Charge carrier solvation and large polaron formation on a polymer chain revealed in model a

Annu.Rev.Phys.Chem.2000.51:129–52Copyright c2000by Annual Reviews.All rights reserved G ENERALIZED B ORN M ODELS OFM ACROMOLECULAR S OLVATION E FFECTSDonald Bashford and David A.CaseDepartment of Molecular Biology,The Scripps Research Institute,La Jolla,California 92037;e-mail:bashford@,case@Key Words solvation energy,continuum dielectricss Abstract It would often be useful in computer simulations to use a simple de-scription of solvation effects,instead of explicitly representing the individual solvent molecules.Continuum dielectric models often work well in describing the thermo-dynamic aspects of aqueous solvation,and approximations to such models that avoid the need to solve the Poisson equation are attractive because of their computational efficiency.Here we give an overview of one such approximation,the generalized Born model,which is simple and fast enough to be used for molecular dynamics simulations of proteins and nucleic acids.We discuss its strengths and weaknesses,both for its fidelity to the underlying continuum model and for its ability to replace explicit con-sideration of solvent molecules in macromolecular simulations.We focus particularly on versions of the generalized Born model that have a pair-wise analytical form,and therefore fit most naturally into conventional molecular mechanics calculations.INTRODUCTIONThere are many circumstances in molecular modeling studies where a simplified description of solvent effects has advantages over the explicit modeling of each solvent molecule.One of the most popular models,especially for water,treats the solvent as a high-dielectric continuum,interacting with charges that are em-bedded in solute molecules of lower dielectric.The solute charge distribution,and its response to the reaction field of the solvent dielectric,can be modeled either by quantum mechanics or by partial atomic charges in a molecular me-chanics description.In spite of the severity of the approximation,this model often gives a good account of equilibrium solvation energetics,and it is widely used to estimate pKs,redox potentials,and the electrostatic contributions to molec-ular solvation energies (for recent reviews,see 1–6).For molecules of arbitrary shape,the Poisson-Boltzmann (PB)equations that describe electrostatic interac-tions in a multiple-dielectric environment are typically solved by finite-difference or boundary-element numerical methods (1,7–12).These can be efficiently solved0066-426X/00/1001-0129$14.00129A n n u . 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F o r p e r s o n a l u s e o n l y .130BASHFORD¥CASEfor small molecules but may become quite expensive for proteins or nucleic acids.For example,the DelphiII program,which is a popular program that computes a finite-difference solution,takes about 25min on a 195-Mhz SGI processor to solve problems on a 1853grid with 600atoms.Obtaining derivatives with respect to atomic positions adds to the time and complexity of the calculation (13).Even though progress continues to be made in numerical solutions,and other approaches may be significantly faster,there is a clear interest in exploring more efficient,if approximate,approaches to this problem.One such simplification that has received considerable recent attention is the generalized Born (GB)approach (14,15).In this model,which is derived below,the electrostatic contribution to the free energy of solvation isG pol =−12 1−1w i ,j q i q jf GB , 1.where q i and q j are partial charges,εw is the solvent dielectric constant,andf GB is a function that interpolates between an “effective Born radius”R i ,when the distance r i j between atoms is short,and r i j itself at large distances (15).In the original model,values for R i were determined by a numerical integration proce-dure,but it has recently been shown that “pair-wise”approximations,in which R i is estimated from a sum over atom pairs,can be nearly as accurate and provide a simplified approach to energies and their derivatives (16–21).In the following sections,we present one derivation of this model and compare it to the underlying continuum dielectric model on which it is based.This is followed by a review of pair-wise parameterizations and of practical applications of GB and closely related approximations.Our emphasis is almost exclusively on the use of this approach to describe aqueous solvation of macromolecules.A comprehensive review of other applications of the GB model has recently appeared (6).GENERALIZED BORN AND RELATED APPROXIMATIONSThe