Aberration correction for analytical in situ TEM - the NTEAM concept. (open access)

Aberration correction for analytical in situ TEM - the NTEAM concept.

Future aberration corrected transmission electron microscopes (TEM) will have a strong impact in materials science, since such microscopes yield information on chemical bonding and structure of interfaces, grain boundaries and lattice defects at an atomic level. Beyond this aberration correction offers new possibilities for in situ experiments performed under controlled temperature, magnetic field, strain etc. at atomic resolution. Such investigations are necessary for solving problems arising from electronic component miniaturization, for example. Significant progress can be expected by means of analytical aberration corrected TEM. These next generation microscopes will be equipped with an aberration corrected imaging system, a monochromator and aberration corrected energy filters. These novel elements have already been designed and partially realized [1,2,3].
Date: March 5, 2002
Creator: Kabius, B.; Allen, C. W. & Miller, D. J.
Object Type: Article
System: The UNT Digital Library
Accelerator physics and technology limitations to ultimate energy and luminosity in very large hadron colliders (open access)

Accelerator physics and technology limitations to ultimate energy and luminosity in very large hadron colliders

The following presents a study of the accelerator physics and technology limitations to ultimate energy and luminosity in very large hadron colliders (VLHCs). The main accelerator physics limitations to ultimate energy and luminosity in future energy frontier hadron colliders are synchrotron radiation (SR) power, proton-collision debris power in the interaction regions (IR), number of events-per-crossing, stored energy per beam and beam-stability [1]. Quantitative estimates of these limits were made and translated into scaling laws that could be inscribed into the particle energy versus machine size plane to delimit the boundaries for possible VLHCs. Eventually, accelerator simulations were performed to obtain the maximum achievable luminosities within these boundaries. Although this study aimed at investigating a general VLHC, it was unavoidable to refer in some instances to the recently studied, [2], 200 TeV center-of-mass energy VLHC stage-2 design (VLHC-2). A more thorough rendering of this work can be found in [3].
Date: December 5, 2002
Creator: al., P. Bauer et
Object Type: Article
System: The UNT Digital Library
Advanced Techniques for Fourier Transform Wavefront Reconstruction (open access)

Advanced Techniques for Fourier Transform Wavefront Reconstruction

The performance of Fourier transform (FT) reconstructors in large adaptive optics systems with Shack-Hartmann sensors and a deformable mirror is analyzed. FT methods, which are derived for point-based geometries, are adapted for use on the continuous systems. Analysis and simulation show how to compensate for effects such as misalignment of the deformable mirror and wavefront sensor gain. Further filtering methods to reduce noise and improve performance are presented. All these modifications can be implemented at the filtering stage, preserving the speed of FT reconstruction. Simulation of a large system shows how compensated FT methods can have equivalent or better performance to slower vector-matrix-multiply reconstructions.
Date: August 5, 2002
Creator: Poyneer, L A
Object Type: Article
System: The UNT Digital Library
Assessing mixtures risks for cleanup and stewardship. (open access)

Assessing mixtures risks for cleanup and stewardship.

The U.S. Department of Energy (DOE) is responsible for addressing contamination from past research, production, and disposal activities at over 100 sites and facilities across the country. Use of emerging science to assess risks for these facilities is the key to defining appropriate solutions. Safely managing contamination is a priority to protect workers in the near term, and sustained protection is a priority for local communities over the long term. The Department conducts its environmental management program with input from a number of groups who have expressed concern about the safety of DOE sites over time and the possible conversion of some lands to other uses. In general, past facility activities and disposal operations have contaminated about 10% of the total collective area of DOE sites while surrounding lands have served as buffer zones. Portions of several sites have been released for other uses, such as wildlife preserves. Soil, surface water, and groundwater have been contaminated in most instances, and on-site waste disposal is targeted for many sites. Wastes and contamination that will remain in the environment are at the heart of ongoing future use and long-term management deliberations. For this reason, oversight groups and local citizens are scrutinizing the …
Date: March 5, 2002
Creator: MacDonell, M. M. & Hertzberg, R.
Object Type: Article
System: The UNT Digital Library
Assessment of Nonnative Invasive Plants in the DOE Oak Ridge National Environmental Research Park (open access)

