Phase-dependent spectral control of pulsed modulation instability via dichromatic seed fields

We investigated experimentally and numerically the spectral control of modulation instability (MI) dynamics via the initial phase relation of two weak seed fields. Specifically, we show how second-order MI dynamics exhibit phase-dependent anti-correlated growth rates of adjacent spectral sidebands. This effect enables a novel method to control MI-based frequency conversion: in contrast to first-order MI dynamics, which exhibit a uniform phase dependence of the growth rates, second-order MI dynamics allow to redistribute the spectral energy, leading to an asymmetric spectrum. Therefore, the presented findings should be very attractive to different applications, such as phase-sensitive amplification or supercontinuum generation initiated by MI.     

Opals: Status and Prospects

The beauty of opals results from a densely packed, highly ordered arrangement of silica spheres with a diameter of several hundred nanometers. Such ordered nanostructures are typical examples of materials called photonic crystals, which can be formed by known microstructuring methods and by self‐assembly. Opals represent a self‐assembly approach to these structured media; such an approach can lead to novel materials for photonics, photocatalysis, and other areas. Although self‐assembly leads to many types of defects, resulting in the surprising and very individual appearance of natural opals, it causes also difficulties in technological applications of opal systems.     

Generating water clusters and other directed graphs

In this paper we will describe an efficient method to generate directed graphs with bounded in- and out-degree. Though developed for the special case of water clusters, which can be modelled as directed graphs with indegree and outdegree at most 2 that have no two directed edges with the same endpoints, the algorithm is also applicable and implemented in the more general context.     

Nowhere-zero flows in low genus graphs

A nowhere-zero k-flow is an assignment of edge directions and integer weights in the range 1,…, k ? 1 to the edges of an undirected graph such that at every vertex the flow in is equal to the flow out. Tutte has conjectured that every bridgeless graph has a nowhere-zero 5-flow. We show that a counterexample to this conjecture, minimal in the class of graphs embedded in a surface of fixed genus, has no face-boundary of length <7. Moreover, in order to prove or disprove Tutte's conjecture for graphs of fixed genus γ, one has to check graphs of order at most 28(γ ? 1) in the orientable case and 14(γ ? 2) in the nonorientable case. So, in particular, it follows immediately that every bridgeless graph of orientable genus ?1 or nonorientable genus ?2 has a nowhere-zero 5-flow. Using a computer, we checked that all graphs of orientable genus ?2 or nonorientable genus ?4 have a nowhere-zero 5-flow.     

A constructive enumeration of fusenes and benzenoids

In this paper, a fast and complete method to constructively enumerate fusenes and benzenoids is given. It is fast enough to construct several million nonisomorphic structures per second. The central idea is to represent fusenes as labelled inner duals and generate them in a two step approach using the canonical construction path method and the homomorphism principle.     

Über die nichtlinearen Glieder im Verschieb ungs-Dehnungsgesetz

Ohne Zusammenfassung     

Messungen zur Ansprechwahrscheinlichkeit und Impulshöhenverteilung eines Sekundärelektronenvervielfachers

The pulse height distribution of a CuBe-secondary electron multiplier has been investigated under the action of single electrons. For an energy interval from 150 eV to 1000 eV the maximum pulse height increases with increasing electron energy (the energy corresponding to maximum yield being 365±10 eV). This shows the statistics of secondary electron emission as being dependant on primary electron energy.     

Proton NMR in the one-dimensional conductor K2Pt(CN) 4Br0.33H2O

The orientation of the proton-proton vectors of the water molecules in the quasi-one-dimensional conductor K₂Pt (CN) ₄Br_0.33H₂O have been determined. Temperature dependent rotations of the water molecules have been observed.     

Electronic properties of YBa2Cu4O8 and Y2Ba4Cu7O15 as probed by NMR/NQR

Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) allow the investigation of electronic properties at the atomic level. We will report on such studies in typical members of the Y-Ba-Cu-O family of high-temperature superconductors, namely YBa₂Cu₄O₈ and Y₂Ba₄Cu₇O₁₅. We will deal with temperature and orientational dependences of Cu and O Knight shifts and spin-lattice relaxation. Topics to be discussed are: (1) Existence of a common electronic spin-susceptibility (a single-spin fluid) in the planes and in the chains of YBa₂Cu₄O₈. (2) Evidence for the existence of a pseudo spin-gap in the anti-ferromagnetic fluctuations in YBa₂Cu₄O₈ and Y₂Ba₄Cu₇O₁₅. (3) Evidence for non-s symmetry of the pair wave function in YBa₂Cu₄O₈. (4) First NQR observation of a strong coupling of inequivalent Cu-O planes in Y₂Ba₄Cu₇O₁₅. (5) Alternative explanations of relaxation and Knight shift.