Temporal evolution of multiple evaporating ribbon sources in a solar flare

We present new results from the Interface Region Imaging Spectrograph showing the dynamic evolution of chromospheric evaporation and condensation in a flare ribbon, with the highest temporal and spatial resolution to date. IRIS observed the entire impulsive phase of the X-class flare SOL2014-09-10T17:45 using a 9.4 second cadence `sit-and-stare' mode. As the ribbon brightened successively at new positions along the slit, a unique impulsive phase evolution was observed for many tens of individual pixels in both coronal and chromospheric lines. Each activation of a new footpoint displays the same initial coronal up-flows of up to ~300 km/s, and chromospheric downflows up to 40 km/s. Although the coronal flows can be delayed by over 1 minute with respect to those in the chromosphere, the temporal evolution of flows is strikingly similar between all pixels, and consistent with predictions from hydrodynamic flare models. Given the large sample of independent footpoints, we conclude that each flaring pixel can be considered a prototypical, `elementary' flare kernel.Comment: Accepted for publication - ApJ letter

Design of functionalized polysiloxanes: synthesis and study on sulfur-containing xerogels with mono- and bifunctional surface layer

Urea- and thiourea-containing trialkoxysilanes were prepared with a high yield and purity. By sol-gel processing of these precursors the new functionalized xerogels were synthesized and characterized by FTIR, elemental analysis, thermal analysis and adsorption method. Mono- and bifunctionalized xerogels were easily prepared by mixing of precursors in the desired ratios together with tetraethyl orthosilicate. Obtained functional polysiloxanes are perspective materials for metal sorption and hybrid catalysis applications

The Three-dimensional Evolution of Rising, Twisted Magnetic Flux Tubes in a Gravitationally Stratified Model Convection Zone

We present three-dimensional numerical simulations of the rise and fragmentation of twisted, initially horizontal magnetic flux tubes which evolve into emerging Omega-loops. The flux tubes rise buoyantly through an adiabatically stratified plasma that represents the solar convection zone. The MHD equations are solved in the anelastic approximation, and the results are compared with studies of flux tube fragmentation in two dimensions. We find that if the initial amount of field line twist is below a critical value, the degree of fragmentation at the apex of a rising Omega-loop depends on its three-dimensional geometry: the greater the apex curvature of a given Omega-loop, the lesser the degree of fragmentation of the loop as it approaches the photosphere. Thus, the amount of initial twist necessary for the loop to retain its cohesion can be reduced substantially from the two-dimensional limit. The simulations also suggest that as a fragmented flux tube emerges through a relatively quiet portion of the solar disk, extended crescent-shaped magnetic features of opposite polarity should form and steadily recede from one another. These features eventually coalesce after the fragmented portion of the Omega-loop emerges through the photosphere.Comment: 17 pages, 17 figures, uses AAS LaTeX macros v5.0. ApJ, in pres

Tracking magnetic bright point motions through the solar atmosphere

High-cadence, multiwavelength observations and simulations are employed for the analysis of solar photospheric magnetic bright points (MBPs) in the quiet Sun. The observations were obtained with the Rapid Oscillations in the Solar Atmosphere (ROSA) imager and the Interferometric Bidimensional Spectrometer at the Dunn Solar Telescope. Our analysis reveals that photospheric MBPs have an average transverse velocity of approximately 1 km s−1, whereas their chromospheric counterparts have a slightly higher average velocity of 1.4 km s−1. Additionally, chromospheric MBPs were found to be around 63 per cent larger than the equivalent photospheric MBPs. These velocity values were compared with the output of numerical simulations generated using the MURAM code. The simulated results were similar, but slightly elevated, when compared to the observed data. An average velocity of 1.3 km s−1 was found in the simulated G-band images and an average of 1.8 km s−1 seen in the velocity domain at a height of 500 km above the continuum formation layer. Delays in the change of velocities were also analysed. Average delays of ∼4 s between layers of the simulated data set were established and values of ∼29 s observed between G-band and Ca II K ROSA observations. The delays in the simulations are likely to be the result of oblique granular shock waves, whereas those found in the observations are possibly the result of a semi-rigid flux tube

Toward Reliable Characterization of Sites With Pronounced Topography and Related Effects on Ground Motion

