703 research outputs found
Effects of non-linearities on magnetic field generation
Magnetic fields are present on all scales in the Universe. While we
understand the processes which amplify the fields fairly well, we do not have a
"natural" mechanism to generate the small initial seed fields. By using fully
relativistic cosmological perturbation theory and going beyond the usual
confines of linear theory we show analytically how magnetic fields are
generated. This is the first analytical calculation of the magnetic field at
second order, using gauge-invariant cosmological perturbation theory, and
including all the source terms. To this end, we have rederived the full set of
governing equations independently. Our results suggest that magnetic fields of
the order of G can be generated (although this depends on the small
scale cut-off of the integral), which is largely in agreement with previous
results that relied upon numerical calculations. These fields are likely too
small to act as the primordial seed fields for dynamo mechanisms.Comment: 21 pages; v2: minor changes, added references; v3: version accepted
for publication in JCA
Averaging Robertson-Walker Cosmologies
The cosmological backreaction arises when one directly averages the Einstein
equations to recover an effective Robertson-Walker cosmology, rather than
assuming a background a priori. While usually discussed in the context of dark
energy, strictly speaking any cosmological model should be recovered from such
a procedure. We apply the Buchert averaging formalism to linear
Robertson-Walker universes containing matter, radiation and dark energy and
evaluate numerically the discrepancies between the assumed and the averaged
behaviour, finding the largest deviations for an Einstein-de Sitter universe,
increasing rapidly with Hubble rate to a 0.01% effect for h=0.701. For the LCDM
concordance model, the backreaction is of the order of Omega_eff~4x10^-6, with
those for dark energy models being within a factor of two or three. The impacts
at recombination are of the order of 10^-8 and those in deep radiation
domination asymptote to a constant value. While the effective equations of
state of the backreactions in Einstein-de Sitter, concordance and quintessence
models are generally dust-like, a backreaction with an equation of state
w_eff<-1/3 can be found for strongly phantom models.Comment: 18 pages, 11 figures, ReVTeX. Updated to version accepted by JCA
Pure kinetic k-essence as the cosmic speed-up
In this paper, we consider three types of k-essence. These k-essence models
were presented in the parametric forms. The exact analytical solutions of the
corresponding equations of motion are found. It is shown that these k-essence
models for the presented solutions can give rise to cosmic acceleration.Comment: 10 pages, typos corrected, main results remain the same, minor
changes to match IJTP accepted versio
Spontaneous regression in alveolar soft part sarcoma: case report and literature review
<p>Abstract</p> <p>Background</p> <p>Sarcomas are a type of malignant tumors that arise from connective tissue. They are most of the time found in extremities</p> <p>Case presentation</p> <p>We are presenting a case of adult male patient, who was found to have huge abdominal mass and multiple gastric and duodenal polyps. Pathological diagnosis for all lesions was Alveolar soft part sarcoma. Although he complained from metastasis to both lungs and right atrium, all these deposits regressed spontaneously. Patient stated that he used some herbs (Teucrium polium, Cat Thyme) prescribed for him. No chemotherapy or radiotherapy was given. The duration of regression was about 5 months before other lesions appeared. Later on, he died secondary to brain metastasis.</p> <p>Conclusion</p> <p>ASPS is a rare type of sarcomas that affect primarily the lower limbs. This tumor does rarely metastasize to the gastrointestinal tract.</p
Infrared effects in inflationary correlation functions
In this article, I briefly review the status of infrared effects which occur
when using inflationary models to calculate initial conditions for a subsequent
hot, dense plasma phase. Three types of divergence have been identified in the
literature: secular, "time-dependent" logarithms, which grow with time spent
outside the horizon; "box-cutoff" logarithms, which encode a dependence on the
infrared cutoff when calculating in a finite-sized box; and "quantum"
logarithms, which depend on the ratio of a scale characterizing new physics to
the scale of whatever process is under consideration, and whose interpretation
is the same as conventional field theory. I review the calculations in which
these divergences appear, and discuss the methods which have been developed to
deal with them.Comment: Invited review for focus section of Classical & Quantum Gravity on
nonlinear and nongaussian perturbation theory. Some improvements compared to
version which will appear in CQG, especially in Sec. 2.3. 30 pages +
references
Core conditions for alpha heating attained in direct-drive inertial confinement fusion
It is shown that direct-drive implosions on the OMEGA laser have achieved core conditions that would lead to significant alpha heating at incident energies available on the National Ignition Facility (NIF) scale. The extrapolation of the experimental results from OMEGA to NIF energy assumes only that the implosion hydrodynamic efficiency is unchanged at higher energies. This approach is independent of the uncertainties in the physical mechanism that degrade implosions on OMEGA, and relies solely on a volumetric scaling of the experimentally observed core conditions. It is estimated that the current best-performing OMEGA implosion [Regan et al., Phys. Rev. Lett. 117, 025001 (2016)10.1103/PhysRevLett.117.025001] extrapolated to a 1.9 MJ laser driver with the same illumination configuration and laser-target coupling would produce 125 kJ of fusion energy with similar levels of alpha heating observed in current highest performing indirect-drive NIF implosions.United States. Department of Energy (DE-FC02-04ER54789)United States. National Nuclear Security Administration (DE-NA0001944
Response to Comment on “Estimating the reproducibility of psychological science”
Gilbert et al. conclude that evidence from the Open Science Collaboration's Reproducibility Project: Psychology indicates high reproducibility, given the study methodology. Their very optimistic assessment is limited by statistical misconceptions and by causal inferences from selectively interpreted, correlational data. Using the Reproducibility Project: Psychology data, both optimistic and pessimistic conclusions about reproducibility are possible, and neither are yet warranted.status: publishe
Tissue distribution of residual antimony in rats treated with multiple doses of meglumine antimoniate
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