Fluid Dynamics and Transfer Processes in Bended Microchannels

Abstract

The understanding of the flow processes in microchannels and micromixers is essential for the design of microfluidic devices like microreactors or analytical equipment. We have performed a systematic numerical CFD-study of mixing and mass transfer in sharp 90° bends and heat transfer in T-joints to obtain a detailed insight into the flow patterns and corresponding transfer processes in a wide range of Reynolds numbers. With increasing flow velocity, the straight laminar flow starts to form symmetrical vortices in the bend, at the entrance of the mixing channel, and in T-joints. The vortices enhance the transport processes like heat and mass transfer in the channels significantly. The influence of the geometry and the flow conditions is shown by an analytical estimation of the relevant forces. The appearance of convective transport processes is used for the definition of microflows, which are controlled by viscous forces and diffusive transfer processes.     

照明相胶和世界市场

Peter Koepff是德国DGF明胶厂的原常务董事,现为新创办的Gelita明胶公司总裁,是明胶生产和管理专家。本编辑部曾向他约稿,为本刊撰写论文,这是一篇题为“Photographic Gelatin and the World Market”的论文,曾在1999年IAG学术报告会上宣读,现在本刊发表。考虑到外语在我国普及的程度和我国明胶界大多数管理干部、科技人员及众多读者都具有一定的英语阅读水平,现摘取主要部分以原文发表,供研究参考。     

What is coded into memory in the absence of outcome feedback?

Although people often have to learn from environments with scarce and highly selective outcome feedback, the question of how nonfeedback trials are represented in memory and affect later performance has received little attention in models of learning and decision making. In this article, the authors use the generalized context model (Nosofsky, 1986) as a vehicle to test contrasting hypotheses about the coding of nonfeedback trials. Data across 3 experiments with selective decision-contingent and selective outcome-contingent feedback provide support for the hypothesis of constructivist coding (Elwin, Juslin, Olsson, & Enkvist, 2007), according to which the outcomes on nonfeedback trials are coded with the most likely outcome, as inferred by the individual. The relation to sampling-based approaches to judgment, and the adaptive significance of constructivist coding, are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Noncentrosymmetric phase of submicron NaNbO<Subscript>3</Subscript> crystallites

The temperature and pressure characteristics of a noncentrosymmetric crystal modification of NaNbO₃ were studied by Raman spectroscopy. A transition towards the bulk-like structure of NaNbO₃ occurs in the temperature range from 280 to 360 °C. High-pressure Raman spectroscopy revealed successive pressure-induced phase transitions at around 2, 6.5 and 10 GPa. Raman scattering profiles recorded above 7 GPa correspond to those reported for the bulk. The temperature-induced spectral changes were completely reversible between −150 and 450 °C. Those induced by pressure were almost reversible from ambient pressure up to 15.9 GPa. Piezoresponse force microscopy demonstrated the occurrence of piezoelectric activity for submicron NaNbO₃ crystals with particle size ranging from 200 to 400 nm. The noncentrosymmetric crystallographic structure plays a critical role for the enhancement of piezoelectricity.     

无线技术最新进展

策略和战术：加工行业中的用户和供应商,就执行工作、合适的用途和厂级无线技术标准所遇到的障碍进行讨论。     

Market-based control of computational systems: introduction to the special issue

We introduce the Special Issue of the journal on the topic of Market-Based Control of Computational Systems. The special issue collects six peer-reviewed papers arising from an International Workshop on the topic held in Liverpool, UK, in September 2008.