Here we present first results of a joint effort undertaken in ongoing European project NERA -JRA1, which aims at establishing scientifically solid and practically acceptable propositions to incorporate surface topography effects in seismic hazard estimates. We assembled a dataset of both ambient vibration and earthquake recordings acquired at 40 European sites with pronounced topography. It comprises a wide variety of sites including populated hills and even extreme cases of unstable rock slopes in Alpine regions. Results of the polarisation analysis for the two sites presented here show the peculiarity of the topographic site effects

Network oscillations at the boundary of an equatorial coronal hole

We investigate intensity oscillations observed simultaneously in the quiet chromosphere and in the corona, above an enhanced network area at the boundary of an equatorial coronal hole. A Fourier analysis is applied to a sequence of images observed in the 171 A and 1600 A passbands of TRACE. Four interesting features above the magnetic network are further investigated by using a wavelet analysis. Our results reveal that, in both the 171 A and 1600 A passbands, oscillations above the magnetic network show a lack of power at high frequencies (5.0-8.3 mHz), and a significant power at low (1.3-2.0 mHz) and intermediate frequencies (2.6-4.0 mHz). The global 5-min oscillation is clearly present in the 4 analyzed features when seen in the 1600 A passband, and is also found with enhanced power in feature 1 (leg of a large coronal loop) and feature 2 (legs of a coronal bright point loop) when seen in the 171 A passband. Two features above an enhanced network element (feature 3 and feature 4) show repeated propagating behaviors with a dominant period of 10 min and 5 min, respectively. We suggest these oscillations are likely to be slow magneto-acoustic waves propagating along inclined magnetic field lines, from the lower solar atmosphere into the corona. The energy flux carried by these waves is estimated of the order of 40 erg cm\^{-2} s\^{-1} for the 171 A passband and is far lower than the energy required to heat the quiet corona. For the 1600 A passband, the energy flux is about 1.4*10^6 erg cm\^{-2} s\^{-1}, which is about one third of the required energy budget for the chromosphere.Comment: 7 pages, 8 figure

A prototype of a large tunable Fabry–Pérot interferometer for solar spectroscopy

Large Fabry-Pérot Interferometers (FPIs) are used in a variety of astronomical instrumentation, including spectro-polarimeters for 4 m class solar telescopes. In this work we comprehensively characterize the cavity of a prototype 150 mm FPI, sporting a novel, fully symmetric design. Of particular interest, we define a new method to properly assess the gravity effects on the interferometer's cavity when the system is used in either the vertical or horizontal configuration, both typical of solar observations. We show that the symmetric design very effectively limits the combined effects of pre-load and gravity forces to only a few nm over a 120 mm diameter illuminated surface, with gravity contributing ~2 nm peak-to-valley (~0.3 nm rms) in either configuration. We confirm a variation of the tilt between the plates of the interferometer during the spectral scan, which can be mitigated with appropriate corrections to the spacing commands. Finally, we show that the dynamical response of the new system fully satisfies typical operational scenarios. We conclude that large, fully symmetric FPIs can be safely used within solar instrumentation in both, horizontal and vertical position, with the latter better suited to limiting the overall volume occupied by such an instrument

(N-Benzoyl-N′-phenyl­thio­urea-κS)chlorido(η4-1,5-cyclo­octa­diene)rhodium(I)

The title compound, [RhCl(C8H12)(C14H12N2OS)], is a rhodium(I) derivative with a functionalized thio­urea ligand. Despite the presence of several heteroatoms, the thio­urea ligand coordinates only in a monodentate fashion via the S atom. The geometry of the coordination sphere is approximately square planar about the RhI atom, with two bonds to the π-electrons of the 1,5-cyclo­octa­diene ligand, one bond to the Cl− ligand and one bond to the S atom of the thio­urea ligand. The mol­ecular structure is stabilized by intra­molecular N—H⋯O and N—H⋯Cl hydrogen bonding. Inter­molecular N—H⋯O hydrogen-bonding inter­actions lead to the formation of layers extending parallel to (011)

Caratteristiche dei dati accelerometrici registrati durante la sequenza sismica aquilana

