6,227 research outputs found
Theoretical limits on magnetic field strengths in low-mass stars
Observations have suggested that some low-mass stars have larger radii than
predicted by 1-D structure models. Some theoretical models have invoked very
strong interior magnetic fields (of order 1 MG or more) as a possible cause of
such large radii. Whether fields of that strength could in principle by
generated by dynamo action in these objects is unclear, and we do not address
the matter directly. Instead, we examine whether such fields could remain in
the interior of a low mass object for a significant time, and whether they
would have any other obvious signatures. First, we estimate timescales for the
loss of strong fields by magnetic buoyancy instabilities. We consider a range
of field strengths and simple morphologies, including both idealized flux tubes
and smooth layers of field. We confirm some of our analytical estimates using
thin flux tube magnetohydrodynamic (MHD) simulations of the rise of buoyant
fields in a fully-convective M-dwarf. Separately, we consider the Ohmic
dissipation of such fields. We find that dissipation provides a complementary
constraint to buoyancy: while small-scale, fibril fields might be regenerated
faster than they rise, the dissipative heating associated with such fields
would in some cases greatly exceed the luminosity of the star. We show how
these constraints combine to yield limits on the internal field strength and
morphology in low-mass stars. In particular, we find that for stars of 0.3
solar masses, no fields in flux tubes stronger than about 800 kG are
simultaneously consistent with both constraints.Comment: 19 pages, 10 figures, accepted to Ap
Enhancing the selection of a model-based clustering with external qualitative variables
In cluster analysis, it can be useful to interpret the partition built from
the data in the light of external categorical variables which were not directly
involved to cluster the data. An approach is proposed in the model-based
clustering context to select a model and a number of clusters which both fit
the data well and take advantage of the potential illustrative ability of the
external variables. This approach makes use of the integrated joint likelihood
of the data and the partitions at hand, namely the model-based partition and
the partitions associated to the external variables. It is noteworthy that each
mixture model is fitted by the maximum likelihood methodology to the data,
excluding the external variables which are used to select a relevant mixture
model only. Numerical experiments illustrate the promising behaviour of the
derived criterion
De lâusage politique du peuple âPadanoâ : la construction dâidentitĂ© dans le cas de la Ligue du Nord
International audienceDans le champ politique, lâappel au « peuple » se focalise sur les principes dâunitĂ©, de faire-valoir de lĂ©gitimitĂ© et de pouvoir. Le cas de la Lega Nord (Ligue du Nord) italienne illustre un processus de construction symbolique dâun peuple et de catĂ©gories « dâautres » polysĂ©miques, variables dans le temps. Le peuple de la Ligue sâest adossĂ© originellement au façonnage dâune identitĂ© « padane ». En dĂ©pit de lâabsence de tout substrat culturel ou gĂ©ographique, la pĂ©rennitĂ© du rĂ©fĂ©rent « padano » tĂ©moigne de lâinstrumentalisation dâun systĂšme de croyances et de reprĂ©sentations qui a longtemps Ă©tĂ© essentiel au maintien de lâunitĂ© du parti et Ă sa capacitĂ© de mobilisation Ă©lectorale. Au fil du temps, toutefois, de nouvelles frontiĂšres sociales et symboliques ont Ă©tĂ© Ă©laborĂ©es Ă partir dâaspects identitaires, socio-Ă©conomiques, politiques et ethniques, complĂ©tĂ©s plus rĂ©cemment par un repositionnement au cĆur de lâespace des droites radicales populistes en Europe. Cette complexitĂ© tient en partie Ă la nature opportuniste et camĂ©lĂ©onienne du rĂ©gional-populisme lĂ©guiste, au grĂ© des reconfigurations et enjeux politiques. Elle tĂ©moigne en outre du statut hybride du mouvement, entre force de coalition gouvernementale et parti dâopposition. Elle illustre enfin la variabilitĂ© des structures dâopportunitĂ©s politiques qui existent au nord et au sud de lâItalie.In ambito politico, lâappello al popolo si focalizza sul principio di unitĂ , di legittimitĂ e potere sovrano. In Italia, il caso della Lega Nord mostra un processo di costruzione di un popolo âsimbolicoâ accompagnato da molteplici categorie âdellâaltroâ in grado di variare nel tempo. Il âpopoloâ leghista si Ăš fatto dapprima portatore di unâidentitĂ âpadanaâ, totalmente priva di un substrato culturale oltre che geografico. Il costante riferimento alla Padania testimonia dunque una strumentalizzazione allâinterno di un sistema di credenze che per molto tempo Ăš stato in grado di mantenere unito il partito e di funzionare come strumento di mobilitazione elettorale. Tuttavia, nel corso del tempo, la Lega Ăš stata in grado di creare nuove barriere sociali e simboliche partendo da aspetti identitari, socio-economici, politici ed etnici. Questo processo di cambiamento si Ăš completato piĂč recentemente attraverso un riposizionamento del partito nellâarea della destra radicale europea. Questi aspetti eterogenei hanno, in parte, a che fare con la natura strategica e camaleontica del regional-populismo leghista. Le stesse caratteristiche mostrano inoltre una natura ibrida del partito, che oscilla tra forza politica allâinterno di una coalizione di governo e partito dâopposizione. Emerge, infine, una capacitĂ di variare le proprie strutture e le proprie strategie nelle diverse aree del Paese (Nord/Sud)
