524 research outputs found
Outcomes of capsulolabral reconstruction for posterior shoulder instability
BACKGROUND: Surgical treatment of isolated posterior shoulder instability-a rare and often misdiagnosed condition-is controversial because of poor outcomes. Failure of physical therapy in symptomatic young athletes requires capsulolabral reconstruction or bone block procedures. The goal of this study was to report the outcomes of patients who have undergone surgical capsulolabral reconstruction and to look for risk factors that contribute to failure of this procedure. MATERIAL AND METHOD: We analyzed the outcomes of 101 patients who underwent capsulolabral reconstruction: 83 included retrospectively, 18 included prospectively. The procedures were performed alone or in combination with capsular shift, labral repair, closure of the rotator interval and notch remplissage. The primary endpoint was failure of the procedure, defined as recurrence of the instability and/or pain. We also determined the outcomes based on specific (Walch-Duplay, modified Rowe) and non-specific (Constant, resumption of activities) scores of shoulder instability. RESULTS: The results were satisfactory despite a high failure rate: 35% in the retrospective cohort with 4.8±2.6 years' follow-up and 22% in the prospective cohort with 1.1±0.3 years' follow-up. The various outcome scores improved significantly. Ninety-two percent of patients returned to work and 80% of athletes returned to their pre-injury level of sports. Eighty-five percent of patients were satisfied or very satisfied after the surgery. No risk factors for failure were identified; however, failures were more common in older patients, those who underwent an isolated procedure and those who had unclassified clinical forms. CONCLUSION: Treatment of posterior shoulder instability by capsulolabral reconstruction leads to good clinical outcomes; however, the recurrence rate is high
Accretion, Growth of Supermassive Black Holes, and Feedback in Galaxy Mergers
Super-Eddington accretion is very efficient in growing the mass of a black
hole: in a fraction of the Eddington time its mass can grow to an arbitrary
large value if the feedback effect is not taken into account. However, since
super-Eddington accretion has a very low radiation efficiency, people have
argued against it as a major process for the growth of the black holes in
quasars since observations have constrained the average accretion efficiency of
the black holes in quasars to be \ga 0.1. In this paper we show that the
observational constraint does not need to be violated if the black holes in
quasars have undergone a two-phase growing process: with a short
super-Eddington accretion process they get their masses inflated by a very
large factor until the feedback process becomes important, then with a
prolonged sub-Eddington accretion process they have their masses increased by a
factor \ga 2. The overall average efficiency of this two-phase process is
then \ga 0.1, and the existence of black holes of by redshift
6 is easily explained. Observational test of the existence of the
super-Eddington accretion phase is briefly discussed.Comment: 11 pages, 4 figures. Submitted to MNRA
The evolution of massive black hole seeds
We investigate the evolution of high redshift seed black hole masses at late
times and their observational signatures. The massive black hole seeds studied
here form at extremely high redshifts from the direct collapse of pre-galactic
gas discs. Populating dark matter halos with seeds formed in this way, we
follow the mass assembly of these black holes to the present time using a
Monte-Carlo merger tree. Using this machinery we predict the black hole mass
function at high redshifts and at the present time; the integrated mass density
of black holes and the luminosity function of accreting black holes as a
function of redshift. These predictions are made for a set of three seed models
with varying black hole formation efficiency. Given the accuracy of current
observational constraints, all 3 models can be adequately fit. Discrimination
between the models appears predominantly at the low mass end of the present day
black hole mass function which is not observationally well constrained.
However, all our models predict that low surface brightness, bulgeless galaxies
with large discs are least likely to be sites for the formation of massive seed
black holes at high redshifts. The efficiency of seed formation at high
redshifts has a direct influence on the black hole occupation fraction in
galaxies at z=0. This effect is more pronounced for low mass galaxies. This is
the key discriminant between the models studied here and the Population III
remnant seed model. We find that there exists a population of low mass galaxies
that do not host nuclear black holes. Our prediction of the shape of the black
hole mass - velocity dispersion relation at the low mass end is in agreement
with the recent observational determination from the census of low mass
galaxies in the Virgo cluster.Comment: MNRAS in pres
Tracing the Reionization-Epoch Intergalactic Medium with Metal Absorption Lines
IGM metal absorption lines observed in z>6 spectra offer the opportunity to
probe early feedback processes, the nature of enriching sources, and the
topology of reionization. We run high-resolution cosmological simulations
including galactic outflows to study the observability and physical properties
of 5 ions (C II, C IV, O I, Si II, Si IV) in absorption between z=8->5. We
apply three cases for ionization conditions: Fully neutral, fully reionized,
and a patchy model based on the flux from the nearest galaxy. We find that our
simulations broadly fit available z~5-6 IGM metal-line data, although all
observations cannot be accommodated with a single ionization condition.
