J. A. Young

Energy-resolved positron annihilation rates for molecules

The development of high resolution positron beams has enabled measurements of annihilation rates for molecules as a function of incident positron energy. Vibrational Feshbach resonances in these spectra provide evidence for the existence of positron-molecule bound states. In this paper we present further studies of this phenomenon. Evidence is presented for positronically excited bound states (i.e., in addition to the ground state) in C{sub 12}H{sub 26} and C{sub 14}H{sub 30}. Measurements of the annihilation spectra of the halomethanes, CH{sub 3}F, CH{sub 3}Cl, and CH{sub 3}Br, exhibit strong resonances that vary significantly with the substituted halogen. Annihilation spectra for linear alkanes and ring molecules are compared. Annihilation spectra and infrared absorption spectra are compared for a number of molecules. Finally, annihilation rate measurements are presented for a variety of molecules at energies {>=}0.5 eV (i.e., above the vibrational resonances). These provide a measure of the annihilation rates in the absence of vibrational resonances.

Analysis and Evaluation of Clinical Communication in the Surgical Intensive Care Unit

For decades, emergency departments have become increasingly unable to meet escalating patient demands. In order to allow emergency departments to operate beyond their designed capacity, major efforts have gone into improving their work-flow, efficiency, and quality of care. Many studies have show that inefficiencies and error in a clinical setting are linked to communications. As a means to improve the quality of care for trauma patients, this study examines the present communication systems for different admission pathways to the University of Virginia’s Surgical Intensive Care Unit (SICU) and recommends a new design for critical operations. The evaluation and analysis of this new design will identify critical factors, including potential communication modalities, implementation details, potential key clinician roles, and in which processes the new system will be useful. Our objective is to design a real-time communication infrastructure for operations within a critical care unit by an informed design process.

Resonant Positron Annihilation on Molecules

At incident positron energies below the threshold for positronium atom formation, there are many cases in which annihilation rates for molecules are far in excess of that possible on the basis of simple two-body collisions. We now understand that this phenomenon is due to positron attachment to molecules mediated by vibrational Feshbach resonances. The attachment enhances greatly the overlap of the positron with molecular electrons and hence increases the probability of annihilation. Furthermore, measurements of the annihilation spectra as a function of incident positron energy provide a means of measuring positron-molecule binding energies. In this paper we present an overview of our current understanding of this process, highlighting key results and discussing outstanding issues that remain to be explained.