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Tribological behaviour of C/C-SiC composites-A review

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Journal of Advanced Ceramics 2016年第1期5卷 1-12页

作者： Parshant KUMAR v.K.srivastava Department of Mechanical Engineering Indian Institute of Technology(BHU) Varanasi-221005 India

Ceramic matrix composites made of carbon fibres and carbon matrix (C/C) are generally used for aircraft structures and brake discs due to their low density, and good thermal, mechanical, and tribological properties. Silicon carbide (SiC) can be introduced to the matrix to improve the performance of C/C composites, because it increases the hardness and thermal stability, and decreases the chemical reactivity, which leads to the improvement of tribological properties of C/C composites. Thus carbon-carbon silicon carbide (C/C-SiC) composites can be used at high temperature for the application of brake discs, friction clutches, etc. C/C-SiC composites are fabricated by three different methods: (i) chemical vapour infiltration (CvI), (ii) polymer infiltration and pyrolysis (PIP), and (iii) liquid silicon infiltration (LSI), among which LSI method is widely used for the fabrication of C/C-SiC composites due to higher mechanical and thermal properties.

关键词： carbon-carbon (C/C) composites coefficient of friction wear

Application of IITM-RANS3D to free-fall water entry of prismatic and non-prismatic finite wedges

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Journal of Hydrodynamics 2023年第3期35卷 417-430页

作者： Shaswat Saincher Kshitij srivastava R.vijayakumar v.Sriram Center for Maritime Experiments to Maritime Experience(ME2ME) Indian Institute of Technology MadrasChennaiIndia Department of Ocean Engineering Indian Institute of Technology MadrasChennaiIndia

High-speed watercraft and ships undergo coupled motions which make the front portion of the hull exit and violently re-enter *** induces short-term slamming loads that may compromise the structural integrity of the *** slamming of the bow can be modeled as straight wedges of different deadrise angles(DRAs)falling into water from different *** advent of computational fluid dynamics has allowed the problem of wedge-slamming to be simulated using the full Navier-Stokes equations thus complementing the pioneering studies based on ***,most researchers are opting to use commercial software to simulate the wedge-impact problem as it allows access to overset meshing algorithms which are robust in modeling the wedge as a moving *** boundary methods(EBMs)offer some advantages over overset meshing in that the mesh only needs to be generated once and Cartesian mesh-based solvers can be ***,the application of EBMs to wedge-impact has been limited in the literature and merits further *** this context,we investigate the applicability of the fast-fictitious-domain(FFD)based embedded boundary treatment to simulate the violent water-entry of *** extend our in-house Navier-Stokes model IITM-RANS3D to handle floating bodies through integration of a rigid-body dynamics solver and an algorithm to embed three-dimensional stereolithography(STL)geometries as solids over a Cartesian *** proposed algorithm is extensively benchmarked against variable DRA wedge-slamming experiments reported in the literature as well as constant DRA wedge-slamming experiments performed *** good agreement is reported in terms of the time-history of hydrodynamic impact pressures measured at various locations on the hull as well as the wedge motion responses thus demonstrating the suitability of FFD for simulating the coupled hydrodynamics of slamming for simplified hull geometries.

关键词： Wedge water entry slamming fast-fictitious-domain IITM-RANS3D experiments

Compositionally Graded Microstructure for Ag-Fe Nanoparticles

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Nano-Micro Letters 2012年第3期4卷 172-175页

作者： Chandan srivastava K.v.L.Sushma Department of Materials Engineering Indian Institute of Science

Ag-Fe nanoparticles with a highly Ag rich average composition were synthesized by the sonochemical ***-iron system exhibits a wide miscibility gap in the bulk ***,a graded compositional profile along the nanoparticle radius was *** at and near the surface of the nanoparticle contained both Ag and Fe *** composition got relatively deficient Fe towards the center of the particle with particle core made up of pure *** of Ag and Fe is confirmed by the absence of diffraction signal corresponding to pure Fe phase and presence of a paramagnetic phase in nanoparticles containing a diamagnetic(Ag)and ferromagnetic(Fe)elements.

