The studies presented in this thesis are in two areas. An investigation of aromatic nitrene molecules using EPR spectroscopy was undertaken. This revealed a general tendency for these molecules to exhibit two forms when trapped in a crystalline lattice. This is qualitatively interpreted as a perturbing effect of nitrogen evolved during generation from the azide. Single crystal experiments were made on 2,4,6-tribromophenyl nitrene, which exhibited an unusually large anisotropy in the zero field splitting, implying a bent structure. Temperature variation of several aromatic nitrene zero field splittings were made. The variation was interpreted as thermal averaging amongst states possessing different zero field parameters. The nature of these states however, could not be inferred. The variation is compared with similar studies. A computer program to least squares fit EPR angular data to a spin Hamiltonian has been written. This programme was used to obtain a description of the angularly dependent EPR data from an aromatic nitrene, and also for a radical species with a large hyperfine interaction. / Science, Faculty of / Chemistry, Department of / Graduate

Two phase transitions have been found in DEM(TCNQ)₂ at 400(3) K and at 442(6) K to 453(6) K using ESR and measurements of the microwave conductivity. These temperatures are less than the values of 415 K and 483 K previously obtained from temperature dependent Guinier measurements. Below 400(3) K two ESR lines, I and II are observed corresponding to the two stacks, B and A, in DEM(TCNQ)₂. Above 400(3) K and below 453(6) K only one line remains with the same g value as line I. The angular dependence of the g value was fitted to g[sub=‖]² = g[sub=⊥] ²cos2θ + g²sinθ and values of g[sub=⊥] = 2.003551(14) and g[sub=‖] = 2.00273015) were obtained. Between 298 K and 442(6) K the conductivity was that of a semiconductor with an exitation energy E[sub=0] = 0.385(52) e.v. The -4k[sub=⌐] phase transition is postulated at 447(9) K. The phase transition at 400(3) K is due to a transfer of spin density from stack A to stack B, and has no effect on the total spin susceptibility or on the conductivity to within the experimental error. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The work described herein falls into three major categories: synthesis of model glycolipids, NMR studies on'model glycolipid'micelles, and application of 2D-NMR spectroscopy in spectral assignment. Three synthetic routes, namely the glycosidation reaction, reductive amination reaction, and amide bond formation have been investigated in relation to their efficiency and convenience in coupling carbohydrates with aliphatic chains. The reaction of amide bond formation was found to be a superior method over the others for the preparation of long alkyl chain derivatives. ¹H-NMR spectroscopy has been utilized to study and detect the micelle formation by the model glycolipids. The studies described illustrate that the ¹H spin-lattice relaxation rate (R-₁) is well suited for the determination of critical micelle concentration providing it is sufficiently high. The contrasting behaviour of R-₁ of the anomeric proton (H-1) of n-octyl β-D-glucoside in relation to that of H-2 and w-CH₃ upon micellization, has been tentatively attributed to the conformational changes accompanying micelle formation. The observed upfield shift of the ¹³C resonances of the alkyl chain has been explained as being due to the increased proportion of trans conformers in the micellar state. The question of the downfield ¹³C shift observed for the sugar resonances has been discussed. Study of N-alkyllactobionamides with ¹H-NMR proved to be difficult due to their extremely low critical micelle concentrations. Application of 2D J-resolved spectroscopy and spin-echo correlated spectroscopy (SECSY) in spectral assignment of unprotected sugar derivatives has been demonstrated. Using above techniques, complete assignment of the sugar region of n-octyl β-D-glucoside and N-hexyllactobionamide has been achieved. / Science, Faculty of / Chemistry, Department of / Graduate

