6,620 Matching Results

Search Results

Electron transfer of carbonylmetalate radical pairs: femtosecond visible spectroscopy of optically excited ion pairs

Description: Charge transfer excitation at 640 nm of the cobaltocenium tetracarbonylcobaltate ion pair, [Cp{sub 2}Co{sup +}{vert_bar}Co(CO){sub 4}{sup -}], was monitored in 1,2- dichloroethane solution by femtosecond transient visible absorption spectroscopy. The absorption prepares a neutral radical pair that can undergo spontaneous back electron transfer, and which shows a double peaked spectrum with features at 760 and 815 nm at 3 ps delay time. Transient decay times of 5.8{+-}0.5 ps were measured by monitoring the decay of Co(CO){sub 4} at 757 nm and 780 nm, and these are assigned to the back electron transfer step. The ET kinetics are consistent with the previously reported rates of electron transfer that were measured for specific vibrational states by picosecond transient IR.
Date: February 1, 1997
Creator: Wen, X.; Spears, K.G.; Wiederrecht, G.P. & Wasielewski, M.R.
Partner: UNT Libraries Government Documents Department

Use of indentation technique to measure elastic modulus of plasma-sprayed zirconia thermal barrier coating

Description: Elastic modulus of an yttria partially stabilized zirconia (YSZ) thermal barrier coating (TBC) was evaluated with a Knoop indentation technique. The measured elastic modulus values for the coating ranged from 68.4 {+-} 22.6 GPa at an indentation load of 50 g to 35.7 {+-} 9.8 at an indentation load of 300 g. At higher loads, the elastic modulus values did not change significantly. This steady-state value of 35.7 GPa for ZrO{sub 2} TBC agreed well with literature values obtained by the Hertzian indentation method. Furthermore, the measured elastic modulus for the TBC is lower than that reported for bulk ZrO{sub 2} ({approx} 190 GPa). This difference is believed to be due to the presence of a significant amount of porosity and microcracks in the TBCs. Hardness was also measured.
Date: January 1, 1997
Creator: Singh, J.P.; Sutaria, M. & Ferber, M.
Partner: UNT Libraries Government Documents Department

Radiotoxicity of neptunium(V) and neptunium(V)-nitrilotriacetic acid (NTA) complexes towards Chelatobacter heintzii

Description: The objective of this work was to investigate the toxicity mechanisms of neptunium and the neptunium-NTA complex towards Chelatobacter heintzii. The results show that metal toxicity of aquo NpO{sub 2}{sup +} may significantly limit growth of Cl heintzii at free metal ion concentrations greater than {approx} 10{sup {minus}5} M. However, neptunium concentrations {ge} 10{sup {minus}4} M do not cause measurable radiotoxicity effects in C. heintzii when present in the form of a neptunium-NTA complex or colloidal/precipitated neptunium-phosphate. The neptunium-NTA complex, which is stable under aerobic conditions, is destabilized by microbial degradation of NTA. When phosphate was present, degradation of NTA led to the precipitation of a neptunium-phosphate phase.
Date: March 10, 1997
Creator: Banaszak, J.E.; Reed, D.T. & Rittmann, B.E.
Partner: UNT Libraries Government Documents Department

Measurement of gas bremsstrahlung from the insertion device beamlines of the advanced photon source

Description: High energy electron storage rings generate energetic bremsstrahlung photons through radiative interaction of the electrons (or positrons) with the residual gas molecules inside the storage ring. The resulting radiation exits at an average emittance angle of (m{sub 0}c{sub 2}/E) radian with respect to the electron beam path, where m{sub 0}c{sup 2} is the rest mass of E the electron and E its kinetic energy. Thus, at straight sections of the storage rings, moving electrons will produce a narrow and intense monodirectional photon beam. At synchrotron radiation facilities, where beamlines are channeled out of the storage ring, a continuous gas bremsstrahlung spectrum, with a maximum energy of the electron beam, will be present. There are a number of compelling reasons that a measurement of the bremsstrahlung characteristics be conducted at the Advanced Photon Source (APS) storage ring. Although the number of residual gas molecules present in the storage ring at typical nTorr vacuum is low, because of the long straight paths of the electrons in the storage ring at APS, significant production of bremsstrahlung will be produced. This may pose a radiation hazard. It is then imperative that personnel be shielded from dose rates due to this radiation. There are not many measurements available for gas bremsstrahlung, especially for higher electron beam energies. The quantitative estimates of gas bremsstrahlung from storage rings as evaluated by Monte Carlo codes also have several uncertainties. They are in general calculated for air at atmospheric pressure, the results of which are then extrapolated to typical storage ring vacuum values (of the order of 10{sup -9} Torr). Realistically, the actual pressure profile can vary inside the narrow vacuum chamber. Also, the actual chemical composition of the residual gas inside the storage ring is generally different from that of air.
Date: March 1, 1997
Creator: Pisharody, M.; Job, P.K. & Magill, S.
Partner: UNT Libraries Government Documents Department

