节理岩体圆形洞室岩爆过程的离散元分析与模拟

采用刚体离散单元法对节理岩体圆形洞室的岩爆过程进行了数值分析与模拟,并与有限元的数值分析结果,岩爆现场实测结果结果进行比较,相当一致。说明采用离散单元法对节理岩体洞室岩爆过程进行数值分析和数值模拟是可行的。     

Use of tortuosity for discriminating electro-facies to interpret the electrical parameters of carbonate reservoir rocks

The electrical parameters of 80 various carbonate rock plugs from a Saudi Arabian reservoir were measured. The results were first analyzed without considering the lithology, and then subsequently lithology was considered. Tortuosity distribution and correlations with other petrophysical parameters were used in differentiating samples of similar electrical properties, called “electro-facies”. Tortuosity distribution indicated two populations of data points one of which corresponded to the oolitic and skeletal-intraclastic lithofacies, referred to as “granular electro-facies”; and the other to the muddy and the dolomitic lithofacies, named “dolomitic-muddy electro-facies”.Three methods were applied to interpret the cementation factor: (1) the Archie; (2) the best fit; and (3) the cementation factor as a function of porosity. Error analysis showed that the Archie cementation factor was not an appropriate method for the studied reservoir rocks. The best fit and the cementation factor as a function of porosity methods yielded more reasonable results and they are recommended over the Archie method.A comparison of the water saturations obtained using the electrical parameters of the overall samples with the water saturations obtained using the parameters of each electro-facies showed significant errors especially in low water saturation zones. This indicates the importance of litho- or electro-facies discrimination in heterogeneous reservoirs.     

Local Groups Online: Political Learning and Participation

Voluntary associations serve crucial roles in local communities and within our larger democratic society. They aggregate shared interests, collective will, and cultivate civic competencies that nurture democratic participation. People active in multiple local groups frequently act as opinion leaders and create “weak” social ties across groups. In Blacksburg and surrounding Montgomery County, Virginia, the Blacksburg Electronic Village (BEV) community computer network has helped to foster nearly universal Internet penetration. Set in this dense Internet context, the present study investigated if and how personal affiliation with local groups enhanced political participation in this high information and communication technology environment. This paper presents findings from longitudinal survey data that indicate as individuals’ uses of information technology within local formal groups increases over time, so do their levels and types of involvement in the group. Furthermore, these increases most often appear among people who serve as opinion leaders and maintain weak social ties in their communities. Individuals’ changes in community participation, interests and activities, and Internet use suggest ways in which group members act upon political motivations and interests across various group types.      

Pharmacokinetics of mefloquine combined with artesunate in children with acute falciparum malaria

To study the biologic role of migration inhibitory factor (MIF), a pleiotropic cytokine, we generated a mouse strain lacking MIF by gene targeting in embryonic stem cells. Analysis of the role of MIF during sepsis showed that MIF-/- mice were resistant to the lethal effects of high dose bacterial lipopolysaccharide (LPS), or Staphylococcus aureus enterotoxin B (SEB) with D-galactosamine and had lower plasma levels of tumor necrosis factor alpha (TNF-alpha) than did wild-type mice, but normal levels of interleukin (IL)-6 and IL-10. When stimulated with LPS and interferon gamma, macrophages from MIF-/- mice showed diminished production of TNF-alpha, normal IL-6 and IL-12, and increased production of nitric oxide. MIF-/- animals cleared gram-negative bacteria Pseudomonas aeruginosa instilled into the trachea better than did wild-type mice and had diminished neutrophil accumulation in their bronchoalveolar fluid compared to the wild-type mice. Thioglycollate elicited peritoneal exudates in uninfected MIF-/- mice, but showed normal neutrophil accumulation. Finally, the findings of enhanced resistance to P. aeruginosa and resistance to endotoxin-induced lethal shock suggest that the counteraction or neutralization of MIF may serve as an adjunct therapy in sepsis.     

Chemical and Mechanical Properties of ZDDP Antiwear Films on Steel and Thermal Spray Coatings Studied by XANES Spectroscopy and Nanoindentation Techniques

X-ray Absorption Near Edge Structure (XANES) has been used to characterize the chemistry of tribochemical wear pads generated from a paraffinic base oil with a zinc-dialkyl-dithiophosphate additive on steel surfaces and high-velocity oxygen fuel (HVOF) thermal spray coatings. The phosphorus K- and L- edge XANES spectra show that the tribofilms formed on steel and the HVOF coatings have the same chemical nature. Also, mechanical properties of these tribofilms were examined by nanoindentation techniques using both Hysitron and Interfacial Force Microscopy (IFM) instruments. The elastic moduli extracted from indentation force-displacement (f-d) curves have demonstrated that tribofilms on steel and HVOF coatings have similar surface topography and mechanical properties.     

结势垒控制肖特基整流管特性分析与建模

在分析结势垒控制肖特基整流管工作机理的基础上，详细讨论器件特性与结构参数的关系；给出了器件优化设计的依据；建立了适用于ＳＰＩＣＥ电路分析程序的等效电路模型。     

Das Grenzflächenverhalten von SiC und seine Anwendung in faserverstärktem Aluminium

The interface Behavior of Sic and its Application to Fiber Reinforced Aluminium SiC barrier layers on carbon fibers can be deposited by thermal decomposition of methyl trichlorosilane. The influence of the CVD parameters on their structure and composition is presented by the results of surface-analytical and electronmicroscopical investigations. During the preparation of fiber reinforced Al chemical reactions and segregation effects result in the formation of undesirabled phases at the interface between matrix and fiber. The stability of the barrier layer is negativly influenced by it.     

Output feedback stabilization of cascaded ODE‐Wave equations with time delay in observation

In this paper, we are concerned with the stabilization of a cascaded ODE‐wave system subject to boundary observation with time delay. Well‐posedness of the open‐loop system is observable to show first. Both observer and predictor systems are designed to estimate the state variable on the time interval [0,t?τ] when the observation is available, and to predict the state variable on the time interval [t?τ,t] when the observation is not available respectively. Next, we transform the original system to the well‐posed and exponentially stable system by the backstepping method. Based on the estimated state variable and the output feedback stabilizing controller using the backstepping method. It is shown that the closed‐loop system is exponentially stable. The numerical simulation is presented to illustrate the effect of the stabilizing controller.     

Management of calcaneonavicular coalition and results

26 cases of calcanconavicular coalitions were treated by resection of the calcanconavicular bar. The endresults were markedly influenced by the age at surgery, while there was no difference between the "bone" and "cartilage" group. The coalition must be recognised if someone examinates a rigid flatfoot.     

Structure degradation of 25Cr35Ni heat-resistant tube associated with surface coking and internal carburization

Microstructures of 25Cr35Ni heat-resistant cracking tube after service were investigated and degradation mechanism of tube material was discussed. Results reveal that three distinguished zones, that is, internal oxide, carbide free, and internally carburized zones, will gradually develop in the inner wall of a cracking tube during service. Carbide free and internally carburized zones are formed primarily in relation to the periodic spalling and regeneration of surface oxide scale, and diffusion velocity of carbon and carbide forming elements in matrix and the solubility limit of carbon in alloy. The formation and growth of filament coke can aggravate structure degradation of the inner wall of the cracking tube, while deposition of lamellar and spheroidal coke may slow structure degradation to some extent. Surface coking and decoking cycles strongly aggravate the structure degradation of tube material and damage the service life of the cracking tube.