Laser spot welding is an ideal process for joining small parts with tight tolerances on weld size, location, and distortion, particularly those with near-by heat sensitive features. It is also key to understanding the overlapping laser spot seam welding process. Rather than attempting to simulate the laser beam-to-part coupling (particularly if a keyhole occurs), it was measured by calorimetry. This data was then used to calculate the thermal and structural response of a laser spot welded SS304 disk using the finite element method. Five combinations of process parameter values were studied. Calculations were compared to experimental data for temperature and distortion profiles measured by thermocouples and surface profiling. Results are discussed in terms of experimental and modeling factors. The authors then suggest appropriate parameters for laser spot welding.

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A MEMS test structure capable of measuring friction between polysilicon surfaces under a variety of test conditions has been refined from previous designs. The device is applied here to measuring friction coefficients of polysilicon surfaces under different environmental, loading, and surface conditions. Two methods for qualitatively comparing friction coefficients ({mu}) using the device are presented. Samples that have been coated with a self-assembled monolayer of the lubricating film perfluorinated-decyltrichorosilane (PFTS) have a coefficient of friction that is approximately one-half that of samples dried using super-critical CO{sub 2} (SCCO{sub 2}) drying. Qualitative results indicate that {mu} is independent of normal pressure. Wear is shown to increase {mu} for both supercritically dried samples and PFTS coated samples, though the mechanisms appear to be different. Super critically dried surfaces appear to degrade continuously with increased wear cycles, while PFTS coated samples reach a steady state friction value after about 10{sup 4} cycles.

The authors have investigated LiNi{sub 0.8}Co{sub 0.2}O{sub 2} (Sumitomo) and LiNi{sub 5/8}Co{sub 1/4}Mn{sub 1/16}Al{sub 1/16}O{sub 2} (Sandia chemical preparation method) cathode powders via in-situ X-ray Diffraction and Cyclic Voltammetry using a coffee-bag type electrochemical cell. Both cathode materials did not show a monoclinic distortion during de-intercalation but sustained the hexagonal structure up to 4.3 V. The doping of Co into the LiNiO{sub 2} structure appears to stabilize this lattice as the hexagonal structure over the full range of charging (up to 4.3 V). The LiNi{sub 5/8}Co{sub 1/4}Mn{sub 1/16}Al{sub 1/16}O{sub 2} cathode material exhibited a 160 mAh/g capacity (to 4.1 V) on its 1{sup st} cycle, while displaying a much smaller volume change (as compared to LiNi{sub 0.8}Co{sub 0.2}O{sub 2}) during de-intercalation. This reduced overall volume change (2.5 vol%) may have important implications for cycle life of this material.

Evaporation is a classical physics problem which, because of its significant importance for many engineering applications, has drawn considerable attention by previous researchers. Classical theoretical models [Ta. I. Frenkel, Kinetic Theory of Liquids, Clarendon Press, Oxford, 1946] represent evaporation in a simplistic way as the escape of atoms with highest velocities from a potential well with the depth determined by the atomic binding energy. The processes taking place in the gas phase above the rapidly evaporating surface have also been studied in great detail [S.I.Anisimov and V. A. Khokhlov, Instabilities in Lasser-Matter Interaction, CRC Press, Boca Raton, 1995]. The description of evaporation utilizing these models is known to adequately characterize drilling with high beam intensity, e.g., >10{sup 7} W/cm{sup 2}. However, the interaction regimes when beam intensity is relatively low, such as during welding or cutting, lack both theoretical and experimental consideration of the evaporation. It was shown recently that if the evaporation is treated in accordance with Anisimov et.al.'s approach, then predicted evaporation recoil should be a substantial factor influencing melt flow and related heat transfer during laser beam welding and cutting. To verify the applicability of this model for low beam intensity interaction, the authors compared the results …

Selectively oxidized vertical cavity surface emitting lasers (VCSELS) have been studied by spectrally resolved near field scanning optical microscopy (NSOM). We have obtained spatially and spectrally resolved images of both subthreshold emission and lasing emission from a selectively oxidized VCSEL operating at a wavelength of 850 nm. Below threshold, highly local high gain regions, emitting local intensity maxima within the active area, were observed; these were found to serve as lasing centers just above threshold. Above threshold, the near field spatial modal distributions of low order transverse modes were identified by spectrally analyzing the emission; these were found to be complex and significantly different from those measured in the far field.

A key step in the construction of high consequence software is its specification in a formal framework. In order to minimize the difficulty and potential for error, a specification should be expressed in a domain language supporting operators and structures that are intrinsic to the class of algorithms one wishes to specify. In this paper the authors describe a language that is suitable for the algorithmic specification of software controllers for a class of reactive systems of which the Bay Area Rapid Transit (BART) system is an instance. The authors then specify an abstract controller for a subset of BART using this language.

The purpose of this paper is to demonstrate how transformation can be used to derive a high integrity implementation of a train controller from an algorithmic specification. The paper begins with a general discussion of high consequence systems (e.g., software systems) and describes how rewrite-based transformation systems can be used in the development of such systems. The authors then discuss how such transformations can be used to derive a high assurance controller for the Bay Area Rapid Transit (BART) system from an algorithmic specification.

