6,420 research outputs found
Social epidemiology
Social epidemiology is the branch of epidemiology concerned with understanding how social and economic characteristics influence states of health in populations. There has been a resurgence recently in interest among epidemiologists about the roles that social and economic factors play in determining health, leading to valuable synergies with the social sciences. The determinants of health commonly studied in social epidemiology include absolute poverty, income inequality, as well as race and discrimination. Recently, social epidemiologists have been at the forefront of conceptual developments within the discipline that view the determinants of health at different levels of social organization. © 2008 Copyright © 2008 Elsevier Inc. All rights reserved
Correlation of Patient Symptoms With Labral and Articular Cartilage Damage in Femoroacetabular Impingement.
BackgroundFemoroacetabular impingement (FAI) can lead to labral and articular cartilage injuries as well as early osteoarthritis of the hip. Currently, the association of patient symptoms with the progression of labral and articular cartilage injuries due to FAI is poorly understood.PurposeTo evaluate the correlation between patient-reported outcome (PRO) scores and cartilage compositional changes seen on quantitative magnetic resonance imaging (MRI) as well as cartilage and labral damage seen during arthroscopic surgery in patients with FAI.Study designCohort study; Level of evidence, 3.MethodsPatients were prospectively enrolled before hip arthroscopic surgery for symptomatic FAI. Patients were included if they had cam-type FAI without radiographic arthritis. All patients completed PRO scores, including the Hip disability and Osteoarthritis Outcome Score (HOOS) and a visual analog scale for pain. MRI with mapping sequences (T1Ï and T2) on both the acetabular and femoral regions was performed before surgery to quantitatively assess the cartilage composition. During arthroscopic surgery, cartilage and labral injury grades were recorded using the Beck classification. Pearson and Spearman correlation coefficients were then obtained to evaluate the association between chondrolabral changes and PRO scores.ResultsA total of 46 patients (46 hips) were included for analysis (mean age, 35.5 years; mean body mass index [BMI], 23.9 kg/m2; 59% male). Increasing BMI was correlated with a more severe acetabular cartilage grade (Ï = 0.37; 95% CI, 0.08-0.65). A greater alpha angle was correlated with an increased labral tear grade (Ï = 0.59; 95% CI, 0.37-0.82) and acetabular cartilage injuries (Ï = 0.61; 95% CI, 0.42-0.80). With respect to PRO scores, increasing femoral cartilage damage in the anterosuperior femoral head region, as measured on quantitative MRI using T1Ï and T2 mapping, correlated with lower (worse) scores on the HOOS Activities of Daily Living (r = 0.35; 95% CI, 0.06-0.64), Symptoms (r = 0.32; 95% CI, 0.06-0.57), and Pain (r = 0.31; 95% CI, 0.06-0.55) subscales. There was no correlation between PRO scores and acetabular cartilage damage or labral tearing found on quantitative MRI or during arthroscopic surgery.ConclusionFemoral cartilage damage, as measured on T1Ï and T2 mapping, appears to have a greater correlation with clinical symptoms than acetabular cartilage damage or labral tears in patients with symptomatic FAI
Lagrangian perturbation theory for a superfluid immersed in an elastic neutron star crust
The inner crust of mature neutron stars, where an elastic lattice of
neutron-rich nuclei coexists with a neutron superfluid, impacts on a range of
astrophysical phenomena. The presence of the superfluid is key to our
understanding of pulsar glitches, and is expected to affect the thermal
conductivity and hence the evolution of the surface temperature. The coupling
between crust and superfluid must also be accounted for in studies of neutron
star dynamics, discussions of global oscillations and associated instabilities.