Assessment of Nonnative Invasive Plants in the DOE Oak Ridge National Environmental Research Park

The Department of Energy (DOE) National Environmental Research Park at Oak Ridge, Tennessee, is composed of second-growth forest stands characteristic of much of the eastern deciduous forest of the Ridge and Valley Province of Tennessee. Human use of natural ecosystems in this region has facilitated the establishment of at least 167 nonnative, invasive plant species on the Research Park. Our objective was to assess the distribution, abundance, impact, and potential for control of the 18 most abundant invasive species on the Research Park. In 2000, field surveys were conducted of 16 management areas on the Research Park (14 Natural Areas, 1 Reference Area, and Walker Branch Watershed) and the Research Park as a whole to acquire qualitative and quantitative data on the distribution and abundance of these taxa. Data from the surveys were used to rank the relative importance of these species using the ''Alien Plant Ranking System, Version 5.1'' developed by the U.S. Geological Survey. Microstegium (Microstegium vimineum) was ranked highest, or most problematic, for the entire Research Park because of its potential impact on natural systems, its tendency to become a management problem, and how difficult it is to control. Microstegium was present in 12 of the 16 …
Date: November 5, 2002
Creator: Drake, S. J.
Object Type: Report
System: The UNT Digital Library
Autophosphorylation of the DNA-Dependent Protein Kinase Catalyticsubunit is Required for Rejoining of DNA Double-Strand Breaks (open access)

Autophosphorylation of the DNA-Dependent Protein Kinase Catalyticsubunit is Required for Rejoining of DNA Double-Strand Breaks

This report is a descriptive journey of the Autophosphorylation of the DNA-Dependent Protein Kinase Catalyticsubunit is Required for Rejoining of DNA Double-Strand Breaks.
Date: June 5, 2002
Creator: Chan, Doug W.; Chen, Benjamin Ping-Chi; Yang, Shun-Jen; Singh,Sheela; Murphy, Michael B.; Kurimasa, Akihiro et al.
Object Type: Article
System: The UNT Digital Library
Background Radioactivity in River and Reservoir Sediments near Los Alamos, New Mexico (open access)

Background Radioactivity in River and Reservoir Sediments near Los Alamos, New Mexico

As part of its continuing Environmental Surveillance Program, regional river and lake-bottom sediments have been collected annually by Los Alamos National Laboratory (the Laboratory) since 1974 and 1979, respectively. These background samples are collected from three drainage basins at ten different river stations and five reservoirs located throughout northern New Mexico and southern Colorado. Radiochemical analyses for these sediments include tritium, strontium-90, cesium-137, total uranium, plutonium-238, plutonium-239,-240, americium-241, gross alpha, gross beta, and gross gamma radioactivity. Detection-limit radioactivity originates as worldwide fallout from aboveground nuclear weapons testing and satellite reentry into Earth's atmosphere. Spatial and temporal variations in individual analyte levels originate from atmospheric point-source introductions and natural rate differences in airborne deposition and soil erosion. Background radioactivity values on sediments reflect this variability, and grouped river and reservoir sediment samples show a range of statistical distributions that appear to be analyte dependent. Traditionally, both river and reservoir analyte data were blended together to establish background levels. In this report, however, we group background sediment data according to two criteria. These include sediment source (either river or reservoir sediments) and station location relative to the Laboratory (either upstream or downstream). These grouped data are statistically evaluated through 1997, and background …
Date: May 5, 2002
Creator: McLin, Stephen G. & Lyons, Dale W.
Object Type: Report
System: The UNT Digital Library
Basin Analysis of the Mississippi Interior Salt Basin and Petroleum System Modeling of the Jurassic Smackover Formation, Eastern Gulf Coastal Plain, Final Report and Topical Reports 5-8 on Smackover Petroleum system and Underdevelopment Reservoirs (open access)

