Showing papers by "Vienna University of Technology published in 1984"

The Defect Correction Approach

Abstract: This is an introductory survey of the defect correction approach which may serve as a unifying frame of reference for the subsequent papers on special subjects.

Elastic-plastic deformation of the rotating solid disk

Abstract: The plane state of stress in a rotating circular disk of elastic-plastic material with linear strain hardening is studied based on Tresca's yield condition and its associated flow rule. The plastic core consists of two parts with different forms of the yield condition. By specializing the results to perfectly plastic material, the usual statically determinate stress distribution is recovered but, since the plastic strain at the axis becomes infinite, these stresses are not meaningful.

A Nonlinear Analysis of the Generic Types of Loss of Stability of the Steady State Motion of a Tractor-Semitrailer∗

Abstract: SUMMARY All different types of loss of stability which occur generically for a tractor semitrailer vehicle are studied when varying two parameters namely the speed V of the vehicle and the position d of the center of mass of the trailer. For a fixed value of d and varying V it turns out that only two cases either a divergence or a Hopf bifurcation can occur typically. By means of a nonlinear analysis the post-bifurcation behavior for both cases is treated showing that it is critical in both cases. This latter result means that the system is an imperfection sensitive one for which the calculation only of the linear stability limit, does not have very much practical meaning, because small perturbations of the system (changes of parameters) can lead to a drastic reduction of the critical speed. Our paper furthermore indicates how a nonlinear investigation of stability problems in vehicle dynamics with no restriction to the number of degrees of freedom of the system can be done in a straight forward manner.

Effects of elastic photoelectron collisions in quantitative XPS

Abstract: A fast Monte Carlo algorithm calculating the effects of elastic photoelectron collisions is presented. The algorithm is applicable to analyzer geometries with axial symmetry and with axis perpendicular to the surface (e.g. the CMA). The calculations were performed for four photoelectron lines: carbon 1s, aluminium 2s, cobalt 3p, and palladium 3d5/2. The following photoelectron characteristics were considered. (i) The angular distribution of photoelectrons leaving the surface. The distribution was found to follow the cosine distribution in practically all considered cases. Taking into account the elastic collisions did not change the shape of the distribution but decreased the photoelectron current leaving the surface, the difference increasing with atomic number of element. (ii) The distribution of emission depths of photoelectrons entering the analyzer. As a result of elastic collisions, more photoelectrons originate from the layer at the surface and less from the deeper layers. Thus, the actual depth of analysis is decreased. (iii) The total photoelectron current entering the analyzer. This current was also decreased by the elastic collisions. The difference reaches 1.6% for carbon 1s line, but increases to 16–19% for palladium 3d5/2 line. An elastic scattering correction in formalism of quantitative XPS is suggested. (iv) The average depth of analysis. This parameter was found to be most significantly affected by elastic scattering of photoelectrons. The depth of analysis was decreased by elastic collisions from 3–5% for carbon 1s line to 60–80% for palladium 3d5/2 line.

Xylitol dehydrogenase from Pachysolen tannophilus

Abstract: NAD-xylitol-dehydrogenase (EC 1.1.1.9) from Pachysolen tannophilus was investigated in relation to xylitol byproduction during xylose fermentation by this yeast. For this purpose the enzyme was partially purified by a combination of affinity chromatography and fast liquid protein chromatography. The enzyme catalyzes an equilibrium reaction which at physiological pH values favours the accumulation of xylitol. The kinetics of the enzyme were shown to be Michaelis-Menten type with respect to both reaction directions. The activity of the enzyme was shown to be under the influence of the ‘catabolic reduction charge’ (NADH/NAD + NADH) and ATP. The apparent equilibrium constant of the enzyme may explain the considerable byproduction of xylitol during xylose fermentation by P. tannophilus .

On laminar steady flow in sinusoidal channels

Abstract: In the present paper a perturbation method is developed in order to study viscous laminar flows through wavy-walled channels. The stream function of the flow is expanded in a series thereby the wall amplitude being the perturbation parameter. The walls of the channel are transformed into parallel straight lines in order to simplify the boundary conditions of the problem on the wall. Flow field and wall-shear stresses are calculated numerically up to the first perturbation order. The position of the beginning separation on the channel walls and the associated critical Reynolds number are determined, as well as the extension of the region of the separated flow. The position of separation and reattachment points are given as functions of Reynolds numbers lying above the critical Reynolds number. The results are discussed and compared with the experimental results of other papers and further theoretical analysis.

Coupled flutter and divergence bifurcation of a double pendulum

Abstract: The loss of stability of the equilibrium position of a double pendulum with follower force loading and elastic end support is studied. At a special parameter combination the linearized system is characterized by a zero root and a pure imaginary pair of eigenvalues. Therefore, the stability problem is a complicated critical case in the sense of Liapunov and requires a non-linear analysis. A complete post-bifurcation investigation of the coupled divergence and flutter motions is given by means of centre manifold theory, and bifurcation diagrams. Among the different types of motions even the appearance of chaotic behavior is shown.

A numerical study of similarity solutions for combined forced and free convection

Abstract: The similarity equations for combined forced and free convection flow over a horizontal plate when the wall temperature is inversely proportional to the square root of the distance from the leading edge are solved by introducing a scaling similar to that for the Blasius equation. The technique is also applied to the local similarity equations for the case of a constant wall temperature.

Linear errors-in-variables models

Abstract: In this paper we are concerned with the statistical analysis of systems, where both, inputs and outputs, are contaminated by errors. Models of this kind are called error-in-variables (EV) models. Let x t * . and y t * denote the “true” inputs and outputs respectively and let xt and yt denote the observed inputs and outputs, then the situation can be illustrated as follows: Thereby ut and vt are the errors of the inputs and the outputs respectively.

