The first two-dimensional Fourier-transform electron spin resonance (2D-FT-ESR) studies of nitroxide-labeled lipids in membrane vesicles are reported. The considerable enhancement this experiment provides for extracting rotational and translational diffusion rates, as well as orientational ordering parameters by means of ESR spectroscopy, is demonstrated. The 2D spectral analysis is achieved using theoretical simulations that are fit to experiments by an efficient and automated nonlinear least squares approach. These methods are applied to dispersions of 1-palmitoyl-2oleoyl-sn-glycerophosphatidylcholine (POPC) model membranes utilizing spin labels 1-palmitoyl-2-(16-doxyl stearoyl) phosphatidylcholine and the 3-doxyl derivative of cholestan-3-one (CSL). Generally favorable agreement is obtained between the results obtained by 2D-FT-ESR on vesicles with the previous results on similar systems studied by continuous wave (cw) ESR on aligned samples. The precision in determining the dynamic and ordering parameters is significantly better for 2D-FT-ESR, even though the cw ESR spectra from membrane vesicles are resolved more poorly than those from well aligned samples. Some small differences in results by the two methods are discussed in terms of limitations of the methods and/or theoretical models, as well as possible differences between dynamic molecular structure in vesicles versus aligned membranes. An interesting observation with CSL/POPC, that the apparent homogeneous linewidths seem to increase in "real time," is tentatively attributed to the effects of slow director fluctuations in the membrane vesicles.

A fast backprojection scheme for parallel beam geometries is proposed. Known as the incremental algorithm, it performs backprojection on a ray-by-ray (beam-by-beam) basis rather than the pixel-by-pixel backprojection in the conventional algorithm. By restructuring a conventional backprojection algorithm, the interdependency of pixel computations (position and value) is transformed to a set of incremental relations for a beam, where a beam is a set of pixels enclosed by two adjacent rays in 2-D computed tomography (CT), and a set of voxels enclosed by four adjacent rays in 3-D CT. To minimize the overhead of searching for the next pixels, a searching flow technique has been developed to implement the first-order and second-order incremental relations for 2-D and 3-D CTs, respectively. The values of all the pixels in each beam (except the first pixel) are computed with additions only, the key idea of the proposed backprojection scheme. The incremental algorithm has been implemented on two different machines and compared to B.F. Shepp and L.A. Logan's (1974) algorithm. The present implementation results show the superiority of this approach over the conventional algorithm.

The γ-brass type phase Pt 2 Zn 11Ϫδ (0.2 < δ < 0.3) was prepared by reaction of the elements in evacuated silica ampoules. The structures of crystals grown in the presence of excess zinc or alternatively excess platinum were determined from single crystal X-ray diffraction intensities and confirmed by Rietveld profile fits. Pt 2 Zn 10.72(1) crystallizes in the space group I43m, a ϭ 908.55(4) pm, Z ϭ 4. The structure refinement converged at R F ϭ 0.0302 for I o > 2σ (I o ) for 293 symmetrically independent intensities and 19 variables. The structure consists of a 26 atom cluster which is comprised of four crystallographically distinct atoms. The Struktur und Eigenschaften von Pt 2 Zn 11؊δ (0.2 < δ < 0.3) vom γ-Messing-TypInhaltsübersicht. Die Phase Pt 2 Zn 11-δ (0.2< δ < 0.3) vom γ-Messing-Typ wurde durch Umsetzung der Elemente in Quarzglasampullen sowohl einphasig als auch im Phasengemenge in Koexistenz mit den Nachbarphasen hergestellt. Die Strukturen von zwei Kristallen wurden aus Röntgen-Beugungsintensitäten bestimmt und durch quantitative Auswertung eines Pulver-Röntgen-Diffraktogramms nach Rietveld bestätigt. Pt 2 Zn 10.72(1) kristallisiert in der Raumgruppe I43m, a ϭ 908.55(4) pm, Z ϭ 4. Die Strukturverfeinerung konvergierte bei R F ϭ 0.0302 mit I o > 2σ (I o ), 293 symmetrisch unabhängigen Reflexen und 19 Variablen.atoms Zn(1), Pt(1), Zn(2) and Zn(3) form an inner tetrahedron IT, an outer tetrahedron OT, an octahedron OH, and a distorted cuboctahedron CO respectively. About 14 % of the Zn(1) sites are unoccupied. Pt 2 Zn 10.73 melts at 1136(2) K. It is a moderate metallic conductor (ρ 298 ϭ 0.2Ϫ0.9 mΩ cm) whose magnetic properties (χ mol ϭ Ϫ4.6 10 Ϫ10 to Ϫ5.4 10 Ϫ10 m 3 mol Ϫ1 ) are dominated by the core diamagnetism of its components.

In this paper, we describe how image reconstruction in Computerized Tomography (CT) can be parallelized on a message-passing multiprocessor. In particular, the results obtained from parallel implementation of 3-D CT image reconstruction for parallel beam geometries on the Intel hypercube, iPSC/2, are presented. A two stage pipelining approach is employed for filtering (convolution) and backprojection. The conventional sequential convolution algorithm is modified such that the symmetry of the filter kernel is fully utilized for parallelization.In the backprojection stage, the 3-D Incremental algorithm, our recently developed backprojection scheme which is shown to be faster than conventional algorithm, is parallelized. The speed-up, defined as (sequential processing time)/(parallel processing time), ranging from 5 to 27, and the efficiency, defined as (speed-up)/(the number of processing elements), ranging from 60% to 92%, have been achieved, depending on the size of image and the number of processing elements employed.

Research on birds has long played an important role in ecological investigations, as birds are relatively easily observed, and their high metabolic rates and diurnal habits make them quite evidently responsive to changes in their environments. A mechanistic understanding of such avian responses requires a better understanding of how variation in physiological state conditions avian behavior and integrates the effects of recent environmental changes. There is a great need for sensor systems that will allow free-flying birds to interact with their environment and make unconstrained decisions about their spatial location at the same time that their physiological state is being monitored in real time. We have developed a miniature needle-based enzymatic sensor system suitable for continuous real-time amperometric monitoring of uric acid levels in unconstrained live birds. The sensor system was constructed with Pt/Ir wire and Ag/AgCl paste. Uricase enzyme was immobilized on a 0.7 mm sensing cavity of Nafion/cellulose inner membrane to minimize the influences of background interferents. The sensor response was linear from 0.05 to 0.6 mM uric acid, which spans the normal physiological range for most avian species. We developed a two-electrode potentiostat system that drives the biosensor, reads the output current, and wirelessly transmits the data. In addition to extensive characterization of the sensor and system, we also demonstrate autonomous operation of the system by collecting in vivo extracellular uric acid measurements on a domestic chicken. The results confirm our needle-type sensor system's potential for real-time monitoring of birds' physiological state. Successful application of the sensor in migratory birds could open up a new era of studying both the physiological preparation for migration and the consequences of sustained avian flight.