A 14-MeV deuterium-tritium (D-T) neutron source for accelerated end-of-life testing of fusion reactor materials has been designed on the basis of a linear two-component collisional plasma system. An intense flux (up to 5 {times} 10{sup 18}/m{sup 2}{center dot}s) of 14-MeV neutrons is produced in a fully ionized high-density (n{sub e} {approx equal} 3 {times} 10{sup 21} m{sup {minus}3}) tritium target by transverse injection of 60 MW of neutral beam power. Power deposited in the target is removed by thermal electron conduction to large end chambers, where it is deposited in gaseous plasma collectors. We show in this paper that the major physics issues have now been experimentally demonstrated. These include magnetohydrodynamic (MHD) equilibrium and stability, microstability, startup, fueling, Spitzer electron thermal conductivity, and power deposition in a gaseous plasma collector. However, an integrated system has not been demonstrated. 28 refs., 8 figs., 2 tabs.

Creating low-energy electrons in the stratosphere by photoelectric emission has the beneficial effect of suppressing ozone destruction by Cl. This is because Cl is converted to Cl{sup {minus}}, which is less reactive. Critical to the success of this scheme is the ability to attach most of the electrons to Cl{sup {minus}} and its hydrates Cl{sup {minus}} (H{sub 2}O). We found that this attachment efficiency is rather high. This is remarkable given the fact that the electron affinity of Cl{sup {minus}} is less than that of NO{sub 3}{minus}. Photoddetachment of NO{sub 3}{minus} is the key factor that leads to this high efficiency. Computer calculations show that ozone increases with electron injection, and most of the electrons end up attaching to Cl{sup {minus}}(H{sub 2}O). We also point out that 40 km, the altitude at which most of the ozone destruction occurs, is also the optimum altitude for injecting photoelectric electrons. 12 refs., 6 figs.

This report discusses the following topics in relationships to plasma simulation: unstructed grids; particle tracking; and field propagation. (LSP)

Soudan 2 is an 1100-ton tracking calorimeter which is being built 713 m underground to search for nucleon decay and to study neutrino and cosmic-ray physics. The detector is assembled from 256 identical 4.3-ton calorimeter modules. Each module consists of finely segmented iron and drift tubes, and records three space coordinates and dE/dx for every tube crossing. It is surrounded on all sides by a 1700 m{sup 2} active shield of proportional tubes. The first atmospheric neutrino interactions and a magnetic monopole search are described. Prospects for cosmic ray studies are summarized.

A model of drilling by high radiance pulsed lasers is described. The model involves a one-dimensional description of heat transport below the bottom of the hole, hydrodynamic expansion of the vapor and compressed air, and light propagation through the vapor. The pressure and energy of the vapor are taken from a separate Saha equilibrium code. The boundary conditions at the vaporization surface include the formation of a transition layer within which macroscopic fluid conditions axe reached. The absorption mechanisms are photoionization and inverse bremsstrahlung. The model has been applied to the case of drilling in stainless steel with green copper laser light, for peak input intensities ranging from 10{sup 8} to 4 {times} 10{sup 10} W/cm{sup 2}. Below 3 {times} 10{sup 8} W/cm{sup 2}, there is negligible absorption in the vapor and ablation increases rapidly with intensity. After decreasing for a short interval beyond this point, the ablation rate then increases steadily with power because of a growing electron thermal conduction to the surface. The experimental ablation rate exhibits a somewhat faster overall growth. It appears comparable to the model at low power but is about five times greater at the highest power.

Traditionally law enforcement agencies have relied on basic measurement and imaging tools, such as tape measures and cameras, in recording a crime scene. A disadvantage of these methods is that they are slow and cumbersome. The development of a portable system that can rapidly record a crime scene with current camera imaging, 3D geometric surface maps, and contribute quantitative measurements such as accurate relative positioning of crime scene objects, would be an asset to law enforcement agents in collecting and recording significant forensic data. The purpose of this project is to develop a feasible prototype of a fast, accurate, 3D measurement and imaging system that would support law enforcement agents to quickly document and accurately record a crime scene.

