729 Matching Results

Search Results

Advanced search parameters have been applied.


Description: Predicting the erosion that results from a gas-solid particle flow in coal energy conversion systems is crucial for the successful operation of coal gasification, magnetohydrodynamic power, and coal-fired turbine facilities. In this study the coupled gas-particle momentum equations are analytically solved to determine the particle trajectories near a plane stagnation point. The momentum equilibration parameter, which is a physical parameter measuring a particle's momentum, is found to be the unique criterion for predicting particle trajectories. It is shown that values of this parameter less than one-fourth identify particles that never impact with a wall. The closed-form solution obtained is used to predict the quantity of material removed from a wall as well as the location of erosion along the wall. The maximum erosion is calculated to occur for the momentum equilibration parameter taking a value of 2.3. The erosion rate is found to be proportional to the particle velocity raised to the exponent of 3.8.
Date: November 1, 1977
Creator: Laitone, J.
Partner: UNT Libraries Government Documents Department


Description: We have suggested that certain plants rich in hydrocarbon-like materials might be cultivated for renewable photosynthetic products. Two species were selected for experimental plantations: Euphorbia lathyris, an annual from seed and Euphorbia tirucalli, a perennial from cuttings, The yield from each species is over 10 barrels of oil/acre/year without genetic or agronomic improvement. In addition to plants, there are trees, such as species of Copaifera in Brazil and other tropical areas, which produce a diesel-like oil upon tapping. Each tree produces approximately 40 liters of hydrocarbon per year, and this material can be used directly by a diesel-powered car. Further efforts to develop plants as alternate energy sources are underway, as well as a continuing search for additional plant species throughout the world which have a similar capability.
Date: May 1, 1980
Creator: Calvin, Melvin
Partner: UNT Libraries Government Documents Department


Description: Equations providing the first and second derivatives of a configuration interaction (CI) energy with respect to an external parameter are provided. We assume no restriction on the form of the CI expansion built from molecular orbitals obtained in a multiconfiguration Hartree-Fock (MCHF) calculation. Also the coupled perturbed multi-configuration Hartree-Fock formalism is presented for a general MCHF wavefunction and provides the first order and second order changes of the molecular orbital expansion coefficients with respect to an external parameter.
Date: September 1, 1980
Creator: Dupuis, M.
Partner: UNT Libraries Government Documents Department

Charge Transfer and Support Effects in Heterogeneous Catalysis

Description: The kinetic, electronic and spectroscopic properties of two‐dimensional oxide‐supported catalysts were investigated in order to understand the role of charge transfer in catalysis. Pt/TiO{sub 2} nanodiodes were fabricated and used as catalysts for hydrogen oxidation. During the reaction, the current through the diode, as well as its I‐V curve, were monitored, while gas chromatography was used to measure the reaction rate. The current and the turnover rate were found to have the same temperature dependence, indicating that hydrogen oxidation leads to the non‐adiabatic excitation of electrons in Pt. A fraction of these electrons have enough energy to ballistically transport through Pt and overcome the Schottky barrier at the interface with TiO{sub 2}. The yield for this phenomenon is on the order of 10{sup ‐4} electrons per product molecule formed, similar to what has been observed for CO oxidation and for the adsorption of many different molecules. The same Pt/TiO{sub 2} system was used to compare currents in hydrogen oxidation and deuterium oxidation. The current through the diode under deuterium oxidation was found to be greater than under hydrogen oxidation by a factor of three. Weighted by the difference in turnover frequencies for the two isotopes, this would imply a chemicurrent yield 5 times greater for D{sub 2} compared to H{sub 2}, contrary to what is expected given the higher mass of D{sub 2}. Reversible changes in the rectification factor of the diode are observed when switching between D{sub 2} and H{sub 2}. These changes are a likely cause for the differences in current between the two isotopes. In the nanodiode experiments, surface chemistry leads to charge flow, suggesting the possibility of creating charge flow to tune surface chemistry. This was done first by exposing a Pt/Si diode to visible light while using it as a catalyst for H{sub 2} oxidation. ...
Date: December 21, 2011
Creator: Hervier, Antoine
Partner: UNT Libraries Government Documents Department

