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Towards paired and coupled electrode reactions for clean organic microreact

Reviews in Applied Electrochemistry Number61Towards paired and coupled electrode reactions for clean organic microreactor electrosynthesesCHRISTOPHER A.PADDON1,MAHITO ATOBE2,TOSHIO FUCHIGAMI2,PING HE3,PAUL WATTS3, STEPHEN J.HASWELL3,GARETH J.PRITCHARD4,STEVEN D.BULL5and FRANK MARKEN5,*1Physical and Theoretical Chemistry Laboratory,Oxford University,Oxford,OX13QZ,UK2Department of Electronic Chemistry,Tokyo Institute of Technology,4259Nagatsuta,Midori-ku,Yokohama,226-8502,Japan3Department of Chemistry,University of Hull,Hull,HU67RX,UK4Department of Chemistry,Loughborough University,Loughborough,Leicestershire,LE113TU,UK5Department of Chemistry,University of Bath,Claverton Down,Bath,BA27AY,UK(*author for correspondence E-mail:F.Marken@)Received24June2005;accepted in revised form13January2006Key words:coupled processes,electrolysis,electrosythesis,microﬂuidics,microreactor,paired reactionsAbstractElectrosynthesis oﬀers a powerful tool for the formation of anion and cation radical intermediates and for driving clean synthetic reactions without the need for additional chemical reagents.Recent advances in microﬂuidic reactor technologies triggered an opportunity for new microﬂow electrolysis reactions to be developed for novel and clean electrosynthetic processes.Naturally,two electrodes,anode and cathode,are required in all electrochemical pro-cesses and combining the two electrode processes into one‘‘paired’’reaction allows waste to be minimised.By decreasing the inter-electrode gap‘‘paired’’reactions may be further‘‘coupled’’by overlapping diﬀusion layers.The concept of‘‘coupling’’electrode processes is new and in some cases coupled processes in micro-ﬂow cells are possible even in the absence of intentionally added electrolyte.The charged intermediates in the inter-electrode gap act as electrolyte and processes become‘‘self-supported’’.Hardly any examples of‘‘coupled’’paired electrochemical processes are known to date and both‘‘paired’’and‘‘coupled’’processes are reviewed here.Coupled electrode processes remain a challenge.In future‘‘pairing’’and‘‘coupling’’electrode processes into more complex reaction sequences will be the key to novel and cleanﬂow-through microreactor processes and to novel chemistry.1.IntroductionElectrosynthesis is based on adding or removing elec-trons with deﬁned energy to/from a chemical process and can be employed to drive a wide range of clean chemical transformations[1,2].The formation of highly reactive intermediates as well as of electrogenerated acids or bases are possible[3,4].In several industrial processes large scale electrosynthetic processes(e.g.in the nylon-6,6synthesis[5])have been successfully applied and specially designed reactor systems have been developed such asﬁlterpress systems,membrane reactors,ﬂuidised bed reactors,or parallel-plateﬂow systems with down to G1mm inter-electrode gaps[5]. In organic synthesis,over the recent years microreac-tor systems have gained popularity[6,7]and they have been applied in syntheses where good reaction control, reactive intermediates,high yields,modularity,and small scale are desirable[8–10].As will be shown in this overview,micro-ﬂow reactor systems are also ideal for electrosyntheses.New types of‘‘paired’’or‘‘cou-pled’’electrosynthetic processes could be developed in future to be conducted in micro-ﬂow systems.However, a better understanding or how to beneﬁcially‘‘pair’’or ‘‘couple’’electrode processes is prerequisite.The main focus of this review is on reaction concepts and examples rather than on cell design and process envi-ronments.All electrochemical reactions occur in pairs(oxidation and reduction),thus obeying the law of electroneutral-ity:the number of electrons added at the cathode must simultaneously be removed at the anode.Often atten-tion is focused on only one of the reactions in a divided cell arrangement or the accompanying reaction at the counter electrode is chosen to be innocuous,not to interfere with starting materials,intermediates,or prod-ucts.In‘‘paired’’electrochemical syntheses both the anodic and cathodic reactions can be matched and contribute to the formation of theﬁnal product(s)as has been emphasised and deﬁned by Baizer[11].UsingJournal of Applied Electrochemistry(2006)36:617–634ÓSpringer2006 DOI10.1007/s10800-006-9122-2paired electrochemical processes to produce chemicals can result in a considerable reduction in energy con-sumption and by pairing electrode processes at a closely spaced anode and cathode,paired electrochemical processes can now be conducted without the need for an intentionally added supporting electrolyte[12].The product is obtained directly by solvent removal and without laborious separation steps,which is of consid-erable beneﬁt in both laboratory scale and commercial processes.In this review a range of‘‘paired’’electrode processes are discussed and different types of processes going from ‘‘uncoupled’’to‘‘strongly coupled’’are compared.The beneﬁts and challenge of coupling electrode processes and possible applications of micro-ﬂow reactor systems for electrosyntheses are highlighted.The future chal-lenge of identifying new‘‘paired’’and‘‘coupled’’pro-cesses and the promise of new chemical reactions under micro-ﬂow electrosynthesis conditions are emphasised.2.Pairing electrosynthetic processesEarly work on‘‘paired electrosynthesis methodology’’was reported in the late1980s particularly by Baizer and co-workers[13].Special cells withﬂow-through opera-tion and novel porous electrodes have been developed [14].There are well-studied examples of paired electro-syntheses such as the formation of ferrocene with a sacriﬁcial iron electrode[15]or the anodic and cathodic transformation of glucose to give gluconic acid and sorbitol[16].This latter process may be classiﬁed as ‘‘divergent’’since two products are obtained from one starting material.In addition,there are many examples for‘‘parallel’’and‘‘convergent’’processes.A method-ology often employed to pair electrode processes is based on the cathodic generation of hydrogen peroxide, H2O2,(or similar peroxo intermediates)from oxygen. Hydrogen peroxide as an intermediate is able to act as an oxidant despite being formed at the cathode and therefore both oxidation and reduction result in the formation of the same product(vide infra).In commercial electrosynthetic processes,pairing electrode processes has always been important.The most prominent example of a paired electrosynthesis is the production of adiponitrile by electrohydrodimerisa-tion of acrylonitrile,which is an industrially important intermediate used in the manufacture of nylon-6,6[17].The Monsanto process may be regarded as a‘‘paired’’process employing a two-phase reaction mixture and was commercialised by utilising an undivided cell consisting of a bipolar stack of carbon steel evaporated on one face with a thin layer of cadmium.Plastic spacers set the inter-electrode gap at2mm.From100–200 electrodes are placed in a single stack,and the assembly installed in a pressure vessel,designed to provide a uniform,two-phase re-circulating aqueous emulsion of acrylonitrile,adiponitrile,and a bisquaternary salt/ phosphate buﬀer system[18].The cell stack is operated at a current density of20A dm)2and3.8V per cell and the power usage at2.4kWh kg)1is less than half that for the corresponding divided cell process (6.0kWh kg)1).For the recovery of the adiponitrile product,a side stream of catholyte is withdrawn from each circulating system,cooled,and counter-currently contacted with excess acrylonitrile in a multistage extraction column.A portion of the aqueous electrolyte in this traditional macroreactor process is also purged from the electrolysis circulating system to remove the organic and metal ion impurities that can adversely aﬀect the reaction selectivity and current eﬃciency. The use of the undivided cell system and two-phase conditions are the keys to high chemical and cost efﬁciency. The overall reaction scheme for this process,which is based on two starting materials(acrylonitrile and hydrogen) reacting at cathode and anode to give adiponitrile as a coupling product,is summarised in Figure1[19].From this reaction scheme the importance of coupling anode and cathode processes is immediately apparent. For processes to be developed it is important to take into consideration the overall reaction scheme including anode and cathode reaction.It is very interesting to ask ‘‘what are the effects of bringing the two electrodes, anode and cathode,even closer together’’?The recent development of new micro-reactor and micro-ﬂow cell technology for synthetic processes[20]is now stimulat-ing further research into electrochemical reactions which proceed in undivided cell reactions and/or under condi-tions where the diﬀusion layer of anode and cathode are made to overlap.Inventing paired syntheses,particularly if they are going to be carried out in undivided cells,presents many intriguing challenges.The raw materials before electrol-ysis must be compatible.The intermediates(or prod-ucts)formed at one electrode must not react irreversibly with the intermediates or products formed at theother Fig.1.Schematic presentation of the Monsanto process[19].618electrode.Above all,an intermediate must not,before reacting,return to the counter electrode and undo the electron transfer(s)that were previously accomplished.For paired electrode processes the selectivity and design of electrodes is important to avoid unwanted reactions and the development of new types of modiﬁed [21]or selective enzyme electrodes [22]will further help to improve this technology.The material used for the electrode often inﬂuences the reaction.The chemical interaction of an electroactive species generated from the substrate and the electrode is a particularly impor-tant factor in the selection of the material for the cathode or anode.Novel materials such as boron-doped diamond [23]or Ebonex [24]are now available to control electrochemical processes and many cases of speciﬁc electrode–substrate interaction exist.The inter-action of graphite with formaldehyde is,for example,a promoting factor in the reductive dimerisation of formaldehyde to ethylene glycol [25].A tin cathode has been found particularly eﬀective for the intramo-lecular coupling of a carbonyl group with an aromatic ring [26].Porous Ebonex can be beneﬁcially employed in processes where anodic solvent decomposition is re-quired (e.g.for the eletrogeneration of acids or bases).The type of electrode material(s)is therefore critical to the selectivity of a process.When considering a paired or coupled process,each electrode may be chosen to support a particular process.The reactor design is crucial for efﬁcient electrosyn-theses.Flow through systems have been proposed with channel geometry [27]or with ﬂow through porous plug electrodes [28].Rather than employing a ﬂow-throughsystem with anode and cathode placed vis-a-vis,elec-trode geometries such as the interdigitated electrode array can be highly eﬀective [29](see Figure 2a).An interdigitated electrode system (arrays of microscopic electrodes made from metal sputtered into patterns onto a substrate)system can now be produced routinely and in extremely small dimensions via advanced lithographic techniques [30].Each electrode has a band geometry with a bandwidth of typically 0.1–100l m and a gap between electrodes of similar size.For the interdigitatedband electrode of equally sized electrodes and gaps,the steady-state feedback current has been determined [31,32]and the approximate (steady state)diﬀusion layer thickness d can be equated in good approximation to the width of the inter-electrode gap between the electrodes,w (Equation 1).d ¼wð1ÞFor all common (uniformly accessible)hydrodynamic electrodes the (steady state)diffusion layer thickness can be expressed based on the Nernst diffusion layer model (Equation 2)[33].d ¼n F A D C Bulk =I limð2ÞIn this expression,d is the diﬀusion layer thickness,n the number of electrons transferred per molecule diﬀusing to the electrode,F the Faraday constant,D the diﬀusion coeﬃcient,C Bulk the bulk concentration,and I lim the mass transport limited current.Forced convection will reduce the diﬀusion layer thickness and therefore increase the current.Typical values for the diﬀusion layer thickness at hydrodynamic electrodes are 10–500l m [34]and in more forceful agitated systems,values down to 1l m [35]and even <0.1l m [36]can be achieved.With reference to Figure 2and by comparing the above two equations it can be seen that ‘‘coupling’’of paired processes will occur when the inter-electrode gap (width w for interdigitated electrodes or height 2h for channel electrodes)approaches approximately 2d .For non-uniformly accessible electrode systems such as the channel electrode (Figure 2b)coupling will be increasing towards the trailing edge of the electrodes (The dotted line is indicating the approximate extend of the diﬀusion layer).On the other hand,increasing the rate of ﬂow through the channel cell will decrease the diﬀusion layer thickness and therefore decouple the processes at anode and cathode (see Figure 3b).Similarly,ﬂow across an interdigitated array electrode will also aﬀect the cou-pling between processes and essentially decouple process at high ﬂow rates (see Figure 3a).There are further types of electrode systems similar to interdigitated band arrays but these are based on porous insulator separated electrodes with ﬂow on both or on only one side of the electrode systems (see Figure 3c).These can be expected to follow similar principles except that convective ﬂow has a smaller eﬀect on the concen-tration proﬁle within the porous insulator or membrane.Finally,in addition to the eﬀect the diﬀusion layer thickness has on processes in micro ﬂow systems,the magnitude of the reaction layer [37]provides a further important parameter for the interaction of the two electrodes and for the pathway of overall chemical processes triggered by the electrochemical process.A full understanding of ‘‘coupled’’electrochemical processes will require a detailed understanding of both diﬀusion layer and reaction layer composition,for example based on a detailed numericalsimulation.Fig.2.Schematic drawing of (a)an interdigitated electrode system and (b)a rectangular duct micro-ﬂow