Low-temperature evolution of the proton magnetic resonance line shape in β-phase palladium hydride

Measurements of the proton magnetic resonance absorption line shape in -phase palladium hydride indicate that there is no short-range ordering associated with the order-disorder phase transition that occurs in the neighborhood of 50 K. However, measurements of the line shape in the range 10–30 K show a change from a Gaussian to a non-Gaussian profile. This effect is not related to the order-disorder phase transition. A possible explanation in terms of thermally assisted tunneling is proposed.     

A method to study the dispersion and orientation of nanoclay tactoids in PET matrix-focused ion beam milling combined with electron microscopy

This paper describes a method to evaluate the dispersion and orientation of nanotactoids in polymer matrix The method involves focused ion beam (FIB) milling of the sample followed by observation of the milled surface under SEM. Compared to conventional TEM techniques, a wider area of the sample can be observed by this method which will give a better representation of the dispersion and orientation of the nanotactoids in the matrix. Both the surface and the cross-section of the sample can be analyzed by this method. However, the FIB milling and imaging conditions need to be optimized to minimize the sample damage.     

Autonomous Navigation of Heavy Construction Equipment

Abstract: A John Deere model 690 excavator, mounted on a Standard Manufacturing Company wheeled undercarriage, has been automated for the purpose of autonomously uncovering and removing unexploded buried ordnance. This paper describes the development effort, with emphasis placed on the autonomous navigation of the excavator system. Accurate navigation is required in order to properly position the excavator system so that it can uncover and remove the target buried munition. Autonomous navigation is accomplished by use of an A_* search algorithm for path planning, an inertial navigation system (INS) integrated with a global positioning system (GPS) for vehicle positioning, and proportional control for path-following. Data gathered from eight navigation test runs show that the excavator, on average, can navigate to within 0.67 m of a goal position and to within 0.021 rad of a goal orientation.     

Atomic layer deposition of hafnium oxide dielectrics on silicon and germanium substrates

Hafnium oxide films have been deposited at 250 °C on silicon and germanium substrates by atomic layer deposition (ALD), using tetrakis-ethylmethylamino hafnium (TEMAH) and water vapour as precursors in a modified Oxford Instruments PECVD system. Self-limiting monolayer growth has been verified, characterised by a growth rate of 0.082 nm/cycle. Layer uniformity is approximately within ±1% of the mean value. MOS capacitors have been fabricated by evaporating aluminium electrodes. CV analysis has been used to determine the bulk and interface properties of the HfO₂, and their dependence on pre-clean schedule, deposition conditions and post-deposition annealing. The dielectric constant of the HfO₂ is typically 18. On silicon, best results are obtained when the HfO₂ is deposited on a chemically oxidised hydrophilic surface. On germanium, best results are obtained when the substrate is nitrided before HfO₂ deposition, using an in-situ nitrogen plasma treatment.     

Immobilized ionic liquids as high-selectivity/high-temperature/high-stability gas chromatography stationary phases

Ionic liquids (ILs) are a class of nonmolecular solvents in which the cation/anion combination can be easily tuned to provide desired chemical and physical properties. When used as stationary phases in gas-liquid chromatography, ionic liquids exhibit dual nature retention selectivity. That is, they are able to separate polar molecules such as a polar stationary phase and nonpolar molecules such as a nonpolar stationary phase. However, issues such as optimization of the wetting ability of the ionic liquid on fused-silica capillaries, the maximum operating temperatures of the stationary phases, and nonuniform film thickness on the wall of the capillary at high temperatures have limited their use in gas chromatography. As described in this paper, these limitations are overcome by cross-linking a new class of ionic liquid monomers by free radical reactions to provide a more durable and robust stationary phase. By lightly cross-linking the ionic liquid stationary phase using a small amount of free radical initiator, high-efficiency capillary columns were produced that are able to endure high temperatures with little column bleed. Two types of cross-linked IL stationary phases are developed. A partially cross-linked stationary phase allows for high-efficiency separations up to temperatures of approximately 280 degrees C. However, by creating a more highly cross-linked stationary phase of geminal dicationic ILs, exclusively, an increase in efficiency is observed at high temperatures allowing for its use over 350 degrees C. In addition, through the use of solvation thermodynamics and interaction parameters, it was shown that the cross-linking/immobilization of the ionic liquid does not affect the selectivity of the stationary phase thereby preserving its dual nature retention behavior.     

Equilibrium partitioning model applied to RDX-halide adduct formation in electrospray ionization mass spectrometry

An equilibrium partitioning model is applied for the first time to the sequential formation of 1:1 and then 2:1 adducts between the high explosive cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX) and halide anions fluoride, chloride, bromide, and iodide in electrospray ionization interface (ESI) mass spectrometry. The equilibrium partitioning model is developed and model calculations are presented to demonstrate the generic behavior of the system, which is in qualitative agreement with the observed changes in 1:1 (RDX-halide) and 2:1 (RDX-halide) responses in ESI-MS. The model is successfully applied to the experimental data with the use of octanol-water partitioning coefficients to predict interior-to-surface partitioning behavior of the complexes in droplets formed in the ESI. The data and model suggest that the significantly more hydrophobic 2:1 complexes are readily observed in ESI-MS, even though their formation constants may be several orders of magnitude less than that of the 1:1 complex. Structures for RDX-halide 1:1 and 2:1 complexes are proposed based on ion-dipole attractions and destabilizing dipole-dipole interactions.     

Forensic analysis of architectural finishes using fourier transform infrared and Raman spectroscopy, part I: the resin bases

The ability of Raman spectroscopy and Fourier transform infrared (FT-IR) microscopy to discriminate between resins used for the manufacture of architectural finishes was examined in a study of 39 samples taken from a commercial resin library. Both Raman and FT-IR were able to discriminate between different types of resin and both split the samples into several groups (six for FT-IR, six for Raman), each of which gave similar, but not identical, spectra. In addition, three resins gave unique Raman spectra (four in FT-IR). However, approximately half the library comprised samples that were sufficiently similar that they fell into a single large group, whether classified using FT-IR or Raman, although the remaining samples fell into much smaller groups. Further sub-division of the FT-IR groups was not possible because the experimental uncertainty was of similar magnitude to the within-group variation. In contrast, Raman spectroscopy was able to further discriminate between resins that fell within the same groups because the differences in the relative band intensities of the resins, although small, were larger than the experimental uncertainty.     

Using the First-Level Caches as Filters to Reduce the Pollution Caused by Speculative Memory References

High-performance processors employ aggressive branch prediction and prefetching techniques to increase performance. Speculative memory references caused by these techniques sometimes bring data into the caches that are not needed by correct execution. This paper proposes the use of the first-level caches as filters that predict the usefulness of speculative memory references. With the proposed technique, speculative memory references bring data only into the first-level caches rather than all levels in the cache hierarchy. The processor monitors the use of the cache blocks in the first-level caches and decides which blocks to keep in the cache hierarchy based on the usefulness of cache blocks. It is shown that a simple implementation of this technique usually outperforms inclusive and exclusive baseline cache hierarchies commonly used by today’s processors and results in IPC performance improvements of up to 10% on the SPEC CPU2000 integer benchmarks.