14,371 research outputs found
Relativistic many-body calculations of the Stark-induced amplitude of the 6P1/2 -7P1/2 transition in thallium
Stark-induced amplitudes for the 6P1/2 - 7P1/2 transition in Tl I are
calculated using the relativistic SD approximation in which single and double
excitations of Dirac-Hartree-Fock levels are summed to all orders in
perturbation theory. Our SD values alpha S = 368 a0 3 and beta S= 298 a 0 3 are
in good agreement with the measurements alpha S=377(8) a 0 3$ and beta S =
313(8) a 0 3 by D. DeMille, D. Budker, and E. D. Commins [Phys. Rev. A 50, 4657
(1994)]. Calculations of the Stark shifts in the 6P1/2 - 7P1/2 and 6P1/2 -
7S1/2 transitions are also carried out. The Stark shifts predicted by our
calculations agree with the most accurate measured values within the
experimental uncertainties for both transitions
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Improved V I Log(gf) Values and Abundance Determinations in the Photospheres of the Sun and Metal-Poor Star HD 84937
New emission branching fraction measurements for 836 lines of the first spectrum of vanadium (V I) are determined from hollow cathode lamp spectra recorded with the National Solar Observatory 1 m Fourier transform spectrometer (FTS) and a high-resolution echelle spectrometer. The branching fractions are combined with recently published radiative lifetimes from laser-induced fluorescence measurements to determine accurate absolute atomic transition probabilities for the 836 lines. The FTS data are also used to extract new hyperfine structure A coefficients for 26 levels of neutral vanadium. These new laboratory data are applied to determine the V abundance in the Sun and metal-poor star HD 84937, yielding log epsilon(V) = 3.956 +/- 0.004 (sigma = 0.037) based on 93 V I lines and log epsilon(V) = 1.89 +/- 0.03 (sigma = 0.07) based on nine Vi lines, respectively, using the Holweger-Muller 1D model. These new V I abundance values for the Sun and HD 84937 agree well with our earlier determinations based upon V II.NASA NNX10AN93GNSF AST-1211055, AST-1211585Astronom
A Linear Iterative Unfolding Method
A frequently faced task in experimental physics is to measure the probability
distribution of some quantity. Often this quantity to be measured is smeared by
a non-ideal detector response or by some physical process. The procedure of
removing this smearing effect from the measured distribution is called
unfolding, and is a delicate problem in signal processing, due to the
well-known numerical ill behavior of this task. Various methods were invented
which, given some assumptions on the initial probability distribution, try to
regularize the unfolding problem. Most of these methods definitely introduce
bias into the estimate of the initial probability distribution. We propose a
linear iterative method, which has the advantage that no assumptions on the
initial probability distribution is needed, and the only regularization
parameter is the stopping order of the iteration, which can be used to choose
the best compromise between the introduced bias and the propagated statistical
and systematic errors. The method is consistent: "binwise" convergence to the
initial probability distribution is proved in absence of measurement errors
under a quite general condition on the response function. This condition holds
for practical applications such as convolutions, calorimeter response
functions, momentum reconstruction response functions based on tracking in
magnetic field etc. In presence of measurement errors, explicit formulae for
the propagation of the three important error terms is provided: bias error,
statistical error, and systematic error. A trade-off between these three error
terms can be used to define an optimal iteration stopping criterion, and the
errors can be estimated there. We provide a numerical C library for the
implementation of the method, which incorporates automatic statistical error
propagation as well.Comment: Proceedings of ACAT-2011 conference (Uxbridge, United Kingdom), 9
pages, 5 figures, changes of corrigendum include
Mapping Exoplanets
The varied surfaces and atmospheres of planets make them interesting places
to live, explore, and study from afar. Unfortunately, the great distance to
exoplanets makes it impossible to resolve their disk with current or near-term
technology. It is still possible, however, to deduce spatial inhomogeneities in
exoplanets provided that different regions are visible at different
times---this can be due to rotation, orbital motion, and occultations by a
star, planet, or moon. Astronomers have so far constructed maps of thermal
emission and albedo for short period giant planets. These maps constrain
atmospheric dynamics and cloud patterns in exotic atmospheres. In the future,
exo-cartography could yield surface maps of terrestrial planets, hinting at the
geophysical and geochemical processes that shape them.Comment: Updated chapter for Handbook of Exoplanets, eds. Deeg & Belmonte. 17
pages, including 6 figures and 4 pages of reference
Dynamics Of Australian Dairy-Food Supply Chain: Strategic Options For Participants In A Deregulated Environment
Following deregulation, participants in Australian dairy-food supply chains are confronted with a more complex and rapidly changing environment. In a study conducted between March 2002 and April 2003, major supermarkets emerged as the dominant power in chain development, with a trend towards greater interdependence and coordination between the chain participants. Future supply chain development will depend on the capabilities of the chain participants in operational and strategic management within the firm, and also in successfully negotiating linkages within the chains. In addition the organizational structures of both the firms and the chains need to be responsive to changing end-user needs and the dynamic business environment
Progress of the Felsenkeller shallow-underground accelerator for nuclear astrophysics
Low-background experiments with stable ion beams are an important tool for
putting the model of stellar hydrogen, helium, and carbon burning on a solid
experimental foundation. The pioneering work in this regard has been done by
the LUNA collaboration at Gran Sasso, using a 0.4 MV accelerator. In the
present contribution, the status of the project for a higher-energy underground
accelerator is reviewed. Two tunnels of the Felsenkeller underground site in
Dresden, Germany, are currently being refurbished for the installation of a 5
MV high-current Pelletron accelerator. Construction work is on schedule and
expected to complete in August 2017. The accelerator will provide intense, 50
uA, beams of 1H+, 4He+, and 12C+ ions, enabling research on astrophysically
relevant nuclear reactions with unprecedented sensitivity.Comment: Submitted to the Proceedings of Nuclei in the Cosmos XIV, 19-24 June
2016, Niigata/Japa
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