Recent advances in fabrication of high-T{sub c} superconductors for electric power applications. (open access)

Recent advances in fabrication of high-T{sub c} superconductors for electric power applications.

The U.S. Department of Energy (DOE) supports an applied superconductivity program entitled ''Superconductivity Program for Electric Power Systems.'' Activities within this program contribute to development of the high-temperature superconductor (HTS) technology needed for industry to proceed with the commercial development of electric power applications such as motors, generators, transformers, transmission cables, and current limiters. Research is conducted in three categories: wire development, systems technology development, and Superconductivity Partnership Initiative (SPI). Wire development activities are devoted to improving the critical current density (J{sub c}) of short-length HTS wires, whereas systems technology development focuses on fabrication of long-length wires, coils, and on magnets. The SPI activities are aimed at development of prototype products. Significant progress has been made in the development of (HTSs) for various applications: some applications have already made significant strides in the marketplace, while others are still in the developmental stages. For successful electric power applications, it is very important that the HTS be fabricated into long-length conductors that exhibit desired superconducting and mechanical properties. Several parameters of the PIT technique must be carefully controlled to obtain the desired properties. Long lengths of Bi-2223 tapes with respectable superconducting properties have been fabricated by a carefully designed thermomechanical treatment process. …
Date: March 25, 1998
Creator: Balachandran, U.
System: The UNT Digital Library
Fracture and Creep of an Al{sub 2}O{sub 3}-SiC(whisker)-TiC(particle) Composite. (open access)

Fracture and Creep of an Al{sub 2}O{sub 3}-SiC(whisker)-TiC(particle) Composite.

High-temperature fracture strength and compressive creep of an electrodischarge-machinable composite, Al{sub 2}O{sub 3}-30.9 vol.% SiC whiskers-23 vol.% TiC particles have been studied to 1200 C and 1450 C, respectively, in inert atmosphere. Microstructures of fractured and deformed specimens were examined by scanning and transmission electron microscopy. Fast fracture occurred at T {le} 1200 C. Steady-state creep was achieved for T > 1350 C at stresses < 80 MPa, with the rate-controlling mechanism being partially unaccommodated grain-boundary sliding, with a stress exponent of {approx}1 and an activation energy of {approx}470 kJ/mol.
Date: February 25, 1998
Creator: de Arellano-Lopez, A. R.
System: The UNT Digital Library
High charge short electron bunches for wakefield accelerator structures development. (open access)

High charge short electron bunches for wakefield accelerator structures development.

The Argonne Wakefield Accelerator group develops accelerating structures based on dielectric loaded waveguides. We use high charge short electron bunches to excite wakefields in dielectric loaded structures, and a second (low charge) beam to probe the wakefields left behind by the drive beam. We report measurements of beam parameters and also initial results of the dielectric loaded accelerating structures. We have studied acceleration of the probe beam in these structures and we have also made measurements on the RF pulses that are generated by the drive beam. Single drive bunches, as well as multiple bunches separated by an integer number of RF periods have been used to generate the accelerating wakefields.
Date: September 25, 1998
Creator: Conde, M. E.
System: The UNT Digital Library
Impact of mental representational systems on design interface. (open access)

Impact of mental representational systems on design interface.

The purpose of the studies conducted at Argonne National Laboratory is to understand the impact mental representational systems have in identifying how user comfort parameters influence how information is to best be presented. By understanding how each individual perceives information based on the three representational systems (visual, auditory and kinesthetic modalities), it has been found that a different approach must be taken in the design of interfaces resulting in an outcome that is much more effective and representative of the users mental model. This paper will present current findings and future theories to be explored.
Date: February 25, 1998
Creator: Brown-VanHoozer, S. A.
System: The UNT Digital Library
Design and construction of a pipeline for transfer of radioactive sodium at Argonne National Laboratory-West. (open access)

Design and construction of a pipeline for transfer of radioactive sodium at Argonne National Laboratory-West.

