Theoretical estimation of thermodynamic properties of the system PS/PPO on the basis of modified combining rule of Sanchez-Lacombe lattice fluid model

The three scaling parameters described in Sanchez-Lacombe lattice fluid theory (SLLFT), T*, P* and rho* of pure polystyrene (PS), pure poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and their mixtures are obtained by fitting corresponding experimental pressure volume-temperature data with equation-of-state of SLLFT. A modified combining rule in SLLFT used to match the volume per mer, v* of the PS/PPO mixtures was advanced and the enthalpy of mixing and Flory-Huggins (FH) interaction parameter were calculated using the new rule. It is found that the difference between the new rule and the old one presented by Sanchez and Lacombe is quite small in the calculation of the enthalpy of mixing and FH interaction parameter and the effect of volume-combining rule on the calculation of thermodynamic properties is much smaller than that of energy-combining rule. But the relative value of interaction parameter changes much due to the new volume-based combining rule. This effect can affect the position of phase diagram very much, which is reported elsewhere [Macromolecules 34 (2001) 6291]

Statistical thermodynamics of polydisperse polymer systems in the framework of lattice fluid model: Effect of molecular weight and its distribution on the spinodal in polymer solution

With the aid of thermodynamics of Gibbs, the expression of the spinodal was derived for the polydisperse polymer-solvent system in the framework of Sanchez-Lacombe Lattice Fluid Theory (SLLFT). For convenience, we considered that a model polydisperse polymer contains three sub-components. According to our calculation, the spinodal depends on both weight-average ((M) over bar (w)) and number-average ((M) over bar (n)) molecular weights of the polydisperse polymer, but the z-average molecular weight ((M) over bar (z)) dependence on the spinodal is invisible. The dependence of free volume on composition, temperature, molecular weight, and its distribution results in the effect of (M) over bar (n) on the spinodal. Moreover, it has been found that the effect of changing (M) over bar (w) on the spinodal is much bigger than that of changing (M) over bar (n) and the extrema of the spinodal increases with the rise of the weight-average molecular weight of the polymer in the solutions with upper critical solution temperature (UCST). However, the effect of polydispersity on the spinodal can be neglected for the polymer with a considerably high weight-average molecular weight. A more simple expression of the spinodal for the polydisperse polymer solution in the framework of SLLFT was also derived under the assumption of upsilon(*)=upsilon(1)(*)=upsilon(2)(*) and (1/r(1)(0))-(1/r(2i)(0))-->(1/r(1)(0)).

Effects of pressure and molecular weight on the miscibility of polystyrene and cyclohexane

With the aid of Sanchez-Lacombe lattice fluid theory (SLLFT), the phase diagrams were calculated for the system cyclohexane (CH)/polystyrene (PS) with different molecular weights at different pressures. The experimental data is in reasonable agreement with SLLFT calculations. The total Gibbs interaction energy, g*(12) for different molecular weights PS at different pressures was expressed, by means of a universal relationship, as g(12)* =f(12)* + (P - P-0) nu*(12) demixing curves were then calculated at fixed (near critical) compositions of CH and PS systems for different molecular weights. The pressures of optimum miscibility obtained from the Gibbs interaction energy are close to those measured by Wolf and coworkers. Furthermore, a reasonable explanation was given for the earlier observation of Saeki et al., i.e., the phase separation temperatures of the present system increase with the increase of pressure for the low molecular weight of the polymer whereas they decrease for the higher molecular weight polymers. The effects of molecular weight, pressure, temperature and composition on the Flory Huggins interaction parameter can be described by a general equation resulting from fitting the interaction parameters by means of Sanchez-Lacombe lattice fluid theory.

Evolution induced catastrophe in a nonlinear dynamical model of material failure

In order to study the failure of disordered materials, the ensemble evolution of a nonlinear chain model was examined by using a stochastic slice sampling method. The following results were obtained. (1) Sample-specific behavior, i.e. evolutions are different from sample to sample in some cases under the same macroscopic conditions, is observed for various load-sharing rules except in the globally mean field theory. The evolution according to the cluster load-sharing rule, which reflects the interaction between broken clusters, cannot be predicted by a simple criterion from the initial damage pattern and even then is most complicated. (2) A binary failure probability, its transitional region, where globally stable (GS) modes and evolution-induced catastrophic (EIC) modes coexist, and the corresponding scaling laws are fundamental to the failure. There is a sensitive zone in the vicinity of the boundary between the GS and EIC regions in phase space, where a slight stochastic increment in damage can trigger a radical transition from GS to EIC. (3) The distribution of strength is obtained from the binary failure probability. This, like sample-specificity, originates from a trans-scale sensitivity linking meso-scopic and macroscopic phenomena. (4) Strong fluctuations in stress distribution different from that of GS modes may be assumed as a precursor of evolution-induced catastrophe (EIC).

