1,765 research outputs found
Infrared continuum observations of the solar atmosphere
The far-infrared wavelengths (10 microns to 1 mm) were used to study the spatial and temporal structure of the solar atmosphere. Observational results were obtained on flares, faculae, sunspots, and on the center-to-limb intensity distribution, as well as on time variability within these regions. A program of precise monitoring of slow variations in the integrated solar luminosity was shown to be feasible, and initial steps to implement observations were completed
Weibel Instabilities in Dense Quantum Plasmas
The quantum effect on the Weibel instability in an unmagnetized plasma is
presented. Our analysis shows that the quantum effect tends to stabilize the
Weibel instability in the hydrodynamic regime, whereas it produces a new
oscillatory instability in the kinetic regime. A novel effect the quantum
damping, which is associated with the Landau damping, is disclosed. The new
quantum Weibel instability may be responsible for the generation of
non-stationary magnetic fields in compact astrophysical objects as well as in
the forthcoming intense laser-solid density plasma experiments.Comment: Submitted to PR
Economics analysis of mitigation strategies for FMD introduction in highly concentrated animal feeding regions
Outbreaks of infectious animal diseases can lead to substantial losses as evidenced by 2003 US BSE (Bovine Spongiform Encephalopathy) event with consequent loss of export markets, and the 2001 UK FMD (Foot and Mouth Disease) outbreak that has cost estimates in the billions. In this paper we present a linked epidemiologic-economic modeling framework which is used to investigate several FMD mitigation strategies under the context of an FMD outbreak in a concentrated cattle feeding region in the US. In this study we extend the literature by investigating the economic effectiveness of some previously unaddressed strategies including early detection, enhanced vaccine availability, and enhanced surveillance under various combinations of slaughter, surveillance, and vaccination. We also consider different disease introduction points at a large feedlot, a backgrounder feedlot, a large grazing herd, and a backyard herd all in the Texas High Plains. In terms of disease mitigation strategies we evaluate the economic effectiveness of: 1. Speeding up initial detection by one week from day 14 to day 7 after initial infection; 2. Speeding up vaccine availability from one week post disease detection to the day of disease detection; 3.Doubling post event surveillance intensity. To examine the economic implications of these strategies we use a two component stochastic framework. The first component is the epidemiologic model that simulates the spread of FMD as affected by control policies and introduction scenarios. The second component is an economics module, which calculates an estimate of cattle industry losses plus the costs of implementing disease control. The results show that early detection of the disease is the most effective mechanism for minimizing the costs of outbreak. Under some circumstances enhanced surveillance also proved to be an effective strategy.Livestock Production/Industries,
GRB 170817A as a Refreshed Shock Afterglow viewed off-axis
Energy injection into the external shock system that generates the afterglow
to a gamma-ray burst (GRB) can result in a re-brightening of the emission. Here
we investigate the off-axis view of a re-brightened refreshed shock afterglow.
We find that the afterglow light-curve, when viewed from outside of the jet
opening angle, could be characterised by a slow rise, or long-plateau, with a
maximum flux determined by the total system energy. Using the broadband
afterglow data for GRB170817A, associated with the gravitational wave detected
binary neutron star merger GW170817, we show that a refreshed shock model with
a simple top-hat jet can reproduce the observed afterglow features. We consider
two particular refreshed shock models: a single episode of energy injection;
and a period of continuous energy injection. The best fit model parameters give
a jet opening angle, for our first or second model of
or deg, an inclination to the
line of sight or deg, an
initial isotropic equivalent kinetic energy orerg and a total/final,
refreshed shock energy orerg. The
first model fitting prefers an initial bulk Lorentz factor ,
with a comparatively low central value of , indicating that,
in this case, the on-axis jet could have been a `failed-GRB'. Alternatively,
our second model is consistent with a bright GRB for an on-axis observer, with
. Due to the low-Lorentz factor or the
jet opening angles at , both models are unable to
reproduce the -ray emission observed in GRB170817A, which would
therefore require an alternative explanation such as cocoon shock-breakout.Comment: 14 pages, 6 figures - Version accepted for publication in ApJ.
Analysis now includes two refreshed shock models and expanded discussio
A search for neutron star-black hole binary mergers in the short Gamma-ray burst population
Short gamma-ray bursts (SGRBs) are now known to be the product of the merger of two compact objects. However, two possible formation channels exist: neutron starâneutron star (NSâNS) or NSâblack hole (BH). The landmark SGRB 170817A provided evidence for the NSâNS channel, thanks to analysis of its gravitational wave signal. We investigate the complete population of SGRBs with an associated redshift (39 events) and search for any divisions that may indicate that an NSâBH formation channel also contributes. Though no conclusive dichotomy is found, we find several lines of evidence that tentatively support the hypothesis that SGRBs with extended emission (EE; seven events) constitute the missing merger population: they are unique in the large energy-band sensitivity of their durations and have statistically distinct energies and host galaxy offsets when compared to regular (non-EE) SGRBs. If this is borne out via future gravitational wave detections, it will conclusively disprove the magnetar model for SGRBs. Furthermore, we identify the first statistically significant anticorrelation between the offsets of SGRBs from their host galaxies and their prompt emission energies
Virtual Supersymmetric Corrections in e^+e^- Annihilation
Depending on their masses, Supersymmetric particles can affect various
measurements in Z decay. Among these are the total width (or consequent
extracted value of ), enhancement or suppression of various flavors,
and left-right and forward-backward asymmetries. The latter depend on squark
mass splittings and are, therefore, a possible test of the Supergravity related
predictions. We calculate leading order corrections for these quantities
considering in particular the case of light photino and gluino where the SUSY
effects are enhanced. In this limit the effect on is appreciable,
the effect on is small, and the effect on the asymmetries is extremely
small.Comment: 11 pages, LaTeX, 3 figures, revised, a reference adde
The obscured hyper-energetic GRB 120624B hosted by a luminous compact galaxy at z = 2.20
Gamma-ray bursts are the most luminous explosions that we can witness in the
Universe. Studying the most extreme cases of these phenomena allows us to
constrain the limits for the progenitor models. In this Letter, we study the
prompt emission, afterglow, and host galaxy of GRB 120624B, one of the
brightest GRBs detected by Fermi, to derive the energetics of the event and
characterise the host galaxy in which it was produced. Following the
high-energy detection we conducted a multi-wavelength follow-up campaign,
including near-infrared imaging from HAWKI/VLT, optical from OSIRIS/GTC, X-ray
observations from the Chandra X-ray Observatory and at
sub-millimetre/millimetre wavelengths from SMA. Optical/nIR spectroscopy was
performed with X-shooter/VLT. We detect the X-ray and nIR afterglow of the
burst and determine a redshift of z = 2.1974 +/- 0.0002 through the
identification of emission lines of [OII], [OIII] and H-alpha from the host
galaxy of the GRB. This implies an energy release of Eiso = (3.0+/-0.2)x10^54
erg, amongst the most luminous ever detected. The observations of the afterglow
indicate high obscuration with AV > 1.5. The host galaxy is compact, with R1/2
< 1.6 kpc, but luminous, at L ~ 1.5 L* and has a star formation rate of 91 +/-
6 Msol/yr as derived from H-alpha. As other highly obscured GRBs, GRB 120624B
is hosted by a luminous galaxy, which we also proof to be compact, with a very
intense star formation. It is one of the most luminous host galaxies associated
with a GRB, showing that the host galaxies of long GRBs are not always blue
dwarf galaxies, as previously thought.Comment: 6 pages, 4 figures, 4 tables; accepted for publication in A&
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