644 research outputs found
Electric current in flares ribbons: observations and 3D standard model
We present for the first time the evolution of the photospheric electric
currents during an eruptive X-class flare, accurately predicted by the standard
3D flare model. We analyze this evolution for the February 15, 2011 flare using
HMI/SDO magnetic observations and find that localized currents in \J-shaped
ribbons increase to double their pre-flare intensity. Our 3D flare model,
developed with the OHM code, suggests that these current ribbons, which develop
at the location of EUV brightenings seen with AIA imagery, are driven by the
collapse of the flare's coronal current layer. These findings of increased
currents restricted in localized ribbons are consistent with the overall free
energy decrease during a flare, and the shape of these ribbons also give an
indication on how much twisted the erupting flux rope is. Finally, this study
further enhances the close correspondence obtained between the theoretical
predictions of the standard 3D model and flare observations indicating that the
main key physical elements are incorporated in the model.Comment: 12 pages, 7 figure
Arbeidsvoorwaardenvorming in het onderwijs: een vergelijking tussen Nederland en Vlaanderen
Hervorming Sociale Regelgevin
Slipping magnetic reconnection during an X-Class solar flare observed by SDO/AIA
We present SDO/AIA observations of an eruptive X-class flare of July 12,
2012, and compare its evolution with the predictions of a 3D numerical
simulation. We focus on the dynamics of flare loops that are seen to undergo
slipping reconnection during the flare. In the AIA 131A observations, lower
parts of 10 MK flare loops exhibit an apparent motion with velocities of
several tens of km/s along the developing flare ribbons. In the early stages of
the flare, flare ribbons consist of compact, localized bright transition-region
emission from the footpoints of the flare loops. A DEM analysis shows that the
flare loops have temperatures up to the formation of Fe XXIV. A series of very
long, S-shaped loops erupt, leading to a CME observed by STEREO. The observed
dynamics are compared with the evolution of magnetic structures in the
"standard solar flare model in 3D". This model matches the observations well,
reproducing both the apparently slipping flare loops, S-shaped erupting loops,
and the evolution of flare ribbons. All of these processes are explained via 3D
reconnection mechanisms resulting from the expansion of a torus-unstable flux
rope. The AIA observations and the numerical model are complemented by radio
observations showing a noise storm in the metric range. Dm-drifting pulsation
structures occurring during the eruption indicate plasmoid ejection and
enhancement of reconnection rate. The bursty nature of radio emission shows
that the slipping reconnection is still intermittent, although it is observed
to persist for more than an hour
The dermal skeleton of the jawless vertebrate Tremataspis mammilata (Osteostraci, stem-Gnathostomata)
Osteostracans are the closest jawless relatives of jawed vertebrates, informing the gradual assembly of the vertebrate mineralised skeleton. Conflicting interpretations of their dermal skeletal histology arise from failure to account for topological variation, obscuring their significance in elucidating vertebrate skeletal evolution. To resolve this, we characterize the cranial and trunk dermal skeleton of a single individual of Tremataspis mammilata (Osteostraci, Thyestiida) at submicron resolution using synchrotron tomography. Our results show that the architecture of the Tremataspis dermal skeleton is, for the most part, conserved over the skeleton and is broadly consistent with previous histological hypotheses based on 2-dimensional thin section study. We resolve debate over the homology of the basal layer, identifying it as osteogenic acellular isopedin rather than odontogenic elasmodine or metaplastic ossification of the stratum compactum of the dermis. We find topological variation between all dermal skeletal elements studied, and particularly between the cranial and postcranial dermal skeleton. This variation can be largely explained by reduction in differentiation due to geometric constraints imposed within smaller skeletal elements, such as scales. Our description of the dermal skeleton of Tremataspis mammilata provides a foundation for interpreting data from cursory topological samples of dermal skeletal diversity obtained in other osteostracans. This reveals general aspects of histological structure that must be primitive for osteostracans and, likely, ancestral jawed vertebrates. Finally, we draw the distinction between hypotheses and descriptions in palaeohistology
