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J.At.Mol.Sci.doi:10.4208/jams.032510.042010a Vol.1,No.3,pp.201-214 August2010Theoretical Raman and IR spectra of tegafur andcomparison of molecular electrostatic potentialsurfaces,polarizability and hyerpolarizability oftegafur with5-ﬂuoro-uracil by density functionaltheoryOnkar Prasad∗,Leena Sinha,and Naveen KumarDepartment of Physics,University of Lucknow,Lucknow,Pin Code-226007,IndiaReceived25March2010;Accepted(in revised version)20April2010Published Online28June2010Abstract.The5-ﬂuoro-1-(tetrahydrofuran-2-yl)pyrimidine-2,4(1H,3H)-dione,also knownas tegafur,is an important component of Tegafur-uracil(UFUR),a chemotherapy drugused in the treatment of cancer.The equilibrium geometries of”Tegafur”and5-ﬂuoro-uracil(5-FU)have been determined and analyzed at DFT level employing the basis set6-311+G(d,p).The molecular electrostatic potential surface which displays the activitycentres of a molecule,has been used along with frontier orbital energy gap,electricmoments,ﬁrst static hyperpolarizability,to interpret the better selectivity of prodrugtegafur over the drug5-FU.The harmonic frequencies of prodrug tegafur have alsobeen calculated to understand its complete vibrational dynamics.In general,a goodagreement between experimental and calculated normal modes of vibrations has beenobserved.PACS:31.15.E-,31.15.ap,33.20.TpKey words:prodrug,polarizability,hyperpolarizability,frontier orbital energy gap,molecular electrostatic potential surface.1IntroductionThe use of a prodrug strategy increases the selectivity and thus results in improved bioavailability of the drug for its intended target.In case of chemotherapy treatments,the reduction of adverse effects is always of paramount importance.The prodrug whichis used to target the cancer cell has a low cytotoxicity,prior to its activation into cytotoxic form in the cell and hence there is a markedly lower chance of it”attacking”the healthy∗Corresponding author.Email address:prasad onkar@lkouniv.ac.in(O.Prasad)/jams201c 2010Global-Science Press202O.Prasad,L.Sinha,and N.Kumar/J.At.Mol.Sci.1(2010)201-214 non-cancerous cells and thus reducing the side-effects associated with the chemothera-peutic agents.Tegafur,a prodrug and chemically known as5-ﬂuoro-1-(tetrahydrofuran-2-yl)pyrimidine-2,4(1H,3H)-dione,is an important component of’Tegafur-uracil’(UFUR), a chemotherapy drug used in the treatment of cancer,primarily bowel cancer.UFUR is a ﬁrst generation Dihydro-Pyrimidine-Dehydrogenase(DPD)inhibitory Flouropyrimidine drug.UFUR is an oral agent which combines uracil,a competitive inhibitor of DPD,with the5-FU prodrug tegafur in a4:1molar ratio.Excess uracil competes with5-FU for DPD, thus inhibiting5-FU catabolism.The tegafur is taken up by the cancer cells and breaks down into5-FU,a substance that kills tumor cells.The uracil causes higher amounts of 5-FU to stay inside the cells and kill them[1–4].The present communication deals with the investigation of the structural,electronic and vibrational properties of tegafur due to its biological and medical importance inﬁeld of cancer treatment.The structure and harmonic frequencies have been determined and analyzed at DFT level employing the basis set6-311+G(d,p).The optimized geometry of tegafur and5-FU and their molecular properties such as equilibrium energy,frontier orbital energy gap,molecular electrostatic potential energy map,dipole moment,polar-izability,ﬁrst static hyperpolarizability have also been used to understand the properties and activity of the drug and prodrug.The normal mode analysis has also been carried out for better understanding of the vibrational dynamics of the molecule under investi-gation.2Computational detailsGeometry optimization is one of the most important steps in the theoretical calculations. The X-ray diffraction data of the tegafur monohydrate and the drug5-FU,obtained from Cambridge Crystallographic Data Center(CCDC)were used to generate the initial co-ordinates of the prodrug tegafur and drug5-FU to optimize the structures.The Becke’s three parameter hybrid exchange functionals[5]with Lee-Yang-Parr correlation func-tionals(B3LYP)[6,7]of the density functional theory[8]and6-311+G(d,p)basis set were chosen.All the calculations were performed using the Gaussian03program[9].TheFigure1:Optimized structure of Tegafur and5-ﬂuoro-uracil at B3LYP/6-311+G(d,p).O.Prasad,L.Sinha,and N.Kumar/J.At.Mol.Sci.1(2010)201-214203Figure2:Experimental and theoretical Raman spectra of Tegafur.model molecular structure of prodrug tegafur and drug5-FU are given in the Fig.1.Pos-itive values of all the calculated vibrational wave numbers conﬁrmed the geometry to be located on true local minima on the potential energy surface.As the DFT hybrid B3LYP functional tends to overestimate the fundamental normal modes of vibration,a scaling factor of0.9679has been applied and a good agreement of calculated modes with ex-perimental ones has been obtained[10,11].The vibrational frequency assignments have been carried out by combining the results of the Gaussview3.07program[12],symmetry considerations and the VEDA4program[13].The Raman intensities were calculated from the Raman activities(Si)obtained with the Gaussian03program,using the following relationship derived from the intensity theory of Raman scattering[14,15]I i=f(v0−v i)4S iv i{1−exp(−hc v i/kT)},(1)where v0being the exciting wave number in cm−1,v i the vibrational wave number of i th normal mode,h,c and k universal constants and f is a suitably chosen common nor-malization factor for all peak intensities.Raman spectra has been calculated according to the spectral database for organic compounds(SDBS)literature,using4880˚A as excit-ing wavelength of laser source with200mW power[16].The calculated Raman and IR spectra have been plotted using the pure Lorentzian band shape with a band width of FWHM of3cm−1and are shown in Fig.2and Fig.3,respectively.204O.Prasad,L.Sinha,and N.Kumar/J.At.Mol.Sci.1(2010)201-214Figure3:Experimental and theoretical IR spectra of Tegafur.The density functional theory has also been used to calculate the dipole moment, mean polarizability<α>and the totalﬁrst static hyperpolarizabilityβ[17,18]are given as for both the molecules in terms of x,y,z components and are given by following equationsµ=(µ2x+µ2y+µ2z)1/2(2)<α>=13αxx+αyy+αzz,(3)βTOTAL=β2x+β2y+β2z1/2=(βxxx+βxyy+βxzz)2+(βyyy+βyxx+βyzz)2+(βzzz+βzxx+βzyy)21/2.(4)Theβcomponents of Gaussian output are reported in atomic units and therefore the calculated values are converted into e.s.u.units(1a.u.=8.3693×10−33e.s.u.).O.Prasad,L.Sinha,and N.Kumar/J.At.Mol.Sci.1(2010)201-214205 3Results and discussion3.1Geometric structureThe electronic structure of prodrug tegafur and the drug5-FU have been investigated, in order to assess the effect of introduction ofﬁve-membered ring having an electron withdrawing carbonyl group to the drug5-FU for better selectivity of target cancer cells. The optimized molecular structures with the numbering scheme of the atoms are shown in Fig. 1.The ground state optimized parameters are reported in Table1.Theﬁve-membered ring in case of tegafur adopts an envelope conformation,with the C(14)atom, acting as theﬂap atom,deviating from the plane through the remaining four carbon atoms.The C-C and C-H bond lengths ofﬁve-membered rings lie in the range1.518˚A ∼1.556˚A and1.091˚A∼1.096˚A respectively.The endocyclic angles ofﬁve-membered ring lie between103.50to108.00whereas there is a sharp rise in the endohedral angle values(129.1◦)at N(6)atom and sharp fall in the angle values(111.3◦)at C(8)atom in the six-membered hetrocyclic ring.The C(7)=O(2)/C(8)=O(3)/C(12)=O(4)bond lengths are equal to1.217/1.211/1.202˚A and are found to be close to the standard C=O bond length(1.220˚A).These calculated bond length,bond angles are in full agreement with those reported in[19,20].The skeleton of tegafur molecule is non-planar while the5-FU skeleton is planar.The optimized parameters agree well with the work reported by Teobald et al.