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We study three different kinds of mesoscopic systems – in the intermediate region between macroscopic and microscopic scales consisting of many interacting constituents: We consider particle entanglement in one-dimensional chains of interacting fermions. By employing a field theoretical bosonization calculation, we obtain the one-particle entanglement entropy in the ground state and its time evolution after an interaction quantum quench which causes relaxation towards non-equilibrium steady states. By pushing the boundaries of the numerical exact diagonalization and density matrix renormalization group computations, we are able to accurately scale to the thermodynamic limit where we make contact to the analytic field theory model. This allows to fix an interaction cutoff required in the continuum bosonization calculation to account for the short range interaction of the lattice model, such that the bosonization result provides accurate predictions for the one-body reduced density matrix in the Luttinger liquid phase. Establishing a better understanding of how to control entanglement in mesoscopic systems is also crucial for building qubits for a quantum computer. We further study a popular scalable qubit architecture that is based on Majorana zero modes in topological superconductors. The two major challenges with realizing Majorana qubits currently lie in trivial pseudo-Majorana states that mimic signatures of the topological bound states and in strong disorder in the proposed topological hybrid systems that destroys the topological phase. We study coherent transport through interferometers with a Majorana wire embedded into one arm. By combining analytical and numerical considerations, we explain the occurrence of an amplitude maximum as a function of the Zeeman field at the onset of the topological phase – a signature unique to MZMs – which has recently been measured experimentally [Whiticar et al., Nature Communications, 11(1):3212, 2020]. By placing an array of gates in proximity to the nanowire, we made a fruitful connection to the field of Machine Learning by using the CMA-ES algorithm to tune the gate voltages in order to maximize the amplitude of coherent transmission. We find that the algorithm is capable of learning disorder profiles and even to restore Majorana modes that were fully destroyed by strong disorder by optimizing a feasible number of gates. Deep neural networks are another popular machine learning approach which not only has many direct applications to physical systems but which also behaves similarly to physical mesoscopic systems. In order to comprehend the effects of the complex dynamics from the training, we employ Random Matrix Theory (RMT) as a zero-information hypothesis: before training, the weights are randomly initialized and therefore are perfectly described by RMT. After training, we attribute deviations from these predictions to learned information in the weight matrices. Conducting a careful numerical analysis, we verify that the spectra of weight matrices consists of a random bulk and a few important large singular values and corresponding vectors that carry almost all learned information. By further adding label noise to the training data, we find that more singular values in intermediate parts of the spectrum contribute by fitting the randomly labeled images. Based on these observations, we propose a noise filtering algorithm that both removes the singular values storing the noise and reverts the level repulsion of the large singular values due to the random bulk.

<p> Displacement transfer between faults and folds has been extensively documented in the Rocky Mountains as an explanation for structural variability along strike producing seemingly similar overall shortenings. A series of subparallel imbricate thrusts and an associated syncline in the Southern Canadian Front ranges at Heart Mountain has been mapped at a scale of 1:16,667. Megascopic, mesoscopic and microscopic evidence supports the contention that the folding observed at Heart Mountain occurred synchronously with thrusting as the result of displacement transfer from the adjacent thrust. </p> <p>Numerical dynamic analyses (NDA) suggest that twinning of calcite grains occurred very early in the deformational history in response to a regional stress field orientation of 246/03, 340/02, and 159/84 for o 1, o2 , and 03 respectively in the Exshaw plate. Megascopic and mesoscopic fabrics indicate similar results. Ambiguous NDA results for the Heart Mountain Syncline are explained using neutral surface folding theories rather than flexural slip theories generally proposed for folding within the Front Ranges. Neutral surface folds are consistent with the deformational model (displacement transfer) proposed. </p> <p>An orthogonal fracture system is pervasive throughout the thesis area. Observations indicate that fractures are oriented parallel and perpendicular to the strike of the Rocky Mountains. Their development is inferred to have taken place in the same regional stress field thought to be responsible for twinning, with fracture opening occurring after the relaxation of tectonic stresses and the removal of substantial amounts of overburden. </p> / Thesis / Bachelor of Science (BSc)

