System-level modeling for geological storage of CO2 (open access)

System-level modeling for geological storage of CO2

One way to reduce the effects of anthropogenic greenhousegases on climate is to inject carbon dioxide (CO2) from industrialsources into deep geological formations such as brine formations ordepleted oil or gas reservoirs. Research has and is being conducted toimprove understanding of factors affecting particular aspects ofgeological CO2 storage, such as performance, capacity, and health, safetyand environmental (HSE) issues, as well as to lower the cost of CO2capture and related processes. However, there has been less emphasis todate on system-level analyses of geological CO2 storage that considergeological, economic, and environmental issues by linking detailedrepresentations of engineering components and associated economic models.The objective of this study is to develop a system-level model forgeological CO2 storage, including CO2 capture and separation,compression, pipeline transportation to the storage site, and CO2injection. Within our system model we are incorporating detailedreservoir simulations of CO2 injection and potential leakage withassociated HSE effects. The platform of the system-level modelingisGoldSim [GoldSim, 2006]. The application of the system model is focusedon evaluating the feasibility of carbon sequestration with enhanced gasrecovery (CSEGR) in the Rio Vista region of California. The reservoirsimulations are performed using a special module of the TOUGH2 simulator,EOS7C, for multicomponent gas mixtures of methane and CO2 or methane andnitrogen. …
Date: April 24, 2006
Creator: Zhang, Yingqi; Oldenburg, Curtis M.; Finsterle, Stefan & Bodvarsson, Gudmundur S.
Object Type: Article
System: The UNT Digital Library
Vacuum-Ultraviolet (VUV) Photoionization of Small Methanol and Methanol-Water Clusters (open access)

Vacuum-Ultraviolet (VUV) Photoionization of Small Methanol and Methanol-Water Clusters

In this work, we report on the vacuum-ultraviolet (VUV) photoionization of small methanol and methanol-water clusters. Clusters of methanol with water are generated via co-expansion of the gas phase constituents in a continuous supersonic jet expansion of methanol and water seeded in Ar. The resulting clusters are investigated by single photon ionization with tunable vacuum-ultraviolet synchrotron radiation and mass analyzed using reflectron mass spectrometry. Protonated methanol clusters of the form (CH3OH)nH+(n = 1-12) dominate the mass spectrum below the ionization energy of the methanol monomer. With an increase in water concentration, small amounts of mixed clusters of the form (CH3OH n(H2O)H+ (n = 2-11) are detected. The only unprotonated species observed in this work are the methanol monomer and dimer. Appearance energies are obtained from the photoionization efficiency (PIE) curves for CH3OH+, (CH3OH)2+, (CH3OH)nH+ (n = 1-9), and (CH3OH)n(H2O)H+ (n = 2-9) as a function of photon energy. With an increasein the water content in the molecular beam, there is an enhancement of photoionization intensity for the methanol dimer and protonated methanol monomer at threshold. These results are compared and contrasted to previous experimental observations.
Date: April 24, 2008
Creator: Kostko, Oleg; Belau, Leonid; Wilson, Kevin R. & Ahmed, Musahid
Object Type: Article
System: The UNT Digital Library
2006 Nevada Test Site Annual Illness and Injury Surveillance Report (open access)

2006 Nevada Test Site Annual Illness and Injury Surveillance Report

The U.S. Department of Energy’s (DOE) commitment to assuring the health and safety of its workers includes the conduct of illness and injury surveillance activities that provide an early warning system to detect health problems among workers. The Illness and Injury Surveillance Program monitors illnesses and health conditions that result in an absence, occupational injuries and illnesses, and disabilities and deaths among current workers.
Date: April 24, 2008
Creator: United States. Department of Energy. Office of Health, Safety, and Security.
Object Type: Report
System: The UNT Digital Library
PBXN-9 Ignition Kinetics and Deflagration Rates (open access)

