Superparallel holographic correlator for ultrafast database searches

We describe a superparallel holographic optical correlator that performs two-dimensional spatial and angular multiplexing simultaneously. The key step in this architecture is the use of a holographic multiplexer to split a query image into many copies before it applies them to the holographic database. A holographic demultiplexer, in conjunction with an aperture, is used to identify the location and the angle of the brightest correlation peak. This architecture uses only O(square root of N) detector elements to search through N unsorted images in a single query. We demonstrate the basic features of this architecture, using three spatial locations with eight angle-multiplexed images in each location.     

Integration of laser-speckle and finite-element techniques of stress analysis

A study of the combined use of laser-speckle and finite-element methods for stress analysis is described. The speckle technique provides displacement data which can be directly input to a finite-element computer program for the determination of stresses. The displacement data can be used as boundary conditions for the examination of a subregion of the structural component to be analyzed. A substantial reduction in computational effort can be realized over conventional finite-element analysis of the entire structure. Also, a sizeable reduction in the required amount of experimental data may occur since direct numerical differentiation of the data is not required for strain evaluation. Acceptable accuracy may be obtained even when experimental displacement data may be too scarce for traditional numerical differentiation. Random error in experimental displacement is illustrated to have localized effects on the calculated stress field. Paper was presented at 1983 SESA Spring Meeting held in Cleveland, OH on May 15–19, 1983.     

Intrinsic stability of a body hovering in an oscillating airflow

We explore the stability of flapping flight in a model system that consists of a pyramid-shaped object hovering in a vertically oscillating airflow. Such a flyer not only generates sufficient aerodynamic force to keep aloft but also robustly maintains balance during free flight. Flow visualization reveals that both weight support and orientational stability result from the periodic shedding of vortices. We explain these findings with a model of the flight dynamics, predict increasing stability for higher center of mass, and verify this counterintuitive fact by comparing top- and bottom-heavy flyers.     

Radionuclide dating and trace element analysis by accelerator mass spectrometry

Accelerator Mass Spectcrometry (AMS) is being used for both radionuclide dating and stable isotope trace element determination with limits of high sensitivity. The areas of applications of radionuclide AMS include oceanography, terrestrial studies, glaciology, hydrology, environmental studies, meteorology, archaeology, anthropology, analysis of crude oils, biomedical and materials sciences, etc. The techniques and applications of radionuclide AMS are reviewed. The applications of stable element AMS include the measurements of trace impurities in electronic and other materials. The techniques and applications of stable element AMS are discussed with particular emphasis on electronic materials such as Si, GaAs, and HgCdTe. The design of the University of North Texas stable element AMS facility built in collaboration with Texas Instruments Incorporated is discussed.Work supported in part by the National Science Foundation Grants No. DMR-8812331 and ECD-9003099, the Office of Naval Research Grants No. N00014-89-J-1309, N00014-89-J-1344, N00014-90-J-1691, and N00014-91-J-1785, Texas Instruments Incorporated, Texas Utilities Electric Inc. International Digital Modeling Corp., North Texas Research Institute, Combustion Engineering Inc., LTV Corporation, the State of Texas Higher Education Coordinating Board — Texas Advanced Technology Research Program, the Robert A. Welch Foundation, and the University of North Texas Organized Research Fund.     

Forward and Inverse Bio-Geochemical Modeling of Microbially Induced Calcite Precipitation in Half-Meter Column Experiments

Microbially induced calcite precipitation (MICP) offers an alternative solution to a wide range of civil engineering problems. Laboratory tests have shown that MICP can immobilize trace metals and radionuclides through co-precipitation with calcium carbonate. MICP has also been shown to improve the undrained shear response of soils and offers potential benefits over current ground improvement techniques that may pose environmental risks and suffer from low “certainty of execution.” Our objective is to identify an effective means of achieving uniform distribution of precipitate in a one-dimensional porous medium. Our approach involves column experiments and numerical modeling of MICP in both forward and inverse senses, using a simplified reaction network, with the bacterial strain Sporoscarcina pasteurii. It was found that the stop-flow injection of a urea- and calcium-rich solution produces a more uniform calcite distribution as compared to a continuous injection method, even when both methods involve flow in opposite direction to that used for bacterial cell emplacement. Inverse modeling was conducted by coupling the reactive transport code TOUGHREACT to UCODE for estimating chemical reaction rate parameters with a good match to the experimental data. It was found, however, that the choice of parameters and data was not sufficient to determine a unique solution, and our findings suggest that additional time and space-varying analytical data of aqueous species would improve the accuracy of numerical modeling of MICP.     

Polyether macrocycles from intramolecular cyclopropanation and ylide formation. Effect of catalyst and coordination

The use of catalytic metal carbene methodology with diazoacetates for the construction in high yield of polyether macrocycles having ring sizes greater than 25 has been achieved by preventing access to gamma-C-H positions for intramolecular insertion. Cyclopropanation is the exclusive outcome of reactions performed with dirhodium(II) catalysts, and product yields of greater than 70% are obtained without resorting to high dilution with solvents. With copper(I) catalysts having multiple sites for polyether coordination, intramolecular oxonium ylide formation occurs at the terminal oxygen, followed by [2,3]-sigmatropic rearrangement of the pendant allyl group, in competition with cyclopropanation. Sodium ion coordination with the reactant diazo compound inhibits oxonium ylide formation in copper-catalyzed reactions. The composite results are consistent with copper serving as a template for the substrate as well as the site in the ether complex for diazo decomposition and subsequent metal carbene reactions.     

A continuous stirred tank reactor investigation of the gas-phase reaction of hydroxyl radicals and toluene

A continuous stirred tank reactor (CSTR) was used to study the gas-phase reaction between HO? and toluene. HO? was generated by the in situ photolysis of nitrous acid. Flow reactor operation at steady-state conditions with a residence time of 20 min allowed investigation of primary and very rapid secondary reactions. CSTR and batch reactor experiments were also performed with selected products. Both gas-phase and aerosol products were identified by chromatography and mass spectroscopy, with total product yields between 55 and 75% of reacted carbon. Toluene reaction products included cresols, nitrocresols, nitrotoluenes, 3,5-dinitrotouluene, benzaldehyde, benzyl nitrate, nitrophenols, methyl-p-benzoquinone, glyoxal, methylglyoxal, formaldehyde, methyl nitrate, PAN, and CO. The fraction of HO? methyl hydrogen abstraction was calculated to be 0.13 ± 0.04. The ratio of reaction rate constants for nitrotoluene versus cresol formation from the HO?-adduct was calculated to be about 3.3 × 10⁴. Also, the ratio of cresol formation versus O₂ addition to the HO?-adduct was estimated to be ≥0.5 for atmospheric conditions. Comparisons of these measurements with previous values and the implications with respect to photochemical kinetics modeling of the atmosphere are discussed.