Browsing by Subject "surface"

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An Audible Demonstration Of The Speed Of Sound In Bubbly Liquids
(2008-10) Wilson, Preston S.; Roy, Ronald A.; Wilson, Preston S.
The speed of sound in a bubbly liquid is strongly dependent upon the volume fraction of the gas phase, the bubble size distribution, and the frequency of the acoustic excitation. At sufficiently low frequencies, the speed of sound depends primarily on the gas volume fraction. This effect can be audibly demonstrated using a one-dimensional acoustic waveguide, in which the flow rate of air bubbles injected into a water-filled tube is varied by the user. The normal modes of the waveguide are excited by the sound of the bubbles being injected into the tube. As the flow rate is varied, the speed of sound varies as well, and hence, the resonance frequencies shift. This can be clearly heard through the use of an amplified hydrophone and the user can create aesthetically pleasing and even musical sounds. In addition, the apparatus can be used to verify a simple mathematical model known as Wood's equation that relates the speed of sound of a bubbly liquid to its void fraction. (c) 2008 American Association of Physics Teachers.
Debris-Covered Glacier Energy Balance Model for Imja-Lhotse Shar Glacier in the Everest Region of Nepal
(2015-12) Rounce, D. R.; Quincey, D. J.; McKinney, D. C.; Rounce, D. R.; McKinney, D. C.
Debris thickness plays an important role in regulating ablation rates on debris-covered glaciers as well as controlling the likely size and location of supraglacial lakes. Despite its importance, lack of knowledge about debris properties and associated energy fluxes prevents the robust inclusion of the effects of a debris layer into most glacier surface energy balance models. This study combines fieldwork with a debris-covered glacier energy balance model to estimate debris temperatures and ablation rates on Imja-Lhotse Shar Glacier located in the Everest region of Nepal. The debris properties that significantly influence the energy balance model are the thermal conductivity, albedo, and surface roughness. Fieldwork was conducted to measure thermal conductivity and a method was developed using Structure from Motion to estimate surface roughness. Debris temperatures measured during the 2014 melt season were used to calibrate and validate a debris-covered glacier energy balance model by optimizing the albedo, thermal conductivity, and surface roughness at 10 debris-covered sites. Furthermore, three methods for estimating the latent heat flux were investigated. Model calibration and validation found the three methods had similar performance; however, comparison of modeled and measured ablation rates revealed that assuming the latent heat flux is zero may overestimate ablation. Results also suggest that where debris moisture is unknown, measurements of the relative humidity or precipitation may be used to estimate wet debris periods, i.e., when the latent heat flux is non-zero. The effect of temporal resolution on the model was also assessed and results showed that both 6 h data and daily average data slightly underestimate debris temperatures and ablation rates; thus these should only be used to estimate rough ablation rates when no other data are available.
Effect of pore structure on capillary condensation in a porous medium
(2009-02) Deinert, M. R.; Parlange, J. Y.; Deinert, M. R.; Deinert, M. R.
The Kelvin equation relates the equilibrium vapor pressure of a fluid to the curvature of the fluid-vapor interface and predicts that vapor condensation will occur in pores or irregularities that are sufficiently small. Past analyses of capillary condensation in porous systems with fractal structure have related the phenomenon to the fractal dimension of the pore volume distribution. Recent work, however, suggests that porous systems can exhibit distinct fractal dimensions that are characteristic of both their pore volume and the surfaces of the pores themselves. We show that both fractal dimensions have an effect on the thermodynamics that governs capillary condensation and that previous analyses can be obtained as limiting cases of a more general formulation.
Evaluation of Micro-Models for Near Surface Dispersion in Reservoirs
(University of Texas at Austin, 1969-07) Gebhard, T.G.; Masch, F.D.
Mechanistic Study Of Plasma Damage Of Low k Dielectric Surfaces
(2007-10) Bao, J. J.; Shi, H. L.; Liu, J. J.; Huang, H.; Ho, P. S.; Goodner, M. D.; Moinpour, M.; Kloster, G. M.; Bao, J. J.; Shi, H. L.
Plasma damage to low k dielectric materials was investigated from a mechanistic point of view. Low k dielectric films were treated by plasma Ar, O-2, N-2/H-2, N-2 and H-2 in a standard RIE chamber and the damage was characterized by Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS), X-Ray Reflectivity (XRR), Fourier Transform Infrared Spectroscopy (FTIR) and Contact Angle measurements. Both carbon depletion and surface densification were observed on the top surface of damaged low k materials while the bulk remained largely unaffected. Plasma damage was found to be a complicated phenomenon involving both chemical and physical effects, depending on chemical reactivity and the energy and mass of the plasma species. A downstream hybrid plasma source with separate ions and atomic radicals was employed to study their respective roles in the plasma damage process. Ions were found to play a more important role in the plasma damage process. The dielectric constant of low k materials can increase up to 20% due to plasma damage and we attributed this to the removal of the methyl group making the low k surface hydrophilic. Annealing was generally effective in mitigating moisture uptake to restore the k value but the recovery was less complete for higher energy plasmas. Quantum chemistry calculation confirmed that physisorbed water in low k materials induces the largest increase of dipole moments in comparison with changes of surface bonding configurations, and is primarily responsible for the dielectric constant increase.
