Theoretical Studies of Nucleation Kinetics and Nanodroplet Microstructure (open access)

Theoretical Studies of Nucleation Kinetics and Nanodroplet Microstructure

The goals of this project were to (1) explore ways of bridging the gap between fundamental molecular nucleation theories and phenomenological approaches based on thermodynamic reasoning, (2) test and improve binary nucleation theory, and (3) provide the theoretical underpinning for a powerful new experimental technique, small angle neutron scattering (SANS) from nanodroplet aerosols, that can probe the compositional structure of nanodroplets. This report summarizes the accomplishments of this project in realizing these goals. Publications supported by this project fall into three general categories: (1) theoretical work on nucleation theory (2) experiments and modeling of nucleation and condensation in supersonic nozzles, and (3) experimental and theoretical work on nanodroplet structure and neutron scattering. These publications are listed and briefly summarized in this report.
Date: January 31, 2009
Creator: Wilemski, Gerald
Object Type: Report
System: The UNT Digital Library
Conceptual Design Report: Nevada Test Site Mixed Waste Disposal Facility Project (open access)

Conceptual Design Report: Nevada Test Site Mixed Waste Disposal Facility Project

Environmental cleanup of contaminated nuclear weapons manufacturing and test sites generates radioactive waste that must be disposed. Site cleanup activities throughout the U.S. Department of Energy (DOE) complex are projected to continue through 2050. Some of this waste is mixed waste (MW), containing both hazardous and radioactive components. In addition, there is a need for MW disposal from other mission activities. The Waste Management Programmatic Environmental Impact Statement Record of Decision designates the Nevada Test Site (NTS) as a regional MW disposal site. The NTS has a facility that is permitted to dispose of onsite- and offsite-generated MW until November 30, 2010. There is not a DOE waste management facility that is currently permitted to dispose of offsite-generated MW after 2010, jeopardizing the DOE environmental cleanup mission and other MW-generating mission-related activities. A mission needs document (CD-0) has been prepared for a newly permitted MW disposal facility at the NTS that would provide the needed capability to support DOE's environmental cleanup mission and other MW-generating mission-related activities. This report presents a conceptual engineering design for a MW facility that is fully compliant with Resource Conservation and Recovery Act (RCRA) and DOE O 435.1, 'Radioactive Waste Management'. The facility, which will …
Date: January 31, 2009
Creator: National Security Technologies, LLC
Object Type: Report
System: The UNT Digital Library
DEGRADATION EVALUATION OF HEAVY WATER DRUMS AND TANKS (open access)

DEGRADATION EVALUATION OF HEAVY WATER DRUMS AND TANKS

Heavy water with varying chemistries is currently being stored in over 6700 drums in L- and K-areas and in seven tanks in L-, K-, and C-areas. A detailed evaluation of the potential degradation of the drums and tanks, specific to their design and service conditions, has been performed to support the demonstration of their integrity throughout the desired storage period. The 55-gallon drums are of several designs with Type 304 stainless steel as the material of construction. The tanks have capacities ranging from 8000 to 45600 gallons and are made of Type 304 stainless steel. The drums and tanks were designed and fabricated to national regulations, codes and standards per procurement specifications for the Savannah River Site. The drums have had approximately 25 leakage failures over their 50+ years of use with the last drum failure occurring in 2003. The tanks have experienced no leaks to date. The failures in the drums have occurred principally near the bottom weld, which attaches the bottom to the drum sidewall. Failures have occurred by pitting, crevice and stress corrosion cracking and are attributable, in part, to the presence of chloride ions in the heavy water. Probable degradation mechanisms for the continued storage of …
Date: July 31, 2009
Creator: Mickalonis, J. & Vormelker, P.
Object Type: Report
System: The UNT Digital Library
LDRD 2009 Annual Report: Laboratory Directed Research and Development Program Activities (open access)

LDRD 2009 Annual Report: Laboratory Directed Research and Development Program Activities

N/A
Date: December 31, 2009
Creator: Looney, J. P. & Fox, K.
Object Type: Report
System: The UNT Digital Library
Membrane Process to Sequester CO2 From Power Plant Flue Gas (open access)

