Article on structural and electronic properties of carbon nanotube tapers, a set of nanostructures comprised of straight tubular sections with decreasing diameters, joined to each other via conical funnels and terminated with a hemispherical cap.

Presented at the 2001 NCPV Program Review Meeting: Comparative studies of dynamics of photoexcited carriers in range of Si-based materials of interest for PV applications.

Presented at the 2001 NCPV Program Review Meeting: Results using light-biasing EBIC are illustrated for dual-junction InGaP/InGaAs solar cells.

Presented at the 2001 NCPV Program Review Meeting: The Thin Film Partnership has organized three National Research Teams in CIS, CdTe, and amorphous silicon.

Presented at the 2001 NCPV Program Review Meeting: Describes performance of 1-kWac CdTe PV array from First Solar operated at NREL from 6/95 to 14/00. This paper describes the performance of a 1-kW{sub ac} CdTe PV array from First Solar (formerly Solar Cells, Inc.) operated at NREL from June 1995 to November 2000. The PV array operating efficiencies over the 5.5-year period were calculated from 15-minute averages to determine changes in seasonal and annual performance. Performance measurements of each module were also made before installing the modules outdoors and again in August 2000 using NREL's indoor SPIRE 240A pulsed solar simulator and the Standard Outdoor Measurement System (SOMS). Although some modules showed increases in efficiency and others decreases, the average efficiency of the modules in the PV array did not change. For modules that showed changes in efficiency, analysis of module I-V parameters indicated that the changes in efficiency were primarily a consequence of changes in fill factor.

We describe a coded-aperture based, gamma-ray imager that uses a unique hybrid germanium detector system. A planar, germanium strip detector, eleven millimeters thick is followed by a coaxial detector. The 19 x 19 strip detector (2 mm pitch) is used to determine the location and energy of low energy events. The location of high energy events are determined from the location of the Compton scatter in the planar detector and the energy is determined from the sum of the coaxial and planar energies. With this geometry, we obtain useful quantum efficiency in a position-sensitive mode out to 500 keV. The detector is used with a 19 x 17 URA coded aperture to obtain spectrally resolved images in the gamma-ray band. We discuss the performance of the planar detector, the hybrid system and present images taken of laboratory sources.

Presented at the 2001 NCPV Program Review Meeting: DOEs Concentrating Solar Power program is investigating the viability of concentrating PV converters as an alternative to thermal conversion devices.

Presented at the 2001 NCPV Program Review Meeting: Energy production and performance of polycrystalline silicon technology photovoltaic modules in the field. Six polycrystalline silicon photovoltaic modules--two apiece from three manufacturers--were simultaneously deployed outdoors on the performance and energy ratings testbed at NREL's Outdoor Test Facility (OTF) in June 2000. In situ electrical performance and energy production from these modules obtained under ambient conditions in the field between June 2000 and August 2001 are compared. The average effective efficiency--derived from module energy out divided by solar energy in calculations averaged on a weekly basis--is analyzed and compared with module current-voltage measurements performed at standard reporting conditions (SRC). The effective efficiencies exhibit seasonal variations correlated with average module temperatures--becoming larger at colder temperatures. The performance ratios (PRs) defined as the effective efficiency divided by the efficiency at SRC, range from 78% to 96%, depending on the module and time of the year. The PRs exhibit seasonal variations that range from 11% to 15%.

Presented at the 2001 NCPV Program Review Meeting: Modeled diffusion of H in 2-step Si{sub 3}N{sub 4} passivation process invoking concept of storage of H. H stored during nitridation is redistributed during subsequent anneal. The modeling results agree with this hypothesis, and the conclusions also appear to concur with the observations.

Presented at the 2001 NCPV Program Review Meeting: Overview of the Fundamental and Exploratory Research project with the DOE Basic Sciences program and the National Center for Photovoltaics. This paper presents an overview of the Fundamental and Exploratory Research project within the U.S. Department of Energy's National Center for Photovoltaics (NCPV). The idea behind the project is to identify, support, evaluate and coordinate an optimal spectrum of complementary projects that either contribute to the fundamental understanding of existing PV technologies or to explore the less conventional, or far out, technological possibilities. Two other programs, one for close collaborative university/industry partnerships in crystalline silicon and an educational/research program involving undergraduates at eight historically black colleges and universities, are also managed under this same task. In sum, this effort represents directed high-risk, long-term basic research targeting possibilities for optimal configurations of low cost, high efficiency, and reliability in PV related devices whatever form they may ultimately take.

