8,128 research outputs found
New model for surface fracture induced by dynamical stress
We introduce a model where an isotropic, dynamically-imposed stress induces
fracture in a thin film. Using molecular dynamics simulations, we study how the
integrated fragment distribution function depends on the rate of change and
magnitude of the imposed stress, as well as on temperature. A mean-field
argument shows that the system becomes unstable for a critical value of the
stress. We find a striking invariance of the distribution of fragments for
fixed ratio of temperature and rate of change of the stress; the interval over
which this invariance holds is determined by the force fluctuations at the
critical value of the stress.Comment: Revtex, 4 pages, 4 figures available upon reques
Theory of the magnetoeletric effect in a lightly doped high-Tc cuprate
In a recent study Viskadourakis et al. discovered that extremely underdoped
La_2CuO_(4+x) is a relaxor ferroelectric and a magnetoelectric material at low
temperatures. It is further observed that the magnetoelectric response is
anisotropic for different directions of electric polarization and applied
magnetic field. By constructing an appropriate Landau theory, we show that a
bi-quadratic magnetoelectric coupling can explain the experimentally observed
polarization dependence on magnetic field. This coupling leads to several novel
low-temperature effects including a feedback enhancement of the magnetization
below the ferroelectric transition, and a predicted magnetocapacitive effect.Comment: 5 pages, 4 figure
Local Ranking Problem on the BrowseGraph
The "Local Ranking Problem" (LRP) is related to the computation of a
centrality-like rank on a local graph, where the scores of the nodes could
significantly differ from the ones computed on the global graph. Previous work
has studied LRP on the hyperlink graph but never on the BrowseGraph, namely a
graph where nodes are webpages and edges are browsing transitions. Recently,
this graph has received more and more attention in many different tasks such as
ranking, prediction and recommendation. However, a web-server has only the
browsing traffic performed on its pages (local BrowseGraph) and, as a
consequence, the local computation can lead to estimation errors, which hinders
the increasing number of applications in the state of the art. Also, although
the divergence between the local and global ranks has been measured, the
possibility of estimating such divergence using only local knowledge has been
mainly overlooked. These aspects are of great interest for online service
providers who want to: (i) gauge their ability to correctly assess the
importance of their resources only based on their local knowledge, and (ii)
take into account real user browsing fluxes that better capture the actual user
interest than the static hyperlink network. We study the LRP problem on a
BrowseGraph from a large news provider, considering as subgraphs the
aggregations of browsing traces of users coming from different domains. We show
that the distance between rankings can be accurately predicted based only on
structural information of the local graph, being able to achieve an average
rank correlation as high as 0.8
Scaling behavior in the dynamics of a supercooled Lennard-Jones mixture
We present the results of a large scale molecular dynamics computer
simulation of a binary, supercooled Lennard-Jones fluid. At low temperatures
and intermediate times the time dependence of the intermediate scattering
function is well described by a von Schweidler law. The von Schweidler exponent
is independent of temperature and depends only weakly on the type of
correlator. For long times the correlation functions show a Kohlrausch behavior
with an exponent that is independent of temperature. This dynamical
behavior is in accordance with the mode-coupling theory of supercooled liquids.Comment: 6 pages, RevTex, three postscript figures available on request,
MZ-Physics-10
Electron-phonon interaction in the t-J model
We derive a t-J model with electron-phonon coupling from the three-band
model, considering modulation of both hopping and Coulomb integrals by phonons.