PBXN-9 Ignition Kinetics and Deflagration Rates

The ignition kinetics and deflagration rates of PBXN-9 were measured using specially designed instruments at LLNL and compared with previous work on similar HMX based materials. Ignition kinetics were measured based on the One Dimensional Time-to-Explosion combined with ALE3D modeling. Results of these experiments indicate that PBXN-9 behaves much like other HMX based materials (i.e. LX-04, LX-07, LX-10 and PBX-9501) and the dominant factor in these experiments is the type of explosive, not the type of binder/plasticizer. In contrast, the deflagration behavior of PBXN-9 is quite different from similar high weight percent HMX based materials (i.e LX-10, LX-07 and PBX-9501). PBXN-9 burns in a laminar manner over the full pressure range studied (0-310 MPa) unlike LX-10, LX-07, and PBX-9501. The difference in deflagration behavior is attributed to the nature of the binder/plasticizer alone or in conjunction with the volume of binder present in PBXN-9.
Date: April 24, 2008
Creator: Glascoe, E; Maienschein, J; Burnham, A; Koerner, J; Hsu, P & Wemhoff, A.
Object Type: Article
System: The UNT Digital Library
Investigation of the Relationship between Green Design and Project Delivery Methods (open access)

Investigation of the Relationship between Green Design and Project Delivery Methods

The selection of the project delivery method (PDM) for any project is critical--it establishes communication, coordination, and contractual issues between the owner, contractor, and designer. With an increase in the number of green design projects, understanding the relationship between the PDM and green design is paramount to project and contract management. It is reasonable to assume that a positive relationship between green design and design-build (DB) exists since both theoretically are intended to foster an integrated, holistic, and collaborative project. This research examines the relationship between the design-bid-build (DBB), construction management (CM), and DB PDMs and green design with the goal of establishing best practices and identifying potential synergies between them. The research collected information by conducting primarily telephone interviews with approximately twenty-five individuals, including owners, contractors, and designers involved in completed green design projects, mainly in the public sector. The interviews developed a general understanding of the current state of knowledge and experience and not a rigorous quantitative analysis. Upon completion of the interviews, the tabulated results were summarized and green project characteristics and project-PDM interactions emerged. Existing published research was evaluated to reveal aspects of PDMs independent of green design. Best practices were ascertained by combining information from …
Date: April 24, 2008
Creator: Bilec, Melissa M. & Ries, Robert J.
Object Type: Report
System: The UNT Digital Library
Modified Visible and Infrared Optical Design for the ITER Upper Ports (open access)

Modified Visible and Infrared Optical Design for the ITER Upper Ports

This document reports the results of a follow-on optical design study of visible-light and infrared optics for the ITER upper ports, performed by LLNL under contract for the US ITER Project Office. The major objectives of this work are to move the viewing aperture closer to the plasma so that the optical path does not cut through any adjacent blanket shield module other than the module designated for the port; move optics forward into the port tube to increase the aperture size and therefore improve the spatial resolution; assess the trade-off between spatial resolution and spatial coverage by reducing the field of view; and create a mechanical model with a neutron labyrinth. Here we show an optical design incorporating all these aspects. The new design fits into a 360 mm ID tube, as did the previous design. The entrance aperture is increased from 10 mm to 21 mm, with a corresponding increase in spatial resolution. The Airy disk diameter for 3.8 {micro}m wavelength IR light is 5.1 mm at the most distant target point in the field of view. The field of view is reduced from 60 toroidal degrees (full toroidal coverage with 6 cameras) to 50 toroidal degrees. The …
Date: April 24, 2008
Creator: Lasnier, C; Seppala, L & Morris, K
Object Type: Report
System: The UNT Digital Library
Phase Transitions Involving Dissociated States of Water at the Electrochemical Ni(111)/H2O Interface (open access)

Phase Transitions Involving Dissociated States of Water at the Electrochemical Ni(111)/H2O Interface

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Date: April 24, 2006
Creator: Taylor, C; Kelly, R & Neurock, M
Object Type: Report
System: The UNT Digital Library
Overview of Modeling and Simulations of Plutonium Aging (open access)

