Capillary forces between sediment particles and an air-water interface

In the vadose zone, air-water interfaces play an important role in particle fate and transport, as particles can attach to the air-water interfaces by action of capillary forces. This attachment can either retard or enhance the movement of particles, depending on whether the air-water interfaces are stationary or mobile. Here we use three standard PTFE particles (sphere, circular cylinder, and tent) and seven natural mineral particles (basalt, granite, hematite, magnetite, mica, milky quartz, and clear quartz) to quantify the capillary forces between an air-water interface and the different particles. Capillary forces were determined experimentally using tensiometry, and theoretically assuming volume-equivalent spherical, ellipsoidal, and circular cylinder shapes. We experimentally distinguished between the maximum capillary force and the snap-off force when the air-water interface detaches from the particle. Theoretical and experimental values of capillary forces were of similar order of magnitude. The sphere gave the smallest theoretical capillary force, and the circular cylinder had the largest force due to pinning of the air-water interface. Pinning was less pronounced for natural particles when compared to the circular cylinder. Ellipsoids gave the best agreement with measured forces, suggesting that this shape can provide a reasonable estimation of capillary forces for many natural particles.     

Losses in GaInAs(P)/InP and GaAlSb(As)/GaSb lasers--The influence of the split-off valence band

GaInAs(P)/InP and GaAlSb(As)/GaSb are interesting material systems for long wavelength optical fiber communication. However lasers fabricated from these materials exhibit a substantially higher temperature dependence of the threshold current than GaAs/ GaAlAs lasers ("T0-problem"). lntervalence band absorption and CHSH-Auger-recombination have been suggested as two possible causes for the strong temperature dependent losses in long wavelength lasers. Both mechanisms, if present, should lead to a population of the split-off valence band. In GaInAsP/InP lasers, we have studied this population by directly observing the radiative high-energy recombination of electrons with holes in the split-off valence band. In the case of the band structure of GaAlSb(As), the band gap energy E0is close or equal to the spin-orbit splitting energy Δ0, which favors hole-Auger recombination and intervalence band absorption, as confirmed by our experimental results.     

Attentional sensitization of unconscious cognition: Task sets modulate subsequent masked semantic priming.

According to classical theories, automatic processes are autonomous and independent of higher level cognitive influence. In contrast, the authors propose that automatic processing depends on attentional sensitization of task-congruent processing pathways. In 3 experiments, the authors tested this hypothesis with a modified masked semantic priming paradigm during a lexical decision task by measuring event-related potentials (ERPs): Before masked prime presentation, participants attended an induction task either to semantic or perceptual stimulus features designed to activate a semantic or perceptual task set, respectively. Semantic priming effects on the N400 ERP component, an electrophysiological index of semantic processing, were obtained when a semantic task set was induced immediately before subliminal prime presentation, whereas a previously induced perceptual task set attenuated N400 priming. Across experiments, comparable results were obtained regardless of the difficulty level and the verbal or nonverbal nature of the induction tasks. In line with the proposed attentional sensitization model, unconscious semantic processing is enhanced by a semantic and attenuated by a perceptual task set. Hence, automatic processing of unconscious stimuli is susceptible to top-down control for optimizing goal-related information processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)