550 research outputs found

    Electronic structure and chemical bonding in Ti2AlC investigated by soft x-ray emission spectroscopy

    Full text link
    The electronic structure of the nanolaminated transition metal carbide Ti2AlC has been investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured Ti L, C K and Al L emission spectra are compared with calculated spectra using ab initio density-functional theory including dipole matrix elements. The detailed investigation of the electronic structure and chemical bonding provides increased understanding of the physical properties of this type of nanolaminates. Three different types of bond regions are identified; the relatively weak Ti 3d - Al 3p hybridization 1 eV below the Fermi level, and the Ti 3d - C 2p and Ti 3d - C 2s hybridizations which are stronger and deeper in energy are observed around 2.5 eV and 10 eV below the Fermi level, respectively. A strongly modified spectral shape of the 3s final states in comparison to pure Al is detected for the buried Al monolayers indirectly reflecting the Ti 3d - Al 3p hybridization. The differences between the electronic and crystal structures of Ti2AlC, Ti3AlC2 and TiC are discussed in relation to the number of Al layers per Ti layer in the two former systems and the corresponding change of the unusual materials properties.Comment: 14 pages, 7 figures; PACS:78.70.En, 71.15.Mb, 71.20.-

    Contrasting Dihydronaphthoquinone Patterns in Closely Related Drosera (Sundew) Species Enable Taxonomic Distinction and Identification

    Get PDF
    Dihydronaphthoquinones are described as constituents of sundews (Drosera), Venus flytraps (Dionaea), and dewy pines (Drosophyllum) for the first time. As in the corresponding naphthoquinones, these reduced derivatives may occur in two regio-isomeric series distinguished by the relative position of a methyl group (at position 2 or 7 in the naphthalene skeleton), depending on the taxon. Species producing plumbagin (2-methyljuglone, 1) do commonly contain the corresponding dihydroplumbagin (5), while species containing ramentaceone (7-methyljuglone, 2) also contain dihydroramentaceone (7-methyl-β-dihydrojuglone, 6). So far, only few species containing plumbagin (1) and dihydroplumbagin (5) additionally form dihydroramentaceone (6) but not ramentaceone (2). Thus, subtle but constant differences in the chemism of closely related and morphologically similar species reliably define and distinguish taxa within D. sect. Arachnopus, which is taken to exemplify their chemotaxonomic utility. The joint presence of quinones and hydroquinones allows observations and predictions on the chemical structures and the reactions of these intriguing natural products

    A High Prevalence of Gastrointestinal Manifestations in Common Variable Immunodeficiency

    Get PDF
    OBJECTIVES: Common variable immunodeficiency (CVID) is associated with a spectrum of autoimmune complications. We studied the prevalence of gastrointestinal (GI) manifestations and infections in patients with CVID. METHODS: Complete clinical data of 132 Finnish patients with CVID (106 probable and 26 possible CVID) followed up between 2007 and 2016 were collected to a structured database. Data on endoscopies, histology, and laboratory studies were retrieved from patient files. RESULTS: Most common referral indications were diarrhea and/or weight loss (47%-67%). Patients with probable CVID had higher fecal calprotectin and a1-antitrypsin and lower blood vitamin B12 than patients with possible CVID. Gastroscopy and colonoscopy were done to 71 (67%) and 63 (59%) patients with probable CVID, respectively. Endoscopies showed that 15% of them had chronic active gastritis and 17% atrophic gastritis and 3% had gastric adenocarcinoma. A celiac sprue-like condition was found in 7 patients (10%), of whom 3 responded to a gluten-free diet. Colonoscopies demonstrated unspecific colitis (14%), ulcerative colitis (8%), microscopic colitis (10%), and Crohn's disease (2%). Colonic polyps were noted in30% of patients, and3% had lower GI malignancies. Thirty-five patients with CVID had bacterial or parasitic gastroenteritis; chronic norovirus was detected in 4 patients with probable CVID. Patients with GI inflammation had higher levels of fecal calprotectin and blood CD81 T lymphocytes but lower counts of CD191CD271 memory B cells and/or CD191 B cells. Immunophenotype with low B-cell counts was associated with higher fecal calprotectin levels. DISCUSSION: Patients with CVID had a high prevalence of GI manifestations and infections of the GI tract. GI inflammation was associated with a distinct immunophenotype and elevated fecal calprotectin.Peer reviewe

