55 research outputs found
Oscillatory Modes of a Prominence-PCTR-Corona Slab Model
Oscillations of magnetic structures in the solar corona have often been
interpreted in terms of magnetohydrodynamic waves. We study the adiabatic
magnetoacoustic modes of a prominence plasma slab with a uniform longitudinal
magnetic field, surrounded by a prominence-corona transition region (PCTR) and
a coronal medium. Considering linear small-amplitude oscillations, the
dispersion relation for the magnetoacoustic slow and fast modes is deduced
assuming evanescent-like perturbations in the coronal medium. In the system
without PCTR, a classification of the oscillatory modes according to the
polarisation of their eigenfunctions is made in order to distinguish modes with
fast-like or slow-like properties. Internal and external slow modes are
governed by the prominence and coronal properties respectively, and fast modes
are mostly dominated by prominence conditions for the observed wavelengths. In
addition, the inclusion of an isothermal PCTR does not substantially influence
the mode frequencies, but new solutions (PCTR slow modes) are present.Comment: Accepted for publication in Solar Physic
Advanced CT imaging features reflect distinct tissue immune profiles and exhibit high prognostic impact on NSCLC
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Oscillatory motions observed in eruptive filaments
Context: The origin of the variable component of the solar wind is of great
intrinsic interest for heliophysics and space-weather, e.g. the initiation of
coronal mass ejections, and the problem of mass loss of all stars. It is also
related to the physics of coronal neutral sheets and streamers, occurring above
lines of magnetic polarity reversal. Filaments and prominences correspond to
the cool coronal component of these regions.
Aims: We examine the dynamical behaviour of these structures where
reconnection and dissipation of magnetic energy in the turbulent plasma are
occurring. The link between the observed oscillatory motions and the eruption
occurrence is investigated in detail for two different events.
Method: Two filaments are analysed using two different datasets: time series
of spectra using a transition region line (He I at 584.33 A) and a coronal line
(Mg X at 609.79 A) measured with CDS on-board SOHO, observed on May 30, 2003,
and time series of intensity and velocity images from the NSO/Dunn Solar
Telescope in the Halpha line on September 18, 1994 for the other. The
oscillatory content is investigated using Fourier transform and wavelet
analysis and is compared to different models.
Results: In both filaments, oscillations are clearly observed, in intensity
and velocity in the He I and Mg X lines, in velocity in Halpha, with similar
periods from a few minutes up to 80 minutes, with a main range from 20 to 30
minutes, cotemporal with eruptions. Both filaments exhibit vertical oscillating
motions. For the filament observed in the UV (He I and Mg X lines), we provide
evidence of damped velocity oscillations, and for the filament observed in the
visible (Halpha line), we provide evidence that parts of the filament are
oscillating, while the filament is moving over the solar surface, before its
disappearance.Comment: Accepted in A&
The Effects of Atmospheric Dispersion on High-Resolution Solar Spectroscopy
We investigate the effects of atmospheric dispersion on observations of the
Sun at the ever-higher spatial resolutions afforded by increased apertures and
improved techniques. The problems induced by atmospheric refraction are
particularly significant for solar physics because the Sun is often best
observed at low elevations, and the effect of the image displacement is not
merely a loss of efficiency, but the mixing of information originating from
different points on the solar surface. We calculate the magnitude of the
atmospheric dispersion for the Sun during the year and examine the problems
produced by this dispersion in both spectrographic and filter observations. We
describe an observing technique for scanning spectrograph observations that
minimizes the effects of the atmospheric dispersion while maintaining a regular
scanning geometry. Such an approach could be useful for the new class of
high-resolution solar spectrographs, such as SPINOR, POLIS, TRIPPEL, and ViSP
Studying Sun-Planet Connections Using the Heliophysics Integrated Observatory (HELIO)
