Peatlands are associated with a range of ecosystem services such as long-term carbon storage and sequestration, biodiversity, and potential water reservoirs, mitigating floods and droughts. However, in the 20th century, large peatland areas in the northern temperate and boreal regions were drained by ditching, primarily to enhance forest and agricultural production and peat harvesting. Drainage of peatland is associated with a reduction in wet tolerant peatland species, reduced long term carbon sequestration and increased carbon emissions, conflicting with the goals of the Convention on Biological Diversity (CBD) and the Paris Agreement. Today, there is a big ongoing effort from society to rewet and restore drained peatlands in Sweden, but post- restoration monitoring to evaluate success are often scarce. Here, I examine the recovery of a restored drained and afforested bog in Southern Sweden, using a pristine area of the bog as the reference target. The aim was to ascertain to what extend the restoration had succeed and its potential to fully recover. During one year pore water quality, water level and peat surface level were monitored. In the fall peat cores were collected to investigate differences in peat physical and elemental and the microbial biomass and composition. I found that there are still considerable differences between restored and reference area, most marked by the deeper water level in the restored area, but this was not due to a reduced capacity of peat oscillation (i.e. the peats ability to expand and shrink to follow the water table. However, the restoration had raised the water table closer to the surface when compared to other drained areas in Sweden. The study also found considerable higher quantities and higher aromaticity of dissolved organic matter (e.g. DOC) in the porewater of the restored area and an overall lower total amount of microbial biomass with altered community composition, with higher relative amounts’ of fungi and G- negative bacteria’s in the restored area. The nutrient profile in the porewater (inorganic N,P,K) were similar to what was found in the reference area. In conclusion, both the hydrological and porewater chemistry status are currently most likely sufficient for wet-dwelling peat mosses to establish. Here, I argue that the restoration effect is noticeable but complete recovery is yet far away and there is a risk of recession towards afforestation if peat mosses fails to re-establish.

The thesis solves vibration of simple combustion engine model as a basic step for evaluating the noise of engine. On the basis of computational model realized in software MBS ADAMS, which contains all significant input parameters, there are found normal velocities of the one cylinder four stroke engine block surfaces. The outputs are then processed into the integral characteristics that define the level of possible emissions for whole acoustic spectre. Two variants of the engine block were solved and in the end the summary of solution approach was made.

Orientador: Marta Cilene Gadotti / Resumo: Este trabalho tem por objetivo o estudo da teoria básica sobre as Equações Diferenciais Funcionais com Retardamento. Enunciaremos e provaremos os resultados clássicos sobre existência e unicidade de solução. E iremos estudar a existência de soluções oscilatórias para equações autônomas escalares. / Abstract: This paper aims to study the basic theory about the Delay Differential Equations. We will enunciate and prove the classic results on existence and uniqueness of solution. And we will study the existence of oscillatory solutions for scalar autonomous equations. / Mestre

In our thesis we focused on demonstrational-experiment-projections and instructions for mechanical oscillations, waves and acoustics. Nevertheless, we did not marginalize other types of tasks linked to experiments. As a starting point of our thesis we used a search of our topic carried out on textbooks for elementary and high schools. This search forms a part of introduction of our thesis. We carried out a considerable part of presented experiments personally during lessons with our students and distilled new experience into the final guidelines of presented experiments. Attachment plays a significant part of the thesis, above all video records of experiments and woorksheets for students. Experiments, with instructions included, update and supplement the subject Practical Course in School Experiments I, which forms part of the compulsory professional preparation of physics teachers at MFF UK. The experiments might therefore serve as an inspiration both for current and future physics teachers. They are synoptically presented in an online Collection of Physics Experiments (fyzikalnipokusy.cz/en).

