96 research outputs found
Solar wind turbulent spectrum at plasma kinetic scales
The description of the turbulent spectrum of magnetic fluctuations in the
solar wind in the kinetic range of scales is not yet completely established.
Here, we perform a statistical study of 100 spectra measured by the STAFF
instrument on the Cluster mission, which allows to resolve turbulent
fluctuations from ion scales down to a fraction of electron scales, i.e. from
km to m. We show that for
(that corresponds approximately to the frequency in the spacecraft frame Hz), all the observed spectra can be described by a general law
, where is
the wave-vector component normal to the background magnetic field and
the electron Larmor radius. This exponential tail found in the solar wind seems
compatible with the Landau damping of magnetic fluctuations onto electrons.Comment: published in APJ, 15 of November 2012 (with reduced "Discussion"
section
Spectra and anisotropy of magnetic fluctuations in the Earth's magnetosheath: Cluster observations
We investigate the spectral shape, the anisotropy of the wave vector
distributions and the anisotropy of the amplitudes of the magnetic fluctuations
in the Earth's magnetosheath within a broad range of frequencies. We present
the first observations of a Kolmogorov-like inertial range of Alfvenic
fluctuations in the magnetosheath flanks, below fci. In the vicinity of fci, a
spectral break is observed, like in solar wind turbulence. Above the break, the
energy of compressive and Alfvenic fluctuations generally follow a power law
with a spectral index between -3 and -2. Concerning the anisotropy of the wave
vector distribution, we observe a change in its nature in the vicinity of ion
characteristic scales: if at MHD scales there is no evidence for a dominance of
a slab (k||>kperp) or 2D (kperp>k||) turbulence, above the spectral break,
(f>fci, kc/wpi>1) the 2D turbulence dominates. This 2D turbulence is observed
in six selected one-hour intervals among which the average proton beta varies
from 0.8 to 9. It is observed for both the transverse and compressive magnetic
fluctuations, independently on the presence of linearly unstable modes at low
frequencies or Alfven vortices at the spectral break. We then analyse the
anisotropy of the magnetic fluctuations in a time dependent reference frame
based on the field B and the flow velocity V directions. Within the range of
the 2D turbulence, at scales [1,30]kc/wpi, and for any beta we find that the
magnetic fluctuations at a given frequency in the plane perpendicular to B have
more energy along the BxV direction. This non-gyrotropy of the fluctuations is
consistent with gyrotropic fluctuations at a given wave vector, with kperp>k||,
which suffer a different Doppler shift along and perpendicular to V in the
plane perpendicular to B.Comment: accepted for publication in Annales Geophysicae (ANGEO) at 29/09/200
Territorialisation sanitaire et décentralisation : état des lieux et enjeux à partir du cas français
Ces derniĂšres dĂ©cennies, les transformations des systĂšmes de santĂ© dans le monde se traduisent par des processus de territorialisation, sous-tendus par trois tendances principales : la rĂ©gulation financiĂšre, le dĂ©veloppement des partenariats et le transfert des compĂ©tences. Dans ce papier, nous resituons tout dâabord le processus de territorialisation dans le cadre plus gĂ©nĂ©ral des questions de dĂ©centralisation, de gouvernance et de gouvernement. En se focalisant sur le cas français, nous analysons ensuite lâarticulation entre la dĂ©centralisation dite fonctionnelle en santĂ© et les processus plus gĂ©nĂ©raux de dĂ©centralisation des institutions. Pour conclure, nous questionnons les enjeux opĂ©rationnels et organisationnels qui en dĂ©coulent.In this paper, we focus on the common trends of transformations of health care systems in the world. Based on the identification of three logics that root these evolutions (financial regulation, development of cooperation and skill/power transfers), we define territorialization as a process. It refers to projects of planning for which actors implement strategies to produce controlled and bounded spaces. In this process, scales, distances enacted through instruments are involved for putting public policy into practice and space. These actions give rise to different forms of territorialization in which different modes of governance, government and uses are embedded. In a second part, we focus on the case of France and the ways instruments have been used to develop public policies. We insist on the disconnections between the political and administrative decentralization with the evolution of the health sector. The general trend of decentralization of French administration during the eighties is characterized by a greater proximity of public decision with citizen, which