887 research outputs found
Singular Liouville fields and spiky strings in \rr^{1,2} and SL(2,\rr)
The closed string dynamics in \rr^{1,2} and SL(2,\rr) is studied within
the scheme of Pohlmeyer reduction. In both spaces two different classes of
string surfaces are specified by the structure of the fundamental quadratic
forms. The first class in \rr^{1,2} is associated with the standard lightcone
gauge strings and the second class describes spiky strings and their conformal
deformations on the Virasoro coadjoint orbits. These orbits correspond to
singular Liouville fields with the monodromy matrixes . The first class
in SL(2,\rr) is parameterized by the Liouville fields with vanishing chiral
energy functional. Similarly to \rr^{1,2}, the second class in SL(2,\rr)
describes spiky strings, related to the vacuum configurations of the
SL(2,\rr)/U(1) coset model.Comment: 37 p. 6 fi
Exploring the Expression of Cardiac Regulators in a Vertebrate Extremophile: The Cichlid Fish Oreochromis (Alcolapia) alcalica
Although it is widely accepted that the cellular and molecular mechanisms of vertebratecardiac development are evolutionarily conserved, this is on the basis of data from only a fewmodel organisms suited to laboratory studies. Here, we investigate gene expression during cardiacdevelopment in the extremophile, non-model fish species, Oreochromis (Alcolapia) alcalica. Wefirst characterise the early development of O. alcalica and observe extensive vascularisation across the yolk prior to hatching. We further investigate heart development by identifying andcloning O. alcalica orthologues of conserved cardiac transcription factors gata4, tbx5, and mef2cfor analysis by in situ hybridisation. Expression of these three key cardiac developmentalregulators also reveals other aspects of O. alcalica development, as these genes are expressed indeveloping blood, limb, eyes, and muscle, as well as the heart. Our data support the notion that O.alcalica is a direct-developing vertebrate that shares the highly conserved molecular regulation ofthe vertebrate body plan. However, the expression of gata4 in O. alcalica reveals interestingdifferences in the development of the circulatory system distinct from that of the well-studiedzebrafish. Understanding the development of O. alcalica embryos is an important step towardsproviding a model for future research into the adaptation to extreme conditions; this is particularlyrelevant given that anthropogenic-driven climate change will likely result in more freshwaterorganisms being exposed to less favourable conditions
Effects of Anomalous Magnetic Moment in the Quantum Motion of Neutral Particle in Magnetic and Electric Fields Produced by a Linear Source in a Conical Spacetime
In this paper we analyse the effect of the anomalous magnetic moment on the
non-relativistic quantum motion of a neutral particle in magnetic and electric
fields produced by linear sources of constant current and charge density,
respectively.Comment: 17 pages, no figur
Detailed Examination of Transport Coefficients in Cubic-Plus-Quartic Oscillator Chains
We examine the thermal conductivity and bulk viscosity of a one-dimensional
(1D) chain of particles with cubic-plus-quartic interparticle potentials and no
on-site potentials. This system is equivalent to the FPU-alpha beta system in a
subset of its parameter space. We identify three distinct frequency regimes
which we call the hydrodynamic regime, the perturbative regime and the
collisionless regime. In the lowest frequency regime (the hydrodynamic regime)
heat is transported ballistically by long wavelength sound modes. The model
that we use to describe this behaviour predicts that as the frequency goes to
zero the frequency dependent bulk viscosity and the frequency dependent thermal
conductivity should diverge with the same power law dependence on frequency.
Thus, we can define the bulk Prandtl number as the ratio of the bulk viscosity
to the thermal conductivity (with suitable prefactors to render it
dimensionless). This dimensionless ratio should approach a constant value as
frequency goes to zero. We use mode-coupling theory to predict the zero
frequency limit. Values of the bulk Prandtl number from simulations are in
agreement with these predictions over a wide range of system parameters. In the
middle frequency regime, which we call the perturbative regime, heat is
transported by sound modes which are damped by four-phonon processes. We call
the highest frequency regime the collisionless regime since at these
frequencies the observing times are much shorter than the characteristic
relaxation times of phonons. The perturbative and collisionless regimes are
discussed in detail in the appendices.Comment: Latex with references in .bib file. 36 pages, 8 figures. Submitted to
J. Stat. Phys. on Sept. 2
Quantitative Treatment of Decoherence
We outline different approaches to define and quantify decoherence. We argue
that a measure based on a properly defined norm of deviation of the density
matrix is appropriate for quantifying decoherence in quantum registers. For a
semiconductor double quantum dot qubit, evaluation of this measure is reviewed.
For a general class of decoherence processes, including those occurring in
semiconductor qubits, we argue that this measure is additive: It scales
linearly with the number of qubits.Comment: Revised version, 26 pages, in LaTeX, 3 EPS figure
First Observation of Coherent Production in Neutrino Nucleus Interactions with 2 GeV
The MiniBooNE experiment at Fermilab has amassed the largest sample to date
of s produced in neutral current (NC) neutrino-nucleus interactions at
low energy. This paper reports a measurement of the momentum distribution of
s produced in mineral oil (CH) and the first observation of coherent
production below 2 GeV. In the forward direction, the yield of events
observed above the expectation for resonant production is attributed primarily
to coherent production off carbon, but may also include a small contribution
from diffractive production on hydrogen. Integrated over the MiniBooNE neutrino
flux, the sum of the NC coherent and diffractive modes is found to be (19.5
1.1 (stat) 2.5 (sys))% of all exclusive NC production at
MiniBooNE. These measurements are of immediate utility because they quantify an
important background to MiniBooNE's search for
oscillations.Comment: Submitted to Phys. Lett.
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Reply to: New Meta- and Mega-analyses of Magnetic Resonance Imaging Findings in Schizophrenia: Do They Really Increase Our Knowledge About the Nature of the Disease Process?
This work was supported by National Institute of Biomedical Imaging and Bioengineering Grant No. U54EB020403 (to the ENIGMA consortium)
Measurement of the B0-anti-B0-Oscillation Frequency with Inclusive Dilepton Events
The - oscillation frequency has been measured with a sample of
23 million \B\bar B pairs collected with the BABAR detector at the PEP-II
asymmetric B Factory at SLAC. In this sample, we select events in which both B
mesons decay semileptonically and use the charge of the leptons to identify the
flavor of each B meson. A simultaneous fit to the decay time difference
distributions for opposite- and same-sign dilepton events gives ps.Comment: 7 pages, 1 figure, submitted to Physical Review Letter
A measurement of the tau mass and the first CPT test with tau leptons
We measure the mass of the tau lepton to be 1775.1+-1.6(stat)+-1.0(syst.) MeV
using tau pairs from Z0 decays. To test CPT invariance we compare the masses of
the positively and negatively charged tau leptons. The relative mass difference
is found to be smaller than 3.0 10^-3 at the 90% confidence level.Comment: 10 pages, 4 figures, Submitted to Phys. Letts.
Measurement of the B0 Lifetime and Oscillation Frequency using B0->D*+l-v decays
The lifetime and oscillation frequency of the B0 meson has been measured
using B0->D*+l-v decays recorded on the Z0 peak with the OPAL detector at LEP.
The D*+ -> D0pi+ decays were reconstructed using an inclusive technique and the
production flavour of the B0 mesons was determined using a combination of tags
from the rest of the event. The results t_B0 = 1.541 +- 0.028 +- 0.023 ps, Dm_d
= 0.497 +- 0.024 +- 0.025 ps-1 were obtained, where in each case the first
error is statistical and the second systematic.Comment: 17 pages, 4 figures, submitted to Phys. Lett.
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