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First principles calculations of the effect of Pt on NiAl surfaceenergy and the site preference of Pt

Description: Pt-modified NiAl is widely used as a coating material in industry. In this study, the surface energies of NiAl with and without Pt are investigated using first-principles calculations. The presence of Pt in NiAl takes the surface electronic states to higher energies, resulting in an increased surface energy, which explains some of the beneficial effects of Pt on the oxidation resistance of NiAl. The electronic structure of NiAl-Pt alloys is also analyzed in terms of the site preference of Pt in NiAl. Results show that Pt bonds strongly to Al, giving its site preference on the Ni site.
Date: March 8, 2007
Creator: Yu, Rong & Hou, Peggy Y.
Partner: UNT Libraries Government Documents Department

Free energy calculations of Cu-Sn interfaces

Description: Excess free energies of solid Cu-Solid Sn and Solid Cu-liquid Sn have been calculated employing an adiabatic switching formalism in a Molecular Dynamics framework. The atomic interactions are described by modified embedded atom method potentials which includes the angular dependence of the electron density to describe bond bending forces necessary to model covalent materials.
Date: December 31, 1995
Creator: Ravelo, R. & Baskes, M.
Partner: UNT Libraries Government Documents Department

Selected Translated Abstracts of Russian-Language Climate-Change Publications, I. Surface Energy Budget

Description: This report presents abstracts (translated into English) of important Russian-language literature concerning the surface energy budget as it relates to climate change. In addition to the bibliographic citations and abstracts translated into English, this report presents the original citations and abstracts in Russian. Author and title indexes are included, to assist the reader in locating abstracts of particular interest.
Date: January 1, 1992
Creator: Ravina, C. B.
Partner: UNT Libraries Government Documents Department

Surface-Energy-Anisotropy-Induced Orientation Effects on RayleighInstabilities in Sapphire

Description: Arrays of controlled-geometry, semi-infinite pore channels of systematically varied crystallographic orientation were introduced into undoped m-plane (10{bar 1}0) sapphire substrates using microfabrication techniques and ion-beam etching and subsequently internalized by solid-state diffusion bonding. A series of anneals at 1700 C caused the breakup of these channels into discrete pores via Rayleigh instabilities. In all cases, channels broke up with a characteristic wavelength larger than that expected for a material with isotropic surface energy, reflecting stabilization effects due to surface-energy anisotropy. The breakup wavelength and the time required for complete breakup varied significantly with channel orientation. For most orientations, the instability wavelength for channels of radius R was in the range of 13.2R-25R, and complete breakup occurred within 2-10 h. To first order, the anneal times for complete breakup scale with the square of the breakup wavelength. Channels oriented along a <11{bar 2}0> direction had a wavelength of {approx} 139R, and required 468 h for complete breakup. Cross-sectional analysis of channels oriented along a <11{bar 2}0> direction showed the channel to be completely bounded by stable c(0001), r{l_brace}{bar 1}012{r_brace}, and s{l_brace}10{bar 1}1{r_brace} facets.
Date: January 1, 2006
Creator: Santala, Melissa & Glaeser, Andreas M.
Partner: UNT Libraries Government Documents Department

Soil Water and Temperature System (SWATS) Handbook

Description: The soil water and temperature system (SWATS) provides vertical profiles of soil temperature, soil-water potential, and soil moisture as a function of depth below the ground surface at hourly intervals. The temperature profiles are measured directly by in situ sensors at the Central Facility and many of the extended facilities of the SGP climate research site. The soil-water potential and soil moisture profiles are derived from measurements of soil temperature rise in response to small inputs of heat. Atmospheric scientists use the data in climate models to determine boundary conditions and to estimate the surface energy flux. The data are also useful to hydrologists, soil scientists, and agricultural scientists for determining the state of the soil.
Date: January 1, 2005
Creator: Bond, D
Partner: UNT Libraries Government Documents Department