underlying physical picture on which the GB approximation is based is the two-dielectric model described above.To obtain the electrostatic potential φin such a model,one should ideally solve the Poisson equation,∇[ε(r )∇φ(r )]=−4πρ(r ),2.where ρis the charge distribution,and the dielectric constant εtakes on the solute molecular dielectric constant εin in the solute interior and the exterior dielectric constant εex elsewhere.For gas phase conditions,εex =1,whereas in solvent conditions,εex =εw ,the dielectric constant of the solvent (here,water);solving Equation 2under these two conditions leads to potentials that can be denoted φsol and φvac ,respectively.The difference between these potentials is the reaction field,φreac =φsol −φvac ,and the electrostatic component of the solvation free energy isG pol =12φreac (r )ρ(r )dV , 3.A n n u . 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F o r p e r s o n a l u s e o n l y .GENERALIZED BORN MODELS 131or if the molecular charge distribution is approximated by a set of partial atomic point charges q i ,G pol =12i q i φreac (r i ). 4.In the case of a simple ion of radius a and charge q ,the potentials can be found analytically and the result is the well-known Born formula (22),G Born =−q 22a 1−1εw. 5.If we imagine a “molecule”consisting of charges q 1···q N embedded in spheres of radii a 1···a N ,and if the separation r i j between any two spheres is sufficiently large in comparison to the radii,then the solvation free energy can be given by a sum of individual Born terms,and pair-wise Coulombic terms:G pol =N i q 2i 2a i 1w −1 +12N i N j =i q i q j r i j 1w −1 , 6.where the factor (1/εw −1)appears in the pair-wise terms because the Coulombicinteractions are rescaled by the change of dielectric constant on going from vacuum to solvent.The goal of GB theory can be thought of as an effort to find a relatively simple analytical formula,resembling Equation 6,which for real molecular geometries will capture,as much as possible,the physics of the Poisson equation.The linearity of the Poisson equation (or the linearized PB equation)assures that G pol will indeed be quadratic in the charges,as both Equations 1and 6assume.However,in calculations of G pol based on direct solution of the Poisson equation,the effect of the dielectric constant is not generally restricted to the form of a prefactor,(1/εw −1),nor is it a general result that the interior dielectric constant,εin ,has no effect.With these caveats in mind,we seek a function f GB ,to be used in Equation 1,such that in the self (i =j )terms,f GB acts as an “effective Born radius,”whereas in the pair-wise terms,f GB becomes an effective interaction distance.The most common form chosen (15)isf GB (r i j )= r 2i j +R i R j exp −r 2i j /4R i R j 12,7.in which the R i are the effective Born radii of the atoms,which generally dependnot only on a i ,the intrinsic atomic radii,but also on the radii and relative positions of all other atoms.Ideally,R i should be chosen so that if one were to solve the Poisson equation for a single charge q i placed at the position of atom i ,and a dielectric boundary determined by all of the molecule’s atoms and their radii,then the self-energy of charge i in its reaction field,q i φreac (r i )/2,would be equal to −(q 2/2R i )(1−1/εw ).Obviously,this procedure per se would have no practical advantage over a direct calculation of G pol using a numerical solution of the Poisson equation.To find a more rapidly calculable approximation for the effective Born radii,we turn to a formulation of electrostatics in terms of integration over energy density.A n n u . 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F o r p e r s o n a l u s e o n l y .132BASHFORD¥CASEDerivation in Terms of Energy DensitiesIn the classical electrostatics of a linearly polarizable media (23),the work required to assemble a charge distribution can be formulated either in terms of a product of the charge distribution with the electric potential,as above,or in terms of the scalar product of the electric field E and the electric displacement D :W =12 ρ(r )φ(r )dV 8.