Method of moments analysis of EM fields in a multilayered spheroid radiated by a thin circular loop antenna

This paper presents derivation and computation of electromagnetic (EM) fields inside a dielectric prolate spheroid radiated by a loop antenna. The dielectric spheroid is considered to be multilayered, and a thin circular loop antenna that is loaded by a voltage source radiates on the top of the prolate spheroid. The multiple interaction of transmitted and reflected waves with the spheroid is characterized by applying the method of moments (MoM) to both the circular loop antenna wire and the stratified spheroidal interfaces. The dyadic Green's function in the expansion form of eigenvector wave functions is used to derive the EM fields, so the formulation is quite compact. Different basis and weighting functions are used inside the method of moments procedure for obtaining in an efficient way the unknown current distributions along the antenna wire and the unknown expansion coefficients of their resulted EM fields. Current distributions and the transmitted fields inside the spheroidal model are computed numerically and the convergence issues are discussed.     

基于LM5117P的降压型直流开关稳压电源设计

降压型直流开关稳压电源是一种单向DC-DC变换器,实现稳定直流降压功能.本系统采用同步降压控制器LM5117P作为电路控制核心,以同步Buck电路作为降压主电路,通过闭环回路反馈设计以及芯片本身的精准采样,将输入电压16V降为5V恒压输出.     

响应面法优化酶法制备花生蛋白的工艺研究

以花生粕为原料,对在乙醇水溶液中利用α-淀粉酶制备花生蛋白的工艺条件进行了研究。探讨乙醇体积分数、加酶量、pH、酶解温度、酶解时间、液料比6个因素对可溶性总糖提取率的影响,试验表明乙醇体积分数、酶解时间、pH和液料比对提取过程影响较大。通过Box-Behnken中心组合试验和响应曲面分析法优化工艺条件:pH 5.95、酶解时间52 min、液料比13.8∶1、乙醇体积分数76%、加酶量0.5%、酶解温度35℃,总糖提取率为13.06%。对此工艺条件进行验证得到蛋白质纯度为70.29%,而单纯的乙醇溶液提取法蛋白质纯度为62.03%。     

核酸适配体技术在食品重金属检测中的应用研究进展

近年来食品中重金属超标对人们健康构成了威胁,所以对食品中重金属检测技术的开发成为了重要研究内容。虽然传统的检测技术对重金属进行了高选择性和高灵敏度的检测,但是仍需要一种简单、快速、有效、成本低廉的方法用于食品安全领域的快速检测。核酸适配体为一段单链DNA或者RNA序列,是经体外筛选技术筛选出的能特异结合蛋白质或其他小分子物质的寡聚核苷酸片段。核酸适配体具有靶分子广、灵敏度高、特异性强、稳定性好等特点,因而被广泛用于食品安全检测领域。本文综述近年来核酸适配体技术对食品中Hg2＋、As3＋、Pb2＋的检测,并对核酸适体技术在食品重金属检测领域的应用前景进行了展望。     

粉质质量指数(FQN)对于评价小麦粉品质的实用价值研究

对85份小麦试样的粉质质量指数(FQN)、评价值和粉质仪的其它测试参数之间的相关关系进行了研究。结果表明：在FQN与评价值之间存在着极显著的相关关系。FQN或评价值与粉质仪其它测试参数之间的相关关系具有非线性的特征。FQN与稳定时间之间存在着极显著的相关关系，可用于反映强筋和中筋小麦粉的筋办和耐揉性。     

Survival of SA11 rotavirus in fresh fruit juices of pineapple, papaya, and honeydew melon

Survival of rotavirus in fresh fruit juices of papaya (Caraca papaya L.), honeydew melon (Cucumis melo L.), and pineapple (Ananas comosus [L.] Merr.) was studied. Clarified juices were prepared from pulps of ripe fruits and sterilized by ultrafiltration. One milliliter of juice from each fruit was inoculated with 20 microl of 1 x 10(6) PFU of SA11 rotavirus and sampled immediately (0-h exposure) and 1 and 3 h later at 28 degrees C. Mean viral titers in juices of papaya (pH 5.1) and honeydew melon (pH 6.3) at 1 and 3 h were not significantly different from titers at 0-h exposure. Mean viral titers in juices from pineapples with ripening color indices of 3 (pH 3.6) and 6 (pH 3.7) at 1-h exposure (color index 3: 4.0 +/- 1.7 x 10(4); color index 6: 2.3 +/- 0.3 x 10(5)) and 3-h exposure (color index 3: 1.1 +/- 0.4 x 10(4); color index 6:1.3 +/- 0.6 x 10(5)) were significantly lower than titers at 0-h exposure (color index 3: 5.7 +/- 2.9 x 10(5); color index 6: 7.4 +/- 1.3 x 10(5)). Virus titers in pineapple juices of color index 3 were significantly lower than titers of the virus in juices of index 6. In cell culture medium (pH 7.4), SA11 titer remained stable over 3 h at 28 degrees C. However, at pH 3.6, the virus titer was reduced to a level not significantly different from that of the virus in pineapple juice of color index 6 (pH 3.7). In conclusion, papaya and honeydew melon juices, in contrast to pineapple juice, have the potential to transmit rotavirus. Inactivation of SA11 virus in pineapple juice can be possibly attributed to low pH and constituent(s) in the juice.     

沙葱及其提取物对肉羊体脂4-烷基支链脂肪酸沉积与分布的影响

本实验旨在研究沙葱及其提取物对肉羊体脂4-烷基支链脂肪酸沉积与分布的影响.选取3月龄体质量((23.67±3.43) kg)相近、体况良好的健康小尾寒羊公羊60只,随机分为4组,每组3个重复,每个重复5只.对照组饲喂基础日粮;实验组以每只羊计,分别在基础日粮中添加沙葱粉10 g/d、沙葱水提物3.4 g/d和沙葱醇提物...     

植物源天然产物对黄曲霉和黄曲霉毒素B_1的抑制作用研究进展

黄曲霉毒素B1(aflatoxin B1,AFB1)是化学物质中致癌性最强的一种,对人和动物的健康具有极大的威胁,尤其是对肝脏的损害。AFB1是谷物和粮油中最为多见的真菌毒素,危害性也最强,长期低剂量的摄入AFB1除了会导致肝脏损伤和诱发肝癌之外,也会损害人体的其他器官。因此,能够有效防护人体免遭AFB1损伤的功能食品和新型保健药物已成为研究重点。近年来,天然产物因其具有生物活性显著、副作用小、多靶点等优点而备受关注,多种植物源天然产物已被报道能够抑制黄曲霉的生长产毒和AFB1的毒性作用。该文主要综述了植物源天然产物对黄曲霉生长产毒和AFB1毒性作用的抑制作用以及其相关抑制机制,为进一步开展AFB1毒性损伤的防护研究工作,开发能降低AFB1对人和动物的毒性损伤的新型保健药物和功能食品提供参考。