I dati accelerometrici relativi alla sequenza sismica de L’Aquila, iniziata con l’evento del 6 Aprile alle ore 1.32 (MW 6.3), provengono dalla rete Rete Accelerometrica Nazionale (RAN), gestita dal Dipartimento della Protezione Civile (DPC) e da una rete temporanea installata il giorno dopo la scossa principale ad opera dell’Istituto Nazionale di Geofisica e Vulcanologia (INGV MI-PV). I dati del DPC sono scaricabili dalla banca dati accelerometrica italiana ITACA (http://itaca.mi.ingv.it), mentre quelli dell'INGV sono accessibili dal sito Internet http://accel.mi.ingv.it/statiche/ABRUZZO-2009/main.html. Il terremoto de L’Aquila è il terzo evento più forte che abbia prodotto registrazioni accelerometriche in Italia, dopo i terremoti dell’Irpinia (1980, MW 6.9) e del Friuli (1976, MW 6.4). Questo evento, insieme alle 12 repliche più forti (MW > 4.0) ha fornito un insieme di dati accelerometrici unico in Italia, in particolare per la presenza di un numero consistente di registrazioni in zona epicentrale ("campo vicino"). Il data set è composto da circa 300 accelerogrammi digitali (di cui 270 provenienti dalla RAN), con un ottimo rapporto segnale/rumore, registrati da circa 70 stazioni, installate in varie condizioni di sito, a distanze comprese fra 0 e 300 km. L'importanza di questo data set, non solo a livello nazionale, è legato al contributo significativo che fornisce nel colmare una lacuna nella distribuzione magnitudo-distanza dei dati strong motion italiani e mondiali, soprattutto per quanto riguarda gli eventi con meccanismo di faglia normale (Ameri et al.; 2009). I dati registrati in campo vicino provengono da un transetto composto da 6 stazioni installato dalla Protezione Civile nel 2001 nella Alta Valle dell’Aterno, con lo scopo di investigare la variabilità del moto sismico rispetto alle condizioni geologiche locali, dalla stazione AQK, installata in prossimità del centro urbano e da una stazione (AQU) appartenente alla rete broad band Mednet (http://mednet.rm.ingv.it/data.php), situata nel castello de L’Aquila. Queste stazioni distano meno di 5 km dall’epicentro dell’evento principale, ricadendo all’interno della proiezione superficiale del piano di rottura. A queste si aggiungono le registrazioni delle repliche, ottenute dalle stazioni della rete temporanea INGV, installata in area epicentrale. In questo lavoro si presenta un resoconto delle principali caratteristiche dello scuotimento del suolo verificatosi durante la sequenza sismica aquilana, attraverso l’analisi dei dati accelerometrici relativi alla scossa principale e alle due repliche più forti. Si discutono in particolare la dipendenza di diversi parametri strong motion dalla distanza, dall’azimuth e dalle condizioni di sito, e l'effetto delle caratteristiche del moto in campo vicino sulla risposta strutturalePublished57-684.1. Metodologie sismologiche per l'ingegneria sismicaN/A or not JCRreserve

Insight into the solar plage chromosphere with DKIST

The strongly coupled hydrodynamic, magnetic, and radiation properties of the plasma in the solar chromosphere makes it a region of the Sun's atmosphere that is poorly understood. We use data obtained with the high-resolution Visible Broadband Imager (VBI) equipped with an H$\beta$ filter and the Visible Spectro-Polarimeter (ViSP) at the Daniel K. Inouye Solar Telescope to investigate the fine-scale structure of the plage chromosphere. To aid the interpretation of the VBI imaging data, we also analyze spectra from the CHROMospheric Imaging Spectrometer on the Swedish Solar Telescope. The analysis of spectral properties, such as enhanced line widths and line depths explains the high contrast of the fibrils relative to the background atmosphere demonstrating that H$\beta$ is an excellent diagnostic for the enigmatic fine-scale structure of the chromosphere. A correlation between the parameters of the H$\beta$ line indicates that opacity broadening created by overdense fibrils could be the main reason for the spectral line broadening observed frequently in chromospheric fine-scale structures. Spectropolarimetric inversions of the ViSP data in the Ca II 8542 {\AA} and Fe I 6301/6302 {\AA} lines are used to construct semiempirical models of the plage atmosphere. Inversion outputs indicate the existence of dense fibrils in the Ca II 8542 {\AA} line. The analyses of the ViSP data show that the morphological characteristics, such as orientation, inclination and length of fibrils are defined by the topology of the magnetic field in the photosphere. Chromospheric maps reveal a prominent magnetic canopy in the area where fibrils are directed towards the observer.Comment: 17 pages, 11 figures, accepted in Ap