Results 1 - 10 of 791
Results 1 - 10 of 791. Search took: 0.062 seconds
|Sort by: date | relevance|
[en] A Medium-Energy Beam Transport (MEBT) line is employed in the SNS linac to match the beam from an RFQ to a DTL and to perform other functions. The MEBT lattice consists of fourteen electromagnetic quadrupoles and other devices. The quads have very small aspect ratios (steel length over aperture diameter), and they are densely packed in the lattice. Significant fringe fields and magnetic interference cause difficulties in beam matching. We have performed 3D simulations of the magnets, computed their optical properties, and compared their performance with what predicted by simple hard edge models. This paper reports our findings and a general solution to the problem.
[en] Isobaric contaminants are often problematical in accelerated negative ion beams for research at certain radioactive ion beam (RIB) and accelerator mass spectrometry (AMS) facilities since their presence in low-intensity rare isotopic beams seriously compromise experimental results. This article describes a non-resonant, laser-based photo-detachment apparatus for use at these facilities, which, according to calculations efficiently removes isobaric contaminants from these beams. The advantage of the system for isobaric contaminant removal over other systems proposed to date lies in its ability to efficiently capture easily transportable energetic negative ion beams with low, intermediate or high energy spreads by a superconducting solenoid magnetic field. The ability to change the diameter of captured beams by adjusting the magnetic field strength permits optimum control of the radial overlap of the laser/negative ion beam profiles over an extended interaction region under high vacuum conditions without retarding optical affect, collision-cooling or capture losses
[en] Horseradish peroxidase (HRP)-TiO2 film electrodes were fabricated by casting the mixture of HRP solution and aqueous titania nanoparticle dispersion onto pyrolytic graphite (PG) electrodes and letting the solvent evaporate. The HRP incorporated in TiO2 films exhibited a pair of well-defined and quasi-reversible cyclic voltammetric peaks at about -0.35 V versus saturated calomel electrode (SCE) in pH 7.0 buffers, characteristic of HRP-Fe(III)/Fe(II) redox couple. The electron exchange between the enzyme and PG electrodes was greatly enhanced in the TiO2 nanoparticle film microenvironment. The electrochemical parameters such as apparent heterogeneous electron transfer rate constant (ks) and formal potential (E deg. ') were estimated by fitting the data of square wave voltammetry with nonlinear regression analysis. The HRP-TiO2 film electrodes were quite stable and amenable to long-time voltammetric experiments. The UV-Vis spectroscopy showed that the position and shape of Soret absorption band of HRP in TiO2 films kept nearly unchanged and were different from those of hemin or hemin-TiO2 films, suggesting that HRP retains its native-like tertiary structure in TiO2 films. The electrocatalytic activity of HRP embedded in TiO2 films toward O2 and H2O2 was studied. Possible mechanism of catalytic reduction of H2O2 with HRP-TiO2 films was discussed. The HRP-TiO2 films may have a potential perspective in fabricating the third-generation biosensors based on direct electrochemistry of enzymes
[en] Urban metabolism analysis has become an important tool for the study of urban ecosystems. The problems of large metabolic throughput, low metabolic efficiency, and disordered metabolic processes are a major cause of unhealthy urban systems. In this paper, I summarize the international research on urban metabolism, and describe the progress that has been made in terms of research methodologies. I also review the methods used in accounting for and evaluating material and energy flows in urban metabolic processes, simulation of these flows using a network model, and practical applications of these methods. Based on this review of the literature, I propose directions for future research, and particularly the need to study the urban carbon metabolism because of the modern context of global climate change. Moreover, I recommend more research on the optimal regulation of urban metabolic systems. Highlights: •Urban metabolic processes can be analyzed by regarding cities as superorganisms. •Urban metabolism methods include accounting, assessment, modeling, and regulation. •Research methodologies have improved greatly since this field began in 1965. •Future research should focus on carbon metabolism and optimal regulation. -- The author reviews research progress in the field of urban metabolism, and based on her literature review, proposes directions for future research
[en] Experience using laser-wire beam profile measurement to perform transverse beam matching in the SNS superconducting linac is discussed. As the SNS beam power is ramped up to 1 MW, transverse beam matching becomes a concern to control beam loss and residual activation in the linac. In our experiments, however, beam loss is not very sensitive to the matching condition. In addition, we have encountered difficulties in performing a satisfactory transverse matching with the envelope model currently available in the XAL software framework. Offline data analysis from multi-particle tracking simulation shows that the accuracy of the current online model may not be sufficient for modeling the SC linac.