Nuclear magnetic resonance absorption and spin-lattice relaxation time measurements have been carried out on the tropolone salt of t-butylamine, (CH₃)₃CN⁺H₃Tr⁻ (Tr ⁻= tropolonate ion, C₇H₅0₂⁻), the choline salts, (CH₃)₃NCH₂CH₂OH. X⁻ (x⁻ = Cl⁻, Br , I , ClO₄ ⁻) and the trimethylamine-phosphorous penta-fluoride adduct, (CH₃)₃NPF₅, in order to study molecular motion and phase transitions in these systems in the solid state. Activation energies and rate parameters associated with the motional processes are reported. Proton magnetic resonance (pmr) absorption second moments and proton spin-lattice relaxation times in the Zeeman frame (T₁) in the temperature range 66K - 425K for the solid (CH₃)₃CNH₃Tr⁻ show that the molecule is rigid on the nmr timescale at the lowest temperature studied, while at higher temperatures rotation of methyls about their C₃ symmetry axes is found to set in first, followed by an additional composite motion involving reorientation of both the t-butyl group and the NH₃ group about the C-N bond. A proton study in the partially deuterated (-ND₃) analogue has enabled the relaxation effects of the latter two motions to be separated, and, by fitting the T₁, data for the two compounds to appropriate relaxation rate expressions, activational energy barriers for the abovementioned motional processes have been determined. It has also been suggested that the t-butyl group and the NH₃ group rotate independently about the C-N bond rather than as one unit. Proton spin-lattice relaxation time measurements in both the Zeeman and rotating frames of reference (T₁ and T₁[sub p]) for the four choline salts and second moments of the pmr absorption for the perchlorate have enabled the following motional processes to be identified: (i) rotation of the methyl groups at low temperatures followed successively by, (ii) the onset of motion of the NMe₃ moiety about the long chain C-N axis (denoted C₃), (iii) general reorientation of the whole choline cation, (iv) additional slow motion of the long chain (CH₂CH₂OH in the case of the chloride and bromide, and (v) diffusion of the choline ion in the case of the iodide and perchlorate. From a quantitative analysis of the and data, activation energies for the above types of motion are determined. A crystal-crystal phase transition known to occur at 353, 364 and 362K in the chloride, bromide and iodide, respectively, has been confirmed. A similar transition has been discovered in the perchlorate, and is found to occur at a much lower temperature (272K). Evidence has also been presented for a further crystal-crystal phase transition in choline iodide at 430K, at which point a "quenching" of the diffusional process is found in this structure. In the adduct (CH₃)₃NPF₅, studies of proton and fluorine nmr absorption spectra and measurements have shown that (i) at 4.2K the molecule is 'rigid1, (ii) C₃ reorientation of one of the methyls and reorientation of the PF₅ group about the P-N bond cause a ¹H and ¹⁹F nmr line narrowing, (iii) this is followed by the C₃ rotation of the other two methyl groups together with the rotation of the (CH₃)₃N group about the P-N bond. These are confirmed by a successful simulation of the observed pmr lineshapes at 4.2K and at 77K. The proton and fluorine T₁ data show the ¹H and ¹⁹F spins to be strongly coupled. A study of fluorine T₁ in the fully deuterated compound, (CD₃)₃NPF₅ has enabled the analysis of the overall T₁ data to be simplified. The observed trends in the T₁ data are seen to be well explained by the theory for a coupled spin system of two unlike spins. / Science, Faculty of / Chemistry, Department of / Graduate

Evidence that recoilless emission and absorption exist may be shown by an experiment in which the source gamma rays are allowed to pass through a suitable absorber to a detector.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by Kenneth Edmund Kreischer. / Ph.D.

A research report submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Medicine Johannesburg, 2018. / The knee is indispensable in everyday life and injuries to it can be debilitating with significant loss of earnings incurred. Clinical diagnosis may not always be made with certainty and Magnetic Resonance Imaging (MRI) helps further elucidate intra-articular injuries. MRI reporting has its shortcomings and may provide spurious results according to the interpretor’s level of experience. This study aims to test the diagnostic reliability of MRI done in a teaching hospital for the evaluation of anterior cruciate ligament and meniscal injuries using arthroscopy as the baseline for comparison. Due to the long waiting times to have surgery we also determined if there was a change in the reliability of an MRI result as time elapsed. A retrospective review of records of patients who had knee arthroscopies at Chris Hani Baragwanath Academic Hospital (Johannesburg, South Africa) from May 2009 to May 2015 was done. Adults (16 − 60 years) with one major episode of trauma to the knee and had MRI done prior to surgery at the above institution were included. Arthroscopy was performed by 2 senior surgeons or by residents under their direct supervision. Arthroscopic findings of anterior cruciate ligament (ACL) and medial (MM) or lateral meniscal (LM) injuries were compared to MRI findings. Data was analysed by STATA version 13.1 to determine injury demographics, sensitivity, specificity and diagnostic accuracy of MRI. The effect of time interval from MRI to surgery on the diagnostic accuracy was determined. A total of 72 patients (74 knees) qualified for review. The median age was 35 years (IQR 26 − 43) with a significant difference between males and females (28 vs 41 years, p = 0.0019). Leading causes of injury were traffic accidents (32.4%), falls (27.0%) and sports injuries (17.6%). Median interval from MRI to surgery was 71.5 days (IQR 29 − 143). The sensitivity of MRI for ACL, MM and LM injuries was (63.6%, 58.8% and 52.6%), specificity (92.7%, 86.0% and 80.0%) and diagnostic accuracy (79.7%, 79.7% and 73.0%) respectively. The patients were divided into subgroups of early (< 6 weeks), intermediate (6 − 16 weeks) and late intervention (> 16 weeks) post-MRI. There were marked differences in the diagnostic accuracy in the three groups for the ACL (70.8% vs 92.6% vs 73.9%) and LM (62.5% vs 81.5% vs 73.9%). This was unremarkable for the MM (75.0% vs 81.5% vs 82.6%). MRI findings correlate well with arthroscopic findings making it a reliable preoperative screening tool for ACL and meniscal injuries. However its diagnostic accuracy appears to change with time. It is apparent that the diagnostic accuracy is higher between 6 − 16 weeks post MRI. A bigger cohort would help determine an ideal waiting time interval without significant depreciation in diagnostic accuracy. / LG2018

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