1,847 research outputs found
Excitation of Na D-line radiation in collisions of sodium atoms with internally excited H2, D2, and N2
Excitation of D-line radiation in collisions of Na atoms with vibrationally excited N2, H2 and D2 was studied in two modulated crossed beam experiments. In both experiments, the vibrational excitation of the molecules was provided by heating the molecular beam source to temperatures in the range of 2000 to 3000 K, which was assumed to give populations according to the Boltzmann expression. In the first experiment, a total rate coefficient was measured as a function of molecular beam temperature, with absolute calibration of the photon detector being made using the black body radiation from the heated molecular beam source. Since heating affects both the internal energy and the collisional kinetic energy, the first experiment could not determine the relative contributions of internal energy transfer versus collisional excitation. The second experiment achieved partial separation of internal versus kinetic energy transfer effects by using a velocity-selected molecular beam. Using two simple models for the kinetic energy dependence of the transfer cross section for a given change in vibrational quantum number, the data from both experiments were used to determine parameters in the models
Non-invasive detection of charge-rearrangement in a quantum dot in high magnetic fields
We demonstrate electron redistribution caused by magnetic field on a single
quantum dot measured by means of a quantum point contact as non-invasive
detector. Our device which is fabricated by local anodic oxidation allows to
control independently the quantum point contact and all tunnelling barriers of
the quantum dot. Thus we are able to measure both the change of the quantum dot
charge and also changes of the electron configuration at constant number of
electrons on the quantum dot. We use these features to exploit the quantum dot
in a high magnetic field where transport through the quantum dot displays the
effects of Landau shells and spin blockade. We confirm the internal
rearrangement of electrons as function of the magnetic field for a fixed number
of electrons on the quantum dot.Comment: 4 pages, 5 figure
A Redshift Survey of Nearby Galaxy Groups: the Shape of the Mass Density Profile
We constrain the mass profile and orbital structure of nearby groups and
clusters of galaxies. Our method yields the joint probability distribution of
the density slope n, the velocity anisotropy beta, and the turnover radius r0
for these systems. The measurement technique does not use results from N-body
simulations as priors. We incorporate 2419 new redshifts in the fields of 41
systems of galaxies with z < 0.04. The new groups have median velocity
dispersion sigma=360 km/s. We also use 851 archived redshifts in the fields of
8 nearly relaxed clusters with z < 0.1. Within R < 2 r200, the data are
consistent with a single power law matter density distribution with slope n =
1.8-2.2 for systems with sigma < 470 km/s, and n = 1.6-2.0 for those with sigma
> 470 km/s (95% confidence). We show that a simple, scale-free phase space
distribution function f(E,L^2) ~ (-E)^(alpha-1/2) L^(-2 \beta) is consistent
with the data as long as the matter density has a cusp. Using this DF, matter
density profiles with constant density cores (n=0) are ruled out with better
than 99.7% confidence.Comment: 22 pages; accepted for publication in the Astrophysical Journa
Algebraic Approach to Shape Invariance
The integrability condition called shape invariance is shown to have an
underlying algebraic structure and the associated Lie algebras are identified.
These shape-invariance algebras transform the parameters of the potentials such
as strength and range. Shape-invariance algebras, in general, are shown to be
infinite-dimensional. The conditions under which they become finite-dimensional
are explored.Comment: Submitted to Physical Review A. Latex file, 9 pages. Manuscript is
also available at http://nucth.physics.wisc.edu/preprints
A spectroscopic study of component C and the extended emission around I Zw 18
Long-slit Keck II, 4m Kitt Peak, and 4.5m MMT spectrophotometric data are
used to investigate the stellar population and the evolutionary status of I Zw
18C, the faint C component of the nearby blue compact dwarf galaxy I Zw 18.
