xv Abstract The aim of this thesis is to investigate the accurate stabilization energy and binding free energy in various non-covalent complexes spanned from small organic molecules to biomolecules. Non-covalent interactions such as H-bonds, π...π stacking and halogen bonds are mainly responsible for understanding of most biological processes, such as small molecule interactions with surface, protein-ligand binding in the cell machinery, etc. In the thesis, different non-covalent complexes such as graphene…electron donor- acceptor complexes, DNA base pair interaction with silica surface, etc, were investigated. The reference stabilization energies were calculated at ab initio level, e.g., CCSD(T)/CBS method wherever possible. On the other hand, more approximated scaled MP2 method (MP2.5/CBS/6-31G*(0.25)) is taken as reference instead of CCSD(T)/CBS due to the size of the complexes. Further, the DFT and MM energies were also tested towards the reference one. The knowledge of non- covalent interaction is required for rationalizing of any association processes in nature which requires accurate description of the free energy change. The state-of- the-art molecular dynamics simulation in full atomic scale and biased metadynamics free energy method is used for binding free energy calculations. The well tempered...

Les personnages des romans d’Elsa Morante (1912-1985) sont analysés du point de vue du rapport apparemment opposé entre leur dimension sociale et leur évidente typisation littéraire. Ces deux pôles, le premier analysé par le recours à certaines notions d’études sociologiques menées par G. Simmel et E. Goffman, le deuxième axé sur la construction au niveau littéraire des personnages, contribuent à mettre en lumière le réalisme de Morante, qui tourne autour des vicissitudes humaines vécues par des « personnages vivants (bien qu’imaginaires) » : la relation avec l’autre et avec soi-même, la recherche d’une identité, grâce et malgré la présence des stigmates, concourent à créer des personnages tout à fait modernes. Les deux parties de cette étude, examinées roman après roman, s’avèrent indispensables et interdépendantes : d’un côté, le réalisme des dynamiques humaines, de l’autre l’univers narratif, fondé sur un incessant travail de réutilisation et de personnalisation des figures stéréotypées et d’éléments identifiables de la tradition littéraire, de la part de l’auteure. / This research focuses on the study of the characters in Elsa Morante's novels. The characters are analysed mostly in relation to the apparently conflictual relationship between their recognizable social dimension and their equally clear literary characterisation. The first aspect is examined with the help of some ideas inspired by the sociological studies carried out by G. Simmel and E. Goffman, while the second is centred on the literary construction of the characters. These two aspects contribute to highlight Morante's understanding of Realism: a concept that revolves around the human events experienced by “living but fictional characters” and that is closely connected to the 20th century. One of the central themes is the relationship with the others and with oneself, together with the search for identity, thanks to and notwithstanding the presence of stigmas. The two dimensions of this study were examined analysing each novel, they are at the same time essential and interdependent: on the one hand we see the realism of human dynamics, analysed with the help of sociological theories, and on the other hand the narrative universe, based on a continuous work of re-use and personalization of stereotypical characters and elements that can be recognised on the basis of literary tradition.

Structures made of plate-like components are common in a variety of industries where the impacts of structural failures are severe. In many cases these structures are surrounded and only partially accessible, such as storage tanks and bridges, making them difficult to inspect frequently. The application of ultrasonic Guided Waves (GWs) in the evaluation and monitoring of relatively large plate-like structures is evermore a feasible option with the continuous development of transducer arrays. The use of transducer arrays is however complex due to directional control and the existence of many GW modes. Aimed at the evaluation of plate-like structures, in this research two piezoelectric transducer arrays respectively capable of omnidirectional and unidirectional control of the fundamental GW shear mode in plates (SH0) with above 20 dB mode purity are successfully designed, produced and validated. Omnidirectionality facilitates full structural evaluation coverage and can lead to defect mapping of large volumes with relatively few transducers. A unidirectional beam with relatively high mode purity facilitates evaluation of specific structural locations. Preference to the SH0 mode was given because of its non-dispersive and in-plane propagation properties making it more suitable than other GW modes to propagation in structures surrounded by fluid material. To enable the array development, a number of monolithic piezoelectric thickness-shear transducers of varied area were characterised with respect to GW mode directionality, amplitude and SH0 mode purity. The characterisation of each thickness-shear transducer allows for optimised superposition manipulation for specific applications. A single characterised shear transducer was selected for use in the development of omnidirectional and unidirectional SH0 mode transducer arrays. To aid development a linear superposition analysis model was produced and used to predict for a circular array design the optimum parameters for omnidirectional SH0 mode transmission with significant mode purity. A range of parameter combinations were evaluated and their predicted influence on array performance was characterised. The same method was employed to optimise a dual row linear array design for the unidirectional transducer array. All results were validated by FE models and later with empirical data. Both developed transducer arrays were characterised with respect to GW mode directionality, magnitude and SH0 mode purity. Both their detection sensitivity to pertinent defects and structures was validated, demonstrating relevance to Non Destructive Evaluation (NDE) and Structural Health Monitoring (SHM) applications.

