Communicating with optical hyperchaos: information encryption and decryption in delayed nonlinear feedback systems

Recent theoretical studies and experimental demonstrations have shown the possibility of using chaos for the encryption of message signals in communication systems. Chaos is generated by systems with delayed nonlinear feedback, which feature hyperchaotic (i.e., of high dimensionality) dynamics. The different ways for the injection of the information in the emitter and the process of the synchronization of the receiver are considered. The analysis of all the possibilities can be used to choose the correct topology of communication systems and, more generally, to explain the behavior of any chaotic systems ruled by nonlinear difference-differential equations.     

Complex Gaussian Multiplicative Chaos

In this article, we study complex Gaussian multiplicative chaos. More precisely, we study the renormalization theory and the limit of the exponential of a complex log-correlated Gaussian field in all dimensions (including Gaussian Free Fields in dimension 2). Our main working assumption is that the real part and the imaginary part are independent. We also discuss applications in 2D string theory; in particular we give a rigorous mathematical definition of the so-called Tachyon fields, the conformally invariant operators in critical Liouville Quantum Gravity with a c = 1 central charge, and derive the original KPZ formula for these fields.     

Silyl Ketene Acetal Chemistry: Steric Limitations in Lewis Acid-Promoted Addition of Ketones

Lewis acid-promoted additions of ketones to silyl ketene acetals is limited sterically with α-branched alkyl groups in the ketone. Cyclic ketones give high yields. Titanium, ferric and aluminum chlorides are effective catalysts.     

Triggered aggregation of PbS nanocrystal dispersions; towards directing the morphology of hybrid polymer films using a removable bilinker ligand

Hybrid polymer films consist of quantum dots (QDs) dispersed in a polymer matrix. A key fundamental challenge that is hindering their optimisation in optoelectronic devices such as hybrid solar cells is overcoming uncontrolled aggregation of the QDs. In an effort to direct aggregation, and trigger self-assembly, we added a bilinker ligand (1,2-ethanedithiol) to dispersed PbS QDs in polymer solutions prior to film deposition by spin casting. Turbidity studies of the PbS QD/1,2-ethanedithiol dispersions enabled a relationship to be established between the extent of 1,2-ethanedithiol-triggered QD aggregation and the nominal fractional coverage of the QDs by 1,2-ethanedithiol. The extent of aggregation (and self-assembly) increased with nominal fraction coverage. Above a value of about 1.0 QD aggregation increased substantially. TEM images showed that at low 1,2-ethanedithiol concentrations triggered assembly of network-like QD structures occurred. At high 1,2-ethanedithiol concentrations the QDs self-assembled into more-ordered micrometre-sized crystals. The results suggest that 1,2-ethanedithiol decreases the inter-QD separation in dispersion as a result of rapid ligand exchange and this process results in QD aggregation as well as self-assembly. The assembled QD structures were successfully trapped within polymer films by spin casting of PbS QD/1,2-ethanedithiol dispersions containing added polystyrene or polytriarylamine.     

Feynman Diagram Theory of Degenerate Birefringent Bragg Diffraction

A Feynman diagram theory for acousto-optic (AO) interaction is established, which supplies a general method to calculate the scattering amplitudes and intensities for both single frequency and multifrequency AO interactions. The method L based on counting the number of allowable Feynman diagrams. Based on this, a complete solution for the scattering amplitudes and intensities an be obtained for any kind of AO interactions, any number of acoustic frequencies, and any final states. A geometrical representation for this Feynman diagram theory of AO interaction is set up too. The theory is ale0 verified by comparing with the experiments.     

New catalysts for the polymerization of cyclic olefins

Various routes to high T_g thermoplastic materials based on the Ziegler-Natta catalyzed polymerization of norbornene-type monomers are described. These routes involve both ring-opening metathesis polymerization (ROMP) and addition polymerization. New catalysts, and a new catalytically-active metal (cobalt), for both ROMP and the addition homopolymerization of norbornene-type monomers are reported.     

A comparison of local structures in crystalline P(EO)3LiCF3SO3 and glyme-LiCF3SO3 systems

The newly discovered crystal structures of CH₃(OCH₂CH₂)OCH₃(LiCF₃SO₃)₂, monoglyme:(LiTf)₂, and CH₃(OCH₂CH₂)₃OCH₃(LiCF₃SO₃)₂, triglyme:(LiTf)₂, are briefly described. The coordination of lithium cations and the CF₃SO₃⁻ anions in these structures is compared with the cation and anion coordination in the crystalline phase of high molecular weight P(EO)₃LiCF₃SO₃. Comparison is also made with the previously reported crystalline phase of CH₃(OCH₂CH₂)₂OCH₃LiCF₃SO₃, diglyme:LiTf. A tendency to form trans-gauche-trans conformations for the bond order -O-C-C-O- is noted in adjacent ethylene oxide sequences interacting with a five-coordinate lithium ion.     

NMR spectroscopy of poly(vinyl chloride) defects. 2. 1H and 13C NMR analysis of the terminal vinyl end group, 1,3-dichlorobutyl end group and chloromethyl branch

We have been able to obtain the ¹H NMR subspectra of most of the major saturated end groups in PVC. In order to assign the terminal vinyl (TV) group, CH₂CH-CHCl-, we synthesized and analyzed the symmetrical model compound 3,5-dichloro-1,6-heptadiene (4) containing a racemic (r) and a meso (m) isomer. They exhibit distinct NMR signals for the vinyl protons, which allowed us to subsequently assign the r diad and the previously unreported m diad terminal vinyl resonances present in very small amounts in commercial PVC. The study of the solvent induced chemical shifts of the vinyl protons in an experimental PVC sample containing an unusually high level of this end group allowed us to further assign it in terms of the terminal rr, rm, mm and mr triads.