1,387 research outputs found
John Chalmers DaCosta (1863-1933): restoration of the old operating table.
John Chalmers DaCosta was an influential chairman and the first Samuel D. Gross Professor of Surgery at Jefferson Medical College in Philadelphia. He was well known throughout the field as a skilled surgeon, passionate speaker, and exceptional writer. In addition to countless accomplishments during his career, DaCosta was deeply dedicated to the preservation and commemoration of surgical history. This ideology was exemplified when he set out on a mission to recover the old wooden operating table used by many of his iconic mentors including Samuel D. Gross, Joseph Pancoast, and William W. Keen. This table was originally used for surgical demonstrations and anatomy lessons in a lecture room of the Ely Building and later in the great amphitheater of the Jefferson Sansom Street Hospital. It was found forgotten in the basement of the College Building and was promptly refurbished, donned with dedicatory plaques, and returned to its honored position in the medical college. Dr. DaCosta also contributed a detailed article recalling the history of the table and the notable leaders in surgery who taught and practiced on its surface. The old table currently stands proudly in the entranceway of the Department of Surgery where it will remain as a cherished symbol of the early beginnings of surgical practice and education
Phase curves of WASP-33b and HD 149026b and a New Correlation Between Phase Curve Offset and Irradiation Temperature
We present new 3.6 and 4.5 Spitzer phase curves for the highly
irradiated hot Jupiter WASP-33b and the unusually dense Saturn-mass planet HD
149026b. As part of this analysis, we develop a new variant of pixel level
decorrelation that is effective at removing intrapixel sensitivity variations
for long observations (>10 hours) where the position of the star can vary by a
significant fraction of a pixel. Using this algorithm, we measure eclipse
depths, phase amplitudes, and phase offsets for both planets at 3.6 and
4.5 . We use a simple toy model to show that WASP-33b's phase offset,
albedo, and heat recirculation efficiency are largely similar to those of other
hot Jupiters despite its very high irradiation. On the other hand, our fits for
HD 149026b prefer a very high albedo and an unusually high recirculation
efficiency. We also compare our results to predictions from general circulation
models, and find that while neither are a good match to the data, the
discrepancies for HD 149026b are especially large. We speculate that this may
be related to its high bulk metallicity, which could lead to enhanced
atmospheric opacities and the formation of reflective cloud layers in localized
regions of the atmosphere. We then place these two planets in a broader context
by exploring relationships between the temperatures, albedos, heat transport
efficiencies, and phase offsets of all planets with published thermal phase
curves. We find a striking relationship between phase offset and irradiation
temperature--the former drops with increasing temperature until around 3400 K,
and rises thereafter. Although some aspects of this trend are mirrored in the
circulation models, there are notable differences that provide important clues
for future modeling efforts
Mapping Exoplanets
The varied surfaces and atmospheres of planets make them interesting places
to live, explore, and study from afar. Unfortunately, the great distance to
exoplanets makes it impossible to resolve their disk with current or near-term
technology. It is still possible, however, to deduce spatial inhomogeneities in
exoplanets provided that different regions are visible at different
times---this can be due to rotation, orbital motion, and occultations by a
star, planet, or moon. Astronomers have so far constructed maps of thermal
emission and albedo for short period giant planets. These maps constrain
atmospheric dynamics and cloud patterns in exotic atmospheres. In the future,
exo-cartography could yield surface maps of terrestrial planets, hinting at the
geophysical and geochemical processes that shape them.Comment: Updated chapter for Handbook of Exoplanets, eds. Deeg & Belmonte. 17
pages, including 6 figures and 4 pages of reference
Diffractive triangulation of radiative point sources
We describe a general method to determine the location of a point source of waves relative to a twodimensional
single-crystalline active pixel detector. Based on the inherent structural sensitivity of
crystalline sensor materials, characteristic detector diffraction patterns can be used to triangulate the
location of a wave emitter. The principle described here can be applied to various types of waves,
provided that the detector elements are suitably structured. As a prototypical practical application of
the general detection principle, a digital hybrid pixel detector is used to localize a source of electrons
for Kikuchi diffraction pattern measurements in the scanning electron microscope. This approach
provides a promising alternative method to calibrate Kikuchi patterns for accurate measurements of
microstructural crystal orientations, strains, and phase distributions
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Attenuation of G{sub 2} cell cycle checkpoint control in human tumor cells is associated with increased frequencies of unrejoined chromosome breaks but not increased cytotoxicity following radiation exposure
The contribution of G{sub 2} cell cycle checkpoint control to ionizing radiation responses was examined in ten human tumor cell lines. Most of the delay in cell cycle progression seen in the first cell cycle following radiation exposure was due to blocks in G{sub 2} and there were large cell line-to-cell line variations in the length of the G{sub 2} block. Longer delays were seen in cell lines that had mutations in p53. There was a highly significant inverse correlation between the length of G{sub 2} delay and the frequency of unrejoined chromosome breaks seen as chromosome terminal deletions in mitosis, and observation that supports the hypothesis that the signal for G{sub 2} delay in mammalian cells is an unrejoined chromosome break. There were also an inverse correlation between the length of G{sub 2} delay and the level of chromosome aneuploidy in each cell line, suggesting that the G{sub 2} and mitotic spindel checkpoints may be linked to each other. Attenuation in G{sub 2} checkpoint control was not associated with alterations in either the frequency of induced chromosome rearrangements or cell survival following radiation exposure suggesting that chromosome rearrangements, the major radiation-induced lethal lesion in tumor cells, form before cells enters G{sub 2}. Thus, agents that act solely to override G{sub 2} arrest should produce little radiosensitization in human tumor cells
The Very Low Albedo of WASP-12b From Spectral Eclipse Observations with
We present an optical eclipse observation of the hot Jupiter WASP-12b using
the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope.
These spectra allow us to place an upper limit of (97.5%
confidence level) on the planet's white light geometric albedo across 290--570
nm. Using six wavelength bins across the same wavelength range also produces
stringent limits on the geometric albedo for all bins. However, our
uncertainties in eclipse depth are 40% greater than the Poisson limit and
may be limited by the intrinsic variability of the Sun-like host star --- the
solar luminosity is known to vary at the level on a timescale of
minutes. We use our eclipse depth limits to test two previously suggested
atmospheric models for this planet: Mie scattering from an aluminum-oxide haze
or cloud-free Rayleigh scattering. Our stringent nondetection rules out both
models and is consistent with thermal emission plus weak Rayleigh scattering
from atomic hydrogen and helium. Our results are in stark contrast with those
for the much cooler HD 189733b, the only other hot Jupiter with spectrally
resolved reflected light observations; those data showed an increase in albedo
with decreasing wavelength. The fact that the first two exoplanets with optical
albedo spectra exhibit significant differences demonstrates the importance of
spectrally resolved reflected light observations and highlights the great
diversity among hot Jupiters.Comment: 8 pages, 4 figures, 1 table, published in ApJL, in pres
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