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Nuclear excitation by electronic transition (NEET).
We present a report on recent measurements using the Advanced Photon Source at Argonne National Laboratory to explore the phenomenon of Nuclear Excitation by Electronic Transition (NEET) in the {sup 189}Os atomic/nuclear system.
Date:
April 28, 1999
Creator:
Ahmad, I.; Dunford, R. W.; Esbensen, H.; Gemmell, D. S.; Kanter, E. P.; Kraessig, B. et al.
Object Type:
Article
System:
The UNT Digital Library
The status of APS, BESSRC, and NEET.
We present a brief summary of the current status of the Advanced Photon Source (APS) at Argonne National Laboratory and of the facilities at two of the APS sectors operated by the Basic Energy Sciences Synchrotrons Radiation Center (BESSRC). This is followed by a report on recent measurements at BESSRC on the phenomenon of Nuclear Excitation by Electronic Transition (NEET).
Date:
March 10, 1999
Creator:
Ahmad, I.; Dunford, R. W.; Esbensen, H.; Gemmell, D. S.; Kanter, E. P.; Kraessig, B. et al.
Object Type:
Article
System:
The UNT Digital Library
Measurement of the {sup 44}Ti half-life and its significance for supernova.
In 1998, we reported the three-laboratory measurement of the {sup 44}Ti half-life which was determined relative to the well known value (5.2714 {+-} 0.0005 yr) of the {sup 60}Co half-life. We have continued the measurement at Argonne and Jerusalem and inclusion of data points for additional two years does not change our published value of 59.0 {+-} 0.6 yr.
Date:
August 28, 1999
Creator:
Ahmad, I.; Greene, J. P.; Kutschera, W. & Paul, M.
Object Type:
Article
System:
The UNT Digital Library
TELEMASP Bulletin, Volume 6, Number 5, August/September 1999
Monthly bulletin issued to address topics related to law enforcement. This issue discusses "Family Violence Units" addressing the documented history of family violence and how to address it.
Date:
August 1999
Creator:
Ahmad, Janice & Mullings, Janet L.
Object Type:
Journal/Magazine/Newsletter
System:
The Portal to Texas History
PARTICLE TRANSPORT AND DEPOSITION IN THE HOT-GAS FILTER AT WILSONVILLE
Particle transport and deposition in the Wilsonville hot-gas filter vessel is studied. The filter vessel contains a total of 72 filters, which are arranged in two tiers. These are modeled by six upper and one lower cylindrical effective filters. An unstructured grid of 312,797 cells generated by GAMBIT is used in the simulations. The Reynolds stress model of FLUENT{trademark} (version 5.0) code is used for evaluating the gas mean velocities and root mean-square fluctuation velocities in the vessel. The particle equation of motion includes the drag, the gravitational and the lift forces. The turbulent instantaneous fluctuation velocity is simulated by a filtered Gaussian white-noise model provided by the FLUENT code. The particle deposition patterns are evaluated, and the effect of particle size is studied. The effect of turbulent dispersion, the lift force and the gravitational force are analyzed. The results show that the deposition pattern depends on particle size. Turbulent dispersion plays an important role in transport and deposition of particles. Lift and gravitational forces affect the motion of large particles, but has no effect on small particles.
Date:
June 24, 1999
Creator:
Ahmadi, Goodarz
Object Type:
Report
System:
The UNT Digital Library
Dynamics of H abstraction from alcohols (CH3OH, C2H5OH and 2-C3H7OH) using velocity map imaging in crossed molecular beams
The crossed beam reactions of ground state Cl ({sup 2}P{sub 3/2}) atoms with alcohols (CH{sub 3}OH, C{sub 2}H{sub 5}OH and 2-C{sub 3}H{sub 7}OH) have been studied using the technique of velocity map imaging (VELMI). The corresponding hydroxyalkyl radical was detected via single photon ionization using 157 nm laser light. The double differential cross sections were obtained at collision energies of 8.7 kcal/mol for methanol, 6.0 and 9.7 kcal/mol for ethanol, and 11.9 kcal/mol for 2-propanol. In all cases, the scattering was predominantly in the backward-sideways direction suggesting direct rebound dynamics, with varying amounts of sideways-scattering. In the case of methanol, the angular distributions were predominantly in the sideways-backward direction with respect to the incoming alcohol beam. Scattering was into the backward hemisphere at the lower collision energy for ethanol, with enhancement of sideways scattering with an increase in collision energy. Isoropanol gave scattering predominantly in the backward direction. Coupling between the translational energy and angular distributions was particularly significant for ethanol at the lower collision energy. All of the translational energy distributions peaked at about 6 kcal/mol and on average 30-40% of the available energy was deposited into product translation for all the alcohols studied. These results are contrasted with …
Date:
September 1, 1999
Creator:
Ahmed, M.; Peterka, D. S. & Suits, A. G.
