Browsing by Author "Wang, Lei"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Measurement of Z Boson Transverse Momentum In Proton-Antiproton Collisions At sqrt(s)=1.96 TeV(2007-03-26) Wang, Lei; Eno, Sarah; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation describes a measurement of the shape of the boson transverse momentum distribution in $p\bar{p}\rightarrow Z/\gamma^{*}\rightarrow e^+e^- +X$ events at a center-of-mass energy of 1.96 TeV. The measurement is made for events with electron-positron mass between $70 < M_{ee} < 110$ GeV/c$^{2}$ and uses 976 pb$^{-1}$ of data collected at the Fermilab Tevatron collider with the D\O\ detector. The shape is measured both for the inclusive sample and for the subset of events containing a boson with large rapidity. The large-rapidity distribution shows better agreement with theory when the calculation is done using traditional Collins-Soper-Sterman resummation than when using a recent resummed form factor with modifications in the small-x region.Item Model Development for Gadolinia-doped Ceria-based Anodes in Solid Oxide Fuel Cells(2014) Wang, Lei; Jackson, Greg S; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Intermediate temperature (500 &ndash 700 °C) solid oxide fuel cells (IT&ndashSOFCs) with gadolinia&ndashdoped ceria (GDC) electrolytes have significant commercial potential due to reduced materials costs for seals and interconnect and improved performance with high oxide&ndashion conductivity at these temperatures. As an SOFC anode component in the reducing anode environments, GDC offers enhanced catalytic activity and tends to suppress carbon deposition in composite Ni/GDC anodes. The current study investigates relevant kinetics on GDC anodes for IT&ndashSOFC applications. Simultaneous electrochemical characterization and X&ndashray photoelectron spectroscopy of thin&ndashfilm Ni/GDC and Au/GDC electrochemical cells provide a basis for understanding pathways for H2 and CO electrochemical oxidation as well as H2O splitting on GDC and GDC composite electrodes. Differences in electrochemical performance of Ni/GDC and Au/GDC electrodes at temperatures below 650 °C reveal limitations of GDC surfaces in promoting electrooxidation under conditions of low polaron (electron) mobility. These results also suggest the role of the metal in promoting hydrogen spillover to facilitate change transfer reactions at the Ni/GDC interface. Variation in OH- concentration at the metal/GDC interface with operating temperature, effective oxygen partial pressure, and electric bias provides valuable insight into the nature of electrochemical and other heterogeneous reactions in IT&ndashSOFC anodes. A detailed kinetic model for the GDC surface reactions and Ni/GDC charge&ndashtransfer reactions of H2 oxidation and H2O electrolysis is developed based on electrochemical characterization and spectroscopic analysis of GDC surface electrochemistry. The thermodynamically consistent kinetic model is able to capture the observed chemical and electrochemical processes on the thin&ndashfilm Ni/GDC electrode. A full three&ndashdimensional IT&ndashSOFC stack model is developed with simplified kinetics to evaluate GDC&ndashbased anode performance with H2 and methane&ndashderived fuels. The stack model explores the effects of operating condition on performance of stacks with GDC electrolytes and Ni/GDC anodes. The parametric study results of stack model provide essential information for optimizing performance of IT&ndashSOFCs stack and guiding IT&ndashSOFC design. Temperature distribution in non&ndashisothermal model result suggests that internal CH4 reforming can be used as an effective thermal management strategy to maintain high current densities and cell voltages and to lower risk to thermo&ndashmechanical degradation.Item Satellite-detected gain in built-up area as a leading economic indicator(IOP Publishing, 2019-10-30) Ying, Qing; Hansen, Matthew C.; Sun, Laixiang; Wang, Lei; Steininger, MarcLeading indicators of future economic activity include measures such as new housing starts, managers purchasing index, money supply, and bond yields. Such macroeconomic and financial indicators hold predictive power in signaling recessionary periods. However, many indicators are constrained by the fact that data are often published with some delay and are subject to constant revision (Bandholz and Funke 2003, Huang et al 2018, Orphanides 2003). In this research, we propose a leading indicator derived from satellite imagery, the expansion of anthropogenic bare ground. Satellite-detected gain in built-up area, a major land cover and land use (LCLU) outcome of anthropogenic bare ground gain (ABGG), provides an inexpensive, consistent, and near-real-time indicator of global and regional macroeconomic change. Our panel data analysis across four major regions of the world from 2001 to 2012 shows that the logarithm of total ABGG, mostly owing to its major LCLU outcome, the expansion of built-up land in either year t, t −1 or t −2, significantly correlated with the year t logarithm of gross domestic product (GDP, de-trended by Hodrick–Prescott filter). Global ABGG between 2001 and 2012 averaged 7875 km2 yr−1, with a peak gain of 11 875 (± 2014 km2 at the 95% confidence interval) in 2006, prior to the 2007–2008 global financial crisis. The curve of global ABGG or its major LCLU outcome of built-up area in year t − 1 accords well with that of the de-trended logarithm of the global GDP in year t. Given the 40 year archive of free satellite data, a growing satellite constellation, advances in machine learning, and scalable methods, this study suggests that analyses of ABGG as a whole or its LCLU outcomes can provide valuable information in near-real time for socioeconomic research, development planning, and economic forecasting.