With the advance in nanotechnology, we are more interested in the "smaller worlds". One of the practical applications of this is to measure a very small displacement or the mass of a nano-mechanical object. To measure such properties, one needs a very sensitive detector. A quantum point contact (QPC) is one of the most sensitive detectors. In a QPC, electrons tunnel one by one through a tunnel junction (a "hole"). The tunnel junction in a QPC consists of a narrow constriction (nm-wide) between two conductors. To measure the properties of a nano-mechanical object (which acts as a harmonic oscillator), we couple it to a QPC. This coupling effects the electrons tunneling through the QPC junction. By measuring the transport properties of the tunneling electrons, we can infer the properties of the oscillator (i.e. the nano-mechanical object). However, this coupling introduces noise, which reduces the measurement precision. Thus, it is very important to understand this source of noise and to study how it effects the measurement process. We theoretically study the transport properties of electrons through a QPC junction, weakly coupled to a vibration mode of a nano-mechanical oscillator via both the position and the momentum of the oscillator. %We study both the position and momentum based coupling. The transport properties that we study consist of the average flow of current through the junction, given by the one-time correlation of the electron tunneling event, and the current noise given by the two-time correlation of the average current, i.e, the variance. The first comprehensive experimental study of the noise spectrum of a detector coupled to a QPC was performed by the group of Stettenheim et al. Their observed spectral features had two pronounced peaks which depict the noise produced due to the coupling of the QPC with the oscillator and in turn provide evidence of the induced feedback loop (back-action). Benatov and Blencowe theoretically studied these spectral features using the Born approximation and the Markovian approximation. In this case the Born approximation refers to second order perturbation of the interaction Hamiltonian. In this approximation, the electrons tunnel independently, i.e., one by one only, and co-tunneling is disregarded. The Markovian approximation does not take into account the past behavior of the system under time evolution. These two approximations also enable one to study the system analytically, and the noise is calculated using the MacDonald formula. Our main aim for this thesis is to find a suitable theoretical model that would replicate the experimental plots from the work of Stettenheim et al. Our work does not use the Markovian approximation. However, we do use the Born approximation. This is justified as long as the coupling between the oscillator and QPC is weak. We first obtain the non-Markovian unconditional master equation for the reduced density matrix of the system. Non-Markovian dynamics enables us to study, in principle, the full memory effects of the system. From the master equation, we then derive analytical results for the current and the current noise. Due to the non-Markovian nature of our system, the electron tunneling parameters are time-dependent. Therefore, we cannot study the system analytically. We thus numerically solve the current noise expression to obtain the noise spectrum. We then compare our noise spectrum with the experimental noise spectrum. We show that our spectral noise results agree better with the experimental evidence compared to the results obtained using the Markovian approximation. We thus conclude that one needs non-Markovian dynamics to understand the experimental noise spectrum of a QPC coupled to a nano-mechanical oscillator. / Physics

The transportation sector is a major contributor to U.S. fuel consumption and emissions. Consequently, assessing the environmental impacts of transportation activities is essential for air-quality improvement programs. Current state-of-the-art models estimate vehicle emissions based on typical urban driving cycles. Most of these models offer simplified mathematical expressions to compute fuel consumption and emission rates based on average link speeds while ignoring transient changes in a vehicle's speed and acceleration level as it travels on a highway network. Alternatively, microscopic models capture these transient effects; however, the application of microscopic models may be costly and time consuming. Also, these tools may require a level of input data resolution that is not available. Consequently, this dissertation attempts to fill the void in energy and emission modeling by a framework for modeling vehicle fuel consumption and emissions mesoscopically. This framework is utilized to develop the VT-Meso model using a number of data sources. The model estimates average light-duty vehicle fuel consumption and emission rates on a link-by-link basis using up to three independent variables, namely: average travel speed, average number of stops per unit