=18π E ·D dV .9.We now introduce the essential approximation used in most forms of GB theory:that the electric displacement is Coulombic in form,and remains so even as the ex-terior dielectric is altered from 1to εw in the solvation process.In other words,the displacement due to the charge of atom i (which for convenience is here presumed to lie on the origin)isD i ≈q i r r3.10.This is called the Coulomb field approximation.In the spherically symmetric case (as in the Born formula),it is exact,but in more complex geometries,there may be substantial deviations,a point to which we turn presently.The work of placing a charge q i at the origin within a molecule whose interior dielectric constant is εin ,surrounded by a medium of dielectric constant εex and in which no other charges have yet been placed,is thenW i =18π (D /ε)·D dV ≈18π in q 2i r 4εin dV +18πex q 2i r 4εex dV .11.The electrostatic component of the solvation energy is found by taking the differ-ence in W i when εex is changed from 1.0to εw ,G pol i =−18π 1−1w ex q ir dV ,12.where the contribution due to the interior region has canceled in the subtraction.1Comparing Equation 12to the Born Formula 5or to Equations 1or 6,we conclude that the effective Born radius should beR −1i =14π ex 1r 4dV .13.1Itmay be noticed that the interior integral contained a singularity at r →0.This a con-sequence of representing the charge distribution as a set of point charges,and similar singularities appear in treatments based on the electrostatic potential.The validity of can-celing out such singularities can be demonstrated by replacement of these point charges by small charged spheres and consideration of the limit as the sphere radii shrink to zero.A n n u . 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F o r p e r s o n a l u s e o n l y .GENERALIZED BORN MODELS 133It is often convenient to rewrite this in terms of an integration over the interior region,excluding a radius a i around the origin,R −1i =a −1i −14π in ,r >a i 1r 4dV ,14.where we have used the fact that the integration of r −4over all space outside radius a is simply 4πa −1.Note that in the case of a monatomic ion,where the molecular boundary is simply the sphere of radius a i ,this equation becomes R i =a i and the Born formula is recovered exactly.The integrals in Equation 13or 14can be calculated numerically by constructing a set of concentric spherical shells around atom i and calculating the fractional area of these shells lying inside or outside the van der Waals volume of the other atoms,j =i (15),or by using a cubic integration lattice (24).Ghosh et al (25)have proposed an alternative approach,in which the Coulomb field is still used in place of the correct field,and Green’s theorem is used to convert the volume integral in Equation 14to a surface integral.At this level,the S-GB (surface-GB)model is formally identical to the model outlined above.(There are potential computational advantages in the surface integral approach,especially for large systems and for evaluating gradients,but these have not yet been exploited.)In practice,empirical short-range and long-range corrections (discussed below)are added to improve agreement with numerical Poisson theory.Solute Dielectrics Other than UnityStrictly speaking,the Coulomb field approximation assures that the internal dielec-tric constant,εin ,does not appear in GB theory;the only dielectric constants that matter are those of the solvent and the vacuum.(See the passage from Equation 11to Equation 12.)However,εin can reappear in an indirect and somewhat deceptive way,in GB-based expressions for energy as a function of solute conformation or intermolecular interaction energies.In such cases,one would like to have a poten-tial of mean force described on the hypersurface of the solute degrees of freedom.Its electrostatic component would bePMF elec =E elec ,ref + G pol (ref →sol ),15.where E elec ,ref is the electrostatic energy of the solute in some reference environ-ment that is chosen so that the calculation can be done simply,and G pol (ref →sol )is the energy of transferring the system from this reference environment to solvent.If the solute is presumed to have an internal dielectric of 1,the obvious choice of reference medium is the vacuum,where E elec ,ref can be calculated by Coulomb’s law,and the usual GB expressions for G pol can be used unchanged for G pol (ref →sol ).However,if the internal dielectric has a value εin that is different from 1,a more convenient choice is a reference medium of dielectric constant εin ,so that Coulomb’s law can again be used.In this case,all occurrencesA n n u . 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F o r p e r s o n a l u s e o n l y .134BASHFORD¥CASEof (1−1/εw )in the GB theory expressions are replaced by (1/εin −1/εw ).The resulting expression for the electrostatic potential of mean force isPMF elec =12 i =j q i q j in r i j −12 i ,j 1in −1wq i q jf GB i j 16.