Membrane Process to Sequester CO2 From Power Plant Flue Gas

The objective of this project was to assess the feasibility of using a membrane process to capture CO2 from coal-fired power plant flue gas. During this program, MTR developed a novel membrane (Polaris™) with a CO2 permeance tenfold higher than commercial CO2-selective membranes used in natural gas treatment. The Polaris™ membrane, combined with a process design that uses a portion of combustion air as a sweep stream to generate driving force for CO2 permeation, meets DOE post-combustion CO2 capture targets. Initial studies indicate a CO2 separation and liquefaction cost of $20 - $30/ton CO2 using about 15% of the plant energy at 90% CO2 capture from a coal-fired power plant. Production of the Polaris™ CO2 capture membrane was scaled up with MTR’s commercial casting and coating equipment. Parametric tests of cross-flow and countercurrent/sweep modules prepared from this membrane confirm their near-ideal performance under expected flue gas operating conditions. Commercial-scale, 8-inch diameter modules also show stable performance in field tests treating raw natural gas. These findings suggest that membranes are a viable option for flue gas CO2 capture. The next step will be to conduct a field demonstration treating a realworld power plant flue gas stream. The first such MTR field …
Date: March 31, 2009
Creator: Merkel, Tim; Amo, Karl; Baker, Richard; Daniels, Ramin; Friat, Bilgen; He, Zhenjie et al.
Object Type: Report
System: The UNT Digital Library
Next Generation Hole Injection/Transport Nano-Composites for High Efficiency OLED Development (open access)

Next Generation Hole Injection/Transport Nano-Composites for High Efficiency OLED Development

The objective of this program is to use a novel nano-composite material system for the OLED anode coating/hole transport layer. The novel anode coating is intended to significantly increase not only hole injection/transport efficiency, but the device energy efficiency as well. Another goal of the Core Technologies Program is the optimization and scale-up of air-stable and cross-linkable novel HTL nano-composite materials synthesis and the development of low-cost, large-scale mist deposition processes for polymer OLED fabrication. This proposed technology holds the promise to substantially improve OLED energy efficiency and lifetime.
Date: July 31, 2009
Creator: Wang, King
Object Type: Report
System: The UNT Digital Library
Electron cooling for low-energy RHIC program (open access)

Electron cooling for low-energy RHIC program

Electron cooling was proposed to increase luminosity of the RHIC collider for heavy ion beam energies below 10 GeV/nucleon. Providing collisions at such energies, termed RHIC 'low-energy' operation, will help to answer one of the key questions in the field of QCD about existence and location of critical point on the QCD phase diagram. The electron cooling system should deliver electron beam of required good quality over energies of 0.9-5 MeV. Several approaches to provide such cooling were considered. The baseline approach was chosen and design work started. Here we describe the main features of the cooling system and its expected performance. We have started design work on a low-energy RHIC electron cooler which will operate with kinetic electron energy range 0.86-2.8 (4.9) MeV. Several approaches to an electron cooling system in this energy range are being investigated. At present, our preferred scheme is to transfer the Fermilab Pelletron to BNL after Tevatron shutdown, and to use it for DC non-magnetized cooling in RHIC. Such electron cooling system can significantly increase RHIC luminosities at low-energy operation.
Date: August 31, 2009
Creator: Fedotov, A.; Ben-Zvi, Ilan; Chang, X.; Kayran, D.; Litvinenko, V. N.; Pendzick, A. et al.
Object Type: Article
System: The UNT Digital Library
Transfer of Physical and Hydraulic Properties Databases to the Hanford Environmental Information System - PNNL Remediation Decision Support Project, Task 1, Activity 6 (open access)

Transfer of Physical and Hydraulic Properties Databases to the Hanford Environmental Information System - PNNL Remediation Decision Support Project, Task 1, Activity 6

