溶液中柔性树枝形高分子的分子动力学模拟

树枝形高分子具有几乎完美的分子结构，含有许多末端基团，并拥有特殊的流变行为使其在生物医药、基因治疗、光电材料等领域有广泛的应用前景。探讨树枝形高分子的代数和链节长度对其静态性质和动力学行为的影响规律，将有助于实现树枝形高分子的结构调控，为其广泛应用提供依据和指导。然而，目前系统研究代数和链节长度的研究仍然较少，还遗留很多问题没有得到解决，尤其是树枝形高分子的动力学行为。因此，本论文使用分子动力学的模拟方法探讨了树枝形高分子的静态性质和动力学行为，获得了如下结果： 1. 树枝形高分子的回转半径Rg满足标度律Rg~N1/5(G+1)2/5P2/5（其中树枝形分子的聚合度是N，代数是G，链节长度是P，子代代数是g。）。 2. 随着代数的增加，树枝形高分子的分形维数增加并接近3.0，静态结构因子和硬球的相似，表明其内部结构发生了由类星形向近球形转化。 3. 随着代数和链节长度的增加，出现了“单元”(monomer)密度几乎不变的区域，这是外层子代链节回折的结果。定量计算表明：树枝形分子的回折能力随着链节长度的增加而增强，随着代数的增加而减弱。 4. 树枝形高分子整体的扩散行为和“单元”的运动满足Zimm标度关系。 5. 树枝形分子各子代的运动速度不同，与内层子代相比，外层子代在短时间内扩散较慢，但其松弛较快。借助Stoke-Einstein扩散方程和链节的空间位阻效应，我们解释了子代速度不同的成因。

Effects of convection and solid wall on the diffusion in microscale convection flows

The diffusive transport properties in microscale convection flows are studied by using the direct simulation Monte Carlo method. The effective diffusion coefficient D is computed from the mean square displacements of simulated molecules based on the Einstein diffusion equation D = x2 t /2t. Two typical convection flows, namely, thermal creep convection and Rayleigh– Bénard convection, are investigated. The thermal creep convection in our simulation is in the noncontinuum regime, with the characteristic scale of the vortex varying from 1 to 100 molecular mean free paths. The diffusion is shown to be enhanced only when the vortex scale exceeds a certain critical value, while the diffusion is reduced when the vortex scale is less than the critical value. The reason for phenomenon of diffusion reduction in the noncontinuum regime is that the reduction effect due to solid wall is dominant while the enhancement effect due to convection is negligible. A molecule will lose its memory of macroscopic velocity when it collides with the walls, and thus molecules are hard to diffuse away if they are confined between very close walls. The Rayleigh– Bénard convection in our simulation is in the continuum regime, with the characteristic length of 1000 molecular mean free paths. Under such condition, the effect of solid wall on diffusion is negligible. The diffusion enhancement due to convection is shown to scale as the square root of the Péclet number in the steady convection regime, which is in agreement with previous theoretical and experimental results. In the oscillation convection regime, the diffusion is more strongly enhanced because the molecules can easily advect from one roll to its neighbor due to an oscillation mechanism. © 2010 American Institute of Physics. doi:10.1063/1.3528310

量子能谱中的长程关联

从可积系统求迹公式出发 ,运用Einstein Brillouin Keller(EBK)量子化条件 ,导出了二维无关联振子系统周期轨道作用量量子化条件 ,由此发现了量子能级与周期轨道之间的对应关系 .这种对应关系表明 ,如果两条能级对应的周期轨道的拓扑相同 ,这两条能级对回归函数的贡献相干 .回归谱中的一个峰是量子能谱中一组与具有相同拓扑的周期轨道相对应的能级之间相干的结果 ,这一组能级间存在着长程关联 .

The generalized second law of thermodynamics in generalized gravity theories

We investigate the generalized second law of thermodynamics (GSL) in generalized theories of gravity. We examine the total entropy evolution with time including the horizon entropy, the non-equilibrium entropy production, and the entropy of all matter, field and energy components. We derive a universal condition to protect the generalized second law and study its validity in different gravity theories. In Einstein gravity (even in the phantom-dominated universe with a Schwarzschild black hole), Lovelock gravity and braneworld gravity, we show that the condition to keep the GSL can always be satisfied. In f ( R) gravity and scalar-tensor gravity, the condition to protect the GSL can also hold because the temperature should be positive, gravity is always attractive and the effective Newton constant should be an approximate constant satisfying the experimental bounds.

