88 Matching Results

Search Results

Advanced search parameters have been applied.

A study of cloud and drizzle properties in the Azores using Doppler Radar spectra

Description: Understanding the onset of coalescence in warm clouds is key in our effort to improve cloud representation in numerical models. Coalescence acts at small scales, and its study requires detailed high-resolution dynamical and microphysical measurements from a comprehensive suite of instruments over a wide range of environmental conditions (e.g., aerosol loading). The first AMF is currently in its second year of a two-year deployment at Graciosa Island in the Azores, offering the opportunity to collect a long data set from a stable land-based platform in a marine stratocumulus regime. In this study, recorded WACR Doppler spectra are used to characterize the properties of Doppler spectra from warm clouds with and without drizzle, and from drizzle only, in an effort to observe the transition (onset) to precipitation in clouds. A retrieval technique that decomposes observed Doppler spectra into their cloud and/or drizzle components is applied in order to quantify drizzle growth.
Date: March 15, 2010
Creator: Luke, E.; Remillard, J. & Kollias, P.
Partner: UNT Libraries Government Documents Department

Effect of underlayer on coalescence of silver islands grown byfiltered cathodic arc deposition

Description: For low-emissivity application on window glass, coalescenceof thin film silver islands is crucial for high transmittance in thevisible andhigh reflectance in the infrared. It is well known that theenergy of ions arriving at the substrate (kinetics) as wells as the typeof underlayer (thermodynamics) affect the nucleation and growth mode.Little is known about coalescence of silver islands synthesized byenergetic condensation, e.g., by filtered cathodic vacuum arc deposition.In this work, the effect of the underlayer on nucleation and growth ofsilver films deposited by filtered cathodic vacuum arc was investigatedby transmission electron microscopy (TEM) and atomic force microscopy(AFM). The results are compared with data obtained on magnetron sputteredfilms. It was found that uncoated and titanium-oxide-coated glass requiremore silver to achieve the same low value of sheet resistance than silveron zinc-oxide-coated glass. This can be associated with the energy ofinteraction between surface and silver atoms. Silver films made bycathodic arc deposition show an earlier onset of island coalescence andformation of short links. It was found that silver islands in energeticdeposition exhibit a reduced aspect ratio compared to evaporation andsputtering. A nominal 0.1 nm niobium underlayer increases the nucleationdensity and promotes coalescence of silver islands, however, a 0.2 nmlayer did not show these features, indicating the need for furtherstudies.
Date: March 1, 2003
Creator: Byon, Eungsun & Anders, Andre
Partner: UNT Libraries Government Documents Department

Localized Scale Coupling and New Educational Paradigms in Multiscale Mathematics and Science

Description: One of the most challenging multi-scale simulation problems in the area of multi-phase materials is to develop effective computational techniques for the prediction of coalescence and related phenomena involving rupture of a thin liquid film due to the onset of instability driven by van der Waals or other micro-scale attractive forces. Accurate modeling of this process is critical to prediction of the outcome of milling processes for immiscible polymer blends, one of the most important routes to new advanced polymeric materials. In typical situations, the blend evolves into an ?emulsion? of dispersed phase drops in a continuous matrix fluid. Coalescence is then a critical factor in determining the size distribution of the dispersed phase, but is extremely difficult to predict from first principles. The thin film separating two drops may only achieve rupture at dimensions of approximately 10 nm while the drop sizes are 0(10 ?m). It is essential to achieve very accurate solutions for the flow and for the interface shape at both the macroscale of the full drops, and within the thin film (where the destabilizing disjoining pressure due to van der Waals forces is proportional approximately to the inverse third power of the local film thickness, h-3). Furthermore, the fluids of interest are polymeric (through Newtonian) and the classical continuum description begins to fail as the film thins ? requiring incorporation of molecular effects, such as a hybrid code that incorporates a version of coarse grain molecular dynamics within the thin film coupled with a classical continuum description elsewhere in the flow domain. Finally, the presence of surface active additions, either surfactants (in the form of di-block copolymers) or surface-functionalized micro- or nano-scale particles, adds an additional level of complexity, requiring development of a distinct numerical method to predict the nonuniform concentration gradients of these additives that ...
Date: June 30, 2013
Creator: LEAL, L. GARY
Partner: UNT Libraries Government Documents Department

Pinch off and reconnection in liquid/liquid flows: joint experimental and numerical studies

