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Northern pike (Esox lucius L) populations have been declining along the east coast of Sweden, including the Gävleborg coast. This negative trend is believed to be caused by factors related to pike recruitment including loss of suitable spawning habitats. The purpose of this study is to gain a deeper understanding for the recruitment process of pike by investigating their preferences when selecting spawning habitats. Data from a rod fishing inventory targeting adult pike was used to estimate pike densities in 20 assumed spawning bays along the coast of Gävleborg. By using the number of pike caught per hour as a measure of pike density I examined how the morphological characteristics of bays and fish communities influenced pike densities during the spawning period in the studied bays. The results suggest that the density of pike (# caught per hour) tend to increase in bays with deeper average depths, larger surface area, and higher densities of sticklebacks. These results contradict the hypothesis in the study and somewhat previous research. Possible explanations for these unexpected findings are discussed, and one theory suggest that the rod fishing method used may have influenced the results. Probably improvements can be made to make the density estimates from the fishing inventory more accurately, especially when comparing bays of varying sizes. Suggestions for enhancing density estimation include adjusting the fishing duration based on bay size or using a specific number of throws per casting rod and defined surface area and then move to next surface area.

Accelerating physics-based simulations has been an evergreen topic across different scientific communities. This dissertation is devoted to this subject addressing bottlenecks in state-of-the-art approaches to the simulation of fluids of large-scale scenes, viscous threads, magnetic fluids, and the simulation of fibers and thin structures. The contributions within the thesis are rooted in mathematical modeling and numerical simulation as well as in machine learning. The first part deals with the simulation of incompressible flow in a multigrid fashion. For the variational viscous equation, geometric multigrid is inefficient. An Unsmoothed Aggregation Algebraic Multigrid method is devised with a multi-color Gauss-Seidel smoother, which consistently solves this equation in a few iterations for various material parameters. This framework is 2.0 to 14.6 times faster compared to the state-of-the-art adaptive octree solver in commercial software for the large-scale simulation of both non-viscous and viscous flow. In the second part, a new physical model is devised to accelerate the macroscopic simulation of magnetic fluids. Previous work is based on the classical Smoothed-Particle Hydrodynamics (SPH) method and a Kelvin force model. Unfortunately, this model results in a force pointing outwards causing significant levitation problems limiting the application of more advanced SPH frameworks such as Divergence-Free SPH (DFSPH) or Implicit Incompressible SPH (IISPH). This shortcoming has been addressed with this new current loop magnetic force model resulting in more stable and fast simulations of magnetic fluids using DFSPH and IISPH. Following a different trajectory, the third part of this thesis aims for the acceleration of iterative solvers widely used to accurately simulate physical systems. We speedup the simulation for rod dynamics with Graph Networks by predicting the initial guesses to reduce the number of iterations for the constraint projection part of a Position-based Dynamics solver. Compared to existing methods, this approach guarantees long-term stability and therefore leads to more accurate solutions.

The thulium fiber laser has gained interest due to its long emission wavelength, large bandwidth (~1.8 – 2.1 µm), high efficiencies (~60 %), and high output power levels both in cw as well as pulsed regimes. Applications like remote sensing, machining, medical tissue ablation, and mid-infrared generation benefit from high peak power thulium laser sources. Pulsed thulium fiber laser systems are advancing rapidly towards higher peak power levels and are becoming the preferred sources for these applications. This dissertation work describes the development of novel nanosecond pulsed thulium fiber laser systems with record high peak power levels targeting mid-infrared generation. The peak power scaling in thulium fiber lasers requires new fiber designs with larger mode field area (MFA) than commercially available step index large mode area (SI-LMA) fibers. Two different prototypes of thulium doped photonic crystal fibers (PCF) were investigated for high peak power generation. The first prototype is a flexible-PCF with MFA twice as large as SILMA fiber and the second prototype is a PCF-rod with six times larger MFA. A robust single stage master oscillator power amplifier (MOPA) source based on flexible-PCF was developed. This source provided narrow linewidth, tunable wavelength, variable pulse duration, high peak power, and high energy nanosecond pulses. The PCF-rod was implemented as a second stage power amplifier. This system generated a record level of ~1 MW peak power output with 6.4 ns pulse-duration at 1 kHz repetition rate. This thulium doped PCF based MOPA system is a state of the art laser source providing high quality nanosecond pulses. iv The single stage MOPA system was successfully implemented to pump a zinc germanium phosphide (ZGP) crystal in an optical parametric oscillator (OPO) cavity to generate 3 - 5 µm wavelengths. The MOPA source was also used to demonstrate backside machining in silicon wafer. The PCF based laser system demonstrated an order of magnitude increase in the peak power achievable in nanosecond thulium doped fiber laser systems, and further scaling appears possible. The increase in peak power will enable additional capabilities for mid-infrared generation and associated applications.

