Hohlraums (measuring 6-mm in diameter by 7-mm in height) have been heated by x-rays from a z-pinch. Over measured x-ray input powers P of 0.7 to 13 TW, the hohlraum radiation temperature T increases from {approximately}55 to {approximately}130 eV, and is in agreement with the Planckian relation P-T{sup 4}. The results suggest that indirect-drive ICF studies involving NIF relevant pulse shapes and <2-mm diameter capsules can he studied using this arrangement.
Technical guidance for performance assessment (PA) of low-level radioactive waste (LLRW) sites is currently dependent upon experimental retardation factors (K{sub D}'s) to predict radionuclide transport. Accurate predictions of waste transport or retardation will require mechanistic models of radionuclide sorption so as to be applicable to a wide range of soil/groundwater environments. To that end, we have investigated Cs{sup +}, Sr{sup +}, and Ba{sup 2+} sorption on several clay and Fe-oxide minerals. Relative metal binding strengths for montmorillonite clay decrease from Ba{sup 2+} to Sr{sup +}, which is similar to that sorption trend noticed for kaolinite. Molecular dynamics simulations for kaolinite suggest that Cs{sup +} is sorbed at aluminol (010) edge sites as an inner-sphere complex and weakly sorbed as an outer-sphere complex on (001) basal surfaces. Sorption is thought to occur on similar sites for smectite clays, however, the basal plane residual charge and its increased basal plane exposure should have a greater influence on metal sorption. On the other hand, phase transformation kinetics (e.g., ferrihydrite to goethite) is a very important control of metal sorption and resorption for Fe-oxides/hydroxides. These results provide a basis for understanding and predicting metal sorption on complex soil minerals.
Experiments at the Z machine generate over four hundred channels of waveform data on each accelerator shot. Most experiments require timing accuracy to better than one nanosecond between multiple distributed recording locations throughout the facility. Experimental diagnostics and high speed data recording equipment are typically located within a few meters of the 200 to 300 terawatt X- ray source produced during Z-pinch experiments. This paper will discuss techniques used to resolve the timing of the several hundred data channels acquired on each shot event and system features which allow viewing of waveforms within a few minutes after a shot. Methods for acquiring high bandwidth signals in a severe noise environment will also be discussed.
A retarding potential energy analyzer having 750 nm diameter, self-aligned grid apertures and micron scale grid separation has been fabricated using polycrystalline silicon and silicon dioxide. High resolution in situ measurements of ion velocity distributions have been demonstrated in inductively coupled argon plasmas. Measurement results agree well with those from a macroscopic analyzer. Important differences are observed in the energies of plasma ions when measured with respect to chamber wall versus those measured with respect to the plasma floating potential. Preliminary measurements under rf bias conditions have also been made and results follow the expected trends.
Technology development efforts are under way to apply chemical sensors to discriminate inert ordnance and clutter from live munitions that remain a threat to reutilization of military ranges. However, the chemical signature is affected by multiple environmental phenomena that can enhance or reduce its presence and transport behavior, and can affect the distribution of the chemical signature in the environment. For example, the chemical can be present in the vapor, aqueous, and solid phases. The distribution of the chemical among these phases, including the spatial distribution, is key in designing appropriate detectors, e.g., gas, aqueous or solid phase sampling instruments. A fundamental understanding of the environmental conditions that affect the chemical signature is needed to describe the favorable and unfavorable conditions of a chemical detector based survey to minimize the consequences of a false negative. UXO source emission measurements are being made to estimate the chemical flux from a limited set of ordnance items. Phase partitioning analysis has been completed to show what the expected concentrations of chemical analytes would be fi-om total concentrations measured in the soil. The soil moisture content in the dry region has been shown to be critical in the attenuation of soil gas concentrations by increased sorption to soil particles. Numerical simulation tools have been adapted to include surface boundary conditions such as solar radiation, surface boundary layer (which is a function of wind speed), precipitation and evaporation, and plant cover/root density to allow transport modeling and evaluate long term processes. Results of this work will provide performance targets for sensor developers and support operational decisions regarding field deployments.
