Dynamics of Quasi-Electrostatic Whistler waves in Earth's Radiation belts

NASA Astrophysics Data System (ADS)

Goyal, R.; Sharma, R. P.; Gupta, D. N.

2017-12-01

A numerical model is proposed to study the dynamics of high amplitude quasi-electrostatic whistler waves propagating near resonance cone angle and their interaction with finite frequency kinetic Alfvén waves (KAWs) in Earth's radiation belts. The quasi-electrostatic character of whistlers is narrated by dynamics of wave propagating near resonance cone. A high amplitude whistler wave packet is obtained using the present analysis which has also been observed by S/WAVES instrument onboard STEREO. The numerical simulation technique employed to study the dynamics, leads to localization (channelling) of waves as well as turbulent spectrum suggesting the transfer of wave energy over a range of frequencies. The turbulent spectrum also indicates the presence of quasi-electrostatic whistlers and density fluctuations associated with KAW in radiation belts plasma. The ponderomotive force of pump quasi-electrostatic whistlers (high frequency) is used to excite relatively much lower frequency waves (KAWs). The wave localization and steeper spectra could be responsible for particle energization or heating in radiation belts.

High-frequency matrix converter with square wave input

DOEpatents

Carr, Joseph Alexander; Balda, Juan Carlos

2015-03-31

A device for producing an alternating current output voltage from a high-frequency, square-wave input voltage comprising, high-frequency, square-wave input a matrix converter and a control system. The matrix converter comprises a plurality of electrical switches. The high-frequency input and the matrix converter are electrically connected to each other. The control system is connected to each switch of the matrix converter. The control system is electrically connected to the input of the matrix converter. The control system is configured to operate each electrical switch of the matrix converter converting a high-frequency, square-wave input voltage across the first input port of the matrix converter and the second input port of the matrix converter to an alternating current output voltage at the output of the matrix converter.

Parametric array technique for microbubble excitation.

PubMed

Vos, Hendrik J; Goertz, David E; van der Steen, Antonius F W; de Jong, Nico

2011-05-01

This study investigates the use of an acoustic parametric array as a means for microbubble excitation. The excitation wave is generated during propagation in a nonlinear medium of two high-frequency carrier waves, whereby the frequency of the excitation wave is the difference frequency of the carrier waves. Carrier waves of around 10 and 25 MHz are used to generate low-frequency waves between 0.5 and 3.5 MHz at amplitudes in the range of 25 to 80 kPa in water. We demonstrate with high-speed camera observations that it is possible to induce microbubble oscillations with the low frequency signal arising from the nonlinear propagation process. As an application, we determined the resonance frequency of Definity contrast agent microbubbles with radius ranging from 1.5 to 5 μm by sweeping the difference frequency in the range from 0.5 to 3.5 MHz.

Observation of High-Frequency Electrostatic Waves in the Vicinity of the Reconnection Ion Diffusion Region by the Spacecraft of the Magnetospheric Multiscale (MMS) Mission

NASA Technical Reports Server (NTRS)

Zhou, M.; Ashour-Abdalla, M.; Berchem, J.; Walker, R. J.; Liang, H.; El-Alaoui, M.; Goldstein, M. L.; Lindqvist, P.-A.; Marklund, G.; Khotyaintsev, Y. V.;

Unprecedentedly Strong and Narrow Electromagnetic Emissions Stimulated by High-Frequency Radio Waves in the Ionosphere

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

Norin, L.; Leyser, T. B.; Nordblad, E.

2009-02-13

Experimental results of secondary electromagnetic radiation, stimulated by high-frequency radio waves irradiating the ionosphere, are reported. We have observed emission peaks, shifted in frequency up to a few tens of Hertz from radio waves transmitted at several megahertz. These emission peaks are by far the strongest spectral features of secondary radiation that have been reported. The emissions are attributed to stimulated Brillouin scattering, long predicted but hitherto never unambiguously identified in high-frequency ionospheric interaction experiments. The experiments were performed at the High-Frequency Active Auroral Research Program (HAARP), Alaska, USA.

Unprecedentedly strong and narrow electromagnetic emissions stimulated by high-frequency radio waves in the ionosphere.

PubMed

Norin, L; Leyser, T B; Nordblad, E; Thidé, B; McCarrick, M

2009-02-13

Experimental results of secondary electromagnetic radiation, stimulated by high-frequency radio waves irradiating the ionosphere, are reported. We have observed emission peaks, shifted in frequency up to a few tens of Hertz from radio waves transmitted at several megahertz. These emission peaks are by far the strongest spectral features of secondary radiation that have been reported. The emissions are attributed to stimulated Brillouin scattering, long predicted but hitherto never unambiguously identified in high-frequency ionospheric interaction experiments. The experiments were performed at the High-Frequency Active Auroral Research Program (HAARP), Alaska, USA.

On the Importance of High Frequency Gravity Waves for Ice Nucleation in the Tropical Tropopause Layer

NASA Technical Reports Server (NTRS)

Jensen, Eric J.

2016-01-01

Recent investigations of the influence of atmospheric waves on ice nucleation in cirrus have identified a number of key processes and sensitivities: (1) ice concentrations produced by homogeneous freezing are strongly dependent on cooling rates, with gravity waves dominating upper tropospheric cooling rates; (2) rapid cooling driven by high-frequency waves are likely responsible for the rare occurrences of very high ice concentrations in cirrus; (3) sedimentation and entrainment tend to decrease ice concentrations as cirrus age; and (4) in some situations, changes in temperature tendency driven by high-frequency waves can quench ice nucleation events and limit ice concentrations. Here we use parcel-model simulations of ice nucleation driven by long-duration, constant-pressure balloon temperature time series, along with an extensive dataset of cold cirrus microphysical properties from the recent ATTREX high-altitude aircraft campaign, to statistically examine the importance of high-frequency waves as well as the consistency between our theoretical understanding of ice nucleation and observed ice concentrations. The parcel-model simulations indicate common occurrence of peak ice concentrations exceeding several hundred per liter. Sedimentation and entrainment would reduce ice concentrations as clouds age, but 1-D simulations using a wave parameterization (which underestimates rapid cooling events) still produce ice concentrations higher than indicated by observations. We find that quenching of nucleation events by high-frequency waves occurs infrequently and does not prevent occurrences of large ice concentrations in parcel simulations of homogeneous freezing. In fact, the high-frequency variability in the balloon temperature data is entirely responsible for production of these high ice concentrations in the simulations.

A study on the prenatal zone of ultrasonic guided waves in plates

NASA Astrophysics Data System (ADS)

Thomas, Tibin; Balasubramaniam, Krishnan

2017-02-01

Low frequency guided wave based inspection is an extensively used method for asset management with the advantage of wide area coverage from a single location at the cost of spatial resolution. With the advent of high frequency guided waves, short range inspections with high spatial resolution for monitoring corrosion under pipe supports and tank annular plates has gained widespread interest and acceptance. One of the major challenges in the application of high frequency guided waves in a short range inspection is to attain the desired modal displacements with respect to the application. In this paper, an investigation on the generation and formation of fundamental S0 mode is carried out through numerical simulation and experiments to establish a prenatal zone for guided waves. The effect of frequency, thickness of the plate and frequency-thickness (f*d) is studied. The investigation reveals the existence of a rudimentary form with similar modal features to the fully developed mode. This study helps in the design and development of a high frequency guided wave generator for particular applications which demands waves with very less sensitivity to the surface and loading during the initial phase which immediately evolves to a more sensitive wave towards the surface on propagation for the detection of shallow defects.

Global Observations of Magnetospheric High-m Poloidal Waves During the 22 June 2015 Magnetic Storm

NASA Technical Reports Server (NTRS)

Le, G.; Chi, P. J.; Strangeway, R. J.; Russell, C. T.; Slavin, J. A.; Takahashi, K.; Singer, H. J.; Anderson, B. J.; Bromund, K.; Fischer, D.;

Global observations of magnetospheric high-m poloidal waves during the 22 June 2015 magnetic storm.

PubMed

Le, G; Chi, P J; Strangeway, R J; Russell, C T; Slavin, J A; Takahashi, K; Singer, H J; Anderson, B J; Bromund, K; Fischer, D; Kepko, E L; Magnes, W; Nakamura, R; Plaschke, F; Torbert, R B

2017-04-28

We report global observations of high- m poloidal waves during the recovery phase of the 22 June 2015 magnetic storm from a constellation of widely spaced satellites of five missions including Magnetospheric Multiscale (MMS), Van Allen Probes, Time History of Events and Macroscale Interactions during Substorm (THEMIS), Cluster, and Geostationary Operational Environmental Satellites (GOES). The combined observations demonstrate the global spatial extent of storm time poloidal waves. MMS observations confirm high azimuthal wave numbers ( m  ~ 100). Mode identification indicates the waves are associated with the second harmonic of field line resonances. The wave frequencies exhibit a decreasing trend as L increases, distinguishing them from the single-frequency global poloidal modes normally observed during quiet times. Detailed examination of the instantaneous frequency reveals discrete spatial structures with step-like frequency changes along L . Each discrete L shell has a steady wave frequency and spans about 1  R E , suggesting that there exist a discrete number of drift-bounce resonance regions across L shells during storm times.

Application of very high harmonic fast waves for off-axis current drive in the DIII-D and FNSF-AT tokamaks

DOE PAGES

Prater, Ronald; Moeller, Charles P.; Pinsker, Robert I.; ...

2014-06-26

Fast waves at frequencies far above the ion cyclotron frequency and approaching the lower hybrid frequency (also called “helicons” or “whistlers”) have application to off-axis current drive in tokamaks with high electron beta. The high frequency causes the whistler-like behavior of the wave power nearly following field lines, but with a small radial component, so the waves spiral slowly toward the plasma center. The high frequency also contributes to strong damping. Modeling predicts robust off-axis current drive with good efficiency compared to alternatives in high performance discharges in DIII-D and Fusion Nuclear Science Facility (FNSF) when the electron beta ismore » above about 1.8%. Detailed analysis of ray behavior shows that ray trajectories and damping are deterministic (that is, not strongly affected by plasma profiles or initial ray conditions), unlike the chaotic ray behavior in lower frequency fast wave experiments. Current drive was found to not be sensitive to the launched value of the parallel index of refraction n||, so wave accessibility issues can be reduced. Finally, use of a traveling wave antenna provides a very narrow n|| spectrum, which also helps avoid accessibility problems.« less

Wave forcing and morphological changes of New Caledonia lagoon islets: Insights on their possible relations

NASA Astrophysics Data System (ADS)

Aucan, Jérôme; Vendé-Leclerc, Myriam; Dumas, Pascal; Bricquir, Marianne

2017-10-01

In the present study, we examine how waves may contribute to the morphological changes of islets in the New Caledonia lagoon. We collected in situ wave data to investigate their characteristics. Three types of waves are identified and quantified: (1) high-frequency waves generated within the lagoon, (2) low-frequency waves originating from swells in the Tasman Sea, and (3) infragravity waves. We found out that high-frequency waves are the dominant forcing on the islets during typical wind events throughout the year, while infragravity waves, likely generated by the breaking of low-frequency waves, dominate during seasonal swell events. During swell events, low-frequency waves can also directly propagate to the islets through channels across the barrier reef, or be tidally modulated across the barrier reef before reaching the islets. Topographic surveys and beach profiles on one islet indicate areas with seasonal morphological changes and other areas with longer, interannual or decadal, erosion patterns. Although more data are needed to validate this hypothesis, we suspect that a relation exists between wave forcing and morphological changes of the islets.

