A Combined Experimental and Computational Approach for the Design of Mold Topography that Leads to Desired Ingot Surface and Microstructure in Aluminum Casting. (open access)

A Combined Experimental and Computational Approach for the Design of Mold Topography that Leads to Desired Ingot Surface and Microstructure in Aluminum Casting.

A method combining features of front-tracking methods and fixed-domain methods is presented to model dendritic solidification of pure materials. To explicitly track the interface growth and shape of the solidifying crystals, a fronttracking approach based on the level set method is implemented. To easily model the heat and momentum transport, a fixed-domain method is implemented assuming a diffused freezing front where the liquid fraction is defined in terms of the level set function. The fixed-domain approach, by avoiding the explicit application of essential boundary conditions on the freezing front, leads to an energy conserving methodology that is not sensitive to the mesh size. To compute the freezing front morphology, an extended Stefan condition is considered. Applications to several classical Stefan problems and two- and three-dimensional crystal growth of pure materials in an undercooled melt including the effects of melt flow are considered. The computed results agree very well with available analytical solutions as well as with results obtained using front-tracking techniques and the phase-field method.
Date: July 12, 2005
Creator: Dr. Zabaras, N. & Tan, L.
System: The UNT Digital Library
Crosscheck of different techniques for two dimensional power spectral density measurements of x-ray optics (open access)

Crosscheck of different techniques for two dimensional power spectral density measurements of x-ray optics

The consistency of different instruments and methods for measuring two-dimensional (2D) power spectral density (PSD) distributions are investigated. The instruments are an interferometric microscope, an atomic force microscope (AFM) and the X-ray Reflectivity and Scattering experimental facility, all available at Lawrence Berkeley National Laboratory. The measurements were performed with a gold-coated mirror with a highly polished stainless steel substrate. It was shown that these three techniques provide essentially consistent results. For the stainless steel mirror, an envelope over all measured PSD distributions can be described with an inverse power-law PSD function. It is also shown that the measurements can be corrected for the specific spatial frequency dependent systematic errors of the instruments. The AFM and the X-ray scattering measurements were used to determine the modulation transfer function of the interferometric microscope. The corresponding correction procedure is discussed in detail. Lower frequency investigation of the 2D PSD distribution was also performed with a long trace profiler and a ZYGO GPI interferometer. These measurements are in some contradiction, suggesting that the reliability of the measurements has to be confirmed with additional investigation. Based on the crosscheck of the performance of all used methods, we discuss the ways for improving the 2D PSD …
Date: July 12, 2005
Creator: Yashchuk, Valeriy V.; Irick, Steve C.; Gullikson, Eric M.; Howells, Malcolm R.; MacDowell, Alastair A.; McKinney, Wayne R. et al.
System: The UNT Digital Library
NEVADA RAIL PROJECT PROGRAMMATIC AGREEMENT (open access)

NEVADA RAIL PROJECT PROGRAMMATIC AGREEMENT

None
Date: July 11, 2005
Creator: Bishop, L.
System: The UNT Digital Library
Neutron Capture and Transmission Measurements and Resonance Parameter Analysis of Niobium (open access)

Neutron Capture and Transmission Measurements and Resonance Parameter Analysis of Niobium

None
Date: July 1, 2005
Creator: Drindak, NJ; Burke, JA; Leinweber, G; Helm, JA; Hoole, JG; Block, RC et al.
System: The UNT Digital Library
Risked Based Inspection (External Conference MaterialsRBI) of Steam Systems (open access)

Risked Based Inspection (External Conference MaterialsRBI) of Steam Systems

This paper describes the implementation of a risk-based inspection program for process and utility steam lines in a large chemical process facility. The paper addresses first the development of an RBI matrix, the likelihood attributes, the consequence scores, and the overall risk in terms of personnel safety and costs. Systems are plotted on the RBI matrix to develop inspection priorities. The RBI ranking is followed by inspection planning, acceptance criteria, and wall thickness inspection techniques, including UT, pulsed eddy current and digital radiography.
Date: July 1, 2005
Creator: GEORGE, ANTAKI
System: The UNT Digital Library
Southern Ocean Iron Experiment (SOFex) (open access)

Southern Ocean Iron Experiment (SOFex)