Production Locale De MĂ©dicaments Issus De La MĂ©decine Et PharmacopĂ©e Traditionnelles : Analyse Des DĂ©terminants De La Survie De LâunitĂ© De Production (UPHARMA))
Introduction: LâaccĂšs durable Ă des mĂ©dicaments de qualitĂ© et abordables par la production locale contribue au dĂ©veloppement sanitaire et socioĂ©conomique dâun pays. LâunitĂ© de production pharmaceutique (UPHRAMA) a Ă©tĂ© crĂ©Ă©e pour pallier Ă ce besoin au Burkina Faso. Cependant, elle rencontre d'Ă©normes difficultĂ©s susceptibles d'entrainer sa fermeture. Objectif: Lâobjectif de cette Ă©tude est dâanalyser les dĂ©terminants de la survie de lâunitĂ© de production de mĂ©dicaments (UPHARMA). MĂ©thodes: La mĂ©thodologie utilisĂ©e a combinĂ© la recherche bibliographique et lâenquĂȘte de terrain qui a consistĂ© en une sĂ©rie dâentretiens. RĂ©sultats/Discussion: Les rĂ©sultats obtenus indiquent que lâunitĂ© n'a pas de personnalitĂ© juridique lui permettant de jouir d'une autonomie dans la gestion de ses activitĂ©s. L'encrage institutionnel ne la permet pas de mener ses activitĂ©s dans une logique d'entreprise commerciale compĂ©titive. Les activitĂ©s de lâunitĂ© se trouvent piĂ©gĂ©es par la procĂ©dure de gestion des actes administratifs et financiĂšres de la fonction publique. Au regard de ce constat, elle doit ĂȘtre envisagĂ©e comme Ă©tant une sociĂ©tĂ© Ă capitaux publics avec une personnalitĂ© juridique ayant une autonomie financiĂšre et de gestion. Conclusion: Au regard des analyses, il ressort que lâunitĂ© est soumise de façon caractĂ©ristique aux principes de lâadministration publique marquĂ© par la subordination, la dĂ©pendance et le contrĂŽle qui reflĂštent le pouvoir de l'Etat. La crĂ©ation dâun nouveau statut juridique, celui dâentreprise publique autonome avec des modes de gestion et de financements adĂ©quats favorisera la mobilisation de ressources pour booster les activitĂ©s de recherche-dĂ©veloppement de nouveaux phytomĂ©dicaments au sein de lâIRSS.
Introduction: Sustainable access to quality and affordable medicines through local production contributes to health and socio-economic development of a country. The pharmaceutical production unit (UPHRARMA) was created to address this issue in Burkina Faso. However, it encounters serious difficulties which could lead to its closure. Objective: The objective of this study is to analyze the determinants of the survival of this production unit. Methods: The method combined a bibliographic review and field survey which consisted of a number of interviews. Results/Discussion: The results showed that the unit has no legal form enabling autonomy in management activities. Its institutional anchor does not allow it to perform its activities as a competitive commercial enterprise. The activities of the unit are trapped by the public procedures of administrative and financial management. In that line, the status of the unit should be revised as a public shareholding company with a legal form allowing financial and management autonomy. Conclusion: Regarding the results, U-PHARAMA is subject to the public administrationâs principles such as subordination, dependence and control. The new legal status will allow an autonomy of a public company with adequate management and financing mechanisms. This will encourage funds raising in order to mobilize resources for boosting research and development of new phytomedicines within the health sciences research institute
Student perspectives on the relationship between a curve and its tangent in the transition from Euclidean Geometry to Analysis
The tangent line is a central concept in many mathematics and science courses. In this paper we describe a model of studentsâ thinking â concept images as well as ability in symbolic manipulation â about the tangent line of a curve as it has developed through studentsâ experiences in Euclidean Geometry and Analysis courses. Data was collected through a questionnaire administered to 196 Year 12 students. Through Latent Class Analysis, the participants were classified in three hierarchical groups representing the transition from a Geometrical Global perspective on the tangent line to an Analytical Local perspective. In the light of this classification, and through qualitative explanations of the studentsâ responses, we describe studentsâ thinking about tangents in terms of seven factors. We confirm the model constituted by these seven factors through Confirmatory Factor Analysis
A formal methodology for integral security design and verification of network protocols
We propose a methodology for verifying security properties of network
protocols at design level. It can be separated in two main parts: context and
