7,590 research outputs found
Global existence of classical solutions to the Vlasov-Poisson system in a three dimensional, cosmological setting
The initial value problem for the Vlasov-Poisson system is by now well
understood in the case of an isolated system where, by definition, the
distribution function of the particles as well as the gravitational potential
vanish at spatial infinity. Here we start with homogeneous solutions, which
have a spatially constant, non-zero mass density and which describe the mass
distribution in a Newtonian model of the universe. These homogeneous states can
be constructed explicitly, and we consider deviations from such homogeneous
states, which then satisfy a modified version of the Vlasov-Poisson system. We
prove global existence and uniqueness of classical solutions to the
corresponding initial value problem for initial data which represent spatially
periodic deviations from homogeneous states.Comment: 23 pages, Latex, report #
Broadband modelling of short gamma-ray bursts with energy injection from magnetar spin-down and its implications for radio detectability
The magnetar model has been proposed to explain the apparent energy injection
in the X-ray light curves of short gamma-ray bursts (SGRBs), but its
implications across the full broadband spectrum are not well explored. We
investigate the broadband modelling of four SGRBs with evidence for energy
injection in their X-ray light curves, applying a physically motivated model in
which a newly formed magnetar injects energy into a forward shock as it loses
angular momentum along open field lines. By performing an order of magnitude
search for the underlying physical parameters in the blast wave, we constrain
the characteristic break frequencies of the synchrotron spectrum against their
manifestations in the available multi-wavelength observations for each burst.
The application of the magnetar energy injection profile restricts the
successful matches to a limited family of models that are self-consistent
within the magnetic dipole spin-down framework.We produce synthetic light
curves that describe how the radio signatures of these SGRBs ought to have
looked given the restrictions imposed by the available data, and discuss the
detectability of these signatures with present-day and near-future radio
telescopes. Our results show that both the Atacama Large Millimetre Array and
the upgraded Very Large Array are now sensitive enough to detect the radio
signature within two weeks of trigger in most SGRBs, assuming our sample is
representative of the population as a whole. We also find that the upcoming
Square Kilometre Array will be sensitive to depths greater than those of our
lower limit predictions.Comment: 15 pages, 4 figures, 6 tables, accepted for publication in MNRA
Constraining properties of GRB magnetar central engines using the observed plateau luminosity and duration correlation
An intrinsic correlation has been identified between the luminosity and
duration of plateaus in the X-ray afterglows of Gamma-Ray Bursts (GRBs;
Dainotti et al. 2008), suggesting a central engine origin. The magnetar central
engine model predicts an observable plateau phase, with plateau durations and
luminosities being determined by the magnetic fields and spin periods of the
newly formed magnetar. This paper analytically shows that the magnetar central
engine model can explain, within the 1 uncertainties, the correlation
between plateau luminosity and duration. The observed scatter in the
correlation most likely originates in the spread of initial spin periods of the
newly formed magnetar and provides an estimate of the maximum spin period of
~35 ms (assuming a constant mass, efficiency and beaming across the GRB
sample). Additionally, by combining the observed data and simulations, we show
that the magnetar emission is most likely narrowly beamed and has 20%
efficiency in conversion of rotational energy from the magnetar into the
observed plateau luminosity. The beaming angles and efficiencies obtained by
this method are fully consistent with both predicted and observed values. We
find that Short GRBs and Short GRBs with Extended Emission lie on the same
correlation but are statistically inconsistent with being drawn from the same
distribution as Long GRBs, this is consistent with them having a wider beaming
angle than Long GRBs.Comment: MNRAS Accepte
On a method to calculate conductance by means of the Wigner function: two critical tests
We have implemented the linear response approximation of a method proposed to
compute the electron transport through correlated molecules based on the
time-independent Wigner function [P. Delaney and J. C. Greer, \prl {\bf 93},
36805 (2004)]. The results thus obtained for the zero-bias conductance through
quantum dot both without and with correlations demonstrate that this method is
either quantitatively nor qualitatively able to provide a correct physical
escription of the electric transport through nanosystems. We present an
analysis indicating that the failure is due to the manner of imposing the
boundary conditions, and that it cannot be simply remedied.Comment: 22 pages, 7 figur
The separation of lactate dehydrogenase X from other lactate dehydrogenase isozymes of mouse testes by affinity chromatography
The hidden X-ray breaks in afterglow light curves
Gamma-Ray Burst (GRB) afterglow observations in the Swift era have a
perceived lack of achromatic jet breaks compared to the BeppoSAX, or pre-Swift
era. Specifically, relatively few breaks, consistent with jet breaks, are
observed in the X-ray light curves of these bursts. If these breaks are truly
missing, it has serious consequences for the interpretation of GRB jet
collimation and energy requirements, and the use of GRBs as standard candles.
