This thesis deals with the current methods available for X-ray structure determination and with the crystal and molecular structure determination of five compounds using these methods. The five compounds are 1) [ 2,3-Bis (dimethylarsino)- 1, 1, 1,4, 4, 4-hexaf luorobut-2-ene-As,As]tricarbonyldiiodotungsten(II),Me₂AsC (CF₃):C (CF₃) AsMe₂WI₂(CO)₃ 2) Dimethylammonium trichlorotris(dimethylsulphoxide}-ruthenate(II) , [ ( (CE₃)₂ SQ)₃ RuCl₃ ]⁻ [ (CH₃)₂ NH ₂]+ 3) Dichlorotetrakis{dimethylsulphoxide)ruthenium(II), (Me₂SO)₄fRuCl₂ 4) 1,3,7-Triraethyl-2,6-dioxypuriae hydrochloride dihydrate (caffeine hydrochloride dihydrate), CH₁₁C1N₄0₂-2H₂0 .5) 1-Acetyl-3-benzamido-2-keto-4- (2,3, 4, 6-tetra-O-acetyl-β-D-glucopyranosyloxy)-Δ³-pyrroline, C ₂₇H₃₀N₂O₁₃ The structures of compounds 1), 2), and 3) were determined by Patterson syntheses, compound 4) by centrosymmetric direct methods and compound 5) by non-centrosymmetric direct methods. All structures were then refined using full-matrix least-sguares procedures. The relevant crystal data for all five compounds can be found in Table A In the tungsten compound [1) the tungsten atom is seven-coordinate with a distorted capped octahedral environment, the capping group being a carbonyl. The capped face consists of the two remaining carbonyl groups and one of the arsenic atoms from the bidentate ligand. The uncapped face contains the two iodine atoms and the remaining arsenic. Crystal data for the five compounds examined atom. The structure of the ruthenium compound [ 2) ] consists of two crystallcgraphically non-equivalent anions in the asymmetric unit linked by hydrogen bonding via dimethylammonium cations. The coordination geometry about the structurally similar anions is essentially that of an octahedron with the DHSO ligands being bonded to Ru via the sulphur atoms. The co-ordination geometry about the ruthenium atom for compound 3) is essentially octahedral with cis chlorine atoms; Of the four DMSO ligands three are S-bonded and one is O-bonded, the O-bonded ligand being trans to a S-bonded ligand. For caffeine hydrochloride [ 4) ] the fused ring system is essentially planar and protonated at the 9-positioh. The crystal contains two types of hydrogen bonding involving 0-H...C1 and N-H...0 interactions. The structure of compound 5) consists of a pyranose ring in the chair conformation with the four 0-acetyl substituents in equatorial positions; the pyranose ring is connected to a planar pyrroline ring via a β-oxygen bridge. / Science, Faculty of / Chemistry, Department of / Graduate

Tesis para optar al grado de Magíster en Lingüística mención Lengua Inglesa / The main purpose of the present study is to compare and determine the degree of coherence between the non-official national second grade EFL program published by the Ministry of Education and the respective EFL textbook (Bounce 2) used by students at state schools in Chile. Through the application of Bloom‟s revised Taxonomy (Anderson & Krathwohl, 2001) and the General Model of Hierarchical Complexity (Commons, Trudeau, Stein, Richards, & Krause, 1998; Commons, 2007), learning task instructions were analyzed and tasks were classified in terms of their levels of complexity. A mixed methodological design has been adopted to provide an exploratory account of patterns observed. The classification of tasks made in the EFL textbook and the EFL program for second graders revealed a mismatch between their tasks‟ levels of cognitive complexity. In addition, the interpretation of results also places both documents at an early childhood level of hierarchical complexity, which does not correspond to second grade learners‟ developmental stage.

No description available.

Call number: LD2668 .T4 1951 E38 / Master of Science

The ROSAT spacecraft is due for launch in June 1990. On board will be an X-Ray Telescope (XRT) and an XUV Wide Field Camera (WFC). The XRT will perform the first ever imaging all sky survey in the 0.1 keV- 2.0 keV wave-band. This will be complemented by the first all sky survey in the 0.062 keV - 0.21 keV wave-band using the WFC. A scientific simulator has been developed to assist the WFC mission in the following areas: 1. Production of representative telemetry to develop and test the ROSAT WFC ground system software. 2. Determination of optimum parameters for several WFC firmware and hardware features. 3. Evaluation of background radiation effects on operational and astrophysical aspects of the WFC mission. The modelling and simulation of the performance aspects of the WFC telescope and its interaction with the predicted environment is described here. The complete model has been implemented as a user orientated software package and can be run to produce scientific telemetry and other simulated output that interface with the ROSAT WFC ground system software. The results of the simulator provide essential foresight into the following: The efficacy of image analysis software. The efficiency of in-orbit WFC low energy (50 keV) electron rejection. Prediction of all sky exposure coverage, the background environment, and minimum source sensitivity.

X-Ray emission techniques have been developed for the analysis of unusual and difficult samples that cannot be analyzed by conventional analytical techniques. Three X-ray techniques have been investigated, including radioisotope-induced X-ray fluorescence (RXRF), proton-induced X-ray emission (PIXE) and high resolution PIXE. Low flux radioisotope X-ray sources have been used to non-destructively characterize the elements present in photographic papers and emulsions. The information obtained has proven valuable for cataloging and preserving photographic prints of historical significance. Radioisotope X-ray sources have also been used in the development of low-cost, portable instrumentation useful for quantitating a variety of toxicological samples, including urine and feces samples to determine the elimination rates of X-ray contrast media containing dysprosium. The PIXE technique has been applied to the analysis of forensic samples, including bullet lead, tissue fragments and thin metal coatings, and has been compared with other non-destructive methods of analysis. Sample preparation techniques and analytical procedures have been developed for general, thin target, quantitative PIXE analysis. These procedures were applied to the analysis of five NBS standard reference materials, and to the analysis of deep-sea ferromanganese nodules. A high resolution (2 eV) PIXE system has been developed to aid in the deconvolution of overlapping X-ray peaks encountered in conventional PIXE spectra. This system has been applied to the measurement of chemical shifts in the X-ray emisson spectra of transition metal compounds.

No description available.

published_or_final_version / abstract / toc / Physics / Master / Master of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

No description available.