Hot Hydrogen Exposure Degradation of the Strength of Mullite

Near-stoichiometric mullite (3Al₂O₃2SiO₂) that contained small amounts of calcium and magnesium was exposed to pure dry hydrogen gas at elevated temperatures. Exposure temperatures were 1050° and 1250°C, and exposure times were up to 500 h. Preferential attack of the aluminosilicate glass that was present in the grain boundaries of the mullite occurred after 125 h at 1250°C. Hydrogen scrubbing of the silica from the glassy grain boundaries and the mullite grains yielded a porous alumina-rich surface. The room-temperature strength increased after short exposure times at 1250°C (up to 125 h) and then decreased by 53% after exposure for 500 h. At 1050°C, all exposure times (25-500 h) decreased the strength. The room-temperature strength of mullite decreased 22% after 500 h in hydrogen at 1050°C. We also observed a rapid 25% strength loss after short exposure times at 1050°C, which was attributed to the calcium/hydrogen-assisted crystallization of the glassy grain-boundary phase.     

High-Resolution 3D Deposition of Electrospun Fibers on Patterned Dielectric Elastomers

Electrostatic patterning has improved the performance of devices incorporating electrospun fibers in a wide variety of applications. However, the impact of process parameters on the final fiber pattern in these systems is rarely analyzed. Herein, a systematic analytical approach is developed to define quantitative metrics related to fiber patterning. Three-dimensional patterned dielectric elastomer collectors are fabricated via solution-casting polydimethylsiloxane with embedded carbon black or liquid metal droplets. Fiber patterning metrics are used to evaluate the effect of collector parameters such as insulating layer thickness, electrical ground surface area, and three-dimensional pattern geometry. Dielectric layer parameters such as conductive material concentration and particle diameter are also investigated. Using this framework, the best-performing collector is shown to improve selectivity 30-fold, uniformity ninefold, reproducibility eightfold, and increase fiber volume by one order of magnitude. Furthermore, eutectic gallium indium liquid metal and scaled-up pattern geometries demonstrate the tunability of this approach and broad applicability of systematic fiber pattern analysis. This rational approach to patterned fiber development can be applied to virtually any method or pattern to better understand the fiber patterning processes.     

The applicability of the PTTL dose re-analysis method to the Harshaw LiF:Mg,Cu,P material

The phototransferred thermoluminescence (PTTL) technique is applied to the Harshaw LiF:Mg,Cu,P material. It is demonstrated that using 254-nm UV light, dose levels as low as 0.2 mGy can be re-estimated. The PTTL efficiency was found to be ～ 6 % in the dose range of 0.2 mGy-1 Gy, and it appears to be dose-independent. This implies that a simple calibration factor could be applied to the PTTL data for the re-estimation of dose levels. It was demonstrated that with a proper choice of the TL readout parameters, and the UV-light irradiation conditions, dose levels that are relevant to personal or environmental dosimetry can be re-estimated.     

Combustion and thermal properties of OctaTMA-POSS/PS composites

Inorganic–organic composites of octa(tetramethylammonium) polyhedral oligomeric silsesquioxanes (OctaTMA-POSS) and polystyrene (PS) were prepared by melt-mixing method. The composites were characterized by Fourier-transform infrared spectrometry (FT-IR), Transmission electronic microscopy (TEM), scanning electronic microscopy (SEM), and thermal gravimetric analysis (TGA). Their flammability was evaluated by cone calorimeter test. The experimental results indicate that OctaTMA-POSS, when present in low ratios (1%–5%, weight ratio) in the composites, can decrease the peak heat release rate (HRR) by 15%, while high ratios of OctaTMA-POSS (20% and 30%) can decrease the peak HRR and the average HRR approximately linearly. Concentration and release rate of carbon monoxide (CO) in the composites combustion are also decreased evidently. Thermal gravimetric analysis under nitrogen and air atmosphere both show that the char yield increases obviously. These advances are attributed to the special properties of OctaTMA-POSS and its dispersion in PS.     