Experimental Breeder Reactor-II (EBR-II), an experimental sodium cooled fast breeder reactor located at Argonne National Laboratory-West (ANL-W), was shut down in 1994, and has since been defueled in preparation for final plant closure. Approximately 100,000 gallons of liquid sodium is contained in the primary and secondary cooling systems of the EBR-II plant. The liquid sodium must be drained from the reactor systems during closure of the plant to place the reactor plant in an industrially and radiologically safe condition for long term storage or dismantlement. Because the liquid sodium is a listed waste under the Resource Conservation Recovery Act (RCRA), it is not suitable for disposal. It therefore must be transferred to the Sodium Process Facility (SPF), which is located approximately nine hundred feet from the reactor complex, where it will be processed into a non-reactive form, suitable for land disposal in Idaho. To facilitate this transfer, a heated pipeline for carrying liquid sodium metal from EBR-II to the SPF was designed and installed. The SPF was originally designed and built to process primary sodium from the Fermi-1 reactor. The sodium is stored at ANL-W in 55 gallon drums. Design of the SPF did not originally accommodate processing of EBR-II …
Date: February 25, 1998
Creator: Baily, C. E.
System: The UNT Digital Library
Laser scattering detection and characterization of defects and machining damage in silicon nitride components. (open access)

Laser scattering detection and characterization of defects and machining damage in silicon nitride components.

It is known that surface and subsurface damage in machined silicon nitride (Si{sub 3}N{sub 4}) ceramic components can significantly affect component strength and lifetime. Because Si{sub 3}N{sub 4} may transmit some light into its subsurface, they have developed an elastic optical scattering technique to provide two-dimensional image data for detecting surface or subsurface defects and machining damage. This technique has been used to analyze diamond-ground Si{sub 3}N{sub 4} specimens subjected to various machining conditions. The results were compared with photomicroscopy data for detect characterization and were correlated with machining conditions.
Date: November 25, 1998
Creator: Sun, J. G.
System: The UNT Digital Library
PNC in hydrogen. different prospects using heliumlike ions. (open access)

PNC in hydrogen. different prospects using heliumlike ions.

The motivation for parity experiments in simple atomic systems is that the atomic physics is known precisely so they directly test the weak interactions. We review the status of the parity experiments that have been done in atomic hydrogen and suggest some possibilities for experiments in helium like ions.
Date: September 25, 1998
Creator: Dunford, R. W.
System: The UNT Digital Library
Imprinting artificial magnetic structures. (open access)

Imprinting artificial magnetic structures.

Recently we created La/Fe multilayers with a helical magnetic structure imprinted from the conditions of growth rather than by the magnetic interactions between layers. Each sublayer was 30{angstrom} thick, and during deposition the sample was rotated in an external field of 3 Oe. a field strong enough to magnetize the Fe layer being deposited but not sufficient to perturb the magnetization of the Fe layers already grown. As a result adjacent Fe layers formed a helical structure with a chirality and periodicity determined by the rotational direction and speed of the substrate and the rate of deposition. Following this discovery, an extensive set of experiments (mainly using Kerr effect magnetometry and polarized neutron reflectivity) was undertaken to ascertain the stability of imprinted magnetic structures, and to understand the onset of magnetization during growth. La/Fe imprinted helical magnetic structures (of different La and Fe thicknesses) were found to be stable in time and to be permanently erased only by magnetic fields larger than 90 Oe.
Date: September 25, 1998
Creator: Lohstroh, W.
System: The UNT Digital Library
Magnetic spiral structures in La/Fe multilayers. (open access)

Magnetic spiral structures in La/Fe multilayers.