Basin Analysis of the Mississippi Interior Salt Basin and Petroleum System Modeling of the Jurassic Smackover Formation, Eastern Gulf Coastal Plain, Final Report and Topical Reports 5-8 on Smackover Petroleum system and Underdevelopment Reservoirs

The Smackover Formation, a major hydrocarbon-producing horizon in the Mississippi Interior Salt Basin (MISB), conformably overlies the Norphlet Formation and is conformably overlain by the Buckner Anhydrite Member of the Haynesville Formation. The Norphlet-Smackover contact can be either gradational or abrupt. The thickness and lithofacies distribution of the Smackover Formation were controlled by the configuration of incipient paleotopography. The Smackover Formation has been subdivided into three informal members, referred to as the lower, middle and upper members.
Date: March 5, 2002
Creator: Mancini, Ernest A.; Puckett, T. Markham; Parcell, William C.; Llinas, Juan Carlos; Kopaska-Merkel, David C. & Townsend, Roger N.
Object Type: Report
System: The UNT Digital Library
Battlefield Utility of Antipersonnel Landmines and Proposed Alternatives (Analysis in Support of the NATO SAS-023 APM Study) (open access)

Battlefield Utility of Antipersonnel Landmines and Proposed Alternatives (Analysis in Support of the NATO SAS-023 APM Study)

This study consists of work done in support of the U.S. delegation to the NATO SAS-023 Antipersonnel Landmine Study Group, supplemented by additional work done for the U.S. Office of the Secretary of Defense Antipersonnel Landmine Alternative Concept Exploration Program (Track III). It explores the battlefield utility of current antipersonnel landmines (APL) in both pure and mixed APL/antitank minefields and evaluates the value of military suggested non-materiel alternatives. The historical record is full of examples where the presence (or absence) of antipersonnel landmines made a critical difference in battle. The current generation of military thinkers and writers lack any significant combat experience employing either mixed or antipersonnel minefields, which leaves a critical gap in available expert advice for policy and decision-makers. Because of this lack of experienced-based professional military knowledge, Lawrence Livermore National Laboratory analyzed the employment of antipersonnel landmines in tactical mixed minefields and in protective antipersonnel minefields. The scientific method was employed where hypotheses were generated from the tactics and doctrine of the antipersonnel landmine era and tested in a simulation laboratory. A high-resolution, U.S. Joint Forces Command combat simulation model (the Joint Conflict and Tactical Simulation--JCATS) was used as the laboratory instrument. A realistic European scenario was …
Date: February 5, 2002
Creator: Crandley, J. F., Jr.; Greenwalt, R. J., Jr.; Magnoli, D. E. & Randazzo, A. S.
Object Type: Report
System: The UNT Digital Library
Beam Effects from an Increase of LINAC Current from 40 ma to 49 Milliamperes (open access)

Beam Effects from an Increase of LINAC Current from 40 ma to 49 Milliamperes

On March 25, 2002 the FNAL Linac had been running at a decreased 40 ma of beam current for some time. Both the 400 MeV Linac and the 8GeV Booster had been tuned to optimum running during that time. Optimum running for the Booster was at 4.1e12 per pulse. Losses at injection and at transition were limiting intensity at the time. By March 26, 2002 the Linac beam current had been increased to 49 ma. The optimum Booster intensity immediately jumped to 4.5e12 per pulse and increased in the next few days to 4.8e12 and 5e12 per pulse. Booster was not retuned until early April when a low-loss 5.0e12 was obtained for stacking operations. Linac current had sagged to 47 ma by then. Measurements were made on the 25th at 40 ma and the 26th and 27th at 49 ma. This is a report and discussion of those measurements.
Date: June 5, 2002
Creator: Tomlin, Ray
Object Type: Report
System: The UNT Digital Library
BSW Well Evaluation Report (open access)

