Structure of the Mimas 5:3 Bending Wave in Saturn's Rings

NASA Astrophysics Data System (ADS)

Sega, Daniel D.; Colwell, Josh E.

2016-10-01

Saturn's moon Mimas is on an inclined orbit with several strong vertical orbital resonances in Saturn's rings. The 5:3 inner vertical resonance with Mimas lies in the outer A ring and produces a prominent spiral bending wave (BW) that propagates away from Mimas. While dozens of density waves in Saturn's rings have been analyzed to determine local surface mass densities and viscosities, the number of bending waves is limited by the requirement for a moon on an inclined orbit and because, unlike the Lindblad resonances that excite density waves, there can be no first order vertical resonances. The Mimas 5:3 BW is the most prominent in the ring system. Bending wave theory was initially developed by Shu et al. (1983, Icarus, 53, 185-206) following the Voyager encounters with Saturn. Later, Gresh et al. (1986, Icarus, 68, 481-502) modeled radio science occultation data of the Mimas 5:3 BW with an imperfect fit to the theory. The multitude of high resolution stellar occultations observed by Cassini UVIS provides an opportunity to reconstruct the full three-dimensional structure of this wave and learn more about local ring properties. Occultations at high elevation angles out of the ring plane are insensitive to the wave structure due to the small angles of the vertical warping of the rings in the wave. They thus reveal the underlying structure in the wave region. There is a symmetric increase in optical depth throughout the Mimas 5:3 BW region. This may be due to an increase in the abundance of small particles without a corresponding increase in surface mass density. We include this feature in a ray-tracing model of the vertical structure of the wave and fit it to multiple UVIS occultations. The observed amplitude of the wave and its damping behavior of are not well-described by the Shu et al. model, which assumes a fluid-like damping mechanism. A different damping behavior of the ring, perhaps radially varying across the wave region due to differences in the particle size distribution and/or structure of the self-gravity wakes in the ring, is needed to match observations.

Gravity waves

NASA Technical Reports Server (NTRS)

Fritts, David

1987-01-01

Gravity waves contributed to the establishment of the thermal structure, small scale (80 to 100 km) fluctuations in velocity (50 to 80 m/sec) and density (20 to 30%, 0 to peak). Dominant gravity wave spectrum in the middle atmosphere: x-scale, less than 100 km; z-scale, greater than 10 km; t-scale, less than 2 hr. Theorists are beginning to understand middle atmosphere motions. There are two classes: Planetary waves and equatorial motions, gravity waves and tidal motions. The former give rise to variability at large scales, which may alter apparent mean structure. Effects include density and velocity fluctuations, induced mean motions, and stratospheric warmings which lead to the breakup of the polar vortex and cooling of the mesosphere. On this scale are also equatorial quasi-biennial and semi-annual oscillations. Gravity wave and tidal motions produce large rms fluctuations in density and velocity. The magnitude of the density fluctuations compared to the mean density is of the order of the vertical wavelength, which grows with height. Relative density fluctuations are less than, or of the order of 30% below the mesopause. Such motions may cause significant and variable convection, and wind shear. There is a strong seasonal variation in gravity wave amplitude. Additional observations are needed to address and quantify mean and fluctuation statistics of both density and mean velocity, variability of the mean and fluctuations, and to identify dominant gravity wave scales and sources as well as causes of variability, both temporal and geographic.

NMR and NQR parameters of ethanol crystal

NASA Astrophysics Data System (ADS)

Milinković, M.; Bilalbegović, G.

2012-04-01

Electric field gradients and chemical shielding tensors of the stable monoclinic crystal phase of ethanol are computed. The projector-augmented wave (PAW) and gauge-including projector-augmented wave (GIPAW) models in the periodic plane-wave density functional theory are used. The crystal data from X-ray measurements, as well as the structures where either all atomic, or only hydrogen atom positions are optimized in the density functional theory are analyzed. These structural models are also studied by including the semi-empirical van der Waals correction to the density functional theory. Infrared spectra of these five crystal models are calculated.

Impulsively Generated Wave Trains in Coronal Structures. II. Effects of Transverse Structuring on Sausage Waves in Pressurelesss Slabs

NASA Astrophysics Data System (ADS)

Li, Bo; Guo, Ming-Zhe; Yu, Hui; Chen, Shao-Xia

2018-03-01

Impulsively generated sausage wave trains in coronal structures are important for interpreting a substantial number of observations of quasi-periodic signals with quasi-periods of order seconds. We have previously shown that the Morlet spectra of these wave trains in coronal tubes depend crucially on the dispersive properties of trapped sausage waves, the existence of cutoff axial wavenumbers, and the monotonicity of the dependence of the axial group speed on the axial wavenumber in particular. This study examines the difference a slab geometry may introduce, for which purpose we conduct a comprehensive eigenmode analysis, both analytically and numerically, on trapped sausage modes in coronal slabs with a considerable number of density profiles. For the profile descriptions examined, coronal slabs can trap sausage waves with longer axial wavelengths, and the group speed approaches the internal Alfvén speed more rapidly at large wavenumbers in the cylindrical case. However, common to both geometries, cutoff wavenumbers exist only when the density profile falls sufficiently rapidly at distances far from coronal structures. Likewise, the monotonicity of the group speed curves depends critically on the profile steepness right at the structure axis. Furthermore, the Morlet spectra of the wave trains are shaped by the group speed curves for coronal slabs and tubes alike. Consequently, we conclude that these spectra have the potential for inferring the subresolution density structuring inside coronal structures, although their detection requires an instrumental cadence of better than ∼1 s.

REVIEWS OF TOPICAL PROBLEMS: The modern view of the nature of the spiral structure of galaxies

NASA Astrophysics Data System (ADS)

Efremov, Yurii N.; Korchagin, V. I.; Marochnik, L. S.; Suchkov, A. A.

1989-04-01

The current state of the Lin-Shu density wave theory is discussed in the light of modern observational data. Much attention is paid to the problem of wave excitation and to the response of the interstellar gas to the wave gravitational potential. It is noted that the major predictions of the density wave theory—the galactic shock waves, the spiral velocity field of stars, and the age gradient across the spiral arms—have become fundamental observational facts at present, so that the density wave theory now has no competition from alternative theories. The nature of flocculent spirals is also discussed since, unlike regular spirals, they are probably not connected with density waves but with the effects of induced star formation in differentially rotating galactic disks.

Metal-ligand delocalization and spin density in the CuCl{sub 2} and [CuCl{sub 4}]{sup 2−} molecules: Some insights from wave function theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Giner, Emmanuel, E-mail: gnrmnl@unife.it; Angeli, Celestino, E-mail: anc@unife.it

2015-09-28

The aim of this paper is to unravel the physical phenomena involved in the calculation of the spin density of the CuCl{sub 2} and [CuCl{sub 4}]{sup 2−} systems using wave function methods. Various types of wave functions are used here, both variational and perturbative, to analyse the effects impacting the spin density. It is found that the spin density on the chlorine ligands strongly depends on the mixing between two types of valence bond structures. It is demonstrated that the main difficulties found in most of the previous studies based on wave function methods come from the fact that eachmore » valence bond structure requires a different set of molecular orbitals and that using a unique set of molecular orbitals in a variational procedure leads to the removal of one of them from the wave function. Starting from these results, a method to compute the spin density at a reasonable computational cost is proposed.« less

Density Fluctuations in the Solar Wind Driven by Alfvén Wave Parametric Decay

NASA Astrophysics Data System (ADS)

Bowen, Trevor A.; Badman, Samuel; Hellinger, Petr; Bale, Stuart D.

2018-02-01

Measurements and simulations of inertial compressive turbulence in the solar wind are characterized by anti-correlated magnetic fluctuations parallel to the mean field and density structures. This signature has been interpreted as observational evidence for non-propagating pressure balanced structures, kinetic ion-acoustic waves, as well as the MHD slow-mode. Given the high damping rates of parallel propagating compressive fluctuations, their ubiquity in satellite observations is surprising and suggestive of a local driving process. One possible candidate for the generation of compressive fluctuations in the solar wind is the Alfvén wave parametric instability. Here, we test the parametric decay process as a source of compressive waves in the solar wind by comparing the collisionless damping rates of compressive fluctuations with growth rates of the parametric decay instability daughter waves. Our results suggest that generation of compressive waves through parametric decay is overdamped at 1 au, but that the presence of slow-mode-like density fluctuations is correlated with the parametric decay of Alfvén waves.

Characterizing bonding patterns in diradicals and triradicals by density-based wave function analysis: A uniform approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Orms, Natalie; Rehn, Dirk; Dreuw, Andreas

Density-based wave function analysis enables unambiguous comparisons of electronic structure computed by different methods and removes ambiguity of orbital choices. Here, we use this tool to investigate the performance of different spin-flip methods for several prototypical diradicals and triradicals. In contrast to previous calibration studies that focused on energy gaps between high and low spin-states, we focus on the properties of the underlying wave functions, such as the number of effectively unpaired electrons. Comparison of different density functional and wave function theory results provides insight into the performance of the different methods when applied to strongly correlated systems such asmore » polyradicals. We also show that canonical molecular orbitals for species like large copper-containing diradicals fail to correctly represent the underlying electronic structure due to highly non-Koopmans character, while density-based analysis of the same wave function delivers a clear picture of bonding pattern.« less

Characterizing bonding patterns in diradicals and triradicals by density-based wave function analysis: A uniform approach

DOE PAGES

Orms, Natalie; Rehn, Dirk; Dreuw, Andreas; ...

2017-12-21

Density-based wave function analysis enables unambiguous comparisons of electronic structure computed by different methods and removes ambiguity of orbital choices. Here, we use this tool to investigate the performance of different spin-flip methods for several prototypical diradicals and triradicals. In contrast to previous calibration studies that focused on energy gaps between high and low spin-states, we focus on the properties of the underlying wave functions, such as the number of effectively unpaired electrons. Comparison of different density functional and wave function theory results provides insight into the performance of the different methods when applied to strongly correlated systems such asmore » polyradicals. We also show that canonical molecular orbitals for species like large copper-containing diradicals fail to correctly represent the underlying electronic structure due to highly non-Koopmans character, while density-based analysis of the same wave function delivers a clear picture of bonding pattern.« less

Experimental investigation on aero-optical aberration of shock wave/boundary layer interactions

NASA Astrophysics Data System (ADS)

Ding, Haolin; Yi, Shihe; Fu, Jia; He, Lin

2016-10-01

After streaming through the flow field which including the expansion, shock wave, boundary, etc., the optical wave would be distorted by fluctuations in the density field. Interactions between laminar/turbulent boundary layer and shock wave contain large number complex flow structures, which offer a condition for studying the influences that different flow structures of the complex flow field have on the aero-optical aberrations. Interactions between laminar/turbulent boundary layer and shock wave are investigated in a Mach 3.0 supersonic wind tunnel, based on nanoparticle-tracer planar laser scattering (NPLS) system. Boundary layer separation/attachment, induced suppression waves, induced shock wave, expansion fan and boundary layer are presented by NPLS images. Its spatial resolution is 44.15 μm/pixel. Time resolution is 6ns. Based on the NPLS images, the density fields with high spatial-temporal resolution are obtained by the flow image calibration, and then the optical path difference (OPD) fluctuations of the original 532nm planar wavefront are calculated using Ray-tracing theory. According to the different flow structures in the flow field, four parts are selected, (1) Y=692 600pixel; (2) Y=600 400pixel; (3) Y=400 268pixel; (4) Y=268 0pixel. The aerooptical effects of different flow structures are quantitatively analyzed, the results indicate that: the compressive waves such as incident shock wave, induced shock wave, etc. rise the density, and then uplift the OPD curve, but this kind of shock are fixed in space position and intensity, the aero-optics induced by it can be regarded as constant; The induced shock waves are induced by the coherent structure of large size vortex in the interaction between turbulent boundary layer, its unsteady characteristic decides the induced waves unsteady characteristic; The space position and intensity of the induced shock wave are fixed in the interaction between turbulent boundary layer; The boundary layer aero-optics are induced by the coherent structure of large size vortex, which result in the fluctuation of OPD.

Modeling and observations of ULF waves trapped in a plasmaspheric density plume

NASA Astrophysics Data System (ADS)

Degeling, A. W.; Zhang, S.; Foster, J. C.; Shi, Q.; Zong, Q. G.; Rankin, R.

2017-12-01

In order for ULF waves to effectively energise radiation belt electrons by drift-resonance, wave power must be significant in regions within the magnetosphere where the ULF wave phase propagation and electron drift directions are roughly aligned. For waves launched along the dayside magnetopause, such a region would be located in the afternoon - dusk sector of the inner magnetosphere. During periods of storm activity and enhanced convection, the plasma density in this region is highly dynamic due to the development of plasmaspheric drainage plume (PDP) structure. This significantly affects the local Alfvén speed, and alters the propagation of ULF waves launched from the magnetopause. It can therefore be expected that the accessibility of ULF wave power for radiation belt energisation is sensitively dependent on the recent history of magnetospheric convection, and the stage of development of the PDP. This is investigated using a 3D model for ULF waves within the magnetosphere in which the plasma density distribution is evolved using an advection model for cold plasma, driven by a (Volland - Stern) convection electrostatic field (resulting in PDP structure). The wave model includes magnetic-field day/night asymmetry, and extends to a paraboloid dayside magnetopause, from which ULF waves are launched at various stages during the PDP development. We find that the plume structure significantly alters the field line resonance (FLR) location, and the turning point for MHD fast waves, introducing strong asymmetry in the ULF wave distribution across the noon meridian. Moreover, the density enhancement within the PDP creates a waveguide or local cavity for MHD fast waves, such that eigenmodes formed allow the penetration of ULF wave power to much lower L within the plume than outside. This may explain satellite observations of the appearance of ULF wave activity within localized density enhancements associated with a PDP. Such an example, made by THEMIS following a geomagnetic storm on October 9, 2013, is described, and compared against the ULF wave model results, for which inputs are constrained by available observations.

Small-scale plasma irregularities in the nightside Venus ionosphere

NASA Astrophysics Data System (ADS)

Grebowsky, J. M.; Curtis, S. A.; Brace, L. H.

1991-12-01

The individual volt-ampere curves from the Pioneer Venus Orbiter electron temperature probe showed evidence for small-scale density irregularities, or short-period plasma waves, in regions of the nightside ionosphere where the Orbiter electric field detector observed waves in its 100-Hz channel. A survey of the nightside volt-ampere curves has revealed several hundred examples of such irregularities. The I-V structures correspond to plasma density structure with spatial scale sizes in the range of about 100-2000 m, or alternatively they could be viewed as waves having frequencies extending toward 100 Hz. They are often seen as isolated events, with spatial extent along the orbit frequently less than 80 km. The density irregularities or waves occur in or near prominent gradients in the ambient plasma concentrations both at low altitudes where molecular ions are dominant and at higher altitudes in regions of reduced plasma density where O(+) is the major ion. Electric field 100-Hz bursts occur simultaneously, with the majority of the structured I-V curves providing demonstrative evidence that at least some of the E field signals are produced within the ionosphere.

Numerical band structure calculations of plasma metamaterials

NASA Astrophysics Data System (ADS)

Pederson, Dylan; Kourtzanidis, Konstantinos; Raja, Laxminarayan

2015-09-01

Metamaterials (MM) are materials engineered to display negative macroscopic permittivity and permeability. These materials allow for designed control over electromagnetic energy flow, especially at frequencies where natural materials do not interact. Plasmas have recently found application in MM as a negative permittivity component. The permittivity of a plasma depends on its electron density, which can be controlled by an applied field. This means that plasmas can be used in MM to actively control the transmission or reflection of incident waves. This work focuses on a plasma MM geometry in which microplasmas are generated in perforations in a metal plate. We characterizethis material by its band structure, which describes its interaction with incident waves. The plasma-EM interactions are obtained by coupling Maxwell's equations to a simplified plasma momentum equation. A plasma density profile is prescribed, and its effect on the band structure is investigated. The band structure calculations are typically done for static structures, whereas our current density responds to the incident waves. The resulting band structures are compared with experimental results.

Quantum coherent switch utilizing commensurate nanoelectrode and charge density periodicities

DOEpatents

Harrison,; Neil, Singleton [Santa Fe, NM; John, Migliori [Los Alamos, NM; Albert, [Santa Fe, NM

2008-08-05

A quantum coherent switch having a substrate formed from a density wave (DW) material capable of having a periodic electron density modulation or spin density modulation, a dielectric layer formed onto a surface of the substrate that is orthogonal to an intrinsic wave vector of the DW material; and structure for applying an external spatially periodic electrostatic potential over the dielectric layer.

Deep structure of the Alborz Mountains by joint inversion of P receiver functions and dispersion curves

NASA Astrophysics Data System (ADS)

Rastgoo, Mehdi; Rahimi, Habib; Motaghi, Khalil; Shabanian, Esmaeil; Romanelli, Fabio; Panza, Giuliano F.

2018-04-01

The Alborz Mountains represent a tectonically and seismically active convergent boundary in the Arabia - Eurasia collision zone, in western Asia. The orogenic belt has undergone a long-lasted tectono-magmatic history since the Cretaceous. The relationship between shallow and deep structures in this complex tectonic domain is not straightforward. We present a 2D velocity model constructed by the assemblage of 1D shear wave velocity (Vs) models from 26 seismic stations, mainly distributed along the southern flank of the Alborz Mountains. The shear wave velocity structure has been estimated beneath each station using joint inversion of P-waves receiver functions and Rayleigh wave dispersion curves. A substantiation of the Vs inversion results sits on the modeling of Bouguer gravity anomaly data. Our velocity and density models show low velocity/density anomalies in uppermost mantle of western and central Alborz at a depth range of ∼50-100 km. In deeper parts of the uppermost mantle (depth range of 100-150 km), a high velocity/density anomaly is located beneath most of the Mountain range. The spatial pattern of these low and high velocity/density structures in the upper mantle is interpreted as the result of post collisional delamination of lower part of the western and central Alborz lithosphere.

Staggering Structure

NASA Image and Video Library

2017-09-06

This view from NASA's Cassini spacecraft shows a wave structure in Saturn's rings known as the Janus 2:1 spiral density wave. Resulting from the same process that creates spiral galaxies, spiral density waves in Saturn's rings are much more tightly wound. In this case, every second wave crest is actually the same spiral arm which has encircled the entire planet multiple times. This is the only major density wave visible in Saturn's B ring. Most of the B ring is characterized by structures that dominate the areas where density waves might otherwise occur, but this innermost portion of the B ring is different. The radius from Saturn at which the wave originates (toward lower-right in this image) is 59,796 miles (96,233 kilometers) from the planet. At this location, ring particles orbit Saturn twice for every time the moon Janus orbits once, creating an orbital resonance. The wave propagates outward from the resonance (and away from Saturn), toward upper-left in this view. For reasons researchers do not entirely understand, damping of waves by larger ring structures is very weak at this location, so this wave is seen ringing for hundreds of bright wave crests, unlike density waves in Saturn's A ring. The image gives the illusion that the ring plane is tilted away from the camera toward upper-left, but this is not the case. Because of the mechanics of how this kind of wave propagates, the wavelength decreases with distance from the resonance. Thus, the upper-left of the image is just as close to the camera as the lower-right, while the wavelength of the density wave is simply shorter. This wave is remarkable because Janus, the moon that generates it, is in a strange orbital configuration. Janus and Epimetheus share practically the same orbit and trade places every four years. Every time one of those orbit swaps takes place, the ring at this location responds, spawning a new crest in the wave. The distance between any pair of crests corresponds to four years' worth of the wave propagating downstream from the resonance, which means the wave seen here encodes many decades' worth of the orbital history of Janus and Epimetheus. According to this interpretation, the part of the wave at the very upper-left of this image corresponds to the positions of Janus and Epimetheus around the time of the Voyager flybys in 1980 and 1981, which is the time at which Janus and Epimetheus were first proven to be two distinct objects (they were first observed in 1966). Epimetheus also generates waves at this location, but they are swamped by the waves from Janus, since Janus is the larger of the two moons. This image was taken on June 4, 2017, with the Cassini spacecraft narrow-angle camera. The image was acquired on the sunlit side of the rings from a distance of 47,000 miles (76,000 kilometers) away from the area pictured. The image scale is 1,730 feet (530 meters) per pixel. The phase angle, or sun-ring-spacecraft angle, is 90 degrees. https://photojournal.jpl.nasa.gov/catalog/PIA21627

On Spatial Structuring of the F2 Layer Studied by the Satellite Radio Sounding of the Ionosphere Disturbed by High-Power HF Radio Waves

NASA Astrophysics Data System (ADS)

Tereshchenko, E. D.; Turyansky, V. A.; Khudukon, B. Z.; Yurik, R. Yu.; Frolov, V. L.

2018-01-01

We present the results of studying the characteristics of the artificial plasma structures excited in the ionospheric F2 region modified by high-power HF radio waves. The experiments were carried out at the Sura heating facility using satellite radio sounding of the ionosphere. The plasma density profile was reconstructed with the highest possible spatial resolution for today, about 4 km. In a direction close to the magnetic zenith of the pump wave, the following phenomena were observed: the formation of a cavity with a 15% lower plasma density at the altitudes of the F2 layer and below; the formation of an area with plasma density increased by 12% at altitudes greater than 400 km. With a long-term quasiperiodic impact of the pump wave on the ionosphere, wavy large-scale electron-density perturbations (the meridional scale λx ≈ 130 km and the vertical scale λz ≈ 440 km) are also formed above the Sura facility. These perturbations can be due to the plasma density modulation by an artificial acoustic-gravity wave with a period of 10.6 m, which was formed by the heat source inside a large-scale cavity with low plasma density; there is generation of the electron density irregularities for the electrons with ΔNe/Ne ≈ 3% in the form of layers having the sizes 10-12 km along and about 24 km across the geomagnetic field, which are found both below and above the F2-layer maximum. The mechanisms of the formation of these plasma structures are discussed.

Axisymmetric Density Waves in Saturn's Rings

NASA Astrophysics Data System (ADS)

Hedman, Matthew; Nicholson, Philip

2018-04-01

Density waves in Saturn's rings are typically tightly wrapped spiral patterns generated by resonances with either Saturn's moons or structures inside the planet. However, between the Barnard and Bessel Gaps in the Cassini Division (i.e. between 120,240 and 120,300 km), there are density variations that appear to form an axisymmetric density wave, which consists of concentric regions of varying density that propagate radially through the rings. Such a wave requires some process that forces ring particles at all longitudes to pass through pericenter at the same time, and so cannot be generated by satellite resonances. Instead this particular wave appears to be excited by interference between a nearby satellite resonance and normal mode oscillations on the inner edge of the Barnard Gap. Similar axisymmetric waves may exist within the Dawes ringlet and the outermost part of the B ring, which are also just interior to resonantly confined edges that exhibit a large number of normal modes. These waves may therefore provide new insights into how resonant perturbations near an edge can propagate through a disk of material.

Small-scale plasma, magnetic, and neutral density fluctuations in the nightside Venus ionosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoegy, W.R.; Brace, L.H.; Kasprazak, W.T.

1990-04-01

Pioneer Venus orbiter measurements have shown that coherent small-scale waves exist in the electron density, the electron temperature, and the magnetic field in the lower ionosphere of Venus just downstream of the solar terminator (Brace et al., 1983). The waves become less regular and less coherent at larger solar zenith angles, and Brace et al. suggested that these structures may have evolved from the terminator waves as they are convected into the nightside ionosphere, driven by the day-to-night plasma pressure gradient. In this paper the authors describe the changes in wave characteristics with solar zenith angle and show that themore » neutral gas also has related wave characteristics, probably because of atmospheric gravity waves. The plasma pressure exceeds the magnetic pressure in the nightside ionosphere at these altitudes, and thus the magnetic field is carried along and controlled by the turbulent motion of the plasma, but the wavelike nature of the thermosphere may also be coupled to the plasma and magnetic structure. They show that there is a significant coherence between the ionosphere, thermosphere, and magnetic parameters at altitudes below about 185 km, a coherence which weakens in the antisolar region. The electron temperature and density are approximately 180{degree} out of phase and consistently exhibit the highest correlation of any pair of variables. Waves in the electron and neutral densities are moderately correlated on most orbits, but with a phase difference that varies within each orbit. The average electron temperature is higher when the average magnetic field is more horizontal; however, the correlation between temperature and dip angle does not extend to individual wave structures observed within a satellite pass, particularly in the antisolar region.« less

Spiral density waves and vertical circulation in protoplanetary discs

NASA Astrophysics Data System (ADS)

Riols, A.; Latter, H.

2018-06-01

Spiral density waves dominate several facets of accretion disc dynamics - planet-disc interactions and gravitational instability (GI) most prominently. Though they have been examined thoroughly in two-dimensional simulations, their vertical structures in the non-linear regime are somewhat unexplored. This neglect is unwarranted given that any strong vertical motions associated with these waves could profoundly impact dust dynamics, dust sedimentation, planet formation, and the emissivity of the disc surface. In this paper, we combine linear calculations and shearing box simulations in order to investigate the vertical structure of spiral waves for various polytropic stratifications and wave amplitudes. For sub-adiabatic profiles, we find that spiral waves develop a pair of counter-rotating poloidal rolls. Particularly strong in the non-linear regime, these vortical structures issue from the baroclinicity supported by the background vertical entropy gradient. They are also intimately connected to the disc's g modes which appear to interact non-linearly with the density waves. Furthermore, we demonstrate that the poloidal rolls are ubiquitous in gravitoturbulence, emerging in the vicinity of GI spiral wakes, and potentially transporting grains off the disc mid-plane. Other than hindering sedimentation and planet formation, this phenomena may bear on observations of the disc's scattered infrared luminosity. The vortical features could also impact on the turbulent dynamo operating in young protoplanetary discs subject to GI, or possibly even galactic discs.

Experimental Study of Internal Waves and Vortices Past 2d Obstacles In A Continuously Stratified Fluid

NASA Astrophysics Data System (ADS)

Mitkin, V.

Experimental investigations of fine and macroscopic structures of density and veloc- ity disturbances generated by a towing cylinder or a vertical strip in a linearly strati- fied liquid are carried out in a rectangular tank. A density gradient field is visualised by different Schlieren methods (direct shadow, 'slit-knife', 'slit-thread', 'natural rain- bow') characterised by a high spatial resolution. Profiles of fluid velocity are visu- alised by density markers U wakes past a vertically descending sugar crystal or an ascending gas bubble. In a fluid at rest the density marker acts as a vertical linear source of internal oscillations, which allows us to measure buoyancy frequency over all depth by the Schlieren instrument directly or by a conductivity probe in a particular point. Sensitive methods reveal a set of high gradient interfaces inside and outside the downstream wake besides well-known large-scale elements: upstream disturbances, attached internal waves and vortices. High gradient interfaces bound compact vor- tices. Vortices moving with respect to environment emit their own systems of internal waves randomising a regular pattern of attached antisymmetric internal waves. But after a rather long time a wave recurrence occurs and a regular but symmetric struc- ture of the longest waves (similar to the pattern of initial attached internal waves) is observed again. Results of studying of the influence of obstacles shape on phase struc- ture and amplitudes of attached internal waves field, vortex formation, their structure and characteristics are presented.

Internal structure of shock waves in disparate mass mixtures

NASA Technical Reports Server (NTRS)

Chung, Chan-Hong; De Witt, Kenneth J.; Jeng, Duen-Ren; Penko, Paul F.

1992-01-01

The detailed flow structure of a normal shock wave for a gas mixture is investigated using the direct-simulation Monte Carlo method. A variable diameter hard-sphere (VDHS) model is employed to investigate the effect of different viscosity temperature exponents (VTE) for each species in a gas mixture. Special attention is paid to the irregular behavior in the density profiles which was previously observed in a helium-xenon experiment. It is shown that the VTE can have substantial effects in the prediction of the structure of shock waves. The variable hard-sphere model of Bird shows good agreement, but with some limitations, with the experimental data if a common VTE is chosen properly for each case. The VDHS model shows better agreement with the experimental data without adjusting the VTE. The irregular behavior of the light-gas component in shock waves of disparate mass mixtures is observed not only in the density profile, but also in the parallel temperature profile. The strength of the shock wave, the type of molecular interactions, and the mole fraction of heavy species have substantial effects on the existence and structure of the irregularities.

Experimental study of a fine structure of 2D wakes and mixing past an obstacle in a continuously stratified fluid

NASA Astrophysics Data System (ADS)

Chashechkin, Yuli. D.; Mitkin, Vladimir V.

2001-10-01

Experimental investigations of fine and macroscopic structures of density and velocity disturbances generated by a towing cylinder or a vertical strip in a linearly stratified liquid are carried out in a rectangular tank. A density gradient field is visualised by different Schlieren methods (direct shadow, 'slit-knife', 'slit-thread', 'natural rainbow') characterised by a high spatial resolution. Profiles of fluid velocity are visualised by density markers — wakes past a vertically descending sugar crystal or an ascending gas bubble. In a fluid at rest, the density marker acts as a vertical linear source of internal oscillations which allows us to measure buoyancy frequency over all depth by the Schlieren instrument directly or by a conductivity probe in a particular point. Sensitive methods reveal a set of high gradient interfaces inside and outside the downstream wake besides well-known large scale elements: upstream disturbances, attached internal waves and vortices. Solitary interfaces located inside the attached internal waves field have no features on their leading and trailing edges. A thickness of interfaces is defined by an appropriate diffusion coefficient and a buoyancy frequency. High gradient interfaces bound compact vortices. Vortices moving with respect to environment emit their own systems of internal waves randomising a regular pattern of attached antisymmetric internal waves. But after a rather long time a wave recurrence occurs and a regular but symmetric structure of the longest waves (similar to the pattern of initial attached internal waves) is observed again. High gradient interfaces and lines of their intersections act as collectors of a dye coming from a compact source or from a coloured liquid volume inside the tank and separate coloured and clear areas.

Genesis of charge orders in high temperature superconductors

PubMed Central

Tu, Wei-Lin; Lee, Ting-Kuo

2016-01-01

One of the most puzzling facts about cuprate high-temperature superconductors in the lightly doped regime is the coexistence of uniform superconductivity and/or antiferromagnetism with many low-energy charge-ordered states in a unidirectional charge density wave or a bidirectional checkerboard structure. Recent experiments have discovered that these charge density waves exhibit different symmetries in their intra-unit-cell form factors for different cuprate families. Using a renormalized mean-field theory for a well-known, strongly correlated model of cuprates, we obtain a number of charge-ordered states with nearly degenerate energies without invoking special features of the Fermi surface. All of these self-consistent solutions have a pair density wave intertwined with a charge density wave and sometimes a spin density wave. Most of these states vanish in the underdoped regime, except for one with a large d-form factor that vanishes at approximately 19% doping of the holes, as reported by experiments. Furthermore, these states could be modified to have a global superconducting order, with a nodal-like density of states at low energy. PMID:26732076

Density Shock Waves in Confined Microswimmers

NASA Astrophysics Data System (ADS)

Tsang, Alan Cheng Hou; Kanso, Eva

2016-01-01

Motile and driven particles confined in microfluidic channels exhibit interesting emergent behavior, from propagating density bands to density shock waves. A deeper understanding of the physical mechanisms responsible for these emergent structures is relevant to a number of physical and biomedical applications. Here, we study the formation of density shock waves in the context of an idealized model of microswimmers confined in a narrow channel and subject to a uniform external flow. Interestingly, these density shock waves exhibit a transition from "subsonic" with compression at the back to "supersonic" with compression at the front of the population as the intensity of the external flow increases. This behavior is the result of a nontrivial interplay between hydrodynamic interactions and geometric confinement, and it is confirmed by a novel quasilinear wave model that properly captures the dependence of the shock formation on the external flow. These findings can be used to guide the development of novel mechanisms for controlling the emergent density distribution and the average population speed, with potentially profound implications on various processes in industry and biotechnology, such as the transport and sorting of cells in flow channels.

Analysis of population structure and genetic history of cattle breeds based on high-density SNP data

USDA-ARS?s Scientific Manuscript database

Advances in single nucleotide polymorphism (SNP) genotyping microarrays have facilitated a new understanding of population structure and evolutionary history for several species. Most existing studies in livestock were based on low density SNP arrays. The first wave of low density SNP studies on cat...

Equatorial waves in the stratosphere of Uranus

NASA Technical Reports Server (NTRS)

Hinson, David P.; Magalhaes, Julio A.

1991-01-01

Analyses of radio occultation data from Voyager 2 have led to the discovery and characterization of an equatorial wave in the Uranus stratosphere. The observed quasi-periodic vertical atmospheric density variations are in close agreement with theoretical predictions for a wave that propagates vertically through the observed background structure of the stratosphere. Quantitative comparisons between measurements obtained at immersion and at emersion yielded constraints on the meridional and zonal structure of the wave; the fact that the two sets of measurements are correlated suggests a wave of planetary scale. Two equatorial wave models are proposed for the wave.

STRONG EVIDENCE FOR THE DENSITY-WAVE THEORY OF SPIRAL STRUCTURE IN DISK GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pour-Imani, Hamed; Kennefick, Daniel; Kennefick, Julia

2016-08-10

The density-wave theory of galactic spiral-arm structure makes a striking prediction that the pitch angle of spiral arms should vary with the wavelength of the galaxy’s image. The reason is that stars are born in the density wave but move out of it as they age. They move ahead of the density wave inside the co-rotation radius, and fall behind outside of it, resulting in a tighter pitch angle at wavelengths that image stars (optical and near-infrared) than those that are associated with star formation (far-infrared and ultraviolet). In this study we combined large sample size with wide range ofmore » wavelengths, from the ultraviolet to the infrared to investigate this issue. For each galaxy we used an optical wavelength image ( B -band: 445 nm) and images from the Spitzer Space Telescope at two infrared wavelengths (infrared: 3.6 and 8.0 μ m) and we measured the pitch angle with the 2DFFT and Spirality codes. We find that the B -band and 3.6 μ m images have smaller pitch angles than the infrared 8.0 μ m image in all cases, in agreement with the prediction of density-wave theory. We also used images in the ultraviolet from Galaxy Evolution Explorer , whose pitch angles agreed with the measurements made at 8 μ m.« less

Gravity wave and tidal structures between 60 and 140 km inferred from space shuttle reentry data

NASA Technical Reports Server (NTRS)

Fritts, David C.; Wang, Ding-Yi; Blanchard, Robert C.

1993-01-01

This study presents an analysis of density measurements made using high-resolution accelerometers aboard several space shuttles at altitudes from 60 to 140 km during reentry into the earth's atmosphere. The observed density fluctuations are interpreted in terms of gravity waves and tides and provide evidence of the importance of such motions well into the thermosphere. Height profiles of fractional density variance reveal that wave amplitudes increase at a rate consistent with observations at lower levels up to about 90 km. The rate of amplitude growth decreases at greater heights, however, and appears to cease above about 110 km. Wave amplitudes are nevertheless large at these heights and suggest that gravity waves may play an important role in forcing of the lower thermosphere.

Filamentation of plasma in the auroral region by an ion-ion instability: A process for the formation of bidimensional potential structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mottez, F.; Chanteur, G.; Roux, A.

1992-07-01

A two-dimensional, explicit, electrostatic particle code is used to investigate the nonlinear behavior of electrostatic ion waves generated by an ion beam flowing through a thermal ion and electron background in a strongly magnetized plasma ({omega}{sub ce} {much gt} {omega}{sub pe} where {omega}{sub ce} and {omega}{sub pe} are the electron gyrofrequency and the plasma frequency). To follow the nonlinear evolution of these ions waves, a long-lasting simulation is run with a large simulation grid: 128 {times} 512{lambda}{sub d}. Beam ions are shown to generate oblique waves. The nonlinear beatings between these oblique waves produce purely transverse waves, which leads tomore » a strong modulation of the density and of the electric potential in a direction transverse to the magnetic field. The transverse scale of these essentially field-aligned filaments is L{sub {perpendicular}} = 10 {rho}{sub i} where {rho}{sub i} is the ion Larmor radius of beam ions. Within these filaments, relatively stable field-aligned density and potential structures develop. The typical size, along the magnetic field, of these structures is L{sub {parallel}} = 10 {lambda}{sub d}, the density is modulated by 30%, and the electric potential is as large as T{sub e} within these structures. Unlike the potential structures that develop in a two-component plasma with downgoing electrons, these structures move upward. These characteristics are in good agreement with the weak double layers recently detected by Viking.« less

The Mass of Saturn's B ring from hidden density waves

NASA Astrophysics Data System (ADS)

Hedman, M. M.; Nicholson, P. D.

2015-12-01

The B ring is Saturn's brightest and most opaque ring, but many of its fundamental parameters, including its total mass, are not well constrained. Elsewhere in the rings, the best mass density estimates come from spiral waves driven by mean-motion resonances with Saturn's various moons, but such waves have been hard to find in the B ring. We have developed a new wavelet-based technique, for combining data from multiple stellar occultations that allows us to isolate the density wave signals from other ring structures. This method has been applied to 5 density waves using 17 occultations of the star gamma Crucis observed by the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft. Two of these waves (generated by the Janus 2:1 and Mimas 5:2 Inner Lindblad Resonances) are visible in individual occultation profiles, but the other three wave signatures ( associated with the Janus 3:2, Enceladus 3:1 and Pandora 3:2 Inner Lindblad Resonances ) are not visible in individual profiles and can only be detected in the combined dataset. Estimates of the ring's surface mass density derived from these five waves fall between 40 and 140 g/cm^2. Surprisingly, these mass density estimates show no obvious correlation with the ring's optical depth. Furthermore, these data indicate that the total mass of the B ring is probably between one-third and two-thirds the mass of Saturn's moon Mimas.

Nonlinear lower hybrid structures in auroral plasmas: comparison of theory with observations

NASA Astrophysics Data System (ADS)

Robinson, P. A.

1999-01-01

Intense, localized lower hybrid wave structures are widely observed in auroral plasmas, often associated with density depletions. Commonly it is concluded without further analysis that these structures are solitons, collapsing wave packets, or other nonlinear entities. Such conclusions are often not justified on theoretical grounds. This review outlines theoretical constraints on field intensity, wave-packet scale length, timescales, and levels of density perturbations that must be met before nonlinear phenomena such as wave collapse and strong turbulence can occur. These criteria are determined within the framework of the modern nucleation scenario for the maintenance of strong turbulence, which involves collapse and dissipation (burnout) of each wave packet, followed by relaxation of its associated density perturbation, then renucleation of further energy into fields trapped in this relaxing perturbation, often leading to further collapse. The criteria are illustrated by applying them to a range of in situ auroral data that have been commonly interpreted in terms of lower hybrid solitons. It will be shown that the data are consistent with some of these criteria, but violate others if packets are all assumed to be observed in the collapse phase. However, theory and observations are consistent within the full nucleation scenario in which packets spend most of their time in the relaxation and renucleation phases, rather than undergoing collapse or burnout.

Wave Propagation Around Coronal Structures: Stratification, Buoyancy, Small Scale Formation

NASA Astrophysics Data System (ADS)

Tomlinson, S. M.; Rappazzo, F.; Velli, M.

2017-12-01

We study the propagation of waves in a coronal medium characterized by stratification and structure in density. temperature and magnetic field. It is well known that average gradients affect the propagation of Alfvén and other MHD waves via reflection, phase mixing, resonant absorption and other coupling phenomena. Here we discuss how the interplay of propagation on inhomogeneous, stratified structures with nonlinear interactions may lead to interesting effects including preferential heating, buoyancy, and plasma acceleration.

Accurately predicting the structure, density, and hydrostatic compression of crystalline β-1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane based on its wave-function-based potential

NASA Astrophysics Data System (ADS)

Song, H.-J.; Huang, F.

2011-09-01

A wave-function-based intermolecular potential of the β phase 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) molecule has been constructed from first principles using the Williams-Stone-Misquitta method and the symmetry-adapted perturbation theory. Using the potential and its derivatives, we have accurately predicted not only the structure and lattice energy of the crystalline β-HMX at 0 K, but also its densities at temperatures of 0-403 K within an accuracy of 1% of density. The calculated densities at pressures within 0-6 GPa excellently agree with the results from the experiments on hydrostatic compression.

Formation of large-scale structures with sharp density gradient through Rayleigh-Taylor growth in a two-dimensional slab under the two-fluid and finite Larmor radius effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goto, R.; Hatori, T.; Miura, H., E-mail: miura.hideaki@nifs.ac.jp

Two-fluid and the finite Larmor effects on linear and nonlinear growth of the Rayleigh-Taylor instability in a two-dimensional slab are studied numerically with special attention to high-wave-number dynamics and nonlinear structure formation at a low β-value. The two effects stabilize the unstable high wave number modes for a certain range of the β-value. In nonlinear simulations, the absence of the high wave number modes in the linear stage leads to the formation of the density field structure much larger than that in the single-fluid magnetohydrodynamic simulation, together with a sharp density gradient as well as a large velocity difference. Themore » formation of the sharp velocity difference leads to a subsequent Kelvin-Helmholtz-type instability only when both the two-fluid and finite Larmor radius terms are incorporated, whereas it is not observed otherwise. It is shown that the emergence of the secondary instability can modify the outline of the turbulent structures associated with the primary Rayleigh-Taylor instability.« less

Gravity Wave Seeding of Equatorial Plasma Bubbles

NASA Technical Reports Server (NTRS)

Singh, Sardul; Johnson, F. S.; Power, R. A.

1997-01-01

Some examples from the Atmosphere Explorer E data showing plasma bubble development from wavy ion density structures in the bottomside F layer are described. The wavy structures mostly had east-west wavelengths of 150-800 km, in one example it was about 3000 km. The ionization troughs in the wavy structures later broke up into either a multiple-bubble patch or a single bubble, depending upon whether, in the precursor wavy structure, shorter wavelengths were superimposed on the larger scale wavelengths. In the multiple bubble patches, intrabubble spacings vaned from 55 km to 140 km. In a fully developed equatorial spread F case, east-west wavelengths from 690 km down to about 0.5 km were present simultaneously. The spacings between bubble patches or between bubbles in a patch appear to be determined by the wavelengths present in the precursor wave structure. In some cases, deeper bubbles developed on the western edge of a bubble patch, suggesting an east-west asymmetry. Simultaneous horizontal neutral wind measurements showed wavelike perturbations that were closely associated with perturbations in the plasma horizontal drift velocity. We argue that the wave structures observed here that served as the initial seed ion density perturbations were caused by gravity waves, strengthening the view that gravity waves seed equatorial spread F irregularities.

Sensitivity of Rogue Waves Predictions to the Oceanic Stratification

NASA Astrophysics Data System (ADS)

Guo, Qiuchen; Alam, Mohammad-Reza

2014-11-01

Oceanic rogue waves are short-lived very large amplitude waves (a giant crest typically followed or preceded by a deep trough) that appear and disappear suddenly in the ocean causing damages to ships and offshore structures. Assuming that the state of the ocean at the present time is perfectly known, then the upcoming rogue waves can be predicted via numerically solving the equations that govern the evolution of the waves. The state of the art radar technology can now provide accurate wave height measurement over large spatial domains and when combined with advanced wave-field reconstruction techniques together render deterministic details of the current state of the ocean (i.e. surface elevation and velocity field) at any given moment of the time with a very high accuracy. The ocean water density is, however, stratified (mainly due to the salinity and temperature differences). This density stratification, with today's technology, is very difficult to be measured accurately. As a result in most predictive schemes these density variations are neglected. While the overall effect of the stratification on the average state of the ocean may not be significant, here we show that these density variations can strongly affect the prediction of oceanic rogue waves. Specifically, we consider a broadband oceanic spectrum in a two-layer density stratified fluid, and study via extensive statistical analysis the effects of strength of the stratification (difference between densities) and the depth of the thermocline on the prediction of upcoming rogue waves.

Fine structure of transient waves in a random medium: The correlation and spectral density functions

NASA Technical Reports Server (NTRS)

Wenzel, Alan R.

1994-01-01

This is essentially a progress report on a theoretical investigation of the propagation of transient waves in a random medium. The emphasis in this study is on applications to sonic-boom propagation, particularly as regards the effect of atmospheric turbulence on the sonic-boom waveform. The analysis is general, however, and is applicable to other types of waves besides sonic-boom waves. The phenomenon of primary concern in this investigation is the fine structure of the wave. A figure is used to illustrate what is meant by finestructure.

Analysis of band structure, transmission properties, and dispersion behavior of THz wave in one-dimensional parabolic plasma photonic crystal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Askari, Nasim; Eslami, Esmaeil, E-mail: eeslami@iust.ac.ir; Mirzaie, Reza

2015-11-15

The photonic band gap of obliquely incident terahertz electromagnetic waves in a one-dimensional plasma photonic crystal is studied. The periodic structure consists of lossless dielectric and inhomogeneous plasma with a parabolic density profile. The dispersion relation and the THz wave transmittance are analyzed based on the electromagnetic equations and transfer matrix method. The dependence of effective plasma frequency and photonic band gap characteristics on dielectric and plasma thickness, plasma density, and incident angle are discussed in detail. A theoretical calculation for effective plasma frequency is presented and compared with numerical results. Results of these two methods are in good agreement.

Cassini RSS occultation observations of density waves in Saturn's rings

NASA Astrophysics Data System (ADS)

McGhee, C. A.; French, R. G.; Marouf, E. A.; Rappaport, N. J.; Schinder, P. J.; Anabtawi, A.; Asmar, S.; Barbinis, E.; Fleischman, D.; Goltz, G.; Johnston, D.; Rochblatt, D.

2005-08-01

On May 3, 2005, the first of a series of eight nearly diametric occultations by Saturn's rings and atmosphere took place, observed by the Cassini Radio Science (RSS) team. Simultaneous high SNR measurements at the Deep Space Network (DSN) at S, X, and Ka bands (λ = 13, 3.6, and 0.9 cm) have provided a remarkably detailed look at the radial structure and particle scattering behavior of the rings. By virtue of the relatively large ring opening angle (B=-23.6o), the slant path optical depth of the rings was much lower than during the Voyager epoch (B=5.9o), making it possible to detect many density waves and other ring features in the Cassini RSS data that were lost in the noise in the Voyager RSS experiment. Ultimately, diffraction correction of the ring optical depth profiles will yield radial resolution as small as tens of meters for the highest SNR data. At Ka band, the Fresnel scale is only 1--1.5 km, and thus even without diffraction correction, the ring profiles show a stunning array of density waves. The A ring is replete with dozens of Pandora and Prometheus inner Lindblad resonance features, and the Janus 2:1 density wave in the B ring is revealed with exceptional clarity for the first time at radio wavelengths. Weaker waves are abundant as well, and multiple occultation chords sample a variety of wave phases. We estimate the surface mass density of the rings from linear density wave models of the weaker waves. For stronger waves, non-linear models are required, providing more accurate estimates of the wave dispersion relation, the ring surface mass density, and the angular momentum exchange between the rings and satellite. We thank the DSN staff for their superb support of these complex observations.

Pseudopotential plane-wave calculation of the structural properties of yttrium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Y.; Chou, M.Y.

1991-11-01

The structural properties of hexagonal-close-packed yttrium are studied by using the plane-wave basis within the pseudopotential method and local-density-functional approximation. By employing a soft'' pseudopotential proposed by Troullier and Martins, satisfactory convergence is achieved with a plane-wave energy cutoff of 30--40 Ry for this early-transition-metal element. The overall results for the structural properties are in good agreement with experiment. It is found that the charge overlap between core and valence electrons has a substantial effect on the accuracy of the calculated structural properties. Two different calculations are performed with and without the outer-core 4{ital p} orbital included as a valencemore » state. In addition, as found in some other local-density calculations, the uncertainty in the results due to different exchange-correlation energy functionals may not be negligible in transition metals.« less

Linear and Nonlinear Coupling of Electrostatic Drift and Acoustic Perturbations in a Nonuniform Bi-Ion Plasma with Non-Maxwellian Electrons

NASA Astrophysics Data System (ADS)

Ali, Gul-e.; Ahmad, Ali; Masood, W.; Mirza, Arshad M.

2017-12-01

Linear and nonlinear coupling of drift and ion acoustic waves are studied in a nonuniform magnetized plasma comprising of Oxygen and Hydrogen ions with nonthermal distribution of electrons. It has been observed that different ratios of ion number densities and kappa and Cairns distributed electrons significantly modify the linear dispersion characteristics of coupled drift-ion acoustic waves. In the nonlinear regime, KdV (for pure drift waves) and KP (for coupled drift-ion acoustic waves) like equations have been derived to study the nonlinear evolution of drift solitary waves in one and two dimensions. The dependence of drift solitary structures on different ratios of ion number densities and nonthermal distribution of electrons has also been explored in detail. It has been found that the ratio of the diamagnetic drift velocity to the velocity of the nonlinear structure determines the existence regimes for the drift solitary waves. The present investigation may be beneficial to understand the formation of solitons in the ionospheric F-region.

CRUST 5.1: A global crustal model at 5° x 5°

USGS Publications Warehouse

Mooney, Walter D.; Laske, Gabi; Masters, T. Guy

1998-01-01

We present a new global model for the Earth's crust based on seismic refraction data published in the period 1948–1995 and a detailed compilation of ice and sediment thickness. An extensive compilation of seismic refraction measurements has been used to determine the crustal structure on continents and their margins. Oceanic crust is modeled with both a standard model for normal oceanic crust, and variants for nonstandard regions, such as oceanic plateaus. Our model (CRUST 5.1) consists of 2592 5° × 5° tiles in which the crust and uppermost mantle are described by eight layers: (1) ice, (2) water, (3) soft sediments, (4) hard sediments, (5) crystalline upper, (6) middle, (7) lower crust, and (8) uppermost mantle. Topography and bathymetry are adopted from a standard database (ETOPO-5). Compressional wave velocity in each layer is based on field measurements, and shear wave velocity and density are estimated using recently published empirical Vp- Vs and Vp-density relationships. The crustal model differs from previous models in that (1) the thickness and seismic/density structure of sedimentary basins is accounted for more completely, (2) the velocity structure of unmeasured regions is estimated using statistical averages that are based on a significantly larger database of crustal structure, (3) the compressional wave, shear wave, and density structure have been explicitly specified using newly available constraints from field and laboratory studies. Thus this global crustal model is based on substantially more data than previous models and differs from them in many important respects. A new map of the thickness of the Earth's crust is presented, and we illustrate the application of this model by using it to provide the crustal correction for surface wave phase velocity maps. Love waves at 40 s are dominantly sensitive to crustal structure, and there is a very close correspondence between observed phase velocities at this period and those predicted by CRUST 5.1. We find that the application of crustal corrections to long-period (167 s) Rayleigh waves significantly increases the variance in the phase velocity maps and strengthens the upper mantle velocity anomalies beneath stable continental regions. A simple calculation of crustal isostacy indicates significant lateral variations in upper mantle density. The model CRUST 5.1 provides a complete description of the physical properties of the Earth's crust at a scale of 5° × 5° and can be used for a wide range of seismological and nonseismological problems.

Nanoscale measurement of Nernst effect in two-dimensional charge density wave material 1T-TaS 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Stephen M.; Luican-Mayer, Adina; Bhattacharya, Anand

Advances in nanoscale material characterization on two-dimensional van der Waals layered materials primarily involve their optical and electronic properties. The thermal properties of these materials are harder to access due to the difficulty of thermal measurements at the nanoscale. In this work, we create a nanoscale magnetothermal device platform to access the basic out-of-plane magnetothermal transport properties of ultrathin van der Waals materials. Specifically, the Nernst effect in the charge density wave transition metal dichalcogenide 1T-TaS 2 is examined on nano-thin flakes in a patterned device structure. It is revealed that near the commensurate charge density wave (CCDW) to nearlymore » commensurate charge density wave (NCCDW) phase transition, the polarity of the Nernst effect changes. Since the Nernst effect is especially sensitive to changes in the Fermi surface, this suggests that large changes are occurring in the out-of-plane electronic structure of 1T-TaS 2, which are otherwise unresolved in just in-plane electronic transport measurements. This may signal a coherent evolution of out-of-plane stacking in the CCDW! NCCDW transition.« less

Charge density wave order in 1D mirror twin boundaries of single-layer MoSe 2

DOE PAGES

Barja, Sara; Wickenburg, Sebastian; Liu, Zhen-Fei; ...

2016-04-18

Here, We provide direct evidence for the existence of isolated, one-dimensional charge density waves at mirror twin boundaries (MTBs) of single-layer semiconducting MoSe 2. Such MTBs have been previously observed by transmission electron microscopy and have been predicted to be metallic in MoSe 2 and MoS 2. Our low-temperature scanning tunnelling microscopy/spectroscopy measurements revealed a substantial bandgap of 100 meV opening at the Fermi energy in the otherwise metallic one-dimensional structures. We found a periodic modulation in the density of states along the MTB, with a wavelength of approximately three lattice constants. In addition to mapping the energy-dependent densitymore » of states, we determined the atomic structure and bonding of the MTB through simultaneous high-resolution non-contact atomic force microscopy. Density functional theory calculations based on the observed structure reproduced both the gap opening and the spatially resolved density of states.« less

Field-induced spin-density wave beyond hidden order in URu2Si2

NASA Astrophysics Data System (ADS)

Knafo, W.; Duc, F.; Bourdarot, F.; Kuwahara, K.; Nojiri, H.; Aoki, D.; Billette, J.; Frings, P.; Tonon, X.; Lelièvre-Berna, E.; Flouquet, J.; Regnault, L.-P.

2016-10-01

URu2Si2 is one of the most enigmatic strongly correlated electron systems and offers a fertile testing ground for new concepts in condensed matter science. In spite of >30 years of intense research, no consensus on the order parameter of its low-temperature hidden-order phase exists. A strong magnetic field transforms the hidden order into magnetically ordered phases, whose order parameter has also been defying experimental observation. Here, thanks to neutron diffraction under pulsed magnetic fields up to 40 T, we identify the field-induced phases of URu2Si2 as a spin-density-wave state. The transition to the spin-density wave represents a unique touchstone for understanding the hidden-order phase. An intimate relationship between this magnetic structure, the magnetic fluctuations and the Fermi surface is emphasized, calling for dedicated band-structure calculations.

A model for the Lin-Shu type density-wave structure of our Galaxy: Line-of-sight and transverse-longitudinal velocities of 242 optically visible open clusters

NASA Astrophysics Data System (ADS)

Griv, E.; Jiang, I.-G.

2015-02-01

In this paper, the fourth in a series, we examine again one of the implications of the Lin-Shu density-wave theory, specifically, the noncircular systematic motion of the Galactic objects. Our previous investigation is extended by analyzing simultaneously both the line-of-sight and transversal velocities of a sample of open clusters for which velocities, distances and ages are available. The ordinary equations of the Oort-Lindblad theory of galactic differential rotation are used. The minor effects caused by the two-dimensional tightly-wound density waves are also taken into account. The published data of 242 currently known optically visible clusters having distances r<3 kpc from the Sun and -200 < z <200 pc from the Galactic plane, and ages 2 × 108 < t < 2 × 109 yr are collected from Dias et al. (2014), excluding extremely far, high-velocity, young and old objects in our fitting. The most noteworthy result is the fact that the parameters of Lin-Shu type density waves estimated from two independent line-of-sight and transversal along the Galactic longitude velocities are nearly equal. We argue that the resemblance of these Galactic wave structures is so remarkable that no doubt is felt as to the theory's truth with respect to these data. The results obtained allow us to conclude that several low-m trailing density-wave patterns with different number of spiral arms m (say, m=1, 2, 3, and 4), pitch angles (about 5o, 8o, 11o, and 14o, respectively) and amplitudes of the perturbed gravitational potential may coexist in the Galaxy. The latter suggests the asymmetric multiarm, not well-organized (``flocculent'') spiral structure of the system. In memory of Professors Alexei M. Fridman (1940-2010) and Chi Yuan (1937-2008)

Suspended liquid particle disturbance on laser-induced blast wave and low density distribution

NASA Astrophysics Data System (ADS)

Ukai, Takahiro; Zare-Behtash, Hossein; Kontis, Konstantinos

2017-12-01

The impurity effect of suspended liquid particles on the laser-induced gas breakdown was experimentally investigated in quiescent gas. The focus of this study is the investigation of the influence of the impurities on the shock wave structure as well as the low density distribution. A 532 nm Nd:YAG laser beam with an 188 mJ/pulse was focused on the chamber filled with suspended liquid particles 0.9 ± 0.63 μm in diameter. Several shock waves are generated by multiple gas breakdowns along the beam path in the breakdown with particles. Four types of shock wave structures can be observed: (1) the dual blast waves with a similar shock radius, (2) the dual blast waves with a large shock radius at the lower breakdown, (3) the dual blast waves with a large shock radius at the upper breakdown, and (4) the triple blast waves. The independent blast waves interact with each other and enhance the shock strength behind the shock front in the lateral direction. The triple blast waves lead to the strongest shock wave in all cases. The shock wave front that propagates toward the opposite laser focal spot impinges on one another, and thereafter a transmitted shock wave (TSW) appears. The TSW interacts with the low density core called a kernel; the kernel then longitudinally expands quickly due to a Richtmyer-Meshkov-like instability. The laser-particle interaction causes an increase in the kernel volume which is approximately five times as large as that in the gas breakdown without particles. In addition, the laser-particle interaction can improve the laser energy efficiency.

Self-organizing Large-scale Structures in Earth's Foreshock Waves

NASA Astrophysics Data System (ADS)

Ganse, U.; Pfau-Kempf, Y.; Turc, L.; Hoilijoki, S.; von Alfthan, S.; Vainio, R. O.; Palmroth, M.

2017-12-01

Earth's foreshock is populated by plasma waves in the ULF regime, assumed to be caused by wave instabilities of shock-reflected particle beams. While in-situ observation of these waves has provided plentiful data of their amplitudes, frequencies, obliquities and relation to local plasma conditions, global-scale structures are hard to grasp from observation data alone. The hybrid-Vlasov simulation system Vlasiator, designed for kinetic modeling of the Earth's magnetosphere, has been employed to study foreshock formation under radial and near-radial IMF conditions on global scales. Structures arising in the foreshock can be comprehensively studied and directly compared to observation results. Our modeling results show that foreshock waves present emergent large-scale structures, in which regions of waves with similar phase exist. At the interfaces of these regions ("spines") we observe high wave obliquity, higher beam densities and lower beam velocities than inside them. We characterize these apparently self-organizing structures through the interplay between wave- and beam properties and present the microphysical mechanisms involved in their creation.

Investigating gravity waves evidences in the Venus upper atmosphere

NASA Astrophysics Data System (ADS)

Migliorini, Alessandra; Altieri, Francesca; Shakun, Alexey; Zasova, Ludmila; Piccioni, Giuseppe; Bellucci, Giancarlo; Grassi, Davide

2014-05-01

We present a method to investigate gravity waves properties in the upper mesosphere of Venus, through the O2 nightglow observations acquired with the imaging spectrometer VIRTIS on board Venus Express. Gravity waves are important dynamical features that transport energy and momentum. They are related to the buoyancy force, which lifts air particles. Then, the vertical displacement of air particles produces density changes that cause gravity to act as restoring force. Gravity waves can manifest through fluctuations on temperature and density fields, and hence on airglow intensities. We use the O2 nightglow profiles showing double peaked structures to study the influence of gravity waves in shaping the O2 vertical profiles and infer the waves properties. In analogy to the Earth's and Mars cases, we use a well-known theory to model the O2 nightglow emissions affected by gravity waves propagation. Here we propose a statistical discussion of the gravity waves characteristics, namely vertical wavelength and wave amplitude, with respect to local time and latitude. The method is applied to about 30 profiles showing double peaked structures, and acquired with the VIRTIS/Venus Express spectrometer, during the mission period from 2006-07-05 to 2008-08-15.

Wavenumber-4 structures observed in the low-latitude ionosphere during low and high solar activity periods using FORMOSAT/COSMIC observations

NASA Astrophysics Data System (ADS)

Onohara, Amelia Naomi; Staciarini Batista, Inez; Prado Batista, Paulo

2018-03-01

The main purpose of this study is to investigate the four-peak structure observed in the low-latitude equatorial ionosphere by the FORMOSAT/COSMIC satellites. Longitudinal distributions of NmF2 (the density of the F layer peak) and hmF2 (ionospheric F2-layer peak height) averages, obtained around September equinox periods from 2007 to 2015, were submitted to a bi-spectral Fourier analysis in order to obtain the amplitudes and phases of the main waves. The four-peak structure in the equatorial and low-latitude ionosphere was present in both low and high solar activity periods. This kind of structure possibly has tropospheric origins related to the tidal waves propagating from below that modulate the E-region dynamo, mainly the eastward non-migrating diurnal tide with wavenumber 3 (DE3, E for eastward). This wave when combined with the migrating diurnal tide (DW1, W for westward) presents a wavenumber-4 (wave-4) structure under a synoptic view. Electron densities observed during 2008 and 2013 September equinoxes revealed that the wave-4 structures became more prominent around or above the F-region altitude peak (˜ 300-350 km). The four-peak structure remains up to higher ionosphere altitudes (˜ 800 km). Spectral analysis showed DE3 and SPW4 (stationary planetary wave with wavenumber 4) signatures at these altitudes. We found that a combination of DE3 and SPW4 with migrating tides is able to reproduce the wave-4 pattern in most of the ionospheric parameters. For the first time a study using wave variations in ionospheric observations for different altitude intervals and solar cycle was done. The conclusion is that the wave-4 structure observed at high altitudes in ionosphere is related to effects of the E-region dynamo combined with transport effects in the F region.

Dynamic response of some tentative compliant wall structures to convected turbulence fields

NASA Technical Reports Server (NTRS)

Nijim, H. H.; Lin, Y. K.

1977-01-01

Some tentative compliant wall structures designed for possible skin friction drag reduction are investigated. Among the structural models considered is a ribbed membrane backed by polyurethane or PVS plastisol. This model is simplified as a beam placed on a viscoelastic foundation as well as on a set of evenly spaced supports. The total length of the beam may be either finite or infinite, and the supports may be either rigid or elastic. Another structural model considered is a membrane mounted over a series of pretensioned wires, also evenly spaced, and the entire membrane is backed by an air cavity. The forcing pressure field is idealized as a frozen random pattern convected downstream at a characteristic velocity. The results are given in terms of the frequency response functions of the system, the spectral density of the structural motion, and the spectral density of the boundary layer pressure including the effect of structural motion. These results are used in a parametric study of structural configurations capable of generating favorable wave lengths, wave amplitudes, and wave speeds in the structural motion for potential drag reduction.

Gravity dual of spin and charge density waves

NASA Astrophysics Data System (ADS)

Jokela, Niko; Järvinen, Matti; Lippert, Matthew

2014-12-01

At high enough charge density, the homogeneous state of the D3-D7' model is unstable to fluctuations at nonzero momentum. We investigate the end point of this instability, finding a spatially modulated ground state, which is a charge and spin density wave. We analyze the phase structure of the model as a function of chemical potential and magnetic field and find the phase transition from the homogeneous state to be first order, with a second-order critical point at zero magnetic field.

A New Comprehensive Model for Crustal and Upper Mantle Structure of the European Plate

NASA Astrophysics Data System (ADS)

Morelli, A.; Danecek, P.; Molinari, I.; Postpischl, L.; Schivardi, R.; Serretti, P.; Tondi, M. R.

2009-12-01

We present a new comprehensive model of crustal and upper mantle structure of the whole European Plate — from the North Atlantic ridge to Urals, and from North Africa to the North Pole — describing seismic speeds (P and S) and density. Our description of crustal structure merges information from previous studies: large-scale compilations, seismic prospection, receiver functions, inversion of surface wave dispersion measurements and Green functions from noise correlation. We use a simple description of crustal structure, with laterally-varying sediment and cristalline layers thickness and seismic parameters. Most original information refers to P-wave speed, from which we derive S speed and density from scaling relations. This a priori crustal model by itself improves the overall fit to observed Bouguer anomaly maps, as derived from GRACE satellite data, over CRUST2.0. The new crustal model is then used as a constraint in the inversion for mantle shear wave speed, based on fitting Love and Rayleigh surface wave dispersion. In the inversion for transversely isotropic mantle structure, we use group speed measurements made on European event-to-station paths, and use a global a priori model (S20RTS) to ensure fair rendition of earth structure at depth and in border areas with little coverage from our data. The new mantle model sensibly improves over global S models in the imaging of shallow asthenospheric (slow) anomalies beneath the Alpine mobile belt, and fast lithospheric signatures under the two main Mediterranean subduction systems (Aegean and Tyrrhenian). We map compressional wave speed inverting ISC travel times (reprocessed by Engdahl et al.) with a non linear inversion scheme making use of finite-difference travel time calculation. The inversion is based on an a priori model obtained by scaling the 3D mantle S-wave speed to P. The new model substantially confirms images of descending lithospheric slabs and back-arc shallow asthenospheric regions, shown in other more local high-resolution tomographic studies, but covers the whole range of the European Plate. We also obtain three-dimensional mantle density structure by inversion of GRACE Bouguer anomalies locally adjusting density and the scaling relation between seismic wave speeds and density. We validate the new comprehensive model through comparison of recorded seismograms with numerical simulations based on SPECFEM3D. This work is a contribution towards the definition of a reference earth model for Europe. To this extent, in order to improve model dissemination and comparison, we propose the adoption of a common exchange format for tomographic earth models based on JSON, a lightweight data-interchange format supported by most high-level programming languages. We provide tools for manipulating and visualising models, described in this standard format, in Google Earth and GEON IDV.

The response of plasma density to breaking inertial gravity wave in the lower regions of ionosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, Wenbo, E-mail: Wenbo.Tang@asu.edu; Mahalov, Alex, E-mail: Alex.Mahalov@asu.edu

2014-04-15

We present a three-dimensional numerical study for the E and lower F region ionosphere coupled with the neutral atmosphere dynamics. This model is developed based on a previous ionospheric model that examines the transport patterns of plasma density given a prescribed neutral atmospheric flow. Inclusion of neutral dynamics in the model allows us to examine the charge-neutral interactions over the full evolution cycle of an inertial gravity wave when the background flow spins up from rest, saturates and eventually breaks. Using Lagrangian analyses, we show the mixing patterns of the ionospheric responses and the formation of ionospheric layers. The correspondingmore » plasma density in this flow develops complex wave structures and small-scale patches during the gravity wave breaking event.« less

Electron wind in strong wave guide fields

NASA Astrophysics Data System (ADS)

Krienen, F.

1985-03-01

The X-ray activity observed near highly powered waveguide structures is usually caused by local electric discharges originating from discontinuities such as couplers, tuners or bends. In traveling waves electrons move in the direction of the power flow. Seed electrons can multipactor in a traveling wave, the moving charge pattern is different from the multipactor in a resonant structure and is self-extinguishing. The charge density in the wave guide will modify impedance and propagation constant of the wave guide. The radiation level inside the output wave guide of the SLAC, 50 MW, S-band, klystron is estimated. Possible contributions of radiation to window failure are discussed.

Comparative In Situ Measurements of Plasma Instabilities in the Equatorial and Auroral Electrojets

NASA Technical Reports Server (NTRS)

Pfaff, Robert F.

2008-01-01

This presentation provides a comparison of in situ measurements of plasma instabilities gathered by rocket-borne probes in the equatorial and auroral electrojets. Specifically, using detailed measurements of the DC electric fields, current density, and plasma number density within the unstable daytime equatorial electrojet from Brazil (Guara Campaign) and in the auroral electrojet from Sweden (ERRIS Campaign), we present comparative observations and general conclusions regarding the observed physical properties of Farley-Buneman two-stream waves and large scale, gradient drift waves. The two stream observations reveal coherent-like waves propagating near the E x B direction but at reduced speeds (nearer to the presumed acoustic velocity) with wavelengths of approximately 5-10m in both the equatorial and auroral electrojet, as measured using the spaced-receiver technique. The auroral electrojet data generally shows extensions to shorter wavelengths, in concert with the fact that these waves are driven harder. With respect to gradient-drift driven waves, observations of this instability are much more pronounced in the equatorial electrojet, given the more favorable geometry for growth provided by the vertical gradient and horizontal magnetic field lines. We present new analysis of Guara rocket observations of electric field and plasma density data that reveal considerable structuring in the middle and lower portion of the electrojet (90-105 km) where the ambient plasma density gradient is unstable. Although the electric field amplitudes are largest (approximately 10-15 mV/m) in the zonal direction, considerable structure (approximately 5-10 mV/m) is also observed in the vertical electric field component as well, implying that the dominant large scale waves involve significant vertical interaction and coupling within the narrow altitude range where they are observed. Furthermore, a detailed examination of the phase of the waveforms show that on some, but not all occasions, locally enhanced eastward fields are associated with locally enhanced upwards (polarization) electric fields. The measurements are discussed in terms of theories involving the non-linear evolution and structuring of plasma waves.

Effect of dust charging and trapped electrons on nonlinear solitary structures in an inhomogeneous magnetized plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Ravinder; Malik, Hitendra K.; Singh, Khushvant

2012-01-15

Main concerns of the present article are to investigate the effects of dust charging and trapped electrons on the solitary structures evolved in an inhomogeneous magnetized plasma. Such a plasma is found to support two types of waves, namely, fast wave and slow wave. Slow wave propagates in the plasma only when the wave propagation angle {theta} satisfies the condition {theta}{>=}tan{sup -1}{l_brace}({radical}((1+2{sigma})-[(n{sub dlh}({gamma}{sub 1}-1))/(1+n{sub dlh}{gamma}{sub 1})])-v{sub 0}/u{sub 0}){r_brace}, where v{sub 0}(u{sub 0}) is the z- (x-) component of ion drift velocity, {sigma} = T{sub i}/T{sub eff}, n{sub dlh} = n{sub d0}/(n{sub el0} + n{sub eh0}), and {gamma}{sub 1}=-(1/{Phi}{sub i0})[(1-{Phi}{sub i0}/1+{sigma}(1-{Phi}{submore » i0}))] together with T{sub i} as ion temperature, n{sub el0}(n{sub eh0}) as the density of trapped (isothermal) electrons, {Phi}{sub i0} as the dust grain (density n{sub d0}) surface potential relative to zero plasma potential, and T{sub eff}=(n{sub elo}+n{sub eho})T{sub el}T{sub eh}/(n{sub elo}T{sub eh}+n{sub eho}T{sub el}), where T{sub el}(T{sub eh}) is the temperature of trapped (isothermal) electrons. Both the waves evolve in the form of density hill type structures in the plasma, confirming that these solitary structures are compressive in nature. These structures are found to attain higher amplitude when the charge on the dust grains is fluctuated (in comparison with the case of fixed charge) and also when the dust grains and trapped electrons are more in number; the same is the case with higher temperature of ions and electrons. Slow solitary structures show weak dependence on the dust concentration. Both types of structures are found to become narrower under the application of stronger magnetic field. With regard to the charging of dust grains, it is observed that the charge gets reduced for the higher trapped electron density and temperature of ions and electrons, and dust charging shows weak dependence on the ion temperature.« less

The microscopic structure of charge density waves in underdoped YBa 2Cu 3O 6.54 revealed by x-ray diffraction

DOE PAGES

E. M. Forgan; Huecker, M.; Blackburn, E.; ...

2015-12-09

Charge density wave (CDW) order appears throughout the underdoped high-temperature cuprate superconductors, but the underlying symmetry breaking and the origin of the CDW remain unclear. We use X-ray diffraction to determine the microscopic structure of the CDWs in an archetypical cuprate YBa 2Cu 3O 6.54 at its superconducting transition temperature ~60 K. We find that the CDWs in this material break the mirror symmetry of the CuO 2 bilayers. The ionic displacements in the CDWs have two components, which are perpendicular and parallel to the CuO 2 planes, and are out of phase with each other. The planar oxygen atomsmore » have the largest displacements, perpendicular to the CuO 2 planes. Our results allow many electronic properties of the underdoped cuprates to be understood. For example, the CDWs will lead to local variations in the electronic structure, giving an explicit explanation of density-wave states with broken symmetry observed in scanning tunnelling microscopy and soft X-ray measurements.« less

The microscopic structure of charge density waves in underdoped YBa2Cu3O6.54 revealed by X-ray diffraction

NASA Astrophysics Data System (ADS)

Forgan, E. M.; Blackburn, E.; Holmes, A. T.; Briffa, A. K. R.; Chang, J.; Bouchenoire, L.; Brown, S. D.; Liang, Ruixing; Bonn, D.; Hardy, W. N.; Christensen, N. B.; Zimmermann, M. V.; Hücker, M.; Hayden, S. M.

