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1. Radio light curves and imaging of the helium nova V445 Puppis reveal seven years of synchrotron emission

   https://doi.org/10.1093/mnras/staa3712  

   Nyamai, M M ; Chomiuk, L ; Ribeiro, V A ; Woudt, P A ; Strader, J ; Sokolovsky, K V ( December 2020 , Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT V445 Puppis is the only helium nova observed to date; its eruption in late 2000 showed high velocities up to 8500 km s−1, and a remarkable bipolar morphology cinched by an equatorial dust disc. Here we present multifrequency radio observations of V445 Pup obtained with the Very Large Array (VLA) spanning 1.5–43.3 GHz, and between 2001 January and 2008 March (days ∼89–2700 after eruption). The radio light curve is dominated by synchrotron emission over these 7 yr, and shows four distinct radio flares. Resolved radio images obtained in the VLA’s A configuration show that the synchrotron emission hugs the equatorial disc, and comparisons to near-IR images of the nova clearly demonstrate that it is the densest ejecta – not the fastest ejecta – that are the sites of the synchrotron emission in V445 Pup. The data are consistent with a model where the synchrotron emission is produced by a wind from the white dwarf impacting the dense equatorial disc, resulting in shocks and particle acceleration. The individual synchrotron flares may be associated with density enhancements in the equatorial disc and/or velocity variations in the wind from the white dwarf. This overall scenario is similar to a common picture of shock production in hydrogen-rich classical novae, but V445 Pup is remarkable in that these shocks persist for almost a decade, much longer than the weeks or months for which shocks are typically observed in classical novae. 

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2. Understanding the Amorphous Lithiation Pathway of the Type I Ba 8 Ge 43 Clathrate with Synchrotron X-ray Characterization

   https://doi.org/10.1021/acs.chemmater.0c03641  

   Dopilka, Andrew ; Childs, Amanda ; Bobev, Svilen ; Chan, Candace K. ( November 2020 , Chemistry of Materials)

   null (Ed.)
3. On stars and spikes: Resolving the skeletal morphology of planktonic Acantharia using synchrotron X-ray nanotomography and deep learning image segmentation

   https://doi.org/10.1016/j.actbio.2023.01.037  

   Raja Somu, Dawn ; Cracchiolo, Timothy ; Longo, Elena ; Greving, Imke ; Merk, Vivian ( March 2023 , Acta Biomaterialia)

   Acantharia ( Acantharea ) are wide-spread marine protozoa, presenting one of the rare examples of stron- tium sulfate mineralization in the biosphere. Their endoskeletons consist of 20 spicules arranged accord- ing to a unique geometric pattern named Müller’s principle. Given the diverse mineral architecture of the Acantharia class, we set out to examine the complex three-dimensional skeletal morphology at the nanometer scale using synchrotron X-ray nanotomography, followed by image segmentation based on deep learning methods. The present study focuses on how the spicules emanate from the robust central junction in the orders Symphyacanthida and Arthracanthida , the geometry of lateral spicule wings as well as pockets of interspicular space, which may be involved in cell compartmentalization. Through these morphometric studies, we observed subtle deviations from the previously described spatial arrangement of the spicules. According to our data, spicule shapes are adjusted in opposite spicules as to accommodate the overall spicule arrangement. In all types examined, previously unknown interspicular interstices were found in areas where radial spicules meet, which could have implications for the crystal growth mecha- nism and overall endoskeletal integrity. A deeper understanding of the spiculogenesis in Acantharia can provide biomimetic routes towards complex inorganic shapes. 

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4. Measurement of the anisotropy power spectrum of the radio synchrotron background

   https://doi.org/10.1093/mnras/stab2865  

   Offringa, A R ; Singal, J ; Heston, S ; Horiuchi, S ; Lucero, D M ( November 2021 , Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We present the first targeted measurement of the power spectrum of anisotropies of the radio synchrotron background, at 140 MHz, where it is the overwhelmingly dominant photon background. This measurement is important for understanding the background level of radio sky brightness, which is dominated by steep-spectrum synchrotron radiation at frequencies below ν ∼ 0.5 GHz and has been measured to be significantly higher than that produced by known classes of extragalactic sources and most models of Galactic halo emission. We determine the anisotropy power spectrum on scales ranging from 2° to 0.2 arcmin with Low-Frequency Array observations of two 18-deg2 fields – one centred on the Northern hemisphere’s coldest patch of radio sky where the Galactic contribution is smallest and the other offset from that location by 15°. We find that the anisotropy power is higher than that attributable to the distribution of point sources above 100 $\mu$Jy in flux. This level of radio anisotropy power indicates that if it results from point sources, those sources are likely at low fluxes and incredibly numerous, and likely clustered in a specific manner. 

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5. Evaluation of quantitative synchrotron radiation micro-X-ray fluorescence in rice grain

   https://doi.org/10.1107/S1600577523000747  

   Limmer, Matt A. ; Webb, Samuel M. ; Seyfferth, Angelia L. ( March 2023 , Journal of Synchrotron Radiation)

   Concentrations of nutrients and contaminants in rice grain affect human health, specifically through the localization and chemical form of elements. Methods to spatially quantify the concentration and speciation of elements are needed to protect human health and characterize elemental homeostasis in plants. Here, an evaluation was carried out using quantitative synchrotron radiation microprobe X-ray fluorescence (SR-µXRF) imaging by comparing average rice grain concentrations of As, Cu, K, Mn, P, S and Zn measured with rice grain concentrations from acid digestion and ICP-MS analysis for 50 grain samples. Better agreement was found between the two methods for high-Zelements. Regression fits between the two methods allowed quantitative concentration maps of the measured elements. These maps revealed that most elements were concentrated in the bran, although S and Zn permeated into the endosperm. Arsenic was highest in the ovular vascular trace (OVT), with concentrations approaching 100 mg kg⁻¹in the OVT of a grain from a rice plant grown in As-contaminated soil. Quantitative SR-µXRF is a useful approach for comparison across multiple studies but requires careful consideration of sample preparation and beamline characteristics.

    

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