No description available.

To fully exploit the potential of gallium nitride (GaN) devices for optoelectronics and power electronic applications, the structures of device need to be investigated and optimized. In particular carrier densities, conductivities and localised charges can have a significant impact to device performances. Electrical scanning probe microscopy techniques, including scanning capacitance microscopy (SCM), conductive atomic force microscopy (C-AFM) and kelvin probe force microscopy (KPFM), were utilized to study the structures of nitride devices such as high electron mobility transistors (HEMTs), light emitting diodes (LEDs) and junction diodes. These results combine with other characterisation techniques to give an enhanced understanding about the nitride structures. Leakage currents are one of the major challenges in HEMTs, especially leakages in buffer layers which deteriorate the breakdown voltage of the devices. To achieve an insulating buffer layer, carbon doping is usually used to compensate the unintentional n-type doping of nitride materials. Here, I show that vertical leakage can originate from the formation of inverted hexagonal pyramidal defects during the low temperature growth of an AlGaN:C strain relief layer. The semi-polar facets of the defects enhanced the oxygen incorporation and led to the formation of leakage pathways which were observed using SCM. Leakage occurring at HEMT surfaces will lead to current collapses of devices. In this work, I discovered nano-cracks on a HEMT surface. C-AFM showed enhanced conductivity along these nano-cracks. A model based on stress relaxation analysis was proposed to explain the drop of surface potential along the nano-cracks. Advances in the quality of epitaxial GaN grown by MOVPE have been facilitated by understanding the formation of defects within the materials and structures. However, hillocks as a specific type of defects have not been intensively studied yet. In this work, three types of hillocks were discovered on GaN p-i-n diodes and a GaN film grown on patterned sapphire substrates. It was found that pits were always present around the centres of hillocks. Multi-microscopy results showed these pits were developed from either an inversion domain or a nano-pipe or a void under the sample surface. Formation of hillocks was usually associated with a change of growth condition, such as an increase in Mg doping or a decrease in growth temperature and gas flows, despite the formation mechanism is still unclear. GaN$_{1-x}$As$_x$ is a highly mismatched alloy semiconductor whose band-gap can be engineered across the whole visible spectrum. For this reason and the potential to achieve high p-type doping, GaN$_{1-x}$As$_x$ is a promising material for optoelectronic applications. However, the growth of GaN$_{1-x}$As$_{x}$ at intermediate As fraction while maintaining a high conductivity and uniformity of the material is still challenging. Two n-GaN/p-GaN$_{1-x}$As$_x$ diodes with different Ga flows were investigated. Both samples demonstrated that highly Mg-doped GaN$_{1-x}$As$_x$ with high As fraction is achievable. However, the samples contained both amorphous and polycrystalline regions. The electrical scanning probe microscopy results suggested the amorphous structure has a lower hole concentration and hence conductivity than the polycrystalline structure. Nevertheless, there is still a lack of understanding about the electrical properties and conduction mechanisms of the GaN$_{1-x}$As$_x$ alloy.

