3,532 research outputs found
Harvesting Thermal Fluctuations: Activation Process Induced by a Nonlinear Chain in Thermal Equilibrium
We present a model in which the immediate environment of a bistable system is
a molecular chain which in turn is connected to a thermal environment of the
Langevin form. The molecular chain consists of masses connected by harmonic or
by anharmonic springs. The distribution, intensity, and mobility of thermal
fluctuations in these chains is strongly dependent on the nature of the springs
and leads to different transition dynamics for the activated process. Thus, all
else (temperature, damping, coupling parameters between the chain and the
bistable system) being the same, the hard chain may provide an environment
described as diffusion-limited and more effective in the activation process,
while the soft chain may provide an environment described as energy-limited and
less effective. The importance of a detailed understanding of the thermal
environment toward the understanding of the activation process itself is thus
highlighted
Deep radio images of the HEGRA and Whipple TeV sources in the Cygnus OB2 region
Context. The modern generation of Cherenkov telescopes has revealed a new
population of gamma-ray sources in the Galaxy. Some of them have been
identified with previously known X-ray binary systems while other remain
without clear counterparts a lower energies. Our initial goal here was
reporting on extensive radio observations of the first extended and yet
unidentified source, namely TeV J2032+4130. This object was originally detected
by the HEGRA telescope in the direction of the Cygnus OB2 region and its nature
has been a matter of debate during the latest years.
Aims. We aim to pursue our radio exploration of the TeV J2032+4130 position
that we initiated in a previous paper but taking now into account the latest
results from new Whipple and MILAGRO TeV telescopes.
Methods. Our investigation is mostly based on interferometric radio
observations with the Giant Metre Wave Radio Telescope (GMRT) close to Pune
(India) and the Very Large Array (VLA) in New Mexico (USA). We also conducted
near infrared observations with the 3.5 m telescope and the OMEGA2000 camera at
the Centro Astronomico Hispano Aleman (CAHA) in Almeria (Spain).
Results. We present deep radio maps centered on the TeV J2032+4130 position
at different wavelengths. In particular, our 49 and 20 cm maps cover a field of
view larger than half a degree that fully includes the Whipple position and the
peak of MILAGRO emission. Our most important result here is a catalogue of 153
radio sources detected at 49 cm within the GMRT antennae primary beam with a
full width half maximum (FWHM) of 43 arc-minute. Moreover, our
multi-configuration VLA images reveal the non-thermal extended emission
previously reported by us with improved angular resolution.Comment: 10 pages, 8 figures, 1 online catalogue. Accepted for publication in
Astronomy & Astrophysic
Contact tracing and epidemics control in social networks
A generalization of the standard susceptible-infectious-removed (SIR)
stochastic model for epidemics in sparse random networks is introduced which
incorporates contact tracing in addition to random screening. We propose a
deterministic mean-field description which yields quantitative agreement with
stochastic simulations on random graphs. We also analyze the role of contact
tracing in epidemics control in small-world networks and show that its
effectiveness grows as the rewiring probability is reduced.Comment: 4 pages, 4 figures, submitted to PR
Comparative analysis of ferroelectric domain statistics via nonlinear diffraction in random nonlinear materials
© 2018 [Optical Society of America]. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved.We present an indirect, non-destructive optical method for domain statistic characterization in disordered nonlinear crystals having homogeneous refractive index and spatially random distribution of ferroelectric domains. This method relies on the analysis of the wave-dependent spatial distribution of the second harmonic, in the plane perpendicular to the optical axis in combination with numerical simulations. We apply this technique to the characterization of two different media, Calcium Barium Niobate and Strontium Barium Niobate, with drastically different statistical distributions of ferroelectric domains.Peer ReviewedPostprint (published version
Radio continuum and near-infrared study of the MGRO J2019+37 region
(abridged) MGRO J2019+37 is an unidentified extended source of VHE gamma-rays
originally reported by the Milagro Collaboration as the brightest TeV source in
the Cygnus region. Its extended emission could be powered by either a single or
several sources. The GeV pulsar AGL J2020.5+3653, discovered by AGILE and
associated with PSR J2021+3651, could contribute to the emission from MGRO
J2019+37, although extrapolation of the GeV spectrum does not explain the
detected multi-TeV flux. Our aim is to identify radio and NIR sources in the
field of the extended TeV source MGRO J2019+37, and study potential
counterparts that could contribute to its emission. We surveyed a region of
about 6 square degrees with the Giant Metrewave Radio Telescope (GMRT) at the
frequency 610 MHz. We also observed the central square degree of this survey in
the NIR Ks-band using the 3.5 m telescope in Calar Alto. Archival X-ray
observations of some specific fields are included. VLBI observations of an
interesting radio source were performed. We explored possible scenarios to
produce the multi-TeV emission from MGRO J2019+37 and studied which of the
sources could be the main particle accelerator. We present a catalogue of 362
radio sources detected with the GMRT in the field of MGRO J2019+37, and the
results of a cross-correlation of this catalog with one obtained at NIR
wavelengths, as well as with available X-ray observations of the region. Some
peculiar sources inside the ~1 degree uncertainty region of the TeV emission
from MGRO J2019+37 are discussed in detail, including the pulsar PSR J2021+3651
and its pulsar wind nebula PWN G75.2+0.1, two new radio-jet sources, the HII
region Sh 2-104 containing two star clusters, and the radio source NVSS
J202032+363158.Comment: 10 pages, 6 figures, 2 tables, accepted for publication in Astronomy
and Astrophysic
Radio continuum and near-infrared study of the MGRO J2019+37 region