Transfer and dissipation of energy during wave group propagation on a gentle beach slope

NASA Astrophysics Data System (ADS)

Padilla, Enrique M.; Alsina, José M.

2017-08-01

The propagation of bichromatic wave groups over a constant 1:100 beach slope and the influence of the group modulation is presented. The modulation is controlled by varying the group frequency, fg, which is shown to remarkably affect the energy transfer to high and low frequency components. The growth of the high frequency (hf) wave skewness increases when fg decreases. This is explained by nonlinear coupling between the primary frequencies, which results in a larger growth of hf components as fg decreases, causing the hf waves to break earlier. Due to high spatial resolution, wave tracking has provided an accurate measurement of the varying breakpoint. These breaking locations are very well described (R2>0.91) by the wave-height to effective-depth ratio (γ). However, for any given Iribarren number, this γ is shown to increase with fg. Therefore, a modified Iribarren number is proposed to include the grouping structure, leading to a considerable improvement in reproducing the measured γ-values. Within the surf zone, the behavior of the Incident Long Wave also depends on the group modulation. For low fg conditions, the lf wave decays only slightly by transferring energy back to the hf wave components. However, for high fg wave conditions, strong dissipation of low frequency (lf) components occurs close to the shoreline associated with lf wave breaking. This mechanism is explained by the growth of the lf wave height, induced partly by the self-self interaction of fg, and partly by the nonlinear coupling between the primary frequencies and fg.

High-frequency plasma-heating apparatus

DOEpatents

Brambilla, Marco; Lallia, Pascal

1978-01-01

An array of adjacent wave guides feed high-frequency energy into a vacuum chamber in which a toroidal plasma is confined by a magnetic field, the wave guide array being located between two toroidal current windings. Waves are excited in the wave guide at a frequency substantially equal to the lower frequency hybrid wave of the plasma and a substantially equal phase shift is provided from one guide to the next between the waves therein. For plasmas of low peripheral density gradient, the guides are excited in the TE.sub.01 mode and the output electric field is parallel to the direction of the toroidal magnetic field. For exciting waves in plasmas of high peripheral density gradient, the guides are excited in the TM.sub.01 mode and the magnetic field at the wave guide outlets is parallel to the direction of the toroidal magnetic field. The wave excited at the outlet of the wave guide array is a progressive wave propagating in the direction opposite to that of the toroidal current and is, therefore, not absorbed by so-called "runaway" electrons.

High-frequency Rayleigh-wave method

USGS Publications Warehouse

Xia, J.; Miller, R.D.; Xu, Y.; Luo, Y.; Chen, C.; Liu, J.; Ivanov, J.; Zeng, C.

2009-01-01

High-frequency (???2 Hz) Rayleigh-wave data acquired with a multichannel recording system have been utilized to determine shear (S)-wave velocities in near-surface geophysics since the early 1980s. This overview article discusses the main research results of high-frequency surface-wave techniques achieved by research groups at the Kansas Geological Survey and China University of Geosciences in the last 15 years. The multichannel analysis of surface wave (MASW) method is a non-invasive acoustic approach to estimate near-surface S-wave velocity. The differences between MASW results and direct borehole measurements are approximately 15% or less and random. Studies show that simultaneous inversion with higher modes and the fundamental mode can increase model resolution and an investigation depth. The other important seismic property, quality factor (Q), can also be estimated with the MASW method by inverting attenuation coefficients of Rayleigh waves. An inverted model (S-wave velocity or Q) obtained using a damped least-squares method can be assessed by an optimal damping vector in a vicinity of the inverted model determined by an objective function, which is the trace of a weighted sum of model-resolution and model-covariance matrices. Current developments include modeling high-frequency Rayleigh-waves in near-surface media, which builds a foundation for shallow seismic or Rayleigh-wave inversion in the time-offset domain; imaging dispersive energy with high resolution in the frequency-velocity domain and possibly with data in an arbitrary acquisition geometry, which opens a door for 3D surface-wave techniques; and successfully separating surface-wave modes, which provides a valuable tool to perform S-wave velocity profiling with high-horizontal resolution. ?? China University of Geosciences (Wuhan) and Springer-Verlag GmbH 2009.

Electromagnetic Ion Cyclotron Waves in the High Altitude Cusp: Polar Observations

NASA Technical Reports Server (NTRS)

Le, Guan; Blanco-Cano, X.; Russell, C. T.; Zhou, X.-W.; Mozer, F.; Trattner, K. J.; Fuselier, S. A.; Anderson, B. J.; Vondrak, Richard R. (Technical Monitor)

2001-01-01

High-resolution magnetic field data from the Polar Magnetic Field Experiment (MFE) show that narrow band waves at frequencies approximately 0.2 to 3 Hz are a permanent feature in the vicinity of the polar cusp. The waves have been found in the magnetosphere adjacent to the cusp (both poleward and equatorward of the cusp) and in the cusp itself. The occurrence of waves is coincident with depression of magnetic field strength associated with enhanced plasma density, indicating the entry of magnetosheath plasma into the cusp region. The wave frequencies are generally scaled by the local proton cyclotron frequency, and vary between 0.2 and 1.7 times local proton cyclotron frequency. This suggests that the waves are generated in the cusp region by the precipitating magnetosheath plasma. The properties of the waves are highly variable. The waves exhibit both lefthanded and right-handed polarization in the spacecraft frame. The propagation angles vary from nearly parallel to nearly perpendicular to the magnetic field. We find no correlation among wave frequency, propagation angle and polarization. Combined magnetic field and electric field data for the waves indicate that the energy flux of the waves is guided by the background magnetic field and points downward toward the ionosphere.

Electromagnetic Ion Cyclotron Waves in the High-Altitude Cusp: Polar Observations

NASA Technical Reports Server (NTRS)

Le, G.; Blanco-Cano, X.; Russell, C. T.; Zhou, X.-W.; Mozer, F.; Trattner, K. J.; Fuselier, S. A.; Anderson, B. J.

2005-01-01

High-resolution magnetic field data from the Polar Magnetic Field Experiment (MFE) show that narrow-band waves at frequencies approx. 0.2-3 Hz are a permanent feature in the vicinity of the polar cusp. The waves have been found in the magnetosphere adjacent to the cusp (both poleward and equatorward of the cusp) and in the cusp itself. The occurrence of waves is coincident with depression of magnetic field strength associated with enhanced plasma density, indicating the entry of magnetosheath plasma into the cusp region. The wave frequencies are generally scaled by the local proton cyclotron frequency and vary between 0.2 and 1.7 times local proton cyclotron frequency. This suggests that the waves are generated in the cusp region by the precipitating magnetosheath plasma. The properties of the waves are highly variable. The waves exhibit both left-handed and right-handed polarization in the spacecraft frame. The propagation angles vary from nearly parallel to nearly perpendicular to the magnetic field. We find no correlation among wave frequency, propagation angle, and polarization. Combined magnetic field and electric field data for the waves indicate that the energy flux of the waves is guided by the background magnetic field and points downward toward the ionosphere.

Monitoring uniform and localized corrosion in reinforced mortar using high-frequency guided longitudinal wages

NASA Astrophysics Data System (ADS)

Ervin, Benjamin L.; Reis, Henrique; Bernhard, Jennifer T.; Kuchma, Daniel A.

2008-03-01

High-frequency guided longitudinal waves have been used in a through-transmission arrangement to monitor reinforced mortar specimens undergoing both accelerated uniform and localized corrosion. High-frequency guided longitudinal waves were chosen because they have the fastest propagation velocity and lowest theoretical attenuation for the rebar/mortar system. This makes the modes easily discernible and gives them the ability to travel over long distances. The energy of the high-frequency longitudinal waves is located primarily in the center of the rebar, leading to less leakage into the surrounding mortar. The results indicate that the guided mechanical waves are sensitive to both forms of corrosion attack in the form of attenuation, with less sensitivity at higher frequencies. Also promising is the ability to discern uniform corrosion from localized corrosion in a through-transmission arrangement by examination of the frequency domain.

Inversion of high frequency surface waves with fundamental and higher modes

USGS Publications Warehouse

Xia, J.; Miller, R.D.; Park, C.B.; Tian, G.

2003-01-01

The phase velocity of Rayleigh-waves of a layered earth model is a function of frequency and four groups of earth parameters: compressional (P)-wave velocity, shear (S)-wave velocity, density, and thickness of layers. For the fundamental mode of Rayleigh waves, analysis of the Jacobian matrix for high frequencies (2-40 Hz) provides a measure of dispersion curve sensitivity to earth model parameters. S-wave velocities are the dominant influence of the four earth model parameters. This thesis is true for higher modes of high frequency Rayleigh waves as well. Our numerical modeling by analysis of the Jacobian matrix supports at least two quite exciting higher mode properties. First, for fundamental and higher mode Rayleigh wave data with the same wavelength, higher modes can "see" deeper than the fundamental mode. Second, higher mode data can increase the resolution of the inverted S-wave velocities. Real world examples show that the inversion process can be stabilized and resolution of the S-wave velocity model can be improved when simultaneously inverting the fundamental and higher mode data. ?? 2002 Elsevier Science B.V. All rights reserved.

