Discrete breathers — Advances in theory and applications

Nonlinear classical Hamiltonian lattices exhibit generic solutions — discrete breathers. They are time-periodic and (typically exponentially) localized in space. The lattices have discrete translational symmetry. Discrete breathers are not confined to certain lattice dimensions. We will introduce the concept of these localized excitations and review their basic properties including dynamical and structural stability. We then focus on advances in the theory of discrete breathers in three directions — scattering of waves by these excitations, persistence of discrete breathers in long transient processes and thermal equilibrium, and their quantization. The second part of this review is devoted to a detailed discussion of recent experimental observations and studies of discrete breathers, including theoretical modelling of these experimental situations on the basis of the general theory of discrete breathers. In particular we will focus on their detection in Josephson junction networks, arrays of coupled nonlinear optical waveguides, Bose–Einstein condensates loaded on optical lattices, antiferromagnetic layered structures, PtCl based single crystals and driven micromechanical cantilever arrays.     

Schnellbestimmung von Halogen und Schwefel in organischen Substanzen mit einer modifizierten Wickbold-Apparatur

Zusammenfassung Die elementaranalytische Bestimmung von Chlor, Brom, Jod, Fluor und Schwefel sowie die Spurenbestimmung dieser Elemente in organischen Substanzen wurde durch wesentliche Vereinfachung des Substanzaufschlusses in einer modifizierten Wickbold-Apparatur (Knallgasverbrennung) bedeutend verbessert und beschleunigt.

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Summary The determination of chlorine, bromine, iodine, fluorine and sulphur including the determination of traces of these elements in organic substances is significantly improved by a modified Wickbold apparatus. The modification permits to introduce a new sample and to rinse the absorber after a finished combustion without turning-off the oxygen-hydrogen flame.

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Alleinhersteller: Fa. Heraeus, Quarzschmelze GmbH., Hanau/Main, Rohrstr.8.     

Cascaded generation of multiply charged optical vortices and spatiotemporal helical beams in a Raman medium

Using an example of a Raman active medium we describe how a common nonlinear process of four-wave mixing can be used to induce strong coupling between the spatial and temporal degrees of freedom in optical waves. This coupling produces several unexpected effects. Amongst those are cascaded excitation of multiply charged optical vortices, spatial focusing in a nonlinearly defocusing medium, and generation of helically shaped spatiotemporal optical solitons.     

Degenerate polarization multiwave mixing between light beams in a solution of rhodamine 6G dye

The characteristics of diffracted waves derived from four- and six-wave mixing in a solution of Rhodamine 6G dye are studied in different combinations ofthe polarization states of waves that participate in wave interaction.     

Modulational instability in a silicon-on-insulator directional coupler: role of the coupling-induced group velocity dispersion

We report frequency conversion experiments in silicon-on-insulator (SOI) directional couplers. We demonstrate that the evanescent coupling between two subwavelength SOI waveguides is strongly dispersive and significantly modifies modulational instability (MI) spectra through the coupling induced group velocity dispersion (GVD). As the separation between two 380-nm-wide silicon photonic wires decreases, the increasing dispersion of the coupling makes the GVD in the symmetric supermode more normal and suppresses the bandwidth of the MI gain observed for larger separations.     

Preparation and properties of liposomes coated with <Emphasis Type="Italic">N</Emphasis>-acylated low-molecular-weight chitosan

Amphiphilic low-molecular-weight chitosan N-acylated with 3-hydroxytetradecanoic acid was synthesized. It was shown that addition of the acylated chitosan changes the surface potential and size of negatively charged liposomal particles, the magnitudes of which depend on the chitosan concentration. Charge neutralization and aggregation of the liposomes occurs at low chitosan concentration. Increasing its concentration produces positive charge on the surface of the liposomes and decreases their size. This increases the stability of the liposomal particles in solution. Liposomes coated with chitosan may be of interest as carriers for genes, vaccines, and drugs.     

Gap polariton solitons

We report the existence, and study mobility and interactions of gap polariton solitons in a microcavity with a periodic potential, where the light field is strongly coupled to excitons. Gap solitons are formed due to the interplay between the repulsive exciton-exciton interaction and cavity dispersion. The analysis is carried out in an analytical form, using the coupled-mode (CM) approximation, and also by means of numerical methods.     

Colorimetric test-systems for creatinine detection based on composite molecularly imprinted polymer membranes

An easy-to-use colorimetric test-system for the efficient detection of creatinine in aqueous samples was developed. The test-system is based on composite molecularly imprinted polymer (MIP) membranes with artificial receptor sites capable of creatinine recognition. A thin MIP layer was created on the surface of microfiltration polyvinylidene fluoride (PVDF) membranes using method of photo-initiated grafting polymerization. The MIP layer was obtained by co-polymerization of a functional monomer (e.g. 2-acrylamido-2-methyl-1-propanesulfonic acid, itaconic acid or methacrylic acid) with N, N′-methylenebisacrylamide as a cross-linker. The choice of the functional monomer was based on the results of computational modeling. The creatinine-selective composite MIP membranes were used for measuring creatinine in aqueous samples. Creatinine molecules were selectively adsorbed by the MIP membranes and quantified using color reaction with picrates. The intensity of MIP membranes staining was proportional to creatinine concentration in an analyzed sample. The colorimetric test-system based on the composite MIP membranes was characterized with 0.25 mM detection limit and 0.25–2.5 mM linear dynamic range. Storage stability of the MIP membranes was estimated as at least 1 year at room temperature. As compared to the traditional methods of creatinine detection the developed test-system is characterized by simplicity of operation, small size and low cost.