185 research outputs found
Diffusive shock acceleration in radiation dominated environments
In this work I describe a numerical method developed, for the first time, for the study of Diffusive Shock Acceleration in astrophysical environments where the radiation pressure dominates over the magnetic pressure. This work is motivated by the overwhelming evidence of the acceleration of particles to high energy in astrophysical objects, traced by the nonâthermal radiation they emit due to interactions with the gas, radiation fields and magnetic fields. The main objective of this work is to create a generic framework to study selfâconsistently the interaction of acceleration at shocks and radiative energy losses and the effect such an interplay has on the particle spectrum and on the radiation they emit, in the case when energy losses determine the maximum achievable energy. I apply the developed method to electrons accelerated in three different types of sources: a Supernova Remnant in the Galactic Centre region, a microquasar, and a galaxy cluster. In all three cases the energy losses due to the interaction of electrons with radiation dominate over synchrotron cooling. I demonstrate that there is a strong impact due to the changing features of the inverse Compton scattering from the Thomson to the Klein-Nishina regime, on both the spectrum of accelerated electrons and their broadband emission. I also consider proton acceleration in galaxy clusters, where the particles lose energy during acceleration due to the interaction with the Cosmic Microwave Background radiation. The secondary products from pair production and photomeson processes interact with the same photon field and the background magnetic field, producing broadband electromagnetic radiation from radio to gamma-rays
Mother-Young Recognition in an Ungulate Hider Species: A Unidirectional Proce
Parentâoffspring recognition is usually crucial for survival of young. In mammals, olfaction often only permits identification at short range, and vocalizations are important at longer distances. Following and hiding antipredator strategies found in newborn mammals may also affect parental recognition mechanisms. We investigated motherâoffspring recognition in fallow deer, an ungulate hider species. We analyzed the structure of adult female and fawn contact calls to determine whether they are individually distinctive and tested for motherâoffspring recognition. Only females (and not fawns) have individualized vocalizations, with the fundamental frequency as the most distinctive parameter. Playback experiments showed that fawns can distinguish the calls of their mothers from those of other females, but mothers could not discriminate their own and alien fawn calls. Thus, the vocal identification process is unidirectional. In followers, motherâoffspring acoustic recognition is mutual, and therefore the different antipredator strategies of newborn mammals may have shaped the modalities of parentâoffspring acoustic recognition
Quality prevails over identity in the sexually selected vocalisations of an ageing mammal
BACKGROUND: Male sexually selected vocalisations generally contain both individuality and quality cues that are crucial in intra- as well as inter-sexual communication. As individuality is a fixed feature whereas male phenotypic quality changes with age, individuality and quality cues may be subjected to different selection pressures over time. Individuality (for example, morphology of the vocal apparatus) and quality (for example, body size and dominance status) can both affect the vocal production mechanism, inducing the same components of vocalisations to convey both kinds of information. In this case, do quality-related changes to the acoustic structure of calls induce a modification of vocal cues to identity from year to year? We investigated this question in fallow deer (Dama dama), in which some acoustic parameters of vocalisations (groans) code for both individuality and quality. RESULTS: We carried out a longitudinal analysis of groan individuality, examining the effects of age and dominance rank on the acoustic structure of groans of the same males recorded during consecutive years. We found both age- and rank-related changes to groans; the minimum values of the highest formant frequencies and the fundamental frequency increased with the age of males and they decreased when males became more dominant. Both age- and rank-related acoustic parameters contributed to individuality. Male quality changed with age, inducing a change in quality-related parameters and thus, a modification of vocal cues to male individuality between years. CONCLUSIONS: The encoding of individuality and quality information in the same components of vocalisations induces a tradeoff between these two kinds of signals over time. Fallow deer vocalisations are honest signals of quality that are not fixed over time but are modified dynamically according to male quality. As they are more reliable cues to quality than to individuality, they may not be used by conspecifics to recognize a given male from one year to another, but potentially used by both sexes to assess male quality during each breeding season
Mother-Young Recognition in an Ungulate Hider Species: A Unidirectional Proce
