Solubility and Diffusion of H2S and CO2 in the Ionic Liquid
Solubility and Diffusion of H2S and CO2in the Ionic Liquid
1-(2-Hydroxyethyl)-3-methylimidazolium Tetra?uoroborate
Mohammad Shokouhi,Mina Adibi,Amir Hossein Jalili,*Masih Hosseini-Jenab,and Ali Mehdizadeh
Gas Science Department,Research Institute of Petroleum Industry(RIPI),National Iranian Oil Company(NIOC),
P.O.Box14665-137,West Blvd.Azadi Sports Complex,Tehran,Iran
The solubilities and diffusion coef?cients of hydrogen sul?de and carbon dioxide gases in the ionic liquid (IL)1-(2-hydroxyethyl)-3-methylimidazolium tetra?uoroborate([hemim][BF4]),at temperatures ranging from (303.15to353.15)K and pressures up to1.1MPa,were determined.The solubility data were correlated using the Krichevsky-Kasarnovsky equation,and Henry’s law constants at different temperatures were obtained.From the solubility data,the partial molar thermodynamic functions of solution such as Gibbs energy,enthalpy,and entropy were calculated.The diffusion coef?cients were obtained for H2S and CO2 using a semi-in?nite volume approach,and a correlation equation with temperature is presented for each gas.A comparison showed that the solubility of H2S was about three times its magnitude,and its diffusion coef?cient is of the same order of magnitude as that of CO2in the IL studied in this work.
Introduction
The acid gases hydrogen sul?de and carbon dioxide are produced along with methane and light hydrocarbons in many oil and gas?elds.1Alkanolamines,especially monoethanola-mine,diethanolamine,and methyldiethanolamine,are the main constituents of aqueous solutions used in industrial natural gas treating plants.1There are some disadvantages in the commercial use of these alkanolamine solutions,including loss of the alkanolamine and transfer of water into the gas stream during the desorption stage and degradation of alkanolamines to form corrosive byproducts,which make the process economically expensive.2
Room-temperature ionic liquids(RTILs)are molten salts that are liquid over a wide temperature range including ambient temperatures.3Their most remarkable characteristic is that they have negligibly small vapor pressure,meaning that ionic liquids (ILs)are essentially nonvolatile,non?ammable,and odorless. They also have high thermal and electrochemical stability. Nowadays,one of the active research areas is to explore task-speci?c ILs4to replace conventional alkanolamine solutions for acid gases(CO2and H2S)removal in gas sweetening processes. An important feature in the evaluation of ILs for potential use in industrial natural-gas treating processes is the knowledge of the solubility and the rate of solubility,that is,diffusion coef?cients of gases at various temperatures and pressures.In the past few years,a growing number of measurements reporting the solubility and diffusion of CO2in various ILs have become available(see,for example,refs5to10).However,experimental data for the solubility and diffusion of hydrogen sul?de in ILs are scarce.Jou and Mather11have reported the solubility of H2S in[bmim][PF6]at temperatures from(298.15to403.15)K and pressures up to9.6MPa.The solubility of H2S in different 1-butyl-3-methylimidazolium based ILs with different anions and in a series of bis(tri?uoromethyl)sulfonylimide ILs with different cations at298.15K and1400kPa is reported by Pomelli et al.12Jalili et al.13have reported the solubility of H2S in[bmim][PF6],[bmim][BF4],and[bmim][Tf2N]at temperatures ranging from(303.15to343.15)K and pressures up to1MPa. Subsequently,they reported14experimental data for the solubility of H2S in[hmim][PF6],[hmim][BF4],and[hmim][Tf2N]at temperatures ranging from(303.15to343.15)K and pressures up to1.1MPa.They have used the obtained data to estimate Henry’s law constants and thermodynamic functions of solution at different temperatures.
This paper focuses on the solubility and diffusion coef?cient of H2S and CO2in the IL([hemim][BF4])at six temperatures from(303.15to353.15)K.The solubilities determined were used to estimate Henry’s law constants and partial molar thermodynamic functions of solution of H2S and CO2at different temperatures.A correlation equation for the obtained solubility, diffusion,and partial molar volume at in?nite dilution data of each gas with temperature is presented here.The density of the IL considered in this work is also reported at six temperatures from(300.71to314.35)K.
Experimental Section
Materials.Carbon dioxide and hydrogen sul?de(c.p.grade 99.5%min)were obtained from Roham Gas Company.
The IL[hemim][BF4]was prepared according to the synthesis method described by Yeon et al.15and Dubreuil and Bazureau.16 A portion of13.9g(0.169mol)of1-methylimidazole(Merck, 99%),distilled over KOH,was added slowly to15.0g(0.186 mol)of freshly distilled2-chloroethanol in a round-bottomed ?ask equipped with a magnetic stirrer and a condenser under nitrogen atmosphere.Then,the mixture was re?uxed at373K for4h.After cooling to343K,the reaction mixture was washed four times using20%of its weight of ethyl acetate.The product was dried in vacuo at343K for8h.The product,1-(2-hydroxyethyl)-3-methylimidazolium chloride([hemim][Cl]),was obtained as a white crystalline solid(17.9g,65%yield).1H NMR(500MHz,D2O,25°C):δ(ppm))3.87(3H,S,NCH3), 3.89(2H,t,NCH2CH2OH),4.28(2H,t,NCH2CH2OH),7.42 (1H,d,H-4),7.47(1H,d,H-5),8.71(1H,S,H-2).
*To whom correspondence should be addressed.E-mail:jaliliah@ripi.ir.
Tel./fax:98-21-44739716.
J.Chem.Eng.Data2010,55,1663–16681663
10.1021/je900716q CCC:$40.75 2010American Chemical Society
Published on Web11/02/2009
A portion of 30.0g (0.185mol)of [hemim][Cl]was reacted with 26.4g (0.24mol)of sodium tetra?uoroborate (NaBF 4)in acetonitrile solvent under nitrogen atmosphere at room temper-ature for 48h.The reaction mixture was cooled to 255K overnight and then ?ltered through a short column of Celite to remove NaCl.The solvent was removed using a rotary evapora-tor,and the residual chloride (AgNO 3)test performed on product was negative.The product,1-(2-hydroxyethyl)-3-methylimida-zolium tetra?uoroborate ([hemim][BF 4]),was obtained as a viscous material (62%yield).Karl Fischer test showing <100ppm of water and the absence of chloride ion con?rmed the product purity (>99.5%).1H NMR (500MHz,D 2O,25°C):δ(ppm))3.83(3H,S,NCH 3),3.87(2H,t,NCH 2CH 2OH),4.24(2H,t,NCH 2CH 2OH),7.38(1H,d,H-4),7.43(1H,d,H-5),8.66(1H,S,H-2).
Apparatus and Procedure.The details of the experimental method for the measurement of gas solubility have previously been presented,13and only a short description will be provided here.In this technique,a known quantity of gaseous solute is contacted with a known quantity of degassed solvent at a constant temperature inside an equilibrium cell of known volume.When the thermodynamic equilibrium is reached,the pressure above the liquid solution is constant and directly related to the solubility of the gas in the liquid.The amount of solute
present in the liquid solution,n solute
l
,is calculated by the difference between two PVT measurements:?rst,when the gas is introduced from the gas container of known volume into the equilibrium cell containing the IL,and second,after thermo-dynamic equilibrium is reached (i.e.,pressure of the autoclave remains constant and no longer changes with time):
n solute l )n total -n solute
g (1)
where n total is the total number of moles of gas (in this case H 2S or CO 2)injected from the gas container into the autoclave and calculated using the following equation:
n total
)V gc RT gc (P i Z i -P f Z f
)
(2)
where V gc denotes the volume of the gas container,Z i and Z f are the compressibility factors corresponding to the initial and ?nal pressures P i and P f ,respectively,in the gas container before and after transferring the gas,and T gc is the temperature of the gas https://www.sodocs.net/doc/4a11828125.html,pressibility factors were calculated using the most accurate PVT data presented by the National Institute of Standards and Technology (NIST)for pure compounds.17n solute g in eq 1is the number of moles of gas solute left in the gas phase and was determined from the following equation:
n solute g )
V g P
ZRT
(3)
where V g is the volume of the gas-phase above the IL phase,T is the equilibrium temperature of the cell,and Z is the compressibility factor of gas solute at P and T .In all experi-ments,before solubility measurements,the IL was dried in vacuo (below 1.0kPa)for about 48h at a temperature of 343K to remove trace amounts of moisture and volatile impurities.The water content of ILs was found to be below 100(10ppm by a Mettler model DL-37Karl Fischer volumetric titrator.The temperature of the equilibrium cell,which was placed inside of a water recirculation bath (Haake,model D8),was measured with a Lutron model TM-917digital thermometer with a 0.01K resolution using a Pt-100sensor inserted into the cell.The pressure of the equilibrium cell was measured using a BD model
D95199pressure transmitter sensor in the range of (0to 1)MPa,
and that of the gas container was measured using a Druck model PTX 1400pressure transmitter sensor in the range of (0to 4)MPa.The pressure sensors were calibrated against a dead-weight gauge and were uncertain to within 0.1%of full scale.