[21].The angle between the hetrocyclic six-membered ring plane andﬁve-membered ring plane represented byζ(N(5)-C(11)-C(15)-C(12))is calculated at126.1◦.It is seen that most of the bond distances are similar in tegafur and5-FU molecules,al-though there are differences in molecular formula.In the six-membered ring all the C-C and C-N bond distances are in the range1.344∼1.457˚A and1.382∼1.463˚A.Accord-ing to our calculations all the carbonyl oxygen atoms carry net negative charges.The signiﬁcance of this is further discussed in terms of its activity in the next section.Table1:Parameters corresponding to optimized geometry at DFT/B3LYP level of theory for Tegafur and5-FUParameters Tegafur5-FUGround state energy(in Hartree)-783.639204-514.200506Frontier orbital energy gap(in Hartree)0.185850.19593Dipole moment(in Debye) 6.43 4.213.2Electronic propertiesThe frontier orbitals,HOMO and LUMO determine the way a molecule interacts with other species.The frontier orbital gap helps characterize the chemical reactivity and ki-netic stability of the molecule.A molecule with a small frontier orbital gap is more po-larizable and is generally associated with a high chemical reactivity,low kinetic stability206O.Prasad,L.Sinha,and N.Kumar/J.At.Mol.Sci.1(2010)201-214 and is also termed as soft molecule[22].The frontier orbital gap in case of prodrug tega-fur is found to be0.27429eV lower than the5-FU molecule.The HOMO is the orbital that primarily acts as an electron donor and the LUMO is the orbital that largely acts as the electron acceptor.The3D plots of the frontier orbitals HOMO and LUMO,electron density(ED)and the molecular electrostatic potential map(MESP)for both the molecules are shown in Fig.4and Fig.5.It can be seen from theﬁgures that,the HOMO is almost distributed uniformly in case of prodrug except the nitrogen atom between the two car-bonyl groups but in case of5-FU the HOMO is spread over the entire molecule.Homo’s of both the molecules show considerable sigma bond character.The LUMO in case of tegafur is found to be shifted mainly towards hetrocyclic ring and the carbonyl group ofﬁve-membered ring and shows more antibonding character as compared to LUMO of 5-FU in which the spread of LUMO is over the entire molecule.The nodes in HOMO’s and LUMO’s are placed almost symmetrically.The ED plots for both molecules show a uniform distribution.The molecular electrostatic potential surface MESP which is a plot of electrostatic potential mapped onto the iso-electron density surface,simultaneously displays molecular shape,size and electrostatic potential values and has been plotted for both the molecules.Molecular electrostatic potential(MESP)mapping is very use-ful in the investigation of the molecular structure with its physiochemical property rela-tionships[22–27].The MESP map in case of tegafur clearly suggests that each carbonyl oxygen atom of theﬁve and six-membered rings represent the most negative potential region(dark red)but theﬂuorine atom seems to exert comparatively small negative po-tential as compared to oxygen atoms.The hydrogen atoms attached to the six andﬁve-membered ring bear the maximum brunt of positive charge(blue region).The MESP of tegafur shows clearly the three major electrophyllic active centres characterized by red colour,whereas the MESP of the5-FU reveals two major electrophyllic active centres,the ﬂuorine atom seems to exert almost neutral electric potential.The values of the extreme potentials on the colour scale for plotting MESP maps of both molecules have been taken same for the sake of comparison and drawing the conclusions.The predominance of green region in the MESP surfaces corresponds to a potential halfway between the two extremes red and dark blue colour.From a closer inspection of various plots given in Fig. 4and Fig.5and the electronic properties listed in Table1,one can easily conclude how the substitution of the hydrogen atom by theﬁve-membered ring containing an electron withdrawing carbonyl group modiﬁes the properties of the drug5-FU.3.3Electric momentsThe dipole moment in a molecule is an important property that is mainly used to study the intermolecular interactions involving the non bonded type dipole-dipole interactions, because higher the dipole moment,stronger will be the intermolecular interactions.The calculated value of dipole moment in case of tegafur is found to be quite higher than the drug5-FU molecule and is attributed due to the presence of an extra highly electron withdrawing carbonyl group.The calculated dipole moment for both the molecules areO.Prasad,L.Sinha,and N.Kumar/J.At.Mol.Sci.1(2010)201-214207Table2:Polarizability data/a.u.for Tegafur at DFT/B3LYP level of theoryPolarizability TegafurαXX173.315αXY-2.494αYY111.365αXZ-4.149αYZ0.399αZZ92.930<α>125.870Table3:Allβcomponents andβTotal for Tegafur calculated at DFT/B3LYP level of theoryPolarizability TegafurβXXX-54.9411βXXY-57.5539βXYY-13.4605βYYY95.0387βXXZ31.8370βXYZ9.2943βYYZ-22.0880βXZZ57.6657βYZZ-21.7419βZZZ-37.3655βTotal(e.s.u.)0.2808×10−30also given in Table1.The lower frontier orbital energy gap and very high dipole moment for the tegafur are manifested in its high reactivity and consequently higher selectivity for the target carcinogenic/tumor cells as compared to5-FU(refer to Table1).According to the present calculations,the mean polarizability of tegafur(125.870/ a.u.,refer to Table2)is found signiﬁcantly higher than5-FU(66.751/a.u.calculated at the same level of theory as well as same basis set).This is related very well to the smaller frontier orbital gaps of tegafur as compared to5-FU[22].The different components of polarizability are reported in the Table2.Theﬁrst static hyperpolarizabilityβcalculated value is found to be appreciably lowered in case of tegafur(0.2808x10−30e.s.u.,refer to Table3)as compared to5-FU(0.6218x10−30e.s.u.calculated at B3LYP/6-311+G(d,p)). Table3presents the different components of static hyperpolarizability.In addition,βval-ues do not seem to follow the same trend asαdoes,with the frontier orbital energy gaps. This behavior could be explained by a poor communication between the two frontier or-bitals of tegafur.Although the HOMO is almost distributed uniformly in case of tegafur208O.Prasad,L.Sinha,and N.Kumar/J.At.Mol.Sci.1(2010)201-214Figure4:Plots of Homo,Lumo and the energy gaps in Tegafur and5-FU.Figure5:Total Density and MESP of Tegafur and5-FU.but the LUMO is found to be shrunk and shifted mainly towards hetrocyclic ring and the carbonyl group ofﬁve-membered ring and shows more antibonding character than the LUMO of5-FU.It may thus be concluded that the higher”selectivity”of the prodrug tegafur as compared to the drug5-FU may be attributed due to the higher dipole mo-ment and lower values of frontier energy band gap coupled with the lowerﬁrst static hyperpolarizability.3.4Vibrational spectral analysisAs the molecule has no symmetry,all the fundamental modes are Raman and IR active. The66fundamental modes of vibrations of tegafur are distributed among the functional and theﬁnger print region.The experimental and computed vibrational wave num-O.Prasad,L.Sinha,and N.Kumar/J.At.Mol.Sci.1(2010)201-214209 bers,their IR and Raman intensities and the detailed description of each normal mode of vibration of the prodrug tegafur,carried out in terms of their contribution to the total potential energy are given in Table4.The calculated Raman and IR spectra of prodrugTable4:Theoretical and experimental a wave numbers(in cm−1)of TegafurExp a Exp a Calc.Calc.Calc.Calc.Assignment of dominantIR Raman(Unscaled(Scaled IR Raman modes in order of Wave no.Wave no.Wave no.Wave no.Intensity Intensity decreasing potentialin cm−1in cm−1in cm−1)in cm−1)energy distribution(PED)3426-3592347779.8317.38υ(N-H)(100)3076310032193115 3.0919.49υ(C-H)R(99)3033-3117301714.2012.97υas methylene(C-H)(82)30333004310730079.8732.29υas methylene(C-H)(90)-29763097299818.5945.83υas methylene(C-H)(80)--3065296720.6530.88υs methylene(C-H)(96)--305029527.8416.11υ(C-H)pr(98)--3044294610.2419.02υs methylene(C-H)(91)2911-3033293624.9745.77υs methylene(C-H)(84)1721-183********.637.65υ(C12=O)pr(90)1693172317821725461.2581.78υ(C8=O)R(72)1668170717661709871.67 3.93υ(C7=O)R(66)165816611701164776.0842.39υ(C9-C10)(66)+β(H17-C10-C9)(11)14711473151114628.71 2.05sc CH2(93)14661469149314457.829.82sc CH2(87)140014381467142042.97 1.93υ(N5-C)10)(23)+β(N5-C10-C9)(13) +υ(N6-C8)(11)+β(N5-C11-H18)(10)140014031450140320.857.15sc(CH2)(88)13621367141913738.94 3.78β(H16-N6-C7)(52)+υ(C=O)R(20) +β(H17-C10-N5)(11)135613401393134971.90 4.40β(H18-C11-N5)(35) +β(H16-N6-C7)(13)1339-138********.7460.20β(H17-C10-C9)(21)+υ(C9-C10)(14) +υ(N5-C10)(13)+υ(N6-C7)(12)--1343130010.26 1.21methylene(C14)wag(62)+methylene(C15)twisting(13)--1337129414.487.82methylene(C15)wag(56)+methylene(C14)twisting(16)1264126113071266 4.21 1.73methylene(C13)wag(56)+methylene(C14),(C15)twisting(16)1264-12991257 1.958.16Methylene twisting(60)1231-12671225199.09 4.95β(H17-C10-N5)(23)+methylene(C13)twisting(15) +υ(N5-C10)(10)1187-1244120485.739.03Ring deformation1179119912281189 4.29 1.65Methylene twisting(40) +(C11-H18)wag(35)--1193115522.238.09methylene(C13)wag(10) +β(H17-C10-C9)(10)210O.Prasad,L.Sinha,and N.Kumar/J.At.Mol.Sci.1(2010)201-214(continued)Exp a Exp a Calc.Calc.Calc.Calc.Assignment of dominantIR Raman(Unscaled(Scaled IR Raman modes in order of Wave no.Wave no.Wave no.Wave no.Intensity Intensity decreasing potentialin cm−1in cm−1in cm−1)in cm−1)energy distribution(PED)1115-11681131134.60 4.73β(H23-C15-C11)(21) +β(H22-C13-C14)(18)β(H16-N6-C7)(17)1115-11571120 5.9920.48υ(N6-C7)(30)+υ(N5-C10)(16) +methylene twisting(14)1065104510621028 3.60 4.26υ(C-C)pr(28)+β(H18-C11-C12)(13) +methylene twisting(11)1087-1126109020.609.14υ(C-C)pr(35)+β(C12-C13-C14)(12) --10139808.56 6.79υ(C-C)pr(54)+methylene wag(25)941942965934 2.79 1.53υ(C-C)pr(20)+β(H18-C11-C15)(17) +methylene twisting(10)9139219268970.27 6.28methylene rocking(33) +υ(C-C)pr(11)--916886 4.1310.06υ(C-C)pr(59)867-896868 2.20 5.99C-H out of plane Ring wag(79)840-8868570.48 4.53β(H16-N6-C7)(20)+β(H17-C10-C9)(13)+methylene(C13)rocking(13) +methylene(C14)twisting(11)--82780011.31 6.48methylene rocking(69)77378281578950.9325.00β(C10-N5-C7)(27)+β(C9-C10-N5)(16) +υ(F-C)(11)749-760736 5.940.73βout(O-C-N)(78)--75473052.72 2.02βout(O-C-N)(77)+(N-H)wag(10) --746722 5.537.78Ring Breathing mode(51)687704728705 1.7330.18methylene rocking(39) +β(O2-C7-N6)(18)-6466686479.5512.38β(O-C-N)(45)+β(F-C-C)(11) -64665863742.75 2.90(N-H)wag(90)608-6266069.55 2.91β(C-C-C)Pr(18)+β(O-C-C)Pr(18) +(N-H)wag(12)--58256320.4212.86βout(C-C-C)Pr(17)+β(C8-N6-C7)(12) +β(C9-C10-N5)(10)542-550532 2.497.84βout(C-C-C)Pr(31)+β(O-C-C)Pr(15)48249051850110.7119.07β(O-C-C)Pr(32)+Pr torsional mode(12) +Ring Tors.mode(12)430-4694548.9916.04Pr tors.mode(31)+β(N-C-N)(23) +β(N5-C10-C9)(10)-421418405 2.01 1.44Pr tors.mode(29)+Ring Tors.mode(17)--4103967.608.21Ring Tors.mode(54)(continued)Exp a Exp a Calc.Calc.Calc.Calc.Assignment of dominant IR Raman(Unscaled(Scaled IR Raman modes in order ofWave no.Wave no.Wave no.Wave no.Intensity Intensity decreasing potential in cm−1in cm−1in cm−1)in cm−1)energy distribution(PED)-38138937719.530.39β(O2-C7-N6)(22)+Ring Tors.