17,833 research outputs found
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http://archive.org/details/energylossofhigh00mosbNAN
Evidence for a developing gap in a 10 Myr old protoplanetary disk
We have developed a self-consistent model of the disk around the nearby 10
Myr old star TW Hya which matches the observed spectral energy distribution and
7mm images of the disk. The model requires a significant dust size evolution
and a partially-evacuated inner disk region, as predicted by theories of planet
formation. The outer disk, which extends to at least 140 AU in radius, is very
optically thick at IR wavelengths and quite massive ~0.06 Msun for the
relatively advanced age of this T Tauri star. This implies long viscous and
dust evolution timescales, although dust must have grown to sizes of order ~1cm
to explain the sub-mm and mm spectral slopes. In contrast, the negligible
near-infrared excess emission of this system requires that the disk be
optically thin inside ~4 AU.This inner region cannot be completely evacuated;
we need ~0.5 lunar mass of ~1 micron particles remaining to produce the
observed 10 micron silicate emission. Our model requires a distinct transition
in disk properties at ~4 AU, separating the inner and outer disk. The inner
edge of the optically-thick outer disk must be heated almost frontally by the
star to account for the excess flux at mid-IR wavelengths. We speculate that
this truncation of the outer disk may be the signpost of a developing gap due
to the effects of a growing protoplanet; the gap is still presumably evolving
because material still resides in it, as indicated by the silicate emission,
the molecular hydrogen emission, and by the continued accretion onto the
central star (albeit at a much lower rate than typical of younger T Tauri
stars). TW Hya thus may become the Rosetta stone for our understanding of the
evolution and dissipation of protoplanetary disks.Comment: 23 pages including 5 figures, Accepted by AP
Lattice study of trapped fermions at unitarity
We present a lattice study of up to N=20 unitary fermions confined to a
harmonic trap. Our preliminary results show better than 1% agreement with high
precision solutions to the many-body Schrodinger equation for up to N=6. We are
able to make predictions for larger N which were inaccessible by the
Hamiltonian approach due to computational limitations. Harmonic traps are used
experimentally to study cold atoms tuned to a Feshbach resonance. We show that
they also provide certain benefits to numerical studies of many-body
correlators on the lattice. In particular, we anticipate that the methods
described here could be used for studying nuclear physics.Comment: 7 pages, 5 figures, presented at the XXVIII International Symposium
on Lattice Field Theory (Lattice 2010), Villasimius, Italy, June 14-19 201
The Situational Judgment Test Validity Void: Describing Participant Response Processes
Situational judgment tests (SJTs) are used to measure important components of professional competence that cannot be assessed via traditional tests of knowledge and skills. Despite their increasing popularity, there is a significant gap in the validity evidence and research on the response process to support how SJTs measure their intended constructs. This study evaluated an SJT to examine: (1) the factors that influence the response process, (2) the role of experience in the response process, (3) the role of contextual features in the response process, and (4) whether individuals attempt to identify the construct being assessed. Thirty participants—15 students and 15 pharmacists—completed a 12-item SJT designed to measure empathy. Each participant engaged in an uninterrupted think-aloud interview while they completed an SJT followed by a cognitive interview that asked specific questions about their decision-making process. Results of the qualitative and quantitative analyses suggest that the SJT response processes include the complex integration of comprehension, retrieval, judgments, and response selections. In addition, job-specific knowledge and experiences comprised a significant portion of the retrieval process. Moreover, there was evidence that SJTs are highly contextual and that item characteristics such as setting, actors, or relationships can influence the response process. There was limited evidence to suggest individuals attempt to identify the construct being assessed. In summary, this study provides a comprehensive evaluation of the response process involved in SJTs using rigorous qualitative methodologies and it contributes to foundational steps to generate the validity evidence necessary to aid in score interpretation and future research.Doctor of Philosoph
Lattice calculation for unitary fermions in a finite box
A fundamental constant in systems of unitary fermions is the so-called
Bertsch parameter, the ratio of the ground state energy for spin paired unitary
fermions to that for free fermions at the same density. I discuss how we
computed this parameter as well as the pairing gap using a recently developed
lattice construction for unitary fermions, by measuring correlation functions
for up to 38 fermions in a finite box. Our calculation illustrates interesting
issues facing the study of many-body states on the lattice, which may
eventually be confronted in QCD calculations as well.Comment: 7 pages, 6 figures, The XXVIII International Symposium on Lattice
Field Theory, Lattice2010, June 14-19, 2010, Villasimius, Ital
Identifying First-person Camera Wearers in Third-person Videos
We consider scenarios in which we wish to perform joint scene understanding,
object tracking, activity recognition, and other tasks in environments in which
multiple people are wearing body-worn cameras while a third-person static
camera also captures the scene. To do this, we need to establish person-level
correspondences across first- and third-person videos, which is challenging
because the camera wearer is not visible from his/her own egocentric video,
preventing the use of direct feature matching. In this paper, we propose a new
semi-Siamese Convolutional Neural Network architecture to address this novel
challenge. We formulate the problem as learning a joint embedding space for
first- and third-person videos that considers both spatial- and motion-domain
cues. A new triplet loss function is designed to minimize the distance between
correct first- and third-person matches while maximizing the distance between
incorrect ones. This end-to-end approach performs significantly better than
several baselines, in part by learning the first- and third-person features
optimized for matching jointly with the distance measure itself
Longitudinal analysis of the developing rhesus monkey brain using magnetic resonance imaging: birth to adulthood.
We have longitudinally assessed normative brain growth patterns in naturalistically reared Macaca mulatta monkeys. Postnatal to early adulthood brain development in two cohorts of rhesus monkeys was analyzed using magnetic resonance imaging. Cohort A consisted of 24 rhesus monkeys (12 male, 12 female) and cohort B of 21 monkeys (11 male, 10 female). All subjects were scanned at 1, 4, 8, 13, 26, 39, and 52Â weeks; cohort A had additional scans at 156Â weeks (3Â years) and 260Â weeks (5Â years). Age-specific segmentation templates were developed for automated volumetric analyses of the T1-weighted magnetic resonance imaging scans. Trajectories of total brain size as well as cerebral and subcortical subdivisions were evaluated over this period. Total brain volume was about 64Â % of adult estimates in the 1-week-old monkey. Brain volume of the male subjects was always, on average, larger than the female subjects. While brain volume generally increased between any two imaging time points, there was a transient plateau of brain growth between 26 and 39Â weeks in both cohorts of monkeys. The trajectory of enlargement differed across cortical regions with the occipital cortex demonstrating the most idiosyncratic pattern of maturation and the frontal and temporal lobes showing the greatest and most protracted growth. A variety of allometric measurements were also acquired and body weight gain was most closely associated with the rate of brain growth. These findings provide a valuable baseline for the effects of fetal and early postnatal manipulations on the pattern of abnormal brain growth related to neurodevelopmental disorders
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