The diffusion coef?cient for the diffusivity of H 2S and CO 2gases into [hemim][BF 4]was measured by the apparatus used in this work for measuring gas solubilities and the method devised by Camper et al.6This way,the diffusion measurements were made through the measurement of pressure with respect to time during the ?rst 20min in which the magnetic stirrer was turned off so that there was a stagnant layer of IL.Some time after 20min,the stirrer was turned on so that the time needed to reach equilibrium would be signi?cantly reduced.This method is based on a semi-in?nite diffusion model,which is developed mathematically by Crank.18The equations needed for the measurement of diffusion coef?cients are introduced below.
The concentration at point x below the surface of a ?uid at time t is de?ned by 18
C )C x )t )0erfc
x
2√Dt +k √πt [i erfc (x 2√Dt
)]
(4)
where C x )t )0is the surface concentration at time t )0,which
is related to surface concentration by eq 5
C x )0)C x )t )0+k √t
(5)
D is the diffusion coef?cient.The rate of gain of the diffusing gas into the semi-in?nite volume is de?ned by 18
(D ?C ?x
)
x )0
)C x )t )0
1
√Dt π
-
√π2√D
k (6)
From eq 6,the cumulative gas that has diffused into the semi-in?nite volume at time t is found using eq 7.18
M t )
∫
t
(D ?C
?x
|x )0
)
dt )√D [
2C x )t )0
t
π-12
kt √π]
)√D ε(7)
The following assumptions were implicitly made while using the semi-in?nite volume approach.(1)Concentration does not vary radially.(2)The volume is considered in?nite in the x >0direction,where x )0at the surface of the IL,for the time interval used in determining the diffusion coef?cient.(3)Joule -Thomson effects are negligible for the time interval used in determining the diffusion coef?cient.(4)The surface concentration at x )0and t >2min is at equilibrium with the gas.Time intervals greater than 2min were used so that any surface adsorption that is not in equilibrium with the gas would not affect the values obtained for the diffusion coef?cients.Assumption 1is naturally valid because the autoclave is a regular cylinder with a uniform circular cross section and also there is no mechanical agitation disturbing the stagnant liquid during diffusion measurement.The validity of assumption 2was checked mathematically for the two systems studied in this work using eq 4to determine the concentration of the solute at the bottom of the autoclave at the ?nal diffusion time.The solute concentration at the bottom of the autoclave was the highest for CO 2at 80°C,where the ratio of the initial surface concentration to the concentration at the bottom of the autoclave was <0.15%.The validity of assumption 3has previously been checked experimentally by Camper et al.6Given that the temperature of the gas before injection is the same as that of the autoclave and thus cooling of the gas is minimum due to
1664Journal of Chemical &Engineering Data,Vol.55,No.4,2010
Joule-Thomson expansion,this was considered a valid as-sumption here,too.In assumption4the nonequilibrium surface adsorption is omitted from our calculations where it gives rise to great uncertainties and has the greatest effect for time intervals,which immediately follow the opening of the valve. The time required for C x)0to?rst be in equilibrium with the gas was obtained from careful examination of Figures2and3 where there is good linear correlation among the data points. The estimated overall uncertainty due to the above assumptions does not exceed(5%.
Results and Discussion
The results of the measurement of the solubility of hydrogen sul?de and carbon dioxide in the IL[hemim][BF4]at temper-atures of(303.15,313.15,323.15,333.15,343.15,and353.15) K and pressures up to about1MPa are summarized in Tables 1and 2.The reliability and accuracy of the method of measurement have been checked in our previous work.13The Krichevsky-Kasarnovsky equation12was used to model the experimental data obtained in this work:
ln(f2x2))ln K h+V2∞(P-P1s)RT(8)
where f2is the fugacity of solute(hydrogen sul?de or carbon dioxide)in the gas phase,x2is the mole fraction of solute in the solvent1,P1s is the saturated vapor pressure of solvent1, K h is Henry’s law constant of gas solute2in solvent1at the pressure P,V2∞is the partial molar volume of gas solute2at in?nite dilution,R is the universal gas constant,and T is the absolute temperature.In this case the vapor pressure of the solvent,the IL,is negligible;the saturated vapor pressure P1s is zero,and f2can be substituted by the fugacity of pure hydrogen sul?de or carbon dioxide gas,f2o.Equation8then can be turned to eq9
ln
f
2
o
x
2
)ln K
h
+
V
2
∞P
RT
(9)
The fugacities of hydrogen sul?de and carbon dioxide were calculated using the most accurate corresponding states used by NIST for pure compounds.17The intercept of Krichevsky-Kasarnovsky plots(that is,plots of ln(f2o/x2)vs P)at each temperature,T,yields ln K h at the speci?ed temperature.The Henry’s law constants are given in Table3for the solubility of H2S and CO2in the IL studied in this work together with their standard deviations.The Henry’s law constants were?t by the equation,
ln(K
h
/MPa))∑i)02A i(T/K)-i(10)
The parameters A i of eq10obtained for H2S and CO2are summarized in Table4.The Henry’s law constants for these two gases,as a function of temperature,are compared with each other in Figure1.It can be observed that the solubility of both gases in the IL decreases by increasing the temperature and hydrogen sul?de is about three times as soluble as carbon dioxide in the IL studied in this work.This later point has previously explained by Pomelli et al.12from molecular point of view using extensive quantum chemical calculations and also by Jalili et al.13by means of obtained experimental thermody-namic functions of solution.The solubility curves also indicate that the solubility of H2S and CO2in the IL studied in this work are typical of that of physical solvents,13therefore obeying the
Table1.Mole Fraction Solubility of Hydrogen Sul?de Gas,x,in [hemim][BF4]
p/kPa x p/kPa x p/kPa x T/K)303.15T/K)313.15T/K)323.15 1360.039(0.0011210.028(0.0011420.026(0.001 1640.048(0.0012350.055(0.0012500.047(0.001 2890.081(0.0013380.076(0.0013500.065(0.001 4620.126(0.0015050.112(0.0014440.083(0.001 5320.144(0.0016410.140(0.0015310.097(0.001 6520.174(0.0027600.162(0.0016060.111(0.001 7030.187(0.0038900.186(0.0016750.123(0.001 8020.208(0.0049690.202(0.0027930.142(0.001 9690.235(0.00410660.217(0.0019310.164(0.001 10270.247(0.00210030.176(0.002 T/K)333.15T/K)343.15T/K)353.15 1550.025(0.0013000.041(0.0011650.020(0.001 2770.045(0.0014080.055(0.0013180.039(0.001 3940.062(0.0015180.070(0.0014420.055(0.001 4950.077(0.0016130.082(0.0016440.079(0.001 6130.096(0.0027550.099(0.0018450.102(0.002 7570.116(0.0028720.115(0.0029640.115(0.002 8680.133(0.0029890.127(0.00210470.126(0.002
10660.137(0.003
Table2.Mole Fraction Solubility of Carbon Dioxide Gas,x,in [hemim][BF4]
p/kPa x p/kPa x p/kPa x T/K)303.15T/K)313.15T/K)323.15 1750.018(0.0011140.008(0.0011190.007(0.001 2330.021(0.0012910.019(0.0013000.019(0.001 3500.033(0.0014080.031(0.0014270.028(0.001 4340.041(0.0025490.043(0.0015710.041(0.001 6450.061(0.0026770.053(0.0028460.059(0.002 7330.068(0.0028080.065(0.0029600.065(0.002 7660.071(0.0039170.071(0.00210640.072(0.002 11020.102(0.00310160.079(0.003
T/K)333.15T/K)343.15T/K)353.15 1250.006(0.0011300.005(0.0011350.004(0.001 3120.018(0.0013250.016(0.0013350.016(0.001 4440.026(0.0014600.025(0.0014790.022(0.001 5970.037(0.0026190.035(0.0016440.032(0.002 7380.045(0.0027680.042(0.0027960.040(0.002 8820.055(0.0029170.051(0.0029500.049(0.002 9990.061(0.00310400.057(0.003
11940.061(0.003
https://www.sodocs.net/doc/4a11828125.html,parison between Henry’s law constants as a function of temperature for the solubility of H2S and CO2in[hemim][BF4]and [emim][BF4]:2,H2S in[hemim][BF4];b,H2S in[bmim][BF4](ref13);
9,H2S in[hmim][BF4](ref14);4,CO2in[hemim][BF4];0,CO2in [emim][BF4](ref19).
