William F. Christensen

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Although the association between exposure to ambient fine particulate matter with aerodynamic diameter < 2.5 microm (PM2.5) and human mortality is well established, the most responsible particle types/sources are not yet certain. In May 2003, the U.S. Environmental Protection Agency's Particulate Matter Centers Program sponsored the Workshop on the Source(More)
Although much of the media attention during presidential election years focuses on polls tracking popular support for the major candidates, the complicated role played by the Electoral College in this multistage election process must be accounted for in order to address the issue of winning the presidency. State-level pre-election polls are used in a manner(More)
OBJECTIVES The aims of this study were to determine the feasibility of obtaining auditory cortex activation evoked by pure tones presented at threshold and suprathreshold hearing levels, to evaluate tonotopicity of the primary auditory cortex, and to determine the effect of stimulus intensity on auditory cortex activation using silent functional magnetic(More)
PURPOSE To evaluate auditory cortex activation evoked by pure-tone stimulus using silent functional magnetic resonance imaging (FMRI). MATERIAL AND METHODS Nine volunteers with normal hearing as determined with pure-tone audiometry were studied. Auditory cortex activation was evoked by pure-tone stimuli presented monaurally at 1,000, 2,000, and 4,000 Hz.(More)
This project has been read by each member of the following graduate committee and by majority vote has been found to be satisfactory. As chair of the candidate's graduate committee, I have read the project of Guinan Lian in its final form and found that (1) its format, citations, and bibliographical style are consistent and acceptable and fulfill university(More)
Functional magnetic resonance imaging (fMRI) allows neuroscientists to assess brain function by evaluating haemodynamic activity (blood flow) when a stimulus is present or absent. In clinical practice, the hearing levels of individuals are determined using an audiometer that allows presentation of a pure-tone of specific intensity and frequency. Functional(More)
Statistical measures for evaluating the similarity of different source apportionment solutions are proposed. The sensitivity of positive matrix factorization to small perturbations in species measurement uncertainty estimates is examined using fine particulate matter measurements on organic carbon, elemental carbon, ions, and metals at the St. Louis-Midwest(More)