distance, and average stop duration. The mesoscopic model utilizes a microscopic vehicle fuel consumption and emission model that was developed at Virginia Tech to compute mode-specific fuel consumption and emission rates. This model, known as VT-Micro, predicts the instantaneous fuel consumption and emission rates of HC, CO and NOx of individual vehicles based on their instantaneous speed and acceleration levels. The mesoscopic model utilizes these link-by-link input parameters to construct a synthetic drive cycle and compute average link fuel consumption and emission rates. After constructing the drive cycle, the model estimates the proportion of time that a vehicle typically spends cruising, decelerating, idling and accelerating while traveling on a link. A series of fuel consumption and emission models are then used to estimate the amount of fuel consumed and emissions of HC, CO, CO2, and NOX emissions for each mode of operation. Subsequently, the total fuel consumed and pollutants emitted by a vehicle while traveling along a segment are estimated by summing across the different modes of operation and dividing by the distance traveled to obtain distance-based average vehicle fuel consumption and emission rates. The models are developed for normal and high emitting vehicles. The study quantifies the typical driver deceleration behavior for incorporation within the model. Since this model constructs a drive cycle which includes a deceleration mode, an accurate characterization of typical vehicle deceleration behavior is critical to the accurate modeling of vehicle emissions. The study demonstrates that while the deceleration rate typically increases as the vehicle approaches its desired final speed, the use of a constant deceleration rate over the entire deceleration maneuver is adequate for environmental modeling purposes. Finally, the study validates the model on a freeway and urban arterial network. The results demonstrate that the model provides accurate estimates of vehicle fuel consumption and emission rates and is adequate for the evaluation of transportation operational projects. / Ph. D.

The study of quantum interference in solid-state systems yields insight in fundamental properties of mesoscopic systems. Electron quantum interference constitutes an important method to explore mesoscopic physics and quantum decoherence. This dissertation focuses on two-dimensional (2D) electron systems in $delta-$Si doped n-type In$_{0.64}$Ga$_{0.36}$As/In$_{0.45}$Al$_{0.55}$As, 2D hole systems in Si-doped p-type GaAs/Al$_{0.35}$Ga$_{0.65}$As and C-doped p-type GaAs/\Al$_{0.24}$Ga$_{0.76}$As heterostructures. The low temperature experiments study the magnetotransport of nano- and micro-scale lithographically defined devices fabricated on the heterostructures. These devices include a single ring interferometer and a ring interferometer array in 2D electron system, Hall bar geometries and narrow wires in 2D hole systems. The single ring interferometer yields pronounced Aharonov-Bohm (AB) oscillations with magnetic flux periodicity of h/e over a wide range of magnetic field. The periodicity was confirmed by Fourier transformation of the oscillations. The AB oscillation amplitude shows a quasi-periodic modulation over applied magnetic field due to local magnetic flux threading through the interferometer arms. Further study of current and temperature dependence of the amplitude of the oscillations indicates that the Thouless energy forms the measure of excitation energies giving quantum decoherence. An in-plane magnetic field was applied to the single ring interferometer to study the Berry's phase and the Aharonov-Casher effect. The ring interferometer array yields both AB oscillations and Altshuler-Aronov-Spivak (AAS) oscillations, the latter with magnetic flux periodicity of h/2e. The AAS oscillations require time-reversal symmetry and hence can be used to qualify time-reversal symmetry breaking. More importantly, the fundamental mesoscopic dephasing length associated with time-reversal symmetry breaking under applied magnetic field, an effective magnetic length, can be obtained by the analysis of the AAS oscillations over magnetic field. A theoretical model for confined ballistic system is confirmed by experimental data fitting. The AAS oscillations are barely resolved above 0.16 T and their amplitude decays with increasing magnetic field. The AB oscillations exist till above 2 T and their amplitude doesn't show the monotonic decay with increasing magnetic field. The different behavior of the AAS and AB oscillations originates in the different symmetries, respectively temporal and spatial, that they are sensitive to. The p-type 2D GaAs system has strong spin-orbit interaction (SOI). Antilocalization in a Hall bar geometry was analyzed by the 2D Hikami-Larkin-Nagaoka (HLN) theory to obtain the spin coherence time and phase coherence time. The 2D hole systems we studied have low density and high mobility, quite different from the 2D electron systems. These high-quality 2D hole systems demonstrate semi-classical ballistic phenomena in mesoscopic structures preferentially to quantum-coherence phenomena. / Ph. D.

