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Articles 1 - 18 of 18
Full-Text Articles in Physical Sciences and Mathematics
Rainbows In The Grass. Ii. Arbitrary Diagonal Incidence, Charles L. Adler, James A. Lock, Richard W. Fleet
Rainbows In The Grass. Ii. Arbitrary Diagonal Incidence, Charles L. Adler, James A. Lock, Richard W. Fleet
Physics Faculty Publications
We consider external reflection rainbow caustic,,; due to the reflection of light from a pendant droplet where the light rays are at an arbitrary angle with respect to the horizontal. We compare this theory to observation of glare spots from, pendant drops on grass; we also consider the potential application of this theory to the determination of liquid surface tension. (C) 2008 Optical Society of America
Scattering Of An Electromagnetic Plane Wave By A Luneburg Lens. Iii. Finely Stratified Sphere Model, James A. Lock
Scattering Of An Electromagnetic Plane Wave By A Luneburg Lens. Iii. Finely Stratified Sphere Model, James A. Lock
Physics Faculty Publications
The parallel iteration procedure for computing scattering by a multilayer sphere is described. The procedure uses a successive doubling strategy applied to four sets of multiple-scattering amplitudes, which is reminiscent of the fast Fourier transform (FFT) algorithm. The procedure is then used to calculate scattering of a plane wave by a modified Luneburg lens. The evolution of the transmission rainbow for the Luneburg lens parameter f > 1 into an orbiting ray for f = 1 and into a series of morphology-dependent resonances for f < 1 is studied, and various features of the scattered intensity as a function of scattering angle are commented on. It is found that some resonances are formed without the presence of an exterior centrifugal barrier to confine them. (C) 2008 Optical Society of America
Scattering Of An Electromagnetic Plane Wave By A Luneburg Lens. Ii. Wave Theory, James A. Lock
Scattering Of An Electromagnetic Plane Wave By A Luneburg Lens. Ii. Wave Theory, James A. Lock
Physics Faculty Publications
The partial wave scattering and interior amplitudes for the interaction of an electromagnetic plane wave with a modified Luneburg lens are derived in terms of the exterior and interior radial functions of the scalar radiation potentials evaluated at the lens surface. A Debye series decomposition of these amplitudes is also performed and discussed. The effective potential inside the lens for the transverse electric polarization is qualitatively examined, and the approximate lens size parameters of morphology-dependent resonances are determined. Finally, the physical optics model is used to calculate wave scattering in the vicinity of the ray theory orbiting condition in order …
Rainbows In The Grass. I. External Reflection Rainbows From Pendant Droplets, James A. Lock, Charles L. Adler, Richard W. Fleet
Rainbows In The Grass. I. External Reflection Rainbows From Pendant Droplets, James A. Lock, Charles L. Adler, Richard W. Fleet
Physics Faculty Publications
In the mid-morning on a sunny day one can sometimes see glare spots associated with uncolored "rainbow" (i.e., fold) caustics due to the sunlight reflected from the surface of dew or guttation drops. We show that these dewdrop reflection rainbows are due to places on the droplet (i.e., from an "inflection circle") where its Gaussian curvature becomes zero. We work out the theory of such caustics with horizontally incident light and present a comparison of the theory to measurements made in the laboratory. (C) 2008 Optical Society of America
Scattering Of An Electromagnetic Plane Wave By A Luneburg Lens. I. Ray Theory, James A. Lock
Scattering Of An Electromagnetic Plane Wave By A Luneburg Lens. I. Ray Theory, James A. Lock
Physics Faculty Publications
For a plane wave incident on either a Luneburg lens or a modified Luneburg lens, the magnitude and phase of the transmitted electric field are calculated as a function of the scattering angle in the context of ray theory. It is found that the ray trajectory and the scattered intensity are not uniformly convergent in the vicinity of edge ray incidence on a Luneburg lens, which corresponds to the semiclassical phenomenon of orbiting. In addition, it is found that rays transmitted through a large-focal-length modified Luneburg lens participate in a far-zone rainbow, the details of which are exactly analytically soluble …
