Arctic Energy Technology Development Laboratory (Part 2) (open access)

Arctic Energy Technology Development Laboratory (Part 2)

Methane (CH{sub 4}) in natural gas is a major energy source in the U.S., and is used extensively on Alaska's North Slope, including the oilfields in Prudhoe Bay, the community of Barrow, and the National Petroleum Reserve, Alaska (NPRA). Smaller villages, however, are dependent on imported diesel fuel for both power and heating, resulting in some of the highest energy costs in the U.S. and crippling local economies. Numerous CH{sub 4} gas seeps have been observed on wetlands near Atqasuk, Alaska (in the NPRA), and initial measurements have indicated flow rates of 3,000-5,000 ft{sup 3} day{sup -1} (60-100 kg CH{sub 4} day{sup -1}). Gas samples collected in 1996 indicated biogenic origin, although more recent sampling indicated a mixture of biogenic and thermogenic gas. In this study, we (1) quantified the amount of CH{sub 4} generated by several seeps and evaluated their potential use as an unconventional gas source for the village of Atqasuk; (2) collected gas and analyzed its composition from multiple seeps several miles apart to see if the source is the same, or if gas is being generated locally from isolated biogenic sources; and (3) assessed the potential magnitude of natural CH{sub 4} gas seeps for future use …
Date: December 31, 2008
Creator: 960443, See OSTI ID Number
Object Type: Report
System: The UNT Digital Library
Arctic Energy Technology Development Laboratory (Part 3) (open access)

Arctic Energy Technology Development Laboratory (Part 3)

Various laboratory tests were carried at the R & D facility of BJ Services in Tomball, TX with BJ Services staff to predict and evaluate the performance of the Ceramicrete slurry for its effective use in permafrost cementing operations. Although other standards such as those of the American Standard for Testing Materials (ASTM) and Construction Specification Institute (CSI) exist, all these tests were standardized by the API. A summary of the tests traditionally used in the cement slurry design as well as the API tests reference document are provided in Table 7. All of these tests were performed within the scope of this research to evaluate properties of the Ceramicrete.
Date: December 31, 2008
Creator: 960443, See OSTI ID Number
Object Type: Report
System: The UNT Digital Library
Functionally Graded Cathodes for Solid Oxide Fuel Cells (open access)

Functionally Graded Cathodes for Solid Oxide Fuel Cells

One primary suspected cause of long-term performance degradation of solid oxide fuels (SOFCs) is the accumulation of chromium (Cr) species at or near the cathode/electrolyte interface due to reactive Cr molecules originating from Cr-containing components (such as the interconnect) in fuel cell stacks. To date, considerable efforts have been devoted to the characterization of cathodes exposed to Cr sources; however, little progress has been made because a detailed understanding of the chemistry and electrochemistry relevant to the Cr-poisoning processes is still lacking. This project applied multiple characterization methods - including various Raman spectroscopic techniques and various electrochemical performance measurement techniques - to elucidate and quantify the effect of Cr-related electrochemical degradation at the cathode/electrolyte interface. Using Raman microspectroscopy the identity and location of Cr contaminants (SrCrO{sub 4}, (Mn/Cr){sub 3}O{sub 4} spinel) have been observed in situ on an LSM cathode. These Cr contaminants were shown to form chemically (in the absence of current flowing through the cell) at temperatures as low as 625 C. While SrCrO{sub 4} and (Mn/Cr){sub 3}O{sub 4} spinel must preferentially form on LSM, since the LSM supplies the Sr and Mn cations necessary for these compounds, LSM was also shown to be an active site for …
Date: December 31, 2006
Creator: Abernathy, Harry & Liu, Meilin
Object Type: Report
System: The UNT Digital Library
Withdrawal from the ABM Treaty: Legal Considerations (open access)

Withdrawal from the ABM Treaty: Legal Considerations

On December 13, 2001, President Bush gave formal notice to Russia, Belarus, Kazakhstan, and the Ukraine that the United States was withdrawing from the Anti-Ballistic Missile Treaty because of the constraints it imposes on the testing of missile defense systems; and six months later, on June 13, 2002, the treaty effectively terminated. The ABM Treaty has been in force since 1972. Pertinent legal questions that have been raised about U.S. withdrawal concern whether the treaty allows it; if so, the procedure to be followed; and, finally, the constitutionality of the President doing so unilaterally without the involvement of the Senate or Congress. This report briefly discusses these issues, as well as the recent federal district court decision in Kucinich v. Bush dismissing a suit by 32 members of the House challenging the constitutionality of the President’s action.
Date: December 31, 2002
Creator: Ackerman, David M.
Object Type: Report
System: The UNT Digital Library
Production Well Performance Enhancement using Sonication Technology (open access)