cell electrode system.6193.Parallel,divergent,and convergent paired electro-organic reactions3.1.Parallel paired electroorganic synthesesThe least complicated approach to a paired electro-chemical process is to use two starting materials which are converted into two products without any chemical interaction during the electrolysis process.There is one prominent example for this type of process which is the formation of phthalide and 4-(t -butyl)benzaldehyde dimethylacetal.In 1999,BASF AG introduced a parallel commercial paired electrosynthesis for the simultaneous formation of two products.Methyl phthalate is cathodically reduced to phthalide while at the anode 4-(t -butyl)tol-uene is oxidised to give 4-(t -butyl)benzaldehyde dime-thylacetal (Figure 4)[38,39].In this process methanol is used both as a reagent and as a solvent.However,overall as much methanol is released from reduction of the diester as is consumed in making 4-(t -butyl)benzal-dehyde dimethylacetal.Protons are simultaneously gen-erated at the anode and consumed at the cathode.3.2.Divergent paired electroorganic synthesesThe use of a single starting material can be beneﬁcial when two distinct products are formed at cathode and anode.In this ‘‘divergent’’process the overall balance ofcharges is maintained and the two products have to be separated post-electrolysis.The paired oxidation of glucose to gluconate with the simultaneous reduction of glucose to sorbitol is an example of a divergent paired,industrial scale electroorganic process.The indirect oxidation by anodically generated bromine of glucose to gluconate is used commercially.The electro-chemical reduction to sorbitol (and mannitol)was for some years an industrial process until a catalytic process replaced it.It was postulated that if the two could be paired into a single undivided ﬂow cell,the economics for each would be improved and full details of this procedure have since been published [40,41].The reaction at the cathode involves the electrochemical hydrogenation of glucose.An indirect oxidant (Br 2)is then electrochemically generated at the anode and oxidises the reactant in the bulk solution.Hydrogen evolution is a side reaction at the cathode (Figure 5).A continuous,electrochemical tubular –stirred tank reac-tor was employed (see Table 1).3.3.Convergent paired electroorganic syntheses Processes in which two starting materials upon oxida-tion and reduction give the same product may be employed in a ‘‘convergent’’process.Although it is unusual for oxidation/reduction processes to yield the same product,there are several examples of this type ofprocess.Fig.3.Schematic drawing of the concentration proﬁle (dotted line)in the presence of strong or weak convective ﬂow (see arrow)for (a)interdigitated electrodes,(b)channel electrodes,and (c)a semi-open ‘‘sandwich’’electrode.Fig.4.Schematic presentation of an industrially applied (BASF AG)paired electrosynthesis of phthalide at the cathode and 4-(t -butyl)benz-aldehyde dimethylacetal at the anode [38,39].6203.3.1.Formation of glyoxalic acidThrough paired electrosynthesis,oxalic acid and glyoxal were separately reduced and oxidised yielding glyoxalic acid [42].In the oxidation process,both chlorine and oxygen gas could be used as an oxidising agent for glyoxal.It was found that the percentage of transfor-mation and selectivity was higher with chlorine gas than with oxygen gas (Figure 6).Overall,this process high-lights the advantages of a paired synthesis with high percentage yield,selectivity,and purity,low waste and a ‘simple’synthesis that is normally very diﬃcult to perform by conventional chemical methods.3.3.2.Formation of 2-alkoxy-tetrahydrofuransIshifune et al.[43]describe the electroreduction of aliphatic esters to form 2-alkoxytetrahydrofurans using a novel electrolysis system (see Table 1).The paired electrolysis system consists of a cathodic reduction of aliphatic esters and an anodic oxidation of THF solvent forming the tetrahydrofuranyl-protected form of a primary alcohol (Figure 7).Ultrasound was employed to continuously unblock the electrodes.An interesting eﬀect of magnesium in the process was postulated.The authors suggest that magnesium ions promote the electroreduction of aliphatic esters which are hardly reduced under usual electroreductive conditions.Over-all,from a synthetic viewpoint,this is a novel example of a paired electrosynthesis yielding protected alcohols directly from aliphatic esters.3.3.3.Formation of propylene oxideInterdigitated coplanar band electrodes were made from platinum ink printed on alumina and their application to the epoxidation of propylene investigated in both a tank cell and ﬂow cell [44],using a convergent paired process.Bromide solutions were saturated in propylene,then the bromide oxidised to bromine at the anode,which then reacts with water to form hypobromous acid.This in turn reacts with propylene to form propylene bromohydrin.The hydroxide ions produced at the cathode were then necessary to complete the overall reaction (Figure 8).The performances of various platinum arrays were investigated.Many factors were found to inﬂuence their results such as the ﬂow conditions,applied voltage,cell temperature,electrolyte concentration and the inter-electrode distance.Experiments were carried out with inter-electrode distances of the different arrays varying between 250l m and 1mm (see Table 1).3.3.4.Formation of benzyl –nitroalkyl adductsChiba and co-workers have reported [45]a benzylic nitroalkylation process,accomplished by the paired reaction of various benzyl phenyl sulﬁdes and nitroalk-anes in the presence of lithium perchlorate.Paired electrolyses were performed in an undivided cell,with divided cells actually giving the desired products in very poor yields (Figures 9and 10).Similar reactions using a benzylphenylether gave no desirednitromethylatedFig.5.Schematic presentation of the paired production of gluconic acid and sorbitol from glucose [40,41].Fig.6.Schematic presentation of the convergent glyoxalic acid electrosynthesis [42].621T a b l e 1.D i v e r g e n t a n d c o n v e r g e n t p a i r e d s y n t h e t i c p r o c e s s e sE x a m p l e /R e f e r e n c e P r o d u c t (s )S t a r t i n g M a t e r i a l (s )C u r r e n t E ﬃc i e n c y (%)A n o d e M a t e r i a l /R e a c t i o n C a t h o d e M a t e r i a l /R e a c t i o n1.S o r b i t o l G l u c o s e 100%f o r b o t h p r o d u c t s G r a p h i t e a n o d e R a n e y N i C a t h o d e [40,41]G l u c o n a t eG l u c o s e ﬁg l u c o n a t e v i a ‘‘B r +’’G l u c o s e ﬁs o r b i t o l v i a e l e c t r o c a t a l y t i c r e d u c t i o n 2.G l y o x a l i c a c i dO x a l i c a c i d 40%y i e l d s o f b o t h p r o d u c t sG r a p h i t e L e a d P l a t e (99.99%)a[42]G l y o x a l G l y o x a l ﬁg l y o x a l i c a c i d v i a C l 2O x a l i c a c i d v i a p r o t o n r e d u c t i o n 3.2-A l k o x y t e t r a -h y d r o f u r a nA l i p h a t i c e s t e r sG e n e r a l a c e t a l p e r c e n t a g e y i e l d 87%P l a t i n u m M a g n e s i u m [43]F o r m a t i o n o f T H F c a t i o n s b y a n o d i c o x i d a t i o nF o r m a t i o n o f t h e a c e t a l v i a c o m b i n a t i o n b e t w e e n t h e a l k o x i d e f o r m e d a t t h e c a t h o d e a n d T H F c a t i o n4.[44]P r o p y l e p o x i d e P r o p y l e n e 68%bb5.V a r i o u s n i t r o a l k y l a t e d c o m p o u n d s V a r i e d b e n z y l s u l ﬁd e s i n c l u d i n g b e n z y l d i t h i o a c e t a l s68–100%G l a s s y c a r b o n a n o d eP l a t i n u m c a t h o d e [45]B e n z y l c a t i o n s g e n e r a t e d b y a n o d i c o x i d a t i o n o f s u l ﬁd e s a n d t h e n t r a p p e d b y n i t r o a l k y l a n i o n s F o r m a t i o n o f n i t r o a l k y l a n i o n s .c6.V a r i o u s n u c l e o p h i l i c s u b s t i t u t e d a r o m a t i c sM e t h o x y a r e n e s w i t h 1H -t e t r a z o l e s 88%d ,eR a d i c a l c a t i o n s o f e l e c t r o n -r i c h a r o m a t i c s g e n e r a t e d a t p l a t i n u m a n o d e P l a t i n u m c a t h o d e [46]N i t r o g e n h e t e r o c y c l i c a n i o n s a c t a s n u c l e o p h i l e s .7.p -B e n z o q u i n o n e H y d r o q u i n o n eB e n z e n e T o t a l c u r r e n t e ﬃc i e n c y ,94%P b O 2P b O 2[47]B e n z e n e a n o d i c a l l y o x i d i s e d .B e n z e n e ‘‘c a t h o d i c a l l y o x i d i s e d ’’u s i n g aC u +/O 2r e d o x s y s t e m 8.P r o t e c t e d h o m o a l l y l i c a l c o h o l sA l l y l b r o m i d e ;b e n z a l d e h y d e a n d N ,N -d i m e t h y l -f o r m a m i d e50–60%fP l a t i n u m G l a s s y c a r b o n [48]A n o d i c a l l y g e n e r a t e d e l e c t r o p h i l e +h o m o a l l y l i c a l c o h o l a t e M e t a l -f r e e a l l y l a t i o n o f b e n z a l d e -h y d e b y a l l y l b r o m i d e r e d u c t i o n .9.2,6-D i m e t h y l -4-a r y l p y r i d i n e -3,5-d i c a r b o n i t r i l eB e n z y l t h i o c y a n a t e ,b e n z y l c h l o r i d e ,p -m e t h y l b e n z y l c h l o r i d e ,o r t o l u e n e 67%P l a t i n u m gP l a t i n u m[49]10.C y a n o a c e t i c a c i dC O 2h 24.7%i P l a t i n u m n e t o r c a r b o n p l a t e s .G e n e r a t i o n o f C H 2C N r a d i c a l s f r o m s o l v e n tP l a t i n u m o r l e a d p l a t e s .C H 2C N R a d i c a l s a r e c o u p l e d w i t h c a t h o d i c C O 2-r e d u c e d s p e c i e s[50]aT y p i c a l d i s t a n c e b e t w e e n t w o e l e c t r o d e s 10m m .A p o l y c a r b o n y l s t y r e n e c a t i o n i c e x c h a n g i n g m e m b r a n e w a s u s e d t o s e p a r a t e t h e a n o d e a n d c a t h o d e c e l l s .bI n t e r d i g i t a t e d c o p l a n a r b a n d e l e c t r o d e s m a d e f r o m p l a t i n u m i n k p r i n t e d o n a l u m i n a .c P a i r e d e l e c t r o l y s e s w e r e p e r f o r m e d i n 3M l i t h i u m p e r c h l o r a t e a n d i n d r y n i t r o m e t h a n e s o l u t i o n s .d T o t a l y i e l d f o r p r o d u c t s A a n d B .P r o d u c t r a t i o 3:2,r e s p e c t i v e l y .e P a i r e d e l e c t r o s y n t h e s i s p e r f o r m e d u s i n g a n u n d i v i d e d c e l l i n a c e t o n i t r i l e s o l v e n t w i t h t e t r a b u t y l a m m o n i u m s a l t o f t h e h e t e r o c y c l i c a n i o n a s t h e e l e c t r o l y t e .f E l e c t r o l y s e s w e r e c o n d u c t e d i n a q u a s i –d i v i d e d c e l l a t a c o n s t a n t c u r r e n t o f 150m A (h i g h e r c u r r e n t d e n s i t i e s c a u s e d t h e p r o d u c t i o n o f s e v e r a l b y -p r o d u c t s );y i e l d r a n g e r e ﬂe c t s p r o d u c t s A –C .g P l a t i n u m e l e c t r o d e s i n a t w o -c o m p a r t m e n t c e l l s e t u p d i v i d e d b y a g l a s s f r i t .A c e t o n i t r i l e s o l v e n t w a s u s e d i n a l l e l e c t r o l y s e s .h S y n t h e s i s o f C A a c t u a l l y i n v o l v e s t h e s o l v e n t ,a c e t o n i t r i l e a n d a t e t r a a l k y l a m m o n i u m s a l t a n i o n .S a t u r a t i o n o f c e l l s w i t h c a r b o n d i o x i d e w a s a c h i e v e d b y c o n t i n u o u s b u b b l i n g o f t h e g a s .i U n d e r c e r t a i n e x p e r i m e n t a l c o n d i t i o n s t h i s r e p r e s e n t e d t h e g r e a t e s t c u r r e n t e ﬃc i e n c y .622Fig.7.Paired electrolysis system of the combination between cathodic reduction of an aliphatic ester and anodic oxidation of THF[43].Fig.8.Schematic presentation of propylene epoxidation process at interdigitated electrodes[44].Fig.9.Overall reaction scheme for the paired benzylic nitroalkylation employing a nitroalkane and a benzylphenylsulﬁde as starting materi-als[45].Fig.10.Schematic presentation of the proposed reaction mechanism of the benzylic nitroalkylation by paired electrolysis [45].623products.The result showed that the benzylic phen-ylsulfanyl group was essential for the electrochemical generation of the corresponding benzyl cation.Addi-tionally,it was reported that the perchlorate electrolyte was presumed to assist the oxidativeﬁssion of the carbon–sulfur bond.In conclusion,paired electrolysis of benzyl sulﬁdes and dithioacetals in lithium perchlorate and nitroalkane solution eﬃciently accomplished the electrooxidative generation of the corresponding benzyl cations at the anode with the simultaneous electrore-ductive generation of a nitroalkyl anion at the cathode. In Figure10the formation of oxidised forms of thi-ophenol and hydrogen as side products are omitted. 3.3.5.Formation of tetrazole anion–methoxyarene cation adductsEvans and co-workers[46]performed coupling reactions with methoxy arenes and1H-tetrazoles.Although the mechanism behind the reaction is not fully explained, the direct coupling of cations produced at the anode and anions produced at the cathode was intended.A convergent paired electrosynthesis is developed in which anions of nitrogen heterocycles are generated at the cathode,and radical cations of electron-rich aromatics are produced at the anode.Reaction between these two electrogenerated species leads to products via nucleo-philic substitution at the aromatic substrate(Figure11). Interestingly,attempts to achieve similar substitution reactions on1,4-dimethoxybenzene using other types of anions(benzoate,triﬂuoracetate,acetate,2,4-dinitro-phenolate,and the anion of diethyl nitromalonate)did not produce satisfactory yields.3.3.6.Formation of p-benzoquinone and hydroquinone from benzeneIto et al.[47]reported the oxidation of aromatics using a paired process(Figure12).Historically,this is theﬁrst reported example of the production of the same product from the same starting material both in the anode and cathode chambers,i.e.a convergent synthesis.A single H-type electrolytic cell with Cu+/Cu2+mediator is required in this procedure and oxygen in contact with the Cu+intermediate is the actual cathodic oxidising reagent.3.3.7.Formation of homoallylic alcoholsThe allylation of an aldehyde in a convergent paired electrolysis under indium-free conditions wasperformed Fig.11.Schematic presentation of a paired coupling process employing anodically generated radical cations and cathodically generated het-erocyclic anions[46].Fig.12.Schematic presentation of the convergent synthesis of p-benzoquinone and hydroquinone via simultaneous anodic and cathodic oxi-dation of benzene[47].624。

