3,641 research outputs found
Random site dilution properties of frustrated magnets on a hierarchical lattice
We present a method to analyze magnetic properties of frustrated Ising spin
models on specific hierarchical lattices with random dilution. Disorder is
induced by dilution and geometrical frustration rather than randomness in the
internal couplings of the original Hamiltonian. The two-dimensional model
presented here possesses a macroscopic entropy at zero temperature in the large
size limit, very close to the Pauling estimate for spin-ice on pyrochlore
lattice, and a crossover towards a paramagnetic phase. The disorder due to
dilution is taken into account by considering a replicated version of the
recursion equations between partition functions at different lattice sizes. An
analysis at first order in replica number allows for a systematic
reorganization of the disorder configurations, leading to a recurrence scheme.
This method is numerically implemented to evaluate the thermodynamical
quantities such as specific heat and susceptibility in an external field.Comment: 26 pages, 11 figure
Excitonic instability and electric-field-induced phase transition towards a two dimensional exciton condensate
We present an InAs-GaSb-based system in which the electric-field tunability
of its 2D energy gap implies a transition towards a thermodynamically stable
excitonic condensed phase. Detailed calculations show a 3 meV BCS-like gap
appearing in a second-order phase transition with electric field. We find this
transition to be very sharp, solely due to exchange interaction, and so, the
exciton binding energy is greatly renormalized even at small condensate
densities. This density gradually increases with external field, thus enabling
the direct probe of the Bose-Einstein to BCS crossover.Comment: LaTex, 11 pages, 3 ps figures, To appear in PR
Exact two-time correlation and response functions in the one-dimensional coagulation-diffusion process by the empty-interval-particle method
The one-dimensional coagulation-diffusion process describes the strongly
fluctuating dynamics of particles, freely hopping between the nearest-neighbour
sites of a chain such that one of them disappears with probability 1 if two
particles meet. The exact two-time correlation and response function in the
one-dimensional coagulation-diffusion process are derived from the
empty-interval-particle method. The main quantity is the conditional
probability of finding an empty interval of n consecutive sites, if at distance
d a site is occupied by a particle. Closed equations of motion are derived such
that the probabilities needed for the calculation of correlators and responses,
respectively, are distinguished by different initial and boundary conditions.
In this way, the dynamical scaling of these two-time observables is analysed in
the longtime ageing regime. A new generalised fluctuation-dissipation ratio
with an universal and finite limit is proposed.Comment: 31 pages, submitted to J.Stat.Mec
Enabling Hyper-Personalisation: Automated Ad Creative Generation and Ranking for Fashion e-Commerce
Homepage is the first touch point in the customer's journey and is one of the
prominent channels of revenue for many e-commerce companies. A user's attention
is mostly captured by homepage banner images (also called Ads/Creatives). The
set of banners shown and their design, influence the customer's interest and
plays a key role in optimizing the click through rates of the banners.
Presently, massive and repetitive effort is put in, to manually create
aesthetically pleasing banner images. Due to the large amount of time and
effort involved in this process, only a small set of banners are made live at
any point. This reduces the number of banners created as well as the degree of
personalization that can be achieved. This paper thus presents a method to
generate creatives automatically on a large scale in a short duration. The
availability of diverse banners generated helps in improving personalization as
they can cater to the taste of larger audience. The focus of our paper is on
generating wide variety of homepage banners that can be made as an input for
user level personalization engine. Following are the main contributions of this
paper: 1) We introduce and explain the need for large scale banner generation
for e-commerce 2) We present on how we utilize existing deep learning based
detectors which can automatically annotate the required objects/tags from the
image. 3) We also propose a Genetic Algorithm based method to generate an
optimal banner layout for the given image content, input components and other
design constraints. 4) Further, to aid the process of picking the right set of
banners, we designed a ranking method and evaluated multiple models. All our
experiments have been performed on data from Myntra (http://www.myntra.com),
one of the top fashion e-commerce players in India.Comment: Workshop on Recommender Systems in Fashion, 13th ACM Conference on
Recommender Systems, 201
On the Importance of Electroweak Corrections for Majorana Dark Matter Indirect Detection
Recent analyses have shown that the inclusion of electroweak corrections can
alter significantly the energy spectra of Standard Model particles originated
from dark matter annihilations. We investigate the important situation where
the radiation of electroweak gauge bosons has a substantial influence: a
Majorana dark matter particle annihilating into two light fermions. This
process is in p-wave and hence suppressed by the small value of the relative
velocity of the annihilating particles. The inclusion of electroweak radiation
eludes this suppression and opens up a potentially sizeable s-wave contribution
to the annihilation cross section. We study this effect in detail and explore
its impact on the fluxes of stable particles resulting from the dark matter
annihilations, which are relevant for dark matter indirect searches. We also
discuss the effective field theory approach, pointing out that the opening of
