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Study of damage behavior and repair effectiveness of patch repaired carbon fiber laminate under quasi-static indentation loading

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Defence Technology（防务技术） 2024年第4期34卷 29-41页

作者： alok kumar Chinmaya kumar Sahoo A.Arockiarajan Department of Applied Mechanics Indian Institute of Technology MadrasChennai 600036India

Damage caused due to low-velocity impacts in composites leads to substantial deterioration in their residual strength and eventually provokes structural *** work presents an experimental investigation on the effects of different patch and parent laminate stacking sequences on the enhancement of impact strength of Carbon Fiber Reinforced Polymers(CFRP)composites by utilising the adhesively bonded external patch repair *** evolution study is also performed with the aid of Acoustic Emission(AE).Two different quasi-isotropic configurations were selected for the parent laminate,viz.,[45°/45°/0°/0°]s and[45°/0°/45°/0°]*** Static Indentation(QSI)test was performed on both the pristine laminates,and damage areas were detected by using the C-scan inspection *** laminates were repaired by using a single-sided patch of two different configurations,viz.,[45°/45°/45°/45°]and[45°/0°/0°/45°],and employing a circular plug to fill the damaged *** different combinations of repaired laminates with two configurations of each parent and patch laminate were produced,which were further subjected to the QSI *** results reveal the effectiveness of the repair method,as all the repaired laminates show higher impact resistance compared to the respective pristine *** of[45°/0°/0°/45°]configuration when repaired by taking[45°/45°/0°/0°]s and[45°/0°/45°/0°]s as parents exhibited 68%and 73%higher peak loads,respectively,than the respective pristine ***,parent and patch of configuration[45°/0°/45°/0°]s and[45°/0°/0°/45°],respectively,attain the highest peak load,whereas[45°/45°/0°/0°]s and[45°/45°/45°/45°]combinations possess the most gradual decrease in the load.

关键词： Carbon fiber reinforced polymers(CFRP) Quasi-isotropic laminate Quasi static indentation(QSI) Acoustic emission(AE) Composite repair

Dual-Core Photonic Crystal Fiber Plasmonic Refractive Index Sensor: A Numerical Analysis

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Photonic Sensors 2019年第2期9卷 151-161页

作者： alok kumar PAUL Ajay Krishno SARKAR Department of Electrical & Electronic Engineering Rajshahi University of Engineering & Technology Rajshahi-6204 Bangladesh

A numerical analysis on dual core photonic crystal fiber (DC-PCF) based surface plasmon resonance (SPR) refractive index sensor is presented. The guiding parameters and required sensing performances are examined with finite element method (FEM) based software under MATLAB environment. According to simulation, it is warranted that the proposed refractive index sensor offers the maximum amplitude sensitivity of 554.9 refractive index unit (RIU-1) and 636.5 RIU 1 with the maximum wavelength sensitivity of 5800nm/RIU and 11 500nm/RIU, and the sensor resolutions of 1.72 ×10^-5RIU and 8.7× 10^-6 RIU, at analyte refractive index (RI) of 1.40 for x- and y-polarized modes, respectively. As the sensing performance in different wavelength ranges is quite high, the proposed sensor can be used in simultaneous detection for different wavelength ranges. Therefore, the proposed device is of a suitable platform for detecting biological, chemical, biochemical, and organic chemical analytes.

关键词： Photonic crystal fiber biosensor refractive index sensor finite element method plasmonic material

Optimal ordering policy for short life-cycle products under credit financing with dynamic adoption in supply chain

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Journal of Management Analytics 2019年第3期6卷 269-301页

作者： Udayan Chanda alok kumar Department of Management BITS PilaniPilaniIndia FORE School of Management New DelhiIndia

Traditional inventory models are mostly ignorant of the life cycle dynamics of a technology product;hence,they often fail to identify different dimensions of inventory *** paper attempts to investigate the relationship between adoption behavior of customers using life cycle dynamics and associated trade credit policies in order to optimize the total inventory *** demand model used in this paper treats sales as a function of awareness diffusion and *** is considered as a function of feedback effects from users/***’s optimal strategies for short life cycle product under credit financing were determined ***,numerical examples have been used to support the theoretical *** results have further been used to gain some managerial insights.