2015-12-01

Charge density wave (CDW) order appears throughout the underdoped high-temperature cuprate superconductors, but the underlying symmetry breaking and the origin of the CDW remain unclear. We use X-ray diffraction to determine the microscopic structure of the CDWs in an archetypical cuprate YBa2Cu3O6.54 at its superconducting transition temperature ~60 K. We find that the CDWs in this material break the mirror symmetry of the CuO2 bilayers. The ionic displacements in the CDWs have two components, which are perpendicular and parallel to the CuO2 planes, and are out of phase with each other. The planar oxygen atoms have the largest displacements, perpendicular to the CuO2 planes. Our results allow many electronic properties of the underdoped cuprates to be understood. For instance, the CDWs will lead to local variations in the electronic structure, giving an explicit explanation of density-wave states with broken symmetry observed in scanning tunnelling microscopy and soft X-ray measurements.

Experimental observation of standing wave effect in low-pressure very-high-frequency capacitive discharges

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Yong-Xin; Gao, Fei; Liu, Jia

2014-07-28

Radial uniformity measurements of plasma density were carried out by using a floating double probe in a cylindrical (21 cm in electrode diameter) capacitive discharge reactor driven over a wide range of frequencies (27–220 MHz). At low rf power, a multiple-node structure of standing wave effect was observed at 130 MHz. The secondary density peak caused by the standing wave effect became pronounced and shifts toward the axis as the driving frequency further to increase, indicative of a much more shortened standing-wave wavelength. With increasing rf power, the secondary density peak shift toward the radial edge, namely, the standing-wave wavelength was increased,more » in good qualitative agreement with the previous theory and simulation results. At higher pressures and high frequencies, the rf power was primarily deposited at the periphery of the electrode, due to the fact that the waves were strongly damped as they propagated from the discharge edge into the center.« less

Quasiparticle interference, quasiparticle interactions, and the origin of the charge density wave in 2 H – NbSe 2

DOE PAGES

Arguello, C. J.; Rosenthal, E. P.; Andrade, E. F.; ...

2015-01-21

We show that a small number of intentionally introduced defects can be used as a spectroscopic tool to amplify quasiparticle interference in 2H-NbSe₂ that we measure by scanning tunneling spectroscopic imaging. We show, from the momentum and energy dependence of the quasiparticle interference, that Fermi surface nesting is inconsequential to charge density wave formation in 2H-NbSe₂. We demonstrate that, by combining quasiparticle interference data with additional knowledge of the quasiparticle band structure from angle resolved photoemission measurements, one can extract the wave vector and energy dependence of the important electronic scattering processes thereby obtaining direct information both about the fermiologymore » and the interactions. In 2H-NbSe₂, we use this combination to confirm that the important near-Fermi-surface electronic physics is dominated by the coupling of the quasiparticles to soft mode phonons at a wave vector different from the charge density wave ordering wave vector.« less

Quasiparticle interference, quasiparticle interactions, and the origin of the charge density wave in 2H-NbSe2.

PubMed

Arguello, C J; Rosenthal, E P; Andrade, E F; Jin, W; Yeh, P C; Zaki, N; Jia, S; Cava, R J; Fernandes, R M; Millis, A J; Valla, T; Osgood, R M; Pasupathy, A N

2015-01-23

We show that a small number of intentionally introduced defects can be used as a spectroscopic tool to amplify quasiparticle interference in 2H-NbSe2 that we measure by scanning tunneling spectroscopic imaging. We show, from the momentum and energy dependence of the quasiparticle interference, that Fermi surface nesting is inconsequential to charge density wave formation in 2H-NbSe2. We demonstrate that, by combining quasiparticle interference data with additional knowledge of the quasiparticle band structure from angle resolved photoemission measurements, one can extract the wave vector and energy dependence of the important electronic scattering processes thereby obtaining direct information both about the fermiology and the interactions. In 2H-NbSe2, we use this combination to confirm that the important near-Fermi-surface electronic physics is dominated by the coupling of the quasiparticles to soft mode phonons at a wave vector different from the charge density wave ordering wave vector.

Determining integral density distribution in the mach reflection of shock waves

NASA Astrophysics Data System (ADS)

Shevchenko, A. M.; Golubev, M. P.; Pavlov, A. A.; Pavlov, Al. A.; Khotyanovsky, D. V.; Shmakov, A. S.

2017-05-01

We present a method for and results of determination of the field of integral density in the structure of flow corresponding to the Mach interaction of shock waves at Mach number M = 3. The optical diagnostics of flow was performed using an interference technique based on self-adjusting Zernike filters (SA-AVT method). Numerical simulations were carried out using the CFS3D program package for solving the Euler and Navier-Stokes equations. Quantitative data on the distribution of integral density on the path of probing radiation in one direction of 3D flow transillumination in the region of Mach interaction of shock waves were obtained for the first time.

Vertical temperature and density patterns in the Arctic mesosphere analyzed as gravity waves

NASA Technical Reports Server (NTRS)

Eberstein, I. J.; Theon, J. S.

1975-01-01

Rocket soundings conducted from high latitude sites in the Arctic mesosphere are described. Temperature and wind profiles and one density profile were observed independently to obtain the thermodynamic structure, the wind structure, and their interdependence in the mesosphere. Temperature profiles from all soundings were averaged, and a smooth curve (or series of smooth curves) drawn through the points. A hydrostatic atmosphere based on the average, measured temperature profile was computed, and deviations from the mean atmosphere were analyzed in terms of gravity wave theory. The vertical wavelengths of the deviations were 10-20 km, and the wave amplitudes slowly increased with height. The experimental data were matched by calculated gravity waves having a period of 15-20 minutes and a horizontal wavelength of 60-80 km. The wind measurements are consistent with the thermodynamic measurements. The results also suggest that gravity waves travel from East to West with a horizontal phase velocity of approximately 60 m sec-1.

Multigap superconductivity in the charge density wave superconductor LaPt2Si2

NASA Astrophysics Data System (ADS)

Das, Debarchan; Gupta, Ritu; Bhattacharyya, A.; Biswas, P. K.; Adroja, D. T.; Hossain, Z.

2018-05-01

The superconducting gap structure of a charge density wave (CDW) superconductor LaPt2Si2 (Tc=1.6 K) having a quasi-two-dimensional crystal structure has been investigated using muon spin rotation/relaxation (μ SR ) measurements in transverse field (TF), zero field (ZF), and longitudinal field (LF) geometries. Rigorous analysis of TF-μ SR spectra in the superconducting state corroborates that the temperature dependence of the effective penetration depth, λL, derived from muon spin depolarization, fits to a two gap s wave model (i.e., s +s wave) suggesting that the Fermi surface contains two gaps of different magnitude rather than an isotropic gap expected for a conventional s wave superconductor. On the other hand, ZF μ SR data do not show any significant change in muon spin relaxation rate above and below the superconducting transition temperature indicating the fact that time-reversal symmetry is preserved in the superconducting state of this material.

Oscillatory interfacial instability between miscible fluids

NASA Astrophysics Data System (ADS)

Shevtsova, Valentina; Gaponenko, Yuri; Mialdun, Aliaksandr; Torregrosa, Marita; Yasnou, Viktar

Interfacial instabilities occurring between two fluids are of fundamental interest in fluid dynamics, biological systems and engineering applications such as liquid storage, solvent extraction, oil recovery and mixing. Horizontal vibrations applied to stratified layers of immiscible liquids may generate spatially periodic waving of the interface, stationary in the reference frame of the vibrated cell, referred to as a "frozen wave". We present experimental evidence that frozen wave instability exists between two ordinary miscible liquids of similar densities and viscosities. At the experiments and at the numerical model, two superimposed layers of ordinary liquids, water-alcohol of different concentrations, are placed in a closed cavity in a gravitationally stable configuration. The density and viscosity of these fluids are somewhat similar. Similar to the immiscible fluids this instability has a threshold. When the value of forcing is increased the amplitudes of perturbations grow continuously displaying a saw-tooth structure. The decrease of gravity drastically changes the structure of frozen waves.

Influence of defects on the charge density wave of ([SnSe] 1+δ) 1(VSe 2) 1 ferecrystals

DOE PAGES

Falmbigl, Matthias; Putzky, Daniel; Ditto, Jeffrey; ...

2015-07-14

A series of ferecrystalline compounds ([SnSe] 1+δ) 1(VSe 2) 1 with varying Sn/V ratios were synthesized using the modulated elemental reactant technique. Temperature-dependent specific heat data reveal a phase transition at 102 K, where the heat capacity changes abruptly. An abrupt increase in electrical resistivity occurs at the same temperature, correlated with an abrupt increase in the Hall coefficient. Combined with the magnitude and nature of the specific heat discontinuity, this suggests that the transition is similar to the charge density wave transitions in transition metal dichalcogenides. An ordered intergrowth was formed over a surprisingly wide compositional range of Sn/Vmore » ratios of 0.89 ≤ 1 + δ ≤ 1.37. X-ray diffraction and transmission electron microscopy reveal the formation of various volume defects in the compounds in response to the nonstoichiometry. The electrical resistivity and Hall coefficient data of samples with different Sn/V ratios show systematic variation in the carrier concentration with the Sn/V ratio. There is no significant change in the onset temperature of the charge density wave transition, only a variation in the carrier densities before and after the transition. Given the sensitivity of the charge density wave transitions of transition metal dichalcogenides to variations in composition, it is very surprising that the charge density wave transition observed at 102 K for ([SnSe] 1.15) 1(VSe 2) 1 is barely influenced by the nonstoichiometry and structural defects. As a result, this might be a consequence of the two-dimensional nature of the structurally independent VSe 2 layers.« less

Ionizing gas breakdown waves in strong electric fields.

NASA Technical Reports Server (NTRS)

Klingbeil, R.; Tidman, D. A.; Fernsler, R. F.

1972-01-01

A previous analysis by Albright and Tidman (1972) of the structure of an ionizing potential wave driven through a dense gas by a strong electric field is extended to include atomic structure details of the background atoms and radiative effects, especially, photoionization. It is found that photoionization plays an important role in avalanche propagation. Velocities, electron densities, and temperatures are presented as a function of electric field for both negative and positive breakdown waves in nitrogen.

Pore-Scale Modeling of Pore Structure Effects on P-Wave Scattering Attenuation in Dry Rocks

PubMed Central

Li, Tianyang; Qiu, Hao; Wang, Feifei

2015-01-01

Underground rocks usually have complex pore system with a variety of pore types and a wide range of pore size. The effects of pore structure on elastic wave attenuation cannot be neglected. We investigated the pore structure effects on P-wave scattering attenuation in dry rocks by pore-scale modeling based on the wave theory and the similarity principle. Our modeling results indicate that pore size, pore shape (such as aspect ratio), and pore density are important factors influencing P-wave scattering attenuation in porous rocks, and can explain the variation of scattering attenuation at the same porosity. From the perspective of scattering attenuation, porous rocks can safely suit to the long wavelength assumption when the ratio of wavelength to pore size is larger than 15. Under the long wavelength condition, the scattering attenuation coefficient increases as a power function as the pore density increases, and it increases exponentially with the increase in aspect ratio. For a certain porosity, rocks with smaller aspect ratio and/or larger pore size have stronger scattering attenuation. When the pore aspect ratio is larger than 0.5, the variation of scattering attenuation at the same porosity is dominantly caused by pore size and almost independent of the pore aspect ratio. These results lay a foundation for pore structure inversion from elastic wave responses in porous rocks. PMID:25961729

Ab Initio study on structural, electronic, magnetic and dielectric properties of LSNO within Density Functional Perturbation Theory

NASA Astrophysics Data System (ADS)

Petersen, John; Bechstedt, Friedhelm; Furthmüller, Jürgen; Scolfaro, Luisa

LSNO (La2-xSrxNiO4) is of great interest due to its colossal dielectric constant (CDC) and rich underlying physics. While being an antiferromagnetic insulator, localized holes are present in the form of stripes in the Ni-O planes which are commensurate with the inverse of the Sr concentration. The stripes are a manifestation of charge density waves with period approximately 1/x and spin density waves with period approximately 2/x. Here, the spin ground state is calculated via LSDA + U with the PAW method implemented in VASP. Crystal structure and the effective Hubbard U parameter are optimized before calculating ɛ∞ within the independent particle approximation. ɛ∞ and the full static dielectric constant (including the lattice polarizability) ɛ0 are calculated within Density Functional Perturbation Theory.

A Note on the Wave Action Density of a Viscous Instability Mode on a Laminar Free-shear Flow

NASA Technical Reports Server (NTRS)

Balsa, Thomas F.

1994-01-01

Using the assumptions of an incompressible and viscous flow at large Reynolds number, we derive the evolution equation for the wave action density of an instability wave traveling on top of a laminar free-shear flow. The instability is considered to be viscous; the purpose of the present work is to include the cumulative effect of the (locally) small viscous correction to the wave, over length and time scales on which the underlying base flow appears inhomogeneous owing to its viscous diffusion. As such, we generalize our previous work for inviscid waves. This generalization appears as an additional (but usually non-negligible) term in the equation for the wave action. The basic structure of the equation remains unaltered.

Orthogonality of embedded wave functions for different states in frozen-density embedding theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zech, Alexander; Wesolowski, Tomasz A.; Aquilante, Francesco

2015-10-28

Other than lowest-energy stationary embedded wave functions obtained in Frozen-Density Embedding Theory (FDET) [T. A. Wesolowski, Phys. Rev. A 77, 012504 (2008)] can be associated with electronic excited states but they can be mutually non-orthogonal. Although this does not violate any physical principles — embedded wave functions are only auxiliary objects used to obtain stationary densities — working with orthogonal functions has many practical advantages. In the present work, we show numerically that excitation energies obtained using conventional FDET calculations (allowing for non-orthogonality) can be obtained using embedded wave functions which are strictly orthogonal. The used method preserves the mathematicalmore » structure of FDET and self-consistency between energy, embedded wave function, and the embedding potential (they are connected through the Euler-Lagrange equations). The orthogonality is built-in through the linearization in the embedded density of the relevant components of the total energy functional. Moreover, we show formally that the differences between the expectation values of the embedded Hamiltonian are equal to the excitation energies, which is the exact result within linearized FDET. Linearized FDET is shown to be a robust approximation for a large class of reference densities.« less

Evidence for a Peierls phase-transition in a three-dimensional multiple charge-density waves solid

PubMed Central

Mansart, Barbara; Cottet, Mathieu J. G.; Penfold, Thomas J.; Dugdale, Stephen B.; Tediosi, Riccardo; Chergui, Majed; Carbone, Fabrizio

2012-01-01

The effect of dimensionality on materials properties has become strikingly evident with the recent discovery of graphene. Charge ordering phenomena can be induced in one dimension by periodic distortions of a material’s crystal structure, termed Peierls ordering transition. Charge-density waves can also be induced in solids by strong coulomb repulsion between carriers, and at the extreme limit, Wigner predicted that crystallization itself can be induced in an electrons gas in free space close to the absolute zero of temperature. Similar phenomena are observed also in higher dimensions, but the microscopic description of the corresponding phase transition is often controversial, and remains an open field of research for fundamental physics. Here, we photoinduce the melting of the charge ordering in a complex three-dimensional solid and monitor the consequent charge redistribution by probing the optical response over a broad spectral range with ultrashort laser pulses. Although the photoinduced electronic temperature far exceeds the critical value, the charge-density wave is preserved until the lattice is sufficiently distorted to induce the phase transition. Combining this result with ab initio electronic structure calculations, we identified the Peierls origin of multiple charge-density waves in a three-dimensional system for the first time. PMID:22451898

Spatial structure of plasma density perturbations, induced in the ionosphere modified by powerful HF radio waves: Review of experimental results

NASA Astrophysics Data System (ADS)

Frolov, Vladimir

2015-06-01

In the review, the results of experimental studies of spatial structure of small-, middle-, and large scale plasma density perturbations induced in the ionosphere by its pumping by powerful HF O-mode (ordinary) radio waves, are analyzed. It is shown that the region with induced plasma density perturbations occupied all ionosphere body from its E-region up to the topside ionosphere in the height and it has the horizontal length of about of 300-500 km. Peculiarities of generation of artificial ionosphere irregularities of different scale-lengths in the magnetic zenith region are stated. Experimental results obtained under conditions of ionosphere periodical pumping when the generation of travel ionosphere disturbances is revealed are also discussed.

Crustal structure of northern Italy from the ellipticity of Rayleigh waves

NASA Astrophysics Data System (ADS)

Berbellini, Andrea; Morelli, Andrea; G. Ferreira, Ana M.

2017-04-01

Northern Italy is a diverse geological region, including the wide and thick Po Plain sedimentary basin, which is bounded by the Alps and the Apennines. The seismically slow shallow structure of the Po Plain is difficult to retrieve with classical seismic measurements such as surface wave dispersion, yet the detailed structure of the region greatly affects seismic wave propagation and hence seismic ground shaking. Here we invert Rayleigh wave ellipticity measurements in the period range 10-60 s for 95 stations in northern Italy using a fully non linear approach to constrain vertical vS,vP and density profiles of the crust beneath each station. The ellipticity of Rayleigh wave ground motion is primarily sensitive to shear-wave velocity beneath the recording station, which reduces along-path contamination effects. We use the 3D layering structure in MAMBo, a previous model based on a compilation of geological and geophysical information for the Po Plain and surrounding regions of northern Italy, and employ ellipticity data to constrain vS,vP and density within its layers. We show that ellipticity data from ballistic teleseismic wave trains alone constrain the crustal structure well. This leads to MAMBo-E, an updated seismic model of the region's crust that inherits information available from previous seismic prospection and geological studies, while fitting new seismic data well. MAMBo-E brings new insights into lateral heterogeneity in the region's subsurface. Compared to MAMBo, it shows overall faster seismic anomalies in the region's Quaternary, Pliocene and Oligo-Miocene layers and better delineates the seismic structures of the Po Plain at depth. Two low velocity regions are mapped in the Mesozoic layer in the western and eastern parts of the Plain, which seem to correspond to the Monferrato sedimentary basin and to the Ferrara-Romagna thrust system, respectively.

Density Effects on Post-shock Turbulence Structure

NASA Astrophysics Data System (ADS)

Tian, Yifeng; Jaberi, Farhad; Livescu, Daniel; Li, Zhaorui; Michigan State University Collaboration; Los Alamos National Laboratory Collaboration; Texas A&M University-Corpus Christi Collaboration

2017-11-01

The effects of density variations due to mixture composition on post-shock turbulence structure are studied using turbulence-resolving shock-capturing simulations. This work extends the canonical Shock-Turbulence Interaction (STI) problem to involve significant variable density effects. The numerical method has been verified using a series of grid and LIA convergence tests, and is used to generate accurate post-shock turbulence data for a detailed flow study. Density effects on post-shock turbulent statistics are shown to be significant, leading to an increased amplification of turbulent kinetic energy (TKE). Eulerian and Lagrangian analyses show that the increase in the post-shock correlation between rotation and strain is weakened in the case with significant density variations (referred to as the ``multi-fluid'' case). Similar to previous single-fluid results and LIA predictions, the shock wave significantly changes the topology of the turbulent structures, exhibiting a symmetrization of the joint PDF of second and third invariant of the deviatoric part of velocity gradient tensor. In the multi-fluid case, this trend is more significant and mainly manifested in the heavy fluid regions. Lagrangian data are also used to study the evolution of turbulence structure away from the shock wave and assess the accuracy of Lagrangian dynamical models.

Spiral density waves in a young protoplanetary disk.

PubMed

Pérez, Laura M; Carpenter, John M; Andrews, Sean M; Ricci, Luca; Isella, Andrea; Linz, Hendrik; Sargent, Anneila I; Wilner, David J; Henning, Thomas; Deller, Adam T; Chandler, Claire J; Dullemond, Cornelis P; Lazio, Joseph; Menten, Karl M; Corder, Stuartt A; Storm, Shaye; Testi, Leonardo; Tazzari, Marco; Kwon, Woojin; Calvet, Nuria; Greaves, Jane S; Harris, Robert J; Mundy, Lee G

2016-09-30

Gravitational forces are expected to excite spiral density waves in protoplanetary disks, disks of gas and dust orbiting young stars. However, previous observations that showed spiral structure were not able to probe disk midplanes, where most of the mass is concentrated and where planet formation takes place. Using the Atacama Large Millimeter/submillimeter Array, we detected a pair of trailing symmetric spiral arms in the protoplanetary disk surrounding the young star Elias 2-27. The arms extend to the disk outer regions and can be traced down to the midplane. These millimeter-wave observations also reveal an emission gap closer to the star than the spiral arms. We argue that the observed spirals trace shocks of spiral density waves in the midplane of this young disk. Copyright © 2016, American Association for the Advancement of Science.

Observation of 1-D time dependent non-propagating laser plasma structures using fluid and PIC codes

NASA Astrophysics Data System (ADS)

Verma, Deepa; Bera, Ratan Kumar; Kumar, Atul; Patel, Bhavesh; Das, Amita

2017-12-01

The manuscript reports the observation of time dependent localized and non-propagating structures in the coupled laser plasma system through 1-D fluid and Particle-In-Cell (PIC) simulations. It is reported that such structures form spontaneously as a result of collision amongst certain exact solitonic solutions. They are seen to survive as coherent entities for a long time up to several hundreds of plasma periods. Furthermore, it is shown that such time dependence can also be artificially recreated by significantly disturbing the delicate balance between the radiation and the density fields required for the exact non-propagating solution obtained by Esirkepov et al., JETP 68(1), 36-41 (1998). The ensuing time evolution is an interesting interplay between kinetic and field energies of the system. The electrostatic plasma oscillations are coupled with oscillations in the electromagnetic field. The inhomogeneity of the background and the relativistic nature, however, invariably produces large amplitude density perturbations leading to its wave breaking. In the fluid simulations, the signature of wave breaking can be discerned by a drop in the total energy which evidently gets lost to the grid. The PIC simulations are observed to closely follow the fluid simulations till the point of wave breaking. However, the total energy in the case of PIC simulations is seen to remain conserved throughout the simulations. At the wave breaking, the particles are observed to acquire thermal kinetic energy in the case of PIC. Interestingly, even after wave breaking, compact coherent structures with trapped radiation inside high-density peaks continue to exist both in PIC and fluid simulations. Although the time evolution does not exactly match in the two simulations as it does prior to the process of wave breaking, the time-dependent features exhibited by the remnant structures are characteristically similar.

Planetary and Gravity Waves in the Mesosphere and Lower Thermosphere

NASA Technical Reports Server (NTRS)

Vincent, R. A.

1985-01-01

Rocket and ground based studies of the mesosphere and lower thermosphere show that waves play an important role in the dynamics of their region. The waves manifest themselves in wind, temperature, density, pressure, ionization and airglow fluctuations in the 80-120 km height range. Rockets have enabled the density and temperature structure to be measured with excellent height resolution, while long term studies of wind motions using MST, partial reflection and meteor radars and, more recently, lidar investigations of temperature and density, have enabled the temporal behaviour of the waves to be better understood. A composite of power spectra is shown of wind motions measured near the mesopause at widely separated locations and illustrates how wave energy is distributed as a function of frequency. The spectra show three distinct parts; (1) a long period section corresponding to periods longer than 24 h; (2) a section between 12 and 24 h priod where the spectra are dominated by narrow; peaks associated with the semidiurnal and diurnal tides and (3) a section at periods less than 12 h where the spectral density decreases montonically (except for the 8 h tidal peak). The long period section is associated with transient planetary scale waves while the short period motions are caused by gravity waves.

Spin waves in planar quasicrystal of Penrose tiling

NASA Astrophysics Data System (ADS)

Rychły, J.; Mieszczak, S.; Kłos, J. W.

2018-03-01

We investigated two-dimensional magnonic structures which are the counterparts of photonic quasicrystals forming Penrose tiling. We considered the slab composed of Ni (or Py) disks embedded in Fe (or Co) matrix. The disks are arranged in quasiperiodic Penrose-like structure. The infinite quasicrystal was approximated by its rectangular section with periodic boundary conditions applied. This approach allowed us to use the plane wave method to find the frequency spectrum of eigenmodes for spin waves and their spatial profiles. The calculated integrated density of states shows more distinctive magnonic gaps for the structure composed of materials of high magnetic contrast (Ni and Fe) and relatively high filling fraction. This proves the impact of quasiperiodic long-range order on the spectrum of spin waves. We also investigated the localization of spin wave eingenmodes resulting from the quasiperiodicity of the structure.

On the interplay between cosmological shock waves and their environment

NASA Astrophysics Data System (ADS)

Martin-Alvarez, Sergio; Planelles, Susana; Quilis, Vicent

2017-05-01

Cosmological shock waves are tracers of the thermal history of the structures in the Universe. They play a crucial role in redistributing the energy within the cosmic structures and are also amongst the main ingredients of galaxy and galaxy cluster formation. Understanding this important function requires a proper description of the interplay between shocks and the different environments where they can be found. In this paper, an Adaptive Mesh Refinement (AMR) Eulerian cosmological simulation is analysed by means of a shock-finding algorithm that allows to generate shock wave maps. Based on the population of dark matter halos and on the distribution of density contrast in the simulation, we classify the shocks in five different environments. These range from galaxy clusters to voids. The shock distribution function and the shocks power spectrum are studied for these environments dynamics. We find that shock waves on different environments undergo different formation and evolution processes, showing as well different characteristics. We identify three different phases of formation, evolution and dissipation of these shock waves, and an intricate migration between distinct environments and scales. Shock waves initially form at external, low density regions and are merged and amplified through the collapse of structures. Shock waves and cosmic structures follow a parallel evolution. Later on, shocks start to detach from them and dissipate. We also find that most of the power that shock waves dissipate is found at scales of k ˜0.5 Mpc^{-1}, with a secondary peak at k ˜8 Mpc^{-1}. The evolution of the shocks power spectrum confirms that shock waves evolution is coupled and conditioned by their environment.

Phase stability in the two-dimensional anisotropic boson Hubbard Hamiltonian

DOE PAGES

Ying, T.; Batrouni, G. G.; Rousseau, V. G.; ...

2013-05-15

The two dimensional square lattice hard-core boson Hubbard model with near neighbor interactions has a ‘checkerboard’ charge density wave insulating phase at half-filling and sufficiently large intersite repulsion. When doped, rather than forming a supersolid phase in which long range charge density wave correlations coexist with a condensation of superfluid defects, the system instead phase separates. However, it is known that there are other lattice geometries and interaction patterns for which such coexistence takes place. In this paper we explore the possibility that anisotropic hopping or anisotropic near neighbor repulsion might similarly stabilize the square lattice supersolid. Lastly, by consideringmore » the charge density wave structure factor and superfluid density for different ratios of interaction strength and hybridization in the ˆx and ˆy directions, we conclude that phase separation still occurs.« less

Planetesimal formation in self-gravitating discs - the effects of particle self-gravity and back-reaction

NASA Astrophysics Data System (ADS)

Gibbons, P. G.; Mamatsashvili, G. R.; Rice, W. K. M.

2014-07-01

We study particle dynamics in self-gravitating gaseous discs with a simple cooling law prescription via two-dimensional simulations in the shearing sheet approximation. It is well known that structures arising in the gaseous component of the disc due to a gravitational instability can have a significant effect on the evolution of dust particles. Previous results have shown that spiral density waves can be highly efficient at collecting dust particles, creating significant local overdensities of particles. The degree of such concentrations has been shown to be dependent on two parameters: the size of the dust particles and the rate of gas cooling. We expand on these findings, including the self-gravity of dust particles, to see how these particle overdensities evolve. We use the PENCIL code to solve the local shearing sheet equations for gas on a fixed grid together with the equations of motion for solids coupled to the gas through an aerodynamic drag force. We find that the enhancements in the surface density of particles in spiral density wave crests can reach levels high enough to allow the solid component of the disc to collapse under its own self-gravity. This produces many gravitationally bound collections of particles within the spiral structure. The total mass contained in bound structures appears nearly independent of the cooling time, suggesting that the formation of planetesimals through dust particle trapping by self-gravitating density waves may be possible at a larger range of radii within a disc than previously thought. So, density waves due to gravitational instabilities in the early stages of star formation may provide excellent sites for the rapid formation of many large, planetesimal-sized objects.

Output characteristics of a 0.14 THz dual sheet beam backward wave oscillator based on a hole-grating slow wave structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, Xiaopin; Yang, Ziqiang; Shi, Zongjun

A novel backward wave oscillator (BWO) based on a hole-grating slow wave structure is proposed as a dual sheet beam millimeter wave radiation source. In this paper, we focus on the output characteristics of a 0.14 THz hole-grating BWO. The output characteristics of the hole-grating BWO, the conventional single-beam grating BWO, and the dual-beam grating BWO are contrasted in detail. 3-D particle-in-cell results indicate that the hole-grating slow wave structure can help to increase the maximum output power as well as lower the operating current density. Meanwhile, the hole-grating BWO shows good insensitivity to the differences between two sheet electronmore » beams. These characteristics make the hole-grating BWO feasible to be a stable millimeter wave radiation source with higher output power.« less

Ultraviolet Laser Lithography of Titania Photonic Crystals for Terahertz-Wave Modulation.

PubMed

Kirihara, Soshu; Nonaka, Koki; Kisanuki, Shoichiro; Nozaki, Hirotoshi; Sakaguchi, Keito

2018-05-18

Three-dimensional (3D) microphotonic crystals with a diamond structure composed of titania microlattices were fabricated using ultraviolet laser lithography, and the bandgap properties in the terahertz (THz) electromagnetic-wave frequency region were investigated. An acrylic resin paste with titania fine particle dispersions was used as the raw material for additive manufacturing. By scanning a spread paste surface with an ultraviolet laser beam, two-dimensional solid patterns were dewaxed and sintered. Subsequently, 3D structures with a relative density of 97% were created via layer lamination and joining. A titania diamond lattice with a lattice constant density of 240 µm was obtained. The properties of the electromagnetic wave were measured using a THz time-domain spectrometer. In the transmission spectra for the Γ-X direction, a forbidden band was observed from 0.26 THz to 0.44 THz. The frequency range of the bandgap agreed well with calculated results obtained using the plane⁻wave expansion method. Additionally, results of a simulation via transmission-line modeling indicated that a localized mode can be obtained by introducing a plane defect between twinned diamond lattice structures.

Electron beam-plasma interaction and electron-acoustic solitary waves in a plasma with suprathermal electrons

NASA Astrophysics Data System (ADS)

Danehkar, A.

2018-06-01

Suprathermal electrons and inertial drifting electrons, so called electron beam, are crucial to the nonlinear dynamics of electrostatic solitary waves observed in several astrophysical plasmas. In this paper, the propagation of electron-acoustic solitary waves (EAWs) is investigated in a collisionless, unmagnetized plasma consisting of cool inertial background electrons, hot suprathermal electrons (modeled by a κ-type distribution), and stationary ions. The plasma is penetrated by a cool electron beam component. A linear dispersion relation is derived to describe small-amplitude wave structures that shows a weak dependence of the phase speed on the electron beam velocity and density. A (Sagdeev-type) pseudopotential approach is employed to obtain the existence domain of large-amplitude solitary waves, and investigate how their nonlinear structures depend on the kinematic and physical properties of the electron beam and the suprathermality (described by κ) of the hot electrons. The results indicate that the electron beam can largely alter the EAWs, but can only produce negative polarity solitary waves in this model. While the electron beam co-propagates with the solitary waves, the soliton existence domain (Mach number range) becomes narrower (nearly down to nil) with increasing the beam speed and the beam-to-hot electron temperature ratio, and decreasing the beam-to-cool electron density ratio in high suprathermality (low κ). It is found that the electric potential amplitude largely declines with increasing the beam speed and the beam-to-cool electron density ratio for co-propagating solitary waves, but is slightly decreased by raising the beam-to-hot electron temperature ratio.

Impact of inhomogeneity on SH-type wave propagation in an initially stressed composite structure

NASA Astrophysics Data System (ADS)

Saha, S.; Chattopadhyay, A.; Singh, A. K.

2018-02-01

The present analysis has been made on the influence of distinct form of inhomogeneity in a composite structure comprised of double superficial layers lying over a half-space, on the phase velocity of SH-type wave propagating through it. Propagation of SH-type wave in the said structure has been examined in four distinct cases of inhomogeneity viz. when inhomogeneity in double superficial layer is due to exponential variation in density only (Case I); when inhomogeneity in double superficial layers is due to exponential variation in rigidity only (Case II); when inhomogeneity in double superficial layer is due to exponential variation in rigidity, density and initial stress (Case III) and when inhomogeneity in double superficial layer is due to linear variation in rigidity, density and initial stress (Case IV). Closed-form expression of dispersion relation has been accomplished for all four aforementioned cases through extensive application of Debye asymptotic analysis. Deduced dispersion relations for all the cases are found in well-agreement to the classical Love-wave equation. Numerical computation has been carried out to graphically demonstrate the effect of inhomogeneity parameters, initial stress parameters as well as width ratio associated with double superficial layers in the composite structure for each of the four aforesaid cases on dispersion curve. Meticulous examination of distinct cases of inhomogeneity and initial stress in context of considered problem has been carried out with detailed analysis in a comparative approach.

General analytic results for nonlinear waves and solitons in molecular clouds

NASA Technical Reports Server (NTRS)

Adams, Fred C.; Fatuzzo, Marco; Watkins, Richard

1994-01-01

We study nonlinear wave phenomena in self-gravitating fluid systems, with a particular emphasis on applications to molecular clouds. This paper presents analytical results for one spatial dimension. We show that a large class of physical systems can be described by theories with a 'charge density' q(rho); this quantity replaces the density on the right-hand side of the Poisson equation for the gravitational potential. We use this formulation to prove general results about nonlinear wave motions in self-gravitating systems. We show that in order for stationary waves to exist, the total charge (the integral of the charge density over the wave profile) must vanish. This 'no-charge' property for solitary waves is related to the capability of a system to be stable to gravitational perturbations for arbitrarily long wavelengths. We find necessary and sufficient conditions on the charge density for the existence of solitary waves and stationary waves. We study nonlinear wave motions for Jeans-type theories (where q(rho) = rho-rho(sub 0)) and find that nonlinear waves of large amplitude are confined to a rather narrow range of wavelengths. We also study wave motions for molecular clouds threaded by magnetic fields and show how the allowed range of wavelengths is affected by the field strength. Since the gravitational force in one spatial dimension does not fall off with distance, we consider two classes of models with more realistic gravity: Yukawa potentials and a pseudo two-dimensional treatment. We study the allowed types of wave behavior for these models. Finally, we discuss the implications of this work for molecular cloud structure. We argue that molecular clouds can support a wide variety of wave motions and suggest that stationary waves (such as those considered in this paper) may have already been observed.

Harmonic plasma waves excitation and structure evolution of intense ion beams in background plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Zhang-Hu, E-mail: zhanghu@dlut.edu.cn; Wang, You-Nian

2016-08-15

The long-term dynamic evolutions of intense ion beams in plasmas have been investigated with two-dimensional electromagnetic particle simulations, taking into account the effect of the two-stream instability between beam ions and plasma electrons. Depending on the initial beam radial density profile and velocity distribution, ring structures may be formed in the beam edge regions. At the later stage of beam-plasma interactions, the ion beams are strongly modulated by the two-stream instability and multiple density spikes are formed in the longitudinal direction. The formation of these density spikes is shown to result from the excitation of harmonic plasma waves when themore » instability gets saturated. Comparisons between the beam cases with initial flat-top and Gaussian radial density profiles are made, and a higher instability growth rate is observed for the flat-top profile case.« less

An open-source framework for analyzing N-electron dynamics. II. Hybrid density functional theory/configuration interaction methodology.

PubMed

Hermann, Gunter; Pohl, Vincent; Tremblay, Jean Christophe

2017-10-30

In this contribution, we extend our framework for analyzing and visualizing correlated many-electron dynamics to non-variational, highly scalable electronic structure method. Specifically, an explicitly time-dependent electronic wave packet is written as a linear combination of N-electron wave functions at the configuration interaction singles (CIS) level, which are obtained from a reference time-dependent density functional theory (TDDFT) calculation. The procedure is implemented in the open-source Python program detCI@ORBKIT, which extends the capabilities of our recently published post-processing toolbox (Hermann et al., J. Comput. Chem. 2016, 37, 1511). From the output of standard quantum chemistry packages using atom-centered Gaussian-type basis functions, the framework exploits the multideterminental structure of the hybrid TDDFT/CIS wave packet to compute fundamental one-electron quantities such as difference electronic densities, transient electronic flux densities, and transition dipole moments. The hybrid scheme is benchmarked against wave function data for the laser-driven state selective excitation in LiH. It is shown that all features of the electron dynamics are in good quantitative agreement with the higher-level method provided a judicious choice of functional is made. Broadband excitation of a medium-sized organic chromophore further demonstrates the scalability of the method. In addition, the time-dependent flux densities unravel the mechanistic details of the simulated charge migration process at a glance. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Study of Linear and Nonlinear Wave Excitation

NASA Astrophysics Data System (ADS)

Chu, Feng; Berumen, Jorge; Hood, Ryan; Mattingly, Sean; Skiff, Frederick

2013-10-01

We report an experimental study of externally excited low-frequency waves in a cylindrical, magnetized, singly-ionized Argon inductively-coupled gas discharge plasma that is weakly collisional. Wave excitation in the drift wave frequency range is accomplished by low-percentage amplitude modulation of the RF plasma source. Laser-induced fluorescence is adopted to study ion-density fluctuations in phase space. The laser is chopped to separate LIF from collisional fluorescence. A single negatively-biased Langmuir probe is used to detect ion-density fluctuations in the plasma. A ring array of Langmuir probes is also used to analyze the spatial and spectral structure of the excited waves. We apply coherent detection with respect to the wave frequency to obtain the ion distribution function associated with externally generated waves. Higher-order spectra are computed to evaluate the nonlinear coupling between fluctuations at various frequencies produced by the externally generated waves. Parametric decay of the waves is observed. This work is supported by U.S. DOE Grant No. DE-FG02-99ER54543.

3D Structure of Iran and Surrounding Areas From The Simultaneous Inversion of Complementary Geophysical Observations

NASA Astrophysics Data System (ADS)

Ammon, C. J.; Maceira, M.; Cleveland, M.

2010-12-01

We present a three-dimensional seismic-structure model of the Arabian-Eurasian collision zone obtained via simultaneous, joint inversion of surface-wave dispersion measurements, teleseismic P-wave receiver functions, and gravity observations. We use a simple, approximate relationship between density and seismic velocities so that the three data sets may be combined in a single inversion. The sensitivity of the different data sets are well known: surface waves provide information on the smooth variations in elastic properties, receiver functions provide information on abrupt velocity contrasts, and gravity measurements provide information on broad-wavenumber shallow density variations and long-wavenumber components of deeper density structures. The combination of the data provides improved resolution of shallow-structure variations, which in turn help produce the smooth features at depth with less contamination from the strong heterogeneity often observed in the upper crust. We also explore geologically based smoothness constraints to help resolve sharp features in the underlying shallow 3D structure. Our focus is on the region surrounding Iran from east Turkey and Iraq in the west, to Pakistan and Afghanistan in the east. We use Bouguer gravity anomalies derived from the global gravity model extracted from the GRACE satellite mission. Surface-wave dispersion velocities in the period range between 7 and 150 s are taken from previously published tomographic maps for the region. Preliminary results show expected strong variations in the Caspian region as well as the deep sediment regions of the Persian Gulf. Regions constrained with receiver-function information generally show sharper crust-mantle boundary structure than that obtained by inversion of the surface waves alone (with thin layers and smoothing constraints). Final results of the simultaneous inversion will help us to better understand one of the most prominent examples of continental collision. Such models also provide an important starting model for time-consuming and fully 3D inversions.

Nonlinear helicons bearing multi-scale structures

NASA Astrophysics Data System (ADS)

Abdelhamid, Hamdi M.; Yoshida, Zensho

2017-02-01

The helicon waves exhibit varying characters depending on plasma parameters, geometry, and wave numbers. Here, we elucidate an intrinsic multi-scale property embodied by the combination of the dispersive effect and nonlinearity. The extended magnetohydrodynamics model (exMHD) is capable of describing a wide range of parameter space. By using the underlying Hamiltonian structure of exMHD, we construct an exact nonlinear solution, which turns out to be a combination of two distinct modes, the helicon and Trivelpiece-Gould (TG) waves. In the regime of relatively low frequency or high density, however, the combination is made of the TG mode and an ion cyclotron wave (slow wave). The energy partition between these modes is determined by the helicities carried by the wave fields.

Generation of intermittent gravitocapillary waves via parametric forcing

NASA Astrophysics Data System (ADS)

Castillo, Gustavo; Falcón, Claudio

2018-04-01

We report on the generation of an intermittent wave field driven by a horizontally moving wave maker interacting with Faraday waves. The spectrum of the local gravitocapillary surface wave fluctuations displays a power law in frequency for a wide range of forcing parameters. We compute the probability density function of the local surface height increments, which show that they change strongly across time scales. The structure functions of these increments are shown to display power laws as a function of the time lag, with exponents that are nonlinear functions of the order of the structure function. We argue that the origin of this scale-invariant intermittent spectrum is the Faraday wave pattern breakup due to its advection by the propagating gravity waves. Finally, some interpretations are proposed to explain the appearance of this intermittent spectrum.

Suppressive Shields Structural Design and Analysis Handbook

DTIC Science & Technology

1977-11-18

of this disturbance to steepen as it passes through the air until it exhibits nearly discontinuous increases in pressure, density, and temperature ...sure. density, and temperature of the reflected wave are all in- creased above the values in the incident wave. The ove-nressure at the wall surface...limiting thickness of concrete at which per- foration will occur can be obtained from Fig. 3-18 and is a function of the coefficient C1, the fragment weight

Bipolaronic charge density waves, polaronic spin density waves and high Tc superconductivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aubry, S.

1992-01-01

At large enough electron phonon coupling, the existence of bipolaronic, polaronic and mixed states is rigorously proven for the adiabatic Holstein model at any dimension and any band filling. The ground-state is one of them which then prove the existence of insulating Bipolaronic Charge Density Waves. The role of the quantum lattice fluctuations is analysed and found to be neglegible in that regime but to become essential in case of phonon softening then favoring the occurence of superconductivity. When a strong Hubbard term is also present, the bipolarons break into polorons and the ground state is expected to be amore » polaronic spin density wave. If the repulsive Hubbard term is comparable to the electron-phonon coupling, the energy for breaking a bipoloron into two polarons can become small and we get instead of these two degenerate structures, a pait of polarons bounded by a spin resonance which we call spin resonant bipolaron''. This resonant bipolaron is still strongly bound, but the role of the quantum lattice fluctuations becomes now very important and yields a sharp broadening of the bandwidth of this resonant bipolarona. Thus, the strong quantum character of these resonant bipolarons could prevent their localization into real space structures which could be insulating bipolaronic CDWs or polaronic SDWS, then favoring the formation of a superconducting coherent state with a possible high {Tc}.« less

Bipolaronic charge density waves, polaronic spin density waves and high {Tc} superconductivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aubry, S.

1992-09-01

At large enough electron phonon coupling, the existence of bipolaronic, polaronic and mixed states is rigorously proven for the adiabatic Holstein model at any dimension and any band filling. The ground-state is one of them which then prove the existence of insulating Bipolaronic Charge Density Waves. The role of the quantum lattice fluctuations is analysed and found to be neglegible in that regime but to become essential in case of phonon softening then favoring the occurence of superconductivity. When a strong Hubbard term is also present, the bipolarons break into polorons and the ground state is expected to be amore » polaronic spin density wave. If the repulsive Hubbard term is comparable to the electron-phonon coupling, the energy for breaking a bipoloron into two polarons can become small and we get instead of these two degenerate structures, a pait of polarons bounded by a spin resonance which we call ``spin resonant bipolaron``. This resonant bipolaron is still strongly bound, but the role of the quantum lattice fluctuations becomes now very important and yields a sharp broadening of the bandwidth of this resonant bipolarona. Thus, the strong quantum character of these resonant bipolarons could prevent their localization into real space structures which could be insulating bipolaronic CDWs or polaronic SDWS, then favoring the formation of a superconducting coherent state with a possible high {Tc}.« less

Competing spin density wave, collinear, and helical magnetism in Fe 1 + x Te

DOE PAGES

Stock, C.; Rodriguez, E. E.; Bourges, P.; ...

2017-04-07

The Fe 1+xTe phase diagram consists of two distinct magnetic structures with collinear order present at low interstitial iron concentrations and a helical phase at large values of x with these phases separated by a Lifshitz point. In this paper, we use unpolarized single-crystal diffraction to confirm the helical phase for large interstitial iron concentrations and polarized single-crystal diffraction to demonstrate the collinear order for the iron-deficient side of the Fe 1+xTe phase diagram. Polarized neutron inelastic scattering shows that the fluctuations associated with this collinear order are predominately transverse at low-energy transfers, consistent with a localized magnetic moment picture.more » We then apply neutron inelastic scattering and polarization analysis to investigate the dynamics and structure near the boundary between collinear and helical orders in the Fe 1+xTe phase diagram. We first show that the phase separating collinear and helical orders is characterized by a spin density wave with a single propagation wave vector of (~0.45, 0, 0.5). We do not observe harmonics or the presence of a charge density wave. The magnetic fluctuations associated with this wave vector are different from the collinear phase, being strongly longitudinal in nature and correlated anisotropically in the (H,K) plane. The excitations preserve the C 4 symmetry of the lattice but display different widths in momentum along the two tetragonal directions at low-energy transfers. Finally, while the low-energy excitations and minimal magnetic phase diagram can be understood in terms of localized interactions, we suggest that the presence of the density wave phase implies the importance of electronic and orbital properties.« less

Competing spin density wave, collinear, and helical magnetism in Fe 1 + x Te

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stock, C.; Rodriguez, E. E.; Bourges, P.

The Fe 1+xTe phase diagram consists of two distinct magnetic structures with collinear order present at low interstitial iron concentrations and a helical phase at large values of x with these phases separated by a Lifshitz point. In this paper, we use unpolarized single-crystal diffraction to confirm the helical phase for large interstitial iron concentrations and polarized single-crystal diffraction to demonstrate the collinear order for the iron-deficient side of the Fe 1+xTe phase diagram. Polarized neutron inelastic scattering shows that the fluctuations associated with this collinear order are predominately transverse at low-energy transfers, consistent with a localized magnetic moment picture.more » We then apply neutron inelastic scattering and polarization analysis to investigate the dynamics and structure near the boundary between collinear and helical orders in the Fe 1+xTe phase diagram. We first show that the phase separating collinear and helical orders is characterized by a spin density wave with a single propagation wave vector of (~0.45, 0, 0.5). We do not observe harmonics or the presence of a charge density wave. The magnetic fluctuations associated with this wave vector are different from the collinear phase, being strongly longitudinal in nature and correlated anisotropically in the (H,K) plane. The excitations preserve the C 4 symmetry of the lattice but display different widths in momentum along the two tetragonal directions at low-energy transfers. Finally, while the low-energy excitations and minimal magnetic phase diagram can be understood in terms of localized interactions, we suggest that the presence of the density wave phase implies the importance of electronic and orbital properties.« less

Competing spin density wave, collinear, and helical magnetism in Fe1 +xTe

NASA Astrophysics Data System (ADS)

Stock, C.; Rodriguez, E. E.; Bourges, P.; Ewings, R. A.; Cao, H.; Chi, S.; Rodriguez-Rivera, J. A.; Green, M. A.

2017-04-01

The Fe1 +xTe phase diagram consists of two distinct magnetic structures with collinear order present at low interstitial iron concentrations and a helical phase at large values of x with these phases separated by a Lifshitz point. We use unpolarized single-crystal diffraction to confirm the helical phase for large interstitial iron concentrations and polarized single-crystal diffraction to demonstrate the collinear order for the iron-deficient side of the Fe1 +xTe phase diagram. Polarized neutron inelastic scattering shows that the fluctuations associated with this collinear order are predominately transverse at low-energy transfers, consistent with a localized magnetic moment picture. We then apply neutron inelastic scattering and polarization analysis to investigate the dynamics and structure near the boundary between collinear and helical orders in the Fe1 +xTe phase diagram. We first show that the phase separating collinear and helical orders is characterized by a spin density wave with a single propagation wave vector of (˜0.45 , 0, 0.5). We do not observe harmonics or the presence of a charge density wave. The magnetic fluctuations associated with this wave vector are different from the collinear phase, being strongly longitudinal in nature and correlated anisotropically in the (H ,K ) plane. The excitations preserve the C4 symmetry of the lattice but display different widths in momentum along the two tetragonal directions at low-energy transfers. While the low-energy excitations and minimal magnetic phase diagram can be understood in terms of localized interactions, we suggest that the presence of the density wave phase implies the importance of electronic and orbital properties.

The modal density of composite beams incorporating the effects of shear deformation and rotary inertia

NASA Astrophysics Data System (ADS)

Bachoo, Richard; Bridge, Jacqueline

2018-06-01

Engineers and designers are often faced with the task of selecting materials that minimizes structural weight whilst meeting the required strength and stiffness. In many cases fibre reinforced composites (FRCs) are the materials of choice since they possess a combination of high strength and low density. Depending on the application, composites are frequently constructed to form long slender beam-like structures or flat thin plate-like structures. Such structures when subjected to random excitation have the potential to excite higher order vibratory modes which can contribute significantly to structure-borne sound. Statistical Energy Analysis (SEA) is a framework for modeling the high frequency vibration of structures. The modal density, which is typically defined as the number of modes per unit Hertz in a frequency band, is a fundamental parameter when applying SEA. This study derives formulas for the modal density of a fibre reinforced composite beam coupled in bending and torsion. The effects of shear deformation and rotary inertia are accounted for in the formulation. The modal density is shown to be insensitive to boundary conditions. Numerical analyses were carried out to investigate the variation of modal density with fibre orientation including and excluding the effects of shear deformation and rotary inertia. It was observed that neglecting such effects leads to underestimating the mode count in a particular frequency band. In each frequency band there exists a fibre orientation for which the modal density is minimized. This angular orientation is shown to be dependent on the shear rigidity as well as the bending, torsional and coupling rigidities. The foregoing observation becomes more pronounced with increasing frequency. The paper also addresses the modal density beyond the wave-mode transition frequency where the beam supports three propagating waves.

Electron cyclotron thruster new modeling results preparation for initial experiments

NASA Technical Reports Server (NTRS)

Hooper, E. Bickford

1993-01-01

The following topics are discussed: a whistler-based electron cyclotron resonance heating (ECRH) thruster; cross-field coupling in the helicon approximation; wave propagation; wave structure; plasma density; wave absorption; the electron distribution function; isothermal and adiabatic plasma flow; ECRH thruster modeling; a PIC code model; electron temperature; electron energy; and initial experimental tests. The discussion is presented in vugraph form.

Role of structural anisotropy of biological tissues in poroelastic wave propagation

PubMed Central

Cardoso, Luis; Cowin, Stephen C.

2011-01-01

Ultrasound waves have a broad range of clinical applications as a non-destructive testing approach in imaging and in the diagnoses of medical conditions. Generally, biological tissues are modeled as an homogenized equivalent medium with an apparent density through which a single wave propagates. Only the first wave arriving at the ultrasound probe is used for the measurement of the speed of sound. However, the existence of a second wave in tissues such as cancellous bone has been reported and its existence is an unequivocal signature of Biot type poroelastic media. To account for the fact that ultrasound is sensitive to microarchitecture as well as density, a fabric-dependent anisotropic poroelastic ultrasound (PEU) propagation theory was recently developed. Key to this development was the inclusion of the fabric tensor - a quantitative stereological measure of the degree of structural anisotropy of bone - into the linear poroelasticity theory. In the present study, this framework is extended to the propagation of waves in several soft and hard tissues. It was found that collagen fibers in soft tissues and the mineralized matrix in hard tissues are responsible for the anisotropy of the solid tissue constituent through the fabric tensor in the model. PMID:22162897

Human Stressors Are Driving Coastal Benthic Long-Lived Sessile Fan Mussel Pinna nobilis Population Structure More than Environmental Stressors.

PubMed

Deudero, Salud; Vázquez-Luis, Maite; Álvarez, Elvira

2015-01-01

Coastal degradation and habitat disruption are severely compromising sessile marine species. The fan shell Pinna nobilis is an endemic, vulnerable species and the largest bivalve in the Mediterranean basin. In spite of species legal protection, fan shell populations are declining. Models analyzed the contributions of environmental (mean depth, wave height, maximum wave height, period of waves with high energy and mean direction of wave source) versus human-derived stressors (anchoring, protection status, sewage effluents, fishing activity and diving) as explanatory variables depicting Pinna nobilis populations at a mesoscale level. Human stressors were explaining most of the variability in density spatial distribution of fan shell, significantly disturbing benthic communities. Habitat protection affected P. nobilis structure and physical aggression by anchoring reveals a high impact on densities. Environmental variables instead played a secondary role, indicating that global change processes are not so relevant in coastal benthic communities as human-derived impacts.

Crustal and mantle structure of the greater Jan Mayen-East Greenland region (NE Atlantic) from combined 3D structural, S-wave velocity, and gravity modeling

NASA Astrophysics Data System (ADS)

Tan, P.; Sippel, J.; Scheck-Wenderoth, M.; Meeßen, C.; Breivik, A. J.

2016-12-01

The study area is located between the Jan Mayen Ridge and the east coast of Greenland. It has a complex geological setting with the ultraslow Kolbeinsey and Mohn's spreading ridges, the anomalously shallow Eggvin Bank, the Jan Mayen Microcontinent (JMMC), and the tectonically active West Jan Mayen Fracture Zone (WJMFZ). In this study, we present the results of forward 3D structural, S-wave velocity, and gravity modeling which provide new insights into the deep crust and mantle structure and the wide-ranging influence of the Iceland Plume. The crustal parts of the presented 3D structural model are mainly constrained by local seismic refraction and reflection data. Accordingly, greatest crustal thicknesses (24 km) are observed on the northern boundary of the JMMC, while the average crustal thickness is 8.5 km and 4 km in the Kolbeinsey and Mohn's Ridge, respectively. The densities of the crustal parts are from previous studies. Additionally, the mantle density is derived from S-wave velocity data (between 50 and 250 km depth), while densities of the lithospheric mantle between the Moho and 50 km are calculated assuming isostatic equilibrium at 250 km depth. This is used as a starting density model which is further developed to obtain a reasonable fit between the calculated and measured (free-air) gravity fields. The observed S-wave tomographic data and the gravity modeling prove that the Iceland plume anomaly in the asthenosphere affects the lithospheric thickness and temperature, from the strongly influenced Middle Kolbeinsey Ridge, to the less affected North Kolbeinsey Ridge (Eggvin Bank), and to the little impacted Mohn's Ridge. Thus, the age-temperature relations of the different mid-ocean ridges of the study area are perturbed to different degrees controlled by the distance from the Iceland Plume. Furthermore, we find that the upper 50 km of lithospheric mantle are thermally affected by the plume only in the southwestern parts of the study area.

Elastic Wave Propagation through Multilayered Media

DTIC Science & Technology

1980-03-01

Distilled ) 20 Water (Heavy,D^O) 19.8 o-Xylene 20 m-Xylene 20 p-Xylene 20 ■■■/ Wavespeed Long. Trans. Surf Density Ref. 10^ cm/sec gm/cm...7 3 Schematic of Three Layer Structure 15 4a Longitudinal Wave Incident on a Water /Lucite Interface 17 4b Longitudinal Wave Incident on a Lucite... Water Interface 17 5a Longitudinal Wave Incident on an Aluminum/ Water Interface 18 5b Longitudinal Wave Incident on a Steel/ Water Interface 18 6a

Planetary wave-like oscillations in the ionosphere retrieved with a longitudinal chain of ionosondes at high northern latitudes

NASA Astrophysics Data System (ADS)

Stray, Nora H.; Espy, Patrick J.

2018-06-01

This paper examines the influence of neutral dynamics on the high latitude ionosphere. Using a longitudinal chain of ionosondes at high northern latitudes (52°-65° N), planetary wave-like structures were observed in the spatial structure of the peak electron density in the ionosphere. Longitudinal wavenumbers S0, S1 and S2 have been extracted from these variations of the F layer. The observed wave activity in wavenumber one and two does not show any significant correlation with indices of magnetic activity, suggesting that this is not the primary driver. In addition, the motion of the S1 ionospheric wave structures parallels that of the S1 planetary waves observed in the winds of the mesosphere-lower-thermosphere derived from a longitudinal array of SuperDARN meteor-radar wind measurements. The time delay between the motions of the wave structures would indicate a indirect coupling, commensurate with the diffusion to the ionosphere of mesospheric atomic oxygen perturbations.

Multi-Point Measurements to Characterize Radiation Belt Electron Precipitation Loss

NASA Astrophysics Data System (ADS)

Blum, L. W.

2017-12-01

Multipoint measurements in the inner magnetosphere allow the spatial and temporal evolution of various particle populations and wave modes to be disentangled. To better characterize and quantify radiation belt precipitation loss, we utilize multi-point measurements both to study precipitating electrons directly as well as the potential drivers of this loss process. Magnetically conjugate CubeSat and balloon measurements are combined to estimate of the temporal and spatial characteristics of dusk-side precipitation features and quantify loss due to these events. To then understand the drivers of precipitation events, and what determines their spatial structure, we utilize measurements from the dual Van Allen Probes to estimate spatial and temporal scales of various wave modes in the inner magnetosphere, and compare these to precipitation characteristics. The structure, timing, and spatial extent of waves are compared to those of MeV electron precipitation during a few individual events to determine when and where EMIC waves cause radiation belt electron precipitation. Magnetically conjugate measurements provide observational support of the theoretical picture of duskside interaction of EMIC waves and MeV electrons leading to radiation belt loss. Finally, understanding the drivers controlling the spatial scales of wave activity in the inner magnetosphere is critical for uncovering the underlying physics behind the wave generation as well as for better predicting where and when waves will be present. Again using multipoint measurements from the Van Allen Probes, we estimate the spatial and temporal extents and evolution of plasma structures and their gradients in the inner magnetosphere, to better understand the drivers of magnetospheric wave characteristic scales. In particular, we focus on EMIC waves and the plasma parameters important for their growth, namely cold plasma density and cool and warm ion density, anisotropy, and composition.

Cylindrical ion-acoustic solitary waves in electronegative plasmas with superthermal electrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eslami, Parvin; Mottaghizadeh, Marzieh

2012-06-15

By using the standard reductive perturbation technique, a three-dimensional cylindrical Kadomtsev-Petviashvili equation (CKPE), which governs the dynamics of ion acoustic solitary waves (IASWs), is derived for small but finite amplitude ion-acoustic waves in cylindrical geometry in a collisionless unmagnetized plasma with kappa distributed electrons, thermal positrons, and cold ions. The generalized expansion method is used to solve analytically the CKPE. The existence regions of localized pulses are investigated. It is found that the solution of the CKPE supports only compressive solitary waves. Furthermore, the effects of superthermal electrons, the ratio of the electron temperature to positron temperature, the ratio ofmore » the positron density to electron density and direction cosine of the wave propagation on the profiles of the amplitudes, and widths of the solitary structures are examined numerically. It is shown these parameters play a vital role in the formation of ion acoustic solitary waves.« less

The propagation of ion-acoustic waves carrying orbital angular momentum in the electron-positron-ion plasmas

NASA Astrophysics Data System (ADS)

Mehdian, H.; Nobahar, D.; Hajisharifi, K.

2018-02-01

Ion-acoustic (IA) waves carrying orbital angular momentum (OAM) are investigated in an unmagnetized, uniform, and collisionless electron-positron-ion (e-p-i) plasma system. Employing the hydrodynamic theory, the paraxial equation in term of ion perturbed number density is derived and discussed about its Laguerre-Gaussian (LG) beam solutions. Obtaining an approximate solution for the electrostatic potential, the IA wave characteristics including helical electric field structure, energy density, and OAM density are theoretically studied. Based on the numerical analysis, the effects of positron concentration, radial and angular mode number as well as beam waist on the obtained potential profile are investigated. It is shown that the depth (height) and width of the LG potential profile wells (barriers) are considerably modify by the variation of positron concentration.

Photoemission study of the electronic structure and charge density waves of Na₂Ti₂Sb₂O

DOE PAGES

Tan, S. Y.; Jiang, J.; Ye, Z. R.; ...

2015-04-30

The electronic structure of Na₂Ti₂Sb₂O single crystal is studied by photon energy and polarization dependent angle-resolved photoemission spectroscopy (ARPES). The obtained band structure and Fermi surface agree well with the band structure calculation of Na₂Ti₂Sb₂O in the non-magnetic state, which indicates that there is no magnetic order in Na₂Ti₂Sb₂O and the electronic correlation is weak. Polarization dependent ARPES results suggest the multi-band and multi-orbital nature of Na₂Ti₂Sb₂O. Photon energy dependent ARPES results suggest that the electronic structure of Na₂Ti₂Sb₂O is rather two-dimensional. Moreover, we find a density wave energy gap forms below the transition temperature and reaches 65 meV atmore » 7 K, indicating that Na₂Ti₂Sb₂O is likely a weakly correlated CDW material in the strong electron-phonon interaction regime. (author)« less

Van Allen Probes observations of structured whistler mode activity and coincident electron Landau acceleration inside a remnant plasmaspheric plume

NASA Astrophysics Data System (ADS)

Woodroffe, J. R.; Jordanova, V. K.; Funsten, H. O.; Streltsov, A. V.; Bengtson, M. T.; Kletzing, C. A.; Wygant, J. R.; Thaller, S. A.; Breneman, A. W.

2017-03-01

We present observations from the Van Allen Probes spacecraft that identify a region of intense whistler mode activity within a large density enhancement outside of the plasmasphere. We speculate that this density enhancement is part of a remnant plasmaspheric plume, with the observed wave being driven by a weakly anisotropic electron injection that drifted into the plume and became nonlinearly unstable to whistler emission. Particle measurements indicate that a significant fraction of thermal (<100 eV) electrons within the plume were subject to Landau acceleration by these waves, an effect that is naturally explained by whistler emission within a gradient and high-density ducting inside a density enhancement.

SLOW MAGNETOACOUSTIC WAVES OBSERVED ABOVE A QUIET-SUN REGION IN A DARK CAVITY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu Jiajia; Zhou Zhenjun; Wang Yuming

Waves play a crucial role in diagnosing the plasma properties of various structures in the solar corona and coronal heating. Slow magnetoacoustic (MA) waves are one of the important types of magnetohydrodynamic waves. In past decades, numerous slow MA waves were detected above active regions and coronal holes, but were rarely found elsewhere. Here, we investigate a 'tornado'-like structure consisting of quasi-periodic streaks within a dark cavity at about 40-110 Mm above a quiet-Sun region on 2011 September 25. Our analysis reveals that these streaks are actually slow MA wave trains. The properties of these wave trains, including phase speed,more » compression ratio, and kinetic energy density, are similar to those of the reported slow MA waves, except that the period of these waves is about 50 s, much shorter than the typical reported values (3-5 minutes).« less

A novel function of WAVE in lamellipodia: WAVE1 is required for stabilization of lamellipodial protrusions during cell spreading.

PubMed

Yamazaki, Daisuke; Fujiwara, Takashi; Suetsugu, Shiro; Takenawa, Tadaomi

2005-05-01

When a cell spreads and moves, reorganization of the actin cytoskeleton pushes the cell membrane, and the resulting membrane protrusions create new points of contact with the substrate and generate the locomotive force. Membrane extension and adhesion to a substrate must be tightly coordinated for effective cell movement, but little is known about the mechanisms underlying these processes. WAVEs are critical regulators of Rac-induced actin reorganization. WAVE2 is essential for formation of lamellipodial structures at the cell periphery stimulated by growth factors, but it is thought that WAVE1 is dispensable for such processes in mouse embryonic fibroblasts (MEFs). Here we show a novel function of WAVE in lamellipodial protrusions during cell spreading. During spreading on fibronectin (FN), MEFs with knockouts (KOs) of WAVE1 and WAVE2 showed different membrane dynamics, suggesting that these molecules have distinct roles in lamellipodium formation. Formation of lamellipodial structures on FN was inhibited in WAVE2 KO MEFs. In contrast, WAVE1 is not essential for extension of lamellipodial protrusions but is required for stabilization of such structures. WAVE1-deficiency decreased the density of actin filaments and increased the speed of membrane extension, causing deformation of focal complex at the tip of spreading edges. Thus, at the tip of the lamellipodial protrusion, WAVE2 generates the membrane protrusive structures containing actin filaments, and modification by WAVE1 stabilizes these structures through cell-substrate adhesion. Coordination of WAVE1 and WAVE2 activities appears to be necessary for formation of proper actin structures in stable lamellipodia.

Cloaks for suppression or enhancement of scattering of diffuse photon density waves

NASA Astrophysics Data System (ADS)

Renthlei, Lalruatfela; Ramakrishna, S. Anantha; Wanare, Harshawardhan

2018-07-01

Enhancement of wave-like characteristics of heavily damped diffuse photon density waves in a random medium by amplification can induce strongly localised resonances. These resonances can be used to either suppress or enhance scattering from an inhomogeneity in the random medium by cloaking the inhomogeneous region by a shell of random medium with the correct levels of absorption or amplification. A spherical core-shell structure consisting of a shell of a random amplifying medium is shown to enhance or suppress specific resonant modes. A shell with an absorbing random medium is also shown to suppress scattering which can also be used for cloaking the core region.

From cluster structures to nuclear molecules: The role of nodal structure of the single-particle wave functions

NASA Astrophysics Data System (ADS)

Afanasjev, A. V.; Abusara, H.

2018-02-01

The nodal structure of the density distributions of the single-particle states occupied in rod-shaped, hyper- and megadeformed structures of nonrotating and rotating N ˜Z nuclei has been investigated in detail. The single-particle states with the Nilsson quantum numbers of the [N N 0 ]1 /2 (with N from 0 to 5) and [N ,N -1 ,1 ]Ω (with N from 1 to 3 and Ω =1 /2 , 3/2) types are considered. These states are building blocks of extremely deformed shapes in the nuclei with mass numbers A ≤50 . Because of (near) axial symmetry and large elongation of such structures, the wave functions of the single-particle states occupied are dominated by a single basis state in cylindrical basis. This basis state defines the nodal structure of the single-particle density distribution. The nodal structure of the single-particle density distributions allows us to understand in a relatively simple way the necessary conditions for α clusterization and the suppression of the α clusterization with the increase of mass number. It also explains in a natural way the coexistence of ellipsoidal mean-field-type structures and nuclear molecules at similar excitation energies and the features of particle-hole excitations connecting these two types of the structures. Our analysis of the nodal structure of the single-particle density distributions does not support the existence of quantum liquid phase for the deformations and nuclei under study.

A Theoretical Study of Love Wave Sensors Based on ZnO–Glass Layered Structures for Application to Liquid Environments

PubMed Central

Caliendo, Cinzia; Hamidullah, Muhammad

2016-01-01

The propagation of surface acoustic Love modes along ZnO/glass-based structures was modeled and analysed with the goal of designing a sensor able to detect changes in the environmental parameters, such as liquid viscosity changes and minute amounts of mass supported in the viscous liquid medium. Love mode propagation was modeled by numerically solving the system of coupled electro-mechanical field equations and Navier–Stokes equations. The phase and group velocities and the attenuation of the acoustic wave propagating along the 30° tilted c-axis ZnO/glass structure contacting a viscous non-conductive liquid were calculated for different ZnO guiding layer thicknesses, added mass thicknesses, and liquid viscosity and density. The three sensor responses, i.e., the wave phase and group velocity, and attenuation changes are calculated for different environmental parameters and related to the sensor velocity and attenuation sensitivities. The resulted sensitivities to liquid viscosity and added mass were optimized by adjusting the ZnO guiding layer thickness corresponding to a sensitivity peak. The present analysis is valuable for the manufacture and application of the ZnO-glass structure Love wave sensors for the detection of liquid properties, such as viscosity, density and mass anchored to the sensor surface. PMID:27918419

Multiconfiguration Pair-Density Functional Theory: A New Way To Treat Strongly Correlated Systems.

