911 research outputs found
Solar and Galactic Cosmic Rays observed by SOHO
Both the Cosmic Ray Flux (CRF) and Solar Energetic Particles (SEPs) have left
an imprint on SOHO technical systems. While the solar array efficiency degraded
irreversibly down to ~77% of its original level over roughly 1 1/2 solar
cycles, Single Event Upsets (SEUs) in the solid state recorder (SSR) have been
reversed by the memory protection mechanism. We compare the daily CRF observed
by the Oulu station with the daily SOHO SEU rate and with the Degradation curve
of the solar arrays. The Oulu CRF and the SOHO SSR SEU rate are both modulated
by the solar cycle and are highly correlated, except for sharp spikes in the
SEU rate, caused by isolated SEP events, which also show up as discontinuities
in the otherwise slowly decreasing solar ray efficiency. This allows to
discriminate between effects with solar and non-solar origin and to compare the
relative strength of both. We find that during solar cycle 23 (1996 Apr 1 --
2008 Aug 31) only 6% of the total number of SSR SEUs were caused by SEPs; the
remaining 94% were due to galactic cosmic rays. During the maximum period of
cycle 23 (2000 Jan 1 -- 2003 Dec 31), the SEP contribution increased to 22%,
and during 2001, the year with the highest SEP rate, to 30%. About 40% of the
total solar array degradation during the 17 years from Jan 1996 through Feb
2013 can be attributed to proton events, i.e. the effect of a series of
short-lived, violent SEP events is comparable to the cycle-integrated damage by
cosmic rays.Comment: 10 pages, 5 figures accepted for publication in Cent. Eur. Astrophys.
Bul
Detection of 3-Minute Oscillations in Full-Disk Ly Emission During A Solar Flare
In this Letter we report the detection of chromospheric 3-minute oscillations
in disk-integrated EUV irradiance observations during a solar flare. A wavelet
analysis of detrended Lyman-alpha (from GOES/EUVS) and Lyman continuum (from
SDO/EVE) emission from the 2011 February 15 X-class flare (SOL2011-02-15T01:56)
revealed a 3-minute period present during the flare's main phase. The
formation temperature of this emission locates this radiation to the flare's
chromospheric footpoints, and similar behaviour is found in the SDO/AIA
1600\AA\ and 1700\AA\ channels, which are dominated by chromospheric continuum.
The implication is that the chromosphere responds dynamically at its acoustic
cutoff frequency to an impulsive injection of energy. Since the 3-minute period
was not found at hard X-ray energies (50-100 keV) in RHESSI data we can state
that this 3-minute oscillation does not depend on the rate of energization of
non-thermal electrons. However, a second period of 120 s found in both hard
X-ray and chromospheric emission is consistent with episodic electron
energization on 2-minute timescales. Our finding on the 3-minute oscillation
suggests that chromospheric mechanical energy should be included in the flare
energy budget, and the fluctuations in the Lyman-alpha line may influence the
composition and dynamics of planetary atmospheres during periods of high
activity.Comment: 6 pages, 5 figures. Accepted for publication in Astrophysics Journal
Letter
A New Method for Detecting Solar Atmospheric Gravity Waves
Internal gravity waves have been observed in the Earth's atmosphere and
oceans, on Mars and Jupiter, and in the Sun's atmosphere. Despite ample
evidence for the existence of propagating gravity waves in the Sun's
atmosphere, we still do not have a full understanding of their characteristics
and overall role for the dynamics and energetics of the solar atmosphere. Here
we present a new approach to study the propagation of gravity waves in the
solar atmosphere. It is based on calculating the three-dimensional
cross-correlation function between the vertical velocities measured at
different heights. We apply this new method to a time series of co-spatial and
co-temporal Doppler images obtained by SOHO/MDI and Hinode/SOT as well as to
simulations of upward propagating gravity wave packets. We show some
preliminary results and outline future developments.Comment: 11 pages, 6 figure
Visualization of Chronic Myocardial Infarction Using the Intravascular Contrast Agent MS-325 (Gadofosveset) in Patients
