The Gueorgi Nadjakov Lecture Negative-U defects in chalcogenide glasses: elusive or non-existent?

The negative-U model for chalcogenide glasses has traditionally been interpreted in terms of charged co-ordination defects that lead to discrete electronic energy levels in the band gap. However, the failure of these levels to be revealed in the optical absorption spectra of pure a-As₂S₃ samples has recently led to a questioning of the actual occurrence of such defects. We therefore review the relevant experimental evidence and point out that, since the density of the charged defects is lower than the density of localized tail states, failure to resolve the former in direct optical spectroscopy does not constitute sufficient grounds for doubting their presence in the material.     

Passive designs and strategies for low-cost housing using simulation-based optimization and different thermal comfort criteria

An optimum design of low-cost housing offers low-income urban inhabitants great opportunities to obtain a shelter at an affordable price and acceptable indoor thermal conditions. In this paper, the design and operation of a low-cost dwelling were numerically optimized using a simulation-based approach. Three multi-objective cost functions including construction cost, thermal comfort performance and 50-year operating cost were applied for naturally ventilated and air-conditioned buildings. Thermal environment inside the house was controlled and assessed by two thermal comfort models. Optimization problems which consist of 18 design parameters and 6 ventilation strategies were examined by two population-based probabilistic optimization algorithms (particle swarm optimization and hybrid algorithm). Optimum designs corresponding to each objective function, differences in optimal solutions, energy saving by the adaptive comfort approach and optimization effectiveness were outlined. The optimization method used in this paper shows a considerable potential of comfort improvement, energy saving and operating cost reduction.     

Relation between the optoelectronic parameters of amorphous hydrogenated silicon films deposited at high temperatures and their microstructure

The optical modulation spectra and photoconductivity of a number of a-Si:H films containing 5–6 at.% hydrogen with different microstructure parameters (R=0.2–0.8) have been investigated. Information about the defect density in the films, spreading of band edges (tailing), the gap width, and the product of the mobility and the lifetime of the electrons has been obtained. The microstructure is shown to have a substantial effect on the optoelectronic parameters of films with low hydrogen content. Fiz. Tekh. Poluprovodn. 32, 121–123 (January 1998)     

On the revolutionary nature of the operant as a unit of behavioral selection.

The term operant is used in many different but related ways. Implicit in most uses is the concept of the operant as a behavioral unit. Historical origins of the operant unit are traced in Skinner's early work on the relational character of behavior as a subject matter in its own right. An operant unit in an individual's repertoire is compared with a species as an evolutionary unit or taxon. It is suggested that usage of the term class in the definition of operants leads to confusion regarding the operant as category vs the operant as taxon. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Flash welding and the testing of shafts

Abstract

This paper describes investigations carried out on a manually operated flash welder, including quality control by mechanical and ultrasonic testing.     

Structural Analysis and Validation of a Smart Pantograph Mast Concept

To progress the development of deployable, lightweight infrastructure for relief and recovery efforts in the aftermath of natural and man‐made disasters, this article develops a proof of concept for a smart mast that leverages the versatility of pantograph systems and advances in sensor, actuator, and informatics technologies. More specifically the article addresses key design criteria of transportability, deployability, global stability, and site responsiveness through the development of analytical expressions and control framework, and reduced‐scale physical model testing. The case study, a three‐tiered tetrahedral mast is composed of three connected sets of planar pantograph systems and deployed by single actuator located between two of the three mast supports. The article discusses the optimum configurations for the individual design criteria and trade‐offs to be made between compactness, overturning, and operational power. The design, construction, and experimentation with a 73‐cm tall fully deployed physical model reinforce the feasibility of the presented smart mast concept.     

Antimicrobial resistance among Campylobacter jejuni isolated from raw poultry meat at retail level in Denmark

Campylobacter jejuni isolated from raw poultry meat collected at retail shops in Denmark in the period 1996-2003 were tested for susceptibility to seven antimicrobial agents. The food samples consisted of raw chicken meat and other raw poultry meat of domestic or imported origin. The highest levels of resistance among C. jejuni were observed for tetracycline, nalidixic acid and ciprofloxacin, whereas macrolide resistance was rarely detected. C. jejuni originating from other poultry meat (mainly duck and turkey meat) exhibited the highest occurrences of antimicrobial resistance monitored; approximately one third of the isolates were tetracycline resistant (N=100). Among chicken meat isolates, the occurrence of tetracycline resistance was significantly higher (P<0.005) in C. jejuni isolated from imported chicken meat (N=88) than in C. jejuni from Danish chicken meat (N=367). The same tendency was observed for chloramphenicol, nalidixic acid and ciprofloxacin (P<0.05). The trends in resistance in the period 1996-2003 among C. jejuni isolates from chicken meat indicate a decrease in the occurrence of resistance towards fluoroquinolones. This may be due to reduced application of fluoroquinolones for food animals. Monitoring of the occurrence of antimicrobial resistance in C. jejuni isolated from raw uncooked poultry has been performed on a yearly basis since 1996, thus providing useful insight into consumer exposure to antimicrobial-resistant C. jejuni.