Excitation of high-frequency surface waves with long duration in the Valley of Mexico

NASA Astrophysics Data System (ADS)

Iida, Masahiro

1999-04-01

During the 1985 Michoacan earthquake (Ms = 8.1), large-amplitude seismograms with extremely long duration were recorded in the lake bed zone of Mexico City. We interpret high-frequency seismic wave fields in the three geotechnical zones (the hill, the transition, and the lake bed zones) in the Valley of Mexico on the basis of a systematic analysis for borehole strong motion recordings. We make identification of wave types for real seismograms. First, amplitude ratios between surface and underground seismograms indicate that predominant periods of the surface seismograms are largely controlled by the wave field incident into surficial layers in the Valley of Mexico. We interpret recorded surface waves as fundamental-mode Love waves excited in the Mexican Volcanic Belt by calculating theoretical amplification for different-scale structures. Second, according to a cross-correlation analysis, the hill and transition seismograms are mostly surface waves. In the lake bed zone, while early portions are noisy body waves, late portions are mostly surface waves. Third, using two kinds of surface arrays with different station intervals, we investigate high-frequency surface-wave propagation in the lake bed zone. The wave propagation is very complicated, depending upon the time section and the frequency band. Finally, on the basis of a statistical time series model with an information criterion, we separate S- and surface-wave portions from lake bed seismograms. Surface waves are dominant and are recognized even in the early time section. Thus high-frequency surface waves with long duration in the Valley of Mexico are excited by the Mexican Volcanic Belt.

MULTI-FLUID APPROACH TO HIGH-FREQUENCY WAVES IN PLASMAS. I. SMALL-AMPLITUDE REGIME IN FULLY IONIZED MEDIUM

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

Martínez-Gómez, David; Soler, Roberto; Terradas, Jaume, E-mail: david.martinez@uib.es

Ideal magnetohydrodynamics (MHD) provides an accurate description of low-frequency Alfvén waves in fully ionized plasmas. However, higher-frequency waves in many plasmas of the solar atmosphere cannot be correctly described by ideal MHD and a more accurate model is required. Here, we study the properties of small-amplitude incompressible perturbations in both the low- and the high-frequency ranges in plasmas composed of several ionized species. We use a multi-fluid approach and take into account the effects of collisions between ions and the inclusion of Hall’s term in the induction equation. Through the analysis of the corresponding dispersion relations and numerical simulations, wemore » check that at high frequencies ions of different species are not as strongly coupled as in the low-frequency limit. Hence, they cannot be treated as a single fluid. In addition, elastic collisions between the distinct ionized species are not negligible for high-frequency waves, since an appreciable damping is obtained. Furthermore, Coulomb collisions between ions remove the cyclotron resonances and the strict cutoff regions, which are present when collisions are not taken into account. The implications of these results for the modeling of high-frequency waves in solar plasmas are discussed.« less

Estimation of near-surface shear-wave velocities and quality factors using multichannel analysis of surface-wave methods

NASA Astrophysics Data System (ADS)

Xia, Jianghai

2014-04-01

This overview article gives a picture of multichannel analysis of high-frequency surface (Rayleigh and Love) waves developed mainly by research scientists at the Kansas Geological Survey, the University of Kansas and China University of Geosciences (Wuhan) during the last eighteen years by discussing dispersion imaging techniques, inversion systems, and real-world examples. Shear (S)-wave velocities of near-surface materials can be derived from inverting the dispersive phase velocities of high-frequency surface waves. Multichannel analysis of surface waves—MASW used phase information of high-frequency Rayleigh waves recorded on vertical component geophones to determine near-surface S-wave velocities. The differences between MASW results and direct borehole measurements are approximately 15% or less and random. Studies show that inversion with higher modes and the fundamental mode simultaneously can increase model resolution and an investigation depth. Multichannel analysis of Love waves—MALW used phase information of high-frequency Love waves recorded on horizontal (perpendicular to the direction of wave propagation) component geophones to determine S-wave velocities of shallow materials. Because of independence of compressional (P)-wave velocity, the MALW method has some attractive advantages, such as 1) Love-wave dispersion curves are simpler than Rayleigh wave's; 2) dispersion images of Love-wave energy have a higher signal to noise ratio and more focused than those generated from Rayleigh waves; and 3) inversion of Love-wave dispersion curves is less dependent on initial models and more stable than Rayleigh waves.

The Polar Plasma Wave Instrument

NASA Technical Reports Server (NTRS)

Gurnett, D. A.; Persoon, A. M.; Randall, R. F.; Odem, D. L.; Remington, S. L.; Averkamp, T. F.; Debower, M. M.; Hospodarsky, G. B.; Huff, R. L.; Kirchner, D. L.

1995-01-01

The Plasma Wave Instrument on the Polar spacecraft is designed to provide measurements of plasma waves in the Earth's polar regions over the frequency range from 0.1 Hz to 800 kHz. Three orthogonal electric dipole antennas are used to detect electric fields, two in the spin plane and one aligned along the spacecraft spin axis. A magnetic loop antenna and a triaxial magnetic search coil antenna are used to detect magnetic fields. Signals from these antennas are processed by five receiver systems: a wideband receiver, a high-frequency waveform receiver, a low-frequency waveform receiver, two multichannel analyzers; and a pair of sweep frequency receivers. Compared to previous plasma wave instruments, the Polar plasma wave instrument has several new capabilities. These include (1) an expanded frequency range to improve coverage of both low- and high-frequency wave phenomena, (2) the ability to simultaneously capture signals from six orthogonal electric and magnetic field sensors, and (3) a digital wideband receiver with up to 8-bit resolution and sample rates as high as 249k samples s(exp -1).

High-frequency modulation of ion-acoustic waves.

NASA Technical Reports Server (NTRS)

Albright, N. W.

1972-01-01

A large amplitude, high-frequency electromagnetic oscillation is impressed on a nonrelativistic, collisionless plasma from an external source. The frequency is chosen to be far from the plasma frequency (in fact, lower). The resulting electron velocity distribution function strongly modifies the propagation of ion-acoustic waves parallel to the oscillating electric field. The complex frequency is calculated numerically.

Frequency-agile THz-wave generation and detection system using nonlinear frequency conversion at room temperature.

PubMed

Guo, Ruixiang; Ikar'i, Tomofumi; Zhang, Jun; Minamide, Hiroaki; Ito, Hiromasa

2010-08-02

A surface-emitting THz parametric oscillator is set up to generate a narrow-linewidth, nanosecond pulsed THz-wave radiation. The THz-wave radiation is coherently detected using the frequency up-conversion in MgO: LiNbO(3) crystal. Fast frequency tuning and automatic achromatic THz-wave detection are achieved through a special optical design, including a variable-angle mirror and 1:1 telescope devices in the pump and THz-wave beams. We demonstrate a frequency-agile THz-wave parametric generation and THz-wave coherent detection system. This system can be used as a frequency-domain THz-wave spectrometer operated at room-temperature, and there are a high possible to develop into a real-time two-dimensional THz spectral imaging system.

Frequency-Wavenumber (FK)-Based Data Selection in High-Frequency Passive Surface Wave Survey

NASA Astrophysics Data System (ADS)

Cheng, Feng; Xia, Jianghai; Xu, Zongbo; Hu, Yue; Mi, Binbin

2018-04-01

Passive surface wave methods have gained much attention from geophysical and civil engineering communities because of the limited application of traditional seismic surveys in highly populated urban areas. Considering that they can provide high-frequency phase velocity information up to several tens of Hz, the active surface wave survey would be omitted and the amount of field work could be dramatically reduced. However, the measured dispersion energy image in the passive surface wave survey would usually be polluted by a type of "crossed" artifacts at high frequencies. It is common in the bidirectional noise distribution case with a linear receiver array deployed along roads or railways. We review several frequently used passive surface wave methods and derive the underlying physics for the existence of the "crossed" artifacts. We prove that the "crossed" artifacts would cross the true surface wave energy at fixed points in the f-v domain and propose a FK-based data selection technique to attenuate the artifacts in order to retrieve the high-frequency information. Numerical tests further demonstrate the existence of the "crossed" artifacts and indicate that the well-known wave field separation method, FK filter, does not work for the selection of directional noise data. Real-world applications manifest the feasibility of the proposed FK-based technique to improve passive surface wave methods by a priori data selection. Finally, we discuss the applicability of our approach.

Frequency-Wavenumber (FK)-Based Data Selection in High-Frequency Passive Surface Wave Survey

NASA Astrophysics Data System (ADS)

Cheng, Feng; Xia, Jianghai; Xu, Zongbo; Hu, Yue; Mi, Binbin

2018-07-01

Passive surface wave methods have gained much attention from geophysical and civil engineering communities because of the limited application of traditional seismic surveys in highly populated urban areas. Considering that they can provide high-frequency phase velocity information up to several tens of Hz, the active surface wave survey would be omitted and the amount of field work could be dramatically reduced. However, the measured dispersion energy image in the passive surface wave survey would usually be polluted by a type of "crossed" artifacts at high frequencies. It is common in the bidirectional noise distribution case with a linear receiver array deployed along roads or railways. We review several frequently used passive surface wave methods and derive the underlying physics for the existence of the "crossed" artifacts. We prove that the "crossed" artifacts would cross the true surface wave energy at fixed points in the f- v domain and propose a FK-based data selection technique to attenuate the artifacts in order to retrieve the high-frequency information. Numerical tests further demonstrate the existence of the "crossed" artifacts and indicate that the well-known wave field separation method, FK filter, does not work for the selection of directional noise data. Real-world applications manifest the feasibility of the proposed FK-based technique to improve passive surface wave methods by a priori data selection. Finally, we discuss the applicability of our approach.

Study of Complex Plasmas with Magnetic Dipoles

DTIC Science & Technology

2017-10-10

variety of collective behavior manifested in a plasma, especially oscillations or waves characterized by high frequency accompanied by the motion of...behavior manifested in a plasma, especially oscillations or waves characterized by high frequency accompanied by the motion of electrons and/or ions...particles characterized by extremely low frequency modes and the collection of plasma particles characterized by high frequency modes. The interaction of

High-frequency surface waves method for agricultural applications

USDA-ARS?s Scientific Manuscript database

A high-frequency surface wave method has been recently developed to explore shallow soil in the vadose zone for agricultural applications. This method is a modification from the conventional multichannel analysis of surface wave (MASW) method that explores near surface soil properties from a couple ...