Silicon (Si) has a strength to density ratio of 3.0({sigma}{sub y}/{delta}=(6.8GPa/2.3g/cc)), an order-of-magnitude higher than titanium, aluminum, or stainless steel. Silicon also demonstrates favorable thermal, optical, and electrical properties making it ideal for use as a structural foundation for autonomous, mesoscopic systems such as nanosatellites. Using Si substrates, a structure that can simultaneously act as a thermal management system, a radiation shield, an optical material, a package, and a semiconductor substrate can be realized.

Finite difference methods for solving the wave equation more accurately capture the physics of waves propagating through the earth than asymptotic solution methods. Unfortunately. finite difference simulations for 3D elastic wave propagation are expensive. We model waves in a 3D isotropic elastic earth. The wave equation solution consists of three velocity components and six stresses. The partial derivatives are discretized using 2nd-order in time and 4th-order in space staggered finite difference operators. Staggered schemes allow one to obtain additional accuracy (via centered finite differences) without requiring additional storage. The serial code is most unique in its ability to model a number of different types of seismic sources. The parallel implementation uses the MP1 library, thus allowing for portability between platforms. Spatial parallelism provides a highly efficient strategy for parallelizing finite difference simulations. In this implementation, one can decompose the global problem domain into one-, two-, and three-dimensional processor decompositions with 3D decompositions generally producing the best parallel speed up. Because i/o is handled largely outside of the time-step loop (the most expensive part of the simulation) we have opted for straight-forward broadcast and reduce operations to handle i/o. The majority of the communication in the code consists of passing subdomain …

The authors present a summary of recent measurements utilizing top quark candidate events extracted from approximately 110 pb{sup -1} of p{bar p} data collected by the CDF and D0 experiments at the Tevatron collider. They report on a new combined Tevatron top quark mass of 174.3 {+-} 5.1 GeV/c{sup 2} which takes into account five separate measurements made by the two experiments. They also demonstrate how the techniques developed for the mass analysis have been applied to further studies of the top quark and the t{bar t} system.

Text of the Hawaiian Supreme Court ruling to uphold same-sex marriages only. Includes concurring opinion of Hawaiian Supreme Court judge.

Prototype current leads incorporating High Temperature Superconductor (HTS) elements have been tested at Fermilab. Fermilab's Tevatron includes about 50 pair of 5 to 6 kA current leads, and Fermilab is investigating the feasibility of replacing some of these conventional leads with HTS leads. The prototype HTS current leads are cooled primarily by a countercurrent flow of liquid nitrogen from the 80 K intercept to the warm end of the leads, but also a small flow of helium gas cools the HTS section from the 4 K level. The HTS current leads carried the design current of 5 kA with good thermal and electrical stability. LN2 flow without current was 0.24 g/set per lead and with 5 kA was 0.53 g/set per lead, corresponding to heat inflows to the 80 K intercept of 46 Watts and 101 Watts, respectively. The heat input to the 4 K level was 0.6 W with no current and 0.7 W +/- 0.1 W per lead with 5 kA current, about 1/8 of the heat load via copper, vapor-cooled leads.

To date most validation techniques are highly biased towards calculations involving symbolic representations of problems. These calculations are either formal (in the case of consistency and completeness checks), or informal in the case of code inspections. The authors believe that an essential type of evidence of the correctness of the formalization process must be provided by (i.e., must originate from) human-based calculation. They further believe that human calculation can by significantly amplified by shifting from symbolic representations to graphical representations. This paper describes their preliminary efforts in realizing such a representational shift.

Water in porous silica glass is a suitable system for investigating the effect of confinement on translational diffusion. These systems are important because of their relevance in catalytic and separation processes. Two factors are to be considered in the case of confined water: (1) the effects of hydrophilic and hydrophobic surfaces on interfacial water and (2) how the dynamics of the hydrogen bond network changes due to the volume of confinement. Here quasi-elastic neutron scattering experiments at room temperature on water filled controlled pore glasses with radius of 15, 24 and 32 {angstrom}, are presented and analyzed using the random-jump diffusion model. Both the average residence time and the mean jump distance increase with decreasing pore radius.

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Over the past several years, extensive databases have been developed for the S-N behavior of various materials used in wind turbine blades, primarily fiberglass composites. These data are typically presented both in their raw form and curve fit to define their average properties. For design, confidence limits must be placed on these descriptions. In particular, most designs call for the 95/95 design values; namely, with a 95% level of confidence, the designer is assured that 95% of the material will meet or exceed the design value. For such material properties as the ultimate strength, the procedures for estimating its value at a particular confidence level is well defined if the measured values follow a normal or a log-normal distribution. Namely, based upon the number of sample points and their standard deviation, a commonly-found table may be used to determine the survival percentage at a particular confidence level with respect to its mean value. The same is true for fatigue data at a constant stress level (the number of cycles to failure N at stress level S{sub 1}). However, when the stress level is allowed to vary, as with a typical S-N fatigue curve, the procedures for determining confidence limits are …

In this paper we analyze the behavior of a gang-scheduling strategy that we are developing for the ASCI Blue-Pacific machines. Using actual job logs for one of the ASCI machines we generate a statistical model of the current workload with hyper Erlang distributions. We then vary the parameters of those distributions to generate various workloads, representative of different operating points of the machine. Through simulation we obtain performance parameters for three different scheduling strategies: (i) first-come first-serve, (ii) gang-scheduling, and (iii) backfilling. Our results show that backfilling, can be very effective for the common operating points in the 60-70% utilization range. However, for higher utilization rates, time-sharing techniques such as gang-scheduling offer much better performance.