This thesis reports our work on transport related problems in mesoscopic physics using analytical as well as numerical techniques. Some of the problems we studied are: effect of interactions and static impurities on the conductance of a ballistic quantum wire[1], aspects of quantum charge pumping [2, 3, 4], DC and AC conductivity of a (dissipative) quantum Hall (edge) line junctions[5, 6], and junctions of three or more Luttinger liquid (LL)quantum wires[7]. This thesis begins with an introductory chapter which gives a brief glimpse of the underlying physical systems and the ideas and techniques used in our studies. In most of the problems we will look at the physical effects caused by e-e interactions and static scattering processes. In the second chapter we study the effects of a static impurity and interactions on the conductance of a 1D-quantum wire numerically. We use the non-equilibrium Green’s function (NEGF) formalism along with a self-consistent Hartree-Fock approximation to numerically study the effects of a single impurity and interactions between the electrons (with and without spin) on the conductance of a quantum wire [1]. We study the variation of the conductance with the wire length, temperature and the strength of the impurity and electron-electron interactions. We find our numerical results to be in agreement with the results obtained from the weak interaction RG analysis. We also discover that bound states produce large density deviations at short distances and have an appreciable effect on the conductance which is not captured by the renormalization group analysis. In the third chapter we use the equations of motion (EOM) for the density matrix and Floquet scattering theory to study different aspects of charge pumping of non-interacting electrons in a one-dimensional system. We study the effects of the pumping frequency, amplitude, band filling and finite bias on the charge pumped per cycle, and the spectra of the charge and energy currents in the leads[2]. The EOM method works for all values of parameters, and gives the complete time-dependences of the current and charge at any site of the system. In particular we study a system with oscillating impurities at several sites and our results agree with Floquet and adiabatic theory where these are applicable, and provides support for a mechanism proposed elsewhere for charge pumping by a traveling potential wave in such systems. For non-adiabatic and strong pumping, the charge and energy currents are found to have a marked asymmetry between the two leads, and pumping can work even against a substantial bias. We also study one-parameter charge pumping in a system where an oscillating potential is applied at one site while a static potential is applied in a different region [3]. Using Floquet scattering theory, we calculate the current up to second order in the oscillation amplitude and exactly in the oscillation frequency. For low frequency, the charge pumped per cycle is proportional to the frequency and therefore vanishes in the adiabatic limit. If the static potential has a bound state, we find that such a state has a significant effect on the pumped charge if the oscillating potential can excite the bound state into the continuum states or vice versa. In the fourth chapter we study the current produced in a Tomonaga-Luttinger liquid (TLL) by an applied bias and by weak, point-like impurity potentials which are oscillating in time[4]. We use bosonization to perturbatively calculate the current up to second order in the impurity potentials. In the regime of small bias and low pumping frequency, both the DC and AC components of the current have power law dependences on the bias and pumping frequencies with an exponent 2K−1 for spinless electrons, where Kis the interaction parameter. For K<1/2, the current grows large for special values of the bias. For non-interacting electrons with K= 1, our results agree with those obtained using Floquet scattering theory for Dirac fermions. We also discuss the cases of extended impurities and of spin-1/2 electrons. In chapter five, we present a microscopic model for a line junction formed by counter or co-propagating single mode quantum Halledges corresponding to different filling factors and calculate the DC [5] and AC[6] conductivity of the system in the diffusive transport regime. The ends of the line junction can be described by two possible current splitting matrices which are dictated by the conditions of both lack of dissipation and the existence of chiral commutation relations between the outgoing bosonic fields. Tunneling between the two edges of the line junction then leads to a microscopic understanding of a phenomenological description of line junctions introduced by Wen. The effect of density-density interactions between the two edges is considered exactly, and renormalization group (RG) ideas are used to study how the tunneling parameter changes with the length scale. The RG analysis leads to a power law variation of the conductance of the line junction with the temperature (or other energy scales) and the line junction may exhibit metallic or insulating phase depending on the strength of the interactions. Our results can be tested in bent quantum Hall systems fabricated recently. In chapter six, we study a junction of several Luttinger Liquid (LL) wires. We use bosonization with delayed evaluation of boundary conditions for our study. We first study the fixed points of the system and discuss RG flow of various fixed points under switching of different ‘tunneling’ operators at the junction. Then We study the DC conductivity, AC conductivity and noise due to tunneling operators at the junction (perturbative).We also study the tunneling density of states of a junction of three Tomonaga-Luttinger liquid quantum wires[7]. and find an anomalous enhancement in the TDOS for certain fixed points even with repulsive e-e interactions.