Estimation of Correlation Distance of Soil Properties by Geostatistics

Random field theory has been used to model the spatial average soil properties, whereas the most widely used, geostatistics, on which also based a common basis (covariance function) has been successfully used to model and estimate natural resource since 1960s. Therefore, geostistics should in principle be an efficient way to model soil spatial variability Based on this, the paper presents an alternative approach to estimate the scale of fluctuation or correlation distance of a soil stratum by geostatistics. The procedure includes four steps calculating experimental variogram from measured data, selecting a suited theoretical variogram model, fitting the theoretical one to the experimental variogram, taking the parameters within the theoretical model obtained from optimization into a simple and finite correlation distance 6 relationship to the range a. The paper also gives eight typical expressions between a and b. Finally, a practical example was presented for showing the methodology.

Vertical Bearing Capacity of a Partially-Embedded Pipeline on Tresca Soils

Slip-line field solutions are presented for the ultimate load of submarine pipelines on a purely cohesive soil obeying Tresca yield criterion, taking into account of pipe embedment and pipe-soil contact friction. The derived bearing capacity factors for a smooth pipeline degenerate into those for the traditional strip-line footing when the embedment approaches zero. Parametric studies demonstrate that the bearing capacity factors for pipeline foundations are significantly influenced by the pipeline embedment and the pipe-soil frictional coefficient. With the increase of pipeline embedment, the bearing capacity factor Nc decreases gradually, and finally reaches the minimum value (4.0) when the embedment equals to pipeline radius. As such, if the pipeline is directly treated as a traditional strip footing, the bearing capacity factor Nc would be over evaluated. The ultimate bearing loads increase with increasing pipeline embedment and pipe-soil frictional coefficient.

Analysis on the spin reorientation of GdFeCo/DyFeCo exchange-coupled double-layer films

In this paper, GdFeCo/DyFeCo exchange-coupled double-layer films used for center aperture type magnetically induced super resolution were investigated through experiments and theoretical calculation. The samples were prepared by magnetron sputtering method. The polar Kerr effect was measured to prove the spin reorientation of the readout layer. Theoretical study of magnetization profiles was performed on the basis of the mean-field theory and the continuum model. The theoretical results showed that the magnetization orientation of the readout layer changed gradually from in-plane to out-of-plane with the rise of the temperature. Theoretical analysis explained the experimental results successfully. (c) 2005 Elsevier B.V. All rights reserved.

基于Berreman矩阵的双折射薄膜光谱响应特性计算

采用Berreman特征矩阵方法，通过数值计算研究了双折射薄膜的反射、透射等光谱响应特性。依据电磁场理论的电场分量、磁场分量的界面连续条件，推导了光波在各向异性双轴薄膜中的Berreman转移矩阵，用以分析含有各向异性介质层的复杂薄膜系统的光学性质。这些矩阵递推关系包含了界面处的多点反射，适用于一般的各向异性的多层膜系统，包括入射媒质或基底为各向异性的情况。在文中给出了各向同性入射媒质双轴各向异性膜层一各向同性基底薄膜系统的计算结果，验证了该计算方法的可行性，以此作为进一步研究各向异性薄膜和相关光学薄膜器

Photoluminescence of low-dimensional semiconductor structures under pressure

Photoluminescence of some low-dimensional semiconductor structures has been investigated under pressure. The measured pressure coefficients of In0.55Al0.45 As/Al0.5Ga0.5As quantum dots with average diameter of 26, 52 and 62 nm are 82, 94 and 98 meV/GPa, respectively. It indicates that these quantum dots are type-I dots. On the other hand, the measured pressure coefficient for quantum dots with 7 nm in size is -17meV/GPa, indicating the type-II character. The measured pressure coefficient for Mn emission in ZnS:Mn nanoparticles is -34.6meV/GPa, in agreement with the predication of the crystal field theory. However, the DA emission is nearly independent on pressure, indicating that this emission is related to the surface defects in ZnS host. The measured pressure coefficient of Cu emission in ZnS: Cu nanoparticles is 63.2 meV/GPa. It implies that the acceptor level introduced by Cu ions has some character of shallow level. The measured pressure coefficient of Eu emission in ZnS:Eu nanoparticles is 24.1 mev/GPa, in contrast to the predication of the crystal field theory. It may be due to the strong interaction between the excited state of Eu ions and the conduction band of ZnS host.