Not enough there, too many here: understanding geographical imbalances in the distribution of the health workforce
Access to good-quality health services is crucial for the improvement of many health outcomes, such as those targeted by the Millennium Development Goals (MDGs) adopted by the international community in 2000. The health-related MDGs cannot be achieved if vulnerable populations do not have access to skilled personnel and to other necessary inputs. This paper focuses on the geographical dimension of access and on one of its critical determinants: the availability of qualified personnel. The objective of this paper is to offer a better understanding of the determinants of geographical imbalances in the distribution of health personnel, and to identify and assess the strategies developed to correct them. It reviews the recent literature on determinants, barriers and the effects of strategies that attempted to correct geographical imbalances, with a focus on empirical studies from developing and developed countries. An analysis of determinants of success and failures of strategies implemented, and a summary of lessons learnt, is included
The aetiology of infectious intestinal disease in the community in Malta
Routine sources of data provide limited information on aetiological agents causing infectious intestinal disease (IID) in the community. A retrospective, age-stratified, cross-sectional, telephone study at community level was performed whereby identified cases were asked to submit stools for analysis. Of a total of 3504 persons who participated, 99 respondents were suffering from IID. Of these, 37.4% (n=37) cases submitted stools for analysis. These samples were analysed for bacteria (Salmonella, Campylobacter, Escherichia coli, Shigella), protozoa and viruses (rotavirus, norovirus). Salmonella goldcoast was identified in 2.7% (n=1 of 37 tested) of cases, rotavirus in 10% (n=3 of 30 tested) of cases and norovirus in 20% (n=6 of 30 tested) of cases. This study describes norovirus being the commonest aetiological cause of IID in the community of Malta, which along with the data from the national surveillance system is of value in planning policies for the control of infectious intestinal disease.peer-reviewe
Structure and magnetism of orthorhombic epitaxial FeMnAs
The molecular beam epitaxy growth of Fe on MnAs/GaAs(001) leads to the formation of an epitaxial FeMnAs phase at the Fe/MnAs interface. The investigation of the structure by high angle annular dark field imaging in a scanning transmission electron microscope reveals an unusual orthorhombic structure, with vacancy ordering. Ab initio calculations show an antiferromagnetic ground state for this orthorhombic FeMnAs.Fil: Demaille, Dominique. Laboratorio Internacional Franco-Argentino en Nanociencias; Francia. Universite Pierre et Marie Curie. Institut des Nanosciences de Paris; FranciaFil: Patriarche, Gilles. Centre National de la Recherche Scientifique; FranciaFil: Helman, Christian. ComisiĂłn Nacional de EnergĂa AtĂłmica; Argentina. Laboratorio Internacional Franco-Argentino en Nanociencias; FranciaFil: Eddrief, Mahmoud. Laboratorio Internacional Franco-Argentino en Nanociencias; Francia. Universite Pierre et Marie Curie. Institut des Nanosciences de Paris; FranciaFil: Etgens, Hugo. Laboratorio Internacional Franco-Argentino en Nanociencias; Francia. Universite Pierre et Marie Curie. Institut des Nanosciences de Paris; FranciaFil: Sacchi, Maurizio. Laboratorio Internacional Franco-Argentino en Nanociencias; Francia. Universite Pierre et Marie Curie. Institut des Nanosciences de Paris; Francia. LâOrme des merisiers Saint-Aubin. Synchrotron SOLEIL; FranciaFil: Llois, Ana Maria. ComisiĂłn Nacional de EnergĂa AtĂłmica; Argentina. Laboratorio Internacional Franco-Argentino en Nanociencias; Francia. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Marangolo, Massimiliano. Laboratorio Internacional Franco-Argentino en Nanociencias; Francia. Universite Pierre et Marie Curie. Institut des Nanosciences de Paris; Franci
Quasistatic evolution in non-associative plasticity - The cap model
International audienceNon-associative elasto-plasticity is the working model of plasticity for soil and rocks mechanics. Yet, it is usually viewed as non-variational. In this work, we prove a contrario the existence of a variational evolution for such a model under a natural capping assumption on the hydrostatic stresses and a less natural mollification of the stress admissibility constraint. The obtained elasto-plastic evolution is expressed for times that are conveniently rescaled
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