Overview of Modeling and Simulations of Plutonium Aging

Computer-aided materials research is now an integral part of science and technology. It becomes particularly valuable when comprehensive experimental investigations and materials testing are too costly, hazardous, or of excessive duration; then, theoretical and computational studies can supplement and enhance the information gained from limited experimental data. Such is the case for improving our fundamental understanding of the properties of aging plutonium in the nuclear weapons stockpile. The question of the effects of plutonium aging on the safety, security, and reliability of the nuclear weapons stockpile emerged after the United States closed its plutonium manufacturing facility in 1989 and decided to suspend any further underground testing of nuclear weapons in 1992. To address this, the Department of Energy's National Nuclear Security Administration (NNSA) initiated a research program to investigate plutonium aging, i.e., the changes with time of properties of Pu-Ga alloys employed in the nuclear weapons and to develop models describing these changes sufficiently reliable to forecast them for several decades. The November 26, 2006 press release by the NNSA summarizes the conclusions of the investigation, '...there appear to be no serious or sudden changes occurring, or expected to occur, in plutonium that would affect performance of pits beyond the …
Date: April 24, 2007
Creator: Schwartz, A J & Wolfer, W G
Object Type: Article
System: The UNT Digital Library
Development of a Versatile Laser Ultrasonic System and Application to On-Line Measurement for Process Control of Wall Thickness and Eccentrictiy of Steel Seamless Mechanical Tubing (open access)

Development of a Versatile Laser Ultrasonic System and Application to On-Line Measurement for Process Control of Wall Thickness and Eccentrictiy of Steel Seamless Mechanical Tubing

Researchers at the Timken Company conceived a project to develop an on-line instrument for wall thickness measurement of steel seamless mechanical tubing based on laser ultrasonic technology. The instrument, which has been installed and tested at a piercing mill, provides data on tube eccentricity and concentricity. Such measurements permit fine-tuning of manufacturing processes to eliminate excess material in the tube wall and therefore provide a more precisely dimensioned product for their customers. The resulting process energy savings are substantial, as is lowered environmental burden. The expected savings are $85.8 million per year in seamless mechanical tube piercing alone. Applied across the industry, this measurement has a potential of reducing energy consumption by 6 x 10{sup 12} BTU per year, greenhouse gas emissions by 0.3 million metric tons carbon equivalent per year, and toxic waste by 0.255 million pounds per year. The principal technical contributors to the project were the Timken Company, Industrial Materials Institute (IMI, a contractor to Timken), and Oak Ridge National Laboratory (ORNL). Timken provided mill access as well as process and metallurgical understanding. Timken researchers had previously developed fundamental ultrasonic analysis methods on which this project is based. IMI developed and fabricated the laser ultrasonic generation and …
Date: April 24, 2002
Creator: Kisner, R. A.; Kercel, S. W.; Damiano, B.; Bingham, P. R.; Gee, T. F.; Tucker, R. W. et al.
Object Type: Report
System: The UNT Digital Library
Final Technical Report on Scaling Models of the Internal Variability of Clouds DoE Grant No. DE-FG02-04ER63773 (open access)

Final Technical Report on Scaling Models of the Internal Variability of Clouds DoE Grant No. DE-FG02-04ER63773

The purpose of this proposal is to gain a better understanding of the space-time correlations of atmospheric fluctuations in clouds through application of methods from statistical physics to high resolution, continuous data sets of cloud observations available at the Department of Energy Atmospheric Radiation Measurement Program archive. In this report we present the accomplishments achieved during the four year period. Starting with the most recent one, we report on two break-throughs in our research that make the fourth year of the project exceptionally successful and markedly outperforming the objectives. The first break-through is on characterization of the structure of cirrus radiative properties at large, intermediate and small, generating cells scales by applying the Fokker-Planck equation method and other methods to ARM millimeter wavelength radar observations collected at the Southern Great Plains site. The second break-through is that we show that different characterizations of the cirrus radiative properties are obtained for different synoptic scale environments. We outline a stochastic approach to investigate the internal structure of radiative properties of cirrus clouds based on empirical modeling and draw conclusions about cirrus dynamical properties in the context of the synoptic environment. Results on the structure of cirrus dynamical properties are consistent with the …
Date: April 24, 2008
Creator: Ivanova, Kristinka
Object Type: Report
System: The UNT Digital Library
Remaining Sites Verification Package for the 118-C-3:3, 105-C French Drains, Waste Site Reclassification Form 2006-016 (open access)

