Thermodynamic and transport properties of spiro-(1,1')-bipyrrolidinium tetrafluoroborate and acetonitrile mixtures:A molecular dynamics study

Organic salts such as spiro-(1,1')-bipyrrolidinium tetrafluoroborate([SBP][BF4]) dissolved in liquid acetonitrile(ACN) are a new kind of organic salt solution,which is expected to be used as an electrolyte in electrical double layer capacitors(EDLCs).To explore the physicochemical properties of the solution,an all-atom force field is established on the basis of AMBER parameter values and quantum mechanical calculations.Molecular dynamics(MD) simulations are carried out to explore the liquid structure and physicochemical properties of [SBP][BF4] electrolyte at room temperature.The computed thermodynamic and transport properties match the available experimental results very well.The microscopic structures of [SBP][BF4] salt solution are also discussed in detail.The method used in this work provides an efficient way of predicting the properties of organic salt solvent as an electrolyte in EDLCs.     

Thermodynamic,transport, and optical properties of dense silver plasma calculated using the GreeKuP code

The transport and optical properties of a dense silver plasma are calculated using our parallel GreeKuP code. The code uses the results of Vienna ab initio simulation package (VASP) as input information and is based upon the Kubo–Greenwood formula. The calculation is performed at the normal density 10.5 g/cm³ and 3 kK ≤ T ≤ 20 kK. Under these conditions, the results are strongly influenced by the presence of the d‐electrons in silver: the real part of dynamic electrical conductivity has a non‐Drude shape, the temperature dependence of thermal conductivity is non‐monotonic, and the Wiedemann–Franz law is violated.     

Thermodynamic properties of noble metal clusters:molecular dynamics simulation

The thermodynamics properties of noble metal clusters Au_N, Ag_N, Cu_N, and Pt_N (N = 80, 106, 140, 180, 216, 256, 312, 360, 408, 500, 628, 736, and 864) are simulated by micro-canonical molecular dynamics simulation technique. The potential energy and heat capacities change with temperature are obtained. The results reveal that the phase transition temperature of big noble metal clusters (N ⩾ 312 for Au, 180 for Ag and Cu, and 360 for Pt) increases linearly with the atom number slowly and approaches gently to bulk crystals. This phenomenon indicates that clusters are intermediate between single atoms and molecules and bulk crystals. But for the small noble clusters, the phase transition temperature changes irregularly with the atom number due to surface effect. All noble metal clusters have negative heat capacity around the solid-liquid phase transition temperature, and hysteresis in the melting/freezing circle is derived in noble metal clusters.     

棱形石墨烯纳米孔道内离子传输性能的分子动力学模拟

纳米通道的尺寸、结构和表面化学对其内部溶液的分布结构和输运性质有着重大影响.本文研究了一种全新的菱形石墨烯纳米通道.这种理想的通道与最近被广泛研究的金属有机框架材料(MOF)的内部结构类似,有着与传统的碳纳米管截然不同的内部结构.本文使用分子动力学模拟的方法研究在不同尺寸的菱形石墨烯纳米通道内的KCl溶液的性质,并将其与同尺寸的单壁碳纳米管进行了比较.研究结果表明在小孔道内(<20?)其内部的溶液结构呈现若干个密度极高的聚集区域,即出现了结晶化的趋势．这一研究结果,将为MOF的结构设计提供思路,从而有望实现类似于生物离子通道的高选择性和高传输能力.     

Thermodynamic and transport properties of itinerant antiferromagnets

In this contribution we present calculations of the specific heat, longitudinal magnetic susceptibility and d.c. conductivity. This latter transport coefficient is calculated in a generalized model taking into account finite life-time effects due to impurity scattering. A gradual transition from a metal to a semiconductor-like behaviour is found.     