BSW Well Evaluation Report

The BSW series wells are located in the Mixed Waste Management Facility and are part of the groundwater monitoring program at Savannah River Site. These wells have had persistent problems that prevent successful sampling that dates back to their installation. Only thirty-two of the fifty-three BSW wells were successfully sampled during 4th quarter, 2001. These problems were previously investigated by looking at field sampling logbooks from 4th quarter 2001 and other background information to try to identify causes for the high rate of sampling failure. Several possible causes were identified and reported in memorandum, SRT-EST-2002-00059. The memorandum recommended that an evaluation be performed on each well to identify problems and their causes and to correct them when possible. Environmental Restoration Division followed up on this recommendation and requested Savannah River Technology Center to perform an evaluation. This report includes the results of the evaluation performed on the BSW wells.
Date: September 5, 2002
Creator: Noonkester, J.V.
Object Type: Report
System: The UNT Digital Library
CALCIUM CARBONATE PRODUCTION BY COCCOLITHOPHORID ALGAE IN LONG TERM, CARBON DIOXIDE SEQUESTRATION (open access)

CALCIUM CARBONATE PRODUCTION BY COCCOLITHOPHORID ALGAE IN LONG TERM, CARBON DIOXIDE SEQUESTRATION

Predictions of increasing levels of anthropogenic carbon dioxide (CO{sub 2}) and the specter of global warming have intensified research efforts to identify ways to sequester carbon. A number of novel avenues of research are being considered, including bioprocessing methods to promote and accelerate biosequestration of CO{sub 2} from the environment through the growth of organisms such as coccolithophorids, which are capable of sequestering CO{sub 2} relatively permanently. Calcium and magnesium carbonates are currently the only proven, long-term storage reservoirs for carbon. Whereas organic carbon is readily oxidized and releases CO{sub 2} through microbial decomposition on land and in the sea, carbonates can sequester carbon over geologic time scales. This proposal investigates the use of coccolithophorids--single-celled, marine algae that are the major global producers of calcium carbonate--to sequester CO{sub 2} emissions from power plants. Cultivation of coccolithophorids for calcium carbonate (CaCO{sub 3}) precipitation is environmentally benign and results in a stable product with potential commercial value. Because this method of carbon sequestration does not impact natural ecosystem dynamics, it avoids controversial issues of public acceptability and legality associated with other options such as direct injection of CO{sub 2} into the sea and ocean fertilization. Consequently, cultivation of coccolithophorids could be carried …
Date: April 5, 2002
Creator: V.J. Fabry, Ph.D.
Object Type: Report
System: The UNT Digital Library
Carbon Resistor Pressure Gauge Calibration at Stresses Up to 1 GPa (open access)

Carbon Resistor Pressure Gauge Calibration at Stresses Up to 1 GPa

Calibration of the 470-Ohm carbon resistor gauge is desired in the low stress region up to 1 GPa. A split-Hopkinson pressure bar, drop tower apparatus, gas pressure chamber, and gas gun have been used to perform the calibration experiments. The gauge behavior at elevated temperature was also investigated by heating the resistors to 200 C at atmospheric pressure while observing the resistance change. The motivation for this calibration work arises from the desire to increase the number of data points in the low stress regime to better establish the accuracy and precision of the gauge. Details of the various calibration arrangements and the results are discussed and compared to calibration curves fit to previously published calibration data. It was found that in most cases, the data from this work fit the calibration curves fit to previously published data rather well.
Date: March 5, 2002
Creator: Vandersall, K S; Niles, A M; Greenwood, D W; Cunningham, B; Garcia, F & Forbes, J W
Object Type: Article
System: The UNT Digital Library
Casting Characteristics of Aluminum Die Casting Alloys (open access)

