4,230 research outputs found
Magnetic flux flow and superconductor stabilization Quarterly report, 1 Jan. - 31 Mar. 1968
Magnetic flux flow and stability of superconducting niobium titanium strip
A 3âD Model of Gas Generation, Migration, and Gas Hydrate Formation at a Young Convergent Margin (Hikurangi Margin, New Zealand)
We present a three-dimensional gas hydrate systems model of the southern Hikurangi subduction margin in eastern New Zealand. The model integrates thermal and microbial gas generation, migration, and hydrate formation. Modeling these processes has improved the understanding of factors controlling hydrate distribution. Three spatial trends of concentrated hydrate occurrence are predicted. The first trend (I) is aligned with the principal deformation front in the overriding Australian plate. Concentrated hydrate deposits are predicted at or near the apexes of anticlines and to be mainly sourced from focused migration and recycling of microbial gas generated beneath the hydrate stability zone. A second predicted trend (II) is related to deformation in the subducting Pacific plate associated with former Mesozoic subduction beneath Gondwana and the modern Pacific-Australian plate boundary. This trend is enhanced by increased advection of thermogenic gas through permeable layers in the subducting plate and focused migration into the Neogene basin fill above Cretaceous-Paleogene structures. The third trend (III) follows the northern margin of the Hikurangi Channel and is related to the presence of buried strata of the Hikurangi Channel system. The predicted trends are consistent with pronounced seismic reflection anomalies related to free gas in the pore space and strength of the bottom-simulating reflection. However, only trend I is also associated with clear and widespread seismic indications of concentrated gas hydrate. Total predicted hydrate masses at the southern Hikurangi Margin are between 52,800 and 69,800 Mt. This equates to 3.4â4.5 Mt hydrate/km2, containing 6.33 Ă 108â8.38 Ă 108 m3/km2 of methane
Gamma-Ray Spectral States of Galactic Black Hole Candidates
OSSE has observed seven transient black hole candidates: GRO J0422+32,
GX339-4, GRS 1716-249, GRS 1009-45, 4U 1543-47, GRO J1655-40, and GRS 1915+105.
Two gamma-ray spectral states are evident and, based on a limited number of
contemporaneous X-ray and gamma-ray observations, these states appear to be
correlated with X-ray states. The former three objects show hard spectra below
100 keV (photon number indices Gamma < 2) that are exponentially cut off with
folding energy ~100 keV, a spectral form that is consistent with thermal
Comptonization. This "breaking gamma-ray state" is the high-energy extension of
the X-ray low, hard state. In this state, the majority of the luminosity is
above the X-ray band, carried by photons of energy ~100 keV. The latter four
objects exhibit a "power-law gamma-ray state" with a relatively soft spectral
index (Gamma ~ 2.5-3) and no evidence for a spectral break. For GRO J1655-40,
the lower limit on the break energy is 690 keV. GRS 1716-249 exhibits both
spectral states, with the power-law state having significantly lower gamma-ray
luminosity. The power-law gamma-ray state is associated with the presence of a
strong ultrasoft X-ray excess (kT ~ 1 keV), the signature of the X-ray high,
soft (or perhaps very high) state. The physical process responsible for the
unbroken power law is not well understood, although the spectra are consistent
with bulk-motion Comptonization in the convergent accretion flow.Comment: 27 pages, 3 figures, uses aaspp.sty and psfig.st
Continuous feedback on a quantum gas coupled to an optical cavity
We present an active feedback scheme acting continuously on the state of a
quantum gas dispersively coupled to a high-finesse optical cavity. The quantum
gas is subject to a transverse pump laser field inducing a self-organization
phase transition, where the gas acquires a density modulation and photons are
scattered into the resonator. Photons leaking from the cavity allow for a
real-time and non-destructive readout of the system. We stabilize the mean
intra-cavity photon number through a micro-processor controlled feedback
architecture acting on the intensity of the transverse pump field. The feedback
scheme can keep the mean intra-cavity photon number constant, in
a range between and , and
for up to 4 s. Thus we can engage the stabilization in a regime where the
system is very close to criticality as well as deep in the self-organized
phase. The presented scheme allows us to approach the self-organization phase
transition in a highly controlled manner and is a first step on the path
towards the realization of many-body phases driven by tailored feedback
mechanisms
Galactic Black Hole Binaries: Multifrequency Connections
We review the recent multifrequency studies of galactic black hole binaries,
aiming at revealing the underlying emission processes and physical properties
in these systems. The optical and infrared observations are important for
determining their system parameters, such as the companion star type, orbital
period and separation, inclination angle and the black hole mass. The radio
observations are useful for studying high energy electron acceleration process,
jet formation and transport. X-ray observations can be used to probe the inner
accretion disk region in order to understand the fundamental physics of the
accretion disk in the strongest gravitational field and the properties of the
black hole. Future higher sensitivity and better resolution instrumentation
will be needed to answer the many fundamental questions that have arisen.Comment: Revised on August 6, 1997, 22 pages, 6 figures, 1 table. Invited
review paper for the 4th Compton Symposium, eds. C. D. Dermer and J. D.
Kurfess, Williamsburg, VA, April, 1997. AIP Conference Proceeding
Magnetic flux flow and superconductor stabilization Quarterly report, Apr. 1 - Jun. 30, 1967
Magnetic flux flow and superconductor stabilizatio
Public Benefits of Undeveloped Lands on Urban Outskirts: Non-Market Valuation Studies and their Role in Land Use Plans
Over the past three decades, the economics profession has developed methods for estimating the public benefits of green spaces, providing an opportunity to incorporate such information into land-use planning. While federal regulations routinely require such estimates for major regulations, the extent to which they are used in local land use plans is not clear. This paper reviews the literature on public values for lands on urban outskirts, not just to survey their methods or empirical findings, but to evaluate the role they have played--or have the potential to play-- in actual land use plans. Based on interviews with authors and representatives of funding agencies and local land trusts, it appears that academic work has had a mixed reception in the policy world. Reasons for this include a lack of interest in making academic work accessible to policy makers, emphasizing revealed preference methods which are inconsistent with policy priorities related to nonuse values, and emphasis on benefit-cost analyses. Nevertheless, there are examples of success stories that illustrate how such information can play a vital role in the design of conservation policies. Working Paper 07-2
The costs of preventing and treating chagas disease in Colombia
Background: The objective of this study is to report the costs of Chagas disease in Colombia, in terms of vector disease control programmes and the costs of providing care to chronic Chagas disease patients with cardiomyopathy.
Methods: Data were collected from Colombia in 2004. A retrospective review of costs for vector control programmes carried out in rural areas included 3,084 houses surveyed for infestation with triatomine bugs and 3,305 houses sprayed with insecticide. A total of 63 patient records from 3 different hospitals were selected for a retrospective review of resource use. Consensus methodology with local experts was used to estimate care seeking behaviour and to complement observed data on utilisation. Findings: The mean cost per house per entomological survey was of 2004), whereas the mean cost of spraying a house with insecticide was 46.4 and 1,028, whereas lifetime costs averaged $11,619 per patient. Chronic Chagas disease patients have limited access to healthcare, with an estimated 22% of patients never seeking care. Conclusion: Chagas disease is a preventable condition that affects mostly poor populations living in rural areas. The mean costs of surveying houses for infestation and spraying infested houses were low in comparison to other studies and in line with treatment costs. Care seeking behaviour and the type of insurance affiliation seem to play a role in the facilities and type of care that patients use, thus raising concerns about equitable access to care. Preventing Chagas disease in Colombia would be cost-effective and could contribute to prevent inequalities in health and healthcare.Wellcome Trus
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