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使用浒苔提取物作为传统混凝剂在黄河水处理混凝行为和絮状物特性的助凝剂的影响

Inﬂuence of using Enteromorpha extract as a coagulant aid on coagulation behavior and ﬂoc characteristics of traditional coagulant in Yellow River water treatmentShuang Zhao,Baoyu Gao ⇑,Xiangzuo Li,Min DongShandong Key Laboratory of Water Pollution Control and Resource Reuse,School of Environmental Science and Engineering,Shandong University,Ji’nan 250100,Shandong,People’s Republic of Chinah i g h l i g h t s"An effective way of the recycle of hazard wastes-Enteromorpha was found."A new kind of coagulant aid-Ee was found and applied in the water treatment process."Coagulation performance could be obviously enhanced when appropriate Ee was dosed."Floc characteristics were signiﬁcantly improved due to Ee addition.a r t i c l e i n f o Article history:Received 24April 2012Received in revised form 21June 2012Accepted 21June 2012Available online 30June 2012Keywords:Coagulant aidEnteromorpha extract Coagulation performance Floc characteristica b s t r a c tA new coagulant aid,Enteromorpha extract (Ee),was used together with traditional coagulants in water treatment process to assess its effect on coagulation behavior and ﬂoc characteristics.Four kinds of alu-minum and ferric coagulants were studied in this article,with the results indicating that aluminum sul-fate (AS)was the optimal coagulant due to its high efﬁciency and perfect cooperation with Ee for given test water.Then coagulation behavior and ﬂoc characteristics of AS coagulation system were studied.Turbidity,UV 254(ultraviolet absorbance at 254nm wavelength)and DOC (dissolved organic carbon)removal efﬁciencies were used to evaluate coagulation effects;and ﬂoc characteristics were investigated in terms of ﬂoc size,strength and recovery ability.The results obtained in this study indicated that the coagulation effect of AS could be signiﬁcantly improved by around 30%when appropriate proportion of Ee was dosed.When AS was used in conjunction with Ee,the generated ﬂocs had bigger sizes and faster growth rate than those generated by AS alone.Meanwhile,the former were also stronger and had better recovery abilities than the latter.The charge neutralization was the dominant mechanism in AS coagula-tion,and Ee displayed good adsorption bridging effect.Consequently,coagulation efﬁciency could be enhanced signiﬁcantly due to the combination of two advantages.Ó2012Elsevier B.V.All rights reserved.1.IntroductionIt is well known that coagulation is the most common process used for particles and organic matter removal in drinking water treatment [1].In this process,coagulants are added to aggregate destabilized dissolved organic matter (DOM)and colloidal particles into larger-sized ﬂocs,and then the ﬂocs can be effectively re-moved in sedimentation processes [2].Due to the effectiveness in treating a wide range of waters at relatively low lost,traditional coagulants (aluminum and ferric salts)become the most com-monly used coagulant in water treatment [3–5].However,recent studies have discovered a number of drawbacks of using tradi-tional coagulants.Alum salts may cause human body disease and ferric salts may cause the unsightly brown staining of equipments [6–8].Therefore,it is necessary to decrease the dosage of tradi-tional coagulants to reduce negative effects.Applying coagulant aids is the most common method to solve above problems,and meanwhile,the water treatment cost can also be cut down by dos-ing appropriate coagulant aids.Coagulant aids can accelerate the ﬂocculation process or strengthen the ﬂoc to make it easier to ﬁl-ter.They can be roughly divided into two categories based on their mechanism of action.Synthetic polymers are the most common coagulant aids,which bind to particles much like coagulants.Oth-ers,generally the inorganic and natural polymers,act as sites of nucleation to speed the formation of ﬂoc.However,it has been1385-8947/$-see front matter Ó2012Elsevier B.V.All rights reserved./10.1016/j.cej.2012.06.097Corresponding author.Tel.:+8653188364832;fax:+8653188364513.E-mail address:baoyugao_sdu@ (B.Gao).reported that synthetic polymers contain contaminants from the manufacturing process that may threaten human health[8,9]. Meanwhile,Synthetic polymers can also react with other chemi-cals added to the water treatment process to form undesirable sec-ondary products[10–12].Natural polymers,which are extracted from plant or animal life,can be workable alternatives to synthetic polymers[13–16].They are biodegradable and also have a wider effective dosage range ofﬂocculation for various colloidal suspen-sions.Therefore,it is indispensable to develop high efﬁcient and low cost natural polymers which were used as coagulant aids for water and wastewater treatment[17–19].Enteromorpha is a kind of green algae,which is known as a dominant species in saline coastal wetlands with high nitrogen levels[20].Enteromorpha can tolerate salinities varying from freshwater to seawater.As a fast growing and opportunistic macro-algae,this species can proliferate in a wide range of abiotic and biotic conditions[21–23].In the summer of2008,Enteromorpha broke out in Yellow Sea and East Sea on a large scale,which posed a threat to the Sailing Competition of the2008Beijing Olympics. The local government had to spend much manpower andﬁnancial resources to carry out the emergency treatment measures against the disaster.But Enteromorpha management is supposed to be a long termﬁght rather than an episode during the29th Olympic Games for China,since it has been gaining in scale during the past 3decades in both marine and estuary environment all over the world.As we all know that waste is a kind of resource that was put in the wrong place.The comprehensive utilization of Enteromorpha is the ultimate way to settle the problem rather than piled them on the beach.But there has not been too much literature about the recycle used method of Enteromorpha at pres-ent since most researches focused on the Enteromorpha biological characteristics[24,25].It was once reported that Enteromorpha can be successfully transformed into biomass oil under appropriate conditions[26],but the cost was higher than the low-level fuel oil existing on market.The higher production cost limits its application and this technology is not suitable for the actual mass production.Enteromorpha is rich in macromolecular substances which can play an positive role in water supply and wastewater treatment,and also it has advantages of containing many active groups,various natural polymers and non-toxic character. Considering all the advantages of Enteromorpha,it is worth trying to apply the extracting solution of Enteromorpha(compound of many kinds of natural polymers)as a coagulant aid in coagulation process of water treatment.It is a tentative try since there is no relevant literature so far.By doing this,we attempt to provide a new solution to the Enteromorpha disaster,on the other hand,a new-style,cheap and non-toxic coagulant aid may be found.In this research,several kinds of aluminum and ferric salts were selected to use in conjunction with Ee in the treatment process of test water.Traditional coagulants were addedﬁrstly at the start of rapid mixing in coagulation process,and then Ee was dosed after 30s.That was denoted as dual-coagulant,which can be displayed in form of coagulant–coagulant aid.The coagulation aid perfor-mance of Enteromorpha extract(Ee)forﬂocculation–sedimenta-tion process was studied through a series of contrast test. Coagulation effects of traditional coagulants and dual-coagulants were comparatively investigated in terms of turbidity,UV254 (ultraviolet absorbance at254nm wavelength)and DOC(dissolved organic carbon)removal efﬁciency.Zeta potential was also researched in order to study the coagulation mechanism. Furthermore,the growth,breakage and re-growth properties of ﬂocs produced in optimal condition were conducted.Based on the coagulation performance andﬂoc properties,the coagulation aid effect of Ee can be found,meanwhile,the coagulation aid mechanism can be discussed.2.Materials and methods2.1.Chemicals and raw waterThe chemicals used in this study including FeCl3Á6H2O,FeS-O4Á7H2O,AlCl3Á6H2O and Al2(SO4)3Á18H2O,which were all pur-chased from Sinopharm Chemical Reagent Co.,Ltd.,Beijing.All reagents used were of analytical grade.Deionized water was used to prepare all solutions.The raw water investigated in the study was sampled from Quehua water works of Jinan city in China in October2011.The properties of the test water were:temperature=19.5–22.5°C, pH=8.17–8.45,turbidity=2.18–2.76NTU,UV254=0.038–0.045cmÀ1,DOC=3.636–4.284mg/L.2.2.Preparation of coagulantsFresh Enteromorpha were gathered fromﬁrst bathing beach of Qingdao,China.They were put into the vacuum drying oven for5h at the constant temperature of70°C after being washed.The dry sample were shattered into powder by magnetic crusher and then passed through100mesh sieve.The screening Enteromorpha and deionized water were mixed at the mass ratio of1:75and then that compound was heated in water bath for4h at the constant tem-perature of90°C[27].The extract of Enteromorpha were centrifu-galized for30min at the speed of5000r/min.Supernatant were collected to measure volume and then diluted with equal volume of deionized water.That was used as the coagulant aid and the dos-age of Ee was metering by volume.Traditional coagulants and dual-coagulants,were compara-tively investigated in this study.The conventional coagulants, FeCl3Á6H2O and FeSO4Á7H2O,were used to prepare iron solutions with deionized water at a concentration of1.0g/L as Fe.Similarly, AlCl3Á6H2O and Al2(SO4)3Á18H2O were used to prepare alum solu-tions at a concentration of1.0g/L as Al.2.3.Jar-testAt a room temperature of20±2°C,Coagulation experiments were conducted by a jar-test apparatus(ZR4–6,Zhongrun Water Industry Technology Development Co.Ltd.,China).The test water of1000mL was poured into each of the1400mL plexiglass beakers and a six-paddled stirrer was used for mixing.The coagulation pro-cedure was as follow:predetermined amount of coagulant or dual-coagulant was dosed after30s rapid stirring of200rpm;after 1.5min,the stirring speed was changed to40rpm with a duration of15min;then after30min of quiescent settling,sample was col-lected from1cm below the surface for measuring.Part of sample was directly used for measuring residual turbidity and zeta poten-tial by using a2100P turbidimeter(Hach,USA)and zeta sizer 3000HSa(Malvern Instruments,UK),respectively.The remaining samples wasﬁltrated by0.45l mﬁber membrane and then was used to test UV254absorbance and DOC.UV254absorbance was analyzed with an UV-754UV/VIS spectrophotometer(Precision Scientiﬁc Instrument Co.Ltd.,Shanghai,China),and DOC was mea-sured by a TOC analyzer(TOC-VCPH,Shimadzu,Japan).2.4.On-line monitoring ofﬂoc formation,breakage and re-growth measurementA laser diffraction instrument Mastersizer2000(Malvern,UK) was used to monitor the evolution ofﬂoc size in coagulation pro-cess.The suspendedﬂoc was monitored through the sample cell of the Mastersizer and then transferred back into the jar by a peri-staltic pump(LEAD-1,Longer Precision Pump,China)using a5mm570S.Zhao et al./Chemical Engineering Journal200–202(2012)569–576internal diameter tube at aﬂow rate of2.0L/h.The pump was de-signed to be located at the downstream of Mastersizer to prevent disturbing theﬂocs prior.The inﬂow and outﬂow tubes were posi-tioned opposite each other at a depth just above the impeller in the holding ports.Size measurements of theﬂoc were taken every half minute in the process of coagulation and the results were recorded automatically by computer.Floc characteristic experiments were carried out under different dosage of(aluminum sulfate)AS and Ee.The coagulation procedure were conducted as follows:(1)a rapid mix step at200rpm for 1.5min;(2)a slow stir step at40rpm for15min;(3)a breakage step for5min200rpm;and(4)a slow stirring at40rpm for a fur-ther15min forﬂocs re-growth.2.5.Characteristic representation ofﬂocIn this study,the median volumetric diameter(d50)was used to denote theﬂoc size.The growth rate was an important representa-tion ofﬂoc characteristic.It was denoted as the slope of rapid growth region.The larger the growth rate,the fasterﬂoc generated. It was calculated as follow[28,29]:growth rate¼D sizeð1ÞFor comparing the strength and re-growth ability ofﬂocs in differ-entﬂocculated systems,ﬂoc strength factor(S f)and recovery factor (R f)were induced.They could be calculated by the following equa-tions[30,31]:S f¼d2d1Â100ð2ÞR f¼d3Àd212Â100ð3Þwhere d1(l m)and d2(l m)represent the stableﬂoc size before and after breakage,while d3represents theﬂoc size after re-growth to the new steady step.The strength factor value indicates the ability ofﬂocs to withstand shear,such that a higher value suggests that theﬂocs are stronger.Meanwhile,the recovery factor is an indica-tive ofﬂoc recoverability,such that a higher value implies that theﬂocs have better re-growth ability after breakage.All the exper-iments were carried out three times and very little variation was observed.3.Results and discussion3.1.Coagulation effect of EeAlthough the Enteromorpha was non-toxic,but the outbreaks of it could block sunshine just as the red tides,and meanwhile the death Enteromorpha would consume oxygen in the sea,so the ﬂoating Enteromorpha may affect the algae growth in seabed.Fur-thermore,the outbreak of Enteromorpha will seriously affect land-scape and the proceeding of water sports.That is the biggest disadvantage that the people want to try to eliminate.Therefore, it is of great signiﬁcance to explore an effective way for compre-hensive utilization of Enteromorpha,as well as for the restoration and improvement of the ecological environment and development of a recycling economy.In this section,Ee was used as a kind of coagulant.Fig.1showed the variation of turbidity,UV254and DOC removal efﬁciency with various Ee dosages.Fig.1showed that the turbidity and UV254removal gradually increased with the increasing Ee dosage,while the removal trend of DOC