支承舱减振性能分析

支承舱是运载火箭与航天器之间的重要连接结构,支承舱的振动特性是力学环境设计需要考虑的因素之一.本文从振动环境控制的角度进行支承舱结构动力学分析,阐述了一种基于支承舱振动特性研究的改善航天器力学环境的方法.在有限元建模过程中,引入了材料级性能试验.计算并比较了不同材料支承舱结构对航天器振动环境的作用,比较了连接面形式对振动环境的影响.基于分析结果给出了进一步研究的建议.     

高效液相色谱法测定磺胺二甲嘧啶的有关物质

目的:用高效液相色谱法测定磺胺二甲嘧啶的有关物质。方法:用Alltima C18(5μm,250 mm×4.6 mm)色谱柱;流动相为13.6 g/L磷酸二氢钾缓冲液(用20 g/L氢氧化钾溶液调节pH至4.50)—甲醇的体积比为55∶45;流速1.0 mL/min;检测波长:275 nm;进样体积:20μL。结果:磺胺二甲嘧啶在80~120μg/mL范围内线性关系良好(r=0.9999),磺胺线性范围为0.15~1μg/mL(r=1.0000),磺胺脒线性范围为0.15~1μg/mL(r=1.0000)。结论:该方法简便、准确、专属性好,可用于磺胺二甲嘧啶含量及有关物质检测。     

带有热沉结构的全镂空光读出红外焦平面阵列

A substrate-free optical readout focal plane array(FPA) operating in 8-12μm with a heat sink structure (HSS) was fabricated and its performance was tested.The temperature distribution of the FPA with an HSS investigated by using a commercial FLIR IR camera shows excellent uniformity.The thermal cross-talk effect existing in traditional substrate-free FPAs was eliminated effectively.The heat sink is fabricated successfully by electroplating copper,which provides high thermal capacity and high thermal conductivity,on the frame of substrate-free FPA. The FPA was tested in the optical-readout system,the results show that the response and NETD are 13.6 grey/K(F / # = 0.8) and 588 mK,respectively.     

Optimization of enzymatic hydrolysis parameters for antioxidant capacity of peptide from goat placenta

The goat placenta protein was hydrolyzed by pepsin and the optimal hydrolysis parameters of strongest antioxidant capacity of peptides were obtained using response surface methodology (RSM). The effects of reaction temperature, pH value and enzyme to substrate (E:S) ratio on the reducing power (RP) of the peptides and degree of hydrolysis (DH) of protein were well fitted to a quadric equation with high determination coefficients. The hydrolysate with optimal RP was predicted to be obtained at: temperature of 36.5 °C, pH value of 1.05, and E:S ratio of 2.03% and 3–10 kDa fraction (10 mg/mL), rich in GLY, GLU, ASP and TYR, was proved to exhibit highest RP, which is equivalent to the RP of 0.189 mg/mL ascorbic acid. The fraction of peptide also showed peroxidation inhibition in linoleic acid oxidation system and had a free radical scavenging ability similar to ascorbic acid (10 μg/mL) in the 1,1-diphenyl-2-picrylhydrazyl (DPPH) system after 17 min.     

Reductionin Listeria monocytogenes,Salmonella enterica and Escherichia coli O157:H7 in vitro and on tomato by sophorolipid and sanitiser as affected by temperature and storage time

Increased consumption of produce by consumers has been attributed to perceived health benefits of postharvest produce. Pathogen control is crucial because periodic occurrences and contamination of tomato and leafy greens have exacerbated food safety risks for consumers. We investigated the effects of temperatures (5 and 25 °C), storage time (30 min and 24 h) for inactivation of Listeria monocytogenes, Salmonella enterica and Escherichia coli O157:H7 by sophorolipid (SL‐p) produced fermentatively using palmitic acid as a co‐substrate at different concentrations in vitro. Reduction in pathogenic bacteria on grape tomato by SL‐p, sanitiser (Lovit) and combinations of SL‐p and sanitiser was determined. Temperature and storage time significantly (P < 0.05) affected pathogen inactivations by SL‐p as pathogen reductions were greater at 25 °C and 24 h than at 5 °C and 30 min of storage. L. monocytogenes was the most sensitive to SL‐p treatment as reductions of 5 log relative to untreated controls were attained at 0.12% of SL‐p. Significant reductions in S. enterica (1.91–3.85 logs) and E. coli O157:H7 (0.87–4.09 logs) were recorded at 2–5% of SL‐p. Lower populations of Salmonella and E. coli O157:H7 were inactivated than L. monocytogenes. On grape tomato, pathogen populations inactivated increased at higher SL‐p levels at 25 °C. Sanitiser and sanitiser + SL‐p reduced bacterial populations on tomato by 5.29–5.76 logs and 0.71–3.3.66 logs, respectively. These results imply the interactions of temperature, storage time and SL‐p significantly (P < 0.05) affected pathogen strain reductions. The combination of SL‐p with sanitiser led to synergistic effect on E. coli O157:H7, but not L. monocytogenes and S. enterica.     

Measuring Deep Metastability and Its Effect on Synchronizer Performance

Present measurement techniques do not allow synchronizer reliability to be measured in the region of most interest, that is, beyond the first half cycle of the synchronizer clock. We describe methods of extending the measurement range, in which the number of metastable events generated is increased by four orders of magnitude and events with long metastable times are selected from the large number of more normal events. The relationship found between input times and the resulting output times is dependent on accurate measurement of input time distributions with deviations of less than 10 ps. We show how the distribution of to clock times at the input can be characterized in the presence of noise and how predictions of failure rates for long synchronizer times can be made. Anomalies such as the increased failure rates in a master-slave synchronizer produced by the back edge of the clock are explained and demonstrated.     

Miller and noise effects in a synchronizing flip-flop

The effects of Miller coupling and thermal noise on a synchronizing flip-flop are described. Data on the metastability characteristics of the flip-flop are gathered and analyzed. True metastability is distinguished from the deterministic region. A worst case mean-time-between-failure bound is established. A simple and accurate test method is presented. A simple jamb latch was used with driving circuits of two different strengths to determine the role of input strength on T_m and τ. The flip-flop was fabricated on a 0.25-μm CMOS process     

Effect of sanitizing treatments on removal of bacteria from cantaloupe surface, and re-contamination with Salmonella

There are many reports of disease due to consumption of cantaloupes contaminated at the surface with enteric pathogens. Salmonella is among the most frequently reported cause of foodborne outbreaks of gastroenteritis in the United States. Research was undertaken to determine the effects of sanitizer and hot water treatments on microbial populations on cantaloupe surfaces and to determine whether prior decontamination of melons by sanitizer treatment affects vulnerability to recontamination by Salmonella. Cantaloupes were sanitized with 200 ppm chlorine or 2.5% hydrogen peroxide solution for 2 min, or hot water (96 degrees C) for 2 min and were held at 5 degrees C for 24 h. Hot water treatments reduced the microbial populations on cantaloupe surface by 4.9 log reduction while H2O2 or chlorine caused approximately 2.6 log unit reduction on cantaloupe surfaces. When sanitized or hot water treated whole cantaloupes were re-inoculated with Salmonella. Higher populations of Salmonella were recovered from sanitized cantaloupes than from the untreated controls; recovery was greater from hot water treated cantaloupes than from cantaloupes treated with chlorine or hydrogen peroxide. The results of this study clearly show that sanitized cantaloupes are susceptible to recontamination if exposed to a human bacterial pathogen during subsequent handling.