1,198 research outputs found
Evaluation and Management of Sleep Disorders in the Hand Surgery Patient.
Despite posing a significant public health threat, sleep disorders remain poorly understood and often underdiagnosed and mismanaged. Although sleep disorders are seemingly unrelated, hand surgeons should be mindful of these because numerous conditions of the upper extremity have known associations with sleep disturbances that can adversely affect patient function and satisfaction. In addition, patients with sleep disorders are at significantly higher risk for severe, even life-threatening medical comorbidities, further amplifying the role of hand surgeons in the recognition of this condition
Paroxysmal eye–head movements in Glut1 deficiency syndrome
Objective:To describe a characteristic paroxysmal eye–head movement disorder that occurs in infants with Glut1 deficiency syndrome (Glut1 DS).Methods:We retrospectively reviewed the medical charts of 101 patients with Glut1 DS to obtain clinical data about episodic abnormal eye movements and analyzed video recordings of 18 eye movement episodes from 10 patients.Results:A documented history of paroxysmal abnormal eye movements was found in 32/101 patients (32%), and a detailed description was available in 18 patients, presented here. Episodes started before age 6 months in 15/18 patients (83%), and preceded the onset of seizures in 10/16 patients (63%) who experienced both types of episodes. Eye movement episodes resolved, with or without treatment, by 6 years of age in 7/8 patients with documented long-term course. Episodes were brief (usually <5 minutes). Video analysis revealed that the eye movements were rapid, multidirectional, and often accompanied by a head movement in the same direction. Eye movements were separated by clear intervals of fixation, usually ranging from 200 to 800 ms. The movements were consistent with eye–head gaze saccades. These movements can be distinguished from opsoclonus by the presence of a clear intermovement fixation interval and the association of a same-direction head movement.Conclusions:Paroxysmal eye–head movements, for which we suggest the term aberrant gaze saccades, are an early symptom of Glut1 DS in infancy. Recognition of the episodes will facilitate prompt diagnosis of this treatable neurodevelopmental disorder.</jats:sec
Simultaneous Estimation of Reflectivity and Geologic Texture: Least-Squares Migration with a Hierarchical Bayesian Model
In many geophysical inverse problems, smoothness assumptions on the underlying geology are utilized to mitigate the effects of poor resolution and noise in the data and to improve the quality of the inferred model parameters. Within a Bayesian inference framework, a priori assumptions about the probabilistic structure of the model parameters impose such a smoothness constraint or regularization. We consider the particular problem of inverting seismic data for the subsurface reflectivity of a 2-D medium, where we assume a known velocity field. In particular, we consider a hierarchical Bayesian generalization of the Kirchhoff-based least-squares migration (LSM) problem. We present here a novel methodology for estimation of both the optimal image and regularization parameters in a least-squares migration setting. To do so we utilize a Bayesian statistical framework that treats both the regularization parameters and image parameters as random variables to be inferred from the data. Hence rather than fixing the regularization parameters prior to inverting for the image, we allow the data to dictate where to regularize. In order to construct our prior model of the subsurface and regularization parameters, we define an undirected graphical model (or Markov random field) where vertices represent reflectivity values, and edges between vertices model the degree of correlation (or lack thereof) between the vertices. Estimating optimal values for the vertex parameters gives us an image of the subsurface reflectivity, while estimating optimal edge strengths gives us information about the local “texture” of the image, which, in turn, may tell us something about the underlying geology. Subsequently incorporating this information in the final model produces more clearly visible discontinuities in the final image. The inference framework is verified on a 2-D synthetic dataset, where the hierarchical Bayesian imaging results significantly outperform standard LSM images.Shell International Exploration and Production B.V.; Massachusetts Institute of Technology. Earth Resources Laboratory (Founding Members Consortium
Iterative estimation of reflectivity and image texture: Least-squares migration with an empirical Bayes approach
In many geophysical inverse problems, smoothness assumptions on the underlying geology are used to mitigate the effects of nonuniqueness, poor data coverage, and noise in the data and to improve the quality of the inferred model parameters. Within a Bayesian inference framework, a priori assumptions about the probabilistic structure of the model parameters can impose such a smoothness constraint, analogous to regularization in a deterministic inverse problem. We have considered an empirical Bayes generalization of the Kirchhoff-based least-squares migration (LSM) problem. We have developed a novel methodology for estimation of the reflectivity model and regularization parameters, using a Bayesian statistical framework that treats both of these as random variables to be inferred from the data. Hence, rather than fixing the regularization parameters prior to inverting for the image, we allow the data to dictate where to regularize. Estimating these regularization parameters gives us information about the degree of conditional correlation (or lack thereof) between neighboring image parameters, and, subsequently, incorporating this information in the final model produces more clearly visible discontinuities in the estimated image. The inference framework is verified on 2D synthetic data sets, in which the empirical Bayes imaging results significantly outperform standard LSM images. We note that although we evaluated this method within the context of seismic imaging, it is in fact a general methodology that can be applied to any linear inverse problem in which there are spatially varying correlations in the model parameter space.MIT Energy Initiative (Shell International Exploration and Production B.V.)ERL Founding Member Consortiu
Youth Single-Sport Specialization in Professional Baseball Players.