The Southern Ocean Iron Experiment (SOFeX) was an experiment decades in the planning. It's implementation was among the most complex ship operations that SIO has been involved in. The SOFeX field expedition was successful in creating and tracking two experimentally enriched areas of the Southern Ocean, one characterized by low silicic acid, one characterized by high silicic acid. Both experimental sites were replete with abundant nitrate. About 100 scientists were involved overall. The major findings of this study were significant in several ways: (1) The productivity of the southern ocean is limited by iron availability. (2) Carbon uptake and flux is therefore controlled by iron availability (3) In spite of low silicic acid, iron promotes non-silicious phytoplankton growth and the uptake of carbon dioxide. (4) The transport of fixed carbon from the surface layers proceeds with a C:N ratio that would indicate differential remineralization of nitrogen at shallow depths. (5) These finding have major implications for modeling of carbon export based on nitrate utilization. (6) The general results of the experiment indicate that, beyond other southern ocean enrichment experiments, iron inputs have a much wider impact of productivity and carbon cycling than previously demonstrated. Scientific presentations: Coale, K., Johnson, K, …
Date: July 28, 2005
Creator: Coale, Kenneth H.
System: The UNT Digital Library
Tailored terahertz pulses from a laser-modulated electronbeam (open access)

Tailored terahertz pulses from a laser-modulated electronbeam

Interaction of an electron beam with a femtosecond laserpulseco-propagating through a wiggler modulates the electronenergieswithin a short slice of the electron bunch comparable with the durationof the laser pulse (Figure 1). Propagating around an electron storagering, this bunch develops a longitudinal density perturbation due to thedispersion of electron trajectories. Figure 1 shows how this createsfemtosecond electron bunch wings which are used for femtosecond x-raylight. In addition, this density perturbation emits temporally andspatially coherent tera-hertz pulses whichare inherently synchronized tothe modulating laser. This gives us a new way to study coherentsynchrotron radaition, and creates an opportunity for tuning the THzemmission specifically for the needs of a given experiment.
Date: July 19, 2005
Creator: Martin, Michael C.; Byrd, John; Hao, Zhao; Robin, David; Sannibale,Fernando; Schoenlein, Robert W. et al.
System: The UNT Digital Library
Meson Correlation Functions at High Temperatures. (open access)

Meson Correlation Functions at High Temperatures.

We present preliminary results for the correlation- and spectral functions of different meson channels on the lattice. The main focus lies on gaining control over cut-off as well as on the finite-volume effects. Extrapolations of screening masses above the deconfining temperature are guided by the result of the free (T = {infinity}) case on the lattice and in the continuum. We study the quenched non-perturbatively improved Wilson-clover fermion as well as the hypercube fermion action which might show less cut-off effects.
Date: July 25, 2005
Creator: Wissel, S.; Datta, S.; Karsch, F.; Laermann, E. & Shcheredin, S.
System: The UNT Digital Library
Positron Annihilation in the Bipositronium Ps2 (open access)

Positron Annihilation in the Bipositronium Ps2

The electron-positron-pair annihilation in the bipositronium PS2 is considered. In particular, the two-, three-, one- and zero-photon annihilation rates are determined to high accuracy. The corresponding analytical expressions are also presented. Also, a large number of bound state properties have been determined for this system.
Date: July 1, 2005
Creator: Bailey, David H. & Frolov, Alexei M.
System: The UNT Digital Library
STATIC QUARK ANTI-QUARK FREE AND INTERNAL ENERGY IN 2-FLAVOR QCD AND BOUND STATES IN THE QGP. (open access)

STATIC QUARK ANTI-QUARK FREE AND INTERNAL ENERGY IN 2-FLAVOR QCD AND BOUND STATES IN THE QGP.

We present results on heavy quark free energies in 2-flavour QCD. The temperature dependence of the interaction between static quark anti-quark pairs will be analyzed in terms of temperature dependent screening radii, which give a first estimate on the medium modification of (heavy quark) bound states in the quark gluon plasma. Comparing those radii to the (zero temperature) mean squared charge radii of chasmonium states indicates that the J/{Psi} may survive the phase transition as a bound state, while {chi}{sub c} and {Psi}{prime} are expected to show significant thermal modifications at temperatures close to the transition. Furthermore we will analyze the relation between heavy quark free energies, entropy contributions and internal energy and discuss their relation to potential models used to analyze the melting of heavy quark bound states above the deconfinement temperature. Results of different groups and various potential models for bound states in the deconfined phase of QCD are compared.
Date: July 25, 2005
Creator: ZANTOW, F. & KACZMAREK, O.
System: The UNT Digital Library
The Qcd Phase Diagram at Finite Density. (open access)

The Qcd Phase Diagram at Finite Density.