Maintaining a contamination free sample preparation lab for biological 14 C AMS requires the same or more diligence as a radiocarbon dating prep lab. Isotope ratios of materials routinely range over 4-8 orders of magnitude in a single experiment, dosing solutions contain thousands of DPM and gels used to separate proteins possess 14 C ratios of 1pMC. Radiocarbon contamination is a legacy of earlier tracer work in most biological laboratories, even if they were never hot labs. Removable surface contamination can be found and monitored using swipes. Contamination can be found on any surface routinely touched: door knobs, light switches, drawer handles, water faucets. In general, all surfaces routinely touched need to be covered with paper, foil, or plastic that can be changed frequently. Shared air supplies can also present problems by distributing hot aerosols throughout a building. Aerosols can be monitored for 14 C content using graphitized coal or fullerene soot mixed with metal powder as an absorber. The monitors can be set out in work spaces for 1-2 weeks and measured by AMS with regular samples. Frequent air changes help minimize aerosol contamination in many cases. Cross contamination of samples can be minimized by using disposable plastic or …

The basic mechanisms of single-event upset are reviewed, including charge collection in silicon junctions and transistors, and properties of single-event upset in CMOS static random access memory (SRAM) cells. The mechanisms are illustrated through the use of three-dimensional device and circuit simulations. Technology trends and implications for commercial devices are discussed.

Recent developments in the application of damped time advance methods to plasma simulations include the synthesis of implicit and explicit adjustably damped'' second order accurate methods for particle motion and electromagnetic field propagation. This paper discusses this method.

The evaluation of the accuracy, precision and lower detection limits of the determination of trace radionuclides in environmental samples can become quite sophisticated and time consuming. This in turn could add significant cost to the analyses being performed. In the present method, a {open_quotes}deficit reduction approach{close_quotes} has been taken to keep costs low, but at the same time provide defensible data. In order to measure the accuracy of a particular method, reference samples are measured over the time period that the actual samples are being analyzed. Using a Lotus spreadsheet, data are compiled and an average accuracy is computed. If pairs of reference samples are analyzed, then precision can also be evaluated from the duplicate data sets. The standard deviation can be calculated if the reference concentrations of the duplicates are all in the same general range. Laboratory blanks are used to estimate the lower detection limits. The lower detection limit is calculated as 4.65 times the standard deviation of a set of blank determinations made over a given period of time. A Lotus spreadsheet is again used to compile data and LDLs over different periods of time can be compared.

The purpose of the research described in this paper was to examine the effects of using longer and heavier tractor-trailer combinations from the standpoint of the individual firm or shipper rather than from the viewpoint of the motor carrier. The objective was to determine the effect of longer combination vehicles (LCVS) not only on shippers freight costs but on their inventory and other logistical costs as well. A sample of companies in selected industries provided data on their principal products, traffic flows, and logistics costs in a mail survey. These data were entered into a computer program called the Freight Transportation Analyzer (FTA) which calculated the component logistics costs associated with shipping by single trailers and by two alternative types of double trailer LCVS. A major finding of the study was that, given sufficient flows of a company`s product in a traffic lane, LCVs would in most cases greatly reduce the total logistics cost of firms that currently ship in single trailer truckload quantities. Annual lane volume, lane distance, and annual lane ton-mileage appeared to be good indicators of whether or not shipping by LCVs would benefit a company, whereas product value had surprisingly little influence on the cost-effectiveness of …

A two-stage model is presented to describe alloy element evaporation rates from molten metal due to transient local heating by an electron beam. The first stage is a simulation of transient phenomena near the melt surface due to periodic heating by a scanning beam, the output of which is the relationship between operating parameters, surface temperature, and evaporation rate. At high scan rates, this can be done using a simple one-dimensional heat transfer model of the surface layer; at lower scan rates, a more complex three-dimensional model with fluid flow and periodic boundary conditions is necessary. The second stage couples this evaporation-surface temperature relationship with a larger steady state heat transfer and fluid flow model of an entire melting hearth or mold, in order to calculate local and total evaporation rates. Predictions are compared with experimental results from Sandia`s 310-kW electron beam melting furnace, in which evaporation rates and vapor compositions were studied in pure titanium and Ti-6%Al-4%V alloy. Evaporation rates were estimated from rate of condensation on a substrate held over the hearth, and were characterized as a function of beam power (150 and 225 kW), scan frequency (30, 115 and 450 Hz) and background pressure (10{sup {minus}3}, 10{sup …

We present results of atomistic simulations of the interaction between self interstitial atoms and vacancies with edge dislocations in BCC iron. The calculations are carried out using molecular dynamics with an energy minimization scheme based on the quasi-Newton approach and use the Finnis-Sinclair interatomic potential for BCC iron developed by Ackland et al. Large anisotropy in the strain field of self interstitials is observed and it causes strong interaction with edge dislocations even when the defect is located on the dislocation glide plane. For vacancies, the relaxation volume is smaller and much more isotropic, which results in a far weaker interaction with the dislocation. A temperature dependent capture radius for vacancies and self interstitials is extracted from the simulations. The difference between the capture radii of vacancies and self interstitials is used to define the sink strength of the dislocation. Large deviations are observed from the predictions of elasticity based on treating point defects as isotropic dilatational centers. Further, the capture radius of edge dislocations in BCC iron is observed to be small and is of the order of l-3 nm for self interstitials.

