6,838 research outputs found
Some Aspects of Measurement Error in Linear Regression of Astronomical Data
I describe a Bayesian method to account for measurement errors in linear
regression of astronomical data. The method allows for heteroscedastic and
possibly correlated measurement errors, and intrinsic scatter in the regression
relationship. The method is based on deriving a likelihood function for the
measured data, and I focus on the case when the intrinsic distribution of the
independent variables can be approximated using a mixture of Gaussians. I
generalize the method to incorporate multiple independent variables,
non-detections, and selection effects (e.g., Malmquist bias). A Gibbs sampler
is described for simulating random draws from the probability distribution of
the parameters, given the observed data. I use simulation to compare the method
with other common estimators. The simulations illustrate that the Gaussian
mixture model outperforms other common estimators and can effectively give
constraints on the regression parameters, even when the measurement errors
dominate the observed scatter, source detection fraction is low, or the
intrinsic distribution of the independent variables is not a mixture of
Gaussians. I conclude by using this method to fit the X-ray spectral slope as a
function of Eddington ratio using a sample of 39 z < 0.8 radio-quiet quasars. I
confirm the correlation seen by other authors between the radio-quiet quasar
X-ray spectral slope and the Eddington ratio, where the X-ray spectral slope
softens as the Eddington ratio increases.Comment: 39 pages, 11 figures, 1 table, accepted by ApJ. IDL routines
(linmix_err.pro) for performing the Markov Chain Monte Carlo are available at
the IDL astronomy user's library, http://idlastro.gsfc.nasa.gov/homepage.htm
Parametric test of a zirconium (4) oxide-polyacrylic acid dual layer hyperfiltration membrane with spacecraft washwater
Performance data consisting of solute rejections and product flux were measured, as dependent on the operation parameters. These parameters and ranges were pressure (500,000 n/m2 to 700,000 n/m2), temperature (74 C to 95 C), velocity (1.6 M/sec to 10 M/sec), and concentration (up to 14x). Tests were carried out on analog washwater. Data presented include rejections of organic materials, ammonia, urea, and an assortment of ions. The membrane used was deposited in situ on a porcelain ceramic substrate
Understanding Differences in Medical Versus Surgical Patients Alerted by the Modified Early Warning Score (MEWS) at Jefferson Hospital
An Early Warning Score (EWS) is a risk-management tool to identify patients experiencing clinical deterioration early, therefore allowing timely treatment to occur. Although EWS scores are recommended for all in-patients, more data is available for patients under general medical services compared to surgical services. This study aims to understand differences between medical versus surgical in-patients who receive a red alert from the Modified Early Warning Score (MEWS) at Jefferson hospital. Patients who received a red MEWS alert during admission and discharged between June 2017 to March 2018 (N=812) were categorized as medical or surgical patients. Patient characteristics were compared using an independent samples t-test (age, alert count) or chi-square test (sex, race, admission source, insurance). Patient outcomes were compared using a binary logistic regression (in-hospital mortality, RRT, sepsis diagnosis, ICU transfer, intubation, discharge to hospice) or a Cox regression model (length of stay), controlling for age, sex, and race. Compared to medical patients, surgical patients were younger by 2.7 years (p=0.026) and more likely to have a Commercial and/or Medicare category of insurance (OR=1.568, p=0.005). Surgical patients were more likely to have ICU transfer (OR=1.487, p=0.013) and intubation post-alert (OR=2.470, p=0.006), while less likely to be discharged early (HR=0.675,
The Cross-Wavelet Transform and Analysis of Quasiperiodic Behavior in the Pearson-Readhead VLBI Survey Sources
We introduce an algorithm for applying a cross-wavelet transform to analysis
of quasiperiodic variations in a time-series, and introduce significance tests
for the technique. We apply a continuous wavelet transform and the
