Browsing by Subject "Ionization"
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Item Chloride ion transport in bridge deck concrete under different curing durations(Texas Tech University, 2004-08) Ghanem, Hassan AkramThe durability of concrete is usually measured by the number of years of maintenance- free service it provides. If a correct prediction has been made of the environmental conditions to which the concrete will be subjected to, concrete can be made to last for its intended service life. The durability of concrete is closely related to its permeability. The permeability dictates the rate at which aggressive agents can penetrate the concrete and attack the steel reinforcement. During winter, ice accumulates on the top surface of concrete slabs and bridge decks. For the purpose of removing the snow and ice, de-icing agents, such as sodium chloride and calcium chloride, are applied. These salts migrate down to the reinforcing steel through small pores in the concrete. Over time, the chlorides in these salts can react with the reinforcing steel, breaking down the passive layer and causing the steel to corrode. In Texas, the specification requirement for wet-mat curing is 8 days for decks with Type I and III cements and 10 days for decks with Type II and I/II cements and for mix designs with fly ash. Once the concrete is cured sufficiently, the deck is allowed to dry for one day. An additional day is typically allowed for any required surface treatment. The main objective of the research is to explore the possibility of opening the bridge decks earlier than 10 to 12 days by decreasing the number of wet mat curing days. For this reason, concrete mixtures typically used in Texas bridge deck were evaluated using numerous tests such as the Ponding test, the Rapid Chloride permeability Test, and the Abrasion Test. This research focuses on the effect of curing on the chloride ion permeability of different mix design. It is expected that the knowledge gained through this work can be used to optimize the number of curing days and age required before full traffic can be allowed on bridge decks in Texas.Item Dynamics of noble gas cluster expansion driven by intense pulses of extreme ultraviolet light(2009-08) Murphy, Brendan Francis, 1976-; Ditmire, Todd R.; Keto, John W.The interaction of intense laser pulses with nanometer scale atomic clusters has been an active area of study since the advent of amplified femtosecond lasers. In the case of infrared irradiation of noble gas clusters, direct field-driven ionization results in the ejection of energetic electrons, high ion charge states, and Coulomb explosion of the ion core of the clusters. These processes result from electron motion driven by the cluster potential and the large ponderomotive potential of the laser field. When extreme ultraviolet (XUV) pulses interact with clusters, the mechanisms responsible for the infrared response are 'turned off' because the ponderomotive potential is very small. We have conducted cluster experiments at 38nm using focused XUV pulses produced by high harmonic generation with a 15TW Ti:Sapphire laser. We measured the charge states and kinetic energy spectra of ions produced in the interaction, and observe substantial ion population up to Xe⁵⁺, with a small number of Xe⁶⁺-Xe⁸⁺ ions produced by collisional ionization by hot plasma electrons. The ion kinetic energy spectrum indicates a hydrodynamic expansion at an ion temperature of 8eV. This is in stark contrast to intense infrared/cluster interactions, where clusters are stripped of electrons to a large degree and expand by Coulomb forces, resulting in far higher ion kinetic energy for similar degrees of ionization.Item Electrical characteristics of breakdown phenomena(Texas Tech University, 2003-12) Haustein, Mark AThe phenomenology of breakdown in gases and liquids, and surface flashover at atmospheric pressures are investigated with high-speed electrical and optical diagnostics. The experiments utilize a 50Q coaxial transmission line system with an axial discharge and a load line to simulate a matched terminating impedance. DC breakdown, and in part pulsed breakdown, are characterized for argon gas, subcooled liquid nitrogen, biodegradable oil and vacuum. The discharge current and voltage are measured via transmission line current sensors and capacitive voltage dividers, which have a working range of 0.1 mA to IkA with temporal resolutions of 300 ps. Light emission is measured by photomultiplier tubes (800 ps risetime) and high speed photography. Some results indicate the presence of prebreakdown events preceding the main self-breakdown. These events occur microseconds before the main breakdown as nanosecond current and luminosity spikes.Item Electrospray ionization