showed a parabola shape.The optimum point was at the dosage of0.1mL/L,in which condition the DOC removal rate was 20.5%.Zeta potential decreased with the increasing Ee dosage and below zero all the time within the whole dose ranges investigated. This indicated that charge neutralization is not the dominate mechanism of Ee.Due to the repulsive force between negative col-loids,theﬂoc was quiet small and hardly to settle down.Therefore, the removal of organic matter was in low levels.Overall,Ee exhib-ited some potential in removing organics,but good coagulation efﬁciency could not be achieved when Ee was used as a coagulant. So the performance of using Ee as a coagulant aid in coagulation process was studied as follow.3.2.Determination of the optimal coagulantAppropriate coagulant will not only improve the efﬂuent water characteristics,but also can decrease the cost of water treatment. In order to ascertain the optimal coagulant for given test water, experiments were performed with aﬁxed coagulant aid(Ee)in conjunction with four traditional coagulants(FeCl3,FeSO4,AlCl3 and Al2(SO4)3).Coagulants doses varied within a range of 2–12mg/L while coagulant aid dose was constant at0.1mL/L. Turbidity,UV254and DOC removal efﬁciency were taken to esti-mate coagulation performance.Results were shown in Fig.2.It can be seen from theﬁgure that the coagulation performance of four coagulants showed signiﬁcant pared with iron salts coagulants,aluminum salts had better coagulation ef-fects with fasterﬂocs growth rates and largerﬂocs sizes.For DOC removal:the removal rates were rather low when iron salts were used and the maximal value was21%,while the removal of DOC can reach34%when aluminum salts were used.The conditions of turbidity and UV254removal efﬁciencies are similar to that of DOC.For aluminum salts coagulants,both of them could provide relatively high performances even at low dosages.Meanwhile the efﬁciencies of coagulation increased with coagulants doses increasing.In case of AlCl3,the application of coagulant aid could improved the performance,but only slightly effect could be ob-served,while the addition of Ee led to a signiﬁcant increase of coagulation performance in Al2(SO4)3system.Consequently, Al2(SO4)3was chosen to carry out the following experiments as the optimal coagulant for the test water.3.3.Determination of the optimal dose of coagulant aidIn this section,the tests were performed with aﬁxed coagulant (AS)based on Section3.2.Optimization tests were conducted to ascertain the optimum Ee dosage for particles and organic matterS.Zhao et al./Chemical Engineering Journal200–202(2012)569–576571removal under the raw water pH conditions.Traditional coagulant (AS)and dual-coagulant(aluminum sulfate–Enteromorpha extract (AS–Ee))were comparatively evaluated in terms of coagulation performance.The variation of coagulation efﬁciencies and zeta po-tential were presented in Fig.3with the coagulant dosages2–12mg/L as Al.When AS was used alone,Fig.3showed that UV254and DOC re-moval efﬁciency increased with alum dosage increasing,but the turbidity removal increased rapidly at a low alum dosage and then decreased slightly as the alum dose further increased.The coagulation with AS has been studied for decades and the coagula-tion mechanisms of it include charge neutralization,precipitation, bridge-aggregation,adsorption and sweep-ﬂocculation[32,33].As shown in Fig.3,the organic matter removal efﬁciency increased as AS dosage increasing,which was in accordance with the increas-ing zeta potential(Fig.3d).The highest organics removal was achieved at the dosage of12mg/L with zeta potential of0.3mV, which indicated that charge neutralization was the dominant mechanism of AS coagulation system.The alkaline test water could produce precipitation of amorphous hydroxide,so the charge neu-tralization was likely to be achieved by adsorbed precipitate. Therefore,efﬁcient turbidity removal still occurred at low dosages, even though the zeta potentials were below zero.When adequate Ee(0.1mL/L,0.3mL/L)was used in conjunction with AS,the turbidity,UV254and DOC removal were higher than that of AS used alone.Especially when Ee dosage was0.3mL/L,the organics removal efﬁciency was signiﬁcantly improved:the UV254and DOC removal rate exceeded47%and44%at the alum dosage of12mg/L,while the removal obtained by AS alone were only37%and35%in the same test condition.Even though higher organic matter removal was obtained,zeta potential was still be-low zero(Fig.3d).That suggested that charge neutralization may be not the dominant mechanism for organics removal by AS–Ee. When AS was dosedﬁrstly,it quickly adsorbed on the surface of the microﬂocs and then neutralized the negative charge on it.So repulsion forces between the colloids became very weak.When Ee was dosed30s after AS,the adsorption bridging ability of it could play a signiﬁcantly positive effect on theﬂocculation process, which could generate largerﬂocs those had preferably settling ability.Therefore,better coagulation efﬁciency could be achieved. But further increase in the dosage of Ee did not cause further ele-vation in the removals of organics:when Ee dosage was0.5mL/L, the coagulation performance was poor and even showed lower le-vel than that of AS used alone.The turbidity removal was about8% lower than that of AS.Since Ee itself was a complicated organic matter,the overdosed Ee in the coagulation system caused the de-crease of organics removal.Meanwhile,in such a situation,zeta potential was underÀ10mV due to larger dose of negatively charged Ee(À35.0mV).Therefore,the stronger inter-particle repulsion and the restrainedﬂocs growth resulted in poor coagula-tion efﬁciency.Consequently,based on theﬁgure and discussion above,it is easy for us to draw the conclusion that the optimal572S.Zhao et al./Chemical Engineering Journal200–202(2012)569–576coagulant aid dosage was 0.3mL/L.Considering the coagulants cost and coagulation performance,the dosage of Ee was constant at 8mg/L for the next ﬂoc characteristic experiments.3.4.Effect of coagulant aid on ﬂoc size and growth rateThe growth proﬁles of ﬂocs were investigated and the results were shown in Fig.4,where the ﬂoc size was represented by med-ian equivalent diameter.Floc growth rate in steady state were adopted to examine the ﬂoc formation process,and the growth rates were shown in Table 1.The dosages of AS were constant at 8mg/L based on Section 3.3,and all the ﬂoc characteristic tests were taken in situation of raw water pH.Fig.4showed that the ﬂoc in the AS ﬂocculation process dis-played a sharp increase in size during the ﬁrst 5min,achieving the largest ﬂoc size of 338.1l m,followed by a steady-state period during the next 15min.The sharp growth of ﬂoc size in the ﬁrst 5min is likely due to the aggregation of particles and the stable phase indicated that the ﬂoc growth and ﬂoc breakage reachedTable 1Flocs growth rates for various doses.Ee dosage (mL/L)0.00.10.30.5Growth rate (l m/min)45.8787.78122.20123.54S.Zhao et al./Chemical Engineering Journal 200–202(2012)569–576573appropriate balance.The sizes of ﬂocs generated by AS–Ee and AS showed the similar variation tendency but the former were larger than the latter.As shown in Fig.4:the ﬂoc sizes at the steady stagewere 334.7l m,570.4l m,717.3l m,743.3l m for 0.0mL/L,0.1mL/L,0.3mL/L,0.5mL/L Ee dosage,respectively.Meanwhile,Table 1indicated that ﬂocs produced by AS–Ee gave faster aggrega-tion than that of AS:at constant alum dose of 8mg/L,the ﬂocs growth rate could achieve 122.20l m /min when 0.3mL/L Ee was used,while the growth rate of ﬂocs produced by AS was only 45.87l m/min.The phenomenon mentioned above may be related to the dom-inate coagulation mechanism.The prime mechanism of AS was charge neutralization [2]while extra adsorption bridge were dom-inating when AS–Ee was used.Ee could promote the growth of ﬂocs by adsorption bridge ability due to natural polymers con-tained in it.This result was in agreement with the observation of Ray and Hogg [33],who had reported that ﬂocs produced by bridging ﬂocculation and charge neutralization can be much largerTable 2Strength and recovery factors of ﬂocs for different Ee dosages.ParameterEe dose (mL/L)0.00.10.30.5Strength factor 37.0840.6469.3975.33Recovery factor19.2625.7346.2255.63574S.Zhao et al./Chemical Engineering Journal 200–202(2012)569–576than those formed simply by charge neutralization.As we can see, when0.3mL/L Ee was used,the generatedﬂocs sizes and growth rate were much lager than those of0.1mL/L Ee applied,but there was no sharp improvement when Ee dosage further increased.The growth curves were almost overlapping when Ee dosage larger than0.5mL/L.This can be explained as follow:The bridge role of Ee can led to the increase of aggregation at the initial aggregation. There were not enough macromolecule matter particles when Ee dosage was small,so the adsorption bridge effect would be enhanced as the increase dosage of Ee.But all particles were positively aggregated and precipitated when Ee dosage larger than 0.5mL/L.Therefore,the due role of extra Ee couldn’t play out. Accordingly,theﬂoc sizes were hardly to further increased.3.5.Effect of coagulant aid onﬂoc breakage and re-growthThe effect of Ee onﬂoc breakage and re-growth was investi-gated in this section.Fig.5showed that in all cases,theﬂocs sizes immediately decreased when the shear was introduced by increas-ing the mixing speed up to200rpm.After the shear period of 5min,d50ofﬂocs was about131l m for AS.When AS–Ee were used,theﬂocs sizes were230l m,493l m,591l m for0.1mL/L, 0.3mL/L,0.5mL/L Ee dosage,respectively.As the shear was re-duced again,theﬂocs began to re-grow.However,irreversible breakage was usually observed.The initialﬂocs sizes were not recovered after breakage:ﬂocs formed by AS re-grew up to 172l m size and when Ee was used besides AS,the corresponding ﬂoc sizes after the re-growth period was312l m,579l m and 682l m for0.1mL/L,0.3mL/L and0.5mL/L Ee dosage,respectively. In order to investigateﬂoc breakage and re-growth in detail, the strength and recovery factors were used to interpret theﬂoc strength and recoverability,and the results were shown in Table2.In parallel,theﬂocs particle size distributions were also analyzed in this section,and the results were shown in Fig.6.Table2indicated that when AS–Ee was used in the coagulation process,the strength of generatedﬂocs were much larger than those of AS used alone:when0.5mL/L Ee was applied in conjunc-tion with AS,theﬂoc strength factor achieved75.33,which is twice larger than that of AS used alone(37.08).Meanwhile,For Fig.6,an apparent shift in the major peak after breakage could be seen for AS,while,comparatively,small extent of shift in the major peak was found of AS–Ee.Since the shift degree represented the ability of resisting shear,large excursion indicated poorﬂocs strength. Therefore,the results of Fig.6was in accordance with the conclu-sion of Table2obtained above.This results agreed with the conclu-sion by Li et al.[30]who found thatﬂocs generated by bridging were stronger than those generated simply by charge neutraliza-tion.Table2also showed that the strength factors increased as the rising dose of Ee with the constant AS dosage.Since there were not enough polymers between the particles when Ee dosage was low,the producedﬂocs were weak.But when the dose of Ee was large,the polymers were adequate to generate strongerﬂocs,so the strength factors became larger.For recovery ability,Table2 showed a gradual uptrend as the Ee dosage increased.The result was consist with the conclusion of Fig.6,which showed that:for AS–Ee,the small peak showed a comparatively apparent shift to the right of the major peak,while minor change could be observed between theﬂoc particle size distributions before and after re-growth of AS.Theﬂoc recovery factors of AS–Ee were larger than that of AS,which may be the result from Ee,which could undergo scission under high shear rate.Meanwhile,the renewed adsorbent polymer could reform on the particle surface whileﬂocs generated by AS were immediately broken when the high shear rate was introduced and then could not recover[33].4.ConclusionIn this study,the coagulation aid effect of Ee was investigated and it was found that Ee could be used as a new kind of coagulant aid due to its notable aid effects.Meanwhile,applying Ee in the water treatmentﬁeld can be a new recycle way of disaster wastes–Enteromorpha.In this paper,AS was selected as the opti-mum coagulant from different traditional coagulants due to its high efﬁciency and perfect cooperation with Ee.The coagulation ef-fect of AS could be improved by around30%when0.3mL/L Ee was dosed.It was also found thatﬂocs generated by AS–Ee had bigger sizes and faster growth rates than that of AS.Meanwhile,the for-mer were also stronger and had better recovery ability than the lat-ter.The results of coagulation andﬂocs characteristic test showed that:the main coagulation mechanism of AS was precipitate charge neutralization,and Ee can play a positive aid role by adsorp-tion bridging in water treatment process.Therefore,better coagu-lation performance of AS–Ee could be achieved by the combination of two advantages.AcknowledgmentsThis study is supported by The Scientiﬁc Technology Research and Development Program of Shandong,China(No. 2010GZX20605)and a grant from the National High Technology Research and Development Program of China(863Program)(No. SQ2009AA06XK1482412).The kind suggestions from the anony-mous reviewers are highly appreciated.References[1]P.Jarvis,B.Jefferson,S.A.Parsons,Breakage,re-growth and fractal nature ofnatural organic matterﬂocs,Environ.Sci.Technol.39(7)(2005)2307–2314.[2]C.Hu,H.Liu,J.Qu,D.Wang,J.Ru,Coagulation behavior of aluminum salts ineutrophic water:signiﬁcance of Al13species and pH 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alum,Turkish J.Eng.Environ.Sci.27(2003)227–236.[18]M.Ozacar,I.A.Sengil,Evaluation of tannin biopolymer as a coagulant aid forcoagulation of colloidal particles,Colloids Surface A:Physicochem.Eng.Aspects229(2002)85–96.S.Zhao et al./Chemical Engineering Journal200–202(2012)569–576575。

