Warning procedures for systems that are improving

Nowadays it is quite usual that systems are correctly maintained. This leads to a decreasing number of failures for the system. In this paper we discuss how to establish warning procedures that take into account features giving the chance of detecting eventual changes of trend in the systems and allowing taking measures before too much damage has actually happened. The proposed procedure is applied to the study of the reliability and maintenance of the railway electric supply system. In this kind of systems, complex and extended, testing the performance of the system and effectiveness of the maintenance tasks has special interest. Copyright © 2007 John Wiley & Sons, Ltd.     

Robust speed estimation and control of an induction motor drive based on artificial neural networks

In this paper, a speed estimation and control scheme of an induction motor drive based on an indirect field‐oriented control is presented. On one hand, a rotor speed estimator based on an artificial neural network is proposed, and on the other hand, a control strategy based on the sliding‐mode controller type is proposed. The stability analysis of the presented control scheme under parameter uncertainties and load disturbances is provided using the Lyapunov stability theory. Finally, simulated results show that the presented controller with the proposed observer provides high‐performance dynamic characteristics and that this scheme is robust with respect to plant parameter variations and external load disturbances. Copyright © 2007 John Wiley & Sons, Ltd.     

Calorimetric Study of the Desorption and Phases of 3He And 4He Adsorbed on Two Layers of H2-plated Graphite Above 0.2K

We have conducted new heat capacity studies of films of ³ He and ⁴ He adsorbed on 2.15 layers of hydrogen plating exfoliated graphite for temperatures T > 0.2K and coverages (n) over the entire first layer and beginning of the second layer. Low-density ³ He films show two-dimensional Fermi fluid behavior with no liquid-vapor condensation below 0.9K. We have mapped the n-T melting tine and estimated monolayer completion density using heat capacity isotherms. By fitting ³ He films' desorption specific heats to a theoretical model, we have calculated the ³ He binding energy (21.3K to 21. 7K) and compare it to a previous measurement for ⁴ He films on the same substrate (25.1K to 25.5K).     

Fixing Letrec: A Faithful Yet Efficient Implementation of Scheme's Recursive Binding Construct

A Scheme letrec expression is easily converted into more primitive constructs via a straightforward transformation given in the Revised⁵ Report. This transformation, unfortunately, introduces assignments that can impede the generation of efficient code. This article presents a more judicious transformation that preserves the semantics of the revised report transformation and also detects invalid references and assignments to left-hand-side variables, yet enables the compiler to generate efficient code. A variant of letrec that enforces left-to-right evaluation of bindings is also presented and shown to add virtually no overhead. A preliminary version of this article was presented at the 2002 Workshop on Scheme and Functional Programming [15].     

Precipitation and densification of magnetic iron compounds from aqueous solutions at room temperature

The advantages of generating stable and compact spinel-type precipitates from aqueous solutions at ambient temperature, instead of the amorphous and voluminous hydroxides obtained by conventional treatment of effluents are supported by experimental evidence. As a first step, the study of magnetite formation by controlled aerial oxidation of ferrous solutions at ambient temperature was considered. The parameters studied were: aerial oxidation intensity, precipitation pH, SO₄²⁻ concentration, initial Fe²⁺ concentration and aging of the sludges. The results suggest a close relation between precipitation pH and the kinetics of conversion of intermediate green rust-II into γ-FeOOH and/or Fe₃O₄. A precipitation pH between 10 and 11 and a well-controlled oxidant environment achieved by a moderate aeration of the solutions promoted suitable physical and chemical stability characteristics of quickly generated magnetite at ambient temperature. Furthermore, the minimum concentration of ferrous ions conducive to magnetite formation will be limited by the preexistent amount of dissolved oxygen in the starting solutions. Generated information was related to a laboratory-scale simulation of the `Recycle Process', but applied to the generation and densification of magnetic sludges. The stability conditions of iron precipitates allowed a better understanding of those transformations that occur in the stages of this process: aerated alkaline precipitation, solid/liquid separation, chemical conditioning of settled solids and their recycling to the precipitation stage.     

The High Temperature Phase Diagram of Single-Layer 3He-4He Mixtures

We present resugts of an extensive investigation with heat capacity measurements of the first layer phases of ³He-⁴He mixtures adsorbed on graphite preplated with two layers of H₂, for a wide range of coverages, and for temperatures between 0.2 K and 2.0 K. We observe the evolution of the twodimensional liquid(L)-vapor(V) coexistence region as a function of the ³He molar fraction(x). The L-V critical points, starting with 0.9 K at x=0, move to lower temperatures and the density of the self-bound liquid decreases as x increases, pointing towards a limiting value of x for L-V coexistence, in agreement with theoretical expectations. At densities higher than those producing L-V coexistence, we observe the onset of transitions to a phase present in the mixtures but apparently absent in the pure isotopic cases. Possible interpretations of the data will be discussed.     

