Compatibility of Lead-Bismuth Eutectic with SiC-Coated Graphite at Elevated Temperature

Uniform coating of β-silicon carbide (β-SiC) was formed over a graphite pellet through slurry-based silicon coating followed by in situ reaction at 1873 K (1600 °C). The coated pellet was exposed to molten lead-bismuth eutectic (LBE) at 1173 K (900 °C) in static condition for 200 h. Weight loss measurement, X-ray diffraction, and secondary electron microscopy–energy-dispersive spectroscopy confirmed that the SiC coating could effectively prevent molten LBE from attacking the inner graphite material.     

Red enhanced YAG:Ce,Pr nanophosphor for white LEDs

Rare earth ion Pr³⁺ was co doped in yellow emitting YAG:Ce nanophosphor to introduce red emission for improving colour rendering property of white LED. Nanocrystalline YAG:Ce, YAG:Ce, Pr was synthesised by a single step auto combustion process. Photoluminescence (PL) emission spectra of YAG:Ce, Pr nanophosphor, when excited by 460?nm blue light, exhibited sharp red emission peaks at 610?nm from Pr³⁺ ions in addition to broad yellow emission from Ce³⁺ peaking at 540?nm due to charge transfer from excited Ce³⁺ 5d band to ³P _J /¹D₂ level of Pr³⁺. Ce³⁺ (yellow) and Pr³⁺ (red) emission decays in tens of nanoseconds and microseconds, respectively. Electroluminescence spectra of blue LED with developed phosphor layer shows colour coordinates (0.30, 0.39) close to ideal white light.     

Formation of nano-rod and nano-particles of polyaniline using Langmuir–Blodgett technique

We present the formation of nano-structures especially nano-rod and nano-particles of polyaniline (PANI) using Langmuir–Blodgett (LB) technique of molecular deposition. Decrease in the pH of the sub-phase of LB trough increases level of doping (protonation) of polyaniline emeraldine base to emeraldine salt and causes doping induced nano-structure formation. High resolution transmission electron microscopy reveals that anisotropic rod like nano-structures of PANI of diameter less than 50 nm are formed at pH 1 while pH 3 induces the formation of dispersed nano-particle of diameter 15 nm. On the contrary, connected lump (aggregation) type nano-structures of PANI are formed at a higher value of pH 6.     

An enhanced method for measuring cardiac output using Doppler color flow echocardiography

An enhanced method for determining cardiac output using Doppler color flow imaging techniques to measure mitral orifice diameter was developed and validated in an experimental model and in clinical patients. In an in vitro circuit model, color jet width correlated well with actual orifice dimension from 12 to 24 mm (r = 0.99). In the clinical application, mitral valve area was calculated as a X b X pi/4 where a and b represent the width of the color flow stream in the mitral orifice just distal to the annulus in apical long-axis (short-diameter) and 4-chamber (90 degrees rotated, long-diameter) views, respectively. Cardiac output was then computed as the product of mitral valve area and time-velocity integral of transmitral flow from the same site. Cardiac output was also measured by thermodilution and conventional echocardiographic methods using diameters and time-velocity integrals from the left ventricular outflow tract. In 30 patients with nonvalvular heart disease, cardiac output measured by thermodilution ranged from 3.40 to 8.40 L/min. Cardiac output was determined in 28 of 30 patients (93%) by the Doppler color flow imaging technique; it ranged from 3.00 to 8.36 L/min and correlated well with thermodilution: y = 0.90x + 0.63, r = 0.91. Cardiac output was determined in 24 of 30 patients by the conventional left ventricular outflow method (80%). The cardiac output measured by the conventional method correlated less closely with thermodilution (r = 0.84), although there was no statistical difference in correlation coefficiencies between the 2 methods. These results indicate that the Doppler color flow imaging technique can be used to enhance the determination of cardiac output by echocardiography, particularly when the conventional method has resulted in technically inadequate recordings.     

On the anisotropic thermal conductivity of shape memory alloy single crystals

Summary This paper addresses the issue of anisotropy in overall thermal conductivity of a shape memory alloy microstructure that is single crystalline in the high temperature austenitic state. The Voigt and Reuss bounds of the thermal conductivity are given. It is shown that the trace of the Voigt bound is independent of the specific variants that may exist and their orientations in the microstructure, whereas it is not so for the Reuss bound. It is also shown that both bounds of a purely self-accomodated martensitic microstructure originating from a cubic parent phase are isotropic and independent of the geometric properties of the variants. The bounds are then applied to the study of orthorhombic martensitic SMAs that are single crystalline in the cubic austenitic state. Using the resolved shear stress approach for variant selection, the impact of anisotropy in the thermal conductivity components of the orthorhombic martensite is studied for a single variant microstructure where the Voigt and Reuss bounds are used as estimates for the thermal conductivity of a cylindrical domain. Their impact on the normalized average steady state temperature and the normalized time taken to attain steady state are studied. This work is the precursor of experimental research on the anisotropy in thermal conductivity of shape memory alloys, of which virtually none exists in the open literature today.     

Fatigue and dielectric properties of undoped and Ce doped PZT thin films

Abstract

Ce doping improves the ferroelectric properties of sol-gel derived PZT thin films by facilitating easier domain wall movement. It also decreases the leakage current densities by reducing the concentration of free carriers through a decrease in concentration of Pb and O vacancies. Ce-PZT films retain good dielectric dispersion characteristics since the concentration of defects and defect dipoles are reduced. Ce doping dramatically improves the fatigue resistance of PZT thin films. We have studied the frequency dependence of fatigue behavior and shown that the loss of polarization due to fatigue follows a universal scaling behavior with N/f², where N is the number of the switching cycles and f is the frequency. The origin of the scaling is attributed to the drift of oxygen vacancies, which is the rate limiting process in the growth of the interface layer responsible for fatigue. Empirical fits for both undoped and cerium doped samples show that switchable polarization follows a stretched exponential decay with time or N/f. Cerium doping is believed to improve fatigue resistance by impeding the motion of oxygen vacancies.