6,654 research outputs found
Interference effects in two-photon ATI by multiple orders high harmonics with random or locked phases
We numerically study 2-photon processes using a set of harmonics from a
Ti:Sapphire laser and in particular interference effects in the Above Threshold
Ionization spectra. We compare the situation where the harmonic phases are
assumed locked to the case where they have a random distribution. Suggestions
for possible experiments, using realistic parameters are discussed.Comment: 11 pages, 13 figures, LaTe
Global Examination of the C+C Reaction Data at Low and Intermediate Energies
We examine the C+C elastic scattering over a wide energy range
from 32.0 to 70.7 MeV in the laboratory system within the framework of the
Optical model and the Coupled-Channels formalism. The C+C system
has been extensively studied within and over this energy range in the past.
These efforts have been futile in determining the shape of the nuclear
potential in the low energy region and in describing the individual angular
distributions, single-angle 50 to 90 excitation functions and
reaction cross-section data simultaneously. In order to address these problems
systematically, we propose a potential that belongs to a family other than the
one used to describe higher energy experimental data and show that it is
possible to use it over this wide energy range. This potential also predicts
the resonances at correct energies with reasonable widths.Comment: 30 pages with 13 eps figues and 3 tables, LaTeX-Revtex
Dynamics of coupled bosonic systems with applications to preheating
Coupled, multi-field models of inflation can provide several attractive
features unavailable in the case of a single inflaton field. These models have
a rich dynamical structure resulting from the interaction of the fields and
their associated fluctuations. We present a formalism to study the
nonequilibrium dynamics of coupled scalar fields. This formalism solves the
problem of renormalizing interacting models in a transparent way using
dimensional regularization. The evolution is generated by a renormalized
effective Lagrangian which incorporates the dynamics of the mean fields and
their associated fluctuations at one-loop order. We apply our method to two
problems of physical interest: (i) a simple two-field model which exemplifies
applications to reheating in inflation, and (ii) a supersymmetric hybrid
inflation model. This second case is interesting because inflation terminates
via a smooth phase transition which gives rise to a spinodal instability in one
of the fields. We study the evolution of the zero mode of the fields and the
energy density transfer to the fluctuations from the mean fields. We conclude
that back reaction effects can be significant over a wide parameter range. In
particular for the supersymmetric hybrid model we find that particle production
can be suppressed due to these effects.Comment: 23 pages, 16 eps-figures, minor changes in the text, references
added, accepted for publication in PR
A milestone toward understanding PDR properties in the extreme environment of LMC-30Dor
More complete knowledge of galaxy evolution requires understanding the
process of star formation and interaction between the interstellar radiation
field and the interstellar medium in galactic environments traversing a wide
range of physical parameter space. Here we focus on the impact of massive star
formation on the surrounding low metallicity ISM in 30 Doradus in the Large
Magellanic Cloud. A low metal abundance, as is the case of some galaxies of the
early universe, results in less ultra-violet shielding for the formation of the
molecular gas necessary for star formation to proceed. The half-solar
metallicity gas in this region is strongly irradiated by the super star cluster
R136, making it an ideal laboratory to study the structure of the ISM in an
extreme environment. Our spatially resolved study investigates the gas heating
and cooling mechanisms, particularly in the photo-dissociation regions where
the chemistry and thermal balance are regulated by far-ultraviolet photons (6
eV< h\nu <13.6 eV).
