4,571 research outputs found
I. The Isotopic Foldy-Wouthuysen Representation and Chiral Symmetry
The paper introduces the isotopic Foldy-Wouthuysen representation. This
representation was used to derive equations for massive interacting fermion
fields. When the interaction Hamiltonian commutes with the matrix, these
equations possess chiral invariance irrespective of whether fermions have mass
or are massless. The isotopic Foldy-Wouthuysen representation preserves the
vector and axial currents irrespective of the fermion mass value. In the Dirac
representation, the axial current is preserved only for massless fermions. In
the isotopic Foldy-Wouthuysen representation, the ground state of fermions
(vacuum) turns out to be degenerate, and therefore there is the possibility of
spontaneously breaking parity (P - symmetry). This study considers the example
of constructing a chirally symmetric quantum electrodynamics framework in the
isotopic Foldy-Wouthuysen representation. A number of physical processes are
calculated in the lowest orders of the perturbation theory. Final results of
the calculations agree with the results of the standard quantum
electrodynamics.Comment: 37 pages, 9 figure
Practice area and work demands in nurses' aides: a cross-sectional study
BACKGROUND: Knowledge of how work demands vary between different practice areas could give us a better understanding of the factors that influence the working conditions in the health services, and could help identify specific work-related challenges and problems in the different practice areas. In turn, this may help politicians, and healthcare administrators and managers to develop healthy work units. The aim of this study was to find out how nurses' aides' perception of demands and control at work vary with the practice area in which the aides are working. METHODS: In 1999, 12 000 nurses' aides were drawn randomly from the member list of the Norwegian Union of Health – and Social Workers, and were mailed a questionnaire. 7478 (62.3 %) filled in the questionnaire. The sample of the present study comprised the 6485 nurses' aides who were not on leave. Respondents working in one practice area were compared with respondents not working in this area (all together). Because of multiple comparisons, 0.01 was chosen as statistical significance level. RESULTS: Total quantitative work demands were highest in somatic hospital departments, nursing homes, and community nurse units. Physical demands were highest in somatic hospital departments and nursing homes. Level of positive challenges was highest in hospital departments and community nurses units, and lowest in nursing homes and homes or apartment units for the aged. Exposure to role conflicts was most frequent in nursing homes, homes or apartment units for the aged, and community nurse units. Exposure to threats and violence was most frequent in psychiatric departments, nursing homes, and institutions for mentally handicapped. Control of work pace was highest in psychiatric departments and institutions for mentally handicapped, and was lowest in somatic hospital departments and nursing homes. Participation in decisions at work was highest in psychiatric departments and community nurse units, and was lowest in somatic hospital departments and nursing homes. CONCLUSION: The demands and control experienced by Norwegian nurses' aides at work vary strongly with the practice area. Preventive workplace interventions should be tailored each area
Probing the subshell closure: factor of the Mg(2) state
The first-excited state ~factor of Mg has been measured relative to
the factor of the Mg() state using the high-velocity
transient-field technique, giving . This new measurement is in
strong disagreement with the currently adopted value, but in agreement with the
-shell model using the USDB interaction. The newly measured factor,
along with and systematics, signal the closure of the subshell at . The possibility that precise -factor
measurements may indicate the onset of neutron admixtures in first-excited
state even-even magnesium isotopes below Mg is discussed and the
importance of precise excited-state -factor measurements on ~shell
nuclei with to test shell-model wavefunctions is noted.Comment: 8 pages, 5 figure
Optimized Large-Scale CMB Likelihood And Quadratic Maximum Likelihood Power Spectrum Estimation
We revisit the problem of exact CMB likelihood and power spectrum estimation
with the goal of minimizing computational cost through linear compression. This
idea was originally proposed for CMB purposes by Tegmark et al.\ (1997), and
here we develop it into a fully working computational framework for large-scale
polarization analysis, adopting \WMAP\ as a worked example. We compare five
different linear bases (pixel space, harmonic space, noise covariance
eigenvectors, signal-to-noise covariance eigenvectors and signal-plus-noise
covariance eigenvectors) in terms of compression efficiency, and find that the
computationally most efficient basis is the signal-to-noise eigenvector basis,
