Central banks use a series of relatively small interest rate changes in adjusting their monetary policy stance. This persistence in interest rate changes is well documented by empirical monetary policy reaction functions that feature a large estimated coefficient for the lagged interest rate. The two hypotheses that explain the size of this large estimated coefficient are monetary policy inertia and serially correlated macro shocks. In the first part of my dissertation, I show that the effect of inertia on the Federal Reserve’s monthly funds rate adjustment is only moderate, and smaller than suggested by previous studies. In the second part, I present evidence that the temporal aggregation of interest rates puts an upward bias on the size of the estimated coefficient for the lagged interest rate. The third part of my dissertation is inspired by recent developments in the housing market and the resulting effect on the overall economy. In this third essay, we show that high loan-to-value mortgage borrowing reduces the effectiveness of monetary policy.

Diss. Stockholm : Handelshögskolan, 2007

Microorganisms have played a critical role in geological processes and in the formation of soils throughout geological time. It is hypothesized that biological activity can also affect soil properties in short engineering time-scales. Bioactivity in sediments is determined by the classical limiting factors (i.e., nutrients, water, C for biomass, temperature and pH) as well as by pore-size geometrical limits and mechanical interactions between bacterial cells and soil particles. These constraints restrict the range of grain size and burial depth where biomediated geochemical processes can be expected in sediments, affect the interpretation of geological processes and the development of engineering solutions such as bioremediation. When biological, geometrical and mechanical limiting factors are satisfied, bioactivity can be designed to alter the mechanical properties of a soil mass, including lowering the bulk stiffness of the pore fluid through controlled gas bio-generation, increasing the shear stiffness of the soil skeleton by biomineralization, and reducing hydraulic conduction through biofilm formation and clogging. Each of these processes can be analyzed to capture the bio-chemo-hydro-mechanical coupling effects, in order to identify the governing equations that can be used for process design. Design must recognize the implications of spatial variability, reversibility and environmental impacts.

In this thesis we empirically examine whether the Turkish stock market is driven by rational bubbles over the period between March 1990 and February 2012. The bubble periods are estimated using a recently developed right-tailed unit root test, the generalized sup augmented Dickey-Fuller test of Phillips, Shi and Yu (2011a). Applying their bubble detection and location strategies to weekly price dividend ratio series, we find strong evidence for the existence of rational bubbles in the Turkish stock market benchmark indices as well as sector indices. Our located bubble periods may give early warning signals of the subsequent Turkish financial crisis.

Experimente mit neuartigen Messverfahren lieferten Daten über die Struktur von transienten Flüssig-keits-Gas-Strömungen für die Entwicklung und Validierung von mikroskopischen, d.h. geometrieunabhängigen Konstitutivbeziehungen zur Beschreibung des Impulsaustauschs zwischen Flüssig-phase und Gasblasen sowie zur Quantifizierung der Häufigkeit von Blasenkoaleszenz und -zerfall. Hierzu wurde eine vertikale Testsektion der Zweiphasentestschleife MTLoop in Rossendorf genutzt, wobei erstmals Gittersensoren mit einer Auflösung von 2-3 mm bei einer Messfrequenz von bis zu 10 kHz angewandt wurden. Dabei wurde die Evolution von Gasgehalts-, Geschwindigkeits- und Bla-sengrößenverteilungen entlang des Strömungsweges und bei schnellen Übergangsprozessen aufge-nommen und so die für die Modellbildung erforderlichen Daten bereitgestellt. Für den Test der Mo-dellbeziehungen wurde ein vereinfachtes Verfahren zur Lösung der Strömungsgleichungen entlang des Strömungswegs erstellt. Es basiert auf der Betrachtung einer größeren Anzahl von Blasengrö-ßenklassen. Die erhaltenen numerische Lösungen haben erstmals gezeigt, dass der bei Erhöhung der Gasvolumenstromdichte stattfindende Übergang von einer Blasenströmung mit Randmaximum zu einem Profil mit Zentrumsmaximum und anschließend zu einer Pfropfenströmung ausgehend von einem einheitlichen Satz physikalisch begründeter und geometrieunabhängiger Konstitutivgleichun-gen modelliert werden kann. Die Modellbeziehungen haben sich in einem abgegrenzten Gebiet der Volumenstromdichten als generalisierungsfähig erwiesen und sind für den Einbau in CFD-Modelle geeignet. Weiterhin wurden Arbeiten zur Kondensation durchgeführt, die direkten Bezug zu den Kon-densationsmodellen haben, die in Thermohydraulik-Codes enthalten sind. Die Untersuchung liefert darüber hinaus experimentelle Daten für die Modellvalidierung hinsichtlich des Verhaltens und des Einflusses nichtkondensierbarer Gase. Hierfür wurden spezielle Sonden für die Bestimmung der Konzentration und für die Lokalisierung von Pfropfen nichtkondensierbarer Gase entwickelt und bei transienten Kondensationsversuchen in einem leicht geneigten Wärmeübertragerrohr eingesetzt.