Atmospheric Radiation Measurement Climate Research Facility Annual Report 2006

Description: This annual report describes the purpose and structure of the ARM Climate Research Facility and ARM Science programs and presents key accomplishments in 2006. Noteworthy scientific and infrastructure accomplishments in 2006 include: • Collaborating with the Australian Bureau of Meteorology to lead the Tropical Warm Pool-International Cloud Experiment, a major international field campaign held in Darwin, Australia • Successfully deploying the ARM Mobile Facility in Niger, Africa • Developing the new ARM Aerial Vehicles Program (AVP) to provide airborne measurements • Publishing a new finding on the impacts of aerosols on surface energy budget in polar latitudes • Mitigating a long-standing double-Intertropical Convergence Zone problem in climate models using ARM data and a new cumulus parameterization scheme.
Date: November 30, 2005
Creator: Roeder, LR
Partner: UNT Libraries Government Documents Department

Roughness length and displacement height derived from building databases

Description: In air quality and meteorological models, the bulk drag and turbulence enhancement due to cities is often parameterized through the roughness length (z{sub 0}) and displacement height (d). These log-law parameters have traditionally been derived from meteorological measurements and building morphological characteristics (e.g., see Grimmond and Oke, 1999). We are in the midst of an effort to characterize the morphological properties of some of the major cities in the western U.S. At this time we have completed the analyses for Los Angeles, Phoenix, and Salt Lake City. We are currently working with datasets from Portland and Houston and anticipate analyzing more than five other cities in the near future. Morphological analysis of 3-D building databases produces a suite of urban canopy parameters that can be incorporated into mesoscale meteorological, surface energy budget, and pollutant dispersion models. Additional computations can be performed to derive roughness length and displacement height using several common morphological formulae described in the literature. This paper summarizes the derivation of roughness length and displacement height for a 12-km{sup 2} section of downtown Los Angeles, 16-km{sup 2} section of downtown Phoenix, and 6-km{sup 2} section of downtown Salt Lake City. We correlate the computed roughness length and displacement height to underlying land use type.
Date: January 1, 2002
Creator: Burian, S. J. (Steven J.); Brown, M. J. (Michael J.) & Velugubantla, S. P. (Srinivas, P.)
Partner: UNT Libraries Government Documents Department

An atomistic study of dynamic brittle fracture in silicon

Description: Dynamic fracture has been modeled using a modified embedded atom method (MEAM) potential for silicon. For Mode I dynamic fracture along (1 1 1) crystallographic planes, the molecular dynamics model predicts crack speeds and fracture energies in agreement with previous experimental results [l]. In this orientation, hcture occurs almost exclusively along (1 1 1) planes for energy release rates up to 30 J/m2. For Mode I fracture oriented initially on (1 10) planes, fracture occurs by cleavage on (1 10) planes for a static energy release rate (J,) less than 8 J/m2. For greater values of J,, the fracture surfaces switch to alternating (111) planes, which is in agreement with previous experimental results [2]. Crack speed predictions for the (1 10) orientation are somewhat In the atomistic simulations, the dynamically propagating cracks generate dislocations, which are primarily produced on the (1 1 1) and (1 10) planes. Differences in the type and quantity of dislocations produced have been observed for different orientations. Molecular dynamics has the ability to calculate the energy consumed by dislocations and other lattice defects produced during fracture and the total surface energy of the main crack, side branches and secondary cracks. The sum of the surface energy and the energy consumed by lattice defects determines the dynamic fracture less than the high speeds observed experimentally. toughness, J(v). The dynamic fkacture toughness has been found to vary linearly with J,. For the (111) orientation with cracks propagating in the [211] direction, J(v) asymptotically approached a value of 1/3 of J,. The remainder of the strain energy that is released during fracture is converted into kinetic energy at the crack tip during the fracture process, which occurs atom by atom.
Date: January 1, 2002
Creator: Swadener, J. G. (John G.); Baskes, M. I. (Michael I.) & Nastasi, Michael Anthony,
Partner: UNT Libraries Government Documents Department

