A variable temperature,tensile testing cryostat

This paper describes a gas spray cryostat for tensile tests, which can also be used with testing instruments where both the crosshead on the top and the hydraulic piston on the bottom are moving simultaneously. A twin tube is used for the heat exchanger together with a ‘Thermocoax’ heater. This provides a short cooling and heating time during temperature change tests. The connexion between sample and load cell is frictionless, without the commonly used seals, and therefore very small forces can be resolved. In order to avoid unwanted deformation of the specimen due to the thermal expansion of the connexion rod, the specimen length is measured and controlled directly.     

微波GaAs功率场效应晶体管稳态温度场的数值模拟

根据微波功率ＧａＡｓ功率场效应晶体管芯片结构特点建立热模型，用有限元法对模型数值求解得到芯片稳态温度分布。分析了影响芯片表面沟道温度的诸因素：功耗、芯片周围环境温度、ＧａＡｓ材热导率、芯片厚度、芯片热源分布及其跨导。     

Finite impulse response utilizing the principle of superposition

A critical parameter in any finite impulse response (FIR) design is the impulse response length, which must be optimized for the given design specifications in order to reduce the size of the filter. To this end, many design algorithms have been introduced, such as Remez exchange, linear programming, and least mean squares. A new algorithm has been derived that is simple, efficient, and accurate for the design of arbitrary filter specifications and requires fewer computations than many other FIR approaches. This paper provides the definition of the basic functions used for the design process. An overview of the design process is given and the design technique used to design filters with tailored passband and stopband responses to yield a near-optimum time length is presented. This design can be very useful when compensating for the effects of a second transducer or other second order effects in surface acoustic wave (SAW) devices. The effects of monotonically increasing sidelobes on the impulse response length are discussed and illustrated. The addition of arbitrary phase response to the filter design process is discussed. The results of the current FIR approach are discussed and compared with other design techniques.     

On some steady state temperature fields in semiinfinite solids with cylindrical heat sources

An integral equation is obtained which describes the steady-state temperature field in a semi-infinite body with internal cylindrical heat sources (for cylinders of an arbitrary shape). For practical calculations a simplified equation is obtained by replacing the integral by a sum of a finite number of terms. The equations were used by the author to develop new methods of calculating the temperature in disc and drum rotors of heat turbines cooled by blowing-off the working fluid through distributed slots.     

A He3 cryostat with charcoal sorption pump for easy control of temperature

We have built the He³ cryostat with a charcoal sorption pump placed inside a small dewar vessel turned upside down and inserted in liquid He⁴·bath. The device is capable of providing any desired temperature within the range from 0.32 K to 3.20 K in a short time and holding it constant for a few hours if the external conditions remain unchanged.     

聚焦超声热疗二维稳态温度场模拟

本文运用差分法求解了聚焦超声加热的二维稳态温度场，比较了声场与不曙度场的特征，分析了耦合层厚度与治疗区大小，位置的关系。     

A note on the steady state downtime distribution of a monotone system

In this note we study the steady state downtime distribution of a monotone system comprising independent components. An exact formula exists for parallel system, but approximations have to be used for other type of systems. Results from Monte Carlo simulations are presented to illustrate the error term by estimating the distribution of the ith downtime of the system by the steady state down time distribution.     

一种用于制冷系统稳定运行时制冷剂分布测试的新方法

介绍制冷系统动态和稳态过程的理论和实验研究现状,总结现有实验研究中的测试方法,并分析各自的优缺点。提出一种相对高效省时的制冷剂回收测试方法,同时介绍这种方法的测试原理、实验步骤,并根据实际测试结果,分析误差产生的原因及避免方法。     

On the steady state unavailability of standby systems

In this paper we study the steady state unavailability of standby systems comprising n identical components of which n − 1 are normally operating and one is in standby, with one repair facility. The components are assumed to have constant failure rates, but arbitrary repair time distribution. Attention is given to the case that the mean time to repair MTTR is relatively small compared to the mean time to failure MTTF, which is the most common situation in practice. Simple approximation formulae are presented and compared with the standard Markov expressions. It is demonstrated that the Markov expressions produce relatively large errors when the coefficient of variation of the repair time distribution is not close to 1. Some easily computed error bounds of the approximation formulae are established.     

