PLEIADES: A Picosecond Compton Scattering X-Ray Source for Advanced Backlighting and Time-Resolved Material Studies (open access)

PLEIADES: A Picosecond Compton Scattering X-Ray Source for Advanced Backlighting and Time-Resolved Material Studies

The PLEIADES (Picosecond Laser-Electron Inter-Action for the Dynamical Evaluation of Structures) facility has produced first light at 70 keV. This milestone offers a new opportunity to develop laser-driven, compact, tunable x-ray sources for critical applications such as diagnostics for the National Ignition Facility and time-resolved material studies. The electron beam was focused to 50 {micro}m rms, at 57 MeV, with 260 C of charge, a relative energy spread of 0.2%, and a normalized emittance of 5 mm mrad horizontally and 13 mm mrad vertically. The scattered 820-nm laser pulse had an energy of 180 mJ and a duration of 54 fs. Initial x-rays were captured with a cooled charge-coupled device using a Cesium Iodide scintillator; the peak photon energy was approximately 78 keV, with a total x-ray flux of 1.3 x 10{sup 6} photons/shot, and the observed angular distribution found to agree very well with three-dimensional codes. Simple K-edge radiography of a tantalum foil showed good agreement with the theoretical divergence-angle dependence of the x-ray energy. Optimization of the x-ray dose is currently underway, with the goal of reaching 10{sup 8} photons per shot and a peak brightness approaching 10{sup 20} photons/mm{sup 2}/mrad{sup 2}/s/0.1%bandwidth.
Date: October 20, 2003
Creator: Gibson, D J; Anderson, S G; Barty, C P; Betts, S M; Booth, R; Brown, W J et al.
Object Type: Article
System: The UNT Digital Library
Multi-scale Science: Supporting Emerging Practice with Semantically Derived Provenance (open access)

Multi-scale Science: Supporting Emerging Practice with Semantically Derived Provenance

Scientific progress is becoming increasingly dependent of our ability to study phenomena at multiple scales and from multiple perspectives. The ability to recontextualize third party data within the semantic and syntactic framework of a given research project is increasingly seen as a primary barrier in multi-scale science. Within the Collaboratory for Multiscale Chemical Science (CMCS) project, we are developing a general-purpose informatics-based approach that emphasizes ''on-demand'' metadata creation, configurable data translations, and semantic mapping to support the rapidly increasing and continually evolving requirements for managing data, metadata, and data relationships in such projects. A concrete example of this approach is the design of the CMCS provenance subsystem. The concept of provenance varies across communities, and multiple independent applications contribute to and use provenance. In CMCS, we have developed generic tools for viewing provenance relationships and for using them to, for example, scope notifications and searches. These tools rely on a configurable concept of provenance defined in terms of other relationships. The result is a very flexible mechanism capable of tracking data provenance across many disciplines and supporting multiple uses of provenance information.
Date: October 20, 2003
Creator: Myers, James D.; Pancerella, Carmen M.; Lansing, Carina S.; Schuchardt, Karen L.; Didier, Brett T. & Ashish, N., Goble, C
Object Type: Article
System: The UNT Digital Library
3D HYDRA Simulations of NIF Targets (open access)

3D HYDRA Simulations of NIF Targets

The performance of NIF target designs is simulated in three dimensions using the HYDRA multiphysics radiation hydrodynamics code. In simulations of a cylindrical NIF hohlraum that include an imploding capsule, the motion of the wall material inside the hohlraum shows a high degree of axisymmetry. Laser radiation is able to propagate through the entrance hole for the required duration of the pulse. Gross hohlraum energetics in the simulation mirror the results from an axisymmetric simulation. A simulation of a copper-doped beryllium ablator NIF capsule carried out over large solid angle resolved the full spectrum of the most dangerous modes that grow from surface roughness. Hydrodynamic instabilities evolve into the weakly nonlinear regime. There is no evidence of low mode jetting driven by nonlinear mode coupling.
Date: October 20, 2000
Creator: Marinak, M. M.; Kerbel, G. D.; Gentile, N. A.; Jones, O.; Pollaine, S.; Dittrich, T. R. et al.
Object Type: Article
System: The UNT Digital Library
A method for repairing amplitude defects in multilayer-coated EUV mask blanks (open access)