Corrective Action Plan for CAU No. 95: Area 15 EPA Farm Laboratory Building, Decontamination and Demolition Closure Activities - Nevada Test Site. Rev. 0

Description: This Corrective Action Plan (CAP) provides the selected corrective action alternative and proposes the closure implementation methodology for the Environmental Protection Agency (EPA) Farm Laboratory Building 15-06 located in Area 15 of the Nevada Test Site (NTS), Nye County, Nevada. The facility is part of the Environmental Restoration Project managed by the U.S. Department of Energy/Nevada Operations Office (DOE/NV) under the Decontamination and Decommissioning (D&D) Subproject which serves to manage and dispose of surplus facilities at the NTS in a manner that will protect personnel, the public, and the environment. It is identified as Corrective Action Unit (CAU) 95 in Appendix III of the Federal Facilities Agreement and Consent Order (FFACO). In July 1997, the DOE/NV verbally requested approval from the Nevada Division of Environmental Protection (NDEP) for the closure schedule to be accelerated. Currently, field activities are anticipated to be completed by September 30, 1997. In order to meet this new schedule NDEP has agreed to review this document as expeditiously as possible. Comments will be addressed in the Closure Report after field activities have been completed, unless significant issues require resolution during closure activities.
Date: November 1997
Creator: Olson, A. L. & Nacht, S. J.
Partner: UNT Libraries Government Documents Department

Corrective action plan for CAU Number 339: Area 12 Fleet Operations, Steam Cleaning Discharge Area, Nevada Test Site

Description: The purpose of this Corrective Action Plan (CAP) is to provide the method for implementing the corrective action alternative as provided in the Corrective Action Decision Document (CADD). Detailed information of the site history and results of previous characterizations can be found in the Work Plan, the Preliminary Investigation Report, and the Phase 2 Characterization Report. Previous characterization investigations were completed as a condition of the Temporary Water Pollution Control Permit issued by the Nevada Division of Environmental Protection (NDEP) on July 14, 1992. The scope of this report is to prepare a CAP based upon the selected remedial alternative for closure of the Area 12, Building 12-16 Fleet Operations steam cleaning discharge area. The effluent discharge area has been impacted by volatile organic compounds (VOCs) and total petroleum hydrocarbons (TPH) as oil. The maximum hydrocarbon and VOC concentrations detected in the Preliminary and Phase 2 Site Characterization Investigations are summarized.
Date: May 1, 1997
Partner: UNT Libraries Government Documents Department

Corrective action plan for CAU No. 404: Roller Coaster Sewage Lagoons and North Disposal Trench, Tonopah Test Range

Description: This Corrective Action Plan (CAP) provides the selected corrective action alternative and proposes the closure implementation methodology for the Roller Coaster Sewage Lagoons and North Disposal Trench Corrective Action Unit (CAU) No. 404. The site is located on the Tonopah Test Range. CAU 404 consists of two Corrective Action Sites (CAS): the Roller Coaster Lagoons (CAS No TA-03-001-TA-RC) and the North Disposal Trench (CAS No TA-21-001-TA-RC). A site map of the lagoons and trench is provided. The Roller Coaster Sewage Lagoons are comprised of two unlined lagoons that received liquid sanitary waste in 1963 from the Operation Roller Coaster Man Camp and debris from subsequent construction and range cleanup activities. The North Disposal Trench was excavated in approximately 1963 and received solid waste and debris from the man camp and subsequent construction and range cleanup activities. A small hydrocarbon spill occurred during the 1995 Voluntary Corrective Action (VCA) activities in an area associated with the North Disposal Trench CAS.
Date: July 1, 1997
Partner: UNT Libraries Government Documents Department

