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Lithographically-directed self-assembly of nanostructures (open access)

Lithographically-directed self-assembly of nanostructures

The combination of lithography and self-assembly provides apowerful means of organizing solution-synthesized nanostructures for awide variety of applications. We have developed a fluidic assembly methodthat relies on the local pinning of a moving liquid contact line bylithographically produced topographic features to concentratenanoparticles at those features. The final stages of the assembly processare controlled first by long-range immersion capillary forces and then bythe short-range electrostatic and Van der Waal's interactions. We havesuccessfully assembled nanoparticles from 50 nm to 2 nm in size usingthis technique and have also demonstrated the controlled positioning ofmore complex nanotetrapod structures. We have used this process toassemble Au nanoparticles into pre-patterned electrode structures andhave performed preliminary electrical characterization of the devices soformed. The fluidic assembly method is capable of very high yield, interms of positioning nanostructures at each lithographically-definedlocation, and of excellent specificity, with essentially no particledeposition between features.
Date: September 21, 2004
Creator: Liddle, J. Alexander; Cui, Yi & Alivisatos, Paul
System: The UNT Digital Library
Quantitative Evaluation of Bio-Aerosol Mass Spectrometry for the Real-Time Detection of Individual Airborne Mycobacterium Tuberculosis H37Ra Particles (open access)

Quantitative Evaluation of Bio-Aerosol Mass Spectrometry for the Real-Time Detection of Individual Airborne Mycobacterium Tuberculosis H37Ra Particles

None
Date: May 21, 2004
Creator: Tobias, H; Schafer, M; Pitesky, M; Horn, J & Frank, M
System: The UNT Digital Library
Near-infrared Adaptive Optics Imaging of the Satellites and Individual Rings of Uranus from the W.M. Keck Observatory (open access)

Near-infrared Adaptive Optics Imaging of the Satellites and Individual Rings of Uranus from the W.M. Keck Observatory

None
Date: January 21, 2004
Creator: Gibbard, S G; de Pater, I & Hammel, H B
System: The UNT Digital Library
FUDGE: A Program for Performing Nuclear Data Testing and Sensitivity Studies (open access)

FUDGE: A Program for Performing Nuclear Data Testing and Sensitivity Studies

We have developed a program called FUDGE that allows one to modify data from LLNL's nuclear database. After modifying data, FUDGE can then be instructed to process the data into the formats used by LLNL's deterministic (ndf) and the Monte Carlo (MCAPM) transport codes. This capability allows users to perform nuclear data sensitivity studies without modification of the transport modeling codes. FUDGE is designed to be user friendly (object-oriented) and fast (the modification and processing typically takes about a minute). It uses Python as a front-end, making it flexible and scriptable. Comparing, plotting and printing of the data are also supported. An overview of FUDGE will be presented as well as examples.
Date: September 21, 2004
Creator: Beck, B R
System: The UNT Digital Library
An Integrated Universal Collapsar Gamma-ray Burst Model (open access)

An Integrated Universal Collapsar Gamma-ray Burst Model

Starting with two assumptions: (1) gamma-ray bursts originate from stellar death phenomena or so called ''collapsars'' and (2) that these bursts are quasi-universal, whereby the majority of the observed variation is due to our perspective of the jet, an integrated gamma-ray burst model is proposed. It is found that several of the key correlations in the data can be naturally explained with this simple picture and another possible correlation is predicted.
Date: January 21, 2004
Creator: Salmonson, J D
System: The UNT Digital Library
Laser- and Radar-based Mission Concepts for Suborbital and Spaceborne Monitoring of Seismic Surface Waves (open access)

Laser- and Radar-based Mission Concepts for Suborbital and Spaceborne Monitoring of Seismic Surface Waves

