586 research outputs found
Pseudospectral methods for atoms in strong magnetic fields
We present a new pseudospectral algorithm for the calculation of the
structure of atoms in strong magnetic fields. We have verified this technique
for one, two and three-electron atoms in zero magnetic fields against
laboratory results and find typically better than one-percent accuracy. We
further verify this technique against the state-of-the-art calculations of
hydrogen, helium and lithium in strong magnetic fields (up to about T) and find a similar level of agreement. The key enabling advantages
of the algorithm are its simplicity (about 130 lines of commented code) and its
speed (about times faster than finite-element methods to achieve
similar accuracy).Comment: 10 pages, version accepted to MNRA
Prospects for precision measurements of atomic helium using direct frequency comb spectroscopy
We analyze several possibilities for precisely measuring electronic
transitions in atomic helium by the direct use of phase-stabilized femtosecond
frequency combs. Because the comb is self-calibrating and can be shifted into
the ultraviolet spectral region via harmonic generation, it offers the prospect
of greatly improved accuracy for UV and far-UV transitions. To take advantage
of this accuracy an ultracold helium sample is needed. For measurements of the
triplet spectrum a magneto-optical trap (MOT) can be used to cool and trap
metastable 2^3S state atoms. We analyze schemes for measuring the two-photon
interval, and for resonant two-photon excitation to high
Rydberg states, . We also analyze experiments on the
singlet-state spectrum. To accomplish this we propose schemes for producing and
trapping ultracold helium in the 1^1S or 2^1S state via intercombination
transitions. A particularly intriguing scenario is the possibility of measuring
the transition with extremely high accuracy by use of
two-photon excitation in a magic wavelength trap that operates identically for
both states. We predict a ``triple magic wavelength'' at 412 nm that could
facilitate numerous experiments on trapped helium atoms, because here the
polarizabilities of the 1^1S, 2^1S and 2^3S states are all similar, small, and
positive.Comment: Shortened slightly and reformatted for Eur. Phys. J.
risk status (Seginer
a b s t r a c t In the present study, we examined demographic differences in time attitudes in a sample of 293 adolescents. Time attitudes were measured using the Adolescent Time Attitude Scale Published by Elsevier Ltd on behalf of The Foundation for Professionals in Services for Adolescents. Time attitudes, one dimension of time perspective, refer to an individual's emotional and evaluative feelings toward the past, the present, and the future, and there is an extensive literature on the relationship between time attitudes and several other variables. For example, researchers have found that time attitudes are related to academic achievement (e.g., Some researchers have proposed that demographic variables both set the stage for and maintain individuals' time perspective
From QCD lattice calculations to the equation of state of quark matter
We describe two-flavor QCD lattice data for the pressure at finite
temperature and zero chemical potential within a quasiparticle model. Relying
only on thermodynamic selfconsistency, the model is extended to nonzero
chemical potential. The results agree with lattice calculations in the region
of small chemical potential.Comment: 5 eps figure
Rearing laying hens in aviaries reduces fearfulness following transfer to furnished cages
Appropriate rearing is essential for ensuring the welfare and productivity of laying hens. Early experience has the potential to affect the development of fearfulness. This study tested whether rearing in aviaries, as opposed to cages, reduces the fearfulness of laying hens after transfer to furnished cages. Fear responses were recorded as avoidance of a novel object in the home cage. Lohmann Selected Leghorns were reared in an aviary system or conventional rearing cages and then transported to furnished cages at 16 weeks, before the onset of lay. Observations of a selection of birds were conducted at 19 (N = 50 independent cages) and 21 (N = 48 independent cages) weeks of age. At 19 and 21 weeks, cage-reared birds showed higher levels of fearfulness indicated by spending more time away from the novel object compared to aviary-reared birds. These results suggest that rearing in an enriched aviary environment reduces fearfulness up to the fifth week after transfer to a new housing system, compared to rearing in cages
Establishing HZ43 A, Sirius B, and RX J185635-3754 as soft X-ray standards: a cross-calibration between the Chandra LETG+HRC-S, the EUVE spectrometer, and the ROSAT PSPC
The absolute calibration of space-borne instruments in the soft X-ray regime
rests strongly on model spectra of hot white dwarfs.