Object Type:
Article
System:
The UNT Digital Library
Fuel-flexible partial oxidation reforming of hydrocarbons for automotive applications.
Micro-reactor tests indicate that our partial oxidation catalyst is fuel-flexible and can reform conventional (gasoline and diesel) and alternative (ethanol, methanol, natural gas) fuels to hydrogen rich product gases with high hydrogen selectivity. Alcohols are reformed at lower temperatures (< 600 C) while alkanes and unsaturated hydrocarbons require slightly higher temperatures. Cyclic hydrocarbons and aromatics have also been reformed at relatively low temperatures, however, a different mechanism appears to be responsible for their reforming. Complex fuels like gasoline and diesel, which are mixtures of a broad range of hydrocarbons, require temperatures of > 700 C for maximum hydrogen production.
Date:
June 7, 1999
Creator:
Ahmed, S.; Carter, J. D.; Kopasz, J. P.; Krumpelt, M. & Wilkenhoener, R.
Object Type:
Article
System:
The UNT Digital Library
Partial Oxidation Fuel Reforming for Automotive Power Systems
For widespread use of fuel cells to power automobiles in the near future, it is necessary to convert gasoline or other transportation fuels to hydrogen on-board the vehicle. Partial oxidation reforming is particularly suited to this application as it eliminates the need for heat exchange at high temperatures. Such reformers offer rapid start and good dynamic performance. Lowering the temperature of the partial oxidation process, which requires the development of a suitable catalyst, can increase the reforming efficiency. Catalytic partial oxidation (or autothermal) reformers and non-catalytic partial oxidation reformers developed by various organizations are presently undergoing testing and demonstration. This paper summarizes the process chemistries as well as recent test data from several different reformers operating on gasoline, methanol, and other fuels.
Date:
September 7, 1999
Creator:
Ahmed, S.; Chalk, S.; Krumpelt, M.; Kumar, R. & Milliken, J.
Object Type:
Article
System:
The UNT Digital Library
Gas-to-liquids synthetic fuels for use in fuel cells : reformability, energy density, and infrastructure compatibility.
The fuel cell has many potential applications, from power sources for electric hybrid vehicles to small power plants for commercial buildings. The choice of fuel will be critical to the pace of its commercialization. This paper reviews the various liquid fuels being considered as an alternative to direct hydrogen gas for the fuel cell application, presents calculations of the hydrogen and carbon dioxide yields from autothermal reforming of candidate liquid fuels, and reports the product gas composition measured from the autothermal reforming of a synthetic fuel in a micro-reactor. The hydrogen yield for a synthetic paraffin fuel produced by a cobalt-based Fischer-Tropsch process was found to be similar to that of retail gasoline. The advantages of the synthetic fuel are that it contains no contaminants that would poison the fuel cell catalyst, is relatively benign to the environment, and could be transported in the existing fuel distribution system.
Date:
September 8, 1999
Creator:
Ahmed, S.; Kopasz, J. P.; Russell, B. J. & Tomlinson, H. L.
Object Type:
Article
System:
The UNT Digital Library
Liquid fuel reformer development.
At Argonne National Laboratory we are developing a process to convert hydrocarbon fuels to a clean hydrogen feed for a fuel cell. The process incorporates a partial oxidation/steam reforming catalyst that can process hydrocarbon feeds at lower temperatures than existing commercial catalysts. We have tested the catalyst with three diesel-type fuels: hexadecane, low-sulfur diesel fuel, and a regular diesel fuel. We achieved complete conversion of the feed to products. Hexadecane yielded products containing 60% hydrogen on a dry, nitrogen-free basis at 800 C. For the two diesel fuels, higher temperatures, >850 C, were required to approach similar levels of hydrogen in the product stream. At 800 C, hydrogen yield of the low sulfur diesel was 32%, while that of the regular diesel was 52%. Residual products in both cases included CO, CO{sub 2}, ethane, ethylene, and methane.
Date:
July 30, 1999
Creator:
Ahmed, S.; Krumpelt, M.; Pereira, C. & Wilkenhoener, R.
