4,258 research outputs found
Quantum Layers over Surfaces Ruled Outside a Compact Set
In this paper, we proved the quantum layer over a surface which is ruled
outside a compact set, asymptotically flat but not totally geodesic admits
ground states
On-board processing for future satellite communications systems: Satellite-Routed FDMA
A frequency division multiple access (FDMA) 30/20 GHz satellite communications architecture without on-board baseband processing is investigated. Conceptual system designs are suggested for domestic traffic models totaling 4 Gb/s of customer premises service (CPS) traffic and 6 Gb/s of trunking traffic. Emphasis is given to the CPS portion of the system which includes thousands of earth terminals with digital traffic ranging from a single 64 kb/s voice channel to hundreds of channels of voice, data, and video with an aggregate data rate of 33 Mb/s. A unique regional design concept that effectively smooths the non-uniform traffic distribution and greatly simplifies the satellite design is employed. The satellite antenna system forms thirty-two 0.33 deg beam on both the uplinks and the downlinks in one design. In another design matched to a traffic model with more dispersed users, there are twenty-four 0.33 deg beams and twenty-one 0.7 deg beams. Detailed system design techniques show that a single satellite producing approximately 5 kW of dc power is capable of handling at least 75% of the postulated traffic. A detailed cost model of the ground segment and estimated system costs based on current information from manufacturers are presented
The Physical Effects of Progenitor Rotation: Comparing Two Long-Duration 3D Core-Collapse Supernova Simulations
We analyse and determine the effects of modest progenitor rotation in the
context of core-collapse supernovae by comparing two separate long-duration
three-dimensional simulations of 9 M progenitors, one rotating with
an initial spin period of 60 seconds and the other non-rotating. We
determine that both models explode early, though the rotating model explodes a
bit earlier. Despite this difference, the asymptotic explosion energies
(10 ergs) and residual neutron star baryon masses (1.3
M) are similar. We find that the proto-neutron star (PNS) core can
deleptonize and cool significantly more quickly. Soon into the evolution of the
rotating model, we witness more vigorous and extended PNS core convection that
early in its evolution envelopes the entire inner sphere, not just a shell.
Moreover, we see a corresponding excursion in both the luminosity and
gravitational-wave strain that may be diagnostic of this observed dramatic
phenomenon. In addition, after bounce the innermost region of the rotating
model seems to execute meridional circulation. The rotationally-induced growth
of the convective PNS region may facilitate the growth of core B-fields by the
dynamo mechanism by facilitating the achievement of the critical Rossby number
condition for substantial growth of a dipole field, obviating the need for
rapid rotation rates to create dipole fields of significance. The next step is
to explore the progenitor-mass and spin dependencies across the progenitor
continuum of the supernova explosion, dynamics, and evolution of PNS convection
and its potential role in the generation of magnetar and pulsar magnetic
fields.Comment: Withdrawn pending further calculation
Microlensing of the Lensed Quasar SDSS0924+0219
We analyze V, I and H band HST images and two seasons of R-band monitoring
data for the gravitationally lensed quasar SDSS0924+0219. We clearly see that
image D is a point-source image of the quasar at the center of its host galaxy.
We can easily track the host galaxy of the quasar close to image D because
microlensing has provided a natural coronograph that suppresses the flux of the
quasar image by roughly an order of magnitude. We observe low amplitude,
uncorrelated variability between the four quasar images due to microlensing,
but no correlated variations that could be used to measure a time delay. Monte
Carlo models of the microlensing variability provide estimates of the mean
stellar mass in the lens galaxy (0.02 Msun < M < 1.0 Msun), the accretion disk
size (the disk temperature is 5 x 10^4 K at 3.0 x 10^14 cm < rs < 1.4 x 10^15
cm), and the black hole mass (2.0 x 10^7 Msun < MBH \eta_{0.1}^{-1/2}
(L/LE)^{1/2} < 3.3 x 10^8 Msun), all at 68% confidence. The black hole mass
estimate based on microlensing is consistent with an estimate of MBH = 7.3 +-
2.4 x 10^7 Msun from the MgII emission line width. If we extrapolate the
best-fitting light curve models into the future, we expect the the flux of
images A and B to remain relatively stable and images C and D to brighten. In
particular, we estimate that image D has a roughly 12% probability of
brightening by a factor of two during the next year and a 45% probability of
brightening by an order of magnitude over the next decade.Comment: v.2 incorporates referee's comments and corrects two errors in the
original manuscript. 28 pages, 10 figures, published in Ap
The Gravitational-Wave Signature of Core-Collapse Supernovae
We calculate the gravitational-wave (GW) signatures of detailed 3D
core-collapse supernova simulations spanning a range of massive stars. Most of
the simulations are carried out to times late enough to capture more than 95%
of the total GW emission. We find that the f/g-mode and f-mode of proto-neutron
star oscillations carry away most of the GW power. The f-mode frequency
inexorably rises as the proto-neutron star (PNS) core shrinks. We demonstrate
that the GW emission is excited mostly by accretion plumes onto the PNS that
energize modal oscillations and also high-frequency (``haze") emission
correlated with the phase of violent accretion. The duration of the major phase
of emission varies with exploding progenitor and there is a strong correlation
between the total GW energy radiated and the compactness of the progenitor.