We study the density of states method to explore the phase diagram of the chiral transition on the temperature and quark chemical potential plane. Four quark flavours are used in the analysis. Though the method is quite expensive small lattices show an indication for a triple-point connecting three different phases on the phase diagram.
Date: July 25, 2005
Creator: Schmidt, C.; Fodor, Z. & Katz, S.
System: The UNT Digital Library
Experimental Investigation of the Structural Scattering Due to Impedance Discontinuities on a Cylindrical Shell (open access)

Experimental Investigation of the Structural Scattering Due to Impedance Discontinuities on a Cylindrical Shell

None
Date: July 29, 2005
Creator: Glotzbecker, RJ; Hambric, SA & Pollack, ML
System: The UNT Digital Library
Performance of a Drum Type Packaging with Urethane Foam Overpack Subjected to Crush and Other Regulatory Tests (open access)

Performance of a Drum Type Packaging with Urethane Foam Overpack Subjected to Crush and Other Regulatory Tests

In order to improve the melt rate of high level waste slurry feed being vitrified in the Savannah River Site's (SRS) Defense Waste Processing Facility (DWPF) Melter, a melter glass pump (pump 1) was installed in the DWPF Melter on February 10, 2004. The glass pump increased melt rate by generating a forced convection within the molten glass pool, thereby increasing the heat transfer from the molten glass to the unmolten feed cold cap that is on top of the glass pool. After operating for over four months, the pump was removed on June 22, 2004 due to indications that it had failed. The removed pump exhibited obvious signs of corrosion, had collapsed inward at the glass exit slots at the melt line, and was dog-legged in the same area. This lead to the pump being redesigned to improve its mechanical integrity (increased wall thickness and strength) while maintaining its hydraulic diameter as large as possible. The improved DWPF glass pump (pump 2) was installed on September 15, 2004. The impact of the new design on pump life, along with analysis of the glass pump's impact on melt rate in the DWPF Melter is discussed in this paper.
Date: July 17, 2005
Creator: Allen, Smith
System: The UNT Digital Library
Identification of Severe Multiple Contingencies in Electric PowerNetworks (open access)

Identification of Severe Multiple Contingencies in Electric PowerNetworks

In this paper we propose a two-stage screening and analysis process for identifying multiple contingencies that may result in very severe disturbances and blackouts. In a screening stage we form an optimization problem to find the minimum change in the network to move the power flow feasibility boundary to the present operating point and that will cause the system to separate with a user-specified power imbalance. The lines identified by the optimization program are used in a subsequent analysis stage to find combinations that may lead to a blackout. This approach is applied to a 30-bus system with encouraging results.
Date: July 1, 2005
Creator: Donde, Vaibhav; Lopez, Vanessa; Lesieutre, Bernard; Pinar, Ali; Yang,Chao & Meza, Juan
System: The UNT Digital Library
HEAVY QUARK FREE ENERGIES AND SCREENING AT FINITE TEMPERATURE AND DENSITY. (open access)

HEAVY QUARK FREE ENERGIES AND SCREENING AT FINITE TEMPERATURE AND DENSITY.

We study the free energies of heavy quarks calculated from Polyakov loop correlation functions in full 2-flavour QCD using the p4-improved staggered fermion action. A small but finite baryon number density is included via Taylor expansion of the fermion determinant in the baryo-chemical potential {mu}. For temperatures above T{sub c} we extract Debye screening masses from the large distance behavior of the free energies and compare their {mu}-dependence to perturbative results.
Date: July 25, 2005
Creator: Doring, M.; Ejiri, S.; Kaczmarek, O.; Karsch, F. & Laermann, E.
System: The UNT Digital Library
Rationale for Measuring Duct Leakage Flows in Large Commercial Buildings (open access)

