395 research outputs found
Real-time Audio-Visual Media Transport over QUIC
We consider the problem of how to transport low-latency, interactive, real-time traffic over QUIC. This is needed to support applications like WebRTC, but difficult to support due to the reliable, unframed, nature of QUIC streams. We review the needs of low-latency real-time applications and how they have been supported in previous protocols, then propose a minimal set of extensions to QUIC to provide such support. Compared to a raw datagram service, our extensions provide meaningful support for partially reliable and real-time flows, in a backwards compatible manner
The evolution of M 2-9 from 2000 to 2010
M 2-9, the Butterfly nebula, is an outstanding representative of extreme
aspherical flows. It presents unique features such as a pair of high-velocity
dusty polar blobs and a mirror-symmetric rotating pattern in the inner lobes.
Imaging monitoring of the evolution of the nebula in the past decade is
presented. We determine the proper motions of the dusty blobs, which infer a
new distance estimate of 1.3+-0.2 kpc, a total nebular size of 0.8 pc, a speed
of 147 km/s, and a kinematical age of 2500 yr. The corkscrew geometry of the
inner rotating pattern is quantified. Different recombination timescales for
different ions explain the observed surface brightness distribution. According
to the images taken after 1999, the pattern rotates with a period of 92+-4 yr.
On the other hand, the analysis of images taken between 1952 and 1977 measures
a faster angular velocity. If the phenomenon were related to orbital motion,
this would correspond to a modest orbital eccentricity (e=0.10+-0.05), and a
slightly shorter period (86+-5 yr). New features have appeared after 2005 on
the west side of the lobes and at the base of the pattern. The geometry and
travelling times of the rotating pattern support our previous proposal that the
phenomenon is produced by a collimated spray of high velocity particles (jet)
from the central source, which excites the walls of the inner cavity of M 2-9,
rather than by a ionizing photon beam. The speed of such a jet would be
remarkable: between 11000 and 16000 km/s. The rotating-jet scenario may explain
the formation and excitation of most of the features observed in the inner
nebula, with no need for additional mechanisms, winds, or ionization sources.
All properties point to a symbiotic-like interacting binary as the central
source of M 2-9.Comment: Accepted for publication on Astronomy and Astrophysics (10 pages, 8
figures
Spectral Energy Distributions and Multiwavelength Selection of Type 1 Quasars
We present an analysis of the mid-infrared (MIR) and optical properties of type 1 (broad-line) quasars detected by the Spitzer Space Telescope. The MIR color-redshift relation is characterized to z ~ 3, with predictions to z = 7. We demonstrate how combining MIR and optical colors can yield even more efficient selection of active galactic nuclei (AGNs) than MIR or optical colors alone. Composite spectral energy distributions (SEDs) are constructed for 259 quasars with both Sloan Digital Sky Survey and Spitzer photometry, supplemented by near-IR, GALEX, VLA, and ROSAT data, where available. We discuss how the spectral diversity of quasars influences the determination of bolometric luminosities and accretion rates; assuming the mean SED can lead to errors as large as 50% for individual quasars when inferring a bolometric luminosity from an optical luminosity. Finally, we show that careful consideration of the shape of the mean quasar SED and its redshift dependence leads to a lower estimate of the fraction of reddened/obscured AGNs missed by optical surveys as compared to estimates derived from a single mean MIR to optical flux ratio
Hot Jupiter Magnetospheres
(Abridged) The upper atmospheres of close-in gas giant exoplanets are
subjected to intense heating/tidal forces from their parent stars.