Journal of Chemical&Engineering Data,Vol.55,No.4,20101665
Henry’s law.Also variations with the temperature of the Henry’s law constant for the solubility of CO2in the conventional IL, 1-ethyl-3-methylimidazolium tetra?uoroborate([emim][BF4]),19 and that of H2S in1-butyl-3-methylimidazolium tetra?uorobo-rate([bmim][BF4])13and1-hexyl-3-methylimidazolium tet-ra?uoroborate([hmim][BF4])14are shown in Figure1.It can be seen that CO2is more soluble in[emim][BF4]than [hemim][BF4].To explain the observed difference in solubility, we measured the density of pure[hemim][BF4]at six temper-atures from(300.71to314.35)K by using a calibrated glass picnometer.The obtained densities are summarized in Table5, which show a good linear correlation with temperature repre-sented by eq11
(F/kg·m-3))-0.00106(T/K)+1.703(11) These values agree within6%of the values obtained by Restolho et al.22from(298.15to328.15)K(listed in Table5 for ease of comparison).Also shown in Table5are the densities of[emim][BF4]at temperatures from(293.15to343.15)K.20 Comparison of these data reveals that the density of [hemim][BF4]is higher than that of[emim][BF4].This can be explained on the basis of the fact that the presence of a hydroxyl group attached to the alkyl chain in[hemim][BF4]gives rise to a stronger attraction between imidazolium cations and also between imidazolium cations and tetra?uoroborate anions via hydrogen bonding.The strong hydrogen bonding attraction causes the cationic and anionic molecular species to join more compactly together in[hemim][BF4]than the corresponding cations and anions in[emim][BF4],which causes the void volume in[hemim][BF4]to be lower than that of[emim][BF4] and thus the density of[hemim][BF4]to be higher than [emim][BF4].The lower void volume in[hemim][BF4]relative to[emim][BF4]may also be one of the important factors for the observed lower solubility of CO2in[hemim][BF4]relative to[emim][BF4].This same reasoning may be used to describe the higher solubility of H2S(Figure1)in the conventional ILs [bmim][BF4]and[hmim][BF4]relative to[hemim][BF4]as long as the densities of both of them are lower than that of [hemim][BF4].We are studying these observations,from mo-lecular point of view,for the solubility of CO2and H2S in functionalized ILs by using a molecular dynamics(MD) simulation and will present the results in the near future. The slope of the Krichevsky-Kasarnovsky plots at each temperature,T,yields V2∞at the speci?ed temperature.The obtained experimental data of partial molar volumes of gas solutes,H2S and CO2,at in?nite dilution,V2∞,are presented in Table3.They were correlated with temperature using the following simple quadratic formula
V
2
∞/m3·mol-1)∑
i)0
2
B
i
(T/K)i(12)
The obtained parameters B i of eq12for H2S and CO2are summarized in Table4.It can be observed from Table3that the V2∞values decrease with temperature from(778·10-6to 8.7·10-6)m3·mol-1for H2S,but in the case of CO2they increase with temperature from(-116·10-6to-81·10-6) m3·mol-1.
The variation with temperature of the solubility of solute(H2S and CO2)studied,expressed in Henry’s law constant,is directly related to the thermodynamic properties of solution which,in the case of gaseous solutes at low pressures,is practically identical to the thermodynamic properties of solution.21The Gibbs energy of solution,corresponding to the change in Gibbs energy when the solute is transferred at constant temperature from the pure perfect gas at the standard pressure to the standard state of in?nite dilution of the solute in the solvent is given by:21
Table3.Thermodynamic Properties of H2S and CO2in the[hemim][BF4]
T K h V2∞·106?sol G∞?sol H∞?sol S∞D·1010 K MPa m3·mol-1kJ·mol-1kJ·mol-1J·mol-1·K-1m2·s-1
H2S
303.15 3.13(0.01778(148.68-22.9-104 1.79(0.03 313.15 4.11(0.01357(169.67-20.2-95.2 2.15(0.04 323.15 5.12(0.03164(510.6-17.5-87.0 2.76(0.13 333.15 6.13(0.0387.4(511.4-15.1-79.5 3.24(0.08 343.157.26(0.0553.5(512.2-12.8-72.6 3.80(0.04 353.157.95(0.088.69(312.9-10.6-66.4 4.41(0.15
CO2
303.1510.8(0.02-116(311.8-13.4-83.1 1.40(0.05 313.1512.8(0.02-105(212.6-12.2-79.1 2.09(0.11 323.1514.7(0.02-98(113.4-11.0-75.5 3.94(0.20 333.1516.3(0.02-93(214.1-9.93-72.2 4.65(0.10 343.1518.1(0.03-85(114.8-8.92-69.2 5.71(0.09 353.1519.8(0.05-81(115.5-7.96-66.57.16(0.18 Table4.Numerical Values of the Parameters of Equations10,12,and16
A0A1A2B0B1B2C0C1C2
H2S
-1.003193744.7-93567453048-308.830.4495242.2436-0.295890.000536
CO2
0.506602718.8-651619-915.84 4.3188-0.00554-19.16680.029210.000127 Table5.Density of[hemim][BF4]and[emim][BF4]as a Function of
Temperature
T F T F T F
K kg·m-3K kg·m-3K kg·m-3
[hemim][BF4]this work[hemim][BF4]ref22[emim][BF4]ref20
300.711384298.151308.0293.151305
303.351380303.151304.7303.151296
304.951379308.151301.4313.151288
307.311376313.151296.1323.151280
310.811373318.151294.7333.151272
314.351369323.151291.5343.151264
328.151288.3
1666Journal of Chemical&Engineering Data,Vol.55,No.4,2010
?
sol
G∞)RT ln(K h P0)(13)
where P0is the standard state pressure.The partial molar differences in enthalpy and entropy between the two states can be obtained by calculating the corresponding partial derivatives of the Gibbs energy with respect to temperature
?
sol H∞)-T2
?
?T(?sol G∞T
))-RT2??T[ln(K h P0)]
(14)
?
sol
S∞)
(?
sol
H∞-?
sol
G∞)
T
(15)
The pressure range considered in this work is not too high to cause Henry’s law constant to be a strong function of pressure, and Henry’s law is weakly dependent on pressure under the speci?ed conditions.Therefore,it does not give rise to large errors if one ignores this pressure dependency.By means of this approximation and using eqs13,14,and15,we estimated the thermodynamic functions of solution at in?nite dilution for H2S and CO2in the IL.The values for the Gibbs energy, enthalpy,and entropy of solution are given in Table3for H2S and CO2in[hemim][BF4]at six discrete temperatures between (303.15and353.15)K.As it can be observed,the?sol G∞values are positive and increase with temperature in a similar manner for the solubility of both gases in IL.The?sol H∞values and ?sol S∞values are negative.Because of strong hydrogen bonding interaction between the H2S and the hydroxyl group of the IL, the magnitudes of?sol H∞values are much greater for the solubility of H2S in the IL than they are in CO2.The variations with temperature of the?sol H∞values and?sol S∞values are positive for H2S and CO2in[hemim][BF4],and they increase with temperature.
