3,769 research outputs found
Global Spinors and Orientable Five-Branes
Fermion fields on an M-theory five-brane carry a representation of the double
cover of the structure group of the normal bundle. It is shown that, on an
arbitrary oriented Lorentzian six-manifold, there is always an Sp(2) twist that
allows such spinors to be defined globally. The vanishing of the arising
potential obstructions does not depend on spin structure in the bulk, nor does
the six-manifold need to be spin or spin-C. Lifting the tangent bundle to such
a generalised spin bundle requires picking a generalised spin structure in
terms of certain elements in the integral and modulo-two cohomology of the
five-brane world-volume in degrees four and five, respectively.Comment: 18 pages, LaTeX; v2: version to appear in JHE
Twisted topological structures related to M-branes
Studying the M-branes leads us naturally to new structures that we call
Membrane-, Membrane^c-, String^K(Z,3)- and Fivebrane^K(Z,4)-structures, which
we show can also have twisted counterparts. We study some of their basic
properties, highlight analogies with structures associated with lower levels of
the Whitehead tower of the orthogonal group, and demonstrate the relations to
M-branes.Comment: 17 pages, title changed on referee's request, minor changes to
improve presentation, typos correcte
Ritual Intuitions: Cognitive Contributions to Judgments of Ritual Efficacy
Lawson and McCauley (1990) have argued that non-cultural regularities in how actions are conceptualized inform and constrain participants' understandings of religious rituals. This theory of ritual competence generates three predictions: 1) People with little or no knowledge of any given ritual system will have intuitions about the potential effectiveness of a ritual given minimal information about the structure of the ritual. 2) The representation of superhuman agency in the action structure will be considered the most important factor contributing to effectiveness. 3) Having an appropriate intentional agent initiate the action will be considered relatively more important than any specific action to be performed. These three predictions were tested in two experiments with 128 North American Protestant college students who rated the probability of various fictitious rituals to be effective in bringing about a specified consequence. Results support Lawson and McCauley's predictions and suggest that expectations regarding ordinary social actions apply to religious rituals.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43718/1/10881_2004_Article_brill_15677095_v1n2_s4.pd
51 Eri and GJ 3305: A 10-15 Myr old binary star system at 30 parsecs
Following the suggestion of Zuckerman et al. (2001, ApJ, 562, L87), we
consider the evidence that 51 Eri (spectral type F0) and GJ 3305 (M0),
historically classified as unrelated main sequence stars in the solar
neighborhood, are instead a wide physical binary system and members of the
young beta Pic moving group (BPMG). The BPMG is the nearest (d < 50 pc) of
several groups of young stars with ages around 10 Myr that are kinematically
convergent with the Oph-Sco-Cen Association (OSCA), the nearest OB star
association. Combining SAAO optical photometry, Hobby-Eberly Telescope
high-resolution spectroscopy, Chandra X-ray data, and UCAC2 catalog kinematics,
we confirm with high confidence that the system is indeed extremely young. GJ
3305 itself exhibits very strong magnetic activity but has rapidly depleted
most of its lithium. The 51 Eri/GJ 3305 system is the westernmost known member
of the OSCA, lying 110 pc from the main subgroups. The system is similar to the
BPMG wide binary HD 172555/CD -64d1208 and the HD 104237 quintet, suggesting
that dynamically fragile multiple systems can survive the turbulent
environments of their natal giant molecular cloud complexes, while still being
imparted high dispersion velocities. Nearby young systems such as these are
excellent targets for evolved circumstellar disk and planetary studies, having
stellar ages comparable to that of the late phases of planet formation.Comment: 27 pages, 7 figures. Accepted for publication in the Astronomical
Journal. For a version with high resolution figures, see
http://www.astro.psu.edu/users/edf/51Eri.pd
Chimeric antigens displaying GPR65 extracellular loops on a soluble scaffold enabled the discovery of antibodies, which recognized native receptor
GPR65 is a proton-sensing G-protein coupled receptor associated with multiple immune-mediated inflammatory diseases, whose function is relatively poorly understood. With few reagents commercially available to probe the biology of receptor, generation of an anti-GPR65 monoclonal antibody was desired. Using soluble chimeric scaffolds, such as ApoE3, displaying the extracellular loops of GPR65, together with established phage display technology, native GPR65 loop-specific antibodies were identified. Phage-derived loop-binding antibodies recognized the wild-type native receptor to which they had not previously been exposed, generating confidence in the use of chimeric soluble proteins to act as efficient surrogates for membrane protein extracellular loop antigens. This technique provides promise for the rational design of chimeric antigens in facilitating the discovery of specific antibodies to GPCRs
Recommended from our members
This article corrects: “Correlation of the NBME Advanced Clinical Examination in EM and the National EM M4 examsâ€?
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Recommended from our members
This article corrects: “Correlation of the NBME Advanced Clinical Examination in EM and the National EM M4 examsâ€?
n/
The evolution of X-ray emission in young stars
We study the relation between age and magnetic activity in late-type pre-main
sequence (PMS) stars, for the first time using mass-stratified subsamples. The
effort is based on the Chandra Orion Ultradeep Project (COUP) which provides
very sensitive and homogenous X-ray data on a uniquely large sample of 481
optically well-characterized low-extinction low-mass members of the Orion
Nebula Cluster, for which individual stellar masses and ages could be
determined. More than 98 percent of the stars in this sample are detected as
X-ray sources. Within the PMS phase for stellar ages in the range
Myr, we establish a mild decay in activity with stellar age roughly as
. On longer timescales, when the Orion stars are
compared to main sequence stars, the X-ray luminosity decay law for stars in
the M mass range is more rapid with over the wide range of ages yr. The
magnetic activity history for M stars with masses is
distinctly different. Only a mild decrease in X-ray luminosity, and even a mild
increase in and , is seen over the 1-100 Myr
range, though the X-ray emission does decay over long timescales on the main
sequence. Together with COUP results on the absence of a rotation-activity
relation in Orion stars, we find that the activity-age decay is strong across
the entire history of solar-type stars but is not attributable to rotational
deceleration during the early epochs. A combination of tachocline and
distributed convective dynamos may be operative in young solar-type stars. The
results for the lowest mass stars are most easily understood by the dominance
of convective dynamos during both the PMS and main sequence phases.Comment: accepted for ApJS, COUP special issu
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