Spectral predictions for pulse interval and width modulation

An expression for the frequency spectrum of pulse interval and width modulation (PIWM) is presented. Experimental results obtained have shown close agreement with spectral predictions from the formula. Performance figures are also included from a practical PIWM optical-fibre transmission system intended for use with TV and video signals.<>     

Rogue Servers

Rogue servers are a constant threat and pose a variety of problems for the IT security team. This article summarises the threats that come from not managing rogue servers and gives prevention and detection tips.     

What difference a decade makes? [management issues]

This paper discusses the results of a survey conducted by a team of researchers from Ashridge Business School that aimed to determine how managers and management practices have changed over the last 10 years. The survey considered a range of issues related to three broad themes, namely, organizational challenges, individual challenges, and the challenges of learning and development. The survey found that for the vast majority of managers in all industry sectors, the pressures of running an organization that is profitable, growing and competitive have not gone away. However, evidence suggests that these issues are perhaps slightly less dominant on the management agenda than in 1994. The survey concluded that there is a good deal that organizations might do to create a better working environment.     

Designing the MPC105 PCI bridge/memory controller

The MPC105 peripheral component interconnection bridge/memory controller provides a platform-specification-compliant bridge between Power PC microprocessors and the PCI bus. With it, designers can create systems using peripherals already designed for a variety of standard PC interfaces. This bridge chip also integrates a secondary cache controller and high-performance memory controller that supports DRAM or synchronous DRAM and ROM or flash ROM     

Experimental results of the erosion of molybdenum due to blistering by He+ bombardment

We report some preliminary measurement of the erosion rate of plasma dumps when bombarded with 100 keV He⁺ ions at high power density ( 1 MW/m²). The expected erosion rates, based on measurements of He blistering that were made at lower power density ( 0.3 MW/m²), indicate a potentially serious problem for fusion reactors. Our tests use a reactorlike power density and produce He blisters at a rate that is slower than predicted by 2 to 4 orders of magnitude, depending on the temperature of the molybdenum target.     

The behavior of small fatigue cracks at notches in corrosive environments

The behavior of small cracks growing out of the roots of blunt notches in compact type specimens of an austenitic steel was characterized under fatigue loading in wet H ₂ plus air environment. The growth rates of cracks in the size range of 0.125 mm to 0.75 mm were up to two orders of magnitude higher than the rates expected for conventional cracks at equal stress intensity range, K. It was also observed that the small cracks grew at these fast rates only in corrosive environments when the loading frequency was 0.02 Hz or less. At a frequency of 10 Hz, the behavior was in agreement with the trend predicted for conventional size cracks.The above observations are rationalized in terms of the breakdown of the concept of a single parameter representation of the crack tip stress and strain field by K or in terms of differences in crack tip environments between small and long cracks for the same bulk environment. A simple engineering model is proposed which adequately represents the observed small crack growth behavior.

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Résumé On a procédé à la caractérisation, sous charges de fatigue en atmosphère humide de H ₂ et d'air, de petites fissures se développant à partir des racines d'entailles arrondies dans des éprouvettes compactes.Les vitesses de croissance des fissures d'une taille allant de 0,125 à 0,750 mm se sont révélé être de deux ordres de grandeur plus grandes que les vitesses prévues dans le cas de fissures conventionnelle, soumises aux mêmes variations de l'intensité de contrainte K. On a également observé que de petites fissures croissaient à ces grandes vitesses seulement dans des atmosphères corrosives, lorsque la fréquence de sollicitation était de 0,02 Hz ou moins. A la fréquence de 10 Hz, le comportement observé s'est trouvé en accord avec les tendances prévues pour des fissures de taille conventionnelle.Les observations ci-dessus sont rationnalisées en un élargissement du concept de représentation monoparamétrique par le facteur K du champ de contraintes et de dilatation à l'extrémité de la fissure, ou en termes des différences rencontrées dans l'environnement local de l'extrémité d'une fissure, selon que celle-ci est longue ou courte, et ce dans un même environnement global.On propose un modèle simple utilisable en pratique, pour représenter de manière adéquate le comportement à la croissance observé pour des petites fissures.

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Metallurgy Department     

RelativizedNC

This paper introduces a notion of relativized depth for circuit families and discusses issues regarding uniform families of relativized circuits. This allows us to define a version of relativizedNC and compare it under various oracles with relativizedL, NL, andP. We see thatNC ₁ is properly contained inL if and only if there exists an oracleA such thatNC ₁ ^A is properly contained inL ^A . There is an oracleA where the hierarchy collapses,NC ₁ ^A = NC ^A , and another whereNC ₁ ^A NC ₂ ^A NC ^A P ^A . We then construct anA so that, for anyk, NC ₁ ^A contains a set not inNSPACE ^A (O(n ^k )), suggesting that the notion of relativized space is too weak or that of relativized depth is too strong.     

Potentiostatic step experiments on pasted Pb-Sb and Pb-Sn-Ca electrodes

A range of cyclic electrochemical experiments have been carried out on electrodes of porous PbO₂ supported on a number of Pb-Sb and Pb-Sn-Ca alloys using micro-computer controlled potentiostatic stepping techniques. The results show that, in certain cases, the differences in electrochemical behaviour of the PbO₂ can be interpreted as being due to the effect of the support alloy.     

Carbon fiber structure and stability studies

A study has been made of the thermal-oxidative stability of several commercially available carbon fibers. Significant differences in the weight loss behavior were observed in air aging studies run on the bare fibers at 600°F (589 K). The stability of high temperature laminates, such as those based on NR-150 polyimide precursor solutions, was found to be directly affected by the stability of the reinforcing carbon fibers. In studies carried out to determine the reasons for carbon fiber instability, residual sodium sulfate was found to be the principle destabilizing factor. A mechanism whereby the sodium sulfate promotes the oxidation of carbon in the presence of air is proposed.