1,077 research outputs found
Identification of Flexural Rigidity in a Kirchhoff Plates Model Using a Convex Objective and Continuous Newton Method
This work provides a detailed theoretical and numerical study of the inverse problem of identifying flexural rigidity in Kirchhoff plate models. From a mathematical standpoint, this inverse problem requires estimating a variable coefficient in a fourth-order boundary value problem.This inverse problem and related estimation problems associated with general plates and shellmodels have been investigated by numerous researchers through an optimization framework using the output least-squares (OLSs) formulation. OLS yields a nonconvex framework and hence it is suitable for investigating only the local behavior of the solution. In this work, we propose a new convex framework for the inverse problem of identifying a variable parameter in a fourth-order inverse problem. Existence results, optimality conditions, and discretization issues are discussed in detail. The discrete inverse problem is solved by using a continuous Newton method. Numerical results show the feasibility of the proposed framework
The Relationship of Coronal Mass Ejections to Streamers
We have examined images from the Large Angle Spectroscopic Coronagraph
(LASCO) to study the relationship of Coronal Mass Ejections (CMEs) to coronal
streamers. We wish to test the suggestion (Low 1996) that CMEs arise from flux
ropes embedded in a streamer erupting, thus disrupting the streamer. The data
span a period of two years near sunspot minimum through a period of increased
activity as sunspot numbers increased. We have used LASCO data from the C2
coronagraph which records Thomson scattered white light from coronal electrons
at heights between 1.5 and 6R_sun. Maps of the coronal streamers have been
constructed from LASCO C2 observations at a height of 2.5R_sun at the east and
west limbs. We have superposed the corresponding positions of CMEs observed
with the C2 coronagraph onto the synoptic maps. We identified the different
kinds of signatures CMEs leave on the streamer structure at this height
(2.5R_sun). We find four types of CMEs with respect to their effect on
streamers:
1. CMEs that disrupt the streamer 2. CMEs that have no effect on the
streamer, even though they are related to it. 3. CMEs that create streamer-like
structures 4. CMEs that are latitudinally displaced from the streamer.
This is the most extensive observational study of the relation between CMEs
and streamers to date. Previous studies using SMM data have made the general
statement that CMEs are mostly associated with streamers, and that they
frequently disrupt it. However, we find that approximately 35% of the observed
CMEs bear no relation to the pre-existing streamer, while 46% have no effect on
the observed streamer, even though they appear to be related to it. Our
conclusions thus differ considerably from those of previous studies.Comment: Accepted, Journal of Geophysical Research. 8 figs, better versions at
http://www.science.gmu.edu/~prasads/streamer.htm
Parents' reported preference scores for childhood atopic dermatitis disease states
BACKGROUND: We sought to elicit preference weights from parents for health states corresponding to children with various levels of severity of atopic dermatitis. We also evaluated the hypothesis that parents with children who had been diagnosed with atopic dermatitis would assign different preferences to the health state scenarios compared with parents who did not have a child with atopic dermatitis. METHODS: Subjects were parents of children aged 3 months to 18 years. The sample was derived from the General Panel, Mommies Sub-Panel, and Chronic Illness Sub-Panel of Harris Interactive. Participants rated health scenarios for atopic dermatitis, asthma, and eyeglasses on a visual analog scale, imagining a child was experiencing the described state. RESULTS: A total of 3539 parents completed the survey. Twenty-nine percent had a child with a history of atopic dermatitis. Mean preference scores for atopic dermatitis were as follows: mild, 91 (95% confidence interval [CI], 90.7 to 91.5); mild/moderate, 84 (95%CI, 83.5 to 84.4); moderate, 73 (95%CI, 72.5 to 73.6); moderate/severe, 61 (95%CI, 60.6 to 61.8); severe, 49 (95% CI, 48.7 to 50.1); asthma, 58 (95%CI, 57.4 to 58.8); and eyeglasses, 87(95%CI, 86.3 to 87.4). CONCLUSIONS: Parents perceive that atopic dermatitis has a negative effect on quality of life that increases with disease severity. Estimates of parents' preferences can provide physicians with insight into the value that parents place on their children's treatment and can be used to evaluate new medical therapies for atopic dermatitis
STEREO and Wind observations of a fast ICME flank triggering a prolonged geomagnetic storm on 5-7 April 2010
On 5 April 2010 an interplanetary (IP) shock was detected by the Wind
spacecraft ahead of Earth, followed by a fast (average speed 650 km/s) IP
coronal mass ejection (ICME). During the subsequent moderate geomagnetic storm
(minimum Dst = -72 nT, maximum Kp=8-), communication with the Galaxy 15
satellite was lost. We link images from STEREO/SECCHI to the near-Earth in situ
observations and show that the ICME did not decelerate much between Sun and
Earth. The ICME flank was responsible for a long storm growth phase. This type
of glancing collision was for the first time directly observed with the STEREO
Heliospheric Imagers. The magnetic cloud (MC) inside the ICME cannot be modeled
with approaches assuming an invariant direction. These observations confirm the
hypotheses that parts of ICMEs classified as (1) long-duration MCs or (2)
magnetic-cloud-like (MCL) structures can be a consequence of a spacecraft
trajectory through the ICME flank.Comment: Geophysical Research Letters (accepted); 3 Figure
Determining the Magnetic Field Orientation of Coronal Mass Ejections from Faraday Rotation
We describe a method to measure the magnetic field orientation of coronal
mass ejections (CMEs) using Faraday rotation (FR). Two basic FR profiles,
Gaussian-shaped with a single polarity or "N"-like with polarity reversals, are
produced by a radio source occulted by a moving flux rope depending on its
orientation. These curves are consistent with the Helios observations,
providing evidence for the flux-rope geometry of CMEs. Many background radio
sources can map CMEs in FR onto the sky. We demonstrate with a simple flux rope
that the magnetic field orientation and helicity of the flux rope can be
determined 2-3 days before it reaches Earth, which is of crucial importance for
space weather forecasting. An FR calculation based on global
magnetohydrodynamic (MHD) simulations of CMEs in a background heliosphere shows
that FR mapping can also resolve a CME geometry curved back to the Sun. We
discuss implementation of the method using data from the Mileura Widefield
Array (MWA).Comment: 22 pages with 9 figures, accepted for publication in Astrophys.
