91 research outputs found
Determination of gas bubble fractionation rates in the deep ocean by laser Raman spectroscopy
Author Posting. © The Authors, 2004. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Marine Chemistry 99 (2006): 12-23, doi:10.1016/j.marchem.2004.10.006.A new deep-sea laser Raman spectrometer (DORISS â Deep Ocean Raman In
Situ Spectrometer) is used to observe the preferential dissolution of CO2 into
seawater from a 50%-50% CO2-N2 gas mixture in a set of experiments that test a
proposed method of CO2 sequestration in the deep ocean. In a first set of
experiments performed at 300 m depth, an open-bottomed 1000 cm3 cube was
used to contain the gas mixture; and in a second set of experiments a 2.5 cm3
funnel was used to hold a bubble of the gas mixture in front of the sampling
optic. By observing the changing ratios of the CO2 and N2 Raman bands we
were able to determine the gas flux and the mass transfer coefficient at 300 m
depth and compare them to theoretical calculations for air-sea gas exchange.
Although each experiment had a different configuration, comparable results
were obtained. As expected, the ratio of CO2 to N2 drops off at an exponential
rate as CO2 is preferentially dissolved in seawater. In fitting the data with
theoretical gas flux calculations, the boundary layer thickness was determined to
be ~42 ÎŒm for the gas cube, and ~165 ÎŒm for the gas funnel reflecting different
boundary layer turbulence. The mass transfer coefficients for CO2 are kL = 2.82
x 10- 5 m/s for the gas cube experiment, and kL = 7.98 x 10- 6 m/s for the gas
funnel experiment.Funding was provided by a grant to
MBARI from the David and Lucile Packard Foundation, and by the U.S. Dept. of Energy Ocean
Carbon Sequestration Program (Grants No. DE-FC26-00NT40929 and DE-FC03-01ER6305)
Quantitative conditional quantum erasure in two-atom resonance fluorescence
We present a conditional quantum eraser which erases the a priori knowledge
or the predictability of the path a photon takes in a Young-type double-slit
experiment with two fluorescent four-level atoms. This erasure violates a
recently derived erasure relation which must be satisfied for a conventional,
unconditional quantum eraser that aims to find an optimal sorting of the system
into subensembles with particularly large fringe visibilities. The conditional
quantum eraser employs an interaction-free, partial which-way measurement which
not only sorts the system into optimal subsystems with large visibility but
also selects the appropriate subsystem with the maximum possible visibility. We
explain how the erasure relation can be violated under these circumstances.Comment: Revtex4, 12pages, 4 eps figures, replaced with published version,
changes in Sec. 3, to appear in Physical Review
Universality of the Lyapunov regime for the Loschmidt echo
The Loschmidt echo (LE) is a magnitude that measures the sensitivity of
quantum dynamics to perturbations in the Hamiltonian. For a certain regime of
the parameters, the LE decays exponentially with a rate given by the Lyapunov
exponent of the underlying classically chaotic system. We develop a
semiclassical theory, supported by numerical results in a Lorentz gas model,
which allows us to establish and characterize the universality of this Lyapunov
regime. In particular, the universality is evidenced by the semiclassical limit
of the Fermi wavelength going to zero, the behavior for times longer than
Ehrenfest time, the insensitivity with respect to the form of the perturbation
and the behavior of individual (non-averaged) initial conditions. Finally, by
elaborating a semiclassical approximation to the Wigner function, we are able
to distinguish between classical and quantum origin for the different terms of
the LE. This approach renders an understanding for the persistence of the
Lyapunov regime after the Ehrenfest time, as well as a reinterpretation of our
results in terms of the quantum--classical transition.Comment: 33 pages, 17 figures, uses Revtex
Leading for gold: social identity leadership processes at the London 2012 Olympic Games
© 2014, © 2014 Taylor & Francis. This paper adopted a social identity approach to explore the media data of leadership figures at the London 2012 Olympic Games. Media data in the form of interviews, speeches/team announcements, and blog posts from leaders integral to the London 2012 Olympic Games were analysed from 100 days prior to, during, and for 30 days following, the Olympic Games. Leaders included Lord Seb Coe, Andy Hunt, and performance directors of TeamGB athletics (Charles van Commenee), cycling (Sir David Brailsford), rowing (David Tanner) and swimming (Michael Scott). An inductive and deductive thematic analysis identified five higher order themes: creation of team identities, team values, team vision, performance consequences and âweâ achieved. The analysis makes a contribution to extant leadership literature by highlighting novel contextually relevant themes surrounding leadership at the London 2012 Olympic Games. Thus, opportunities for future research and application are outlined
Characteristics of the Moveable Middle: Opportunities Among Adults Open to COVID-19 Vaccination
Introduction: Focusing on subpopulations that express the intention to receive a COVID-19 vaccination but are unvaccinated may improve the yield of COVID-19 vaccination efforts. Methods: A nationally representative sample of 789,658 U.S. adults aged â„18 years participated in the National Immunization Survey Adult COVID Module from May 2021 to April 2022. The survey assessed respondentsâ COVID-19 vaccination status and intent by demographic characteristics (age, urbanicity, educational attainment, region, insurance, income, and race/ethnicity). This study compared composition and within-group estimates of those who responded that they definitely or probably will get vaccinated or are unsure (moveable middle) from the first and last month of data collection. Results: Because vaccination uptake increased over the study period, the moveable middle declined among persons aged â„18 years. Adults aged 18â39 years and suburban residents comprised most of the moveable middle in April 2022. Groups with the largest moveable middles in April 2022 included persons with no insurance (10%), those aged 18â29 years (8%), and those with incomes below poverty (8%), followed by non-Hispanic Native Hawaiian or other Pacific Islander (7%), non-Hispanic multiple or other race (6%), non-Hispanic American Indian or Alaska Native persons (6%), non-Hispanic Black or African American persons (6%), those with below high school education (6%), those with high school education (5%), and those aged 30â39 years (5%). Conclusions: A sizable percentage of adults open to receiving COVID-19 vaccination remain in several demographic groups. Emphasizing engagement of persons who are unvaccinated in some racial/ethnic groups, aged 18â39 years, without health insurance, or with lower income may reach more persons open to vaccination
Late Winter Biogeochemical Conditions Under Sea Ice in the Canadian High Arctic
With the Arctic summer sea-ice extent in decline, questions are arising as to how changes in sea-ice dynamics might affect biogeochemical cycling and phenomena such as carbon dioxide (CO2) uptake and ocean acidification. Recent field research in these areas has concentrated on biogeochemical and CO2 measurements during spring, summer or autumn, but there are few data for the winter or winterâspring transition, particularly in the High Arctic. Here, we present carbon and nutrient data within and under sea ice measured during the Catlin Arctic Survey, over 40 days in March and April 2010, off Ellef Ringnes Island (78° 43.11âČ N, 104° 47.44âČ W) in the Canadian High Arctic. Results show relatively low surface water (1â10 m) nitrate (<1.3 ”M) and total inorganic carbon concentrations (mean±SD=2015±5.83 ”mol kgâ1), total alkalinity (mean±SD=2134±11.09 ”mol kgâ1) and under-ice pCO2sw (mean±SD=286±17 ”atm). These surprisingly low wintertime carbon and nutrient conditions suggest that the outer Canadian Arctic Archipelago region is nitrate-limited on account of sluggish mixing among the multi-year ice regions of the High Arctic, which could temper the potential of widespread under-ice and open-water phytoplankton blooms later in the season
New insights into the genetic etiology of Alzheimer's disease and related dementias
Characterization of the genetic landscape of Alzheimer's disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/'proxy' AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE Δ4 allele
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