Determination of the average orientation of DNA in the octopus sperm Eledone cirrhossa through polarized light scattering

The coupled-dipole approximation has been used to model polarized light-scattering data obtained from the sperm of the octopus Eledone cirrhosa. Mueller scattering-matrix elements (which describe how a sample alters the intensity and degree of polarization of scattered light) were measured as a function of angle. The sample was modeled as a helical fiber believed to correspond to a DNA protein complex. It was necessary to propose an inherent anisotropy in the polarizability of the fiber in order to fit the data. The direction of the principle axes of the polarizability were determined by comparing the model with experimental data. The results suggest that the 2-nm DNA fibers are perpendicular to the thick fiber that defines the helical geometry of the octopus sperm head.     

Observations of directional gamma prime coarsening during engine operation

Two alloys, NASAIR 100 and a modified NASAIR 100 called Alloy 3, were run as turbine blades in an experimental ground-based Garrett TFE731 engine for up to 200 hours. The stress induced directional coarsening of γ′ (rafting) that developed during engine testing was analyzed and compared to previous research from laboratory tests. The blades were found to have formed a lamellar structure, the lamellae being normal to the centrifugal stress axis over much of the span. However, near the surfaces, the blades were found to have formed lamellae parallel to the centrifugal stress axis for certain cycles. Representative photomicrographs of the blades and the effects of stress and temperature on lamellae formation are shown.     

Mechanisms of protection induced by attenuated simian immunodeficiency virus. IV. Protection against challenge with virus grown in autologous simian cells

Attenuated simian immunodeficiency virus (SIV) induces potent protection against infection with wild-type virus, but the mechanism of this immunity remains obscure. Allogeneic antibodies, which arise within animals as a result of SIV infection, might protect against challenge with exogenous SIV grown in allogeneic cells. To test this hypothesis, eight macaques were infected with attenuated SIV and subsequently challenged with wild-type SIV grown in autologous cells or heterologous cells. The results clearly demonstrated that animals infected with attenuated SIV are protected against wild-type SIV grown in autologous or heterologous cells. Thus, the hypothesis that live attenuated SIV protects by the induction of allogeneic antibodies is not tenable.     

Relation between the time to achieve the lower limit of the APTT therapeutic range and recurrent venous thromboembolism during heparin treatment for deep vein thrombosis

BACKGROUND: Randomized trials have demonstrated the importance of achieving adequate heparinization early in the course of therapy. Recently, some authors reported a pooled analysis of selected studies in the literature that suggested that there is no convincing evidence that the risk of recurrent venous thromboembolism is critically dependent on achieving a therapeutic activated partial thromboplastin time result at 24 to 48 hours. METHODS: We provide the analyses of patient groups entered into our series of 3 consecutive double-blind randomized trials evaluating initial heparin therapy for proximal deep venous thrombosis. RESULTS: Logistic regression analysis of the patient groups receiving the less intense initial intravenous heparin dose of 30,000 U/24 h demonstrated that subtherapy for 24 hours predicted the onset of venous thromboembolic events. Failure to achieve a therapeutic activated partial thromboplastin time by 24 hours was associated with a 23.3% frequency of venous thromboembolism vs 4% to 6% for those whose activated partial thromboplastin time exceeded the therapeutic threshold by 24 hours (P=.02). Time-to-event analysis shows the increased frequency of recurrent venous thromboembolic events during the period of study in patients who were subtherapeutic for 24 hours compared with those who were therapeutic (P=.001). CONCLUSIONS: Our findings reaffirm the clinical importance of rapidly achieving therapeutic levels of heparin. Patients who failed to achieve the therapeutic threshold by 24 hours were at an increased risk of subsequent recurrent venous thromboembolism. These findings are independently supported by the results of a randomized trial comparing different intensities of initial heparin treatment by continuous infusion.     

Simulation of flow control in the meniscus of a continuous casting mold with opposing alternating current magnetic fields

A numerical simulation was performed for a novel electromagnetic stirring system that employs two rotating magnetic fields. The system controls stirring flow in the meniscus region of a continuous casting mold independently from the stirring induced within the remaining volume of the mold by a main electromagnetic stirring (M-EMS) system. This control is achieved by applying to the meniscus region an alternating current-stirring modifier (AC-SM) whose direction of rotation is opposite to that of the main magnetic field produced by the M-EMS. The model computes values and spatial distributions of electromagnetic parameters and fluid flow in stirred pools of mercury in cylindrical and square pools. Also predicted are the relationships between electromagnetics and fluid flows pertinent to a dynamic equilibrium of the opposing stirring swirls in the meniscus region. Results of the numerical simulation compared well with the measurements obtained from experiments with mercury pools.