Crystallization and preliminary X-ray analysis of neoagarobiose hydrolase from Saccharophagus degradans 2-40

Many agarolytic bacteria degrade agar polysaccharide into the disaccharide unit neoagarobiose [O-3,6-anhydro-α-L-galactopyranosyl-(1→3)-D-galactose] using various β-agarases. Neoagarobiose hydrolase is an enzyme that acts on the α-1,3 linkage in neoagarobiose to yield D-galactose and 3,6-anhydro-L-galactose. This activity is essential in both the metabolism of agar by agarolytic bacteria and the production of fermentable sugars from agar biomass for bioenergy production. Neoagarobiose hydrolase from the marine bacterium Saccharophagus degradans 2-40 was overexpressed in Escherichia coli and crystallized in the monoclinic space group C2, with unit-cell parameters a = 129.83, b = 76.81, c = 90.11 Å, β = 101.86°. The crystals diffracted to 1.98 Å resolution and possibly contains two molecules in the asymmetric unit

Predicting retention among application users with online ensemble learning models

Most service providing companies consider customer retention as the most important asset for improving profitability. Even for services and applications without paying customers the retention of users is essential, as more advertisement impressions are generated and the reputation of the brand strengthens. The ability to foresee which users will be retained and which are likely to churn is therefore highly valuable for any expanding company. Forza Football is one of the world’s most popular football live score applications with millions of weekly active users. New data of application activity among users arrives sequentially in the form of a stream. To predict future user activities, a model must be able to adapt to seasonal drifts in activity. The model must furthermore remain scalable and time efficient when analyzing new instance arrivals, given that the size of each instance is several million observations. Motivated by these requirements, this thesis approaches a data stream of previous user activities to predict the activities of upcoming instances. State-of-the-art ensemble classification methods are acclimatized to an online learning environment to incorporate both historical and current information in a computationally low-cost manner. Various predictive models are proposed which obtains accurate predictions that are efficient in terms of storage and computational time. The models are stable in detecting and adjusting to concept drifts

Pd-nanoalloys for hydrogen sensing: Multiscale modeling of thermodynamic and optical properties

Hydrogen sensing based on Pd nanoalloys has shown great promise in the past decades and could potentially be part of a solution that enables a safe future hydrogen economy. There are, however, remaining challenges related to, e.g., long-term stability and a need for further optimization of these systems. To efficiently span the possible combinations of alloyants, composition, and nanostructure geometry, computational methods are invaluable. This thesis focuses on two aspects of sensor optimization: surface segregation and hydrogen sensitivity, using multi-scale modeling approaches.Alloying with metals such as Au and Cu is necessary to overcome issues related to hysteresis and CO poisoning. At the same time, it introduces additional difficulties related to the chemical order such as surface segregation, which is directly related to long-term stability. In this thesis, the surface composition of Pd alloyed with Au or Cu is studied as a function of H2 pressure using Monte Carlo simulations based on cluster expansions parametrized against ab-initio calculations. For Pd-Au, an increased H2 concentration abruptly switches the surface from Au to Pd dominant. For Pd-Cu, the change with H2 concentration is much more gradual\ua0with non-monotonic tendencies, with an overall surplus of Pd in most conditions.The sensing principle is based on the shift in optical response upon H absorption. The magnitude of the sensor readout at a certain H2 pressure depends on nanoparticle geometry and alloy composition. In this thesis, extinction spectra are calculated for Pd-Au-H nanodisks using electrodynamic simulations and the corresponding H sensitivity is analyzed. It is found that the H sensitivity depends on the nanodisk diameter, mainly due to the interplay between a localized surface plasmon and an interband transition which becomes more apparent for smaller nanodisks

Analyses of EMC- & Grid-connected Filters in an Electric Power-train

Abstract Epiroc have had a need to investigate the EMC and LCL-filters that are currently placed and operating in a lot of their vehicles. They have questioned whether or not their currently used capacitor and inductor-based filters are working adequately in filtering unwanted noise or if there could be a risk of wear to the system with prolonged operation and if any improvements could be made. This thesis has, with the help of Epiroc and extensive research, examined these questions in detail by conducting measurements on a drill rig vehicle at Epiroc’s facilities in Örebro. The thesis dives into areas such as Electromagnetic interference, electrical noise prevention methods and signal processing. The measurements indicated that both of the filters work and do filter unwanted noise, differences can be seen in the overall noise level. There are however some ideas outlined in this thesis that potentially could help increase the noise suppression of the filters

Evaluation of the Concentration and Enantiomeric Purity of Selected Free Amino Acids in Fermented Malt Beverages (Beers)