Neuropsychological abnormalities among HIV-infected individuals in a community-based sample.

The purpose of this study was to determine the nature and extent of neuropsychological abnormalities among HIV-infected individuals and to examine the interrelationships between measures of cognitive functions and the factors that predict neuropsychological abnormalities. The study focused on cross-sectional data gathered in a multidisciplinary research clinic from 200 HIV-infected (HIV+) men and women recruited from primary medical care settings. Composite scores representing six cognitive domains were derived from the neuropsychological test data. Scores of memory, fluency, spatial, and frontal functions could be predicted by independent assessment of participants' verbal and psychomotor speed abilities. Basic verbal ability itself was predicted by education, race, and handedness, whereas speed was predicted by age, CD4+ cell counts, and a lifetime history of major depression. This model of effects is consistent with the hypothesis that psychomotor slowing is central to mild cognitive disorder in HIV infection and that such changes are associated with markers of the severity of systemic infection. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Validation of Lag Time and Growth Rate Models for Salmonella Typhimurium: Acceptable Prediction Zone Method

ABSTRACT: The prediction bias (B_f) and accuracy (A_f) factors are the most widely used measures of performance of predictive models for food pathogens. However, B_f and A_f have limitations that can produce inaccurate assessments of model performance. Consequently, an objective of the current study was to develop a method for quantifying model performance that overcomes limitations of B_f and A_f. Performance of published lag time and growth rate models for Salmonella Typhimurium were evaluated for data used in model development and for data not used in model development but that were inside (interpolation) or outside (extrapolation) the response surface of the models. In addition, performance of published models for growth of Escherichia coli O157:H7 was evaluated for data used in model development. Observed and predicted values were compared using B_f, A_f, and pRE, a new performance factor that quantified the proportion of relative errors (RE) in an acceptable prediction zone from an RE of‐0.3 (fail‐safe) to 0.15 (fail‐dangerous). A decision diagram based on criteria for test data and model performance was used to validate the models. When B_f and A_f were used to quantify model performance, all models were validated. In contrast, when pRE was used to evaluate model performance, 2 models for S. Typhimurium and both models for E. coli O157:H7 failed validation. Overall, pRE was a more sensitive and reliable indicator of model performance than B_f and A_f because unacceptable pRE, which indicated a performance problem, were obtained for 8 of 20 evaluations, all of which had acceptable B_f and A_f. Alimitation of pRE was the inability to distinguish between global and regional prediction problems. However, when used in combination with an RE plot, pRE provided a complete evaluation of model performance that overcame limitations of B_f and A_f.     

GSE: A flexible,yet efficient,encapsulation for IP over DVB‐S2 continuous generic streams

The second‐generation specification for Digital Video Broadcast over Satellite, DVB‐S2, defines an improved and adaptive physical layer. A new framing structure at the link layer, known as the generic stream (GS), is introduced offering an alternative to the well‐known MPEG transport stream (TS). This paper presents the requirements for and the design of an encapsulation protocol to transport IPv4 and IPv6 datagrams and other network protocol packets directly over DVB‐S2 using this GS profile. The resulting generic stream encapsulation (GSE) is a novel method that provides flexible encapsulation with support for fragmentation. A flexible extension header format allows GSE to carry additional header information, suitable for enhanced features, such as link layer encryption and IP header compression. The paper assesses GSE performance by simulation using realistic traffic profiles and attenuation fading. This demonstrates considerable improvement in efficiency compared with the MPE/MPEG‐2 TS, especially when used with adaptive coding and modulation (ACM). Although designed for DVB‐S2 systems, the new encapsulation is suitable for other second‐generation physical layer standards. Copyright © 2008 John Wiley & Sons, Ltd.     

努尔苏丹2030年规划(2)——策略性干预

本文介绍了英国空间句法公司于2020年为哈萨克斯坦首都努尔苏丹市制定的规划设计方案,着重介绍了为实现2030年规划愿景所需要的战略性设计干预内容。具体包括:(1)宜居性,改善关键社会基础设施的可达性;(2)可持续性,通过翻新现有建筑物来减少能源消耗;(3)健康,鼓励步行与非机动车出行,改善医疗、公共交通和体育设施的易得性;减少城市对汽车的依赖,并创建舒适、有吸引力的城市空间网络。