Zur Kenntnis der Proteine und der lyotropen Reihen

Ohne Zusammenfassung     

Multiple scattering of an obliquely incident plane acoustic wave from a grating of immersed cylindrical shells

The study of the interaction of acoustic waves with cylindrical structures has numerous applications including the ultrasonic nondestructive testing of materials. In this paper, using a new mathematical model presented for the scattering of obliquely incident plane acoustic waves from a grating of immersed cylindrical shells, a detailed study of the resonant interaction of A-wave resonances originating from the shells is conducted. The nature of A-wave resonances and the effect of center-to-center distance of the shells on these resonances are examined. It is observed that this resonant interaction not only results in the splitting of A-wave resonances, but also causes an increase in resonance amplitudes. This interaction phenomenon is not seen in Rayleigh, whispering gallery and guided wave resonances. It is also shown that increasing the angle of wave incidence to the grating weakens the A-wave resonant interactions. The numerical results obtained from the mathematical model are compared to experimental results available in the literature for gratings composed of two and three aluminum shells. The numerical results are in very good agreement with their experimental counterparts.     

Correlation between helical surface waves and guided modes of an infinite immersed elastic cylinder

Scattering of obliquely incident plane acoustic waves from immersed infinite solid elastic cylinders is a complex phenomenon that involves generation of various types of surface waves on the body of the cylinder. Mitri [F.G. Mitri, Acoustic backscattering enhancement resulting from the interaction of an obliquely incident plane wave with an infinite cylinder, Ultrasonics 50 (2010) 675-682] recently showed that for a solid aluminum cylinder, there exist acoustic backscattering enhancements at a normalized frequency of ka?0.1. The incidence angle α_c at which these enhancements are observed lies between the first (longitudinal) and second (shear) coupling angles of the cylinder. He also confirmed the observations previously reported by the authors that there exist backscattering enhancements of the dipole mode at large angles of incidence where no wave penetration into the cylinder is expected. In this paper, physical explanations are provided for the aforementioned observations by establishing a correlation between helical surface waves generated by oblique insonification of an immersed infinite solid elastic cylinder and the longitudinal and flexural guided modes that can propagate along the cylinder. In particular, it is shown that the backscattering enhancement observed at ka?0.1 is due to the excitation of the first longitudinal guided mode travelling at the bar velocity along the cylinder. It is also demonstrated that the dipole resonance mode observed at incidence angles larger than the Rayleigh coupling angle is associated with the first flexural guided mode of the cylinder. The correlation established between the scattering and propagation problems can be used in both numerical and experimental studies of interaction of mechanical waves with cylinders.     

A compact UHV package for microfabricated ion-trap arrays with direct electronic air-side access

We have demonstrated a new apparatus for operating microfabricated ion-trap arrays in a compact ultra-high-vacuum setup with excellent optical and electrical access. The approach uses conventional components, materials and techniques in a unique fashion. The microtrap chip is mounted on a modified ceramic leadless chip carrier, the conductors of which serve as the vacuum feedthrough. The chip carrier is indium-sealed to stainless-steel components to form vacuum seals, resulting in short electrical path lengths of ≤20 mm from the trap electrodes under vacuum to air side. The feedthrough contains conductors for the radio-frequency trap drive, as well as 42 conductors for DC electrodes. Vacuum pressures of ～1 × 10^?11 mbar are achieved, and ions have been confined and laser cooled in a microtrap chip. The apparatus enables accurate measurements of radio-frequency voltage amplitudes on the trap electrodes, yielding an excellent agreement between measured and modelled trap efficiencies. This feature is of significant use in establishing initial operation of new devices. The principle of the connectivity scheme presented here is applicable to larger ceramic chip carriers containing many more conductors.     

Three-level Decomposition Approach for Solving Feedstock Problems on Microcomputers

Many decision support systems for feedstock companies include an option for the solution of large linear programming problems. A three-level decomposition algorithm is presented which substantially improves the solution times for such linear programming problems. When decisions must be made on the addition of new raw materials or extra quantities of existing raw materials to feed mixes, the usual approach is to use parametric linear programming. A new approach to this decision problem, based on the results of the three-level decomposition algorithm, is presented in the paper. Finally, implementation issues and the computational performance of the new approaches on real-world problems are discussed.     