Recent International R&D Activities in the Extraction of Uranium from Seawater

Description: A literature survey has been conducted to collect information on the International R&D activities in the extraction of uranium from seawater for the period from the 1960s till the year of 2010. The reported activities, on both the laboratory scale bench experiments and the large scale marine experiments, were summarized by country/region in this report. Among all countries where such activities have been reported, Japan has carried out the most advanced large scale marine experiments with the amidoxime-based system, and achieved the collection efficiency (1.5 g-U/kg-adsorbent for 30 days soaking in the ocean) that could justify the development of industrial scale marine systems to produce uranium from seawater at the price competitive with those from conventional uranium resources. R&D opportunities are discussed for improving the system performance (selectivity for uranium, loading capacity, chemical stability and mechanical durability in the sorption-elution cycle, and sorption kinetics) and making the collection of uranium from seawater more economically competitive.
Date: March 15, 2010
Creator: Rao, Linfeng
Partner: UNT Libraries Government Documents Department


Description: The prospects are shrinking rapidly for a future for society based on liquid hydrocarbons as a major source of energy. Among the wide array of alternative sources that are currently undergoing scrutiny, much attention is attracted to the photolysis of water to produce hydrogen and oxygen gases. Water, the starting material, does not suffer from lack of abundance, and there is every likelihood that the environmental consequences of water splitting will be negligible. Solar radiation is the obvious candiate for the ultimate energy source, but of course water cannot be photolyzed directly by the relatively low-energy wave-lengths, greater than 300 nm, that penetrate the earth's atmosphere. Nevertheless, the photolysis of water to produce O{sub 2} and reduced substances, with reduction potentials equivalent to that of H{sub 2}, is accomplished efficiently using sunlight by higher plant photosynthesis. There are even organisms that, under special conditions, will evolve H{sub 2} gas photosynthetically, but not efficiently when coupled with O{sub 2} production. To produce a molecule of O{sub 2} from water requires the removal of four electrons from two H{sub 2}O molecules.
Date: January 1, 1980
Creator: Sauer, Kenneth
Partner: UNT Libraries Government Documents Department

Acoustic Emission Precursors of M6.0 2004 Parkfield and M7.0 1989Loma Prieta Earthquakes

Description: Two recent strike-slip earthquakes on the San Andreas Fault(SAF) in California, the M6.0 2004 Parkfield and M7.0 1989 Loma Prietaevents, revealed peaks in the acoustic emission (AE) activity in thesurrounding crust several months prior to the main events. Earthquakesdirectly within the SAF zone were intentionally excluded from theanalysis. The observed increase in AE is assumed to be a signature of theincreasing stress level in the surrounding crust, while the peak andsubsequent decrease in AE starting several months prior to the mainevents is attributed to damage-induced softening processes as discussedherein. Further, distinctive zones of low seismic activity surroundingthe epicentral regions in the pre-event time period are present for thetwo studied events. Both AE increases in the crust surrounding apotential future event and the development of a low-seismicity epicentralzone can be regarded as promising precursory information that could helpsignal the arrival of large earthquakes.
Date: February 1, 2005
Creator: Korneev, Valeri
Partner: UNT Libraries Government Documents Department