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Fatigue and Healing Characterization of Asphalt Mixtures

Fatigue and Healing Characterization of Asphalt Mixtures Yong-Rak Kim1;D.N.Little,P.E.,F.ASCE2;and R.L.Lytton,P.E.,F.ASCE3Abstract:This paper investigates the effect of the processes on fatigue fracture and fracture healing during controlled-strain,dynamic mechanical analysis͑DMA͒testing.Sand asphalt samples were fabricated with two SHRP-classiﬁed binders:AAD-1and AAM-1.DMA testing was performed at25°C and at10Hz.The mechanical response during DMA testing was monitored using three different damage indicators:͑1͒change in dynamic modulus;͑2͒change in pseudo stiffness;and͑3͒change in dissipated strain energy.When either of these parameters are plotted versus the number of load cycles,two inﬂection points are apparent that deﬁne a signiﬁcant change in sample behavior due to damage.The second inﬂection point is a reasonable deﬁnition of failure,as it is strongly correlated with the peak of the plot of phase angle versus load repetitions.Furthermore,the phase angle drops precipitously at the second inﬂection point.By performing controlled-strain torsional fatigue tests at three different strain levels,each great enough to induce damage,a reproducible fatigue relationship͑number of load cycles as a function of stress level͒is developed.The introduction of several rest periods during testing lengthened fatigue life.Successful development of this testing method is suggested as a potential speciﬁcation-type test method because of its efﬁciency,reproducibility,and reliability.DOI:10.1061/͑ASCE͒0899-1561͑2003͒15:1͑75͒CE Database keywords:Fatigue;Fracture;Damage;Asphalt mixes.IntroductionA precise understanding of the fatigue behavior of asphalt mix-tures is required in order to improve asphalt mixture design and hot mix performance.However,accurate prediction and evalua-tion of fatigue is a difﬁcult task not only because of the complex nature of fatigue phenomena but also because of characteristics of fatigue testing,namely,that it is expensive and time-consuming.The deﬁnition of fatigue life͑the number of loading cycles to failure͒,especially in the controlled-strain mode,is a controver-sial issue.Among many options open to researchers,a50%loss in stiffness or modulus from the initial value was used by Hicks et al.͑1993͒;Williams͑1998͒;Smith and Hesp͑2000͒;and oth-ers.Other criteria based on changes in dissipated energy including dissipated energy ratio or damage accumulation ratio were se-lected in studies by Rowe͑1993͒;Rowe and Bouldin͑2000͒;and Anderson et al.͑2001͒.In particular,Reese͑1997͒proposed evaluation of changes in the phase angle during fatigue testing. According to his argument,a point showing the maximum phase angle is a reasonable fatigue failure point,since the phase angle versus time curve shows a rapid loss of phase angle when asphalt mixtures stop accumulating distress.A series of studies by Lee ͑1996͒;Kim et al.͑1997͒;and Lee et al.͑2000͒suggested a new failure criterion using50%loss in pseudo stiffness.The pseudo stiffness can be reasonably used to represent damage accumula-tion due to repeated fatigue loading,as it eliminates linear vis-coelastic time-dependency,which does not induce damage.Based on a reasonable deﬁnition of fatigue failure,a fatigue life prediction model can be developed.In general,there are two main approaches:phenomenological and mechanistic.The phe-nomenological fatigue model is simple to use;however,it does not account for damage evolution throughout the fatigue process. On the other hand,mechanistic models are based on fracture me-chanics or damage mechanics.This approach is inherently more complex than the phenomenological approach but is more widely accepted because it uses material properties based on stress-strain relationships.Recently,Lee et al.͑2000͒successfully developed a fatigue performance prediction model of asphalt concrete based on an elastic-viscoelastic correspondence principle and con-tinuum damage mechanics.The fatigue cracks generally initiate as microcracks and grow as dictated by a crack propagation process including coalescence of the microcracks.Several studies by Kim͑1988͒;Kim et al.͑1990,1994,1995͒;and Bahia et al.͑1999͒have shown that the microcracks heal during rest periods.In particular,Bahia et al.͑1999͒showed signiﬁcant effects of rest periods on fatigue dam-age recovery in dynamic shear rheometer͑DSR͒tests using vari-ous binders.Quantitative analysis of healing was conducted in those studies,and the healing effect was signiﬁcant,producing increased fatigue life.In this study,dynamic mechanical analysis͑DMA͒was con-ducted to characterize fatigue damage and healing in asphalt mix-tures under controlled-strain,torsional testing.The impetus of the DMA testing was work performed by Goodrich͑1988,1991͒; Christensen and Anderson͑1992͒;and Smith and Hesp͑2000͒. Differences between this study and those studies include the sample geometry used,the sample composition,and the loading1Graduate Research Assistant,Texas Transportation Institute,Texas A&M Univ.,College Station,TX77843-3135.2Professor,Dept.of Civil Engineering,Texas A&M Univ.,College Station,TX77843-3135.3Professor,Dept.of Civil Engineering,Texas A&M Univ.,College Station,TX77843-3135.Note.Associate Editor:Donald W.Christensen,Jr.Discussion open until July1,2003.Separate discussions must be submitted for individual papers.To extend the closing date by one month,a written request must beﬁled with the ASCE Managing Editor.The manuscript for this paper was submitted for review and possible publication on May23,2001; approved on December13,2001.This paper is part of the Journal ofdistributions in the samples and to make calculation easier.Sand asphalt mixtures were employed so that samples could be tested at an intermediate͑realistic performance͒temperature͑25°C͒. Successful development of the methodology will allow one to analyze fatigue behavior in asphalt mixtures more accurately using a comprehensive investigation of fatigue performance and to develop a simple model for predicting the fatigue performance. Theoretical BackgroundExtended Correspondence Principle for Torsional Shear ModeSchapery͑1984͒proposed the extended elastic-viscoelastic corre-spondence principle͑CP͒,which is applicable to both linear and nonlinear viscoelastic materials.Schapery stated that constitutive equations for certain viscoelastic media are identical to those for the elastic cases,but stresses and strains are not necessarily physi-cal quantities in the viscoelastic body.Instead,they are pseudo variables.Torsional shear pseudo strain is deﬁned as␥Rϵ1G R͵0t G͑tϪ␰͒ץ␥ץ␰d␰(1)where␥R(t)ϭpseudo strain in the shear mode;G Rϭreference shear modulus that is an arbitrary constant;G(t)ϭshear relax-ation modulus;and␥ϭtime-dependent shear strain.For linear vis-coelastic materials,a torsional shear stress-shear strain relation-ship can be expressed as␶L VE͑t͒ϭ͵0t G͑tϪ␰͒ץ␥ץ␰d␰(2)where␶L VE(t)ϭcalculated linear viscoelastic stress.With the use of the deﬁnition of pseudo strain in Eq.͑1͒,Eq.͑2͒can be rewrit-ten as follows:␶L VE͑t͒ϭG R␥R͑t͒(3) It is noted that the calculation of pseudo strain requires the ex-pression of the relaxation modulus as a function of time.The extended correspondence principle accounts for time-dependency properties and separates the viscoelastic relaxation mechanism from damage accumulation in viscoelastic materials, e.g.,asphalt mixtures.Stress-strain relations for many linear and nonlinear viscoelastic materials can be represented by elastic-like equations through the use of pseudo variables.Specimens that experience signiﬁcant damage exhibit such damage in the form of hysteretic loops when plotted in the stress–pseudo strain domain. Damage accumulation can be demonstrated by observing changes in the loop area and loop secant slope during mechanical tests such as fatigue testing.Based on the relationship between the pseudo strain and physi-cal stress,Kim et al.͑1994,1995͒introduced a simple parameter, secant pseudo stiffness(S R,or simply pseudo stiffness͒that,to-gether with the rate of change of pseudo-strain energy,can quan-titatively measure microdamage.Pseudo stiffness represents the change in the slope of loops between physical stress and pseudo strain.The decrease in pseudo stiffness indicates damage growth due to repeated cyclic loading.Pseudo stiffness is expressed as␶m where S Rϭpseudo stiffness;␥m Rϭpeak pseudo strain in each physical stress–pseudo strain cycle;and␶mϭphysical stress cor-responding to␥m R.Pseudo Strain CalculationPseudo strain is an essential parameter for applying Schapery’s extended correspondence principle to the hysteretic stress-strain behavior of viscoelastic materials.As shown in Eq.͑1͒,the cal-culation of pseudo strain can be performed by presenting the re-laxation modulus and the strain as analytical functions of time and integrating the product of these functions.The constant cyclic shear strain,␥0,with zero mean strain can be simply represented as an analytical harmonic sinusoidal func-tion.The analytical representation of this shear strain component at time t is␥͑t͒ϭ␥0sin͑␻tϩ␪͒H͑t͒(5) where␥0ϭshear strain amplitude;␻ϭangular velocity;␪ϭregression constant;and H(t)ϭheaviside step function.The regression constant is necessary to match the analytical functions of strain history with measured strain data at the same loading time.Substituting Eq.͑5͒within the deﬁnition of pseudo strain in Eq.͑1͒analytically yields the respective pseudo strain at current time t as␥R͑t͒ϭ1G R͓␥0͉G*͉sin͑␻tϩ␪ϩ␾͔͒(6)where␾ϭphase angle.For simplicity of analysis,the value of the reference shear modulus,G R,is typically assumed to be unity, and Eq.͑6͒can be rewritten as␥R͑t͒ϭ␥0͉G*͉sin͑␻tϩ␪ϩ␾͒(7) As can be seen from this equation,the pseudo strain calculation requires knowledge of the linear viscoelastic dynamic modulus and phase angle.These mechanical properties can be determined from constitutive testing such as static creep,relaxation,and/or dynamic frequency sweep testing.Therefore,pseudo strain at any time can be easily predicted with a well-deﬁned strain history as a function of time and two material properties:dynamic modulus and phase angle.In the study of fatigue,only the peak pseudo strain within each cycle is typically used.The pseudo strain reaches the peak pseudo strain in each cycle when the sine function in Eq.͑7͒becomes1:␥m R͑t͒ϭ␥0͉G*͉(8) where␥m Rϭpeak pseudo strain during each cycle.Thus,the peak pseudo strain at any loading cycle can be easily obtained when-ever the dynamic modulus and the strain amplitude are known.Determination of Relaxation Modulus and Dynamic PropertiesViscoelastic materials subjected to a constant strain experience relaxation so that the stress gradually decreases.Stress relaxation is classiﬁed as a basic material property together with creep in viscoelastic materials.As can be seen in Eq.