53,249 research outputs found
A model for the time uncertainty measurements in the Auger surface detector array
The precise determination of the arrival direction of cosmic rays is a
fundamental prerequisite for the search for sources or the study of their
anisotropies on the sky. One of the most important aspects to achieve an
optimal measurement of these directions is to properly take into account the
measurement uncertainties in the estimation procedure. In this article we
present a model for the uncertainties associated with the time measurements in
the Auger surface detector array. We show that this model represents well the
measurement uncertainties and therefore provides the basis for an optimal
determination of the arrival direction. With this model and a description of
the shower front geometry it is possible to estimate, on an event by event
basis, the uncertainty associated with the determination of the arrival
directions of the cosmic rays
Analytical BPS Maxwell-Higgs vortices
We have established a prescription for the calculation of analytical vortex
solutions in the context of generalized Maxwell-Higgs models whose overall
dynamics is controlled by two positive functions of the scalar field. We have
also determined a natural constraint between these functions and the Higgs
potential allowing the existence of axially symmetric
Bogomol'nyi-Prasad-Sommerfield (BPS) solutions possessing finite energy.
Furthermore, when the generalizing functions are chosen suitably, the
nonstandard BPS equations can be solved exactly. We have studied some examples,
comparing them with the usual Abrikosov-Nielsen-Olesen (ANO) solution. The
overall conclusion is that the analytical self-dual vortices are well-behaved
in all relevant sectors, strongly supporting the generalized models they belong
themselves. In particular, our results mimic well-known properties of the usual
(numerical) configurations, as localized energy density, while contributing to
the understanding of topological solitons and their description by means of
analytical methods.Comment: 8 pages, 4 figure
Universal and deterministic manipulation of the quantum state of harmonic oscillators: a route to unitary gates for Fock State qubits
We present a simple quantum circuit that allows for the universal and
deterministic manipulation of the quantum state of confined harmonic
oscillators. The scheme is based on the selective interactions of the referred
oscillator with an auxiliary three-level system and a classical external
driving source, and enables any unitary operations on Fock states, two-by-two.
One circuit is equivalent to a single qubit unitary logical gate on Fock states
qubits. Sequences of similar protocols allow for complete, deterministic and
state-independent manipulation of the harmonic oscillator quantum state.Comment: 4 pages, 4 figure
A Bayesian estimate of the CMB-large-scale structure cross-correlation
Evidences for late-time acceleration of the Universe are provided by multiple
probes, such as Type Ia supernovae, the cosmic microwave background (CMB) and
large-scale structure (LSS). In this work, we focus on the integrated
Sachs--Wolfe (ISW) effect, i.e., secondary CMB fluctuations generated by
evolving gravitational potentials due to the transition between, e.g., the
matter and dark energy (DE) dominated phases. Therefore, assuming a flat
universe, DE properties can be inferred from ISW detections. We present a
Bayesian approach to compute the CMB--LSS cross-correlation signal. The method
is based on the estimate of the likelihood for measuring a combined set
consisting of a CMB temperature and a galaxy contrast maps, provided that we
have some information on the statistical properties of the fluctuations
affecting these maps. The likelihood is estimated by a sampling algorithm,
therefore avoiding the computationally demanding techniques of direct
evaluation in either pixel or harmonic space. As local tracers of the matter
distribution at large scales, we used the Two Micron All Sky Survey (2MASS)
galaxy catalog and, for the CMB temperature fluctuations, the ninth-year data
release of the Wilkinson Microwave Anisotropy Probe (WMAP9). The results show a
dominance of cosmic variance over the weak recovered signal, due mainly to the
shallowness of the catalog used, with systematics associated with the sampling
algorithm playing a secondary role as sources of uncertainty. When combined
with other complementary probes, the method presented in this paper is expected
to be a useful tool to late-time acceleration studies in cosmology.Comment: 21 pages, 15 figures, 4 tables. We extended the previous analyses
including WMAP9 Q, V and W channels, besides the ILC map. Updated to match
accepted ApJ versio
Coherent State Path Integrals in the Weyl Representation
We construct a representation of the coherent state path integral using the
Weyl symbol of the Hamiltonian operator. This representation is very different
from the usual path integral forms suggested by Klauder and Skagerstan in
\cite{Klau85}, which involve the normal or the antinormal ordering of the
Hamiltonian. These different representations, although equivalent quantum
mechanically, lead to different semiclassical limits. We show that the
semiclassical limit of the coherent state propagator in Weyl representation is
involves classical trajectories that are independent on the coherent states
width. This propagator is also free from the phase corrections found in
\cite{Bar01} for the two Klauder forms and provides an explicit connection
between the Wigner and the Husimi representations of the evolution operator.Comment: 23 page
Dynamical evolution of V-type asteroids in the central main belt
V-type asteroids are associated with basaltic composition, and are supposed
to be fragments of crust of differentiated objects. Most V-type asteroids in
the main belt are found in the inner main belt, and are either current members
of the Vesta dynamical family (Vestoids), or past members that drifted away.
However, several V-type photometric candidates have been recently identified in
the central and outer main belt.
The origin of this large population of V-type objects is not well understood.
Since it seems unlikely that Vestoids crossing the 3J:-1A mean-motion resonance
with Jupiter could account for the whole population of V-type asteroids in the
central and outer main belt, origin from local sources, such as the parent
bodies of the Eunomia, and of the Merxia and Agnia asteroid families, has been
proposed as an alternative mechanism.