Modulating the Surface Environment of Lead Sulfide Quantum Dots to Manipulate Energy Transfer across the Inorganic–organic Interface
(2020-05) Lee, Inki; Roberts, Sean
Elucidating the mechanism behind energy transport is essential to improving the efficiency of energy related functions. In our project, we attempt to uncover the nature of energy transfer dynamics between lead sulfide quantum dots (PbS QDs) and surface bound perylene diimide (PDI) molecules. The two species are energetically aligned in such a way that energy can transfer between them even though they absorb in different regions of the light spectrum. Using transient absorption spectroscopy, we selectively excited the PbS QDs and observed how the system relaxes on a femtosecond timescale. We found that PbS QD transfers an excited electron to PDI within 30 picoseconds to create a radical PDI anion. Furthermore, we can make this process faster or slower by adding cinnamate molecules to the QD surface, which serve to move the energy levels of PbS QDs up and down. This means that we can change the energetic alignment between PbS QD and PDI by synthetically modifying the surface’s electronic environment. This realization is significant because it adds an additional degree of control to preparing energy devices. We believe that this will help in guiding future designs to engineer light harvesting materials.
No Evidence of Morning or Large-Scale Drizzle On Titan
(2008-05) Kim, Sang J.; Trafton, L. M.; Geballe, Thomas R.; Trafton, L. M.
Widespread methane precipitation on Titan has been predicted by several authors since methane saturation in the upper troposphere was measured by the Huygens probe over its landing site. Recently, observational evidence of widespread morning drizzle has been suggested based on detection of a dark morning site in surface-subtracted 2 mu m spectroimages obtained from ground-based observations. We have obtained similar new spectroimages of Titan observed at Gemini-North Observatory at several rotational phase angles and have analyzed them using the same image processing technique. By comparing images at different phases, we show that the presumed dark drizzling regions in the surface-subtracted images are mainly negative renditions of bright surface regions. No evidence of spectroscopically verifiable drizzling is apparent in our cloudless Titan images. At present, constraining models of Titan's hydrological cycle to produce a diurnal response would be premature.
Presentation: When the Earth Quakes
(Environmental Science Institute, 2000-08-25) Marrett, Randall; Environmental Science Institute
Process Planning and Automation for Additive-Subtractive Solid Freeform Fabrication
(1998) Pinilla, J. Miguel; Kao, Ju-Hsien; Prinz, Fritz B.
New additive-subtractive processes promise to enhance SFF capability from prototyping to true low-volume production. However, to maintain the same degree of process automation as in currently available processes like SLA or SLS, more sophisticated planning and execution systems need to be developed. The system we present in this paper consists of two parts. The first is an off-line planner that decomposes a CAD model into 3D manufacturable volumes called "single-step geometries", arranges these geometries into a graph representation called" adjacency graphs", and automatically generates deposition and machining codes for each single-step geometry. The second is an on-line system that handles asynchronous multi-part building, job-shop scheduling, process control and run-time execution. Communication between these two stages is through a "process description language". The goal of this paper is to present a framework for planning and execution for additive/subtractive processes, outline the issues involved in developing such an environment, and report on the progress made in this direction at the Rapid Prototyping Laboratory of Stanford University.
The Role Of The Magnetorotational Instability In The Sun
(2014-05) Kagan, Daniel; Wheeler, J. Craig; Kagan, Daniel; Wheeler, J. Craig
We calculate growth rates for nonaxisymmetric instabilities including the magnetorotational instability (MRI) throughout the Sun. We first derive a dispersion relation for nonaxisymmetric instability including the effects of shear, convective buoyancy, and three diffusivities (thermal conductivity, resistivity, and viscosity). We then use a solar model evolved with the stellar evolution code MESA and angular velocity profiles determined by Global Oscillations Network Group helioseismology to determine the unstable modes present at each location in the Sun and the associated growth rates. The overall instability has unstable modes throughout the convection zone and also slightly below it at middle and high latitudes. It contains three classes of modes: large-scale hydrodynamic convective modes, large-scale hydrodynamic shear modes, and small-scale magnetohydrodynamic shear modes, which may be properly called MRI modes. While large-scale convective modes are the most rapidly growing modes in most of the convective zone, MRI modes are important in both stably stratified and convectively unstable locations near the tachocline at colatitudes theta < 53 degrees. Nonaxisymmetric MRI modes grow faster than the corresponding axisymmetric modes; for some poloidal magnetic fields, the nonaxisymmetric MRI growth rates are similar to the angular rotation frequency Omega, while axisymmetric modes are stabilized. We briefly discuss the saturation of the field produced by MRI modes, finding that the implied field at the base of the convective zone in the Sun is comparable to that derived based on dynamos active in the tachocline and that the saturation of field resulting from the MRI may be of importance even in the upper convection zone.