arXiv subjects

S. Banerjee

Publications and source records attributed to S. Banerjee.

At least 91 records · Page 5Linked to original sources

arXiv2012

Scanning microscopies of superconductors at very low temperatures

We discuss basics of scanning tunneling microscopy and spectroscopy (STM/S) of the superconducting state with normal and superconducting tips. We present a new method to measure the local variations in the Andreev reflection amplitude between a superconducting tip and the sample. This method is termed Scanning Andreev Reflection Spectroscopy (SAS). We also briefly discuss vortex imaging with STM/S under an applied current through the sample, and show the vortex lattice as a function of the angle between the magnetic field and sample's surface.

cond-mat.supr-con↗

arXiv2011

Precise measurement of the top quark mass in the dilepton channel at D0

We measure the top quark mass (mt) in ppbar collisions at a center of mass energy of 1.96 TeV using dilepton ttbar->W+bW-bbar->l+nubl-nubarbbar events, where l denotes an electron, a muon, or a tau that decays leptonically. The data correspond to an integrated luminosity of 5.4 fb-1 collected with the D0 detector at the Fermilab Tevatron Collider. We obtain mt = 174.0 +- 1.8(stat) +- 2.4(syst) GeV, which is in agreement with the current world average mt = 173.3 +- 1.1 GeV. This is currently the most precise measurement of mt in the dilepton channel.

hep-ex↗

arXiv2011

Spatiotemporal evolution in a (2+1)-dimensional chemotaxis model

Simulations are performed to investigate the nonlinear dynamics of a (2+1)-dimensional chemotaxis model of Keller-Segel (KS) type with a logistic growth term. Because of its ability to display auto-aggregation, the KS model has been widely used to simulate self-organization in many biological systems. We show that the corresponding dynamics may lead to a steady-state, divergence in a finite time as well as the formation of spatiotemporal irregular patterns. The latter, in particular, appear to be chaotic in part of the range of bounded solutions, as demonstrated by the analysis of wavelet power spectra. Steady states are achieved with sufficiently large values of the chemotactic coefficient $(χ)$ and/or with growth rates $r$ below a critical value $r_c$. For $r > r_c$, the solutions of the differential equations of the model diverge in a finite time. We also report on the pattern formation regime for different values of $χ$, $r$ and the diffusion coefficient $D$.

physics.bio-ph↗

arXiv2011

Synchronization of spatiotemporal semiconductor lasers and its application in color image encryption

Optical chaos is a topic of current research characterized by high-dimensional nonlinearity which is attributed to the delay-induced dynamics, high bandwidth and easy modular implementation of optical feedback. In light of these facts, which adds enough confusion and diffusion properties for secure communications, we explore the synchronization phenomena in spatiotemporal semiconductor laser systems. The novel system is used in a two-phase colored image encryption process. The high-dimensional chaotic attractor generated by the system produces a completely randomized chaotic time series, which is ideal in the secure encoding of messages. The scheme thus illustrated is a two-phase encryption method, which provides sufficiently high confusion and diffusion properties of chaotic cryptosystem employed with unique data sets of processed chaotic sequences. In this novel method of cryptography, the chaotic phase masks are represented as images using the chaotic sequences as the elements of the image. The scheme drastically permutes the positions of the picture elements. The next additional layer of security further alters the statistical information of the original image to a great extent along the three-color planes. The intermediate results during encryption demonstrate the infeasibility for an unauthorized user to decipher the cipher image. Exhaustive statistical tests conducted validate that the scheme is robust against noise and resistant to common attacks due to the double shield of encryption and the infinite dimensionality of the relevant system of partial differential equations.