A two-dimensional model is developed to simulate discharge of a lithium/thionyl chloride primary battery. The model accounts for not only transport of species and charge, but also the electrode porosity variations and the electrolyte flow induced by the volume reduction caused by electrochemical reactions. Numerical simulations are performed using a finite volume method of computational fluid dynamics. The predicted discharge curves for various temperatures are compared to the experimental data with excellent agreement. Moreover, the simulation results. in conjunction with computer visualization and animation techniques, confirm that cell utilization in the temperature and current range of interest is limited by pore plugging or clogging of the front side of the cathode as a result of LiCl precipitation. The detailed two-dimensional flow simulation also shows that the electrolyte is replenished from the cell header predominantly through the separator into the front of the cathode during most parts of the discharge, especially for higher cell temperatures.
The International Energy Agency (IEA) is an energy forum for 24 industrialized countries and was established in 1974 as an autonomous body within the Organization for Economic Cooperation and Development (OECD). The IEA Photovoltaic Power Systems (PVPS) program implementing agreement was signed in 1993, and renewed for another five years in 1998. Twenty-two countries are collaborating under the auspices of the IEA in the PVPS to address common technical and informational barriers that often limit the rate at which photovoltaic technologies advance into the markets. Task V of the IEA PVPS is entitled "Grid Interconnection of Building-Integrated and Other Dispersed Photovoltaic Power Systems." The task sponsored a workshop in September 1997 on grid-interconnection of photovoltaic systems and is planning a second workshop to address impacts of more penetration of dispersed systems into the utility grid. This paper will summarize the accomplishments of Task V over the last five years and will detail the planned work for the next three years.
There now exist close to 20 years of history in the application of Probabilistic Risk Assessment (PRA) for the analysis of fire risk at nuclear power plants. The current methods are based on various assumptions regarding fire phenomena, the impact of fire on equipment and operator response, and the overall progression of a fire event from initiation through final resolution. Over this same time period, a number of significant fire incidents have occurred at nuclear power plants around the world. Insights gained from US experience have been used in US studies as the statistical basis for establishing fire initiation frequencies both as a function of the plant area and the initiating fire source.To a lesser extent, the fire experience has also been used to assess the general severity and duration of fires. However, aside from these statistical analyses, the incidents have rarely been scrutinized in detail to verify the underlying assumptions of fire PRAs. This paper discusses an effort, under which a set of fire incidents are being reviewed in order to gain insights directly relevant to the methods, data, and assumptions that form the basis for current fire PRAs. The paper focuses on the objectives of the effort, the specific fire events being reviews methodology, and anticipated follow-on activities.
The sensitivity of surface acoustic wave (SAW) sensors has been enhanced by increasing the active surface area of these devices. Electrodepositions of Ni, Pd, and Pt in a mass-transport-limited mode with trace foreign metals yield highly dendritic crystal structures of uniform macroscopic thickness. The concentration of metal ions, supporting electrolyte, agitation, and additives greatly impact the crystal morphology of the deposit. This methodology can be used simply and economically to provide high-area films in selective regions.
This paper improves on some of the limitations of conventional safety assessment and decision analysis methods. It develops a top-down mathematical method for expressing imprecise individual metrics as possibilistic or fuzzy numbers and shows how they may be combined (aggregated) into an overall metric, also portraying the inherent uncertainty. Both positively contributing and negatively contributing factors are included. Metrics are weighted according to significance of the attribute and evaluated as to contribution toward the attribute. Aggregation is performed using exponential combination of the metrics, since the accumulating effect of such factors responds less and less to additional factors. This is termed soft mathematical aggregation. Dependence among the contributing factors is accounted for by incorporating subjective metrics on overlap of the factors and by correspondingly reducing the overall contribution of these combinations to the overall aggregation. Decisions corresponding to the meaningfulness of the results are facilitated in several ways. First, the results are compared to a soft threshold provided by a sigmoid function. Second, information is provided on input ''Importance'' and ''Sensitivity,'' in order to know where to place emphasis on controls that may be necessary. Third, trends in inputs and outputs are tracked in order to add important information to the decision process. The methodology has been implemented in software.