(compare with Equation 1).At long distances,where f GB goes to r i j ,the εin de-pendence disappears.It should be emphasized that εin appears in these formulaenot so much because it is the internal dielectric constant as because it is the ex-ternal dielectric constant of the reference environment.In particular,GB theory,because of its Coulomb field approximation,and in contrast to Poisson-equation theory,cannot capture the tendency of solvation to increase the dipole moment of a dipolar solute,thus enhancing its solubility,through the use of an internal dielectric constant.Of course,such effects can be captured by methods that ex-plicitly couple some other theory of solute polarizability to GB theory,e.g.though quantum mechanical descriptions of the solute (6).Incorporation of Salt EffectsGB models have not traditionally considered salt effects,but the model can be extended to low salt concentrations at the Debye-Huckel level by the following arguments (21).The basic idea of the GB approach can be viewed as an inter-polation formula between analytical solutions for a single sphere and for widely separated spheres.For the latter,the solvation contribution in the Poisson model becomesG pol =− 1−e −κr i j wq i q jr i j ,17.where κis the Debye-H¨u ckel screening parameter.The first term removes the gas-phase interaction energy,and the second term replaces it with a screened Coulombpotential.For a single spherical ion,the result is (26,27)G pol =−12 1−1εwq 2a −q 2κ2εw (1+κb ),18.where a is the radius of the sphere and b is the radial distance to which salt ionsare excluded,so that b −a is the ion-exclusion radius.To a close extent,these two limits can be obtained by the simple substitution1−1w → 1−e −κf GBw19.in Equation 1.This reduces directly to Equation 17for large distances,and thesalt-dependent terms become,as r i j goes to zero,−q 2i κ2εw 1+12κR i 20.A n n u . 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F o r p e r s o n a l u s e o n l y .GENERALIZED BORN MODELS 135through terms in κ2.To terms linear in κ,Equations 20and 18agree,but the quadratic terms differ by the replacement of b with 1/2(R i ).In practice,Equation 19gives salt effects that are slightly larger than those predicted by finite-difference linearized PB calculations,but which are strongly correlated with them.One likely reason is that the GB model outlined here does not have the concept of an ion-exclusion radius and,hence,tends to overestimate salt effects (compared with the usual PB model)by allowing counterions to approach more closely to the solute than they should.A simple ad hoc modification that leads to acceptable results can be obtained by a simple scaling of κby 0.73in Equation 19(21).Figure 1compares linearized PB and GB estimates of the effect of monovalent added salt on the solvation energy of a 10-bp DNA duplex.The GB model is clearly capturing most of the behavior of linearized PB,especially at low salt concentrations.It is worth emphasizing that the linearized PB model itself is an imperfect model for salt effects (28),so that Equation 20should only be viewed as a rough approximation;it does,nonetheless,introduce the exponential screening of long-range Coulomb interactions,which is one of the hallmarks of salt effects.Limitations and Variations of the GB ModelThe crux of the GB approximation for the self-energy terms and effective radii is the Coulomb field approximation,Equation 10,and this is also the main source of its deviation from solvation energies calculated using solutions of thePoissonFigure 1Difference in the solvation energy at finite and zero added salt for a 10-bp DNA duplex,calculated by numerical solutions to the linearized PB model,and from Equation 38.(Data from Reference 21.)A n n u . 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F o r p e r s o n a l u s e o n l y .136BASHFORD¥CASEequation.In general,the electric displacement generated by a charge q i located at a position r i within the low dielectric cavity of the solute will consist of a Coulomb field and a reaction field component D reac ,the latter being a consequence of the nonuniformity of the dielectric environment.The reaction field contains no Coulombic singularities within the molecular interior and is usually fairly smoothly varying within this region.If the dielectric boundary between solvent and solute is sharp,which is the usual assumption,then D reac can be thought of as arising from an induced surface charge density on the dielectric boundary.In spherically symmetric cases,such as the case analyzed in the original Born theory,D is given exactly by the Coulomb field (D reac is zero),and GB solvation goes over into Poisson-equation solvation.Schaefer &Froemmel (29)have an-alyzed