The influence of the coordinate reduction on the identification of the joint dynamic properties

A problem of establishing a theoretical model of a joint from the measured frequency-response function (FRF) data is discussed in this paper. The model of the joint is considered as a coupled dynamic stiffness matrix, which generally includes six degrees of freedom (DoFs). For two types of least-squares solution the terms of use are clarified. The effect of coordinate reduction on the identification results is demonstrated numerically. Also the effect of added noise is studied. Using a substructure synthesis method and the identified joint dynamic properties the assembly response is reconstructed.     

Growth of recrystallised grains in 1.8% Si steel in temperature range 650 to 850°C

Three different types of grain growth were observed: uniform growth producing a regular microstructure; fast individual grain growth and finally a fast secondary recrystallisation initiated by the decarburisation of steel. Uniform growth follows parabolic kinetics. Above appr. 800°C a lower rate of growth is observed than it would be expected by extrapolation from lower temperature. Individual grain growth occurs in areas depleted of cementite and austenite and follows also parabolic kinetics. Nuclea for this type of growth are produced by the coalescence of smaller grains with similar space orientation. An apparent activation energy of 26 kJ/mole was determined for the process of coalescence, while for the uniform growth of recrystallised grains an apparent activation energy of 171 kJ/mole was established. Experimental data show that the texture rich with grains of orientation near to (111) in strips plane results from the greater density of such grains in recrystallised steel and the resulting faster formation of near (111) nuclea of sufficient size suitable for fast growth.     

Schrifttumsberichte

Ohne Zusammenfassung     

Basic Properties of the Projective Product with Application to Products of Column-Allowable Nonnegative Matrices

We use basic properties of the projective product to obtain exponential bounds for the Lipschitz constant associated with the projective product of column-allowable nonnegative matrices. We obtain similar bounds for the associated linear tangent maps. Date received: May 14, 1998. Date revised: November 18, 1999.     

Distribution of the carbide phase in the viscoplastic layer during the rotational friction-welding of various steels

The paper presents the viscoplastic phenomena observed during the rotational friction-welding process of high-speed steel M2 (AISI SAE) with carbon steel 1060 (AISI SAE). The structure, phase composition and distribution of the carbide phase in the friction plane and adjoining zones are examined by using optical microscopy (OM) with a system for quantitative analysis, and scanning electron microscopy (SEM) in addition to EDS analysis. The experimentally-checked mathematical relationship is suggested for the calculation of the radial movements of the carbide phase, immediately next to the friction plane. On the basis of qualitative and quantitative evaluation of the microstructural and rheological appearances, a model of carbide phase distribution is also established in the viscoplastic and viscous layers in the area of the friction plane.     

Optimization of geometry for lateral buckling process of a cantilever beam in the elastic region

Using the large displacement theory (theory of the third order according to Chwalla), the paper deals with lateral buckling process of a slender, elastic cantilever beam with a changeable cross-sectional area and represents it with a system of nonlinear differential equations. Based on a mathematical model of the lateral buckling process which considers the geometric and boundary conditions, an optimal geometry of a cantilever beam is obtained using the calculus of variation. A comparison between the properties of the beam with optimized geometry and those of a referential beam with a constant cross section is shown. The main feature of the optimized geometry beam is a constant maximal reference stress, obtained by the deformation energy theory, along the whole length of the beam in a deflected form which means that in terms of stability the material is completely exploited. The result of this feature is, besides higher critical load, also higher carrying capacity of the optimal geometry beam in the postbuckling region.     

Improvement of the stoichiometric network analysis for determination of instability conditions of complex nonlinear reaction systems

Stoichiometric network analysis (SNA), a known method for analyzing complex reaction systems including biochemical ones, is improved and applied to a nonlinear process studied far from equilibrium in a continuously fed, well stirred tank reactor (CSTR). A particular attention is focused on the determination of the narrow range of the control parameter values where the main steady state is unstable and where different dynamic states can be simulated numerically. The instability region, the most important feature of nonlinear reaction systems, is calculated as a function of the SNA parameters (current rates and reciprocal concentrations of intermediate species in the steady state) and simplified by retaining only the dominant terms. Since the number of the current rates is usually larger than the number of linearly independent equations to be used for their calculation, it is shown here that the current rates can be replaced with a smaller number of reaction rates at the steady state. These rates are related to the experimental data in a simple manner. The instability condition is also written as a function of dimensionless parameters derived from the SNA. This general approach is applied to a model of the Bray–Liebhafsky (BL) reaction having seven reactions without direct autocatalysis or autoinhibition, studied under CSTR conditions. Since the model has six intermediate species, it would be very difficult to analyze its instability condition by the conventional procedure, where a sixth order characteristic equation would have to be solved. On the other hand, the instability condition, obtained easily by the improved SNA, locates correctly the oscillatory region using numerical integration. Other dynamic states found earlier with a larger model of the BL reaction, such as mixed-mode oscillations, period doubling and chaos, are also obtained within the theoretically predicted oscillatory region. Thus, besides the general advantages of the improved stoichiometric network analysis as a method appropriate for the examination of complex nonlinear reactions, we show that the various mentioned dynamic states can be obtained by a very simple variant of the model of the BL reaction realized under CSTR conditions.     

Vitamin C and plasma triglycerides in experimental animals and in humans

A chronic latent vitamin C deficiency in guinea pigs enhances triglyceride concentration in blood plasma but does not markedly alter the composition of fatty acids in serum and hepatal triglycerides. An addition of 0·5% ascorbic acid to the diet of golden hamsters tends to normalise alimentary hypertriglyceridemia provoked by a high-glucose fat-free diet not containing vitamin C. A daily administration of 2 × 500 mg of an effervescent ascorbic acid for three months to subjects aged between 50 and 75 who were in a state of a seasonal vitamin C deficiency resulted in a significant depression of triglyceridemia. The hypotriglyceridemic effect of ascorbic acid depended on the starting plasma concentration of triglycerides: the higher the initial triglyceridemia, the more striking the hypotriglyceridemic effect. An administration of 2 × 500 mg of effervescent ascorbic acid every 24 h to a selected group of subjects with an initial triglyceridemia above 200 mg % for the duration of one year brought about a very significant decline of triglyceridemia, and this still persisted six weeks following cessation of ascorbic acid administration. An intervention of vitamin C at the level of triglyceride splitting enzymes is presumed.     

Determination of testosterone esters and nortestosterone esters in animal blood serum by LC-MS/MS

A sensitive and robust confirmatory method for determination of steroid esters in blood serum is essential for reliable monitoring of possible illegal use of steroid hormones as growth promoters in meat production. A previously used sample preparation methodology was improved. The procedure consists of protein precipitation and removal of phospholipids by dispersive SPE Supel? QuE Z-Sep (Sigma-Aldrich) followed by clean-up on alumina column and LC-MS/MS measurement. The modified method has been validated according to Commission Decision 2002/657/EC. Validation parameters for determination of six testosterone esters and five nortestosterone esters in bovine and porcine blood serum are presented in this article. Decision limits for all analytes were observed in the range 10–20 pg mL^?1. The method described is considerably robust for bovine and porcine serum analyses and can be applied both for screening and confirmatory determination in routine residue monitoring.