Variations in O I absorbers among sight lines seen by Becker et al. (2006)
suggest significant neutral IGM patches down to z~6. Strong C IV absorbers at
z~6 may be the result of ionization by their parent galaxy. Our outflows have
typical speeds of ~200 km/s and mass loading factors of ~6. Such high mass
loading is critical for enriching the IGM to the observed levels while
curtailing star formation to match the observed z~6 rest-frame UV luminosity
function. The volume filling factor of metals increases during this epoch, but
only reaches ~1% for Z>10^(-3) Zsolar by z=5. C IV is an ideal tracer of IGM
metals at z~5-6, with dropping global ionization fractions to either higher or
lower redshifts. This results in a strongly increasing global Omega(C IV) from
z=8->5, in contrast to its relative constancy from z=5->2. Our simulations do
not support widespread early IGM enrichment from e.g. Pop III stars. High-z
absorbers arise from metals on their first outward journey from galaxies, at
distances less than 50 kpc. The galaxies responsible for early IGM enrichment
have typical M*=10^(7.0-8.5) Msolar.Comment: Accepted to MNRAS, 34 pages, 24 figures, 1 table (Sections 5.5,
6.3.1, & 6.3.2 added as well as 5 figures and 1 table
Ab-initio prediction of the electronic and optical excitations in polythiophene: isolated chains versus bulk polymer
We calculate the electronic and optical excitations of polythiophene using
the GW approximation for the electronic self-energy, and include excitonic
effects by solving the electron-hole Bethe-Salpeter equation. Two different
situations are studied: excitations on isolated chains and excitations on
chains in crystalline polythiophene. The dielectric tensor for the crystalline
situation is obtained by modeling the polymer chains as polarizable line
objects, with a long-wavelength polarizability tensor obtained from the
ab-initio polarizability function of the isolated chain. With this model
dielectric tensor we construct a screened interaction for the crystalline case,
including both intra- and interchain screening. In the crystalline situation
both the quasi-particle band gap and the exciton binding energies are
drastically reduced in comparison with the isolated chain. However, the optical
gap is hardly affected. We expect this result to be relevant for conjugated
polymers in general.Comment: 15 pages including 4 figures; to appear in Phys. Rev. B, 6/15/200
Formation of Supermassive Black Holes
Evidence shows that massive black holes reside in most local galaxies.
Studies have also established a number of relations between the MBH mass and
properties of the host galaxy such as bulge mass and velocity dispersion. These
results suggest that central MBHs, while much less massive than the host (~
0.1%), are linked to the evolution of galactic structure. In hierarchical
cosmologies, a single big galaxy today can be traced back to the stage when it
was split up in hundreds of smaller components. Did MBH seeds form with the
same efficiency in small proto-galaxies, or did their formation had to await
the buildup of substantial galaxies with deeper potential wells? I briefly
review here some of the physical processes that are conducive to the evolution
of the massive black hole population. I will discuss black hole formation
processes for `seed' black holes that are likely to place at early cosmic
epochs, and possible observational tests of these scenarios.Comment: To appear in The Astronomy and Astrophysics Review. The final
publication is available at http://www.springerlink.co
Supramolecular heterostructures formed by sequential epitaxial deposition of two-dimensional hydrogen-bonded arrays
Two-dimensional (2D) supramolecular arrays provide a route to the spatial control of the chemical functionality of a surface, but their deposition is in almost all cases limited to a monolayer termination. Here we investigated the sequential deposition of one 2D array on another to form a supramolecular heterostructure and realize the growth—normal to the underlying substrate—of distinct ordered layers, each of which is stabilized by in-plane hydrogen bonding. For heterostructures formed by depositing terephthalic acid or trimesic acid on cyanuric acid/melamine, we have determined, using atomic force microscopy under ambient conditions, a clear epitaxial arrangement despite the intrinsically distinct symmetries and/or lattice constants of each layer. Structures calculated using classical molecular dynamics are in excellent agreement with the orientation, registry and dimensions of the epitaxial layers. Calculations confirm that van der Waals interactions provide the dominant contribution to the adsorption energy and registry of the layers
Changing morphology of metallic monolayers via temperature controlled heteroepitaxial growth
Compressed representation of a partially defined integer function over multiple arguments
In OLAP (OnLine Analitical Processing) data are analysed in an n-dimensional cube. The cube may be represented as a partially defined function over n arguments. Considering that often the function is not defined everywhere, we ask: is there a known way of representing the function or the points in which it is defined, in a more compact manner than the trivial one
Animal Models of Dyssynchrony
Cardiac resynchronization therapy (CRT) is an important therapy for patients with heart failure and conduction pathology, but the benefits are heterogeneous between patients and approximately a third of patients do not show signs of clinical or echocardiographic response. This calls for a better understanding of the underlying conduction disease and resynchronization. In this review, we discuss to what extent established and novel animal models can help to better understand the pathophysiology of dyssynchrony and the benefits of CRT
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