Migpore,a code package for the estimation of migration of radioactive species in a porous medium

In the event of an accidental leakage of high level radioactive waste buried deep in repositories surrounded by rock, the build up of the concentration of the radioactive species within the rock needs to be assessed. Towards this, we follow the model of Chen and Li and provide a numerical code to solve the relevant partial differential equations using a compact finite difference scheme.     

Analysis of charge density and Fermi level of AlInSb/InSb single-gate high electron mobility transistor

A compact model is proposed to derive the charge density of the AlInSb/InSb HEMT devices by considering the variation of Fermi level, the first subband, the second subband and sheet carrier charge density with applied gate voltage. The proposed model considers the Fermi level dependence of charge density and vice versa. The analytical results generated by the proposed model are compared and they agree well with the experimental results. The developed model can be used to implement a physics based compact model for an InSb HEMT device in SPICE applications.     

Comparison of inter- and intra-chromosomal aberrations in blood samples exposed to different dose rates of gamma radiation

Peripheral blood samples obtained from a normal healthy volunteer were exposed in vitro to gamma radiation with various doses at different dose rates of 1.0, 0.1 and 0.0014 Gy min(-1). The exposed samples were analysed for different chromosomal aberrations such as dicentrics (DC), centric rings (CR) and double-minutes (DM). The ratio of DC chromosomes (inter) to the total number of centric rings (CR) and double-minutes (DM) (CR + DM = intra) were analysed for all the three dose rates. The study showed that the frequency of inter-arm chromosomal aberrations was more then three times higher than that observed with intra-arm chromosomal aberrations in samples exposed at a dose rate of 1.0 and 0.1 Gy min (-1). However, the frequency of inter- and intra-arm chromosomal aberrations were almost same (ratio 1:1) in samples exposed at a dose rate of 0.0014 Gy min(-1). This paper discusses the usefulness of the ratio of inter- and intra-arm chromosome aberration in finding out whether the sample was exposed to high or low dose rate radiation.     

Simulation of microphysical structure associated with tropical cloud clusters using mesoscale model and comparison with TRMM observations

An attempt has been made in the present study to examine the microphysical structure of a non‐squall Tropical Cloud Cluster (TCC). Three‐dimensional model simulations of cloud microphysical structure associated with a non‐squall TCC occurred on 26 October 2005 over the South Bay of Bengal have been carried out. The initial conditions for the model simulations were improved by incorporating upper air radiosonde observations and Indian Mesosphere Stratosphere Troposphere (MST) radar wind observations through analysis nudging. The horizontal and vertical distribution of the cloud hydrometeor fields observed from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) are compared to those simulated by a mesoscale model using a sophisticated microphysical scheme. Substantial differences are noticed in the amounts of cloud microphysical parameters, with simulated values of hydrometeors being higher than TMI retrievals. Spatial distribution of Cloud Liquid Water (CLW) and Rain Water (RNW) from TMI and model simulations correspond well with each other. The cloud microphysical structure during the initial and mature phases of the storm is also investigated. Comparisons of horizontal and vertical reflectivity structure from the TRMM‐Precipitation Radar (PR) and those simulated by the model show reflectivity cores of values greater than 30 dBZ. The TRMM‐PR echo tops are 3–4 km higher than the simulated echo tops. The 24 hr accumulated precipitation from model simulations are then verified with the combined rainfall product from the TRMM observations.     

A surface potential based drain current model for asymmetric double gate MOSFETs

In this paper, we present a generic surface potential based current voltage (I-V) model for doped or undoped asymmetric double gate (DG) MOSFET. The model is derived from the 1-D Poisson’s equation with all the charge terms included and the channel potential is solved for the asymmetric operation of DG MOSFET based on the Newton-Raphson iterative method. A noncharge sheet based drain current model based on the Pao-Sah’s double integral method is formulated in terms of front and back gate surface potentials at the source and drain end. The model is able to clearly show the dependence of the front and back surface potential and the drain current on the terminal voltages, gate oxide thicknesses, channel doping concentrations and the Silicon body thickness and a good agreement is observed with the 2-D numerical simulation results.     