This paper presents results of coupled thermal-hydrological-mechanical (THM) simulations of two field-scale tests that are part of the thermal testing program being conducted by the Yucca Mountain Site Characterization Project. The two tests analyzed are the Drift-Scale Test (DST) which is sited in an alcove of the Exploratory Studies Facility at Yucca Mountain, Nevada, and the Large Block Test (LBT) which is sited at Fran Ridge, near Yucca Mountain, Nevada. Both of these tests were designed to investigate coupled thermal-mechanical-hydrological-chemical (TMHC) behavior in a fractured, densely welded ash-flow tuff. The geomechanical response of the rock mass forming the DST and the LBT is analyzed using a coupled THM model. A coupled model for analysis of the DST and LBT has been formulated by linking the 3DEC distinct element code for thermal-mechanical analysis and the NUFT finite element code for thermal-hydrologic analysis. The TH model (NUFT) computes temperatures at preselected times using a model that extends from the surface to the water table. The temperatures computed by NUFT are input to 3DEC, which then computes stresses and deformations. The distinct element method was chosen to permit the inclusion of discrete fractures and explicit modeling of fracture deformations. Shear deformations and normal …

Presented at the 2001 NCPV Program Review Meeting: Electron microscopy studies of MOVPE layers of materials that are potential 1-eV bandgap semiconductors for solar cells.

Presented at the 2001 NCPV Program Review Meeting: Measurements of backsheet moisture permeation and encapsulant-substrate adhesion. At the March 2001 NCPV workshop on ''Moisture Ingress and High-Voltage Isolation'', industry participants identified several properties associated with PV module durability that are critical for commercial success. These include interface conductivity, adhesion of encapsulants to substrate materials as a function of in-service exposure conditions, and moisture permeation through backsheet materials as a function of temperature. Electrical data is discussed in a companion paper; adhesion and water vapor transmission rate (WVTR) measurements are presented herein.

By thermally cycling through their transformation temperature range, coarse-grained, polymorphic materials can be deformed superplastically, owing to the emergence of transformation mismatch plasticity (or transformation superplasticity) as a deformation mechanism. This mechanism is investigated under biaxial stress conditions during thermal cycling of unalloyed titanium, Ti-6Al-4V, and their composites (Ti/10 vol.% TiC{sub p}, Ti-6Al-4V/10 vol% TiC{sub p} and Ti-6Al-4V/5 vol.% TiB{sub w}). During gas-pressure dome bulging experiments, the dome height was measured as a function of forming time. Adapting existing models of biaxial doming to the case of transformation superplasticity where the strain-rate sensitivity is unity, we verify the operation of this deformation mechanism in all experimental materials, and compare the biaxial results to uniaxial thermal cycling results on the same materials. Finally, existing thickness distribution models are compared with experimentally measured profiles.

Major improvements in models of chemically peculiar stars have been achieved in the past few years. With these new models it has been possible to test quantitatively some of the processes involved in the formation of abundance anomalies and their effect on stellar structure. The models of metallic A (Am) stars have shown that a much deeper mixing has to be present to account for observed abundance anomalies. This has implications on their variability, which these models also reproduce qualitatively. These models also have implications for other chemically inhomogeneous stars such as HgMn B stars which are not known to be variable and {lambda} Booetis stars which can be. The study of the variability of chemically inhomogeneous stars can provide unique information on the dynamic processes occurring in many types of stars in addition to modeling of the evolution of their surface composition.

