20,474 research outputs found
No well-defined remnant Fermi surface in Sr2CuO2Cl2
In angle-resolved photoelectron spectra of the antiferromagnetic insulators
Ca2CuO2Cl2 and Sr2CuO2Cl2 a sharp drop of the spectral intensity of the
lowest-lying band is observed along a line in k space equivalent to the Fermi
surface of the optimally doped high-temperature superconductors. This was
interpreted as a signature of the existence of a remnant Fermi surface in the
insulating phase of the high-temperature superconductors. In this paper it is
shown that the drop of the spectral intensity is not related to the spectral
function but is a consequence of the electron-photon matrix elementComment: 4 pages, 3 figure
Oral History: Provenance and Intellectual Access
In the second half of the twentieth century, resea·rchers in all fields of study have become more sensitive to documentary gaps, especially the paucity of materials by and about social non-elites. With increasing frequency, oral history projects have been carried out to add these forgotten voices to the historical record and thereby create what may be termed new historical evidence. In the words of one public historian, a new and integrative paradigm is crafted out of such initiatives, whereby the oral testimonies of the heretofore ignored are synthesized with the documentation of the powerful. The result is, at least in theory, a more balanced and faithful view of society and history. Such a self-conscious effort to reshape history is troubling to many researchers, those who must interpret these new records as well as those whose job it is to expose and render their context. Nevertheless, despite its critics, oral history has become a popular method of inquiry and has earned a degree of historiographical significance
Analytic Methods for Optimizing Realtime Crowdsourcing
Realtime crowdsourcing research has demonstrated that it is possible to
recruit paid crowds within seconds by managing a small, fast-reacting worker
pool. Realtime crowds enable crowd-powered systems that respond at interactive
speeds: for example, cameras, robots and instant opinion polls. So far, these
techniques have mainly been proof-of-concept prototypes: research has not yet
attempted to understand how they might work at large scale or optimize their
cost/performance trade-offs. In this paper, we use queueing theory to analyze
the retainer model for realtime crowdsourcing, in particular its expected wait
time and cost to requesters. We provide an algorithm that allows requesters to
minimize their cost subject to performance requirements. We then propose and
analyze three techniques to improve performance: push notifications, shared
retainer pools, and precruitment, which involves recalling retainer workers
before a task actually arrives. An experimental validation finds that
precruited workers begin a task 500 milliseconds after it is posted, delivering
results below the one-second cognitive threshold for an end-user to stay in
flow.Comment: Presented at Collective Intelligence conference, 201
Meteorology of Jupiter's Equatorial Hot Spots and Plumes from Cassini
We present an updated analysis of Jupiter's equatorial meteorology from
Cassini observations. For two months preceding the spacecraft's closest
approach, the Imaging Science Subsystem (ISS) onboard regularly imaged the
atmosphere. We created time-lapse movies from this period in order to analyze
the dynamics of equatorial hot spots and their interactions with adjacent
latitudes. Hot spots are quasi-stable, rectangular dark areas on
visible-wavelength images, with defined eastern edges that sharply contrast
with surrounding clouds, but diffuse western edges serving as nebulous
boundaries with adjacent equatorial plumes. Hot spots exhibit significant
variations in size and shape over timescales of days and weeks. Some of these
changes correspond with passing vortex systems from adjacent latitudes
interacting with hot spots. Strong anticyclonic gyres present to the south and
southeast of the dark areas appear to circulate into hot spots. Impressive,
bright white plumes occupy spaces in between hot spots. Compact cirrus-like
'scooter' clouds flow rapidly through the plumes before disappearing within the
dark areas. These clouds travel at 150-200 m/s, much faster than the 100 m/s
hot spot and plume drift speed. This raises the possibility that the scooter
clouds may be more illustrative of the actual jet stream speed at these
latitudes. Most previously published zonal wind profiles represent the drift
speed of the hot spots at their latitude from pattern matching of the entire
longitudinal image strip. If a downward branch of an equatorially-trapped
Rossby waves controls the overall appearance of hot spots, however, the
westward phase velocity of the wave leads to underestimates of the true jet
stream speed.Comment: 33 pages, 11 figures; accepted for publication in Icarus; for
supplementary movies, please contact autho
A very deep Chandra observation of Abell 1795: The Cold Front and Cooling Wake
We present a new analysis of very deep Chandra observations of the galaxy
cluster Abell 1795. Utilizing nearly 750 ks of net ACIS imaging, we are able to
resolve the thermodynamic structure of the Intracluster Medium (ICM) on length
scales of ~ 1 kpc near the cool core. We find several previously unresolved
structures, including a high pressure feature to the north of the BCG that
appears to arise from the bulk motion of Abell 1795's cool core. To the south
of the cool core, we find low temperature (~ 3 keV), diffuse ICM gas extending
for distances of ~ 50 kpc spatially coincident with previously identified
filaments of H-alpha emission. Gas at similar temperatures is also detected in
adjacent regions without any H-alpha emission. The X-ray gas coincident with
the H-alpha filament has been measured to be cooling spectroscopically at a
rate of ~ 1 Solar Masses/ yr, consistent with measurements of the star
formation rate in this region as inferred from UV observations, suggesting that
the star formation in this filament as inferred by its H and UV
emission can trace its origin to the rapid cooling of dense, X-ray emitting
gas. The H-alpha filament is not a unique site of cooler ICM, however, as ICM
at similar temperatures and even higher metallicities not cospatial with
H emission is observed just to the west of the H-alpha filament,
suggesting that it may have been uplifted by Abell 1795's central active
galaxy. Further simulations of cool core sloshing and AGN feedback operating in
concert with one another will be necessary to understand how such a dynamic
cool core region may have originated and why the H-alpha emission is so
localized with respect to the cool X-ray gas despite the evidence for a
catastrophic cooling flow.Comment: 14 Pages, 10 Figures, Resubmitted to ApJ after first referee report,
Higher Resolution Figures available upon reques
Defocus test and defocus correction in full-field optical coherence tomography
We report experimental evidence and correction of defocus in full-field OCT
of biological samples due to mismatch of the refractive index of biological
tissues and water. Via a metric based on the image quality, we demonstrate that
we are able to compensate this index-induced defocus and to recover a sharp
image in depth.Comment: 7 pages, 3 figures, minor changes, 1 figure adde
Renal secretion of organic anions and cations
Renal secretion of organic anions and cations. The renal proximal tubule actively transports charged, potentially toxic xenobiotics from blood to lumen. Basolateral uptake of organic anions is indirectly coupled to the sodium gradient through Na-dicarboxylate cotransport and dicar-boxylate-organic anion exchange. Upon entry, a significant fraction of intracellular organic anion is sequestered within vesicles. Disruption of the cellular microtubular network can lead to both diminished vesicular movement and reduced transepithelial secretion. Luminal efflux of organic anions is energetically downhill, but carrier mediated. Both anion exchange and potential driven transport are present, but neither completely accounts for transport from cell to lumen. For organic cations, basolateral entry is downhill via potential driven facilitated diffusion. Intracellular sequestration of organic cations in vesicles is substantial, but its role in secretion is uncertain. Multiple carriers are available to drive organic cations uphill into the tubular lumen. The classical system indirectly taps the energy of the luminal Na gradient to drive organic cation efflux via Na+-H+ and proton-organic cation exchange. In addition, the multidrug resistance ATPase can pump organic cations into the tubular lumen. Thus, although much detailed information has been added over the last 50 years, it is not yet possible to provide a detailed, quantitative understanding of these important excretory systems
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