70 research outputs found
In Situ XAS and XRPD Parametric Rietveld Refinement To Understand Dealumination of Y Zeolite Catalyst
No full textResilience profiles across context: A latent profile analysis in a German, Greek, and Swiss sample of adolescents
No full textThe present study investigated resilience profiles (based on levels of symptoms of anxiety and depression and five dimensions of protective factors) of 1,160 students from Germany (n = 346, 46.0% females, Mage = 12.77, SDage = 0.78), Greece (n = 439, 54.5% females, Mage = 12.68, SDage = 0.69), and Switzerland (n = 375, 44.5% females, Mage = 12.29, SDage = 0.88) using latent profile analyses. We also checked for measurement invariance and investigated the influence of gender and migration on class membership. A three-profilesolution was found for Switzerland (nonresilient 22.1%, moderately resilient 42.9%, untroubled 34.9%), and a four-profile-solution was the best fitting model for Germany (nonresilient 15.7%, moderately resilient 44.2%, untroubled 27.3%, resilient 12.7%) and Greece (nonresilient 21.0%, moderately resilient 30.8%, untroubled 24.9%, resilient 23.3%). Measurement invariance did not hold across the three countries. Profile differences regarding class membership predictions were detected for Germany and Greece, but none for Switzerland. Results implicate that resilience profiles are highly contextually sensitive, and resilience research findings should not be generalized considering the particularity of contexts, people, and outcomes. © 2022 Janousch et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Influence of crystallographic orientation of biogenic calcite on <i>in situ</i> Mg XANES analyses
No full textMicro X-ray absorption near-edge spectroscopy at the Mg <i>K</i>-edge is a useful technique for acquiring information about the environment of Mg<sup>2+</sup> in biogenic calcite. These analyses can be applied to shell powders or intact shell structures. The advantage of the latter is that the XANES analyses can be applied to specific areas, at high (e.g. micrometre) spatial resolution, to determine the environment of Mg<sup>2+</sup> in a biomineral context. Such in situ synchrotron analysis has to take into account the potential effect of crystallographic orientation given the anisotropy of calcite crystals and the polarized nature of X-rays. Brachiopod shells of species with different crystallographic orientations are used to assess this crystallographic effect on <i>in situ</i> synchrotron measurements at the Mg <i>K</i>-edge. Results show that, owing to the anisotropy of calcite, <i>in situ</i> X-ray absorption spectra (XAS) are influenced by the crystallographic orientation of calcite crystals with a subsequent potentially erroneous interpretation of Mg<sup>2+</sup> data. Thus, this study demonstrates the importance of crystallography for XAS analyses and, therefore, the necessity to obtain crystallographic information at high spatial resolution prior to spectroscopic analysis
Magnesium in the lattice of calcite-shelled brachiopods
No full textPalaeoclimate information is often extracted from Rhynchonelliform brachiopod shell calcite, in particular the inner secondary layer, via the δ18O composition, which is a proxy for seawater temperature. Compared to δ18O, the potential for Mg/Ca ratio, as a brachiopod seawater temperature proxy, has been neglected. The use of Mg/Ca ratio as a temperature proxy assumes that, with increasing temperature, more Mg substitutes for Ca in the calcite lattice. Brachiopod shells, like all biominerals, are composites of organic and inorganic components. This raises the possibility that magnesium is hosted by the organic components. Alternatively, magnesium may be present as a separate mineral phase, rather than a true component of the calcite lattice, or incorporated into calcite in non-ideal or variable coordination. Here we use synchrotron X-ray absorption Near Edge Spectroscopy (XANES) at the Mg K-edge to determine the local environment of magnesium in two species of brachiopod with low Mg-calcite shells, Terebratulina retusa and Notosaria nigricans and one species with a high Mg-calcite shell, Novocrania anomala. XANES at the Mg K-edge of a suite of Mg-bearing standards fingerprints the local environment of magnesium in the brachiopod shell powders as well as in situ analyses. In all cases, it is evident that magnesium is not hosted by organic components but is within the inorganic component of the shell. These data support the possibility of using brachiopod Mg/Ca ratios as a temperature proxy
Reduction of selenite on corroded iron: a micro-spectroscopic study
No full textUnder anoxie conditions zero-valent iron can react with water to produce hydrogen gas and magnetite or green rust, a highly reactive mineral phase that can induce reduction processes and thus control the speciation, the
solubility, toxicity and the mobility of redox sensitive elements in (nuclear) waste repositories. In this study micro
X-ray fluorescence (micro-XRF) and micro X-ray absorption spectroscopy (micro-XAS) were used to investigate
the speciation of selenium that immobilized in the presence of Fe(0) and an anoxie synthetic groundwater solution.
