6,245 research outputs found
TeV gamma rays and cosmic rays from the nucleus of M87, a mis-aligned BL Lac object
The unresolved nuclear region of M87 emits strong non-thermal emission from
radio to X-rays. Assuming this emission to originate in the pc scale jet
aligned at to the line of sight, we interpret this
emission in the context of the Synchrotron Proton Blazar (SPB) model. We find
the observed nuclear jet emission to be consistent with M87 being a mis-aligned
BL Lac Object and predict gamma-ray emission extending up to at least 100 GeV
at a level easily detectable by GLAST and MAGIC, and possibly by VERITAS
depending on whether it is high-frequency or low-frequency peaked. Predicted
neutrino emission is below the sensitivity of existing and planned neutrino
telescopes. Ultra-high energy neutrons produced in pion photoproduction
interactions decay into protons after escaping from the host galaxy. Because
energetic protons are deflected by the intergalactic magnetic field, the
protons from the decay of neutrons emitted in all directions, including along
the jet axis where the Doppler factor and hence emitted neutron energies are
higher, can contribute to the observed ultra-high energy cosmic rays. We
consider the propagation of these cosmic ray protons to Earth and conclude that
M87 could account for the observed flux if the extragalactic magnetic field
topology were favourable.Comment: 17 pages, 6 figures. 3 additional references plus minor changes,
acctepted for publication in Astroparticle Physic
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.
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
Marine reservoir corrections : St. Helena, South Atlantic Ocean
We present the first marine reservoir age and ∆R 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 ∆R 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 artilleryman’s button, together with other artifacts found in a midden, demonstrate association of the mollusk shells with a narrow historic period of AD 1815–1835
Who Should be Interviewed in Surveys of Household Income?
This study tests the null hypothesis that it is sufficient to interview only the household head to obtain accurate information on household income. Results show that using a husband’s estimate of his wife’s income does not produce statistically reliable results for poverty analysis. Estimates of the wife’s income provided by the husband and wife are in agreement in only six percent of households. While limiting interviews to one person has the advantage of reducing the time and expense of household surveys, this appears detrimental in terms of accuracy, and may lead to incorrect conclusions on the determinants of poverty.Africa, gender, household dynamics, household surveys, Malawi, poverty, Agricultural Finance,
Formation of Atomic Carbon Chains from Graphene Nanoribbons
The formation of one-dimensional carbon chains from graphene nanoribbons is
investigated using it ab initio molecular dynamics. We show under what
conditions it is possible to obtain a linear atomic chain via pulling of the
graphene nanoribbons. The presence of dimers composed of two-coordinated carbon
atoms at the edge of the ribbons is necessary for the formation of the linear
chains, otherwise there is simply the full rupture of the structure. The
presence of Stone-Wales defects close to these dimers may lead to the formation
of longer chains. The local atomic configuration of the suspended atoms
indicates the formation of single and triple bonds, which is a characteristic
of polyynes.Comment: 4 pages, 5 figure
Some Thoughts about the Conservation of Scanning Electron Microscopic Preparations of Diatoms in a Museum Repository
The Scanning electron microscope (SEM) is now an indispensable tool for the study and the description of diatoms. Many new species have been described from SEM preparations and problems now arise with the preservation of designated types and other comparative material. Moisture contributes to the deterioration of diatom stubs. Special care must be taken to store stubs in vacuum desiccators in order to keep heavy metal coatings from peeling from the siliceous surfaces of diatoms. One alternative is to mount the designated type on a coverglass so that it can be inverted, mounted in Hyrax and preserved indefinitely for light microscopic observation. It is recommended that additional prepared slides and dried material be deposited in a museum repository, along with the designated type, so that it may be used for future SEM study
Preliminary results of fast neutron treatments in carcinoma of the pancreas
A group of 30 patients with adenocarcinoma of the pancreas including some patients with very advanced disease, were treated with the so-called mixed beam modality employing photon treatments three times per week and neutron treatments twice a week. Two hundred Rads or equivalent Rads (RBE 3.3) were given in daily fractions aiming at a total dose of 6000 Rads in 6 to 8 weeks. The treatments were well tolerated and significant palliation was achieved in 26 to 30 cases. Twelve months survival was 33 percent with a median survival of 7 months or 210 days. Treatment techniques and localization procedures are discussed
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
SHCal13 Southern Hemisphere calibration, 0–50,000 years cal BP
The Southern Hemisphere SHCal04 radiocarbon calibration curve has been updated with the addition of new data sets extending measurements to 2145 cal BP and including the ANSTO Younger Dryas Huon pine data set. Outside the range of measured data, the curve is based upon the Northern Hemisphere data sets as presented in IntCal13, with an interhemispheric offset averaging 43 ± 23 yr modeled by an autoregressive process to represent the short-term correlations in the offset
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