788 research outputs found
All-optical combiner-splitter and gating devices based on straight waveguides
A two-mode optical combiner-splitter device is designed based on all straight waveguides that maintains the integrity of the two modes during propagation and allows for an analytic analysis. The design analysis has the potential to improve the precision of the device fabrication. The design is used in an analytic optical gate based on a nonlinear Mach-Zehnder interferometer. The design reduces the size of a previously proposed device and simplifies its analysis
Projecting the Economic Impact of the Fayetteville Shale Play for 2005-2008
This study projects the general economic impact from exploration and development activities related to the Fayetteville Shale. The Fayetteville Shale is an unconventional gas reservoir located on the Arkansas side of the Arkoma Basin, ranging in thickness from 50 to 325 feet and ranging in depth from 1,500 to 6,500 feet. The Fayetteville Shale is aerially extensive and may be present across numerous counties in central and eastern Arkansas, including the counties of Cleburne, Conway, Faulkner, Independence, Johnson, St. Francis, Prairie, Van Buren, White, and Woodruff
Triple-Star Candidates Among the Kepler Binaries
We present the results of a search through the photometric database of
eclipsing Kepler binaries (Prsa et al. 2011; Slawson et al. 2011) looking for
evidence of hierarchical triple star systems. The presence of a third star
orbiting the binary can be inferred from eclipse timing variations. We apply a
simple algorithm in an automated determination of the eclipse times for all
2157 binaries. The "calculated" eclipse times, based on a constant period
model, are subtracted from those observed. The resulting O-C (observed minus
calculated times) curves are then visually inspected for periodicities in order
to find triple-star candidates. After eliminating false positives due to the
beat frequency between the ~1/2-hour Kepler cadence and the binary period, 39
candidate triple systems were identified. The periodic O-C curves for these
candidates were then fit for contributions from both the classical Roemer delay
and so-called "physical" delay, in an attempt to extract a number of the system
parameters of the triple. We discuss the limitations of the information that
can be inferred from these O-C curves without further supplemental input, e.g.,
ground-based spectroscopy. Based on the limited range of orbital periods for
the triple star systems to which this search is sensitive, we can extrapolate
to estimate that at least 20% of all close binaries have tertiary companions.Comment: 19 pages, 13 figures, 3 tables; ApJ, 2013, 768, 33; corrected Fig. 7,
updated references, minor fixes to tex
Survey of the Labor Market for New Ph.D. Hires in Economics 2005-2006
This year, the survey questionnaire was sent to 372 organizations. Questionnaires were returned by 150 (40.3 percent) for a response rate that was lower than the 2004-05-survey response rate of 49.1 percent. Of this yearâs responses, 102 (68.0 percent) were from those who responded to last yearâs survey; 48 (32.0 percent) came from new respondents. Among the academic institutions responding, the distribution of highest degrees offered was as follows: Ph.D.â32.0 percent; Masterâ14.7 percent; Bachelorâ39.3 percent. The remaining 14.0 percent did not indicate their highest degree offered. One of the respondents was a non-academic organization. The responses are reported for all respondents (including the non-academic institution and schools that did not report âhighest degree offeredâ), and separately for Ph.D. degree-granting institutions and for schools whose highest degree offered is the Bachelor or Master degree. Data for institutions in the National Research Councilâs Research Doctorate Report, 1995, are reported as a subset of Ph.D. degree-granting schools. They are referred to as the Top 30
Survey of the Labor Market for New Ph.D. Hires in Economics 2004-2005
This year, the survey questionnaire was sent to 371 organizations. Questionnaires were returned by 182 (49.1 percent) for a response rate that was higher than the 2003-04-survey response rate of 48.4 percent. Of this yearâs responses, 120 (65.9 percent) were from among those who responded to last yearâs survey; 62 (34.1 percent) came from new respondents. Among the academic institutions responding, the distribution of highest degrees offered was as follows: Ph.D.â44.5 percent; Masterâ13.2 percent; Bachelorâ33.0 percent. The remaining 9.3 percent did not indicate their highest degree offered. Two of the respondents were non-academic organizations. The responses are reported for all respondents (including the non-academic institutions and schools that did not report âhighest degree offeredâ), and separately for Ph.D. degree-granting institutions and for schools whose highest degree offered is the Bachelor or Master degree. Data for institutions in the National Research Councilâs Research Doctorate Report, 1995, are reported as a subset of Ph.D. degree-granting schools. They are referred to as the Top 30
Survey of the Labor Market for New Ph.D. Hires in Economics 2006-2007
This year, the survey questionnaire was sent to 385 organizations. Questionnaires were returned by 160 (41.6 percent) for a response rate that was higher than the 2005-06-survey response rate of 40.3 percent. Of this yearâs responses, 92 (57.9 percent) were from those who responded to last yearâs survey; 68 (42.1 percent) came from new respondents. Among the academic institutions responding, the distribution of highest degrees offered was as follows: Ph.D.â41.3 percent; Masterâ20.0 percent; Bachelorâ38.8 percent. The responses are reported for all respondents, and separately for Ph.D. degree-granting institutions and for schools whose highest degree offered is the Bachelor or Master degree. Data for institutions in the National Research Councilâs Research Doctorate Report, 1995, are reported as a subset of Ph.D. degree-granting schools. They are referred to as the Top 30
