The Experts below are selected from a list of 195 Experts worldwide ranked by ideXlab platform
Juan F Arratia - One of the best experts on this subject based on the ideXlab platform.
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concurrent observations at the magnetic equator of small scale irregularities and large scale depletions associated with equatorial spread f
Journal of Geophysical Research, 2015Co-Authors: Dustin A Hickey, C R Martinis, F S Rodrigues, R H Varney, Marco Milla, M J Nicolls, A Stromme, Juan F ArratiaAbstract:In 2014 an all-sky imager (ASI) and an Advanced Modular Incoherent Scatter Radar consisting of 14 panels (AMISR-14) system were installed at the Jicamarca Radio Observatory. The ASI measures airglow depletions associated with large-scale equatorial spread F irregularities (10–500 km), while AMISR-14 detects small-scale irregularities (0.34 m). This study presents simultaneous observations of equatorial spread F (ESF) irregularities at 50–200 km scale sizes using the all-sky imager, at 3 m scale sizes using the JULIA (Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere) radar, and at 0.34 m scales using the AMISR-14 radar. We compare data from the three instruments on the night of 20–21 August 2014 by locating the radar Scattering Volume in the optical images. During this night no topside plumes were observed, and we only compare with bottomside ESF. AMISR-14 had five beams perpendicular to the magnetic field covering ~200 km in the east-west direction at 250 km altitude. Comparing the radar data with zenith ASI measurements, we found that most of the echoes occur on the western wall of the depletions with fewer echoes observed the eastern wall and center, contrary to previous comparisons of topside plumes that showed most of the echoes in the center of depleted regions. We attribute these differences to the occurrence of irregularities produced at submeter scales by the lower hybrid drift instability. Comparisons of the ASI observations with JULIA images show similar results to those found in the AMISR-14 and ASI comparison.
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concurrent observations at the magnetic equator of small scale irregularities and large scale depletions associated with equatorial spread f
arXiv: Space Physics, 2015Co-Authors: Dustin A Hickey, C R Martinis, F S Rodrigues, R H Varney, Marco Milla, M J Nicolls, A Stromme, Juan F ArratiaAbstract:In 2014 an all-sky imager (ASI) and an Advanced Modular Incoherent Scatter Radar consisting of 14 panels (AMISR-14) system were installed at the Jicamarca Radio Observatory. The ASI measures airglow depletions associated with large-scale equatorial spread F irregularities (10s-100s km), while AMISR-14 detects small-scale irregularities (0.34 m). This study presents simultaneous observations of equatorial spread F (ESF) irregularities at 10-100 km scales using the all sky-imager, at 3 m scales using the JULIA (Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere) radar, and at 0.34 m scales using the AMISR-14 radar. We compare data from the three instruments on the night of 20-21 August, 2014 by locating the radar Scattering Volume in the optical images. During this night no topside plumes were observed, and we only compare with bottomside ESF. AMISR-14 had five beams perpendicular to the magnetic field covering ~200 km in the east-west direction at 250 km altitude. Comparing the radar data with zenith ASI measurements, we found that most of the echoes occur on the western wall of the depletions with fewer echoes observed the eastern wall and center, contrary to previous comparisons of topside plumes that showed most of the echoes in the center of depleted regions. We attribute these differences to the occurrence of irregularities produced at sub-meter scales by the lower-hybrid-drift instability. Comparisons of the ASI observations with JULIA images show similar results to those found in the AMISR-14 and ASI comparison.
Lilo D Pozzo - One of the best experts on this subject based on the ideXlab platform.
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a small angle Scattering environment for in situ ultrasound studies
Soft Matter, 2018Co-Authors: David Li, Yuyin Xi, Ivan Pelivanov, Matthew Odonnell, Lilo D PozzoAbstract:Ultrasonic devices are common tools in laboratory and industrial settings to produce cavitation events for cleaning, emulsification, cell lysis and other materials applications. Effects of sonication at the macroscopic scale can be visible while effects at the molecular and nano-scales are not easily probed and, therefore, not fully understood. We present a new small angle Scattering sample environment designed specifically to study structural changes occurring in various types of dispersions at the nano-scale due to ultrasonic acoustic waves. The sample environment features two face-to-face high-intensity focused ultrasound transducers coaxially aligned and normal to the neutron/X-ray beam propagation direction. A third broadband transducer is fixed beneath the Scattering Volume to acoustically monitor for cavitation events. By correlating acoustic data to Scattering data, measured structural changes can be correlated to changes in parameters such as frequency, acoustic pressure, or cavitation pressure threshold. Several example applications of colloidal systems effectively influenced by ultrasound fields are also presented to demonstrate the capabilities of the device and to motivate future work on in situ Scattering analysis of ultrasound materials processing methods.
Dustin A Hickey - One of the best experts on this subject based on the ideXlab platform.