which is closely related to the Karhunen-Loeve and Principal Component
transforms, in agreement with previous suggestions. For this basis, the
information in 6836 unmasked \WMAP\ sky map pixels can be compressed into a
smaller set of 3102 modes, with a maximum error increase of any single
multipole of 3.8\% at , and a maximum shift in the mean values of a
joint distribution of an amplitude--tilt model of 0.006. This
compression reduces the computational cost of a single likelihood evaluation by
a factor of 5, from 38 to 7.5 CPU seconds, and it also results in a more robust
likelihood by implicitly regularizing nearly degenerate modes. Finally, we use
the same compression framework to formulate a numerically stable and
computationally efficient variation of the Quadratic Maximum Likelihood
implementation that requires less than 3 GB of memory and 2 CPU minutes per
iteration for , rendering low- QML CMB power spectrum
analysis fully tractable on a standard laptop.Comment: 13 pages, 13 figures, accepted by ApJ
Bubble, Bubble, Flow and Hubble: Large Scale Galaxy Flow from Cosmological Bubble Collisions
We study large scale structure in the cosmology of Coleman-de Luccia bubble
collisions. Within a set of controlled approximations we calculate the effects
on galaxy motion seen from inside a bubble which has undergone such a
collision. We find that generically bubble collisions lead to a coherent bulk
flow of galaxies on some part of our sky, the details of which depend on the
initial conditions of the collision and redshift to the galaxy in question.
With other parameters held fixed the effects weaken as the amount of inflation
inside our bubble grows, but can produce measurable flows past the number of
efolds required to solve the flatness and horizon problems.Comment: 30 pages, 8 figures, pdftex, minor corrections and references adde
Bayesian Power Spectrum Analysis of the First-Year WMAP data
We present the first results from a Bayesian analysis of the WMAP first year
data using a Gibbs sampling technique. Using two independent, parallel
supercomputer codes we analyze the WMAP Q, V and W bands. The analysis results
in a full probabilistic description of the information the WMAP data set
contains about the power spectrum and the all-sky map of the cosmic microwave
background anisotropies. We present the complete probability distributions for
each C_l including any non-Gaussianities of the power spectrum likelihood.
While we find good overall agreement with the previously published WMAP
spectrum, our analysis uncovers discrepancies in the power spectrum estimates
at low l multipoles. For example we claim the best-fit Lambda-CDM model is
consistent with the C_2 inferred from our combined Q+V+W analysis with a 10%
probability of an even larger theoretical C_2. Based on our exact analysis we
can therefore attribute the "low quadrupole issue" to a statistical
fluctuation.Comment: 5 pages. 4 figures. For additional information and data see
http://www.astro.uiuc.edu/~iodwyer/research#wma
New Evidence for Efficient Collisionless Heating of Electrons at the Reverse Shock of a Young Supernova Remnant
Although collisionless shocks are ubiquitous in astrophysics, certain key
aspects of them are not well understood. In particular, the process known as
collisionless electron heating, whereby electrons are rapidly energized at the
shock front, is one of the main open issues in shock physics. Here we present
the first clear evidence for efficient collisionless electron heating at the
reverse shock of Tycho's supernova remnant (SNR), revealed by Fe-K diagnostics
using high-quality X-ray data obtained by the Suzaku satellite. We detect
K-beta (3p->1s) fluorescence emission from low-ionization Fe ejecta excited by
energetic thermal electrons at the reverse shock front, which peaks at a
smaller radius than Fe K-alpha (2p->1s) emission dominated by a relatively
highly-ionized component. Comparison with our hydrodynamical simulations
implies instantaneous electron heating to a temperature 1000 times higher than
expected from Coulomb collisions alone. The unique environment of the reverse
shock, which is propagating with a high Mach number into rarefied ejecta with a
low magnetic field strength, puts strong constraints on the physical mechanism
responsible for this heating, and favors a cross-shock potential created by
charge deflection at the shock front. Our sensitive observation also reveals
that the reverse shock radius of this SNR is about 10% smaller than the
previous measurement using the Fe K-alpha morphology from the Chandra
observations. Since strong Fe K-beta fluorescence is expected only from
low-ionization plasma where Fe ions still have many 3p electrons, this feature
is key to diagnosing the plasma state and distribution of the immediate
postshock ejecta in a young SNR.Comment: 7 pages, 9 figures, resubmitted to ApJ with minor changes following
the referee repor
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