Strömungsvisualisierung mit Texturen

Visualisation of Flow with the Aid of Textures Many new methods of flow visualisation have been developed in recent years. One of the most promising approaches is the visualisation of flow with the aid of textures. Textures are graphic structures containing directional information. They can be calculated with the Line Integral Convolution (LIC) algorithm developed by Cabral and Leedom, according to which pixel-oriented random entry fields are convoluted along integral lines. This paper uses the LIC algorithm for texture generation. Known procedures for texture generation and for spatial representation of textures are considered and extended by the authors' own work. Textures are compared with traditional approaches, which use flow lines and vector arrows for flow visualisation, and evaluated. In their presentation of the topic the authors use a easily comprehensible representation which the user can readily reproduce rather than an exact mathematical-statistical analysis of texture generation.     

Temperature dependence of the magnetic volume susceptibility of human breast fat tissue: an NMR study

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Proton resonance frequency shift (PRFS)-based MR thermometry (MRT) is hampered by heat-induced susceptibility changes when applied in tissues containing fat, e.g., the human breast. In order to assess the impact of fat susceptibility changes on PRFS-based MRT during thermal therapy in the human breast, reliable knowledge of the temperature dependence of the magnetic volume susceptibility of fat, dχ_fat/dT, is a prerequisite. In this work we have measured dχ_fat/dT of human breast fat tissue, using a double-reference method to ensure invariance to temperature-induced changes in the proton electron screening constant.     

Inhibition of reinforcing effects of morphine and naloxone-precipitated opioid withdrawal by novel glycine site and uncompetitive NMDA receptor antagonists

The glycine site (MRZ 2/570 and L-701,324), and uncompetitive (MRZ 2/579) NMDA receptor antagonists inhibited morphine-produced behaviors related to drug-abuse. The expression of morphine dependence was blocked by pretreatment with all three compounds (3-7.5 mg/kg); the effects of glycine/NMDA antagonists were not dose-dependent. Mice which were morphine-free for 3 days still displayed a significant severity of the withdrawal syndrome when challenged again with naloxone. This extinction of a residual morphine dependence was markedly diminished by treatment with similar doses of NMDA receptor antagonists at the test following the wash-out period. The rewarding impact of morphine was investigated in rats using the place preference (CPP) paradigm. All NMDA receptor antagonists (2.5-10 mg/kg) inhibited both the acquisition and expression of morphine-induced CPP. Once established, morphine-induced CPP was observed until 2 weeks after conditioning. NMDA receptor antagonists given for 3 days after the end of conditioning did not influence the extinction of morphine-induced CPP. Microdialysis studies revealed that the behaviorally effective doses of MRZ 2/579 resulted in a brain concentration close to its in vitro potency as an NMDA receptor antagonist. These data suggest that novel glycine site and uncompetitive NMDA receptor antagonists may have therapeutic potential in the treatment of opioid abuse.     

新拌水泥浆体中邻近胶凝材料粒子表面最近间距分布的解析解

依据Torquato的最邻近表面函数公式, 推导了新拌水泥浆体邻近水泥粒子表面最近间距分布的解析解, 并采用计算机模拟生成了1个水泥浆体结构模型, 选取邻近粒子表面最近间距概率密度分布曲线、 区间概率曲线和累计概率分布曲线这3个函数检验模拟结果与理论结果之间的差别。结果表明, 该解析解与计算机模拟实验结果吻合良好。利用该解析解, 以Rosin-Rammler分布为例, 研究了胶凝材料细度以及水胶比对邻近水泥粒子表面最近间距分布及其平均值的影响。结果显示, 水泥细度对邻近粒子表面最近间距平均值的影响高于水胶比的影响。邻近粒子表面最近间距解析解的获得, 不但为基于不同粒径分布以及尺度范围粉体之间搭配的高粉体初始堆积密度的实现提供了依据, 而且对多尺度模拟方法中选取各级模型的尺度、 量化粉煤灰浆体中粉煤灰颗粒的微集料效应、 了解邻近集料间的交互作用程度以及界面重叠程度等问题具有参考价值。     

Bounded delay for a free address

 The problem is to let n processes concurrently and repeatedly search for free addresses in a range of m addresses. The search must be wait-free: a searching process finds an address in a bounded number of steps. Three solutions are presented. The first one has large atomic actions. The second one is only correct if m≧(r+1) ⋅ n where r is the maximum number of used addresses. The third solution is always partially correct. It is wait-free if m>r+2 ⋅ n. This solution has a worst-case waiting time quadratic in n and an amortized waiting time linear in n, even linear in the number of active processes. Received February 2, 1994/January 24, 1995     

Stop-flow programmable selectivity with a dual-column ensemble of microfabricated etched silicon columns and air as carrier gas

A series-coupled ensemble of microfabricated GC columns made by dry reactive ion etching of silicon substrates is evaluated for use with pneumatic selectivity enhancement techniques for targeted pairs of volatile organic compounds. Each column is 3.0 m long with a 150 miceom wide by 240 microm deep cross section. Dynamic coating was used to prepare a nonpolar column with a dimethyl polysiloxane stationary phase and a moderately polar column with a trifluoropropylmethyl polysiloxane stationary phase. Each column generates 5000-6000 theoretical plates. The columns are operated in series with the nonpolar column connected to a split inlet, the polar column connected to a flame ionization detector, and a valve connected between the column junction point and the inlet to the first column. When the valve is closed, the effluent from the first column passes directly into the second column. When the valve is open, both ends of the first column are at the inlet pressure, and flow stops in this column while increased flow is obtained in the second column. For analyte pairs that are separated by the first column but coelute from the column ensemble, the valve is opened for a few seconds after the first component of the pair has passed into the second column but the second component is still in the first column. The result is enhanced separation of the pair in the ensemble chromatogram. Relatively thick cross-linked stationary-phase films are used to increase retention for volatile compounds. The combination of air carrier gas and stationary-phase film thickness in the range 1-2 microm requires the use of relatively low average carrier gas velocities (typically less than 10 cm/s) for adequate resolving power of the column ensemble. Selectivity enhancement under isothermal conditions for a 14-component mixture of volatile organic compounds is demonstrated where neither of the columns alone nor the column ensemble without selectivity enhancement could obtain a complete separation.