the s-wave is missed at the level of dimension-six operators and only encoded
by higher orders.Comment: 25 pages, 6 figures. Minor corrections to match version published in
JCA
Development and Recovery of Stress-Induced Elastic Anisotropy During Cyclic Loading Experiment on Westerly Granite
International audienceIn the upper crust, where brittle deformation mechanisms dominate, the development of Q4 Q5 crack networks subject to anisotropic stress fields generates stress-induced elastic anisotropy. Here a rock specimen of Westerly granite was submitted to differential stress cycles (i.e., loading and unloading) of increasing amplitudes, up to failure and under upper crustal conditions. Combined records of strains, acoustic emissions, and P and S elastic wave anisotropies demonstrate that increasing differential stress promotes crack opening, sliding, and propagation subparallel to the main compressive stress orientation. However, the significant elastic anisotropies observed during loading (≥20%) almost vanish upon stress removal, demonstrating that in the absence of stress, crack-related elastic anisotropy remains limited (≤10%). As a consequence, (i) crack-related elastic anisotropies measured in the crust will likely be a strong function of the level of differential stress, and consequently (ii) continuous monitoring of elastic wave velocity anisotropy along faults could shed light on the mechanism of stress accumulation during interseismic loading. Plain Language Summary In the upper crust, large strains are accommodated by brittle deformation mechanisms, leading to macroscopic faults embedded within a substantially damaged rock medium. The development of crack damage affects both the strength and the elastic and transport properties of rocks. Nowadays, the evolution of rock elastic properties is commonly used to estimate the direction of the maximum stress along faults and evaluate seismic hazard of seismogenic area. Up to Q6 now, stress-induced anisotropy was expected to be irreversible and observable by geophysics method even after unloading or exhumation of the rocks. In this study, we demonstrate for the first time that unloading induces an almost complete recovery of both stress-induced anisotropy and stress-induced damage. Our results suggest that elastic properties estimated from wave velocity measurement could then underestimate both damage and anisotropy of the crust under shallow depth conditions
Design, Synthesis, Biological Evaluation, and Structure–Activity Relationships of Substituted Phenyl 4-(2-Oxoimidazolidin-1-yl)benzenesulfonates as New Tubulin Inhibitors Mimicking Combretastatin A-4
International audienc
Effects of nonnative species on the stability of riverine fish communities
ResearchDespite the increasing ubiquity of biological invasions worldwide, little is known
about the scale-dependent effects of nonnative species on real-world ecological dynamics.
Here, using an extensive time series dataset of riverine fish communities across different
biogeographic regions of the world, we assessed the effects of nonnative species
on the temporal variability and synchrony in abundance at different organizational levels
(population, metapopulation, community and metacommunity) and spatial scales
(stream reach and river basin). At the reach scale, we found that populations of nonnative
species were more variable over time than native species, and that this effect scaled
up to the community level – significantly destabilizing the dynamics of riverine fish
communities. Nonnative species not only contributed to reduced community stability,
but also increased variability of native populations. By contrast, we found no effect of
nonnative species dominance on local interspecific synchrony among native species. At
the basin scale, nonnative metapopulations were again more variable than the native
ones. However, neither native metapopulations nor metacommunities showed differences
in temporal variability or synchrony as nonnative species dominance increased
basin-wide. This suggests a ‘dilution effect’ where the contribution to regional stability
of local native populations from sites displaying low levels of invasion reduced the
destabilizing effects of nonnative species. Overall, our results indicate that accounting
for the destabilizing effect of nonnative species is critical to understanding native species
persistence and community stabilityinfo:eu-repo/semantics/publishedVersio
Anomalous Lattice Vibrations of Single and Few-Layer MoS2
Molybdenum disulfide (MoS2) of single and few-layer thickness was exfoliated
on SiO2/Si substrate and characterized by Raman spectroscopy. The number of
S-Mo-S layers of the samples was independently determined by contact-mode
atomic-force microscopy. Two Raman modes, E12g and A1g, exhibited sensitive
thickness dependence, with the frequency of the former decreasing and that of
the latter increasing with thickness. The results provide a convenient and
reliable means for determining layer thickness with atomic-level precision. The
opposite direction of the frequency shifts, which cannot be explained solely by
van der Waals interlayer coupling, is attributed to Coulombic interactions and
possible stacking-induced changes of the intralayer bonding. This work
exemplifies the evolution of structural parameters in layered materials in
changing from the 3-dimensional to the 2-dimensional regime.Comment: 14 pages, 4 figure
Fermions and Disorder in Ising and Related Models in Two Dimensions
The aspects of phase transitions in the two-dimensional Ising models modified
by quenched and annealed site disorder are discussed in the framework of
fermionic approach based on the reformulation of the problem in terms of
integrals with anticommuting Grassmann variables.Comment: 11 pages, 1 table, no figures. The discussion is merely based on a
talk given at the International Bogoliubov Conference on Problems of
Theoretical and Mathematical Physics, MIRAS--JINR, Moscow--Dubna, Russia,
August 21--27, 200
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