Structural investigation of polydiacetylenes: A variable temperature solid state13C CP/MAS NMR study

The spectral features in the solid state¹³C CP/MAS NMR of poly (1,1,6,6-tetraphenylhexadiyn diamine) (poly(THD)) are compared with X-ray diffraction. The NMR data suggests that acetylenic carbons are nonequivalent in the unit cell resulting in two resonances. On the other hand, a single acetylenic carbon resonance was observed for poly (1,6-di-N-carbozolyl-2,4-hexadiyne) (poly(DCH)). The orientation of side groups in the crystal structures of poly(DCH) and poly(THD) are responsible for equivalence and nonequivalence of acetylenic carbons. The structural changes due to thermochromic transitions are monitored by variable temperature solid state NMR. The solid state VT NMR data suggest that the backbone and side chain conformations of blue phase and red phases of poly(bis-n-propyl urethane of 5,7-dodecadin-1,12-diol) (poly(PUDO)) are distinctly different. For the first time, we present a solid state NMR spectrum showing the presence of both the blue and red phases of this polymer at the thermochromic transition temperature (ca. 115–125°C).     

A corresponding-states principle for the equation of state of hard-convex-body fluids

A theoretically based corresponding-states principle is developed for the equation of state of hard-convex-body fluids. For all the fluids considered, the excess compressibility factor, reduced by means of a parameter which can be determined analytically. lies on a single curve whose analytical expression can be obtained from the equation of state of the hard-sphere fluid.     

Stress analysis in a functionally graded disc under mechanical loads and a steady state temperature distribution

An analytical thermoelasticity solution for a disc made of functionally graded materials (FGMs) is presented. Infinitesimal deformation theory of elasticity and power law distribution for functional gradation are used in the solution procedure. Some relative results for the stress and displacement components along the radius are presented due to internal pressure, external pressure, centrifugal force and steady state temperature. From the results, it is found that the grading indexes play an important role in determining the thermomechanical responses of FG disc and in optimal design of these structures.     

The prediction of steady state heat flux and related temperature profiles in pressurized superfluid helium II

To design superconducting magnets cooled by pressurized superfluid helium II, it is necessary to know the heat transfer characteristics of steady state heat flux in the cryogen. This study shows the calculation used to obtain these characteristics using the universal Gorter-Mellink equation proposed by Soloski et al. The calculated results agree fairly well with the data obtained in this study.     

The diamagnetic current limit in the steady state MIGMA

The diamagnetic field produced by the ions circulating in the MIGMA fusion reactor has been discussed for the case of a ring magnet. An expression for the diamagnetic current and its distribution in the magnet gap has been derived in terms of the basic MIGMA parameters. It is shown, with the magnet code POISSON, that the diamagnetic field can be substantially reduced and the usable central ion density can be exceeded by one order of magnitude with the aid of correction coils which carry opposite currents and are located in the magnet gap close to the region where the diamagnetic currents are flowing.     

Theoretical assessment of the steady state diffusion cell test

The steady state diffusion cell test is often used to determine the chloride ion diffusion coefficient in cementitious materials. It involves the measurement of the flux of chloride ions through a specimen under near steady state conditions. It has been noted that such a test may also provide data which characterises the chloride binding capacity of the specimen. In this work a numerical model of chloride diffusion subject to the effects of chloride binding is used to assess the effect of deviations from the steady state on the data obtained from a diffusion cell test. It is noted that there will be a tendency to underestimate the diffusion coefficient, although good practice should limit this error. The predicted error in the chloride binding isotherm is smaller than that in the diffusion coefficient. Furthermore, the influence of errors in the effective porosity on model predictions is limited as the resulting effect on the values of the calculated parameters describing chloride diffusion and binding counteract each other.     

A corresponding-states principle for the equation of state of linear homonuclear fused-hard-sphere fluids

A theoretically based corresponding-states principle previously developed for the equation of state of hard-convex-body fluids is extended to rigid linear homonuclear fused-hard-sphere fluids. Effective volumes and shapes are introduced in order to account for the nonconvexity of the molecules. The excess compressibility factor, reduced by means of a parameter which can be determined analytically, is a common function of the effective packing fraction. The analytical expression for the function can be obtained from the equation of state of the hard-sphere fluid. Existing simulation data for diatomics, triatomics and tetraatomics show excellent agreement with the corresponding-states principle.     

Governing equations for the steady state creep in orthotropic materials

Summary A general constitutive equation for creep deformation is presented based upon the concept of tensorial internal variables. The consequences of the theory of tensor functions representation are discussed with respect to the evolution equations. In a particular case of steady evolution of internal variables the governing equation for the secondary creep rate is derived in terms of a scalar inelastic potential. The material parameters required to characterize the stationary creep behaviour of the orthotropic composite are obtained from the unidirectional tension creep tests performed on a glass woven fabric xylok composite. Further check on the theory is made for the bidirectionally loaded specimens.With 4 Figures