Målet med detta arbete var att ta fram ett nytt trådmagasin till Sund Birstas α-kompaktor som är bättre ur ett säkerhets- samt ekonomiskt perspektiv. En kompaktor är en bindmaskin som komprimerar och binder samman valstrådrullar för att förhindra trassel samt underlätta förvararing och fraktning. Trådmagasinets huvudsakliga uppgift är att hålla kompaktorns bindtråd konstant sträckt för att förhindra att trassel uppstår bakom kompaktorn. Under arbetets konceptgenereringsfas togs delkoncept fram för ackumulering av tråd, lyftmekanismer samt förflyttningsmekanisker. Därefter togs 12 helhetskoncept fram som utvärderades först vid ett seminarium med Sund Birsta för att få värdefulla insikter kring koncepten. Därefter utvärderades koncepten med en Pughs-matris där koncepten jämfördes utifrån kriterier från Sund Birsta samt krav från kravspecifikationen. Det koncept som valdes ut från utvärderingen är en konstruktion som tillåter att användaren trär tråden igenom magasinet från golvnivå samt bidrar till en sänkning med 33% på kraften kompaktorns matarverk matar tråden med. En elmotor hjälper till att hålla tråden sträckt samt ladda magasinet genom att lyfta upp två rörliga brythjul. Det slutgiltiga konceptet utvecklades ytterligare för att kunna möjliggöra att allt arbete ska ske från golvnivå och därmed öka säkerheten. En CAD-modell togs slutligen fram för att illustrera konceptets utformning och funktion. / The goal of this project was to develop a new wire magazine for Sund Birsta´s α-compactor that is better from a safety and economical perspective. A coil compactor is a binding machine that compresses and binds together rod wire coils to prevent tangling and facilitate storage and transportation. The wire magazines main task is to keep the compactor’s binding wire constantly tense to prevent tangling from occuring behind the compactor. During the projects concept generation phase, subconcepts for lifting mechanisms, accumulation of wire and movement mechanisms was sketched. Thereafter 12 overall concepts was developed which was evaluated first at a seminar with Sund Birsta to gain valueble knowledge regarding the concepts. The concepts was thereafter evaluated with a Pughs-matrix where the concepts was compared with each other regarding to how well they met the demands set by Sund Birsta and from the requirements specification. The concept which was chosen from the evaluation is a construction which lets the user pull the wire through the magazine from ground level, and it lowers the force required for the compactor´s feeding unit with 33%. A electric motor helps keeping the wire tense and load the magazine by lifting up two movable wire wheels.

The proponents of non-conventional lightning protection devices claim that these devices are superior to the conventional Franklin Rod. Lack of systematic study and insufficient field data make it difficult to compare the non-conventional lightning protection devices with the conventional ones. Previously, the performance of various air terminals was studied by comparing the emission current through various dissipation devices in the MSU High Voltage Laboratory. The study of emission current from the air terminals gives an idea about the space charge developing over them. However, it does not show the behavior of air terminals to attract or repel lightning strikes. The present study presents the measurements of critical flashover (CFO) voltage of the air terminals. The CFO voltage shows the ability of an air terminal to attract or reduce the chance of lightning strike to the protected object.

After over a decade of its discovery, the Electroretinogram (ERG) still remains the objective tool that is conventionally used in assessment of retinal function in health and disease. Although there is ongoing research in developing ERG recording techniques, interpretation and clinical applications, there is still a limited understanding on how each photoreceptor class contribute to the ERG waveform and their role and/or susceptibilities in various retinal diseases still remains unclear. Another limitation with currently used conventional testing protocols in a clinical setting is the requirement of an adaptation period which is time consuming. Furthermore, the ERG responses derived in this manner are recorded under different stimulus conditions, thus, making comparison of these signals difficult. To address these issues and develop a new testing method, we employed silent substitution paradigm in obtaining cone- and rod- isolating ERGs using sine- and square- wave temporal profiles. The ERGs achieved in this manner were shown to be photoreceptor-selective. Furthermore, these responses did not only provide the functional index of photoreceptors but their contributions to their successive postreceptoral pathways. We believe that the substitution stimuli used in this thesis could be a valuable tool in functional assessment of individual photoreceptor classes in normal and pathological conditions. Furthermore, we speculate that this method of cone/rod activity isolation could possibly be used in developing faster and efficient photoreceptor-selective testing protocols without the need of adaptation. / Bradford School of Optometry and Vision Sciences scholarship

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