关键词： Nanoparticles Electron Microscopy Ag-Fe Miscibility gap Solid solution Microstructure

Effect of hydrogen plasma treatment on the growth and microstructures of multiwalled carbon nanotubes

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Nano-Micro Letters 2010年第1期2卷 42-48页

作者： S.K.srivastava v.D.vankar v.Kumar Department of Physics Indian Institute of Technology Delhi National Physical Laboratory Dr.K.S.Krishnan Marg

The effect of hydrogen plasma treatment of iron oxide films on the growth and microstructure of carbon nanotubes(CNTs)by microwave plasma enhanced chemical vapor deposition process has been *** plasma was characterized in-situ using optical emission *** of the films was examined by scanning electron *** analysis was carried out by high resolution transmission electron microscopy(HRTEM)equipped with energy dispersive X-ray spectroscopy(EDS)and micro-diffraction *** is found that oxide films without H_2 plasma pretreatment or treated for lesser time resulted in CNT films with high percentage of carbonaceous particles and with embedded particles/nanorods distributed discontinuously in the cavity of the *** embedded particles were found to be of iron carbide(Fe-C)as confirmed by HRTEM,EDS and micro-diffraction *** observations suggested that the iron oxide particles had poor catalytic action for CNT growth and in-situ reduction of oxide clusters to Fe by hydrogen plasma plays a key role in discontinuous filling of the nanotubes by the catalytic particles.

关键词： Carbon nanotubes Chemical vapor deposition Iron carbide MPECvD

Investigating the impact of atmospheric parameters on sea ice variability in and around Svalbard

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Advances in Polar Science 2023年第2期34卷 125-143页

作者： Dency v PANICKER Bhasha vACHHARAJANI Rohit srivastava Department of Physics School of Energy TechnologyPandit Deendayal Energy UniversityGandhinagarGujaratIndia Department of Mathematics School of TechnologyPandit Deendayal Energy UniversityGandhinagarGujaratIndia

Recent research has shown that winter warmings are phenomenally high compared to summer warmings over the poles,especially over the *** the current scenario into account,this paper attempts to understand the atmospheric variables causing sea ice variability over and around the region of Svalbard for seasons;winter,spring,summer and autumn for the span of 42 years(1979-2021).The variability in atmospheric and oceanic parameters namely temperature,precipitation,wind speed,and sea surface salinity are analysed over inter-spatial,inter-seasonal and inter-annual *** are characterized by inter-annual increasing trend in *** 1981-1990 the rise from the decadal mean is found to be 0.39 K·a^(-1),during 1991-2000 it is 0.20 K·a^(-1),during 2001-2010 it is 0.04 K·a^(-1) and during 2011-2020 it is 0.23 K·a^(-1).Interestingly while considering inter-spatial domains,the region southwest to Svalbard seems to be wetter(0.05 mm·(10 a)-1)compared to its northeast(-0.03 mm·(10 a)-1).Across all the three domains,wind speeds are highest during autumn and then decrease subsequently through summer,spring and are least during *** is predominantly from the south,and hence it is suspected to carry hot Atlantic ***,the significant role of salinity in the ocean also plays a key role in governing the fate of sea ice *** long-term forecasts of temperature over seaice of Svalbard are alarming especially for the winter ice(r=-0.84).Correlation matrices between atmospheric and sea ice parameters are shown to gain a better understanding on their inter relation.

关键词： Svalbard northeast Svalbard southwest Svalbard temperature precipitation wind speed sea ice concentration

Biologics in the management of pediatric inflammatory bowel disease:When and what to choose

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World Journal of Clinical Pediatrics 2025年第1期14卷 21-45页

作者： Arghya Samanta Anshu srivastava Department of Pediatric Gastroenterology Sanjay Gandhi Postgraduate Institute of Medical SciencesLucknow 226014Uttar PradeshIndia

Pediatric inflammatory bowel disease(PIBD)is a chronic inflammatory disorder of the gastrointestinal tract,with rising global incidence and *** the past two decades,biologics have added to the therapeutic armamentarium and revolutionized the approach to treatment of inflammatory bowel *** available biologics include monoclonal antibodies which target inflammatory cytokines(anti-tumor necrosis factor alpha,anti-interleukin 12/23)or recruitment of leucocytes to the gastrointestinal tract(anti-alpha4beta7 integrin)and small molecules(Janus kinase inhibitors,sphingosine 1-phosphate-inhibitors)which modify the proinflammatory *** their potential disease-modifying ability,recent pediatric guidelines from the West have advocated upfront use of biologics in appropriate clinical scenarios as a top-down approach rather than the conventional step-up *** real-world studies are available regarding the clinical efficacy of biologics in PIBD,there is paucity of long-term outcome and safety data in ***,little information is available about the best approach in the newly industrialized-developing countries where PIBD is rising but at the same time,infections are prevalent and resources are *** this review,we summarize the efficacy and safety profile of biologics and small molecule drugs and discuss the challenges in the management of PIBD,especially in the developing world,and future directions.