͑2͒,the calculation of linear viscoelastic stress and the corresponding pseudo strain re-quires the relaxation modulus as a function of time.The relax-ation modulus in the shear mode is deﬁned asG͑t͒ϵ␶͑t͒␥s(9)␶(t )ϭshear stress response;and ␥s ϭapplied static constant shear strain.The relaxation modulus as a function of time is typically de-termined from laboratory relaxation tests by measuring resulting stress under the applied constant strain.An alternative way to deﬁne static relaxation properties is by dynamic frequency sweep testing within the linear viscoelastic region.This is based on the theory of linear viscoelasticity inferring correspondence between frequency domain and time domain.In cyclic load laboratory test-ing,viscoelastic materials normally respond with dynamic prop-erties such as storage modulus due to the elastic characteristic,loss modulus due to the viscous property,and phase angle be-tween stress and strain due to time-dependency.The storage and loss modulus can be used to produce the complex modulus and the phase angle:G *ϭG ЈϩiG Љ(10)␾ϭtan Ϫ1ͩG ЉG Јͪ(11)where G *ϭcomplex shear modulus;G Јϭstorage shear modulus;G Љϭloss shear modulus;and ␾ϭphase angle.The dynamic shear modulus is deﬁned as an absolute value of the complex shear modulus and/or by monitoring the ratio of the peak stress to the peak strain at each cycle:͉G *͉ϵͱ͑G Ј͒2ϩ͑G Љ͒2ϭ␶0␥0(12)where ͉G *͉ϭdynamic shear modulus;␶0ϭpeak stress measured at each cycle;and ␥0ϭapplied cyclic strain amplitude.Eq.͑12͒can be deﬁned in both linear and nonlinear viscoelastic behaviors.However,the linear viscoelastic dynamic modulus is determined by measuring stress,strain,and/or storage and loss modulus within the linear viscoelastic region.Data plots between the modulus and frequency require a curve-ﬁtting function to be used in calculation of linear viscoelas-tic stress and pseudo strain in the constitutive equation.Among many curve-ﬁtting techniques,the Prony series representation has been frequently adopted because the Prony series ﬁts the data more precisely and is more efﬁcient in mathematical operations.The Prony series representations ͑Christensen 1982͒of storage and loss modulus as a function of frequency areG Ј͑␻͒ϭG ϱϩ͚i ϭ1nG i ␻2␳i 2␻2␳i 2ϩ1(13)G Љ͑␻͒ϭ͚i ϭ1nG i ␻␳i␻2␳i 2ϩ1(14)where G ϱϭlong-time equilibrium modulus;G t ϭregression con-stants;␳i ϭrelaxation times;␻ϭfrequency in radian;andn ϭnumber of dashpots in the model.The regression constants in Eqs.͑13͒and ͑14͒can be deter-mined by a so-called collocation method,which is a matching procedure between the measured data and the analytical represen-tation at several points.More detailed information on the collo-cation method is given by Huang ͑1993͒.Given parameters from a Prony series representation deter-mined from the dynamic frequency sweep test,static relaxation modulus as a function of time can be illustrated by the following generalized Maxwell model:nAs can be seen in Eq.͑15͒,the static relaxation modulus is easily formulated by using the material parameters G ϱ,G i ,and ␳i ,which are determined from linear viscoelastic dynamic fre-quency sweep testing.Testing Method and MaterialsAll tests were conducted in the torsional shear,strain-controlled mode.According to a study by Reese ͑1997͒,torsional loading produces a better simulation of damage due to trafﬁc than bend-ing.A cylindrical rather than a rectangular sample,which has been a typical testing geometry for DMA,was adopted in this study to avoid complex stress distributions and for easy data analysis.Fig.1shows the cylindrical DMA sample conﬁguration.Test data ͑applied displacement and corresponding torque ͒were collected by a data acquisition ͑DAQ ͒system with a 16-bit mul-tichannel board.Stresses and strains used in the analysis were average values calculated from the following equations:␥ϭR ␸H(16)␶ϭ2T ␲R 3(17)where R ϭradius of cylinder;H ϭlength of cylinder;␸ϭactuatorangular displacement;and T ϭtransducer torque.Each sample was mounted in the DMA instrument,and the chamber was closed and allowed to equilibrate to the desired testing temperature.All the tests were begun after at least a 20min period of equilibration at the test temperature.Materials and Sample FabricationTwo SHRP-classiﬁed binders,AAD-1and AAM-1,were selected for this study,and some of their rheological material properties are shown in Table 1.The pure binders were mixed with Ottawa sand to form a sand-asphalt mixture capable of maintaining itsFig.1.Cylindrical sample with holders in DMAfacilitates fabrication of a homogenous mixture.Eight percent binder by weight of dry sand was mixed and compacted at pre-determined mixing and compaction temperatures.The8%asphalt content was selected as a reasonable,arbitrary value to provide an average‘‘ﬁlm thickness’’of approximately10microns.The term ‘‘ﬁlm thickness’’is used with the understanding that it is a con-troversial term.The mixing and compaction temperatures were determined according to AASHTO T209and were160and 142°C for AAD-1and164and152°C for AAM-1,respectively. Each sample was compacted in a specially fabricated mold͑Fig. 2͒.The loose sand asphalt mixture was evenly distributed into themold and compacted by applying static pressure.The11.5grams of loose sand asphalt was determined by trial and error to provide the mass necessary to produce a specimen geometry50mm long and12mm in diameter.A sample holder capable of properly securing the cylindrical sample was developed.Epoxy glue was used to secure the sand-asphalt sample to the holder. Description of Laboratory Tests and ResultsA torsional shear strain sweep test,which deﬁnes mechanical be-havior responding to a continuously increasing strain,was per-formed with two objectives:͑1͒to determine a strain level satis-fying linear viscoelasticity in terms of homogeneity;and͑2͒to investigate strain levels producing maximum shear stress and peak phase ing a strain level within the linear viscoelas-tic region,dynamic frequency sweep tests were performed to ob-tain a master relaxation curve representing the time-dependent properties of the mixture.Strain-controlled torsional shear cyclic tests were then performed at several strains.Each testing scheme is illustrated in Fig.3.Dynamic Shear Strain Sweep TestDynamic strains beginning at0.0065%were applied on replicate samples,and corresponding values of shear modulus were moni-tored as shown in Fig.4.In the theory of linear viscoelasticity,the homogeneity concept indicates that the ratio of stress response to any applied strain is independent of strain magnitude.This char-acteristic can be adopted to the strain sweep test by monitoring the dynamic modulus,͉G*͉,as the strain increases.If the dy-namic modulus does not drop more than10%from its initialTable1.Binder Rheological Material Properties͑Measured Using Dynamic Shear Rheometer at1.59Hz͒TEMPERATURE10°C25°C40°CBinder GradeDM a͑MPa͒PA b͑degrees͒DM͑MPa͒PA͑degrees͒DM͑MPa͒PA͑degrees͒AAD-1AR-4000 4.2560.28690.01978 AAM-1AC-201536 1.2570.05276 Dynamic modulus.b Phaseangle.paction mold assembly for samplefabricationvalue,linear viscoelasticity holds ͑Marasteanu and Anderson 2000͒.Since the strain dependency is a function of temperature and frequency,strain sweep tests were performed at different tem-peratures and frequencies as shown in Fig.4.Any strain can be selected for constitutive testing such as dynamic frequency sweep testing,as the strain is within the linear viscoelastic region over a speciﬁed range of temperature and frequency.Mechanical strength and resistance to increasing strain were investigated by conducting the dynamic strain sweep tests begin-ning at a relatively high strain,0.04%.Testing was continued until sample failure.As shown in Fig.5,maximum shear stress was recorded at approximately 0.7–0.8%strain,while the peak phase angle was measured at approximately 1.0%strain.AAM-1showed much higher maximum shear stress than AAD-1,which demonstrates that AAM-1is stiffer than AAD-1.The test result provides a basic idea for determining a reasonable range of strain levels for fatigue testing,and it deﬁnes mechanical responses due to increasing strain.Fig.6is developed from Fig.5in order to investigate stress levels induced at each strain level.The stress level at each strain was calculated by dividing measured stress at each strain by peak stress.Fig.6shows that AAM-1experiences a higher stress than AAD-1at the same strain level.Dynamic Frequency Sweep TestBased on strain sweep testing results,frequency sweep tests were performed at low strains—no damage.In an attempt to predict relaxation behavior over a long time domain,testing was doneatFig.4.Representative dynamic strain sweep test results at different temperatures andfrequenciesFig.5.Test results from shear strain sweep test ͑25°C͒Fig.7.Master curves and Prony series ﬁtting ͑25°C͒Fig.8.Converted relaxation modulus plots from frequency sweepseveral different temperatures ͑10,25,and 40°C ͒and the time-temperature superposition concept was applied.Fig.7shows master curves of each mixture at 25°C after superposition in the frequency domain and curve ﬁtting with a Prony series.The fre-quency domain master curves were then converted to time do-main relaxation moduli,which is shown in Fig.8.As can be seen in this ﬁgure,the position of relaxation curves further demon-strates that AAM-1is stiffer than AAD-1.Torsional Controlled-Strain Cyclic TestStrain-controlled torsional shear cyclic tests were conducted at three different strain levels:0.20,0.28,and 0.40%at 25°C and 10Hz.Typical hysteretic stress-strain behavior resulting from the cyclic loading is presented in Fig.9at two selected cycles,the 80th and the 3,000th.Stress-strain loops shifted downward with the reduction of dissipated energy,which is determined from the area inside the stress-strain curve.The effect of the damage accu-mulation in a specimen was also investigated using pseudo strain,as described in Fig.10.The changes in area and slope of the hysteresis loop during continuous cyclic loading reﬂect that mi-crodamage has occurred.The propensity for microdamage occur-rence in different mixtures can be determined by measuring the difference in secant slopes ͑pseudo stiffness ͒of the stress–pseudo strain plots during fatigue testing.This method has been used successfully in differentiating the fatigue-resistance potentials of variousbinders.Fig.9.Stress-strain hysteresisloopsFig.11.Fatigue plots based on three different indicators ofdamageFig.12.Typical trend ͑conceptual ͒of strain-controlled fatiguetestsFig.13.Number of loading cycles versus normalized dynamic modulus and phase angle during fatigue testing at different strainA representative data set at a 0.40%strain for AAD-1is com-pared in Fig.11using three different indicators of damage,namely,reduction in normalized values of:͑1͒pseudo stiffness ͑PS ͒;͑2͒dynamic modulus ͑DM ͒;and ͑3͒dissipated strain energy ͑DSE ͒.Normalized values,the ratio of each indicator at certain loading cycles to the initial value,were used to eliminate variabil-ity among the indicators.Each indicator showed reduction due to damage accumulation and reached ﬁrst and second inﬂection points at a certain number of loading cycles.The three damage indicators showed