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concurrent observations at the magnetic equator of small scale irregularities and large scale depletions associated with equatorial spread f
Journal of Geophysical Research, 2015Co-Authors: Dustin A Hickey, C R Martinis, F S Rodrigues, R H Varney, Marco Milla, M J Nicolls, A Stromme, Juan F ArratiaAbstract:In 2014 an all-sky imager (ASI) and an Advanced Modular Incoherent Scatter Radar consisting of 14 panels (AMISR-14) system were installed at the Jicamarca Radio Observatory. The ASI measures airglow depletions associated with large-scale equatorial spread F irregularities (10–500 km), while AMISR-14 detects small-scale irregularities (0.34 m). This study presents simultaneous observations of equatorial spread F (ESF) irregularities at 50–200 km scale sizes using the all-sky imager, at 3 m scale sizes using the JULIA (Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere) radar, and at 0.34 m scales using the AMISR-14 radar. We compare data from the three instruments on the night of 20–21 August 2014 by locating the radar Scattering Volume in the optical images. During this night no topside plumes were observed, and we only compare with bottomside ESF. AMISR-14 had five beams perpendicular to the magnetic field covering ~200 km in the east-west direction at 250 km altitude. Comparing the radar data with zenith ASI measurements, we found that most of the echoes occur on the western wall of the depletions with fewer echoes observed the eastern wall and center, contrary to previous comparisons of topside plumes that showed most of the echoes in the center of depleted regions. We attribute these differences to the occurrence of irregularities produced at submeter scales by the lower hybrid drift instability. Comparisons of the ASI observations with JULIA images show similar results to those found in the AMISR-14 and ASI comparison.
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concurrent observations at the magnetic equator of small scale irregularities and large scale depletions associated with equatorial spread f
arXiv: Space Physics, 2015Co-Authors: Dustin A Hickey, C R Martinis, F S Rodrigues, R H Varney, Marco Milla, M J Nicolls, A Stromme, Juan F ArratiaAbstract:In 2014 an all-sky imager (ASI) and an Advanced Modular Incoherent Scatter Radar consisting of 14 panels (AMISR-14) system were installed at the Jicamarca Radio Observatory. The ASI measures airglow depletions associated with large-scale equatorial spread F irregularities (10s-100s km), while AMISR-14 detects small-scale irregularities (0.34 m). This study presents simultaneous observations of equatorial spread F (ESF) irregularities at 10-100 km scales using the all sky-imager, at 3 m scales using the JULIA (Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere) radar, and at 0.34 m scales using the AMISR-14 radar. We compare data from the three instruments on the night of 20-21 August, 2014 by locating the radar Scattering Volume in the optical images. During this night no topside plumes were observed, and we only compare with bottomside ESF. AMISR-14 had five beams perpendicular to the magnetic field covering ~200 km in the east-west direction at 250 km altitude. Comparing the radar data with zenith ASI measurements, we found that most of the echoes occur on the western wall of the depletions with fewer echoes observed the eastern wall and center, contrary to previous comparisons of topside plumes that showed most of the echoes in the center of depleted regions. We attribute these differences to the occurrence of irregularities produced at sub-meter scales by the lower-hybrid-drift instability. Comparisons of the ASI observations with JULIA images show similar results to those found in the AMISR-14 and ASI comparison.
Vincent K Shen - One of the best experts on this subject based on the ideXlab platform.
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a methodology to calculate small angle Scattering profiles of macromolecular solutions from molecular simulations in the grand canonical ensemble
Journal of Chemical Physics, 2018Co-Authors: Harold W Hatch, Marco A Blanco, Joseph E Curtis, Vincent K ShenAbstract:The theoretical framework to evaluate small-angle Scattering (SAS) profiles for multi-component macromolecular solutions is re-examined from the standpoint of molecular simulations in the grand-canonical ensemble, where the chemical potentials of all species in solution are fixed. This statistical mechanical ensemble resembles more closely Scattering experiments, capturing concentration fluctuations that arise from the exchange of molecules between the Scattering Volume and the bulk solution. The resulting grand-canonical expression relates Scattering intensities to the different intra- and intermolecular pair distribution functions, as well as to the distribution of molecular concentrations on the Scattering Volume. This formulation represents a generalized expression that encompasses most of the existing methods to evaluate SAS profiles from molecular simulations. The grand-canonical SAS methodology is probed for a series of different implicit-solvent, homogeneous systems at conditions ranging from dilute to concentrated. These systems consist of spherical colloids, dumbbell particles, and highly flexible polymer chains. Comparison of the resulting SAS curves against classical methodologies based on either theoretical approaches or canonical simulations (i.e., at a fixed number of molecules) shows equivalence between the different Scattering intensities so long as interactions between molecules are net repulsive or weakly attractive. On the other hand, for strongly attractive interactions, grand-canonical SAS profiles deviate in the low- and intermediate-q range from those calculated in a canonical ensemble. Such differences are due to the distribution of molecules becoming asymmetric, which yields a higher contribution from configurations with molecular concentrations larger than the nominal value. Additionally, for flexible systems, explicit discrimination between intra- and inter-molecular SAS contributions permits the implementation of model-free, structural analysis such as Guinier's plots at high molecular concentrations, beyond what the traditional limits are for such analysis.