The magnetic properties of La/Fe multilayers were tested by magneto-optical Kerr effect and polarized neutron reflectometry. The experiments indicated that above a layer thickness t{sub la} = 25{angstrom} the magnetic state of the virgin sample is represented by a spiral-like arrangement of magnetizations of subsequent Fe layers, whereas each Fe layer itself is ferromagnetic. Polarized neutron reflectometry shows that the helix has predominantly one chirality over the entire surface area of several cm{sup 2}. Tine magnetic spiral structure is imprinted during the growth process by rotating the sample in a small residual magnetic field. External magnetic field of 90 Oe are sufficient to erase the magnetic structure irreversibly.
Date: September 25, 1998
Creator: Lohstroh, W.
System: The UNT Digital Library
High-spin states in {sup 71}As, {sup 72}Se, and {sup 72}Br. (open access)

High-spin states in {sup 71}As, {sup 72}Se, and {sup 72}Br.

The {sup 16}O + {sup 58}Ni reaction was used to study yrast and non-yrast excitations in {sup 71}As, {sup 72}Se, and {sup 72}Br. High-spin yrast and negative-parity non-yrast bands were observed in {sup 72}Se. The F{sub 7/2} proton extruder orbital was identified in {sup 71}As. The odd-even staggering in the {pi}g{sub 9/2}{nu}g{sub 9/2} decoupled band in {sup 72}Br is compared with similar structures in heavier Br isotopes.
Date: August 25, 1998
Creator: Fotiades, N.
System: The UNT Digital Library
Determining Pu-239 content by resonance transmission analysis using a filtered reactor beam. (open access)

Determining Pu-239 content by resonance transmission analysis using a filtered reactor beam.

A novel technique has been developed at Argonne National Laboratory to determine the {sup 239}Pu content in EBR-II blanket elements using resonance transmission analysis (RTA) with a filtered reactor beam. The technique uses cadmium and gadolinium filters along with a {sup 239}Pu fission chamber to isolate the 0.3 eV resonance in {sup 239}Pu. In the energy range from 0.1 to 0.5 eV, the total microscopic cross-section of {sup 239}Pu is significantly larger than the cross-sections of {sup 238}U and {sup 235}U. This large difference in cross-section allows small amounts of {sup 239}Pu to be detected in uranium samples. Tests using a direct beam from a 250 kW TRIGA reactor have been performed with stacks of depleted uranium and {sup 239}Pu foils. Preliminary measurement results are in good agreement with the predicted results up to about two weight percent of {sup 239}Pu in the sample. In addition, measured {sup 239}Pu masses were in agreement with actual sample masses with uncertainties less than 3.8 percent.
Date: November 25, 1998
Creator: Klann, R. T.
System: The UNT Digital Library
Quantum Monte Carlo calculations of light nuclei. (open access)

Quantum Monte Carlo calculations of light nuclei.

Quantum Monte Carlo calculations using realistic two- and three-nucleon interactions are presented for nuclei with up to eight nucleons. We have computed the ground and a few excited states of all such nuclei with Greens function Monte Carlo (GFMC) and all of the experimentally known excited states using variational Monte Carlo (VMC). The GFMC calculations show that for a given Hamiltonian, the VMC calculations of excitation spectra are reliable, but the VMC ground-state energies are significantly above the exact values. We find that the Hamiltonian we are using (which was developed based on {sup 3}H, {sup 4}He, and nuclear matter calculations) underpredicts the binding energy of p-shell nuclei. However our results for excitation spectra are very good and one can see both shell-model and collective spectra resulting from fundamental many-nucleon calculations. Possible improvements in the three-nucleon potential are also be discussed.
Date: August 25, 1998
Creator: Pieper, S. C.
System: The UNT Digital Library
Large NMR signals and polarization asymmetries. (open access)

Large NMR signals and polarization asymmetries.

A large modulation in the series Q-meter can lead to nonlinear NMR signals and asymmetric polarization values. With a careful circuit analysis the nonlinearity can be estimated and corrections to polarization can be determined as a function of the strength of the modulation. We describe the recent LAMPF polarized proton target experiment, its NMR measurement and corrections to the measured polarizations.
Date: November 25, 1998
Creator: Penttila, S. I.
System: The UNT Digital Library
A numerical study of short residence time FCC riser flows with a new flow/kinetics modeling technique. (open access)

A numerical study of short residence time FCC riser flows with a new flow/kinetics modeling technique.

