12,378 research outputs found
Quantum Equivalence of Massive Antisymmetric Tensor Field Models in Curved Space
We study the effective actions for massive rank-2 and rank-3 antisymmetric
tensor field models in curved space-time. These models are classically
equivalent to massive vector field and massive scalar field with minimal
coupling to gravity respectively. We prove that effective action for massive
rank-2 antisymmetric tensor field is exactly equal to one for massive vector
field and effective action for massive rank-3 antisymmetric tensor field is
exactly equal to one for massive scalar field. Prove is based on an identity
for mass-dependent zeta-functions associated with Laplacians acting on
-forms.Comment: 8 pages, REVTeX fil
A decision tree model to estimate the value of information provided by a groundwater quality monitoring network
Groundwater contaminated with nitrate poses a serious health risk to infants when this contaminated water is used for culinary purposes. To avoid this health risk, people need to know whether their culinary water is contaminated or not. Therefore, there is a need to design an effective groundwater monitoring network, acquire information on groundwater conditions, and use acquired information to inform management options. These actions require time, money, and effort. This paper presents a method to estimate the value of information (VOI) provided by a groundwater quality monitoring network located in an aquifer whose water poses a spatially heterogeneous and uncertain health risk. A decision tree model describes the structure of the decision alternatives facing the decision-maker and the expected outcomes from these alternatives. The alternatives include (i) ignore the health risk of nitrate-contaminated water, (ii) switch to alternative water sources such as bottled water, or (iii) implement a previously designed groundwater quality monitoring network that takes into account uncertainties in aquifer properties, contaminant transport processes, and climate (Khader, 2012). The VOI is estimated as the difference between the expected costs of implementing the monitoring network and the lowest-cost uninformed alternative. We illustrate the method for the Eocene Aquifer, West Bank, Palestine, where methemoglobinemia (blue baby syndrome) is the main health problem associated with the principal contaminant nitrate. The expected cost of each alternative is estimated as the weighted sum of the costs and probabilities (likelihoods) associated with the uncertain outcomes resulting from the alternative. Uncertain outcomes include actual nitrate concentrations in the aquifer, concentrations reported by the monitoring system, whether people abide by manager recommendations to use/not use aquifer water, and whether people get sick from drinking contaminated water. Outcome costs include healthcare for methemoglobinemia, purchase of bottled water, and installation and maintenance of the groundwater monitoring system. At current methemoglobinemia and bottled water costs of 0.6/baby/day, the decision tree results show that the expected cost of establishing the proposed groundwater quality monitoring network exceeds the expected costs of the uninformed alternatives and there is no value to the information the monitoring system provides. However, the monitoring system will be preferred to ignoring the health risk or using alternative sources if the methemoglobinemia cost rises to 2.3/baby/day. Similarly, the monitoring system has value if the system can more accurately report actual aquifer concentrations and the public more fully abides by manager recommendations to use/not use the aquifer. The system also has value if it will serve a larger population or if its installation costs can be reduced, for example using a smaller number of monitoring wells. The VOI analysis shows how monitoring system design, accuracy, installation and operating costs, public awareness of health risks, costs of alternatives, and demographics together affect the value of implementing a system to monitor groundwater quality
Health economic analysis of laparoscopic lavage versus Hartmann's procedure for diverticulitis in the randomized DILALA trial
BACKGROUND: Open surgery with resection and colostomy (Hartmann's procedure) has been the standard treatment for perforated diverticulitis with purulent peritonitis. In recent years laparoscopic lavage has emerged as an alternative, with potential benefits for patients with purulent peritonitis, Hinchey grade III. The aim of this study was to compare laparoscopic lavage and Hartmann's procedure with health economic evaluation within the framework of the DILALA (DIverticulitis – LAparoscopic LAvage versus resection (Hartmann's procedure) for acute diverticulitis with peritonitis) trial. METHODS: Clinical effectiveness and resource use were derived from the DILALA trial and unit costs from Swedish sources. Costs were analysed from the perspective of the healthcare sector. The study period was divided into short‐term analysis (base‐case A), within 12 months, and long‐term analysis (base‐case B), from inclusion in the trial throughout the patient's expected life. RESULTS: The study included 43 patients who underwent laparoscopic lavage and 40 who had Hartmann's procedure in Denmark and Sweden during 2010–2014. In base‐case A, the difference in mean cost per patient between laparoscopic lavage and Hartmann's procedure was €–8983 (95 per cent c.i. –16 232 to –1735). The mean(s.d.) costs per patient in base‐case B were €25 703(27 544) and €45 498(38 928) for laparoscopic lavage and Hartmann's procedure respectively, resulting in a difference of €–19 794 (95 per cent c.i. –34 657 to –4931). The results were robust as demonstrated in sensitivity analyses. CONCLUSION: The significant cost reduction in this study, together with results of safety and efficacy from RCTs, support the routine use of laparoscopic lavage as treatment for complicated diverticulitis with purulent peritonitis
The Relationship Between Baryons and Dark Matter in Extended Galaxy Halos
The relationship between gas-rich galaxies and Ly-alpha absorbers is
addressed in this paper in the context of the baryonic content of galaxy halos.
