63 research outputs found
Multibranch Bogoliubov-Bloch spectrum of a cigar shaped Bose condensate in an optical lattice
We study properties of excited states of an array of weakly coupled
quasi-two-dimensional Bose condensates by using the hydrodynamic theory. The
spectrum of the axial excited states strongly depends on the coupling among the
various discrete radial modes in a given symmetry. By including mode-coupling
within a given symmetry, the complete excitation spectrum of axial
quasiparticles with various discrete radial nodes are presented. A single
parameter which determines the strength of the mode coupling is identified. The
excitation spectrum in the zero angular momentum sector can be observed by
using the Bragg scattering experiments.Comment: to apper in Phys. Rev.
Collective modes of Fermi superfluid containing vortices along the BEC-BCS crossover
Using the coarse-grain averaged hydrodynamic approach, we calculate all low
energy transverse excitation spectrum of a rotating Fermi superfluid containing
vortex lattices for all regimes along the BEC-BCS crossover. In the fast
rotating regime, the molecular BEC enters into the lowest Landau level, but the
superfluid in the unitarity and the BCS regimes occupies many low-lying Landau
levels. The difference between the breathing mode frequencies at the BEC and
unitarity limit shrinks to zero as the rotation speed approaches the radial
trap frequency, in contrast to the finite difference in the non-rotating
systems.Comment: To appear in Physical Review
Design of Low Offset and High Speed CMOS Comparator for Analog to Digital Converter
In today’s world everything is digitized but nature is analog, so it is necessary to have such a device which converts analog signal into digital and for this analog to digital converter is required. Now a day’s ADC’s require lesser power, better slew rate, high speed and less offset. Performance limiting component for ADC’s are amplifiers and comparators in which comparator is the most important.This paper presents the design of low offset low power dissipation and high speed comparator. The proposed comparator consists of a preamplifier stage, decision stage and self biased output buffer stage. The proposed design uses a low power current mirror circuitry for providing a highly biased current. The circuit is designed using 90nm CMOS process for a supply voltage of 1V and reference voltage of 0.5V and power consumption is approximately 300?W. Keywords: CMOS Comparator, Current Mirror, Pre Amplifier, Output Buffe
Design of Low Voltage Improved performance Current Mirror
This paper proposes a low voltage current mirror circuit with low input impedance and high output impedance. These improvements are obtained by adding an amplifier which provides biasing voltage to the transistors. Its operation and results are compared with conventional and cascode current mirror circuits. The circuits are designed using Tanner EDA Tool in 90nm CMOS technology with 0.8V supply voltage. Simulation results shows that the minimum output voltage is reduced to 0.1 V, also input resistance is reduced to 0.179k? and consumes only 46µW power. Keywords: Current mirror, Input resistance Output resistance, Input compliance voltage, Output compliance voltage
Bragg spectroscopy of a cigar shaped Bose condensate in optical lattices
We study properties of excited states of an array of weakly coupled
quasi-two-dimensional Bose condensates by using the hydrodynamic theory. We
calculate multibranch Bogoliubov-Bloch spectrums and its corresponding
eigenfunctions. The spectrum of the axial excited states and its eigenfunctions
strongly depends on the coupling among various discrete radial modes within a
given symmetry. This mode coupling is due to the presence of radial trapping
potential. The multibranch nature of the Bogoliubov-Bloch spectrum and its
dependence on the mode-coupling can be realized by analyzing dynamic structure
factor and momentum transferred to the system in Bragg spectroscopy
experiments. We also study dynamic structure factor and momentum transferred to
the condensate due to the Bragg spectroscopy experiment.Comment: 7 pages, 5 figures, to appear in Journal of Physics B: Atomic,
Molecular & Optical Physic
Magnetotransport properties of a magnetically modulated two-dimensional electron gas with the spin-orbit interaction
We study the electrical transport properties of a two-dimensional electron
gas with the Rashba spin-orbit interaction in presence of a constant
perpendicular magnetic field which is weakly modulated by , where and with
is the modulation period. We obtain the analytical expressions of the diffusive
conductivities for spin-up and spin-down electrons. The conductivities for
spin-up and spin-down electrons oscillate with different frequencies and
produce beating patterns in the amplitude of the Weiss and Shubnikov-de Haas
oscillations. We show that the Rashba strength can be determined by analyzing
the beating pattern in the Weiss oscillation. We find a simple equation which
determines the Rashba spin-orbit interaction strength if the number of Weiss
oscillations between any two successive nodes is known from the experiment. We
compare our results with the electrically modulated 2DEG with the Rashba
interaction. For completeness, we also study the beating pattern formation in
the collisional and the Hall conductivities.Comment: 11 pages, 5 figures, re-written with new result
Model Independent Foreground Power Spectrum Estimation using WMAP 5-year Data
In this paper, we propose & implement on WMAP 5-year data, a model
independent approach of foreground power spectrum estimation for multifrequency
observations of CMB experiments. Recently a model independent approach of CMB
power spectrum estimation was proposed by Saha et al. 2006. This methodology
demonstrates that CMB power spectrum can be reliably estimated solely from WMAP
data without assuming any template models for the foreground components. In the
current paper, we extend this work to estimate the galactic foreground power
spectrum using the WMAP 5 year maps following a self contained analysis. We
apply the model independent method in harmonic basis to estimate the foreground
power spectrum and frequency dependence of combined foregrounds. We also study
the behaviour of synchrotron spectral index variation over different regions of
the sky. We compare our results with those obtained from MEM foreground maps
which are formed in pixel space. We find that relative to our model independent
estimates MEM maps overestimates the foreground power close to galactic plane
and underestimates it at high latitudes.Comment: 12 pages, 4 figure
First results from RHIC-PHENIX
The PHENIX experiment consists of a large detector system located at the newly commissioned relativistic heavy ion collider (RHIC) at the Brookhaven National Laboratory. The primary goal of the PHENIX experiment is to look for signatures of the QCD prediction of a deconfined high-energy-density phase of nuclear matter quark gluon plasma. PHENIX started data taking for Au+Au collisions at √sNN = 130 GeV in June 2000. The signals from the beam-beam counter (BBC) and zero degree calorimeter (ZDC) are used to determine the centrality of the collision. A Glauber model reproduces the ZDC spectrum reasonably well to determine the participants in a collision. Charged particle multiplicity distribution from the first PHENIX paper is compared with the other RHIC experiment and the CERN, SPS results. Transverse momentum of photons are measured in the electro-magnetic calorimeter (EMCal) and preliminary results are presented. Particle identification is made by a time of flight (TOF) detector and the results show clear separation of the charged hadrons from each other
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