642 research outputs found
Automated LASCO CME catalog for solar cycle 23: are CMEs scale invariant?
In this paper we present the first automatically constructed LASCO CME
catalog, a result of the application of the Computer Aided CME Tracking
software (CACTus) on the LASCO archive during the interval September 1997 -
January 2007. We have studied the CME characteristics and have compared them
with similar results obtained by manual detection (CDAW CME catalog). On
average CACTus detects less than 2 events per day during solar minimum up to 8
events during maximum, nearly half of them being narrow (< 20 degrees).
Assuming a correction factor, we find that the CACTus CME rate is surprisingly
consistent with CME rates found during the past 30 years. The CACTus statistics
show that small scale outflow is ubiquitously observed in the outer corona. The
majority of CACTus-only events are narrow transients related to previous CME
activity or to intensity variations in the slow solar wind, reflecting its
turbulent nature. A significant fraction (about 15%) of CACTus-{\it only}
events were identified as independent events, thus not related to other CME
activity. The CACTus CME width distribution is essentially scale invariant in
angular span over a range of scales from 20 to 120 degrees while previous
catalogues present a broad maximum around 30 degrees. The possibility that the
size of coronal mass outflows follow a power law distribution could indicate
that no typical CME size exists, i.e. that the narrow transients are not
different from the larger well-defined CMEs.Comment: 13 pages. ApJ, accepte
Gel spinning of porous poly(methyl methacrylate)) fibres
Solutions of poly(methyl methacrylate) in 1-butanol demix on cooling. By solution extrusion, fibres are produced which have an oriented porosity. The relation between this morphology, the phase diagram and the extrusion procedure is discussed
On the ultraviolet signatures of small scale heating in coronal loops
Studying the statistical properties of solar ultraviolet emission lines could
provide information about the nature of small scale coronal heating. We expand
on previous work to investigate these properties. We study whether the
predicted statistical distribution of ion emission line intensities produced by
a specified heating function is affected by the isoelectronic sequence to which
the ion belongs, as well as the characteristic temperature at which it was
formed. Particular emphasis is placed on the strong resonance lines belonging
to the lithium isoelectronic sequence. Predictions for emission lines observed
by existing space-based UV spectrometers are given. The effects on the
statistics of a line when observed with a wide-band imaging instrument rather
than a spectrometer are also investigated. We use a hydrodynamic model to
simulate the UV emission of a loop system heated by nanoflares on small,
spatially unresolved scales. We select lines emitted at similar temperatures
but belonging to different isoelectronic groups: Fe IX and Ne VIII, Fe XII and
Mg X, Fe XVII, Fe XIX and Fe XXIV. Our simulations confirm previous results
that almost all lines have an intensity distribution that follows a power-law,
in a similar way to the heating function. However, only the high temperature
lines best preserve the heating function's power law index (Fe XIX being the
best ion in the case presented here). The Li isoelectronic lines have different
statistical properties with respect to the lines from other sequences, due to
the extended high temperature tail of their contribution functions. However,
this is not the case for Fe XXIV which may be used as a diagnostic of the
coronal heating function. We also show that the power-law index of the heating
function is effectively preserved when a line is observed by a wide-band
imaging instrument rather than a spectromenter
Energy Distribution of Micro-events in the Quiet Solar Corona
Recent imaging observations of EUV line emissions have shown evidence for
frequent flare-like events in a majority of the pixels in quiet regions of the
solar corona. The changes in coronal emission measure indicate impulsive
heating of new material to coronal temperatures. These heating or evaporation
events are candidate signatures of "nanoflares" or "microflares" proposed to
interpret the high temperature and the very existence of the corona. The energy
distribution of these micro-events reported in the literature differ widely,
and so do the estimates of their total energy input into the corona. Here we
analyze the assumptions of the different methods, compare them by using the
same data set and discuss their results.
We also estimate the different forms of energy input and output, keeping in
mind that the observed brightenings are most likely secondary phenomena. A
rough estimate of the energy input observed by EIT on the SoHO satellite is of
the order of 10% of the total radiative output in the same region. It is
considerably smaller for the two reported TRACE observations. The discrepancy
can be explained partially by different thresholds for flare detection. There
is agreement on the slope and the absolute value of the distribution if the
same method were used and a numerical error corrected. The extrapolation of the
power law to unobserved energies that are many orders of magnitude smaller
remains questionable. Nevertheless, these micro-events and unresolved smaller
events are currently the best source of information on the heating process of
the corona
Coronal Alfvén speed determination : consistency between seismology using AIA/SDO transverse loop oscillations and magnetic extrapolation
Two transversely oscillating coronal loops are investigated in detail during a flare on the 6th September 2011 using data from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics
Observatory (SDO).We compare two independent methods to determine the Alfvén speed inside these loops. Through the period of oscillation and loop length information about the Alfvén speed inside each loop is deduced seismologically. This is compared with the Alfvén speed profiles deduced from magnetic extrapolation and spectral methods using AIA bandpass. We find that for both loops the two methods are consistent. Also, we find that the average Alfvén speed based on loop travel time is not necessarily a good measure to compare with the seismological result, which explains earlier reported discrepancies. Instead, the effect of density and magnetic stratification on the wave mode has to be taken into account. We discuss the implications of combining seismological, extrapolation and spectral methods in deducing the physical properties of coronal loops
Preliminary Results on Irradiance Measurements from Lyra and Swap
International audienceThe first and preliminary results of the photometry of Large Yield Radiometer (LYRA) and Sun Watcher using Active Pixel system detector and Image Processing (SWAP) onboard PROBA2 are presented in this paper. To study the day-to-day variations of LYRA irradiance, we have compared the LYRA irradiance values (observed Sun as a star) measured in Aluminum filter channel (171 Å-500 Å) with spatially resolved full-disk integrated intensity values measured with SWAP (174 Å) and Ca II K 1 Å index values (ground-based observations from NSO/Sac Peak) for the period from 01 April 2010 to 15 Mar 2011. We found that there is a good correlation between these parameters. This indicates that the spatial resolution of SWAP complements the high temporal resolution of LYRA. Hence SWAP can be considered as an additional radiometric channel. Also the K emission index is the integrated intensity (or flux) over a 1 Å band centered on the K line and is proportional to the total emission from the chromosphere; this comparison clearly explains that the LYRA irradiance variations are due to the various magnetic features, which are contributing significantly. In addition to this we have made an attempt to segregate coronal features from full-disk SWAP images. This will help to understand and determine the actual contribution of the individual coronal feature to LYRA irradiance variations
Achieving thoracic oncology data collection in Europe : a precursor study in 35 countries
Background: A minority of European countries have participated in international comparisons with high level data on lung cancer. However, the nature and extent of data collection across the continent is simply unknown, and without accurate data collection it is not possible to compare practice and set benchmarks to which lung cancer services can aspire. Methods: Using an established network of lung cancer specialists in 37 European countries, a survey was distributed in December 2014. The results relate to current practice in each country at the time, early 2015. The results were compiled and then verified with co-authors over the following months. Results: Thirty-five completed surveys were received which describe a range of current practice for lung cancer data collection. Thirty countries have data collection at the national level, but this is not so in Albania, Bosnia- Herzegovina, Italy, Spain and Switzerland. Data collection varied from paper records with no survival analysis, to well-established electronic databases with links to census data and survival analyses. Conclusion: Using a network of committed clinicians, we have gathered validated comparative data reporting an observed difference in data collection mechanisms across Europe. We have identified the need to develop a welldesigned dataset, whilst acknowledging what is feasible within each country, and aspiring to collect high quality data for clinical research
- …