PYTHIA status report
Recent improvements in the PYTHIA event generator are summarized: new hard subprocesses, γ*γ* physics, QCD final-state showers, and more.
The Lund Model
Preface 1. Relativistic kinematics, electromagnetic fields and the method of virtual quanta 2. The harmonic oscillator and the quantum field 3. The vacuum as a dielectric medium and renormalisation 4. Deep inelastic scattering and the parton model 5. The classical motion of the massless relativistic string 6. The decay kinematics of the massless relativistic string 7. A stochastic process for string decay 8. The properties of the Lund model fragmentation formulae: external part formulas 9. The internal part fragmentation formulae and their relations to the unitarity equations of Regge theory 10. The dynamical analogues of the Lund model fragmentation formulae 11. Flavour and transverse momentum generation, and the vector to pseudoscalar meson ratio 12. Heavy quark fragmentation and Baryon production 13. The Hanbury-Brown-Twiss-effect and polarisation in the Lund model 14. The Lund gluon model, the kinematics and the decay properties 15. Gluon emission via the Bremsstrahlung process 16. Multigluon emission, the dipole moment and parton coherence cascade models 17. The lambda measure in the leading log, and the modified lead log approximation of perturbative QCD 18. The parton model and QCD 19. Inelastic lepto-production in the Lund model, the soft radiation model and heretical structure functions 20. Hadronic interaction models References Index.
Numerical analysis of surface crack propagation in flexible pavements using XFEM and cohesive zone model
Surface initiated (top-down) cracking in the longitudinal direction of pavements has become a predominant mode of failure in thick asphalt pavements. Most previous researchers studied crack propagation using the traditional Linear Elastic Fracture Mechanics (LEFM) method by calculating the stress intensity factor around the crack tip. In this paper, Extended Finite Element Method (XFEM) was used to study the key factors causing surface initiated crack propagation under surface tension and/or shear. A two-dimensional (2-D) finite element (FE) model for a two-lane flexible pavement was built to predict pavement responses and crack propagation potential under various scenarios. It was found that surface tension is the major driving force for crack propagation when the crack is at some distance away from tire loading. The results show that the distance from the location of crack to tire loading, the depth and direction of the crack, and the modulus ratio between the hot-mix asphalt (HMA) layer and the base layer have significant influences on crack propagation under surface tension. On the other hand, this study shows that shear stress can induce surface initiated crack propagation near the loading area as the shear resistance of material becomes low at the high temperature.