817 research outputs found
The OARSI histopathology initiative – recommendations for histological assessments of osteoarthritis in the rat
SummaryObjectiveDuring the development of disease-modifying osteoarthritis (OA) drugs, rat models of OA are frequently used for a first assessment of in vivo efficacy. The most efficacious compound in the rat model may then be tested in a larger animal model before entering human trials. The aim of this study was to describe a histologic scoring system for use in different models of OA in rats that allows standardization and comparison of results obtained by different investigators.MethodsThe experience of the authors with current scoring systems and the range of lesions observed in rat and human OA studies were considered in recommending this common paradigm for rat histologic scoring. Considerations were made for reproducibility and ease of use for new scorers. Additional scoring paradigms may be employed to further identify specific effects of some disease-modifying drugs.ResultsAlthough the described scoring system is more complex than the modified Mankin scores, which are recommended for some other species, the reliability study showed that it is easily understood and can be reproducibly used, even by inexperienced scorers.ConclusionsThe scoring paradigm described here has been found to be sufficiently sensitive to discriminate between treatments and to have high reproducibility. Therefore we recommend its use for evaluation of different rat OA models as well as assessment of disease-modifying effects of treatments in these models
Dynamics of earthquake nucleation process represented by the Burridge-Knopoff model
Dynamics of earthquake nucleation process is studied on the basis of the
one-dimensional Burridge-Knopoff (BK) model obeying the rate- and
state-dependent friction (RSF) law. We investigate the properties of the model
at each stage of the nucleation process, including the quasi-static initial
phase, the unstable acceleration phase and the high-speed rupture phase or a
mainshock. Two kinds of nucleation lengths L_sc and L_c are identified and
investigated. The nucleation length L_sc and the initial phase exist only for a
weak frictional instability regime, while the nucleation length L_c and the
acceleration phase exist for both weak and strong instability regimes. Both
L_sc and L_c are found to be determined by the model parameters, the frictional
weakening parameter and the elastic stiffness parameter, hardly dependent on
the size of an ensuing mainshock. The sliding velocity is extremely slow in the
initial phase up to L_sc, of order the pulling speed of the plate, while it
reaches a detectable level at a certain stage of the acceleration phase. The
continuum limits of the results are discussed. The continuum limit of the BK
model lies in the weak frictional instability regime so that a mature
homogeneous fault under the RSF law always accompanies the quasi-static
nucleation process. Duration times of each stage of the nucleation process are
examined. The relation to the elastic continuum model and implications to real
seismicity are discussed.Comment: Title changed. Changes mainly in abstract and in section 1. To appear
in European Physical Journal
Novel NN interaction and the spectroscopy of light nuclei
Nucleon-nucleon (NN) phase shifts and the spectroscopy of nuclei
are successfully described by an inverse scattering potential that is separable
with oscillator form factors.Comment: 4 pages, 1 figure, 13 table
Superconductivity and Charge Density Wave in a Quasi-One-Dimensional Spin Gap System
We consider a model of spin-gapped chains weakly coupled by Josephson and
Coulomb interactions. Combining such non-perturbative methods as bosonization
and Bethe ansatz to treat the intra-chain interactions with the Random Phase
Approximation for the inter-chain couplings and the first corrections to this,
we investigate the phase diagram of this model. The phase diagram shows both
charge density wave ordering and superconductivity. These phases are seperated
by a line of critical points which exhibits an approximate an SU(2) symmetry.
