25,738 research outputs found
Very Extended and at low levels, Gravity and Supergravity
We define a level for a large class of Lorentzian Kac-Moody algebras. Using
this we find the representation content of very extended and
(i.e. ) at low levels in terms of and
representations respectively. The results are consistent with the conjectured
very extended and symmetries of gravity and maximal supergravity
theories given respectively in hep-th/0104081 and hep-th/0107209. We explain
how these results provided further evidence for these conjectures.Comment: 16 pages, plain tex (equation 3.3 modified and one reference
expanded
Anomalous isotopic predissociation in the F³Πu(v=1) state of O₂
Using a tunable, narrow-bandwidth vacuum-ultraviolet source based on third-harmonic generation from excimer-pumped dye-laser radiation, the F³Πu←X³Σg-(1,0)photoabsorption cross sections of ¹⁶O₂ and ¹⁸O₂ have been recorded in high resolution. Rotational analyses have been performed and the resultant F(v=1) term values fitted to the ³Π Hamiltonian of Brown and Merer [J. Mol. Spectrosc. 74, 488 (1979)]. A large rotationless isotope effect is observed in the F(v=1)predissociation, wherein the Lorentzian linewidth component for ¹⁸O₂ is a factor of ∼50 smaller than the corresponding ¹⁶O₂linewidth. This effect, a consequence of the nonadiabatic rotationless predissociation mechanism, is described using a coupled-channel treatment of the strongly Rydberg-valence-mixed 3Πu states. Significant J, e/f-parity, and sublevel dependencies observed in the isotopic F(v=1) rotational widths are found to derive from an indirect predissociation mechanism involving an accidental degeneracy with the E³Σ−u(v=3) level, itself strongly predissociated by ³Σ−u Rydberg-valence interactions, together with L-uncoupling (rotational) interactions between the Rydberg components of the F and E states. Transitions into the E(v=3) level are observed directly for the first time, specifically in the ¹⁸O₂ spectrumPartial support
was provided by an NSF International Opportunities for Scientists
and Engineers Program Grant No. INT-9513350, and
Visiting Fellowships for G.S. and J.B.W. at the Australian
National University
Effect of abdominal binding on respiratory mechanics during exercise in athletes with cervical spinal cord injury
West CR, Goosey-Tolfrey VL, Campbell IG, Romer LM. Effect of
abdominal binding on respiratory mechanics during exercise in athletes
with cervical spinal cord injury. J Appl Physiol 117: 36–45, 2014. First
published May 22, 2014; doi:10.1152/japplphysiol.00218.2014.—We
asked whether elastic binding of the abdomen influences respiratory
mechanics during wheelchair propulsion in athletes with cervical
spinal cord injury (SCI). Eight Paralympic wheelchair rugby players
with motor-complete SCI (C5-C7) performed submaximal and maximal
incremental exercise tests on a treadmill, both with and without
abdominal binding. Measurements included pulmonary function,
pressure-derived indices of respiratory mechanics, operating lung
volumes, tidal flow-volume data, gas exchange, blood lactate, and
symptoms. Residual volume and functional residual capacity were
reduced with binding (77 18 and 81 11% of unbound, P 0.05),
vital capacity was increased (114 9%, P 0.05), whereas total lung
capacity was relatively well preserved (99 5%). During exercise,
binding introduced a passive increase in transdiaphragmatic pressure,
due primarily to an increase in gastric pressure. Active pressures
during inspiration were similar across conditions. A sudden, sustained
rise in operating lung volumes was evident in the unbound condition,
and these volumes were shifted downward with binding.
Expiratory flow limitation did not occur in any subject and there
was substantial reserve to increase flow and volume in both
conditions. V ˙ O2 was elevated with binding during the final stages
of exercise (8 –12%, P 0.05), whereas blood lactate concentration
was reduced (16 –19%, P 0.05). V ˙ O2/heart rate slopes were
less steep with binding (62 35 vs. 47 24 ml/beat, P 0.05).
Ventilation, symptoms, and work rates were similar across conditions.