We present Herschel observations of far-infrared fine-structure lines
obtained with PACS and SPIRE/FTS. We have combined atomic fine-structure lines
from Herschel and Spitzer observations with ground-based CO data to provide
diagnostics on the properties and the structure of the gas by modeling it with
the Meudon PDR code. We derive the spatial distribution of the radiation field,
the pressure, the size, and the filling factor of the photodissociated gas and
molecular clouds. We find a range of pressure of ~ 10^5 - 1.7x10^6 cm^{-3} K
and a range of incident radiation field G_UV ~ 10^2 - 2.5x10^4 through PDR
modeling. Assuming a plane-parallel geometry and a uniform medium, we find a
total extinction of 1-3 mag , which correspond to a PDR cloud size of 0.2 to
3pc, with small CO depth scale of 0.06 to 0.5pc. We also determine the three
dimensional structure of the gas. (Abridged)Comment: 20 pages, 23 figures, accepted in A&
Nkx2-5 and Sarcospan genetically interact in the development of the muscular ventricular septum of the heart
The muscular ventricular septum separates the flow of oxygenated and de-oxygenated blood in air-breathing vertebrates. Defects within it, termed muscular ventricular septal defects (VSDs), are common, yet less is known about how they arise than rarer heart defects. Mutations of the cardiac transcription factor NKX2-5 cause cardiac malformations, including muscular VSDs. We describe here a genetic interaction between Nkx2-5 and Sarcospan (Sspn) that affects the risk of muscular VSD in mice. Sspn encodes a protein in the dystrophin-glycoprotein complex. Sspn knockout (Sspn(KO)) mice do not have heart defects, but Nkx2-5(+/−)/Sspn(KO) mutants have a higher incidence of muscular VSD than Nkx2-5(+/−) mice. Myofibers in the ventricular septum follow a stereotypical pattern that is disrupted around a muscular VSD. Subendocardial myofibers normally run in parallel along the left ventricular outflow tract, but in the Nkx2-5(+/−)/Sspn(KO) mutant they commonly deviate into the septum even in the absence of a muscular VSD. Thus, Nkx2-5 and Sspn act in a pathway that affects the alignment of myofibers during the development of the ventricular septum. The malalignment may be a consequence of a defect in the coalescence of trabeculae into the developing ventricular septum, which has been hypothesized to be the mechanistic basis of muscular VSDs
A Survey of Atomic Carbon [C I] in High-redshift Main-Sequence Galaxies
We present the first results of an ALMA survey of the lower fine structure
line of atomic carbon [C I](^3P_1\,-\,^{3}P_0) in far infrared-selected
galaxies on the main sequence at in the COSMOS field. We compare our
sample with a comprehensive compilation of data available in the literature for
local and high-redshift starbursting systems and quasars. We show that the [C
I]() luminosity correlates on global scales with the
infrared luminosity similarly to low- CO transitions. We report
a systematic variation of L'_{\rm [C\,I]^3P_1\,-\, ^3P_0}/ as a
function of the galaxy type, with the ratio being larger for main-sequence
galaxies than for starbursts and sub-millimeter galaxies at fixed .
The L'_{\rm [C\,I]^3P_1\,-\, ^3P_0}/ and / mass ratios are similar for main-sequence galaxies and for
local and high-redshift starbursts within a 0.2 dex intrinsic scatter,
suggesting that [C I] is a good tracer of molecular gas mass as CO and dust. We
derive a fraction of %
of the total carbon mass in the atomic neutral phase. Moreover, we estimate the
neutral atomic carbon abundance, the fundamental ingredient to calibrate [C I]
as a gas tracer, by comparing L'_{\rm [C\,I]^3P_1\,-\, ^3P_0} and available
gas masses from CO lines and dust emission. We find lower [C I] abundances in
main-sequence galaxies than in starbursting systems and sub-millimeter
galaxies, as a consequence of the canonical and gas-to-dust
conversion factors. This argues against the application to different galaxy
populations of a universal standard [C I] abundance derived from highly biased
samples.Comment: 14 pages + Appendix. Accepted for publication in ApJ. All the data
tables in Appendix will be also released in electronic forma
Two--Electron Atoms in Short Intense Laser Pulses
We discuss a method of solving the time dependent Schrodinger equation for
atoms with two active electrons in a strong laser field, which we used in a
previous paper [A. Scrinzi and B. Piraux, Phys. Rev. A 56, R13 (1997)] to
calculate ionization, double excitation and harmonic generation in Helium by
short laser pulses. The method employs complex scaling and an expansion in an
explicitly correlated basis. Convergence of the calculations is documented and
error estimates are provided. The results for Helium at peak intensities up to
10^15 W/cm^2 and wave length 248 nm are accurate to at least 10 %. Similarly
accurate calculations are presented for electron detachment and double
excitation of the negative hydrogen ion.Comment: 14 pages, including figure
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