12,477 research outputs found
Pion mass effects on axion emission from neutron stars through NN bremsstrahlung processes
The rates of axion emission by nucleon-nucleon bremsstrahlung are calculated
with the inclusion of the full momentum contribution from a nuclear one pion
exchange (OPE) potential. The contributions of the neutron-neutron (nn),
proton-proton (pp) and neutron-proton (np) processes in both the nondegenerate
and degenerate limits are explicitly given. We find that the finite momentum
corrections to the emissivities are quantitatively significant for the
non-degenerate regime and temperature-dependent, and should affect the existing
axion mass bounds. The trend of these nuclear effects is to diminish the
emissivities
Self-bound models of compact stars and recent mass-radius measurements
The exact composition of a specific class of compact stars, historically
referred to as "neutron stars", is still quite unknown. Possibilities ranging
from hadronic to quark degrees of freedom, including self-bound versions of the
latter have been proposed. We specifically address the suitability of strange
star models (including pairing interactions) in this work, in the light of new
measurements available for four compact stars. The analysis shows that these
data might be explained by such an exotic equation of state, actually selecting
a small window in parameter space, but still new precise measurements and also
further theoretical developments are needed to settle the subject.Comment: To appear in PR
Coherent Topological Charge Structure in Models and QCD
In an effort to clarify the significance of the recent observation of
long-range topological charge coherence in QCD gauge configurations, we study
the local topological charge distributions in two-dimensional sigma
models, using the overlap Dirac operator to construct the lattice topological
charge. We find long-range sign coherence of topological charge along extended
one-dimensional structures in two-dimensional spacetime. We discuss the
connection between the long range topological structure found in and
the observed sign coherence along three-dimensional sheets in four-dimensional
QCD gauge configurations. In both cases, coherent regions of topological charge
form along membrane-like surfaces of codimension one. We show that the Monte
Carlo results, for both two-dimensional and four-dimensional gauge theory,
support a view of topological charge fluctuations suggested by Luscher and
Witten. In this framework, the observed membranes are associated with
boundaries between ``k-vacua,'' characterized by an effective local value of
which jumps by across the boundary.Comment: 26 page
Gene Targeting Without DSB Induction Is Inefficient in Barley
Double strand-break (DSB) induction allowed efficient gene targeting in barley (Hordeum vulgare), but little is known about efficiencies in its absence. To obtain such data, an assay system based on the acetolactate synthase (ALS) gene was established, a target gene which had been used previously in rice and Arabidopsis thaliana. Expression of recombinases RAD51 and RAD54 had been shown to improve gene targeting in A. thaliana and positive-negative (P-N) selection allows the routine production of targeted mutants without DSB induction in rice. We implemented these approaches in barley and analysed gene targeting with the ALS gene in wild type and RAD51 and RAD54 transgenic lines. In addition, P-N selection was tested. In contrast to the high gene targeting efficiencies obtained in the absence of DSB induction in A. thaliana or rice, not one single gene targeting event was obtained in barley. These data suggest that gene targeting efficiencies are very low in barley and can substantially differ between different plants, even at the same target locus. They also suggest that the amount of labour and time would become unreasonably high to use these methods as a tool in routine applications. This is particularly true since DSB induction offers efficient alternatives. Barley, unlike rice and A. thaliana has a large, complex genome, suggesting that genome size or complexity could be the reason for the low efficiencies. We discuss to what extent transformation methods, genome size or genome complexity could contribute to the striking differences in the gene targeting efficiencies between barley, rice and A. thaliana
Bird's-eye view on Noise-Based Logic
Noise-based logic is a practically deterministic logic scheme inspired by the
randomness of neural spikes and uses a system of uncorrelated stochastic
processes and their superposition to represent the logic state. We briefly
discuss various questions such as (i) What does practical determinism mean?
(ii) Is noise-based logic a Turing machine? (iii) Is there hope to beat (the
dreams of) quantum computation by a classical physical noise-based processor,
and what are the minimum hardware requirements for that? Finally, (iv) we
address the problem of random number generators and show that the common belief
that quantum number generators are superior to classical (thermal) noise-based
generators is nothing but a myth.Comment: paper in pres
Curvature energy effects on strange quark matter nucleation at finite density
We consider the effects of the curvature energy term on thermal strange quark
matter nucleation in dense neutron matter. Lower bounds on the temperature at
which this process can take place are given and compared to those without the
curvature term.Comment: PlainTex, 6 pp., IAG-USP Rep.5
Manipulation and generation of synthetic satellite images using deep learning models
Generation and manipulation of digital images based on deep learning (DL) are receiving increasing attention for both benign and malevolent uses. As the importance of satellite imagery is increasing, DL has started being used also for the generation of synthetic satellite images. However, the direct use of techniques developed for computer vision applications is not possible, due to the different nature of satellite images. The goal of our work is to describe a number of methods to generate manipulated and synthetic satellite images. To be specific, we focus on two different types of manipulations: full image modification and local splicing. In the former case, we rely on generative adversarial networks commonly used for style transfer applications, adapting them to implement two different kinds of transfer: (i) land cover transfer, aiming at modifying the image content from vegetation to barren and vice versa and (ii) season transfer, aiming at modifying the image content from winter to summer and vice versa. With regard to local splicing, we present two different architectures. The first one uses image generative pretrained transformer and is trained on pixel sequences in order to predict pixels in semantically consistent regions identified using watershed segmentation. The second technique uses a vision transformer operating on image patches rather than on a pixel by pixel basis. We use the trained vision transformer to generate synthetic image segments and splice them into a selected region of the to-be-manipulated image. All the proposed methods generate highly realistic, synthetic, and satellite images. Among the possible applications of the proposed techniques, we mention the generation of proper datasets for the evaluation and training of tools for the analysis of satellite images. (c) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI
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