Time series of monthly mean Collm mesosphere/lower thermosphere winds 1979 - 2008 are analyses with respect to a possible correlation with North Atlantic Oscillation (NAO) and Southern Oscillation (SO) indices. There is a positive correlation with both indices until the middle 1990s, but later the correlation decreases or even reverses. Owing to the coupling of the SO with the NAO the change of correlation occurs broadly at the same time. The change of correlation is probably connected with changes of the middle atmosphere mean dynamics. / Zeitreihen von Monatsmittelwerten des Windes in der Mesosphäre/unteren Thermosphäre über Collm werden auf mögliche Korrelationen mit der Nordatlantischen Oszillation (NAO) und der Südlichen Oszillation (SO) hin untersucht. Während eine positive Korrelation bis in die 1990er Jahre existiert, schwächt sich diese in der Folge ab und kehrt sich teilweise um. Da NAO und SO gekoppelt sind, erfolgen diese Änderungen etwa zur selben Zeit. Die Änderung der Kopplung steht wahrscheinlich in Verbindung mit einer generellen Änderung der Dynamik der mittleren Atmosphäre.

Compared to single-mode VCSELs, multimode VCSELs have not received much attention in models and characterizations for functional parameters, despite making up the majority of commercially available VCSELs [1]. In particular, the extraction of the linewidth enhancement factor for multimode VCSELs has been overlooked, likely due to difficulties in measurement. Additionally, multimode models for VCSELs have, until recently, omitted spectral characteristics such as linewidth [2]. This is the first work to report a measured linewidth enhancement factor value (lower bound) for a multimode VCSEL. A characterization for the functional parameters of a red multimode vertical-cavity surface-emitting laser (VCSEL) is shown herein. The extracted values form a complete working set of parameters for the laser rate equations. The techniques employed for extracting values include frequency responses, power versus current fittings, and optical spectral measurements. From the frequency responses at various bias currents, the relaxation oscillation frequency and damping factor are found. The power versus current curve is fitted to find parameters including the modal spontaneous emission rate and carrier density at threshold. The spectral measurements are used for evaluating the linewidth enhancement factor (LEF) also known as the alpha factor or Henry factor. These 5 methods have been applied previously to characterizing single-mode VCSELs [3]–[5]. The experimentally extracted parameters herein are important for creating accurate models and simulations for multimode VCSELs. Improved multimode VCSEL models are necessary for improving optical communication, especially for short-range optical interconnects [2]. The measured parameters for the characterized VCSEL are comparable to similar single-mode VCSELs characterized in other works. This is promising because multi-mode VCSELs have higher output power than their single-mode counterparts, thus these results may aid in improving short-range optical interconnects.

Recently, some new technologies (e.g., downsizing, turbocharging) have been widely used in spark-ignition (SI) engines to achieve higher efficiencies and less emissions. However, the improved power density and in-cylinder pressure promote more engine knock, causing violent pressure oscillations and threatening engine integrity. Therefore, it is imperative to study engine knocking combustion more than ever; In-depth understandings of knock mechanism and characteristics are of utmost importance for controlling knock. With this emphasis, this thesis implements systematic studies to bridge the gap between knocking combustion characteristics and knock suppressing strategies. To investigate knock with optical and laser diagnostics, an optical compression-ignition (CI) engine was modified to operate under SI mode. A home-made metal liner with multiple spark plugs was used to trigger more controllable knock events via different spark strategies. Up to six pressure sensors were installed to collect the pressure signals from different sides. Next, the relationships between in-cylinder pressure, knock intensity, pressure fluctuation, heat release, and measurement location are analyzed to study the knock mechanism, influential factors, and measurement methods. The findings indicate a trade-off between the mass fraction and temperature of end-gas. The effects of compression ratio and fuel octane number are also explored. Moreover, the multichannel pressure monitoring is synchronized with high-speed imaging to investigate the flame propagation and knock development processes regarding the different spark strategies. The results give insights into the in-cylinder temperature inhomogeneity and how it affects the spatial distribution of auto-ignition sites. Furthermore, a new method is proposed to detect the local pressure fluctuations by setting a series of virtual flame monitors instead of pressure sensors. The results validate that this method provides a convenient and reliable way to study knock oscillations. Finally, this study presents a hydraulically actuated VCR (variable compression ratio) piston design to address knock challenges. The numerical simulation results show this VCR piston has a good adaptability and could help achieve high engine efficiencies, while keeping reasonable peak pressure to avoid heavy knock at high loads. However, more analysis work still needs to be implemented on its practical applications, e.g., the thermal stress and frictions under different operating conditions.

