287,874 research outputs found
Femtosecond x rays from laser-plasma accelerators
Relativistic interaction of short-pulse lasers with underdense plasmas has
recently led to the emergence of a novel generation of femtosecond x-ray
sources. Based on radiation from electrons accelerated in plasma, these sources
have the common properties to be compact and to deliver collimated, incoherent
and femtosecond radiation. In this article we review, within a unified
formalism, the betatron radiation of trapped and accelerated electrons in the
so-called bubble regime, the synchrotron radiation of laser-accelerated
electrons in usual meter-scale undulators, the nonlinear Thomson scattering
from relativistic electrons oscillating in an intense laser field, and the
Thomson backscattered radiation of a laser beam by laser-accelerated electrons.
The underlying physics is presented using ideal models, the relevant parameters
are defined, and analytical expressions providing the features of the sources
are given. Numerical simulations and a summary of recent experimental results
on the different mechanisms are also presented. Each section ends with the
foreseen development of each scheme. Finally, one of the most promising
applications of laser-plasma accelerators is discussed: the realization of a
compact free-electron laser in the x-ray range of the spectrum. In the
conclusion, the relevant parameters characterizing each sources are summarized.
Considering typical laser-plasma interaction parameters obtained with currently
available lasers, examples of the source features are given. The sources are
then compared to each other in order to define their field of applications.Comment: 58 pages, 41 figure
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Small-Scale Food Animal Production and Antimicrobial Resistance: Mountain, Molehill, or Something in-between?
SummarySmall-scale food animal production is widely practiced around the globe, yet it is often overlooked in terms of the environmental health risks. Evidence suggests that small-scale food animal producers often employ the use of antimicrobials to improve the survival and growth of their animals, and that this practice leads to the development of antimicrobial resistance (AMR) that can potentially spread to humans. The nature of human-animal interactions in small-scale food animal production systems, generally practiced in and around the home, likely augments spillover events of AMR into the community on a scale that is currently unrecognized and deserves greater attention. https://doi.org/10.1289/EHP2116
Abundances in Sagittarius: present state and perspectives for the use of VLT
Sagittarius, the nearest external galaxy, will be amenable to detailed
abundance studies with VLT and other 8m class telescopes. Such data, in
conjuction with the similar data of our own galaxy, will allow a deeper
understanding of chemical evolution. Our study conducted with NTT shows the
presence of metal-rich stars with radial velocities compatible with Sagittarius
membership and of stars as metal-poor as [Fe/H]=-1.5. In this talk I shall
address the way in which VLT instruments will allow to clarify this intricate
situation.Comment: Invited talk at the ESO VLT Opening Symposium, Antofagasta, March 1-4
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Semi-Classical Wavefunction Perspective to High-Harmonic Generation
We introduce a semi-classical wavefunction (SCWF) model for strong-field
physics and attosecond science. When applied to high harmonic generation (HHG),
this formalism allows one to show that the natural time-domain separation of
the contribution of ionization, propagation and recollisions to the HHG process
leads to a frequency-domain factorization of the harmonic yield into these same
contributions, for any choice of atomic or molecular potential. We first derive
the factorization from the natural expression of the dipole signal in the
temporal domain by using a reference system, as in the quantitative
rescattering (QRS) formalism [J. Phys. B. 43, 122001 (2010)]. Alternatively, we
show how the trajectory component of the SCWF can be used to express the
factorization, which also allows one to attribute individual contributions to
the spectrum to the underlying trajectories
Autism, the Integrations of 'Difference' and the Origins of Modern Human Behaviour
It is proposed here that the archaeological evidence for the emergence of 'modern behaviour' (160,000-40,000 bp) can best be explained as the rise of cognitive variation within populations through social mechanisms for integrating 'different minds', rather than by the development of a single 'modern human mind'. Autism and the autistic spectrum within human populations are used as an example of 'different minds' which when integrated within society can confer various selective benefits. It is proposed that social mechanisms for incorporating autistic difference are visible in the archaeological record and that these develop sporadically from 160,000 years bp in association with evidence for their consequences in terms of technological innovations, improved efficiency in technological and natural spheres and innovative thinking. Whilst other explanations for the emergence Of modern human behaviour may also contribute to observed changes, it is argued that the incorporation of cognitive differences played a significant role in the technological, social and symbolic expression of 'modern' behaviour