The development of a suborbital or spaceborne system to monitor seismic waves poses an intriguing prospect for advancing the state of seismology. This capability would enable an unprecedented global mapping of the velocity structure of the earth's crust, understanding of earthquake rupture dynamics and wave propagation effects, and event source location, characterization and discrimination that are critical for both fundamental earthquake research and nuclear non-proliferation applications. As part of an ongoing collaboration between LLNL and JPL, an advanced mission concept study assessed architectural considerations and operational and data delivery requirements, extending two prior studies by each organization--a radar-based satellite system (JPL) for earthquake hazard assessment and a feasibility study of space- or UAV-based laser seismometer systems (LLNL) for seismic event monitoring. Seismic wave measurement requirements include lower bounds on detectability of specific seismic sources of interest and wave amplitude accuracy for different levels of analysis, such as source characterization, discrimination and tomography, with a 100 {micro}m wave amplitude resolution for waves nominally traveling 5 km/s, an upper frequency bound based on explosion and earthquake surface displacement spectra, and minimum horizontal resolution (1-5 km) and areal coverage, in general and for targeted observations. For a radar system, corresponding engineering and operational …
Date: September 21, 2004
Creator: Foxall, W; Schultz, C A & Tralli, D M
System: The UNT Digital Library
MATRIX PRODUCT VARIATIONAL FORMULATION FOR LATTICE GAUGE THEORY. (open access)

MATRIX PRODUCT VARIATIONAL FORMULATION FOR LATTICE GAUGE THEORY.

For hamiltonian lattice gauge theory, we introduce the matrix product ansatz inspired from density matrix renormalization group. In this method, wavefunction of the target state is assumed to be a product of finite matrices. As a result, the energy becomes a simple function of the matrices, which can be evaluated using a computer. The minimum of the energy function corresponds to the vacuum state. We show that the S = 1/2 Heisenberg chain model are well described with the ansatz. The method is also applied to the two-dimensional S = 1/2 Heisenberg and U(1) plaquette chain models.
Date: September 21, 2004
Creator: SUGIHARA,T.
System: The UNT Digital Library
Feature Subset Selection, Class Separability, and Genetic Algorithms (open access)

Feature Subset Selection, Class Separability, and Genetic Algorithms

The performance of classification algorithms in machine learning is affected by the features used to describe the labeled examples presented to the inducers. Therefore, the problem of feature subset selection has received considerable attention. Genetic approaches to this problem usually follow the wrapper approach: treat the inducer as a black box that is used to evaluate candidate feature subsets. The evaluations might take a considerable time and the traditional approach might be unpractical for large data sets. This paper describes a hybrid of a simple genetic algorithm and a method based on class separability applied to the selection of feature subsets for classification problems. The proposed hybrid was compared against each of its components and two other feature selection wrappers that are used widely. The objective of this paper is to determine if the proposed hybrid presents advantages over the other methods in terms of accuracy or speed in this problem. The experiments used a Naive Bayes classifier and public-domain and artificial data sets. The experiments suggest that the hybrid usually finds compact feature subsets that give the most accurate results, while beating the execution time of the other wrappers.
Date: January 21, 2004
Creator: Cantu-Paz, E
System: The UNT Digital Library
Open Midplane Dipole Design for Lhc Ir Upgrade. (open access)

Open Midplane Dipole Design for Lhc Ir Upgrade.

The proposed luminosity upgrade of the Large Hadron Collider (LHC), now under construction, will bring a large increase in the number of secondary particles from p-p collisions at the interaction point (IP). Energy deposition will be so large that the lifetime and quench performance of interaction region (IR) magnets may be significantly reduced if conventional designs are used. Moreover, the cryogenic capacity of the LHC will have to be significantly increased as the energy deposition load on the interaction region (IR) magnets by itself will exhaust the present capacity. We propose an alternate open midplane dipole design concept for the dipole-first optics that mitigates these issues. The proposed design takes advantage of the fact that most of the energy is deposited in the midplane region. The coil midplane region is kept free of superconductor, support structure and other material. Initial energy deposition calculations show that the increase in temperature remains within the quench tolerance of the superconducting coils. In addition, most of the energy is deposited in a relatively warm region where the heat removal is economical. We present the basic concept and preliminary design that includes several innovations.
Date: January 21, 2004
Creator: Gupta, R.; Anerella, M.; Harrison, M.; Schmalzle, J. & Mokhov, N.
System: The UNT Digital Library
Rapid Degradation of Alkanethiol-Based Self-Assembled Monolayers on Gold in Ambient Laboratory Conditions (open access)

