An order for asymmetry in copulas, and implications for risk management

We investigate symmetry properties of bivariate copulas. For this, we introduce an order of asymmetry, as well as measures of asymmetry which are monotone in that order. As for applications, we show that asymmetry does occur in real financial data. This implies that in finance and risk management, asymmetric models should be favored against the usual symmetric ones

An order for asymmetry in copulas, and implications for risk management

We investigate symmetry properties of bivariate copulas. For this, we introduce an order of asymmetry, as well as measures of asymmetry which are monotone in that order. As for applications, we show that asymmetry does occur in real financial data. This implies that in finance and risk management, asymmetric models should be favored against the usual symmetric ones

Quantum-mechanical wavepacket transport in quantum cascade laser structures

We present a viewpoint of the transport process in quantum cascade laser structures in which spatial transport of charge through the structure is a property of coherent quantum-mechanical wavefunctions. In contrast, scattering processes redistribute particles in energy and momentum but do not directly cause spatial motion of charge.Comment: 6 pages, 5 figures included in tex, to appear in Physical Review

Ultrafast modulation of electronic structure by coherent phonon excitations

Femtosecond x-ray absorption spectroscopy with a laser-driven high-harmonic source is used to map ultrafast changes of x-ray absorption by femtometer- scale coherent phonon displacements. In LiBH4, displacements along an Ag phonon mode at 10 THz are induced by impulsive Raman excitation and give rise to oscillatory changes of x-ray absorption at the Li K edge. Electron density maps from femtosecond x-ray diffraction data show that the electric field of the pump pulse induces a charge transfer from the BH4− to neighboring Li+ ions, resulting in a differential Coulomb force that drives lattice vibrations in this virtual transition state