(21) Tors.(O4-C11-C13-C12)(12)-352364352 3.228.17Tors.(F1-C8-C10-C9)(59) +Tors.(O3-N6-C9-C8)(10)-319312302 1.680.76β(C10-C9-F1)(26)+β(C8-N6-C7)(18) +β(C10-N5-C11)(29)+β(C10-N5-C7)(12)--2872787.10 4.57Ring Tors.(24)+βout(C10-C9-F1)(22) +β(C15-C11-N5)(20)--2432360.17 1.90Pr tors.mode(32)+Ring Tors.(30) +βout(C10-C9-F1)(12)--230223 1.08 1.61Pr tors.mode(30) +β(C10-N5-C11)(29)--166160 4.74 3.08Ring Tors.(64)--152147 2.75 4.58Pr tors.mode(20)+Tors.(C15-C11-N5-C7)(19)+Ring Tors(10)+β(C10-N5-C11)(10)--1281230.78 3.22Tors.(C15-C11-N5-C7)(35)+Ring Tors.(33)+Pr tors.mode(17)--7471 1.78 1.29Tors.(C14-C15-C11-N5)(61) +β(C11-N5-C10)(10)--6159 1.36 1.94Ring Tors.(36)+Tors.(C15-C11-N5-C7)(35)--4543 1.18 1.74Tors.(C11-C7-C10-N5)(67) +Tors.(C12-C11-N5-C7)(11)The experimental IR and Raman data have been taken from http://riodb01.ibase.aist.go.jp/sdbs website.Note:υ:stretching;υs:symmetric stretching;υas:asymmetric stretching;β:in plane bending;βout:out of plane bending;Tors:torsion;sc:scissoring;ωag:wagging;Pr:Five-membered ring;Ring:Hetroaromatic six-membered ring tegafur agree well with the experimental spectral data taken from the Spectral Database for Organic Compounds(SDBS)[16].3.4.1N-H vibrationsThe N-H stretching of hetrocyclic six-membered ring of tegafur is calculated at3477 cm−1.As expected,this is a pure stretching mode and is evident from P.E.D.table con-tributing100%to the total P.E.D.,and is assigned to IR wave number at3426cm−1.The discrepancy in the calculated and experimental N-H stretching wave number is due to the intermolecular hydrogen bonding.The mode calculated at637cm−1represents the pure N-H wagging mode which is assigned well with the peak at646cm−1in Raman spectra.3.4.2C-C and C-H vibrationsC-C stretching are observed as mixed modes in the frequency range1600cm−1to980 cm−1for tegafur with general appearance of C-H and C-C stretching modes and are in good agreement with experimentally observed frequencies.C-C stretches are calcu-lated to be1090,980,934and886cm−1.The functional group region in aromatic het-rocyclic compounds exhibits weak multiple bands in the region3100∼3000cm−1.The six-membered ring stretching vibrations as well as the C-H symmetric and asymmet-ric stretching vibrations of methylene group in tegafur are found in the region3125to 2925cm−1.In the present investigation,the strengthening and contraction of C-H bond C(10)-H(17)=108.147pm in hetrocyclic six-membered ring may have caused the C-H stretching peak to appear at3115cm−1having almost100%contribution to total P.E.D. in calculation.This C-H stretching vibration is assigned to the3076cm−1IR spectra. The calculated peaks at3017,3007,2998cm−1and2967cm−1are identiﬁed as methylene asymmetric and symmetric stretching vibrations with more than80%contribution to the total P.E.D.are matched moderately and have been assigned at3033cm−1in the IR and at3004and2976cm−1in Raman spectra respectively.The calculated peaks in the frequency range1475∼1400cm−1of tegafur correspond methylene scissoring modes with more than85%contribution to the total P.E.D.are as-signed at1471/1473and1466/1469cm−1in the IR/Raman spectra.Methylene wagging calculated at1300cm−1(62%P.E.D.),1294and1266cm−1(56%P.E.D.each),show con-siderable mixing with methylene twisting mode,whereas dominant twisting modes are calculated at1257cm−1and1189cm−1with60%and40%contribution to P.E.D.The mode calculated at897,800and705cm−1are identiﬁed as methylene rocking with their respective33%,69%and39%contribution to the total P.E.D.3.4.3Ring vibrationsThe calculated modes at868cm−1and722cm−1represent the pure six-membered ring wagging and breathing modes.As expected the skeletal out of plane deformations/ the torsional modes appear dominantly below the600cm−1.The mode calculated at 789cm−1represent mixed mode with(C-C-N)and(C-N-C)in-plane bending and F-C stretching and corresponds to Raman/IR mode at782/773cm−1.The experimental wave number at646cm−1in Raman spectra is assigned to the in-plane(O-C-N)and(F-C-C) bending at647cm−1.3.4.4C=O vibrationsThe appearance of strong bands in Raman and IR spectra around1700to1880cm−1show the presence of carbonyl group and is due to the C=O stretch.The frequency of the stretch due to carbonyl group mainly depends on the bond strength which in turn depends upon inductive,conjugative,ﬁeld and steric effects.The three strong bands in the IR spectra at 1721,1693and1668cm−1are due to C=O stretching vibrations corresponding to the three C=O groups at C(12),C(8)and C(7)respectively in tegafur.These bands are calculatedat1771,1725and1709cm−1.The discrepancy between the calculated and the observed frequencies may be due to the intermolecular hydrogen bonding.4ConclusionsThe equilibrium geometries of tegafur and5-FU and harmonic frequencies of tegafur molecule under investigation have been analyzed at DFT/6-311+G(d,p)level.In general, a good agreement between experimental and calculated normal modes of vibrations has been was observed.The skeleton of optimized tegafur molecule is non-planar.The lower frontier orbital energy gap and the higher dipole moment values make tegafur the more reactive and more polar as compared to the drug5-FU and results in improved target cell selectivity.The molecular electrostatic potential surface andﬁrst static hyperpolarizabil-ity have also been employed successfully to explain the higher activity of tegafur over its drug5-FU.The present study of tegafur and the corresponding drug in general may lead to the knowledge of chemical properties which are likely to improve absorption of the drug and the major metabolic pathways in the body and allow the modiﬁcation of the structure of new chemical entities(drug)for the improved bioavailability. Acknowledgments.We would like to thank Prof.Jenny Field for providing the crystal data of Tegafur and5-FU from Cambridge Crystallographic data centre(CCDC),U.K. and Prof.M.H.Jamroz for providing his VEDA4software.References[1]L.W.Li,D.D.Wang,D.Z.Sun,M.Liu,Y.Y.Di,and H.C.Yan,Chinese Chem.Lett.18(2007)891.[2] D.Engel, A.Nudelman,N.Tarasenko,I.Levovich,I.Makarovsky,S.Sochotnikov,I.Tarasenko,and A.Rephaeli,J.Med.Chem.51(2008)314.[3]Z.Zeng,X.L.Wang,Y.D.Zhang,X.Y.Liu,W H Zhou,and N.F.Li,Pharmaceutical Devel-opment and Technology14(2009)350.[4]ura,A Azucena,C Carmen,and G Joaquin,Therapeutic Drug Monitoring25(2003)221.[5] A.D.Becke,J.Chem.Phys.98(1993)5648.[6] C.Lee,W.Yang,and R.G.Parr,Phys.Rev.B37(1988)785.[7] B.Miehlich,A.Savin,H.Stoll,and H.Preuss,Chem.Phys.Lett.157(1989)200.[8]W.Kohn and L.J.Sham,Phys.Rev.140(1965)A1133.[9]M.J.Frisch,G.W.Trucks,H.B.Schlegel,et al.,Gaussian03,Rev.C.01(Gaussian,Inc.,Wallingford CT,2004).[10] A.P.Scott and L.Random,J.Phys.Chem.100(1996)16502.[11]P.Pulay,G.Fogarasi,G.Pongor,J.E.Boggs,and A.Vargha,J.Am.Chem.Soc.105(1983)7037.[12]R.Dennington,T.Keith,lam,K.Eppinnett,W.L.Hovell,and R.Gilliland,GaussView,Version3.07(Semichem,Inc.,Shawnee Mission,KS,2003).[13]M.H.Jamroz,Vibrational Energy Distribution Analysis:VEDA4Program(Warsaw,Poland,2004).[14]G.Keresztury,S.Holly,J.Varga,G.Besenyei,A.Y.Wang,and J.R.Durig,Spectrochim.Acta49A(1993)2007.[15]G.Keresztury,Raman spectroscopy theory,in:Handbook of Vibrational Spectroscopy,Vol.1,eds.J.M.Chalmers and P.R.Grifﬁth(John Wiley&Sons,New York,2002)pp.1.[16]http://riodb01.ibase.aist.go.jp/sdbs/(National Institute of Advanced Industrial Scienceand Technologys,Japan)[17] D.A.Kleinman,Phys,Rev.126(1962)1977.[18]J.Pipek and P.Z.Mezey,J.Chem.Phys.90(1989)4916.[19]dd,Introduction to Physical Chemistry,third ed.(Cambridge University Press,Cam-bridge,1998).[20] F.H.Allen,O.Kennard,and D.G.Watson,J.Chem.Soc.,Perkin Trans.2(S1)(1987)12.[21] B.Blicharska and T.Kupka,J.Mol.Struct.613(2002)153.[22]I.Fleming,Frontier Orbitals and Organic Chemical Reactions(John Wiley and Sons,NewYork,1976)pp.5-27.[23]J.S.Murray and K.Sen,Molecular Electrostatic Potentials,Concepts and Applications(El-sevier,Amsterdam,1996).[24]I.Alkorta and J.J.Perez,Int.J.Quant.Chem.57(1996)123.[25] E.Scrocco and J.Tomasi,Advances in Quantum Chemistry,Vol.11(Academic Press,NewYork,1978)pp.115.[26] F.J.Luque,M.Orozco,P.K.Bhadane,and S.R.Gadre,J.Phys.Chem.97(1993)9380.[27]J.Sponer and P.Hobza,Int.J.Quant.Chem.57(1996)959.。

