John H. Konnert

Crystalline Ordering in Silica and Germania Glasses

The diffraction patterns of both silica and germania glasses are consistent with a structure in which nearly all of the atoms belong to tridymite-like regions of up to about 20 angstroms or more that are bonded efficiently together in a manner analogous to that found in twinned crystals.

Sound absorbing diffusor

Disclosed herein is an improved sound absorbing diffusor device wherein the surface designed to face the sound source includes a plurality of sound absorbing wells of equal widths but different depths separated by thin sound absorbing dividers. The depths of the individual wells are based upon the quadratic-residue number theory sequence which is used in acoustic design. The wells are covered with an open weave fabric adhered thereover which fabric is specifically chosen for its ability to allow sound to pass therethorugh to the wells and dividers. Tests performed on the inventive sound absorbing diffusor have revealed significant reduction in sound levels of reflected sounds over that which would accrue from a flat absorptive panel.

Observation of Growth Steps, Spiral Dislocations and Molecular Packing on the Surface of Lysozyme Crystals with the Atomic Force Microscope

The (110) faces of lysozyme crystals in their mother liquor have been investigated using an atomic force microscope (AFM) in height mode. Crystal growth and dissolution steps, as well as simultaneous growth and dissolution in pits, have been observed. Screw dislocations were also observed but the fine structure has not yet been investigated. Images that may possess molecular resolution were obtained and compared with theoretical images based on the crystallographic structure and the effects of arbitrary tip profiles. Crystallographic periodicities of 38 and 112 A were observed. A recurring feature is a centered periodic array of minima that may be associated with one of the two nearly planar sheets of molecules present in the crystal that are parallel to the (110) faces.

The advancement and structure of growth steps on thaumatin crystals visualized by atomic force microscopy at molecular resolution

Abstract Using in situ atomic force microscopy (AFM) we have recorded the incorporation, on the nanometer scale, of molecules into growth steps of macromolecular crystals grown from solution. From these investigations we were able to deduce the fine structure of the growth step edges and the surface layer of the {101} faces of tetragonal thaumatin crystals. Although the height of the growth step corresponds to unit cells of eight molecules, step advancement occurs by ordered addition of individual protein molecules rather than molecular clusters. Advancement of growth steps in specific directions, which is anisotropic, occurs by formation of one-dimensional nuclei of varying sizes which generate subkinks on the step edges. Incorporation of molecules into kinks occurs through the same kind of nucleation process. The crystal surface as a whole is created from molecular chains parallel with the surface. Models for the packing of protein molecules comprising the surface layer, the structure of the step edges, and the structure of two-dimensional nuclei were developed which are consistent with the AFM images.

Acoustical diffusing and absorbing cinder blocks

Disclosed are embodiments of structural acoustical cinder blocks including blocks which are intended to be assembled together through the use of mortar to provide a diffusor of desired shape and configuration. Each diffusor includes a plurality of wells, the depths of which are determined through the use of number theory sequences, such as, for example, the quadratic-residue sequence developed by Karl Frederick Gauss. The surface irregularities formed in the blocks are unique in that they provide a flat power spectrum and constant scattered energy in the diffraction directions. Each of the blocks also includes a low frequency sound absorbing chamber. As the blocks are installed, a structural stacked bond is formed on both the diffusor face and the rear structural face. If desired, a single block may be made which includes an entire sequence of wells and dividers.

Comparison of radial distribution function for silica glass with those for various bonding topologies: Use of correlation function

Radial distribution functions (RDFs) calculated from the bonding topologies of quartz, cristobalite, tridymite and a 1412 atom model of silica glass (35 A in diameter) have been compared with the experimental RDF for silica glass. The functions, 4πr3(ϱ(r)−ϱ0), computed over the range 0 < r < 20 A from the known structures of quartz, cristobalite, tridymite and the 1412 atom model have been compared with the corresponding function for silica glass by means of correlation functions, giving 0.26, 0.69, 0.82 and 0.91, respectively (0.00 would indicate no correlation, and 1.00, perfect positive correlation). Cristobalite and tridymite are composed entirely of six-membered rings of silicate tetrahedra, whereas the model contains both six- and five-membered rings in a ratio of 2.6:1. The correlation coefficients suggest that the six-membered rings of the type present in tridymite play a dominant role in silica glass, but that other ring sizes are important and result in the higher correlation coefficient for the 1412 atom model. While the correspondence in RDFs is encouraging, the model RDF does not fit the experimental curve to within the accuracy of the experiment. Perhaps the model is not large enough to represent adequately, in a statistical fashion, all the configurations present in a macroscopic sample.