The selenium immobilization was accompanied by the formation of a green rust corrosion layer. Micro-XRF
revealed that a Se-rich layer is present along the iron surfaces that were exposed to the Se(IV) solution. Micro-XAS
experiments at the Se K-edge showed that Se(IV) was reduced to elemental Se(0). Thus, the reactivity of zero-valent
and green rust should to be considered in assessing the long-term fate of selenium in nuclear waste repositories.
Psychometric properties of the Resilience Scale for Adolescents (READ) and Measurement Invariance Across Two Different German-Speaking Samples
No full textThe Resilience Scale for Adolescents (READ) is a highly rated scale for measuring protective factors of resilience. Even though the READ has been validated in several different cultural samples, no studies have validated the READ across samples in German from Switzerland and Germany. The purpose of this study was to explore the construct validity of the German READ version in two samples from two different countries and to test the measurement invariance between those two samples. A German sample (n = 321, M = 12.74, SD = 0.77) and a German-speaking Swiss sample (n = 349, M = 12.67, SD = 0.69) of seventh graders completed the READ, Hopkins Symptom Checklist (HSCL-25), Rosenberg Self-Esteem Scale (RSE), General Self-Efficacy Scale, and Satisfaction with Life Scale (SWL). The expected negative correlations between READ and HSCL-25 and the positive correlations between RSE, self-efficacy, and SWL were supported. Furthermore, the results of the measurement invariance demonstrated that the originally proposed five-dimensional structure is equal in the German and Swiss samples, and it can be assumed that the same construct was assessed by excluding one item. The five-factor, 27-item solution is a valid and reliable self-report measure of protective factors between two German-speaking samples
Spatial distribution of oxygen vacancies in Cr-doped SrTiO3 during an electric-field-driven insulator-to-metal transition
No full textSpatially resolved x-ray fluorescence maps are presented that show the introduction and the evolution of oxygen vacancies in chromium-doped strontium titanate during an electric-field-driven insulator-to-metal transition. The vacancies are introduced at the anode and diffuse through the crystal toward the cathode. The spatial distribution of vacancies is explained by a model describing the electrical breakdown as a percolation process. Strong differences in the vacancy distribution were found when the transition took place in air and in a hydrogen-enriched atmosphere. In air, the vacancies disappeared from the surface, whereas in the reducing hydrogen atmosphere, they remained at the surface. © 2009 American Institute of Physics.</p
Internalizing and externalizing symptoms in adolescents with and without experiences of physical parental violence, a latent profile analysis on violence resilience
No full textQuestionnaire data from a cross-sectional study on social resilience in adolescence, with a sample of N = 1,974 Swiss seventh grade high school students ages 12–14 (M = 11.76; SD = 0.65) was used to identify and compare violence resilience profiles. Person-centered latent profile analysis (LPA) was applied and allowed for the grouping of adolescents into profiles of internalizing (depression/anxiety, dissociation) and externalizing symptoms (peer aggression, peer victimization, classroom disruption) and differentiation of adolescents with (n = 403) and without (n = 1,571) physical parental violence experiences. Subsequently, a multinomial logistic regression analysis was conducted to further investigate the sociodemographic predictors of violence resilience profiles. With LPA, we identified four distinct profiles for both adolescent groups (with and without parental physical violence experiences). The results showed three particularly burdened profiles of adolescents, one with higher externalizing and one with higher internalizing symptoms, which did not occur simultaneously to the same extent. Furthermore, the third profile contained adolescents with both elevated internalizing and externalizing symptoms, the comorbid profile. The fourth profile consisted of the majority of adolescents, who exhibited little or no internalizing and externalizing symptoms, the so-called no/low symptomatic profile. A differentiated view of the symptoms can create added value regarding the understanding of violence resilience. Moreover, in the multinomial logistic regression, significant associations were found between the profiles and adolescents’ gender in the group of adolescents with parental physical violence experiences, but none were found in relation to sociocultural status and migration background