Crossing the phantom divide in brane cosmology with curvature corrections and brane-bulk energy transfer

We consider the Randall-Sundrum brane-world model with bulk-brane energy transfer where the Einstein-Hilbert action is modified by curvature correction terms: a four-dimensional scalar curvature from induced gravity on the brane, and a five-dimensional Gauss-Bonnet curvature term. It is remarkable that these curvature terms will not change the dynamics of the brane universe at low energy. Parameterizing the energy transfer and taking the dark radiation term into account, we find that the phantom divide of the equation of state of effective dark energy could be crossed, without the need of any new dark energy components. Fitting the two most reliable and robust SNIa datasets, the 182 Gold dataset and the Supernova Legacy Survey (SNLS), our model indeed has a small tendency of phantom divide crossing for the Gold dataset, but not for the SNLS dataset. Furthermore, combining the recent detection of the SDSS baryon acoustic oscillations peak (BAO) with lower matter density parameter prior, we find that the SNLS dataset also mildly favors phantom divide crossing.

Antikaon condensation and in-medium kaon and antikaon production in protoneutron stars

Antikaon condensation and kaon and antikaon production in protoneutron stars are investigated in a chiral hadronic model (also referred to as the FST model in this paper). The effects of neutrino trapping on protoneutron stars are analyzed systematically. It is shown that neutrino trapping makes the critical density of K- condensation delay to higher density and (K) over bar (0) condensation not occur. The equation of state (EOS) of (proto)neutron star matter with neutrino trapping is stiffer than that without neutrino trapping, As a result, the maximum masses of (proto)neutron stars with neutrino trapping are larger than those without neutrino trapping. If hyperons are taken into account, antikaon does not form a condensate in (Proto)neutron stars. Meanwhile, the corresponding EOS becomes much softer, and the maximum masses of (proto)neutron stars are smaller than those without hyprons. Finally, our results illustrate that the Q values for K+ and K- production in (proto)neutron stars are not sensitive to neutrino trapping and inclusion of hyperons.

Entropy of Kaluza-Klein black hole from Kerr/CFT correspondence

We extend the recently proposed Kerr/CFT correspondence to examine the dual conformal field theory of four-dimensional Kaluza-Klein black hole in Einstein-Maxwell-Dilaton theory. For the extremal Kaluza-Klein black hole, the central charge and temperature of the dual conformal field are calculated following the approach of Guica, Hartman, Song and Strominger. Meanwhile, we show that the microscopic entropy given by the Cardy formula agrees with Bekenstein-Hawking entropy of extremal Kaluza-Klein black hole. For the non-extremal case, by studying the near-region wave equation of a neutral massless scalar field, we investigate the hidden conformal symmetry of Kaluza-Klein black hole, and find the left and right temperatures of the dual conformal field theory. Furthermore, we find that the entropy of non-extremal Kaluza-Klein black hole is reproduced by Cardy formula. (C) 2010 Elsevier B.V. All rights reserved.

Center of mass energy and system-size dependence of photon production at forward rapidity at RHIC

We present the multiplicity and pseudorapidity distributions of photons produced in Au + Au and Cu + Cu collisions at root(NN)-N-s = 62.4 and 200 GeV. The photons are measured in the region -3.7 < eta < -2.3 using the photon Multiplicity detector in the STAR experiment at RHIC. The number of photons produced per average number of participating nucleon pairs increases with the beam energy and is independent of (lie collision centrality. For collisions with similar average numbers of participating nucleons the photon multiplicities are observed to be similar for An + Au and Cu + Cu collisions at a given beam energy. The ratios of the number of charged particles to photons in the measured pseudorapidity range are found to be 1.4 +/- 0.1 and 1.2 +/- 0.1 for root(NN)-N-s = 62.4 and 200 GeV, respectively. The energy dependence of this ratio could reflect varying contributions from baryons to charged particles, while mesons are the dominant contributors to photon production in the given kinematic region. The photon pseudorapidity distributions normalized by average number of participating nucleon pairs, when plotted as a function of eta-Y-beam, are found to follow a longitudinal scaling independent of centrality and colliding ion species at both beam energies. (C) 2009 Elsevier B.V. All rights reserved.

The electrochemical behavior of a system with a limited number of molecules

In this paper, based on Einstein relationship between diffusion and random walk, the electrochemical behavior of a system with a limited number of molecules was simulated and explored theoretically. The transition of the current vs time responses from discrete to continuous was clearly obtained as the number of redox molecules increased from 10 to 10(6).

Synthesis of Aromatic Oxide-Oxadiazoles Containing Pyridine Ring and Study on Their Spectral Properties

In order to explore new highly organic electroluminescent materials, six symmetrical aromatic oxide-oxadiazoles containing pyridine ring 4a similar to 4f were synthesized through cyclization of substituted benzoic acid (2) with 2,6-dihydrazide pyridine (3) by "one-pot" method in POCl3. Their structures were confirmed by MS, IR, H-1 NMR techniques and elemental analysis. The fluorescence spectra of the target compounds showed that the A,m ranged from 347 to 507 nm, and the maximum A,m were close to 384 nm, which showed that these compounds have good fluorescence with strong fluorescence intensity. When the 5-Br group was introduced into the aromatic ring (4e and 4f), the fluorescent emission wavelength took place Einstein shift, and the fluorescent intensity decreased a little. Using quinine bisulphate as a reference, the fluorescence quantum yields were all tested, and the introduction of 5-Br group had no visible effect on fluorescence quantum yield.

