105 research outputs found
Gauge Theories on Deformed Spaces
The aim of this review is to present an overview over available models and
approaches to non-commutative gauge theory. Our main focus thereby is on gauge
models formulated on flat Groenewold-Moyal spaces and renormalizability, but we
will also review other deformations and try to point out common features. This
review will by no means be complete and cover all approaches, it rather
reflects a highly biased selection.Comment: v2 references added; v3 published versio
Quantum Corrections for Translation-Invariant Renormalizable Non-Commutative Phi^4 Theory
In this paper we elaborate on the translation-invariant renormalizable Phi^4
theory in 4-dimensional non-commutative space which was recently introduced by
the Orsay group. By explicitly performing Feynman graph calculations at one
loop and higher orders we illustrate the mechanism which overcomes the UV/IR
mixing problem and ultimately leads to a renormalizable model. The obtained
results show that the IR divergences are also suppressed in the massless case,
which is of importance for the gauge field theoretic generalization of the
scalar field model.Comment: 18 pages, v2: slightly extended version including a new section on
one-loop renormalization, v3: minor revisio
Automated search for star clusters in large multiband surveys: II. Discovery and investigation of open clusters in the Galactic plane
Automated search for star clusters in J,H,K_s data from 2MASS catalog has
been performed using the method developed by Koposov et. al (2008). We have
found and verified 153 new clusters in the interval of the galactic latitude
-24 < b < 24 degrees. Color excesses E(B-V), distance moduli and ages were
determined for 130 new and 14 yet-unstudied known clusters. In this paper, we
publish a catalog of coordinates, diameters, and main parameters of all the
clusters under study. A special web-site available at http://ocl.sai.msu.ru has
been developed to facilitate dissemination and scientific usage of the results.Comment: 9 pages, 3 tables, 5 figures, accepted to Astronomy Letter
Automated search for galactic star clusters in large multiband surveys: I. Discovery of 15 new open clusters in the Galactic anticenter region
Aims: According to some estimations, there are as many as 100000 open
clusters in the Galaxy, but less than 2000 of them have been discovered,
measured, and cataloged. We plan to undertake data mining of multiwavelength
surveys to find new star clusters. Methods: We have developed a new method to
search automatically for star clusters in very large stellar catalogs, which is
based on convolution with density functions. We have applied this method to a
subset of the Two Micron All Sky Survey catalog toward the Galactic anticenter.
We also developed a method to verify whether detected stellar groups are real
star clusters, which tests whether the stars that form the spatial density peak
also fall onto a single isochrone in the color-magnitude diagram. By fitting an
isochrone to the data, we estimate at the same time the main physical
parameters of a cluster: age, distance, color excess. Results: For the present
paper, we carried out a detailed analysis of 88 overdensity peaks detected in a
field of degrees near the Galactic anticenter. From this analysis,
15 overdensities were confirmed to be new open clusters and the physical and
structural parameters were determined for 12 of them; 10 of them were
previously suspected to be open clusters by Kronberger (2006) and Froebrich
(2007). The properties were also determined for 13 yet-unstudied known open
clusters, thus almost tripling the sample of open clusters with studied
parameters in the anticenter. The parameters determined with this method showed
a good agreement with published data for a set of well-known clusters.Comment: accepted to A&
Rotation curve bifurcations as indicators of close recent galaxy encounters
Rotation curves of interacting galaxies often show that velocities are either
rising or falling in the direction of the companion galaxy. We seek to
reproduce and analyse these features in the rotation curves of simulated
equal-mass galaxies suffering a one-to-one encounter, as possible indicators of
close encounters. Using simulations of major mergers in 3D, we study the time
evolution of these asymmetries in a pair of galaxies, during the first passage.