Production Well Performance Enhancement using Sonication Technology

The objective of this project was to develop a sonic well performance enhancement technology that focused on near wellbore formation damage. In order to successfully achieve this objective, a three-year project was defined. The entire project was broken into four tasks. The overall objective of all this was to foster a better understanding of the mechanisms involved in sonic energy interactions with fluid flow in porous media and adapt such knowledge for field applications. The fours tasks are: • Laboratory studies • Mathematical modeling • Sonic tool design and development • Field demonstration The project was designed to be completed in three years; however, due to budget cuts, support was only provided for the first year, and hence the full objective of the project could not be accomplished. This report summarizes what was accomplished with the support provided by the US Department of Energy. Experiments performed focused on determining the inception of cavitation, studying thermal dissipation under cavitation conditions, investigating sonic energy interactions with glass beads and oil, and studying the effects of sonication on crude oil properties. Our findings show that the voltage threshold for onset of cavitation is independent of transducer-hydrophone separation distance. In addition, thermal dissipation under …
Date: December 31, 2005
Creator: Adewumi, Michael A.; Ityokumbul, M. Thaddeus; Watson, Robert W.; Eltohami, Eltohami; Farias, Mario; Heckman, Glenn et al.
Object Type: Report
System: The UNT Digital Library
Advanced Measurement and Modeling Techniques for Improved SOFC Cathodes (open access)

Advanced Measurement and Modeling Techniques for Improved SOFC Cathodes

The goal of this project was to develop an improved understanding of factors governing performance and degradation of mixed-conducting SOFC cathodes. Two new diagnostic tools were developed to help achieve this goal: (1) microelectrode half-cells for improved isolation of cathode impedance on thin electrolytes, and (2) nonlinear electrochemical impedance spectroscopy (NLEIS), a variant of traditional impedance that allows workers to probe nonlinear rates as a function of frequency. After reporting on the development and efficacy of these tools, this document reports on the use of these and other tools to better understand performance and degradation of cathodes based on the mixed conductor La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} (LSC) on gadolinia or samaria-doped ceria (GDC or SDC). We describe the use of NLEIS to measure O{sub 2} exchange on thin-film LSC electrodes, and show that O{sub 2} exchange is most likely governed by dissociative adsorption. We also describe parametric studies of porous LSC electrodes using impedance and NLEIS. Our results suggest that O{sub 2} exchange and ion transport co-limit performance under most relevant conditions, but it is O{sub 2} exchange that is most sensitive to processing, and subject to the greatest degradation and sample-to-sample variation. We recommend further work that focuses on …
Date: December 31, 2006
Creator: Adler, Stuart; Dunyushkina, L.; Huff, S.; Lu, Y. & Wilson, J.
Object Type: Report
System: The UNT Digital Library
Optical Properties and Wave Propagation in Semiconductor-Based Two-Dimensional Photonic Crystals (open access)

Optical Properties and Wave Propagation in Semiconductor-Based Two-Dimensional Photonic Crystals

This work is a theoretical investigation on the physical properties of semiconductor-based two-dimensional photonic crystals, in particular for what concerns systems embedded in planar dielectric waveguides (GaAs/AlGaAs, GaInAsP/InP heterostructures, and self-standing membranes) or based on macro-porous silicon. The photonic-band structure of photonic crystals and photonic-crystal slabs is numerically computed and the associated light-line problem is discussed, which points to the issue of intrinsic out-of-lane diffraction losses for the photonic bands lying above the light line. The photonic states are then classified by the group theory formalism: each mode is related to an irreducible representation of the corresponding small point group. The optical properties are investigated by means of the scattering matrix method, which numerically implements a variable-angle-reflectance experiment; comparison with experiments is also provided. The analysis of surface reflectance proves the existence of selection rules for coupling an external wave to a certain photonic mode. Such rules can be directly derived from symmetry considerations. Lastly, the control of wave propagation in weak-index contrast photonic-crystal slabs is tackled in view of designing building blocks for photonic integrated circuits. The proposed designs are found to comply with the major requirements of low-loss propagation, high and single-mode transmission. These notions are then collected …
Date: December 31, 2002
Creator: Agio, Mario
Object Type: Thesis or Dissertation
System: The UNT Digital Library
The MACHO Project Large Magellanic Cloud Variable Star Inventory. XIII. Fourier Parameters for the First Overtone RR Lyrae Variables and the LMC Distance (open access)

