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Ashish Kumar

Publications and source records attributed to Ashish Kumar.

85 records · Page 5Linked to original sources
arXiv2013

Cognitive Radios: A Survey of Methods for Channel State Prediction

This paper discusses the need for Cognitive Radio ability in view of the physical scarcity of wireless spectrum for communication. A background of the Cognitive Radio technology is presented and the aspect of 'channel state prediction' is focused upon. Hidden Markov Models (HMM) have been traditionally used to model the wireless channel behavior but it suffers from certain limitations. We discuss few techniques of channel state prediction using machine-learning methods and will extend the Conditional Random Field (CRF) procedure to this field.

cs.NI↗
arXiv2013

Some Efficient Solutions to Yao's Millionaire Problem

We present three simple and efficient protocol constructions to solve Yao's Millionaire Problem when the parties involved are non-colluding and semi-honest. The first construction uses a partially homomorphic Encryption Scheme and is a 4-round scheme using 2 encryptions, 2 homomorphic circuit evaluations (subtraction and XOR) and a single decryption. The second construction uses an untrusted third party and achieves a communication overhead linear in input bit-size with the help of an order preserving function.Moreover, the second construction does not require an apriori input bound and can work on inputs of different bit-sizes. The third construction does not use a third party and, even though, it has a quadratic communication overhead, it is a fairly simple construction.

cs.CR↗
arXiv2013

Prospects for a Heavy Vector-Like Charge 2/3 Quark T search at the LHC with \sqrt{s}=14 TeV and 33 TeV. "A Snowmass 2013 Whitepaper"

We present the prospects for the discovery or exclusion of heavy vector-like charge 2/3 quarks, T, in proton-proton collisions at two center-of-mass energies, 14 and 33 TeV at the LHC. In this note, the pair production of T quark and its antiparticle, with decays to W boson and a b quark (Wb), a top quark and the Higgs boson (tH), and a top quark and Z boson (tZ) are investigated. Higgs boson decays to $b\bar b$ and $W^+W^-$ final states are selected for this study.

hep-ex↗
arXiv2013

System and Methods for Converting Speech to SQL

This paper concerns with the conversion of a Spoken English Language Query into SQL for retrieving data from RDBMS. A User submits a query as speech signal through the user interface and gets the result of the query in the text format. We have developed the acoustic and language models using which a speech utterance can be converted into English text query and thus natural language processing techniques can be applied on this English text query to generate an equivalent SQL query. For conversion of speech into English text HTK and Julius tools have been used and for conversion of English text query into SQL query we have implemented a System which uses rule based translation to translate English Language Query into SQL Query. The translation uses lexical analyzer, parser and syntax directed translation techniques like in compilers. JFLex and BYACC tools have been used to build lexical analyzer and parser respectively. System is domain independent i.e. system can run on different database as it generates lex files from the underlying database.

cs.CL↗
arXiv2013

Ion beam generated surface ripples: new insight in the underlying mechanism

A new hydrodynamic mechanism is proposed for the ion beam induced surface patterning on solid surfaces. Unlike the standard mechanisms based on the ion beam impact generated erosion and mass redistribution at the free surface (proposed by Bradley-Harper (BH) and its extended theories), the new mechanism proposes that the ion beam induced saltation and creep processes, coupled with incompressible solid flow in amorphous layer, leads to the formation of ripple patterns at the amorphous/crystalline (a/c) interface and hence at the free surface. Ion beam stimulated solid flow inside the amorphous layer controls the wavelength, where as the amount of material transported and re-deposited at a/c interface control the amplitude of ripples. The new approach is verified by designed experiments and supported by the discrete simulation method.

cond-mat.mtrl-sci↗
arXiv2011

A Search for the Higgs Boson in H->ZZ->2leptons 2jets Mode

A search for the Standard Model Higgs boson decaying to two Z bosons with subsequent decay to a final state with two leptons and two quark-jets, H->ZZ->2l 2jets, where \ell = e, μ, is discussed. It is based on an integrated luminosity of 1 fb-1 of proton-proton collision data at center of mass energy sqrt(s) = 7 TeV collected by the CMS experiment at the LHC. The data are compared to the expected Standard Model backgrounds. No evidence for the Higgs boson is found and upper limits are placed on its production cross section over the range of masses between 200 GeV and 600 GeV.