学术交际英语第一部分第4章

eg.3 对该电路作一定量分析是很复杂的。 W: Quantitative analysis of this circuit is complicated. R: A quantitative analysis of this circuit is complicated.
3）Overuse of articles
4）Confusion of “a” and “an”
eg.1 这里应该使用8伏的电池。 W: A 8-volt battery should be used here. R: An 8-volt battery should be used here. eg.2 在这里我们使用一个S形的管子。 W: A S-shaped tube is used here. R: An S-shaped tube is used here. eg.3 这是一个单位。 W: This is an unit. R: This is a unit.
eg.8 通过观察一种新药对病人的影响才能看出它的治疗效果。 W: Through observing the effect of a new kind of drug to patient, one can see its efficiency of cure. R: By observing the effect of a new drug on patients, one can see its therapeutic effect. eg.9 我们在讨论微分方程的时候，将把注意力集中在一次方程上。 W: During our discussion of differential equations, we shall restrict our attention to equations of the first degree. R: In our discussion of differential equations, we shall restrict our attention to equations of the first degree. eg.10 除了该电子外，氢原子还含有一个正质子。 W: Except the electron, hydrogen atom also contains a positive proton. R: In addition to the electron, a hydrogen atom also contains a positive proton.

中考英语作文评分标准及评分说明四川

中考英语作文评分标准及评分说明四川全文共3篇示例，供读者参考篇1Scoring Criteria and Explanation for Middle School English Composition in SichuanThe middle school English composition in Sichuan is an important part of the standardized test for students. The composition test aims to assess the students' English writing skills, vocabulary, grammar, coherence, and creativity. In order to evaluate the students' work fairly and accurately, the examiners use a specific scoring criteria and provide detailed explanations for each score.Scoring Criteria:1. Content (30 points): The content refers to the topic relevance, originality, and coherence of the composition. The students should stick to the topic, present their ideas clearly, and develop the content logically.2. Vocabulary and Grammar (25 points): The vocabulary and grammar score assesses the students' use of vocabulary, sentence structure, and grammar accuracy. The students shoulddemonstrate a good range of vocabulary and use them appropriately in sentences with correct grammar.3. Organization (20 points): The organization score evaluates the coherence and cohesion of the composition. The students should use appropriate paragraph structures, transitions, and connectives to ensure the smooth flow of ideas.4. Creativity (15 points): The creativity score measures the students' ability to present their ideas in an original and engaging way. The students should use imaginative language, examples, and descriptions to make their composition more interesting.5. Language Use (10 points): The language use score focuses on the students' language proficiency, including pronunciation, intonation, and fluency. The students should demonstrate a clear and natural use of English language.Explanation for each score:1. Excellent (100-90): The composition demonstrates a deep understanding of the topic, original ideas, coherent organization, rich vocabulary, accurate grammar, and creative language use. The writing is engaging, persuasive, and error-free.2. Good (89-80): The composition shows a clear understanding of the topic, coherent structure, varied vocabulary, mostly accurate grammar, and some creative language use. The writing is interesting and well-developed with minor errors.3. Average (79-70): The composition presents a basic understanding of the topic, somewhat coherent organization, limited vocabulary, some grammar errors, and little creativity. The writing is somewhat engaging but lacks depth and originality.4. Below average (69-60): The composition demonstrates a weak understanding of the topic, poor organization, limited vocabulary, frequent grammar errors, and lack of creativity. The writing is dull, disjointed, and difficult to follow.5. Poor (59-0): The composition shows a lack of understanding of the topic, incoherent organization, repetitive vocabulary, numerous grammar errors, and no creativity. The writing is confusing, incomprehensible, and full of mistakes.In conclusion, the scoring criteria for the middle school English composition in Sichuan provide a clear and detailed assessment of the students' writing abilities. By following the scoring guidelines and explanations, the examiners can evaluate the students' work objectively and fairly. It is important for thestudents to pay attention to these criteria and strive to improve their writing skills in order to achieve higher scores in the composition test.篇2Grading Criteria and Scoring Explanation for the Middle School English Composition in Sichuan ProvinceThe English composition is an important part of the middle school entrance exam in Sichuan Province. It not only tests the students' language ability but also evaluates their thinking skills and creativity. In order to ensure a fair and accurate assessment of the students' writing, a detailed grading criteria and scoring explanation are provided below.1. Content and Organization (30 points)- Ideas: The composition should have a clear main idea and supporting details that are relevant to the topic. (10 points)- Organization: The composition should have a logical structure with a clear introduction, body paragraphs, and conclusion. (10 points)- Development: The ideas should be well-developed with examples, explanations, and details to support the main points.(10 points)2. Vocabulary and Grammar (30 points)- Vocabulary: The composition should demonstrate a range of vocabulary, including words and phrases that are appropriate for the topic. (15 points)- Grammar: The composition should have correct grammar usage, including verb tenses, subject-verb agreement, and sentence structure. (15 points)3. Language Use and Fluency (20 points)- Clarity: The composition should be clear and easy to understand, with smooth transitions between ideas. (10 points)- Fluency: The composition should be well-written with a variety of sentence structures and language devices. (10 points)4. Creativity and Originality (20 points)- Creativity: The composition should show creativity in the use of language, ideas, and organization. (10 points)- Originality: The composition should be original and unique, showing the student's personal thoughts and perspectives. (10 points)Scoring Explanation:- Excellent (26-30 points): The composition demonstrates a high level of proficiency in all aspects. It is well-organized, with clear ideas, accurate grammar, and a wide range of vocabulary. The language use is fluent and engaging, showing creativity and originality.- Good (21-25 points): The composition is well-written with minor errors in content, vocabulary, or grammar. It shows a good understanding of the topic and demonstrates creativity and originality.- Fair (16-20 points): The composition has some weaknesses in content, vocabulary, or grammar. It may lack clarity or organization, but still conveys the main ideas. It shows some creativity and originality.- Needs Improvement (15 points or below): The composition has significant errors in content, vocabulary, or grammar. It may be unclear or poorly organized, with limited creativity and originality.In conclusion, the grading criteria and scoring explanation provide a clear framework for evaluating the students' English compositions in the middle school entrance exam in Sichuan Province. By focusing on content, vocabulary, grammar, language use, creativity, and originality, the examiners can assess the students' writing skills accurately and fairly.篇3Grading Criteria and Explanation for English Composition in the Middle School Entrance Examination in SichuanEnglish composition is an important part of the middle school entrance examination in Sichuan. It is aimed at assessing students' ability to express ideas clearly and coherently in English. In order to ensure fairness and consistency in grading, a set of grading criteria and explanations have been established for English compositions.1. Content (30 points)- Relevance: Does the composition address the giventopic/task?- Completeness: Is the composition well-developed with relevant details and examples?- Originality: Does the composition show creativity and original thinking?2. Organization (20 points)- Introduction: Does the composition have a clear and engaging introduction?- Body: Is the main idea supported with well-organized paragraphs and logical transitions?- Conclusion: Does the composition have a satisfactory conclusion that ties back to the main idea?3. Vocabulary and Grammar (20 points)- Vocabulary: Is a wide range of vocabulary used appropriately and accurately?- Grammar: Are grammatical structures used correctly, including verb tenses, pronouns, and sentence structures?4. Cohesion and Coherence (15 points)- Cohesion: Are cohesive devices (e.g., transition words, pronouns) used effectively to connect ideas?- Coherence: Is the composition logically and clearly organized?5. Creativity and Style (15 points)- Creativity: Does the composition show originality and creativity in ideas and language use?- Style: Is the composition written in a clear and engaging style that holds the reader's attention?Explanation of Grading- Excellent (26-30 points): The composition is outstanding in all aspects, with a clear and original idea, well-developed content, excellent organization, precise vocabulary and grammar, effective cohesion and coherence, and creative style.- Good (21-25 points): The composition is good in most aspects, with a relevant idea, well-developed content, good organization, mostly accurate vocabulary and grammar, adequate cohesion and coherence, and a clear style.- Average (15-20 points): The composition is average in most aspects, with a somewhat relevant idea, basic content, average organization, basic vocabulary and grammar, some cohesion and coherence issues, and a basic style.- Below Average (0-14 points): The composition is below average in most aspects, with an irrelevant or incomplete idea,poor content, weak organization, limited vocabulary and grammar, lack of cohesion and coherence, and a basic style.In conclusion, the grading criteria and explanations for English composition in the middle school entrance examination in Sichuan are designed to assess students' ability to communicate effectively in English. By following these criteria, examiners can ensure fairness and consistency in grading, and students can understand the expectations for their compositions.。

冲刺讲义

一、Listening Comprehension（听力）Exercise oneSection A:1. Me? Just a little.我？只听懂一点点4. Don’t mention it. （借钱）不客气5. It is really unimaginable. 真的超出想象Section B:6. classmates 同学7. Last Christmas. 上个圣诞节见的面9. USD＄280.280美元10. He hadn’t realized he was speeding. 他还没有意识到超速15. Carry his groceries home. 帮他把杂货带回家Exercise twoSection A:3. perhaps I got to read through them again.也许我该再看一遍4. yes, identical同一的ones. 是的，是同卵双胞胎Section B:9. they try to be friendly to them.他们尽力对他们友好10. at 2:00 两点12. his car was hit from behind.他的车尾被撞了（追尾了）13. he has to finish his report 他得完成他的报告14. See the Niagara.游览尼亚加拉瀑布15. In a bookstore 在书店16. a timetable of events.参观时刻表17. they live far away.他家住得很远（500公里）Exercise threeSection A:2. yes, it is worth your while to do so.是的。

值得你去做3. oh, I am sorry, I didn’t notice it.对不起，我没注意到5. How much do you want to change?你想兑换多少零钱？Section B:8. long holidays attract her 长假期吸引她10. a book store 书店（没提到）12. a couple of items 几件东西13. he is tired of厌倦his work 他厌倦邮局的工作14. sample cutting 切片样品（标本）16. he once gave a book as a present他曾经送他人一本书作为礼物五年前出版的一本小说18. she planned house and other buildings她设计房子和其他建筑物19. the architects were men 建筑设计师都是男的20. storage buildings（她主要设计）仓库Exercise fourSection A:1. no, it is really freezing 是的，天气真寒冷2. maybe tomorrow if I hurry up 如果快些，也许明天能完成Section B:6. it has plenty of light 房间光线很好7. to see a new type of boiler来看新款的热水器9. in the women’s dormitory.在女生宿舍10. their schoolmates 他们的同学16. they may support the employers他们会支持雇主17. a third party would impose a settle 第三方来裁决Exercise fiveSection A:1. no, I don’t mind at all 我一点也不介意3. thank you for saying so很感激你这麽说5. I’m afraid I don’t我恐怕不喜欢Section B:6. toothpaste, coffee and a doll 牙膏，咖啡，洋娃娃12. a bookstore书店16. receptionist and guest接待员和顾客。

植物油中内源性成分的抗氧化作用

马宇晨，王光宜，刘乐乐，等. 植物油中内源性成分的抗氧化作用[J]. 食品工业科技，2023，44（24）：119−130. doi:10.13386/j.issn1002-0306.2023040195MA Yuchen, WANG Guangyi, LIU Lele, et al. Antioxidant Effects of Endogenous Components in Vegetable Oils[J]. Science and Technology of Food Industry, 2023, 44(24): 119−130. (in Chinese with English abstract). doi: 10.13386/j.issn1002-0306.2023040195· 研究与探讨 ·植物油中内源性成分的抗氧化作用马宇晨，王光宜，刘乐乐，李红艳*（南昌大学食品科学与资源挖掘全国重点实验室，江西南昌 330047）摘　要：本研究通过在复配植物油中添加不同的植物油内源性抗氧化物（生育酚、植物甾醇、多酚和角鲨烯），研究不同植物油内源性成分对植物油的抗氧化作用。

采用Schaal 烘箱加速实验，通过脂肪酸组成、酸价、过氧化值、茴香胺值、总氧化值等氧化稳定性指标的变化，评价内源性抗氧化物对复配油氧化稳定性的影响。

结果表明，生育酚和多酚单独作用时抗氧化效果明显，且随浓度的增加而增强。

生育酚和角鲨烯组合作用时，随着生育酚和角鲨烯浓度的升高，呈现先拮抗后协同效应，当生育酚含量大于480 mg/kg ，角鲨烯的存在会显著提高生育酚的抗氧化能力（P <0.05）。

从加速氧化的结果来看，未经预处理去除抗氧化成分的复配油脂肪酸组成只有微小的变化，经过预处理的复配油脂肪酸组成变化范围较大。

经过预处理的复配油酸价和总氧化值在氧化前后的变化量也显著高于未经预处理的复配油（P <0.05），添加生育酚和多酚后，复配油的氧化稳定性得到提高，表明内源性抗氧化成分含量虽少，但对延缓植物油氧化过程起到了至关重要的作用。

教材知识解读选择性必修第二册 Unit 1 Science and Scientists

Ⅰ.认阅读单词1．cholera n．霍乱2．diarrhoea n．腹泻3．dehydration n．脱水4．contradictory adj.相互冲突的；对立的；不全都的5．germ n．微生物；细菌；病菌6．pump n．泵；抽水机；打气筒7．water pump水泵8．household n．一家人；家庭；同住一所(套)房子的人9．raw adj.未煮的；生的；未经处理的；原始的10．statistic n．[pl.]统计数字；统计资料；统计学11．epidemiology n．流行病学12．microscope n．显微镜13．protein n．蛋白质14．cell n．细胞；小房间；单间牢房15．virus n．病毒16．vaccine n．疫苗17．framework n．框架；结构18．theoretical framework理论框架19．rainbow n．彩虹20．concrete n．混凝土adj.混凝土制的；的确的；具体的21．plasma n．血浆22．aerospace n．航空航天工业23．patriotic adj.爱国的24．mechanical adj.机械的；发动机的；机器的25．mechanic n．机械师；机械修理工26．aviation n．航空制造业；航空；飞行27．jet n．喷气式飞机28．missile n．导弹29．astronomer n．天文学家30．astronomy n．天文学31．telescope n．望远镜Ⅱ.记重点单词1．severe adj.极为恶劣的；格外严峻的；严峻的2．subscribe v i.认购(股份)；定期订购；定期交纳(会费)3．suspect v t.& v i.怀疑；疑有；不信任n．犯罪嫌疑人；可疑对象4．blame v t.把……归咎于；责怪；指责n．责怪；指责5．handle n．把手；拉手；柄v t.处理；搬动；操纵(车辆、动物、工具等)；(用手)触碰6．link n．联系；纽带v t.把……连接起来；相关联7．substantial adj.大量的；价值巨大的；重大的8．decrease n．削减；降低；削减量v t.& v i.(使大小、数量等)削减；减小；降低9．transform v t.使改观；使转变形态v i.转变；转变10．thinking n．思想；思维；见解11．finding n．发觉；调查结果；(法律)判决12．initial adj.最初的；开头的；第一的13．solid adj.牢靠的；固体的；坚实的n．固体14．cast v t.(cast，cast)投射；向……投以(视线、笑容等)；投掷15．shadow n．阴影；影子；背光处16．pour v t.倒出；倾泻；斟(饮料)17．leadership n．领导；领导地位；领导才能18．trace v t.追溯；追踪；查出n．痕迹；遗迹；踪迹19．outstanding adj.优秀的；杰出的；明显的20．abstract adj.抽象的；理论上的n．(文献等的)摘要21．concept n．概念；观念22．besides prep.除……之外(还) ad v.而且；此外23．brilliant adj.聪颖的；绝妙的；光明的24．furthermore ad v.此外；再者25．fault n．弱点；过错26．shift n．转变；转换；轮班v i.& v t.转移；挪动；转向Ⅲ.知拓展单词1．frustrated adj.懊恼的；懊丧的；失意的→frustrate v t.使懊恼；使懊丧→frustration n．懊丧；懊恼；挫败2．infection n．感染；传染→infect v t.使感染；传染→infectious adj.感染的；传染的3．proof n．证据；证明；检验→prove v t.证明link v．证明是4．multiple adj.数量多的；多种多样的→multiply v i.& v t.乘；繁殖5．intervention n．介入；出面；干涉→intervene v i.干扰；介入6．pure adj.洁净的；纯的；纯粹的→purely ad v.完全地；纯粹地→purify v t.净化；使……洁净7．defend v t.保卫；防守；辩解→defense/defence n．防备；保卫；爱护8．assistant n．助理；助手→assist v t.& v i.挂念；帮忙→assistance n．挂念；帮忙；救济9．gifted adj.有天赋的；有天才的；天资聪慧的→gift n．礼物；天赋10．steady adj.稳定的；平稳的；稳步的→steadily ad v.稳定地；持续地11．vivid adj.生动的；鲜亮的；丰富的→vividly ad v.生动地；逼真地；鲜亮地1．idiom n．习语；成语2．ignore v t.忽视3．illegal adj.非法的；不合法的4．immediately ad v.马上5．immigration n．移民6．import v t.& n．进口；输入7．impression n．印象；感觉8．incorrect adj.不正确的；错误的Ⅳ.背核心短语1．once and for all最终地；彻底地2．subscribe to同意；赞同3．thanks to幸亏；由于4．break out(战斗、打斗等不开心的事情)突然开头；爆发5．in charge of主管；掌管6．come down患(病)；染上(小病)7．above all最重要的是；尤其是8．die from/of死于9．in time准时；迟早10．be likely to do sth 很可能做某事Ⅴ.悟经典句式1．Cholera used to be one of the most feared diseases in the world，until a British doctor，John Snow，showed how it could be overcome.(until引导的时间状语从句)在英国医生约翰·斯诺向人们呈现如何战胜霍乱之前，霍乱曾是世界上最令人恐惊的疾病之一。

