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Atomic Layer Deposition for SRF Cavities
We have begun using Atomic Layer Deposition (ALD) to synthesize a variety of surface coatings on coupons and cavities as part of an effort to produce rf structures with significantly better performance and yield than those obtained from bulk niobium, The ALD process offers the possibility of conformally coating complex cavity shapes with precise layered structures with tightly constrained morphology and chemical properties. Our program looks both at the metallurgy and superconducting properties of these coatings, and also their performance in working structures. Initial results include: 1) evidence from point contact tunneling showing magnetic oxides can be a significant limitation to high gradient operation, 2) experimental results showing the production sharp niobium/oxide interfaces from a high temperature bake of ALD coated Al2O3 on niobium surfaces, 3) results from ALD coated structures.
Date:
May 1, 2009
Creator:
Norem, J; Pellin, M J; Antoine, C Z; Ciovati, G; Kneisel, P; Reece, C E et al.
Object Type:
Article
System:
The UNT Digital Library
Atomic Physics Processes Important to the Understanding of the Scrape-Off Layer of Tokamaks
The region between the well-confined plasma and the vessel walls of a magnetic confinement fusion research device, the scrape-off layer (SOL), is typically rich in atomic and molecular physics processes. The most advanced magnetic confinement device, the magnetically diverted tokamak, uses a magnetic separatrix to isolate the confinement zone (closed flux surfaces) from the edge plasma (open field lines). Over most of their length the open field lines run parallel to the separatrix, forming a thin magnetic barrier with the nearby vessel walls. In a poloidally-localized region, the open field lines are directed away from the separatrix and into the divertor, a region spatially separated from the separatrix where intense plasma wall interaction can occur relatively safely. Recent data from several tokamaks indicate that particle transport across the field lines of the SOL can be somewhat faster than previously thought. In these cases, the rate at which particles reach the vessel wall is comparable to the rate to the divertor from parallel transport. The SOL can be thin enough that the recycling neutrals and sputtered impurities from the wall may refuel or contaminate the confinement zone more efficiently than divertor plasma wall interaction. Just inside the SOL is a confinement …
Date:
May 1, 2002
Creator:
West, W. P.; Goldsmith, B.; Evans, T. E. & Olson, R. J.
Object Type:
Article
System:
The UNT Digital Library
Atomic resolution transmission electron microscopy of the intergranular structure of a Y{sub 2}O{sub 3}-silicon nitride ceramic
High-resolution transmission electron microscopy (HRTEM) employing focus-variation phase-reconstruction methods is used to image the atomic structure of grain boundaries in a silicon nitride ceramic at a resolution of 0.8 Angstrom
Date:
May 1, 2002
Creator:
Ziegler, A.; Kisielowski, C.; Hoffmann, M. J. & Ritchie, R. O.
Object Type:
Article
System:
The UNT Digital Library
Atomic Structure of Twin Boundaries in CdTe
Using the combination of high-resolution transmission electron microscopy, first-principles density-functional total energy calculations, and image simulations, we determined the atomic structure of lamellar twin and double-positioning twin boundaries in CdTe. We find that the structure of lamellar twin boundaries has no dangling bonds or wrong bonds; thus, it results in negligible effects on the electronic properties. The structure of double-positioning twin boundaries, however, contain both Cd and Te dangling bonds, and therefore produce energy states in the bandgap that are detrimental to the electronic properties of CdTe.
Date:
May 1, 2003
Creator:
Yan, Y.; Jones, K. M. & Al-Jassim, M. M.
