231 research outputs found
Tidal evolution of exo-planetary systems: WASP-50, GJ 1214 and CoRoT-7
We perform numerical simulations to investigate tidal evolution of two
single-planet systems, that is, WASP-50 and GJ 1214 and a two-planet system
CoRoT-7. The results of orbital evolution show that tidal decay and
circularization may play a significant role in shaping their final orbits,
which is related to the initial orbital data in the simulations. For GJ 1214
system, different cases of initial eccentricity are also considered as only an
upper limit of its eccentricity (0.27) is shown, and the outcome suggests a
possible maximum initial eccentricity (0.4) in the adopted dynamical model.
Moreover, additional runs with alternative values of dissipation factor
are carried out to explore tidal evolution for GJ 1214b, and these
results further indicate that the real of GJ 1214b may be much
larger than its typical value, which may reasonably suggest that GJ 1214b bears
a present-day larger eccentricity, undergoing tidal circularization at a slow
rate. For the CoRoT-7 system, tidal forces make two planets migrating towards
their host star as well as producing tidal circularization, and in this process
tidal effects and mutual gravitational interactions are coupled with each
other. Various scenarios of the initial eccentricity of the outer planet have
also been done to investigate final planetary configuration. Tidal decay
arising from stellar tides may still work for each system as the eccentricity
decreases to zero, and this is in association with the remaining lifetime of
each planet used to predict its future.Comment: 9 pages, 12 figures, accepted for publication in "SCIENCE CHINA
Physics,Mechanics & Astronomy
Homogeneizacion reiterada de un problema de contorno unidimensional
The asymptotic homogenization method is applied to homogenize a one-dimensional family of elliptic boundary value problems with periodic and rapidly oscillating coefficients which depend on two fast variables. The homogenized problem, the local problems and the corresponding effective coefficient are obtained. A necessary and sufficient condition for constructing an asymptotic solution with periodic terms is demonstrated. Based on a Maximum Principle the proximity between the solutions of the homogenized and original problems is proved. Some numerical computations are used to illustrate the mathematical justificationEl metodo de homogeneizacion asintotica es aplicado para homogeneizar una familia unidimensional de problemas elıpticos, con coeficientes periodicos y rapidamente oscilantes que dependen de dos variables rapidas. El problema homogeneizado, los problemas locales y los correspondientes coeficientes efectivos son obtenidos. Una condicion necesaria y suficiente para la construccion de una solucion asintotica con terminos periodicos es demostrada. Basados en el principio del maximo, se demuestra la proximidad entre la soluci´on del problema homogeneizado y la del problema original. Se propone un ejemplo numerico para ilustrar la justificacion matematica
Deep X-ray and radio observations of the first outburst of the young magnetar Swift J1818.0-1607
Swift J1818.0-1607 is a radio-loud magnetar with a spin period of 1.36 s and
a dipolar magnetic field strength of B~3E14 G, which is very young compared to
the Galactic pulsar population. We report here on the long-term X-ray
monitoring campaign of this young magnetar using XMM-Newton, NuSTAR, and Swift
from the activation of its first outburst in March 2020 until October 2021, as
well as INTEGRAL upper limits on its hard X-ray emission. The 1-10 keV magnetar
spectrum is well modeled by an absorbed blackbody with a temperature of
kT_BB~1.1 keV, and apparent reduction in the radius of the emitting region from
~0.6 to ~0.2 km. We also confirm the bright diffuse X-ray emission around the
source extending between ~50'' and ~110''. A timing analysis revealed large
torque variability, with an average spin-down rate nudot~-2.3E-11 Hz^2 that
appears to decrease in magnitude over time. We also observed Swift J1818.0-1607
with the Karl G. Jansky Very Large Array (VLA) on 2021 March 22. We detected
the radio counterpart to Swift J1818.0-1607 measuring a flux density of S_v =
4.38+/-0.05 mJy at 3 GHz, and a half ring-like structure of bright diffuse
radio emission located at ~90'' to the west of the magnetar. We tentatively
suggest that the diffuse X-ray emission is due to a dust scattering halo and
that the radio structure may be associated with the supernova remnant of this
young pulsar, based on its morphology.Comment: 19 pages, 8 figures, accepted for publication on Ap
Anisotropy and chemical composition of ultra-high energy cosmic rays using arrival directions measured by the Pierre Auger Observatory
The Pierre Auger Collaboration has reported evidence for anisotropy in the
distribution of arrival directions of the cosmic rays with energies
eV. These show a correlation with the distribution
of nearby extragalactic objects, including an apparent excess around the
direction of Centaurus A. If the particles responsible for these excesses at
are heavy nuclei with charge , the proton component of the
sources should lead to excesses in the same regions at energies . We here
report the lack of anisotropies in these directions at energies above
(for illustrative values of ). If the anisotropies
above are due to nuclei with charge , and under reasonable
assumptions about the acceleration process, these observations imply stringent
constraints on the allowed proton fraction at the lower energies
Advanced functionality for radio analysis in the Offline software framework of the Pierre Auger Observatory
The advent of the Auger Engineering Radio Array (AERA) necessitates the
development of a powerful framework for the analysis of radio measurements of
cosmic ray air showers. As AERA performs "radio-hybrid" measurements of air
shower radio emission in coincidence with the surface particle detectors and
