Physical Sciences and Mathematics Commons^™

Self-Consistent Calculations Of Strain-Induced Band Gap Changes In Semiconducting (N, 0) Carbon Nanotubes, Pavan Kumar Valavala, Douglas R. Banyai, Max Seel, Ranjit Pati

Department of Physics Publications

First-principles density-functional calculations of the electronic structure, energy band gaps (E_g), and strain-induced band gap changes in moderate-gap single-walled (n,0) carbon nanotubes (SWNTs) are presented. It is confirmed that (n,0) SWNTs fall into two classes depending upon n mod 3=1 or 2. E_g is always lower for “mod 1” than for “mod 2” SWNTs of similar diameter. For n<10, strong curvature effects dominate E_g; from n=10 to 17, the E_g oscillations, amplified due to σ−π mixing, decrease and can be explained very well with a tight-binding model which includes trigonal warping. Under strain, the two families of semiconducting …

Drizzle Rates Versus Cloud Depths For Marine Stratocumuli, A. B. Kostinski

Department of Physics Publications

Marine stratocumuli make a major contribution to Earth’s radiation budget. Drizzle in such clouds can greatly affect their albedo, lifetime and fractional coverage, so drizzle rate prediction is important. Here we examine a question: does a drizzle rate (R) depend on cloud depth (H) and/or drop number concentration n in a simple way? This question was raised empirically in several recent publications and an approximate H3/n dependence was observed. Here we suggest a simple explanation for H3 scaling from viewing the drizzle rate as a sedimenting volume fraction ( f ) of water drops (radius r) in air, i.e. R …

The Effect Of Clustering On The Uncertainty Of Differential Reflectivity Measurements, A. R. Jameson, A. B. Kostinski

Department of Physics Publications

One of the most important avenues of recent meteorological radar research is the application of polarization techniques to improve radar rainfall estimation. A keystone in many of these methods is the so-called differential reflectivity Z_DR, the ratio of the reflectivity factor Z_H at horizontal polarization backscattered from a horizontally polarized transmission to that corresponding to a vertically polarized transmission Z_V. For such quantitative applications, it is important to understand the statistical accuracy of observations of Z_DR. The underlying assumption of all past estimations of meteorological radar uncertainties is that the signals obey Rayleigh …

Enrichment Of Surface-Active Compounds In Coalescing Cloud Drops, Ilya Taraniuk, Alexander Kostinski, Yinon Rudich

Department of Physics Publications

Surfactants often found in tropospheric aerosols, can affect the onset and development of clouds. Due to high dilution during droplet growth, the effects of surfactants on cloud microphysical processes have been mostly neglected. However, while cloud growth by coalescence conserves the combined volume of all cloud droplets, it reduces the combined surface area. This could lead to enrichment of water‐insoluble surfactants (WIS) and to reduced surface tension of droplets forming in warm processes. Measurements of individual raindrops reveal the presence of water insoluble surfactants. Our field and laboratory studies as well as simple theoretical arguments suggest that by causing varying …

Measurements Of The Vapor Pressure Of Supercooled Water Using Infrared Spectroscopy, Will Cantrell, Eli Ochshorn, Alexander Kostinski, Keith Bozin

Department of Physics Publications

Measurements are presented of the vapor pressure of supercooled water utilizing infrared spectroscopy, which enables unambiguous verification that the authors’ data correspond to the vapor pressure of liquid water, not a mixture of liquid water and ice. Values of the vapor pressure are in agreement with previous work. Below −13°C, the water film that is monitored to determine coexistence of liquid water (at one temperature) and ice (at another, higher, temperature) de-wets from the hydrophilic silicon prism employed in the authors’ apparatus. The de-wetting transition indicates a quantitative change in the structure of the supercooled liquid.

