6,003 research outputs found
The pion parton distribution function in the valence region
The parton distribution function of the pion in the valence region is
extracted in a next-to-leading order analysis from Fermilab E-615 pionic
Drell-Yan data. The effects of the parameterization of the pion's valence
distributions are examined. Modern nucleon parton distributions and nuclear
corrections were used and possible effects from higher twist contributions were
considered in the analysis. In the next-to-leading order analysis, the high-
dependence of the pion structure function differs from that of the leading
order analysis, but not enough to agree with the expectations of pQCD and
Dyson-Schwinger calculations.Comment: 5 pages, 4 figures, submitted to Phys. Rev.
Marine reservoir corrections : St. Helena, South Atlantic Ocean
We present the first marine reservoir age and âR determination for the island of St. Helena using marine mollusk radiocarbon dates obtained from an historical context of known age. This represents the first marine reservoir age and âR determination in the southern Atlantic Ocean within thousands of kilometers of the island. The depletion of 14C in the shells indicates a rather larger reservoir age for that portion of the surface Atlantic than models indicate. The implication is that upwelling old water along the Namibian coast is transported for a considerable distance, although it is likely to be variable on a decadal timescale. An artillerymanâs button, together with other artifacts found in a midden, demonstrate association of the mollusk shells with a narrow historic period of AD 1815â1835
Electron-beam-induced shift in the apparent position of a pinned vortex in a thin superconducting film
When an electron beam strikes a superconducting thin film near a pinned
vortex, it locally increases the temperature-dependent London penetration depth
and perturbs the circulating supercurrent, thereby distorting the vortex's
magnetic field toward the heated spot. This phenomenon has been used to
visualize vortices pinned in SQUIDs using low-temperature scanning electron
microscopy. In this paper I develop a quantitative theory to calculate the
displacement of the vortex-generated magnetic-flux distribution as a function
of the distance of the beam spot from the vortex core. The results are
calculated using four different models for the spatial distribution of the
thermal power deposited by the electron beam.Comment: 9 pages, 6 figures, resubmitted to PRB with referee-suggested
revisions, includes new paragraph on numerical evaluatio
Chasing the second gamma-ray bright isolated neutron star: 3EG J1835+5918/RX J1836.2+5925
The EGRET telescope aboard NASAs Compton GRO has repeatedly detected 3EG
J1835+5918, a bright and steady source of high-energy gamma-ray emission with
no identification suggested until recently. The long absence of any likely
counterpart for a bright gamma-ray source located 25 degrees off the Galactic
plane initiated several attempts of deep observations at other wavelengths. We
report on counterparts in X-rays on a basis of a 60 ksec ROSAT HRI image. In
order to conclude on the plausibility of the X-ray counterparts, we reanalyzed
data from EGRET at energies above 100 MeV and above 1 GeV, including data up to
CGRO observation cycle 7. The gamma-ray source location represents the latest
and probably the final positional assessment based on EGRET data. The X-ray
counterparts were studied during follow-up optical identification campaigns,
leaving only one object to be likely associated with the gamma-ray source 3EG
J1835+5918. This object, RX J1836.2+5925, has the characteristics of an
isolated neutron star and possibly of a radio-quiet pulsar.Comment: 5 pages, 3 figures. To appear in the Proceedings of the 270.
WE-Heraeus Seminar on Neutron Stars, Pulsars and Supernova Remnants, Jan.
21-25, 2002, Physikzentrum Bad Honnef, eds W. Becker, H. Lesch & J. Truemper.
Proceedings are available as MPE-Report 27
Non-thermal high-energy emission from colliding winds of massive stars
Colliding winds of massive star binary systems are considered as potential
sites of non-thermal high-energy photon production. This is motivated merely by
the detection of synchrotron radio emission from the expected colliding wind
location. Here we investigate the properties of high-energy photon production
in colliding winds of long-period WR+OB-systems. We found that in the
dominating leptonic radiation process anisotropy and Klein-Nishina effects may
yield spectral and variability signatures in the gamma-ray domain at or above
the sensitivity of current or upcoming gamma-ray telescopes. Analytical
formulae for the steady-state particle spectra are derived assuming diffusive
particle acceleration out of a pool of thermal wind particles, and taking into
account adiabatic and all relevant radiative losses. For the first time we
include their advection/convection in the wind collision zone, and distinguish
two regions within this extended region: the acceleration region where spatial
diffusion is superior to convective/advective motion, and the convection region
defined by the convection time shorter than the diffusion time scale. The
calculation of the Inverse Compton radiation uses the full Klein-Nishina cross
section, and takes into account the anisotropic nature of the scattering
process. This leads to orbital flux variations by up to several orders of
magnitude which may, however, be blurred by the geometry of the system. The
calculations are applied to the typical WR+OB-systems WR 140 and WR 147 to
yield predictions of their expected spectral and temporal characteristica and
to evaluate chances to detect high-energy emission with the current and
upcoming gamma-ray experiments. (abridged)Comment: 67 pages, 24 figures, submitted to Ap
Serving Innovation in Scholarly Communication with the Open Platform âDigital Peer Publishing"
The internet causes a continuous emergence of novel forms of scholarly communication and collaboration. Electronic publishing provides a means for representing eventual outcomes of these processes, i.e. all types of content such as papers and advanced forms of media. Electronic journals are often chosen as an adequate publishing format because they simultaneously deliver content in a well-known manner but, at the same time, allow extending traditional publishing with innovative features. The initiative Digital Peer Publishing (DiPP) provides technological, organizational and legal frameworks and tools that help to incubate and proliferate such innovative publishing projects. The hosting platform reflects principles of a Service Oriented Architecture. It combines, via Web Services, already established components such as an OAI repository (Fedora) and a Web Content Management System (Plone) with customized workflows for document processing, conversion and distribution. As an open platform it is capable of integrating external tools and services or acts itself as a service provider. It is therefore disposed for supplementing research infrastructures with electronic publishing
Tuning the exciton g-factor in single InAs/InP quantum dots
Photoluminescence data from single, self-assembled InAs/InP quantum dots in
magnetic fields up to 7 T are presented. Exciton g-factors are obtained for
dots of varying height, corresponding to ground state emission energies ranging
from 780 meV to 1100 meV. A monotonic increase of the g-factor from -2 to +1.2
is observed as the dot height decreases. The trend is well reproduced by sp3
tight binding calculations, which show that the hole g-factor is sensitive to
confinement effects through orbital angular momentum mixing between the
light-hole and heavy-hole valence bands. We demonstrate tunability of the
exciton g-factor by manipulating the quantum dot dimensions using pyramidal InP
nanotemplates
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