Copper-induced changes in the properties of arsenic chalcogenides

The influence of the presence of Cu in the amount between 1% and 6% in arsenic chalcogenide glasses is examined through a study of the electronic energy levels by means of x-ray photoelectron and x-ray emission spectroscopy, through an investigation of the low-energy tunneling systems by means of phonon echoes at 0.37 K, and through an examination of the photodarkening and the photoinduced dichroism caused by polarized Ar⁺ laser irradiation. Possible links between the various effects are examined. The Cu atoms become an integral part of the amorphous lattice structure and strongly influence the photodarkening, but they do not have a significant effect on the tunneling systems or the dichroism. It is concluded that the tunneling levels and the dichroism involve only local configurations, while the photodarkening involves larger-scale areas of the lattice. Fiz. Tekh. Poluprovodn. 32, 976–981 (August 1998)     

Thermal Monitoring of Self-Checking Systems

With the increasing power density in integrated systems resulting from scaling down, the occurrence of field failures due to overheating has considerably increased. Faulty operation can be prevented by on-line temperature monitoring. This paper deals with questions of on-line temperature monitoring in safety-critical systems. First the possible temperature sensors are reviewed and basic principles of self-checking systems including such sensors are detailed, then a new temperature sensor cell with extremely good parameters designed especially for DfTT applications is presented. The basic questions of integrating thermal sensors into self-checking systems are also discussed.     

An Extraction of the Dominant Rotor-Stator Interaction Modes by the Use of Proper Orthogonal Decomposition （POD）

The Proper Orthogonal Decomposition method is applied to the instantaneous velocity field within the rotor-stator inter-row region of a high-speed high-pressure centrifugal compressor. The processed data come from experiments and numerical simulations. In comparison with a Fourier transform, the POD gives the best modal approximation for both initial fields, in terms of the energy expressed on any given number of modes to be taken into account: to reach 98% of the total energy of the velocity field, the required number of POD modes is around nine times smaller than the number of Fourier harmonics. The individual POD modes are given and show that the unsteady rotor-stator interaction is already present in the very first modes.     

Hypergeometric Functions and Parabolic Partial Differential Equations

We investigate the summability of formal power series solutions of parabolic linear partial differential equations with exponential coefficients.2000 Mathematics Subject Classification. 35C10, 35C20.This research was supported by a Marie Curie Fellowship of the European Community program Improving Human Research Potential under contract number HPMF-CT-2002-01818.     

Unsteady rotor-stator interaction in high speed compressor and turbine stages

The blade row interaction can alter the time-mean flow and therefore be of interest for aerodynamic design analysis. Whereas results within low subsonic turbomachines are quite numerous in the literature, there have been far fewer works which give results of blade row interaction within high speed cases. Two cases are related in this paper. First, the effects of an incoming wake on the rotor flow field of a transonic compressor are analyzed. The blade row interaction proved to be positive regarding the total pressure ratio, but negative regarding the losses. The second case concerns a transonic turbine. Particular emphasis is placed on the assessment of the deterministic correlations included in the Averaged Passage Equation System.     

Steam conditioning after low temperature dyring

The purpose of this study was to investigate the response of saturated water vapour steaming on boards from Scots pine and Norway spruce. Steaming treatment of the predried boards were done in a laboratory chamber equipped with a 1.5 kW electric water boiler. The experiments were performed mainly at 100°C in saturated steam and the relation between temperature and moisture pickup as well as stress relaxation was studied. The results showed that steaming is a very efficient process to relax stress and equalise moisture gradients in boards. The gain of time is considerable; steaming takes only about 10% of traditional conditioning time at lower temperatures. The temperature rise is correlated to moisture pickup from surface condensation resulting in the possibility of estimating the increase of moisture content during steaming from measurements of temperature.     

Time-varying analysis methods and models for the respiratory and cardiac system coupling in graded exercise

The analysis of heart period series is a difficult task especially under graded exercise conditions. From all the information present in these series, we are the most interested in the coupling between respiratory and cardiac systems, known as respiratory sinus arrythmia. In this paper, we show that precise patterns concerning the respiratory frequency can be extracted from the heart period series. An evolutive model is introduced in order to achieve tracking of the main respiratory-related frequencies and their time-varying amplitudes. Since respiration acts to modulate the sinus rhythm, we relate the frequencies and amplitudes to this modulation by analyzing in detail its nonlinear transformation giving the heart period signal. This analysis is performed assuming stationary conditions but also in the realistic case where the mean heart period, the amplitude, and the frequency of the respiration are time-varying. Since this paper is devoted to the theoretical and complete presentation of the method used in a physiological study published elsewhere, the capabilities of our method will be illustrated in a realistic simulated case.     

Zn(MgBe)Se ultraviolet photodetectors

We present the growth and characterization of blue-violet and ultraviolet photodetectors based on ZnSe and Zn(Mg)BeSe compounds. Structures are grown by molecular beam epitaxy on (001) GaAs substrates. Three types of photodetectors have been fabricated. Zn(Mg)BeSe p-i-n photodiodes exhibit a high response of 0.17 A/W with a rejection rate of 10⁴ and a wavelength cutoff of 450 nm. Schottky barrier photodiodes based on planar geometry devices display a very flat response above the band gap with a rejection rate above 10³. High responses with quantum efficiency higher than 50% have been obtained. The wavelength cutoff can be tuned from 460 (ZnSe) to 380 nm (ZnMgBeSe), which leads to visible blind devices. Detectivities from 2.0 10¹⁰ (ZnMgBeSe) to 1.3 10¹⁰ mHz^1/2W⁻¹ (ZnSe) have also been measured. Metal-semiconductor-metal devices, recently fabricated, exhibit a spectral response very similar to Schottky devices. Quantum efficiencies of 40% are easily obtained in these devices with a rejection rate of 10³.