PubMed

Gagliardi, Laura; Truhlar, Donald G; Li Manni, Giovanni; Carlson, Rebecca K; Hoyer, Chad E; Bao, Junwei Lucas

2017-01-17

The electronic energy of a system provides the Born-Oppenheimer potential energy for internuclear motion and thus determines molecular structure and spectra, bond energies, conformational energies, reaction barrier heights, and vibrational frequencies. The development of more efficient and more accurate ways to calculate the electronic energy of systems with inherently multiconfigurational electronic structure is essential for many applications, including transition metal and actinide chemistry, systems with partially broken bonds, many transition states, and most electronically excited states. Inherently multiconfigurational systems are called strongly correlated systems or multireference systems, where the latter name refers to the need for using more than one ("multiple") configuration state function to provide a good zero-order reference wave function. This Account describes multiconfiguration pair-density functional theory (MC-PDFT), which was developed as a way to combine the advantages of wave function theory (WFT) and density functional theory (DFT) to provide a better treatment of strongly correlated systems. First we review background material: the widely used Kohn-Sham DFT (which uses only a single Slater determinant as reference wave function), multiconfiguration WFT methods that treat inherently multiconfigurational systems based on an active space, and previous attempts to combine multiconfiguration WFT with DFT. Then we review the formulation of MC-PDFT. It is a generalization of Kohn-Sham DFT in that the electron kinetic energy and classical electrostatic energy are calculated from a reference wave function, while the rest of the energy is obtained from a density functional. However, there are two main differences with respent to Kohn-Sham DFT: (i) The reference wave function is multiconfigurational rather than being a single Slater determinant. (ii) The density functional is a function of the total density and the on-top pair density rather than being a function of the spin-up and spin-down densities. In work carried out so far, the multiconfigurational wave function is a multiconfiguration self-consistent-field wave function. The new formulation has the advantage that the reference wave function has the correct spatial and spin symmetry and can describe bond dissociation (of both single and multiple bonds) and electronic excitations in a formally and physically correct way. We then review the formulation of density functionals in terms of the on-top pair density. Finally we review successful applications of the theory to bond energies and bond dissociation potential energy curves of main-group and transition metal bonds, to barrier heights (including pericyclic reactions), to proton affinities, to the hydrogen bond energy of water dimer, to ground- and excited-state charge transfer, to valence and Rydberg excitations of molecules, and to singlet-triplet splittings of radicals. We find that that MC-PDFT can give accurate results not only with complete-active-space multiconfiguration wave functions but also with generalized-active-space multiconfiguration wave functions, which are practical for larger numbers of active electrons and active orbitals than are complete-active-space wave functions. The separated-pair approximation, which is a special case of generalized active space self-consistent-field theory, is especially promising. MC-PDFT, because it requires much less computer time and storage than pure WFT methods, has the potential to open larger and more complex strongly correlated systems to accurate simulation.

Density and pressure variability in the mesosphere and thermosphere

NASA Technical Reports Server (NTRS)

Davis, T. M.

1986-01-01

In an effort to isolate the essential physics of the mesosphere and the thermosphere, a steady one-dimensional density and pressure model has been developed in support of related NASA activities, i.e., projects such as the AOTV and the Space Station. The model incorporates a zeroth order basic state including both the three-dimensional wind field and its associated shear structure, etc. A first order wave field is also incorporated in period bands ranging from about one second to one day. Both basic state and perturbation quantities satsify the combined constraints of mass, linear momentum and energy conservation on the midlatitude beta plane. A numerical (iterative) technique is used to solve for the vertical wind which is coupled to the density and pressure fields. The temperature structure from 1 to 1000 km and the lower boundary conditions are specified using the U.S. Standard Atmosphere 1976. Vertical winds are initialized at the top of the Planetary Boundary Layer using Ekman pumping values over flat terrain. The model also allows for the generation of waves during the geostrophic adjustment process and incorporates wave nonlinearity effects.

Density and temperature structure over northern Europe

NASA Technical Reports Server (NTRS)

Philbrick, C. R.; Schmidlin, F. J.; Grossmann, K. U.; Lange, G.; Offermann, D.; Baker, K. D.; Krankowsky, D.; Von Zahn, U.

1985-01-01

During the Energy Budget Campaign, a number of profiles of the density and temperature were obtained to study the structure and variability of the atmosphere. The measurements were made using rocketborne instrumentation launched from Esrange, Sweden, and Andoya Rocket Range, Norway, during November and December 1980. The techniques included meteorological temperature sondes, passive falling sphere, accelerometer instrumented falling spheres, density gauges, mass spectrometers and infrared emission experiments. The instruments provided data covering the altitude range from 20 to 150 km. The measurements were made during periods which have been grouped into three categories by level of geomagnetic activity. Analysis has been made to compare the results and to examine the wave features and variations in the vertical profiles for scales ranging between hundreds of meters and tens of kilometers. Most of the features observed fit qualitatively within the range expected for internal gravity waves. However, the features in the profiles during one of the measurement periods are unusual and may be due to aurorally generated shock waves. The geomagnetic storm conditions caused temperature increases in the lower thermosphere which maximized in the 120-140 km region.

The structure of ion-acoustic waves in a low-frequency three-component electron-ion space plasma with two-electron populations

NASA Astrophysics Data System (ADS)

Govender, G.; Moolla, S.

2018-07-01

Low-frequency ion-acoustic waves are analysed on the ion time-scale, in a three-component electron-ion space plasma. The solitary waves propagate in the positive x direction relative to an ambient magnetic field ěc {B}_0 which forms static background for a configuration consisting of cool fluid ions and both warm and hot Boltzmann-distributed electrons with temperatures T_{ic}, T_{ew} and T_{eh}, respectively. We derive linear dispersion relation for the waves by introducing first-order density, pressure and velocity perturbations into the ion fluid equations. Additionally, the variation in the nonlinear structure of the waves are investigated by carrying out a full parametric analysis utilising our numerical code. Our results reveal that ion-acoustic waves exhibit well-defined nonlinear spikes at speeds of M≥ 2.25 and an electric field amplitude of E_0=0.85. It is also shown that low wave speeds (M≤ 2), higher densities of the hot electrons, antiparallel drifting of the cool fluid ions, and increased ion temperatures all lead to significant dispersive effects. The ion-acoustic plasma waves featured in this paper have forms that are consistent with those classified as the type-A and type-B broadband electrostatic noise (BEN) observed in the data obtained from earlier satellite missions.

Quantum linear magnetoresistance in NbTe2

NASA Astrophysics Data System (ADS)

Chen, Hongxiang; Li, Zhilin; Fan, Xiao; Guo, Liwei; Chen, Xiaolong

2018-07-01

NbTe2 is a quasi-2D layered semimetal with charge density wave ground state showing a distorted-1T structure at room temperature. Here we report the anisotropic magneto-transport properties of NbTe2. An anomalous linear magnetoresistance up to 30% at 3 K in 9 T was observed, which can be well explained by a quantum linear magnetoresistance model. Our results reveal that a large quasi-2D Fermi surface and small Fermi pockets with linearly dispersive bands coexist in NbTe2. The comparison with the isostructural TaTe2 provides more information about the band structure evolution with charge density wave transitions in NbTe2 and TaTe2.

Structural, electronic and vibrational properties of lanthanide monophosphide at high pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Panchal, J. M., E-mail: amitjignesh@yahoo.co.in; Department of Physics, University School of Sciences, Gujarat University, Ahmedabad 380009, Gujarat; Joshi, Mitesh

2016-05-06

A first-principles plane wave self-consistent method with the ultra-soft-pseudopotential scheme in the framework of the density functional theory (DFT) is performed to study structural, electronic and vibrational properties of LaP for Rock-salt (NaCl/Bl) and Cesium-chloride (CsCl/B2) phases. The instability of Rock-salt (NaCl/Bl) phases around the transition is discussed. Conclusions based on electronic energy band structure, density of state, phonon dispersion and phonon density of states in both phases are outlined. The calculated results are consistence and confirm the successful applicability of quasi-harmonic phonon theory for structural instability studies for the alloys.

Fabric dependence of wave propagation in anisotropic porous media

PubMed Central

Cowin, Stephen C.; Cardoso, Luis

2012-01-01

Current diagnosis of bone loss and osteoporosis is based on the measurement of the Bone Mineral Density (BMD) or the apparent mass density. Unfortunately, in most clinical ultrasound densitometers: 1) measurements are often performed in a single anatomical direction, 2) only the first wave arriving to the ultrasound probe is characterized, and 3) the analysis of bone status is based on empirical relationships between measurable quantities such as Speed of Sound (SOS) and Broadband Ultrasound Attenuation (BUA) and the density of the porous medium. However, the existence of a second wave in cancellous bone has been reported, which is an unequivocal signature of poroelastic media, as predicted by Biot’s poroelastic wave propagation theory. In this paper the governing equations for wave motion in the linear theory of anisotropic poroelastic materials are developed and extended to include the dependence of the constitutive relations upon fabric - a quantitative stereological measure of the degree of structural anisotropy in the pore architecture of a porous medium. This fabric-dependent anisotropic poroelastic approach is a theoretical framework to describe the microarchitectural-dependent relationship between measurable wave properties and the elastic constants of trabecular bone, and thus represents an alternative for bone quality assessment beyond BMD alone. PMID:20461539

Structure of the charge density wave in cuprate superconductors: Lessons from NMR

NASA Astrophysics Data System (ADS)

Atkinson, W. A.; Ufkes, S.; Kampf, A. P.

2018-03-01

Using a mix of numerical and analytic methods, we show that recent NMR 17O measurements provide detailed information about the structure of the charge-density wave (CDW) phase in underdoped YBa2Cu3O6 +x . We perform Bogoliubov-de Gennes (BdG) calculations of both the local density of states and the orbitally resolved charge density, which are closely related to the magnetic and electric quadrupole contributions to the NMR spectrum, using a microscopic model that was shown previously to agree closely with x-ray experiments. The BdG results reproduce qualitative features of the experimental spectrum extremely well. These results are interpreted in terms of a generic "hot-spot" model that allows one to trace the origins of the NMR line shapes. We find that four quantities—the orbital character of the Fermi surface at the hot spots, the Fermi surface curvature at the hot spots, the CDW correlation length, and the magnitude of the subdominant CDW component—are key in determining the line shapes.

Advanced Multivariate Inversion Techniques for High Resolution 3D Geophysical Modeling (Invited)

NASA Astrophysics Data System (ADS)

Maceira, M.; Zhang, H.; Rowe, C. A.

2009-12-01

We focus on the development and application of advanced multivariate inversion techniques to generate a realistic, comprehensive, and high-resolution 3D model of the seismic structure of the crust and upper mantle that satisfies several independent geophysical datasets. Building on previous efforts of joint invesion using surface wave dispersion measurements, gravity data, and receiver functions, we have added a fourth dataset, seismic body wave P and S travel times, to the simultaneous joint inversion method. We present a 3D seismic velocity model of the crust and upper mantle of northwest China resulting from the simultaneous, joint inversion of these four data types. Surface wave dispersion measurements are primarily sensitive to seismic shear-wave velocities, but at shallow depths it is difficult to obtain high-resolution velocities and to constrain the structure due to the depth-averaging of the more easily-modeled, longer-period surface waves. Gravity inversions have the greatest resolving power at shallow depths, and they provide constraints on rock density variations. Moreover, while surface wave dispersion measurements are primarily sensitive to vertical shear-wave velocity averages, body wave receiver functions are sensitive to shear-wave velocity contrasts and vertical travel-times. Addition of the fourth dataset, consisting of seismic travel-time data, helps to constrain the shear wave velocities both vertically and horizontally in the model cells crossed by the ray paths. Incorporation of both P and S body wave travel times allows us to invert for both P and S velocity structure, capitalizing on empirical relationships between both wave types’ seismic velocities with rock densities, thus eliminating the need for ad hoc assumptions regarding the Poisson ratios. Our new tomography algorithm is a modification of the Maceira and Ammon joint inversion code, in combination with the Zhang and Thurber TomoDD (double-difference tomography) program.

Single-cycle high-intensity electromagnetic pulse generation in the interaction of a plasma wakefield with regular nonlinear structures.

PubMed

Bulanov, S S; Esirkepov, T Zh; Kamenets, F F; Pegoraro, F

2006-03-01

The interaction of regular nonlinear structures (such as subcycle solitons, electron vortices, and wake Langmuir waves) with a strong wake wave in a collisionless plasma can be exploited in order to produce ultrashort electromagnetic pulses. The electromagnetic field of the nonlinear structure is partially reflected by the electron density modulations of the incident wake wave and a single-cycle high-intensity electromagnetic pulse is formed. Due to the Doppler effect the length of this pulse is much shorter than that of the nonlinear structure. This process is illustrated with two-dimensional particle-in-cell simulations. The considered laser-plasma interaction regimes can be achieved in present day experiments and can be used for plasma diagnostics.

Self-interaction corrected LDA + U investigations of BiFeO3 properties: plane-wave pseudopotential method

NASA Astrophysics Data System (ADS)

Yaakob, M. K.; Taib, M. F. M.; Lu, L.; Hassan, O. H.; Yahya, M. Z. A.

2015-11-01

The structural, electronic, elastic, and optical properties of BiFeO3 were investigated using the first-principles calculation based on the local density approximation plus U (LDA + U) method in the frame of plane-wave pseudopotential density functional theory. The application of self-interaction corrected LDA + U method improved the accuracy of the calculated properties. Results of structural, electronic, elastic, and optical properties of BiFeO3, calculated using the LDA + U method were in good agreement with other calculation and experimental data; the optimized choice of on-site Coulomb repulsion U was 3 eV for the treatment of strong electronic localized Fe 3d electrons. Based on the calculated band structure and density of states, the on-site Coulomb repulsion U had a significant effect on the hybridized O 2p and Fe 3d states at the valence and the conduction band. Moreover, the elastic stiffness tensor, the longitudinal and shear wave velocities, bulk modulus, Poisson’s ratio, and the Debye temperature were calculated for U = 0, 3, and 6 eV. The elastic stiffness tensor, bulk modulus, sound velocities, and Debye temperature of BiFeO3 consistently decreased with the increase of the U value.

Simulated GOLD Observations of Atmospheric Waves

NASA Astrophysics Data System (ADS)

Correira, J.; Evans, J. S.; Lumpe, J. D.; Rusch, D. W.; Chandran, A.; Eastes, R.; Codrescu, M.

2016-12-01

The Global-scale Observations of the Limb and Disk (GOLD) mission will measure structures in the Earth's airglow layer due to dynamical forcing by vertically and horizontally propagating waves. These measurements focus on global-scale structures, including compositional and temperature responses resulting from dynamical forcing. Daytime observations of far-UV emissions by GOLD will be used to generate two-dimensional maps of the ratio of atomic oxygen and molecular nitrogen column densities (ΣO/N2 ) as well as neutral temperature that provide signatures of large-scale spatial structure. In this presentation, we use simulations to demonstrate GOLD's capability to deduce periodicities and spatial dimensions of large-scale waves from the spatial and temporal evolution observed in composition and temperature maps. Our simulations include sophisticated forward modeling of the upper atmospheric airglow that properly accounts for anisotropy in neutral and ion composition, temperature, and solar illumination. Neutral densities and temperatures used in the simulations are obtained from global circulation and climatology models that have been perturbed by propagating waves with a range of amplitudes, periods, and sources of excitation. Modeling of airglow emission and predictions of ΣO/N2 and neutral temperatures are performed with the Atmospheric Ultraviolet Radiance Integrated Code (AURIC) and associated derived product algorithms. Predicted structure in ΣO/N2 and neutral temperature due to dynamical forcing by propagating waves is compared to existing observations. Realistic GOLD Level 2 data products are generated from simulated airglow emission using algorithm code that will be implemented operationally at the GOLD Science Data Center.

Influence of the spatially inhomogeneous gap distribution on the quasiparticle current in c-axis junctions involving d-wave superconductors with charge density waves.

PubMed

Ekino, T; Gabovich, A M; Suan Li, Mai; Szymczak, H; Voitenko, A I

2016-11-09

The quasiparticle tunnel current J(V) between the superconducting ab-planes along the c-axis and the corresponding conductance [Formula: see text] were calculated for symmetric junctions composed of disordered d-wave layered superconductors partially gapped by charge density waves (CDWs). Here, V is the voltage. Both the checkerboard and unidirectional CDWs were considered. It was shown that the spatial spread of the CDW-pairing strength substantially smears the peculiarities of G(V) appropriate to uniform superconductors. The resulting curves G(V) become very similar to those observed for a number of cuprates in intrinsic junctions, e.g. mesas. In particular, the influence of CDWs may explain the peak-dip-hump structures frequently found for high-T c oxides.

Self consistent solution of Schrödinger Poisson equations and some electronic properties of ZnMgO/ZnO hetero structures

NASA Astrophysics Data System (ADS)

Uslu, Salih; Yarar, Zeki

2017-02-01

The epitaxial growth of quantum wells composed of high quality allows the production and application to their device of new structures in low dimensions. The potential profile at the junction is determined by free carriers and by the level of doping. Therefore, the shape of potential is obtained by the electron density. Energy level determines the number of electrons that can be occupied at every level. Energy levels and electron density values of each level must be calculated self consistently. Starting with V(z) test potential, wave functions and electron densities for each energy levels can be calculated to solve Schrödinger equation. If Poisson's equation is solved with the calculated electron density, the electrostatic potential can be obtained. The new V(z) potential can be calculated with using electrostatic potential found beforehand. Thus, the obtained values are calculated self consistently to a certain error criterion. In this study, the energy levels formed in the interfacial potential, electron density in each level and the wave function dependence of material parameters were investigated self consistently.

Recent Progress in Brillouin Scattering Based Fiber Sensors

PubMed Central

Bao, Xiaoyi; Chen, Liang

2011-01-01

Brillouin scattering in optical fiber describes the interaction of an electro-magnetic field (photon) with a characteristic density variation of the fiber. When the electric field amplitude of an optical beam (so-called pump wave), and another wave is introduced at the downshifted Brillouin frequency (namely Stokes wave), the beating between the pump and Stokes waves creates a modified density change via the electrostriction effect, resulting in so-called the stimulated Brillouin scattering. The density variation is associated with a mechanical acoustic wave; and it may be affected by local temperature, strain, and vibration which induce changes in the fiber effective refractive index and sound velocity. Through the measurement of the static or dynamic changes in Brillouin frequency along the fiber one can realize a distributed fiber sensor for local temperature, strain and vibration over tens or hundreds of kilometers. This paper reviews the progress on improving sensing performance parameters like spatial resolution, sensing length limitation and simultaneous temperature and strain measurement. These kinds of sensors can be used in civil structural monitoring of pipelines, bridges, dams, and railroads for disaster prevention. Analogous to the static Bragg grating, one can write a moving Brillouin grating in fibers, with the lifetime of the acoustic wave. The length of the Brillouin grating can be controlled by the writing pulses at any position in fibers. Such gratings can be used to measure changes in birefringence, which is an important parameter in fiber communications. Applications for this kind of sensor can be found in aerospace, material processing and fine structures. PMID:22163842

Recent progress in Brillouin scattering based fiber sensors.

PubMed

Bao, Xiaoyi; Chen, Liang

2011-01-01

Brillouin scattering in optical fiber describes the interaction of an electro-magnetic field (photon) with a characteristic density variation of the fiber. When the electric field amplitude of an optical beam (so-called pump wave), and another wave is introduced at the downshifted Brillouin frequency (namely Stokes wave), the beating between the pump and Stokes waves creates a modified density change via the electrostriction effect, resulting in so-called the stimulated Brillouin scattering. The density variation is associated with a mechanical acoustic wave; and it may be affected by local temperature, strain, and vibration which induce changes in the fiber effective refractive index and sound velocity. Through the measurement of the static or dynamic changes in Brillouin frequency along the fiber one can realize a distributed fiber sensor for local temperature, strain and vibration over tens or hundreds of kilometers. This paper reviews the progress on improving sensing performance parameters like spatial resolution, sensing length limitation and simultaneous temperature and strain measurement. These kinds of sensors can be used in civil structural monitoring of pipelines, bridges, dams, and railroads for disaster prevention. Analogous to the static Bragg grating, one can write a moving Brillouin grating in fibers, with the lifetime of the acoustic wave. The length of the Brillouin grating can be controlled by the writing pulses at any position in fibers. Such gratings can be used to measure changes in birefringence, which is an important parameter in fiber communications. Applications for this kind of sensor can be found in aerospace, material processing and fine structures.

Study of plasma-based stable and ultra-wideband electromagnetic wave absorption for stealth application

NASA Astrophysics Data System (ADS)

Xuyang, CHEN; Fangfang, SHEN; Yanming, LIU; Wei, AI; Xiaoping, LI

2018-06-01

A plasma-based stable, ultra-wideband electromagnetic (EM) wave absorber structure is studied in this paper for stealth applications. The stability is maintained by a multi-layer structure with several plasma layers and dielectric layers distributed alternately. The plasma in each plasma layer is designed to be uniform, whereas it has a discrete nonuniform distribution from the overall view of the structure. The nonuniform distribution of the plasma is the key to obtaining ultra-wideband wave absorption. A discrete Epstein distribution model is put forward to constrain the nonuniform electron density of the plasma layers, by which the wave absorption range is extended to the ultra-wideband. Then, the scattering matrix method (SMM) is employed to analyze the electromagnetic reflection and absorption of the absorber structure. In the simulation, the validation of the proposed structure and model in ultra-wideband EM wave absorption is first illustrated by comparing the nonuniform plasma model with the uniform case. Then, the influence of various parameters on the EM wave reflection of the plasma are simulated and analyzed in detail, verifying the EM wave absorption performance of the absorber. The proposed structure and model are expected to be superior in some realistic applications, such as supersonic aircraft.

Resonance in fast-wave amplitude in the periphery of cylindrical plasmas and application to edge losses of wave heating power in tokamaks

DOE PAGES

Perkins, R. J.; Hosea, J. C.; Bertelli, N.; ...

2016-07-01

Heating magnetically confined plasmas using waves in the ion-cyclotron range of frequencies typically requires coupling these waves over a steep density gradient. Furthermore, this process has produced an unexpected and deleterious phenomenon on the National Spherical Torus eXperiment (NSTX): a prompt loss of wave power along magnetic field lines in front of the antenna to the divertor. Understanding this loss may be key to achieving effective heating and expanding the operational space of NSTX-Upgrade. Here, we propose that a new type of mode, which conducts a significant fraction of the total wave power in the low-density peripheral plasma, is drivingmore » these losses. We demonstrate the existence of such modes, which are distinct from surface modes and coaxial modes, in a cylindrical cold-plasma model when a half wavelength structure fits into the region outside the core plasma. The latter condition generalizes the previous hypothesis regarding the occurence of the edge losses and may explain why full-wave simulations predict these losses in some cases but not others. If valid, this condition implies that outer gap control is a potential strategy for mitigating the losses in NSTX-Upgrade in addition to raising the magnetic field or influencing the edge density.« less

A finite element model of a MEMS-based surface acoustic wave hydrogen sensor.

PubMed

El Gowini, Mohamed M; Moussa, Walied A

2010-01-01

Hydrogen plays a significant role in various industrial applications, but careful handling and continuous monitoring are crucial since it is explosive when mixed with air. Surface Acoustic Wave (SAW) sensors provide desirable characteristics for hydrogen detection due to their small size, low fabrication cost, ease of integration and high sensitivity. In this paper a finite element model of a Surface Acoustic Wave sensor is developed using ANSYS12© and tested for hydrogen detection. The sensor consists of a YZ-lithium niobate substrate with interdigital electrodes (IDT) patterned on the surface. A thin palladium (Pd) film is added on the surface of the sensor due to its high affinity for hydrogen. With increased hydrogen absorption the palladium hydride structure undergoes a phase change due to the formation of the β-phase, which deteriorates the crystal structure. Therefore with increasing hydrogen concentration the stiffness and the density are significantly reduced. The values of the modulus of elasticity and the density at different hydrogen concentrations in palladium are utilized in the finite element model to determine the corresponding SAW sensor response. Results indicate that with increasing the hydrogen concentration the wave velocity decreases and the attenuation of the wave is reduced.

Propagation of radio frequency waves through density fluctuations

NASA Astrophysics Data System (ADS)

Valvis, S. I.; Papagiannis, P.; Papadopoulos, A.; Hizanidis, K.; Glytsis, E.; Bairaktaris, F.; Zisis, A.; Tigelis, I.; Ram, A. K.

2017-10-01

On their way to the core of a tokamak plasma, radio frequency (RF) waves, excited in the vacuum region, have to propagate through a variety of density fluctuations in the edge region. These fluctuations include coherent structures, like blobs that can be field aligned or not, as well as turbulent and filamentary structures. We have been studying the effect of fluctuations on RF propagation using both theoretical (analytical) and computational models. The theoretical results are being compared with those obtained by two different numerical codes ``a Finite Difference Frequency Domain code and the commercial COMSOL package. For plasmas with arbitrary distribution of coherent and turbulent fluctuations, we have formulated an effective dielectric permittivity of the edge plasma. This permittivity tensor is then used in numerical simulations to study the effect of multi-scale turbulence on RF waves. We not only consider plane waves but also Gaussian beams in the electron cyclotron and lower hybrid range of frequencies. The analytical theory and results from simulations on the propagation of RF waves will be presented. Supported in part by the Hellenic National Programme on Controlled Thermonuclear Fusion associated with the EUROfusion Consortium and by DoE Grant DE-FG02-91ER-54109.

The distribution of seismic velocities and attenuation in the earth. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Hart, R. S.

1977-01-01

Estimates of the radial distribution of seismic velocities and density and of seismic attenuation within the earth are obtained through inversion of body wave, surface wave, and normal mode data. The effect of attenuation related dispersion on gross earth structure, and on the reliability of eigenperiod identifications is discussed. The travel time baseline discrepancies between body waves and free oscillation models are examined and largely resolved.

Band dependence of charge density wave in quasi-one-dimensional Ta2NiSe7 probed by orbital magnetoresistance

NASA Astrophysics Data System (ADS)

He, Jiaming; Zhang, Yiran; Wen, Libin; Yang, Yusen; Liu, Jinyu; Wu, Yueshen; Lian, Hailong; Xing, Hui; Wang, Shun; Mao, Zhiqiang; Liu, Ying

2017-07-01

Ta2NiSe7 is a quasi-one-dimensional (quasi-1D) transition-metal chalcogenide with Ta and Ni chain structures. An incommensurate charge-density wave (CDW) in this quasi-1D structure was well studied previously using tunnelling spectrum, X-ray, and electron diffraction, whereas its transport property and the relation to the underlying electronic states remain to be explored. Here, we report our results of the magnetoresistance (MR) on Ta2NiSe7. A breakdown of Kohler's rule is found upon entering the CDW state. Concomitantly, a clear change in curvature in the field dependence of MR is observed. We show that the curvature change is well described by the two-band orbital MR, with the hole density being strongly suppressed in the CDW state, indicating that the p orbitals from Se atoms dominate the change in transport through CDW transition.

Traveling waves in a continuum model of 1D schools

NASA Astrophysics Data System (ADS)

Oza, Anand; Kanso, Eva; Shelley, Michael

2017-11-01

We construct and analyze a continuum model of a 1D school of flapping swimmers. Our starting point is a delay differential equation that models the interaction between a swimmer and its upstream neighbors' wakes, which is motivated by recent experiments in the Applied Math Lab at NYU. We coarse-grain the evolution equations and derive PDEs for the swimmer density and variables describing the upstream wake. We study the equations both analytically and numerically, and find that a uniform density of swimmers destabilizes into a traveling wave. Our model makes a number of predictions about the properties of such traveling waves, and sheds light on the role of hydrodynamics in mediating the structure of swimming schools.

Probability and Quantum Paradigms: the Interplay

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kracklauer, A. F.

Since the introduction of Born's interpretation of quantum wave functions as yielding the probability density of presence, Quantum Theory and Probability have lived in a troubled symbiosis. Problems arise with this interpretation because quantum probabilities exhibit features alien to usual probabilities, namely non Boolean structure and non positive-definite phase space probability densities. This has inspired research into both elaborate formulations of Probability Theory and alternate interpretations for wave functions. Herein the latter tactic is taken and a suggested variant interpretation of wave functions based on photo detection physics proposed, and some empirical consequences are considered. Although incomplete in a fewmore » details, this variant is appealing in its reliance on well tested concepts and technology.« less

Probability and Quantum Paradigms: the Interplay

NASA Astrophysics Data System (ADS)

Kracklauer, A. F.

2007-12-01

Since the introduction of Born's interpretation of quantum wave functions as yielding the probability density of presence, Quantum Theory and Probability have lived in a troubled symbiosis. Problems arise with this interpretation because quantum probabilities exhibit features alien to usual probabilities, namely non Boolean structure and non positive-definite phase space probability densities. This has inspired research into both elaborate formulations of Probability Theory and alternate interpretations for wave functions. Herein the latter tactic is taken and a suggested variant interpretation of wave functions based on photo detection physics proposed, and some empirical consequences are considered. Although incomplete in a few details, this variant is appealing in its reliance on well tested concepts and technology.

Elastic precursor wave decay in shock-compressed aluminum over a wide range of temperature

NASA Astrophysics Data System (ADS)

Austin, Ryan A.

2018-01-01

The effect of temperature on the dynamic flow behavior of aluminum is considered in the context of precursor wave decay measurements and simulations. In this regard, a dislocation-based model of high-rate metal plasticity is brought into agreement with previous measurements of evolving wave profiles at 300 to 933 K, wherein the amplification of the precursor structure with temperature arises naturally from the dislocation mechanics treatment. The model suggests that the kinetics of inelastic flow and stress relaxation are governed primarily by phonon scattering and radiative damping (sound wave emission from dislocation cores), both of which intensify with temperature. The manifestation of these drag effects is linked to low dislocation density ahead of the precursor wave and the high mobility of dislocations in the face-centered cubic lattice. Simulations performed using other typical models of shock wave plasticity do not reproduce the observed temperature-dependence of elastic/plastic wave structure.

Deciphering the embedded wave in Saturn's Maxwell ringlet

NASA Astrophysics Data System (ADS)

French, Richard G.; Nicholson, Philip D.; Hedman, Mathew M.; Hahn, Joseph M.; McGhee-French, Colleen A.; Colwell, Joshua E.; Marouf, Essam A.; Rappaport, Nicole J.

2016-11-01

The eccentric Maxwell ringlet in Saturn's C ring is home to a prominent wavelike structure that varies strongly and systematically with true anomaly, as revealed by nearly a decade of high-SNR Cassini occultation observations. Using a simple linear "accordion" model to compensate for the compression and expansion of the ringlet and the wave, we derive a mean optical depth profile for the ringlet and a set of rescaled, background-subtracted radial wave profiles. We use wavelet analysis to identify the wave as a 2-armed trailing spiral, consistent with a density wave driven by an m = 2 outer Lindblad resonance (OLR), with a pattern speed Ωp = 1769.17° d-1 and a corresponding resonance radius ares = 87530.0 km. Estimates of the surface mass density of the Maxwell ringlet range from a mean value of 11g cm-2 derived from the self-gravity model to 5 - 12gcm-2 , as inferred from the wave's phase profile and a theoretical dispersion relation. The corresponding opacity is about 0.12 cm2 g-1, comparable to several plateaus in the outer C ring (Hedman, M.N., Nicholson, P.D. [2014]. Mont. Not. Roy. Astron. Soc. 444, 1369-1388). A linear density wave model using the derived wave phase profile nicely matches the wave's amplitude, wavelength, and phase in most of our observations, confirming the accuracy of the pattern speed and demonstrating the wave's coherence over a period of 8 years. However, the linear model fails to reproduce the narrow, spike-like structures that are prominent in the observed optical depth profiles. Using a symplectic N-body streamline-based dynamical code (Hahn, J.M., Spitale, J.N. [2013]. Astrophys. J. 772, 122), we simulate analogs of the Maxwell ringlet, modeled as an eccentric ringlet with an embedded wave driven by a fictitious satellite with an OLR located within the ring. The simulations reproduce many of the features of the actual observations, including strongly asymmetric peaks and troughs in the inward-propagating density wave. We argue that the Maxwell ringlet wave is generated by a sectoral normal-mode oscillation inside Saturn with ℓ = m = 2 , similar to other planetary internal modes that have been inferred from density waves observed in Saturn's C ring (Hedman, M.N., Nicholson, P.D. [2013]. Astron. J. 146, 12; Hedman, M.N., Nicholson, P.D. [2014]. Mont. Not. Roy. Astron. Soc. 444, 1369-1388). Our identification of a third m = 2 mode associated with saturnian internal oscillations supports the suggestions of mode splitting by Fuller et al. (Fuller, J., Lai, D., Storch, N.I. [2014]. Icarus 231, 34-50) and Fuller (Fuller, J. [2014]. Icarus 242, 283-296). The fitted amplitude of the wave, if it is interpreted as driven by the ℓ = m = 2 f-mode, implies a radial amplitude at the 1 bar level of ∼ 50 cm, according to the models of Marley and Porco (Marley, M.S., Porco, C.C. [1993]. Icarus 106, 508).

Strong wave/mean-flow coupling in baroclinic acoustic streaming

NASA Astrophysics Data System (ADS)

Chini, Greg; Michel, Guillaume

2017-11-01

Recently, Chini et al. demonstrated the potential for large-amplitude acoustic streaming in compressible channel flows subjected to strong background cross-channel density variations. In contrast with classic Rayleigh streaming, standing acoustic waves of O (ɛ) amplitude acquire vorticity owing to baroclinic torques acting throughout the domain rather than via viscous torques acting in Stokes boundary layers. More significantly, these baroclinically-driven streaming flows have a magnitude that also is O (ɛ) , i.e. comparable to that of the sound waves. In the present study, the consequent potential for fully two-way coupling between the waves and streaming flows is investigated using a novel WKBJ analysis. The analysis confirms that the wave-driven streaming flows are sufficiently strong to modify the background density gradient, thereby modifying the leading-order acoustic wave structure. Simulations of the wave/mean-flow system enabled by the WKBJ analysis are performed to illustrate the nature of the two-way coupling, which contrasts sharply with classic Rayleigh streaming, for which the waves can first be determined and the streaming flows subsequently computed.

On the nature of fast sausage waves in coronal loops

NASA Astrophysics Data System (ADS)

Bahari, Karam

2018-05-01

The effect of the parameters of coronal loops on the nature of fast sausage waves are investigated. To do this three models of the coronal loop considered, a simple loop model, a current-carrying loop model and a model with radially structured density called "Inner μ" profile. For all the models the Magnetohydrodynamic (MHD) equations solved analytically in the linear approximation and the restoring forces of oscillations obtained. The ratio of the magnetic tension force to the pressure gradient force obtained as a function of the distance from the axis of the loop. In the simple loop model for all values of the loop parameters the fast sausages wave have a mixed nature of Alfvénic and fast MHD waves, in the current-carrying loop model with thick annulus and low density contrast the fast sausage waves can be considered as purely Alfvénic wave in the core region of the loop, and in the "Inner μ" profile for each set of the parameters of the loop the wave can be considered as a purely Alfvénic wave in some regions of the loop.

Silicone-Based Triboelectric Nanogenerator for Water Wave Energy Harvesting.

PubMed

Xiao, Tian Xiao; Jiang, Tao; Zhu, Jian Xiong; Liang, Xi; Xu, Liang; Shao, Jia Jia; Zhang, Chun Lei; Wang, Jie; Wang, Zhong Lin

2018-01-31

Triboelectric nanogenerator (TENG) has been proven to be efficient for harvesting water wave energy, which is one of the most promising renewable energy sources. In this work, a TENG with a silicone rubber/carbon black composite electrode was designed for converting the water wave energy into electricity. The silicone-based electrode with a soft texture provides a better contact with the dielectric film. Furthermore, a spring structure is introduced to transform low-frequency water wave motions into high-frequency vibrations. They together improve the output performance and efficiency of TENG. The output performances of TENGs are further enhanced by optimizing the triboelectric material pair and tribo-surface area. A spring-assisted TENG device with the segmented silicone rubber-based electrode structure was sealed into a waterproof box, which delivers a maximum power density of 2.40 W m -3 , as triggered by the water waves. The present work provides a new strategy for fabricating high-performance TENG devices by coupling flexible electrodes and spring structure for harvesting water wave energy.

Determination of Fluid Density and Viscosity by Analyzing Flexural Wave Propagations on the Vibrating Micro-Cantilever

PubMed Central

Kim, Deokman; Hong, Seongkyeol; Park, Junhong

2017-01-01

The determination of fluid density and viscosity using most cantilever-based sensors is based on changes in resonant frequency and peak width. Here, we present a wave propagation analysis using piezoelectrically excited micro-cantilevers under distributed fluid loading. The standing wave shapes of microscale-thickness cantilevers partially immersed in liquids (water, 25% glycerol, and acetone), and nanoscale-thickness microfabricated cantilevers fully immersed in gases (air at three different pressures, carbon dioxide, and nitrogen) were investigated to identify the effects of fluid-structure interactions to thus determine the fluid properties. This measurement method was validated by comparing with the known fluid properties, which agreed well with the measurements. The relative differences for the liquids were less than 4.8% for the densities and 3.1% for the viscosities, and those for the gases were less than 6.7% for the densities and 7.3% for the viscosities, showing better agreements in liquids than in gases. PMID:29077005

Measurements and modeling of radio frequency field structures in a helicon plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, C. A.; Chen, Guangye; Arefiev, A. V.

2011-01-01

Measurements of the radio frequency (rf) field structure, plasma density, and electron temperature are presented for a 1 kW argon helicon plasma source. The measured profiles change considerably when the equilibrium magnetic field is reversed. The measured rf fields are identified as fields of radially localized helicon waves, which propagate in the axial direction. The rf field structure is compared to the results of two-dimensional cold plasma full-wave simulations for the measured density profiles. Electron collision frequency is adjusted in the simulations to match the simulated and measured field profiles. The resulting frequency is anomalously high, which is attributed tomore » the excitation of an ion-acoustic instability. The calculated power deposition is insensitive to the collision frequency and accounts for most of the power supplied by the rf-generator.« less

Lunar Structure from Coda Wave Interferometry

NASA Astrophysics Data System (ADS)

Nunn, Ceri; Igel, Heiner

2017-04-01

As part of the Apollo lunar missions, four seismometers were deployed on the near-side of the Moon between 1969 and 1972, and operated continuously until 1977. There are many difficulties associated with determining lunar structure from these records. As a result, many properties of the moon, such as the thickness, density and porosity of the crust are poorly constrained. This hampers our ability to determine the structure, geochemical composition of the moon, its evolution, and ultimately the evolution of the solar system. We explore the use of coda wave interferometry to reconstruct the near surface structure within the strongly scattering lunar crust.

Many-body instabilities and mass generation in slow Dirac materials

NASA Astrophysics Data System (ADS)

Triola, Christopher; Zhu, Jian-Xin; Migliori, Albert; Balatsky, Alexander V.

2015-07-01

Some Kondo insulators are expected to possess topologically protected surface states with linear Dirac spectrum: the topological Kondo insulators. Because the bulk states of these systems typically have heavy effective electron masses, the surface states may exhibit extraordinarily small Fermi velocities that could force the effective fine structure constant of the surface states into the strong coupling regime. Using a tight-binding model, we study the many-body instabilities of these systems and identify regions of parameter space in which the system exhibits spin density wave and charge density wave order.

Another self-similar blast wave: Early time asymptote with shock heated electrons and high thermal conductivity

NASA Technical Reports Server (NTRS)

Cox, D. P.; Edgar, R. J.

1982-01-01

Accurate approximations are presented for the self-similar structures of nonradiating blast waves with adiabatic ions, isothermal electrons, and equation ion and electron temperatures at the shock. The cases considered evolve in cavities with power law ambient densities (including the uniform density case) and have negligible external pressure. The results provide the early time asymptote for systems with shock heating of electrons and strong thermal conduction. In addition, they provide analytical results against which two fluid numerical hydrodynamic codes can be checked.

Generalization of the Kohn-Sham system that can represent arbitrary one-electron density matrices

DOE PAGES

Hubertus J. J. van Dam

2016-04-27

Density functional theory is currently the most widely applied method in electronic structure theory. The Kohn-Sham method, based on a fictitious system of noninteracting particles, is the workhorse of the theory. The particular form of the Kohn-Sham wave function admits only idempotent one-electron density matrices whereas wave functions of correlated electrons in post-Hartree-Fock methods invariably have fractional occupation numbers. Here we show that by generalizing the orbital concept and introducing a suitable dot product as well as a probability density, a noninteracting system can be chosen that can represent the one-electron density matrix of any system, even one with fractionalmore » occupation numbers. This fictitious system ensures that the exact electron density is accessible within density functional theory. It can also serve as the basis for reduced density matrix functional theory. Moreover, to aid the analysis of the results the orbitals may be assigned energies from a mean-field Hamiltonian. This produces energy levels that are akin to Hartree-Fock orbital energies such that conventional analyses based on Koopmans' theorem are available. Lastly, this system is convenient in formalisms that depend on creation and annihilation operators as they are trivially applied to single-determinant wave functions.« less

Mechanical and Thermophysical Properties of Cubic Rock-Salt AlN Under High Pressure

NASA Astrophysics Data System (ADS)

Lebga, Noudjoud; Daoud, Salah; Sun, Xiao-Wei; Bioud, Nadhira; Latreche, Abdelhakim

2018-03-01

Density functional theory, density functional perturbation theory, and the Debye model have been used to investigate the structural, elastic, sound velocity, and thermodynamic properties of AlN with cubic rock-salt structure under high pressure, yielding the equilibrium structural parameters, equation of state, and elastic constants of this interesting material. The isotropic shear modulus, Pugh ratio, and Poisson's ratio were also investigated carefully. In addition, the longitudinal, transverse, and average elastic wave velocities, phonon contribution to the thermal conductivity, and interesting thermodynamic properties were predicted and analyzed in detail. The results demonstrate that the behavior of the elastic wave velocities under increasing hydrostatic pressure explains the hardening of the corresponding phonons. Based on the elastic stability criteria under pressure, it is found that AlN with cubic rock-salt structure is mechanically stable, even at pressures up to 100 GPa. Analysis of the Pugh ratio and Poisson's ratio revealed that AlN with cubic rock-salt structure behaves in brittle manner.

Photoemission study of the electronic structure and charge density waves of Na2Ti2Sb2O.

PubMed

Tan, S Y; Jiang, J; Ye, Z R; Niu, X H; Song, Y; Zhang, C L; Dai, P C; Xie, B P; Lai, X C; Feng, D L

2015-04-30

The electronic structure of Na2Ti2Sb2O single crystal is studied by photon energy and polarization dependent angle-resolved photoemission spectroscopy (ARPES). The obtained band structure and Fermi surface agree well with the band structure calculation of Na2Ti2Sb2O in the non-magnetic state, which indicates that there is no magnetic order in Na2Ti2Sb2O and the electronic correlation is weak. Polarization dependent ARPES results suggest the multi-band and multi-orbital nature of Na2Ti2Sb2O. Photon energy dependent ARPES results suggest that the electronic structure of Na2Ti2Sb2O is rather two-dimensional. Moreover, we find a density wave energy gap forms below the transition temperature and reaches 65 meV at 7 K, indicating that Na2Ti2Sb2O is likely a weakly correlated CDW material in the strong electron-phonon interaction regime.

Topographically induced internal solitary waves in a pycnocline: Ultrasonic probes and stereo-correlation measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dossmann, Yvan, E-mail: yvan.dossmann@anu.edu.au; CNRM-GAME, UMR3589 METEO-FRANCE and CNRS, 42 avenue Gaspard Coriolis, 31057 Toulouse Cedex 01; Laboratoire d’Aérologie, 14 avenue Edouard Belin, 31400 Toulouse

Internal solitary waves (ISWs) are large amplitude stable waves propagating in regions of high density gradients such as the ocean pycnocline. Their dynamics has often been investigated in two-dimensional approaches, however, their three-dimensional evolution is still poorly known. Experiments have been conducted in the large stratified water tank of CNRM-GAME to study the generation of ISWs in two academic configurations inspired by oceanic regimes. First, ultrasonic probes are used to measure the interfacial displacement in the two configurations. In the primary generation case for which the two layers are of constant density, the generation of ISWs is investigated in twomore » series of experiments with varying amplitude and forcing frequency. In the secondary generation case for which the lower layer is stratified, the generation of ISWs from the impact of an internal wave beam on the pycnocline and their subsequent dynamics is studied. The dynamics of ISWs in these two regimes accords well with analytical approaches and numerical simulations performed in analogous configurations. Then, recent developments of a stereo correlation technique are used to describe the three-dimensional structure of propagating ISWs. In the primary generation configuration, small transverse effects are observed in the course of the ISW propagation. In the secondary generation configuration, larger transverse structures are observed in the interfacial waves dynamics. The interaction between interfacial troughs and internal waves propagating in the lower stratified layer are a possible cause for the generation of these structures. The magnitude of these transverse structures is quantified with a nondimensional parameter in the two configurations. They are twice as large in the secondary generation case as in the primary generation case.« less

Liquid density analysis of sucrose and alcoholic beverages using polyimide guided Love-mode acoustic wave sensors

NASA Astrophysics Data System (ADS)

Turton, Andrew; Bhattacharyya, Debabrata; Wood, David

2006-02-01

A liquid density sensor using Love-mode acoustic waves has been developed which is suitable for use in the food and drinks industries. The sensor has an open flat surface allowing immersion into a sample and simple cleaning. A polyimide waveguide layer allows cheap and simple fabrication combined with a robust chemically resistant surface. The low shear modulus of polyimide allows thin guiding layers giving a high sensitivity. A dual structure with a smooth reference device exhibiting viscous coupling with the wave, and a patterned sense area to trap the liquid causing mass loading, allows discrimination of the liquid density from the square root of the density-viscosity product (ρη)0.5. Frequency shift and insertion loss change were proportional to (ρη)0.5 with a non-linear response due to the non-Newtonian nature of viscous liquids at high frequencies. Measurements were made with sucrose solutions up to 50% and different alcoholic drinks. A maximum sensitivity of 0.13 µg cm-3 Hz-1 was achieved, with a linear frequency response to density. This is the highest liquid density sensitivity obtained for acoustic mode sensors to the best of our knowledge.

Shear-horizontal surface acoustic wave phononic device with high density filling material for ultra-low power sensing applications

NASA Astrophysics Data System (ADS)

Richardson, M.; Sankaranarayanan, S. K. R. S.; Bhethanabotla, V. R.

2014-06-01

Finite element simulations of a phononic shear-horizontal surface acoustic wave (SAW) sensor based on ST 90°-X Quartz reveal a dramatic reduction in power consumption. The phononic sensor is realized by artificially structuring the delay path to form an acoustic meta-material comprised of a periodic microcavity array incorporating high-density materials such as tantalum or tungsten. Constructive interference of the scattered and secondary reflected waves at every microcavity interface leads to acoustic energy confinement in the high-density regions translating into reduced power loss. Tantalum filled cavities show the best performance while tungsten inclusions create a phononic bandgap. Based on our simulation results, SAW devices with tantalum filled microcavities were fabricated and shown to significantly decrease insertion loss. Our findings offer encouraging prospects for designing low power, highly sensitive portable biosensors.

Dynamic Structure Factor: An Introduction

NASA Astrophysics Data System (ADS)

Sturm, K.

1993-02-01

The doubly differential cross-section for weak inelastic scattering of waves or particles by manybody systems is derived in Born approximation and expressed in terms of the dynamic structure factor according to van Hove. The application of this very general scheme to scattering of neutrons, x-rays and high-energy electrons is discussed briefly. The dynamic structure factor, which is the space and time Fourier transform of the density-density correlation function, is a property of the many-body system independent of the external probe and carries information on the excitation spectrum of the system. The relation of the electronic structure factor to the density-density response function defined in linear-response theory is shown using the fluctuation-dissipation theorem. This is important for calculations, since the response function can be calculated approximately from the independent-particle response function in self-consistent field approximations, such as the random-phase approximation or the local-density approximation of the density functional theory. Since the density-density response function also determines the dielectric function, the dynamic structure can be expressed by the dielectric function.

Nonlinear interaction of kinetic Alfven wave and whistler: Turbulent spectra and anisotropic scaling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar Dwivedi, Navin; Sharma, R. P.

2013-04-15

In this work, we are presenting the excitation of oblique propagating whistler wave as a consequence of nonlinear interaction between whistler wave and kinetic Alfven wave (KAW) in intermediate beta plasmas. Numerical simulation has been done to study the transient evolution of magnetic field structures of KAW when the nonlinearity arises due to ponderomotive effects by taking the adiabatic response of the background density. Weak oblique propagating whistler signals in these nonlinear plasma density filaments (produced by KAW localization) get amplified. The spectral indices of the power spectrum at different times are calculated with given initial conditions of the simulations.more » Anisotropic scaling laws for KAW and whistlers are presented. The relevance of the present investigation to solar wind turbulence and its acceleration is also pointed out.« less

Persistent Charge-Density-Wave Order in Single-Layer TaSe2.

PubMed

Ryu, Hyejin; Chen, Yi; Kim, Heejung; Tsai, Hsin-Zon; Tang, Shujie; Jiang, Juan; Liou, Franklin; Kahn, Salman; Jia, Caihong; Omrani, Arash A; Shim, Ji Hoon; Hussain, Zahid; Shen, Zhi-Xun; Kim, Kyoo; Min, Byung Il; Hwang, Choongyu; Crommie, Michael F; Mo, Sung-Kwan

2018-02-14

We present the electronic characterization of single-layer 1H-TaSe 2 grown by molecular beam epitaxy using a combined angle-resolved photoemission spectroscopy, scanning tunneling microscopy/spectroscopy, and density functional theory calculations. We demonstrate that 3 × 3 charge-density-wave (CDW) order persists despite distinct changes in the low energy electronic structure highlighted by the reduction in the number of bands crossing the Fermi energy and the corresponding modification of Fermi surface topology. Enhanced spin-orbit coupling and lattice distortion in the single-layer play a crucial role in the formation of CDW order. Our findings provide a deeper understanding of the nature of CDW order in the two-dimensional limit.

Oblique ion-acoustic cnoidal waves in two temperature superthermal electrons magnetized plasma

NASA Astrophysics Data System (ADS)

Panwar, A.; Ryu, C. M.; Bains, A. S.

2014-12-01

A study is presented for the oblique propagation of ion acoustic cnoidal waves in a magnetized plasma consisting of cold ions and two temperature superthermal electrons modelled by kappa-type distributions. Using the reductive perturbation method, the nonlinear Korteweg de-Vries equation is derived, which further gives the solutions with a special type of cnoidal elliptical functions. Both compressive and rarefactive structures are found for these cnoidal waves. Nonlinear periodic cnoidal waves are explained in terms of plasma parameters depicting the Sagdeev potential and the phase curves. It is found that the density ratio of hot electrons to ions μ significantly modifies compressive/refractive wave structures. Furthermore, the combined effects of superthermality of cold and hot electrons κ c , κ h , cold to hot electron temperature ratio σ, angle of propagation and ion cyclotron frequency ωci have been studied in detail to analyze the height and width of compressive/refractive cnoidal waves. The findings in the present study could have important implications in understanding the physics of electrostatic wave structures in the Saturn's magnetosphere where two temperature superthermal electrons are present.

Self-consistent Model of Magnetospheric Ring Current and Propagating Electromagnetic Ion Cyclotron Waves. 2. Wave Induced Ring Current Precipitation and Thermal Electron Heating

NASA Technical Reports Server (NTRS)

Khazanov, G. V.; Gamayunov, K. V.; Gallagher, D. L.; Kozyra, J. U.; Liemohn, M. W.

2007-01-01

This paper continues presentation and discussion of the results from our new global self-consistent theoretical model of interacting ring current ions and propagating electromagnetic ion cyclotron waves [Khazanov et al., 2006]. To study the effects of electromagnetic ion cyclotron wave propagation and refraction on the wave induced ring current precipitation and heating of the thermal plasmaspheric electrons, we simulate the May 1998 storm. The main findings after a simulation can be summarized as follows. Firstly, the wave induced ring current precipitation exhibits quite a lot of fine structure, and is highly organized by location of the plasmapause gradient. The strongest fluxes of about 4 x 10(exp 6) (cm(raised dot) s(raised dot) sr(raised dot) (sup -1)) are observed during the maill and early recovery phases of the storm. The very interesting and probably more important finding is that in a number of cases the most intense precipitating fluxes are not connected to the most intense waves in simple manner. The characteristics of the wave power spectral density distribution over the wave normal angle are extremely crucial for the effectiveness of the ring current ion scattering. Secondly, comparison of the global proton precipitating patterns with the results from RAM [Kozyra et al., 1997a] reveals that although we observe a qualitative agreement between the localizations of the wave induced precipitations in the models, there is no quantitative agreement between the magnitudes of the fluxes. The quantitative differences are mainly due to a qualitative difference between the characteristics of the wave power spectral density distributions over the wave normal angle in RAM and in our model. Thirdly, the heat fluxes to plasmaspheric electrons caused by Landau resonate energy absorption from electromagnetic ion cyclotron waves are observed in the postnoon-premidnight MLT sector, and can reach the magnitude of 10(exp 11) eV/(cm(sup 2)(raised dot)s). The Coulomb energy degradation of the RC H(+) and O(+) ions maximizes at about 10(exp 11) (eV/(cm(sup 2) (raised dot) s), and typically leads to electron energy deposition rates of about 2(raised dot) 10(exp 10) (eV/(cm(sup 2)(raised dot)s) which are observed during two periods; 32-48 hours, and 76-86 hours after 1 May, 0000 UT. The theoretically derived spatial structure of the thermal electron heating caused by interaction of the ring current with the plasmasphere is strongly supported by concurrent and conjugate plasma measurements from the plasmasphere, ring current, and topside ionosphere [Gurgiolo et al., 2005]. Finally, the wave induced intense electron heating has a structure of the spot-like patches along the most enhanced density gradients in the plasmasphere boundary layer and can be a possible driver to the observed but still not explained small-scale structures of enhanced emissions in the stable auroral red arcs.

Strong enhancement of s -wave superconductivity near a quantum critical point of Ca 3 Ir 4 Sn 13

DOE PAGES

Biswas, P. K.; Guguchia, Z.; Khasanov, R.; ...

2015-11-11

We repormore » t microscopic studies by muon spin rotation/relaxation as a function of pressure of the Ca 3 Ir 4 Sn 13 and Sr 3Ir 4Sn 13 system displaying superconductivity and a structural phase transition associated with the formation of a charge density wave (CDW). Our findings show a strong enhancement of the superfluid density and a dramatic increase of the pairing strength above a pressure of ≈ 1.6 GPa giving direct evidence of the presence of a quantum critical point separating a superconducting phase coexisting with CDW from a pure superconducting phase. The superconducting order parameter in both phases has the same s-wave symmetry. In spite of the conventional phonon-mediated BCS character of the weakly correlated (Ca 1-xSr x) 3Ir 4Sn 13 system the dependence of the effective superfluid density on the critical temperature puts this compound in the “Uemura” plot close to unconventional superconductors. This system exemplifies that conventional BCS superconductors in the presence of competing orders or multi-band structure can also display characteristics of unconventional superconductors.« less

Non-autonomous matter-wave solitons in hybrid atomic-molecular Bose-Einstein condensates with tunable interactions and harmonic potential

NASA Astrophysics Data System (ADS)

Wang, Deng-Shan; Liu, Jiang; Wang, Lizhen

2018-03-01

In this paper, we investigate matter-wave solitons in hybrid atomic-molecular Bose-Einstein condensates with tunable interactions and external potentials. Three types of time-modulated harmonic potentials are considered and, for each of them, two groups of exact non-autonomous matter-wave soliton solutions of the coupled Gross-Pitaevskii equation are presented. Novel nonlinear structures of these non-autonomous matter-wave solitons are analyzed by displaying their density distributions. It is shown that the time-modulated nonlinearities and external potentials can support exact non-autonomous atomic-molecular matter-wave solitons.

Shock-wave structure based on the Navier-Stokes-Fourier equations.

PubMed

Uribe, F J; Velasco, R M

2018-04-01

We use the Navier-Stokes-Fourier constitutive equations to study plane shock waves in dilute gases. It is shown that the experimental information on the normalized density profiles can be fit by using the so-called soft sphere model, in which the viscosity and thermal conductivity are proportional to a power of the temperature.

Shock-wave structure based on the Navier-Stokes-Fourier equations

NASA Astrophysics Data System (ADS)

Uribe, F. J.; Velasco, R. M.

2018-04-01

We use the Navier-Stokes-Fourier constitutive equations to study plane shock waves in dilute gases. It is shown that the experimental information on the normalized density profiles can be fit by using the so-called soft sphere model, in which the viscosity and thermal conductivity are proportional to a power of the temperature.

The Density-wave Theory and Spiral Structures by Looking at Spiral Arms through a Multi-wavelength StudyHamed Pour-Imani1,2, Daniel Kennefick1,2, Julia Kennefick1,2, Mohamed Shameer Abdeen1,2, Eric Monson1,2, Douglas W. Shields1,2, B. L. Davis31Department of Physics, University of Arkansas, Fayetteville, AR 72701, USA2Arkansas Center for Space & Planetary Sciences, Univ. of Arkans

NASA Astrophysics Data System (ADS)

Pour-Imani, Hamed; Kennefick, Daniel; Kennefick, Julia; Shameer Abdeen, Mohammad; Monson, Erick; Shields, Douglas William; Davis, Benjamin L.

2018-01-01

The density-wave theory of spiral structure, though first proposed as long ago as the mid-1960s by C.C. Lin and F. Shu, continues to be challenged by rival theories, such as the manifold theory. One test between these theories which has been proposed is that the pitch angle of spiral arms for galaxies should vary with the wavelength of the image in the density-wave theory, but not in the manifold theory. The reason is that stars are born in the density wave but move out of it as they age. In this study, we combined large sample size with a wide range of wavelengths to investigate this issue. For each galaxy, we used wavelength FUV151nm, U-band, H-alpha, optical wavelength B-band and infrared 3.6 and 8.0μm. We measured the pitch angle with the 2DFFT and Spirality codes (Davis et al. 2012; Shields et al. 2015). We find that the B-band and 3.6μm images have smaller pitch angles than the infrared 8.0μm image in all cases, in agreement with the prediction of the density-wave theory. We also find that the pitch angle at FUV and H-alpha are close to the measurements made at 8.0μm. The Far-ultraviolet wavelength at 151nm shows very young, very bright UV stars still in the star-forming region (they are so bright as to be visible there and so short-lived that they never move out of it). We find that for both sets of measurements (2dFFT and Spirality) the 8.0μm, H-alpha and ultraviolet images agree in their pitch angle measurements, suggesting that they are, in fact, sensitive to the same region. By contrast, the 3.6μm and B-band images are uniformly tighter in pitch angle measurements than these wavelengths, suggesting that the density-wave picture is correct.

Waves in the middle and upper atmosphere of Mars as seen by the Radio Science Experiment MaRS on Mars Express

NASA Astrophysics Data System (ADS)

Tellmann, S.; Paetzold, M.; Häusler, B.; Hinson, D. P.; Peter, K.; Tyler, G. L.

2017-12-01

Atmospheric waves play a crucial role in the Martian atmosphere. They are responsible for the redistribution of momentum, energy and dust and for the coupling of the different atmospheric regions on Mars. Almost all kinds of waves have been observed in the lower atmosphere (e.g. stationary and transient waves, baroclinic waves as well as migrating and non-migrating thermal tides, gravity waves, etc...). Atmospheric waves are also known to exist in the middle atmosphere of Mars ( 70-120 km, e.g. by the SPICAM instrument on Mars Express). In the thermosphere, thermal tides have been observed e.g. by radio occultation or accelerometer measurements on MGS. Recently, the NGIMS instrument on MAVEN reported gravity waves in the thermosphere of Mars. Radio Science profiles from the Mars Express Radio Science experiment MaRS on Mars Express can analyse the temperature, pressure and neutral number density profiles in the lower atmosphere (from a few hundred metres above the surface up to 40-50 km) and electron density profiles in the ionosphere of Mars. Wavelike structures have been detected below the main ionospheric layers (M1 & M2) and in the topside of the ionosphere. The two coherent frequencies of the MaRS experiment allow to discriminate between plasma density fluctuations in the ionosphere and Doppler related frequency shifts caused by spacecraft movement. A careful analysis of the observed electron density fluctuations in combination with sensitivity studies of the radio occultation technique will be used to classify the observed fluctuations. The MaRS experiment is funded by DLR under grant 50QM1401.

Waves in the middle and upper atmosphere of Mars as seen by the Radio Science Experiment MaRS on Mars Express

NASA Astrophysics Data System (ADS)

Tellmann, Silvia Anna; Paetzold, Martin; Häusler, Bernd; Hinson, David P.; Peter, Kerstin; Tyler, G. Leonard

2017-10-01

Atmospheric waves play a crucial role for the dynamics in the Martian atmosphere. They are responsible for the redistribution of momentum, energy and dust and the coupling of the different atmospheric regions on Mars.Almost all kinds of waves have been observed in the lower atmosphere (e.g. stationary and transient waves, baroclinic waves as well as migrating and non-migrating thermal tides, and gravity waves). Atmospheric waves are also known to exist in the middle atmosphere of Mars (~70-120 km, e.g. by the SPICAM instrument on Mars Express). In the thermosphere, thermal tides have been observed e.g. by radio occultation or accelerometer measurements on MGS. Recently, the NGIMS instrument on MAVEN reported gravity waves in the thermosphere of Mars.Radio Science profiles from the Mars Express Radio Science experiment MaRS on Mars Express can analyse the temperature, pressure and neutral number density profiles in the lower atmosphere (from a few hundred metres above the surface up to ~ 40-50 km) and electron density profiles in the ionosphere of Mars.Wavelike structures have been detected below the main ionospheric layers (M1 & M2) and in the topside of the ionosphere. The two coherent frequencies of the MaRS experiment allow to discriminate between plasma density fluctuations in the ionosphere and Doppler related frequency shifts caused by spacecraft movement.A careful analysis of the observed electron density fluctuations in combination with sensitivity studies of the radio occultation technique will be used to classify the observed fluctuations.The MaRS experiment is funded by DLR under grant 50QM1401.

Charge Density Wave and Narrow Energy Gap at Room Temperature in 2D Pb 3–xSb 1+xS 4Te 2-δ with Square Te Sheets

DOE PAGES

Chen, Haijie; Malliakas, Christos D.; Narayan, Awadhesh; ...

2017-07-17

We report a new two-dimensional compound Pb 3–xSb 1+xS 4Te 2-δ has a charge density wave (CDW) at room temperature. The CDW is incommensurate with q-vector of 0.248(6)a* + 0.246(8)b* + 0.387(9)c* for x = 0.29(2) and d = 0.37(3) due to positional and occupational long range ordering of Te atoms in the sheets. The modulated structure was refined from the single crystal X-ray diffraction data with a superspace group Pmore » $$\\bar{1}$$(αβγ)0 using (3 + 1)-dimensional crystallography. The resistivity increases with decreasing temperature, suggesting semiconducting behavior. The transition temperature (T CDW) of the CDW is ~ 345 K above which the Te square sheets become disordered with no q-vector. Lastly, first-principles density functional theory calculations on the undistorted structure and an approximate commensurate supercell reveal that the gap is due to the structure modulation.« less

Derivation of force field parameters for SnO2-H2O surface systems from plane-wave density functional theory calculations.

PubMed

Bandura, A V; Sofo, J O; Kubicki, J D

2006-04-27

Plane-wave density functional theory (DFT-PW) calculations were performed on bulk SnO2 (cassiterite) and the (100), (110), (001), and (101) surfaces with and without H2O present. A classical interatomic force field has been developed to describe bulk SnO2 and SnO2-H2O surface interactions. Periodic density functional theory calculations using the program VASP (Kresse et al., 1996) and molecular cluster calculations using Gaussian 03 (Frisch et al., 2003) were used to derive the parametrization of the force field. The program GULP (Gale, 1997) was used to optimize parameters to reproduce experimental and ab initio results. The experimental crystal structure and elastic constants of SnO2 are reproduced reasonably well with the force field. Furthermore, surface atom relaxations and structures of adsorbed H2O molecules agree well between the ab initio and force field predictions. H2O addition above that required to form a monolayer results in consistent structures between the DFT-PW and classical force field results as well.

Charge Density Wave and Narrow Energy Gap at Room Temperature in 2D Pb 3–xSb 1+xS 4Te 2-δ with Square Te Sheets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Haijie; Malliakas, Christos D.; Narayan, Awadhesh

We report a new two-dimensional compound Pb 3–xSb 1+xS 4Te 2-δ has a charge density wave (CDW) at room temperature. The CDW is incommensurate with q-vector of 0.248(6)a* + 0.246(8)b* + 0.387(9)c* for x = 0.29(2) and d = 0.37(3) due to positional and occupational long range ordering of Te atoms in the sheets. The modulated structure was refined from the single crystal X-ray diffraction data with a superspace group Pmore » $$\\bar{1}$$(αβγ)0 using (3 + 1)-dimensional crystallography. The resistivity increases with decreasing temperature, suggesting semiconducting behavior. The transition temperature (T CDW) of the CDW is ~ 345 K above which the Te square sheets become disordered with no q-vector. Lastly, first-principles density functional theory calculations on the undistorted structure and an approximate commensurate supercell reveal that the gap is due to the structure modulation.« less

Charge Density Wave and Narrow Energy Gap at Room Temperature in 2D Pb3-xSb1+xS4Te2-δ with Square Te Sheets.

PubMed

Chen, Haijie; Malliakas, Christos D; Narayan, Awadhesh; Fang, Lei; Chung, Duck Young; Wagner, Lucas K; Kwok, Wai-Kwong; Kanatzidis, Mercouri G

2017-08-16

We report a new two-dimensional compound, Pb 3-x Sb 1+x S 4 Te 2-δ , that has a charge density wave (CDW) at room temperature. The CDW is incommensurate with q-vector of 0.248(6)a* + 0.246(8)b* + 0.387(9)c* for x = 0.29(2) and δ = 0.37(3) due to positional and occupational long-range ordering of Te atoms in the sheets. The modulated structure was refined from the single-crystal X-ray diffraction data with a superspace group P1̅(αβγ)0 using (3 + 1)-dimensional crystallography. The resistivity increases with decreasing temperature, suggesting semiconducting behavior. The transition temperature (T CDW ) of the CDW is ∼345 K, above which the Te square sheets become disordered with no q-vector. First-principles density functional theory calculations on the undistorted structure and an approximate commensurate supercell reveal that the gap is due to the structure modulation.

Current-wave spectra coupling project. Volume III. Cumulative distribution of forces on structures subjected to the combined action of currents and random waves for potential OTEC sites: (A) Keahole Point, Hawaii, 100 year hurricane; (B) Punta Tuna, Puerto Rico, 100 year hurricane; (C) New Orleans, Louisiana, 100 year hurricane; (D) West Coast of Florida, 100 year hurricane. [CUFOR code

DOE Office of Scientific and Technical Information (OSTI.GOV)

Venezian, G.; Bretschneider, C.L.

1980-08-01

This volume details a new methodology to analyze statistically the forces experienced by a structure at sea. Conventionally a wave climate is defined using a spectral function. The wave climate is described using a joint distribution of wave heights and periods (wave lengths), characterizing actual sea conditions through some measured or estimated parameters like the significant wave height, maximum spectral density, etc. Random wave heights and periods satisfying the joint distribution are then generated. Wave kinetics are obtained using linear or non-linear theory. In the case of currents a linear wave-current interaction theory of Venezian (1979) is used. The peakmore » force experienced by the structure for each individual wave is identified. Finally, the probability of exceedance of any given peak force on the structure may be obtained. A three-parameter Longuet-Higgins type joint distribution of wave heights and periods is discussed in detail. This joint distribution was used to model sea conditions at four potential OTEC locations. A uniform cylindrical pipe of 3 m diameter, extending to a depth of 550 m was used as a sample structure. Wave-current interactions were included and forces computed using Morison's equation. The drag and virtual mass coefficients were interpolated from published data. A Fortran program CUFOR was written to execute the above procedure. Tabulated and graphic results of peak forces experienced by the structure, for each location, are presented. A listing of CUFOR is included. Considerable flexibility of structural definition has been incorporated. The program can easily be modified in the case of an alternative joint distribution or for inclusion of effects like non-linearity of waves, transverse forces and diffraction.« less

Dimensional Effects on the Charge Density Waves in Ultrathin Films of TiSe 2

DOE PAGES

Chen, P.; Chan, Y. -H.; Wong, M. -H.; ...

2016-09-20

Charge density wave (CDW) formation in solids is a critical phenomenon involving the collective reorganization of the electrons and atoms in the system into a wave structure, and it is expected to be sensitive to the geometric constraint of the system at the nanoscale. Here, we study the CDW transition in TiSe 2, a quasi-two-dimensional layered material, to determine the effects of quantum confinement and changing dimensions in films ranging from a single layer to multilayers. Of key interest is the characteristic length scale for the transformation from a two-dimensional case to the three-dimensional limit. Angle-resolved photoemission (ARPES) measurements ofmore » films with thicknesses up to six layers reveal substantial variations in the energy structure of discrete quantum well states; however, the temperature-dependent band-gap renormalization converges at just three layers. The results indicate a layer-dependent mixture of two transition temperatures and a very-short-range CDW interaction within a three-dimensional framework.« less

Pair-density waves, charge-density waves, and vortices in high-Tc cuprates

NASA Astrophysics Data System (ADS)

Dai, Zhehao; Zhang, Ya-Hui; Senthil, T.; Lee, Patrick A.

2018-05-01

A recent scanning tunneling microscopy (STM) experiment reports the observation of a charge-density wave (CDW) with a period of approximately 8a in the halo region surrounding the vortex core, in striking contrast to the approximately 4a period CDWs that are commonly observed in the cuprates. Inspired by this work, we study a model where a bidirectional pair-density wave (PDW) with period 8 is at play. This further divides into two classes: (1) where the PDW is a competing state of the d -wave superconductor and can exist only near the vortex core where the d -wave order is suppressed and (2) where the PDW is the primary order, the so-called "mother state" that persists with strong phase fluctuations to high temperature and high magnetic field and lies behind the pseudogap phenomenology. We study the charge-density wave structures near the vortex core in these models. We emphasize the importance of the phase winding of the d -wave order parameter. The PDW can be pinned by the vortex core due to this winding and become static. Furthermore, the period-8 CDW inherits the properties of this winding, which gives rise to a special feature of the Fourier transform peak, namely, it is split in certain directions. There is also a line of zeros in the inverse Fourier transform of filtered data. We propose that these are key experimental signatures that can distinguish between the PDW-driven scenario from the more mundane option that the period-8 CDW is primary. We discuss the pro's and con's of the options considered above. Finally, we attempt to place the STM experiment in the broader context of pseudogap physics of underdoped cuprates and relate this observation to the unusual properties of x-ray scattering data on CDW carried out to very high magnetic field.

Transport of phase space densities through tetrahedral meshes using discrete flow mapping

NASA Astrophysics Data System (ADS)

Bajars, Janis; Chappell, David J.; Søndergaard, Niels; Tanner, Gregor

2017-01-01

Discrete flow mapping was recently introduced as an efficient ray based method determining wave energy distributions in complex built up structures. Wave energy densities are transported along ray trajectories through polygonal mesh elements using a finite dimensional approximation of a ray transfer operator. In this way the method can be viewed as a smoothed ray tracing method defined over meshed surfaces. Many applications require the resolution of wave energy distributions in three-dimensional domains, such as in room acoustics, underwater acoustics and for electromagnetic cavity problems. In this work we extend discrete flow mapping to three-dimensional domains by propagating wave energy densities through tetrahedral meshes. The geometric simplicity of the tetrahedral mesh elements is utilised to efficiently compute the ray transfer operator using a mixture of analytic and spectrally accurate numerical integration. The important issue of how to choose a suitable basis approximation in phase space whilst maintaining a reasonable computational cost is addressed via low order local approximations on tetrahedral faces in the position coordinate and high order orthogonal polynomial expansions in momentum space.

