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Stability analysis of a thin-walled cylinder in turning operation using the semi-discretization method

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Acta Mechanica Sinica 2014年第2期30卷 214-222页

作者： arnab chanda Achim Fischer Peter Eberhard Santosha Kumar Dwivedy Institute of Engineering and Computational Mechanics University of Stuttgart

In this work, the stability of a flexible thin cylindrical workpiece in turning is analyzed. A process model is derived based on a finite element representation of the workpiece flexibility and a nonlinear cutting force law. Repeated cutting of the same surface due to overlapping cuts is modeled with the help of a time delay. The stability of the so obtained system of periodic delay differential equations is then determined using an approximation as a time-discrete system and Floquet theory. The time-discrete system is obtained using the semi-discretization method. The method is implemented to analyze the stability of two different workpiece models of different thicknesses for different tool positions with respect to the jaw end. It is shown that the stability chart depends on the tool position as well as on the thickness.

关键词： Machine tools Stability Chatter

Fibrinogen’s potential role in connecting cerebrovascular abnormalities with glymphatic dysfunction in Alzheimer’s disease

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Neural Regeneration Research 2025年第1期20卷 203-204页

作者： Vishal Singh arnab Choudhury Hyung Jin Ahn Department of Pharmacology Physiology and NeurosciencesRutgers-New Jersey Medical SchoolNewarkNJUSA Brain Health Institute Rutgers UniversityPiscatawayNJUSA

Alzheimer’s disease(AD)stands out as the primary manifestation of age-related dementia,portraying a chronic neurodegenerative disorder distinguished by the accumulation of fibrillar amyloid-β(Aβ)plaques and neurofibrillary tangles of hyperphosphorylated ***,from a clinical standpoint,AD presents itself as a complex condition with a spectrum of dysfunctions rather than a singular pathological *** often-overlooked aspect of the disease is the presence of extensive cerebrovascular abnormalities,given that the majority of AD patients experience altered cerebral blood flow,damaged vasculature,increased microinfarcts and *** models of AD further support this observation,showing cerebrovascular dysfunction such as impaired cerebral blood flow and altered cerebrovascular reactivity(Tataryn et al.,2021;Gareau et al.,2023).

关键词： cerebrovascular dysfunction Alzheimer

The meridional circulation of the Sun: Observations, theory and connections with the solar dynamo

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Science China(Physics,Mechanics & Astronomy) 2021年第3期64卷 46-72页

作者： arnab Rai Choudhuri Department of Physics Indian Institute of ScienceBangalore560012India

The meridional circulation of the Sun, which is observed to be poleward at the surface, should have a return flow at some depth. Since large-scale flows like the differential rotation and the meridional circulation are driven by turbulent stresses in the convection zone, these flows are expected to remain confined within this zone. Current observational(based on helioseismology)and theoretical(based on dynamo theory) evidences point towards an equatorward return flow of the meridional circulation at the bottom of the convection zone. Assuming the mean values of various quantities averaged over turbulence to be axisymmetric,we study the large-scale flows in solar-like stars on the basis of a 2D mean field theory. Turbulent stresses in a rotating star can transport angular momentum, setting up a differential rotation. The meridional circulation arises from a slight imbalance between two terms which try to drive it in opposite directions: a thermal wind term(arising out of the higher efficiency of convective heat transport in the polar regions) and a centrifugal term(arising out of the differential rotation). To make these terms comparable,the poles of the Sun should be slightly hotter than the equator. We discuss the important role played by the meridional circulation in the flux transport dynamo model. The poloidal field generated by the Babcock-Leighton process at the surface is advected poleward, whereas the toroidal field produced at the bottom of the convection zone is advected equatorward. The fluctuations in the meridional circulation(with coherence time of about 30-40 yr) help in explaining many aspects of the irregularities in the solar cycle. Finally, we discuss how the Lorentz force of the dynamo-generated magnetic field can cause periodic variations in the large-scale flows with the solar cycle.

