Qing Liang

Effect of Manganese Doping on Oxygen Storage Capacity of Ceria-Zirconia Mixed Oxides

CeO22ZrO22MnO x mixed oxide series were prepared by sol2gel method . CO pulse and CO2O2 cycle measure2 ments were carried out to examine the oxygen storage complete capacity (OSCC) and dynamic oxygen storage capacity (OSC) of the samples . The doping method brought about strong interactions between manganese oxide and ceria , both in the bulk and on the surface . Only a small part of Mn cations are incorporated into the ceria lattice to form solid solutions and the remaining are left on the surface as finely dispersed Mn3O4 . The OSC behaviors of the materials are influenced by the doping amount of Mn and the solubility of Mn in the CeO2 lattice . The OSC is more easily affected by available cont2 ents of oxygen storage components when the measurement frequency is low. Comparatively , the concentration of lattice de2 fects , which affects the mobility of bulk oxygen , is the determining factor under high frequency.

Role of Surface Adsorption in Fast Oxygen Storage/Release of CeO2 - ZrO2 Mixed Oxides

Abstract Four kinds of CeO 2 -ZrO 2 mixed oxides, i.e., a physical mixture of ceria and zirconia (CZP), zirconia-coated ceria (ZCC), ceria-coated zirconia (CCZ) and a chemical mixture of ceria and zirconia (CZC), were prepared. The oxygen storage capacity (OSC) measurements at 500 °C were performed under transient and stationary reaction conditions. All the curves of CO 2 evolution during CO-O 2 cycles presented a bimodal shape. The first peak was primarily the result of the reaction of CO with the oxygen from the oxides, which was mainly determined by the nature of the material. The second peak was mostly related to the CO 2 adsorption behavior and was highly influenced by the surface area and the number of surface active sites. As a result, OSC activity of the samples followed in the order of CZC > CCZ > ZCC ≈ CZP.

Image extrapolation for patient-specific CT dose determination based on scout images

Monte Carlo (MC) simulation based on a patient’s computed tomography (CT) images is a promising way to retroactively determine patient-specific dose from CT scans. CT scans generally include only a portion of the patient’s body; however, photon interactions in regions adjacent to the scan region contribute to the overall scan dose. Thus, the CT images alone, which do not include these adjacent regions, are insufficient for determining dose. In fact, dose underestimation, especially at the scan edge, occurs when the adjacent regions are not accounted for. In this work, the dose underestimation without the scatter region is demonstrated, and the size of the scatter region required to provide sufficient simulated scatter was determined with mathematical phantom studies. For a simple cylindrical water phantom, up to a 25% underestimation of dose was found when no scatter region was used, and a 40 mm scatter region was determined to be required to eliminate this error for scans performed with both the 40 mm and 5 mm collimation sizes. In addition, four different image extrapolation methods based on CT images and scout images were proposed for a chest CT scan of an anthropomorphic phantom. The dose was calculated with the chest images only and the chest images plus the four types of extrapolated images. The results were compared with the dose calculated using whole body images of the anthropomorphic phantom. The image extrapolation methods, especially the ones based on scout images, were shown to improve the dose calculation accuracy under both step-shoot scan mode and helical scan mode. Keywords: CT, patient-specific dose, Monte Carlo, image extrapolation, scout images