A method for repairing amplitude defects in multilayer-coated EUV mask blanks

EUV mask blanks are fabricated by depositing a reflective Mo/Si multilayer film onto super-polished substrates. Localized defects in this thin film coating can significantly perturb the reflected field and produce errors in the printed image. Ideally one would want to manufacture defect-free mask blanks; however, this may be very difficult to achieve in practice. One practical way to increase the yield of mask blanks is to be able to repair a significant number of the defects in the multilayer coating. In this paper we present a method for repairing defects that are near the top surface of the coating; we call these amplitude defects because they predominantly attenuate the amplitude of the reflected field. Although the discussion is targeted to the application of manufacturing masks for EUV lithography, the conclusions and results are also applicable to understanding the optical effects of multilayer erosion, including ion-induced multilayer erosion and condenser erosion in EUVL steppers.
Date: October 20, 2003
Creator: Barty, A.; Hau-Riege, S.; Stearns, D.; Clift, M.; Mirkarimi, P.; Gullikson, E. et al.
Object Type: Article
System: The UNT Digital Library
Pulse requirements for electron diffraction imaging of single biological molecules (open access)

Pulse requirements for electron diffraction imaging of single biological molecules

The pulse requirements for electron diffraction imaging of single biological molecules are calculated. We find that the electron fluence and pulse length requirements imposed by the damage limit and by the need to classify the diffraction patterns according to their angular orientation cannot be achieved with today's electron beam technology. A simple analytical model shows that the pulse requirements cannot be achieved due to beam broadening due to spacecharge effects.
Date: October 20, 2004
Creator: Hau-Riege, S; London, R & Chapman, H
Object Type: Report
System: The UNT Digital Library
On the Utility of Antiprotons as Drivers for Inertial Confinement Fusion (open access)

On the Utility of Antiprotons as Drivers for Inertial Confinement Fusion

By contrast to the large mass, complexity and recirculating power of conventional drivers for inertial confinement fusion (ICF), antiproton annihilation offers a specific energy of 90MJ/{micro}g and thus a unique form of energy packaging and delivery. In principle, antiproton drivers could provide a profound reduction in system mass for advanced space propulsion by ICF. We examine the physics underlying the use of antiprotons ({bar p}) to drive various classes of high-yield ICF targets by the methods of volumetric ignition, hotspot ignition and fast ignition. The useable fraction of annihilation deposition energy is determined for both {bar p}-driven ablative compression and {bar p}-driven fast ignition, in association with 0-D and 1-D target burn models. Thereby, we deduce scaling laws for the number of injected antiprotons required per capsule, together with timing and focal spot requirements. The kinetic energy of the injected antiproton beam required to penetrate to the desired annihilation point is always small relative to the deposited annihilation energy. We show that heavy metal seeding of the fuel and/or ablator is required to optimize local deposition of annihilation energy and determine that a minimum of {approx}3x10{sup 15} injected antiprotons will be required to achieve high yield (several hundred megajoules) in …
Date: October 20, 2003
Creator: Perkins, L J; Orth, C D & Tabak, M
Object Type: Report
System: The UNT Digital Library
DETECTION OF TWO MASSIVE CO SYSTEMS IN 4C 41.17 AT z=3.8 (open access)