Surface Energy Balance System (SEBS) Handbook

Description: A Surface Energy Balance System (SEBS) has been installed collocated with each deployed ECOR system at the Southern Great Plains (SGP), North Slope of Alaska (NSA), Tropical Western Pacific (TWP), ARM Mobile Facility 1 (AMF1), and ARM Mobile Facility 2 (AMF2). The surface energy balance system consists of upwelling and downwelling solar and infrared radiometers within one net radiometer, a wetness sensor, and soil measurements. The SEBS measurements allow the comparison of ECOR sensible and latent heat fluxes with the energy balance determined from the SEBS and provide information on wetting of the sensors for data quality purposes.
Date: February 14, 2011
Creator: Cook, DR
Partner: UNT Libraries Government Documents Department

Surface Energy Anisotropy Effects on Pore-Channel Stability:Rayleigh Instabilities in m-Plane Sapphire

Description: Internal, high-aspect-ratio pore channels with their long axes parallel to the m(10{bar 1}0) plane of sapphire were generated through sequential application of photolithography, ion-beam etching and solid-state diffusion bonding. The axial orientation of channels within the m plane was systematically varied to sample a range of bounding-surface crystallographies. The morphologic evolution of these pore channels during anneals at 1700 C was recorded by postanneal optical microscopy. The development and growth of periodic axial variations in the pore channel radius was observed, and ultimately led to the formation of discrete pores. The wavelength and average pore spacing, assumed to reflect the kinetically dominant perturbation wavelength, varied with the in-plane pore channel orientation, as did the time for complete channel breakup. Results are compared to those previously obtained when pore channels were etched into c(0001)-plane sapphire and annealed under similar conditions. The results indicate a strong effect of surface stability on the evolution behavior.
Date: September 7, 2005
Creator: Santala, Melissa K. & Glaeser, Andreas M.
Partner: UNT Libraries Government Documents Department

Modified epoxy coatings on mild steel: A study of tribology and surface energy.

Description: A commercial epoxy was modified by adding fluorinated poly (aryl ether ketone) and in turn metal micro powders (Ni, Al, Zn, and Ag) and coated on mild steel. Two curing agents were used; triethylenetetramine (curing temperatures: 30 oC and 70 oC) and hexamethylenediamine (curing temperature: 80 oC). Variation in tribological properties (dynamic friction and wear) and surface energies with varying metal powders and curing agents was evaluated. When cured at 30 oC, friction and wear decreased significantly due to phase separation reaction being favored but increased when cured at 70 oC and 80 oC due to cross linking reaction being favored. There was a significant decrease in surface energies with the addition of modifiers.
Date: August 2009
Creator: Dutta, Madhuri
Partner: UNT Libraries

Application of Electron Backscattered Diffraction (EBSD) and Atomic Force Microscopy (AFM) to Determine Texture, Microtexture, and Grain Boundary Energies in Ceramics

Description: Crystallographic orientations in alumina (Al<sub>2</sub>0<sub>3</sub>) and magnesium aluminate spinel (MgAl<sub>2</sub>0<sub>4</sub>) were obtained using electron backscattered diffraction (EBSD) patterns. The texture and mesotexture (grain boundary misorientations) were random and no special boundaries were observed. The relative grain boundary energies were determined by thermal groove geometries using atomic force microscopy (AFM) to identify relationships between the grain boundary energies and misorientations.
Date: May 19, 1999
Creator: Glass, S.J.; Rohrer, G.S.; Saylor, D.M. & Vedula, V.R.
Partner: UNT Libraries Government Documents Department

Triangular step instability and 2D/3D transition during the growth of strained Ge films on Si(100)

Description: We show that an activation energy barrier exists to the formation of wavy step edges due to stress-driven 2D instability. The barrier height and the barrier width depend sensitively on the surface stress anisotropy and step free energy. The large misfit strain of Ge films significantly reduces the barrier by lowering the S{sub B} step energy, inducing S{sub A} steps to undergo a triangular instability even during low temperature growth of Ge on Si(100). The step instability results in a novel arrangement of stress domains, and the interaction between the domains causes a spatial variation of surface strain with a surprisingly large influence on the energy barrier for island nucleation. Calculations indicate a dramatic enhancement in the nucleation of 3D islands at the apex regions of triangular steps, in good agreement with our experimental measurements.
Date: April 1, 1995
Creator: Chen, K.M.; Jesson, D.E.; Pennycook, S.J.; Mostoller, M.; Kaplan, T.; Thundat, T. et al.
Partner: UNT Libraries Government Documents Department

The Argonne boundary layer experiments facility : using minisodars to complement a wind profiler network.