The purpose of the Spallation Neutron Source Project (SNS) is to generate low-energy neutrons (ambient [{approximately}200 meV] and cold [{approximately}50 meV]) which can be used by up to 18 neutron beam lines to study the structure and functionality of materials. The neutrons are generated by the spallation process initiated by the interactions of 1-GeV protons with a Hg target. These neutrons are reflected by a Pb reflector and are moderated by 2 water (ambient) and 2 super critical hydrogen (cryogenic) moderators. The pulse structure for the 1 MW proton beam is 60 Hertz and < 0.7 {micro}s/pulse. The facility must be upgradable to higher power levels (2- and 4- MW) with minimal operational interruptions. Although not included in the current funding or baseline, a second target station and associated support structure which will be designed to utilize cold neutrons is also considered to be an upgrade that must be incorporated with minimal impact on operations.

Generating a volumetric heat source in solid deuterium hydride, HD, allows the formation of a spherical crystalline shell of HD inside a transparent plastic shell. Pumping the infra-red (IR) collisionally induced vibration-rotation band of solid HD contained inside a transparent plastic shell generates the volumetric heat source in the HD lattice. HD layers 150 - 250 {micro}m thick formed near the triple point have a surface roughness rms between l-3 {micro}m and become rougher with decreasing temperature. Solid growth dynamics have a significant impact on the quality of the resultant layer.

A vibrating sample technique was used to study the elastic behavior of the magnetic vortex system in YBa{sub 2}Cu{sub 3}O{sub 7} single crystal. The setup consists of a system of two weakly coupled mechanical oscillators (transducer, sample), the frequency and Q of which depends sensitively on the frequencies of the two subsystems as well as the coupling between both. By sweeping a magnetic field at temperatures below the superconducting transition temperature {Tc} the authors observe pronounced attenuation peaks of temperature-dependent characteristic field strengths H{sub 1} and H{sub 2}. These fields mark temperature-dependent points of constant elasticity of the vortex-ensemble. Since softening precedes the melting of the vortex-lattice by approaching H{sub o1} as well as H{sub o2}, the observed angular dependence of H{sub 1} and H{sub 2} is interpreted as due to reentrant softening as precursor to reentrant melting.

Nonmethane hydrocarbons (NMHCs) are precursors to oxidant formation. They are oxidized by hydroxyl radical (OH), forming a complex mixture of peroxy radicals that oxidize NO to NO{sub 2} without consuming ozone (O{sub 3}) and thus allow O{sub 3} to increase in the atmospheric boundary layer. The reactivities of the NMHCs that compose biogenic and anthropogenic emissions vary greatly. For example, isoprene, which is emitted by deciduous vegetation, has an atmospheric lifetime with respect to oxidation by OH of about 20 min in polluted air ([OH] = 10{sup 7} radicals cm{sup {minus}3}). The atmospheric lifetimes of 2-methylpropene, 2-methylbutane, and the xylenes, which are found in vehicle emissions, are approximately 30 min, 7 hr, and 1.5 hr, respectively. The authors made measurements of the NMHCs at a surface site and aloft aboard the Battelle Gulfstream (G-1) aircraft, as part of an air quality study in the Phoenix area during May 1998. Diurnal variations in the NMHC distributions and their propene-equivalent concentrations are used to examine origins and reactivities of the air masses that were sampled at the surface site.

This report reflects the results of heat treatment under various conditions on as-grown and ion implanted GaN. The PL spectrums of as-grown GaN and GaN with 400 A AlN cap were almost identical. This fact allows one to use PL analysis without AlN stripping. As-grown GaN and ion implanted with Mg and Si crystals were annealed at 1300 C for 10 minutes in three different conditions: in flowing argon gas; in flowing ultra high purity nitrogen; and in a quartz capsule sealed with nitrogen gas. The results of PL, RBS, SEM and TEM analysis show an advantage of GaN high temperature annealing in quartz capsules with nitrogen ambient as compared to annealing in argon and nitrogen gas flow. Encapsulation with nitrogen over-pressure prevents the decomposition of the GaN crystal and the AlN capping film, and allows one to achieve optical activation of implanted Mg and Si after 1300 C annealing.

