调用氦物性程序对10K下透平喷嘴的气动性进行数值模拟及分析

针对EAST用俄制氦透平D在2008年5月至8月一轮实验中出现的抱轴问题,采用Fluent数值模拟的方法调用氦物性Fortran程序,按透平D喷嘴环的设计工况对其流场进行模拟,并通过得到的近真实流场,分析了因为加工偏差引起的流场不均匀性程度,从而验证了喷嘴环的加工问题也是引起透平工作稳定性的一个重要原因.     

氦透平膨胀机膨胀端机理与控制分析

为实现氦透平膨胀机的自动控制,据透平膨胀端的结构,从控制的角度,采用一元稳定流动理论来简化模型,分析了氦气经过喷嘴、工作叶轮和扩压器的机理,得到了压力与流量、流速等的关系。据此引出两个透平的主控变量:透平转速和入口阀开度,详细阐述了一种透平转速设定值的计算方法,列举了几个影响因子及其确定方法,并给出了转速设定值预处理的流出图。最后针对入口阀提出了一种基于转速和影响因子的控制方法。     

基于PLC的氦透平膨胀机控制系统设计

首先分析了氦制冷机和透平的工作流程,再从透平的众多参数中分析得出被控变量。以提高透平运行效率和制冷量为指导依据,设计了透平转速和入口阀的控制方案,并通过对比说明设计方案的优越性。最后考虑到透平的安全运行,设立了报警与保护信号,同时也对转速设定值进行了预处理,根据设计方案,采用模块化的编程思想设计了PLC的控制程序。     

氦透平膨胀机特性分析及转速控制方法

介绍了透平的几个重要特性:效率、特性比、制动方式以及制冷量的调节,并分析了各个特性的特点和意义。结合理论,给出了4种氦透平膨胀机的转速控制方法,详细说明了转速设定值的计算方法、计算流程及参数确定的方法,并分析说明了其优缺点。最后总结对比分析了几种方法在控制过程中设定值、控制器、执行机构上的差异,为实现氦透平膨胀机的PLC控制提供参考。     

Magnetopolarons on the surface of helium films

The energy spectrum of the surface electrons on liquid helium films in the presence of a perpendicular applied magnetic field is determined in different approaches within second order perturbation theory. The influence of the electron-ripplon interaction on the Landau levels are studied for arbitrary strength of the magnetic field and several values of the coupling constant. Current theories of the polaron ground-state and cyclotron resonance are compared to the exact weak-coupling results obtained. We found a shift down in the cyclotron resonance frequency due to polaron effects.     

Kinetic properties of surface electrons over liquid helium under strong electron-electron interaction

The mobility and lifetime of ground-level electrons are studied experimentally in a two-dimensional electron system at the surface of liquid helium at temperatures of0.4 to1.4 K and charge concentrations of (2.8–12.0) × 10⁸ cm^–2. It is shown that for fairly low temperature and high concentration where the frequency of interelectronic collisions is much higher than that of electron-ripplon ones, the so-called complete control condition is realized in the electron system, i.e., when the average drift velocity of electrons and the effective electron temperature can be introduced. This model is found to describe well the kinetic properties of surface electrons in the range of charge concentrations up to 4×10⁸ cm^–2, where the one-particle approach is no longer applicable. For the value of parameter =e²(n_s)^1/2/T=47 that corresponds to a strong electron-electron interaction, the lifetime is found to increase sharply and the short-range order typical of a liquid state appears in the two-dimensional electron layer.     

Improved surface properties of D2 steel by laser surface alloying

The wear and the high-temperature oxidation resistance of the D2 steel (Fe-1.5 C-12 Cr-0.95 Mo-0.9 V-0.3 Mn) were increased by laser surface alloying after coating the surface with SiC or Cr₃C₂ powder. The surface alloys exhibit two microstructures: hypoeutectic and hypereutectic, respectively, all containing iron solid solutions and iron-chromium carbides, (Fe,Cr)₇C₃. The oxidation resistance of these alloys was measured in isothermal and cyclic conditions, and was shown to increase with silicon or chromium additions, particularly due to the formation of a chromia scale with excellent behaviour during thermal shoks. The surface alloy obtained with Cr₃C₂ also has shown a better resistance to wear due to its hypereutectic microstructure.     

Solution of a direct problem of heat exchange between a cooled turbine blade and a gas by the pivot method

Using the pivot method we solve a third-order differential equation that describes the heat exchange of a gas with a cooled turbine blade.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 21, No. 3, pp. 531–536, September, 1971.     