physics.optics↗

arXiv2011

Upper-hybrid wave driven Alfvenic turbulence in magnetized dusty plasmas

The nonlinear dynamics of coupled electrostatic upper-hybrid (UH) and Alfven waves (AWs) is revisited in a magnetized electron-ion plasma with charged dust impurities. A pair of nonlinear equations that describe the interaction of UH wave envelopes (including the relativistic electron mass increase) and the density as well as the compressional magnetic field perturbations associated with the AWs is solved numerically to show that many coherent solitary patterns can be excited and saturated due to modulational instability of unstable UH waves. The evolution of these solitary patterns is also shown to appear in the states of spatiotemporal coherence, temporal as well as spatiotemporal chaos due to collision and fusion among the patterns in stochastic motion. Furthermore, these spatiotemporal features are demonstrated by the analysis of wavelet power spectra. It is found that a redistribution of wave energy takes place to higher harmonic modes with small wavelengths which, in turn, results into the onset of Alfvenic turbulence in dusty magnetoplasmas. Such a scenario can occur in the vicinity of Saturn's magnetosphere as many electrostatic solitary structures have been observed there by the Cassini spacecraft.

physics.plasm-ph↗

arXiv2010

Cooperative ordering of superparamagnetic ZnO nanograins

In this paper we have tried to understand the precise nature of magnetism in ZnO nanoparticles. Cooling field dependence of magnetic hysteresis and coercive field was observed for high temperature annealed sample indicating cooperative magnetic correlation and ordering within the agglomerated nanograins. The increasing induced internal magnetic field along the direction of external field for the high temperature annealed sample has been fitted with the modified Weiss-Brillouin model indicating emergence of long range intergrain interaction among the superparamagnetic grains. We propose a simple idea that explains the reduction of magnetisation due to vortex state like flux closure situation.

cond-mat.mtrl-sci↗

arXiv2010

Search for pair production of the scalar top quark in the electron-muon final state

We report the result of a search for the pair production of the lightest supersymmetric partner of the top quark ($\tilde{t}_1$) in $p\bar{p}$ collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider corresponding to an integrated luminosity of 5.4 fb$^{-1}$. The scalar top quarks are assumed to decay into a $b$ quark, a charged lepton, and a scalar neutrino ($\tildeν$), and the search is performed in the electron plus muon final state. No significant excess of events above the standard model prediction is detected, and improved exclusion limits at the 95% C.L. are set in the the ($M_{\tilde{t}_1}$,$M_{\tildeν}$) mass plane.

hep-ex↗

arXiv2010

Determination of the width of the top quark

We extract the total width of the top quark, Gamma_t, from the partial decay width Gamma(t -> W b) measured using the t-channel cross section for single top quark production and from the branching fraction B(t -> W b) measured in ttbar events using up to 2.3 fb^-1 of integrated luminosity collected by the D0 Collaboration at the Tevatron ppbar Collider. The result is Gamma_t = 1.99 +0.69 -0.55 GeV, which translates to a top-quark lifetime of tau_t = (3.3 +1.3 -0.9) x 10^-25 s. Assuming a high mass fourth generation b' quark and unitarity of the four-generation quark-mixing matrix, we set the first upper limit on |Vtb'| < 0.63 at 95% C.L.

hep-ex↗

arXiv2010

Variations in magnetic properties of nanostructured nickel

The magnetic properties of carbon nanotube encapsulated nickel nanowires (C.E. nanowires of diameter ~ 10 nm), and its comparison to other forms of Ni are carried out in this work. The saturation magnetization (M_s) and coercivity (H_c) for C.E. nanowires are 1.0 emu/g and 230 Oe. The temperature dependence of coercivity follows T^0.77 dependence indicating a superparamagnetic behavior. The field-cooled and zero-field-cooled plots indicate that the blocking temperature (T_B) ~ 300 K. These altered magnetic properties of C.E. nanowires are mainly due to the nanoscale confinement effect from carbon nanotube encapsulation. The shape and magnetic environment enhance the total magnetic anisotropy of C.E. nanowires by a factor of four.

cond-mat.mes-hall↗

arXiv2010

Dirac Point Degenerate with Massive Bands at a Topological Quantum Critical Point

