Electron doped Ca10(Pt3As8)(Fe2As2)5 and Ca10(Pt4As8)(Fe2As2)5 - High Tc superconductors with skutterudite intermediary layers

It has been argued that the very high transition temperatures of the highest Tc cuprate superconductors are facilitated by enhanced CuO2 plane coupling through the (Bi,Tl,Hg)-O intermediary layers. Whether enhanced coupling through intermediary layers can also influence Tc in the iron arsenide superconductors has never been tested due the lack of appropriate systems for study. Here we report the crystal structures and properties of two iron arsenide superconductors, Ca10(Pt3As8)(Fe2As2)5 (the 10-3-8 phase) and Ca10(Pt4As8)(Fe2As2)5 (the 10-4-8 phase). Based on -Ca-(PtnAs8)-Ca-Fe2As2- layer stacking, the most important difference in the structures lies in the structural and electronic characters of the intermediary platinum arsenide layers. Electron doping through partial substitution of Pt for Fe in the Fe2As2 layers leads to Tc of 11 K in the 10-3-8 phase and 25 K in the 10-4-8 phase. Using the chemical concepts of Zintl ion electron counting and the stability of Pt in the 5d8 configuration we argue that the dramatic difference in Tc arises because the intermediary layer is semiconducting in the 10-3-8 phase but metallic in the 10-4-8 phase, leading to enhanced interlayer coupling in the 10-4-8 phase. The results suggest that metallic intermediary layers may offer a new road to higher Tc in iron arsenide superconductors

Comparing computer-generated and pathologist-generated tumour segmentations for immunohistochemical scoring of breast tissue microarrays

BACKGROUND: Tissue microarrays (TMAs) have become a valuable resource for biomarker expression in translational research. Immunohistochemical (IHC) assessment of TMAs is the principal method for analysing large numbers of patient samples, but manual IHC assessment of TMAs remains a challenging and laborious task. With advances in image analysis, computer-generated analyses of TMAs have the potential to lessen the burden of expert pathologist review. METHODS: In current commercial software computerised oestrogen receptor (ER) scoring relies on tumour localisation in the form of hand-drawn annotations. In this study, tumour localisation for ER scoring was evaluated comparing computer-generated segmentation masks with those of two specialist breast pathologists. Automatically and manually obtained segmentation masks were used to obtain IHC scores for thirty-two ER-stained invasive breast cancer TMA samples using FDA-approved IHC scoring software. RESULTS: Although pixel-level comparisons showed lower agreement between automated and manual segmentation masks (κ=0.81) than between pathologists' masks (κ=0.91), this had little impact on computed IHC scores (Allred; [Image: see text]=0.91, Quickscore; [Image: see text]=0.92). CONCLUSIONS: The proposed automated system provides consistent measurements thus ensuring standardisation, and shows promise for increasing IHC analysis of nuclear staining in TMAs from large clinical trials

Chromospheric Velocities of a C-class Flare

We use high spatial and temporal resolution observations from the Swedish Solar Telescope to study the chromospheric velocities of a C-class flare originating from active region NOAA 10969. A time-distance analysis is employed to estimate directional velocity components in H-alpha and Ca II K image sequences. Also, imaging spectroscopy has allowed us to determine flare-induced line-of-sight velocities. A wavelet analysis is used to analyse the periodic nature of associated flare bursts. Time-distance analysis reveals velocities as high as 64 km/s along the flare ribbon and 15 km/s perpendicular to it. The velocities are very similar in both the H-alpha and Ca II K time series. Line-of-sight H-alpha velocities are red-shifted with values up to 17 km/s. The high spatial and temporal resolution of the observations have allowed us to detect velocities significantly higher than those found in earlier studies. Flare bursts with a periodicity of approximately 60 s are also detected. These bursts are similar to the quasi-periodic oscillations observed at hard X-ray and radio wavelength data. Some of the highest velocities detected in the solar atmosphere are presented. Line-of-sight velocity maps show considerable mixing of both the magnitude and direction of velocities along the flare path. A change in direction of the velocities at the flare kernel has also been detected which may be a signature of chromospheric evaporation.Comment: Accepted for publication in Astronomy and Astrophysics, 5 figure