基于分子动力学模拟流体输运性质的稳定性分析

利用线性响应理论对Ar流体输运参数进行了分子动力学模拟,结果发现:导热系数和黏度会随着自相关积分函数积分时间的增加而产生剧烈波动,而扩散系数却相对稳定. 针对积分稳定性这一问题,对导热系数和黏度中的热流密度和应力张量进行了分解分析,发现含分子间作用力项是影响稳定性的最大因素. 从牛顿力学出发对作用力项的影响机理进行了分析,指明减小这种影响的最主要方法是使在体系进行统计输运参数前达到稳定平衡状态,即最小的预平衡步数应该满足使体系达到该状态下熵最大或者能量最低,并尽量减小温度对体系的影响. 同时,还对模拟盒尺寸、统计步长等因素对积分稳定性的影响进行了分析,给出了保持稳定性的建议. 关键词： 分子动力学 输运性质 自相关函数 稳定性     

Finite temperature effect on mechanical properties of graphene sheets with various grain boundaries

The mechanical properties of graphene sheets with various grain boundaries are studied by molecular dynamics method at finite temperatures.The finite temperature reduces the ultimate strengths of the graphenes with different types of grain boundaries.More interestingly,at high temperatures,the ultimate strengths of the graphene with the zigzagorientation grain boundaries at low tilt angles exhibit different behaviors from those at lower temperatures,which is determined by inner initial stress in grain boundaries.The results indicate that the finite temperature,especially the high one,has a significant effect on the ultimate strength of graphene with grain boundaries,which gives a more in-depth understanding of their mechanical properties and could be useful for potential graphene applications.     

Thermal transport properties of defective graphene:A molecular dynamics investigation

In this work the thermal transport properties of graphene nanoribbons with randomly distributed vacancy defects are investigated by the reverse non-equilibrium molecular dynamics method. We find that the thermal conductivity of the graphene nanoribbons decreases as the defect coverage increases and is saturated in a high defect ratio range. Further analysis reveals a strong mismatch in the phonon spectrum between the unsaturated carbon atoms in 2-fold coordination around the defects and the saturated carbon atoms in 3-fold coordination, which induces high interfacial thermal resistance in defective graphene and suppresses the thermal conductivity. The defects induce a complicated bonding transform from sp2 to hybrid sp–sp2network and trigger vibration mode density redistribution, by which the phonon spectrum conversion and strong phonon scattering at defect sites are explained. These results shed new light on the understanding of the thermal transport behavior of graphene-based nanomaterials with new structural configurations and pave the way for future designs of thermal management phononic devices.     

Thermodynamic properties of molecular fluid mixtures of hard ellipsoids

Thermodynamic properties of molecular fluid mixtures of hard ellipsoids are calculated. Numerical results are given for equation of state and excess-free energy of the binary mixture of both additive and non-additive hard ellipsoids. It is found that the equation of state and free energy of mixtures increase with increase of anisotropy parameterx ₀.     

Thermodynamic and transport properties of SmS under high pressure

We measured transport and thermodynamic properties of the valence-fluctuating phase of SmS up to 8.5 kbar, and found a bump structure in the temperature dependence of the electrical resistivity and a Schottky-type anomaly in the temperature dependence of the thermal expansion coefficient at a characteristic temperature T₀. We also observed that the absolute value of the Hall constant rapidly increases below T₀. From these results, we argue that the steep rise of the electrical resistivity below T₀ is inherent to golden SmS and can be ascribed to the decrease in the carrier concentration possibly due to the pseudo gap formation.     

On the properties of a periodic fluid

The Born-Green equation is used to clarify and estimate the error introduced into Monte Carlo and molecular dynamics simulations of dense fluids by the use of periodic boundary conditions. This theory is applied to the Lennard-Jones fluid and the theoretical predictions are found to be in reasonable agreement with experiment. The implications for size dependence of pressure, for anisotropy of the radial distribution function, for size dependence of the supercooling limit for crystal nucleation, and for the orientations of nucleated crystals are discussed.This research was supported under grants MPS73-04743 and MPS73-04922 of the National Science Foundation, Washington D.C.     