    On dimension reduction in Gaussian filters

    Full text link
    A priori dimension reduction is a widely adopted technique for reducing the computational complexity of stationary inverse problems. In this setting, the solution of an inverse problem is parameterized by a low-dimensional basis that is often obtained from the truncated Karhunen-Loeve expansion of the prior distribution. For high-dimensional inverse problems equipped with smoothing priors, this technique can lead to drastic reductions in parameter dimension and significant computational savings. In this paper, we extend the concept of a priori dimension reduction to non-stationary inverse problems, in which the goal is to sequentially infer the state of a dynamical system. Our approach proceeds in an offline-online fashion. We first identify a low-dimensional subspace in the state space before solving the inverse problem (the offline phase), using either the method of "snapshots" or regularized covariance estimation. Then this subspace is used to reduce the computational complexity of various filtering algorithms - including the Kalman filter, extended Kalman filter, and ensemble Kalman filter - within a novel subspace-constrained Bayesian prediction-and-update procedure (the online phase). We demonstrate the performance of our new dimension reduction approach on various numerical examples. In some test cases, our approach reduces the dimensionality of the original problem by orders of magnitude and yields up to two orders of magnitude in computational savings

    Exposure to potentially morally injurious events in U.K. health and social care workers during COVID-19: Associations with PTSD and complex PTSD

    Get PDF
    OBJECTIVE: Health and social care workers (HSCWs) have been shown to be at risk of exposure to potentially morally injurious events (PMIEs) and mental health problems during the COVID-19 pandemic. This study aimed to examine associations between exposure to PMIEs and meeting threshold criteria for probable posttraumatic stress disorder (PTSD) and probable complex PTSD (CPTSD) in U.K. HSCWs immediately after the peak of the first COVID-19 wave. METHOD: Frontline HSCWs from across the United Kingdom working in diverse roles in hospitals, nursing or care homes, and other community settings were recruited to the Frontline-COVID study via social media. Participants (n = 1,056) completed a cross-sectional online survey (May 27, 2020-July 23, 2020) which assessed exposure to PMIEs (nine-item Moral Injury Events Scale), and meeting symptom thresholds for probable PTSD and probable CPTSD (International Trauma Questionnaire). RESULTS: PMIEs related to witnessing others' wrongful actions and betrayal events were more commonly endorsed than perceived self-transgressions. The rate of probable International Classification of Diseases, 11th Revision (ICD-11) PTSD was 8.3%, and of probable ICD-11 CPTSD was 14.2%. Betrayal-related PMIEs were a significant predictor of probable PTSD or probable CPTSD, together with having been redeployed during the pandemic. The only variable that differentially predicted probable CPTSD as compared with probable PTSD was not having had reliable access to personal protective equipment; none of the PMIE types were differential predictors for screening positive for probable PTSD versus probable CPTSD. CONCLUSIONS: Exposure to PIMEs could be important for PTSD and CPTSD development. Interventions for moral injury in HSCWs should be investigated. (PsycInfo Database Record (c) 2023 APA, all rights reserved)

    Electronic structure investigation of Ti3AlC2, Ti3SiC2, and Ti3GeC2 by soft-X-ray emission spectroscopy

    Full text link
    The electronic structures of epitaxially grown films of Ti3AlC2, Ti3SiC2 and Ti3GeC2 have been investigated by bulk-sensitive soft X-ray emission spectroscopy. The measured high-resolution Ti L, C K, Al L, Si L and Ge M emission spectra are compared with ab initio density-functional theory including core-to-valence dipole matrix elements. A qualitative agreement between experiment and theory is obtained. A weak covalent Ti-Al bond is manifested by a pronounced shoulder in the Ti L-emission of Ti3AlC2. As Al is replaced with Si or Ge, the shoulder disappears. For the buried Al and Si-layers, strongly hybridized spectral shapes are detected in Ti3AlC2 and Ti3SiC2, respectively. As a result of relaxation of the crystal structure and the increased charge-transfer from Ti to C, the Ti-C bonding is strengthened. The differences between the electronic structures are discussed in relation to the bonding in the nanolaminates and the corresponding change of materials properties.Comment: 15 pages, 8 figure
    corecore