This report documents the requirements for transferring physical and hydraulic property data compiled by PNNL into the Hanford Environmental Information System (HEIS). The Remediation Decision Support (RDS) Project is managed by Pacific Northwest National Laboratory (PNNL) to support Hanford Site waste management and remedial action decisions by the U.S. Department of Energy and one of their current site contractors - CH2M-Hill Plateau Remediation Company (CHPRC). The objective of Task 1, Activity 6 of the RDS project is to compile all available physical and hydraulic property data for sediments from the Hanford Site, to port these data into the Hanford Environmental Information System (HEIS), and to make the data web-accessible to anyone on the Hanford Local Area Network via the so-called Virtual Library.1 These physical and hydraulic property data are used to estimate parameters for analytical and numerical flow and transport models that are used for site risk assessments and evaluation of remedial action alternatives. In past years efforts were made by RDS project staff to compile all available physical and hydraulic property data for Hanford sediments and to transfer these data into SoilVision{reg_sign}, a commercial geotechnical software package designed for storing, analyzing, and manipulating soils data. Although SoilVision{reg_sign} has proven …
Date: March 31, 2009
Creator: Rockhold, Mark L. & Middleton, Lisa A.
Object Type: Report
System: The UNT Digital Library
The Role of Natural Organic Matter and Mineral Colloids in the Transport of Contaminants through Heterogeneous Vadose-Zone Environments (open access)

The Role of Natural Organic Matter and Mineral Colloids in the Transport of Contaminants through Heterogeneous Vadose-Zone Environments

Our research was guided by a key objective of the Environmental Management Science Program (EMSP), which is to improve conceptual and predictive models for contaminant movement in complex vadose zone environments. In this report, increases in the understanding of colloidcontaminant interactions, colloid mobilization, and colloid deposition within unsaturated soils are cited as requisite needs for predicting contaminant fate and distribution in the vadose zone. We addressed these needs by pursuing three key goals: 1. Identify the mechanisms that govern OM and mineral-colloid reaction and transport in heterogeneous, unsaturated porous media; 2. Quantify the role of OM and mineral colloids in scavenging and facilitating the transport of contaminants of concern to DOE; and 3. Develop and test a mathematical model suitable for simulating the movement of OM- and colloid-associated contaminants through heterogeneous, unsaturated porous media.
Date: January 31, 2009
Creator: Saiers, James & Ryan, Joseph
Object Type: Report
System: The UNT Digital Library
Synthesis and Evaluation of CO2 Thickeners Designed with Molecular Modeling (open access)

Synthesis and Evaluation of CO2 Thickeners Designed with Molecular Modeling

The objective of this research was to use molecular modeling techniques, coupled with our prior experimental results, to design, synthesize and evaluate inexpensive, non-fluorous carbon dioxide thickening agents. The first type of thickener that was considered was associating polymers. Typically, these thickeners are copolymers that contain a highly CO{sub 2}-philic monomer, and a small concentration of a CO{sub 2}-phobic associating monomer. Yale University was solely responsible for the synthesis of a second type of thickener; small, hydrogen bonding compounds. These molecules have a core that contains one or more hydrogen-bonding groups, such as urea or amide groups. Non-fluorous, CO{sub 2}-philic functional groups were attached to the hydrogen bonding core of the compound to impart CO{sub 2} stability and macromolecular stability to the linear 'stack' of these compounds. The third type of compound initially considered for this investigation was CO{sub 2}-soluble surfactants. These surfactants contain conventional ionic head groups and composed of CO{sub 2}-philic oligomers (short polymers) or small compounds (sugar acetates) previously identified by our research team. Mobility reduction could occur as these surfactant solutions contacted reservoir brine and formed mobility control foams in-situ. The vast majority of the work conducted in this study was devoted to the copolymeric thickeners …
Date: August 31, 2009
Creator: Enick, Robert; Beckman, Erick & Johnson, J. Karl
Object Type: Report
System: The UNT Digital Library
Water and Energy Sustainability: A Balance of Government Action and Industry Innovation (open access)

Water and Energy Sustainability: A Balance of Government Action and Industry Innovation

By completing the tasks and subtasks of the project, the Ground Water Protection Council (GWPC) through its state regulatory agency members and oil and gas industry partners, will bring attention to water quality and quantity issues and make progress toward water and energy sustainability though enhanced water protection and conservation thus enhancing the viability of the domestic fossil fuel industry. The project contains 4 major independent Tasks. Task 1 - Work Plan: Water-Energy Sustainability: A Symposium on Resource Viability. Task 2 - Work Plan: A Regional Assessment of Water and Energy Sustainability. Task 3 - Work Plan: Risk Based Data Management System-Water Water and Energy Module. Task 4 - Work Plan: Identification and Assessment of States Regulatory Programs Regarding Geothermal Heating and Cooling Systems. Each task has a specific scope (details given).
Date: December 31, 2009
Creator: Grunewald, Ben
Object Type: Report
System: The UNT Digital Library
Homogeneous and Heterogeneous Reaction and Transformation of Hg and Trace Metals in Combustion Systems (open access)