Object Type:
Article
System:
The UNT Digital Library
Fuel processing for fuel cell powered vehicles.
A number of auto companies have announced plans to have fuel cell powered vehicles on the road by the year 2004. The low-temperature polymer electrolyte fuel cells to be used in these vehicles require high quality hydrogen. Without a hydrogen-refueling infrastructure, these vehicles need to convert the available hydrocarbon fuels into a hydrogen-rich gas on-board the vehicle. Earlier analysis has shown that fuel processors based on partial oxidation reforming are well suited to meet the size and weight targets and the other performance-related needs of on-board fuel processors for light-duty fuel cell vehicles (1).
Date:
January 22, 1999
Creator:
Ahmed, S.; Wilkenhoener, R.; Lee, S. H. D.; Carter, J. D.; Kumar, R. & Krumpelt, M.
Object Type:
Article
System:
The UNT Digital Library
Protected silver coatings for flashlamp-pumped Nd: glass amplifiers
None
Date:
July 1, 1999
Creator:
Ahre, D; Erlandson, A; Farmer, J; Fix, D; Gregg, H; Marshall, C et al.
Object Type:
Article
System:
The UNT Digital Library
Recombination Lifetime of InxGa1-xAs Alloys Used in Thermophotovoltaic Converters
The family of ternary compounds of composition InxGa1-xAs are of considerable interest for thermophotovoltaic energy converters. The recombination lifetimes of the various compositions are critical to the successful application of these materials as efficient converters. Here we will describe experimental results on the composition. In0.53Ga0.47 that is lattice-matched to InP. We will also describe lifetime results on the compositions In0.68Ga0.32As, with bandgap of 0.60 eV to compositions In0.78Ga0.22As with a bandgap of 0.50 eV. Double heterostructure confinement devices have been made over a range of both n- and p-type doping. These results are preliminary, but the goal is to obtain the radiative and Auger recombination coefficients for the alloys in this composition range.
Date:
February 16, 1999
Creator:
Ahrenkiel, R. K.; Ellingson, R.; Johnston, S.; Webb, J.; Carapella, J. & Wanlass, M.
Object Type:
Article
System:
The UNT Digital Library
Characterizing Composition Modulations in InAs/AIAs Short-Period Superlattices
The formation of quantum wires has much interest due to their novel electronic properties which may lead to enhanced optoelectronic device performance and greater photovoltaic efficiencies. One method of forming these structures is through spontaneous lateral modulation found during the epitaxial growth of III/V alloys. In this paper, we report and summarize our investigations on the formation of lateral moduation in the MBE grown InAlAs/InP(001) system. This system was grown as a short-period superlattice where n-monolayers of InAs are deposited followed by m-Monolayers of AlAs (with n and m~2) and this sequence is repeated to grown a low strain InAlAs ternary alloy on InP(001) that exhibits lateral modulation. Films were grown under a variety of condition (growth temperature, effective alloy composition, superlattice period, and growth rate). These films have been extensively analyzed using X-ray diffraction, atomic force microscopy, and transmission electron microscopy (TEM) and microcharacterization, in addition to photon-based spectroscopes. Here we present results of several microstructural characterizations using a wide range of TEM-based techniques, and compare them to results from the other methods to obtain a unified understanding of composition modulation. Two strong points consistently emerge: 1) The lateral modulation wavelength is insensitive to growth temperature and effective alloy …
Date:
April 26, 1999
Creator:
Ahrenkiel, S. P.; Follstaedt, D. M.; Jones, E. D.; Lee, S. R.; Mascarenhas, A.; Mirecki-Millunchick, J. et al.
Object Type:
Article
System:
The UNT Digital Library
Photoluminescence Studies of Lateral Composition Modulated Short-Period AlAs/InAs Superlattices
We present low temperature photoluminescence data for a series of spontaneous lateral composition modulation in (AlAs){sub m}/(InAs){sub n} short period superlattices on InP with differing average lattice constants, i.e., varying global strain. The low temperature photoluminescence peak energies were found to be much lower than the corresponding energy expected for the equivalent In{sub x}Al{sub 1{minus}x}As alloy. The bandgap energy reductions are found to approach 500 meV and this reduction is found to correlated with the strength of the composition modulation wave amplitude.
Date:
January 4, 1999
Creator:
Ahrenkiel, S. P.; Follstaedt, D. M.; Jones, E. D.; Lee, S. R.; Mascarenhas, A.; Mirecki-Millunchick, J. et al.
Object Type:
Article
System:
The UNT Digital Library
High Intensity Performance of the Brookhaven AGS.