Chemical research at Argonne National Laboratory

Description: Argonne National Laboratory is a research and development laboratory located 25 miles southwest of Chicago, Illinois. It has more than 200 programs in basic and applied sciences and an Industrial Technology Development Center to help move its technologies to the industrial sector. At Argonne, basic energy research is supported by applied research in diverse areas such as biology and biomedicine, energy conservation, fossil and nuclear fuels, environmental science, and parallel computer architectures. These capabilities translate into technological expertise in energy production and use, advanced materials and manufacturing processes, and waste minimization and environmental remediation, which can be shared with the industrial sector. The Laboratory`s technologies can be applied to help companies design products, substitute materials, devise innovative industrial processes, develop advanced quality control systems and instrumentation, and address environmental concerns. The latest techniques and facilities, including those involving modeling, simulation, and high-performance computing, are available to industry and academia. At Argonne, there are opportunities for industry to carry out cooperative research, license inventions, exchange technical personnel, use unique research facilities, and attend conferences and workshops. Technology transfer is one of the Laboratory`s major missions. High priority is given to strengthening U.S. technological competitiveness through research and development partnerships with industry that capitalize on Argonne`s expertise and facilities. The Laboratory is one of three DOE superconductivity technology centers, focusing on manufacturing technology for high-temperature superconducting wires, motors, bearings, and connecting leads. Argonne National Laboratory is operated by the University of Chicago for the U.S. Department of Energy.
Date: April 1, 1997
Partner: UNT Libraries Government Documents Department

Prospects for using high power x-rays as a volumetric heat source

Description: Third-generation, high-intensity, x-ray synchrotron radiation sources are capable of producing high heat-flux x-ray beams. In many applications finding ways to handle these powers is viewed as a burden. However, there are some technological applications where the deep penetration length of the x-rays may find beneficial uses as a volumetric heat source. In this paper the authors discuss the prospects for using high power x-rays for volumetric heating and report some recent experimental results. The particular applications they focus on are welding and surface heat treatment. The radiation source is an undulator at the Advanced Photon Source (APS). Results of preliminary tests on aluminum, aluminum metal matrix composites, and steel will be presented.
Date: September 1, 1997
Creator: Rosenberg, R.A.; Farrell, W. & Ma, Q.
Partner: UNT Libraries Government Documents Department

Traffic characterization and modeling of wavelet-based VBR encoded video

Description: Wavelet-based video codecs provide a hierarchical structure for the encoded data, which can cater to a wide variety of applications such as multimedia systems. The characteristics of such an encoder and its output, however, have not been well examined. In this paper, the authors investigate the output characteristics of a wavelet-based video codec and develop a composite model to capture the traffic behavior of its output video data. Wavelet decomposition transforms the input video in a hierarchical structure with a number of subimages at different resolutions and scales. the top-level wavelet in this structure contains most of the signal energy. They first describe the characteristics of traffic generated by each subimage and the effect of dropping various subimages at the encoder on the signal-to-noise ratio at the receiver. They then develop an N-state Markov model to describe the traffic behavior of the top wavelet. The behavior of the remaining wavelets are then obtained through estimation, based on the correlations between these subimages at the same level of resolution and those wavelets located at an immediate higher level. In this paper, a three-state Markov model is developed. The resulting traffic behavior described by various statistical properties, such as moments and correlations, etc., is then utilized to validate their model.
Date: July 1, 1997
Creator: Kuo, Yu; Jabbari, B. & Zafar, S.
Partner: UNT Libraries Government Documents Department

On the implementation of a modified Sag-Szekeres quadrature method

Description: The authors describe a modified Sag-Szekeres multidimensional quadrature algorithm and discuss its implementation as a general-purpose library procedure on serial and parallel architectures. Examples illustrate its effectiveness for both smooth and singular integrands. The procedure has been implemented as a parallel library routine, running on transputer-based systems, as part of Esprit project P2528: Supernode II; (see Plowman (1992)). This routine is scheduled to appear in the quadrature section of the Liverpool-NAG Transputer Software Library. The authors give here some results obtained using this routine, to demonstrate the rapid convergence obtained with both smooth and singular integrands, and to demonstrate the routine`s effectiveness on a parallel NIMD architecture.
Date: July 1997
Creator: Lyness, J. N. & Delves, L. M.
Partner: UNT Libraries Government Documents Department

