3,823 research outputs found
Innovations and Trends in Pension Plan Coverage, Pension Type and Plan Design
In this paper, we outline recent trends in employer pension pIan structure in the United States, focusing on plan coverage, plan type and pension plan design. We then identify the key factors that we believe will shape company-sponsored pension design in the future, drawing conclusions from a review of recent research and practice. Finally, we offer a cautious prognosis about the future of pension pIan coverage, pIan type and pIan design, focusing on the role of labor force aging, as well as anticipated developments in the business environment and anticipated changes in public policy
Aberration of the Cosmic Microwave Background
The motion of the solar system barycenter with respect to the cosmic
microwave background (CMB) induces a very large apparent dipole component into
the CMB brightness map at the 3 mK level. In this Letter we discuss another
kinematic effect of our motion through the CMB: the small shift in apparent
angular positions due to the aberration of light. The aberration angles are
only of order beta ~0.001, but this leads to a potentially measurable
compression (expansion) of the spatial scale in the hemisphere toward (away
from) our motion through the CMB. In turn, this will shift the peaks in the
acoustic power spectrum of the CMB by a factor of order 1 +/- beta. For current
CMB missions, and even those in the foreseeable future, this effect is small,
but should be taken into account. In principle, if the acoustic peak locations
were not limited by sampling noise (i.e., the cosmic variance), this effect
could be used to determine the cosmic contribution to the dipole term.Comment: 3 pages, 1 figure, comments welcome. Submitted to ApJ Letter
Temperature variations of the disorder-induced vortex-lattice melting landscape
Differential magneto-optical imaging of the vortex-lattice melting process in
Bi_2Sr_2CaCu_2O_8 crystals reveals unexpected effects of quenched disorder on
the broadening of the first-order phase transition. The melting patterns show
that the disorder-induced melting landscape T_m(H,r) is not fixed, but rather
changes dramatically with varying field and temperature along the melting line.
The changes in both the scale and shape of the landscape are found to result
from the competing contributions of different types of quenched disorder which
have opposite effects on the local melting transition.Comment: 4 pages of text and 3 figures. Accepted for Publication in Physical
Review Letter
Collisions of Free Floating Planets with Evolved Stars in Globular Clusters
We estimate the rate of collisions between stars and free-floating planets
(FFPs) in globular clusters, in particular the collision of FFPs with red giant
branch (RGB) stars. Recent dynamical simulations imply that the density of such
objects could exceed million per cubic parsec near the cores of rich globular
clusters. We show that in these clusters 5-10 per cents of all RGB stars near
the core would suffer a collision with a FFP, and that such a collision can
spin up the RGB star's envelope by an order of magnitude. In turn, the higher
rotation rates may lead to enhanced mass-loss rates on the RGB, which could
result in bluer horizontal branch (HB) stars. Hence, it is plausible that the
presence of a large population of FFPs in a globular cluster can influence the
distribution of stars on the HB of that cluster to a detectable degree.Comment: 10 pages, Accepted by ApJ Letter
Dynamic Creation and Annihilation of Metastable Vortex Phase as a Source of Excess Noise
The large increase in voltage noise, commonly observed in the vicinity of the
peak-effect in superconductors, is ascribed to a novel noise mechanism. A
strongly pinned metastable disordered vortex phase, which is randomly generated
at the edges and annealed into ordered phase in the bulk, causes large
fluctuations in the integrated critical current of the sample. The excess noise
due to this dynamic admixture of two distinct phases is found to display
pronounced reentrant behavior. In the Corbino geometry the injection of the
metastable phase is prevented and, accordingly, the excess noise disappearsComment: 5 pages 3 figures. Accepted for publication in Europhysics letter
A lung retention model based on Michaelis-Menten-like kinetics.
A Michaelis-Menten (MM)-like kinetic model for pulmonary clearance and retention of insoluble dusts was developed and validated by comparing our predictions with experimental data from F344 rats. Published data from inhalation studies involving accumulation and elimination of photocopy test toner, antimony trioxide, carbon black, and diesel exhaust particles were investigated. Numerical integration techniques were used to solve mass balance relationships based upon dust retention in a single lung compartment and clearance via an MM-like kinetic process. The model fit most of the experimental data well. The parameters of MM-like clearance kinetics, which had been derived strictly from the elimination phase, accurately predicted dust retention during the elimination as well as accumulation phases. Furthermore, parameters estimated from one study could accurately predict retention of the same dust in other studies. Particle density and gender of the animals had no effect on the goodness of fit of model predictions. This study suggests that MM-like kinetics offer a reasonable description of particle clearance from the pulmonary region of the rat lung that is more parsimonious than existing particle-clearance models and therefore more suitable for use with small amounts of data
Production of Millisecond Dips in Sco X-1 Count Rates by Dead Time Effects
Chang et al. (2006) reported millisecond duration dips in the X-ray intensity
of Sco X-1 and attributed them to occultations of the source by small
trans-Neptunian objects (TNOs). We have found multiple lines of evidence that
these dips are not astronomical in origin, but rather the result of high-energy
charged particle events in the RXTE PCA detectors. Our analysis of the RXTE
data indicates that at most 10% of the observed dips in Sco X-1 could be due to
occultations by TNOs, and, furthermore, we find no positive or supporting
evidence for any of them being due to TNOs. We therefore believe that it is a
mistake to conclude that any TNOs have been detected via occultation of Sco
X-1.Comment: Submitted to ApJ; uses emulateapj.cls, 8 pages with 8 figure
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