involves more action for local authorities. A structured vision of decentralization appears only at the beginning of 2010s based on potential differentiation of standard on the territory and the possibility for regions to provide guidance to others local authorities. During these periods, health sector remains on the sidelines of the legislative evolution. Although regional level was defined as the structuring level of organization for health care in the hospital law of 1991, regionalization of public health policy really operated in 2009 with the Patients, Health and Territories Law (HPST) creating regional health agencies. These ones, with the legal personality are a type of functional decentralization, which are submitted to state monitoring. Concentrating the decision-making power at the regional level and breaking down barriers between sectoral policies, this law simplified local organization of health sector governance. It is operated in a regional health plan which relies on contractual partnerships with a lot of actors including local authorities which became a major actor to decline the plan at the local level. In a third part, we discuss the stakes, options and problems that actors have to face in the current stage of decentralization. Combined with deconcentration of others services, overlapping, cross-financing occurred and involved lower clarity of administrative organization. Two major stakes are identified. Firstly, the capabilities for actors to form a wide coalition sharing objectives and keeping up with changes in stakeholderâs dynamics, like political changeovers and budget cuts. Secondly, a better coordination of actors, in order to create favorable conditions for cooperation and complementarities
Whistler mode waves and the electron heat flux in the solar wind: Cluster observations
The nature of the magnetic field fluctuations in the solar wind between the
ion and electron scales is still under debate. Using the Cluster/STAFF
instrument, we make a survey of the power spectral density and of the
polarization of these fluctuations at frequencies Hz, during five
years (2001-2005), when Cluster was in the free solar wind. In of
the selected data, we observe narrow-band, right-handed, circularly polarized
fluctuations, with wave vectors quasi-parallel to the mean magnetic field,
superimposed on the spectrum of the permanent background turbulence. We
interpret these coherent fluctuations as whistler mode waves. The life time of
these waves varies between a few seconds and several hours. Here we present,
for the first time, an analysis of long-lived whistler waves, i.e. lasting more
than five minutes. We find several necessary (but not sufficient) conditions
for the observation of whistler waves, mainly a low level of the background
turbulence, a slow wind, a relatively large electron heat flux and a low
electron collision frequency. When the electron parallel beta factor
is larger than 3, the whistler waves are seen along the
heat flux threshold of the whistler heat flux instability. The presence of such
whistler waves confirms that the whistler heat flux instability contributes to
the regulation of the solar wind heat flux, at least for 3, in the slow wind, at 1 AU.Comment: The Astrophysical Journal, 2014, in pres
Rock fall photogrammetric monitoring in the active crater of Piton de la Fournaise volcano, la Reunion Island
International audienceThe collapse of the active crater at Piton de la Fournaise volcano, La Reunion Island, 5th April 2007, offers a rare opportunity to observe frequent rock fall and granular landslides, and test new monitoring techniques. Events concern volumes ranging from single blocks to more massive cliff collapse. The purpose of the presentation is two fold: first, we present a comparison between a Digital Terrain Model (DTM) obtained prior to crater collapse and a DTM extracted from aerial photographs shot in October 2010 (before the eruptive crisis of November 2009 and January 2010). This provides an assessment of morphological changes at the scale of the crater. The second purpose is to describe slope instabilities on the south-western flank of the crater observed since October 2009. These ground-based observations were obtained from a pair of photogrammetric stations deployed along the northern and eastern edges of the crater. These works were conducted within UNDERVOLC project. With this monitoring system we mapped zones affected by rockfalls (departure and accumulation areas) and propose a first estimate of volumes of lava produced by the eruption affecting the inside of the crater since January 2
Les déserts médicaux en Ile-de-France
Mangeney Catherine. Les déserts médicaux en Ile-de-France. In: Villes en parallÚle. Documents, n°6,2018. Financiarisation de la ville et liberté du politique. Séminaire Analyse et Politique de la Ville - année 2018-2019. pp. 27-29
