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

New technique to measure the cavity defects of Fabry-Perot interferometers

(Abridged): We define and test a new technique to accurately measure the cavity defects of air-spaced FPIs, including distortions due to the spectral tuning process typical of astronomical observations. We further develop a correction technique to maintain the shape of the cavity as constant as possible during the spectral scan. These are necessary steps to optimize the spectral transmission profile of a two-dimensional spectrograph using one or more FPIs. We devise a generalization of the techniques developed for the so-called phase-shifting interferometry to the case of FPIs. The technique is applicable to any FPI that can be tuned via changing the cavity spacing ($z$-axis), and can be used for any etalon regardless of the coating' reflectivity. The major strength of our method is the ability to fully characterize the cavity during a spectral scan, allowing for the determination of scan-dependent modifications of the plates. As a test, we have applied this technique to three 50 mm diameter interferometers, with cavity gaps ranging between 600 micron and 3 mm, coated for use in the visible range. We obtain accurate and reliable measures of the cavity defects of air-spaced FPIs, and of their evolution during the entire spectral scan. Our main, and unexpected, result is that the relative tilt between the two FPI plates varies significantly during the spectral scan, and can dominate the cavity defects; in particular, we observe that the tilt component at the extremes of the scan is sensibly larger than at the center of the scan. Exploiting the capability of the electronic controllers to set the reference plane at any given spectral step, we develop a correction technique that allows the minimization of the tilt during a complete spectral scan. The correction remains highly stable over long periods, well beyond the typical duration of astronomical observations.Comment: 15 pages, 20+ figures, accepted for publication in A&A. Two additional movies are available in the online version of the pape

TRACE and ground-based observations of microflares

We present high temporal and spatial resolution, multiwavelength observations of small-scale activity phenomena. The data were obtained during a coordinated campaign between ground-based and space observatories. Our analysis supports the concept that small flares are just miniature flares, i.e. that the same physical processes are at work, but that it is mandatory to have an excellent resolution in order to clearly identify them. In particular, we find that chromospheric downward motions are a very distinctive characteristic of the flare phenomenon even in tiny events

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

Anchoring selenido-carbonyl ruthenium clusters to functionalised silica xerogels

Silica Xerogels containing carbonyl Ru3Se2 nido clusters were prepared in three different ways. The simple dispersion of [Ru3(mu3-Se)2(CO)7(PPh 3)2] via sol gel process produces an inhomogeneous material; by contrast, homogeneous xerogels were obtained by reaction of [Ru3(mu3-Se)2(CO)8(PPh 3)] with functionalised xerogels containing grafted diphenylphosphine moieties and by reaction of [Ru3(CO)12] with a xerogel containing grafted phosphine-selenide groups. The reaction between [Ru3(CO)12] and dodecyldiphenylphosphine selenide led to the formation of four selenido carbonyl clusters, which are soluble in hydrocarbon solvents and can be deposited as thin films from their solution by slow evaporation. Xerogéis de silica contendo carbonilas metálicas polinucleares (clusters) com estrutura nido Ru3Se2 foram preparadas através de três rotas diferentes. A simples dispersão do cluster [Ru3(mi3-Se)2(CO)7(PPh 3)2] pelo processo sol gel produz um material não homogêneo. Xerogéis homogêneos foram obtidos através da reação de [Ru3(mi3-Se)2(CO)8(PPh 3)] com xerogéis funcionalizados contendo fragmentos difenilfosfino enxertados, e pela reação do [Ru3(CO)12] com um xerogel contendo grupos fosfinoseleneto enxertados. A reação entre [Ru3(CO)12] e seleneto de dodecildifenilfosfinoseleneto resultou na formação de quatro clusters contendo ligantes carbonil e seleneto, solúveis em solventes apolares e que podem ser empregados na confecção de filmes

Record Processing in ITACA, the New Italian Strong-Motion Database

The development of the new Italian strong-motion database ITACA (ITalian AC-celerometric Archive, http://itaca.mi.ingv.it) is in progress under the sponsorship of the National Department of Civil Protection (DPC) within Project S4, in the framework of DPC-INGV 2007–2009 research agreement. This work started from the alpha version of ITACA [8], where 2,182 3-component records from 1,004 earthquakes, mainly recorded by the National Accelerometric Network, RAN, operated by DPC, were processed and included in the database. Earthquake metadata, recording station information and reports on the available geologicalgeophysical information of 452 recording sites, corresponding to about 70% of the total, were also included. Subsequently, ITACA has been updated and will reach its final stage by the end of Project S4, around mid-2010, with additional features, improved information about recording stations, and updated records, including the Mw6.3 L’Aquila earthquake. All records were re-processed with respect to the alpha version [9], with a special care to preserve information about late-triggered events and to ensure compatibility of corrected records, i.e., velocity and displacement traces obtained by the first and second integral of the corrected acceleration should not be affected by unrealistic trends. After a short introduction of ITACA and its most relevant features and statistics, this paper mainly deals with the newly adopted processing scheme, with reference to the problems encountered and the solutions that have been devised

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