24 resultados para 0399 Other Chemical Sciences


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Islam, Development, Ecology,

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Radiometric determination methods, such as alpha spectrometry require long counting times when low activities are to be determined. Mass spectrometric techniques as Inductively Coupled Plasma Mass Spectrometry (ICP-MS), Thermal Ionisation Mass Spectrometry (TIMS) and Accelerator Mass Spectrometry (AMS) have shown several advantages compared to traditional methods when measuring long-lived radionuclides. Mass spectrometric methods for determination of very low concentrations of elemental isotopes, and thereby isotopic ratios, have been developed using a variety of ion sources. Although primarily applied to the determination of the lighter stable element isotopes and radioactive isotopes in geological studies, the techniques can equally well be applied to the measurement of activity concentrations of long-lived low-level radionuclides in various samples using “isotope dilution” methods such as those applied in inductively coupled plasma mass spectrometry (ICP-MS). Due to the low specific activity of long-lived radionuclides, many of these are more conveniently detected using mass spectrometric techniques. Mass spectrometry also enables the individual determination of Pu-239 and Pu-240, which cannot be obtained by alpha spectrometry. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) are rapidly growing techniques for the ultra-trace analytical determination of stable and long-lived isotopes and have a wide potential within environmental science, including ecosystem tracers and radio ecological studies. Such instrumentation, of course needs good radiochemical separation, to give best performance. The objectives of the project is to identify current needs and problems within low-level determination of long-lived radioisotopes by ICP-MS, to perform intercalibration and development and improvement of ICP-MS methods for the measurement of radionuclides and isotope ratios and to develop new methods based on modified separation chemistry applied to new auxiliary equipment.

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This thesis is primarily concerned with the enzyme- catalysed synthesis of sulfoxides using reductase and dioxygenase enzymes. Chapter 1 provides an introduction to the topic of redox chemistry with particular emphasis on the application of reductase and dioxygenase enzymes in organosulfur chemistry. Earlier literature methods for the production of enantiopure sulfoxides are reviewed. A brief discussion of the methods used for the determination of enantiomeric excess and absolute configuration is provided. Chapter 2 contains results obtained using a range of whole-cell bacteria each using a dimethyl sulfoxide reductase enzyme. The synthesis of a series of racemic sulfoxides and the development of appropriate CSPHPLC analytical methods is discussed. Kinetic resolutions of a series of sulfoxides have been achieved. Chapter 3 contains a presentation of results using dioxygenase enzymes as biocatalysts for the asymmetric sulfoxidation of dialkyl sulfoxides including thioacetal sulfoxides. A new range of monosulfoxides, cis-dihydrodiols and cis- dihydrodiol sulfoxides have been isolated in enantiopure form. Chapter 4 is focussed on the application of chiral sulfoxides in synthesis. A new chemoenzymatic route to diol sulfoxide enantiomers and the derived enantiopure phenols and catechols is discussed. The application of chemically synthesised sulfoxide enantiomers in the production of hydroxy sulfoxides is reported. Chapter 5 provides a full experimental section where the synthesis of sulfides and racemic sulfoxides is included. The methods used in the isolation and characterisation of bioproducts from the biotransformation are discussed and full experimental details given.

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A simple method for absolute frequency measurements of molecular transitions in the mid-infrared region is reported. The method is based on a cw singly-resonant optical parametric oscillator (SRO), which is tunable from 3.2 to 3.45 µm. The mid- infrared frequency of the SRO is referenced to an optical frequency comb through its pump and signal beams. Sub-Doppler spectroscopy and absolute frequency measurement of the P(7) transition of the ν3 band of CH4 are demonstrated.

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This paper describes the cost-benefit analysis of digital long-term preservation (LTP) that was carried out in the context of the Finnish National Digital Library Project (NDL) in 2010. The analysis was based on the assumption that as many as 200 archives, libraries, and museums will share an LTP system. The term ‘system’ shall be understood as encompassing not only information technology, but also human resources, organizational structures, policies and funding mechanisms. The cost analysis shows that an LTP system will incur, over the first 12 years, cumulative costs of €42 million, i.e. an average of €3.5 million per annum. Human resources and investments in information technology are the major cost factors. After the initial stages, the analysis predicts annual costs of circa €4 million. The analysis compared scenarios with and without a shared LTP system. The results indicate that a shared system will have remarkable benefits. At the development and implementation stages, a shared system shows an advantage of €30 million against the alternative scenario consisting of five independent LTP solutions. During the later stages, the advantage is estimated at €10 million per annum. The cumulative cost benefit over the first 12 years would amount to circa €100 million.