Deep Arecibo HI observations are presented of two gas-rich spiral galaxies
within 125 kpc projected distance of a Ly-alpha absorber at a similar velocity.
The galaxies investigated are close to edge-on and the absorbers lie almost
along their major axes, allowing for a comparison of the Ly-alpha absorber
velocities with galactic rotation. This comparison is used to examine whether
the absorbers are diffuse gas rotating with the galaxies' halos, outflow
material from the galaxies, or intergalactic gas in the low redshift cosmic
web. The results indicate that if the gas resides in the galaxies' halos it is
not rotating with the system and possibly counter-rotating. In addition, simple
geometry indicates the gas was not ejected from the galaxies and there are no
gas-rich satellites detected down to 3.6 - 7.5 x 10^6 Msun, or remnants of
satellites to 5-6 x 10^{18} cm^{-2}. The gas could potentially be infalling
from large radii, but the velocities and distances are rather high compared to
the high velocity clouds around the Milky Way. The most likely explanation is
the galaxies and absorbers are not directly associated, despite the vicinity of
the spiral galaxies to the absorbers (58-77 kpc from the HI edge). The spiral
galaxies reside in a filament of intergalactic gas, and the gas detected by the
absorber has not yet come into equilibrium with the galaxy. These results also
indicate that the massive, extended dark matter halos of spiral galaxies do not
commonly have an associated diffuse baryonic component at large radii.Comment: Accepted by AJ, 33 pages preprint format, see
http://www.astro.lsa.umich.edu/~mputman/putman1.pdf for a higher resolution
versio
Evidence for Proportionate Partition Between the Magnetic Field and Hot Gas in Turbulent Cassiopeia A
We present a deep X-ray observation of the young Galactic supernova remnant
Cas A, acquired with the ROSAT High Resolution Imager. This high dynamic range
(232 ks) image reveals low-surface-brightness X-ray structure, which appears
qualitatively similar to corresponding radio features. We consider the
correlation between the X-ray and radio morphologies and its physical
implications. After correcting for the inhomogeneous absorption across the
remnant, we performed a point by point (4" resolution) surface brightness
comparison between the X-ray and radio images. We find a strong (r = 0.75)
log-log correlation, implying an overall relationship of . This is
consistent with proportionate partition (and possibly equipartition) between
the local magnetic field and the hot gas --- implying that Cas A's plasma is
fully turbulent and continuously amplifying the magnetic field.Comment: 8 pages with embedded bitmapped figures, Accepted by ApJ Letters
5/1/9
k-dependent spectrum and optical conductivity near metal-insulator transition in multi-orbital Hubbard bands
We apply the dynamical mean field theory (DMFT) in the iterative perturbation
theory(IPT) to doubly degenerate eg bands and triply degenerate tg bands on a
simple cubic lattice and calculate the spectrum and optical conductivity in
arbitrary electron occupation. The spectrum simultaneously shows the effects of
multiplet structure and DMFT together with the electron ionization and affinity
levels of different electron occupations, coherent peaks at the Fermi energy in
the metallic phase and a gap at an integer filling of electrons for
sufficiently large Coulomb U. We also calculate the critical value of the
Coulomb U for degenerate orbitals.Comment: 8 pages, 6 figure
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