The Heliophysics Integrated Observatory (HELIO) is a software infrastructure involving a collection of web services, heliospheric data sources (e.g., solar, planetary, etc.), and event catalogues – all of which are accessible through a unified front end. In this paper we use the HELIO infrastructure to perform three case studies based on solar events that propagate through the heliosphere. These include a coronal mass ejection that intersects both Earth and Mars, a solar energetic particle event that crosses the orbit of Earth, and a high-speed solar wind stream, produced by a coronal hole, that is observed in situ at Earth (L1). A ballistic propagation model is run as one of the HELIO services and used to model these events, predicting if they will interact with a spacecraft or planet and determining the associated time of arrival. The HELIO infrastructure streamlines the method used to perform these kinds of case study by centralising the process of searching for and visualising data, indicating interesting features on the solar disk, and finally connecting remotely observed solar features with those detected by in situ solar wind and energetic particle instruments. HELIO represents an important leap forward in European heliophysics infrastructure by bridging the boundaries of traditional scientific domains
The Solar Orbiter Science Activity Plan: translating solar and heliospheric physics questions into action
Solar Orbiter is the first space mission observing the solar plasma both in situ and remotely, from a close distance, in and out of the ecliptic. The ultimate goal is to understand how the Sun produces and controls the heliosphere, filling the Solar System and driving the planetary environments. With six remote-sensing and four in-situ instrument suites, the coordination and planning of the operations are essential to address the following four top-level science questions: (1) What drives the solar wind and where does the coronal magnetic field originate?; (2) How do solar transients drive heliospheric variability?; (3) How do solar eruptions produce energetic particle radiation that fills the heliosphere?; (4) How does the solar dynamo work and drive connections between the Sun and the heliosphere? Maximising the mission’s science return requires considering the characteristics of each orbit, including the relative position of the spacecraft to Earth (affecting downlink rates), trajectory events (such as gravitational assist manoeuvres), and the phase of the solar activity cycle. Furthermore, since each orbit’s science telemetry will be downloaded over the course of the following orbit, science operations must be planned at mission level, rather than at the level of individual orbits. It is important to explore the way in which those science questions are translated into an actual plan of observations that fits into the mission, thus ensuring that no opportunities are missed. First, the overarching goals are broken down into specific, answerable questions along with the required observations and the so-called Science Activity Plan (SAP) is developed to achieve this. The SAP groups objectives that require similar observations into Solar Orbiter Observing Plans, resulting in a strategic, top-level view of the optimal opportunities for science observations during the mission lifetime. This allows for all four mission goals to be addressed. In this paper, we introduce Solar Orbiter’s SAP through a series of examples and the strategy being followed
Elective Cancer Surgery in COVID-19-Free Surgical Pathways During the SARS-CoV-2 Pandemic: An International, Multicenter, Comparative Cohort Study.
PURPOSE: As cancer surgery restarts after the first COVID-19 wave, health care providers urgently require data to determine where elective surgery is best performed. This study aimed to determine whether COVID-19-free surgical pathways were associated with lower postoperative pulmonary complication rates compared with hospitals with no defined pathway. PATIENTS AND METHODS: This international, multicenter cohort study included patients who underwent elective surgery for 10 solid cancer types without preoperative suspicion of SARS-CoV-2. Participating hospitals included patients from local emergence of SARS-CoV-2 until April 19, 2020. At the time of surgery, hospitals were defined as having a COVID-19-free surgical pathway (complete segregation of the operating theater, critical care, and inpatient ward areas) or no defined pathway (incomplete or no segregation, areas shared with patients with COVID-19). The primary outcome was 30-day postoperative pulmonary complications (pneumonia, acute respiratory distress syndrome, unexpected ventilation). RESULTS: Of 9,171 patients from 447 hospitals