7,624 research outputs found
Model independent study of massive lepton elastic scattering on the proton, beyond the Born approximation
Model independent expressions for all polarization observables in elastic scattering are obtained, taking into account the lepton mass and
including the two-photon exchange contribution. The spin structure of the
matrix element is parametrized in terms of six independent complex amplitudes,
functions of two independent kinematical variables. General statements about
the influence of the two--photon--exchange terms on the differential cross
section and on polarization observables are given. Polarization effects have
been investigated for the case of a longitudinally polarized lepton beam and
polarized nucleon in the final state.Comment: 28 pages, 3 figure
Disentangling the Hercules stream
Using high-resolution spectra of nearby F and G dwarf stars, we have
investigated the detailed abundance and age structure of the Hercules stream.
We find that the stars in the stream have a wide range of stellar ages,
metallicities, and element abundances. By comparing to existing samples of
stars in the solar neighbourhood with kinematics typical of the Galactic thin
and thick disks we find that the properties of the Hercules stream distinctly
separate into the abundance and age trends of the two disks. Hence, we find it
unlikely that the Hercules stream is a unique Galactic stellar population, but
rather a mixture of thin and thick disk stars. This points toward a dynamical
origin for the Hercules stream, probably caused by the Galactic bar.Comment: Accepted for publication in ApJ Letter
A pure S-wave covariant model for the nucleon
Using the manifestly covariant spectator theory, and modeling the nucleon as
a system of three constituent quarks with their own electromagnetic structure,
we show that all four nucleon electromagnetic form factors can be very well
described by a manifestly covariant nucleon wave function with zero orbital
angular momentum. Since the concept of wave function depends on the formalism,
the conclusions of light-cone theory requiring nonzero angular momentum
components are not inconsistent with our results. We also show that our model
gives a qualitatively correct description of deep inelastic scattering,
unifying the phenomenology at high and low momentum transfer. Finally we review
two different definitions of nuclear shape and show that the nucleon is
spherical in this model, regardless of how shape is defined.Comment: 20 pages and 10 figures; greatly expanded version with new fits and
discussion of DIS; similar to published versio
Calibration of the CH and CN Variations Among Main Sequence Stars in M71 and in M13
An analysis of the CN and CH band strengths measured in a large sample of M71
and M13 main sequence stars by Cohen (1999a,b) is undertaken using synthetic
spectra to quantify the underlying C and N abundances. In the case of M71 it is
found that the observed CN and CH band strengths are best matched by the
{\it{identical}} C/N/O abundances which fit the bright giants, implying: 1)
little if any mixing is taking place during red giant branch ascent in M71, and
2) a substantial component of the C and N abundance inhomogeneities is in place
before the main sequence turn-off. The unlikelihood of mixing while on the main
sequence requires an explanation for the abundance variations which lies
outside the present stars (primordial inhomogeneities or intra-cluster self
enrichment). For M13 it is shown that the 3883\AA CN bands are too weak to be
measured in the spectra for any reasonable set of expected compositions. A
similar situation exists for CH as well. However, two of the more luminous
program stars do appear to have C abundances considerably greater than those
found among the bright giants thereby suggesting deep mixing has taken place on
the M13 red giant branch.Comment: 14 pages, 4 figures, accepted for publication by A
Search for evidence of two photon contribution in elastic electron proton data
We reanalyze the most recent data on elastic electron proton scattering. We
look for a deviation from linearity of the Rosenbluth fit to the differential
cross section, which would be the signature of the presence of two photon
exchange. The two photon contribution is parametrized by a one parameter
formula, based on symmetry arguments. The present data do not show evidence for
such deviation.Comment: 15 pages 3 figures More details on the fitting procedure, more
explicit explanation
Tracing the Galactic thick disk to Solar metallicities
We show that the Galactic thick disk reaches at least solar metallicities,
and that it experienced strong chemical enrichment during a period of ~3 Gyr,
ending around 8-9 Gyr ago. This finding puts further constraints on the
relation and interface between the thin and thick disks, and their formation
processes. Our results are based on a detailed elemental abundance analysis of
261 kinematically selected F and G dwarf stars in the solar neighborhood: 194
likely members of the thick disk and 67 likely members of the thin disk, in the
range -1.3<[Fe/H]<+0.4.Comment: Accepted for publication in ApJ Letter
Mira's wind explored in scattering infrared CO lines
