Magnetic deflection techniques have been employed to measure proton angular distributions from some (d,p) and (t,p) reactions. In many cases the distributions exhibit typical stripping patterns and their analysis in terms of plane wave and distorted wave theories of stripping has enabled spin and parity assignments to be made for a number of excited nuclear levels. These theories are briefly outlined in Chapter 1 of this thesis and the experimental procedures are described in Chapter 2. The (d,p) reaction has been studied at an incident energy of 3 MeV with target nuclei B¹⁰, B¹¹, C¹², C¹⁴ and O¹⁶ and an account of this investigation is given in Chapter 3. Although the plane wave theory gives a good account of the angular distributions corresponding to the low-Q transitions (say Q ≤ 2 MeV) it is not a good approximation for the high-Q transitions. This is in accord with Wilkinson's suggestion that distortion effects should be quite small even at low deuteron bombarding energies providing also that the reaction Q-value is low. Agreement with the high-Q ground state distribution for B¹¹ could only be obtained with distorted wave theory if a cut-off radius were used. This may indicate the need for taking into account finite range effects in this theory. The Se⁷⁶(d,p)Se⁷⁷ reaction has been studied at 7.8 MeV bombarding energy and eleven angular distributions corresponding to the ground and ten excited states of Se⁷⁷ have been analysed using distorted wave theory. This investigation is described in Chapter 4. Deuteron and proton elastic scattering measurements have also been made from Se⁷⁶ and Se⁷⁷, respectively. The optical model potentials required to describe the stripping distributions are found to be entirely consistent with those derived from the elastic scattering data. In Chapter 5 an account is given of a systematic study of the (t,p) reaction for target nuclei B¹⁰, B¹¹, C¹², C¹⁴, O¹⁸, Si²⁸, Si²⁹ and Ca⁴⁰. This investigation was carried out at triton energies between 8 and 13 MeV. In the majority of cases the angular distributions are observed to be strongly forward peaked and these have been analysed in terms of Newn's plane wave theory of double stripping. With the exception of the B¹⁰(t,p)B¹² and C¹²(t,p)C¹⁴ reactions the agreement in general is found to be very satisfactory. In addition to the ground state, nine excited states of B¹³ were observed and information on the spins and parities of six of them have been obtained. The excitation energies of only four excited states were previously known. C¹⁶ had not previously been observed and the present investigation has shown this to be stable by 4.25 MeV against neutron emission, in good agreement with the predicitons of Zel'dovich. The ground state was confirmed to be O⁺ and the first excited state at 1.753 MeV excitation is probably 2⁺. The delayed neutron emission for C¹⁶ has also been studied and its measured half-life found to be 0.74 ± 0.03 seconds. Angular distributions were measured for the ground and nine excited states of O¹⁸ and ground and four excited states of O²⁰. Only one state, at 4.45 MeV excitation in O¹⁸, could not be interpreted by a double stripping process. Spin-parity assignments from the reactions Si²⁸(t,p)Si³⁰, Si²⁹(t,p)Si³¹ and Ca⁴⁰(t,p)Ca⁴² are in good agreement with earlier measurements. The Be¹¹ nucleus has been studied using the Be⁹(t,p)Be¹¹ reaction at 6 and 10 MeV triton energies. This investigation is described in Chapter 6. At the higher bombarding energy six energy levels of Be¹¹ were observed and three of these were found to have natural widths in excess of 10 keV. Proton distributions were measured at both energies for the ground and first excited states. Their interpretation in terms of a double-stripping mechanism is complicated by the presence of large backward peaks but the distributions are not inconsistent with the spins of 1/2 ^- and 1/2 ⁺, respectively, predicted by Talmi and Unna. Angular distributions from the C¹²(t,α)B¹¹ reaction at 10 MeV triton energy were also studied in an attempt to obtain information on the spins and parities of some of the states in B¹¹ which are involved in the beta-decay of Be¹¹. In Chapter 7 an account is given of triton elastic scattering measurements made at incident energies 6.4, 6.8 and 7.2 MeV from C¹², O¹⁶, O¹⁸, F¹⁹ and Ca⁴⁰. Only the scattering from F¹⁹ and Ca⁴⁰ can be described by the optical model, although the optical parameters are ambiguous. The scattering distributions from O¹⁶ at all three energies exhibit large backward peaks suggestive of compound resonance scattering. Optical model parameters derived from the triton scattering data have been uesd by Rook and Mitra to analyse the proton distributions from Ca⁴⁰(t,p)Ca⁴², using distorted wave theory. A brief account of the results is given in Appendix C.

Made available in DSpace on 2015-03-05T18:11:57Z (GMT). No. of bitstreams: 0 Previous issue date: 12 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Nesta dissertação de mestrado, procuro mostrar a contribuição de determinadas concepções de organização textual para a representação do texto realizada pelo modelo da Rhetorical Structure Theory – RST (Mann; Thompson, 1988). A RST é uma teoria que explica a estrutura textual por meio de um modelo de relações que se estabelecem, recursivamente, entre partes do texto consideradas pelo analista como núcleos e satélites. Porém, apesar de abarcar a coerência retórica relacional, a RST, como teoria, não lida com outras concepções que dêem conta do processo complexo de organização textual. Dessa forma, como modelo, ela representa o texto de forma limitada. Neste trabalho, investigo a possibilidade de a RST ser associada a determinadas concepções de organização textual, como a relação entre texto e contexto e o processo estratégico top-down de formação do texto. Para tanto, realizo uma investigação em duas partes: uma teórica e uma de análise. Na parte teórica, apresento um quadro teórico que embasa as concepções de / In this master’s degree paper work, I aim to show the contribution of some conceptions of textual organization to the text representing process carried out by Rhetorical Structure Theory – RST (Mann; Thompson, 1988). RST is a theory that explains the text structure by postulating a model of relations which recursively hold between parts of text labeled nucleus or satellite by the analyst. However, even accounting for the rhetorical relational coherence, RST, as a theory, doesn’t include other conceptions to account for the complex process of textual organization. Thus, as a model, it produces a limited text representation. In this paper work, I investigate the possibility of associating RST with some conceptions of textual organization, like the relationship between text and context and the top-down strategic process of text construction. To do so, I carry out an investigation in two parts: a theoretical one and an analytical one. In the theoretical part, I show a theoretical framework that supports the conce

