Modeling the interaction of milking frequency and nutrition on mammary gland growth and lactation

A mathematical model of biological mechanisms regulating lactation is constructed. In particular, the model allows prediction of the effect of milking frequency on milk yield and mammary regression, and the interaction of nutrition and milking frequency in determining yield. Possible interactions of nutrition with milking frequency on alveolar dynamics are highlighted. The model is based upon the association of prolonged engorgement (as a consequence of milk accumulation) of active secretory alveoli with changes in gene expression that result in impairment and, ultimately, cessation of milk secretion. The emptying of alveoli at milking, following alveolar contraction induced by oxytocin, prevents this process and also allows quiescent alveoli to reactivate. Prolonged engorgement results in apoptosis of the secretory cells and, hence, regression of the mammary gland. Milk yield is linked to alveolar populations, with secretion rates being modulated by nutrition and udder fill effects. The model was used to investigate different management scenarios, and is in agreement with experimental results. The model shows that while milking frequency drives alveolar population, and therefore potential milk production, actual production varies considerably with nutrition. A significant portion of the loss associated with once-daily milking was due to udder fill rather than loss of secretory tissue. The model showed qualitative agreement with experimental data, on the acute and chronic effects of temporary once-daily milking.     

GPS发展动态(译文)

由于全球卫星定位系统在从手提电脑到加强型火炮炮弹等装备上的广泛使用，对其电子抗干扰功能(ECCM)的需求变得非常明显。为了加快布置下一代GPS安全系统，美洛杉机空军基地NAVSTAR联合项目办公室(JPO)正致力于寻求方案来加快发展GPS的接收机使用组件的可选性和抗欺骗性组件(GRAASM，或称为GRAM—SAASM)     

GPS近期发展动态

最近，NAVSPECWARCOM(美国海军特种作战司令部)所属机构将对微型水下GFS接收机MUGR进行野外试验。这仅是GPS众多技术升级工作之一。为介绍该工作的广泛领域及GPS对军民两用技术领域的渗透。本文选择了几项近期GPS应用项目以便读者窥视该技术在当今和未来的地位。     

程控环境下的软件修补及对交换系统可靠性的影响

本文着重讲述有关软件修补的种种概念。文中介绍软件维护的概念，研究软件修补处理对交换系统可靠性的影响。     

澳大利亚芒特伊萨矿山公司希尔顿选矿厂的方铅矿回收问题研究

介绍了芒特伊萨矿山有限公司在希尔顿选矿厂矿样采用Ｘ－射线光电子光谱（ＸＰＳ）法所做的表面分析结果。同时论述了在取样时间内所得浮选速率数据。取样时的矿浆化学测定包括Ｅｈ、ＰＨ、溶解氧、温度、溶解的金属离子分析和用乙二胺四醋酸（ＥＤ－ＴＡ）可萃取的金属离子。     

AI-200型被动红外探测器寿命问题研究

本文利用实验统计数学推导了ＡＩ－２００型被动红外探测器的平均寿命。分析了在重庆地区使用中寿命缩短的主要原因，并给出了相应技术措施。     

Delivery of cefotaxime to the brain via intranasal administration

The purpose of this study was to investigate the plausibility of delivery of cefotaxime to the brain via intranasal administration. In vitro permeation studies were carried out using Franz diffusion cells, and the effect of different concentrations of chitosan (0.1% w/v and 0.25% w/v) on drug permeation across the bovine olfactory mucosa was determined. Samples were collected from the receiver compartment at different time points and analyzed using HPLC. The amount of cefotaxime that permeated across the olfactory mucosa when 0.25% w/v of chitosan was used as a permeation enhancer was ~1.5- and ~2-fold higher at the end of the first hour and second hour, respectively, over control (29.56 ± 6.18 μg/cm(2)). There was no significant enhancement in drug permeation when 0.1% w/v chitosan was used as the permeation enhancer. Pharmacokinetic studies were carried out using Sprague-Dawley rats. Cefotaxime solution with 0.25% w/v chitosan (40 mg/kg) was administered intravenously (i.v.) to rats in groups 1 and 3 and intranasally to those in group 2 and 4. The time course of drug in the brain was investigated by performing microdialysis in rats of groups 1 and 2. Blood samples were withdrawn from rats in groups 3 and 4, and cefotaxime in plasma was analyzed using HPLC after extraction with a hydrochloric acid-chloroform:1-pentanol (3:1) and phosphate buffer solvent system. Pharmacokinetic parameters were calculated using the trapezoidal rule. The results imply that the drug levels attained in the brain following i.v. and intranasal administrations were comparable. These results suggest that intranasal administration of cefotaxime could be a potential method of delivering antibacterial agents because of it being noninvasive and patient compliant.