Casting Characteristics of Aluminum Die Casting Alloys

The research program investigates the casting characteristics of selected aluminum die casting alloys. Specifically, the alloys' tendencies towards die soldering and sludge formation, and the alloys' fluidity and machinability are evaluated. It was found that: When the Fe and Mn contents of the alloy are low; caution has to be taken against possible die soldering. When the alloy has a high sludge factor, particularly a high level of Fe, measures must be taken to prevent the formation of large hardspots. For this kind of alloy, the Fe content should be kept at its lowest allowable level and the Mn content should be at its highest possible level. If there are problems in die filling, measures other than changing the alloy chemistry need to be considered first. In terms of alloy chemistry, the elements that form high temperature compounds must be kept at their lowest allowable levels. The alloys should not have machining problems when appropriate machining techniques and machining parameters are used.
Date: February 5, 2002
Creator: Makhlouf, Makhlouf M. & Apelian, Diran
Object Type: Report
System: The UNT Digital Library
Cesium-137 in the Sediments of Fourmile Creek (open access)

Cesium-137 in the Sediments of Fourmile Creek

The Nonproliferation Technology Section (NTS) was requested by the Environmental Restoration Division (ER) to aid in completing ground-truth measurements of aerial overflight data in support of the Integrator Operable Unit (IOU) program at the Savannah River Site (SRS). The IOU's at the SRS are under investigation as a possible pathway for the release of contamination from past SRS activities to off-unit receptors and the environment. The IOU's are defined as surface water bodies and associated wetlands, including the water, sediment and related biota. The objective of the IOU program is to: assess the risk to potential human and ecological receptors from IOU contamination; evaluate the impact of inactive and active waste units and operating facilities on the IOU quality; determine if IOU early actions, including reprioritization of operable units implementation schedules, are necessary; and complete the remedial investigation/feasibility study process, defining the nature and extent of IOU contamination, remedial action objectives, and final remediation goals.
Date: December 5, 2002
Creator: Beals, D.M.
Object Type: Report
System: The UNT Digital Library
Chamber wall response to target implosion in inertial fusion reactors : new and critical assessments. (open access)

Chamber wall response to target implosion in inertial fusion reactors : new and critical assessments.

The chamber walls in inertial fusion energy (IFE) reactors are exposed to harsh conditions following each target implosion. Key issues of the cyclic IFE operation include intense photon and ion deposition, wall thermal and hydrodynamic evolution, wall erosion and fatigue lifetime, and chamber clearing and evacuation to ensure desirable conditions prior to target implosion. Several methods for wall protection have been proposed in the past, each having its own advantages and disadvantages. These methods include use of solid bare walls, gas-filled cavities, and liquid walls/jets. Detailed models have been developed for reflected laser light, emitted photons, and target debris deposition and interaction with chamber components and have been implemented in the comprehensive HEIGHTS software package. The hydrodynamic response of gas filled cavities and photon radiation transport of the deposited energy has been calculated by means of new and advanced numerical techniques. Fragmentation models of liquid jets as a result of the deposited energy have also been developed, and the impact on chamber clearing dynamics has been evaluated. The focus of this study is to critically assess the reliability and the dynamic response of chamber walls in various proposed protection methods for IFE systems. Of particular concern is the effect on …
Date: August 5, 2002
Creator: Hassanein, A. & Morozov, V.
Object Type: Article
System: The UNT Digital Library
Characterization of high performance electrochemical systems for portable power. Final report for period September 15, 1993 - December 31, 2001 (open access)

Characterization of high performance electrochemical systems for portable power. Final report for period September 15, 1993 - December 31, 2001