The MACHO Project Large Magellanic Cloud Variable Star Inventory. XIII. Fourier Parameters for the First Overtone RR Lyrae Variables and the LMC Distance

Shapes of RR Lyrae light curves can be described in terms of Fourier coefficients which past research has linked with physical characteristics such as luminosity, mass and temperature. Fourier coefficients have been derived for the V and R light curves of 785 overtone RR Lyrae variables in 16 MACHO fields near the bar of the LMC. In general, the Fourier phase differences {phi}{sub 21}, {phi}{sub 31} and {phi}{sub 41} increase and the amplitude ratio R{sub 21} decreases with increasing period. The coefficients for both the V and R magnitudes follow these patterns, but the phase differences for the R curves are on average slightly greater, and their amplitudes are about 20% smaller, than the ones for the V curves. The {phi}{sub 31} and R{sub 21} coefficients have been compared with those of the first overtone RR Lyrae variables in the Galactic globular clusters NGC 6441, M107, M5, M3, M2, {omega} Centauri and M68. The results indicate that many of the LMC variables have properties similar to the ones in M2, M3, M5 and the Oosterhoff type I variables in {omega} Cen, but they are different from the Oosterhoff type II variables in {omega} Cen. Equations derived from hydrodynamic pulsation models …
Date: December 31, 2003
Creator: Alcock, C.; Alves, D.; Axelrod, T.; Becker, A.; Bennett, D.; Clement, C. et al.
Object Type: Article
System: The UNT Digital Library
Scalable Computational Chemistry: New Developments and Applications (open access)

Scalable Computational Chemistry: New Developments and Applications

The computational part of the thesis is the investigation of titanium chloride (II) as a potential catalyst for the bis-silylation reaction of ethylene with hexaclorodisilane at different levels of theory. Bis-silylation is an important reaction for producing bis(silyl) compounds and new C-Si bonds, which can serve as monomers for silicon containing polymers and silicon carbides. Ab initio calculations on the steps involved in a proposed mechanism are presented. This choice of reactants allows them to study this reaction at reliable levels of theory without compromising accuracy. The calculations indicate that this is a highly exothermic barrierless reaction. The TiCl{sub 2} catalyst removes a 50 kcal/mol activation energy barrier required for the reaction without the catalyst. The first step is interaction of TiCl{sub 2} with ethylene to form an intermediate that is 60 kcal/mol below the energy of the reactants. This is the driving force for the entire reaction. Dynamic correlation plays a significant role because RHF calculations indicate that the net barrier for the catalyzed reaction is 50 kcal/mol. They conclude that divalent Ti has the potential to become an important industrial catalyst for silylation reactions. In the programming part of the thesis, parallelization of different quantum chemistry methods is …
Date: December 31, 2002
Creator: Alexeev, Yuri
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Optical Sensors for Post Combustion Control in Electric Arc Furnace Steelmaking (TRP 9851) (open access)

Optical Sensors for Post Combustion Control in Electric Arc Furnace Steelmaking (TRP 9851)

Working in collaboration with Stantec Global Technologies, Process Metrix Corporation, and The Timken Company, Sandia National Laboratories constructed and evaluated a novel, laser-based off-gas sensor at the electric arc furnace facility of Timken's Faircrest Steel Plant (Canton, Ohio). The sensor is based on a mid-infrared tunable diode laser (TDL), and measures the concentration and temperature of specific gas species present in the off-gas emanating from the EAF. The laser beam is transmitted through the gas stream at the fourth hole of the EAF, and provides a real-time, in situ measurement that can be used for process optimization. Two sets of field tests were performed in parallel with Stantec's extractive probe off-gas system, and the tests confirm the TDL sensor's operation and applicability for electric steel making. The sensor measures real-time, in situ line-of-sight carbon monoxide (CO) concentrations between 5% and 35% CO, and measures off-gas temperature in the range of 1400 to 1900 K. In order to achieve commercial-ready status, future work is required to extend the sensor for simultaneous CO and CO{sub 2} concentration measurements. In addition, long-term endurance tests including process optimization must be completed.
Date: December 31, 2003
Creator: Allendorf, Sarah W.; Ottesen, David K.; Green, Robert W.; Hardesty, Donald R.; Kolarik, Robert; Goodfellow, Howard et al.
Object Type: Report
System: The UNT Digital Library
A Hybrid Hydrologic-Geophysical Inverse Technique For The Assessment And Monitoring Of Leachates In The Vadose Zone (open access)

