A New Albite Microanalytical Reference Material from Piz Beverin for Na, Al and Si Determination, and the Potential for New K-Feldspar Reference Materials

Determination of alkali elements is important to Earth scientists, yet suitable and reliable microanalytical reference materials are lacking. This paper proposes a new albite reference material and evaluates the potential for future K-feldspar reference materials. The proposed Piz Beverin albite reference material from Switzerland yields a homogeneous composition at the centimetre- to micrometre-scale for Si, Al and Na with \u3c 2000 μg g-1 total trace elements (mostly heterogeneously distributed Ca, K and Sr). EPMA and LA-ICP-MS measurements confirm a composition of 99.5(2)% albite component, which is supported further by bulk XRF measurements. A round robin evaluation involving nine independent EPMA laboratories confirms its composition and homogeneity for Si, Al and Na. In addition, a set of five distinct clear K-feldspar samples was evaluated as possible reference materials. The first two crystals of adular and orthoclase yield unacceptable inhomogeneities with \u3e 2% relative local variations of Na, K and Ba contents. The three other investigated sets of K-feldspar crystals are yellow sanidine crystals from Itrongay (Madagascar). Despite distinct compositions, EPMA confirms they are each homogeneous at the centimetre to micrometre scale for Si, Al and K and have no apparent inclusions; further investigation to find larger amounts of these materials is therefore justified

Direct tomography imaging for inelastic x-ray scattering experiments at high pressure

A method to separate the non-resonant inelastic X-ray scattering signal of a micro-metric sample contained inside a diamond anvil cell (DAC) from the signal originating from the high-pressure sample environment is described. Especially for high-pressure experiments, the parasitic signal originating from the diamond anvils, the gasket and/or the pressure medium can easily obscure the sample signal or even render the experiment impossible. Another severe complication for high-pressure non-resonant inelastic X-ray measurements, such as X-ray Raman scattering spectroscopy, can be the proximity of the desired sample edge energy to an absorption edge energy of elements constituting the DAC. It is shown that recording the scattered signal in a spatially resolved manner allows these problems to be overcome by separating the sample signal from the spurious scattering of the DAC without constraints on the solid angle of detection. Furthermore, simple machine learning algorithms facilitate finding the corresponding detector pixels that record the sample signal. The outlined experimental technique and data analysis approach are demonstrated by presenting spectra of the Si L-2,L-3-edge and O K-edge of compressed alpha-quartz. The spectra are of unprecedented quality and both the O K-edge and the Si L-2,L-3-edge clearly show the existence of a pressure-induced phase transition between 10 and 24 GPa.Peer reviewe

Berechnung einiger Eigenschaften von SiO2-haltigen wässrigen Fluiden und Gläsern auf atomarer Ebene

Disordered silicate materials occur in nature as melts, glasses and silica species in aqueous fluids. It is therefore of great importance in numerous branches of geosciences. Understanding the relation between the atomic-scale structure of disordered silicate materials and their macroscopic properties such as melt viscosity or silica solubility in water is one of the fundamental aims of experimental investigation of these materials. Ab initio modeling provides atomic-scale insight into both the structure and macroscopic properties, and thereby contributes to our understanding of disordered silicate materials. The present work investigates several structural and dynamical properties of silicate glasses and silica species in aqueous fluids by means of ab initio molecular dynamics (MD) and post-run evaluation tools.Ungeordnete silikatische Materialien kommen in der Natur vor in Form von Schmelzen und Gläsern sowie als Silikatspezies in wässriger Lösung. Diese Materialien sind von großer Bedeutung in verschiedenen Bereichen der Geowissenschaften. Es ist eines der grundlegenden Ziele in der Untersuchung solcher Materialien, die Zusammenhänge zwischen der atomaren Struktur und makroskopischen Eigenschaften wie zum Beispiel der Viskosität von Schmelzen oder der Löslichkeit von SiO2 in Wasser besser zu verstehen. Die ab initio Modellierung gibt Einblicke auf der atomaren Skala in Struktur und Eigenschaften. Sie trägt somit zum Verständnis von ungeordnetem silikatischem Material bei. Mit den Mitteln der ab initio molekulardynamischen Modellierung und nachgeordneten Auswertungsalgorithmen untersucht die vorliegende Arbeit einige strukturelle und dynamische Eigenschaften von Silikatgläsern und Silikatspezies in wässriger Lösung

Kodierung von LPC-Parametern für die mechanokutane Sprachvermittlung

Zusammenfassung: In dieser Studienarbeit wurde eine Zuordnung von verschiedenen mechanokutanen Vibrationsreizen zu den LPC-Parametern entwickelt. Dazu wurde ein Satz von neun gut unterscheidbaren und erlernbaren Reizen einer Dauer von 50ms aus dem Amplituden-Frequenzfeld 0-600um / 60-600Hz erarbeitet. Die Erlernbarkeit wurde anhand von Tests mit verschiedenen Testpersonen bestätigt. Die Reize wurden nach ihrem Fühlstärkeeindruck geordnet. Damit wurde gewährleistet, daß bei einer Zuordnung dieser Reize zu den gleichverteilten LPC-Koeffizienten ein ]bertragungs- und Berechnungsfehler sich minimal auf die Informationsaufnahme des Gehörgeschädigten auswirkt. Auf der Suche nach einem physiologischen Modell zur Beschreibung des Fühlstärkeeindrucks wurden die mechanische Hautimpedanz und die Fühlschwelle bei einer Reizdauer von 50ms bestimmt. Über die Hautimpedanz konnte die mechanische Leistung der Reize errechnet werden. Weiterhin wurde gezeigt, daß die Verständlichkeit der Reize bei einer Verkürzung der Reizdauer auf 33ms bzw. 25ms nur wenig sinkt

