Optimizing rod window width in positron emission tomography

A technique determines the optimal window width for orbiting rod transmission studies in positron emission tomography (PET). Windowing reduces noise in orbiting rod transmission studies. Lines-of-response (LOR) which intersect the rods generate primarily true coincidence events. LOR which pass far from the rods generate random and scatter events. Since the angular position of the orbiting rods is known in real-time, LOR which produce mostly noise are gated off. When optimally determined, the rod window width maximizes the noise equivalent counts (NEC) collected in the transmission study. Transaxial rod projection profiles of trues, randoms, and scatter produce NEC versus window width plots. For the ECAT EXACT line of PET systems and a 20-cm water cylinder, optimal is five LOR wide.     

Azaaurones as Potent Antimycobacterial Agents Active against MDR- and XDR-TB

Herein we report the screening of a small library of aurones and their isosteric counterparts, azaaurones and N-acetylazaaurones, against Mycobacterium tuberculosis. Aurones were found to be inactive at 20 μm , whereas azaaurones and N-acetylazaaurones emerged as the most potent compounds, with nine derivatives displaying MIC₉₉ values ranging from 0.4 to 2.0 μm . In addition, several N-acetylazaaurones were found to be active against multidrug-resistant (MDR) and extensively drug-resistant (XDR) clinical M. tuberculosis isolates. The antimycobacterial mechanism of action of these compounds remains to be determined; however, a preliminary mechanistic study confirmed that they do not inhibit the mycobacterial cytochrome bc1 complex. Additionally, microsomal metabolic stability and metabolite identification studies revealed that N-acetylazaaurones are deacetylated to their azaaurone counterparts. Overall, these results demonstrate that azaaurones and their N-acetyl counterparts represent a new entry in the toolbox of chemotypes capable of inhibiting M. tuberculosis growth.     

电厂蒸汽回路系统中腐蚀损伤的决定论预测

局部腐蚀,包括点腐蚀、应力腐蚀开裂和腐蚀疲劳是导致电厂发电装置损伤的重要原因,它们诱发50%以上的意外停机事故。迄今,腐蚀破坏的预测一直沿用经验和统计的方法,但是,由于已证实该方法的适用性和其结果的准确性欠佳,故不宜作为例行检修规程的基础。本文提出了预测局部腐蚀损伤的决定论方法,并使用这个方法说明点腐蚀如何引发低压蒸汽轮机涡轮盘Wilson线下游部位的应力腐蚀开裂(SCC),我们的计算表明SCC的萌发与扩展对蒸汽小氧含量、冷凝液膜的环境和涡轮盘所承受的应力这三个因素敏感。     

The use of channel flow cells for electrochemical kinetic studies in high temperature aqueous solutions

It has been shown that, for the case of one-step reactions of arbitrary order, the relationship between the average current density and the limiting current density on a working electrode mounted on the inner radius of an annular flow channel of arbitrary length obeys, with great accuracy, the same relations as does a reaction on a uniformly accessible surface. This allows us to combine the advantages of non-uniformly accessible surfaces (high sensitivity, and no need to use rotating contacts) with the advantages of uniformly accessible surface systems (simple treatment of experimental data). This feature can be very important when investigating systems at high temperatures and pressures, where RDEs are difficult to employ. Using this approach, and by employing previously measured polarization data, the kinetic parameters (exchange current density and anodic transfer coefficient) for the oxidation of hydrogen on platinized nickel in 0.1 M NaOH + 0.7 × 10⁻³ m H₂ at temperatures between 25 °C and 300 °C have been derived. The anodic transfer coefficient is found to be almost temperature independent with a value of 0.43. The exchange current density displays Arrhenius behavior with temperature, increasing from 1.9 × 10⁻⁴ A cm⁻² at 25 °C to 3.9 × 10⁻³ A cm⁻² at 300 °C.     

Continuous visual information may be important after all: A failure to replicate Thomson (1983).

