Una solución numérica eficiente para problemas dinámicos de mecánica de la fractura

XIV Congreso nacional de Ingeniería Mecánica, celebrado en Leganés en 2000Los problemas de Mecánica de la Fractura pueden estudiarse usando la formulación clásica de elementos de contorno combinada con la subdivisión del dominio por medio de contornos internos artificiales que no están únicamente definidos. La necesidad de emplear subregiones desaparece cuando se combinan la ecuación integral clásica y la ecuación integral en tracciones. Una de las principales dificultades que se derivan del uso de la representación integral de las tracciones es la evaluación de las integrales hipersingulares. En este trabajo las integrales hipersingulares se transforn1an analíticamente en integrales regulares que pueden evaluarse numéricamente. Se presenta la formulación e implementación efectiva de esta formulación mixta para problemas dinámicos armónicos tridimensionales de Mecánica de la Fractura. Se utiliza por primera vez la representación integral tridimensional de las tracciones para problemas de este tipo. Los ejemplos numéricos muestran la eficacia del modelo propuesto. Los resultados se comparan con los obtenidos por otros autores utilizando diferentes procedimientos.Ministerio de Educación y Cultura PB96-l 380Ministerio de Educación y Cultura PB96-l 322-C03-0

On-shelļ methods for perturbative QCD

We present new on-shell techniques for the calculation of colour ordered helicity amplitudes in QCD. We review the methods of on-shell recursion and the MHV rules before applying them to tree-level processes within the Standard Model. The MHV rules are applied to QCD corrections to Higgs amplitudes in the heavy top quark limit at tree- level, generating simple n֊point expressions for specific helicity configurations as well as developing more generally applicable recursion relations. We then generalise the on-shell recursion relations for massless QCD to include massive propagating particles and apply them to amplitudes with massive scalar particles, vector bosons and fermions. We then apply on-shell methods to compute the cut-constructible parts of 1-loop Higgs plus multi-gluon amplitudes fixing the remaining rational terms through Feynman diagrams. In all cases we find that the on-shell methods generate simpler analytic expressions than the traditional off-shell methods

Perturbative QCD in event generation

This thesis is concerned with the simulation of particle physics processes involving strong interactions in modern event generators. New algorithms to reinstate colour in colour- ordered amplitudes through colour dressing are presented and their analytical and numerical properties are discussed in detail. The colour-dressed Berends-Giele recursive relations are extended to the full Standard Model Lagrangian and implemented into the numerical program Comix for large multiplicity matrix element computation. New algorithms for phase space integration are proposed, whereof one is capable to effectively couple colour and momentum sampling. Comparisons to other high-multiplicity generators are shown. QCD parton evolution and the CKKW algorithm to correctly include real next-to-leading order corrections are revisited. New types of jet measures are proposed for the merging of matrix elements and parton showers and their analytical and numerical properties are discussed. The implementation into the event generator Sherpa is presented using two different types of matrix element generators. Corresponding results and comparisons are shown. A further comparison between different types of merging algorithms is presented, including various numerical codes, which implement different merging approaches. Finally, the implementation of BFKL evolution in a Markovian approach is introduced and corresponding results from a numerical simulation are presented. Implications on event generation for current and future colliders are discussed throughout

Acta Societatis Scientiarum Fennicae

Julkaisu kuuluu kokonaisuuteen, jonka osat julkaistu vuosina 1842-1926 [i.e. 1930]Date information: 1842-1926 [i.e. 1930