全国大学英语CET四级考试试题及解答参考(2025年)

2025年全国大学英语CET四级考试复习试题及解答参考一、写作（15分）Part I Writing (30 points)Directions: For this part, you are allowed 30 minutes to write a short essay on the topic “The Impact of Artificial Intelligence on Daily Life.” You should start your essay with a brief introduction to the topic, then give specific examples to illustrate your point, and finally, provide a conclusion with your personal view. Your essay should be about 120 to 150 words but no less than 100 words.Writing Sample:The advent of artificial intelligence (AI) has revolutionized our daily lives in numerous ways. From smart homes to advanced medical diagnosis, AI has become an integral part of modern society.In smart homes, AI systems like voice assistants and smart security cameras enhance our convenience and safety. These systems learn from our habits and preferences, making our homes more comfortable and efficient. Moreover, in the healthcare sector, AI algorithms are being used to analyze medical images and identify potential diseases at an early stage, which can significantly improvepatient outcomes.However, the rise of AI also brings challenges. For example, job displacement is a major concern, as AI can perform certain tasks more efficiently than humans. Additionally, there are ethical questions about privacy, data security, and the potential misuse of AI technology.In conclusion, while AI has brought substantial benefits to our daily lives, we must also address its challenges to ensure a balanced and ethical integration of AI into our society.Writing Analysis:•Introduction: The essay starts with a clear introduction to the topic of AI and its impact on daily life, providing a broad perspective.•Body Paragraphs: The body of the essay presents two distinct impacts of AI:•The positive impact of AI in smart homes and healthcare.•The negative impacts of job displacement and ethical concerns.•Conclusion: The essay concludes with a balanced view, acknowledging both the benefits and challenges of AI, and emphasizing the need for ethical considerations.•Structure and Coherence: The essay has a clear structure and is well-organized, making the flow of ideas easy to follow.•Length: The essay meets the required word count, with 120 words, demonstrating the writer’s ability to convey the main points concisely.二、听力理解-短篇新闻（选择题，共7分）第一题News:In recent years, global attention has been drawn to the rapid development of electric vehicles (EVs). According to a recent report by the International Energy Agency (IEA), the number of electric vehicles on the roads worldwide reached 13 million in 2021, up from just 2 million in 2015. The report also indicates that by 2030, the number of electric vehicles is expected to surpass 145 million.Question 1:What has the number of electric vehicles on the roads reached as of 2021 according to the recent report by the IEA?A) 1 millionB) 13 millionC) 2 millionAnswer: BQuestion 2:How many years is it mentioned from 2015 to 2021 in the report?A) 5 yearsB) 6 yearsC) 7 yearsAnswer: BQuestion 3:What is the expected number of electric vehicles by 2030 according to the report?A) 13 millionB) 2 millionC) 145 millionAnswer: C第二题News Item 1:A new study reveals that the global use of electric scooters has increased significantly in recent years. These scooters are becoming a popular form of transportation in cities around the world. However, the study also highlights the environmental and safety concerns associated with the rapid growth in electric scooter usage.Cities are faced with the challenge of managing the increased demand for parking spaces, as well as the potential risks of accidents involving these scooters. Improved infrastructure and regulations are being considered to address these issues.Questions:1、What is the primary topic of the news item?A. The decline of traditional scootersB. The environmental impact of electric scootersC. The safety concerns of using electric scootersD. The rise in global use of electric scooters2、“These scooters are becoming a popular form of transportation in cities around the world.” Which of the following is true regarding the use of electric scooters?A. They are only popular in developed countries.B. They have no environmental impact.C. They are causing a decrease in car usage.D. They have become a common mode of transportation globally.3、“Improved infrastructure and regulations are being considered to address these issues.” What is the implied issue that needs to be addressed?A. The overuse of public transportation.B. The need for more parking spaces for cars.C. The decline in bicycle usage.D. The potential safety risks and management challenges posed by electric scooters.Answers:1.D2.D3.D三、听力理解-长对话（选择题，共8分）First QuestionConversationA: Hey, Sarah! Did you finish listening to the podcast this morning?B: Yeah, I did. It was quite fascinating. Have you checked the transcript on their webpage?A: Not yet. I plan to review what we heard today after work. By the way, I was thinking it would be nice to form a study circle this semester.B: That sounds like a good idea. Could you host a meeting this weekend?A: Sure, I can. I’ll prepare some questio ns for us to discuss, and you can bring in your notes. It’ll make our learning more productive.B: Great! Should we stick to the topics in the podcast or choose something else?A: Let’s talk about the topics in the podcast first. That way, it’ll help us understand the context better.B: Sounds perfect. I have a couple of questions for you. How long have you been listening to podcasts?A: Since about a year now. I find it’s a great way to learn English while doing something productive.B: I agree. What’s your favorite podcast?A: Hmm, I really like “The Economist Briefing.” It covers current events and history, which are topics I find interesting.B: Nice choice. I’m a fan of “TED Talks Daily.” It’s a bit different from “The Economist Briefing” but still educational.A: That’s true. We can switch up the topics as we like. What are youstudying?B: I’m majoring in international relations. The podcast really helps me get more insights into what I’m studying.A: That’s awesome. What about yo ur plans for the future?B: I hope to travel around Europe for my study abroad program next year, so I’m trying to learn more European languages. It would be a great opportunity to practice my English as well.A: That sounds exciting! This weekend, let’s m eet for an hour at my place, okay?B: Sure, that works for me.Q1. What is one reason Sarah likes listening to this podcast?a)To practice her English.b)To pass CET-4.c)To prepare for a trip.d)To learn her major subject.Answer: aQ2. How long has the speaker been listening to podcasts?a)One yearb)Two yearsc)Three yearsd)Half a yearAnswer: aQ3. Who does the speaker admire for choosing “TED Talks Daily”?a)Sarahb) A friendc) A professord)Another studentAnswer: aQ4. What will they do this weekend?a)Meet for an hour at the speaker’s place.b)Join a club activity.c)Go to a coffee shop.d)Attend a lecture on English.Answer: aQuestion 2:Why does Liu feel a bit nervous about the exam?A) He is preparing for it for too long.B) He hasn’t studied hard enough.C) His friends are also enrolled in CET-4 course classes.D) He needs to take a break soon.Answer: AQuestion 3:What advice does Amy give to Liu?A) Enroll in a CET-4 course class.B) Review the past papers.C) Study every day.D) Take a break.Answer: BQuestion 4:What can be inferred about Liu from the conversation?A) He is confident about the exam.B) He has been preparing for the exam for a long time.C) He is ready for the upcoming exam.D) He doesn’t like studying hard.Answer: B四、听力理解-听力篇章（选择题，共20分）第一题Directions: In this section, you will hear a passage. Listen carefully and answer the questions that follow.Passage:In today’s fast-paced digital world, it has become increasingly important for businesses to adopt technologies that improve their efficiency and customer satisfaction. The rise of artificial intelligence (AI) and machine learning (ML) has led to significant advancements in the field of business operations. Companies are now exploring various ways to integrate these technologies to enhance their processes.1、What aspect of business operations has seen significant advancements dueto AI and ML integration?A) Customer serviceB) LogisticsC) Financial managementD) A2、Why is the adoption of AI and ML technologies regarded as important for businesses?A) To reduce operational costsB) To improve customer satisfactionC) To increase operational efficiencyD) C3、Which of the following is NOT an example of how businesses can integrate AI and ML?A) Enhancing predictive analyticsB) Automating routine tasksC) Increasing manual data entryD) C第二题Passage 1The globalization of the economy has brought about significant changes in the world, and one area that has been heavily affected is the sports industry. In this essay, we will explore how globalization has impacted the sports industry,focusing on the growth of international sports events and the role of sports in global culture.1、Why is globalization having a profound impact on the sports industry?A) Because it allows sports to be practiced anywhere in the world.B) Because it has led to the growth of international sports events.C) Because it has changed the way people culture around the world.D) Because it has increased the salaries of professional athletes.2、Which of the following is not mentioned as a change brought about by globalization in the sports industry?A) The increase in cross-cultural interactions.B) The decline in local sports teams.C) The rise of regional sports leagues.D) The increase in global fan bases for various sports.3、What is the main argument made by the essay about the role of sports in global culture?A) Sports have a单一 focus on winning and losing.B) Sports help to foster national pride and identity.C) Sports have become a way for countries to cooperatively compete.D) Sports have lost their relevance due to increased commercialization.Answer Key:1、B2、BThird Question: Listening Comprehension - Listening PassagePassage:Welcome to our final research trip to India. We are in a small village in the state of Kerala, known for its rich cultural heritage and scenic beauty. The village, named Paravoor, has a population of approximately 15,000. Today, we focus on the local economy, which is largely dependent on farming, tourism, and small-scale industries. Currently, the village is facing several challenges, including water scarcity and lack of proper infrastructure. The government plans to implement a new irrigation project, which will provide a significant boost to the agricultural sector. In addition, the village is promoting eco-tourism to diversify its economic base. However, these initiatives require support and investment from both the government and the local community.1、Which of the following is NOT a challenge facing Paravoor Village?A、Water scarcityB、Lack of proper infrastructureC、Dependence on large-scale industriesD、C、2、What is the villagers’ plan to diversify their economic base?A、Developing new industriesB、Promoting eco-tourismC、Increasing agricultural production3、Which of the following is a potential benefit of the new irrigation project?A、It will help diversify the local economy.B、It will improve the infrastructure.C、It will provide water to the entire state.D、C、五、阅读理解-词汇理解（填空题，共5分）第一题Reading PassageAlice, receiving a ring, was extremely pleased. Her father promptly asked, “Have you made up your mind, my dear?” “Not quite,” said Alice ominously, stepping out of her ring. “But I will do so directly,” she declared.With a faint shiver of delight, the father experienced her civil but firm decision and then together they went to bet {?1?} her little servant girl a seventeen-pound horse. While they were thus occupied, the children saw their disagreement. The richest and keenest-uprisinguchepest, perfectly struck their fancy, and though their(Game) competitive position was, by no means, satisfactory, they had no objection to feel very sorry for the seller.1、civil A. 非常高兴的B. 礼貌的；文明的C. 无数的；无休止的D. 非常出色的2、competititive A. 竞争性的；竞赛的B. 嫉妒的；充满敌意的C. 令人厌恶的；讨厌的D. 无能的；不称职的3、keen A. 苦涩的；尖利的B. 明锐的；敏锐的C. 高兴的；愉快的D. 枯燥的；乏味的4、Ominous A. 不吉利的；不祥的B. 温和的；文雅的C. 欢快的；愉快的D. 兴奋的；激动的5、shiver A. 战栗；发抖B. 淡水C. 快速降雨D. 柔软的动物答案:1、B2、A3、B4、A5、A第二题Directions: Read the following text and complete the sentences below. There is one word or phrase missing in each sentence. Choose the most appropriate word or phrase from the options given below each sentence.Reading Passage:The rapid growth of technology has profoundly transformed our social fabric. From the emergence of the internet to the advent of smartphones, our daily interactions and work routines have been fundamentally altered. These technological advancements have not only facilitated instant communication but also expanded our access to information. However, this shift comes with its own set of challenges. For instance, while the internet provides a vast array of resources, it also exposes us to misinformation and the need for digital literacy is increasingly important. Moreover, the reliance on technology in the workplace has raised concerns about job security, as automation and artificial intelligence continue to evolve and change the nature of work.1、The word “fabric” (Line 1) most closely r elates to the following word: _[Options: a) fabric b) structure c) society d) clothing_]•1、c) society2、The phrase “emergence of the internet” (Line 3) can be replaced with which of the following: _[Options: a) the start of the internet b) the appearance of the internet c) the deployment of the internet d) the invention of the internet_]•2、b) the appearance of the internet3、The word “instant” (Line 4) is synonymous with: _[Options: a) immediate b) brief c) quick d) rapid_]•3、a) immediate4、The challenge mentioned in the passage regarding the internet is: _[Options: a) accessing information b) exposure to misinformation c) maintaining digital literacy d) balancing physical and digital interactions_]•4、b) exposure to misinformation5、The phrase “nature of work” (Line 7) refers to: _[Options: a) the quality of work b) the purpose of work c) the essence of work d) the value of work_]•5、c) the essence of work六、阅读理解-长篇阅读（选择题，共10分）第一题Reading Passage OneIt is widely accepted that education is of great importance to all people. However, there are many arguments on its necessity. While some people believe it is important to receive an education, others argue that education is not essential in one’s life.One of the main arguments for education is that it offers opportunities for personal development. With a good education, individuals can acquire the knowledge and skills needed to succeed in life. They can also improve theircritical thinking abilities and make informed decisions. Furthermore, an education can help individuals become more adaptable and flexible, enabling them to thrive in a changing world.Opponents of education argue that people can succeed without it. They cite examples of successful individuals who dropped out of school, such as Steve Jobs and比尔·盖茨. They believe that talent and opportunities can compensate for a lack of formal education.In the following passage, there are some statements about education. Choose the most suitable answer for each of the following questions.Questions 1-51、Which of the following is the main issue discussed in the reading passage?A. The benefits of educationB. The drawbacks of educationC. The importance of personal developmentD. The relationship between education and success2、What do the proponents of education believe about the role of education in personal development?A. Education hinders personal growth.B. Education does not contribute to skill acquisition.C. Education improves critical thinking and decision-making skills.D. Education makes individuals less adaptable.3、What is the main argument against education mentioned in the passage?A. Education limits personal development.B. Successful individuals can compensate for a lack of education.C. Education stifles creativity and innovation.D. Education takes away opportunities for self-betterment.4、Which of the following does the reading passage NOT mention as a reason for supporting education?A. Increased opportunities for employment.B. Enhanced critical thinking abilities.C. Improved adaptability and flexibility.D. Theernenment in international cooperation.5、What is the author’s attitude towards the debate on education?A. The author believes that education is unnecessary.B. The author supports the idea that education is essential for personal development.C. The author prefers talent and opportunities over education.D. The author is neutral on the issue of education.Answer Key:1、A2、C3、B4、D5、B第二题Passage:The concept of cloud computing has been discussed for decades, but it has only recently become a practical solution for businesses and individuals. Itall began with the idea of using the Internet as a transmission medium for data and applications. As technology advanced, the costs of storage and bandwidth became more affordable, making cloud computing a viable option. Today, cloud services range from simple file storage to complex application delivery, and they are accessible via web browsers or special software applications.The benefits of cloud computing are numerous. First, there is no need for costly hardware or maintenance. Cloud providers handle all the backend operations, ensuring that the service runs smoothly without requiring any intervention from users. Second, cloud services are highly scalable, meaning they can handle sudden increases in demand without additional investment. Third, cloud computing encourages collaboration and mobility, as users can access data and applications from anywhere with an internet connection. Finally, cloud services often come with robust security features, which are continuously updated, minimizing the risk of data breaches.However, cloud computing also comes with challenges. Security remains a significant concern, as data is stored remotely and vulnerable to cyberattacks. Additionally, there is the issue of data sovereignty, where data stored outside a country’s borders may be subject to the laws of that country. Furthermore, some companies may be hesitant to switch to cloud services due to the lack of control over their data, a common concern known as “control issues.”Questions:1、What is the main idea of the passage?a) The history of cloud computing.b) The benefits and challenges of cloud computing.c) The security concerns of cloud computing.d) The scalability of cloud computing.2、Why did cloud computing become practical recently?a) Because of the decreased costs of storage and bandwidth.b) Because of the widespread availability of the Internet.c) Because of the advancement in technology.d) Because of the decreasing demand for hardware.3、What are the benefits of cloud computing mentioned in the passage?a) No need for costly hardware, scalability, collaboration and mobility, and robust security features.b) High scalability, easy maintenance, and data sovereignty.c) Low costs, easy access, and increased data security.d) Remote access, data availability, and decreased bandwidth requirements.4、Which of the following is a challenge of cloud computing?a) The lack of mobility.b) The high costs of hardware.c) The security risks associated with remote data storage.d) The limited availability of web browsers.5、What is the common concern known as “control issues” mentioned in the passage?a) Users have no control over their data.b) Users have control over their data, but it is stored remotely.c) Data stored outside a country’s borders may be subject to the laws of that country.d) Users can choose to control their data through special software applications.Answers:1、b) The benefits and challenges of cloud computing.2、a) Because of the decreased costs of storage and bandwidth.3、a) No need for costly hardware, scalability, collaboration and mobility, and robust security features.4、c) The security risks associated with remote data storage.5、a) Users have no control over their data.七、阅读理解-仔细阅读（选择题，共20分）First Reading Comprehension Part AReading PassageThe following is a passage about the importance of exercise for mental health and productivity. This passage is followed by some questions to which the answers can be found in the passage.In today’s fast-paced world, stress has become an integral part of our lives. It’s essential to find ways to manage and reduce stress to maintain both our mental and physical health. One effective way to combat stress is through regularexercise. Research has consistently shown that physical activity can have a profound impact on our mental well-being and productivity.1.Physical activity has been found to:A) improve mental healthB) enhance productivityC) both improve mental health and enhance productivityD) have no effect on mental health2.The passage primarily discusses:A) the negative impact of stress on mental healthB) the benefits of exercise in reducing stressC) the effectiveness of various stress management techniquesD) the effects of different types of stress on the body3.It is mentioned that physical activity can have a “profound impact” on our:A) attention spanB) moodC) ability to sleepD) All of the above4.The word “integral” in the first paragraph most closely means:A) essentialB) foundationC) simpleD) occasional5.According to the passage, what is one effective way to combat stress?A) Avoiding situations that cause stressB) Seeking professional helpC) Regular physical activityD) Meditating for a few minutes dailyOptions:1、C2、B3、D4、A5、C第二题阅读下面的文章，然后回答问题。