A high-order 3-D spectral-element method for the forward modelling and inversion of gravimetric data—Application to the western Pyrenees

NASA Astrophysics Data System (ADS)

Martin, Roland; Chevrot, Sébastien; Komatitsch, Dimitri; Seoane, Lucia; Spangenberg, Hannah; Wang, Yi; Dufréchou, Grégory; Bonvalot, Sylvain; Bruinsma, Sean

2017-04-01

We image the internal density structure of the Pyrenees by inverting gravity data using an a priori density model derived by scaling a Vp model obtained by full waveform inversion of teleseismic P-waves. Gravity anomalies are computed via a 3-D high-order finite-element integration in the same high-order spectral-element grid as the one used to solve the wave equation and thus to obtain the velocity model. The curvature of the Earth and surface topography are taken into account in order to obtain a density model as accurate as possible. The method is validated through comparisons with exact semi-analytical solutions. We show that the spectral-element method drastically accelerates the computations when compared to other more classical methods. Different scaling relations between compressional velocity and density are tested, and the Nafe-Drake relation is the one that leads to the best agreement between computed and observed gravity anomalies. Gravity data inversion is then performed and the results allow us to put more constraints on the density structure of the shallow crust and on the deep architecture of the mountain range.

Density of the Human Body in Gravity Contrasting Tectonic Blocks of Earth

NASA Astrophysics Data System (ADS)

Kochemasov, G. G.

Short duration cosmic experiments with humans in reduced gravity might be compared with results of practically time unlimited (many thousand of years!) existence of man in conditions of planetary tectonic blocks with rather small gravity gradient. These blocks with differing planetary radii are formed in the terrestrial globe (as well as in other celestial bodies) as a result of its movement in an elliptical orbit inevitably causing inertia-gravity warping waves. Depending on the wavelengths, Earth is tectonically dichotomic (wave1, 2π R-structure), sectoral (wave2, π R-structure) and granular (wave4, π R/2-structure) [1]. Alternations of uplifts (+) and subsidences (-) in rotating Earth requires an equilibration of angular momenta of different levels blocks by differing densities of composing them objects. ``Objects'' are geological as well as biological ones. Oceans (-) are filled with dense basaltic rocks, continents (+) are built by less dense granites (andesites, on average). Homo sapiens, widely spread over Earth, equally accommodates himself to conditions of tectonic blocks with differing radii (densities). The most pronounced (amplitudinal) tectonic dichotomy is an opposition of the subsided (-) western pacific hemisphere to the uplifted (+) eastern continental hemisphere. Recently populated (12 to 3 thousand years ago) America and Pacific made migrating mongoloids denser (higher the Rohrer's index* of Indians and Polynesians) than inhabitants of native Asia. Asia itself is a sector of the planetary sectoral π R-structure of the eastern hemisphere with the center at the Pamirs-Hindukush. Around this center converge 2 uplifted sectors (Africa-Mediterranean ++, Asian +) separated by 2 subsided ones (Eurasian -, Indoceanic - -). The 4 great races developed on these sectors have their own ``body density'' characteristics. The uplifted Africa bears ``light'' negroids, subsided Eurasia ``heavy'' europeoids. In the former USSR population of the Asian sector (+) has less mineralized bones and less Fe/Mn in hairs (thus less dense hairs) than population of the Eurasian sector (-) [2]. The differentiation of the great races can be traced to the gene level: frequencies of their Rh-system genetic markers are clearly different. the ratio of man's weight to his height in the cube power (can be used also the simple ratio of man's weight to his height, that means the ``linear density'' of man). References : [1] Kochemasov G. G. Theorems of wave planetary tectonics // Geophys. Res. Abstr., V. 1, # 3, 1999,700; [2] Alexeeva T. I. Geographical environment and human biology // Moscow, Mysl, 1977, 302 pp. (in Russian).

Eddy, drift wave and zonal flow dynamics in a linear magnetized plasma

PubMed Central

Arakawa, H.; Inagaki, S.; Sasaki, M.; Kosuga, Y.; Kobayashi, T.; Kasuya, N.; Nagashima, Y.; Yamada, T.; Lesur, M.; Fujisawa, A.; Itoh, K.; Itoh, S.-I.

2016-01-01

Turbulence and its structure formation are universal in neutral fluids and in plasmas. Turbulence annihilates global structures but can organize flows and eddies. The mutual-interactions between flow and the eddy give basic insights into the understanding of non-equilibrium and nonlinear interaction by turbulence. In fusion plasma, clarifying structure formation by Drift-wave turbulence, driven by density gradients in magnetized plasma, is an important issue. Here, a new mutual-interaction among eddy, drift wave and flow in magnetized plasma is discovered. A two-dimensional solitary eddy, which is a perturbation with circumnavigating motion localized radially and azimuthally, is transiently organized in a drift wave – zonal flow (azimuthally symmetric band-like shear flows) system. The excitation of the eddy is synchronized with zonal perturbation. The organization of the eddy has substantial impact on the acceleration of zonal flow. PMID:27628894

Development of smart wave mitigation structure using array of poles (Conference Presentation)

NASA Astrophysics Data System (ADS)

Asanuma, Hiroshi

2017-05-01

This paper describes reduction of water flow velocity by array of poles as a new wave mitigation structure. This structure is based on tsunami mitigation coastal forest. As natural forests have many problems such as low fraction of trees, low visibility of ocean waves, low strength, long of time to grow, and so on. To cope with these problems, a new wave mitigation structure has been developed, which are intended to add better capability of high wave or tsunami mitigation effect to actual ones by optimizing various parameters such as configuration, distribution density and material properties. In this study, the effect of type of material and its combination were mainly investigated. According to the results, reduction rate of the flow velocity increases with increasing number of rows for each material up to a certain level, and that of poles having lower Young's modulus is generally higher than that of those having higher Young's modulus. The effect of combination of materials was also investigated and drastic increase of mitigation effect was found when soft and hard poles were combined.

Lunar Structure from Ambient Noise and Coda Wave Interferometry

NASA Astrophysics Data System (ADS)

Nunn, C.; Igel, H.

2016-12-01

As part of the Apollo lunar missions, four seismometers were deployed on the near-side of the Moon between 1969 and 1972, and operated continuously until 1977. There are many difficulties associated with determining lunar structure from these records. As a result, many properties of the moon, such as the thickness, density and porosity of the crust are poorly constrained. This hampers our ability to determine the structure, geochemical composition of the moon, its evolution, and ultimately the evolution of the solar system. We explore the use of ambient noise and coda wave interferometry to reconstruct the near surface structure within the strongly scattering lunar crust.

Implementation of density functional theory method on object-oriented programming (C++) to calculate energy band structure using the projector augmented wave (PAW)

NASA Astrophysics Data System (ADS)

Alfianto, E.; Rusydi, F.; Aisyah, N. D.; Fadilla, R. N.; Dipojono, H. K.; Martoprawiro, M. A.

2017-05-01

This study implemented DFT method into the C++ programming language with object-oriented programming rules (expressive software). The use of expressive software results in getting a simple programming structure, which is similar to mathematical formula. This will facilitate the scientific community to develop the software. We validate our software by calculating the energy band structure of Silica, Carbon, and Germanium with FCC structure using the Projector Augmented Wave (PAW) method then compare the results to Quantum Espresso calculation’s results. This study shows that the accuracy of the software is 85% compared to Quantum Espresso.

Magnetosheath Filamentary Structures

NASA Astrophysics Data System (ADS)

Rojas-Castillo, D. I.; Blanco-Cano, X.; Omidi, N.; Kajdic, P.

2014-12-01

The terrestrial magnetosheath is full of highly perturbed plasma. The inhomogeneity of this region leads to temperature anisotropies that can originate waves; e.g, mirror mode and ion cyclotron waves. Other structures like the magnetosheath filamentary structures (MFS) can also be present. These are structures reported from results of global hybrid simulations by Omidi et al. (2014) that are formed in the quasi-parallel region of the bow shock and they are convected into the magnetosheath. The MFS are characterized by field aligned enhancements of density and temperature that are anti-correlated. In this work we analyze magnetic field and plasma data from the THEMIS mission to explore the possible existence of MFS.

Electronic band structure and charge density wave transition in quasi-2D KMo6O17 purple bronze

NASA Astrophysics Data System (ADS)

Valbuena, M. A.; Avila, J.; Vyalikh, D. V.; Guyot, H.; Laubschat, C.; Molodtsov, S. L.; Asensio, M. C.

2008-03-01

High resolution angle-resolved photoemission of quasi-2D KMo6O17 purple bronze has been performed in the range from room temperature to 130 K, slightly above the charge density wave (CDW) transition (Tc = 110 K), and down to 35 K (well below Tc). In this paper we report a detailed study of how electronic band structure is affected by this transition driven by the hidden nesting scenario. The expected spectroscopic fingerprints of the CDW phase transition have been found and discussed according to the hidden one dimension and the development of a quasi-commensurate CDW. The excellent agreement between theory and our experimental results makes of potassium purple bronze a reference system for studying this type of instabilities.

Drift-Alfven wave mediated particle transport in an elongated density depression

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vincena, Stephen; Gekelman, Walter

Cross-field particle transport due to drift-Alfven waves is measured in an elongated density depression within an otherwise uniform, magnetized helium plasma column. The depression is formed by drawing an electron current to a biased copper plate with cross-field dimensions of 28x0.24 ion sound-gyroradii {rho}{sub s}=c{sub s}/{omega}{sub ci}. The process of density depletion and replenishment via particle flux repeats in a quasiperiodic fashion for the duration of the current collection. The mode structure of the wave density fluctuations in the plane perpendicular to the background magnetic field is revealed using a two-probe correlation technique. The particle flux as a function ofmore » frequency is measured using a linear array of Langmuir probes and the only significant transport occurs for waves with frequencies between 15%-25% of the ion cyclotron frequency (measured in the laboratory frame) and with perpendicular wavelengths k{sub perpendicular}{rho}{sub s}{approx}0.7. The frequency-integrated particle flux is in rough agreement with observed increases in density in the center of the depletion as a function of time. The experiments are carried out in the Large Plasma Device (LAPD) [Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] at the Basic Plasma Science Facility located at the University of California, Los Angeles.« less

Planetesimal formation in self-gravitating discs - dust trapping by vortices

NASA Astrophysics Data System (ADS)

Gibbons, P. G.; Mamatsashvili, G. R.; Rice, W. K. M.

2015-11-01

The mechanism through which metre-sized boulders grow to km-sized planetesimals in protoplanetary discs is a subject of active research, since it is critical for planet formation. To avoid spiralling into the protostar due to aerodynamic drag, objects must rapidly grow from cm-sized pebbles, which are tightly coupled to the gas, to large boulders of 1-100 m in diameter. It is already well known that overdensities in the gaseous component of the disc provide potential sites for the collection of solids, and that significant density structures in the gaseous component of the disc (e.g. spiral density waves) can trap solids efficiently enough for the solid component of the disc to undergo further gravitational collapse due to their own self-gravity. In this work, we employ the PENCIL CODE to conduct local shearing sheet simulations of massive self-gravitating protoplanetary discs, to study the effect of anticyclonic transient vortices, or eddies, on the evolution of solids in these discs. We find that these types of structures are extremely efficient at concentrating small and intermediate-sized dust particles with friction times comparable to, or less than, the local orbital period of the disc. This can lead to significant over-densities in the solid component of the disc, with density enhancements comparable to, and even higher, than those within spiral density waves; increasing the rate of gravitational collapse of solids into bound structures.

Molding acoustic, electromagnetic and water waves with a single cloak

PubMed Central

Xu, Jun; Jiang, Xu; Fang, Nicholas; Georget, Elodie; Abdeddaim, Redha; Geffrin, Jean-Michel; Farhat, Mohamed; Sabouroux, Pierre; Enoch, Stefan; Guenneau, Sébastien

2015-01-01

We describe two experiments demonstrating that a cylindrical cloak formerly introduced for linear surface liquid waves works equally well for sound and electromagnetic waves. This structured cloak behaves like an acoustic cloak with an effective anisotropic density and an electromagnetic cloak with an effective anisotropic permittivity, respectively. Measured forward scattering for pressure and magnetic fields are in good agreement and provide first evidence of broadband cloaking. Microwave experiments and 3D electromagnetic wave simulations further confirm reduced forward and backscattering when a rectangular metallic obstacle is surrounded by the structured cloak for cloaking frequencies between 2.6 and 7.0 GHz. This suggests, as supported by 2D finite element simulations, sound waves are cloaked between 3 and 8 KHz and linear surface liquid waves between 5 and 16 Hz. Moreover, microwave experiments show the field is reduced by 10 to 30 dB inside the invisibility region, which suggests the multi-wave cloak could be used as a protection against water, sonic or microwaves. PMID:26057934

Molding acoustic, electromagnetic and water waves with a single cloak.

PubMed

Xu, Jun; Jiang, Xu; Fang, Nicholas; Georget, Elodie; Abdeddaim, Redha; Geffrin, Jean-Michel; Farhat, Mohamed; Sabouroux, Pierre; Enoch, Stefan; Guenneau, Sébastien

2015-06-09

We describe two experiments demonstrating that a cylindrical cloak formerly introduced for linear surface liquid waves works equally well for sound and electromagnetic waves. This structured cloak behaves like an acoustic cloak with an effective anisotropic density and an electromagnetic cloak with an effective anisotropic permittivity, respectively. Measured forward scattering for pressure and magnetic fields are in good agreement and provide first evidence of broadband cloaking. Microwave experiments and 3D electromagnetic wave simulations further confirm reduced forward and backscattering when a rectangular metallic obstacle is surrounded by the structured cloak for cloaking frequencies between 2.6 and 7.0 GHz. This suggests, as supported by 2D finite element simulations, sound waves are cloaked between 3 and 8 KHz and linear surface liquid waves between 5 and 16 Hz. Moreover, microwave experiments show the field is reduced by 10 to 30 dB inside the invisibility region, which suggests the multi-wave cloak could be used as a protection against water, sonic or microwaves.

Large scale atmospheric waves in the Venus mesosphere as seen by the VeRa Radio Science instrument on Venus Express

NASA Astrophysics Data System (ADS)

Tellmann, Silvia; Häusler, Bernd; Hinson, David P.; Tyler, G. Leonard; Andert, Thomas P.; Bird, Michael K.; Imamura, Takeshi; Pätzold, Martin; Remus, Stefan

2015-04-01

Atmospheric waves on all spatial scales play a crucial role in the redistribution of energy, momentum, and atmospheric constituent in planetary atmosphere and are thought to be involved in the development and maintenance of the atmospheric superrotation on Venus. The Venus Express Radio-Science Experiment VeRa sounded the Venus neutral atmosphere and ionosphere in Earth occultation geometry using the spacecraft radio subsystem at two coherent frequencies. Radial profiles of neutral number density, covering the altitude range 40-90 km, are then converted to vertical profiles of temperature and pressure, assuming hydrostatic equilibrium. The extensive VeRa data set enables us to study global scale atmospheric wave phenomena like thermal tides in the mesosphere and troposphere. A pronounced local time dependency of the temperature is found in the mesosphere at different altitude levels. Wave-2 structures dominate the low latitude range in the upper mesosphere while the higher latitudes show a strong wave-1 structure at the top of the cloud layer. The investigation of these wave structures provides valuable information about the energy transport in the atmosphere.

Nonlocal theory of electromagnetic wave decay into two electromagnetic waves in a rippled density plasma channel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sati, Priti; Tripathi, V. K.

Parametric decay of a large amplitude electromagnetic wave into two electromagnetic modes in a rippled density plasma channel is investigated. The channel is taken to possess step density profile besides a density ripple of axial wave vector. The density ripple accounts for the momentum mismatch between the interacting waves and facilitates nonlinear coupling. For a given pump wave frequency, the requisite ripple wave number varies only a little w.r.t. the frequency of the low frequency decay wave. The radial localization of electromagnetic wave reduces the growth rate of the parametric instability. The growth rate decreases with the frequency of lowmore » frequency electromagnetic wave.« less

Charge density wave behavior and order-disorder in the antiferromagnetic metallic series Eu (Ga1 -xAlx)4

NASA Astrophysics Data System (ADS)

Stavinoha, Macy; Cooley, Joya A.; Minasian, Stefan G.; McQueen, Tyrel M.; Kauzlarich, Susan M.; Huang, C.-L.; Morosan, E.

2018-05-01

The solid solution Eu (Ga1-xAlx) 4 was grown in single crystal form to reveal a rich variety of crystallographic, magnetic, and electronic properties that differ from the isostructural end compounds EuGa4 and EuAl4, despite the similar covalent radii and electronic configurations of Ga and Al. Here we report the onset of magnetic spin reorientation and metamagnetic transitions for x =0 -1 evidenced by magnetization and temperature-dependent specific heat measurements. TN changes nonmonotonously with x , and it reaches a maximum around 20 K for x =0.50 , where the a lattice parameter also shows an extreme (minimum) value. Anomalies in the temperature-dependent resistivity consistent with charge density wave behavior exist only for x =0.50 and 1. Density functional theory calculations show increased polarization between the Ga-Al covalent bonds in the x =0.50 structure compared to the end compounds, such that crystallographic order and chemical pressure are proposed as the causes of the charge density wave behavior.

Broken Time-Reversal Symmetry in Strongly Correlated Ladder Structures

NASA Astrophysics Data System (ADS)

Troyer, Matthias

2004-03-01

A decade after the first detailed numerical investigations of strongly correlated ladder models, exotic and interesting phases are still being discovered. Besides charge and spin density wave states with broken translational symmetry, and resonating valence bond (RVB) type superconductivity, a time reversal symmetry borken phase was recently found at half filling [J.B. Marston et al., Phys. Rev. Lett 89, 056404 (2002)]. In this talk I will present our recent results of density matrix renormalization group (DMRG) calculations [Phys. Rev. Lett. 90, 186401 (2003)], where we provide, for the first time, in a doped strongly correlated system (two-leg ladder), a controlled theoretical demonstration of the existence of this state in which long-range ordered orbital currents are arranged in a staggered pattern. This phase, which we found to coexist with a charge density wave, is known in the literature under the names ``staggered flux phase'', ``orbital antiferromagnetism'' or ``d-density wave (DDW)''. This brings us closer to recent proposals that this order might be realized in the enigmatic pseudogap phase of the cuprate high temperature superconductors.

Microstructural Design for Stress Wave Energy Management

DTIC Science & Technology

2013-04-01

Polyurea based foam 7 4) Controlling transmission and reflection of pressure and shear waves in a multilayered anisotropic structure 10 5... Polyurea based foam consists of several factors including high energy absorption, light weight, higher elastic modulus to density ratio (compared with... Polyurea ), and collapsible voids under extreme loading. Pure Polyurea offers unique properties such as increased shear stiffness under large pressure

Nonlinear MHD Waves in a Prominence Foot

NASA Astrophysics Data System (ADS)

Ofman, L.; Knizhnik, K.; Kucera, T.; Schmieder, B.

2015-11-01

We study nonlinear waves in a prominence foot using a 2.5D MHD model motivated by recent high-resolution observations with Hinode/Solar Optical Telescope in Ca ii emission of a prominence on 2012 October 10 showing highly dynamic small-scale motions in the prominence material. Observations of Hα intensities and of Doppler shifts show similar propagating fluctuations. However, the optically thick nature of the emission lines inhibits a unique quantitative interpretation in terms of density. Nevertheless, we find evidence of nonlinear wave activity in the prominence foot by examining the relative magnitude of the fluctuation intensity (δI/I ˜ δn/n). The waves are evident as significant density fluctuations that vary with height and apparently travel upward from the chromosphere into the prominence material with quasi-periodic fluctuations with a typical period in the range of 5-11 minutes and wavelengths <2000 km. Recent Doppler shift observations show the transverse displacement of the propagating waves. The magnetic field was measured with the THEMIS instrument and was found to be 5-14 G. For the typical prominence density the corresponding fast magnetosonic speed is ˜20 km s-1, in qualitative agreement with the propagation speed of the detected waves. The 2.5D MHD numerical model is constrained with the typical parameters of the prominence waves seen in observations. Our numerical results reproduce the nonlinear fast magnetosonic waves and provide strong support for the presence of these waves in the prominence foot. We also explore gravitational MHD oscillations of the heavy prominence foot material supported by dipped magnetic field structure.

Hydrodynamic instabilities at an oblique interface: Experiments and Simulations

NASA Astrophysics Data System (ADS)

Douglas-Mann, E.; Fiedler Kawaguchi, C.; Trantham, M. A.; Malamud, G.; Wan, W. C.; Klein, S. R.; Kuranz, C. C.

2017-10-01

Hydrodynamic instabilities are important phenomena that occur in high-energy-density systems, such as astrophysical systems and inertial confinement fusion experiments, where pressure, density, and velocity gradients are present. Using a 30 ns laser pulse from the Omega EP laser system, a steady shock wave is driven into a target. A Spherical Crystal Imager provides high-resolution x-ray radiographs to study the evolution of complex hydrodynamic structures. This experiment has a light-to-heavy interface at an oblique angle with a precision-machined perturbation. The incident shock wave deposits shear and vorticity at the interface causing the perturbation to grow via Richtmyer-Meshkov and Kelvin-Helmholtz processes. We present results from analysis of radiographic data and hydrodynamics simulations showing the evolution of the shock and unstable structure. This work is supported by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, Grant Number DE-NA0002956 and the National Science Foundation through the Basic Plasma Science and Engineering program and LILAC.

Properties of density and magnetic fluctuations occurring in density striations in the new LAPD

NASA Astrophysics Data System (ADS)

Maggs, J. E.; Morales, G. J.

2001-10-01

Previous studies of density striations (long, narrow magnetic-field-aligned density depletions) in the LAPD plasma device at UCLA revealed an eigenmode structure to fluctuations driven by the pressure gradient in the striation wall (Maggs and Morales, Phys. Plasmas, 4, 1997). The nature of these fluctuations depended on the plasma beta external to the striation, with shear Alfvén wave turbulence developing at betas less than the mass ratio and drift-Alfvén waves at betas above the mass ratio. These fluctuations were found to have a direct connection to turbulence observed at the plasma edge. The new LAPD is 18 meters in length with a background field up to twice previously attainable values. We report on the properties of fluctuations associated with density striations in the new device over a wider range of beta, and compare them to previous results. The behavior of fluctuations in density striations created in flared-field and magnetic-mirror geometries will also be presented. Research sponsored by ONR and NSF

Wave Structures in Thermospheric Density from Satellite Electrostatic Triaxial Accelerometer Measurements.

DTIC Science & Technology

1987-06-04

Testud , J. (1970) Gravity waves generated diring magnetic substorms, .1. Atmos. Terr. Phys., 32:1793. .6 t9, "-€ according to their horizontal...auroral oval during polar substorms, J. Geophys. Res., 74:5721. 7. Testud , J. P., Amayenc, P., and Blanc, M. (1975) Middle and low latitude effects of...1730. 13. Bertin, F.J., Testud , J., Kersley, L., and Rees, P. R. (1978) The meteorological jet stream as a source of medium scale gravity waves in

Stochastic three-wave interaction in flaring solar loops

NASA Technical Reports Server (NTRS)

Vlahos, L.; Sharma, R. R.; Papadopoulos, K.

1983-01-01

A model is proposed for the dynamic structure of high-frequency microwave bursts. The dynamic component is attributed to beams of precipitating electrons which generate electrostatic waves in the upper hybrid branch. Coherent upconversion of the electrostatic waves to electromagnetic waves produces an intrinsically stochastic emission component which is superposed on the gyrosynchrotron continuum generated by stably trapped electron fluxes. The role of the density and temperature of the ambient plasma in the wave growth and the transition of the three wave upconversion to stochastic, despite the stationarity of the energy source, are discussed in detail. The model appears to reproduce the observational features for reasonable parameters of the solar flare plasma.

Focusing guided waves using surface bonded elastic metamaterials

NASA Astrophysics Data System (ADS)

Yan, Xiang; Zhu, Rui; Huang, Guoliang; Yuan, Fuh-Gwo

2013-09-01

Bonding a two-dimensional planar array of small lead discs on an aluminum plate with silicone rubber is shown numerically to focus low-frequency flexural guided waves. The "effective mass density profile" of this type of elastic metamaterials (EMMs), perpendicular to wave propagation direction, is carefully tailored and designed, which allows rays of flexural A0 mode Lamb waves to bend in succession and then focus through a 7 × 9 planar array. Numerical simulations show that Lamb waves can be focused beyond EMMs region with amplified displacement and yet largely retained narrow banded waveform, which may have potential application in structural health monitoring.

Structure-driven turbulence in ``No man's Land''

NASA Astrophysics Data System (ADS)

Kosuga, Yusuke; Diamond, Patrick

2012-10-01

Structures are often observed in many physical systems. In tokamaks, for example, such structures are observed as density blobs and holes. Such density blobs and holes are generated at the tokamak edge, where strong gradient perturbations generate an outgoing blob and an incoming hole. Since density holes can propagate from the edge to the core, such structures may play an important role in understanding the phenomenology of the edge-core coupling region, so-called ``No Man's Land.'' In this work, we discuss the dynamics of such structures in real space. In particular, we consider the dynamics of density blobs and holes in the Hasegawa-Wakatani system. Specific questions addressed here include: i) how these structures extract free energy and enhance transport? how different is the relaxation driven by such structures from that driven by linear drift waves? ii) how these structures interact with shear flows? In particular, how these structures interact with a shear layer, which can absorb structures resonantly? iii) how can we calculate the coupled evolution of structures and shear flows? Implications for edge-core coupling problem are discussed as well.

Superradiant Ka-band Cherenkov oscillator with 2-GW peak power

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rostov, V. V.; Romanchenko, I. V.; Pedos, M. S.

The generation of a 2-GW microwave superradiance (SR) pulses has been demonstrated at 29-GHz using a single-mode relativistic backward-wave oscillator possessing the beam-to-wave power conversion factor no worse than 100%. A record-breaking radiation power density in the slow-wave structure (SWS) of ∼1.5 GW/cm{sup 2} required the use of high guiding magnetic field (7 T) decreasing the beam losses to the SWS in strong rf fields. Despite the field strength at the SWS wall of 2 MV/cm, a single-pass transmission mode of a short SR pulse in the SWS allows one to obtain extremely high power density in subnanosecond time scale due tomore » time delay in the development of the breakdown phenomena.« less

Computational research on lithium ion battery materials

NASA Astrophysics Data System (ADS)

Tang, Ping

Crystals of LiFePO4 and related materials have recently received a lot of attention due to their very promising use as cathodes in rechargeable lithium ion batteries. This thesis studied the electronic structures of FePO 4 and LiMPO4, where M=Mn, Fe, Co and Ni within the framework of density-functional theory. The first study compared the electronic structures of the LiMPO 4 and FePO4 materials in their electrochemically active olivine form, using the LAPW (linear augmented plane wave) method [1]. A comparison of results for various spin configurations suggested that the ferromagnetic configuration can serve as a useful approximation for studying general features of these systems. The partial densities of states for the LiMPO4 materials are remarkably similar to each other, showing the transition metal 3d states forming narrow bands above the O 2p band. By contrast, in absence of Li, the majority spin transition metal 3d states are well-hybridized with the O 2p band in FePO4. The second study compared the electronic structures of FePO4 in several crystal structures including an olivine, monoclinic, quartz-like, and CrVO4-like form [2,3]. For this work, in addition to the LAPW method, PAW (Projector Augmented Wave) [4], and PWscf (plane-wave pseudopotential) [5] methods were used. By carefully adjusting the computational parameters, very similar results were achieved for the three independent computational methods. Results for the relative stability of the four crystal structures are reported. In addition, partial densities of state analyses show qualitative information about the crystal field splittings and bond hybridizations and help rationalize the understanding of the electrochemical and stability properties of these materials.

Adsorbate Diffusion on Transition Metal Nanoparticles

DTIC Science & Technology

2015-01-01

different sizes and shapes using density functional theory calculations. We show that nanoparticles bind adsorbates more strongly than the...structure theoretical methods, a quantitative study with accurate density functional theory (DFT) calculations is still missing. Here, we perform a...functional theory . The projector augmented wave (PAW) potentials29,30 were used for electron- ion interactions and the generalized gradient approximation

Internal Wave Apparatus for Copepod Behavior Assays

NASA Astrophysics Data System (ADS)

Jung, S.; Haas, K. A.; Webster, D. R.

2015-11-01

Internal waves are ubiquitous features in coastal marine environments and have been observed to mediate vertical distributions of zooplankton in situ. Internal waves are generated through oscillations of the pycnocline in stratified waters and thereby create fine-scale hydrodynamic cues that copepods and other zooplankton are known to sense, such as fluid density gradients and velocity gradients (quantified as shear deformation rate). The role of copepod behavior in response to cues associated with internal waves is largely unknown. Thus, a coupled quantification of copepod behavior and hydrodynamic cues will provide insight to the bio-physical interaction and the role of biological versus physical forcing in mediating organism distributions. We constructed a laboratory-scale internal wave apparatus to facilitate fine-scale observations of copepod behavior in flows that replicate in situ conditions of internal waves in a two-layer stratification. Three cases are chosen with density jump ranging between 0.75 - 1.5 kg/m3. Analytical analysis of the two-layer system provides guidance of the target forcing frequency to generate a standing internal wave with a single dominate frequency of oscillation. Flow visualization and signal processing of the interface location are used to quantify the wave characteristics. A copepod behavior assay is conducted, and sample trajectories are analyzed to identify copepod response to internal wave structure.

Topological entanglement Rényi entropy and reduced density matrix structure.

PubMed

Flammia, Steven T; Hamma, Alioscia; Hughes, Taylor L; Wen, Xiao-Gang

2009-12-31

We generalize the topological entanglement entropy to a family of topological Rényi entropies parametrized by a parameter alpha, in an attempt to find new invariants for distinguishing topologically ordered phases. We show that, surprisingly, all topological Rényi entropies are the same, independent of alpha for all nonchiral topological phases. This independence shows that topologically ordered ground-state wave functions have reduced density matrices with a certain simple structure, and no additional universal information can be extracted from the entanglement spectrum.

Topological Entanglement Rényi Entropy and Reduced Density Matrix Structure

NASA Astrophysics Data System (ADS)

Flammia, Steven T.; Hamma, Alioscia; Hughes, Taylor L.; Wen, Xiao-Gang

2009-12-01

We generalize the topological entanglement entropy to a family of topological Rényi entropies parametrized by a parameter α, in an attempt to find new invariants for distinguishing topologically ordered phases. We show that, surprisingly, all topological Rényi entropies are the same, independent of α for all nonchiral topological phases. This independence shows that topologically ordered ground-state wave functions have reduced density matrices with a certain simple structure, and no additional universal information can be extracted from the entanglement spectrum.

Macroalgal communities on multi-stressed coral reefs in the Caribbean: Long-term changes, spatial variations, and relationships with environmental variables

NASA Astrophysics Data System (ADS)

Sangil, Carlos; Guzman, Hector M.

2016-11-01

Long-term changes in macroalgal cover, spatial variation between macroalgal communities, and relationships with environmental variables and benthic groups were assessed in coral reefs along the Caribbean coast of Panama. Sampling was conducted in two regions: Western and Central. Data collected between 2000 and 2012 showed a continuous increase in macroalgal abundance, although patterns differed according to region and site. There were differences in macroalgal communities between regions, as well as within regions between different wave-exposure levels. There were also differences between sites within regions exposed to the same level of wave action. Multivariate analysis found that wave exposure along with herbivore density (Echinometra viridis) and sedimentation were the variables that explained most of the variability between communities. Other variables such as Echinometra lucunter and Diadema antillarum densities, fish density, productivity, and live coral cover had significant relationships with community structure, but explained less of the variability.

Pinning of topological solitons at extrinsic defects in a quasi one-dimensional charge density wave

NASA Astrophysics Data System (ADS)

Razzaq, Samad; Wippermann, Stefan; Tae Hwan Kim Collaboration; Han Woong Yeom Collaboration

Quasi one-dimensional (1D) electronic systems are known to exhibit exotic physical phenomena, such as, e.g., Jahn Teller distortions, charge density wave (CDW) formation and non-Fermi liquid behavior. Solitonic excitations of the charge density wave ordered ground state and associated topological edge states in atomic wires are presently the focus of increasing attention. We carried out a combined ab initio and scanning tunneling microscopy (STM) study of solitonic and non-solitonic phase defects in the In/Si(111) atomic wire array. While free solitons move too fast to be imaged directly in STM, they can become trapped at extrinsic de- fects within the wire. We discuss the detailed atomistic structure of the responsible extrinsic defects and trapped solitons. Our study highlights the key role of coupled theory-experimental investigations in order to understand also the elusive fast moving solitons. S. W. gratefully acknowledges financial support from the German Research Foundation (DFG), Grant No. FOR1700.

Extended adiabatic blast waves and a model of the soft X-ray background. [interstellar matter

NASA Technical Reports Server (NTRS)

Cox, D. P.; Anderson, P. R.

1981-01-01

An analytical approximation is generated which follows the development of an adiabatic spherical blast wave in a homogeneous ambient medium of finite pressure. An analytical approximation is also presented for the electron temperature distribution resulting from coulomb collisional heating. The dynamical, thermal, ionization, and spectral structures are calculated for blast waves of energy E sub 0 = 5 x 10 to the 50th power ergs in a hot low-density interstellar environment. A formula is presented for estimating the luminosity evolution of such explosions. The B and C bands of the soft X-ray background, it is shown, are reproduced by such a model explosion if the ambient density is about .000004 cm, the blast radius is roughly 100 pc, and the solar system is located inside the shocked region. Evolution in a pre-existing cavity with a strong density gradient may, it is suggested, remove both the M band and OVI discrepancies.

Short and long periodic atmospheric variations between 25 and 200 km

NASA Technical Reports Server (NTRS)

Justus, C. G.; Woodrum, A.

1973-01-01

Previously collected data on atmospheric pressure, density, temperature and winds between 25 and 200 km from sources including Meteorological Rocket Network data, ROBIN falling sphere data, grenade release and pitot tube data, meteor winds, chemical release winds, satellite data, and others were analyzed by a daily difference method and results on the distribution statistics, magnitude, and spatial structure of gravity wave and planetary wave atmospheric variations are presented. Time structure of the gravity wave variations were determined by the analysis of residuals from harmonic analysis of time series data. Planetary wave contributions in the 25-85 km range were discovered and found to have significant height and latitudinal variation. Long period planetary waves, and seasonal variations were also computed by harmonic analysis. Revised height variations of the gravity wave contributions in the 25 to 85 km height range were computed. An engineering method and design values for gravity wave magnitudes and wave lengths are given to be used for such tasks as evaluating the effects on the dynamical heating, stability and control of spacecraft such as the space shuttle vehicle in launch or reentry trajectories.

An integrated geophysical study of north African and Mediterranean lithospheric structure

NASA Astrophysics Data System (ADS)

Dial, Paul Joseph

1998-07-01

This dissertation utilizes gravity and seismic waveform modeling techniques to: (1) determine models of lithospheric structure across northern African through gravity modeling and (2) determine lithospheric and crustal structure and seismic wave propagation characteristics across northern Africa and the Mediterranean region. The purpose of the gravity investigation was to construct models of lithospheric structure across northern Africa through the analysis of gravity data constrained by previous geological and geophysical studies. Three lithospheric models were constructed from Bouguer gravity data using computer modeling, and the gravity data was wavelength-filtered to investigate the relative depth and extent of the structures associated with the major anomalies. In the Atlas Mountains area, the resulting earth models showed slightly greater crustal thickness than those of previous studies if a low density mantle region is not included in the models. However, if a low density mantle region (density = 3.25 g/cm3) was included beneath the Atlas, the earth models showed little crustal thickening (38 km), in accord with previous seismic studies. The second portion of the research consisted of seismic waveform modeling of regional and teleseismic events to determine crustal and lithospheric structure across northern Africa and the Mediterranean. A total of 174 seismograms (145 at regional distances (200--1400 km) and 29 with epicentral distances exceeding 1900 km) were modeled using 1-D velocity models and a reflectivity code. At regional distances from four stations surrounding the western Mediterranean basin (MAL, TOL, PTO and AQU) and one station near the Red Sea (HLW), 1-D velocity models can satisfactorily model the relative amplitudes of both the Pnl and surface wave portions of the seismograms. Modeling of propagation paths greater than 1900 km was also conducted across northern Africa and the Mediterranean. The results indicate that the S-wave velocity model of Corchete et al. (1995) is more appropriate for the Iberian Peninsula, southwestern Mediterranean basin and northwest African coast than the other models tested. This model was better able to predict both the timing and amplitudes of the observed Sn and surface wave components on the observed seismograms. (Abstract shortened by UMI.)

Impurity-induced modulations in PdxNbSe3 coupled to charge-density-wave formation

NASA Astrophysics Data System (ADS)

Xue, Q.; Gong, Y.; Drake, D. L.; Qian, J.; Coleman, R. V.

1996-01-01

Very dilute amounts of Pd in PdxNbSe3 introduce long-range electronic modulations of wavelength 7b0, 4b0, 3b0, and 2b0 at room temperature as the Pd concentration increases in the range x=0.002 to x=0.02 while the low-temperature charge-density waves (CDW's) initially remain unchanged. For x>=0.02 the low-temperature CDW's are quenched while the NbSe3 structure remains intact, and the high-temperature modulations disappear, indicating a clear correlation between the two effects. The magnetoquantum oscillations due to magnetic breakdown first detect the band-structure shift followed by the sudden quenching of the nested Fermi surface sheets. The atomic force microscope scans show substantial charge transfer between chains caused by the Pd doping.

Hybridization wave as the cause of the metal-insulator transition in rare earth nickelates

NASA Astrophysics Data System (ADS)

Park, Hyowon; Marianetti, Chris A.; Millis, Andrew J.

2012-02-01

The metal-insulator transition driven by varying rare earth (Re) ion in ReNiO3 has been a longstanding challenge to materials theory. Experimental evidence suggesting charge order is seemingly incompatible with the strong Mott-Hubbard correlations characteristic of transition metals. We present density functional, Hartree-Fock and Dynamical Mean field calculations showing that the origin of the insulating phase is a hybridization wave, in which a two sublattice ordering of the oxygen breathing mode produces two Ni sites with almost identical Ni d-charge densities but very different magnetic moments and other properties. The high temperature crystal structure associated with smaller Re ions such as Lu is shown to be more susceptible to the distortion than the high temperature structure associated with larger Re ions such as La.

Acoustic metamaterials: From local resonances to broad horizons

PubMed Central

Ma, Guancong; Sheng, Ping

2016-01-01

Within a time span of 15 years, acoustic metamaterials have emerged from academic curiosity to become an active field driven by scientific discoveries and diverse application potentials. This review traces the development of acoustic metamaterials from the initial findings of mass density and bulk modulus frequency dispersions in locally resonant structures to the diverse functionalities afforded by the perspective of negative constitutive parameter values, and their implications for acoustic wave behaviors. We survey the more recent developments, which include compact phase manipulation structures, superabsorption, and actively controllable metamaterials as well as the new directions on acoustic wave transport in moving fluid, elastic, and mechanical metamaterials, graphene-inspired metamaterials, and structures whose characteristics are best delineated by non-Hermitian Hamiltonians. Many of the novel acoustic metamaterial structures have transcended the original definition of metamaterials as arising from the collective manifestations of constituent resonating units, but they continue to extend wave manipulation functionalities beyond those found in nature. PMID:26933692

C/NOFS Satellite Electric Field and Plasma Density Observations of Plasma Instabilities Below the Equatorial F-Peak -- Evidence for Approximately 500 km-Scale Spread-F "Precursor" Waves Driven by Zonal Shear Flow and km-Scale, Narrow-Banded Irregularities

NASA Technical Reports Server (NTRS)

Pfaff, R.; Freudenreich, H.; Klenzing, J.; Liebrecht, C.; Valladares, C.

2011-01-01

As solar activity has increased, the ionosphere F-peak has been elevated on numerous occasions above the C/NOFS satellite perigee of 400km. In particular, during the month of April, 2011, the satellite consistently journeyed below the F-peak whenever the orbit was in the region of the South Atlantic anomaly after sunset. During these passes, data from the electric field and plasma density probes on the satellite have revealed two types of instabilities which had not previously been observed in the C/NOFS data set (to our knowledge): The first is evidence for 400-500km-scale bottomside "undulations" that appear in the density and electric field data. In one case, these large scale waves are associated with a strong shear in the zonal E x B flow, as evidenced by variations in the meridional (outward) electric fields observed above and below the F-peak. These undulations are devoid of smaller scale structures in the early evening, yet appear at later local times along the same orbit associated with fully-developed spread-F with smaller scale structures. This suggests that they may be precursor waves for spread-F, driven by a collisional shear instability, following ideas advanced previously by researchers using data from the Jicamarca radar. A second new result (for C/NOFS) is the appearance of km-scale irregularities that are a common feature in the electric field and plasma density data that also appear when the satellite is below the F -peak at night. The vector electric field instrument on C/NOFS clearly shows that the electric field component of these waves is strongest in the zonal direction. These waves are strongly correlated with simultaneous observations of plasma density oscillations and appear both with, and without, evidence of larger-scale spread-F depletions. These km-scale, quasi-coherent waves strongly resemble the bottomside, sinusoidal irregularities reported in the Atmosphere Explorer satellite data set by Valladares et al. [JGR, 88, 8025, 1983]. We interpret these new observations in terms of fundamental plasma instabilities associated with the unstable, nighttime equatorial ionosphere.

Small-Scale Structure in Saturn's Rings

NASA Astrophysics Data System (ADS)

Rehnberg, Morgan

2017-08-01

The rings of Saturn are the largest and most complex in the Solar System. Decades of observation from ground- and space-based observatories and spacecraft missions have revealed the broad structure of the rings and the intricate interactions between the planet's moons and its rings. Stellar occultations observed by the Ultraviolet Imaging Spectrograph's High Speed Photometer onboard the Cassini spacecraft now enable the direct study of the small-scale structure that results from these interactions. In this dissertation, I present three distinct phenomena resulting from the small-scale physics of the rings. Many resonance locations with Saturn's external satellites lie within the main (A and B) rings. Two of these satellites, Janus and Epimetheus, have a unique co-orbital relationship and move radially to switch positions every 4.0 years. This motion also moves the resonance locations within the rings. As the spiral density waves created at these resonances interact, they launch an enormous solitary wave every eight years. I provide the first-ever observations of this never-predicted phenomenon and detail a possible formation mechanism. Previous studies have reported a population of kilometer-scale aggregates in Saturn's F ring, which likely form as a result of self-gravitation between ring particles in Saturn's Roche zone. I expand the known catalog of features in UVIS occultations and provide the first estimates of their density derived from comparisons with the A ring. These features are orders of magnitude less dense than previously believed, a fact which reconciles them with detections made by other means. Theory and indirect observations indicate that the smallest regular structures in the rings are wavelike aggregates called self-gravity wakes. Using the highest-resolution occulta- tions, I provide the first-ever direct detection of these features by identifying the gaps that represent the minima of the wakes. I demonstrate that the distribution of these gaps is con- sistent with the broad brightness asymmetries previously observed in the rings. Furthermore, the presence of spiral density waves affects the formation of self-gravity waves.

Ice shelf structure from dispersion curve analysis of passive-source seismic data, Ross Ice Shelf, Antarctica

NASA Astrophysics Data System (ADS)

Diez, A.; Bromirski, P. D.; Gerstoft, P.; Stephen, R. A.; Anthony, R. E.; Aster, R. C.; Cai, C.; Nyblade, A.; Wiens, D.

2015-12-01

An L-shaped array of three-component short period seismic stations was deployed at the Ross Ice Shelf, Antarctica approximately 100 km south of the ice edge, near 180° longitude, from November 18 through 28, 2014. Polarization analysis of data from these stations clearly shows propagating waves from below the ice shelf for frequencies below 2 Hz. Energy above 2 Hz is dominated by Rayleigh and Love waves propagating from the north. Frequency-slowness plots were calculated using beamforming. Resulting Love and Rayleigh wave dispersion curves were inverted for the shear wave velocity profile, from which we derive a density profile. The derived shear wave velocity profiles differ within the firn for the inversions using Rayleigh and Love wave dispersion curves. This difference is attributed to an effective anisotropy due to fine layering. The layered structure of firn, ice, water, and ocean floor results in a characteristic dispersion curve pattern below 7 Hz. We investigate the observed structures in more detail by forward modeling of Rayleigh wave dispersion curves for representative firn, ice, water, sediment structures. Rayleigh waves are observed when wavelengths are long enough to span the distance from the ice shelf surface to the seafloor. Our results show that the analysis of high frequency Rayleigh waves on an ice shelf has the ability to resolve ice shelf thickness, water column thickness, and the physical properties of the underlying ocean floor using passive-source seismic data.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ofman, L.; Knizhnik, K.; Kucera, T.

We study nonlinear waves in a prominence foot using a 2.5D MHD model motivated by recent high-resolution observations with Hinode/Solar Optical Telescope in Ca ii emission of a prominence on 2012 October 10 showing highly dynamic small-scale motions in the prominence material. Observations of Hα intensities and of Doppler shifts show similar propagating fluctuations. However, the optically thick nature of the emission lines inhibits a unique quantitative interpretation in terms of density. Nevertheless, we find evidence of nonlinear wave activity in the prominence foot by examining the relative magnitude of the fluctuation intensity (δI/I ∼ δn/n). The waves are evidentmore » as significant density fluctuations that vary with height and apparently travel upward from the chromosphere into the prominence material with quasi-periodic fluctuations with a typical period in the range of 5–11 minutes and wavelengths <2000 km. Recent Doppler shift observations show the transverse displacement of the propagating waves. The magnetic field was measured with the THEMIS instrument and was found to be 5–14 G. For the typical prominence density the corresponding fast magnetosonic speed is ∼20 km s{sup −1}, in qualitative agreement with the propagation speed of the detected waves. The 2.5D MHD numerical model is constrained with the typical parameters of the prominence waves seen in observations. Our numerical results reproduce the nonlinear fast magnetosonic waves and provide strong support for the presence of these waves in the prominence foot. We also explore gravitational MHD oscillations of the heavy prominence foot material supported by dipped magnetic field structure.« less

Three dimensional dust-acoustic solitary waves in an electron depleted dusty plasma with two-superthermal ion-temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borhanian, J.; Shahmansouri, M.

2013-01-15

A theoretical investigation is carried out to study the existence and characteristics of propagation of dust-acoustic (DA) waves in an electron-depleted dusty plasma with two-temperature ions, which are modeled by kappa distribution functions. A three-dimensional cylindrical Kadomtsev-Petviashvili equation governing evolution of small but finite amplitude DA waves is derived by means of a reductive perturbation method. The influence of physical parameters on solitary wave structure is examined. Furthermore, the energy integral equation is used to study the existence domains of the localized structures. It is found that the present model can be employed to describe the existence of positive asmore » well as negative polarity DA solitary waves by selecting special values for parameters of the system, e.g., superthermal index of cold and/or hot ions, cold to hot ion density ratio, and hot to cold ion temperature ratio. This model may be useful to understand the excitation of nonlinear DA waves in astrophysical objects.« less

Capillary wave theory of adsorbed liquid films and the structure of the liquid-vapor interface

NASA Astrophysics Data System (ADS)

MacDowell, Luis G.

2017-08-01

In this paper we try to work out in detail the implications of a microscopic theory for capillary waves under the assumption that the density is given along lines normal to the interface. Within this approximation, which may be justified in terms of symmetry arguments, the Fisk-Widom scaling of the density profile holds for frozen realizations of the interface profile. Upon thermal averaging of capillary wave fluctuations, the resulting density profile yields results consistent with renormalization group calculations in the one-loop approximation. The thermal average over capillary waves may be expressed in terms of a modified convolution approximation where normals to the interface are Gaussian distributed. In the absence of an external field we show that the phenomenological density profile applied to the square-gradient free energy functional recovers the capillary wave Hamiltonian exactly. We extend the theory to the case of liquid films adsorbed on a substrate. For systems with short-range forces, we recover an effective interface Hamiltonian with a film height dependent surface tension that stems from the distortion of the liquid-vapor interface by the substrate, in agreement with the Fisher-Jin theory of short-range wetting. In the presence of long-range interactions, the surface tension picks up an explicit dependence on the external field and recovers the wave vector dependent logarithmic contribution observed by Napiorkowski and Dietrich. Using an error function for the intrinsic density profile, we obtain closed expressions for the surface tension and the interface width. We show the external field contribution to the surface tension may be given in terms of the film's disjoining pressure. From literature values of the Hamaker constant, it is found that the fluid-substrate forces may be able to double the surface tension for films in the nanometer range. The film height dependence of the surface tension described here is in full agreement with results of the capillary wave spectrum obtained recently in computer simulations, and the predicted translation mode of surface fluctuations reproduces to linear order in field strength an exact solution of the density correlation function for the Landau-Ginzburg-Wilson Hamiltonian in an external field.

Ab initio study on rare-earth iron-pnictides RFeAsO (R = Pr, Nd, Sm, Gd) in low-temperature Cmma phase

NASA Astrophysics Data System (ADS)

Eryigit, Resul; Gurel, Tanju; Erturk, Esra; Lukoyanov, A. V.; Akcay, Guven; Anisimov, V. I.

2014-03-01

We present density functional theory calculations on iron-based pnictides RFeAsO (R = Pr, Nd, Sm, Gd). The calculations have been carried out using plane-waves and projector augmented wave (PAW) pseudopotential approach. Structural, magnetic and electronic properties are studied within generalized gradient approximation (GGA) and also within GGA+U in order to investigate the influence of electron correlation effects. Low-temperature Cmma structure is fully optimized by GGA considering both non-magnetic and magnetic cells. We have found that spin-polarized structure improves the agreement with experiments on equilibrium lattice parameters, particularly c lattice parameter and Fe-As bond-lengths. Electronic band structure, total density of states, and spin-dependent orbital-resolved density of states are also analyzed in the frameworks of GGA and GGA+U and discussed. For all materials, by including on-site Coulomb correction, rare earth 4f states move away from the Fermi level and the Fermi level features of the systems are found to be mostly defined by the 3d electron-electron correlations in Fe. This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK Project No. TBAG-111T796) and the Russian Foundation for Basic Research (Project No. 12-02-91371-CT_a).

Sub-structure formation in starless cores

NASA Astrophysics Data System (ADS)

Toci, C.; Galli, D.; Verdini, A.; Del Zanna, L.; Landi, S.

2018-02-01

Motivated by recent observational searches of sub-structure in starless molecular cloud cores, we investigate the evolution of density perturbations on scales smaller than the Jeans length embedded in contracting isothermal clouds, adopting the same formalism developed for the expanding Universe and the solar wind. We find that initially small amplitude, Jeans-stable perturbations (propagating as sound waves in the absence of a magnetic field) are amplified adiabatically during the contraction, approximately conserving the wave action density, until they either become non-linear and steepen into shocks at a time tnl, or become gravitationally unstable when the Jeans length decreases below the scale of the perturbations at a time tgr. We evaluate analytically the time tnl at which the perturbations enter the non-linear stage using a Burgers' equation approach, and we verify numerically that this time marks the beginning of the phase of rapid dissipation of the kinetic energy of the perturbations. We then show that for typical values of the rms Mach number in molecular cloud cores, tnl is smaller than tgr, and therefore density perturbations likely dissipate before becoming gravitational unstable. Solenoidal modes grow at a faster rate than compressible modes, and may eventually promote fragmentation through the formation of vortical structures.

The excitation of spiral density waves through turbulent fluctuations in accretion discs - II. Numerical simulations with MRI-driven turbulence

NASA Astrophysics Data System (ADS)

Heinemann, T.; Papaloizou, J. C. B.

2009-07-01

We present fully three-dimensional local simulations of compressible magneto-rotational instability (MRI) turbulence with the object of studying and elucidating the excitation of the non-axisymmetric spiral density waves that are observed to always be present in such simulations. They are potentially important for affecting protoplanetary migration through the action of associated stochastic gravitational forces and producing residual transport in MHD inactive regions through which they may propagate. The simulations we perform are with zero net flux and produce mean activity levels corresponding to the Shakura & Syunyaev α ~ 5 × 10-3, being at the lower end of the range usually considered in accretion disc modelling. We reveal the nature of the mechanism responsible for the excitation of these waves by determining the time-dependent evolution of the Fourier transforms of the participating state variables. The dominant waves are found to have no vertical structure and to be excited during periodically repeating swings in which they change from leading to trailing. The initial phase of the evolution of such a swing is found to be in excellent agreement with that expected from the WKBJ theory developed in a preceding paper by Heinemann & Papaloizou. However, shortly after the attainment of the expected maximum wave amplitude, the waves begin to be damped on account of the formation of weak shocks. As expected from the theory, the waves are seen to shorten in radial wavelength as they propagate. This feature enables non-linear dissipation to continue in spite of amplitude decrease. As a consequence, the waves are almost always seen to be in the non-linear regime. We demonstrate that the important source terms causing excitation of the waves are related to a quantity that reduces to the potential vorticity for small perturbations from the background state with no vertical dependence. We find that the root mean square density fluctuations associated with the waves are positively correlated with both this quantity and the general level of hydromagnetic turbulence. The mean angular momentum transport associated with spiral density waves generated in our simulations is estimated to be a significant fraction of that associated with the turbulent Reynolds stress.

Theoretical investigations on structural, elastic and electronic properties of thallium halides

NASA Astrophysics Data System (ADS)

Singh, Rishi Pal; Singh, Rajendra Kumar; Rajagopalan, Mathrubutham

2011-04-01

Theoretical investigations on structural, elastic and electronic properties, viz. ground state lattice parameter, elastic moduli and density of states, of thallium halides (viz. TlCl and TlBr) have been made using the full potential linearized augmented plane wave method within the generalized gradient approximation (GGA). The ground state lattice parameter and bulk modulus and its pressure derivative have been obtained using optimization method. Young's modulus, shear modulus, Poisson ratio, sound velocities for longitudinal and shear waves, Debye average velocity, Debye temperature and Grüneisen parameter have also been calculated for these compounds. Calculated structural, elastic and other parameters are in good agreement with the available data.

Effect of wave localization on plasma instabilities

NASA Astrophysics Data System (ADS)

Levedahl, William Kirk

1987-10-01

The Anderson model of wave localization in random media is involved to study the effect of solar wind density turbulence on plasma processes associated with the solar type III radio burst. ISEE-3 satellite data indicate that a possible model for the type III process is the parametric decay of Langmuir waves excited by solar flare electron streams into daughter electromagnetic and ion acoustic waves. The threshold for this instability, however, is much higher than observed Langmuir wave levels because of rapid wave convection of the transverse electromagnetic daughter wave in the case where the solar wind is assumed homogeneous. Langmuir and transverse waves near critical density satisfy the Ioffe-Reigel criteria for wave localization in the solar wind with observed density fluctuations -1 percent. Numerical simulations of wave propagation in random media confirm the localization length predictions of Escande and Souillard for stationary density fluctations. For mobile density fluctuations localized wave packets spread at the propagation velocity of the density fluctuations rather than the group velocity of the waves. Computer simulations using a linearized hybrid code show that an electron beam will excite localized Langmuir waves in a plasma with density turbulence. An action principle approach is used to develop a theory of non-linear wave processes when waves are localized. A theory of resonant particles diffusion by localized waves is developed to explain the saturation of the beam-plasma instability. It is argued that localization of electromagnetic waves will allow the instability threshold to be exceeded for the parametric decay discussed above.

Anisotropy-driven transition from the Moore-Read state to quantum Hall stripes

NASA Astrophysics Data System (ADS)

Zhu, Zheng; Sodemann, Inti; Sheng, D. N.; Fu, Liang

2017-05-01

We investigate the nature of the quantum Hall liquid in a half-filled second Landau level (n =1 ) as a function of band mass anisotropy using numerical exact diagonalization and density matrix renormalization group methods. We find increasing the mass anisotropy induces a quantum phase transition from the Moore-Read state to a charge density wave state. By analyzing the energy spectrum, guiding center structure factors, and by adding weak pinning potentials, we show that this charge density wave is a unidirectional quantum Hall stripe, which has a periodicity of a few magnetic lengths and survives in the thermodynamic limit. We find smooth profiles for the guiding center occupation function that reveal the strong coupling nature of the array of chiral Luttinger liquids residing at the stripe edges.

Simulation Analysis of Zero Mean Flow Edge Turbulence in LAPD

NASA Astrophysics Data System (ADS)

Friedman, Brett Cory

I model, simulate, and analyze the turbulence in a particular experiment on the Large Plasma Device (LAPD) at UCLA. The experiment, conducted by Schaffner et al. [D. Schaffner et al., Phys. Rev. Lett. 109, 135002 (2012)], nulls out the intrinsic mean flow in LAPD by limiter biasing. The model that I use in the simulation is an electrostatic reduced Braginskii two-fluid model that describes the time evolution of density, electron temperature, electrostatic potential, and parallel electron velocity fluctuations in the edge region of LAPD. The spatial domain is annular, encompassing the radial coordinates over which a significant equilibrium density gradient exists. My model breaks the independent variables in the equations into time-independent equilibrium parts and time-dependent fluctuating parts, and I use experimentally obtained values as input for the equilibrium parts. After an initial exponential growth period due to a linear drift wave instability, the fluctuations saturate and the frequency and azimuthal wavenumber spectra become broadband with no visible coherent peaks, at which point the fluctuations become turbulent. The turbulence develops intermittent pressure and flow filamentary structures that grow and dissipate, but look much different than the unstable linear drift waves, primarily in the extremely long axial wavelengths that the filaments possess. An energy dynamics analysis that I derive reveals the mechanism that drives these structures. The long k|| ˜ 0 intermittent potential filaments convect equilibrium density across the equilibrium density gradient, setting up local density filaments. These density filaments, also with k || ˜ 0, produce azimuthal density gradients, which drive radially propagating secondary drift waves. These finite k|| drift waves nonlinearly couple to one another and reinforce the original convective filament, allowing the process to bootstrap itself. The growth of these structures is by nonlinear instability because they require a finite amplitude to start, and they require nonlinear terms in the equations to sustain their growth. The reason why k|| ˜ 0 structures can grow and support themselves in a dynamical system with no k|| = 0 linear instability is because the linear eigenmodes of the system are nonorthogonal. Nonorthogonal eigenmodes that individually decay under linear dynamics can transiently inject energy into the system, allowing for instability. The instability, however, can only occur when the fluctuations have a finite starting amplitude, and nonlinearities are available to mix energy among eigenmodes. Finally, I attempt to figure out how many effective degrees of freedom control the turbulence to determine whether it is stochastic or deterministic. Using two different methods - permutation entropy analysis by means of time delay trajectory reconstruction and Proper Orthogonal Decomposition - I determine that more than a few degrees of freedom, possibly even dozens or hundreds, are all active. The turbulence, while not stochastic, is not a manifestation of low-dimensional chaos - it is high-dimensional.

Variational Optimization of the Second-Order Density Matrix Corresponding to a Seniority-Zero Configuration Interaction Wave Function.

PubMed

Poelmans, Ward; Van Raemdonck, Mario; Verstichel, Brecht; De Baerdemacker, Stijn; Torre, Alicia; Lain, Luis; Massaccesi, Gustavo E; Alcoba, Diego R; Bultinck, Patrick; Van Neck, Dimitri

2015-09-08

We perform a direct variational determination of the second-order (two-particle) density matrix corresponding to a many-electron system, under a restricted set of the two-index N-representability P-, Q-, and G-conditions. In addition, we impose a set of necessary constraints that the two-particle density matrix must be derivable from a doubly occupied many-electron wave function, i.e., a singlet wave function for which the Slater determinant decomposition only contains determinants in which spatial orbitals are doubly occupied. We rederive the two-index N-representability conditions first found by Weinhold and Wilson and apply them to various benchmark systems (linear hydrogen chains, He, N2, and CN(-)). This work is motivated by the fact that a doubly occupied many-electron wave function captures in many cases the bulk of the static correlation. Compared to the general case, the structure of doubly occupied two-particle density matrices causes the associate semidefinite program to have a very favorable scaling as L(3), where L is the number of spatial orbitals. Since the doubly occupied Hilbert space depends on the choice of the orbitals, variational calculation steps of the two-particle density matrix are interspersed with orbital-optimization steps (based on Jacobi rotations in the space of the spatial orbitals). We also point to the importance of symmetry breaking of the orbitals when performing calculations in a doubly occupied framework.

Determination of structure parameters in strong-field tunneling ionization theory of molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao Songfeng; Jin Cheng; College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou, Gansu 730070

2010-03-15

In the strong field molecular tunneling ionization theory of Tong et al. [Phys. Rev. A 66, 033402 (2002)], the ionization rate depends on the asymptotic wave function of the molecular orbital from which the electron is removed. The orbital wave functions obtained from standard quantum chemistry packages in general are not good enough in the asymptotic region. Here we construct a one-electron model potential for several linear molecules using density functional theory. We show that the asymptotic wave function can be improved with an iteration method and after one iteration accurate asymptotic wave functions and structure parameters are determined. Withmore » the new parameters we examine the alignment-dependent tunneling ionization probabilities for several molecules and compare with other calculations and with recent measurements, including ionization from inner molecular orbitals.« less

A View into Saturn through its Natural Seismograph

NASA Astrophysics Data System (ADS)

Mankovich, Christopher

2018-04-01

Saturn's nonradial oscillations perturb the orbits of ring particles. The C ring is fortuitous in that it spans several resonances with Saturn's fundamental acoustic (f-) modes, and its moderate optical depth allows the characterization of wave features using stellar occultations. The growing set of C-ring waves with precise pattern frequencies and azimuthal order m measured from Cassini stellar occultations (Hedman & Nicholson 2013, 2014; French et al. 2016) provides new constraints on Saturn's internal structure, with the potential to aid in resolving long-standing questions about the planet's distribution of helium and heavier elements, its means of internal energy transport, and its rotation state.We construct Saturn interior models and calculate mode eigenfrequencies, mapping the planet mode frequencies to resonant locations in the rings to compare with the locations of observed spiral density and vertical bending waves in the C ring. While spiral density waves at low azimuthal order (m=2-3) appear strongly affected by resonant coupling between f-modes and deep g-modes (Fuller 2014), the locations of waves with higher azimuthal order can be fit with a spectrum of pure f-modes for Saturn models with adiabatic envelopes and realistic equations of state. Notably, several newly observed density waves and bending waves (Nicholson et al., in preparation) align with outer Lindblad and outer vertical resonances for non-sectoral (m!=l) Saturn f-modes of relatively high angular degree, and we present normal mode identifications for these waves. We assess the range of resonance locations in the C and D rings allowed for the spectrum of f-modes given gravity field constraints, point to other resonance locations that should experience strong forcing, and use the full set of observed waves to estimate Saturn's bulk rotation rate.

Density functional theory calculations of III-N based semiconductors with mBJLDA

NASA Astrophysics Data System (ADS)

Gürel, Hikmet Hakan; Akıncı, Özden; Ünlü, Hilmi

2017-02-01

In this work, we present first principles calculations based on a full potential linear augmented plane-wave method (FP-LAPW) to calculate structural and electronic properties of III-V based nitrides such as GaN, AlN, InN in a zinc-blende cubic structure. First principles calculation using the local density approximation (LDA) and generalized gradient approximation (GGA) underestimate the band gap. We proposed a new potential called modified Becke-Johnson local density approximation (MBJLDA) that combines modified Becke-Johnson exchange potential and the LDA correlation potential to get better band gap results compared to experiment. We compared various exchange-correlation potentials (LSDA, GGA, HSE, and MBJLDA) to determine band gaps and structural properties of semiconductors. We show that using MBJLDA density potential gives a better agreement with experimental data for band gaps III-V nitrides based semiconductors.

Branches of electrostatic turbulence inside solitary plasma structures in the auroral ionosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Golovchanskaya, Irina V.; Kozelov, Boris V.; Chernyshov, Alexander A.

2014-08-15

The excitation of electrostatic turbulence inside space-observed solitary structures is a central topic of this exposition. Three representative solitary structures observed in the topside auroral ionosphere as large-amplitude nonlinear signatures in the electric field and magnetic-field-aligned current on the transverse scales of ∼10{sup 2}–10{sup 3} m are evaluated by the theories of electrostatic wave generation in inhomogeneous background configurations. A quantitative analysis shows that the structures are, in general, effective in destabilizing the inhomogeneous energy-density-driven (IEDD) waves, as well as of the ion acoustic waves modified by a shear in the parallel drift of ions. It is demonstrated that the dominatingmore » branch of the electrostatic turbulence is determined by the interplay of various driving sources inside a particular solitary structure. The sources do not generally act in unison, so that their common effect may be inhibiting for excitation of electrostatic waves of a certain type. In the presence of large magnetic-field-aligned current, which is not correlated to the inhomogeneous electric field inside the structure, the ion-acoustic branch becomes dominating. In other cases, the IEDD instability is more central.« less

Introduction to Density Functional Theory: Calculations by Hand on the Helium Atom

ERIC Educational Resources Information Center

Baseden, Kyle A.; Tye, Jesse W.

2014-01-01

Density functional theory (DFT) is a type of electronic structure calculation that has rapidly gained popularity. In this article, we provide a step-by-step demonstration of a DFT calculation by hand on the helium atom using Slater's X-Alpha exchange functional on a single Gaussian-type orbital to represent the atomic wave function. This DFT…

Quantum-shutter approach to tunneling time scales with wave packets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamada, Norifumi; Garcia-Calderon, Gaston; Villavicencio, Jorge

2005-07-15

The quantum-shutter approach to tunneling time scales [G. Garcia-Calderon and A. Rubio, Phys. Rev. A 55, 3361 (1997)], which uses a cutoff plane wave as the initial condition, is extended to consider certain type of wave packet initial conditions. An analytical expression for the time-evolved wave function is derived. The time-domain resonance, the peaked structure of the probability density (as the function of time) at the exit of the barrier, originally found with the cutoff plane wave initial condition, is studied with the wave packet initial conditions. It is found that the time-domain resonance is not very sensitive to themore » width of the packet when the transmission process occurs in the tunneling regime.« less

Coincident structural and magnetic order in BaFe 2 ( As 1 - x P x ) 2 revealed by high-resolution neutron diffraction

DOE PAGES

Allred, J. M.; Taddei, K. M.; Bugaris, D. E.; ...

2014-09-19

We present neutron dffraction analysis of BaFe 2(As 1-xP x) 2 over a wide temperature (10 to 300 K) and compositional (0.11 < x < 0.79) range, including the normal state, the magnetically ordered state, and the superconducting state. The paramagnetic to spin-density wave and orthorhombic to tetragonal transitions are first order and coincident within the sensitivity of our measurements (~ 0:5 K). Extrapolation of the orthorhombic order parameter down to zero suggests that structural quantum criticality cannot exist at compositions higher than x = 0.28, which is much lower than values determined using other methods, but in good agreementmore » with our observations of the actual phase stability range. Lastly, the onset of spin-density wave order shows a stronger structural anomaly than the charge-doped system in the form of an enhancement of the c/a ratio below the transition.« less

Electromagnetic modulation of the ultrasonic signal for nondestructive detection of small defects and ferromagnetic inclusions in thin wall structures

NASA Astrophysics Data System (ADS)

Finkel, Peter

2008-03-01

We report on new nondestructive evaluation technique based on electromagnetic modulation of ultrasonic signal for detection of the small crack, flaws and inclusions in thin-walled parts. The electromagnetically induced high density current pulse produces stresses which alter the ultrasonic waves scanning the part with the defect and modulate ultrasonic signal. The excited electromagnetic field can produces crack-opening due to Lorentz forces that increase the ultrasonic reflection. The Joule heating associated with the high density current, and consequent thermal stresses may cause both crack-closure, as well as crack-opening, depending on various factors. Experimental data is presented here for the case of a small crack near holes in thin-walled structures. The measurements were taken at 2-10 MHz with a Lamb wave wedge transducer. It is shown that electromagnetic transient modulation of the ultrasonic echo pulse tone-burst suggest that this method could be used to enhance detection of small cracks and ferromagnetic inclusions in thin walled metallic structures.

Design and Analysis of Tubular Permanent Magnet Linear Wave Generator

PubMed Central

Si, Jikai; Feng, Haichao; Su, Peng; Zhang, Lufeng

2014-01-01

Due to the lack of mature design program for the tubular permanent magnet linear wave generator (TPMLWG) and poor sinusoidal characteristics of the air gap flux density for the traditional surface-mounted TPMLWG, a design method and a new secondary structure of TPMLWG are proposed. An equivalent mathematical model of TPMLWG is established to adopt the transformation relationship between the linear velocity of permanent magnet rotary generator and the operating speed of TPMLWG, to determine the structure parameters of the TPMLWG. The new secondary structure of the TPMLWG contains surface-mounted permanent magnets and the interior permanent magnets, which form a series-parallel hybrid magnetic circuit, and their reasonable structure parameters are designed to get the optimum pole-arc coefficient. The electromagnetic field and temperature field of TPMLWG are analyzed using finite element method. It can be included that the sinusoidal characteristics of air gap flux density of the new secondary structure TPMLWG are improved, the cogging force as well as mechanical vibration is reduced in the process of operation, and the stable temperature rise of generator meets the design requirements when adopting the new secondary structure of the TPMLWG. PMID:25050388

Design and analysis of tubular permanent magnet linear wave generator.

PubMed

Si, Jikai; Feng, Haichao; Su, Peng; Zhang, Lufeng

2014-01-01

Due to the lack of mature design program for the tubular permanent magnet linear wave generator (TPMLWG) and poor sinusoidal characteristics of the air gap flux density for the traditional surface-mounted TPMLWG, a design method and a new secondary structure of TPMLWG are proposed. An equivalent mathematical model of TPMLWG is established to adopt the transformation relationship between the linear velocity of permanent magnet rotary generator and the operating speed of TPMLWG, to determine the structure parameters of the TPMLWG. The new secondary structure of the TPMLWG contains surface-mounted permanent magnets and the interior permanent magnets, which form a series-parallel hybrid magnetic circuit, and their reasonable structure parameters are designed to get the optimum pole-arc coefficient. The electromagnetic field and temperature field of TPMLWG are analyzed using finite element method. It can be included that the sinusoidal characteristics of air gap flux density of the new secondary structure TPMLWG are improved, the cogging force as well as mechanical vibration is reduced in the process of operation, and the stable temperature rise of generator meets the design requirements when adopting the new secondary structure of the TPMLWG.