Spectral Time Moment Analysis Of Microgel Deswelling: Effect Of The Heating Rate, Kiril A. Streletzky, John T. Mckenna
Spectral Time Moment Analysis Of Microgel Deswelling: Effect Of The Heating Rate, Kiril A. Streletzky, John T. Mckenna
Physics Faculty Publications
Microgel nanoparticles were synthesized in aqueous solutions of neutral polymer hydroxypropylcellulose (HPC) through the self-association of amphiphilic HPC molecules and the subsequent cross linking at room temperature. Dynamic Light Scattering was used to study the transport properties of HPC microgels below and above the volume phase transition. Highly nonexponential, multimodal microgel spectra were observed and successfully analyzed by spectral time moment analysis. This article expands earlier results and focuses on the effect of the heating rate on microgel deswelling. During the fast heating two identified microgel modes with apparent hydrodynamic radii (RH) of 25–30 nm and 400–650 nm collapse into …
Turbulent Dispersion In Cloudy Boundary Layers, Remco A. Verzijlbergh, Harmen J.J. Jonker, Thijs Heus, J. Vilà-Guerau De Arellano
Turbulent Dispersion In Cloudy Boundary Layers, Remco A. Verzijlbergh, Harmen J.J. Jonker, Thijs Heus, J. Vilà-Guerau De Arellano
Physics Faculty Publications
Compared to dry boundary layers, dispersion in cloud-topped boundary layers has received less attention. In this LES based numerical study we investigate the dispersion of a passive tracer in the form of Lagrangian particles for four kinds of atmospheric boundary layers: 1) a dry convective boundary layer (for reference), 2) a "smoke" cloud boundary layer in which the turbulence is driven by radiative cooling, 3) a stratocumulus topped boundary layer and 4) a shallow cumulus topped boundary layer. We show that the dispersion characteristics of the smoke cloud boundary layer as well as the stratocumulus situation can be well understood …
Structure Of The Catalytic Trimer Of Methanococcus Jannaschii Aspartate Transcarbamoylase In An Orthorhombic Crystal Form, Jacqueline Vitali, Michael J. Colaneri
Structure Of The Catalytic Trimer Of Methanococcus Jannaschii Aspartate Transcarbamoylase In An Orthorhombic Crystal Form, Jacqueline Vitali, Michael J. Colaneri
Physics Faculty Publications
Crystals of the catalytic subunit of Methanococcus jannaschii aspartate transcarbamoylase in an orthorhombic crystal form contain four crystallographically independent trimers which associate in pairs to form stable staggered complexes that are similar to each other and to a previously determined monoclinic C2 form. Each subunit has a sulfate in the central channel. The catalytic subunits in these complexes show flexibility, with the elbow angles of the monomers differing by up to 7.4 degrees between crystal forms. Moreover, there is also flexibility in the relative orientation of the trimers around their threefold axis in the complexes, with a difference of 4 …
Mixing In Shallow Cumulus Clouds Studied By Lagrangian Particle Tracking, Thijs Heus, Gertjan Van Dijk, Harmen J.J. Jonker, Harry E.A. Van Den Akker
Mixing In Shallow Cumulus Clouds Studied By Lagrangian Particle Tracking, Thijs Heus, Gertjan Van Dijk, Harmen J.J. Jonker, Harry E.A. Van Den Akker
Physics Faculty Publications
Mixing between shallow cumulus clouds and their environment is studied using large-eddy simulations. The origin of in-cloud air is studied by two distinct methods: 1) by analyzing conserved variable mixing diagrams (Paluch diagrams) and 2) by tracing back cloud-air parcels represented by massless Lagrangian particles that follow the flow. The obtained Paluch diagrams are found to be similar to many results in the literature, but the source of entrained air found by particle tracking deviates from the source inferred from the Paluch analysis. Whereas the classical Paluch analysis seems to provide some evidence for cloud-top mixing, particle tracking shows that …