A theory of weak bisimulation for core cml

J.Functional Programming1(1):1–000,January1993c1993Cambridge University Press1A Theory of Weak Bisimulation for Core CMLWILLIAM FERREIRA†Computing LaboratoryUniversity of CambridgeMATTHEW HENNESSY AND ALAN JEFFREY‡School of Cognitive and Computing SciencesUniversity of Sussex1IntroductionThere have been various attempts to extend standard programming languages with con-current or distributed features,(Giacalone et al.,1989;Holmstr¨o m,1983;Nikhil,1990). Concurrent ML(CML)(Reppy,1991a;Reppy,1992;Panangaden&Reppy,1996)is a practical and elegant example.The language Standard ML is extended with two new type constructors,one for generating communication channels,and the other for delayed com-putations,and a new function for spawning concurrent threads of computation.Thus the language has all the functional and higher-order features of ML,but in addition pro-grams also have the ability to communicate with each other by transmitting values along communication channels.In(Reppy,1992),a reduction style operational semantics is given for a subset of CML calledλcv,which may be viewed as a concurrent version of the call-by-valueλ-calculus of(Plotkin,1975).Reppy’s semantics gives reduction rules for whole programs,not for program fragments.It is not compositional,in that the semantics of a program is not deﬁned in terms of the semantics of its subterms.Reppy’s semantics is designed to prove properties about programs(for example type safety),and not about program fragments(for example equational reasoning).In this paper we construct a compositional operational semantics in terms of a labelled †William Ferreira was funded by a CASE studentship from British Telecom.‡This work is carried out in the context of EC BRA7166CONCUR2.2W.Ferreira,M.Hennessy and A.S.A.Jeffreytransition system,for a core subset of CML which we callµCML.This semantics not only describes the evaluation steps of programs,as in(Reppy,1992),but also their communi-cation potentials in terms of their ability to input and output values along communication channels.This semantics extends the semantics of higher-order processes(Thomsen,1995) with types andﬁrst-class functions.We then proceed to demonstrate the usefulness of this semantics by using it to deﬁne a version of weak bisimulation,(Milner,1989),suitable forµCML.We prove that,modulo the usual problems associated with the choice operator of CCS,our chosen equivalence is preserved by allµCML contexts and therefore may be used as the basis for reasoning about CML programs.In this paper we do not investigate in detail the resulting theory but conﬁne ourselves to pointing out some of its salient features;for example standard identities one would expect of a call-by-valueλ-calculus are given and we also show that certain algebraic laws common to process algebras,(Milner,1989),hold.We now explain in more detail the contents of the remainder of the paper.In Section2we describeµCML,a monomorphically typed core subset of CML,which nonetheless includes base types for channel names,booleans and integers,and type con-structors for pairs,functions,and delayed computations which are known as events.µCML also includes a selection of the constructs and constants for manipulating event types,such as and for constructing basic events for sending and receiving values, for combining delayed computations,for selecting between delayed compu-tations,and a function for launching new concurrent threads of computation within a program.The major omission is thatµCML has no facility for generating new channel names.However we believe that this can be remedied by using techniques common to the π-calculus,(Milner,1991;Milner et al.,1992;Sangiorgi,1992).In the remainder of this section we present the operational semantics ofµCML in terms of a labelled transition system.In order to describe all possible states which can arise dur-ing the computation of a well-typedµCML program we need to extend the language.This extension is twofold.Theﬁrst consists in adding the constants of event type used by Reppy in(Reppy,1992)to deﬁneλcv,i.e.constants to denote certain delayed computations.This extended language,which we callµCML cv,essentially coincides with theλcv,the lan-guage used in(Reppy,1992),except for the omissions cited above.However to obtain a compositional semantics we make further extensions toµCML cv.We add a parallel oper-ator,commonly used in process algebras,which allows us to use programs in place of the multisets of programs of(Reppy,1992).Theﬁnal addition is more subtle;we include inµCML cv expressions which correspond to the ed versions of Reppy’s constants for representing delayed computations.Thus the labelled transition system uses as states programs from a language which we call µCML.This language is a superset ofµCML cv,which is our version of Reppy’sλcv, which in turn is a superset ofµCML,our mini-version of CML.The following diagramA Theory of Weak Bisimulation for Core CML3indicates the relationships between these languages:µCMLλcvCMLIn Section3we discuss semantic equivalences deﬁned on the labelled transition of Sec-tion2.We demonstrate the inadequacies of the obvious adaptations of strong and weak bisimulation equivalence,(Milner,1989),and then consider adaptations of higher-order and irreﬂexive bisimulations from(Thomsen,1995).Finally we suggest a new variation called hereditary bisimulation equivalence which overcomes some of the problems en-countered with using higher-order and irreﬂexive bisimulations.In Section4we show that hereditary bisimulation is preserved by allµCML contexts.This is an application of the proof method originally suggested in(Howe,1989)but the proof is further complicated by the fact that hereditary bisimulations are deﬁned in terms of pairs of relations satisfying mutually dependent properties.In Section5we brieﬂy discuss the resulting algebraic theory ofµCML expressions.This paper is intended only to lay the foundations of this theory and so here we simply indicate that our theory extends both that of call-by-valueλ-calculus(Plotkin,1975)and process algebras(Milner,1989).In Section6we show that,up to weak bisimulation equivalence,our semantics coincides with the reduction semantics forλcv presented in(Reppy,1992).This technical result ap-plies only to the common sub-language,namelyµCML cv.In Section7we brieﬂy consider other approaches to the semantics of CML and related languages and we end with some suggestions for further work.2The LanguageIn this section we introduce our languageµCML,a subset of Concurrent ML(Reppy, 1991a;Reppy,1992;Panangaden&Reppy,1996).We describe the syntax,including a typing system,and an operational semantics in terms of a labelled transition system. Unfortunately,there is not enough space in this paper to provide an introduction to pro-gramming in CML:see(Panangaden&Reppy,1996)for a discussion of the design and philosophy of CML.The type expressions for our language are given by:A::A A A A A AThus we have three base types,,and;the latter two are simply examples of useful base types and one could easily include more.These types are closed under four con-structors:pairing,function space,and the less common and type constructors.4W.Ferreira,M.Hennessy and A.S.A.JeffreyOur language may be viewed as a typedλ-calculus augmented with the type constructors A for communication channels sending and receiving data of type A,and A for constructing delayed computations of type A.Let Chan A be a type-indexed family of disjoint sets of channel names,ranged over by k, and let Var denote a set of variables ranged over by x,y and z.The expressions ofµCML are given by the following abstract syntax:e f g Exp::v ce e e e e e x e e eev w Val::x y e x k01c Const::The main syntactic category is that of Exp which look very much like the set of expressions for an applied call-by-value version of theλ-calculus.There are the usual pairing,let-binding and branching constructors,and two forms of application:the application of one expression to another,ee,the application of a constant to an expression,ce.There is also a syntactic category of value expressions Val,used in giving a semantics to call-by-value functions and communicate-by-value channels.They are restricted in form: either a variable,a recursively deﬁned function,x y e,or a predeﬁned literal value for the base types.We will use some syntax sugar,writing y e for x y e when x does not occur in e,and e;f for x e f when x does not occur in f. Finally there are a small collection of constant functions.These consist of a representa-tive sample of constants for manipulating objects of base type,,which could easily be extended,the projection functions and,together with the set of constants for manipulating delayed computations taken directly from(Reppy,1992):and,for constructing delayed computations which can send and receive values,,for constructing alternatives between delayed computations,,for spawning new computational threads,,for launching delayed computations,,for combining delayed computations,,for a delayed computation which always deadlocks,and,for a delayed computation which immediately terminates with a value. Note that there is no method for generating channel names other than using the predeﬁned set of names Chan A.There are two constructs in the language which bind occurrences of variables,xe1e2where free occurrences of x in e2are bound and x y e where free oc-currences of both x and y in e are bound.We will not dwell on the precise deﬁnitions of free and bound variables but simply use f v e to denote the set of variables which have free occurrences in e.If f v e/0then e is said to be a closed expression,which we sometimes refer to as a program.We also use the standard notation of e v x to denote the substitution of the value v for all free occurrences of x in e where bound names may be changed in order to avoid the capture of free variables in v.(Since we are modelling aA Theory of Weak Bisimulation for Core CML5:A B A:A A:A B B:A A::A A A::::A A B B:A A:A:A AFigure1a.Type rules forµCML constant functionsx yΓx:A y:BΓ:Γ:Γx y e:A BΓe:AΓf:BΓe:AΓe f:BΓe:AΓx:A f:BΓe f g:A6W.Ferreira,M.Hennessy and A.S.A.Jeffreythis reduction semantics are of the form:CτCwhere C C are conﬁgurations which combine a closed expression with a run-time envi-ronment necessary for its evaluation,andτis Milner’s notation for a silent action.However this semantics is not compositional as the reductions of an expression can not be deduced directly from the reductions of it constituent components.Here we give a compositional operational semantics with four kinds of judgements:eτe,representing a one step evaluation or reduction,e v e,representing the production of the value v,with a side effect e,e k?x e,representing the potential to input a value x along the channel k,ande k!v e,representing the output of the value v along the channel k.These are formally deﬁned in Figure2,but weﬁrst give an informal overview.In order to deﬁne these relations we introduce extra syntactic constructs.These are introduced as required in the overview but are summarized in Figure3.The rules for one step evaluation or reduction have much in common with those for a standard call-by-valueλ-calculus.But in addition a closed expression e of type A should evaluate to a value of type A and it is this production of values which is the subject of the second kind of judgement.HoweverµCML expressions can spawn subprocesses before returning a value,so we have to allow expressions to continue evaluation even after they have returned a result.For example in the expression:0a;aone possible reduction is(whereτindicates a sequence ofτ-reductions):0a;aτa?11a!0where the process returns the value1before outputting0.For this reason we need a reduc-tion e v e rather than the more usual termination e v.The following diagram illustrates all of the possible transitions from this expression:0a;aτa!0τa?vva!0vA Theory of Weak Bisimulation for Core CML7 judgements of the operational semantics apply to these conﬁgurations.The second,more common in work on process algebras,(Bergstra&Klop,1985;Milner,1989),extends the syntax of the language being interpreted to encompass conﬁgurations.We choose the latter approach and one extra construct we add to the language is a parallel operator,e f.This has the same operational rules as in CCS,allowing reduction of both processes:eαee fαe fand communication between the processes:e k!v ef k?x fe fτe v x fThe assymetry is introduced by termination(a feature missing from CCS).A CML process has a main thread of control,and only the main thread can return a value.By convention, we write the main thread on the right,so the rule is:f v feαeSecondly,e may have spawned some concurrent processes before returning a function,and these should carry on evaluation,so we use the silent rule for constant application:e v e8W.Ferreira,M.Hennessy and A.S.A.JeffreyThe well-typedness of the operational semantics will ensure that v is a function of the appropriate type,.With this method of representing newly created computation threads more of the rules corresponding toβ-reduction in a call-by-valueλ-calculus may now be given.To evaluate an application expression e f,ﬁrst e is evaluated to a value of functional form and then the evaluation of f is initiated.This is represented by the rules:eαee fτe yf g(In fact we use a slightly more complicated version of the latter rule as functions are al-lowed to be recursive.)Continuing with the evaluation of e f,we now evaluate f to a value which is then substituted into g for y.This is represented by the two rules:fτfx f gτf g v xThe evaluation of the application expression c f is similar;f is evaluated to a value and then the constant c is applied to the resulting