We have observed the intermediate regions of the circumstellar envelope of
Mira (o Ceti) in photospheric light scattered by three vibration-rotation
transitions of the fundamental band of CO, from low-excited rotational levels
of the ground vibrational state, at an angular distance of beta = 2"-7" away
from the star. The data were obtained with the Phoenix spectrometer mounted on
the 4 m Mayall telescope at Kitt Peak. The spatial resolution is approximately
0.5" and seeing limited. Our observations provide absolute fluxes, leading to
an independent new estimate of the mass-loss rate of approximately 3e-7
Msun/yr, as derived from a simple analytic wind model. We find that the
scattered intensity from the wind of Mira for 2" < beta < 7" decreases as
beta^-3, which suggests a time constant mass-loss rate, when averaged over 100
years, over the past 1200 years.Comment: accepted for publication in the Astrophysical Journa
Aircraft engine fleet monitoring using Self-Organizing Maps and Edit Distance
International audienceAircraft engines are designed to be used during several tens of years. Ensuring a proper operation of engines over their lifetime is therefore an important and difficult task. The maintenance can be improved if efficient procedures for the understanding of data flows produced by sensors for monitoring purposes are implemented. This paper details such a procedure aiming at visualizing in a meaningful way successive data measured on aircraft engines and finding for every possible request sequence of data measurement similar behaviour already observed in the past which may help to anticipate failures. The core of the procedure is based on Self-Organizing Maps (SOM) which are used to visualize the evolution of the data measured on the engines. Rough measurements can not be directly used as inputs, because they are influenced by external conditions. A preprocessing procedure is set up to extract meaningful information and remove uninteresting variations due to change of environmental conditions. The proposed procedure contains four main modules to tackle these difficulties: environmental conditions normalization (ECN), change detection and adaptive signal modeling (CD), visualization with Self-Organizing Maps (SOM) and finally minimal Edit Distance search (SEARCH). The architecture of the procedure and of its modules is described in this paper and results on real data are also supplied
Toward a precision, complexity-informed cultural policy design: Structural bottlenecks to culture-led development in Skaraborg, Sweden
We analyze the spatial-temporal dynamics of cultural vibrancy in the Swedish sub-region of Skaraborg. Our database consists of 4170 geo-localized cultural activities and facilities, mapped between October 2013 and March 2014. We make use of the TWC methodology for the dynamic simulation of the evolution of geo-localized activity starting from an observed distribution of events, and of the AutoCM ANN architecture to understand how cultural variables are related to the rest of the Skaraborg socio-economy. We find that cultural vibrancy in Skaraborg is likely characterized by a 'flaring' pattern of initial, widespread activity followed by a re-concentration into the main local urban hubs. The deep reason behind this unsuccessful developmental trajectory is the lack of centrality of cultural production in the local socio-economy, and of integration across cultural production sectors. This is in turn due also to structural bottlenecks of a non-cultural nature such as insufficient access of women to higher education. We make a case for the necessity to develop a new precision cultural policy design approach founded upon the science of complexity for both policy design and assessment, and we provide and illustrate a first technical toolkit to this purpose.(c) 2022 Elsevier B.V. All rights reserved
A nonlinear, data-driven, ANNs-based approach to culture-led development policies in rural areas: The case of Gjakove and Pee districts, Western Kosovo
We develop a computational approach to the analysis of cultural vibrancy and to the role of the cultural and cre-ative sectors in the socio-economic organization of two districts of Western Kosovo, Gjakove and Pee. Our anal-ysis is built on a geolocalized mapping of the cultural activities and facilities, and on the main socio-economic variables for the two districts, and makes use of innovative data analysis techniques: Theory of Impossible Words (TIW), the Topological Weighted Centroid (TWC), and the AutoCM ANN. We find that the dynamics of cul-tural vibrancy of the territory is mainly driven by the competing attraction pulls of the nearby countries of Serbia and Albania, that also form the region's main and often conflicting ethnicities, and that such dynamics are likely to further polarize in the future. We also find that the cultural system plays a marginal role in the territory's socio-economic organization. This situation makes a case for a more active role of cultural policy in shaping future local developmental models in rural areas and in acting as an agent of social cohesion.(c) 2022 Elsevier Ltd. All rights reserved
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