Analysis of a hybrid noise control system for a duct

This letter proposes the combination of a passive muffler and an active noise control system for the control of very high‐level noise in ducts used with large industrial fans and similar equipment. The analysis of such a hybrid system is presented making use of electroacoustic analogies and the transfer matrix method. It turns out that a passive muffler upstream of the input microphone can indeed lower the acoustic pressure and, hence, the power requirement of the auxiliary source. The parameter that needs to be optimized (or maximized) for this purpose is a certain velocity ratio that can readily be evaluated in a closed form, making it more or less straightforward to synthesize the configuration of an effective passive muffler to go with the active noise control system.

Low Voltage Firing Characteristics of a Simple Triggered Vacuum Gap

The firing characteristics of the simple triggered vacuum gap (TVG) using lead zirconate titanate as dielectric material in the triggered gap are described. This TVG has a long life of about 2000 firings without appreciable deterioration of the electrical properties for main discharge currents upto 3 kA and is much superior to these made with Supramica (Mycalex Corporation of America) and silicon carbide as used in our earlier investigations. The effects of the variation of trigger voltage, trigger curcit, trigger pulse duration, trigger pulse energy, main gap voltage, main gap separation and main circuit energy on the firing characteristics have been studied. Trigger resistance progressively decreases with the number of firings of the trigger gap and as well as of the main gap. This decrease in the trigger resistance is more pronounced for main discharge currents exceeding 10 kA. The minimum trigger current required for reliable firing decreases with increase of trigger voltage upto a threshold value of 1.2 kV and there-onwards saturates at 3.0 A. This value is less than that obtained with Supramica as dielectric material. One hundred percent firing probability of the TVG at main gap voltages as low as 50 V is possible and this low voltage breakdown of the main gap appears to be similar to the breakdown at low pressures between moving plasma by other workers. and the cold electrodes immersed in it, as reported.

Assembly and inspection of liquid crystal on silicon devices

Liquid crystal on silicon (LCOS) is one of the most exciting technologies, combining the optical modulation characteristics of liquid crystals with the power and compactness of a silicon backplane. The objective of our work is to improve cell assembly and inspection methods by introducing new equipment for automated assembly and by using an optical inspection microscope. A Suss-Micro'Tec Universal device bonder is used for precision assembly and device packaging and an Olympus BX51 high resolution microscope is employed for device inspection. ©2009 Optical Society of America.

Bragg diffraction of multilayer volume holographic gratings under ultrashort laser pulse readout

The multilayer coupled wave theory is extended to systematically investigate the diffraction properties of multilayer volume holographic gratings (MVHGs) under ultrashort laser pulse readout. Solutions for the diffracted and transmitted intensities, diffraction efficiency, and the grating bandwidth are obtained in transmission MVHGs. It is shown that the diffraction characteristics depend not only on the input pulse duration but also on the number and thickness of grating layers and the gaps between holographic layers. This analysis can be implemented as a useful tool to aid with the design of multilayer volume grating-based devices employed in optical communications, pulse shaping, and processing. (C) 2008 Optical Society of America

Dynamic behaviour of gas jets in laser cutting

The efficiency and overall quality of a laser cutting operation is highly dependent on the assist gas parameters. The desire to cut thicker material has led to the observation of small process operating windows for thicker sections. The gas jet delivery and subsequent dynamical behaviour have significant effects on the cutting operation as the sample thickness increases. To date, few workers have examined the dynamical behaviour of the gas jet. This paper examines the characteristics of oxygen gas jets during CO2 laser cutting of steel. Particular emphasis is placed on the mass transfer effects that are operating within the kerf. Oxygen concentration levels within a model kerf are measured for various laser cutting set-ups. The results show a substantial reduction in oxygen concentration within the kerf. A system for oxygen concentration maintenance is described and cutting results from this system are compared with conventional techniques for cutting steels in the range 10 to 20mm thick. A theoretical analysis of turbulent mass transfer within a kerf is presented and compared with experiment.

