19,362 research outputs found
Adjustment of the basin-scale circulation at 26 degrees N to variations in Gulf Stream, deep western boundary current and Ekman transports as observed by the Rapid array
The Rapid instrument array across the Atlantic Ocean along 26 degrees N provides unprecedented monitoring of the basin-scale circulation. A unique feature of the Rapid array is the combination of full-depth moorings with instruments measuring temperature, salinity, pressure time series at many depths with co-located bottom pressure measurements so that dynamic pressure can be measured from surface to bottom. Bottom pressure measurements show a zonally uniform rise (and fall) of bottom pressure of 0.015 dbar on a 5 to 10 day time scale, suggesting that the Atlantic basin is filling and draining on a short time scale. After removing the zonally uniform bottom pressure fluctuations, bottom pressure variations at 4000 m depth against the western boundary compensate instantaneously for baroclinic fluctuations in the strength and structure of the deep western boundary current so there is no basin-scale mass imbalance resulting from variations in the deep western boundary current. After removing the mass compensating bottom pressure, residual bottom pressure fluctuations at the western boundary just east of the Bahamas balance variations in Gulf Stream transport. Again the compensation appears to be especially confined close to the western boundary. Thus, fluctuations in either Gulf Stream or deep western boundary current transports are compensated in a depth independent (barotropic) manner very close to the continental slope off the Bahamas. In contrast, compensation for variations in wind-driven surface Ekman transport appears to involve fluctuations in both western basin and eastern basin bottom pressures, though the bottom pressure difference fluctuations appear to be a factor of 3 too large, perhaps due to an inability to resolve small bottom pressure fluctuations after removal of larger zonal average, baroclinic, and Gulf Stream pressure components. For 4 tall moorings where time series dynamic height (geostrophic pressure) profiles can be estimated from sea surface to ocean bottom and bottom pressure can be added, there is no general correlation between surface dynamic height and bottom pressure. Dynamic height on each mooring is strongly correlated with sea surface height from satellite observations and the variability in both dynamic height and satellite sea surface height decrease sharply as the western boundary is approached
Applying black hole perturbation theory to numerically generated spacetimes
Nonspherical perturbation theory has been necessary to understand the meaning
of radiation in spacetimes generated through fully nonlinear numerical
relativity. Recently, perturbation techniques have been found to be successful
for the time evolution of initial data found by nonlinear methods. Anticipating
that such an approach will prove useful in a variety of problems, we give here
both the practical steps, and a discussion of the underlying theory, for taking
numerically generated data on an initial hypersurface as initial value data and
extracting data that can be considered to be nonspherical perturbations.Comment: 14 pages, revtex3.0, 5 figure
Modelling surface acoustic wave modulation of the carrier concentration in quantum cascade lasers for broadband tuneability
Mopra CO Observations of the Bubble HII Region RCW120
We use the Mopra radio telescope to test for expansion of the molecular gas
associated with the bubble HII region RCW120. A ring, or bubble, morphology is
common for Galactic HII regions, but the three-dimensional geometry of such
objects is still unclear. Detected near- and far-side expansion of the
associated molecular material would be consistent with a three-dimensional
spherical object. We map the transitions of CO,
CO, CO, and CO, and detect emission from all
isotopologues. We do not detect the masing lines of
CHOH at 108.8939 GHz. The strongest CO emission is from the
photodissociation region (PDR), and there is a deficit of emission toward the
bubble interior. We find no evidence for expansion of the molecular material
associated with RCW120 and therefore can make no claims about its geometry. The
lack of detected expansion is roughly in agreement with models for the
time-evolution of an HII region like RCW120, and is consistent with an
expansion speed of . Single-position CO spectra show
signatures of expansion, which underscores the importance of mapped spectra for
such work. Dust temperature enhancements outside the PDR of RCW120 coincide
with a deficit of emission in CO, confirming that these temperature
enhancements are due to holes in the RCW120 PDR. H emission shows that
RCW120 is leaking of the ionizing photons into the interstellar
medium (ISM) through PDR holes at the locations of the temperature
enhancements. H-alpha emission also shows a diffuse "halo" from leaked photons
not associated with discrete holes in the PDR. Overall of all
ionizing photons are leaking into the nearby ISM.Comment: 35 pages, 14 figures. Accepted to Ap
Strategic Network Formation with Attack and Immunization
Strategic network formation arises where agents receive benefit from
connections to other agents, but also incur costs for forming links. We
consider a new network formation game that incorporates an adversarial attack,
as well as immunization against attack. An agent's benefit is the expected size
of her connected component post-attack, and agents may also choose to immunize
themselves from attack at some additional cost. Our framework is a stylized
model of settings where reachability rather than centrality is the primary
concern and vertices vulnerable to attacks may reduce risk via costly measures.