Time resolution of the plastic scintillator strips with matrix photomultiplier readout for J-PET tomograph
Recent tests of a single module of the Jagiellonian Positron Emission
Tomography system (J-PET) consisting of 30 cm long plastic scintillator strips
have proven its applicability for the detection of annihilation quanta (0.511
MeV) with a coincidence resolving time (CRT) of 0.266 ns. The achieved
resolution is almost by a factor of two better with respect to the current
TOF-PET detectors and it can still be improved since, as it is shown in this
article, the intrinsic limit of time resolution for the determination of time
of the interaction of 0.511 MeV gamma quanta in plastic scintillators is much
lower. As the major point of the article, a method allowing to record
timestamps of several photons, at two ends of the scintillator strip, by means
of matrix of silicon photomultipliers (SiPM) is introduced. As a result of
simulations, conducted with the number of SiPM varying from 4 to 42, it is
shown that the improvement of timing resolution saturates with the growing
number of photomultipliers, and that the 2 x 5 configuration at two ends
allowing to read twenty timestamps, constitutes an optimal solution. The
conducted simulations accounted for the emission time distribution, photon
transport and absorption inside the scintillator, as well as quantum efficiency
and transit time spread of photosensors, and were checked based on the
experimental results. Application of the 2 x 5 matrix of SiPM allows for
achieving the coincidence resolving time in positron emission tomography of
0.170 ns for 15 cm axial field-of-view (AFOV) and 0.365 ns
for 100 cm AFOV. The results open perspectives for construction of a
cost-effective TOF-PET scanner with significantly better TOF resolution and
larger AFOV with respect to the current TOF-PET modalities.Comment: To be published in Phys. Med. Biol. (26 pages, 17 figures
Evolution of the human fear-circuitry and acute sociogenic pseudoneurological symptoms: The Neolithic balanced-polymorphism hypothesis
In light of the increasing threat of large-scale massacres such as terrorism against non-combatants (civilians), more attention is warranted not only to posttraumatic stress disorder (PTSD) but also to acute sociogenic pseudoneurological ("conversion") symptoms, especially epidemic sociogenic symptoms. We posit that conversion disorders are etiologically related to specific evolutionary pressures (inescapable threats to life) in the late stage of the human environment of evolutionary adaptedness (EEA). Bracha et al. have recently argued that from the neuroevolutionary perspective, medically unexplained efferent vasovagal syncope and medically unexplained craniofacial musculoskeletal pain in young otherwise healthy individuals, may be taxonomized as stress and fear-circuitry disorders. In the present article, we extend neuroevolutionary perspectives to acute pseudoneurological sociogenic ("conversive") symptoms: psychogenic non-epileptic attacks ("pseudoseizures"), epidemic sociogenic disorders (DSM-IV-TR Epidemic "Hysteria"), conversive motor deficits (pseudo-paralysis and pseudo-cerebellar symptoms), and psychogenic blindness. We hypothesize that these perplexing pseudoneurological stress-triggered symptoms, which constitute psychopathology in extant humans, are traceable to allele-variant polymorphisms which spread during the Neolithic EEA. During Neolithic warfare, conversive symptoms may have increased the survival odds for some non-combatants by visually (i.e., "non-verbally") signaling to predatory conspecifics that one does not present a danger. This is consistent with the age and sex pattern of conversive disorders. Testable and falsifiable predictions are presented; e.g., at the genome-transcriptome interface, one of the major oligogenic loci involved in conversive spectrum disorders may carry a developmentally sensitive allele in a stable polymorphism (balanced polymorphism) in which the gene expression mechanism is gradually suppressed by pleiotropic androgens especially dehydroxyepiandrosterone sulfate (DHEA-S). Taxonomic implications for the much-needed rapprochement between the forthcoming Diagnostic and Statistical Manual for Mental Disorders, Fifth Edition (DSM-V) and the International Classification of Diseases (ICD) are discussed
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