Laminar heat transfer enhancement downstream of a backward facing step by using a pulsating flow

This study is motivated by the need to devise means to enhance heat transfer in configurations, like the back step, that appear in certain types of MEMS that involve fluid flow and that are not very efficient from the thermal transfer point of view. In particular, the work described in this paper studies the effect that a prescribed flow pulsation (defined by two control parameters: velocity pulsation frequency and pressure gradient amplitude at the inlet section) has on the heat transfer rate behind a backward facing step in the unsteady laminar 2-D regime. The working fluid that we have considered is water with temperature dependent viscosity and thermal conductivity. We have found that, for inlet pressure gradients that avoid flow reversal at both the upstream and downstream boundary conditions, the time-averaged Nusselt number behind the step depends on the two above mentioned control parameters and is always larger than in the steady-state case. At Reynolds 100 and pulsating at the resonance frequency, the maximum time-averaged Nusselt number in the horizontal wall region located behind the step whose length is four times the step height is 55% larger than in the steady-case. Away from the resonant pulsation frequency, the time-averaged Nusselt number smoothly decreases and approaches its steady-state value.     

Identification of a Candida glabrata homologue of the S. cerevisiae VRG4 gene,encoding the Golgi GDP-mannose transporter

Mannoproteins on the cell wall of yeast and fungi help regulate cell shape, porosity, and cell-cell interactions, including those required for attachment to host cells by fungal pathogens. The mannose-containing oligosaccharides on proteins and lipids are extended in the Golgi by glycosyltransferases that use GDP-mannose as the sugar substrate. A membrane-bound transporter that, in Saccharomyces cerevisiae, is encoded by the VRG4 gene catalyses delivery of GDP-mannose into the lumen of the Golgi. We report here the cloning of the homologous VRG4 gene from the pathogenic yeast, Candida glabrata, by functional complementation of an S. cerevisiae vrg4 mutant. The sequence of the CgVrg4 protein displays significant homology to GDP-mannose transporters from other yeast, fungi, protozoa, and plants. CgVRG4 fully complements the glycosylation defect and other cell wall associated vrg4 mutant phenotypes. Like ScVRG4, CgVRG4 is essential for the viability of C. glabrata. These results suggest that, as in S. cerevisiae, CgVrg4p accounts for all of the GDP-mannose transport activity in the Golgi lumen.     

Low-Power and Compact CMOS APS Circuits for Hybrid Cryogenic Infrared Fast Imaging

This brief presents a complete set of CMOS basic building blocks for low-cost scanning infrared (IR) cryogenic imagers. Low-power and compact novel circuits are proposed for single-capacitor integration and correlated double sampling, embedded pixel test, pixel charge-multiplexing and video composition and buffering. In order to validate the new basic building blocks, experimental results are reported in standard 0.35-mum CMOS technology for a 50 mum x 100 mum active pixel cell operating at 77 K. Based on the proposed circuits, IR imagers capable of capturing up to 256 x 2560 pixels at 25 fps can be implemented.     

Nucleation and crystallization of PET droplets dispersed in an amorphous PC matrix

The present work compares the nucleation and crystallization process of poly(ethylene terephthalate) (PET) in bulk and when it is finely dispersed in a polycarbonate (PC) matrix. Two types of 80/20 PC/PET immiscible blends were prepared by twin-screw extrusion at different screw rotation rates in order to produce fine dispersions of PET. The results indicate that the finer the dispersion, the greater the inhibition of the crystallization of the PET droplets. These results are explained by demonstrating (through self-nucleation experiments) that a fractionated crystallization process was developed in the dispersed PET, since the number of PET particles was much greater than the number of heterogeneities originally present in the bulk polymer. The dispersion of PET into droplets also affects its crystallization rate during isothermal crystallization at high temperatures and its reorganization capacity during heating. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1725–1735, 1998     

Assessment of parameters influencing fiber characteristics of chitosan nanofiber membrane to optimize fiber mat production

Electrospun chitosan nanofiber mats have been obtained using chitosan solutions in a mixture of trifluoroacetic acid and dichloromethane. The relationship between processing parameters (solvent composition, polymer concentration in the solution, feeding rate, applied voltage, traveling distance between the needle, and the collector) and fiber morphology was studied. Taguchi's methodology was followed to determine which parameters have the strongest influence on mean fiber diameter and fiber homogeneity. Chitosan nanofibers obtained with this procedure were water soluble due to the protonation of amine side groups but were successfully neutralized by immersion in calcium carbonate solutions. It was established that fiber diameter is mainly determined by the solution concentration and the distance from the needle to the collector while other parameters have less influence. The set of parameters that produce the thinnest fibers were a concentration of 8 wt%, a TFA/DCM ratio of 80:20 (v/v%), a voltage of 30 kV, a flow rate of 6.0 mL/h, a gap distance of 10 cm, using a needle diameter of 0.5, allowing to produce randomly oriented mats with a mean fiber thickness of 66 nm. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Overview of the drug approval process.

Reviewed a database sponsored by the National Institutes of Health (NIH) that lists all clinical trials currently underway indicated that there are at least 400 investigational drugs in various stages of development for central nervous system (CNS) disorders, such as major depression, schizophrenia, Alzheimer's disease, and social anxiety disorder (NIH, 2002). Of the 65 new drugs approved in 2001, 10 were drugs for (CNS indications (S. Briggs et al., 2002). Given this level of activity, psychologists might benefit from an overview of the drug development process that would further their understanding of the dynamics involved in bringing a drug into the market. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of ultrasound on the permeability of D2O through cellulose membranes

The effect of ultrasound energy on the permeability of water through cellulose membranes was studied using deuterium oxide (D2O) as a tracer. The same membrane was used for control (no ultrasound) and ultrasound experiments in a sequential reversal design. Transfer of D2O to a 2% albumin solution was measured in a glass dializing cell with membrane area of 11 cm2. Ultrasonic energy was supplied for 45 min by a hydrosonic bath (Linden Laboratories) at an intensity of 0.18 watt/cm2, an energy level commonly used for therapeutic purposes. Statistical analysis showed a significant increase in water transfer due to the ultrasound treatment irrespective of the sequence of application of ultrasound. It was concluded that ultrasound energy increases water permeability through cellulose dializing membranes. Whether or not increased water permeability is the operating mechanism underlying the beneficial effects of ultrasonic bath therapy remains unanswered.     

Porcine pericardial membrane subjected to tensile testing: preliminary study of the process of selecting tissue for use in the construction of cardiac bioprostheses

The durability of cardiac bioprostheses is limited fundamentally by structural failure due to mechanical fatigue and calcification. In the present report, we analyze, using an in vitro hydraulic simulator to test tensile strength, the mechanical behavior of porcine pericardium for the purpose of establishing the criteria for selecting the biomaterial, taking into account both morphological criteria (thickness and homogeneity of the specimens) and mechanical criteria (stress at breaking point), using the epidemiological model of paired samples. The stress at breakage was found to range widely from 24.07 MPa to 100.29 MPa, although we observed no statistically significant differences when comparing the mean results in the different regions and zones of the pericardium being studies. The application of the selection criteria in the present series resulted in an excellent mathematical fit in terms of the stress/elongation (R ² > 0.95), making it possible to establish, by means of linear regression, the prediction of the tensile strength in one zone on the basis of the values observed in its paired specimen. © 2001 Kluwer Academic Publishers