Fluid Catalytic Cracking (FCC) technology is the most important process used by the refinery industry to convert crude oil to valuable lighter products such as gasoline. New and modified processes are constantly developed by refinery companies to improve their global competitiveness and meet more stringent environmental regulations. Short residence time FCC riser reactor is one of the advanced processes that the refining industry is actively pursuing because it can improve the yield selectivity and efficiency of an FCC unit. However, as the residence time becomes shorter, the impact of the mixing between catalyst and feed oil at the feed injection region on the product yield becomes more significant. Currently, most FCC computer models used by the refineries perform sophisticated kinetic calculations on simplified flow field and can not be used to evaluate the impact of fluid mixing on the performance of an FCC unit. Argonne National Laboratory (AFL) is developing a computational fluid dynamic (CFD) code ICRKFLO for FCC riser flow modeling. The code, employing hybrid hydrodynamic-chemical kinetic coupling techniques, is used to investigate the effect of operating and design conditions on the product yields of FCC riser reactors. Numerical calculations were made using the code to examine the impacts …
Date: August 25, 1998
Creator: Chang, S. L.
System: The UNT Digital Library
Laser system for a subpicosecond electron linac. (open access)

Laser system for a subpicosecond electron linac.

At the Argonne Chemistry Division efforts are underway to develop a sub-picosecond electron beam pulse radiolysis facility for chemical studies. The target output of the accelerator is to generate electron pulses that can be adjusted from 3nC in .6ps to 100nC in 45ps. In conjunction with development of the accelerator a state-of-the-art ultrafast laser system is under construction that will drive the linac's photocathode and provide probe pulses that are tunable from the UV to IR spectral regions.
Date: September 25, 1998
Creator: Crowell, R. A.
System: The UNT Digital Library
The measurement of the mass of the W boson from the Tevatron. (open access)

The measurement of the mass of the W boson from the Tevatron.

This paper presents measurements of the mass of the W vector boson from the CDF and D0 experiments using data collected at {radical}s = 1.8 TeV during the 1994-1995 data taking run. CDF finds a preliminary mass of M{sub W} = 80.43 {+-} 0.16 GeV and D0 measures a mass of M{sub W} = 80.44 {+-} 0.12 GeV.
Date: August 25, 1998
Creator: Thurman-Keup, R.
System: The UNT Digital Library
The role of selected f ions in the suppression of high-Tc superconductivity. (open access)

The role of selected f ions in the suppression of high-Tc superconductivity.

The initial observations of superconductivity at temperatures above 77 K in copper-oxide based materials was surprising from a variety of different perspectives. Among the unexpected findings were reports of superconductivity for the series RBa{sub 2}Cu{sub 3}O{sub 7} where R is a rare earth (Y, Nd-Tm), which may carry a large, local magnetic moment. Superconductivity was subsequently demonstrated for all 4f analogs in this series except Ce, Pr, and Tb. In addition to the RBa{sub 2}Cu{sub 3}O{sub 7} series, there are several other CuO based series of superconductors that are formed by substituting R ions. The most studied of these are listed in Table 1, together with the f ions that form isostructural compounds and their superconducting critical temperatures (T{sub c}). The presence of an R ion with a large magnetic moment does not significantly influence the superconductivity. In contrast, even the presence of small concentrations of magnetic impurity ions in a conventional superconductor inhibits superconductivity by interfering with the formation of Cooper pairs. Most R ions substitute into an isostructural series with no observable effect on the superconducting properties of the material. As can be seen from Table 1, there are notable exceptions to this observation. In particular, the rare-earth …
Date: September 25, 1998
Creator: Soderholm, L.
System: The UNT Digital Library
A numerical investigation of the scale-up effects on flow, heat transfer, and kinetics processes of FCC units. (open access)

A numerical investigation of the scale-up effects on flow, heat transfer, and kinetics processes of FCC units.

