94 research outputs found
Can Galactic Observations Be Explained by a Relativistic Gravity Theory?
We consider the possibility of an alternative gravity theory explaining the
dynamics of galactic systems without dark matter. From very general assumptions
about the structure of a relativistic gravity theory we derive a general
expression for the metric to order . This allows us to compare the
predictions of the theory with various experimental data: the Newtonian limit,
light deflection and retardation, rotation of galaxies and gravitational
lensing. Our general conclusion is that the possibility for any gravity theory
to explain the behaviour of galaxies without dark matter is rather improbable.Comment: 12p, REVTeX 3.
The Star-Forming Galaxy Contribution to the Cosmic MeV and GeV Gamma-Ray Background
While star-forming galaxies could be major contributors to the cosmic GeV
-ray background, they are expected to be MeV-dim because of the "pion
bump" falling off below ~100 MeV. However, there are very few observations of
galaxies in the MeV range, and other emission processes could be present. We
investigate the MeV background from star-forming galaxies by running one-zone
models of cosmic ray populations, including Inverse Compton and bremsstrahlung,
as well as nuclear lines (including Al), emission from core-collapse
supernovae, and positron annihilation emission, in addition to the pionic
emission. We use the Milky Way and M82 as templates of normal and starburst
galaxies, and compare our models to radio and GeV--TeV -ray data. We
find that (1) higher gas densities in high-z normal galaxies lead to a strong
pion bump, (2) starbursts may have significant MeV emission if their magnetic
field strengths are low, and (3) cascades can contribute to the MeV emission of
starbursts if they emit mainly hadronic -rays. Our fiducial model
predicts that most of the unresolved GeV background is from star-forming
galaxies, but this prediction is uncertain by an order of magnitude. About ~2%
of the claimed 1 MeV background is diffuse emission from star-forming galaxies;
we place a firm upper limit of <~10% based on the spectral shape of the
background. The star-formation contribution is constrained to be small, because
its spectrum is peaked, while the observed background is steeply falling with
energy through the MeV-GeV range.Comment: Published in ApJ, 27 pages, emulateapj format. Readers may be
interested in the concurrent paper by Chakraborty and Fields
(arXiv:1206.0770), a calculation of the Inverse Compton background from
star-forming galaxie
Recovery of heat shock-triggered released apoplastic Ca2+ accompanied by pectin methylesterase activity is required for thermotolerance in soybean seedlings
Synthesis of heat shock proteins (HSPs) in response to heat shock (HS) is essential for thermotolerance. The effect of a Ca2+ chelator, EGTA, was investigated before a lethal HS treatment in soybean (Glycine max) seedlings with acquired thermotolerance induced by preheating. Such seedlings became non-thermotolerant with EGTA treatment. The addition of Ca2+, Sr2+ or Ba2+ to the EGTA-treated samples rescued the seedlings from death by preventing the increased cellular leakage of electrolytes, amino acids, and sugars caused by EGTA. It was confirmed that EGTA did not affect HSP accumulation and physiological functions but interfered with the recovery of HS-released Ca2+ concentration which was required for thermotolerance. Pectin methylesterase (PME, EC 3.1.1.11), a cell wall remodelling enzyme, was activated in response to HS, and its elevated activity caused an increased level of demethylesterified pectin which was related to the recovery of the HS-released Ca2+ concentration. Thus, the recovery of HS-released Ca2+ in Ca2+-pectate reconstitution through PME activity is required for cell wall remodelling during HS in soybean which, in turn, retains plasma membrane integrity and co-ordinates with HSPs to confer thermotolerance
Gamma Ray Bursts as standard candles to constrain the cosmological parameters
Gamma Ray Bursts (GRBs) are among the most powerful sources in the Universe:
they emit up to 10^54 erg in the hard X-ray band in few tens of seconds. The
cosmological origin of GRBs has been confirmed by several spectroscopic
measurements of their redshifts, distributed in the range 0.1-6.3. These two
properties make GRBs very appealing to investigate the far Universe. The
energetics implied by the observed fluences and redshifts span at least four
orders of magnitudes. Therefore, at first sight, GRBs are all but standard
candles. But there are correlations among some observed quantities which allow
us to know the total energy or the peak luminosity emitted by a specific burst
with a great accuracy. Through these correlations, GRBs become "known" candles
to constrain the cosmological parameters. One of these correlation is between
the rest frame peak spectral energy E_peak and the total energy emitted in
gamma--rays E_gamma, properly corrected for the collimation factor. Another
correlation, discovered very recently, relates the total GRB luminosity L_iso,
its peak spectral energy E_peak and a characteristic timescale T_0.45, related
to the variability of the prompt emission. It is based only on prompt emission
properties, it is completely phenomenological, model independent and
assumption--free. The constraints found through these correlations on the
Omega_M and Omega_Lambda parameters are consistent with the concordance model.