Radiation Torque Exerted On A Spheroid: Analytical Solution, Feng Xu, James A. Lock, Gérard Gouesbet, Cameron Tropea
Radiation Torque Exerted On A Spheroid: Analytical Solution, Feng Xu, James A. Lock, Gérard Gouesbet, Cameron Tropea
Physics Faculty Publications
As a companion work to our previous study [F. Xu, , Phys. Rev. E. 75, 026613 (2007)] on radiation force prediction for a homogeneous spheroid, we provide in this paper the analytical solution to the radiation torque exerted by an arbitrarily shaped beam on a spheroid, which can be prolate or oblate, transparent or absorbing. Calculations based upon this theoretical development are performed for both linearly and circularly polarized incident beams, and the results are compared to those of a sphere. Stable orientations of spheroids inside a linearly and a circularly polarized Gaussian beam are predicted. We analyze two physical …
Spectral Time Moment Analysis Of Microgel Structure And Dynamics, Kiril A. Streletzky, John T. Mckenna, Rami Mohieddine
Spectral Time Moment Analysis Of Microgel Structure And Dynamics, Kiril A. Streletzky, John T. Mckenna, Rami Mohieddine
Physics Faculty Publications
The structure and dynamics of crosslinked nanoparticles (microgels) made out of hydroxypropylcellulose (HPC) polymer chains were studied using dynamic light scattering spectroscopy. The microgel light scattering spectra were found to be highly nonexponential requiring a spectral time moment analysis in which the spectra were fit to a sum of stretched exponentials. Each term offers three parameters for analysis and represents a single spectral mode. At room temperature microgel spectra reveal three modes. Two faster modes are almost diffusive and correspond to apparent sizes of 25 and 450–650 nm. The slowest mode is independent of scattering angle and is reminiscent of …
A Refined View Of Vertical Mass Transport By Cumulus Convection, Harmen J.J. Jonker, Thijs Heus, Peter P. Sullivan
A Refined View Of Vertical Mass Transport By Cumulus Convection, Harmen J.J. Jonker, Thijs Heus, Peter P. Sullivan
Physics Faculty Publications
The purpose of this letter is to show that the traditional view of transport by shallow cumulus clouds needs important refinement. On the basis of a straightforward geometrical analysis of Large Eddy Simulation results of shallow cumulus clouds, we conclude (1) that the upward mass transport by clouds is strongly dominated by regions close to the edge of clouds rather than by the core region of clouds and (2) that the downward mass transport is dominated by processes just outside the cloud. The latter finding contradicts the accepted view of a uniformly descending dry environment. We therefore advocate a refined …
Investigation Of Magnetic Interactions In Large Arrays Of Magnetic Nanowires, Petru S. Fodor, G. M. Tsoi, L. W. Wenger
Investigation Of Magnetic Interactions In Large Arrays Of Magnetic Nanowires, Petru S. Fodor, G. M. Tsoi, L. W. Wenger
Physics Faculty Publications
The magnetic interactions in large arrays of ordered magnetic nanowires with 12-48 nm diameter and 55-95 nm spacing were investigated using modified Henkel plots. The measurements for nanowire arrays ac demagnetized with the field applied parallel to the nanowire axis (the easy magnetization axis) indicate that the dominant interaction during the switching process is the magnetostatic coupling between the nanowires. Nevertheless, while the strength of the magnetostatic interactions increases with the magnetic moment associated with the nanowires, the increase is not linear with respect to the volume of the nanowires. Moreover, the dependence of the remanence curves on the field …
Elastically Induced Coexistence Of Surface Reconstructions, Jessica E. Bickel, Normand A. Modine, Chris Pearson, Joanna Mirecki Millunchick
Elastically Induced Coexistence Of Surface Reconstructions, Jessica E. Bickel, Normand A. Modine, Chris Pearson, Joanna Mirecki Millunchick
Physics Faculty Publications
