<p>In this thesis the magnetic and structural properties of ultra-thin 3d transition metals films have been investigated, in particular Fe, Ni and Co films. X-ray Magnetic Circular Dichroism (XMCD) has provided element specific spin (m_s ) and orbital (m_l ) moments per atom by utilizing the magneto optic sum-rules. Element specific hysteresis curves have been measured by means of X-ray Resonant Magnetic Scattering (XRMS), and the local crystallographic structure has been investigated using Extended X-ray Absorption Fine Structure (EXAFS). </p><p>By performing XMCD on Fe/Ag(100) we observe a spin reorientation from in-plane to out-of-plane as the Fe thickness is lowered. At temperatures below 300K it occurs around 5-7 mono layers (ML) of Fe. While reorienting the magnetization out-of-plane the orbital moment increases with 125% but only a minor increase (5%) of the spin moment is observed. Extended X-ray Absorption Fine Structure (EXAFS) measurements indicate that films 6 ML and thicker have a bulk-like bcc structure. For the thin out-of-plane films, the local crystallographic structure is more complicated. </p><p>The spin reorientation of the Au/Co/Au tri-layer system has been studied as a function of temperature, Co layer and Au cap thickness. An unexpected behavior of the orbital moment upon spin reorientation is found in these systems. An ex-situ prepared sample shows a smooth spin reorientation from an in-plane to an out-of-plane easy magnetization direction as the temperature is lowered from 300K to 200K. In-situ prepared samples have also been investigated and a novel phase diagram has been identified. The Au/Co interface has been explored during the Au capping by means of photoemission measurements. </p><p>In the bi- and tri-layer system of Fe and Ni we have been able to manipulate the spin reorientation by varying the Fe and Ni thickness. A novel non-collinear interlayer exchange interaction for 3d ferro magnets in direct contact has been discovered for a set of samples. This exchange interaction is found to be strongly dependant on the preparation conditions.</p>

Microbial electrochemical systems (MESs) have attracted much research attention in recent years due to their promising applications in renewable energy generation, bioremediation, and wastewater treatment. In a MES, microorganisms interact with electrodes via electrons, catalyzing oxidation and reduction reactions at the anode and the cathode. The bacterial community of a high power mixed consortium MESs (maximum power density is 6.5W/m��) was analyzed by using denature gradient gel electrophoresis (DGGE) and 16S DNA clone library methods. The bacterial DGGE profiles were relatively complex (more than 10 bands) but only three brightly dominant bands in DGGE results. These results indicated there are three dominant bacterial species in mixed consortium MFCs. The 16S DNA clone library method results revealed that the predominant bacterial species in mixed culture is Geobacter sp (66%), Arcobacter sp and Citrobacter sp. These three bacterial species reached to 88% of total bacterial species. This result is consistent with the DGGE result which showed that three bright bands represented three dominant bacterial species. Exoelectrogenic bacterial strain SX-1 was isolated from a mediator-less microbial fuel cell by conventional plating techniques with ferric citrate as electron acceptor under anaerobic conditions. Phylogenetic analysis of the 16S rDNA sequence revealed that it was related to the members of Citrobacter genus with Citrobacter sp. sdy-48 being the most closely related species. The bacterial strain SX-1 produced electricity from citrate, acetate, glucose, sucrose, glycerol, and lactose in MFCs with the highest current density of 205 mA/m�� generated from citrate. Cyclic voltammetry analysis indicated that membrane associated proteins may play an important role in facilitating electron transfer from the bacteria to the electrode. This is the first study that demonstrates that Citrobacter species can transfer electrons to extracellular electron acceptors. Citrobacter strain SX-1 is capable of generating electricity from a wide range of substrates in MFCs. This finding increases the known diversity of power generating exoelectrogens and provids a new strain to explore the mechanisms of extracellular electron transfer