Entropic Aspects Of Supercooled Droplet Freezing, Alexander Kostinski, Will Cantrell

Department of Physics Publications

The freezing of supercooled water droplets in the atmosphere, with an emphasis on the entropic aspects of the problem, is examined. Supercooled water is a metastable state and, therefore, the associated phase transition must be irreversible. Temperature-dependent heat capacities of supercooled water and ice are used to calculate the entropy difference. That difference is then used to establish a lower bound on the amount of latent heat that can be liberated by the freezing droplets. The calculation is compared with tabulated values of the latent heat of fusion with surprising results. Based on a novel physical picture of the freezing …

Origin Of Negative Differential Resistance In A Strongly Coupled Single Molecule-Metal Junction Device, Ranjit Pati, Mike Mcclain, Anirban Bandyopadhyay

Department of Physics Publications

A new mechanism is proposed to explain the origin of negative differential resistance (NDR) in a strongly coupled single molecule-metal junction. A first-principles quantum transport calculation in a Fe-terpyridine linker molecule sandwiched between a pair of gold electrodes is presented. Upon increasing the applied bias, it is found that a new phase in the broken symmetry wave function of the molecule emerges from the mixing of occupied and unoccupied molecular orbitals. As a consequence, a nonlinear change in the coupling between the molecule and the lead is evolved resulting in NDR. This model can be used to explain NDR in …

Ice Nucleation And Overseeding Of Ice In Volcanic Clouds, Adam J. Durant, R. A. Shaw, William I. Rose, Y. Mi, G. G. J. Ernst

Department of Geological and Mining Engineering and Sciences Publications

Water is the dominant component of volcanic gas emissions, and water phase transformations, including the formation of ice, can be significant in the dynamics of volcanic clouds. The effectiveness of volcanic ash particles as ice-forming nuclei (IN) is poorly understood and the sparse data that exist for volcanic ash IN have been interpreted in the context of meteorological, rather than volcanic clouds. In this study, single-particle freezing experiments were carried out to investigate the effect of ash particle composition and surface area on water drop freezing temperature. Measured freezing temperatures show only weak correlations with ash IN composition and surface …

Magnetic Properties Of One-Dimensional Ni/Cu And Ni/Al Multilayered Nanowires: Role Of Nonmagnetic Spacers, Partha Pratim Pal, Ranjit Pati

Department of Physics Publications

We have used density functional theory within spin-polarized local density approximation to investigate the equilibrium structure, electronic, and magnetic properties of one-dimensional Ni/Cu and Ni/Al multilayered nanowires. In particular, we look into the subtle changes in the magnetic properties of the nanowires with the change in the width of the nonmagnetic spacer. Our calculations yield the magnitude of cohesive energy in both the systems to decrease with the increase in the concentration of the nonmagnetic spacer, suggesting that Ni rich nanowires are more stable. Analysis of the magnetic moment per Ni atom (μ_av) in the Ni/Cu hybrid multilayered …

Giant Intrinsic Carrier Mobilities In Graphene And Its Bilayer, S. V. Morozov, K. S. Novoselov, M. I. Katsnelson, F. Schedin, D. C. Elias, John A. Jaszczak, A. K. Geim

Department of Physics Publications

We have studied temperature dependences of electron transport in graphene and its bilayer and found extremely low electron-phonon scattering rates that set the fundamental limit on possible charge carrier mobilities at room temperature. Our measurements show that mobilities higher than 200,000 cm²/V s are achievable, if extrinsic disorder is eliminated. A sharp (threshold-like) increase in resistivity observed above ∼200K is unexpected but can qualitatively be understood within a model of a rippled graphene sheet in which scattering occurs on intraripple flexural phonons.

Aerosols' Influence On The Interplay Between Condensation, Evaporation And Rain In Warm Cumulus Cloud, O. Altaratz, I. Koren, T. Reisin, A. B. Kostinski, Graham Feingold, Z. Levin, Y. Yin

Department of Physics Publications

A numerical cloud model is used to study the influence of aerosol on the microphysics and dynamics of moderate-sized, coastal, convective clouds that develop under the same meteorological conditions. The results show that polluted convective clouds start their precipitation later and precipitate less than clean clouds but produce larger rain drops. The evaporation process is more significant at the margins of the polluted clouds (compared to the clean cloud) due to a higher drop surface area to volume ratio and it is mostly from small drops. It was found that the formation of larger raindrops in the polluted cloud is …

Numerical Analysis Of Elliptic Inverse Problems With Interior Data, Mark Gockenbach