Thermodynamic properties of multicomponent mixtures near the liquid-vapor critical point

A new method has been proposed to describe the physical properties of multicomponent mixtures near their critical points. The method is based on the transition from the experimental thermodynamic variables to scaling fields, is applicable to a mixture with any number of the components, and is, thus, universal. For the previously studied methane-propane-pentane mixture, it has been shown that the anomalies of the specific heat at a constant volume and derivative (?P/?T)_ρ,x can be quantitatively described in this approach in a wide vicinity of a critical point, including noncritical isochores.     

Phenomenological models for nitrogen transport in tissues

Summary Transfer mechanisms and critical pressures are essential elements in decompression calculations and staged procedures. By coupling a multitissue transfer model to fitted critical pressures, decompression data can be synthesized for rapid numerical implementation in applications. Parametric fits to the critical nitrogen pressures are generated for the six tissue compartments (5, 10, 20, 40, 80, 120 min) at seal-evel with both linear and constant-pressure ratio extrapolations to altitude conveniently effected with the barometer equation. The macroscopic model used to transfer nitrogen in tissues is described and functional forms of the fit equations are motivated. Accurate exponential representations for mantle pressures and the well-known Cross altitude factors are also generated. Fitted critical tensions vary inversely as the approximate fourth root of the tissue half-life and increase linearly with depth. Air mantle pressures decrease exponentially with altitude and inverse temperature. Using bounce dive constraints, a set of single-tissue decay coefficients, which increase logarithmically with depth, are extracted from depth-dependent decompression criteria and contrasted with corresponding multitissue decay parameters. Bend statistics and a decompression titration experiment, which predicts decreasing critical ratios at depth, are discussed. Overlapping predictions of the models and correlations with experiment are identified.

---

Riassunto I meccanismi di trasferimento e le pressioni critiche sono elementi essenziali nei calcoli della decompressione e nelle procedure a stadi. Accoppiando un modello di trasferimento a molti tessuti e pressioni critiche adattate, i dati di decompressione possono essere sintetizzati per un rapido incremento numerico nelle applicazioni. Approssimazioni parametriche alle pressioni critiche dell'azoto sono generate per sei componenti del tessuto (5, 10, 20, 40, 80, 120 min) a livello del mare con estrapolazioni sia lineari che a pressione costante del rapporto ad un'altitudine convenientemente ottenuta con l'equazione barometro. Si descrive il modello macroscopico per trasferire azoto nei tessuti e si forniscono le motivazioni delle forme funzionali delle equazioni di approssimazione. Sono anche prodotte accurate rappresentazioni esponenziali per pressioni mantello ed i ben noti fattori di altitudine di Cross. Le tensioni critiche approssimate variano inversamente come la radice quarta approssimata della vita media del tessuto ed aumentano in maniera lineare con la profondità. Le pressioni del mantello d'aria diminuiscono esponenzialmente con l'altitudine e la temperatura inverse. Usando costanti di immersione di rimbalzo, un gruppo di coefficienti di decadimento di singoli tessuti, che aumentano logaritmicamente con la profondità, è estratto dai criteri di decompressione dipendenti dalla profondità ed è in contrasto con il parametro di decadimento a molti tessuti. La statistica dei piegamenti ed un esperimento di titolazione della decompressione, che prevede rapporti critici decrescenti in profondità, sono discussi. Si identificano le previsioni sovrapposte dei modelli e correlazioni con l'esperimento.

     

The viscosity of normal butane,isobutane and their mixtures

The paper reports measurements of the viscosity of normal butane and isobutane at atmospheric pressure in the temperature range 25–195°C. In addition, the viscosity of mixtures of the two gases has been determined in the more limited temperature range 25–100°C. The absolute accuracy of the viscosity data is estimated as ±0.2%, whereas the ratio of the viscosity of the two pure components is determined with an uncertainty of ±0.1%. The viscosity data allow the evaluation of the diffusion coefficients for the n-butane-i-butane system.The experimental data demonstrate that there are discernible differences between the intermolecular potentials for the pair-interactions n-C₆H₁₀-n-C₄H₁₀; and i-C₄H₁₀-i-C₄H₁₀. All of the experimental data can be correlated within their experimental uncertainty with the aid of the extended law of corresponding states developed by Kestin, Ro and Wakeham. The optimum values of the two scaling parameters, σ_ij and ?_ij, for each interaction which secure this agreement are determined.     

