68,987 research outputs found
Research in the field of molecular collision phenomena using molecular beam techniques Final report
Aerodynamic molecular beam interactions with solid surface
Generalizations of the Abstract Boundary singularity theorem
The Abstract Boundary singularity theorem was first proven by Ashley and
Scott. It links the existence of incomplete causal geodesics in strongly
causal, maximally extended spacetimes to the existence of Abstract Boundary
essential singularities, i.e., non-removable singular boundary points. We give
two generalizations of this theorem: the first to continuous causal curves and
the distinguishing condition, the second to locally Lipschitz curves in
manifolds such that no inextendible locally Lipschitz curve is totally
imprisoned. To do this we extend generalized affine parameters from
curves to locally Lipschitz curves.Comment: 24 page
Astrometric Microlensing Constraints on a Massive Body in the Outer Solar System with Gaia
A body in Solar orbit beyond the Kuiper belt exhibits an annual parallax that
exceeds its apparent proper motion by up to many orders of magnitude. Apparent
motion of this body along the parallactic ellipse will deflect the angular
position of background stars due to astrometric microlensing ("induced
parallax"). By synoptically sampling the astrometric position of background
stars over the entire sky, constraints on the existence (and basic properties)
of a massive nearby body may be inferred. With a simple simulation, we estimate
the signal-to-noise for detecting such a body -- as function of mass,
heliocentric distance, and ecliptic latitude -- using the anticipated
sensitivity and temporal cadences from Gaia (launch 2011). A Jupiter-mass
(M_Jup) object at 2000 AU is detectable by Gaia over the whole sky above
5-sigma, with even stronger constraints if it lies near the ecliptic plane.
Hypotheses for the mass (~3M_Jup), distance (~20,000 AU) and location of the
proposed perturber ("Planet X") which gives rise to long-period comets may be
testable.Comment: 17 pages, 6 figures. Figures revised, new figure added, minor text
revisions. Accepted to ApJ, to appear in the Dec 10, 2005 issue (v635
Persistent junk solutions in time-domain modeling of extreme mass ratio binaries
In the context of metric perturbation theory for non-spinning black holes,
extreme mass ratio binary (EMRB) systems are described by distributionally
forced master wave equations. Numerical solution of a master wave equation as
an initial boundary value problem requires initial data. However, because the
correct initial data for generic-orbit systems is unknown, specification of
trivial initial data is a common choice, despite being inconsistent and
resulting in a solution which is initially discontinuous in time. As is well
known, this choice leads to a "burst" of junk radiation which eventually
propagates off the computational domain. We observe another unintended
consequence of trivial initial data: development of a persistent spurious
solution, here referred to as the Jost junk solution, which contaminates the
physical solution for long times. This work studies the influence of both types
of junk on metric perturbations, waveforms, and self-force measurements, and it
demonstrates that smooth modified source terms mollify the Jost solution and
reduce junk radiation. Our concluding section discusses the applicability of
these observations to other numerical schemes and techniques used to solve
distributionally forced master wave equations.Comment: Uses revtex4, 16 pages, 9 figures, 3 tables. Document reformatted and
modified based on referee's report. Commentary added which addresses the
possible presence of persistent junk solutions in other approaches for
solving master wave equation
Delayed Recombination
Under the standard model for recombination of the primeval plasma, and the
cold dark matter model for structure formation, recent measurements of the
first peak in the angular power spectrum of the cosmic microwave background
temperature indicate the spatial geometry of the universe is nearly flat. If
sources of Lya resonance radiation, such as stars or active galactic nuclei,
were present at z ~ 1000 they would delay recombination, shifting the first
peak to larger angular scales, and producing a positive bias in this measure of
space curvature. It can be distinguished from space curvature by its
suppression of the secondary peaks in the spectrum.Comment: submitted to ApJ
Neuropsychological and functional outcomes in recent-onset major depression, bipolar disorder and schizophrenia-spectrum disorders: a longitudinal cohort study
Functional disability is the lead contributor to burden of mental illness. Cognitive deficits frequently limit functional recovery, although whether changes in cognition and disability are longitudinally associated in recent-onset individuals remains unclear. Using a prospective, cohort design, 311 patients were recruited and assessed at baseline. One hundred and sixty-seven patients met eligibility criteria (M = 21.5 years old, s.d. = 4.8) and returned for follow-up (M = 20.6 months later, s.d. = 7.8). Two-hundred and thirty participants were included in the final analysis, comprising clinically stable patients with major depression (n = 71), bipolar disorder (BD; n = 61), schizophrenia-spectrum disorders (n = 35) and 63 healthy controls. Neuropsychological functioning and self-rated functional disability were examined using mixed-design, repeated-measures analysis, across diagnoses and cognitive clusters, covarying for relevant confounds. Clinical, neuropsychological and functional changes did not differ between diagnoses (all P40.05). Three reliable neuropsychological subgroups emerged through cluster analysis, characterized by psychomotor slowing, improved sustained attention, and improved verbal memory. Controlling for diagnosis and changes in residual symptoms, clusters with improved neuropsychological functioning observed greater reductions in functional disability than the psychomotor slowing cluster, which instead demonstrated a worsening in disability (Po0.01). Improved sustained attention was independently associated with greater likelihood of follow-up employment (Po0.01). Diagnosis of BD uniquely predicted both follow-up employment and independent living. Neuropsychological course appears to be independently predictive of subjective and objective functional outcomes. Importantly, cognitive phenotypes may reflect distinct pathophysiologies shared across major psychiatric conditions, and be ideal targets for personalized early intervention
Volumetric microvascular imaging of human retina using optical coherence tomography with a novel motion contrast technique
Phase variance-based motion contrast imaging is demonstrated using a spectral domain optical coherence tomography system for the in vivo human retina. This contrast technique spatially identifies locations of motion within the retina primarily associated with vasculature. Histogram-based noise analysis of the motion contrast images was used to reduce the motion noise created by transverse eye motion. En face summation images created from the 3D motion contrast data are presented with segmentation of selected retinal layers to provide non-invasive vascular visualization comparable to currently used invasive angiographic imaging. This motion contrast technique has demonstrated the ability to visualize resolution-limited vasculature independent of vessel orientation and flow velocity
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