794 research outputs found
Phase diagram of three-leg ladders at strong coupling along the rungs
A phase diagram of the t-J three-leg ladder as a function of hole dopping is
derived in the limit where the coupling parameters along the rungs,
and , are taken to be much larger than those along the legs,
and At large exchange coupling along the rungs,
, there is a transition from a low-dopping
Luttinger liquid phase into a Luther-Emery liquid at a critical hole
concentration . In the opposite case,
, there as a sequence of three Luttinger
liquid phases (LLI, LLII and LLIII) as a function of hole dopping.Comment: 9 pages, 15 figure
Learning the Imaging Model of Speed-of-Sound Reconstruction via a Convolutional Formulation
Speed-of-sound (SoS) is an emerging ultrasound contrast modality, where
pulse-echo techniques using conventional transducers offer multiple benefits.
For estimating tissue SoS distributions, spatial domain reconstruction from
relative speckle shifts between different beamforming sequences is a promising
approach. This operates based on a forward model that relates the sought local
values of SoS to observed speckle shifts, for which the associated image
reconstruction inverse problem is solved. The reconstruction accuracy thus
highly depends on the hand-crafted forward imaging model. In this work, we
propose to learn the SoS imaging model based on data. We introduce a
convolutional formulation of the pulse-echo SoS imaging problem such that the
entire field-of-view requires a single unified kernel, the learning of which is
then tractable and robust. We present least-squares estimation of such
convolutional kernel, which can further be constrained and regularized for
numerical stability. In experiments, we show that a forward model learned from
k-Wave simulations improves the median contrast of SoS reconstructions by 63%,
compared to a conventional hand-crafted line-based wave-path model. This
simulation-learned model generalizes successfully to acquired phantom data,
nearly doubling the SoS contrast compared to the conventional hand-crafted
alternative. We demonstrate equipment-specific and small-data regime
feasibility by learning a forward model from a single phantom image, where our
learned model quadruples the SoS contrast compared to the conventional
hand-crafted model. On in-vivo data, the simulation- and phantom-learned models
respectively exhibit impressive 7 and 10 folds contrast improvements over the
conventional model
Axially and spherically symmetric solitons in warm plasma
We study the existence of stable axially and spherically symmetric plasma
structures on the basis of the new nonlinear Schrodinger equation (NLSE)
accounting for nonlocal electron nonlinearities. The numerical solutions of
NLSE having the form of spatial solitions are obtained and their stability is
analyzed. We discuss the possible application of the obtained results to the
theoretical description of natural plasmoids in the atmosphere.Comment: 10 pages, two columns, 5 eps figures, RevTeX 4.1; several new
references are added and some typos are corrected; a variant to be published
in Journal of Plasma Physic
Quantum exchange interaction of spherically symmetric plasmoids
We study nano-sized spherically symmetric plasma structures which are radial
nonlinear oscillations of electrons in plasma. The effective interaction of
these plasmoids via quantum exchange forces between ions is described. We
calculate the energy of this interaction for the case of a dense plasma. The
conditions when the exchange interaction is attractive are examined and it is
shown that separate plasmoids can form a single object. The application of our
results to the theoretical description of stable atmospheric plasma structures
is considered.Comment: 11 pages in LaTeX2e, two columns, 2 eps figures; paper was
significantly revised, more realistic values for plasma parameters are used,
several references were added; matches version to be published in J. Atm.
Solar-Terr. Phy
Container solutions for HPC Systems: A Case Study of Using Shifter on Blue Waters
Software container solutions have revolutionized application development
approaches by enabling lightweight platform abstractions within the so-called
"containers." Several solutions are being actively developed in attempts to
bring the benefits of containers to high-performance computing systems with
their stringent security demands on the one hand and fundamental resource
sharing requirements on the other.