Short reflections on the history of African communication

This article aims to propose a chronological subdivision in the history of African communication. African communication today is one of the most important axes for implementing development strategies, sustaining education, health, and schooling programmes, and so on. However, many of these programmes fail due to a lack of or ineffective communication between international organisations, local elite and lay people. The reasons for this situation must be found in Africa’s history of communication, which has undergone radical transformations in its different phases. Using the functionalist analysis drawn up by Jakobson, this article proposes a new chronological subdivision of Africa’s history of communication, reflecting on the current contradictions in contemporary communication in Africa.

Body size differs in workers produced across time and is associated with variation in the quantity and composition of larval food in Nannotrigona perilampoides (Hymenoptera, Meliponini)

Although variation in body size has been recently reported in stingless bees (Meliponini), empirical evidence evaluating possible factors related to such variation is lacking, and thus it is not clear if it may have an adaptive significance. We evaluated if variation in the body size and weight of workers of stingless bees fluctuates across a seasonal pattern and if this could be related to characteristics of the food consumed during the larval stage. The weight of larval provisions, their protein, and sugar content were evaluated in four colonies of Nannotrigona perilampoides every 2 months across 1 year. Worker-destined larvae from the same combs were allowed to develop and were sampled as callow workers to determine their weight and size using morphometric data. The weight and size of workers were highly correlated and varied across the seasons in established colonies, suggesting that size variation cycles across the year in stingless bees. An increase in the protein content and, to a lesser degree, the quantity of larval food were positively linked to variation in body weight and size; food with richer protein content resulted in larger and heavier workers. This study provides the first evidence of an effect of the quantity and composition of larval food on the size of workers in stingless bees. Although body weight and size of workers differed across seasons, they were not readily noticeable as changes seem to occur as a continuum across the year. Since size polymorphism was of a larger magnitude across time but not within age cohorts and as it was highly determined by food resources, it may not be an adaptive feature in stingless bees. However, more studies are needed to determine the role of the cyclical change in worker body size on colony performance and thus its adaptive significance in stingless bees.

D'objet de risée à symbole de l'Amérique : la télévision à travers le cinéma américain (1970 à 1999)

Cette analyse dresse le portrait des différentes représentations de la télévision à travers le cinéma américain de 1970 à 1999. Ce travail porte sur un corpus de quatorze films et s’intéresse à quatre dimensions de la télévision : l’appareil électrique, le téléspectateur, le contenu et l’univers professionnel. Les hypothèses soulevées sont que la télévision est majoritairement présentée de façon négative, que les représentations s’inscrivent dans un contexte culturel précis et qu’il y a un consensus entre les écrits universitaires et les cinéastes au sujet de l’écran cathodique. Bien que certaines critiques soient récurrentes d’une décennie à l’autre, il y a une évolution des représentations. Dans les années 1970, la télévision est un objet de risée. Son contenu est caricaturé et les professionnels qui travaillent pour la télévision sont personnifiés comme des êtres incompétents. Dans les années 1980, le petit écran est montré comme un objet dangereux. Sa très grande popularité en ferait un puissant diffuseur idéologique qui transforme tout en spectacle même la mort. Cette même popularité servira de prétexte aux cinéastes des années 1990 pour utiliser la télévision comme symbole de l’Amérique. Le portrait est peu flatteur : une Amérique corrompue, violente et en manque d’idéaux. Cette analyse montre également qu’au fil des décennies, les mêmes idées circulent entre cinéastes et penseurs américains. Enfin, cette attitude par rapport à la télévision est d’ailleurs symptomatique d’un mépris de l’élite intellectuel envers l’art populaire.