cross-wavelet algorithm to the Pearson-Readhead VLBI survey sources using data
obtained from the University of Michigan 26-m parabloid at observing
frequencies of 14.5, 8.0, and 4.8 GHz. Thirty of the sixty-two sources were
chosen to have sufficient data for analysis, having at least 100 data points
for a given time-series. Of these thirty sources, a little more than half
exhibited evidence for quasiperiodic behavior in at least one observing
frequency, with a mean characteristic period of 2.4 yr and standard deviation
of 1.3 yr. We find that out of the thirty sources, there were about four time
scales for every ten time series, and about half of those sources showing
quasiperiodic behavior repeated the behavior in at least one other observing
frequency.Comment: Revised version, accepted by ApJ. 17 pages, 13 figures, color figures
included as gifs, seperate from the text. The addition of statistical
significance tests has resulted in modifying the technique and results, but
the broad conclusion remain the same. A high resolution version may be found
at http://www.astro.lsa.umich.edu/obs/radiotel/prcwdata.htm
Structure and expression of two nuclear receptor genes in marsupials: insights into the evolution of the antisense overlap between the Ī±-thyroid hormone receptor and Rev-erbĪ±
<p>Abstract</p> <p>Background</p> <p>Alternative processing of Ī±-thyroid hormone receptor (TRĪ±, NR1A1) mRNAs gives rise to two functionally antagonistic nuclear receptors: TRĪ±1, the Ī±-type receptor, and TRĪ±2, a non-hormone binding variant that is found only in mammals. TRĪ±2 shares an unusual antisense coding overlap with mRNA for Rev-erbĪ± (NR1D1), another nuclear receptor protein. In this study we examine the structure and expression of these genes in the gray short-tailed opossum, <it>Monodelphis domestica</it>, in comparison with that of eutherian mammals and three other marsupial species, <it>Didelphis virginiana, Potorous tridactylus </it>and <it>Macropus eugenii</it>, in order to understand the evolution and regulatory role of this antisense overlap.</p> <p>Results</p> <p>The sequence, expression and genomic organization of mRNAs encoding TRĪ±1 and Rev-erbĪ± are very similar in the opossum and eutherian mammals. However, the sequence corresponding to the TRĪ±2 coding region appears truncated by almost 100 amino acids. While expression of TRĪ±1 and Rev-erbĪ± was readily detected in all tissues of <it>M. domestica </it>ages 0 days to 18 weeks, TRĪ±2 mRNA was not detected in any tissue or stage examined. These results contrast with the widespread and abundant expression of TRĪ±2 in rodents and other eutherian mammals. To examine requirements for alternative splicing of TRĪ± mRNAs, a series of chimeric minigenes was constructed. Results show that the opossum TRĪ±2-specific 5' splice site sequence is fully competent for splicing but the sequence homologous to the TRĪ±2 3' splice site is not, even though the marsupial sequences are remarkably similar to core splice site elements in rat.</p> <p>Conclusions</p> <p>Our results strongly suggest that the variant nuclear receptor isoform, TRĪ±2, is not expressed in marsupials and that the antisense overlap between TRĪ± and Rev-erbĪ± thus is unique to eutherian mammals. Further investigation of the TRĪ± and Rev-erbĪ± genes in marsupial and eutherian species promises to yield additional insight into the physiological function of TRĪ±2 and the role of the associated antisense overlap with Rev-erbĪ± in regulating expression of these genes.</p
Three-Dimensional Spin-Orbit Coupling in a Trap
We investigate the properties of an atom under the influence of a synthetic
three-dimensional spin-orbit coupling (Weyl coupling) in the presence of a
harmonic trap. The conservation of total angular momentum provides a
numerically efficient scheme for finding the spectrum and eigenfunctions of the
system. We show that at large spin-orbit coupling the system undergoes
dimensional reduction from three to one dimension at low energies, and the
spectrum is approximately Landau level-like. At high energies, the spectrum is
approximately given by the three-dimensional isotropic harmonic oscillator. We
explore the properties of the ground state in both position and momentum space.
