No description available.

L’étude des réaction (a,g) d’intérêt astrophysique est vaste. Ces réactions ont un rôle important dans la phase de fusion d’hélium des étoiles, dans la nucléosynthèse au moment du big bang ainsi que dans une grande partie des scénarios d'explosions stellaires. L’étude des réactions (a,g) impliquant des faisceaux stables peut être réalisée de diverse façon. Je me suis concentrée sur deux d'entre elles. La première est l’étude en cinématique directe en détectant les rayons gamma produits. C'est ce que j'ai fait durant ma thèse pour mesurer la section efficace de 7Li(a,g)11B. Cette réaction a été étudiée au cours des années pour différentes raisons en astrophysique nucléaire. Par exemple, il a été postule que cette réaction pourrait résoudre, au moment de la nucléosynthèse du big bang, le problème du Lithium. Il est clair, aujourd'hui, que ce n'est pas la solution, cependant, elle a un rôle dans la production de boron lors des supernovae de type Ic. Une autre façon d’étudier les réactions (a,g) est d'utiliser la cinématique inverse. L’idée est d'envoyer un faisceau d'ions lourd sur une cible d’hélium. Ce type de cinématique permet de détecter, avec une bonne efficacité, le noyau lourd de recul produit si le faisceau qui n'a pas interagit avec la cible, en est correctement séparé. Les séparateurs de masses, comme St. George, sont construit dans ce but. St. George sera impliquer dans la mesure de sections efficaces de réaction d’importance pour le processus s comme 16O(a,g)20Ne. / The study of (a,g) reactions of astrophysical interest is quite vast. These reactions play an important role in the quiescent Helium burning phase of stars, in big bang nucleosynthesis and in most explosive stellar scenarios. The studies of (a,g) reactions involving stable beams are performed in various ways. I have been concentrating on two of them. The first one is studying these reactions in direct kinematics by detecting the produced gamma rays. This is what I did during my thesis to measure the cross section of 7Li(a,g)11B. It has been studied throughout the years for several purposes in nuclear astrophysics. For example, it was postulated it could solve the big bang nucleosynthesis Lithium problem. Nowadays, it is clear it does not.However, this reaction plays a role in the production of Boron during type Ic Supernovae. Another way to study (a,g) reactions is to use inverse kinematics. The idea is to send a heavy element beam on a Helium target. This kind of kinematics allows for the detection, with good efficiency, of the heavy recoil product if the beam that did not interact in the target is properly separated. Recoil mass separators, like St. George, are built for this purpose. St. George will be involved in measuring cross sections of reaction important for the s-process like 16O(a,g)20Ne.

Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Please refer to full text. / AFRIKAANSE OPSOMMING: Sien asb volteks vir opsomming

No description available.

Virtual knot theory, introduced by Kauffman, is a generalization of classical knot theory of interest because its finite-type invariant theory is potentially a topological interpretation of Etingof and Kazhdan's theory of quantization of Lie bi-algebras. Classical knots inject into virtual knots}, and flat virtual knots is the quotient of virtual knots which equates the real positive and negative crossings, and in this sense is complementary to classical knot theory within virtual knot theory. We classify flat virtual tangles with no closed components and give bases for its ``infinitesimal'' algebras. The classification of the former can be used as an invariant on virtual tangles with no closed components and virtual braids. In a subsequent paper, we will show that the infinitesimal algebras are the target spaces of any universal finite-type invariants on the respective variants of the flat virtual tangles.

The photoionization of the beryllium-like isoelectronic series has been studied. The bound state wave functions of the target ions were built with CIV3 program. The relativistic Breit-Pauli R-matrix method was used to calculate the cross sections in the photon energy range between the ionization threshold and 1s24f7/2 threshold for each ion. For the total cross sections of Be, B+, C+2, N+3, and O+4, our results match experiment well. The comparison between the present work and other theoretical works are also discussed. We show the comparison with our LS results as it indicates the importance of relativistic effects on different ions. In the analysis, the resonances converging to 1s22lj and 1s23lj were identified and characterized with quantum defects, energies and widths using the eigenphase sum methodology. We summarize the general appearance of resonances along the resonance series and along the isoelectronic sequence. Partial cross sections are also reported systematically along the sequence. All calculations were performed on the NERSC system.

Photoionization cross section calculations are performed for the ground ([Ne]3s23p63d 2D ) and the first two excited ([Ne]3s23p63d 2D and [Ne]3s23p64s 2S ) states of potassium-like transition metal ions (Sc+2, Ti+3, V+4, Cr+5, Mn+6, Fe+7), along with photoionization calculations for K-like Ca+ ions in the ground ([Ne]3s23p64s 2S ) state and the first two excited ([Ne]3s23p63d 2D and [Ne]3s23p63d 2D ) states. The discrete N-electron final state ion system orbitals are generated using the computer program AUTOSTRUCTURE; 24 configurations are included in the configuration-interaction (CI) calculation for transition metal ions, and 30 configurations for the case of Ca+ ions. The initial and final (N+1)-electron wavefunctions are generated using R-matrix along with photoionization cross sections. In addition to the non-relativistic (LS-coupling) R-matrix, we have used the relativistic (Breit-Pauli) R -matrix method to carry out these calculations to focus on relativistic effects. Relativistic and non-relativistic results are compared to demonstrate the influence of relativistic effects. The prominent 3p → 3d giant resonances are analyzed and identified, and our calculated positions and widths are compared with experimental results for K-like ions such as Ca+, Sc+2 and Ti+3. In the case of lower Z (22  Z  20) ions (Ca+, Sc+2 and Ti+3), the photoionization cross section spectra are dominated by the giant (3p  3d excitation) resonances, while in cases of higher Z (26  Z  23) ions (V+4, Cr+5, Mn+6 and Fe+7), the 3p  3d resonances lie below the ionization threshold, and the cross sections are dominated by 3p53d nd and 3p53d n’s Rydberg series of resonances. Comparison of the Ca+, Sc+2 and Ti3+ results with available theoretical and experimental data shows good agreement.

No description available.

No description available.

Virtual knot theory, introduced by Kauffman, is a generalization of classical knot theory of interest because its finite-type invariant theory is potentially a topological interpretation of Etingof and Kazhdan's theory of quantization of Lie bi-algebras. Classical knots inject into virtual knots}, and flat virtual knots is the quotient of virtual knots which equates the real positive and negative crossings, and in this sense is complementary to classical knot theory within virtual knot theory. We classify flat virtual tangles with no closed components and give bases for its ``infinitesimal'' algebras. The classification of the former can be used as an invariant on virtual tangles with no closed components and virtual braids. In a subsequent paper, we will show that the infinitesimal algebras are the target spaces of any universal finite-type invariants on the respective variants of the flat virtual tangles.