Imaging-based Parametric Resonance in an Optical Dipole Atom Trap

We report sensitive detection of parametric resonances in a high-density sample of ultracold $^{87}Rb$ atoms confined to a far-off-resonance optical dipole trap. Fluorescence imaging of the expanded ultracold atom cloud after a period of parametric excitation shows significant modification of the atomic spatial distribution and has high sensitivity compared with traditional measurements of parametrically-driven trap loss. Using this approach, a significant shift of the parametric resonance frequency is observed, and attributed to the anharmonic shape of the dipole trap potential

A scaling law for light scattering from dense and cold atomic ensembles

We calculate the differential cross section of polarized light scattering from a cold and dense atomic ensemble. The regularities in the transformation of the cross section when increasing the size of the atomic ensemble are analyzed numerically. We show that for typical experimental conditions, an approximate scaling law can be obtained. Very good agreement is found in a comparison with experimental data on the size dependence of a dense and cold cloud of 87$Rb atoms.Comment: Submitted to Journal of Modern Optics, Special issue on the Proceedings of the Colloquium on the Physics of Quantum Electronic

The behaviour of roof gable walls under the effect of earthquake load

In this study, the effect of earthquake loads on roof gable walls and the behaviours of these roof gable walls are investigated. In preparation of the study, two experiments on cradle roof system which gets and does not get any loads off the roof members were carried out in all. The experiments were performed on the shaking table in Earthquake Research Department of General Directorate of Disaster Affairs. Through the experiments, some considerable results were obtained on the behaviours of roof gable walls under the effect of horizontal dynamic loads. The results obtained at the end of these examinations are given and discussed. Furthermore, suggestions to make the brick gable walls more reliable against the loads of earthquake are given. When the results of the experiments were generally taken into consideration, it was realized that the gable walls in both roof systems would partly or completely collapse even under the effect of a little horizontal dynamic load

Some features of flow and particle transport in porous structures

There has been a growing interest in the study of porous and complex flow structures due to its impact in technology. This concerns not only environmental but also diagnostic and therapeutic exposure in medical research. Physics of flow within porous structures is especially important to model transport and deposition of viruses, pollutants and drugs deep in these structures. In this work we analyze numerically low and medium Reynolds number flows in axisymmetric cylindrical duct surrounded by a torus. We also consider three different particle sizes (0.02, 0.1 and 20 micron) for possible physiological and environmental applications

Spectral Dependence of Coherent Backscattering of Light in a Narrow-Resonance Atomic System

We report a combined theoretical and experimental study of the spectral and polarization dependence of near resonant radiation coherently backscattered from an ultracold gas of 85Rb atoms. Measurements in an approximately 6 MHz range about the 5s^{2}S_{1/2}- 5p^{2}P_{3/2}, F=3 - F'=4 hyperfine transition are compared with simulations based on a realistic model of the experimental atomic density distribution. In the simulations, the influence of heating of the atoms in the vapor, magnetization of the vapor, finite spectral bandwidth, and other nonresonant hyperfine transitions are considered. Good agreement is found between the simulations and measurements.Comment: 10 pages, 12 figur