We analyze the Chandra LETG+HRC-S observations of the white dwarfs HZ43 A and
Sirius B and of the neutron star RX J185635-3754 in order to resolve current
uncertainties in the soft X-ray spectral fluxes and photospheric parameters of
the three stars. We have obtained improved parameters for which fit the
observations from the optical to the soft X-ray regime. Our approach allows us
to quote their absolute spectral fluxes at selected wavelengths which may aid
the calibration of other space-borne instruments.Comment: 15 pages, 9 figure
Pseudospectral Calculation of Helium Wave Functions, Expectation Values, and Oscillator Strength
The pseudospectral method is a powerful tool for finding highly precise
solutions of Schr\"{o}dinger's equation for few-electron problems. We extend
the method's scope to wave functions with non-zero angular momentum and test it
on several challenging problems. One group of tests involves the determination
of the nonrelativistic electric dipole oscillator strength for the helium
S P transition. The result achieved, , is
comparable to the best in the literature.
Another group of test applications is comprised of well-studied leading order
finite nuclear mass and relativistic corrections for the helium ground state. A
straightforward computation reaches near state-of-the-art accuracy without
requiring the implementation of any special-purpose numerics.
All the relevant quantities tested in this paper -- energy eigenvalues,
S-state expectation values and bound-bound dipole transitions for S and P
states -- converge exponentially with increasing resolution and do so at
roughly the same rate. Each individual calculation samples and weights the
configuration space wave function uniquely but all behave in a qualitatively
similar manner. Quantum mechanical matrix elements are directly and reliably
calculable with pseudospectral methods.
The technical discussion includes a prescription for choosing coordinates and
subdomains to achieve exponential convergence when two-particle Coulomb
singularities are present. The prescription does not account for the wave
function's non-analytic behavior near the three-particle coalescence which
should eventually hinder the rate of the convergence. Nonetheless the effect is
small in the sense that ignoring the higher-order coalescence does not appear
to affect adversely the accuracy of any of the quantities reported nor the rate
at which errors diminish.Comment: 24 pages, 12 figures, 6 tables. To be submitted to Physical Review A.
LANL identifier 'LA-UR-11-10986
Swift X-Ray Observations of Classical Novae. II. The Super Soft Source sample
The Swift GRB satellite is an excellent facility for studying novae. Its
rapid response time and sensitive X-ray detector provides an unparalleled
opportunity to investigate the previously poorly sampled evolution of novae in
the X-ray regime. This paper presents Swift observations of 52
Galactic/Magellanic Cloud novae. We included the XRT (0.3-10 keV) X-ray
instrument count rates and the UVOT (1700-8000 Angstroms) filter photometry.
Also included in the analysis are the publicly available pointed observations
of 10 additional novae the X-ray archives. This is the largest X-ray sample of
Galactic/Magellanic Cloud novae yet assembled and consists of 26 novae with
super soft X-ray emission, 19 from Swift observations. The data set shows that
the faster novae have an early hard X-ray phase that is usually missing in
slower novae. The Super Soft X-ray phase occurs earlier and does not last as
long in fast novae compared to slower novae. All the Swift novae with
sufficient observations show that novae are highly variable with rapid
variability and different periodicities. In the majority of cases, nuclear
burning ceases less than 3 years after the outburst begins. Previous
relationships, such as the nuclear burning duration vs. t_2 or the expansion
velocity of the eject and nuclear burning duration vs. the orbital period, are
shown to be poorly correlated with the full sample indicating that additional
factors beyond the white dwarf mass and binary separation play important roles
in the evolution of a nova outburst. Finally, we confirm two optical phenomena
that are correlated with strong, soft X-ray emission which can be used to
further increase the efficiency of X-ray campaigns.Comment: Accepted to ApJ Supplements. Full data for Table 2 and Figure 17
available in the electronic edition. New version of the previously posted
paper since the earlier version was all set in landscape mod
- …