(abridged) MGRO J2019+37 is an unidentified extended source of VHE gamma-rays
originally reported by the Milagro Collaboration as the brightest TeV source in
the Cygnus region. Its extended emission could be powered by either a single or
several sources. The GeV pulsar AGL J2020.5+3653, discovered by AGILE and
associated with PSR J2021+3651, could contribute to the emission from MGRO
J2019+37, although extrapolation of the GeV spectrum does not explain the
detected multi-TeV flux. Our aim is to identify radio and NIR sources in the
field of the extended TeV source MGRO J2019+37, and study potential
counterparts that could contribute to its emission. We surveyed a region of
about 6 square degrees with the Giant Metrewave Radio Telescope (GMRT) at the
frequency 610 MHz. We also observed the central square degree of this survey in
the NIR Ks-band using the 3.5 m telescope in Calar Alto. Archival X-ray
observations of some specific fields are included. VLBI observations of an
interesting radio source were performed. We explored possible scenarios to
produce the multi-TeV emission from MGRO J2019+37 and studied which of the
sources could be the main particle accelerator. We present a catalogue of 362
radio sources detected with the GMRT in the field of MGRO J2019+37, and the
results of a cross-correlation of this catalog with one obtained at NIR
wavelengths, as well as with available X-ray observations of the region. Some
peculiar sources inside the ~1 degree uncertainty region of the TeV emission
from MGRO J2019+37 are discussed in detail, including the pulsar PSR J2021+3651
and its pulsar wind nebula PWN G75.2+0.1, two new radio-jet sources, the HII
region Sh 2-104 containing two star clusters, and the radio source NVSS
J202032+363158.Comment: 10 pages, 6 figures, 2 tables, accepted for publication in Astronomy
and Astrophysic
Role of Sterile Neutrino Warm Dark Matter in Rhenium and Tritium Beta Decays
Sterile neutrinos with mass in the range of one to a few keV are important as
extensions of the Standard Model of particle physics and are serious dark
matter (DM) candidates. This DM mass scale (warm DM) is in agreement with both
cosmological and galactic observations. We study the role of a keV sterile
neutrino through its mixing with a light active neutrino in Rhenium 187 and
Tritium beta decays. We pinpoint the energy spectrum of the beta particle, 0 <
T_e < (Q_{beta} - m_s), as the region where a sterile neutrino could be
detected and where its mass m_s could be measured. This energy region is at
least 1 keV away rom the region suitable to measure the mass of the light
active neutrino, located near the endpoint Q_{beta} . The emission of a keV
sterile neutrino in a beta decay could show up as a small kink in the spectrum
of the emitted beta particle. With this in view, we perform a careful
calculation of the Rhenium and Tritium beta spectra and estimate the size of
this perturbation by means of the dimensionless ratio R of the sterile neutrino
to the active neutrino contributions. We comment on the possibility of
searching for sterile neutrino signatures in two experiments which are
currently running at present, MARE and KATRIN, focused on the Rhenium 187 and
Tritium beta decays respectively.Comment: 16 pages, 10 figures. Version to appear in Nucl. Phys. B. Results and
conclusions unchange
Design of the Ethiopian and plough using structural analysis validated with finite element analysis
Oral vaccination of cattle with heat inactivated Mycobacterium bovis does not compromise bovine TB diagnostic tests
AbstractIn this study we investigated whether oral uptake of a heat inactivated M. bovis wildlife vaccine by domestic cattle induced systemic immune responses that compromised the use of tuberculin or defined antigens in diagnostic tests for bovine TB. Positive skin test and blood-based IFN-Îł release assay (IGRA) results were observed in all calves vaccinated via the parenteral route (i.e. intramuscular). In contrast, no positive responses to tuberculin or defined antigens were observed in either the skin test or IGRA test when performed in calves vaccinated via the oral route. In conclusion, our results suggest that the heat inactivated M. bovis vaccine could be used to vaccinate wildlife in a baited form in conjunction with the following in cattle: (i) continuation of existing tuberculin skin testing or novel skin test formats based on defined antigens; and (ii) the use of IGRA tests utilizing tuberculin or defined antigens
Theoretical overview on high-energy emission in microquasars
Microquasar (MQ) jets are sites of particle acceleration and synchrotron
emission. Such synchrotron radiation has been detected coming from jet regions
of different spatial scales, which for the instruments at work nowadays appear
as compact radio cores, slightly resolved radio jets, or (very) extended
structures. Because of the presence of relativistic particles and dense photon,
magnetic and matter fields, these outflows are also the best candidates to
generate the very high-energy (VHE) gamma-rays detected coming from two of
these objects, LS 5039 and LS I +61 303, and may be contributing significantly
to the X-rays emitted from the MQ core. In addition, beside electromagnetic
radiation, jets at different scales are producing some amount of leptonic and
hadronic cosmic rays (CR), and evidences of neutrino production in these
objects may be eventually found. In this work, we review on the different
physical processes that may be at work in or related to MQ jets. The jet
regions capable to produce significant amounts of emission at different
wavelengths have been reduced to the jet base, the jet at scales of the order
of the size of the system orbital semi-major axis, the jet middle scales (the
resolved radio jets), and the jet termination point. The surroundings of the
jet could be sites of multiwavelegnth emission as well, deserving also an
insight. We focus on those scenarios, either hadronic or leptonic, in which it
seems more plausible to generate both photons from radio to VHE and high-energy
neutrinos. We briefly comment as well on the relevance of MQ as possible
contributors to the galactic CR in the GeV-PeV range.Comment: Astrophysics & Space Science, in press (invited talk in the
conference: The multimessenger approach to the high-energy gamma-ray
sources", Barcelona/Catalonia, in July 4-7); 10 pages, 6 figures, 2 tables
(one reference corrected
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