仓库容量有限条件下的随机存贮管理

建立了一种仓库容量有限条件下,订货后到货时间为随机变量的允许缺货单商品存贮模型,给出最佳订货点满足的积分方程,并通过例子说明可借助Matlab来求解该模型。然后推广到多种商品情形,最后讨论了商品销售速率随机情况下模型的建立和求解。     

Low-cost solid FeS lubricant as a possible alternative to MoS<Subscript>2</Subscript> for producing Fe-based friction materials

Three reaction systems of MoS₂-Fe, FeS-Fe, and FeS-Fe-Mo were designed to investigate the use of FeS as an alternative to MoS₂ for producing Fe-based friction materials. Samples were prepared by powder metallurgy, and their phase compositions, microstructures, mechanical properties, and friction performance were characterized. The results showed that MoS₂ reacts with the matrix to produce iron-sulfides and Mo when sintered at 1050℃. Iron-sulfides produced in the MoS₂-Fe system were distributed uniformly and continuously in the matrix, leading to optimal mechanical properties and the lowest coefficient of friction among the systems studied. The lubricity observed was hypothesized to originate from the iron-sulfides produced. The FeS-Fe-Mo system showed a phase composition, porosity, and density similar to those of the MoS₂-Fe system, but an uneven distribution of iron-sulfides and Mo in this system resulted in less-optimal mechanical properties. Finally, the FeS-Fe system showed the poorest mechanical properties among the systems studied because of the lack of Mo reinforcement. In friction tests, the formation of a sulfide layer contributed to a decrease in coefficient of friction (COF) in all of the samples.     

Trends of the precipitation acidity over China during 1992–2006

The trends of the precipitation acidity from 1992 to 2006 were studied, based on the long-term acid rain observations at 74 sites in China. The results show that there was no remarkable change or extension of acid rain area (i.e., with annual mean of precipitation pH<5.6) during the 15 years. The largest and continuous acid rain area exists in the south of the Yangtze River, while the acid rain areas north of the Yangtze River remain separate. The severe acid rain area (i.e., with annual mean of precipitation pH<4.5) exists mainly in the south of the Yangtze River. The overall precipitation acidity for the 74 stations showed different trends before 1999 and after 2000. In the period 1992–1999, the precipitation acidity at most of the sites remained steady or showed a decreasing trend. After 2000, however, an increasing trend of the precipitation acidity was observed at many sites in North China, Central China, East China, and South China. As a result, the pattern of acid rain area changed during 1992–2006. The precipitation over North China, Central China, and South China became more acidified in the 15 years, with more pronounced trends in North China and the north of Central China. A slight decrease in the precipitation acidity was found in Southwest China, an area characterized as severest acid rain area for about two decades after the early 1980s. Consequently, the center of severe acid rain area in the south of the Yangtze River moved eastwards. The non-hydrogen conductivity (NHC), which is defined as the difference between the measured precipitation conductivity and the H+ conductivity calculated from measured pH, was estimated and treated as a proxy of soluble ions in precipitation. The result shows that the overall trend of the NHC before 1999 was pronounced and positive, while the trend after 2000 was inconspicuous or slightly negative. During 2000–2006, the change rate of pH was positively correlated to that of the NHC at 21 sites, implying that the increasing acidities found at these sites may partly be attributed to the decrease in the concentration of airborne particulate matter in recent years.     

厨房里的阿诗玛：彝族撒尼人食物体系的符号化表述

饮食在地理区位上的表述是＂菜系＂,而当以＂族群文化＂对饮食进行分类时,诸多的＂民族菜＂就已经端上了人类学家的＂餐桌＂。在文化旅游的背景下,为吸引游客进行＂舌尖上的探访＂,＂民族风味＂在原生状态的味觉传承中,又加入了＂文化想象＂的符号化流转,对饮食进行着符号化的表述与传播。文章以彝族撒尼人食物体系的符号化表述为个案,观察＂阿诗玛文化＂是如何在＂厨房＂与＂餐桌＂之间刻写食物的故事,呈现那个＂厨房里的阿诗玛＂。     

微重力状态下细水雾雾场特性仿真

针对细水雾灭火在载人航天器安全中的应用,采用计算流体动力学（CFD）的方法进行了研究.在建立压力旋流喷嘴液膜式雾化模型及微重力场雾滴运动轨迹模型的基础上,利用计算流体动力学仿真软件FLUENT中的离散相模型（DPM）分析了微重力状态下细水雾雾场特性,包括微重力下细水雾的雾化图形、速度以及雾粒直径分布.仿真结果表明：微重...     

ICU病人褥疮的预防和护理

褥疮是临床常见的并发症之一,因ICU病人大多为长期卧床病人,患病率更高。文章通过对文献资料和临床实践的分析,对褥疮的预防与护理进行综述,并提出提高ICU病人褥疮的预防与护理水平的方法。     

Is the polydispersity exponent of the hyperbranched polymers the 3/2 or 5/2？

Dendrimers and hyperbranched polymers have re- ceived much attention in recent decade due to their novel physical and chemical properties, such as multi- ple end groups, high solubility, and reduced viscosities relative to their linear counterparts, and h…     

Infection of Wolbachia may improve the olfactory response of Drosophila

The endosymbiotic bacterium Wolbachia infects various insects and is primarily known for its ability to manipulate host reproduction.Recent investigations reveal that Wolbachia also affects the activity of somatic cells.We here demonstrated by trap method and T-maze that Wolbachia infection had signifi-cant impact on the olfactory response of Drosophila simulans.Wolbachia-infected flies took shorter time to enter the food trap and were more sensitive to odorant in T-maze than those uninfected controls.The t...     

一类复合系统稳定性分析

考虑一类复合系统的稳定性问题，得到类似于线性规划的结果。     

氨活塞式双级制冷压缩机轴功率和单位轴功率制冷量的计算

根据生产厂家[2]提供的产品样本和A．C．Cleland[3]提出的制冷剂热力学参数快速求值的方法，采用计算机绘制活塞式双级制冷压缩机在实际工况下的轴功率和单位轴功率制冷量变化曲线，计算和拟合出双级制冷压缩机轴功率数学模型，为实现制冷系统节能提供理论依据。