N-Methyl-N-Allylpyrrolidinium Based Ionic Liquids for Solvent-Free Dye-Sensitized Solar Cells

We prepared four new ionic liquids consisting of N-methyl-N-allylpyrrolidinium cation in conjunction with anions including iodide, nitrate, thiocyanate, and dicyanamide, respectively, and measured their physical properties of density, viscosity, and conductivity. Owing to the relatively lower melting point of electroactive N-methyl-N-allylpyrrolidinium iodide, in combination with three other nonelectroactive ionic liquids, we could construct solvent-free electrolytes possessing high iodide concentrations for dye-sensitized solar cells. We correlated temperature-dependent electrolyte viscosity with molar conductivity and triiodide mobility through applying an empirical Walden's rule and a modified Stokes-Einstein equation, respectively. We have further found that these anions (nitrate, thiocyanate, and dicyanamide) have different influences on surface states and electron transport in the mesoporous titania film, resulting in different photovoltages and photocurrents of dye-sensitized solar cells.

Diffusion-limited kinetics modeling of one-step polyimide formation

A diffusion-limited kinetic model was developed to describe the imidization of one-step polythioetherimide formation based on an endgroup diffusion model. The changes of conversion and viscosity during the imidization were monitored with thermogravimetric analysis and dynamic stress rheometry, respectively. It was observed that the imidization rate began to decelerate after a fast early stage, whereas the viscosity in the system increased dramatically after a period of low value. Amic acid and imide formations concurrently take place in the one-step polyimide formation, but the formation of amic acid is much slower than that of imide and is the rate-limiting step of imidization. When a second-order kinetic model was used to describe the imidization, the effect of viscosity on the diffusion resistance of reactive groups needed to be included. In order to predict the change of viscosity during the imidization, the Lipshitz-Macosko model was modified and introduced into the diffusion-limited kinetic model by the Stokes-Einstein equation. The comparison of the modeled results with experimental data indicated that the diffusion-limited kinetic model and the modified Lipshitz-Macosko model were able to efficiently predict the changes of conversion and viscosity with temperature and time during the one-step polythioetherimide formation. (C) 2001 John Wiley & Sons, Inc.

STUDY ON MEASUREMENT OF DIFFUSION-COEFFICIENT OF LI ATOM IN LIQUID ALUMINUM

The tess potential-concentration curve was first applied to measure the concentration of an alloy. Attempt to use the V-c curve of Al-Li alloy in measuring the diffusion coeffictent of Li atom in liquid aluminium with anode chronopotentiometry at 720℃, was made and D_(Li/Al=4.94×10~(-5)cm~2·s~(-1) was obtained. The value is well consistent wish the theoretical value, D_(Li/Al)=4.85×10~(-5)cm~2·s~(-1) in terms of Stokes-Einstein equation.

Li在液态Al中扩散系数的测定研究

首次尝试利用开路电位-浓度曲线法测定合金的浓度,并用阳极计时电位法快速测定Li在液态Al中的扩散系数,720℃下Li在液态Al中的扩散系数D_(Li/Al)=4.94×10~(-5)cm~2·s~(-1),与根据Stokes-Einstein方程计算得到的理论值D_(Li/Al)=4.85×10~(-5)cm~2·s~(-1)相吻合。

Pretreatment Method for Nitrogen Isotopic Analysis of Nitrate in Seawater

A suitable method for the pretreutment of dissolved nitrate samples in seawaters for nitrogen isotopic analysis was established. First, the seawater samples were processed by removing nitrite and amonium. Then Devard's alloy was added in sample for conversion of dissolved nitrate to ammonium. The sample was distilled, and then the ammonium condensate was collected with zeolite. after distillation, the collected condensate was filtered and prepared for determining nitropic values. Some tests of the method were conducted. The distillation condition, the influence of salinity on nitrogen isotopic analysis, absorption of ammonium onto zeolite and an improved method on a large volume of seawater were discussed in this study. The results showed that the distillation step had an average recovery of (104.9 +/- 4.2) % (n = 6) when distillating every 300 mL aliquot of the sample under a strong alkaline condition with 0.5 g devard's alloy and a distillation time of 30 min. The nitrogen isotopic fractionation decreased markedly when salinity was increased from 0% to 0.5%; further increase(1% - 3.5%) showed little effect. The adsorption rate of ammonium onto zeolite had a high yield of (95.96 +/- 1.08) % (n = 6) in average. An improved collection method was used to process a large volume of seawater with several distillations, and had good effect on analysis. The method had been applied to analyze water samples collected from Changjiang estuary. The analytical results indicate that the method is suitable for delta N-15 analysis of dissolved nitrate in seawaters. The present method could provide valuable information about the source and cycle mechanism of dissolved nitrogen in estuary waters.