The Brookhaven AGS provides 24 GeV protons for a multi-user program of fixed-target high energy physics experiments, such as the study of extremely rare Kaon decays. Up to 7 x 10{sup 13} protons are slowly extracted over 2.2 seconds each 5.1 seconds. The muon storage ring of the g-2 experiment is supplied with bunches of 7 x 10{sup 12} protons. Since the completion of the a 1.9 GeV Booster synchrotron and installation of a new high-power rf system and transition jump system in the AGS various modes of operation have been explored to overcome space charge limits and beam instabilities at these extreme beam intensities. Experiments have been done using barrier cavities to enable accumulation of debunched beam in the AGS as a potential path to significantly higher intensities. We report on the present understanding of intensity limitations and prospects for overcoming them.
Date:
March 29, 1999
Creator:
Ahrens, L. A.; Alessi, J.; Blaskiewicz, M.; Brennan, J. M.; Brown, K.; Gardner, C. et al.
Object Type:
Article
System:
The UNT Digital Library
Performance of the AGS Transition Jump System.
The transition jump system has been indispensable to the high intensity proton operation of the AGS complex. Nevertheless, transition crossing remains one of the major hurdles as the accelerator complex intensity is pushed upward. To enhance the performance of the system ''quadrupole pumping'' in the Booster is used to minimize the necessary longitudinal dilution of the beam on the AGS injection porch. During the transition jump sextupole correctors at strategic locations are pulsed to minimize the effects of the chromatic non-linearity of the jump system. The available instrumentation for diagnosing the performance of the system will be described, along with installed hardware to counter the non-linear effects of the transition jump system.
Date:
March 29, 1999
Creator:
Ahrens, L. A.; Brennan, J. M.; Glenn, J. W.; Roser, T. & Van Asselt, W. K.
Object Type:
Article
System:
The UNT Digital Library
AGS Resonant Extraction With High Intensity Beams.
The Brookhaven AGS third integer resonant extraction system allows the AGS to provide high quality, high intensity 25.5 GeV/c proton beams simultaneously to four target stations and as many as 8 experiments. With the increasing intensities (over 7 x 10{sup 13} protons/pulse) and associated longer spill periods (2.4 to 3 seconds long), we continue to run with low losses and high quality low modulation continuous current beams.[1] Learning to extract and transport these higher intensity beams has required a process of careful modeling and experimentation. We have had to learn how to correct for various instabilities and how to better match extraction and the transport lines to the higher emittance beams being accelerated in the AGS. Techniques employed include ''RF'' methods to smooth out momentum distributions and fine structure. We will present results of detailed multi-particle tracking modeling studies which enabled us to develop a clear understanding of beam loss mechanisms in the transport and extraction process. We will report on our status, experiences, and the present understanding of the intensity limitations imposed by resonant extraction and transport to fixed target stations.
Date:
March 29, 1999
Creator:
Ahrens, L.; Brown, K.; Glenn, J. W.; Roser, T.; Tsoupas, N. & Vanasselt, W.
Object Type:
Article
System:
The UNT Digital Library
Molecular size and structure in pyridine extracts of upper Freeport coal as separated by M41S sieving.
The determination of the structure of coal has long been of interest due to its crucial importance in research on reactivity and processing. However, the chemically and physically heterogeneous nature of coals makes determination of the chemical nature of even the building blocks complicated, since the molecular structure and molecular weight distribution are not dependent on a single molecule or repeat unit as in technical polymers or biopolymers, but on a complex mixture of molecules and potential connections between them which may vary among coals. Coal extracts have long been used to obtain coal material in solution form that can readily be characterized. However, what part of the total coal structure these extracts represent is not completely known. Pyridine has been a particularly good solvent for coal; for example, the extractability of Upper Freeport has been shown to be as high 30%. Although pyridine extracts of coal have been referred to as solutions, there is good evidence that they are not truly solvated, but are dispersions which are polydisperse in particle size. The particle sizes may span the size range from clusters of small molecules (a few {angstrom}) to extended clusters of large particles (a few hundred {angstrom}), not unlike …
Date:
July 2, 1999
Creator:
Ahrens, M.; Hunt, J. E.; Winans, R. E. & Xu, L.
