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Chinese Physics B 2015年第10期24卷 604-611页

作者： Gopi Krishna Saramekala Sarvesh Dubey pramod.kumar tiwari Department of Electronics and Communication Engineering National Institute of Technology Shri Ramswaroop Memorial University

In this paper, a surface potential based threshold voltage model of fully-depleted（FD） recessed-source/drain（Re-S/D）silicon-on-insulator（SOI） metal-oxide semiconductor field-effect transistor（MOSFET） is presented while considering the effects of high-k gate-dielectric material induced fringing-field. The two-dimensional（2D） Poisson＇s equation is solved in a channel region in order to obtain the surface potential under the assumption of the parabolic potential profile in the transverse direction of the channel with appropriate boundary conditions. The accuracy of the model is verified by comparing the model＇s results with the 2D simulation results from ATLAS over a wide range of channel lengths and other parameters,including the dielectric constant of gate-dielectric material.

关键词： recessed-source/drain (Re-S/D) high-k gate-material fringing field and SCEs

On-current modeling of short-channel double-gate(DG) MOSFETs with a vertical Gaussian-like doping profile

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Journal of Semiconductors 2013年第5期34卷 46-53页

作者： Sarvesh Dubey pramod.kumar tiwari S.Jit Department of Electronics Engineering Indian Institute of Technology(BHU)Varanasi-221005India Department of Electronics and Communication Engineering National Institute of Technology Rourkela-769008India

An analytic drain current model is presented for doped short-channel double-gate MOSFETs with a Gaussian-like doping profile in the vertical direction of the channel. The present model is valid in linear and satura- tion regions of device operation. The drain current variation with various device parameters has been demonstrated. The model is made more physical by incorporating the channel length modulation effect. Parameters like transcon- ductance and drain conductance that are important in assessing the analog performance of the device have also been formulated. The model results are validated by numerical simulation results obtained by using the commercially available ATLAS^TM, a two dimensional device simulator from SILVACO.

关键词： drain current DG MOSFET transconductance drain conductance

Analytical model for subthreshold current and subthreshold swing of short-channel double-material-gate MOSFETs with strained-silicon channel on silicon–germanium substrates

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Journal of Semiconductors 2014年第10期35卷 30-36页

作者： pramod.kumar tiwari Gopi Krishna Saramekala Sarvesh Dubey Anand kumar Mukhopadhyay National Institute of Technology Rourkela Department of Electronics and Communication Engineering Faculty of Electronics and Communication SRM University

The present work gives some insight into the subthreshold behaviour of short-channel double-material- gate strained-silicon on silicon-germanium MOSFETs in terms of subthreshold swing and off-current. The formu- lation of subthreshold current and, thereupon, the subthreshold swing have been done by exploiting the expression of potential distribution in the channel region of the device. The dependence of the subthreshold characteristics on the device parameters, such as Ge mole fraction, gate length ratio, work function of control gate metal and gate length, has been tested in detail. The analytical models have been validated by the numerical simulation results that were obtained from the device simulation software ATLASTM by Silvaco Inc.

关键词： strained-Si channel Si1-xGex substrate dual-metal gate subthreshold current subthreshold swing

Analog and radio-frequency performance analysis of silicon-nanotube MOSFETs

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Journal of Semiconductors 2016年第6期37卷 60-63页

作者： pramod.kumar tiwari mukesh kumar ramavathu sakru naik gopi krishna saramekala Department of Electronics and Communication Engineering National Institute of TechnologyRourkela-769008OdishaIndia

This work presents a comparative study of the influence of various parameters on the analog and RF properties of silicon-nanotube MOSFETs and nanowire-based gate-all-around（GAA） *** important analog and RF performance parameters of SiNT FETs and GAA MOSFETs,namely drain current（/d）,transconductance to drain current ratio（g_m/I_d）,I_（on）/I_（off）,the cut-off frequency（f_T） and the maximum frequency of oscillation（/max） are evaluated with the help of Y- and H-parameters which are obtained from a 3-D device simulator,ATLAS^（TM）.It is found that the silicon-nanotube MOSFETs have far more superior analog and RF characteristics（g_m/I_d,f_T and /max） compared to the nanowire-based gate-all-around GAA *** silicon-nanotube MOSFET shows an improvement of ~2.5 and 3 times in the case of f_T and /max values respectively compared with the nanowire-based gate-all-around（GAA） MOSFET.

