1,772 research outputs found
Quantum initial condition sampling for linearized density matrix dynamics: Vibrational pure dephasing of iodine in krypton matrices
This paper reviews the linearized path integral approach for computing time
dependent properties of systems that can be approximated using a mixed
quantum-classical description. This approach is applied to studying vibrational
pure dephasing of ground state molecular iodine in a rare gas matrix. The
Feynman-Kleinert optimized harmonic approximation for the full system density
operator is used to sample initial conditions for the bath degrees of freedom.
This extremely efficient approach is compared with alternative initial
condition sampling techniques at low temperatures where classical initial
condition sampling yields dephasing rates that are nearly an order of magnitude
too slow compared with quantum initial condition sampling and experimental
results.Comment: 20 pages and 8 figure
The Role of Magnetic Field Dissipation in the Black Hole Candidate Sgr A*
The compact, nonthermal radio source Sgr A* at the Galactic Center appears to
be coincident with a 2.6 million solar mass point-like object. Its energy
source may be the release of gravitational energy as gas from the interstellar
medium descends into its potential well. Simple attempts at calculating the
spectrum and flux based on this picture have come close to the observations,
yet have had difficulty in accounting for the low efficiency in this source.
There now appear to be two reasons for this low conversion rate: (1) the plasma
separates into two temperatures, with the protons attaining a significantly
higher temperature than that of the radiating electrons, and (2) the magnetic
field, B, is sub-equipartition, which reduces the magnetic bremsstrahlung
emissivity, and therefore the overall power of Sgr A*. We investigate the
latter with improvement over what has been attempted before: rather than
calculating B based on a presumed model, we instead infer its distribution with
radius empirically with the requirement that the resulting spectrum matches the
observations. Our ansatz for B(r) is motivated in part by earlier calculations
of the expected magnetic dissipation rate due to reconnection in a compressed
flow. We find reasonable agreement with the observed spectrum of Sgr A* as long
as its distribution consists of 3 primary components: an outer equipartition
field, a roughly constant field at intermediate radii (~1000 Schwarzschild
radii), and an inner dynamo (more or less within the last stable orbit for a
non-rotating black hole) which increases B to about 100 Gauss. The latter
component accounts for the observed sub-millimiter hump in this source.Comment: 33 pages including 2 figures; submitted to Ap
Utilisation of One Health Approaches in the Surveillance and Mitigation of Risks of Animal Derived Infections in Tanzania: Attitudinal Profiles of Human and Animal Health Experts
Low angular momentum flow model of Sgr A* activity
Sgr A* is the closest massive black hole and can be observed with the highest
angular resolution. Nevertheless, our current understanding of the accretion
process in this source is very poor. The inflow is almost certainly of low
radiative efficiency and it is accompanied by a strong outflow and the flow is
strongly variable but the details of the dynamics are unknown. Even the amount
of angular momentum in the flow is an open question. Here we argue that low
angular momentum scenario is better suited to explain the flow variability. We
present a new hybrid model which describes such a flow and consists of an outer
spherically symmetric Bondi flow and an inner axially symmetric flow described
through MHD simulations. The assumed angular momentum of the matter is low,
i.e. the corresponding circularization radius in the equatorial plane of the
flow is just above the innermost stable circular orbit in pseudo-Newtonian
potential. We compare the radiation spectrum from such a flow to the broad band
observational data for Sgr A*.Comment: Proceedings of the AHAR 2008 Conference: The Universe under the
Microscope; Astrophysics at High Angular Resolution, Bad Honef
Neutralino dark matter vs galaxy formation
Neutralino dark matter may be incompatible with current cold dark matter
models with cuspy dark halos, because excessive synchrotron radiation may
originate from neutralino annihilations close to the black hole at the galactic
center.Comment: 6 pages, 3 figures, talk given at "Sources and detection of dark
matter in the Universe", Marina del Rey, CA, February 23-25, 200
Stochastic reconstruction of sandstones
A simulated annealing algorithm is employed to generate a stochastic model
for a Berea and a Fontainebleau sandstone with prescribed two-point probability
function, lineal path function, and ``pore size'' distribution function,
respectively. We find that the temperature decrease of the annealing has to be
rather quick to yield isotropic and percolating configurations. A comparison of
simple morphological quantities indicates good agreement between the
reconstructions and the original sandstones. Also, the mean survival time of a
random walker in the pore space is reproduced with good accuracy. However, a
more detailed investigation by means of local porosity theory shows that there
may be significant differences of the geometrical connectivity between the
reconstructed and the experimental samples.Comment: 12 pages, 5 figure
Massive transfusion protocol optimization
Hemorrhage is the leading cause of mortality in trauma, accounting for up to 80% of intraoperative trauma mortalities and nearly half of the deaths that occur within 24 hours of traumatic injury. The timely and appropriate administration of blood products in hemorrhage control is paramount to adequate resuscitation efforts. Given the need for rapid delivery of products, appropriate product infusion ratios, and adjunctive therapies for control of hemorrhage and anticoagulation reversal, it is essential that facilities have and maintain a Massive Transfusion Protocol. The goal of this project was to create a Massive Transfusion Protocol for our facility that incorporated current literature, involved buy-in from all involved departments, and optimized blood product ordering and delivery in the emergency setting. To this end, a literature search was performed, and a protocol was drafted which focused on single entry point ordering, and automated product delivery until massive transfusion was halted. Elective orders were also incorporated for easy requesting of coagulation reversal agents and pro-clotting factors. The final draft of the protocol was submitted to the hospital transfusion committee for approval and then incorporated into an EHR order set. Staff training was performed in all involved departments before deployment. Outcome measurement is ongoing but it is anticipated that this updated protocol will decrease time between disposition of major bleed and arrival of blood products at the bedside. It is also expected that this protocol will decrease the amount of crystalloid products given to major bleeding patients by increasing efficiency of blood product delivery
Psychosocial Stress and Prostate Cancer: A Theoretical Model
African-American men are more likely to develop and die from prostate cancer than are European-American men; yet, factors responsible for the racial disparity in incidence and mortality have not been elucidated. Socioeconomic disadvantage can lead to psychosocial stress and may be linked to negative lifestyle behaviors. Regardless of socioeconomic position, African-American men routinely experience racism-induced stress. We propose a theoretical framework for an association between psychosocial stress and prostate cancer. With the context of history and culture, we further propose that psychosocial stress may partially explain the variable incidence of prostate cancer between these diverse groups. Psychosocial stress may negatively impact teh immune system leaving the individual susceptible to malingnancies. Behavioral responses to psychosocial stress are amenable to change. If psychosocial stress is found to negatively impact prostate cancer risk, interventions may be designed to modify reactions to environmental demands
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