5,687 research outputs found
Spurious Eccentricities of Distorted Binary Components
I discuss the effect of physical distortion on the velocities of close binary
components and how we may use the resulting distortion of velocity curves to
constrain some properties of binary systems, such as inclination and mass
ratio. Precise new velocities for 5 Cet convincingly detect these distortions
with their theoretically predicted phase dependence. We can even use such
distortions of velocity curves to test Lucy's theory of convective gravity
darkening. The observed distortions for TT Hya and 5 Cet require the contact
components of those systems to be gravity darkened, probably somewhat more than
predicted by Lucy's theory but clearly not as much as expected for a radiative
star. These results imply there is no credible evidence for eccentric orbits in
binaries with contact components. I also present some speculative analyses of
the observed properties of a binary encased in a non-rotating common envelope,
if such an object could actually exist, and discuss how the limb darkening of
some recently calculated model atmospheres for giant stars may bias my resuts
for velocity-curve distortions, as well as other results from a wide range of
analyses of binary stars.Comment: 14 pp, 2 tables, 12 fig; under review by Ap
Outcome after introduction of laparoscopic appendectomy in children: A cohort study
INTRODUCTION: Acute appendicitis in children is common and the optimal treatment modality is still debated, even if recent data suggest that laparoscopic surgery may result in shorter postoperative length of stay without an increased number of complications. The aim of the study was to compare the outcome of open and laparoscopic appendectomies during a transition period. MATERIALS AND METHODS: This was a retrospective cohort study with prospectively collected data. All patients who underwent an operation for suspected appendicitis at the Astrid Lindgren Children's Hospital in Stockholm between 2006 and 2010 were included in the study. RESULTS: 1745 children were included in this study, of whom 1010 had a laparoscopic intervention. There were no significant differences in the rate of postoperative abscesses, wound infections, readmissions or reoperations between the two groups. The median operating time was longer for laparoscopic appendectomy than for open appendectomy, 51 vs. 37minutes (p<0.05). The postoperative length of stay was similar in the two groups. A simple comparison between the groups suggested that laparoscopic appendectomy had a shorter median postoperative length of stay, 43 vs. 57hours (p<0.05). However, there was a trend in time for a shorter postoperative length of stay, and a trend for more of the procedures to be performed laparoscopically over time so on regression analysis, the apparent decrease in length of stay with laparoscopy could be ascribed to the general trend toward decreased length of stay over time, with no specific additional effect of laparoscopy. CONCLUSIONS: Our data show no difference in outcome between open and laparoscopic surgery for acute appendicitis in children in regard of complications. The initial assumption that the patients treated with laparoscopic surgery had a shorter postoperative stay was not confirmed with linear regression, which showed that the assumed difference was due only to a trend toward shorter postoperative length of stay over time, regardless of the surgical intervention
Modeling Porous Dust Grains with Ballistic Aggregates. II. Light Scattering Properties
We study the light scattering properties of random ballistic aggregates
constructed in Shen et al. (Paper I). Using the discrete-dipole-approximation,
we compute the scattering phase function and linear polarization for random
aggregates with various sizes and porosities, and with two different
compositions: 100% silicate and 50% silicate-50% graphite. We investigate the
dependence of light scattering properties on wavelength, cluster size and
porosity using these aggregate models. We find that while the shape of the
phase function depends mainly on the size parameter of the aggregates, the
linear polarization depends on both the size parameter and the porosity of the
aggregates, with increasing degree of polarization as the porosity increases.
