888 research outputs found
Reconnection Outflows and Current Sheet Observed with Hinode/XRT in the 2008 April 9 "Cartwheel CME" Flare
Supra-arcade downflows (SADs) have been observed with Yohkoh/SXT (soft X-rays
(SXR)), TRACE (extreme ultra-violet (EUV)), SoHO/LASCO (white light),
SoHO/SUMER (EUV spectra), and Hinode/XRT (SXR). Characteristics such as low
emissivity and trajectories which slow as they reach the top of the arcade are
consistent with post-reconnection magnetic flux tubes retracting from a
reconnection site high in the corona until they reach a lower-energy magnetic
configuration. Viewed from a perpendicular angle, SADs should appear as
shrinking loops rather than downflowing voids. We present XRT observations of
supra-arcade downflowing loops (SADLs) following a coronal mass ejection (CME)
on 2008 April 9 and show that their speeds and decelerations are consistent
with those determined for SADs. We also present evidence for a possible current
sheet observed during this flare that extends between the flare arcade and the
CME. Additionally, we show a correlation between reconnection outflows observed
with XRT and outgoing flows observed with LASCO.Comment: 32 pages, 23 figures, Accepted for publication by the Astrophysical
Journal (Oct. 2010
Quantitative Examination of a Large Sample of Supra-Arcade Downflows in Eruptive Solar Flares
Sunward-flowing voids above post-coronal mass ejection (CME) flare arcades
were first discovered using the soft X-ray telescope (SXT) aboard Yohkoh and
have since been observed with TRACE (extreme ultra-violet (EUV)), SOHO/LASCO
(white light), SOHO/SUMER (EUV spectra), and Hinode/XRT (soft X-rays (SXR)).
Supra-arcade downflow (SAD) observations suggest that they are the
cross-sections of thin flux tubes retracting from a reconnection site high in
the corona. Supra-arcade downflowing loops (SADLs) have also been observed
under similar circumstances and are theorized to be SADs viewed from a
perpendicular angle. Previous studies have presented detailed SAD observations
for a small number of flares. In this paper we present a substantial SADs and
SADLs flare catalog. We have applied semi-automatic detection software to
several of these events to detect and track individual downflows thereby
providing statistically significant samples of parameters such as velocity,
acceleration, area, magnetic flux, shrinkage energy, and reconnection rate. We
discuss these measurements, how they were obtained, and potential impact on
reconnection models.Comment: Submitted to ApJ -- 33 pages, 13 figure
X-ray Reflection By Photoionized Accretion Discs
We present the results of reflection calculations that treat the relevant
physics with a minimum of assumptions. The temperature and ionization structure
of the top five Thomson depths of an illuminated disc are calculated while also
demanding that the atmosphere is in hydrostatic equilibrium. In agreement with
Nayakshin, Kazanas & Kallman, we find that there is a rapid transition from hot
to cold material in the illuminated layer. However, the transition is usually
not sharp so that often we find a small but finite region in Thomson depth
where there is a stable temperature zone at T \sim 2 x 10^{6} K due to
photoelectric heating from recombining ions. As a result, the reflection
spectra often exhibit strong features from partially-ionized material,
including helium-like Fe K lines and edges. We find that due to the highly
ionized features in the spectra these models have difficulty correctly
parameterizing the new reflection spectra. There is evidence for a spurious
correlation in the ASCA energy range, where is the reflection
fraction for a power-law continuum of index , confirming the suggestion
of Done & Nayakshin that at least part of the R-Gamma correlation reported by
Zdziarski, Lubinski & Smith for Seyfert galaxies and X-ray binaries might be
due to ionization effects. Although many of the reflection spectra show strong
ionized features, these are not typically observed in most Seyfert and quasar
X-ray spectra.Comment: 16 pages, accepted by MNRAS, Fig. 8 is in colour Figures and tables
changed by a code update. Conclusions unchange
Transition Region Emission from Solar Flares during the Impulsive Phase
There are relatively few observations of UV emission during the impulsive
phases of solar flares, so the nature of that emission is poorly known. Photons
produced by solar flares can resonantly scatter off atoms and ions in the
corona. Based on off-limb measurements by SOHO/UVCS, we derive the O VI
1032 luminosities for 29 flares during the impulsive phase and the
Ly luminosities of 5 flares, and we compare them with X-ray
luminosities from GOES measurements. The upper transition region and lower
transition region luminosities of the events observed are comparable. They are
also comparable to the luminosity of the X-ray emitting gas at the beginning of
the flare, but after 10-15 minutes the X-ray luminosity usually dominates. In
some cases we can use Doppler dimming to estimate flow speeds of the O VI
emitting gas, and 5 events show speeds in the 40 to 80 range.
