1,077 research outputs found
Enhancement of solar heavy nuclei at high energies in the 4 July 1974 event
Relative abundances of energetic nuclei in the 4 July 1974 solar event are presented. The results show a marked enhancement of abundances that systematically increase with nuclear charge numbers in the range of the observation, 6 less than or equal to Z less than or equal to 26 for energies above 15 MeV/nucleon. While such enhancements are commonly seen below 10 MeV/nucleon, most observations at higher energies are found to be consistent with solar system abundances. The energy spectrum of oxygen is observed to be significantly steeper than most other solar events studied in this energy region. It is proposed that these observations are characteristic of particle populations at energies approximately 1 MeV/nucleon, and that the anomalous features observed here may be the result of the high energy extension of such a population that is commonly masked by other processes or populations that might occur in larger solar events
Calibration of a gamma-ray telescope using tagged position annihilation photons
Measurements of detection efficiency, angular resolution, and energy resolution properties of a gamma ray telescope used to study celestial gamma rays from balloon flight altitudes are described. Nearly monochromatic photons produced at the National Bureau of Standards tagged photon facility were used for the calibration. Details of the photon beam configuration and properties and results of the measurements made at photon energies of 15.1 and 31.1 MeV are presented. Finally, the data are compared with a Monte Carlo analysis of the instrument properties
Nuclear composition and energy spectra in the 12 April 1969 solar particle event
Nuclear composition for several multicharged nuclei and energy spectra for hydrogen, helium, and medium nuclei measured in solar particle even
Searches for gamma ray emission from radio pulsars
Searches were made for pulsed high energy (E 35 MeV) gamma radiation from 43 pulsars using the SAS-2 data base and radio parameters. No positive results were found, and the upper limits are consistent with the concept that gamma ray production efficiency increases with increasing apparent age. Two limits suggest that efficiency cannot be a simple function of apparent age beyond 10,000,000 years
Conductance of a single-atom carbon chain with graphene leads
We study the conductance of an interconnect between two graphene leads formed
by a single-atom carbon chain. Its dependence on the chemical potential and the
number of atoms in the chain is qualitatively different from that in the case
of normal metal leads. Electron transport proceeds via narrow resonant states
in the wire. The latter arise due to strong reflection at the junctions between
the chain and the leads, which is caused by the small density of states in the
leads at low energy. The energy dependence of the transmission coefficient near
resonance is asymmetric and acquires a universal form at small energies. We
find that in the case of leads with the zigzag edges the dispersion of the edge
states has a significant effect on the device conductance.Comment: 9 pages, 4 figure
Coupling of hydrodynamics and quasiparticle motion in collective modes of superfluid trapped Fermi gases
At finite temperature, the hydrodynamic collective modes of superfluid
trapped Fermi gases are coupled to the motion of the normal component, which in
the BCS limit behaves like a collisionless normal Fermi gas. The coupling
between the superfluid and the normal components is treated in the framework of
a semiclassical transport theory for the quasiparticle distribution function,
combined with a hydrodynamic equation for the collective motion of the
superfluid component. We develop a numerical test-particle method for solving
these equations in the linear response regime. As a first application we study
the temperature dependence of the collective quadrupole mode of a Fermi gas in
a spherical trap. The coupling between the superfluid collective motion and the
quasiparticles leads to a rather strong damping of the hydrodynamic mode
already at very low temperatures. At higher temperatures the spectrum has a
two-peak structure, the second peak corresponding to the quadrupole mode in the
normal phase.Comment: 14 pages; v2: major changes (effect of Hartree field included
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