1,512 research outputs found
Yet another surprise in the problem of classical diamagnetism
The well known Bohr-van Leeuwen Theorem states that the orbital diamagnetism
of classical charged particles is identically zero in equilibrium. However,
results based on real space-time approach using the classical Langevin equation
predicts non-zero diamagnetism for classical unbounded (finite or infinite)
systems. Here we show that the recently discovered Fluctuation Theorems,
namely, the Jarzynski Equality or the Crooks Fluctuation Theorem surprisingly
predict a free energy that depends on magnetic field as well as on the friction
coefficient, in outright contradiction to the canonical equilibrium results.
However, in the cases where the Langevin approach is consistent with the
equilibrium results, the Fluctuation Theorems lead to results in conformity
with equilibrium statistical mechanics. The latter is demonstrated analytically
through a simple example that has been discussed recently.Comment: 6 pages, 6 figure
Spectral properties of a short-range impurity in a quantum dot
The spectral properties of the quantum mechanical system consisting of a
quantum dot with a short-range attractive impurity inside the dot are
investigated in the zero-range limit. The Green function of the system is
obtained in an explicit form. In the case of a spherically symmetric quantum
dot, the dependence of the spectrum on the impurity position and the strength
of the impurity potential is analyzed in detail. It is proven that the
confinement potential of the dot can be recovered from the spectroscopy data.
The consequences of the hidden symmetry breaking by the impurity are
considered. The effect of the positional disorder is studied.Comment: 30 pages, 6 figures, Late
Classical Integrable 2-dim Models Inspired by SUSY Quantum Mechanics
A class of integrable 2-dim classical systems with integrals of motion of
fourth order in momenta is obtained from the quantum analogues with the help of
deformed SUSY algebra. With similar technique a new class of potentials
connected with Lax method is found which provides the integrability of
corresponding 2-dim hamiltonian systems. In addition, some integrable 2-dim
systems with potentials expressed in elliptic functions are explored.Comment: 19 pages, LaTeX, final version to be published in J.Phys.
A nilpotent symmetry of quantum gauge theories
For the Becchi-Rouet-Stora-Tyutin (BRST) invariant extended action for any
gauge theory, there exists another off-shell nilpotent symmetry. For linear
gauges, it can be elevated to a symmetry of the quantum theory and used in the
construction of the quantum effective action. Generalizations for nonlinear
gauges and actions with higher order ghost terms are also possible.Comment: RevTeX, 9 pages, several changes to include generalizations to
quartic and higher ghost terms and non-linear gauges. Abstract changed. Final
version to be publishe
Particles Sliding on a Fluctuating Surface: Phase Separation and Power Laws
We study a system of hard-core particles sliding downwards on a fluctuating
one-dimensional surface which is characterized by a dynamical exponent . In
numerical simulations, an initially random particle density is found to coarsen
and obey scaling with a growing length scale . The structure
factor deviates from the Porod law in some cases. The steady state is unusual
in that the density-segregation order parameter shows strong fluctuations. The
two-point correlation function has a scaling form with a cusp at small argument
which we relate to a power law distribution of particle cluster sizes. Exact
results on a related model of surface depths provides insight into the origin
of this behaviour.Comment: 5 pages, 5 Postscript figure
N-nitroso-N-ethylurea activates DNA damage surveillance pathways and induces transformation in mammalian cells
Abstract
Background
The DNA damage checkpoint signalling cascade sense damaged DNA and coordinates cell cycle arrest, DNA repair, and/or apoptosis. However, it is still not well understood how the signalling system differentiates between different kinds of DNA damage. N-nitroso-N-ethylurea (NEU), a DNA ethylating agent induces both transversions and transition mutations.
Methods
Immunoblot and comet assays were performed to detect DNA breaks and activation of the canonical checkpoint signalling kinases following NEU damage upto 2 hours. To investigate whether mismatch repair played a role in checkpoint activation, knock-down studies were performed while flow cytometry analysis was done to understand whether the activation of the checkpoint kinases was cell cycle phase specific. Finally, breast epithelial cells were grown as 3-dimensional spheroid cultures to study whether NEU can induce upregulation of vimentin as well as disrupt cell polarity of the breast acini, thus causing transformation of epithelial cells in culture.
