Evaluation of performance enhancing proxies in internet over satellite

Performance enhancing proxies (PEPs) are widely used to improve the performance of TCP over high delay‐bandwidth product links and links with high error probability. In this paper we analyse the performance of using TCP connection splitting in combination with web caching via traces obtained from a commercial satellite system. We examine the resulting performance gain under different scenarios, including the effect of caching, congestion, random loss and file sizes. We show, via analysing our measurements, that the performance gain from using splitting is highly sensitive to random losses and the number of simultaneous connections, and that such sensitivity is alleviated by caching. On the other hand, the use of a splitting proxy enhances the value of web caching in that cache hits result in much more significant performance improvement over cache misses when TCP splitting is used. We also compare the performance of using different versions of HTTP in such a system. Copyright © 2003 John Wiley & Sons, Ltd.     

A model for accurate predictions of self-diffusivities in liquid metals, semimetals, and semiconductors

By combining the modified Stokes-Einstein formula with the authors’ model for the melting-point viscosity, the authors present a model for accurate predictions of self-diffusivity of liquid metallic elements. The model is expressed in terms of well-known physical quantities and has been applied to various liquid metallic elements for which experimental data are available. The results of calculations show that agreement with experimental data is excellent; the uncertainties in the calculations of the self-diffusivities in various liquid metallic elements are equal to the uncertainties associated with experimental measurements. Also, the authors propose an expression for the temperature dependence of self-diffusivity in liquid metallic elements in terms of melting-point temperature. Using the model, self-diffusivity data are predicted for liquid iron, cobalt, nickel, titanium, aluminum, magnesium, silicon, and so forth.     

The importance of IT security

Security and the ‘will to survive’ are basic instincts which are evident in all aspects of life. Businesses in general, exhibit and practice these instincts with varying degrees of success.     

Synthesizing robust systems

Systems should not only be correct but also robust in the sense that they behave reasonably in unexpected situations. This article addresses synthesis of robust reactive systems from temporal specifications. Existing methods allow arbitrary behavior if assumptions in the specification are violated. To overcome this, we define two robustness notions, combine them, and show how to enforce them in synthesis. The first notion applies to safety properties: If safety assumptions are violated temporarily, we require that the system recovers to normal operation with as few errors as possible. The second notion requires that, if liveness assumptions are violated, as many guarantees as possible should be fulfilled nevertheless. We present a synthesis procedure achieving this for the important class of GR(1) specifications, and establish complexity bounds. We also present an implementation of a special case of robustness, and show experimental results.     

Modeling large reversible electric-field-induced strain in ferroelectric materials using 90° orientation switching

Reversible large electric-field-induced strain caused by reversible orientation switchings in BaTiO3 is modeled using the Landau's theory of phase transition. A triple well free energy function is constructed. Each of its minima is associated with one of the polarization orientations involved. Nonlinear constitu- tive laws accounting for reversible orientation switchings and electrostriction effects are obtained by using thermodynamic equilibrium conditions. Hysteretic dynamics of one-dimensional structures is described by coupled nonlinear differential equations. Double hysteretic loops in the electric and me- chanic fields are both successfully modeled. Giant reversible electrostriction is modeled as a conse-quence of reversible orientation switchings via electro-mechanical couplings. Comparisons with ex-perimental results reported in literatures are presented.     

Long latency postural reflexes are under supraspinal dopaminergic control

Scaling of posturally stabilizing long latency (LL) reflexes in tibialis anterior muscles induced by "toe-up" rotational perturbations is abnormal in standing patients with Parkinson's disease. To investigate the contribution of dopaminergic pathways to abnormal scaling, we studied LL reflexes in 22 patients with selective hypodopaminergic syndromes: 10 psychiatric patients taking chronic neuroleptic medication (7 with mild parkinsonism), 8 patients with young-onset Parkinson's disease, and 4 patients with MPTP-induced parkinsonism. Results were compared with those of 10 healthy controls. Stimuli consisted of (a) 10 serial (predictable) perturbations of 4 degrees amplitude, (b) 10 serial (predictable) perturbations of 10 degrees amplitude, and (c) 20 randomly mixed (unpredictable) perturbations of either 4 or 10 degrees amplitude. In normal subjects, LL reflex amplitudes were adapted to match predictable variations in stimulus size, whereas under unpredictable conditions a "default" response emerged that anticipated the 10 degrees perturbation. LL reflex scaling under predictable conditions was intact in patients with neuroleptic-induced parkinsonism and young-onset Parkinson's disease, but the large default LL response under unpredictable conditions was absent. In patients with MPTP-induced parkinsonism, LL reflex scaling was absent during both predictable and unpredictable conditions. We conclude that abnormal scaling of posturally stabilizing LL reflexes is related to decreased supraspinal dopaminergic influence.     