[en] A variety of ISOL targets for generation of radioactive ion beams have been successfully developed at the Holifield Radioactive Ion Beam Facility. Short-lived ion species generated from fast release targets made up of fibrous materials such as HfO2, and coated low-density carbon foam target matrices such as UC2/RVCF targets have been applied in important research programs of nuclear physics and astrophysics. In this paper, computer modeling of the HRIBF targets are introduced, and the computation results are coincident with the experimental measurements. These studies provide a cost effective method to understand beam power deposition as well as temperature distribution in ISOL target presently utilized at the HRIBF and predict the capability of high power ISOL target designs and the temperature profiles with other target materials and geometries for the future facility upgrade
[en] The most recent beam dynamics studies at the Spallation Neutron Source (SNS) linac, including major beam loss reduction efforts in the normal conducting linac and in the superconducting linac (SCL), and the simulation and measurement of longitudinal beam halo and longitudinal acceptance at the entrance of the SCL are discussed. Oscillation of the beam centroid around the linac synchronous phase and the phase adiabatic damping curves in the SNS linac are investigated with linac longitudinal models and measured with all the linac beam phase monitors.
[en] For the purpose of evaluating the detection of small hepatocellular carcinoma (HCC) and morphologic features thereof using dynamic CT (D-CT) and dynamic MRI (D-MRI), and for evaluating the same with respect to histologic differentiation in particular, 50 patients with 70 histologically verified sites of nodular HCC less than 20 mm in diameter were examined as subjects. Results were compared utilizing the χ2 test. The detection rate of small sites of HCC with early-phase D-MRI (56%) was slightly higher than that using early-phase D-CT (49%), whereas detection rate using delayed-phase D-CT (59%) was slightly higher than that using delayed-phase D-MRI (53%). The capsular pattern of small HCC nodules (diameter 10 mm or greater but less than 20 mm) was better visualized using D-MRI than D-CT (visualized in 51% and 27%, respectively; p<0.05). The mosaic pattern was likewise better visualized using D-MRI than D-CT (20% and 4%, respectively; p<0.05). The detection rate of sites of well differentiated HCC was significantly lower than that for moderately differentiated HCC (38% and 81%, respectively; p<0.05), as was the rate of capsular visualization (6% and 48%, respectively; p<0.05). These findings suggest that the rate of tumor detection and visualization of morphologic features are dependent on tumor size as well as the histologic grade of the tumor. (author)
[en] BiFeO_3 (BFO) nanoparticles was synthesized via sol–gel technique, and successfully loaded with small sizes of gold nanoparticles (Au NPs) by impregnation-reduction method to extremely enhance the BFO photocatalytic activity. The obviously stronger optical absorption of Au/BFO observed from the UV–vis diffuse reflectance spectrum confirmed that the surface plasmon resonance (SPR) effect occured on the surface of Au NPs. And the surface plasmon-induced localized electric field could allow the formation of electron/hole pairs in the near surface region of BFO which can migrate to the surface without undergoing electron/hole (e"−/h"+) pair recombination. The more electrons and holes formed, the more ·OH will be generated to decompose the CR solution. When the gold loading in Au/BFO nanoparticles is 3.36 wt%, the obtained Au/BFO catalyst exhibits best photocatalytic activity evaluated by photocatalysis degradation of Congo red (CR) solution under the visible light irradiation.