value.This is represented by the two rulesfτfc fτfδc vHere,borrowing the notation of(Reppy,1992),we use the functionδto represent the effect of applying the constant c to the value v.This effect depends on the constant in question and we have already seen one instance of this rule,for the constant,which result from the fact thatδv v.The deﬁnition ofδfor all constants in the language is given in Figure2f.For the constants associated with the base types this is self-explanatory; the others will be explained below as the constant in question is considered.Note that because of the introduction of into the language we can treat all constants uniformly, unlike(Reppy,1992)where and have to considered in a special manner.In order to implement the standard left-to-right evaluation of pairs of expressions we introduce a new value v w representing a pair which has been fully evaluated.Then to evaluate e f:ﬁrst allow e to evaluate:eαee fτe xf v xThese value pairs may then be used by being applied to functions of type A B.For example the following inferences result from the deﬁnition of the functionδfor the constants and:e v w eeτe m nIt remains to explain how delayed computations,i.e.programs of type A,are han-dled.It is important to realise that expressions of type A represent potential rather than actual computations and this potential can only be activated by an application of theA Theory of Weak Bisimulation for Core CML9eαee fαe feαee f gαe f geαee fαef fαfe f v e fFigure2a.Operational semantics:static rules ge1αege1ge2αegeαeceτeδc v e ee f gτe ge v ee fτe yfg v xv x y g e v ee fτef v xe k?x ef k!v fv vΛk?k?x x10W.Ferreira,M.Hennessy and A.S.A.Jeffreye f g Exp::v ce e e e e e x e e eev w Val::x y e x k01c Const::Figure3a.Syntax ofµCMLv w Val::v v gege GExp::v!v v?ge v ge geΛA vFigure3b.Syntax ofµCML cve f g Exp::ge e eFigure3c.Syntax ofµCMLconstant,of type A A.Thus for example the expression k is of type A and represents a delayed computation which has the potential to receive a value of type A along the channel k.The expression k can actually receive such a value v along channel k,or more accurately can evaluate to such a value,provided some other computation thread can send the value along channel k.The semantics of is handled by introducing a new constructor for values.For certain kinds of expressions ge of type A,which we call guarded expressions,let ge be a value of type A;this represents a delayed computation which when launched initiates a new computation thread which evaluates the expression ge.Then the expression ge reduces in one step to the expression ge.More generally the evaluation of the expressione proceeds as follows:First evaluate e until it can produce a value:eτeeτe geNote that here,as always,the production of a value may have as a side-effect the generation of a new computation thread e and this is launched concurrently with the delayed compu-tation ge.Also both of these rules are instances of more general rules already considered. Theﬁrst is obtained from the rule for the evaluation of applications of the form ce and the second by deﬁningδge to be ge.The precise syntax for guarded expressions will emerge by considering what types of values of the form e can result from the evaluation of expressions of type from the basic languageµCML.The constant is of type A A and thereforethe evaluation of the expression e proceeds byﬁrst evaluating e to a value of type A until it returns a value k,and then returning a delayed computation consisting of an event which can receive any value of type A on the channel k.To represent this event we extend the syntax further by letting k?be a guarded expression for any k and A,with the associated rule:e k eeτe k!vIt is these two new expressions k?and k!v which perform communication between compu-tation threads.Formally k!v is of type and we have the axiom:k?k?x xTherefore in general input moves are of the form e k?x f where e:B and x:A f:B. Communication can now be modelled as in CCS by the simultaneous occurrence of input and output actions:e k?x ef k!v feτeΛobtained,once more,by deﬁningδto beΛ.The constant is of type A A B B.The evaluation of e proceeds in the standard way by evaluating e until it produces a value,which must be of the form ge v,where ge is a guarded expression of type A and v has type A B.Then the evaluation of e continues by the construction of the new delayed computation ge v.Bearing in mind the fact that the production of values can generate new computation threads,this is formally represented by the inference rule:e ge v ege vαveThe construct,of type A A,evaluates its argument to a value v,and thenreturns a trivial a delayed computation;this computation,when activated,immediately evaluates to the value v.In order to represent these trivial computations we introduce a new constructor for guarded expressions,A and the semantics of is then captured by the rule:e v eA vτvThe choice construct e is a choice between delayed computations as has the type A A A.To interpret it we introduce a new choice constructor ge1ge2where ge1and ge2are guarded expressions of the same type.Then e pro-ceeds by evaluating e until it can produce a value,which must be of the form ge1ge2, and the evaluation continues by constructing the delayed computation ge1ge2.This is represented by the rule:e ge1ge2ege2αege1ge2αeΓv:AΓw:BΓge:AΓv:AΓw:AΓv?:AΓge:AΓv:A BΓge1ge2:AΓA v:AΓe:AΓf:BΓτ:A Γv:AΓk?x:AΓw:Bof the form e k ?xf where f may be an open expression we need to consider relations over open expressions.Let an open type-indexed relation R be a family of relations R ΓA such that if e R ΓA f then Γe :A and Γf :A .We will often elide the subscripts from relations,for example writing e R f for e R ΓA f when context makes the type obvious.Let a closed type-indexed relation R be an open type-indexed relation where Γis everywhere the empty context,and can therefore be elided.For any closed type-indexed relation R ,let its open extension R be deﬁned as:e R x :A Bf iff e v x R B f v x for allv :AA closed type-indexed relation R is structure preserving iff:if v R A w and A is a base type then v w ,if v 1v 2R A 1A 2w 1w 2then v i R A i w i ,if ge 1R A ge 2then ge 1R A ge 2,andif v R A B v then for all w :A we have vw R B v w .With this notation we can now deﬁne strong bisimulations over µCML expressions.A closed type-indexed relation R is a ﬁrst-order strong simulation iff it is structure-preserving and the following diagram can be completed:e 1R e 2e 1R e 2ase 1lRe 2lsince the deﬁnition of strong bisimulation demands that the actions performed by expres-sions match up to syntactic identity.This counter-example can also be reproduced using only µCML contexts:kx121kx21since the left hand side can perform the move:kx12τk !x12but this can only be matched by the right hand side up to strong bisimulation:kx21τk !x21In fact,it is easy to verify that the only ﬁrst-order strong bisimulation which is a congruence for µCML is the identity relation.To ﬁnd a satisfactory treatment of bisimulation for µCML,we need to look to higher-order bisimulation ,where the structure of the labels is accounted for.To this end,given a closed type-indexed relation R ,deﬁne its extension to labels R l as:v R l A wk !v R l A k !wkChan BThen R is a higher-order strong simulation iff it is structure-preserving and the followingdiagram can be completed:e 1R e 2e 1R e 2aswhere l 1R l l 2e 1l 1Re 2l 2lotherwise.Then R is a ﬁrst-order weak simulation iff it is structure-preserving and the following diagram can be completed:e 1R e 2e 1R e 2ase 1lRe 2ˆl Let1be the largest ﬁrst-order weak bisimulation.Proposition 3.31is an equivalence.ProofSimilar to the proof of Proposition 3.1.Unfortunately,1is not a congruence,for the same reason as 1,and so we can attempt the same modiﬁcation.R is a higher-order weak simulation iff it is structure-preserving and the following diagram can be completed:e 1R e 2e 1R e 2aswhere l 1R ll 2e 1l 1Re 2ˆl 2Lethbe the largest higher-order weak bisimulation.Proposition 3.4h is an equivalence.ProofSimilar to the proof of Proposition 3.1.However,h is still not a congruence,for the usual reason that weak bisimulation equiva-lence is not a congruence for CCS summation.Recall from (Milner,1989)that in CCS 0τ0but a 00a 0τ0.We can duplicate this counter-example in µCML since the CCS operator corresponds to the µCML operator and 0corresponds to Λ.However may only be applied to guarded expressions and therefore we need a guarded expressionwhich behaves like τ0;the required expression is A Λ.Thus:ΛhA Λsince the right hand side has only one reduction:A ΛτΛτΛbut:Λk !0hA Λk !0because the only reduction of Λk !0is Λk !0k !0ΛΛand:A Λk !0τΛτΛThis counter-example can also be replicated using the restricted syntax of µCML.We have:hsince the left hand side has only one reduction:ΛΛand the right hand side can match this with:A ΛΛand we have seen:ΛhA ΛHowever:k 0hk 0since the left hand side has only one reduction:k 0τΛk !0whereas the right hand side has the reduction:k 0τA Λk !0A ﬁrst attempt to rectify this is to adapt Milner’s observational equivalence for µCML,and to deﬁne h as the smallest symmetric relation such that the following diagram can be completed:e 1he 2e 1he 2aswhere l 1h ll 2e 1l 1he 2l 2Proposition 3.5h is an equivalence.ProofSimilar to the proof of Proposition 3.1.This attempt fails,however,since it only looks at the ﬁrst move of a process,and not at theﬁrst moves of any processes in its transitions.Thus,the above µCML counter-example for h being a congruence also applies to h ;i.e.hbut:k 0hk 0This failure was ﬁrst noted in (Thomsen,1995)for CHOCS.Thomsen’s solution to this problem is to require that τ-moves can always be matched by at least one τ-move,which produces his deﬁnition of an irreﬂexive simulation as a structure-preserving relation where the following diagram can be completed:e 1R e 2e 1R e 2aswhere l 1R l l 2e 1l 1Re 2l 2Letibe the largest irreﬂexive bisimulation.Proposition 3.6iis a congruence.ProofThe proof that i is an equivalence is similar to the proof of Proposition 3.1.The proof that it is a congruence is similar to the proof of Theorem 4.7in the next section.However this relation is rather too strong for many purposes,for example 12i111since the right hand side can perform more τ-moves than the left hand side.This is similar to the problem in CHOCS where a τP i a P .In order to ﬁnd an appropriate deﬁnition of bisimulation for µCML,we observe that µCML only allows to be used on guarded expressions ,and not on arbitrary expressions.We can thus ignore the initial τ-moves of all expressions except for guarded expressions.For this reason,we have to provide two equivalences:one on terms where we are not interested in initial τ-moves,and one on terms where we are.A pair of closed type-indexed relations R R n R s form a hereditary simulation (we call R n an insensitive simulation and R s a sensitive simulation )iff R s is structure-preserving and we can complete the following diagrams:e 1R ne 2e 1R ne 2aswhere l 1R sll 2e 1l 1R ne 2ˆl 2and:e 1R se 2e 1R se 2aswhere l 1R s l l 2e 1l 1R ne 2l 2Let n sbe the largest hereditary bisimulation.Note that we require R s to be structure-preserving because it is used to compare the labels in transitions,which may contain ab-stractions or guarded events.In the operational semantics of µCML expressions,guarded expressions can only appear in labels,and not as the residuals of transitions.This explains why in the deﬁnition of n labels are compared with respect to the sensitive relation s whereas the insensitive relation is used for the residuals.For example,if ge 1n s ge 2then we have:xge 1nxge 2since once either side is applied to an argument,their ﬁrst action will be a τ-step.On the other hand:ge 1nge 2sinceis precisely the construct which allows us to embed ge 1and ge 2in acontext.Theorem 3.7s is a congruence for µCML ,andnis a congruence for µCML.ProofThe proof that s and n are equivalences is similar to the proof of Proposition 3.1.The proof that they form congruences is the subject of the next section.Proposition 3.8The equivalences on µCML have the following strict inclusions:1shh111x1xk k i h k12s i1111n s x1xh n1h h x1xwhere:x x(Note that this settles an open question(Thomsen,1995)as to whether i is the largestcongruence contained in h.)It is the operator which differentiates between the two equivalences n and h.Howeverin order to demonstrate the difference we need to be able to apply to guarded expressionswhich can spontaneously evolve,i.e.performτ-moves.The onlyµCML constructor for guarded expressions which allows this is A,and in turn occurrences of this can only begenerated by theµCML constructor.Therefore:Proposition3.9For the subset ofµCML without and A,n is the same as h,and s is the same as h.ProofFrom Proposition3.8n h.For the subset ofµCML without and A,deﬁne R s as:v w v h w ge1ge2ge1h ge2v1w v2w v1h v2Then since no event without A can perform aτ-move,and since the only initial moves ofv i w areβ-reductions,we can show that h R s forms an hereditary bisimulation,and so h n.From this it is routine to show that s h.Unfortunately we have not been able to show that n is the largestµCML congruence con-tained in weak higher-order bisimulation equivalence.However we do have the following characterisation:Theorem3.10n is the largest higher-order weak bisimulation which respectsµCML contexts.ProofBy deﬁnition,n is a higher-order weak bisimulation,and we have shown that it respectsµCML contexts.All that remains is to show that it is the largest such.Let R be a higher-order weak bisimulation which respectsµCML contexts.Then deﬁne: R n R v1w e2v1R v2v2wτe2e1v2w v1R v2v1wτe1R s v w v R w ge1ge2ge1R ge2v1w v2w v1R v2We will now show that R n R s forms an hereditary simulation,from which we can de-duce R R n n.。