The long-term objective of research has been to perform the enabling materials research necessary for the development of a battery oriented to the consumer market with special requirements in terms of safety, cycling life, and high specific energy and power. We have discovered novel processing of V{sub 2}O{sub 5} gels that leads to aerogel (ARG) and xerogel (XRG) films with specific energy and Li insertion capacity that are much higher than for other amorphous or crystalline forms of V{sub 2}O{sub 5}. We have also found that the new materials will host Mg{sup +2} and other cations which should be the basis for novel high-energy, high-power consumer battery systems. The investigation has examined (1) low-temperature synthesis of V{sub 2}O{sub 5} aerogel host materials, (2) characterization of insertion of Mg{sup 2+}, Zn{sup 2+}, and Al{sup 3+} into the V{sub 2}O{sub 5} hosts, (3) anode materials for the new systems, and alternate anode materials to replace the intrinsically unsafe lithium metal for lithium batteries, and (4) the feasibility of safer, nonaqueous, high-performance battery designs.
Date: September 5, 2002
Creator: Smyrl, W. H. & Owens, B. B.
Object Type: Report
System: The UNT Digital Library
CHEMICALLY BONDED CEMENTS FROM BOILER ASH AND SLUDGE WASTES. PHASE I REPORT AUGUST 1997 - JULY 1998 (open access)

CHEMICALLY BONDED CEMENTS FROM BOILER ASH AND SLUDGE WASTES. PHASE I REPORT AUGUST 1997 - JULY 1998

In exploring methods to recycle boiler ash (BA) and waste water treatment sludge (WWTS), by-products generated from Keyspan's power plants, into commercially viable materials, we synthesized chemically bonded cements (CBC) offering the following three specific characteristics; (1) immobilization of hazardous heavy metals, such as Pb, Ni, and V, (2) rapid hardening and setting properties, and (3) development of high mechanical strength. The CBCs were prepared through an acid-base reaction between these by-products acting as the solid base reactants and the sodium polyphosphate solution as the cement-forming acid reactant, followed by a hydrating reaction. Furthermore, two additives, the calcium aluminate cements (CAC) and the calcium silicate cements (CSC) were incorporated into the CBC systems to improve their properties. Using a CBC formulation consisting of 53.8 wt% WWTS, 23.1 wt% CSC, and 23.1 wt% [40 wt% -(-NaPO{sub 3}-)-{sub n}]{sub 2} the Toxicity Characteristics Leaching Procedure (TCLP) tests showed that the concentrations of Pb, Ni, and V metals leached out from the specimens were minimal. This formulation originally contained {approx} 28800 mg/kg of Pb, {approx} 6300 mg/kg of Ni, and {approx} 11130 mg/kg of V; the amounts leaching into the acid extraction fluid were only 0.15 mg/L of Pb, 0.15 mg/L of Ni, …
Date: August 5, 2002
Creator: SUGAMA,T. & YAGER,K.A.
Object Type: Report
System: The UNT Digital Library
Clean Metal Casting (open access)

Clean Metal Casting

The objective of this project is to develop a technology for clean metal processing that is capable of consistently providing a metal cleanliness level that is fit for a given application. The program has five tasks: Development of melt cleanliness assessment technology, development of melt contamination avoidance technology, development of high temperature phase separation technology, establishment of a correlation between the level of melt cleanliness and as cast mechanical properties, and transfer of technology to the industrial sector. Within the context of the first task, WPI has developed a standardized Reduced Pressure Test that has been endorsed by AFS as a recommended practice. In addition, within the context of task1, WPI has developed a melt cleanliness sensor based on the principles of electromagnetic separation. An industrial partner is commercializing the sensor. Within the context of the second task, WPI has developed environmentally friendly fluxes that do not contain fluorine. Within the context of the third task, WPI modeled the process of rotary degassing and verified the model predictions with experimental data. This model may be used to optimize the performance of industrial rotary degassers. Within the context of the fourth task, WPI has correlated the level of melt cleanliness at …
Date: February 5, 2002
Creator: Makhlouf, Makhlouf M. & Apelian, Diran
Object Type: Report
System: The UNT Digital Library
Comparison of MTI and Ground Truth Sea Surface Temperatures at Nauru (open access)

Comparison of MTI and Ground Truth Sea Surface Temperatures at Nauru

This report evaluates MTI-derived surface water temperature near the tropical Pacific island of Nauru. The MTI sea-surface temperatures were determined by the Los Alamos National Laboratory based on the robust retrieval.
Date: September 5, 2002
Creator: Kurzeja, R.
Object Type: Report
System: The UNT Digital Library
Contributions of inelastically scattered electrons to defect images. (open access)

Contributions of inelastically scattered electrons to defect images.