similar behavior.The rate of change in strain energy dissipation precisely charted damage accumulation during fatigue testing.Fig.12illustrates a typical trend for strain-controlled fatigue tests.The ﬁrst inﬂection point ͑FIP ͒is an indi-cator of a signiﬁcant change in fatigue behavior,deﬁning a de-creasing rate of stiffness changes from that point.A plot of phase angle versus loading cycles helps to explain the meaning and signiﬁcance of the second inﬂection point ͑SIP ͒,as shown in Fig.13.Fig.13illustrates the change in dynamic modulus and phase angle due to damage accumulation at different strain levels.The normalized dynamic modulus was used to eliminate sample-to-sample variability.A maximum phase angle followed by a pre-cipitous drop was consistently observed at or near the second inﬂection point.In an attempt to ﬁnd the normalized dynamic modulus and the corresponding number of loading cycles at two inﬂectionpoints,Fig.14.Remaining stiffness at ﬁrst and second inﬂection points ͑AAD-1͒Fig.15.Remaining stiffness at ﬁrst and second inﬂection pointsFig.16.Cross-plot between number of loading cycles at second inﬂection points and number of loading cycles at peak phaseangleFig.17.Applied strain versus number of loading cycles tofailureregression analysis using third-order polynomials was conducted.Two separated regression analyses were used to determine two different inﬂection points with acceptable accuracy.The normal-ized dynamic moduli at the ﬁrst and second inﬂection points are plotted in Fig.14for AAD-1and in Fig.15for AAM-1.Approxi-mately 45–55%of the stiffness reduction was observed at the ﬁrst inﬂection points,while the second inﬂection points corresponded to 70–80%stiffness reduction.The observed number of loading cycles at the second inﬂection points from the regression analysis was compared with the number of loading cycles at the maximum phase angle.Fig.16demonstrates that the number of loading cycles at the maximum phase angle is consistent with that at the second inﬂection point,which is adopted as a point of fatigue failure in this study.This representation of fatigue is considerably more accurate and logical than simply determining failure as an arbitrary condition, e.g.,when 50%of the initial stiffness is reached.The number of loading cycles to failure at each strain level was plotted on a log-log scale in Fig.17.AAD-1,as expected,showed higher fatigue resistance and correspondingly longer fa-tigue life than AAM-1under the strain-controlled test mode.The number of loading cycles to failure for both binders,AAD-1and AAM-1,were correlated with stress levels determined from the shear strain sweep test,as shown in Fig.18.It can be inferred that fatigue life is dependent on the stress level applied and shows ahigh correlation (R 2ϭ0.96)with stress level.A simple power relationship was determined to derive the correlation between fa-tigue life and the stress level:N f ϭA ͑SL ͒ϪB (18)where N f ϭfatigue life;SL ϭstress level;and A and B ϭregressionconstants.The measured fatigue life was cross-plotted with the predicted fatigue life,which is calculated using regression Eq.͑18͒in Fig.19.Only a small deviation from the line of equality is observed,even though the regression model is quite simple.The strength of this approach is the suggestion that a small number of strain sweep tests,which are much simpler and easier to perform than a fatigue test,may be all that is needed to determine the fatigue resistance potential of each binder.The accuracy of the fatigue life prediction model can be improved by considering viscoelastic mechanical properties such as the slope of the curve,the dynamic modulus,and the phase angle,which are determined from the constitutive tests.In an attempt to validate the effect of microdamage healing due to rest periods,torsional shear cyclic tests with rest periods were conducted at 0.28%strain.Two-minute rest periods were applied ten times during the tests.Each rest period was introduced at equal damage levels for each mixture.Since the mixture with AAM-1fatigues twice as fast as the mixture with AAD-1,the rest periods occurred every 1,000cycles for the mixture with AAD-1and every 500cycles for the mixture with AAM-1͑Fig.20͒.Fig.19.Measured versus predicted number of loading cycles tofailureFig.20.Plots of normalized dynamic modulus versus normalizedFig.21.Normalized dynamic modulus versus number of loading cycles with and without rest periods ͑AAD-1͒Fig.22.Normalized dynamic modulus versus number of loadingAfter the last rest period,continuous cyclic loading to failure was applied.Figs.21and22illustrate the effects of microdamage healing due to rest periods.It is observed that the dynamic modu-lus increases after the rest period,and this resulted in an increase in fatigue life.The fatigue life increases in Figs.21and22rep-resent the healing effect due to ten2min rest periods.Average increases in fatigue life measured on replicate samples were8.7 and23.9%for AAD-1and AAM-1,respectively.The binder AAM-1shows better healing potential than AAD-1,which is con-sistent with results shown in previous studies,although AAM-1 has a higher viscosity than the AAD-1.Little et al.͑1999͒studied the mechanism of fracture and healing of asphalt mixtures based on surface energy measurements.The experimental results dem-onstrate an inverse relationship between the healing potential and Lifshitz–Van der Waals surface energy and a direct relationship between the healing potential and acid-base surface energy.The fact that AAM-1shows a higher healing potential than AAD-1is consistent with the fact that it has a higher acid-base surface energy and much lower Lifshitz–Van der Waals surface energy than AAD-1.Concluding RemarksFatigue fracture and microdamage healing of binder-rich cylindri-cal sand-asphalt mixtures were evaluated successfully by per-forming DMA tests on two SHRP-classiﬁed binders,AAD-1and AAM-1.Successful development of this protocol could result in a potential speciﬁcation-type test method because of its rapidity, repeatability,and accuracy.The described approach can be ex-panded to other SHRP-classiﬁed binders and even modiﬁed bind-ers to investigate their fatigue fracture resistance and healing po-tential.Based on the study,the following conclusions can be drawn:1.Dynamic mechanical analysis can be effectively used tocharacterize the fatigue behavior of asphalt binders and mas-tics in torsional fatigue.2.Three different damage parameters proved to be effective asmonitors of fatigue damage during torsional loading:͑1͒a decay in pseudo stiffness;͑2͒a loss of dynamic modulus;and͑3͒a change in dissipated strain energy.3.Plots relating damage as monitored by the three damage pa-rameters showed consistent relationships with two inﬂection points.The second inﬂection point,associated with approxi-mately a70–80%reduction in dynamic modulus and consis-tent with the peak in the phase angle versus number of load cycles for a speciﬁc material,is a reasonable deﬁnition of fatigue failure.4.Healing during several rest periods introduced at equal levelsof damage for the two systems studied increased the fatigue life,as deﬁned by the second inﬂection point,of the two asphalt systems.Asphalt AAM-1is a substantially better healer than asphalt AAD-1.This is in consistent agreement with previous studies on the fatigue and healing characteris-tics of these binders.AcknowledgmentsThe writers would like to acknowledge Western Research Insti-tute and Federal Highway Administration for theirﬁnancial sup-port.ReferencesTransportation Research Record1766,Transportation Research Board,Washington,D.C.,48–56.Bahia,H.,Zhai,H.,Bonnetti,K.,and Kose,S.͑1999͒.‘‘Non-linear vis-coelastic and fatigue properties of asphalt binders.’’J.Assn.Asphalt Paving Technologists,68,1–34.Christensen,R.M.͑1982͒.Theory of viscoelasticity:an introduction, Academic,New York.Christensen,D.W.,and Anderson,D.A.͑1992͒.‘‘Interpretation of dy-namic mechanical test data for paving grade asphalt cements.’’J.Assn.of Asphalt Paving Technologists,61,67–116.Goodrich,J.L.͑1988͒.‘‘Asphalt and polymer modiﬁed asphalt properties related to the performance of asphalt concrete mixes.’’J.Assn.As-phalt Paving Technologists,57,116–175.Goodrich,J.L.͑1991͒.‘‘Asphaltic binder rheology,asphalt concrete rhe-ology,and asphalt concrete mix properties.’’J.Assn.Asphalt Paving Technologists,60,80–120.Hicks,R.G.,Finn,F.N.,Monismith,C.L.,and Leahy,R.B.͑1993͒.‘‘Validation of SHRP binder speciﬁcation through mix testing.’’J.Assn.Asphalt Paving Technologists,62,565–614.Huang,Y.H.͑1993͒.Pavement analysis and design,Prentice-Hall, Englewood Cliffs,N.J.Kim,Y.R.͑1988͒.‘‘Evaluation of healing and constitutive modeling of asphalt concrete by means of the theory of nonlinear viscoelasticity and damage mechanics.’’PhD thesis,Texas A&M Univ.,College Sta-tion,Tex.Kim,Y.R.,Lee,Y.C.,and Lee,H.J.͑1995͒.‘‘Correspondence principle for characterization of asphalt concrete.’’J.Mater.Civ.Eng.,7͑1͒, 59–68.Kim,Y.R.,Lee,H.J.,and Little,D.N.͑1997͒.‘‘Fatigue characterization of asphalt concrete using viscoelasticity and continuum damage theory.’’J.Assn.Asphalt Paving Technologists,66,520–569. Kim,Y.R.,and Little,D.N.͑1990͒.‘‘One-dimensional constitutive mod-eling of asphalt concrete.’’J.Eng.Mech.,116͑4͒,751–772.Kim,Y.R.,Whitmoyer,S.L.,and Little,D.N.͑1994͒.‘‘Healing in asphalt concrete pavements:is it real?’’Transportation Research Record1454,Transportation Research Board,Washington,D.C.,89–96.Lee,H.J.͑1996͒.‘‘Uniaxial constitutive modeling of asphalt concrete using viscoelasticity and continuum damage theory.’’PhD thesis, North Carolina State Univ.,Raleigh,N.C.Lee,H.J.,Daniel,J.S.,and Kim,Y.R.͑2000͒.‘‘Continuum damage mechanics–based fatigue model of asphalt concrete.’’J.Mater.Civ.Eng.,12͑2͒,105–112.Little,D.N.,Lytton,L.R.,Williams,D.A.,and Kim,Y.R.͑1999͒.‘‘An analysis of the mechanism of microdamage healing based on the ap-plication of micromechanicsﬁrst principles of fracture and healing.’’J.Assn.Asphalt Paving Technologists,68,501–542. Marasteanu,M.O.,and Anderson,D.A.͑2000͒.‘‘Establishing linear viscoelastic conditions for asphalt binders.’’Transporation Research Record1728,Transportation Research Board,Washington,D.C.,1–6. Reese,R.͑1997͒.‘‘Properties of aged asphalt binder related to asphalt concrete fatigue life.’’J.Assn.Asphalt Paving Technologists,66, 604–632.Rowe,G.M.͑1993͒.‘‘Performance of asphalt mixtures in the trapezoidal fatigue test.’’J.Assn.Asphalt Paving Technologists,62,344–384. Rowe,G.M.,and Bouldin,M.G.͑2000͒.‘‘Improved techniques to evaluate the fatigue resistance of asphaltic mixes.’’Proc.,2nd En-raphalt and Eurobitume Congress,Barcelona.Schapery,R.A.͑1984͒.‘‘Correspondence principles and a generalized J-integral for large deformation and fracture analysis of viscoelastic media.’’Int.J.Fract.,25,195–223.Smith,B.J.,and Hesp,S.͑2000͒.‘‘Crack pinning in asphalt mastic and concrete:regular fatigue studies.’’Transporation Research Record 1728,Transportation Research Board,Washington,D.C.,75–81. Williams,D.A.͑1998͒.‘‘Microdamage healing in asphalt concretes:re-。