Stochastische Approximation konvexer Polygone

Abstract: Let K be a convex polygon with perimeter L and area F. Denote the perimeter of the convex hull of n uniformly and independently distributed points in K by Ln and by Fn its area. As n tends to infinity, $$L - E(L_n ) = C_1 (K)/\sqrt n + o(1/n^{1 - \varepsilon } )$$ for any fixed ɛ>0 and $$F - E(F_n ) = C_2 (K)\log n/n + O(1/n),$$ where the constants C1(K) and C2(K) are given explicitly. This generalizes a result of Renyi and Sulanke.

Thermodynamics and kinetics of Zr(Fe1−xMnx)2Hx and the storage compound Ti0.8Zr0.2MnCrH3

Abstract: Thermodynamic and kinetic data for hydrogen absorption in Zr(Fe1−xMnx)2 and Ti0.8Zr0.2CrMn, which is one of the most promising hydrogen storage materials, are presented. The data were obtained from measurements performed using a high pressure microbalance. The macroscopic rate constants obey an Arrhenius law, and comparison with the hydrogen self-diffusion coefficient of Ti0.8Zr0.2MnCrH3 recently measured by Hempelmann and coworkers suggests that the rate-limiting step in the absorption kinetics is the α-β phase transition rather than the comparatively fast hydrogen diffusion in the bulk.

Transmission electron microscope observations of brown rot caused by Fomitopsis pinicola with respect to osmiophilic particles

Abstract: Changes in pinewood tracheids during decay by the brown rot fungus Fomitopsis pinicola were observed in the transmission electron microscope for a cultivation period of 80 days. It was found that F. pinicola normally caused degradation of carbohydrates over the entire cell wall with the cell wall contours maintained, but more rarely was capable of a complete degradation of the cell walls including the middle lamella and the cell corners. This indicates that some hyphae may have a ligninolytic enzyme system. The occurrence of osmiophilic particles in the protoplasm of hyphae and in wood cell walls was observed from early decay stages. They were randomly distributed in the wood and their distribution, being an indicator of carbohydrate depolymerization, permits this type of decay to be observed in the transmission electron microscope. The origin and function of the osmiophilic particles is discussed with respect to what is known about the enzymes of wood decay. Furthermore, the curve of weight loss is discussed in connection with earlier findings concerning wood decay and with the appearance of the osmiophilic particles.

μ/ρ Algorithm valid for 1 keV ≤ E ≤ 50 keV and 11 ≤ Z ≤ 83

Abstract: Mass absorption coefficients can be calculated by this algorithm with programmable pocket calculators giving a standard deviation of about 5% when compared with McMaster's tables.

Application of the virtual pulse generator method to real-time correction of counting losses in high-rate gamma ray spectroscopy

Abstract: The virtual pulse generator method of counting loss correction [1] has been installed and tested on the high counting rate gamma ray spectroscopy system of KORONA, a high flux neutron generator facility for 14 MeV neutron activation analysis. It is shown that this system may be used for gamma ray spectroscopy up to counting rates of 8 × 10 5 cps. Counting losses due to dead time and pulse pile-up are determined and corrected in real time by means of suitably adapted correcting factors which are transferred to the multichannel analyzer as variable increments.

The Physical Parameters

Abstract: The basic semiconductor equations, the derivation of which we have thoroughly discussed in Chapter 2, just determine the structure of the set of equations which we shall have to solve in order to simulate the internal behavior of a device. Process modeling, as sketched in Chapter 3, delivers information about the geometry of a device and the distribution of dopants, whieh can also be considered to be a physical Parameter. As we have already noticed, a couple of additional physical parameters are inherently associated with the basic semiconductor equations. Any quantitative, or even qualitative, Simulation of a device relies heavily on applicable models for these parameters. In addition, a mathematieal characterization of the problem of solving the basic semiconductor equations is only fqasible with at least qualitative knowledge of the associated parameters (e.g. sign, smoothness, order of magnitude). Therefore, we shall discuss in this chapter the most important models for the physical parameters. A review has also been presented in [4.41].

Transient elastic waves in a wedge-shaped layer

Abstract: The theory of generalized ray is applied to analyzing transient elastic waves in a layered half-space with non-parallel interface. The propagation, reflection and refraction of longitudinal (P-) and transverse (SV-) waves which are generated by a line source in the surface layer of a two layer model are considered, each of the two homogeneous and isotropic layers having different density and inverse of wave speeds. Generalized ray integrals for multi-reflected rays in the top layer are formulated by using two rotated coordinate systems, one for each interface, and are expressed in terms of local wave slowness along each interface. Through a series of transformations of the local slowness, all ray integrals are expressible in a common slowness variable. Special attention is given to wave mode changes during reflection. The arrival time of each ray is then determined from the stationary value of the phase function with common slowness of the ray integral. Arrivals of head waves corresponding to rays refracted at a fast bottom are calculated from proper branch points of the Cagniard-mapping.

Quantitative XPS analysis considering elastic scattering

Abstract: Up to now the equations for both quantitative XPS analysis and those for the determination of reduced thicknesses of thin overlayers have been derived according to the assumption of a well-defined photoelectron escape length. Escape length distributions are caused by a variety of influences. The consequences of this are demonstrated by the example of thin overlayers. Additionally, an approximation is developed which accounts for elastic electron scattering. The ratio Λ/λel of mean free path is the characteristic quantity of this approximation, which is quantified by comparison of Monte Carlo calculations and thin film experiments. This approximation allows us to conclude that elastic electron scattering does not influence quantitative XPS analysis, so long as it is performed without any kind of references.