A 2‐D surface‐potential‐based threshold voltage model for short channel asymmetric heavily doped DG MOSFETs

In recent times, transistors with heavily doped body have generated much interest because of junctionless channel. In addition, proper threshold voltage regulation requires adjustment of the channel doping, as a result of which most of the compact models become invalid as they consider an intrinsic body. In this paper, a compact surface‐potential‐based threshold voltage model is developed for short channel asymmetric double‐gate metal–oxide–semiconductor field‐effect transistors with heavily/lightly doped channel. The 2‐D surface potential is computed and compared with Technology Computer Aided Design, and a relative error of 2–4 % was obtained. The threshold voltage is solved from 2‐D Poisson's equation using ‘virtual cathode’ method, and a good agreement is observed with the numerical simulations. Also, the model is compared with a reference model and a better result is obtained for heavily doped channel. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of underlap and gate length on device performance of an AlInN/GaN underlap MOSFET

We investigate the performance of an 18 nm gate length AlInN/GaN heterostructure underlap double gate MOSFET, using 2D Sentaurus TCAD simulation. The device uses lattice-matched wideband Al_0.83In_0.17N and narrowband GaN layers, along with high-k Al₂O₃ as the gate dielectric. The device has an ultrathin body and is designed according to the ITRS specifications. The simulation is done using the hydrodynamic model and interface traps are also considered. Due to the large two-dimensional electron gas (2DEG) density and high velocity, the maximal drain current density achieved is very high. Extensive device simulation of the major device performance metrics such as drain induced barrier lowering (DIBL), subthreshold slope (SS), delay, threshold voltage (V_t), I_on/I_off ratio and energy delay product have been done for a wide range of gate and underlap lengths. Encouraging results for delay, I_on, DIBL and energy delay product are obtained. The results indicate that there is a need to optimize the I_off and SS values for specific logic design. The proposed AlInN/GaN heterostructure underlap DG MOSFET shows excellent promise as one of the candidates to substitute currently used MOSFETs for future high speed applications.     

Improvement of Transmission Control Protocol for High Bandwidth Applications

Transmission control protocol (TCP) is the widely and dominantly used protocol in today’s internet. A very recent implementation of congestion control algorithm is BBR by Google. Bottleneck bandwidth and round-trip time (BBR) is a congestion control algorithm which is created with the aim of increasing throughput and reducing delay. The congestion control protocols mentioned previously try to determine congestion limits by filling router queues. BBR drains the router queues at the bottleneck by sending exactly at the bottleneck link rate. This is done by the BBR through pacing rate which infers the delivery rate of the receiver and uses this as the estimated bottleneck bandwidth. But when the data rate is high, in the startup phase itself pipe becomes full and leads to some degradation in the Access Point of wireless environments by inducing losses specific to this environment. So the current pacing rate is not suitable for producing higher throughputs. Therefore, in the proposed system named R-BBR, this startup gain should be lower than the current startup gain which eventually would reduce pacing rate to reduce queue pressure in the sink node during the startup phase. The startup phase of BBR is modified to solve the problem of pipe full under high data rate. R-BBR has been evaluated over a wide range of wired as well as wireless networks by varying different factors like startup gain, congestion window, and pacing rate. It is inferred that R-BBR performs better than BBR with significant performance improvement.

     

Simple but efficient synthesis of bis(indolyl)methanes by the condensation reaction of substituted benzaldehydes with indole over mesoporous ZrO<Subscript>2</Subscript>–MgO green catalysts under solvent free conditions

Solid base catalytic materials such as ZrO₂, MgO, ZrO₂–MgO were prepared by either precipitation or impregnation method and characterized by, BET, CO₂-TPD, PXRD, FT-IR, ICP-OES and TEM techniques. These catalysts were used for the synthesis of bis(indolyl)methanes by the condensation of different benzaldehydes with indole under solvent free conditions in shorter reaction times (20 min) at moderate temperature (70?°C). ZrO₂/MgO catalyst was found to be highly basic and also resulted in high yields of bis(indolyl)methanes up to ~99%. This methodology offers several advantages such as high quality yields, easy procedure, mild and environmentally benign conditions. TEM studies revealed that ZrO₂–MgO is mesoporous (25–45 nm) in nature. ZrO₂–MgO catalysts were found to be economical, efficient and were found to be highly active, recyclable and reusable up to six reaction cycles without much loss of their activity.