6,185 research outputs found
The nature of turbulence in OMC1 at the star forming scale: observations and simulations
Aim: To study turbulence in the Orion Molecular Cloud (OMC1) by comparing
observed and simulated characteristics of the gas motions.
Method: Using a dataset of vibrationally excited H2 emission in OMC1
containing radial velocity and brightness which covers scales from 70AU to
30000AU, we present the transversal structure functions and the scaling of the
structure functions with their order. These are compared with the predictions
of two-dimensional projections of simulations of supersonic hydrodynamic
turbulence.
Results: The structure functions of OMC1 are not well represented by power
laws, but show clear deviations below 2000AU. However, using the technique of
extended self-similarity, power laws are recovered at scales down to 160AU. The
scaling of the higher order structure functions with order deviates from the
standard scaling for supersonic turbulence. This is explained as a selection
effect of preferentially observing the shocked part of the gas and the scaling
can be reproduced using line-of-sight integrated velocity data from subsets of
supersonic turbulence simulations. These subsets select regions of strong flow
convergence and high density associated with shock structure. Deviations of the
structure functions in OMC1 from power laws cannot however be reproduced in
simulations and remains an outstanding issue.Comment: 12 pages, 8 figures, accepted A&A. Revised in response to referee.
For higher resolution, see http://www.astro.phys.au.dk/~maikeng/sim_paper
Electric potential distributions at the interface between plasmasheet clouds
At the interface between two plasma clouds with different densities, temperatures, and/or bulk velocities, there are large charge separation electric fields which can be modeled in the framework of a collisionless theory for tangential discontinuities. Two different classes of layers were identified: the first one corresponds to (stable) ion layers which are thicker than one ion Lamor radius; the second one corresponds to (unstable) electron layers which are only a few electron Larmor radii thick. It is suggested that these thin electron layers with large electric potential gradients (up to 400 mV/m) are the regions where large-amplitude electrostatic waves are spontaneously generated. These waves scatter the pitch angles of the ambient plasmasheet electron into the atmospheric loss cone. The unstable electron layers can therefore be considered as the seat of strong pitch angle scattering for the primary auroral electrons
Interplanetary boundary layers at 1 AU
The structure and nature of discontinuities in the interplanetary magnetic field at 1 AU in the period March 18, 1971 to April 9, 1971, is determined by using high-resolution magnetic field measurements from Explorer 34. The discontinuities that were selected for this analysis occurred under a variety of interplanetary conditions at an average rate of 0.5/hr. This set does not include all discontinuities that were present, but the sample is large and it is probably representative. Both tangential and rotational discontinuities were identified, the ratio of TD's to RD's being approximately 3 to 1. Tangential discontinuities were observed every day, even among Alfvenic fluctuations. The structure of most of the boundary layers was simple and ordered, i.e., the magnetic field usually changed smoothly and monotonically from one side of the boundary layer to the other
Legami curati - legami curanti. 'Cliniche della concertazione' e violenze di quartiere
Mahdi ha ventisei anni, è alto e di corporatura atletica ed è cieco in quanto vittima di un’aggressione in cui ha perso la vista. Una situazione come questa descritta, mette al lavoro una rete complessa che associa professionisti dell’aiuto, della cura, dell’educazione e del controllo, al di là di ciò che questi stessi operatori possono immaginare. La metodologia della “Clinica della Concertazione”, intesa come “Laboratorio di etica comunicazionale applicata”, riconosce a Mahdi e ai vari membri della sua famiglia il ruolo di architetti di questa rete. Se i professionisti non resistono a questa costruzione collettiva, vedranno disporsi numerosi sistemi relazionali in equilibrio di cui potranno sfruttare le risorse in un processo ricostruttore di legami. Più che un dispositivo descrittivo, la Clinica della Concertazione è un dispositivo terapeutico creativo retto da regole aleatorie che sfuggono a un progetto di padronanza assoluta. Si tratta, in un dibattito che non esclude alcun membro di questo collettivo ma, proprio al contrario, promotore di tutti i passi estensivi, di differenziare senza dissociare, con tutte le persone interessate ciò che apparterrà alla sfera privata da ciò che apparterrà alla sfera pubblica, riconoscendo la legittimità delle dinamiche compensative vendicative e delle dinamiche protettrici delle generazioni future, individuando le loro articolazioni, le loro compatibilità e incompatibilità permettendo lo sviluppo preferibilmente, di quelle che sono ricostruttrici e preventive. Résumé Mahdi a vingt-six ans, il est grand et de stature athlétique. Il est aveugle. Il a été victime d’une agression qui lui a ôté la vue. Une situation comme celle de Mahdi met au travail un réseau complexe associant des professionnels de l’aide, du soin, de l’éducation et du contrôle, au-delà de ce que ces mêmes professionnels peuvent imaginer. La Méthodologie de la « Clinique de Concertation », en tant que « Laboratoire d’éthique communicationelle appliquée», reconnaît que Mahdi et les membres de sa famille font d’emblée partie des architectes de ce réseau. Si les professionnels ne résistent pas à cette construction collective, ils verront se disposer plusieurs systèmes relationnels en équilibre dont ils pourront exploiter les ressources dans des processus reconstructeurs de liens. Plus qu’un dispositif descriptif, la « Clinique de Concertation » est un dispositif thérapeutique créatif régi par des règles aléatoires échappant à un projet de maîtrise absolue. Il s’agit, dans un débat collectif n’excluant aucun membre de ce même collectif, bien au contraire, promoteur de toutes les démarches extensives, de différencier sans dissocier, avec toutes les personnes intéressées ce qui va appartenir à la sphère privée de ce qui va appartenir