Article on dynamic conductance of carbon nanotubes.

We present a new computed tomography method, the low third derivative (LTD) method, that is particularly suited for reconstructing the spatial distribution of gas concentrations from path-integral data for a small number of optical paths. The method finds a spatial distribution of gas concentrations that (1) has path integrals that agree with measured path integrals, and (2) has a low third spatial derivative in each direction, at every point. The trade-off between (1) and (2) is controlled by an adjustable parameter, which can be set based on analysis of the path-integral data. The method produces a set of linear equations, which can be solved with a single matrix multiplication if the constraint that all concentrations must be positive is ignored; the method is therefore extremely rapid. Analysis of experimental data from thousands of concentration distributions shows that the method works nearly as well as Smooth Basis Function Minimization (the best method previously available), yet is 100 times faster.

The nonlinear Poisson-Boltzmann (PB) equation is solved using Pseudo Transient Continuation. The PB solver is constructed by modifying the nonlinear diffusion module of a 3D, massively parallel, unstructured-grid, finite element, radiation-hydrodynamics code. The solver also computes the electrostatic energy and evaluates the force on a user-specified contour. Either Dirichlet or mixed boundary conditions are allowed. The latter specifies surface charges, approximates far-field conditions, or linearizes conditions ''regulating'' the surface charge. The code may be run in either Cartesian, cylindrical, or spherical coordinates. The potential and force due to a conical probe interacting with a flat plate is computed and the result compared with direct force measurements by chemical force microscopy.

The authors have completed a set of gamma-ray pulse height benchmark experiments using a high purity germanium detector to measure absolute counting rate spectra from {sup 60}Co, {sup 137}Cs and {sup 57}Co isotopic sources. The detector was carefully shielded and collimated so that the geometry of the system was completely known. The measured absolute pulse height spectrum counting rates as a function of detector position relative to the source are compared to energy deposit spectra calculated using the Monte Carlo radiation transport code COG. They present here a small subset of our results. The agreement between the calculated and measured spectra and known sources of discrepancies will be discussed.

This article presents the light curves of 21 gravitational microlensing events from the first six years of the MACHO Project gravitational microlensing survey that are likely examples of lensing by binary systems.

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An alternative to the conventional see-saw mechanism is proposed to explain the origin of small neutrino masses in supersymmetric theories. The masses and couplings of the right-handed neutrino field are suppressed by supersymmetry breaking, in a way similar to the suppression of the Higgs doublet mass, $\mu$. New mechanisms for light Majorana, Dirac and sterile neutrinos arise, depending on the degree of suppression. Superpartner phenomenology is greatly altered by the presence of weak scale right-handed sneutrinos, which may have a coupling to a Higgs boson and a left-handed sneutrino. The sneutrino spectrum and couplings are quite unlike the conventional case - the lightest sneutrino can be the dark matter and predictions are given for event rates at upcoming halo dark matter direct detection experiments. Higgs decays and search strategies are changed. Copious Higgs production at hadron colliders can result from cascade decays of squarks and gluinos.

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Mineral nucleation at a Langmuir film interface has been studied by synchrotron x-ray scattering. Diluted calcium bicarbonate solutions were used as subphases for arachidic and stearic acid monolayers, compressed in a Langmuir trough. Self-assembly of the monolayer template is observed directly, and subsequent crystal growth monitored in-situ.

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The fundamental differences between energetic composites and energetic materials made from a monomolecular approach are the energy density attainable and the energy release rates. For the past 4 years, we have been exploiting sol-gel chemistry as a route to process energetic materials on a microstructural scale. At the last ISA conference, we described four specific sol-gel approaches to fabricating energetic materials and presented our early work and results on two methods - solution crystallization and powder addition. Here, we detail our work on a third approach, energetic nanocomposites. Synthesis of thermitic types of energetic nanocomposites are presented using transition and main group metal-oxide skeletons. Results on characterization of structure and performance will also be given.

A multi-channel quadrupole array has been proposed to increase beam intensity and reduce space charge effects in a Heavy Ion Fusion Driver. A single array unit composed of several quadrupole magnets, each with its own beam line, will be placed within a ferromagnetic accelerating core whose cost is directly affected by the array size. A large number of focusing arrays will be needed along the accelerating path. The use of a superconducting quadrupole magnet array will increase the field and reduce overall cost. We report here on the design of a compact 3 x 3 superconducting quadrupole magnet array. The overall array diameter and length including the cryostat is 900 x 700 mm. Each of the 9 quadrupole magnets has a 78 mm warm bore and an operating gradient of 50 T/m over an effective magnetic length of 320 mm.

