Experimental Investigation of the Thermal Performance of Graphite Foam for Evaporator Enhancement in Both Pool Boiling and an FC-72 Thermosyphon

High-conductivity graphite foam is investigated for use as a surface enhancement for improved thermal performance in both pool boiling and an FC-72 thermosyphon. The influences of heat load and fluid level on the overall system thermal performance including surface superheat, effective heat transfer coefficient, and thermal resistance are examined. The thermal resistance of the foam heat sink is found to be extremely low at a minimum of 0.024 K/W, well below that of many other methods. The featured low thermal resistance is the primary benefit of this system. The thermal resistance is found to rise with increasing heat flux, but still remains advantageously low and exhibits excellent potential for high heat flux dissipation with low surface superheat, making it suitable for thermal management of advanced electronics.     

Equilibrium pressure measurements in the Li-N-H system by static manometric method

The equilibrium pressure over the phase mixture (Li₂NH + LiNH₂ + LiH) was measured from 343 to 683 K by static manometric method. The plot of ln (p_eq/p⁰) versus (1/T) showed three distinct temperature regions with different slopes. Analysis of the equilibrium gas composition in each temperature regions revealed that the equilibrium gas is a mixture of H₂, NH₃ and N₂ below 443 K whereas above 443 K, the equilibrium gas is mainly H₂. The enthalpy and entropy of the reaction of H₂ with Li₂NH to form LiNH₂ and LiH are found to be −55.0 ± 1.3 kJ?mol⁻¹ and −86 ± 2 J?K⁻¹?mol⁻¹, respectively at 523 K, where LiNH₂ exists in the solid state and −18.5 ± 0.5 kJ?mol⁻¹ and −26 ± 1 J?K⁻¹?mol⁻¹, respectively at 658 K, where LiNH₂ exists in the liquid state. The enthalpy and entropy of melting of solid LiNH₂ are calculated as 36.5 ± 1.4 kJ?mol⁻¹ and 60 ± 2 J?K⁻¹?mol⁻¹, respectively.     

Some studies on the warm solid- and hollow-extrusion of sintered powder metallurgical copper preforms

The warm extrusion of sintered P/M preforms of electrolytically pure copper has been investigated for extrusion strains of 0.35, 0.5, 0.66 and 0.81 for the solid configuration and 0.43, 0.62, 0.85 and 1.09 for the tubular configuration at temperatures of 303, 363, 433, 493 and 563 K with densities of 7.45 and 7.90 g cm⁻³ for the solid configuration and 7.0 and 7.7 g cm⁻³ for the tubular configuration. Force requirements and microstructural property evaluation have been attempted. Using the standard axial ring-compression test on the initial preforms, the plastic properties were evaluated to enable the computation of theoretical forces. The actual forces were compared with these theoretical forces and a correction factor, φ, then determined. The influence of strain, temperature and the geometry in ensuring near to theoretical density of the extrudates has been assessed.     

Disk diffusion susceptibility testing of dermatophytes with imidazoles

Flupirtine belongs to the class of triaminopyridines and is successfully applied clinically as a non-opiate analgesic drug with additional muscle relaxant properties. Recently it was reported that flupirtine acts like an antagonist of the N-methyl-D-aspartate (NMDA) receptor complex in neuronal cells both in vitro and in vivo. Here we have used primary cortical cells from rat embryos to demonstrate that this compound is also neuroprotective against the toxic effects caused by the prion agent PrPSc and lead acetate (Pb). These two agents display pleiotropic effects on neurons, which include activation of the NMDA receptor complex. At concentrations above 30 microM the toxic-peptide fragment of PrPSc causes apoptotic fragmentation of DNA and is consequently neurotoxic. Pb is neurotoxic at concentrations above 10 microM. Co-administration of flupirtine (10 microM) with either of these agents resulted in reduced neurotoxicity. These data indicate that the cytoprotective effect of flupirtine is measurable in vitro against these noxious agents which show their effects, including modulation of the NMDA receptor complex, pleiotropically.     

Influence of scattering and two-photon absorption on the optical loss in GaAs-Al/sub 2/O/sub 3/ nonlinear waveguides measured using femtosecond pulses

The influence of scattering and two-photon absorption on the optical loss in GaAs-Al/sub 2/O/sub 3/ semiconductor nonlinear waveguides has been studied using femtosecond pulses. By deploying a scattering technique, loss coefficients were evaluated over an extended wavelength range of 1.3-2.1 /spl mu/m in the near-infrared. A systematic study involving intensity and wavelength dependence of the loss revealed the presence of two-photon absorption for wavelengths below 1.6 /spl mu/m. A simple nonlinear transmission study enabled the separation of the two-photon absorption coefficient from scattering and linear absorption. The calculated two-photon absorption coefficients were /spl sim/9-20 cm/GW.     

AC impedance study on the activation mechanism of aluminium by indium and zinc in 3.5% NaCl medium

Activation of aluminium by In³⁺ and Zn²⁺ ions in chloride media has been investigated by using potentiodynamic polarisation, potential vs. time measurements, electrochemical impedance spectroscopy and scanning electron microscopy studies. It is suggested that indium exhibits In⁺ and In²⁺ intermediates during the dissolution and redeposition processes. Incorporation of any of these lower valent ions changes the defect structure of the passive film, leading to an increase in anionic vacancies and a decrease in the number of electrons, promoting active dissolution of aluminium. The role of zinc is to moderate localised attack by increasing the electron concentration and cation mobility, thereby lowering the corrosion rate at activated sites.     