Enjeux et défis des zonages prescriptifs de l'action publique, l'exemple des zonages déficitaires en medecins généralistes en France
In France, as in other countries in the world, the difficulties of spatial accessibility to healthcare supply has been a central issue and a priority for public health policies for two decades. Since 2005, French legislation has provided that, in each region, areas considered to be in deficit in terms of medical provision must be identified. Doctors who practice or who come to settle there can benefit from a certain number of public aids, the objective being to promote a better geographical distribution of healthcare supply. Faced with the limited effectiveness of this public policy, the measures implemented are regularly called into question, as is the methodology for delimiting "doctor zoning". This thesis is devoted to questioning this zoning methodology. A preliminary socio-historical detour retracing the process of genesis of this instrument of public action allows us to understand that current physician zoning, in its purely incentive form, is a compromise tool shaped in part by pragmatic issues of which it cannot be disregard. I then demonstrate why, as an instrument of a public policy of positive discrimination, the issues of equity and social and/or spatial justice are essential to the instrument and I explain how current zoning methods are largely conditioned by a presupposition, more fantasized than proven, of a link between territories with difficulties in spatial accessibility to general practitioners and socially disadvantaged territories. So much so that current zoning methods are based on social criteria as much as on the measurement of levels of spatial accessibility to care, which distorts the very function of this zoning, which we no longer know if it targets areas in difficulty of access to care or if it only targets areas in social difficulty. In this thesis, I reintegrate the social dimension of needs into the measurement of levels of spatial accessibility to general practitioners in order to identify, based on the Ile-de-France case, the territories where populations have the most potential difficulties with spatial accessibility et general practitioners taking into account their social characteristics. I explain the underlying choices of the measurement method. Proceeding by scenarios, I show that in Ăle-de-France, the reality represented differs very significantly according to the parameters integrated into the measurement model, thus underlining the importance of "repoliticizing" the measurement (even before the selection stage) since the norms produced by the underlying choices draw implicitly (while they should translate explicitly) a specific vision of where we want to go. I also show that it is possible to re-politicize the step of selection of the "portions of spaces" that will be included - or excluded - from zoning by basing it, more than it is done today, on the characteristics of the populations concerned, on a desire to articulate public policies and on the constraints that are imposed on zoning today to establish its potential effectiveness (acceptability by health professionals). My modeling also illustrates that proceeding by scenarios makes it possible to propose several possibilities of the reality of which we seek to produce a representation. This makes it possible to mobilize quantification as a tool of government and not as an idealized tool of proof, by testing - in a dispassionate manner - the geographical and population impact of different intention or political claim. Thus, my modeling shows, for example, that beyond moral questions, feasibility or induced risks, making zoning coercive rather than simply incentive could have few operational effects in Ăle-de-France, especially if the zoning is retained in its current contours.En France, comme ailleurs dans le monde, la lutte contre les difficultĂ©s d'accessibilitĂ© spatiale aux soins constitue depuis deux dĂ©cennies un enjeu central et une prioritĂ© des politiques publiques de santĂ©. Depuis 2005, la lĂ©gislation française prĂ©voit que, dans chaque rĂ©gion, soient dĂ©limitĂ©es des zones considĂ©rĂ©es comme en dĂ©ficit en matiĂšre d'offre mĂ©dicale. Les mĂ©decins qui y exercent ou qui viennent s'y installer peuvent bĂ©nĂ©ficier d'un certain nombre d'aides publiques, l'objectif Ă©tant de favoriser une meilleure rĂ©partition gĂ©ographique des professionnels de santĂ© de ville. Face au constat d'efficacitĂ© limitĂ©e de cette politique publique, les mesures mises en Ćuvre sont rĂ©guliĂšrement remises en cause de mĂȘme que la mĂ©thodologie de dĂ©limitation du « zonage mĂ©decins ». Cette thĂšse est consacrĂ©e Ă questionner cette mĂ©thodologie de zonage. Un dĂ©tour socio-historique prĂ©alable retraçant