Laser stabilitron

We consider a new method for producing intensity stabilization of cw lasers. This method incorporates negative feedback from a nonlinear saturable absorber to provide wideband noise-reduction and may produce an output beam for which shot noise is below the quantum limit. This new method can be used with a large variety of cw lasers and is particularly applicable to frequency-stabilized lasers which are locked to absorption lines.Permanent address: Institute of Laser Physics, Novosibirsk 630090, Russia     

Subchronic oral toxicity (six months) of carboxyethylgermanium sesquioxide [(HOOCCH2CH2Ge)2O3]n in rats

After briefly renewing toxicological data on germanium compounds, the authors report on the subchronic oral toxicity of carboxyethylgermanium sesquioxide in rats. During six months, male and female animals received 1 g kg^?1. day^?1. No particular toxic symptoms, and no behaviour problems except a small decrease of body weight in male rats, at the end of the six-month experimentation period, were observed. A significant decrease of erythropoiesis and some significant changes in leucocyte ratios were demonstrated. The main marked effect was a moderate renal dysfunction characterized by a tubular disease with the presence of cylinders, swelling of tubulus cells and flocculus deposits. Germanium urinary excretion was constant and linked to the received dose. Six months later, no preferential accumulation in organs was evident.     

Towards an Operational Model for Prevention and Treatment of Asthma Attacks

Asthma is one of the major chronic diseases in many countries. At present there is no cure for asthma, but medical advances can help to reduce the chances of attacks of the condition. Efficient care for asthma involves complexity, uncertainty, variability and the use of scarce resources, and these are the same conditions that indicate a possible use for the modelling approach of operational research. This paper is concerned with a pilot model that was developed through joint work by medical professionals and operational researchers. The development of the model is explained and illustrative results indicate the potential value of the modelling approach for the care of asthma in the community.     

Certification of the sulphur content of three rapeseed reference materials

Summary The sulphur content of three rapeseed reference materials has been certified on the basis of measurements made by inductively coupled plasma-optical emission spectroscopy, isotope-dilution mass spectrometry and ion chromatography. Their suitability for the calibration of x-ray fluorescence spectrometers used for measuring sulphur in rapeseed samples was established.     

Line Narrowing of a Tunable High Pressure CO2 Laser by Means of an Improved Non-Littrow Cavity

A model is reported to foresee ,for different mirror choices, the spectral properties of a high pressure, frequency tunable, CO₂ laser, operating with a non-Littrow grating mounting. The calculations show a larger frequency selectivity for not collimated plane cavities. The model is experimentally verified in a suitable high pressure laser. In particular narrowed linewidths less than 300MHz ( FWHM) are obtained.     

Arc erosion reduction on electrical contacts using transversecurrent injection

Electrical contact lifetime is often directly determined by arc erosion. A method for reducing are erosion was developed consisting of injecting from an external current source an additional electrical current flowing parallel to the contact surface. This method was examined in three are environments using the additional transverse electrical current with a density less than 1 A/mm²: 1) automobile ignition contacts; 2) pulsed air arc; and 3) low pressure (P=100 mTorr) arc in nitrogen, SEM and X-ray examination showed that application of a transverse current in a contact during arcing changed the phase composition and microstructure of the contact surface. Under optimal conditions, the microstructure which is formed is significantly more erosion resistant than without the transverse current injection     

Multiple-scattering-theory analysis of XANES spectra of SO2 adsorbed on Cu(100)

The sulphur K-edge x-ray absorption spectra of SO₂ multilayer and of SO₂ submonolayer adsorbed on Cu(100) are analysed. It is found that the dominant spectral features are of a molecular origin. The results support earlier findings that the SO₂ molecule stands perpendicular to the surface. Use of non-selfconsistent potentials does not lead to a good quantitative agreement between theory and experiment.     

Gain saturation in quantum-well heterostructures

The effect of radiation gain saturation in quantum-well heretostructures was investigated in the system GaAs—AlGaAs with regard to the spectral line broadening and the type of radiation polarization. Belarusian State University, 4, F. Skorina Ave., Minsk, 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 797–800, November–December, 1997.     

Optimum parameters for the generalized ADI method

Summary. In the context of the generalized ADI method, we are concerned with the problem of finding in the set of rational functions r with numerator degree m and denominator degree n an element that minimizes where E,F are disjoint real intervals. By extending a recent analysis by Levin and Saff, we present an explicit formula for choosing the pair (m,n) for given m +n. Furthermore, we provide a characterization of and a Remes type algorithm for its determination. Extensive numerical computations furnish some comparison of with asymptotically optimal solutions based on Fejér-Walsh and Leja-Bagby points. Received September 6, 1996 / revised version received June 30, 1997     

Fairness in Scheduling

On-line machine scheduling has been studied extensively, but the fundamental issue of fairness in scheduling is still mostly open. In this paper we explore the issue in settings where there are long-lived processes which should be repeatedly scheduled for various tasks throughout the lifetime of a system. For any such instance we develop a notion ofdesiredload of a process, which is a function of the tasks it participates in. Theunfairnessof a system is the maximum, taken over all processes, of the difference between the desired load and the actual load.An example of such a setting is thecarpool problemsuggested by Fagin and Williams [IBM Journal of Research and Development27(2) (1983), 133–139]. In this problem, a set ofnpeople form a carpool. On each day a subset of the people arrive and one of them is designated as the driver. A scheduling rule is required so that the driver will be determined in a “fair” way.We investigate this problem under various assumptions on the input distribution. We also show that the carpool problems can capture several other problems of fairness in scheduling.