Non-contact atomic force microscopy imaging of TiO2(100) surfaces

Atomically resolved non-contact fm mode atomic force microscopy images have been obtained from TiO₂(100) surfaces. The 1×1 surface is observed, as well as the 1×3 phase previously imaged with STM. The morphology of the latter reconstruction consists of (110) microfacets. An additional reconstruction with 1×3 symmetry is observed, which is assigned to a phase intermediate between the 1×1 and 1×3-microfacet terminations.     

A microscopic description of inelastic 12C scattering from 208Pb

Heavy-ion inelastic scattering is described microscopically by using an effective nucleon-nucleon interaction and RPA hole-particle wave functions. The relative cross sections for different multipoles can be sensitive to the range of the interaction. The strength is determined by fitting elastic scattering. The model is used to analyze 98 MeV ¹²C ions exciting ²⁰⁸Pb. The range required is shorter than that for the bare interaction between nucleons. Collective model fits are also presented for comparison.     

A shortest path algorithm in robotics and its implementation on the FPS T-20 hypercube

A broad class of problems involving the optimal control of robot arms can be formulated as dynamic programming problems whose structure is particularly attractive for parallel processing. For certain simple cost functions the dynamic programming formulation reduces to determining the shortest path through a network. This algorithm has been implemented on a Floating Point Systems' T-20 hypercube computer. An analysis of the performance of the algorithm provides several important insights into the interplay between problem size and the number of processors in a parallel computer. The results also underscore the potential for parallel computers in real-time control applications.This work was supported in part by the Office of Naval Research, Contract N 00014-86-K-0693.     

The infrared spectra of pyridine N-oxide complexes of transition metal perchlorates in relation to their structures

The infrared spectra of the complexes [M(pyO)₆](ClO₄)₂ (pyO = pyridine N-oxide; M = Mn, Fe, Co, Ni, Zn) are discussed. Assignments of v(M-O) and other significant vibrations are based on the band shifts induced by deuteration of the heterocyclic ring and the effects of metal ion substitution. Earlier spectroscopic evidence suggesting distortion from regular octahedral site symmetry is discounted by the far-infrared spectra. In agreement with recent crystallographic evidence for O_h site symmetry in these complexes, one infrared-active v(M-O) band is expected and observed. The effects on the spectra of structural distortion in the 6-coordinate Cu^II complex [Cu(pyO)₆](ClO₄)₂, reduced coordination number in the 4-coordinate complex [Cu(pyO)₄](C1O₄)₂, and increased cationic charge in the Ga^III complex [Ga(pyO)₆](C1O₄)₃are discussed.     

Application of the νD/νH ratio to the assignment of C-H(D) and ring vibrations in the infrared spectra of imidazole and its deuterated analogues

The IR spectra (4000-150 cm^?1)of imidazole and its I-, 2,4,5- and 1,2,4,5-deuterated analogues are discussed. All twenty-one fundamental IR active imidazole vibrations are assigned by employing the ν^D/ν^H ratio which is defined as the ratio between the frequencies of corresponding IR bands in the spectra of a ring-deuterated heterocyclic (or aromatic) molecule and its normal analogue. The results suggest that some previously reported assignments require revision.     

A numerical examination of shear banding and simple shear non-coaxial flow rules

Strain localisation and shear band formation is frequently observed during the handling and flow of dense phase particulate materials. However, a complete understanding of how shear bands form and what happens inside shear bands is still lacking. In order to address this problem, discrete particle simulations have been carried out to examine the detailed processes that occur at the grain scale associated with the initiation and development of shear bands. To reliably identify the continuum model applicable within a shear band is difficult due to the small number of particles/contacts involved. However, it is normally accepted that the mode of deformation within a shear band is one of simple shear. Consequently, simple shear simulations have been performed in order to determine the evolution of the stress tensor, dilation rate, and the principal directions of stress and strain-rate. It is demonstrated that the corresponding non-coaxial flow rule is equivalent to that suggested by Tatsuoka et al. (Géotechnique 38 148 (1988)). Furthermore, at fully developed flow when there is no further change in volume, the stress and strain-rate directions are coaxial and the flow rule is that proposed by Hill (The Mathematical Theory of Plasticity (Oxford University Press, 1950) p. 294).