As part of the effort to modernize safeguards equipment, the IAEA is continuing to acquire and install equipment for upgrading obsolete surveillance systems with digital technology; and providing remote-monitoring capabilities where and when economically justified. Remote monitoring is expected to reduce inspection effort, particularly at storage facilities and reactor sites. Remote monitoring technology will not only involve surveillance, but will also include seals, sensors, and other unattended measurement equipment. The experience of Lawrence Livermore National Laboratory (LLNL) with the Argus Security System offers lessons for the design, deployment, and maintenance of remote monitoring systems. Argus is an integrated security system for protection of high-consequence U.S. Government assets, including nuclear materials. Argus provides secure transmission of sensor data, administrative data, and video information to support intrusion detection and access control functions. LLNL developed and deployed the Argus system on its own site in 1988. Since that time LLNL has installed, maintained, and upgraded Argus systems at several Department of Energy and Department of Defense sites in the U.S. and at the original LLNL site. Argus has provided high levels of reliability and integrity, and reduced overall life-cycle cost through incremental improvements to hardware and software. This philosophy permits expansion of functional …

The National Ignition Facility (NIF) requires that pulses from each of the 192 laser beams be positioned on target with an accuracy of 50 {micro}m rms. Beam quality must be sufficient to focus a total of 1.8 MJ of 0.351-{micro}m light into a 600-{micro}m-diameter volume. An optimally flat beam wavefront can achieve this pointing and focusing accuracy. The control system corrects wavefront aberrations by performing closed-loop compensation during laser alignment to correct for gas density variations. Static compensation of flashlamp-induced thermal distortion is established just prior to the laser shot. The control system compensates each laser beam at 10 Hz by measuring the wavefront with a 77-lenslet Hartmann sensor and applying corrections with a 39-actuator deformable mirror. The distributed architecture utilizes SPARC AXi computers running Solaris to perform real-time image processing of sensor data and PowerPC-based computers running VxWorks to compute mirror commands. A single pair of SPARC and PowerPC processors accomplishes wavefront control for a group of eight beams. The software design uses proven adaptive optic control algorithms that are implemented in a multi-tasking environment to economically control the beam wavefronts in parallel. Prototype tests have achieved a closed-loop residual error of 0.03 waves rms. aberrations, the spot size …

This paper introduces the DesignersWorkbench, a semi-immersive virtual environment for two-handed modeling, sculpting and analysis tasks. The paper outlines the fundamental tools, design metaphors and hardware components required for an intuitive real-time modeling system. As companies focus on streamlining productivity to cope with global competition, the migration to computer-aided design (CAD), computer-aided manufacturing (CAM), and computer-aided engineering (CAE) systems has established a new backbone of modern industrial product development. However, traditionally a product design frequently originates from a clay model that, after digitization, forms the basis for the numerical description of CAD primitives. The DesignersWorkbench aims at closing this technology or ''digital gap'' experienced by design and CAD engineers by transforming the classical design paradigm into its filly integrated digital and virtual analog allowing collaborative development in a semi-immersive virtual environment. This project emphasizes two key components from the classical product design cycle: freeform modeling and analysis. In the freeform modeling stage, content creation in the form of two-handed sculpting of arbitrary objects using polygonal, volumetric or mathematically defined primitives is emphasized, whereas the analysis component provides the tools required for pre- and post-processing steps for finite element analysis tasks applied to the created models.

Transformation superplasticity is a deformation mechanism induced by thermally-cycling a polymorphic material through the phase transformation range while simultaneously applying an external biasing stress. Unlike microstructural superplasticity, which requires a fine, equiaxed grain structure, this mechanism can be applied to coarse-grained alloys and composites. In this article, we review our research on transformation superplasticity of Ti-6Al-4V/TiB-whisker reinforced composites, during thermal cycling through the titanium {alpha}/{beta} transformation range. The composites exhibit Newtonian flow and superplastic extension under these conditions. We describe the constitutive behavior of composites containing 0, 5 and 10 vol% reinforcing whiskers, and consider the effects of load transfer from matrix to whisker on superplastic deformation using existing rheological models. Additionally, strain hardening due to gradual whisker alignment is observed, and rationalized in terms of increased load transfer for aligned whiskers.

