Nonrelativistic dyon-dyon scattering

The nonrelativistic problem of the scattering of two dyons (including the case of electron scattering by magnetic monopoles) is systematically studied, both classically and quantum mechanically, with a view toward the discrimination between various combinations of electric and magnetic charges. We analyze the classical cross section with particular attention to the interesting phenomena which occur for large angle scattering, the “rainbows” and “glory,” where the cross section becomes infinite. Quantum mechanically, we find that these infinities do not occur and that, when the partial wave scattering amplitude is summed, a very elaborate structure emerges for the cross section, which depends sensitively upon the electric and magnetic charges of the particles, as well as on their relative speed. We further discuss a large modification, leading to spin flip and nonflip amplitudes, due to the dipole moments of the particles. Numerical results are presented for a variety of values of these parameters. In principle, these results could be used to distinguish the δ-ray distributions produced by the various species of electrically and magnetically charged particles. Quite apart from the experimental implications of our numerical results, we have made a number of theoretical improvements and extensions. Numbered among these are the consideration of dyons and particles having dipole moments, and the explicit demonstration, based on the methods of angular momentum, that the differential cross section is independent of the choice of singularity line.     

One-dimensional BeH2 polymers: infrared spectra and theoretical calculations

Laser-ablated beryllium atoms react with H2 upon co-condensation in excess hydrogen and neon to form BeH2 and (BeH2)2, which are identified through isotopic substitution and DFT calculations. Unreacted Be atoms isolated in solid neon or hydrogen are excited to the 1P0 state and react further with H2 to enhance the BeH2 and (BeH2)2 concentrations and produce (BeH2)n polymers. The series of strong infrared-active parallel Be-H-Be bridge-bond stretching modes observed for (BeH2)n polymers suggests one-dimensional structures, and this conclusion is supported by DFT calculations. The computed polymerization energy per BeH2 unit is about 33 kcal/mol.     

Matrix infrared spectra and density functional theory calculations of molybdenum hydrides

Laser-ablated Mo atoms react with H2 upon condensation in excess argon, neon, and hydrogen. The molybdenum hydrides MoH, MoH2, MoH4, and MoH6 are identified by isotopic substitution (H2, D2, HD, H2 + D2) and by comparison with vibrational frequencies calculated by density functional theory. The MoH2 molecule is bent, MoH4 is tetrahedral, and MoH6 appears to have the distorted trigonal prism structure.     

FTIR spectroscopic studies of the matrix photoionization and photolysis products of methylene halides

Matrix photoionization of methylene bromide produced absorptions at 1019, 897, and 788 cm^?1 identified previously as CBr₂⁺, CHBr₂⁺, and CHBr₂. High-resolution FTIR spectra revealed overlapping 1/2/1 triplets for natural bromine isotopes with individual linewidths near 0.2 cm^?1. New absorptions at 3121, 2897, and 1345 cm^?1 are assigned to the (CH₂Br⁺)Br cation complex which yields CHBr₂⁺ on photolysis. A substantially increased yield of the CHCl₂⁺ species made possible observation of the CH stretching mode at 3033 cm^?1 and the symmetric CCl₂ stretching mode at 845 cm^?1 along with the previously observed stronger 1291- and 1044-cm^?1 fundamentals. The high resolution and enhanced signal-to-noise capability of the FTIR are clearly demonstrated in this investigation.     

An electron microscopic study of the archaeal feast/famine regulatory protein 5. Fourier filtration of images

Microcrystals of the feast/famine regulatory protein (FFRP) pot0434017 (FL11) were prepared by sonicating larger crystals. Using the microcrystals a cryo-electron micrograph was obtained, which showed a hexagonal packing of cylinder-like assemblies of FL11. This micrograph was processed by selecting, in the Fourier space, spots reflecting the crystal lattice, thereby removing the noise. The microcrystal was not totally free from distortion, and cylinders in local clusters adopted slightly different orientations. Thus, 25 hexagonal units closest to the ideal, each containing a cylinder at the center surrounded by six others, were manually selected. The averaged image was further processed to yield a perfect six-fold symmetry. These processed images, and some of the original images too, show bridges connecting cylinders, each corresponding to two pairs of N-domains, protruding from the two cylinders and contacting between them in the X-ray structure.     

The signature operator at 2

It is well known that the signature operator on a manifold defines a K-homology class which is an orientation after inverting 2. Here we address the following puzzle: What is this class localized at 2, and what special properties does it have? Our answers include the following:

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the K-homology class Δ_M of the signature operator is a bordism invariant;

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the reduction mod 8 of the K-homology class of the signature operator is an oriented homotopy invariant;

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the reduction mod 16 of the K-homology class of the signature operator is not an oriented homotopy invariant.

     

Dielectron widths of the Gamma(1S,2S,3S) resonances

We determine the dielectron widths of the Gamma(1S), Gamma(2S), and Gamma(3S) resonances with better than 2% precision by integrating the cross section of e+e- -->Gamma over the e+e- center-of-mass energy. Using e+e- energy scans of the Gamma resonances at the Cornell Electron Storage Ring and measuring Gamma production with the CLEO detector, we find dielectron widths of 1.252+/-0.004(sigma(stat))+/-0.019(sigma(syst)) keV, 0.581+/-0.004+/-0.009 keV, and 0.413+/-0.004+/-0.006 keV for the Gamma(1S), Gamma(2S), and Gamma(3S), respectively.