The nature of the generic chemical structures found in patents is described, with a discussion of the types of statement commonly found in them. The available representations for such structures are reviewed, with particular note being given to the suitability of the representation for searching files of such structures. Requirements for the unambiguous representation of generic structures in an "ideal" storage and retrieval system are discussed. The basic principles of the theory of formal languages are reviewed, with particular consideration being given to parsing methods for context-free languages. The Grammar and parsing of computer programming languages, as an example of artificial formal languages, is discussed. Applications of formal language theory to chemistry and information work are briefly reviewed. GENSAL, a formal language for the unambiguous description of generic structures from patents, is presented. It is designed to be intelligible to a chemist or patent agent, yet sufficiently ABSTRACT formaLised to be amenabLe to computer anaLysis. DetaiLed description is given of the facilities it provides for generic structure representation, and there is discussion of its Limitations and the principLes behind its design. A connection-tabLe-based internaL representation for generic structures, caLLed an ECTR (Extended Connection Table Representation) is presented. It is designed to represent generic structures unambiguousLy, and to be generated automatically from structures encoded in GENSAL. It is compared to other proposed representations, and its implementation using data types of the programming Language PascaL described. An interpreter program which generates an ECTR from structures encoded in a subset of the GENSAL Language is presented. The principles of its operation are described. Possible applications of GENSAL outside the area of patent documentation are discussed, and suggestions made for further work on the development of a generic structure storage and retrieval system based on GENSAL and ECTRs.

CIVINS / Approved for public release; distribution is unlimited / The utility of present Autonomous Underwater Vehicles (AUVs) is limited by their on-board energy storage capability. Research indicates that rechargeable batteries will continue to be the AUV power source of choice for at least the near future. Thus, a need exists in both military and commercial markets for a universal, industry-standard underwater AUV recharge system. A novel solution using a linear coaxial wound transformer (LCWT) inductive coupling mounted on the AUV and a vertical docking cable is investigated. The docking cable may be deployed from either a fixed docking station or a mobile "tanker AUV". A numerical simulation of the simplified system hydrodynamics was created in MATLAB and used to evaluate the mechanical feasibility of the proposed system. The simulation tool calculated cable tension and AUV oscillation subsequent to the docking interaction. A prototype LCWT coupling was built and tested in saltwater to evaluate the power transfer efficiency of the system. The testing indicated that the surrounding medium has little effect on system performance. Finally, an economic analysis was conducted to determine the impact of the proposed system on the present military and commercial AUV markets. The recharge system creates substantial cost-savings, mainly by reducing support ship requirements. An effective AUV recharge system will be an important element of the Navy's net-centric warfare concept, as well as a valuable tool for commercial marine industries. / Lieutenant Commander, United States Navy

