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Transient liquid phase bonding of Aluminium-based MMCsAskew, John Russell January 2000 (has links)
No description available.
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An investigation on the dispersion of TiBâ†2 ceramic phase in molten Al alloysDometakis, Christopher January 1997 (has links)
No description available.
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Generation and characterisation of some molecular compounds of the group 13 metalsHimmel, Hans-Jörg January 2000 (has links)
No description available.
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The effect of microscopic residual stress on the deformation of polycrystalsJames, Karen Elizabeth January 2001 (has links)
No description available.
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The application of algorithm-based fault tolerance to VLSI processor arraysDavall, Rosemarie Anne Regina January 1995 (has links)
No description available.
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Variation in human tissue inhibitor of metalloproteinase 1 gene and its effect on the control of connective tissue remodelling in cardiovascular diseaseLamlum, Hanan January 2000 (has links)
No description available.
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Manufacture and Characterization of Fiber Reinforced Epoxy for Application in Cowling Panels of Recreational Aircraft2014 April 1900 (has links)
In this study, glass and Kevlar® fibers reinforced epoxy composites were manufactured and characterized using different techniques. The effect of thermal exposure on the flexural properties of the composites was investigated to ascertain its suitability for the intended application in cowling panels of light engine aircraft. Thermogravimetric analysis (TGA) was carried out on both reinforced and unreinforced epoxy resin to evaluate their thermal stability at elevated temperatures. Dynamic mechanical thermal analysis was carried out to evaluate the effects of thermal exposure, applied strain and frequency on the dynamic mechanical response of the composites. The effects of the applied resin hardener and thermal exposure on the flexural strength, flexural modulus and dynamic impact response of the composites were also investigated. The flexural properties were determined using 3-point bending test, while the impact test was carried out using Split Hopkinson Pressure Bar (SHPB). TGA analysis of the reinforced and unreinforced epoxy showed no significant weight loss until the test samples were heated above 250°C in an inert atmosphere. Dynamic Mechanical Thermal Analysis (DMTA) on the composites indicated the glass transition temperature to lie between 80 and 100°C.
The results of the flexural and impact tests showed that the mechanical integrity of both glass and Kevlar® fiber reinforced epoxy composites remained unimpaired by radiative or convective heat exposure for up to 3 h until the exposure temperature exceeded 200°C. This is much higher than the service temperature of cowling panels of light engine recreational aircrafts. When the manufactured fiber reinforced epoxy composites were exposed to temperature above 200°C matrix degradation occurred, which became very significant when the exposure temperature was higher than 250°C. Extensive delamination and matrix cracking occurred when the composites were exposed to the temperature range 250°C - 300°C for 1 h. Fiber-matrix debonding was not observed in the composite except after failure under impact loading. This is evidence of the fact that the epoxy matrix was adequately wetted by both the glass and Kevlar® fibers resulting in the strong fiber/matrix interfacial bonding. While the Kevlar® reinforced epoxy displayed a better damage tolerance under flexural and impact loading, glass fiber reinforced epoxy showed higher strength but lower damage tolerance. Glass fiber reinforced epoxy also showed more resistance to damage under exposure to thermal flux than Kevlar® reinforced epoxy. Under impact loading, the Kevlar® reinforced composite failed by delamination with no fiber rupture, whereas the glass fiber reinforced epoxy failed by matrix cracking, debonding, fiber rupture and fiber pullout.
The results from this research have established the effect of radiative and convective thermal exposure on the mechanical behavior of the fabricated Kevlar® fiber and glass reinforced epoxy composites. The maximum temperature reached on the inner surface of the cowling panels of a typical light engine recreational aircraft due to heat radiations from the engine block has been estimated to be about 65°C. This is lower than the glass transition temperature of the epoxy matrix as obtained from DMTA. The low temperature rise is due to inflow cooling air into the cowling chamber in flight. The results of the current investigations suggest the suitability of composite materials for the intended application. The intensity of thermal exposure, to which the materials will be exposed in such application, may not cause any significant damage to the mechanical integrity of the composite. However, since the difference between the possible exposure temperature and the glass transition temperature is only a little over 20°C, a layer of thermal insulator on the inner surface of the cowling made of fiber reinforced epoxy will be desirable to further sustain the mechanical integrity of the composites when selected for use as choice materials for cowling panels of light engine aircraft.