Aloe vera incorporated biomimetic nanofibrous scaffold: a regenerative approach for skin tissue engineering

Aloe vera (AV) is one of the medicinal herbs with a well-established spectrum of wound healing, antimicrobial and anti-inflammatory property. AV-mediated therapeutics present significant tissue regenerative activity by modulating the inflammatory and proliferative phases of wound healing. The purpose of the present work was to combine the biological properties of AV and the advantages of electrospun meshes to prepare a potent transdermal biomaterial. The polycaprolactone (PCL) containing 5 and 10 wt % of lyophilized powder of AV was studied for electrospinning into nanoscale fiber mats and compared with PCL/Collagen blend for dermal substitutes. SEM revealed the average diameters of PCL, PCL-AV 5 %, PCL-AV 10 % and PCL/Collagen nanofiber scaffolds in the range of 519 ± 28, 264 ± 46, 215 ± 63 and 249 ± 52 nm, respectively. PCL-AV 10 % nanofiber scaffolds showed finer fiber morphology with improved hydrophilic properties and higher tensile strength of 6.28 MPa with a Young’s modulus of 16.11 MPa desirable for skin tissue engineering. The nanofibers were then used to investigate differences in biological responses in terms of proliferation and cell morphology of mice dermal fibroblasts. It was found that PCL-AV 10 % nanofibrous matrix favored cell proliferation compared to other scaffolds which almost increased linearly by (p ≤ 0.01) 17.79 % and (p ≤ 0.01) 21.28 % compared to PCL on sixth and ninth day. CMFDA dye expression, secretion of collagen and F-actin expression were significantly increased in PCL-AV 10 % scaffolds compared to other nanofibrous scaffolds. The obtained results proved that the PCL-AV 10 % nanofibrous scaffold is a potential biomaterial for skin tissue regeneration.     

Elastomeric electrospun scaffolds of poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide-<Emphasis Type="Italic">co</Emphasis>-trimethylene carbonate) for myocardial tissue engineering

In myocardial tissue engineering the use of synthetically bioengineered flexible patches implanted in the infarcted area is considered one of the promising strategy for cardiac repair. In this work the potentialities of a biomimetic electrospun scaffold made of a commercial copolymer of (l)-lactic acid with trimethylene carbonate (P(l)LA-co-TMC) are investigated in comparison to electrospun poly(l)lactic acid. The P(l)LA-co-TMC scaffold used in this work is a glassy rigid material at room temperature while it is a rubbery soft material at 37°C. Mechanical characterization results (tensile stress–strain and creep-recovery measurements) show that at 37°C electrospun P(l)LA-co-TMC displays an elastic modulus of around 20 MPa and the ability to completely recover up to 10% of deformation. Cell culture experiments show that P(l)LA-co-TMC scaffold promotes cardiomyocyte proliferation and efficiently preserve cell morphology, without hampering expression of sarcomeric alpha actinin marker, thus demonstrating its potentialities as synthetic biomaterial for myocardial tissue engineering.     

Evaluation of the Biocompatibility of PLACL/Collagen Nanostructured Matrices with Cardiomyocytes as a Model for the Regeneration of Infarcted Myocardium

Pioneering research suggests various modes of cellular therapeutics and biomaterial strategies for myocardial tissue engineering. Despite several advantages, such as safety and improved function, the dynamic myocardial microenvironment prevents peripherally or locally administered therapeutic cells from homing and integrating of biomaterial constructs with the infarcted heart. The myocardial microenvironment is highly sensitive due to the nanoscale cues that it exerts to control bioactivities, such as cell migration, proliferation, differentiation, and angiogenesis. Nanoscale control of cardiac function has not been extensively analyzed in the field of myocardial tissue engineering. Inspired by microscopic analysis of the ventricular organization in native tissue, a scalable in‐vitro model of nanoscale poly(L ‐lactic acid)‐co ‐poly(? ‐caprolactone)/collagen biocomposite scaffold is fabricated, with nanofibers in the order of 594 ± 56 nm to mimic the native myocardial environment for freshly isolated cardiomyocytes from rabbit heart, and the specifically underlying extracellular matrix architecture: this is done to address the specificity of the underlying matrix in overcoming challenges faced by cellular therapeutics. Guided by nanoscale mechanical cues provided by the underlying random nanofibrous scaffold, the tissue constructs display anisotropic rearrangement of cells, characteristic of the native cardiac tissue. Surprisingly, cell morphology, growth, and expression of an interactive healthy cardiac cell population are exquisitely sensitive to differences in the composition of nanoscale scaffolds. It is shown that suitable cell–material interactions on the nanoscale can stipulate organization on the tissue level and yield novel insights into cell therapeutic science, while providing materials for tissue regeneration.     

Analog Circuit Fault Detection Using Location of Poles

A method for detection of parametric faults occurring in linear analog circuits based on location of poles of the Circuit Under Test (CUT) is proposed. In the proposed method, the value of each component of the CUT is varied within its tolerance limit using monte carlo simulation. The upper and lower bounds of magnitude, phase angle, real part and imaginary part of all poles of the CUT are obtained. While testing, the locations of poles are obtained. If any one or more of the poles lies outside the tolerance limit then the CUT is declared faulty. The effectiveness of the proposed method is validated through two benchmark circuits like second order sallenkey band pass filter and fourth order leapfrog low pass filter.