deviations from the Coulomb-field approximation for the case of charges at arbitrary positions within a spherical dielectric boundary,a case for which an-alytical solutions of the Poisson equation are available (26).They found that the Coulomb field approximation leads to significant errors in both self-energies and in the screening of charge-charge interactions,and they proposed an image-charge approximation for D reac that is very successful in recovering the energetic behavior of the exact Poisson model.Some additional quantitative sense of the limitations of the Coulomb field ap-proximation can be gained by considering the case of a charge near a planar dielectric boundary (Figure 2).This can be thought of as the infinite-radius limit of the situation where a charge is a distance d below the surface of a spherical macromolecule with a large radius (R d )and a dielectric constant εin ,and the macromolecule is transferred from an external medium of dielectric constant εin to a medium of dielectric constant εw .The electrostatic potential can be found exactly by the method of images (23).φz >0=q εin r 1+q εin r 2φz <0=q ex r 1,21.whereq =−qεex −εin ex in q =q 2εexex in .22.The reaction field in the z >0region corresponding to a change of εex from εin to εw isφreac =q εin r 2=−q εw −εin εw +εin1εin r 2,23.A n n u . 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F o r p e r s o n a l u s e o n l y .GENERALIZED BORN MODELS137Figure 2A point charge q near a dielectric interface at z =0.The dielectric constant is εin or εex in the positive or negative z regions,respectively.The potential on the +z side is a sum of the Coulomb potential of the real charge q at z =d ,and an image charge q at z =−d .The potential on the −z side is the Coulomb potential of an image charge q at z =d .The distances of an arbitrary point r from the z =d and z =−d charge locations are denoted as r 1and r 2,respectively.where the r 1term has canceled in the subtraction of the potential in the εex =εin case from the potential in the εex =εw case.The electrostatic solvation energy can be found using Equation 4,G pol (exact )=−q 24d εw −εin εin (εw +εin )=−q 24d 1εin −1εw11+εin /εw .24.The corresponding formula for the solvation energy according to the Coulomb-field approximation and an integration of the energy density difference over the“exterior”(z <0)region can be obtained using Equation 12:G pol (Coulomb )= 1in −1w 18πz <0q 2r 2=−q 28d 1in −1w .25.Note that in the usual case where εw εin ,the magnitude of G pol is underesti-mated by a factor of almost 2compared with the exact expression,Equation 24,although the form of the dielectric-constant dependence,a factor of (1/εin −1/εw ),is approximately correct.This suggests that for charges buried somewhat below the surface of large macromolecules,the |W i |of Equation 11may be underestimated,and thus the effective Born radii overestimated because of the Coulomb-field ap-proximation.Of course the methods of approximating density integrals (such asA n n u . 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F o r p e r s o n a l u s e o n l y .138BASHFORD¥CASEthe pair-wise descreening approximation decribed below)will also affect the re-sults.On the other hand,most of the solvation energy of a macromolecule will be due to charged or highly polar groups that protrude into solvent,and for these groups,GB theory may be expected to work nearly as well as for analogous groups in small molecules.Luo et al (30)have also examined errors arising from replacing the true field with a Coulomb approximation.Essentially,they assume that E ≈E vac /d F ,where E vac is the vacuum Coulomb field and d F is a screening parameter having different values in the interior region or exterior regions.In the centrosymmetric case,d F is identical to the dielectric constant,but for more general shapes,it is a parameter to be optimized to provide realistic solvation energies.This leads toG pol =−18πεw −1d Fex E 2vac dV .26.Noting that in the Coulomb field approximation D =E vac ,this expression is similarto Equation 12with (1−1/εw )replaced by (εw −1)/d F .Its other difference from GB theory is that this expression is used for the entire solvation energy,implicitly including charge-charge interactions terms rather than using a formula such as Equation 7.On a number of test cases,it was found to give good agreement with Poisson calculations,but the numerical integration required had roughly the same computational cost as solving the Poisson equation numerically.The limitations of both the density integration methods and the Coulomb field