1,158 research outputs found
Phase transition of a Bose gas in a harmonic potential
We consider a dilute Bose gas confined by a harmonic potential. We define an
appropriate thermodynamic limit and analyze the properties of the phases and
phase transition in this limit. Critical properties in the presence of the
potential are found to be different from, though simply related, to those in
the usual translationally invariant case. We argue that the properties of
magnetically trapped rubidium\cite{Wieman} and sodium\cite{ketterle} gases (in
which Bose-Einstein condensation has been recently observed) are well
approximated by our thermodynamic limit except in a narrow window of
temperature around the critical temperature. We also consider the effect of the
confining potential on the non-equilibrium dynamics following a rapid quench to
the ordered side and give a scaling description of the late time universal
dynamics.Comment: 10 page
Superfluid Insulator Transitions of Hard-Core Bosons on the Checkerboard Lattice
We study hard-core bosons on the checkerboard lattice with nearest neighbour
unfrustrated hopping and `tetrahedral' plaquette charging energy .
Analytical arguments and Quantum Monte Carlo simulations lead us to the
conclusion that the system undergoes a zero temperature () quantum phase
transition from a superfluid phase at small to a large Mott
insulator phase with = 1/4 for a range of values of the chemical
potential . Further, the quarter-filled insulator breaks lattice
translation symmetry in a characteristic four-fold ordering pattern, and
occupies a lobe of finite extent in the - phase diagram. A Quantum
Monte-Carlo study slightly away from the tip of the lobe provides evidence for
a direct weakly first-order superfluid-insulator transition away from the tip
of the lobe. While analytical arguments leads us to conclude that the
transition {\em at} the tip of the lobe belongs to a different landau-forbidden
second-order universality class, an extrapolation of our numerical results
suggests that the size of the first-order jump does not go to zero even at the
tip of the lobe.Comment: published versio
Persistent supersolid phase of hard-core bosons on the triangular lattice
We study hard-core bosons with unfrustrated hopping () and nearest
neighbour repulsion () on the triangular lattice. At half-filling, the
system undergoes a zero temperature () quantum phase transition from a
superfluid phase at small to a supersolid at in units of
. This supersolid phase breaks the lattice translation symmetry in a
characteristic pattern, and is remarkably
stable--indeed, a smooth extrapolation of our results indicates that the
supersolid phase persists for arbitrarily large .Comment: 4 pages, 5 figures, two column forma
Fabrication and Characterization of High Surface Area Gold Electrodes
High surface area gold electrodes are very good substrates for biosensors, catalysis and drug delivery. Their performance is characterized by good sensitivity, low detection limit and high signal. As a result, extensive research is being carried out in this field using different approaches of fabrication to generate high surface area porous electrodes of different morphology, pore size and structure. The morphology of the electrodes can be changed based on whether the approach involves a template or not, types of metal deposition, method and time of dealloying etc. The deposition of metal can be carried out using various approaches such as electroless deposition, electrochemical deposition, combination of electroless and electrochemical deposition, pulsed laser deposition, laser deposition etc. These electrodes can then be used in electrochemical measurements and their performance compared with an unmodified flat gold electrode.
We used a template based approach, combined with electrochemical deposition, to fabricate macroporous, macro-nanoporous and nanoporous gold electrodes. To generate nanopores, in case of macro-nanoporous and nanoporous gold electrodes, we used gold-silver alloy electrochemical deposition method, followed by chemical dealloying. The morphology of electrodes was later observed under HITACHI Scanning Electron Microscope (SEM) and their elemental composition studied using HITACHI Energy Dispersion Spectroscopy (EDS). The electrodes were used in electrochemical measurements and their voltammetric data was compared. These measurements involved the determination of surface area, faradaic current using redox molecules with fast and slow electron transfer and charging current in KCl. Surface adsorption of dopamine was studied and detection of dopamine in the presence of ascorbic acid was carried out
Permutation-Symmetric Multicritical Points in Random Antiferromagnetic Spin Chains
The low-energy properties of a system at a critical point may have additional
symmetries not present in the microscopic Hamiltonian. This letter presents the
theory of a class of multicritical points that provide an interesting example
of this in the phase diagrams of random antiferromagnetic spin chains. One case
provides an analytic theory of the quantum critical point in the random
spin-3/2 chain, studied in recent work by Refael, Kehrein and Fisher
(cond-mat/0111295).Comment: Revtex, 4 pages (2 column format), 2 eps figure
Long term Ultra-Violet Variability of Seyfert galaxies
Flux variability is one of the defining characteristics of Seyfert galaxies,
a class of active galactic nuclei (AGN). Though these variations are observed
over a wide range of wavelengths, results on their flux variability
characteristics in the ultra-violet (UV) band are very limited. We present here
the long term UV flux variability characteristics of a sample of fourteen
Seyfert galaxies using data from the International Ultraviolet Explorer
acquired between 1978 and 1995. We found that all the sources showed flux
variations with no statistically significant difference in the amplitude of UV
flux variation between shorter and longer wavelengths. Also, the flux
variations between different near-UV (NUV, 1850 - 3300 A) and far-UV (FUV, 1150
- 2000 A) passbands in the rest frames of the objects are correlated with no
time lag. The data show indications of (i) a mild negative correlation of UV
variability with bolometric luminosity and (ii) weak positive correlation
between UV variability and black hole mass. At FUV, about 50% of the sources
show a strong correlation between spectral indices and flux variations with a
hardening when brightening behaviour, while for the remaining sources the
correlation is moderate. In NUV, the sources do show a harder when brighter
trend, however, the correlation is either weak or moderate.Comment: Accepted by Journal of Astrophysics and Astronom
Comment on "Spin Transport properties of the quantum one-dimensional non-linear sigma model"
In a recent preprint (cond-mat/9905415), Fujimoto has used the Bethe ansatz
to compute the finite temperature, zero frequency Drude weight of spin
transport in the quantum O(3) non-linear sigma model in a magnetic field . We show here that, contrary to his claims, the results are in accord
with earlier semiclassical results (Sachdev and Damle, cond-mat/9610115). We
also comment on his 1/N expansion, and show that it does not properly describe
the long-time correlations.Comment: 4 page
Comparison of salivary IgA levels in caries free and caries active children
Purpose: The aim of the study was to compare the salivary IgA levels and dental caries status in caries active and caries free children.Methods: Thirty children in the age group of 8-10 years were selected and divided into two groups, Group I caries free (dfs=0) and Group II caries active (dfs>10). Whole salivary IgA level was estimated using radial immunodiffusion method.Results: Whole salivary IgA levels were significantly higher in caries free children as compared to caries active children.Conclusions: Naturally occurring salivary IgA antibodies can play an important role in immunological control of dental caries.Key Words: Salivary IgA, dental caries, mutans streptococc
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