Object Type:
Article
System:
The UNT Digital Library
Audit Guide: Auditing and Investigating the Internal Control of Government Purchase Card Programs (Superseded by GAO-04-87G)
Guidance issued by the General Accounting Office with an abstract that begins "This publication has been superseded by GAO-04-87G, Audit Guide: Auditing and Investigating the Internal Control of Government Purchase Card Programs, November 2003. The federal government of the United States--the largest and most complex organization in the world--expended approximately $15 billion through federal organizations' purchase card programs in fiscal year 2002. As the steward of taxpayer dollars, federal agencies are accountable for how purchase cards are used and how the funds are spent. To that end, federal agencies are responsible for establishing and maintaining internal control to provide reasonable assurance that (1) the goals and objectives of the purchase card program are met and (2) safeguards against fraudulent, improper, and abusive purchases are adequate. Recent congressional testimony and Inspector General and GAO reports show that some federal agencies do not have adequate internal control over their purchase card programs. Without effective internal control, management has little assurance that fraudulent, improper, and abusive purchases are being prevented or, if occurring, are being promptly detected with appropriate corrective actions taken. A key element of internal control is monitoring that assesses the quality of performance over time and ensures that the findings …
Date:
May 1, 2003
Creator:
United States. General Accounting Office.
Object Type:
Text
System:
The UNT Digital Library
Audit Report "Department of Energy Efforts to Manage Information Technology Resources in an Energy-Efficient and Environmentally Responsible Manner"
The American Recovery and Reinvestment Act of 2009 emphasizes energy efficiency and conservation as critical to the Nation's economic vitality; its goal of reducing dependence on foreign energy sources; and, related efforts to improve the environment. The Act highlights the significant use of various forms of energy in the Federal sector and promotes efforts to improve the energy efficiency of Federal operations. One specific area of interest is the increasing demand for Federal sector computing resources and the corresponding increase in energy use, with both cost and environmental implications. The U.S. Environmental Protection Agency reported that, without aggressive conservation measures, data center energy consumption alone is expected to double over the next five years. In our report on Management of the Department's Data Centers at Contractor Sites (DOE/IG-0803, October 2008) we concluded that the Department of Energy had not always improved the efficiency of its contractor data centers even when such modifications were possible and practical. Despite its recognized energy conservation leadership role, the Department had not always taken advantage of opportunities to reduce energy consumption associated with its information technology resources. Nor, had it ensured that resources were managed in a way that minimized impact on the environment. In …
Date:
May 1, 2009
Creator:
unknown
Object Type:
Report
System:
The UNT Digital Library
Automated Demand Response Strategies and Commissioning Commercial Building Controls
California electric utilities have been exploring the use of dynamic critical peak pricing (CPP) and other demand response programs to help reduce peaks in customer electric loads. CPP is a new electricity tariff design to promote demand response. This paper begins with a brief review of terminology regarding energy management and demand response, followed by a discussion of DR control strategies and a preliminary overview of a forthcoming guide on DR strategies. The final section discusses experience to date with these strategies, followed by a discussion of the peak electric demand savings from the 2005 Automated CPP program. An important concept identified in the automated DR field tests is that automated DR will be most successful if the building commissioning industry improves the operational effectiveness of building controls. Critical peak pricing and even real time pricing are important trends in electricity pricing that will require new functional tests for building commissioning.
Date:
May 1, 2006
Creator:
Piette, Mary Ann; Watson, David; Motegi, Naoya; Kiliccote, Sila & Linkugel, Eric
Object Type:
Article
System:
The UNT Digital Library
Autonomic Healing of Epoxy Using Micro-Encapsulated Dicyclopentadiene
The autonomic healing ability of an epoxy adhesive containing micro-encapsulated dicyclopentadiene (DCPD) was evaluated. The epoxy resin used was Epon 828 cured with either Versamid 140 or diethylenetriamine (DETA). Variables included total weight percent of microcapsules (MCs) and catalyst, as well as the catalyst to DCPD ratio. The degree of healing was determined by the fracture toughness before and after ''healing'' using double-cantilever beam analysis. It was found that the degree of self-healing was most directly related to the contact area (i.e. crack width) during healing. Temperature also played a significant role. Observed differences between the results of this study and those in literature are discussed.
Date:
May 1, 2003
Creator:
THOMA, STEVEN G.; GIUNTA, RACHEL K.; STAVIG, MARK E.; EMERSON, JOHN A. & MORALES, ALFREDO M.
