A dislocation-based model for variant selection during the γ-to-α′ transformation

A phase transformation model is described for variant selection during the austenite-to-martensite transformation. The model depends entirely on the presence of glide dislocations in the deformed austenite. The direct correlation between the 24 slip systems of the Bishop and Hill (B-H) crystal plasticity model and the 24 〈112〉 rotation axes of the Kurdjumov-Sachs (K-S) orientation relationship is employed. Two selection criteria, based on slip activity and permissible dislocation reactions, govern the variants that are chosen to represent the final transformation texture. The development of the model via analysis of the experimental results of Liu and Bunge is described. The model is applied to the four distinct strain paths: (1) plane strain rolling, (2) axisymmetric extension, (3) axisymmetric compression, and (4) simple shear. Experimental deformation and transformation textures were produced for comparison purposes via appropriate deformation and quenching procedures. In each case, the transformation texture predicted using the dislocation reaction model is in excellent agreement with the experimental findings.     

Fluorescence monitoring of ATP-stimulated, endothelium-derived nitric oxide production in channels of a poly(dimethylsiloxane)-based microfluidic device

Intracellular nitric oxide (NO) production in a microfluidic endothelium is detected using fluorescence microscopy. Bovine pulmonary artery endothelial cells (bPAECs) were loaded with the fluorescence probe diaminodifluorofluorescein diacetate (DAF-FM DA), and the subsequent fluorescent DAF-FM DA/NO adduct was measured. Solutions of bradykinin, a well-known stimulus of endothelium-derived NO, activated nitric oxide synthase (NOS) in the immobilized bPAECs. This activation was inhibited using l-nitro arginine methyl ester (L-NAME), a competitive inhibitor of NOS. Importantly, the NO production was also stimulated with adenosine triphosphate (ATP) using concentrations as low as 1 microM. Previous reports on stimulating NO production using an immobilized endothelium in microfluidic channels were limited by the requirement of ATP concentrations of at least 100 microM, a value that is not physiologically relevant. The ability to monitor NO production with ATP concentrations that are similar to in vivo levels of ATP in the microcirculation represents a major advance in the use of microfluidic technology as an in vitro model of the microcirculation.     

Dynamic monitoring of glutathione in erythrocytes, without a separation step, in the presence of an oxidant insult

A method for the quantitative determination of the antioxidant form of glutathione (GSH) in red blood cells (RBCs) is described that does not require separation of the analyte of interest from the complex cellular matrix. The measurement portion of the analysis is performed using fluorescence spectrophotometry after monochlorobimane (a recognized probe for GSH) is added to a mixture containing RBCs and glutathione transferase (GST). This method was employed to determine the GSH concentration (0.042 +/- 0.002 mM) in a solution of 1% RBCs obtained from rabbits (n = 6). When spiked with authentic GSH (0.50 micromol), 99.8% of the GSH was recovered. Addition of GST to the sample mixture enabled most measurements to be made after 5-10 min of reaction time. Importantly, a decrease in GSH was measured upon the addition of a recognized oxidant (diamide) to the RBC sample followed by a subsequent return to normal levels of GSH. The ability of the GSH to recover from the oxidant attack occurred in a dose-dependent manner, requiring 30 and 90 min to recover from oxidant insults of 20 and 40 microM diamide, respectively. The antioxidant capabilities of the GSH were able to be monitored in real time, thus providing a method to dynamically monitor the ability of the RBC to maintain homeostasis in a complex matrix.     

Bias-dependent linear scalable millimeter-wave FET model

This paper describes a measurement-based bias-dependent linear equivalent circuit field-effect-transistor/high-electron-mobility-transistor model that is accurate to at least 100 GHz and scalable up to 12 parallel gate fingers and from 100 to 1000 μm total gate width. A new and accurate technique for extracting the Z-shell parameters has been developed, and the scaling rules for all the parasitic elements have been determined. The intrinsic equivalent circuit element values are determined at each bias point in V_ge-V_ds space and interpolated by splines between points     

Growth of aluminum nitride single crystals under thermal explosion conditions

The process of aluminum nanopowder combustion in air under thermal explosion conditions has been studied. It is established that the presence of a constant magnetic field with an induction of 0.4 T favors the formation of aluminum nitride single crystals under non-steady-state combustion conditions.     

Neutron Diffraction and Finite-Element Analysis of Thermal Residual Stresses on Diffusion-Bonded Silicon Carbide-Molybdenum Joints

Various approaches can be used to minimize residual stresses in ceramic-metal joining, such as a refractory-metal interlayer in a hot-pressed joint. Nonetheless, it is still necessary to characterize the stresses at and near the interface between the interlayer and the ceramic, as a function of the hot-pressing parameters. This study combines two techniques to assess the stress distribution of hot-pressed silicon carbide-molybdenum joints: neutron diffraction and finite-element (FEM) analysis. The results demonstrate that the joining temperature greatly influences the final stress distribution, and that significant stress accommodation is achieved by controlling the cooling rate of the diffusion couples. FEM analysis provides a broad view of stress distribution profiles, whereas experimental stress values that are obtained via neutron diffraction allow a better assessment of the effects of parameters that are not easily reproduced using a mathematical model.     

Voltage distortion in distribution feeders with nonlinear loads

The voltage of three real-life 13.8 kV feeders supplying customers with nonlinear loads was analyzed by means of computer simulations. Three classes of nonlinear loads were considered. Each class is characteristic for different types of AC to DC converters such as the input DC supply used for adjustable-speed-drives, battery chargers, PCs, TVs and electronically ballasted lights. The analysis is based on the determination of the most harmonic susceptible busses and their response to each harmonic frequency. A new expeditive method that takes into account the background harmonic voltage phasor, and an equivalent bus impedance was developed and used to compute the maximum nonlinear loads that yields VTHD=5%, (voltage total harmonic distortion). The main conclusion of this work is that when mitigation methods are not used, for a 15 kV class feeder with a maximum 10 MVA installed load, the total nonlinear residential load should not exceed 300 kW if the ITHD<90% (current total harmonic distortion), and 100 kW if ITHD>100%