Location of Staphylococcus aureus within the experimentally infected bovine udder and the expression of capsular polysaccharide type 5 in situ

The objective of this study was to locate Staphylococcus aureus in the bovine udder and to investigate the expression of capsular polysaccharide type 5 (CP5) in situ in both the early and chronic stages of experimental intramammary S. aureus infections. Bovine udder tissue was obtained in early and chronic stages of intramammary infection; i.e., 24 to 96 h and 122 d after experimental intramammary infection with S. aureus Newbould 305. The presence and location of S. aureus was investigated by Gram staining of tissue sections. The expression of CP5 by S. aureus in situ was investigated by immunochemical staining of tissue sections with specific antibodies against CP5. Both in the early and chronic stages of infection, S. aureus was located within the lumen of alveoli or lactiferous ducts, in association with the epithelium, and within phagocytic cells. The staphylococci were mainly observed in clusters and often in the presence of polymorphonuclear neutrophils. Expression of CP5 by S. aureus was observed both in the early and chronic stages of infection. In general, CP5-positive S. aureus were located in alveoli and in association with the mammary epithelium. In the chronic infection, CP5-positive S. aureus were also located deep in the interstitial tissue. These results indicate that--both in early and chronic stages of experimental S. aureus mastitis--colonization of the mammary epithelia and invasion into the interstitial tissue occurs and that CP5 is expressed by S. aureus Newbould 305 in situ. The invasion of S. aureus in the interstitial tissue and the expression of CP5 probably help the bacteria to withstand the host defense mechanisms.     

Asymptotic analysis of temporal-difference learning algorithms with constant step-sizes

The mean-square asymptotic behavior of temporal-difference learning algorithms with constant step-sizes and linear function approximation is analyzed in this paper. The analysis is carried out for the case of discounted cost function associated with a Markov chain with a finite dimensional state-space. Under mild conditions, an upper bound for the asymptotic mean-square error of these algorithms is determined as a function of the step-size. Moreover, under the same assumptions, it is also shown that this bound is linear in the step size. The main results of the paper are illustrated with examples related to M/G/1 queues and nonlinear AR models with Markov switching. Editor: Robert Schapire     

Reduced numerical integration in thermal transient finite element analysis

The stability and accuracy of the so-called “ga-family”, two level time integration algorithms for thermal transient problems are considered. In particular, the influence on the solution characteristics of the order of numerical integration rule employed in the evaluation of the element matrices is examined. Consideration is restricted to the four node bilinear and eight node biquadratic isoparametric elements. The time integration schemes considered in detail are the Crank Nicolson, Galerkin, Modified Galerkin and Euler Backward algorithms. The stability of each process is related to both the eigenproperties of the conductivity and heat capacity matrices and to the eigenvalue spectrum of the thermal equation system. It is shown that inaccuracies and instabilities can arise in solution which are associated with the poor prediction of the element properties by reduced numerical integration rules. For eight node biquadratic elements, the source of error is the inadequate modelling of the eigenvalue spectrum of the heat capacity matrix by reduced quadrature; with both full and reduced integration rules providing very similar values for the conductivity (or stiffness matrix). However, for four node bilinear elements, reduced quadrature can result in an inadequate representation of both the conductivity and heat capacity matrices. It is shown that these inaccuracies are confined to the higher thermal frequencies which can be dominant in the initial stages of a transient response and cause deterioration of the numerical solution. Therefore an “adaptive” scheme is proposed in which a full integration order is used for the first few timesteps, after which a reduced integration rule is employed. Recommendations are made for the selection of time integration algorithms, quadrature rules and element dimensioning which are substantiated by the solution of several numerical examples.     

Computer-oriented method for linearization of dynamic models of active spatial mechanisms

A new computer oriented method for linearized dynamic model construction of open-chain active mechanisms is developed. The method is an extension of an existing algorithm for automatic setting of nonlinear dynamic models [1,2], based on general theorems of mechanics. The developed procedure involves vectorial algebraic recursive relations, but not numerical differentiation and other numerical operations which cause cumulative computing errors. Such a method is of essential importance in manipulation robot control synthesis when small perturbations are present. The results of application of the algorithm to three joints of a 6 degrees-of-freedom manipulator system are given.     

Structural changes during pressing of fine nickel powders

Structural changes that take place during pressing of carbonyl powder of nickel are discussed. Particular attention has been paid both to the formation and state of the oxide powder surface during this process.