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Articles 1 - 12 of 12
Full-Text Articles in Physics
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
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 (Eg), 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. Eg is always lower for “mod 1” than for “mod 2” SWNTs of similar diameter. For n<10, strong curvature effects dominate Eg; from n=10 to 17, the Eg 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
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
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 ZDR, the ratio of the reflectivity factor ZH at horizontal polarization backscattered from a horizontally polarized transmission to that corresponding to a vertically polarized transmission ZV. For such quantitative applications, it is important to understand the statistical accuracy of observations of ZDR. 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
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
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
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
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 …
Magnetic Properties Of One-Dimensional Ni/Cu And Ni/Al Multilayered Nanowires: Role Of Nonmagnetic Spacers, Partha Pratim Pal, Ranjit Pati
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 (μav) 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
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
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 …
Studies Of Spatial Clustering Of Inertial Particles In Turbulence, Ewe Wei Saw
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
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). …