Determination of atomic positions using electron nanodiffraction patterns from overlapping regions: Si[110]

Abstract A procedure for determining atomic positions is described that utilizes electron nanodiffraction patterns from overlapping regions. The technique is applied using experimental data collected for Si[110] with a beam 4 A in diameter. Autocorrelation functions are calculated for each beam position and correlated with theoretical functions. The positions of the Si atoms are established with an accuracy of ±0.2 A, and images with 1 A resolution are computed for individual beam positions. It is also demonstrated how the technique may be used to determine, with similar resolution, the structure of noncrystalline regions adjacent to crystalline regions.

Determining the molecular-packing arrangements on protein crystal faces by atomic force microscopy

Previous atomic force microscopy (AFM) studies and periodic bond-chain (PBC) analyses of tetragonal lysozyme crystals have suggested that the (110) face consists of chains of molecules related to one another by 43 axes parallel to the crystal face. In this study, high-resolution AFM images of the (110) face were obtained and analyzed in order to verify this prediction. A computer program was employed which constructs the theoretical AFM image corresponding to a specific crystallographic molecular-packing arrangement and AFM tip shape. The packing arrangement and tip shape were varied in order to obtain the maximum possible correlation between experimental and theoretical images. The prediction from PBC analysis of an arrangement involving 43 helices was confirmed in this manner, while the alternate arrangement, consisting of molecules related to one another by 21 axes, was not observed. However, the surface structure was found to differ significantly even from this crystallographic arrangement. The molecules were found to pack slightly closer about what will become the 43 axes within the interior of the crystal, suggesting the occurrence of surface reconstruction or rearrangement on the tetragonal lysozyme (110) face. This study represents a new approach for more precise determination of the molecular-packing arrangements on protein crystal faces employing AFM.

Structural Ordering in Amorphous TbFe2 and YFe2

Total neutron scattering data were collected on sputtered YFe2 at 298 K and TbFe2 at 423 K with a wavelength of 0.7 A. The TbFe2 data were collected above the magnetic ordering temperature of 383 K. In addition, the elastic neutron scattering of TbFe2 was measured with the use of a pyrolytic graphite analyzer at a wavelength of 1.5 A, and its total X-ray scattering was measured with Mo radiation and a silicon-lithium drifted detector. Experimental radial distribution functions, with statistical error limits, were calculated. Errors due to an incorrect background, scaling of the data and termination effects were minimized. The scale and shape of the experimental background and the coordination numbers, internuclear distances and disorder parameters, for the first six coordination spheres, have been determined. The contribution of paramagnetic inelastic scattering from TbFe2 to the total neutron scattering is quite appreciable. The shape of the background scattering, which goes through a maximum, is indicative of residual coherence and suggests short-range magnetic ordering where neighboring atom spins are aligned. These effects are not observed in YFe2, nor in the elastic TbFe2 data. The metallic glasses have a structural topology which is quite different from that found in their crystalline analogues. The transition-metal substructure, consisting of corner-sharing tetrahedra, is the only aspect of the crystalline topology preserved in the amorphous phase. The structural parameters suggest a tendency of the rare-earth atoms to cluster, thereby decreasing the number of Fe nearest neighbors relative to the crystalline structure.

Image reconstruction using electron microdiffraction patterns from overlapping regions

Abstract An image reconstruction procedure is described that utilizes electron microdiffraction patterns from overlapping regions. The autocorrelation function is calculated for an array of beam positions surrounding the sample area of interest, and the beam positions that maximize each autocorrelation vector are identified. Such maxima occur with the beam centered midway between the related atoms, and, thus, each maximum serves to identify the positions of two atoms. Atomic resolution images are constructed from microdiffraction patterns calculated for crystalline silicon viewed along the [110] direction, and for a thin slice from a model of amorphous silica (SiO 2 ). Comparisons are made with dark-field images calculated for annular detector data.