计算机科技情报检索通讯网的排队分析

本文从计算机科技情报检索通讯网的一种设计方案中提出数学模型,并用排队论方法计算用户从终端发送一个信息到数据库(贮存科技情报资料)直到获得应答的平均时间,即平均系统时间,给出了解析算法.目的是为此类计算机通讯网的设计合理性提供依据,亦是对网作出性能评估。     

一类Fork—Join排队网络的弱极限定理

借助于概率测度弱收敛理论，对Ｎ台并联Ｆｏｒｋ－Ｊｏｉｎ联队网络进行了较为详细的研究，得到了响应时间，队长和离去过程等排队指标的弱收敛定理。对一般型Ｆｏｒｋ－Ｊｏｉｎ网络，提出了一种新的研究方法，并针对某一类型Ｆｏｒｋ－Ｊｏｉｎ网络给出了响应时间的弱收敛定理。     

In vitro human nail penetration and kinetics of panthenol

The in vitro absorption of panthenol into and through the human nail was examined in this study. Panthenol, the alcohol form of pantothenic acid (vitamin B5), is believed to act as a humectant and improve the flexibility and strength of nails. A liquid nail treatment formulated with panthenol (2%) was compared to a solution of panthenol (2%) in water. Fingernail specimens were dosed daily for 7 days with either the nail treatment (non-lacquer film forming) formulation or aqueous solution with sampling performed every 24 h. Panthenol concentrations were determined in the dorsal surface, interior (by drilling and removal) and in the supporting bed under the human nail. Panthenol levels in the dorsal nail (R(2) = 0.87; P < 0.001), nail interior (R(2) = 0.94; P < 0.001) and nail supporting bed (R(2) = 0.79; P < 0.003) showed a significant linear increase with each day of dosing. Significantly more panthenol was delivered into the interior nail and supporting bed by a nail treatment formulation than from an aqueous solution. The film acts not only as a reservoir of panthenol, but also acts to increase the hydration of the nail and the thermodynamic activity of panthenol as well, thereby enhancing diffusion.     

Benecol®—一种有效、安全降低血清胆固醇水平的独特食品配料

在世界范围内,心血管疾病——冠心病(CHD)、中风、周围动脉疾病的患病数量正在增加.据世界卫生组织(WHO)统计估计,每年大约有1600万人死于各种形式的心血管疾病.高血清胆固醇是导致各种心血管疾病的主要危险因素之一.近来,通过饮食方法如功能食品来降低胆固醇水平已经引起了极大关注.植物甾醇和植物甾烷醇是动物胆固醇的植物等价物,因为它们在植物细胞中的作用与胆固醇在动物细胞中的作用是一样的.如果在日常的饮食当中含有足量的植物甾醇或植物甾烷醇,则它们可以有效地降低胃肠道中对胆固醇的吸收量,从而降低血清胆固醇浓度.植物甾烷醇酯是世界上第一个基于植物甾醇的降低胆固醇的商业食品配料.1995年芬兰首次生产出添加植物甾烷醇酯的降胆固醇食品.如今,在全世界的24个国家销售Benecol品牌的各种植物甾烷醇酯强化食品,包括植物黄油、酸奶、牛奶、橙汁、通心粉等.Benecol食品含有植物甾烷醇酯,专门针对想通过饮食方法降低血清胆固醇水平的人群.植物甾烷醇酯的安全性已经得到了严格的安全性测试,并得到了40多项人体临床研究的证实.国际专业团体已经充分肯定了植物甾烷醇酯食品的降低胆固醇的功效.     

多类顾客多服务台强占重复优先排队系统的弱收敛极限探讨

用概率测度弱收敛的理论对多类顾客多服务台强占重复优先排队系统进行了研究，获得了其系统中负荷过程、离去过程和队长过程的弱收敛极限在什么情况下存在，在什么情况下不存在。     

随机服务系统一般模型的仿真和应用

本文提出了多服务台随机服务系统的一般模型,给出了仿真框图及通用计算程序.对某 些系统的仿真结果进行理论分析和计算.分析表明:对有理论计算公式的系统,理论值和仿 真结果基本一致;对难以用解析理论加以处理的系统,计算机仿真可提供数值解.最后介绍了 该仿真模型在机械加工自动线设计中的应用.     

Fusion of a recombinant antibody fragment with a homo-amino-acid polymer: effects on biophysical properties and prolonged plasma half-life

Chemical conjugation of small recombinant proteins with polyethylene glycol (PEG) is an established strategy to extend their typically short circulation times to a therapeutically useful range. We have investigated the production of a genetic fusion with a glycine-rich homo-amino-acid polymer (HAP) as an alternative way to attach a solvated random chain with large hydrodynamic volume. The anti-HER2 Fab fragment 4D5 was used as a model system and fused with either 100 or 200 residue polymers of the repetitive sequence (Gly(4)Ser)(n) to its light chain. Both fusion proteins were successfully produced in the periplasm of Escherichia coli and obtained as homogeneous preparations after two-step affinity chromatography via the His(6) tag fused to the heavy chain and the Strep-tag II fused to the extended light chain. Both modified Fab fragments showed binding activity towards the HER2 antigen indistinguishable from the conventional recombinant Fab fragment. When compared with the unfused Fab fragment, a significantly increased hydrodynamic volume, by ca. 120%, was observed during gel filtration for the 200 residue HAP fusion protein and, to a lesser extent, in the case of the 100 residue HAP. Difference CD measurements revealed a characteristic random coil spectrum for the 100 and 200 residue HAP fusion moieties. Finally, pharmacokinetic experiments were carried out in mice after radioiodination of the recombinant Fab fragments. Although the 100 residue HAP fusion showed a behavior very similar to the unfused Fab fragment, with a terminal plasma half-life of ca. 2 h, the 200 residue HAPylated Fab fragment gave rise to a significantly prolonged half-life of ca. 6 h. While this moderate effect may so far be most beneficial for specialized medical applications, such as in vivo imaging, the genetic engineering of optimized HAP sequences should yield pharmacokinetic properties similar to PEGylation, yet without necessitating in vitro modification steps.     