As it was explained in the previous section,the diffusion measurements were made through the measurement of the variation of pressure with time from(2to20)min in which the magnetic stirrer was turned off.The pressure drop during the measurement of the diffusion coef?cient varied from(0.23to 0.22)MPa.The surface concentrations,C x)0,of the solute(H2S or CO2)and the cumulative gas,which has diffused into semi-
in?nite volume at time t,M t,were calculated using the measured pressures at time t and the Henry’s law constant.Figure2shows how C x)0varies with the square root of time(eq5),and Figure 3shows the plot of M t versusε,where the diffusion coef?cient was found from the slope squared(eq7)for H2S in [hemim][BF4]at303.15K as an example.The diffusion coef?cients calculated using the method described in the previous section are listed in Table3.They were correlated with temperature using eq16,and the obtained parameters C i for H2S and CO2are summarized in Table4.
(D/cm2·s-1))∑i)02C i(T/K)i(16) It can be observed that the diffusion coef?cients of both gases in the IL increase with increasing temperature as long as the viscosity of the IL decreases.The diffusion coef?cients of the two gases in the IL are approximately equal at about313K, and the difference between them increases by increasing the temperature.The van der Waals radii of both gases are approximately equal.Thus,the factor,which determines the diffusion coef?cient of H2S to be larger than that of CO2in the IL at the lower temperature region,is the lower molecular weight
of H2S relative to CO2.However,at higher temperatures the diffusion coef?cient of H2S is lower than that of CO2.This behavior may be explained on the basis of the fact that as long as the force constant of the S s H bond in H2S(4.28N·cm-1) is about four times lower than that of C d O bond in CO2(16 N·cm-1),the molecular size of H2S increases much more rapidly with temperature than that of CO2,which gives rise to the observed trend.
Conclusion
New experimental data for the solubility,molar volume at in?nite dilution,and diffusion coef?cients of hydrogen sul?de and carbon dioxide gases in a functionalized IL[hemim][BF4] not previously reported in the literature have been measured and presented in this work.The solubility of carbon dioxide in [hemim][BF4]is lower than that of[emim][BF4],which is a conventional IL.The solubility of both gases in the IL studied in this work is of a physical nature.The solubility and diffusion coef?cient of hydrogen sul?de in the IL are greater than those of carbon dioxide,indicating that this solvent can be used for the separation of these two gases from each other.The density of the IL at six temperatures was also reported,which
indicates Figure2.Surface concentration for H2S in[hemim][BF4]at303.15K as a function of the square root of time(eq
5).
Figure3.Plot of M t versusε)2C x)t)0(t/π)1/2-(1/2)ktπ1/2for H2S in [hemim][BF4]at303.15K(eq7).
Journal of Chemical&Engineering Data,Vol.55,No.4,20101667
that it is higher than that of corresponding IL,[emim][BF4], containing no hydroxyl functional group.
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Received for review September2,2009.Accepted October12,2009. We are thankful to the research council of the Research Institute of Petroleum Industry(RIPI)and also to the Research and Development of the National Iranian Oil Company(NIOC)for their support of this work.
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汽车灯光使用技巧
简单但决不能忽视！汽车灯光使用技巧 首先我们来看看汽车的灯光系统，关系到行车驾驶的主要有行车灯、近光灯、远光灯、雾灯、转向灯、倒车灯等几种。下面我们就逐个看看它的正确使用方法。 行车灯：也就是我们俗称的“小灯”，一般都是灯光开关的第一挡，这时车内的仪表灯全部点亮，车头和车尾也会点亮两盏小灯，这两盏灯的亮度不大，主要是为了让车身四角能被看见。一般在天色渐暗、雨天或在地下停车场等阴暗地方，都应该亮起这个灯。 近光灯：夜间在市区行车时使用。近光灯和远光灯都叫大灯。一方面城市的道路都有路灯照明，不需要远光灯来探照远处的路面，只需看清车前的路面状况即可；另一方面市区道路车流量大，开远光灯的话不仅在会车时造成对方车辆眩目，而且对马路两边行人的视线也有影响。在大雨、大雪等能情况下，不仅能见度非常低，而且车辆的制动距离也会增加很多，所以此时最好打开近光灯，让其他车辆在最远的距离就能发现自己。 远光灯：远光灯亮起时，车内仪表板上会亮起醒目的蓝色灯号以作提示。在荒郊野外或是没有路灯照明的公路上比较适合使用远光灯，但要记住会车的时候应该换回近光，以免造成对方司机眩目。如果道路上车辆很多，在靠近前方车辆时最好切换到近光模式，这样可以减少对前车驾驶员的干扰。 很多驾驶员在高速公路上超车时喜欢按喇叭，其实由于在车速较快时车辆的发动机噪音和风噪都很大，按喇叭前车是很难听到的，尤其是那些货车，所以在超车时按喇叭，不如把灯光拨杆向上拨动几下，用远光灯提示前方的车辆。 转向灯：转向灯最基本的用途便是在车辆转弯时给出其它车辆和路人转弯的信号，以提醒别人注意。有时候转向灯也可在狭窄的地方充当照明作用，以便司机观察两旁的障碍物。两边转向灯同时开启的时候起警示兼示宽作用。当在没有中央隔离带的道路上左转驶出所在公路，调头或者靠边停车时，应该提前打转向灯，并且把大灯切换到近光灯，因为如果开着远光灯打转向灯，对面的行人和车辆受大灯的炫目，很难看到转向灯的闪烁。 危险报警闪光灯：就是我们常说的“双闪”、“双蹦灯”，它作为一种信号，主要是用来提醒其他车辆与行人注意本车发生了特殊情况。那么，什么情况下使用双蹦灯呢？一是在道路上发生故障或者发生交通事故时，二是牵引故障机动车时，牵引车和被牵引车均应当开启危险报警闪光灯。有些朋友在遇到雾、雨、雪、沙尘、冰雹等能见度较差的气象条件时喜欢打开双蹦灯，不过此时转向灯就失去转向提示功能，所以这种情况下最好使用近光灯和雾灯，尽量不要使用双蹦灯，如果使用的话，在变道转向时一定要多观察前后情况。另外，机动车在道路上行驶时，不能随意开启危险报警闪光灯。 雾灯：从名称上就很容易理解，雾灯是在大雾天气里使用的灯光信号，雾灯在雾中的穿透力更强，因此更容易让车辆或行人及早注意到。有些朋友在雾天行驶时
哈佛大学留学申请书范文
哈佛大学留学申请书范文 通过学习留学申请书范文可以帮助大家熟悉申请文书写作的规范，今天给大家提供一篇申请哈佛大学的申请文书范文，希看对大家有所帮助。 Of all the characters that I' ve " met" through books and movies, two stand out as people that I most want to emulate. They are Attacus Finch from T o Kill A Mockingbird and Dr. Archibald " Moonlight" Graham from Field of Dreams. They appeal to me because they embody what I strive to be. They are influential people in small towns who have a direct positive effect on those around them. I, too, plan to live in a small town after graduating from college, and that positive effect is something I must give in order to be satisfied with my life. Both Mr. Finch and Dr. Graham are strong supporting characters in wonderful stories. They symbolize good, honesty, and wisdom. When the story of my town is written I want to symbolize those things. The base has been formed for me to live a productive, helpful life. As an Eagle Scout I represent those things that Mr. Finch and Dr. Graham represent. In the child/adolescent world I am Mr. Finch and Dr. Graham, but soon I' ll be entering the adult world, a world in which I' m not yet prepared to lead.