Alkali dimers on the surface of liquid helium

A recent paper by Ancilottoet al. (Zeitschrift für Physik B, in press), presented calculations of adsorption energies and the geometry of a surface dimple for alkali atoms bound to the surfaces of quantum liquids (⁴He,³He, H₂). Here we present a study of the adsorption of two alkali dimers (Li₂, Na₂) on the surface of liquid helium. The calculations employ a model of an abrupt interface formulated by Ancilotto et al. as well as one using a diffuse interface. Our conclusion its that the dimers are bound to the surface more strongly than their respective monomers. In the case of dimers there is an additional degree of freedom-the orientation of the molecular axis relative to the surface. We study the influence of molecular anisotropy on adsorption by comparing the cases of erect and spinning flat orientations and conclude that the latter is energetically favored.     

Electron-ripplon scattering on the surface of liquid helium

We use an adiabatic development of the electron wave function to calculate the scattering matrix elements for the electron-ripplon interaction. In this treatment the nonadiabatic terms in the total Schrödinger equation are responsible for the scattering. Our calculation shows that the magnitude of the scattering matrix element for this interaction depends critically on the magnitude of the electron wave function at the surface.     

Heat capacity of helium submonolayers on a nonuniform surface

Data of McCormick, Goodstein, and Dash, and Stewart and Dash, for heat capacities of³He and⁴He films on Ar-plated copper in the submonolayer region have been analyzed on the basis of a model of a long-range variation of adsorption potential. This variation allows the adatoms to form small islands on the surface. The total heat capacity of the film is the sum of two contributions, one a Fermi-like contribution due to surface heterogeneity, and the other a two-dimensional Debye-like contribution due to molecular vibrations. The data are roughly consistent with a Debye temperature of 32K for all the⁴He data and 38 K for the³He data. The role of surface heterogeneity in the heat capacity of films is briefly discussed.     

Wetting properties of liquid helium on rubidium metal

Wetting properties of liquid helium on rubidium metal have been investigated in the temperature range 1.0–1.7 K using a heat conduction method. The rubidium surface is found to be wetted under saturated vapor conditions. Prewetting transitions have been observed for rather weak offsets from saturation, indicating that rubidium is close to the nonwetting limit at T = 0 K. Presumably because of substrate inhomogeneities, the prewetting transitions are experimentally found to be continuous and hysteretic. No evidence for the prewetting critical point has been found up to 1.7 K. The prewetting line verifies a simple linear relation between the liquid-vapour surface tension and the two third power of the chemical potential offset, but does not conform quantitatively to the simple model currently used.On leave of Rochester University.Laboratoire de L'Ecole Normale Supérieure et de l'Universté Pierre et Marie Curie, associé au CNRS (URA 18).     

Standing surface waves on helium induced by second sound. Observations and calculations

Standing waves of second sound in superfluid helium deform the free helium surface. Schlieren observations on cylindrical cavities with vertical axis give the wave patterns predicted by Sorbello. Calculations and experiments show that the deformation is stationary, with only a very small time-dependent component. At low second-sound levels the wave amplitude is proportional to intensity. At higher levels the relation of wave height to second-sound intensity becomes nonlinear and when a critical value is reached, the waves break. Their height then increases abruptly, and the dominant wave number doubles.     

Influence of surface modification by 2-aminothiophenol on optoelectronics properties of ZnO nanoparticles

In this study, a precipitation method was used to synthesise ZnO nanoparticles using suitable precursors. An efficient surface modification method was proposed in order to reduce the agglomeration among synthesised small sized ZnO nanoparticles using 2-aminothiophenol as a capping agent. This article briefly investigated the effects of capping agent like 2-aminothiophenol on the optoelectronic properties of ZnO nanoparticles. The modified effectivity of 2-aminothiophenol has been examined on the nanosized ZnO nanoparticle for fluorescence and UV–visible (UV–vis) studies. The mechanism was studied for ZnO nanoparticles light emitting capability under different conditions. By facilitating the capping of ZnO with 2-aminothiophenol, fluorescence emission of the surface defects vanishes and ultraviolet (UV) emission increases. Surface capping by 2-aminothiophenol effectively covers most of the surface defects of ZnO and results in quenching of the visible region. The UV–vis absorption spectra of modified ZnO nanoparticles has been influenced by modified ZnO nanoparticles as a result of surface modification; where marked blue shift in absorption edge results. By surface modification of ZnO nanoparticles, change in optoelectronics properties has opened the new scope and possibilities to explore and fine tune the optical character of the modified ZnO for various optoelectronics applications such as UV laser.     

