No description available.

No description available.

No description available.

An original method is presented as an efficient technique for characterizing polymers, and understanding the kinetics of the polymerization reactions The Automatic Continuous Online Monitoring of Polymerization Reactions (ACOMP) method developed at Tulane University involves following one or more characteristics of a polymerization reaction: monomer conversion, different molecular weight averages, intrinsic viscosity, etc By performing an automatic withdrawal and dilution of the polymer solution to create a small stream which flows through a detector train, including light scattering, viscometer, refractive index, Ultraviolet/Visible detectors, a continuum of data points can be obtained, allowing powerful analysis methods to be developed The goal of this work is to expand ACOMP to new polymerization reactions, such as free radical copolymerization, controlled radical polymerization, inverse emulsion polymerization, both to achieve a complete physical characterization of the polymers synthesized and a better understanding of the reaction mechanisms. For each of the reactions ACOMP brings significant innovations in the analysis of the kinetics. Other new methods, such as Automatic Continuous Mixing (ACM) and Simultaneous Multiple Sample Light Scattering (SMSLS) are also used, as well as traditional multi-detector Size Exclusion Chromatography (SEC) As an immediate consequence it is hoped that the information on reaction kinetics and mechanisms offer a better fundamental knowledge, control and ability to optimize reactions. At the industrial scale, online monitoring should allow a more efficient use of resources, energy, reactor and personnel time as well as a higher product quality / acase@tulane.edu

acase@tulane.edu

This dissertation is comprised of three projects associated with cholesteric liquid crystals. Each project was motivated by observations in liquid crystalline deoxyribonucleic acid (lcDNA). The first project is a Monte Carlo study of defects in planar cholesterics. A microscopic model is used to obtain defects and defect energies. The second project is a microscopic model for the cholesteric to hexagonal transition observed in lcDNA. The model is solved in the mean-field and forms for the twist wave vector and its associated elastic modulus are obtained. The model is also used to obtain expressions for the elastic constants. The third project is a computational study of cholesteric liquid crystals under high magnetic fields. Differential equations obtained from the free energy of defects are solved numerically. The solutions obtained provide theoretical justification for structure observed in lcDNA under 9.4 Tesla fields. / Source: Dissertation Abstracts International, Volume: 55-11, Section: B, page: 4916. / Major Professor: David H. Van Winkle. / Thesis (Ph.D.)--The Florida State University, 1994.

Thesis (Ph.D.)--Brown University, 2008. / Vita. Advisor : Xingsheng Sean Ling. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

Fundamental observations of molecular hydrogen (H₂) in dark clouds, star forming regions, and radiation-dominated environments are presented, modeled, and interpreted. Through a weak infrared absorption line spectrum, the abundance of cold H₂ in dark molecular clouds and star forming regions is measured directly and compared with the abundance of its most commonly cited surrogate, CO. The derived abundance of CO is between 1.5 and 2.5 x 10⁻⁴ for the sample. The CO molecule thus represents about ⅓ of the total carbon budget in dense clouds. Also detected via infrared line absorption is the pivotal molecular ion H⁺₃ , yielding a direct measure of the cosmic ray ionization rate of H₂ in dark molecular clouds (between 1 and 5 x 10⁻¹⁷ s⁻¹), a process that instigates the complex ion-neutral chemical pathways that form many of the 120+ known molecular species deep inside interstellar clouds. These timely tests of theory are applied to the detailed submillimeter-wave study of the ρ Ophiuchi star forming cloud and photodissociation front, allowing partial disentanglement of the complicated physical and chemical structure of a star forming cloud. Yet H₂ and H⁺₃ continue to surprise and delight us with more mysteries. The formation, excitation and survival of molecules in unusual & hostile environments is highlighted by the discoveries of H⁺₃ in circumstellar disks of early-type stars, and of fluorescing H₂ in two harshly-irradiated filaments of the Crab Nebula. The role of H⁺₃ as a possible tracer of planet formation, and the evolution of H₂ in the interstellar medium is discussed. The study of H₂ in hostile environments is extended to the ensemble properties of extragalactic star forming regions, and applied to the Arp 299 merger system as a unique probe of the feedback of newly-formed hot stars, their fossil remains, and the molecular material which formed them.

The First Negative (1N) band emission of the molecular nitrogen ion, N⁺₂ , is one of the most prominent features of the terrestrial dayglow spectrum. However, past N⁺₂ studies have encountered problems in validating the intensity of this emission. Also, some anomalous characteristics of the dayglow 1N spectrum remain unexplained, such as a highly developed rotational and vibrational structure. These anomalies appear to be due to the charge exchange reaction: O⁺ + N₂ → N⁺₂ + O, which dominates N⁺₂ ion production at high altitudes. This thesis examines dayglow 1N spectra acquired by the Arizona Airglow Experiment (GLO) flown on the space shuttle mission STS-74. In the analysis the emission is separated into two components. First is the emission from ions produced by photoionization and electron bombardment. Second is emission from ions produced by the charge exchange reaction, which cannot be modeled. The first source is evaluated and subtracted from the observed spectrum. The remaining emission is then used to derive empirical parameters related to the charge exchange reaction. These parameters can be used to estimate the 1N emission rate expected from the thermosphere, based on model atmosphere predictions. This emission rate can be used to determine the dayside O⁺ concentration using the GLO observations.