Rapid Degradation of Alkanethiol-Based Self-Assembled Monolayers on Gold in Ambient Laboratory Conditions

Self-assembled monolayers (SAMs) consisting of alkanethiols and similar sulfur-containing molecules on noble metal substrates are extensively used and explored for various chemical and biological surface-functionalization in the scientific community. SAMs consisting of thiol- or disulfide-containing molecules adsorbed on gold are commonly used due to their ease of preparation and stability. However, the gold-thiolate bond is easily and rapidly oxidized under ambient conditions, adversely affecting SAM quality and structure. Here, the oxidation of dodecanethiol on gold is explored for various 12-hour exposures to ambient laboratory air and light. SAM samples are freshly prepared, air-exposed, and stored in small, capped vials. X-ray photoelectron spectroscopy (XPS) reveals nearly complete oxidation of the thiolate in air-exposed samples, and a decrease in carbon signal on the surface. Near-edge X-ray absorption fine structure spectroscopy (NEXAFS) at the Carbon K-edge shows a loss of upright orientational order upon air-exposure. Alternatively, the oxidation of the thiolate is minor when SAMs are stored in limited-air-containing small 15 ml vials. Thus, care must be taken to avoid SAM degradation by ensuring alkanethiolates on gold have sufficient durability for each intended environment and application.
Date: July 21, 2004
Creator: Willey, T M; Vance, A L; van Buuren, T; Bostedt, C; Terminello, L J & Fadley, C S
System: The UNT Digital Library
Compensation for Bunch Emittance in a Magnetization and Space Charge Dominated Beam. (open access)

Compensation for Bunch Emittance in a Magnetization and Space Charge Dominated Beam.

In order to obtain sufficient cooling rates for the Relativistic Heavy Ion Collider (RHIC) electron cooling, a bunched beam with high bunch charge, high repetition frequency and high energy is required and it is necessary to use a ''magnetized'' beam, i.e., an electron beam with non-negligible angular momentum. Applying a longitudinal solenoid field on the cathode can generate such a beam, which rotates around its longitudinal axis in a field-free region. This paper suggests how a magnetized beam can be accelerated and transported from a RF photocathode electron gun to the cooling section without significantly increasing its emittance. The evolution of longitudinal slices of the beam under a combination of space charge and magnetization is investigated, using paraxial envelope equations and numerical simulations. We find that we must modify the traditional method of compensating for emittance as used for normal non-magnetized beam with space charge to account for magnetization. The results of computer simulations of successful compensation are presented. Alternately, we show an electron bunch density distribution for which all slices propagate uniformly and which does not require emittance compensation.
Date: June 21, 2004
Creator: Chang, X.; Ben-Zvi, Ilan & Kewisch, J.
System: The UNT Digital Library
Proceedings of the 26th Seismic Research Review: Trends in Nuclear Explosion Monitoring (open access)

Proceedings of the 26th Seismic Research Review: Trends in Nuclear Explosion Monitoring

These proceedings contain papers prepared for the 26th Seismic Research Review: Trends in Nuclear Explosion Monitoring, held 21-23 September, 2004 in Orlando, Florida. These papers represent the combined research related to ground-based nuclear explosion monitoring funded by the National Nuclear Security Administration (NNSA), Defense Threat Reduction Agency (DTRA), Air Force Research Laboratory (AFRL), US Army Space and Missile Defense Command, and other invited sponsors. The scientific objectives of the research are to improve the United States capability to detect, locate, and identify nuclear explosions. The purpose of the meeting is to provide the sponsoring agencies, as well as potential users, an opportunity to review research accomplished during the preceding year and to discuss areas of investigation for the coming year. For the researchers, it provides a forum for the exchange of scientific information toward achieving program goals, and an opportunity to discuss results and future plans. Paper topics include: seismic regionalization and calibration; detection and location of sources; wave propagation from source to receiver; the nature of seismic sources, including mining practices; hydroacoustic, infrasound, and radionuclide methods; on-site inspection; and data processing.
Date: September 21, 2004
Creator: Chavez, Francesca C.; Benson, Jody; Hanson, Stephanie; Mark, Carol & Wetovsky, Marvin A.
System: The UNT Digital Library
Reducing Complexity in Parallel Algebraic Multigrid Preconditioners (open access)

