The effect of acoustic diffraction and acoustic attenuation on the dynamic range of acoustooptic Bragg cells

A three-dimensional model for the propagation of finite acoustic waves in nonlinear media is developed. This model implicitly includes the effects of acoustic attenuation and divergence due to diffraction. The generation of intermodulation products in the case of a two-tone input signal is numerically analyzed. It is found that acoustic diffraction can have a significant effect on the dynamic range of a Bragg cell if the acoustic field extends well into the Fraunhofer region. Inclusion of the effect of diffraction in the model predicts a dynamic range that can be considerably larger than the value obtained by using the infinite plane wave assumption. It is shown that acoustic attenuation significantly reduces the level of the acoustic intermodulation products relative to the level of the fundamental modes. This also increases the dynamic range. The influence of these effects on design considerations for Bragg cells is discussed.     

Thermoelastic coefficients of alpha quartz

Experimental measurements of alpha quartz thermal expansion as reported in the literature have been critically analyzed. A recommended set of best measured values over the temperature range -50 degrees C to +150 degrees C have been determined, as have values for the coefficient of thermal linear expansion (CTE) and the thermoelastic coefficients. The impact of using the coefficients on determinations of quartz material temperature coefficients and on the calculation of temperature coefficients of frequency for the case of the AT-cut is discussed.     

A volume-perturbation approach to the problem of Rayleigh wave scattering at a rectangular groove

The problem of scattering of Rayleigh waves at a rectangular groove is addressed. Grooves are known to excite bulk waves upon scattering and, hence, are potential sources (albeit secondary) in bulk-acoustic-wave (BAW) devices. The groove is formulated as a volume perturbation of the geometry. A modal method is used, and the results of Rayleigh wave reflection as well as bulk wave radiation are obtained and compared with the results available in the literature. The method is compared with the boundary perturbation formulation. The equivalence of the boundary perturbation method and the volume perturbation method is shown.     

The effect of appraisers in estimating metabolic rate with the Edholm scale

A study was made of the appraisers' effect on the estimation of metabolic rate with the Edholm scale and a table of the ISO 7243 heat stress standard. The appraisers, five experienced and five inexperienced persons, estimated the metabolic rate of three different work tasks from videotapes. Analysis of variance indicated significant ( [Formula: see text] ) differences in the appraisers' recordings of the activities. The appraisers were grouped according to the similarity of the estimated values they gave. The groups thus contained both experienced and inexperienced appraisers, and it was not possible to classify the appraisers into experienced and inexperienced groups according to their earlier experience. The metabolic rates according to the Edholm scale were higher than according to the ISO 7243 table. The differences in metabolic rates given by the individual observers varied from 38 to 118 W/m(2). The variations in the estimation of metabolic rates were greater when the Edholm scale was used. This variation caused considerable variation also in the predicted mean vote, PMV index. It is recommended that the appraisers be selected carefully, because it is not possible to know whether a randomly selected appraiser is an 'average' or an 'extreme' appraiser without a test. Before conducting extensive field surveys where several appraisers estimate the metabolic rates, it would be useful to arrange training in order to calibrate the levels of the Edholm scale as well as ISO method among the appraisers because training clearly unified the estimation.     

Operator stress and monitoring practices

This study attempted to identify the major sources of work-related stress among telephone operators, with special emphasis on computer monitoring and telephone surveillance. A cross-sectional random sample of over 700 telephone operators participated in a questionnaire survey (response rate = 88%). The survey included items designed to measure perceived stress, management practices, specific job stressors and monitoring preferences. Call-time pressure items were most strongly linked to job stress by operators, with 70% reporting that difficulty in serving a customer well and still keeping call-time down contributed to their feelings of stress to a large or very large extent. About 55% of operators reported that telephone monitoring contributed to their feelings of job stress. If given the opportunity, 44% of operators stated they would prefer not to be monitored by telephone at all, while 23% stated they would prefer some monitoring; 33% had no preference. The setting of inappropriate individual-call-time objectives, which may be consistently unachievable for some operators and which create conflict between management demands for quantity and quality and also between workers values concerning quality and productivity demands, appears to be the most stress-inducing aspect of the job. In terms of telephone surveillance, the issues of timeliness and specificity of feedback appear to be less important than call-time pressure.     

试析中专计算机教学中如何提高学生能力水平

在以往中专计算机教学中比较重视理论知识,而忽视了对学生实际操作能力的培养,导致中专计算机专业毕业生在社会中就业中没有足够的竞争力。所以加强中专教学中学生能力的培养是非常必要的。本文主要对如何加强中专计算机教学中学生的创新能力、抽象思维能力、自学能力以及应用能力进行了深入的分析。     

Effect of singeing on the texture and histological appearance of pig skin

Singeing of pigs is a necessary process in the manufacture of Wiltshire bacon, but it is a very energy-demanding process. As a preliminary to the development of less expensive methods, the effect of singeing was examined. Skin samples were taken from thirty pig carcasses before and after the singeing process. The changes in the skin were followed by texture measurements, analyses of soluble collagen content and histological measurements of the depth of the effect on the skin microscopically observable. For more detailed histological studies, five carcasses were followed through the slaughtering processes and samples were taken immediately after death, after scalding and de-hairing, after singeing and after removal of the charred skin. The results show that the desired changes in the skin are due to the heat denaturation of the collagen. The same effect is seen after 10 minutes' exposure to water at 60°C. It is therefore possible to change the skin structure at a lower, and less energy-expensive, temperature, but then the hair left from the de-hairing process has to be removed in another way.     

Hot cutting of goat carcasses following early post-mortem high temperature ageing

Hot cutting of goat sides into bone-in joints, such as leg, shoulder and loin, 3 h after the sides were left hanging at an ambient temperature of 34°C with (treatment II) or without (treatment I) subsequent chilling prior to freezing did not adversely affect colour of meat, tenderness, cooking loss or water-holding capacity compared with normal chilling. The latter process (treatment III) significantly (P < 0·05) increased evaporative weight loss from the sides. Differences in colour, shear force, evaporative weight loss, cooking loss, drip loss from the leg joint and water-holding capacity between treatment I, where sides were hung at room temperature for 3h, and treatment II, where sides were given an additional chilling period of 21h after hanging, were not significant. These findings indicate that, in countries with ambient temperatures above 30°C, goat sides or carcasses can be cut hot after a 3h hanging period at ambient temperature and subsequently frozen without deterioration in the quality or processing properties of the meat.     

Tenderization of beef with bacterial collagenase

The feasibility of using a purified collagenase produced by Clostridium histolyticum as a meat tenderizer was studied. Experiments were conducted with enzymes in model systems to compare collagenase with the currently used plant proteinases, papain, bromelain and ficin. Collagenase was shown to have a greater activity in hydrolyzing insoluble collagen than salt-soluble-protein (SSP) and highest activity between 40° and 60°C, with little to no activity above 60°C. Collagenase was added to raw steaks and steaks were placed in bags and cooked in a water bath to 6.5°C. Tenderness was evaluated by analyzing components of Warner-Bratzler shear-deformation curves. The results suggested that addition of NaCl or a combination of CaCl(2), NaCl and collagenase would cause equivalent tenderization. The lack of a significant tenderization due to collagenase could be related to a lack of sensitivity in the shear evaluation or an effect on the enzyme activity due to the meat environment.