The zero energy modes problem of the nine-node lagrangian degenerated shell element

The nine-node Lagrangian degenerated shell element under reduced integration exhibits excellent performance, provided that no zero energy modes develop. The zero energy modes developed by the general curved-distorted element are identified and the conditions under which they develop are described. A simple scheme of artificial stiffening of the element to eliminate zero energy modes is investigated. An alternative method of stabilizing the system by means of special stabilizing elements without introducing stiffening effects is developed. In the course of the development of this method, a simple technique to avoid membrane locking and to simultaneously eliminate any zero energy modes in undistorted cylindrical elements is introduced.     

Maximum entropy two-station cyclic queues with multiple general servers

Summary The efficient implementation and extension of various approximate methods for general queueing networks require the study of two-station cyclic queues. In this paper maximum entropy formalism is used to analyse two-station cyclic queues with multiple general servers and a fixed number of jobs. New robust one step recursions for the queue length distribution are derived and asymptotic connections to infinite capacity queues are established. Links with Birth-Death and global balance solutions are determined and extensions to load dependent servers with Bernoulli feedback are presented. Numerical examples provide useful information on how critically system behaviour is affected by the distributional form of service times and simple bounds for typical performance measures such as throughout and mean queue length are defined. Moreover, the utility of the work as a building block for the approximate analysis of a general central server model is demonstrated.Some of the material included in this paper has been orally presented to the International Workshop on Computer Performance Evaluation, 28–30 April 1986, Sophia-Antipolis (INRIA), France [1]This work is jointly supported by Science and Engineering Research Council (SERC), UK and Metron Technology Ltd., UK, under grants GR/D/12422 and GR/AA/772, respectively     

Wind forces on porous elevated panels

Agricultural nets are used in fruit and ornamentals production as covering material in various light structures such as anti-hail and/or anti-frost shields, windbreaks, and coverings of shading or anti-insect structures. There is limited information in the existing standards for the calculation of wind loads on structures with permeable cladding like nets. Moreover, there are few experimental data concerning the wind pressure distribution around air permeable structures. For this reason, the wind-pressure distributions over permeable claddings need to be systematically investigated by field experiments and numerical simulations. In the present work, special full-scale field tests were designed and carried out to measure the wind pressures on experimental scale panels covered by various types of nets and by film. The film covering was functioning as impermeable reference material, for comparative purposes. The forces were measured at a central independent segment of the panel suspended on specially designed spring units by using displacement transducers. The measurements were compared to data obtained from a similar structure covered with impermeable plastic film and against the provisions of relevant standards. The full scale measurements were also compared to computational results obtained by CFD simulations.     

Machine locking of degenerated thin shell elements

The degenerated shell element is one of the most efficient elements for analysing shell structures. However, it is known to result in rather stiff models when used in thin element applications. The phenomena associated with this behaviour are known as locking phenomena. This paper analyses the machine locking mechanism developed in thin to very thin Lagrangian and serendipity elements. The machine related locking phenomenon is distinguished from the shear and membrane locking phenomena. A remedy for the pure machine locking problem is developed for the two elements. The proposed remedy is based on the technique of the modified transverse shear modulus. It is also extended to control shear locking. The proposed technique is shown to completely eliminate machine locking. Also, it is shown to effectively alleviate stiffening effects due to the presence of spurious shear strain.     

LRD and SRD traffic: review of results and open issues for the batch renewal process

The batch renewal process is the least-biased choice of process given only the measures of count correlation and interval correlation at all lags.

This paper reviews the batch renewal process, both for LRD (long-range-dependent) traffic and for SRD (short-range-dependent) traffic in the discrete space–discrete time domain, and in the wider context of general traffic in that domain. It shows some applications of the batch renewal process in simple queues and in queueing network models. The paper concludes with open research problems and issues arising from the discussion.     

