9,616 research outputs found
RAM: A Relativistic Adaptive Mesh Refinement Hydrodynamics Code
We have developed a new computer code, RAM, to solve the conservative
equations of special relativistic hydrodynamics (SRHD) using adaptive mesh
refinement (AMR) on parallel computers. We have implemented a
characteristic-wise, finite difference, weighted essentially non-oscillatory
(WENO) scheme using the full characteristic decomposition of the SRHD equations
to achieve fifth-order accuracy in space. For time integration we use the
method of lines with a third-order total variation diminishing (TVD)
Runge-Kutta scheme. We have also implemented fourth and fifth order Runge-Kutta
time integration schemes for comparison. The implementation of AMR and
parallelization is based on the FLASH code. RAM is modular and includes the
capability to easily swap hydrodynamics solvers, reconstruction methods and
physics modules. In addition to WENO we have implemented a finite volume module
with the piecewise parabolic method (PPM) for reconstruction and the modified
Marquina approximate Riemann solver to work with TVD Runge-Kutta time
integration. We examine the difficulty of accurately simulating shear flows in
numerical relativistic hydrodynamics codes. We show that under-resolved
simulations of simple test problems with transverse velocity components produce
incorrect results and demonstrate the ability of RAM to correctly solve these
problems. RAM has been tested in one, two and three dimensions and in
Cartesian, cylindrical and spherical coordinates. We have demonstrated
fifth-order accuracy for WENO in one and two dimensions and performed detailed
comparison with other schemes for which we show significantly lower convergence
rates. Extensive testing is presented demonstrating the ability of RAM to
address challenging open questions in relativistic astrophysics.Comment: ApJS in press, 21 pages including 18 figures (6 color figures
Relationship between depressive symptom severity and emergency department use among low-income, depressed homebound older adults aged 50 years and older
Namkee G. Choi, and C. Nathan Marti are with The University of Texas at Austin, Austin, TX, USA. -- Martha L. Bruce is with the Weill Cornell Medical College, White Plains, NY, USA. -- Mark E. Kunik is with the VA HSRD Houston Center of Excellence, Michael E. DeBakey VA Medical Center, Houston, TX, USA, and Baylor College of Medicine, Houston, TX, USA, and VA South Central Mental Illness Research, Education and Clinical Center, Houston, TX, USA.Background: Previous research found a high prevalence of depression, along with chronic illnesses and disabilities, among older ED patients. This study examined the relationship between depressive symptom severity and the number of ED visits among low-income homebound older adults who participated in a randomized controlled trial of telehealth problem-solving therapy (PST).
Methods: The number of and reasons for ED visits were collected from the study participants (n=121 at baseline) at all assessment points—baseline and 12- and 24-week follow-ups. Depressive symptoms were measured with the 24-item Hamilton Rating Scale for Depression (HAMD). All multivariable analyses examining the relationships between ED visits and depressive symptoms were conducted using zero-inflated Poisson regression models.
Results: Of the participants, 67.7% used the ED at least once and 61% of the visitors made at least one return visit during the approximately 12-month period. Body pain (not from fall injury and not including chest pain) was the most common reason. The ED visit frequency at baseline and at follow-up was significantly positively associated with the HAMD scores at the assessment points. The ED visit frequency at follow-up, controlling for the ED visits at baseline, was also significantly associated with the HAMD score change since baseline.
Conclusions: The ED visit rate was much higher than those reported in other studies. Better education on self-management of chronic conditions, depression screening by primary care physicians and ED, and depression treatment that includes symptom management and problem-solving skills may be important to reduce ED visits among medically ill, low-income homebound adults.
Trial registration
ClinicalTrials.gov Identifier: NCT00903019Psycholog
Relative pleopod length as an indicator of size at sexual maturity in slipper (Scyllarides squammosus) and spiny Hawaiian (Panulirus marginatus) lobsters
Body size at gonadal maturity is described for females of the slipper lobster (Scyllarides squammosus) (Scyllaridae) and the endemic Hawaiian spiny lobster (Panulirus marginatus) (Palinuridae) based on microscopic examination
of histological preparations of ovaries. These data are used to validate several morphological metrics (relative
exopodite length, ovigerous condition) of functional sexual maturity. Relative exopodite length (“pleopod length”) produced consistent estimates of size at maturity when evaluated with a newly derived statistical application for estimating size at the morphometric maturation point (MMP) for the population, identified as the midpoint of a sigmoid
function spanning the estimated boundaries of overlap between the largest immature and smallest adult animals.