现代汽车大灯的使用及操作
现代汽车大灯的使用及操作 汽车灯光的使用与行车安全有着直接的关系，本期《菜鸟进阶课堂》，我们一起来聊聊汽车大灯以及其使用方法。 汽车大灯也称汽车前照灯，主要担负夜间行车的照明工作，可以说是汽车的“眼睛”。
汽车大灯包括远光灯和近光灯，远光和近光灯的作用都是用来照亮车辆前方道路。区别是，一个照射的近，一个照射的比较远。通常情况下，近光灯的照射距离约30-40米，照射范围大约160°，远光灯则光线较为集中，亮点大，可以照射到更高更远的地方(照射距离根据大灯材质不同会有差异)。 ●怎么看自己是开近光灯还是远光灯? 可能很多人觉得不可思议，开没开远光灯还不知道啊! 但现实情况，确实存在一些车主在开车过程中并不知道自己开了远光灯。
看有没有开远光灯很简单，虽然远光灯和近光灯的标志很像，但还是很好区别的。如上图所示，左边的带直线的是远光灯的标志，斜向下线条的右侧图标就是近光灯的标志。（部分车型近光灯开启不会有仪表指示） ●为什么夜间会车要切换近光灯? 因为远光的角度太高，很容易晃到对面来车和周围行人的眼镜，影响他们的视线，从而给行车带来很大的安全隐患。另外，会车开远光灯也是一种不礼貌的驾驶行
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哈佛大学推荐必读书籍 20本名著缩短你和名校见的距离
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汽车车灯图解大全doc资料
汽车车灯图解大全
来自汽车之家 示廓灯 示廓灯定义：示廓灯也叫示宽灯，俗称小灯。光从字面上看，“示”是警示的意思;“廓”有轮廓之意，所以示廓灯是一种警示标志的车灯，用来提醒其它车辆注意的示意灯。这种灯一般安装在汽车顶部的边缘处，这既能表示汽车高度又能表示宽度。安全标准规定在车高高于三米的汽车必须安装示廓灯。
示廓灯使用：示廓灯的颜色为前白后红，如下图所示，将灯光开关开至第一挡时，前后亮的灯就是示廓类。示廓灯用于在傍晚行驶时，让别的车辆看见。当你从后视镜看不清楚后边的时候，就该点亮小灯，特别是下雨天。但是很多司机会用示廓灯代替近光灯在黑暗中行车，这是很危险的，因为示宽灯并无法照亮前方道路。
《交通法》相关规定：第六十条机动车在道路上发生故障或者发生交通事故，妨碍交通又难以移动的，应当按照规定开启危险报警闪光灯并在车后50米至100米处设置警告标志，夜间还应当同时开启示廓灯和后位灯。夜间发生故障或事故未开示廓灯和后位灯的罚款200。
近光灯、远光灯 近光灯定义：近光灯就是为了近距离照明，设计要求就是照射范围大(160°)，照射距离短，聚光度也无法调节。近光灯的照射距离约有30-40米左右。远光灯的照射高度比近光灯要高，因此能够照亮更高更远的物体.根据实验得知：夜间以55公里/小时速度行驶时，发现情况立即踩制动，停车距离正好30米。即当在近光灯照射范围内发现情况到立即停车，车与物体之间已无间隙。当然这是在车况、路况及驾驶员反应均良好情形下，如果高于这一车速，车况、路况较差和驾驶员疲劳反应时间长等情况下，其结果可想而知了。因此，夜间行车一定要控制车速。在平坦宽阔、视线良好的道路上使用远光灯时，车速可适当加快;而在会车又遇上路面不平或转弯或桥梁或窄路或交叉路口等复杂情况时应减速慢行，车速一般控制在40公里/小时以内。 示宽灯的下一档就是大灯，也就是远近光灯。它的主要作用是汽车行驶时照明，原车的远近光不可以同时打开，也就是远近灯光的切换，切换手柄在方向盘左下侧，上下拨动可以切换远近光。经改装了的灯，打开近光时近光亮，打开远光时远近光同时亮。
图解小汽车灯光使用
西凤瘦马 17:31:07 只要听到是“会车”和“跟车”就一定是近光灯，记住这个就能和“近远光变换（四次）”区分开了，就不用记其它的了。 西凤瘦马 18:02:24 教练说其实这个考试其实是有死规律的： 1、一定是：开启大灯（比亚迪车灯杆按钮向上扭两个格） 2、一定是：变成远光灯（比亚迪车灯杆向车头的方向按下去，仪表盘里会看到一个蓝色的灯的图标； 注意：这里有个问题，就是怕前一个人下车的时候把灯不小心给弄在远光上，教练说最好上车时借扶方向盘的时机，用指头不经意间轻轻把灯杆往上抬一抬，就是保证灯光模拟考试前车灯一定是在近光状态上的） 3、一定是：变回近光灯（刚才按了下去、现在再板回来，那个蓝色图标会消失） 4、会有两个情况： 一是：让你再变成远光（向下按）、再变回近光， 二是：远近光交替闪四下（向下按的时候轻一些，只要出现蓝色图标就松，如是四下，ok） 5、接着上面会有几种情况（都在近光下）： 一是：车坏了，扭回一格、打开红色的警示灯（方向盘右边） 二是：雾天，打开雾灯（方向盘左边）、再打开警示灯（方向盘右边） 6、模拟考试完毕，一定是：关掉所有灯（从右到左，按回、扭回即可） 下来就进入起步了（最关键的！）：打左方向灯（向下拨杆，仪表盘上会看到）、踩下离合、挂一档，松手刹，慢松离合（安全员没说就别加油，哪天有一个兄弟觉得学得好，加了油就让安全员弄死了）、慢打方向就走了。 路上一切听安全员的（无非是加减档，打方向盘，打转向灯），人家没说绝不要踩刹车（哪怕眼看着要撞上也别踩，那是安全员的责任，哪天有一个兄弟一激动，就是这样死的） 图解小汽车灯光应用图片源自网络
拨杆式灯光开关如上图所示。在雾天里我们必须开启行车灯及前后雾灯，必要时还可以打开近光灯。大多数车辆的自动灯光开关在雾天里并不给力，还是手动打开相应车灯比较靠谱。 旋钮式灯光开关如图所示。把灯光开关旋钮旋转到相应位置能打开行车灯或远光灯。前后雾灯是通过按钮来分别开启的。 行车灯：行车灯也叫做示宽灯，它的作用是使车辆的四个角为人所见，亮度没有大灯那么高。在雨天、天色昏暗或者在地下停车场时应亮起此灯。行车灯亮起时，仪表盘上会亮起如图所示的标志。
哈佛大学及案例教学法
哈佛大学及案例教学法 哈佛案例闻名遐迩，但书本上的研读和课堂的感受是大不相同的，我们这次美国游学，有幸在哈佛大学上一堂原滋原味的哈佛案例课，金李老师用详尽数据，激情飞扬的讲解，让大家都投身于其中，对案例发授课感受深刻，这里我就将哈佛的案例较学法做一些延伸，希望对我们今后学习和管理都有所帮助。 哈佛案例教学的发展历程 当哈佛商学院在 1908 年成立时，案例教学还只是学院第一任院长Edwin F. Gay 的一个想法。 Gay 想设计一种方法进行课堂教学，可以围绕商业管理中的现实问题进行讨论。 1911 年， Arch Wilkinson Shaw 开始教授经营策略这门课，在这门课里他给学生提出了商业经理们所遇到的现实问题。这些尝试可以说是哈佛商学院历史上第一次案例教学。哈佛商学院在 1921 年出版了其第一本案例集，“通用鞋业公司”，由院长助理 Dean Clinton 编写。 这些年来，案例的构思与编写方式都发生了很多的变化，内容也逐渐覆盖了整个商业领域。但案例教学依旧保留了最初的灵魂，即哈佛商学院是如何进行案例教学的——“通过行动来学习，”主管案例编写的高级讲师 Michael J. Roberts 表示，“作为教授，我们必须将复杂的商业问题提炼，并将其引入到课堂中。作为学生，他们希望借