The quasi-linear bands in the topologically trivial skutterudite insulator CoSb$_3$ are studied under adiabatic, symmetry-conserving displacement of the Sb sublattice. In this cubic, time-reversal and inversion symmetric system, a transition from trivial insulator to topological point Fermi surface system occurs through a critical point in which massless (Dirac) bands are {\it degenerate} with massive bands. Spin-orbit coupling does not alter the character of the transition. The mineral skutterudite (CoSb$_3$) is very near the critical point in its natural state.

cond-mat.str-el↗

arXiv2010

How Gold nanoparticle acquires magnetism? - Formation of large orbital moment at the interface

In this paper, we have tried to find out the origin of magnetism in Gold nanoparticles (Au- NPs). We observe that upon incorporating Gold nanoparticles (Au-NPs) in Fe3O4 nanoparticle medium the net magnetisation increases compared to the pure Fe3O4 nanoparticle medium. This increase of magnetization can be attributed to the large orbital magnetic moment formation at the Au/magnetic particle interface indicating that magnetism observed in Au-NPs is an interfacial effect. This interfacial effect has been supported by the observation of sudden transition from positive saturated magnetisation to a negative diamagnetic contribution as a function of magnetic field on citrate coated gold Au-NPs.

cond-mat.mtrl-sci↗

arXiv2010

Using Grid Files for a Relational Database Management System

This paper describes our experience with using Grid files as the main storage organization for a relational database management system. We primarily focus on the following two aspects. (i) Strategies for implementing grid files efficiently. (ii) Methods for efficiency evaluating queries posed to a database organized using grid files.

cs.DB↗

arXiv2010

Spatiotemporal chaos and the dynamics of coupled Langmuir and ion-acoustic waves in plasmas

A simulation study is performed to investigate the dynamics of coupled Langmuir waves (LWs) and ion-acoustic waves (IAWs) in an unmagnetized plasma. The effects of dispersion due to charge separation and the density nonlinearity associated with the IAWs, are considered to modify the properties of Langmuir solitons, as well as to model the dynamics of relatively large amplitude wave envelopes. It is found that the Langmuir wave electric field, indeed, increases by the effect of ion-wave nonlinearity (IWN). Use of a low-dimensional model, based on three Fourier modes shows that a transition to temporal chaos is possible, when the length scale of the linearly excited modes is larger than that of the most unstable ones. The chaotic behaviors of the unstable modes are identified by the analysis of Lyapunov exponent spectra. The space-time evolution of the coupled LWs and IAWs shows that the IWN can cause the excitation of many unstable harmonic modes, and can lead to strong IAW emission. This occurs when the initial wave field is relatively large or the length scale of IAWs is larger than the soliton characteristic size. Numerical simulation also reveals that many solitary patterns can be excited and generated through the modulational instability (MI) of unstable harmonic modes. As time goes on, these solitons are seen to appear in the spatially partial coherence (SPC) state due to the free ion-acoustic radiation as well as in the state of spatiotemporal chaos (STC) due to collision and fusion in the stochastic motion. The latter results the redistribution of initial wave energy into a few modes with small length scales, which may lead to the onset of Langmuir turbulence in laboratory as well as space plasmas.

physics.plasm-ph↗

arXiv2010

Temporal dynamics in the one-dimensional quantum Zakharov equations for plasmas

The temporal dynamics of the quantum Zakharov equations (QZEs) in one spatial dimension, which describes the nonlinear interaction of quantum Langmuir waves (QLWs) and quantum ion-acoustic waves (QIAWs) is revisited by considering their solution as a superposition of three interacting wave modes in Fourier space. Previous results in the literature are modified and rectified. Periodic, chaotic as well as hyperchaotic behaviors of the Fourier-mode amplitudes are identified by the analysis of Lyapunov exponent spectra and the power spectrum. The periodic route to chaos is explained through an one-parameter bifurcation analysis. The system is shown to be destabilized via a supercritical Hopf-bifurcation. The adiabatic limits of the fully spatio-temporal and reduced systems are compared from the viewpoint of integrability properties.

