408 research outputs found
Determination of particulate sizes in ceramic powders by electron microscopy
Ceramic powders of small particulate size can be characterized by electron microscopy. The usual methods of powder preparation were tested and compared. The data are analyzed in two ways
Physical properties of interplanetary grains
Morphological analyses of micrometeorite craters found on lunar rocks and laboratory simulation experiments are used to formulate a meteoritic interplanetary dust particle for optical scattering calculations that is roughly spherical and has a density of 2g cm/3. The model particle has chondritic elemental abundances and also contains a high content of finely dispersed carbon
Die Bildung in der Gesellschaft der Wiener Moderne
Zu Beginn des 20. Jahrhunderts fand in Österreich ein enormer Entwicklungs- und Veränderungsprozess statt. In der Politik befand sich die Habsburgermonarchie an der Schwelle zur Demokratie. Die Industrialisierung führte zu einer Veränderung der Arbeitswelten. Die starke Urbanisierung in Wien stellte an die Stadtplanung hohe Ansprüche. Kunst und Kultur motivierten revolutionären Veränderungen. Moderne Architektur, Musik, Literatur, Malerei sowie die Psychoanalyse waren Ausdruck zeitgenössischer Strömungen und nicht Abglanz der Vergangenheit. Das Junge Wien (Loos, Schönberg, Mahler, Schiele, Kokoschka, Hofmannsthal, Schnitzler und Freud) versuchte sich unabhängig von ihrem kulturellen und familiären Wurzeln neu zu definieren. Ihre bahnbrechenden Ideen waren nicht nur von künstlerischer Qualität, sondern vielmehr vom Interesse an den Menschen und seinem Dasein geprägt. Triebstrukturen, das Seelenleben sowie Denkmuster wurden analysiert und im Zuge dessen offen über Liebe, Leidenschaft, Sexualität und Tod diskutiert.
Setzt man sich mit der Bildung der Gesellschaft in der Wiener Moderne auseinander, so darf man die Leistungen der „Wiener Schule“ nicht außer Acht lassen. Es wäre jedoch unzureichend, Bildung auf die Intellektuellen jener Zeit zu projizieren. In meiner Diplomarbeit möchte ich interdisziplinär und gesellschaftskritisch Grundideen und Befindlichkeiten der Menschen während der Wiener Moderne darstellen. Der Schwerpunkt meiner Bildungsanalyse liegt auf der Gesellschaftsstruktur und ihren Netzwerken. Die Einbeziehung aller Schichten (Adel, Bürgertum, Arbeiter sowie Frauen) und möglichst vieler Bildungsinstitutionen (staatliche, kulturelle und disziplinäre) basiert jedoch nicht aus einem Vollständigkeitswahn heraus, sondern auf der Tatsache, dass diese interdependent agieren und somit erst zusammen ein vollständiges und erklärendes Bild der Bildungswirklichkeit der Wiener Moderne darstellen.At the beginning of the 20th Century Vienna went through enormous political, economical, social and cultural changes. The focus of my analyses lies on the different social classes - nobility, Boureoisie, Working class- and on academic, cultural and disciplinal institutions. They act interdependently and create the educational landscape of the Wiener Moderne
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Oxygen behaviour in the process of float glass manufacturing
By means of solid electrolyte probes the oxygen content was determined in inert gas atmosphere and in the tin melt. The probes can be used within a temperature range of 500 °C for tin melt and of 600 °C for inert gas atmosphere up to 1100 °C. Α higher emf value causes an oxygen decrease, a lower emf value leads to an oxygen increase in the system. From the measured emf values the oxygen partial pressures in the inert gas atmosphere and the oxygen contents in the tin melt can be calculated by means of the respective mathematical relations.
The investigations confirmed that the leveling of an oxygen-unsaturated tin melt is very time-consuming if forming gas of 10 vol.% H2 is used. However, at temperatures above 700 °C (900 °C may be best) the oxygen unsaturated tin melt is reached relatively quickly. At 500 and 600 °C the melt will stay in the oxygen-saturated state for days. Setting of an oxygen-unsaturated Sn melt is most efficient under pure hydrogen. If the Sn melt is covered by a glass melt, the oxygen content above the glass melt and in the tin melt is always higher than without the glass. Small amounts of oxygen are steadily transferred from the glass melt to the atmosphere and to the tin.