Fluid Catalytic Cracking (FCC) technology is the most important process used by the refinery industry to convert crude oil to valuable lighter products such as gasoline. Process development is generally very time consuming especially when a small pilot unit is being scaled-up to a large commercial unit because of the lack of information to aide in the design of scaled-up units. Such information can now be obtained by analysis based on the pilot scale measurements and computer simulation that includes controlling physics of the FCC system. A Computational fluid dynamic (CFD) code, ICRKFLO, has been developed at Argonne National Laboratory (ANL) and has been successfully applied to the simulation of catalytic petroleum cracking risers. It employs hybrid hydrodynamic-chemical kinetic coupling techniques, enabling the analysis of an FCC unit with complex chemical reaction sets containing tens or hundreds of subspecies. The code has been continuously validated based on pilot-scale experimental data. It is now being used to investigate the effects of scaled-up FCC units. Among FCC operating conditions, the feed injection conditions are found to have a strong impact on the product yields of scaled-up FCC units. The feed injection conditions appear to affect flow and heat transfer patterns and the …
Date: August 25, 1998
Creator: Chang, S. L.
System: The UNT Digital Library
Resonant excitation of plasma wakefields using multiple electron bunches. (open access)

Resonant excitation of plasma wakefields using multiple electron bunches.

We plan to resonantly excite plasma wakefields using a train of electron bunches separated by an-integer number of plasma wavelengths. The multiple electron bunches are generated by a photocathode based RF gun by splitting the laser beam into temporally separated pulses. The amplitude of the wakefields generated by the sequence of bunches is expected to be higher than that generated if all charge had been in only one bunch, because this single bunch would be considerably longer than the individual sub-bunches due to space charge effects in our gun.
Date: September 25, 1998
Creator: Conde, M. E.
System: The UNT Digital Library
Adaptive Remote-Sensing Techniques Implementing Swarms of Mobile Agents (open access)

Adaptive Remote-Sensing Techniques Implementing Swarms of Mobile Agents

In many situations, stand-off remote-sensing and hazard-interdiction techniques over realistic operational areas are often impractical "and difficult to characterize. An alternative approach is to implement an adap- tively deployable array of sensitive agent-specific devices. Our group has been studying the collective be- havior of an autonomous, multi-agent system applied to chedbio detection and related emerging threat applications, The current physics-based models we are using coordinate a sensor array for mukivanate sig- nal optimization and coverage as re,alized by a swarm of robots or mobile vehicles. These intelligent control systems integrate'glob"ally operating decision-making systems and locally cooperative learning neural net- works to enhance re+-timp operational responses to dynarnical environments examples of which include obstacle avoidance, res~onding to prevailing wind patterns, and overcoming other natural obscurants or in- terferences. Collectively',tkensor nefirons with simple properties, interacting according to basic community rules, can accomplish complex interconnecting functions such as generalization, error correction, pattern recognition, sensor fusion, and localization. Neural nets provide a greater degree of robusmess and fault tolerance than conventional systems in that minor variations or imperfections do not impair performance. The robotic platforms would be equipped with sensor devices that perform opticaI detection of biologicais in combination with multivariate chemical analysis tools …
Date: November 25, 1998
Creator: Asher, R. B.; Cameron, S. M.; Loubriel, G. M.; Robinett, R. D.; Stantz, K. M.; Trahan, M. W. et al.
System: The UNT Digital Library
Fatigue and fracture of fiber composites under combined interlaminar stresses (open access)