We consider the effects of a magnetic field on the system. We apply the theory
to the material Sr_2 Ca_12 Cu_24 O_41 and suggest further experiments.Comment: 14 pages, 7 figure; submitted to PRB; Revised with new version:
references added; section on the flux state remove
Homogeneous Fermion Superfluid with Unequal Spin Populations
For decades, the conventional view is that an s-wave BCS superfluid can not
support uniform spin polarization due to a gap in the quasiparticle
excitation spectrum. We show that this is an artifact of the dismissal of
quasiparticle interactions in the conventional approach at the
outset. Such interactions can cause triplet fluctuations in the ground state
and hence non-zero spin polarization at "magnetic field" . The
resulting ground state is a pairing state of quasiparticles on the ``BCS
vacuum". For sufficiently large , the spin polarization of at unitarity
has the simple form . Our study is motivated by the recent
experiments at Rice which found evidence of a homogenous superfluid state with
uniform spin polarization.Comment: 4 pages, 3 figure
Electronic Collective Modes and Superconductivity in Layered Conductors
A distinctive feature of layered conductors is the presence of low-energy
electronic collective modes of the conduction electrons. This affects the
dynamic screening properties of the Coulomb interaction in a layered material.
We study the consequences of the existence of these collective modes for
superconductivity. General equations for the superconducting order parameter
are derived within the strong-coupling phonon-plasmon scheme that account for
the screened Coulomb interaction. Specifically, we calculate the
superconducting critical temperature Tc taking into account the full
temperature, frequency and wave-vector dependence of the dielectric function.
We show that low-energy plasmons may contribute constructively to
superconductivity. Three classes of layered superconductors are discussed
within our model: metal-intercalated halide nitrides, layered organic materials
and high-Tc oxides. In particular, we demonstrate that the plasmon contribution
(electronic mechanism) is dominant in the first class of layered materials. The
theory shows that the description of so-called ``quasi-two-dimensional
superconductors'' cannot be reduced to a purely 2D model, as commonly assumed.
While the transport properties are strongly anisotropic, it remains essential
to take into account the screened interlayer Coulomb interaction to describe
the superconducting state of layered materials.Comment: Final version (minor changes) 14 pages, 6 figure
The Oregon Experiment — Effects of Medicaid on Clinical Outcomes
Background: Despite the imminent expansion of Medicaid coverage for low-income adults, the effects of expanding coverage are unclear. The 2008 Medicaid expansion in Oregon based on lottery drawings from a waiting list provided an opportunity to evaluate these effects. Methods: Approximately 2 years after the lottery, we obtained data from 6387 adults who were randomly selected to be able to apply for Medicaid coverage and 5842 adults who were not selected. Measures included blood-pressure, cholesterol, and glycated hemoglobin levels; screening for depression; medication inventories; and self-reported diagnoses, health status, health care utilization, and out-of-pocket spending for such services. We used the random assignment in the lottery to calculate the effect of Medicaid coverage. Results: We found no significant effect of Medicaid coverage on the prevalence or diagnosis of hypertension or high cholesterol levels or on the use of medication for these conditions. Medicaid coverage significantly increased the probability of a diagnosis of diabetes and the use of diabetes medication, but we observed no significant effect on average glycated hemoglobin levels or on the percentage of participants with levels of 6.5% or higher. Medicaid coverage decreased the probability of a positive screening for depression (−9.15 percentage points; 95% confidence interval, −16.70 to −1.60; P=0.02), increased the use of many preventive services, and nearly eliminated catastrophic out-of-pocket medical expenditures. Conclusions: This randomized, controlled study showed that Medicaid coverage generated no significant improvements in measured physical health outcomes in the first 2 years, but it did increase use of health care services, raise rates of diabetes detection and management, lower rates of depression, and reduce financial strain.United States. Dept. of Health and Human Services. Office of the Assistant Secretary for Planning and EvaluationCalifornia HealthCare FoundationNational Institute on Aging (P30AG012810)National Institute on Aging (RC2AGO36631)National Institute on Aging (R01AG0345151)John D. and Catherine T. MacArthur FoundationRobert Wood Johnson FoundationAlfred P. Sloan FoundationSmith Richardson FoundationUnited States. Social Security Administration (5 RRC 08098400-03-00, to the National Bureau of Economic Research as part of the Retirement Research Consortium of the Social Security Administration)Centers for Medicare & Medicaid Services (U.S.