助这些提炼的经验来进行推断。所以，我们需要选择好的案例并保证其实用性。” 哈佛商学院每年大概编写 350 个案例，涉及各种科目。案例覆盖了商业问题中很广的区域，有时并紧跟时代潮流，例如电子商务。与课程中的问题相吻合是案例编写的一个重要参考因素。 Roberts 列举了案例编写最开始要考虑的四个要素： 1 、案例所围绕体现的问题； 2 、学生使用该案例所需做的分析； 3 、案例具有足够的数据方便进行分析； 4 、数据从哪里能够获得。 案例的编写可以由问题驱动，例如当有一个教授想通过一个案例来说明一个问题，教授便需要找到一个公司的案例可以用来阐明强调他所要阐述的问题。其他案例是通过公司 / 产业 / 管理者来驱动的，有时通过教授所做的研究，例如对公司的研究，或只是通过研究一些事与人，从中得到体会，认为这些故事也许可以成为一个有趣的案例。在这些情况下，案例编写者在编写案例最初时并没有一个清晰的关于问题的轮廓。“关键是从现实中找到一个片段可以引出所要研究探讨的核心问题。” Roberts 解释到。 找到现实场景经常是一个艰苦的过程，因为这需要准确识别一个商业问题所涉及的各个方面，并能够激发课堂讨论并有助于学习。举个例子，教创业学这门课程的教授想讲授条款书的相关知识，教授开始设想一个企业家接受了风险投资的条款书，“从那，” Roberts 建
汽车仪表盘指示灯图解
1、车辆基本情况提示标识 平常常见的并最常使用的图标有：车门提示、手刹提示、安全带提示、发动机自检、润滑油情况检查、ABS系统检查、安全气囊检查、蓄电池提示以及燃油量提示这么几种。 另外，还有一些标识是因为相关车型仪表盘设计的原因而产生的，比如说水温显示标识，在现代老款悦动、东风日产骊威等没有水温表的车型上，这些标识就充当显示车辆水温是否正常的功能，一般情况下，蓝色和绿色表示水温低，红色表示水温高，不显示任何颜色表示水温合适。
刚才在说常用标识的时候提到了安全带未系提示标识，而有些对安全要求比较高的车型，会分开提醒主、副驾驶位置的人安全带是否系好安全带。 2、灯光信息提示标识 在仪表盘中除了刚才提示的一些关于车辆安全方面的标识外，还有一部分也是非常重要的，它的存在甚至关系我们驾车的安全，那就是灯光提示标识。不过这里也需要提醒您一下，如果看到仪表盘上灯光表示亮起的时候可能实际上相应的灯光没有亮，因此就需要我们在使用的过程中勤检查灯光是否正常，因为特别是在夜间开车，没有灯光、甚至不正确使用灯光都会有交通事故的隐患存在。
说到这里也请各位车主朋友能够在合适的时间恰当的使用车辆灯光，比如夜间就要开车灯；远光灯尽量不要长时间开启等，错误的使用车辆灯光可能会给自己以及车辆造成不必要的麻烦。 3、变速箱/车辆行驶状态提示标识 多数车型的自动变速箱车型为了能让车主更好的控制车辆也设计了不同的模式来保证不同使用者的需求，下面几个标识就是代表。
一般自动变速箱的车型会在仪表盘上面有一些提示标识，比如大众独有的换挡提醒标识、变速箱的SNOW雪地模式等。 此外，对于一些注重运动风格的车型来说还会有一些驾驶模式的选择，你可以通过仪表盘上的图标来了解目前车辆处于什么样的驾驶模式，一般这种标识都是直接显示相关模式的英文，总结来看主要有“Sport运动、Comfortable舒适、ECO经济等几种”
新手如何正确使用汽车灯光
新手如何正确使用汽车灯光 汽车灯光的正确使用很少人会在夜间学车，所以刚刚从驾校毕业的新手虽然考过了交规，对于汽车灯光的使用还是不太清楚，导致不该开灯的时候乱开，该开的时候又不开。有人觉得汽车用灯很简单，可是在马路上，就是有人不会用。 第一，示廓灯。 打开此灯，在前面，有两个小灯会亮，在后面，尾灯会亮，在车内，仪表盘灯会亮，音响、空调背景灯亮。 使用范围，用此灯照明是“照不明”的，因此，此灯的作用并不是车外照明，而是车内照明，如在夜间要看行车电脑数据等等，另外，根据规定，如果车辆在夜间出现事故，停在路边时，应设立警示牌，打开此灯及紧急报警灯。 第二，大灯。 所谓大灯，也就是远近光灯，原车的远近光不可以同时打开，也就是远近灯光的切换，切换手柄在方向盘左下侧，上下拨动可以切换远近光。经改装了的灯，打开近光时近光亮，打开远光时远近光同时亮。 使用范围，按照要求，车灯的开启随同路灯的开启，也就是当路灯打开时，必需开启近光灯。如遇没有路灯的路段，应当在晚七点开启灯光。根据要求，有路灯的路段只可以开启近光灯，不可以开启远光灯（因为远光灯晃人眼睛）。如遇没有路灯的路段，原则上可以开启远光灯，但我一般也不开启远光灯。因为打开远光灯后会晃前方车辆、对面车辆前排人员的眼睛，也会晃对面行人的眼睛。相信很多人都被晃过，真的很难受。所以，在这种路段上我的做法一般是打开远光看清楚前方路段的情况就切换到近光，走一段，如有必要，就再小开一下远光，然后及时关掉。 第三，前雾灯。 打开此灯，前面的两个雾灯亮。此灯不可以在灯光开关关闭时拔起，但可以在示廓灯段拔起，也可以在大灯段拔起。 使用范围，故名思义，雾灯应当在有雾的天气开启，当没有雾的晴天夜晚，不应开启雾灯。好多司机都有个不良习惯，就是一开灯就把前后雾灯一起打开了，其实这样做并不能增加很多的照明，但却很严重地晃了前方、对面车辆前排人员的眼睛，造成光污染。这种做法是很不对的。但同时再补充一句，雾灯不应和远光灯同时使用，而是可以和近光同时使用。因为真的在雾里的时候，越是开远光灯越是晃得你眼前一片白，什么都看不到，这时，穿透力强的雾灯才真的起了作用。 第四、后雾灯。 打开此灯，后雾灯同时亮起，使用范围同前雾灯。不过补充一点，好多新同学都不知道绝大多数车都只有一个后雾灯。因为后雾灯有眩目的作用（就是会晃后面车辆的人的眼睛），所以后雾灯只设计了一个。极少数车型现在也有双后雾灯，但像宝来的大众车型，都只有一个后雾灯，在左侧。 第五，转向灯光组合。 向下拨是左转，向右拨是右转，上下拨是切换远近灯光，向上抬一下，是“变换”远近灯光（就
汽车灯光亮度调节方法
汽法车灯光亮度调节方法 汽车的车灯在夜晚的时候，如果能亮一点可能在夜间行车的安全性可以大大提高，那么是否有办法能让汽车的灯光调亮呢? 有的人在黄昏或者晚上用车比在白天频繁，那么你可曾想过汽车的灯光是否可以调亮呢?众所周知车辆的灯光是汽车主机厂设计好的。但是如果你感觉不够亮可以通过一些简单的办法提高。 一、灯本身存在问题。 比如灯罩内部过脏;使用伪劣灯罩，外部磨毛褪色，都会影响发光。可以将灯罩拆下来做清洁，或干脆更换; 二、灯泡的功率小和照明电路设计问题的改造相对复杂一些。 很多车前大灯仍在使用功率为的白炽灯，功率相对较小;一些车的前大灯是直接由车辆总电路上分出线束送电的，大灯得到的电压比总电路电压要低1-2伏。普通白炽灯通过灯内的金属钨在真空环境下发光获得亮度，但是金属钨在真空环境下通电，产生光的同时也产生钨蒸气，造成亮度逐渐下降，灯光越用越暗。 如果想提高车前灯的亮度，不要直接更换大功率灯泡，那样有可能造成电路过热甚至烧毁。而应在更换大功率灯泡的同时，改变电路。现在市场上流行的改装方式中有一种可操作性较好： 一是将原车大灯接口对插一个外装电路，通过车辆电瓶直接给前大灯送电，可以保证足够的电压;二是将原车大灯电路改变后作为开关电路使用，此方式可以把车辆前灯更换成卤素灯，亮度大大提高，夜间行车安全性也大大提高。 经常在黄昏和黎明驾驶车辆的驾驶员可以考虑在车辆前面安装两个小而亮的灯光，又好看又安全。