Estimates of the MMP were related to matched (same-year) characterizations of sexual maturity based on ovigerous
condition — a more conventional measure of functional maturity previously used to characterize maturity for the two lobster species. Both measures of functional maturity were similar for the respective species and were within 5% and 2% of one another for slipper and spiny lobster,
respectively. The precision observed for two shipboard collection series of pleopod-length data indicated that the
method is reliable and not dependent on specialized expertise. Precision of maturity estimates for S. squammosus with the pleopod-length metric was similar
to that for P. marginatus with any of the other measures (including conventional evidence of ovigerous condition)
and greatly exceeded the precision of estimates for S. squammosus based on ovigerous condition alone. The two
measures of functional maturity averaged within 8% of the estimated size at gonadal maturity for the respective species. Appendage-to-body size proportions, such as the pleopod length metric, hold great promise, particularly for species of slipper lobsters like S. squammosus for which there exist no other reliable conventional morphological measures of sexual maturity. Morphometric proportions
also should be included among the factors evaluated when assessing size at sexual maturity in spiny lobster stocks;
previously, these proportions have been obtained routinely only for brachyuran crabs within the Crustacea
Nursing in Hell: The Experience of Providing Care During and After Hurricane Katrina
Hurricane Katrina, a Category Four hurricane, made landfall on August 29, 2005, along the Gulf Coast of Mississippi and Louisiana. The strength and the extent of winds resulted in the worst destruction and the largest storm surge in the history of the United States. Within hours after the hurricane hit, the earthen levees in New Orleans were breached and 80% of the city became submerged in up to 20 feet of water. Health care workers and patients were stranded in hospitals, where they experienced extreme environmental conditions. The death toll was reported at, 1836 persons, and the damage was estimated at 200 billion dollars. No one in the United States was prepared for a disaster of this magnitude.
The purpose of the study was to describe nurses’ experience of caring for patients in Mississippi and Louisiana during and after Hurricane Katrina. An existential phenomenological research method was used. Face-to-face, digitally recorded interviews were conducted with a purposeful, networking sample of nine Registered Nurses. Transcribed narratives were analyzed by the researcher and members of an interdisciplinary research team using a hermeneutical approach developed by Pollio and applied to nursing research by Thomas. Each interview was examined to identify themes.
The experience of providing care was grounded within the context of caring. The themes that emerged were 1) Fear, 2) Ethical Conflicts, 3) Blurred Boundaries, 4) Isolation/Connection, 5) Powerlessness/Power, and 6) No Hope/Hope. Descriptions of the environment were woven throughout every narrative, and it was described as overwhelming. The nurses in this study experienced terror, chaos, danger, threat, and isolation while providing care to patients. During this ordeal, basic physiological needs were not met. The nurses experienced physical exhaustion and some became patients.
The findings from this study point out the inadequacies of local, state, and national government and hospital administrators related to disaster preparedness. The findings also illuminate areas where nursing education could be improved, policies to protect nurses could be implemented, and areas needed for future research related to emergency preparedness
Hot Settling Accretion Flow onto a Spinning Black Hole
We study the structure and properties of hot MHD accretion onto a Kerr black
hole. In such a system, the hole is magnetically coupled to the inflowing gas
and exerts a torque onto the accretion flow. A hot settling flow can form
around the hole and transport the angular momentum outward, to the outer edge
of the flow. Unlike other hot flows, such as advection- and
convection-dominated flows and inflow-outflow solutions (ADAFs, CDAFs, and
ADIOS), the properties of the hot settling flow are determined by the spin of
the central black hole, but are insensitive to the mass accretion rate.
Therefore, it may be possible to identify rapidly spinning BHs simply from
their broad-band spectra.
Observationally, the hot settling flow around a Kerr hole is somewhat similar
to other hot flows in that they all have hard, power-law spectra and relatively
low luminosities. Thus, most black hole candidates in the low/hard and,
perhaps, intermediate X-ray state may potentially accrete via the hot settling
flow. However, a settling flow will be somewhat more luminous than
ADAFs/CDAFs/ADIOS, will exhibit high variability in X-rays, and may have
relativistic jets. This suggests that galactic microquasars and active galactic
nuclei may be powered by hot settling flows. We identify several galactic X-ray
sources as the best candidates.Comment: 7 pages, 1 figure. Submitted to Ap
Optical and near-infrared observations of the microquasar V4641 Sagittarii during the 1999 September outburst
We present photometric and spectroscopic optical and near-infrared (NIR)
observations (Based on observations collected at the European Southern
Observatory, Chile (ESO ID 63.H-0493 and 64.H-0382)) taken during the outburst
of the microquasar V4641 Sgr = SAX J1819.3-2525 (in'tzand et al., 2000) in
September 1999. We observed an increase in the J-Ks colour between 5 and 8 days
after the outburst, which we interpret as likely evidence for the presence of
dust around the source. We also observed an extraordinarily strong, broad and
variable H_alpha line, with a velocity width of 4560 km/s suggesting the
presence of a high-velocity outflow component. We constrain the distance of the
system between 3 and 8 kpc, locating it further away than previously derived
from radio observations (Hjellming et al., 2000), but consistent with Orosz et
al. (2001). We then discuss the nature of this system, showing that the
companion star is either a B3-A2 main sequence star, or a B3-A2 sub-giant
crossing the Hertzsprung gap. The system is therefore an Intermediate or High
Mass X-ray Binary System (IMXB or HMXB). The distance derived by these
optical/NIR observations implies that the jets observed by Hjellming et al.
(2000) would then exhibit apparent velocities of ~ 10 c. We finally discuss the
possibility of an interaction between the jets and surroundings of the source,
and also of this source being a ``microblazar''.Comment: 7 pages, 6 figures, accepted for publication in MNRA
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