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We herein demonstrate the cause of well-observed variant transport behaviors for apparently identical colloids in porous media under conditions of colloid-collector repulsion (unfavorable attachment conditions). We demonstrate that variant colloid transport behavior under unfavorable conditions can be explained by inherently variable colloid residence times prior to arrest on grains (collectors). We demonstrate that the residence time distributions derived from particle trajectory simulations incorporating representative nanoscale heterogeneity provide quantitative prediction of colloid transport under unfavorable conditions. We quantitatively predict hyper-exponential retention profiles in glass beads from representative nanoscale heterogeneity determined for glass, and we qualitatively predict nonmonotonic retention profiles in quartz sand from an estimated representative nanoscale heterogeneity for quartz. We also demonstrate that the transition from hyper-exponential to nonmonotonic profiles among glass beads versus quartz sand under otherwise equivalent conditions is primarily driven by greater grain angularity and consequent greater length and number of grain to grain contacts in quartz sand relative to glass beads. That continuum-scale transport behaviors emerge from upscaling of simulated pore-scale colloid residence times corroborates the utility of representative nanoscale heterogeneity for quantitative prediction of colloid transport under unfavorable conditions.

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Abstract: The fatigue performance of the high-strength magnesium alloy AZ 80 is studied in air as well as in aqueous 0.5 and 3.5% NaCl solutions. The effect of mechanical surface treatments, specifically mechanical polishing, shot peening, and roller burnishing on the S-N curves, is investigated using an electropolished surface as a reference. While mechanical polishing as well as shot peening improves fatigue performance in air, no improvement is observed in NaCl solutions. However, roller burnishing, which combines a smooth surface finish with residual compressive stresses in sufficient depths, leads to outstanding fatigue performance even in 3.5% NaCl solution.

We investigate the influence of carrier relaxation on the emission dynamics of a semiconductor microcavity laser. The structure is optically excited with energies of 1.477 down to 1.346 eV (resonant excitation). The stimulated emission dynamics clearly becomes faster for decreasing excitation energy and the influence of the light hole on the emission dynamics is demonstrated. Theoretical calculations reproduce the results only if the nonequilibrium carrier dynamics is treated on the basis of a microscopic model.

The Larmor precession of polarized electron spins in a transverse magnetic field causes a synchronized pulsing of the stimulated emission of a semiconductor microcavity. Alternating right- and left-handed circularly polarized pulses are emitted by the vertical cavity laser after excitation of the In0.04Ga0.96As quantum wells in the resonator with circularly polarized pulses of a picosecond Ti: sapphire laser. The excitation geometry is the Voigt geometry with the magnetic field in the plane of the quantum wells and the optical axis in growth direction. The non-equilibrium carrier and the coupled laser dynamics are successfully analyzed with a microscopic theory.

A simple new pump geometry for optical excitation of microcavities and vertical-cavity surface-emitting lasers is presented. The technique circumvents the high reflectivity of the cavity stop band by excitation through the substrate at a large angle of incidence. Under these conditions, the reflectivity of the bottom Bragg reflector is small, and optical pumping at any desired photon energy becomes possible. Experimental results for optical excitation with this new geometry are compared with resonant optical pumping through the cavity mode.

Deprotonation of (I) leads to the endo‐configurated allyl anion (II) exclusively.