An analytical solution for transient gas flow in a multi-wellsystem

Description: Soil vapor extraction (SVE) combined with air injectionprovides an efficient way for the cleanup of vadose zone contaminated byvolatile organic chemicals (VOCs). A successful design of an SVE system,however, relies on a good knowledge of the induced gas flow field in thevadose zone. Analytical solutions are available to help understand thegas flow field at steady-state. However, most SVE systems must pass atransient period before reaching steady (or quasi-steady) state and thelength of the period should be system-specific. This paper presents ananalytical solution for transient gas flow in a vadose zone withextraction and injection wells. The transient solution approaches thesteady-state solution as time increases. Calculations have shown that fora shallow well (screened in a depth of less than 10 m) in a vadose zonewith an air permeability of 1 darcy (10-12 m2) or larger, the systemreaches steady-state in just several hours. Decreasing the airpermeability or increasing the screen depth increases the time to reachsteady-state. In practical applications the transient solution may berelatively insignificant in an SVE design. However, the solution can beimportant in site characterization through pneumatic tests. A procedureis provided for applying the dimensionless solution in estimating airpermeability and air-filled porosity. An example is also given to use thetransient solution for verifying numerical codes.
Date: May 25, 2006
Creator: Shan, Chao
Partner: UNT Libraries Government Documents Department

High-Pressure Catalytic Reactions of C6 Hydrocarbons on PlatinumSingle-Crystals and nanoparticles: A Sum Frequency Generation VibrationalSpectroscopic and Kinetic Study

Description: Catalytic reactions of cyclohexene, benzene, n-hexane, 2-methylpentane, 3-methylpentane, and 1-hexene on platinum catalysts were monitored in situ via sum frequency generation (SFG) vibrational spectroscopy and gas chromatography (GC). SFG is a surface specific vibrational spectroscopic tool capable of monitoring submonolayer coverages under reaction conditions without gas-phase interference. SFG was used to identify the surface intermediates present during catalytic processes on Pt(111) and Pt(100) single-crystals and on cubic and cuboctahedra Pt nanoparticles in the Torr pressure regime and at high temperatures (300K-450K). At low pressures (<10{sup -6} Torr), cyclohexene hydrogenated and dehydrogenates to form cyclohexyl (C{sub 6}H{sub 11}) and {pi}-allyl C{sub 6}H{sub 9}, respectively, on Pt(100). Increasing pressures to 1.5 Torr form cyclohexyl, {pi}-allyl C{sub 6}H{sub 9}, and 1,4-cyclohexadiene, illustrating the necessity to investigate catalytic reactions at high-pressures. Simultaneously, GC was used to acquire turnover rates that were correlated to reactive intermediates observed spectroscopically. Benzene hydrogenation on Pt(111) and Pt(100) illustrated structure sensitivity via both vibrational spectroscopy and kinetics. Both cyclohexane and cyclohexene were produced on Pt(111), while only cyclohexane was formed on Pt(100). Additionally, {pi}-allyl c-C{sub 6}H{sub 9} was found only on Pt(100), indicating that cyclohexene rapidly dehydrogenates on the (100) surface. The structure insensitive production of cyclohexane was found to exhibit a compensation effect and was analyzed using the selective energy transfer (SET) model. The SET model suggests that the Pt-H system donates energy to the E{sub 2u} mode of free benzene, which leads to catalysis. Linear C{sub 6} (n-hexane, 2-methylpentane, 3-methylpentane, and 1-hexene) hydrocarbons were also investigated in the presence and absence of excess hydrogen on Pt(100). Based on spectroscopic signatures, mechanisms for catalytic isomerization and dehydrocyclization of n-hexane were identified. The structure sensitivity of benzene hydrogenation on shape controlled platinum nanoparticles was also studied. The nanoparticles showed similar selectivities to those found for Pt(111) and Pt(100) single-crystals. ...
Date: December 19, 2007
Creator: Bratlie, Kaitlin
Partner: UNT Libraries Government Documents Department

Complexation of Actinides in Solution: Thermodynamic Measurementsand Structural Characterization

Description: This paper presents a brief introduction of the studies of actinide complexation in solution at Lawrence Berkeley National Laboratory. An integrated approach of thermodynamic measurements and structural characterization is taken to obtain fundamental understanding of actinide complexation in solution that is of importance in predicting the behavior of actinides in separation processes and environmental transport.
Date: February 1, 2007
Creator: Rao, L.
Partner: UNT Libraries Government Documents Department

Electronic structure characterization and bandgap engineeringofsolar hydrogen materials