Preparation and properties of surface textured ZnO: Al films by direct current pulse magnetron sputtering

Transparent conductive surface textured Al-doped zinc oxide (ZnO:Al, AZO) thin films were prepared on glass substrates by direct current pulse magnetron sputtering at substrate temperature of 270 °C and post-etching in NaOH solution at room temperature. The effects of Ar flow rate on the structural, optical, electrical properties and light trapping ability were investigated systematically. With the increasing of Ar flow rate from 10 to 50 sccm, different surface features ranging from honeycomb-like to crater-like structures were observed. The relationship between surface textured structures and Ar flow rate was discussed. The AZO film deposited with Ar flow rate in 50 sccm displayed fine optoelectronic properties, improved figure of merit and effective surface textured structures for light trapping, which could be applied as a transparent conducting electrode in silicon-based thin film solar cells.     

Dependence of helium II viscosity properties on oscillation frequency

The causes of a discrepancy in the results of measurements of He II viscosity below T 1.6 k obtained with different measurement methods are investigated. It is shown that to obtain correct results in oscillation experiments, the condition _ph should obtain, where is the depth of viscous wave penetration and _ph is the phonon free path length. Results of viscosity measurements at different ratios /_ph (by a wire viscometer) are presented. It is shown that for the condition _ph, the results obtained are in good agreement with the results of Andronikashvili (in which /_ph > 100). If the mentioned relation is not satisfied, then, as the value of the ratio /_ph is decreased, the value measured for the viscosity is increasingly lower than the results of Andronikashvili.     

The lifetime of interacting ripplons on the surface of superfluid helium

Ripplons, or quantised surface waves, are known to exist on the surface of superfluid⁴He. We follow the work of previous authors and describe these excitations by quantising the classical expressions for the energy of such surface waves. The resulting quantum mechanical Hamiltonian consists of a term describing free ripplons, together with an additional term (cubic in the ripplon variables) which induces the mutual scattering of ripplons and has the effect of causing any one ripplon to have a finite lifetime. We present here a many body calculation which investigates the lifetimes of ripplons at a temperatureT=0 and the lifetimes of acoustic ripplons at a finite temperature. In these two limits our calculation agrees with separate calculations performed by previous authors carried out at the two limits; however our calculations readily allow a sensible interpolation between these limits. We report hitherto unsuspected divergences in the calculations at finite temperature and we comment on the relevance of such calculations to the results of recent experiments which yield information on the ripplon lifetimes.     

Effect of Kapitza resistance on standing surface waves in superfluid helium

We analyze theoretically the resonant frequencies of standing surface waves produced by second sound in⁴He. In particular, we show that an empirical heat transfer coefficient involved in a recently proposed boundary condition can be related to Kapitza resistance. We also calculate the heat flux within the helium and deduce that the height of the surface waves is strongly frequency dependent.     

Continuous direct tablet compression: effects of impeller rotation rate,total feed rate and drug content on the tablet properties and drug release

Context: Continuous processing is becoming popular in the pharmaceutical industry for its cost and quality advantages.

Objective: This study evaluated the mechanical properties, uniformity of dosage units and drug release from the tablets prepared by continuous direct compression process.

Materials and methods: The tablet formulations consisted of acetaminophen (3–30% (w/w)) pre-blended with 0.25% (w/w) colloidal silicon dioxide, microcrystalline cellulose (69–96% (w/w)) and magnesium stearate (1% (w/w)). The continuous tableting line consisted of three loss-in-weight feeders and a convective continuous mixer and a rotary tablet press. The process continued for 8?min and steady state was reached within 5?min. The effects of acetaminophen content, impeller rotation rate (39–254?rpm) and total feed rate (15 and 20?kg/h) on tablet properties were examined.

Results and discussion: All the tablets complied with the friability requirements of European Pharmacopoeia and rapidly released acetaminophen. However, the relative standard deviation of acetaminophen content (10% (w/w)) increased with an increase in impeller rotation rate at a constant total feed rate (20?kg/h). A compression force of 12?kN tended to result in greater tablet hardness and subsequently a slower initial acetaminophen release from tablets when compared with those made with the compression force of about 8?kN.

Conclusions: In conclusion, tablets could be successfully prepared by a continuous direct compression process and process conditions affected to some extent tablet properties.     

硫掺杂TiO_2光催化剂的研究

采用溶胶-凝胶法制备了硫掺杂二氧化钛粉体(S-TiO2),采用XRD、Nano-series Sizer、FT-IR、UV-Vis、PL等方法对其进行表征和分析。结果表明,S掺杂抑制了TiO2从锐钛矿相向金红石相的转变,减小了粒子间的团聚,拓展了TiO2对可见光的吸收范围,有效地抑制了光生电子-空穴对的复合。光催化降解亚甲基蓝(MB)的实验表明,n(S)∶n(Ti)=0.14,450℃烧结的S-TiO2粉体具有最佳光催化性能,在普通日光灯下对亚甲基蓝的降解率3h达74.12%,明显优于德国Degussa公司生产的P25纯TiO2光催化剂对亚甲基蓝的降解率31.89%。