Description: Liquid/liquid systems appear in applications involving transport, mixing, and separation of petroleum, chemical, and waste products. Breakup and coalescence transitions often determine flow regimes as well as reaction and separation rates. Because they occur over very small time and length scales compared with the larger scales that dominate the flow, they are difficult to quantify experimentally and simulate numerically. Thus far, no accurate models exist for engineers to predict these flows. Experiments and computations were performed so that accurate engineering models can be developed. Jet pinch off and drop coalescence were examined in mixtures of water/glycerin and silicone oil. Index matching, laser sheet illumination, and the PIV method were applied to obtain visualization and velocity field sequences through transitions. The computations used a novel, physically-based method that captures interface breakup and coalescence automatically without resorting to ad-hoc cut-and-connect methods. To achieve enhanced accuracy near transitions, new adaptive time and space meshes were developed. The computations were validated through direct comparison with the experiments. The detailed results should lead to improved understanding of transition behavior. This understanding is needed to develop engineering models of multiphase flows. Such predictive models will lead to extensive cost savings in device and process design.
Date: September 26, 2005
Creator: Longmire, Ellen K. & Lowengrub, John S.
Partner: UNT Libraries Government Documents Department

Towards a Scalable Fully-Implicit Fully-coupled Resistive MHD Formulation with Stabilized FE Methods

Description: This paper presents an initial study that is intended to explore the development of a scalable fully-implicit stabilized unstructured finite element (FE) capability for low-Mach-number resistive MHD. The discussion considers the development of the stabilized FE formulation and the underlying fully-coupled preconditioned Newton-Krylov nonlinear iterative solver. To enable robust, scalable and efficient solution of the large-scale sparse linear systems generated by the Newton linearization, fully-coupled algebraic multilevel preconditioners are employed. Verification results demonstrate the expected order-of-acuracy for the stabilized FE discretization of a 2D vector potential form for the steady and transient solution of the resistive MHD system. In addition, this study puts forth a set of challenging prototype problems that include the solution of an MHD Faraday conduction pump, a hydromagnetic Rayleigh-Bernard linear stability calculation, and a magnetic island coalescence problem. Initial results that explore the scaling of the solution methods are presented on up to 4096 processors for problems with up to 64M unknowns on a CrayXT3/4. Additionally, a large-scale proof-of-capability calculation for 1 billion unknowns for the MHD Faraday pump problem on 24,000 cores is presented.
Date: June 3, 2009
Creator: Shadid, J N; Pawlowski, R P; Banks, J W; Chacon, L; Lin, P T & Tuminaro, R S
Partner: UNT Libraries Government Documents Department

Novel SiGe Coherent Island Coarsening: Ostwald Ripening, Elastic Interactions, and Coalescence

Description: Real-time measurements of island coarsening during SiGe/Si (001) deposition reveal unusual kinetics. In particular, the mean island volume increases superlinearly with time, while the areal density of islands decreases at a faster-than-linear rate. Neither observation is consistent with standard considerations of Ostvvald ripening. We attribute our observed kinetics to the effect of elastic interactions in the densely growing island array. Island coalescence likely plays an important role as well.
Date: June 30, 1999
Creator: Chason, E.; Floro, J.A.; Freund, L.B.; Hwang, R.Q.; Lucadamo, G.A.; Sinclair, M. et al.
Partner: UNT Libraries Government Documents Department

Experimental and Analytical Research on Fracture Processes in ROck

Description: Experimental studies on fracture propagation and coalescence were conducted which together with previous tests by this group on gypsum and marble, provide information on fracturing. Specifically, different fracture geometries wsere tested, which together with the different material properties will provide the basis for analytical/numerical modeling. INitial steps on the models were made as were initial investigations on the effect of pressurized water on fracture coalescence.
Date: February 27, 2009
Creator: Einstein, Herbert H..; Miller, Jay & Silva, Bruno
Partner: UNT Libraries Government Documents Department

Hydrodynamic effects on coalescence.

Description: The goal of this project was to design, build and test novel diagnostics to probe the effect of hydrodynamic forces on coalescence dynamics. Our investigation focused on how a drop coalesces onto a flat surface which is analogous to two drops coalescing, but more amenable to precise experimental measurements. We designed and built a flow cell to create an axisymmetric compression flow which brings a drop onto a flat surface. A computer-controlled system manipulates the flow to steer the drop and maintain a symmetric flow. Particle image velocimetry was performed to confirm that the control system was delivering a well conditioned flow. To examine the dynamics of the coalescence, we implemented an interferometry capability to measure the drainage of the thin film between the drop and the surface during the coalescence process. A semi-automated analysis routine was developed which converts the dynamic interferogram series into drop shape evolution data.
Date: October 1, 2006
Creator: Dimiduk, Thomas G.; Bourdon, Christopher Jay; Grillet, Anne Mary; Baer, Thomas A.; de Boer, Maarten Pieter; Loewenberg, Michael (Yale University, New Haven, CT) et al.
Partner: UNT Libraries Government Documents Department