Homogeneous and Heterogeneous Reaction and Transformation of Hg and Trace Metals in Combustion Systems

The overall goal of this project was to produce a working dynamic model to predict the transformation and partitioning of trace metals resulting from combustion of a broad range of fuels. The information provided from this model will be instrumental in efforts to identify fuels and conditions that can be varied to reduce metal emissions. Through the course of this project, it was determined that mercury (Hg) and arsenic (As) would be the focus of the experimental investigation. Experiments were therefore conducted to examine homogeneous and heterogeneous mercury oxidation pathways, and to assess potential interactions between arsenic and calcium. As described in this report, results indicated that the role of SO{sub 2} on Hg oxidation was complex and depended upon overall gas phase chemistry, that iron oxide (hematite) particles contributed directly to heterogeneous Hg oxidation, and that As-Ca interactions occurred through both gas-solid and within-char reaction pathways. Modeling based on this study indicated that, depending upon coal type and fly ash particle size, vaporization-condensation, vaporization-surface reaction, and As-CaO in-char reaction all play a role in arsenic transformations under combustion conditions.
Date: August 31, 2009
Creator: Helble, J.; Smith, Clara & Miller, David
Object Type: Report
System: The UNT Digital Library
A University Consortium on Low Temperature Combustion for High Efficiency, Ultra-Low Emission Engines (open access)

A University Consortium on Low Temperature Combustion for High Efficiency, Ultra-Low Emission Engines

The objective of the University consortium was to investigate the fundamental processes that determine the practical boundaries of Low Temperature Combustion (LTC) engines and develop methods to extend those boundaries to improve the fuel economy of these engines, while operating with ultra low emissions. This work involved studies of thermal effects, thermal transients and engine management, internal mixing and stratification, and direct injection strategies for affecting combustion stability. This work also examined spark-assisted Homogenous Charge Compression Ignition (HCCI) and exhaust after-treatment so as to extend the range and maximize the benefit of Homogenous Charge Compression Ignition (HCCI)/ Partially Premixed Compression Ignition (PPCI) operation. In summary the overall goals were:  Investigate the fundamental processes that determine the practical boundaries of Low Temperature Combustion (LTC) engines.  Develop methods to extend LTC boundaries to improve the fuel economy of HCCI engines fueled on gasoline and alternative blends, while operating with ultra low emissions.  Investigate alternate fuels, ignition and after-treatment for LTC and Partially Premixed compression Ignition (PPCI) engines.
Date: December 31, 2009
Creator: Assanis, Dennis N.; Atreya, Arvind; Chen, Jyh-Yuan; Cheng, Wai K.; Dibble, Robert W.; Edwards, Chris et al.
Object Type: Report
System: The UNT Digital Library
Implementation of longitudinal dynamics with barrier RF in BETACOOL and comparison to ESME (open access)

Implementation of longitudinal dynamics with barrier RF in BETACOOL and comparison to ESME

The barrier bucket RF system is successfully used on Recycler storage ring at Fermilab. The special program code ESME was used for numerical simulation of longitudinal phase space manipulations. This program helps optimizing the various regimes of operation in the Recycler and increasing the luminosity in the colliding experiments. Electron and stochastic cooling increases the phase space density in all degrees of freedom. In the case of a small phase space volume the intrabeam scattering introduces coupling between the transverse and longitudinal temperatures of the antiproton beam. For numerical simulations of the cooling processes at the Recycler, a new model of the barrier buckets was implemented in the BETACOOL code. The comparison between ESME and BETACOOL codes for a stationary and moving barrier buckets is presented. This article also includes an application of the barrier bucket numerical model for simulation of the luminosity distribution for RHIC colliding experiments. These simulations take into account the specific longitudinal distribution of the bunch and the vertex size of the detector.
Date: August 31, 2009
Creator: Smirnov, A.; Fedotov, A.; Sidorin, A.; Krestnikov, D.; Bhat, C. & Prost, L.
Object Type: Article
System: The UNT Digital Library
Project Response To ASME Question for Comparison of Pure Oxy-Firing to Diluted Oxy-Firing (open access)