A maximum entropy priority approximation for a stableG/G/1 queue

Summary The principle of maximum entropy is used under two different sets of mean value constraints to analyse a stableG/G/1 queue withR priority classes under preemptive-resume (PR) and non-preemptive head-of-line (HOL) scheduling disciplines. New one-step recursions for the maximum entropy state probabilities are established and closed form approximations for the marginal queue length distribution per priority class are derived. To expedite the utility of the maximum entropy solutions exact analysis, based on the generalised exponential (GE) distribution, is used to approximate the marginal mean queue length and idle state probability class constraints for both the PR and HOLG/G/1 priority queues. Moreover, these results are used as building blocks in order to provide new approximate formulae for the mean and coefficient of variation of the effective priority service-time and suggest a maximum entropy algorithm for general open queueing networks with priorities in the context of the reduced occupancy approximation (ROA) method. Numerical examples illustrate the accuracy of the proposed maximum entropy approximations in relation to simulations involving different interarrival-time and service-time distributions per class. Comments on the extension of the work to more complex types of queueing systems are included.This work is sponsored in part by the Science and Engineering Research Council (SERC), UK, under grant GR/D/12422 and in part by the Ministry of Higher Education of the Algerian Government     

Stochastic Analysis of Deterministic Routing Algorithms in the Presence of Self-Similar Traffic

Many performance models for deterministic routing in multicomputer interconnection networks have been derived and analyzed under the assumption of the traditional Poisson stochastic arrival process, which is inherently unable to capture traffic self-similarity revealed by many real-world parallel applications. In an effort towards understanding the network performance under various traffic loads and different design alternatives, this paper presents an analytical model for dimension-ordered routing in k-ary n-cubes when subjected to self-similar traffic. As the service time, blocking probability and waiting time experienced by a message vary from a dimension to another, the design of such a model for dimension-ordered routing poses greater challenges. The developed analytical model is then used to investigate the efficiency of two different ways to organize virtual channels for deterministic routing and to evaluate the impact of self-similar traffic with various Hurst parameters on network performance.     

Tracing correlations of corrosion products and microclimate data on outdoor bronze monuments by Principal Component Analysis

Although the corrosion of outdoor bronzes has been extensively studied for the last decades, there is no quantitative correlation of corrosion products to microclimatic factors. The present work aims to demonstrate how Principal Component Analysis (PCA) can serve this purpose. Thirty corrosion product samples were collected from the bronze monument of Theodoros Kolokotronis (Nafplio, Greece) and analysed using X-Ray Diffractometry (XRD). The quantitative XRD data together with data on surface orientation and exposure to rain or wind were treated by PCA and three distinct groups were found. Each group includes samples of similar composition and microclimate characteristics showing that PCA may give useful information on corrosion mechanisms.     

The σ-hole phenomenon of halogen atoms forms the structural basis of the strong inhibitory potency of C5 halogen substituted glucopyranosyl nucleosides towards glycogen phosphorylase b

C5 halogen substituted glucopyranosyl nucleosides (1-(β-D-glucopyranosyl)-5-X-uracil; X=Cl, Br, I) have been discovered as some of the most potent active site inhibitors of glycogen phosphorylase (GP), with respective K(i) values of 1.02, 3.27, and 1.94 μM. The ability of the halogen atom to form intermolecular electrostatic interactions through the σ-hole phenomenon rather than through steric effects alone forms the structural basis of their improved inhibitory potential relative to the unsubstituted 1-(β-D-glucopyranosyl)uracil (K(i) =12.39 μM), as revealed by X-ray crystallography and modeling calculations exploiting quantum mechanics methods. Good agreement was obtained between kinetics results and relative binding affinities calculated by QM/MM-PBSA methodology for various substitutions at C5. Ex vivo experiments demonstrated that the most potent derivative (X=Cl) toward purified GP has no cytotoxicity and moderate inhibitory potency at the cellular level. In accordance, ADMET property predictions were performed, and suggest decreased polar surface areas as a potential means of improving activity in the cell.