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%。     

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.     

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。     

Preparation and characterisation of water-soluble phytosterol nanodispersions

The purpose of this study was to prepare and characterise water-soluble phytosterol nanodispersions for food formulation. The effects of several factors were examined: four different types of organic phases (hexane, isopropyl alcohol, ethanol and acetone), the organic to aqueous phase ratio and conventional homogenisation vs. high-pressure homogenisation. We demonstrated the feasibility of phytosterol nanodispersions production using an emulsification–evaporation technique. The results showed that hexane was able to produce the smallest particle size at a mean diameter of approximately 50 nm at monomodal distribution. Phytosterol nanodispersions prepared with a higher homogenisation pressure and a higher organic to aqueous phase ratio resulted in significantly larger phytosterol nanoparticles (P < 0.05). Phytosterol loss after high-pressure homogenisation ranged from 3% to 28%, and losses increased with increasing homogenisation pressure. Elimination of the organic phase by evaporation resulted in a phytosterol loss of 0.5–9%.     

Enhancement of activity and sulfur resistance of CeO2 supported on TiO2-SiO2 for the selective catalytic reduction of NO by NH3

A series of novel metal-oxide-supported CeO(2) catalysts were prepared via the wet impregnation method, and their NH(3)-SCR activities were investigated. The Ce/TiO(2)-SiO(2) catalyst with a Ti/Si mass ratio of 3/1 exhibited superior NH(3)-SCR activity and high N(2) selectivity in the temperature range of 250-450 °C. The characterization results revealed that the activity enhancement was correlated with the properties of the support material. Cerium was highly dispersed on the TiO(2)-SiO(2) binary metal oxide support, and the interaction of Ti and Si resulted in greater conversion of Ce(4+) to Ce(3+) on the surface of the catalyst compared to that on the single metal oxide supports. As a result of in the increased number of acid sites on Ce/TiO(2)-SiO(2) that resulted from the addition of SiO(2), the NH(3) adsorption capacity was significantly improved. All of these factors played significant roles in the high SCR activity. More importantly, Ce/TiO(2)-SiO(2) exhibited strong resistance to SO(2) and H(2)O poisoning. After the addition of SiO(2), the number of Lewis-acid sites was not decreased, but the number of Br?nsted-acid sites on the TiO(2)-SiO(2) carrier was increased. The introduction of SiO(2) further weakened the alkalinity over the surface of the Ce/TiO(2)-SiO(2) catalyst, which resulted in sulfate not easily accumulating on the surface of the Ce/TiO(2)-SiO(2) catalyst in comparison with Ce/TiO(2).     

The extreme xerophilic mould Xeromyces bisporus--growth and competition at various water activities

Little is known about the mould, Xeromyces bisporus, unique in its strong xerophilicity and ability to grow at water activity (a_w) 0.62, lower than for any other known organism. The linear growth rates of one fast and one slow-growing strain of X. bisporus were assessed at 20, 25, 30 and 37 °C on solid agar media containing a mixture of glucose and fructose to reduce a_w to 0.94, 0.88, 0.84, 0.80, 0.76 and 0.66. Growth rates of xerophilic species closely related to X. bisporus, viz. Chrysosporium inops, C. xerophilum and Monascus eremophilus, were also assessed. Optimal conditions for growth of both X. bisporus strains were approx. 0.84 a_w and 30 °C, despite FRR 2347 growing two- to five-fold faster than CBS 185.75. X. bisporus FRR 2347 even grew well at 0.66 a_w (0.48 mm/day). C. inops and C. xerophilum were more tolerant of high a_w than X. bisporus, and could be differentiated from each other based on: the faster growth of C. xerophilum; its preference for temperatures ≥ 30 °C and a_w ≥ 0.94 (c.f. ≤ 25 °C and ~ 0.88 a_w for C. inops); and its ability to grow at 0.66 a_w, which is the lowest a_w reported to date for this species. M. eremophilus grew slowly (max. 0.4 mm/day) even in its optimal conditions of ~ 0.88 a_w and 25 °C. To investigate the competitive characteristics of X. bisporus at low a_w, both X. bisporus strains were grown in dual-culture with xerotolerant species Aspergillus flavus and Penicillium roqueforti, and xerophilic species A. penicillioides, C. inops, C. xerophilum and Eurotium chevalieri, on glucose-fructose agar plates at 0.94, 0.84, 0.80 and 0.76 a_w and at 25 °C. Growth rates and types of interactions were assessed. Excretion of inhibitory substances acting over a long-range was not observed by any species; inhibitors acting over a short-range that temporarily slowed competitors' growth or produced a protective zone around the colony were occasionally observed for A. penicillioides, C. inops and C. xerophilum. Instead, rapid growth relative to the competitor was the most common means of dominance. The xerotolerant species, A. flavus and P. roqueforti were dominant over X. bisporus at 0.94 a_w. E. chevalieri was often dominant due to its rapid growth over the entire a_w range. At a_w < 0.80, X. bisporus was competitive because it grew faster than the other species examined. This supports the concept that its ideal environmental niche is sugary foods with low a_w.     

Effect of nano-TiO<Subscript>2</Subscript> addition on the microstructure and bonding strengths of Sn3.5Ag0.5Cu composite solder BGA packages with immersion Sn surface finish

The effects of nano-TiO₂ particles on the interfacial microstructures and bonding strength of Sn3.5Ag0.5Cu composite solder joints in ball grid array packages with immersion Sn surface finishes have been investigated. Metallography reveals that addition of nano-TiO₂ particle retarded wicker-Cu₆Sn₅ IMC formed in the Sn3.5Ag0.5Cu composite solder joints. The thickness of the interfacial intermetallic compounds of the solder joint was reduced with increased additions of nano-TiO₂ particles (0.25–1.0 wt%), but further additions up to 1.25 wt% decreased the beneficial influence. This indicates that the presence of a small amount of nano-TiO₂ particles is effective in suppressing the growth of the intermetallic compounds layer. In addition, the shear strength of the soldered joints was improved by larger nano-TiO₂ particle additions, with the peak shear strength occurring at 1.0 wt% of nano-TiO₂ particles into the Sn3.5Ag0.5Cu solder. The fracture mode also changed with increased amounts of nano-TiO₂ particles.