Fabrication,characterization and low‐velocity impact testing of hybrid sandwich composites with polyurethane/layered silicate foam cores

A series of nanophased hybrid sandwich composites based on polyurethane/montmorillonite (PU/MMT) has been fabricated and characterized. Polyaddition reaction of the polyol premix with 4,4′‐diphenylmethane diisocyanate was applied to obtain nanophased PU foams, which were then used for fabrication of sandwich panels. It has been found that the incorporation of MMT resulted in higher number of PU cells with smaller dimensions and higher anisotropy index (cross sections RI and RII). The obtained materials exhibited improved parameters in terms of thermal insulation properties. The results also show that nanophased sandwich structures are capable of withstanding higher peak loads than those made of neat PU foam cores when subject to low‐velocity impact despite their lower density than that of neat PU foams. This is especially significant for multi‐impact recurrences within the threshold loads and energies studied. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Effects of gender-related geometrical characteristics of aorta–iliac bifurcation on hemodynamics and macromolecule concentration distribution

Aorta–iliac bifurcation has been anatomically shown to be asymmetric. Also, statistical data reveal differences in the structural features of average male and female aorta–iliac bifurcation. In the present work, numerical simulations of the macromolecule transport at the aorta–iliac bifurcation are performed. The transport phenomena within the lumen and the arterial wall are coupled. The arterial wall is modeled as a four-layer porous wall, representing endothelium, intima, internal elastic lamina (IEL), and media layers. The layers are all treated as macroscopically homogeneous porous media with uniform morphological properties. The Staverman filtration coefficient is incorporated to account for selective permeability of each porous layer to macromolecules. Different geometrical attributes of the aorta–iliac bifurcation are studied, i.e. asymmetry and gender-dependence. Profiles of macromolecule concentration distributions are obtained for different cases. The results are discussed with regard to the shear stress distribution, which is believed to be one of the key factors in atherogenesis. The present study appears to be the first one to discuss the effects of gender and geometrical characteristics (e.g. asymmetry) on the transport phenomena at the aorta–iliac bifurcation.     

Modeling and optimization of a large-scale slurry bubble column reactor for producing 10,000 bbl/day of Fischer-Tropsch liquid hydrocarbons

A user-friendly simulator based on a comprehensive computer model for slurry bubble column reactors (SBCRs) for Fischer-Tropsch (F-T) synthesis, taking into account the hydrodynamics, kinetics, heat transfer, and mass transfer was developed. The hydrodynamic and mass transfer data obtained in our laboratories under typical F-T conditions along with those available in the literature were correlated using Back Propagation Neural Network and empirical correlations with high confidence levels. The data used covered wide ranges of reactor geometry, gas distributor, and operating conditions. All reactor partial differential equations, equation parameters and boundary conditions were simultaneously solved numerically.The simulator was systematically used to predict the effects of reactor geometry (inside diameter and height) as well as superficial gas velocity and catalyst concentration on the performance of a large-scale SBCR provided with cooling pipes and operating under F-T conditions with cobalt-supported catalyst and H₂/CO = 2. The performance of the SBCR was expressed in terms of CO conversion, liquid hydrocarbon yield, catalyst productivity, and space time yield. The simulator was also used to optimize the reactor geometry and operating conditions in order to produce 10,000 barrels/day (bbl/day) of liquid hydrocarbons.     

A self-calibration technique for wide tuning range PLLs

This paper presents a new calibration technique applicable for wide tuning range phase locked loops (PLLs) using very low gain voltage controlled oscillators (VCO). This technique uses the PLL main loop for the coarse and fine tuning of the VCO. Instead of using two loops which has been reported in previous works, in this work the VCO tuning voltage is used to calibrate the VCO switch capacitor array. Since the proposed calibration circuit operates in a closed loop form, it can be used for channel selection as well as adjusting for process, voltage and temperature variations. In addition, the calibration circuit has been used to set the VCO tail current in order to optimize VCO phase noise. A prototype frequency synthesizer has been designed in 0.18-μm CMOS process to work for a frequency range from 2.4 to 2.72 GHz. Simulation results show that using the proposed technique, a spur level of ?60 dB at 5 MHz offset from carrier was achieved while having negligible power overhead.     

