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Collocated crystal sizes and mineral identities are critical for interpreting textural relationships in rocks and testing geological hypotheses, but it has been previously impossible to unambiguously constrain these properties using in situ instruments on Mars rovers. Here, we demonstrate that diffracted and fluoresced x-rays detected by the PIXL instrument (an x-ray fluorescence microscope on the Perseverance rover) provide information about the presence or absence of coherent crystalline domains in various minerals. X-ray analysis and multispectral imaging of rocks from the Séítah formation on the floor of Jezero crater shows that they were emplaced as coarsely crystalline igneous phases. Olivine grains were then partially dissolved and filled by finely crystalline or amorphous secondary silicate, carbonate, sulfate, and chloride/oxychlorine minerals. These results support the hypothesis that Séítah formation rocks represent olivine cumulates altered by fluids far from chemical equilibrium at low water-rock ratios.

We present a synthesis of PIXL elemental data and SHERLOC Raman spectra collected on two targets investigated by the Perseverance rover during the first year of its exploration of Jezero Crater, Mars. The Bellegarde target (in the Máaz formation) and Dourbes target (in the Séítah formation) exhibit distinctive mineralogies that are an ideal case study for in situ analysis by SHERLOC and PIXL. Each instrument alone produces valuable data about the chemistry and spatial distribution of mineral phases at the sub-millimeter scale. However, combining data from both instruments provides a more robust interpretation that overcomes the limitations of either instrument, for example: 1) Detection of correlated calcium and sulfur in Bellegarde by PIXL is corroborated by the co-located detection of calcium sulfate by SHERLOC. 2) Detection of sodium and chlorine in Dourbes is consistent with either chloride or oxychlorine salts, but SHERLOC does not detect perchlorate or chlorate. 3) A Raman peak at 1120 cm−1 in Dourbes could be sulfate or pyroxene, but elemental abundances from PIXL at that location are a better match to pyroxene. This study emphasizes the importance of analyzing co-located data from both instruments together, to obtain a more complete picture of sub-millimeter-scale mineralogy measured in situ in Jezero crater, Mars, by the Perseverance rover.

Tumours are abnormal growths of cells that reproduce by redirecting essential nutrients and resources from surrounding tissue. Changes to cell metabolism that trigger the growth of tumours are reflected in subtle differences between the chemical composition of healthy and malignant cells. We used LA-ICP-MS imaging to investigate whether these chemical differences can be used to spatially identify tumours and support detection of primary colorectal tumours in anatomical pathology. First, we generated quantitative LA-ICP-MS images of three colorectal surgical resections with case-matched normal intestinal wall tissue and used this data in a Monte Carlo optimisation experiment to develop an algorithm that can classify pixels as tumour positive or negative. Blinded testing and interrogation of LA-ICP-MS images with micrographs of haematoxylin and eosin stained and Ki67 immunolabelled sections revealed Monte Carlo optimisation accurately identified primary tumour cells, as well as returning false positive pixels in areas of high cell proliferation. We analysed an additional 11 surgical resections of primary colorectal tumours and re-developed our image processing method to include a random forest regression machine learning model to correctly identify heterogenous tumours and exclude false positive pixels in images of non-malignant tissue. Our final model used over 1.6 billion calculations to correctly discern healthy cells from various types and stages of invasive colorectal tumours. The imaging mass spectrometry and data analysis methods described, developed in partnership with clinical cancer researchers, have the potential to further support cancer detection as part of a comprehensive digital pathology approach to cancer care through validation of a new chemical biomarker of tumour cells.

In the paper by Jones et al. (2020), the authors have noted that an incorrect value was published for the calibrated Fe3+/Fe for the rafted pumice sample from the 2012 Havre eruption. The correct value is 0.257 (0.010) and is included in the updated Table 2 below and updated in the inset in Fig. 3(c) (overleaf). (Table Presented).

Background and Aims X-ray fluorescence microscopy (XFM) is a powerful technique to elucidate the distribution of elements within plants. However, accumulated radiation exposure during analysis can lead to structural damage and experimental artefacts including elemental redistribution. To date, acceptable dose limits have not been systematically established for hydrated plant specimens. • Methods Here we systematically explore acceptable dose rate limits for investigating fresh sunflower (Helianthus annuus) leaf and root samples and investigate the time–dose damage in leaves attached to live plants. • Key Results We find that dose limits in fresh roots and leaves are comparatively low (4.1 kGy), based on localized disintegration of structures and element-specific redistribution. In contrast, frozen-hydrated samples did not incur any apparent damage even at doses as high as 587 kGy. Furthermore, we find that for living plants subjected to XFM measurement in vivo and grown for a further 9 d before being reimaged with XFM, the leaves display elemental redistribution at doses as low as 0.9 kGy and they continue to develop bleaching and necrosis in the days after exposure. • Conclusions The suggested radiation dose limits for studies using XFM to examine plants are important for the increasing number of plant scientists undertaking multidimensional measurements such as tomography and repeated imaging using XFM.

Electrochemical water splitting to generate hydrogen has been identified as a possible solution to the storage of intermittent renewable energy. However there are still challenges remaining in the development of stable electrocatalysts for the oxygen evolution half-reaction. Here we investigate the effects that the oxygen evolution reaction (OER) has on an electrodeposited Ni(OH)2 catalyst operated under alkaline conditions. The electrocatalyst was characterised by established methods including cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy both before and after the OER to identify changes that may have occurred in the structure and/or composition of the catalyst. In addition, synchrotron X-ray absorption near edge structure mapping was used to generate spatially resolved maps of the species present within the Ni(OH)2 catalyst and how they change in a heterogeneous manner into a NiO species after the OER. When compared to the morphological data it suggests that changes in the morphology after the OER can be correlated to the formation of NiO within the newly formed clusters that were generated across the electrocatalyst.

Optical devices, where light controls light, are of interest to the computing and communications industries due to their potential to vastly improve information capacity and processing speed. One such device is an optical logic gate, based on the interactions of low divergence fields in photorefractive media. Presently, bright solitons in self-focusing photorefractive media offer one attractive possibility. A wide variety of other low divergence fields have also been outlined in recent literature, however, no theoretical model of a single bright soliton propagating in unbiased selfdefocusing photorefractive media is currently available. Evidence is presented of self-defocusing photorefractive media as an intensity dependent Gradient-Index (GRIN) lens with a negative power. Using this model, we outline conditions for the change in the complex beam parameter, and consequently the area and wavefront curvature, of the Gaussian beam to be minimised as it propagates through the selfdefocusing media. This is the first instance where self-defocusing photorefractive media has been modelled as an intensity dependent GRIN lens, and where a low divergence field propagating through unbiased self-defocusing media with a constant complex Gaussian beam parameter has been described.