628 research outputs found
The interaction between transpolar arcs and cusp spots
Transpolar arcs and cusp spots are both auroral phenomena which occur when the interplanetary magnetic field is northward. Transpolar arcs are associated with magnetic reconnection in the magnetotail, which closes magnetic flux and results in a âwedgeâ of closed flux which remains trapped, embedded in the magnetotail lobe. The cusp spot is an indicator of lobe reconnection at the high-latitude magnetopause; in its simplest case, lobe reconnection redistributes open flux without resulting in any net change in the open flux content of the magnetosphere. We present observations of the two phenomena interactingâi.e., a transpolar arc intersecting a cusp spot during part of its lifetime. The significance of this observation is that lobe reconnection can have the effect of opening closed magnetotail flux. We argue that such events should not be rare
Among once-daily regimens, single tablet regimens (STRs) are associated with better adherence
Previous published evidences showed that taking HAART once-daily (OD) is associated to better adherence when compared to BID or TID regimens. However, no further studies investigated whether, among OD regimens, adherence levels can be differently influenced. Aim of the study was to evaluate levels of self-reported adherence in HIV+ people according to type of HAART dosing (STR, OD with more than one pill or BID). To limit reporting biases, the study was performed in five different non-clinic settings covering North and Central Italy. A total of 230 patients on stable HAART were asked to complete a semi-structured, anonymous questionnaire reporting their attitude toward HAART, their adherence and the acceptability of their regimen. Self-perception of adherence was also investigated with a single item for comparison with real adherence behavior. Most of the subjects were males (66%) with a mean age of 46 years, with higher education level (72%) and a long history of HIV infection (mean 13.6 years). 17% of patients were on a first-line regimen. 21% reported to miss at least one dose during the past week (STR: 6%; OD >1 pill 23% and BID 21%; p<0.05). People taking STR and BID tend to report less discontinuations (all the drug of the day for at least 3 times in a month) compared to OD>1 pill (6 and 4% vs 11%). People taking therapies other than HAART reported similar adherence levels of people taking only HAART, even when stratified for dosing groups. Even people judging their adherence as ‘optimal’ or ‘very good’, 10 and 17% respectively, reported having missed a dose during the last week. At stepwise regression model, optimal adherence was correlated to being male (OR: 2.38; 95% CI: 1.19–4.74), younger (OR: 3.04; 95% CI: 1.01–9.13) and with a shorter HIV infection (OR: 3.58; 95% CI: 1.04–12.38). People taking simpler once-daily STR tend to report better adherence than people taking OD>1 pill or BID. Perception of optimal adherence is largely variable among HIV-infected people taking HAART, although only a minority of subjects showing less than perfect adherence do judge their behavior as ‘optimal’
The interaction between transpolar arcs and cusp spots
Transpolar arcs and cusp spots are both auroral phenomena which occur when
the interplanetary magnetic field is northward. Transpolar arcs are associated
with magnetic reconnection in the magnetotail, which closes magnetic flux and
results in a "wedge" of closed flux which remains trapped, embedded in the
magnetotail lobe. The cusp spot is an indicator of lobe reconnection at the
high-latitude magnetopause; in its simplest case, lobe reconnection
redistributes open flux without resulting in any net change in the open flux
content of the magnetosphere. We present observations of the two phenomena
interacting--i.e., a transpolar arc intersecting a cusp spot during part of its
lifetime. The significance of this observation is that lobe reconnection can
have the effect of opening closed magnetotail flux. We argue that such events
should not be rare
Origin of molecular oxygen in Comet 67P/Churyumov-Gerasimenko
Molecular oxygen has been detected in the coma of comet
67P/Churyumov-Gerasimenko with abundances in the 1-10% range by the ROSINA-DFMS
instrument on board the Rosetta spacecraft. Here we find that the radiolysis of
icy grains in low-density environments such as the presolar cloud may induce
the production of large amounts of molecular oxygen. We also show that
molecular oxygen can be efficiently trapped in clathrates formed in the
protosolar nebula, and that its incorporation as crystalline ice is highly
implausible because this would imply much larger abundances of Ar and N2 than
those observed in the coma. Assuming that radiolysis has been the only O2
production mechanism at work, we conclude that the formation of comet
67P/Churyumov-Gerasimenko is possible in a dense and early protosolar nebula in
the framework of two extreme scenarios: (1) agglomeration from pristine
amorphous icy grains/particles formed in ISM and (2) agglomeration from
clathrates that formed during the disk's cooling. The former scenario is found
consistent with the strong correlation between O2 and H2O observed in 67P/C-G's
coma while the latter scenario requires that clathrates formed from ISM icy
grains that crystallized when entering the protosolar nebula.Comment: The Astrophysical Journal Letters, in pres
Polar cap arcs from the magnetosphere to the ionosphere: kinetic modelling and observations by Cluster and TIMED
On 1 April 2004 the GUVI imager onboard the TIMED spacecraft spots an
isolated and elongated polar cap arc. About 20 min later, the Cluster
satellites detect an isolated upflowing ion beam above the polar cap.