à la sphère publique, tout en reconnaissant la légitimité des dynamiques compensatoires vengeresses et des dynamiques protectrices des générations futures, en repérant leurs articulations, leurs compatibilités et leurs incompatibilités, de développer préférentiellement celles qui sont reconstructrices et préventives. Abstract Mahdi is twenty-six years old, he is tall and athletic. He is blind, because he was attacked. This kind of situation puts at work a complex network of professionals of help, care, education and control, beyond everything they can expect. The methodology of the « Clinic of Concertation », as a « Laboratory of applied communicational ethics », recognises that Mahdi and the members of his family are directly part of this network. If the professionals do not resist to this collective construction, they will see laying out different relational systems in balance from which they can exploit the resources in the process of reconstructive links. More than a narrative device, the "Clinic of Concertation" is a creative therapeutic device governed by random rules beyond an absolute mastery. It is, in a collective discussion that does not exclude any member of the collective, but on the contrary, that promotes every extensive step, about differentiating without dissociating, with all interested persons, what will belong to the private sphere and what will belong to the public sphere, while recognizing the legitimacy of the compensatory dynamics of revenge and the protective dynamics of future generations, by identifying their joints, their compatibilities and their incompatibilities, by developing preferentially those reconstructive and preventive
Magnetic and structural properties of nanocrystalline PrCo
The structure and magnetic properties of nanocrystalline PrCo obtained
from high energy milling technique are investigated by X-ray diffraction, Curie
temperature determination and magnetic properties measurements are reported.
The as-milled samples have been annealed in a temperature range of 1023 K to
1273 K for 30 mn to optimize the extrinsic properties. The Curie temperature is
349\,K and coercive fields of 55\,kOe at 10\,K and 12\,kOe at 293\,K are
obtained on the samples annealed at 1023\,K. A simulation of the magnetic
properties in the framework of micromagnetism has been performed in order to
investigate the influence of the nanoscale structure. A composite model with
hard crystallites embedded in an amorphous matrix, corresponding to the
as-milled material, leads to satisfying agreement with the experimental
magnetization curve. [ K. Younsi, V. Russier and L. Bessais, J. Appl. Phys.
{\bf 107}, 083916 (2010)]. The microscopic scale will also be considered from
DFT based calculations of the electronic structure of Co compounds,
where = (Y, Pr) and = 2,3 and 5.Comment: To be published in J. Phys.: Conference Series in the JEMS 2010
special issue. To be found once published at
http://iopscience.iop.org/1742-659
The roman catholic church and contraception
The official position regarding the use of artificial means of family planning varies from religion to religion. With its steadfast opposition to the use of any form of contraception or sterilization, the Roman Catholic Church puts its 1.2 billion followers worldwide in the difficult dilemma of either adhering to the teaching of their church and thereby risk an unwanted pregnancy, or ignoring that teaching and use an artificial method of family planning, but thereby become marginalized by their church. Pope Francis has made a number of statements and actions indicating that their might be a possibility of some changes in the teaching of the Roman Catholic Church regarding a number of issues re-lated to the family, such as divorce, remarriage, gays and women’s rights. However he has continued to reaffirm the Church’s opposition to the use of any artificial method of family planning and has reiterated on a number of occasions that the Church will only allow the so called natural methods. This essay argues that in the opinion of the author, the time has come for the Roman Catholic hierarchy to revise this outdated position and allow catholics to resort to modern methods for limiting the size of their family, which is some-thing that a large percentage of the catholics are doing already anyway
Observations of spatial and velocity structure in the Orion Molecular Cloud
Observations are reported of H2 IR emission in the S(1) v=1-0 line at 2.121
microns in the Orion Molecular Cloud, OMC1, using the GriF instrument on the
Canada-France-Hawaii Telescope. GriF is a combination of adaptive optics and
Fabry-Perot interferometry, yielding a spatial resolution of 0.15" to 0.18" and
a velocity discrimination as high as 1 km/s. Thanks to the high spatial and
velocity resolution of the GriF data, 193 bright H2 emission regions can be
identified in OMC1. The general characteristics of these features are described
in terms of radial velocities, brightness and spatial displacement of maxima of
velocity and brightness, the latter to yield the orientation of flows in the
plane of the sky. Strong spatial correlation between velocity and bright H2
emission is found and serves to identify many features as shocks. Important
results are: (i) velocities of the excited gas illustrate the presence of a
zone to the south of BN-IRc2 and Peak 1, and the west of Peak 2, where there is
a powerful blue-shifted outflow with an average velocity of -18 km/s. This is
shown to be the NIR counterpart of an outflow identified in the radio from
source I, a very young O-star. (ii) There is a band of weak velocity features
(<5 km/s) in Peak 1 which may share a common origin through an explosive event,
in the BN-IRc2 region, with the fast-moving fingers (or bullets) to the NW of
OMC1. (iii) A proportion of the flows are likely to represent sites of low mass
star formation and several regions show multiple outflows, probably indicative
of multiple star formation within OMC1. The high spatial and velocity
resolution of the GriF data show these and other features in more detail than
has previously been possible.Comment: 27 pages, 19 figures, submitted to A&A Version 2: Several additions,
including a section on protostellar candidates in OMC1, have been made based
on the referee's suggestions v3: corrected typograph
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