1.0 THz GaN IMPATT Source: Effect of Parasitic Series Resistance

The degradation of high-frequency characteristics of a 1.0-THz double-drift region (DDR) impact avalanche transit time (IMPATT) diode based on wurtzite gallium nitride (Wz-GaN), due to the influence of parasitic series resistance, has been investigated. A two-dimensional (2-D) large-signal (L-S) simulation method based on a non-sinusoidal voltage excitation (NSVE) model has been used for this purpose. A comprehensive model of series resistance has been developed by considering the influence of skin effect, and the said model has been incorporated in the 2-D L-S simulation for studying the effect of RF power output and DC to RF conversion efficiency of the device. Results indicate 24.2–35.9% reduction in power output and efficiency due to the RF power dissipation in the positive series resistance. However, the device can still deliver 191.7–202.9 mW peak RF power to the load at 1.0 THz with 8.48–6.41% conversion efficiency. GaN IMPATT diodes are capable of generating higher RF power at around 1 THz than conventional diodes, but the effect of parasitic series resistance causes havoc reduction in power output and efficiency. The nature of the parasitic resistance is studied here in the level of device fabrication and optimization, which to our knowledge is not available at present.     

Experimental approach to probe into mechanisms of high-temperature erosion of NbB2-ZrO2

In the backdrop of potential applications of boride-based materials in high-speed supersonic aircrafts, the present investigation probes in comprehending the mechanisms of high-temperature erosive wear of spark plasma sintered NbB₂-ZrO₂ composite. The solid particle erosion experiments were performed at different temperatures starting from room temperature (25°C) to 800°C using Al₂O₃ particles (50 μm). The air-erodent particle mixture was impinged toward the target surface at normal impact with a velocity of 50 m/s. The detailed microstructural analysis using HRTEM reveals the generation and accumulation of a large number of dislocations within NbB₂ and ZrO₂ grains of the eroded surfaces. Such observations indicate the activation of dislocation plasticity during erosion at 800°C. XRD-based analyses provided residual stress-based interpretation for the enhancement of erosion resistance at high temperatures. In contrast, substantial material loss via brittle failure, involving the generation and intersection of the lateral/radial cracks, was recorded after room temperature erosion. In case of erosion at 400°C and 800°C, the residual stress relaxes as a consequence of high-temperature exposure prior to erosion. The accumulation of dislocations near the crater region and shot peening phenomena play a dominant role in decreasing erosion rate with increasing erosion test temperature.     

Synthesis and characterization of CdS doped TiO2 nanocrystalline powder: A spectroscopic study

This report aimed to study the effect of CdS doping in TiO₂ on the phase transformation of TiO₂ from anatase to rutile using X-ray diffraction (XRD) and Raman spectroscopy. CdS-doped TiO₂ nanocomposites have been prepared and characterized using Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). We have observed that contrary to bare TiO₂, phase transformation of TiO₂ from anatase to rutile is hindered when doped with CdS at high temperature. Raman spectroscopy is found to be more sensitive for detection of the surface of TiO₂ as compared to XRD.     

Modeling of SO(2) scrubbing in spray towers

The present article aims at developing simple realistic models in order to describe the gaseous removal process of SO(2) by absorption with and without chemical reaction in spray towers. Effects of droplet size, droplet velocity, superficial gas velocity, liquid flow rate and tower height on the performance of such a system are theoretically predicted. Model calculations bring out some very interesting facets of gas scrubbing as functions of droplet diameter and velocity. Four distinct regimes, viz. droplet lean, dense droplet, rigid droplet and droplet inertia controlling regimes, are found important in spray scrubbing process. Model calculation also elucidates the existence of rigid droplet (sphere) for a distinct droplet size at a specific droplet velocity. Theoretical considerations reveal that best performance can be achieved in the droplet inertia-controlling regime. Effect of turbulence on scrubbing is also considered for modeling. The model development and experimental data are limited to use of water-soluble alkaline scrubbing. However, the predicted values agree reasonably well with the available experimental data at lower gas and liquid flow rates for relatively smaller droplets. Models can also be applied to any gas-liquid spray absorption process subject to the assumptions and conditions necessary to describe the specific physico-chemical hydrodynamics of the system. However, incorporation of various droplet interactions can further refine the models for better prediction of removal efficiency.     