This work is concerned with the theoretical description of the Scanning Gate Microscopy (SGM) in general and with solving particular models of the quantum point contact (QPC) nanostructure, analytically and numerically. SGM is an experimental technique, which measures the conductance of a nanostructure, while a charged AFM tip is scanned above its surface. It gives many interesting results, such as lobed and branched images, interference fringes and a chequerboard pattern. A generally applicable theory, allowing for unambiguous interpretation of the results, is still missing. Using the Lippman-Schwinger scattering theory, we have developed a perturbative description of non-invasive SGM signal. First and second order expressions are given, pertaining to the ramp- and plateau-regions of the conductance curve. The maps of time-reversal invariant (TRI) systems, tuned to the lowest conductance plateau, are related to the Fermi-energy charge density. In a TRI system with a four-fold spatial symmetry and very wide leads, the map is also related to the current density, on any plateau. We present and discuss the maps calculated for two analytically solvable models of the QPC and maps obtained numerically, with Recursive Green Function method, pointing to the experimental features they reproduce and to the fundamental difficulties in obtaining good plateau tuning which they reveal.

In this study, seismic interferometry is used to analyze dynamic processes in the Earth’s shallow subsurface caused by environmental processes and ground shaking. In the first part of the thesis, the feasibility of a passive monitoring with ambient seismic noise at the pilot site for CO2 injection in Ketzin is investigated. Monitoring the expansion of the CO2 plume is essential for the characterization of the reservoir as well as the detection of potential leakage. From June 2008 until August 2013, more than 67000 tons of CO2 were injected into a saline aquifer at a depth of about 650 m. Passive seismic data recorded at a seismic network around the injection site was cross-correlated in a frequency range of 0.5-4.5 Hz over a period of 4 years. The frequency band of 0.5-0.9 Hz, in which surface waves exhibit a high sensitivity at the depth of the reservoir, is not suitable for monitoring purposes as it is only weakly excited. In a frequency range of 1.5-3 Hz, periodic velocity variations with a period of approximately one year are found that cannot be caused by the CO2 injection. The prominent propagation direction of the noise wave field indicates a wind farm as the dominant source providing the temporally stable noise field. This spacial stability excludes variations of the noise source distribution as a spurious cause of velocity variations. Based on an amplitude decrease associated with time windows towards later parts of the coda, the variations must be generated in the shallow subsurface. A comparison to groundwater level data reveals a direct correlation between depth of the groundwater level and the seismic velocity. The influence of ground frost on the seismic velocities is documented by a sharp increase of velocity when the maximum daily temperature stays below 0 C. Although the observed periodic changes and the changes due to ground frost affect only the shallow subsurface, they mask potential signals of material changes from the reservoir depths. To investigate temporal seismic velocity changes due to earthquake-related processes and environmental forcing in northern Chile, 8 years of ambient seismic noise recorded by the Integrated Plate Boundary Observatory Chile (IPOC) are analyzed. By autocorrelating the ambient seismic noise field, approximations of the Green’s functions are retrieved and velocity changes are measured with Coda Wave Interferometry. At station PATCX, seasonal changes of seismic velocity caused by thermal stress as well as transient velocity