Remaining Sites Verification Package for the 118-C-3:3, 105-C French Drains, Waste Site Reclassification Form 2006-016

The 118-C-3:3 french drains received condensate from the steam heating system in the 105-C Reactor Building. The 118-C-3:3 french drain meets the remedial action objectives specified in the Remaining Sites ROD. The results demonstrate that residual contaminant concentrations do not preclude any future uses and allow for unrestricted use of shallow zone soils. The results also demonstrate that residual contaminant concentrations are protective of groundwater and the Columbia River.
Date: April 24, 2006
Creator: Carlson, R. A.
Object Type: Report
System: The UNT Digital Library
Center for Gyrokinetic Particle Simulation of Turbulent Transport in Burning Plasma (open access)

Center for Gyrokinetic Particle Simulation of Turbulent Transport in Burning Plasma

The UCLA work on this grant was to design and help implement an object-oriented version of the GTC code, which is written in Fortran90. The GTC code is the main global gyrokinetic code used in this project, and over the years multiple, incompatible versions have evolved. The reason for this effort is to allow multiple authors to work together on GTC and to simplify future enhancements to GTC. The effort was designed to proceed incrementally. Initially, an upper layer of classes (derived types and methods) was implemented which called the original GTC code 'under the hood.' The derived types pointed to data in the original GTC code, and the methods called the original GTC subroutines. The original GTC code was modified only very slightly. This allowed one to define (and refine) a set of classes which described the important features of the GTC code in a new, more abstract way, with a minimum of implementation. Furthermore, classes could be added one at a time, and at the end of the each day, the code continued to work correctly. This work was done in close collaboration with Y. Nishimura from UC Irvine and Stefan Ethier from PPPL. Ten classes were ultimately …
Date: April 24, 2008
Creator: Decyk, Viktor K.
Object Type: Report
System: The UNT Digital Library
Remaining Sites Verification Package for the 100-B-1 Surface Chemical and Solid Waste Dumping Area, Waste Site Reclassification Form 2006-003 (open access)

Remaining Sites Verification Package for the 100-B-1 Surface Chemical and Solid Waste Dumping Area, Waste Site Reclassification Form 2006-003

The 100-B-1 waste site was a dumping site that was divided into two areas. One area was used as a laydown area for construction materials, and the other area was used as a chemical dumping area. The 100-B-1 Surface Chemical and Solid Waste Dumping Area site meets the remedial action objectives specified in the Remaining Sites ROD. The results demonstrate that residual contaminant concentrations support future unrestricted land uses that can be represented by a rural-residential scenario. The results also demonstrate that residual contaminant concentrations are protective of groundwater and the Columbia River.
Date: April 24, 2006
Creator: Carlson, R. A.
Object Type: Report
System: The UNT Digital Library
Reactive Transport Modeling of Geologic CO{sub 2} Sequestration in Saline Aquifers: The Influence of Intra-Aquifer Shales and the Relative Effectiveness of Structural, Solubility, and Mineral Trapping During Prograde and Retrograde Sequestration (open access)

Reactive Transport Modeling of Geologic CO{sub 2} Sequestration in Saline Aquifers: The Influence of Intra-Aquifer Shales and the Relative Effectiveness of Structural, Solubility, and Mineral Trapping During Prograde and Retrograde Sequestration