The present limited sample of bursts and the lack of low redshift events,
necessary to calibrate these correlations, makes the cosmological constraints
obtained with GRBs still large compared to those obtained with other
cosmological probes (e.g. SNIa or CMB). However, the newly born field of
GRB--cosmology is very promising for the future.Comment: 39 pages, 23 figures, 2 tables. Accepted for publication in the New
Journal of Physics focus issue, "Focus on Gamma--Ray bursts in the Swift Era"
(Eds. D. H. Hartmann, C. D. Dermer, J. Greiner
Essentially biased: why people are fatalistic about genes
We propose that people are genetic essentialistsâthat is, they tend to think of genetic attributions as being immutable, of a specific etiology, natural, and dividing people into homogenous and discrete groups. Although there are rare conditions where genes operate in these kinds of deterministic ways, people overgeneralize from these to the far more common conditions where genes are not at all deterministic. These essentialist biases are associated with some harmful outcomes such as racism, sexism, pessimism in the face of illnesses, political polarization, and support for eugenics, while at the same time they are linked with increased tolerance and sympathy for gay rights, mental illness, and less severe judgments of responsibility for crime. We will also discuss how these essentialist biases connect with the burgeoning direct-to-consumer genomics industry and various kinds of genetic engineering. Overall, these biases appear rather resistant to efforts to reduce them, although genetics literacy predicts weaker essentialist tendencies
Comparison of supraintercondylar and supracondylar femur fractures treated with condylar buttress plates
Impact of telehealth on general practice contacts: findings from the whole systems demonstrator cluster randomised trial
Identification and reconstruction of low-energy electrons in the ProtoDUNE-SP detector
Measurements of electrons from interactions are crucial for the Deep
Underground Neutrino Experiment (DUNE) neutrino oscillation program, as well as
searches for physics beyond the standard model, supernova neutrino detection,
and solar neutrino measurements. This article describes the selection and
reconstruction of low-energy (Michel) electrons in the ProtoDUNE-SP detector.
ProtoDUNE-SP is one of the prototypes for the DUNE far detector, built and
operated at CERN as a charged particle test beam experiment. A sample of
low-energy electrons produced by the decay of cosmic muons is selected with a
purity of 95%. This sample is used to calibrate the low-energy electron energy
scale with two techniques. An electron energy calibration based on a cosmic ray
muon sample uses calibration constants derived from measured and simulated
cosmic ray muon events. Another calibration technique makes use of the
theoretically well-understood Michel electron energy spectrum to convert
reconstructed charge to electron energy. In addition, the effects of detector
response to low-energy electron energy scale and its resolution including
readout electronics threshold effects are quantified. Finally, the relation
between the theoretical and reconstructed low-energy electron energy spectrum
is derived and the energy resolution is characterized. The low-energy electron
selection presented here accounts for about 75% of the total electron deposited
energy. After the addition of lost energy using a Monte Carlo simulation, the
energy resolution improves from about 40% to 25% at 50~MeV. These results are
used to validate the expected capabilities of the DUNE far detector to
reconstruct low-energy electrons.Comment: 19 pages, 10 figure
Impact of cross-section uncertainties on supernova neutrino spectral parameter fitting in the Deep Underground Neutrino Experiment
A primary goal of the upcoming Deep Underground Neutrino Experiment (DUNE) is
to measure the MeV neutrinos produced by a Galactic
core-collapse supernova if one should occur during the lifetime of the
experiment. The liquid-argon-based detectors planned for DUNE are expected to
be uniquely sensitive to the component of the supernova flux, enabling
a wide variety of physics and astrophysics measurements. A key requirement for
a correct interpretation of these measurements is a good understanding of the
energy-dependent total cross section for charged-current
absorption on argon. In the context of a simulated extraction of
supernova spectral parameters from a toy analysis, we investigate the
impact of modeling uncertainties on DUNE's supernova neutrino
physics sensitivity for the first time. We find that the currently large
theoretical uncertainties on must be substantially reduced
before the flux parameters can be extracted reliably: in the absence of
external constraints, a measurement of the integrated neutrino luminosity with
less than 10\% bias with DUNE requires to be known to about 5%.
The neutrino spectral shape parameters can be known to better than 10% for a
20% uncertainty on the cross-section scale, although they will be sensitive to
uncertainties on the shape of . A direct measurement of
low-energy -argon scattering would be invaluable for improving the
theoretical precision to the needed level.Comment: 25 pages, 21 figure
Highly-parallelized simulation of a pixelated LArTPC on a GPU
The rapid development of general-purpose computing on graphics processing units (GPGPU) is allowing the implementation of highly-parallelized Monte Carlo simulation chains for particle physics experiments. This technique is particularly suitable for the simulation of a pixelated charge readout for time projection chambers, given the large number of channels that this technology employs. Here we present the first implementation of a full microphysical simulator of a liquid argon time projection chamber (LArTPC) equipped with light readout and pixelated charge readout, developed for the DUNE Near Detector. The software is implemented with an end-to-end set of GPU-optimized algorithms. The algorithms have been written in Python and translated into CUDA kernels using Numba, a just-in-time compiler for a subset of Python and NumPy instructions. The GPU implementation achieves a speed up of four orders of magnitude compared with the equivalent CPU version. The simulation of the current induced on 10^3 pixels takes around 1 ms on the GPU, compared with approximately 10 s on the CPU. The results of the simulation are compared against data from a pixel-readout LArTPC prototype
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