Vesicle propulsion in haptotaxis: A local model

We study theoretically vesicle locomotion due to haptotaxis. Haptotaxis is referred to motion induced by an adhesion gradient on a substrate. The problem is solved within a local approximation where a Rayleigh-type dissipation is adopted. The dynamical model is akin to the Rousse model for polymers. An invariant formulation is used to solve a dynamical model which includes a kind of dissipation due to bond breaking/restoring with the substrate. For a stationary situation where the vesicle acquires a constant drift velocity, we formulate the propulsion problem in terms of a nonlinear eigenvalue (the a priori unknown drift velocity) one of Barenblat-Zeldovitch type. A counting argument shows that the velocity belongs to a discrete set. For a relatively tense vesicle, we provide an analytical expression for the drift velocity as a function of relevant parameters. We find good agreement with the full numerical solution. Despite the oversimplification of the model it allows the identification of a relevant quantity, namely the adhesion length, which turns out to be crucial also in the nonlocal model in the presence of hydrodynamics, a situation on which we have recently reported (I. Cantat and C. Misbah, Phys. Rev. Lett. 83, 235 (1999)) and which constitutes the subject of a forthcoming extensive study. Received 10 February 2000     

Measurement of temperature and velocity fields in a heater unit by liquid crystal thermometry and particle image velocimetry

Temperature and velocity fields in a heating unit for automobiles are measured through a model experiment in water tunnel using flow visualizations and image analysis to investigate the mixing mechanism of the flow that has passed through the heater and not passed through it inside the unit. The temperature fields are measured by the liquid crystal visualization technique combined with the field calibration using full color spline fitting technique, and the velocity fields are evaluated by a particle imaging technique with a cross-correlation algorithm. These results indicate an enhanced flow mixing at larger mix-door angles, which results in a shorter mixing distance of temperature and velocity downstream of the mix door. The enhanced flow mixing is caused by the high velocity fluctuations created by the flow separation over the mix door.     

Direct observation of variations of optical properties in single quantum dots by using time-resolved near-field scanning optical microscope

We study the variations of optical properties of self-assembled In_0.5Ga_0.5As single quantum dots (QDs) in the spatial and time domains by combining a near-field scanning optical microscope with an ultrafast pulsed laser. Through the examinations of several tens of QDs, we find that the variations of photoluminescence (PL) intensity strongly depend on the condition of the initial carrier creation. The differences in quantum efficiency and those in the carrier flow rate into QDs cause the large distribution of PL intensity when the carriers are excited in the barrier layers. From the results of time-resolved PL decay measurements, we find that there are two types of QDs exhibiting quite different PL decay profiles.     

Fiber-in-tube solid-phase microextraction: a fibrous rigid-rod heterocyclic polymer as the extraction medium

A novel “fiber-in-tube” configuration has been applied to the extraction tube of solid phase microextraction (SPME), and the direct coupling of the extraction process to liquid chromatography (LC) has been accomplished for the analysis of n-butylphthalate in wastewater. By using this fiber-in-tube SPME/LC system the preconcentration factor for the phthalate was about 160 with 20 min extraction and no interference peak was observed in the chromatogram. The results also showed the potential applications of this fiber-in-tube SPME/LC for the analysis of sub-ppb level (i.e., lower than 1 ng/mL) of various organic analytes in aqueous sample matrix without a large solvent consumption during the preconcentration process.     

Novel carbon-carbon bond-forming reactions using carbocations produced from substituted propargyl silyl ethers by the action of TMSOTf.

Highly useful carbon-carbon bond forming reactions using stable allenyl, propargyl, or allyl-propargyl hybrid cations have been developed. These carbocations could be generated from silyl 1-(pi-donor)-substituted propargyl ethers by the action of trimethylsilyl trifluoromethanesulfonate in dichloromethane at -78 degrees C to room temperature and could be attacked nucleophilically by electron rich arenes, allylsilanes, or enol silyl ethers, giving rise to allenes, alkynes, and their derivatives. A novel method for regio- and stereoselective synthesis of conjugated enynes utilizing allyl-propargyl hybrid cations has also been established.     

Aromatization of enamines promoted by a stoichiometric amount of palladium(II) salts: a novel method for the synthesis of aromatic amines.

Enamines (1a-r) prepared from cyclohexanones, cyclohexane-1,3-diones, or tetralones led to arylamines (2a-r) in one pot when treated with a stoichiometric amount of palladium salts [PdCl2-(MeCN)2] in acetonitrile in the presence of triethylamine at room temperature or at elevated temperature, in some cases for 5 min to 2 h. The initial electrophilic attack of palladium chloride on the beta-carbon of the enamines led to a sigma-palladium species (8) which triggered a series of reactions (-->9-->10-->11-->12) destined for aromatization to give 2a-r in good yields. The intervention of such a sigma-palladium species has been attested by a trapping experiment. On the basis of this reaction mechanism, we have developed another new process capable of transforming acyclic compounds having 6-en-2-one frameworks (16, 23, 25) to arylamines (2s-u) when their enamines were treated under the similar conditions as above, featuring again the formation of sigma-palladium species such as 8 as the initial key intermediate.     

Mechanochemical Synthesis of LaOX (X=Cl, Br) and Their Solid State Solutions

A mixture of lanthanum oxide (La₂O₃), chloride (LaCl₃), and bromide (LaBr₃) was ground in air by a planetary ball mill to investigate synthesis of lanthanum oxychloride (LaOCl), oxybromide (LaOBr), and their solid solutions, LaOCl_1−xBr_x (0≤x≤1, Δx=0.25). The synthesizing reactions proceed with an increase in grinding time. Unit cell dimensions, a, c, and lattice volume of the solutions evolve linearly with an increase in x in the LaOCl_1−xBr_x series. Comparing unit cell dimensions of LaOX synthesized by mechanochemical reaction to those of LaOX synthesized by solid-state reaction at high temperature, there is no difference in the length of c, while a is shortened slightly. This may be attributed to the complex cation layer of (LaO)ⁿ⁺_n, with a close relationship to a of the cell dimensions, being affected by the intensive grinding.