TestingFrequencyMultipliersandDividers

Testing Frequency Multipliers and DividersAuthor: Adrian JonesDate: February 2000IntroductionFrequency multipliers and dividers are key components of modern radio frequency (RF) and microwave systems. They are generally used in signal generation and frequency synthesis applications. These devices can be awkward to characterize due to the frequency conversion between input and output - several pieces of test equipment are usually needed.This paper reviews current techniques for measuring the main parameters of multipliers and dividers, focusing on areas where special considerations are required. In particular, output return loss and phase noise are covered. The application of a microwave system analyzer to multiplier and divider measurements is introduced. Several examples are given to illustrate fast measurements of conversion gain suitable for tuning and manufacturing environments.Common measurement techniquesThe most basic measurement setup consists of a signal generator and spectrum analyzer. This can be used in an elementary fashion to determine the following parameters.Operating window (Input power and frequency)Output powerOutput harmonicsMeasuring these parameters manually over a band of frequencies can be a laborious process and it is common to perform a quasi - swept measurement using a sweeper and the maximum hold facility on the spectrum analyzer. This works well as long as the harmonics of interest do not overlap.Phase noise measurementsThe phase noise of multipliers and dividers is a major concern especially when they are the building blocks of frequency synthesizers. The output phase noise of a multiplier or divider is ideally given by:where L IN and L OUT are single sideband phase noise expressed in decibels with respect to the carrier in a 1Hz bandwidth (dBc/Hz). Dividers improve the phase noise whereas multipliers degrade it. In real devices, the output phase noise is limited by a noise floor. This can be measured by many methods, but most of these require a reference signal significantly better than the device under test.This problem can be overcome with a quadrature mixing method where the devices are measured in pairs (Figure 1). The signal generator phase noise adds to both paths of the measurement, but by adding a variable delay into one of the paths is canceled at the phase detector, leaving just the sum of the additional noise from the two devices. If three devices are available, they can be measured in all combinations to reveal the noise of each individual device. It is particularly important to ensure that only the desired output harmonic reaches the phase detector. The phase detector can be calibrated with a beat note method using another signal generator to drive one of the devices.Input and output return lossComplex RF subsystems are often designed by a team of engineers. To reduce integration problems when the building blocks are connected together, input and output return loss are commonly specified for each block of circuitry.The input match of a divider or multiplier can be measured over the input frequency range using any conventional technique, for example an autotester (return loss bridge) and scalar analyzer. When using a broadband device such as an autotester to measure multipliers and dividers beware of backfire of the output frequency or harmonics causing errors. Ensure that the power at the device input is correct during the measurement, as the input match is a function of input level. When measuring output return loss, it is important that the multiplier or divider is in its normal operating state. A small signal measurement with an autotester or vector network analyzer (VNA) may give false results, as the operating conditions of the non linear parts of the device will be different. Figure 2 shows a possible set-up. The device output is used as excitation for the measurement. A mismatched line is used to reflect power back to the device and the standing wave pattern is used to determine the output match.If the output is loaded with a variable phase short circuit, problems can arise with some devices, especially digital dividers, which could stop running. In this case, a pad can be inserted before the short to provide a controlled mismatch. The forward power on the line is sampled with a directional coupler. By adjusting the length of the mismatched line, the maxima and minima of the standing wave can be observed on a spectrum analyzer tuned to the output frequency. The ratio of maximum to minimum is the voltage standing wave ratio (VSWR) on the line. The return loss of the device under test is given bywhere L pad is the loss of the pad in dB. Errors in this measurement can be analyzed with reference to the flow graph shown in Figure 3.DUT reflection coefficient GsCoupler transmission coefficient TCoupling coefficient CCoupler directivity DPad transmission coefficient T padSliding short reflection angle PThe sliding short is modeled as lossless. The analysis will not be included, but the main result is summarized in the following table. This assumes no pad.As a rule of thumb, the coupler directivity needs to be 10 to 20dB better than the output return loss being measured.Automated measurementsConsiderable time can be saved by automating the preceding measurements with general purpose interface bus (GPIB) compatible instruments and a controller. This technique is very flexible, and a system can be contrived to measure almost any parameter versus frequency, power, time etc.As an example, Figure 4 shows a relatively simple set-up to search for an interesting characteristic in a comb generator. The time varying capacitance in a step recovery diode (SRD) based comb generator makes it easy to inadvertently produce a parametric amplifier. The parametric gain can cause peaks in the noise floor, or even oscillations, generally at half the input frequency, and is often referred to as period doubling instability. In trying to construct a multiplier, a divider has been produced!Considerable difficulties can be experienced in proving the effect has been eliminated as it happens over a narrow range of drive levels and frequencies. A GPIB controlled system can plot regions of period doubling against frequency and drive power - a typical result is shown in Figure 5. This can save substantial development time.Fast swept frequency techniquesRF engineers like to see plots of characteristics against frequency. Even continuous wave (CW) multipliers need to be characterized over frequency to allow for component tolerances and temperature change. For manufacturing, real time tuning and rapid development applications, fast swept measurements are desired.A scalar analyzer can be used to measure divider and multiplier output power, but the high levels of harmonics can cause large errors with broadband detectors. Most spectrum analyzers with tracking generators and vector network analyzers cannot handle frequency conversion devices without external hardware.What is needed is a synchronized source and receiver with the required frequency relationship. Microwave system analyzersThe Microwave System Analyzer (MSA) is new class of instrument which provides the solution by combining a signal generator and spectrum analyzer with an inbuilt controller (Figure 6). In addition, a high accuracy scalar analyzer is included.In most tracking generators, the signal is derived by mixing the spectrum analyzer local oscillator (LO), which only allows frequency offsets to be generated. However if the source and receiver are independently generated, any frequency relationship can be obtained. With a MSA the relationship between the source and receiver frequencies is determined by a scale and offset control. The instrument can be configured into two modes: spectrum analyzer with full band tracking generator (to 24GHz), and scalar analyzer with a tuned receiver input.In spectrum analyzer mode, the frequency range at the receiver is entered and the source frequency is scaled and offset. The instrument acts like a spectrum analyzer with a scaled and offset tracking generator. This mode is convenient for measuring dividers as the scale is simply the divide ratio.In scalar analyzer mode, the source frequencies are entered and the receiver frequency is scaled and offset. This is convenient for frequency multipliers, where the scale is the harmonic number. The instrument acts like a scalar analyzer, except the input is tuned and of high dynamic range. The tuned input can be combined with scalar detectors to measure conversion gain.Example measurements on frequency multipliers and dividers using a MSAAs an example of the spectrum analyzer mode, Figure 7 shows a screen shot of a measurement of the output power of a frequency divider (divide ratio = 8). The MSA scale control has been set to 8 such that the source tracks at 8 times the spectrum analyzer frequency. The frequency scale is annotated in source frequency units. The plot is overlaid with a swept measurement of the output second harmonic level (i.e. scale = 4).As an example of the scalar analyzer mode, Figure 8 shows a comparison of the 2nd and 3rd harmonic measurement of a multiplier. A balanced multiplier is used, which generates a signal rich in odd harmonics and suppresses even harmonics. A dual channel measurement is shown. The measurements are live, and swept alternately. The scale control on each channel has been set equal to the required harmonic number. For example, the 2nd harmonic channel has scale set to 2 such that the spectrum analyzer frequency is always twice the source frequency. The scales are annotated in spectrum analyzer units (output frequency).Measurement accuracy and calibrationThe uncertainties in multiplier and divider conversion measurements must be considered separately at the input and output as the frequencies are different. At the device input, the source level accuracy, cable loss and source match are the dominant factors in uncertainty of incidentinput power. At the device output, receiver level accuracy, load match and cable loss limit the accuracy of the output level measurement.The input cable loss can be compensated for by performing a user power calibration at the end of the cable. The instrument automatically sets the front panel level high enough to compensate for the cable loss. The source match can be improved by increasing the power level and adding 50 ohm attenuators.A through path calibration can be performed over the source or receiver frequency range. The choice depends on the uncertainties at each side of the device under test. The receiver level accuracy is generally worse than the source level accuracy and a calibration over the receiver frequency range is most suitable. This reduces the spectrum analyzer reference level uncertainty to approach that of the source.Characterizing integrated assemblies containing frequency multipliers and dividers Frequency multipliers and dividers are rarely stand alone devices, and are usually part of an integrated system. As an example, Figure 9 shows a comb generator and voltage tuned filter assembly. This circuit takes the VHF signal from a high quality oscillator and selects the 3rd, 4th or 5th harmonic to provide a 1.5 to 3GHz signal.A MSA can be used to perform a swept measurement of the entire signal chain. The speed of the measurement allows the effect of adjustments to the circuit to be seen in “real time”. Figure 10 shows the 3rd harmonic response of the signal chain measured on a MSA - the response can be observed as the voltage tuned filters are adjusted.ConclusionThis paper has reviewed techniques for measuring the key parameters of frequency multipliers and dividers. In particular methods for measuring phase noise and output match have been studied. The flexibility of GPIB controlled techniques was illustrated with the example of a period doubling search on a comb generator.Fast, swept frequency measurements can be made using a microwave system analyzer. It has been shown how this instrument can be used to measure the output level and harmonics of multipliers and dividers. In this application, the instrument is faster and more convenient than using a separate signal generator and spectrum analyzer, which is important in tuning and manufacturing environments. It is also superior to using a scalar analyzer as the tuned receiver can be used to reject unwanted harmonics.。

计算机b类刊物与会议分类信息

108.
Neural Networks
NN
9/12
2
109.
International Journal of Knowledge-Based and Intelligent Engineering Systems
KES
月刊
110.
AIE
月刊
111.
Computational Intelligence: An International Journal
JPDC
月
0.43
33.
ACMTransactions onEmbedded Computing Systems
TECS
月
34.
IEEETransactions onSystems, Man and Cybernetics
SMC
月
A:0.98
B:1.538
C:0.885
35.
ACMTransactions onAutonomous and Adaptive Systems
月刊
0.185
4.
IEEETransactions onReliability
季
0.8
5.
ACM Transactions on information and system security
季
6.
Journal ofInformation Technology
月
1.239
7.
IEEE Transaction on Information Theory
TVLSI
月
0.771
30.
IEEETransactions onComputer-Aided Design of Integrated Circuits and Systems

机器人技术路线图：从互联网到机器人(A Roadmap for US Robotics)

68
4.1. Architecture and Representations 68
4.2. Control and Planning
68
4.3. Perception 69
4.4. Robust, High-Fidelity Sensors
69
4.5. Novel Mechanisms and High-Performance Actuators 69
2. Strategic Findings 52
2.1. Principal Markets and Drivers
53
2.2. Near-Term Opportunities and Factors Affecting Commercialization 54
ii
A Roadmap for U.S. Robotics – From Internet to Robotics
May 21, 2009
A Roadmap for US Robotics
From Internet to Robotics
Organized by
Georgia Institute of Technology University of Southern California
Johns Hopkins University University of lvania University of California, Berkeley Rensselaer Polytechnic Institute University of Massachusetts, Amherst
2.5. Human-Robot Interfaces 76
2.6. Communications and Networking 76