in 55 countries, 2,481 were operated on in COVID-19-free surgical pathways. Patients who underwent surgery within COVID-19-free surgical pathways were younger with fewer comorbidities than those in hospitals with no defined pathway but with similar proportions of major surgery. After adjustment, pulmonary complication rates were lower with COVID-19-free surgical pathways (2.2% v 4.9%; adjusted odds ratio [aOR], 0.62; 95% CI, 0.44 to 0.86). This was consistent in sensitivity analyses for low-risk patients (American Society of Anesthesiologists grade 1/2), propensity score-matched models, and patients with negative SARS-CoV-2 preoperative tests. The postoperative SARS-CoV-2 infection rate was also lower in COVID-19-free surgical pathways (2.1% v 3.6%; aOR, 0.53; 95% CI, 0.36 to 0.76). CONCLUSION: Within available resources, dedicated COVID-19-free surgical pathways should be established to provide safe elective cancer surgery during current and before future SARS-CoV-2 outbreaks
Elective cancer surgery in COVID-19-free surgical pathways during the SARS-CoV-2 pandemic: An international, multicenter, comparative cohort study
PURPOSE As cancer surgery restarts after the first COVID-19 wave, health care providers urgently require data to determine where elective surgery is best performed. This study aimed to determine whether COVID-19–free surgical pathways were associated with lower postoperative pulmonary complication rates compared with hospitals with no defined pathway. PATIENTS AND METHODS This international, multicenter cohort study included patients who underwent elective surgery for 10 solid cancer types without preoperative suspicion of SARS-CoV-2. Participating hospitals included patients from local emergence of SARS-CoV-2 until April 19, 2020. At the time of surgery, hospitals were defined as having a COVID-19–free surgical pathway (complete segregation of the operating theater, critical care, and inpatient ward areas) or no defined pathway (incomplete or no segregation, areas shared with patients with COVID-19). The primary outcome was 30-day postoperative pulmonary complications (pneumonia, acute respiratory distress syndrome, unexpected ventilation). RESULTS Of 9,171 patients from 447 hospitals in 55 countries, 2,481 were operated on in COVID-19–free surgical pathways. Patients who underwent surgery within COVID-19–free surgical pathways were younger with fewer comorbidities than those in hospitals with no defined pathway but with similar proportions of major surgery. After adjustment, pulmonary complication rates were lower with COVID-19–free surgical pathways (2.2% v 4.9%; adjusted odds ratio [aOR], 0.62; 95% CI, 0.44 to 0.86). This was consistent in sensitivity analyses for low-risk patients (American Society of Anesthesiologists grade 1/2), propensity score–matched models, and patients with negative SARS-CoV-2 preoperative tests. The postoperative SARS-CoV-2 infection rate was also lower in COVID-19–free surgical pathways (2.1% v 3.6%; aOR, 0.53; 95% CI, 0.36 to 0.76). CONCLUSION Within available resources, dedicated COVID-19–free surgical pathways should be established to provide safe elective cancer surgery during current and before future SARS-CoV-2 outbreaks
Oscillations in a solar filament: first observation of long periods in the HeI 584.33 Å line, modelling and diagnostic
Three long observations of filaments were carried out in the 584.33 Å
HeI
line during
MEDOC campaigns in November
2003 and November 2004, by the Coronal Diagnostic Spectrometer
onboard SOHO. Their duration was 15-16 h and the
temporal resolution was 20 s, allowing measurements of the entire range of
periodicities theoretically expected in a filament (particularly both the short
periods, less than 10 min, and the long ones, more than 40 min). Fourier analysis of the Doppler velocities in the filament
allows us to detect
oscillations over a wide range, and particularly very slow
velocity oscillations (5-6 h) that were not detected previously.
We test an earlier interpretation of these velocity oscillations in
the prominence model of Joarder & Roberts (1993, A&A, 277, 225), who
treat the prominence as a slab. We used a
systematic method
to identify the six
fundamental modes
predicted by the model among the numerous frequencies detected. Identification of these modes
– and especially the slowest one, the slow kink mode – provides a complete
diagnostic of the filament
in terms of the Alfvén speed,
temperature, and angle between the magnetic field and the main
axis of the filament.
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