DETECTION OF TWO MASSIVE CO SYSTEMS IN 4C 41.17 AT z=3.8

We have detected CO(4-3) in the z=3.8 radio galaxy 4C 41.17 with the IRAM Interferometer. The CO is in two massive (M{sub dyn} {approx}> 2.5 x 10{sup 11} M{sub {circle_dot}}) systems separated by 1.8 (13 kpc), and by 400 km s{sup -1} in velocity, which coincide with two different dark lanes in a deep Ly{alpha} image. One CO component coincides with the cm-radio core of the radio galaxy, and its redshift is close to that of the He II {lambda} 1640 AGN line. The second CO component is near the base of a cone-shaped region southwest of the nucleus, which resembles the emission-line cones seen in nearby AGN and starburst galaxies. The characteristics of the CO sources and their mm/submm dust continuum are similar to those found in ultraluminous IR galaxies and in some high-z radio galaxies and quasars. The fact that 4C 41.17 contains two CO systems is further evidence for the role of mergers in the evolution of galaxies at high redshift.
Date: October 20, 2004
Creator: DeBreuck, C; Downes, D; Neri, R; van Breugel, W; Reuland, M; Omont, A et al.
Object Type: Article
System: The UNT Digital Library
New York State Code Adoption Analysis: Lighting Requirements (open access)

New York State Code Adoption Analysis: Lighting Requirements

The adoption of the IECC 2003 Energy code will include a set of Lighting Power Density (LPD) values that are effectively a subset of the values in Addendum g to the ASHRAE/IESNA/ANSI 90.1-2001 Standard which will soon be printed as part of the 90.1-2004 version. An analysis of the effectiveness of this adoption for New York State can be provided by a direct comparison of these values with existing LPD levels represented in the current IECC 2000 code, which are themselves a subset of the current ASHRAE/IESNA/ANSI 90.1-2001 Standard (without addenda). Because the complete ASHRAE 2001 and 2004 sets of LPDs are supported by a set of detailed models, they are best suited to provide the basis for an analysis comparison of the two code levels of lighting power density stringency. It is important to note that this kind of analysis is a point-to-point comparison where a fixed level of real world activity is assumed. It is understood that buildings are not built precisely to code levels and that actual percentage of compliance above and below codes will vary among individual buildings and building types. However, without specific knowledge of this real world activity for all buildings in existence and …
Date: October 20, 2004
Creator: Richman, Eric E.
Object Type: Report
System: The UNT Digital Library
X-Ray Spectropolarimetry Studies at the Nevada Terawatt Facility and LLNL EBIT (open access)

X-Ray Spectropolarimetry Studies at the Nevada Terawatt Facility and LLNL EBIT

Recent results from x-pinches at the NTF provide experimental evidence for the existence of strong electron beams in x-pinch plasmas and motivate the development of a new diagnostic, x-ray spectropolarimetry, for investigating the anisotropy of such plasmas. This diagnostic is based on theoretical modeling of polarization-dependent spectra measured simultaneously by spectrometers with different sensitivity to polarization. Results of the first polarization-sensitive experiments at the NTF are presented. K-shell emission from Ti x-pinches is recorded simultaneously by two identical spectrometers with the dispersion plane perpendicular and parallel to the discharge axis. The spectroscopic analysis of more than eight Ti x-pinch shots show how spectropolarimetry complements the usual diagnostics of a z-pinch plasma. The polarization-sensitive spectra, generated by a Maxwellian electron beam at LLNL EBIT have been collected and analyzed. These data make an important contribution to the plasma polarization spectroscopy program at the NTF. In particular, the study of multiply-charged Ti ion spectra help in the interpretation of the polarization-sensitive spectra from Ti x-pinches at the NTF.
Date: October 20, 2001
Creator: Shlyaptseva, A S; Kantsyrev, V L; Bauer, B S; Neill, P; Harris, C; Fedin, D A et al.
Object Type: Article
System: The UNT Digital Library
Photonuclear Benchmarks with a Comparison of COG and MCNPX Results (open access)

Photonuclear Benchmarks with a Comparison of COG and MCNPX Results

The Nuclear Data Section of the International Atomic Energy Agency (IAEA) has distributed an evaluated photonuclear data library in standard ENDF-6 format that is intended for use in transport codes. This ''IAEA Photonuclear Data Library'' consists of a number of individual ASCII text files for various elements that have been recently processed into the single binary (COG data library) file ''COGPNUC'' with corresponding changes to the COG code for use in transport calculations involving photonuclear reactions.
Date: October 20, 2003
Creator: Heinrichs, D P & Lent, E M
Object Type: Article
System: The UNT Digital Library
A Model and Controller Reduction Method for Robust Control Design (open access)