le processus de genĂšse de cet instrument d'action publique permet de comprendre que le zonage mĂ©decins actuel, dans sa forme purement incitative, est un outil de compromis façonnĂ© en partie par des enjeux pragmatiques dont il ne peut ĂȘtre fait abstraction. Je dĂ©montre ensuite pourquoi, en tant qu'instrument d'une politique publique de discrimination positive, les enjeux d'Ă©quitĂ© et de justice sociale et/ou spatiale s'imposent Ă l'instrument et j'explicite en quoi les mĂ©thodes de zonage actuelles sont largement conditionnĂ©es par un prĂ©supposĂ© plus fantasmĂ© qu'avĂ©rĂ© d'un lien entre territoires en difficultĂ© d'accessibilitĂ© spatiale aux mĂ©decins gĂ©nĂ©ralistes et territoires socialement dĂ©favorisĂ©s. A tel point que les mĂ©thodes de zonage actuelles reposent sur des critĂšres sociaux autant que sur la mesure des niveaux d'accessibilitĂ© spatiale aux soins ce qui dĂ©nature la fonction mĂȘme de ce zonage dont on ne sait plus s'il cible des territoires en difficultĂ© d'accĂšs aux soins ou bien s'il ne cible plus que des territoires en difficultĂ© sociale. Dans cette thĂšse, je rĂ©intĂšgre la dimension sociale des besoins au sein de la mesure des niveaux d'accessibilitĂ© spatiale aux mĂ©decins afin d'identifier, Ă partir du cas francilien, les territoires oĂč les populations ont le plus de difficultĂ©s potentielles d'accessibilitĂ© spatiale aux mĂ©decins gĂ©nĂ©ralistes compte tenu de leurs caractĂ©ristiques sociales. J'explicite les choix sous-jacents de la mĂ©thode de mesure. En procĂ©dant par scĂ©narios, je montre qu'en Ăle-de-France, la rĂ©alitĂ© reprĂ©sentĂ©e diffĂšre trĂšs sensiblement selon les paramĂštres intĂ©grĂ©s au modĂšle de mesure, soulignant ainsi l'importance à « repolitiser » la mesure (avant mĂȘme l'Ă©tape de sĂ©lection) puisque les normes produites par les choix opĂ©rĂ©s dessinent implicitement (alors qu'ils devraient traduire explicitement) une vision spĂ©cifique de lĂ oĂč l'on souhaite aller. Je montre Ă©galement qu'il est possible de repolitiser l'Ă©tape de sĂ©lection des « portions d'espaces » qui seront intĂ©grĂ©es - ou exclues - du zonage en la fondant, plus que cela n'est fait aujourd'hui, sur les caractĂ©ristiques des populations concernĂ©es, sur une volontĂ© d'articulation des diffĂ©rentes politiques publiques et sur les contraintes qui s'imposent aujourd'hui au zonage pour asseoir son efficacitĂ© potentielle (acceptabilitĂ© par les professionnels de santĂ©). Mes modĂ©lisations illustrent Ă©galement que procĂ©der par scĂ©narios permet de proposer plusieurs possibles de la rĂ©alitĂ© dont on cherche Ă produire une reprĂ©sentation. Cela permet de mobiliser la quantification bien comme un outil de gouvernement et non pas comme un outil de preuve idĂ©alisĂ©, en testant - de maniĂšre dĂ©passionnĂ©e - l'impact gĂ©ographique et populationnel de telle ou telle intention ou revendication politique. Ainsi, mes modĂ©lisations montrent par exemple, qu'au-delĂ des questions morales, de faisabilitĂ© ou de risques induits, rendre le zonage coercitif pourrait n'avoir que peu d'effets opĂ©rationnels en Ăle-de-France, surtout si le zonage est conservĂ© dans ses contours actuels
Le zonage mĂ©decins en France : genĂšse dâun instrument dâaction publique Ă dimension territoriale
En France, comme ailleurs, la lutte contre les difficultĂ©s dâaccĂšs aux soins constitue depuis plusieurs annĂ©es une prioritĂ© des politiques publiques de santĂ©. Depuis 2005, un « zonage mĂ©decins » rĂ©glementaire cible les territoires dĂ©ficitaires en mĂ©decins gĂ©nĂ©ralistes, oĂč les mĂ©decins sont Ă©ligibles Ă diffĂ©rentes aides publiques. Dans une approche socio-historique, cet article vise Ă dĂ©crire la genĂšse de cet instrument dâaction publique et Ă en retracer le processus dâĂ©mergence lente et hĂ©sitante dans un paysage dâintĂ©rĂȘts complexes et contradictoires. Dans un contexte de refonte du zonage mĂ©decins et de remise en question rĂ©currente de sa pertinence, ce dĂ©tour historique permet mieux comprendre que le zonage actuel, dans sa forme purement incitative, est un outil de compromis façonnĂ© en partie par des enjeux pragmatiques dont il ne peut ĂȘtre fait abstraction
Physician zoning in France: the genesis of a public action instrument with a territorial dimension
Politiques de rationalisation de lâoffre de soins et mobilitĂ©: Chapitre 7
International audienceLes politiques de rationalisation de lâoffre de soins reposent largement sur la mesure de lâaccessibilitĂ© spatiale aux soins. Cette derniĂšre, au fil des Ă©volutions mĂ©thodologiques et technologiques, considĂšre de maniĂšre de plus en plus intĂ©grĂ©e le concept de mobilitĂ©. Celui-ci reste nĂ©anmoins insuffisamment mobilisĂ© pour questionner lâapproche domo-centrĂ©e des mesures et tenir compte des diffĂ©rentiels sociaux de mobilitĂ© des populations
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