http://rudar.ruc.dk/handle/1800/33 2012-02-07T05:27:01Z http://rudar.ruc.dk/handle/1800/2012 Title: Netstøtte til undervisning i naturvidenskab - Hvad mener de studerende om netstøtte til kurser med laboratoriearbejde og regneopgaver Authors: Josephsen, Jens Abstract: Artiklen handler om de muligheder, der ligger i anvendelsen af nogle forskelligartede EDB-baserede hjælpemidler i kursusundervisning inden for naturvidenskab. Disse værktøjer er især karakteriserede derved, at de giver en respons (regner noget ud, sammenligner, finder en oplysning, giver et svar) på den studerendes input På baggrund af erfaringer med en udviklet praksis i et indledende kemikursus ved RUC beskrives nogle anvendte IKT-ressourcer, som på forskellig måde indgår i dialogen mellem lærer og studerende og mellem de studerende indbyrdes og giver feedback til den studerendes læreprocesser. Der anvendes bl.a. "skræddersyede" interaktive programmer der beskæftiger sig med kemiske reaktioner og som kan simulere laboratoriearbejde. Via sit design giver et sådant program samme feedback på en beskrevet kemisk operation, som de studerende kender fra laboratoriet og kan derved på en måde udvide den dyre laboratorietid. 2006-01-01T00:00:00Z http://rudar.ruc.dk/handle/1800/1955 Title: Photostability of the solar cell dye sensitizer N719: electrochemical synthesis of some arylsulfones and aminobenzoquinones Authors: Nour-Mohammadi, Farahnaz Abstract: The photostability of the sensitizer dye [Ru(dcbpyH)2(NCS)2] (Bu4N)2 (referred to as N719) was investigated in a simple model system instead of a complete nanocrystaline dye sensitized titanium dioxide solar cells (nc-DSSC). The applied model system consisted of N719 dyed titanium dioxide nanoparticles, suspended in a cuvette containing acetonitrile as the solvent which were illuminated with 532/525 nm monochromatic light of different light intensity. Under these experimental conditions and in the absence of any redox couple as a regenerative electron donor, the number of mole of photodegradation products: [RuL2(CN)2], [RuL2(NCS)(CN)] and [RuL2(NCS)(ACN)] increased almost linearly as a function of increasing mole of absorbed photons. The total quantum yields of these degradation products, Φdeg showed light intensity dependence, being higher at low light intensities and smaller at higher intensities. This light intensity dependency of the quantum yield was attributed to the back electron transfer reaction rate between the titanium dioxide conduction band electrons and the oxidized dye cation. Photoinduced absorption spectroscopy (PIA) was used to measure the back electron transfer reaction rate, kback at the same light intensities as used in the model experiments. The PIA measurements showed that kback increased with increasing light intensities. By applying the equation kdeg = Φdeg × kback to the experimentally obtained total quantum yields and back electron transfer rates it was possible to calculate an average value for the oxidative degradation rate of the N719 dye attached to the TiO2 nanoparticles, kdeg = 4 × 10–2 s–1 . Heating and illumination of the model system in the presence of 4-tert-butylpyridine (4-TBP), the commonly used additive in nc-DSSC, revealed the possible involvement of the dye in a substitution reaction with 4-TBP with the formation of the substitution product [Ru(dcbpyH)2(NCS)(4-TBP)] –, Bu4N+. It was also found that the amount of the additive substituted product formed under illumination increases upon adsorption of the dye on TiO2 nanoparticles. Quantum yield measurements of the substitution product under different experimental conditions directed us to conclude that the main part of the substitution product is formed through the oxidized state of the dye, S+. The quantum yield of the substitution reaction initiated from the dye oxidized state was φ+ sub (TiO2) = 7.1 × 10–5 . Based on this value the rate of the hotosubstitution reaction was calculated to be k+ sub(TiO2) = 0.07 M–1s–1. The influence of the photosubstitution reaction on the N719 dye lifetime was discussed based on the k+ sub(TiO2 ) value and the literature values of the dye regeneration reaction, kreg between the oxidized dye, S+ and iodide. 2005-01-01T00:00:00Z http://rudar.ruc.dk/handle/1800/1646 Title: Responses of marine plankton to pollutant stress: integrated community studies of structure and function Authors: Hjorth, Morten Abstract: The thesis analyses effects of pollutants on natural plankton communities on the basis of three independent mesocosm experiments and a series of laboratory experiments performed in Denmark and Greenland. The work focus on integrating functional and structural measures of community responses to reveal indirect effects and co-effects with the abiotic environment on three trophic levels, namely bacteria, phytoplankton and zooplankton. The role of mesocosms and community studies in risk assessment and their usefulness in integrating ecological knowledge into ecotoxicology is discussed with examples of work done on natural communities of phytoplankton and zooplankton. Abiotic conditions such as UV light and nutrient concentrations are shown to influence pollutant effects. 2005-10-01T00:00:00Z http://rudar.ruc.dk/handle/1800/1174 Title: Chemometrics as a tool to analyse complex chemical mixtures: environmental forensics and fate of oil spills Authors: Christensen, Jan H. Abstract: Chemical characterisation of contaminant mixtures is important for environmental forensics and risk assessment. The great challenge in future research lies in developing suitable, rapid, reliable and objective methods for analysis of the composition of complex chemical mixtures. This thesis describes the development of such methods for assessing the identity (chemical fingerprinting) and fate (e.g. biodegradation) of petroleum hydrocarbon mixtures. The methods comply with the general concept that suitable methods must be rapid and inexpensive, objective with limited human intervention and at the same time must consider a substantial fraction of compounds in the complex mixture. A combination of a) limited sample preparation, b) rapid chemical screening analysis, c) fast and semi-automatic pre-processing, d) comprehensive multivariate statistical data analysis and e) objective data evaluation was used throughout the thesis. 2005-01-01T00:00:00Z