12,310 research outputs found
On the physical processes which lie at the bases of time variability of GRBs
The relative-space-time-transformation (RSTT) paradigm and the interpretation
of the burst-structure (IBS) paradigm are applied to probe the origin of the
time variability of GRBs. Again GRB 991216 is used as a prototypical case,
thanks to the precise data from the CGRO, RXTE and Chandra satellites. It is
found that with the exception of the relatively inconspicuous but
scientifically very important signal originating from the initial ``proper
gamma ray burst'' (P-GRB), all the other spikes and time variabilities can be
explained by the interaction of the accelerated-baryonic-matter pulse with
inhomogeneities in the interstellar matter. This can be demonstrated by using
the RSTT paradigm as well as the IBS paradigm, to trace a typical spike
observed in arrival time back to the corresponding one in the laboratory time.
Using these paradigms, the identification of the physical nature of the time
variablity of the GRBs can be made most convincingly. It is made explicit the
dependence of a) the intensities of the afterglow, b) the spikes amplitude and
c) the actual time structure on the Lorentz gamma factor of the
accelerated-baryonic-matter pulse. In principle it is possible to read off from
the spike structure the detailed density contrast of the interstellar medium in
the host galaxy, even at very high redshift.Comment: 11 pages, 5 figure
The EMBH model in GRB 991216 and GRB 980425
This is a summary of the two talks presented at the Rome GRB meeting by C.L.
Bianco and R. Ruffini. It is shown that by respecting the Relative Space-Time
Transformation (RSTT) paradigm and the Interpretation of the Burst Structure
(IBS) paradigm, important inferences are possible: a) in the new physics
occurring in the energy sources of GRBs, b) on the structure of the bursts and
c) on the composition of the interstellar matter surrounding the source.Comment: 8 pages, 3 figures, in the Proceedings of the "Third Rome Workshop on
Gamma-Ray Bursts in the Afterglow Era", 17-20 September 2002, M. Feroci, F.
Frontera, N. Masetti, L. Piro (editors
GRB 970228 Within the EMBH Model
We consider the gamma-ray burst of 1997 February 28 (GRB 970228) within the
ElectroMagnetic Black Hole (EMBH) model. We first determine the value of the
two free parameters that characterize energetically the GRB phenomenon in the
EMBH model, that is to say the dyadosphere energy,
ergs, and the baryonic remnant mass in units of ,
. Having in this way estimated the
energy emitted during the beam-target phase, we evaluate the role of the
InterStellar Medium (ISM) number density (n) and of the ratio between the effective emitting area and the total surface area of the GRB
source, in reproducing the observed profiles of the GRB 970228 prompt emission
and X-ray (2-10 keV energy band) afterglow. The importance of the ISM
distribution three-dimensional treatment around the central black hole is also
stressed in this analysis.Comment: 4 pages, 1 figure, to appear in the Proceedings of the Los Alamos
"Gamma Ray Burst Symposium" in Santa Fe, New Mexico, September 8-12 2003 (AIP
Conf. Ser.), CHAPTER: GRB Connection to Supernova
Prevalence of aster yellows (AY) and elm yellows (EY) group phytoplasmas in symptomatic grapevines in three areas of northern Italy
Flavescence doree (FD) and others important grapevine yellows (GY) diseases are known to occur in northern Italy. In this communication we report the results of an extended survey of naturally yellows diseased grapevines growing in three provinces of northern Italy, Vicenza, Brescia and Pavia. The plants were sampled at the end of June and the beginning of August. Direct PCR assay using group-specific primers for universal phytoplasma 16S rDNA amplification or for amplification of 16S rDNA from 16SrI (aster yellows and related phytoplasmas), 16SrIII (X-disease and related phytoplasmas) and 16SrV (elm yellows and related phytoplasmas) phytoplasma groups, and RFLP analysis of amplified DNA, were conducted. Phytoplasmas belonging to group 16SrV were detected only in grapevines in the Vicenza province; whereas, phytoplasmas belonging to group 16SrI subgoup G were found in grapevines in all three provinces
Electromagnetic emission of white dwarf binary mergers
It has been recently proposed that the ejected matter from white dwarf (WD)
binary mergers can produce transient, optical and infrared emission similar to
the "kilonovae" of neutron star (NS) binary mergers. To confirm this we
calculate the electromagnetic emission from WD-WD mergers and compare with
kilonova observations. We simulate WD-WD mergers leading to a massive, fast
rotating, highly magnetized WD with an adapted version of the
smoothed-particle-hydrodynamics (SPH) code Phantom. We thus obtain initial
conditions for the ejecta such as escape velocity, mass and initial position
and distribution. The subsequent thermal and dynamical evolution of the ejecta
is obtained by integrating the energy-conservation equation accounting for
expansion cooling and a heating source given by the fallback accretion onto the
newly-formed WD and its magneto-dipole radiation. We show that magnetospheric
processes in the merger can lead to a prompt, short gamma-ray emission of up to
erg in a timescale of - s. The bulk of the ejecta
initially expands non-relativistically with velocity and then it
accelerates to due to the injection of fallback accretion energy. The
ejecta become transparent at optical wavelengths around days
post-merger with a luminosity - erg s. The X-ray
emission from the fallback accretion becomes visible around -
day post-merger with a luminosity of erg s. We also predict
the post-merger time at which the central WD should appear as a pulsar
depending on the value of the magnetic field and rotation period.Comment: 12 pages, Accepted for publication in JCA
Indole-3-acetic acid regulates the central metabolic pathways in Escherichia coli.