A Model and Controller Reduction Method for Robust Control Design

A bifurcation subsystem based model and controller reduction approach is presented. Using this approach a robust {micro}-synthesis SVC control is designed for interarea oscillation and voltage control based on a small reduced order bifurcation subsystem model of the full system. The control synthesis problem is posed by structured uncertainty modeling and control configuration formulation using the bifurcation subsystem knowledge of the nature of the interarea oscillation caused by a specific uncertainty parameter. Bifurcation subsystem method plays a key role in this paper because it provides (1) a bifurcation parameter for uncertainty modeling; (2) a criterion to reduce the order of the resulting MSVC control; and (3) a low order model for a bifurcation subsystem based SVC (BMSVC) design. The use of the model of the bifurcation subsystem to produce a low order controller simplifies the control design and reduces the computation efforts so significantly that the robust {micro}-synthesis control can be applied to large system where the computation makes robust control design impractical. The RGA analysis and time simulation show that the reduced BMSVC control design captures the center manifold dynamics and uncertainty structure of the full system model and is capable of stabilizing the full system and achieving satisfactory …
Date: October 20, 2003
Creator: Yue, M. & Schlueter, R.
Object Type: Article
System: The UNT Digital Library
A shallow subsurface controlled release facility in Bozeman, Montana, USA, for testing near surface CO2 detection techniques and transport models (open access)

A shallow subsurface controlled release facility in Bozeman, Montana, USA, for testing near surface CO2 detection techniques and transport models

A controlled field pilot has been developed in Bozeman, Montana, USA, to study near surface CO2 transport and detection technologies. A slotted horizontal well divided into six zones was installed in the shallow subsurface. The scale and CO2 release rates were chosen to be relevant to developing monitoring strategies for geological carbon storage. The field site was characterized before injection, and CO2 transport and concentrations in saturated soil and the vadose zone were modeled. Controlled releases of CO2 from the horizontal well were performed in the summers of 2007 and 2008, and collaborators from six national labs, three universities, and the U.S. Geological Survey investigated movement of CO2 through the soil, water, plants, and air with a wide range of near surface detection techniques. An overview of these results will be presented.
Date: October 20, 2009
Creator: Spangler, L.H.; Dobeck, L.M.; Nehrir, A.; Humphries, S.; Barr, J.; Keith, C. et al.
Object Type: Article
System: The UNT Digital Library
Direct Photonic-Plasmonic Coupling and Routing in Single Nanowires (open access)

Direct Photonic-Plasmonic Coupling and Routing in Single Nanowires

Metallic nanoscale structures are capable of supporting surface plasmon polaritons (SPPs), propagating collective electron oscillations with tight spatial confinement at the metal surface. SPPs represent one of the most promising structures to beat the diffraction limit imposed by conventional dielectric optics. Ag nano wires have drawn increasing research attention due to 2D sub-100 nm mode confinement and lower losses as compared with fabricated metal structures. However, rational and versatile integration of Ag nanowires with other active and passive optical components, as well as Ag nanowire based optical routing networks, has yet to be achieved. Here, we demonstrate that SPPs can be excited simply by contacting a silver nanowire with a SnO2 nanoribbon that serves both as an unpolarized light source and a dielectric waveguide. The efficient coupling makes it possible to measure the propagation-distance-dependent waveguide spectra and frequency-dependent propagation length on a single Ag nanowire. Furthermore, we have demonstrated prototypical photonic-plasmonic routing devices, which are essential for incorporating low-loss Ag nanowire waveguides as practical components into high-capacity photonic circuits.
Date: October 20, 2009
Creator: Yan, Rouxue; Pausauskie, Peter; Huang, Jiaxing & Yang, Piedong
Object Type: Article
System: The UNT Digital Library
Tissue architecture: the ultimate regulator of breast epithelial function (open access)

