Article discussing research on the response of carbon nanotubes to a tensile load.

The PEP-II High Energy Ring (HER), a 9 GeV electron storage ring, has been in commissioning since spring 1997. Initial beam commissioning activities focused on systems checkout and commissioning and on determining the behavior of the machine systems at high beam currents. This phase culminated with the accumulation of 0.75 A of stored beam-sufficient to achieve design luminosity--in January 1998 after 3.5 months of beam time. Collisions with the 3 GeV positron beam of the Low Energy Ring (LER) were achieved in Summer of 1998. At high beam currents, collective instabilities have been seen. Since then, commissioning activities for the HER have shifted in focus towards characterization of the machine and a rigorous program to understand the machine and the beam dynamics is presently underway.

Most accelerator magnets for applications in the field range up to 9 T utilize NbTi superconductor and a cosine theta coil design. For fields above 9 T, it is necessary to use Nb{sub 3}Sn or other strain sensitive materials, and other coil geometries that are more compatible with these materials must be considered. This paper describes their recent efforts to design a series of racetrack coil magnets that will provide experimental verification of this alternative magnet design for a dual aperture dipole magnet with the goal of reaching a field level of 15 T, will be described. The experimental program, which consists of a series of steps leading to a high field accelerator quality magnet, will be presented. Fabrication of a racetrack dipole magnet utilizing Nb{sub 3}Sn superconductor and a wind and react approach will be presented.

In support of data quality objectives for the INEEL Stored Waste Examination Pilot Plant (SWEPP) a series of 208-liter (55-gallon) waste drums containing inorganic sludge have been sampled and destructively analyzed. The drums were non-destructively assayed by the SWEPP PAN system and the SWEPP Gamma-Ray Spectrometer (SGRS) prior to sampling. This paper reports some of the conclusions from the destructive versus NDA comparisons, and additionally presents the results of an on-going effort to use the destructive analyses to validate absolute efficiency curves calculated using Monte-Carlo and analytical modeling for the SGRS. Destructive analysis results are available from radiochemical assay of 128 sludge-containing drums. The content codes represented are CC001 (42 items), CC002 (8), CC007 (48), CC800 (16), CC803 (3), and CC807 (11.) Each drum had two full-length vertical cores removed from designated radial positions. The entire length of each core was composited and submitted for analysis. All of the core composites were analyzed radiochemically for Am-241, Pu-239/240, and Pu-238, and by inductively-coupled mass spectrometry (ICPMS) for U-235 and U-238. Not only have the destructive analysis results been useful in documenting the performance of both the SGRS and the PAN system, but also have allowed the determination of certain absolute counting …

Regulatory agencies governing the disposal of nuclear waste require that the waste be appropriately characterized prior to disposition. The most important aspect of the characterization process, establishing radionuclide content, is often achieved by nondestructive assay (NDA). For NDA systems to be approved for use in these applications, measurement uncertainty must be established. Standard “propagation of errors” methods provide a good starting point for considering the uncertainty analysis of NDA systems for nuclear waste. However, as compared with other applications (e.g., nuclear material accountability), using NDA systems for nuclear waste measurements presents some unique challenges. These challenges, stemming primarily from the diverse nature of the waste materials encountered, carry over into the uncertainty analysis as well. This paper reviews performance measures appropriate for the assessment of NDA uncertainty, describes characteristics of nuclear waste measurements that contribute to difficulties in assessing uncertainty, and outlines some statistics based methods for incorporating variability in waste characteristics in an uncertainty analysis.

New experiments using an array of high purity germanium detectors and fast liquid scintillation detectors has been performed to observe the radiation emitted from the induced fission of 235U with a beam of thermal neutrons. The experiment was performed at the Argonne National Laboratory Intense Pulsed Neutron Source. Preliminary observations of the data are presented. A nondestructive analysis system for the characterization of DOE spent nuclear fuel based on these new data is presented.

Galvanic corrosion behavior of A 516 steel coupled to alloy C-22 and Ti Gr-12, respectively was evaluated in an acidic brine (pH {approx} 2.75) at 30 C, 60 C and 80 C using zero resistance ammeter method. A limited number of experiments were also performed in a neutral brine involving A 516 steel/alloy C-22 couple. The steady-state galvanic current and galvanic potential were measured as functions of anode-to-cathode (A/C) area ratio and electrode distance. Results indicate that the galvanic current was gradually reduced as the A/C area ratio was increased. No systematic trend on the effect of A/C area ratio on the galvanic potential was observed. Also, no significant effect of electrode distance on the galvanic current and galvanic potential was evident. In general, increased galvanic current was noticed with increasing temperature. The limited data obtained in the neutral brine indicate that the galvanic current was reduced in this environment, compared to that in the acidic brine. Optical microscopic examination was performed on all tested specimens to evaluate the extent of surface damage resulting from galvanic interaction. A 516 steel suffered from general corrosion and crevice corrosion in all environments tested. Very light crevice corrosion mark was observed with alloy …

In an organization where there are many DBAs working with many instances and databases on many machines with many developers - how do you manage all of this without total chaos? This paper will outline how the central Database Support organization at Lockheed Martin Energy Systems in Oak Ridge, TN manages more than 250 instances on more than 90 systems with a variety of operating systems. This discussion will include how tasks and responsibilities are divided between System DBAs, Application Project DBAs, and developers. The use of standards as well as local routines to maintain the systems will be discussed. Information on the type of communications used to keep the different groups informed and up-to-date will also be presented.