Our main results are: (a) the rotation curve asymmetries appear right at
pericentre of the first passage, (b) the significant disturbed rotation
velocities occur within a small time interval, of ~ 0.5 Gyr h^-1, and therefore
the presence of bifurcation in the velocity curve could be used as an indicator
of the pericentre occurrence. These results are in qualitative agreement with
previous findings for minor mergers and fly-byes.Comment: 4 pages, 7 figure
Study of Microscopic Residual Stresses in an Extruded Aluminium Alloy Sample after Thermal Treatment
Abstract: A method is proposed to calculate the microscopic residual stresses in extruded cylindrical samples of non-ageing aluminium alloy 5083 (Al–Mg), arising from quenching in fresh water from 530°C. We start from the premise that the alloy is single-phase and non-isotropic on a microscopic scale; it consists of many grains that exhibit different mechanical response depending on their crystallographic orientation and neighboring grains. Microscopic residual stresses depend on the applied heat treatment, microstructure and mechanical strength of the individual grains. The stresses were calculated from neutron diffraction data. Genetic programming algorithms were used to calculate microscopic residual stresses, considering that each diffraction peak describes the stress distribution of a group of grains having a certain orientation, size and environment. The algorithm assigns a stress value to each grain according to the distribution of the diffraction peaks and the microstructural parameters of these grains.This work was supported by the Madrid Regional Government-FEDER grant Y2018/NMT-4668 (Micro-Stress-MAP-CM) and the project MAT2017-83825-C4-1-R. We would also like to express our gratitude to FLNR-JINP for the beam time allocated on the FSD instrument, and to the HeuristicLab Software developers
A New Approach to Non-Commutative U(N) Gauge Fields
Based on the recently introduced model of arXiv:0912.2634 for non-commutative
U(1) gauge fields, a generalized version of that action for U(N) gauge fields
is put forward. In this approach to non-commutative gauge field theories, UV/IR
mixing effects are circumvented by introducing additional 'soft breaking' terms
in the action which implement an IR damping mechanism. The techniques used are
similar to those of the well-known Gribov-Zwanziger approach to QCD.Comment: 11 pages; v2 minor correction
Commutative limit of a renormalizable noncommutative model
Renormalizable models on Moyal space have been obtained by
modifying the commutative propagator. But these models have a divergent "naive"
commutative limit. We explain here how to obtain a coherent such commutative
limit for a recently proposed translation-invariant model. The mechanism relies
on the analysis of the uv/ir mixing in general Feynman graphs.Comment: 11 pages, 3 figures, minor misprints being correcte
Kinematics and physical properties of Southern interacting galaxies: the minor merger AM 2306-721
We present an observational study about the effects of the interactions in
the kinematics, stellar population and abundances of the components of the
galaxy pair AM2306-721. Rotation curves for the main and companion galaxies
were obtained, showing a deprojected velocity amplitude of 175 km/s and 185
km/s, respectively. The interaction between the main and companion galaxies was
modeled using numerical N-body/hydrodynamical simulations, with the result
indicating that the current stage of the merger would be about 250 Myr after
perigalacticum. The spatial variation in the distribution of the stellar
population components in both galaxies was analysed by fitting combinations of
stellar population models of different age groups. The central region of main
galaxy is dominated by an old (5-10 Gyr) population, while significant
contributions from a young (200 Myr) and intermediate (1 Gyr) components are
found in the disk, being enhanced in the direction of the tidal features. The
stellar population of the companion galaxy is overall much younger, being
dominated by components with 1 Gyr or less, quite widely spread over the whole
disk. Spatial profiles of the oxygen abundance were obtained from the a grid of
photoionization models using the R23 line ratio. The disk of the main galaxy
shows a clear radial gradient, while the companion galaxy presents an oxygen
abundance relatively homogeneous across the disk. The absence of an abundance
gradient in the secondary galaxy is interpreted in terms of mixing by gas flows
from the outer parts to the center of the galaxy due to the gravitational
interaction with the more massive primary.Comment: 13 pages, 12 figures, accepted for publication on MNRA
Bottom up ethics - neuroenhancement in education and employment
Neuroenhancement involves the use of neurotechnologies to improve cognitive, affective or behavioural functioning, where these are not judged to be clinically impaired. Questions about enhancement have become one of the key topics of neuroethics over the past decade. The current study draws on in-depth public engagement activities in ten European countries giving a bottom-up perspective on the ethics and desirability of enhancement. This informed the design of an online contrastive vignette experiment that was administered to representative samples of 1000 respondents in the ten countries and the United States. The experiment investigated how the gender of the protagonist, his or her level of performance, the efficacy of the enhancer and the mode of enhancement affected support for neuroenhancement in both educational and employment contexts. Of these, higher efficacy and lower performance were found to increase willingness to support enhancement. A series of commonly articulated claims about the individual and societal dimensions of neuroenhancement were derived from the public engagement activities. Underlying these claims, multivariate analysis identified two social values. The Societal/Protective highlights counter normative consequences and opposes the use enhancers. The Individual/Proactionary highlights opportunities and supports use. For most respondents these values are not mutually exclusive. This suggests that for many neuroenhancement is viewed simultaneously as a source of both promise and concern
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