Rationale for Measuring Duct Leakage Flows in Large Commercial Buildings

Industry-wide methods of assessing duct leakage are based on duct pressurization tests, and focus on ''high pressure'' ducts. Even though ''low pressure'' ducts can be a large fraction of the system and tend to be leaky, few guidelines or construction specifications require testing these ducts. We report here on the measured leakage flows from ten large commercial duct systems at operating conditions: three had low leakage (less than 5% of duct inlet flow), and seven had substantial leakage (9 to 26%). By comparing these flows with leakage flows estimated using the industry method, we show that the latter method by itself is not a reliable indicator of whole-system leakage flow, and that leakage flows need to be measured.
Date: July 1, 2005
Creator: Wray, Craig P.; Diamond, Richard C. & Sherman, Max H.
System: The UNT Digital Library
A Combined Experimental and Computational Approach for the Design of Mold Topography that Leads to Desired Ingot Surface and Microstructure in Aluminum Casting. (open access)

A Combined Experimental and Computational Approach for the Design of Mold Topography that Leads to Desired Ingot Surface and Microstructure in Aluminum Casting.

A thermomechanical study of the effects of mold topography on the solidification of Aluminum alloys at early times is provided. The various coupling mechanisms between the solid-shell and mold deformation and heat transfer at the mold/solid-shell interface during the early stages of Aluminum solidification on molds with uneven topographies are investigated. The air-gap nucleation time, the stress evolution and the solid-shell growth pattern are examined for different mold topographies to illustrate the potential control of Aluminum cast surface morphologies during the early stages of solidification using proper design of mold topographies. The unstable shell growth pattern in the early solidification stages results mainly from the unevenness of the heat flux between the solid-shell and the mold surface. This heat flux is determined by the size of the air-gaps formed between the solidifying shell and mold surface or from the value of the contact pressure. Simulation results show that a sinusoidal mold surface with a smaller wavelength leads to nucleation of air-gaps at earlier times. In addition, the unevenness in the solid-shell growth pattern decreases faster for a smaller wavelength. Such studies can be used to tune mold surfaces for the control of cast surface morphologies.
Date: July 12, 2005
Creator: Dr. Zabaras, N. & Tan, L.
System: The UNT Digital Library
Distributed Generation with Heat Recovery and Storage (open access)

Distributed Generation with Heat Recovery and Storage

Electricity generated by distributed energy resources (DER) located close to end-use loads has the potential to meet consumer requirements more efficiently than the existing centralized grid. Installation of DER allows consumers to circumvent the costs associated with transmission congestion and other non-energy costs of electricity delivery and potentially to take advantage of market opportunities to purchase energy when attractive. On-site thermal power generation is typically less efficient than central station generation, but by avoiding non-fuel costs of grid power and utilizing combined heat and power (CHP) applications, i.e., recovering heat from small-scale on-site generation to displace fuel purchases, then DER can become attractive to a strictly cost-minimizing consumer. In previous efforts, the decisions facing typical commercial consumers have been addressed using a mixed-integer linear programme, the DER Customer Adoption Model(DER-CAM). Given the site s energy loads, utility tariff structure, and information (both technical and financial) on candidate DER technologies, DER-CAM minimizes the overall energy cost for a test year by selecting the units to install and determining their hourly operating schedules. In this paper, the capabilities of DER-CAM are enhanced by the inclusion of the option to store recovered low-grade heat. By being able to keep an inventory of heat …
Date: July 29, 2005
Creator: Siddiqui, Afzal; Marnay, Chris; Firestone, Ryan M. & Zhou, Nan
System: The UNT Digital Library
RARE KAON DECAYS. (open access)

RARE KAON DECAYS.

Lepton flavor violation (LFV) experiments have probed sensitivities corresponding to mass scales of well over 100 TeV, making life difficult for models predicting accessible LFV in kaon decay and discouraging new dedicated experiments of this type.
Date: July 19, 2005
Creator: LITTENBERG, L.
System: The UNT Digital Library
A Compact High Gradient Pulsed Magnetic Quadpole (open access)

