Thermodynamic and kinetic properties of phonons in cylindrical quantum dots

The Green's function technique, suitable for analyses of spatially deformed structures, is developed in this paper and applied to phonon system. The thermodynamic and kinetic phonon properties of cylindrical quantum dots are analysed using a developed method. As a consequence of the applied new method the configurational dependence of diffusion coefficient and dot's density were included into calculations. Maximum of diffusion and minimum of density is located in central part of the cylindrical quantum dot. All thermodynamic and kinetic characteristics of quantum dot are exponentially small at low temperatures. The low phonons specific heat as well as the low thermal conductivity lead to conclusion that in cylindrical quantum dots exist more convenient conditions for appearance of electron superconductivity.     

Diffusion thermopower due to interface roughness-induced piezoelectric scattering in lattice-mismatched semiconductor quantum wells

We calculate the diffusion thermopower for a degenerate two-dimensional electron gas in real lattice-mismatched semiconductor quantum wells (QWs) at low temperatures. We consider explicitly two scattering mechanisms: (i) the surface roughness-induced piezoelectric effect, a new important scattering source, arising due to a large fluctuating density of roughness-induced piezoelectric charges and (ii) the surface roughness. The scattering parameter p of energy dependence of the momentum relaxation time and the diffusion thermopower S^d, of each of the mechanisms separately and also when both the mechanisms are combined, are calculated as a function of electron concentration and well width. The diffusion thermopower, as a function of electron concentration, due to piezoelectric field shows a change in sign for lower concentrations. Interestingly, the diffusion thermopower, due to this mechanism, as a function of well width also shows a change in sign and it is dominant for larger well widths. The numerical calculations are presented for In_0.2Ga_0.8As/GaAs and AlN/GaN QWs. The piezoelectric mechanism is expected to be very important in systems with large piezoelectric constant and lattice mismatch.     

H32.685N16.8430O3.0和H8.154N4.5770O3.0炸药爆轰参数的数值模拟

用Gibbs自由能最小原理,通过解化学平衡方程组,求解HNO型炸药H32·685N16·8430O3·0(70/30Hydrazine/HydrazineNitrate)和H8·154N4·5770O3·0(21/79Hydrazine/HydrazineNitrate)爆轰产物系统的平衡组分,计算结果与用BKW和LJD方法计算的结果相近。以Ree修正的WCA状态方程并考虑Ross软球修正的硬球微扰理论作为爆轰气相产物的物态方程,用自编的程序对H32·685N16·8430O3·0和H8·154N4·5770O3·0炸药爆轰参数作了预言,爆轰CJ点的爆速、爆压和爆温的计算结果与实验值吻合得很好。     

Further studies of the reaction kernel structure and stabilization of jet diffusion flames

The structure of axisymmetric laminar jet diffusion flames of ethane, ethylene, acetylene, and propane in quasi-quiescent air has been studied numerically in normal earth gravity (1g) and zero gravity (0g). The time-dependent full Navier–Stokes equations with buoyancy were solved using an implicit, third-order accurate numerical scheme, including a C₃-chemistry model and an optically thin-media radiation model for heat losses. Observations of the flames were also made at the NASA Glenn 2.2-Second Drop Tower. For all cases of the fuels and gravity levels investigated, a peak reactivity spot, i.e., reaction kernel, was formed in the flame base, thereby holding a trailing diffusion flame. The location of the reaction kernel with respect to the burner rim depended inversely on the reaction-kernel reactivity or velocity. In the C₂ and C₃ hydrocarbon flames, the H₂–O₂ chain reactions were important at the reaction kernel, yet the CH₃ + O → CH₂O + H reaction, a dominant contributor to the heat-release rate in methane flames studied previously, did not outweigh other exothermic reactions. Instead of the C₁-route oxidation pathway in methane flames, the C₂ and C₃ hydrocarbon fuels dehydrogenated on the fuel side and acetylene was a major hydrocarbon fragment burning at the reaction kernel. The reaction-kernel correlations between the reactivity (the heat-release or oxygen-consumption rate) and the velocity, obtained previously for methane, were developed further for various fuels in more universal forms using variables related to local Damköhler numbers and Peclet numbers.     

