High Forest or Wood Pasture: A model of Large Herbivores' impact on European Lowland Vegetation

Natural forest dynamics is a foundational topic of forest science. A new Wood Pasture hypothesis considering large herbivore as driving force in forest ecosystem is now challenging the traditional High Forest hypothesis, in which vegetation is regarded as main driving force. In this study, a model-based approach is applied to investigate differences between these two hypotheses and the determine factors in the system. A theoretical landscape of 1 km²formed by 100*100 cells is set up with 100 vegetation patches and free moving herbivores on. Our null hypothesis that herbivores make no difference in vegetation dynamics especially at canopy level is rejected. It is found that synchronization of herbivore behaviors is the most influencing factor of how a landscape might be shaped. It is also found that landscape could be a mosaic of both high forest and wood pasture depends on large herbivore’s herd size

Factors affecting the microstructure of porous ceramics

In this study, porous ceramics were produced by using two methods: the polymeric sponge and foam method. Astudy of the effect of viscosity on the characteristics of the final product produced using the polymeric sponge method revealed that the microstructure of porous ceramics is highly affected by the viscosity of the slurry. The optimal ratio between porosity and the strength of the porous material was achieved by subsequently repeating the immersing and drying processes. Astudy of the porous material obtained using the foam method revealed that the pore size and foam volume can be controlled by varying the amounts of anhydride and thermal blowing agent. The problem related to foam collapsing was solved by using a thermal blowing agent. The microstructure of the samples was characterized by SEM

Utveckling av en energieffektiv luftningsstrategi vid Käppalaverket, Lidingö : Development of an energy-effective aeration strategy at Käppala WWTP, Lidingö

Detta examensarbete utreder möjligheterna att utveckla en energieffektiv luftningsstrategi i en aktivslamprocess. Arbetet innehåller först en litteraturstudie där forskningsläget gås igenom. Därefter följer en optimeringsstudie i Matlab, en simuleringsstudie i en förenklad variant av Benchmark Simulation Model No 1 (BSM1) och en redogörelse för ett fullskaleförsök vid Käppalaverket.    Resultaten från optimeringsstudien visar att, under vissa förutsättningar, är ett konstant luftflöde energioptimalt. Simuleringsstudierna visar att en minskning av energiförbrukningen på upp till 16%  kan uppnås, då luftflödet hålls konstant, jämfört med att hålla ett konstant ammoniumbörvärde. Preliminära resultat från fullskaleförsöken indikerar att ett konstant luftflöde kan minska luftförbrukningen men en längre utvärdering bör genomföras för att få mer tillförlitliga resultat. Slutsatsen från detta arbete är att den utvecklade metodiken kan vara intressanta alternativ till en överordnad reglering av ammoniumkoncentrationen och bör därför studeras vidare

Reduction of free fatty acids in waste oil for biodiesel production by glycerolysis: investigation and optimization of process parameters

Influence of the process parameters for the industrially relevant reaction of free fatty acid (FFA) with glycerol is investigated. Furthermore, several drying techniques are investigated and a novel method is suggested that can provide more realistic experimental conditions. Silica as an absorbent is found to be a more suitable method for water removal than distillation or carrier gas. Using response surface methodology, important parameters are identified and optimal conditions found. Empirical correlation is developed to account for the most important parameters. Both oil:glycerol ratio and temperature have optimal values for which the highest conversion can be achieved. Interestingly, the highest conversion can be obtained at 220°C; above this temperature the conversion decreases. It is found that the influence of oil:glycerol ratio also exhibits anomalous behavior, where conversion is constant and decreases above a certain value. At optimal conditions, the FFA is reduced to 1.6% from the initial 8.6%

Nanocomposite permanent magnetic materials Nd-Fe-B type: The influence of nanocomposite on magnetic properties

The influence on the magnetic properties of nanocristalline ribbons and powders has character of microstructure, between others – the grain size volume of hard and soft magnetic phases and their distribution. Magnetic properties of ribbons and powders depend mainly on their chemical composition and parameters of their heat treatment [1]. Technology of magnets from nanocristalline ribbon consists of the following process: preparing the Nd-Fe- B alloy, preparing the ribbon, powdering of the ribbon, heat treatment of the powder and finally preparing the magnets. Nanocomposite permanent magnet materials based on Nd-Fe- B alloy with Nd low content are a new type of permanent magnetic material. The microstructure of this nanocomposite permanent magnet is composed of a mixture of magnetically soft and hard phases which provide so called exchange coupling effect

PMMA-Y2O3 (Eu3+) nanocomposites: Optical and mechanical properties

The results of a study related to the processing and characterization of poly(methyl methacrylate) (PMMA)-Y2O3 (Eu3+) nanocomposites are presented herein. The nanocomposite samples were prepared using a laboratory mixing molder with different contents of Eu-ion doped Y2O3 nanophosphor powder. The influence of particle content on the optical and dynamic mechanical properties of the nanocomposites was investigated. The intensity of the luminescence emission spectra increased as the nanophosphor content in the composite increased. The results of dynamic mechanical analysis revealed that the storage modulus, loss modulus and glass transition temperature (T-g) of the polymer composites increased with increasing content of the nanophosphor powder. The microhardness data also confirmed that the hardness number increased with nanoparticles concentration in the PMMA nanocomposites. The obtained results revealed a relatively linear relationship between T-g and the Vickers hardness

Healing efficiency of polystyrene electrospun nanofibers with Grubbs' catalyst in thermosetting composite

The study presents a novel method for the protection of Grubbs' catalyst, by incorporation in polystyrene fibres via electrospinning technique. Epoxy-glass fibre composite with embedded self-healing agents (polystyrene fibres with Grubbs' and microcapsules with dicyclopentadiene) was processed. Fibres retained pale purple colour during processing, revealing that fibres provided good protection of the catalyst from the amine hardener. The influence of self-healing agents' content and thermal treatment on self-healing efficiency was investigated. Fourier transform infrared spectroscopy revealed that a polydicyclopentadiene formed at the healed interface. Thermal analysis revealed that bleed' at the healing sites from different samples had similar concentration of polydicyclopentadiene, indicating that the same amount of the catalyst has been provided to dicyclopentadiene for polymerization. This finding lead to assumption that electrospun polymer fibres enabled good dispersion of the catalyst in the composites. The low energy impact tests of the samples showed a recovery of 90% after 24h at room temperature and up to 111% after repeated heating cycles