Optical and other property changes of M-50 bearing steel surfaces for different lubricants and additive prior to scuffing

An ester lubricant base oil containing one or more standard additives to protect against wear, corrosion, and oxidation was used in an experimental ball/plate elastohydrodynamic contact under load and speed conditions such as to induce scuffing failure in short times. Both the ball and the plate were of identically treated M-50 steel. After various periods of operating time the wear track on the plate was examined with an interference microscope of plus or minus 30 A depth resolution and sometimes also with a scanning ellipsometer and an Auger spectrometer. The optically deduced surface profiles varied with wavelength, indicating the presence of surface coatings, which were confirmed by the other instruments. As scuffing was approached, a thin (approximately A) oxide layer and a carbide layer formed in the wear track in particular when tricresylphosphate antiwear additive was present in the lubricant. The rates of the formation of these layers and their reactivity toward dilute alcholic HCl depended strongly on the lubricant and additives. Based on these results suggestions for improved formulations and a test method for bearing reliability could be proposed

Von der Arithmetik zur Algebra

Arithmetik ist mehr als das Berechnen von Termwerten, Algebra ist mehr als das Umformen von Termen: Bereits in der Arithmetik kann das inhaltliche Verständnis für Algebra geweckt werden. Die Struktur einer Situation spiegelt sich in der Struktur von Termen wider, und Terme können als universales Werkzeug für die Darstellung strukturgleicher Situationen verwendet werden. Dazu werden Aufgabenformate vorgestellt, die das inhaltliche Verständnis für Terme und Termstrukturen anbahnen können

Funktionale Zusammenhänge auf den Punkt gebracht. Oder: Warum sich Funktionen nicht gerne „verschieben“ lassen

Beim Thema „Funktionen“ fokussiert der Mathematikunterricht häufig auf die Betrachtung von Graphen und deren Charakteristika unter Verwendung algebraischer Werkzeuge. Schülerformulierungen wie „Ich verschiebe die Funktion“ lassen erkennen, dass ein problematisches Verständnis von Funktionen im Sinne graphischer Objekte vorliegt. Der Beitrag stellt Überlegungen an, wie die Formalisierung der Abhängigkeit von Größen stärker ins Blickfeld gerückt werden kann und illustriert dies an Aufgabenformate

Characterization of lubricated bearing surfaces operated under high loads

The composition and surface profiles of M-50 steel surfaces were measured after operation at high loads in a bearing contact simulator. An ester lubricant (trimethyolpropane triheptanoate) was used with and without various additives. Optical profiles were obtained + or - to 30 depth resolution with a phase-locked interference microscope in 10 micron diameter areas within and outside the wear tracks. Optical constants and surface film thickness were measured in the same areas with an electronic scanning ellipsometer. Film composition was measured with a scanning Auger electron spectrometer. It is concluded that metal oxide formation is accelerated within the wear tracks

Aufgabenadäquates Rechnen bei Dezimalbrüchen oder Warum vermeintlich einfache Aufgaben so fehlerträchtig sind

In diesem Beitrag werden in Bezug auf das flexible Rechnen mit Dezimalbrüchen zwei Aspekte beschrieben: Einerseits typische Fehler von Schülerinnen und Schülern, die auf ein nicht aufgabenadäquates Arbeiten hindeuten, und andererseits Ansätze zur Entwicklung von Aufgaben, die das flexible Rechnen mit Dezimalbrüchen fördern können

The effects of online content structure on attention & memory: exploring optimal structure for news on corporate web sites

The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file.Title from title screen of research.pdf file viewed on (December 14, 2006)Includes bibliographical references.Vita.Thesis (M.A.) University of Missouri-Columbia 2005.Dissertations, Academic -- University of Missouri--Columbia -- Journalism.This study examined the effects of online content structure on attention and memory as indicators to overall communication effectiveness. For the purposes of this study, content structure was defined as either Bite-Snack-Meal (BSM), which involved presentation of information through several clickable hyperlinks, or traditional, inverted pyramid news writing without hyperlinks. The design was a mixed 2 (content structure) x 6 (article) repeated measures design. Heart rate was collected during a 10 second baseline period and during stimulus exposure. A multiple choice recognition test and a short answer cued recall test were utilized to measure memory. Attention and encoding were tested by submitting the data to a repeated measures ANOVA. Findings suggest that content structure does impact allocation of cognitive resources for controlled attention. BSM requires less effort and fewer cognitive resources allocated during exposure with no significant memory differences