fluorescence telescopes of the Pierre Auger Observatory, the radio analysis
functionality had to be incorporated in the existing hybrid analysis solutions
for fluoresence and surface detector data. This goal has been achieved in a
natural way by extending the existing Auger Offline software framework with
radio functionality. In this article, we lay out the design, highlights and
features of the radio extension implemented in the Auger Offline framework. Its
functionality has achieved a high degree of sophistication and offers advanced
features such as vectorial reconstruction of the electric field, advanced
signal processing algorithms, a transparent and efficient handling of FFTs, a
very detailed simulation of detector effects, and the read-in of multiple data
formats including data from various radio simulation codes. The source code of
this radio functionality can be made available to interested parties on
request.Comment: accepted for publication in NIM A, 13 pages, minor corrections to
author list and references in v
Search for First Harmonic Modulation in the Right Ascension Distribution of Cosmic Rays Detected at the Pierre Auger Observatory
We present the results of searches for dipolar-type anisotropies in different
energy ranges above eV with the surface detector array of
the Pierre Auger Observatory, reporting on both the phase and the amplitude
measurements of the first harmonic modulation in the right-ascension
distribution. Upper limits on the amplitudes are obtained, which provide the
most stringent bounds at present, being below 2% at 99% for EeV
energies. We also compare our results to those of previous experiments as well
as with some theoretical expectations.Comment: 28 pages, 11 figure
Photoperiodic Modulation of Circadian Clock and Reproductive Axis Gene Expression in the Pre-Pubertal European Sea Bass Brain
The acquisition of reproductive competence requires the activation of the brain-pituitary-gonad (BPG) axis, which in most vertebrates, including fishes, is initiated by changes in photoperiod. In the European sea bass long-term exposure to continuous light (LL) alters the rhythm of reproductive hormones, delays spermatogenesis and reduces the incidence of precocious males. In contrast, an early shift from long to short photoperiod (AP) accelerates spermatogenesis. However, how photoperiod affects key genes in the brain to trigger the onset of puberty is still largely unknown. Here, we investigated if the integration of the light stimulus by clock proteins is sufficient to activate key genes that trigger the BPG axis in the European sea bass. We found that the clock genes clock, npas2, bmal1 and the BPG genes gnrh, kiss and kissr share conserved transcription factor frameworks in their promoters, suggesting co-regulation. Other gene promoters of the BGP axis were also predicted to be co-regulated by the same frameworks. Co-regulation was confirmed through gene expression analysis of brains from males exposed to LL or AP photoperiod compared to natural conditions: LL fish had suppressed gnrh1, kiss2, galr1b and esr1, while AP fish had stimulated npas2, gnrh1, gnrh2, kiss2, kiss1rb and galr1b compared to NP. It is concluded that fish exposed to different photoperiods present significant expression differences in some clock and reproductive axis related genes well before the first detectable endocrine and morphological responses of the BPG axis.European Community [222719 - LIFECYCLE]; Foundation for Science and Technology of Portugal (FCT) [SFRH/BPD/66742/2009, PEst-C/MAR/LA0015/2011]; Valencian Regional Goverment [Prometeo II/2014/051]; Spanish Ministry of Science and Innovation (MICINN) [CSD 2007-0002]info:eu-repo/semantics/publishedVersio
Does the Establishment of Sustainable Use Reserves Affect Fire Management in the Humid Tropics?
Tropical forests are experiencing a growing fire problem driven by climatic change, agricultural expansion and forest degradation. Protected areas are an important feature of forest protection strategies, and sustainable use reserves (SURs) may be reducing fire prevalence since they promote sustainable livelihoods and resource management. However, the use of fire in swidden agriculture, and other forms of land management, may be undermining the effectiveness of SURs in meeting their conservation and sustainable development goals. We analyse MODIS derived hot pixels, TRMM rainfall data, Terra-Class land cover data, socio-ecological data from the Brazilian agro-census and the spatial extent of rivers and roads to evaluate whether the designation of SURs reduces fire occurrence in the Brazilian Amazon. Specifically, we ask (1) a. Is SUR location (i.e., de facto) or (1) b. designation (i.e. de jure) the driving factor affecting performance in terms of the spatial density of fires?, and (2), Does SUR creation affect fire management (i.e., the timing of fires in relation to previous rainfall)? We demonstrate that pre-protection baselines are crucial for understanding reserve performance. We show that reserve creation had no discernible impact on fire density, and that fires were less prevalent in SURs due to their characteristics of sparser human settlement and remoteness, rather than their status de jure. In addition, the timing of fires in relation to rainfall, indicative of local fire management and adherence to environmental law, did not improve following SUR creation. These results challenge the notion that SURs promote environmentally sensitive fire-management, and suggest that SURs in Amazonia will require special attention if they are to curtail future accidental wildfires, particularly as plans to expand the road infrastructure throughout the region are realised. Greater investment to support improved fire management by farmers living in reserves, in addition to other fire users, will be necessary to help ameliorate these threats
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