Simulating Solidification in Metals at High Pressure: The Drive to Petascale Computing

Description: We investigate solidification in metal systems ranging in size from 64,000 to 524,288,000 atoms on the IBM BlueGene/L computer at LLNL. Using the newly developed ddcMD code, we achieve performance rates as high as 103 TFlops, with a performance of 101.7 TFlop sustained over a 7 hour run on 131,072 cpus. We demonstrate superb strong and weak scaling. Our calculations are significant as they represent the first atomic-scale model of metal solidification to proceed, without finite size effects, from spontaneous nucleation and growth of solid out of the liquid, through the coalescence phase, and into the onset of coarsening. Thus, our simulations represent the first step towards an atomistic model of nucleation and growth that can directly link atomistic to mesoscopic length scales.
Date: July 26, 2006
Creator: Streitz, F; Glosli, J & Patel, M
Partner: UNT Libraries Government Documents Department

TEM studies of laterally overgrown GaN layers grown on non-polarsubstrates

Description: Transmission electron microscopy (TEM) was used to study pendeo-epitaxial GaN layers grown on polar and non-polar 4H SiC substrates. The structural quality of the overgrown layers was evaluated using a number of TEM methods. Growth of pendeo-epitaxial layers on polar substrates leads to better structural quality of the overgrown areas, however edge-on dislocations are found at the meeting fronts of two wings. Some misorientation between the 'seed' area and wing area was detected by Convergent Beam Electron Diffraction. Growth of pendeo-epitaxial layers on non-polar substrates is more difficult. Two wings on the opposite site of the seed area grow in two different polar directions with different growth rates. Most dislocations in a wing grown with Ga polarity are 10 times wider than wings grown with N-polarity making coalescence of these layers difficult. Most dislocations in a wing grown with Ga polarity bend in a direction parallel to the substrate, but some of them also propagate to the sample surface. Stacking faults formed on the c-plane and prismatic plane occasionally were found. Some misorientation between the wings and seed was detected using Large Angle Convergent Beam Diffraction.
Date: January 5, 2006
Creator: Liliental-Weber, Z.; Ni, X. & Morkoc, H.
Partner: UNT Libraries Government Documents Department

In Situ Transmission Electron Microscopy Heating Studies of Particle Coalescence and Microstructure Evolution in Nanosized Ceramics

Description: Final report on in-situ transmission microscopy heating studies of particle coalescence and microstructure evolution in nanosized ceramics. Report includes summary of work on particle shape changes and stress effects, and novel infiltration techniques in the processing of alumina based ceramics.
Date: June 2, 2006
Partner: UNT Libraries Government Documents Department

Structural Defects in Laterally Overgrown GaN Layers Grown onNon-polar Substrates

Description: Transmission electron microscopy was used to study defects in lateral epitaxial layers of GaN which were overgrown on a template of a-plane (11{und 2}0) GaN grown on (1{und 1}02) r-plane Al2O3. A high density of basal stacking faults is formed in these layers because the c-planes of wurtzite structure are arranged along the growth direction. Density of these faults is decreasing at least by two orders of magnitude lower in the wings compared to the seed areas. Prismatic stacking faults and threading dislocations are also observed, but their densities drastically decrease in the wings. The wings grow with opposite polarities and the Ga-wing width is at least 6 times larger than N-wing and coalescence is rather difficult. Some tilt and twist was detected using Large Angle Convergent Beam Electron Diffraction.
Date: February 14, 2007
Creator: Liliental-Weber, Z.; Ni, X. & Morkoc, H.
Partner: UNT Libraries Government Documents Department

Analysis of the growth of strike-slip faults using effective medium theory

Description: Increases in the dimensions of strike-slip faults including fault length, thickness of fault rock and the surrounding damage zone collectively provide quantitative definition of fault growth and are commonly measured in terms of the maximum fault slip. The field observations indicate that a common mechanism for fault growth in the brittle upper crust is fault lengthening by linkage and coalescence of neighboring fault segments or strands, and fault rock-zone widening into highly fractured inner damage zone via cataclastic deformation. The most important underlying mechanical reason in both cases is prior weakening of the rocks surrounding a fault's core and between neighboring fault segments by faulting-related fractures. In this paper, using field observations together with effective medium models, we analyze the reduction in the effective elastic properties of rock in terms of density of the fault-related brittle fractures and fracture intersection angles controlled primarily by the splay angles. Fracture densities or equivalent fracture spacing values corresponding to the vanishing Young's, shear, and quasi-pure shear moduli were obtained by extrapolation from the calculated range of these parameters. The fracture densities or the equivalent spacing values obtained using this method compare well with the field data measured along scan lines across the faults in the study area. These findings should be helpful for a better understanding of the fracture density/spacing distribution around faults and the transition from discrete fracturing to cataclastic deformation associated with fault growth and the related instabilities.
Date: October 15, 2009
Creator: Aydin, A. & Berryman, J.G.
Partner: UNT Libraries Government Documents Department