Theory of modeling and simulation

THEORY OF MODELING AND SIMULATIONby Bernard P. Zeigler, Herbert Praehofer, Tag Gon Kim2nd Edition, Academic Press, 2000, ISBN: 0127784551Given the many advances in modeling and simulation in the last decades, the need for a widely accepted framework and theoretical foundation is becoming increasingly necessary. Methods of modeling and simulation are fragmented across disciplines making it difficult to re-use ideas from other disciplines and work collaboratively in multidisciplinary teams. Model building and simulation is becoming easier and faster through implementation of advances in software and hardware. However, difficult and fundamental issues such as model credibility and interoperation have received less attention. These issues are now addressed under the impetus of the High Level Architecture (HLA) standard mandated by the U.S. DoD for all contractors and agencies.This book concentrates on integrating the continuous and discrete paradigms for modeling and simulation. A second major theme is that of distributed simulation and its potential to support the co-existence of multiple formalisms in multiple model components. Prominent throughout are the fundamental concepts of modular and hierarchical model composition. These key ideas underlie a sound methodology for construction of complex system models.The book presents a rigorous mathematical foundation for modeling and simulation. It provides a comprehensive framework for integrating various simulation approaches employed in practice, including such popular modeling methods as cellular automata, chaotic systems, hierarchical block diagrams, and Petri Nets. A unifying concept, called the DEVS Bus, enables models to be transparently mapped into the Discrete Event System Specification (DEVS). The book shows how to construct computationally efficient, object-oriented simulations of DEVS models on parallel and distributed environments. In designing integrative simulations, whether or not they are HLA compliant, this book provides the foundation to understand, simplify and successfully accomplish the task.MODELING HUMAN AND ORGANIZATIONAL BEHAVIOR: APPLICATION TO MILITARY SIMULATIONSEditors: Anne S. Mavor, Richard W. PewNational Academy Press, 1999, ISBN: 0309060966. Hardcover - 432 pages.This book presents a comprehensive treatment of the role of the human and the organization in military simulations. The issue of representing human behavior is treated from the perspective of the psychological and organizational sciences. After a thorough examination of the current military models, simulations and requirements, the book focuses on integrative architectures for modeling theindividual combatant, followed by separate chapters on attention and multitasking, memory and learning, human decision making in the framework of utility theory, models of situation awareness and enabling technologies for their implementation, the role of planning in tactical decision making, and the issue of modeling internal and external moderators of human behavior.The focus of the tenth chapter is on modeling of behavior at the unit level, examining prior work, organizational unit-level modeling, languages and frameworks. It is followed by a chapter on information warfare, discussing models of information diffusion, models of belief formation and the role of communications technology. The final chapters consider the need for situation-specific modeling, prescribe a methodology and a framework for developing human behavior representations, and provide recommendations for infrastructure and information exchange.The book is a valuable reference for simulation designers and system engineers.HANDBOOK OF SIMULATOR-BASED TRAININGby Eric Farmer (Ed.), Johan Reimersma, Jan Moraal, Peter JornaAshgate Publishing Company, 1999, ISBN: 0754611876.The rapidly expanding area of military modeling and simulation supports decision making and planning, design of systems, weapons and infrastructure. This particular book treats the third most important area of modeling and simulation – training. It starts with thorough analysis of training needs, covering mission analysis, task analysis, trainee and training analysis. The second section of the book treats the issue of training program design, examining current practices, principles of training and instruction, sequencing of training objectives, specification of training activities and scenarios, methodology of design and optimization of training programs. In the third section the authors introduce the problem of training media specification and treat technical issues such as databases and models, human-simulator interfaces, visual cueing and image systems, haptic, kinaesthetic and vestibular cueing, and finally, the methodology for training media specification. The final section of the book is devoted to training evaluation, covering the topics of performance measurement, workload measurement, and team performance. In the concluding part the authors outline the trends in using simulators for training.The primary audience for this book is the community of managers and experts involved in training operators. It can also serve as useful reference for designers of training simulators.CREATING COMPUTER SIMULATION SYSTEMS:An Introduction to the High Level Architectureby Frederick Kuhl, Richard Weatherly, Judith DahmannPrentice Hall, 1999, ISBN: 0130225118. - 212 pages.Given the increasing importance of simulations in nearly all aspects of life, the authors find that combining existing systems is much more efficient than building newer, more complex replacements. Whether the interest is in business, the military, or entertainment or is even more general, the book shows how to use the new standard for building and integrating modular simulation components and systems. The HLA, adopted by the U.S. Department of Defense, has been years in the making and recently came ahead of its competitors to grab the attention of engineers and designers worldwide. The book and the accompanying CD-ROM set contain an overview of the rationale and development of the HLA; a Windows-compatible implementation of the HLA Runtime Infrastructure (including test software). It allows the reader to understand in-depth the reasons for the definition of the HLA and its development, how it came to be, how the HLA has been promoted as an architecture, and why it has succeeded. Of course, it provides an overview of the HLA examining it as a software architecture, its large pieces, and chief functions; an extended, integrated tutorial that demonstrates its power and applicability to real-world problems; advanced topics and exercises; and well-thought-out programming examples in text and on disk.The book is well-indexed and may serve as a guide for managers, technicians, programmers, and anyone else working on building simulations.HANDBOOK OF SIMULATION:Principles, Methodology, Advances, Applications, and Practiceedited by Jerry BanksJohn Wiley & Sons, 1998, ISBN: 0471134031. Hardcover - 864 pages.Simulation modeling is one of the most powerful techniques available for studying large and complex systems. This book is the first ever to bring together the top 30 international experts on simulation from both industry and academia. All aspects of simulation are covered, as well as the latest simulation techniques. Most importantly, the book walks the reader through the various industries that use simulation and explains what is used, how it is used, and why.This book provides a reference to important topics in simulation of discrete- event systems. Contributors come from academia, industry, and software development. Material is arranged in sections on principles, methodology, recent advances, application areas, and the practice of simulation. Topics include object-oriented simulation, software for simulation, simulation modeling,and experimental design. For readers with good background in calculus based statistics, this is a good reference book.Applications explored are in fields such as transportation, healthcare, and the military. Includes guidelines for project management, as well as a list of software vendors. The book is co-published by Engineering and Management Press.ADVANCES IN MISSILE GUIDANCE THEORYby Joseph Z. Ben-Asher, Isaac YaeshAIAA, 1998, ISBN 1-56347-275-9.This book about terminal guidance of intercepting missiles is oriented toward practicing engineers and engineering students. It contains a variety of newly developed guidance methods based on linear quadratic optimization problems. This application-oriented book applies widely used and thoroughly developed theories such LQ and H-infinity to missile guidance. The main theme is to systematically analyze guidance problems with increasing complexity. Numerous examples help the reader to gain greater understanding of the relative merits and shortcomings of the various methods. Both the analytical derivations and the numerical computations of the examples are carried out with MATLAB Companion Software: The authors have developed a set of MATLAB M-files that are available on a diskette bound into the book.CONTROL OF SPACECRAFT AND AIRCRAFTby Arthur E. Bryson, Jr.Princeton University Press, 1994, ISBN 0-691-08782-2.This text provides an overview and summary of flight control, focusing on the best possible control of spacecraft and aircraft, i.e., the limits of control. The minimum output error responses of controlled vehicles to specified initial conditions, output commands, and disturbances are determined with specified limits on control authority. These are determined using the linear-quadratic regulator (LQR) method of feedback control synthesis with full-state feedback. An emphasis on modeling is also included for the design of control systems. The book includes a set of MATLAB M-files in companion softwareMATHWORKSInitial information MATLAB is given in this volume to allow to present next the Simulink package and the Flight Dynamics Toolbox, providing for rapid simulation-based design. MATLAB is the foundation for all the MathWorks products. Here we would like to discus products of MathWorks related to the simulation, especially Code Generation tools and Dynamic System Simulation.Code Generation and Rapid PrototypingThe MathWorks code generation tools make it easy to explore real-world system behavior from the prototyping stage to implementation. Real-Time Workshop and Stateflow Coder generate highly efficient code directly from Simulink models and Stateflow diagrams. The generated code can be used to test and validate designs in a real-time environment, and make the necessary design changes before committing designs to production. Using simple point-and-click interactions, the user can generate code that can be implemented quickly without lengthy hand-coding and debugging. Real-Time Workshop and Stateflow Coder automate compiling, linking, and downloading executables onto the target processor providing fast and easy access to real-time targets. By automating the process of creating real-time executables, these tools give an efficient and reliable way to test, evaluate, and iterate your designs in a real-time environment.Real-Time Workshop, the code generator for Simulink, generates efficient, optimized C and Ada code directly from Simulink models. Supporting discrete-time, multirate, and hybrid systems, Real-Time Workshop makes it easy to evaluate system models on a wide range of computer platforms and real-time environments.Stateflow Coder, the standalone code generator for Stateflow, automatically generates C code from Stateflow diagrams. Code generated by Stateflow Coder can be used independently or combined with code from Real-Time Workshop.Real-Time Windows Target, allows to use a PC as a standalone, self-hosted target for running Simulink models interactively in real time. Real-Time Windows Target supports direct I/O, providing real-time interaction with your model, making it an easy-to-use, low-cost target environment for rapid prototyping and hardware-in-the-loop simulation.xPC Target allows to add I/O blocks to Simulink block diagrams, generate code with Real-Time Workshop, and download the code to a second PC that runs the xPC target real-time kernel. xPC Target is ideal for rapid prototyping and hardware-in-the-loop testing of control and DSP systems. It enables the user to execute models in real time on standard PC hardware.By combining the MathWorks code generation tools with hardware and software from leading real-time systems vendors, the user can quickly and easily perform rapid prototyping, hardware-in-the-loop (HIL) simulation, and real-time simulation and analysis of your designs. Real-Time Workshop code can be configured for a variety of real-time operating systems, off-the-shelf boards, and proprietary hardware.The MathWorks products for control design enable the user to make changes to a block diagram, generate code, and evaluate results on target hardware within minutes. For turnkey rapid prototyping solutions you can take advantage of solutions available from partnerships between The MathWorks and leading control design tools:q dSPACE Control Development System: A total development environment forrapid control prototyping and hardware-in-the-loop simulation;q WinCon: Allows you to run Real-Time Workshop code independently on a PC;q World Up: Creating and controlling 3-D interactive worlds for real-timevisualization;q ADI Real-Time Station: Complete system solution for hardware-in-the loopsimulation and prototyping.q Pi AutoSim: Real-time simulator for testing automotive electronic control units(ECUs).q Opal-RT: a rapid prototyping solution that supports real-time parallel/distributedexecution of code generated by Real-Time Workshop running under the QNXoperating system on Intel based target hardware.Dynamic System SimulationSimulink is a powerful