755 research outputs found
Are constant loop widths an artifact of the background and the spatial resolution?
We study the effect of the coronal background in the determination of the
diameter of EUV loops, and we analyze the suitability of the procedure followed
in a previous paper (L\'opez Fuentes, Klimchuk & D\'emoulin 2006) for
characterizing their expansion properties. For the analysis we create different
synthetic loops and we place them on real backgrounds from data obtained with
the Transition Region and Coronal Explorer (\textit{TRACE}). We apply to these
loops the same procedure followed in our previous works, and we compare the
results with real loop observations. We demonstrate that the procedure allows
us to distinguish constant width loops from loops that expand appreciably with
height, as predicted by simple force-free field models. This holds even for
loops near the resolution limit. The procedure can easily determine when loops
are below resolution limit and therefore not reliably measured. We find that
small-scale variations in the measured loop width are likely due to
imperfections in the background subtraction. The greatest errors occur in
especially narrow loops and in places where the background is especially bright
relative to the loop. We stress, however, that these effects do not impact the
ability to measure large-scale variations. The result that observed loops do
not expand systematically with height is robust.Comment: Accepted for publication in Ap
Tzitzeica solitons versus relativistic CalogeroâMoser three-body clusters
We establish a connection between the hyperbolic relativistic CalogeroâMoser systems and a class of soliton solutions to the Tzitzeica equation (also called the DoddâBulloughâZhiberâShabatâMikhailov equation). In the 6N-dimensional phase space Omega of the relativistic systems with 2N particles and N antiparticles, there exists a 2N-dimensional PoincarĂ©-invariant submanifold OmegaP corresponding to N free particles and N bound particle-antiparticle pairs in their ground state. The Tzitzeica N-soliton tau functions under consideration are real valued and obtained via the dual Lax matrix evaluated in points of OmegaP. This correspondence leads to a picture of the soliton as a cluster of two particles and one antiparticle in their lowest internal energy state
French translation and validation of the Jefferson Scale of Empathy - Health Professions Student version
Background: Background: Jefferson Scale of Empathy is one of the most widely used tools worldwide to assess empathy.
The extended version for Health Professions Students (JSE HPS) has not yet been translated into French. Objective:
The aim of our study was to translate the JSE HPS into French and assess the psychometric properties of this new
version (JSE HPS Fr). Methods: The JSE HPS was translated according to international recommendations. The main
psychometric qualities (test-retest reliability, internal consistency, floor and ceiling effects and construct validity) were studied in a sample of physiotherapy students. Participants provided general information (age, gender, year of study) and completed the JSE HPS Fr and the Questionnaire of Cognitive and Affective Empathy (QCAE). Participants were also asked to complete the JSE-HPS-Fr again one week later to assess its test-retest reliability. Results: 408 students (161 males and 247 females; mean age: 21.3 years) participated. The JSE HPS Fr demonstrated good test-retest reliability for the total score (ICC=0.81) and good internal consistency (α Cronbach: 0.79). The JSE HPS also showed good convergent validity with the QCAE questionnaire (r=0.41, p<0.05). No floor or ceiling effects were observed. Conclusions: The results indicate that the JSE HPS Fr is a valid and reliable tool to assess the level of empathy of French-speaking physiotherapy students
Final Report: Theory of Advanced High Efficiency Concentrator Cells
The goal of this project was to begin -developing accurate, and ultimately predictive, device models for III-V concentrator cells. The project consisted of extending a one-dimensional numerical device model previously developed at Purdue to III-V solar cells. We also began verifying the accuracy of the code by comparing computed and measured solar cell characteristics. Gallium arsenide was selected because it is the most mature III-V technology and because GaAs solar cells have demonstrated high conversion efficiency [l,2,3]. The present device model should be useful in optimizing GaAs solar cells and forms a foundation that can be extended to other III-V homo- and heterostructure solar cells. The numerical device model developed in this work solves Poissonâs equation simultaneously with the electron and hole continuity equations without making common assumptions such as low-level injection, piece-wise uniform doping, neglect of space-charge recombination, etc. Materials models for GaAs solar cells (e. g. intrinsic carrier concentration, carrier mobilities, lifetimes, optical absorption and reflection coefficients, etc.) were compiled, evaluated, and in some cases extended. These materials models were then implemented into the numerical device model. The device model was also extended to analyze optical absorption and reflection from bare and anti-reflection (AR) coated cells. To test the GaAs cell model, we compared its predictions to measured results for an N+P cell (the shallow homojunction cell reported by Fan and co-workers) and a P+N cell (fabricated by Borrego and co-workers). In general, good agreement between theory and experiment was obtained for both concentrated and unconcentrated conditions. Although detailed comparisons of the modelâs predictions with measured results continue, the present model is a useful tool for GaAs cell design and optimization
Liquid transport in scale space
International audienceWhen a liquid stream is injected into a gaseous atmosphere, it destabilizes and continuously passes through different states characterized by different morphologies. Throughout this process, the flow dynamics may be different depending on the region of the flow and the scales of the involved liquid structures. Exploring this multi-scale, multi-dimensional phenomenon requires some new theoretical tools, some of which need yet to be elaborated. Here, a new analytical framework is proposed on the basis of two-point statistical equations of the liquid volume fraction. This tool, which originates from single phase turbulence, allows us notably to decompose the fluxes of liquid in flowâposition space and scale space. Direct numerical simulations of liquidâgas turbulence decaying in a triply periodic domain are then used to characterize the time and scale evolution of the liquid volume fraction. It is emphasized that two-point statistics of the liquid volume fraction depend explicitly on the geometrical properties of the liquidâgas interface and in particular its surface density. The stretch rate of the liquidâgas interface is further shown to be the equivalent for the liquid volume fraction (a non-diffusive scalar) of the scalar dissipation rate. Finally, a decomposition of the transport of liquid in scale space highlights that non-local interactions between non-adjacent scales play a significant role
