45,799 research outputs found
Southwest Research Institute assistance to NASA in biomedical areas of the technology utilization program Cumulative quarterly report, 1 Oct. 1967 - 31 Mar. 1968
Quarterly operations summary of center for selective dissemination of biomedical information within Technology Utilization progra
Production of a Prompt Photon in Association with Charm at Next-to-Leading Order in QCD
A second order, , calculation in perturbative quantum
chromodynamics of the two particle inclusive cross section is presented for the
reaction for large values of the
transverse momentum of the prompt photon and charm quark. The combination of
analytic and Monte Carlo integration methods used here to perform phase-space
integrations facilitates imposition of photon isolation restrictions and other
selections of relevance in experiments. Differential distributions are provided
for various observables. Positive correlations in rapidity are predicted.Comment: 27 pages in RevTex plus 14 figures in one compressed PS fil
Spitzer Observations of Gamma-Ray Burst Host Galaxies: A Unique Window into High Redshift Chemical Evolution and Star-formation
We present deep Spitzer 3.6 micron observations of three z~5 GRB host
galaxies. Our observations reveal that z~5 GRB hosts are a factor of 3 less
luminous than the median rest-frame V-band luminosity of spectroscopically
confirmed z~5 galaxies in the GOODS fields and the UDF. The strong connection
between GRBs and massive star formation implies that not all star-forming
galaxies at these redshifts are currently being accounted for in deep surveys
and GRBs provide a unique way to measure the contribution to the star-formation
rate density from galaxies at the faint end of the galaxy luminosity function.
By correlating the co-moving star-formation rate density with co-moving GRB
rates at lower redshifts, we estimate a lower limit to the star-formation rate
density of 0.12+/-0.09 and 0.09+/-0.05 M_sun/yr/Mpc^3 at z~4.5 and z~6,
respectively. Finally, we provide evidence that the average metallicity of
star-forming galaxies evolves as (stellar mass density)^(0.69+/-0.17) between
and , probably indicative of the loss of a significant
fraction of metals to the intergalactic medium, particularly in low-mass
galaxies.Comment: ApJ, in pres
CP Violation and Arrows of Time Evolution of a Neutral or Meson from an Incoherent to a Coherent State
We study the evolution of a neutral meson prepared as an incoherent equal
mixture of and . Denoting the density matrix by \rho(t) =
{1/2} N(t) [\1 + \vec{\zeta}(t) \cdot \vec{\sigma} ] , the norm of the state
is found to decrease monotonically from one to zero, while the magnitude
of the Stokes vector increases monotonically from zero to
one. This property qualifies these observables as arrows of time. Requiring
monotonic behaviour of for arbitrary values of and
yields a bound on the CP-violating overlap , which is similar to, but weaker than, the known unitarity
bound. A similar requirement on yields a new bound,
which is particularly effective in limiting
the CP-violating overlap in the - system. We obtain the Stokes
parameter which shows how the average strangeness of the beam
evolves from zero to . The evolution of the Stokes vector from
to has a resemblance to an order
parameter of a system undergoing spontaneous symmetry breaking.Comment: 13 pages, 6 figures. Inserted conon "." in title; minor change in
text. To appear in Physical review
Southwest Research Institute assistance to NASA in biomedical areas of the technology utilization program Quarterly progress report, 1 Jul. - 30 Sep. 1968
Southwest Research Institute activites in NASA technology utilization program for biomedical use, 1 Jul. - 30 Sep. 196
Southwest Research Institute assistance to NASA in biomedical areas of the technology utilization program Cumulative quarterly report, 1 Apr. - 30 Jun. 1968
Biomedical applications of NASA science and technolog
325 MHz VLA Observations of Ultracool Dwarfs TVLM 513-46546 and 2MASS J0036+1821104
We present 325 MHz (90 cm wavelength) radio observations of ultracool dwarfs
TVLM 513-46546 and 2MASS J0036+1821104 using the Very Large Array (VLA) in June
2007. Ultracool dwarfs are expected to be undetectable at radio frequencies,
yet observations at 8.5 GHz (3.5 cm) and 4.9 GHz (6 cm) of have revealed
sources with > 100 {\mu}Jy quiescent radio flux and > 1 mJy pulses coincident
with stellar rotation. The anomalous emission is likely a combination of
gyrosynchrotron and cyclotron maser processes in a long-duration, large-scale
magnetic field. Since the characteristic frequency for each process scales
directly with the magnetic field magnitude, emission at lower frequencies may
be detectable from regions with weaker field strength. We detect no significant
radio emission at 325 MHz from TVLM 513-46546 or 2MASS J0036+1821104 over
multiple stellar rotations, establishing 2.5{\sigma} total flux limits of 795
{\mu}Jy and 942 {\mu}Jy respectively. Analysis of an archival VLA 1.4 GHz
observation of 2MASS J0036+1821104 from January 2005 also yields a
non-detection at the level of < 130 {\mu}Jy . The combined radio observation
history (0.3 GHz to 8.5 GHz) for these sources suggests a continuum emission
spectrum for ultracool dwarfs which is either flat or inverted below 2-3 GHz.
Further, if the cyclotron maser instability is responsible for the pulsed radio
emission observed on some ultracool dwarfs, our low-frequency non-detections
suggest that the active region responsible for the high-frequency bursts is
confined within 2 stellar radii and driven by electron beams with energies less
than 5 keV.Comment: 11 pages, 5 figures, submitted to A
Spin Dependence of Massive Lepton Pair Production in Proton-Proton Collisions
We calculate the transverse momentum distribution for the production of
massive lepton-pairs in longitudinally polarized proton-proton reactions at
collider energies within the context of perturbative quantum chromodynamics.
For values of the transverse momentum Q_T greater than roughly half the pair
mass Q, Q_T > Q/2, we show that the differential cross section is dominated by
subprocesses initiated by incident gluons, provided that the polarized gluon
density is not too small. Massive lepton-pair differential cross sections
should be a good source of independent constraints on the polarized gluon
density, free from the experimental and theoretical complications of photon
isolation that beset studies of prompt photon production. We provide
predictions for the spin-averaged and spin-dependent differential cross
sections as a function of Q_T at energies relevant for the Relativistic Heavy
Ion Collider (RHIC) at Brookhaven, and we compare these with predictions for
real prompt photon production.Comment: 34 pages, RevTeX including 17 figures in .ps file
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