Tissue architecture: the ultimate regulator of breast epithelial function

A problem in developmental biology that continues to take center stage is how higher organisms generate diverse tissues and organs given the same cellular genotype. In cell and tumor biology, the key question is not the production of form, but its preservation: how do tissues and organs maintain homeostasis, and how do cells within tissues lose or overcome these controls in cancer? Undoubtedly, mechanisms that maintain tissue specificity should share features with those employed to drive formation of the tissues. However, they are unlikely to be identical. At a simplistic level, developmental pathways may be thought of as a series of extremely rapid short-term events. Each new step depends on what came before, and the outcome is the organism itself at birth. All organs, with a few notable exceptions, such as the mammary gland and the brain, 'arrive' together and are complete when the organism is born. In mice and humans, these events occur in a mere 21 days and 9 months respectively. The stability of the differentiated state and the homeostasis of the organism, on the other hand, will last 40-110 times longer. How does the organism achieve this feat? How are tissues maintained? These questions also relate fundamentally …
Date: October 20, 2003
Creator: Bissell, Mina J; Rizki, Aylin & Mian, Saira
Object Type: Article
System: The UNT Digital Library
Form CJ-7, Annual Parole Survey: 2009 (open access)

Form CJ-7, Annual Parole Survey: 2009

Blank parole data survey containing a series of questions related to the parole population in a particular location, with instructions for filling out the survey.
Date: October 20, 2009
Creator: United States. Bureau of Justice Statistics.
Object Type: Text
System: The UNT Digital Library
Photoinduced Charge and Energy Transfer Processes in Molecular Aggregates (open access)

Photoinduced Charge and Energy Transfer Processes in Molecular Aggregates

This project involved the experimental probing of the electronic excited states generated by photoinduced (center-to-center) electron and energy transfer processes in several classes of transition metal donor/acceptor (D/A) complexes. Some of the general properties inferred from these studies should be useful in the design of new systems for energy conversion applications. Pursuit of the project goals has involved the determination of electron transfer efficiencies and the detailed study of variations in the electronic spectra of D/A complexes. This has resulted in the study of some very fundamental issues of photoinduced charge transfer and the identification of some of the constraints on its efficiency. The experimental studies of the competition between the degradative non-radiative unimolecular relaxation of transition metal excited states and their transfer of charge from these excited states to external acceptors have involved a range of techniques such as transient decay kinetics, photoacoustic calorimetry and transient or stationary state spectroscopy. The substrates synthesized for these studies were selected to provide model systems, or series of model systems to probe the validity of models of electronic excited states and their reactivity. The work during the last few years has focused largely, but not exclusively, on the use of emission spectral …
Date: October 20, 2009
Creator: Endicott, John F.
Object Type: Report
System: The UNT Digital Library
Grays River Watershed Restoration Status Report 2007, May 1, 2007 - October 30, 2008. (open access)

Grays River Watershed Restoration Status Report 2007, May 1, 2007 - October 30, 2008.

The Bonneville Power Administration (BPA) Project 2003-013-00, 'Grays River Watershed Restoration', began in FY04 and continues into FY09. This status report is intended to summarize accomplishments during the period 1 May 2007 through 30 October 2008. Accomplishments are summarized by Work Elements, as detailed in the Statement of Work (see BPA's project management database PISCES). The Pacific Northwest National Laboratory (PNNL) is collaborating with the Columbia River Estuary Task Force (CREST) on implementation of the Grays River Restoration Project. The Grays River is vitally important to the recovery of Lower Columbia River (LCR) chum salmon because it currently has the most viable population remaining in the LCR region. The Grays River watershed is also important to the recovery of salmon and steelhead in the LCR ecosystem. Today, numbers of naturally spawning salmon and steelhead have declined to levels far below historical numbers because of habitat limiting factors that include but are not limited to the lack of habitat connectivity, diversity, channel stability, riparian function and altered stream flow conditions. The objective of this project is to restore habitat-forming processes to enhance salmon and steelhead populations in the Grays River, following recommendations developed during the FY04-06 BPA-sponsored Grays River Watershed Assessment …
Date: October 20, 2008
Creator: Hanrahan, Tim
Object Type: Report
System: The UNT Digital Library
Utah Heavy Oil Program (open access)