In the 1990s, significant experience has been gained with high-speed passenger rail technologies. On the one hand, high speed versions of conventional-configuration trains, such as the French TGV, have proven themselves in service; on the other hand, magnetic levitation (maglev) trains such as the German Transrapid, which some expected to supplant conventional trains in some high speed applications, have not yet proven themselves and face a problematic future. This is because of maglev's high capital cost, the magnetic drag which it introduces, and the high development risks associated with this complex technology. This paper examines a new form of high-speed train expected to be capable of speeds of 300 mph, the Maglift Monorail. The Maglift Monorail was developed by simplifying and improving two well-understood technologies--wheelsets and LIMs--and then integrating them. The solution is a vehicle with flangeless wheels mounted in two axes, powered by a high-efficiency and light-weight LIM, positioned to give magnetic lift (maglift), i.e., electromagnetic force in the vertical direction which reduces the vehicle weight on the suspension, and thereby reduces static and rolling drag. Maglift can be considered a form of maglev as it uses the same electromagnetic forces to lift and propel the vehicle. This solution is presented in a Spanish-designed monorail system which has a unique suspension designed to minimize friction while giving great stability and turning capability. This monorail vehicle is propelled by the Seraphim motor (Segmented Rail Phased Induction Motor) which virtually eliminates magnetic drag and provides significant maglift. The Maglift Monorail achieves lower operating costs and a greater overall reduction in drag than conventional noncontact maglev does, and it does so without incurring maglev's high capital costs or its technology development risks.
There are currently two proposed standards for agent communication languages, namely, KQML (Finin, Lobrou, and Mayfield 1994) and the FIPA ACL. Neither standard has yet achieved primacy, and neither has been evaluated extensively in an open environment such as the Internet. It seems prudent therefore to design a general-purpose agent communications facility for new agent architectures that is flexible yet provides an architecture that accepts many different specializations. In this paper we exhibit the salient features of an agent communications architecture based on distributed metaobjects. This architecture captures design commitments at a metaobject level, leaving the base-level design and implementation up to the agent developer. The scope of the metamodel is broad enough to accommodate many different communication protocols, interaction protocols, and knowledge sharing regimes through extensions to the metaobject framework. We conclude that with a powerful distributed object substrate that supports metaobject communications, a general framework can be developed that will effectively enable different approaches to agent communications in the same agent system. We have implemented a KQML-based communications protocol and have several special-purpose interaction protocols under development.
When one considers the possibility of clandestine production of nuclear materials, one must consider the nature of the state. A Nuclear Weapon State (NWS) already has production facilities, and even though these might be safeguarded, the NWS could more easily hide the activities than could a Non-Nuclear Weapon State (NNWS). In this paper, some of the properties of production facilities are discussed in relation to how this would relate to vulnerability to detection. The observable and methods of detection are discussed, as well as the possibility that significant help by another country could totally eliminate one or more of the steps needed for a complete production cycle.
We present the results of molecular dynamics simulations of very long model polymer chains analyzed by various experimentally relevant techniques. The segment motion of the chains is found to be in very good agreement with the reptation model. We also calculated the plateau modulus G0N. The predictions of the entanglement length Ne from G0N and from the mean square displacement of the chain segments disagree by a factor of about 2.2(2), indicating an error in the prefactor in the standard formula for G0N. We show that recent neutron spin echo measurements were carried out for chain lengths which are too small to allow for a correct determination of Ne.
It became clear during the workshop that the applicability of commercial satellite imagery to the verification of future regional arms control agreements is limited at this time. Non-traditional security topics such as environmental protection, natural resource management, and the development of infrastructure offer the more promising applications for commercial satellite imagery in the short-term. Many problems and opportunities in these topics are regional, or at least multilateral, in nature. A further advantage is that, unlike arms control and nonproliferation applications, cooperative use of imagery in these topics can be done independently of the formal Middle East Peace Process. The value of commercial satellite imagery to regional arms control and nonproliferation, however, will increase during the next three years as new, more capable satellite systems are launched. Aerial imagery, such as that used in the Open Skies Treaty, can also make significant contributions to both traditional and non-traditional security applications but has the disadvantage of requiring access to national airspace and potentially higher cost. There was general consensus that commercial satellite imagery is under-utilized in the Middle East and resources for remote sensing, both human and institutional, are limited. This relative scarcity, however, provides a natural motivation for collaboration in non-traditional security topics. Collaborations between scientists, businesses, universities, and non-governmental organizations can work at the grass-roots level and yield contributions to confidence building as well as scientific and economic results. Joint analysis projects would benefit the region as well as establish precedents for cooperation.
Preliminary experimental and modeling study of injection and transport of high current electron beams in current-neutralized background gas has been performed. Initial analysis of the results indicates that high current triaxial ring diode operates very reproducibly in the pinch mode. High current density beam can be injected efficiently into the drift region, using azimuthal guide field with reduced intensity near the injection region. This was shown to improve the effectiveness of capturing the beam for the transport. The transport length was insufficient to measure losses, such as would arise from scattering with the background gas.