Aircraft measurements of nitrogen dioxide and peroxyacyl nitrates using luminol chemiluminescence with fast capillary gas chromatography

Description: Peroxyacyl nitrates (PANs) and nitrogen dioxide (NO{sub 2}) are important trace gas species associated with photochemical air pollution. The PANs are in thermal equilibrium with the peroxyacetyl radical and NO{sub 2}. Because PANs are trapped peroxy radicals, they are an important indicator species of the photochemical age of an air parcel, as well as being a means of long-range transporting of NO{sub 2}, leading to the formation of regional ozone and other oxidants. Typically, PANs are measured by using a gas chromatograph with electron-capture detection (ECD). Once automated, this method has been shown to be reliable and quite sensitive, allowing the levels of PANs to be measured at low parts per trillion in the troposphere. Unfortunately, a number of other atmospheric gases also have strong ECD signals or act as inferences and limit the speed in which the analysis can be completed. Currently, the shortest analysis time for PAN is approx. 5 minutes with ECD. The authors recent examined the luminol detection of NO{sub 2} and PANs using gas capillary chromatography for rapid monitoring of these important trace gases. Analysis of the PANs (PAN, PPN, and PBN) and NO{sub 2} in one minute has been demonstrated in laboratory studies by using this approach. Reported here are modifications of this instrument for aircraft operation and preliminary results from test flights taken near Pasco, Washington in August of 1997.
Date: September 1997
Creator: Gaffney, J. S.; Marley, N. A. & Drayton, P. J.
Partner: UNT Libraries Government Documents Department

Crystal structure of (Li{sub 0.5}K{sub 0.5}){sub 2}CO{sub 3} by neutron powder diffraction analysis

Description: The crystal structure of (Li{sub 0.5}K{sub 0.5}){sub 2}CO{sub 3} was determined by neutron powder diffraction. A final weighted R-factor of 4.54% was obtained for the refinement of 2,373 reflections by the Rietveld method from a sample synthesized using {sup 7}Li{sub 2}CO{sub 3} and K{sub 2}CO{sub 3} (99.9% pure). Slight distortion of the CO{sub 3}{sup 2{minus}} units in the monoclinic cell was observed; the O(1)-C-O(2) angle and C-O(3) length are larger than those for the other C-O bonds and O-C-O angles. These local-structure characteristics can be explained by the difference in the ionic size of Li{sup +} and K{sup +}, and the different electrostatic interactions between the cations and CO{sub 3}{sup 2{minus}} units. (Li{sub 0.5}K{sub 0.5}){sub 2}CO{sub 3} is important as a material for molten carbonate fuel cells.
Date: August 1, 1997
Creator: Idemoto, Yasushi; Richardson, J.W. Jr.; Loong, C.K.; Koura, Nobuyuki & Kohara, Shinji
Partner: UNT Libraries Government Documents Department

Derivation of Hamiltonians for accelerators

Description: In this report various forms of the Hamiltonian for particle motion in an accelerator will be derived. Except where noted, the treatment will apply generally to linear and circular accelerators, storage rings, and beamlines. The generic term accelerator will be used to refer to any of these devices. The author will use the usual accelerator coordinate system, which will be introduced first, along with a list of handy formulas. He then starts from the general Hamiltonian for a particle in an electromagnetic field, using the accelerator coordinate system, with time t as independent variable. He switches to a form more convenient for most purposes using the distance s along the reference orbit as independent variable. In section 2, formulas will be derived for the vector potentials that describe the various lattice components. In sections 3, 4, and 5, special forms of the Hamiltonian will be derived for transverse horizontal and vertical motion, for longitudinal motion, and for synchrobetatron coupling of horizontal and longitudinal motions. Hamiltonians will be expanded to fourth order in the variables.
Date: September 12, 1997
Creator: Symon, K.R.
Partner: UNT Libraries Government Documents Department

Radium separation through complexation by aqueous crown ethers and ion exchange or solvent extraction