Fly Eye radar: detection through high scattered media

NASA Astrophysics Data System (ADS)

Molchanov, Pavlo; Gorwara, Ashok

2017-05-01

Longer radio frequency waves better penetrating through high scattered media than millimeter waves, but imaging resolution limited by diffraction at longer wavelength. Same time frequency and amplitudes of diffracted waves (frequency domain measurement) provides information of object. Phase shift of diffracted waves (phase front in time domain) consists information about shape of object and can be applied for reconstruction of object shape or even image by recording of multi-frequency digital hologram. Spectrum signature or refracted waves allows identify the object content. Application of monopulse method with overlap closely spaced antenna patterns provides high accuracy measurement of amplitude, phase, and direction to signal source. Digitizing of received signals separately in each antenna relative to processor time provides phase/frequency independence. Fly eye non-scanning multi-frequency radar system provides simultaneous continuous observation of multiple targets and wide possibilities for stepped frequency, simultaneous frequency, chaotic frequency sweeping waveform (CFS), polarization modulation for reliable object detection. Proposed c-band fly eye radar demonstrated human detection through 40 cm concrete brick wall with human and wall material spectrum signatures and can be applied for through wall human detection, landmines, improvised explosive devices detection, underground or camouflaged object imaging.

Investigation of ELF/VLF waves created by a "beat-wave" HF ionospheric heating at high latitudes

NASA Astrophysics Data System (ADS)

Shumilov, Oleg; Tereshchenko, Evgeniy; Kasatkina, Elena; Gomonov, Alexandr

2015-04-01

The generation of extremely low frequency (ELF, 3-3000 Hz) and very low frequency (VLF, 3-30 kHz) electromagnetic waves by modulated ionospheric high frequency (HF, 2-30 MHz) heating is one of the main directions of ionospheric modification experiments. In this work, we present observations of ELF waves generated during a "beat-wave" heating experiments at the EISCAT heating facility. ELF waves were registered with the ELF receiver located at Lovozero (68 N, 35 E), 660 km east from the EISCAT Tromso heating facility (69.6 N, 19.2 E). Frequency shifts between the generated beat-wave and received ELF waves were detected in all sessions. It is shown that the amplitudes of ELF waves depend on the auroral electrojet current strength. Our results showing a strong dependence of ELF signal intensities on the substorm development seem to support the conclusion that electrojet currents may affect the BW generation of ELF/VLF waves.

High Frequency Acoustic Propagation using Level Set Methods

DTIC Science & Technology

2007-01-01

solution of the high frequency approximation to the wave equation. Traditional solutions to the Eikonal equation in high frequency acoustics are...the Eikonal equation derived from the high frequency approximation to the wave equation, ucuH ∇±=∇ )(),( xx , with the nonnegative function c(x...For simplicity, we only consider the case ucuH ∇+=∇ )(),( xx . Two difficulties must be addressed when solving the Eikonal equation in a fixed

Simple equations guide high-frequency surface-wave investigation techniques

USGS Publications Warehouse

Xia, J.; Xu, Y.; Chen, C.; Kaufmann, R.D.; Luo, Y.

2006-01-01

We discuss five useful equations related to high-frequency surface-wave techniques and their implications in practice. These equations are theoretical results from published literature regarding source selection, data-acquisition parameters, resolution of a dispersion curve image in the frequency-velocity domain, and the cut-off frequency of high modes. The first equation suggests Rayleigh waves appear in the shortest offset when a source is located on the ground surface, which supports our observations that surface impact sources are the best source for surface-wave techniques. The second and third equations, based on the layered earth model, reveal a relationship between the optimal nearest offset in Rayleigh-wave data acquisition and seismic setting - the observed maximum and minimum phase velocities, and the maximum wavelength. Comparison among data acquired with different offsets at one test site confirms the better data were acquired with the suggested optimal nearest offset. The fourth equation illustrates that resolution of a dispersion curve image at a given frequency is directly proportional to the product of a length of a geophone array and the frequency. We used real-world data to verify the fourth equation. The last equation shows that the cut-off frequency of high modes of Love waves for a two-layer model is determined by shear-wave velocities and the thickness of the top layer. We applied this equation to Rayleigh waves and multi-layer models with the average velocity and obtained encouraging results. This equation not only endows with a criterion to distinguish high modes from numerical artifacts but also provides a straightforward means to resolve the depth to the half space of a layered earth model. ?? 2005 Elsevier Ltd. All rights reserved.

High-frequency Plasma Waves Associated with Magnetic Reconnection in the Solar Wind

NASA Astrophysics Data System (ADS)

Wang, Y.

2015-12-01

Activities of high-frequency plasma waves associated with magnetic reconnection in the solar wind observed by Time Domain Sampler (TDS) experiments on STEREO/WAVES are preliminarily analyzed. The TDS instrument can provide burst mode electric fields data with as long as 16384 sample points at 250 kHz sampling rate. In all 1120 suspected reconnection events, it is found that the most commonly occurred waves are neither ion acoustic waves, electrostatic solitary waves, nor Langmuir/upper hybrid waves, but Bernstein-like waves with harmonics of the electron cyclotron frequency. In addition, to each type of waves, Langmuir/upper hybrid waves reveal the largest occurrence rate in the reconnection region than in the ambient solar wind. These results indicate that Bernstein-like waves and Langmuir/upper hybrid waves might play important roles in the reconnection associated particle heating processes and they might also influence the dissipation of magnetic reconnection.

Extremely frequency-widened terahertz wave generation using Cherenkov-type radiation.

PubMed

Suizu, Koji; Koketsu, Kaoru; Shibuya, Takayuki; Tsutsui, Toshihiro; Akiba, Takuya; Kawase, Kodo

2009-04-13

Terahertz (THz) wave generation based on nonlinear frequency conversion is promising way for realizing a tunable monochromatic bright THz-wave source. Such a development of efficient and wide tunable THz-wave source depends on discovery of novel brilliant nonlinear crystal. Important factors of a nonlinear crystal for THz-wave generation are, 1. High nonlinearity and 2. Good transparency at THz frequency region. Unfortunately, many nonlinear crystals have strong absorption at THz frequency region. The fact limits efficient and wide tunable THz-wave generation. Here, we show that Cherenkov radiation with waveguide structure is an effective strategy for achieving efficient and extremely wide tunable THz-wave source. We fabricated MgO-doped lithium niobate slab waveguide with 3.8 microm of thickness and demonstrated difference frequency generation of THz-wave generation with Cherenkov phase matching. Extremely frequency-widened THz-wave generation, from 0.1 to 7.2 THz, without no structural dips successfully obtained. The tuning frequency range of waveguided Cherenkov radiation source was extremely widened compare to that of injection seeded-Terahertz Parametric Generator. The tuning range obtained in this work for THz-wave generation using lithium niobate crystal was the widest value in our knowledge. The highest THz-wave energy obtained was about 3.2 pJ, and the energy conversion efficiency was about 10(-5) %. The method can be easily applied for many conventional nonlinear crystals, results in realizing simple, reasonable, compact, high efficient and ultra broad band THz-wave sources.

Device and method for imaging of non-linear and linear properties of formations surrounding a borehole

DOEpatents

Johnson, Paul A; Tencate, James A; Le Bas, Pierre-Yves; Guyer, Robert; Vu, Cung Khac; Skelt, Christopher

2013-11-05

In some aspects of the disclosure, a method and an apparatus is disclosed for investigating material surrounding the borehole. The method includes generating a first low frequency acoustic wave within the borehole, wherein the first low frequency acoustic wave induces a linear and a nonlinear response in one or more features in the material that are substantially perpendicular to a radius of the borehole; directing a first sequence of high frequency pulses in a direction perpendicularly with respect to the longitudinal axis of the borehole into the material contemporaneously with the first acoustic wave; and receiving one or more second high frequency pulses at one or more receivers positionable in the borehole produced by an interaction between the first sequence of high frequency pulses and the one or more features undergoing linear and nonlinear elastic distortion due to the first low frequency acoustic wave to investigate the material surrounding the borehole.

Nonextensive statistics and skin depth of transverse wave in collisional plasma

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

Hashemzadeh, M., E-mail: hashemzade@gmail.com

Skin depth of transverse wave in a collisional plasma is studied taking into account the nonextensive electron distribution function. Considering the kinetic theory for charge particles and using the Bhatnagar-Gross-Krook collision model, a generalized transverse dielectric permittivity is obtained. The transverse dispersion relation in different frequency ranges is investigated. Obtaining the imaginary part of the wave vector from the dispersion relation, the skin depth for these frequency ranges is also achieved. Profiles of the skin depth show that by increasing the q parameter, the penetration depth decreases. In addition, the skin depth increases by increasing the electron temperature. Finally, itmore » is found that in the high frequency range and high electron temperature, the penetration depth decreases by increasing the collision frequency. In contrast, by increasing the collision frequency in a highly collisional frequency range, the skin depth of transverse wave increases.« less

High-frequency waves in the corona due to null points

NASA Astrophysics Data System (ADS)

Santamaria, I. C.; Khomenko, E.; Collados, M.; de Vicente, A.

2017-06-01

This work aims to understand the behavior of non-linear waves in the vicinity of a coronal null point. In previous works we have shown that high-frequency waves are generated in such a magnetic configuration. This paper studies those waves in detail in order to provide a plausible explanation of their generation. We demonstrate that slow magneto-acoustic shock waves generated in the chromosphere propagate through the null point and produce a train of secondary shocks that escape along the field lines. A particular combination of the shock wave speeds generates waves at a frequency of 80 mHz. We speculate that this frequency may be sensitive to the atmospheric parameters in the corona and therefore can be used to probe the structure of this solar layer. Movies attached to Figs 2 and 4 are available at http://www.aanda.org

High-frequency guided ultrasonic waves for hidden defect detection in multi-layered aircraft structures.

PubMed

Masserey, Bernard; Raemy, Christian; Fromme, Paul

2014-09-01

Aerospace structures often contain multi-layered metallic components where hidden defects such as fatigue cracks and localized disbonds can develop, necessitating non-destructive testing. Employing standard wedge transducers, high frequency guided ultrasonic waves that penetrate through the complete thickness were generated in a model structure consisting of two adhesively bonded aluminium plates. Interference occurs between the wave modes during propagation along the structure, resulting in a frequency dependent variation of the energy through the thickness with distance. The wave propagation along the specimen was measured experimentally using a laser interferometer. Good agreement with theoretical predictions and two-dimensional finite element simulations was found. Significant propagation distance with a strong, non-dispersive main wave pulse was achieved. The interaction of the high frequency guided ultrasonic waves with small notches in the aluminium layer facing the sealant and on the bottom surface of the multilayer structure was investigated. Standard pulse-echo measurements were conducted to verify the detection sensitivity and the influence of the stand-off distance predicted from the finite element simulations. The results demonstrated the potential of high frequency guided waves for hidden defect detection at critical and difficult to access locations in aerospace structures from a stand-off distance. Copyright © 2014 The Authors. Published by Elsevier B.V. All rights reserved.