mass spectrometric techniques for the study of molecular recognition(2005) Sherman, Courtney Lawrence; Brodbelt, Jennifer S.Item High Rydberg states and ionization potential of carbon(Texas Tech University, 1997-05) Glynn, Patrick ToddThe ionization potential (IP) as well as the coupling and interactions occurring between the states converging to each of the spin-orbit split states of the ground state of the ion core are analyzed using resonance enhanced multiphoton ionization (REMPI) spectroscopy. Although this is not the first time that the IP for carbon has been measured, the measurement was made to an as yet unseen level of accuracy. Additionally, this is the first time that the interseries interactions have been analyzed for the 2pnp states of carbon. This was accomplished by first exciting from the 2s22p2 3Pj (1 = 0, 1,2) ground state up to the 2p3s 3Pj (1 = 0, 1,2) intermediate state with a vacuum ultraviolet (VUV) photon. This enabled a second transition up to the Rydberg states for the respective transitions. The Rydberg states were scanned from a principal quantum number of about 30 to well beyond the ionization limit. From the analysis of these states, the ionization limit for the series converging to the2P1/2 state of the excited core is determined to an accuracy of ±0.05 cm-1. Additionally, the series interactions occurring within the Rydberg series excited from the 2p3s 3Pj and 2p3s 3P0 states were analyzed to yield quantum defects, interaction matrix elements, and relative dipole matrix elements for comparison to theoretical calculations.Item Low noise avalanche photodiodes with an impact-ionization-engineered multiplication region(2002-08) Wang, Shuling, 1972-; Campbell, JoeAn avalanche photodiode (APD) is frequently the photodetector of choice in high-bit-rate, long-haul fiber optic communication systems due to its higher sensitivity, relative to a PIN photodiode, afforded by its internal gain. However, this can only be accomplished given that the multiplication noise is low. Impactionization-engineering (I2 E) is a novel approach that incorporates materials with different impact ionization threshold energies (Eth) into the multiplication region of APDs for low noise, high gain, and low dark current. A series of multiplication region structures with record-low multiplication noise were developed on both GaAs and InP substrates; an excess noise level comparable to silicon APDs was achieved on I2 E structures grown on GaAs. Unlike “superlattice” or “staircase” structures, the band gap continuities are not involved in the working mechanism of I2 E APDs. Monte Carlo simulation has revealed the spatial modulation effect of the impact ionization events in these heterostructure devices, which makes the ionization process more deterministic than in homojunctions, thus yielding lower noise. These low-noise I2 E multiplication region structures are promising in improving APD performance once they are implemented into SACM structures, with working wavelengths including 800-900nm, 1.3µm, and 1.55µm.Item Synthesis of Calix[4]arene ligands with multiple proton-ionizable groups for complexation of multivalent metal ions(Texas Tech University, 2004-05) Fernandez, Fernando AdolfoA series of new conformationally mobile tri-ionizable calix[4]arenes has been prepared for the complexation of trivalent lanthanide ions by matching the metal ion charge (3+) with the same number of proton-ionizable groups. The A-(X)sulfonyI carboxamide group, -C(0)NHS02X, was chosen as the proton-ionizable function because its acidity may be tuned by variation of X. Three series of new di-ionizable calix[4]arene-l,3-crown-5 ethers have been prepared in the cone, 1,3-aItemate and partial cone conformations to probe the influence of conformation, acidity variations and the crown ether ring size in solvent extraction of metal ions. A dansyl fluorescent group was coupled to di-ionizable calix[4]arene-l,3- crown-5 to produce potential fluorogenic ligands.Item X-ray preionization for triggering spark gaps(Texas Tech University, 1986-05) Ingram, Michael WrightThe use of a cold field emission flash x-ray tube for spark gap triggering is described, along with measurements of the ionization produced by the tube in nitrogen and argon. For the ionization measurements, the tube is mounted on an ionization chamber constructed to measure the ionization vs. distance travelled in the gas. The pressures of interest are 1, 3, and 5 atmospheres. The tube is then mounted on a spark gap and the x-rays are used to trigger the gap. The delay and jitter are measured at various percentages of the self-breakdown voltage for pressures of 1, 3, and 5 atmospheres. The contributions of the gas ionization and photoelectron emission from the electrodes are considered.