关键词： inventory stage-wise diffusion unfavorable information short life cycle trade credit

Slip flow of micropolar fluid through a permeable wedge due to the effects of chemical reaction and heat source/sink with Hall and ionslip currents:an analytic approach

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Propulsion and Power Research 2020年第3期9卷 289-303页

作者： Khilap Singh alok kumar Pandey Manoj kumar Department of Mathematics Statisticsand Computer ScienceG.B.Pant University of Agriculture and TechnologyPantnagar263145UttarakhandIndia Department of Mathematics Graphic Era Deemed to Be UniversityDehradun248002UttarakhandIndia

This study focuses on the combined impact of heat source/sink and chemical reaction on slip flow of micropolar fluid through a permeable wedge in the existence of Hall and ion-slip *** governing highly non-lincar PDEs were altered into a set of non-linear coupled ODEs by using similarity *** transformation method(DTM)has been implemented in transformed ODEs *** comparison with previous literatures was performed and the data of this study was found to be in accordance with each *** analytical solutions for skin-friction coefficients(surface drag forces),Nussclt and Sherwood numbers are depicted through graphs and *** study of boundary layer flow over a wedge surface plays an imperative role in the field of aerodynamics,heat exchanger,ground water pollution and geothermal system etc.

关键词： Chemical reaction Differential transformation method(DTM) Hall current and ion slip Heat source/sink Micropolar fluid Slip velocity

Modeling the effect of time delay in implementation of mitigation policies on the control of atmospheric greenhouse gases

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International Journal of Biomathematics 2023年第8期16卷 75-108页

作者： alok kumar Verma Maitri Verma Department of Mathematics School of Physical and Decision Science Babasaheb Bhimrao Ambedkar University Lucknow India

Mitigation of the enhanced greenhouse gas(GHG)concentrations in the Earth's atmosphere is imperative to meet the climate change mitigation *** of many countries are developing and implementing various mitigation strategies to reduce their GHG ***,a time delay between the formulation and implementation of these mitigation policies can affect their effectiveness in controlling greenhouse gas levels in the *** work presents a nonlinear mathematical model to investigate the effect of application of mitigation strategies and the delay involved in their implementation over the reduction of atmospheric greenhouse *** model formulation,it is assumed that the mitigation strategies work two-fold;first they reduce the GHG emission rate from the anthropogenic source and second they increase the removal rate of greenhouse gas from the atmosphere.A comprehensive stability analysis of the proposed model system is made to examine its long-term *** model analysis shows that an increase in the implementation rate of mitigation strategies and their efficiencies to cut down the GHG emission rate from point sources and increase the GHG uptake rate lead to reduction in equilibrium GHG *** is found that a long delay in the execution of mitigation policies can destabilize the system dynamics and leads to the generation of periodic *** expression for the threshold value of the delay parameter at which periodic oscillations arise via Hopf-bifurcation is *** stability and direction of bifurcating periodic solutions are discussed.A sensitivity analysis is performed to investigate the effect of changes in key parameters over system dynamics.

关键词： Mathematical model greenhouse gases global warming mitigation strategies time delay Hopf-bifurcation

Numerical solution of micropolar fluid flow via stretchable surface with chemical reaction and melting heat transfer using Keller-Box method

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Propulsion and Power Research 2021年第2期10卷 194-207页

作者： Khilap Singh alok kumar Pandey Manoj kumar Department of Mathematics Statistics and Computer ScienceG.B.Pant University of Agriculture and TechnologyPantnagarUttarakhand263145India Department of Mathematics Graphic Era Deemed to be UniversityDehradunUttarakhand248002India

The main theme of this research is to find the numerical results of stagnation point flow of micropolar fluid over a porous stretchable surface due to the physical effects of internal heat generation/absorption,melting heat transfer and chemical reaction via Keller-Box method(KBM).The graphs and tables are depicted and explained for various embedded *** range of melting heat transfer parameter is 0≤M≤3,the range of chemical reaction parameter is 0≤K_(r)≤1 whereas the values of space-temperature dependent heat source/sink parameters lies in-0:4≤Q≤0:4 and-2≤Q*≤*** upshots of the current problem illustrate that at fluid-solid interface,rate of HMT(heat and mass transfer)declined on escalating the values of stretching ***,as the values of internal heat source/sink parameter increases,heat transfer rate declines at fluid-solid interface.