Scanning tunneling microscopy of Sb-capped GaAs shows the coexistence of different surface reconstructions. The majority of the surface consists of an α2(2×4) reconstruction typically observed for GaAs(001) surfaces. At step edges, an α(4×3) reconstruction, common for GaSb(001), is observed. We argue that strain couples the surface reconstruction to the film morphology. Density functional theory calculations show that the (2×4) reconstruction is stabilized in GaSb films when the lattice parameter is constrained to that of GaAs, as happens in the middle of a terrace, while the (4×3) reconstruction is stabilized when the lattice parameter is allowed to relax toward that of …
Dipole In A Magnetic Field, Work, And Quantum Spin, Robert J. Deissler
Dipole In A Magnetic Field, Work, And Quantum Spin, Robert J. Deissler
Physics Faculty Publications
The behavior of an atom in a nonuniform magnetic field is analyzed, as well as the motion of a classical magnetic dipole (a spinning charged ball) and a rotating charged ring. For the atom it is shown that, while the magnetic field does no work on the electron-orbital contribution to the magnetic moment (the source of translational kinetic energy being the internal energy of the atom), whether or not it does work on the electron- spin contribution to the magnetic moment depends on whether the electron has an intrinsic rotational kinetic energy associated with its spin. A rotational kinetic energy …
Subsiding Shells Around Shallow Cumulus Clouds, Thijs Heus, Harmen J.J. Jonker
Subsiding Shells Around Shallow Cumulus Clouds, Thijs Heus, Harmen J.J. Jonker
Physics Faculty Publications
In this study large-eddy simulations (LES) are used to gain more knowledge on the shell of subsiding air that is frequently observed around cumulus clouds. First, a detailed comparison between observational and numerical results is presented to better validate LES as a tool for studies of microscale phenomena. It is found that horizontal cloud profiles of vertical velocity, humidity, and temperature are in good agreement with observations. They show features similar to the observations, including the presence of the shell of descending air around the cloud. Second, the availability of the complete 3D dataset in LES has been exploited to …
Atomic Size Mismatch Strain Induced Surface Reconstructions, Jessica E. Bickel, Normand A. Modine, Anton Van Der Ven, Joanna Mirecki Millunchick
Atomic Size Mismatch Strain Induced Surface Reconstructions, Jessica E. Bickel, Normand A. Modine, Anton Van Der Ven, Joanna Mirecki Millunchick
Physics Faculty Publications
The effects of lattice mismatch strain and atomic size mismatch strain on surface reconstructions are analyzed using density functional theory. These calculations demonstrate the importance of an explicit treatment of alloying when calculating the energies of alloyed surface reconstructions. Lattice mismatch strain has little impact on surface dimer ordering for the α2(2×4) reconstruction of GaAs alloyed with In. However, atomic size mismatch strain induces the surface In atoms to preferentially alternate position, which, in turn, induces an alternating configuration of the surface anion dimers. These results agree well with experimental data for α2(2×4) domains in InGaAs∕GaAs surfaces.
Crystal Structure Of The Catalytic Trimer Of Methanococcus Jannaschii Aspartate Transcarbamoylase, Jacqueline Vitali, Michael Colaneri Colaneri, Evan Kantrowitz
Crystal Structure Of The Catalytic Trimer Of Methanococcus Jannaschii Aspartate Transcarbamoylase, Jacqueline Vitali, Michael Colaneri Colaneri, Evan Kantrowitz
Physics Faculty Publications
The catalytic trimer of Methanococcus jannaschii aspartate transcarbamoylase is extremely heat stable, maintaining 75% of its activity after heat treatment for 60 min at 75 degrees C. We undertook its structural analysis in order to understand the molecular basis of its thermostability and gain insight on how its catalytic function adapts to high temperature. Several structural elements potentially contributing to thermostability were identified. These include: (i) changes in the amino acid composition such as a decrease in the thermolabile residues Gln and Asn, an increase in the charged residues Lys and Glu, an increase in Tyr and a decrease in …