1,932 research outputs found
The Light Curve of the Weakly-Accreting T Tauri Binary KH 15D from 2005-10: Insights into the Nature of its Protoplanetary Disk
Photometry of the unique pre-main sequence binary system KH 15D is presented,
spanning the years 2005-2010. This system has exhibited photometric variations
and eclipses over the last 50 years caused by a precessing circumbinary disk.
Advancement of the occulting edge across the binary orbit has continued and the
photospheres of both stars are now completely obscured at all times. The system
is now visible only by scattered light, and yet it continues to show a periodic
variation on the orbital cycle with an amplitude exceeding two magnitudes. This
variation, which depends only on the binary phase, has likely been present in
the data since at least 1995. It can, by itself, account for shoulders on the
light curve prior to ingress and following egress, obviating the need for
components of extant models such as a scattering halo around star A or forward
scattering from a fuzzy disk edge. A plausible source for the variable
scattering component is reflected light from the far side of a warped occulting
disk. We have detected color changes in V-I of several tenths of a magnitude to
both the blue and red that occur during times of minima. These may indicate the
presence of a third source of light (faint star) within the system, or a change
in the reflectance properties of the disk as the portion being illuminated
varies with the orbital motion of the stars. The data support a picture of the
circumbinary disk as a geometrically thin, optically thick layer of perhaps mm
or cm-sized particles that has been sculpted by the binary stars and possibly
other components into a decidedly nonplanar configuration. A simple (infinitely
sharp) knife-edge model does a good job of accounting for all of the recent
(2005-2010) occultation data.Comment: To appear in The Astronomical Journa
Bipolar jets produced by a spectroscopic binary
We present evidence that the spectroscopically identified bipolar jets of the
pre-main sequence binary KH 15D are a common product of the whole binary
system, rather than being launched from either star individually. They may be
launched from the innermost part of the circumbinary disk (CBD) or may result
from the merging of two outflows driven by the individual stars. This evidence
is based on high-resolution H-alpha and [OI] 6300A line profiles obtained
during eclipse phases of this nearly edge-on system. The occultation of star A
(the only currently visible star) by the disk strongly suppresses the stellar
H-alpha and continuum emission and allows one to study the faint redshifted and
blueshifted emission components of the bipolar jets. The strongest evidence for
jet production by the whole binary system comes from the observed radial
velocity symmetry of the two jet components relative to the systemic velocity
of the binary, in combination with current accretion models from the CBD onto a
binary system.Comment: ApJ Letters, in press [6 pages
Complex Variability of the H Emission Line Profile of the T Tauri Binary System KH 15D: The Influence of Orbital Phase, Occultation by the Circumbinary Disk, and Accretion Phenomenae
We have obtained 48 high resolution echelle spectra of the pre-main sequence
eclipsing binary system KH~15D (V582 Mon, P = 48.37 d, 0.6, M
= 0.6 M, M = 0.7 M). The eclipses are caused by a
circumbinary disk seen nearly edge on, which at the epoch of these observations
completely obscured the orbit of star B and a large portion of the orbit of
star A. The spectra were obtained over five contiguous observing seasons from
2001/2002 to 2005/2006 while star A was fully visible, fully occulted, and
during several ingress and egress events. The H line profile shows
dramatic changes in these time series data over timescales ranging from days to
years. A fraction of the variations are due to "edge effects" and depend only
on the height of star A above or below the razor sharp edge of the occulting
disk. Other observed variations depend on the orbital phase: the H
emission line profile changes from an inverse P Cygni type profile during
ingress to an enhanced double-peaked profile, with both a blue and red emission
component, during egress. Each of these interpreted variations are complicated
by the fact that there is also a chaotic, irregular component present in these
profiles. We find that the complex data set can be largely understood in the
context of accretion onto the stars from a circumbinary disk with gas flows as
predicted by the models of eccentric T Tauri binaries put forward by Artymowicz
& Lubow, G\"{u}nther & Kley, and de Val-Borro et al. In particular, our data
provide strong support for the pulsed accretion phenomenon, in which enhanced
accretion occurs during and after perihelion passage.Comment: accepted to Ap
Learning Direct Optimization for scene understanding
We develop a Learning Direct Optimization (LiDO) method for the refinement of
a latent variable model that describes input image x. Our goal is to explain a
single image x with an interpretable 3D computer graphics model having scene
graph latent variables z (such as object appearance, camera position). Given a
current estimate of z we can render a prediction of the image g(z), which can
be compared to the image x. The standard way to proceed is then to measure the
error E(x, g(z)) between the two, and use an optimizer to minimize the error.
However, it is unknown which error measure E would be most effective for
simultaneously addressing issues such as misaligned objects, occlusions,
textures, etc. In contrast, the LiDO approach trains a Prediction Network to
predict an update directly to correct z, rather than minimizing the error with
respect to z. Experiments show that our LiDO method converges rapidly as it
does not need to perform a search on the error landscape, produces better
solutions than error-based competitors, and is able to handle the mismatch
between the data and the fitted scene model. We apply LiDO to a realistic
synthetic dataset, and show that the method also transfers to work well with
real images
Qualitative evaluation of a practice-based experience pilot program for master of pharmacy students in Scotland
Objective. To determine the views of pharmacists in central Scotland regarding experiential education for MPharm students. Methods. A thematic analysis was completed by Ms. Gillian Hendry and Dr. Sally Wiggins of interviews conducted with ten practicing pharmacists paired with first-year master of pharmacy (MPharm) students during the 2011-2012 academic year. Relevant comments from the interviews were manually sorted in a Microsoft Excel spreadsheet to bring similarly themed material together to facilitate the identification and naming of recurring themes and subthemes. Results. The pharmacists were unanimous in their opinion that experiential education was valuable for MPharm students and, in particular, that it helped students to develop self-confidence. The pharmacists derived personal satisfaction in developing mentor/mentee relationships with students. They also recognized the value that students provided to the workforce as well as the educational value to themselves in supervising students. The participantsâ primary dissatisfaction was that the pharmacy workflow limited the time they could spend mentoring students. Conclusion. The results provide guidance to the academic community and the pharmacy practice community in the United Kingdom (UK) regarding the design and integration of experiential education courses in MPharm degree programs
Surveying the Feasibility of a Voluntary Beef Checkoff: Do Demographics and Attitudes Matter?