Description: The Argonne Boundary Layer Experiments (ABLE) facility, located in south central Kansas, east of Wichita, is devoted primarily to investigations of and within the planetary boundary layer (PBL), including the dynamics of the mixed layer during both day and night; effects of varying land use and land form; the interactive role of precipitation, runoff, and soil moisture; storm development; and energy budgets on scales of 10 to 100 km. Located entirely within the Walnut River watershed, ABLE provides intense measurements within the northeast quadrant (Fig. 1) of the Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) of the Atmospheric Radiation Measurement (ARM) Program (Stokes and Schwarz, 1994). By combining the continuous measurements of ABLE with ancillary continuous measurements of, for example, the ARM and the Global Energy Water cycle Experiment (GEWEX) (Kinster and Shukla, 1990) programs, ABLE provides a platform within which shorter, more intensive studies, such as those conducted by the Cooperative Atmosphere-Surface Exchange Studies (CASES) Program, can realize the full benefit of a wide variety of atmospheric measurements on many scales; this allows the study of hypothesized features of PBL development and dynamics, including frontal dynamics, nocturnal boundary development and breakdown, urban heat island effects, precipitation enhancement, and modification of the surface energy budget partitioning.
Date: June 5, 1998
Creator: Coulter, R. L.
Partner: UNT Libraries Government Documents Department

The coexistence curve of finite charged nuclear matter

Description: The multifragmentation data of the ISiS Collaboration and the EOS Collaboration are examined. Fisher's droplet formalism, modified to account for Coulomb energy, is used to determine the critical exponents {tau} and {sigma}, the surface energy coefficient c{sub 0}, the pressure-temperature-density coexistence curve of finite nuclear matter and the location of the critical point.
Date: January 1, 2001
Creator: Elliott, J.B.; Moretto, L.G.; Phair, L.; Wozniak, G.J.; Beaulieu, L.; Breuer, H. et al.
Partner: UNT Libraries Government Documents Department

Theoretical approaches and experimental evidence for liquid-vapor phase transitions in nuclei

Description: The leptodermous approximation is applied to nuclear systems for T &gt; 0. The introduction of surface corrections leads to anomalous caloric curves and to negative heat capacities in the liquid-gas coexistence region. Clusterization in the vapor is described by associating surface energy to clusters according to Fisher's formula. The three-dimensional Ising model, a leptodermous system par excellence, does obey rigorously Fisher's scaling up to the critical point. Multifragmentation data from several experiments including the ISiS and EOS Collaborations, as well as compound nucleus fragment emission at much lower energy follow the same scaling, thus providing the strongest evidence yet of liquid-vapor coexistence.
Date: January 1, 2001
Creator: Moretto, L.G.; Elliott, J.B.; Phair, L.; Wozniak, G.J.; Mader, C.M. & Chappars, A.
Partner: UNT Libraries Government Documents Department

A Sensitivity Study of the Urban Effect on a Regional-Scale Model: An Idealized Case

Description: Urban infrastructure impacts the surface and atmospheric properties, such as wind, temperature, turbulence and radiation budgets. The well-recognized urban heat island phenomenon, characterized by the temperature contrast between the city and the surrounding rural area, is one such impact. Many field experiments have been conducted to study the urban heat island effect, which is typically most intense under clear sky and weak ambient wind conditions at night. In some cases, a cool island may even exist during the day. To consider these urban effects in a numerical model with horizontal grid resolution on the order of kilometers, some sort of parameterization is required to account for the sub-grid building impacts on these effects. To this end, Brown and Williams (1998) have developed an urban parameterization by extending Yamada's (1982) forest canopy scheme to include drag, turbulent production, anthropogenic and rooftop heating effects, and radiation balance in a mesoscale model. In this study, we further modify this urban parameterization by adding the rooftop surface energy equation to eliminate a simplifying assumption that the rooftop is at the same temperature as the air. The objective of this work is to assess the impact of individual process of this modified urban canopy parameterization for the urban heat island phenomenon.
Date: May 30, 2000
Creator: Chin, H. N. S.; Leach, M. J. & Brown, M. J.
Partner: UNT Libraries Government Documents Department

