Discrete element modelling of pebble beds: With application to uniaxial compression tests of ceramic breeder pebble beds

In this paper, a discrete element simulation scheme for pebble beds in fusion blankets is presented. Each individual pebble is considered as one element obeying equilibrium conditions under contact forces. We study not only the rearrangement of particles but also the overall behaviour of an assembly under the action of macroscopic compressive stresses. Using random close packing as initial configurations, the discrete element simulation of the uniaxial compression test has been quantitatively compared to experiments. This method yields the distribution of the inter-particle contact forces. Moreover, the micro-macro relations have been investigated to relate the microscopic information, such as the maximum contact force and the coordination number inside the assembly, to the macroscopic stress variables.     

Novel recognition mechanisms in biological adhesion

Molecular recognition is generally thought of in terms of bond formation between unique sites on host and complementary guest molecules, but recent studies have revealed new complexities in biological recognition at cell. Adhesion between cell surfaces similarly involves specific interactions between analogous ligands and receptors. Recent force measurements, however, suggest that cell adhesion proteins may bind via multiple interaction sites that can form in a sequential manner. Other studies further show that in some instances, the principal recognition event may not be receptor–ligand docking, but the assembly of a complex pattern of many receptors and ligands.     

Equilibrium bond lengths, force constants and vibrational frequencies of MnF2, FeF2, CoF2, NiF2, and ZnF2 from least-squares analysis of gas-phase electron diffraction data

The least-squares analysis of the electron diffraction data for MnF₂, FeF₂, CoF₂, NiF₂ and ZnF₂ was carried out in terms of a cubic potential function. The obtained equilibrium bond lengths (in Å) are r_e(Mn–F)=1.797(6), r_e(Fe–F)=1.755(6), r_e(Co–F)=1.738(6), r_e(Ni–F)=1.715(7), and r_e(Zn–F)=1.729(7). The determined force constants and the corresponding vibrational frequencies are listed. The bond length r_e(Cu–F)=1.700(14) Å for CuF₂ was estimated and the variations of bond lengths for the first-row transition metal difluorides were discussed in light of their electronic structure.     

Measurements of Forces and Temperature Fields in High-Speed Machining of 6061-T6 Aluminum Alloy

This study focuses on experimental modeling of dry high-speed machining at 30 m/s cutting velocity using 6061-T6 aluminum alloy. A modified Hopkinson bar apparatus is employed to simulate orthogonal machining, a focused array of mercury–cadmium–tellurium infrared detectors is used to measure the temperature distribution around the tool tip, and a three-component quartz force transducer is utilized in measuring the cutting and feed forces. The resulting measurements confirm the assumption of steady-state cutting and allow for estimation of the partition of cutting work into heating, shear, and momentum changes in the chip. In an earlier study, measurements of temperature distributions showed little heating of the finished surface. Therefore, a study of the temperature fields generated during machining with a cutting tool that has a wear-land was performed. The wear-land contributes significantly to the heating of the workpiece and, at this speed, is the most likely mechanism for the generation of residual stresses and a temperature rise on the finished surface.     

Analysis of energy and force of Pt adatom on Pt (0 0 1) surface by MAEAM

The energy and perpendicular force of a Pt adatom on Pt (0 0 1) surface have been calculated by MAEAM. With increasing the distance of the adatom from the surface, the energy and force maps can be classified into four regions: repulsive region, transformed region, strongly attractive region and weakly attractive region. In repulsive region, the maximum (minimum) values of the energy and repulsive force appear on the top (hole) of the first layer atoms of Pt (0 0 1) surface due to stronger pair-potential interaction. In other regions, the energy and force maps are more complicated than those in repulsive region due to the effects of the many body interactions and nonspherical distribution of the electrons of the atoms in crystal. The most stable position is 0.1664 nm above the hole of the first layer atoms for a Pt adatom on Pt (0 0 1) surface.     

Hypersonic jet control effectiveness

The present study aims to identify some of the parameters which determine the upstream extent and the lateral spreading of the separation front around an under-expanded transverse jet on a slender blunted cone. The tests were conducted in the Cranfield hypersonic facility at , to and at , . Air was used as the working gas for both the freestream and the jet. Schlieren pictures were used for the visualisation of the three-dimensional structures around the jet. Pressure, normal force and pitching moment measurements were conducted to quantitatively study the interaction region and its effects on the vehicle. An analytical algorithm has been developed to predict the shape of the separation front around the body. Received 18 August 1995 / Accepted 27 June 1996     

Empirical correlation between the stretching force constant and the bond order for nitrogen-oxygen systems

The stretching force constant correlates satisfactorily with theWiberg's bond order,K(N-O)=11.791 [p(N-O)]–9.565, with a correlation coefficient of 0.958, for nitrogen—oxygen systems.

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Empirische Korrelation zwischen der Kraftkonstante der Streckschwingung und der Bindungsordnung in Stickstoff-Sauerstoff-Systemen (Kurze Mitteilung)

Zusammenfassung Die KraftkonstanteK der Streckschwingung läßt sich in befriedigender Weise mit derWibergschen Bindungsordnungp korrelieren:K(N-O)=11.791 [p(N-O)]-9.565. Für Stickstoff-Sauerstoff-Systeme beträgt der Korrelationskoeffizient 0.958.

     

Protonen-Spin-Gitter-Relaxation und interne Beweglichkeit von Molekülen

Relaxation rates can be used as assignment tool in NMR-spectroscopy; even conformational changes in the cyclic peptide alkaloid frangulanin (1) can be monitored by proton-relaxation measurements. The results are compared with a force-field calculation of (1).

     

Untersuchungen über die Abhängigkeit der Carbonylfrequenz monosubstituierter Benzophenone von der Polarität des Lösungsmittels

IR-spectroscopic studies have been performed on monosubstituted benzophenones (2-, 3-, 4-NO₂; 2-, 3-, 4-Cl; 2-, 3-, 4-NH₂). The carbonyl frequency of the ketones have been measured in various solvents. The force constants and HMO-bonding orders have been calculated. It has been tried to find a correlation between solvent polarity and the strength of the carbonyl bonding resp. favoured conformations of the two aromatic rings.