Utah Heavy Oil Program

The Utah Heavy Oil Program (UHOP) was established in June 2006 to provide multidisciplinary research support to federal and state constituents for addressing the wide-ranging issues surrounding the creation of an industry for unconventional oil production in the United States. Additionally, UHOP was to serve as an on-going source of unbiased information to the nation surrounding technical, economic, legal and environmental aspects of developing heavy oil, oil sands, and oil shale resources. UHOP fulGilled its role by completing three tasks. First, in response to the Energy Policy Act of 2005 Section 369(p), UHOP published an update report to the 1987 technical and economic assessment of domestic heavy oil resources that was prepared by the Interstate Oil and Gas Compact Commission. The UHOP report, entitled 'A Technical, Economic, and Legal Assessment of North American Heavy Oil, Oil Sands, and Oil Shale Resources' was published in electronic and hard copy form in October 2007. Second, UHOP developed of a comprehensive, publicly accessible online repository of unconventional oil resources in North America based on the DSpace software platform. An interactive map was also developed as a source of geospatial information and as a means to interact with the repository from a geospatial setting. …
Date: October 20, 2009
Creator: Bauman, J.; Burian, S.; Deo, M.; Eddings, E.; Gani, R.; Goel, R. et al.
Object Type: Report
System: The UNT Digital Library
Lightning Arrestor Connectors Production Readiness (open access)

Lightning Arrestor Connectors Production Readiness

The Lightning Arrestor Connector (LAC), part “M”, presented opportunities to improve the processes used to fabricate LACs. The A## LACs were the first production LACs produced at the KCP, after the product was transferred from Pinnellas. The new LAC relied on the lessons learned from the A## LACs; however, additional improvements were needed to meet the required budget, yield, and schedule requirements. Improvement projects completed since 2001 include Hermetic Connector Sealing Improvement, Contact Assembly molding Improvement, development of a second vendor for LAC shells, general process improvement, tooling improvement, reduction of the LAC production cycle time, and documention of the LAC granule fabrication process. This report summarizes the accomplishments achieved in improving the LAC Production Readiness.
Date: October 20, 2008
Creator: Marten, Steve; Linder, Kim; Emmons, Jim; Gomez, Antonio; Hasam, Dawud & Maurer, Michelle
Object Type: Report
System: The UNT Digital Library
Interfacial Structures of Acidic and Basic Aqueous Solutions (open access)

Interfacial Structures of Acidic and Basic Aqueous Solutions

Phase-sensitive sum-frequency vibrational spectroscopy was used to study water/vapor interfaces of HCl, HI, and NaOH solutions. The measured imaginary part of the surface spectral responses provided direct characterization of OH stretch vibrations and information about net polar orientations of water species contributing to different regions of the spectrum. We found clear evidence that hydronium ions prefer to emerge at interfaces. Their OH stretches contribute to the 'ice-like' band in the spectrum. Their charges create a positive surface field that tends to reorient water molecules more loosely bonded to the topmost water layer with oxygen toward the interface, and thus enhances significantly the 'liquid-like' band in the spectrum. Iodine ions in solution also like to appear at the interface and alter the positive surface field by forming a narrow double-charge layer with hydronium ions. In NaOH solution, the observed weak change of the 'liquid-like' band and disappearance of the 'ice-like' band in the spectrum indicates that OH{sup -} ions must also have excess at the interface. How they are incorporated in the interfacial water structure is however not clear.
Date: October 20, 2008
Creator: Tian, C.; Ji, N.; Waychunas, G. & Shen, Y.R.
Object Type: Article
System: The UNT Digital Library
Transport of Parallel Momentum by Toroidal Ion Temperature Gradient Instability near Marginality (open access)

Transport of Parallel Momentum by Toroidal Ion Temperature Gradient Instability near Marginality

The turbulent angular momentum flux carried by ions resonant with toroidal ion temperature gradient(ITG) instability is calculated via quasilinear calculation using the phase-space conserving gyrokinetic equation in the laboratory frame. The results near ITG marginality indicate that the inward turbulent equipartition (TEP) momentum pinch [Hahm T.S. et al 2007 Phys. Plasmas 14 072302] remains as the most robust part of pinch. In addition, ion temperature gradient driven momentum flux is inward for typical parameters, while density gradient driven momentum flux is outward as in the previous kinetic result in slab geometry [Diamond P.H. et al 2008 Phys. Plasmas 15 012303].
Date: October 20, 2009
Creator: Yoon, E. S. & Hahm, T. S.
Object Type: Report
System: The UNT Digital Library
CMM Technology (open access)