Atomic/ionized hydrogen (H) layers are sufficiently rarefied that magnetic
pressure may dominate gas pressure for expected planetary magnetic field
strength. We examine the magnetospheric structure using a 3D isothermal
magnetohydrodynamic model that includes: a static "dead zone" near the magnetic
equator containing magnetically confined gas; a "wind zone" outside the
magnetic equator in which thermal pressure gradients and the
magneto-centrifugal-tidal effect give rise to transonic outflow; and a region
near the poles where sufficiently strong tidal forces may suppress transonic
outflow. Using dipole field geometry, we estimate the size of the dead zone to
be ~1-10 planetary radii for a range of parameters. To understand appropriate
base conditions for the 3D isothermal model, we compute a 1D thermal model in
which photoelectric heating from the stellar Lyman continuum is balanced by
collisionally-excited Lyman {\alpha} cooling. This 1D model exhibits a H layer
with temperatures T=5000-10000K down to pressures of 10-100 nbar. Using the 3D
isothermal model, we compute H column densities and Lyman {\alpha} transmission
spectra for parameters appropriate to HD 209458b. Line-integrated transit
depths of 5-10% can be achieved for the above base conditions. Strong magnetic
fields increase the transit signal while decreasing the mass loss, due to
higher covering fraction and density of the dead zone. In our model, most of
the transit signal arises from magnetically confined gas, some of which may be
outside the L1 equipotential. Hence the presence of gas outside the L1
equipotential does not directly imply mass loss. Lastly, we discuss the domain
of applicability for the magnetic wind model described in this paper and in the
Roche-lobe overflow model.Comment: 26 pages, 17 figures (5 color), 2 appendices; submitted to ApJ;
higher resolution version available at
http://www.astro.virginia.edu/~gbt8f/HotJupMag_fullres_astroph.pd
HST NICMOS Observations of the Polarization of NGC 1068
We have observed the polarized light at 2 micron in the center of NGC 1068
with HST NICMOS Camera 2. The nucleus is dominated by a bright, unresolved
source, polarized at a level of 6.0 pm 1.2% with a position angle of 122degr pm
1.5degr. There are two polarized lobes extending up to 8'' northeast and
southwest of the nucleus. The polarized flux in both lobes is quite clumpy,
with the maximum polarization occurring in the southwest lobe at a level of 17%
when smoothed to 0.23'' resolution. The perpendiculars to the polarization
vectors in these two lobes point back to the intense unresolved nuclear source
to within one 0.076'' Camera 2 pixel, thereby confirming that this is the
illuminating source of the scattered light and therefore the probable AGN
central engine. Whereas the polarization of the nucleus is probably caused by
dichroic absorption, the polarization in the lobes is almost certainly caused
by scattering, with very little contribution from dichroic absorption. Features
in the polarized lobes include a gap at a distance of about 1'' from the
nucleus toward the southwest lobe and a ``knot'' of emission about 5''
northeast of the nucleus. Both features had been discussed by ground-based
observers, but they are much better defined with the high spatial resolution of
NICMOS. The northeast knot may be the side of a molecular cloud that is facing
the nucleus, which cloud may be preventing the expansion of the northeast radio
lobe at the head of the radio synchrotron-radiation-emitting jet. We also
report the presence of two ghosts in the Camera 2 polarizers. These had not
been detected previously (Hines et al. 2000) because they are relatively faint
and require observations of a source with a large dynamic range.Comment: 17 pages, 4 figure
Community-Led Response to Address Economic Vulnerability due to COVID-19 with, for, and by Transgender Women of Color: A Qualitative Pilot Evaluation
PURPOSE: Intersectional stigma fuels inequities among transgender women of color, which have been exacerbated by coronavirus disease 2019 (COVID-19). This study evaluated a community-led emergency assistance program for transgender women of color.
METHODS: We conducted a pilot program evaluation (n=8).
RESULTS: Retention was 87.5% over the follow-up. Funds were primarily used for bills, food, and housing. Requesting and receiving funds was described as somewhat to extremely easy. Participants identified the need for economic empowerment components in future programming, specifically gender affirmation, skill-building for education and employment, and entrepreneurial opportunities.
CONCLUSION: Findings highlight the need to invest in community-led strategies to address inequities experienced by transgender women of color
HST Snapshot Survey of Post-AGB Objects
The results from a Hubble Space Telescope (HST) snapshot survey of post-AGB
objects are shown. The aim of the survey is to complement existing HST images
of PPN and to connect various types of nebulosities with physical and chemical
properties of their central stars. Nebulosities are detected in 15 of 33
sources. Images and photometric and geometric measurements are presented. For
sources with nebulosities we see a morphological bifurcation into two groups,
DUPLEX and SOLE, as previous studies have found. We find further support to the
previous results suggesting that this dichotomy is caused by a difference in
optical thickness of the dust shell. The remaining 18 sources are classified as
stellar post-AGB objects, because our observations indicate a lack of
nebulosity. We show that some stellar sources may in fact be DUPLEX or SOLE
based on their infrared colors. The cause of the differences among the groups
are investigated. We discuss some evidence suggesting that high progenitor-mass
AGB stars tend to become DUPLEX post-AGB objects. Intermediate progenitor-mass
AGB stars tend to be SOLE post-AGB objects. Most of the stellar sources
probably have low mass progenitors and do not seem to develop nebulosities
during the post-AGB phase and therefore do not become planetary nebulae.Comment: 21 pages, 11 figure
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