Optimal bed net use for a dengue disease model with mosquito seasonal pattern

Controversial results concerning the effectiveness of bed net in reducing dengue fever transmission make further research necessary in this direction. At this aim, we consider a mathematical model of dengue transmission where the use by individuals of insecticide‐treated bed nets is taken into account, combined or not with insecticide spraying. Furthermore, as climatic factors play a key role in mosquito‐borne diseases, we model the effect of seasonality through a periodic mosquito birth rate. We numerically investigate some specific scenarios according to different rainfall and mean temperature values. We set an optimal control problem to minimize the number of human infections and the cost of efforts placed into bed net adoption and maintenance and insecticide spraying. To assess the most appropriate strategy to eliminate dengue with minimum costs, we perform a comparative cost‐effectiveness analysis, which also shows how the cost‐benefit of intervention efforts is affected by changes in the amplitude of seasonal variation. One general result is that in any case the combination of bed net use and insecticide spraying produces the highest ratio of infections averted, whereas in terms of cost‐benefit only spraying campaigns should be implemented in control programs for regions with no large seasonality.     

Theoretical study of the in-plane components of the 13C shielding tensors in condensed aromatic hydrocarbons

The Pople model for chemical shielding is applied to calculate the in-plane components of the ¹³C shielding tensors of condensed aromatic hydrocarbons. The wave functions are evaluated using the MNDO method and the calculated results are supported by the very good agreement with the experimental results in the few cases in which experimental information is available.The relationship found between the calculated bond orders and the in-plane components of the ¹³C shielding tensors suggest that the experimental study of the ¹³C shielding tensors in these compounds may provide a powerful technique for studying aromaticity. The in-plane components are found to be directly affected by the degree of delocalization of the -electrons in the adjacent bonds. Rules are given for estimating the orientation of the two in-plane components of the shielding tensor.     

不同形状孔阵屏蔽效应的分析

 屏蔽效应的研究对于防御电磁干扰，保证电子系统的正常工作是非常重要的。计算了屏蔽腔上开有不同形状的孔阵时对屏蔽效应的影响，分析比较了各种不同孔间距对屏蔽效应的影响。计算结果表明，圆形孔阵的穿透系数最小，方形孔阵次之，蜂巢形孔阵较大，但频谱分布基本一致。而对于哑铃形孔阵，由于孔面形状差异较大，孔面处磁流分布变化也较大，不仅穿透系数比前三者都大，而且高频时穿透系数的频率分布也发生较大改变。另外，随着孔阵中孔间距变大，孔之间的互耦减弱，耦合进屏蔽腔内的场强也变小。     

基于操作便捷性和安全性的可变功能应急产品应急效能评估

为更全面地评估可变功能应急产品的应急效能,降低因应急效能问题导致的财产损失和人员伤亡的可能性,同时也为该类产品的设计开发提供技术支持,提出了可变功能应急产品的应急效能评估方法.首先,根据可变功能应急产品的自身特点和使用环境情况,构建以操作时间、操作难度、使用安全性为基础的可变功能应急产品的应急效能评估指标体系.在此基础上,引入层次-熵权法确定评估指标的权重,并通过保守型效用函数统一量纲,建立可变功能应急产品的应急效能评估模型,为基于再设计策略的可变功能应急产品的设计开发提供评判依据.最后以两款多功能自救座椅为案例,验证所提出方法的可行性.     

Some properties of generalized secant integrals: extended definition and recurrence relations

Line sources with slab shields represent typical source–shield configurations in gamma-ray attenuation problems. Such shielding problems often lead to the generalized secant integrals of the form

Recently, the author has developed rapidly convergent infinite-series representation of generalized secant integrals involving incomplete gamma functions. The validity of this representation was established for zero and positive values of the integral parameter a (a0). In this paper the definition is extended to include negative real a values. It is demonstrated that the introduced series representation is still valid. In addition, general recurrence relations are established that allow precise calculation of the integral for negative a values.     