We have made measurements of the contribution of inelastically scattered electrons to images of dislocations in Ni{sub 3}Ga and nanometer-sized defects in ion-irradiated Au under weak-beam dark-field diffraction conditions [1]. The purpose is to determine the conditions for data acquisition required to eventually make detailed and quantitative comparisons to simulations of images for various defect models, thus determining defect structure, composition, and local strain field. Such image simulations usually consider only elastically scattered electrons, and thus it is important to understand and possibly eliminate the contribution of inelastically scattered electrons to the experimental images for quantitative comparisons with image simulations. Experimental data have been acquired with either JEOL 2010F or 3000F microscopes, both equipped with Gatan Imaging Filter electron spectrometers. Samples examined in the 2010F were Au, ion-irradiated to low dose (10{sup 11}Kr ions at 1 MeV energy) to form individual defects (1-10nm sized Frank dislocation loops and partial stacking fault tetrahedra). Samples examined in the 3000F were Ni{sub 3}Ga with long dislocation defects. Imaging conditions included weak-beam dark-field with deviation parameter generally > 0.2 nm{sup -1}. Energy filter slit width was set to 10 eV and centered on the zero loss peak in both instruments to obtain images produced …
Date: March 5, 2002
Creator: Kirk, M. A.; Twesten, R.; Martin, S. P.; Hetherington, C. J. D. & Jenkins, M. L.
Object Type: Article
System: The UNT Digital Library
Controlling the morphology of nanocrystal-polymer composites for solar cells (open access)

Controlling the morphology of nanocrystal-polymer composites for solar cells

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Date: June 5, 2002
Creator: Huynh, Wendy U.; Dittmer, Janke J.; Libby, William C.; Whiting, Gregory L. & Alivisatos, A. Paul
Object Type: Article
System: The UNT Digital Library
A cosmic perspective from Lapland in 2001 (open access)

A cosmic perspective from Lapland in 2001

A convergence of ideas, observations and technology have led to the greatest period of cosmological discovery yet. Over the past three years we have determined the basic features of our Universe. We are now challenged to make sense of what we have found. The outcome of planned experiments and observations as well as new ideas will be required. If we succeed, ours truly will be a Golden Age of Cosmology.
Date: December 5, 2002
Creator: Turner, Michael s.
Object Type: Article
System: The UNT Digital Library
A density functional theory study of the oxidation of methanol to formaldehyde over vanadia supported on silica, titania, and zirconia (open access)

A density functional theory study of the oxidation of methanol to formaldehyde over vanadia supported on silica, titania, and zirconia

Density functional theory was used to investigate the mechanism and kinetics of methanol oxidation to formaldehyde over vanadia supported on silica, titania, and zirconia. The catalytically active site was modeled as an isolated VO{sub 4} unit attached to the support. The calculated geometry and vibrational frequencies of the active site are in good agreement with experimental measurements both for model compounds and oxide-supported vanadia. Methanol adsorption is found to occur preferentially with the rupture of a V-O-M bond (M = Si, Ti, Zr) and with preferential attachment of a methoxy group to V. The vibrational frequencies of the methoxy group are in good agreement with those observed experimentally as are the calculated isobars. The formation of formaldehyde is assumed to occur via the transfer of an H atom of a methoxy group to the O atom of the V=O group. The activation energy for this process is found to be in the range of 199-214 kJ/mol and apparent activation energies for the overall oxidation of methanol to formaldehyde are predicted to lie in the range of 112-123 kJ/mol, which is significantly higher than that found experimentally. Moreover, the predicted turnover frequency (TOF) for methanol oxidation is found to be essentially …
Date: September 5, 2002
Creator: Khaliullin, Rustam Z. & Bell, Alexis T.
Object Type: Article
System: The UNT Digital Library