physics.plasm-ph↗

arXiv2010

NaAlSi: a self-doped semimetallic superconductor with free electrons and covalent holes

The layered ternary sp conductor NaAlSi, possessing the iron-pnictide "111" crystal structure, superconducts at 7 K. Using density functional methods, we show that this compound is an intrinsic (self-doped) low-carrier-density semimetal with a number of unusual features. Covalent Al-Si valence bands provide the holes, and free-electron-like Al 3s bands, which propagate in the channel between the neighboring Si layers, dip just below the Fermi level to create the electron carriers. The Fermi level (and therefore the superconducting carriers) lies in a narrow and sharp peak within a pseudogap in the density of states. The small peak arises from valence bands which are nearly of pure Si, quasi-two-dimensional, flat, and coupled to Al conduction bands. Isostructural NaAlGe, which is not superconducting above 1.6 K, has almost exactly the same band structure except for one missing piece of small Fermi surface. Certain deformation potentials induced by Si and Na displacements along the c-axis are calculated and discussed. It seems likely that the mechanism of pairing is related to that of several other lightly doped two-dimensional nonmagnetic semiconductors (TiNCl, ZrNCl, HfNCl), which is not well understood but apparently not of phonon origin.

cond-mat.supr-con↗

arXiv2009

Inverse magnetocaloric effect in polycrystalline La$_{0.125}$Ca$_{0.875}$MnO$_{3}$

Recently the inverse magnetocaloric effect is observed for different compounds. However there is very rare for any manifestation of the effect to be seen in manganites. We have found inverse magnetocaloric effect in the case of polycrystalline La$_{0.125}$Ca$_{0.875}$MnO$_{3}$. Such phenomenon is attributed to the stabilization of antiferromagnetic state associated with inherent magnetic inhomogeneous phases for this compound.

cond-mat.mtrl-sci↗

arXiv2009

Enhanced magnetism, memory and aging in Gold-Iron oxide nanoparticle composites

In this report we present systematic magnetic studies of pure iron oxide nanoparticles and gold iron oxide nanocomposite with increasing Au particle size/content. For the magnetic studies of these samples we have measured: (1) zero field cooled (ZFC) and field cooled (FC) magnetization, (2) ac susceptibility, (3) magnetization vs field at various temperatures, (4) thermoremanant magnetization relaxation (TRM) and zero field cooled magnetization relaxation (ZFCM) at fixed temperature for various wait times tw for studying the aging effect, (5) magnetization memory effect and (6) exchange bias as a function of cooling field. The detailed magnetic measurement analysis indicates that the pure Fe3O4 nanoparticles sample behaves like a superparamagnet and on incorporation of gold (Au) nanoparticles the nanocomposite system slowly evolves from superparamagnetic to superspin glass state. The memory and aging effect enhances with the increase of the Au nanoparticle size/content. The most important observation in this study is the enhancement of magnetization with the incorporation of Au nanoparticles. The enhancement increases with the increase in the Au content in the nanocomposite. We have explained the cause of this enhancement of magnetization as due to large orbital magnetic moment formation at the Au/magnetic particle interface.

cond-mat.mtrl-sci↗

arXiv2009

Gyrosonics a Novel Stimulant for Autonomic Nervous System

Gyrosonics refers to novel audio binaural stimulus that produces rotational perceptions of sound movement in head at a particular predetermined frequency. Therapeutic effect observed with this is considered to be associated with modification of arousal of autonomic nervous system. The heart rate variability (HRV), non-invasive measure of autonomic nervous system, has been measured for group of 30 subjects for pre- and post- gyrosonic installation. The time- and frequency- domain analysis of HRV results show overall decrease in sympathetic response and increase in para- sympathetic response due to listening of gyro sonics.

physics.med-ph↗