A realistic approach for modeling permeability of fibrous media: 3-D imaging coupled with CFD simulation

Determining permeability of fibrous media is of great importance to many industries. While there are several 2-D and 3-D analytical models developed for predicting the permeability of fibrous disordered media, there are not many numerical works that compare the predictions of these models with that of real media. In this work, we present a series of numerical simulations performed on the microstructure of a real fibrous media. An efficient procedure is presented for reconstructing 3-D images from the 2-D images of the real fibrous media and processing them for the purpose of performing fluid flow simulation. Digital volumetric imaging (DVI) of a typical hydroentangled fibrous fabric is obtained, as an example, and its permeability is computed. These results are compared with those obtained from the analytical equations given in the literature. In particular, it was found that permeability of a typical hydroentangled material can be closely predicted by the layered anisotropic models.     

Time-resolved cryotransmission electron microscopy

We describe a new technique, time-resolved cryotransmission electron microscopy (TRC-TEM), that can be used to study changes in microstructure occurring during dynamic processes such as phase transitions and chemical reactions. The sample is prepared on an electron microscope grid maintained at a fixed temperature in a controlled atmosphere. The dynamic process is induced on the grid by a change in pH, salt, or reactant concentration by rapid mixing with appropriate solutions. Alternatively, induction is by rapid change of specimen temperature, or by controlled evaporation of a volatile component. We call such procedures on-the-grid processing. The dynamic process is permitted to run for a defined time and then the thin-film specimen is thermally fixed by plunging into liquid ethane at its freezing point, producing a cryotransmission electron microscopy specimen. By repeating this procedure with varying delays between induction and sample fixation, we can observe transient microstructures. We demonstrate the use of TRC-TEM to study the intermediate structures that form during the transitions between Lα, I_II, and H_II liquid crystalline phases in phospholipid systems. We also identify several other possible applications of the technique.     

国外天基雷达的发展趋势

天基雷达工作在较高的高度,能够不受日照和天气条件的限制,全天候、全天时的对地、对空进行探测,具有可见光和红外遥感系统不可比拟的优点.文中介绍了国外天基雷达的发展水平,以及天基雷达在功能和平台上的多样性,分析了天基雷达系统及其未来发展趋势.     

含氧化叔胺侧基的水溶性酚醛树脂的合成与成像性能

本实验通过一锅、两步法制备改性酚醛树脂．首先利用环氧酚醛树脂F-44与二甲胺反应，得到叔胺化酚醛树脂，叔胺化树脂被双氧水氧化后得到最终目标产物，即含强极性氧化叔胺基团的酚醛树脂．实验表明，该新型树脂易溶于水和一些强极性溶荆，如四氢呋喃、乙二醇独甲醚和N，N-二甲基甲酰胺等．在热的作用下，树脂能够分解并失去水溶性，但仍可溶于一些有机溶剂．由该树脂与830nm激光增感染料匹配使用，树脂体系对红外光敏感，并能够通过中性水显影得到较为清晰的阴图型图像，表明该树脂有望用于免化学处理热敏激光成像领域．     

Nonhuman primate neuroimaging and cocaine medication development.

Given the important role of the dopamine transporter (DAT) in the addictive properties of cocaine, the development and use of compounds that target the DAT represents a reasonable approach for the pharmacological treatment of cocaine abuse. The present report describes a series of studies conducted in nonhuman primates that evaluated the effectiveness of DAT inhibitors in reducing cocaine self-administration. In addition, drug substitution studies evaluated the abuse liability of the DAT inhibitors. Positron emission tomography neuroimaging studies quantified DAT occupancy at behaviorally relevant doses, characterized the time-course of drug uptake in brain, and documented drug-induced changes in cerebral blood flow as a model of brain activation. Selective DAT inhibitors were effective in reducing cocaine use but high (>70%) levels of DAT occupancy were associated with significant reductions in cocaine self-administration. The selective DAT inhibitors were reliably self-administered but rates of responding were lower than those maintained by cocaine even at higher levels of DAT occupancy. A profile of slow rate of drug uptake in brain accompanied by a gradual increase in extracellular dopamine may account for the more limited reinforcing effectiveness of the DAT inhibitors. Selective serotonin transporter (SERT) inhibitors were also effective in reducing cocaine use and blocked cocaine-induced brain activation and increases in extracellular dopamine. Coadministration of SERT inhibitors with a selective DAT inhibitor was more effective than the DAT inhibitor administered alone, even at comparable levels of DAT occupancy. The results indicate that combined inhibition of DAT and SERT may be a viable approach to treat cocaine addiction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A multispectral imaging technique to determine concentration profiles of myoglobin derivatives during meat oxygenation