Time resolved scanning Kerr microscopy (TRSKM) has been used to study a number of different magnetic systems. Firstly, partially built hard disk writer structures, with a multilayered yoke formed from 4 repeats of a NiFe(~1 nm)/CoFe(50 nm) bilayer, and with three coil windings underneath, were studied by TRSKM with unipolar driving pulses. Dynamic images of the in-plane magnetization suggest an underlying closure domain equilibrium state. This state is found to be modified by application of a bias magnetic field and also during pulse cycling, leading to different magnetization rotation and relaxation behaviour within the tip region. Studies of a further three yokes with the same stack structure, but with only one coil winding at different positions beneath the yoke, yielded dynamic images of “flux beaming” in a channel parallel to the driving field. The magnetic contrast was strongest when the active coil was located near the centre of the yoke, while relaxation after removal of the excitation was most complete when the active coil was located near the confluence region. These results confirm the need for a multi-turn coil to ensure effective flux propagation along the entire length of the yoke. Furthermore, a structure with a NiFe/CoFe/Ru/NiFe/CoFe synthetic antiferromagnetic (SAF) yoke was studied as a bipolar current pulse with 1MHz repetition rate was delivered to the coil. The component of magnetization parallel to the symmetry axis of the yoke was compared at the pole and above a coil winding in the centre of the yoke. The two responses are in phase as the pulse rises, but the pole piece lags the yoke as the pulse falls. The Kerr signal is smaller within the yoke than within the confluence region during pulse cycling. This suggests funneling of flux into the confluence region. Dynamic images acquired at different time delays showed that the relaxation is faster in the centre of the yoke than in the confluence region, perhaps due to the different magnetic anisotropy in these regions. Although the SAF yoke is designed to support a single domain to aid flux conduction, no obvious flux beaming was observed, suggesting the presence of a more complicated domain structure. The SAF yoke writer hence provides relatively poor flux conduction but good control of rise time compared to single layer and multi-layered yokes studied previously. Secondly, vortex dynamics within arrays of square ferromagnetic nano-elements have been studied using TRSKM with coherent microwave excitation. It is shown that TRSKM can be used to detect vortex gyration in square nanomagnets with a lateral size (250nm) that is smaller than the diameter (300nm) of the focused laser beam. In an array with large element separation and negligible dipolar interaction, TRSKM images acquired at a fixed point in the microwave cycle reveal differences in the phase of the dynamic response of individual nanomagnets. While some variation in phase can be attributed to dispersion in the size and shape of elements, the circulation and polarization of the vortex are also shown to influence the phase. In an array with element separation smaller than the optical spot size, strong magneto optical response was observed within small clusters of elements. Micromagnetic simulations performed for 2 x 2 arrays of elements show that a certain combination of circulation and polarization values is required to generate the observed magneto-optical contrast. Thirdly, polar TRSKM has been used to directly observe magnetostatically coupled transverse domain walls (TDWs) in a pair of closely spaced, curved nanowires (NWs). Kerr images of the precessional response revealed a minimum in the Kerr signal due to the TDW in the region of closest NW separation. When the TDWs were ejected from the NW pair, the minimum in the Kerr signal was no longer observed. By imaging this transition, the static decoupling field was estimated to lie between 38 and 48 Oe, in good agreement with a simple micromagnetic model. This work provides a novel technique by which DC and microwave assisted decoupling fields of TDWs may be explored in NW pairs of different width, separation, and curvature. Fourth, time resolved magneto-optical Kerr effect and phase modulated X-ray ferromagnetic resonance measurements have been performed on a CoO/Py bilayer for different temperatures, RF frequency, and CoO thickness. Kerr hysteresis loops did not show any evidence of exchange bias for temperatures between 200K and 330K for any thickness of CoO, but the coercivity was found to increase with increasing CoO thickness and decreasing temperature. Magneto-optical FMR and XFMR data showed some asymmetry with respect to the sign of the bias field, but the amplitude of the signals decreased rapidly with decreasing temperature. The results are consistent with the appearance of frustrated antiferromagnetic order within the CoO during field cooling.

No description available.

Call number: LD2668 .T4 1951 O8 / Master of Science

Call number: LD2668 .T4 1951 P73 / Master of Science

A Dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. 28 October 2016. / Energy storage has become an important issue for society, there is a need for affordable and efficient devices that can store energy optimally. Supercapacitors are energy storage devices that can solve society’s energy storage problem. They can store the energy generated by renewable energy systems. In this work approaches will be studied that may be used to estimate capacitance of materials that can be used as the electrode of these devices. These materials must have high energy density, which will address one of the limitations of supercapacitors. To estimate the capacitance of the double layer, the double layer theory and ab initio numerical tools based on density functional theory (DFT) are used. The ab initio tools work with periodic systems, when charging the system one violates the periodicity of the system. This is overcome by using the effective screening medium method, which prevents energy divergent of the system. In this work different configurations of the water molecules are used to average the different orientations of water molecules in the electrolyte. The Pt(111) electrode is used, and electrolyte of sodium ion and water. In different configurations the sodium ion in the electrolyte is located at different positions. The capacitances calculated using two different approaches that we developed in this work are comparable to previously estimated capacitance. This is achieved by using minimal computational efforts. We obtained capacitance within that range. Double layer capacitance can be estimated to a good accuracy with the methods developed in this work. Though there are improvements that can be made on the methods that have been developed in this work to better estimate the double layer capacitance. And also more research has to be done in this field to come up with a theory that will accurately estimate capacitance. At the moment calculating the double layer capacitance is not trivial due to the lack of theory that describe the processes taking place at the surface of the electrode where the capacitance is calculated. / LG2017