Results
We report a novel finding that NEU causes activation of major checkpoint signalling kinases, Chk1 and Chk2. This activation is temporally controlled with Chk2 activation preceding Chk1 phosphorylation, and absence of cross talk between the two parallel signalling pathways, ATM and ATR. Damage caused by NEU leads to the temporal formation of both double strand and single strand breaks. Activation of checkpoints following NEU damage is cell cycle phase dependent wherein Chk2 is primarily activated during G2-M phase whilst in S phase, there is immediate Chk1 phosphorylation and delayed Chk2 response. Surprisingly, the mismatch repair system does not play a role in checkpoint activation, at doses and duration of NEU used in the experiments. Interestingly, NEU caused disruption of the well-formed polarised spheroid archithecture and upregulation of vimentin in three-dimensional breast acini cultures of non-malignant breast epithelial cells upon NEU treatment indicating NEU to have the potential to cause early transformation in the cells.
Conclusion
NEU causes damage in mammalian cells in the form of double strand and single strand breaks that temporally activate the major checkpoint signalling kinases without the occurrence of cross-talk between the pathways. NEU also appear to cause transformation in three-dimensional spheroid cultures.http://deepblue.lib.umich.edu/bitstream/2027.42/109493/1/12885_2013_Article_4466.pd
Thermodynamics of Plasmaballs and Plasmarings in 3+1 Dimensions
We study localized plasma configurations in 3+1 dimensional massive field
theories obtained by Scherk-Schwarz compactification of 4+1 dimensional CFT to
predict the thermodynamic properties of localized blackholes and blackrings in
Scherk-Schwarz compactified using the AdS/CFT correspondence. We
present an exact solution to the relativistic Navier-Stokes equation in the
thin ring limit of the fluid configuration. We also perform a thorough
numerical analysis to obtain the thermodynamic properties of the most general
solution. Finally we compare our results with the recent proposal for the phase
diagram of blackholes in six flat dimensions and find some similarities but
other differences.Comment: 18 pages, 11 figures, latex; v2: Typos corrected and new references
adde
Plasmarings as dual black rings
We construct solutions to the relativistic Navier-Stokes equations that
describe the long wavelength collective dynamics of the deconfined plasma phase
of N=4 Yang Mills theory compactified down to d=3 on a Scherk-Schwarz circle
and higher dimensional generalisations. Our solutions are stationary, axially
symmetric spinning balls and rings of plasma. These solutions, which are dual
to (yet to be constructed) rotating black holes and black rings in
Scherk-Schwarz compactified AdS(5) and AdS(6), and have properties that are
qualitatively similar to those of black holes and black rings in flat five
dimensional supergravity.Comment: 40 pages, 40 figures. (v2) Correction to black brane equation of
state, additional reference
Topological mass mechanism and exact fields mapping
We present a class of mappings between models with topological mass mechanism
and purely topological models in arbitrary dimensions. These mappings are
established by directly mapping the fields of one model in terms of the fields
of the other model in closed expressions. These expressions provide the
mappings of their actions as well as the mappings of their propagators. For a
general class of models in which the topological model becomes the BF model the
mappings present arbitrary functions which otherwise are absent for
Chern-Simons like actions. This work generalizes the results of [1] for
arbitrary dimensions.Comment: 11 page
Pauli equation and the method of supersymmetric factorization
We consider different variants of factorization of a 2x2 matrix
Schroedinger/Pauli operator in two spatial dimensions. They allow to relate its
spectrum to the sum of spectra of two scalar Schroedinger operators, in a
manner similar to one-dimensional Darboux transformations. We consider both the
case when such factorization is reduced to the ordinary 2-dimensional SUSY QM
quasifactorization and a more general case which involves covariant
derivatives. The admissible classes of electromagnetic fields are described and
some illustrative examples are given.Comment: 18 pages, Late
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