19,394 research outputs found
Seed Magnetic Fields Generated by Primordial Supernova Explosions
The origin of the magnetic field in galaxies is an open question in
astrophysics. Several mechanisms have been proposed related, in general, with
the generation of small seed fields amplified by a dynamo mechanism. In
general, these mechanisms have difficulty in satisfying both the requirements
of a sufficiently high strength for the magnetic field and the necessary large
coherent scales. We show that the formation of dense and turbulent shells of
matter, in the multiple explosion scenario of Miranda and Opher (1996, 1997)
for the formation of the large-scale structures of the Universe, can naturally
act as a seed for the generation of a magnetic field. During the collapse and
explosion of Population III objects, a temperature gradient not parallel to a
density gradient can naturally be established, producing a seed magnetic field
through the Biermann battery mechanism. We show that seed magnetic fields can be produced in this multiple explosion scenario on
scales of the order of clusters of galaxies (with coherence length ) and up to on scales of galaxies ().Comment: Accepted for publication in MNRAS, 5 pages (MN plain TeX macros v1.6
file). Also available at http://www.iagusp.usp.br/~oswaldo (click "OPTIONS"
and then "ARTICLES"
Multiplicative local linear hazard estimation and best one-sided cross-validation
This paper develops detailed mathematical statistical theory of a new class of cross-validation techniques of local linear kernel hazards and their multiplicative bias corrections. The new class of cross-validation combines principles of local information and recent advances in indirect cross-validation. A few applications of cross-validating multiplicative kernel hazard estimation do exist in the literature. However, detailed mathematical statistical theory and small sample performance are introduced via this paper and further upgraded to our new class of best one-sided cross-validation. Best one-sided cross-validation turns out to have excellent performance in its practical illustrations, in its small sample performance and in its mathematical statistical theoretical performance
Mott transition in the Hubbard model away from particle-hole symmetry
We solve the Dynamical Mean Field Theory equations for the Hubbard model away
from the particle-hole symmetric case using the Density Matrix Renormalization
Group method. We focus our study on the region of strong interactions and
finite doping where two solutions coexist. We obtain precise predictions for
the boundaries of the coexistence region. In addition, we demonstrate the
capabilities of this precise method by obtaining the frequency dependent
optical conductivity spectra.Comment: 4 pages, 4 figures; updated versio
A generalized vortex lattice method for subsonic and supersonic flow applications
If the discrete vortex lattice is considered as an approximation to the surface-distributed vorticity, then the concept of the generalized principal part of an integral yields a residual term to the vorticity-induced velocity field. The proper incorporation of this term to the velocity field generated by the discrete vortex lines renders the present vortex lattice method valid for supersonic flow. Special techniques for simulating nonzero thickness lifting surfaces and fusiform bodies with vortex lattice elements are included. Thickness effects of wing-like components are simulated by a double (biplanar) vortex lattice layer, and fusiform bodies are represented by a vortex grid arranged on a series of concentrical cylindrical surfaces. The analysis of sideslip effects by the subject method is described. Numerical considerations peculiar to the application of these techniques are also discussed. The method has been implemented in a digital computer code. A users manual is included along with a complete FORTRAN compilation, an executed case, and conversion programs for transforming input for the NASA wave drag program
Probing neutrino transition magnetic moments with coherent elastic neutrino-nucleus scattering
We explore the potential of current and next generation of coherent elastic
neutrino-nucleus scattering (CENS) experiments in probing neutrino
electromagnetic interactions. On the basis of a thorough statistical analysis,
we determine the sensitivities on each component of the Majorana neutrino
transition magnetic moment (TMM), , that
follow from low-energy neutrino-nucleus experiments. We derive the sensitivity
to neutrino TMM from the first CENS measurement by the COHERENT
experiment, at the Spallation Neutron Source. We also present results for the
next phases of COHERENT using HPGe, LAr and NaI[Tl] detectors and for reactor
neutrino experiments such as CONUS, CONNIE, MINER, TEXONO and RED100. The role
of the CP violating phases in each case is also briefly discussed. We conclude
that future CENS experiments with low-threshold capabilities can improve
current TMM limits obtained from Borexino data.Comment: 25 pages, 8 figures, 2 tables, analysis updated; conclusions
unchanged; references added; matches published versio
- …