Description: Bandgap, band edge positions as well as the overall band structure of semiconductors are of crucial importance in photoelectrochemical and photocatalytic applications. The energy position of the band edge level can be controlled by the electronegativity of the dopants, the pH of the solution (flatband potential variation of 60 mV per pH unit), as well as by quantum confinement effects. Accordingly, band edges and bandgap can be tailored to achieve specific electronic, optical or photocatalytic properties. Synchrotron radiation with photon energy at or below 1 keV is giving new insight into such areas as condensed matter physics and extreme ultraviolet optics technology. In the soft x-ray region, the question tends to be, what are the electrons doing as they migrated between the atoms. In this paper, I will present a number of soft x-ray spectroscopic study of nanostructured 3d metal compounds Fe{sub 2}O{sub 3} and ZnO.
Date: November 1, 2007
Creator: Guo, Jinghua
Partner: UNT Libraries Government Documents Department

[(eta5-PentamethylcyclopentadienylYb(III)(5,5'-dimethyl-2,2-bipyridyl)mu-OH)2(mu 2-trifluoromethylsulfanato-O,O')][tetraphenylborate](5,5'-dimethyl-2,2-bipyridyl)

Description: The title compound C{sub 81}H{sub 88}BF{sub 3}N{sub 6}O{sub 5}SYb{sub 2}, crystallizes as a half-sandwich complex with a bridging inner-sphere trifluoro-methane sulfonate as well as two bridging hydroxide groups. there is uncoordinated 5,5{prime}-dimethyl-2,2{prime}-bipyridine in the crystal structure. The bound bipyridine ligands have N-C-C{prime}-n{prime} torsion angles of 12-13{sup o}. The triply bridged Yb centers are 3.5990(4) Angstroms apart. The Yb-N bonds range from 2.389(6)-2.424(5) Angstroms.
Date: January 23, 2008
Creator: Kazhdan, Daniel
Partner: UNT Libraries Government Documents Department

Nanocrystal Solar Cells

Description: This dissertation presents the results of a research agenda aimed at improving integration and stability in nanocrystal-based solar cells through advances in active materials and device architectures. The introduction of 3-dimensional nanocrystals illustrates the potential for improving transport and percolation in hybrid solar cells and enables novel fabrication methods for optimizing integration in these systems. Fabricating cells by sequential deposition allows for solution-based assembly of hybrid composites with controlled and well-characterized dispersion and electrode contact. Hyperbranched nanocrystals emerge as a nearly ideal building block for hybrid cells, allowing the controlled morphologies targeted by templated approaches to be achieved in an easily fabricated solution-cast device. In addition to offering practical benefits to device processing, these approaches offer fundamental insight into the operation of hybrid solar cells, shedding light on key phenomena such as the roles of electrode-contact and percolation behavior in these cells. Finally, all-inorganic nanocrystal solar cells are presented as a wholly new cell concept, illustrating that donor-acceptor charge transfer and directed carrier diffusion can be utilized in a system with no organic components, and that nanocrystals may act as building blocks for efficient, stable, and low-cost thin-film solar cells.
Date: December 15, 2006
Creator: Gur, Ilan
Partner: UNT Libraries Government Documents Department

Numerical simulation of leakage from a geologic disposal reservoirfor CO2, with transitions between super- and sub-criticalconditions

