Two-dimensional motion of a set of particles in a free surface flow with image processing

A method to analyze bed load with image processing was developed. The motion of coarse spherical particles on a mobile bed entrained by a shallow turbulent flow down a steep channel was filmed with a high-speed camera. The water free surface and the particle positions were detected combining classical image processing algorithms. We developed a particle-tracking algorithm to calculate all particle trajectories and motion regimes, rolling or saltation. At constant slope, the contribution of the rolling particles to the solid discharge only slightly differed when the particle supply was increased. At a slope of 10%, it represented about 40%. In contrast, rolling became the major regime when the slope increased, at a slope of 15% it represented up to 80% of the total solid discharge.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Mortar physical properties evolution in extrusion flow

Extrusion is not a common way to form firm cement-based material. Due to material frictional behaviour, drainage phenomenon appears and leads to process blockage. The properties of the extrusion multiphase flow of such specific materials have to be highlighted to understand the properties of the process flow. An extrudible mortar is formulated according to extrusion criteria provided by literature tests developed to describe the evolution of the paste undergoing extrusion. To study the relationship between flow properties, extrusion force and material consolidation, a technique based on the measurement of paste hardness in the billet zone is developed. Measurements of the local paste density and flow visualisation are also performed. Results show that in the range of used ram velocities, filtration occurs between fluid and solid phases. This creates zones of preferential flow and of non-flowing consolidated material. Paper presented at the 3rd Annual European Rheology Conference held on April 27–29, 2006, Crete, Greece.     

Measurement of the Zeta Potential of Oil Drops with the Spinning Tube Zetameter

The spinning tube zetameter, an apparatus which was utilized up to now to keep a gas bubble from settling while electrophoretic measurement was carried out, can be used to measure the zeta potential of an oil drop as well. This piece of equipment is brought into play for estimating the influence of various formulation variables (pH, ionic strength, surfactant type or mixture) on the zeta potentials of oil drops. The results are compared to those reported in the literature.     

Dispersion and orientation of single-walled carbon nanotubes in a chromonic liquid crystal

A post-synthesis alignment of individual single-walled carbon nanotubes (SWCNTs) is desirable for translating their unique anisotropic properties to a macroscopic scale. Here, we demonstrate excellent dispersion, orientation and concomitant-polarised photoluminescence of SWCNTs in a nematic chromonic liquid crystal. The methods to obtain stable suspension are described, and order parameters of the liquid crystal matrix and of the nanotubes are measured independently.     

Proton Catalysis in the Redox Responsivity of a Mini‐Sized Photochromic Diarylethene

A thermally irreversible dithienylethene (DTE) photochrom can be turned into a thermally reversible one in presence of Cu^II triflate. A ring opening (DTEC closed→DTEO open) occurs through the formation of a copper‐containing fast transient intermediate. Stopped‐flow experiments monitored at 410 and 780 nm have allowed to show that the stoichiometry of this intermediate is DTE/Cu=1:1. At longer monitoring times (i.e., several seconds after mixing), the intermediate undergoes a slow decay while the residual DTEC closed form opens. A joint detailed kinetic and electrochemical analysis has unveiled a proton catalysis scenario in which electron transfer between DTEC and Cu^II, ligand exchange, protonation‐deprotonation equilibria of the cation radicals and ring opening are embedded into two main reaction cycles. At the beginning of the reaction, Cu^II is reduced into Cu^I and DTE is degraded without ring opening. Then, as the reaction progresses, the triflic acid released from the Cu^II reduction switches‐on a propagation cycle during which ring opens without any more Cu^II consumption. Cyclic voltammetry, spectro‐electrochemical measurements, delayed photocoloration experiments in presence of Cu^II and acid–base additions have confirmed the main features of the proton catalysis.     

Gas-Phase Structure of Amyloid-β (12 – 28) Peptide Investigated by Infrared Spectroscopy, Electron Capture Dissociation and Ion Mobility Mass Spectrometry

The gas-phase structures of doubly and triply protonated Amyloid-β_12-28 peptides have been investigated through the combination of ion mobility (IM), electron capture dissociation (ECD) mass spectrometry, and infrared multi-photon dissociation (IRMPD) spectroscopy together with theoretical modeling. Replica-exchange molecular dynamics simulations were conducted to explore the conformational space of these protonated peptides, from which several classes of structures were found. Among the low-lying conformers, those with predicted diffusion cross-sections consistent with the ion mobility experiment were further selected and their IR spectra simulated using a hybrid quantum mechanical/semiempirical method at the ONIOM DFT/B3LYP/6-31 g(d)/AM1 level. In ECD mass spectrometry, the c/z product ion abundance (PIA) has been analyzed for the two charge states and revealed drastic differences. For the doubly protonated species, N – C_α bond cleavage occurs only on the N and C terminal parts, while a periodic distribution of PIA is clearly observed for the triply charged peptides. These PIA distributions have been rationalized by comparison with the inverse of the distances from the protonated sites to the carbonyl oxygens for the conformations suggested from IR and IM experiments. Structural assignment for the amyloid peptide is then made possible by the combination of these three experimental techniques that provide complementary information on the possible secondary structure adopted by peptides. Although globular conformations are favored for the doubly protonated peptide, incrementing the charge state leads to a conformational transition towards extended structures with 3₁₀- and α-helix motifs.      

Small Changes Have Consequences: Lessons from Tetrabenzyltitanium and ‐zirconium Surface Organometallic Chemistry

Homoleptic benzyl derivatives of titanium and zirconium have been grafted onto silica that was dehydroxylated at 200 and 700 °C, thereby affording bi‐grafted and mono‐grafted single‐site species, respectively, as shown by a combination of experimental techniques (IR, MAS NMR, EXAFS, and elemental analysis) and theoretical calculations. Marked differences between these compounds and their neopentyl analogues are discussed and rationalized by using DFT. These differences were assigned to the selectivity of the grafting process, which, depending on the structure of the molecular precursors, led to different outcomes in terms of the mono‐ versus bi‐grafted species for the same surface concentration of silanol species. The benzylzirconium derivatives were active towards ethylene polymerization in the absence of an activator and the bi‐grafted species displayed higher activity than their mono‐grafted analogues. In contrast, the benzyltitanium and neopentylzirconium counterparts were not active under similar reaction conditions.     

A Novel One- and Zero-Dimensional Model for Turbulent Jet Ignition

Flow, Turbulence and Combustion - Turbulent jet ignition (TJI) is a promising combustion technology for burning highly diluted air-fuel mixtures. Computationally efficient models to assess the...     

Auditory discrimination of force of impact

The auditory discrimination of force of impact was measured for three groups of listeners using sounds synthesized according to first-order equations of motion for the homogenous, isotropic bar [Morse and Ingard (1968). Theoretical Acoustics pp. 175-191]. The three groups were professional percussionists, nonmusicians, and individuals recruited from the general population without regard to musical background. In the two-interval, forced-choice procedure, listeners chose the sound corresponding to the greater force of impact as the length of the bar varied from one presentation to the next. From the equations of motion, a maximum-likelihood test for the task was determined to be of the form Δlog A + αΔ log f > 0, where A and f are the amplitude and frequency of any one partial and α = 0.5. Relative decision weights on Δ log f were obtained from the trial-by-trial responses of listeners and compared to α. Percussionists generally outperformed the other groups; however, the obtained decision weights of all listeners deviated significantly from α and showed variability within groups far in excess of the variability associated with replication. Providing correct feedback after each trial had little effect on the decision weights. The variability in these measures was comparable to that seen in studies involving the auditory discrimination of other source attributes.