关键词： analog and RF SiNT MOSFETs GAA MOSFETs unity gain frequency unity power frequency

Reliability assessment of deep excavations in spatially random cohesion weakening friction strengthening massive rocks:Application to nuclear repositories

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Underground Space 2023年第6期13卷 48-73页

作者： Akshay kumar Gaurav tiwari Department of Civil Engineering Indian Institute of Technology KanpurKanpurUttar Pradesh 208016India

An augmented methodology is developed to estimate the reliability of deep excavations along spatially variable massive rock masses using the cohesion weakening friction strengthening(CWFS)*** parameters of the CWFS model were initially identified using Sobol’s global sensitivity analysis based on their influence on the displacements and excavation damage zone around *** probability of failure was estimated by performing Mont–Carlo Simulations on random finite difference models of excavations generated via MATLAB-FLAC2D coupling,considering the spatial variation of these sensitive *** variation was modeled by generating anisotropic random fields of sensitive CWFS parameters via the recently developed Fourier series method and updated correlations suggested by Walton(2019).The proposed methodology was demonstrated for a proposed deep nuclear waste repository to be located in *** from the developed methodology were systematically compared with those of traditional reliability(ignoring spatial variation)and deterministic methods(ignoring uncertainty).Although the developed methodology was computationally complex,it was judged to be the most realistic due to the realistic consideration of heterogeneous distributions of rock *** methodologies underestimate/overestimate the excavation performance due to negligence of uncertainty and spatial ***,a parametric analysis was performed using developed methodology by varying the initial friction angle,scale of fluctuations(SOFs)and dilation *** effect of initial friction angle was observed to be more pronounced on the probability of failures as compared to SOFs and dilation *** observations were made related to the excavation damage zone(EDZ)development quantified using yield area ratio.

关键词： Deep excavations Brittle failures CWFS model Sobol’s sensitivity Moving least square response surface Fourier series random field

Robertson-Walker cosmological models with perfect fluid in general relativity

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Research in Astronomy and Astrophysics 2011年第7期11卷 767-775页

作者： Rishi kumar tiwari Department of Mathematics Govt.Model Science College Rewa(M.P.) 486001India

Einstein＇s field equations with variable gravitational and cosmological constants are considered in the presence of perfect fluid for a Robertson-Walker universe by assuming the cosmological term to be proportional to R-m（R is a scale factor and m is a constant）.A variety of solutions is *** physical significance of the cosmological models has also been discussed.

关键词： cosmological parameters—cosmology:variable cosmological term

Jackknife based generalized resampling reliability approach for rock slopes and tunnels stability analyses with limited data:Theory and applications

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Journal of Rock Mechanics and Geotechnical Engineering 2022年第3期14卷 714-730页

作者： Akshay kumar Gaurav tiwari Department of Civil Engineering IIT KanpurIndia

An efficient resampling reliability approach was developed to consider the effect of statistical uncertainties in input properties arising due to insufficient data when estimating the reliability of rock slopes and *** approach considers the effect of uncertainties in both distribution parameters(mean and standard deviation)and types of input ***,the approach was generalized to make it capable of analyzing complex problems with explicit/implicit performance functions(PFs),single/multiple PFs,and correlated/non-correlated input *** couples resampling statistical tool,***,with advanced reliability tools like Latin hypercube sampling(LHS),Sobol’s global sensitivity,moving least square-response surface method(MLS-RSM),and Nataf’s *** developed approach was demonstrated for four cases encompassing different *** were compared with a recently developed bootstrap-based resampling reliability *** results show that the approach is accurate and significantly efficient compared with the bootstrap-based *** proposed approach reflects the effect of statistical uncertainties of input properties by estimating distributions/confidence intervals of reliability index/probability of failure(s)instead of their fixed-point ***,sufficiently accurate results were obtained by considering uncertainties in distribution parameters only and ignoring those in distribution types.

关键词： Statistical uncertainty Resampling reliability Moving least square response surface(MLSRSM) Sobol’s global sensitivity Correlation coefficient

Climatology, trend of aerosol-cloud parameters and their correlation over the Northern Indian Ocean

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Geoscience Frontiers 2023年第4期14卷 173-186页

作者： Harshbardhan kumar Shani tiwari Academy of Scientific and Innovative Research(AcSIR) Ghaziabad201002India Aerosol and Cloud Research Lab Geological Oceanography DivisionCSIR–National Institute of OceanographyGoa403004India