Reducing Complexity in Parallel Algebraic Multigrid Preconditioners

Algebraic multigrid (AMG) is a very efficient iterative solver and preconditioner for large unstructured linear systems. Traditional coarsening schemes for AMG can, however, lead to computational complexity growth as problem size increases, resulting in increased memory use and execution time, and diminished scalability. Two new parallel AMG coarsening schemes are proposed, that are based on solely enforcing a maximum independent set property, resulting in sparser coarse grids. The new coarsening techniques remedy memory and execution time complexity growth for various large three-dimensional (3D) problems. If used within AMG as a preconditioner for Krylov subspace methods, the resulting iterative methods tend to converge fast. This paper discusses complexity issues that can arise in AMG, describes the new coarsening schemes and examines the performance of the new preconditioners for various large 3D problems.
Date: September 21, 2004
Creator: De Sterck, H; Yang, U M & Heys, J
System: The UNT Digital Library
Comparison of Four Parallel Algorithms For Domain Decomposed Implicit Monte Carlo (open access)

Comparison of Four Parallel Algorithms For Domain Decomposed Implicit Monte Carlo

We consider two existing asynchronous parallel algorithms for Implicit Monte Carlo (IMC) thermal radiation transport on spatially decomposed meshes. The two algorithms are from the production codes KULL from Lawrence Livermore National Laboratory and Milagro from Los Alamos National Laboratory. Both algorithms were considered and analyzed in an implementation of the KULL IMC package in ALEGRA, a Sandia National Laboratory high energy density physics code. Improvements were made to both algorithms. The improved Milagro algorithm performed the best by scaling nearly perfectly out to 244 processors.
Date: December 21, 2004
Creator: Brunner, T A; Urbatsch, T J; Evans, T M & Gentile, N A
System: The UNT Digital Library
Comments on Cosmic Censorship in AdS/CFT (open access)

Comments on Cosmic Censorship in AdS/CFT

Recently Hertog, Horowitz, and Maeda (HHM) (hep-th/0310054) have proposed that cosmic censorship can be violated in the AdS/CFT context. They argue that for certain initial data there is insufficient energy available to make a black hole whose horizon is big enough to cloak the singularity that forms. We have investigated this proposal in the models HHM discuss and have thus far been unable to find initial data that provably satisfy this criterion, despite our development of an improved lower bound on the size of the singular region. This is consistent with recent numerical results (hep-th/0402109). For certain initial data, the energies of our configurations are not far above the lower bound on the requisite black hole mass, and so it is possible that in the exact time development naked singularities do form. We go on to argue that the finite radius cut-off AdS_5 situation discussed by HHM displays instabilities when the full 10D theory is considered. We propose an AdS_3 example that may well be free of this instability.
Date: March 21, 2004
Creator: Hubeny, Veronika E.; Liu, Xiao; Rangamani, Mukund & Shenker, Stephen
System: The UNT Digital Library
Effect of Nitrate on the Repassivation Potential of Alloy 22 in Chloride Containing Environment (open access)

Effect of Nitrate on the Repassivation Potential of Alloy 22 in Chloride Containing Environment

The study of Alloy 22 was undertaken in several selected nitrate/chloride (NO{sub 3}{sup -}/Cl{sup -}) electrolytes with chloride concentrations [Cl{sup -}] of 1.0, 3.5 and 6.0 molal with [NO{sub 3}{sup -}]/[Cl{sup -}] ratios of 0.05, 0.15 and 0.5 at temperatures up to 100 C. The repassivation potentials increased with increase in [NO{sub 3}{sup -}]/[Cl{sup -}] ratio and decreased with increase in temperature. The absolute [Cl{sup -}] was found to have less of an effect on the repassivation potential compared with temperature and the [NO{sub 3}{sup -}]/[Cl{sup -}]. Regression analyses were carried out to describe the relationship between the repassivation potential, temperature, [Cl{sup -}] and [NO{sub 3}{sup -}] for the conditions tested.
Date: September 21, 2004
Creator: Ilevbare, G.; King, K.; Gordon, S.; Elayat, H.; Gdowski, G. & Summers, T.
System: The UNT Digital Library
Quantum physics in neuroscience and psychology: A neurophysicalmodel of the mind/brain interaction (open access)

