92,473 research outputs found
Inconsistencies between lifetime and polarizability measurements in Cs
Electric-dipole matrix elements for 6p-nd, n=5, 6, 7 transitions in cesium
are calculated using a relativistic all-order method. The resulting matrix
elements are used to evaluate 5d lifetimes and 6p polarizabilities. The data
are compared with experimental lifetime and polarizability measurements made by
different groups. Domination of the 6p scalar polarizabilities by 5d-6p dipole
matrix elements facilitates an exacting consistency check of 5d lifetime and 6p
polarizability data. Values of 5d-6p matrix elements obtained from experimental
5d lifetime data are found to be inconsistent with those inferred from 6p
polarizabilities derived from experimental Stark shift data. Our ab initio
calculated 6p polarizabilities agree well with experimental determinations.Comment: 5 pages, submitted to Physical Review
A Lifecourse Approach to Long-Term Sickness Absence-A Cohort Study
This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Polarizabilities of Si^{2+}: a benchmark test of theory and experiment
We have calculated electric-dipole polarizabilities of the 3s^2 ^1S_0, 3s3p
^3P_0, and 3s3p ^1P_1 states of the Si^{2+} ion using recently developed
configuration interaction + all-order method. Detailed evaluation of the
uncertainties of the final results is carried out. Our value for the ground
state electric-dipole polarizability 11.670(13) a.u. is in excellent agreement
with the resonant excitation Stark ionization spectroscopy value 11.669(9) a.u.
[Komara et al., J. Phys. B 38, 87 (2005); Mitroy, Phys. Rev. A 78, 052515
(2008)]. This work represents the most precise benchmark test to date of theory
and experiment in divalent atoms. The near cancellation of the ns^2 ^1S_0
ground state and the lowest nsnp ^3P_0 polarizabilities previously observed in
B+, Al+, In+, Tl+, and Pb^{2+} is also found in Si^{2+} ion.Comment: 6 page
Milton Keynes - preliminary estimates of regional traffic flows in 1981
The Milton Keynes Development Corporation and their planning
consultants have asked the College Transport Group to investigate the
scale of likely regional traffic flows into and out of Milton Keynes.
At this stage the emphasis is on providing information for the preparation
of a Master Plan for the city itself, rather than detailed traffic
estimates for planning transport systems in the surrounding region.
Population estimates for 1981 have been obtained from County
Councils for areas within a 20 mile radius of the new city, and the
proportions attracted to Milton Keynes for work and shopping assessed
using gravity model techniques. Separate estimates have been made of
work journeys from the city to regional employment and to London.
Possible upper and lower limits to these forecasts are included to
account for many uncertainties in the absolute and relative growth of
population, employment and shopping opportunities in the city itself and
in the surrounding region. The results are presented as traffic flews
into and out of octant sectors around the city. Flows to the east are
greater than to the west with work trip flows of the order of 2,500 person
trips each way in the most heavily loaded sectors. A 1981 city population
of 150,000 is likely to produce at least 1,500 daily commuters to London
using the fast rail service, with an additional 200 commuters from the region
using Milton Keynes railway station
Modeling charge transport in C60-based self-assembled monolayers for applications in field-effect transistors
We have investigated the conductance properties of C60-containing
self-assembled monolayers (SAMs), which are used in organic field-effect
transistors, employing a combination of molecular-dynamics simulations,
semiempirical electronic structure calculations and Landauer transport theory.
The results reveal the close relation between the transport characteristics and
the structural and electronic properties of the SAM. Furthermore, both local
pathways of charge transport in the SAMs and the influence of structural
fluctuations are analyzed.Comment: 10 figure
FARM-LEVEL EVALUATION OF ALTERNATIVE POLICY APPROACHES TO REDUCE NITRATE LEACHING FROM MIDWEST AGRICULTURE
Policies to reduce nitrate leaching are evaluated using a mixed integer linear programming model of a representative Michigan cash grain farm. At spring 1993 prices, elimination of the current deficiency payment program is found to be more efficient at reducing leaching than a nitrogen input tax, a tax credit on biologically fixed nitrogen, a rotation payment, or obligatory use of the Integrated Farm Management Program Option (IFMPO). However, elimination of the deficiency payment program would significantly reduce farm income. Modeling risk management and nitrate leaching dynamics are useful extensions of this research, as is estimating the benefits from averting nitrate leaching.Agricultural and Food Policy,
Radio emission from the massive stars in the Galactic Super Star Cluster Westerlund 1
Current mass-loss rate estimates imply that main sequence winds are not
sufficient to strip away the H-rich envelope to yield Wolf-Rayet (WR) stars.
The rich transitional population of Westerlund 1 (Wd 1) provides an ideal
laboratory to observe mass-loss processes throughout the transitional phase of
stellar evolution. An analysis of deep radio continuum observations of Wd 1 is
presented. We detect 18 cluster members. The radio properties of the sample are
diverse, with thermal, non-thermal and composite thermal/non-thermal sources
present. Mass-loss rates are ~10^{-5} solar mass/year across all spectral
types, insufficient to form WRs during a massive star lifetime, and the stars
must undergo a period of enhanced mass loss. The sgB[e] star W9 may provide an
example, with a mass-loss rate an order of magnitude higher than the other
cluster members, and an extended nebula of density ~3 times the current wind.
This structure is reminiscent of luminous blue variables, and one with evidence
of two eras of high, possibly eruptive, mass loss. Three OB supergiants are
detected, implying unusually dense winds. They also may have composite spectra,
suggesting binarity. Spatially resolved nebulae are associated with three of
the four RSGs and three of the six YHGs in the cluster, which are due to
quiescent mass loss rather than outbursts. For some of the cool star winds, the
ionizing source may be a companion star though the cluster radiation density is
sufficiently high to provide the necessary ionizing radiation. Five WR stars
are detected with composite spectra, interpreted as arising in colliding-wind
binaries.Comment: 15 pages, 6 figures. Accepted for publication in Astronomy and
Astrophysic
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