In this study, we address a series of fundamental questions regarding the processes and effectiveness of geologic CO{sub 2} sequestration in saline aquifers. We begin with the broadest: what is the ultimate fate of CO{sub 2} injected into these environments? Once injected, it is immediately subject to two sets of competing processes: migration processes and sequestration processes. In terms of migration, the CO{sub 2} moves by volumetric displacement of formation waters, with which it is largely immiscible; by gravity segregation, which causes the immiscible CO{sub 2} plume to rise owing to its relatively low density; and by viscous fingering, owing to its relatively low viscosity. In terms of sequestration, some fraction of the rising plume will dissolve into formation waters (solubility trapping); some fraction may react with formation minerals to precipitate carbonates (mineral trapping); and the remaining portion eventually reaches the cap rock, where it migrates up-dip, potentially accumulating in local topographic highs (structural trapping). Although this concept of competing migration/sequestration processes is intuitively obvious, identifying those sub-processes that dominate the competition is by no means straightforward. Hence, at present there are large uncertainties associated with the ultimate fate of injected CO{sub 2} (Figure 1). Principal among these: can a …
Date: April 24, 2001
Creator: Johnson, J. W.; Nitao, J. J.; Steefel, C. I. & Knauss, K. G.
Object Type: Article
System: The UNT Digital Library
Electron Cyclotron Heating and Current Drive for Maintaining Minimum q in Negative Central Shear Discharges (open access)

Electron Cyclotron Heating and Current Drive for Maintaining Minimum q in Negative Central Shear Discharges

Toroidal plasmas created with negative magnetic shear in the core region offer advantages in terms of MHD stability properties. These plasmas, transiently created in several tokamaks, have exhibited high performance as measured by normalized stored energy and neutron production rates. A critical issue with extending the duration of these plasmas is the need to maintain the off-axis-peaked current distribution required to support the minimum in the safety factor q at large radii. We present equilibrium and transport simulations that explore the use of electron cyclotron heating and current drive to maintain this negative shear configuration. Using parameters consistent with DIII-D tokamak operation, we find that with sufficiently high injected power, it is possible to achieve steady-state conditions employing well aligned electron cyclotron and bootstrap current drive in fully non-inductively current-driven configurations.
Date: April 24, 2003
Creator: Casper, T. A.; Kaiser, T. B.; Jong, R. A.; LoDestro, L. L.; Moller, J.; Pearlstein, L. D. et al.
Object Type: Article
System: The UNT Digital Library
The REBUS-MCNP Linkage. (open access)

The REBUS-MCNP Linkage.

The Reduced Enrichment Research and Test Reactor (RERTR) Program uses the REBUS-PC computer code to provide reactor physics and core design information such as neutron flux distributions in space, energy, and time, and to track isotopic changes in fuel and neutron absorbers with burnup. REBUS-PC models the complete fuel cycle including shuffling capability. REBUS-PC evolved using the neutronic capabilities of multi-group diffusion theory code DIF3D 9.0, but was extended to apply the continuous energy Monte Carlo code MCNP for one-group fluxes and cross-sections. The linkage between REBUS-PC and MCNP has recently been modernized and extended, as described in this manual. REBUS-PC now calls MCNP via a system call so that the user can apply any valid MCNP executable. The interface between REBUS-PC and MCNP requires minimal changes to an existing MCNP model, and little additional input. The REBUS-MCNP interface can also be used in conjunction with DIF3D neutronics to update an MCNP model with fuel compositions predicted using a DIF3D based depletion.
Date: April 24, 2009
Creator: Stevens, J. G.
Object Type: Report
System: The UNT Digital Library
Wind-To-Hydrogen Energy Pilot Project (open access)