Aerosols are one of the important atmospheric constituents and exert indirect impact on climate through the modification of microphysical and radiative properties of clouds that in turn perturb the precipitation ***,the long term quantification of changes in aerosol and cloud characteristics and their interactions on both temporal as well as spatial scale will provide a crucial information for the better assessment of future climate *** present study,18 years(2003-2020)MODerate Resolution Imaging Spectro-radiometer(MODIS)derived aerosol-cloud dataset over the Northern Indian Ocean(NIO)were analysed to assess climatology and trend of aerosol,cloud characteristics and their *** found a strong heterogeneity in spatio-temporal variation of aerosol and cloud parameters over the NIO that are more prominent for the coastal *** climatological mean of aerosol loading is found high(AOD≥0.5)over the outflow region along the Indian sub-continent and low(AOD≤0.2)over the northern equatorial open *** climatological mean of cloud properties shows dominance of optically thicker deep convective(CTP700 hPa and CTT>273 K)over the northwestern Arabian Sea(AS).Similarly,bigger effective radii(>17µm)observed along the equatorial open ocean whereas smaller CER(0.

关键词： Aerosol Cloud properties Northern Indian Ocean Climatology Trend Correlation

A Bayesian multi-model inference methodology for imprecise momentindependent global sensitivity analysis of rock structures

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Journal of Rock Mechanics and Geotechnical Engineering 2024年第3期16卷 840-859页

作者： Akshay kumar Gaurav tiwari Department of Civil Engineering Indian Institute of Technology(IIT)KanpurKanpur208016India

Traditional global sensitivity analysis(GSA)neglects the epistemic uncertainties associated with the probabilistic characteristics(*** of distribution type and its parameters)of input rock properties emanating due to the small size of datasets while mapping the relative importance of properties to the model *** paper proposes an augmented Bayesian multi-model inference(BMMI)coupled with GSA methodology(BMMI-GSA)to address this issue by estimating the imprecision in the momentindependent sensitivity indices of rock structures arising from the small size of input *** methodology employs BMMI to quantify the epistemic uncertainties associated with model type and parameters of input *** estimated uncertainties are propagated in estimating imprecision in moment-independent Borgonovo’s indices by employing a reweighting approach on candidate probabilistic *** proposed methodology is showcased for a rock slope prone to stress-controlled failure in the Himalayan region of *** proposed methodology was superior to the conventional GSA(neglects all epistemic uncertainties)and Bayesian coupled GSA(B-GSA)(neglects model uncertainty)due to its capability to incorporate the uncertainties in both model type and parameters of *** Borgonovo’s indices estimated via proposed methodology provide the confidence intervals of the sensitivity indices instead of their fixed-point estimates,which makes the user more informed in the data collection *** performed with the varying sample sizes suggested that the uncertainties in sensitivity indices reduce significantly with the increasing sample *** accurate importance ranking of properties was only possible via samples of large ***,the impact of the prior knowledge in terms of prior ranges and distributions was significant;hence,any related assumption should be made carefully.

关键词： Bayesian inference Multi-model inference Statistical uncertainty Global sensitivity analysis(GSA) Borgonovo’s indices Limited data

Cloning ＆ sequence identification of Hsp27 gene and expression analysis of the protein on thermal stress in Lucilia cuprina

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Insect Science 2016年第4期23卷 555-568页

作者： Manish K. Singh pramod K. tiwari Center for Genomics Molecular & Human Genetics Jiwaji University Gwafior 474011 Cytogenetics Laboratory Department of Zoology Banaras Hindu University Varanasi 221005 India

Hsp27, a highly conserved small molecular weight heat shock protein, is widely known to be developmentally regulated and heat inducible. Its role in thermotolerance is also implicated. This study is a sequel of our earlier studies to understand the molecular organization of heat shock genes/proteins and their role in development and thermal adaptation in a sheep pest, Lucilia cuprina （blowfly）, which exhibits unusually high adaptability to a variety of environmental stresses, including heat and chemicals. In this report our aim was to understand the evolutionary relationship of Lucilia hsp27 gene/protein with those of other species and its role in thermal adaptation. We sequence characterized the Lchsp27 gene （coding region） and analyzed its expression in various larval and adult tissues under normal as well as heat shock conditions. The nucleotide sequence analysis of 678 bps long-coding region of Lchsp27 exhibited closest evolutionary proximity with Drosophila （90.09%）, which belongs to the same order, Diptera. Heat shock caused significant en- hancement in the expression ofLchsp27 gene in all the larval and adult tissues examined, however, in a tissue specific manner. Significantly, in Malpighian tubules, while the heatinduced level ofhsp27 transcript （mRNA） appeared increased as compared to control, the protein level remained unaltered and nuclear localized. We infer that Lchsp27 may have significant role in the maintenance of cellular homeostasis, particularly, during summer months, when the fly remains exposed to high heat in its natural habitat.

关键词： heat shock protein Hsp27 Lucilia cuprina thermal stress