Description: The effect of three water-soluble, unsubstituted crown ethers (15-crown-5 (15C5), 18-crown-6 (18C6) and 21-crown-7 (21C7)) on the uptake of Ca, Sr, Ba and Ra cations by a sulfonic acid cation exchange resin, and on the extraction of the same cations by xylene solutions of dinonylnaphthalenesulfonic acid (HDNNS) from aqueous hydrochloric acid solutions has been investigated. The crown ethers enhance the sorption of the larger cations by the ion exchange resin, thereby improving the resin selectivity over calcium, a result of a synergistic interaction between the crown ether and the ionic functional groups of the resin. Similarly, the extraction of the larger alkaline earth cations into xylene by HDNNS is strongly synergized by the presence of the crown ethers in the aqueous phase. Promising results for intra-Group IIa cation separations have been obtained using each of the three crown ethers as the aqueous ligands and the sulfonic acid cation exchange resin. Even greater separation factors for the radium-calcium couple have been measured with the crown-ethers and HDNNS solutions in the solvent extraction mode. The application of the uptake and extraction results to the development of radium separation schemes is discussed and a possible flowchart for the determination of {sup 226}Ra/{sup 228}Ra in natural waters is presented.
Date: November 1, 1997
Creator: Chiarizia, R.; Dietz, M.L.; Horwitz, E.P. & Burnett, W.C.
Partner: UNT Libraries Government Documents Department

Wavy Taylor vortices in plane Couette flow

Description: Path-following techniques applied to a spectral approximation of the solution of the Navier-Stokes Equations have revealed the existence of a new class of solutions to the plane Couette flow problem.
Date: August 1997
Creator: Conley, A. J. & Keller, H. B.
Partner: UNT Libraries Government Documents Department

Mitigation of sub-surface crack propagation in railroad rails by laser surface modification

Description: The authors address the mitigation of sub-surface crack propagation in railroad rails via laser surface modification. The goal is to reduce the shear forces from rail-wheel friction, which contribute significantly to the nucleation and propagation of cracks in the sub-surface region at rail gage corners. Microhardness scans and tensile tests were performed on samples from cross-sections of unused and heavily used rail heads. The results of these tests indicate that the severe cyclic plastic deformation that occurs at the gage corners, during service, significantly hardens the sub-surface region there, which leads to cracking. Laser glazing, the rapid melting and rapid solidification of a thin surface layer, was used to reduce the friction coefficient of rail steel. The advantages of this process are that specific regions of the rail surface can be targeted; the treatment does not wash away as the currently used liquid lubricants do; it is more environmentally sound than liquid lubricants; and it can be applied in service, during re-work or during rail fabrication. A number of laser treatments were conducted on AISI 1080 steel plates, similar to rail steel, from which friction samples were extracted. Static block-on-ring friction experiments performed on a variety of laser treated surfaces showed reductions in the friction coefficient by about 25% relative to untreated surfaces at loads corresponding to prototypic rail service loads. The authors laser-glazed two areas on the top surface of a 6-ft length of rail with multiple pass treatments, one with adjacent passes overlapping, and one with adjacent passes separated by 1 mm. Friction measurements were made after they were subjected to 20,000 run-in cycles. The laser treatments remained intact after these cycles. Reductions of friction coefficient of ca. 40%, relative to untreated surfaces, were observed, corresponding to a reduction in the calculated mixed mode crack propagation rate by ...
Date: October 1, 1997
Creator: DiMelfi, R.J.; Sanders, P.G.; Hunter, B.; Eastman, J.A.; Leong, K.; Kramer, J.M. et al.
Partner: UNT Libraries Government Documents Department

Quantum Monte Carlo calculations for light nuclei

Description: Quantum Monte Carlo calculations of ground and low-lying excited states for nuclei with A {le} 8 have been made using a realistic Hamiltonian that fits NN scattering data. Results for more than two dozen different (J{sup {pi}}, T) p-shell states, not counting isobaric analogs, have been obtained. The known excitation spectra of all the nuclei are reproduced reasonably well. Density and momentum distributions and various electromagnetic moments and form factors have also been computed. These are the first microscopic calculations that directly produce nuclear shell structure from realistic NN interactions.
Date: October 1, 1997
Creator: Wiringa, R.B.
Partner: UNT Libraries Government Documents Department