Monitoring of corrosion damage using high-frequency guided ultrasonic waves

NASA Astrophysics Data System (ADS)

Chew, D.; Fromme, P.

2014-03-01

Due to adverse environmental conditions corrosion can develop during the life cycle of industrial structures, e.g., offshore oil platforms, ships, and desalination plants. Both pitting corrosion and generalized corrosion leading to wall thickness loss can cause the degradation of the integrity and load bearing capacity of the structure. Structural health monitoring of corrosion damage in difficult to access areas can in principle be achieved using high frequency guided waves propagating along the structure from accessible areas. Using standard ultrasonic transducers with single sided access to the structure, high frequency guided wave modes were generated that penetrate through the complete thickness of the structure. Wall thickness reduction was induced using accelerated corrosion in a salt water bath. The corrosion damage was monitored based on the effect on the wave propagation and interference of the different modes. The change in the wave interference was quantified based on an analysis in the frequency domain (Fourier transform) and was found to match well with theoretical predictions for the wall thickness loss. High frequency guided waves have the potential for corrosion damage monitoring at critical and difficult to access locations from a stand-off distance.

Monitoring of corrosion damage using high-frequency guided ultrasonic waves

NASA Astrophysics Data System (ADS)

Chew, D.; Fromme, P.

2015-03-01

Due to adverse environmental conditions corrosion can develop during the life cycle of industrial structures, e.g., offshore oil platforms, ships, and desalination plants. Both pitting corrosion and generalized corrosion leading to wall thickness loss can cause the degradation of the integrity and load bearing capacity of the structure. Structural health monitoring of corrosion damage in difficult to access areas can in principle be achieved using high frequency guided waves propagating along the structure from accessible areas. Using standard ultrasonic transducers with single sided access to the structure, high frequency guided wave modes were generated that penetrate through the complete thickness of the structure. Wall thickness reduction was induced using accelerated corrosion in a salt water bath. The corrosion damage was monitored based on the effect on the wave propagation and interference of the different modes. The change in the wave interference was quantified based on an analysis in the frequency domain (Fourier transform) and was found to match well with theoretical predictions for the wall thickness loss. High frequency guided waves have the potential for corrosion damage monitoring at critical and difficult to access locations from a stand-off distance.

A current drive by using the fast wave in frequency range higher than two timeslower hybrid resonance frequency on tokamaks

NASA Astrophysics Data System (ADS)

Kim, Sun Ho; Hwang, Yong Seok; Jeong, Seung Ho; Wang, Son Jong; Kwak, Jong Gu

2017-10-01

An efficient current drive scheme in central or off-axis region is required for the steady state operation of tokamak fusion reactors. The current drive by using the fast wave in frequency range higher than two times lower hybrid resonance (w>2wlh) could be such a scheme in high density, high temperature reactor-grade tokamak plasmas. First, it has relatively higher parallel electric field to the magnetic field favorable to the current generation, compared to fast waves in other frequency range. Second, it can deeply penetrate into high density plasmas compared to the slow wave in the same frequency range. Third, parasitic coupling to the slow wave can contribute also to the current drive avoiding parametric instability, thermal mode conversion and ion heating occured in the frequency range w<2wlh. In this study, the propagation boundary, accessibility, and the energy flow of the fast wave are given via cold dispersion relation and group velocity. The power absorption and current drive efficiency are discussed qualitatively through the hot dispersion relation and the polarization. Finally, those characteristics are confirmed with ray tracing code GENRAY for the KSTAR plasmas.

Comparing the Robustness of High-Frequency Traveling-Wave Tube Slow-Wave Circuits

NASA Technical Reports Server (NTRS)

Chevalier, Christine T.; Wilson, Jeffrey D.; Kory, Carol L.

2007-01-01

A three-dimensional electromagnetic field simulation software package was used to compute the cold-test parameters, phase velocity, on-axis interaction impedance, and attenuation, for several high-frequency traveling-wave tube slow-wave circuit geometries. This research effort determined the effects of variations in circuit dimensions on cold-test performance. The parameter variations were based on the tolerances of conventional micromachining techniques.

A low-frequency wave motion mechanism enables efficient energy transport in carbon nanotubes at high heat fluxes.

PubMed

Zhang, Xiaoliang; Hu, Ming; Poulikakos, Dimos

2012-07-11

The great majority of investigations of thermal transport in carbon nanotubes (CNTs) in the open literature focus on low heat fluxes, that is, in the regime of validity of the Fourier heat conduction law. In this paper, by performing nonequilibrium molecular dynamics simulations we investigated thermal transport in a single-walled CNT bridging two Si slabs under constant high heat flux. An anomalous wave-like kinetic energy profile was observed, and a previously unexplored, wave-dominated energy transport mechanism is identified for high heat fluxes in CNTs, originated from excited low frequency transverse acoustic waves. The transported energy, in terms of a one-dimensional low frequency mechanical wave, is quantified as a function of the total heat flux applied and is compared to the energy transported by traditional Fourier heat conduction. The results show that the low frequency wave actually overtakes traditional Fourier heat conduction and efficiently transports the energy at high heat flux. Our findings reveal an important new mechanism for high heat flux energy transport in low-dimensional nanostructures, such as one-dimensional (1-D) nanotubes and nanowires, which could be very relevant to high heat flux dissipation such as in micro/nanoelectronics applications.

Application of nonlinear deterministic decomposition to the prediction and energy dissipation of long-crested irregular ocean surface waves

NASA Astrophysics Data System (ADS)

Meza Conde, Eustorgio

The Hybrid Wave Model (HWM) is a deterministic nonlinear wave model developed for the computation of wave properties in the vicinity of ocean wave measurements. The HWM employs both Mode-Coupling and Phase Modulation Methods to model the wave-wave interactions in an ocean wave field. Different from other nonlinear wave models, the HWM decouples the nonlinear wave interactions from ocean wave field measurements and decomposes the wave field into a set of free-wave components. In this dissertation the HWM is applied to the prediction of wave elevation from pressure measurements and to the quantification of energy during breaking of long-crested irregular surface waves. 1.A transient wave train was formed in a two-dimensional wave flume by sequentially generating a series of waves from high to low frequencies that superposed at a downstream location. The predicted wave elevation using the HWM based on the pressure measurement of a very steep transient wave train is in excellent agreement with the corresponding elevation measurement, while that using Linear Wave Theory (LWT) has relatively large discrepancies. Furthermore, the predicted elevation using the HWM is not sensitive to the choice of the cutoff frequency, while that using LWT is very sensitive. 2.Several transient wave trains containing an isolated plunging or spilling breaker at a prescribed location were generated in a two-dimensional wave flume using the same superposition technique. Surface elevation measurements of each transient wave train were made at locations before and after breaking. Applying the HWM nonlinear deterministic decomposition to the measured elevation, the free-wave components comprising the transient wave train were derived. By comparing the free-wave spectra before and after breaking it is found that energy loss was almost exclusively from wave components at frequencies higher than the spectral peak frequency. Even though the wave components near the peak frequency are the largest, they do not significantly gain or lose energy after breaking. It was also observed that wave components of frequencies significantly below or near the peak frequency gain a small portion of energy lost by the high-frequency waves. These findings may have important implications to the ocean wave energy budget.

Nonlinear heating of ions by electron cyclotron frequency waves

NASA Astrophysics Data System (ADS)

Zestanakis, P. A.; Hizanidis, K.; Ram, A. K.; Kominis, Y.

2010-11-01

We study the nonlinear interaction of ions with electron cyclotron (EC) wave packets in a magnetized plasma. Previous studies have shown that such interactions with high frequency electrostatic lower hybrid waves can lead to coherent energization of ions. It requires the frequency bandwidth of the wave packet to be broader than the ion cyclotron frequency [1,2]. For the electromagnetic high frequency EC waves we have developed a more general theory, based on the Lie transform canonical perturbation method [3,4]. We apply the theory to the case of two overlapping EC beams. The wave frequency of each beam is assumed to be frequency modulated with a modulation bandwidth comparable to the ion cyclotron frequency. We present results for both X-mode and O-mode and illustrate the conditions for ion energization. [4pt] [1] D. Benisti, A. K. Ram, and A. Bers, Phys. Plasmas 5, 3224 (1998). [0pt] [2] A. K. Ram, A. Bers, and D. Benisti , J. Geophys. Res. 103, 9431 (1998). [0pt] [3] J.R. Cary and A.N. Kaufman, Phys. Fluids 24, 1238 (1981). [0pt] [4] R.L. Dewar, J. Phys A-Math. Gen 9, 2043 (1976).

Low-Frequency Waves in HF Heating of the Ionosphere

NASA Astrophysics Data System (ADS)

Sharma, A. S.; Eliasson, B.; Milikh, G. M.; Najmi, A.; Papadopoulos, K.; Shao, X.; Vartanyan, A.

2016-02-01

Ionospheric heating experiments have enabled an exploration of the ionosphere as a large-scale natural laboratory for the study of many plasma processes. These experiments inject high-frequency (HF) radio waves using high-power transmitters and an array of ground- and space-based diagnostics. This chapter discusses the excitation and propagation of low-frequency waves in HF heating of the ionosphere. The theoretical aspects and the associated models and simulations, and the results from experiments, mostly from the HAARP facility, are presented together to provide a comprehensive interpretation of the relevant plasma processes. The chapter presents the plasma model of the ionosphere for describing the physical processes during HF heating, the numerical code, and the simulations of the excitation of low-frequency waves by HF heating. It then gives the simulations of the high-latitude ionosphere and mid-latitude ionosphere. The chapter also briefly discusses the role of kinetic processes associated with wave generation.

Role of the Ionosphere in the Generation of Large-Amplitude Ulf Waves at High Latitudes

NASA Astrophysics Data System (ADS)

Tulegenov, B.; Guido, T.; Streltsov, A. V.

2014-12-01

We present results from the statistical study of ULF waves detected by the fluxgate magnetometer in Gakona, Alaska during several experimental campaigns conducted at the High Frequency Active Auroral Research Program (HAARP) facility in years 2011-2013. We analyzed frequencies of ULF waves recorded during 26 strongly disturbed geomagnetic events (substorms) and compared them with frequencies of ULF waves detected during magnetically quite times. Our analysis demonstrates that the frequency of the waves carrying most of the power almost in all these events is less than 1 mHz. We also analyzed data from the ACE satellite, measuring parameters of the solar wind in the L1 Lagrangian point between Earth and Sun, and found that in several occasions there is a strong correlation between oscillations of the magnetic field in the solar wind and oscillations detected on the ground. We also found several cases when there is no correlation between signals detected on ACE and on the ground. This finding suggests that these frequencies correspond to the fundamental eigenfrequency of the coupled magnetosphere-ionosphere system. The low frequency of the oscillations is explained by the effect of the ionosphere, where the current is carried by ions through highly collisional media. The amplitude of these waves can reach significant magnitude when the system is driven by the external driver (for example, the solar wind) with this particular frequency. When the frequency of the driver does not match the frequency of the system, the waves still are observed, but their amplitudes are much smaller.