Effects of the antithyroid agent propylthiouracil in a partial life cycle assay with zebrafish

Some ubiquitous pollutants of the aquatic environment, such as PCBs or other polyhalogenated aromatic hydrocarbons, may disrupt the thyroid hormone system. In a partial life cycle assay with zebrafish (Danio rerio), we studied the effects of the reference compound propylthiouracil (PTU) on reproduction, growth and development, histopathology of some target tissues, and plasma thyroid hormone levels. PTU induced a concentration-dependent increase of egg production with a concomitant decrease of mature oocyte size but had no effect on fertilization rate or hatching. In F1, serious dysmorphogenesis was found in 4 dph larvae at the highest PTU level tested (100 mg/L), and there was a dose-dependent decrease in body length and weight at 42 dph (significant at 100 mg/L PTU). At this time, there was also a decreased scale thickness, suggesting inhibited metamorphosis, detectable at 1 mg/L PTU and higher. PTU also induced activation of the thyroid follicles in a concentration-dependent way, in juveniles associated with hyperemia in the thyroid area, and depletion of liver glycogen. Effects in adults were associated with decreased circulating levels of the thyroid hormones T3 and T4. These observations indicate that disruption of the thyroid hormone system may affect the fitness of these aquatic organisms. The zebrafish model may contribute to the identification of thyroid hormone disrupting activity in water samples and also in the interpretation of histological observations in free-ranging fish species.     

Hepatic metabolism of 2-hydroxy-4-methylthiobutyrate in growing lambs

This study was undertaken to determine how, and where, 2-hydroxy-4-methylthiobutyrate (HMTBA) can augment Met metabolism in lambs. Four lambs (initial body weight of 50 kg, SE = 2, and 6 mo of age) prepared with catheters in the mesenteric, portal, hepatic, and jugular veins plus the aorta, were fed at 1.5× maintenance on a grass hay, barley, fish meal, molasses/pre-mix (5:3:1:1, as fed) diet, supplied as hourly meals. Lambs were infused for 10 h with [methyl-²H₃]Met (0.11 mmol/h) in a jugular vein and p-aminohippurate into the mesenteric vein. From 1 h onwards, successive 3-h infusions of saline (control), 0.55 mg/min (3.67 μmol/min), and 4.44 mg/min (29.6 μmol/min) of HMTBA were also infused into the mesenteric vein. Plasma, sampled continuously, was collected every 20 min during the last 60 min of each infusion. All infused HMTBA was recovered at the portal vein with 25% extracted subsequently by the liver. Portal appearance of total Cys and Met was unaltered by HMTBA infusion, but net splanchnic appearance of Cys increased (0.04, 0.08, 0.23 mmol/h, SEM = 0.05), whereas Met decreased (0.14, −0.01, −0.21 mmol/h, SED = 0.05). Despite this, arterial Met increased (27.0, 30.7, 51.5 μM, SEM = 2.1) as did Met irreversible loss rate (27.6, 28.7, 40.1 μmol/h, SEM = 0.51), equivalent to 40% of the HMTBA reentering the plasma after conversion to Met. These data indicate that, in ruminants, HMTBA is probably converted to Met within peripheral tissues; that is, where the metabolic need for Met exists.     

Absorption and digestive tract metabolism of 2-hydroxy-4-methylthiobutanoic acid in lambs

Anabolic availability of the hydroxyl methionine analog, 2-hydroxy-4-methylthiobutanoic acid (HMTBA), given as oral doses to lambs, was quantified both directly as appearance in the portal vein and as synthesis to Met by digestive tract tissues. Eight lambs, prepared with vascular catheters in the mesenteric and portal veins plus the aorta, received twice daily for 7 d either 0.46 g or 2 g of HMTBA. On d 7, [1-¹³C]HMTBA was supplied as 1 oral dose while [methyl-²H₃]Met was infused into the jugular vein. Peak absorption as HMTBA occurred 70 to 90 min after the oral dose. All digestive tract tissues converted HMTBA to Met, equivalent to 24% of the Met provided by the diet for the larger HMTBA dose. Overall, total availability of HMBTA averaged 17.9% of the dose (range 10.6 to 27.9%), with 12.5% (range 7 to 22%) as absorbed HMBTA and the remainder as Met synthesized by digestive tract tissues. Release of ¹³CO₂ into the portal vein accounted for another 23% of the dose. In all digestive tract tissues, the d-isomer was present in a smaller proportion than in the dose. In terms of whole-body kinetics, HMTBA loss from the plasma followed first-order kinetics, with a mean biological half-life of 76 min. Using this value, a simple model was devised to estimate HMTBA absorption based on peripheral plasma samples. When compared with direct measures of absorption, the model gave a slope of 0.81 (R² = 0.68) and offers a practical means to test HMTBA availability to animals.