Even though amino acids are important trace components in the brewing of beers, they have not been extensively evaluated in these beverages. Studies involving the enantiomeric composition of these amino acids are even less prevalent. A brief summary of the brewing process for malt beverages is given. The total concentration and enantiomeric composition of three amino acids (leucine, phenylalanine, and proline) were determined in 25 different beers. Proline tended to have the highest average absolute concentration and the lowest percentage of the D-enantiomer in most samples. In some cases the relative amounts of D-phenylalanine and D-leucine exceeded 10% of the individual amino acids. The enantiomeric composition of the amino acids in different beer samples did not vary as extensively as the absolute concentrations. The reason for the concentration differences between proline and the other amino acids is discussed. A knowledge of amino acid concentrations and enantiomeric compositions appears to be useful in characterizing specific beers and brewing processes

Naturvetenskaplig utbildning för hållbar utveckling? : en longitudinell studie av hur studenter på grundskollärarprogrammet utvecklar för miljöundervisning relevanta kunskaper i naturkunskap

Swedish with summary in EnglishIn this study the concept of sustainable development is discussed and what contribution a science teacher can make. Some scientific concepts relevant for environmental education are defined. To understand the concepts mean to be able to explain phenomena and to be able to use the conceptions as tools when discussing complex environmental issues. The ability to discuss complex issues is discussed. The aims of study were to study how student teachers in a programme oriented towards science for the first seven years in school develop scientific understanding and ability to discuss complex issues. Another aim was to relate the students’ experience of their own learning and the teaching to what they learn. Data were collected mainly by questionnaires and interviews. The whole student group answered questionnaires three times and about 15 students were interviewed three times. In the questionnaires the students answered questions about some ecological concepts. Their knowledge about causes and consequences of two global environmental issues were tested. They drew concept maps illustrating how complex they look upon an issue. In the interviews the students were asked about the teaching and their learning. They discussed a complex issue dealing with weather or not it is ethical to use surplus heat from a crematorium in the far heating system. The teachers were asked about the courses and about the students’ learning. Several learning projects could be identified. All the students had the intention to become teachers for young pupils. Parallel to this they wanted to pass the exams and to understand. Depending on the learning projects the students interpreted both the questions they were asked and the relevance of the contents in the science courses. This could explain why a majority of the students did not develop understanding of the investigated concepts. Most students did not use much science as a tool for decision-making when discussing the complex issue. There was a discrepancy between the students' learning projects and the teachers' learning projects for the students. When the students experienced this gap they went into rote learning to pass the exams. Those students whose learning project was to understand developed a better scientific understanding

High-performance Liquid Chromatographic and Capillary Electrophoretic Enantioseparation of Plant Growth Regulators and Related Indole Compounds using Macrocyclic Antibiotics as Chiral Selectors

Enantioseparation of plant growth regulators, such as 3-(3-indolyl)-butyric acid, abscisic acid and structurally related molecules including a variety of substituted tryptophan compounds, has been achieved by HPLC and/or CE. The covalently bonded macrocyclic antibiotics, teicoplanin, ristocetin A and vancomycin, were used as chiral stationary phases (CSPs) in HPLC. Most of the racemates were baseline resolved in the reversed-phase mode (EtOH-H2O) using the teicoplanin CSP. The chiral recognition mechanism is discussed in regard to the structure of the analytes. In CE, the three aforementioned macrocyclic antibiotics were used as chiral additives in a phosphate run buffer. The effect of pH and the concentration of the organic modifiers were considered. The results obtained by HPLC and CE were compared. © 2001 Elsevier Science B.V

Varietal Differences in the Total and Enantiomeric Composition of Theanine in Tea

Theanine is the main amino acid component in tea. It usually constitutes between 1 and 2% of the dry weight of the tea leaves. It is as prevalent in tea as all other free amino acids combined. Both enantiomers of theanine were found to have a similar sweet taste, with little or no aftertaste. It was found that black and half-green teas (except for Formosa Oolong) contained as much, or more, theanine as green teas. No correlation was found between the absolute concentration of theanine in tea and its enantiomeric composition. An inverse correlation was found between certain grades of tea (e.g., pekoe, Flowery Orange Pekoe, etc.) and the percent of D-theanine present. This could provide the basis for a reproducible, scientific method to grade and/or evaluate teas. Theanine slowly racemizes in aqueous solution. It also undergoes hydrolysis, particularly at basic pH values. By monitoring these processes, information may be gleaned on the production, storage, handling, and shipping of tea and tea products

Highly Enantioselective HPLC Separations using the Covalently Bonded Macrocyclic Antibiotic, Ristocetin A, Chiral Stationary Phase

The macrocyclic glycopeptide, ristocetin A, was covalently bonded to a silica gel support and evaluated as a liquid chromatographic (LC) chiral stationary phase (CSP). Over 230 racemates were resolved in either the reversed-phase mode, the normal-phase mode, or the polar-organic mode. The retention behavior and selectivity of this CSP were examined in each mode. Optimization of separations on this column is discussed. The ristocetin A CSP appeared to be complimentary to other glycopeptide CSPs (i.e., vancomycin and teicoplanin). Column stability was excellent. The CSP was not irreversibly altered when going from one mobile phase mode to another