The physiological changes induced by indoleacetic acid (IAA) treatment were investigated in the totally sequenced Escherichia coli K-12 MG1655. DNA macroarrays were used to measure the mRNA levels for all the 4290 E. coli protein-coding genes; 50 genes (1-1 %) exhibited significantly different expression profiles. In particular, genes involved in the tricarboxylic acid cycle, the glyoxylate shunt and amino acid biosynthesis (leucine, isoleucine, valine and proline) were up-regulated, whereas the fermentative adhE gene was down-regulated. To confirm the indications obtained from the macroarray analysis the activity of 34 enzymes involved in central metabolism was measured; this showed an activation of the tricarboxylic acid cycle and the glyoxylate shunt. The malic enzyme, involved in the production of pyruvate, and pyruvate dehydrogenase, required for the channelling of pyruvate into acetyl-CoA, were also induced in IAA-treated cells. Moreover, it was shown that the enhanced production of acetyl-CoA and the decrease of NADH/NAD+ ratio are connected with the molecular process of the IAA response. The results demonstrate that IAA treatment is a stimulus capable of inducing changes in gene expression, enzyme activity and metabolite level involved in central metabolic pathways in E. col
Unanswered Questions in the Electroweak Theory
This article is devoted to the status of the electroweak theory on the eve of
experimentation at CERN's Large Hadron Collider. A compact summary of the logic
and structure of the electroweak theory precedes an examination of what
experimental tests have established so far. The outstanding unconfirmed
prediction of the electroweak theory is the existence of the Higgs boson, a
weakly interacting spin-zero particle that is the agent of electroweak symmetry
breaking, the giver of mass to the weak gauge bosons, the quarks, and the
leptons. General arguments imply that the Higgs boson or other new physics is
required on the TeV energy scale. Indirect constraints from global analyses of
electroweak measurements suggest that the mass of the standard-model Higgs
boson is less than 200 GeV. Once its mass is assumed, the properties of the
Higgs boson follow from the electroweak theory, and these inform the search for
the Higgs boson. Alternative mechanisms for electroweak symmetry breaking are
reviewed, and the importance of electroweak symmetry breaking is illuminated by
considering a world without a specific mechanism to hide the electroweak
symmetry.
For all its triumphs, the electroweak theory has many shortcomings. . . .Comment: 31 pages, 20 figures; prepared for Annual Review of Nuclear and
Particle Science (minor changes
ATLAS RPC Quality Assurance results at INFN Lecce
The main results of the quality assurance tests performed on the Resistive
Plate Chamber used by the ATLAS experiment at LHC as muon trigger chambers are
reported and discussed.
Since July 2004, about 270 RPC units has been certified at INFN Lecce site
and delivered to CERN, for being integrated in the final muon station of the
ATLAS barrel region.
We show the key RPC characteristics which qualify the performance of this
detector technology as muon trigger chamber in the harsh LHC enviroments.
These are dark current, chamber efficiency, noise rate, gas volume
tomography, and gas leakage.Comment: Comments: 6 pages, 1 table, 9 figures Proceedings of XXV Physics in
Collision-Prague, Czech Republic, 6-9 July 200
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