A Hybrid Hydrologic-Geophysical Inverse Technique For The Assessment And Monitoring Of Leachates In The Vadose Zone

At many DOE facilities, the presence of radioactive wastes and other contaminants within the vadose zone poses a serious and ongoing threat to public health and safety. In many cases these contaminants have been introduced directly to the vadose zone through releases on the surface or in shallow pits, and through leaking storage facilities. To reduce the environmental risks these wastes pose, the DOE is currently considering two fundamentally different approaches. The first involves remediation by treating contaminants in-place while the second, and more economically feasible being examined by DOE, involves in-situ immobilization of the wastes. Immobilization would be achieved through both injection of subsurface grout barriers to block transport pathways and installation of surface caps to prevent additional water infiltration into contaminated formations. A necessary requirement of both remediation approaches is the need to obtain information on the spatial distributions of the hydraulic and transport properties, the amount of contamination in place, and flow and transport processes that are occurring. With this information in hand, informed decisions can be made in order to optimize the remediation process for each particular case. In particular, these capabilities could result in reduced remediation costs, as well as providing necessary data to illustrate …
Date: December 31, 2000
Creator: Alumbaugh, David L.
Object Type: Report
System: The UNT Digital Library
Major Leadership Election Contests in the House of Representatives, 94th-111th Congresses (open access)

Major Leadership Election Contests in the House of Representatives, 94th-111th Congresses

This report contains data on votes for Speaker of the House for the 94th through 110th Congresses and elections in party conferences or caucuses for major leaders within each party for the 94th through 111th Congresses. It reflects actual balloting on the House floor for Speaker and in the Democratic Caucus and Republican Conference for other positions.
Date: December 31, 2008
Creator: Amer, Mildred
Object Type: Report
System: The UNT Digital Library
Membership of the 111th Congress: A Profile (open access)

Membership of the 111th Congress: A Profile

This report presents a profile of the membership of the 111th Congress. Statistical information is included on selected characteristics of Members, including data on party affiliation, average age and length of service, occupation, religious affiliation, gender, ethnicity, foreign births, and military service.
Date: December 31, 2008
Creator: Amer, Mildred
Object Type: Report
System: The UNT Digital Library
Corner rounding in EUV photoresist: tuning through molecular weight, PAG size, and development time (open access)

Corner rounding in EUV photoresist: tuning through molecular weight, PAG size, and development time

In this paper, the corner rounding bias of a commercially available extreme ultraviolet photoresist is monitored as molecular weight, photoacid generator (PAG) size, and development time are varied. These experiments show that PAG size influences corner biasing while molecular weight and development time do not. Large PAGs are shown to exhibit less corner biasing, and in some cases, lower corner rounding, than small PAGs. In addition, heavier resist polymers are shown to exhibit less corner rounding than lighter ones.
Date: December 31, 2009
Creator: Anderson, Christopher; Daggett, Joe & Naulleau, Patrick
Object Type: Article
System: The UNT Digital Library
Modeling Brine-Rock Interactions in an Enhanced Geothermal System Deep Fractured Reservoir at Soultz-Sous-Forets (France) - A Joint Approach Using Two Geochemical Codes: Frachem and Toughreact (open access)

Modeling Brine-Rock Interactions in an Enhanced Geothermal System Deep Fractured Reservoir at Soultz-Sous-Forets (France) - A Joint Approach Using Two Geochemical Codes: Frachem and Toughreact