Microearthquake (MEQ) occurrence surrounding the injection well DV11 in Unit 18 of the Southeast (SE) Geysers is investigated. Seismicity rates are compared to the injection rate, and to flow rates in nearby steam extraction wells, which were monitored during the Unit 18 Cooperative Injection Test in 1994 and 1995. The seismicity rate is seen to mirror both injection and production rates, although a time lag sometimes occurs. Waveform cross-correlation is performed for the MEQs in the DV11 area, and the events grouped into clusters based on waveform similarity. Relative location techniques applied to the events in two of these clusters show 7 events grouped into a volume of about 25 m in diameter, at an elevation of about -0.65 km msl and 5 events grouped into a vertically-oriented linear feature about 100 m in length, at about -1.8 km msl.

The built-in electric field in polycrystalline CuInSe{sub 2} (CIS) near gold co-planar contacts was quantitatively revealed for the first time by the photomixing technique. A He-Ne laser beam was focused locally on the CIS sample near one of its contact. While both dc dark and photo-currents showed ohmic behavior, the high frequency ac current was non-zero for zero applied dc bias, which reveals a built-in electric field of {approx}1000V/cm. The capability of the photomixing technique to probe local charge transport properties is expected to be very useful for, e.g., the quantitative evaluation of the quality of ohmic contacts and the investigation of electric field induced p-n junction formation in CIS and related materials.

Regulatory agencies governing the disposal of nuclear waste require that the waste be appropriately characterized prior to disposition. The most important aspect of the characterization process, establishing radionuclide content, is often achieved by nondestructive assay (NDA). For NDA systems to be approved for use in these applications, measurement uncertainty must be established. Standard �propagation of errors� methods provide a good starting point for considering the uncertainty analysis of NDA systems for nuclear waste. However, as compared with other applications (e.g., nuclear material accountability), using NDA systems for nuclear waste measurements presents some unique challenges. These challenges, stemming primarily from the diverse nature of the waste materials encountered, carry over into the uncertainty analysis as well. This paper reviews performance measures appropriate for the assessment of NDA uncertainty, describes characteristics of nuclear waste measurements that contribute to difficulties in assessing uncertainty, and outlines some statistics based methods for incorporating variability in waste characteristics in an uncertainty analysis.

An adaptive, variable block-size readout technique for use with multiple, sixteen-channel CAMAC ADCs with a FERA-bus readout has been developed and designed. It can be used to read data from experiments with or without coincidence, i.e. singles, without having to change the readout protocol. Details of the implementation are discussed and initial results are presented. Further applications of the adaptive readout are also discussed.

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It was shown that the accuracy of results for wires moved laterally from mesh edges can be greatly improved by taking account of the behavior of the field in the vicinity of the wire. Also, the distance to the end of the wire can be adjusted within a cell by using a general second-order difference form for the derivative. Making the wire location completely independent of the mesh would require the additional ability to tilt the wire with respect to the edges. This seems to be a considerably more difficult problem than moving the wires laterally, since the component of the mesh field parallel to the wire gets mixed with the larger radial electric field due to charge on the wire. Simply averaging the mesh fields did not seem to work well, except in the case where the wire was tilted in one coordinate plane, and the mesh fields above and below the plane of the wire, on edges orthogonal to the wire normal, could be averaged. Further study is needed to develop a more general capability to tilt a wire with respect to the mesh.

This article discusses tunneling rate fluctuations induced by nonlinear resonances. The authors investigate the tunneling process between two symmetric stable islands of a forced pendulum Hamiltonian in the weak chaos regime.

Marty brittle fracture evaluation procedures include plasticity corrections to elastically computed stress intensity factors. These corrections, which are based on the existence of a plastic zone in the vicinity of the crack tip, can overestimate the plasticity effect for a crack embedded in a stress concentration region in which the elastically computed stress exceeds the yield strength of the material in a localized zone. The interactions between the crack, which acts to relieve the high stresses driving the crack, plasticity effects in the stress concentration region, and the nature and source of the loading are examined by formulating explicit flaw finite element models for a crack emanating from the root of a notch located in a panel subject to an applied tensile stress. The results of these calculations provide conditions under which a crack-tip plasticity correction based on the Irwin plastic zone size overestimates the plasticity effect. A failure assessment diagram (FAD) curve is used to characterize the effect of plasticity on the crack driving force and to define a less restrictive plasticity correction for cracks at notch roots when load-controlled boundary conditions are imposed. The explicit flaw finite element results also demonstrate that stress intensity factors associated with load-controlled …