Exploring impulsive solar magnetic energy release and particle acceleration with focused hard X-ray imaging spectroscopy

How impulsive magnetic energy release leads to solar eruptions and how those eruptions are energized and evolve are vital unsolved problems in Heliophysics. The standard model for solar eruptions summarizes our current understanding of these events. Magnetic energy in the corona is released through drastic restructuring of the magnetic field via reconnection. Electrons and ions are then accelerated by poorly understood processes. Theories include contracting loops, merging magnetic islands, stochastic acceleration, and turbulence at shocks, among others. Although this basic model is well established, the fundamental physics is poorly understood. HXR observations using grazing-incidence focusing optics can now probe all of the key regions of the standard model. These include two above-the-looptop (ALT) sources which bookend the reconnection region and are likely the sites of particle acceleration and direct heating. The science achievable by a direct HXR imaging instrument can be summarized by the following science questions and objectives which are some of the most outstanding issues in solar physics (1) How are particles accelerated at the Sun? (1a) Where are electrons accelerated and on what time scales? (1b) What fraction of electrons is accelerated out of the ambient medium? (2) How does magnetic energy release on the Sun lead to flares and eruptions? A Focusing Optics X-ray Solar Imager (FOXSI) instrument, which can be built now using proven technology and at modest cost, would enable revolutionary advancements in our understanding of impulsive magnetic energy release and particle acceleration, a process which is known to occur at the Sun but also throughout the Universe

Low-Tech Riparian and Wet Meadow Restoration Increases Vegetation Productivity and Resilience Across Semiarid Rangelands

Restoration of riparian and wet meadow ecosystems in semiarid rangelands of the western United States is a high priority given their ecological and hydrological importance in the region. However, traditional restoration approaches are often intensive and costly, limiting the extent over which they can be applied. Practitioners are increasingly trying new restoration techniques that are more cost‐effective, less intensive, and can more practically scale up to the scope of degradation. Unfortunately, practitioners typically lack resources to undertake outcome‐based evaluations necessary to judge the efficacy of these techniques. In this study, we use freely available, satellite remote sensing to explore changes in vegetation productivity (normalized difference vegetation index) of three distinct, low‐tech, riparian and wet meadow restoration projects. Case studies are presented that range in geographic location (Colorado, Oregon, and Nevada), restoration practice (Zeedyk structures, beaver dam analogs, and grazing management), and time since implementation. Restoration practices resulted in increased vegetation productivity of up to 25% and increased annual persistence of productive vegetation. Improvements in productivity with time since restoration suggest that elevated resilience may further enhance wildlife habitat and increase forage production. Long‐term, documented outcomes of conservation are rare; we hope our findings empower practitioners to further monitor and explore the use of low‐tech methods for restoration of ecohydrologic processes at meaningful spatial scales

The origins of estrogen receptor alpha-positive and estrogen receptor alpha-negative human breast cancer

Current hormonal therapies have benefited millions of patients with breast cancer. Their success, however, is often temporary and limited to a subset of patients whose tumors express estrogen receptor alpha (ER). The therapies are entirely ineffective in ER-negative disease. Recent studies suggest that there are many biological pathways and alterations involved in determining whether ER is expressed and how it is regulated during breast cancer evolution. Improving hormonal therapies, in addition to perfecting current strategies, will also target these newly discovered pathways and alterations, and others yet to be found. The present commentary will briefly highlight a few important observations and unanswered questions regarding ER status and growth regulation during breast cancer evolution, which hopefully will help to stimulate new thinking and progress in this important area of medial research

Multiwavelength observations of a giant flare on CN Leonis I. The chromosphere as seen in the optical spectra