Ultra-low velocity zones beneath the Philippine and Tasman Seas revealed by a trans-dimensional Bayesian waveform inversion

NASA Astrophysics Data System (ADS)

Pachhai, Surya; Dettmer, Jan; Tkalčić, Hrvoje

2015-11-01

Ultra-low velocity zones (ULVZs) are small-scale structures in the Earth's lowermost mantle inferred from the analysis of seismological observations. These structures exhibit a strong decrease in compressional (P)-wave velocity, shear (S)-wave velocity, and an increase in density. Quantifying the elastic properties of ULVZs is crucial for understanding their physical origin, which has been hypothesized either as partial melting, iron enrichment, or a combination of the two. Possible disambiguation of these hypotheses can lead to a better understanding of the dynamic processes of the lowermost mantle, such as, percolation, stirring and thermochemical convection. To date, ULVZs have been predominantly studied by forward waveform modelling of seismic waves that sample the core-mantle boundary region. However, ULVZ parameters (i.e. velocity, density, and vertical and lateral extent) obtained through forward modelling are poorly constrained because inferring Earth structure from seismic observations is a non-linear inverse problem with inherent non-uniqueness. To address these issues, we developed a trans-dimensional hierarchical Bayesian inversion that enables rigorous estimation of ULVZ parameter values and their uncertainties, including the effects of model selection. The model selection includes treating the number of layers and the vertical extent of the ULVZ as unknowns. The posterior probability density (solution to the inverse problem) of the ULVZ parameters is estimated by reversible jump Markov chain Monte Carlo sampling that employs parallel tempering to improve efficiency/convergence. First, we apply our method to study the resolution of complex ULVZ structure (including gradually varying structure) by probabilistically inverting simulated noisy waveforms. Then, two data sets sampling the CMB beneath the Philippine and Tasman Seas are considered in the inversion. Our results indicate that both ULVZs are more complex than previously suggested. For the Philippine Sea data, we find a strong decrease in S-wave velocity, which indicates the presence of iron-rich material, albeit this result is accompanied with larger parameter uncertainties than in a previous study. For the Tasman Sea data, our analysis yields a well-constrained S-wave velocity that gradually decreases with depth. We conclude that this ULVZ represents a partial melt of iron-enriched material with higher melt content near its bottom.

Density functional theory calculations of 95Mo NMR parameters in solid-state compounds.

PubMed

Cuny, Jérôme; Furet, Eric; Gautier, Régis; Le Pollès, Laurent; Pickard, Chris J; d'Espinose de Lacaillerie, Jean-Baptiste

2009-12-21

The application of periodic density functional theory-based methods to the calculation of (95)Mo electric field gradient (EFG) and chemical shift (CS) tensors in solid-state molybdenum compounds is presented. Calculations of EFG tensors are performed using the projector augmented-wave (PAW) method. Comparison of the results with those obtained using the augmented plane wave + local orbitals (APW+lo) method and with available experimental values shows the reliability of the approach for (95)Mo EFG tensor calculation. CS tensors are calculated using the recently developed gauge-including projector augmented-wave (GIPAW) method. This work is the first application of the GIPAW method to a 4d transition-metal nucleus. The effects of ultra-soft pseudo-potential parameters, exchange-correlation functionals and structural parameters are precisely examined. Comparison with experimental results allows the validation of this computational formalism.

DOE Office of Scientific and Technical Information (OSTI.GOV)

EL-Shamy, E. F., E-mail: emadel-shamy@hotmail.com; Department of Physics, College of Science, King Khalid University, P.O. 9004, Abha; Al-Asbali, A. M., E-mail: aliaa-ma@hotmail.com

A theoretical investigation is carried out to study the propagation and the head-on collision of dust-acoustic (DA) shock waves in a strongly coupled dusty plasma consisting of negative dust fluid, Maxwellian distributed electrons and ions. Applying the extended Poincaré–Lighthill–Kuo method, a couple of Korteweg–deVries–Burgers equations for describing DA shock waves are derived. This study is a first attempt to deduce the analytical phase shifts of DA shock waves after collision. The impacts of physical parameters such as the kinematic viscosity, the unperturbed electron-to-dust density ratio, parameter determining the effect of polarization force, the ion-to-electron temperature ratio, and the effective dustmore » temperature-to-ion temperature ratio on the structure and the collision of DA shock waves are examined. In addition, the results reveal the increase of the strength and the steepness of DA shock waves as the above mentioned parameters increase, which in turn leads to the increase of the phase shifts of DA shock waves after collision. The present model may be useful to describe the structure and the collision of DA shock waves in space and laboratory dusty plasmas.« less

Three-Dimensional Sensitivity Kernels of Z/H Amplitude Ratios of Surface and Body Waves

NASA Astrophysics Data System (ADS)

Bao, X.; Shen, Y.

2017-12-01

The ellipticity of Rayleigh wave particle motion, or Z/H amplitude ratio, has received increasing attention in inversion for shallow Earth structures. Previous studies of the Z/H ratio assumed one-dimensional (1D) velocity structures beneath the receiver, ignoring the effects of three-dimensional (3D) heterogeneities on wave amplitudes. This simplification may introduce bias in the resulting models. Here we present 3D sensitivity kernels of the Z/H ratio to Vs, Vp, and density perturbations, based on finite-difference modeling of wave propagation in 3D structures and the scattering-integral method. Our full-wave approach overcomes two main issues in previous studies of Rayleigh wave ellipticity: (1) the finite-frequency effects of wave propagation in 3D Earth structures, and (2) isolation of the fundamental mode Rayleigh waves from Rayleigh wave overtones and converted Love waves. In contrast to the 1D depth sensitivity kernels in previous studies, our 3D sensitivity kernels exhibit patterns that vary with azimuths and distances to the receiver. The laterally-summed 3D sensitivity kernels and 1D depth sensitivity kernels, based on the same homogeneous reference model, are nearly identical with small differences that are attributable to the single period of the 1D kernels and a finite period range of the 3D kernels. We further verify the 3D sensitivity kernels by comparing the predictions from the kernels with the measurements from numerical simulations of wave propagation for models with various small-scale perturbations. We also calculate and verify the amplitude kernels for P waves. This study shows that both Rayleigh and body wave Z/H ratios provide vertical and lateral constraints on the structure near the receiver. With seismic arrays, the 3D kernels afford a powerful tool to use the Z/H ratios to obtain accurate and high-resolution Earth models.

Non-perturbative aspects of particle acceleration in non-linear electrodynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burton, David A.; Flood, Stephen P.; Wen, Haibao

2015-04-15

We undertake an investigation of particle acceleration in the context of non-linear electrodynamics. We deduce the maximum energy that an electron can gain in a non-linear density wave in a magnetised plasma, and we show that an electron can “surf” a sufficiently intense Born-Infeld electromagnetic plane wave and be strongly accelerated by the wave. The first result is valid for a large class of physically reasonable modifications of the linear Maxwell equations, whilst the second result exploits the special mathematical structure of Born-Infeld theory.

Effect of wave localization on plasma instabilities. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Levedahl, William Kirk

1987-01-01

The Anderson model of wave localization in random media is involved to study the effect of solar wind density turbulence on plasma processes associated with the solar type III radio burst. ISEE-3 satellite data indicate that a possible model for the type III process is the parametric decay of Langmuir waves excited by solar flare electron streams into daughter electromagnetic and ion acoustic waves. The threshold for this instability, however, is much higher than observed Langmuir wave levels because of rapid wave convection of the transverse electromagnetic daughter wave in the case where the solar wind is assumed homogeneous. Langmuir and transverse waves near critical density satisfy the Ioffe-Reigel criteria for wave localization in the solar wind with observed density fluctuations -1 percent. Numerical simulations of wave propagation in random media confirm the localization length predictions of Escande and Souillard for stationary density fluctations. For mobile density fluctuations localized wave packets spread at the propagation velocity of the density fluctuations rather than the group velocity of the waves. Computer simulations using a linearized hybrid code show that an electron beam will excite localized Langmuir waves in a plasma with density turbulence. An action principle approach is used to develop a theory of non-linear wave processes when waves are localized. A theory of resonant particles diffusion by localized waves is developed to explain the saturation of the beam-plasma instability. It is argued that localization of electromagnetic waves will allow the instability threshold to be exceeded for the parametric decay discussed above.

Investigation of traveling ionospheric disturbances

NASA Technical Reports Server (NTRS)

Grossi, M.; Estes, R. D.

1981-01-01

Maximum entropy power spectra of the ionospheric electron density were constructed to enable PINY to compare them with the power independently obtained by PINY with in situ measurements of ionospheric electron density and neutral species performed with instrumentation carried by the Atmospheric Explorer (AE) satellite. This comparison corroborated evidence on the geophysical reality of the alleged electron density irregularities detected by the ASTP dual frequency Doppler link. Roughly half of the localized wave structures which are confined to dimensions of 1800 km or less (as seen by an orbiting Doppler baseline) were found to be associated with the larger crest of the geomagnetic anomaly in the Southern (winter) Hemisphere in the morning. The observed nighttime structures are also associated with local peaks in the electron density.

Generation Mechanism of Nonlinear Rayleigh Surface Waves for Randomly Distributed Surface Micro-Cracks.

PubMed

Ding, Xiangyan; Li, Feilong; Zhao, Youxuan; Xu, Yongmei; Hu, Ning; Cao, Peng; Deng, Mingxi

2018-04-23

This paper investigates the propagation of Rayleigh surface waves in structures with randomly distributed surface micro-cracks using numerical simulations. The results revealed a significant ultrasonic nonlinear effect caused by the surface micro-cracks, which is mainly represented by a second harmonic with even more distinct third/quadruple harmonics. Based on statistical analysis from the numerous results of random micro-crack models, it is clearly found that the acoustic nonlinear parameter increases linearly with micro-crack density, the proportion of surface cracks, the size of micro-crack zone, and the excitation frequency. This study theoretically reveals that nonlinear Rayleigh surface waves are feasible for use in quantitatively identifying the physical characteristics of surface micro-cracks in structures.

Nonlinear structures and anomalous transport in partially magnetized E×B plasmas

DOE PAGES

Janhunen, Salomon; Smolyakov, Andrei; Chapurin, Oleksandr; ...

2017-12-29

Nonlinear dynamics of the electron-cyclotron instability driven by the electron E x B current in a crossed electric and magnetic field is studied. In the nonlinear regime, the instability proceeds by developing a large amplitude coherent wave driven by the energy input from the fundamental cyclotron resonance. Further evolution shows the formation of the long wavelength envelope akin to the modulational instability. Simultaneously, the ion density shows the development of a high-k content responsible for wave focusing and sharp peaks on the periodic cnoidal wave structure. Here, it is shown that the anomalous electron transport (along the direction of themore » applied electric field) is dominated by the long wavelength part of the turbulent spectrum.« less

Wide-range simulation of elastoplastic wave fronts and failure of solids under high-speed loading

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saveleva, Natalia, E-mail: saveleva@icmm.ru; Bayandin, Yuriy, E-mail: buv@icmm.ru; Naimark, Oleg, E-mail: naimark@icmm.ru

2015-10-27

The aim of this paper is numerical study of deformation processes and failure of vanadium under shock-wave loading. According developed statistical theory of solid with mesoscopic defects the constitutive equations were proposed in terms of two structural variables characterizing behavior of defects ensembles: defect density tensor and structural scaling parameter. On the basis of wide-range constitutive equations the mathematical model of deformation behavior and failure of vanadium was developed taking into account the bond relaxation mechanisms, multistage of fracture and nonlinearity kinetic of defects. Results of numerical simulation allow the description of the major effects of shock wave propagation (elasticmore » precursor decay, grow of spall strength under grow strain rate)« less

Generation Mechanism of Nonlinear Rayleigh Surface Waves for Randomly Distributed Surface Micro-Cracks

PubMed Central

Ding, Xiangyan; Li, Feilong; Xu, Yongmei; Cao, Peng; Deng, Mingxi

2018-01-01

This paper investigates the propagation of Rayleigh surface waves in structures with randomly distributed surface micro-cracks using numerical simulations. The results revealed a significant ultrasonic nonlinear effect caused by the surface micro-cracks, which is mainly represented by a second harmonic with even more distinct third/quadruple harmonics. Based on statistical analysis from the numerous results of random micro-crack models, it is clearly found that the acoustic nonlinear parameter increases linearly with micro-crack density, the proportion of surface cracks, the size of micro-crack zone, and the excitation frequency. This study theoretically reveals that nonlinear Rayleigh surface waves are feasible for use in quantitatively identifying the physical characteristics of surface micro-cracks in structures. PMID:29690580

Damping of Resonantly Forced Density Waves in Dense Planetary Rings

NASA Astrophysics Data System (ADS)

Lehmann, Marius; Schmidt, Jürgen; Salo, Heikki

2016-10-01

We address the stability of resonantly forced density waves in dense planetary rings.Already by Goldreich and Tremaine (1978) it has been argued that density waves might be unstable, depending on the relationship between the ring's viscosity and the surface mass density. In the recent paper (Schmidt et al. 2016) we have pointed out that when - within a fluid description of the ring dynamics - the criterion for viscous overstability is satisfied, forced spiral density waves become unstable as well. In this case, linear theory fails to describe the damping.We apply the multiple scale formalism to derive a weakly nonlinear damping relation from a hydrodynamical model.This relation describes the resonant excitation and nonlinear viscous damping of spiral density waves in a vertically integrated fluid disk with density dependent transport coefficients. The model consistently predicts linear instability of density waves in a ring region where the conditions for viscous overstability are met. In this case, sufficiently far away from the Lindblad resonance, the surface mass density perturbation is predicted to saturate to a constant value due to nonlinear viscous damping. In general the model wave damping lengths depend on a set of input parameters, such as the distance to the threshold for viscous overstability and the ground state surface mass density.Our new model compares reasonably well with the streamline model for nonlinear density waves of Borderies et al. 1986.Deviations become substantial in the highly nonlinear regime, corresponding to strong satellite forcing.Nevertheless, we generally observe good or at least qualitative agreement between the wave amplitude profiles of both models. The streamline approach is superior at matching the total wave profile of waves observed in Saturn's rings, while our new damping relation is a comparably handy tool to gain insight in the evolution of the wave amplitude with distance from resonance, and the different regimes of wave formation and the dependence on the parameters of the model.

Inversion of Surface Wave Phase Velocities for Radial Anisotropy to an Depth of 1200 km

NASA Astrophysics Data System (ADS)

Xing, Z.; Beghein, C.; Yuan, K.

2012-12-01

This study aims to evaluate three dimensional radial anisotropy to an depth of 1200 km. Radial anisotropy describes the difference in velocity between horizontally polarized Rayleigh waves and vertically polarized Love waves. Its presence in the uppermost 200 km mantle has well been documented by different groups, and has been regarded as an indicator of mantle convection which aligns the intrinsically anisotropic minerals, largely olivine, to form large scale anisotropy. However, there is no global agreement on whether anisotropy exists in the region below 200 km. Recent models also associate a fast vertically polarized shear wave with vertical upwelling mantle flow. The data used in this study is the globally isotropic phase velocity models of fundamental and higher mode Love and Rayleigh waves (Visser, 2008). The inclusion of higher mode surface wave phase velocity provides sensitivities to structure at depth that extends to below the transition zone. While the data is the same as used by Visser (2008), a quite different parameterization is applied. All the six parameters - five elastic parameters A, C, F, L, N and density - are now regarded as independent, which rules out possible biased conclusions induced by scaling relation method used in several previous studies to reduce the number of parameters partly due to limited computing resources. The data need to be modified by crustal corrections (Crust2.0) as we want to look at the mantle structure only. We do this by eliminating the perturbation in surface wave phase velocity caused by the difference in crustal structure with respect to the referent model PREM. Sambridge's Neighborhood Algorithm is used to search the parameter space. The introduction of such a direct search technique pales the traditional inversion method, which requires regularization or some unnecessary priori restriction on the model space. On the contrary, the new method will search the full model space, providing probability density function of each anisotropic parameter and the corresponding resolution.

Observational Signatures of Parametric Instability at 1AU

NASA Astrophysics Data System (ADS)

Bowen, T. A.; Bale, S. D.; Badman, S.

2017-12-01

Observations and simulations of inertial compressive turbulence in the solar wind are characterized by density structures anti-correlated with magnetic fluctuations parallel to the mean field. This signature has been interpreted as observational evidence for non-propagating pressure balanced structures (PBS), kinetic ion acoustic waves, as well as the MHD slow mode. Recent work, specifically Verscharen et al. (2017), has highlighted the unexpected fluid like nature of the solar wind. Given the high damping rates of parallel propagating compressive fluctuations, their ubiquity in satellite observations is surprising and suggests the presence of a driving process. One possible candidate for the generation of compressive fluctuations in the solar wind is the parametric instability, in which large amplitude Alfvenic fluctuations decay into parallel propagating compressive waves. This work employs 10 years of WIND observations in order to test the parametric decay process as a source of compressive waves in the solar wind through comparing collisionless damping rates of compressive fluctuations with growth rates of the parametric instability. Preliminary results suggest that generation of compressive waves through parametric decay is overdamped at 1 AU. However, the higher parametric decay rates expected in the inner heliosphere likely allow for growth of the slow mode-the remnants of which could explain density fluctuations observed at 1AU.

ARPES study of the evolution of band structure and charge density wave properties in RTe3 ( R=Y , La, Ce, Sm, Gd, Tb, and Dy)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hussain, Zahid; Brouet, Veronique; Yang, Wanli

2008-01-16

We present a detailed angle-resolved photoemission spectroscopy (ARPES) investigation of the RTe3 family, which sets this system as an ideal"textbook" example for the formation of a nesting driven charge density wave (CDW). This family indeed exhibits the full range of phenomena that can be associated to CDWinstabilities, from the opening of large gaps on the best nested parts of Fermi surface (up to 0.4 eV), to the existence of residual metallic pockets. ARPES is the best suited technique to characterize these features, thanks to its unique ability to resolve the electronic structure in k space. An additional advantage of RTe3more » is that theband structure can be very accurately described by a simple two dimensional tight-binding (TB) model, which allows one to understand and easily reproduce many characteristics of the CDW. In this paper, we first establish the main features of the electronic structure by comparing our ARPES measurements with the linear muffin-tinorbital band calculations. We use this to define the validity and limits of the TB model. We then present a complete description of the CDW properties and of their strong evolution as a function of R. Using simple models, we are able to reproduce perfectly the evolution of gaps in k space, the evolution of the CDW wave vector with R, and the shape of the residual metallic pockets. Finally, we give an estimation of the CDWinteraction parameters and find that the change in the electronic density of states n (EF), due to lattice expansion when different R ions are inserted, has the correct order of magnitude to explain the evolution of the CDW properties.« less

Spatial localization of resistive drift wave structure in tokamak edge plasmas with an embedded magnetic island

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Shilin; Qu, Hongpeng; Li, Jiquan, E-mail: lijq@energy.kyoto-u.ac.jp

Resistive drift wave instability is investigated numerically in tokamak edge plasma confined by sheared slab magnetic field geometry with an embedded magnetic island. The focus is on the structural characteristics of eigenmode inside the island, where the density profile tends to be flattened. A transition of the dominant eigenmode occurs around a critical island width w{sub c}. For thin islands with a width below w{sub c}, two global long wavelength eigenmodes with approximately the same growth rate but different eigenfrequency are excited, which are stabilized by the magnetic island through two-dimensional mode coupling in both x and y (corresponding tomore » radial and poloidal in tokamak) directions. On the other hand, a short wavelength eigenmode, which is destabilized by thick islands with a width above w{sub c}, dominates the edge fluctuation, showing a prominent structural localization in the region between the X-point and the O-point of the magnetic island. The main destabilization mechanism is identified as the mode coupling in the y direction, which is similar to the so-called toroidal coupling in tokamak plasmas. These three eigenmodes may coexist in the drift wave fluctuation for the island with a width around w{sub c}. It is demonstrated that the structural localization results mainly from the quasilinear flattening of density profile inside the magnetic island.« less

In situ Observations of Magnetosonic Waves Modulated by Background Plasma Density

NASA Astrophysics Data System (ADS)

Yu, X.; Yuan, Z.; Huang, S.; Wang, D.; Funsten, H. O.

2017-12-01

We report in situ observations by the Van Allen Probe mission that magnetosonic (MS) waves are clearly relevant to appear relevant to the background plasma number density. As the satellite moved across dense and tenuous plasma alternatively, MS waves occurred only in lower density region. As the observed protons with 'ring' distributions provide free energy, local linear growth rates are calculated and show that magnetosonic waves can be locally excited in tenuous plasma. With variations of the background plasma density, the temporal variations of local wave growth rates calculated with the observed proton ring distributions, show a remarkable agreement with those of the observed wave amplitude. Therefore, the paper provides a direct proof that background plasma densities can modulate the amplitudes of magnetosonic waves through controlling the wave growth rates.

Finite element simulation of core inspection in helicopter rotor blades using guided waves.

PubMed

Chakrapani, Sunil Kishore; Barnard, Daniel; Dayal, Vinay

2015-09-01

This paper extends the work presented earlier on inspection of helicopter rotor blades using guided Lamb modes by focusing on inspecting the spar-core bond. In particular, this research focuses on structures which employ high stiffness, high density core materials. Wave propagation in such structures deviate from the generic Lamb wave propagation in sandwich panels. To understand the various mode conversions, finite element models of a generalized helicopter rotor blade were created and subjected to transient analysis using a commercial finite element code; ANSYS. Numerical simulations showed that a Lamb wave excited in the spar section of the blade gets converted into Rayleigh wave which travels across the spar-core section and mode converts back into Lamb wave. Dispersion of Rayleigh waves in multi-layered half-space was also explored. Damage was modeled in the form of a notch in the core section to simulate a cracked core, and delamination was modeled between the spar and core material to simulate spar-core disbond. Mode conversions under these damaged conditions were examined numerically. The numerical models help in assessing the difficulty of using nondestructive evaluation for complex structures and also highlight the physics behind the mode conversions which occur at various discontinuities. Copyright © 2015 Elsevier B.V. All rights reserved.

Vibrational Power Flow Analysis of Rods and Beams

NASA Technical Reports Server (NTRS)

Wohlever, James Christopher; Bernhard, R. J.

1988-01-01

A new method to model vibrational power flow and predict the resulting energy density levels in uniform rods and beams is investigated. This method models the flow of vibrational power in a manner analogous to the flow of thermal power in a heat conduction problem. The classical displacement solutions for harmonically excited, hysteretically damped rods and beams are used to derive expressions for the vibrational power flow and energy density in the rod and beam. Under certain conditions, the power flow in these two structural elements will be shown to be proportional to the energy density gradient. Using the relationship between power flow and energy density, an energy balance on differential control volumes in the rod and beam leads to a Poisson's equation which models the energy density distribution in the rod and beam. Coupling the energy density and power flow solutions for rods and beams is also discussed. It is shown that the resonant behavior of finite structures complicates the coupling of solutions, especially when the excitations are single frequency inputs. Two coupling formulations are discussed, the first based on the receptance method, and the second on the travelling wave approach used in Statistical Energy Analysis. The receptance method is the more computationally intensive but is capable of analyzing single frequency excitation cases. The traveling wave approach gives a good approximation of the frequency average of energy density and power flow in coupled systems, and thus, is an efficient technique for use with broadband frequency excitation.

Linear Transformation of Electromagnetic Wave Beams of the Electron-Cyclotron Range in Toroidal Magnetic Configurations

NASA Astrophysics Data System (ADS)

Khusainov, T. A.; Shalashov, A. G.; Gospodchikov, E. D.

2018-05-01

The field structure of quasi-optical wave beams tunneled through the evanescence region in the vicinity of the plasma cutoff in a nonuniform magnetoactive plasma is analyzed. This problem is traditionally associated with the process of linear transformation of ordinary and extraordinary waves. An approximate analytical solution is constructed for a rather general magnetic configuration applicable to spherical tokamaks, optimized stellarators, and other magnetic confinement systems with a constant plasma density on magnetic surfaces. A general technique for calculating the transformation coefficient of a finite-aperture wave beam is proposed, and the physical conditions required for the most efficient transformation are analyzed.

Planetesimal formation in self-gravitating discs

NASA Astrophysics Data System (ADS)

Gibbons, P. G.; Rice, W. K. M.; Mamatsashvili, G. R.

2012-10-01

We study particle dynamics in local two-dimensional simulations of self-gravitating accretion discs with a simple cooling law. It is well known that the structure which arises in the gaseous component of the disc due to a gravitational instability can have a significant effect on the evolution of dust particles. Previous results using global simulations indicate that spiral density waves are highly efficient at collecting dust particles, creating significant local overdensities which may be able to undergo gravitational collapse. We expand on these findings using a range of cooling times to mimic the conditions at a large range of radii within the disc. Here we use the PENCIL code to solve the 2D local shearing sheet equations for gas on a fixed grid together with the equations of motion for solids coupled to the gas solely through aerodynamic drag force. We find that spiral density waves can create significant enhancements in the surface density of solids, equivalent to 1-10 cm sized particles in a disc following the profiles of Clarke around an ˜1 M⊙ star, causing it to reach concentrations several orders of magnitude larger than the particles mean surface density. We also study the velocity dispersion of the particles, finding that the spiral structure can result in the particle velocities becoming highly ordered, having a narrow velocity dispersion. This implies low relative velocities between particles, which in turn suggest that collisions are typically low energy, lessening the likelihood of grain destruction. Both these findings suggest that the density waves that arise due to gravitational instabilities in the early stages of star formation provide excellent sites for the formation of large, planetesimal-sized objects.

Computational studies on scattering of radio frequency waves by density filaments in fusion plasmas

NASA Astrophysics Data System (ADS)

Ioannidis, Zisis C.; Ram, Abhay K.; Hizanidis, Kyriakos; Tigelis, Ioannis G.

2017-10-01

In modern magnetic fusion devices, such as tokamaks and stellarators, radio frequency (RF) waves are commonly used for plasma heating and current profile control, as well as for certain diagnostics. The frequencies of the RF waves range from ion cyclotron frequency to the electron cyclotron frequency. The RF waves are launched from structures, like waveguides and current straps, placed near the wall in a very low density, tenuous plasma region of a fusion device. The RF electromagnetic fields have to propagate through this scrape-off layer before coupling power to the core of the plasma. The scrape-off layer is characterized by turbulent plasmas fluctuations and by blobs and filaments. The variations in the edge density due to these fluctuations and filaments can affect the propagation characteristics of the RF waves—changes in density leading to regions with differing plasma permittivity. Analytical full-wave theories have shown that scattering by blobs and filaments can alter the RF power flow into the core of the plasma in a variety of ways, such as through reflection, refraction, diffraction, and shadowing [see, for example, Ram and Hizanidis, Phys. Plasmas 23, 022504 (2016), and references therein]. There are changes in the wave vectors and the distribution of power-scattering leading to coupling of the incident RF wave to other plasma waves, side-scattering, surface waves, and fragmentation of the Poynting flux in the direction towards the core. However, these theoretical models are somewhat idealized. In particular, it is assumed that there is step-function discontinuity in the density between the plasma inside the filament and the background plasma. In this paper, results from numerical simulations of RF scattering by filaments using a commercial full-wave code are described. The filaments are taken to be cylindrical with the axis of the cylinder aligned along the direction of the ambient magnetic field. The plasma inside and outside the filament is assumed to be cold. There are three primary objectives of these studies. The first objective is to validate the numerical simulations by comparing with the analytical results for the same plasma description—a step-function discontinuity in density. A detailed comparison of the Poynting flux shows that numerical simulations lead to the same results as those from the theoretical model. The second objective is to extend the simulations to take into account a smooth transition in density from the background plasma to the interior of the filament. The ensuing comparison shows that the deviations from the results of the theoretical model are quite small. The third objective is to consider the scattering process for situations well beyond a reasonable theoretical analysis. This includes scattering off multiple filaments with different densities and sizes. Simulations for these complex arrangements of filaments show that, in spite of the obvious limitations, the essential physics of RF scattering is captured by the analytical theory for a single filament.

Valley density-wave (VDW) and Superconductivity in Iron-Pnictides

NASA Astrophysics Data System (ADS)

Cvetkovic, Vladimir; Tesanovic, Zlatko

2009-03-01

One of the experimentally observed features of iron-pnictide superconductors is the structural transition and SDW ordering occurring at almost the same temperature. Starting from a tight-binding model [1], we construct an effective theory for iron-pnictides with the distinctive two hole and two electron Fermi surfaces. This theory is then mapped onto a negative-U Hubbard model with additional orbital and spin flavors [2]. We demonstrate that the superconducting instability of the attractive Hubbard model --- valley density-wave (VDW) --- corresponds to the observed structural and SDW orders. The deviations from perfect nesting between the hole and electron Fermi surfaces are mapped onto the Zeeman field which causes portions of Fermi surface to remain ungapped. The origin of pnictide superconductivity in this model, and its ties to the VDW are discussed. [1] V. Cvetkovic and Z. Tesanovic, http://arxiv.org/abs/0804.4678. [2] V. Cvetkovic and Z. Tesanovic, http://arxiv.org/abs/0808.3742.

Plasmon Geometric Phase and Plasmon Hall Shift

NASA Astrophysics Data System (ADS)

Shi, Li-kun; Song, Justin C. W.

2018-04-01

The collective plasmonic modes of a metal comprise a simple pattern of oscillating charge density that yields enhanced light-matter interaction. Here we unveil that beneath this familiar facade plasmons possess a hidden internal structure that fundamentally alters its dynamics. In particular, we find that metals with nonzero Hall conductivity host plasmons with an intricate current density configuration that sharply departs from that of ordinary zero Hall conductivity metals. This nontrivial internal structure dramatically enriches the dynamics of plasmon propagation, enabling plasmon wave packets to acquire geometric phases as they scatter. At boundaries, these phases accumulate allowing plasmon waves that reflect off to experience a nonreciprocal parallel shift. This plasmon Hall shift, tunable by Hall conductivity as well as plasmon wavelength, displaces the incident and reflected plasmon trajectories and can be readily probed by near-field photonics techniques. Anomalous plasmon geometric phases dramatically enrich the nanophotonics toolbox, and yield radical new means for directing plasmonic beams.

Hidden Order and Dimensional Crossover of the Charge Density Waves in TiSe 2

DOE PAGES

Chen, P.; Chan, Y. -H.; Fang, X. -Y.; ...

2016-11-29

Charge density wave (CDW) formation, a key physics issue for materials, arises from interactions among electrons and phonons that can also lead to superconductivity and other competing or entangled phases. The prototypical system TiSe 2, with a particularly simple (2 × 2 × 2) transition and no Kohn anomalies caused by electron-phonon coupling, is a fascinating but unsolved case after decades of research. Our angle-resolved photoemission measurements of the band structure as a function of temperature, aided by first-principles calculations, reveal a hitherto undetected but crucial feature: a (2 × 2) electronic order in each layer sets in at ~232more » K before the widely recognized three-dimensional structural order at ~205 K. The dimensional crossover, likely a generic feature of such layered materials, involves renormalization of different band gaps in two stages.« less

Steady states and outbreaks of two-phase nonlinear age-structured model of population dynamics with discrete time delay.

PubMed

Akimenko, Vitalii; Anguelov, Roumen

2017-12-01

In this paper we study the nonlinear age-structured model of a polycyclic two-phase population dynamics including delayed effect of population density growth on the mortality. Both phases are modelled as a system of initial boundary values problem for semi-linear transport equation with delay and initial problem for nonlinear delay ODE. The obtained system is studied both theoretically and numerically. Three different regimes of population dynamics for asymptotically stable states of autonomous systems are obtained in numerical experiments for the different initial values of population density. The quasi-periodical travelling wave solutions are studied numerically for the autonomous system with the different values of time delays and for the system with oscillating death rate and birth modulus. In both cases it is observed three types of travelling wave solutions: harmonic oscillations, pulse sequence and single pulse.

Topological sound in active-liquid metamaterials

NASA Astrophysics Data System (ADS)

Souslov, Anton; van Zuiden, Benjamin C.; Bartolo, Denis; Vitelli, Vincenzo

2017-11-01

Liquids composed of self-propelled particles have been experimentally realized using molecular, colloidal or macroscopic constituents. These active liquids can flow spontaneously even in the absence of an external drive. Unlike spontaneous active flow, the propagation of density waves in confined active liquids is not well explored. Here, we exploit a mapping between density waves on top of a chiral flow and electrons in a synthetic gauge field to lay out design principles for artificial structures termed topological active metamaterials. We design metamaterials that break time-reversal symmetry using lattices composed of annular channels filled with a spontaneously flowing active liquid. Such active metamaterials support topologically protected sound modes that propagate unidirectionally, without backscattering, along either sample edges or domain walls and despite overdamped particle dynamics. Our work illustrates how parity-symmetry breaking in metamaterial structure combined with microscopic irreversibility of active matter leads to novel functionalities that cannot be achieved using only passive materials.

High-resolution angle-resolved photoemission study of electronic structure and charge-density wave formation in HoTe3

NASA Astrophysics Data System (ADS)

Liu, Guodong; Wang, Chenlu; Zhang, Yan; Hu, Bingfeng; Mou, Daixiang; Yu, Li; Zhao, Lin; Zhou, Xingjiang; Wang, Nanlin; Chen, Chuangtian; Xu, Zuyan

We performed high-resolution angle-resolved photoemission spectroscopy (ARPES) measurement on high quality crystal of HoTe3, an intriguing quasi-two-dimensional rare-earth-element tritelluride charge-density-wave (CDW) compound. The main features of the electronic structure in this compound are established by employing a quasi-CW laser (7eV) and a helium discharging lamp (21.22 eV) as excitation light sources. It reveals many bands back folded according to the CDW periodicity and two incommensurate CDW gaps created by perpendicular Fermi surface (FS) nesting vectors. A large gap is found to open in well nested regions of the Fermi surface sheets, whereas other Fermi surface sections with poor nesting remain ungapped. In particular, some peculiar features are identified by using our ultra-high resolution and bulk sensitive laser-ARPES.

Magnetic Ordering of Erbium and Uranium NICKEL(2) SILICON(2) by Neutron Scattering

NASA Astrophysics Data System (ADS)

Lin, Hong

The magnetic ordering has been studied in UNi _2Si_2 and erbium single crystals by elastic neutron scattering. Abundant results are given regarding the magnetic structure, magnetic phase transitions, and the effect of a magnetic field on these properties. Three ordered phases are observed in UNi _2Si_2. They have been determined to be an incommensurate longitudinal spin density wave with a magnetic wave vector around q = 0.74c ^* in the high temperature phase, a simple body-centred antiferromagnet in the intermediate temperature phase, and a square wave in the low temperature phase. This square wave can be viewed equivalently as a longitudinal spin density wave with q = 2/3c ^* superimposed on a ferromagnetic component. Hysteresis and sample dependence are observed in the low-temperature phase transition. The two lower temperature phase transitions are both first order. The transition to paramagnetism is second order with a critical exponent beta = 0.35 +/- 0.03. When a magnetic field is applied along the c axis, the intermediate temperature phase is destabilised and disappears above a field of 3.5T. Although there is no new phase induced by the field, there exists a reentrant point where the three ordered phases can coexist. Erbium has three distinct ordered phases: the cone phase at low temperatures, the c-axis modulated (CAM) phase at higher temperatures, and the intermediate phase with moments modulated both along c and perpendicular to c. Within these phases the modulation of the moments may lock in to the lattice. The observed weak harmonics of the wave vector q in the basal plane for the cone phase and the q = 1/4c^* structure in the intermediate phase can be explained by a basal-plane spin slip model. The effect of magnetic field along the c axis on the magnetic structure is to stabilise the cone phase and to destabilise the intermediate phase. A new lock-in structure with q = 1/4c^* in the cone phase is induced by fields above 1.8T. The presence of the field also stabilises the lock-in structure with q = 2/7c^* in both the intermediate and the CAM phases.

Generation of internal solitary waves by frontally forced intrusions in geophysical flows.

PubMed

Bourgault, Daniel; Galbraith, Peter S; Chavanne, Cédric

2016-12-06

Internal solitary waves are hump-shaped, large-amplitude waves that are physically analogous to surface waves except that they propagate within the fluid, along density steps that typically characterize the layered vertical structure of lakes, oceans and the atmosphere. As do surface waves, internal solitary waves may overturn and break, and the process is thought to provide a globally significant source of turbulent mixing and energy dissipation. Although commonly observed in geophysical fluids, the origins of internal solitary waves remain unclear. Here we report a rarely observed natural case of the birth of internal solitary waves from a frontally forced interfacial gravity current intruding into a two-layer and vertically sheared background environment. The results of the analysis carried out suggest that fronts may represent additional and unexpected sources of internal solitary waves in regions of lakes, oceans and atmospheres that are dynamically similar to the situation examined here in the Saguenay Fjord, Canada.

Electronic, thermoelectric and transport properties of cesium cadmium trifluoride: A DFT study

NASA Astrophysics Data System (ADS)

Abraham, Jisha Annie; Pagare, G.; Sanyal, Sankar P.

2018-04-01

The full potential linearized augmented plane wave method based on density functional theory is employed to investigate the electronic structure of CsCdF3. The electronic properties of this compound have been studied from the band structure plot and density of states. The presence of indirect energy gap reveals its insulating nature. Using constant relaxation time, the electrical conductivity, electronic thermal conductivity, Seebeck coefficient and figure of merit are calculated by using Boltzmann transport theory. We have also studied the temperature dependence of thermoelectric properties of this compound.

In-situ Measurements of the Direction of Propagation of Pump Waves

NASA Astrophysics Data System (ADS)

James, H. G.; Bernhardt, P. A.; Leyser, T.; Siefring, C. L.

2017-12-01

In the course of an experiment to modify the ionosphere, the direction of pump wave propagation is affected by density gradients in the horizontal and vertical directions, fundamentally affecting wave-energy transport. Horizontal gradients on various scales may await a modification attempt as a preexisting state of the ionosphere and/or be changed by the deposition of heater radio-frequency energy. In the results from the Radio Receiver Instrument (RRI) in the enhanced Polar Outflow Probe (e-POP), we have recorded on the order of 100 flights over ionospheric heaters revealing a variety of processes that high-frequency pump waves experience in the ionosphere. E-POP flies on the Canadian satellite CASSIOPE in an elliptic (320 x 1400 km), highly-inclined (81°) orbit. High frequency measurements have been/are being made near SPEAR, HAARP, Sura, EISCAT Heating and Arecibo. Electromagnetic waves from ground-based heaters are detected by the two, orthogonal, 6-m dipoles on the RRI. The high input impedance of the RRI means that the dipoles act as voltage probes, from which the electric field of incoming waves can be simply computed. When combined with cold-magnetoplasma electric-field theory, the relationship of voltages on the two orthogonal dipoles is used to deduce the direction of arrival of an incoming wave in three dimensions. We illustrate the technique by its application to analysis of signals from different transmitters. These results show a variety of pump-wave propagation directions, indicating the complexity of density structure within which modification might take place. Such complexity illustrates the importance of three-dimensional models of density in the vicinity of modification.

Satellite and Ground Signatures of Kinetic and Inertial Scale ULF Alfven Waves Propagating in Warm Plasma in Earth's Magnetosphere

NASA Astrophysics Data System (ADS)

Rankin, R.; Sydorenko, D.

2015-12-01

Results from a 3D global numerical model of Alfven wave propagation in a warm multi-species plasma in Earth's magnetosphere are presented. The model uses spherical coordinates, accounts for a non-dipole magnetic field, vertical structure of the ionosphere, and an air gap below the ionosphere. A realistic density model is used. Below the exobase altitude (2000 km) the densities and the temperatures of electrons, ions, and neutrals are obtained from the IRI and MSIS models. Above the exobase, ballistic (originating from the ionosphere and returning to ionosphere) and trapped (bouncing between two reflection points above the ionosphere) electron populations are considered similar to [Pierrard and Stegen (2008), JGR, v.113, A10209]. Plasma parameters at the exobase provided by the IRI are the boundary conditions for the ballistic electrons while the [Carpenter and Anderson (1992), JGR, v.97, p.1097] model of equatorial electron density defines parameters of the trapped electron population. In the simulations that are presented, Alfven waves with frequencies from 1 Hz to 0.01 Hz and finite azimuthal wavenumbers are excited in the magnetosphere and compared with Van Allen Probes data and ground-based observations from the CARISMA array of ground magnetometers. When short perpendicular scale waves reflect form the ionosphere, compressional Alfven waves are observed to propagate across the geomagnetic field in the ionospheric waveguide [e.g., Lysak (1999), JGR, v.104, p.10017]. Signals produced by the waves on the ground are discussed. The wave model is also applied to interpret recent Van Allen Probes observations of kinetic scale ULF waves that are associated with radiation belt electron dynamics and energetic particle injections.

Observations and Modeling of Thermal Structure in the Lower Atmosphere and the Upward Propagation of Tides into the Thermosphere

NASA Technical Reports Server (NTRS)

Wilson, R. J.; Kahre, M.

2017-01-01

Thermal tides are the atmospheric response to diurnally varying thermal forcing resulting from radiative and convective heat transfer from the surface and from aerosol and gaseous heating within the atmosphere. Tides include sun-synchronous (migrating) waves driven in response to solar heating and additional non-migrating waves resulting from longitudinal variations in the distributions of topography, dust aerosol and water ice clouds. The systematic spatial mapping of temperature over 5 Mars years by the Mars Climate Sounder (MCS) has yielded a well-defined climatology of seasonally-varying temperature structures in the lower atmosphere, from 5 to 80 km. Tide theory and Mars global circulation model (MGCM) simulations are a fruitful framework for relating temperature observations to thermal forcing by aerosol fields [1]. The analysis of density and temperature fields derived from MAVEN IUVS and NGIMS observations have revealed the presence of predominantly zonal wave 2 and 3 features at altitudes of 100-170 km that are almost certainly non-migrating tides propagating upward from the lower atmosphere [2,3]. In this presentation we will use the MCS climatology and MGCM simulations to relate the density variations seen by MAVEN with the seasonally varying tide activity in the lower atmosphere. Large amplitude perturbations in density are most sensitive to the tide components with the longest vertical wavelengths in temperature, which are well resolved in MCS observations.

Application of Sub-Bottom Profiler to Study Riverbed Structure and Sediment Density

NASA Astrophysics Data System (ADS)

Rui, Wang; Changzheng, Li; Xiaofei, Yan

2018-03-01

In this pater, we present a study on the riverbed structure and sediment density in-situ test by using sub-bottom profiler. Compared with traditional direct observation methods, the sub-bottom profiler method based on sonar technology is non-contact, low-disturbance and high-efficient. We finish the investigation of several sections in Sanmenxia and Xiaolangdi reservoirs, which located on the main channel of lower reaches of Yellow River. Collected data show a detailed layered structure of the riverbed sediment which believed caused by sedimentary processes in different periods. Further more, we analyse the reflection coefficient of water-sediment interface and inverse the sediment density data from the raw wave record. The inversion method is based on the effective density fluid model and Kozeny-Carman formula. The comparison of the inversion results and sample tests shows that the in-situ test is reliable and useable.

The structure of the magnetosphere as deduced from magnetospherically reflected whistlers

NASA Technical Reports Server (NTRS)

Edgar, B. C.

1972-01-01

Very low frequency (VLF) electromagnetic wave phenomenon called the magnetospherically reflected (MR) whistler was investigated. VLF (0.3 to 12.5 kHz) data obtained from the Orbiting Geophysical Observatories 1 and 3 from October 1964 to December 1966 were used. MR whistlers are produced by the dispersive propagation of energy from atmospheric lightning through the magnetosphere to the satellite along ray paths which undergo one or more reflections due to the presence of ions. The gross features of MR whistler frequency-time spectrograms are explained in terms of propagation through a magnetosphere composed of thermal ions and electrons and having small density gradients across L-shells. Irregularities observed in MR spectra were interpreted in terms of propagation through field-aligned density structures. Trough and enhancement density structures were found to produce unique and easily recognizable signatures in MR spectra. Sharp cross-field density dropoff produces extra traces in MR spectrograms.

DFT-BASED AB INITIO STUDY OF THE ELECTRONIC AND OPTICAL PROPERTIES OF CESIUM BASED FLUORO-PEROVSKITE CsMF3 (M = Ca AND Sr)

NASA Astrophysics Data System (ADS)

Harmel, M.; Khachai, H.; Ameri, M.; Khenata, R.; Baki, N.; Haddou, A.; Abbar, B.; UǦUR, Ş.; Omran, S. Bin; Soyalp, F.

2012-12-01

Density functional theory (DFT) is performed to study the structural, electronic and optical properties of cubic fluoroperovskite AMF3 (A = Cs; M = Ca and Sr) compounds. The calculations are based on the total-energy calculations within the full-potential linearized augmented plane wave (FP-LAPW) method. The exchange-correlation potential is treated by local density approximation (LDA) and generalized gradient approximation (GGA). The structural properties, including lattice constants, bulk modulus and their pressure derivatives are in very good agreement with the available experimental and theoretical data. The calculations of the electronic band structure, density of states and charge density reveal that compounds are both ionic insulators. The optical properties (namely: the real and the imaginary parts of the dielectric function ɛ(ω), the refractive index n(ω) and the extinction coefficient k(ω)) were calculated for radiation up to 40.0 eV.

Development of Extended Ray-tracing method including diffraction, polarization and wave decay effects

NASA Astrophysics Data System (ADS)

Yanagihara, Kota; Kubo, Shin; Dodin, Ilya; Nakamura, Hiroaki; Tsujimura, Toru

2017-10-01

Geometrical Optics Ray-tracing is a reasonable numerical analytic approach for describing the Electron Cyclotron resonance Wave (ECW) in slowly varying spatially inhomogeneous plasma. It is well known that the result with this conventional method is adequate in most cases. However, in the case of Helical fusion plasma which has complicated magnetic structure, strong magnetic shear with a large scale length of density can cause a mode coupling of waves outside the last closed flux surface, and complicated absorption structure requires a strong focused wave for ECH. Since conventional Ray Equations to describe ECW do not have any terms to describe the diffraction, polarization and wave decay effects, we can not describe accurately a mode coupling of waves, strong focus waves, behavior of waves in inhomogeneous absorption region and so on. For fundamental solution of these problems, we consider the extension of the Ray-tracing method. Specific process is planned as follows. First, calculate the reference ray by conventional method, and define the local ray-base coordinate system along the reference ray. Then, calculate the evolution of the distributions of amplitude and phase on ray-base coordinate step by step. The progress of our extended method will be presented.

Saturn's Internal Structure: A View through its Natural Seismograph

NASA Astrophysics Data System (ADS)

Mankovich, Christopher; Marley, Mark S.; Fortney, Jonathan J.; Movshovitz, Naor

2017-10-01

Saturn's nonradial oscillations perturb the orbits of ring particles. The C ring is fortuitous in that it spans several resonances with Saturn's fundamental acoustic (f-) modes, and its moderate optical depth allows the characterization of wave features using stellar occultations. The growing set of C-ring waves with precise pattern frequencies and azimuthal order m measured from Cassini stellar occultations (Hedman & Nicholson 2013, 2014; French et al. 2016) provides new constraints on Saturn's internal structure, with the potential to resolve long-standing questions about the planet's distribution of helium and heavier elements, its means of internal energy transport, and its rotation state.We construct Saturn interior models and calculate mode eigenfrequencies, mapping the planet mode frequencies to resonant locations in the rings to compare with the locations of observed spiral density and vertical bending waves in the C ring. While spiral density waves at low azimuthal order (m=2-3) appear strongly affected by resonant coupling between f-modes and deep g-modes (Fuller 2014), the locations of waves with higher azimuthal order can be fit reasonably well with a spectrum of pure f-modes for Saturn models with adiabatic envelopes and realistic equations of state. In particular, four observed bending waves (Nicholson et al., DPS 2016) align with outer vertical resonances for non-sectoral (m≠l) Saturn f-modes of relatively high angular degree, and we present preliminary identifications of these. We assess the range of resonance locations in the C and D rings allowed for the spectrum of f-modes given gravity field constraints and discuss what role a realistic helium distribution in the planet might play.

Electron Heating and Acceleration from High Amplitude Driven Alfvén Waves in the LAPD

NASA Astrophysics Data System (ADS)

Auerbach, David; Carter, Troy; Brugman, Brian

2006-10-01

High amplitude (δB/B ˜1 %) shear Alfvén waves are generated in the Large Plasma Device Upgrade (LAPD) at UCLA, and elevated electron temperatures and high energy electrons are observed using triple probes and Langmuir current traces. The Poynting flux of the observed waves is calculated, and wave power is compared to estimates of power input required to cause the observed heating. Theoretical calculations of power transfer from wave to plasma due to Landau damping and collisional heating are also presented and compared to experimental measurements. Heating by antenna near field effects is also being explored. The density and potential structures of these waves are explored using interferometer and triple probe measurements. Applications to Auroral generation and plasma heating are discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wardaya, P. D., E-mail: pongga.wardaya@utp.edu.my; Noh, K. A. B. M., E-mail: pongga.wardaya@utp.edu.my; Yusoff, W. I. B. W., E-mail: pongga.wardaya@utp.edu.my

This paper discusses a new approach for investigating the seismic wave velocity of rock, specifically carbonates, as affected by their pore structures. While the conventional routine of seismic velocity measurement highly depends on the extensive laboratory experiment, the proposed approach utilizes the digital rock physics view which lies on the numerical experiment. Thus, instead of using core sample, we use the thin section image of carbonate rock to measure the effective seismic wave velocity when travelling on it. In the numerical experiment, thin section images act as the medium on which wave propagation will be simulated. For the modeling, anmore » advanced technique based on artificial neural network was employed for building the velocity and density profile, replacing image's RGB pixel value with the seismic velocity and density of each rock constituent. Then, ultrasonic wave was simulated to propagate in the thin section image by using finite difference time domain method, based on assumption of an acoustic-isotropic medium. Effective velocities were drawn from the recorded signal and being compared to the velocity modeling from Wyllie time average model and Kuster-Toksoz rock physics model. To perform the modeling, image analysis routines were undertaken for quantifying the pore aspect ratio that is assumed to represent the rocks pore structure. In addition, porosity and mineral fraction required for velocity modeling were also quantified by using integrated neural network and image analysis technique. It was found that the Kuster-Toksoz gives the closer prediction to the measured velocity as compared to the Wyllie time average model. We also conclude that Wyllie time average that does not incorporate the pore structure parameter deviates significantly for samples having more than 40% porosity. Utilizing this approach we found a good agreement between numerical experiment and theoretically derived rock physics model for estimating the effective seismic wave velocity of rock.« less

Convolute laminations — a theoretical analysis: example of a Pennsylvanian sandstone

NASA Astrophysics Data System (ADS)

Visher, Glenn S.; Cunningham, Russ D.

1981-03-01

Data from an outcropping laminated interval were collected and analyzed to test the applicability of a theoretical model describing instability of layered systems. Rayleigh—Taylor wave perturbations result at the interface between fluids of contrasting density, viscosity, and thickness. In the special case where reverse density and viscosity interlaminations are developed, the deformation response produces a single wave with predictable amplitudes, wavelengths, and amplification rates. Physical measurements from both the outcropping section and modern sediments suggest the usefulness of the model for the interpretation of convolute laminations. Internal characteristics of the stratigraphic interval, and the developmental sequence of convoluted beds, are used to document the developmental history of these structures.

A Self-Consistent Model of the Interacting Ring Current Ions and Electromagnetic Ion Cyclotron Waves, Initial Results: Waves and Precipitating Fluxes

NASA Technical Reports Server (NTRS)

Khazanov, G. V.; Gamayunov, K. V.; Jordanova, V. K.; Krivorutsky, E. N.

2002-01-01

Initial results from a newly developed model of the interacting ring current ions and ion cyclotron waves are presented. The model is based on the system of two kinetic equations: one equation describes the ring current ion dynamics, and another equation describes wave evolution. The system gives a self-consistent description of the ring current ions and ion cyclotron waves in a quasilinear approach. These equations for the ion phase space distribution function and for the wave power spectral density were solved on aglobal magnetospheric scale undernonsteady state conditions during the 2-5 May 1998 storm. The structure and dynamics of the ring current proton precipitating flux regions and the ion cyclotron wave-active zones during extreme geomagnetic disturbances on 4 May 1998 are presented and discussed in detail.

Lidar observations of wave-like structure in the atmospheric sodium layer

NASA Technical Reports Server (NTRS)

Rowlett, J. R.; Gardner, C. S.; Richter, E. S.; Sechrist, C. F., Jr.

1978-01-01

The University of Illinois (Urbana) lidar system has been developed to study the atmospheric sodium layer near 90 km altitude through the mechanism of resonance scattering. The photocount data are processed using digital smoothing filters to obtain continuous estimates of the sodium density versus altitude. The filter cutoff frequency is related to the height resolution and accuracy of the estimated profile. Lidar photocount data processed using this filtering technique show wave-like structures in the sodium layer which move downward with time. The waves have typical wavelengths of 3-15 km and phase velocities of less than 1 m/sec. The movement of these structures seems to be independent of the motion of the bottomside of the layer, which also has been observed to move up or down by as much as 2 km over a period of a few hours.

Shock wave boundary layer interaction on suction side of compressor profile in single passage test section

NASA Astrophysics Data System (ADS)

Flaszynski, Pawel; Doerffer, Piotr; Szwaba, Ryszard; Kaczynski, Piotr; Piotrowicz, Michal

2015-11-01

The shock wave boundary layer interaction on the suction side of transonic compressor blade is one of the main objectives of TFAST project (Transition Location Effect on Shock Wave Boundary Layer Interaction). In order to investigate the flow structure on the suction side of a profile, a design of a generic test section in linear transonic wind tunnel was proposed. The experimental and numerical results for the flow structure investigations are shown for the flow conditions as the existing ones on the suction side of the compressor profile. Near the sidewalls the suction slots are applied for the corner flow structure control. It allows to control the Axial Velocity Density Ratio (AVDR), important parameter for compressor cascade investigations. Numerical results for Explicit Algebraic Reynolds Stress Model with transition modeling are compared with oil flow visualization, schlieren and Pressure Sensitive Paint. Boundary layer transition location is detected by Temperature Sensitive Paint.

Equatorial magnetic Rossby waves — evidence for a thin, strongly-buoyant stratified layer in earth's core

NASA Astrophysics Data System (ADS)

Knezek, Nicholas; Buffett, Bruce

2017-04-01

A low density stratified layer at the top of Earth's core has been proposed by many authors on the basis of chemical and thermodynamic arguments and has implications for Earth's thermal history, core energetics, and core-mantle interactions. Past studies claiming to detect a layer using perturbations in seismic wave speeds are contentious due to the extremely small magnitude of the detected signal. Recently, several studies have instead argued for the existence of a stratified layer by hypothesizing that oscillations in the observed geomagnetic field arise from waves propagating in the layer. In particular, 60 year oscillations in dipole strength have been attributed to global MAC waves, and 8 year oscillations of secular acceleration have been attributed to equatorially-trapped waves. We use a new hybrid finite-volume and Fourier numerical method we developed to model magnetohydrodynamic waves in a thin layer and show that a thin, strongly buoyant layer can produce equatorially-trapped waves with similar structures and periods to the observed 8 year signal. Using these simulated wave structures, we provide additional evidence for the existence of several propagating wave modes and place constraints on estimates for the wave periods, stratified layer thickness, and strength of buoyancy within the layer.

Plasma waves in the magnetic hole

NASA Technical Reports Server (NTRS)

Lin, Naiguo; Kellogg, P. J.; MacDowall, R.; Balogh, A.; Forsyth, R. J.; Phillips, J. L.; Pick, M.

1995-01-01

Magnetic holes in the solar wind, which are characterized by isolated local depressions in the magnetic field magnitude, have been observed previously. The Unified Radio and Plasma Wave (URAP) instrument of Ulysses has found that within such magnetic structures, electrostatic waves at kHz frequency and ultralow frequency electromagnetic waves are often excited and seen as short duration wave bursts. Most of these bursts occur near the ambient electron plasma frequency, which suggests that the waves are Langmuir waves. Such waves are usually excited by electron streams. Some evidence of the streaming of energetic electrons required for exciting Langmuir waves has been observed. These electrons may have originated at sources near the Sun, which would imply that the magnetic structures containing the waves would exist as long channels formed by field and plasma conditions near the Sun. On the other hand, the electrons could be suprathermal 'tails' from wave collapse processes occurring near the spacecraft. In either case, the Langmuir waves excited in the magnetic holes provide a measurement of the plasma density inside the holes. Low frequency electromagnetic waves, having frequencies of a fraction of the local electron cyclotron frequency, sometimes accompany the Langmuir waves observed in magnetic holes. Waves excited in this frequency range are very likely to be whistler-mode waves. They may have been excited by an electron temperature anisotropy which has been observed in the vicinity of the magnetic holes or generated through the decay of Langmuir waves.

First principles predictions of electronic and elastic properties of BaPb2As2 in the ThCr2Si2-type structure

NASA Astrophysics Data System (ADS)

Bourourou, Y.; Amari, S.; Yahiaoui, I. E.; Bouhafs, B.

2018-01-01

A first-principles approach is used to predicts the electronic and elastic properties of BaPb2As2 superconductor compound, using full-potential linearized augmented plane wave plus local orbitals (FP-L/APW+lo) scheme within the local density approximation LDA. The calculated equilibrium structural parameter a agree well with the experiment while the c/a ratio is far away from the experimental result. The band structure, density of states, together with the charge density and chemical bonding are discussed. The calculated elastic constants for our compound indicate that it is mechanically stable at ambient pressure. Polycrystalline elastic moduli (Young's, Bulk, shear Modulus and the Poisson's ratio) were calculated according to the Voigte-Reusse-Hill (VRH) average.

Thermodynamical study of boron doped CeX{sub 3} (X=Pd, Rh)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Ramesh; Dwivedi, Shalini; Sharma, Yamini, E-mail: sharma.yamini62@gmail.com

2016-05-06

The structural, electronic, thermal, and optical properties of cubic non magnetic CeX{sub 3}(X=Pd, Rh) compounds which crystallize in the Au{sub 3}Cu structure have been studied using the projected augmented wave (PAW) method within the density functional theory (DFT) with generalized gradient approximation (GGA) for exchange correlation potential. In this paper we have calculated the band structure which are interpreted using the density of states. The optical properties such as extinction coefficients clearly illustrate the changes in CeX{sub 3} due to intercalation of boron. Lattice instability is observed in CePd{sub 3}B from the calculated dynamical properties.

Midlatitude sporadic-E layers

NASA Technical Reports Server (NTRS)

Miller, K. L.; Smith, L. G.

1976-01-01

The partially transparent echo from midlatitude sporadic E layers was recorded by ionosondes between the blanketing frequency and the maximum frequency. The theory that the midlatitude sporadic E layers are not uniform in the horizontal plane but contain localized regions of high electron density was evaluated using data obtained by incoherent scatter radar and found to provide a satisfactory explanation. The main features of midlatitude sporadic E layers are consistent with the convergence of metallic ions as described by the wind shear theory applied to gravity waves and tides. The interference of gravity waves with other gravity waves and tides can be recognized in the altitudes of occurrence and the structure of the layers. Small scale horizontal irregularities are attributed in some cases to critical level effects and in others to fluid instabilities. The convergence of a meteor trail can, under some circumstances, account for localized enhancement of the electron density in the layer.

Excitation of propagating magnetization waves by microstrip antennas

NASA Astrophysics Data System (ADS)

Dmitriev, V. F.; Kalinikos, B. A.

1988-11-01

We discuss the self-consistent theory of excitation of dipole-exchange magnetization waves by microstrip antennas in a metal-dielectric-ferrite-dielectric-metal stratified structure, magnetized under an arbitrary angle to the surface. Spin-wave Green's functions are derived, describing the response of the spin-system to a spatially inhomogeneous varying magnetic field. The radiative resistance of microstrip antenna is calculated. In this case the distribution of surface current density in the antenna is found on the basis of the analytic solution of a singular integral equation. The nature of the effect of metallic screens and redistributed surface current densities in the antenna on the frequency dependence of the resistive radiation is investigated. Approximate relations are obtained, convenient for practical calculations of radiative resistance of microstrip antennas both in a free and in a screened ferromagnetic film. The theoretical calculations are verified by data of experiments carried out on monocrystalline films of iron-yttrium garnet.

Absorption of acoustic waves by sunspots. II - Resonance absorption in axisymmetric fibril models

NASA Technical Reports Server (NTRS)

Rosenthal, C. S.

1992-01-01

Analytical calculations of acoustic waves scattered by sunspots which concentrate on the absorption at the magnetohydrodynamic Alfven resonance are extended to the case of a flux-tube embedded in a uniform atmosphere. The model is based on a flux-tubes of varying radius that are highly structured, translationally invariant, and axisymmetric. The absorbed fractional energy is determined for different flux-densities and subphotospheric locations with attention given to the effects of twist. When the flux is highly concentrated into annuli efficient absorption is possible even when the mean magnetic flux density is low. The model demonstrates low absorption at low azimuthal orders even in the presence of twist which generally increases the range of wave numbers over which efficient absorption can occur. Resonance absorption is concluded to be an efficient mechanism in monolithic sunspots, fibril sunspots, and plage fields.

Importance of Relativistic Effects and Electron Correlation in Structure Factors and Electron Density of Diphenyl Mercury and Triphenyl Bismuth.

PubMed

Bučinský, Lukáš; Jayatilaka, Dylan; Grabowsky, Simon

2016-08-25

This study investigates the possibility of detecting relativistic effects and electron correlation in single-crystal X-ray diffraction experiments using the examples of diphenyl mercury (HgPh2) and triphenyl bismuth (BiPh3). In detail, the importance of electron correlation (ECORR), relativistic effects (REL) [distinguishing between total, scalar and spin-orbit (SO) coupling relativistic effects] and picture change error (PCE) on the theoretical electron density, its topology and its Laplacian using infinite order two component (IOTC) wave functions is discussed. This is to develop an understanding of the order of magnitude and shape of these different effects as they manifest in the electron density. Subsequently, the same effects are considered for the theoretical structure factors. It becomes clear that SO and PCE are negligible, but ECORR and scalar REL are important in low- and medium-order reflections on absolute and relative scales-not in the high-order region. As a further step, Hirshfeld atom refinement (HAR) and subsequent X-ray constrained wavefunction (XCW) fitting have been performed for the compound HgPh2 with various relativistic and nonrelativistic wave functions against the experimental structure factors. IOTC calculations of theoretical structure factors and relativistic HAR as well as relativistic XCW fitting are presented for the first time, accounting for both scalar and spin-orbit relativistic effects.

Exact solutions of magnetohydrodynamics for describing different structural disturbances in solar wind

NASA Astrophysics Data System (ADS)

Grib, S. A.; Leora, S. N.

2016-03-01

We use analytical methods of magnetohydrodynamics to describe the behavior of cosmic plasma. This approach makes it possible to describe different structural fields of disturbances in solar wind: shock waves, direction discontinuities, magnetic clouds and magnetic holes, and their interaction with each other and with the Earth's magnetosphere. We note that the wave problems of solar-terrestrial physics can be efficiently solved by the methods designed for solving classical problems of mathematical physics. We find that the generalized Riemann solution particularly simplifies the consideration of secondary waves in the magnetosheath and makes it possible to describe in detail the classical solutions of boundary value problems. We consider the appearance of a fast compression wave in the Earth's magnetosheath, which is reflected from the magnetosphere and can nonlinearly overturn to generate a back shock wave. We propose a new mechanism for the formation of a plateau with protons of increased density and a magnetic field trough in the magnetosheath due to slow secondary shock waves. Most of our findings are confirmed by direct observations conducted on spacecrafts (WIND, ACE, Geotail, Voyager-2, SDO and others).

Magnetospheric Multiscale Observations of an Ion Diffusion Region With Large Guide Field at the Magnetopause: Current System, Electron Heating, and Plasma Waves

NASA Astrophysics Data System (ADS)

Zhou, M.; Berchem, J.; Walker, R. J.; El-Alaoui, M.; Goldstein, M. L.; Lapenta, G.; Deng, X.; Li, J.; Le Contel, O.; Graham, D. B.; Lavraud, B.; Paterson, W. R.; Giles, B. L.; Burch, J. L.; Torbert, R. B.; Russell, C. T.; Strangeway, R. J.; Zhao, C.; Ergun, R. E.; Lindqvist, P.-A.; Marklund, G.

2018-03-01

We report Magnetospheric Multiscale (MMS) observations of a reconnecting current sheet in the presence of a weak density asymmetry with large guide field at the dayside magnetopause. An ion diffusion region (IDR) was detected associated with this current sheet. Parallel current dominated over the perpendicular current in the IDR, as found in previous studies of component reconnection. Electrons were preferentially heated parallel to the magnetic field within the IDR. The heating was manifested as a flattop distribution below 400 eV. Two types of electromagnetic electron whistler waves were observed within the regions where electrons were heated. One type of whistler wave was associated with nonlinear structures in E|| with amplitudes up to 20 mV/m. The other type was not associated with any structures in E||. Poynting fluxes of these two types of whistler waves were directed away from the X-line. We suggest that the nonlinear evolution of the oblique whistler waves gave rise to the solitary structures in E||. There was a perpendicular super-Alfvénic outflow jet that was carried by magnetized electrons. Intense electrostatic lower hybrid drift waves were localized in the current sheet center and were probably driven by the super-Alfvénic electron jet, the velocity of which was approximately equal to the diamagnetic drift of demagnetized ions. Our observations suggest that the guide field significantly modified the structures (Hall electromagnetic fields and current system) and wave properties in the IDR.

Efficient EM Simulation of GCPW Structures Applied to a 200-GHz mHEMT Power Amplifier MMIC

NASA Astrophysics Data System (ADS)

Campos-Roca, Yolanda; Amado-Rey, Belén; Wagner, Sandrine; Leuther, Arnulf; Bangert, Axel; Gómez-Alcalá, Rafael; Tessmann, Axel

2017-05-01

The behaviour of grounded coplanar waveguide (GCPW) structures in the upper millimeter-wave range is analyzed by using full-wave electromagnetic (EM) simulations. A methodological approach to develop reliable and time-efficient simulations is proposed by investigating the impact of different simplifications in the EM modelling and simulation conditions. After experimental validation with measurements on test structures, this approach has been used to model the most critical passive structures involved in the layout of a state-of-the-art 200-GHz power amplifier based on metamorphic high electron mobility transistors (mHEMTs). This millimeter-wave monolithic integrated circuit (MMIC) has demonstrated a measured output power of 8.7 dBm for an input power of 0 dBm at 200 GHz. The measured output power density and power-added efficiency (PAE) are 46.3 mW/mm and 4.5 %, respectively. The peak measured small-signal gain is 12.7 dB (obtained at 196 GHz). A good agreement has been obtained between measurements and simulation results.

Modelling of deep gaps created by giant planets in protoplanetary disks

NASA Astrophysics Data System (ADS)

Kanagawa, Kazuhiro D.; Tanaka, Hidekazu; Muto, Takayuki; Tanigawa, Takayuki

2017-12-01

A giant planet embedded in a protoplanetary disk creates a gap. This process is important for both theory and observation. Using results of a survey for a wide parameter range with two-dimensional hydrodynamic simulations, we constructed an empirical formula for the gap structure (i.e., the radial surface density distribution), which can reproduce the gap width and depth obtained by two-dimensional simulations. This formula enables us to judge whether an observed gap is likely to be caused by an embedded planet or not. The propagation of waves launched by the planet is closely connected to the gap structure. It makes the gap wider and shallower as compared with the case where an instantaneous wave damping is assumed. The hydrodynamic simulations show that the waves do not decay immediately at the launching point of waves, even when the planet is as massive as Jupiter. Based on the results of hydrodynamic simulations, we also obtained an empirical model of wave propagation and damping in cases of deep gaps. The one-dimensional gap model with our wave propagation model is able to reproduce the gap structures in hydrodynamic simulations well. In the case of a Jupiter-mass planet, we also found that the waves with a smaller wavenumber (e.g., m = 2) are excited and transport the angular momentum to a location far away from the planet. The wave with m = 2 is closely related with a secondary wave launched by a site opposite from the planet.

ULF Waves in the Ionospheric Alfven Resonator: Modeling of MICA Observations

NASA Astrophysics Data System (ADS)

Streltsov, A. V.; Tulegenov, B.

2017-12-01

We present results from a numerical study of physical processes responsible for the generation of small-scale, intense electromagnetic structures in the ultra-low-frequency range frequently observed in the close vicinity of bright discrete auroral arcs. In particular, our research is focused on the role of the ionosphere in generating these structures. A significant body of observations demonstrate that small-scale electromagnetic waves with frequencies below 1 Hz are detected at high latitudes where the large-scale, downward magnetic field-aligned current (FAC) interact with the ionosphere. Some theoretical studies suggest that these waves can be generated by the ionospheric feedback instability (IFI) inside the ionospheric Alfven resonator (IAR). The IAR is the region in the low-altitude magnetosphere bounded by the strong gradient in the Alfven speed at high altitude and the conducting bottom of the ionosphere (ionospheric E-region) at low altitude. To study ULF waves in this region we use a numerical model developed from reduced two fluid MHD equations describing shear Alfven waves in the ionosphere and magnetosphere of the earth. The active ionospheric feedback on structure and amplitude of magnetic FACs that interact with the ionosphere is implemented through the ionospheric boundary conditions that link the parallel current density with the plasma density and the perpendicular electric field in the ionosphere. Our numerical results are compared with the in situ measurements performed by the Magnetosphere-Ionosphere Coupling in the Alfven Resonator (MICA) sounding rocket, launched on February 19, 2012 from Poker Flat Research Range in Alaska to measure fields and particles during a passage through a discreet auroral arc. Parameters of the simulations are chosen to match actual MICA parameters, allowing the comparison in the most precise and rigorous way. Waves generated in the numerical model have frequencies between 0.30 and 0.45 Hz, while MICA measured similar waves in the range from 0.18 to 0.50 Hz. These results prove that the IFI driven inside the IAR by a system of large-scale upward-downward currents is the main mechanism responsible for the generation of small-scale intense ULF waves in the vicinity of discrete auroral arcs.

Electrostatic lower hybrid waves excited by electromagnetic whistler mode waves scattering from planar magnetic-field-aligned plasma density irregularities

NASA Technical Reports Server (NTRS)

Bell, T. F.; Ngo, H. D.

1990-01-01

This paper presents a theoretical model for electrostatic lower hybrid waves excited by electromagnetic whistler mode waves propagating in regions of the magnetosphere and the topside ionosphere, where small-scale magnetic-field-aligned plasma density irregularities are thought to exist. In this model, the electrostatic waves are excited by linear mode coupling as the incident electromagnetic whistler mode waves scatter from the magnetic-field-aligned plasma density irregularities. Results indicate that high-amplitude short-wavelength (5 to 100 m) quasi-electrostatic whistler mode waves can be excited when electromagnetic whistler mode waves scatter from small-scale planar magnetic-field-aligned plasma density irregularities in the topside ionosphere and magnetosphere.

Ion-acoustic and electron-acoustic type nonlinear waves in dusty plasmas

NASA Astrophysics Data System (ADS)

Volosevich, A.-V.; Meister, C.-V.

