An improved covariance assignment theory for discrete systems

For discrete systems, the set of all state covariances X which can be assigned to the closed-loop system via a dynamic controller is characterized explicitly. For any assignable state covariance X , the set of all controllers that assign this X to the closed-loop system is parameterized with an arbitrary orthonormal matrix U of proper dimension     

Optimal Hybrid Control for Structures

A new method for integrated design of passive and active elements is presented. Rather than the existing qualitative selection of parameters for passive elements, a quantitative approach is proposed that finds optimal active and passive parameters with respect to an H₂/H_∞ performance requirement. This new approach automatically yields passive designs when the given performance limits are high enough and active (hybrid) designs when the given performance constraints are stringent. Furthermore, our algorithm finds the special performance requirement (the peak of the frequency response) that cannot be satisfied by any passive design. Hence this article shows how to determine when control is required rather than assuming a priori that it is or is not required. A simple design method given herein yields either passive, active, or hybrid designs depending only on the level of the performance constraints that are specified in the statement of the problem.     

Atomistic Origin of the Enhanced Crystallization Speed and n‐Type Conductivity in Bi‐doped Ge‐Sb‐Te Phase‐Change Materials

Phase‐change alloys are the functional materials at the heart of an emerging digital‐storage technology. The GeTe‐Sb₂Te₃ pseudo‐binary systems, in particular the composition Ge₂Sb₂Te₅ (GST), are one of a handful of materials which meet the unique requirements of a stable amorphous phase, rapid amorphous‐to‐crystalline phase transition, and significant contrasts in optical and electrical properties between material states. The properties of GST can be optimized by doping with p‐block elements, of which Bi has interesting effects on the crystallization kinetics and electrical properties. A comprehensive simulational study of Bi‐doped GST is carried out, looking at trends in behavior and properties as a function of dopant concentration. The results reveal how Bi integrates into the host matrix, and provide insight into its enhancement of the crystallization speed. A straightforward explanation is proposed for the reversal of the charge‐carrier sign beyond a critical doping threshold. The effect of Bi on the optical properties of GST is also investigated. The microscopic insight from this study may assist in the future selection of dopants to optimize the phase‐change properties of GST, and also of other PCMs, and the general methods employed in this work should be applicable to the study of related materials, for example, doped chalcogenide glasses.     

38—THE EFFECTS OF PLANAR CRIMP IN THE MEASUREMENT OF THE MECHANICAL PROPERTIES OF FIBRES,FILAMENTS, AND YARNS

A theoretical investigation of the tensile, flexural and torsional behaviour of crimped filaments has been made; the relationships describing the filament behaviour are presented in graphical and in analytical form, and are verified experimentally. Two results are of particular importance in routine textile testing: it is shown that the Young's modulus of staple fibres measured with a tensile-testing machine is not subject to significant error caused by crimp; and a new expression is proposed which enables the optimum tension for the routine yarn-crimp test to be calculated.     

Integrating instrumentation and control design

Instrument precision is characterized by its signal-to-noise ratio, employing a new noise model. In this paper, this measure of precision of each instrument is used to characterize instrumentation, and an integration is achieved by jointly optimizing the feedback control law and the instrument signal-to-noise ratios to meet control system performance requirements. Iterative algorithms are proposed to find locally optimal solutions. Assuming that the signal-to-noise ratio is directly related to the instrumentation cost, this integration provides a systematic procedure to design a low cost control system. More importantly, this procedure identifies the performance-limiting components of a control system, identifies where to spend money on a system, and generates component design requirements from closed loop system performance criteria.     

Mild traumatic brain injury--the Fife perspective

Excretion was studied of catecholamines and diphenilamine (DOPA) in 310 patients with carcinoma of the stomach and large intestine and 43 patients with non-malignant diseases. The oncological patients showed decrease in activity of the mediator link of the sympathoadrenal system (SAS) as well as its reserves but there was no association with sex, age, location or histological structure. Three types of SAS functioning were identified, such as compensation, overstrain and emaciation. Surgical intervention led to activation of the hormonal link and exhaustion of the system's reserves. Two kinds of sympathoadrenal response to stress were described--adequate and inadequate. In the former type, phases of stress remain as they are, unchanged, as are time periods of formation thereof, while under the latter one time periods of the phases formation or formation thereof get disordered.     

Studying hidden curricula: developing a perspective in the light of postmodern insights

This article provides an overview of research into the hidden curriculum. Following a consideration of functionalist, liberal and critical research studies, I focus in particular on recent insights which have arisen from postmodern thinking. In the light of postmodernism, I identify a personal perspective on how to study the hidden curriculum which moves beyond the established boundaries of discrete research paradigms.