We find the ground state has spin textures with oscillations set by the
spin-orbit length scale
Dust SEDs in the era of Herschel and Planck: a Hierarchical Bayesian fitting technique
We present a hierarchical Bayesian method for fitting infrared spectral
energy distributions (SEDs) of dust emission to observed fluxes. Under the
standard assumption of optically thin single temperature (T) sources the dust
SED as represented by a power--law modified black body is subject to a strong
degeneracy between T and the spectral index beta. The traditional
non-hierarchical approaches, typically based on chi-square minimization, are
severely limited by this degeneracy, as it produces an artificial
anti-correlation between T and beta even with modest levels of observational
noise. The hierarchical Bayesian method rigorously and self-consistently treats
measurement uncertainties, including calibration and noise, resulting in more
precise SED fits. As a result, the Bayesian fits do not produce any spurious
anti-correlations between the SED parameters due to measurement uncertainty. We
demonstrate that the Bayesian method is substantially more accurate than the
chi-square fit in recovering the SED parameters, as well as the correlations
between them. As an illustration, we apply our method to Herschel and sub
millimeter ground-based observations of the star-forming Bok globule CB244.
This source is a small, nearby molecular cloud containing a single low-mass
protostar and a starless core. We find that T and beta are weakly positively
correlated -- in contradiction with the chi-square fits, which indicate a
T-beta anti-correlation from the same data-set. Additionally, in comparison to
the chi-square fits the Bayesian SED parameter estimates exhibit a reduced
range in values.Comment: 20 pages, 9 figures, ApJ format, revised version matches ApJ-accepted
versio
Force of Beauty or Object of Desire? The Priming Effects of Makeup Video Advertisements on Self-Objectification in College Women
Women are too often valued for their beauty and have shifted their focus from character to body improvement (Brumberg, 1998). Objectification theory (Frederickson & Roberts, 1997) posits that sexual objectification socializes females to evaluate themselves based on looks. Self-objectification is the attempt to control this external perception by monitoring oneās physical appearance. Women are more likely to think āHow do I look?ā than āWhat am I capable of?ā
The priming effects of positive and negative body-focused makeup advertisements on college-aged womenās level of self-objectification were examined in two separate studies. In study one, 87 participants viewing positive vs. negative advertisements reported more traits and abilities; this was especially true for high self-objectifiers. Participants viewing positive advertisements reported more positive emotions, suggesting the salutary role that positive messaging may play. Results were replicated in study two, with 172 participants who viewed positive vs. negative advertisements reporting significantly fewer body shape statements, more trait and abilities, as well as more physical competence statements. In addition, individuals who viewed advertisements with non-objectifying content responded with a significantly greater number of positively valenced statements and significantly fewer negative statements about themselves in comparison to women who viewed objectifying advertisements. These results suggest that marketers should eschew advertising that sexually objectifies women and promotes unattainable beauty goals. Future research should evaluate cumulative and long-term effects of advertisement and examine whether exposure that leads to lower levels of objectification also minimizes negative consequences associated with objectifying media influences (e.g., body shame, depression, eating disorder)
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Scale Effects between Body Size and Limb Design in Quadrupedal Mammals
Recently the metabolic cost of swinging the limbs has been found to be much greater than previously thought, raising the possibility that limb rotational inertia influences the energetics of locomotion. Larger mammals have a lower mass-specific cost of transport than smaller mammals. The scaling of the mass-specific cost of transport is partly explained by decreasing stride frequency with increasing body size; however, it is unknown if limb rotational inertia also influences the mass-specific cost of transport. Limb length and inertial properties ā limb mass, center of mass (COM) position, moment of inertia, radius of gyration, and natural frequency ā were measured in 44 species of terrestrial mammals, spanning eight taxonomic orders. Limb length increases disproportionately with body mass via positive allometry (length ā body mass0.40); the positive allometry of limb length may help explain the scaling of the metabolic cost of transport. When scaled against body mass, forelimb inertial properties, apart from mass, scale with positive allometry. Fore- and hindlimb mass scale according to geometric similarity (limb mass ā body mass1.0), as do the remaining hindlimb inertial properties. The positive allometry of limb length is largely the result of absolute differences in limb inertial properties between mammalian subgroups. Though likely detrimental to locomotor costs in large mammals, scale effects in limb inertial properties appear to be concomitant with scale effects in sensorimotor control and locomotor ability in terrestrial mammals. Across mammals, the forelimb's potential for angular acceleration scales according to geometric similarity, whereas the hindlimb's potential for angular acceleration scales with positive allometry.</p
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