Here we address the issue of X-ray breaks which are possibly 'hidden' and
hence the light curves are misinterpreted as being single power-laws. We show
how a number of precedents, including GRB 990510 & GRB 060206, exist for such
hidden breaks and how, even with the well sampled light curves of the Swift
era, these breaks may be left misidentified. We do so by synthesising X-ray
light curves and finding general trends via Monte Carlo analysis. Furthermore,
in light of these simulations, we discuss how to best identify achromatic
breaks in afterglow light curves via multi-wavelength analysis.Comment: 4 pages, contributed talk, submitted to the proceedings of Gamma Ray
Bursts 2007, Santa Fe, New Mexico, November 5-9 200
The Peculiar Multi-Wavelength Evolution Of V1535 Sco
We present multi-wavelength observations of the unusual nova V1535 Sco
throughout its outburst in 2015. Early radio observations were consistent with
synchrotron emission, and early X-ray observations revealed the presence of
high-energy (>1 keV) photons. These indicated that strong shocks were present
during the first ~2 weeks of the nova's evolution. The radio spectral energy
distribution was consistent with thermal emission from week 2 to week 6.
Starting in week 7, the radio emission again showed evidence of synchrotron
emission and there was an increase in X-ray emission, indicating a second shock
event. The optical spectra show evidence for at least two separate outflows,
with the faster outflow possibly having a bipolar morphology. The optical and
near infrared light curves and the X-ray measurements of the hydrogen column
density indicated that the companion star is likely a K giant.Comment: 20 pages, 13 figures, under review at ApJ, updated to match the most
recent version submitted to the refere
Molecfit: A general tool for telluric absorption correction. I. Method and application to ESO instruments
Context: The interaction of the light from astronomical objects with the
constituents of the Earth's atmosphere leads to the formation of telluric
absorption lines in ground-based collected spectra. Correcting for these lines,
mostly affecting the red and infrared region of the spectrum, usually relies on
observations of specific stars obtained close in time and airmass to the
science targets, therefore using precious observing time. Aims: We present
molecfit, a tool for correcting for telluric absorption lines based on
synthetic modelling of the Earth's atmospheric transmission. Molecfit is
versatile and can be used with data obtained with various ground-based
telescopes and instruments. Methods: Molecfit combines a publicly available
radiative transfer code, a molecular line database, atmospheric profiles, and
various kernels to model the instrument line spread function. The atmospheric
profiles are created by merging a standard atmospheric profile representative
of a given observatory's climate, of local meteorological data, and of
dynamically retrieved altitude profiles for temperature, pressure, and
humidity. We discuss the various ingredients of the method, its applicability,
and its limitations. We also show examples of telluric line correction on
spectra obtained with a suite of ESO Very Large Telescope (VLT) instruments.
Results: Compared to previous similar tools, molecfit takes the best results
for temperature, pressure, and humidity in the atmosphere above the observatory
into account. As a result, the standard deviation of the residuals after
correction of unsaturated telluric lines is frequently better than 2% of the
continuum. Conclusion: Molecfit is able to accurately model and correct for
telluric lines over a broad range of wavelengths and spectral resolutions.
(Abridged)Comment: 18 pages, 13 figures, 5 tables, accepted for publication in Astronomy
and Astrophysic
Approach to equilibrium in adiabatically evolving potentials
For a potential function (in one dimension) which evolves from a specified
initial form to a different asymptotically, we study the
evolution, in an overdamped dynamics, of an initial probability density to its
final equilibeium.There can be unexpected effects that can arise from the time
dependence. We choose a time variation of the form
. For a , which is
double welled and a which is simple harmonic, we show that, in
particular, if the evolution is adiabatic, the results in a decrease in the
Kramers time characteristics of . Thus the time dependence makes
diffusion over a barrier more efficient. There can also be interesting
resonance effects when and are two harmonic potentials
displaced with respect to each other that arise from the coincidence of the
intrinsic time scale characterising the potential variation and the Kramers
time.Comment: This paper contains 5 page
Where AD plants wildly grow: the spatio-temporal diffusion of agricultural biogas production in the Czech Republic
There is fundamental agreement about the environmental benefits of renewable energy technologies, but unintended consequences arising from their deployment are frequent sources of conflicts. The Czech Republic has committed itself to supply 13.5% of its electricity consumption from renewable sources by 2020. High state incentives for renewable energies have been provided to achieve this target, however critical questions can be asked about the appropriateness of the design of the supporting frameworks which caused a boom in photo-voltaic (PV) installations on agricultural land, as well as a boom in the installation of agricultural anaerobic digestion (AD) plants fuelled by dedicated energy crops. This paper analyses the diffusion of agricultural AD plants in the Czech Republic, focusing especially on locational characteristics in relation to the quality of agricultural land, agricultural and population census data. Statistical analysis of those spatial datasets show that agricultural AD plants are mostly located in less favourable agricultural areas, in regions having recently experienced a reduction in cattle breeding, and in regions with significant increases of sowing areas of green maize. These findings suggests shortcomings in the supporting policy for AD plants in the Czech Republic, resulting in unintended environmental consequences, and missed opportunities to enhance energy self-sufficiency and resilience in the countryside
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