Object Type:
Report
System:
The UNT Digital Library
Autothermal Reforming of Renewable Fuels
The conversion of biomass into energy and chemicals is a major research and technology challenge of this century, comparable to petroleum processing in the last century. Recently we have successfully transformed both volatile liquids and nonvolatile liquids and solids into syngas with no carbon formation in autothermal catalytic reactors with residence times of ~10 milliseconds. In the proposed research program we explore the mechanisms of these processes and their extensions to other biomass sources and applications by examining different feeds, catalysts, flow conditions, and steam addition to maximize production of either syngas or chemicals. We will systematically study the catalytic partial oxidation in millisecond autothermal reactors of solid biomass and the liquid products formed by pyrolysis of solid biomass. We will examine alcohols, polyols, esters, solid carbohydrates, and lignocellulose to try to maximize formation of either hydrogen and syngas or olefins and oxygenated chemicals. We will explore molecules and mixtures of practical interest as well as surrogate molecules that contain the functional groups of biofuels but are simpler to analyze and interpret. We will examine spatial profiles within the catalyst and transient and periodic operation of these reactors at pressures up to 10 atm to obtain data from which to …
Date:
May 1, 2009
Creator:
Schmidt, Lanny D
Object Type:
Report
System:
The UNT Digital Library
B-hadron lifetimes and Delta Gamma at the Tevatron
The authors present new results on the lifetimes and widths of B hadrons based on 300-450 pb{sup -1} of data collected by CDF and D0 at the Fermilab Tevatron. Lifetimes were measured in semileptonic decays as well as fully reconstructed hadronic modes. A new measurement of the width difference between B{sub s} CP eigenstates, {Delta}{Lambda}/{bar {Lambda}}, in B{sub s} decays to J/{psi}{phi} is also presented.
Date:
May 1, 2005
Creator:
Lipton, R. J.
Object Type:
Article
System:
The UNT Digital Library
B Lifetimes and Mixing
The Tevatron experiments, CDF and D0, have produced a wealth of new B-physics results since the start of Run II in 2001. We've observed new B-hadrons, seen new effects, and increased many-fold the precision with which we know the properties of b-quark systems. In these proceedings, we will discuss two of the most fruitful areas in the Tevatron B-physics program: lifetimes and mixing. We'll examine the experimental issues driving these analyses, present a summary of the latest results, and discuss prospects for the future.
Date:
May 1, 2009
Creator:
Evans, Harold G.
Object Type:
Article
System:
The UNT Digital Library
B lifetimes and mixing at the Tevatron
The authors present recent results on b-hadron lifetimes and mixing obtained from the analysis of the data collected at the Tevatron Collider by the CDF and D0 Collaborations in the period 2002-2004. Many lifetime measurements have been updated since the Summer 2004 conferences, sometimes improving significantly the accuracy. Likewise the measurement of the B{sub d} oscillation frequency has been updated. New limits on the B{sub s} oscillation frequency have been determined using for the first time Run II data.
Date:
May 1, 2005
Creator:
Bedeschi, Franco
Object Type:
Article
System:
The UNT Digital Library
B(s) Mixing, Delta Gamma(s) and CP Violation at the Tevatron
The authors discuss the results from the Tevatron experiments on mixing and CP violation in the B{sub s}{sup 0}-{bar B}{sub s}{sup 0} system, with particular emphasis to the updated measurements of the decay-width difference {Delta}{Lambda}{sub s} and the first measurement of the CP-violating phase {beta}{sub s} using flavor tagging information. They also briefly review the charge asymmetry measurements in semileptonic B{sub s}{sup 0} decays and in B{sup {+-}} {yields} J/{psi}K{sup {+-}} decays.
Date:
May 1, 2008
Creator:
Di Giovanni, Gian Piero
Object Type:
Article
System:
The UNT Digital Library
B(s) physics at CDF and D0
Run II at the Tevatron has seen an explosion of results related to the B{sub s} meson, ranging from tests of QCD models, to probes of electro-weak symmetry breaking, to direct searches for new physics effects. I will briefly summarize the CDF and D0 B{sub s}-physics programs, describing the suitability of the detectors for doing this kind of physics, and pointing out how our knowledge of important quantities has improved through Run II measurements.
Date:
May 1, 2007
Creator:
Evans, Harold G.
