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.

Article on O(N) real-space method for ab initio quantum transport calculations and application to carbon nanotube-metal contacts.

Article discussing the I' potential of the human auditory brainstem response to paired click stimuli.

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Scientists in the Physical Biosciences Division of the Ernest Orlando Berkeley National Laboratory (Berkeley Lab) studying transition metals in proteins with fluorescence-detected L-edge absorption spectroscopy have found the measurements to be extremely challenging. The difficulty is that the metal centers are present in very dilute concentrations so that their weak fluorescence is often obscured by strong background signals carbon and oxygen. To solve this problem, the Berkeley group has been working with researchers from the Advanced Detector Group at the Lawrence Livermore National Laboratory on an energy-dispersive superconducting tunnel junction x-ray detector. These devices in principle have the energy resolution needed to reveal the metal signal. The most recent results with the latest version of the detector on Beamline 4.0.1-2 at the Advanced Light Source (ALS) illustrate the promise of the cryogenic detector strategy not only for this application but also for spectroscopy of other types of dilute samples. Transition-metal complexes are key elements in many biologically important processes that are catalyzed by proteins (enzymes), photosynthesis being a prime example. The changes in that occur in electronic structure throughout a catalytic cycle are the subject of much research aimed at understanding the mechanisms of these processes. L-edge x-ray spectroscopy offers …

The Lawrence Berkeley National Laboratory has developed a device that measures the water content of wood chips, pulp and brown stock for the paper industry. This device employs a permanent magnet as the central part of a NMR measurement system. This report describes the magnet and the NMR measurement system. The results of water content measurements in wood chips in a magnetic field of 0.47 T are presented.

The Idaho National Engineering and Environmental Laboratory (INEEL) is dedicated to finding solutions to problems related to the environment, energy, economic competitiveness, and national security. In an effort to attract and retain the expertise needed to accomplish these challenges, the INEEL is developing a program of broad educational opportunities that makes continuing education readily available to all laboratory employees, beginning in the K–12 environment and progressing through post-graduate education and beyond. One of the most innovative educational approaches being implemented at the laboratory is the application of STELLA© dynamic learning environments, which facilitate captivating K–12 introductions to the complex energy and environmental challenges faced by global societies. These simulations are integrated into lesson plans developed by teachers in collaboration with INEEL scientists and engineers. This approach results in an enjoyable and involved learning experience, and an especially positive introduction to the application of science to emerging problems of great social and environmental consequence.

Large distributed systems, such as computational grids,require a large amount of monitoring data be collected for a variety oftasks, such as fault detection, performance analysis, performance tuning,performance prediction and scheduling. Ensuring that all necessarymonitoring is turned on and that the data is being collected can be avery tedious and error-prone task. We have developed an agent-basedsystem to automate the execution of monitoring sensors and the collectionof event data.

Adaptive management consists in patterning human sustenancewithin the constraints of Earth and biological systems whose behavior isinherently uncertain and difficult to control. For successful adaptivemanagement, a mind-set recognizing the limitations of science isneeded.

We describe the goals and research program leading to the Heavy Ion Integrated Research Experiment (IRE). We review the basic constraints which lead to a design and give examples of parameters and capabilities of an IRE. We also show design tradeoffs generated by the systems code IBEAM.

Transmission Electron Microscopy developed from an imagingtool into a quantitative electron beam characterization tool that locallyaccesses structure, chemistry, and bonding in materials with sub Angstromresolution. Experiments utilize coherently and incoherently scatteredelectrons. In this contribution, the interface between gallium nitrideand sapphire as well as thin silicon gate oxides are studied tounderstand underlying physical processes and the strength of thedifferent microscopy techniques. An investigation of the GaN/sapphireinterface benefits largely from the application of phase contrastmicroscopy that makes it possible to visualize dislocation corestructures and single columns of oxygen and nitrogen at a closest spacingof 85 pm. In contrast, it is adequate to investigate Si/SiOxNy/poly-Siinterfaces with incoherently scattered electrons and electronspectroscopy because amorphous and poly crystalline materials areinvolved. Here, it is demonstrated that the SiOxNy/poly-Si interface isrougher than the Si/SiOx interface, that desirable nitrogen diffusiongradients can be introduced into the gate oxide, and that a nitridationcoupled with annealing increases its physical width while reducing theequivalent electrical oxide thickness to values approaching 1.2 nm.Therefore, an amorphous SiNxOy gate dielectric seems to be a suitablesubstitute for traditional gate oxides to further increase device speedby reducing dimensions in Si technology.

Idaho National Laboratory is experimenting with electrical neutron generators, as potential replacements for californium-252 radioisotopic neutron sources in its PINS prompt gamma-ray neutron activation analysis (PGNAA) system for the identification of military chemical warfare agents and explosives. In addition to neutron output, we have recently measured the x-ray output of the Thermo Scientific P385 deuterium-deuterium neutron generator. X-rays are a normal byproduct from a neutron generator and depending on their intensity and energy they can interfere with gamma rays from the object under test, increase gamma-spectrometer dead time, and reduce PGNAA system throughput. The P385 x-ray energy spectrum was measured with a high-purity germanium (HPGe) detector, and a broad peak is evident at about 70 keV. To identify the source of the x-rays within the neutron generator assembly, it was scanned by collimated scintillation detectors along its long axis. At the strongest x-ray emission points, the generator also was rotated 60° between measurements. The scans show the primary source of x-ray emission from the P385 neutron generator is an area 60 mm from the neutron production target, in the vicinity of the ion source. Rotation of the neutron generator did not significantly alter the x-ray count rate, and the x-ray …

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.

In this study, we address a series of fundamental questions regarding the processes and effectiveness of geologic CO{sub 2} sequestration in saline aquifers. We begin with the broadest: what is the ultimate fate of CO{sub 2} injected into these environments? Once injected, it is immediately subject to two sets of competing processes: migration processes and sequestration processes. In terms of migration, the CO{sub 2} moves by volumetric displacement of formation waters, with which it is largely immiscible; by gravity segregation, which causes the immiscible CO{sub 2} plume to rise owing to its relatively low density; and by viscous fingering, owing to its relatively low viscosity. In terms of sequestration, some fraction of the rising plume will dissolve into formation waters (solubility trapping); some fraction may react with formation minerals to precipitate carbonates (mineral trapping); and the remaining portion eventually reaches the cap rock, where it migrates up-dip, potentially accumulating in local topographic highs (structural trapping). Although this concept of competing migration/sequestration processes is intuitively obvious, identifying those sub-processes that dominate the competition is by no means straightforward. Hence, at present there are large uncertainties associated with the ultimate fate of injected CO{sub 2} (Figure 1). Principal among these: can a …

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.