4,542 research outputs found
Quantum thermodynamics at critical points during melting and solidification processes
We systematically explore and show the existence of finite-temperature
continuous quantum phase transition (CTQPT) at a critical point, namely, during
solidification or melting such that the first-order thermal phase transition is
a special case within CTQPT. Infact, CTQPT is related to chemical reaction
where quantum fluctuation (due to wavefunction transformation) is caused by
thermal energy and it can occur maximally for temperatures much higher than
zero Kelvin. To extract the quantity related to CTQPT, we use the ionization
energy theory and the energy-level spacing renormalization group method to
derive the energy-level spacing entropy, renormalized Bose-Einstein
distribution and the time-dependent specific heat capacity. This work
unambiguously shows that the quantum phase transition applies for any finite
temperatures.Comment: To be published in Indian Journal of Physics (Kolkata
Lifetime Measurements in 120Xe
Lifetimes for the lowest three transitions in the nucleus Xe have
been measured using the Recoil Distance Technique. Our data indicate that the
lifetime for the transition is more than a factor of
two lower than the previously adopted value and is in keeping with more recent
measurements performed on this nucleus. The theoretical implications of this
discrepancy and the possible reason for the erroneous earlier results are
discussed. All measured lifetimes in Xe, as well as the systematics of
the lifetimes of the 2 states in Xe isotopes, are compared with
predictions of various models. The available data are best described by the
Fermion Dynamic Symmetry Model (FDSM).Comment: 9 pages, RevTeX, 3 figures with Postscript file available on request
at [email protected], [email protected]. Submitted to Phys.
Rev.
Observation of Superfluid Flow in a Bose-Einstein Condensed Gas
We have studied the hydrodynamic flow in a Bose-Einstein condensate stirred
by a macroscopic object, a blue detuned laser beam, using nondestructive {\em
in situ} phase contrast imaging. A critical velocity for the onset of a
pressure gradient has been observed, and shown to be density dependent. The
technique has been compared to a calorimetric method used previously to measure
the heating induced by the motion of the laser beam.Comment: 4 pages, 5 figure
Bonn Potential and Shell-Model Calculations for 206,205,204Pb
The structure of the nuclei 206,205,204Pb is studied interms of shell model
employing a realistic effective interaction derived from the Bonn A
nucleon-nucleon potential. The energy spectra, binding energies and
electromagnetic properties are calculated and compared with experiment. A very
good overall agreement is obtained. This evidences the reliability of our
realistic effective interaction and encourages use of modern realistic
potentials in shell-model calculations for heavy-mass nuclei.Comment: 4 pages, 4 figures, submitted to Physical Review
A Large Mass Hierarchy from a Small Extra Dimension
We propose a new higher-dimensional mechanism for solving the Hierarchy
Problem. The Weak scale is generated from a large scale of order the Planck
scale through an exponential hierarchy. However, this exponential arises not
from gauge interactions but from the background metric (which is a slice of
AdS_5 spacetime). This mechanism relies on the existence of only a single
additional dimension. We demonstrate a simple explicit example of this
mechanism with two three-branes, one of which contains the Standard Model
fields. The experimental consequences of this scenario are new and dramatic.
There are fundamental spin-2 excitations with mass of weak scale order, which
are coupled with weak scale as opposed to gravitational strength to the
standard model particles. The phenomenology of these models is quite distinct
from that of large extra dimension scenarios; none of the current constraints
on theories with very large extra dimensions apply.Comment: 9 pages, LaTe
Alpha-decay Rates of Yb and Gd in Solar Neutrino Detectors
The -decay rates for the nuclides Yb
and Gd have been estimated from transmission probabilities
in a systematic -nucleus potential and from an improved fit to
-decay rates in the rare-earth mass region. Whereas -decay of
Gd in natural gadolinium is a severe obstacle for the use of gadolinium
as a low-energy solar-neutrino detector, we show that
-decay does not contribute significantly to the background in a
ytterbium detector. An extremely long -decay lifetime of Yb
is obtained from calculation, which may be close to the sensitivity limit in a
low-background solar neutrino detector.Comment: 12 pages, 1 figure; An author name was correcte
The ORNATE India project: Building research capacity and capability to tackle the burden of diabetic retinopathy-related blindness in India
The ORNATE India project is an interdisciplinary, multifaceted United Kingdom (UK)–India collaborative study aimed to build research capacity and capability in India and the UK to tackle the burden of diabetes-related visual impairment. For 51 months (October 2017–December 2021), this project built collaboration between six institutions in the UK and seven in India, including the Government of Kerala. Diabetic retinopathy (DR) screening models were evaluated in the public system in Kerala. An epidemiological study of diabetes and its complications was conducted through 20 centers across India covering 10 states and one union territory. The statistical analysis is not yet complete. In the UK, risk models for diabetes and its complications and artificial intelligence-aided tools are being developed. These were complemented by joint studies on various aspects of diabetes between collaborators in the UK and India. This interdisciplinary team enabled increased capability in several workstreams, resulting in an increased number of publications, development of cost-effective risk models, algorithms for risk-based screening, and policy for state-wide implementation of sustainable DR screening and treatment programs in primary care in Kerala. The increase in research capacity included multiple disciplines from field workers, administrators, project managers, project leads, screeners, graders, optometrists, nurses, general practitioners, and research associates in various disciplines. Cross-fertilization of these disciplines enabled the development of several collaborations external to this project. This collaborative project has made a significant impact on research capacity development in both India and the UK
Vortex Nucleation in a Stirred Bose-Einstein Condensate
We studied the nucleation of vortices in a Bose-Einstein condensate stirred
by a laser beam. We observed the vortex cores using time-of-flight absorption
imaging. By varying the size of the stirrer, we observed either discrete
resonances or a broad response as a function of the frequency of the stirrer's
motion. Stirring beams small compared to the condensate size generated vortices
below the critical rotation frequency for the nucleation of surface modes,
suggesting a local mechanism of generation. In addition, we observed the
centrifugal distortion of the condensate due to the rotating vortex lattice and
found evidence for bent vortices
A stacking-fault based microscopic model for platelets in diamond
We propose a new microscopic model for the planar defects in
diamond commonly called platelets. This model is based on the formation of a
metastable stacking fault, which can occur because of the ability of carbon to
stabilize in different bonding configurations. In our model the core of the
planar defect is basically a double layer of three-fold coordinated
carbon atoms embedded in the common diamond structure. The properties of
the model were determined using {\it ab initio} total energy calculations. All
significant experimental signatures attributed to the platelets, namely, the
lattice displacement along the direction, the asymmetry between the
and the directions, the infrared absorption peak
, and broad luminescence lines that indicate the introduction of
levels in the band gap, are naturally accounted for in our model. The model is
also very appealing from the point of view of kinetics, since naturally
occurring shearing processes will lead to the formation of the metastable
fault.Comment: 5 pages, 4 figures. Submitted for publication on August 2nd, 200
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