graphical simulation tool for modeling nonlinear dynamic systems and developing control strategies. With support for linear, nonlinear, continuous-time, discrete-time, multirate, conditionally executed, and hybrid systems, Simulink lets you model and simulate virtually any type of real-world dynamic system. Using the powerful simulation capabilities in Simulink, the user can create models, evaluate designs, and correct design flaws before building prototypes.Simulink provides a graphical simulation environment for modeling dynamic systems. It allows to build quickly block diagram models of dynamic systems. The Simulink block library contains over 100 blocks that allow to graphically represent a wide variety of system dynamics. The block library includes input signals, dynamic elements, algebraic and nonlinear functions, data display blocks, and more. Simulink blocks can be triggered, enabled, or disabled, allowing to include conditionally executed subsystems within your models.FLIGHT DYNAMICS TOOLBOX – FDC 1.2report by Marc RauwFDC is an abbreviation of Flight Dynamics and Control. The FDC toolbox for Matlab and Simulink makes it possible to analyze aircraft dynamics and flight control systems within one softwareenvironment on one PC or workstation. The toolbox has been set up around a general non-linear aircraft model which has been constructed in a modular way in order to provide maximal flexibility to the user. The model can be accessed by means of the graphical user-interface of Simulink. Other elements from the toolbox are analytical Matlab routines for extracting steady-state flight-conditions and determining linearized models around user-specified operating points, Simulink models of external atmospheric disturbances that affect the motions of the aircraft, radio-navigation models, models of the autopilot, and several help-utilities which simplify the handling of the systems. The package can be applied to a broad range of stability and control related problems by applying Matlab tools from other toolboxes to the systems from FDC 1.2. The FDC toolbox is particularly useful for the design and analysis of Automatic Flight Control Systems (AFCS). By giving the designer access to all models and tools required for AFCS design and analysis within one graphical Computer Assisted Control System Design (CACSD) environment the AFCS development cycle can be reduced considerably. The current version 1.2 of the FDC toolbox is an advanced proof of concept package which effectively demonstrates the general ideas behind the application of CACSD tools with a graphical user- interface to the AFCS design process.MODELING AND SIMULATION TERMINOLOGYMILITARY SIMULATIONTECHNIQUES & TECHNOLOGYIntroduction to SimulationDefinitions. Defines simulation, its applications, and the benefits derived from using the technology. Compares simulation to related activities in analysis and gaming.DOD Overview. Explains the simulation perspective and categorization of the US Department of Defense.Training, Gaming, and Analysis. Provides a general delineation between these three categories of simulation.System ArchitecturesComponents. Describes the fundamental components that are found in most military simulations.Designs. Describes the basic differences between functional and object oriented designs for a simulation system.Infrastructures. Emphasizes the importance of providing an infrastructure to support all simulation models, tools, and functionality.Frameworks. Describes the newest implementation of an infrastructure in the forma of an object oriented framework from which simulation capability is inherited.InteroperabilityDedicated. Interoperability initially meant constructing a dedicated method for joining two simulations for a specific purpose.DIS. The virtual simulation community developed this method to allow vehicle simulators to interact in a small, consistent battlefield.ALSP. The constructive, staff training community developed this method to allow specific simulation systems to interact with each other in a single joint training exercise. HLA. This program was developed to replace and, to a degree, unify the virtual and constructive efforts at interoperability.JSIMS. Though not labeled as an interoperability effort, this program is pressing for a higher degree of interoperability than have been achieved through any of the previous programs.Event ManagementQueuing. The primary method for executing simulations has been various forms of queues for ordering and releasing combat events.Trees. Basic queues are being supplanted by techniques such as Red-Black and Splay trees which allow the simulation store, process, and review events more efficiently than their predecessors.Event Ownership. Events can be owned and processed in different ways. Today's preference for object oriented representations leads to vehicle and unit ownership of events, rather than the previous techniques of managing them from a central executive.Time ManagementUniversal. Single processor simulations made use of a single clocking mechanism to control all events in a simulation. This was extended to the idea of a "master clock" during initial distributed simulations, but is being replaced with more advanced techniques in current distributed simulation.Synchronization. The "master clock" too often lead to poor performance and required a great deal of cross-simulation data exchange. Researchers in the Parallel Distributed Simulation community provided several techniques that are being used in today's training environment.Conservative & Optimistic. The most notable time management techniques are conservative synchronization developed by Chandy, Misra, and Bryant, and optimistic synchronization (or Time Warp) developed by David Jefferson.Real-time. In addition to being synchronized across a distributed computing environment, many of today's simulators must also perform as real-time systems. These operate under the additional duress of staying synchronized with the human or system clock perception of time.Principles of ModelingScience & Art. Simulation is currently a combination of scientific method and artistic expression. Learning to do this activity requires both formal education and watching experienced practitioners approach a problem.Process. When a team of people undertake the development of a new simulation system they must follow a defined process. This is often re-invented for each project, but can better be derived from experience of others on previous projects.Fundamentals. Some basic principles have been learned and relearned by members of the simulation community. These have universal application within the field and allow new developers to benefit from the mistakes and experiences of their predecessors.Formalism. There has been some concentrated effort to define a formalism for simulation such that models and systems are provably correct. These also allow mathematical exploration of new ideas in simulation.Physical ModelingObject Interaction. Military object modeling is be divided into two pieces, the physical and the behavioral. Object interactions, which are often viewed as 'physics based', characterize the physical models.Movement. Military objects are often very mobile and a great deal of effort can be given to the correct movement of ground, air, sea, and space vehicles across different forms of terrain or through various forms of ether.Sensor Detection. Military object are also very eager to interact with each other in both peaceful and violent ways. But, before they can do this they must be able to perceive each other through the use of human and mechanical sensors.Engagement. Encounters with objects of a different affiliation often require the application of combat engagement algorithms. There are a rich set of these available to the modeler, and new ones are continually being created.Attrition. Object and unit attrition may be synonymous with engagement in the real world, but when implemented in a computer environment they must be separated to allow fair combat exchanges. Distributed simulation systems are more closely replicating real world activities than did their older functional/sequential ancestors, but the distinction between engagement and attrition are still important. Communication. The modern battlefield is characterized as much by communication and information exchange as it is by movement and engagement. This dimension of the battlefield has been largely ignored in previous simulations, but is being addressed in the new systems under development today.More. Activities on the battlefield are extremely rich and varied. The models described in this section represent some of the most fundamental and important, but they are only a small fraction of the detail that can be included in a model.Behavioral ModelingPerception. Military simulations have historically included very crude representations of human and group decision making. One of the first real needs for representing the human in the model was to create a unique perception of the battlefield for each group, unit, or individual.Reaction. Battlefield objects or units need to be able to react realistically to various combat environments. These allow the simulation to handle many situations without the explicit intervention of a human operator.Planning. Today we look for intelligent behavior from simulated objects. Once form of intelligence is found in allowing models to plan the details of a general operational combat order, or to formulate a method for extracting itself for a difficult situation.Learning. Early reactive and planning models did not include the capability to learn from experience. Algorithms can be built which allow units to become more effective as they become more experienced. They also learn the best methods for operating on a specific battlefield or under specific conditions.Artificial Intelligence. Behavioral modeling can benefit from the research and experience of the AI community. Techniques of value include: Intelligent Agents, Finite State Machines, Petri Nets, Expert and Knowledge-based Systems, Case Based Reasoning, Genetic Algorithms, Neural Networks, Constraint Satisfaction, Fuzzy Logic, and Adaptive Behavior. An introduction is given to each of these along with potential applications in the military environment.Environmental ModelingTerrain. Military objects are heavily dependent upon the environment in which they operate. The representation of terrain has been of primary concern because of its importance and the difficulty of managing the amount of data required. Triangulated Irregular Networks (TINs) are one of the newer techniques for managing this problem. Atmosphere. The atmosphere plays an important role in modeling air, space, and electronic warfare. The effects of cloud cover, precipitation, daylight, ambient noise, electronic jamming, temperature, and wind can all have significant effects on battlefield activities.Sea. The surface of the ocean is nearly as important to naval operations as is terrain to army operations. Sub-surface and ocean floor representations are also essential for submarine warfare and the employment of SONAR for vehicle detection and engagement.Standards. Many representations of all of these environments have been developed.Unfortunately, not all of these have been compatible and significant effort is being given to a common standard for supporting all simulations. Synthetic Environment Data Representation and Interchange Specification (SEDRIS) is the most prominent of these standardization efforts.Multi-Resolution ModelingAggregation. Military commanders have always dealt with the battlefield in an aggregate form. This has carried forward into simulations which operate at this same level, omitting many of the details of specific battlefield objects and events.Disaggregation. Recent efforts to join constructive and virtual simulations have required the implementation of techniques for cross the boundary between these two levels of representation. Disaggregation attempts to generate an entity level representation from the aggregate level by adding information. Conversely, aggregation attempts to create the constructive from the virtual by removing information.Interoperability. It is commonly accepted that interoperability in these situations is best achieved though disaggregation to the lowest level of representation of the models involved. In any form the patchwork battlefield seldom supports the same level of interoperability across model levels as is found within models at the same level of resolution.Inevitability. Models are abstractions of the real world generated to address a specific problem. Since all problems are not defined at the same level of physical representation, the models built to address them will be at different levels. The modeling an simulation problem domain is too rich to ever expect all models to operate at the same level. Multi-Resolution Modeling and techniques to provide interoperability among them are inevitable.Verification, Validation, and AccreditationVerification. Simulation systems and the models within them are conceptual representations of the real world. By their very nature these models are partially accurate and partially inaccurate. Therefore, it is essential that we be able to verify that the model constructed accurately represents the important parts of the real world we are try to study or emulate.Validation. The conceptual model of the real world is converted into a software program. This conversion has the potential to introduce errors or inaccurately represent the conceptual model. Validation ensures that the software program accurately reflects the conceptual model.Accreditation. Since all models only partially represent the real world, they all have limited application for training and analysis. Accreditation defines the domains and。