Aims. The aim of this study was to evaluate the potential of visualizing chronic myocardial infarction in patients using the intravascular CA MS-325 (gadofosveset, EPIX Pharmaceuticals, Mass, USA). Methods. Nine patients were enrolled in a clinical phase II multicenter trial for MRCA and perfusion imaging using MS-325. They had objective evidence of chronic myocardial infarction as visualized by previously performed late gadolinium (Gd) enhancement imaging (LGE) with a conventional extracellular Gd-DTPA CA (Magnevist, Bayer Healthcare, Germany, 0.2 mmol/kg/body weight) serving as reference standard. A prepulse-optimized LGE study was performed immediately and at several time points after injection of MS-325 (0.05 mmol/kg/body weight). The number and localization of segments demonstrating LGE with MS-325 as well as signal intensities were compared with the reference standard (Gd-DTPA). Results. Using MS-325, LGE could be detected at every time point in all 9 patients. The accuracy of LGE with MS-325 as compared to LGE with Gd-DTPA was highest 54 ± 4 minutes after contrast injection, resulting in a sensitivity of 84% with a specificity of 98%. Conclusion. The intravascular CA MS-325 has the potential to visualize chronic myocardial infarction. However, in comparison with Gd-DTPA, the transmural extent and the number of segments are smaller
BOLD cardiovascular magnetic resonance at 3.0 tesla in myocardial ischemia
Background: The purpose of this study was to determine the ability of Blood Oxygen Level Dependent (BOLD) cardiovascular magnetic resonance (CMR) to detect stress-inducible myocardial ischemic reactions in the presence of angiographically significant coronary artery disease (CAD).
Methods: Forty-six patients (34 men; age 65 ± 9 years,) with suspected or known coronary artery disease underwent CMR at 3Tesla prior to clinically indicated invasive coronary angiography. BOLD CMR was performed in 3 short axis slices of the heart at rest and during adenosine stress (140 μg/kg/min) followed by late gadolinium enhancement (LGE) imaging. In all 16 standard myocardial segments, T2* values were derived at rest and under adenosine stress. Quantitative coronary angiography served as the standard of reference and defined normal myocardial segments (i.e. all 16 segments in patients without any CAD), ischemic segments (i.e. supplied by a coronary artery with ≥50% luminal narrowing) and non-ischemic segments (i.e. supplied by a non-significantly stenosed coronary artery in patients with significant CAD).
Results: Coronary angiography demonstrated significant CAD in 23 patients. BOLD CMR at rest revealed significantly lower T2* values for ischemic segments (26.7 ± 11.6 ms) compared to normal (31.9 ± 11.9 ms; p < 0.0001) and non-ischemic segments (31.2 ± 12.2 ms; p = 0.0003). Under adenosine stress T2* values increased significantly in normal segments only (37.2 ± 14.7 ms; p < 0.0001).
Conclusions: Rest and stress BOLD CMR at 3Tesla proved feasible and differentiated between ischemic, non-ischemic, and normal myocardial segments in a clinical patient population. BOLD CMR during vasodilator stress identified patients with significant CAD
A steady-state supersonic downflow in the transition region above a sunspot umbra
We investigate a small-scale (~1.5 Mm along the slit), supersonic downflow of about 90 km s-1 in the transition region above the lightbridged sunspot umbra in AR 11836. The observations were obtained with the Interface Region Spectrograph (IRIS) on 2013 September 2 from 16:40 to 17:59 UT. The downflow shows up as redshifted "satellite" lines of the Si iv and O iv transition region lines and is remarkably steady over the observing period of nearly 80 min. The downflow is not visible in the chromospheric lines, which only show an intensity enhancement at the location of the downflow. The density inferred from the line ratio of the redshifted satellites of the O iv lines (Ne = 1010.6 ± 0.25 cm-3) is only a factor 2 smaller than the one inferred from the main components (Ne = 1010.95 ± 0.20 cm-3). Consequently, this implies a substantial mass flux (~5 × 10-7 g cm-2 s-1), which would evacuate the overlying corona on timescales close to 10 s. We interpret these findings as evidence of a stationary termination shock of a supersonic siphon flow in a cool loop that is rooted in the central umbra of the spot. The movie is available in electronic form at http://www.aanda.or
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