The Selectivity of Chemical Reactions Disguised by Diffusion. Part I: Chemical Selectivity Disguised by Mixing

A mixing-reaction model (MIRE) is used to develop criteria, readily accessible by experiment, which permit the chemist to decide whether and when mixing effects influence the product distribution in competitive consecutive or parallel reactions. The validity of these criteria is demonstrated by comparison of prediction and experiment in the examples used.     

Optimal investment policy of an insurance firm

In this paper we consider an investment problem by an insurance firm. As in the classical model of collective risk, it is assumed that premium payments are received deterministically from policyholders at a constant rate, while the claim process is determined by a compound Poisson process. We introduce a conversion mechanism of funds from cash into investments and vice versa. Contrary to the conventional collective risk model we do not assume a ruin barrier. Instead we introduce conversion costs to account for the problems implicit in reaching the zero boundary. The objective of the firm is to maximize its net profit by selecting an appropriate investment strategy. A diffusion approximation is suggested in order to obtain tractable results for a general claim size distribution.     

Partial filling ofd-band of nickel on hydrogen diffusion

Summary It is seen that low-temperature annealing of nickel wires forbids the complete filling in of thed-band of nickel when the latter is subjected to cathodic-hydrogen diffusion. At a certain low-temperature range irreversible changes occur in the orientation of the surface planes of nickel which persist even if the temperature is raised to the room temperature. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Performance of profiled single noise barriers covered with quadratic residue diffusers

The paper describes an investigation about the acoustic performance of noise barriers with quadratic residue diffuser (QRD) tops, and with T-, Arrow-, Cylindrical and Y-shape profiles. A 2D boundary element method (BEM) is used to calculate the barrier insertion loss. The results of rigid and with absorptive coverage are also calculated for comparisons. Using QRD on the top surface of almost all barrier models presented here is found to improve the efficiency of barriers compare with using absorptive coverage at the examined receiver positions. T-shape and Arrow-shape barriers are also found to provide better performance than other shapes of barriers. The best shape of barriers for utilising QRD among the tested models is the T-shape profile barrier. It is found that reducing the design frequency of QRD shifts the performance improvement towards lower frequency, and therefore the most efficient model for traffic noise is a barrier covered with a QRD tuned to around 400 Hz.     

Common Intersection Points of Bulk Modulus for Liquefied Natural Gas (LNG) Mixtures

During recent developments on the theories and experimental techniques of compressed liquids and liquid mixtures, it has been revealed that there exist some regularities. Among these, the regularity found by Huang and O'Connell is that the isotherms of reduced bulk modulus of compressed liquids as a function of molar volume intersect at a common point. This intersection is a useful tool for evaluating the reliability of an equation of state (EOS) for producing equilibrium properties of matter. This paper also deals with an extension of the above regularity to some liquefied natural gas (LNG) mixtures including: N₂+CH₄, N₂+C₂H₆, CH₄+C₂H₆, CH₄+C₃H₈, and CH₄+C₄H₁₀ at different temperatures. The present work gives a theoretical analysis for the common bulk modulus point in terms of a statistical‐mechanical equation of state for mixtures. In addition, we have calculated excess molar volume of N₂+CH₄ mixture in terms of temperature and compared it with experimental values.     

用TNT的{D,ρ0}实验数据对爆轰的ZND理论的检验

爆轰产物中或多或少含有固态碳 ,一相的排平物态方程被推广为两相的之后 ,以某种炸药的一条已知等熵线为参考曲线 ,就可以用来估算其各种初始装药密度下的爆轰参数 .用产物中含碳量较多的TNT的 {D ,ρ0 }实验数据与理论估算值相比较 ,可以对爆轰的ZND理论的假设进行检验 .检验的结果再一次表明 ,爆轰的ZND理论的假设是成立的 ,并且排平物态方程是恰当的爆轰产物的物态方程 .