The Role of Therapeutic Leukapheresis in Hyperleukocytotic AML

Purpose: Hyperleukocytosis in AML with leukostasis is a serious life-threatening condition leading to a high early mortality which requires immediate cytoreductive therapy. Therapeutic leukapheresis is currently recommended by the American Society of Apheresis in patients with a WBC>100 G/l with signs of leukostasis, but the role of prophylactic leukapheresis before clinical signs of leukostasis occur is unclear. Patients: We retrospectively analyzed the role of leukapheresis in 52 patients (median age 60 years) with hyperleukocytotic AML with and without clinical signs of leukostasis. Since leukapheresis was performed more frequently in patients with signs of leukostasis due to the therapeutic policy in our hospital, we developed a risk score for early death within seven days after start of therapy (EDd7) to account for this selection bias and to independently measure the effect of leukapheresis on EDd7. Results: 20 patients received leukapheresis in combination to chemotherapy compared to 32 patients who received chemotherapy only. In a multivariate logistic regression model for the estimation of the probability of EDd7 thromboplastin time and creatinine remained as independent significant parameters and were combined to create an EDd7 risk score. The effect of leukapheresis on EDd7 was evaluated in a bivariate logistic regression together with the risk score. Leukapheresis did not significantly change early mortality in all patients with a WBC >= 100 G/l. Discussion: Prophylactic leukapheresis in hyperleukocytotic patients with and without leukostasis did not improve early mortality in our retrospective study. Larger and prospective clinical trials are needed to validate the risk score and to further explore the role of leukapheresis in AML with hyperleukocytosis

Structural and dynamical properties of supercritical H2O-SiO2 fluids studied by ab initio molecular dynamics

In this study we report the structure of supercritical H2O-SiO2 fluid composed of 50 mol% H2O and 50 mol% SiO2 at 3000 K and 2400 K. investigated by means of ab initio molecular dynamics of models comprising 192 and 96 atoms. The density is set constant to 138 g/cm(3), which yields a pressure of 4.3 GPa at 3000 K and 3.6 GPa at 2400 K. Throughout the trajec[ories, water molecules are formed and dissociated via the network modifying reaction 2 SiOH = SiOSi + H2O The calculation of the reaction constant K- [OH](2)/[H2O][O2-] is carried out on the basis of the experimentally relevant Q '' species notation and agrees well with an extrapolation of experimental data to 3000 K. After quench from 3000 K to 2400 K, the degree of polymerization of the silicate network in the 192-atom models increases noticeably within several tens of picoseconds, accompanied by release of molecular H2O. An unexpected opposite trend is observed in smaller 96-atom models, due to a finite size effect, as several uncorrelated models of 192 and 96 atoms indicate. The temperature-dependent slowing down of the H2O-silica interaction dynamics is described on the basis of the bond autocorrelation function. (C) 2016 Elsevier B.V. All rights reserved

Density of amorphous GeO2GeO_{2} to 133 GPa with possible pyritelike structure and stiffness at high pressure

Germanium oxide is a prototype network-forming oxide with pressure-induced structural changes similar to those found in crystals and amorphous silicate oxides at high pressure. Studying density and coordination changes in amorphous GeO2 allows for insight into structural changes in silicate oxides at very high pressure, with implications for the properties of planetary magmas. Here, we report the density of germanium oxide glass up to 133 GPa using the x-ray absorption technique, with very good agreement with previous experimental data at pressure below 40 GPa and recent calculation up to 140 GPa. Our data highlight four distinct compressibility domains, corresponding to changes of the local structure of GeO2. Above 80 GPa, our density data show a compressibility and bulk modulus similar to the counterpart crystal phase, and we propose that a compact distorted sixfold coordination, similar to the structural motif of the pyritelike crystalline GeO2 polymorph, is likely to be stable in that pressure range. Our density data point to a smooth continuous evolution of the average coordination for pressure above 20 GPa with persistent sixfold coordination, without sharp density or density slope discontinuities. These observations are in very good agreement with theoretical calculations and spectroscopic measurements, and our results indicate that glasses and melts may behave similarly to their high-pressure solid counterparts with comparable densities, compressibility, and possibly average coordination

Vibrational properties of silica species in MgO-SiO2 glasses obtained from ab initio molecular dynamics

We report the vibrational properties of silica species in magnesio-silicate glasses, obtained from ab initio molecular dynamics. The mode-projection method employed in this study decomposes the vibrational density of states of silica species into subspectra resulting from normal-mode-like vibrations of mainly two fundamental structural subunits: the SiO44- tetrahedron and the Si- O-Si bridging oxygen (BO). This decomposition reveals the mode-specific frequency shifts as a function of tetrahedral polymerization. The method is validated by application to crystalline Mg2SiO4 at 300 K, and by comparison to results obtained from normal mode analysis (NMA). Our main findings are: (1) The frequency of the spectroscopically important tetrahedral symmetric stretching mode v(1)(TET) of Q(1)- to Q(4)-species is in general lower than commonly assumed. The Q(2)-species shows a double instead of a single peak. (2) The BO asymmetric stretching mode v(3)(BO) contributes to the vibrational density in the region 900-1200 cm(-1). If this contribution is not considered in the fitting of Raman intensity in the high-frequency region between 800 cm(-1) and 1200 cm(-1) and spectra are explained by tetrahedral contributions of Q(n)-species only, then the degree of polymerization of a glass is likely to be overestimated. (3) The Si2O76- dimer, which is an important structural unit in silica-poor MgO-SiO2 glasses, possesses a specific ethane-like symmetric stretching vibration at about 935 cm(-1).(C) 2012 Elsevier B.V. All rights reserved