Equivalent Cylinder Systems Representing the Soil Matrix in Diffusion-Reaction Models for an Aggregated Soil

The structure of an aggregated soil or a dual-porosity medium is characterized by a function called the generalized surface-area-to-volume ratio, which can be measured as a distance distribution. For an isotropic structure the distance measurements may be done in the digitized image of a cross-section. A diffusion-reaction process in the soil matrix can be described by means of an equivalent cylinder system which preserves the generalized surface-area-to-volume ratio of the structure. The contribution of each cylinder radius is described by a weight function, which is obtained by transforming the measured cross-sectional distance distribution. In order to test the method, a diffusion-reaction model from the literature has been applied to spheres with a lognormal radius distribution and to an irregular, generated structure. Both geometries can be represented by just a few cylinder radii and cylinder weights. The method works best for dual-porosity structures with a convex shape. Deviations occur if parts of the matrix structure have a concave shape.     

出流角对旋转涡轮叶片前缘气膜冷却影响

基于频闪拍照和稳态液晶测温技术,实验研究了不同气膜孔出流角对旋转态整级涡轮叶片前缘外壁面的气膜冷却特性的影响。实验中,叶片前缘处的主流雷诺数为6.3378×104。实验转速为574 r/min,对应的旋转数为0.0018。平均吹风比从0.5变化到1.25。射流采用N2,其对应的密度比为1.04。结果表明:展向平均气膜冷效是随吹风比的增加而单调增加的,其中最佳吹风比为M=1.25。对于所有吹风比,在-4.3相似文献   

Benchmarking of maintenance performance: a case study in two manufacturers of furniture

When profit margins of a plant are decreasing, the need forreliable and efficient maintenance policy becomes more important.Measuring maintenance performance is important for companiesto recognize whether their planned goals are achieved or not.Also, such measurements can be utilized for benchmarking, whichis one of the tools for never-ending improvement. But, theseobjectives cannot be achieved without well-documented data ofthe relevant variables. Better data coverage and quality isnecessary for following maintenance performance developmentand it would, in many cases, clarify the ambiguity concerningthe main problem in the context, namely that neither the productionnor maintenance department can show what effect maintenancehas on profitability. A more effective maintenance policy indirectly implies improvementsin product quality and manufacturing process effectiveness.Elongation of the production time, i.e. reducing the downtimedue to failures, planned replacements and repair, in additionto the improvement in the total maintenance activities, arealso some of the results that can be expected when an efficientmaintenance policy is used. Measuring and monitoring maintenanceperformance measures is required partly for detecting, and eventuallytreating as soon as possible, undesirable changes and partlyto make benchmarking with the best in the branch, which savesappreciable economic losses for companies. In this paper, a model for how to identify the measurable variables,which are needed to develop measures for monitoring maintenanceperformance behaviour systematically, is developed. Five maintenanceperformance measures are proposed and applied. An additionalmodel for systematically analysing the trend of maintenanceperformance measures, for an overall assessment of the company'ssituation, is presented. Two case studies in manufacturers offurniture are conducted to verify these models.     

企业管理的有效性、管理效率与管理变迁

为了客观公正地评价一个企业的管理有效性,本文深入挖掘了企业管理有效性概念的内涵与外延,并提出根据管理有效性的内涵确定管理效益指标体系,根据它的外延确定管理绩效的测算方法这一基本原则。基于此项原则,建立了管理前沿、管理效率和管理变迁的数理概念和测算方法。利用数据包络分析模型对我国30个省市自治区工业企业2002、2003年的管理效率以及2003年的管理变迁的评测结果表明:同时考察管理效率和管理变迁这两个技术指标,可以更客观、更全面地评价一个企业的管理有效性。     

极值分布和威布尔分布异常数据的检验方法

本文对威布尔分布的极值分布异常数据的检验给出了一系列的方法，首先，导入了极值分布下一般Ｄｉｘｏｎ型统计量的精确分布，同时还给出了改进的Ｇ型统计量，及它们的分位点表。最后本文提出了一个新的统计量；Ｆ型统计量，并用Ｍｏｎｔｅ－Ｃａｒｌｏ模拟的方法给出其分位点表，从而首次给出威布尔分布异常值的直接检验方法。本文进一步讨论了这些检验方法的功效，且表明Ｆ型检验是最优的。