Project Response To ASME Question for Comparison of Pure Oxy-Firing to Diluted Oxy-Firing

High flame temperature oxy-combustion and low flame temperature oxy-combustion are the two primary types of oxy-combustion, which is the combustion of fossil fuel with oxygen instead of air. High flame temperature oxy-combustion results in increased radiant energy, but heat flux at the water walls has been demonstrated to be maintained within design parameters. Less fossil fuel is used, so less CO{sub 2} is produced. Latent and sensible heat can be partially recovered from the compressors. CO{sub 2} capture costs are decreased. Evenly distributed heat avoids creating hot spots. The NETL IPR capture system can capture 100% of the CO{sub 2} when operating at steady state. New boiler designs for high flame temperature oxy-combustion can take advantage of the higher flame temperatures. High flame temperature oxy-combustion with IPR capture can be retrofitted on existing plants. High flame temperature oxy-combustion has significantly improved radiant heat transfer compared to low flame temperature oxy-combustion, but heat flux at the water walls can be controlled. High flame temperature oxy-combustion used with the NETL's Integrated Pollutant Removal System can capture 95%-100% of the CO{sub 2} with heat recovery. These technologies create CO{sub 2} capture cost savings, and are applicable to new design and existing design boilers.
Date: August 31, 2009
Creator: Schoenfield, Mark & Ochs, Tom
Object Type: Report
System: The UNT Digital Library
An Integrated Solid-State LED Luminaire for General Lighting (open access)

An Integrated Solid-State LED Luminaire for General Lighting

A strong systems approach to designing and building practical LED-based replacement lamps is lacking. The general method of taking high-performance LEDs and marrying them to standard printed circuit boards, drivers and a heat sink has fallen short of the promise of LED lighting. In this program, a top-down assessment of requirements and a bottom-up reinvention of LED sources, electronics, optics and mechanics have resulted in the highest performance lamp possible. The team, comprised of Color Kinetics, the leaders in LED lighting and Cree, the leaders in LED devices took an approach to reinvent the package, the driver and the overall form and aesthetic of a replacement source. The challenge was to create a new benchmark in LED lighting - the resultant lamp, a PAR38 equivalent, met the light output, color, color quality and efficacy marks set out in the program as well as being dimmable, which is important for market acceptance. The approach combined the use of multiple source die, a chip-on-board approach, a very efficient driver topology, the use of both direct emission and phosphor conversion, and a unique faceted optic to avoid the losses, artifacts and hotspots of lensed approaches. The integral heat sink provided a mechanical base …
Date: March 31, 2009
Creator: Dowling, Kevin; Lys, Fritz Morgan Ihor; Datta, Mike; Keller, Bernd & Yuan, Thomas
Object Type: Report
System: The UNT Digital Library
Well-to-wheels energy use and greenhouse gas emissions analysis of plug-in hybrid electric vehicles. (open access)

Well-to-wheels energy use and greenhouse gas emissions analysis of plug-in hybrid electric vehicles.

Researchers at Argonne National Laboratory expanded the Greenhouse gases, Regulated Emissions, and Energy use in Transportation (GREET) model and incorporated the fuel economy and electricity use of alternative fuel/vehicle systems simulated by the Powertrain System Analysis Toolkit (PSAT) to conduct a well-to-wheels (WTW) analysis of energy use and greenhouse gas (GHG) emissions of plug-in hybrid electric vehicles (PHEVs). The WTW results were separately calculated for the blended charge-depleting (CD) and charge-sustaining (CS) modes of PHEV operation and then combined by using a weighting factor that represented the CD vehicle-miles-traveled (VMT) share. As indicated by PSAT simulations of the CD operation, grid electricity accounted for a share of the vehicle's total energy use, ranging from 6% for a PHEV 10 to 24% for a PHEV 40, based on CD VMT shares of 23% and 63%, respectively. In addition to the PHEV's fuel economy and type of on-board fuel, the marginal electricity generation mix used to charge the vehicle impacted the WTW results, especially GHG emissions. Three North American Electric Reliability Corporation regions (4, 6, and 13) were selected for this analysis, because they encompassed large metropolitan areas (Illinois, New York, and California, respectively) and provided a significant variation of marginal generation …
Date: March 31, 2009
Creator: Elgowainy, A.; Burnham, A.; Wang, M.; Molburg, J.; Rousseau, A. & Systems, Energy
Object Type: Report
System: The UNT Digital Library
Chemical Looping Combustion Kinetics (open access)