On the isotropic and anisotropic thermal conductivity of metallic hollow sphere structures
No full textMetallic hollow sphere structures (MHSS) combine the well-known advantages of cellular metals with the excellent material properties of solid base metals. The basic cell is a hollow sphere. Metallic hollow sphere structures can be assembled by sintering, soldering, or adhesive bonding. The macroscopic thermal property and, more specifically, the thermal conductivity is an essential material property. The objective of this work is to address the thermal conductivity of MHSS in dependence of the geometrical parameters of a single sphere and the ordering scheme of the assembled structure with a special focus on isotropy and anisotropy. From a macroscopic point of view, which is often used within the engineering design process, the characterization of the properties of MHSS demand an approximative description coming out of a homogenization. Within this paper the unit cell approach is used. The numerical analysis is done on the basis of a parameterized 3D-CAD model enabling the variation of the sphere size and wall thickness as well as the geometry of the interconnection between spheres. Periodic boundary conditions are applied. Results for the macroscopic thermal conductivity are presented for regular-packed (CP, BCC, FCC, and HCP) as well as randomly packed unit cells representing sintered or soldered MHSS. The anisotropy is discussed by the 3 × 3 thermal conductivity tensor.No Full Tex
A Comparison of 4<i>f vs</i> 5<i>f</i> Metal−Metal Bonds in (CpSiMe<sub>3</sub>)<sub>3</sub>M−ECp* (M = Nd, U; E = Al, Ga; Cp* = C<sub>5</sub>Me<sub>5</sub>): Synthesis, Thermodynamics, Magnetism, and Electronic Structure
No full textReaction of (CpSiMe3)3U or (CpSiMe3)3Nd with (Cp*Al)4 or Cp*Ga (Cp* = C5Me5) afforded the isostructural complexes (CpSiMe3)3M−ECp* (M = U, E = Al (1); M = U, E = Ga (2); M = Nd, E = Al (3); M = Nd, E = Ga (4)). In the case of 1 and 2 the complexes were isolated in 39 and 90% yields, respectively, as crystalline solids and were characterized by single-crystal X-ray diffraction, variable-temperature 1H NMR spectroscopy, elemental analysis, variable-temperature magnetic susceptibility, and UV−visible−NIR spectroscopy. In the case of 3 and 4, the complexes were observed by variable-temperature 1H NMR spectroscopy but were not isolated as pure materials. Comparison of the equilibrium constants and thermodynamic parameters ΔH and ΔS obtained by 1H NMR titration methods revealed a much stronger U−Ga interaction in 2 than the Nd−Ga interaction in 4. Competition reactions between (CpSiMe3)3U and (CpSiMe3)3Nd indicate that Cp*Ga selectively binds U over Nd in a 93:7 ratio at 19 °C and 96:4 at −33 °C. For 1 and 3, comparison of 1H NMR peak intensities suggests that Cp*Al also achieves excellent U(III)/Nd(III) selectivity at 21 °C. The solution electronic spectra and solid-state temperature-dependent magnetic susceptibilities of 1 and 2, in addition to X-ray absorption near-edge structure (XANES) measurements from scanning transmission X-ray microscopy (STXM) of 1, are consistent with those observed for other U(III) coordination complexes. DFT calculations using five different functionals were performed on the model complexes Cp3M−ECp (M = Nd, U; E = Al, Ga), and empirical fitting of the values for Cp3M−ECp allowed the prediction of binding energy estimates for Cp*Al compounds 1 and 3. NBO/NLMO bonding analyses on Cp3U−ECp indicate that the bonding consists predominantly of a E→U σ-interaction arising from favorable overlap between the diffuse ligand lone pair and the primarily 7s/6d acceptor orbitals on U(III), with negligible U→E π-donation. The overall experimental and computational bonding analysis suggests that Cp*Al and Cp*Ga behave as good σ-donors in these systems
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