Wind-To-Hydrogen Energy Pilot Project

WIND-TO-HYDROGEN ENERGY PILOT PROJECT: BASIN ELECTRIC POWER COOPERATIVE In an effort to address the hurdles of wind-generated electricity (specifically wind's intermittency and transmission capacity limitations) and support development of electrolysis technology, Basin Electric Power Cooperative (BEPC) conducted a research project involving a wind-to-hydrogen system. Through this effort, BEPC, with the support of the Energy & Environmental Research Center at the University of North Dakota, evaluated the feasibility of dynamically scheduling wind energy to power an electrolysis-based hydrogen production system. The goal of this project was to research the application of hydrogen production from wind energy, allowing for continued wind energy development in remote wind-rich areas and mitigating the necessity for electrical transmission expansion. Prior to expending significant funding on equipment and site development, a feasibility study was performed. The primary objective of the feasibility study was to provide BEPC and The U.S. Department of Energy (DOE) with sufficient information to make a determination whether or not to proceed with Phase II of the project, which was equipment procurement, installation, and operation. Four modes of operation were considered in the feasibility report to evaluate technical and economic merits. Mode 1 - scaled wind, Mode 2 - scaled wind with off-peak, Mode …
Date: April 24, 2009
Creator: Rebenitsch, Ron; Bush, Randall; Boushee, Allen; Stevens, Brad G.; Williams, Kirk D.; Woeste, Jeremy et al.
Object Type: Report
System: The UNT Digital Library
Interim Letter Report - Verification Survey Results for Activities Performed in March 2009 for the Vitrification Test Facility Warehouse at the West Valley Demonstration Project, Ashford, New York (open access)

Interim Letter Report - Verification Survey Results for Activities Performed in March 2009 for the Vitrification Test Facility Warehouse at the West Valley Demonstration Project, Ashford, New York

The objective of the verification activities was to provide independent radiological surveys and data for use by the Department of Energy (DOE) to ensure that the building satisfies the requirements for release without radiological controls.
Date: April 24, 2009
Creator: Estes, B.D.
Object Type: Report
System: The UNT Digital Library
Local scrape-off layer control using biased electrodes in NSTX (open access)

Local scrape-off layer control using biased electrodes in NSTX

An experiment was designed to test the theory that biased electrodes can affect the local scrape-off layer (SOL) width by creating a strong radial ExB drift [Cohen, R.H. and Ryutov, D.D, Nucl. Fusion 37, 621 (1997)]. These electrodes were located near the outer midplane in the SOL of the National Spherical Torus Experiment (NSTX). The electrodes were biased at up to �100 Volts, and the radial profile of the plasma between them was measured by an array of Langmuir probes. The biasing caused large changes in the local SOL profiles at least qualitatively consistent with this theory.
Date: April 24, 2009
Creator: Zweben, S. J.; Maqueda, R. J.; Roquemore, A. L.; Bush, C. E.; Kaita, R.; Marsala, R. J. et al.
Object Type: Report
System: The UNT Digital Library
Probing the hydrogen-bond network of water via time-resolved soft x-ray spectroscopy (open access)

Probing the hydrogen-bond network of water via time-resolved soft x-ray spectroscopy

We report time-resolved studies of hydrogen bonding in liquid H2O, in response to direct excitation of the O-H stretch mode at 3 mu m, probed via soft x-ray absorption spectroscopy at the oxygen K-edge. This approach employs a newly developed nanofluidic cell for transient soft x-ray spectroscopy in liquid phase. Distinct changes in the near-edge spectral region (XANES) are observed, and are indicative of a transient temperature rise of 10K following transient laser excitation and rapid thermalization of vibrational energy. The rapid heating occurs at constant volume and the associated increase in internal pressure, estimated to be 8MPa, is manifest by distinct spectral changes that differ from those induced by temperature alone. We conclude that the near-edge spectral shape of the oxygen K-edge is a sensitive probe of internal pressure, opening new possibilities for testing the validity of water models and providing new insight into the nature of hydrogen bonding in water.
Date: April 24, 2009
Creator: Huse, Nils; Wen, Haidan; Nordlund, Dennis; Szilagyi, Erzsi; Daranciang, Dan; Miller, Timothy A. et al.
Object Type: Article
System: The UNT Digital Library
Fast Pulsing Neutron Generators for Security Application (open access)

