1,110 research outputs found
Finite Size Scaling, Fisher Zeroes and N=4 Super Yang-Mills
We investigate critical slowing down in the local updating continuous-time
Quantum Monte Carlo method by relating the finite size scaling of Fisher Zeroes
to the dynamically generated gap, through the scaling of their respective
critical exponents. As we comment, the nonlinear sigma model representation
derived through the hamiltonian of our lattice spin model can also be used to
give a effective treatment of planar anomalous dimensions in N=4 SYM. We
present scaling arguments from our FSS analysis to discuss quantum corrections
and recent 2-loop results, and further comment on the prospects of extending
this approach for calculating higher twist parton distributions.Comment: Lattice 2004(spin), Fermilab, June 21-26, 2004; 3 pages, 4 figure
An efficient compressive sensing based PS-DInSAR method for surface deformation estimation
Permanent scatterers differential interferometric synthetic aperture radar (PS-DInSAR) is a
technique for detecting surface micro-deformation, with an accuracy at the centimeter to millimeter
level. However, its performance is limited by the number of SAR images available (normally more than
20 are needed). Compressive Sensing (CS) has been proven to be an effective signal recovery method
with only a very limited number of measurements. Applying CS to PS-DInSAR, a novel
CS-PS-DInSAR method is proposed to estimate the deformation with fewer SAR images. By analyzing
the PS-DInSAR process in detail, first the sparsity representation of deformation velocity difference is
obtained; then, the mathematical model of CS-PS-DInSAR is derived and the restricted isometry
property (RIP) of the measurement matrix is discussed to validate the proposed CS-PS-DInSAR in
theory. The implementation of CS-PS-DInSAR is achieved by employing basis pursuit algorithms to
estimate the deformation velocity. With the proposed method, DInSAR deformation estimation can be
achieved by a much smaller number of SAR images, as demonstrated by simulation result
Non-Markovian dynamics for an open two-level system without rotating wave approximation: Indivisibility versus backflow of information
By use of the two measures presented recently, the indivisibility and the
backflow of information, we study the non-Markovianity of the dynamics for a
two-level system interacting with a zero-temperature structured environment
without using rotating wave approximation (RWA). In the limit of weak coupling
between the system and the reservoir, and by expanding the time-convolutionless
(TCL) generator to the forth order with respect to the coupling strength, the
time-local non-Markovian master equation for the reduced state of the system is
derived. Under the secular approximation, the exact analytic solution is
obtained and the sufficient and necessary conditions for the indivisibility and
the backflow of information for the system dynamics are presented. In the more
general case, we investigate numerically the properties of the two measures for
the case of Lorentzian reservoir. Our results show the importance of the
counter-rotating terms to the short-time-scale non-Markovian behavior of the
system dynamics, further expose the relations between the two measures and
their rationality as non-Markovian measures. Finally, the complete positivity
of the dynamics of the considered system is discussed
Quasi-normal modes of warped black holes and warped AdS/CFT correspondence
We analytically calculate the quasi-normal modes of various perturbations of
spacelike stretched and null warped black holes. From AdS/CFT
correspondence, these quasi-normal modes are expected to appear as the poles in
momentum space of retarded Green functions of dual operators in CFT at finite
temperature. We find that this is indeed the case, after taking into account of
the subtle identification of quantum numbers. The subtlety comes from the fact
that only after appropriate coordinate transformation the asymptotic geometries
of warped black holes are the same as the ones of warped spacetimes. We
show that in general the quasi-normal modes are in good agreement with the
prediction of the warped AdS/CFT correspondence, up to a constant factor. As a
byproduct, we compute the conformal dimensions of boundary operators dual to
the perturbations. Our result gives strong support to the conjectured warped
AdS/CFT correspondence.Comment: 26 pages; typos corrected, references added; more clarifications,
match the version to appear in JHE
From crystal to amorphopus: a novel route towards unjamming in soft disk packings
It is presented a numerical study on the unjamming packing fraction of bi-
and polydisperse disk packings, which are generated through compression of a
monodisperse crystal. In bidisperse systems, a fraction f_+ = 40% up to 80% of
the total number of particles have their radii increased by \Delta R, while the
rest has their radii decreased by the same amount. Polydisperse packings are
prepared by changing all particle radii according to a uniform distribution in
the range [-\Delta R,\Delta R]. The results indicate that the critical packing
fraction is never larger than the value for the initial monodisperse crystal,
\phi = \pi/12, and that the lowest value achieved is approximately the one for
random close packing. These results are seen as a consequence of the interplay
between the increase in small-small particle contacts and the local crystalline
order provided by the large-large particle contacts.Comment: two columns, 14 pages, 12 figures, accepted for publication in Eur.
Phys. J.
A Quantitative Model of Energy Release and Heating by Time-dependent, Localized Reconnection in a Flare with a Thermal Loop-top X-ray Source
We present a quantitative model of the magnetic energy stored and then
released through magnetic reconnection for a flare on 26 Feb 2004. This flare,
well observed by RHESSI and TRACE, shows evidence of non-thermal electrons only
for a brief, early phase. Throughout the main period of energy release there is
a super-hot (T>30 MK) plasma emitting thermal bremsstrahlung atop the flare
loops. Our model describes the heating and compression of such a source by
localized, transient magnetic reconnection. It is a three-dimensional
generalization of the Petschek model whereby Alfven-speed retraction following
reconnection drives supersonic inflows parallel to the field lines, which form
shocks heating, compressing, and confining a loop-top plasma plug. The
confining inflows provide longer life than a freely-expanding or
conductively-cooling plasma of similar size and temperature. Superposition of
successive transient episodes of localized reconnection across a current sheet
produces an apparently persistent, localized source of high-temperature
emission. The temperature of the source decreases smoothly on a time scale
consistent with observations, far longer than the cooling time of a single
plug. Built from a disordered collection of small plugs, the source need not
have the coherent jet-like structure predicted by steady-state reconnection
models. This new model predicts temperatures and emission measure consistent
with the observations of 26 Feb 2004. Furthermore, the total energy released by
the flare is found to be roughly consistent with that predicted by the model.
Only a small fraction of the energy released appears in the super-hot source at
any one time, but roughly a quarter of the flare energy is thermalized by the
reconnection shocks over the course of the flare. All energy is presumed to
ultimately appear in the lower-temperature T<20 MK, post-flare loops
Tumor initiating cells in Esophageal squamous cell carcinomas express high levels of CD44
10.1371/journal.pone.0021419PLoS ONE66
Charged pion form factor between Q^2=0.60 and 2.45 GeV^2. II. Determination of, and results for, the pion form factor
The charged pion form factor, Fpi(Q^2), is an important quantity which can be
used to advance our knowledge of hadronic structure. However, the extraction of
Fpi from data requires a model of the 1H(e,e'pi+)n reaction, and thus is
inherently model dependent. Therefore, a detailed description of the extraction
of the charged pion form factor from electroproduction data obtained recently
at Jefferson Lab is presented, with particular focus given to the dominant
uncertainties in this procedure. Results for Fpi are presented for
Q^2=0.60-2.45 GeV^2. Above Q^2=1.5 GeV^2, the Fpi values are systematically
below the monopole parameterization that describes the low Q^2 data used to
determine the pion charge radius. The pion form factor can be calculated in a
wide variety of theoretical approaches, and the experimental results are
compared to a number of calculations. This comparison is helpful in
understanding the role of soft versus hard contributions to hadronic structure
in the intermediate Q^2 regime.Comment: 18 pages, 11 figure
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