Flow, combustion and emissions in a four-valve spark-ignition engine fuelled by compressed natural gas.

Imperial Users onl

Multiferroic hexagonal HoMnO3 films

The fundamental properties of hexagonal multiferric HoMnO3 films have been thoroughly investigated. The films are grown by pulsed laser deposition on Y:ZrO2(111) substrates. High quality epitaxial HoMnO3 films of 25 { 1000 nm thickness were successfully prepared. The film properties are compared to those of single-crystals. The magnetization measurements revealed that the films show a deviating magnetic behavior from the single-crystals in several ways. For instance, the films have a weakened antiferromagnetic Ho3+ order confirmed from magnetic susceptibility. The difierences are likely to be related to the modified (mostly larger) lattice parameters of films. An approximate phase diagram in comparison with the single-crystal's one is constructed. For multiferroicity investigations, Second Harmonic Generation (SHG; in collaboration with the group of M. Fiebig) has been employed. By SHG, the ferroelectric polar order of the films is obviously confirmed. The ferroelectric switching at room temperature could be clearly demonstrated, whereas leakage of films requires generally a more sophisticated approach.Die fundamentalen Eigenschaften von hexagonalen multiferroischen HoMnO3 Schichten werden eingehend untersucht. Die dünnen Schichten wurden mittels gepulster Laserdeposition auf Y:ZrO2(111)-Substraten gewachsen. Hochwertige epitaktische HoMnO3-Dünnschichten von 25 { 1000 nm Dicke wurden erfolgreich hergestellt. Die Dünnschichteigenschaften werden mit denen von Einkristallen verglichen. Die Magnitisierungsmessungen ergeben, dass die dünnen Schichten ein von den Einkristallen in verschiedener Weise abweichendes magnetischen Verhalten zeigen. Zum Beispiel haben die dünnen Schichten eine abgeschwächte antiferromagntetische Ho3+ Ordnung, die durch die magnetische Suszeptibilität bestätigt wird. Die Unterschiede sind wahrscheinlich auf die veränderten (meistens grösseren) Gitterparameter der dünnen Schichten zurückzuführen. Ein Phasendiagramm wird zum Vergleich mit Einkristallen konstruiert. Durch Second Harmonic Generation (SHG; in Zusammenarbeit mit der Gruppe von M. Fiebig) wird die ferroelektrische Ordnung der dünnen Schichten eindeutig bestätigt. Das ferroelektrische Umschalten bei Raumtemperatur kann eindeutig nachgewiesen werden, wobei durch den Leckstrom der dünnen Schichten allgemein eine detailliertere Vorgehensweise benötigt wird

A Novel Approach to Ontology Management

The term ontology is defined as the explicit specification of a conceptualization. While much of the prior research has focused on technical aspects of ontology management, little attention has been paid to the investigation of issues that limit the widespread use of ontologies and the evaluation of the effectiveness of ontologies in improving task performance. This dissertation addresses this void through the development of approaches to ontology creation, refinement, and evaluation. This study follows a multi-paper model focusing on ontology creation, refinement, and its evaluation. The first study develops and evaluates a method for ontology creation using knowledge available on the Web. The second study develops a methodology for ontology refinement through pruning and empirically evaluates the effectiveness of this method. The third study investigates the impact of an ontology in use case modeling, which is a complex, knowledge intensive organizational task in the context of IS development. The three studies follow the design science research approach, and each builds and evaluates IT artifacts. These studies contribute to knowledge by developing solutions to three important issues in the effective development and use of ontologies

Investigations of the RNi2Ge2 intermetallic compounds by X-ray resonant magnetic scattering

The x-ray magnetic scattering (XRMS) intensities of the Gd, Tb, Dy, Ho, Er, and Tm L2,3 edges were investigated using two isostructural samples [Gd1/4Tb1/4Dy1/4Ho 1/4]Ni2Ge2 and [Gd1/3Er1/3Tm 1/3]Ni2Ge2 in order to elucidate systematics in the underlying resonance process. Taken together with theoretical linearized augmented planewave (LAPW) calculations employing LDA + U, we found that the XRMS intensity at the heavy rare-earth L edges is strongly related to the 4f-5d exchange interaction and that the branching ratio arises from the effects of spin orbit coupling in the 5d band. For Gd, the 4f-5 d exchange interaction is large and dominant over not only the spin orbit coupling but also other interactions. Therefore, the XRMS intensity of Gd L3 and L2 edges most closely reflects the state of 4f moments.;In the pure GdNi2Ge2 compound, large antiferromagnetic (AFM) domains were found, comparable to the x-ray beam size. Single domain scattering was measured carefully with a very small beam size for various azimuth angles and temperatures. From this measurement, a second transition at 16 K in bulk measurements was identified as a transformation from a collinear squared-up structure at high temperature, to a tilted helical structure below 16 K. Since the XRMS scattering cross-section is strongly dependent on the magnetic moment direction, the AFM domain structure was imaged by the XRMS intensity.;From single domain scattering data, the ratio of the spin moments in the collinear and the spiral structure of GdNi2Ge2 at the second magnetic transition temperature were derived and used to estimate the magnetic anisotropy energy of Gd. Surprisingly, the estimated magnetic anisotropy energy of Gd in this compound is much higher than that of pure Gd metal (about a order of magnitude). This is expected to be the effect of the anisotropy in 5d conduction band. More theoretical study is necessary to understand this observation