Signatures of impulsive localized heating in the temperature distribution of multi-stranded coronal loops

We study the signatures of different coronal heating regimes on the differential emission measure (DEM) of multi-stranded coronal loops by means of hydrodynamic simulations. We consider heating either uniformly distributed along the loops or localized close to the chromospheric footpoints, in both steady and impulsive conditions. Our simulations show that condensation at the top of the loop forms when the localized heating is impulsive with a pulse cadence time shorter than the plasma cooling time, and the pulse energy is below a certain threshold. A condensation does not produce observable signatures in the global DEM structure. Conversely, the DEM coronal peak is found sensitive to the pulse cadence time. Our simulations can also give an explanation of the warm overdense and hot underdense loops observed by TRACE, SOHO and Yohkoh. However, they are unable to reproduce both the transition region and the coronal DEM structure with a unique set of parameters, which outlines the need for a more realistic description of the transition region.Comment: 31 pages, 7 figure

Velocity measurements for a solar active region fan loop from Hinode/EIS observations

The velocity pattern of a fan loop structure within a solar active region over the temperature range 0.15-1.5 MK is derived using data from the EUV Imaging Spectrometer (EIS) on board the Hinode satellite. The loop is aligned towards the observer's line-of-sight and shows downflows (redshifts) of around 15 km/s up to a temperature of 0.8 MK, but for temperatures of 1.0 MK and above the measured velocity shifts are consistent with no net flow. This velocity result applies over a projected spatial distance of 9 Mm and demonstrates that the cooler, redshifted plasma is physically disconnected from the hotter, stationary plasma. A scenario in which the fan loops consist of at least two groups of "strands" - one cooler and downflowing, the other hotter and stationary -- is suggested. The cooler strands may represent a later evolutionary stage of the hotter strands. A density diagnostic of Mg VII was used to show that the electron density at around 0.8 MK falls from 3.2 x 10^9 cm^-3 at the loop base, to 5.0 x 10^8 cm^-3 at a projected height of 15 Mm. A filling factor of 0.2 is found at temperatures close to the formation temperature of Mg VII (0.8 MK), confirming that the cooler, downflowing plasma occupies only a fraction of the apparent loop volume. The fan loop is rooted within a so-called "outflow region" that displays low intensity and blueshifts of up to 25 km/s in Fe XII 195.12 A (formed at 1.5 MK), in contrast to the loop's redshifts of 15 km/s at 0.8 MK. A new technique for obtaining an absolute wavelength calibration for the EIS instrument is presented and an instrumental effect, possibly related to a distorted point spread function, that affects velocity measurements is identified.Comment: 42 pages, 15 figures, submitted to Ap

A prototype large-angle photon veto detector for the P326 experiment at CERN

The P326 experiment at the CERN SPS has been proposed with the purpose of measuring the branching ratio for the decay K^+ \to \pi^+ \nu \bar{\nu} to within 10%. The photon veto system must provide a rejection factor of 10^8 for \pi^0 decays. We have explored two designs for the large-angle veto detectors, one based on scintillating tiles and the other using scintillating fibers. We have constructed a prototype module based on the fiber solution and evaluated its performance using low-energy electron beams from the Frascati Beam-Test Facility. For comparison, we have also tested a tile prototype constructed for the CKM experiment, as well as lead-glass modules from the OPAL electromagnetic barrel calorimeter. We present results on the linearity, energy resolution, and time resolution obtained with the fiber prototype, and compare the detection efficiency for electrons obtained with all three instruments.Comment: 8 pages, 9 figures, 2 tables. Presented at the 2007 IEEE Nuclear Science Symposium, Honolulu HI, USA, 28 October - 3 November 200

Innate immune modulation by GM-CSF and IL-3 in health and disease

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and inteleukin-3 (IL-3) have long been known as mediators of emergency myelopoiesis, but recent evidence has highlighted their critical role in modulating innate immune effector functions in mice and humans. This new wealth of knowledge has uncovered novel aspects of the pathogenesis of a range of disorders, including infectious, neoplastic, autoimmune, allergic and cardiovascular diseases. Consequently, GM-CSF and IL-3 are now being investigated as therapeutic targets for some of these disorders, and some phase I/II clinical trials are already showing promising results. There is also pre-clinical and clinical evidence that GM-CSF can be an effective immunostimulatory agent when being combined with anti-cytotoxic T lymphocyte-associated protein 4 (anti-CTLA-4) in patients with metastatic melanoma as well as in novel cancer immunotherapy approaches. Finally, GM-CSF and to a lesser extent IL-3 play a critical role in experimental models of trained immunity by acting not only on bone marrow precursors but also directly on mature myeloid cells. Altogether, characterizing GM-CSF and IL-3 as central mediators of innate immune activation is poised to open new therapeutic avenues for several immune-mediated disorders and define their potential in the context of immunotherapies

Evidence for Steady Heating: Observations of an Active Region Core with Hinode and TRACE