科技英语翻译1

驱动这些机器的动力装置是一台50马力的感应电动机。
► 2）通顺易懂 ► 译文的语言符合译语语法结构及表达习惯，容易为读者所理解和接受。
► A. When a person sees, smells, hears or touches something, then he is perceiving.
2. Cramped(狭窄的) conditions means that passengers’ legs cannot move around freely.
空间狭窄，旅客的两腿就不能自由活动。
3. All bodies are known to possess weight and occupy space.
忠实、通顺（普遍观点）
► 科技英语文章特点：(well-knit structure;tight logic;various styles)结构严谨，逻辑严密，文体多样
1. 科技翻译的标准：准确规范，通顺易懂，简洁明晰 1）准确规范
所谓准确，就是忠实地，不折不扣地传达原文的全部信息内容。所谓规范，就是译文要符合所涉及的科学技或某个专业领域的专业语言表
实验结果等，而不是介绍这是这些结果，理论或现象是由谁发明或发现的。
► In this section, a process description and a simplified process flowsheet are given for each DR process to illustrate the types of equipment used and to describe the flow of materials through the plant. The discussion does not mention all the variations of the flowsheet which may exist or the current status of particular plants. In the majority of the DR processes described in this section, natural gas is reformed in a catalyst bed with steam or gaseous reduction products from the reduction reactor. Partial oxidation processes which gasify liquid hydrocarbons, heavy residuals and coal are also discussed. The reformer and partial oxidation gasifier are interchangeable for several of the DR processes.

《计算机维修工》考证面试题(The computer repairman examines the interview questions)

