1,620 research outputs found
Signatures of two-step impurity mediated vortex lattice melting in Bose-Einstein Condensates
We simulate a rotating 2D BEC to study the melting of a vortex lattice in
presence of random impurities. Impurities are introduced either through a
protocol in which vortex lattice is produced in an impurity potential or first
creating the vortex lattice in the absence of random pinning and then cranking
up the (co-rotating) impurity potential. We find that for a fixed strength,
pinning of vortices at randomly distributed impurities leads to the new states
of vortex lattice. It is unearthed that the vortex lattice follow a two-step
melting via loss of positional and orientational order. Also, the comparisons
between the states obtained in two protocols show that the vortex lattice
states are metastable states when impurities are introduced after the formation
of an ordered vortex lattice. We also show the existence of metastable states
which depend on the history of how the vortex lattice is created.Comment: Accepted in Euro. Phys. Let
A phenomenological model for magnetoresistance in granular polycrystalline colossal magnetoresistive materials: the role of spin polarised tunnelling at the grain boundaries
It has been observed that in bulk and polycrystalline thin films of collossal
magnetoresistive (CMR) materials the magnetoresistance follows a different
behaviour compared to single crystals or single crystalline films below the
ferromagnetic transition temperature Tc. In this paper we develop a
phenomenological model to explain the magnetic field dependence of resistance
in granular CMR materials taking into account the spin polarised tunnelling at
the grain boundaries. The model has been fitted to two systems, namely,
La0.55Ho0.15Sr0.3MnO3 and La1.8Y0.5Ca0.7Mn2O7. From the fitted result we have
separated out, in La0.55Ho0.15Sr0.3MnO3, the intrinsic contribution from the
intergranular contribution to the magnetoresistance coming from spin polarised
tunnelling at the grain boundaries. It is observed that the temperature
dependence of the intrinsic contribution to the magnetoresistance in
La0.55Ho0.15Sr0.3MnO3 follows the prediction of double exchange model for all
values of field.Comment: 14 pages + 5 figures, postscript (to appear in Journal of Applied
Physics
Singularity: Raychaudhuri Equation once again
I first recount Raychaudhuri's deep involvement with the singularity problem
in general relativity. I then argue that precisely the same situation has
arisen today in loop quantum cosmology as obtained when Raychaudhuri discovered
his celebrated equation. We thus need a new analogue of the Raychaudhuri
equation in quantum gravity.Comment: 11 pages, Contribution to Special issue of Pramana on Raychaudhuri
Equation at Cross-roads, edited by Naresh Dadhich, Pankaj Joshi and Probir
Ro
Boosted Top Quark Signals for Heavy Vector Boson Excitations in a Universal Extra Dimension Model
In view of the fact that the Kaluza-Klein (KK) modes in a model with
a Universal Extra Dimension (UED), could mimic supersymmetry signatures at the
LHC, it is necessary to look for the KK modes, which have no analogues
in supersymmetry. We discuss the possibility of searching for heavy
vector boson resonances -- especially the -- through their decays to a
highly-boosted top quark-antiquark pair using recently-developed top-jet
tagging techniques in the hadronic channel. It is shown that signals
from the gluon resonance are as efficient a discovery mode at the LHC
as dilepton channels from the and resonances.Comment: 22 pages, 8 embedded figure
Peak effect in laser ablated DyBa2Cu3O7-d films at microwave frequencies at subcritical currents
In this paper we report the observation of a peak in the microwave surface
resistance (at frequencies ~10GHz) of laser ablated DyBa2Cu3O7-d films in
magnetic field ranging from 2 to 9kOe (||c) close to the superconducting
transition temperature (Tc(H)). The exact nature of peak is sample dependent
but it follows a general behaviour. The peak shifts to lower temperature when
the magnetic field is increased. It has strong frequency dependence and the
peak is pronounced at frequencies close to the depinning frequency of the flux
line lattice. From the observed temperature and field dependence we argue that
this peak is associated with the order disorder transition of the flux line
lattice close to Tc(H).Comment: 8 pages, 2 pages (accepted for publication in JAP, Intermag symposium
proceeding
Using Jet Substructure at the LHC to Search for the Light Higgs Bosons of the CP-Violating MSSM
The CP-violating version of the Minimal Supersymmetric Standard Model (MSSM)
is an example of a model where experimental data do not preclude the presence
of light Higgs bosons in the range around 10 -- 110 GeV. Such light Higgs
bosons, decaying almost wholly to b-bbar pairs, may be copiously produced at
the LHC, but would remain inaccessible to conventional Higgs searches because
of intractable QCD backgrounds. We demonstrate that a significant number of
these light Higgs bosons would be boosted strongly enough for the pair of
daughter -jet pairs to appear as a single `fat' jet with substructure.
Tagging such jets could extend the discovery potential at the LHC into the
hitherto-inaccessible region for light Higgs bosons.Comment: LaTeX, 33 pages, 5 eps figures and 5 tables embedded. minor changes,
to appear in Physical Review
A Minimal Model of Signaling Network Elucidates Cell-to-Cell Stochastic Variability in Apoptosis
Signaling networks are designed to sense an environmental stimulus and adapt
to it. We propose and study a minimal model of signaling network that can sense
and respond to external stimuli of varying strength in an adaptive manner. The
structure of this minimal network is derived based on some simple assumptions
on its differential response to external stimuli. We employ stochastic
differential equations and probability distributions obtained from stochastic
simulations to characterize differential signaling response in our minimal
network model. We show that the proposed minimal signaling network displays two
distinct types of response as the strength of the stimulus is decreased. The
signaling network has a deterministic part that undergoes rapid activation by a
strong stimulus in which case cell-to-cell fluctuations can be ignored. As the
strength of the stimulus decreases, the stochastic part of the network begins
dominating the signaling response where slow activation is observed with
characteristic large cell-to-cell stochastic variability. Interestingly, this
proposed stochastic signaling network can capture some of the essential
signaling behaviors of a complex apoptotic cell death signaling network that
has been studied through experiments and large-scale computer simulations. Thus
we claim that the proposed signaling network is an appropriate minimal model of
apoptosis signaling. Elucidating the fundamental design principles of complex
cellular signaling pathways such as apoptosis signaling remains a challenging
task. We demonstrate how our proposed minimal model can help elucidate the
effect of a specific apoptotic inhibitor Bcl-2 on apoptotic signaling in a
cell-type independent manner. We also discuss the implications of our study in
elucidating the adaptive strategy of cell death signaling pathways.Comment: 9 pages, 6 figure
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