hep-ex↗
arXiv2011

Measurements of W/Z Production in Association with Jets at D0

Understanding the associated production of jets and vector bosons is of paramount importance for the top quark physics, for the Higgs boson and for many new physics searches. In this contribution, recent measurements of W/Z+jets and Z+b-jets processes by the D0 experiment are presented. The measurements are compared to theoretical predictions from next-to-leading order (NLO) perturbative QCD calculations where available, and to several Monte Carlo model predictions.

hep-ex↗
arXiv2011

Spin dephasing in III-V nanowires

We use semiclassical Monte Carlo approach to investigate spin polarized transport in InP and InSb nanowires. Spin dephasing in III-V channels is caused due to D'yakonov- Perel (DP) relaxation and due to Elliott-Yafet (EY) relaxation. The DP relaxation occurs because of bulk inversion asymmetry (Dresselhaus spin-orbit interaction) and structural inversion asymmetry (Rashba spin-orbit interaction). The injection polarization direction studied is that along the length of the channel. The dephasing rate is found to be very strong for InSb as compared to InP which has larger spin dephasing lengths. The ensemble averaged spin components vary differently for both InP and InSb nanowires. The steady state spin distribution also shows a difference between the two III-V nanowires.

cond-mat.mes-hall↗
arXiv2011

Spin dephasing in Silicon Germanium nanowires

We study spin polarized transport in silicon germanium nanowires using a semiclassical monte carlo approach. Spin depolarization in the channel is caused due to D'yakonov-Perel (DP) relaxation associated with Rashba spin orbit coupling and due to Elliott- Yafet (EY) relaxation. We investigate the dependence of spin dephasing on germanium mole fraction in silicon germanium nanowires. The spin dephasing lengths decrease with an increase in the germanium mole fraction. We also find that the temperature has a strong influence on the dephasing rate and spin relaxation lengths increase with decrease in temperature. The ensemble averaged spin components and the steady state distribution of spin components vary with initial polarization.

cond-mat.mes-hall↗
arXiv2011

Spin Relaxation in Germanium Nanowires

We use semiclassical Monte Carlo approach along with spin density matrix calculations to model spin polarized electron transport. The model is applied to germanium nanowires and germanium two dimensional channels to study and compare spin relaxation between them. Spin dephasing in germanium occurs because of Rashba Spin Orbit Interaction (structural inversion asymmetry) which gives rise to D'yakonov-Perel(DP) relaxation. In germanium spin flip scattering due to Elliot-Yafet(EY) mechanism also leads to spin relaxation. The spin relaxation tests for both 1-D and 2-D channels are carried out at different values of temperature and driving electric field and the variation in spin relaxation length is recorded. Spin relaxation length in a nanowire is found to be much higher than that in a 2-D channel due to suppression of DP relaxation in a nanowire. At lower temperatures the spin relaxation length increases. This suggests that spin relaxation in germanium occurs slowly in a 1-D channel (nanowires) and at lower temperatures. The electric field dependence of spin relaxation length was found to be very weak.

cond-mat.mes-hall↗
arXiv2011

Spin Relaxation in Silicon Nanowires

We simulate spin polarized transport of electrons along a silicon nanowire and along a silicon two dimensional channel. Spin density matrix calculations are used along with the semi-classical Monte Carlo approach to model spin evolution along the channel. Spin dephasing in silicon is caused due to Rashba Spin Orbit Interaction (structural inversion asymmetry) which gives rise to D'yakonov-Perel' relaxation. Spin relaxation length in a nanowire is found to be an order of magnitude higher than that in a 2-D channel. The effect of driving electric field on spin relaxation is also investigated. These results obtained are essential for design of spintronics based devices.

cond-mat.mes-hall↗
arXiv2009

Prospects for the first Top pair cross section measurement in the semileptonic and dilepton channels at CMS

Although the top quark has been discovered in 1995 and studied extensively by the Tevatron experiments, the top quark will remain special for years to come due to unique opportunities it offers. Because of the large top-antitop production cross section and high luminosity, the LHC would be a Top factory, producing a large sample of top quarks even at the initial low luminosities. This will enable a rich program of top quark physics to be explored, both within the Standard Model and using top quarks as probes of physics beyond the Standard Model. Prospects for the observation of top pair production in the proton-proton collisions at the center of mass energy $\sqrt{s}$=10 TeV in the dilepton and lepton+jets final state are discussed. The emphasis is put on analysis strategies for the early phase of CMS operation with data corresponding to integrated luminosities of 10-20 pb$^{-1}$ considering a realistic detector performance.

hep-ex↗