The US Government has declared that approximately 50 tons of plutonium is surplus to US needs and should be set aside for eventual disposition. The US is currently following a dual path for the disposition of this plutonium: immobilization and irradiation of mixed-oxide fuel. Some fraction of this plutonium material that is undesirable for use in mixed-oxide fuel will be immobilized in a titanate ceramic and disposed of in a geologic repository for high level waste. The reminder of Pu will be fabricated into mixed-oxide fuel and irradiated in domestic light-water reactors. The resulting spent fuel would also be disposed of in a geologic repository for high level waste. The proposed US repository would be at the Yucca Mountain site in Nevada. Plutonium present in the disposal forms, either ceramics or spent fuel, must remain isolated from the biosphere over the geologic repository regulatory performance period, which is currently 10,000 years. Contamination of the biosphere could result from slow dissolution of the disposal forms followed by transport of the dissolution products into the biosphere by flowing ground water. Measurable amounts of apparently soluble plutonium can be released if plutonium dioxide is exposed to water under some conditions. Furthermore, recent studies …

Important preconditions for wide acceptance of virtual reality (VR) systems include their comfort, ease and naturalness to use. Most existing trackers super from discomfort-related issues. For example, body-based trackers (hand controllers, joysticks, helmet attachments, etc.) restrict spontaneity and naturalness of motion, while ground-based devices (e.g., hand controllers) limit the workspace by literally binding an operator to the ground. There are similar problems with controls. This paper describes using real-time video with registered depth information (from a commercially available camera) for virtual reality navigation. Camera-based setup can replace cumbersome trackers. The method includes selective depth processing for increased speed, and a robust skin-color segmentation for accounting illumination variations.

This report describes development of processes for cladding APT Target tungsten components with a thin layer (0.127-mm) of Alloy 718, Alloy 600 or 316L stainless steel alloy. The application requires that the cladding be thermally bonded to the tungsten in order to transfer heat generated in the tungsten volume to a surrounding coolant. High temperature diffusion bonding using the hot isostatic processing (HIP) technique was selected as the method for creating a metallurgical bond between pure tungsten tubes and rods and the cladding materials. Bonding studies using a uniaxially loaded vacuum hot press were conducted in preliminary experiments to determine acceptable time-temperature conditions for diffusion bonding. The results were successfully applied in cladding tungsten rods and tubes with these alloys. Temperatures 800-810 C were suitable for cladding tungsten with Alloy 600 and 316L stainless steel alloy, whereas tungsten was clad with Alloy 718 at 1020 C.

This presentation will be a broad survey of progress in induction technology over the past four years. Much work has been done on accelerators for hydrodynamic test radiography and other applications. Solid-state pulsers have been developed which can provide unprecedented flexibility and precision in pulse format and accelerating voltage for both ion and electron induction machines. Induction linacs can now be built which can operate with MHz repetition rates. Solid-state technology has also made possible the development of fast kickers for precision control of high current beams. New insulator technology has been developed which will improve conventional induction linacs in addition to enabling a new class of high gradient induction linacs.

The National Ignition Facility (NIF) is an inertial confinement fusion project being built at Lawrence Livermore National Laboratory (LLNL) for the Department of Energy (DOE). The project is comprised of two buildings and the high technology equipment. The NIF houses 192 separate laser beams that generate approximately two megajoules of energy and 500 terawatts of power. The laser beams travel through a large optical system that contains over 7,500 large-aperture optical components (40 cm by 40 cm) and approximately 30,000 small-aperture optical components (less than 20 cm diameter). The NIF laser will be enclosed in a building that is approximately 200 meters in length (l) by 100 meters in width (w) by 15 meters in height (h) scheduled for completion by the end of 2002. A 0.5 mm target will be positioned inside a 10 meter sphere in the Target Building which measures approximately 35 meters (l) by 90 meters (w) by 30 meters (h). To achieve optimum laser operation the optics will require precision positioning and alignment. As a result, the mechanical components that support the optics require accurate positioning. State-of-the-art surveying, measuring techniques, and uncertainty and error analyses are being used to measure the control network and mechanical …

The edge plasma plays key roles in tokamak devices: generates the edge transport-barrier yielding the L-H core confinement transition, distributes the core charged-particle energy to surrounding material surfaces, shields the core from impurities, and removes helium ash in fusion plasmas. The transport of density, momentum, and energy in the near-separatrix edge region, and the corresponding self-consistent electrostatic potential, require a two-dimensional description, here incorporated into the UEDGE code. In the direction across the B-field, both turbulent transport and classical cross-field flows are important. The role of classical flows is analyzed in detail in the presence of an assumed diffusive turbulent transport. Results and explanations are given for the generation of radial electric field near the separatrix, edge plasma asymmetries and differences between double-null DIII-D and NSTX devices, comparisons with DIII-D diagnostics for single-null divertor, and core/edge transport coupling.

