153 research outputs found
Gamma-ray emission from pulsars
We have attempted to devise a scheme by which it may be possible to identify pulsars which are likely to be γ-ray pulsars. We apply this test to a representative population of pulsars and identify the likely candidates for γ emission. We also discuss some individual cases including the Crab and Vela pulsars
Globular clusters as gamma ray sources
There are indications now that globular clusters contain a large number of low magnetic field millisecond pulsars. Since
millisecond pulsars are expected to emit γ -rays due to curvature radiation, it is likely that globular clusters will themselves be
sources of γ -rays bright enough to be detectable by present day instruments. Using the expression derived by Scharlemann,
Arons & Fawley (1978) of the energy acquired by the electrons moving along the open magnetic field lines of the pulsars we
have calculated the likely luminosity of γ -rays from globular clusters. We discuss our results in the light of the calculations
reported in the literature based on some of the other models
Gravitational Lensing Bound On The Average Redshift Of Gamma Ray Bursts In Models With Evolving Lenses
Identification of gravitationally lensed Gamma Ray Bursts (GRBs) in the BATSE
4B catalog can be used to constrain the average redshift of the GRBs.
In this paper we investigate the effect of evolving lenses on the of
GRBs in different cosmological models of universe. The cosmological parameters
$\Omega$ and $\Lambda$ have an effect on the of GRBs. The other factor
which can change the of GRBs is higher in evolving model of galaxies as compared to
non-evolving models of galaxies.Comment: 23 pages,one plain LaTeX file with three postscript figures This is
modified version with recent BATSE efficiency parameter and with the latest F
paramete
Constraint On The Cosmological Constant From Gravitational Lenses In An Evolutionary Model Of Galaxies
We study the effect of the cosmological constant on the statistical
properties of gravitational lenses in flat cosmologies (Omega_{0}+lambda_{0} =
1). It is shown that some of the lens observables are strongly affected by the
cosmological constant, especially in a low--density universe, and its existence
might be inferred by a statistical study of the lenses. In particular, the
optical depth of the lens distribution may be used best for this purpose
without depending much on the lens model. We calculate the optical depth
(probabilty of a beam encountering with a lens event) for a source in a new
picture of galaxy evolution based on number evolution in addition to pure
luminosity evolution. It seems that present day galaxies result from the
merging of a large number of building blocks. We have tried to put limit on the
cosmological constant in this new picture of galaxy evolution. This
evolutionary model of galaxies permits larger value of cosmological constant.Comment: Latex file with two figures, 24 page
Gravitational lensing constraint on the cosmic equation of state
Recent redshift-distance measurements of Type Ia supernovae (SNe Ia) at
cosmological distances suggest that two-third of the energy density of the
universe is dominated by dark energy component with an effective negative
pressure. This dark energy component is described by the equation of state
. We use gravitational lensing statistics to
constrain the equation of state of this dark energy. We use ,
image separation distribution function of lensed quasars, as a tool to probe
. We find that for the observed range of ,
should lie between in order to have five lensed quasars
in a sample of 867 optical quasars. This limit is highly sensitive to lens and
Schechter parameters and evolution of galaxies.Comment: Modified results and inclusion of calculations with new set of
parameter
Geological Field Trips
This field trip guide organized in the framework of the Goldschmidt Conference 2013, held in Florence from
August 25 to 30, 2013, is here presented.
The two-days field trip, shows some of the many geological, naturalistic and cultural features in the Fiorano
area (Modena), in which history, geology and passion for Ferrari come together in a perfect marriage.
The first excursion day is dedicated to visit the Natural Reserve of Salse di Nirano, where the mud volcanoes,
produced by the cold mud, salt water and hydrocarbons - mainly methane- can be observed.
The second day is devoted to visit the Ferrari Museum and goes on at the Spezzano Castle, hosting the Ceramics
Museum. Clays are, in fact, abundant in the hilly margin, where they form badlands, characteristic narrow crests
washed out by running waters. In the Castle there is also a Balsamic Vinegar producing Consortium, it’s a peculiar
and typical product of Modena province. The itinerary ends with the tour to Enzo Ferrari’s Birthplace at Modena
Large Scale Benchmark of Materials Design Methods
Lack of rigorous reproducibility and validation are major hurdles for
scientific development across many fields. Materials science in particular
encompasses a variety of experimental and theoretical approaches that require
careful benchmarking. Leaderboard efforts have been developed previously to
mitigate these issues. However, a comprehensive comparison and benchmarking on
an integrated platform with multiple data modalities with both perfect and
defect materials data is still lacking. This work introduces
JARVIS-Leaderboard, an open-source and community-driven platform that
facilitates benchmarking and enhances reproducibility. The platform allows
users to set up benchmarks with custom tasks and enables contributions in the
form of dataset, code, and meta-data submissions. We cover the following
materials design categories: Artificial Intelligence (AI), Electronic Structure
(ES), Force-fields (FF), Quantum Computation (QC) and Experiments (EXP). For
AI, we cover several types of input data, including atomic structures,
atomistic images, spectra, and text. For ES, we consider multiple ES
approaches, software packages, pseudopotentials, materials, and properties,
comparing results to experiment. For FF, we compare multiple approaches for
material property predictions. For QC, we benchmark Hamiltonian simulations
using various quantum algorithms and circuits. Finally, for experiments, we use
the inter-laboratory approach to establish benchmarks. There are 1281
contributions to 274 benchmarks using 152 methods with more than 8 million
data-points, and the leaderboard is continuously expanding. The
JARVIS-Leaderboard is available at the website:
https://pages.nist.gov/jarvis_leaderboar
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