Emerging technologies in the field of "Test & Measurement" have recently enabled the development of the Rapidly Adaptable Instrumentation Tester (RAIT). Based on software developed with LabVIEW®, the RAIT design enables quick reconfiguration to test and calibrate a wide variety of telemetry systems. The consequences of inadequate testing could be devastating if a telemetry system were to fail during an expensive flight mission. Supporting both open-bench testing as well as automated test sequences, the RAIT has significantly lowered total time required to test and calibrate a system. This has resulted in an overall lower per unit testing cost than has been achievable in the past.
Chemical detection of gaseous species at very low vapor pressures is possible for materials with very low, saturation vapor pressures. A saturation vapor pressure implies equilibrium with the solid or liquid phase of the material. Thus partitioning of the gaseous species into a phase such as a polymer, will result in a very large concentration of the species in the solid phase and greatly enhanced ability to detect this species. The concentration in the polymer of the species to be detected is limited by the volubility of the species in that phase. In this presentation we discuss such a situation were 2-nitro-diphenylamine (2NDPA) is detected in the gas phase at room temperature at the few parts per trillion level.
A new equivalent-circuit model for the thickness shear mode resonator with a surface viscoelastic layer will be described. This model is valid only in the vicinity of a film resonance but is a reasonable approximation away from resonance. A simple resonant parallel circuit containing a resistor, a capacitor, and an inductor represents the electrical impedance of the film. These elements describe the film's viscous power dissipation, elastic energy storage, and kinetic energy storage, respectively. Resonator response comparisons between this lumped- element model and the general transmission-line model show good agreement over a range of film phase conditions and not just near film resonance. Under certain conditions, it will be shown that two peaks in the admittance magnitude are observed for operation at film resonance.
The sensitivity of surface acoustic wave (SAW) sensors has been enhanced by increasing the active surface area of these devices, Electrodepositions of Ni, Pd, and Pt in a mass-transport-limited mode with trace foreign metals yield highly dendritic crystal structures of uniform macroscopic thickness. The concentration of metal ions, supporting electrolyte, agitation, and additives greatly impact the crystal morphology of the deposit. This methodology can be used simply and economically to provide high-area films in selective regions.
We report experimental results suggesting that mobile protons are generated at strained Si-O-Si bonds near the Si/SiO2 interface during annealing in forming gas. Our data further suggest that the presence of the top Si layer plays a crucial role in the mobile H+ generation process. Finally, we show that the diffusion of the reactive species (presumably H2 or H0) towards the H+ generation sites occurs laterally along the buried oxide layer, and can be impeded significantly due to the presence of trapping sites in the buried oxide.
The balance-of-system (BOS) of a photovoltaic installation includes the array structure, trackers, ac and dc wiring, overcur-rent protection, disconnects, interconnects, inverters, charge controllers, energy storage and system controllers. The inverter (sometimes called power-conditioning subsystem (PCS), power conditioner or static power converter) is the key electrical power-handling component of a photovoltaic (PV) power system that has, ac loads. This paper will focus on the inverter and its related functions as the critical electrical BOS element in photovoltaic systems. An evolutionary summary for inverter hardware development, primarily in the US, will shed light on the paths that have been taken to arrive at today's state-of-the-technology. Recent developments, integrated packaging and opportunities for practical technology and hardware advancements will be presented. This paper will also touch on elementary battery issues as they relate to inverters and their control functions. Batteries are also critical, but often misunderstood, BOS components in stand- alone systems.
During the Cold War the handling of Soviet military nuclear wastes was a classified topic--kept secret to hide the status and readiness of Soviet military forces. Following the end of the Cold War information about the handling of nuclear wastes by agencies of the Former Soviet Union (FSU) became available. The US Government response to the disclosure of disposal of radioactive wastes into the Arctic Ocean and into rivers that drain into the Arctic Ocean was the finding of the Arctic Nuclear Waste Assessment Program (ANWAP) in the Office of Naval Research (ONR). Projects were aided by ANWAP to study the behavior, transport, and fate of radionuclides in the Arctic Ocean. One of the research teams, the Risk Assessment Integration Group (RAIG) assessed the potential risks to humans and to the environment, particularly in the US Alaskan Arctic.