Holocene carbon-cycle dynamics based on CO2 trapped in ice at Taylor Dome, Antarctica
A high-resolution ice-core record of atmospheric CO2 concentration over the Holocene epoch shows that the global carbon cycle has not been in steady state during the past 11,000 years. Analysis of the CO2 concentration and carbon stable-isotope records, using a one-dimensional carbon-cycle model,uggests that changes in terrestrial biomass and sea surface temperature were largely responsible for the observed millennial-scale changes of atmospheric CO2 concentrations
An Empirically Derived Three-Dimensional Laplace Resonance in the Gliese 876 Planetary System
We report constraints on the three-dimensional orbital architecture for all
four planets known to orbit the nearby M dwarf Gliese 876 based solely on
Doppler measurements and demanding long-term orbital stability. Our dataset
incorporates publicly available radial velocities taken with the ELODIE and
CORALIE spectrographs, HARPS, and Keck HIRES as well as previously unpublished
HIRES velocities. We first quantitatively assess the validity of the planets
thought to orbit GJ 876 by computing the Bayes factors for a variety of
different coplanar models using an importance sampling algorithm. We find that
a four-planet model is preferred over a three-planet model. Next, we apply a
Newtonian MCMC algorithm to perform a Bayesian analysis of the planet masses
and orbits using an n-body model in three-dimensional space. Based on the
radial velocities alone, we find that a 99% credible interval provides upper
limits on the mutual inclinations for the three resonant planets
( for the "c" and "b" pair and for
the "b" and "e" pair). Subsequent dynamical integrations of our posterior
sample find that the GJ 876 planets must be roughly coplanar
( and ), suggesting the amount of
planet-planet scattering in the system has been low. We investigate the
distribution of the respective resonant arguments of each planet pair and find
that at least one argument for each planet pair and the Laplace argument
librate. The libration amplitudes in our three-dimensional orbital model
supports the idea of the outer-three planets having undergone significant past
disk migration.Comment: 19 pages, 11 figures, 8 tables. Accepted to MNRAS. Posterior samples
available at https://github.com/benelson/GJ87
Is the incidence of depressive disorders increased following cerebral concussion?
Q: Is the incidence of depressive disorders increased following cerebral concussion? Evidence-based answer: yes, in some populations. Youth and adolescents with self-reported history of concussion had increased risk of depressive disorders (strength of recommendation [SOR]: B, based on a prospective cohort study and a retrospective cohort study). Evidence was inconsistent for college athletes. Athletes with â„ 3 concussions exhibited more depressive disorders, but no association was observed for those with 1 or 2 concussions compared to nonconcussion injuries (SOR: B, based on a cross-sectional study, a small prospective cohort study, and a case-control study). In semiprofessional and professional athletes, evidence was variable and may be sport related. Retired rugby players with a history of concussion showed no increase in depression compared to controls with no concussion history (SOR: B, based on a case-control study). Retired football players with previous concussions displayed increased incidence of depression, especially after â„ 3 concussions (SOR: B, based on a prospective cohort study and a small case-control study). There is a significant risk of bias in these studies because of their reliance on self-reported concussions, differing definitions of depression, and possible unmeasured confounders in the study designs, making a causative relationship between concussion and depression unclear.Jason W. Deck, MD; Thomas Kern, MD; LaMont Cavanagh, MD; Matthew Bartow, DO; Franklin T. Perkins III, MD (Department of Family and Community Medicine, OU-TU School of Community Medicine, University of Oklahoma Health Sciences Center, Tulsa); Toni Hoberecht, MA, MLIS, AHIP; Alyssa Migdalski, MLIS (Schusterman Library, University of Oklahoma-Tulsa
Independent control of polar and azimuthal anchoring
Monte Carlo simulation, experiment and continuum theory are used to examine
the anchoring exhibited by a nematic liquid crystal at a patterned substrate
comprising a periodic array of rectangles that, respectively, promote vertical
and planar alignment. It is shown that the easy axis and effective anchoring
energy promoted by such surfaces can be readily controlled by adjusting the
design of the pattern. The calculations reveal rich behavior: for strong
anchoring, as exhibited by the simulated system, for rectangle ratios
the nematic aligns in the direction of the long edge of the rectangles, the
azimuthal anchoring coefficient changing with pattern shape. In weak anchoring
scenarios, however, including our experimental systems, preferential anchoring
is degenerate between the two rectangle diagonals. Bistability between
diagonally-aligned and edge-aligned arrangement is predicted for intermediate
combinations of anchoring coefficient and system length-scale.Comment: 12 pages, 12 figure
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