Model studies of Rayleigh instabilities via microdesigned interfaces

Description: The energetic and kinetic properties of surfaces play a critical role in defining the microstructural changes that occur during sintering and high-temperature use of ceramics. Characterization of surface diffusion in ceramics is particularly difficult, and significant variations in reported values of surface diffusivities arise even in well-studied systems. Effects of impurities, surface energy anisotropy, and the onset of surface attachment limited kinetics (SALK) are believed to contribute to this variability. An overview of the use of Rayleigh instabilities as a means of characterizing surface diffusivities is presented. The development of models of morphological evolution that account for effects of surface energy anisotropy is reviewed, and the potential interplay between impurities and surface energy anisotropy is addressed. The status of experimental studies of Rayleigh instabilities in sapphire utilizing lithographically introduced pore channels of controlled geometry and crystallography is summarized. Results of model studies indicate that impurities can significantly influence both the spatial and temporal characteristics of Rayleigh instabilities; this is attributed at least in part to impurity effects on the surface energy anisotropy. Related model experiments indicate that the onset of SALK may also contribute significantly to apparent variations in surface diffusion coefficients.
Date: October 17, 2000
Creator: Glaeser, Andreas M.
Partner: UNT Libraries Government Documents Department

On the Sensitivity of Atmospheric Model Implied Ocean Heat Transport to the Dominant Terms of the Surface Energy Balance

Description: The oceanic meridional heat transport (T{sub o}) implied by an atmospheric General Circulation Model (GCM) can help evaluate a model's readiness for coupling with an ocean GCM. In this study we examine the T{sub o} from benchmark experiments of the Atmospheric Model Intercomparison Project, and evaluate the sensitivity of T{sub o} to the dominant terms of the surface energy balance. The implied global ocean TO in the Southern Hemisphere of many models is equatorward, contrary to most observationally-based estimates. By constructing a hybrid (model corrected by observations) T{sub o}, an earlier study demonstrated that the implied heat transport is critically sensitive to the simulated shortwave cloud radiative effects, which have been argued to be principally responsible for the Southern Hemisphere problem. Systematic evaluation of one model in a later study suggested that the implied T{sub o} could be equally as sensitive to a model's ocean surface latent heat flux. In this study we revisit the problem with more recent simulations, making use of estimates of ocean surface fluxes to construct two additional hybrid calculations. The results of the present study demonstrate that indeed the implied T{sub o} of an atmospheric model is very sensitive to problems in not only the surface net shortwave, but the latent heat flux as well. Many models underestimate the shortwave radiation reaching the surface in the low latitudes, and overestimate the latent heat flux in the same region. The additional hybrid transport calculations introduced here could become useful model diagnostic tests as estimates of implied ocean surface fluxes are improved.
Date: November 3, 2004
Creator: Gleckler, P J
Partner: UNT Libraries Government Documents Department

Fundamentals of reservoir surface energy as related to surface properties, wettability, capillary action, and oil recovery from fractured reservoirs by spontaneous imbibition

