Role of carrier depletion effects and material properties in advanced microscale thermal modeling of N-GaInP–Si/p-GaAs–C heterojunction bipolar transistor (HBT) devices

Ab initio calculations were performed to determine the width of the depletion regions in a N-GaInP/p-GaAs heterojunction bipolar transistor (HBT), by constructing the energy band diagrams for the GaInP emitter, and the ‘degenerate' p-doped GaAs base region. The depletion regions were established as the regions of primary heat generation inside the HBT. A detailed thermal model of a 2 μm × 16.5 μm emitter, with two rows of three such emitters per device has been developed using finite difference analysis (FDA). Care has been taken to incorporate the contact metallization and fine geometry, including the representative collector and base mesa structures. The thermal conductivity of the materials involved were carefully established as functions of temperature. Additionally, the temperature profile across the active region of the device was characterized using emission spectroscopy. Close agreement was found between the results from the thermal model and physical measurements. This paper establishes the rationale for appropriating suitable regions inside the active device as sources for heat generation––Joule heat, Thomson heat and Recombinant heat, along with a brief discussion of the causes for their generation.     

Improve Performance of Wireless Sensor Network Clustering Using Mobile Relay

Wireless Personal Communications - Wireless sensor networks sense events, collect data and forward it to the infrastructural node, called sink, for further processing and assessment. The...     

Grid-independent large-eddy simulation of turbulent wake flow using explicit differential filters

Journal of Mechanical Science and Technology - Large-eddy simulations (LES) using explicit filtering are performed to obtain grid-independent solutions of turbulent wake flow behind a circular...     

Synthesis and optical characterization of ZnO nanoparticles capped with 2-aminothiols

ZnO nanoparticles were synthesized by precipitation method. To reduce the agglomeration among small ZnO nanoparticles, an efficient surface modification method was proposed using 2-aminothiols as a capping agent. The effect of capping reagent is investigated on optoelectronics properties of ZnO. The capping of ZnO with 2-aminothiol leads to the shift in fluorescence intensity and also effected the UV–vis spectra of ZnO. The strategy exposed new dimensions to fine tune the fluorescence signatures of the ZnO.     

Computational Analysis of Particle Nucleation in Dilution Tunnels: Effects of Flow Configuration and Tunnel Geometry

Measurement of fine particle emission from combustion sources is important to understand their health effects, and to develop emissions regulations. Dilution sampling is the most commonly used technique to measure particle number distribution because it simulates the mixing and cooling of combustion exhaust with atmospheric air, which drives nucleation and condensation of semi volatile material. Experiments suggest that the measured size distribution is dependent on the dilution ratio used and the tunnel design. In the present work, computational analysis using a large-eddy-simulation (LES) based model is performed to investigate the effect of tunnel flow and geometric parameters on H₂SO₄-H₂O binary nucleation inside dilution tunnels. Model predictions suggest that the experimental trends are likely due to differences in the intensity of turbulent mixing inside the tunnels. It is found that the interaction of dilution air and combustion exhaust in the mixing layer greatly impacts the extent of nucleation. In general, a cross-flow interaction with enhanced turbulent mixing leads to greater number of nucleation-mode particles than an axial-flow interaction of combustion sample and dilution air.

Copyright 2014 American Association for Aerosol Research     

Medium Optimization for Enhanced Production of Protease with Industrially Desirable Attributes from Bacillus subtilis K-1

Microbial proteases due to their huge application potential have attracted considerable research attention and account for more than 60% of the worldwide enzyme sales. However, large-scale industrial application of proteases is hindered due to their poor performance under relatively hostile industrial conditions (extremes of temperature, pH) and the high production cost. In the current study, the production of a thermostable and wide-range pH stable protease was accomplished from a newly isolated Bacillus subtilis K-1 strain using cost-effective agricultural residues. Process optimization for protease production was conducted by employing one-variable-at-a-time and statistical approaches. The most significant variables for protease production were identified as incubation time, soybean meal, mustard cake, and wheat bran. Optimization of these variables by central composite design of response surface methodology resulted in a substantial protease yield enhancement (112%). Exploitation of agricultural wastes as substrates may pave the way for cost-effective production of protease with industrially desirable attributes.     