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osmotic virial coefficients for model protein and colloidal solutions importance of ensemble constraints in the analysis of light Scattering data
Journal of Chemical Physics, 2012Co-Authors: Daniel W Siderius, William P Krekelberg, Christopher J Roberts, Vincent K ShenAbstract:Protein-protein interactions in solution may be quantified by the osmotic second virial coefficient (OSVC), which can be measured by various experimental techniques including light Scattering. Analysis of Rayleigh light Scattering measurements from such experiments requires identification of a Scattering Volume and the thermodynamic constraints imposed on that Volume, i.e., the statistical mechanical ensemble in which light Scattering occurs. Depending on the set of constraints imposed on the Scattering Volume, one can obtain either an apparent OSVC, A(2,app), or the true thermodynamic OSVC, B(22)(osm), that is rigorously defined in solution theory [M. A. Blanco, E. Sahin, Y. Li, and C. J. Roberts, J. Chem. Phys. 134, 225103 (2011)]. However, it is unclear to what extent A(2,app) and B(22)(osm) differ, which may have implications on the physical interpretation of OSVC measurements from light Scattering experiments. In this paper, we use the multicomponent hard-sphere model and a well-known equation of state to directly compare A(2,app) and B(22)(osm). Our results from the hard-sphere equation of state indicate that A(2,app) underestimates B(22)(osm), but in a systematic manner that may be explained using fundamental thermodynamic expressions for the two OSVCs. The difference between A(2,app) and B(22)(osm) may be quantitatively significant, but may also be obscured in experimental application by statistical uncertainty or non-steric interactions. Consequently, the two OSVCs that arise in the analysis of light Scattering measurements do formally differ, but in a manner that may not be detectable in actual application.
Olga Korotkova - One of the best experts on this subject based on the ideXlab platform.
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theory of weak Scattering of stochastic electromagnetic fields from deterministic and random media
Physical Review A, 2010Co-Authors: Zhisong Tong, Olga KorotkovaAbstract:The theory of Scattering of scalar stochastic fields from deterministic and random media is generalized to the electromagnetic domain under the first-order Born approximation. The analysis allows for determining the changes in spectrum, coherence, and polarization of electromagnetic fields produced on their propagation from the source to the Scattering Volume, interaction with the scatterer, and propagation from the scatterer to the far field. An example of Scattering of a field produced by a {delta}-correlated partially polarized source and scattered from a {delta}-correlated medium is provided.
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effect of the pair structure factor of a particulate medium on scalar wave Scattering in the first born approximation
Optics Letters, 2009Co-Authors: Serkan Sahin, Olga KorotkovaAbstract:Using Scattering matrices and the angular spectrum representation of waves, we develop the analytical theory of Scattering of random scalar waves from random collections of particles, valid under the first Born approximation. We demonstrate that in the calculation of far-field statistics, such as the spectral density and the spectral degree of coherence, the knowledge of the pair-structure factor of the collection is crucial. We illustrate our analytical approach by considering a numerical example involving Scattering of two partially correlated plane waves from a random distribution of spheres. © 2009 Optical Society of America OCIS codes: 030.0030, 290.5825. Wave Scattering from particulate media is always discussed under a number of assumptions with regard to the properties of illumination as well as of individual particles and the collection as a whole [1–4]. Owing to such simplifying assumptions only a few characteristics of the scattered field are usually considered. In particular, in a majority of cases the incident radiation is assumed to be a monochromatic or polychromatic plane wave, either scalar or electromagnetic. Such simplification is not adequate in a number of practical situations, for instance, when either spatial distribution of illumination is not uniform and/or its coherence properties are not perfect. On the other hand, in the description of random collections of particles it is usually assumed that the Scattering potentials of the individual particles are deterministic functions of space and frequency, and their collective properties are determined by the structure factor—a quantity that accounts for the modification of the intensity of a plane wave that is incident at and scattered from the collection along two fixed directions and at a given frequency. However, structure factor cannot provide information about how the correlations in the incident wave are modified on Scattering. This very fact limits Scattering to the case of the incident plane wave and to the calculation of spectral properties of the scattered waves alone. Moreover, with knowledge of only the Scattering potential of a single particle and of the structure factor, it is impossible to determine the coherence properties of the scattered field. Even in the case of a deterministic collection of scatterers the coherence properties of scattered waves may, generally, change [5]. In this Letter we develop the theory of Scattering of scalar fields with arbitrary spectral and coherence properties from random collections of particles (deterministic potentials, random locations), which we characterize by a pair-structure factor (cf. [6]). The pair-structure factor is a generalization of the conventional structure factor accounting for the change in correlation properties of light at two given directions of incidence and two given directions of Scattering. We stress that the knowledge of the pairstructure factor makes it possible to predict not only spectral but also coherence properties of scattered waves, even in the case when the incident wave has a more complex structure than a plane wave. Let us consider a collection of N identical particles with Scattering potentials fr ; as deterministic functions of position r =x , y , z and frequency but with centers randomly distributed in Scattering Volume V. The Scattering potential of a particle is a simple function of the index of refraction nr, namely,