Chemical Looping Combustion Kinetics

One of the most promising methods of capturing CO{sub 2} emitted by coal-fired power plants for subsequent sequestration is chemical looping combustion (CLC). A powdered metal oxide such as NiO transfers oxygen directly to a fuel in a fuel reactor at high temperatures with no air present. Heat, water, and CO{sub 2} are released, and after H{sub 2}O condensation the CO{sub 2} (undiluted by N{sub 2}) is ready for sequestration, whereas the nickel metal is ready for reoxidation in the air reactor. In principle, these processes can be repeated endlessly with the original nickel metal/nickel oxide participating in a loop that admits fuel and rejects ash, heat, and water. Our project accumulated kinetic rate data at high temperatures and elevated pressures for the metal oxide reduction step and for the metal reoxidation step. These data will be used in computational modeling of CLC on the laboratory scale and presumably later on the plant scale. The oxygen carrier on which the research at Utah is focused is CuO/Cu{sub 2}O rather than nickel oxide because the copper system lends itself to use with solid fuels in an alternative to CLC called 'chemical looping with oxygen uncoupling' (CLOU).
Date: March 31, 2009
Creator: Eyring, Edward & Konya, Gabor
Object Type: Text
System: The UNT Digital Library
Improvement plans for the RHIC/AGS on-line model environments (open access)

Improvement plans for the RHIC/AGS on-line model environments

The on-line models for Relativistic Ion Collider (RHIC) and the RHIC pre-injectors (the AGS and the AGS Booster) can be thought of as containing our best collective knowledge of these accelerators. As we improve these on-line models we are building the framework to have a sophisticated model-based controls system. Currently the RHIC on-line model is an integral part of the controls system, providing the interface for tune control, chromaticity control, and non-linear chromaticity control. What we discuss in this paper is our vision of the future of the on-line model environment for RHIC and the RHIC preinjectors. Although these on-line models are primarily used as Courant-Snyder parameter calculators using live machine settings, we envision expanding these environments to encompass many other problem domains.
Date: August 31, 2009
Creator: Brown, K. A.; Ahrens, L.; Beebe-Wang, J.; Morris, J.; Nemesure, S.; Robert-Demolaize, G. et al.
Object Type: Article
System: The UNT Digital Library
2008 Photoions, Photoionization & Photodetachment Gordon Research Conference January 27-February 1, 2008 (open access)

2008 Photoions, Photoionization & Photodetachment Gordon Research Conference January 27-February 1, 2008

This conference brings together scientists interested in a range of basic phenomena linked to the ejection and scattering of electrons from atoms, molecules, clusters, liquids and solids by absorption of light. Photoionization, a highly sensitive probe of both structure and dynamics, can range from perturbative single-photon processes to strong-field highly non-perturbative interactions. It is responsible for the formation and destruction of molecules in astrophysical and plasma environments and successfully used in advanced analytical techniques. Positive ions, which can be produced and studied most effectively using photoionization, are the major components of all plasmas, vital constituents of flames and important intermediates in many chemical reactions. Negative ions are significant as transient species and, when photodetached, the corresponding neutral species often undergoes remarkable, otherwise non-observable, dynamics. The scope of the meeting spans from novel observations in atomic and molecular physics, such as Coulomb Crystals, highly excited states and cold Rydberg plasmas, to novel energy resolved or ultrafast time-resolved experiments, photoionization in strong laser fields, theoretical method development for electron scattering, photoionization and photodetachment and more complex phenomena such as charge transfer and DNA and protein conductivity, important for biological and analytical applications.
Date: March 31, 2009
Creator: GRay, Klaus Muller-Dethefs Nancy Ryan
Object Type: Article
System: The UNT Digital Library
Dynamic Simulation and Optimization of Nuclear Hydrogen Production Systems (open access)

