8,662 research outputs found
Determination of Dark Matter Halo Mass from Dynamics of Satellite Galaxies
We show that the mass of a dark matter halo can be inferred from the
dynamical status of its satellite galaxies. Using 9 dark-matter simulations of
halos like the Milky Way (MW), we find that the present-day substructures in
each halo follow a characteristic distribution in the phase space of orbital
binding energy and angular momentum, and that this distribution is similar from
halo to halo but has an intrinsic dependence on the halo formation history. We
construct this distribution directly from the simulations for a specific halo
and extend the result to halos of similar formation history but different
masses by scaling. The mass of an observed halo can then be estimated by
maximizing the likelihood in comparing the measured kinematic parameters of its
satellite galaxies with these distributions. We test the validity and accuracy
of this method with mock samples taken from the simulations. Using the
positions, radial velocities, and proper motions of 9 tracers and assuming
observational uncertainties comparable to those of MW satellite galaxies, we
find that the halo mass can be recovered to within 40%. The accuracy can
be improved to within 25% if 30 tracers are used. However, the dependence
of the phase-space distribution on the halo formation history sets a minimum
uncertainty of 20% that cannot be reduced by using more tracers. We
believe that this minimum uncertainty also applies to any mass determination
for a halo when the phase space information of other kinematic tracers is used.Comment: Accepted for publication in ApJ, 18 pages, 13 figure
PAM-HC: A Bayesian Nonparametric Construction of Hybrid Control for Randomized Clinical Trials Using External Data
It is highly desirable to borrow information from external data to augment a
control arm in a randomized clinical trial, especially in settings where the
sample size for the control arm is limited. However, a main challenge in
borrowing information from external data is to accommodate potential
heterogeneous subpopulations across the external and trial data. We apply a
Bayesian nonparametric model called Plaid Atoms Model (PAM) to identify
overlapping and unique subpopulations across datasets, with which we restrict
the information borrowing to the common subpopulations. This forms a hybrid
control (HC) that leads to more precise estimation of treatment effects
Simulation studies demonstrate the robustness of the new method, and an
application to an Atopic Dermatitis dataset shows improved treatment effect
estimation
Flexural Behavior of RC Beams Under Combined Effects of AcidāSalt Mist and Carbon Dioxide
The coupling effects of hydrochloric acid mist, carbon dioxide, and salt mist rich in Clā and SO42ā on the degradation of reinforcement concrete (RC) beams were researched with the simulation of colliery ground environment (CGE) and experimental investigation. The results indicated that carbonation of concrete and corrosion of rebar increased slowly as the maximum width of crack became \u3c0.5 mm. Meanwhile, the flexural carrying capacity of the deteriorated beam decreased slightly, while the concrete strength got a small increase first and a large decrease of more than 20% quickly. As the width of crack exceeded 0.5 mm, each target changed rapidly except the carbonation depth. Because of the interaction of deteriorated concrete and corroded rebar, the crack width, and flexural behavior of the beams have discrete correlation with the corrosion of rebar. The failure mode of beams changed from the crushing of compression concrete to the yielding of rebar
Gene Copy Number Analysis for Family Data Using Semiparametric Copula Model
Gene copy number changes are common characteristics of many genetic disorders. A new technology, array comparative genomic hybridization (a-CGH), is widely used today to screen for gains and losses in cancers and other genetic diseases with high resolution at the genome level or for specific chromosomal region. Statistical methods for analyzing such a-CGH data have been developed. However, most of the existing methods are for unrelated individual data and the results from them provide explanation for horizontal variations in copy number changes. It is potentially meaningful to develop a statistical method that will allow for the analysis of family data to investigate the vertical kinship effects as well. Here we consider a semiparametric model based on clustering method in which the marginal distributions are estimated nonparametrically, and the familial dependence structure is modeled by copula. The model is illustrated and evaluated using simulated data. Our results show that the proposed method is more robust than the commonly used multivariate normal model. Finally, we demonstrated the utility of our method using a real dataset
The experience of long-stay patients in a forensic psychiatric hospital in China: a qualitative study
open access articleBackground
Long stay in forensic psychiatric hospitals is common in patients who are defined as ānot criminally responsible on account of mental disorderā. However, little is known about how these patients experience and perceive the long stay within these settings. The aim of this study is to explore the perception and needs of long-stay patients in forensic psychiatric hospitals in China.
Methods
In-depth semi-structured interviews were conducted with 21 participants who had lived in the forensic psychiatry hospital for more than 8āyears. We used thematic analysis strategies to analyse the qualitative data.
Results
Participantsā perceptions clustered seven themes: hopelessness, loneliness, worthlessness, low mood, sleep disturbances, lack of freedom, and lack of mental health intervention.
Conclusions
The views and opinions expressed by long-stay patients showed that psychological distress is prevailing in forensic psychiatric hospitals. Adequate and effective care and mental health interventions are recommended to be tailored for their special needs
Poynting vector, energy density and energy velocity in anomalous dispersion medium
The Poynting vector, energy density and energy velocity of light pulses
propagating in anomalous dispersion medium (used in WKD-like experiments) are
calculated. Results show that a negative energy density in the medium
propagates along opposite of incident direction with such a velocity similar to
the negative group velocity while the direction of the Poynting vector is
positive. In other words, one might say that a positive energy density in the
medium would propagate along the positive direction with a speed having
approximately the absolute valueof the group velocity. We further point out
that neither energy velocity nor group velocity is a good concept to describe
the propagation process of light pulse inside the medium in WKD experiment
owing to the strong accumulation and dissipation effects.Comment: 6 page
- ā¦