Furthermore, the effects of air, H2O vapour, CO and CO2 on the system were investigated in detail. Α rather complicated behaviour in inert gas atmosphere and in the melt was observed. It depends on doping, temperature and type of inert gas atmosphere. Carrying SO2 in the carrier gas stream (forming gas and H2, respectively) leads to changes of oxygen content both in the tin melt and in the gas phase. The equilibrium state in the Sn melt is reached more slowly than in the gas phase. The emf curve for the gas phase falls below that of the tin melt, i.e. the main part of SO2 is decomposed in the gas atmosphere and only then is available as oxygen for the Sn melt. The restoration of the starting state of oxygen in both phases takes much time (about 40 h). However, at the Sn surface and at the wall of the vessel there are depositions consisting of SnS2, SnS and SnO2.
As a further impurity in the floating chamber H2S is considered. The measurements show that there are no essential changes in oxygen behaviour in the system. The Sn melt, however, is strongly interspersed with SnS, such that it is no longer suitable for the float glass process. For the float glass process a tin melt unsaturated with oxygen is required. If saturation is achieved, SnO2 is formed, which is deposited as slag onto the tin surface, and thus is detrimental to the float glass process.
Oxygen dissolved in tin can be removed by the addition of an dement, the oxide of which is more stable than that of the oxide of tin. Na, Mg, C and Zr are used as deoxidation agents. Using Zr, which is dissolved in Sn, a nearly oxygen-free melt is obtained, too. The advantage of the use of this getter consists in the fact that no slag is formed on the Sn surface. The introduction of a getter into the production process of float glass manufacture could lead to an essential improvement of the process technology
Realisierung von optischen Talbot- und Talbot-Lau-Teppichen
In den letzten Jahren haben Talbot- und Talbot-Lau-Effekte, zwei Beugungseffekte im optischen Nahfeld, zunehmend an Bedeutung gewonnen und Anwendung in mehreren Bereichen der modernen Physik gefunden. So wurden diese Effekte mit Licht, Röntgenstrahlung, Plasmonen, Atomen und großen Molekülen nachgewiesen und Zusammenhänge zu anderen Phänomenen der Wellenpaketdynamik hergestellt.
Die spezielle Darstellungen der Effekte oft Talbot- oder Talbot-Lau-Teppiche genannt wurden mehrfach theoretisch diskutiert und experimentell mit Atomen und Elektronen demonstriert. Diese feinen fraktalen Strukturen wurden jedoch noch nie mit Licht aufgelöst und experimentell nachgewiesen. In dieser Arbeit werden mit Licht erstellte Talbot- und Talbot-Lau-Teppiche demonstriert.
Nach einer historischen Heranführung an den Talbot- und den Talbot-Lau-Effekt (Abschnitt I), wird die Beugung im Nah- und Fernfeld allgemein behandelt. Die folgenden Kapitel widmen sich der speziellen mathematischen Betrachtung und der physikalische Grundlage (Abschnitt II). Anschließend wird die Möglichkeit zur numerischen Berechnung der beiden Effekte gezeigt (Abschnitt III).