approximation are also addressed in the electrostatic component of the SEED method for docking small molecular fragments to a macromolecular receptor (31).The desolvation of the receptor by the low dielectric of the ligand is taken to be the integral of D 2/(8π)over the ligand volume,and D is assumed not to change on ligand binding,as in conventional GB theory.The integration is done numerically using a cubic lattice,and the user can choose whether to estimate D by the Coulomb field approximation,as in GB theory,or to calculate it by a finite difference solution of the Poisson equation for the ligand-free receptor.In its use of a D obtained by solving the Poisson equation,this method is similar in spirit to the SEDO approximation described below,except that the latter is based on solvation energy density rather than D 2.Solvation Energy DensityIn Equation 12,the solvation energy is expressed as the volume integral of an energy density that is zero within the solute volume,so that the integral need only run over the solvent volume.This could be thought of as a solvation energy density,but it is only by virtue of the Coulomb field approximation that it falls to zero in the solute region.It is possible to give a more rigorous definition of solvation energy density that does not depend on approximations (32).In classical continuum electrostatics,an important problem is to find the energy change caused by placing a dielectricA n n u . 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F o r p e r s o n a l u s e o n l y .object within some volume,in the electric field of a fixed set of charges outside that volume.This is essentially the same as the present solvation problem:We seek the change of energy associated with changing the dielectric constant of the region outside the molecule V ex ,from εvac to εw ,in the presence of the atomic partial charges,which remain fixed in the molecular interior.Denoting the electric field and displacement before the dielectric alteration as E vac and D vac ,and after the alteration as E sol and D sol ,respectively,the energy change isG pol =18π (E sol ·D sol −E vac ·D vac )dV ,27.where the volume integration runs over all space.It can be shown (23)that Equation 27can be transformed intoG pol =18π (E sol ·D vac −D sol ·E vac )dV ing D =εE ,it can be seen that the integrand falls to zero in the molecular interior because the dielectric constant there does not change (i.e.E sol ·εin E vac −εin E sol ·E vac =0).One can then writeG pol =exS (r )dV ,29.where the integral runs only over the exterior region,and S is the solvation energydensity,defined byS =18π(E sol ·D vac −D sol ·E vac ).30.No approximations have been introduced up until this point,and Equations 29and 30are fully equivalent to Equation 3.Of course,if one introduces the Coulomb field approximation,Equation 10,into the expression for S ,the GB theory expression for self energies is obtained.A different approximation based on S and oriented toward estimating desol-vation effects in intermolecular interactions has recently been proposed by Arora &Bashford (32).Suppose one would like to calculate the effect of the approach of a second molecule on the solvation energy of the first molecule.The effect of the low dielectric of the second molecule on the solvation energy density S of the first is twofold.First,S will go to zero in the interior of the second molecule,in other words a portion of S will be occluded.Second,in the solvent region near the second molecule,there will be some rearrangement of S .The approximation is to include the first effect but neglect the second.This means that one can precalculate S by solving the Poisson equation and differentiating the potential to obtain the field and displacement in both vacuum and solvent,for the first molecule alone.Then the desolvation effect of a second molecule can be obtained byG desol =−mol 2S mol 1dV .31.A n n u . R e v . P h y s . C h e m . 2000.51:129-152. D o w n l o a d e d f r o m w w w .a n n u a l r e v i e w s .o r g A c c e s s p r o v i d e d b y N e w Y o r k U n i v e r s i t y - B o b s t L i b r a r y o n 09/24/15. F o r p e r s o n a l u s e o n l y .。