Characterization of hole circularity in pulsed Nd:YAG laser micro-drilling of TiN–Al2O3 composites

In micro-manufacturing, circularity of a drilled hole at entry and exit are important attributes which greatly influence the quality of a drilled hole. This study investigates the effect of five parameters in the circularity of drilled holes in pulsed Nd:YAG laser micro-drilling process. The drilling operation has been carried out on titanium nitride–alumina (TiN–Al₂O₃) composite, an important electroconductive ceramics suitable for wear and heating applications. The effect of various process parameters like lamp current, pulse frequency, pulse width, air pressure, and focal length of Nd:YAG laser micro-drilling on hole circularity at entry and exit has been investigated through response-surface-methodology-based experimental study. The parametric combination for optimal hole circularity at entry and exit has also been evaluated.     

Herd-level prevalence of Johne's disease in Utah and adjacent areas of the intermountain west as detected by a bulk-tank milk surveillance project

The objectives of this study were to estimate the dairy herd-level prevalence of Johne's disease (JD) in Utah and nearby areas of the intermountain west and to estimate the sensitivity of a single bulk-tank milk test for JD detection. Two milk samples from all bulk tanks on the study farms were collected 1 mo apart. Samples were frozen and shipped to a laboratory for JD testing. An ELISA to measure total IgG antibody specific against Mycobacterium avium ssp. paratuberculosis, the etiological agent that causes JD, and a quantitative real-time PCR to detect M. avium ssp. paratuberculosis DNA were used; both tests were designed for bulk milk. Of the dairy farms in the study area, 170/246 (69%) participated. Positive JD results were found in bulk milk from 67/170 (39%) of dairy farms in Utah and adjacent areas. There were 138 JD-positive bulk-tank results from 241 bulk-tank samples from the 67 positive herds. The sensitivity of the bulk milk testing for detection of JD was 138/241(57%). From the 103 JD-negative farms, 235 bulk-tank samples tested negative for JD. The probability of false-negative results on a single bulk-milk sample was (1 - 0.57) = 0.43. For farms with 1 bulk tank, 2 samples collected 1 mo apart, with both samples testing negative (by both ELISA and quantitative real-time PCR) for JD, the true-negative probability was [1 - (0.43)(2)] = (1 - 0.18) = 82%. For farms with at least 2 bulk tanks, at least 4 samples tested, with all results negative for JD, the true-negative probability was at least 97%. Results support other estimates that prevalence of JD has increased over the last 15 to 20 yr. However, the prevalence detected was 3 times that from a recent report where 13% of dairy herds in the western US were positive. The increase in JD suggests that current control programs, at least as applied, are not effective. Bulk milk testing is a practical way to screen dairy herds for presence of JD. Studies are needed regarding the use of individual cow milk tests for accuracy, practicality, and effectiveness in reducing the prevalence of JD in dairy herds.     

Antihyperlipidemic effect of sesame (Sesamum indicum L.) protein isolate in rats fed a normal and high cholesterol diet

The dietary influence of sesame protein isolate (protein content 91.5%), produced from dehulled, defatted sesame meal, on blood and tissue lipid profile and lipid peroxidation has been assessed in normal and hypercholesterolemic rats. To evaluate their hypocholesterolemic and antioxidative activity in vivo, we fed 18% sesame protein isolate with or without 2% cholesterol in comparison with casein to rats for 28 d. We determined plasma total protein, total cholesterol, high-density lipoprotein (HDL)-cholesterol, low-density lipoprotein (LDL)-cholesterol, triacylglycerol as well as susceptibility of plasma and erythrocyte membrane lipid to oxidation ex vivo. Liver tissue lipid, cholesterol, phospholipids, and lipid peroxidations were also determined. The total cholesterol, LDL-cholesterol and triacylglycerol levels were significantly reduced in the sesame protein isolate and isolate containing cholesterol group than the corresponding control casein groups. HDL-cholesterol level was also increased in sesame protein isolate (41%) and protein isolate containing cholesterol group (38%) than the corresponding control casein and casein containing cholesterol groups. There was 49% and 64% lowering of plasma lipid peroxidation as well as 36% and 56% lowering of lipoprotein oxidation susceptibility (LOS) in the 2 experimental groups (sesame protein isolate and isolate containing cholesterol group) than the corresponding control (casein and casein containing cholesterol) groups. There was significant lowering of erythrocyte membrane lipid peroxidation (68% and 63% lowering in sesame protein isolate and isolate containing cholesterol groups) and liver lipid peroxidation (61% and 76% lowering in the 2 experimental groups than the corresponding control casein groups). Therefore, our results indicate that sesame protein isolate decreases cholesterol concentration in plasma, increases HDL-cholesterol, and also decreases plasma and erythrocyte membrane lipid peroxidation with or without cholesterol fed diet in rats.     

