Publications

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Although battery technology is relatively mature, power sources continue to impose serious limitations for small, portable, mobile, or remote applications. A potentially attractive alternative to batteries is chemical fuel-to-electric conversion. Chemical fuels have volumetric energy densities 4 to 10 times those of batteries. However, realizing this advantage requires efficient chemical fuel-to-electric conversion. Direct electrochemical conversion would be the ideal, but, for most fuels, is generally not within the state-of-the-science. Next best, chemical-to-thermal-to-electric conversion can be attractive if efficiencies can be kept high. This small investigative project was an exploration into the feasibility of a novel hybrid (i.e., thermal-electrochemical) micropower converter of high theoretical performance whose demonstration was thought to be within near-term reach. The system is comprised of a hydrogen concentration electrochemical cell with physically identical hydrogen electrodes as anode and cathode, with each electrode connected to physically identical hydride beds each containing the same low-enthalpy-of-formation metal hydride. In operation, electrical power is generated by a hydrogen concentration differential across the electrochemical cell. This differential is established via coordinated heating and passive cooling of the corresponding hydride source and sink. Heating is provided by the exothermic combustion (i.e., either flame combustion or catalytic combustion) of a chemical fuel. Upon hydride source depletion, the role of source and sink are reversed, heating and cooling reversed, electrodes commutatively reversed, cell operation reversed, while power delivery continues unchanged. This 'regenerative flip' of source and sink hydride beds can be cycled continuously until all available heating fuel is consumed. Electricity is efficiently generated electrochemically, but hydrogen is not consumed, rather the hydrogen is regeneratively cycled as an electrochemical 'working fluid'.

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Interstratification-periodic or nonperiodic stacking of two different silicate layers along a c*-axis-is common in phyllosilicates. Published evidence indicates that some interstratified minerals precipitate directly from aqueous solutions. In this paper, we have demonstrated, based on chaos theory, that both periodic and nonperiodic interstratification can autonomously arise from simple kinetics of mineral growth from a solution. Growth of a mixed-layer mineral is assumed to proceed layer by layer, and each layer starts with the formation of a base (Si, Al)-O tetrahedral sheet, whose structural configuration in a-b dimensions determines the type of new layer that forms. The sequence of layer stacking can be described by a one-dimensional map (i.e., a difference equation), which accounts for two competing factors: (1) the affinity of each end-member structural component for attaching to the surface of the preceding layer, and (2) the strain energy created by stacking next to each other two silicate layers with different structural configurations. Chaotic (or nonperiodic) interstratification emerges when the contacting solution becomes slightly supersaturated with respect to both structural components. The transition from one interstratification pattern to another reflects a change in chemical environment during mineral crystallization. Our model can successfully predict the occurrence of mixed-layer phyllosilicates and the associated layer stacking sequences observed in both hydrothermal alteration and sediment diagenesis. The model suggests that the diagenetic transition of smectite → nonperiodic illite/smectite → ordered illite/smectite → illite may reflect relative changes in the saturation degree of pore water with respect to two end-member phases as a result of increasing burial temperatures. © 2006 Elsevier Inc. All rights reserved.

Measurements within 10% accuracy of the dynamic dipole polarizabilities α (λ) for five nonrefractory metal atoms (Mg, Ag, Al, Cu, and Au) at laser wavelengths of λ=532 and 1064 nm are presented using electrical explosion of thin wires in vacuum and a novel laser probing integrated-phase technique. The technique is based on single-wavelength interferometry and does not require axial symmetry of the tested object. Theoretical prediction of α (λ) for wavelengths λ=355, 532, and 1064 nm, as well as the static dipole polarizabilities αst, are also presented. An agreement within 20% was obtained between calculated data, recommended static polarizabilities αst, and the measured dynamic polarizabilities α (532 nm) and α (1064 nm). © 2006 The American Physical Society.