Functional near-infrared neuroimaging.

Functional near-infrared spectroscopy (fNIR) is a neroimaging modality that enables continuous, noninvasive, and portable monitoring of changes in blood oxygenation and blood volume related to human brain function. Over the last decade, studies in the laboratory have established that fNIR spectroscopy provides a veridical measure of oxygenation and blood flow in the brain. Our recent findings indicate that fNIR can effectively monitor cognitive tasks such as attention, working memory, target categorization, and problem solving. These experimental outcomes compare favorably with functional magnetic resonance imaging (fMRI) studies, and in particular, with the blood oxygenation level dependent signal. Since fNIR can be implemented in the form of a wearable and minimally intrusive device, it has the capacity to monitor brain activity under real life conditions and in everyday environments. Moreover, the fNIR system is amenable to integration with other established physiological and neurobehavioral measures, including electroencephalogram, eye tracking, pupil reflex, heart rate variability, respiration, and electrodermal activity.     

Analytical characterization of heat transport through biological media incorporating hyperthermia treatment

Modeling and understanding heat transport and temperature variations within biological tissues and body organs are key issues in medical thermal therapeutic applications, such as hyperthermia cancer treatment. The biological media can be treated as a blood saturated tissue represented by a porous matrix. A comprehensive analytical investigation of bioheat transport through the tissue/organ is carried out including thermal conduction in tissue and vascular system, blood–tissue convective heat exchange, metabolic heat generation and imposed heat flux. Utilizing local thermal non-equilibrium model in porous media theory, exact solutions for blood and tissue phase temperature profiles as well as overall heat exchange correlations are established for the first time, for two primary tissue/organ models representing isolated and uniform temperature conditions, while incorporating the pertinent effective parameters, such as volume fraction of the vascular space, ratio of the blood and the tissue matrix thermal conductivities, interfacial blood–tissue heat exchange, tissue/organ depth, arterial flow rate and temperature, body core temperature, imposed hyperthermia heat flux, metabolic heat generation, and blood physical properties. A simplified solution based on the local thermal equilibrium between the tissue and the blood is also presented.     

Application of a generic bow-tie based risk analysis framework on risk management of sea ports and offshore terminals

Ports and offshore terminals are critical infrastructure resources and play key roles in the transportation of goods and people. With more than 80 percent of international trade by volume being carried out by sea, ports and offshore terminals are vital for seaborne trade and international commerce. Furthermore in today's uncertain and complex environment there is a need to analyse the participated risk factors in order to prioritise protective measures in these critically logistics infrastructures. As a result of this study is carried out to support the risk assessment phase of the proposed Risk Management (RM) framework used for the purpose of sea ports and offshore terminals operations and management (PTOM). This has been fulfilled by integration of a generic bow-tie based risk analysis framework into the risk assessment phase as a backbone of the phase. For this reason Fault Tree Analysis (FTA) and Event Tree Analysis (ETA) are used to analyse the risk factors associated within the PTOM. This process will eventually help the port professionals and port risk managers to investigate the identified risk factors more in detail. In order to deal with vagueness of the data Fuzzy Set Theory (FST) and possibility approach are used to overcome the disadvantages of the conventional probability based approaches.     

Spray drying microencapsulation of natural canthaxantin using soluble soybean polysaccharide as a carrier

Microencapsulation of canthaxanthin produced by Dietzia natronolimnaea HS-1 using soluble soybean polysaccharide (SSPS) as a wall material by spray drying method was studied. The SSPS showed very good ability for microencapsulation of canthaxanthin due to its emulsifying properties. The effects of the ratios of core to wall on characteristics of microcapsules were investigated at ratios of 0.25, 0.50, 0.75, and 1.00. The best ratio of core to wall was 0.25 because the microcapsules prepared with this ratio had the smallest size in droplets (0.78 μm) and microcapsules (7.94 μm), also they had the highest microencapsulation efficiency (90.1%) and the lowest losing during process (10.3%). The stability of microcapsules was examined at 25°C in light and dark during 16 weeks of storage. The degradation of canthaxanthin was more retarded by microencapsulation and greater canthaxanthin stability was observed in dark than light condition. The results showed the oxidation was more suppressed for the microcapsules prepared from the emulsion having smaller droplets.