Moreover, the total GW emissions vary by as much as three orders of magnitude
from star to star. For black-hole formation, the GW signal tapers off slowly
and does not manifest the haze seen for the exploding models. For such failed
models, we also witness the emergence of a spiral shock motion that modulates
the GW emission at a frequency near 100 Hertz that slowly increases as
the stalled shock sinks. We find significant angular anisotropy of both the
high- and low-frequency (memory) GW emissions, though the latter have very
little power.Comment: submitted to PR
Course-based Science Research Promotes Learning in Diverse Students at Diverse Institutions
Course-based research experiences (CREs) are powerful strategies for spreading learning and improving persistence for all students, both science majors and nonscience majors. Here we address the crucial components of CREs (context, discovery, ownership, iteration, communication, presentation) found across a broad range of such courses at a variety of academic institutions. We also address how the design of a CRE should vary according to the background of student participants; no single CRE format is perfect. We provide a framework for implementing CREs across multiple institutional types and several disciplines throughout the typical four years of undergraduate work, designed to a variety of student backgrounds. Our experiences implementing CREs also provide guidance on overcoming barriers to their implementation
Cognitive-Behavioral Therapy Augmentation of SSRI Reduces Cortisol Levels in Older Adults with Generalized Anxiety Disorder: A Randomized Clinical Trial
Objectives: Elevated cortisol in stress and aging, such as has been seen in late-life anxiety disorders, is postulated to accelerate cognitive and physiological decline in this large and increasing population. Selective serotonin-reuptake inhibitors (SSRIs) and cognitive behavior therapy (CBT) are both effective treatments for Generalized Anxiety Disorder (GAD) in older adults. On the other hand, there is very little research examining the effect of combining these therapies on peak cortisol levels. For the current analyses, we examined the effectiveness of CBT augmentation on peak cortisol levels in older adults diagnosed with GAD.
Methods: The sample consisted of 42 individuals with late-life GAD who received an acute course of the SSRI escitalopram and then entered a 16-week randomized phase. Twenty-one participants were randomized to receive 16 sessions of CBT in addition to continuing escitalopram and the remaining 21 participants continued on escitalopram without CBT. Generalized Estimating Equations were performed to assess the effectiveness of CBT augmentation on peak cortisol levels (30 minutes after waking).
Results: Older adults with GAD who received both escitalopram and CBT demonstrated a significant reduction in peak cortisol levels at post-treatment compared to the group who received escitalopram without CBT augmentation.
Conclusions: CBT augmentation of SSRI treatment reduced peak cortisol levels for older adults with GAD. Since persistently high cortisol levels in aging are thought to increase age-related cognitive and medical problems, our findings suggest that there may be a benefit to health and cognition of CBT augmentation for late-life anxiety disorders
Designing MPAs for food security in open-access fisheries
Food security remains a principal challenge in the developing tropics where communities rely heavily on marine-based protein. While some improvements in fisheries management have been made in these regions, a large fraction of coastal fisheries remain unmanaged, mismanaged, or use only crude input controls. These quasi-open-access conditions often lead to severe overfishing, depleted stocks, and compromised food security. A possible fishery management approach in these institution-poor settings is to implement fully protected marine protected areas (MPAs). Although the primary push for MPAs has been to solve the conservation problems that arise from mismanagement, MPAs can also benefit fisheries beyond their borders. The literature has not completely characterized how to design MPAs under diverse ecological and economic conditions when food security is the objective. We integrated four key biological and economic variables (i.e., fish population growth rate, fish mobility, fish price, and fishing cost) as well as an important aspect of reserve design (MPA size) into a general model and determined their combined influence on food security when MPAs are implemented in an open-access setting. We explicitly modeled open-access conditions that account for the behavioral response of fishers to the MPA; this approach is distinct from much of the literature that focuses on assumptions of “scorched earth” (i.e., severe over-fishing), optimized management, or an arbitrarily defined fishing mortality outside the MPA’s boundaries. We found that the MPA size that optimizes catch depends strongly on economic variables. Large MPAs optimize catch for species heavily harvested for their high value and/or low harvesting cost, while small MPAs or no closure are best for species lightly harvested for their low value and high harvesting cost. Contrary to previous theoretical expectations, both high and low mobility species are expected to experience conservation benefits from protection, although, as shown previously, greater conservation benefits are expected for low mobility species. Food security benefits from MPAs can be obtained from species of any mobility. Results deliver both qualitative insights and quantitative guidance for designing MPAs for food security in open-access fisheries
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