requirements analysis and informal verification; and formal representation and
procedural verification. It is an iterative process where the early steps are
simpler than the last ones. Therefore, the effort required for detecting flaws
is proportional to the complexity of the associated attack. Thus, we avoid
wasting valuable resources for simple flaws that can be detected early in the
verification process. In order to illustrate the advantages provided by our
methodology, we also analyze three real protocols
Slipping magnetic reconnection, chromospheric evaporation, implosion, and precursors in the 2014 September 10 X1.6-class solar flare
© 2016. The American Astronomical Society. All rights reserved.. We investigate the occurrence of slipping magnetic reconnection, chromospheric evaporation, and coronal loop dynamics in the 2014 September 10 X-class flare. Slipping reconnection is found to be present throughout the flare from its early phase. Flare loops are seen to slip in opposite directions toward both ends of the ribbons. Velocities of 20-40 km s-1 are found within time windows where the slipping is well resolved. The warm coronal loops exhibit expanding and contracting motions that are interpreted as displacements due to the growing flux rope that subsequently erupts. This flux rope existed and erupted before the onset of apparent coronal implosion. This indicates that the energy release proceeds by slipping reconnection and not via coronal implosion. The slipping reconnection leads to changes in the geometry of the observed structures at the Interface Region Imaging Spectrograph slit position, from flare loop top to the footpoints in the ribbons. This results in variations of the observed velocities of chromospheric evaporation in the early flare phase. Finally, it is found that the precursor signatures, including localized EUV brightenings as well as nonthermal X-ray emission, are signatures of the flare itself, progressing from the early phase toward the impulsive phase, with the tether-cutting being provided by the slipping reconnection. The dynamics of both the flare and outlying coronal loops is found to be consistent with the predictions of the standard solar flare model in three dimensions
On the Spatial Coherence of Magnetic Ejecta: Measurements of Coronal Mass Ejections by Multiple Spacecraft Longitudinally Separated by 0.01 AU
Measurements of coronal mass ejections (CMEs) by multiple spacecraft at small
radial separations but larger longitudinal separations is one of the ways to
learn about the three-dimensional structure of CMEs. Here, we take advantage of
the orbit of the Wind spacecraft that ventured to distances of up to 0.012
astronomical units (au) from the Sun-Earth line during the years 2000 to 2002.
Combined with measurements from ACE, which is in a tight halo orbit around L1,
the multipoint measurements allow us to investigate how the magnetic field
inside magnetic ejecta (MEs) changes on scales of 0.005 - 0.012 au. We identify
21 CMEs measured by these two spacecraft for longitudinal separations of 0.007
au or more. We find that the time-shifted correlation between 30-minute
averages of the non-radial magnetic field components measured at the two
spacecraft is systematically above 0.97 when the separation is 0.008 au or
less, but is on average 0.89 for greater separations. Overall, these newly
analyzed measurements, combined with 14 additional ones when the spacecraft
separation is smaller, point towards a scale length of longitudinal magnetic
coherence inside MEs of 0.25 - 0.35 au for the magnitude of the magnetic field
but 0.06 - 0.12 au for the magnetic field components. This finding raises
questions about the very nature of MEs. It also highlights the need for
additional "mesoscale" multi-point measurements of CMEs with longitudinal
separations of 0.01 - 0.2 au.Comment: Published in ApJL, 6 page
Representing addition and subtraction : learning the formal conventions
The study was designed to test the effects of a structured intervention in teaching children to represent addition and subtraction. In a post-test only control group design, 90 five-year-olds experienced the intervention entitled Bi-directional Translation whilst 90 control subjects experienced typical teaching. Post-intervention testing showed some significant differences between the two groups both in terms of being able to effect the addition and subtraction operations and in being able to determine which operation was appropriate. The results suggest that, contrary to historical practices, children's exploration of real world situations should precede practice in arithmetical symbol manipulation
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