In the reachability benefit model without attack or immunization, the set of
equilibria is the empty graph and any tree. The introduction of attack and
immunization changes the game dramatically; new equilibrium topologies emerge,
some more sparse and some more dense than trees. We show that, under a mild
assumption on the adversary, every equilibrium network with agents contains
at most edges for . So despite permitting topologies denser
than trees, the amount of overbuilding is limited. We also show that attack and
immunization don't significantly erode social welfare: every non-trivial
equilibrium with respect to several adversaries has welfare at least as that of
any equilibrium in the attack-free model.
We complement our theory with simulations demonstrating fast convergence of a
new bounded rationality dynamic which generalizes linkstable best response but
is considerably more powerful in our game. The simulations further elucidate
the wide variety of asymmetric equilibria and demonstrate topological
consequences of the dynamics e.g. heavy-tailed degree distributions. Finally,
we report on a behavioral experiment on our game with over 100 participants,
where despite the complexity of the game, the resulting network was
surprisingly close to equilibrium.Comment: The short version of this paper appears in the proceedings of WINE-1
Barriers to the dissemination of four harm reduction strategies: a survey of addiction treatment providers in Ontario
A sample of service providers at addictions agencies' in Ontario were interviewed by telephone to assess attitudes toward, anticipated internal and external barriers to implementing, and expected benefits of four harm reduction strategies: needle exchange, moderate drinking goals, methadone treatment, and provision of free condoms to clients. Respondents were also asked to define harm reduction, list its most important elements, and describe what they find most troubling and most appealing about harm reduction. Attitudes toward harm reduction in general and the services provided at each agency were also assessed. Results indicated that the service providers surveyed had positive attitudes toward each of the four harm reduction strategies and harm reduction in general, and the majority of respondents were aware of the benefits associated with each strategy. Almost all of the agencies surveyed allowed for moderate drinking outcomes in the treatment of alcohol problems, and most agencies provided free condoms to clients. In terms of barriers, anticipated negative community reaction to needle exchange, methadone treatment, and free condoms was a major concern for the majority of respondents. Lack of staff, of funding, or anticipated staff resistance were also cited as potential barriers to introducing these strategies. In the case of methadone maintenance, the unavailability of a qualified physician was listed as the primary constraint. Implications for future efforts directed at encouraging the adoption of these strategies and suggestions for future research are discussed
Future Intentions Regarding Quitting and Reducing Cigarette Use in a Representative Sample of Canadian Daily Smokers: Implications for Public Health Initiatives
Pre-cessation reduction is associated with quitting smoking. However, many smokers reduce the amount consumed but may not quit altogether. Using a representative sample of adult current daily smokers, this project explored future intentions of smokers regarding cigarette consumption. This information is important because it can provide a framework within which to plan tobacco cessation initiatives. A random digit dialing telephone survey was conducted of 889 Canadian current daily smokers, 18 years and older. The response rate was 65% (of households with a smoker in residence, 65% agreed to participate). Analyses focused on the 825 respondents who smoked at least 10 cigarettes per day at some point in their lives. As part of this survey, respondents were asked their future plans about their smoking (maintain, increase, reduce, quit). Of these 825 respondents, the majority of respondents had plans to change their cigarette use, with 55% planning to quit, 18.8% to reduce and 22.5% to maintain the amount they smoked (3.4% did not know and 2 respondents planned to increase). Most smokers who planned to reduce their smoking saw it as a step towards quitting smoking completely. These results present a picture of smokers, the majority of whom appear to be in some form of transition. Many smokers planned to reduce, of which the overwhelming majority saw their reduction as a step towards quitting. Opportunities exist to capitalize on these intentions to change in efforts to promote tobacco cessation
Advanced tracking systems design and analysis
The results of an assessment of several types of high-accuracy tracking systems proposed to track the spacecraft in the National Aeronautics and Space Administration (NASA) Advanced Tracking and Data Relay Satellite System (ATDRSS) are summarized. Tracking systems based on the use of interferometry and ranging are investigated. For each system, the top-level system design and operations concept are provided. A comparative system assessment is presented in terms of orbit determination performance, ATDRSS impacts, life-cycle cost, and technological risk
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