The second most common cause of cancer deaths in the developed world is bowel cancer. Improving the ability to detect and classify lesions as early as possible, allows treatment earlier. The work presented in this thesis is structured around the following detailed aims:Development of high frequency, broadband µUS (micro-ultrasound) imaging transducers through optimization of ultra-thinning processes for lithium niobate (LNO) and fabrication of novel ‘mass-spring’ matching layers using carefully controlled vacuum deposition is demonstrated. The effectiveness of this technique was quantified by applying multiple matching layers to 3 mm diameter 45 MHz LNO µUS transducers using carefully controlled vacuum deposition. The bandwidth of single mass-spring layer µUS transducer was measured to be 46% with an insertion loss of 21 dB. The bandwidth and insertion loss of a multiple matching layer µUS transducer was measured to be 59% and 18 dB respectively. The values were compared with an unmatched transducer which had a bandwidth and insertion loss of 28% and 34 dB respectively. All the experimentally measured values were in agreement with unidimensional acoustic model predictions. µUS tools that can detect and measure microscopic changes in precancerous tissue using a mouse small bowel model with an oncogenic mutation was developed. µUS transducer was used to test the hypothesis that the intestinal tissue morphology of WT (wild type) and ApcMin/+ (adenomatous polyposis coli) diverges with progressing age intervals (60, 90 and 120 days) of mice. A high frequency ultrasound scanning system was designed and the experiments were performed ex vivo using a focused 45 MHz, f-# = 2.85, µUS transducer. The data collected by scanning was used to compute the backscatter coefficients (BSC) and acoustic impedance (Z) of WT and ApcMin/+ mice. The 2D and 3D ultrasound images showed that µUS detects polyps < 500 µm in the scan plane. The measured values of BSC and Z showed differences between normal and precancerous tissue. The differences detected in precancerous murine intestine and human tissue using µUS were correlated with high resolution 3D optical imaging. This novel approach may provide a powerful adjunct to screening endoscopy for improved identification and monitoring, allowing earlier treatment of otherwise undetectable lesions.

Thesis (M. Sc. (Soil Science)) --University of Limpopo, 2019 / Many conventional laboratory methods are used to characterise spatial and temporal variation of soil properties in order to understand soil quality for different purposes. Currently there is a high demand for accurate soil information by land users. Therefore there is a need to develop a rapid, inexpensive, non-destructive and accurate technique that could compensate or replace conventional laboratory methodologies. Remote sensing has the potential to serve as an alternative approach to characterise soil properties due to its advantages over conventional laboratory methods such as it is rapid, non-destructive and it has low cost. The objectives of this study were to: (i) evaluate the ability of proximal soil sensing to characterise soil properties namely organic matter, soil moisture content, macronutrients, soil texture, cation exchange capacity (CEC), and pH. (ii) Identify bands of relevance from proximal soil sensing (300-2400 nm) that can provide acceptable reflectance variation for different levels of selected soil properties. (iii) Evaluate the performance of models developed from multispectral space-borne image in characterising selected soil properties. In this study spectroradiometer (proximal sensor) and worldview 2 satellite images (space-borne) were the two remote sensing techniques used to collect information about soil at Syferkuil experimental farm of the University of Limpopo. Visible and near infrared spectral data of 98 soil samples were collected at the study site using Analytical spectral device (ASD) field spectroradiometer. Spectral reflectance from spectroradiometer and those extracted from worldview 2 satellite image were used to develop prediction models of selected soil properties using Partial least square regression (PLSR). Bands of relevance were also identified from PLSR models developed from spectral data acquired by spectroradiometer. The results showed that estimation accuracy of PLSR models developed using spectral data from proximal soil sensing were excellent (Category A) for clay, sand, soil organic matter (SOM), and soil moisture content, while good prediction accuracy (Category B) was observed for other soil properties such as silt, ammonium, nitrate, active acidity (pHw), calcium, magnesium, phosphorus, potassium, sulphur, CEC, and reserve acidity (pHKCl). Then, relevant bands which contributed greatly in the prediction of these soil attributes were selected from the electromagnetic spectrum, the range was from 451 nm to 2400 nm. These bands fall within visible, shortwave infrared and near-infrared x regions of electromagnetic spectrum. In addition all selected soil properties were approximately quantitatively estimated using spectral data from satellite image. Based on the results obtained it can be concluded that proximal soil sensing has the ability to predict selected soil properties with various accuracies and it can be used as an alternative technique to characterise soil properties of South African soils. Soil predicting models developed from proximal soil sensing data also showed that there are bands of relevance within spectral range of 451 nm to 2400 nm. However more work is required for space-borne sensing before it can be used as one of the soil characterisation methods since its prediction accuracy was low as compared to that of hyperspectral proximal soil sensing. Keywords: Space-borne sensing; proximal soil sensing; soil characterisation.

