652 research outputs found
Essential Metalloelement Chelates Facilitate Repair of Radiation Injury
Treatment with essential metalloelement (Cu, Fe, Mn, and Zn) chelates or combinations of them before and/or after radiation injury is a useful approach to overcoming radiation injury. No other agents are known to increase survival when they are used to treat after irradiation, in a radiorecovery treatment paradigm. These chelates may be useful in facilitating de novo syntheses of essential metalloelement-dependent enzymes required to repair radiation injury. Reports of radioprotection, which involves treatment before irradiation, with calcium-channel blockers, acyl Melatonin homologs, and substituted anilines, which may serve as
chelating agents after biochemical modification in vivo, as well as Curcumin, which is a chelating agent, have been included in this review. These inclusions are intended to suggest additional approaches to combination treatments that may be useful in facilitating radiation recovery. These approaches to radioprotection and
radiorecovery offer promise in facilitating recovery from radiation-induced injury experienced by patients
undergoing radiotherapy for neoplastic disease and by individuals who experience environmental,
occupational, or accidental exposure to ultraviolet, x-ray, or γ-ray radiation. Since there are no existing
treatments of radiation-injury intended to facilitate tissue repair, studies of essential metalloelement chelates
and combinations of them, as well as combinations of them with existing organic radioprotectants, seem
worthwhile
The afterglow of GRB050709 and the nature of the short-hard gamma-ray bursts
The final chapter in the long-standing mystery of the gamma-ray bursts (GRBs)
centres on the origin of the short-hard class, suspected on theoretical grounds
to result from the coalescence of neutron star or black hole binary systems.
Numerous searches for the afterglows of short-hard bursts have been made,
galvanized by the revolution in our understanding of long-duration GRBs that
followed the discovery in 1997 of their broadband (X-ray, optical, and radio)
afterglow emission. Here we present the discovery of the X-ray afterglow of a
short-hard burst whose accurate position allows us to unambiguously associate
it with a star-forming galaxy at redshift z=0.160, and whose optical lightcurve
definitively excludes a supernova association. Together with results from three
other recent short-hard bursts, this suggests that short-hard bursts release
much less energy than the long-duration GRBs. Models requiring young stellar
populations, such as magnetars and collapsars, are ruled out, while coalescing
degenerate binaries remain the most promising progenitor candidates.Comment: Nature in press (Oct 6 issue). 23 pages, 4 figure
The optical afterglows and host galaxies of three short/hard gamma-ray bursts
Short GRBs are commonly thought to originate from the merging of double
compact object binaries but direct evidence for this scenario is still missing.
Optical observations of short GRBs allow us to measure redshifts, firmly
identify host galaxies, characterize their properties, and accurately localize
GRBs within them. Multiwavelength observations of GRB afterglows provide useful
information on the emission mechanisms at work. These are all key issues that
allow one to discriminate among different models of these elusive events. We
carried out photometric observations of the short/hard GRB 051227, GRB 061006,
and GRB 071227 with the ESO-VLT starting from several hours after the explosion
down to the host galaxy level several days later. For GRB 061006 and GRB 071227
we also obtained spectroscopic observations of the host galaxy. We compared the
results obtained from our optical observations with the available X-ray data of
these bursts. For all the three above bursts, we discovered optical afterglows
and firmly identified their host galaxies. About half a day after the burst,
the optical afterglows of GRB 051227 and GRB 061006 present a decay
significatly steeper than in the X-rays. In the case of GRB 051227, the optical
decay is so steep that it likely indicates different emission mechanisms in the
two wavelengths ranges. The three hosts are blue, star forming galaxies at
moderate redshifts and with metallicities comparable to the Solar one. The
projected offsets of the optical afterglows from their host galaxies centers
span a wide range, but all afterglows lie within the light of their hosts and
present evidence for local absorption in their X-ray spectra. We discuss our
findings in light of the current models of short GRB progenitors.Comment: Accepted for publication by A&A. 11 pages, 9 figures; v2: minor
changes and new version of Fig.
Multimessenger astronomy with the Einstein Telescope
Gravitational waves (GWs) are expected to play a crucial role in the
development of multimessenger astrophysics. The combination of GW observations
with other astrophysical triggers, such as from gamma-ray and X-ray satellites,
optical/radio telescopes, and neutrino detectors allows us to decipher science
that would otherwise be inaccessible. In this paper, we provide a broad review
from the multimessenger perspective of the science reach offered by the third
generation interferometric GW detectors and by the Einstein Telescope (ET) in
particular. We focus on cosmic transients, and base our estimates on the
results obtained by ET's predecessors GEO, LIGO, and Virgo.Comment: 26 pages. 3 figures. Special issue of GRG on the Einstein Telescope.