关键词： Chemical reaction Implicit finite difference Keller-Box method(KBM) Internal heat generation/absorption Heat and mass transfer(HMT) Melting heat transfer Porous medium

Upper ocean high resolution regional modeling of the Arabian Sea and Bay of Bengal

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Acta Oceanologica Sinica 2019年第5期38卷 32-50页

作者： Dwivedi Suneet Mishra alok kumar Srivastava Atul K Banerjee Centre of Atmospheric and Ocean Studies and M N Saha Centre of Space Studies University of Allahabad

In this paper, effort is made to demonstrate the quality of high-resolution regional ocean circulation model in realistically simulating the circulation and variability properties of the northern Indian Ocean(10°S–25°N,45°–100°E) covering the Arabian Sea(AS) and Bay of Bengal(BoB). The model run using the open boundary conditions is carried out at 10 km horizontal resolution and highest vertical resolution of 2 m in the upper *** surface and sub-surface structure of hydrographic variables(temperature and salinity) and currents is compared against the observations during 1998–2014(17 years). In particular, the seasonal variability of the sea surface temperature, sea surface salinity, and surface currents over the model domain is studied. The highresolution model's ability in correct estimation of the spatio-temporal mixed layer depth(MLD) variability of the AS and BoB is also shown. The lowest MLD values are observed during spring(March-April-May) and highest during winter(December-January-February) seasons. The maximum MLD in the AS(BoB) during December to February reaches 150 m (67 m). On the other hand, the minimum MLD in these regions during March-April-May becomes as low as 11–12 m. The influence of wind stress, net heat flux and freshwater flux on the seasonal variability of the MLD is discussed. The physical processes controlling the seasonal cycle of sea surface temperature are investigated by carrying out mixed layer heat budget analysis. It is found that air-sea fluxes play a dominant role in the seasonal evolution of sea surface temperature of the northern Indian Ocean and the contribution of horizontal advection, vertical entrainment and diffusion processes is small. The upper ocean zonal and meridional volume transport across different sections in the AS and BoB is also computed. The seasonal variability of the transports is studied in the context of monsoonal currents.

关键词： Indian Ocean modeling Arabian Sea and Bay of Bengal mixed layer depth transport

Synthesis of Co3O4 Nanoparticles Wrapped Within Full Carbon Matrix as an Anode Material for Lithium Ion Batteries

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Acta Metallurgica Sinica(English Letters) 2018年第2期31卷 164-170页

作者： Subhalaxmi Mohapatra Shantikumar V.Nair alok kumar Rai Amrita Centre for Nanosciences and Molecular Medicine Amrita Vishwa Vidyapeetham Amrita University Kochi Kerala 682041 India

A facile polyol-assisted pyro-synthesis method was used to synthesize Co3O4 nanoparticles embedded into carbon matrix without using any conventional carbon source. The surface analysis by scanning electron microscopy showed that the Co3O4 nanoparticles（-20 ± 5 nm） are tightly enwrapped within the carbon matrix. CHN analysis determined the carbon content was only 0.11% in the final annealed sample. The Co3O4@carbon exhibited high capacities and excellent cycling performance as an anode at various current rates（such as 914.4 and 515.5 mAh g^-1 at 0.25 and1.0 C, respectively, after 50 cycles; 318.2 mAh g^-1 at a high current rate of 5.0 C after 25 cycles）. This superior electrochemical performance of the electrode can be attributed to the various aspects, such as,（1） the existence of carbon matrix, which acts as a flexible buffer to accommodate the volume changes during Li^＋ion insertion/deinsertion and facilitates the fast Li^＋and electron transfer and（2） the anchoring of Co3O4 nanoparticles within the carbon matrix prevents particles agglomeration.

关键词： Co3O4 Carbon matrix Pyro-synthesis Anode Lithium ion battery

An improved reverse time migration for subsurface imaging over complex geological structures:A numerical study

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Energy Geoscience

Energy Geoscience 2024年第2期5卷 290-297页

作者： alok kumar Routa Priya Ranjan Monahty Department of Applied Geophysics IIT(ISM)DhanbadJharkhandIndia

In seismic exploration,it is a critical task to image and interpret different seismic signatures over complex geology due to strong lateral velocity contrast,steep reflectors,overburden strata and dipping *** understand the behavior of these seismic signatures,nowadays Reverse Time Migration(RTM)technique is used extensively by the oil&gas *** the extrapolation phase of RTM,the source wavefield needs to be saved,which needs high storage memory and large computing *** two are the main obstacles of RTM for production *** order to overcome these disadvantages,in this study,a second-generation improved RTM technique is *** this improved form,a shift operator is introduced at the time of imaging condition of RTM algorithm which is performed automatically both in space and time *** effort is made to produce a better-quality image by minimizing the computational time as well as numerical *** proposed method is applied over various benchmark models and validated by implementing over one field data set from the Jaisalmer Basin,*** the analysis,it is observed that the method consumes a minimum of 45%less storage space and reduce the execution time by 20%,as compared to conventional *** proposed RTM is found to work efficiently in comparison to the conventional RTM both in terms of imaging quality and minimization of numerical artefacts for all the benchmark models as well as field data.

关键词： Imaging condition Reverse time migration(RTM) Seismic imaging Velocity-depth model Wave propagation