135 research outputs found
Using the Dipolar and Quadrupolar Moments to Improve Solar-Cycle Predictions Based on the Polar Magnetic Fields
The solar cycle and its associated magnetic activity are the main drivers
behind changes in the interplanetary environment and Earth's upper atmosphere
(commonly referred to as space weather and climate). In recent years there has
been an effort to develop accurate solar cycle predictions, leading to nearly a
hundred widely spread predictions for the amplitude of solar cycle 24. Here we
show that cycle predictions can be made more accurate if performed separately
for each hemisphere, taking advantage of information about both the dipolar and
quadrupolar moments of the solar magnetic field during minimum
Simulations of the Kelvin-Helmholtz instability driven by coronal mass ejections in the turbulent corona
Recent high resolution AIA/SDO images show evidence of the development of the
Kelvin-Helmholtz instability, as coronal mass ejections (CMEs) expand in the
ambient corona. A large-scale magnetic field mostly tangential to the interface
is inferred, both on the CME and on the background sides. However, the magnetic
field component along the shear flow is not strong enough to quench the
instability. There is also observational evidence that the ambient corona is in
a turbulent regime, and therefore the criteria for the development of the
instability are a-priori expected to differ from the laminar case. To study the
evolution of the Kelvin-Helmholtz instability with a turbulent background, we
perform three-dimensional simulations of the incompressible magnetohydrodynamic
equations. The instability is driven by a velocity profile tangential to the
CME-corona interface, which we simulate through a hyperbolic tangent profile.
The turbulent background is generated by the application of a stationary
stirring force. We compute the instability growth-rate for different values of
the turbulence intensity, and find that the role of turbulence is to attenuate
the growth. The fact that the Kelvin-Helmholtz instability is observed, sets an
upper limit to the correlation length of the coronal background turbulence
Management of Elbow Dislocations in the National Football League.
Background: Although much literature exists regarding the treatment and management of elbow dislocations in the general population, little information is available regarding management in the athletic population. Furthermore, no literature is available regarding the postinjury treatment and timing of return to play in the contact or professional athlete.
Purpose: To review the clinical course of elbow dislocations in professional football players and determine the timing of return to full participation.
Study Design: Case series; Level of evidence, 4.
Methods: All National Football League (NFL) athletes with elbow dislocations from 2000 through 2011 who returned to play during the season were identified from the NFL Injury Surveillance System (NFL ISS). Roster position, player activity, use of external bracing, and clinical course were reviewed. Mean number of days lost until full return to play was determined for players with elbow dislocations who returned in the same season.
Results: From 2000 to 2011, a total of 62 elbow dislocations out of 35,324 injuries were recorded (0.17%); 40 (64.5%) dislocations occurred in defensive players, 12 (19.4%) were in offensive players; and 10 (16.1%) were during special teams play. Over half of the injuries (33/62, 53.2%) were sustained while tackling, and 4 (6.5%) patients required surgery. A total of 47 (75.8%) players who sustained this injury were able to return in the same season. For this group, the mean number of days lost in players treated conservatively (45/47) was 25.1 days (median, 23.0 days; range, 0.0-118 days), while that for players treated operatively (2/47) was 46.5 days (median, 46.5 days; range, 29-64 days). Mean return to play based on player position was 25.8 days for defensive players (n = 28; median, 21.5 days; range, 3.0-118 days), 24.1 days for offensive players (n = 11; median, 19 days; range, 2.0-59 days), and 25.6 days for special teams players (n = 8; median, 25.5 days; range, 0-44 days).
Conclusion: Elbow dislocations comprise less than a half of a percent of all injuries sustained in the NFL. Most injuries occur during the act of tackling, with the majority of injured athletes playing a defensive position. Players treated nonoperatively missed a mean of 25.1 days, whereas those managed operatively missed a mean of 46.5 days
Influence of Coronal Abundance Variations
During the final year of this program we concentrated on understanding the how to constrain the models with the best available observations. Work on developing accurate temperature and density diagnostics fkom TRACE and CDS together with constrained fits of non-potential force free fields will be extremely useful in the guiding the next generation of coronal models. The program has produced three fully operation numerical codes that model multi-species of ions in coronal loops: Static models and constant flow models. The time dependent numerical models have not been completed. We have extended the steady flow investigations to study the effect these flows have on coronal structure as observed with TRACE. Coronal observations derive from heavy-ion emission; thus, we focus on the extent to which flow may modify coronal abundances by examining the heavy-ion abundance stratification within long-lived loops. We discuss the magnitudes of the physical effects modeled and compare simulated results with TRACE observations. These results can have a profound effect on the interpretation of TRACE observations
The Minimum of Solar Cycle 23: As Deep as It Could Be?
In this work we introduce a new way of binning sunspot group data with the
purpose of better understanding the impact of the solar cycle on sunspot
properties and how this defined the characteristics of the extended minimum of
cycle 23. Our approach assumes that the statistical properties of sunspots are
completely determined by the strength of the underlying large-scale field and
have no additional time dependencies. We use the amplitude of the cycle at any
given moment (something we refer to as activity level) as a proxy for the
strength of this deep-seated magnetic field.
We find that the sunspot size distribution is composed of two populations:
one population of groups and active regions and a second population of pores
and ephemeral regions. When fits are performed at periods of different activity
level, only the statistical properties of the former population, the active
regions, is found to vary.
Finally, we study the relative contribution of each component (small-scale
versus large-scale) to solar magnetism. We find that when hemispheres are
treated separately, almost every one of the past 12 solar minima reaches a
point where the main contribution to magnetism comes from the small-scale
component. However, due to asymmetries in cycle phase, this state is very
rarely reached by both hemispheres at the same time. From this we infer that
even though each hemisphere did reach the magnetic baseline, from a
heliospheric point of view the minimum of cycle 23 was not as deep as it could
have been
Temperature and Emission-Measure Profiles Along Long-Lived Solar Coronal Loops Observed with TRACE
We report an initial study of temperature and emission measure distributions
along four steady loops observed with the Transition Region and Coronal
Explorer (TRACE) at the limb of the Sun. The temperature diagnostic is the
filter ratio of the extreme-ultraviolet 171-angstrom and 195-angstrom
passbands. The emission measure diagnostic is the count rate in the
171-angstrom passband. We find essentially no temperature variation along the
loops. We compare the observed loop structure with theoretical isothermal and
nonisothermal static loop structure.Comment: 10 pages, 3 postscript figures (LaTeX, uses aaspp4.sty). Accepted by
ApJ Letter
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