Application of high-resolution linear Radon transform for Rayleigh-wave dispersive energy imaging and mode separating

USGS Publications Warehouse

Luo, Y.; Xia, J.; Miller, R.D.; Liu, J.; Xu, Y.; Liu, Q.

2008-01-01

Multichannel Analysis of Surface Waves (MASW) analysis is an efficient tool to obtain the vertical shear-wave profile. One of the key steps in the MASW method is to generate an image of dispersive energy in the frequency-velocity domain, so dispersion curves can be determined by picking peaks of dispersion energy. In this paper, we image Rayleigh-wave dispersive energy and separate multimodes from a multichannel record by high-resolution linear Radon transform (LRT). We first introduce Rayleigh-wave dispersive energy imaging by high-resolution LRT. We then show the process of Rayleigh-wave mode separation. Results of synthetic and real-world examples demonstrate that (1) compared with slant stacking algorithm, high-resolution LRT can improve the resolution of images of dispersion energy by more than 50% (2) high-resolution LRT can successfully separate multimode dispersive energy of Rayleigh waves with high resolution; and (3) multimode separation and reconstruction expand frequency ranges of higher mode dispersive energy, which not only increases the investigation depth but also provides a means to accurately determine cut-off frequencies.

Artificial excitation of ELF waves with frequency of Schumann resonance

NASA Astrophysics Data System (ADS)

Streltsov, A. V.; Guido, T.; Tulegenov, B.; Labenski, J.; Chang, C.-L.

2014-11-01

We report results from the experiment aimed at the artificial excitation of extremely low-frequency (ELF) electromagnetic waves with frequencies corresponding to the frequency of Schumann resonance. Electromagnetic waves with these frequencies can form a standing pattern inside the spherical cavity formed by the surface of the Earth and the ionosphere. In the experiment the ELF waves were excited by heating the ionosphere with X-mode HF electromagnetic waves generated at the High Frequency Active Auroral Research Program (HAARP) facility in Alaska. The experiment demonstrates that heating of the ionosphere can excite relatively large-amplitude electromagnetic waves with frequencies in the range 7.8-8.0 Hz when the ionosphere has a strong F layer, the frequency of the HF radiation is in the range 3.20-4.57 MHz, and the electric field greater than 5 mV/m is present in the ionosphere.

Excitation of half-integer up-shifted decay channel and quasi-mode in plasma edge for high power electron Bernstein wave heating scenario

NASA Astrophysics Data System (ADS)

Ali Asgarian, M.; Abbasi, M.

2018-04-01

Electron Bernstein waves (EBW) consist of promising tools in driving localized off-axis current needed for sustained operation as well as effective selective heating scenarios in advanced over dense fusion plasmas like spherical tori and stellarators by applying high power radio frequency waves within the range of Megawatts. Here some serious non-linear effects like parametric decay modes are highly expect-able which have been extensively studied theoretically and experimentally. In general, the decay of an EBW depends on the ratio of the incident frequency and electron cyclotron frequency. At ratios less than two, parametric decay leads to a lower hybrid wave (or an ion Bernstein wave) and EBWs at a lower frequency. For ratios more than two, the daughter waves constitute either an electron cyclotron quasi-mode and another EBW or an ion wave and EBW. However, in contrast with these decay patterns, the excitation of an unusual up-shifted frequency decay channel for the ratio less than two is demonstrated in this study which is totally different as to its generation and persistence. It is shown that this mode varies from the conventional parametric decay channels which necessarily satisfy the matching conditions in frequency and wave-vector. Moreover, the excitation of some less-known local non-propagating quasi-modes (virtual modes) through weak-turbulence theory and their contributions to energy leakage from conversion process leading the reduction in conversion efficiency is assessed.

Joint inversion of high-frequency surface waves with fundamental and higher modes

USGS Publications Warehouse

Luo, Y.; Xia, J.; Liu, J.; Liu, Q.; Xu, S.

2007-01-01

Joint inversion of multimode surface waves for estimating the shear (S)-wave velocity has received much attention in recent years. In this paper, we first analyze sensitivity of phase velocities of multimodes of surface waves for a six-layer earth model, and then we invert surface-wave dispersion curves of the theoretical model and a real-world example. Sensitivity analysis shows that fundamental mode data are more sensitive to the S-wave velocities of shallow layers and are concentrated on a very narrow frequency band, while higher mode data are more sensitive to the parameters of relatively deeper layers and are distributed over a wider frequency band. These properties provide a foundation of using a multimode joint inversion to define S-wave velocities. Inversion results of both synthetic data and a real-world example demonstrate that joint inversion with the damped least-square method and the singular-value decomposition technique to invert high-frequency surface waves with fundamental and higher mode data simultaneously can effectively reduce the ambiguity and improve the accuracy of S-wave velocities. ?? 2007.

Optical image and laser slope meter intercomparisons of high-frequency waves

NASA Technical Reports Server (NTRS)

Lubard, S. C.; Krimmel, J. E.; Thebaud, L. R.; Evans, D. D.; Shemdin, O. H.

1980-01-01

Spectral analyses of optical images of the ocean surface, obtained by a digital video system, are presented and compared with wave data measured simultaneously by the JPL Waverider-mounted laser slope meter. The image analyses, which incorporate several new ideas, provide two-dimensional wave number spectra of slope, covering wavelengths from 10 cm to 10 m. These slope spectra are converted to wave height spectra by a new technique which includes the effects of sky radiance gradients. Space-time spectra are also presented for waves whose frequencies are less than 2 Hz. The JPL slope frequency spectra are compared with image wave number spectra which have been converted to frequency spectra by use of the gravity wave dispersion relation. Results of comparisons between the frequency spectra obtained from the two different measurements show reasonable agreement for frequencies less than 3 Hz.

Bending, longitudinal and torsional wave transmission on Euler-Bernoulli and Timoshenko beams with high propagation losses.

PubMed

Wang, X; Hopkins, C

2016-10-01

Advanced Statistical Energy Analysis (ASEA) is used to predict vibration transmission across coupled beams which support multiple wave types up to high frequencies where Timoshenko theory is valid. Bending-longitudinal and bending-torsional models are considered for an L-junction and rectangular beam frame. Comparisons are made with measurements, Finite Element Methods (FEM) and Statistical Energy Analysis (SEA). When beams support at least two local modes for each wave type in a frequency band and the modal overlap factor is at least 0.1, measurements and FEM have relatively smooth curves. Agreement between measurements, FEM, and ASEA demonstrates that ASEA is able to predict high propagation losses which are not accounted for with SEA. These propagation losses tend to become more important at high frequencies with relatively high internal loss factors and can occur when there is more than one wave type. At such high frequencies, Timoshenko theory, rather than Euler-Bernoulli theory, is often required. Timoshenko theory is incorporated in ASEA and SEA using wave theory transmission coefficients derived assuming Euler-Bernoulli theory, but using Timoshenko group velocity when calculating coupling loss factors. The changeover between theories is appropriate above the frequency where there is a 26% difference between Euler-Bernoulli and Timoshenko group velocities.

Wave Transformation over a Fringing Coral Reef and the Importance of Low-Frequency Waves and Offshore Water Levels to Runup and Island Overtopping

NASA Astrophysics Data System (ADS)

Cheriton, O. M.; Storlazzi, C. D.; Rosenberger, K. J.

2016-02-01

Low-lying, reef-fringed islands are susceptible to sea-level rise and often subjected to overwash and flooding during large wave events. To quantify wave dynamics and wave-driven water levels on fringing coral reefs, wave gauges and a current meter were deployed for 5 months across two shore-normal transects on Roi-Namur, an atoll island in the Republic of the Marshall Islands. These observations captured two large wave events that had maximum wave heights greater than 6 m and peak periods of 16 s over the fore reef. The larger event coincided with a peak spring tide, leading to energetic, highly-skewed infragravity (0.04-0.004 Hz) and very low frequency (0.004-0.001 Hz) waves at the shoreline, which reached heights of 1.0 and 0.7 m, respectively. Water surface elevations, combined with wave runup, exceeded 3.7 m at the innermost reef flat adjacent to the toe of the beach, resulting in flooding of inland areas. This overwash occurred during a 3-hr time window that coincided with high tide and maximum low-frequency reef flat wave heights. The relatively low-relief characteristics of this narrow reef flat may further drive shoreline amplification of low-frequency waves due to resonance modes. These results demonstrate how the coupling of high offshore water levels with low-frequency reef flat wave energetics can lead to large impacts along atoll and fringing reef-lined shorelines, such as island overwash. These observations lend support to the hypothesis that predicted higher sea levels will lead to more frequent occurrences of both extreme shoreline runup and island overwash, threatening the sustainability of these islands.

Observations of wave transformation over a fringing coral reef and the importance of low-frequency waves and offshore water levels to runup, overwash, and coastal flooding

NASA Astrophysics Data System (ADS)

Cheriton, Olivia M.; Storlazzi, Curt D.; Rosenberger, Kurt J.

2016-05-01

Many low-lying tropical islands are susceptible to sea level rise and often subjected to overwash and flooding during large wave events. To quantify wave dynamics and wave-driven water levels on fringing coral reefs, a 5 month deployment of wave gauges and a current meter was conducted across two shore-normal transects on Roi-Namur Island in the Republic of the Marshall Islands. These observations captured two large wave events that had waves with maximum heights greater than 6 m with peak periods of 16 s over the fore reef. The larger event coincided with a peak spring tide, leading to energetic, highly skewed infragravity (0.04-0.004 Hz) and very low frequency (0.004-0.001 Hz) waves at the shoreline, which reached heights of 1.0 and 0.7 m, respectively. Water surface elevations, combined with wave runup, reached 3.7 m above the reef bed at the innermost reef flat adjacent to the toe of the beach, resulting in flooding of inland areas. This overwash occurred during a 3 h time window that coincided with high tide and maximum low-frequency reef flat wave heights. The relatively low-relief characteristics of this narrow reef flat may further drive shoreline amplification of low-frequency waves due to resonance modes. These results (1) demonstrate how the coupling of high offshore water levels with low-frequency reef flat wave energetics can lead to large impacts along fringing reef-lined shorelines, such as island overwash, and (2) lend support to the hypothesis that predicted higher sea levels will lead to more frequent occurrences of these extreme events, negatively impacting coastal resources and infrastructure.