关于车辆前大灯目前还有一种更好的改装方法，只是价格昂贵。那就是氙气大灯。灯的亮度可以达到日光的效果。使用这样的灯，驾驶员在夜晚驾驶车辆的视觉疲劳大大降低，安全性也有所提高
哈佛大学Stephen M. Walt__论良好学术写作能力的培养
论良好学术写作能力的培养 Stephen M. Walt (哈佛) 过去安德鲁·苏利文（Andrew Sullivan）曾在其新建的、独立的新闻网站 Daily Dish上，主持了一个有趣的话题：为什么学术著作常常不堪卒读。和某些人一样，让自己的学术写 作更清晰易懂，并且试图把那种价值观灌输给学生，因此我饶有兴趣地参加了话题。 对于初学者来讲，我认为问题不在于没有人鼓励未来学者把文章写好。例如，就我自 己而言，我有幸在本科生时就在斯坦福大学和乔治·亚历克斯一起搞研究，在研究生阶段，在伯克利大学和肯尼斯·沃尔兹一起搞研究，两位都一再强调培养良好写作能力的重要性。沃尔兹对研究生的论文或学位论文修改不多，但他一旦发现我的写作中有佶屈聱牙、冗长 乏味、条理不清或明显的逻辑混乱，他都会明确地给我指出来。他还公开谈到写作在研究 生课程中的重要性，鼓励学生阅读写作方面的书籍，如福勒《现代英语用法》，他对像象 鼻虫那样大量出现于学术著作的时髦新词汇嗤之以鼻。 我认为这个问题也不在于刊物或大学出版社的编辑水平差。我在十多个学术期刊发表 过论文，在一家著名的大学出版社和两家不同的商业出版商出版过书，也在许多媒体上发 表过文章。我打过交道的编辑或文字编辑几乎都热心助人，一些人还相当优秀。事实上， 在我的记忆中，在近三十年里，我的稿子只有一次真正被一位编辑毙掉（实际上是一位实 习生干的），还好杂志在文章发表前给我挽回了损失。 那么，为什么学术写作如此拙劣？ 学术写作有时很困难的原因之一是因为正在研究的课题很复杂，难度较大，很难用普 通的语言解释。我对哲学家努力解决有关道德、时间、认识论这一类问题抱有更多的同情，因为这类问题天生就很棘手，用些玄虚的措辞极易失去读者。但那也不是无法避免的。一 些哲学家也尽力用十分浅显的笔调著述非常深奥的、重要的问题。但读者仍然要专注思考，才能理解人家在说些什么，但那种难度倒不是作者有意为之。 第二个原因是许多学者不能理解论证的逻辑和演示的逻辑之间的差异。具体来讲，学 者细述解决某个特定问题的过程并不一定就是向读者解释这个答案的最好的方式。但一些 文章和稿件常常有点像研究说明：“首先我们先做文献综述，然后我们得到了以下的假设， 然后我们收集这些数据或研究这些案例，再然后我们对这些资料加以分析，并得到了如下 结果，第二天我们进行鲁棒性检验，这就是我们下一步要做的。”
图解小汽车灯光使用
图解小汽车灯光应用 灯光操作杆通常在方向盘左侧下方，其长度与方向盘半径相当，便于在手握方向盘时操作，可控制远近光切换，左右转向灯和灯光开启和前后雾灯的开启与关闭（多数车辆）。其使用方法是 拨杆式灯光开关如上图所示。在雾天里我们必须开启行车灯及前后雾灯，必要时还可以打开近光灯。大多数车辆的自动灯光开关在雾天里并不给力，还是手动打开相应车灯比较靠谱。 开关：在控制杆上，有转动开关，一般有两个，靠外侧的是灯光开启开关，有三个档，分别为关-（示宽灯）小灯-大灯（远、近光灯）；内侧的转动开关可控制前后雾灯的开启和关闭。 转向：三个档位，左-关-右，以方向盘为表盘，顺时针方推控制杆，为开启左转向灯，转向结束后可随方向盘回位，也可手动拔回，逆时针拔动，为开启右转向灯。
远近光切换：两个档位，通常放在近光位置，以方向盘为参照，打开大灯开关后，向下推动，为开启远光灯，此时，开启远光，仪表盘上蓝色灯图标常亮。向上提动，开启近光，仪表盘上，蓝色图标灭，在近光位置，向上提动，为会车提醒灯（远光灯亮）起到提醒作用。手松开后，自动回到近光位置，（若灯光开关未开启，灯光关闭）。 旋钮式灯光开关如图所示。把灯光开关旋钮旋转到相应位置能打开行车灯或远光灯。前后雾灯是通过按钮来分别开启的。 汽车照明系统是否进行正确的指向调整，不仅关乎实际的照射效果，也关乎车辆行驶的安全，大街上经常能看到一些车的近光灯调得很高，使对面车辆产生眩光，非常影响安全。同时，如果不能正确调节车大灯指向，也会影响车大灯的照射范围，以及路面的照射效果。即使是更换一些升级的卤素灯泡，也最好检查一下车大灯是否正确指向，因为灯丝位置的细微变化，也会导致车大灯光型的巨大变化。
图解小汽车灯光使用及灯光使用技巧
汽车灯光的操作一般是通过灯光操作杆来调节的。 灯光操作杆通常在方向盘左侧下方，其长度与方向盘半径相当，便于在手握方向盘时操作，可控制远近光切换，左右转向灯和灯光开启和前后雾灯的开启与关闭（多数车辆）。其使用方法是 开关：在控制杆上，有转动开关，一般有两个，靠外侧的是灯光开启开关，有三个档，分别为关-（示宽灯）小灯-大灯（远、近光灯）；内侧的转动开关可控制前后雾灯的开启和关闭。 转向：三个档位，左-关-右，以方向盘为表盘，顺时针方推控制杆，为开启左转向灯，转向结束后可随方向盘回位，也可手动拔回，逆时针拔动，为开启右转向灯。 远近光切换：两个档位，通常放在近光位置，以方向盘为参照，打开大灯开关后，向下推动，为开启远光灯，此时，开启远光，仪表盘上蓝色灯图标常亮。向上提动，开启近光，仪表盘上，蓝色图标灭，在近光位置，向上提动，为会车提醒灯（远光灯亮）起到提醒作用。手松开后，自动回到近光位置，（若灯光开关未开启，灯光关闭）。
汽车照明系统是否进行正确的指向调整，不仅关乎实际的照射效果，也关乎车辆行驶的安全，大街上经常能看到一些车的近光灯调得很高，使对面车辆产生眩光，非常影响安全。同时，如果不能正确调节车大灯指向，也会影响车大灯的照射范围，以及路面的照射效果。即使是更换一些升级的卤素灯泡，也最好检查一下车大灯是否正确指向，因为灯丝位置的细微变化，也会导致车大灯光型的巨大变化。下面的调整汽车照明系统方法不需要借助特殊的设备和仪器，但却能获得正确的指向照明。 需要准备的东西：卷尺、封口胶，十字螺丝和内六角套筒 步骤1：首先，找到一块地面水平且又有垂直白色墙面的场地――地下停车场里就很好。正对白色墙面，将车直着慢慢开过去，并在车头最大限度贴近墙面的位置停住。在墙面上对应车头中心线的位置（对”MM“，就是中网的头标中心点），划一条垂直线（注：为了避免涂鸭别人的墙面，我建议用胶带黏贴，方便去除）。然后，直线倒车，在车头灯距离墙面2 5英尺处停住（即约7.6米处） 步骤2：进行如下两项测量 测量A：测量车灯外罩的几何中心点到地面的高度
汽车灯光的正确使用方法!