Implications of the unusual redox behavior exhibited by the heteropolyanion [EuP{sub 5}W{sub 30}O{sub 110}]{sup 12{minus}}

Description: Materials containing more than one electroactive species may exhibit a variety of unusual properties, including mixed or intermediate valence, and their related phenomena. Intermediate valence arises when localized orbitals, notably valence f-states, interact in a bonding fashion with delocalized, molecular orbitals in the same material. Electrons are viewed to be rapidly hopping between these two very different kinds of orbitals, and it is their relative residence times that are interpreted as a non-integral valence. Whereas there has been considerable efforts expended to understand this unusual behavior, these efforts have not proven successful, largely because the problem is many-bodied and is usually studied on infinite band states, often in chemically complex systems. The authors report here on the novel electrochemical behavior of the heteropolyanion [EuP{sub 5}W{sub 30}O{sub 110}]{sup 12}, and examine the valence of Eu in both the oxidized and reduced form of the anion, as determined from Eu L{sub 3}-edge X-ray absorption near edge structure (XANES). The results demonstrate that, with careful electrochemical control, Eu in this ion may become intermediate valent. Such a result would provide an entirely new and unique approach to longstanding questions related to the phenomenon of intermediate valence.
Date: August 1, 1997
Creator: Antonio, M.R. & Soderholm, L.
Partner: UNT Libraries Government Documents Department

Computational experience with a dense column feature for interior-point methods

Description: Most software that implements interior-point methods for linear programming formulates the linear algebra at each iteration as a system of normal equations. This approach can be extremely inefficient when the constraint matrix has dense columns, because the density of the normal equations matrix is much greater than the constraint matrix and the system is expensive to solve. In this report the authors describe a more efficient approach for this case, that involves handling the dense columns by using a Schur-complement method and conjugate gradient interaction. The authors report numerical results with the code PCx, into which the technique now has been incorporated.
Date: August 1, 1997
Creator: Wenzel, M.; Czyzyk, J. & Wright, S.
Partner: UNT Libraries Government Documents Department

Integrated monitoring and surveillance system demonstration project: Phase I accomplishments

Description: The authors present the results of the Integrated Monitoring and Surveillance System (IMSS) demonstration project Phase I efforts. The rationale behind IMSS development is reviewed and progress in each of the 5 basic tasks is detailed. Significant results include decisions to use Echelon LonWorks networking protocol and Microsoft Access for the data system needs, a preliminary design for the plutonium canning system glovebox, identification of facilities and materials available for the demonstration, determination of possibly affected facility documentation, and a preliminary list of available sensor technologies. Recently imposed changes in the overall project schedule and scope are also discussed and budgetary requirements for competition of Phase II presented. The results show that the IMSS demonstration project team has met and in many cases exceeded the commitments made for Phase I deliverables.
Date: January 15, 1997
Creator: Aumeier, S.E.; Walters, B.G. & Crawford, D.C.
Partner: UNT Libraries Government Documents Department

Report to users of ATLAS

Description: This report covers the following topics: (1) status of the ATLAS accelerator; (2) progress in R and D towards a proposal for a National ISOL Facility; (3) highlights of recent research at ATLAS; (4) the move of gammasphere from LBNL to ANL; (5) Accelerator Target Development laboratory; (6) Program Advisory Committee; (7) ATLAS User Group Executive Committee; and (8) ATLAS user handbook available in the World Wide Web. A brief summary is given for each topic.
Date: March 1, 1997
Creator: Ahmad, I. & Glagola, B.
Partner: UNT Libraries Government Documents Department

Surface roughening, columnar growth and intrinsic stress formation in amorphous CuTi films

Description: The growth of amorphous CuTi films, prepared by electron beam evaporation, is investigated by Scanning Tunneling Microscopy (STM), Small Angle Neutron Scattering (SANS) and in situ measurements of intrinsic mechanical stresses (ISM). In early growth stages the films develop compressive stresses and, with increasing film thickness, a crossover to tensile stresses. In the same thickness range the STM investigations show a change in the growth mode. The experiments suggest a transition from planar growth with statistical surface roughening to columnar growth.
Date: November 1, 1997
Creator: Huelsen, U.V.; Geyer, U. & Thiyagarajan, P.
Partner: UNT Libraries Government Documents Department