708 research outputs found
Alien Registration- Mallen, Agnes M. (Portland, Cumberland County)
https://digitalmaine.com/alien_docs/21914/thumbnail.jp
Alien Registration- Mallen, Agnes M. (Portland, Cumberland County)
https://digitalmaine.com/alien_docs/21914/thumbnail.jp
The EXPLORE Project I: A Deep Search for Transiting Extrasolar Planets
(Abridged) We discuss the design considerations of the EXPLORE (EXtra-solar
PLanet Occultation REsearch) project, a series of transiting planet searches
using 4-m-class telescopes to continuously monitor a single field of stars in
the Galactic Plane in each ~2 week observing campaign. We discuss the general
factors which determine the efficiency and the number of planets found by a
transit search, including time sampling strategy and field selection. The
primary goal is to select the most promising planet candidates for radial
velocity follow-up observations. We show that with very high photometric
precision light curves that have frequent time sampling and at least two
detected transits, it is possible to uniquely solve for the main parameters of
the eclipsing system (including planet radius) based on several important
assumptions about the central star. Together with a measured spectral type for
the star, this unique solution for orbital parameters provides a powerful
method for ruling out most contaminants to transiting planet candidates. For
the EXPLORE project, radial velocity follow-up observations for companion mass
determination of the best candidates are done on 8-m-class telescopes within
two or three months of the photometric campaigns. This same-season follow-up is
made possible by the use of efficient pipelines to produce high quality light
curves within weeks of the observations. We conclude by presenting early
results from our first search, EXPLORE I, in which we reached <1% rms
photometric precision (measured over a full night) on ~37,000 stars to I <=
18.2.Comment: accepted by ApJ. Main points unchanged but more thorough discussion
of some issues. 36 pages, including 14 figure
Multifractal nature of ocular aberration dynamics of the human eye
Ocular monochromatic aberrations display dynamic behavior even when the eye is fixating on a stationary stimulus. The fluctuations are commonly characterized in the frequency domain using the power spectrum obtained via the Fourier transform. In this paper we used a wavelet-based multifractal analytical approach to provide a more in depth analysis of the nature of the aberration fluctuations. The aberrations of five subjects were measured at 21 Hz using an open-view Shack-Hartmann sensor. We show that the aberration dynamics are multifractal. The most frequently occurring Hölder exponent for the rms wavefront error, averaged across the five subjects, was 0.31 ± 0.10. This suggests that the time course of the aberration fluctuations is antipersistant. Future applications of multifractal analysis are discussed
What does a primary care annual review for RA include? A national GP survey
Letter to the edito
Applying quantitative bias analysis to estimate the plausible effects of selection bias in a cluster randomised controlled trial: secondary analysis of the Primary care Osteoarthritis Screening Trial (POST).
BACKGROUND: Selection bias is a concern when designing cluster randomised controlled trials (c-RCT). Despite addressing potential issues at the design stage, bias cannot always be eradicated from a trial design. The application of bias analysis presents an important step forward in evaluating whether trial findings are credible. The aim of this paper is to give an example of the technique to quantify potential selection bias in c-RCTs. METHODS: This analysis uses data from the Primary care Osteoarthritis Screening Trial (POST). The primary aim of this trial was to test whether screening for anxiety and depression, and providing appropriate care for patients consulting their GP with osteoarthritis would improve clinical outcomes. Quantitative bias analysis is a seldom-used technique that can quantify types of bias present in studies. Due to lack of information on the selection probability, probabilistic bias analysis with a range of triangular distributions was also used, applied at all three follow-up time points; 3, 6, and 12 months post consultation. A simple bias analysis was also applied to the study. RESULTS: Worse pain outcomes were observed among intervention participants than control participants (crude odds ratio at 3, 6, and 12 months: 1.30 (95% CI 1.01, 1.67), 1.39 (1.07, 1.80), and 1.17 (95% CI 0.90, 1.53), respectively). Probabilistic bias analysis suggested that the observed effect became statistically non-significant if the selection probability ratio was between 1.2 and 1.4. Selection probability ratios of > 1.8 were needed to mask a statistically significant benefit of the intervention. CONCLUSIONS: The use of probabilistic bias analysis in this c-RCT suggested that worse outcomes observed in the intervention arm could plausibly be attributed to selection bias. A very large degree of selection of bias was needed to mask a beneficial effect of intervention making this interpretation less plausible
The EXPLORE Project: A Deep Search for Transiting Extra-Solar Planets
Searching for transits provides a very promising technique for finding
close-in extra-solar planets. Transiting planets present the advantage of
allowing one to determine physical properties such as mass and radius
unambiguously. The EXPLORE (EXtra-solar PLanet Occultation REsearch) project is
a transit search project carried out using wide-field CCD imaging cameras on
4-m class telescopes, and 8-10m class telescopes for radial velocity
verification of the photometric candidates. We describe some of the
considerations that go into the design of the EXPLORE transit search to
maximize the discovery rate and minimize contaminating objects that mimic
transiting planets. We show that high precision photometry (2 to 10 millimag)
and high time sampling (few minutes) are crucial for sifting out contaminating
signatures, such as grazing binaries. We have completed two searches using the
8k MOSAIC camera at the CTIO4m and the CFH12k camera at CFHT, with runs
covering 11 and 16 nights, respectively. We obtained preliminary light curves
for approximately 47,000 stars with better than ~1% photometric precision. A
number of light curves with flat-bottomed eclipses consistent with being
produced by transiting planets has been discovered. Preliminary results from
follow-up spectroscopic observations using the VLT UVES spectrograph and the
Keck HIRES spectrograph obtained for a number of the candidates are presented.
Data from four of these can be interpreted consistently as possible planet
candidates, although further data are still required for definitive
confirmations.Comment: 11 pages. To appear in the Proceedings of the SPIE conference:
Astronomical Telescopes and Instrumentatio
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