reductions are observed in the frequency range of 4-6 Hz. Sudden velocity drops occur at times of mostly earthquake-induced ground describing the seismic velocity variations based on continuous observations of the local ground acceleration. The model assumes that not only the shaking of large earthquakes causes velocity drops, but any small vibrations continuously induce minor velocity variations that are immediately compensated by healing in the steady state. The shaking effect is accumulated over time and best described by the integrated envelope of the ground acceleration over one day, which is the temporal resolution of the velocity measurements. In the model, the amplitude of the velocity reduction as well as the recovery time are proportional to the strength of the excitation. The increase of coseismic velocity change and recovery time with increasing excitation is confirmed by laboratory tests with ultrasound. Despite having only two free scaling parameters, the model fits the data of the shaking-induced velocity variation in remarkable detail. Additionally, a linear trend is observed that might be related to a recovery process from one or more earthquakes before the measurement period. A clear relationship between ground shaking and induced velocity reductions is not visible at other stations. The outstanding sensitivity of PATCX to ground shaking and thermal stress can be attributed to the special geological setting of the station, where the subsurface material consists of a relatively loose conglomerate with high pore volume leading to stronger nonlinearity compared to the other IPOC stations. / In dieser Studie werden mit Hilfe von seismischer Interferometrie kleinste dynamische Prozesse in der Erdkruste beobachtet, welche beispielsweise durch umweltbedingte oder anthropogene Einflüsse sowie Bodenerschütterungen hervorgerufen werden können. Im ersten Teil der Arbeit werden Änderungen in der seismischen Geschwindigkeit am Pilotstandort für CO2-Speicherung in Ketzin untersucht. In einer Tiefe von 650m wurden dort zwischen Juni 2008 und August 2013 über 67000 Tonnen CO2 eingelagert. In einem Frequenzbereich vom 0,05-4,5 Hz wurden Kreuzkorrelationen des seismischen Hintergrundrauschens an einem kleinräumigen Netzwerk über einen Zeitraum von 4 Jahren berechnet. Der Frequenzbereich zwischen 0,5 und 0,9 Hz weist eine hohe Sensitivität von Oberflächenwellen in der Tiefe des Reservoirs auf, ist aber nur sehr schwach angeregt und eignet sich deswegen nicht für die Analyse. In einem Frequenzbereich von 1,5-3 Hz zeigen sich periodische Geschwindigkeitsänderungen mit einer Periode von einem Jahr, welche nicht durch die Einlagerung von CO2 erzeugt werden können. Eine Analyse des seismischen Hintergrundrauschens zeigt, dass dieses über den gesamten Zeitraum hinweg hauptsächlich aus der Richtung eines Windparks kommt. Durch die Stabilität des Wellenfeldes können Änderungen in den Quellpositionen, welche sich in scheinbaren Geschwindigkeitsänderungen zeigen können, ausgeschlossen werden. Eine Amplitudenabnahme der Geschwindigkeitsänderungen hin zu späteren Zeitfenstern in der Coda lässt auf oberflächennahe Prozesse als Ursache schließen. Ein Vergleich zwischen den jährlichen Geschwindigkeitsänderungen mit Schwankungen im Grundwasserspiegel zeigt eine direkte Korrelation. Ein sprunghafter Anstieg in der Geschwindigkeit zeigt sich im Winter, wenn die Tageshöchsttemperaturen unter den Gefrierpunkt sinken und der Boden zufriert. Obwohl Bodenfrost und Änderungen im Grundwasserspiegel nur einen sehr oberflächennahen Bereich betreffen, so überdecken sie dennoch mögliche Signale durch die Einlagerung von CO2. Im zweiten Teil der Arbeit werden Geschwindigkeitsänderungen in Nordchile untersucht, welche durch erdbebeninduzierte Prozesse und umweltbedingte Einflüsse hervorgerufen werden. Dazu wurden über einen Zeitraum von 8 Jahren Autokorrelationen des seismischen Hintergrundrauschens des IPOC Netzwerkes (Integrated Plate Boundary Observatory Chile) berechnet und mit seismischer Interferometrie ausgewertet. An der Station PATCX können in einem Frequenzbereich von 4-6 Hz periodische Geschwindigkeitsänderungen beobachet werden, welche durch thermisch induzierte Dehnung hervorgerufen werden. Außerdem treten transiente Geschwindigkeitsabnamen nach Bodenerschütterungen auf, welche hauptsächlich von Erdbeben verursacht werden. Die seismische Geschwindigkeit kehrt daraufhin langsam wieder auf ihr vorheriges Niveau zurück. Für die Geschwindigkeitsänderungen wurde ein empirisches Modell entwickelt, welches auf Messungen der lokalen Bodenerschütterung basiert. Dabei wird angenommen, dass nicht nur große erdbebeninduzierte, sondern auch kleinste Bodenerschütterungen einen Abfall der Geschwindigkeit erzeugen, welche wiederum innerhalb kürzester Zeit durch Heilung in den Gleichgewichtszustand zurückkehrt. Dabei summieren sich die Effekte durch die Bodenerschütterungen mit der Zeit auf und werden am besten mit dem Integral der lokalen Bodenbeschleunigung über die Messwerte eines Tages beschrieben. Die Diskretisierung von einem Tag entspricht der zeitlichen Auflösung in der Messung der Geschwindigkeitsänderungen. Sowohl die Amplitude der Geschwindigkeitsabnahme als auch die Zeit bis der Gleichgewichtszustand wieder erreicht ist (Heilungszeit) werden im Modell als proportinal zur Größe der Anregung angenommen. Eine Korrelation der Heilungszeit und der Amplitude der koseismischen Geschwindigkeitsabnahme mit der Größe der Anregung konnte mit Hilfe von Laboruntersuchungen mit Ultraschall bestätigt werden. Mit nur zwei Parametern beschreibt das Modell die transienten Geschwindigkeitsänderungen in bemerkenswerter Genauigkeit. Desweiteren beinhaltet das Modell einen linearen Verlauf in den Geschwindigkeitsänderungen, welcher vermutlich durch einen Heilungsprozess hervorgerufen wird, der auf ein oder mehrere Erdbeben vor dem Messzeitraum folgte. Eine Beziehung zwischen Bodenerschütterung und Geschwindigkeitsänderung ist an anderen Stationen des IPOC Netzwerkes nicht erkennbar. Die herausragende Sensitivität von PATCX im Hinblick auf Bodenerschütterung und thermische Dehnung kann den speziellen geologischen Gegebenheiten an der Station zugeschrieben werden. Bei dem dort vorliegenden Material handelt es sich um ein relativ loses Konglomerat mit großem Porenvolumen, welches ein starkes nichtlineares Verhalten aufweist, was an anderen IPOC Stationen nicht zu erwarten ist.

Nous avons étudié la formation de nanogaps par électromigration dans des nanofils d'or. Cette technique consiste à provoquer la rupture d'un nanofil en lui appliquant de fortes densités de courant et peut être utilisée pour la caractérisation électrique de nano-objets. L'étude en temps réel du processus d'électromigration par microscopie à force atomique a permis d'apporter un éclairage nouveau de la dynamique du processus. En effet, il apparaît que la structure globale du dispositif est définie dans les premiers temps de l'électromigration et nous avons montré que cette structure est directement liée à la microstructure du film métallique. Pour la première fois, des nanogaps ont été élaborés par électromigration dans des films monocristallins. Malgré l'absence de joints de grain, il est possible de former des nanogaps dans un matériau épitaxié. L'utilisation de ces matériaux permet d'obtenir des nanogaps avec une morphologie plus reproductible. Les propriétés de transports des nanogaps obtenus à partir de films polycristallins ont été caractérisées. Les caractéristiques obtenues présentent toutes des signatures particulières, attribuées à la présence d'agrégats d'or provenant de la procédure d'électromigration et/ou de polymères issus du procédé de nanofabrication. Ces résultats montrent la difficulté à réaliser des mesures à l'échelle de la molécule unique.