β-hydroxyacyl-coa-dehydrogenase (HADH) activity of unfrozen and frozen—thawed frog (Rana esculenta) legs

The β-hydroxyacyl-CoA-dehydrogenase (HADH) activity of unfrozen and thawed frog legs was investigated. The enzyme was extracted by either immersing frog legs in phosphate buffer 0.1 M, pH 6.0 at 25°C for 15 min or pressing them between trichinoscopy glasses. The enzyme activity was assayed using acetoacetyl-CoA as substrate and measured spectrophotometrically at 340 nm. It was possible by both extraction methods to distinguish between thawed and unfrozen samples although when the juice was obtained by pressing the HADH activity of the dilution was ～ 1.5 times higher than that obtained by immersion. The HADH activity was significantly higher (P≤0·001) in frozen-thawed frogs than in unfrozen legs because during freezing there is a release of HADH. No significative differences were found in the HADH activity in samples frozen in the temperature range -10 to -196°C. HADH activity was not affected by the storage time in crushed ice up to 6 days.     

Yeast exo-β-glucanases can be used as efficient and readily detectable reporter genes in Saccharomyces cerevisiae

Yeast exo-1,3-β-glucanases are secretable proteins whose function is basically trophic and may also be involved in cell wall glucan hydrolytic processes. Since fluorescein di(β-D -glucopyranoside) is a fluorogenic substrate detectable and quantifiable by flow cytometry, it was used for testing the ability of the EXG1 gene product of Saccharomyces cerevisiae and its homologous gene in Candida albicans to function as reporter genes. These open reading frames were coupled to different promoters in multicopy plasmids, and exoglucanase activity quantified at flow cytometry. Exoglucanases were found to be useful tools for the study of promoter regions in S. cerevisiae. This technique has the advantage over other reporter gene systems—such as β-galactosidase fusions—that it does not require permeabilization of yeast cells and therefore it allows the recovery of viable cells—by sorting—after flow cytometry analysis.     

Copper bioavailability from breakfasts containing tea. Influence of the addition of milk

The influence of drinking tea on copper bioavailability is unclear, particularly when tea is consumed with food. A breakfast meal containing white bread, margarine, strawberry jam, cheese and tea, with or without milk, was digested in; vitro and the dialysis of copper investigated. Reference breakfasts were prepared with water and water with milk. Copper dialysability (percentage of copper dialysed) was markedly increased by tea. The influence of adding milk to tea was not significant. A second study was carried out in rats using the breakfasts containing tea and water. They were spiked with ⁶⁴Cu and given orally to the animals in a single dose. Whole-body ⁶⁴Cu retention was measured over a 4-day period after administration. In order to determine the true absorption of ⁶⁴Cu a control group of rats received the dose intraperitioneally. The results in vivo indicate a tendency to higher absorption and retention of ⁶⁴Cu with tea. Liver ⁶⁴Cu retention was significantly elevated by tea. Therefore, the presence of tea in a breakfast meal favours the formation of soluble low-molecular-weight ligands which can be absorbed and retained by rats. The concomitant increase in liver copper retetition may be associated with higher bioavailability and/or lower copper mobilisation.     

Aflatoxin B1 contamination of shrimp feeds and its effect on growth and hepatopancreas of pre-adult Penaeus monodon

A survey of aflatoxin B₁ (AFLB₁) levels in commonly used commercial shrimp finisher feeds in the Philippines showed a various range of values from not detected to 120 μg kg^?1 using high-performance thin-layer chromatography. Six experimental diets were prepared to contain various levels of AFLB₁ based on survey results to determine the effects of such contamination in pre-adult shrimp Penaeus monodon (17.5 ± 0.6 g). Results showed that shrimps fed diets containing AFLB₁ greater than or equal to 73.8 μg kg^?1 gave comparatively poor growth rate and higher susceptibility to shell diseases. No AFLB₁ residues were detected in sampled whole shrimp tissues after 62 days of exposure to AFLB₁ containing diets indicating a low potential for transmission of the toxin from edible shrimp tissues to consumers. Histopathological alterations in the hepatopancreas of shrimp chronically exposed to AFLB, were observed in all samples. The degree of alterations correlated with the level of AFLB₁. Based on growth performance, pre-adult shrimps can tolerate AFLB₁ levels of up to 52.3 μg kg^?1 in the feeds although histopathological changes were already evident in the tissues of shrimps given diets with 26.5 μg kg^?1 AFLB₁.     

透同光路指示光的CO_2激光器

报导封离型可透同光路指示光的ＣＯ２激光器的研制，并给出了其电流—工作特性曲线。对需可见光作同光路指示的ＣＯ２激光应用整机的开发，开辟了一条新的途径。     

四方向上的任意角度扇形数字滤波器的设计

具有任意角度（扇形所围成的角度）和任意方向（扇形所取方向）的扇形数字滤波器在图像数据压缩和地质、地震等方面的数据处理中有着广泛的应用。目前，大多数的工作多集中于水平及垂直方向的９０°扇形数字滤波器的设计，因而有必要研究任意方向上的任意角度的扇形数字滤波器的设计。本文介绍利用ＭｃＣｌｅｌｌａｎ交换法设计具有垂直，水平及±４５°方向上的任意角度的扇形数字滤波器的设计方法，垂直水平方向上的扇形滤波器的设     

直接序列扩展频谱中伪码优选研究

本文从最优化理论和工程实际出发，全面分析和完善了直接序列扩展频谱中伪码的数学模型，在此基础上，建立了一种较准确的伪码优选数学模型，并探讨了合适的搜索算法。     

从江苏苏南数字微波线路看广播电视专用网发展前景

新建微波干线电路采用高质量的数字微波设备是广电部科技工作会议的精神之一。本文介绍了江苏苏南数字微波线路，并从方案确定、技术实现、设备选型等方面进行分析比较，从而得到一个合理的整体方案。本文还着重阐述了数字传输的关键设备－编码器的现状与发展趋势，提出广播电视专用网多功能应用的设想。     

任意型一维FIR数字滤波器设计新方法

本文介绍了一种设计任意型（宽带、窄带、低阶、高阶、低通、高通、带通、带阻）一维FIR数字滤波器新方法．给出设计不同类型滤波器的统一方法。各种类型滤波器脉冲响应的设计公式简单、计算方便。该方法消除了Gibbs现象．不仅克服了优化设计中收敛速度、设计精度及初值选取等问题，而且减少设计高阶滤波器的时间。最后，本文给出了各种类型滤波器设计的仿真结果。