把你想发明的东西介绍给大家英语作文

把你想发明的东西介绍给大家英语作文全文共3篇示例，供读者参考篇1A World-Changing Invention: The Universal TranslatorHey everyone! I have this really cool idea for an invention that could honestly change the world. Hear me out – it's going to sound kind of crazy at first, but just stick with me.Imagine being able to understand any language in the world just like that. No more struggling through language classes or getting lost in translation. My invention, which I'm calling the Universal Translator, would instantly translate any spoken or written language into your native tongue in real-time. How awesome would that be?Just think about how much easier communication would become across the globe. Cultural and language barriers would basically disappear overnight. People from completely different backgrounds could understand each other perfectly. It could help prevent misunderstandings that lead to conflicts. Heck, we might even make first contact with aliens someday, and this babywould let us communicate with them! Okay, maybe that's a little far-fetched, but you get the idea.So how would this Universal Translator work exactly? Well, the core technology would involve some seriously advanced speech recognition, natural language processing, and machine translation powered by artificial intelligence. Basically, the device would first identify and transcribe the spoken words into text using speech recognition. Then, an AI translation model would take that text, analyze its meaning and context, and translate it into the desired output language. Finally, a voice synthesis component would articulate the translation out loud.For translating written text, it would use optical character recognition to extract the words from images or documents first before feeding it into the AI translation pipeline. The user interface would be super simple – you could just point your smartphone camera at some text and it would overlay the translation right on top in augmented reality mode. Or for voice, you'd just enable translation mode and it would work like a real-time interpreter whispering in your ear.Now I know what you're thinking – we already have translation apps and devices that can sort of do this, right? Yeah, that's true to some extent. But here's the thing – those existingtools rely mostly on phrase-based statistical translation which isn't perfect. They struggle with less common languages, idioms, context, and just generally sound quite unnatural.My Universal Translator, on the other hand, would use the latest transformer-based neural machine translation models which are way more advanced. These can better understand the full meaning and context behind phrases to produce natural, fluent translations that sound like they came from a native speaker. The AI model would be trained on a massive dataset of translated texts and speech across hundreds of languages to a crazy level of accuracy.I'm picturing integrating this core translation tech into different form factors – like wireless earbuds for voice translation, smart glasses for augmented reality text overlays, or even a handheld scanner for menus, signs, you name it. It could be built into smartphones, car navigation systems, video calling apps –basically anywhere translation would be useful.Just imagine going on vacation and being able to chat with the locals in their native tongue effortlessly. Or being a doctor and communicating directly with patients to better understand their symptoms, no interpreter needed. Businesses could expand globally without worrying about language barriers. Maybe itcould even help unite the world by allowing people from different cultures to understand each other.Of course, bringing a sci-fi invention like this to reality wouldn't be easy. There are some major challenges I'd need to overcome:First off, building AI translation models that work for hundreds of languages at human levels of accuracy is insanely difficult from a machine learning perspective. I'd need teams of computational linguists and engineers to create and train these massively complex neural networks. Not to mention the resources to feed them absolutely gigantic datasets of transcribed speech and text across all these languages.Secondly, the speech recognition, optical character recognition, and audio synthesis aspects would require pretty advanced multimodal AI too. It's one thing to translate plain text, but understanding speech with all its ambiguities and accents adds another layer of complexity.Third, I'd have to figure out the hardware and form factor side of things to integrate all these AI capabilities into small, power-efficient devices people can actually carry around conveniently. Things like specialized AI chipsets, energy-efficientprocessors, microphones, and compact optics and displays. That's a big hardware and engineering challenge in itself.Then of course, the elephant in the room – I'd need a LOT of money and resources to make this happen! I'm talking billions of dollars to hire the AI researchers, engineers, linguists, and teams required to pull this off. Fundraising from investors and navigating intellectual property would be super difficult for a teenager like me.Despite all these hurdles though, I truly think the Universal Translator is an invention that's worth pursuing. The potential impacts on communication, education, diplomacy, business –you name it – would be just astronomical. Maybe it's naive for a kid to dream this big, but I believe the benefits to society would be invaluable.So those are my ideas for revolutionizing how we communicate across languages and cultures! Let me know what you think – would a Universal Translator be helpful or not? What other huge challenges am I not considering? I'd love to get your perspectives. Who knows, maybe with some hard work and a lot of luck, this crazy idea could become a reality someday!篇2The Incredible MemVR: A Revolutionary Learning HeadsetHave you ever struggled to memorize important facts or concepts? Do you find it challenging to stay focused during long study sessions? Well, get ready for a game-changing invention that will revolutionize the way we learn and retain information –the MemVR!As a student constantly juggling between classes, extracurricular activities, and social life, I've often found myself frustrated by the limitations of traditional learning methods. Sitting hunched over textbooks for hours on end, trying to cram information into my brain, only to forget most of it a few days later, is an experience all too familiar to many of us.But what if there was a way to make learning not only more effective but also engaging and fun? That's where the MemVR comes in – a groundbreaking virtual reality headset designed specifically for educational purposes.Imagine being able to step into a fully immersive virtual environment tailored to the subject you're studying. Instead of staring at dry diagrams in a textbook, you could explore a 3D model of the human body, zooming in on individual organs and observing their functions in real-time. Or picture yourself walking through a virtual reconstruction of ancient Rome,witnessing historical events unfold before your eyes, and truly understanding the cultural context behind them.The MemVR's unique selling point lies in its ability to leverage the power of experiential learning. Research has shown that we retain information better when we actively engage with it, rather than passively consuming it. By creating immersive simulations that allow users to interact with concepts and scenarios, the MemVR taps into our brain's natural ability to learn through experience, making the process not only more effective but also incredibly captivating.But the MemVR isn't just about visuals; it's a multi-sensory experience. Imagine learning about music theory by actually composing and playing virtual instruments, or studying chemistry by manipulating virtual molecules and observing their reactions. The possibilities are endless, and the potential for enhancing our understanding and retention is truly remarkable.One of the key features of the MemVR is its adaptability to different learning styles. Some students thrive with visual aids, while others prefer hands-on activities or auditory cues. The MemVR caters to all these preferences by offering a range of customizable learning environments and interactive tools. Whether you're a kinesthetic learner who prefers physicalsimulations or an auditory learner who benefits from narrated explanations, the MemVR has you covered.But the MemVR isn't just for individual learning; it also opens up a world of collaborative possibilities. Imagine being able to connect with classmates or even experts from around the globe in a shared virtual space, where you can work together on projects, engage in discussions, and exchange ideas in a truly immersive setting. This not only fosters teamwork and communication skills but also creates a dynamic and engaging learning community.Of course, one might wonder about the potential side effects of prolonged virtual reality exposure. However, the MemVR has been designed with safety in mind. Its ergonomic design and advanced eye-tracking technology minimize strain and discomfort, while built-in timers and reminders encourage regular breaks to prevent excessive use.Furthermore, the MemVR's software incorporates educational best practices and proven learning techniques. From spaced repetition to gamification elements, the MemVR ensures that users not only enjoy the experience but also retain the information effectively.Imagine the impact the MemVR could have on education. No longer would students be confined to the limitations of textbooks and traditional classrooms. Instead, they could explore vast virtual worlds, pushing the boundaries of their imagination and curiosity. Learning would become an adventure, a journey of discovery, and a truly unforgettable experience.But the potential applications of the MemVR extend far beyond the classroom. Training simulations for various professions, from healthcare to aviation, could benefit greatly from the immersive and interactive nature of the MemVR. Imagine medical students being able to practice complex surgical procedures in a risk-free virtual environment, or pilots training for emergency scenarios without ever leaving the ground.The MemVR represents a revolution in the way we approach learning and knowledge acquisition. It's not just a headset; it's a gateway to a world of limitless possibilities, where education becomes an immersive, engaging, and truly transformative experience.So, who's ready to embark on this incredible journey? With the MemVR, the future of learning is closer than you think. Let'sembrace this revolutionary technology and unlock the full potential of our minds, one virtual adventure at a time.篇3A Revolutionary Invention to Simplify Our LivesHave you ever felt like there just aren't enough hours in the day to get everything done? As students, we're constantly juggling classes, homework, extracurricular activities, social lives, and for some of us, jobs or family responsibilities too. It can be overwhelming trying to stay on top of it all. That's why I've invented something that I believe could be a real game-changer when it comes to better managing our time and reducing stress levels. Let me tell you all about it!My invention is a smart virtual assistant that I call "TempoAI." It's an artificial intelligence program that essentially acts as your own personal task manager and schedule optimizer. Using advanced algorithms and machine learning, TempoAI analyzes your daily commitments, priorities, and goals to create a customized and dynamic schedule that makes the most efficient use of your time.Here's how it works: you start by inputting all of your recurring events and responsibilities into the TempoAI app –things like your class schedule, work shifts, practice times for clubs or sports, and any other regular commitments. You'll also enter important deadlines, like due dates for assignments and projects. TempoAI takes all of this data and starts building out a basic weekly calendar for you.But TempoAI doesn't stop there. It then prompts you to prioritize which activities and tasks are most important to you. Do you want to ensure you get 8 hours of sleep each night? Make that a high priority. Need to reserve 2 hours daily for your part-time job? TempoAI will block that time. Want to spend at least an hour at the gym 5 days a week? Just let the AI know and it will schedule it in at optimal times based on your other commitments.The true power of TempoAI, however, comes from its ability to make dynamic adjustments to your schedule as needed. Let's say you have a huge research paper due at the end of the month for one of your classes. You input the deadline and TempoAI will provide recommendations on how to break down the work over several days, scheduling incremental mini-deadlines for completing research, drafting sections, revising, etc. If you end up falling behind on your self-imposed timeline, TempoAI willrecognize this and reshuffle your schedule to ensure you can get back on track without conflicts.TempoAI can also learn your personal habits over time through manual inputs and integrations with smart home devices and wearable tech. For example, it might notice that you tend to be most productive in the morning hours before noon. It would then prioritize scheduling。