Al{sub 2}Cu thin films ({approximately}382 nm) are fabricated by melting and resolidifying Al/Cu bilayers in the presence of a {approximately}3 nm Al{sub 2}O{sub 3} passivating layer. X-ray Photoelectron Spectroscopy (XPS) measures a 1.0 eV shift of the Cu2p{sub 3/2} peak and a 1.6 eV shift of the valence band relative to metallic Cu upon Al{sub 2}Cu formation. Scanning Electron Microscopy (SEM) and Electron Back-Scattered Diffraction (EBSD) show that the Al{sub 2}Cu film is composed of 30--70 {mu}m wide and 10--25 mm long cellular grains with (110) orientation. The atomic composition of the film as estimated by Energy Dispersive Spectroscopy (EDS) is 67{+-}2% Al and 33{+-}2% Cu. XPS scans of Al{sub 2}O{sub 3}/Al{sub 2}Cu taken before and after air exposure indicate that the upper Al{sub 2}Cu layers undergo further oxidation to Al{sub 2}O{sub 3} even in the presence of {approximately}5 nm Al{sub 2}O{sub 3}. The majority of Cu produced from oxidation is believed to migrate below the Al{sub 2}O{sub 3} layers, based upon the lack of evidence for metallic Cu in the XPS scans. In contrast to Al/Cu passivated with Al{sub 2}O{sub 3}, melting/resolidifying the Al/Cu bilayer without Al{sub 2}O{sub 3} results in phase-segregated dendritic film growth.

Wind-energy researchers at Sandia National Laboratories have developed a new, light-weight, modular data acquisition system capable of acquiring long-term, continuous, multi-channel time-series data from operating wind-turbines. New hardware features have been added to this system to make it more flexible and permit programming via telemetry. User-friendly Windows-based software has been developed for programming the hardware and acquiring, storing, analyzing, and archiving the data. This paper briefly reviews the major components of the system, summarizes the recent hardware enhancements and operating experiences, and discusses the features and capabilities of the software programs that have been developed.

This study examines adhesion between silane-coated micromachined surfaces that are exposed to humid conditions. Our quantitative values for interfacial adhesion energies are determined from an in-situ optical measurement of deformations in partly-adhered cantilever beams. We coated micromachined cantilevers with either ODTS (C{sub 18}H{sub 37}SiCl{sub 3}) or FDTS (C{sub 8}F{sub 17}C{sub 2}H{sub 4}SiCl{sub 3}) with the objective of creating hydrophobic surfaces whose adhesion would be independent of humidity. In both cases, the adhesion energy is significantly lower than for uncoated, hydrophilic surfaces. For relative humidities (RH) less than 95% (ODTS) and 80% (FDTS) the adhesion energy was extremely low and constant. In fact, ODTS-coated beams exposed to saturated humidity conditions and long (48 hour) exposures showed only a factor of two increase in adhesion energy. Surprisingly, FDTS coated beams, which initially have a higher contact angle (115{degree}) with water than do ODTS coated beams (112{degree}), proved to be much more sensitive to humidity. The FDTS coated surfaces showed a factor of one hundred increase in adhesion energy after a seven hour exposure to 90% RH. Atomic force microscopy revealed agglomerated coating material after exposed to high RH, suggesting a redistribution of the monolayer film. This agglomeration was more prominent for FDTS …

We show that for general input sets linear feedback shift registers (LFSRS) do not provide compression comparable to current, standard algorithms, at least not on the current, standard input files. Rather, LFSRS provide performance on a par with simple, run-length encoding schemes. We exercised three different ways of using LFSRS on the Canterbury, Canterbury Oarge set, the Calgory Corpora, and on three, large graphics files of our own.

Typical laboratory testing of Polycrystalline Diamond Compact (PDC) bits is performed on relatively rigid setups. Even in hard rock, PDC bits exhibit reasonable life using such testing schemes. Unfortunately, field experience indicates otherwise. In this paper, the authors show that introducing compliance in testing setups provides better simulation of actual field conditions. Using such a scheme, they show that chatter can be severe even in softer rock, such as sandstone, and very destructive to the cutters in hard rock, such as sierra white granite.

The connection is made between the normal-coordinate structural decomposition (NSD) and the vibronic molecular states and spectra of porphyrins. NSD is a procedure that provides a description of the distortion of a porphyrin from a D{sub 4h} symmetric reference structure in terms of equivalent displacements along the normal coordinates. Expressions for the optical absorption spectra with vibrational structure are developed with these NSD-determined deformations as parameters, and the expressions are applied to the UV-visible absorption spectra porphyrins.