2003-04-01

In the present work, two three-dimensional nonlinear theoretical models of electrostatic solitary waves are investigated within the frame of magnetohydrodynamics. Both times, a multi-component plasma is considered, which consists of hot electrons with a rather flexible distribution function, hot ions with Boltzmann-type distribution, and (negatively as well as positively charged) dust. Additionally, cold ion beams are taken into account in the model to study ion-acoustic structures (IAS), and cold electron beams are included into the model to investigate electron-acoustic structures (EAS). The numerical results of the considered theoretical models allow to make the following conclusions: 1) Electrostatic structures with negative potential (of rarefaction type) are formed both in the IAS model and in the EAS model, but structures with negative potential (of compressional type) are formed in the IAS model only. 2) The intervals of various plasma parameters (velocities of ion and electron beams, temperatures, densities of the plasma components, ions' masses), for which the existence of IAS and EAS solitary waves and structures is possible, are calculated. 3) Further, the parameters of the electrostatic structures (wave amplitudes, scales along and perpendicular to the magnetic field, velocities) are estimated. 4) The application of the present numerical simulation for multi-component plasmas to various astrophysical systems under different physical conditions is discussed.

Propagation of gaseous detonation waves in a spatially inhomogeneous reactive medium

NASA Astrophysics Data System (ADS)

Mi, XiaoCheng; Higgins, Andrew J.; Ng, Hoi Dick; Kiyanda, Charles B.; Nikiforakis, Nikolaos

2017-05-01

Detonation propagation in a compressible medium wherein the energy release has been made spatially inhomogeneous is examined via numerical simulation. The inhomogeneity is introduced via step functions in the reaction progress variable, with the local value of energy release correspondingly increased so as to maintain the same average energy density in the medium and thus a constant Chapman-Jouguet (CJ) detonation velocity. A one-step Arrhenius rate governs the rate of energy release in the reactive zones. The resulting dynamics of a detonation propagating in such systems with one-dimensional layers and two-dimensional squares are simulated using a Godunov-type finite-volume scheme. The resulting wave dynamics are analyzed by computing the average wave velocity and one-dimensional averaged wave structure. In the case of sufficiently inhomogeneous media wherein the spacing between reactive zones is greater than the inherent reaction zone length, average wave speeds significantly greater than the corresponding CJ speed of the homogenized medium are obtained. If the shock transit time between reactive zones is less than the reaction time scale, then the classical CJ detonation velocity is recovered. The spatiotemporal averaged structure of the waves in these systems is analyzed via a Favre-averaging technique, with terms associated with the thermal and mechanical fluctuations being explicitly computed. The analysis of the averaged wave structure identifies the super-CJ detonations as weak detonations owing to the existence of mechanical nonequilibrium at the effective sonic point embedded within the wave structure. The correspondence of the super-CJ behavior identified in this study with real detonation phenomena that may be observed in experiments is discussed.

A single-phase elastic hyperbolic metamaterial with anisotropic mass density.

PubMed

Zhu, R; Chen, Y Y; Wang, Y S; Hu, G K; Huang, G L

2016-06-01

Wave propagation can be manipulated at a deep subwavelength scale through the locally resonant metamaterial that possesses unusual effective material properties. Hyperlens due to metamaterial's anomalous anisotropy can lead to superior-resolution imaging. In this paper, a single-phase elastic metamaterial with strongly anisotropic effective mass density has been designed. The proposed metamaterial utilizes the independently adjustable locally resonant motions of the subwavelength-scale microstructures along the two principal directions. High anisotropy in the effective mass densities obtained by the numerical-based effective medium theory can be found and even have opposite signs. For practical applications, shunted piezoelectric elements are introduced into the microstructure to tailor the effective mass density in a broad frequency range. Finally, to validate the design, an elastic hyperlens made of the single-phase hyperbolic metamaterial is proposed with subwavelength longitudinal wave imaging illustrated numerically. The proposed single-phase hyperbolic metamaterial has many promising applications for high resolution damage imaging in nondestructive evaluation and structural health monitoring.

EVOLUTION OF FAST MAGNETOACOUSTIC PULSES IN RANDOMLY STRUCTURED CORONAL PLASMAS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, D.; Li, B.; Pascoe, D. J.

2015-02-01

We investigate the evolution of fast magnetoacoustic pulses in randomly structured plasmas, in the context of large-scale propagating waves in the solar atmosphere. We perform one-dimensional numerical simulations of fast wave pulses propagating perpendicular to a constant magnetic field in a low-β plasma with a random density profile across the field. Both linear and nonlinear regimes are considered. We study how the evolution of the pulse amplitude and width depends on their initial values and the parameters of the random structuring. Acting as a dispersive medium, a randomly structured plasma causes amplitude attenuation and width broadening of the fast wavemore » pulses. After the passage of the main pulse, secondary propagating and standing fast waves appear. Width evolution of both linear and nonlinear pulses can be well approximated by linear functions; however, narrow pulses may have zero or negative broadening. This arises because narrow pulses are prone to splitting, while broad pulses usually deviate less from their initial Gaussian shape and form ripple structures on top of the main pulse. Linear pulses decay at an almost constant rate, while nonlinear pulses decay exponentially. A pulse interacts most efficiently with a random medium with a correlation length of about half of the initial pulse width. This detailed model of fast wave pulses propagating in highly structured media substantiates the interpretation of EIT waves as fast magnetoacoustic waves. Evolution of a fast pulse provides us with a novel method to diagnose the sub-resolution filamentation of the solar atmosphere.« less

Intrinsic superspin Hall current

NASA Astrophysics Data System (ADS)

Linder, Jacob; Amundsen, Morten; Risinggârd, Vetle

2017-09-01

We discover an intrinsic superspin Hall current: an injected charge supercurrent in a Josephson junction containing heavy normal metals and a ferromagnet generates a transverse spin supercurrent. There is no accompanying dissipation of energy, in contrast to the conventional spin Hall effect. The physical origin of the effect is an antisymmetric spin density induced among transverse modes ky near the interface of the superconductor arising due to the coexistence of p -wave and conventional s -wave superconducting correlations with a belonging phase mismatch. Our predictions can be tested in hybrid structures including thin heavy metal layers combined with strong ferromagnets and ordinary s -wave superconductors.

Nonlocal theory of beam-driven electron Bernstein waves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jain, V.K.; Tripathi, V.K.

A nonlocal theory of electron Bernstein waves driven unstable by an axial beam (V = V/sub b/z-italic-circumflex) of finite width has been developed. Assuming a parabolic density profile for the background plasma, an equation describing the mode structure of the wave is obtained in the slab geometry. The eigenfunctions are found to be Hermite polynomials. Expressions for the growth rates of the instabilities caused by Cerenkov and slow cyclotron interactions are derived. The results of the theory are applied to explain some of the experimental observations of Jain and Christiansen (Phys. Lett. A 82, 127 (1981)).

Simultaneous measurements of density field and wavefront distortions in high speed flows

NASA Astrophysics Data System (ADS)

George, Jacob; Jenkins, Thomas; Trolinger, James; Hess, Cecil; Buckner, Benjamin

2017-09-01

This paper presents results from simultaneous measurements of fluid density and the resulting wavefront distortions in a sonic underexpanded jet. The density measurements were carried out using Rayleigh scattering, and the optical distortions were measured using a wavefront sensor based on phase shifting interferometry. The measurements represent a preliminary step toward relating wavefront distortions to a specific flow structure. The measured density field is used to compute the phase distortions using a wave propagation model based on a geometric-optics approximation, and the computed phase map shows moderate agreement with that obtained using the wavefront sensor.

Pondermotive versus mirror force in creation of the filamentary cavities in auroral plasma

NASA Technical Reports Server (NTRS)

Singh, Nagendra

1994-01-01

Recently rocket observations on spikelets of lower-hybrid waves along with strong density cavities and transversely heated ions were reported. The observed thin filamentary cavities oriented along the magnetic field in the auroral plasma have density depletions up to several tens of percent. These observations have been interpreted in terms of a theory for lower-hybrid wave condensation and collapse. The modulational instability leading to the wave consensation of the lower-hybrid waves yields only weak density perturbations, which cannot explain the above strong density depletions. The wave collapse theory is based on the nonlinear pondermotive force in a homogeneous ambient plasma and the density depletion is determined by the balance between the wave pressure (pondermotive force) and the plasma pressure. In the auroral plasma, the balance is achieved in a time tau(sub wc) equal to or less than 1 ms. It is shown here that the mirror force, acting on the transversely heated ions at a relatively long time scale, is an effective mechanism for creating the strong plasma cavities. We suggest that the process of wave condensation, through the pondermotive force causing generation of short wavelength waves from relatively long wavelength waves, is a dominant process until the former waves evolve and become effective in the transverse heating of ions. As soon as this happens, mirror force on ions becomes an important factor in the creation of the density cavities, which may further trap and enhance the waves. Results from a model of cavity formation by transverse ion heating show that the observed depletions in the density cavities can be produced by the heating rates determined by the observed wave amplitudes near the lower-hybrid frequency. It is found that the creation of a strong density cavity takes a few minutes.

Nonlinear electrostatic solitary waves in electron-positron plasmas

NASA Astrophysics Data System (ADS)

Lazarus, I. J.; Bharuthram, R.; Moolla, S.; Singh, S. V.; Lakhina, G. S.

2016-02-01

The generation of nonlinear electrostatic solitary waves (ESWs) is explored in a magnetized four component two-temperature electron-positron plasma. Fluid theory is used to derive a set of nonlinear equations for the ESWs, which propagate obliquely to an external magnetic field. The electric field structures are examined for various plasma parameters and are shown to yield sinusoidal, sawtooth and bipolar waveforms. It is found that an increase in the densities of the electrons and positrons strengthen the nonlinearity while the periodicity and nonlinearity of the wave increases as the cool-to-hot temperature ratio increases. Our results could be useful in understanding nonlinear propagation of waves in astrophysical environments and related laboratory experiments.

OGO 5 observations of Pc 5 waves - Particle flux modulations

NASA Technical Reports Server (NTRS)

Kokubun, S.; Kivelson, M. G.; Mcpherron, R. L.; Russell, C. T.; West, H. I., Jr.

1977-01-01

An investigation is conducted concerning the modulations of particle fluxes associated with Pc 5 waves in the region beyond the plasmapause. A study of thermal flux modulations indicates that some of the density enhancements observed are not spatial structures but are spurious features caused by temporal flux variations associated with hydromagnetic waves. A resonance model of the energetic particle flux modulations is discussed. Energetic particle modulations are also considered. The reported observations reveal that modulations are dominant at energies of about 100 keV for electrons and at 100 keV to 1 MeV for protons. This may indicate that the bounce resonance interaction is not important for Pc 5 waves.

Study of cavity type antenna structure of large-area 915 MHz ultra-high frequency wave plasma device based on three-dimensional finite difference time-domain analysis

NASA Astrophysics Data System (ADS)

Chang, Xijiang; Kunii, Kazuki; Liang, Rongqing; Nagatsu, Masaaki

2013-11-01

A large-area planar plasma source with a resonant cavity type launcher driven by a 915 MHz ultra-high frequency wave was developed. Theoretical analysis with the three-dimensional finite difference time-domain simulation was carried out to determine the optimized launcher structure by analyzing the resonant transverse magnetic mode in the resonant cavity. Numerical result expects that the resonant electric field distribution inside the cavity dominantly consists of the TM410 mode. The resonant cavity type launcher having 8 holes in an octagonal geometry was designed to fit the resonant transverse magnetic mode. Adjusting 8 hole positions of the launcher to the field pattern of the resonant TM410 mode, we found that the plasma density increased about 40%˜50% from 1.0˜1.1 × 1011 cm-3 to ˜1.5 × 1011 cm-3 at the same incident power of 2.5 kW, compared with the previous results with the launcher having 6 holes in the hexagonal geometry. It is also noted that the electron density changes almost linearly with the incident wave power without any mode jumps.

Evolution of solitary density waves in stellar winds of early-type stars: A simple explanation of discrete absorption component behavior

NASA Technical Reports Server (NTRS)

Waldron, Wayne L.; Klein, Larry; Altner, Bruce

1994-01-01

We model the evolution of a density shell propagating through the stellar wind of an early-type star, in order to investigate the effects of such shells on UV P Cygni line profiles. Unlike previous treatments, we solve the mass, momentum, and energy conservation equations, using an explicit time-differencing scheme, and present a parametric study of the density, velocity, and temperature response. Under the assumed conditions, relatively large spatial scale, large-amplitude density shells propagate as stable waves through the supersonic portion of the wind. Their dynamical behavior appears to mimic propagating 'solitary waves,' and they are found to accelerate at the same rate as the underlying steady state stellar wind (i.e., the shell rides the wind). These hydrodynamically stable structures quantitatively reproduce the anomalous 'discrete absorption component' (DAC) behavior observed in the winds of luminous early-type stars, as illustrated by comparisons of model predictions to an extensive International Ultraviolet Explorer (IUE) time series of spectra of zeta Puppis (O4f). From these comparisons, we find no conclusive evidence indicative of DACs accelerating at a significantly slower rate than the underlying stellar wind, contrary to earlier reports. In addition, these density shells are found to be consistent within the constraints set by the IR observations. We conclude that the concept of propagating density shells should be seriously reconsidered as a possible explanation of the DAC phenomenon in early-type stars.

Ionospheric Tomography Using Faraday Rotation of Automatic Dependant Surveillance Broadcast UHF Signals

NASA Astrophysics Data System (ADS)

Cushley, A. C.

2013-12-01

The proposed launch of a satellite carrying the first space-borne ADS-B receiver by the Royal Military College of Canada (RMCC) will create a unique opportunity to study the modification of the 1090 MHz radio waves following propagation through the ionosphere from the transmitting aircraft to the passive satellite receiver(s). Experimental work successfully demonstrated that ADS-B data can be used to reconstruct two dimensional (2D) electron density maps of the ionosphere using computerized tomography (CT). The goal of this work is to evaluate the feasibility of CT reconstruction. The data is modelled using Ray-tracing techniques. This allows us to determine the characteristics of individual waves, including the wave path and the state of polarization at the satellite receiver. The modelled Faraday rotation (FR) is determined and converted to total electron content (TEC) along the ray-paths. The resulting TEC is used as input for computerized ionospheric tomography (CIT) using algebraic reconstruction technique (ART). This study concentrated on meso-scale structures 100-1000 km in horizontal extent. The primary scientific interest of this thesis was to show the feasibility of a new method to image the ionosphere and obtain a better understanding of magneto-ionic wave propagation. Multiple feature input electron density profile to ray-tracing program. Top: reconstructed relative electron density map of ray-trace input (Fig. 1) using TEC measurements and line-of-sight path. Bottom: reconstructed electron density map of ray-trace input using quiet background a priori estimate.

Plasma turbulence and coherent structures in the polar cap observed by the ICI-2 sounding rocket

NASA Astrophysics Data System (ADS)

Spicher, A.; Miloch, W. J.; Clausen, L. B. N.; Moen, J. I.

2015-12-01

The electron density data from the ICI-2 sounding rocket experiment in the high-latitude F region ionosphere are analyzed using the higher-order spectra and higher-order statistics. Two regions of enhanced fluctuations are chosen for detailed analysis: the trailing edge of a polar cap patch and an electron density enhancement associated with particle precipitation. While these two regions exhibit similar power spectra, our analysis reveals that their internal structures are significantly different. The structures on the edge of the polar cap patch are likely due to nonlinear wave interactions since this region is characterized by intermittency and significant coherent mode coupling. The plasma enhancement subjected to precipitation, however, exhibits stronger random characteristics with uncorrelated phases of density fluctuations. These results suggest that particle precipitation plays a fundamental role in ionospheric plasma structuring creating turbulent-like structures. We discuss the physical mechanisms that cause plasma structuring as well as the possible processes for the low-frequency part of the spectrum in terms of plasma instabilities.

The thin section rock physics: Modeling and measurement of seismic wave velocity on the slice of carbonates

NASA Astrophysics Data System (ADS)

Wardaya, P. D.; Noh, K. A. B. M.; Yusoff, W. I. B. W.; Ridha, S.; Nurhandoko, B. E. B.

2014-09-01

This paper discusses a new approach for investigating the seismic wave velocity of rock, specifically carbonates, as affected by their pore structures. While the conventional routine of seismic velocity measurement highly depends on the extensive laboratory experiment, the proposed approach utilizes the digital rock physics view which lies on the numerical experiment. Thus, instead of using core sample, we use the thin section image of carbonate rock to measure the effective seismic wave velocity when travelling on it. In the numerical experiment, thin section images act as the medium on which wave propagation will be simulated. For the modeling, an advanced technique based on artificial neural network was employed for building the velocity and density profile, replacing image's RGB pixel value with the seismic velocity and density of each rock constituent. Then, ultrasonic wave was simulated to propagate in the thin section image by using finite difference time domain method, based on assumption of an acoustic-isotropic medium. Effective velocities were drawn from the recorded signal and being compared to the velocity modeling from Wyllie time average model and Kuster-Toksoz rock physics model. To perform the modeling, image analysis routines were undertaken for quantifying the pore aspect ratio that is assumed to represent the rocks pore structure. In addition, porosity and mineral fraction required for velocity modeling were also quantified by using integrated neural network and image analysis technique. It was found that the Kuster-Toksoz gives the closer prediction to the measured velocity as compared to the Wyllie time average model. We also conclude that Wyllie time average that does not incorporate the pore structure parameter deviates significantly for samples having more than 40% porosity. Utilizing this approach we found a good agreement between numerical experiment and theoretically derived rock physics model for estimating the effective seismic wave velocity of rock.

The structural, electronic and dynamic properties of the L1{sub 2}- type Co{sub 3}Ti alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arikan, Nihat; Özduran, Mustafa

2014-10-06

The structural, electronic and dynamic properties of the cubic Co{sub 3}Ti alloy in L1{sub 2} structure have been investigated using a pseudopotential plane wave (PP-PW) method within the generalized gradient approximation proposed by Perdew–Burke–Ernzerhof (GGA-PBE). The structural properties, including the lattice constant, the bulk modulus and its pressure derivative agree reasonably with the previous results. The density of state (DOS), projected density of state (PDOS) and electronic band structure are also reported. The DOS shows that Co{sub 3}Ti alloy has a metallic character since the energy bands cross the Fermi level. The density of states at Fermi level mainly comesmore » from the Co-3d states. Phonon dispersion curves and their corresponding total densities of states were obtained using a linear response in the framework of the density functional perturbation theory. All computed phonon frequencies are no imaginer and thus, Co{sub 3}Ti alloy is dynamically stable. The zone center phonon modes have been founded to be 9.307, 9.626 and 13.891 THz for Co{sub 3}Ti.« less

Acoustic waves in the solar atmosphere. VII - Non-grey, non-LTE H(-) models

NASA Technical Reports Server (NTRS)

Schmitz, F.; Ulmschneider, P.; Kalkofen, W.

1985-01-01

The propagation and shock formation of radiatively damped acoustic waves in the solar chromosphere are studied under the assumption that H(-) is the only absorber; the opacity is non-grey. Deviations from local thermodynamic equilibrium (LTE) are permitted. The results of numerical simulations show the depth dependence of the heating by the acoustic waves to be insensitive to the mean state of the atmosphere. After the waves have developed into shocks, their energy flux decays exponentially with a constant damping length of about 1.4 times the pressure scale height, independent of initial flux and wave period. Departures from LTE have a strong influence on the mean temperature structure in dynamical chromosphere models; this is even more pronounced in models with reduced particle density - simulating conditions in magnetic flux tubes - which show significantly increased temperatures in response to mechanical heating. When the energy dissipation of the waves is sufficiently large to dissociate most of the H(-) ions, a strong temperature rise is found that is reminiscent of the temperature structure in the transition zone between chromosphere and corona; the energy flux remaining in the waves then drives mass motions.

Anisotropic S-wave velocity structure from joint inversion of surface wave group velocity dispersion: A case study from India

NASA Astrophysics Data System (ADS)

Mitra, S.; Dey, S.; Siddartha, G.; Bhattacharya, S.

2016-12-01

We estimate 1-dimensional path average fundamental mode group velocity dispersion curves from regional Rayleigh and Love waves sampling the Indian subcontinent. The path average measurements are combined through a tomographic inversion to obtain 2-dimensional group velocity variation maps between periods of 10 and 80 s. The region of study is parametrised as triangular grids with 1° sides for the tomographic inversion. Rayleigh and Love wave dispersion curves from each node point is subsequently extracted and jointly inverted to obtain a radially anisotropic shear wave velocity model through global optimisation using Genetic Algorithm. The parametrization of the model space is done using three crustal layers and four mantle layers over a half-space with varying VpH , VsV and VsH. The anisotropic parameter (η) is calculated from empirical relations and the density of the layers are taken from PREM. Misfit for the model is calculated as a sum of error-weighted average dispersion curves. The 1-dimensional anisotropic shear wave velocity at each node point is combined using linear interpolation to obtain 3-dimensional structure beneath the region. Synthetic tests are performed to estimate the resolution of the tomographic maps which will be presented with our results. We envision to extend this to a larger dataset in near future to obtain high resolution anisotrpic shear wave velocity structure beneath India, Himalaya and Tibet.

PAREMD: A parallel program for the evaluation of momentum space properties of atoms and molecules

NASA Astrophysics Data System (ADS)

Meena, Deep Raj; Gadre, Shridhar R.; Balanarayan, P.

2018-03-01

The present work describes a code for evaluating the electron momentum density (EMD), its moments and the associated Shannon information entropy for a multi-electron molecular system. The code works specifically for electronic wave functions obtained from traditional electronic structure packages such as GAMESS and GAUSSIAN. For the momentum space orbitals, the general expression for Gaussian basis sets in position space is analytically Fourier transformed to momentum space Gaussian basis functions. The molecular orbital coefficients of the wave function are taken as an input from the output file of the electronic structure calculation. The analytic expressions of EMD are evaluated over a fine grid and the accuracy of the code is verified by a normalization check and a numerical kinetic energy evaluation which is compared with the analytic kinetic energy given by the electronic structure package. Apart from electron momentum density, electron density in position space has also been integrated into this package. The program is written in C++ and is executed through a Shell script. It is also tuned for multicore machines with shared memory through OpenMP. The program has been tested for a variety of molecules and correlated methods such as CISD, Møller-Plesset second order (MP2) theory and density functional methods. For correlated methods, the PAREMD program uses natural spin orbitals as an input. The program has been benchmarked for a variety of Gaussian basis sets for different molecules showing a linear speedup on a parallel architecture.

Critical Role of the Exchange Interaction for the Electronic Structure and Charge-Density-Wave Formation in TiSe2

NASA Astrophysics Data System (ADS)

Hellgren, Maria; Baima, Jacopo; Bianco, Raffaello; Calandra, Matteo; Mauri, Francesco; Wirtz, Ludger

2017-10-01

We show that the inclusion of screened exchange via hybrid functionals provides a unified description of the electronic and vibrational properties of TiSe2 . In contrast to local approximations in density functional theory, the explicit inclusion of exact, nonlocal exchange captures the effects of the electron-electron interaction needed to both separate the Ti -d states from the Se -p states and stabilize the charge-density-wave (CDW) (or low-T ) phase through the formation of a p -d hybridized state. We further show that this leads to an enhanced electron-phonon coupling that can drive the transition even if a small gap opens in the high-T phase. Finally, we demonstrate that the hybrid functionals can generate a CDW phase where the electronic bands, the geometry, and the phonon frequencies are in agreement with experiments.

PLANET-DISK INTERACTION IN THREE DIMENSIONS: THE IMPORTANCE OF BUOYANCY WAVES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu Zhaohuan; Stone, James M.; Rafikov, Roman R., E-mail: zhzhu@astro.princeton.edu, E-mail: jstone@astro.princeton.edu, E-mail: rrr@astro.princeton.edu

2012-10-20

We carry out local three-dimensional (3D) hydrodynamic simulations of planet-disk interaction in stratified disks with varied thermodynamic properties. We find that whenever the Brunt-Vaeisaelae frequency (N) in the disk is non-zero, the planet exerts a strong torque on the disk in the vicinity of the planet, with a reduction in the traditional 'torque cutoff'. In particular, this is true for adiabatic perturbations in disks with isothermal density structure, as should be typical for centrally irradiated protoplanetary disks. We identify this torque with buoyancy waves, which are excited (when N is non-zero) close to the planet, within one disk scale heightmore » from its orbit. These waves give rise to density perturbations with a characteristic 3D spatial pattern which is in close agreement with the linear dispersion relation. The torque due to these waves can amount to as much as several tens of percent of the total planetary torque, which is not expected based on analytical calculations limited to axisymmetric or low-m modes. Buoyancy waves should be ubiquitous around planets in the inner, dense regions of protoplanetary disks, where they might possibly affect planet migration.« less

Quantitative examination of demineralized and remineralized dental lesions using photothermal radiometry and modulated luminescence

NASA Astrophysics Data System (ADS)

Hellen, Adam; Mandelis, Andreas; Finer, Yoav; Amaechi, Bennett

2010-02-01

The development of photothermal techniques to detect thermal waves in biological tissue has occurred with a concomitant advancement in the extraction of material thermophysical properties and knowledge regarding the internal structure of a medium. Human molars (n=37) were subjected to demineralization in acid gel (pH 4.5, 10 days), followed by incubation in different fluoride-containing remineralization solutions. PTR-LUM frequency scans (1 Hz - 1 kHz) were performed prior to and during demineralization and remineralization treatments. Transverse Micro-Radiography (TMR) analysis followed at treatment conclusion. A coupled diffuse-photon-density-wave and thermal-wave theoretical model was used to quantitatively evaluate changes in thermal and optical properties of sound, demineralized and remineralized enamel. Amplitude increase and phase lag decrease in demineralized samples were consistent with higher scatter of the diffuse-photon density field and thermal wave confinement to near-surface regions. A remineralized sample illustrates a complex interplay between surface and subsurface processes, confining the thermal-wave centroid toward the dominating layer. PTR-LUM sensitivity to changes in tooth mineralization coupled with optical and thermal property extraction illustrates the technique's potential for non-destructive evaluation of multi-layered turbid media.

Enhanced control of light and sound trajectories with three-dimensional gradient index lenses

NASA Astrophysics Data System (ADS)

Chang, T. M.; Dupont, G.; Enoch, S.; Guenneau, S.

2012-03-01

We numerically study the focusing and bending effects of light and sound waves through heterogeneous isotropic cylindrical and spherical devices. We first point out that transformation optics and acoustics show that the control of light requires spatially varying anisotropic permittivity and permeability, while the control of sound is achieved via spatially anisotropic density and isotropic compressibility. Moreover, homogenization theory applied to electromagnetic and acoustic periodic structures leads to such artificial (although not spatially varying) anisotropic permittivity, permeability and density. We stress that homogenization is thus a natural mathematical tool for the design of structured metamaterials. To illustrate the two-step geometric transform-homogenization approach, we consider the design of cylindrical and spherical electromagnetic and acoustic lenses displaying some artificial anisotropy along their optical axis (direction of periodicity of the structural elements). Applications are sought in the design of Eaton and Luneburg lenses bending light at angles ranging from 90° to 360°, or mimicking a Schwartzchild metric, i.e. a black hole. All of these spherical metamaterials are characterized by a refractive index varying inversely with the radius which is approximated by concentric layers of homogeneous material. We finally propose some structured cylindrical metamaterials consisting of infinitely conducting or rigid toroidal channels in a homogeneous bulk material focusing light or sound waves. The functionality of these metamaterials is demonstrated via full-wave three-dimensional computations using nodal elements in the context of acoustics, and finite edge-elements in electromagnetics.

Methods in the study of discrete upper hybrid waves

NASA Astrophysics Data System (ADS)

Yoon, P. H.; Ye, S.; Labelle, J.; Weatherwax, A. T.; Menietti, J. D.

2007-11-01

Naturally occurring plasma waves characterized by fine frequency structure or discrete spectrum, detected by satellite, rocket-borne instruments, or ground-based receivers, can be interpreted as eigenmodes excited and trapped in field-aligned density structures. This paper overviews various theoretical methods to study such phenomena for a one-dimensional (1-D) density structure. Among the various methods are parabolic approximation, eikonal matching, eigenfunction matching, and full numerical solution based upon shooting method. Various approaches are compared against the full numerical solution. Among the analytic methods it is found that the eigenfunction matching technique best approximates the actual numerical solution. The analysis is further extended to 2-D geometry. A detailed comparative analysis between the eigenfunction matching and fully numerical methods is carried out for the 2-D case. Although in general the two methods compare favorably, significant differences are also found such that for application to actual observations it is prudent to employ the fully numerical method. Application of the methods developed in the present paper to actual geophysical problems will be given in a companion paper.

Competition of density waves and quantum multicritical behavior in Dirac materials from functional renormalization

NASA Astrophysics Data System (ADS)

Classen, Laura; Herbut, Igor F.; Janssen, Lukas; Scherer, Michael M.

2016-03-01

We study the competition of spin- and charge-density waves and their quantum multicritical behavior for the semimetal-insulator transitions of low-dimensional Dirac fermions. Employing the effective Gross-Neveu-Yukawa theory with two order parameters as a model for graphene and a growing number of other two-dimensional Dirac materials allows us to describe the physics near the multicritical point at which the semimetallic and the spin- and charge-density-wave phases meet. With the help of a functional renormalization group approach, we are able to reveal a complex structure of fixed points, the stability properties of which decisively depend on the number of Dirac fermions Nf. We give estimates for the critical exponents and observe crucial quantitative corrections as compared to the previous first-order ɛ expansion. For small Nf, the universal behavior near the multicritical point is determined by the chiral Heisenberg universality class supplemented by a decoupled, purely bosonic, Ising sector. At large Nf, a novel fixed point with nontrivial couplings between all sectors becomes stable. At intermediate Nf, including the graphene case (Nf=2 ), no stable and physically admissible fixed point exists. Graphene's phase diagram in the vicinity of the intersection between the semimetal, antiferromagnetic, and staggered density phases should consequently be governed by a triple point exhibiting first-order transitions.

Spin density waves predicted in zigzag puckered phosphorene, arsenene and antimonene nanoribbons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Xiaohua; Zhang, Xiaoli; Wang, Xianlong

2016-04-15

The pursuit of controlled magnetism in semiconductors has been a persisting goal in condensed matter physics. Recently, Vene (phosphorene, arsenene and antimonene) has been predicted as a new class of 2D-semiconductor with suitable band gap and high carrier mobility. In this work, we investigate the edge magnetism in zigzag puckered Vene nanoribbons (ZVNRs) based on the density functional theory. The band structures of ZVNRs show half-filled bands crossing the Fermi level at the midpoint of reciprocal lattice vectors, indicating a strong Peierls instability. To remove this instability, we consider two different mechanisms, namely, spin density wave (SDW) caused by electron-electronmore » interaction and charge density wave (CDW) caused by electron-phonon coupling. We have found that an antiferromagnetic Mott-insulating state defined by SDW is the ground state of ZVNRs. In particular, SDW in ZVNRs displays several surprising characteristics:1) comparing with other nanoribbon systems, their magnetic moments are antiparallelly arranged at each zigzag edge and almost independent on the width of nanoribbons; 2) comparing with other SDW systems, its magnetic moments and band gap of SDW are unexpectedly large, indicating a higher SDW transition temperature in ZVNRs; 3) SDW can be effectively modified by strains and charge doping, which indicates that ZVNRs have bright prospects in nanoelectronic device.« less

Investigation of the Presence of Charge Order in Magnetite by Measurement of the Sprin Wave Spectrum

DOE Office of Scientific and Technical Information (OSTI.GOV)

McQueeny, R. J.; Yethiraj, Mohana; Montfrooij, W.

Inelastic neutron scattering results on magnetite (Fe{sub 3}O{sub 4}) show a large splitting in the acoustic spin wave branch, producing a 7 meV gap midway to the Brillouin zone boundary at q = (0,0,1/2) and {h_bar}{omega} = 43 meV. The splitting occurs below the Verwey transition temperature, where a metal-insulator transition occurs simultaneously with a structural transformation, supposedly caused by the charge ordering on the iron sublattice. The wavevector (0,0,1/2) corresponds to the superlattice peak in the low symmetry structure. The dependence of the magnetic superexchange on changes in the crystal structure and ionic configurations that occur below the Verweymore » transition affect the spin wave dispersion. To better understand the origin of the observed splitting, several Heisenberg models intended to reproduce the pair-wise variation of the magnetic superexchange arising from both small crystalline distortions and charge ordering were studied. None of the models studied predicts the observed splitting, whose origin may arise from charge-density wave formation or magnetoelastic coupling.« less

Properties of Langmuir wave bursts associated with magnetic holes

NASA Technical Reports Server (NTRS)

MacDowall, R. J.; Lin, N.; Kellogg, P. J.; Phillips, J. L.; Neugebauer, M.; Balogh, A.; Forsyth, R. J.

1995-01-01

The radio and plasma wave receivers on the Ulysses spacecraft have detected thousands of short-duration bursts of waves at approximately the electron plasma frequency. These wave events believed to be Langmuir waves are usually less than approximately 5 minutes in duration. They occur in or at the boundaries of depletions in the magnetic field amplitude known as magnetic holes. Using the 16 sec time resolution provided by the plasma frequency receiver, it is possible to examine the density structure inside of magnetic holes. Even higher time resolutions are sometimes available from the radio receiver data. The Ulysses observations show that these wave bursts occur more frequently at high heliographic latitudes; the occurrence rates depend on both latitude and distance from the Sun. We review the statistics for the wave events, compare them to magnetic and plasma parameters, and review the reasons for the more frequent occurrence at high heliographic latitudes.

Negative refraction of elastic waves at the deep-subwavelength scale in a single-phase metamaterial.

PubMed

Zhu, R; Liu, X N; Hu, G K; Sun, C T; Huang, G L

2014-11-24

Negative refraction of elastic waves has been studied and experimentally demonstrated in three- and two-dimensional phononic crystals, but Bragg scattering is impractical for low-frequency wave control because of the need to scale the structures to manageable sizes. Here we present an elastic metamaterial with chiral microstructure made of a single-phase solid material that aims to achieve subwavelength negative refraction of elastic waves. Both negative effective mass density and modulus are observed owing to simultaneous translational and rotational resonances. We experimentally demonstrate negative refraction of the longitudinal elastic wave at the deep-subwavelength scale in the metamaterial fabricated in a stainless steel plate. The experimental measurements are in good agreement with numerical simulations. Moreover, wave mode conversion related with negative refraction is revealed and discussed. The proposed elastic metamaterial may thus be used as a flat lens for elastic wave focusing.

Monitoring the Groningen gas field by seismic noise interferometry

NASA Astrophysics Data System (ADS)

Zhou, Wen; Paulssen, Hanneke

2017-04-01

The Groningen gas field in the Netherlands is the world's 7th largest onshore gas field and has been producing from 1963. Since 2013, the year with the highest level of induced seismicity, the reservoir has been monitored by two geophone strings at reservoir level at about 3 km depth. For borehole SDM, 10 geophones with a natural frequency of 15-Hz are positioned from the top to bottom of the reservoir with a geophone spacing of 30 m. We used seismic interferometry to determine, as accurately as possible, the inter-geophone P- and S-wave velocities from ambient noise. We used 1-bit normalization and spectral whitening, together with a bandpass filter from 3 to 400 Hz. After that, for each station pair, the normalized cross-correlation was calculated for 6 seconds segments with 2/3 overlap. These segmented cross-correlations were stacked for every 1 hour, 24(hours)*33(days) segments were obtained for each station pair. The cross-correlations show both day-and-night and weekly variations reflecting fluctuations in cultural noise. The apparent P-wave travel time for each geophone pair is measured from the maximum of the vertical component cross-correlation for each of the hourly stacks. Because the distribution of these (24*33) picked travel times is not Gaussian but skewed, we used Kernel density estimations to obtain probability density functions of the travel times. The maximum likelihood travel times of all the geophone pairs was subsequently used to determine inter-geophone P-wave velocities. A good agreement was found between our estimated P velocity structure and well logging data, with difference less than 5%. The S-velocity structure was obtained from the east-component cross-correlations. They show both the direct P- and S-wave arrivals and, because of the interference, the inferred S-velocity structure is less accurate. From the 9(3x3)-component cross-correlations for all the geophone pairs, not only the direct P and S waves can be identified, but also reflected waves within the reservoir for some of the cross-correlations. It is concluded that noise interferometry can be used to determine the seismic velocity structure from deep borehole data.

Density variation effect on multi-ions with kinetic Alfven wave around cusp region—a kinetic approach

NASA Astrophysics Data System (ADS)

Tamrakar, Radha; Varma, P.; Tiwari, M. S.

2018-01-01

The kinetic Alfven waves in the presence of homogeneous magnetic field plasma with multi-ions effect are investigated. The dispersion relation and normalised damping rate are derived for low-β plasma using kinetic theory. The effect of density variation of H+, He+ and O+ ions is observed on frequency and damping rate of the wave. The variation of frequency (ω) and normalised damping rate (γ / Ω_{H^{ +}} ) of the wave are studied with respect to k_{ \\bot} ρj, where k_{ \\bot} is the perpendicular wave number, ρj is the ion gyroradius and j denotes H+, He+ and O+ ions. The variation with k_{ \\bot} ρj is considered over wide range. The parameters appropriate to cusp region are used for the explanation of results. It is found that with hydrogen and helium ions gyration, the frequency of wave is influenced by the density variation of H+ and He+ ions but remains insensitive to the change in density of O+ ions. For oxygen ion gyration, the frequency of wave varies over a short range only for O+ ion density variation. The wave shows damping at lower altitude due to variation in density of lighter H+ and He+ ions whereas at higher altitude only heavy O+ ions contribute in wave damping. The damping of wave may be due to landau damping or energy transfer from wave to particles. The present study signifies that the both lighter and heavier ions dominate differently to change the characteristics of kinetic Alfven wave and density variation is also an important parameter to understand wave phenomena in cusp region.

A Weakly Nonlinear Model for the Damping of Resonantly Forced Density Waves in Dense Planetary Rings

NASA Astrophysics Data System (ADS)

Lehmann, Marius; Schmidt, Jürgen; Salo, Heikki

2016-10-01

In this paper, we address the stability of resonantly forced density waves in dense planetary rings. Goldreich & Tremaine have already argued that density waves might be unstable, depending on the relationship between the ring’s viscosity and the surface mass density. In the recent paper Schmidt et al., we have pointed out that when—within a fluid description of the ring dynamics—the criterion for viscous overstability is satisfied, forced spiral density waves become unstable as well. In this case, linear theory fails to describe the damping, but nonlinearity of the underlying equations guarantees a finite amplitude and eventually a damping of the wave. We apply the multiple scale formalism to derive a weakly nonlinear damping relation from a hydrodynamical model. This relation describes the resonant excitation and nonlinear viscous damping of spiral density waves in a vertically integrated fluid disk with density dependent transport coefficients. The model consistently predicts density waves to be (linearly) unstable in a ring region where the conditions for viscous overstability are met. Sufficiently far away from the Lindblad resonance, the surface mass density perturbation is predicted to saturate to a constant value due to nonlinear viscous damping. The wave’s damping lengths of the model depend on certain input parameters, such as the distance to the threshold for viscous overstability in parameter space and the ground state surface mass density.

Investigation of the spatial structure and developmental dynamics of near-Earth plasma perturbations under the action of powerful HF radio waves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Belov, A. S., E-mail: alexis-belov@yandex.ru

2015-10-15

Results of numerical simulations of the near-Earth plasma perturbations induced by powerful HF radio waves from the SURA heating facility are presented. The simulations were performed using a modified version of the SAMI2 ionospheric model for the input parameters corresponding to the series of in-situ SURA–DEMETER experiments. The spatial structure and developmental dynamics of large-scale plasma temperature and density perturbations have been investigated. The characteristic formation and relaxation times of the induced large-scale plasma perturbations at the altitudes of the Earth’s outer ionosphere have been determined.

Density functional study of molecular interactions in secondary structures of proteins.

PubMed

Takano, Yu; Kusaka, Ayumi; Nakamura, Haruki

2016-01-01

Proteins play diverse and vital roles in biology, which are dominated by their three-dimensional structures. The three-dimensional structure of a protein determines its functions and chemical properties. Protein secondary structures, including α-helices and β-sheets, are key components of the protein architecture. Molecular interactions, in particular hydrogen bonds, play significant roles in the formation of protein secondary structures. Precise and quantitative estimations of these interactions are required to understand the principles underlying the formation of three-dimensional protein structures. In the present study, we have investigated the molecular interactions in α-helices and β-sheets, using ab initio wave function-based methods, the Hartree-Fock method (HF) and the second-order Møller-Plesset perturbation theory (MP2), density functional theory, and molecular mechanics. The characteristic interactions essential for forming the secondary structures are discussed quantitatively.

Geophysical Exploration Technologies for the Deep Lithosphere Research: An Education Materials for High School Students

NASA Astrophysics Data System (ADS)

Xu, H.; Xu, C.; Luo, S.; Chen, H.; Qin, R.

2012-12-01

The science of Geophysics applies the principles of physics to study of the earth. Geophysical exploration technologies include the earthquake seismology, the seismic reflection and refraction methods, the gravity method, the magnetic method and the magnetotelluric method, which are used to measure the interior material distribution, their structure and the tectonics in the lithosphere of the earth. Part of the research project in SinoProbe-02-06 is to develop suitable education materials for carton movies targeting the high school students and public. The carton movies include five parts. The first part includes the structures of the earth's interior and variation in their physical properties that include density, p-wave, s-wave and so on, which are the fundamentals of the geophysical exploration technologies. The second part includes the seismology that uses the propagation of elastic waves through the earth to study the structure and the material distribution of the earth interior. It can be divided into earthquake seismology and artifice seismics commonly using reflection and refraction. The third part includes the magnetic method. Earth's magnetic field (also known as the geomagnetic field)extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun. The aim of magnetic survey is to investigate subsurface geology on the basis of anomalies in the Earth's magnetic field resulting from the magnetic properties of the underlying rocks. The magnetic method in the lithosphere attempts to use magnetic disturbance to analyse the regional geological structure and the magnetic boundaries of the crust. The fourth part includes the gravity method. A gravity anomaly results from the inhomogeneous distribution of density of the Earth. Usually gravity anomalies contain superposed anomalies from several sources. The long wave length anomalies due to deep density contrasts are called regional anomalies. They are important for understanding the large-scale structure of the earth's crust under major geographic features, such as mountain ranges, oceanic ridges and subduction zones. Short wave length residual anomalies are due to shallow anomalous masses that may be of interest for commercial exploitation. The last part is the magnetotellurics (MT), which is an electromagnetic geophysical method of imaging the earth's subsurface by measuring natural variations of electrical and magnetic fields at the Earth's surface. The long-period MT technique is used to exploration deep crustal. MT has been used to investigate the distribution of silicate melts in the Earth's mantle and crust and to better understand the plate-tectonic processes.

Ab-initio calculation for cation vacancy formation energy in anti-fluorite structure

NASA Astrophysics Data System (ADS)

Saleel, V. P. Saleel Ahammad; Chitra, D.; Veluraja, K.; Eithiraj, R. D.

2018-04-01

Lithium oxide (Li2O) has been suggested as a suitable breeder blanket material for fusion reactors. Li+ vacancies are created by neutron irradiation, forming bulk defect complex whose extra character is experimentally unclear. We present a theoretical study of Li2O using density functional theory (DFT) with a plane-wave basis set. The generalized gradient approximation (GGA) and local-density approximation (LDA) were used for exchange and correlation. Here we address the total energy for defect free, cation defect, cation vacancy and vacancy formation energy in Li2O crystal in anti-fluorite structure.

Structural, electronic and magnetic properties of Pr-based filled skutterudites: A first principle study

NASA Astrophysics Data System (ADS)

Yadav, Priya; Nautiyal, Shashank; Verma, U. P.

2018-04-01

Ternary skutterudites materials exhibit good electronic properties due to the unpaired d- and f- electrons of the transition and rare-earth metals, respectively. In this communication, we have performed the structural optimization of Pr-based filled skutterudite (PrCo4P12) for the first time and obtained the electronic band structure, density of states and magnetic moments by using the full-potential linearized augmented plane wave (FP-LAPW) method based on density functional theory (DFT). Our obtained magnetic moment of PrCo4P12 is ˜ 1.8 µB in which main contribution is due to Pr atom. Behavior of this material is metallic and it is most stable in body centered cubic (BCC) structure.

Laboratory-Scale Internal Wave Apparatus for Studying Copepod Behavior

NASA Astrophysics Data System (ADS)

Jung, S.; Webster, D. R.; Haas, K. A.; Yen, J.

2016-02-01

Internal waves are ubiquitous features in coastal marine environments and have been observed to mediate vertical distributions of zooplankton in situ. Internal waves create fine-scale hydrodynamic cues that copepods and other zooplankton are known to sense, such as fluid density gradients and velocity gradients (quantified as shear deformation rate). The role of copepod behavior in response to cues associated with internal waves is largely unknown. The objective is to provide insight to the bio-physical interaction and the role of biological versus physical forcing in mediating organism distributions. We constructed a laboratory-scale internal wave apparatus to facilitate fine-scale observations of copepod behavior in flows that replicate in situ conditions of internal waves in two-layer stratification. Two cases were chosen with density jump of 1 and 1.5 sigma-t units. Analytical analysis of the two-layer system provided guidance to the target forcing frequency needed to generate a standing internal wave with a single dominate frequency of oscillation. Flow visualization and signal processing of the interface location were used to quantify the wave characteristics. The results show a close match to the target wave parameters. Marine copepod (mixed population of Acartia tonsa, Temora longicornis, and Eurytemora affinis) behavior assays were conducted for three different physical arrangements: (1) no density stratification, (2) stagnant two-layer density stratification, and (3) two-layer density stratification with internal wave motion. Digitized trajectories of copepod swimming behavior indicate that in the control (case 1) the animals showed no preferential motion in terms of direction. In the stagnant density jump treatment (case 2) copepods preferentially moved horizontally, parallel to the density interface. In the internal wave treatment (case 3) copepods demonstrated orbital trajectories near the density interface.

Systematic investigation of structural, electronic, optical and thermal properties of ternary MoAlB; an ab initio approach

NASA Astrophysics Data System (ADS)

Rajpoot, Priyanka; Rastogi, Anugya; Verma, U. P.

2018-02-01

Structural, electronic, optical and thermal properties of molybdenum aluminum boride (MoAlB) have been analyzed systematically using the full potential linearized augmented plane wave method based on density functional theory at ambient condition as well as high pressure and high temperature. Density of states and band structure calculation reflect the metallic character of MoAlB. In addition to this, the electron charge density calculation reveals the strong covalent bonding, in between ‘B’ atoms as well as ‘Mo’ and ‘B’ atoms. Optical parameters exhibit anisotropic nature and MoAlB become transparent in ultraviolet region for the radiation of energy above 25 eV. The thermal properties were investigated by using the quasi-harmonic Debye model at high temperature and high pressure.

Plasma modification of spoof plasmon propagation along metamaterial-air interfaces

NASA Astrophysics Data System (ADS)

Lee, R.; Wang, B.; Cappelli, M. A.

2017-12-01

We report on measurements of the shift in resonance frequency of "spoof" surface plasmon polariton propagation along a 2-D metamaterial slow-wave structure induced by a gaseous plasma near the metamaterial/air interface. A transmission line circuit model for the metamaterial structure interprets the introduction of a plasma as a decrease in unit cell capacitance, causing a shift in the plasmon dispersion to higher frequency. We show through simulations and experiments that the effects of this shift at the resonance frequency and attenuation below and above resonance depend on the plasma density. The shifts recorded experimentally are small owing to the low plasma densities generated near the structure, ˜ 10 11 cm - 3 , but simulations show that a shift of ˜ 3 % of the resonance frequency can be generated at plasma densities of ˜ 10 12 cm - 3 .

Experimental studies of interactions between Alfv'en waves and striated density depletions in the LAPD

NASA Astrophysics Data System (ADS)

Auerbach, D. W.; Carter, T. A.; Vincena, S.

2008-11-01

Satellite measurements in the earth's magnetosphere have associated Alfv'en frequency fluctuations with density depletions striated along the geomagnetic field. This poster presents laboratory studies in the LADP experiment at UCLA modeling this phenomena. Density depletions are pre-formed in the plasma column by selectively blocking a portion of the drive beam, and Alfv'en waves are driven in the cavity by means of an inserted antenna. Relevant experimental parameters include an ion cyclotron radius around a mm, alfven parallel wavelength several meters, electron inertial length around 6 mm, and electron thermal speeds about a third of the alfv'en speed. We report here on modifications to the wave propagation due to the density depletion. We also report on the details of the interactions between the driven wave and the secondary drift-alfv'en wave instabilities that arise on the density boundary, including wave-wave interactions and possible turbulent broadening effects on the main wave.

Validation of Ionosonde Electron Density Reconstruction Algorithms with IONOLAB-RAY in Central Europe

NASA Astrophysics Data System (ADS)

Gok, Gokhan; Mosna, Zbysek; Arikan, Feza; Arikan, Orhan; Erdem, Esra

2016-07-01

Ionospheric observation is essentially accomplished by specialized radar systems called ionosondes. The time delay between the transmitted and received signals versus frequency is measured by the ionosondes and the received signals are processed to generate ionogram plots, which show the time delay or reflection height of signals with respect to transmitted frequency. The critical frequencies of ionospheric layers and virtual heights, that provide useful information about ionospheric structurecan be extracted from ionograms . Ionograms also indicate the amount of variability or disturbances in the ionosphere. With special inversion algorithms and tomographical methods, electron density profiles can also be estimated from the ionograms. Although structural pictures of ionosphere in the vertical direction can be observed from ionosonde measurements, some errors may arise due to inaccuracies that arise from signal propagation, modeling, data processing and tomographic reconstruction algorithms. Recently IONOLAB group (www.ionolab.org) developed a new algorithm for effective and accurate extraction of ionospheric parameters and reconstruction of electron density profile from ionograms. The electron density reconstruction algorithm applies advanced optimization techniques to calculate parameters of any existing analytical function which defines electron density with respect to height using ionogram measurement data. The process of reconstructing electron density with respect to height is known as the ionogram scaling or true height analysis. IONOLAB-RAY algorithm is a tool to investigate the propagation path and parameters of HF wave in the ionosphere. The algorithm models the wave propagation using ray representation under geometrical optics approximation. In the algorithm , the structural ionospheric characteristics arerepresented as realistically as possible including anisotropicity, inhomogenity and time dependence in 3-D voxel structure. The algorithm is also used for various purposes including calculation of actual height and generation of ionograms. In this study, the performance of electron density reconstruction algorithm of IONOLAB group and standard electron density profile algorithms of ionosondes are compared with IONOLAB-RAY wave propagation simulation in near vertical incidence. The electron density reconstruction and parameter extraction algorithms of ionosondes are validated with the IONOLAB-RAY results both for quiet anddisturbed ionospheric states in Central Europe using ionosonde stations such as Pruhonice and Juliusruh . It is observed that IONOLAB ionosonde parameter extraction and electron density reconstruction algorithm performs significantly better compared to standard algorithms especially for disturbed ionospheric conditions. IONOLAB-RAY provides an efficient and reliable tool to investigate and validate ionosonde electron density reconstruction algorithms, especially in determination of reflection height (true height) of signals and critical parameters of ionosphere. This study is supported by TUBITAK 114E541, 115E915 and Joint TUBITAK 114E092 and AS CR 14/001 projects.

Effect of shock waves on the statistics and scaling in compressible isotropic turbulence

NASA Astrophysics Data System (ADS)

Wang, Jianchun; Wan, Minping; Chen, Song; Xie, Chenyue; Chen, Shiyi

2018-04-01

The statistics and scaling of compressible isotropic turbulence in the presence of large-scale shock waves are investigated by using numerical simulations at turbulent Mach number Mt ranging from 0.30 to 0.65. The spectra of the compressible velocity component, density, pressure, and temperature exhibit a k-2 scaling at different turbulent Mach numbers. The scaling exponents for structure functions of the compressible velocity component and thermodynamic variables are close to 1 at high orders n ≥3 . The probability density functions of increments of the compressible velocity component and thermodynamic variables exhibit a power-law region with the exponent -2 . Models for the conditional average of increments of the compressible velocity component and thermodynamic variables are developed based on the ideal shock relations and are verified by numerical simulations. The overall statistics of the compressible velocity component and thermodynamic variables are similar to one another at different turbulent Mach numbers. It is shown that the effect of shock waves on the compressible velocity spectrum and kinetic energy transfer is different from that of acoustic waves.

Construction of CASCI-type wave functions for very large active spaces.

PubMed

Boguslawski, Katharina; Marti, Konrad H; Reiher, Markus

2011-06-14

We present a procedure to construct a configuration-interaction expansion containing arbitrary excitations from an underlying full-configuration-interaction-type wave function defined for a very large active space. Our procedure is based on the density-matrix renormalization group (DMRG) algorithm that provides the necessary information in terms of the eigenstates of the reduced density matrices to calculate the coefficient of any basis state in the many-particle Hilbert space. Since the dimension of the Hilbert space scales binomially with the size of the active space, a sophisticated Monte Carlo sampling routine is employed. This sampling algorithm can also construct such configuration-interaction-type wave functions from any other type of tensor network states. The configuration-interaction information obtained serves several purposes. It yields a qualitatively correct description of the molecule's electronic structure, it allows us to analyze DMRG wave functions converged for the same molecular system but with different parameter sets (e.g., different numbers of active-system (block) states), and it can be considered a balanced reference for the application of a subsequent standard multi-reference configuration-interaction method.

Rapid Multi-Damage Identification for Health Monitoring of Laminated Composites Using Piezoelectric Wafer Sensor Arrays

PubMed Central

Si, Liang; Wang, Qian

2016-01-01

Through the use of the wave reflection from any damage in a structure, a Hilbert spectral analysis-based rapid multi-damage identification (HSA-RMDI) technique with piezoelectric wafer sensor arrays (PWSA) is developed to monitor and identify the presence, location and severity of damage in carbon fiber composite structures. The capability of the rapid multi-damage identification technique to extract and estimate hidden significant information from the collected data and to provide a high-resolution energy-time spectrum can be employed to successfully interpret the Lamb waves interactions with single/multiple damage. Nevertheless, to accomplish the precise positioning and effective quantification of multiple damage in a composite structure, two functional metrics from the RMDI technique are proposed and used in damage identification, which are the energy density metric and the energy time-phase shift metric. In the designed damage experimental tests, invisible damage to the naked eyes, especially delaminations, were detected in the leftward propagating waves as well as in the selected sensor responses, where the time-phase shift spectra could locate the multiple damage whereas the energy density spectra were used to quantify the multiple damage. The increasing damage was shown to follow a linear trend calculated by the RMDI technique. All damage cases considered showed completely the developed RMDI technique potential as an effective online damage inspection and assessment tool. PMID:27153070

Shock-wave studies of anomalous compressibility of glassy carbon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Molodets, A. M., E-mail: molodets@icp.ac.ru; Golyshev, A. A.; Savinykh, A. S.

2016-02-15

The physico-mechanical properties of amorphous glassy carbon are investigated under shock compression up to 10 GPa. Experiments are carried out on the continuous recording of the mass velocity of compression pulses propagating in glassy carbon samples with initial densities of 1.502(5) g/cm{sup 3} and 1.55(2) g/cm{sup 3}. It is shown that, in both cases, a compression wave in glassy carbon contains a leading precursor with amplitude of 0.135(5) GPa. It is established that, in the range of pressures up to 2 GPa, a shock discontinuity in glassy carbon is transformed into a broadened compression wave, and shock waves are formedmore » in the release wave, which generally means the anomalous compressibility of the material in both the compression and release waves. It is shown that, at pressure higher than 3 GPa, anomalous behavior turns into normal behavior, accompanied by the formation of a shock compression wave. In the investigated area of pressure, possible structural changes in glassy carbon under shock compression have a reversible character. A physico-mechanical model of glassy carbon is proposed that involves the equation of state and a constitutive relation for Poisson’s ratio and allows the numerical simulation of physico-mechanical and thermophysical properties of glassy carbon of different densities in the region of its anomalous compressibility.« less

Ground testing of bioconvective variables such as morphological characterizations and mechanisms which regulate macroscopic patterns

NASA Technical Reports Server (NTRS)

Johnson, Adriel D.

1992-01-01

Conditions simulating low- and high-gravity, reveal changes in macroscopic pattern formation in selected microorganisms, but whether these structures are gravity dependent is not clear. Two theories have been identified in the fluid dynamics community which support macroscopic pattern formation. The first one is gravity dependent (fluid density models) where small concentrated regions of organisms sink unstably, and the second is gravity independent (wave reinforcement theory) where organisms align their movements in concert, such that either their swimming strokes beat in phase or their vortices entrain neighbors to follow parallel paths. Studies have shown that macroscopic pattern formation is consistent with the fluid density models for protozoa and algae and wave reinforcement hypothesis for caprine spermatozoa.

On performing of interference technique based on self-adjusting Zernike filters (SA-AVT method) to investigate flows and validate 3D flow numerical simulations

NASA Astrophysics Data System (ADS)

Pavlov, Al. A.; Shevchenko, A. M.; Khotyanovsky, D. V.; Pavlov, A. A.; Shmakov, A. S.; Golubev, M. P.

2017-10-01

We present a method for and results of determination of the field of integral density in the structure of flow corresponding to the Mach interaction of shock waves at Mach number M = 3. The optical diagnostics of flow was performed using an interference technique based on self-adjusting Zernike filters (SA-AVT method). Numerical simulations were carried out using the CFS3D program package for solving the Euler and Navier-Stokes equations. Quantitative data on the distribution of integral density on the path of probing radiation in one direction of 3D flow transillumination in the region of Mach interaction of shock waves were obtained for the first time.

Numerical simulation and analysis of electromagnetic-wave absorption of a plasma slab created by a direct-current discharge with gridded anode

NASA Astrophysics Data System (ADS)

Yuan, Chengxun; Tian, Ruihuan; Eliseev, S. I.; Bekasov, V. S.; Bogdanov, E. A.; Kudryavtsev, A. A.; Zhou, Zhongxiang

2018-03-01

In this paper, we present investigation of a direct-current discharge with a gridded anode from the point of view of using it as a means of creating plasma coating that could efficiently absorb incident electromagnetic (EM) waves. A single discharge cell consists of two parallel plates, one of which (anode) is gridded. Electrons emitted from the cathode surface are accelerated in the short interelectrode gap and are injected into the post-anode space, where they lose acquired energy on ionization and create plasma. Numerical simulations were used to investigate the discharge structure and obtain spatial distributions of plasma density in the post-anode space. The numerical model of the discharge was based on a simple hybrid approach which takes into account non-local ionization by fast electrons streaming from the cathode sheath. Specially formulated transparency boundary conditions allowed performing simulations in 1D. Simulations were carried out in air at pressures of 10 Torr and higher. Analysis of the discharge structure and discharge formation is presented. It is shown that using cathode materials with lower secondary emission coefficients can allow increasing the thickness of plasma slabs for the same discharge current, which can potentially enhance EM wave absorption. Spatial distributions of electron density obtained during simulations were used to calculate attenuation of an incident EM wave propagating perpendicularly to the plasma slab boundary. It is shown that plasma created by means of a DC discharge with a gridded anode can efficiently absorb EM waves in the low frequency range (6-40 GHz). Increasing gas pressure results in a broader range of wave frequencies (up to 500 GHz) where a considerable attenuation is observed.

Färoe-Iceland Ridge Experiment: 1. Crustal structure of northeastern Iceland

USGS Publications Warehouse

Staples, Robert K.; White, Robert S.; Brandsdottir, Bryndis; Menke, William; Maguire, Peter K.H.; McBride, John H.

1997-01-01

Results from the Färoe-Iceland Ridge Experiment (FIRE) constrain the crustal thickness as 19 km under the Northern Volcanic Zone of Iceland and 35 km under older Tertiary areas of northeastern Iceland. The Moho is defined by strong P wave and S wave reflections. Synthetic seismogram modeling of the Moho reflection indicates mantle velocities of at least 8.0 km/s beneath the Tertiary areas of northeastern Iceland and at least 7.9 km/s beneath the neovolcanic zone. Crustal diving rays resolve the structure of the upper and lower crust. Surface P wave velocities are 1.1–4.0 km/s in Quaternary rocks and are rather higher, 4.4–4.7 km/s, in the Tertiary basalts that outcrop elsewhere. The highest crustal P wave velocities observed directly from diving rays are 7.1 km/s, from rays that turn at 24 km depth. Velocities of 7.35 km/s at the base of the crust are inferred from extrapolation of the lower crustal velocity gradient (0.024 s−1). A Poisson's ratio of approximately 0.27, equivalent to an S wave to P wave travel time ratio of 1.78, is measured throughout the crust east of the neovolcanic zone. The Poisson's ratio and the steep Moho topography (in places up to 30° from the horizontal) indicate that the entire crust outside the neovolcanic zone is cool (<800°C). Gravity data are well matched by a velocity/density conversion of our seismic crustal model and indicate a region of low mantle density beneath the neovolcanic zone, believed to be due to elevated mantle temperatures. The crustal thickness in the neovolcanic zone is consistent with geochemical estimates of the melt generation, placing constraints on the flow within the Iceland mantle plume.

Density-induced suppression of the {alpha}-particle condensate in nuclear matter and the structure of {alpha}-cluster states in nuclei

DOE Office of Scientific and Technical Information (OSTI.GOV)

Funaki, Y.; Horiuchi, H.; International Institute for Advanced Studies, Kizugawa 619-0225

2008-06-15

At low densities, with decreasing temperatures, in symmetric nuclear matter {alpha} particles are formed, which eventually give raise to a quantum condensate with four-nucleon {alpha}-like correlations (quartetting). Starting with a model of {alpha} matter, where undistorted {alpha} particles interact via an effective interaction such as the Ali-Bodmer potential, the suppression of the condensate fraction at zero temperature with increasing density is considered. Using a Jastrow-Feenberg approach, it is found that the condensate fraction vanishes near saturation density. Additionally, the modification of the internal state of the {alpha} particle due to medium effects will further reduce the condensate. In finite systems,more » an enhancement of the S-state wave function of the center-of-mass orbital of {alpha}-particle motion is considered as the correspondence to the condensate. Wave functions have been constructed for self-conjugate 4n nuclei that describe the condensate state but are fully antisymmetrized on the nucleonic level. These condensate-like cluster wave functions have been successfully applied to describe properties of low-density states near the n{alpha} threshold. Comparison with orthogonality condition model calculations in {sup 12}C and {sup 16}O shows strong enhancement of the occupation of the S-state center-of-mass orbital of the {alpha} particles. This enhancement is decreasing if the baryon density increases, similar to the density-induced suppression of the condensate fraction in {alpha} matter. The ground states of {sup 12}C and {sup 16}O show no enhancement at all, thus a quartetting condensate cannot be formed at saturation densities.« less

Electronic structure of BaNi2As2

NASA Astrophysics Data System (ADS)

Zhou, Bo; Xu, Min; Zhang, Yan; Xu, Gang; He, Cheng; Yang, L. X.; Chen, Fei; Xie, B. P.; Cui, Xiao-Yu; Arita, Masashi; Shimada, Kenya; Namatame, Hirofumi; Taniguchi, Masaki; Dai, X.; Feng, D. L.

2011-01-01

BaNi2As2, with a first-order phase transition around 131 K, is studied by the angle-resolved photoemission spectroscopy. The measured electronic structure is compared to the local-density approximation calculations, revealing similar large electronlike bands around M¯ and differences along Γ¯-X¯. We further show that the electronic structure of BaNi2As2 is distinct from that of the sibling iron pnictides. Particularly, there is no signature of band folding, indicating no collinear spin-density-wave-related magnetic ordering. Moreover, across the strong first-order phase transition, the band shift exhibits a hysteresis, which is directly related to the significant lattice distortion in BaNi2As2.

Hardrock Elastic Physical Properties: Birch's Seismic Parameter Revisited

NASA Astrophysics Data System (ADS)

Wu, M.; Milkereit, B.

2014-12-01

Identifying rock composition and properties is imperative in a variety of fields including geotechnical engineering, mining, and petroleum exploration, in order to accurately make any petrophysical calculations. Density is, in particular, an important parameter that allows us to differentiate between lithologies and estimate or calculate other petrophysical properties. It is well established that compressional and shear wave velocities of common crystalline rocks increase with increasing densities (i.e. the Birch and Nafe-Drake relationships). Conventional empirical relations do not take into account S-wave velocity. Physical properties of Fe-oxides and massive sulfides, however, differ significantly from the empirical velocity-density relationships. Currently, acquiring in-situ density data is challenging and problematic, and therefore, developing an approximation for density based on seismic wave velocity and elastic moduli would be beneficial. With the goal of finding other possible or better relationships between density and the elastic moduli, a database of density, P-wave velocity, S-wave velocity, bulk modulus, shear modulus, Young's modulus, and Poisson's ratio was compiled based on a multitude of lab samples. The database is comprised of isotropic, non-porous metamorphic rock. Multi-parameter cross plots of the various elastic parameters have been analyzed in order to find a suitable parameter combination that reduces high density outliers. As expected, the P-wave velocity to S-wave velocity ratios show no correlation with density. However, Birch's seismic parameter, along with the bulk modulus, shows promise in providing a link between observed compressional and shear wave velocities and rock densities, including massive sulfides and Fe-oxides.

Magnetic Fluctuations in Pair-Density-Wave Superconductors

NASA Astrophysics Data System (ADS)

Christensen, Morten H.; Jacobsen, Henrik; Maier, Thomas A.; Andersen, Brian M.

2016-04-01

Pair-density-wave superconductivity constitutes a novel electronic condensate proposed to be realized in certain unconventional superconductors. Establishing its potential existence is important for our fundamental understanding of superconductivity in correlated materials. Here we compute the dynamical magnetic susceptibility in the presence of a pair-density-wave ordered state and study its fingerprints on the spin-wave spectrum including the neutron resonance. In contrast to the standard case of d -wave superconductivity, we show that the pair-density-wave phase exhibits neither a spin gap nor a magnetic resonance peak, in agreement with a recent neutron scattering experiment on underdoped La1.905 Ba0.095 CuO4 [Z. Xu et al., Phys. Rev. Lett. 113, 177002 (2014)].

Enhanced NMR Discrimination of Pharmaceutically Relevant Molecular Crystal Forms through Fragment-Based Ab Initio Chemical Shift Predictions.

PubMed

Hartman, Joshua D; Day, Graeme M; Beran, Gregory J O

2016-11-02

Chemical shift prediction plays an important role in the determination or validation of crystal structures with solid-state nuclear magnetic resonance (NMR) spectroscopy. One of the fundamental theoretical challenges lies in discriminating variations in chemical shifts resulting from different crystallographic environments. Fragment-based electronic structure methods provide an alternative to the widely used plane wave gauge-including projector augmented wave (GIPAW) density functional technique for chemical shift prediction. Fragment methods allow hybrid density functionals to be employed routinely in chemical shift prediction, and we have recently demonstrated appreciable improvements in the accuracy of the predicted shifts when using the hybrid PBE0 functional instead of generalized gradient approximation (GGA) functionals like PBE. Here, we investigate the solid-state 13 C and 15 N NMR spectra for multiple crystal forms of acetaminophen, phenobarbital, and testosterone. We demonstrate that the use of the hybrid density functional instead of a GGA provides both higher accuracy in the chemical shifts and increased discrimination among the different crystallographic environments. Finally, these results also provide compelling evidence for the transferability of the linear regression parameters mapping predicted chemical shieldings to chemical shifts that were derived in an earlier study.

Enhanced NMR Discrimination of Pharmaceutically Relevant Molecular Crystal Forms through Fragment-Based Ab Initio Chemical Shift Predictions

PubMed Central

2016-01-01

Chemical shift prediction plays an important role in the determination or validation of crystal structures with solid-state nuclear magnetic resonance (NMR) spectroscopy. One of the fundamental theoretical challenges lies in discriminating variations in chemical shifts resulting from different crystallographic environments. Fragment-based electronic structure methods provide an alternative to the widely used plane wave gauge-including projector augmented wave (GIPAW) density functional technique for chemical shift prediction. Fragment methods allow hybrid density functionals to be employed routinely in chemical shift prediction, and we have recently demonstrated appreciable improvements in the accuracy of the predicted shifts when using the hybrid PBE0 functional instead of generalized gradient approximation (GGA) functionals like PBE. Here, we investigate the solid-state 13C and 15N NMR spectra for multiple crystal forms of acetaminophen, phenobarbital, and testosterone. We demonstrate that the use of the hybrid density functional instead of a GGA provides both higher accuracy in the chemical shifts and increased discrimination among the different crystallographic environments. Finally, these results also provide compelling evidence for the transferability of the linear regression parameters mapping predicted chemical shieldings to chemical shifts that were derived in an earlier study. PMID:27829821

Theoretical calculation of electron-positron momentum density in YBa 2Cu 3O 7-δ

NASA Astrophysics Data System (ADS)

Massidda, S.

1990-07-01

We present calculations of the electron-positron momentum density for the high- Tc superconductor YBa 2Cu 3O 7-δ for δ=0 and for the insulating parent compound YBa 2Cu 3O 6, based on first-principle electronic structure calculations performed within the local density approximation (LDA) using the full potential linearized augmented plane wave (FLAPW) method. Our results indicate a small overlap of the positron wave function with the CuO 2 plane electrons and, as a consequence, relatively small signals due to the related Fermi surfaces. By contrast, the present calculations show, after the folding of Umklapp terms according to Lock, Crisp and West, clear Fermi surface breaks arising from the Cu-O chain bands. No general agreement with existing experiments allows a clear definition of Fermi surface structures in the latter. A comparison of the calculated momentum with the experimental two-dimensional angular correlation of annihilation radiation (2D-ACAR) recently measured in Geneva shows an overall agreement for the insulating compound, despite the spurious LDA metallic state, and possibly suggests the importance of O vacancies in experiments performed on non-stoichiometric YBa 2Cu 3O 7-δ samples.

MGS Radio Science Electron Density Profiles: Interannual Variability and Implications for the Martian Neutral Atmosphere

NASA Technical Reports Server (NTRS)

Bougher, S. W.; Engel, S.; Hinson, D. P.; Murphy, J. R.

2004-01-01

Martian electron density profiles provided by the Mars Global Surveyor (MGS) Radio Science (RS) experiment over the 95-200 km altitude range indicate what the height of the electron peak and the longitudinal structure of the peak height are sensitive indicators of the physical state of the Mars lower and upper atmospheres. The present analysis is carried out on five sets of occultation profiles, all at high solar zenith angles (SZA). Variations spanning 2 Martian years are investigated near aphelion conditions at high northern latitudes (64.7 - 77.6 N) making use of four of these data sets. A mean ionospheric peak height of 133.5 - 135 km is obtained near SZA = 78 - 82 deg.; a corresponding mean peak density of 7.3 - 8.5 x l0(exp 4)/ qu cm is also measured during solar moderate conditions at Mars. Strong wave number 2 - 3 oscillations in peak heights are consistently observed as a function of longitude over the 2 Martian years. These observed ionospheric features are remarkably similar during aphelion conditions 1 Martian year apart. This year-to-year repeatability in the thermosphere-ionosphere structure is consistent with that observed in multiyear aphelion temperature data of the Mars lower atmosphere. Coupled Mars general circulation model (MGCM) and Mars thermospheric general circulation model (MTGCM) codes are run for Mars aphelion conditions, yielding mean and longitude variable ionospheric peak heights that reasonably match RS observations. A tidal decomposition of MTGCM thermospheric densities shows that observed ionospheric wave number 3 features are linked to a non-migrating tidal mode with semidiurnal period (sigma = 2) and zonal wave number 1 (s = -1) characteristics. The height of this photochemically determined ionospheric peak should be monitored regularly.