Thermodynamic and transport properties of superconducting Mg10B2

Transport and thermodynamic properties of a sintered pellet of the newly discovered MgB2 superconductor have been measured to determine the characteristic critical magnetic fields and critical current densities. Both resistive transition and magnetization data give similar values of the upper critical field, Hc2, with magnetization data giving dHc2/dT = 0.44 T/K at the transition temperature of Tc = 40.2 K. Close to the transition temperature, magnetization curves are thermodynamically reversible, but at low temperatures the trapped flux can be on the order of 1 T. The value of dHc/dT at Tc is estimated to be about 12 mT/K, a value similar to classical superconductors like Sn. Hence, the Ginzburg-Landau parameter kappa approximately 26. Estimates of the critical supercurrent density, Jc, using hysteresis loops and the Bean model, give critical current densities on the order of 10(5) A/cm2. Hence the supercurrent coupling through the grain boundaries is comparable to intermetallics like Nb3Sn.     

基于基液连续假设的大体系Cu-H2O纳米流体输运特性的模拟研究

分子动力学模拟是研究纳米流体的输运特性的重要手段, 但计算量庞大. 为研究能体现流动传热过程的大体系纳米流体的输运特性, 本文对基液采用连续介质假设, 将基液的势能拟合在纳米团簇的势能中, 大幅度减小了计算量, 使得大体系输运特性的模拟成为可能, 且模拟结果与多组实验结果吻合较好. 采用此方法模拟研究了速度梯度剪切对Cu-H₂O纳米流体颗粒聚集过程和聚集特性的影响, 进而对Cu-H₂O纳米流体在流动传热过程中的热导率和黏度进行了模拟计算, 定量揭示了宏观流动传热过程中不同的速度梯度、速度、平均温度和温度梯度对于Cu-H₂O纳米流体热导率和黏度的影响.     

Theory of the Robin quantum wall in a linear potential. II. Thermodynamic properties

A theoretical analysis of the thermodynamic properties of the Robin wall characterized by the extrapolation length Λ in the electric field that pushes the particle to the surface is presented both in the canonical and two grand canonical representations and in the whole range of the Robin distance with the emphasis on its negative values which for the voltage‐free configuration support negative‐energy bound state. For the canonical ensemble, the heat capacity at exhibits a nonmonotonic behavior as a function of the temperature T with its pronounced maximum unrestrictedly increasing for the decreasing fields as and its location being proportional to . For the Fermi‐Dirac distribution, the specific heat per particle is a nonmonotonic function of the temperature too with the conspicuous extremum being preceded on the T axis by the plateau whose magnitude at the vanishing is defined as , with N being a number of the particles. The maximum of is the largest for and, similar to the canonical ensemble, grows to infinity as the field goes to zero. For the Bose‐Einstein ensemble, a formation of the sharp asymmetric feature on the ‐T dependence with the increase of N is shown to be more prominent at the lower voltages. This cusp‐like dependence of the heat capacity on the temperature, which for the infinite number of bosons transforms into the discontinuity of , is an indication of the phase transition to the condensate state. Some other physical characteristics such as the critical temperature and ground‐level population of the Bose‐Einstein condensate are calculated and analyzed as a function of the field and extrapolation length. Qualitative and quantitative explanation of these physical phenomena is based on the variation of the energy spectrum by the electric field.     

A comparative study of optic phonon-like excitations in liquid mixtures and molten salts

We report a study of collective excitations in an equimolar Lennard–Jones liquid mixture KrAr and a molten salt NaCl within the parameter-free generalized collective modes (GCM) approach. It is shown that the high-frequency propagating modes in liquid KrAr and molten NaCl correspond to optic phonon-like excitations, caused by fast mass-concentration (charge in NaCl) fluctuations. Dispersion curves for optic collective excitations are discussed.