YBa{sub 2}Cu{sub 3}O{sub 2} (YBCO) films have been deposited on buffered metal substrates by Metal Organic Chemical Vapor Deposition (MOCVD). Cube-textured nickel substrates were fabricated by a thermomechanical process. Epitaxial CeO{sub 2}films were deposited on these substrates by thermal evaporation. Nickel alloy substrates with biaxially-textured Yttria-Stabilized Zirconia (YSZ) buffer layers deposited by Ion Beam Assisted Deposition were also prepared. Highly biaxially-textured YBCO films were deposited by MOCVD on both types of metal substrates. A critical current density greater than 10{sup 5} A/cm{sup 2} at 77 K has been achieved in YBCO films on metal substrates.

Modern computers make possible a new blending of systems, man, and cybernetics in the detailed simulation of large sociotechnical systems. Several such simulations are currently under development at Los Alamos National Laboratory and elsewhere. When deployed, they will affect the daily lives of hundreds of millions of people and the allocation of billions of dollars. Whether they are deployed depends entirely on their perceived usefulness, which in turn depends on answers to the following: What kinds of questions does the simulation address and what kinds of solutions does it provide? How can the solutions be validated? Is simulation more cost-effective than other methods? Answers to these questions lead us to define a useful simulation as one which efficiently provides correct, robust estimates required by decision-making needs, together with well understood variability for the outcomes in hypothetical situations. This paper examines the implications of this criterion for the design o f TRANSIMS, a regional transportation network simulation, and by extension, for simulations of other sociotechnical systems.

Assertions by the Russian military that all of their nuclear weapons are secure against theft and that nuclear units within the military are somehow insulated from the problems plaguing the Russian military should not be accepted uncritically. Accordingly, we should not give unwarranted credence to the pronouncements of military figures like Cal.-Gen. Igor Valynkin, Chief of the Defense Ministry's 12th Main Directorate, which oversees the country's nuclear arsenal. He contends that ''Russian nuclear weapons are under reliable supervision'' and that ''talk about the unreliability of our control over nuclear weapons has only one pragmatic goal--to convince international society that the country is incapable of maintaining nuclear safety and to introduce international oversight over those weapons, as it is done, for example, in Iraq.'' While the comparison to Iraq is preposterous, many analysts might agree with Valynkin's sanguine appraisal of the security of Russia's nuclear weapons. In contrast, I argue that the numerous difficulties confronting the military as a whole should cause concern in the West over the security of the Russian nuclear arsenal.

A high temperature furnace (up to 1500 C) has been designed specifically for use with high-energy synchrotron radiation using Debeye-Scherrer transmission geometry. This allows for full bulk sampling and a low thermal gradient (< 1 C/mm) and a controlled environment (inert to oxidizing). Unlike flat plate geometry, the transmission geometry allows for solid-liquid as well as solid-solid phase transitions to be explored. A comparison between image plate and charged-coupled detector (CCD) system will be discussed. The potential is to collect quantifiable powder patterns under a second. Data collected on the tetragonal to cubic transition in the RhTi systems demonstrate the capabilities for performing quantitative time resolved high temperature powder diffraction.

Primary surface recuperators (PSRs) are compact heat-exchangers made from thin-foil type 347 austenitic stainless steel, which boost the efficiency of land-based gas turbine engines. Solar Turbines uses foil folded into a unique corrugated pattern to maximize the primary surface area for efficient heat transfer between hot exhaust gas on one side, and the compressor discharge air on the other side of the foil. Allegheny-Ludlum produces 0.003 - 0.0035 in. thick foil for a range of current turbine engines using PSRs that operate at up to 660 degrees C. Laboratory-scale processing modification experiments recently have demonstrated that dramatic improvements can be achieved in the creep resistance of such typical 347 stainless steel foils. The modified processing enables fine NbC carbide precipitates to develop during creep at 650-700 degrees C, which provides strength even with a fine grain size. Such improved creep-resistance is necessary for advanced turbine systems that will demand greater materials performance and reliability at higher operating conditions. The next challenges are to better understand the nature of the improved creep resistance in these 347 stainless steel foil, and to achieve similar improvements with scale-up to commercial foil production.

{alpha}-axis oriented EuBa{sub 2}Cu{sub 3}O{sub 7} films have been irradiated with high energy heavy ions in different configurations to study the possible pinning role of the artificial defects in this kind of samples. The original pinning limiting mechanism of the samples is not essentially altered what the irradiation is parallel to the CuO{sub 2} planes. However, when it is deviated from this direction, an increase in critical current density and a change in pinning force are observed when the magnetic field is parallel to the columnar defects at values around the matching field.