A Self-Consistent Quantum Field Theory for Random Lasing

The spatial formation of coherent random laser modes in strongly scattering disordered random media is a central feature in the understanding of the physics of random lasers. We derive a quantum field theoretical method for random lasing in disordered samples of complex amplifying Mie resonators which is able to provide self-consistently and free of any fit parameter the full set of transport characteristics at and above the laser phase transition. The coherence length and the correlation volume respectively is derived as an experimentally measurable scale of the phase transition at the laser threshold. We find that the process of stimulated emission in extended disordered arrangements of active Mie resonators is ultimately connected to time-reversal symmetric multiple scattering in the sense of photonic transport while the diffusion coefficient is finite. A power law is found for the random laser mode diameters in stationary state with increasing pump intensity.

Ideal charge-density-wave order in the high-field state of superconducting YBCO

The existence of charge-density-wave (CDW) correlations in cuprate superconductors has now been established. However, the nature of the CDW ground state has remained uncertain because disorder and the presence of superconductivity typically limit the CDW correlation lengths to only a dozen unit cells or less. Here we explore the field-induced 3D CDW correlations in extremely pure detwinned crystals of YBa2Cu3O2(YBCO) ortho-II and ortho-VIII at magnetic fields in excess of the resistive upper critical field (Hc2) where superconductivity is heavily suppressed. We observe that the 3D CDW is unidirectional and possesses a long in-plane correlation length as well as significant correlations between neighboring CuO2planes. It is significant that we observe only a single sharply defined transition at a critical field proportional toHc2, given that the field range used in this investigation overlaps with other high-field experiments including quantum oscillation measurements. The correlation volume is at least two to three orders of magnitude larger than that of the zero-field CDW. This is by far the largest CDW correlation volume observed in any cuprate crystal and so is presumably representative of the high-field ground state of an “ideal” disorder-free cuprate.

In vivo identification of soft biological tissues using MR imaging

Soft biological tissues constituting the human body are individually investigated regarding the identification of their mechanical properties. This study proposes an identification process of human legs tissues by coupling Magnetic Resonance Imaging (MRI) images with different levels of stocking used as mechanical loading. This loading may be compared with a compression around the whole leg section. The identification method relies on one hand on MRI image processing (digital image correlation, volume extraction, etc.) and on the other hand on a Finite Element Model combined with an optimization algorithm.

X-Ray Characterization of Defects in Irradiated Iron

ABSTRACTWe report on a thorough X-ray study of irradiation induced defects in iron. Single crystals were irradiated at 4.6 K with reactor neutrons and at 90 K with 2 MeV electrons. After irradiation and subsequent thermal annealing, we measured the defect induced diffuse scattering of X-rays (Huang scattering) and the small angle scattering of synchrotron radiation. Simultaneously, lattice parameter and electrical resistivity changes were measured. The single defect properties are determined from low dose electron irradiated samples and yield the lattice distortions, i.e., the volume change and defect symmetry as described by the force dipole tensor. Excellent agreement of the experimental results with calculated values from literature is observed. After neutron irradiation, defects are correlated within displacement cascades. The correlations for vacanciesand interstitials are described by a spatial correlation volume. These results are compared with computer simulations usingthe Marlowe code. During thermal annealing the irradiation induced defects agglomerate at characteristic temperatures and we observe changes in the spatial correlations of the defects. There is a clear difference between electron and neutron irradiated samples concerning defect recovery in stage 1.