Beam loading compensation requirement for multibatch coalescing in Fermilab Main Injector

Description: Fermilab collider Run IIa requires 36 proton bunches with intensities 270E9ppb and 36 antiproton bunches with intensities 40-70E9ppb[1]. Currently the proton bunches are produced by coalescing 5-7 53MHz bunches into one 53MHz bunch and repeating this process a total of 36 times. It is necessary to coalesce each group of 5-7 bunches (called a ''batch'') on independent cycles mainly because of beam loading. The beam loading requirements that would allow us to coalesce 4 proton batches at a time are presented.
Date: July 24, 2001
Creator: al., J. Dey et
Partner: UNT Libraries Government Documents Department

Visualization of Solution Gas Drive in Viscous Oil, SUPRI TR-126

Description: Several experimental studies of solution gas drive are available in this report. Almost all of the studies have used light oil. Solution gas drive behavior, especially in heavy oil reservoirs, is poorly understood. Experiments were performed in which pore-scale solution gas drive phenomena were viewed in water/carbon dioxide and viscous oil/carbon dioxide systems. A new pressure vessel was designed and constructed to house silicon-wafer micromodels that previously operated at low (<3 atm) pressure. The new apparatus is used for the visual studies. Several interesting phenomena were viewed. The repeated nucleation of gas bubbles was observed at a gas-wet site occupied by dirt. Interestingly, the dissolution of a gas bubble into the liquid phase was previously recorded at the same nucleation site. Gas bubbles in both systems grew to span one ore more pore bodies before mobilization. Liquid viscosity affected the ease with which gas bubbles coalesced. More viscous solutions result in slower rates of coalescence. The transport of solid particles on gas-liquid interfaces was also observed.
Date: July 23, 2001
Creator: George, D.S. & Kovscek, A.R.
Partner: UNT Libraries Government Documents Department

Behavior of nanocrystalline Xe precipitates in Al under 1 MeV electron irradiation.

Description: Crystalline nanoprecipitates of Xe have been produced by ion implantation into high purity Al at 300 K. With an off-zone axis TEM imaging technique, the nanocrystals may be clearly structure imaged against a nearly featureless background. Under the 1 MeV electron irradiation employed for the HREM observation, Xe nanocrystals exhibit a number of readily observed physical phenomena including migration within the matrix, changes in shape, faulting, melting, crystallization and coalescence. The various phenomena observed as changes in the Xe nanocrystals reflect changes of matrix cavity-surface structure. The Xe nanocrystal thus allows investigation indirectly into changes in interface morphology at the atomic level, resulting in this instance from electron irradiation damage. Such changes have heretofore been inaccessible to observation.
Date: March 10, 1999
Creator: Allen, C. W.; Birtcher, R. C.; Donnelly, S. E.; Furuya, K.; Mitsuishi, K. & Song, M.
Partner: UNT Libraries Government Documents Department

Azimuthal anisotropy in Au+Au collisions at {radical}s{sub NN} = 200 GeV

Description: The results from the STAR Collaboration on directed flow (v{sub 1}), elliptic flow (v{sub 2}), and the fourth harmonic (v{sub 4}) in the anisotropic azimuthal distribution of particles from Au+Au collisions at {radical}s{sub NN} = 200 GeV are summarized and compared with results from other experiments and theoretical models. Results for identified particles are presented and fit with a Blast Wave model. For v{sub 2}, scaling with the number of constituent quarks and parton coalescence is discussed. For v{sub 4}, scaling with v{sub 22} and quark coalescence predictions for higher harmonic flow is discussed. The different anisotropic flow analysis methods are compared and nonflow effects are extracted from the data. For v{sub 2}, scaling with the number of constituent quarks and parton coalescence are discussed. For v{sub 2}{sup 2} and quark coalescence are discussed.
Date: September 29, 2004
Creator: Adams, J.; Aggarwal, M.M.; Ahammed, Z.; Amonett, J.; Anderson, B.D.; Akhipkin, D. et al.
Partner: UNT Libraries Government Documents Department