The O VI emission could originate in gas evaporating to fill the X-ray flare
loops, in heated chromospheric gas at the footpoints, or in heated prominence
material in the coronal mass ejection. All three sources may contribute in
different events or even in a single event, and the relative timing of UV and
X-ray brightness peaks, the flow speeds, and the total O VI luminosity favor
each source in one or more events.Comment: 18 pages, 8 figures, 3 table
Magnetic Reconnection with Asymmetry in the Outflow Direction
Magnetic reconnection with asymmetry in the outflow direction occurs in the
Earth's magnetotail, coronal mass ejections, flux cancellation events,
astrophysical disks, spheromak merging experiments, and elsewhere in nature and
the laboratory. A control volume analysis is performed for the case of steady
antiparallel magnetic reconnection with asymmetric downstream pressure, which
is used to derive scaling relations for the outflow velocity from each side of
the current sheet and the reconnection rate. Simple relationships for outflow
velocity are presented for the incompressible case and the case of symmetric
downstream pressure but asymmetric downstream density. Asymmetry alone is not
found to greatly affect the reconnection rate. The flow stagnation point and
magnetic field null do not coincide in a steady state unless the pressure
gradient is negligible at the flow stagnation point.Comment: 12 pages, 8 figures. Submitted to JGR. Any comments will be
appreciate
Inter-rater reliability of data elements from a prototype of the Paul Coverdell National Acute Stroke Registry
<p>Abstract</p> <p>Background</p> <p>The Paul Coverdell National Acute Stroke Registry (PCNASR) is a U.S. based national registry designed to monitor and improve the quality of acute stroke care delivered by hospitals. The registry monitors care through specific performance measures, the accuracy of which depends in part on the reliability of the individual data elements used to construct them. This study describes the inter-rater reliability of data elements collected in Michigan's state-based prototype of the PCNASR.</p> <p>Methods</p> <p>Over a 6-month period, 15 hospitals participating in the Michigan PCNASR prototype submitted data on 2566 acute stroke admissions. Trained hospital staff prospectively identified acute stroke admissions, abstracted chart information, and submitted data to the registry. At each hospital 8 randomly selected cases were re-abstracted by an experienced research nurse. Inter-rater reliability was estimated by the kappa statistic for nominal variables, and intraclass correlation coefficient (ICC) for ordinal and continuous variables. Factors that can negatively impact the kappa statistic (i.e., trait prevalence and rater bias) were also evaluated.</p> <p>Results</p> <p>A total of 104 charts were available for re-abstraction. Excellent reliability (kappa or ICC > 0.75) was observed for many registry variables including age, gender, black race, hemorrhagic stroke, discharge medications, and modified Rankin Score. Agreement was at least moderate (i.e., 0.75 > kappa ≥; 0.40) for ischemic stroke, TIA, white race, non-ambulance arrival, hospital transfer and direct admit. However, several variables had poor reliability (kappa < 0.40) including stroke onset time, stroke team consultation, time of initial brain imaging, and discharge destination. There were marked systematic differences between hospital abstractors and the audit abstractor (i.e., rater bias) for many of the data elements recorded in the emergency department.</p> <p>Conclusion</p> <p>The excellent reliability of many of the data elements supports the use of the PCNASR to monitor and improve care. However, the poor reliability for several variables, particularly time-related events in the emergency department, indicates the need for concerted efforts to improve the quality of data collection. Specific recommendations include improvements to data definitions, abstractor training, and the development of ED-based real-time data collection systems.</p
Optical Sensing Method for Screening Disease in Melon Seeds by Using Optical Coherence Tomography
We report a noble optical sensing method to diagnose seed abnormalities using optical coherence tomography (OCT). Melon seeds infected with Cucumber green mottle mosaic virus (CGMMV) were scanned by OCT. The cross-sectional sensed area of the abnormal seeds showed an additional subsurface layer under the surface which is not found in normal seeds. The presence of CGMMV in the sample was examined by a blind test (n = 140) and compared by the reverse transcription-polymerase chain reaction. The abnormal layers (n = 40) were quantitatively investigated using A-scan sensing analysis and statistical method. By utilizing 3D OCT image reconstruction, we confirmed the distinctive layers on the whole seeds. These results show that OCT with the proposed data processing method can systemically pick up morphological modification induced by viral infection in seeds, and, furthermore, OCT can play an important role in automatic screening of viral infections in seeds
Are in-Hospital Delays Important Obstacles in Thrombolytic Therapy Following Acute Ischemic Stroke?
Real Time Animation of Virtual Humans: A Trade-off Between Naturalness and Control
Virtual humans are employed in many interactive applications using 3D virtual environments, including (serious) games. The motion of such virtual humans should look realistic (or ‘natural’) and allow interaction with the surroundings and other (virtual) humans. Current animation techniques differ in the trade-off they offer between motion naturalness and the control that can be exerted over the motion. We show mechanisms to parametrize, combine (on different body parts) and concatenate motions generated by different animation techniques. We discuss several aspects of motion naturalness and show how it can be evaluated. We conclude by showing the promise of combinations of different animation paradigms to enhance both naturalness and control
Plasmoids in Reconnecting Current Sheets: Solar and Terrestrial Contexts Compared
Magnetic reconnection plays a crucial role in violent energy conversion
occurring in the environments of high electrical conductivity, such as the
solar atmosphere, magnetosphere, and fusion devices. We focus on the
morphological features of the process in two different environments, the solar
atmosphere and the geomagnetic tail. In addition to indirect evidence that
indicates reconnection in progress or having just taken place, such as auroral
manifestations in the magnetosphere and the flare loop system in the solar
atmosphere, more direct evidence of reconnection in the solar and terrestrial
environments is being collected. Such evidence includes the reconnection inflow
near the reconnecting current sheet, and the outflow along the sheet
characterized by a sequence of plasmoids. Both turbulent and unsteady
Petschek-type reconnection processes could account for the observations. We
also discuss other relevant observational consequences of both mechanisms in
these two settings. While on face value, these are two completely different
physical environments, there emerge many commonalities, for example, an Alfven
speed of the same order of magnitude, a key parameter determining the
reconnection rate. This comparative study is meant as a contribution to current
efforts aimed at isolating similarities in processes occurring in very
different contexts in the heliosphere, and even in the universe.Comment: 21 pages, 9 figures, in press at J. Geophys. Res. (Space Physics),
for the special NESSC section on Comparative Aspects of Magnetic Reconnectio
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