The magnetization processes of antiferromagnetically (AF) coupled Co/Pt multilayers on extended substrates and of Co/Pd multilayers deposited on arrays of 58 nm spheres are investigated via magnetic force microscopy at room temperature by imaging the domain configuration in magnetic fields. Adding AF exchange to such perpendicular anisotropy systems changes the typical energy balance that controls magnetic band domain formation, thus resulting in two competing reversal modes for the system. In the ferromagnetic (FM) dominated regime the magnetization forms FM band domains, vertically correlated. By applying a magnetic field, a transition from band to bubble domains is observed. In the AF-exchange dominated regime, by applying a field or varying the temperature it is possible to alter the magnetic correlation from horizontal (AF state) to vertical (FM state) via the formation of specific multidomain states, called metamagnetic domains. A theoretical model, developed for complex multilayers is applied to the experimentally studied multilayer architecture, showing a good agreement. Magnetic nanoparticles have attracted considerable interest in recent years due to possible applications in high density data storage technology. Requirements are a well defined and localized magnetic switching behavior and a large thermal stability in zero fields. The thermal stability of [Co/Pt]N multilayers with different numbers of repeats (N), deposited on nanospheres is studied by magnetic viscosity measurements. The magnetic activation volume, representing the effect of thermal activation on the switching process, is estimated. It is found that the activation volume is much smaller than the volume of the nanosphere and almost independent of the number of bilayers supporting an inhomogeneous magnetization reversal process.

An equilibrium multielectron bubble (MEB) in liquid helium is a fascinating object with a spherical two-dimensional electron gas on its surface. After it was first observed a few decades ago, a plethora of physical properties of MEBs, for example, a tunable surface electron density, have been predicted. In this thesis, we will discuss two new methods to create MEBs in liquid helium. Before the discussion, the way to generate a large number of electrons in a low temperature system will be discussed, including thermionic emission and field emission in helium. In the first new method to make MEBs, we used a dome-shaped cell filled with superfluid helium in which an MEB was created and confined at the dome. The lifetime of the MEB was substantially longer than the previously reported observations of MEBs. In the second method, MEBs were extracted from the vapor sheath around an electrically heated tungsten filament submerged in liquid helium, either by a high electric field (up to 15 kV/cm) or by a sudden increase of a negative pressure in liquid helium. High-speed photography was used to capture the MEB's motion. A method to determine the number of electrons was developed by monitoring the oscillations of the MEBs. Finally, an electromagnetic trap was designed to localize the MEBs created using the second method, which was important for future studies of the properties of MEBs. / Physics

Le liner métallique à confiner le matériau combustible des plaques GenIV doit, pour tenir son rôle, supporter « l'agression » des flux de neutrons rapides et d’impuretés implantées (produits de fission, hélium). Le travail de thèse présenté a contribué à la compréhension des mécanismes de fragilisation dans les métaux sous irradiation : il propose un modèle pour la nucléation et la croissance de bulles de gaz tels que l’hélium. L’approche utilisée couple une démarche de modélisation à une démarche expérimentale. Des mesures de relâchement obtenues par les techniques de spectrométrie de masse (TDS) et d’analyse par la réaction nucléaire (NRA) ainsi que des caractérisations par microscopie électronique en transmission (MET) ont été réalisées. Le développement d’un modèle simplifié de dynamique d’amas a permis d’interpréter le couplage entre la dynamique de relâchement de l’hélium et celle des bulles. Ce modèle a permis d’une part, de simuler les expériences d’implantation/récuit à partir d’un jeu de grandeurs physiques cohérentes avec celle de la littérature, et d’autre part, de mettre en évidence un couplage fort entre les concentrations des espèces libres (atomes d’hélium et lacunes) et la composition moyenne des bulles. Les dynamiques singulières de relâchement du gaz observées expérimentalement ont pu être expliquées par le mûrissement d’une population de bulles, initialement « surpressurisées », qui poursuivent leur croissance en réduisant leur concentration totale et leur pression / The metal liner dedicated to continue the fuel assembly of the Gas Fast Reactor, is intended to resist to a fast neutron flux and the implantation of impurities such as helium and the fission products. This PhD work contributes to the understanding of one of the mechanisms inducing the metal embrittlement under irradiation; it deals with a model that predicts the nucleation and growth of gas bubbles, such as helium, into a metal. The approach of the thesis relies on both theoretical and experimental works. The gas release measurements have been performed with the Nuclear Reaction Analysis (NRA) method and the Thermal Desorption Spectrometry (TDS); the bubbles characterization performed by Transmission Electronic Microscopy (TEM). The development of a simple model for the description of the cluster dynamic (clusters composed by defects and gas atoms) proposes some explanations for the coupling between the dynamics of the helium release and the bubbles evolution. This model enables to simulate the implantation experiments and the following annealing sequences, with a relevant physical dataset and coherent with the literature. Moreover it enhances the strong inference between the species concentration into the bulk (vacancies and helium atoms) and the mean composition of the bubbles. The peculiar dynamics of the gas release observed during the experiments, initially rapid and then significantly reduced , would be due to the ripening of the bubbles, pressurized after the room temperature implantation, which keep on growing and reducing their concentration and internal pressure

Conn., Yale Univ., Diss.--New Haven, 2005. / Kopie, ersch. im Verl. UMI, Ann Arbor, Mich. - Enth. 3 Beitr.

Thesis (M.S.); Submitted to the University of California, Berkeley, 210 Hearst Mining Memorial Bldg., Berkeley, CA 94720 (US); 15 Dec 2003. / Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--54116" Li, Sonny X. USDOE Director. Office of Science. Basic Energy Sciences (US) 12/15/2003. Report is also available in paper and microfiche from NTIS.