Microfluidic chip for spatially and temporally controlled biochemical gradient generation in standard cell-culture Petri dishes

This paper reports the development, modeling, and testing of an original microfluidic chip capable of generating both time-evolving and spatially varying gradients in standard Petri dishes. It consists of three sets of five independently controlled parallel channels, and its architecture allows the generation of complex gradient profiles that can be flexibly positioned and dynamically altered in an open cell-chamber environment. A detailed fabrication protocol for the production of these chips using multilayer soft lithography is reported. A comprehensive computational model is also presented based on COMSOL Multiphysics software that includes both diffusion and advection of the fluid as it exits the microchannels. The results of the simulation are successfully applied to model single-channel experiments. The chip is then tested in multi-channel mode, and its ability to produce complex spatially varied concentration profiles is demonstrated. The achievement of steady state of the gradient profile in less than 5 min also allows for the dynamic variation of the profile. Finally, we apply the present chip architecture to investigate the migration of mouse neutrophils in an Interleukin-8 gradient. We report quantitatively on cell migration driven by Interleukin-8 gradient and provide migration speed distribution.     

提高DC-DC变换器效率用高单元密度屏蔽栅功率MOSFET

本文介绍了飞兆半导体公司最新开发的高单元密度、屏蔽栅功率MOSFET的结构。这种屏蔽栅结构有助于建立电荷平衡,从而减少MOSFET的通态电阻和栅电荷。这种新技术能使通态电阻比前一代减少50%以上。为进一步改善器件特性,一种肖特基器件也被单片集成在这种新型MOSFET中,使得反向恢复电荷减少了将近20%。上述措施直接减小了在高频、大电流和高输入电压下非常关键的体二极管损耗。该新型器件在典型的同步降压变换器应用中,能提供1.5%的最高效率改进。     

Modelling material separation processes in bulk recycling

Increasing environmental concerns about the disposal of mass produced products have resulted in efforts to recover value from components and materials before discarding such products. Methods include incineration, disassembly or de-manufacturing and bulk recycling. This paper investigates several cases of the problem of selecting the best sequence for recovery of materials by bulk recycling. A solution procedure for determining the optimal sequence for isolating all target materials present in a given batch based on dynamic programming is presented. A modification for targeting specific materials in a batch is discussed. Additional constraints arising from the operation of such facilities are also discussed. The general problem of target material identification is presented and a procedure for selecting a profitable target material mix, along with a numerical illustration, is documented. Finally, the integrated consideration of bulk recycling and disassembly for evaluating product disposal costs is presented.     

Synthesis and characterization of nanocrystalline zinc aluminate spinel powder by sol–gel method

Single-phase nanocrystalline zinc aluminate (ZnAl₂O₄) spinel powder has been synthesized by the sol–gel method. Zinc aluminate nanoparticles were formed at 600 °C, which is at much lower temperature than by solid state reactions. Formation of ZnAl₂O₄ and their particle size depend on the calcination temperature. Calcination temperature also affects the specific surface area and pore volume. The nanocrystalline zinc aluminate was characterized by powder X-ray diffraction, FT-IR spectroscopy, thermal gravimetric analysis, diffuse reflectance spectroscopy, surface area measurements, field emission scanning electron microscopy coupled with energy dispersive X-ray analysis and transmission electron microscopy. Catalytic reactivity of nanocrystalline zinc aluminate was tested for the reduction of 4-nitrophenol to 4-aminophenol using NaBH₄.     

Ice Thrust in Reservoirs

We undertook a three-year program to measure the magnitude of static ice forces in four reservoirs located in central and northern Quebec. These static forces may be generated by a temperature change or may arise from such other mechanisms as water level variations, wind, and current drag force. Field observations have revealed two important facts: (1) ice covers have circumferential cracks caused either by water level variations or thermal contraction, and (2) the static ice forces are, in some instances, sufficient to trigger an instability of the broken ice covers by buckling. Noting that an ice cover cannot transmit a force to a structure larger than its own resistance, we derive an upper bound for static forces by determining the in-plane compression force at which a fragmented ice cover collapses. Empirical formulas are presented for three typical structure shapes: retaining walls, sluice gates, and piers. These formulas correlate well with the field data collected from the four dam sites, and suggest that the maximum ice thrust may simply be defined as a function of ice thickness and contact geometry.     

Open-circuit to short-circuit switching: method for lifetime measurement in solar cells

A new method is suggested for measurement of lifetime of photoinjected carriers in the base layer of a p-n junction solar cell. The cell is switched from the open-circuit to the shortcircuit mode of operation by using a negative voltage pulse. C.R.O. trace of the output voltage pulse provides a direct means for lifetime measurement.     

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A study on video semantics; overview,challenges, and applications

Multimedia Tools and Applications - Due to the increase in surveillance systems, there is a massive increase in surveillance data. As of now, the key challenge for video surveillance systems is...