Lactobacillus fermentum isolated from human colonic mucosal biopsy inhibits the growth and adhesion of enteric and foodborne pathogens

A number of Lactobacillus species are used as probiotic strains in order to benefit health. We have isolated L. fermentum from human colonic mucosal biopsy samples that possess antimicrobial activities against entroinvasive and foodborne pathogens such as Escherichia coli, Salmonella paratyphi A, Shigella sonnei, Staphylococcus aureus, Enterococcus faecalis, Proteus mirabilis, Pseudomonas aeruginosa, and Vibrio sp. In addition to lactic acid, L. fermentum secretes antimicrobial proteinacious compound(s) that was found to be active even at neutral pH (pH 7.0). The compound was sensitive to heat treatment and trypsin digestion. Lactobacillus fermentum inhibited the adhesion of enteropathogens to intestinal epithelial cells in vitro. Isolated cell surface associated proteins (SAPs) from L. fermentum were sufficient for the adhesion exclusions of enteropathogenic E. coli. Our results indicate that L. fermentum produces antimicrobial compounds and SAPs to inhibit the growth and adhesion of enteropathogens, respectively.     

Antioxidative effect of conjugated linolenic acid in diabetic and non-diabetic blood: an in vitro study

The present study examined the in vitro antioxidant activity of conjugated octadecatrienoic fatty acid (9cis, 11 trans, 13 trans-18:3), alpha-eleostearic acid present in karela seed oil (Momordica charantia) at about 55% level. The in vitro antioxidant properties of alpha-eleostearic acid are investigated on oxidative modification of human plasma, low-density lipoprotein (LDL) and erythrocyte membrane lipid. Blood samples are collected from diabetic and non-diabetic (normal) healthy individuals. alpha-eleostearic acid is added at 0.05% and 0.1% concentrations to plasma, LDL and erythrocyte membrane isolated from the respective blood samples and peroxidations are determined against control samples. A significant increase of respective peroxidation levels has been observed in diabetic control blood than the non-diabetic control blood. alpha-eleostearic acid has decreased lipid peroxidation level against control samples in a dose dependent manner. The present findings suggest that CLnA, 9cis, 11trans, 13trans-18:3 is a potentially effective antioxidant that can protect plasma, low density lipoprotein and erythrocyte membrane from oxidation which may be effective in reducing the risk of coronary heart disease in diabetes mellitus.     

Predictive equations for CO2 emission factors for coal combustion, their applicability in a thermal power plant and subsequent assessment of uncertainty in CO2 estimation

The emission of carbon dioxide varies systematically with the rank and type of coal combusted. Hence use of a single default emission factor proposed by IPCC (Inter Governmental Panel on Climate Change) for entire categories coals may not be appropriate option to obtain a reliable estimate of carbon dioxide emission level or towards the preparation of national carbon dioxide inventory. Even predictive equations developed based on the coals of different origin may not work well with coals of a specific origin. Several linear predictive equations were thus developed separately for coking and non-coking coals of Indian origin for the estimation of carbon dioxide emission utilizing basic coal parameters such as VM, FC, GCV and NCV on different basis. Large numbers of authenticated data set were used for multiple regression analysis and good correlations were obtained. Those equations were also validated with different data sets of Indian coals. Its applicability towards estimation of CO₂ emission from power plant was also studied and uncertainty in CO₂ estimation is revealed. The developed equations may be utilized to get a realistic estimate of carbon dioxide emission with specific cases where Indian coals are mostly used.