Object Type:
Article
System:
The UNT Digital Library
B spectroscopy at Tevatron
Recent results on heavy flavor spectroscopy from the CDF and D0 experiments are reported in this contribution. Using up to 1 fb{sup -1} of accumulated luminosity per experiment, properties of X(3872), excited B** states, and the B{sub c} meson are measured. Also included are measurements of production rates for ground state b hadrons in p{bar p} collisions.
Date:
May 1, 2006
Creator:
Kravchenko, I.
Object Type:
Article
System:
The UNT Digital Library
B-Tagging at CDF and D0, lessons for LHC
The identification of jets resulting from the fragmentation and hadronization of b quarks is an important part of high-p{sub T} collider physics. The methods used by the CDF and D0 collaborations to perform this identification are described, including the calibration of the efficiencies and fake rates. Some thoughts on the application of these methods in the LHC environment are also presented.
Date:
May 1, 2006
Creator:
Wright, Thomas
Object Type:
Article
System:
The UNT Digital Library
B0(S) mixing, lifetime difference and rare decays at the Tevatron
Recent results on B{sub s}{sup 0} mixing, lifetime difference and rare decays obtained by the CDF and D0 collaborations using the data samples collected at the Tevatron Collider in the period 2002-2005 are presented.
Date:
May 1, 2005
Creator:
Burdin, Sergey
Object Type:
Article
System:
The UNT Digital Library
B0(s) mixing studies at the Tevatron
Measurement of the B{sub s}{sup 0} oscillation frequency via B{sub s}{sup 0} mixing analysis provides a powerful constraint on CKM matrix elements. This note briefly reviews the motivation behind these analyses and describes the various steps that go into a mixing measurement. Recent results on B{sub s}{sup 0} mixing obtained by the CDF and D0 collaborations using the data samples collected at Tevatron Collider in the period 2002-2005 are presented.
Date:
May 1, 2006
Creator:
Naimuddin, M. D. & U., /Delhi
Object Type:
Article
System:
The UNT Digital Library
Backward Integration of the Equations of Motion to Correct for Free Surface Perturbations
Window and free surface interfaces perturb the flow in compression wave experiments. The velocity of these interfaces is routinely measured in shock-compression experiments using interferometry (i.e., VISAR). Interface perturbations often must be accounted for before meaningful material property results can be obtained. For shockless experiments when stress is a single valued function of strain, the governing equations of motion are hyperbolic and can be numerically integrated forward or backward in either time or space with assured stability. Using the VISAR results as ''initial conditions'' the flow fields are integrated backward in space to the interior of the specimen where the VISAR interface has not perturbed the flow at earlier times and results can be interpreted as if the interface had not been present. This provides a rather exact correction for free surface perturbations. The method can also be applied to window interfaces by selecting the appropriate initial conditions. Applications include interpreting Z-accelerator ramp wave experiments. The method applies to multiple layers and multiple reverberations. For an elastic-plastic material model the flow is dissipative and the governing equations are parabolic. When the parabolic terms are small, the equations also can be successfully integrated backward in space. This is verified by using …
Date:
May 1, 2001
Creator:
HAYES,DENNIS BREWSTER
Object Type:
Report
System:
The UNT Digital Library
Bankruptcy Reform: Value of Credit Counseling Requirements Is Not Clear
Testimony issued by the Government Accountability Office with an abstract that begins "The Bankruptcy Abuse Prevention and Consumer Protection Act of 2005 requires individuals to receive credit counseling before filing for bankruptcy and to take a debtor education course before having debts discharged. Concerns were raised that the new requirements could expose consumers to abusive practices by credit counseling agencies or become barriers to filing for bankruptcy. This testimony is based on GAO's report issued last month, and addresses (1) the process of approving counseling and education providers, (2) the content and results of the counseling and education sessions, (3) the fees charged, and (4) the availability of and challenges to accessing services. To address these issues, GAO reviewed Trustee Program data and application case files, and interviewed a wide range of individuals and groups involved in the bankruptcy process."
Date:
May 1, 2007
Creator:
United States. Government Accountability Office.
