2,880 research outputs found
Emergent electrodynamics from the Nambu model for spontaneous Lorentz symmetry breaking
After imposing the Gauss law constraint as an initial condition upon the
Hilbert space of the Nambu model, in all its generic realizations, we recover
QED in the corresponding non-linear gauge A_{\mu}A^{\mu}=n^{2}M^{2}. Our result
is non-perturbative in the parameter M for n^{2}\neq 0 and can be extended to
the n^{2}=0 case. This shows that in the Nambu model, spontaneous Lorentz
symmetry breaking dynamically generates gauge invariance, provided the Gauss
law is imposed as an initial condition. In this way electrodynamics is
recovered, with the photon being realized as the Nambu-Goldstone modes of the
spontaneously broken symmetry, which finally turns out to be non-observableComment: 17 page
An Overview of Variational Integrators
The purpose of this paper is to survey some recent advances in variational
integrators for both finite dimensional mechanical systems as well as continuum
mechanics. These advances include the general development of discrete
mechanics, applications to dissipative systems, collisions, spacetime integration algorithms,
AVI’s (Asynchronous Variational Integrators), as well as reduction for
discrete mechanical systems. To keep the article within the set limits, we will only
treat each topic briefly and will not attempt to develop any particular topic in
any depth. We hope, nonetheless, that this paper serves as a useful guide to the
literature as well as to future directions and open problems in the subject
Evolution of Binary Stars in Multiple-Population Globular Clusters - II. Compact Binaries
We present the results of a survey of N-body simulations aimed at exploring
the evolution of compact binaries in multiple-population globular clusters.We
show that as a consequence of the initial differences in the structural
properties of the first-generation (FG) and the second-generation (SG)
populations and the effects of dynamical processes on binary stars, the SG
binary fraction decreases more rapidly than that of the FG population. The
difference between the FG and SG binary fraction is qualitatively similar to
but quantitatively smaller than that found for wider binaries in our previous
investigations.The evolution of the radial variation of the binary fraction is
driven by the interplay between binary segregation, ionization and ejection.
Ionization and ejection counteract in part the effects of mass segregation but
for compact binaries the effects of segregation dominate and the inner binary
fraction increases during the cluster evolution. We explore the variation of
the difference between the FG and the SG binary fraction with the distance from
the cluster centre and its dependence on the binary binding energy and cluster
structural parameters. The difference between the binary fraction in the FG and
the SG populations found in our simulations is consistent with the results of
observational studies finding a smaller binary fraction in the SG population.Comment: 9 pages, 12 figures. Accepted for publication in MNRA
Evolution of Binary Stars in Multiple-Population Globular Clusters
The discovery of multiple stellar populations in globular clusters has
implications for all the aspects of the study of these stellar systems. In this
paper, by means of N-body simulations, we study the evolution of binary stars
in multiple-population clusters and explore the implications of the initial
differences in the spatial distribution of different stellar populations for
the evolution and survival of their binary stars. Our simulations show that
initial differences between the spatial distribution of first-generation (FG)
and second-generation (SG) stars can leave a fingerprint in the current
properties of the binary population. SG binaries are disrupted more efficiently
than those of the FG population resulting in a global SG binary fraction
smaller than that of the FG. As for surviving binaries, dynamical evolution
produces a difference between the SG and the FG binary binding energy
distribution with the SG population characterized by a larger fraction of high
binding energy (more bound) binaries. We have also studied the dependence of
the binary properties on the distance from the cluster centre. Although the
global binary fraction decreases more rapidly for the SG population, the local
binary fraction measured in the cluster inner regions may still be dominated by
SG binaries. The extent of the differences between the surviving FG and SG
binary binding energy distribution also varies radially within the cluster and
is larger in the cluster inner regions.Comment: 10 pages, 12 figures. Accepted for publication in MNRA
A survey of UV-excess AGNs in the South Galactic Pole
Spectra, position, magnitudes and colors are presented for 485 faint (B<20.5)
emission line objects selected with the ultraviolet-excess (UVX) criterion on a
area of 24.6 sq. deg in the South Galactic Pole. The objects were selected from
the analysis of pixel-to-pixel stacking of COSMOS scans of UKST U, J and R
plates. The candidates were observed with the Meudon-ESO Fiber Optics System
(MEFOS) at the ESO 3.6m telescope. 429 type 1 AGNs have been identified (373 in
the redshift range 0.3<z<2.2). This sample has allowed the measure of a
difference on the QSO clustering evolution in comparison with that found for
galaxies (La Franca et al 1998). The region is part of the ESO Imaging Survey
(EIS) and of the 2dF QSO redshift survey.Comment: 32 pages, 19 figures. To appear on A&AS, revised after minor comment
Shyness and Psychological Adjustment During Adolescence: The Moderating Role of Parenting Style
Although shyness constitutes a risk factor for maladjustment, parenting style may influence these developmental trajectories during childhood. Little is known about the role of parental style in the relationship between shyness and psychological adjustment during adolescence.Aims: To explore the relationship between shyness and parenting style and to analyse the moderating role of the quality of parenting in the relationship between shyness and internalizing difficulties during adolescence.Method: 787 11 to 19 year-old participants (divided in early and late adolescents) were recruited for this study. Participants completed Revised Cheek and Buss Shyness Scale, Parental Bonding Instrument and internalizing scale of Youth Self Report.Results: Shy adolescents perceived parents to be less warm and close, less encouraging of their autonomy and independence, and more overprotective and intrusive than did other participants. During early-adolescence participants who perceived their parents as supportive and not intrusive showed significantly fewer internalizing problems related to shynes
Histopathological diagnosis and surgical complications following bilateral anal sacculectomy for the treatment of unilateral canine apocrine gland anal sac adenocarcinoma - 35 cases (2019-2023)
OBJECTIVES: To report the histopathological diagnosis of both anal sacs in dogs undergoing bilateral anal sacculectomy for the treatment of unilateral apocrine gland anal sac adenocarcinoma and to compare the surgical complication rate associated with this procedure in this population with previously published literature.MATERIALS AND METHODS: Records were retrospectively reviewed for dogs that underwent bilateral anal sacculectomy for the treatment of apparently unilateral apocrine gland anal sac adenocarcinoma, at a single institute between 2019 and 2023. Clinical staging, surgical treatment, histological findings, intra- and postoperative complications were evaluated.RESULTS: Thirty-five dogs were included. Only five of 35 (14%) dogs were found to have histologically normal contralateral anal sacs. Non-neoplastic anal sac disease was found in 23 of 35 (66%) dogs and bilateral apocrine gland anal sac adenocarcinoma was seen in seven of 35 (20%) dogs. None of the dogs diagnosed with bilateral neoplasia had evidence of bilateral neoplasia before surgery despite a thorough work-up. Complications attributable to the primary tumour removal were seen in 9% of dogs intraoperatively and 14% of dogs postoperatively, commonly tumour capsule disruption and surgical site infection, respectively.CLINICAL SIGNIFICANCE: Bilateral anal sac disease was diagnosed histologically in the majority of presumed normal anal sacs, with 20% of cases being found to have bilateral apocrine gland anal sac adenocarcinoma. The surgical complication rates of this cohort were comparable to those reported for unilateral anal sacculectomy alone. These findings promote and encourage the use of bilateral anal sacculectomy in cases of suspected unilateral anal sac neoplasia.</p
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