756 research outputs found
Introductory Notes to Algebraic Statistics
These are the notes of a short course on algebraic
statistics, a new discipline across the fields of statistical modeling
and computational commutativa algebra. The basics of the
theory are provided together with brief reference to applications to
design of experiments, to exponential and graphical models, and
to computational biology
A Stochastic Model for the Luminosity Fluctuations of Accreting Black Holes
In this work we have developed a new stochastic model for the fluctuations in
lightcurves of accreting black holes. The model is based on a linear
combination of stochastic processes and is also the solution to the linear
diffusion equation perturbed by a spatially correlated noise field. This allows
flexible modeling of the power spectral density (PSD), and we derive the
likelihood function for the process, enabling one to estimate the parameters of
the process, including break frequencies in the PSD. Our statistical technique
is computationally efficient, unbiased by aliasing and red noise leak, and
fully accounts for irregular sampling and measurement errors. We show that our
stochastic model provides a good approximation to the X-ray lightcurves of
galactic black holes, and the optical and X-ray lightcurves of AGN. We use the
estimated time scales of our stochastic model to recover the correlation
between characteristic time scale of the high frequency X-ray fluctuations and
black hole mass for AGN, including two new `detections' of the time scale for
Fairall 9 and NGC 5548. We find a tight anti-correlation between the black hole
mass and the amplitude of the driving noise field, which is proportional to the
amplitude of the high frequency X-ray PSD, and we estimate that this parameter
gives black hole mass estimates to within ~ 0.2 dex precision, potentially the
most accurate method for AGN yet. We also find evidence that ~ 13% of AGN
optical PSDs fall off flatter than 1 / f^2, and, similar to previous work, find
that the optical fluctuations are more suppressed on short time scales compared
to the X-rays, but are larger on long time scales, suggesting the optical
fluctuations are not solely due to reprocessing of X-rays.Comment: 22 pages, 10 figures, resubmitted to match accepted version, in press
at Ap
Refined system parameters and TTV study of transiting exoplanetary system HAT-P-20
This work is supported by National Natural Science Foundation of China through grants No. U1531121, No. 10873031 and No. 11473066.We report new photometric observations of the transiting exoplanetary system HAT-P-20, obtained using CCD cameras at Yunnan Observatories and Ho Koon Nature Education cum Astronomical Centre, China, from 2010 to 2013, and Observatori Ca l'Ou, Sant Marti Sesgueioles, Spain, from 2013 to 2015. The observed data are corrected for systematic errors according to the coarse de-correlation and SYSREM algorithms, so as to enhance the signal of the transit events. In order to consistently model the star spots and transits of this exoplanetary system, we develop a highly efficient tool STMT based on the analytic models of Mandel & Agol and Montalto et al. The physical parameters of HAT-P-20 are refined by homogeneously analyzing our new data, the radial velocity data, and the earlier photometric data in the literature with the Markov chain Monte Carlo technique. New radii and masses of both host star and planet are larger than those in the discovery paper due to the discrepancy of the radius among K-dwarfs between predicted values by standard stellar models and empirical calibration from observations. Through the analysis of all available mid-transit times calculated with the normal model and spotted model, we conclude that the periodic transit timing variations in these transit events revealed by employing the normal model are probably induced by spot crossing events. From the analysis of the distribution of occulted spots by HAT-P-20b, we constrain the misaligned architecture between the planetary orbit and the spin of the host star.Publisher PDFPeer reviewe
Non-B DB: a database of predicted non-B DNA-forming motifs in mammalian genomes
Although the capability of DNA to form a variety of non-canonical (non-B) structures has long been recognized, the overall significance of these alternate conformations in biology has only recently become accepted en masse. In order to provide access to genome-wide locations of these classes of predicted structures, we have developed non-B DB, a database integrating annotations and analysis of non-B DNA-forming sequence motifs. The database provides the most complete list of alternative DNA structure predictions available, including Z-DNA motifs, quadruplex-forming motifs, inverted repeats, mirror repeats and direct repeats and their associated subsets of cruciforms, triplex and slipped structures, respectively. The database also contains motifs predicted to form static DNA bends, short tandem repeats and homo(purine•pyrimidine) tracts that have been associated with disease. The database has been built using the latest releases of the human, chimp, dog, macaque and mouse genomes, so that the results can be compared directly with other data sources. In order to make the data interpretable in a genomic context, features such as genes, single-nucleotide polymorphisms and repetitive elements (SINE, LINE, etc.) have also been incorporated. The database is accessed through query pages that produce results with links to the UCSC browser and a GBrowse-based genomic viewer. It is freely accessible at http://nonb.abcc.ncifcrf.gov