Parentâoffspring recognition is usually crucial for survival of young. In mammals, olfaction often only permits identification at short range, and vocalizations are important at longer distances. Following and hiding antipredator strategies found in newborn mammals may also affect parental recognition mechanisms. We investigated motherâoffspring recognition in fallow deer, an ungulate hider species. We analyzed the structure of adult female and fawn contact calls to determine whether they are individually distinctive and tested for motherâoffspring recognition. Only females (and not fawns) have individualized vocalizations, with the fundamental frequency as the most distinctive parameter. Playback experiments showed that fawns can distinguish the calls of their mothers from those of other females, but mothers could not discriminate their own and alien fawn calls. Thus, the vocal identification process is unidirectional. In followers, motherâoffspring acoustic recognition is mutual, and therefore the different antipredator strategies of newborn mammals may have shaped the modalities of parentâoffspring acoustic recognition
Fallow bucks attend to vocal cues of motivation and fatigue
Breeding vocalizations can provide up-to-date information about callers. During the rut, fallow buck calling rates vary in response to their nearest neighbors, and vocal fatigue is linked to body condition loss. We found that fallow bucks perceive higher calling rates as a greater threat and that bucks were sensitive to declines in the quality of the calls of other males. Over the breeding season, fallow bucks gain information from changing calls to continually assess the condition and motivation of conspecific
Acceleration and radiation of ultra-high energy protons in galaxy clusters
Clusters of galaxies are believed to be capable to accelerate protons at
accretion shocks to energies exceeding 10^18 eV. At these energies, the losses
caused by interactions of cosmic rays with photons of the Cosmic Microwave
Background Radiation (CMBR) become effective and determine the maximum energy
of protons and the shape of the energy spectrum in the cutoff region. The aim
of this work is the study of the formation of the energy spectrum of
accelerated protons at accretion shocks of galaxy clusters and of the
characteristics of their broad band emission. The proton energy distribution is
calculated self-consistently via a time-dependent numerical treatment of the
shock acceleration process which takes into account the proton energy losses
due to interactions with the CMBR. We calculate the energy distribution of
accelerated protons, as well as the flux of broad-band emission produced by
secondary electrons and positrons via synchrotron and inverse Compton
scattering processes. We find that the downstream and upstream regions
contribute almost at the same level to the emission. For the typical parameters
characterising galaxy clusters, the synchrotron and IC peaks in the spectral
energy distributions appear at comparable flux levels. For an efficient
acceleration, the expected emission components in the X-ray and gamma-ray band
are close to the detection threshold of current generation instruments, and
will be possibly detected with the future generation of detectors.Comment: 9 pages, 13 figures, submitted to Astronomy & Astrophysic
Sources of UHECRs in view of the TUS and JEM-EUSO experiments
The origin of ultra-high-energy cosmic rays (UHECRs) is one of the most
intriguing problems of modern cosmic ray physics. We briefly review the main
astrophysical models of their origin and the forthcoming orbital experiments
TUS and JEM-EUSO, and discuss how the new data can help one solve the
long-standing puzzle.Comment: 4 pages; prepared for ECRS-2012 (http://ecrs2012.sinp.msu.ru/); v2: a
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Production Risk Evaluation Program (PREP) Summary
Nuclear weapons have been produced in the US since the early 1950s by a network of contractor-operated Department of Energy (DOE) facilities collectively known as the Nuclear Weapon Complex (NWC). Recognizing that the failure of an essential process might stop weapon production for a substantial period of time, the DOE Albuquerque Operations office initiated the Production Risk Evaluation Program (PREP) at Sandia National Laboratories (SNL) to assess quantitatively the potential for serious disruptions in the NWC weapon production process. PREP was conducted from 1984-89. This document is an unclassified summary of the effort
Micro-beam and pulsed laser beam techniques for the micro-fabrication of diamond surface and bulk structures
Micro-fabrication in diamond is involved in a wide set of emerging
technologies, exploiting the exceptional characteristics of diamond for
application in bio-physics, photonics, radiation detection. Micro ion-beam
irradiation and pulsed laser irradiation are complementary techniques, which
permit the implementation of complex geometries, by modification and
functionalization of surface and/or bulk material, modifying the optical,
electrical and mechanical characteristics of the material. In this article we
summarize the work done in Florence (Italy) concerning ion beam and pulsed
laser beam micro-fabrication in diamond.Comment: 14 pages, 5 figure
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