Minor corrections include
Measurement of the Helicity Fractions of W Bosons from Top Quark Decays Using Fully Reconstructed top-antitop Events with CDF II
We present a measurement of the fractions F_0 and F_+ of longitudinally
polarized and right-handed W bosons in top quark decays using data collected
with the CDF II detector. The data set used in the analysis corresponds to an
integrated luminosity of approximately 318 pb -1. We select ttbar candidate
events with one lepton, at least four jets, and missing transverse energy. Our
helicity measurement uses the decay angle theta*, which is defined as the angle
between the momentum of the charged lepton in the W boson rest frame and the W
momentum in the top quark rest frame. The cos(theta*) distribution in the data
is determined by full kinematic reconstruction of the ttbar candidates. We find
F_0 = 0.85 +0.15 -0.22 (stat) +- 0.06 (syst) and F_+ = 0.05 +0.11 -0.05 (stat)
+- 0.03 (syst), which is consistent with the standard model prediction. We set
an upper limit on the fraction of right-handed W bosons of F_+ < 0.26 at the
95% confidence level.Comment: 11 pages, 2 figures, submitted to Phys. Rev.
Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s) = 1.96 TeV
We present a measurement of the top quark pair production cross section in
ppbar collisions at sqrt(s)=1.96 TeV using 318 pb^{-1} of data collected with
the Collider Detector at Fermilab. We select ttbar decays into the final states
e nu + jets and mu nu + jets, in which at least one b quark from the t-quark
decays is identified using a secondary vertex-finding algorithm. Assuming a top
quark mass of 178 GeV/c^2, we measure a cross section of 8.7 +-0.9 (stat)
+1.1-0.9 (syst) pb. We also report the first observation of ttbar with
significance greater than 5 sigma in the subsample in which both b quarks are
identified, corresponding to a cross section of 10.1 +1.6-1.4(stat)+2.0-1.3
(syst) pb.Comment: Accepted for publication in Physics Review Letters, 7 page
Top quark mass measurement using the template method at CDF
We present a measurement of the top quark mass in the lepton+jets and
dilepton channels of decays using the template method. The data
sample corresponds to an integrated luminosity of 5.6 fb of
collisions at Tevatron with TeV, collected with the CDF II
detector. The measurement is performed by constructing templates of three
kinematic variables in the lepton+jets and two kinematic variables in the
dilepton channel. The variables are two reconstructed top quark masses from
different jets-to-quarks combinations and the invariant mass of two jets from
the decay in the lepton+jets channel, and a reconstructed top quark mass
and , a variable related to the transverse mass in events with two
missing particles, in the dilepton channel. The simultaneous fit of the
templates from signal and background events in the lepton+jets and dilepton
channels to the data yields a measured top quark mass of Comment: submitted to Phys. Rev.
Search for the Higgs boson in events with missing transverse energy and b quark jets produced in proton-antiproton collisions at s**(1/2)=1.96 TeV
We search for the standard model Higgs boson produced in association with an
electroweak vector boson in events with no identified charged leptons, large
imbalance in transverse momentum, and two jets where at least one contains a
secondary vertex consistent with the decay of b hadrons. We use ~1 fb-1
integrated luminosity of proton-antiproton collisions at s**(1/2)=1.96 TeV
recorded by the CDF II experiment at the Tevatron. We find 268 (16) single
(double) b-tagged candidate events, where 248 +/- 43 (14.4 +/- 2.7) are
expected from standard model background processes. We place 95% confidence
level upper limits on the Higgs boson production cross section for several
Higgs boson masses ranging from 110 GeV/c2 to 140 GeV/c2. For a mass of 115
GeV/c2 the observed (expected) limit is 20.4 (14.2) times the standard model
prediction.Comment: 8 pages, 2 figures, submitted to Phys. Rev. Let
Observation and Mass Measurement of the Baryon
We report the observation and measurement of the mass of the bottom, strange
baryon through the decay chain , where
, , and .
Evidence for observation is based on a signal whose probability of arising from
the estimated background is 6.6 x 10^{-15}, or 7.7 Gaussian standard
deviations. The mass is measured to be (stat.) (syst.) MeV/.Comment: Minor text changes for the second version. Accepted by Phys. Rev.
Let
Search for New Particles Leading to Z+jets Final States in Collisions at TeV
We present the results of a search for new particles that lead to a \Z boson
plus jets in collisions at TeV using the Collider
Detector at Fermilab (CDF II). A data sample with a luminosity of 1.06 \ifb\
collected using \Z boson decays to and is used. We describe a
completely data-based method to predict the dominant background from
standard-model \Z+jet events. This method can be similarly applied to other
analyses requiring background predictions in multi-jet environments, as shown
when validating the method by predicting the background from +jets in \ttbar
production. No significant excess above the background prediction is observed,
and a limit is set using a fourth generation quark model to quantify the
acceptance. Assuming and using a leading-order
calculation of the cross section, quark masses below 268 \gev/c^2
are excluded at 95% confidence level.Comment: To be submitted to PR
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