Flares on dM stars contain plasmas at very different temperatures and thus affect a wide wavelength range in the electromagnetic spectrum. While the coronal properties of flares are studied best in X-rays, the chromosphere of the star is observed best in the optical and ultraviolet ranges. Therefore, multiwavelength observations are essential to study flare properties throughout the atmosphere of a star. We analysed simultaneous observations with UVES/VLT and XMM-Newton of the active M5.5 dwarf CN Leo (Gl 406) exhibiting a major flare. The optical data cover the wavelength range from 3000 to 10000 Angstrom. From our optical data, we find an enormous wealth of chromospheric emission lines occurring throughout the spectrum. We identify a total of 1143 emission lines, out of which 154 are located in the red arm, increasing the number of observed emission lines in this red wavelength range by about a factor of 10. Here we present an emission line list and a spectral atlas. We also find line asymmetries for H I, He I, and Ca II lines. For the last, this is the first observation of asymmetries due to a stellar flare. During the flare onset, there is additional flux found in the blue wing, while in the decay phase, additional flux is found in the red wing. We interpret both features as caused by mass motions. In addition to the lines, the flare manifests itself in the enhancement of the continuum throughout the whole spectrum, inverting the normal slope for the net flare spectrum.Comment: 15 pages, accepted by A&

Near-Ultraviolet Spectra of Flares on YZ CMi

Near-ultraviolet spectroscopic data obtained with the HST STIS instrument on the dMe flare star YZ Canis Minoris (YZ CMi) were analyzed. Flare and quiet intervals were identified from the broadband near-UV light curve, and the spectrum of each flare was separately extracted. Mg II and Fe II line profiles show similar behavior during the flares. Two large flares allowed time-resolved spectra to be analyzed, revealing a very broad component to the Mg II k line profile in at least one flare spectrum (F9b). If interpreted as a velocity, this component requires chromospheric material to be moving with FWHM ~ 250 km/sec, implying kinetic energy far in excess of the radiative energy. The Mg II k flare line profiles were compared to recent radiative hydrodynamic models of flare atmospheres undergoing electron beam heating. The models successfully predict red enhancements in the line profile with typical velocity of a few km/sec, but do not reproduce the flares showing blue enhancements, or the strongly broadened line observed in flare F9b. A more complete calculation of redistribution into the line wings, including the effect of collisions with the electron beam, may resolve the origin of the excess line broadening.Comment: 29 pages, 12 figures; accepted to PAS

New Insights into White-Light Flare Emission from Radiative-Hydrodynamic Modeling of a Chromospheric Condensation

(abridged) The heating mechanism at high densities during M dwarf flares is poorly understood. Spectra of M dwarf flares in the optical and near-ultraviolet wavelength regimes have revealed three continuum components during the impulsive phase: 1) an energetically dominant blackbody component with a color temperature of T $\sim$ 10,000 K in the blue-optical, 2) a smaller amount of Balmer continuum emission in the near-ultraviolet at lambda $<$ 3646 Angstroms and 3) an apparent pseudo-continuum of blended high-order Balmer lines. These properties are not reproduced by models that employ a typical "solar-type" flare heating level in nonthermal electrons, and therefore our understanding of these spectra is limited to a phenomenological interpretation. We present a new 1D radiative-hydrodynamic model of an M dwarf flare from precipitating nonthermal electrons with a large energy flux of $10^{13}$ erg cm$^{-2}$ s$^{-1}$. The simulation produces bright continuum emission from a dense, hot chromospheric condensation. For the first time, the observed color temperature and Balmer jump ratio are produced self-consistently in a radiative-hydrodynamic flare model. We find that a T $\sim$ 10,000 K blackbody-like continuum component and a small Balmer jump ratio result from optically thick Balmer and Paschen recombination radiation, and thus the properties of the flux spectrum are caused by blue light escaping over a larger physical depth range compared to red and near-ultraviolet light. To model the near-ultraviolet pseudo-continuum previously attributed to overlapping Balmer lines, we include the extra Balmer continuum opacity from Landau-Zener transitions that result from merged, high order energy levels of hydrogen in a dense, partially ionized atmosphere. This reveals a new diagnostic of ambient charge density in the densest regions of the atmosphere that are heated during dMe and solar flares.Comment: 50 pages, 2 tables, 13 figures. Accepted for publication in the Solar Physics Topical Issue, "Solar and Stellar Flares". Version 2 (June 22, 2015): updated to include comments by Guest Editor. The final publication is available at Springer via http://dx.doi.org/10.1007/s11207-015-0708-