from bacteria to electrode. The wide range of substrate utilization by SX-1 increases the application potential of MFCs in renewable energy generation and waste treatment. Anode properties are critical for the performance of microbial electrolysis cells (MECs). Inexpensive Fe nanoparticle modified graphite disks were used as anodes to preliminarily investigate the effects of nanoparticles on the performance of Shewanella oneidensis MR-1 in MECs. Results demonstrated that average current densities produced with Fe nanoparticle decorated anodes were up to 5.9-fold higher than plain graphite anodes. Whole genome microarray analysis of the gene expression showed that genes encoding biofilm formation were significantly up-regulated as a response to nanoparticle decorated anodes. Increased expression of genes related to nanowires, flavins and c-type cytochromes indicate that enhanced mechanisms of electron transfer to the anode may also have contributed to the observed increases in current density. The majority of the remaining differentially expressed genes were associated with electron transport and anaerobic metabolism demonstrating a systemic response to increased power loads. The carbon nanotube (CNT) is another form of nano materials. Carbon nanotube (CNT) modified graphite disks were used as anodes to investigate the effects of nanostructures on the performance S. oneidensis MR-1 in microbial electrolysis cells (MECs). The current densities produced with CNT decorated anodes were up to 5.6-fold higher than plain graphite anodes. Global transcriptome analysis showed that cytochrome c genes associated with extracellular electron transfer are up-expressed by CNT decorated anodes, which is the leading factor to contribute current increase in CNT decorated anode MECs. The up regulated genes encoded to flavin also contribute to current enhancement in CNT decorated anode MECs. / Graduation date: 2013

We carried out systematic neutron scattering experiments to investigate the magnetic properties and their relationship to the high-$T_c$ superconductivity, when the materials are tuned from their antiferromagnetic (AF) parent compounds to the superconducting regime. We observed resonance mode in the electron doped cuprate Nd$_{1.85}$Ce$_{0.15}$CuO$_4$, demonstrating that the resonance is a general phenomenon in cuprate superconductors regardless of hole- or electron-doping. In Pr$_{0.88}$LaCe$_{0.12}$CuO$_4$, the local susceptibility displays two distinct energy scales that are broadly consistent with the bosonic modes revealed by scanning tunneling microscopy experiments. These results indicate the presence of very strong electron spin excitations couplings in electron doped cuprates. Shortly after the discovery of high-$T_c$ superconductivity in the Fe pnictides, we discovered that the magnetic phase diagram of CeFeAsO$_{1-x}$F$_x$ is remarkably similar to that of the cuprates. Besides CeFeAsO, similar magnetic and lattice structures are also observed in PrFeAsO and SrFe$_2$As$_2$ systems. Neutron scattering measurements show that in SrFe$_2$As$_2$, the spectrum of magnetic excitations consists of a Bragg peak at the elastic position, a spin gap, and sharp spin-wave excitations at higher energies. Based on the observed dispersion relation, we estimated the effective magnetic exchange coupling using a Heisenberg model. In order to study the nature of the exchange interactions in the parent compound of Fe pnictides, we studied the high energy spin-wave excitations in CaFe$_2$As$_2$. Although the spin waves in the entire Brillouin zone can be described by an effective three-dimensional anisotropic Heisenberg Hamiltonian, the magnetism in this system is neither purely local nor purely itinerant; rather it is a complicated mix of the two. When the Fe pnictide is tuned into superconducting regime with doping, the low energy spin fluctuation is dominated by a resonance mode. In the optimally electron doped BaFe$_{1.9}$Ni$_{0.1}$As$_2$, application of a magnetic field that suppresses the superconductivity and superconducting gap energy also reduces the intensity and energy of the resonance. These results suggest that the energy of the resonance is proportional to the electron pairing energy, and thus indicate that spin fluctuations are intimately related to the mechanism of high $T_c$ superconductivity.