The beef checkoff, a generic marketing program, funded through producer assessments, may soon be been ruled unconstitutional. Several states have proceeded toward voluntary checkoffs to replace the broadly supported mandatory program. These factors raise the question: Is a voluntary beef checkoff feasible? A choice experiment, employing cheap talk and certainty calibration is conducted on a mail survey to 2,950 Oklahoma cattle producers. Several checkoff designs are examined, and participation in either a state or federal checkoff appears sufficient to initiate a checkoff. Producers prefer checkoff expenditure to be heavy in advertising, favor a per-head fee less than one dollar and are not strongly influenced by a minimum participation rate. Several demographics correlate with checkoff preferences including: higher household income, membership in certain farm groups and veal production. Attitudes regarding the current checkoff correlate strongly with preferences for a voluntary program.Department of Agricultural Economic
Subaru HDS Transmission Spectroscopy of the Transiting Extrasolar Planet HD 209458b
We have searched for absorption in several common atomic species due to the
atmosphere or exosphere of the transiting extrasolar planet HD 209458b, using
high precision optical spectra obtained with the Subaru High Dispersion
Spectrograph (HDS). Previously we reported an upper limit on H alpha absorption
of 0.1% (3 sigma) within a 5.1\AA band. Using the same procedure, we now report
upper limits on absorption due to the optical transitions of Na D, Li, H alpha,
H beta, H gamma, Fe, and Ca. The 3 sigma upper limit for each transition is
approximately 1% within a 0.3\AA band (the core of the line), and a few tenths
of a per cent within a 2\AA band (the full line width). The wide-band results
are close to the expected limit due to photon-counting (Poisson) statistics,
although in the narrow-band case we have encountered unexplained systematic
errors at a few times the Poisson level. These results are consistent with all
previously reported detections and upper limits, but are significantly more
sensitive.Comment: 10 pages, 9 figure
\u3ci\u3e Phenytoin reduces 5-ala mediated fluorescence in glioblastoma cells \u3c/i\u3e
Glioblastoma multiforme (GBM) is a devastating form of cancer, and essentially all GBM tumors recur causing fatality. A new surgical technique, fluorescence-guided resection of GBM using 5-aminolevulinic acid (5-ala), improves the extent of resection and positively impacts the length and quality of patient survival. The fluorescence achieved in neoplastic tissue depends directly on the accumulation of porphyrins derived from the metabolism of the 5-ala prodrug within the cancer cell. However, 5-ala induced fluorescence has been reported to be inconsistent. In an effort to determine the cause of the inconsistent fluorescence, the authors investigated the effect of medications commonly prescribed to brain tumor patients on 5-ala induced fluorescence. A model was developed to quantify intracellular porphyrin accumulation using a U87MG GBM cell line constitutively expressing yellow fluorescent protein (YFP-U87). 5-ala mediated fluorescence within the cells was standardized to cell number via the fluorescence emission spectra ratio of porphyrin (405 nm) to YFP (525 nm). 5-ala induced accumulation of porphyrins was measured after treating YFP-U87 cells with phenytoin, dexamethasone, or desipramine for 3 days. After a 6 hour incubation with 5-ala, no significant difference in porphyrin accumulation was observed in cells treated with dexamethasone or desipramine. Phenytoin, however, significantly reduced the accumulation of fluorescent porphyrins within the YFP-U87 cell line by nearly 30% compared to the control. To optimize fluorescence during surgery and improve patient survival these results suggest that further investigations are warranted to determine the effects of commonly administered medications on 5-ala fluorescence-guided resection of GBM
PKS 1830-211: A Face-On Spiral Galaxy Lens
We present new Hubble Space Telescope images of the gravitational lens PKS
1830-211, which allow us to characterize the lens galaxy and update the
determination of the Hubble constant from this system. The I-band image shows
that the lens galaxy is a face-on spiral galaxy with clearly delineated spiral
arms. The southwestern image of the background quasar passes through one of the
spiral arms, explaining the previous detections of large quantities of
molecular gas and dust in front of this image. The lens galaxy photometry is
consistent with the Tully-Fisher relation, suggesting the lens galaxy is a
typical spiral galaxy for its redshift. The lens galaxy position, which was the
main source of uncertainty in previous attempts to determine H_0, is now known
precisely. Given the current time delay measurement and assuming the lens
galaxy has an isothermal mass distribution, we compute H_0 = 44 +/- 9 km/s/Mpc
for an Omega_m = 0.3 flat cosmological model. We describe some possible
systematic errors and how to reduce them. We also discuss the possibility
raised by Courbin et al. (2002), that what we have identified as a single lens
galaxy is actually a foreground star and two separate galaxies.Comment: 21 pp., 4 figs., accepted by ApJ, section added to discuss related
work by Courbin et al. (astro-ph/0202026
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