While the modulation of the hopping integrals dominates, the modulation of the
Coulomb integrals cannot be neglected. The model explains the experimentally
observed anomalous softening of the half-breathing mode upon doping and a
weaker softening of the breathing mode. It is shown that other phonons are not
strongly influenced, and, in particular, the coupling to a buckling mode is not
strong in this model.Comment: 4 pages, RevTeX, 3 eps figures; final version with minor correction
Competing magnetic fluctuations in Sr3Ru2O7 probed by Ti doping
We report the effect of nonmagnetic Ti4+ impurities on the electronic and
magnetic properties of Sr3Ru2O7. Small amounts of Ti suppress the
characteristic peak in magnetic susceptibility near 16 K and result in a sharp
upturn in specific heat. The metamagnetic quantum phase transition and related
anomalous features are quickly smeared out by small amounts of Ti. These
results provide strong evidence for the existence of competing magnetic
fluctuations in the ground state of Sr3Ru2O7. Ti doping suppresses the low
temperature antiferromagnetic interactions that arise from Fermi surface
nesting, leaving the system in a state dominated by ferromagnetic fluctuations.Comment: 5 pages, 4 figures, 1 tabl
Three-loop HTL gluon thermodynamics at intermediate coupling
We calculate the thermodynamic functions of pure-glue QCD to three-loop order
using the hard-thermal-loop perturbation theory (HTLpt) reorganization of
finite temperature quantum field theory. We show that at three-loop order
hard-thermal-loop perturbation theory is compatible with lattice results for
the pressure, energy density, and entropy down to temperatures .
Our results suggest that HTLpt provides a systematic framework that can used to
calculate static and dynamic quantities for temperatures relevant at LHC.Comment: 24 pages, 13 figs. 2nd version: improved discussion and fixing typos.
Published in JHE
Electronic structure of Pr_{2-x}Ce_xCuO_4 studied via ARPES and LDA+DMFT+\Sigma_k
The electron-doped Pr(2-x)Ce(x)CuO(4) (PCCO) compound in the pseudogap regime
(x~0.15) was investigated using angle-resolved photoemission spectroscopy
(ARPES) and the generalized dynamical mean-field theory (DMFT) with the
k-dependent self-energy (LDA+DMFT+\Sigma_k). Model parameters (hopping integral
values and local Coulomb interaction strength) for the effective one-band
Hubbard model were calculated by the local density approximation (LDA) with
numerical renormalization group method (NRG) employed as an "impurity solver"
in DMFT computations. An "external" k-dependent self-energy \Sigma_k was used
to describe interaction of correlated conducting electrons with short-range
antiferromagnetic (AFM) pseudogap fluctuations. Both experimental and
theoretical spectral functions and Fermi surfaces (FS) were obtained and
compared demonstrating good semiquantitative agreement. For both experiment and
theory normal state spectra of nearly optimally doped PCCO show clear evidence
for a pseudogap state with AFM-like nature. Namely, folding of quasiparticle
bands as well as presence of the "hot spots" and "Fermi arcs" were observed.Comment: 4 pages, 4 figures, as accepted to PRB Rapid Communications. Title is
changed by Editor
A model-based approach to recovering the structure of a plant from images
We present a method for recovering the structure of a plant directly from a
small set of widely-spaced images. Structure recovery is more complex than
shape estimation, but the resulting structure estimate is more closely related
to phenotype than is a 3D geometric model. The method we propose is applicable
to a wide variety of plants, but is demonstrated on wheat. Wheat is made up of
thin elements with few identifiable features, making it difficult to analyse
using standard feature matching techniques. Our method instead analyses the
structure of plants using only their silhouettes. We employ a generate-and-test
method, using a database of manually modelled leaves and a model for their
composition to synthesise plausible plant structures which are evaluated
against the images. The method is capable of efficiently recovering accurate
estimates of plant structure in a wide variety of imaging scenarios, with no
manual intervention
Three-loop HTL QCD thermodynamics
The hard-thermal-loop perturbation theory (HTLpt) framework is used to
calculate the thermodynamic functions of a quark-gluon plasma to three-loop
order. This is the highest order accessible by finite temperature perturbation
theory applied to a non-Abelian gauge theory before the high-temperature
infrared catastrophe. All ultraviolet divergences are eliminated by
renormalization of the vacuum, the HTL mass parameters, and the strong coupling
constant. After choosing a prescription for the mass parameters, the three-loop
results for the pressure and trace anomaly are found to be in very good
agreement with recent lattice data down to , which are
temperatures accessible by current and forthcoming heavy-ion collision
experiments.Comment: 27 pages, 11 figures; corresponds with published version in JHE
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