Hybrid methods for function generation

A method of function generation is discussed based on the use of hybrid digital analogue techniques. A brief description of a quantizer is given together with some experimental results. The purpose of this unit is to give the derivative with respect to time (in quantized form) of a variable. Units of this type used in conjunction with pulse modulators, which are also described, are shown to be capable of performing a wide variety of analytic functions. The application to correlation functions, using magnetic core storage for time delays, is also discussed. Another application is a fast analogue/digital converter with an incremental bit resolution time of one micro-second. The possibility of extending the application to generation of arbitrary functions of one or more variable is considered and one possible form of instrumentation, based on the use of magnetic core storage, is described

Coulomb blockade in silicon based structures at temperatures up to 50 K

Coulomb blockade has been observed in the current-voltage characteristics of structures fabricated in silicon germanium delta-doped material at temperatures up to 50 K. This is consistent with the estimated effective tunnel capacitance of 10 aF which is significantly smaller than the reported capacitances of tunnel junctions made from Al or GaAs/AlGaAs heterostructures

Healthcare workers in Saudi Arabia (KSA) perceive stress differently according to gender but not in cortisol levels - an immunoassay study

Background: Working in the healthcare sector is generally regarded as stress inductive, which hampers performance, yet one demanding constant accuracy. This dichotomy has led to numerous investigations on the impact from perceived stress on hospital workers but focused primarily on employing psychological methods to determine perceived stress. This study sought to employ an arguably more objective measure of chronic stress on female healthcare professionals in Saudi Arabia, by assaying the concentration of hair cortisol (HCC) in parallel with stress questionnaires. Methods: Pharmacists, nurses and lab workers participated in providing hair samples. Cortisol levels were subsequently quantified using immunoassay methods. Investigations considered the variables of age, gender, and smoking, hair coloring or bleaching or working in shifts on both stress perception and HCC. Results: On average chronic stress was perceived comparably between the different healthcare professions and not differ significantly against the female control group. However, chronic stress differed significantly between genders within the healthcare profession. In contrast, HCC levels showed no direct relation to stress perception with respect to either gender or profession. HCC did, however, show steady decreases with respect to age, as an indirect measure of experience, that contrasted against the identical scores for stress perception. Finally, night shifts, smoking or hair colouring did not produce a significant change on HCC in the healthcare cohorts. Conclusions: Women in the healthcare profession perceive stress higher irrespective of profession compared to men. Also show a pattern of decreasing levels of cortisol with increasing age despite reporting similar stress perception against younger participants

Fast C-V method to mitigate effects of deep levels in CIGS doping profiles

In this work, methods to determine more accurate doping profiles in semiconductors is explored where trap-induced artifacts such as hysteresis and doping artifacts are observed. Specifically in CIGS, it is shown that this fast capacitance-voltage (C-V) approach presented here allows for accurate doping profile measurement even at room temperature, which is typically not possible due to the large ratio of trap concentration to doping. Using deep level transient spectroscopy (DLTS) measurement, the deep trap responsible for the abnormal C-V measurement above 200 K is identified. Importantly, this fast C-V can be used for fast evaluation on the production line to monitor the true doping concentration, and even estimate the trap concentration. Additionally, the influence of high conductance on the apparent doping profile at different temperature is investigated

Gauge Invariant Effective Stress-Energy Tensors for Gravitational Waves

It is shown that if a generalized definition of gauge invariance is used, gauge invariant effective stress-energy tensors for gravitational waves and other gravitational perturbations can be defined in a much larger variety of circumstances than has previously been possible. In particular it is no longer necessary to average the stress-energy tensor over a region of spacetime which is larger in scale than the wavelengths of the waves and it is no longer necessary to restrict attention to high frequency gravitational waves.Comment: 11 pages, RevTe

Growth variation effects in SiGe-based quantum cascade lasers

Epitaxial growth of SiGe quantum cascade (QC) lasers has thus far proved difficult, and nonabrupt Ge profiles are known to exist. We model the resulting barrier degradation by simulating annealing in pairs of quantum wells (QWs). Using a semiclassical charge transport model, we calculate the changes in scattering rates and transition energy between the lowest pair of subbands. We compare results for each of the possible material configurations for SiGe QC lasers. The effects are most severe in n-type (001) Si-rich systems due to the large effective electron mass, and in p-type systems due to the coexistence of light holes and heavy holes. The lower effective mass and conduction band offset of (111) oriented systems minimizes the transition energy variation, and a large interdiffusion length (Ld = 1.49 nm) is tolerated with respect to the scattering rate. Ge-rich systems are shown to give the best tolerance with respect to subband separation (Ld = 3.31 nm), due also to their low effective mass

Different types of X-ray bursts from GRS 1915+105 and their origin

We report the X-ray observations of the Galactic X-ray transient source GRS 1915+105 with the PPCs of the Indian X-ray Astronomy Experiment(IXAE) onboard the Indian satellite IRS-P3 during 1997 June - August, which have revealed the presence of four types of intense X-ray bursts. All the observed bursts have a slow exponential rise, a sharp linear decay, and they can broadly be put in two classes: irregular and quasi-regular bursts in one class, and regular bursts in another class. The regular bursts are found to have two distinct time scales and they persist over extended durations. There is a strong correlation between the preceding quiescent time and the burst duration for the quasi-regular and irregular bursts. No such correlation is found for the regular bursts. The ratio of average flux during the burst time to the average flux during the quiescent phase is high and variable for the quasi- regular and irregular bursts while it is low and constant for the regular bursts. We suggest that the peculiar bursts that we have seen are charact- eristic of the change of state of the source. The source can switch back and forth between the low-hard state and the high-soft state near critical accretion rates in a very short time scale. A test of the model is presented using the publicly available 13-60 keV RXTE/PCA data for irregular and regular bursts concurrent with our observations.Comment: 13 pages, 12 figures, Accepted in APJ, emulateapj style use