The Influence of Modulational Instability on Energy Exchange in Coupled Sine-Gordon Equations

We consider a two-component system of coupled sine-Gordon equations, particular solutions of which represent a continuum generalization of periodic energy exchange in a system of coupled pendulums. Weakly nonlinear solutions describing periodic energy exchange between waves traveling in the two components are governed, depending on the length scale of the amplitude variation, either by two nonlocally coupled nonlinear Schrödinger equations, with different transport terms due to the group velocity, or by a model that is nondispersive to the leading order. Using both asymptotic analysis and numerical simulations, we show that the effects of dispersion significantly influence the structure of these solutions, causing modulational instability and the formation of localized structures but preserving the pattern of energy exchange between the components.     

Stress intensity factors for cracks in grooved rolls used for hot-rolling

A procedure is described for the calculation of stress intensity factors for surface cracks in a section roll. Results are given in terms of the load acting on the roll and the average pressure acting on the roll/workpiece interface. It is noted that the load acting on the roll can be determined for individual cases by experimentally measuring the deformation of the roll stands: this obviates the necessity of relying on theoretical estimates of the roll/workpiece pressure. The stresses in the uncracked roll are determined using an axisymmetric finite element model. However, for the subsequent calculation of stress intensity factors the analysis is reduced to a plane strain model. It is shown that it may not be necessary to carry out finite element stress analyses on cracked rolls to determine stress intensity factors.     

The structure of a propagating MgAl2O4/MgO interface: linked atomic- and μm-scale mechanisms of interface motion

To understand how a new phase forms between two reactant layers, MgAl₂O₄ (spinel) has been grown between MgO (periclase) and Al₂O₃ (corundum) single crystals under defined temperature and load. Electron backscatter diffraction data show a topotaxial relationship between the MgO reactant and the MgAl₂O₄ reaction product. These MgAl₂O₄ grains are misoriented from perfect alignment with the MgO substrate by ~2–4°, with misorientation axes concentrated in the interface plane. Further study using atomic resolution scanning transmission electron microscopy shows that in 2D the MgAl₂O₄/MgO interface has a periodic configuration consisting of curved segments (convex towards MgO) joined by regularly spaced misfit dislocations occurring every ~4.5 nm (~23 atomic planes). This configuration is observed along the two equivalent [1 0 0] directions parallel to the MgAl₂O₄/MgO interface, indicating that the 3D geometry of the interface is a grid of convex protrusions of MgAl₂O₄ into MgO. At each minimum between the protrusions is a misfit dislocation. This geometry results from the coupling between long-range diffusion, which supplies Al³⁺ to and removes Mg²⁺ from the reaction interface, and interface reaction, in which climb of the misfit dislocations is the rate-limiting process. The extra oxygen atoms required for dislocation climb were likely derived from the reactant MgO, leaving behind oxygen vacancies that eventually form pores at the interface. The pores are dragged along by the propagating reaction interface, providing additional resistance to interface motion. The pinning effect of the pores leads to doming of the interface on the scale of individual grains.     

Rapid Scan Infrared Fourier Transform Spectroscopy

The characteristic asorption, reflection, or emission of particu lar frequencies of IR radiation has been used extensively over the last two decades to identify compounds and mixtures and to investigate intermolecular and intramolecular interactions. It is probably true to say that IR spectroscopy is the most widely used instrumental technique in analytical chemistry today. This is due to a variety of reasons, including the ease of operation of many IR spectrometers, the ease in which a sample may be classified according to its chemical class from its IR spectrum, the variety of states in which a compound may be investigated, the availability of libraries of IR spectra for the unique identification of a sample, and the accuracy to which quantitative analysis may be carried out.     

Fette, ?le, und Wachse

Ohne Zusammenfassung     

Influence of chemical modification (bromination) on structure and charge transport in poly(N-vinylcarbazole)

Bromine has been randomly substituted in the 3 or 6 position of the pendant carbazole group of poly(N-vinylcarbazole) using N-bromosuccinimide in chlorobenzene solution. X-ray diffraction indicated that this substitution interferes with the interchain interactions in the amorphous polymer eliminating the unusual degree of chain parallelism and destroying the ability to crystallize. Charge carrier photogeneration and mobility measurements show that holes are still the majority carrier in the bromine-substituted polymer but both generation and mobility are substantially reduced compared to the unsubstituted polymer. It has not been possible to separate the influence of pendant group electronic structure from that of bulk chain conformation in this modification of the polymer photoconductive properties.