无线通信基础知识讨论(Discussion on basic knowledge of wireless communication)

无线通信基础知识讨论（Discussion on basic knowledge ofwireless communication）The coherent time is the maximum time difference range for the channel to remain constant. The coherent bandwidth is similar to the maximum frequency difference range where the channel remains constant. To understand this concept from the angle of comparative image: diversity time diversity requirements two launch time should be greater than the channel coherence time, i.e. if the launch time is less than the coherence time of the channel, the signal is the two launch will experience the same fading diversity, anti fading effect does not exist, the coherence bandwidth can be understood from frequency diversity.5. What are the definitions of frequency selective fading, flat fading, fast fading and slow fading?Frequency selective fading and flat fading are defined by relative coherent bandwidth. The larger the signal bandwidth is, the more obvious the frequency selective fading is, and the more sensitive to multipath, the more serious the ISI is.Fast fading and slow fading are defined by relative coherent time. The larger the symbol time or code time, the faster fading (but it can be very good against frequency selective fading).These two types of decline are contradictory and should be considered when designing a system.6, wireless communication books are on the top7, multipath channel modeling requires that multipath should be independent. How should independence be reflected in channel modeling? This should also be the case for MIMO channels and multiuser channels.The correlation coefficients of the two paths are as small as possible, or modeled separately according to what is said above.8, MIMO channel modeling, sometimes required to consider the correlation between antennas, and how this correlation should be modeled?Firstly, the correlation coefficient matrix is constructed, and then the Chol is decomposed. The matrix obtained by the decomposition is multiplied by the signal of each antenna.Biezs was published at 20:53 2006-10-25[quote] or 2006-10-25 20:42 published by [i]lucatt0415[/i] in(but it's good against frequency selective fading).These two types of decline are contradictory and should be considered when designing a system.[/quote]Can you explain why these two types of decline are contradictory?Biezs was published at 20:56 2006-10-25[quote] or 2006-10-25 20:42 published by [i]lucatt0415[/i] inThe correlation coefficients of the two paths are as small as possible, or modeled separately according to what is said above. [/quote]The relative coefficient of the two paths as small as possible is our goal, but I'm not sure what the so-called "individual modeling" means. For example, what does this single modeling mean for the traditional Jakes model?Lucatt0415 was published at 23:39 2006-10-25Can you explain why these two types of decline are contradictory?The reasons are as follows: the coherence bandwidth requirements of signal bandwidth less than the channel against frequency selective fading, which requires bandwidth as small as possible, from the time it is symbolic time or chip time as large as possible, but with the increase of symbol or of the chip cycle, and when the channel phase do when a long time, it is difficult to fight against fast fading so, the design of the system should fully consider the application object system, reasonable design parameters.Lucatt0415 was published at 23:44 2006-10-25Or in accordance with the MIMO modeling method is better, that is, the use of coefficient correlation matrix for Chol decomposition, and then use the decomposed matrix multiplied by two signals,Individual modeling does not necessarily guarantee that the two paths are uncorrelated.SWAs was published in 2006-10-26 08:46Large scale fading is mainly path loss, which can be approximated by free space propagation model, but some characteristics are different, such as fading index, and so onWhat are the factors associated with the lognormal variance of shadow fading? How much is the typical value?OFDM system is used to discuss the guiding role of coherent time and coherent bandwidth in practical system design.In addition to the fading characteristics of wireless channel, which is different from wired channel, we must consider, such as multi user shared channel, multiple access methods are discussed, the discussion on the basis of the understanding of great help. A good subject. I hope you will have a heated discussion.Lucatt0415 was published in 2006-10-26 08:54The three effects of the wireless channel are missing:Three effects of wireless channelShadow effect, near far effect and Doppler effect(1) shadow effect: when the electric wave is disturbed by undulating terrain, buildings, vegetation and other obstacles on the propagation path, the half blind zone of electromagnetic field will be produced(2): Near far effect due to random mobility receiving users, mobile users and the distance between the base station and then low change, if the mobile users transmit power, then arrive at the base station signal is strong if different from the base station near strong signal, far from the base station signal is weak. In which the base station receiver appears strong stronger and the weak weaker and strong weak phenomenon. This is the reason for power control(3) Doppler effect: because of the high speed motion of the mobile user in the receiving state, the propagation frequency is diffused, and the diffusion degree is directly proportional to the user's moving speed.Lcj2212916 was published at 18:23 2006-10-26What are the characteristics of wireless (mobile) channels?Turn from:[url]/tongxin/wjaspx/wuxianxindao detexing.aspx[/url]Radio waves in different frequency bands have different propagation modes and characteristics.The mobile communication system to work in the VHF and UHF bands, radio wave propagation is the main way of space, namely direct wave, refraction wave, wave scattering and their synthesis wave.In the land mobile system, the mobile station is in the city or in the buildings in the complex terrain area, the antenna will receive signals from multiple paths came, coupled with the mobile station itself, the wireless channel between the mobile station and the base station is changeable and difficult to control.In analog wired channels, the typical signal-to-noise ratio is about 46dB, that is, the signal level is 40000 times higher than the noise level, and for the wired channel, the quality of transmission is controllable. By selecting the right materials and careful processing, you can ensure that there is a relatively stable electrical environment in the wired transmission system. As a result, the signal-to-noise ratio usually does not exceed 1~2dB in a wired transmission line. Only when a line has been running for a long period of time, will the loss of the line gradually reach 10~15dB, so in this case, the line will need to be updated.In terrestrial mobile radio channels, a sudden drop in signal intensity, known as fading, is frequent, with a depth of about 30dB.In urban environments, the number of signals received by a mobile station on a fast moving vehicle can decline significantly within a second. This kind of fading seriously deteriorates the quality of received signals and affects the reliability of communications.In the cellular mobile environment, the same frequency interference is a problem that must be paid attention to. When fading occurs, the signal to be received may be weaker than the interference signal from the same frequency cell base station, so the receiver will easily lock on the wrong signal.The analog mobile communication adopts FM signal, and the capture effect of FM mode has a certain inhibitory effect on the same frequency interference. The fading phenomenon will significantly change the characteristics of FM signal and weaken its capture effect. For digital transmission, fading will greatly increase bit error rate (BER).The fading characteristics of mobile channels depend on the propagation environment of radio waves. Different environments, their propagation characteristics are not the same.A large city with many tall buildings, for example, has a very different spread environment compared to a flat open country, and the mobile channel characteristics vary greatly. The communication environment itself is quite complex, which makes the mobile channel characteristics is very complex.It is spread in different environment, led directly to the multipath delay size have obvious difference, if we want totransmit high-speed data, T symbol period should be as small as possible, but the smaller the T, the ability to resist multipath delay is weak, resulting in a OFDM, it is because the symbol period in OFDM system because of the parallel transmission of variable length, which can effectively resist the multipath delay.Complex and harsh propagation conditions are the characteristics of mobile channels. In order to maintain acceptable transmission quality under such propagation conditions, a variety of technical measures must be adopted to counteract the adverse effects of fading. Therefore, a variety of anti fading technologies have been developed, including diversity, spread spectrum / frequency hopping, equalization, interleaving and error correction coding. In addition, the signal transmission mode, such as modulation mode, will also have a certain adaptability to fading in the channel.[[i] this post was finally edited by sreight at 19:14 2006-10-26 on [/i]]Lcj2212916 was published at 20:29 2006-10-26Provide two reference materials, the basic knowledge written in more detail, the Xi'an electronics division of the big lesson plans!!!We mainly discuss large scale and small scale fading and general modeling of channelBiezs was published at 22:21 2006-10-26[quote] or 2006-10-25 23:44 published by [i]lucatt0415[/i] inOr in accordance with the MIMO modeling method is better, that is, the use of coefficient correlation matrix for Chol decomposition, and then use the decomposed matrix multiplied by two signals,Individual modeling does not necessarily guarantee that the two paths are uncorrelated. [/quote]Could you give me a reference to what you call this modeling approach? Thank youSnakehl was published at 12:57 2006-10-27See friends upstairs discussed so warm, I can not help but make little excitement, ha ha; on the number of points, some things I don't agree, now summarized as follows:1) the coherent bandwidth of the channel,The concept of coherent time, first of all, how to deduce from the theoretical point of view, that is, from the formula point of view, so as to deepen the understanding of the nature of the two, this is very important, you can refer to relevant literature.The coherence bandwidth: first of all, this is caused by multipath transmission channel, the received signal amplitude frequency response to keep the relevant strongest in thefrequency interval within a certain interval is called coherent bandwidth; it is called frequency selective or flat fading, is compared with the emission signal bandwidth itself, has nothing to do with the emission signal symbol cycle;For coherent time, the relative motion of the two sides of the motion leads to the frequency spread of the received signal. From the point of view of time, the channel remains the strongest correlation in the relevant time interval. The term "time selectivity", i.e., "fast change" or "slow change", is the correlation between the symbol cycle of the transmitted signal and the relevant time. It is independent of the transmitted symbol bandwidth;For the above two, the former is from frequency domain to time domain, and the latter is better understood from frequency domain to time domain;2) for channel modeling, whether MIMO or not, whether or not, are the first to establish a single path channel model; many modeling methods, mainly uses two methods, one is SOS, the second is the classical Doppler power spectrum using the impulse response method based on the modeling; a relatively simple method. The classic clarcle is an example, but it is mainly based on various correction models, so that it can better satisfy the higher order statistical characteristics of the channel. As long as the establishment of the single channel model, can test the various test statistics, general two order statistics can meet the standard, modeling the MIMO channel model, can be independent if relevant, is simple and a correlation matrix can be either launch or receive antennacorrelation;3) in addition to say is: various characteristics and modeling methods of wireless channel, although the wireless communication for so many years, but always feel to understand the channel is not easy, a warm welcome into the depth of up to a theoretical point of view to discuss;The above only personal opinions are for reference only!SWAs was published at 13:41 2006-10-27About coherent bandwidth (time) itself is a fuzzy concept, in brief, within certain bandwidth (time) interval, the channel response remains almost constant, with a variety of factors. Almost the same multiple standards, such as 3dB standard, to thoroughly understand may want to consider with the corresponding domain, such as profile and Doppler spectrum, and some books directly to the corresponding domain reciprocal relationship. The key is to understand its influence on the design of communication system, what factors need to be considered, such as the design of the OFDM system, to take the number of band spacing, take a little more good, take a little less good, the length of cyclic prefix with long, what is the effect of a little more, what is the impact of the smaller. As for coherent bandwidth, what is the bottom of the specific value? It may not matter much.Biezs was published at 15:24 2006-10-28[quote] or 2006-10-27 12:57 published by [i]snakehl[/i] inFrequency selective or flat fading is comparable to the bandwidth of the transmitted signal itself, independent of the symbol period of the transmitted signal [/quote]Basically agree with this statement, but is there no relation between the signal cycle of the transmitted signal and the bandwidth of the signal? I have always felt that there is a certain relationship between the two, such as B ~ 1/TBiezs was published at 16:30 2006-10-28About single path Rayleigh fading channel modeling methods, what are the classic reference books or paper, for everyone to recommend it? Are there any friends on the page who study channel modeling?How can the independence of multipath Rayleigh fading channels and multiuser channels be guaranteed? Take the traditional Jakes model for example, how do we generate independent fading?Snakehl was published at 10:13 2006-10-30Post an article about channel modeling. I used, we can refer to!To improve academic exchange, the article is free!The phoenix trees rain at 10:19 2006-11-16Block fading channels mean that the intensity of the receivedsignal changes over the time period of the magnitude of the symbol timeA slow fading channel means that the strength of the received signal remains constant over multiple symbol cyclesNumbman was published at 11:15 2006-11-16The wireless mobile channel, the Doppler shift of mobile station itself generated by the movement.Coherent time means that at this time the channel changes can be viewed as invariant.There are three effects, the propagation loss of radio waves in free space, which is called large-scale fadingShadow fading refers to fading caused by changes in propagation environment, also known as medium scale fadingMultiple fading refers to various kinds of reflection, diffraction and diffraction, which cause signals to reach the receiving end after multiple paths. The delay, fading and phase of each component are different, also called small scale fadingYangsheng0328 was published at 13:35 2006-11-17Relative to a finite channel,What are the characteristics of wireless (mobile) channels?Relative to the cable channel. The characteristics of wireless channel: 1. (multipath frequency selective fading; 2 corresponding), time-varying channels (corresponding to the time selective fading). From the channel model can be seen, the cable channel corresponding to the constant parameter channel (path delay, fading, Chi Hengding), and the corresponding wireless channel the model of time-varying channel (multipath fading, the amplitude varies with time, delay changes with the environment).2, the loss in wireless channel is generally divided into three levels, large scale (also called path loss), mesoscale (shadow fading) and small scale fading. What are the causes of the three losses? What are the characteristics of each? Shadow fading is generally modeled, and why is it distributed? What are the commonly used probability distributions in small-scale fading analysis?The propagation of electromagnetic waves to energy loss (and the transmission distance is proportional to the frequency). This is known as the large scale loss; slow fading is generally a geographical environment (caused by obstructions). While the fast fading (small scale fading) is caused by multipath.4, what is the coherent time? What is coherent bandwidth?The coherence time is due to the time-varying channel (Doppler frequency shift)Coherent bandwidth is caused by multipath (frequency selective fading). In the coherent bandwidth, the amplitude of thefrequency component of the signal will not be attenuated to a small even 0., so that the signal will not suffer much5. What are the definitions of frequency selective fading, flat fading, fast fading and slow fading?1,2,4 has instructionsYangsheng0328 was published at 14:02 2006-11-17What are the characteristics of a wireless (mobile) channel relative to a finite channel?Relative to the cable channel. The characteristics of wireless channel: 1. (multipath frequency selective fading; 2 corresponding), time-varying channels (corresponding to the time selective fading). From the channel model can be seen, the cable channel corresponding to the constant parameter channel (path delay, fading, Chi Hengding), and the corresponding wireless channel the model of time-varying channel (multipath fading, the amplitude varies with time, delay changes with the environment).2, the loss in wireless channel is generally divided into three levels, large scale (also called path loss), mesoscale (shadow fading) and small scale fading. What are the causes of the three losses? What are the characteristics of each? Shadow fading is generally modeled, and why is it distributed? What are the commonly used probability distributions in small-scale fading analysis?The propagation of electromagnetic waves to energy loss (and the transmission distance is proportional to the frequency). This is known as the large scale loss; slow fading is generally a geographical environment (caused by obstructions). While the fast fading (small scale fading) is caused by multipath.4, what is the coherent time? What is coherent bandwidth?The coherence time is due to the time-varying channel (Doppler frequency shift)Coherent bandwidth is caused by multipath (frequency selective fading). In the coherent bandwidth, the amplitude of the frequency component of the signal will not be attenuated to a small even 0., so that the signal will not suffer much5. What are the definitions of frequency selective fading, flat fading, fast fading and slow fading?1,2,4 has instructionsKarmark was published at 16:23 2006-11-171, what are the characteristics of a wireless (mobile) channel relative to a finite channel?The radio (mobile) channel is a variable statistical channel, whose channel transfer function varies with time and can only be considered in terms of its statistical characteristics2, the loss in wireless channel is generally divided into threelevels, large scale (also called path loss), mesoscale (shadow fading) and small scale fading. What are the causes of the three losses? What are the characteristics of each? Shadow fading is generally modeled, and why is it distributed? What are the commonly used probability distributions in small-scale fading analysis?Large scale loss is mainly caused by refraction and diffraction of radio waves in the course of transmission. It has the characteristics of slow change over time;Shadow fading is generally modeled as a Gauss exponential distribution Want to know the formula can look at the relevant parts of the mobile communication principleSmall scale fading is mainly due to the complex environment around the end accept scattering caused by the movement of very tiny caused by receiving level very big change (minus 30 to minus 40dB), can be modeled as Rayleigh (no horizon component) or Rician distribution (with Los component)4, what is the coherent time? What is coherent bandwidth?Coherence time, the interval between the first arrival of a symbol and the last time it arrivesThe coherence bandwidth is the reciprocal of the coherence timeBiezs was published at 21:36 2006-11-17[quote] or 2006-11-17 16:23 published by [i]karmark[/i] in1, what are the characteristics of a wireless (mobile) channel relative to a finite channel?The radio (mobile) channel is a variable statistical channel, whose channel transfer function varies with time and can only be considered in terms of its statistical characteristics2, wireless channel loss is generally divided into three levels, large scale (also known as path loss), medium, [/quote]Finally, the concept of error, please see the previous replies, or access to mobile communications principles of teaching materials.Kangyatou was published at 20:10 2007-1-17The understanding of the channel is the foundation and the most critical problem of communication. Any system implementation can be realized on the basis of fully understanding the channel and the simulation channel。

声学场景和事件的检测及分类

7002018年9月Rev.Lett.,2011,106(21):213902.[22]Mellin S D,Nordin G P.Limits of scalar diﬀraction the-ory and an iterative angular spectrum algorithm forﬁnite aperture diﬀractive optical element design[J].Opt.Ex-press,2001,8(13):705–722.[23]Gerchberg R W,Saxton W O.A practical algorithm forthe determination of phase from image and diﬀraction plane pictures[J].Optik,1972,35(2):237–250.[24]St-Hilaire P.Phase proﬁles for holographic stereograms[J].Opt.Eng.,1995,34(1):83–90.[25]Gallagher N C,Liu B.Method for computing kinoformsthat reduces image reconstruction error[J].Appl.Opt., 1973,12(10):2328–2335.[26]Fienup J R.Iterative method applied to image reconstruc-tion and to computer-generated holograms[J].Opt.Eng., 1980,19(3):297–305.[27]Wyrowski F,Bryngdahl O.Iterative fourier-transform al-gorithm applied to computer holography[J].J.Opt.Soc.Am.A.,1988,5(7):1058–1065.[28]Wyrowski F,Bryngdahl O.Digital holography as partof diﬀractive optics[J].Rep.Prog.Phys.,1991,54(12): 1481–1571.........................................................................................................⋄声学新闻和动态⋄声学场景和事件的检测及分类随着计算机听觉场景分析领域的发展，声学场景和事件的检测、分类得到了越来越多的关注。

