Graduation date: 1990

No description available.

No description available.

Thesis (Ph.D.)--Tufts University, 1995. / Adviser: Nak-Ho Sung. Submitted to the Dept. of Chemical Engineering. Includes bibliographical references. Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Nitrogen oxides control the global formation of ozone in the lower atmosphere and influence the much higher levels of ozone formed in areas subjected to photochemical air pollution. As an important member of the nitrogen oxide family, N02 plays a significant role in serving as the only known source of ozone (through photolysis) in the lower atmosphere and as sink for HO via the formation of nitric acid. Ozone can be destroyed by reaction with another member of the nitrogen oxide family, nitric oxide (NO), to reform N02. This cycle between NO, N02 and 03 is known as the NOx-03 photostationary state (PSS). Imbalances in this cycle have been used to calculate ambient levels of oxidants (such as R02 and H02) responsible for ozone production. Consequently, accurate N02 measurements are critical to making meaningful measurements of the imbalances in the NOx-03 photostationary states (PSS). A low pressure laser-excited fluorescence technique (FAGE) for the direct determination of atmospheric N02 has been developed. This technique has been explored with both a Nd-YAG laser (1.4 W, 532nm, 30Hz) and a Cu-vapor (1.2 W, 511nm, 5.6kHz) laser. The detection limits for these instruments, under laboratory conditions and a signal collection time of 20s (lOs each signal and background), have been determined to be 450 and 350pptv N02, respectively. In these systems, the background was measured by chemically reducing N02 with FeS04°7H20. Ambient measurements of the NOx-03 photostationary state (PSS) were undertaken on a rooftop monitoring site in downtown Portland, Oregon. N02 was monitored with the Cu-vapor system. Nitric oxide and ozone were monitored with standard instruments. Data for three days in 1990 are presented. Overall these data sets clearly show that despite daily changes in concentration of NO, N02 and 0 3 of factors of 4-10 each, the PSS remains relatively constant to within -50%. This is in itself strong confIrmation of the primary importance of the NOx-03 photo stationary state in controlling the concentrations of these species at these levels. In addition, these experiments also serve to demonstrate that the monitoring instruments, including FAGE-N02, are not subject to serious interferences or artifacts at these concentration levels.

No description available.

A novel detector for ultra-high energy cosmic rays, and its prototype are discussed. It detects events with primary energy greater than 100 PeV. (1 PeV = 1000 TeV; 1EeV = 1000 PeV.) The detector operates by sensing the near-ultraviolet scintillation light of ionized nitrogen molecules created by the passage of ionizing particles in extensive air showers. (The concept is loosely based on the highly successful Fly's Eye detector situated at Dugway, Utah.) Typical events should consist of 1 to 100 EeV primary energy showers, with near-vertical cores, passing through the detector's field-of-view at distances of 1 to 20 km. The optical field of view of the hypothetical detector would be 60 degrees wide by several (≈ 3) degrees high and would look in a near-horizontal direction at a distant mountain range or other suitably dark background roughly 20 Ian away. A typical good location would be the rim of a canyon, looking slightly downward at the other side. The field-of-view would be subdivided into 3 or more thinner ''wedges'', 60 degrees wide by, perhaps, 1 degree high. A single detector provides timing and brightness information only. Three widely-separated detectors with overlapping fields-of-view provide sufficient data to determine the core location, the zenith and azinruthal angles of the core axis, and the absolute luminosity of the cascade. Interpretation of the luminosity data would be a challenge, but it should be possible to estimate primary energy from it. The advantage of this new scheme is the enormous effective detector area per relatively low-cost detector module. Each triplet of detectors "sees" 300 square km with a typical core axis acceptance of roughly 1 sr. The construction and testing of a prototype unit has been accomplished. The field-of-view was 41 degrees wide by 2 degrees high. Light was collected by a 4.7 square meter mirror and focused onto a wave-shifter PMT system. 8 events with primary energies in the 0.1 to 1 EeV range were observed in an 8.5 hour period. Representative events are shown and preliminary data analysis is discussed.

by Chow Kim-fung. / Bibliography: leaves 112-114 / Thesis (M.Ph.)--Chinese University of Hong Kong, 1985

This thesis describes several aspects of cosmic ray composition studies using the Utah Fly's Eye and High Resolution Fly's Eye (HiRes) detectors. The Fly's Eye detector utilises the atmospheric fluorescence technique to measure the development of cosmic ray cascades as they pass through the atmosphere. This is complementary to the surface array technique, as used by the Akeno experiment in Japan, which measures the electromagnetic and muon content of air showers at a single observation level. For some time it was thought that Fly's Eye and Akeno gave inconsistent composition results. In Chapter 4 I show that the inconsistency is due, for the most part, to a difference in the assumptions made about hadronic interactions. In Chapter 5 I present analysis of the composition between 10^17 and 10^18 eV using the prototype High Resolution Fly's Eye (HiRes) detector in coincidence with the Michigan Muon Array (MIA). The hybrid nature of these measurements gives us more information about cosmic ray showers than either technique on its own. The consistency or otherwise of the composition measured by the two detectors is discussed. Finally, in Chapter 6, I discuss a method of extracting the total proton-proton cross section from the cosmic ray data. This information is of interest because it is derived at centre of mass energies much higher (by at least an order of magnitude) than those currently accessible by collider experiments. I present a preliminary calculation of the cross section using the HiRes/MIA hybrid data set. / Thesis (Ph.D.)--Department of Physics and Mathematical Physics, 2001.

A fiber optic fluorometer utilizing a double-fiber optic probe was constructed. The absolute fluorescence signal and effective collection efficiency are approximately one fifth those of typical cuvette fluorometers and agree with those predicted by theory. A quinine sulfate calibration curve shows linearity from a detection limit of 10 pg/mL to 10 μg/mL. Single- and double-fiber probe configurations were also compared. The double-fiber configuration provided better detection limits due to its superior signal-to-background ratio. A discussion of sensor methodology for the monitoring of reaction intermediates is presented and a simple kinetic model for predicting the time dependent response of such sensors is developed. Two possible mechanisms for the Fujiwara reaction with chloroform are discussed. The effect of pyridine, water, and base concentrations on reaction kinetics was evaluated to develop single-phase Fujiwara reagent mixtures for both fluorometric and spectrophotometric determinations of chloroform. A unique "continuous-exposure" apparatus allowing vapor phase transport of chloroform from an aqueous sample to a conventional cuvette was constructed. The spectrophotometric detection limit for chloroform is 11 ng/mL and the method was shown to be suitable for the analysis of tap water. Two fiber optic chemical sensors (FOCS) for the detection of chloroform were developed. An aliquot of the optimized fluorometric reagent solution is held in contact with the fiber optic probe within a light-tight enclosure and is isolated from a bulk sample by a trapped headspace. One FOCS utilizes 1.3 mL of reagent held in a reservoir and the other utilizes a 10-μL drop of reagent suspended on the sensing tips of the fiber optic probe. Chloroform vapor from the sample migrates into the FOCS and reacts with the reagent to produce a fluorescent reaction intermediate which is monitored at 590 nm; the rate of increase in the fluorescence signal is related to chloroform concentration. Both FOCSs give detection limits better than 0.1 ng/mL. The response and total measurement times are comparable for the two FOCSs, and the duration of the linear response is limited by inner-filter effects. The response to a number of volatile GPHHCs including the trihalomethanes are reported. Analyses of tap water for chloroform with the reservoir FOCS and GC/MS were in excellent agreement. / Graduation date: 1992