De nos jours, la production agricole est soumise à certaines restrictions avec l'objectif de contrôler limpact environnemental et les volumes de production. Ces restrictions ont entrainé des modifications du niveau d'intensification de la production. En ce qui concerne lélevage des ruminants, le niveau d'intensification est défini par le chargement (animaux/ha) et la fertilisation minérale (kg/ha). La réforme de la Politique Agricole Commune (PAC) en 1992 a instauré des « méthodes de production agricole compatibles avec les exigences de la protection de l'environnement ainsi que l'entretien de l'espace naturel » (Règlement (CEE) N° 2078/92 du Conseil du 30 juin 1992, J.O.C.E. N°L 215 du 30/7/92 ; MRW, 1997). La réduction du niveau d'intensification de la production se trouvait parmi ces mesures. En élevage viandeux, elle était encouragée par l'octroi de primes aux éleveurs ne dépassant pas un seuil de chargement de 2 UGB/ha. Ces primes permettaient de compenser la perte de production due à la réduction du niveau dintensification. De plus, des primes à l'extensification pouvaient être obtenues pour les chargements inférieurs à 1,4 UGB/ha. Ces mesures, conjointement au système des quotas, ont permis de maîtriser aussi le volume de la production à grande échelle. Actuellement, suite au principe du découplage décidé lors de la réforme à mi parcours de lAgenda 2000 en juin 2003 et qui correspond aux dernières réformes de la PAC, loctroi de primes nest plus lié au volume des productions, mais bien à la surface. Chaque exploitant doit disposer de « droits » quil doit activer en justifiant les superficies correspondantes. Ces droits sont calculés sur base des superficies et des animaux qui ont donné lieu à un paiement daides directes au cours des années de références 2000, 2001 et 2002. Une fois les droits justifiés et un ensemble de conditions appelées « conditionnalité », liées à lenvironnement (Directive Nitrate), à la sécurité alimentaire et au bien-être des animaux, respectés, lexploitant pourra obtenir le «paiement unique». Les Etats Membres peuvent choisir de découpler certaines productions comme cest le cas pour les vaches allaitantes en Belgique. De plus, les règlements liés à la « Directive Nitrate » ont permis de mieux prendre en compte les effluents délevage et ont provoqué une diminution de la fertilisation azotée susceptible de diminuer la production, lazote étant le premier minéral limitant pour la croissance végétale. Cependant, dans les prairies pâturées, on constate souvent un bilan azoté positif. Lazote en excès est susceptible de sortir du système en étant lessivé sous forme de nitrate avec un risque de pollution environementale. La réduction de l'intensification de la production obtenue soit par une réduction de la fertilisation azotée soit par la réduction du chargement ou les deux facteurs conjugués, peut provoquer une diminution des déjections déposées sur les parcelles et une réduction du bilan azoté. On peut ainsi obtenir une réduction de la pollution des eaux (notamment par les nitrates) ainsi que les émissions des composants azotés volatils (ammoniac et oxyde nitreux). Les résultats dune série d'essais menés pendant six années consécutives sur des prairies pâturées par les principaux types de spéculation bovine, la vache allaitante, la vache laitière et le taurillon, sont présentés et discutés dans cette thèse. Le fil conducteur des essais a été un protocole semblable dans ces trois spéculations. Ce protocole visait à comparer d'une part, la réduction de 33% de la fertilisation azotée sans réduction du chargement et d'autre part, le rapport entre ces deux systèmes et un système sans apport d'azote minéral. Les paramètres étudiés ont été les performances zootechniques, phytotechniques, le bilan azoté et, pour les spéculations des vaches laitières et des taurillons, les reliquats azotés dans le sol. En plus, dans la spéculation "taurillon", les trois lots soumis au pâturage ont été comparés à un lot engraissé en stabulation.