The modeling of coupled thermal, hydrological, and chemical (THC) processes in geothermal systems is complicated by reservoir conditions such as high temperatures, elevated pressures and sometimes the high salinity of the formation fluid. Coupled THC models have been developed and applied to the study of enhanced geothermal systems (EGS) to forecast the long-term evolution of reservoir properties and to determine how fluid circulation within a fractured reservoir can modify its rock properties. In this study, two simulators, FRACHEM and TOUGHREACT, specifically developed to investigate EGS, were applied to model the same geothermal reservoir and to forecast reservoir evolution using their respective thermodynamic and kinetic input data. First, we report the specifics of each of these two codes regarding the calculation of activity coefficients, equilibrium constants and mineral reaction rates. Comparisons of simulation results are then made for a Soultz-type geothermal fluid (ionic strength {approx}1.8 molal), with a recent (unreleased) version of TOUGHREACT using either an extended Debye-Hueckel or Pitzer model for calculating activity coefficients, and FRACHEM using the Pitzer model as well. Despite somewhat different calculation approaches and methodologies, we observe a reasonably good agreement for most of the investigated factors. Differences in the calculation schemes typically produce less difference …
Date: December 31, 2006
Creator: Andre, Laurent; Spycher, Nicolas; Xu, Tianfu; Vuataz, Francois-D. & Pruess, Karsten
Object Type: Report
System: The UNT Digital Library
Department of Defense Facilities Energy Conservation Policies and Spending (open access)

Department of Defense Facilities Energy Conservation Policies and Spending

This report reviews energy conservation legislation and Executive Ordrs that apply to the Department of Defense, directives and instructions to the military departments and agencies on implementing the legislation and orders, Defense spending on facility energy over the last decade, annual Defense appropriations that fund energy-conservation improvements, and Defense energy conservation investments.
Date: December 31, 2008
Creator: Andrews, Anthony
Object Type: Report
System: The UNT Digital Library
Results Of The Excreta Bioassay Quality Control Program For April 1, 2007 Through March 31, 2008 (open access)

Results Of The Excreta Bioassay Quality Control Program For April 1, 2007 Through March 31, 2008

A total of 79 urine samples, 3 blank fecal and 5 spiked artificial fecal samples were submitted during the report period (April 1, 2007 through March 31, 2008) to General Engineering Laboratories, South Carolina by the Hanford Internal Dosimetry Program (IDP) to check the accuracy, precision, and detection levels of their analyses. Urine analyses for tritium, Sr, 238Pu, 239Pu, 241Am, 243Am 235U, 238U, elemental uranium and fecal analyses for 241Am, 238Pu and 239Pu were tested this year. The number of QC urine samples submitted during the report period represented 1.8% of the total samples submitted. In addition to the samples provided by IDP, GEL was also required to conduct their own QC program, and submit the results of analyses to IDP. About 35% of the analyses processed by GEL during the third year of this contract were quality control samples. GEL tested the performance of 24 radioisotopes, all of which met or exceeded the specifications in the Statement of Work within statistical uncertainty (Table 4). IDP concluded that GEL was performing well for all analyses tested, and concerns identified earlier were satisfactorily resolved.
Date: December 31, 2008
Creator: Antonio, Cheryl L.
Object Type: Report
System: The UNT Digital Library
Supported, Alkali-Promoted Cobalt Oxide Catalysts for NOx Removal from Coal Combustion Flue Gases (open access)

Supported, Alkali-Promoted Cobalt Oxide Catalysts for NOx Removal from Coal Combustion Flue Gases

A series of cobalt oxide catalysts supported on alumina ({gamma}-Al{sub 2}O{sub 3}) were synthesized with varying contents of cobalt and of added alkali metals, including lithium, sodium, potassium, rubidium, and cesium. Unsupported cobalt oxide catalysts and several cobalt oxide catalysts supported ceria (CeO{sub 2}) with varying contents of cobalt with added potassium were also prepared. The catalysts were characterized with UV-visible spectroscopy and were examined for NO{sub x} decomposition activity. The CoO{sub x}/Al{sub 2}O{sub 3} catalysts and particularly the CoO{sub x}/CeO{sub 2} catalysts show N{sub 2}O decomposition activity, but none of the catalysts (unsupported Co{sub 3}O{sub 4} or those supported on ceria or alumina) displayed significant, sustained NO decomposition activity. For the Al{sub 2}O{sub 3}-supported catalysts, N{sub 2}O decomposition activity was observed over a range of reaction temperatures beginning about 723 K, but significant (>50%) conversions of N{sub 2}O were observed only for reaction temperatures >900 K, which are too high for practical commercial use. However, the CeO{sub 2}-supported catalysts display N{sub 2}O decomposition rates similar to the Al{sub 2}O{sub 3}-supported catalysts at much lower reaction temperatures, with activity beginning at {approx}573 K. Conversions of >90% were achieved at 773 K for the best catalysts. Catalytic rates per cobalt atom …
Date: December 31, 2005
Creator: Argyle, Morris D.
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
The Federal Budget: Current and Upcoming Issues (open access)