1 MeV electron irradiation of solid Xe nanoclusters in Al : an in-situ HRTEM study.

Description: Thin film samples of a simple embedded nanocluster system consisting of solid Xe precipitates in Al have been subjected to 1 MeV electron irradiation in a high-voltage electron microscope. High-resolution images have been recorded on videotape in order to monitor the changes to the system resulting from the passage of electrons through the film. Inspection of the video recordings (in some cases frame-by-frame) reveals that complex, rapid processes occur under the electron beam. These include, movement of small clusters, coalescence of neighboring clusters, shape changes, the apparent melting and resolidification of the Xe, and the creation and annealing of extended defects within the Xe lattice. A tentative interpretation of some of the observations is presented in terms of the electron-induced displacement processes at the surface of the clusters.
Date: December 5, 1997
Creator: Donnelly, S. E.; Furuya, K.; Song, M.; Birtcher, R. C. & Allen, C. W.
Partner: UNT Libraries Government Documents Department

3-D Cavern Enlargement Analyses

Description: Three-dimensional finite element analyses simulate the mechanical response of enlarging existing caverns at the Strategic Petroleum Reserve (SPR). The caverns are located in Gulf Coast salt domes and are enlarged by leaching during oil drawdowns as fresh water is injected to displace the crude oil from the caverns. The current criteria adopted by the SPR limits cavern usage to 5 drawdowns (leaches). As a base case, 5 leaches were modeled over a 25 year period to roughly double the volume of a 19 cavern field. Thirteen additional leaches where then simulated until caverns approached coalescence. The cavern field approximated the geometries and geologic properties found at the West Hackberry site. This enabled comparisons are data collected over nearly 20 years to analysis predictions. The analyses closely predicted the measured surface subsidence and cavern closure rates as inferred from historic well head pressures. This provided the necessary assurance that the model displacements, strains, and stresses are accurate. However, the cavern field has not yet experienced the large scale drawdowns being simulated. Should they occur in the future, code predictions should be validated with actual field behavior at that time. The simulations were performed using JAS3D, a three dimensional finite element analysis code for nonlinear quasi-static solids. The results examine the impacts of leaching and cavern workovers, where internal cavern pressures are reduced, on surface subsidence, well integrity, and cavern stability. The results suggest that the current limit of 5 oil drawdowns may be extended with some mitigative action required on the wells and later on to surface structure due to subsidence strains. The predicted stress state in the salt shows damage to start occurring after 15 drawdowns with significant failure occurring at the 16th drawdown, well beyond the current limit of 5 drawdowns.
Date: March 1, 2002
Creator: EHGARTNER, BRIAN L. & SOBOLIK, STEVEN R.
Partner: UNT Libraries Government Documents Department

Dislocation Multiplication in the Early Stage of Deformation in Mo Single Crystals

Description: Initial dislocation structure in annealed high-purity Mo single crystals and deformation substructure in a crystal subjected to 1% compression have been examined and studied using transmission electron microscopy (TEM) techniques in order to investigate dislocation multiplication mechanisms in the early stage of plastic deformation. The initial dislocation density is in a range of 10{sup 6} {approx} 10{sup 7} cm{sup -2}, and the dislocation structure is found to contain many grown-in superjogs along dislocation lines. The dislocation density increases to a range of 10{sup 8} {approx} 10{sup 9} cm{sup -2}, and the average jog height is also found to increase after compressing for a total strain of 1%. It is proposed that the preexisting jogged screw dislocations can act as (multiple) dislocation multiplication sources when deformed under quasi-static conditions. The jog height can increase by stress-induced jog coalescence, which takes place via the lateral migration (drift) of superjogs driven by unbalanced line-tension partials acting on link segments of unequal lengths. The coalescence of superjogs results in an increase of both link length and jog height. Applied shear stress begins to push each link segment to precede dislocation multiplication when link length and jog height are greater than critical lengths. This ''dynamic'' dislocation multiplication source is suggested to be crucial for the dislocation multiplication in the early stage of plastic deformation in Mo.
Date: March 2, 2000
Creator: Hsiung, L. & Lassila, D.H.
Partner: UNT Libraries Government Documents Department

Topical Report: Task 2.3 "Aphron Shell Hydrophobicity"

Description: Various methods were investigated to measure the oil-wetting character of transient bubbles under static and dynamic conditions, in order to determine the roles played by bubble and micellar agglomeration, coalescence and adhesion to mineral surfaces.
Date: October 28, 2004
Creator: Fosdick, Miranda & Growcock, Fred
Partner: UNT Libraries Government Documents Department