<p>Most of the heavy-duty machines, in particular construction vehicles, employ hydraulically actuated functions that are used to perform multiple tasks with elevated power requirements. Such high-power demand motivates the Original Equipment Manufacturers (OEMs) to minimize the costs associated with energy consumption through the design of such hydraulic systems. The human-machine interaction (human factors) and the efficiency of the hydraulic control system are considered key elements towards a successful design. The interaction between the operator and the machine considerably affects the performance of construction machines. In order to maintain high levels of productivity, the operators require comfort and effortless controllability of the multiple hydraulic functions. The comfort requirement can include limited shocks and oscillations while operating the machines (while driving and controlling the implement motion), cabin accessories (AC, radio, cameras, etc.) and accessibility to the instrumentation. Besides, the operators have to control multiple functions simultaneously in an efficient manner while maintaining high levels of productivity. Consequently, the operators require smooth controllability of such functions. Such demand can largely affect the efficiency of the expected hydraulic control system and can induce additional costs and complexity. The OEMs are therefore forced to find a balance between efficiency and operators’ requirements to be competitive on the market. As a result, the currently adopted hydraulic architectures rely on purely hydraulic components to ensure robustness and functionality of the hydraulic functions at the expenses of limited performance and high-power consumption. In this dissertation, electro-hydraulic components are employed to induce improvements of the commercially available solutions while still complying with the operators’ demands and energy efficiency. To this end, this work tackles the weaknesses of traditional hydraulic architectures and it proposes alternative solutions to overcome their limitations. Two full-size wheel loaders are used to study the behavior of the existing system and later to implement the proposed variations. First, the development of an innovative ride control feature to improve the operators’ comfort is presented. Experimental results show the proposed strategy having better comfort performances compared to the purely hydraulic solution. Besides, the electro-hydraulic alternative does not demand the costly additional components the commercial solution instead requires. Second, this work faces the concern for efficiency of the present hydraulic architecture. The most diffused hydraulic system for the studied category of construction machines, commonly known as Load Sensing (LS), is sized to work most efficiently for elevated power conditions. During this work, an electronically controlled hydraulic supply unit and a flow-sharing method are used to reduce the hydraulic power consumption in the regions where the traditional LS system is less efficient. With a simple and cost-effective modification, the presented control strategy can induce an efficiency improvement over a wide range of operating conditions. Third, this dissertation proposes an operator-assistance feature to potentially increase the overall productivity and reduce the operator’s stress. An online estimation algorithm was developed to predict the payload weight of the transported material inside the bucket and the pushing forces during a typical loading cycle. The calculated payload mass provides an estimate of the user’s productivity level and it is extremely advantageous when the loaded material should reach a certain target weight. The developed estimation algorithm can also support an optimized autonomous excavation process, which can progressively limit the operator-machine interaction.</p>

Zeitreihen von Monatsmittelwerten des Windes in der Mesosphäre/unteren Thermosphäre über Collm werden auf mögliche Korrelationen mit der Nordatlantischen Oszillation (NAO) und der Südlichen Oszillation (SO) hin untersucht. Während eine positive Korrelation bis in die 1990er Jahre existiert, schwächt sich diese in der Folge ab und kehrt sich teilweise um. Da NAO und SO gekoppelt sind, erfolgen diese Änderungen etwa zur selben Zeit. Die Änderung der Kopplung steht wahrscheinlich in Verbindung mit einer generellen Änderung der Dynamik der mittleren Atmosphäre.

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