Quantum physics in neuroscience and psychology: A neurophysicalmodel of the mind/brain interaction

Neuropsychological research on the neural basis of behavior generally posits that brain mechanisms will ultimately suffice to explain all psychologically described phenomena. This assumption stems from the idea that the brain is made up entirely of material particles and fields, and that all causal mechanisms relevant to neuroscience can therefore be formulated solely in terms of properties of these elements. Thus terms having intrinsic mentalistic and/or experiential content (e.g., ''feeling,'' ''knowing,'' and ''effort'') are not included as primary causal factors. This theoretical restriction is motivated primarily by ideas about the natural world that have been known to be fundamentally incorrect for more than three quarters of a century. Contemporary basic physical theory differs profoundly from classical physics on the important matter of how the consciousness of human agents enters into the structure of empirical phenomena. The new principles contradict the older idea that local mechanical processes alone can account for the structure of all observed empirical data. Contemporary physical theory brings directly and irreducibly into the overall causal structure certain psychologically described choices made by human agents about how they will act. This key development in basic physical theory is applicable to neuroscience, and it provides neuroscientists and psychologists with …
Date: September 21, 2004
Creator: Schwartz, Jeffrey M.; Stapp, Henry P. & Beauregard, Mario
System: The UNT Digital Library
Virtual Building Environments (VBE) - Applying Information Modeling to Buildings (open access)

Virtual Building Environments (VBE) - Applying Information Modeling to Buildings

A Virtual Building Environment (VBE) is a ''place'' where building industry project staffs can get help in creating Building Information Models (BIM) and in the use of virtual buildings. It consists of a group of industry software that is operated by industry experts who are also experts in the use of that software. The purpose of a VBE is to facilitate expert use of appropriate software applications in conjunction with each other to efficiently support multidisciplinary work. This paper defines BIM and virtual buildings, and describes VBE objectives, set-up and characteristics of operation. It informs about the VBE Initiative and the benefits from a couple of early VBE projects.
Date: June 21, 2004
Creator: Bazjanac, Vladimir
System: The UNT Digital Library
2003 Archaea: Ecology, Metabolism and Molecular Biology (open access)

2003 Archaea: Ecology, Metabolism and Molecular Biology

The Gordon Research Conference (GRC) on 2003 Archaea: Ecology, Metabolism and Molecular Biology was held at Proctor Academy, Andover, NH from August 3-8, 2003. The Conference was well-attended with 150 participants (attendees list attached). The attendees represented the spectrum of endeavor in this field coming from academia, industry, and government laboratories, both U.S. and foreign scientists, senior researchers, young investigators, and students. In designing the formal speakers program, emphasis was placed on current unpublished research and discussion of the future target areas in this field. There was a conscious effort to stimulate lively discussion about the key issues in the field today. Time for formal presentations was limited in the interest of group discussions. In order that more scientists could communicate their most recent results, poster presentation time was scheduled. Attached is a copy of the formal schedule and speaker program and the poster program. In addition to these formal interactions, ''free time'' was scheduled to allow informal discussions. Such discussions are fostering new collaborations and joint efforts in the field. I want to personally thank you for your support of this Conference. As you know, in the interest of promoting the presentation of unpublished and frontier-breaking research, Gordon Research …
Date: September 21, 2004
Creator: Shand, Richard F.
System: The UNT Digital Library
Pursuing Scalability for hypre's Conceptual Interfaces (open access)