The Federal Budget: Current and Upcoming Issues

This report examines changes to the Federal Budget for Fiscal Years 2008-2010. The report considers the factors that have an effect on various budgetary functions and decisions. The report specifically focuses on the effect of the 2007-2008 financial recession on the budget, but also considers more long-term fiscal issues such as health care for retiring Baby-Boomers.
Date: December 31, 2009
Creator: Austin, D. Andrew & Levit, Mindy R.
Object Type: Report
System: The UNT Digital Library
Beam Intensity Expectations for a 200 Mev/U 400 KW Radioactive Beam Driver Accelerator. (open access)

Beam Intensity Expectations for a 200 Mev/U 400 KW Radioactive Beam Driver Accelerator.

The expected radioactive ion production rate for a 200 MeV/u 400 kW driver linac using four different production methods is discussed. For each isotope the optimum method is identified and the rate is calculated based on different model assumptions, empirical observation and extrapolations. The results are compared to the rates expected for a 550 MeV proton driver machine with a beam power of 50 kW, as well as the full RIA facility with a 400 MeV/u 400 kW production linac.
Date: December 31, 2006
Creator: Back, B. B.; Jiang, C. L. & Physics
Object Type: Report
System: The UNT Digital Library
High-Precision Floating-Point Arithmetic in ScientificComputation (open access)

High-Precision Floating-Point Arithmetic in ScientificComputation

At the present time, IEEE 64-bit floating-point arithmetic is sufficiently accurate for most scientific applications. However, for a rapidly growing body of important scientific computing applications, a higher level of numeric precision is required: some of these applications require roughly twice this level; others require four times; while still others require hundreds or more digits to obtain numerically meaningful results. Such calculations have been facilitated by new high-precision software packages that include high-level language translation modules to minimize the conversion effort. These activities have yielded a number of interesting new scientific results in fields as diverse as quantum theory, climate modeling and experimental mathematics, a few of which are described in this article. Such developments suggest that in the future, the numeric precision used for a scientific computation may be as important to the program design as are the algorithms and data structures.
Date: December 31, 2004
Creator: Bailey, David H.
Object Type: Article
System: The UNT Digital Library
A Pseudo-Random Number Generator Based on Normal Numbers (open access)

A Pseudo-Random Number Generator Based on Normal Numbers

In a recent paper, Richard Crandall and the present author established that each of a certain class of explicitly given real constants, uncountably infinite in number, is b-normal, for an integer that appears in the formula defining the constant. A b-normal constant is one where every string of m digits appears in the base-b expansion of the constant with limiting frequency b{sup -m}. This paper shows how this result can be used to fashion an efficient and effective pseudo-random number generator, which generates successive strings of binary digits from one of the constants in this class. The resulting generator, which tests slightly faster than a conventional linear congruential generator, avoids difficulties with large power-of-two data access strides that may occur when using conventional generators. It is also well suited for parallel processing--each processor can quickly and independently compute its starting value, with the collective sequence generated by all processors being the same as that generated by a single processor.
Date: December 31, 2004
Creator: Bailey, David H.
Object Type: Report
System: The UNT Digital Library
A Strong Hot Spot Theorem (open access)

A Strong Hot Spot Theorem

A real number alpha is said to be b-normal if every m-long string of digits appears in the base-b expansion of alpha with limiting frequency b-m. We prove that alpha is b-normal if and only if it possesses no base-b ''hot spot''. In other words, alpha is b-normal if and only if there is no real number y such that smaller and smaller neighborhoods of y are visited by the successive shifts of the base-b expansion of alpha with larger and larger frequencies, relative to the lengths of these neighborhoods
Date: December 31, 2005
Creator: Bailey, David H. & Misiurewicz, Michal
Object Type: Article
System: The UNT Digital Library