We have designed a multispectral imaging acquisition system to measure the relative concentration values of myoglobin forms inside meat during oxygenation. Images at 474, 525, 572 and 610 nm are used to compute the concentration of reduced myoglobin, oxymyoglobin and metmyoglobin with a spatial resolution of 0.0125 mm/pixel. From these images, pigment concentration profiles as a function of oxygenation time and depth beneath the surface were obtained. A model describing the diffusion of oxygen and the consumption of reduced myoglobin is numerically tested versus the measured concentration profiles. The model accurately fits the data with a Mean Root Squared Error equal to 0.253%. Precise definitions for position and width of pigment layers based in concentration profiles are given. The results suggest that multispectral imaging techniques combined with precise control and measurement of sample temperature and oxygen partial pressure will permit detailed studies of the myoglobin chemistry during oxygenation.     

Iterative Step-Like Reconstruction of Stratified Dielectric Media from Multifrequency Reflected-Field Data

We describe in this paper a frequency domain microwave method to reconstruct the permittivity profile of layered dielectric half-space. The inversion algorithm is based on the iterative Newton–Kantorovitch procedure applied to the Riccati nonlinear differential equation. To obtain a correction term to the initial profile, the integral equation relating to a small change of the profile function and corresponding change of the reflection coefficient is solved twice, with different systems of expanding functions for the unknown profile. The first set of functions is utilized to determine positions of the reflecting interfaces between layers. The second set represented by the Heaviside step functions provides the profile correction term completing the iteration. The proposed approach is valid for the essentially band-limited input data, that is, when both low- and high-frequency information is not available. This alleviates practical implementation especially from the viewpoint of antenna design, dielectric rods fed by TEM horns are used as transmitting/receiving antennas. Some numerical and experimental examples are presented for the input data in the frequency range of 1–4GHz, which demonstrate validity and robustness of the method for the complicated highly contrasted dielectric profiles.     

时间相关单光子计数记录快速荧光寿命图像

基于时间相关单光子计数(TCSPC)的荧光寿命成像(FLIM)的获取时间取决于成像的图像尺寸、样品寿命的精度及样品计数率.对于高密度荧光团样品,如染色组织或植物细胞,当前可用的样品计数率与TCSPC荧光寿命成像技术最高的计数率接近.该文描述了在高计数率下TCSPC性能,并估计计数损失及堆积效应.结果表明,整个体系的寿命误差比预料的要小.因此,TCSPC FLIM可在获取时间低于1 s的情况下记录寿命图像.为增加FLIM时间序列记录,利用存储交换技术,在采集下一个光子期间读取正在记录的数据,使用两个平行TCSPC模块,可以每秒两幅图像记录荧光寿命时间序列.该技术可应用于活体植物组织叶绿素的瞬态测量.     

Ladars for construction assessment and update

Work at the National Institute of Standards and Technology (NIST) on laser radar imaging of a construction site is described. The objective of the NIST research is to make measurements required in a construction project quicker and cheaper than current practice and to do so without impacting existing operations. This can be done by developing techniques for real-time assessment and documentation in terms of 3-D as-built models of the construction process. Once developed, this technology may be used for other applications such as condition assessment of a hazardous environment where human intervention would be impossible.