The Gainers Strike: Capitalist Offensive, Militancy, and the Politics of Industrial Relations in Canada

The history of Alberta's meatpacking workers is closely connected with the broader historical struggles of the working class in North America. Like their counterparts from the packinghouses in Toronto and Montreal, the workers of Calgary and Edmonton organized and fought for union recognition between 1911 and 1920, thus joining a labour revolt that was spreading throughout Europe and North America in the wake of World War I and the October Revolution. They faced stiff resistance.

Commitment of women industrial workers with special reference to electronics industry in Kerala

In this study of workers of the two industrial units, it has been found that the women workers are more committed to the organization than the men workers. The organizational commitment has been a popular research topic among organizational sociologists, industrial psychologists and labour relations specialists. Much of the early research was directed on organizational commitment of men workers and studies on organizational commitment of women workers were less when compared to that of men workers. The results of this study is partially supported by the findings of Aranya and Jacobson (1975) who found that parental responsibility is linked with maintaining stable patterns of employment.

"Profile of Industrial workers in Kerala - A Comparative Study of the Socioeconomic Profile of Workers in Traditional and Modern Industries

The objective of this study is to assess the changes that have been taking place in the socio-economic profile of organized industrial workers of Kerala in the context of the changes that have been taking place in the state's industrial structure. with this object in view, the study seeks to find out the similarities and differences in the profile of workers belonging to two Segments of factory sector industries in Kerala viz., modern and traditional segments. It also seeks to examine the factors leading to the differences in profile, if any, and their consequences. As noted earlier, the profile of workers may be influenced both by external societal factors and by internal factors like the difference in industrial structure and the technologies used. It is proposed to assess the relative importance of these two groups of factors. In drawing up the profile, we seek to find out whether the workers belonging to the organised sector of industry in Kerala particularly the more modern sector have begun to form a ‘select group‘ in the Kerala society and the total work force. Wherever possible, it is proposed to compare the profile of the Kerala workers with those of workers in other states of India. As an incidental objective, it is also proposed to find out to the extent possible, whether trends towards labour embourgeoisement and class shifting have begun to set in among the industrial workers of Kerala, particularly among the workers in the modern industries as a result of their relative affluence and their middle class socioeconomic background. besides, the study seeks to find out whether there is any difference in the class consciousness of workers belonging to these two segments of organized industry, arising from the differences in their economic status and social background.

The institutional environment and its influence on political options to Protect Winnipeg’s Female garments Workers against the impact of globalization

The principal objective of this paper is to identify the relationship between the re­sults of the Canadian policies implemented to protect female workers against the impact of globalization on the garment industry and the institutional setting in which this labour market is immersed in Winnipeg. This research paper begins with a brief summary of the institutional theory appro­ach that sheds light on the analysis of the effects of institutions on the policy options to protect female workers of the Winnipeg garment industry. Next, this paper identi­fies the set of beliefs, formal procedures, routines, norms and conventions that cha­racterize the institutional environment of the female workers of Winnipeg’s garment industry. Subsequently, this paper descri­bes the impact of free trade policies on the garment industry of Winnipeg. Afterward, this paper presents an analysis of the ba­rriers that the institutional features of the garment sector in Winnipeg can set to the successful achievement of policy options addressed to protect the female workforce of this sector. Three policy options are considered: ethical purchasing; training/retraining programs and social engage­ment support for garment workers; and protection of migrated workers through promoting and facilitating bonds between Canada’s trade unions and trade unions of the labour sending countries. Finally, this paper concludes that the formation of isolated cultural groups inside of factories; the belief that there is gender and race discrimination on the part of the garment industry management against workers; the powerless social conditions of immi­grant women; the economic rationality of garment factories’ managers; and the lack of political will on the part of Canada and the labour sending countries to set effective bilateral agreements to protect migrate wor­kers, are the principal barriers that divide the actors involved in the garment industry in Winnipeg. This division among the prin­cipal actors of Winnipeg’s garment industry impedes the change toward more efficient institutions and, hence, the successful achievement of policy options addressed to protect women workers.