ACM期刊及会议文献列表

ACM期刊及会议文献列表 ACM 期刊清单1 ACM Computing Surveys (CSUR)2 ACM Journal of Computer Documentation (JCD)3 ACM Letters on Programming Languages and Systems (LOPLAS)4 Journal of Educational Resources in Computing (JERIC)5 Journal of Experimental Algorithmics (JEA)6 Journal of the ACM (JACM) ACM 杂志清单1 Communications of the ACM2 Crossroads3 StandardView4 Ubiquity5 eLearn6 intelligence7 interactions8 netWorker ACM学报清单1 ACM Transactions on Asian Language Information Processing (TALIP)2 ACM Transactions on Computational Logic (TOCL)3 ACM Transactions on Computer Systems (TOCS)4 ACM Transactions on Computer-Human Interaction (TOCHI)5 ACM Transactions on Database Systems (TODS)6 ACM Transactions on Design Automation of Electronic Systems (TODAES)7 ACM Transactions on Graphics (TOG)8 ACM Transactions on Information Systems (TOIS)9 ACM Transactions on Information and System Security (TISSEC)10 ACM Transactions on Internet Technology (TOIT)11 ACM Transactions on Mathematical Software (TOMS)12 ACM Transactions on Modeling and Computer Simulation (TOMACS)13 ACM Transactions on Programming Languages and Systems (TOPLAS)14 ACM Transactions on Software Engineering and Methodology (TOSEM)15 IEEE/ACM Transactions on Networking (TON) ACM会议清单1 ACM Policy2 ACM Southeast Regional Conference3 ACM/CSC-ER4 Computer graphics, virtual reality, visualisation and interaction in Africa5 International Conference on Autonomous Agents6 ACM International Conference Proceeding Series7 Analysis of Neural Net Applications Conference8 Annual Simulation Symposium9 Aspect-oriented software development10 International Conference on APL11 with EDA Technofair Design Automation Conference Asia and South Pacific12 Architectural Support for Programming Languages and Operating Systems13 ACM SIGACCESS Conference on Assistive Technologies14 AVI15 Creativity and Cognition16 International Conference on Compilers, Architecture and Synthesis for Embedded Systems17 Computer Architecture Workshop18 Conference on Computer and Communications Security19 Consortium for Computing Sciences in Colleges20 Contemporary Computing in Ukraine21 Conference On Computing Frontiers22Computers, Freedom and Privacy23 Code Generation and Optimization24 Conference on Human Factors in Computing Systems25 Conference on Information and Knowledge Management26 Conference On Information Technology Education27 International Conference on Hardware Software Codesign28 Annual Workshop on Computational Learning Theory29 Applications, Technologies, Architectures,and Protocols for Computer Communication30 Special Interest Group on Computer Personnel Research Annual Conference31 Symposium on Computers and the Quality of Life32 ACM Annual Computer Science Conference33 Computer Supported Cooperative Work34 ACM Conference on Universal Usability35 Collaborative Virtual Environments36 Annual ACM IEEE Design Automation Conference37 Designing Augmented Reality Environments38 Design, Automation, and Test in Europe39 Distributed event-based systems40 Workshop on Discrete Algothrithms and Methods for MOBILE Computing and Communications41 Symposium on Designing Interactive Systems41 International Conference on Digital Libraries43 Data Mining And Knowledge Discovery44 Data Warehousing and OLAP45 International Symposium on Databases for Parallel and Distributed Systems46 Designing Pleasurable Products And Interfaces47 ACM Workshop On Digital Rights Management48 DSL49 Designing For User Experiences50 Document Engineering51 Workshop on Dynamic and Adaptive Compilation and Optimization53 Electronic Commerce54 Ethics in the Computer Age55 OOPSLA workshop on eclipse technology eXchange56 European Design and Test Conference57 International Conference On Embedded Software58 Annual ERLANG Workshop59 Eye Tracking Research & Application60 ACM SIGOPS European Workshop61 European Design Automation Conference62 Workshop on Formal Methods in Security Engineering63 Formal Methods in Software Practice64 Formal Ontology in Information Systems65 Functional Programming Languages and Computer Architecture66 International Symposium on Field Programmable Gate Arrays67 Genetic And Evolutionary Computation Conference68 Geographic Information Systems69 Great Lakes Symposium on VLSI70 GRAPHICON71 Computer graphics and interactive techniques in Austalasia and South East Asia72 Conference on Supporting Group Work73 History of Medical Informatics74 History of Programming Languages75 History of Personal Workstations76 History of Scientific and Numeric Computation77 Conference on Hypertext and Hypermedia78 SIGGRAPH/EUROGRAPHICS Workshop On Graphics Hardware79 Haskell80 Hypercube Concurrent Computers and Applications81 International Conference on Artificial Intelligence and Law82 International Conference on Computer Aided Design83 International Conference on Information and Computation Economies84 International Conference on Functional Programming85 International Conference on Information Systems86 ICMI87 International Conference on Supercomputing88 International Conference on Software Engineering89 International Conference On Service Oriented Computing90 Interaction Design And Children91 International conference on Industrial and engineering applications of artificial intelligence and expert systems92 Internet Measurement Conference93 Workshop on I/O in Parallel and Distributed Systems94 Information Processing In Sensor Networks95 Information Quality in Informational Systems96 International Workshop on Information Retrieval with Asia Languages97 International Workshop on Real-time Ada Issues98 International Conference on Computer Architecture99 International Symposium on Low Power Electronics and Design100 International Symposium on Methodologies for Intelligent Systems101 International Symposium on Memory Management102 International Symposium on Physical Design103 International Software Process Workshop 104 International Conference on Symbolic and Algebraic Computation105 International Symposium on Systems Synthesis106 International Symposium on Software Testing and Analysis107 Annual Joint Conference Integrating Technology into Computer Science Education108 International Conference on Intelligent User Interfaces109 Interpreters, Virtual Machines And Emulators110 International Workshop on Software Specifications & Design111 Information security curriculum development112 Java Grande Conference113 International Conference On Knowledge Capture114 Conference on Knowledge Discovery in Data115 Language, Compiler and Tool Support for Embedded Systems116 Conference on LISP and Functional Programming117 International Conference On Mobile Data Management118 International Symposium on Microarchitecture119 International Multimedia Conference120 ACM International Workshop On Multimedia Databases121 Memory System Performance122 International Workshop on Modeling Analysis and Simulation of Wireless and Mobile Systems123 Multiple-Valued Logic124 Multimedia Middleware Workshop125 International Conference on Mobile Computing and Networking126 International Workshop on Data Engineering for Wireless and Mobile Access127 International Symposium on Mobile Ad Hoc Networking & Computing128 International Conference On Mobile Systems, Applications And Services129 International Workshop on Network and Operating System Support for Digital Audio and Video130 Non-Photorealistic Animation and Rendering131 New Paradigms in Information Visualization and Manipulation131 New Security Paradigms Workshop132 Network and System Support for Games133 International Workshop on Object-Oriented Database Systems134 Conference on Object Oriented Programming Systems Languages and Applications135 OOPWORK136 PACT137 Workshop on Parallel and Distributed Simulation138 International Symposium on Parallel Symbolic Computation139 Workshop on Program Analysis for Software Tools and Engineering140 Participatory Design141 ACM/SIGPLAN Workshop Partial Evaluation and Semantics-Based Program Manipulation142 Conference on Programming Language Design and Implementation143 Annual ACM Symposium on Principles of Distributed Computing144 Symposium on Principles of Database Systems145 ACM Workshop On Principles Of Mobile Computing146 Annual Symposium on Principles of Programming Languages147 International Conference on Principles and Practice of Declarative Programming 148 Symposium on Principles and Practice of Parallel Programming149 Principles and Practice of Parallel Programming150 Parallel Rendering Symposium151 Parallel and large-data visualization and graphics152 ACM Workshop on Role Based Access Control153 Annual Conference on Research in Computational Molecular Biology154 Workshop On Rule-Based Programming155 Symposium on Applied Computing156 Symposium on Access Control Models and Technologies157 Workshop on Security of ad hoc and Sensor Networks158 SBCCI159 Conference on High Performance Networking and Computing160 Symposium on Computer Animation161 Symposium on Compiler Construction162 Spring Conference on Computer Graphics163 Annual Symposium on Computational Geometry164 Software Configuration Management Workshop165 Simulation of Computer Networks166 Conference On Embedded Networked Sensor Systems167 Software Engineering Symposium on Practical Software Development Environments 168 Symposium on Environments and Tools for Ada169 Symposium on Interactive 3D Graphics170 Annual International Conference on Ada171 Technical Symposium on Computer Science Education172 ACM Special Interest Group for Design of Communications173 SIGFORTH174 International Conference on Computer Graphics and Interactive Techniques175 Annual ACM Conference on Research and Development in Information Retrieval176 Joint International Conference on Measurement and Modeling of Computer Systems 177 International Conference on Management of Data178 SIGPLAN179 Symposium on Small Systems180 Foundations of Software Engineering181 User Services Conference182 International Workshop on System-Level Interconnect Prediction183 Symposium on Language Issues in Programming Environments184 ACM Symposium on Solid Modeling and ApplicationsSymposium on Discrete Algorithms185 ACM Symposium on Operating Systems Principles186 ACM Symposium on Parallel Algorithms and Architectures187 Symposium on Parallel and Distributed Tools188 Symposium on Software Reusability189 Annual ACM Symposium on Theory of Computing190 Software Visualization191 SIGGRAPH Video Review192 Symposium on Symbolic and Algebraic Manipulation193 Richard Tapia Celebration Of Diversity In Computing194 Theoretical Aspects Of Rationality And Knowledge195Timing Issues In The Specification And Synthesis Of Digital Systems196 Trends and Direction in Expert Systems197 Types In Languages Design And Implementation198 Symposium on User Interface Software and Technology199 Virtual reality, archeology, and cultural heritage200 IEEE Visualization201 Virtual Reality Modeling Language Symposium202 Virtual Reality Software and Technology203 Symposium on Volume Visualization204 International Conference on Work activities Coordination and Collaboration 205 Washington Ada Symposium206 Workshop On Web Information And Data Management207 Wireless Mobile Applications And Services On Wlan Hotspots208 International Workshop on Mobile Commerce209 Wireless Mobile Internet210 Workshop on Rapid Malcode211 Workshop on Software and Performance212 Workshop on Self-healing systems213 Workshop on Parallel & Distributed Debugging214 Workshop On Privacy In The Electronic Society215 Wireless Security216 Winter Simulation Conference217 International Workshop on Wireless Sensor Networks and Applications218 Workshop on Universal Accessibility of Ubiquitous Computing219 International World Wide Web Conference220 3D technologies for the World Wide Web221 International Workshop on Wireless Mobile Multimedia222 Workshop On XML Security。

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InteractiveSoundSynthesisforLargeScaleEnvironmentsNikunjRaghuvanshi∗MingC.Lin†DepartmentofComputerScienceUniversityofNorthCarolinaatChapelHill

AbstractWepresentaninteractiveapproachforgeneratingrealisticphysically-basedsoundsfromrigid-bodydynamicsimulations.Weusespring-masssystemstomodeleachobject’slocaldeformationandvibration,whichwedemonstratetobeanadequateapproxi-mationforcapturingphysicaleffectssuchasmagnitudeofimpactforces,locationofimpact,androllingsounds.Noassumptionismadeaboutthemeshconnectivityortopology.Surfacemeshesusedforrigid-bodydynamicsimulationareutilizedforsoundsimu-lationwithoutanymodiﬁcations.Weuseresultsinauditorypercep-tionandanovelpriority-basedqualityscalingschemetoenablethesystemtomeetvariable,stringenttimeconstraintsinareal-timeap-plication,whileensuringminimalreductionintheperceivedsoundquality.Withthisapproach,wehaveobserveduptoanorderofmagnitudespeed-upcomparedtoanimplementationwithouttheacceleration.Asaresult,weareabletosimulatemoderatelycom-plexsimulationswithuptohundredsofsoundingobjectsatover100framespersecond(FPS),makingthistechniquewellsuitedforinteractiveapplicationslikegamesandvirtualenvironments.Furthermore,weutilizeOpenALandEAXTMonCreativeSoundBlasterAudigy2TMcardsforfasthardware-acceleratedpropaga-tionmodelingofthesynthesizedsound.

CRCategories:H.5.5[InformationInterfacesandPresenta-tion]:SoundandMusicComputing—Modeling,Methodologiesandtechniques;I.3.5[ComputerGraphics]:ComputationalGe-ometryandObjectModeling—Physicallybasedmodeling;I.3.7[ComputerGraphics]:Three-DimensionalGraphicsandRealism—Animation;

Keywords:SoundSynthesis,Rigid-BodySimulation,OpenAL1IntroductionMostinteractiveapplicationstodayemployrecordedsoundclipsforprovidingsoundscorrespondingtoobjectinteractionsinascene.Althoughthisapproachhastheadvantagethatthesoundsarereal-isticandthesound-generationprocessisquitefast,therearemanyphysicaleffectswhichcannotbecapturedbysuchatechnique.Forinstance,inatypicalcollisionbetweentwoobjects,theloudnessandtimbreofthesoundisdeterminedbythemagnitudeandlo-cationoftheimpactforces–aplatesoundsverydifferentlywhenstruckontheedgecomparedtowhenitisstruckinthemiddle.Con-sequently,ifthecollisionscenariochangesslightly,thesoundex-hibitsacorrespondingchange.Suchsubtleeffectscanaddsubstan-tialrealismtoatypicalscenebyavoidingtherepetitivenesscom-montorecordedsoundclips.However,developingasystemwhichproducessoundusingphysically-basedprinciplesinrealtimeposes

∗nikunj@cs.unc.edu

†lin@cs.unc.edu

Figure1:Numerousdicefallonathree-octavexylophoneinclosesuccession,playingoutthesong“TheEntertainer”(seethevideo).Ouralgorithmisabletoproducethecorrespondingmusicaltonesatmorethan500FPSforthiscomplexscene,withaudiogenerationtaking10%ofthetotalCPUtime,ona3.4GHzPentium-4Laptopwith1GBRAM.

substantialdifﬁculties.Theforemostrequirementisthepresenceofanefﬁcientdynamicsenginewhichinformsthesoundsystemofobjectcollisionsandtheforcesinvolved.Forthiswork,wehavedevelopedafastandrobustrigid-bodysimulator,butmanypresentdaygamesmeetthisrequirement.Givenadynamicssimulator,themainchallengeistosynthesizethesoundefﬁcientlyenoughtoplayinrealtimewhiletakingonlyasmallportionofthetotalrunningtime,whichisusuallydominatedbygraphicsandrigid-bodysim-ulation.TypicallythesoundsystemcanonlyaffordafewhundredCPUcyclesperobjectpersoundsampleformanyinteractiveappli-cations.

MainResults:Inthispaper,wepresentanapproachwhichmeetstheinteractiveperformancerequirementsoutlinedabove,whileen-suringhighrealismandﬁdelityofthesoundproduced.Givenanobject’sgeometryandafewmaterialparameters,weconstructaspring-massmodelapproximatingtheobject’ssurface.Weshowthatalthoughaspring-masssystemisacoarserapproximationthanFEMmodelsusedinpriorapproaches[ChaigneandDoutaut1997;O’Brienetal.2001;O’Brienetal.2002],itisanadequatemodeltocapturethesmall-scalesurfacevibrationsthatleadtothegener-ationofsoundinnature.Weshowhowthisformulationyieldsananalyticalsolutiontotheequationofmotionforthesurfaceoftheobject.However,anaiveimplementationofsuchanapproachcanhan-dleonlyafew(lessthanten)soundingobjectsinrealtime.Wealsopresentseveralaccelerationtechniques.Theincreasedcom-putationalefﬁciencyisachievedbyexploitingauditoryperception,whichensuresthattheresultingdegradationinperceivedqualityisminimal.Inaddition,thesoundqualityandtheassociatedcomputa-tionalcostforeachobjectisscaleddynamicallyinapriority-basedschemewhichguaranteesthatthetotalsoundproductionmeets