In the present thesis, the properties at ferromagnet/semiconductor interfaces, relevant for semiconductor spintronics applications, are addressed. Semiconductor spintronics refers to the possibility of storing information using the electron spin, additional to the electron charge, for enhanced flexibility in nanoscale semiconductor devices. The system under focus is the Fe/ZnSe(001) heterostructure, where ZnSe is a wide gap semiconductor ideally compatible with GaAs. The heterostructures are grown on GaAs(001) substrates by molecular beam epitaxy. From various electron-beam based diffraction, spectroscopy and microscopy techniques, it is shown that Fe grows epitaxially and predominantly in a layer-by-layer mode on ZnSe(001) with no presence of chemically reacted phases or interdiffusion. An in-plane uniaxial magnetic anisotropy (UMA) is detected for thin Fe films on ZnSe(001) by magnetometry, thus opposing the cubic symmetry of bcc Fe. From first principles calculations, the unidirectional sp3-bonds from ZnSe are shown to induce this uniaxiality. Moreover, an in-plane anisotropic lattice relaxation of Fe is found experimentally, seemingly as a consequence of the sp3-bonds, giving an additional UMA contribution via magneto-elastic coupling. It is proposed that these two effects are responsible for the much-debated UMA observed in Fe/semiconductor structures in general. The interface magnetism is probed by x-ray magnetic circular dichroism and Mössbauer spectroscopy. It is found that the magnetic moment at the interface is comparable or even enhanced with respect to the bulk Fe. These two experiments are believed to provide the first unambiguous proof of a persistent bulk magnetic moment at a transition metal/semiconductor interface. Spin-polarised transport measurements are performed on Fe/ZnSe/FeCo magnetic tunnel junctions. A magnetoresistance of 16% is found at low temperature, which evidences both the existence of interface spin polarisation, as inferred from the bulk magnetic moment above, and that the spin polarisation can be transmitted across the semiconductor barrier layer.

Ni-Co-Mn-In system is a new type of magnetic shape memory alloys (MSMAs) where the first order structural and magnetic phase transitions overlap. These materials can generate large reversible shape changes due to magnetic-field-induced martensitic transformation, and exhibit magneto-caloric effect and magnetoresistance. Ni-Co-Mn-Sn alloys are inexpensive alternatives of the Ni-Co-Mn-In alloys. In both materials, austenite has higher magnetization levels than martensite. Fe-Mn-Ga is another MSMA system, however, whose magnetization trend is opposite to those of the Ni-Co-Mn-X (In-Sn) systems upon phase transformation. The MSMAs have attracted great interest in recent years, and their magnetic and thermo-mechanical properties need to be further investigated. In the present study, the effects of indium concentration, cooling, and annealing on martensitic transformation and magnetic response of single crystalline Ni-Co-Mn-In alloys were investigated. Increasing indium content reduced the martensitic transformation start (Ms) temperature, while increasing temperature hysteresis and saturation magnetization. Increasing annealing temperature led to an increase in the Ms temperature whereas annealing at 400 degrees C and 500 degrees C led to the kinetic arrest of austenite. Cooling after solution heat treatment also notably affected the transformation temperatures and magnetization response. While the transformation temperatures increased in the oil quenched samples compared to those in the water quenched samples, these temperatures decreased in furnace cooled samples due to the kinetic arrest. The possible reasons for the kinetic arrest are: atomic order changes, or precipitate formation. Shape memory and superelastic response, and magnetic field-induced shape recovery behavior of sintered Ni43Co7Mn39Sn11 polycrystalline alloys were also examined. The microstructural analysis showed the existence of small pores, which seem to increase the damage tolerance of the sintered polycrystalline samples. The recoverable transformation strain, irrecoverable strain and transformation temperature hysteresis increased with stress upon cooling under stress. Moreover, magnetic-field-induced strain due to the field-induced phase transformation was confirmed to be 0.6% at 319K. Almost perfect superelastic response was obtained at 343K. A magnetic entropy change of 22 J kg-1 K-1 were determined at 219K from magneto-caloric effect measurements which were conducted on annealed Ni43Co7Mn39Sn11 ribbons. Magnetic characteristics and martensitic transformation behavior of polycrystalline Fe-Mn-Ga alloys were also examined. Cast alloys at various compositions were undergone homogenization heat treatments. It was verified by magnetization measurements that the alloys heat treated at 1050 degrees C shows martensitic transformation. The heat treatment time was determined to be 1 day or 1 week depending on the compositions.