Description: The critical point of CO2 is at temperature and pressureconditions of Tcrit = 31.04oC, Pcrit = 73.82 bar. At lower (subcritical)temperatures and/or pressures, CO2 can exist in two different phases, aliquid and a gaseous state, as well as in two-phase mixtures of thesestates. Disposal of CO2 into brine formations would be made atsupercritical pressures. However, CO2 escaping from the storage reservoirmay migrate upwards towards regions with lower temperatures andpressures, where CO2 would be in subcritical conditions. An assessment ofthe fate of leaking CO2 requires a capability to model not onlysupercritical but also subcritical CO2, as well as phase changes betweenliquid and gaseous CO2 in sub-critical conditions. We have developed amethodology for numerically simulating the behavior of water-CO2 mixturesin permeable media under conditions that may include liquid, gaseous, andsupercritical CO2. This has been applied to simulations of leakage from adeep storage reservoir in which a rising CO2 plume undergoes transitionsfrom supercritical to subcritical conditions. We find strong coolingeffects when liquid CO2 rises to elevations where it begins to boil andevolve a gaseous CO2 phase. A three-phase zone forms (aqueous - liquid -gas), which over time becomes several hundred meters thick as decreasingtemperatures permit liquid CO2 to advance to shallower elevations. Fluidmobilities are reduced in the three-phase region from phase interferenceeffects. This impedes CO2 upflow, causes the plume to spread outlaterally, and gives rise to dispersed CO2 discharge at the land surface.Our simulations suggest that temperatures along a CO2 leakage path maydecline to levels low enough so that solid water ice and CO2 hydratephases may be formed.
Date: April 13, 2003
Creator: Pruess, Karsten
Partner: UNT Libraries Government Documents Department

Assessing the Importance and Impact of Glycomics and Glycosciences Phase II

Description: Glycans form one of the four basic classes of macromolecules in living systems, along with nucleic acids, proteins, and lipids. They are composed of individual sugar units that can be linked to one another in multiple ways, enabling them to form complex three-dimensional structures. In living systems, glycans are involved in myriad processes that are part of normal cellular physiology, development, and signaling, as well as in the development of both chronic and infectious diseases. Because of their ubiquity on cell surfaces, they are key components of biological interfaces and are involved in molecular recognition and signaling. They are also important molecules in cell adhesion and cell movement. Meanwhile, glycans on proteins inside cells participate in the cell’s responses to incoming signals, for example by helping to modulate gene expression and protein functions. Glycan polymers such as cellulose are important components of plant cell walls. Understanding how such walls are assembled and how they can be deconstructed is fundamental to basic plant biology, but also in the development of applications such as efficient conversion of biomass into fuels. Glycan polymers derived from plants and other organisms can also serve as sources of new materials with wide-ranging applications from tissue engineering scaffolds to flexible electronic displays. Achieving an understanding of the structures and functions of glycans is fundamental to understanding biology. The National Research Council report resulting from this project, Transforming Glycoscience: A Roadmap for the Future, discusses the impact glycoscience can have across health, energy, and materials science and lays out a roadmap of research goals whose achievement could help the field become a widely-recognized and integrated discipline rather than a niche area studied by a small number of specialists. Despite advances, gaps remain in the current suite of tools for investigating glycans and these tools often require expert users ...
Date: February 7, 2013
Creator: Zolandz, Dorothy
Partner: UNT Libraries Government Documents Department

Exploiting Universality in Atoms with Large Scattering Lengths

Description: The focus of this research project was atoms with scattering lengths that are large compared to the range of their interactions and which therefore exhibit universal behavior at sufficiently low energies. Recent dramatic advances in cooling atoms and in manipulating their scattering lengths have made this phenomenon of practical importance for controlling ultracold atoms and molecules. This research project was aimed at developing a systematically improvable method for calculating few-body observables for atoms with large scattering lengths starting from the universal results as a first approximation. Significant progress towards this goal was made during the five years of the project.
Date: May 31, 2012
Creator: Braaten, Eric
Partner: UNT Libraries Government Documents Department

Current Titles

Description: This booklet is published for those interested in current research being conducted at the National Center for Electron Microscopy. The NCEM is a DOE-designated national user facility and is available at no charge to qualified researchers. Access is controlled by an external steering committee. Interested researchers may contact Jane Cavlina, Administrator, at 510/486-6036.
Date: June 1, 2006
Partner: UNT Libraries Government Documents Department