Observations of wave transformation over a fringing coral reef and the importance of low-frequency waves and offshore water levels to runup, overwash, and coastal flooding

USGS Publications Warehouse

Cheriton, Olivia; Storlazzi, Curt; Rosenberger, Kurt

2016-01-01

Many low-lying tropical islands are susceptible to sea level rise and often subjected to overwash and flooding during large wave events. To quantify wave dynamics and wave-driven water levels on fringing coral reefs, a 5 month deployment of wave gauges and a current meter was conducted across two shore-normal transects on Roi-Namur Island in the Republic of the Marshall Islands. These observations captured two large wave events that had waves with maximum heights greater than 6 m with peak periods of 16 s over the fore reef. The larger event coincided with a peak spring tide, leading to energetic, highly skewed infragravity (0.04–0.004 Hz) and very low frequency (0.004–0.001 Hz) waves at the shoreline, which reached heights of 1.0 and 0.7 m, respectively. Water surface elevations, combined with wave runup, reached 3.7 m above the reef bed at the innermost reef flat adjacent to the toe of the beach, resulting in flooding of inland areas. This overwash occurred during a 3 h time window that coincided with high tide and maximum low-frequency reef flat wave heights. The relatively low-relief characteristics of this narrow reef flat may further drive shoreline amplification of low-frequency waves due to resonance modes. These results (1) demonstrate how the coupling of high offshore water levels with low-frequency reef flat wave energetics can lead to large impacts along fringing reef-lined shorelines, such as island overwash, and (2) lend support to the hypothesis that predicted higher sea levels will lead to more frequent occurrences of these extreme events, negatively impacting coastal resources and infrastructure.

Large-amplitude ULF waves at high latitudes

NASA Astrophysics Data System (ADS)

Guido, T.; Tulegenov, B.; Streltsov, A. V.

2014-11-01

We present results from the statistical study of ULF waves detected by the fluxgate magnetometer in Gakona, Alaska during several experimental campaigns conducted at the High Frequency Active Auroral Research Program (HAARP) facility in years 2011-2013. We analyzed frequencies of ULF waves recorded during 26 strongly disturbed geomagnetic events (substorms) and compared them with frequencies of ULF waves detected during magnetically quiet times. Our analysis demonstrates that the frequency of the waves carrying most of the power in almost all these events is less than 1 mHz. We also analyzed data from the ACE satellite, measuring parameters of the solar wind in the L1 Lagrangian point between Earth and Sun, and found that in several occasions there is a strong correlation between oscillations of the magnetic field in the solar wind and oscillations detected on the ground. We also found several cases when there is no correlation between signals detected on ACE and on the ground. This finding suggests that these frequencies correspond to the fundamental eigenfrequency of the coupled magnetosphere-ionosphere system, and the amplitude of these waves can reach significant magnitude when the system is driven by the external driver (for example, the solar wind) with this particular frequency. When the frequency of the driver does not match the frequency of the system, the waves still are observed, but their amplitudes are much smaller.

A coupling modulation model of capillary waves from gravity waves: Theoretical analysis and experimental validation

NASA Astrophysics Data System (ADS)

Chen, Pengzhen; Wang, Xiaoqing; Liu, Li; Chong, Jinsong

2016-06-01

According to Bragg theory, capillary waves are the predominant scatterers of high-frequency band (such as Ka-band) microwave radiation from the surface of the ocean. Therefore, understanding the modulation mechanism of capillary waves is an important foundation for interpreting high-frequency microwave remote sensing images of the surface of the sea. In our experiments, we discovered that modulations of capillary waves are significantly larger than the values predicted by the classical theory. Further, analysis shows that the difference in restoring force results in an inflection point while the phase velocity changes from gravity waves region to capillary waves region, and this results in the capillary waves being able to resonate with gravity waves when the phase velocity of the gravity waves is equal to the group velocity of the capillary waves. Consequently, we propose a coupling modulation model in which the current modulates the capillary wave indirectly by modulating the resonant gravity waves, and the modulation of the former is approximated by that of the latter. This model very effectively explains the results discovered in our experiments. Further, based on Bragg scattering theory and this coupling modulation model, we simulate the modulation of normalized radar cross section (NRCS) of typical internal waves and show that the high-frequency bands are superior to the low-frequency bands because of their greater modulation of NRCS and better radiometric resolution. This result provides new support for choice of radar band for observation of wave-current modulation oceanic phenomena such as internal waves, fronts, and shears.

The impact of gravity waves and cloud nucleation threshold on stratospheric water and tropical tropospheric cloud fraction

NASA Astrophysics Data System (ADS)

Schoeberl, Mark; Dessler, Andrew; Ye, Hao; Wang, Tao; Avery, Melody; Jensen, Eric

2016-08-01

Using the Modern Era Retrospective-Analysis for Research and Applications (MERRA) and MERRA-2 reanalysis winds, temperatures, and anvil cloud ice, we explore the impact of varying the cloud nucleation threshold relative humidity (RH) and high-frequency gravity waves on stratospheric water vapor (H2O) and upper tropical tropopause cloud fraction (TCF). Our model results are compared to 2008/2009 winter TCF derived from Cloud-Aerosol Lidar with Orthogonal Polarization and H2O observations from the Microwave Limb Sounder (MLS). The RH threshold affects both model H2O and TCF, while high-frequency gravity waves mostly impact TCF. Adjusting the nucleation RH and the amplitude of high-frequency gravity waves allows us to tune the model to observations. Reasonable observational agreement is obtained with a nucleation threshold between 130% and 150% RH consistent with airborne observations. For the MERRA reanalysis, we lower the tropopause temperature by 0.5 K roughly consistent with GPS radio occultation measurements and include ~0.1 K high-frequency gravity wave temperature oscillations in order to match TCF and H2O observations. For MERRA-2 we do not need to adjust the tropopause temperature nor add gravity waves, because there are sufficient high-frequency temperature oscillations already present in the MERRA-2 reanalysis to reproduce the observed TCF.

Surface Josephson plasma waves in layered superconductors above the plasma frequency: evidence for a negative index of refraction.

PubMed

Golick, V A; Kadygrob, D V; Yampol'skii, V A; Rakhmanov, A L; Ivanov, B A; Nori, Franco

2010-05-07

We predict a new branch of surface Josephson plasma waves (SJPWs) in layered superconductors for frequencies higher than the Josephson plasma frequency. In this frequency range, the permittivity tensor components along and transverse to the layers have different signs, which is usually associated with negative refraction. However, for these frequencies, the bulk Josephson plasma waves cannot be matched with the incident and reflected waves in the vacuum, and, instead of the negative-refractive properties, abnormal surface modes appear within the frequency band expected for bulk modes. We also discuss the excitation of high-frequency SJPWs by means of the attenuated-total-reflection method.

Gravitational waves produced by compressible MHD turbulence from cosmological phase transitions

NASA Astrophysics Data System (ADS)

Peter, Niksa; Martin, Schlederer; Günter, Sigl

2018-07-01

We calculate the gravitational wave spectrum produced by magneto-hydrodynamic turbulence in a first order phase transitions. We focus in particular on the role of decorrelation of incompressible (solenoidal) homogeneous isotropic turbulence, which is dominated by the sweeping effect. The sweeping effect describes that turbulent decorrelation is primarily due to the small scale eddies being swept with by large scale eddies in a stochastic manner. This effect reduces the gravitational wave signal produced by incompressible MHD turbulence by around an order of magnitude compared to previous studies. Additionally, we find a more complicated dependence for the spectral shape of the gravitational wave spectrum on the energy density sourced by solenoidal modes (magnetic and kinetic). The high frequency tail follows either a k ‑5/3 or a k ‑8/3 power law for large and small solenoidal turbulence density parameter, respectively. Further, magnetic helicity tends to increase the gravitational wave energy at low frequencies. Moreover, we show how solenoidal modes might impact the gravitational wave spectrum from dilatational modes e.g. sound waves. We find that solenoidal modes greatly affect the shape of the gravitational wave spectrum due to the sweeping effect on the dilatational modes. For a high velocity flow, one expects a k ‑2 high frequency tail, due to sweeping. In contrast, for a low velocity flow and a sound wave dominated flow, we expect a k ‑3 high frequency tail. If neither of these limiting cases is realized, the gravitational wave spectrum may be a broken power law with index between  ‑2 and  ‑3, extending up to the frequency at which the source is damped by viscous dissipation.

Grating formation by a high power radio wave in near-equator ionosphere

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

Singh, Rohtash; Sharma, A. K.; Tripathi, V. K.

2011-11-15

The formation of a volume grating in the near-equator regions of ionosphere due to a high power radio wave is investigated. The radio wave, launched from a ground based transmitter, forms a standing wave pattern below the critical layer, heating the electrons in a space periodic manner. The thermal conduction along the magnetic lines of force inhibits the rise in electron temperature, limiting the efficacy of heating to within a latitude of few degrees around the equator. The space periodic electron partial pressure leads to ambipolar diffusion creating a space periodic density ripple with wave vector along the vertical. Suchmore » a volume grating is effective to cause strong reflection of radio waves at a frequency one order of magnitude higher than the maximum plasma frequency in the ionosphere. Linearly mode converted plasma wave could scatter even higher frequency radio waves.« less

Beam-plasma instabilities and the beam-plasma discharge

NASA Technical Reports Server (NTRS)

Kellogg, P. J.; Boswell, R. W.

1986-01-01

Using a new waves on magnetized beams and turbulence (WOMBAT) 0-450 eV electron gun, measurements bearing on the generation of beam-plasma discharge (BPD) are made. The new gun has a narrower divergence angle than the old, and the BPD ignition current is found to be proportional to the cross-sectional area of the plasma. The high-frequency instabilities are identified with the two Trivelpiece-Gould modes, (1959). The upper frequency is identified as a Cerenkov resonance with the upper Trivelpiece-Gould mode, and the lower frequency with a cyclotron resonance with the lower mode, in agreement with theoretical expectations. Convective growth rates are found to be small. A mechanism involving the conversion of a convective instability to an absolute one by trapping of the unstable waves in the density perturbations of the low-frequency waves, is suggested for the low-frequency wave control of the onset of the high frequency precursors to the BPD.

Rogue waves generation in a left-handed nonlinear transmission line with series varactor diodes

NASA Astrophysics Data System (ADS)

Onana Essama, B. G.; Atangana, J.; Biya Motto, F.; Mokhtari, B.; Cherkaoui Eddeqaqi, N.; Kofane, Timoleon C.