<p>Acetolactate synthase (ALS) and acetohydroxyacid synthase (AHAS) are two thiamin diphosphate (ThDP)-dependent enzymes that catalyze the formation of acetolactate from two molecules of pyruvate. In addition to acetolactate, AHAS can catalyze the formation of acetohydroxybutyrate from pyruvate and α-ketobutyrate. When formed by AHAS, these compounds are important precursors to the essential amino acids valine and isoleucine. Conversely, ALS forms acetolactate as a precursor to 2,3‑butanediol, a product formed in an alternative pathway to mixed acid fermentation.</p> <p>While these enzymes catalyze the same reaction, they have been found to be quite different. Such differences include: biological function, pH optimum, cofactor requirements, reaction kinetics and quaternary structure. Importantly, AHAS has been identified as the target of the widely-used sulfonylurea and imidazolinone herbicides, which has led to many structural and kinetic studies on AHAS enzymes from plants, bacteria, and fungi. ALS, on the other hand, has only been identified in bacteria, and has largely not seen such extensive characterization. Finally, although some bacteria contain both enzymes, they have never been studied in detail from the same organism. </p> <p>Here, the ALS and AHAS enzymes from <i>Klebsiella pneumoniae</i> were studied using steady-state kinetic analyses, X-ray crystallography, site-directed and site‑saturation mutagenesis, and cell growth complementation assays to i) compare the kinetic parameters of each enzyme, ii) compare the active sites to probe their differences in substrate profile and iii) test the ability of ALS to function in place of AHAS <i>in vivo</i>.</p>

Naturally fractured reservoirs are generally extremely complex. The aim of characterisation and modelling of such reservoirs is to construct numerical models of rock and fractures, preparing input data for reliable stimulation and fluid flow simulation analyses. This requires the knowledge of different fracture heterogeneities and their correlations at well locations and inter-well regions. This study addresses the issues of how to integrate different information from various field data sources and construct comprehensive discrete fracture networks for naturally fractured reservoir. The methodology combines several mathematical and artificial intelligent techniques, which include statistics, geostatistics, fuzzy neural network, stochastic simulation and simulated annealing global optimisation. The study has contributed to knowledge in characterisation and modelling of naturally fractured reservoirs in several ways. It has developed: .An effective and data-dependant fracture characterisation procedure. It examines all the conventional reservoir data sources and their roles towards characterisation of different fracture properties. The procedure has the advantage of being both comprehensive and flexible. It is able to integrate all multi-scaled and diverse fracture information from the different data sources. .An improved hybrid stochastic generation algorithm for modelling discrete fracture networks. The stochastic simulation is able to utilise both discrete and continuum fracture information. It could simulate not only complicated distributions for fracture properties (e.g. multimodal circular statistics and non-parametric distributions) but also their correlations. In addition, with the incorporation of artificial fuzzy neural simulation, discrete multifractal geometry of fracture size and fracture density distribution map could be evaluated and modelled. Compared to most of the previous fracture modelling approach, this model is more flexible and comprehensive. .An improved conditional global optimisation model for modelling discrete fracture networks. The hybrid model takes full advantages of the advanced fracture characterisation using geostatistical and fuzzy neural analyses. Discrete fractures are treated individually and yet continuum information could be modelled. Compared to the stochastic simulation approach, this model produces more representative fracture networks. Compared to the conventional optimisation programs, this model is more versatile and contains superior objective function.

<p>This report is the result of a Master Thesis work that has been performed between October 2003 and March 2004. The purpose of the work was to evaluate a part of the signal chain in a product of Micronic Laser Systems AB. The evaluation was performed to obtain the characterisation for the signal chain, such as impedances and crosstalk. </p><p>The work started with a literature study in order to refresh and increase the knowledge that was needed before the practical work. Then measurements, computer aided simulations and comparisons between these were performed. </p><p>Measurements were performed using TDR (Time Domain Reflectometry). The results showed the impedance levels along the signal chain. This was interesting since it showed how well the different parts in the system are matched. Unmatched parts result in reflections that disturb the transmitted signal and contribute to crosstalk, which also was measured. </p><p>Simulations were done using ADS (Advance Design System), a tool from Agilent Technologies Inc. A substantial part of the simulation work was to build models of the real system. These models have been used for simulation. The simulation results were then compared to the measurement results. </p><p>The results show that the system can be better matched concerning the channel impedance. There are large variations in impedance levels along the signal chain, resulting in signal reflections. Another effect studied is crosstalk between channels. Measurements and simulations showed the presence of crosstalk but it seems to be a minor problem in the current machine.</p>