Description: The objective of this project is to increase oil recovery from fractured reservoirs through improved fundamental understanding of the process of spontaneous imbibition by which oil is displaced from the rock matrix into the fractures. Spontaneous imbibition is fundamentally dependent on the reservoir surface free energy but this has never been investigated for rocks. In this project, the surface free energy of rocks will be determined by using liquids that can be solidified within the rock pore space at selected saturations. Thin sections of the rock then provide a two-dimensional view of the rock minerals and the occupant phases. Saturations and oil/rock, water/rock, and oil/water surface areas will be determined by advanced petrographic analysis and the surface free energy which drives spontaneous imbibition will be determined as a function of increase in wetting phase saturation. The inherent loss in surface free energy resulting from capillary instabilities at the microscopic (pore level) scale will be distinguished from the decrease in surface free energy that drives spontaneous imbibition. A mathematical network/numerical model will be developed and tested against experimental results of recovery versus time over broad variation of key factors such as rock properties, fluid phase viscosities, sample size, shape and boundary conditions. Two fundamentally important, but not previously considered, parameters of spontaneous imbibition, the capillary pressure acting to oppose production of oil at the outflow face and the pressure in the nonwetting phase at the no-flow boundary versus time, will also be measured and modeled. Simulation and network models will also be tested against special case solutions provided by analytic models. In the second stage of the project, application of the fundamental concepts developed in the first stage of the project will be demonstrated. The fundamental ideas, measurements, and analytic/numerical modeling will be applied to mixed-wet rocks. Imbibition measurements will include ...
Date: February 1, 2006
Creator: Morrow, Norman R.; Fischer, Herbert; Li, Yu; Mason, Geoffrey; Ruth, Douglas; Seth, Siddhartha et al.
Partner: UNT Libraries Government Documents Department

Plasma Synthesis of Nanoparticles for Nanocomposite Energy Applications

Description: The nanocomposite energy applications for plasma reactor produced nanoparticles are reviewed. Nanoparticles are commonly defined as particles less than 100 nm in diameter. Due to this small size, nanoparticles have a high surface-to-volume ratio. This increases the surface energy compared to the bulk material. The high surface-to-volume ratio and size effects (quantum effects) give nanoparticles distinctive chemical, electronic, optical, magnetic and mechanical properties from those of the bulk material. Nanoparticles synthesis can be grouped into 3 broad approaches. The first one is wet phase synthesis (sol-gel processing), the second is mechanical attrition, and the third is gas-phase synthesis (aerosol). The properties of the final product may differ significantly depending on the fabrication route. Currently, there are no economical large-scale production processes for nanoparticles. This hinders the widespread applications of nanomaterials in products. The Idaho National Laboratory (INL) is engaging in research and development of advanced modular hybrid plasma reactors for low cost production of nanoparticles that is predicted to accelerate application research and enable the formation of technology innovation alliances that will result in the commercial production of nanocomposites for alternative energy production devices such as fuel cells, photovoltaics and electrochemical double layer capacitors.
Date: September 1, 2008
Creator: Kong, Peter C. & Kawczak, Alex W.
Partner: UNT Libraries Government Documents Department

Impact of Geoengineering Schemes on the Global Hydrological Cycle

Description: The rapidly rising CO{sub 2} level in the atmosphere has led to proposals of climate stabilization via 'Geoengineering' schemes that would mitigate climate change by intentionally reducing the solar radiation incident on earth's surface. In this paper, we address the impact of these climate stabilization schemes on the global hydrological cycle, using equilibrium simulations from an atmospheric general circulation model coupled to a slab ocean model. We show that insolation reductions sufficient to offset global-scale temperature increases lead to a decrease in the intensity of the global hydrologic cycle. This occurs because solar forcing is more effective in driving changes in global mean evaporation than is CO{sub 2} forcing of a similar magnitude. In the model used here, the hydrologic sensitivity, defined as the percentage change in global mean precipitation per degree warming, is 2.4% for solar forcing, but only 1.5% for CO{sub 2} forcing. Although other models and the climate system itself may differ quantitatively from this result, the conclusion can be understood based on simple considerations of the surface energy budget and thus is likely to be robust. Compared to changing temperature by altering greenhouse gas concentrations, changing temperature by varying insolation results in larger changes in net radiative fluxes at the surface; these are compensated by larger changes in latent and sensible heat fluxes. Hence the hydrological cycle is more sensitive to temperature adjustment via changes in insolation than changes in greenhouse gases. This implies that an alteration in solar forcing might offset temperature changes or hydrological changes from greenhouse warming, but could not cancel both at once.
Date: December 7, 2007
Creator: Bala, G; Duffy, P & Taylor, K
Partner: UNT Libraries Government Documents Department