Hydrolysis of citrus peel naringin by recombinant α‐L‐rhamnosidase from Clostridium stercorarium

The citrus fruit processing industry generates substantial quantities of waste rich in glycosylated phenolic substances such as naringin, which are a valuable natural source of polyphenols as well as L‐rhamnopyranose. Naringin is the major polyphenol in bitter orange peel and its hydrolysis by α‐L ‐rhamnosidase (EC 3.2.1.40) catalyzes the cleavage of the terminal rhamnosyl groups to form prunin and rhamnose. In this work, a recombinant α‐L ‐rhamnosidase from C. stercorarium was shown to be suitable for narigin hydrolysis. The recombinant rhamnosidase was found to be relatively stable at 60 °C, and a residual activity close to 50% after 180 min of incubation was demonstrated. The purified enzyme established hydrolysis of naringin extracted from citrus peel waste (CPW). The result indicated that recombinant α‐L ‐rhamnosidase has industrial applicability and is an interesting candidate for producing rhamnose from citrus peel. Copyright © 2010 Society of Chemical Industry     

Influence of surface modification by 2-aminothiophenol on optoelectronics properties of ZnO nanoparticles

In this study, a precipitation method was used to synthesise ZnO nanoparticles using suitable precursors. An efficient surface modification method was proposed in order to reduce the agglomeration among synthesised small sized ZnO nanoparticles using 2-aminothiophenol as a capping agent. This article briefly investigated the effects of capping agent like 2-aminothiophenol on the optoelectronic properties of ZnO nanoparticles. The modified effectivity of 2-aminothiophenol has been examined on the nanosized ZnO nanoparticle for fluorescence and UV–visible (UV–vis) studies. The mechanism was studied for ZnO nanoparticles light emitting capability under different conditions. By facilitating the capping of ZnO with 2-aminothiophenol, fluorescence emission of the surface defects vanishes and ultraviolet (UV) emission increases. Surface capping by 2-aminothiophenol effectively covers most of the surface defects of ZnO and results in quenching of the visible region. The UV–vis absorption spectra of modified ZnO nanoparticles has been influenced by modified ZnO nanoparticles as a result of surface modification; where marked blue shift in absorption edge results. By surface modification of ZnO nanoparticles, change in optoelectronics properties has opened the new scope and possibilities to explore and fine tune the optical character of the modified ZnO for various optoelectronics applications such as UV laser.     

Mixing and flame structures inferred from OH-PLIF for conventional and low-temperature diesel engine combustion

The structure of first- and second-stage combustion is investigated in a heavy-duty, single-cylinder optical engine using chemiluminescence imaging, Mie-scatter imaging of liquid-fuel, and OH planar laser-induced fluorescence (OH-PLIF) along with calculations of fluorescence quenching. Three different diesel combustion modes are studied: conventional non-diluted high-temperature combustion (HTC) with either (1) short or (2) long ignition delay, and (3) highly diluted low-temperature combustion (LTC) with early fuel injection. For the short ignition delay HTC condition, the OH fluorescence images show that second-stage combustion occurs mainly on the fuel jet periphery in a thickness of about 1 mm. For the long ignition delay HTC condition, the second-stage combustion zone on the jet periphery is thicker (5-6 mm). For the early-injection LTC condition, the second-stage combustion is even thicker (20-25 mm) and occurs only in the down-stream regions of the jet. The relationship between OH concentration and OH-PLIF intensity over a range of equivalence ratios is estimated from quenching calculations using collider species concentrations predicted by chemical kinetics simulations of combustion. The calculations show that both OH concentration and OH-PLIF intensity peak near stoichiometric mixtures and fall by an order of magnitude or more for equivalence ratios less than 0.2-0.4 and greater than 1.4-1.6. Using the OH fluorescence quenching predictions together with OH-PLIF images, quantitative boundaries for mixing are established for the three engine combustion modes.