15,205 research outputs found
The 1973-1984 Solar Modulation of Cosmic Ray Nuclei
As a continuation of the program of solar modulation studies, new measurements were carried out with the cosmic ray telescope on the Earth satellite IMP-8, of the intensity time variations and the energy spectra of galactic cosmic ray protons, helium, carbon and oxygen from 1980 through 1984 including the recent solar maximum. In order to test the applicability of a steady state model of solar modulation during a period which includes times of rapidly changing modulation, these fluxes were equated with the predictions of a conventional model of solar modulation which assumes equilibrium between modulation mechanisms. It is found that for a reasonable range of variations of the diffusion coefficient the model predictions can be made to agree with the measurements at essentially all times during the studied period. The model can account also for the observed hysteresis effects between cosmic rays of different rigidities
The high-pressure behavior of CaMoO4
We report a high-pressure study of tetragonal scheelite-type CaMoO4 up to 29
GPa. In order to characterize its high-pressure behavior, we have combined
Raman and optical-absorption measurements with density-functional theory
calculations. We have found evidence of a pressure-induced phase transition
near 15 GPa. Experiments and calculations agree in assigning the high-pressure
phase to a monoclinic fergusonite-type structure. The reported results are
consistent with previous powder x-ray-diffraction experiments, but are in
contradiction with the conclusions obtained from earlier Raman measurements,
which support the existence of more than one phase transition in the pressure
range covered by our studies. The observed scheelite-fergusonite transition
induces significant changes in the electronic band gap and phonon spectrum of
CaMoO4. We have determined the pressure evolution of the band gap for the low-
and high-pressure phases as well as the frequencies and pressure dependences of
the Raman-active and infrared-active modes. In addition, based upon
calculations of the phonon dispersion of the scheelite phase, carried out at a
pressure higher than the transition pressure, we propose a possible mechanism
for the reported phase transition. Furthermore, from the calculations we
determined the pressure dependence of the unit-cell parameters and atomic
positions of the different phases and their room-temperature equations of
state. These results are compared with previous experiments showing a very good
agreement. Finally, information on bond compressibility is reported and
correlated with the macroscopic compressibility of CaMoO4. The reported results
are of interest for the many technological applications of this oxide.Comment: 36 pages, 10 figures, 8 table
On the Gromov-Witten invariants of the moduli of bundles on a surface.
Depto. de Ălgebra, GeometrĂa y TopologĂaFac. de Ciencias MatemĂĄticasTRUEpu
Gluino signals in 4jet events and vertex tagging at LEP1
Heavy flavour tagging provides a broad range of possibilities in testing QCD
features at LEP. We present here a study of 4jets events at LEP I where the
so-called light gluinos could be directly produced. We show that microvertex
techniques offer a unique chance to exploit simple kinematical distributions in
order to optimise the signal coming from gluino production with respect to the
background of ordinary QCD events. Our results indicate that experimental
analyses along the lines suggested here can exclude or reveal the presence of a
gluino for masses up to 10 GeV and lifetimes below 10 sec. We also point
out that a large fraction of gluino events could decay in configurations
carrying large missing energy, so to escape the usual selection criteria of
4jet samples. In our study, mass effects of quarks and gluinos have been taken
into account exactly. Our results are independent from both the jet algorithm
and its resolution parameter.}Comment: 28 pages, 9 figures embedded with epsfig, Latex. Major revision
taking into account latest bounds. Version to appear in Zeit. f. Phys.
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