98 research outputs found
Oxygen ion energization by waves in the high altitude cusp and mantle
We present a comparative study of low frequency electric field spectral
densities and temperatures observed by the Cluster spacecraft in the high
altitude cusp/mantle region. We compare the relation between the O+
temperature and wave intensity at the oxygen gyrofrequency at each
measurement point and find a clear correlation. The trend of the correlation
agrees with the predictions by both an asymptotic mean-particle theory and a
test-particle approach. The perpendicular to parallel temperature ratio is
also consistent with the predictions of the asymptotic mean-particle theory.
At times the perpendicular temperature is significantly higher than predicted
by the models. A simple study of the evolution of the particle distributions
(conics) at these altitudes indicates that enhanced perpendicular
temperatures would be observed over many RE after heating ceases.
Therefore, sporadic intense heating is the likely explanation for cases with
high temperature and comparably low wave activity. We observe waves of
sufficient amplitude to explain the highest observed temperatures, while the
theory in general overestimates the temperature associated with the highest
observed wave activity, indicating that such high wave activity is very
sporadic
O<sup>+</sup> transport in the dayside magnetosheath and its dependence on the IMF direction
Recent studies have shown that the escape of oxygen ions (O+) into the
magnetosheath along open magnetic field lines from the terrestrial cusp and
mantle is significant. We present a study of how O+ transport in the
dayside magnetosheath depends on the interplanetary magnetic field (IMF)
direction. There are clear asymmetries in the O+ flows for southward and
northward IMF. The asymmetries can be understood in terms of the different
magnetic topologies that arise due to differences in the location of the
reconnection site, which depends on the IMF direction. During southward IMF,
most of the observed magnetosheath O+ is transported downstream. In
contrast, for northward IMF we observe O+ flowing both downstream and
equatorward towards the opposite hemisphere. We observe evidence of dual-lobe
reconnection occasionally taking place during strong northward IMF
conditions, a mechanism that may trap O+ and bring it back into the
magnetosphere. Its effect on the overall escape is however small: we estimate
the upper limit of trapped O+ to be 5%, a small number considering that
ion flux calculations are rough estimates. The total O+ escape flux is
higher by about a factor of 2 during times of southward IMF, in agreement
with earlier studies of O+ cusp outflow
From InSb Nanowires to Nanocubes: Looking for the Sweet Spot
High aspect ratios are highly desired to fully exploit the one-dimensional properties of indium antimonide nanowires. Here we systematically investigate the growth mechanisms and find parameters leading to long and thin nanowires. Variation of the V/III ratio and the nanowire density are found to have the same influence on the “local” growth conditions and can control the InSb shape from thin nanowires to nanocubes. We propose that the V/III ratio controls the droplet composition and the radial growth rate and these parameters determine the nanowire shape. A sweet spot is found for nanowire interdistances around 500 nm leading to aspect ratios up to 35. High electron mobilities up to 3.5 × 10^4 cm^2 V^(–1) s^(–1) enable the realization of complex spintronic and topological devices
Acute HCV in a cohort of HIVB-positive men - Outcomes and response to pegylated interferon-alpha 2b and ribavirin
The 55th Annual Meeting of the American Association for the Study of Liver Diseases, Boston, Massachusetts, USA, 29 October-November, 2004. In Hepatology, 2004, v. 40 n. suppl. 1, p. 327A, abstract no. 37
O<sup>+</sup> transport in the dayside magnetosheath and its dependence on the IMF direction
Recent studies have shown that the escape of oxygen ions (O<sup>+</sup>) into the
magnetosheath along open magnetic field lines from the terrestrial cusp and
mantle is significant. We present a study of how O<sup>+</sup> transport in the
dayside magnetosheath depends on the interplanetary magnetic field (IMF)
direction. There are clear asymmetries in the O<sup>+</sup> flows for southward and
northward IMF. The asymmetries can be understood in terms of the different
magnetic topologies that arise due to differences in the location of the
reconnection site, which depends on the IMF direction. During southward IMF,
most of the observed magnetosheath O<sup>+</sup> is transported downstream. In
contrast, for northward IMF we observe O<sup>+</sup> flowing both downstream and
equatorward towards the opposite hemisphere. We observe evidence of dual-lobe
reconnection occasionally taking place during strong northward IMF
conditions, a mechanism that may trap O<sup>+</sup> and bring it back into the
magnetosphere. Its effect on the overall escape is however small: we estimate
the upper limit of trapped O<sup>+</sup> to be 5%, a small number considering that
ion flux calculations are rough estimates. The total O<sup>+</sup> escape flux is
higher by about a factor of 2 during times of southward IMF, in agreement
with earlier studies of O<sup>+</sup> cusp outflow
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