861 research outputs found
DESENVOLVIMENTOECONĂMICO E POLĂTICA INDUSTRIAL E TECNOLĂGICA: A VISĂO DO PROFESSOR FABIO ERBER
Universality of electron-positron distributions in extensive air showers
Using a large set of simulated extensive air showers, we investigate
universality features of electron and positron distributions in
very-high-energy cosmic-ray air showers. Most particle distributions depend
only on the depth of the shower maximum and the number of particles in the
cascade at this depth. We provide multi-dimensional parameterizations for the
electron-positron distributions in terms of particle energy, vertical and
horizontal momentum angle, lateral distance, and time distribution of the
shower front. These parameterizations can be used to obtain realistic
electron-positron distributions in extensive air showers for data analysis and
simulations of Cherenkov radiation, fluorescence signal, and radio emission.Comment: 13 pages, 22 figures, 1 tabl
Magnetic Lensing near Ultramagnetized Neutron Stars
Extremely strong magnetic fields change the vacuum index of refraction. This
induces a lensing effect that is not unlike the lensing phenomenon in strong
gravitational fields. The main difference between the two is the polarization
dependency of the magnetic lensing, a behaviour that induces a handful of
interesting effects. The main prediction is that the thermal emission of
neutron stars with extremely strong magnetic fields is polarized - up to a few
percent for the largest fields known. This potentially allows a direct method
for measuring their magnetic fields.Comment: To appear in MNRAS, 12 pages, 9 figure
Dysregulation of the intrinsic apoptotic pathway mediates megakaryocytic hyperplasia in myeloproliferative neoplasms
published_or_final_versio
Plasma Magnetosphere Formation Around Oscillating Magnetized Neutron Stars
The notion of death line of rotating pulsars is applied to model of
oscillating neutron stars. It is shown that the magnetosphere of typical
non-rotating oscillating stars may not contain secondary plasma to support the
generation of radio emission in the region of open field lines of plasma
magnetosphere.Comment: Accepted for publication in Astrophysics & Space Scienc
Asymptotic conditions of motion for radiating charged particles
Approximate asymptotic conditions on the motion of compact, electrically
charged particles are derived within the framework of general relativity using
the Einstein- Infeld-Hoffmann (EIH) surface integral method. While
superficially similar to the Abraham-Lorentz and Lorentz-Dirac (ALD) equations
of motion, these conditions differ from them in several fundamental ways. They
are not equations of motion in the usual sense but rather a set of conditions
which these motions must obey in the asymptotic future of an initial value
surface. In addition to being asymptotic, these conditions of motion are
approximate and apply, as do the original EIH equations, only to slowly moving
systems. Also, they do not admit the run- away solutions of these other
equations. As in the original EIH work, they are integrability conditions
gotten from integrating the empty-space (i.e., source free) Einstein-Maxwell
equations of general relativity over closed two-surfaces surrounding the
sources of the fields governed by these equations. No additional ad hoc
assumptions, such as the form of a force law or the introduction of inertial
reaction terms, needed to derive the ALD equations are required for this
purpose. Nor is there a need for any of the infinite mass renormalizations that
are required in deriving these other equations.Comment: 15 page
Radiation in Lorentz violating electrodynamics
Synchrotron radiation is analyzed in the classical effective Lorentz
invariance violating model of Myers-Pospelov. Within the full far-field
approximation we compute the electric and magnetic fields, the angular
distribution of the power spectrum and the total emitted power in the m-th
harmonic, as well as the polarization. We find the appearance of rather
unexpected and large amplifying factors, which go together with the otherwise
negligible naive expansion parameter. This opens up the possibility of further
exploring Lorentz invariance violations by synchrotron radiation measurements
in astrophysical sources where these amplifying factors are important.Comment: Presented at the Second Mexican Meeting on Theoretical and
Experimental Physics, El Colegio Nacional, Mexico City, 6-10 September 200
StreptomeDB 2.0 - An extended resource of natural products produced by streptomycetes
Over the last decades, the genus Streptomyces has stirred huge interest in the scientific community as a source of bioactive compounds. The majority of all known antibiotics is isolated from these bac-terial strains, as well as a variety of other drugs such as antitumor agents, immunosuppressants and antifungals. To the best of our knowledge, Strep-tomeDB was the first database focusing on com-pounds produced by streptomycetes. The new ver-sion presented herein represents a major step for-ward: its content has been increased to over 4000 compounds and more than 2500 host organisms. In addition, we have extended the background in-formation and included hundreds of new manually curated references to literature. The latest update features a unique scaffold-based navigation system, which enables the exploration of the chemical diver-sity of StreptomeDB on a structural basis. We have included a phylogenetic tree, based on 16S rRNA se-quences, which comprises more than two-thirds of the included host organisms. It enables visualizing the frequency, appearance, and persistence of com-pounds and scaffolds in an evolutionary context. Ad-ditionally, we have included predicted MS- and NMR-spectra of thousands of compounds for assignment of experimental data. The database is freely acces-sible vi
Limits on models of the ultrahigh energy cosmic rays based on topological defects
An erratum exists for this article. Please see the description link below for details.Using the propagation of ultrahigh energy nucleons, photons, and electrons in the universal radiation backgrounds, we obtain limits on the luminosity of topological defect scenarios for the origin of the highest energy cosmic rays. The limits are set as a function of the mass of the X particles emitted by the cosmic strings or other defects, the cosmological evolution of the topological defects, and the strength of the extragalactic magnetic fields. The existing data on the cosmic ray spectrum and on the isotropic 100 MeV gamma-ray background limit significantly the parameter space in which topological defects can generate the flux of the highest energy cosmic rays, and rule out models with the standard X-particle mass of 10Âčâ¶GeV and higher.R. J. Protheroe and Todor Stane
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