Pursuing Scalability for hypre's Conceptual Interfaces

The software library hypre provides high performance preconditioners and solvers for the solution of large, sparse linear systems on massively parallel computers as well as conceptual interfaces that allow users to access the library in the way they naturally think about their problems. These interfaces include a stencil-based structured interface (Struct); a semi-structured interface (semiStruct), which is appropriate for applications that are mostly structured, e.g. block structured grids, composite grids in structured adaptive mesh refinement applications, and overset grids; a finite element interface (FEI) for unstructured problems, as well as a conventional linear-algebraic interface (IJ). It is extremely important to provide an efficient, scalable implementation of these interfaces in order to support the scalable solvers of the library, especially when using tens of thousands of processors. This paper describes the data structures, parallel implementation and resulting performance of the IJ, Struct and semiStruct interfaces. It investigates their scalability, presents successes as well as pitfalls of some of the approaches and suggests ways of dealing with them.
Date: July 21, 2004
Creator: Falgout, R D; Jones, J E & Yang, U M
System: The UNT Digital Library
Comparison of LiFePO4 from different sources (open access)

Comparison of LiFePO4 from different sources

The lithium iron phosphate chemistry is plagued by the poor conductivity and slow diffusion in the solid phase. In order to alleviate these problems, various research groups have adopted different strategies including decreasing the particle sizes, increasing the carbon content, and adding dopants. In this study, we obtained LiFePO{sub 4} powders and/or electrodes from six different sources and used a combined model-experimental approach to compare the performance. Samples ranged from 0.4% to 15% ''in-situ'' carbon. In addition, particle sizes varied by as much as an order of magnitude between samples. The study detailed in this manuscript allows us to provide insight into the relative importance of the conductivity of the samples compared to the particle size, the impact of having a distribution in particle sizes, and ideas for making materials in order to maximize the power capability of this chemistry.
Date: June 21, 2004
Creator: Striebel, Kathryn; Shim, Joongpyo; Srinivasan, Venkat & Newman, John
System: The UNT Digital Library
2003 Plant Cell Walls Gordon Conference (open access)

2003 Plant Cell Walls Gordon Conference

This conference will address recent progress in many aspects of cell wall biology. Molecular, genetic, and genomic approaches are yielding major advances in our understanding of the composition, synthesis, and architecture of plant cell walls and their dynamics during growth, and are identifying the genes that encode the machinery needed to make their biogenesis possible. This meeting will bring together international scientists from academia, industry and government labs to share the latest breakthroughs and perspectives on polysaccharide biosynthesis, wood formation, wall modification, expansion and interaction with other organisms, and genomic & evolutionary analyses of wall-related genes, as well as to discuss recent ''nanotechnological'' advances that take wall analysis to the level of a single cell.
Date: September 21, 2004
Creator: Cosgrove, Daniel J.
System: The UNT Digital Library
Electroweak and higgs physics at D0 (open access)

Electroweak and higgs physics at D0

We present recent results from the D0 experiment on W and Z boson production using {approx} 50 pb{sup -1} of Run II data recorded at the center of mass energy of 1.96 TeV at the Fermilab Tevatron. Initial studies of W/Z + 2 jets production that are relevant to Higgs searches are also discussed.
Date: January 21, 2004
Creator: Varelas, Nikos
System: The UNT Digital Library
A Multilayered Box Model for Calculating Preliminary RemediationGoals in Soil Screening (open access)

A Multilayered Box Model for Calculating Preliminary RemediationGoals in Soil Screening

In the process of screening a soil against a certain contaminant, we define the health-risk based preliminary remediation goal (PRG) as the contaminant concentration above which some remedial action may be required. PRG is thus the first standard (or guidance) for judging a site. An over-estimated PRG (a too-large value) may cause us to miss some contaminated sites that can threaten human health and the environment. An under-estimated PRG (a too-small value), on the other hand, may lead to unnecessary cleanup and waste tremendous resources. The PRGs for soils are often calculated on the assumption that the contaminant concentration in soil does not change with time. However, that concentration usually decreases with time as a result of different chemical and transport mechanisms. The static assumption thus exaggerates the long-term exposure dose and results in a too-small PRG. We present a box model that considers all important transport processes and obeys the law of mass conservation. We can use the model as a tool to estimate the transient contaminant concentrations in air, soil and groundwater. Using these concentrations in conjunction with appropriate health risk parameters, we may estimate the PRGs for different contaminants. As an example, we calculated the tritium PRG …
Date: May 21, 2004
Creator: Shan, Chao & Javandel, Iraj
System: The UNT Digital Library