Strong electron correlations in electronic structure theory are purely quantum effects arising as a result of degeneracies in molecules and materials, and exhibit significantly different yet interesting characters than do weak correlations. Although weak correlations have recently been able to be described very efficiently and accurately within single particle pictures, less known are good prescriptions for treating strong correlations efficiently. Brute-force calculations of strong correlations in wave function theories tend to be very computationally-intensive, and are usually limited to small molecules for applications. Breaking symmetry in a mean-field approximation is an efficient alternative to acquire strong correlations with, in many cases, qualitatively accurate results. The symmetry broken in quantum chemistry has been traditionally of spin, in so-called unrestricted methods, which typically break spatial symmetry as a consequence, and vice versa, in most situations. In this work, we present a novel approach to accurately describing strong correlations with a mean-field cost by means of Hartree- Fock-Bogoliubov (HFB) theory. We are inspired by the number-symmetry-breaking in HFB, which, with an attractive particle interaction, accounts for strong correlations, while maintaining spin and spatial symmetry. We show that this attractive interaction must be restricted to the chemically-relevant orbitals in an active space to obtain physically meaningful results. With such constraints, our constrained pairing mean-field theory (CPMFT) can accurately describe potential energy curves of various strongly-correlated molecular systems, by cleanly separating strong and weak correlations. To achieve the correct dissociation limits in hetero-atomic molecules, we have modified our CPMFT functional by adding asymptotic constraints. We also include weak correlations by combining CPMFT with density functional theory for chemically accurate results, and reveal the connection between CPMFT and traditional unrestricted methods. The similarity between CPMFT and unrestricted methods leads us to the idea of constrained active space unrestricted mean-field approaches. Motivated by CPMFT, we partially retrieve spin-symmetry that has been fully broken in unrestricted methods. We allow symmetry breaking only in an active space. This constrained unrestricted Hartree-Fock (CUHF) is an interpolation between two extrema: the fully broken-symmetry solution and the symmetry preserved solution. This thesis defines the theory behind and reports the results of CUHF. We first show that, if an active space is chosen to include only open-shell electrons, CUHF reduces to restricted open-shell Hartree-Fock (ROHF), and such CUHF proves in many ways significantly

Density-functional theory has become an indispensible tool for studying matter on the atomic level, being routinely applied across diverse disciplines from solid-state physics to chemistry and molecular biology. Its failure to account for dispersion interactions has spurred intensive research over the past decade. In this thesis, a semilocal density-functional approximation including dispersion is developed by combining standard functionals for exchange and correlation with the nonempirical “exchange-hole dipole moment“ (XDM) dispersion model of Becke and Johnson. With a minimum of empiricism, the method accurately describes all types of noncovalent interactions, from the extremely weak dispersion forces in rare-gas systems to the hydrogen bonding and stacking interactions responsible for the structure and function of biological macromolecules such as DNA and proteins. The method is compatible with a wide variety of standard Gaussian basis sets, and is easily applied to any system that can be modeled with density-functional theory.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第14868号 / 工博第3136号 / 新制||工||1470(附属図書館) / 27290 / UT51-2009-K664 / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 榊 茂好, 教授 今堀 博, 教授 杉野目 道紀 / 学位規則第4条第1項該当

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23220号 / 工博第4864号 / 新制||工||1759(附属図書館) / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 佐藤 啓文, 教授 佐藤 徹, 教授 田中 勝久 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

This paper investigated the change in corporate debt levels in South Africa from 1994 to 2016. Included is an analysis of factors that companies take into consideration when determining the company's capital structure. This study used data from companies, largely from the mining sector, within sectors listed on the Johannesburg Stock Exchange (JSE), including chemicals, general industries, oil and gas. Four different leverage measures were used to determine the change in capital structure for the period under review, as well as six of the most commonly used determinants of capital structure. A high-level interpretation of the results reflected the following; a slight but relatively consistent increase in the use of debt relative to equity over the period for both the total sample and the mining sector. An increase in the use of long- relative to short term debt was also found, as well as a convergence between the use of current and non-current liabilities. Results from the analysis of the capital structure determinants varied, with some showing statistical significance. Asset tangibility was positively correlated to debt, while profitability and growth had a negative relationship. The relationship between company size, tax and cost of debt and leverage was varied.

Over the years electronic structure theory has proven to be a powerful method with which one can probe the behaviour of materials, making it possible to predict properties that are difficult to measure experimentally. The numerical tools needed for these methods are always in need of development, since the desire to calculate more complex materials pushes this field forward. This thesis contains work on both this implementational and developmental aspects. In the first part we investigate the structural properties of the 6d transition metals using the exact muffin-tin orbitals method. It is found that these elements behave similarly to their lighter counterparts, except for a few deviations. In these cases we argue that it is relativistic effects that cause this anomalous behaviour. In the second part we assess the Padé approximant, which is used in several methods where one wants to include many-body effects into the electronic structure. We point out difficulties that can occur when using this approximant, and propose and evaluate methods for their solution. / <p>QC 20130219</p>

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