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Effect of Intermolecular Interactions on the Carbon 1s Near Edge X-ray Absorption Fine Structure (NEXAFS) Spectroscopy of n-Alkanes2012 November 1900 (has links)
“Matrix effects” in Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy are the spectroscopic changes induced by intermolecular interactions, providing sensitivity to local structure and order in solids and liquids. This project aims to identify the effect of intermolecular interactions caused by different n-alkane solid state structures on their NEXAFS spectra. Changes to the carbon 1s NEXAFS spectra are studied as a function of their solid state structure and organization. Two experimental approaches were proposed in this project. In the first approach, different n-alkane crystal structures (orthorhombic, monoclinic, etc.) are examined which arise as a function of n-alkane chain length. In the second approach, changes observed through the pre-melting point order-disorder phase transition found in n-alkanes are examined. This work will explore the characteristic spectroscopic differences observed between n-alkanes in different crystalline forms as well as in the disordered phase below the melting points.
In this project, well-ordered diamond shape n-alkane single crystals were obtained by solution casting, using experimental conditions optimized for each n-alkane. As circularly polarized radiation will average the effect of molecular orientation, circularly polarized radiation was used to obtain the NEXAFS spectra of n-alkanes. However, in the analysis of the NEXAFS spectra of n-alkanes recorded with the left circularly polarized X-rays, a significant linear polarization contamination was found. Therefore, linearly polarized X-rays were used to acquire angle dependent NEXAFS spectra, where the X-ray polarization was deliberately aligned along the principal axes (X, Y) of the n-alkane crystal.
It was observed that the room temperature carbon 1s NEXAFS spectrum of n-octacosane (C28H58) was different from that of the other n-alkanes, n-tetracosane (C24H50), n-tricosane (C23H48) and n-tetracontane (C40H82). This difference can be attributed due to the different crystal packing of n-octacosane (C28H58 - monoclinic) relative to the other n-alkanes (triclinic and orthorhombic), suggesting different intermolecular interactions (matrix effects) in n-octacosane (C28H58).
The analysis of the temperature dependent NEXAFS spectra of n-alkanes reveals that samples of the short chain n-alkane crystals, specially n-tricosane (C23H48), n-tetracosane (C24H50) and n-octacosane (C28H58), sublimed in the STXM microscope. Changes observed in the carbon 1s NEXAFS spectra of n-tetracontane (C40H82) with temperature were attributed to the order-disorder transition. This further illustrates the existence of matrix effects in the NEXAFS spectra of n-alkanes.
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Modelling of ecosystem change on rehabilitated ash disposal sites based on selected bio-indicators / A. SnymanSnyman, Anchen January 2006 (has links)
Finding a common language in describing and interpreting multivariate data
associated with rehabilitation and disturbance ecology, has became a major
challenge.
The main objective of this study is to find and evaluate mathematical models
to describe ecosystem change based on selected indicators of change.
Existing data from a previous rehabilitation project on Hendrina Power Station
(Mpumalanga, South Africa) was used as a database for this study and this
study aims to report on the development of models concentrating on radar
graphs and a model based on matrix mathematics.
The main groups of organisms selected for the construction of models, were
vegetation, soil mesofauna and ant species. The datasets were limited to
some indicative species and their mean abundances were determined. The
grids that were used were randomly chosen and the models were
constructed.
Radar graphs were constructed to model the suite of species identified,
through a sensitivity analysis, to indicate possible rehabilitation success over
time and was applied to the different rehabilitation ages. The surface areas
under the radar graphs were determined and compared for the different
rehabilitation ages in the same year of survey. Correlation graphs were drawn
between the surface area and the rehabilitation ages. These graphs did not
indicate much relevance in indicating rehabilitation success, but the radar
graphs proved to be good indicators of change in abundance of the selected
species over time.
iv
The vegetation species, Eragrostis curvula, was the only species that showed
a strong significant positive relationship with rehabilitation age and could be
considered a good rehabilitation species and indicator of rehabilitation
success. After the evaluation of this model, Eragrostis curvula, and two
additional ant species, Tetramorium setigerum and Lepisiota laevis, were
added. These species that were added, showed an increase in abundance
over time, as found in a previous study. These radar graphs also did not
indicate much relevance and it can be concluded that the radar graphs can
only be used for a visual representation of the changes in abundance of the
relevant species over time.
This study also refers to a matrix model. This model focused on the
interactions between the different variables selected. The percentage carbon
in the soil were also added to the list of species. Model fitting graphs were
constructed and correlations were drawn between the species that had
significant values in the interaction table. This model could be useful for future
studies, but more data and replication is necessary, over a longer period of
time. This will serve to eliminate possible shortcomings of the model. / Thesis (M. Environmental Science (Biodiversity and Conservation Biology))--North-West University, Potchefstroom Campus, 2007.
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Characterisation and ionisation modelling of matrices in MALDI mass spectrometryAllwood, Daniel Anthony January 1998 (has links)
No description available.
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