Im Folgenden wird ein optisches Nahfeldinterferometer beschrieben, das es ermöglicht Interferenzstreifen in Abhängigkeit von ihrem Abstand zum beugenden Gitter zu messen. Es wird gezeigt, wie durch Beleuchtung mit monochromatischem parallelem Licht eine feine Interferenzstruktur, der sogenannte Talbot-Teppich, entsteht. (Abschnitt IV)
Anschließend wird vorgeführt, wie sich durch Erweiterung des Experiments um ein weiteres Gitter und der Verwendung einer unkollimierten Lichtquelle ein sogenannter Talbot-Lau-Teppich erzeugen lässt. (Abschnitt IV)
In einem eigenen Abschnitt wird Erstellung und Anwendungsmöglichkeiten eines interaktiven Demonstrationsexperiments zum Talbot-Effekt vorgestellt. (Abschnitt V)
Auf die Bedeutung der beiden Effekte in der modernen Physik wird im abschließenden Abschnitt der Arbeit mit einigen Beispielen eingegangen. (Abschnitt VI)
Als Anhang findet sich ein englischsprachiger Artikel, der die Ergebnisse dieser Arbeit zusammenfasst und in Optics Express 2009 veröffentlicht wurde. (Abschnitt VIII)In recent years two diffraction effects in the optical near field, the Talbot effect and the Talbot-Lau effect, became increasingly important and have found application in the field of modern physics. The effects were verified with light, x-rays, plasmons, atoms as well as large molecules. Furthermore they were connected to other phenomena of wave packet dynamics as well.
Special visualizations of these effects are often referred as Talbot carpets or Talbot-Lau carpets. They are repeatedly discussed theoretically and experimentally shown with atoms and electrons. These detailed, fractal structures have never been resolved experimentally with light. This thesis demonstrates Talbot carpets as well as Talbot-Lau carpets generated with light.
After a historical approach to the Talbot effect and the Talbot-Lau effect (Section I), the diffraction in the near field and far field is treated in general. Thereby a special treatment of the mathematical analysis and the physical basics are given (Section II). Afterwards the implementation of numerical calculations of the effects are illustrated with examples (Section III).
The section is followed by the description of a visual near field interferometer that allows to capture interference fringes as a function of their distance from the diffracting grating. It is shown how a fine interference structure, called Talbot carpet, is formed by the illumination with monochromatic parallel light (Section IV).
Subsequently it is shown, by extending the experiment with another grating and using an uncollimated light source, how a so-called Talbot-Lau-carpet is obtained (Section IV).
In a separate section the preparation and applications of an interactive demonstration experiment on the Talbot effect is presented (Section V).
The importance of the two effects to modern physics is discussed in the final section of the thesis including some examples (Section VI).
The results of this thesis were published in Optics Express (2009). A copy of the article is given in the appendix (Section VIII)
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Electrochemical determination of the oxygen activity in tin melts by means of the solid electrolyte method
The measurements of oxygen activity in the tin melt were carried out under inert (light oxidizing) as well as under reducing (N2 with 2 vol.% H2 and 10 vol% H2, respectively) conditions. As solid electrolyte (SE) material Y2O3-, CaO- and MgO-stabilized zirconia was used in the form of a long tube closed at one end. Α short SE tube closed at one end within an alumina tube was applied as industrial probe. The galvanic cells worked with a Pt/air and Me/MeO reference electrode and with electrical leads of steel, tantalum as well as rhenium wires. Under inert conditions (argon with 30 vol.ppm O2) a saturation of the tin with oxygen is always obtained and SnO2 is formed. Under reducing conditions the saturation of the melt with oxygen does not take place and no SnO2 is formed. An equilibrium is adjusted between oxygen in the atmosphere and solute oxygen in the melt. At extremely low oxygen contents no equilibrium will be achieved. The lower operating temperatures of the probes were between 500 and 700 °C. The data taken from the literature were confirmed by EMF measurements (solubility of oxygen in liquid tin, molar free solution enthalpy of oxygen in tin, molar free standard enthalpy of formation of SnO2). This kind of investigations is new as to the behaviour of the tin melt under forming gas and the defined addition of elements and compounds to the tin melt (Na2SnO3, Na2O, Na, Fe2O3, Fe, MgO, Mg). Under reducing conditions and the addition of sodium or magnesium to the tin melt a quick decline of the oxygen activity can be recognized at the moment of addition. The melt becomes strongly deoxidized by the addition of these metals. The subsequent processes of deoxidation, which are different from metal to metal, have still to be investigated. No change of the oxygen activity in the melt was observed by addition of iron in the ppm range to the tin melt.
For the measurements alumina and a fireclay brick were used as crucible materials. The tin surface was either in immediate contact with the gas phase or was covered with a float glass melt. The oxygen activity of the tin melt was influenced by the crucible material and the float glass melt, too
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