From Polyesters to Polyamides Via O?N Acyl Migration: An Original Multi‐Transfer Reaction

A new strategy for the synthesis of polyamides from polyesters of hydroxyl‐containing amino acids using a multi O N acyl transfer reaction was developed. This original approach allowed the synthesis of three generations of polymers from the same starting monomer. The polymerization of N‐benzyloxycarbonyl‐serine and its γ‐homologated derivative provided the Z‐protected polyesters; then the water‐soluble polycationic polyesters were obtained by removal of the Z‐protecting group; and finally the polyamides were obtained by a base‐induced multi O N acyl transfer, both in aqueous or organic medium. The key step transfer reaction was monitored by the disappearance and appearance of characteristic NMR proton signals and IR bands of polyesters and polyamides.

     

Reversibility and irreversibility from an initial value formulation

From a time evolution equation for the single particle distribution function derived from the N-particle distribution function (A. Muriel, M. Dresden, Physica D 101 (1997) 297), an exact solution for the 3D Navier–Stokes equation – an old problem – has been found (A. Muriel, Results Phys. 1 (2011) 2). In this Letter, a second exact conclusion from the above-mentioned work is presented. We analyze the time symmetry properties of a formal, exact solution for the single-particle distribution function contracted from the many-body Liouville equation. This analysis must be done because group theoretic results on time reversal symmetry of the full Liouville equation (E.C.G. Sudarshan, N. Mukunda, Classical Mechanics: A Modern Perspective, Wiley, 1974). no longer applies automatically to the single particle distribution function contracted from the formal solution of the N-body Liouville equation. We find the following result: if the initial momentum distribution is even in the momentum, the single particle distribution is reversible. If there is any asymmetry in the initial momentum distribution, no matter how small, the system is irreversible.     

Computational polarization imaging from a single speckle image

We experimentally demonstrate that imaging of the degree of polarization (DOP) can be achieved from a single intensity image acquired under coherent illumination. This computational technique is based on the analysis of the speckle characteristics in a statistically homogeneous neighborhood of the pixel. Over a variety of samples obtained experimentally, we show that a simple calibration step allows this method to quickly and simply provide correct estimated values of the DOP, with precision in agreement with theoretical predictions. It is shown that unlike linear polarimetric contrast imaging, this method remains valid on birefringent samples.     

A convenient synthesis of 5-arylamino-4H-pyran-4-ones using palladium-catalyzed amination

A concise approach to 5-arylamino-4H-pyran-4-ones is described via palladium-catalyzed amination reaction. The methodology involved in this Letter is based on protection/deprotection protocols and on manipulation of the 5-hydroxy group of readily available kojic acid. It would provide a new entry to a range of 5-arylamino-4H-pyran-4-ones via Buchwald-Hartwig-type amination reaction on 4H-pyran-4-one unit.     

Pyridinium encapsulation within a novel cyano-footed pyrogallol[4]arene nanocapsule

A novel polar solvent-soluble tetra-functionalised cyano-footed calixarene forms a dimeric capsule, sealed via a hydrogen-bonding network between the two macrocycles, a single water molecule and a chloride anion, resulting in the encapsulation of a pyridinium guest, as shown in both solution and the solid state.     

Is the critical Reynolds number universal?

This paper is devoted to checking whether the critical Reynolds number is universal in identical conditions for the flow of different fluids. The laminar-turbulent transition in a circular pipe flow has been tested experimentally. The flows of inert gases (He, Ne, Ar, Kr, Xe), molecular gases (N₂, CO, CO₂, SF₆), and two similar liquids (H₂O, D₂O) have been tested. A considerable, up to 40%, difference in critical Reynolds numbers was observed. The possible reasons for nonuniversality of the critical Reynolds number are discussed.     

Computer simulation of an all-optical coherent code division multiple-access network

This article presents a simulation technique for the analysis of all-optical coherent code division multiple-access asynchronous networks, Graphical results are given showing the signal evolution at different parts of the network, and the various sources of noise that degrade the overall performance are pointed out, including the influence of fiber dispersion, laser biasing, and chirp.     

Detection of enantiomers in dissymmetric biaryls with chiral shift reagents

Methoxycarbonyl groups in racemic biphenyls show separation of the methyl proton magnetic resonance signals in the presence of large amounts of chiral shift reagents.