Künstlich hergestellte OberflÄchenschichten auf Glas

Zusammenfassung Der Verfasser führt in erster Reihe die Me\ergebnisse des Brechungsindex mittels der polarimetrischen Methode und mittels der Methode der kleinsten Ablenkung auf Prismen aus den verschiedenen Glassorten (Tabelle II) und auf den 20 Jahre alten Prismen vor und nach dem frischen Polieren (Tabelle III und IV) an. Der Schwerpunkt dieser polarimetrischen Messungen liegt in den Studien der künstlich hergestellten OberflÄchenschichten auf den Glasprismen. Die Tabellen V und VI geben die Me\ergebnisse von Studien der OberflÄchenschichten, welche künstlich mit einer chemischen Einwirkung 1,0-norm. NaOH- und H₂SO₄-Lösungen erzielt wurden. Die H₂SO₄ bildet auf der GlasoberflÄche eine dünne OberflÄchenschicht, welche das Glas vor der Einwirkung der SÄure schützt. Diese OberflÄchenschicht macht das Glas widerstandsfÄhig gegen die SÄuren. Demgegenüber bildet die NaOH-Lösung keine solche Schicht, welche das Glas schützen würde; daher korrodieren die Alkalilösungen (NaOH) das Glas. Weitere Untersuchungen haben bewiesen, da\ die NaOH-Lösung die OberflÄchenschicht auflöst, und zwar auf dem Crownglasprisma schneller als auf dem Flintglas. Auf dem Quarz, der einer vierstündigen Einwirkung NaOHund H₂SO₄-Lösungen ausgesetzt wurde, konnte keine Änderung auf der OberflÄche festgestellt werden. Ein Beweis der Anwesenheit der OberflÄchenschichten auf dem Glas sind die Interferenzerscheinungen des Lichtes. Aus der Interferenzfarbe wurde die Dicke der OberflÄchenschicht auf dem Flintglas ca. 2,10^–4 mm berechnet. Aus dem Vorliegenden ist ersichtlich, da\ die polarimetrischen Messungen sich als wertvolle Hilfsmittel für die Untersuchung der OberflÄchenschichten auf dem Glas und den verschiedenen Stoffen bewÄhren.     

Steady compressible Navier–Stokes equations with large potential forces via a method of decomposition

We investigate the steady compressible Navier–Stokes equations near the equilibrium state v = 0, ρ = ρ₀ (v the velocity, ρ the density) corresponding to a large potential force. We introduce a method of decomposition for such equations: the velocity field v is split into a non-homogeneous incompressible part u (div (ρ₀u) = (0) and a compressible (irrotational) part ∇ϕ. In such a way, the original complicated mixed elliptic–hyperbolic system is split into several ‘standard’ equations: a Stokes-type system for u, a Poisson-type equation for ϕ and a transport equation for the perturbation of the density σ = ρ − ρ₀. For ρ₀ = const. (zero potential forces), the method coincides with the decomposition of Novotny and Padula [21]. To underline the advantages of the present approach, we give, as an example, a ‘simple’ proof of the existence of isothermal flows in bounded domains with no-slip boundary conditions. The approach is applicable, with some modifications, to more complicated geometries and to more complicated boundary conditions as we will show in forthcoming papers. © 1998 B.G. Teubner Stuttgart–John Wiley & Sons Ltd.     

A multimodal analytical toolkit to resolve correlated reaction pathways: the case of nanoparticle formation in zeolites

Unraveling the complex, competing pathways that can govern reactions in multicomponent systems is an experimental and technical challenge. We outline and apply a novel analytical toolkit that fully leverages the synchronicity of multimodal experiments to deconvolute causal from correlative relationships and resolve structural and chemical changes in complex materials. Here, simultaneous multimodal measurements combined diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and angular dispersive X-ray scattering suitable for pair distribution function (PDF), X-ray diffraction (XRD) and small angle X-ray scattering (SAXS) analyses. The multimodal experimental data was interpreted via multi-level analysis; conventional analyses of each data series were integrated through meta-analysis involving non-negative matrix factorization (NMF) as a dimensional reduction algorithm and correlation analysis. We apply this toolkit to build a cohesive mechanistic picture of the pathways governing silver nanoparticle formation in zeolite A (LTA), which is key to designing catalytic and separations-based applications. For this Ag-LTA system, the mechanisms of zeolite dehydration, framework flexing, ion reduction, and cluster and nanoparticle formation and transport through the zeolite are elucidated. We note that the advanced analytical approach outline here can be applied generally to multimodal experiments, to take full advantage of the efficiencies and self-consistencies in understanding complex materials and go beyond what can be achieved by conventional approaches to data analysis.

Multimodal in situ experimental data probing a complex reaction have been integrated via a multi-level analysis involving non-negative matrix factorization and correlation analysis. This strategy can be applied generally to multimodal experiments.     

Innovative technique for the direct determination of proteins in calcified aortic valves

Aortal valve mineralization very frequently causes a genesis of aortic stenosis, which is the most often surgically treated heart disease. Hydroxyapatite deposits have been identified as one of the causes leading to the loss of elasticity of the aortic valves. It is known that phosphates/calcium is accumulated in valve tissues during mineralization, but the mechanism of this process remains unclear. The work is focused mainly on the study of protein composition of mineralized aortic valves by nano-liquid chromatography electrospray ionization in a quadrupole orthogonal acceleration time-of-flight mass spectrometry. New methodological approach based on direct enzymatic digestion of proteins contained in hydroxyapatite deposits was developed for the study of pathological processes connected with osteogenesis. Our objectives were to simplify the traditional analytical protocols of sample preparation and to analyze the organic components of the explanted aortic valves for significant degenerative aortic stenosis. The study of aortic valve mineralization on the molecular level should contribute to understanding this process, which should consequently lead to effective prevention as well as to new ways of treatment of this grave disease.

$C^\infty$ regularity of the free boundary for a two-dimensional optimal compliance problem

We study the regularizing effect of perimeter penalties for a problem of optimal compliance in two dimensions. In particular, we consider minimizers of

Three-element zoom lens with fixed distance between focal points

This work deals with a theoretical analysis of zoom lenses with a fixed distance between focal points. Equations are derived for the primary (paraxial) design of the basic parameters of a three-element zoom lens. It is shown that the number of optical elements for such a lens must be larger than two.