Speckle dynamics under ergodicity breaking

Abstract Laser speckle contrast imaging (LSCI) is a well-known and versatile approach for the non-invasive visualization of flows and microcirculation localized in turbid scattering media, including biological tissues. In most conventional implementations of LSCI the ergodic regime is typically assumed valid. However, most composite turbid scattering media, especially biological tissues, are non-ergodic, containing a mixture of dynamic and static centers of light scattering. In the current study, we examined the speckle contrast in different dynamic conditions with the aim of assessing limitations in the quantitative interpretation of speckle contrast images. Based on a simple phenomenological approach, we introduced a coefficient of speckle dynamics to quantitatively assess the ratio of the dynamic part of a scattering medium to the static one. The introduced coefficient allows one to distinguish real changes in motion from the mere appearance of static components in the field of view. As examples of systems with static/dynamic transitions, thawing and heating of Intralipid samples were studied by the LSCI approach

Cosmic Ray Cutoff Rigidities during Geomagnetic Storms: A Comparison of Magnetospheric Models

CR geomagnetic cutoff rigidities in the magnetic field of two different empirical models of the magnetosphere—Tsyganenko 1989 (Ts89) and Tsyganenko 1996 (Ts96)—have been determined by the method of trajectory computations for two magnetic storms of January 23–31, 1985, and November 23–29, 1986, when anomalies were observed on the satellites and processing systems operated intermittently. A comparison of geo-magnetic cutoff rigidities in Ts89 and Ts96 models indicated that the difference between these rigidities during the above storms can reach 0.5 GV at midlatitude stations