3,886 research outputs found
SELF-DUAL SUPERGRAVITIES
The N-extended supersymmetric self-dual Poincar\'e supergravity equations
provide a natural local description of supermanifolds possessing hyperk\"ahler
structure. These equations admit an economical formulation in chiral
superspace. A reformulation in harmonic superspace encodes self-dual
supervielbeins and superconnections in a graded skew-symmetric supermatrix
superfield prepotential satisfying generalised Cauchy-Riemann conditions. A
recipe is presented for extracting explicit self-dual supervielbeins and
superconnections from such `analytic' prepotentials. We demonstrate the method
by explicitly decoding a simple example of superfield prepotential, analogous
to that corresponding to the Taub-NUT solution. The superspace we thus
construct is an interesting supersymmetric deformation of flat space,
having flat `body' and constant curvature `soul'.Comment: 14 pages, latex fil
Radiative corrections in processes at the SSC
We discuss radiative corrections for interactions in the SSC environment.
Based on the theory of Yennie, Frautschi and Suura, we develop appropriate
Monte Carlo event generators to compute the background electromagnetic
radiation. Our results indicate that multiple-photon effects must be taken into
account in the study of SSC physics such as Higgs decay.Comment: UTHEP-92-0901, 15 pages (incl. 3 figures), LaTeX (Talk presented at
the XXXII Cracow School of Theoretical Physics, Zakopane, June 1992
The contribution of lesion location to upper limb deficit after stroke
BACKGROUND: Motor deficit after stroke is related to regional anatomical damage. OBJECTIVE: To examine the influence of lesion location on upper limb motor deficit in chronic patients with stroke. METHODS: Lesion likelihood maps were created from T1-weighted structural MRI in 33 chronic patients with stroke with either purely subcortical lesions (SC, n=19) or lesions extending to any of the cortical motor areas (CM, n=14). We estimated lesion likelihood maps over the whole brain and applied multivoxel pattern analysis to seek the contribution weight of lesion likelihood to upper limb motor deficit. Among 5 brain regions of interest, the brain region with the greatest contribution to motor deficit was determined for each subgroup. RESULTS: The corticospinal tract was most likely to be damaged in both subgroups. However, while damage in the corticospinal tract was the best indicator of motor deficit in the SC patients, motor deficit in the CM patients was best explained by damage in brain areas activated during handgrip. CONCLUSIONS: Quantification of structural damage can add to models explaining motor outcome after stroke, but assessment of corticospinal tract damage alone is unlikely to be sufficient when considering patients with stroke with a wide range of lesion topography
Observational Constraints on the Ages of Molecular Clouds and the Star-Formation Timescale: Ambipolar-Diffusion--Controlled or Turbulence-Induced Star Formation?
We revisit the problem of the star formation timescale and the ages of
molecular clouds. The apparent overabundance of star-forming molecular clouds
over clouds without active star formation has been thought to indicate that
molecular clouds are "short-lived" and that star formation is "rapid". We show
that this statistical argument lacks self-consistency and, even within the
rapid star-formation scenario, implies cloud lifetimes of approximately 10 Myr.
We discuss additional observational evidence from external galaxies that
indicate lifetimes of molecular clouds and a timescale of star formation of
approximately 10 Myr . These long cloud lifetimes in conjunction with the rapid
(approximately 1 Myr) decay of supersonic turbulence present severe
difficulties for the scenario of turbulence-controlled star formation. By
contrast, we show that all 31 existing observations of objects for which the
linewidth, the size, and the magnetic field strength have been reliably
measured are in excellent quantitative agreement with the predictions of the
ambipolar-diffusion theory. Within the ambipolar-diffusion-controlled star
formation theory the linewidths may be attributed to large-scale non-radial
cloud oscillations (essentially standing large-amplitude, long-wavelength
Alfven waves), and the predicted relation between the linewidth, the size, and
the magnetic field is a natural consequence of magnetic support of
self-gravitating clouds.Comment: 7 pages, 2 figures, uses emulateapj; accepted for publication in Ap
Ambipolar-Diffusion Timescale, Star-Formation Timescale, and the Ages of Molecular Clouds: Is There a Discrepancy?
We re-examine critically the estimates of the duration of different phases of
star formation and the lifetimes of molecular clouds, based on the ages of
T-Tauri stars, age spreads of stars in clusters, and statistics of pre-stellar
cores. We show that all available observational data are consistent with
lifetimes of molecular clouds comparable to 10 Myr, as well as with the
predictions of the theory of self-initiated, ambipolar-diffusion--controlled
star formation. We conclude that there exists no observational support for
either "young" molecular clouds or "rapid" star formation.Comment: Accepted for publication in the Astrophysical Journal. 5 pages, 4
figures, uses emulateapj.cl
Renormalization Group Improved Exponentiation of Soft Gluons in QCD
We extend the methods of Yennie, Frautschi and Suura to QCD for the summation
of soft gluon effects in which infrared singularities are cancelled to all
orders in . An explicit formula for the respective \rngp improved
exponentiated cross section is obtained for q+\bbar{{q'}}\to q+\bbar{{q'}}+
n(G) at SSC energies. Possible applications are discussed.Comment: 7 pages (1 figure not included, available on request) LATEX,
UTHEP-93-040
Can fully automated detection of corticospinal tract damage be used in stroke patients?
We compared manual infarct definition, which is time-consuming and open to bias, with an automated abnormal tissue detection method in measuring corticospinal tract-infarct overlap volumes in chronic stroke patients to help predict motor outcome
Multiple photon effects in scattering at SSC energies
The Monte Carlo program SSCYFS2 is used in conjunction with available parton
distribution functions to calculate the effects of multiple photon radiation on
pp scattering at SSC energies. Effects relevant to precision SSC physics such
as Higgs discovery and exploration are illustrated.Comment: LaTeX file, uses phyzzx, 7pp + 5 LaTeX figure
Multiple Gluon Effects in at FNAL Energies: Semi-Analytical Results
We apply our Yennie-Frautschi-Suura exponentiated cross section formulas for
the parton processes q + {^(} \bar q {^)}{^\prime} \ra q{^\prime}{^\prime} +
{^(} \bar q {^)}{^\prime}{^\prime}{^\prime} + n(G) to the process q + \bar q
\ra t + \bar t + n(G) at FNAL energies, where G is a QCD gluon. We use
semi-analytical methods to compute the ratio ,
where is our soft gluon YFS exponentiated cross section and
is the Born cross section. For TeV, we get
, respectively, for for example. These results are
not inconsistent with the recent observations by CDF and D0.Comment: 6 pages, latex replaces postscript at archiver's reques
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