Hydrogen has a great potential to become a wide-scale, carbon free, sustainable energy carrier of the future. However its implementation and final utilization especially in mobile applications is still limited because of several technological and socio-economical barriers, mainly to do with safe, efficient storage of hydrogen with high gravimetric and volumetric storage capacities. Physisorption into nanoporous materials is an attractive option as it benefits from rapid, fully reversible adsorption/desorption and can store significant amounts of hydrogen at more moderate temperature and pressures conditions than conventional liquefaction (20.3 K) or compression (350‒700 bar). Nevertheless, the critical challenge exists to define the experimental methods that allow accurate hydrogen sorption determination and reduce discrepancies in measurements between different laboratories. This thesis presents an investigation of the experimental methodology of hydrogen sorption in porous materials. A set of nanoporous samples and characterisation techniques have been tested rigorously to explore experimental uncertainty and provide universally reproducible procedures. The validity of the standard methods and some new approaches for experimental data collection and analysis are presented. High repeatability of gas sorption isotherms measured gravimetrically and volumetrically at 77 K on reference TE 7 III carbon beads sample has been demonstrated in-house. A study has been conducted between seven laboratories to evaluate the reproducibility of nitrogen/hydrogen isotherms at 77 K according to a defined test protocol. Statistical analysis yields very good agreement between nitrogen and hydrogen sorption results. The Brunauer-Emmett-Teller surface area of 777.8 ± 6.2 m2 g-1 and Dubinin-Radushkevich micropore volume of 0.3766 ± 0.0078 cm3 g-1, have been determined. The excess hydrogen sorption capacities are found to be 1.65 ± 0.04 wt% and 2.33 ± 0.007 wt% for 1 bar and 20 bar hydrogen pressure, respectively. This study concludes that the accuracy of hydrogen sorption measurements have been pushed forward and methodology proposed here could contribute to improvements in certification of future hydrogen sorption methods.

The specific activities of citrate synthase and malate dehydrogenase extracted from mature green fruit of Lycopersicon esculentum, fell 60% during the first two weeks of a twelve week experiment in which the fruit were stored in an atmosphere designed to inhibit ethylene synthesis. Throughout the remainder of the experiment, the specific activities were relatively constant. In the initial two week period, the specific activity of NADP-linked malic enzyme rose by 400%, malic acid concentration fell by 50%, while the concentration of citric acid rose by 20%. Those features of ripening such as the de novo synthesis of lycopene and polygalacturonase, which were thought to depend on ethylene for initiation of response, could not be detected until the fruit were removed to a normal atmosphere. Additionally, citrate synthase and malate dehydrogenase from mature green tomato fruit stored in the presence or absence of ethylene, showed similar trends in specific activity, and the presence of the olefin made no significant difference to the rate of loss of enzyme specific activity. The purification and partial characterisation of citrate synthase from Lycopersicon esculentum is described. The enzyme is a dimer with sub-units of similar size and a total Mr of approximately. 100,000. The characterisation revealed no obvious regulatory features that would easily account for the fall in specific activity. Sub-cellular fractionation studies demonstrated unequivocally that the site of organic acid metabolism was the mitochondrion. Citrate synthase, NAD-dependent isocitrate dehydrogenase and NAD-dependent malic enzyme were shown to be located exclusively in the mitochondrion, while malate dehydrogenase was located both in the cytosol and the mitochondrion. All these enzymes including cytosolic malate dehydrogenase exhibited the co-ordinated fall in specific activity described above. A hypothesis is proposed which includes a novel coarse control of the citric acid cycle and related enzymes, as an early indicator of senescence.

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