MEMS microfluidic systems are becoming increasingly popular as a way to integrate sample preparation and biological assays on a single substrate. The resulting reduction in manual operations and reduced reagent use can lead to significant cost savings in performing biological tests. The authors have explored the use of small scale dielectrophoresis and electrophoresis as a way to manipulate DNA for sample preparation in DNA-based assays. The use of electric fields to manipulate DNA is readily achieved in MEMS devices using standard photolithography techniques to add electrodes to etched flow channels. Dielectrophoresis allows for manipulation of cells and DNA independently of the liquid. This ability is useful in small, valveless fluidic microchips. An advantage of the use of the dielectrophoretic force over an electrophoretic force is that dielectrophoresis works equally well using an AC field, thus reducing trapping of small ions and mitigating electrochemical effects at the electrodes. However, the dielectrophoretic force on the DNA is a function of the volume of the particle; thus, there is a lower practical limit to use of the dielectrophoretic force. Consequently they have also explored methods of manipulating smaller DNA fragments using what they refer to as a stepped electrophoresis method.

The nature of the interface between CuInSe{sub 2} (CIS) and the chemical bath deposited CdS layer has been investigated. We show that heat-treating the absorbers in Cd- or Zn-containing solutions in the presence of ammonium hydroxide sets up a chemical reaction which facilitates an extraction of Cu from the lattice and an in-diffusion of Cd. The characteristics of devices made in this manner suggest that the reaction generates a thin, n-doped region in the absorber. It is quite possible that the CdS/CuInSe{sub 2} device is a buried, shallow junction with a CdS window layer, rather than a heterojunction. We have used these ideas to develop methods for fabricating devices without CdS or Cd. A 14.2% efficiency ZnO/CIGS device was obtained through aqueous treatment in Zn solutions.

Using defect thermodynamics, we discuss physical factors that affect doping limits in semiconductors. The dependencies of the defect formation enthalpy on the atomic chemical potentials and on the electron Fermi energy are demonstrated. These dependencies, in particular on the Fermi energy, lead to spontaneous formation of charge-compensating defects that can limit doping. Experimental data compiled for III-V, II-VI, and I-III-VI2 compounds support this view and further provide insight into the connections among different host materials. We argue that what matters is not the magnitude of the band gap that determines the dopability of a material, but rather, the relative position of the conduction-band minimum (in the case of n-doping) and the valence-band maximum (in the case of p-doping) with respect to vacuum.

The effect of B and C additions up to 0.4 at. % on glass formation and mechanical properties of a Zr-base alloy Vitreloy 105 was studied using various techniques. All alloys were prepared by arc melting and drop casting. Boron additions increase the glass forming ability by lowering T_m and increasing T_g. Carbon additions only lower T_m, but do not affect T_g. B and C additions occupy free space and do not harden the glass phase.

This work describes simple but comprehensive constitutive equations that model a number of physical phenomena exhibited by dry porous geological materials and metals. Moreover, formulas have been developed for robust numerical integration of the evolution equations at the element level that can be easily implemented into standard computer programs for dynamic response of materials.

A new position-sensing X-ray detector operated in integrate-readout mode has been recently designed and characterized. Due to the peculiar working principle of the new detector, the charge handling capability, that is the maximum charge that can be stored in a pixel, is related to the operating conditions of the device. In particular the amplitude of the barriers that confine the signal electrons during the integration phase depends on the applied drift field and on the field perturbation superposed to it. A detailed experimental characterization of the charge handling capability as a function of these parameters has been carried out.

A high-energy, transverse momentum cut-off, solution of QCD is outlined. Regge pole and single gluon properties of the pomeron are directly related to the confinement and chiral symmetry breaking properties of the hadron spectrum. This solution, which corresponds to a supercritical phase of Reggeon Field Theory, may only be applicable to QCD with a very special quark content.

Inductively coupled plasma (ICP) etching characteristics of GaSb and AIGaAsSb have been investigated in BC13/Ar and Clz/Ar plasmas. The etch rates and selectivity between GaSb and AIGaAsSb are reported as functions of plasma chemistry, ICP power, RF self-bias, and chamber pressure. It is found that physical sputtering resorption of the etch products plays a dominant role in BC13/Ar ICP etching, while in Clz/Ar plasma, the chemical reaction dominates the etching. GaSb etch rates exceeding 2 ~rnhnin are achieved in Clz/Ar plasmas with smooth surfaces and anisotropic profiles. In BC13/Ar plasmas, etch rates of 5100 Mmin and 4200 Mmin are obtained for GaSb and AIGaAsSb, respectively. The surfaces of both GaSb and AIGaAsSb etched in BC13/Ar plasmas remain smooth and stoichiometric over the entire range of plasma conditions investigated. This result is attributed to effective removal of etch products by physical sputtering. For a wide range of plasma conditions, the selectivity between GaSb and AIGaAsSb is close to unity, which is desirable for fabricating etched mirrors and gratings for Sb-based mid-IR laser diodes.