Sum-Frequency Generation from Chiral Media and Interfaces

Description: Sum frequency generation (SFG), a second-order nonlinear optical process, is electric-dipole forbidden in systems with inversion symmetry. As a result, it has been used to study chiral media and interfaces, systems intrinsically lacking inversion symmetry. This thesis describes recent progresses in the applications of and new insights into SFG from chiral media and interfaces. SFG from solutions of chiral amino acids is investigated, and a theoretical model explaining the origin and the strength of the chiral signal in electronic-resonance SFG spectroscopy is discussed. An interference scheme that allows us to distinguish enantiomers by measuring both the magnitude and the phase of the chiral SFG response is described, as well as a chiral SFG microscope producing chirality-sensitive images with sub-micron resolution. Exploiting atomic and molecular parity nonconservation, the SFG process is also used to solve the Ozma problems. Sum frequency vibrational spectroscopy is used to obtain the adsorption behavior of leucine molecules at air-water interfaces. With poly(tetrafluoroethylene) as a model system, we extend the application of this surface-sensitive vibrational spectroscopy to fluorine-containing polymers.
Date: February 13, 2006
Creator: Ji, Na
Partner: UNT Libraries Government Documents Department

Molecular Foundry Workshop draws overflow crowd to BerkeleyLab

Description: Nanoscale science and technology is now one of the top research priorities in the United States. With this background, it is no surprise that an overflow crowd or more than 350 registrants filled two auditoriums to hear about and contribute ideas for the new Molecular Foundry during a two-day workshop at the Lawrence Berkeley National Laboratory (Berkeley Lab). Scheduled to open for business at Berkeley Labin early 2006, the Molecular Foundry is one of three Nanoscale Science Research Centers (NSRCs) put forward for funding by the DOE's Office of Basic Energy Sciences (BES).
Date: November 27, 2002
Creator: Robinson, Art
Partner: UNT Libraries Government Documents Department

Multiplicative or t1 Noise in NMR Spectroscopy

Description: The signal in an NMR experiment is highly sensitive to fluctuations of the environment of the sample. If, for example, the static magnetic field B{sub 0}, the amplitude and phase of radio frequency (rf) pulses, or the resonant frequency of the detection circuit are not perfectly stable and reproducible, the magnetic moment of the spins is altered and becomes a noisy quantity itself. This kind of noise not only depends on the presence of a signal, it is in fact proportional to it. Since all the spins at a particular location in a sample experience the same environment at any given time, this noise primarily affects the reproducibility of an experiment, which is mainly of importance in the indirect dimensions of a multidimensional experiment, when intense lines are suppressed with a phase cycle, or for difference spectroscopy techniques. Equivalently, experiments which are known to be problematic with regard to their reproducibility, like flow experiments or experiments with a mobile target, tend to be affected stronger by multiplicative noise. In this article it is demonstrated how multiplicative noise can be identified and characterized using very simple, repetitive experiments. An error estimation approach is developed to give an intuitive, yet quantitative understanding of its properties. The consequences for multidimensional NMR experiments are outlined, implications for data analysis are shown, and strategies for the optimization of experiments are summarized.
Date: January 25, 2005
Creator: Granwehr, Josef
Partner: UNT Libraries Government Documents Department

Fabrication of Yttria stabilized zirconia thin films on poroussubstrates for fuel cell applications

Description: A process for the deposition of yttria stabilized zirconia (YSZ) films, on porous substrates, has been developed. These films have possible applications as electrolyte membranes in fuel cells. The films were deposited from colloidal suspensions through the vacuum infiltration technique. Films were deposited on both fully sintered and partially sintered substrates. A critical cracking thickness for the films was identified and strategies are presented to overcome this barrier. Green film density was also examined, and a method for improving green density by changing suspension pH and surfactant was developed. A dependence of film density on film thickness was observed, and materials interactions are suggested as a possible cause. Non-shorted YSZ films were obtained on co-fired substrates, and a cathode supported solid oxide fuel cell was constructed and characterized.
Date: June 16, 2003
Creator: Leming, Andres
Partner: UNT Libraries Government Documents Department