Curvature rate approach to the evaluation of the stiffness distribution in plate-like structures

A procedure for identifying the bending stiffness distribution in plate-like structures is presented. The algorithm is based on the correlation between a parameter called curvature increased factor (CIF) and the bending stiffness of the plate, D. Accurate correlation can be achieved only by considering the effect of the redistribution of internal forces and moments due to the damage on the curvature distribution. In order to achieve this goal, the study offers an iterative procedure, which eliminates the effect of the moment redistribution from the CIF and eventually correlates accurately between CIF and D. The curvature rate is evaluated from the displacement mode shape using a 2D smoothing technique. The procedure takes into account the presence of random errors and the limited number of measured nodes. The procedure?s effectiveness, reliability, and range of applicability are demonstrated using numerical examples.     

Untersuchung der Strukturbildung in Kolloidsystemen mit der Paramagnetsonde

Zusammenfassung Mit Hilfe der Paramagnetsondemethode wurden Strukturumwandlungen im System Tween-80-Wasser und Natriumdodecylsulfat-Wasser untersucht. Die ?nderung der Relaxationszeit wird mit der ?nderung der Makroeigenschaften des Systems verglichen.     

Analysis of long-term distributions of calibration parameters and calibration intervals for an atomic absorption spectrophotometer

 A combination of "black box" and "calendar-time" methods for the determination of calibration intervals of an analytical measuring instrument is discussed. Since the methods require information on the distributions of the calibration parameters, such information is described for an atomic absorption spectrophotometer, as an example. The hypotheses on the normal distribution of the calibration parameters are tested using the ω²-criterion and accepted at 0.90–0.95 levels of confidence. Corresponding control charts are designed for indication of warning and action limits of the calibration parameters, and diagnoses of outliers in further calibrations. Control charts indicate also when the calibration should be done according to the full program of the equipment manufacturer. Received: 15 April 2000 / Accepted: 24 July 2000     

Comparative modulation analysis of electron spin echo signals from oxidized chlorophyll a in vitro and P 700 centres in chloroplasts

A comparative analysis of electron spin echo modulation effects from ¹⁴N nuclei of pyrrole rings for Chla⁺ and P 700⁺ has been performed, yielding parameters of quadrupole and isotropic hyperfine couplings with nitrogen nuclei in these paramagnetic centres.     

Experimental study of different control methods for hypersonic air inlets

An experimental study of different control methods for hypersonic air inlets aimed at ensuring reliable starting of these apparatuses and improving their operating characteristics in the range of Mach numbers 2 to 8 is reported. Conditions for boundary-layer separation and possibilities for preventing this separation by using modified diffuser configurations and/or perforation bleedage are examined. An air-inlet model was tested for operation in an intermittent wind tunnel and in a blow-down wind tunnel respectively in the Mach-number ranges 2 to 6 and 5 to 8. Distributions of static and total air pressures on the walls of the model and in several cross sections were measured, together with air flow coefficients and total-pressure recovery coefficients. Perforation bleedage is shown to offer an efficient means to facilitate air-inlet starting. Perforation bleed has enabled a more than two-fold increase in the air flow coefficient on the model with sidewalls. A perforation-bleed panel installed closer to the air-inlet throat proved to be more efficient. The possibility of sudden starting of the air-inlet apparatus was checked in the intermittent wind tunnel; it was shown that, here, sudden starting could be realized. The data obtained in the intermittent wind tunnel proved to be consistent with data obtained in the blow-down wind tunnel with up to 150-ms blowdown time. This work was supported by the International Scientific and Engineering Center (Contract No. 887) and by MBDA, France.     

Investigation of temperature fields in supersonic flow behind a backward-facing step

The results of numerical modelling and experimental investigations of high-enthalpy turbulent flows in the neighborhood of 90-degree backward-facing steps at the Mach numbers M_∞ = 2–4 are presented. The experiments were conducted in the hot-shot wind tunnel IT-302M of ITAM SB RAS. The computations were carried out on the basis of the full Favres-averaged Navier — Stokes equations augmented by the Wilcox turbulence model. The temperature factor influence on the flow structure in the separated zone and temperature distributions was investigated numerically for different Mach numbers. The wall temperature is shown to affect significantly the quantity and sizes of recirculation vortices as well as the temperature distribution in the zone of flow separation and reattachment. The computational results are compared with experimental data on the pressure distribution on the model surface and the wave structure of the flow.     

Lifetime of the traceability chain in chemical measurement

Since the uncertainty of each link in the traceability chain (measuring analytical instrument, reference material or other measurement standard) changes over the course of time, the chain lifetime is limited. The lifetime in chemical analysis is dependent on the calibration intervals of the measuring equipment and the shelf-life of the certified reference materials (CRMs) used for the calibration of the equipment. It is shown that the ordinary least squares technique, used for treatment of the calibration data, is correct only when uncertainties in the certified values of the measurement standards or CRMs are negligible. If these uncertainties increase (for example, close to the end of the calibration interval or shelf-life), they are able to influence significantly the calibration and measurement results. In such cases regression analysis of the calibration data should take into account that not only the response values are subjects to errors, but also the certified values. As an end-point criterion of the traceability chain destruction, the requirement that the uncertainty of a measurement standard should be a source of less then one-third of the uncertainty in the measurement result is applicable. An example from analytical practice based on the data of interlaboratory comparisons of ethanol determination in beer is discussed. Received: 5 October 2000 Accepted: 3 December 2000     

Multiple Dirichlet Series and Moments of Zeta and L-Functions

This paper develops an analytic theory of Dirichlet series in several complex variables which possess sufficiently many functional equations. In the first two sections it is shown how straightforward conjectures about the meromorphic continuation and polar divisors of certain such series imply, as a consequence, precise asymptotics (previously conjectured via random matrix theory) for moments of zeta functions and quadratic L-series. As an application of the theory, in a third section, we obtain the current best known error term for mean values of cubes of cent ral values of Dirichlet L-series. The methods utilized to derive this result are the convexity principle for functions of several complex-variables combined with a knowledge of groups of functional equations for certain multiple Dirichlet series.