Background: An increasing number of youth baseball athletes are specializing in playing baseball at younger ages.
Purpose: The purpose of our study was to describe the age and prevalence of single-sport specialization in a cohort of current professional baseball athletes. In addition, we sought to understand the trends surrounding single-sport specialization in professional baseball players raised within and outside the United States (US).
Study Design: Cross-sectional study; Level of evidence, 3.
Methods: A survey was distributed to male professional baseball athletes via individual team athletic trainers. Athletes were asked if and at what age they had chosen to specialize in playing baseball at the exclusion of other sports, and data were then collected pertaining to this decision. We analyzed the rate and age of specialization, the reasons for specialization, and the athlete\u27s perception of injuries related to specialization.
Results: A total of 1673 professional baseball athletes completed the survey, representing 26 of the 30 Major League Baseball (MLB) organizations. Less than half (44.5%) of professional athletes specialized in playing a single sport during their childhood/adolescence. Those who reported specializing in their youth did so at a mean age of 14.09 ± 2.79 years. MLB players who grew up outside the US specialized at a significantly earlier age than MLB players native to the US (12.30 ± 3.07 vs 14.89 ± 2.24 years, respectively;
Conclusion: This study challenges the current trends toward early youth sport specialization, finding that the majority of professional baseball athletes studied did not specialize as youth and that those who did specialize did so at a mean age of 14 years. With the potential cumulative effects of pitching and overhead throwing on an athlete\u27s arm, the trend identified in this study toward earlier specialization within baseball is concerning
Strong WW scattering in unitary gauge
A method to embed models of strong scattering in unitary gauge
amplitudes is presented that eliminates the need for the effective
approximation (EWA) in the computation of cross sections at high energy
colliders.The cross sections obtained from the U-gauge amplitudes include the
distributions of the final state fermions in , which
cannot be obtained from the EWA. Since the U-gauge method preserves the
interference of the signal and the gauge sector background amplitudes, which is
neglected in the EWA, it is more accurate, especially if the latter is
comparable to or bigger than the signal, as occurs for instance at small angles
because of Coulomb singularities. The method is illustrated for on-shell
scattering and for .Comment: 14 pages, Latex with 2 epsf-embedded postscript figure
Scalar Top Quark as the Next-to-Lightest Supersymmetric Particle
We study phenomenologically the scenario in which the scalar top quark is
lighter than any other standard supersymmetric partner and also lighter than
the top quark, so that it decays to the gravitino via stop -> W^+ b G. In this
case, scalar top quark events would seem to be very difficult to separate from
top quark pair production. However, we show that, even at a hadron collider, it
is possible to distinguish these two reactions. We show also that the
longitudinal polarization of the final gives insight into the scalar top
and wino/Higgsino mixing parameters.Comment: 18 pages, LaTeX, 7 figures, minor typographical correction
Gauge invariant formulation of strong WW scattering
Models of strong scattering in the -wave can be represented in a
gauge invariant fashion by defining an effective scalar propagator that
represents the strong scattering dynamics. The \sigma(qq \ra qqWW) signal may
then be computed in U-gauge from the complete set of tree amplitudes, just as
in the standard model, without using the effective approximation (EWA). The
U-gauge ``transcription'' has a wider domain of validity than the EWA, and it
provides complete distributions for the final state quanta, including
experimentally important jet distributions that cannot be obtained from the
EWA. Starting from the usual formulation in terms of unphysical Goldstone boson
scattering amplitudes, the U-gauge transcription is verified by using BRS
invariance to construct the complete set of gauge and Goldstone boson
amplitudes in gauge.Comment: single LaTeX file, no figures, 12 page
Phase-Coherent Transport through a Mesoscopic System: A New Probe of Non-Fermi-Liquid Behavior
A novel chiral interferometer is proposed that allows for a direct
measurement of the phase of the transmission coefficient for transport through
a variety of mesoscopic structures in a strong magnetic field. The effects of
electron-electron interaction on this phase is investigated with the use of
finite-size bosonization techniques combined with perturbation theory
resummation. New non-Fermi-liquid phenomena are predicted in the FQHE regime
that may be used to distinguish experimentally between Luttinger and Fermi
liquids.Comment: 4 pages, 3 figures, Revte
Infrared catastrophe and tunneling into strongly correlated electron systems: Perturbative x-ray edge limit
The tunneling density of states exhibits anomalies (cusps, algebraic
suppressions, and pseudogaps) at the Fermi energy in a wide variety of
low-dimensional and strongly correlated electron systems. We argue that in many
cases these spectral anomalies are caused by an infrared catastrophe in the
screening response to the sudden introduction of a new electron into the system
during a tunneling event. A nonperturbative functional-integral method is
introduced to account for this effect, making use of methods developed for the
x-ray edge singularity problem. The formalism is applicable to lattice or
continuum models of any dimensionality, with or without translational
invariance. An approximate version of the technique is applied to the 1D
electron gas and the 2D Hall fluid, yielding qualitatively correct results.Comment: 6 page
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