Dynamic Simulation and Optimization of Nuclear Hydrogen Production Systems

This project is part of a research effort to design a hydrogen plant and its interface with a nuclear reactor. This project developed a dynamic modeling, simulation and optimization environment for nuclear hydrogen production systems. A hybrid discrete/continuous model captures both the continuous dynamics of the nuclear plant, the hydrogen plant, and their interface, along with discrete events such as major upsets. This hybrid model makes us of accurate thermodynamic sub-models for the description of phase and reaction equilibria in the thermochemical reactor. Use of the detailed thermodynamic models will allow researchers to examine the process in detail and have confidence in the accurary of the property package they use.
Date: July 31, 2009
Creator: Barton, Paul I.; Kaximi, Mujid S.; Bollas, Georgios & Munoz, Patricio Ramirez
Object Type: Report
System: The UNT Digital Library
Heterogeneous Reburning By Mixed Fuels (open access)

Heterogeneous Reburning By Mixed Fuels

Recent studies of heterogeneous reburning, i.e., reburning involving a coal-derived char, have elucidated its variables, kinetics and mechanisms that are valuable to the development of a highly efficient reburning process. Young lignite chars contain catalysts that not only reduce NO, but they also reduce HCN that is an important intermediate that recycles to NO in the burnout zone. Gaseous CO scavenges the surface oxides that are formed during NO reduction, regenerating the active sites on the char surface. Based on this mechanistic information, cost-effective mixed fuels containing these multiple features has been designed and tested in a simulated reburning apparatus. Remarkably high reduction of NO and HCN has been observed and it is anticipated that mixed fuel will remove 85% of NO in a three-stage reburning process.
Date: March 31, 2009
Creator: Hall, Anderson
Object Type: Report
System: The UNT Digital Library
Fast Tree: Computing Large Minimum-Evolution Trees with Profiles instead of a Distance Matrix (open access)

Fast Tree: Computing Large Minimum-Evolution Trees with Profiles instead of a Distance Matrix

Gene families are growing rapidly, but standard methods for inferring phylogenies do not scale to alignments with over 10,000 sequences. We present FastTree, a method for constructing large phylogenies and for estimating their reliability. Instead of storing a distance matrix, FastTree stores sequence profiles of internal nodes in the tree. FastTree uses these profiles to implement neighbor-joining and uses heuristics to quickly identify candidate joins. FastTree then uses nearest-neighbor interchanges to reduce the length of the tree. For an alignment with N sequences, L sites, and a different characters, a distance matrix requires O(N^2) space and O(N^2 L) time, but FastTree requires just O( NLa + N sqrt(N) ) memory and O( N sqrt(N) log(N) L a ) time. To estimate the tree's reliability, FastTree uses local bootstrapping, which gives another 100-fold speedup over a distance matrix. For example, FastTree computed a tree and support values for 158,022 distinct 16S ribosomal RNAs in 17 hours and 2.4 gigabytes of memory. Just computing pairwise Jukes-Cantor distances and storing them, without inferring a tree or bootstrapping, would require 17 hours and 50 gigabytes of memory. In simulations, FastTree was slightly more accurate than neighbor joining, BIONJ, or FastME; on genuine alignments, FastTree's …
Date: July 31, 2009
Creator: N. Price, Morgan; S. Dehal, Paramvir & P. Arkin, Adam
Object Type: Article
System: The UNT Digital Library
Exact Lattice Supersymmetry (open access)

Exact Lattice Supersymmetry

We provide an introduction to recent lattice formulations of supersymmetric theories which are invariant under one or more real supersymmetries at nonzero lattice spacing. These include the especially interesting case of N = 4 SYM in four dimensions. We discuss approaches based both on twisted supersymmetry and orbifold-deconstruction techniques and show their equivalence in the case of gauge theories. The presence of an exact supersymmetry reduces and in some cases eliminates the need for fine tuning to achieve a continuum limit invariant under the full supersymmetry of the target theory. We discuss open problems.
Date: March 31, 2009
Creator: Catterall, Simon; Kaplan, David B. & Unsal, Mithat
Object Type: Article
System: The UNT Digital Library