Conducted 2 experiments with 20 undergraduates in an attempt to replicate the findings of J. A. Thomson (1980; see also PA, Vol 71:3021), which suggest that visual information useful in the control of movement persists for up to 8 sec after visual occlusion. Little evidence was found for an 8-sec visual representation of the environment layout, which indicates that there is no substitute for continuous visual information in the control of movement. Methodological and statistical problems with Thomson's work are discussed. (9 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Integral methods for flow in a conical centrifuge

A set of through-thickness averaged equations for momentum and strain rate are derived for the problem of axi-symmetric free-surface flow within a spinning cone. The expressions are independent of the choice of constitutive law and can therefore be used for modeling the flow of a variety of materials within an industrial conical centrifuge. By assuming a through-thickness velocity profile the distribution of flow thickness and average velocity over the internal surface of the cone can be obtained. The approach has been validated for thin Newtonian viscous flow by comparison with full three-dimensional solutions of the Navier–Stokes equations obtained with a commercial CFD package. The averaged equations provide an accurate prediction of the flow thickness, velocity and the length of the zones of influence of inlet and outlet boundary conditions.     

DC SQUID Spectrometers for NMR

We report experiments in which we have used DC SQUIDs in pulsed NMR spectrometers to observe directly the free precession of nuclear spins. A broadband spectrometer, which operates in flux-locked loop mode with a bandwidth of 3.4 MHz using a SQUID with additional positive feedback and an untuned superconducting input circuit, has been used to observe NMR signals from platinum powder at frequencies of 38, 65, 85, 240 and 513 kHz. The performance is compared with a second system in which a DC SQUID is operated open loop as a small signal rf amplifier with a series tank input circuit tuned at 1 MHz.     

Prediction of corrosion product stability in high-temperature aqueous systems

Calculated thermodynamic data for metal oxidation/oxide reduction reactions of Fe, Ni, Co and Cu, and for formation, oxidation and reduction of NiFe₂O₄, CoFe₂O₄, CuFeO₂ and CuFe₂O₄, are examined for aqueous systems containing dissolved hydrogen and oxygen at temperatures up to 300°C. The data are presented as equilibrium partial pressures of oxygen and hydrogen for specific reactions. This information is used to predict which solids are stable in an equilibrium system containing known concentrations of oxygen and hydrogen, and in a non-equilibrium system in which γ and neutron radiation fields cause the concentrations of oxygen and hydrogen to be much greater than the equilibrium values. Results of X-ray diffraction studies of corrosion products filtered from the heat-transport system of the Douglas Point Generating Station are compared with phase stability predictions.     

The electrochemistry of silver in KOH at elevated temperatures—IV. AC impedance study

The ac impedance properties of silver in 1 mol kg^?1 KOH were studied under potentiostatic conditions over the temperature range 295–478 K. Measurements were obtained over the frequency range 0.5 Hz–5 kHz, and were analyzed in terms of equivalent in terms of equivalent circuits. It was shown that provision for surface roughness is required for a satisfactory explanation of the impedance data. Values for the double layer capacity and the concentration AgO^? ions at the electrode surface could generally then be obtained. At potentials corresponding to the formation of Ag₂O, it is demonstrated that both diffusion in solution and diffusion in the oxide film are operative. At elevated temperatures, the rate of growth of Ag₂O centres is controlled partly by diffusion in the oxide and party by a reaction step at the growing interfaces of the centers. The subsequent formation of Ag₂O₂, at all temperatures in the range studied, is interpreted on the basis of an electrocrystallisation impedance.     

The growth of iron oxide films on carbon steel and platinum surfaces in LiOH and NaOH solutions at 285°C

The corrosion products formed on carbon steel exposed to 1 mol/l LiOH and NaOH at 285°C in titanium autoclaves have been investigated using scanning electron microscopic and X-ray diffraction techniques. The effect of galvanically coupling the carbon steel to platinum was also studied. In LiOH both Fe₃O₄ and α-LiFeO₂ were found to form on the carbon steel surface but only α-LiFeO₂ was observed to nucleate on platinum in this solution. In NaOH solution both Fe₃O₄ and FeTiO₃ were identified on the metal surface. Galvanic coupling to platinum decreased the amount of α-LiFeO₂ and FeTiO₃ formed on carbon steel surfaces.