In this paper we develop Lagrangian perturbation theory for this problem,
paying attention to key issues like superfluid entrainment, potential vortex
pinning, dissipative mutual friction and the star's magnetic field. We also
discuss the nature of the core-crust interface. The results provide a
theoretical foundation for a range of interesting astrophysical applications.Comment: 13 pages, no figures, to appear in MNRA
The Crustal Rigidity of a Neutron Star, and Implications for PSR 1828-11 and other Precession Candidates
We calculate the crustal rigidity parameter, b, of a neutron star (NS), and
show that b is a factor 40 smaller than the standard estimate due to Baym &
Pines (1971). For a NS with a relaxed crust, the NS's free-precession frequency
is directly proportional to b. We apply our result for b to PSR 1828-11, a 2.5
Hz pulsar that appears to be precessing with period 511 d. Assuming this 511-d
period is set by crustal rigidity, we show that this NS's crust is not relaxed,
and that its reference spin (roughly, the spin for which the crust is most
relaxed) is 40 Hz, and that the average spindown strain in the crust is 5
\times 10^{-5}. We also briefly describe the implications of our b calculation
for other well-known precession candidates.Comment: 44 pages, 10 figures, submitted to Ap
Collisionless shock acceleration of narrow energy spread ion beams from mixed species plasmas using 1 m lasers
Collisionless shock acceleration of protons and C ions has been
achieved by the interaction of a 10 W/cm, 1 m laser with a
near-critical density plasma. Ablation of the initially solid density target by
a secondary laser allowed for systematic control of the plasma profile. This
enabled the production of beams with peaked spectra with energies of 10-18
MeV/a.m.u. and energy spreads of 10-20 with up to 3x10 particles within
these narrow spectral features. The narrow energy spread and similar velocity
of ion species with different charge-to-mass ratio are consistent with
acceleration by the moving potential of a shock wave. Particle-in-cell
simulations show shock accelerated beams of protons and C ions with
energy distributions consistent with the experiments. Simulations further
indicate the plasma profile determines the trade-off between the beam charge
and energy and that with additional target optimization narrow energy spread
beams exceeding 100 MeV/a.m.u. can be produced using the same laser conditions.Comment: Accepted for publication in Physical Review Accelerators and Beam
Dynamics of Quantum Vorticity in a Random Potential
I study the dynamics of a superfluid vortex in a random potential, as in the
inner crust of a neutron star. Below a critical flow velocity of the ambient
superfluid, a vortex is effectively immobilized by lattice forces even in the
limit of zero dissipation. Low-velocity, translatory motion is not dynamically
possible, a result with important implications for understanding neutron star
precession and the dynamical properties of superfluid nuclear matter.Comment: Physical Review Letters, final versio
Neutron Star Structure and the Neutron Radius of 208Pb
We study relationships between the neutron-rich skin of a heavy nucleus and
the properties of neutron-star crusts. Relativistic effective field theories
with a thicker neutron skin in Pb have a larger electron fraction and a
lower liquid-to-solid transition density for neutron-rich matter. These
properties are determined by the density dependence of the symmetry energy
which we vary by adding nonlinear couplings between isoscalar and isovector
mesons. An accurate measurement of the neutron radius in Pb---via
parity violating electron scattering---may have important implications for the
structure of neutron stars.Comment: 5 pages 3 figures, added additional evidence of model independence,
Phys. Rev. Letters in pres
Pulsar Constraints on Neutron Star Structure and Equation of State
With the aim of constraining the structural properties of neutron stars and
the equation of state of dense matter, we study sudden spin-ups, glitches,
occurring in the Vela pulsar and in six other pulsars. We present evidence that
glitches represent a self-regulating instability for which the star prepares
over a waiting time. The angular momentum requirements of glitches in Vela
indicate that at least 1.4% of the star's moment of inertia drives these
events. If glitches originate in the liquid of the inner crust, Vela's
`radiation radius' must exceed ~12 km for a mass of 1.4 solar masses.
Observational tests of whether other neutron stars obey this constraint will be
possible in the near future.Comment: 5 pages, including figures. To appear in Physical Review Letter
Search for T Violation in Charm Meson Decays
Using data from the FOCUS (E831) experiment, we have searched for T violation
in charm meson decays using the four-body decay channels , , and . The T violation asymmetry is obtained using triple-product
correlations and assuming the validity of the CPT theorem. We find the
asymmetry values to be
,
, and
.
Each measurement is consistent with no T violation. New measurements of the
CP asymmetries for some of these decay modes are also presented.Comment: 17 pages,6 figures,submitted to Phys.Lett.
Thermodynamical Study on the Heavy-Fermion Superconductor PrOs4Sb12: Evidence for Field-Induced Phase Transition
We report measurements of low-temperature specific heat on the 4f^2-based
heavy-fermion superconductor PrOs4Sb12. In magnetic fields above 4.5 T in the
normal state, distinct anomalies are found which demonstrate the existence of a
field-induced ordered phase (FIOP). The Pr nuclear specific heat indicates an
enhancement of the 4f magnetic moment in the FIOP. Utilizing a Maxwell
relation, we conclude that anomalous entropy, which is expected for a
single-site quadrupole Kondo model, is not concealed below 0.16 K in zero
field. We also discuss two possible interpretations of the Schottky-like
anomaly at ~3 K, i.e., a crystalline-field excitation or a hybridization gap
formation.Comment: 5 pages with 5 figures, a note with two references added in proo
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