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1
Coherence relations
Introduction
In this paper, I would like to address a methodological question that starts from the following observation: There is a growing number of corpus studies in the area of the use of coherence relations and discourse markers in natural texts. Most of these studies try to establish a relationship between the coherence relations found in the text and the discourse markers used to signal them linguistically, very often inter-clausal connectives (Degand 1996, 1998; Grote, Lenke & Stede 1997; Knott 1996; Mann & Thompson 1992; Oversteegen 1997; Pit, Pander Maat & Sanders 1997; Pander Maat & Sanders 1995, Sanders 1997). However, the results of these studies are hardly ever straightforward to compare. The main reason for this is that the methods used to classify both the coherence relations and their linguistic markers are very often divergent and in the best cases only partially overlapping. So, in order to enable comparison of the different studies, there is a need for clear and explicit classification criteria. In this paper, I will try to set out a number of such (operationalisable) elements that could function as tools in the categorisation task.
The goal will be reached if the categorisation criteria are formulated in such an explicit way that they can be applied by different analysts to all kinds of h assistant at the Belgian National Fund for Scientific Research (F.N.R.S.). 29
justification, motivation, evidence, conclusion, etc. Furthermore, a distinction can be made between (i) epistemic (knowledge of a fact leads to conclusion of a belief), and (ii) speechact relations (a fact leads to the utterance of a speech-act). • _Textual / sequential relations establish a sequential, text organising relation between ideationally and interpersonally only loosely or indirectly related adjacent discourse segments. Examples are: list, joint, etc. or any other ideational or interpersonal relations when they are used as comment, digression, excursus, etc.
2
From connective relation
to
coherence
While the characterisation of these relational domains is general enough so as to account for all different kinds of discourse structures, this generality poses a number of problems as soon as one starts to work with natural texts. Most of the time there is agreement on proto~.'pical examples (very often built-up examples for purposes of illustration), but in actual text analysis one gets rapidly confronted with an important number of ambiguous cases. That is, when one tries to establish what type of coherence relations are present in the text, it becomes rapidly impossible to classify found relations on the basis of these definitions alone. Different elements may account for these problems: (i) coherence relations are not always marked linguistically, (ii) there is no one to one mapping between coherence relation and linguistic discourse marker, and (iii) there is no general consensus on the type of linguistic constructions that may function as discourse markers (connectives, prepositions, adverbials, intonation patterns, cue phrases, etc.). In the literature, connectives are generally considered to be prototypical linguistic markers of coherence relations. In this paper, I will then concentrate on the problems that arise when one tries to relate to each other the discourse domains as described above, the coherence relations and the connectives that may signal these coherence relations. This will be exemplified on the hand of causal constructions.
A classical approach to coherence relations is to classify them into relational or discourse domains: semantic v s . pragmatic (van Dijk 1979; Sanders 1992; Pander Maat & Sanders 1995), content v s . epistemic vs. speech-act (Sweetser 1990), external vs. internal (Halliday & Hasan 1985, Martin 1992), subject matter vs. presentational (Mann & Thompson 1988), ideational vs. interpersonal vs. textual (Degand 1996, Maier & Hovy 1993), ideational vs. rhetorical vs. sequential (Redeker 1991). These classifications all account for the fact that there are different types of coherence relations that exist at several "levels", "strata", "planes" or "domains" of the discourse. It is striking to note that there is a great amount of agreement between the authors with respect to the different general types of coherence relations. They can be grossly characterised as follows: ® Ideational / semantic / content / external / subject matter relations establish a link between discourse units that denote states of affairs in the world described in the discourse. Examples are: cause, sequence, contrast, etc. Interpersonal / pragmatic / internal / presentational / rhetorical relations establish a link between the illocutionary meaning of one of the discourse units with the Iocutionary meaning of the other. Examples are: