Dynamics of high-angle grain boundary YBCO Josephson junctions

This thesis describes experimental investigations of properties of high-angle YBa2Cu3O7−δ(YBCO)bicrystal Josephson junctions and SQUIDs fabricated on SrTiO3-substrates. The main focus of theinvestigation has been on the effects of the predominant d-wave symmetry of the superconductingwavefunction in YBCO on transport properties and dynamics.At a high-angle grain-boundary interface between two high-temperature superconductors Andreevstates can form, the current carried by these states hasπ-periodic component which flows in a direc-tion opposite of the usual Josephson current. Asymmetric high-angle grain boundaries also exhibit acritical current which is four orders of magnitude lower than symmetric lower-angle junctions, thiscan be attributed to the node-lobe arrangement of the the superconducting order parameter.High-angle grain-boundary dc-SQUIDs that have been studied which exhibit unusual dynamicssuch as a relative ”shift” of the positions of the positive and negative modulation and a highly non-sinusoidal dependence on the external field. This behavior vanished when moving to very narrowjunctions. These result are explained using a semi-classical model which assumes the presence ofa2ndharmonic in the current-phase relation. Numerical simulations confirm that this model is inqualitative agreement with experimental results.The properties of sub-micron sized junctions have also been studied. These exhibit some un-usual behavior. These junctions have been used to study the tunnelling spectra since the high normalresistance means that it is possible to study energies close to the gap.Finally, some general properties of high-angle Josephson Junctions are discussed. It is arguedthat some seemingly inconsistent experimental results can be explained using a multi-channel modelwhich accounts for the wiggling and faceting of the interface

Dynamics of high-angle grain boundary YBCO Josephson junctions

This thesis describes experimental investigations of properties of high-angle YBa2Cu3O7−δ(YBCO)bicrystal Josephson junctions and SQUIDs fabricated on SrTiO3-substrates. The main focus of theinvestigation has been on the effects of the predominant d-wave symmetry of the superconductingwavefunction in YBCO on transport properties and dynamics.At a high-angle grain-boundary interface between two high-temperature superconductors Andreevstates can form, the current carried by these states hasπ-periodic component which flows in a direc-tion opposite of the usual Josephson current. Asymmetric high-angle grain boundaries also exhibit acritical current which is four orders of magnitude lower than symmetric lower-angle junctions, thiscan be attributed to the node-lobe arrangement of the the superconducting order parameter.High-angle grain-boundary dc-SQUIDs that have been studied which exhibit unusual dynamicssuch as a relative ”shift” of the positions of the positive and negative modulation and a highly non-sinusoidal dependence on the external field. This behavior vanished when moving to very narrowjunctions. These result are explained using a semi-classical model which assumes the presence ofa2ndharmonic in the current-phase relation. Numerical simulations confirm that this model is inqualitative agreement with experimental results.The properties of sub-micron sized junctions have also been studied. These exhibit some un-usual behavior. These junctions have been used to study the tunnelling spectra since the high normalresistance means that it is possible to study energies close to the gap.Finally, some general properties of high-angle Josephson Junctions are discussed. It is arguedthat some seemingly inconsistent experimental results can be explained using a multi-channel modelwhich accounts for the wiggling and faceting of the interface

An Adaptive Finite Element/Finite Difference Domain Decomposition Method for Applications in Microwave Imaging

A new domain decomposition method for Maxwell’s equations in conductive media is presented. Using this method, reconstruction algorithms are developed for the determination of the dielectric permittivity function using time-dependent scattered data of an electric field. All reconstruction algorithms are based on an optimization approach to find the stationary point of the Lagrangian. Adaptive reconstruction algorithms and space-mesh refinement indicators are also presented. Our computational tests show the qualitative reconstruction of the dielectric permittivity function using an anatomically realistic breast phantom

Particle-level simulations of flocculation in a fiber suspension flowing through a diffuser

We investigate flocculation in dilute suspensions of rigid, straight fibers in a decelerating flow field of a diffuser. We carry out numerical studies using a particle-level simulation technique that takes into account the fiber inertia and the non-creeping fiber-flow interactions. The fluid flow is governed by the Reynolds-averaged Navier-Stokes equations with the standard k-omega eddy-viscosity turbulence model. A one-way coupling between the fibers and the flow is considered with a stochastic model for the fiber dispersion due to turbulence. The fibers interact through short-range attractive forces that cause them to aggregate into flocs when fiber-fiber collisions occur. We show that ballistic deflection of fibers greatly increases the flocculation in the diffuser. The inlet fiber kinematics and the fiber inertia are the main parameters that affect fiber flocculation in the pre-diffuser region

Thermal capability of electric vehicle PMSM with different slot areas via thermal network analysis

In this paper, the effect that a varied stator slot size has on the efficiency and thermal capability of a permanent magnet synchronous machine for an electric vehicle, is evaluated and quantified. A machine with four differently sized slot areas was electromagnetically evaluated with finite element analysis, and thermally with a lumped parameter network model. By decreasing the slot size while keeping other dimensions fixed, the core losses reduce due to the wider magnetic path, whereas the winding losses increase. Additionally, a higher maximum torque is reached due to reduced saturation. Results are compared in the machine\u27s torque-speed operating area regarding machine-part and total losses, continuous torque and transient overload capability, as well as during 19 low, middle and high-speed drive cycles regarding energy losses and peak winding temperature. The largest slot showed the lowest winding losses and thus the highest thermally limited torque capability. In contrast, the energy losses with the largest slot were the highest in 13 of the drive cycles, and the lowest in 11 of them with the smallest slot due to its lower part load (i.e. core) losses. The smallest slot would also result in the lowest material cost since it has the least copper

Automatic test suite generation for PMCFG grammars

We present a method for finding errors in formalized natural language grammars, by automatically and systematically generating test cases that are intended to be judged by a human oracle. The method works on a per-construction basis; given a construction from the grammar, it generates a finite but complete set of test sentences (typically tens or hundreds), where that construction is used in all possible ways. Our method is an alternative to using a corpus or a treebank, where no such completeness guarantees can be made. The method is language-independent and is implemented for the grammar formalism PMCFG, but also works for weaker grammar formalisms. We evaluate the method on a number of different grammars for different natural languages, with sizes ranging from toy examples to real-world grammars

Using Valued Booleans to Find Simpler Counterexamples in Random Testing of Cyber-Physical Systems

We propose a new logic of valued Booleans for writing properties which are not just true or false but compute how severely they are falsified. The logic is reminiscent of STL or MTL but gives the tester control over what severity means in the particular problem domain. We use this logic to simplify failing test inputs in the context of random testing of cyber-physical systems and show that it improves the quality of counterexamples found. The logic of valued Booleans might also be used as an alternative to the standard robust semantics of STL formulas in optimization-based approaches to falsification

Constraint Grammar as a SAT problem

We represent Constraint Grammar (CG) as a Boolean satisfiability (SAT) problem. Encoding CG in logic brings some new features to the grammars. The rules are interpreted in a more declarative way, which makes it possible to abstract away from details such as cautious context and ordering. A rule is allowed to affect its context words, which makes the number of the rules in a grammar potentially smaller. Ordering can be preserved or discarded; in the latter case, we solve eventual rule conflicts by finding a solution that discards the least number of rule applications. We test our implementation by parsing texts in the order of 10,000s–100,000s words, using grammars with hundreds of rules

Comparison of Exact and Approximate methods for the Vehicle Routing Problem with Time Windows

This paper presents a comparison of two approaches for solving the vehicle routing problem with time windows (VRPTW). Scheduling of vehicles for pickup and delivery is a common problem in logistics and may be expressed as VRPTW, for which both exact and approximate techniques are available. It is therefore interesting to compare such techniques to evaluate their performance and figure what is the best option based on the instance features and size. In this work, we compared Mixed Integer Linear Programming (MILP) with Set-Based Particle Swarm optimization (S-PSO). Both algorithms are tested on the full 56 instances of the Solomon dataset. The results show that the two algorithms perform similarly for lower number of customers while there are significant differences for the cases with higher number of customers. For higher number of customers MILP consistently performs as good as or better than S-PSO for the clustered data, both with short and long scheduling horizons, while the S-PSO outperforms MILP in most cases with random and mixed random clustered data with long scheduling horizons. Furthermore when the algorithms perform the same with regards to the main objective (number of vehicles), MILP generally achieves a better result in the second objective (distance traveled)

Water quality modelling: microbial risks associated with manure on pasture and arable land

While agricultural activities, such as the application of manure on arable land and animal grazing on pastures, provide economic and environmental benefits, they may also pose microbial risks to water sources. The aim of this paper was to study the microbial fate and transport in an agricultural catchment and recipient water source through further development of the hydrological model HYPE. Hydrological modelling was combined with hydrodynamic modelling to simulate the fate and transport of Salmonella spp., verotoxin-producing Escherichia coli O157:H7 and Cryptosporidium parvum in an agricultural catchment of a drinking water source, Lake Vombsj\uf6n, in Sweden. This approach was useful to study the influence of different processes on the pathogen fate and transport, and to interpret the relative changes in the simulated concentrations. Sensitivity analysis indicated that the largest uncertainties in the model were associated with the estimation of pathogen loads, parameterisation of the pathogen processes, and simulation of partitioning between surface runoff and infiltration. The proposed modelling approach is valuable for assessing the relative effect of different risk-reducing interventions