In this paper, we discuss the benefits and short-comings of such solutions
when deployed on real HPC systems and applied to production scientific
applications.We highlight use cases that are either enabled by or significantly
benefit from such solutions. We discuss the efforts by HPC system
administrators and support staff to support users of these type of workloads on
HPC systems not initially designed with these workloads in mind focusing on
NCSA's Blue Waters system.Comment: 8 pages, 7 figures, in PEARC '18: Proceedings of Practice and
Experience in Advanced Research Computing, July 22--26, 2018, Pittsburgh, PA,
US
Field-Induced Magnetic Order in Quantum Spin Liquids
We study magnetic field-induced three-dimensional ordering transitions in
low-dimensional quantum spin liquids, such as weakly coupled, antiferromagnetic
spin-1/2 Heisenberg dimers and ladders. Using stochastic series expansion
quantum Monte Carlo simulations, thermodynamic response functions are obtained
down to ultra-low temperatures. We extract the critical scaling exponents which
dictate the power-law dependence of the transition temperature on the applied
magnetic field. These are compared with recent experiments on candidate
materials and with predictions for the Bose-Einstein condensation of magnons
obtained in mean-field theory.Comment: RevTex, 4 pages with 5 figure
Full-length messenger RNA sequences greatly improve genome annotation
Background: Annotation of eukaryotic genomes is a complex endeavor that requires the
integration of evidence from multiple, often contradictory, sources. With the ever-increasing
amount of genome sequence data now available, methods for accurate identification of large
numbers of genes have become urgently needed. In an effort to create a set of very high-quality
gene models, we used the sequence of 5,000 full-length gene transcripts from Arabidopsis to
re-annotate its genome. We have mapped these transcripts to their exact chromosomal locations
and, using alignment programs, have created gene models that provide a reference set for this
organism.
Results: Approximately 35% of the transcripts indicated that previously annotated genes needed
modification, and 5% of the transcripts represented newly discovered genes. We also discovered
that multiple transcription initiation sites appear to be much more common than previously
known, and we report numerous cases of alternative mRNA splicing. We include a comparison of
different alignment software and an analysis of how the transcript data improved the previously
published annotation.
Conclusions: Our results demonstrate that sequencing of large numbers of full-length
transcripts followed by computational mapping greatly improves identification of the complete
exon structures of eukaryotic genes. In addition, we are able to find numerous introns in the
untranslated regions of the genes
Dark sectors 2016 Workshop: community report
This report, based on the Dark Sectors workshop at SLAC in April 2016,
summarizes the scientific importance of searches for dark sector dark matter
and forces at masses beneath the weak-scale, the status of this broad
international field, the important milestones motivating future exploration,
and promising experimental opportunities to reach these milestones over the
next 5-10 years
Simplified Models for LHC New Physics Searches
This document proposes a collection of simplified models relevant to the
design of new-physics searches at the LHC and the characterization of their
results. Both ATLAS and CMS have already presented some results in terms of
simplified models, and we encourage them to continue and expand this effort,
which supplements both signature-based results and benchmark model
interpretations. A simplified model is defined by an effective Lagrangian
describing the interactions of a small number of new particles. Simplified
models can equally well be described by a small number of masses and
cross-sections. These parameters are directly related to collider physics
observables, making simplified models a particularly effective framework for
evaluating searches and a useful starting point for characterizing positive
signals of new physics. This document serves as an official summary of the
results from the "Topologies for Early LHC Searches" workshop, held at SLAC in
September of 2010, the purpose of which was to develop a set of representative
models that can be used to cover all relevant phase space in experimental
searches. Particular emphasis is placed on searches relevant for the first
~50-500 pb-1 of data and those motivated by supersymmetric models. This note
largely summarizes material posted at http://lhcnewphysics.org/, which includes
simplified model definitions, Monte Carlo material, and supporting contacts
within the theory community. We also comment on future developments that may be
useful as more data is gathered and analyzed by the experiments.Comment: 40 pages, 2 figures. This document is the official summary of results
from "Topologies for Early LHC Searches" workshop (SLAC, September 2010).
Supplementary material can be found at http://lhcnewphysics.or
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