Fast Pulsing Neutron Generators for Security Application

Active neutron interrogation has been demonstrated to be an effective method of detecting shielded fissile material. A fast fall-time/fast pulsing neutron generator is needed primarily for differential die-away technique (DDA) interrogation systems. A compact neutron generator, currently being developed in Lawrence Berkeley National Laboratory, employs an array of 0.6-mm-dia apertures (instead of one 6-mm-dia aperture) such that gating the beamlets can be done with low voltage and a small gap to achieve sub-microsecond ion beam fall time and low background neutrons. Arrays of 16 apertures (4x4) and 100 apertures (10x10) have been designed and fabricated for a beam extraction experiment. The preliminary results showed that, using a gating voltage of 1200 V and a gap distance of 1 mm, the fall time of extracted ion beam pulses is approximately 0.15 mu s at beam energies of 1000 eV.
Date: April 24, 2009
Creator: Ji, Q.; Regis, M. & Kwan, J. W.
Object Type: Article
System: The UNT Digital Library
Study of metallic materials for solid oxide fuel cell interconnect applications. (open access)

Study of metallic materials for solid oxide fuel cell interconnect applications.

Metallic interconnect acts as a gas separator and a gas distributor and therefore, it needs to function adequately in two widely different environments. The interconnect material will be exposed to air on one side and natural gas or coal-derived synthesis gas on the other side. The viable material for the interconnect application must be resistant not only to oxidation but also carburization in hydrocarbon containing low-oxygen environments. In addition, the scales that develop on the exposed surfaces must possess adequate electrical conductivity for them to function as current leads over long service life of the fuel cell. This report addresses five topics of interest for the development of metallic interconnects with adequate performance in fuel cells for long service life. The research conducted over the years and the conclusions reached were used to identify additional areas of research on materials for improved performance of components, especially metallic interconnects, in the complex fuel cell environments. This report details research conducted in the following areas: measurement of area specific electrical resistivity, corrosion performance in dual gas environments by experiments using alloy 446, long term corrosion performance of ferritic and austenitic alloys in hydrogen and methane-reformed synthesis fuel-gas environments, approaches to reduce the …
Date: April 24, 2009
Creator: Natesan, K. & Zeng, Z.
Object Type: Report
System: The UNT Digital Library
Restructuring of hex-Pt(100) under CO gas environments: formation of 2-D nanoclusters (open access)

Restructuring of hex-Pt(100) under CO gas environments: formation of 2-D nanoclusters

The atomic-scale restructuring of hex-Pt(100) induced by carbon monoxide with a wide pressure range was studied with a newly designed chamber-in-chamber high-pressure STM and theoretical calculations. Both experimental and DFT calculation results show that CO molecules are bound to Pt nanoclusters through a tilted on-top configuration with a separation of {approx}3.7-4.1 {angstrom}. The phenomenon of restructuring of metal catalyst surfaces induced by adsorption, and in particular the formation of small metallic clusters suggests the importance of studying structures of catalyst surfaces under high pressure conditions for understanding catalytic mechanisms.
Date: April 24, 2009
Creator: Tao, Feng; Dag, Sefa; Wang, Lin-Wang; Liu, Zhi; Butcher, Derek; Salmeron, Miquel et al.
Object Type: Article
System: The UNT Digital Library
Pressure-induced Breaking of Equilibrium Flux Surfaces in the W7AS Stellarator (open access)

Pressure-induced Breaking of Equilibrium Flux Surfaces in the W7AS Stellarator

Calculations are presented for two shots in the W7AS stellarator which differ only in the magnitude of the current in the divertor control coil, but have very different values of experimentally attainable β (<β> ≈ 2.7% versus <β> ≈ 1.8%). Equilibrium calculations find that a region of chaotic magnetic field line trajectories fills approximately the outer 1/3 of the cross-section in each of these configurations. The field lines in the stochastic region are calculated to behave as if the flux surfaces are broken only locally near the outer midplane and are preserved elsewhere. The calculated magnetic field line diffusion coefficients in the stochastic regions for the two shots are consistent with the observed differences in the attainable β, and are also consistent with the differences in the reconstructed pressure profiles.
Date: April 24, 2007
Creator: A. Reiman, M.C. Zarnstorff, D. Monticello, A. Weller, J. Geiger, and the W7-AS Team
Object Type: Article
System: The UNT Digital Library