Isolated Electrostatic Structures Observed Throughout the Cluster Orbit: Relationship to Magnetic Field Strength
Isolated electrostatic structures are observed throughout much of the 4 Re by
19.6 Re Cluster orbit. These structures are observed in the Wideband plasma
wave instrument's waveform data as bipolar and tripolar pulses. These
structures are observed at all of the boundary layers, in the solar wind and
magnetosheath, and along auroral field lines at 4.5-6.5 Re. Using the Wideband
waveform data from the various Cluster spacecraft we have carried out a survey
of the amplitudes and time durations of these structures and how these
quantities vary with the local magnetic field strength. Such a survey has not
been carried out before, and it reveals certain characteristics of solitary
structures in a finite magnetic field, a topic still inadequately addressed by
theories. We find that there is a broad range of electric field amplitudes at
any specific magnetic field strength, and there is a general trend for the
electric field amplitudes to increase as the strength of the magnetic field
increases over a range of 5 to 500 nT. We provide a possible explanation for
this trend that releates to the structures being Bernstein-Greene-Kruskal mode
solitary waves. There is no corresponding dependence of the duration of the
structures on the magnetic field strength, although a plot of these two
quantities reveals the unexpected result that with the exception of the
magnetosheath, all of the time durations for all of the other regions are
comparable, wheras the magnetosheath time durations clearly are in a different
category of much smaller time duration. We speculate that this implies the
structures are much smaller in size.Comment: 24 pages plus 8 figures; paper presented at Spatio-Temporal Analysis
and Multipoint Measurements in Space (STAMMS) conference, held in Orleans,
France on 12-16 May 200
The Impact of New EUV Diagnostics on CME-Related Kinematics
We present the application of novel diagnostics to the spectroscopic
observation of a Coronal Mass Ejection (CME) on disk by the Extreme Ultraviolet
Imaging Spectrometer (EIS) on the Hinode spacecraft. We apply a recently
developed line profile asymmetry analysis to the spectroscopic observation of
NOAA AR 10930 on 14-15 December 2006 to three raster observations before and
during the eruption of a 1000km/s CME. We see the impact that the observer's
line-of-sight and magnetic field geometry have on the diagnostics used.
Further, and more importantly, we identify the on-disk signature of a
high-speed outflow behind the CME in the dimming region arising as a result of
the eruption. Supported by recent coronal observations of the STEREO
spacecraft, we speculate about the momentum flux resulting from this outflow as
a secondary momentum source to the CME. The results presented highlight the
importance of spectroscopic measurements in relation to CME kinematics, and the
need for full-disk synoptic spectroscopic observations of the coronal and
chromospheric plasmas to capture the signature of such explosive energy release
as a way of providing better constraints of CME propagation times to L1, or any
other point of interest in the heliosphere.Comment: Accepted to appear in Solar Physics Topical Issue titled "Remote
Sensing of the Inner Heliosphere". Manuscript has 14 pages, 5 color figures.
Movies supporting the figures can be found in
http://download.hao.ucar.edu/pub/mscott/papers/Weathe
Does fix the Electromagnetic Form Factor at ?
We show that the decay is a reliable
source of information for the electromagnetic form factor of the pion at
by using general arguments to estimate, or
rather, put upper bounds on, the background processes that could spoil this
extraction. We briefly comment on the significance of the resulting
.Comment: 10 pages revtex manuscript, one figure--not included, U. of MD PP
#94-00
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