285 WattPOLYCRYSTALLINE SOLAR MODULEIEC-STP-Wfw-NO1.01-Rev 2017©Copyright 2017 Suntech Power17.4%3800Pa 5400PaExtended wind and snow load testsModule certified towithstand extreme wind (3800 Pascal) and snow loads (5400 Pascal) *High module conversion efficiencyModule efficiency up to 17.4% achieved throughadvanced cell technology and manufacturing capabilities 2%Suntech current sorting processSystem output maximized by reducing mismatch losses up to 2% with modules sorted & packaged by amperage PID ResistantHigh PID resistantAdvanced cell technology and qualified materials lead to high resistance to PIDWithstanding harsh environmentReliable quality leads to a better sustainability even in harsh environment like desert, farm and coastlineCertifications and standards:0/+5W Positive tolerancePositive tolerance of up to 5W delivers higher output reliablityIEC 61215, IEC 61730, conformity to CESTP285 - 20/WfwSTP280 - 20/Wfw STP275 - 20/WfwSuperpoly * Please refer to Suntech Standard Module Installation Manual for details. **WEEE only for EU market.*** Please refer to Suntech Product Near-coast Installation Manual for details. **** Please refer to Suntech Product Warranty for details.Advanced Polycrystalline Perc technologyThe Perc cell uses back surface passivation and local BSFtechnology, which can improve cell efficiency by a large margin.IEC-STP-Vem-NO1.01-Rev 2014E-mail:***********************Current-Voltage & Power-Voltage Curve (285-20)Dealer informationMechanical CharacteristicsSolar Cell Polycrystalline silicon 6 inches No. of Cells 60 (6 × 10)Dimensions 1650 × 992 × 35mm (64.96 × 39.1 × 1.4 inches)Weight 18.3 kgs (40.3 lbs.)Front Glass 3.2 mm (0.13 inches) tempered glass Frame Anodized aluminium alloy Junction Box IP68 rated (3 bypass diodes)Output CablesTUV (2Pfg1169:2007)4.0 mm 2 (0.006 inches 2), symmetrical lengths (-) 1000mm (39.4 inches) and (+) 1000 mm (39.4 inches)ConnectorsMC4 compatibleTemperature CharacteristicsNominal Operating Cell Temperature (NOCT )45±2°C Temperature Coefficient of Pmax -0.41 %/°C Temperature Coefficient of Voc-0.33 %/°C Temperature Coefficient of Isc0.067 %/°CIEC-STP-Wfw-NO1.01-Rev 20171000 W/m800 W/m600 W/m400 W/m200 W/mInformation on how to install and operate this product is available in the installation instruction. All values indicated in this data sheet are subject to change without prior announcement. The specifications may vary slightly. All specifications are in accordance with standard EN 50380. Color differences of the modules relative to the figures as well as discolorations of/in the modules which do not impair their proper functioning are possible and do not constitute a deviation from the specification.STC: lrradiance 1000 W/m , module temperature 25 °C, AM=1.5;Best in Class AAA solar simulator (IEC 60904-9) used, power measurement uncertainty is within +/- 3%NOCT: Irradiance 800 W/m , ambient temperature 20 °C, AM=1.5, wind speed 1 m/s;Best in Class AAA solar simulator (IEC 60904-9) used, power measurement uncertainty is within +/- 3%。

到9月9日，社保基金正式进入股市整整3个月，按照有关规定，社保基金必须通过基金管理公司在三个月内完成建仓，并且其持仓市值要达到投资组合总市值80%的水平。

与此前大受追捧的QFII概念相比，社保基金及其所持有的股票显然低调得多，但是在西南证券分析师田磊看来，至少就目前来看，社保基金无论是在资金规模，还是在持股数量上明显都强于境外投资者，其投资理念和行为更可能给市场带来影响。

基金操作的社保基金的选股思路并不侧重某个行业，而更看重企业本身的发展和成长性，并且现阶段的企业经营业绩和走势也不是基金重点考虑的方面。

目前入市的社保基金都是委托南方、博时、华夏、鹏华、长盛、嘉实6家基金管理公司管理。

社保基金大致是被分为14个组合由以上6家管理公司分别管理，每个组合都有一个三位数的代码，第一位代表投资方向，其中“1”指股票投资、“2”指债券投资；第三位数字则代表基金公司名称，其中“1”为南方、“2”为博时、“3”为华夏、“4”为鹏华、“5”为长盛、“6”为嘉实；另有107、108组合主要运作社保基金此前一直持有的中石化股票，分别由博时与华夏基金公司管理。

在许多社保基金介入的股票中经常可以看到开放式基金的身影，例如在被社保基金大量持有的安阳钢铁(600569)的前10大股东中，其第2、6、7、8、9大股东均为开放式基金，而社保基金则以持股500多万股位列第3大股东。

类似的情况也出现在社保基金103组合所持有的华菱管线(000932)上，其第二大股东即为鹏华行业成长证券投资基金，社保基金则以200多万股的持仓量位列第7大股东，此外，在其前10大股东中还有5家是封闭式基金。

对此，某基金公司人士解释说，在获得社保基金管理人资格后，6家基金公司成立了专门的机构理财部门负责社保基金的投资管理，但是其研究、交易系统等则与公募基金共用一个平台，因此社保基金和开放式基金在选股时才会如此一致。

针对“社保概念股”的走势，国盛证券的分析师王剑认为，虽然社保基金此次委托入市资金超过百亿元，但大部分投向是债券，而且由于社保基金的特殊地位，因此基金管理公司对社保基金的操纵策略应该是以“集中持股，稳定股价”为主，不大可能博取太高的收益。

Refrigerant 22 is now the most
common refrigerant for a wide
range of temperature,
including low temperature, -
41oC being possible without
negative
evaporator
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Fine liquid filters are fitted to protect the small orifices in expansion valves.
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Any clogging of one of these reveals itself by a cooling of the liquid pipe downstream of the filter.
The essential component of a typical seal is a carbon ring, stationary and sealed to the gland cover, with a flat surface against which is pressed the rotating face of a cast iron ring secured to the shaft.
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Therefore it can evaporate at low temperature in the evaporator and condense at high temperature in the condenser.
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Thus it will be seen that heat that is transferred from the air to the evaporator is then pumped round the system until it reaches the condenser where it is transferred or rejected to the sea water.