Millimeter-wave imaging diagnostics systems on the EAST tokamak (invited)

NASA Astrophysics Data System (ADS)

Zhu, Y. L.; Xie, J. L.; Yu, C. X.; Zhao, Z. L.; Gao, B. X.; Chen, D. X.; Liu, W. D.; Liao, W.; Qu, C. M.; Luo, C.; Hu, X.; Spear, A. G.; Luhmann, N. C.; Domier, C. W.; Chen, M.; Ren, X.; Tobias, B. J.

2016-11-01

Millimeter-wave imaging diagnostics, with large poloidal span and wide radial range, have been developed on the EAST tokamak for visualization of 2D electron temperature and density fluctuations. A 384 channel (24 poloidal × 16 radial) Electron Cyclotron Emission Imaging (ECEI) system in F-band (90-140 GHz) was installed on the EAST tokamak in 2012 to provide 2D electron temperature fluctuation images with high spatial and temporal resolution. A co-located Microwave Imaging Reflectometry (MIR) will be installed for imaging of density fluctuations by December 2016. This "4th generation" MIR system has eight independent frequency illumination beams in W-band (75-110 GHz) driven by fast tuning synthesizers and active multipliers. Both of these advanced millimeter-wave imaging diagnostic systems have applied the latest techniques. A novel design philosophy "general optics structure" has been employed for the design of the ECEI and MIR receiver optics with large aperture. The extended radial and poloidal coverage of ECEI on EAST is made possible by innovations in the design of front-end optics. The front-end optical structures of the two imaging diagnostics, ECEI and MIR, have been integrated into a compact system, including the ECEI receiver and MIR transmitter and receiver. Two imaging systems share the same mid-plane port for simultaneous, co-located 2D fluctuation measurements of electron density and temperature. An intelligent remote-control is utilized in the MIR electronics systems to maintain focusing at the desired radial region even with density variations by remotely tuning the probe frequencies in about 200 μs. A similar intelligent technique has also been applied on the ECEI IF system, with remote configuration of the attenuations for each channel.

Compressive and rarefactive double layers in non-uniform plasma with q-nonextensive distributed electrons

NASA Astrophysics Data System (ADS)

Shan, S. Ali; Saleem, H.

2018-05-01

Electrostatic solitary waves and double layers (DLs) formed by the coupled ion acoustic (IA) and drift waves have been investigated in non-uniform plasma using q-nonextensive distribution function for the electrons and assuming ions to be cold Ti< Te. It is found that both compressive and rarefactive nonlinear structures (solitary waves and DLs) are possible in such a system. The steeper gradients are supportive for compressive solitary (and double layers) and destructive for rarefactive ones. The q-nonextensivity parameter q and the magnitudes of gradient scale lengths of density and temperature have significant effects on the amplitude of the double layers (and double layers) as well as on the speed of these structures. This theoretical model is general which has been applied here to the F-region ionosphere for illustration.

Structural, elastic, electronic, optical and thermoelectric properties of the Zintl-phase Ae3AlAs3 (Ae = Sr, Ba)

NASA Astrophysics Data System (ADS)

Benahmed, A.; Bouhemadou, A.; Alqarni, B.; Guechi, N.; Al-Douri, Y.; Khenata, R.; Bin-Omran, S.

2018-05-01

First-principles calculations were performed to investigate the structural, elastic, electronic, optical and thermoelectric properties of the Zintl-phase Ae3AlAs3 (Ae = Sr, Ba) using two complementary approaches based on density functional theory. The pseudopotential plane-wave method was used to explore the structural and elastic properties whereas the full-potential linearised augmented plane wave approach was used to study the structural, electronic, optical and thermoelectric properties. The calculated structural parameters are in good consistency with the corresponding measured ones. The single-crystal and polycrystalline elastic constants and related properties were examined in details. The electronic properties, including energy band dispersions, density of states and charge-carrier effective masses, were computed using Tran-Blaha modified Becke-Johnson functional for the exchange-correlation potential. It is found that both studied compounds are direct band gap semiconductors. Frequency-dependence of the linear optical functions were predicted for a wide photon energy range up to 15 eV. Charge carrier concentration and temperature dependences of the basic parameters of the thermoelectric properties were explored using the semi-classical Boltzmann transport model. Our calculations unveil that the studied compounds are characterised by a high thermopower for both carriers, especially the p-type conduction is more favourable.

Pressure-induced electronic topological transitions in the charge-density-wave material In 4 Se 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yuhang; Song, Liyan; Shao, Xuecheng

2017-08-01

High-pressure in situ angle dispersive X-ray diffraction (ADXRD) measurements were performed on the charge-density-wave (CDW) material In4Se3 up to 48.8 GPa. Pressure-induced structural changes were observed at 7.0 and 34.2 GPa, respectively. Using the CALYPSO methodology, the first high-pressure phase was solved as an exotic Pca21 structure. The compressional behaviors of the initial Pnnm and the Pca21 phases were all determined. Combined with first-principle calculations, we find that, unexpectedly, the Pnnm phase probably experiences twice electronic topological transitions (ETTs), from the initial possible CDW state to a semimetallic state at about 2.3 GPa and then back to a possible CDWmore » state at around 3.5 GPa, which was uncovered for the first time in CDW systems. In the both possible CDW states, pressure provokes a decrease of band-gap. The observation of a bulk metallic state was ascribed to structural transition to the Pca21 phase. Besides, based on electronic band structure calculations, the thermoelectric property of the Pnnm phase under compression was discussed. Our results show that pressure play a dramatic role in tuning In4Se3's structure and transport properties.« less

Initial Results of the Spread F Experiment (SpreadFEx): Overview and Evidence of Possible Gravity Wave Excitation of Equatorial Plasma Bubbles

NASA Astrophysics Data System (ADS)

Fritts, D. C.

2007-05-01

The Spread F Experiment (SpreadFEx) was performed in Brazil by Brazilian and U.S. researchers during two ~20- day periods extending from September to November 2005. We employed extensive ground-based and space- based observations of gravity waves, plasma structures, electron densities, and mean atmospheric and ionospheric conditions using airglow, digisonde, VHF and meteor radar, balloon, GPS and satellite instrumentation at multiple sites in Brazil and with GUVI aboard the TIMED satellite. These measurements focused on deep convection, gravity waves, and plasma bubble structures. This comprehensive data set has provided the first promising indications of the specific roles of gravity waves arising from deep convection and other sources in contributing to the seeding of equatorial spread F and plasma bubbles extending to high altitudes. This talk will summarize the campaign results related to possible neutral atmosphere seeding of spread F and plasma bubbles during these observations. Specifically, our measurements have revealed significant neutral density (and related wind and temperature) perturbations extending from ~80 km well into the thermosphere and ionosphere. Many of these appear to arise from deep convection over the Amazon basin. Others occurring at larger scales under magnetically-disturbed conditions may have auroral or other higher-latitude sources. Both appear to lead, on occasion, to sufficiently large perturbations of the bottomside F layer to trigger plasma bubbles extending to much higher altitudes thereafter. Upon completion of our analyses, we believe that these observations will yield the first persuasive evidence of the role of neutral atmosphere gravity waves in the seeding of equatorial plasma bubbles.

Numerical Simulation of Internal Waves in the Andaman Sea

NASA Astrophysics Data System (ADS)

Mohanty, Sachiko; Devendra Rao, Ambarukhana

2017-04-01

The interactions of barotropic tides with irregular bottom topography generate internal waves with high amplitude known as large-amplitude internal waves (LAIW) in the Andaman Sea. These waves are an important phenomena in the ocean due to their influence on the density structure and energy transfer into the region. These waves are also important in submarine acoustics, underwater navigation, offshore structures, ocean mixing, biogeochemical processes, etc. over the shelf-slope region. In the present study, energetics analysis of M2 internal tides over the Andaman Sea is carried out in detail by using a three-dimensional MIT general circulation ocean model (MITgcm). In-situ observations of temperature, conductivity and currents with high temporal resolution are used to validate the model simulations. From the spectral energy estimate of density, it is found that the peak estimate is associated with the semi-diurnal frequency at all the depths in both observations and model simulations. The baroclinic velocity characteristics, suggests that a multi-mode features of baroclinic tides are present at the buoy location. To understand the generation and propagation of internal tides over this region, energy flux and barotropic-to-baroclinic M2 tidal energy conversion rates are examined. The model simulation suggests that the internal tide is generated at multiple sites and propagate off of their respective generation sources. Most of the energy propagation in the Andaman Sea follows the 1000m isobath. The maximum horizontal kinetic energy follows the energy flux pattern over the domain and the available potential energy is found to be maximum in the north of the Andaman Sea.

Resolvability of regional density structure and the road to direct density inversion - a principal-component approach to resolution analysis

NASA Astrophysics Data System (ADS)

Płonka, Agnieszka; Fichtner, Andreas

2017-04-01

Lateral density variations are the source of mass transport in the Earth at all scales, acting as drivers of convective motion. However, the density structure of the Earth remains largely unknown since classic seismic observables and gravity provide only weak constraints with strong trade-offs. Current density models are therefore often based on velocity scaling, making strong assumptions on the origin of structural heterogeneities, which may not necessarily be correct. Our goal is to assess if 3D density structure may be resolvable with emerging full-waveform inversion techniques. We have previously quantified the impact of regional-scale crustal density structure on seismic waveforms with the conclusion that reasonably sized density variations within the crust can leave a strong imprint on both travel times and amplitudes, and, while this can produce significant biases in velocity and Q estimates, the seismic waveform inversion for density may become feasible. In this study we perform principal component analyses of sensitivity kernels for P velocity, S velocity, and density. This is intended to establish the extent to which these kernels are linearly independent, i.e. the extent to which the different parameters may be constrained independently. We apply the method to data from 81 events around the Iberian Penninsula, registered in total by 492 stations. The objective is to find a principal kernel which would maximize the sensitivity to density, potentially allowing for as independent as possible density resolution. We find that surface (mosty Rayleigh) waves have significant sensitivity to density, and that the trade-off with velocity is negligible. We also show the preliminary results of the inversion.

Density waves in granular flow

NASA Astrophysics Data System (ADS)

Herrmann, H. J.; Flekkøy, E.; Nagel, K.; Peng, G.; Ristow, G.

Ample experimental evidence has shown the existence of spontaneous density waves in granular material flowing through pipes or hoppers. Using Molecular Dynamics Simulations we show that several types of waves exist and find that these density fluctuations follow a 1/f spectrum. We compare this behaviour to deterministic one-dimensional traffic models. If positions and velocities are continuous variables the model shows self-organized criticality driven by the slowest car. We also present Lattice Gas and Boltzmann Lattice Models which reproduce the experimentally observed effects. Density waves are spontaneously generated when the viscosity has a nonlinear dependence on density which characterizes granular flow.

Shock-wave-like structures induced by an exothermic neutralization reaction in miscible fluids

NASA Astrophysics Data System (ADS)

Bratsun, Dmitry; Mizev, Alexey; Mosheva, Elena; Kostarev, Konstantin

2017-11-01

We report shock-wave-like structures that are strikingly different from previously observed fingering instabilities, which occur in a two-layer system of miscible fluids reacting by a second-order reaction A +B →S in a vertical Hele-Shaw cell. While the traditional analysis expects the occurrence of a diffusion-controlled convection, we show both experimentally and theoretically that the exothermic neutralization reaction can also trigger a wave with a perfectly planar front and nearly discontinuous change in density across the front. This wave propagates fast compared with the characteristic diffusion times and separates the motionless fluid and the area with anomalously intense convective mixing. We explain its mechanism and introduce a new dimensionless parameter, which allows to predict the appearance of such a pattern in other systems. Moreover, we show that our governing equations, taken in the inviscid limit, are formally analogous to well-known shallow-water equations and adiabatic gas flow equations. Based on this analogy, we define the critical velocity for the onset of the shock wave which is found to be in the perfect agreement with the experiments.

A projection-free method for representing plane-wave DFT results in an atom-centered basis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dunnington, Benjamin D.; Schmidt, J. R., E-mail: schmidt@chem.wisc.edu

2015-09-14

Plane wave density functional theory (DFT) is a powerful tool for gaining accurate, atomic level insight into bulk and surface structures. Yet, the delocalized nature of the plane wave basis set hinders the application of many powerful post-computation analysis approaches, many of which rely on localized atom-centered basis sets. Traditionally, this gap has been bridged via projection-based techniques from a plane wave to atom-centered basis. We instead propose an alternative projection-free approach utilizing direct calculation of matrix elements of the converged plane wave DFT Hamiltonian in an atom-centered basis. This projection-free approach yields a number of compelling advantages, including strictmore » orthonormality of the resulting bands without artificial band mixing and access to the Hamiltonian matrix elements, while faithfully preserving the underlying DFT band structure. The resulting atomic orbital representation of the Kohn-Sham wavefunction and Hamiltonian provides a gateway to a wide variety of analysis approaches. We demonstrate the utility of the approach for a diverse set of chemical systems and example analysis approaches.« less

Time-frequency energy density precipitation method for time-of-flight extraction of narrowband Lamb wave detection signals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Y., E-mail: thuzhangyu@foxmail.com; Huang, S. L., E-mail: huangsling@tsinghua.edu.cn; Wang, S.

The time-of-flight of the Lamb wave provides an important basis for defect evaluation in metal plates and is the input signal for Lamb wave tomographic imaging. However, the time-of-flight can be difficult to acquire because of the Lamb wave dispersion characteristics. This work proposes a time-frequency energy density precipitation method to accurately extract the time-of-flight of narrowband Lamb wave detection signals in metal plates. In the proposed method, a discrete short-time Fourier transform is performed on the narrowband Lamb wave detection signals to obtain the corresponding discrete time-frequency energy density distribution. The energy density values at the center frequency formore » all discrete time points are then calculated by linear interpolation. Next, the time-domain energy density curve focused on that center frequency is precipitated by least squares fitting of the calculated energy density values. Finally, the peak times of the energy density curve obtained relative to the initial pulse signal are extracted as the time-of-flight for the narrowband Lamb wave detection signals. An experimental platform is established for time-of-flight extraction of narrowband Lamb wave detection signals, and sensitivity analysis of the proposed time-frequency energy density precipitation method is performed in terms of propagation distance, dispersion characteristics, center frequency, and plate thickness. For comparison, the widely used Hilbert–Huang transform method is also implemented for time-of-flight extraction. The results show that the time-frequency energy density precipitation method can accurately extract the time-of-flight with relative error of <1% and thus can act as a universal time-of-flight extraction method for narrowband Lamb wave detection signals.« less

Time-frequency energy density precipitation method for time-of-flight extraction of narrowband Lamb wave detection signals.

PubMed

Zhang, Y; Huang, S L; Wang, S; Zhao, W

2016-05-01

The time-of-flight of the Lamb wave provides an important basis for defect evaluation in metal plates and is the input signal for Lamb wave tomographic imaging. However, the time-of-flight can be difficult to acquire because of the Lamb wave dispersion characteristics. This work proposes a time-frequency energy density precipitation method to accurately extract the time-of-flight of narrowband Lamb wave detection signals in metal plates. In the proposed method, a discrete short-time Fourier transform is performed on the narrowband Lamb wave detection signals to obtain the corresponding discrete time-frequency energy density distribution. The energy density values at the center frequency for all discrete time points are then calculated by linear interpolation. Next, the time-domain energy density curve focused on that center frequency is precipitated by least squares fitting of the calculated energy density values. Finally, the peak times of the energy density curve obtained relative to the initial pulse signal are extracted as the time-of-flight for the narrowband Lamb wave detection signals. An experimental platform is established for time-of-flight extraction of narrowband Lamb wave detection signals, and sensitivity analysis of the proposed time-frequency energy density precipitation method is performed in terms of propagation distance, dispersion characteristics, center frequency, and plate thickness. For comparison, the widely used Hilbert-Huang transform method is also implemented for time-of-flight extraction. The results show that the time-frequency energy density precipitation method can accurately extract the time-of-flight with relative error of <1% and thus can act as a universal time-of-flight extraction method for narrowband Lamb wave detection signals.

Dynamic instabilities in strongly correlated VSe2 monolayers and bilayers

NASA Astrophysics Data System (ADS)

Esters, Marco; Hennig, Richard G.; Johnson, David C.

2017-12-01

With the emergence of graphene and other two-dimensional (2D) materials, transition-metal dichalcogenides have been investigated intensely as potential 2D materials using experimental and theoretical methods. VSe2 is an especially interesting material since its bulk modification exhibits a charge-density wave (CDW), the CDW is retained even for few-layer nanosheets, and monolayers of VSe2 are predicted to be ferromagnetic. In this work, we show that electron correlation has a profound effect on the magnetic properties and dynamic stability of VSe2 monolayers and bilayers. Including a Hubbard-U term in the density-functional-theory calculations strongly affects the magnetocrystalline anisotropy in the 1 T -VSe2 structure while leaving the 2 H -polytype virtually unchanged. This demonstrates the importance of electronic correlations for the electrical and magnetic properties of 1 T -VSe2 . The Hubbard-U term changes the dynamic stability and the presence of imaginary modes of ferromagnetic 1 T -VSe2 while affecting only the amplitudes in the nonmagnetic phase. The Fermi surface of nonmagnetic 1 T -VSe2 allows for nesting along the CDW vector, but it plays no role in ferromagnetic 1 T -VSe2 . Following the eigenvectors of the soft modes in nonmagnetic 1 T -VSe2 monolayers yields a CDW structure with a 4 ×4 supercell and Peierls-type distortion in the atomic positions and electronic structure. The magnetic order indicates the potential for spin-density-wave structures.

Density Functional Calculations for the Neutron Star Matter at Subnormal Density

NASA Astrophysics Data System (ADS)

Kashiwaba, Yu; Nakatsukasa, Takashi

The pasta phases of nuclear matter, whose existence is suggested at low density, may influence observable properties of neutron stars. In order to investigate properties of the neutron star matter, we calculate self-consistent solutions for the ground states of slab-like phase using the microscopic density functional theory with Bloch wave functions. The calculations are performed at each point of fixed average density and proton fraction (\\bar{ρ },Yp), varying the lattice constant of the unit cell. For small Yp values, the dripped neutrons emerge in the ground state, while the protons constitute the slab (crystallized) structure. The shell effect of protons affects the thickness of the slab nuclei.

Prestack density inversion using the Fatti equation constrained by the P- and S-wave impedance and density

NASA Astrophysics Data System (ADS)

Liang, Li-Feng; Zhang, Hong-Bing; Dan, Zhi-Wei; Xu, Zi-Qiang; Liu, Xiu-Juan; Cao, Cheng-Hao

2017-03-01

Simultaneous prestack inversion is based on the modified Fatti equation and uses the ratio of the P- and S-wave velocity as constraints. We use the relation of P-wave impedance and density (PID) and S-wave impedance and density (SID) to replace the constant Vp/Vs constraint, and we propose the improved constrained Fatti equation to overcome the effect of P-wave impedance on density. We compare the sensitivity of both methods using numerical simulations and conclude that the density inversion sensitivity improves when using the proposed method. In addition, the random conjugate-gradient method is used in the inversion because it is fast and produces global solutions. The use of synthetic and field data suggests that the proposed inversion method is effective in conventional and nonconventional lithologies.

HELIOSEISMIC HOLOGRAPHY OF SIMULATED SUNSPOTS: MAGNETIC AND THERMAL CONTRIBUTIONS TO TRAVEL TIMES.

PubMed

Felipe, T; Braun, D C; Crouch, A D; Birch, A C

2016-10-01

Wave propagation through sunspots involves conversion between waves of acoustic and magnetic character. In addition, the thermal structure of sunspots is very different than that of the quiet Sun. As a consequence, the interpretation of local helioseismic measurements of sunspots has long been a challenge. With the aim of understanding these measurements, we carry out numerical simulations of wave propagation through sunspots. Helioseismic holography measurements made from the resulting simulated wavefields show qualitative agreement with observations of real sunspots. We use additional numerical experiments to determine, separately, the influence of the thermal structure of the sunspot and the direct effect of the sunspot magnetic field. We use the ray approximation to show that the travel-time shifts in the thermal (non-magnetic) sunspot model are primarily produced by changes in the wave path due to the Wilson depression rather than variations in the wave speed. This shows that inversions for the subsurface structure of sunspots must account for local changes in the density. In some ranges of horizontal phase speed and frequency there is agreement (within the noise level in the simulations) between the travel times measured in the full magnetic sunspot model and the thermal model. If this conclusion proves to be robust for a wide range of models, it would suggest a path toward inversions for sunspot structure.

HELIOSEISMIC HOLOGRAPHY OF SIMULATED SUNSPOTS: MAGNETIC AND THERMAL CONTRIBUTIONS TO TRAVEL TIMES

PubMed Central

Felipe, T.; Braun, D. C.; Crouch, A. D.; Birch, A. C.

2018-01-01

Wave propagation through sunspots involves conversion between waves of acoustic and magnetic character. In addition, the thermal structure of sunspots is very different than that of the quiet Sun. As a consequence, the interpretation of local helioseismic measurements of sunspots has long been a challenge. With the aim of understanding these measurements, we carry out numerical simulations of wave propagation through sunspots. Helioseismic holography measurements made from the resulting simulated wavefields show qualitative agreement with observations of real sunspots. We use additional numerical experiments to determine, separately, the influence of the thermal structure of the sunspot and the direct effect of the sunspot magnetic field. We use the ray approximation to show that the travel-time shifts in the thermal (non-magnetic) sunspot model are primarily produced by changes in the wave path due to the Wilson depression rather than variations in the wave speed. This shows that inversions for the subsurface structure of sunspots must account for local changes in the density. In some ranges of horizontal phase speed and frequency there is agreement (within the noise level in the simulations) between the travel times measured in the full magnetic sunspot model and the thermal model. If this conclusion proves to be robust for a wide range of models, it would suggest a path toward inversions for sunspot structure. PMID:29670301

HELIOSEISMIC HOLOGRAPHY OF SIMULATED SUNSPOTS: MAGNETIC AND THERMAL CONTRIBUTIONS TO TRAVEL TIMES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Felipe, T.; Braun, D. C.; Crouch, A. D.

Wave propagation through sunspots involves conversion between waves of acoustic and magnetic character. In addition, the thermal structure of sunspots is very different than that of the quiet Sun. As a consequence, the interpretation of local helioseismic measurements of sunspots has long been a challenge. With the aim of understanding these measurements, we carry out numerical simulations of wave propagation through sunspots. Helioseismic holography measurements made from the resulting simulated wavefields show qualitative agreement with observations of real sunspots. We use additional numerical experiments to determine, separately, the influence of the thermal structure of the sunspot and the direct effectmore » of the sunspot magnetic field. We use the ray approximation to show that the travel-time shifts in the thermal (non-magnetic) sunspot model are primarily produced by changes in the wave path due to the Wilson depression rather than variations in the wave speed. This shows that inversions for the subsurface structure of sunspots must account for local changes in the density. In some ranges of horizontal phase speed and frequency there is agreement (within the noise level in the simulations) between the travel times measured in the full magnetic sunspot model and the thermal model. If this conclusion proves to be robust for a wide range of models, it would suggest a path toward inversions for sunspot structure.« less

The effects of shock wave compaction on the transition temperatures of A15 structure superconductors

NASA Technical Reports Server (NTRS)

Otto, G. H.

1974-01-01

Several superconductors with the A15 structure exhibit a positive pressure coefficient, indicating that their transition temperatures increase with applied pressure. Powders of the composition Nb3Al, Nb3Ge, Nb3(Al0.75Ge0.25), and V3Si were compacted by explosive shock waves. The superconducting properties of these materials were measured before and after compaction and it was found that regardless of the sign of the pressure coefficient, the transition temperature is always lowered. The decrease in transition temperature is associated with a decrease in the particle diameter. The shock wave passage through a 3Nb:1Ge powder mixture leads to the formation of at least one compound (probably Nb5Ge3). However, the formation of the A15 compound Nb3Ge is not observed. Elemental niobium powder can be compacted by converging shock waves close to the expected value of the bulk density. Under special circumstances a partial remelting in the center of the sample is observed.

Optical Rogue Waves in Vortex Turbulence.

PubMed

Gibson, Christopher J; Yao, Alison M; Oppo, Gian-Luca

2016-01-29

We present a spatiotemporal mechanism for producing 2D optical rogue waves in the presence of a turbulent state with creation, interaction, and annihilation of optical vortices. Spatially periodic structures with bound phase lose stability to phase unbound turbulent states in complex Ginzburg-Landau and Swift-Hohenberg models with external driving. When the pumping is high and the external driving is low, synchronized oscillations are unstable and lead to spatiotemporal vortex-mediated turbulence with high excursions in amplitude. Nonlinear amplification leads to rogue waves close to turbulent optical vortices, where the amplitude tends to zero, and to probability density functions (PDFs) with long tails typical of extreme optical events.

Parabolic equation for nonlinear acoustic wave propagation in inhomogeneous moving media

NASA Astrophysics Data System (ADS)

Aver'yanov, M. V.; Khokhlova, V. A.; Sapozhnikov, O. A.; Blanc-Benon, Ph.; Cleveland, R. O.

2006-12-01

A new parabolic equation is derived to describe the propagation of nonlinear sound waves in inhomogeneous moving media. The equation accounts for diffraction, nonlinearity, absorption, scalar inhomogeneities (density and sound speed), and vectorial inhomogeneities (flow). A numerical algorithm employed earlier to solve the KZK equation is adapted to this more general case. A two-dimensional version of the algorithm is used to investigate the propagation of nonlinear periodic waves in media with random inhomogeneities. For the case of scalar inhomogeneities, including the case of a flow parallel to the wave propagation direction, a complex acoustic field structure with multiple caustics is obtained. Inclusion of the transverse component of vectorial random inhomogeneities has little effect on the acoustic field. However, when a uniform transverse flow is present, the field structure is shifted without changing its morphology. The impact of nonlinearity is twofold: it produces strong shock waves in focal regions, while, outside the caustics, it produces higher harmonics without any shocks. When the intensity is averaged across the beam propagating through a random medium, it evolves similarly to the intensity of a plane nonlinear wave, indicating that the transverse redistribution of acoustic energy gives no considerable contribution to nonlinear absorption.

Intermolecular shielding contributions studied by modeling the 13C chemical-shift tensors of organic single crystals with plane waves

PubMed Central

Johnston, Jessica C.; Iuliucci, Robbie J.; Facelli, Julio C.; Fitzgerald, George; Mueller, Karl T.

2009-01-01

In order to predict accurately the chemical shift of NMR-active nuclei in solid phase systems, magnetic shielding calculations must be capable of considering the complete lattice structure. Here we assess the accuracy of the density functional theory gauge-including projector augmented wave method, which uses pseudopotentials to approximate the nodal structure of the core electrons, to determine the magnetic properties of crystals by predicting the full chemical-shift tensors of all 13C nuclides in 14 organic single crystals from which experimental tensors have previously been reported. Plane-wave methods use periodic boundary conditions to incorporate the lattice structure, providing a substantial improvement for modeling the chemical shifts in hydrogen-bonded systems. Principal tensor components can now be predicted to an accuracy that approaches the typical experimental uncertainty. Moreover, methods that include the full solid-phase structure enable geometry optimizations to be performed on the input structures prior to calculation of the shielding. Improvement after optimization is noted here even when neutron diffraction data are used for determining the initial structures. After geometry optimization, the isotropic shift can be predicted to within 1 ppm. PMID:19831448

Anisotropic Magnetohydrodynamic Turbulence Driven by Parametric Decay Instability: The Onset of Phase Mixing and Alfvén Wave Turbulence

NASA Astrophysics Data System (ADS)

Shoda, Munehito; Yokoyama, Takaaki

2018-06-01

We conduct a 3D magnetohydrodynamic (MHD) simulation of the parametric decay instability of Alfvén waves and resultant compressible MHD turbulence, which is likely to develop in the solar wind acceleration region. Because of the presence of the mean magnetic field, the nonlinear stage is characterized by filament-like structuring and anisotropic cascading. By calculating the timescales of phase mixing and the evolution of Alfvén wave turbulence, we have found that the early nonlinear stage is dominated by phase mixing, while the later phase is dominated by imbalanced Alfvén wave turbulence. Our results indicate that the regions in the solar atmosphere with large density fluctuation, such as the coronal bottom and wind acceleration region, are heated by phase-mixed Alfvén waves, while the other regions are heated by Alfvén wave turbulence.

Shock wave structure in rarefied polyatomic gases with large relaxation time for the dynamic pressure

NASA Astrophysics Data System (ADS)

Taniguchi, Shigeru; Arima, Takashi; Ruggeri, Tommaso; Sugiyama, Masaru

2018-05-01

The shock wave structure in rarefied polyatomic gases is analyzed based on extended thermodynamics (ET). In particular, the case with large relaxation time for the dynamic pressure, which corresponds to large bulk viscosity, is considered by adopting the simplest version of extended thermodynamics with only 6 independent fields (ET6); the mass density, the velocity, the temperature and the dynamic pressure. Recently, the validity of the theoretical predictions by ET was confirmed by the numerical analysis based on the kinetic theory in [S Kosuge and K Aoki: Phys. Rev. Fluids, Vol. 3, 023401 (2018)]. It was shown that numerical results using the polyatomic version of ellipsoidal statistical model agree with the theoretical predictions by ET for small or moderately large Mach numbers. In the present paper, first, we compare the theoretical predictions by ET6 with the ones by kinetic theory for large Mach number under the same assumptions, that is, the gas is polytropic and the bulk viscosity is proportional to the temperature. Second, the shock wave structure for large Mach number in a non-polytropic gas is analyzed with the particular interest in the effect of the temperature dependence of specific heat and the bulk viscosity on the shock wave structure. Through the analysis of the case of a rarefied carbon dioxide (CO2) gas, it is shown that these temperature dependences play important roles in the precise analysis of the structure for strong shock waves.

Lamb Wave Assessment of Fatigue and Thermal Damage in Composites

NASA Technical Reports Server (NTRS)

Seale, Michael D.; Smith, Barry T.; Prosser, W. H.

2004-01-01

Among the various techniques available, ultrasonic Lamb waves offer a convenient method of evaluating composite materials. Since the Lamb wave velocity depends on the elastic properties of a structure, an effective tool exists to monitor damage in composites by measuring the velocity of these waves. Lamb wave measurements can propagate over long distances and are sensitive to the desired in-plane elastic properties of the material. This paper describes two studies which monitor fatigue damage and two studies which monitor thermal damage in composites using Lamb waves. In the fatigue studies, the Lamb wave velocity is compared to modulus measurements obtained using strain gage measurements in the first experiment and the velocity is monitored along with the crack density in the second. In the thermal damage studies, one examines samples which were exposed to varying temperatures for a three minute duration and the second includes rapid thermal damage in composites by intense laser beams. In all studies, the Lamb wave velocity is demonstrated to be an excellent method to monitor damage in composites.

Cd in SnO: Probing structural effects on the electronic structure of doped oxide semiconductors through the electric field gradient at the Cd nucleus

NASA Astrophysics Data System (ADS)

Errico, Leonardo A.; Rentería, Mario; Petrilli, Helena M.

2007-04-01

We perform an ab initio study of the electric field gradient (EFG) at the nucleus of Cd impurities at substitutional Sn sites in crystalline SnO. The full-potential linearized-augmented plane wave and the projector augmented wave methods used here allow us to treat the electronic structure of the doped system and the atomic relaxations introduced by the impurities in the host in a fully self-consistent way using a supercell approach in a state-of-the-art way. Effects of the impurity charge state on the electronic and structural properties are also discussed. Since the EFG is a very subtle quantity, its determination is very useful to probe ground-state properties such as the charge density. We show that the EFG is very sensitive to structural relaxations induced by the impurity. Our theoretical predictions are compared with available experimental results.

Transition from Propagating Polariton Solitons to a Standing Wave Condensate Induced by Interactions

NASA Astrophysics Data System (ADS)

Sich, M.; Chana, J. K.; Egorov, O. A.; Sigurdsson, H.; Shelykh, I. A.; Skryabin, D. V.; Walker, P. M.; Clarke, E.; Royall, B.; Skolnick, M. S.; Krizhanovskii, D. N.

2018-04-01

We explore phase transitions of polariton wave packets, first, to a soliton and then to a standing wave polariton condensate in a multimode microwire system, mediated by nonlinear polariton interactions. At low excitation density, we observe ballistic propagation of the multimode polariton wave packets arising from the interference between different transverse modes. With increasing excitation density, the wave packets transform into single-mode bright solitons due to effects of both intermodal and intramodal polariton-polariton scattering. Further increase of the excitation density increases thermalization speed, leading to relaxation of the polariton density from a solitonic spectrum distribution in momentum space down to low momenta, with the resultant formation of a nonequilibrium condensate manifested by a standing wave pattern across the whole sample.

Transition from Propagating Polariton Solitons to a Standing Wave Condensate Induced by Interactions.

PubMed

Sich, M; Chana, J K; Egorov, O A; Sigurdsson, H; Shelykh, I A; Skryabin, D V; Walker, P M; Clarke, E; Royall, B; Skolnick, M S; Krizhanovskii, D N

2018-04-20

We explore phase transitions of polariton wave packets, first, to a soliton and then to a standing wave polariton condensate in a multimode microwire system, mediated by nonlinear polariton interactions. At low excitation density, we observe ballistic propagation of the multimode polariton wave packets arising from the interference between different transverse modes. With increasing excitation density, the wave packets transform into single-mode bright solitons due to effects of both intermodal and intramodal polariton-polariton scattering. Further increase of the excitation density increases thermalization speed, leading to relaxation of the polariton density from a solitonic spectrum distribution in momentum space down to low momenta, with the resultant formation of a nonequilibrium condensate manifested by a standing wave pattern across the whole sample.

The non-Gaussian joint probability density function of slope and elevation for a nonlinear gravity wave field. [in ocean surface

NASA Technical Reports Server (NTRS)

Huang, N. E.; Long, S. R.; Bliven, L. F.; Tung, C.-C.

1984-01-01

On the basis of the mapping method developed by Huang et al. (1983), an analytic expression for the non-Gaussian joint probability density function of slope and elevation for nonlinear gravity waves is derived. Various conditional and marginal density functions are also obtained through the joint density function. The analytic results are compared with a series of carefully controlled laboratory observations, and good agreement is noted. Furthermore, the laboratory wind wave field observations indicate that the capillary or capillary-gravity waves may not be the dominant components in determining the total roughness of the wave field. Thus, the analytic results, though derived specifically for the gravity waves, may have more general applications.

Fast Ion and Thermal Plasma Transport in Turbulent Waves in the Large Plasma Device (LAPD)

NASA Astrophysics Data System (ADS)

Zhou, Shu

2011-10-01

The transport of fast ions and thermal plasmas in electrostatic microturbulence is studied. Strong density and potential fluctuations (δn / n ~ δϕ / kTe ~ 0 . 5 , f ~5-50 kHz) are observed in the LAPD in density gradient regions produced by obstacles with slab or cylindrical geometry. Wave characteristics and the associated plasma transport are modified by driving sheared E ×B drift through biasing the obstacle, and by modification of the axial magnetic fields (Bz) and the plasma species. Cross-field plasma transport is suppressed with small bias and large Bz, and is enhanced with large bias and small Bz. Suppressed cross-field thermal transport coincides with a 180° phase shift between the density and potential fluctuations in the radial direction, while the enhanced thermal transport is associated with modes having low mode number (m = 1) and long radial correlation length. Large gyroradius lithium ions (ρfast /ρs ~ 10) orbit through the turbulent region. Scans with a collimated analyzer and with Langmuir probes give detailed profiles of the fast ion spatial-temporal distribution and of the fluctuating fields. Fast-ion transport decreases rapidly with increasing fast-ion gyroradius. Background waves with different scale lengths also alter the fast ion transport: Beam diffusion is smaller in waves with smaller structures (higher mode number); also, coherent waves with long correlation length cause less beam diffusion than turbulent waves. Experimental results agree well with gyro-averaging theory. When the fast ion interacts with the wave for most of a wave period, a transition from super-diffusive to sub-diffusive transport is observed, as predicted by diffusion theory. A Monte Carlo trajectory-following code simulates the interaction of the fast ions with the measured turbulent fields. Good agreement between observation and modeling is observed. Work funded by DOE and NSF and performed at the Basic Plasma Science Facility.

Particle simulation of electromagnetic emissions from electrostatic instability driven by an electron ring beam on the density gradient

NASA Astrophysics Data System (ADS)

Horký, Miroslav; Omura, Yoshiharu; Santolík, Ondřej

2018-04-01

This paper presents the wave mode conversion between electrostatic and electromagnetic waves on the plasma density gradient. We use 2-D electromagnetic code KEMPO2 implemented with the generation of density gradient to simulate such a conversion process. In the dense region, we use ring beam instability to generate electron Bernstein waves and we study the temporal evolution of wave spectra, velocity distributions, Poynting flux, and electric and magnetic energies to observe the wave mode conversion. Such a conversion process can be a source of electromagnetic emissions which are routinely measured by spacecraft on the plasmapause density gradient.

Annular wave packets at Dirac points in graphene and their probability-density oscillation.

PubMed

Luo, Ji; Valencia, Daniel; Lu, Junqiang

2011-12-14

Wave packets in graphene whose central wave vector is at Dirac points are investigated by numerical calculations. Starting from an initial Gaussian function, these wave packets form into annular peaks that propagate to all directions like ripple-rings on water surface. At the beginning, electronic probability alternates between the central peak and the ripple-rings and transient oscillation occurs at the center. As time increases, the ripple-rings propagate at the fixed Fermi speed, and their widths remain unchanged. The axial symmetry of the energy dispersion leads to the circular symmetry of the wave packets. The fixed speed and widths, however, are attributed to the linearity of the energy dispersion. Interference between states that, respectively, belong to two branches of the energy dispersion leads to multiple ripple-rings and the probability-density oscillation. In a magnetic field, annular wave packets become confined and no longer propagate to infinity. If the initial Gaussian width differs greatly from the magnetic length, expanding and shrinking ripple-rings form and disappear alternatively in a limited spread, and the wave packet resumes the Gaussian form frequently. The probability thus oscillates persistently between the central peak and the ripple-rings. If the initial Gaussian width is close to the magnetic length, the wave packet retains the Gaussian form and its height and width oscillate with a period determined by the first Landau energy. The wave-packet evolution is determined jointly by the initial state and the magnetic field, through the electronic structure of graphene in a magnetic field. © 2011 American Institute of Physics

Global Simulation of Electromagnetic Ion Cyclotron Waves

NASA Technical Reports Server (NTRS)

Khazanov, George V.; Gallagher, D. L.; Kozyra, J. U.

2007-01-01

It is very well known that the effects of electromagnetic ion cyclotron (EMIC) waves on ring current (RC) ion and radiation belt (RB) electron dynamics strongly depend on such particle/wave characteristics as the phase-space distribution function, frequency, wave-normal angle, wave energy, and the form of wave spectral energy density. The consequence is that accurate modeling of EMIC waves and RC particles requires robust inclusion of the interdependent dynamics of wave growth/damping, wave propagation, and particles. Such a self-consistent model is being progressively developed by Khazanov et al. This model is based on a system of coupled kinetic equations for the RC and EMIC wave power spectral density along with the ray tracing equations. We will discuss the recent progress in understanding EMIC waves formation mechanisms in the inner magnetosphere. This problem remains unsettled in spite of many years of experimental and theoretical studies. Modern satellite observations by CRRES, Polar and Cluster still do not reveal the whole picture experimentally since they do not stay long enough in the generation region to give a full account of all the spatio-temporal structure of EMIC waves. The complete self-consistent theory taking into account all factors significant for EMIC waves generation remains to be developed. Several mechanisms are discussed with respect to formation of EMIC waves, among them are nonlinear modification of the ionospheric reflection by precipitating energetic protons, modulation of ion-cyclotron instability by long-period (Pc3/4) pulsations, reflection of waves from layers of heavy-ion gyroresonances, and nonlinearities of wave generation process. We show that each of these mechanisms have their attractive features and explains certain part experimental data but any of them, if taken alone, meets some difficulties when compared to observations. We conclude that development of a refined nonlinear theory and further correlated analysis of modern satellite and ground-based data is needed to solve this very intriguing problem.

Global Simulation of Electromagnetic Ion Cyclotron Waves

NASA Technical Reports Server (NTRS)

Khazanov, G. V.; Gamayunov, K.; Gallagher, D. L.; Kozyra, J. U.

2007-01-01

It is well known that the effects of electromagnetic ion cyclotron (EMIC) waves on ring current (RC) ion and radiation belt (RB) electron dynamics strongly depend on such particle/wave characteristics as the phase-space distribution function, frequency, wave-normal angle, wave energy, and the form of wave spectral energy density. The consequence is that accurate modeling of EMIC waves and RC particles requires robust inclusion of the interdependent dynamics of wave growth/damping, wave propagation, and particles. Such a self-consistent model is being progressively developed by Khazanov et al. [2002 - 2007]. This model is based on a system of coupled kinetic equations for the RC and EMIC wave power spectral density along with the ray tracing equations. We will discuss the recent progress in understanding EMIC waves formation mechanisms in the inner magnetosphere. This problem remains unsettled in spite of many years of experimental and theoretical studies. Modern satellite observations by CRRES, Polar and Cluster still do not reveal the whole picture experimentally since they do not stay long enough in the generation region to give a full account of all the spatio-temporal structure of EMIC waves. The complete self-consistent theory taking into account all factors significant for EMIC waves generation remains to be developed. Several mechanisms are discussed with respect to formation of EMIC waves, among them are nonlinear modification of the ionospheric reflection by precipitating energetic protons, modulation of ion-cyclotron instability by long-period (Pc3/4) pulsations, reflection of waves from layers of heavy-ion gyroresonances, and nonlinearities of wave generation process. We show that each of these mechanisms have their attractive features and explains certain part experimental data but any of them, if taken alone, meets some difficulties when compared to observations. We conclude that development of a refined nonlinear theory and further correlated analysis of modern satellite and ground-based data is needed to solve this very intriguing problem.

Superluminal and negative delay times in isotropic-anisotropic one-dimensional photonic crystal

NASA Astrophysics Data System (ADS)

Ouchani, N.; El Moussaouy, A.; Aynaou, H.; El Hassouani, Y.; El Boudouti, E. H.; Djafari-Rouhani, B.

2017-11-01

In this work, we investigate the possibility of superluminal and negative delay times for electromagnetic wave propagation in a linear and passive periodic structure consisting of alternating isotropic and anisotropic media. This phenomenon is due to the birefringence of the anisotropic layers of the structure. By adjusting the orientations of these layers, the delay times of transmitted waves can be controlled from subluminality to superluminality and vice versa. Numerical results indicate that the apparent superluminal propagation of light occurs inside the photonic band-gaps when the principal axes of the anisotropic layers are parallel or perpendicular to the fixed axes. For other orientations of these layers, tunneling and superluminal regimes appear inside the photonic bandgaps and in the allowed bands for frequencies close to the transmission minima. The effect of the number of unit cells of the photonic crystal structure on the propagation of light with superluminal and negative delay times is also investigated. We show that the structure exhibits the Hartman effect in which the tunneling delay time of the electromagnetic wave through the photonic band-gap of the structure converges asymptotically to a finite value with increasing the number of layers. The Green's function approach has been used to derive the transmission and reflection coefficients, the density of states, and the delay times of electromagnetic waves propagating through the structure. The control of the magnitude and the sign of the delay time of light propagation represent a key point in slow and fast light technologies. The proposed structure in this study represents a new system for controlling the delay times of wave propagation without a need of active or non-linear media as well as lossy or asymmetric periodic structures.

Magnetosonic solitons in semiconductor plasmas in the presence of quantum tunneling and exchange correlation effects

NASA Astrophysics Data System (ADS)

Hussain, S.; Mahmood, S.

2018-01-01

Low frequency magnetosonic wave excitations are investigated in semiconductor hole-electron plasmas. The quantum mechanical effects such as Fermi pressure, quantum tunneling, and exchange-correlation of holes and electrons in the presence of the magnetic field are considered. The two fluid quantum magnetohydrodynamic model is used to study magnetosonic wave dynamics, while electric and magnetic fields are coupled via Maxwell equations. The dispersion relation of the magnetosonic wave in electron-hole semiconductor plasma propagating in the perpendicular direction of the magnetic field is obtained, and its dispersion effects are discussed. The Korteweg-de Vries equation (KdV) for magnetosonic solitons is derived by employing the reductive perturbation method. For numerical analysis, the plasma parameters are taken from the semiconductors such as GaAs, GaSb, GaN, and InP already existing in the literature. It is found that the phase velocity of the magnetosonic wave is increased with the inclusion of exchange-correlation force in the model. The soliton dip structures of the magnetosonic wave in GaN semiconductor plasma are obtained, which satisfy the quantum plasma conditions for electron and hole fluids. The magnetosonic soliton dip structures move with speed less than the magnetosonic wave phase speed in the lab frame. The effects of exchange-correlation force in the model and variations of magnetic field intensity and electron/hole density on the magnetosonic wave dip structures are also investigated numerically for illustration.

Large-scale structure of randomly jammed spheres

NASA Astrophysics Data System (ADS)

Ikeda, Atsushi; Berthier, Ludovic; Parisi, Giorgio

2017-05-01

We numerically analyze the density field of three-dimensional randomly jammed packings of monodisperse soft frictionless spherical particles, paying special attention to fluctuations occurring at large length scales. We study in detail the two-point static structure factor at low wave vectors in Fourier space. We also analyze the nature of the density field in real space by studying the large-distance behavior of the two-point pair correlation function, of density fluctuations in subsystems of increasing sizes, and of the direct correlation function. We show that such real space analysis can be greatly improved by introducing a coarse-grained density field to disentangle genuine large-scale correlations from purely local effects. Our results confirm that both Fourier and real space signatures of vanishing density fluctuations at large scale are absent, indicating that randomly jammed packings are not hyperuniform. In addition, we establish that the pair correlation function displays a surprisingly complex structure at large distances, which is however not compatible with the long-range negative correlation of hyperuniform systems but fully compatible with an analytic form for the structure factor. This implies that the direct correlation function is short ranged, as we also demonstrate directly. Our results reveal that density fluctuations in jammed packings do not follow the behavior expected for random hyperuniform materials, but display instead a more complex behavior.

Supporting Structure of the LSD Wave in an Energy Absorption Perspective

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fukui, Akihiro; Hatai, Keigo; Cho, Shinatora

In Repetitively Pulsed (RP) Laser Propulsion, laser energy irradiated to a vehicle is converted to blast wave enthalpy during the Laser Supported Detonation (LSD) regime. Based on the measured post-LSD electron number density profiles by two-wavelength Mach Zehnder interferometer in a line-focusing optics, electron temperature and absorption coefficient were estimated assuming Local Thermal Equilibrium. A 10J/pulse CO{sub 2} laser was used. As a result, laser absorption was found completed in the layer between the shock wave and the electron density peak. Although the LSD-termination timing was not clear from the shock-front/ionization-front separation in the shadowgraph images, there observed drastic changesmore » in the absorption layer thickness from 0.2 mm to 0.5 mm and in the peak heating rate from 12-17x10{sup 13} kW/m{sup 3} to 5x10{sup 13} kW/m{sup 3} at the termination.« less

Remote sensing the plasmasphere, plasmapause, plumes and other features using ground-based magnetometers

NASA Astrophysics Data System (ADS)

Menk, Frederick; Kale, Zoë; Sciffer, Murray; Robinson, Peter; Waters, Colin; Grew, Russell; Clilverd, Mark; Mann, Ian

2014-11-01

The plasmapause is a highly dynamic boundary between different magnetospheric particle populations and convection regimes. Some of the most important space weather processes involve wave-particle interactions in this region, but wave properties may also be used to remote sense the plasmasphere and plasmapause, contributing to plasmasphere models. This paper discusses the use of existing ground magnetometer arrays for such remote sensing. Using case studies we illustrate measurement of plasmapause location, shape and movement during storms; refilling of flux tubes within and outside the plasmasphere; storm-time increase in heavy ion concentration near the plasmapause; and detection and mapping of density irregularities near the plasmapause, including drainage plumes, biteouts and bulges. We also use a 2D MHD model of wave propagation through the magnetosphere, incorporating a realistic ionosphere boundary and Alfvén speed profile, to simulate ground array observations of power and cross-phase spectra, hence confirming the signatures of plumes and other density structures.

Magnetoacoustic Waves and the Kelvin-Helmholtz Instability in a Steady Asymmetric Slab. I: The Effects of Varying Density Ratios

NASA Astrophysics Data System (ADS)

Barbulescu, M.; Erdélyi, R.

2018-06-01

Recent observations have shown that bulk flow motions in structured solar plasmas, most evidently in coronal mass ejections (CMEs), may lead to the formation of Kelvin-Helmholtz instabilities (KHIs). Analytical models are thus essential in understanding both how the flows affect the propagation of magnetohydrodynamic (MHD) waves, and what the critical flow speed is for the formation of the KHI. We investigate both these aspects in a novel way: in a steady magnetic slab embedded in an asymmetric environment. The exterior of the slab is defined as having different equilibrium values of the background density, pressure, and temperature on either side. A steady flow and constant magnetic field are present in the slab interior. Approximate solutions to the dispersion relation are obtained analytically and classified with respect to mode and speed. General solutions and the KHI thresholds are obtained numerically. It is shown that, generally, both the KHI critical value and the cut-off speeds for magnetoacoustic waves are lowered by the external asymmetry.

Wave propagation in equivalent continuums representing truss lattice materials

DOE PAGES

Messner, Mark C.; Barham, Matthew I.; Kumar, Mukul; ...

2015-07-29

Stiffness scales linearly with density in stretch-dominated lattice meta-materials offering the possibility of very light yet very stiff structures. Current additive manufacturing techniques can assemble structures from lattice materials, but the design of such structures will require accurate, efficient simulation methods. Equivalent continuum models have several advantages over discrete truss models of stretch dominated lattices, including computational efficiency and ease of model construction. However, the development an equivalent model suitable for representing the dynamic response of a periodic truss in the small deformation regime is complicated by microinertial effects. This study derives a dynamic equivalent continuum model for periodic trussmore » structures suitable for representing long-wavelength wave propagation and verifies it against the full Bloch wave theory and detailed finite element simulations. The model must incorporate microinertial effects to accurately reproduce long wavelength characteristics of the response such as anisotropic elastic soundspeeds. Finally, the formulation presented here also improves upon previous work by preserving equilibrium at truss joints for simple lattices and by improving numerical stability by eliminating vertices in the effective yield surface.« less

Externally driven magnetic granular layers at a liquid/air interface: self-organization, flows and magnetic order

NASA Astrophysics Data System (ADS)

Snezhko, Alexey

2007-03-01

Collective dynamics and pattern formation in ensembles of magnetic microparticles suspended at the liquid/air interface and subjected to an alternating magnetic field are studied. Experiments reveal a new type of nontrivially ordered dynamic self-assembled structures (``snakes'') emerging in such systems in a certain range of field magnitudes and frequencies. These remarkable structures are directly related to surface waves in the liquid generated by the collective response of magnetic microparticles to the alternating magnetic field. In addition, a large-scale vortex flows are induced in the vicinity of the dynamic structures. Some features of the self-localized snake structures can be understood in the framework of an amplitude equation for parametric waves coupled to the conservation law equation describing the evolution of the magnetic particle density. Self-assembled snakes have a complex magnetic order: the segments of the snake exhibit long-range antiferromagnetic ordering mediated by the surface wave, while each segment is composed of ferromagnetically aligned chains of microparticles. A phenomenological model describing magnetic behavior of the magnetic snakes in external magnetic fields is proposed.

Tidal waves within the thermosphere. [emphasizing wave dissipation and diffusion

NASA Technical Reports Server (NTRS)

Volland, H.; Mayr, H. G.

1974-01-01

The eigenfunctions of the atmosphere (the Hough functions within the lower atmosphere below about 100 km) change their structure and their propagation characteristics within the thermosphere due to dissipation effects such as heat conduction, viscosity, and ion drag. Wave dissipation can be parameterized to a first-order approximation by a complex frequency, the imaginary term of which simulates an effective ion drag force. It is shown how the equivalent depth, the attenuation, and the vertical wavelength of the predominant symmetric diurnal tidal modes change with height as functions of effective ion drag. The boundary conditions of tidal waves are discussed, and asymptotic solutions for the wave parameters like pressure, density, temperature, and wind generated by a heat input proportional to the mean pressure are given. Finally, diffusion effects upon the minor constituents within the thermosphere are described.

Lattice vibrations in the Frenkel-Kontorova model. I. Phonon dispersion, number density, and energy

NASA Astrophysics Data System (ADS)

Meng, Qingping; Wu, Lijun; Welch, David O.; Zhu, Yimei

2015-06-01

We studied the lattice vibrations of two interpenetrating atomic sublattices via the Frenkel-Kontorova (FK) model of a linear chain of harmonically interacting atoms subjected to an on-site potential using the technique of thermodynamic Green's functions based on quantum field-theoretical methods. General expressions were deduced for the phonon frequency-wave-vector dispersion relations, number density, and energy of the FK model system. As the application of the theory, we investigated in detail cases of linear chains with various periods of the on-site potential of the FK model. Some unusual but interesting features for different amplitudes of the on-site potential of the FK model are discussed. In the commensurate structure, the phonon spectrum always starts at a finite frequency, and the gaps of the spectrum are true ones with a zero density of modes. In the incommensurate structure, the phonon spectrum starts from zero frequency, but at a nonzero wave vector; there are some modes inside these gap regions, but their density is very low. In our approximation, the energy of a higher-order commensurate state of the one-dimensional system at a finite temperature may become indefinitely close to the energy of an incommensurate state. This finding implies that the higher-order incommensurate-commensurate transitions are continuous ones and that the phase transition may exhibit a "devil's staircase" behavior at a finite temperature.

Laboratory Characterization of Talley Brick

DTIC Science & Technology

2011-08-01

specimen’s wet, bulk, or “as-tested” density. Results from these determinations are provided in Table 1. Measurements of posttest water content1...ASTM 2005d). Based on the appropriate values of posttest water content, wet density, and an assumed grain density of 2.89 Mg/m3, values of dry... Posttest Axial P Radial P Axial S Radial S Wet Water Dry Degree of ’Wave ’Wave ’Wave \\Vave Test Density Conte-nt, Density, Porosity, Saturation

Empirical relationships among resilience indicators on Micronesian reefs

USGS Publications Warehouse

Mumby, P.J.; Bejarano, S.; Golbuu, Y.; Steneck, R.S.; Arnold, S.N.; van Woesik, R.; Friedlander, A.M.

2013-01-01

A process-orientated understanding of ecosystems usually starts with an exploratory analysis of empirical relationships among potential drivers and state variables. While relationships among herbivory, algal cover, and coral recruitment, have been explored in the Caribbean, the nature of such relationships in the Pacific appears to be variable or unclear. Here, we examine potential drivers structuring the benthos and herbivorous fish assemblages of outer-shelf reefs in Micronesia (Palau, Guam and Pohnpei). Surveys were stratified by wave exposure and protection from fishing. High biomass of most herbivores was favoured by high wave exposure. High abundance of large-bodied scarids was associated with low turf abundance, high coral cover, and marine reserves. The remaining herbivores were more abundant in reefs with low coral cover, possibly because space and hence food limitation occur in high-coral-cover reefs. Rugosity had no detectable effect on herbivorous fish abundance once differences in exposure and coral cover were accounted for. At identical depths, high wave exposure was associated with greater volumes (cover × canopy height) of macroalgae and algal turfs, which most likely resulted from high primary productivity driven by flow. In exposed areas, macroalgal cover declined as the acanthurid biomass increased. The volume of algal turfs was negatively associated with coral cover and herbivore biomass. In turn, high coral cover and herbivore biomass are likely to intensify grazing. The density of juvenile corals was variable where macroalgal cover was low but was confined to lower densities where macroalgal cover was high. High coral cover and density of juvenile corals were favoured in sheltered habitats. While a weak positive relationship was found between scarid biomass and juvenile coral density, we hypothesise that high scarid densities may hinder juvenile density through increased corallivory. New hypotheses emerged that will help clarify the role of acanthurids, wave exposure, and corallivory in driving the recovery of Pacific coral communities.

Self-injection of electrons in a laser-wakefield accelerator by using longitudinal density ripple

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dahiya, Deepak; Sharma, A. K.; Sajal, Vivek

By introducing a longitudinal density ripple (periodic modulation in background plasma density), we demonstrate self-injection of electrons in a laser-wakefield accelerator. The wakefield driven plasma wave, in presence of density ripple excites two side band waves of same frequency but different wave numbers. One of these side bands, having smaller phase velocity compared to wakefield driven plasma wave, preaccelerates the background plasma electrons. Significant number of these preaccelerated electrons get trapped in the laser-wakefield and further accelerated to higher energies.

Resolvability of regional density structure

NASA Astrophysics Data System (ADS)

Plonka, A.; Fichtner, A.

2016-12-01

Lateral density variations are the source of mass transport in the Earth at all scales, acting as drivers of convectivemotion. However, the density structure of the Earth remains largely unknown since classic seismic observables and gravityprovide only weak constraints with strong trade-offs. Current density models are therefore often based on velocity scaling,making strong assumptions on the origin of structural heterogeneities, which may not necessarily be correct. Our goal is to assessif 3D density structure may be resolvable with emerging full-waveform inversion techniques. We have previously quantified the impact of regional-scale crustal density structure on seismic waveforms with the conclusion that reasonably sized density variations within thecrust can leave a strong imprint on both travel times and amplitudes, and, while this can produce significant biases in velocity and Q estimates, the seismic waveform inversion for density may become feasible. In this study we performprincipal component analyses of sensitivity kernels for P velocity, S velocity, and density. This is intended to establish theextent to which these kernels are linearly independent, i.e. the extent to which the different parameters may be constrainedindependently. Since the density imprint we observe is not exclusively linked to travel times and amplitudes of specific phases,we consider waveform differences between complete seismograms. We test the method using a known smooth model of the crust and seismograms with clear Love and Rayleigh waves, showing that - as expected - the first principal kernel maximizes sensitivity to SH and SV velocity structure, respectively, and that the leakage between S velocity, P velocity and density parameter spaces is minimal in the chosen setup. Next, we apply the method to data from 81 events around the Iberian Penninsula, registered in total by 492 stations. The objective is to find a principal kernel which would maximize the sensitivity to density, potentially allowing for independent density resolution, and, as the final goal, for direct density inversion.

Structure of the crust and upper mantle in the western United States

USGS Publications Warehouse

Pakiser, L.C.

1963-01-01

Seismic waves generated by underground nuclear and chemical explosions have been recorded in a network of nearly 2,000 stations in the western conterminous United States as a part of the VELA UNIFORM program. The network extends from eastern Colorado to the California coastline and from central Idaho to the border of the United States and Mexico. The speed of compressional waves in the upper-mantle rocks ranges from 7.7 km/sec in the southern part of the Basin and Range province to 8.2 km/sec in the Great Plains province. In general, the speed of compressional waves in the upper-mantle rocks tends to be nearly the same over large areas within individual geologic provinces. Measured crustal thickness ranges from less than 20 km in the Central Valley of California to 50 km in the Great Plains province. Changes in crustal thickness across provincial boundaries are not controlled by regional altitude above sea level unless the properties of the upper mantle are the same across those boundaries. The crust tends to be thick in regions where the speed of compressional waves in the upper-mantle rocks (and presumably the density) is high, and tends to be relatively thin where the speed of compressional waves in the upper-mantle rocks (and density) is lower. With in the Basin and Range province, crustal thickness seems to vary directly with regional altitude above sea level. Evidence that a layer of intermediate compressional-wave speed exists in the lower part of the crust has been accumulated from seismic waves that have traveled least-time paths, as well as secondary arrivals (particularly reflections). On a scale that includes many geologic provinces, isostatic compensation is related largely to variations in the density of the upper- mantle rocks. Within geologic provinces or adjacent provinces, isostatic compensation may be related to variations in the thickness of crustal layers. Regions of thick crust and dense upper mantle have been relatively stable in Cenozoic time. Regions of thinner crust and low-density upper mantle have had a Cenozoic history of intense diastrophism and silicic volcanism.

Systematic structure of the neutron drip-line {sup 22}C nucleus

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ismail, Atef; Cheong, Lee Yen; Yahya, Noorhana

2014-10-24

In the present work we systematically discuss the nuclear structure of the the heaviest particle-bound carbon isotope, {sup 22}C. The ground state wave function of the carbon isotope is calculated using the {sup 20}C core plus two-valence neutron based on a phenomenological mean-field MF potential. We apply the deduced wave function to provide the nuclear matter density which is necessary in the calculations of the total reaction cross section. Calculations show that there is a reasonable good description of the experimental binding energy BE and root-mean square RMS radius. The exotic structure and configuration of the ground state carbon isotopemore » is explained and a consistent explanation on the two-neutron halo (Borromean) nucleus is given.« less

Tunable band-stop plasmonic waveguide filter with symmetrical multiple-teeth-shaped structure.

PubMed

Wang, Hongqing; Yang, Junbo; Zhang, Jingjing; Huang, Jie; Wu, Wenjun; Chen, Dingbo; Xiao, Gongli

2016-03-15

A nanometeric plasmonic filter with a symmetrical multiple-teeth-shaped structure is investigated theoretically and numerically. A tunable wide bandgap is achievable by adjusting the depth and number of teeth. This phenomenon can be attributed to the interference superposition of the reflected and transmitted waves from each tooth. Moreover, the effects of varying the number of identical teeth are also discussed. It is found that the bandgap width increases continuously with the increasing number of teeth. The finite difference time domain method is used to simulate and compute the coupling of surface plasmon polariton waves with different structures in this Letter. The plasmonic waveguide filter that we propose here may have meaningful applications in ultra-fine spectrum analysis and high-density nanoplasmonic integration circuits.

Negative refraction, surface modes, and superlensing effect via homogenization near resonances for a finite array of split-ring resonators.

PubMed

Farhat, M; Guenneau, S; Enoch, S; Movchan, A B

2009-10-01

We present a theoretical and numerical analysis of liquid surface waves (LSWs) localized at the boundary of a phononic crystal consisting of split-ring resonators (SRRs). We first derive the homogenized parameters of the fluid-filled structure using a three-scale asymptotic expansion in the linearized Navier-Stokes equations. In the limit when the wavelength of the LSW is much larger than the typical heterogeneity size of the phononic crystal, we show that it behaves as an artificial fluid with an anisotropic effective shear modulus and a dispersive effective-mass density. We then analyze dispersion diagrams associated with LSW propagating within an infinite array of SRR, for which eigensolutions are sought in the form of Floquet-Bloch waves. The main emphasis is given to the study of localized modes within such a periodic fluid-filled structure and to the control of low-frequency stop bands associated with resonances of SRRs. Considering a macrocell, we are able to compute the dispersion of LSW supported by a semi-infinite phononic crystal of SRRs. We find that the dispersion of this evanescent mode nearly sits within the first stop band of the doubly periodic structure. We further discover that it is linked to the frequency at which the effective-mass density of the homogenized phononic crystal becomes negative. We demonstrate that this surface mode displays the hallmarks of all-angle negative refraction and it leads to a superlensing effect. Last, we note that our homogenization results for the velocity potential can be applied mutatis mutandis to designs of electromagnetic and acoustic superlenses for transverse electric waves propagating in arrays of infinite conducting SRRs and antiplane shear waves in arrays of cracks shaped as SRRs.

Mantle discontinuities mapped by inversion of global surface wave data

NASA Astrophysics Data System (ADS)

Khan, A.; Boschi, L.; Connolly, J.

2009-12-01

We invert global observations of fundamental and higher order Love and Rayleigh surface-wave dispersion data jointly at selected locations for 1D radial profiles of Earth's mantle composition, thermal state and anisotropic structure using a stochastic sampling algorithm. Considering mantle compositions as equilibrium assemblages of basalt and harzburgite, we employ a self-consistent thermodynamic method to compute their phase equilibria and bulk physical properties (P, S wave velocity and density). Combining these with locally varying anisotropy profiles, we determine anisotropic P and S wave velocities to calculate dispersion curves for comparison with observations. Models fitting data within uncertainties, provide us with a range of profiles of composition, temperature and anisotropy. This methodology presents an important complement to conventional seismic tomograpy methods. Our results indicate radial and lateral gradients in basalt fraction, with basalt depletion in the upper and enrichment of the upper part of the lower mantle, in agreement with results from geodynamical calculations, melting processes at mid-ocean ridges and subduction of chemically stratified lithosphere. Compared with PREM and seismic tomography models, our velocity models are generally faster in the upper transition zone (TZ), and slower in the lower TZ, implying a steeper velocity gradient. While less dense than PREM, density gradients in the TZ are also steeper. Mantle geotherms are generally adiabatic in the TZ, whereas in the upper part of the lower mantle stronger lateral variations are observed. The TZ structure, and thus location of the phase transitions in the Olivine system as well as their physical properties, are found to be controlled to a large degree by thermal rather than compositional variations. The retrieved anistropy structure agrees with previous studies indicating positive as well as laterally varying upper mantle anisotropy, while there is little evidence for anisotropy in and below the TZ.

The role of density discontinuity in the inviscid instability of two-phase parallel flows

NASA Astrophysics Data System (ADS)

Behzad, M.; Ashgriz, N.

2014-02-01

We re-examine the inviscid instability of two-phase parallel flows with piecewise linear velocity profiles. Although such configuration has been theoretically investigated, we employ the concept of waves resonance to physically interpret the instability mechanism as well as the essential role of density discontinuity in the flow. Upon performing linear stability analysis, we demonstrate the existence of neutrally stable "density" and "density-vorticity" waves which are emerged due to the density jump in the flow, in addition to the well-known vorticity waves. Such waves are capable of resonating with each other to form unstable modes in the flow. Although unstable modes in this study are classified as the "shear instability" type, we demonstrate that they are not necessarily of the Rayleigh type. The results also show that the density can have both stabilizing and destabilizing effects on the flow stability. We verify that the difference in the resonating pair of neutral waves leads to such distinct behavior of the density variation.

Observation of Landau quantization and standing waves in HfSiS

NASA Astrophysics Data System (ADS)

Jiao, L.; Xu, Q. N.; Qi, Y. P.; Wu, S.-C.; Sun, Y.; Felser, C.; Wirth, S.

2018-05-01

Recently, HfSiS was found to be a new type of Dirac semimetal with a line of Dirac nodes in the band structure. Meanwhile, Rashba-split surface states are also pronounced in this compound. Here we report a systematic study of HfSiS by scanning tunneling microscopy/spectroscopy at low temperature and high magnetic field. The Rashba-split surface states are characterized by measuring Landau quantization and standing waves, which reveal a quasilinear dispersive band structure. First-principles calculations based on density-functional theory are conducted and compared with the experimental results. Based on these investigations, the properties of the Rashba-split surface states and their interplay with defects and collective modes are discussed.

Alfven resonance mode conversion in the Phaedrus-T current drive experiments: Modelling and density fluctuations measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vukovic, M.; Harper, M.; Breun, R.

1995-12-31

Current drive experiments on the Phaedrus-T tokamak performed with a low field side two-strap fast wave antenna at frequencies below {omega}{sub cH} show loop volt drops of up to 30% with strap phasing (0, {pi}/2). RF induced density fluctuations in the plasma core have also been observed with a microwave reflectometer. It is believed that they are caused by kinetic Alfven waves generated by mode conversion of fast waves at the Alfven resonance. Correlation of the observed density fluctuations with the magnitude of the {Delta}V{sub loop} suggest that the {Delta}V{sub loop} is attributable to current drive/heating due to mode convertedmore » kinetic Alfven waves. The toroidal cold plasma wave code LION is used to model the Alfven resonance mode conversion surfaces in the experiments while the cylindrical hot plasma kinetic wave code ISMENE is used to model the behavior of kinetic Alfven waves at the Alfven resonance location. Initial results obtained from limited density, magnetic field, antenna phase, and impurity scans show good agreement between the RF induced density fluctuations and the predicted behavior of the kinetic Alfven waves. Detailed comparisons between the density fluctuations and the code predictions are presented.« less

Wave energy analysis based on simulation wave data in the China Sea

NASA Astrophysics Data System (ADS)

Gao, Zhan-sheng; Qian, Yu-hao; Sui, Yu-wei; Chen, Xuan; Zhang, Da

2018-05-01

In the current world, where human beings are severely plagued by environmental problems and energy crisis, the full and reasonable utilization of marine new energy resources will contribute to alleviating the energy crisis, contributing to global energy-saving, emission reduction and environmental protection, thus to promote sustainable development. In this study, we firstly simulated a 10-year (1991-2000) 6-hourly wave data of the China Sea, by using the Simulating WAves Nearshore (SWAN) wave model nested with WAVEWATCH-III (WW3) wave model forced with Cross-Calibrated, Multi-Platform (CCMP) wind data. Considering the value size and stability of the wave energy density, we analyzed the overall characteristics of the China Sea wave energy with using the simulation wave data. Results show that: (1) The wave energy density in January and October is distinctly higher than that in April and July. The large center of annual average Wave energy density is located in the north of the South China Sea (of about 12-16 kW/m). (2) Synthetically considering the value size and stability of the wave energy density and stability, the energy-rich area is found to be located in the north region of the South China Sea.

Heating and background plasma modification associated with large amplitude kinetic Alfv'en wave launch in LAPD

NASA Astrophysics Data System (ADS)

Carter, T. A.; Auerbach, D. W.; Brugman, B. T.

2007-11-01

Large amplitude kinetic Alfv'en waves (δB/B ˜1% > k/k) are generated in the Large Plasma Device (LAPD) at UCLA using loop antennas. Substantial electron heating is observed, localized to the wave current channels. The Poynting flux associated with the Alfv'en waves is substantial and the observed heating may be at least in part due to collisional and Landau damping of these waves. However, heating by antenna near inductive electric fields may also be responsible for the observations. A discussion of both possibilities will be presented, including measurements of near fields of the antenna. The heating structures the background plasma and results in the excitation of drift-Alfv'en waves. These drift waves then interact with the incident Alfv'en wave, causing sideband generation which results in a nearly broadband state at high wave power. This process may represent an alternate mechanism by which unidirectional kinetic Alfv'en waves can nonlinearly generate a turbulent spectrum. In addition to electron heating, evidence for background density modification and electron acceleration is observed and will be presented.

