Adaptive instant record signals applied to detection with time reversal operator decomposition

Time reversal arrays are becoming common tools whether for detection or tomography. These applications require the measurement of the response from the array to one or several receivers. The most natural way to record the impulse responses for several sources is to generate pulses successively from each emitting point and record simultaneously the signals from the receivers. However, this method is very time consuming or inefficient in terms of signal-to-noise ratio. To overcome this limitation quasi-orthogonal pseudonoise signals like Kasami sequences can be used. For guided wave propagation, a very high degree of orthogonality between the signal is necessary to allow an accurate measure of the whole multipath structure of the transfer function. Hence, in this work, we propose a new family of pseudo-orthogonal signals that is adapted to the environment and more specifically, to highly dispersive media. These adaptive instant records signals are used experimentally to detect targets using the time reversal operator decomposition method. The accuracy of the 15 x 15 transfer functions acquired simultaneously, and therefore the detection capability, are demonstrated in an experimental ultrasonic waveguide as a small-scale model of shallow water propagation including bottom absorption and reverberation.     

Synthesis and reactions of polymer-bound Ph3P=C=C=O: a quick route to tenuazonic acid and other optically pure 5-substituted tetramates

Polystyrene-bound cumulated ylide Ph3PCCO was prepared on a large scale in two steps. It reacts with Grignard compounds, amines and alcohols to give immobilized acyl, amide and ester ylides, respectively. Their Wittig reactions lead to alkenes free of phosphane oxide. Optically pure 5-substituted tetramates were obtained from reactions of resin-bound Ph3PCCO with alpha-ammonium esters in one step. The mycotoxin (-)-tenuazonic acid was accordingly prepared in just three steps.     

A concise stereocontrolled formal total synthesis of (+/-)-podophyllotoxin using sulfoxide chemistry

A short stereoselective formal total synthesis of (+/-)-podophyllotoxin has been carried out from a sulfoxide, using a one-pot tandem conjugate addition/aldol/electrophilic aromatic substitution reaction to form a tetralin, which was converted into picropodophyllin in two steps.     

Diffusion of asymmetric swimmers

Particles moving along curved trajectories will diffuse if the curvature fluctuates sufficiently in either magnitude or orientation. We consider particles moving at a constant speed with either a fixed or a Gaussian distributed magnitude of curvature. At small speeds the diffusivity is independent of the speed. At larger particle speeds, the diffusivity depends on the speed through a novel exponent. We apply our results to intracellular transport of vesicles. In sharp contrast to thermal diffusion, the effective diffusivity increases with vesicle size and so may provide an effective means of intracellular transport.     

Concentration of sodium ion as the determining factor for the association of dansyl amino acids with the teicoplanin molecule in reversed-phase liquid chromatography

The mechanism of the binding of D,L dansyl amino acids to teicoplanin was investigated. Na+ was used as an indicator of the interactions between the solutes and teicoplanin. The number (n) of sodium ions, Na+, excluded from the solute-teicoplanin interface when analyte transfer occurred was determined. A thermodynamic study and enthalpy-entropy compensation were performed to further explore the interaction mechanism. From these results, it was shown that teicoplanin was balanced between 2 conformational states characterized by distinct enantioselective properties. This approach indicates that liquid chromatography (LC) is a useful tool to extract physicochemical and molecular information from retention data. Thus, LC can be used as a complementary technique with the conventional techniques of molecular interaction analysis.     

Macrocyclic diiminodipyrromethane complexes: structural analogues of Pac-Man porphyrins

The complexation of palladium(II) by a unique family of [2+2] diiminodipyrromethane macrocycles yields compounds that adopt structures reminiscent of Pac-Man porphyrins.     

Exploring the origins of the power-law properties of energy landscapes: An egg-box model

Multidimensional potential energy landscapes (PELs) have a Gaussian distribution for the energies of the minima, but at the same time the distribution of the hyperareas for the basins of attraction surrounding the minima follows a power-law. To explore how both these features can simultaneously be true, we introduce an “egg-box” model. In these model landscapes, the Gaussian energy distribution is used as a starting point and we examine whether a power-law basin area distribution can arise as a natural consequence through the swallowing up of higher-energy minima by larger low-energy basins when the variance of this Gaussian is increased sufficiently. Although the basin area distribution is substantially broadened by this process, it is insufficient to generate power-laws, highlighting the role played by the inhomogeneous distribution of basins in configuration space for actual PELs.