Fatigue and fracture of fiber composites under combined interlaminar stresses

As part of efforts to develop a three-dimensional failure model for composites, a study of failure and fatigue due to combined interlaminar stresses was conducted. The combined stresses were generated using a hollow cylindrical specimen, which was subjected to normal compression and torsion. For both glass and carbon fiber composites, normal compression resulted in a significant enhancement in the interlaminar shear stress and strain at failure. Under moderate compression levels, the failure mode transitioned from elastic to plastic. The observed failure envelope could not be adequately captured using common ply- level failure models. Alternate modeling approaches were examined and it was found that a pressure-dependent failure criterion was required to reproduce the experimental results. The magnitude of the pressure-dependent terms of this model was found to be material dependent. The interlaminar shear fatigue behavior of a carbon/epoxy system was also studied using the cylindrical specimen. Preliminary results indicate that a single S/N curve which is normalized for interlaminar shear strength may be able to reproduce the effects of both temperature and out-of-plane compression on fatigue life. The results demonstrate that there are significant gains to be made in improving interlaminar strengths of composite structures by applying out-of-plane compression. This effect …
Date: June 25, 1998
Creator: DeTeresa, S J; Freeman, D C & Groves, S E
System: The UNT Digital Library
Atomistic simulations for multiscale modeling in bcc metal (open access)

Atomistic simulations for multiscale modeling in bcc metal

Quantum-based atomistic simulations are being used to study fundamental deformation and defect properties relevant to the multiscale modeling of plasticity in bcc metals at both ambient and extreme conditions. Ab initio electronic-structure calculations on the elastic and ideal-strength properties of Ta and Mo help constrain and validate many-body interatomic potentials used to study grain boundaries and dislocations. The predicted C(capital Sigma)5 (310)[100] grain boundary structure for Mo has recently been confirmed in HREM measurements. The core structure, (small gamma) surfaces, Peierls stress, and kink-pair formation energies associated with the motion of a/2(111) screw dislocations in Ta and Mo have also been calculated. Dislocation mobility and dislocation junction formation and breaking are currently under investigation.
Date: September 25, 1998
Creator: Belak, J.; Moriarty, J.A.; Soderlind, P.; Xu, W.; Yang, L.H. & Zhu
System: The UNT Digital Library
Collaboratory for support of scientific research (open access)

Collaboratory for support of scientific research

Collaboration is an increasingly important aspect of magnetic fusion energy research. With the increased size and cost of experiments needed to approach reactor conditions, the numbers being constructed has become limited. In order to satisfy the desire for many groups to conduct research on these facilities, we have come to rely more heavily on collaborations. Fortunately, at the same time, development of high performance computers and fast and reliable wide area networks has provided technological solutions necessary to support the increasingly distributed work force without the need for relocation of entire research staffs. Development of collaboratories, collaborative or virtual laboratories, is intended to provide the capability needed to interact from afar with colleagues at multiple sites. These technologies are useful to groups interacting remotely during experimental operations as well as to those involved in the development of analysis codes and large scale simulations The term ``collaboratory`` refers to a center without walls in which researchers can perform their studies without regard to geographical location - interacting with colleagues, accessing instrumentation, sharing data and computational resources, and accessing information from digital libraries [1],[2]. While it is widely recognized that remote collaboration is not a universal replacement for personal contact, it does …
Date: June 25, 1998
Creator: Casper, T. A.; Meyer, W. H. & Moller, J. M.
System: The UNT Digital Library
Strongly-driven laser plasma coupling (open access)

Strongly-driven laser plasma coupling

An improved understanding of strongly-driven laser plasma coupling is important for optimal use of the National Ignition Facility (NIF) for both inertial fusion and for a variety of advanced applications. Such applications range from high energy x- ray sources and high temperature hohlraums to fast ignition and laser radiography. We discuss a novel model for the scaling of strongly-driven stimulated Brillouin and Raman scattering. This model postulates an intensity dependent correlation length associated with spatial incoherence due to filamentation and stimulated forward scattering. We first motivate the model and then relate it to a variety of experiments. Particular attention is paid to high temperature hohlraum experiments, which exhibited low to modest stimulated Brillouin scattering even though this instability was strongly driven. We also briefly discuss the strongly nonlinear interaction physics for efficient generation of high energy electrons either _ by irradiating a large plasma with near quarter-critical density or by irradiating overdense targets with ultra intense laser
Date: June 25, 1998
Creator: Suter, L; Afeyan, B; Campbell, E M; Decker, C D; Kruer, W L; Moody, J et al.
System: The UNT Digital Library