Object Type:
Article
System:
The UNT Digital Library
Phase Diagram of Iron, Revised-Core Temperatures
Shock-wave experiments on iron preheated to 1,573 K conducted from 14 to 73 GPa, yield new data for sound velocities of the {gamma}- and liquid-phases. Melting was observed in the highest pressure ({approximately} 71 {+-} 2 GPa) experiments at calculated shock temperatures of 2,775 {+-} 160 K. This single crossing of the {gamma}-liquid boundary measured here agrees closely with the {gamma}-iron melting line determined by Boehler [1993], Saxena et al. [1993], and Jephcoat and Besedin [1997]. This {gamma}-iron melting curve is {approximately} 300 C lower than that of Shen et al. [1998b] at 80 GPa.
Date:
January 27, 1999
Creator:
Ahrens, T.J.; Chen, G.Q. & Holland, K.G.
Object Type:
Article
System:
The UNT Digital Library
Improving paper machine efficiency through on-line control of stock delivery, headbox and forming hydrodynamics
None
Date:
September 30, 1999
Creator:
Aidun, Cyrus K.
Object Type:
Report
System:
The UNT Digital Library
Overview of small optics for the National Ignition Facility
LLNL's project to construct the National Ignition Facility (NIF), a 192 beam laser system capable of generating enough light energy necessary to achieve fusion ignition, will require 26,641 small optics, many of which will be supplied in the form of cleaned, tested and aligned assemblies. These assemblies will be built to print, cleaned to specifications, and tested to performance specifications, ready to be installed in the laser system. A wide range of potential suppliers will participate in the manufacture of these sophisticated opto-mechanical systems. The injection laser system requires 7,440 precision optical components manufactured to state of the art performance specifications. In addition to 550 aspheric lenses, almost 2,000 precision spherical elements are required. Wave-fronts are specified in terms of P-V, RMS and RMS Gradient wave-front error, with strict requirements on the filtering and resolution which is required. Precision polarizers, high reflectors, leaking mirrors, high damage threshold coatings and cleanliness levels of 50 to 100 are also specified for this section of the NIF laser. The alignment and diagnostics systems for the NIF require 19,201 optics, many of which have requirements that exceed those of the injection laser system. All of these optics will be purchased using the ISO 10110 …
Date:
July 1, 1999
Creator:
Aikens, D & Bissinger, H D
Object Type:
Article
System:
The UNT Digital Library
Implementation of ISO 10110 optics drawing standards for the National Ignition Facility
The National Ignition Facility (NIF) project elected to implement ISO 10110 standard for the specifications of NIF optics drawings in 1996. More than 7,000 NIF large optics and 20,000 NIF small optics will be manufactured based on ISO 10110 indications. ISO 10110 standard meets many of the needs of the NIF optics specifications. It allows the optical engineer to quantify and clearly communicate the desired optical specifications. While no single drawing standard specifies all the requirements of high energy laser system, a combination of ISO 10110 standard with detailed notes make it possible to apply international drawing standards to the NIF laser system. This paper will briefly describe LLNL's interpretation and implementation of the ISO 10110 drawing standard, present some examples of NIF optics drawings, and discuss pros and cons of the indications from the perspective of this application. Emphasis will be given to the surface imperfection specifications, known as 5/, for the NIF optics.
Date:
July 1, 1999
Creator:
Aikens, D M; English, R E & Wang, D Y
Object Type:
Article
System:
The UNT Digital Library
Surface figure and roughness tolerances for NIF optics and the interpretation of the gradient, P-V wavefront and RMS specifications
In a high energy laser system such as the National Ignition Facility (NIF), the ability to focus light into as small a spot as possible at the highest possible fluence is highly dependent on the quality of the optics used in the system. Typically, surface form errors and transmitted and reflected wavefront errors are specified in terms of a peak-to-valley wavefront error (P-V), or occasionally in terms of an RMS wavefront error (RMS) 1 . It has been shown, however, that the parameter that most closely correlates with beam focusability is neither of these, but the RMS of the gradients of the wavefront error (RMS Gradient). Further, the spatial frequency of the wavefront error plays a significant role in the way that a given error effects the performance of the laser system, so careful attention must be paid to how the spatial filtering is both specified and accomplished. Since ISO 10110 has no specific provisions for a gradient specification, LLNL has developed its own notation and procedures for these critical specifications. In evaluating surface figure errors as specified by the NIF drawings, modern phase modulating interferometers (PMI) will be used. In addition to performing QA testing of the optics, LLNL …
Date:
July 1, 1999
Creator:
Aikens, D M; English, R E; House, W; Lawson, J K; Nichols, M A & Whistler, W T
Object Type:
Article
System:
The UNT Digital Library