Velocity oscillations in actin-based motility

We present a simple and generic theoretical description of actin-based motility, where polymerization of filaments maintains propulsion. The dynamics is driven by polymerization kinetics at the filaments' free ends, crosslinking of the actin network, attachment and detachment of filaments to the obstacle interfaces and entropic forces. We show that spontaneous oscillations in the velocity emerge in a broad range of parameter values, and compare our findings with experiments.Comment: 5 pages, 6 figure

Crystalline and disordered state of poly(dihexylsilylene) copolymers

A systematic comparison of random copolymers, derived from poly(dihexylsilylene) (PDHS) by incorporation of monomeric units with shorter unbranched alkyl side chains, has been carried out based on calorimetry, variable temperature UV spectroscopy, and 29Si MAS (magic angle spinning) solid state NMR investigations. Also, hexylmethylsilylene units and branched monomers have been copolymerized. Up to 10% comonomer with shorter linear side chains (i. e., pentyl to propyl) could be incorporated into PDHS without impeding the all-trans order of the crystalline phase. In this case, the UV absorption maximum of the crystalline low-temperature phase was affected only slightly according to the length and fraction of the comonomer side chains. A less ordered crystal structure (λmax = 345-355 nm) was observed when the content of comonomers with shorter side chains was about 20%. Yet, all these materials form conformationally disordered mesophases. A clear disordering transition and corresponding thermochromism was not observed any more when 50% of propyl side chains were incorporated. The order of the crystalline and the mesophase is also strongly perturbed if only a small fraction (4%) of the side chains are branched at C2

Assessing the Zone of Comfort in Stereoscopic Displays using EEG

The conflict between vergence (eye movement) and accommodation (crystalline lens deformation) occurs in every stereoscopic display. It could cause important stress outside the "zone of comfort", when stereoscopic effect is too strong. This conflict has already been studied using questionnaires, during viewing sessions of several minutes. The present pilot study describes an experimental protocol which compares two different comfort conditions using electroencephalography (EEG) over short viewing sequences. Analyses showed significant differences both in event-related potentials (ERP) and in frequency bands power. An uncomfortable stereoscopy correlates with a weaker negative component and a delayed positive component in ERP. It also induces a power decrease in the alpha band and increases in theta and beta bands. With fast responses to stimuli, EEG is likely to enable the conception of adaptive systems, which could tune the stereoscopic experience according to each viewer

Progressive Low-Grade Metamorphism of a Black Shale Formation, Central Swiss Alps, with Special Reference to Pyrophyllite and Margarite Bearing Assemblages

The unmetamorphosed equivalents of the regionally metamorphosed clays and marls that make up the Alpine Liassic black shale formation consist of illite, irregular mixed-layer illite/montmorillonite, chlorite, kaolinite, quartz, calcite, and dolomite, with accessory feldspars and organic material. At higher grade, in the anchizonal slates, pyrophyllite is present and is thought to have formed at the expense of kaolinite; paragonite and a mixed-layer paragonite/muscovite presumably formed from the mixed-layer illite/montmorillonite. Anchimetamorphic illite is poorer in Fe and Mg than at the diagenetic stage, having lost these elements during the formation of chlorite. Detrital feldspar has disappeared. In epimetamorphic phyllites, chloritoid and margarite appear by the reactions pyrophyllite + chlorite = chloritoid + quartz + H2O and pyrophyllite + calcite ± paragonite = margarite + quartz + H2O + CO2, respectively. At the epi-mesozone transition, paragonite and chloritoid seem to become incompatible in the presence of carbonates and yield the following breakdown products: plagioclase, margarite, clinozoisite (and minor zoisite), and biotite. The maximum distribution of margarite is at the epizone-mesozone boundary; at higher metamorphic grade margarite is consumed by a continuous reaction producing plagioclase. Most of the observed assemblages in the anchi-and epizone can be treated in the two subsystems MgO (or FeO)-Na2O−CaO−Al2O3−(KAl3O5−SiO2−H2O−CO2). Chemographic analyses show that the variance of assemblages decreases with increasing metamorphic grade. Physical conditions are estimated from calibrated mineral reactions and other petrographic data. The composition of the fluid phase was low in XCO2 throughout the metamorphic profile, whereas XCH4 was very high, particularly in the anchizone where aH2O was probably as low as 0.2. P-T conditions along the metamorphic profile are 1-2 kb/200-300 °C in the anchizone (Glarus Alps), and 5 kb/500-550 °C at the epi-mesozone transition (Lukmanier area). Calculated geothermal gradients decrease from 50 °C/km in the anchimetamorphic Glarus Alps to 30 °C/km at the epi-mesozone transition of the Lukmanier are