Department of Mathematical Sciences Publications

A number of algorithms have been proposed and analyzed for estimating a coefficient in an elliptic boundary value problem when interior data is available. Most of the analysis has been done for the simple scalar BVP

-Δ a Δ u = f in Ω,

a (∂ u / ∂ n) g on ∂ Ω

However, some methods and the associated analysis have been extended to the problem of estimating the Lamé moduli in the system of linear, isotropic elasticity. Under certain idealized conditions, convergence of estimates to the exact Lame moduli has been proved for two techniques, the output …

Studies Of Spatial Clustering Of Inertial Particles In Turbulence, Ewe Wei Saw

Dissertations, Master's Theses and Master's Reports - Open

We present studies of the spatial clustering of inertial particles embedded in turbulent flow. A major part of the thesis is experimental, involving the technique of Phase Doppler Interferometry (PDI). The thesis also includes significant amount of simulation studies and some theoretical considerations. We describe the details of PDI and explain why it is suitable for study of particle clustering in turbulent flow with a strong mean velocity. We introduce the concept of the radial distribution function (RDF) as our chosen way of quantifying inertial particle clustering and present some original works on foundational and practical considerations related to it. …

Electronic Properties Of Zig-Zag Carbon Nanotubes : A First-Principles Study, Pavan Kumar Valavala

Dissertations, Master's Theses and Master's Reports - Open

Carbon nanotube (CNT) is a one dimensional (1-D) nanostructured material, which has been the focal point of research over the past decade for intriguing applications ranging from nanoelectronics to chemical and biological sensors. Using a first-principles gradient corrected density functional approach, we present a comprehensive study of the geometry and energy band gap in zig-zag semi-conducting (n,0) carbon nanotubes (CNT) to resolve some of the conflicting findings. Our calculations confirm that the single wall (n,0) CNTs fall into two distinct classes depending upon n mod 3 equal to 1 (smaller band gaps) or 2 (larger gaps). …

Erupted Magma Volume Estimates At Santiaguito And Pacaya Volcanoes, Guatemala Using Digital Elevation Models , Kelly S. Durst

Dissertations, Master's Theses and Master's Reports - Open

High resolution digital elevation models (DEMs) of Santiaguito and Pacaya volcanoes, Guatemala, were used to estimate volume changes and eruption rates between 1954 and 2001. The DEMs were generated from contour maps and aerial photography, which were analyzed in ArcGIS 9.0®. Because both volcanoes were growing substantially over the five decade period, they provide a good data set for exploring effective methodology for estimating volume changes. The analysis shows that the Santiaguito dome complex grew by 0.78 ± 0.07 km³ (0.52 ± 0.05 m³ s^-1) over the 1954-2001 period with nearly all the growth occurring on …

Manual Pumping Test Method For Characterizing The Productivity Of Drilled Wells Equipped With Rope Pumps, Essa L. Gross

Dissertations, Master's Theses and Master's Reports - Open

Since the introduction of the rope-pump in Nicaragua in the 1990s, the dependence on wells in rural areas has grown steadily. However, little or no attention is paid to rope-pump well performance after installation. Due to financial restraints, groundwater resource monitoring using conventional testing methods is too costly and out of reach of rural municipalities. Nonetheless, there is widespread agreement that without a way to quantify the changes in well performance over time, prioritizing regulatory actions is impossible. A manual pumping test method is presented, which at a fraction of the cost of a conventional pumping test, measures the specific …

Digital Processing And Data Compilation Approach For Using Remotely Sensed Imagery To Identify Geological Lineaments In Hard-Rock Terrains : An Application For Groundwater Explorations In Nicaragua , Jill N. Bruning

Dissertations, Master's Theses and Master's Reports - Open

Sustainable yields from water wells in hard-rock aquifers are achieved when the well bore intersects fracture networks. Fracture networks are often not readily discernable at the surface. Lineament analysis using remotely sensed satellite imagery has been employed to identify surface expressions of fracturing, and a variety of image-analysis techniques have been successfully applied in “ideal” settings. An ideal setting for lineament detection is where the influences of human development, vegetation, and climatic situations are minimal and hydrogeological conditions and geologic structure are known. There is not yet a well-accepted protocol for mapping lineaments nor have different approaches been compared in …