Rapid solidification experiment on Fe-Cr-Mo-Mn-Si-C alloy was performed to investigate metastable phases formed during the solidification. A wide range of cooling rate was used to analyse the sample from melt spinning technique (~107 K/s) to water quenching method (~102 K/s). A single phase featureless structure was obtaind initially in the melt spinning experiment for 77Fe-8Cr-6Mn-5Si-4C alloy. Reduction of C and addition of Mo led to form a complete featureless structure for 2.85 mm rod for 72.8Fe-8Cr-5Mo-6Mn-5Si-3.2C. Subsequent investigation of influence of Mo, Cr and Mn on the single phase featureless structure concludes that 7.5 mm thick complete featureless phase could be formed at 63.8Fe-15Cr-7Mo-6Mn-5Si-3.2C alloy composition. In a separate attempt, powder samples of 40 μm dia. size complete featureless powders were produced for three slightly different compostions for the same alloy system. Characterisation of the featureless phases reveals that it could be a single phase metastable structure of ε phase or austenitic solid solution with high amount of alloying element dissolved in it. Subsequent heat treatment of this featureless phase of the rod and the powder at different temperatures formed bainitic ferrite with fine carbides dispersed in the austenitic matrix. Hardness values measured on featureless phase found to have influenced by the alloying element specially Mo, Cr and Mn. In an attempet to improve clean melting condition to extend the featureless phase and to form amorphous, an elliptic short arc lamp vaccum furnace was designed with 10 kW lamp power. Around 30 g of iron based alloy system was melted and cast as a 7 mm rod sample in a copper mould. Design details of new mirror and the lamp furnace are presented. In a separate study, influence of the melt temperature on Al-Y and Al-Si alloys were investigated by levitaion casting in a silver mould at around 2000 K/s cooling rate. Plate like structure of Al8Y3 primary phase was observed at low melt temperature with small percentage of peritectic transformation of Al8Y3 and liquid melt into Al9Y2. A pre-dentritic star like crystal of Al3Y was observed in a fine eutectic matrix at very high melt temperature. Amount and number of primary Si crystals formed in a unit area during the solidification increases as the melt temperature increases. / QC 20100805

Efficiency and innovative problem solving are contradictory requirements for productdevelopment (PD), and both requirements must be satisfied in companies that strive to remainor to become competitive. Efficiency is strongly related to ”doing things right”, whereasinnovative problem solving and creativity is focused on ”doing the right things”.Engineering design, which is a sub-process within PD, can be viewed as problem solving or adecision-making process. New technologies in computer science and new software tools openthe way to new approaches for the solution of mechanical problems. Product datamanagement (PDM) technology and tools can enable concurrent engineering (CE) bymanaging the formal product data, the relations between the individual data objects, and theirrelation to the PD process. Many engineering activities deal with the relation betweenbehavior and shape. Modern CAD systems are highly productive tools for conceptembodiment and detailing. The finite element (FE) method is a general tool used to study thephysical behavior of objects with arbitrary shapes. Since a modern CAD technology enablesdesign modification and change, it can support the innovative dimension of engineering aswell as the verification of physical properties and behavior. Concepts and detailed solutionshave traditionally been evaluated and verified with physical testing. Numerical modeling andsimulation is in many cases a far more time efficient method than testing to verify theproperties of an artifact. Numerical modeling can also support the innovative dimension ofproblem solving by enabling parameter studies and observations of real and syntheticbehavior. Simulation-driven design is defined as a design process where decisions related tothe behavior and performance of the artifact are significantly supported by computer-basedproduct modeling and simulation.A framework for product modeling, that is based on a modern CAD system with fullyintegrated FE modeling and simulation functionality provides the engineer with tools capableof supporting a number of engineering steps in all life-cycle phases of a product. Such aconceptual framework, that is based on a moderately coupled approach to integratecommercial PDM, CAD, and FE software, is presented. An object model and a supportingmodular modeling methodology are also presented. Two industrial cases are used to illustratethe possibilities and some of the opportunities given by simulation-driven design with thepresented methodology and framework. / QC 20100810

