STJ X-ray detectors with titanium sublayer

Superconducting tunnel junctions (STJs) with the structure Ti/Nb/Al, AlO_x/Al/Nb/NbN and corresponding layer thickness 30/100/8/13/150/30 nm were investigated as X-ray detectors at T=1.35 K. STJs with one active electrode in which the response of the other one is suppressed due to trapping layer on the surface opposite to the tunnel barrier have a number of potential advantages. The best line width (FWHM) is 78 eV for 6400 μm² junction. Contribution of the electronic noise is about 50 eV. The intrinsic detector line width is less than 60 eV. The collected charge from inactive electrode is more than 8 times less than that from the active one. Titanium proved to be an appropriate material for a sublayer and a trap.     

Variational Lyapunov method and stability analysis for impulsive delay differential equations

In the paper, employing the variational Lyapunov method, stability and instability properties in terms of two measures for impulsive delay differential equations with fixed moments of impulsive effects are discussed. Some stability and instability criteria are obtained. These results much generalize the known ones. Some examples are given to illustrate the advantages of them as well.     

A generalized boundary integral equation for isotropic heat conduction with spatially varying thermal conductivity

In this paper we derive a generalized fundamental solution for the BEM solution of problems of steady state heat conduction with arbitrarily spatially varying thermal conductivity. This is accomplished with the aid of a singular nonsymmetric generalized forcing function, D, with special sampling properties. Generalized fundamental solutions, E, are derived as locally radially symmetric responses to this nonsymmetric singular forcing function, D, at a source point ξ. Both E and D are defined in terms of the thermal conductivity of the medium. Although locally radially symmetric, E varies within the domain as the source point, ξ changes position. A boundary integral equation is formulated. Examples of generalized fundamental solutions are provided for various thermal conductivities along with the corresponding forcing function, D. Here, four numerical examples are provided. Excellent results are obtained with our formulation for variations of thermal conductivity ranging from quadratic and cubic in one dimension to exponential in two dimensions. Problems are solved in regular and irregular regions. Current work is under way investigating extensions of this general approach to further applications where nonhomogeneous property variations are an important consideration.     

Condensation heat transfer of binary refrigerant mixtures of R22 and R114 inside a horizontal tube with internal spiral grooves

An experimental study of the condensation of pure and mixed refrigerants of R22 and R114 inside a spirally grooved horizontal copper tube has been carried out. A double-tube counterflow condenser in the pressure range 3–21 bar and at a mass flow-rate 26–70 kg h⁻¹ was used. The axial distributions of refrigerant, tube wall and cooling water temperatures, wall heat flux density and vapour quality are shown graphically. The variation of tube wall temperature around the circumference of the tube is also shown. The local Nusselt number depends on the molar fraction, whereas the average Nusselt number can be correlated by an equation which is modified from a previously established equation for pure refrigerants inside a horizontal smooth tube. The frictional pressure drop evaluated is correlated well by the Lockhart-Martinelli parameters and is independent of the concentration of the mixture.     

Fabrication and application of relaxed buffer layers

Principles involved in the fabrication of compositionally graded, relaxed buffer layers with low threading dislocation densities are discussed. It is recognized that two key elements are important in controlling the kinetics of lattice relaxation. A bulk strain dependent surface roughness study is described as an application using the relaxed buffers, where an asymmetric behavior of the surface roughness with respect to the sign of strain is observed and explained as a result of strain induced changes in surface step energies.     

Kinetics of epitaxial growth and roughening

We review some recent results on epitaxial growth and surface roughening. Particular emphasis is placed on the concept of the critical island size in submonolayer growth and on the existence of scaling in both the submonolayer and multilayer growth regimes. The use of scaling ideas as well as Monte Carlo simulations and continuum equations is shown to be effective in understanding experimental results for submonolayer growth and surface roughening.     

Hydrodynamic characteristics of a butterfly valve — Prediction of torque characteristics

This study has focused on the prediction of torque characteristics of butterfly valves and we propose a prediction equation derived from theoretical investigation and experimental results. The free-streamline theory is applied to the prediction of the torque characteristics because the flow separation was confirmed on the rear surface by flow visualization. Actual valves are affected by the duct wall. These effects are considered as the change of attack angles and approaching velocities of the flows. Thus, the correction for these effects is added to the theoretical torque equation obtained by the free-streamline theory. The results of our prediction are shown to be successful comparing with the experimental results.     

Uniformly optimal control of linear time-varying systems

An optimal control problem is formulated in the context of linear, discrete-time, time-varying systems. The cost is the supremum, over all exogenous inputs in a weighted ball, of the sum of the weighted energies of the plant's input and output. The controller is required to be causal and to achieve internal stability. Existence of an optical controller is proved and a formula for the minimum cost is derived.     

Heat capacity of the water-lithium bromide system and the water-lithium bromide-zinc bromide-lithium chloride system at high temperatures

The heat capacities of the water-lithium bromide system were measured in the temperature range 313.15–433.15 K. Those of the water-lithium bromide-zinc bromide-lithium chloride system wer also measured in the temperature range 373.15–433.15 K. On the basis of the experimental data, an empirical formula for the water-lithium bromide system was obtained by the least-squares method. The calculated values from the empirical formula were in good agreement with literature values obtained in the range of low temperatures. In addition, the heat capacity data obtained for the water-lithium bromide-zinc bromide-lithium chloride system were compared with the calculated values from Ueda's equation which is applicable at low temperatures, and they agreed well.     

Bubble size distribution in a flotation column

The bubbles that were generated in a flotation column were measured. The bubble size distributions were obtained both for air-water and air-water-coal systems. The size distribution pattern was fitted to different equations. It was found that the bubble size distribution in both the flotation and cleaning zones follows the Rosin-Rommler equation used to describe the particle size distribution in crushing. This study indicates that bubbles in the cleaning zone are always larger than those of the flotation zone and finer bubbles are generated when a mixture of frothers is used instead of individual frothers.