A 2-day workshop ''Physical and Chemical Property Measurements for the Gas Hydrate R&D Community'' was held on 17-18 September 2001. Putting together this workshop was a joint effort by LLNL, MBARI and the USGS, Menlo Park. Twenty-two people from a wide variety of institutions and backgrounds participated. An additional eighteen people were forced to cancel at the last minute due to the events of 11 September 2001. The premise of the workshop was that progress in nearly every aspect of gas hydrate research depends fundamentally on the availability of high-quality property data and the development of laboratory insights into the physics and chemistry that govern gas hydrates in nature. One objective of the workshop was to develop a dialogue between laboratory scientists who make property measurements of gas hydrates and scientists who use these data for quantitative modeling. A second objective was to help facilitate research among experimentalists and the acquisition of reliable gas hydrate properties. The latter focused mainly, but not exclusively, on researchers from institutions in the San Francisco Bay Area to energize a community that has a geographic advantage in collaborative relationships. The workshop was successful at meeting both of these objectives, although the unique perspectives of …

The Task Group on Computational Modelling for Explicit Analyses in the ASME Boiler and Pressure Vessel Code committee was set up in August 2008 to develop a quantitative finite element modelling guidance document for the explicit dynamic analysis of energy-limited events. This guidance document will be referenced in the ASME Boiler and Pressure Vessel Code Section III Division 3 and NRC Regulatory Guide 7.6 as a means by which the quality of a finite element model may be judged. In energy limited events, which the guidance document will address, ductile metallic materials will suffer significant plastic strains to take full advantage of their energy absorption capacity. Accuracy of the analyses in predicting large strains is therefore essential. One of the issues that this guidance document will address is the issue of the quality of a finite element mesh, and in particular, mesh refinement to obtain a convergent solution. That is, for a given structure under a given loading using a given type of element, what is the required mesh density to achieve sufficiently accurate results. One portion of the guidance document will be devoted to a series of element convergence studies that can aid designers in establishing the mesh refinement …

Abstract – The AGR-1 irradiation experiment contains seventy-two individual cylindrical fuel compacts (25 mm long x 12.5 mm diameter) each containing approximately 4100 TRISO-coated uranium oxycarbide fuel particles. The experiment accumulated 620 effective full power days in the Advanced Test Reactor at the Idaho National Laboratory with peak burnups exceeding 19% FIMA. An extensive post-irradiation examination campaign will be performed on the AGR-1 fuel in order to characterize the irradiated fuel properties, assess the in-pile fuel performance in terms of coating integrity and fission metals release, and determine the fission product retention behavior during high temperature accident testing. PIE experiments will include dimensional measurements of fuel and irradiated graphite, burnup measurements, assessment of fission metals release during irradiation, evaluation of coating integrity using the leach-burn-leach technique, microscopic examination of kernel and coating microstructures, and accident testing of the fuel in helium at temperatures up to 1800°C. Activities completed to date include opening of the irradiated capsules, measurement of fuel dimensions, and gamma spectrometry of selected fuel compacts.

The Russian Research Reactor Fuel Return (RRRFR) Program, under the U.S. Department of Energy’s Global Threat Reduction Initiative, began returning Russian-supplied high-enriched uranium (HEU) spent nuclear fuel (SNF), stored at Russian-designed research reactors throughout the world, to Russia in January 2006. During the first years of making HEU SNF shipments, it became clear that the modes of transportation needed to be expanded from highway and railroad to include sea and air to meet the extremely aggressive commitment of completing the first series of shipments by the end of 2010. The first shipment using sea transport was made in October 2008 and used a non-Russian flagged vessel. The Russian government reluctantly allowed a one-time use of the foreign-owned vessel into their highly secured seaport, with the understanding that any future shipments would be made using a vessel owned and operated by a Russian company. ASPOL-Baltic of St. Petersburg, Russia, owns and operates a small fleet of vessels and has a history of shipping nuclear materials. ASPOL-Baltic’s vessels were licensed for shipping nuclear materials; however, they were not licensed to transport SNF materials. After a thorough review of ASPOL Baltic’s capabilities and detailed negotiations, it was agreed that a contract would be …

Oregon State University (OSU) and the Idaho National Laboratory (INL) are currently collaborating on a test program which entails hydro-mechanical testing of a generic plate type fuel element, or standard fuel element (SFE), for the purpose of qualitatively demonstrating mechanical integrity of uranium-molybdenum monolithic plates as compared to that of uranium aluminum dispersion, and aluminum fuel plates due to hydraulic forces. This test program supports ongoing work conducted for/by the fuel development program and will take place at OSU in the Hydro-Mechanical Fuel Test Facility (HMFTF). Discussion of a preliminary test matrix, SFE design, measurement and instrumentation techniques, and facility description are detailed in this paper.