关键词： astrophysical plasma solar physics Sun:solar magnetism Sun:helioseismology fluid flow:rotational

Spatio-temporal evaluation of Zr plasma parameters in a single-beam-splitting double-pulse laser-induced plasma

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Plasma Science and Technology 2021年第2期23卷 47-56页

作者： arnab SARKAR Manjeet SINGH Fuel Chemistry Division Bhabha Atomic Research CentreMumbai 400085India Homi Bhabha National Institute AnushaktinagarMumbai 400094India

The plasma shielding effect is one of the major weaknesses of laser-induced breakdown spectroscopy(LIBS)as it causes non-linearity in signal *** LIBS is typically carried out in constant laser energy,this non-linearity causes a reduction in *** this work,we systematically examine laser-induced plasma,formed by two different excitation source modes,*** pulse(SP)-excitation and single-beam-splitting double-pulse(SBS-DP)-excitation over Zr-2.5%Nb *** two most important plasma parameters influencing the emission line intensity,plasma temperature(Te)and electron density(Ne)were studied and compared for both modes of laser *** of the results conclusively demonstrates that due to the splitting of the laser energy in the SBS-DP mode,the plasma shielding effect is significantly *** reduced plasma shielding translates to an increased laser–sample coupling under SBS-DP *** imaging of the total intensity of the laser-induced plasma in both excitation modes was also *** study shows how the plasma shielding effect can be reduced to improve the analytical quality of the LIBS methodology.

关键词： LIBS single-beam-splitting double pulse spatial-temporal evolution plasma temperature electron density

Realizing unipolar and bipolar intrinsic skyrmions in MXenes from high-fidelity first-principles calculations

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npj Computational Materials 2023年第1期9卷 553-564页

作者： arnab Kabiraj Santanu Mahapatra Nano-Scale Device Research Laboratory Department of Electronic Systems EngineeringIndian Institute of Science(IISc)BangaloreBengaluru 560012India

Magnetic skyrmions,which are topologically protected tiny spin textures,have emerged as information carriers in energy-efficient logic and memory *** are commonly realized by inducing large Dzyaloshinskii–Moriya interaction(DMI)in the interface of heavy metal *** the advent of two-dimensional magnetism,it is being envisioned to host intrinsic skyrmions in a monolayer,which will be free from any interfacial defect and stacking *** using high-fidelity exchange-correlation functional-based first-principles calculations,we investigate such a possibility in methodically designed non-centrosymmetric MXene *** a search space of about 3000 materials,our customized high-throughput computational pipeline systematically harnesses out-of-the-plane and in-plane magnetism along with strong DMI to realize typical‘unipolar’skyrmions in 78 materials and exotic‘bipolar’skyrmions in 13 *** and atomistic Monte Carlo simulations further reveal that skyrmions in some of these materials may be stable at room temperature without any external magnetic *** study may pave the way for the practical realization of skyrmions-based information technology.

关键词： field intrinsic principles

Time-resolved evaluation of uranium plasma in different atmospheres by laser-induced breakdown spectroscopy

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Plasma Science and Technology 2018年第12期20卷 65-74页

作者： Manjeet SINGH arnab SARKAR Fuel Chemistry Division Bhabha Atomic Research CentreMumbai 400 085India Homi Bhabha National Institute AnushaktinagarMumbai 400 094India

This work reports spectroscopic studies of uranium containing plasma generated in air and argon environments. The 532 nm Q-switched Nd：YAG laser generates the optical breakdown plasma, which was recorded by a spectrometer and an intensified charge coupled device having a resolution of 25 pm. Neutral and ionized uranium lines in the wavelength range of 385.8-391.9 nm indicate significant width and shift variations during the first few microseconds. Electron temperature and density of the plasma are determined using the Boltzmann plot and the Saha-Boltzmann equation at various time delay. The study reveals the power law decay pattern of electron temperature and density, which changes to exponential decay pattern if large gate- width is used to acquire the signal, due to an averaging effect.