Contrary to previous studies, we argue that monomer size has negligible effects
on the light scattering properties of ballistic aggregates, as long as the
constituent monomer is smaller than the incident wavelength up to
2*pi*a_0/lambda\sim 1.6 where a_0 is the monomer radius. Previous claims for
such monomer size effects are in fact the combined effects of size parameter
and porosity. Finally, we present aggregate models that can reproduce the phase
function and polarization of scattered light from the AU Mic debris disk and
from cometary dust, including the negative polarization observed for comets at
scattering angles 160<theta<180 deg. These aggregates have moderate porosities,
P\sim 0.6, and are of sub-micron-size for the debris disk case, or micron-size
for the comet case.Comment: Submitted to ApJ. Scattering properties can be downloaded at
http://www.astro.princeton.edu/~draine/SDJ2009.html Target geometries are at
http://www.astro.princeton.edu/~draine/agglom.htm
Integrated waveguides and deterministically positioned nitrogen vacancy centers in diamond created by femtosecond laser writing
Diamond's nitrogen vacancy (NV) center is an optically active defect with
long spin coherence times, showing great potential for both efficient nanoscale
magnetometry and quantum information processing schemes. Recently, both the
formation of buried 3D optical waveguides and high quality single NVs in
diamond were demonstrated using the versatile femtosecond laser-writing
technique. However, until now, combining these technologies has been an
outstanding challenge. In this work, we fabricate laser written photonic
waveguides in quantum grade diamond which are aligned to within micron
resolution to single laser-written NVs, enabling an integrated platform
providing deterministically positioned waveguide-coupled NVs. This fabrication
technology opens the way towards on-chip optical routing of single photons
between NVs and optically integrated spin-based sensing
An Optical Study of BG Geminorum: An Ellipsoidal Binary with an Unseen Primar Star
We describe optical photometric and spectroscopic observations of the bright
variable BG Geminorum. Optical photometry shows a pronounced ellipsoidal
variation of the K0 I secondary, with amplitudes of ~0.5 mag at VRI and a
period of 91.645 days. A deep primary eclipse is visible for wavelengths <
4400A; a shallower secondary eclipse is present at longer wavelengths. Eclipse
timings and the radial velocity curve of the K0 secondary star indicate an
interacting binary where a lobe-filling secondary, M_2 ~ 0.5 Msun, transfers
material into a extended disk around a massive primary, M_1 ~ 4.5 Msun. The
primary star is either an early B-type star or a black hole. If it did contain
a black hole, BG Gem would be the longest period black hole binary known by a
factor of 10, as well as the only eclipsing black hole binary system.Comment: 27 pages, includes 8 figures and 5 tables, accepted to A
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Building more accurate decision trees with the additive tree.
The expansion of machine learning to high-stakes application domains such as medicine, finance, and criminal justice, where making informed decisions requires clear understanding of the model, has increased the interest in interpretable machine learning. The widely used Classification and Regression Trees (CART) have played a major role in health sciences, due to their simple and intuitive explanation of predictions. Ensemble methods like gradient boosting can improve the accuracy of decision trees, but at the expense of the interpretability of the generated model. Additive models, such as those produced by gradient boosting, and full interaction models, such as CART, have been investigated largely in isolation. We show that these models exist along a spectrum, revealing previously unseen connections between these approaches. This paper introduces a rigorous formalization for the additive tree, an empirically validated learning technique for creating a single decision tree, and shows that this method can produce models equivalent to CART or gradient boosted stumps at the extremes by varying a single parameter. Although the additive tree is designed primarily to provide both the model interpretability and predictive performance needed for high-stakes applications like medicine, it also can produce decision trees represented by hybrid models between CART and boosted stumps that can outperform either of these approaches
Expert-Augmented Machine Learning
Machine Learning is proving invaluable across disciplines. However, its
success is often limited by the quality and quantity of available data, while
its adoption by the level of trust that models afford users. Human vs. machine
performance is commonly compared empirically to decide whether a certain task
should be performed by a computer or an expert. In reality, the optimal
learning strategy may involve combining the complementary strengths of man and
machine. Here we present Expert-Augmented Machine Learning (EAML), an automated
method that guides the extraction of expert knowledge and its integration into
machine-learned models. We use a large dataset of intensive care patient data
to predict mortality and show that we can extract expert knowledge using an
online platform, help reveal hidden confounders, improve generalizability on a
different population and learn using less data. EAML presents a novel framework
for high performance and dependable machine learning in critical applications
Learning from an Electronic Chart Testbed
Over the past five years, the Canadian Hydrographic Service’s Electronic Chart Testbed has provided insights into the way an electronic chart (EC) will handle chart data — and from this the appropriate form for the Hydrographic Office to provide and electronic chart database; it has stimulated suggestions about how the display should be designed; it has provided a practical model for use in planning IHO specifications — and followed on to test these by implementing them; and it has shared in giving mariners demonstrations of some of the eventual capabilities of ECDIS, so that they can start thinking about what they need from it. This paper describes planning the Testbed; lessons from early tests; initial ideas on electronic chart data and on display design; and the reactions from mariners who saw the Testbed among six electronic charts on board the Norwegian ship LANCE during the 1988 North Sea Project
Absolute instruments and perfect imaging in geometrical optics
We investigate imaging by spherically symmetric absolute instruments that
provide perfect imaging in the sense of geometrical optics. We derive a number
of properties of such devices, present a general method for designing them and
use this method to propose several new absolute instruments, in particular a
lens providing a stigmatic image of an optically homogeneous region and having
a moderate refractive index range.Comment: 20 pages, 9 image
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