Potential Benefits of Exercise on Blood Pressure and Vascular Function
Physical activity seems to enhance cardiovascular fitness during the course of the lifecycle, improve blood pressure, and is associated with decreased prevalence of hypertension and coronary heart disease. It may also delay or prevent age-related increases in arterial stiffness. It is unclear if specific exercise types (aerobic, resistance, or combination) have a better effect on blood pressure and vascular function. This review was written based on previous original articles, systematic reviews, and meta-analyses indexed on PubMed from years 1975 to 2012 to identify studies on different types of exercise and the associations or effects on blood pressure and vascular function. In summary, aerobic exercise (30 to 40 minutes of training at 60% to 85% of predicted maximal heart rate, most days of the week) appears to significantly improve blood pressure and reduce augmentation index. Resistance training (three to four sets of eight to 12 repetitions at 10 repetition maximum, 3 days a week) appears to significantly improve blood pressure, whereas combination exercise training (15 minutes of aerobic and 15 minutes of resistance, 5 days a week) is beneficial to vascular function, but at a lower scale. Aerobic exercise seems to better benefit blood pressure and vascular function
Breakage of a thoracic epidural catheter during its removal -A case report-
The breakage of an epidural catheter is a rare complication during the removal of a thoracic epidural catheter. There are many causes to breakage of an epidural catheter, such as the characteristics of the catheter itself, patient's factors (anatomy, position during insertion and removal of the catheter, and the BMI), and the difficulty of the procedure. Surgical removal is considered if there is a possibility that the retained catheter might cause neurological problems. We experienced a breakage of an epidural catheter during its removal, which led to surgical intervention. To prevent the catheter breakage during its removal, the catheter should be withdrawn without excessive tension. In addition, an understanding of the patient's anatomy is essential
Active Galaxies in the UV
In this article we present different aspects of AGN studies demonstrating the
importance of the UV spectral range. Most important diagnostic lines for
studying the general physical conditions as well as the metalicities in the
central broad line region in AGN are emitted in the UV. The UV/FUV continuum in
AGN excites not only the emission lines in the immediate surrounding but it is
responsible for the ionization of the intergalactic medium in the early stages
of the universe. Variability studies of the emission line profiles of AGN in
the UV give us information on the structure and kinematics of the immediate
surrounding of the central supermassive black hole as well as on its mass
itself.Comment: 29 pages, 13 figures, Ap&SS in pres
The Lick AGN Monitoring Project: Alternate Routes to a Broad-line Region Radius
It is now possible to estimate black hole masses across cosmic time, using
broad emission lines in active galaxies. This technique informs our views of
how galaxies and their central black holes coevolve. Unfortunately, there are
many outstanding uncertainties associated with these "virial" mass estimates.
One of these comes from using the accretion luminosity to infer a size for the
broad-line region. Incorporating the new sample of low-luminosity active
galaxies from our recent monitoring campaign at Lick Observatory, we
recalibrate the radius-luminosity relation with tracers of the accretion
luminosity other than the optical continuum. We find that the radius of the
broad-line region scales as the square root of the X-ray and Hbeta
luminosities, in agreement with recent optical studies. On the other hand, the
scaling appears to be marginally steeper with narrow-line luminosities. This is
consistent with a previously observed decrease in the ratio of narrow-line to
X-ray luminosity with increasing total luminosity. The radius of the broad-line
region correlates most tightly with Hbeta luminosity, while the X-ray and
narrow-line relations both have comparable scatter of a factor of two. These
correlations provide useful alternative virial BH masses in objects with no
detectable optical/UV continuum emission, such as high-redshift galaxies with
broad emission lines, radio-loud objects, or local active galaxies with
galaxy-dominated continua.Comment: 8 pages, 1 figure, accepted for publication in Ap
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