Photoluminescence of doped ZnS nanoparticles under hydrostatic pressure

The pressure dependence of the photoluminescence from ZnS : Mn2+, ZnS : Cu2+, and ZnS : Eu2+ nanoparticles were investigated under hydrostatic pressure up to 6 GPa at room temperature. Both the orange emission from the T-4(1) - (6)A(1) transition of Mn2+ ions and the blue emission from the DA pair transition in the ZnS host were observed in the Mn-doped samples. The measured pressure coefficients are -34.3(8) meV/GPa for the Mn-related emission and -3(3) meV/GPa for the DA band, respectively. The emission corresponding to the 4f(6)5d(1) - 4f(7) transition of Eu2+ ions and the emission related to the transition from the conduction band of ZnS to the t(2) level of Cu2+ ions were observed in the Eu- and Cu-doped samples, respectively. The pressure coefficient of the Eu-related emission was found to be 24.1(5) meV/GPa, while that of the Cu-related emission is 63.2(9) meV/GPa. The size dependence of the pressure coefficients for the Mn-related emission was also investigated. The Mn emission shifts to lower energies with increasing pressure and the shift rate (the absolute value of the pressure coefficient) is larger in the ZnS : Mn2+ nanoparticles than in bulk. Moreover, the absolute pressure coefficient increases with the decrease of the particle size. The pressure coefficients calculated based on the crystal field theory are in agreement with the experimental results. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Pressure dependence of Mn2+ luminescence in differently sized ZnS : Mn nanoparticles

The pressure behavior of Mn2+ emission in the 10-, 4.5-, 3.5-, 3-, and 1-nm-sized ZnS:Mn2+ nanoparticles is investigated. The emission shifts to lower energies with increasing pressure, and the shift rate (the absolute value of the pressure coefficient) is larger in the ZnS:Mn2+ nanoparticles than in bulk. The pressure coefficient increases with the decrease in particle size with the 1-nm-sized particles as an exception. Pressure coefficient calculations based on the crystal field theory are in agreement with the experimental results. The pressure dependence of the emission intensity is also size dependent. For nanoparticles 1 and 3 nm in size, the luminescence intensity of Mn2+ decreases dramatically with increasing pressure, while, for bulk and particles with average sizes of 3.5, 4.5, and 10 nm, the luminescence intensity of Mn2+ is virtually unchanged at different pressures. The bandwidth increases faster with increasing pressure for smaller particles. This is perhaps due to the fact that there are more Mn2+ ions at the near-surface sites and because the phonon frequency is greater for smaller particles. These new phenomena provide some insight into the luminescence behavior of Mn2+ in ZnS:Mn2+ nanoparticles.

Temperature and pressure dependences of the Mn2+ and donor-acceptor emissions in ZnS : Mn2+ nanoparticles

Temperature and pressure dependent measurements have been performed on 3.5 nm ZnS:Mn2+ nanoparticles. As temperature increases, the donor-acceptor (DA) emission of ZnS:Mn2+ nanoparticles at 440 nm shifts to longer wavelengths while the Mn2+ emission (T-4(1)-(6)A(1)) shifts to shorter wavelengths. Both the DA and Mn2+ emission intensities decrease with temperature with the intensity decrease of the DA emission being much more pronounced. The intensity decreases are fit well with the theory of thermal quenching. As pressure increases, the Mn2+ emission shifts to longer wavelengths while the DA emission wavelength remains almost constant. The pressure coefficient of the DA emission in ZnS:Mn2+ nanoparticles is approximately -3.2 meV/GPa, which is significantly smaller than that measured for bulk materials. The relatively weak pressure dependence of the DA emission is attributed to the increase of the binding energies and the localization of the defect wave functions in nanoparticles. The pressure coefficient of Mn2+ emission in ZnS:Mn2+ nanoparticles is roughly -34.3 meV/GPa, consistent with crystal field theory. The results indicate that the energy transfer from the ZnS host to Mn2+ ions is mainly from the recombination of carriers localized at Mn2+ ions. (C) 2002 American Institute of Physics.

Pressure dependence of Mn2+ fluorescence in ZnS : Mn2+ nanoparticles

The photoluminescence of Mn2+ in ZnS:Mn2+ nanoparticles with an average size of 4.5 nm has been measured under hydrostatic pressure from 0 to 6 GPa. The emission position is red-shifted at a rate of -33.3+/-0.6meV/GPa, which is in good agreement with the calculated value of -30.4meV/GPa using the crystal field theory. (C) 2000 Elsevier Science B.V. All rights reserved.

PHOTOLUMINESCENCE INVESTIGATIONS OF CD1-XMNXTE UNDER HYDROSTATIC-PRESSURE

The photoluminescence of Cd1-xMnxTe with x=0.25, 0.40, and 0.60 is investigated at 77 K and different pressures. The pressure coefficients of the photoluminescence bands Cd0.75Mn0.25Te and Cd0.6Mn0.4Te are found to be positive and the magnitudes are about 8 X 10(-3) eV/kbar, which is in good agreement with the pressure coefficients of the interband transition. The pressure coefficient of the photoluminescence bands for Cd0.4Mn0.6Te is found to be -6 X 10(-3) eV/kbar, which is quite different from the pressure coefficient of the interband transition. The possible transition mechanism is discussed in terms of group theory and crystal field theory.