A Compact High Gradient Pulsed Magnetic Quadpole

A design for a high gradient, low inductance pulsed quadrupole magnet is presented. The magnet is a circular current dominated design with a circular iron return yoke. Conductor angles are determined by a method of direct multipole elimination which theoretically eliminates the first four higher order multipole field components. Coils are fabricated from solid round film-insulated conductor, wound as a single layer ''non-spiral bedstead'' coil having a diagonal leadout entirely within one upturned end. The coils are wound and stretched straight in a special winder, then bent in simple fixtures to form the upturned ends.
Date: July 5, 2005
Creator: Shuman, D.; Faltens, A.; Kajiyama, Y.; Kireeff-Covo, M. & Seidl, P.
System: The UNT Digital Library
Challenges of Investigating Fluid-Elastic Lock-In of a Shallow Cavity and a Cantilevered Beam at Low Mach Numbers (open access)

Challenges of Investigating Fluid-Elastic Lock-In of a Shallow Cavity and a Cantilevered Beam at Low Mach Numbers

This report was prepared to talk about Challenges of Investigating Fluid-Elastic Lock-In of a Shallow Cavity and a Cantilevered Beam at Low Mach Numbers
Date: July 29, 2005
Creator: Cody, K Lai-Fook; Hambric, SA & Pollack, ML
System: The UNT Digital Library
Testing the dynamics of B ->pi pi and constraints onalpha (open access)

Testing the dynamics of B ->pi pi and constraints onalpha

In charmless nonleptonic B decays to {pi}{pi} or {rho}{rho}, the ''color allowed'' and ''color suppressed'' tree amplitudes can be studied in a systematic expansion in {alpha}{sub s}(m{sub b}) and {Lambda}{sub QCD}/m{sub b}. At leading order in this expansion their relative strong phase vanishes. The implications of this prediction are obscured by penguin contributions. They propose to use this prediction to test the relative importance of the various penguin amplitudes using experimental data. The present B {yields} {pi}{pi} data suggest that there are large corrections to the heavy quark limit, which can be due to power corrections to the tree amplitudes, large up-penguin amplitude, or enhanced weak annihilation. Because the penguin contributions are smaller, the heavy quark limit is more consistent with the B {yields} {rho}{rho} data, and its implications may become important for the extraction of {alpha} from this mode in the future.
Date: July 7, 2005
Creator: Grossman, Yuval; Hocker, Andreas; Ligeti, Zoltan & Pirjol, Dan
System: The UNT Digital Library
NNDC PERSPECTIVE ON NUCLEAR REACTION DATABASES AND ORELA. (open access)

NNDC PERSPECTIVE ON NUCLEAR REACTION DATABASES AND ORELA.

We discuss perspective of the National Nuclear Data Center on nuclear reaction databases, focusing on contributions from the ORELA machine over more than 3 decades. We conclude that ORELA had profound impact on nuclear reaction databases, in particular CSISRS and ENDF. In addition, ORELA contributed considerable amount of data included in the recent Atlas of Neutron Resonances, along with data of critical importance for nuclear reaction model calculations by codes such as EMPIRE.
Date: July 14, 2005
Creator: OBLOZINSKY, P.
System: The UNT Digital Library
Quantum Dots-based Reverse Phase Protein Microarray (open access)

Quantum Dots-based Reverse Phase Protein Microarray

CdSe nanocrystals, also called quantum dots (Qdots) are a novel class of fluorophores, which have a diameter of a few nanometers and possess high quantum yield, tunable emission wavelength and photostability. They are an attractive alternative to conventional fluorescent dyes. Quantum dots can be silanized to be soluble in aqueous solution under biological conditions, and thus be used in bio-detection. In this study, we established a novel Qdot-based technology platform that can perform accurate and reproducible quantification of protein concentration in a crude cell lysate background. Protein lysates have been spiked with a target protein, and a dilution series of the cell lysate with a dynamic range of three orders of magnitude has been used for this proof-of-concept study. The dilution series has been spotted in microarray format, and protein detection has been achieved with a sensitivity that is at least comparable to standard commercial assays, which are based on horseradish peroxidase (HRP) catalyzed diaminobenzidine (DAB) chromogenesis. The data obtained through the Qdot method has shown a close linear correlation between relative fluorescence unit and relative protein concentration. The Qdot results are in almost complete agreement with data we obtained with the well-established HRP-DAB colorimetric array (R{sup 2} = 0.986). …
Date: July 15, 2005
Creator: Shingyoji, Masato; Gerion, Daniele; Pinkel, Dan; Gray, Joe W. & Chen, Fanqing
System: The UNT Digital Library