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Radio spectral index from NVSS and TGSS

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Research in Astronomy and Astrophysics 2019年第7期19卷 59-66页

作者： Prabhakar tiwari National Astronomical Observatories Chinese Academy of Sciences

I extract the radio spectral index,α,from 541 195 common sources observed in the 150 MHz TIFR GMRT Sky Survey(TGSS) and the 1.4 GHz NRAO VLA Sky Survey(NVSS).This large common source catalog covers about 80% of the *** flux density limits in these surveys are such that the observed galaxies are presumably hosts of active galactic nuclei(AGNs).I confirm the steepening of αwith increasing flux density for this large sample and provide a parametric fit between α and flux ***,I divide the data into low flux(LF) and high flux(HF) density samples with roughly equal numbers of *** LF sample contains all galaxies below 100 m Jy TGSS and 20 m Jy NVSS flux density and the HF sample is all galaxies above 100 m Jy TGSS and 20 m Jy NVSS.I observe an increase in α with source size(TGSS measured),saturating for large sizes to 0.89 ± 0.22 and 0.76 ± 0.21 for the LF and HF sources,respectively.I discuss the observed results and possible physical mechanisms to explain observedα dependence with source size for LF and HF samples.

关键词： galaxies:high-redshift galaxies:active galactic nuclei

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

LRS Bianchi Type-II Cosmological Model with a Decaying Lambda Term

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Chinese Physics Letters 2012年第1期29卷 35-37页

作者： R.K.tiwari D.tiwari Pratibha Shukla Department of Mathematics Govt.Model Science College RewaM.P.486001India

We consider a locally rotationally symmetric(LRS)Bianchi type-Ⅱspacetime with a perfect fluid and a variable cosmological constant∧.To solve the Einstein field equations we consider the cosmological term∧to be proportional to R^(-m) with R being the scale factor and m a constant[***.D 58(1998)043506].In this model we obtain∧~H^(2),∧~(R)/R and Larnbda~t^(-2),in agreement with the main dynamical laws for the decay of∧.The physical significance of the cosmological model is also discussed.

关键词： Bianchi Cosmo perfect

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

Ionic polymer-metal composite mechanoelectric transduction:effect of impedance

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International Journal of Smart and Nano Materials 2012年第4期3卷 275-295页

作者： Rashi tiwari Mechanical and Aerospace Engineering Department Cornell UniversityIthacaNYUSA

Ionic polymer–metal composites(IPMCs)are commonly used as soft actuators due to their electromechanical ***,the reverse phenomenon,***’s ability to generate charge on application of mechanical strain(mechanoelectric response),is not very well *** concept of mechanoelectric transduction and its dependence on complex IPMC architecture comprising of electrode,polymer and composite layer is illustrated with a phenomenological *** impedance model takes into account the charge transport inside the polymer and layer properties in terms of their *** model lucidly indicates the significance of capacitance in IPMC *** impedance model is used for studying IPMC step and frequency response and the effect of IPMC capacitance on its application as energy harvester.

关键词： ionic polymer-metal composite capacitance impedance mechanoelectric response

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

Modelling and analysis of COVID-19 epidemic in India

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Journal of Safety Science and Resilience 2020年第2期1卷 135-140页

作者： Alok tiwari Department of Energy Science and Engineering IIT BombayMumbai 400076India

COVID-19 epidemic is declared as the public health emergency of international concern by the World Health Organisation in the last week of March *** disease originated from China in December 2019 has already caused havoc around the world,including *** first case in India was reported on 30th January 2020,with the cases crossing 4 million on the day paper was *** pandemic has caused more than 80,000 fatalities with 3 million *** lockdown of the nation for two months,immediate isolation of infected cases and app-based tracing of infected are some of the proactive steps taken by the *** a better understanding of the evolution of COVID-19 in the world,study on evolution and growth of cases in India could not be *** understand the same,one of the compartment model:Susceptible-Infectious-Quarantined-Recovered(SIQR)is *** rate and doubling rate of the total reported positive cases in the country had crossed 75%and 25 days,*** is also estimated that there is a strong positive correlation between testing rate and detection of new cases up to 6 million tests per *** the SIQR modelling effective reproduction number,epidemic doubling rate and infected to quarantined ratio is determined to check the temporal evolution of the pandemic in the *** reproduction number that was at its peak during first half of the April is gradually converging to *** is also estimated using this model that with each detected cases in India,there could be 10-50 undetected *** every mathematical model,this model also has some *** make this model more robust,a technique with weighted parameter that can avoid a person with a strong immune system to be equally vulnerable to the infection,can be worked *** learning algorithms can also be used to train our model with the data of other countries to make the analysis and prediction more precise and accurate.

关键词： Mathematical modelling SIQR COVID 19 Reproduction number India

Coupling effect of pond ash and polypropylene fiber on strength and durability of expansive soil subgrades:An integrated experimental and machine learning approach

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Journal of Rock Mechanics and Geotechnical Engineering 2021年第5期13卷 1101-1112页

作者： Nitin tiwari Neelima Satyam Department of Civil Engineering Indian Institute of Technology IndoreIndoreIndia

This study explores the coupling effect of pond ash(PA)and polypropylene(PP)fiber to control the strength and durability of expansive *** PA is used to chemically treat the expansive soil and PP fiber is adopted as reinforcement against tensile *** sustainable use of PA and PP fiber are demonstrated by performing mechanical(*** compressive strength,split tensile strength and ultrasonic pulse velocity),chemical(pH value,electrical conductivity and calcite content),and microstructural analyses before and after 2nd,4th,6th,8th and 10th freezing-thawing(F-T)*** curing methods with 7 d,14 d and 28 d curing periods are considered to reinforce the 5%,10%,15%and 20%PA-stabilized expansive soil with 0.25%,0.5%and 1%PP *** order to develop predictive models for mechanical and durability parameters,the experimental data are processed utilizing artificial neural network(ANN),in association with the leave-one-out cross-validation(LOOCV)as a resampling method and three different activation *** mechanical and durability properties of the PA-stabilized expansive soil subgrades are increased with PP fiber *** results of ANN modeling predict the mechanical properties perfectly,and the correlation coefficient(R)approaches up to 0.96.

关键词： Expansive soil subgrades Waste utilization Freezing-thawing(F-T) Microstructural assessment Pond ash(PA) Polypropylene(PP)fiber