Hydrogen H and H emission lines are detected in the spectra of I
Zw 18C, implying that ionizing massive stars are present. High signal-to-noise
Keck II spectra of different regions in I Zw 18C reveal H, H
and higher order hydrogen lines in absorption. Several techniques are used to
constrain the age of the stellar population in I Zw 18C. Ages derived from two
different methods, one based on the equivalent widths of the H,
H emission lines and the other on H, H absorption lines
are consistent with a 15 Myr instantaneous burst model. We find that a small
extinction in the range = 0.20 -- 0.65 mag is needed to fit the observed
spectral energy distribution of I Zw 18C with that model. In the case of
constant star formation, all observed properties are consistent with stars
forming continuously between ~ 10 Myr and < 100 Myr ago. We use all available
observational constraints for I Zw 18C, including those obtained from Hubble
Space Telescope color-magnitude diagrams, to argue that the distance to I Zw 18
should be as high as ~ 15 Mpc. The deep spectra also reveal extended ionized
gas emission around I Zw 18. H emission is detected as far as 30" from
it. To a B surface brightness limit of ~ 27 mag arcsec we find no
observational evidence for extended stellar emission in the outermost regions,
at distances > 15" from I Zw 18.Comment: 38 pages, 11 Postscript figures, accepted for publication in the
Astrophysical Journa
A search for broad infrared recombination lines in NGC 1068
We report infrared spectroscopy of the prototypical Seyfert 2 galaxy NGC
1068, aiming at detection of broad components of hydrogen recombination lines
that originate in the obscured broad-line region. Using the Short Wavelength
Spectrometer on board the Infrared Space Observatory, we have observed for the
first time the regions of Brackett beta 2.626um and Pfund alpha 7.460um, and
present improved data for Brackett alpha 4.052um. No significant broad
components are detected, implying an equivalent visual extinction to the
broad-line region of at least 50 magnitudes and an obscuring column density of
at least 10^23 cm^-2. While consistent with a highly obscured broad-line
region, as required by the classical unified scenario, these limits are not yet
significant enough to discriminate strongly between different torus models or
to constrain properties of the gas causing the very large X-ray obscuration. We
discuss the systematic limitations of infrared broad-line region searches and
suggest that Brackett alpha may often be the most favorable transition for
future searches.Comment: aastex (V4), 4 eps figures. Accepted by Ap
Semiclassical wave equation and exactness of the WKB method
The exactness of the semiclassical method for three-dimensional problems in
quantum mechanics is analyzed. The wave equation appropriate in the
quasiclassical region is derived. It is shown that application of the standard
leading-order WKB quantization condition to this equation reproduces exact
energy eigenvalues for all solvable spherically symmetric potentials.Comment: 13 page
Occurrence and determinants of parental psychosocial stress and mental health disorders in parents and their children in early childhood: rationale, objectives, and design of the population-based SKKIPPI cohort study
Purpose: The postnatal period is a vulnerable time for parents and children but epidemiological and health care utilisation data for Germany on parental mental health during early childhood is scarce. This protocol describes the rationale, aim and study design of a population-based cohort study to assess the occurrence and determinants of psychosocial stress and mental health disorders, as well as the use and cost of health care and social services in early childhood.
Methods: As part of the collaborative SKKIPPI project, we will contact a random sample of 30,000 infants listed in the residents’ registration offices of three German towns and we expect to include 6,000 mother–child pairs. Both parents are invited to fill out an online screening questionnaire. Mothers with indications of psychosocial stress will be interviewed to assess mental health disorders, regulatory problems of their children, as well as health care and social services utilisation, with a follow-up assessment after 6 months.
Results: After description of sociodemographic and health data, we will analyse occurrences, patterns, and potential determinants (maternal age, social status, household factors, migration status etc.) of psychosocial stress and mental health disorders in the mothers and their children in early childhood.
Conclusions: Our study will identify potential risk and protective factors for postnatal mental health and health care utilization of psychosocially burdened families. This will help to improve prevention and treatment strategies to strengthen the parent–child relationship, to reduce persisting vulnerability of children, and to improve health care and social services.
Trial registration: The study has been registered in the German Clinical Trial Registry on February 8th 2019 (DRKS-ID: DRKS00016653)
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