Effective investigative analysis requires proper selection of sample-collection procedures, preservation, and analysis methods. To achieve these objectives it is essential to tailor the collection and analysis methods to the application requirements, which are constrained by different parameters such as analysis time, sample concentration, matrix interferences, and analyte stability (e.g., surface activity (''stickiness'') and chemical reactivity). In addition, method optimization must be accomplished without compromising sample integrity. Maintaining sample integrity requires minimizing and characterizing contamination as well as reducing sample degradation and loss to prevent both false positive and negative detection, respectively. When specific constraints are defined, depending on target chemical(s) and application scenarios, it is sometimes necessary to modify or develop new equipment and methods to best satisfy the application requirements. For this work, we are interested in real-time monitoring of airborne chemicals, which are commonly referred to as volatile organic compounds (VOC). Although there are a number of techniques for remote analysis of VOCs, many of these applications do not provide the specificity and sensitivity needed in real-time application scenarios. For example, spectroscopic techniques are capable of providing low part-per-billion volume/volume (ppb v/v) detection if a compound is distributed over a large area, however, they provide limited compound structural …

We use regional waveform data from the Nevada Test Site (NTS) to investigate phenomenological relationships between recorded amplitude and explosion yield as well as test regional depth estimation procedures. Our goal is to better understand the performance of seismic observables in other regions of monitoring interest, especially at small magnitudes (m{sub b}<<4.5). Some of the topics we are studying include: stable yield estimation, depth estimation, and M{sub g}:m{sub b} performance. We use Lawrence Livermore National Laboratory's NTS explosion database, which consists of several hundred events ranging from {approx}200 to {approx}1500-m depth and yields ranging from a few tenths of a kiloton to the megaton range. In addition to the broadband explosion data, we have a large dataset of well-located earthquakes on the test site with depths ranging from 2 to 17 km and magnitudes ranging between M{sub w}1.5 and 5.7. For yield estimation the relation between teleseismic body wave magnitude (mb) and nuclear explosion yield has been studied extensively over the past several decades for a number of test sites for large (>1 kt) explosions. In this paper we will look at broadband coda, P{sub g,} and L{sub g} from over 260 nuclear explosions to study yield estimation capability by …

We have undertaken an adaptive optics imaging survey of extrasolar planetary systems and stars showing interesting radial velocity trends from high precision radial velocity searches. Adaptive Optics increases the resolution and dynamic range of an image, substantially improving the detectability of faint close companions. This survey is sensitive to objects less luminous than the bottom of the main sequence at separations as close as 1 inch. We have detected stellar companions to the planet bearing stars HD 114762 and Tau Boo. We have also detected a companion to the non-planet bearing star 16 Cyg A.

The Permian Salado Formation in the Delaware Basin of New Mexico is an extensively studied evaporite deposit because it is the host formation for the Waste Isolation Pilot Plant, a repository for transuranic wastes. Geologic and hydrologic studies of the Salado conducted since the mid-1970's have led to the development of a conceptual model of the hydrogeology of the formation that involves far-field permeability in anhydrite layers and at least some impure halite layers. Pure halite layers and some impure halite layers may not possess an interconnected pore network adequate to provide permeability. Pore pressures are probably very close to lithostatic pressure. In the near field around an excavation, dilation, creep, and shear have created and/or enhanced permeability and decreased pore pressure. Whether flow occurs in the far field under natural gradients or only after some threshold gradient is reached is unknown. If far-field flow does occur, mean pore velocities are probably on the order of a meter per hundreds of thousands to tens of millions of years. Flow dimensions inferred from most hydraulic-test responses are subradial, which is believed to reflect channeling of flow through fracture networks, or portions of fractures, that occupy a diminishing proportion of the radially …

The 20th International Congress of Theoretical and Applied Mechanics, ICTAM2000, was held in Chicago, IL, from August 27 - September 2, 2000. It was 32 years since the last of these congresses had been held in USA. A record number of researchers in the mechanical engineering sciences attended and presented their work. The Congress provided an opportunity for the US mechanics community to act as international hosts. Several universities, professional societies, private foundations and individuals, and Federal agencies provided financial support for the Congress.