Reduction of Adjacent Channel Interference in the Standard (AM) Broadcast Band

Side channel interference has been a problem in the standard (AM) broadcast band since the advent of radio broadcasting. The two major contributing factors are: 1) radiation of audio-frequency components greater than 5 kHz, and 2) receivers having poor selectivity characteristics. Other more or less controllable factors are overmodulation of the carrier and inherent distortion in the transmitter.     

Thin Film Adhesion: Effect of Glow Discharge on Substrate

Glow discharge treatment of soda lime glass and silica substrates prior to depositing copper films in oil-free ultra high vacuum as well as in conventional vacuum has been found to increase film adhesion suggesting that gross contamination removal is not the only effect of importance in this method of improving film adhesion. There is evidence from Auger electron emission spectroscopy for sorption of gas from the discharge into the substrate surface layers. Desorption of gases from the substrate also appears to take place. A difference in electron emission from a variety of insulating surfaces following glow discharge was observed in a scanning electron microscope, the sign of the change depending on the nature of the discharge gas. No sputtered material from system components could be detected on the substrate and there was no detectable micro-roughening nor net surface electric charge.     

Birefringent omnidirectional reflector

Anisotropic optical coatings offer unique polarizing properties, unmatched by conventional isotropic devices. Here we demonstrate the fabrication of a birefringent omnidirectional reflector, a type of photonic crystal, which exhibits complete reflection of radiation at 1.1 microm for all incidence angles and polarizations. The thin-film device was deposited from electron-beam evaporated silicon, with refractive-index variation arising from atomic-scale porosity created with glancing-angle deposition. Birefringence was found to enhance the performance of the device compared with its isotropic counterpart by enlarging the photonic bandgap region of omnidirectional reflection.     

Refinement preserving approximations for the design and verification of heterogeneous systems

Embedded systems are electronic devices that function in the context of a real environment, by sensing and reacting to a set of stimuli. Because of their close interaction with the environment, and to simplify their design, different parts of an embedded system are best described using different notations and different techniques. In this case, we say that the system is heterogeneous. We informally refer to the notation and the rules that are used to specify and verify the elements of heterogeneous systems and their collective behavior as a model of computation. In this paper, we consider different classes of relationships between models of computation and discuss their preservation properties with respect to the model's refinement relation and composition operator. In particular, we focus on abstraction and refinement relationships in the form of abstract interpretations and introduce the notion of conservative approximation. We show that, unlike abstract interpretations, conservative approximations preserve refinement verification results from an abstract to a concrete model while avoiding false positives. We also characterize the relationship between abstract interpretations and conservative approximations, and derive necessary and sufficient conditions to obtain a conservative approximation from a pair of abstract interpretations. In addition, we use the inverse of a conservative approximation to identify components that can be used indifferently in several models, thus enabling reuse across models of computation. The concepts described in this paper are illustrated with examples from continuous time and discrete time models of computation.     

Commercial activated carbon for the catalytic production of hydrogen via the sulfur-Iodine thermochemical water splitting cycle

Eight commercial activated carbon catalysts were examined for their catalytic activity to decompose hydroiodic acid (HI) to produce hydrogen; a key reaction in the sulfur-iodine (S-I) thermochemical water splitting cycle. Activity was examined under a temperature ramp from 473 to 773 K. No statistically significant correlation was found between the measured catalyst sample properties and catalytic activity. Four of the eight samples were examined for one week of continuous operation at 723 K. All samples appeared to be stable over the period of examination.     

The metallurgy,mechanics, modelling and assessment of dissimilar material brazed joints

At the heart of any procedure for modelling and assessing the design or failure of dissimilar material brazed joints there must be a basic understanding of the metallurgy and mechanics of the joint. This paper is about developing this understanding and addressing the issues faced with modelling and predicting failure in real dissimilar material brazed joints and the challenges still to be overcome in many cases. An understanding of the key metallurgical features of such joints in relation to finite element modelling is presented in addition to a study of the mechanics and stress state at an abrupt interface between two materials. A discussion is also presented on why elastic singularities do not exist based on a consideration of the assumption of an abrupt change in material properties and plasticity in the vicinity of the joint. In terms of modelling real dissimilar material brazed joints; there are several barriers to accurately capturing the stress state in the region of the joint and across the brazed layer and these are discussed in relation to a metallurgical study of a real dissimilar material brazed joint. However, this does not preclude using a simplified modelling approach with a representative braze layer in design and failure assessment away from the interface. In addition modelling strategies and techniques for assessing the various failure mechanisms of dissimilar material brazed joints are discussed. The findings from this paper are applicable to dissimilar material brazed joints found in a range of applications; however the references listed are primarily focussed on work in fusion research and development.     

Designing intelligent systems to handle system failures: Enhancing explanatory power with less restrictive user interfaces and deep explanations

This research empirically investigates the design choices that can be made to facilitate problem solving when intelligent systems fail. One way is to provide deep explanations, which are explanations that justify system actions. Another way is to manipulate system restrictiveness of the user interface. An experiment was conducted to investigate the effectiveness of deep explanation support, as well as manipulations of system restrictiveness. Results suggest that the less restrictive system was more effective for problem‐solving situations where system failure occurred. In addition, deep explanations were found to be somewhat helpful in system understanding, and this, in turn, led to improved problem‐solving performance.     

Field Measurements of Mean Velocity Characteristics of a Large-Diameter Swirling Jet

Full-scale field acoustic Doppler velocimeter measurements of the radial, axial, and tangential flow components were undertaken in a large-diameter turbulent swirling jet generated by a raft-mounted axial flow-mixing propeller discharging through a draft tube during isothermal and stratified conditions. The results were compared with classical jet theory and showed significant differences in the zone of flow establishment though similar behavior in the zone where established flow was found. It was concluded that the efflux from the axial flow-mixing propeller could not be described adequately by conventional jet theory due to the jet size and swirling characteristics.     

Book reviews

In some parts of Europe, stone wall field boundaries pervade agricultural landscapes, yet despite their prominence there has been very little research into field boundary walls anywhere. However, these anthropogenic features within cultural landscapes may offer insights into current debates on ‘novel’ ecosystems because of their artifice, their longevity in the landscape particularly in remote or exposed regions, and their morphology. In a review of the available, published literature in Europe, it was found that no publications exist that examine or illustrate specific ecological characteristics of field boundary stone walls, despite this longevity. Using examples from Ireland, where these structures are locally abundant, this paper aims first to draw attention to the poorly representative literature on this topic, and thus stimulate research that will detail the potential ecological characteristics of these ancient forms of field boundary. It then briefly explores the potential for these walls to be considered as ‘novel’ ecosystems within current debates on the issue.