The purpose of this thesis has been to investigate the elastic properties of an fcc FeMg alloy with 10 at.% magnesium under high pressure. Recent research has shown that magnesium can be a possible candidate for light element impurities in the Earth’s inner core, something that was previously not considered possible because of the low miscibility of magnesium in iron at ambient pressure. Gaining knowledge about the composition of the Earth’s core can help us better understand such phenomena as seismic activity and the fluctuations of the Earth’s magnetic field. The elastic constants of the FeMg alloy was calculated using ab-initio methods based on Density Functional Theory. The Exact Muffin-Tin Orbitals method was used in conjunction with the Coherent Potential Approximation. The FeMg alloy was found to be overall considerably softer than pure iron, and the softening effect on the elastic constants was also found to increase with pressure. The results also showed that 10% Mg alloying increased the anisotropy with about 40% compared to pure iron.

The diesel engine is growing in popularity due to its energy efficiency and solving the emissions issues associated with diesel engine exhaust would clear the way for further growth. The key pollutants are NOx, particulate matter and unburned hydrocarbons. Selective catalytic reduction (SCR) catalysis is likely the best choice for NOx control. In SCR, NH3 selectively reacts with NOx to form N2 – the selectivity refers to NH3 reacting with NOx instead of the abundant O2. Urea is used as the NH3 source, being injected into the exhaust as an aqueous solution where the urea decomposes and NH3 is generated. Spatial resolution characterization techniques have been gaining attention in the catalysis field because of the higher level of information provided. In this thesis, a new spatial resolution technique, called SpaciFTIR (spatially-resolved, capillary-inlet Fourier transform infra-red spectroscopy), was developed, which overcomes the interference of water in the detection of NH3 in an earlier developed technique, SpaciMS (spatially-resolved, capillary-inlet mass spectrometry). With the new test method, three SCR topics were addressed. First, the three key SCR reactions were spatially resolved. These are the standard SCR reaction (2NO + 2NH3 + 1/2O2 = 2N2 + 3H2O), the fast SCR reaction (NO + NO2 + 2NH3 = 2N2 + 3H2O), and NO2-SCR, (6NO2 + 8NH3 = 7N2 + 12H2O). Results show that in the presence of NO2, but at a NO2/NOx ratio < 0.5, the fast SCR reaction proceeds followed by the standard SCR reaction, i.e. in series. If the NO2/NOx ratio exceeds 0.5, the NO2-SCR and fast SCR reactions occur in parallel. Compared to the standard integral test method, this spatial resolution technique clearly showed such trends. Secondly, the spatial resolution technique was used to characterize the effects of thermal aging on catalyst performance. It was found that for a highly aged catalyst, there was a radial activity profile due to an inhomogeneous temperature distribution in the process of aging. Aging effects on various key SCR reactions, i.e. NO oxidation, NH3 oxidation, and the reduction reactions, were studied. Last but not least, for the purpose of passive SCR system development, transient NH3 storage profiles along the monolith channel were measured with SpaciFTIR. Passive SCR is a system where the NH3 is generated on an upstream catalyst, such as a three-way catalyst or lean-NOx trap, instead of via urea injection. In such a system, NH3 is therefore not constantly being fed to the SCR catalyst, but “arrives” in pulses. Factors such temperature, NH3 concentration, pulsing time, flow rate and thermal aging were investigated. For the first time, NH3 migration was observed and its effect on SCR reactions along the length of catalyst was studied.