The Magnetic Environment of a Stealth Coronal Mass Ejection
Interest in stealth coronal mass ejections (CMEs) is increasing due to their relatively high occurrence rate and space weather impact. However, typical CME signatures such as extreme-ultraviolet dimmings and post-eruptive arcades are hard to identify and require extensive image processing techniques. These weak observational signatures mean that little is currently understood about the physics of these events. We present an extensive study of the magnetic field configuration in which the stealth CME of 2011 March 3 occurred. Three distinct episodes of flare ribbon formation are observed in the stealth CME source active region (AR). Two occurred prior to the eruption and suggest the occurrence of magnetic reconnection that builds the structure that will become eruptive. The third occurs in a time close to the eruption of a cavity that is observed in STEREO-B 171 Ă
data; this subsequently becomes part of the propagating CME observed in coronagraph data. We use both local (Cartesian) and global (spherical) models of the coronal magnetic field, which are complemented and verified by the observational analysis. We find evidence of a coronal null point, with field lines computed from its neighborhood connecting the stealth CME source region to two ARs in the northern hemisphere. We conclude that reconnection at the null point aids the eruption of the stealth CME by removing the field that acted to stabilize the preeruptive structure. This stealth CME, despite its weak signatures, has the main characteristics of other CMEs, and its eruption is driven by similar mechanisms
Observation of the Halo of NGC 3077 Near the "Garland" Region Using the Hubble Space Telescope
We report the detection of upper main sequence stars and red giant branch
stars in the halo of an amorphous galaxy, NGC3077. The observations were made
using Wide Field Planetary Camera~2 on board the Hubble Space Telescope. The
red giant branch luminosity function in I-band shows a sudden discontinuity at
I = 24.0 +- 0.1 mag. Identifying this with the tip of the red giant branch
(TRGB), and adopting the calibration provided by Lee, Freedman, & Madore (1993)
and the foreground extinction of A_B = 0.21 mag, we obtain a distance modulus
of (m-M)_0 = 27.93 +- 0.14(random) +- 0.16(sys). This value agrees well with
the distance estimates of four other galaxies in the M81 Group. In addition to
the RGB stars, we observe a concentration of upper main sequence stars in the
halo of NGC3077, which coincides partially with a feature known as the
``Garland''. Using Padua isochrones, these stars are estimated to be <150 Myrs
old. Assuming that the nearest encounter between NGC3077 and M81 occurred 280
Myrs ago as predicted by the numerical simulations (Yun 1997), the observed
upper main sequence stars are likely the results of the star formation
triggered by the M81-NGC3077 tidal interaction.Comment: 15 pages, 8 figures. Accepted for publication in Astrophysical
Journa
The Magnetic Topology of Coronal Mass Ejection sources
In an attempt to test current initiation models of coronal mass ejections
(CMEs), with an emphasis on the magnetic breakout model, we inspect the
magnetic topology of the sources of 26 CME events in the context of their
chromospheric and coronal response in an interval of approximately nine hours
around the eruption onset. First, we perform current-free (potential)
extrapolations of photospheric magnetograms to retrieve the key topological
ingredients, such as coronal magnetic null points. Then we compare the
reconnection signatures observed in the high cadence and high spatial
resolution of the Transition Region And Coronal Explorer (TRACE) images with
the location of the relevant topological features. The comparison reveals that
only seven events can be interpreted in terms of the breakout model, which
requires a multi-polar topology with pre-eruption reconnection at a coronal
null. We find, however, that a larger number of events (twelve) can not be
interpreted in those terms. No magnetic null is found in six of them. Seven
other cases remain difficult to interpret. We also show that there are no
systematic differences between the CME speed and flare energies of events under
different interpretations.Comment: Accepted for publication in Ap
Kristallstruktur einer racemischen Lipid-Doppelschicht bestimmt mit Synchrotronstrahlung
Tracking Solar Active Region Outflow Plasma from its Source to the near-Earth Environment
Seeking to establish whether active region upflow material contributes to the
slow solar wind, we examine in detail the plasma upflows from Active Region
(AR)10978, which crossed the Sun's disc in the interval 8 to 16 December, 2007
during Carrington rotation (CR)2064. In previous work, using data from the
Hinode/EUV Imaging Spectrometer, upflow velocity evolution was extensively
studied as the region crossed the disc while a linear force-free magnetic
extrapolation was used to confirm aspects of the velocity evolution and to
establish the presence of quasi-separatrix layers at the upflow source areas.
The plasma properties, temperature, density and first ionisation potential bias
(FIP-bias) were measured with the spectrometer during the disc passage of the
active region. Global potential field source surface (PFSS) models showed that
AR 10978 was completely covered by the closed field of a helmet streamer that
is part of the streamer belt. Thus it is not clear how any of the upflowing
AR-associated plasma could reach the source surface at 2.5 R(Sun)and contribute
to the slow solar wind. However a detailed examination of solar-wind in-situ
data obtained by the Advanced Composition Explorer (ACE) spacecraft at the L1
point shows that the increase in O^7+/O^6+, C^6+/C^5+ and Fe/O - a FIP-bias
proxy - are present before the heliospheric current sheet crossing. These
increases, along with an accompanying reduction in proton velocity and an
increase in density are characteristic of both AR and slow-wind plasma. Finally
we describe a two-step reconnection process by which some of the upflowing
plasma from the AR could reach the heliosphere
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