7,555 research outputs found
Attack of the Clones: Legislative Approaches to Human Cloning in the United States
The legal concerns involving the application of cloning technology to humans should be of utmost concern, as the area is extremely complex. Cloning could potentially have great benefits or disastrous effects. Lawmakers have been careful to make certain that the legislation passed is comprehensive and useful for regulation of the ever-changing field of cloning. From debates on whether reproductive or therapeutic cloning should be permitted or banned, to concerns as to who has jurisdiction over cloning, the battle to develop cloning legislation has been difficult. However, this iBrief argues that the currently-proposed federal legislation is constitutional
Gaia FGK Benchmark Stars: Effective temperatures and surface gravities
Large Galactic stellar surveys and new generations of stellar atmosphere
models and spectral line formation computations need to be subjected to careful
calibration and validation and to benchmark tests. We focus on cool stars and
aim at establishing a sample of 34 Gaia FGK Benchmark Stars with a range of
different metallicities. The goal was to determine the effective temperature
and the surface gravity independently from spectroscopy and atmospheric models
as far as possible. Fundamental determinations of Teff and logg were obtained
in a systematic way from a compilation of angular diameter measurements and
bolometric fluxes, and from a homogeneous mass determination based on stellar
evolution models. The derived parameters were compared to recent spectroscopic
and photometric determinations and to gravity estimates based on seismic data.
Most of the adopted diameter measurements have formal uncertainties around 1%,
which translate into uncertainties in effective temperature of 0.5%. The
measurements of bolometric flux seem to be accurate to 5% or better, which
contributes about 1% or less to the uncertainties in effective temperature. The
comparisons of parameter determinations with the literature show in general
good agreements with a few exceptions, most notably for the coolest stars and
for metal-poor stars. The sample consists of 29 FGK-type stars and 5 M giants.
Among the FGK stars, 21 have reliable parameters suitable for testing,
validation, or calibration purposes. For four stars, future adjustments of the
fundamental Teff are required, and for five stars the logg determination needs
to be improved. Future extensions of the sample of Gaia FGK Benchmark Stars are
required to fill gaps in parameter space, and we include a list of suggested
candidates.Comment: Accepted by A&A; 34 pages (printer format), 14 tables, 13 figures;
language correcte
Comments on ISR method in modern experiment and influence of final state radiation
We study the effect of final state radiation in the process , in the kinematical conditions of BaBar and BESIII experiment. We show
that this effect could be large, in particular in the low region ( is
the photon energy fraction) and should be taken into account.Comment: 8 pages, 5 figure
Significant Gamma Lines from Inert Higgs Dark Matter
One way to unambiguously confirm the existence of particle dark matter and
determine its mass would be to detect its annihilation into monochromatic
gamma-rays in upcoming telescopes. One of the most minimal models for dark
matter is the inert doublet model, obtained by adding another Higgs doublet
with no direct coupling to fermions. For a mass between 40 and 80 GeV, the
lightest of the new inert Higgs particles can give the correct cosmic abundance
of cold dark matter in agreement with current observations. We show that for
this scalar dark matter candidate, the annihilation signal of monochromatic
\gamma\gamma and Z\gamma final states would be exceptionally strong. The energy
range and rates for these gamma-ray line signals make them ideal to search for
with the soon upcoming GLAST satellite.Comment: 4 pages, 3 figures; minor changes and text improvements; references
updated; published versio
Two-component model for the axial form factor of the nucleon
The axial form factor of the nucleon is studied in a two-component model
consisting of a three-quark intrinsic structure surrounded by a meson cloud.
The experimental data in the space-like region are well reproduced with a
minimal number of parameters. The results are similar to those obtained from a
dipole fit up to 1 GeV, but they surprisingly show a zero between 2 and 3
GeV. Such behavior, predicted by the present model completely disagrees
with the dipole parametrization. The theoretical expression for the form factor
is then analytically extrapolated to the time-like region, giving the first
predictions in this regime. This kinematical region is especially interesting
for present and future colliders.Comment: 12 pages 2 figures Final version to appear in Phys. Rev.
Quantum phase transitions in disordered dimerized quantum spin models and the Harris criterion
We use quantum Monte Carlo simulations to study effects of disorder on the
quantum phase transition occurring versus the ratio g=J/J' in square-lattice
dimerized S=1/2 Heisenberg antiferromagnets with intra- and inter-dimer
couplings J and J'. The dimers are either randomly distributed (as in the
classical dimer model), or come in parallel pairs with horizontal or vertical
orientation. In both cases the transition violates the Harris criterion,
according to which the correlation-length exponent should satisfy nu >= 1. We
do not detect any deviations from the three-dimensional O(3) universality class
obtaining in the absence of disorder (where nu = 0.71). We discuss special
circumstances which allow nu<1 for the type of disorder considered here.Comment: 4+ pages, 3 figure
Search for evidence of two photon contribution in elastic electron proton data
We reanalyze the most recent data on elastic electron proton scattering. We
look for a deviation from linearity of the Rosenbluth fit to the differential
cross section, which would be the signature of the presence of two photon
exchange. The two photon contribution is parametrized by a one parameter
formula, based on symmetry arguments. The present data do not show evidence for
such deviation.Comment: 15 pages 3 figures More details on the fitting procedure, more
explicit explanation
Asymptotics of the deuteron form factors in the nucleon model and JLab experiments
Using the instant form dynamics of Poincar\'e invariant quantum mechanics and
the modified relativistic impulse approximation proposed previously we
calculate asymptotics of electromagnetic form factors for the deuteron
considered as two--nucleon system. We show that today experiment on the elastic
-scattering has reached asymptotic regime. The possible range of momentum
transfer when the quark degrees of freedom could be seen in future JLab
experiments is estimated. The explicit relation between the behavior of
deuteron wave function at and the form factors asymptotics is obtained.
The conditions on wave functions to give the asymptotics predicted by QCD and
quark counting rules are formulated.Comment: 9 pages, 1 figur
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