Previous observations have not been able to exclude the possibility that high temperature active region loops are actually composed of many small scale threads that are in various stages of heating and cooling and only appear to be in equilibrium. With new observations from the EUV Imaging Spectrometer (EIS) and X-ray Telescope (XRT) on \textit{Hinode} we have the ability to investigate the properties of high temperature coronal plasma in extraordinary detail. We examine the emission in the core of an active region and find three independent lines of evidence for steady heating. We find that the emission observed in XRT is generally steady for hours, with a fluctuation level of approximately 15% in an individual pixel. Short-lived impulsive heating events are observed, but they appear to be unrelated to the steady emission that dominates the active region. Furthermore, we find no evidence for warm emission that is spatially correlated with the hot emission, as would be expected if the high temperature loops are the result of impulsive heating. Finally, we also find that intensities in the "moss", the footpoints of high temperature loops, are consistent with steady heating models provided that we account for the local expansion of the loop from the base of the transition region to the corona. In combination, these results provide strong evidence that the heating in the core of an active region is effectively steady, that is, the time between heating events is short relative to the relevant radiative and conductive cooling times.Comment: Minor changes based on the final report from the referee; Movies are available from the first autho

Regularity of higher codimension area minimizing integral currents

This lecture notes are an expanded version of the course given at the ERC-School on Geometric Measure Theory and Real Analysis, held in Pisa, September 30th - October 30th 2013. The lectures aim to explain the main steps of a new proof of the partial regularity of area minimizing integer rectifiable currents in higher codimension, due originally to F. Almgren, which is contained in a series of papers in collaboration with C. De Lellis (University of Zurich).Comment: This text will appear in "Geometric Measure Theory and Real Analysis", pp. 131--192, Proceedings of the ERC school in Pisa (2013), L. Ambrosio Ed., Edizioni SNS (CRM Series

Comparing extrapolations of the coronal magnetic field structure at 2.5 solar radii with multi-viewpoint coronagraphic observations

The magnetic field shapes the structure of the solar corona but we still know little about the interrelationships between the coronal magnetic field configurations and the resulting quasi-stationary structures observed in coronagraphic images (as streamers, plumes, coronal holes). One way to obtain information on the large-scale structure of the coronal magnetic field is to extrapolate it from photospheric data and compare the results with coronagraphic images. Our aim is to verify if this comparison can be a fast method to check systematically the reliability of the many methods available to reconstruct the coronal magnetic field. Coronal fields are usually extrapolated from photospheric measurements typically in a region close to the central meridian on the solar disk and then compared with coronagraphic images at the limbs, acquired at least 7 days before or after to account for solar rotation, implicitly assuming that no significant changes occurred in the corona during that period. In this work, we combine images from three coronagraphs (SOHO/LASCO-C2 and the two STEREO/SECCHI-COR1) observing the Sun from different viewing angles to build Carrington maps covering the entire corona to reduce the effect of temporal evolution to ~ 5 days. We then compare the position of the observed streamers in these Carrington maps with that of the neutral lines obtained from four different magnetic field extrapolations, to evaluate the performances of the latter in the solar corona. Our results show that the location of coronal streamers can provide important indications to discriminate between different magnetic field extrapolations.Comment: Accepted by A&A the 20th of May, 201

Searches for Physics Beyond the Standard Model at Colliders

All experimental measurements of particle physics today are beautifully described by the Standard Model. However, there are good reasons to believe that new physics may be just around the corner at the TeV energy scale. This energy range is currently probed by the Tevatron and HERA accelerators and selected results of searches for physics beyond the Standard Model are presented here. No signals for new physics have been found and limits are placed on the allowed parameter space for a variety of different particles.Comment: Proceedings for 2007 Europhysics Conference on High Energy Physics, Manchester, July 200

Search for photospheric footpoints of quiet Sun transition region loops

CONTEXT:The footpoints of quiet Sun Transition Region (TR) loops do not seem to coincide with the photospheric magnetic structures appearing in traditional low-sensitivity magnetograms. AIMS: To look for the so-far unidentified photospheric footpoints of TR loops using G-band bright points (BPs) as proxies for photospheric magnetic field concentrations. METHODS: Comparison of TR measurements with SoHO/SUMER and photospheric magnetic field observations obtained with the Dutch Open Telescope. RESULTS: Photospheric BPs are associated with bright TR structures, but they seem to avoid the brightest parts of the structure. BPs appear in regions that are globally redshifted, but they avoid extreme velocities. TR explosive events are not clearly associated with BPs. CONCLUSIONS: The observations are not inconsistent with the BPs being footpoints of TR loops, although we have not succeeded to uniquely identify particular BPs with specific TR loops.Comment: Accepted for publication in A&A. 10 pages, 10 figures. Due to size limitations, the quality of fig3 is not goo

A global fit to determine the pseudoscalar mixing angle and the gluonium content of the eta' meson

We update the values of the eta-eta' mixing angle and of the eta' gluonium content by fitting our measurement R_phi = BR(phi to eta' gamma)/ BR(phi to eta gamma) together with several vector meson radiative decays to pseudoscalars (V to P gamma), pseudoscalar mesons radiative decays to vectors (P to V gamma) and the eta' to gamma gamma, pi^0 to gamma gamma widths. From the fit we extract a gluonium fraction of Z^2_G = 0.12 +- 0.04, the pseudoscalar mixing angle psi_P = (40.4 +- 0.6) degree and the phi-omega mixing angle psi_V = (3.32 +- 0.09) degree. Z^2_G and psi_P are fairly consistent with those previously published. We also evaluate the impact on the eta' gluonium content determination of future experimental improvements of the eta' branching ratios and decay width.Comment: 13 pages, 7 figures to submit to JHE