Controlling the properties of self-assembled nanostructures requires controlling their shape. Size-dependent shape transitions, frequently observed at nanolength scales, are commonly attributed to edge energy effects. To rigorously test such theories against experiment, quantitative atomistic calculations of edge energies are essential, yet none exist. I describe a fundamental ambiguity in the atomistic definition of edge energies, propose a definition based on equimolar dividing surfaces, and present an atomistic calculation of edge energies for Pd clusters. © 2006 The American Physical Society.

The influence of thermal stratification on autoignition at constant volume and high pressure is studied by direct numerical simulation (DNS) with detailed hydrogen/air chemistry. Parametric studies on the effect of the initial amplitude of the temperature fluctuations, the initial length scales of the temperature and velocity fluctuations, and the turbulence intensity are performed. The combustion mode is characterized using the diagnostic measures developed in Part I of this study. Specifically, the ignition front speed and the scalar mixing timescales are used to identify the roles of molecular diffusion and heat conduction in each case. Predictions from a multizone model initialized from the DNS fields are presented and differences are explained using the diagnostic tools developed. © 2005 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

The influence of thermal stratification on autoignition at constant volume and high pressure is studied by direct numerical simulation (DNS) with detailed hydrogen/air chemistry with a view to providing better understanding and modeling of combustion processes in homogeneous charge compression-ignition engines. Numerical diagnostics are developed to analyze the mode of combustion and the dependence of overall ignition progress on initial mixture conditions. The roles of dissipation of heat and mass are divided conceptually into transport within ignition fronts and passive scalar dissipation, which modifies the statistics of the preignition temperature field. Transport within ignition fronts is analyzed by monitoring the propagation speed of ignition fronts using the displacement speed of a scalar that tracks the location of maximum heat release rate. The prevalence of deflagrative versus spontaneous ignition front propagation is found to depend on the local temperature gradient, and may be identified by the ratio of the instantaneous front speed to the laminar deflagration speed. The significance of passive scalar mixing is examined using a mixing timescale based on enthalpy fluctuations. Finally, the predictions of the multizone modeling strategy are compared with the DNS, and the results are explained using the diagnostics developed. © 2005 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Proliferation of degrees-of-freedom has plagued discontinuous Galerkin methodology from its inception over 30 years ago. This paper develops a new computational formulation that combines the advantages of discontinuous Galerkin methods with the data structure of their continuous Galerkin counterparts. The new method uses local, element-wise problems to project a continuous finite element space into a given discontinuous space, and then applies a discontinuous Galerkin formulation. The projection leads to parameterization of the discontinuous degrees-of-freedom by their continuous counterparts and has a variational multiscale interpretation. This significantly reduces the computational burden and, at the same time, little or no degradation of the solution occurs. In fact, the new method produces improved solutions compared with the traditional discontinuous Galerkin method in some situations. © 2005 Elsevier B.V. All rights reserved.

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In this paper, we report spatially resolved temperature profiles along the legs of working V-shaped electrothermal (ET) actuators using a surface Raman scattering technique. The Raman probe provides nonperturbing optical data with a spatial resolution of 1.2 μm, which is required to observe the 3-μm-wide actuator beams. A detailed uncertainty analysis reveals that our Raman thermometry of polycrystalline silicon is performed with fidelity of ±10 to 11 K when the peak location of the Stokes-shifted optical phonon signature is used as an indicator of temperature. This level of uncertainty is sufficient for temperature mapping of many working thermal MEMS devices which exhibit characteristic temperature differences of several hundred Kelvins. To our knowledge, these are the first quantitative and spatially resolved temperature data available for thermal actuator structures. This new temperature data set can be used for validation of actuator thermal design models and these new results are compared with finite-difference simulations of actuator thermal performance. © 2006 IEEE.

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What will be the effect of Iraqi domestic instability on Iraqi oil production Negotiations for Iranian nuclear technology on Iranian oil supplies Saudi commitment to expanded oil production President Putin's policies on Russian oil and natural gas supplies President Chavez's policies on Venezuelan oil supplies Instability in Nigeria Higher oil prices on world economic growth Effect of economic growth on oil demand in China, India, U.S., etc. Higher oil prices on non-OPEC oil supplies