关键词： Biologics Children Inflammatory bowel disease Therapeutic drug monitoring Dual biologic

Photoconductivity and surface chemical analysis of ZnO thin films deposited by solution-processing techniques for nano and microstructure fabrication

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Journal of Semiconductors 2013年第3期34卷 12-16页

作者： v.K.Dwivedi P.srivastava G.vijaya Prakash Nanophotonics Laboratory Department of PhysicsIndian Institute of Technology DelhiHauz khasNew Delhi-110 016India Nanostech Laboratory Department of PhysicsIndian Institute of Technology DelhiHauz khasNew Delhi-110 016India Nanophotonics Laboratory Department of PhysicsIndian Institute of Technology DelhiHauz khasNew Delhi-110016India

The fabrication of zinc oxide(ZnO) from inexpensive solution-processing techniques,namely,electrochemical deposition and electrospinning were explored on various conducting and mesoporous semiconducting *** conditions were derived for template- and self-assisted nano/micro structures and composites. ZnO thin films were annealed at a fixed temperature under ambient conditions and characterised using physical and optical *** photocurrent response in the Uv region shows a fast rise and double decay behaviour with a fast component followed by a slow oscillatory *** results were correlated with surface chemical analysis from X-ray photoelectron *** characterisation details reveal the importance of fabrication parameter optimisation for useful low-cost optoelectronic applications.

关键词： zinc oxide electrochemical deposition surface analysis X-ray photoelectron spectroscopy photocurrent response optoelectronic applications

Pd-gate MOS sensor for detection of methanol and propanol

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Journal of Natural Gas Chemistry 2011年第2期20卷 123-127页

作者： Preeti Pandey J. K. srivastava v. N. Mishra R. Dwivedi Center for Research in Microelectronics Department of Electronics Engineering Institute of Technology Banaras Hindu University

The present paper focused on the detection of methanol and propanol using Pd-gate metal-oxide-semiconductor （MOS） sensor. Surface mor- phology and composition of the gate film were studied by scanning electron microscopy （SEM） and atomic force microscopy （AFM）. The response of the sensor for propanol and methanol was measured as shift in capacitance-voltage （C-v） and conductance-voltage （G-v） curves of the MOS structure. The sensitivity of the sensor towards methanol was found to be greater than that towards propanol. It was 58.2% for methanol and 32% for propanol （at 0.6 v, 1 MHz） in terms of capacitance measurements, while in terms of conductance results the sensitivity was found to be 57.2% for methanol and 38.9% for propanol at 1 kHz. The discontinuities or cracks present in the microstructure of the gate material are believed to be mainly responsible for the high sensitivity of the sensor, going with the decomposition of gas molecules and subsequent hydrogen permeation through Pd.

关键词： MOS structure gas sensor palladium cracks sensitivity

Structural and micro structural studies of PbO-doped SnO_2 sensor for detection of methanol, propanol and acetone

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Journal of Natural Gas Chemistry 2011年第2期20卷 179-183页

作者： J. K. srivastava Preeti Pandey v. N. Mishra R. Dwivedi Center for Research in Microelectronics Department of Electronics Engineering Institute of Technology Banaras Hindu University

In the present work the structural information of PbO-doped SnO2 thick film sensor has been investigated with X-ray diffractometer （XRD） and scanning electron microscope （SEM）. Initially, SnO2 powder was derived using sol-gel process and was subsequently doped with PbO and ground up to nanosized particles. A suitable gas sensor structure was fabricated on 1′′×1′′ alumina substrate using thick film technology. The necessary paste for screen printing was also developed. SEM results showed sol-gel derived powder gets more agglomerated in the thick film form. The sensitivity of the sensor has been investigated at different temperatures （150 ？C？350 ？C） upon exposure to methanol, propanol and acetone, yielding a maximum at 250 ？C for acetone with 1 wt% PbO-doping while at 350 ？C for propanol with 3 wt% PbO-doping of the sensor. The reduction of particle size to nanometers （validated through XRD） leads to a dramatic improvement in sensitivity of sensors for the chosen organic vapors. The results also correlate well with the microstructural properties of the material and the dopant.

关键词： gas sensor nanosized SnO2 Sol-gel thick film