Semiclassical dynamics of spin density waves

NASA Astrophysics Data System (ADS)

Chern, Gia-Wei; Barros, Kipton; Wang, Zhentao; Suwa, Hidemaro; Batista, Cristian D.

2018-01-01

We present a theoretical framework for equilibrium and nonequilibrium dynamical simulation of quantum states with spin-density-wave (SDW) order. Within a semiclassical adiabatic approximation that retains electron degrees of freedom, we demonstrate that the SDW order parameter obeys a generalized Landau-Lifshitz equation. With the aid of an enhanced kernel polynomial method, our linear-scaling quantum Landau-Lifshitz dynamics (QLLD) method enables dynamical SDW simulations with N ≃105 lattice sites. Our real-space formulation can be used to compute dynamical responses, such as the dynamical structure factor, of complex and even inhomogeneous SDW configurations at zero or finite temperatures. Applying the QLLD to study the relaxation of a noncoplanar topological SDW under the excitation of a short pulse, we further demonstrate the crucial role of spatial correlations and fluctuations in the SDW dynamics.

Advanced capabilities for materials modelling with Quantum ESPRESSO

NASA Astrophysics Data System (ADS)

Giannozzi, P.; Andreussi, O.; Brumme, T.; Bunau, O.; Buongiorno Nardelli, M.; Calandra, M.; Car, R.; Cavazzoni, C.; Ceresoli, D.; Cococcioni, M.; Colonna, N.; Carnimeo, I.; Dal Corso, A.; de Gironcoli, S.; Delugas, P.; DiStasio, R. A., Jr.; Ferretti, A.; Floris, A.; Fratesi, G.; Fugallo, G.; Gebauer, R.; Gerstmann, U.; Giustino, F.; Gorni, T.; Jia, J.; Kawamura, M.; Ko, H.-Y.; Kokalj, A.; Küçükbenli, E.; Lazzeri, M.; Marsili, M.; Marzari, N.; Mauri, F.; Nguyen, N. L.; Nguyen, H.-V.; Otero-de-la-Roza, A.; Paulatto, L.; Poncé, S.; Rocca, D.; Sabatini, R.; Santra, B.; Schlipf, M.; Seitsonen, A. P.; Smogunov, A.; Timrov, I.; Thonhauser, T.; Umari, P.; Vast, N.; Wu, X.; Baroni, S.

2017-11-01

Quantum EXPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the-art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudopotential and projector-augmented-wave approaches. Quantum EXPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement their ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software.

Advanced capabilities for materials modelling with Quantum ESPRESSO.

PubMed

Giannozzi, P; Andreussi, O; Brumme, T; Bunau, O; Buongiorno Nardelli, M; Calandra, M; Car, R; Cavazzoni, C; Ceresoli, D; Cococcioni, M; Colonna, N; Carnimeo, I; Dal Corso, A; de Gironcoli, S; Delugas, P; DiStasio, R A; Ferretti, A; Floris, A; Fratesi, G; Fugallo, G; Gebauer, R; Gerstmann, U; Giustino, F; Gorni, T; Jia, J; Kawamura, M; Ko, H-Y; Kokalj, A; Küçükbenli, E; Lazzeri, M; Marsili, M; Marzari, N; Mauri, F; Nguyen, N L; Nguyen, H-V; Otero-de-la-Roza, A; Paulatto, L; Poncé, S; Rocca, D; Sabatini, R; Santra, B; Schlipf, M; Seitsonen, A P; Smogunov, A; Timrov, I; Thonhauser, T; Umari, P; Vast, N; Wu, X; Baroni, S

2017-10-24

Quantum EXPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the-art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudopotential and projector-augmented-wave approaches. Quantum EXPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement their ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software.

Advanced capabilities for materials modelling with Quantum ESPRESSO.

PubMed

Andreussi, Oliviero; Brumme, Thomas; Bunau, Oana; Buongiorno Nardelli, Marco; Calandra, Matteo; Car, Roberto; Cavazzoni, Carlo; Ceresoli, Davide; Cococcioni, Matteo; Colonna, Nicola; Carnimeo, Ivan; Dal Corso, Andrea; de Gironcoli, Stefano; Delugas, Pietro; DiStasio, Robert; Ferretti, Andrea; Floris, Andrea; Fratesi, Guido; Fugallo, Giorgia; Gebauer, Ralph; Gerstmann, Uwe; Giustino, Feliciano; Gorni, Tommaso; Jia, Junteng; Kawamura, Mitsuaki; Ko, Hsin-Yu; Kokalj, Anton; Küçükbenli, Emine; Lazzeri, Michele; Marsili, Margherita; Marzari, Nicola; Mauri, Francesco; Nguyen, Ngoc Linh; Nguyen, Huy-Viet; Otero-de-la-Roza, Alberto; Paulatto, Lorenzo; Poncé, Samuel; Giannozzi, Paolo; Rocca, Dario; Sabatini, Riccardo; Santra, Biswajit; Schlipf, Martin; Seitsonen, Ari Paavo; Smogunov, Alexander; Timrov, Iurii; Thonhauser, Timo; Umari, Paolo; Vast, Nathalie; Wu, Xifan; Baroni, Stefano

2017-09-27

Quantum ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudo-potential and projector-augmented-wave approaches. Quantum ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement theirs ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software. © 2017 IOP Publishing Ltd.

Local Real-Space View of the Achiral 1 T -TiSe2 2 ×2 ×2 Charge Density Wave

NASA Astrophysics Data System (ADS)

Hildebrand, B.; Jaouen, T.; Mottas, M.-L.; Monney, G.; Barreteau, C.; Giannini, E.; Bowler, D. R.; Aebi, P.

2018-03-01

The transition metal dichalcogenide 1 T -TiSe2 -two-dimensional layered material undergoing a commensurate 2 ×2 ×2 charge density wave (CDW) transition with a weak periodic lattice distortion (PLD) below ≈200 K . Scanning tunneling microscopy (STM) combined with intentionally introduced interstitial Ti atoms allows us to go beyond the usual spatial resolution of STM and to intimately probe the three-dimensional character of the PLD. Furthermore, the inversion-symmetric achiral nature of the CDW in the z direction is revealed, contradicting the claimed existence of helical CDW stacking and associated chiral order. This study paves the way to a simultaneous real-space probing of both charge and structural reconstructions in CDW compounds.

Mantle Flow in the Western United States Constrained by Seismic Anisotropy

NASA Astrophysics Data System (ADS)

Niday, W.; Humphreys, E.

2017-12-01

Shear wave splitting, caused by the lattice preferred orientation (LPO) of olivine crystals under shear deformation, provide a useful constraint on numerical models of mantle flow. Although it is sometimes assumed that shear wave splitting fast directions correspond with mantle flow directions, this is only true in simple shear flows that do not vary strongly with space or time. Observed shear wave splitting in the western United States is complex and inconsistent with simple shear driven by North American and Pacific plate motion, suggesting that the effects of time-dependent subduction history and spatial heterogeneity are important. Liu and Stegman (2011) reproduce the pattern of fast seismic anomalies below the western US from Farallon subduction history, and Chaparro and Stegman (2017) reproduce the circular anisotropy field below the Great Basin. We extend this to consider anisotropic structure outside the Great Basin and evaluate the density and viscosity of seismic anomalies such as slabs and Yellowstone. We use the mantle convection code ASPECT to simulate 3D buoyancy-driven flow in the mantle below the western US, and predict LPO using the modeled flow fields. We present results from a suite of models varying the sub-lithospheric structures of the western US and constraints on density and viscosity variations in the upper mantle.

Study of cavity type antenna structure of large-area 915 MHz ultra-high frequency wave plasma device based on three-dimensional finite difference time-domain analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Xijiang; Graduate School of Science and Engineering, Shizuoka University, 3-5-1 Johoku, Hamamatsu 432-8561; Kunii, Kazuki

2013-11-14

A large-area planar plasma source with a resonant cavity type launcher driven by a 915 MHz ultra-high frequency wave was developed. Theoretical analysis with the three-dimensional finite difference time-domain simulation was carried out to determine the optimized launcher structure by analyzing the resonant transverse magnetic mode in the resonant cavity. Numerical result expects that the resonant electric field distribution inside the cavity dominantly consists of the TM{sub 410} mode. The resonant cavity type launcher having 8 holes in an octagonal geometry was designed to fit the resonant transverse magnetic mode. Adjusting 8 hole positions of the launcher to the fieldmore » pattern of the resonant TM{sub 410} mode, we found that the plasma density increased about 40%∼50% from 1.0∼1.1 × 10{sup 11} cm{sup −3} to ∼1.5 × 10{sup 11} cm{sup −3} at the same incident power of 2.5 kW, compared with the previous results with the launcher having 6 holes in the hexagonal geometry. It is also noted that the electron density changes almost linearly with the incident wave power without any mode jumps.« less

Evidence of m = 1 density mode (plasma cam) in Saturn's rotating magnetosphere

NASA Astrophysics Data System (ADS)

Goldstein, J.; Waite, J. H.; Burch, J. L.; Livi, R.

2016-03-01

Cassini field and plasma data measured in the rotating Saturn Longitude System 3 (SLS3) coordinate system show positive evidence of structure whose dominant azimuthal wave number is m = 1: a long-lived, nonaxisymmetric, cam-shaped, global plasma distribution in Saturn's magnetosphere. Previous studies have identified evidence of this plasma cam in wave-derived electron density data and in Cassini Plasma Spectrometer (CAPS) W+ ion counts data. In this paper we report the first comprehensive analysis of CAPS ion moments data to identify the m = 1 density cam. We employ a multiyear, multispecies database of 685,678 CAPS density values, binned into a 1 RS by 4.8° discretized grid, spanning 4-19 RS. Fourier (harmonic) analysis shows that at most radial distances the dominant azimuthal mode is m = 1, for both W+ and H+ ion distributions. The majority (63%) of m = 1 ion peaks are clustered in an SLS3 quadrant centered at 330°. The plasma cam's existence has important implications for the global interchange-driven convection cycle and is a clue to solving the mystery of the rotational periodicities in Saturn's magnetosphere.

Comparison of fine structures of electron cyclotron harmonic emissions in aurora

NASA Astrophysics Data System (ADS)

LaBelle, J.; Dundek, M.

2015-10-01

Recent discoveries of higher harmonic cyclotron emissions in aurora occurring under daylight conditions motivated the modification of radio receivers at South Pole Station, Antarctica, to measure fine structure of such emissions during two consecutive austral summers, 2013-2014 and 2014-2015. The experiment recorded 347 emission events over 376 days of observation. The seasonal distribution of these events reveals that successively higher harmonics require higher solar zenith angles for occurrence, as expected if they are generated at the matching condition fuh = Nfce, which for higher N requires higher electron densities which are associated with higher solar zenith angles. This result implies that generation of higher harmonics from lower harmonics via wave-wave processes explains only a minority of events. Detailed examination of 21 cases in which two harmonics occur simultaneously shows that in almost all events the higher harmonic comes from higher altitudes, and only for a small fraction of events is it plausible that the frequencies of the fine structures of the emissions are correlated and in exact integer ratio. This observation puts an upper bound of 15-20% on the fraction of emissions which can be explained by wave-wave interactions involving Z mode waves at fce and, combined with consideration of source altitudes, puts an upper bound of 75% on the fraction explained by coalescence of Z mode waves at 2fce. Taken together, these results suggest that the dominant mechanism for the higher harmonics is independent generation at the matching points fuh = Nfce and that the wave-wave interaction mechanisms explain a relatively small fraction of events.

Collective transport for active matter run-and-tumble disk systems on a traveling-wave substrate

DOE PAGES

Sándor, Csand; Libál, Andras; Reichhardt, Charles; ...

2017-01-17

Here, we examine numerically the transport of an assembly of active run-and-tumble disks interacting with a traveling-wave substrate. We show that as a function of substrate strength, wave speed, disk activity, and disk density, a variety of dynamical phases arise that are correlated with the structure and net flux of disks. We find that there is a sharp transition into a state in which the disks are only partially coupled to the substrate and form a phase-separated cluster state. This transition is associated with a drop in the net disk flux, and it can occur as a function of themore » substrate speed, maximum substrate force, disk run time, and disk density. Since variation of the disk activity parameters produces different disk drift rates for a fixed traveling-wave speed on the substrate, the system we consider could be used as an efficient method for active matter species separation. Within the cluster phase, we find that in some regimes the motion of the cluster center of mass is in the opposite direction to that of the traveling wave, while when the maximum substrate force is increased, the cluster drifts in the direction of the traveling wave. This suggests that swarming or clustering motion can serve as a method by which an active system can collectively move against an external drift.« less

Collective transport for active matter run-and-tumble disk systems on a traveling-wave substrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sándor, Csand; Libál, Andras; Reichhardt, Charles

Here, we examine numerically the transport of an assembly of active run-and-tumble disks interacting with a traveling-wave substrate. We show that as a function of substrate strength, wave speed, disk activity, and disk density, a variety of dynamical phases arise that are correlated with the structure and net flux of disks. We find that there is a sharp transition into a state in which the disks are only partially coupled to the substrate and form a phase-separated cluster state. This transition is associated with a drop in the net disk flux, and it can occur as a function of themore » substrate speed, maximum substrate force, disk run time, and disk density. Since variation of the disk activity parameters produces different disk drift rates for a fixed traveling-wave speed on the substrate, the system we consider could be used as an efficient method for active matter species separation. Within the cluster phase, we find that in some regimes the motion of the cluster center of mass is in the opposite direction to that of the traveling wave, while when the maximum substrate force is increased, the cluster drifts in the direction of the traveling wave. This suggests that swarming or clustering motion can serve as a method by which an active system can collectively move against an external drift.« less

Solid-state structures and properties of scandium hydride; hydrogen storage and switchable mirrors application

NASA Astrophysics Data System (ADS)

Khodja, Khadidja; Bouhadda, Youcef; Seddik, Larbi; Benyelloul, Kamel

2016-05-01

First-principles calculation has been performed on the rare earth hydride ScH2 for hydrogen storage and switchable mirror applications, using the pseudo-potentials and plane waves based on the density-functional theory (DFT). The electronic and structural properties are studied within both local-density and generalized gradient approximations for exchange energy. The formation energy and the optical properties have been investigated and discussed. Our calculated results are generally in good agreement with theoretical and experimental data. Contribution to the topical issue "Materials for Energy Harvesting, Conversion and Storage (ICOME 2015) - Elected submissions", edited by Jean-Michel Nunzi, Rachid Bennacer and Mohammed El Ganaoui

Electric Field and Plasma Density Observations of Irregularities and Plasma Instabilities in the Low Latitude Ionosphere Gathered by the C/NOFS Satellite

NASA Technical Reports Server (NTRS)

Pfaff, Robert F.; Freudenreich, H.; Rowland, D.; Klenzing, J.; Liebrecht, C.

2012-01-01

The Vector Electric Field Investigation (VEFI) on the C/NOFS equatorial satellite provides a unique data set which includes detailed measurements of irregularities associated with the equatorial ionosphere and in particular with spread-F depletions. We present vector AC electric field observations gathered on C/NOFS that address a variety of key questions regarding how plasma irregularities, from meter to kilometer scales, are created and evolve. The talk focuses on occasions where the ionosphere F-peak has been elevated above the C/NOFS satellite perigee of 400 km as solar activity has increased. In particular, during the equinox periods of 2011, the satellite consistently journeyed below the F-peak whenever the orbit was in the region of the South Atlantic anomaly after sunset. During these passes, data from the electric field and plasma density probes on the satellite have revealed two types of instabilities which had not previously been observed in the C/NOFS data set: The first is evidence for 400-500km-scale bottomside "undulations" that appear in the density and electric field data. In one case, these large scale waves are associated with a strong shear in the zonal E x B flow, as evidenced by variations in the meridional (outward) electric fields observed above and below the F-peak. These undulations are devoid of smaller scale structures in the early evening, yet appear at later local times along the same orbit associated with fully-developed spread-F with smaller scale structures. This suggests that they may be precursor waves for spread-F, driven by a collisional shear instability, following ideas advanced previously by researchers using data from the Jicamarca radar. A second result is the appearance of km-scale irregularities that are a common feature in the electric field and plasma density data that also appear when the satellite is near or below the F-peak at night. The vector electric field instrument on C/NOFS clearly shows that the electric field component of these waves is strongest in the zonal direction. These waves are strongly correlated with simultaneous observations of plasma density oscillations and appear both with, and without, evidence of larger-scale spread-F depletions. These km-scale, quasi-coherent waves strongly resemble the bottomside, sinusoidal irregularities reported in the Atmosphere Explorer satellite data set by Valladares et al. and are believed to cause scintillations of VHF radiowaves. We interpret these new observations in terms of fundamental plasma instabilities associated with the unstable, nighttime equatorial ionosphere.

Observation of helicon wave with m = 0 antenna in a weakly magnetized inductively coupled plasma source

NASA Astrophysics Data System (ADS)

Ellingboe, Bert; Sirse, Nishant; Moloney, Rachel; McCarthy, John

2015-09-01

Bounded whistler wave, called ``helicon wave,'' is known to produce high-density plasmas and has been exploited as a high density plasma source for many applications, including electric propulsion for spacecraft. In a helicon plasma source, an antenna wrapped around the magnetized plasma column launches a low frequency wave, ωce/2 >ωhelicon >ωce/100, in the plasma which is responsible for maintaining high density plasma. Several antenna designs have been proposed in order to match efficiently the wave modes. In our experiment, helicon wave mode is observed using an m = 0 antenna. A floating B dot probe, compensated to the capacitively coupled E field, is employed to measure axial-wave-field-profiles (z, r, and θ components) in the plasma at multiple radial positions as a function of rf power and pressure. The Bθ component of the rf-field is observed to be unaffected as the wave propagates in the axial direction. Power coupling between the antenna and the plasma column is identified and agrees with the E, H, and wave coupling regimes previously seen in M =1 antenna systems. That is, the Bz component of the rf-field is observed at low plasma density as the Bz component from the antenna penetrates the plasma. The Bz component becomes very small at medium density due to shielding at the centre of the plasma column; however, with increasing density, a sudden ``jump'' occurs in the Bz component above which a standing wave under the antenna with a propagating wave away from the antenna are observed.

Nonlinear propagation of ion-acoustic waves in electron-positron-ion plasma with trapped electrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alinejad, H.; Sobhanian, S.; Mahmoodi, J.

2006-01-15

A theoretical investigation has been made for ion-acoustic waves in an unmagnetized electron-positron-ion plasma. A more realistic situation in which plasma consists of a negatively charged ion fluid, free positrons, and trapped as well as free electrons is considered. The properties of stationary structures are studied by the reductive perturbation method, which is valid for small but finite amplitude limit, and by pseudopotential approach, which is valid for large amplitude. With an appropriate modified form of the electron number density, two new equations for the ion dynamics have been found. When deviations from isothermality are finite, the modified Korteweg-deVries equationmore » has been found, and for the case that deviations from isothermality are small, calculations lead to a generalized Korteweg-deVries equation. It is shown from both weakly and highly nonlinear analysis that the presence of the positrons may allow solitary waves to exist. It is found that the effect of the positron density changes the maximum value of the amplitude and M (Mach number) for which solitary waves can exist. The present theory is applicable to analyze arbitrary amplitude ion-acoustic waves associated with positrons which may occur in space plasma.« less

Ionospheric tomography using Faraday rotation of Automatic Dependent Surveillance Broadcast (UHF) signals Ionospheric Measurement From ADS-B Signals

NASA Astrophysics Data System (ADS)

Cushley, Alex Clay

The proposed launch of a CubeSat carrying the first space-borne ADS-B receiver by RMCC will create a unique opportunity to study the modification of radio waves following propagation through the ionosphere as the signals propagate from the transmitting aircraft to the passive satellite receiver(s). Experimental work is described which successfully demonstrated that ADS-B data can be used to reconstruct two-dimensional electron density maps of the ionosphere using techniques from computerized tomography. Ray-tracing techniques are used to determine the characteristics of individual waves, including the wave path and the state of polarization at the satellite receiver. The modelled Faraday rotation is determined and converted to TEC along the ray-paths. The resulting TEC is used as input for CIT using ART. This study concentrated on meso-scale structures 100--1000 km in horizontal extent. The primary scientific interest of this thesis was to show the feasibility of a new method to image the ionosphere and obtain a better understanding of magneto-ionic wave propagation. Keywords: Automatic Dependent Surveillance-Broadcast (ADS-B), Faraday rotation, electromagnetic (EM) waves, radio frequency (RF) propagation, ionosphere (auroral, irregularities, instruments and techniques), electron density profile, total electron content (TEC), computer ionospheric tomography (CIT), algebraic reconstruction technique (ART).

Local Fitting of the Kohn-Sham Density in a Gaussian and Plane Waves Scheme for Large-Scale Density Functional Theory Simulations.

PubMed

Golze, Dorothea; Iannuzzi, Marcella; Hutter, Jürg

2017-05-09

A local resolution-of-the-identity (LRI) approach is introduced in combination with the Gaussian and plane waves (GPW) scheme to enable large-scale Kohn-Sham density functional theory calculations. In GPW, the computational bottleneck is typically the description of the total charge density on real-space grids. Introducing the LRI approximation, the linear scaling of the GPW approach with respect to system size is retained, while the prefactor for the grid operations is reduced. The density fitting is an O(N) scaling process implemented by approximating the atomic pair densities by an expansion in one-center fit functions. The computational cost for the grid-based operations becomes negligible in LRIGPW. The self-consistent field iteration is up to 30 times faster for periodic systems dependent on the symmetry of the simulation cell and on the density of grid points. However, due to the overhead introduced by the local density fitting, single point calculations and complete molecular dynamics steps, including the calculation of the forces, are effectively accelerated by up to a factor of ∼10. The accuracy of LRIGPW is assessed for different systems and properties, showing that total energies, reaction energies, intramolecular and intermolecular structure parameters are well reproduced. LRIGPW yields also high quality results for extended condensed phase systems such as liquid water, ice XV, and molecular crystals.

Projected quasiparticle theory for molecular electronic structure

NASA Astrophysics Data System (ADS)

Scuseria, Gustavo E.; Jiménez-Hoyos, Carlos A.; Henderson, Thomas M.; Samanta, Kousik; Ellis, Jason K.

2011-09-01

We derive and implement symmetry-projected Hartree-Fock-Bogoliubov (HFB) equations and apply them to the molecular electronic structure problem. All symmetries (particle number, spin, spatial, and complex conjugation) are deliberately broken and restored in a self-consistent variation-after-projection approach. We show that the resulting method yields a comprehensive black-box treatment of static correlations with effective one-electron (mean-field) computational cost. The ensuing wave function is of multireference character and permeates the entire Hilbert space of the problem. The energy expression is different from regular HFB theory but remains a functional of an independent quasiparticle density matrix. All reduced density matrices are expressible as an integration of transition density matrices over a gauge grid. We present several proof-of-principle examples demonstrating the compelling power of projected quasiparticle theory for quantum chemistry.

Structural, elastic and electronic properties of transition metal carbides ZnC, NbC and their ternary alloys ZnxNb1-xC

NASA Astrophysics Data System (ADS)

Zidi, Y.; Méçabih, S.; Abbar, B.; Amari, S.

2018-02-01

We have investigated the structural, electronic and elastic properties of transition-metal carbides ZnxNb1-xC alloys in the range of 0 ≤ x ≤ 1 using the density functional theory (DFT). The full potential linearized augmented plane wave (FP-LAPW) method within a framework of the generalized gradient approximation (GGA) and GGA + U (where U is the Hubbard correlation terms) approach is used to perform the calculations presented here. The lattice parameters, the bulk modulus, its pressure derivative and the elastic constants were determined. We have obtained Young's modulus, shear modulus, Poisson's ratio, anisotropy factor by the aid of the calculated elastic constants. We discuss the total and partial densities of states and charge densities.

Structural, Electronic and Elastic Properties of Half-Heusler Alloys CrNiZ (Z = Al, Si, Ge and As)

NASA Astrophysics Data System (ADS)

Zitouni, A.; Benstaali, W.; Abbad, A.; Lantri, T.; Bouadjemi, B.; Aziz, Z.

2018-06-01

In the present work, a self-consistent ab-initio calculation using the full- potential linearized augmented plane wave (FP-LAPW) method within the framework of the spin-polarized density functional theory (DFT) was used to study the structural, electronic, magnetic and elastic properties of the half Heusler alloys CrNiZ (Z = Al, Si, Ge and As) in three phases ( α, β and γ phases). The generalized gradient approximation (GGA) described by Perdew-Burke-Ernzerhof (PBE) was used. The results obtained for the spin-polarized band structure and the density of states show a halfmetallic behavior for the four compounds. The elastic constants ( C ij ) show that our compounds are ductile, stiff and anisotropic.

Gravity waves in Titan's atmosphere

NASA Technical Reports Server (NTRS)

Friedson, A. James

1994-01-01

Scintillations (high frequency variations) observed in the radio signal during the occultation of Voyager 1 by Titan (Hinson and Tyler, 1983) provide information concerning neutral atmospheric density fluctuations on scales on hundreds of meters to a few kilometers. Those seen at altitudes higher than 25 km above the surface were interpreted by Hinson and Tyler as being caused by linear, freely propagating (energy-conserving) gravity waves, but this interpretation was found to be inconsistent with the scintillation data below the 25-km altitude level. Here an attempt is made to interpret the entire scintillation profile between the surface and the 90-km altitude level in terms of gravity waves generated at the surface. Numerical calculations of the density fluctuations caused by two-dimensional, nonhydrostatic, finite-amplitude gravity waves propagating vertically through Titan's atmosphere are performed to produce synthetic scintillation profiles for comparison with the observations. The numerical model accurately treats the effects of wave transience, nonlinearity, and breakdown due to convective instability in the overturned part of the wave. The high-altitude scintillation data were accurately recovered with a freely propagating wave solution, confirming the analytic model of Hinson and Tyler. It is found that the low-altitude scintillation data can be fit by a model where a component of the gravity waves becomes convectively unstable and breaks near the 15 km level. The large-scale structure of the observed scintillation profile in the entire altitude range between 5 and 85 km can be simulated by a model where the freely propagating and breaking waves are forced at the surface simultaneously. Further analysis of the Voyager 1 Titan low-altitude scintillation data, using inversion theory appropriate for strong scattering, could potentially remove some of the ambiguities remaining in this analysis and allow a better determination of the strength and source of the waves.

Mott Transition in GdMnO3: an Ab Initio Study

NASA Astrophysics Data System (ADS)

Ferreira, W. S.; Moreira, E.; Frazão, N. F.

2018-04-01

Orthorhombic GdMnO3 is studied using density functional theory considering the pseudo-potential plane-wave method within local-spin-density approximation, LSDA. The electronic band structure and density of states, for several hydrostatic pressures, are studied. The Mott transition was observed at 60 GPa. Calculated lattice parameters are close to the experimental measurements, and some indirect band gaps (S→Γ) were obtained within the LSDA level of calculation, between the occupied O-2 p and unoccupied Gd-4 f states. The variation of the gap reduces with increasing pressure, being well fitted to a quadratic function.

Dense solar wind cloud geometries deduced from comparisons of radio signal delay and in situ plasma measurements

NASA Technical Reports Server (NTRS)

Landt, J. A.

1974-01-01

The geometries of dense solar wind clouds are estimated by comparing single-location measurements of the solar wind plasma with the average of the electron density obtained by radio signal delay measurements along a radio path between earth and interplanetary spacecraft. Several of these geometries agree with the current theoretical spatial models of flare-induced shock waves. A new class of spatially limited structures that contain regions with densities greater than any observed in the broad clouds is identified. The extent of a cloud was found to be approximately inversely proportional to its density.

Blast-wave density measurements

NASA Astrophysics Data System (ADS)

Ritzel, D. V.

Applications of a densitometer to obtain time-resolved data on the total density in blast-wave flows are described. A beta-source (promethium-147) is separated by a gap from a scintillator and a photomultiplier tube (PMT). Attenuation of the radiation beam by the passing blast wave is due to the total density in the gap volume during the wave passage. Signal conditioning and filtering methods permit the system to output linearized data. Results are provided from use of the system to monitor blast waves emitted by detonation of a 10.7 m diameter fiberglass sphere containing 609 tons of ammonium nitrate/fuel oil at a 50.6 m height. Blast wave density data are provided for peak overpressure levels of 245, 172 and 70 kPa and distances of 183, 201 and 314 m from ground zero. Data resolution was of high enough quality to encourage efforts to discriminate dust and gasdynamic phenomena within passing blast waves.

Lower hybrid wave phenomena associated with density depletions

NASA Technical Reports Server (NTRS)

Seyler, C. E.

1994-01-01

A fluid description of lower hybrid, whistler and magnetosonic waves is applied to study wave phenomena near the lower hybrid resonance associated with plasma density depletions. The goal is to understand the nature of lower hybrid cavitons and spikelets often associated with transverse ion acceleration events in the auroral ionosphere. Three-dimensional simulations show the ponderomotive force leads to the formation of a density cavity (caviton) in which lower hybrid wave energy is concentrated (spikelet) resulting in a three-dimensional collapse of the configuration. Plasma density depletions of the order of a few percent are shown to greatly modify the homogeneous linear properties of lower hybrid waves and account for many of the observed features of lower hybrid spikelets.

K-P-Burgers equation in negative ion-rich relativistic dusty plasma including the effect of kinematic viscosity

NASA Astrophysics Data System (ADS)

Dev, A. N.; Deka, M. K.; Sarma, J.; Saikia, D.; Adhikary, N. C.

2016-10-01

The stationary solution is obtained for the K-P-Burgers equation that describes the nonlinear propagations of dust ion acoustic waves in a multi-component, collisionless, un-magnetized relativistic dusty plasma consisting of electrons, positive and negative ions in the presence of charged massive dust grains. Here, the Kadomtsev-Petviashvili (K-P) equation, three-dimensional (3D) Burgers equation, and K-P-Burgers equations are derived by using the reductive perturbation method including the effects of viscosity of plasma fluid, thermal energy, ion density, and ion temperature on the structure of a dust ion acoustic shock wave (DIASW). The K-P equation predictes the existences of stationary small amplitude solitary wave, whereas the K-P-Burgers equation in the weakly relativistic regime describes the evolution of shock-like structures in such a multi-ion dusty plasma.

On the correct implementation of Fermi-Dirac statistics and electron trapping in nonlinear electrostatic plane wave propagation in collisionless plasmas

NASA Astrophysics Data System (ADS)

Schamel, Hans; Eliasson, Bengt

2016-05-01

Quantum statistics and electron trapping have a decisive influence on the propagation characteristics of coherent stationary electrostatic waves. The description of these strictly nonlinear structures, which are of electron hole type and violate linear Vlasov theory due to the particle trapping at any excitation amplitude, is obtained by a correct reduction of the three-dimensional Fermi-Dirac distribution function to one dimension and by a proper incorporation of trapping. For small but finite amplitudes, the holes become of cnoidal wave type and the electron density is shown to be described by a ϕ ( x ) 1 / 2 rather than a ϕ ( x ) expansion, where ϕ ( x ) is the electrostatic potential. The general coefficients are presented for a degenerate plasma as well as the quantum statistical analogue to these steady state coherent structures, including the shape of ϕ ( x ) and the nonlinear dispersion relation, which describes their phase velocity.

Acoustic imaging and mirage effects with high transmittance in a periodically perforated metal slab

NASA Astrophysics Data System (ADS)

Zhao, Sheng-Dong; Wang, Yue-Sheng; Zhang, Chuanzeng

2016-11-01

In this paper, we present a high-quality superlens to focus acoustic waves using a periodically perforated metallic structure which is made of zinc and immersed in water. By changing a geometrical parameter gradually, a kind of gradient-index phononic crystal lens is designed to attain the mirage effects. The acoustic waves can propagate along an arc-shaped trajectory which is precisely controlled by the angle and frequency of the incident waves. The negative refraction imaging effect depends delicately on the transmittance of the solid structure. The acoustic impedance matching between the solid and the liquid proposed in this article, which is determined by the effective density and group velocity of the unit-cell, is significant for overcoming the inefficiency problem of acoustic devices. This study focuses on how to obtain the high transmittance imaging and mirage effects based on the adequate material selection and geometrical design.

Mapping the Milky Way Galaxy with LISA

NASA Technical Reports Server (NTRS)

McKinnon, Jose A.; Littenberg, Tyson

2012-01-01

Gravitational wave detectors in the mHz band (such as the Laser Interferometer Space Antenna, or LISA) will observe thousands of compact binaries in the galaxy which can be used to better understand the structure of the Milky Way. To test the effectiveness of LISA to measure the distribution of the galaxy, we simulated the Close White Dwarf Binary (CWDB) gravitational wave sky using different models for the Milky Way. To do so, we have developed a galaxy density distribution modeling code based on the Markov Chain Monte Carlo method. The code uses different distributions to construct realizations of the galaxy. We then use the Fisher Information Matrix to estimate the variance and covariance of the recovered parameters for each detected CWDB. This is the first step toward characterizing the capabilities of space-based gravitational wave detectors to constrain models for galactic structure, such as the size and orientation of the bar in the center of the Milky Way

Plasma and energetic particle structure upstream of a quasi-parallel interplanetary shock

NASA Technical Reports Server (NTRS)

Kennel, C. F.; Scarf, F. L.; Coroniti, F. V.; Russell, C. T.; Wenzel, K.-P.; Sanderson, T. R.; Van Nes, P.; Smith, E. J.; Tsurutani, B. T.; Scudder, J. D.

1984-01-01

ISEE 1, 2 and 3 data from 1978 on interplanetary magnetic fields, shock waves and particle energetics are examined to characterize a quasi-parallel shock. The intense shock studied exhibited a 640 km/sec velocity. The data covered 1-147 keV protons and electrons and ions with energies exceeding 30 keV in regions both upstream and downstream of the shock, and also the magnitudes of ion-acoustic and MHD waves. The energetic particles and MHD waves began being detected 5 hr before the shock. Intense halo electron fluxes appeared ahead of the shock. A closed magnetic field structure was produced with a front end 700 earth radii from the shock. The energetic protons were cut off from the interior of the magnetic bubble, which contained a markedly increased density of 2-6 keV protons as well as the shock itself.

Directional Acoustic Wave Manipulation by a Porpoise via Multiphase Forehead Structure

NASA Astrophysics Data System (ADS)

Zhang, Yu; Song, Zhongchang; Wang, Xianyan; Cao, Wenwu; Au, Whitlow W. L.

2017-12-01

Porpoises are small-toothed whales, and they can produce directional acoustic waves to detect and track prey with high resolution and a wide field of view. Their sound-source sizes are rather small in comparison with the wavelength so that beam control should be difficult according to textbook sonar theories. Here, we demonstrate that the multiphase material structure in a porpoise's forehead is the key to manipulating the directional acoustic field. Computed tomography (CT) derives the multiphase (bone-air-tissue) complex, tissue experiments obtain the density and sound-velocity multiphase gradient distributions, and acoustic fields and beam formation are numerically simulated. The results suggest the control of wave propagations and sound-beam formations is realized by cooperation of the whole forehead's tissues and structures. The melon size significantly impacts the side lobes of the beam and slightly influences the main beams, while the orientation of the vestibular sac mainly adjusts the main beams. By compressing the forehead complex, the sound beam can be expanded for near view. The porpoise's biosonar allows effective wave manipulations for its omnidirectional sound source, which can help the future development of miniaturized biomimetic projectors in underwater sonar, medical ultrasonography, and other ultrasonic imaging applications.

A numerical study of shock wave reflections on low density foam

NASA Astrophysics Data System (ADS)

Baer, M. R.

1992-06-01

A continuum mixture theory is used to describe shock wave reflections on low density open-cell polyurethane foam. Numerical simulations are compared to the shock tube experiments of Skews (1991) and detailed wave fields are shown of a shock wave interacting with a layer of foam adjacent to a rigid wall boundary. These comparisons demonstrate that a continuum mixture theory describes well the shock interactions with low density foam.

First principle study of structural, electronic and fermi surface properties of aluminum praseodymium

NASA Astrophysics Data System (ADS)

Shugani, Mani; Aynyas, Mahendra; Sanyal, S. P.

2018-05-01

We present a structural, Electronic and Fermi surface properties of Aluminum Praseodymium (AlPr) using First-principles density functional calculation by using full potential linearized augmented plane wave (FP-LAPW) method within generalized gradient approximation (GGA). The ground state properties along with electronic and Fermi surface properties are studied. It is found that AlPr is metallic and the bonding between Al and Pr is covalent.

High power microwave source with a three dimensional printed metamaterial slow-wave structure.

PubMed

French, David M; Shiffler, Don

2016-05-01

For over the last decade, the concept of metamaterials has led to new approaches for considering the interaction of radiation with complex structures. However, practical manifestations of such a device operating at high power densities have proven difficult to achieve due to the resonant nature of metamaterials and the resultant high electric fields, which place severe constraints on manufacturing the slow wave structures. In this paper, we describe the first experimental manifestation of a high power microwave device utilizing a metallic slow wave structure (metamaterial-like) fabricated using additive manufacturing. The feasibility of utilizing additive manufacturing as a technique for building these relatively complicated structures has thus been demonstrated. The MW class microwave source operates in the C-band and shows frequency tunablility with electron beam voltage. The basic electromagnetic characteristics of this device, the construction using additive manufacturing, and the basic performance as a microwave oscillator are considered. Due to the tunable nature of the device, it shows promise not only as an oscillator but also as a microwave amplifier. Therefore, the dispersive characteristics and a discussion of the anticipated gain is included as it relates to an amplifier configuration.

High power microwave source with a three dimensional printed metamaterial slow-wave structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

French, David M.; Shiffler, Don

2016-05-15

For over the last decade, the concept of metamaterials has led to new approaches for considering the interaction of radiation with complex structures. However, practical manifestations of such a device operating at high power densities have proven difficult to achieve due to the resonant nature of metamaterials and the resultant high electric fields, which place severe constraints on manufacturing the slow wave structures. In this paper, we describe the first experimental manifestation of a high power microwave device utilizing a metallic slow wave structure (metamaterial-like) fabricated using additive manufacturing. The feasibility of utilizing additive manufacturing as a technique for buildingmore » these relatively complicated structures has thus been demonstrated. The MW class microwave source operates in the C-band and shows frequency tunablility with electron beam voltage. The basic electromagnetic characteristics of this device, the construction using additive manufacturing, and the basic performance as a microwave oscillator are considered. Due to the tunable nature of the device, it shows promise not only as an oscillator but also as a microwave amplifier. Therefore, the dispersive characteristics and a discussion of the anticipated gain is included as it relates to an amplifier configuration.« less

Kohn Anomaly and Phase Stability in Group VB Transition Metals

DOE PAGES

Landa, Alexander; Soderlind, Per; Naumov, Ivan; ...

2018-03-26

In the periodic table, only a few pure metals exhibit lattice or magnetic instabilities associated with Fermi surface nesting, the classical examples being α-U and Cr. Whereas α-U displays a strong Kohn anomaly in the phonon spectrum that ultimately leads to the formation of charge density waves (CDWs), Cr is known for its nesting-induced spin density waves (SDWs). Recently, it has become clear that a pronounced Kohn anomaly and the corresponding softening in the elastic constants is also the key factor that controls structural transformations and mechanical properties in compressed group VB metals—materials with relatively high superconducting critical temperatures. Thismore » article reviews the current understanding of the structural and mechanical behavior of these metals under pressure with an introduction to the concept of the Kohn anomaly and how it is related to the important concept of Peierls instability. We review both experimental and theoretical results showing different manifestations of the Kohn anomaly in the transverse acoustic phonon mode TA (ξ00) in V, Nb, and Ta. Specifically, in V the anomaly triggers a structural transition to a rhombohedral phase, whereas in Nb and Ta it leads to an anomalous reduction in yield strength.« less

Kohn Anomaly and Phase Stability in Group VB Transition Metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Landa, Alexander; Soderlind, Per; Naumov, Ivan

In the periodic table, only a few pure metals exhibit lattice or magnetic instabilities associated with Fermi surface nesting, the classical examples being α-U and Cr. Whereas α-U displays a strong Kohn anomaly in the phonon spectrum that ultimately leads to the formation of charge density waves (CDWs), Cr is known for its nesting-induced spin density waves (SDWs). Recently, it has become clear that a pronounced Kohn anomaly and the corresponding softening in the elastic constants is also the key factor that controls structural transformations and mechanical properties in compressed group VB metals—materials with relatively high superconducting critical temperatures. Thismore » article reviews the current understanding of the structural and mechanical behavior of these metals under pressure with an introduction to the concept of the Kohn anomaly and how it is related to the important concept of Peierls instability. We review both experimental and theoretical results showing different manifestations of the Kohn anomaly in the transverse acoustic phonon mode TA (ξ00) in V, Nb, and Ta. Specifically, in V the anomaly triggers a structural transition to a rhombohedral phase, whereas in Nb and Ta it leads to an anomalous reduction in yield strength.« less

Turbulent mixing and fluid transport within Florida Bay seagrass meadows

NASA Astrophysics Data System (ADS)

Hansen, Jennifer C. R.; Reidenbach, Matthew A.

2017-10-01

Seagrasses serve an important function in the ecology of Florida Bay, providing critical nursery habitat and a food source for a variety of organisms. They also create significant benthic structure that induces drag, altering local hydrodynamics that can influence mixing and nutrient dynamics. Thalassia testudinum seagrass meadows were investigated to determine how shoot density and morphometrics alter local wave conditions, the generation of turbulence, and fluid exchange above and within the canopy. Sparsely vegetated and densely vegetated meadows were monitored, with shoot densities of 259 ± 26 and 484 ± 78 shoots m-2, respectively. The temporal and spatial structure of velocity and turbulence were measured using acoustic Doppler velocimeters and an in situ particle image velocimetry (PIV) system positioned both above and within the seagrass canopy. The retention of fluid within the canopy was determined by examining e-folding times calculated from the concentration curves of dye plumes released within the seagrass canopy. Results show that a shear layer with an inflection point develops at the top of the seagrass canopy, which generates instabilities that impart turbulence into the seagrass meadow. Compared to the overlying water column, turbulence was enhanced within the sparse canopy due to flow interaction with the seagrass blades, but reduced within the dense canopy. Wave generated oscillatory motion penetrated deeper into the canopy than unidirectional currents, enhancing fluid exchange. Both shoot density and the relative magnitude of wave- versus current-driven flow conditions were found to be important controls on turbulent exchange of water masses across the canopy-water interface.

Lithosphere-asthenosphere interaction beneath the western United States from the joint inversion of body-wave traveltimes and surface-wave phase velocities

USGS Publications Warehouse

Obrebski, M.; Allen, R.M.; Pollitz, F.; Hung, S.-H.

2011-01-01

The relation between the complex geological history of the western margin of the North American plate and the processes in the mantle is still not fully documented and understood. Several pre-USArray local seismic studies showed how the characteristics of key geological features such as the Colorado Plateau and the Yellowstone Snake River Plains are linked to their deep mantle structure. Recent body-wave models based on the deployment of the high density, large aperture USArray have provided far more details on the mantle structure while surface-wave tomography (ballistic waves and noise correlations) informs us on the shallow structure. Here we combine constraints from these two data sets to image and study the link between the geology of the western United States, the shallow structure of the Earth and the convective processes in mantle. Our multiphase DNA10-S model provides new constraints on the extent of the Archean lithosphere imaged as a large, deeply rooted fast body that encompasses the stable Great Plains and a large portion of the Northern and Central Rocky Mountains. Widespread slow anomalies are found in the lower crust and upper mantle, suggesting that low-density rocks isostatically sustain part of the high topography of the western United States. The Yellowstone anomaly is imaged as a large slow body rising from the lower mantle, intruding the overlying lithosphere and controlling locally the seismicity and the topography. The large E-W extent of the USArray used in this study allows imaging the 'slab graveyard', a sequence of Farallon fragments aligned with the currently subducting Juan de Fuca Slab, north of the Mendocino Triple Junction. The lithospheric root of the Colorado Plateau has apparently been weakened and partly removed through dripping. The distribution of the slower regions around the Colorado Plateau and other rigid blocks follows closely the trend of Cenozoic volcanic fields and ancient lithospheric sutures, suggesting that the later exert a control on the locus of magmato-tectonic activity today. The DNA velocity models are available for download and slicing at http://dna.berkeley.edu. ?? 2011 The Authors Geophysical Journal International ?? 2011 RAS.

Quasiparticle conductance-voltage characteristics for break junctions involving d-wave superconductors: charge-density-wave effects.

PubMed

Ekino, T; Gabovich, A M; Suan Li, Mai; Szymczak, H; Voitenko, A I

2017-12-20

Quasiparticle tunnel conductance-voltage characteristics (CVCs), [Formula: see text], were calculated for break junctions (BJs) made up of layered d-wave superconductors partially gapped by charge-density waves (CDWs). The current is assumed to flow in the ab-plane of electrodes. The influence of CDWs is analyzed by comparing the resulting CVCs with CVCs calculated for BJs made up of pure d-wave superconductors with relevant parameters. The main CDW-effects were found to be the appearance of new CVC peculiarities and the loss of CVC symmetry with respect to the V-sign. Tunnel directionality was shown to be one of the key factors in the formation of [Formula: see text] dependences. In particular, the orientation of electrodes with respect to the current channel becomes very important. As a result, [Formula: see text] can acquire a large variety of forms similar to those for tunnel junctions between superconductors with s-wave, d-wave, and mixed symmetry of their order parameters. The diversity of peculiarities is especially striking at finite temperatures. In the case of BJs made up of pure d-wave superconductors, the resulting CVC can include a two-peak gap-driven structure. The results were compared with the experimental BJ data for a number of high-T c oxides. It was shown that the large variety of the observed current-voltage characteristics can be interpreted in the framework of our approach. Thus, quasiparticle tunnel currents in the ab-plane can be used as an additional mean to detect CDWs competing with superconductivity in cuprates or other layered superconductors.

Quasiparticle conductance-voltage characteristics for break junctions involving d-wave superconductors: charge-density-wave effects

NASA Astrophysics Data System (ADS)

Ekino, T.; Gabovich, A. M.; Li, Mai Suan; Szymczak, H.; Voitenko, A. I.

2017-12-01

Quasiparticle tunnel conductance-voltage characteristics (CVCs), G(V) , were calculated for break junctions (BJs) made up of layered d-wave superconductors partially gapped by charge-density waves (CDWs). The current is assumed to flow in the ab-plane of electrodes. The influence of CDWs is analyzed by comparing the resulting CVCs with CVCs calculated for BJs made up of pure d-wave superconductors with relevant parameters. The main CDW-effects were found to be the appearance of new CVC peculiarities and the loss of CVC symmetry with respect to the V-sign. Tunnel directionality was shown to be one of the key factors in the formation of G(V) dependences. In particular, the orientation of electrodes with respect to the current channel becomes very important. As a result, G(V) can acquire a large variety of forms similar to those for tunnel junctions between superconductors with s-wave, d-wave, and mixed symmetry of their order parameters. The diversity of peculiarities is especially striking at finite temperatures. In the case of BJs made up of pure d-wave superconductors, the resulting CVC can include a two-peak gap-driven structure. The results were compared with the experimental BJ data for a number of high-T c oxides. It was shown that the large variety of the observed current-voltage characteristics can be interpreted in the framework of our approach. Thus, quasiparticle tunnel currents in the ab-plane can be used as an additional mean to detect CDWs competing with superconductivity in cuprates or other layered superconductors.

Systematic theoretical investigation of the zero-field splitting in Gd(III) complexes: Wave function and density functional approaches

NASA Astrophysics Data System (ADS)

Khan, Shehryar; Kubica-Misztal, Aleksandra; Kruk, Danuta; Kowalewski, Jozef; Odelius, Michael

2015-01-01

The zero-field splitting (ZFS) of the electronic ground state in paramagnetic ions is a sensitive probe of the variations in the electronic and molecular structure with an impact on fields ranging from fundamental physical chemistry to medical applications. A detailed analysis of the ZFS in a series of symmetric Gd(III) complexes is presented in order to establish the applicability and accuracy of computational methods using multiconfigurational complete-active-space self-consistent field wave functions and of density functional theory calculations. The various computational schemes are then applied to larger complexes Gd(III)DOTA(H2O)-, Gd(III)DTPA(H2O)2-, and Gd(III)(H2O)83+ in order to analyze how the theoretical results compare to experimentally derived parameters. In contrast to approximations based on density functional theory, the multiconfigurational methods produce results for the ZFS of Gd(III) complexes on the correct order of magnitude.

Theoretical exploration of competing phases of lattice Bose gases in a cavity

NASA Astrophysics Data System (ADS)

Liao, Renyuan; Chen, Huang-Jie; Zheng, Dong-Chen; Huang, Zhi-Gao

2018-01-01

We consider bosonic atoms loaded into optical lattices with cavity-mediated infinite-range interactions. Competing short- and global-range interactions cultivate a rich phase diagram. With a systematic field-theoretical perspective, we present an analytical construction of a global ground-state phase diagram. We find that the infinite-range interaction enhances the fluctuation of the number density. In the strong-coupling regime, we find four branches of elementary excitations, with two being "particlelike" and two being "holelike," and that the excitation gap becomes soft at the phase boundary between compressible phases and incompressible phases. We derive an effective theory describing compressible superfluid and supersolid states. To complement this perturbative study, we construct a self-consistent mean-field theory and find numerical results consistent with our theoretical analysis. We map out the phase diagram and find that a charge density wave may undergo a structure phase transition to a different charge density wave before it finally enters into the supersolid phase driven by increasing the hopping amplitude.

Coordinated Radio, Electron, and Waves Experiment (CREWE) for the NASA Comet Rendezvous and Asteroid Flyby (CRAF) instrument

NASA Technical Reports Server (NTRS)

Scudder, Jack D.

1992-01-01

The Coordinated Radio, Electron, and Waves Experiment (CREWE) was designed to determine density, bulk velocity and temperature of the electrons for the NASA Comet Rendezvous and Asteroid Flyby Spacecraft, to define the MHD-SW IMF flow configuration; to clarify the role of impact ionization processes, to comment on the importance of anomalous ionization phenomena (via wave particle processes), to quantify the importance of wave turbulence in the cometary interaction, to establish the importance of photoionization via the presence of characteristic lines in a structured energy spectrum, to infer the presence and grain size of significant ambient dust column density, to search for the theoretically suggested 'impenetrable' contact surface, and to quantify the flow of heat (in the likelihood that no surface exists) that will penetrate very deep into the atmosphere supplying a good deal of heat via impact and charge exchange ionization. This final report provides an instrument description, instrument test plans, list of deliverables/schedule, flight and support equipment and software schedule, CREWE accommodation issues, resource requirements, status of major contracts, an explanation of the non-NASA funded efforts, status of EIP and IM plan, descope options, and Brinton questions.

Delocalization of charge and current in a chiral quasiparticle wave packet

NASA Astrophysics Data System (ADS)

Sarkar, Subhajit

2018-03-01

A chiral quasiparticle wave packet (c-QPWP) is defined as a conventional superposition of chiral quasiparticle states corresponding to an interacting electron system in two dimensions (2D) in the presence of Rashba spin-orbit coupling (RSOC). I investigate its internal structure via studying the charge and the current densities within the first-order perturbation in the electron-electron interaction. It is found that the c-QPWP contains a localized charge which is less than the magnitude of the bare charge and the remaining charge resides at the system boundary. The amount of charge delocalized turns out to be inversely proportional to the degenerate Fermi velocity v0(=√{α2+2 μ /m }) when RSOC (with strength α ) is weak, and therefore externally tunable. For strong RSOC, the magnitudes of both the delocalized charge and the current further strongly depend on the direction of propagation of the wave packet. Both the charge and the current densities consist of an anisotropic r-2 tail away from the center of the wave packet. Possible implications of such delocalizations in real systems corresponding to 2D semiconductor heterostructure are also discussed within the context of particle injection experiments.

New probe of dark-matter properties: gravitational waves from an intermediate-mass black hole embedded in a dark-matter minispike.

PubMed

Eda, Kazunari; Itoh, Yousuke; Kuroyanagi, Sachiko; Silk, Joseph

2013-05-31

An intermediate-mass black hole (IMBH) may have a dark-matter (DM) minihalo around it and develop a spiky structure within less than a parsec from the IMBH. When a stellar mass object is captured by the minihalo, it eventually infalls into such an IMBH due to gravitational wave backreaction which in turn could be observed directly by future space-borne gravitational wave experiments such as eLISA and NGO. In this Letter, we show that the gravitational wave (GW) detectability strongly depends on the radial profile of the DM distribution. So if the GW is detected, the power index, that is, the DM density distribution, would be determined very accurately. The DM density distribution obtained would make it clear how the IMBH has evolved from a seed black hole and whether the IMBH has experienced major mergers in the past. Unlike the γ-ray observations of DM annihilation, GW is just sensitive to the radial profile of the DM distribution and even to noninteracting DM. Hence, the effect we demonstrate here can be used as a new and powerful probe into DM properties.

CARS measurement of vibrational and rotational temperature with high power laser and high speed visualization of total radiation behind hypervelocity shock waves of 5-7km/s

NASA Astrophysics Data System (ADS)

Sakurai, Kotaro; Bindu, Venigalla Hima; Niinomi, Shota; Ota, Masanori; Maeno, Kazuo

2010-09-01

Coherent Anti-Stokes Raman Spectroscopy (CARS) method is commonly used for measuring molecular structure or condition. In the aerospace technology, this method is applies to measure the temperature in thermic fluid with relatively long time duration of millisecond or sub millisecond. On the other hand, vibrational/rotational temperatures behind hypervelocity shock wave are important for heat-shield design in phase of reentry flight. The non-equilibrium flow with radiative heating from strongly shocked air ahead of the vehicles plays an important role on the heat flux to the wall surface structure as well as convective heating. In this paper CARS method is applied to measure the vibrational/rotational temperature of N2 behind hypervelocity shock wave. The strong shock wave in front of the reentering space vehicles can be experimentally realigned by free-piston, double-diaphragm shock tube with low density test gas. However CARS measurement is difficult for our experiment. Our measurement needs very short pulse which order of nanosecond and high power laser for CARS method. It is due to our measurement object is the momentary phenomena which velocity is 7km/s. In addition the observation section is low density test gas, and there is the strong background light behind the shock wave. So we employ the CARS method with high power, order of 1J/pulse, and very short pulse (10ns) laser. By using this laser the CARS signal can be acquired even in the strong radiation area. Also we simultaneously try to use the CCD camera to obtain total radiation with CARS method.

Acoustic Imaging of Snowpack Physical Properties

NASA Astrophysics Data System (ADS)

Kinar, N. J.; Pomeroy, J. W.

2011-12-01

Measurements of snowpack depth, density, structure and temperature have often been conducted by the use of snowpits and invasive measurement devices. Previous research has shown that acoustic waves passing through snow are capable of measuring these properties. An experimental observation device (SAS2, System for the Acoustic Sounding of Snow) was used to autonomously send audible sound waves into the top of the snowpack and to receive and process the waves reflected from the interior and bottom of the snowpack. A loudspeaker and microphone array separated by an offset distance was suspended in the air above the surface of the snowpack. Sound waves produced from a loudspeaker as frequency-swept sequences and maximum length sequences were used as source signals. Up to 24 microphones measured the audible signal from the snowpack. The signal-to-noise ratio was compared between sequences in the presence of environmental noise contributed by wind and reflections from vegetation. Beamforming algorithms were used to reject spurious reflections and to compensate for movement of the sensor assembly during the time of data collection. A custom-designed circuit with digital signal processing hardware implemented an inversion algorithm to relate the reflected sound wave data to snowpack physical properties and to create a two-dimensional image of snowpack stratigraphy. The low power consumption circuit was powered by batteries and through WiFi and Bluetooth interfaces enabled the display of processed data on a mobile device. Acoustic observations were logged to an SD card after each measurement. The SAS2 system was deployed at remote field locations in the Rocky Mountains of Alberta, Canada. Acoustic snow properties data was compared with data collected from gravimetric sampling, thermocouple arrays, radiometers and snowpit observations of density, stratigraphy and crystal structure. Aspects for further research and limitations of the acoustic sensing system are also discussed.

Pair density waves in superconducting vortex halos

NASA Astrophysics Data System (ADS)

Wang, Yuxuan; Edkins, Stephen D.; Hamidian, Mohammad H.; Davis, J. C. Séamus; Fradkin, Eduardo; Kivelson, Steven A.

2018-05-01

We analyze the interplay between a d -wave uniform superconducting and a pair-density-wave (PDW) order parameter in the neighborhood of a vortex. We develop a phenomenological nonlinear sigma model, solve the saddle-point equation for the order-parameter configuration, and compute the resulting local density of states in the vortex halo. The intertwining of the two superconducting orders leads to a charge density modulation with the same periodicity as the PDW, which is twice the period of the charge density wave that arises as a second harmonic of the PDW itself. We discuss key features of the charge density modulation that can be directly compared with recent results from scanning tunneling microscopy and speculate on the role PDW order may play in the global phase diagram of the hole-doped cuprates.

The Space-Time Scales of Variability in Oceanic Thermal Structure Off the Central California Coast.

DTIC Science & Technology

1983-12-01

SST and sea- surface salinity (SSS) boundaries extracted from the shipboard (2m) thermalsalinograph (T/S) records (Figs. 23, 24, and 25). For these... extracted for comparison. At 175m the density gradient is sufficient to support vigorous internal wave activity in this region. As a result, the predominant... VB2 (VB squared) profiles were calculated from density profiles taken from each phase at a common location (Fig. 149). The location is approximately

Detection of Propagating Fast Sausage Waves through a Detailed Analysis of a Zebra Pattern Fine Structure in a Solar Radio Burst

NASA Astrophysics Data System (ADS)

Kaneda, K.; Misawa, H.; Iwai, K.; Masuda, S.; Tsuchiya, F.; Katoh, Y.; Obara, T.

2017-12-01

Recent observations have revealed that various modes of magnetohydrodynamic (MHD) waves are ubiquitous in the corona. In imaging observations in EUV, propagating fast magnetoacoustic waves are difficult to observe due to the lack of time resolution. Quasi-periodic modulation of radio fine structures is an important source of information on these MHD waves. Zebra patterns (ZPs) are one of such fine structures in type IV bursts, which consist of several parallel stripes superimposed on the background continuum. Although the generation mechanism of ZPs has been discussed still, the most favorable model of ZPs is so-called double plasma resonance (DPR) model. In the DPR model, the frequency separation between the adjacent stripes (Δf) is determined by the plasma density and magnetic field in their source. Hence, the variation of Δf in time and frequency represents the disturbance in their source region in the corona. We report the detection of propagating fast sausage waves through the analysis of a ZP event on 2011 June 21. The variation of Δf in time and frequency was obtained using highly resolved spectral data from the Assembly of Metric-band Aperture Telescope and Real-time Analysis System (AMATERAS). We found that Δf increases with the increase of emission frequency as a whole, which is consistent with the DPR model. Furthermore, we also found that irregularities in Δf are repetitively drifting from the high frequency side to the low frequency side. Their frequency drift rate was 3 - 8 MHz/s and the repetitive frequency was several seconds. Assuming the ZP generation by the DPR model, the drifting irregularities in Δf correspond to propagating disturbances in plasma density and magnetic field with speeds of 3000 - 8000 km/s. Taking account of these facts, the observed modulations in Δf can be explained by fast sausage waves propagating through the corona. We will also discuss the plasma conditions in the corona estimated from the observational results.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Verma, U. P.; Nayak, V.

Quantum mechanical first principle calculations have been performed to study the electronic and structural properties of TiN and TiAs in zinc blende (ZB) and rock salt (RS) structures. The full-potential linearized augmented plane wave (FP-LAPW) method has been used within the framework of density functional theory (DFT). The exchange correlation functional has been solved employing generalized gradient approximation (GGA). Our predicted results for lattice constants are in good agreement with the earlier findings. The electronic band structures of TiX are metallic in both the phases.

Dissipative ion-cyclotron oscillitons in a form of solitons with chirp in Earth's low-altitude ionosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kovaleva, I. Kh.

2012-10-15

In this paper, we consider theoretically nonlinear ion-cyclotron gradient-drift dissipative structures (oscillitons) in low ionospheric plasmas. Similar to Nonlinear Optics and Condensed Matter Physics, the Ginzburg-Landau equation for the envelope of electric wave fields is derived, and solutions for oscillitons in the form of solitons with chirp are examined. The whole dissipative structure constitutes a soliton with a moving charge-neutral density hump. Conditions for excitation and properties of the structures are considered.

3D Density Structure of Oceanic Lithosphere Affected by A Plume: A Case Study from the Greater Jan Mayen-East Greenland Region (NE Atlantic)

NASA Astrophysics Data System (ADS)

Tan, P.; Sippel, J.; Breivik, A. J.; Scheck-Wenderoth, M.; Meeßen, C.

2017-12-01

Unraveling the density structure of the oceanic lithosphere north of Iceland is key for understanding the effects of the Iceland Plume on the mid-ocean ridges of the greater Jan Mayen-East Greenland Region. We use a data-integrative approach for 3D gravity modeling to develop new insights into the crust and upper mantle density structure of this region. First, we obtain the 3D density structure of the sediments and crust from interpretations of regional reflection and refraction seismic lines. Then, the temperature and density structure of the mantle between 50 and 250 km are derived from a published shear-wave velocity (Vs) tomography model. To assess the density configuration between the Moho and 50 km depth, we follow a combined forward and inverse 3D gravity modeling approach. The Vs tomography and derived density of the deeper mantle (>50 km depth) reveal that the low-density anomaly related to the Iceland plume gets weaker with increasing distance from the plume, i.e. from the strongly influenced Middle Kolbeinsey Ridge (MKR) to the Mohn's Ridge. The West Jan Mayen Fracture Zone is identified as a main mantle density contrast, indicative of differences in the thermal evolution of the ridge systems it separates. Beneath the MKR region, the low-density anomaly at depths of >50 km continues upwards into the uppermost mantle, where its lateral dimensions narrow considerably. This elongated density anomaly is consistent with a basement high and indicates a channelization of the Iceland plume effects. The NE-SW elongated mantle anomaly does not, however, coincide with the topographical NNE-SSW striking ridge axis. Thus, the modelled plume-affected oceanic lithosphere reveals discrepancies with the half-space cooling model. We discuss the 3D density model in terms of such spatial relations between deeper mantle anomalies and the shallow crustal structure.

Phase mixing of Alfvén waves in axisymmetric non-reflective magnetic plasma configurations

NASA Astrophysics Data System (ADS)

Petrukhin, N. S.; Ruderman, M. S.; Shurgalina, E. G.

2018-02-01

We study damping of phase-mixed Alfvén waves propagating in non-reflective axisymmetric magnetic plasma configurations. We derive the general equation describing the attenuation of the Alfvén wave amplitude. Then we applied the general theory to a particular case with the exponentially divergent magnetic field lines. The condition that the configuration is non-reflective determines the variation of the plasma density along the magnetic field lines. The density profiles exponentially decreasing with the height are not among non-reflective density profiles. However, we managed to find non-reflective profiles that fairly well approximate exponentially decreasing density. We calculate the variation of the total wave energy flux with the height for various values of shear viscosity. We found that to have a substantial amount of wave energy dissipated at the lower corona, one needs to increase shear viscosity by seven orders of magnitude in comparison with the value given by the classical plasma theory. An important result that we obtained is that the efficiency of the wave damping strongly depends on the density variation with the height. The stronger the density decrease, the weaker the wave damping is. On the basis of this result, we suggested a physical explanation of the phenomenon of the enhanced wave damping in equilibrium configurations with exponentially diverging magnetic field lines.

Arbitrary amplitude dust kinetic Alfvén solitary waves in the presence of polarization force

NASA Astrophysics Data System (ADS)

Singh, Manpreet; Kaur, Nimardeep; Saini, N. S.

2018-02-01

In this investigation, the effect of polarization force on dust kinetic Alfvén solitary waves (DKASWs) in a magnetized dusty plasma consisting of dust fluid, electrons, and positively charged ions is studied. By incorporating density non-uniformity and polarization force in the fluid model equations, the energy balance equation is derived, and from the expression for Sagdeev pseudopotential, the existence conditions for solitary structures in terms of Mach number are determined. From the numerical analysis of Sagdeev pseudopotential, compressive and rarefactive DKASWs at sub- and super-Alfvénic speeds are observed. These waves are significantly affected by varying polarization force, angle of propagation, plasma beta, and Mach number.

A new class of exact solutions of the Klein-Gordon equation of a charged particle interacting with an electromagnetic plane wave in a medium

NASA Astrophysics Data System (ADS)

Varró, Sándor

2014-01-01

Exact solutions are presented of the Klein-Gordon equation of a charged particle moving in a transverse monochromatic plasmon wave of arbitrary high amplitude, which propagates in an underdense plasma. These solutions are expressed in terms of Ince polynomials, forming a doubly infinite set, parametrized by discrete momentum components of the charged particle’s de Broglie wave along the polarization vector and along the propagation direction of the plasmon radiation. The envelope of the exact wavefunctions describes a high-contrast periodic structure of the particle density on the plasma length scale, which may have relevance in novel particle acceleration mechanisms.

Arbitrary electron acoustic waves in degenerate dense plasmas

NASA Astrophysics Data System (ADS)

Rahman, Ata-ur; Mushtaq, A.; Qamar, A.; Neelam, S.

2017-05-01

A theoretical investigation is carried out of the nonlinear dynamics of electron-acoustic waves in a collisionless and unmagnetized plasma whose constituents are non-degenerate cold electrons, ultra-relativistic degenerate electrons, and stationary ions. A dispersion relation is derived for linear EAWs. An energy integral equation involving the Sagdeev potential is derived, and basic properties of the large amplitude solitary structures are investigated in such a degenerate dense plasma. It is shown that only negative large amplitude EA solitary waves can exist in such a plasma system. The present analysis may be important to understand the collective interactions in degenerate dense plasmas, occurring in dense astrophysical environments as well as in laser-solid density plasma interaction experiments.

Background-Oriented Schlieren for Large-Scale and High-Speed Aerodynamic Phenomena

NASA Technical Reports Server (NTRS)

Mizukaki, Toshiharu; Borg, Stephen; Danehy, Paul M.; Murman, Scott M.; Matsumura, Tomoharu; Wakabayashi, Kunihiko; Nakayama, Yoshio

2015-01-01

Visualization of the flow field around a generic re-entry capsule in subsonic flow and shock wave visualization with cylindrical explosives have been conducted to demonstrate sensitivity and applicability of background-oriented schlieren (BOS) for field experiments. The wind tunnel experiment suggests that BOS with a fine-pixel imaging device has a density change detection sensitivity on the order of 10(sup -5) in subsonic flow. In a laboratory setup, the structure of the shock waves generated by explosives have been successfully reconstructed by a computed tomography method combined with BOS.

The role of lower-hybrid-wave collapse in the auroral ionosphere.

PubMed

Schuck, P W; Ganguli, G I; Kintner, P M

2002-08-05

In regions where lower-hybrid solitary structures (LHSS) are observed, the character of auroral lower-hybrid turbulence (LHT) (0-20 kHz) is investigated using the amplitude probability distribution of the electric field. The observed probability distributions are accurately described by a Rayleigh distribution with two degrees of freedom. The statistics of the LHT exhibit no evidence of the global modulational instability or self-similar wave collapse. We conclude that nucleation and resonant scattering in preexisting density depletions are the processes responsible for LHSS in auroral LHT.

Ring dynamics

NASA Technical Reports Server (NTRS)

Borderies, Nicole

1989-01-01

Theoretical models of planetary-ring dynamics are discussed in a detailed analytical review and illustrated with graphs and diagrams. The streamline concept is introduced, and the phenomena associated with the transport of angular momentum are described. Particular attention is then given to (1) broad rings like those of Saturn (shepherding, density-wave excitation, gaps, bending-wave excitation, multiringlet structures, inner-edge shepherding, and the possibility of polar rings around Neptune), (2) narrow rings like those of Uranus (shepherding, ring shapes, and a self-gravity model of rigid precession), and (3) ring arcs like those seen in stellar-occultation observations of Neptune.

The internal caustic structure of illuminated liquid droplets

NASA Technical Reports Server (NTRS)

Lock, James A.; Hovenac, Edward A.

1991-01-01

The internal electric field of an illuminated liquid droplet is studied in detail using both wave theory and ray theory. The internal field obtains its maximum values on the caustics within the droplet. Ray theory is used to determine the equations of these caustics and the density of rays on them. The Debye series expansion of the interior field Mie amplitudes is used to calculate the wave theory version of these caustics. The physical interpretation of the sources of stimulated Raman scattering and fluorescence emission within a liquid droplet is then given.

Clues to the Formation of Spiral Structure in M51 from the Ages and Locations of Star Clusters

NASA Astrophysics Data System (ADS)

Chandar, Rupali; Chien, L.-H.; Meidt, Sharon; Querejeta, Miguel; Dobbs, Clare; Schinnerer, Eva; Whitmore, Bradley C.; Calzetti, Daniela; Dinino, Daiana; Kennicutt, Robert C.; Regan, Michael

2017-08-01

We determine the spatial distributions of star clusters at different ages in the grand-design spiral galaxy M51 using a new catalog based on multi-band images taken with the Hubble Space Telescope (HST). These distributions, when compared with the spiral structure defined by molecular gas, dust, young and old stars, show the following sequence in the inner arms: dense molecular gas (and dust) defines the inner edge of the spiral structure, followed by an overdensity of old stars and then young stellar clusters. The offset between gas and young clusters in the inner arms is consistent with the expectations for a density wave. Clusters as old as a few hundred Myr remain concentrated close to the spiral arms, although the distributions are broader than those for the youngest clusters, which is also consistent with predictions from density wave simulations. The outermost portion of the west arm is different from the rest of the spiral structure in that it contains primarily intermediate-age (≈ 100{--}400 {Myr}) clusters; we believe that this is a “material” arm. We have identified four “feathers,” stellar structures beyond the inner arms that have a larger pitch angle than the arms. We do not find age gradients along any of the feathers, but the least coherent feathers appear to have the largest range of cluster ages.

Stable operating regime for traveling wave devices

DOEpatents

Carlsten, Bruce E.

2000-01-01

Autophase stability is provided for a traveling wave device (TWD) electron beam for amplifying an RF electromagnetic wave in walls defining a waveguide for said electromagnetic wave. An off-axis electron beam is generated at a selected energy and has an energy noise inherently arising from electron gun. The off-axis electron beam is introduced into the waveguide. The off-axis electron beam is introduced into the waveguide at a second radius. The waveguide structure is designed to obtain a selected detuning of the electron beam. The off-axis electron beam has a velocity and the second radius to place the electron beam at a selected distance from the walls defining the waveguide, wherein changes in a density of the electron beam due to the RF electromagnetic wave are independent of the energy of the electron beam to provide a concomitant stable operating regime relative to the energy noise.