CMM Technology

This project addressed coordinate measuring machine (CMM) technology and model-based engineering. CMM data analysis and delivery were enhanced through the addition of several machine types to the inspection summary program. CMM hardware and software improvements were made with the purchases of calibration and setup equipment and new model-based software for the creation of inspection programs. Kansas City Plant (KCP) personnel contributed to and influenced the development of dimensional metrology standards. Model-based engineering capabilities were expanded through the development of software for the tolerance analysis of piece parts and for the creation of model-based CMM inspection programs and inspection plans and through the purchase of off-the-shelf software for the tolerance analysis of mechanical assemblies. An obsolete database application used to track jobs in Precision Measurement was replaced by a web-based application with improved query and reporting capabilities. A potential project to address the transformation of the dimensional metrology enterprise at the Kansas City Plant was identified.
Date: October 20, 2008
Creator: Ward, Robert C.
Object Type: Report
System: The UNT Digital Library
From Artificial Atoms to Nanocrystal Molecules: Preparation and Properties of More Complex Nanostructures (open access)

From Artificial Atoms to Nanocrystal Molecules: Preparation and Properties of More Complex Nanostructures

Quantum dots, which have found widespread use in fields such as biomedicine, photovoltaics, and electronics, are often called artificial atoms due to their size-dependent physical properties. Here this analogy is extended to consider artificial nanocrystal molecules, formed from well-defined groupings of plasmonically or electronically coupled single nanocrystals. Just as a hydrogen molecule has properties distinct from two uncoupled hydrogen atoms, a key feature of nanocrystal molecules is that they exhibit properties altered from those of the component nanoparticles due to coupling. The nature of the coupling between nanocrystal atoms and its response to vibrations and deformations of the nanocrystal molecule bonds are of particular interest. We discuss synthetic approaches, predicted and observed physical properties, and prospects and challenges toward this new class of materials.
Date: October 20, 2009
Creator: Choi, Charina L & Alivisatos, A. Paul
Object Type: Article
System: The UNT Digital Library
A STUDY ON LEGIONELLA PNEUMOPHILA, WATER CHEMISTRY, AND ATMOSPHERIC CONDITIONS IN COOLING TOWERS AT THE SAVANNAH RIVER SITE (open access)

A STUDY ON LEGIONELLA PNEUMOPHILA, WATER CHEMISTRY, AND ATMOSPHERIC CONDITIONS IN COOLING TOWERS AT THE SAVANNAH RIVER SITE

Legionnaires disease is a pneumonia caused by the inhalation of the bacterium Legionella pneumophila. The majority of illnesses have been associated with cooling towers since these devices can harbor and disseminate the bacterium in the aerosolized mist generated by these systems. Historically, Savannah River Site (SRS) cooling towers have had occurrences of elevated levels of Legionella in all seasons of the year and in patterns that are difficult to predict. Since elevated Legionella in cooling tower water are a potential health concern a question has been raised as to the best control methodology. In this work we analyze available chemical, biological, and atmospheric data to determine the best method or key parameter for control. The SRS 4Q Industrial Hygiene Manual, 4Q-1203, 1 - G Cooling Tower Operation and the SRNL Legionella Sampling Program, states that 'Participation in the SRNL Legionella Sampling Program is MANDATORY for all operating cooling towers'. The resulting reports include L. pneumophila concentration information in cells/L. L. pneumophila concentrations >10{sup 7} cells/L are considered elevated and unsafe so action must be taken to reduce these densities. These remedial actions typically include increase biocide addition or 'shocking'. Sometimes additional actions are required if the problem persists including increase …
Date: October 20, 2009
Creator: Smith, C. & Brigmon, R.
Object Type: Article
System: The UNT Digital Library