关键词： uranium laser induced plasma plasma parameter temporal evaluation electron temperature electron density LIBS

Laser-induced plasma electron number density:Stark broadening method versus the Saha-Boltzmann equation

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Plasma Science and Technology 2017年第2期19卷 43-51页

作者： arnab SARKAR Manjeet SINGH Fuel Chemistry Division Bhabha Atomic Research CentreMumbai 400 085India

We report spectroscopic studies on plasma electron number density of laser-induced plasma produced by ns-Nd：YAG laser light pulses on an aluminum sample in air at atmospheric pressure. The effect of different laser energy and the effect of different laser wavelengths were compared. The experimentally observed line profiles of neutral aluminum have been used to extract the excitation temperature using the Boltzmann plot method, whereas the electron number density has been determined from the Stark broadened as well as using the Saha-Boltzmann equation （SBE）. Each approach was also carried out by using the AI emission line and Mg emission lines. It was observed that the,SBE method generated a little higher electron number density value than the Stark broadening, method, but within the experimental uncertainty range. Comparisons of Ne determined by the two methods show the presence of a linear relation which is independent of laser energy or laser wavelength. These results show the applicability of the SBE method for Are determination, especially when the system does not have any pure emission lines whose electron impact factor is known, Also use of Mg lines gives superior results than Al lines.

关键词： plasma parameter laser induced plasma plasma electron density Saha-Boltzmannmethod Stark broadening method

High-throughput design of functional-engineered MXene transistors with low-resistive contacts

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npj Computational Materials 2022年第1期8卷 1917-1929页

作者： Sirsha Guha arnab Kabiraj Santanu Mahapatra Nano-Scale Device Research Laboratory Department of Electronic Systems EngineeringIndian Institute of Science(IISc)BangaloreBangalore560012India

Two-dimensional material-based transistors are being extensively investigated for CMOS(complementary metal oxide semiconductor)technology extension;nevertheless,downscaling appears to be challenging owing to high metal-semiconductor contact ***,we propose a functional group-engineered monolayer transistor architecture that takes advantage of MXenes’natural material chemistry to offer low-resistive *** design an automated,high-throughput computational pipeline that first performs hybrid density functional theory-based calculations to find 16 sets of complementary transistor configurations by screening more than 23,000 materials from an MXene database and then conducts self-consistent quantum transport calculations to simulate their current-voltage characteristics for channel lengths ranging from 10 nm to 3 *** of these devices has been found to meet the requirements of the international roadmap for devices and systems(IRDS)for several benchmark metrics(on current,power dissipation,delay,and subthreshold swing).The proposed balanced-mode,functional-engineered MXene transistors may lead to a realistic solution for the sub-decananometer technology scaling by enabling doping-free intrinsically low contact resistance.

关键词： functional complementary doping

A Hybrid Offline-Online Approach to Adaptive Downlink Resource Allocation Over LTE

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IEEE/CAA Journal of Automatica Sinica 2019年第3期6卷 766-777页

作者： Satish Kumar Rajesh Devaraj arnab Sarkar IEEE the Department of Computer Science and Engineering IIT Guwahati

Radio resource management mechanisms in current and future wireless networks is expected to face an enormous challenge due to the ever increasing demand for bandwidth and latency sensitive applications on mobile devices. This is because an optimal resource allocation scheme which attempts to multiplex the available bandwidth in order to maximize Quality of service(QoS), will pose an exponential computational burden at eNodeB. In order to minimize such computational overhead, this work proposes a hybrid offline-online resource allocation strategy which effectively allocates all the available resources among flows such that their QoS requirements are satisfied. The flows are firstly classified into priority buckets based on real-time criticality factors. During the offline phase, the scheduler attempts to maintain the system load within a pre-specified safe threshold value by selecting an appropriate number of buckets. This offline selection procedure makes use of supervisory control theory of discrete event systems to synthesize an offline scheduler. Next, we have devised an online resource allocation strategy which runs on top of the offline policy and attempts to minimize the impact of the inherent variability in wireless networks. Simulation results show that the proposed scheduling framework is able to provide satisfactory QoS to all end users in most practical scenarios.

关键词： Discrete event systems (DES) hybrid scheduling long term evolution (LTE) quality of service (QoS) radio resource management supervisory control