Performance evaluation of advanced industrial SPECT system with diverging collimator.

An advanced industrial SPECT system with 12-fold-array diverging collimator was developed for flow visualization in industrial reactors and was discussed in the previous study. The present paper describes performance evaluation of the SPECT system under both static- and dynamic- flow conditions. Under static conditions, the movement of radiotracer inside the test reactor was compared with that of color tracer (blue ink) captured with a high-speed camera. The comparison of the reconstructed images obtained with the radiotracer and the SPECT system showed fairly good agreement with video-frames of the color tracer obtained with the camera. Based on the results of the performance evaluation, it is concluded that the SPECT system is suitable for investigation and visualization of flows in industrial flow reactors.

Development of advanced industrial SPECT system with 12-gonal diverging-collimator.

Industrial single photon emission computed tomography (SPECT) is a promising diagnosis technique to investigate the dynamic behavior of process media. In the present study, a 12-gonal industrial SPECT system was developed using diverging collimators, and its performance was compared with those of hexagonal and 24-gonal systems. Of all of the systems, the 12-gonal type showed the best performance, providing (1) a detection-efficiency map without edge artifacts, (2) the best image resolution, and (3) reconstruction images that correctly furnish multi-source information. Based on the performance of the three different types of configurations, a SPECT system with 12-gonal type configuration was found most suitable for investigating and visualization of flow dynamics in industrial process systems.

Study on the validation of the computer fluid dynamics modeling for a continuously flowing water vessel with the industrial SPECT using a radiotracer.

The industrial Single Photon Emission Computerized Tomography (SPECT) system comprised of 30 sets of lead collimated 2 in. NaI(Tl) detectors was built and utilized for measuring the spatial distribution of radiotracers as a function of time at a predefined cross-sectional level of a tank with a diameter of 300 mm and a height of 780 mm. In a stable flow condition, a radiotracer was injected into the upstream of a tank and then the measurement data were processed for the two dimensional concentration mapping of the radiotracers with a time step of 1s. The images were compared with numerical simulation results obtained from the Computational Fluid Dynamics modeling that has been incorporated with several different kinds of turbulence models. The comparison shows one model gives a better result than any others in terms of the similarity of the radiotracer distribution pattern. This study demonstrates the significant possibility of industrial SPECT technology for visualizing flow characteristics in a multi-dimensional way and for validating the CFD modeling.

A feasibility study on gamma-ray tomography by Monte Carlo simulation for development of portable tomographic system.

The electron beam X-ray tomographic scanner has been used in industrial and medical field since it was developed two decades ago. However, X-ray electron beam tomography has remained as indoor equipment because of its bulky hardware of X-ray generation devices. By replacing X-ray devices of electron beam CT with a gamma-ray source, a tomographic system can be a portable device. This paper introduces analysis and simulation results on industrial gamma-ray tomographic system with scanning geometry similar to electron beam CT. The gamma-ray tomographic system is introduced through the geometrical layout and analysis on non-uniformly distributed problem. The proposed system adopts clamp-on type device to actualize portable industrial system. MCNPx is used to generate virtual experimental data. Pulse height spectra from F8 tally of MCNPx are obtained for single channel counting data of photo-peak and gross counting. Photo-peak and gross counting data are reconstructed for the cross-sectional image of simulation phantoms by ART, Total Variation algorithm and ML-EM. Image reconstruction results from Monte Carlo simulation show that the proposed tomographic system can provide the image solution for industrial objects. Those results provide the preliminary data for the tomographic scanner, which will be developed in future work.

Preparation of radioactive core-shell type 198Au@SiO2 nanoparticles as a radiotracer for industrial process applications.

Silica-coated gold nanoparticles produced by gamma-ray irradiation were bombarded with neutrons in a nuclear reactor in order to activate gold nuclides into Au-198 emitting gamma radiation of 0.412-1.088 MeV. The particle size ranges from 20 to 200 nm. The physical integrity of the particles was examined by TEM before and after the neutron irradiation and the silica-gold particles were not affected in terms of structural appearance under gamma radiation environment. The gamma emitting NPs can be utilized as a tracer in petrochemical and refinery industrial processes where the internal temperature is extremely high and the conventional organic radioactive labeled compound would be decomposed.

Structure of the catalytic domain of human phosphodiesterase 5 with bound drug molecules.