Integrated optical components on atom chips

We report on the integration of small-scale optical components into silicon wafers for use in atom chips. We present an on-chip fibre-optic atom detection scheme that can probe clouds with small atom numbers. The fibres can also be used to generate microscopic dipole traps. We describe our most recent results with optical microcavities and show that a sufficiently high finesse can be achieved to enable single-atom detection on an atom chip. The key components have been fabricated by etching directly into the atom chip silicon substrate.     

On the stress singularities in the plane elasticity of the composite wedge

This paper examines the composite, two-dimensional, linear elastic wedge for singular stresses at its vertex. A full range of wedge boundary and matching conditions is considered. Using separation of variables on the Airy stress function, the usual determinant conditions for singularities of the formO(r ^-) asr 0 are established and further conditions are derived for singularities of the formO(r ^- lnr) asr 0. The order of the determinant involved in these conditions depends upon the number of materials comprising the wedge. Two systematic methods of expanding the determinant for theN-material wedge are presented.

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Résumé Ce papier examine le coin composé, linéaire et élastique, en deux dimensions, pour déterminer les contraintes singulières à son sommet. On va considérer la rangée totale des conditions aux limites du coin, et les conditions correspondantes dans le coin. On se sert de la séparation des variables de la fonction de contrainte d'Airy, pour déterminer les conditions usuelles sur le déterminant pour les singularités de la formeO(r ^-) quandr 0, et on dérive des conditions additionnelles pour les singularités de la formeO(r ^- lnr) quandr 0. L'ordre du déterminant impliqué dans ces conditions dépend du nombre des matériaux dans le coin. D'abord on propose deux méthodes systématiques de développer le déterminant du coin deN-matériaux.

     

Ten-deg off-axis test for shear properties in fiber composites

A combined theoretical and experimental investigation was conducted to assess the suitability of the 10-deg off-axis tensile-test specimen for the intralaminar-shear characterization of unidirectional composites. Composite mechanics, a combined-stress failure criterion and a finiteelement analysis were used to determine theoretically the stress-strain variation across the specimen width and the relative stress and strain magnitudes at the 10-deg plane. Strain gages were used to measure the strain variation across the specimen width at specimen midlength and near the end tabs. Specimens from Mod-I/epoxy. T-300/epoxy, and S-glass/epoxy were used in the experimental program. It was found that the 10-deg off-axis tensile-test specimen is suitable for intralaminar-shear characterization and it, is recommended that it should be considered as a possible standard test specimen for such a characterization.     

Inelastic neutron scattering from amorphous solids

Utilization of the inelastic neutron scattering technique for the study of the dynamics of amorphous solids is discussed. Excitation energies of interest range from a fraction of a milli-electron-volt (meV) to several hundred meV. For coherent scatterers, the scattering-vector dependence of the cross section gives information on the correlation between the motions of different atoms. Progress in the application of the technique to several classes of materials is reviewed, and the possibilities offered by the new generation of pulsed-spallation neutron sources are considered. Existing instrumentation on presently operating sources should already be able to measure wide-ranging scattering functions for comparison to model predictions for several types of amorphous solids. Higher flux sources, now at the proposal stage, would allow greater detail in the scattering to be observed and thus aid in discriminating between models.     

A study of three-nucleon transfer reactions on 17O

The reactions ¹⁷O(¹¹B, ⁸Li)²⁰Ne, ¹⁷O(¹²C, ⁹Be)²⁰Ne and ¹⁷O(¹³C, ¹⁰B)²⁰F have been studied using beams of 115 MeV ¹¹B and ¹²C and 105 MeV ¹³C incident on a gas target. Shell-model calculations have been performed for ²⁰Ne and ²⁰F, for comparison with the experimental data. It is found that the data can be interpreted using the shell model spectroscopic factors and a semi-classical reaction theory. We justify the use of the latter by applying it to the cases of three-nucleon transfer on ¹⁶O. Spin assignments are suggested for previously unidentified states in ²⁰F.