《计算机维修工》考证面试题（The computer repairman examinesthe interview questions）What are the main brands of computer motherboard today? What are the three main types of motherboard chips?Key points: main board includes: INTEL, microstar, asus, pan UK, technical jia, master teck, elite, lenovo, etcMotherboard chips are: INTEL, VIA, SIS, etc2. Why does Cache Cache increase the speed of data exchange between CPU and memory?Key points: (1) the CPU is fast and the memory is slower than the CPU; When the CPU goes directly to the memory access data, the memory speed cannot keep up with the CPU speed.(2) when processing other tasks in the CPU, the data in memory can be exchanged with the data in the CACHE.(3) when the CPU needs to access data, it can exchange data directly with the CACHE without having to deal with memory.3. The main board chip can be divided into north and south Bridges. How about the division of labor between them?Key points: (1) the north bridge is generally located near the high-speed equipment (CPU, memory, AGP, etc.) and is responsible for the management of high-speed equipment.(2) nanqiao is generally located near the expansion slot and IDE and FDD, and is responsible for the management of low-speed equipment (I/O) equipment.4. What is the BIOS? In what memory? What are the main functions?Key points: (1) the BIOS is the basic input and output system, which is stored in the EEPROM (electric eraser).(2) main function: BIOS interrupt program, BIOS system setup program, POST power self-check, BIOS system to start the bootstrap program.5. Briefly describe the steps and precautions to upgrade the BIOS.Key points: (1) make a system disk, including FLASH BIOS upgrade tools.(2) prepare a new BIOS program(3) after shutdown, the FLASH BIOS jump switch set to be writable(4) start with the prepared floppy disk and run the upgrade tool(5) save the BIOS to the floppy disk, insert the new BIOS data disk, select update BIOS data, enter the new BIOS file name, complete.(6) change the jumper to read only status (7) to restart andenter CMOS for settingWhat is the meaning of AGP? Why use AGP?Key points: (1) AGP: graphics acceleration port.(2) PCI is too slow to satisfy 3D graphics, images and animations.(3) the transmission speed of AGP is much higher than that of PCI, which can meet 3D demand.7. Name the steps to remove CMOS?Key points: (1) turn off the computer (2) to unplug the power (3) to open the box (4) to find the CMOS jumper(5) pull the jumper from 1-2, insert 2-3 stitches for 5 seconds, and then reconnect back to 1-2(6) return the chassis, power supply and restartWhat is the meaning of plug and play? How to use plug and play function? Is it necessary to drive the plug and play device to the motherboard? Why?Key points: (1) automatic setting, allocation of resources, automatic installation of hardware.(2) open the case or plug the new device directly into the expansion slot or interface and start the computer. (3) notnecessarily.(4) if WINDOWS can identify the new device and has the driver of the device, it can automatically drive the device.(5) if WINDOWS cannot identify the new device, or the driver is not set, then the device driver must be installed manually.9. What are the main considerations for selecting the main board? Why?Key points: (1) quality (2) compatibility (3) performance (4) upgrade expansibility (5) after-sales service (6) price10. Brief description of cpus produced by mainstream Intel and AMD in the market? How to guide users to buy CPU correctly?Key points: (1) AMD Thunderbird 1.4 GHZ (266 / scattered)AMD thunderbird processor, 1.4ghz, 266MHZ front-end bus, SocketA architecture 0.18 micron(2) AMD Athlon XP 2000 + (box)Palomino core, main frequency (MHz) 1670, 256 L2, 128L1(3) Intel Pentium iv2.553 GHz (box)Using the Northwood core, 512K level 2 cache, the front-end bus is increased to 533MHz. 13 Socket 478(4) cy young 1.8 G (Socket478)1.8 GHz, Socket478, Willamette core, 1.8 micron L2 cache 128 kWhat is the meaning of CPU overfrequency? How to do overfrequency? What should be noticed in the process of overfrequency?(1) the meaning of CPU overfrequency is: the working frequency beyond the CPU calibration(2) use the super frequency jump line on the main board for overfrequency(3) use CMOS setup for overfrequency(4) note: gradually increase the frequency and increase the voltage appropriatelyThe frequency of AGP graphics card is set to the same as the external frequency to upgrade the BIOS to the highest versionIf the system is not stable, try a new fan12. A brief description of mainstream memory in the current market. The main performance indicators and characteristics of memory are pointed out.Key points: (1) the new motherboard USES DDR memory and RDRAM, for example; DDR400 / PC3200, RDRAM400(2) the sales of SDRAM memory on the market are also good, mainly to upgrade the old machines, such as PC100, PC133, etc(3) major brands include: SAMSUNG, hyundai (HY), KINGMAX, KINGSTON, etc(4) main performance indexes: capacity, working frequency, access speed, etc(5) DDR memory is 184 lines, voltage is 2.5 V, and there is a plug gapThe SDRAM memory is 168 lines, voltage is 3.3 V, and there are two plug gaps below13. The relationship between the access speed of DDR memory, the working frequency and the specification model is pointed out.Key points: (1) access speed = 1 / work frequency, and the number behind DDR = 2 * working frequency(2) for example: DDR400 / PC3200 memory, working frequency = 400/2 = 200MHzAccess speed = 1/200M = 5 nanoseconds14. What are the main possible reasons for the floppy disk to be unable to read and write in the floppy drive? How?Main points: (1) floppy disk failure (2) soft drive failure (3) floppy disk and floppy drive have fault (4) write protection(5) use substitution method to judge, open and write protection15. What should be paid attention to with floppy and floppy disks? What operation is most likely to cause floppy disk and floppy disk head damage? How to prevent it?Main points: (1) the floppy disk (2) cannot be inserted or taken out when the light is on(3) keep the workplace clean (4) and keep good storageWhat are the most likely causes of hard disk damage? How can I extend the life of the hard disk?Main points: (1) frequent switch machine (2) vibration during work17. After a long period of computer use, a large amount of debris will be generated on the hard disk. Why? What are the effects of debris on computer work? How to solve the fragmentation problem?Key points: (1) a large number of files are deleted and written to the hard disk(2) the speed drops, even causing the computer to be unstable(3) to defragment the hard disk regularly18. In the general working environment, the hard disk can't be opened and repaired directly. Why? A 10G hard disk, if there is a small bad way around 4G, how can you handle it properly?Key points: (1) the environment in the maintenance site cannot meet the requirements (there is more dust).(2) partition: 4G precent zone, 4G left and right zone, 4G after division, no second area.19. The capacity of a hard disk is 10G, which is divided into three zones: c-4g, d-3g, e-3g; Describe the operation steps of this hard disk partition?Key points: (1) restart the computer to DOS (2) input command FDISK (3) select FAT32(4) delete logical partitions after partitioning, remove extension partitions, and finally delete primary partitions(5) establish primary partition, build extension partition, and finally establish logical partition(6) set the activity partition (7) to restart the computer20. The BOOT sector BOOT of hard disk is vulnerable to virus damage and how to prevent it? If it has been destroyed by the virus, how to solve it?Key points: (1) use anti-virus software to backup BOOT (2) to prevent the firewall of anti-virus software(3) to set up CMOS, it is forbidden to modify the BOOT (4) to make backup with other software(5) use anti-virus software to restore BOOT (6) to useanti-virus software to kill virus (7)21. Briefly describe the operation steps to restore the registry files of the last five boot days?Main points: (1) start to DOS (2) input command SCANREG/RESTORE(3) select the registry file (4) of a startup day to ensure the recovery of the return key22. How does cd-rom work? CD - RW drive?Points: (1) laser laser through condenser will light on CDS, concave and convex surface on the disc will light reflection to the polarizer, then polarizer light beam to the light sensor, again by laser diode drive into 0, 1, signal.(2) cd-rw drive is a type of recorder that can be read, writable, and rewritable23. What is the size of the hard disk buffer? Explain the role of the hard disk buffer?Key points: (1) 2MB (2) to increase the speed of data exchange between memory and hard disk24. The monitor cannot display, what are the possible causes? How?Main points: (1) bad display (2) display card bad (3) bad transmission line (4) bad interface (5) generally can be solved by substitution method25.What are the main performance indicators of graphics card? How to select AGP graphics card?Key points: (1) maximum resolution (2) color number (3) refresh frequency (4) performance (5) need(6) display (7) price (8) brand26. What are the interfaces and types of keyboard and mouse? How to choose?Key points: (1) standard interface, PS / 2 interface, USB interface (2) mechanical, capacitive and film type(3) electromechanical, photoelectric (4) price, brand, quality, demand, performance, etc27. Describe the main performance indicators and sound card selection of sound CARDS?Key points: (1) sampling precision (2) sampling frequency (3) interface (4) (4) channel number (5) interface type(6) middle and high-end sound CARDS mainly include: innovation (Creative)28. What issues should be paid attention to in the selection of cases? What are the current output voltage of the ATX chassis power supply?Key points: (1) color (2) appearance modeling (3) robustness (4) extensibility (5) heat dissipation space(6) electromagnetic shielding (7) power supply quality (8) + / -5, + / -12, + / -3.329. Briefly describe the basic configuration and performance indicators of mainstream computers in the market.Main points: (1) CPU: INTEL P4 2G (2) main board: asus P4B (3) memory: DDR400 / PC3200 256G(4) hard disk: Maxine diamond seven generation 60G (5) display: SONY 17 "flatWhat are the mainstream printers on the market? Describe their strengths and weaknesses.Key points: (1) type: needle, inkjet, laser (2) manufacturers: epson, HP, Canon, etc(3) the advantages of the needle: the ability to print wax paper, print the same multipage and cost low costDisadvantages: slow speed, low accuracy, large noiseInkjet advantage: the price is cheap, color, precision is the disadvantage of the needle: the cost of consumables is high, the life is shorterAdvantages of laser: fast speed, high precision and low noise: high price31. Briefly describe the approach of CMOS entry, and what are the main components of CMOS? What are some of the items that you usually need to revise?Key points: (1) the method of CMOS entry is: restart the computer, press DEL or CTRL + ALT + ESC, etc(2) basic CMOS setup easily sets the CPU BIOS feature to set the chip set parameter SettingsThe PNP/PCI parameter setting is set by the power management settingPassword set IDE automatic detection and save and exit(3) automatic hard disk detection, virus detection Settings, starting sequence, password, password entry mode, whether the motherboard is effective, and the type of data transmission protocol is set.32. After the computer is turned on, there is no reaction. Whatare the possible causes for the failure? How to solve it?Key points: (1) the power supply problem (2) no electricity (3) the main board problem (4) the power switch problem (5) is used for the replacement judgment and solution (abbreviated).33. After the computer is switched on, the power indicator and indicator light are on. The hard disk has been working normally, but it has not been shown. What causes this failure? What should be done?Main points: (1) bad display (2) graphics card bad (3) bad transmission line (4) bad interface(5) the substitution method is used to determine and resolve (abbreviated)34.What are the common failures of the printer? How to judge?Main points: (1) inkjet printer: no ink, judgment method: indicating lightPaper card, judge method: paper card can not get out of the printerPrint head move not spirit, judge method: several indicator light is all bright(2) needle printer: broken needle, judgment method: printedword has blank lineThe color band is bad or unknown, the method of judgment: the word cannot be displayed or very vaguePrint head move not spirit, judge method: several indicator light is all bright(3) laser printer: no toner, judgment method: the printed word will be blurred or incompletePaper card, judge method: paper card can not get out of the printerHow to determine computer power failure?Key points: (1) test with multimeter (2) test with replacement method (abbreviated) (3) test with interpolation method (abbreviated)36. What are the more popular anti-virus software now? How to use it?Key points: (1) currently, the popular antivirus software mainly includes: KV300, ruixing anti-virus, kingsoft poison(2) install anti-virus software on the computer and runanti-virus softwareChoose a dish or folder that you want to kill and poison or poisonNote the difference between "clearing the virus" and "deleting the files that are infected by the virus"If you can't kill the virus in WINDOWS, then use the anti-virus software to start the computer and kill it under the DOS37. What causes the most damage to the optical drive? How to prevent it?Key points: (1) poor quality CD (2) poor working environment(3) automatic kinetic energy (4) prevention: prevention according to the above method38. At present, many websites on the Internet will modify the registration form to make Internet explorer not working properly and how to prevent it? What if it has been modified?Key points: (1) backup the registry, install anti-virus software, and use some small tool software to protect it(2) restore the registry, manually modify the registry, and use some small tool software on the Internet for reduction39. What are the laws and regulations regarding the protection of computer software in China? What is the main content?Key points: (1) the computer software protection ordinance and the regulations of the People's Republic of China on the protection of computer information system.(2) legitimate computer software is protected by law, and the use of non-legitimate software is a tort.(3) the computer on the network information and the registered user and password protected by law, through improper means to steal online information and the registered user and password is a kind of method of behavior.Intermediate computer maintenance skills assessment planTest items:Item 1 name: (host and external connection)Use tools to remove wires from each peripherals to the computer host and then reconnect.Item 2: (main engine removal)Remove the card and chip specified in the computer and reinstall it.Item 3: (installation of Windows operating system)Install Windows operating system and driver from hard disk format.Item 4: (error judgment and resolution -- interview)Three questions were randomly selected for the interview.Total time limit:(1) preparation time: 5 min(2) official operation time: 60 min(3) total time: 65 min(4) timing method: after the preparation is completed, the unified order begins the formal operation, which is timed by one of the reviewers.Test scores:1. The ratio of the examineers to the examineers is 1:5.2. Requirements and responsibilities of the assessor:(1) the role of the assessor is to release process instructions and supervise the test personnel's operation.(2) the comments and instructions issued by the assessor to the examineers must be accurate, clear, standardized, concise and to the point, and they are operable.(3) the examinees who violate the rules of the examination and do not follow the process instructions should be warned, and the second violation should be cancelled and the examinee should be disqualified.(4) the assessor should pay attention to the operation safety of the examinees, prevent the operation procedures and the operation of the safety of the person and equipment, and deduct the points as appropriate. The serious person should cancel his examination and decide that the examineer failed the exam.(5) during the examination, one of the assessor is responsible for the timing.(6) each of the five examineers is responsible for one of the assessor s.(7) when grading, the assessor should be odd, 3 or 5.(8) in the evaluation, the assessor shall not prompt the examinees in any way and shall not have any comments on inductive deduction. When in dispute, the candidate must be avoided.(9) when grading, the assessor must indicate the reason for the deduction on the score sheet.(10) after the grading, the assessor should hand over the assessment form to the overall score and no change will be made.Grading methods:A percentage score is applied to the test scores.(2) exam scores applicants every project should score by at least three grade appraisal personnel independence, eachproject exam scores for examination and assessment of all personnel to points of arithmetic mean, finally combined scores for the project.A passing grade of 60 or more.Grading criteria:1. Scoring principles:According to the grading standard score, the score which meets the standard grading requirements is not graded according to the standard score, which is calculated according to the distribution of points.The scale of the test: 100 pointsScore factor score criteria scoreUnplug 2 out of the connecting line, and the method and sequence are correct2 open the case 2 and the method is correctPull out the card 2 and pull out, and the method is correctRemove the CPU fan and CPU 5, and the method is correctRemove 2 out of memory 2 and pull out, and the method is correctRemove the data transmission line and power line 2 of the harddisk, and the method is correctInstall the data transmission line and power line 3 of the hard disk to complete the installation, and the method is correct8 installation memory 3 complete installation, and the method is correctInstall the CPU fan and CPU 5, and the method is correctInstall network card 3 to complete the installation, and the method is correctInstall the machine box 3, and the method is correct12 connect the host and peripherals to complete the installation, method and order correctlyThe C disk is formatted and formatted, and the method is correct14 WINDOWS installation 10 complete installation, and the method is correctThe installation of the install 5 of the network card driver is complete and the method is correct16 sound card driver installation 5 complete installation, and the method is correct17 add protocol: IPX/SPX, NetBEUI 2 completes addition, and the method is correctThe file on the Microsoft network is added with the printer share 2, and the method is correctSet the IP address: 10.13.45. X 2 completes the setting, and the method is correct20. Setting up DNS configuration: 202.96.125.106 2 completes the setting, and the method is correctSet the gateway: 10.13.45.1 2 complete the setting, and the method is correctQuestions 1, 10 are graded according to the integrity of the answersInterview questions 2. 10 according to the completeness of the answerQuestions 3, 10 are graded according to the integrity of the answers。