The results suggest that abdominal binding shifts tidal
breathing to lower lung volumes without influencing flow limitation,
symptoms, or exercise tolerance. Changes in respiratory
mechanics with binding may benefit O2 transport capacity by an
improvement in central circulatory function.This article has been made available through the Brunel Open Access Publishing Fund
Globular Cluster Population of Hickson Compact Group 22a and 90c
We present the first measurement of the globular cluster populations of
galaxies in Hickson compact groups, in order to investigate the effect of these
high density environments on the formation and evolution of globular cluster
systems. Based on V and R band images that we obtained of HCG 22a and HCG 90c
with the ESO New Technology Telescope (NTT), we find a total globular cluster
population of for HCG 22a and for 90c. The specific
frequency for HCG 22a was found to be and for HCG 90c. A power-law fit to the globular cluster radial profile of HCG
22a yields and for HCG 90c we found . A comparison of the globular cluster radial profiles with
the surface brightness of the parent galaxy shows that the globular cluster
systems are at least as extended as the halo light. The measured values for the
specific frequency are consistent with a scenario in which the host galaxies
were in a low density ``field-like'' environment when they formed their
globular cluster systems.Comment: 28 pages, 13 figures, 3 tables, accepted for publication in the
Astrophysical Journa
Fermi surface of the colossal magnetoresistance perovskite La_{0.7}Sr_{0.3}MnO_{3}
Materials that exhibit colossal magnetoresistance (CMR) are currently the
focus of an intense research effort, driven by the technological applications
that their sensitivity lends them to. Using the angular correlation of photons
from electron-positron annihilation, we present a first glimpse of the Fermi
surface of a material that exhibits CMR, supported by ``virtual crystal''
electronic structure calculations. The Fermi surface is shown to be
sufficiently cubic in nature that it is likely to support nesting.Comment: 5 pages, 5 PS figure
Shot-Noise Signatures of 0.7 Structure and Spin in a Quantum Point Contact
We report simultaneous measurement of shot noise and dc transport in a
quantum point contact as a function of source-drain bias, gate voltage, and
in-plane magnetic field. Shot noise at zero field exhibits an asymmetry related
to the 0.7 structure in conductance. The asymmetry in noise evolves smoothly
into the symmetric signature of spin-resolved electron transmission at high
field. Comparison to a phenomenological model with density-dependent level
splitting yields good quantitative agreement.Comment: related papers at http://marcuslab.harvard.ed
Duality Symmetries and G^{+++} Theories
We show that the non-linear realisations of all the very extended algebras
G^{+++}, except the B and C series which we do not consider, contain fields
corresponding to all possible duality symmetries of the on-shell degrees of
freedom of these theories. This result also holds for G_2^{+++} and we argue
that the non-linear realisation of this algebra accounts precisely for the form
fields present in the corresponding supersymmetric theory. We also find a
simple necessary condition for the roots to belong to a G^{+++} algebra.Comment: 35 pages. v2: 2 appendices added, other minor corrections. v3: tables
corrected, other minor changes, one appendix added, refs. added. Version
published in Class. Quant. Gra
On the value of wikipedia as a gateway to the web
By linking to external websites, Wikipedia can act as a gateway to the Web. To date, however, little is known about the amount of traffic generated by Wikipedia's external links. We fill this gap in a detailed analysis of usage logs gathered from Wikipedia users' client devices. Our analysis proceeds in three steps: First, we quantify the level of engagement with external links, finding that, in one month, English Wikipedia generated 43M clicks to external websites, in roughly even parts via links in infoboxes, cited references, and article bodies. Official links listed in infoboxes have by far the highest click-through rate (CTR), 2.47% on average. In particular, official links associated with articles about businesses, educational institutions, and websites have the highest CTR, whereas official links associated with articles about geographical content, television, and music have the lowest CTR. Second, we investigate patterns of engagement with external links, finding that Wikipedia frequently serves as a stepping stone between search engines and third-party websites, effectively fulfilling information needs that search engines do not meet. Third, we quantify the hypothetical economic value of the clicks received by external websites from English Wikipedia, by estimating that the respective website owners would need to pay a total of $7-13 million per month to obtain the same volume of traffic via sponsored search. Overall, these findings shed light on Wikipedia's role not only as an important source of information, but also as a high-traffic gateway to the broader Web ecosystem
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