Management Systems: the End of the Beginning?

For many years quality managers have been striving to merge the requirements of management systems into business as usual. Traditional paper-based formats have made this very difficult to achieve. However, the advance of technology and the transfer of information to the electronic medium have provided new opportunities. In the new medium the EFQM Business Excellence Model may be used as a navigational tool to finally solve this problem.     

Physical Modelling of Transport Phenomena in a Delta‐shaped,Four‐strand Tundish with Flow Modifiers

Experiments were conducted in a full‐scale physical model of a delta‐shaped, four‐strand tundish to study the effect of flow modifiers on tundish performance. Two different types of flow modifiers were studied; an existing flow‐modifier and a turbulence‐inhibitor. Their effects were quantified by measuring residence times of fluid in the tundish and residual ratios of inclusions. Although the Turbulence‐Inhibitor appeared to be more effective in guiding flows than the flow‐modifier, the latter gave the longer average residence times and smaller residence time differences between the inner and outer nozzles, which resulted in a higher residual ratio of inclusions.     

Fluid flows in metallurgy—Friend or foe?

Fluid flows are an integral part of many metallurgical processing operations. They affect the viability, effectiveness, and efficiency of many reactors, be they physical or chemical, in nature. The performance characteristics of blast furnaces, steelmaking vessels, ladles, tundishes, and the molds of continuous casting machines are all strongly influenced by such flows of fluids. Similarly, the question of liquid metal quality, and cast microstructures, is bound up with the way fluids have flowed and interacted. In all these aspects, the evolution in our techniques and abilities to model single- and multiphase flows and their attendant heat- and mass-transfer processes has contributed significantly to our understanding, and ability, to control these processes, to design improvements, and to develop new processes. To be ignorant of such matters can doom a processing operation to the scrap heap of metallurgical failures. This article reviews some of the more important aspects of flows in metallurgical reactor systems associated with steel and aluminum processing, by way of a series of typical examples. Roderick I.L. Guthrie is the Director of the McGill Metals Processing Centre (MMPC) and the Macdonald Professor of Metallurgy in the Department of Mining and Metallurgical Engineering, McGill University (Montreal). Leaving Durham Cathedral School, as Head Chorister, in 1953, he later graduated from Nottingham High School in 1960, took an honors degree in metallurgy at the Royal School of Mines, Imperial College, in 1963, and went on to obtain a doctorate in process metallurgy in 1967, under the guidance of Professors Richardson and Bradshaw of the Nuffield and John Percy Research Groups. Since then, Dr. Guthrie has carried out pioneering research in process engineering metallurgy, on a multitude of topics related to the processing of iron and steel, and of light metals. As well as some 350 papers written in collaboration with his many graduate students, he also wrote the textbooks “Engineering in Process Metallurgy” and “The Properties of Liquid Metals” published by Oxford University Press, in 1990. Something of an inventor, Guthrie presently holds some 150 patents on a variety of inventions, one of which is in use, worldwide, for the detection of inclusions in liquid aluminum (LiMCA). Most recently, an in-situ sensor for the three-dimensional scanning of inclusions in liquid steel has been successfully accomplished, also based on the electric sensing zone technique, again in close collaboration with industrial colleagues. Dr. Guthrie’s most recent research interests are concerned with the high-speed, near-net-shape casting of sheet materials via twin-roll, and single belt, casting machines, and the possibility of bulk amorphous sheet materials. His career of 30 years at McGill University has been interspersed with 20 summers as a full-time research consultant to the steel and aluminum industries, plus a number of Visiting Professorships at the Universities of Tohoku, NTH, KTH, Carnegie Mellon, Greenwich, and Guildford. Dr. Guthrie is a Fellow of the Canadian Institute of Mining, a Fellow of the Royal Society of Canada, a Fellow of the Canadian Academy of Engineering, and a Distinguished Member of the Iron and Steel Society. He has been the recipient of numerous Best Paper Awards, including two Henry Marion Howe Medals of the ASM, two John Chipman Awards of the ISS, two Extractive Metallurgy Awards of the TMS, and three Light Metal Awards of TMS and CIM. He has served on the Board of Directors of the Metallurgical Society of Canadian Institute of Mining, Metals and Petroleum Engineers, being its President in 1992.