牺牲性能英语作文

牺牲性能英语作文The Sacrifice of Performance。

In today's fast-paced world, the pursuit of performance and success has become a common goal for many people. Whether it's in the workplace, in sports, or in academics, the pressure to perform at a high level is ever-present. However, in the quest for performance, many individuals may find themselves sacrificing other aspects of their lives, such as their health, relationships, and overall well-being.One of the most common sacrifices that people make in pursuit of performance is their physical health. Many individuals push themselves to the limit in order toachieve their goals, often neglecting their own physicalwell-being in the process. This can lead to a variety of health issues, including stress, fatigue, and burnout. In extreme cases, it can even lead to serious medicalconditions such as heart disease, high blood pressure, and diabetes. In the long run, sacrificing physical health forthe sake of performance is not sustainable and can have serious consequences.Another area where people often sacrifice in thepursuit of performance is their mental health. The pressure to perform at a high level can take a toll on one's mental well-being, leading to anxiety, depression, and other mental health issues. In some cases, individuals may even resort to unhealthy coping mechanisms, such as substance abuse, in order to deal with the stress and pressure of performance. Sacrificing mental health for the sake of performance can have long-lasting effects and can impact one's overall quality of life.In addition to physical and mental health, many individuals also sacrifice their relationships in pursuit of performance. The demands of high-performance careers and other pursuits can often lead to neglect of family and friends, leading to strained relationships and feelings of isolation. This can have a significant impact on one's overall happiness and well-being, as strong social connections are essential for a fulfilling life.Furthermore, the pursuit of performance can also lead to sacrificing one's overall sense of balance and well-being. Many individuals become so focused on achievingtheir goals that they neglect other important aspects of their lives, such as hobbies, relaxation, and self-care. This can lead to feelings of emptiness and dissatisfaction, as well as a lack of fulfillment in life.In conclusion, while the pursuit of performance is a noble goal, it is important to recognize the potential sacrifices that may come with it. It is essential to prioritize one's physical and mental health, as well as maintain strong relationships and a sense of balance in life. By doing so, individuals can achieve their goals while also leading a fulfilling and well-rounded life. It is important to remember that true success is not just about performance, but also about overall well-being and happiness.。

牺牲性能英语作文高中

牺牲性能英语作文高中Sacrificing Performance for a Greater Good。

In today's society, there is a growing emphasis on the importance of sacrificing performance for the greater good. This concept is particularly relevant in the context of high school education, where students are often faced with the dilemma of whether to prioritize their own academic success or contribute to the well-being of their community. While some may argue that sacrificing performance for the greater good is a noble and selfless act, others may argue that it is ultimately detrimental to the individual'sfuture prospects. In this essay, I will explore both perspectives and provide my own insights on this complex issue.On one hand, sacrificing performance for the greater good can be seen as a selfless and noble act. Byprioritizing the needs of others over one's own,individuals can make a meaningful and positive impact ontheir community. For example, a high school student may choose to spend their time volunteering at a local charity instead of studying for an upcoming exam. While this decision may result in a lower grade, it can also lead to a sense of fulfillment and satisfaction that comes from helping others in need. In this way, sacrificing performance for the greater good can foster a sense of empathy, compassion, and social responsibility in individuals, which are all valuable qualities thatcontribute to a more harmonious and inclusive society.On the other hand, sacrificing performance for the greater good can have negative implications for the individual's future prospects. In today's competitive world, academic performance is often closely linked to future opportunities such as college admissions and career prospects. By prioritizing the needs of others over their own academic success, individuals may be putting themselves at a disadvantage in the long run. For example, a student who consistently sacrifices their academic performance in favor of community service may struggle to gain admissionto a top-tier university or secure a competitive job in thefuture. In this way, sacrificing performance for the greater good can be seen as a short-sighted decision that ultimately limits the individual's potential for personal and professional growth.In my opinion, the issue of sacrificing performance for the greater good is a complex and multifaceted one that does not have a one-size-fits-all solution. While it is important to prioritize the needs of others and contribute to the well-being of our communities, it is also crucial to strike a balance between selflessness and self-care. Rather than viewing these two priorities as mutually exclusive, individuals should strive to find ways to integrate them into their lives in a way that allows them to make a positive impact on others while also pursuing their own goals and aspirations.In conclusion, sacrificing performance for the greater good is a complex issue that requires careful consideration and thoughtful reflection. While it is important to prioritize the needs of others and contribute to the well-being of our communities, it is also crucial to considerthe long-term implications of such decisions on our own personal and professional growth. By finding a balance between selflessness and self-care, individuals can make a meaningful and positive impact on their communities while also pursuing their own goals and aspirations.。

工业机器人英汉词汇

工业机器人英汉词汇Aabrasive wheel 砂轮绝对精度absolute accuracy交流变频器驱动AC inverter drive加速性能 acceleration performance加速时间acceleration time准确定位accurate positioning适应控制adaptive controladaptive robot 适应机器⼈附加轴additional axis附加负载additional loadadditional mass附加质量附加操作additional operation㬵黏剂密封adhesive sealingadvanced collision avoidance高级碰撞避免航空航天工业 aerospace industryagricultural robot农业机器人air robot 空中机器人air tube 空气管alignment pose 校准位姿全电动工业机器人 all-electric industrial robotant colony algorithm蚁群算法 anthropomorphic robot 拟人机器人应用程序application program圆弧示教arc teachingarc welding 点焊，电弧焊弧焊机器人arc welding purpose robot电弧焊机器人arc welding robotarch motion 圆弧运动arm 手臂手臂配置arm configuration关节模型articulated model铰接式机器人，关节(形)机器人 articulated robot关节结构articulated structure人工智能artificial intelligence流水线，装配线assembly lineassembly robot 装配机器人atomization air雾化空气attained pose 实到位姿增强现实技术 augmented reality technologyauto part 汽车零件自动码垛automated palletizingautomated production 自动化生产automatic assembly line自动装配线自动控制automatic control末端执行器自动更换装置 automatic end effector exchanger自动物流运输automatic logistics transportautomatic mode 自动模式自动操作automatic operation自动换刀automatic tool changerautomatically controlled自动控制automation technology 自动化技术汽车行业automotive industry辅助轴电缆auxiliary axis cableaxis 轴axis movement 轴运动BBase 机座机座坐标系base coordinate system机座安装面base mounting surfacebeltless structure无带结构bend motion 弯曲运动big data 大数据bio-inspired robotics仿生机器人制动过滤器brake filter制动电阻brake resistor内置碰撞检测功能 built-in collision detection feature内置控制器built-in controller内置梯形图逻辑处理 built-in ladder logic processingbus cable 总线电缆C电缆干扰cable interferencecamera sensor 相机传感器基于相机的工件定位 camera-based part locationCartesian coordinate笛卡尔坐标系笛卡尔坐标机器人 Cartesian coordinate robot直⻆坐标机器人cartesian robot儿童看护机器人child care robotclean room 洁净室clean room robot 清洁室机器人cloud computing 云计算云存储技术cloud storage technology协作机器人collaborative robot彩色触摸屏color touch screencombustible gas 可燃气体command pose 指令位姿commissioning 试运行communication feature 通信功能communication protocol 通信协议紧凑式六臂机器人compact six-axis robotcompliance 柔顺性component placemen 元件贴装复合材料composite materialcompound movement 复合运动compressed air 压缩空气计算机数控computer numerical control计算机数控机床 computer numerical control machine计算机数控系统 computer numerical control systemcomputing control 计算控制computing power 计算能力构形configuration无缝连接connect seamlessly可连接控制器connectable controllerconsumable part 中小型零部件消费类电子产品consumer electronicscontinuous path 连续路径连续路径控制continuous path control轨迹控制continuous- path controlled控制算法control algorithmcontrol electronics电子控制装置control movement 控制运动control program 控制程序control scheme 控制方案control system 控制系统控制器机柜;控制柜 controller cabinet控制器系统面板 controller system panel (CSP)人机协作 cooperation of humans and machines坐标变换 coordinate transformation核心竞争力core competitiveness对应关节corresponding joint曲线示教curve teaching网络物理系统cyber-physical systemcycle 循环cycle time 循环时间圆柱坐标系 cylindrical coordinate systemcylindrical joint圆柱关节圆柱坐标机器人cylindrical robotD达芬奇手术机器人 DaVinci surgical robot电弧焊机器人 dedicated arc welding robot防护等级degree of protectiondegrees of freedom 自由度Delta并联关节机器人 Delta parallel joint robotDelta robot Delta机器人DexTAR教育机器人 DexTAR educational robotdie-casting machine压铸机数字动力digital power直接空气管路direct air line直接耦合direct coupling直接驱动direct drive残障辅助机器人 disability auxiliary robotdisplacement machine 变位机距离准确度distance accuracy距离重复性distance repeatability分布关节distributed jointDOF 自由度double-arm SCARA robot 双臂SCARA机器人 drawing machine 拉丝机drift of pose accuracy位姿准确度漂移位姿重复性漂移 drift of pose repeatability伺服驱动器轴drive controller for axesdrive controller伺服驱动器drive mechanism 驱动机构drive power supply驱动电源驱动比drive ratio驱动单元drive unitdriving device驱动装置dual arm 双臂。

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August 12, 1998
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Contents
1 Introduction
1.1 1.2 1.3 1.4 Contributions . . . . . . . Jitter . . . . . . . . . . . . Potential Jitter Reduction Hypotheses . . . . . . . . Teleconferencing Systems Delay Bu ering . . . . . . Processor Performance . . Real-time Performance . . Network Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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5 Real-time Priority Experiments
5.1 Speci c Experimental Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 5.2 Results and Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 5.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
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7 Quality 8 An Example: Videoconference Quality
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8.1 The Region of Acceptable Videoconference Quality . . . . . . . . . . . . . . . . . . . . . . . . 26 8.2 Predicting Jitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2
8.3 Predicting Latency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4 Predicting Data Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5 Predicting Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.1 Present Videoconference Assumptions . . . . . . . . . . . . . . 8.5.2 Future High-Performance Processors and High-Speed Networks 8.5.3 Future Users . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5.4 Future Processor and Network Load . . . . . . . . . . . . . . .
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9 Conclusions 10 Future Work
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3
Abstract
Multimedia applications have the potential to enhance work for teams of users collaborating across distances. Jitter hampers the e ectiveness of these multimedia applications. Jitter is the variation in the end-to-end delay of data sent from one user to another. Jitter can cause silent gaps in the playout of an audio stream such as in an audioconference, or a choppy appearance to a video stream for a videoconference. We experimentally measure the e ects of three jitter reduction techniques: high-performance processors, real-time priorities and high-speed networks. We incorporate our jitter measurements into a general model for multimedia application quality. Our model allows us to explore how advances in networks and processors will improve application quality compared with real-time priorities. As an example, we apply our model to a videoconference. We nd high-performance processors, real-time priorities and high-speed networks all signi cantly reduce jitter under conditions of heavy processor and network load. For the next ve years, processor and network improvements alone will not reduce jitter enough to eliminate the need for application bu ering techniques. Hon a LAN, real-time priorities can reduce jitter enough to eliminate the need for application bu ering today. On a WAN, especially the Internet, real-time priorities may not be available on all routers, reducing the e ectiveness of real-time priorities in reducing jitter. In this case, bu ering techniques may still be needed.
The E ects of High-Performance Processors, Real-Time Priorities and High-Speed Networks on Jitter in a Multimedia Stream
Mark Claypool claypool@ Worcester Polytechnic Institute Computer Science Department Joe Habermann John Riedl fhabermann,riedlg@ University of Minnesota Computer Science Department
Computer Science Technical Report Series
WORCESTER POLYTECHNIC INSTITUTE