汽车灯光的正确使用方法！ 过夜生活是现代人的重要习性特征，在夜间开车自然也就成了每个驾驶者必然会有的经历。据统计，夜间开车由于视线较差，对行车前方的判断力有所下降，因此容易出现紧张、恐惧的心理，出事几率大大增加。除此以外，不懂得正确使用灯光信号也是导致意外的一个重要因素。 新手由于经验不足，缺乏对即时情况的迅速有效判断，加之心理紧张，出现险情甚至发生事故的概率较大。而在夜间行车时，由于光线昏暗视野较差，许多潜伏的险情愈加威胁到这些刚刚开车不久的人。然而，不管发生在白天或黑夜的事故，都有相当一部分是不懂得正确使用灯光信号导致的。最常见的例子便是行车时突然变道而不打转向灯，或是拐弯的同时才将转向灯打开，没有一点提前量，使得后面的车辆措手不及。因此，学会正确使用灯光信号的重要性不言而喻。 车辆灯光的使用 汽车的灯光包括行车灯、近光灯、远光灯、雾灯、转向灯、倒车灯等几种。 行车灯：灯光开关的第一挡，这时车内的仪表灯全部点亮，车头和车尾也会点亮两盏小灯，这两盏灯的亮度不大，主要是为了让车身四角能被看见。一般在天色渐暗、雨天或在地下停车场等阴暗地方，都应该亮起这个灯。 近光灯：夜间在市区行车时使用。一方面城市的道路都有路灯照明，不需要远光灯来探照远处的路面，只需看清车前的路面状况即可；另一方面市区道路车流量大，开远光灯的话不仅在会车时造成对方车辆眩目，而且对马路两边行人的视线也有影响。 远光灯：在荒郊野外或是没有路灯照明的公路上比较适合使用远光灯，但要记住会车的时候应该换回近光，以免造成对方司机眩目。远光灯亮起时，车内仪表板上会亮起醒目的蓝色灯号以作提示。 转向灯：转向灯最基本的用途便是在车辆转弯时给出其它车辆和路人转弯的信号，以提醒别人注意。有时候转向灯也可在狭窄的地方充当照明作用，以便司机观察两旁的障碍物。两边转向灯同时开启的时候起警示兼示宽作用。 雾灯：顾名思义，雾灯是在大雾天气里使用的灯光信号，雾灯在雾中的穿透力更强，因此更容易让车辆或行人及早注意到。 倒车灯：倒车的时候车尾会有白色的倒车灯亮起，一方面可以照亮车尾的路面、障碍物，减少倒车时的盲区，另一方面也是对车尾行人的提醒。 灯光使用的对与错 首先来讲一下在日常行车时，一些正确使用灯光信号的例子。
哈佛格式范文
Diversity and global manager Introduction In today’s hyper-complex marketplace, every organization confronts the challenge on how to take the most advantage of the international trends to promote the overall efficiency and effect of businesses and maximize profitability. In fact, diversity has become an overwhelmingly important trend that attracts global attention, especially the human resource diversity. Generally speaking, it is a crucially important fact on organizational performance that weather the employees at all levels are well-trained, dedicated and loyal at their works. The first section demonstrates the key benefits and drawbacks of diversity, which are important for the decision-making of all companies. In the second section, the traits of global managers and their significance are discussed, which are professional background, profound management experiences, global insights and extraordinary leadership. In the last part, the link between diversity and global managers is analyzed from two aspects, and several recommendations are proposed accordingly. Diversity Diversity can be seen everywhere and the processes of most operations have a close relationship with diversity. From the very beginning, materials and manufacturing devices are outsourced from foreign regions to make commodity, advanced technology and inventions are bought to production in many ways, then, multinational workforce take their works in teams and solve problems together, in addition, attentions are paid to specific cultures to attract consumers in different countries and promotions are designed in accordance with habits of the target consumers of different nationalities. Diversity is so significant in resent days that any company can do nothing but come up with great ideas to manage diversity and take the most use of the trend. Diversity management emerges as a result of the rapid process of globalization, especially in the human resource sector such as age, religion, race, gender, culture and specialty,
汽车灯光正确使用
汽车灯光正确使用! 大家对市区违法使用远光灯、车辆交汇不变光都深恶痛绝，很多人不知道怎样正确地使用汽车灯光，也有很多人以为灯总是越亮越好，以为只要自己的灯光亮了，自己就是安全了。即使知道一直开远光灯不好，也不知道应该怎么用。当然也有一部分是在炫耀他的灯高级。下面摘录一些正确使用汽车灯光的方法，希望对不会用的TX有所帮助，通过我们的努力，逐步改变绍兴的夜间行车环境。（呵呵，我原来也是FQ一族，别人不变灯，我也一直照他，后来发现你一直闪他，他却是一脸的茫然，人家根本不知道。 车辆灯光的使用： 车辆的灯光不仅仅是在光线不足的情况下提供照明，而更重要的是起到警示作用，即使在白天，人们也会首先注意到亮着灯的车辆，不管是行人还是其他车辆的司机。因此，在北欧的一些国家，法律规定白天行车也要亮灯，以减少事故。在阴天或天刚刚黑的情况下使用灯光是一个很好的习惯。有些人说还能看见路，只是光线稍暗，不用开灯，这是错误的做法，这时开灯不是为你照亮，而是提醒前面车辆的司机注意后车。（注意：这里所说的开的灯，是指示宽灯） 汽车的灯光包括行车灯、近光灯、远光灯、雾灯、转向灯、倒车灯等几种。 行车灯： 也称示宽灯，俗称小灯，灯光开关的第一挡，这时车内的仪表灯全部点亮，车头和车尾也会点亮两盏小灯，这两盏灯的亮度不大，主要是为了让车身四角能被看见。一般在天色渐暗、雨天或在地下停车场等阴暗地方，都应该亮起这个灯，有利于后方车辆识别车辆宽度，防止超车和会车时，因轮廓不清而发生事故。上面所说的白天也开的就是这个灯！示宽灯的灯光在夜间距离100m以外应能看清楚。车前面的示宽灯的灯光为白色或橙色，车后面的灯光则为红色或橙色。一般在汽车前后的左右外侧各装一只示宽灯，共四只。但是，有些大型载重车及通道式大客车上，还在车身中部外侧再加装左右一只。灯丝的功率为20W左右。 行车灯车内指示标识： 前照灯： 近光灯和远光灯一起组成汽车的前照灯，也称前大灯、头灯。是汽车的眼睛，是夜间行车的必须，是全车灯的“心脏”部位。近光灯和远光灯通常采用双丝灯泡，其中远光灯丝为45～60W，近光灯丝为20～50W。前照灯应保证汽车前方100m以内的路面上有明亮而均匀的照明，有些汽车的照明距离已达150m～270m。 前照灯应使驾驶员能清楚辨明路面上的任何障碍物，并具有防眩目装置，防止夜间会车时因使对方驾驶员目眩而肇事，使用时应注意以下几点： （1）在夜间没有路灯或路灯照明不良的条件下须开启汽车前照灯并使用远光灯，以保证驾
哈佛大学的写作教程 3.How to Do a Close Reading
How to Do a Close Reading The process of writing an essay usually begins with the close reading of a text. Of course, the writer's personal experience may occasionally come into the essay, and all essays depend on the writer's own observations and knowledge. But most essays, especially academic essays, begin with a close reading of some kind of text—a painting, a movie, an event—and usually with that of a written text. When you close read, you observe facts and details about the text. You may focus on a particular passage, or on the text as a whole. Your aim may be to notice all striking features of the text, including rhetorical features, structural elements, cultural references; or, your aim may be to notice only selected features of the text—for instance, oppositions and correspondences, or particular historical references. Either way, making these observations constitutes the first step in the process of close reading. The second step is interpreting your observations. What we're basically talking about here is inductive reasoning: moving from the observation of particular facts and details to a conclusion, or interpretation, based on those observations. And, as with inductive reasoning, close reading requires careful gathering of data (your observations) and careful thinking about what these data add up to. How to Begin: 1. Read with a pencil in hand, and annotate the text. "Annotating" means underlining or highlighting key words and phrases—anything that strikes you as surprising or significant, or that raises questions—as well as making notes in the margins. When we respond to a text in this way, we not only force ourselves to pay close attention, but we also begin to think with the author about the evidence—the first step in moving from reader to writer. Here's a sample passage by anthropologist and naturalist Loren Eiseley. It's from his essay called "The Hidden Teacher." . . . I once received an unexpected lesson from a spider. It happened far away on a rainy morning in the West. I had come up a long gulch looking for fossils, and there, just at eye level, lurked a huge yellow-and-black orb spider, whose web was moored to the tall spears of buffalo grass at the edge of the arroyo. It was her universe, and her senses did not extend beyond the lines and spokes of the great wheel she inhabited. Her extended claws could feel every vibration throughout that delicate structure. She knew the tug of wind, the fall of a raindrop, the flutter of a trapped moth's wing. Down one spoke of the web ran a stout ribbon of gossamer on which she could hurry out to investigate her prey. Curious, I took a pencil from my pocket and touched a strand of the web. Immediately there was a response. The web, plucked by its menacing occupant, began to vibrate until it was a blur. Anything that had brushed claw or wing against that amazing snare would be thoroughly entrapped. As the vibrations slowed, I could see the owner fingering her guidelines for signs of struggle. A pencil point was an intrusion into this universe for which no precedent existed. Spider was circumscribed by spider ideas; its universe was spider universe. All outside was irrational, extraneous, at best raw material for spider. As I proceeded on my way along the gully, like a vast impossible