Phosphodiesterases (PDEs) are a superfamily of enzymes that degrade the intracellular second messengers cyclic AMP and cyclic GMP. As essential regulators of cyclic nucleotide signalling with diverse physiological functions, PDEs are drug targets for the treatment of various diseases, including heart failure, depression, asthma, inflammation and erectile dysfunction. Of the 12 PDE gene families, cGMP-specific PDE5 carries out the principal cGMP-hydrolysing activity in human corpus cavernosum tissue. It is well known as the target of sildenafil citrate (Viagra) and other similar drugs for the treatment of erectile dysfunction. Despite the pressing need to develop selective PDE inhibitors as therapeutic drugs, only the cAMP-specific PDE4 structures are currently available. Here we present the three-dimensional structures of the catalytic domain (residues 537-860) of human PDE5 complexed with the three drug molecules sildenafil, tadalafil (Cialis) and vardenafil (Levitra). These structures will provide opportunities to design potent and selective PDE inhibitors with improved pharmacological profiles.

Molecular basis for the local conformational rearrangement of human phosphoserine phosphatase.

Human phosphoserine phosphatase (HPSP) regulates the levels of glycine and d-serine, the putative co-agonists for the glycine site of the NMDA receptor in the brain. Here, we describe the first crystal structures of the HPSP in complexes with the competitive inhibitor 2-amino-3-phosphonopropionic acid (AP3) at 2.5 A, and the phosphate ion (Pi) and the product uncompetitive inhibitor l-serine (HPSP.l-Ser.Pi) at 2.8 A. The complex structures reveal that the open-closed environmental change of the active site, generated by local rearrangement of the alpha-helical bundle domain, is important to substrate recognition and hydrolysis. The maximal extent of this structural rearrangement is shown to be about 13 A at the L4 loop and about 25 degrees at the helix alpha3. Both the structural change and mutagenesis data suggest that Arg-65 and Glu-29 play an important role in the binding of the substrate. Interestingly, the AP3 binding mode turns out to be significantly different from that of the natural substrate, phospho-l-serine, and the HPSP.l-Ser.Pi structure provides a structural basis for the feedback control mechanism of serine. These analyses allow us to provide a clear model for the mechanism of HPSP and a framework for structure-based drug development.

Crystallization and preliminary X-ray crystallographic analysis of enoyl-acyl carrier protein reductase from Helicobacter pylori.

Enoyl-acyl carrier protein reductase (ENR) catalyzes the NADH-dependent stereospecific reduction of alpha,beta-unsaturated fatty acids bound to the acyl-carrier protein. ENR from Helicobacter pylori has been overexpressed in Escherichia coli and has been crystallized in the presence of its cofactor NADH and the inhibitor triclosan (or its analogue diclosan) at 296 K using polyethylene glycol (PEG) 400 as a precipitant. For the triclosan (or diclosan) complex, diffraction data to 2.5 (or 2.3) A resolution have been collected using synchrotron X-rays. The crystals belong to the monoclinic space group P2(1), with unit-cell parameters a = 73.35, b = 94.91, c = 75.38 A, beta = 106.21 degrees for the triclosan complex (or a = 73.25, b = 95.07, c = 75.02 A, beta = 106.53 degrees for the diclosan complex). The asymmetric unit contains one homotetramer, with a corresponding V(M) of 2.10 A(3) Da(-1) and a solvent content of 41% by volume.

Crystallization and preliminary X-ray crystallographic analysis of UDP-N-acetylglucosamine acyltransferase from Helicobacter pylori.

Lipid A, a constituent of lipopolysaccharides, is essential for the growth and virulence of most Gram-negative bacteria. This makes its biosynthetic enzymes potential targets for development of new antibacterial agents. The first step of lipid A biosynthesis is catalyzed by the enzyme UDP-N-acetylglucosamine acyltransferase (LpxA). LpxA from the pathogenic bacterium Helicobacter pylori has been overexpressed in Escherichia coli and crystallized at 297 K using ammonium sulfate and sodium/potassium tartrate as precipitants in the presence of a detergent. Diffraction data to 2.1 A resolution have been collected from a native crystal. The crystal belongs to space group P6(3)22, with unit-cell parameters a = b = 90.69, c = 148.20 A. The asymmetric unit contains one subunit of LpxA, with a crystal volume per protein mass (V(M)) of 2.87 A(3) Da(-1) and a solvent content of 57.1%.