The 8.2 ka cooling event caused by Laurentide ice saddle collapse
The 8.2 ka event was a period of abrupt cooling of 1–3 °C across large parts of the Northern Hemisphere, which lasted for about 160 yr. The original hypothesis for the cause of this event has been the outburst of the proglacial Lakes Agassiz and Ojibway. These drained into the Labrador Sea in ∼0.5–5 yr and slowed the Atlantic Meridional Overturning Circulation, thus cooling the North Atlantic region. However, climate models have not been able to reproduce the duration and magnitude of the cooling with this forcing without including additional centennial-length freshwater forcings, such as rerouting of continental runoff and ice sheet melt in combination with the lake release. Here, we show that instead of being caused by the lake outburst, the event could have been caused by accelerated melt from the collapsing ice saddle that linked domes over Hudson Bay in North America. We forced a General Circulation Model with time varying meltwater pulses (100–300 yr) that match observed sea level change, designed to represent the Hudson Bay ice saddle collapse. A 100 yr long pulse with a peak of 0.6 Sv produces a cooling in central Greenland that matches the 160 yr duration and 3 °C amplitude of the event recorded in ice cores. The simulation also reproduces the cooling pattern, amplitude and duration recorded in European Lake and North Atlantic sediment records. Such abrupt acceleration in ice melt would have been caused by surface melt feedbacks and marine ice sheet instability. These new realistic forcing scenarios provide a means to reconcile longstanding mismatches between proxy data and models, allowing for a better understanding of both the sensitivity of the climate models and processes and feedbacks in motion during the disintegration of continental ice sheets
Coherent Radio Pulses From GEANT Generated Electromagnetic Showers In Ice
Radio Cherenkov radiation is arguably the most efficient mechanism for
detecting showers from ultra-high energy particles of 1 PeV and above. Showers
occuring in Antarctic ice should be detectable at distances up to 1 km. We
report on electromagnetic shower development in ice using a GEANT Monte Carlo
simulation. We have studied energy deposition by shower particles and
determined shower parameters for several different media, finding agreement
with published results where available. We also report on radio pulse emission
from the charged particles in the shower, focusing on coherent emission at the
Cherenkov angle. Previous work has focused on frequencies in the 100 MHz to 1
GHz range. Surprisingly, we find that the coherence regime extends up to tens
of Ghz. This may have substantial impact on future radio-based neutrino
detection experiments as well as any test beam experiment which seeks to
measure coherent Cherenkov radiation from an electromagnetic shower. Our study
is particularly important for the RICE experiment at the South Pole.Comment: 44 pages, 29 figures. Minor changes made, reference added, accepted
for publication in Phys. Rev.
Geophysical constraints on mirror matter within the Earth
We have performed a detailed investigation of geophysical constraints on the
possible admixture of mirror matter inside the Earth. On the basis of the
Preliminary Reference Earth Model (PREM) -- the `Standard Model' of the Earth's
interior -- we have developed a method which allows one to compute changes in
various quantities characterising the Earth (mass, moment of inertia, normal
mode frequencies etc.)due to the presence of mirror matter. As a result we have
been able to obtain for the first time the direct upper bounds on the possible
concentration of the mirror matter in the Earth. In terms of the ratio of the
mirror mass to the Earth mass a conservative upper bound is . We then analysed possible mechanisms (such as lunar and solar tidal
forces, meteorite impacts and earthquakes) of exciting mirror matter
oscillations around the Earth centre. Such oscillations could manifest
themselves through global variations of the gravitational acceleration at the
Earth's surface. We conclude that such variations are too small to be observed.
Our results are valid for other types of hypothetical matter coupled to
ordinary matter by gravitation only (e.g. the shadow matter of superstring
theories).Comment: 25 pages, in RevTeX, to appear in Phys.Rev.
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