Cluster observations show that the ions are accelerated upward by a
quasi-stationary electric field. The field-aligned potential drop is
estimated to about 700 V and the upflowing ions are accompanied by a tenuous
population of isotropic protons with a temperature of about 500 eV.
<br><br>
The magnetic footpoints of the ion outflows observed by Cluster are situated
in the prolongation of the polar cap arc observed by TIMED GUVI. The
upflowing ion beam and the polar cap arc may be different signatures of the
same phenomenon, as suggested by a recent statistical study of polar cap ion
beams using Cluster data.
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We use Cluster observations at high altitude as input to a quasi-stationary
magnetosphere-ionosphere (MI) coupling model. Using a Knight-type
current-voltage relationship and the current continuity at the topside
ionosphere, the model computes the energy spectrum of precipitating
electrons at the top of the ionosphere corresponding to the generator
electric field observed by Cluster. The MI coupling model provides a
field-aligned potential drop in agreement with Cluster observations of
upflowing ions and a spatial scale of the polar cap arc consistent with the
optical observations by TIMED. The computed energy spectrum of the
precipitating electrons is used as input to the Trans4 ionospheric transport
code. This 1-D model, based on Boltzmann's kinetic formalism, takes into
account ionospheric processes such as photoionization and electron/proton
precipitation, and computes the optical and UV emissions due to
precipitating electrons. The emission rates provided by the Trans4 code are
compared to the optical observations by TIMED. They are similar in size and
intensity. Data and modelling results are consistent with the scenario of
quasi-static acceleration of electrons that generate a polar cap arc as they
precipitate in the ionosphere. The detailed observations of the acceleration
region by Cluster and the large scale image of the polar cap arc provided by
TIMED are two different features of the same phenomenon. Combined together,
they bring new light on the configuration of the high-latitude magnetosphere
during prolonged periods of Northward IMF. Possible implications of the
modelling results for optical observations of polar cap arcs are also
discussed
A multi-satellite study of accelerated ionospheric ion beams above the polar cap
This paper presents a study of nearly field-aligned outflowing ion beams observed on the Cluster satellites over the polar cap. Data are taken at geocentric radial distances of the order of 5&ndash;9 <i>R<sub>E</sub></i>. The distinction is made between ion beams originating from the polar cusp/cleft and beams accelerated almost along the magnetic field line passing by the spacecraft. Polar cusp beams are characterized by nearly field-aligned proton and oxygen ions with an energy ratio E<sub>O+</sub> / E<sub>H+</sub>, of the order of 3 to 4, due to the ion energy repartition inside the source and to the latitudinal extension of the source. Rapid variations in the outflowing ion energy are linked with pulses/modifications of the convection electric field. Cluster data allow one to show that these perturbations of the convection velocity and the associated ion structures propagate at the convection velocity. <P style="line-height: 20px;"> In contrast, polar cap local ion beams are characterized by field-aligned proton and oxygen ions with similar energies. These beams show the typical inverted V structures usually observed in the auroral zone and are associated with a quasi-static converging electric field indicative of a field-aligned electric field. The field-aligned potential drop fits well the ion energy profile. The simultaneous observation of precipitating electrons and upflowing ions of similar energies at the Cluster orbit indicates that the spacecraft are crossing the mid-altitude part of the acceleration region. In the polar cap, the parallel electric field can thus extend to altitudes higher than 5&nbsp;Earth radii. A detailed analysis of the distribution functions shows that the ions are heated during their parallel acceleration and that energy is exchanged between H<sup>+</sup> and O<sup>+</sup>. Furthermore, intense electrostatic waves are observed simultaneously. These observations could be due to an ion-ion two-stream instability
Faire lâUnion. La refondation des parties de droite aprĂšs les Ă©lections de 2002
Un nouveau parti de droite, pour le moment dénommé UMP, a été mis en place entre des deux tours de
l'élection présidentielle. Cet article se donne pour objectif d'analyser les enjeux de cette transformation.
La genĂšse de l'UMP permet de saisir dans quelle mesure un parti poli-tique peut ĂȘtre conçu comme la
connexion d'un ensemble de systÚmes de coopération organisés autour de postes à conquérir. En effet,
l'impératif d'unification de la droite française est lié au décalage persistant existant entre les systÚmes
de coopération législatif et présidentiel. Mais les questions soulevées par cette fusion partisane (l'UMP
inclut le RPR, DL et une majeure partie de l'UDF) montrent que cette vision ne peut suffire et que les
partis ne sont pas seulement des systÚmes de coopération mais aussi des systÚmes de production.
DĂšs lors, leurs logiques d'organisation internes pĂšsent sur ce travail de transformation du social en
politique, de la plu-ralité en homogénéité. Dans le cas de l'UMP, il s'agit d'abord de mettre en commun
des modes de fonctionnement, en particulier de définir la place et la légitimité accordées
respectivement aux adhérents et aux élus, mais aussi d'organiser l'expression de la pluralité
idéologique par la mise en place de courants
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