Non-negative matrix analysis for effective feature extraction in X-ray spectromicroscopy

X-Ray absorption spectromicroscopy provides rich information on the chemical organization of materials down to the nanoscale. However, interpretation of this information in studies of "natural" materials such as biological or environmental science specimens can be complicated by the complex mixtures of spectroscopically complicated materials present. We describe here the shortcomings that sometimes arise in previously-employed approaches such as cluster analysis, and we present a new approach based on non-negative matrix approximation (NNMA) analysis with both sparseness and cluster-similarity regularizations. In a preliminary study of the largescale biochemical organization of human spermatozoa, NNMA analysis delivers results that nicely show the major features of spermatozoa with no physically erroneous negative weightings or thicknesses in the calculated image

Microscale analysis of metal uptake by argillaceous rocks using positive matrix factorization of microscopic X-ray fluorescence elemental maps

Argillaceous rocks are considered in most European countries as suitable host rock formations for the deep geological disposal of high-level radioactive waste (HLW). The most important chemical characteristic in this respect is their generally strong radionuclide retention property due to the high sorption capacity. Consequently, the physico-chemical parameters of these processes have to be studied in great detail. Synchrotron radiation microscopic X-ray fluorescence (SR µ-XRF) has sufficient sensitivity to study these processes on the microscale without the necessity of the application of radioactive substances. The present study focuses on the interaction between the escaped ions and the host-rock surrounding the planned HLW repository. SR µ-XRF measurements were performed on thin sections subjected to sorption experiments using 5 µm spatial resolution. Inactive Cs(I), Ni(II), Nd(III) and natural U(VI) were selected for the experiments chemically representing key radionuclides. The thin sections were prepared on high-purity silicon wafers from geochemically characterized cores of Boda Claystone Formation, Hungary. Samples were subjected to 72-hour sorption experiments with one ion of interest added. The µ-XRF elemental maps taken usually on several thousand pixels indicate a correlation of Cs and Ni with Fe- and K-rich regions suggesting that these elements are predominantly taken up by clay-rich phases. U and Nd was found to be bound not only to the clayey matrix, but the cavity filling minerals also played important role in the uptake. Multivariate methods were found to be efficient tools for extracting information from the elemental distribution maps even when the clayey matrix and fracture infilling regions were examined in the same measured area. By using positive matrix factorization as a new approach the factors with higher sorption capacity could be identified and with additional mineralogical information the uptake capacity of the different mineral phases could be quantified. The results were compared with cluster analysis when the regions dominated by different mineral phases are segmented. The multivariate approach based on µ-XRF to identify the minerals was validated using microscopic X-ray diffraction

Biolabile ferrous iron bearing nanoparticles in glacial sediments

Glaciers and ice sheets are a significant source of nanoparticulate Fe, which is potentially important in sustaining the high productivity observed in the near-coastal regions proximal to terrestrial ice cover. However, the bioavailability of particulate iron is poorly understood, despite its importance in the ocean Fe inventory. We combined high-resolution imaging and spectroscopy to investigate the abundance, morphology and valence state of particulate iron in glacial sediments. Our results document the widespread occurrence of amorphous and Fe(II)-rich and Fe(II)-bearing nanoparticles in Arctic glacial meltwaters and iceberg debris, compared to Fe(III)-rich dominated particulates in an aeolian dust sample. Fe(II) is thought to be highly biolabile in marine environments. Our work shows that glacially derived Fe is more labile than previously assumed, and consequently that glaciers and ice sheets are therefore able to export potentially bioavailable Fe(II)-containing nanoparticulate material to downstream ecosystems, including those in a marine setting. Our findings provide further evidence that Greenland Ice Sheet meltwaters may provide biolabile particulate Fe that may fuel the large summer phytoplankton bloom in the Labrador Sea, and that Fe(II)-rich particulates from a region of very high productivity downstream of a polar ice sheet may be glacial in origin

Combining μXANES and μXRD mapping to analyse the heterogeneity in calcium carbonate granules excreted by the earthworm Lumbricus terrestris

The use of fluorescence full spectral micro-X-ray absorption near-edge structure (μXANES) mapping is becoming more widespread in the hard energy regime. This experimental method using the Ca K-edge combined with micro-X-ray diffraction (μXRD) mapping of the same sample has been enabled on beamline I18 at Diamond Light Source. This combined approach has been used to probe both long- and short-range order in calcium carbonate granules produced by the earthworm Lumbricus terrestris. In granules produced by earthworms cultured in a control artificial soil, calcite and vaterite are observed in the granules. However, granules produced by earthworms cultivated in the same artificial soil amended with 500 p.p.m. Mg also contain an aragonite. The two techniques, μXRD and μXANES, probe different sample volumes but there is good agreement in the phase maps produced

Pricing determinants of primary issues of agribusiness receivables certificates, issued from 2012 to 2019

Os Certificados de Recebíveis do Agronegócio (CRA) são títulos de crédito privado, em que empresas do agronegócio os emitem a fim de financiar seus investimentos em insumos, maquinários e produtos. Este estudo teve como objetivo identificar as variáveis consideradas quando da emissão de CRA, analisando os fatores que influenciam o spread na formação dos preços nas emissões primárias de CRA. A hipótese a ser confirmada foi de que a avaliação de rating das emissoras seria impactante na precificação. Para alcançar esse objetivo, foi utilizada base de dados contendo todas as emissões primárias de CRA, emitidas desde 2012 até dezembro de 2019, distribuídas via Instrução CVM nº 400. Dessa forma, foi avaliado o comportamento das emissões a partir de dados sobre rating, agência de rating, tempo de duração do papel, indexador, além do valor total das emissões e PIB e taxa básica de juros dos anos de emissão. Como resultados da pesquisa, foi confirmada a hipótese de que o rating das emissoras tem impacto na precificação, sendo diretamente proporcional ao spread. Além disso, constatou-se que a taxa de juros básica é inversamente proporcional ao spread e a presença de uma taxa pré-fixada, como remuneração dos papéis, é diretamente proporcional ao spread.Agribusiness Receivables Certificates (CRA) are private credit bonds, which agribusiness companies issue in order to finance their investments in inputs, machinery and products. This study aimed to identify the variables considered when issuing CRA, analyzing the factors that influence the spread in the formation of prices in primary issues of CRA. The hypothesis to be confirmed was that the rating assessment of the issuers would have an impact on pricing. To achieve this goal, a database was used containing all CRA primary issues, issued from 2012 to December 2019, distributed via CVM Instruction No. 400. Thus, the behavior of issues was evaluated based on data on rating, agency rating, duration, index, in addition to the total value of issues and GDP and basic interest rate for the years of issuance. As a result of the research, the hypothesis that the rating of the issuers has an impact on pricing, being directly proportional to the spread, was confirmed. In addition, it was found that the basic interest rate is inversely proportional to the spread and the presence of a pre-fixed rate, as remuneration for the papers, is directly proportional to the spread