In this work we investigated the dynamical evolution of the V-type
photometric candidates in the central main belt, under the effect of
gravitational and non-gravitational forces. Our results show that dynamical
evolution from the parent bodies of the Eunomia and Merxia/Agnia families on
timescales of 2 Byr or more could be responsible for the current orbital
location of most of the low-inclined V-type asteroids.Comment: 16 pages, 10 figures, 3 tables. Accepted for publication in MNRA
Dynamical evolution and chronology of the Hygiea asteroid family
The asteroid (10) Hygiea is the fourth largest asteroid of the Main Belt, by
volume and mass, and it is the largest member of its own family. Previous works
investigated the long-term effects of close encounters with (10) Hygiea of
asteroids in the orbital region of the family, and analyzed the taxonomical and
dynamical properties of members of this family. In this paper we apply the
high-quality SDSS-MOC4 taxonomic scheme of DeMeo and Carry (2013) to members of
the Hygiea family core and halo, we obtain an estimate of the minimum time and
number of encounter necessary to obtain a (or 99.7%) compatible
frequency distribution function of changes in proper caused by close
encounters with (10) Hygiea, we study the behavior of asteroids near secular
resonance configurations, in the presence and absence of the Yarkovsky force,
and obtain a first estimate of the age of the family based on orbital diffusion
by the Yarkovsky and YORP effects with two methods.
The Hygiea family is at least 2 Byr old, with an estimated age of Myr and a relatively large initial ejection velocity field,
according to the approach of Vokrouhlick\'{y} et al. (2006a, b). Surprisingly,
we found that the family age can be shortened by 25% if the dynamical
mobility caused by close encounters with (10) Hygiea is also accounted for,
which opens interesting new research lines for the dynamical evolution of
families associated with massive bodies. In our taxonomical analysis of the
Hygiea asteroid family, we also identified a new V-type candidate: the asteroid
(177904) (2005 SV5). If confirmed, this could be the fourth V-type object ever
to be identified in the outer main belt.Comment: 13 page, 15 figures, and 4 table
Observational Constraints on Visser's Cosmological Model
Theories of gravity for which gravitons can be treated as massive particles
have presently been studied as realistic modifications of General Relativity,
and can be tested with cosmological observations. In this work, we study the
ability of a recently proposed theory with massive gravitons, the so-called
Visser theory, to explain the measurements of luminosity distance from the
Union2 compilation, the most recent Type-Ia Supernovae (SNe Ia) dataset,
adopting the current ratio of the total density of non-relativistic matter to
the critical density () as a free parameter. We also combine the SNe
Ia data with constraints from Baryon Acoustic Oscillations (BAO) and CMB
measurements. We find that, for the allowed interval of values for ,
a model based on Visser's theory can produce an accelerated expansion period
without any dark energy component, but the combined analysis (SNe Ia + BAO +
CMB) shows that the model is disfavored when compared with CDM model.Comment: 6 pages, 4 figure
Response of key stress-related genes of the seagrass Posidonia oceanica in the vicinity of submarine volcanic vents
Submarine volcanic vents are being used as natural laboratories to assess the effects of increased ocean acidity and carbon dioxide (CO2) concentration on marine organisms and communities. However, in the vicinity of volcanic vents other factors in addition to CO2, which is the main gaseous component of the emissions, may directly or indirectly confound the biota responses to high CO2. Here we used for the first time the expression of antioxidant and stress-related genes of the seagrass Posidonia oceanica to assess the stress levels of the species. Our hypothesis is that unknown factors are causing metabolic stress that may confound the putative effects attributed to CO2 enrichment only. We analyzed the expression of 35 antioxidant and stress-related genes of P. oceanica in the vicinity of submerged volcanic vents located in the islands of Ischia and Panarea, Italy, and compared them with those from control sites away from the influence of vents. Reverse-transcription quantitative polymerase chain reaction (RT-qPCR) was used to characterize gene expression patterns. Fifty-one percent of genes analyzed showed significant expression changes. Metal detoxification genes were mostly down-regulated in relation to controls at both Ischia and Panarea, indicating that P. oceanica does not increase the synthesis of heavy metal detoxification proteins in response to the environmental conditions present at the two vents. The up-regulation of genes involved in the free radical detoxification response (e.g., CAPX, SODCP and GR) indicates that, in contrast with Ischia, P. oceanica at the Panarea site faces stressors that result in the production of reactive oxygen species, triggering antioxidant responses. In addition, heat shock proteins were also activated at Panarea and not at Ischia. These proteins are activated to adjust stress-accumulated misfolded proteins and prevent their aggregation as a response to some stressors, not necessarily high temperature. This is the first study analyzing the expression of target genes in marine plants living near natural CO2 vents. Our results call for contention to the general claim of seagrasses as "winners" in a high-CO2 world, based on observations near volcanic vents. Careful consideration of factors that are at play in natural vents sites other than CO2 and acidification is required. This study also constitutes a first step for using stress-related genes as indicators of environmental pressures in a changing ocean.project HighGrass "High-CO2 effects on seagrass photosynthetic ecophysiology" [PTDC/MAREST/3687/2012]; MIUR Italian flagship project RITMARE; ESF COST Action "Seagrass Productivity: from genes to ecosystem management
- …