Object Type:
Text
System:
The UNT Digital Library
BARRIER ISSUES TO THE UTILIZATION OF BIOMASS
The Energy & Environmental Research Center (EERC) is conducting a project to examine the fundamental issues limiting the use of biomass in small industrial steam/power systems in order to increase the future use of this valuable domestic resource. Specifically, the EERC is attempting to elucidate the ash-related problems--grate clinkering and heat exchange surface fouling--associated with cofiring coal and biomass in grate-fired systems. Utilization of biomass in stoker boilers designed for coal can be a cause of concern for boiler operators. Boilers that were designed for low-volatile fuels with lower reactivities can experience damaging fouling when switched to higher-volatile and more reactive lower-rank fuels, such as when cofiring biomass. Higher heat release rates at the grate can cause more clinkering or slagging at the grate because of higher temperatures. Combustion and loss of volatile matter can start too early with biomass fuels compared to design fuel, vaporizing alkali and chlorides which then condense on rear walls and heat exchange tube banks in the convective pass of the boiler, causing noticeable increases in fouling. In addition, stoker-fired boilers that switch to biomass blends may encounter new chemical species such as potassium sulfates and various chlorides in combination with different flue gas temperatures …
Date:
May 1, 2002
Creator:
Gunderson, Jay R.; Folkedahl, Bruce C.; Schmidt, Darren D.; Weber, Greg F. & Zygarlicke, Christopher J.
Object Type:
Report
System:
The UNT Digital Library
BARRIER ISSUES TO THE UTILIZATION OF BIOMASS
In summary, stoker-fired boilers that cofire or switch to biomass fuel may potentially have to deal with ash behavior issues such as production of different concentrations and quantities of fine particulate or aerosols and ash-fouling deposition. Stoker boiler operators that are considering switching to biomass and adding potential infrastructure to accommodate the switch may also at the same time be looking into upgrades that will allow for generating additional power for sale on the grid. This is the case for the feasibility study being done currently for a small (<1-MW) stoker facility at the North Dakota State Penitentiary, which is considering not only the incorporation of a lower-cost biomass fuel but also a refurbishing of the stoker boiler to burn slightly hotter with the ability to generate more power and sell excess energy on the grid. These types of fuel and boiler changes can greatly affect ash behavior issues.
Date:
May 1, 2001
Creator:
Weber, Greg F. & Zygarlicke, Christopher J.
Object Type:
Report
System:
The UNT Digital Library
Barrier RF system and applications in Main Injector
A novel broadband RF system--the barrier RF--has been designed, fabricated and installed in the Fermilab Main Injector (MI). It uses nanocrystal magnetic alloy called Finemet and high voltage fast MOSFET switches. The system delivers {+-}10 kV square pulses at 90 kHz. It can stack two proton batches injected from the Booster and squeeze them into the size of one so that the bunch intensity is increased. The high intensity beams have been successfully accelerated to 120 GeV with small losses. The problem of large longitudinal emittance growth is under investigation. A second system will be installed during the fall shutdown and be tested for the so-called fast stacking scheme to continuously stack up to 12 Booster batches in the MI. This system is also used for cleaning up the leaking-out dc beams from slip stacking to reduce beam loss. This work is part of the US-Japan collaborative agreement.
Date:
May 1, 2005
Creator:
Chou, W.; Wildman, D. & Takagi, A.
Object Type:
Article
System:
The UNT Digital Library
Basic Electropolishing Process Research and Development in Support of Improved Reliable Performance SRF Cavities for the Future Accelerator
Future accelerators require unprecedented cavity performance, which is strongly influenced by interior surface nanosmoothness. Electropolishing is the technique of choice to be developed for high-field superconducting radiofrequency cavities. Electrochemical impedance spectroscopy (EIS) and related techniques point to the electropolishing mechanism of Nb in a sulfuric and hydrofluoric acid electrolyte of controlled by a compact surface salt film under F- diffusion-limited mass transport control. These and other findings are currently guiding a systematic characterization to form the basis for cavity process optimization, such as flowrate, electrolyte composition and temperature. This integrated analysis is expected to provide optimum EP parameter sets for a controlled, reproducible and uniform surface leveling for Nb SRF cavities.
Date:
May 1, 2009
Creator:
H. Tian, C.E. Reece,M.J. Kelley
Object Type:
Article
System:
The UNT Digital Library