2014-07-01

We investigate the electromagnetic wave behavior and its characterization using collective variables technique. Second-order dispersion, first- and second-order nonlinearities, which strongly act in a left-handed nonlinear transmission line with series varactor diodes, are taken into account. Four frequency ranges have been found. The first one gives the so-called energetic soliton due to a perfect combination of second-order dispersion and first-order nonlinearity. The second frequency range presents a dispersive soliton leading to the collapse of the electromagnetic wave at the third frequency range. But the fourth one shows physical conditions which are able to provoke the appearance of wave trains generation with some particular waves, the rogue waves. Moreover, we demonstrate that the number of rogue waves increases with frequency. The soliton, thereafter, gains a relative stability when second-order nonlinearity comes into play with some specific values in the fourth frequency range. Furthermore, the stability conditions of the electromagnetic wave at high frequencies have been also discussed.

Excitation and trapping of lower hybrid waves in striations

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

Borisov, N.; Institute of Terrestrial Magnetism, Ionosphere and Radio Waves Propagation; Honary, F.

2008-12-15

The theory of lower hybrid (LH) waves trapped in striations in warm ionospheric plasma in the three-dimensional case is presented. A specific mechanism of trapping associated with the linear transformation of waves is discussed. It is shown analytically that such trapping can take place in elongated plasma depletions with the frequencies below and above the lower hybrid resonance frequency of the ambient plasma. The theory is applied mainly to striations generated artificially in ionospheric modification experiments and partly to natural plasma depletions in the auroral upper ionosphere. Typical amplitudes and transverse scales of the trapped LH waves excited in ionosphericmore » modification experiments are estimated. It is shown that such waves possibly can be detected by backscattering at oblique sounding in very high frequency (VHF) and ultra high frequency (UHF) ranges.« less

Stimulated Brillouin scatter in a magnetized ionospheric plasma.

PubMed

Bernhardt, P A; Selcher, C A; Lehmberg, R H; Rodriguez, S P; Thomason, J F; Groves, K M; McCarrick, M J; Frazer, G J

2010-04-23

High power electromagnetic waves transmitted from the HAARP facility in Alaska can excite low-frequency electrostatic waves by magnetized stimulated Brillouin scatter. Either an ion-acoustic wave with a frequency less than the ion cyclotron frequency (f(CI)) or an electrostatic ion cyclotron (EIC) wave just above f(CI) can be produced. The coupled equations describing the magnetized stimulated Brillouin scatter instability show that the production of both ion-acoustic and EIC waves is strongly influenced by the wave propagation relative to the background magnetic field. Experimental observations of stimulated electromagnetic emissions using the HAARP transmitter have confirmed that only ion-acoustic waves are excited for propagation along the magnetic zenith and that EIC waves can only be detected with oblique propagation angles. The ion composition can be obtained from the measured EIC frequency.

The theory and method of variable frequency directional seismic wave under the complex geologic conditions

NASA Astrophysics Data System (ADS)

Jiang, T.; Yue, Y.

2017-12-01

It is well known that the mono-frequency directional seismic wave technology can concentrate seismic waves into a beam. However, little work on the method and effect of variable frequency directional seismic wave under complex geological conditions have been done .We studied the variable frequency directional wave theory in several aspects. Firstly, we studied the relation between directional parameters and the direction of the main beam. Secondly, we analyzed the parameters that affect the beam width of main beam significantly, such as spacing of vibrator, wavelet dominant frequency, and number of vibrator. In addition, we will study different characteristics of variable frequency directional seismic wave in typical velocity models. In order to examine the propagation characteristics of directional seismic wave, we designed appropriate parameters according to the character of direction parameters, which is capable to enhance the energy of the main beam direction. Further study on directional seismic wave was discussed in the viewpoint of power spectral. The results indicate that the energy intensity of main beam direction increased 2 to 6 times for a multi-ore body velocity model. It showed us that the variable frequency directional seismic technology provided an effective way to strengthen the target signals under complex geological conditions. For concave interface model, we introduced complicated directional seismic technology which supports multiple main beams to obtain high quality data. Finally, we applied the 9-element variable frequency directional seismic wave technology to process the raw data acquired in a oil-shale exploration area. The results show that the depth of exploration increased 4 times with directional seismic wave method. Based on the above analysis, we draw the conclusion that the variable frequency directional seismic wave technology can improve the target signals of different geologic conditions and increase exploration depth with little cost. Due to inconvenience of hydraulic vibrators in complicated surface area, we suggest that the combination of high frequency portable vibrator and variable frequency directional seismic wave method is an alternative technology to increase depth of exploration or prospecting.

Dichromatic Langmuir waves in degenerate quantum plasma

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

Dubinov, A. E., E-mail: dubinov-ae@yandex.ru; Kitayev, I. N.

2015-06-15

Langmuir waves in fully degenerate quantum plasma are considered. It is shown that, in the linear approximation, Langmuir waves are always dichromatic. The low-frequency component of the waves corresponds to classical Langmuir waves, while the high-frequency component, to free-electron quantum oscillations. The nonlinear problem on the profile of dichromatic Langmuir waves is solved. Solutions in the form of a superposition of waves and in the form of beatings of its components are obtained.

Tunable short-wavelength spin wave excitation from pinned magnetic domain walls

PubMed Central

Van de Wiele, Ben; Hämäläinen, Sampo J.; Baláž, Pavel; Montoncello, Federico; van Dijken, Sebastiaan

2016-01-01

Miniaturization of magnonic devices for wave-like computing requires emission of short-wavelength spin waves, a key feature that cannot be achieved with microwave antennas. In this paper, we propose a tunable source of short-wavelength spin waves based on highly localized and strongly pinned magnetic domain walls in ferroelectric-ferromagnetic bilayers. When driven into oscillation by a microwave spin-polarized current, the magnetic domain walls emit spin waves with the same frequency as the excitation current. The amplitude of the emitted spin waves and the range of attainable excitation frequencies depend on the availability of domain wall resonance modes. In this respect, pinned domain walls in magnetic nanowires are particularly attractive. In this geometry, spin wave confinement perpendicular to the nanowire axis produces a multitude of domain wall resonances enabling efficient spin wave emission at frequencies up to 100 GHz and wavelengths down to 20 nm. At high frequency, the emission of spin waves in magnetic nanowires becomes monochromatic. Moreover, pinning of magnetic domain wall oscillators onto the same ferroelectric domain boundary in parallel nanowires guarantees good coherency between spin wave sources, which opens perspectives towards the realization of Mach-Zehnder type logic devices and sensors. PMID:26883893

High-frequency shear-horizontal surface acoustic wave sensor

DOEpatents

Branch, Darren W

2013-05-07

A Love wave sensor uses a single-phase unidirectional interdigital transducer (IDT) on a piezoelectric substrate for leaky surface acoustic wave generation. The IDT design minimizes propagation losses, bulk wave interferences, provides a highly linear phase response, and eliminates the need for impedance matching. As an example, a high frequency (.about.300-400 MHz) surface acoustic wave (SAW) transducer enables efficient excitation of shear-horizontal waves on 36.degree. Y-cut lithium tantalate (LTO) giving a highly linear phase response (2.8.degree. P-P). The sensor has the ability to detect at the pg/mm.sup.2 level and can perform multi-analyte detection in real-time. The sensor can be used for rapid autonomous detection of pathogenic microorganisms and bioagents by field deployable platforms.

High-frequency shear-horizontal surface acoustic wave sensor

DOEpatents

Branch, Darren W

2014-03-11

A Love wave sensor uses a single-phase unidirectional interdigital transducer (IDT) on a piezoelectric substrate for leaky surface acoustic wave generation. The IDT design minimizes propagation losses, bulk wave interferences, provides a highly linear phase response, and eliminates the need for impedance matching. As an example, a high frequency (.about.300-400 MHz) surface acoustic wave (SAW) transducer enables efficient excitation of shear-horizontal waves on 36.degree. Y-cut lithium tantalate (LTO) giving a highly linear phase response (2.8.degree. P-P). The sensor has the ability to detect at the pg/mm.sup.2 level and can perform multi-analyte detection in real-time. The sensor can be used for rapid autonomous detection of pathogenic microorganisms and bioagents by field deployable platforms.

Insight into large-scale topography on analysis of high-frequency Rayleigh waves

NASA Astrophysics Data System (ADS)

Ping, Ping; Chu, Risheng; Chong, Jiajun; Ni, Sidao; Zhang, Yu

2018-03-01

The dispersion of surface waves could be biased in regions where topography is comparable to the wavelength. We investigate the effects on high-frequency Rayleigh waves propagating in a typical massif model through numerical simulations. High-frequency Rayleigh waves have relatively higher signal-to-noise ratios (SNR) using the Q component in the LQT coordinate system, perpendicular to the local free surface in these topographic models. When sources and stations are located at different sides of the massif, the conventional dispersion image overestimates phase velocities of Rayleigh waves, as much as 25% with topographic height/width ratio (H/r) > 0.5. The dispersion perturbation is more distinctive for fundamental modes. Using a two-layer model, the thickness deviation (ΔD/D) may be significant in surface-wave inversion due to the variation of H/r and the thickness of the first layer. These phenomena cannot be ignored in surface-wave interpretations, nevertheless they are trivial for the source and stations located at the same side of the massif.

Generation of whistler waves by continuous HF heating of the upper ionosphere

NASA Astrophysics Data System (ADS)

Vartanyan, A.; Milikh, G. M.; Eliasson, B.; Najmi, A. C.; Parrot, M.; Papadopoulos, K.

2016-07-01

Broadband VLF waves in the frequency range 7-10 kkHz and 15-19 kHz, generated by F region CW HF ionospheric heating in the absence of electrojet currents, were detected by the DEMETER satellite overflying the High Frequency Active Auroral Research Program (HAARP) transmitter during HAARP/BRIOCHE campaigns. The VLF waves are in a frequency range corresponding to the F region lower lybrid (LH) frequency and its harmonic. This paper aims to show that the VLF observations are whistler waves generated by mode conversion of LH waves that were parametrically excited by HF-pump-plasma interaction at the upper hybrid layer. The paper discusses the basic physics and presents a model that conjectures (1) the VLF waves observed at the LH frequency are due to the interaction of the LH waves with meter-scale field-aligned striations—generating whistler waves near the LH frequency; and (2) the VLF waves at twice the LH frequency are due to the interaction of two counterpropagating LH waves—generating whistler waves near the LH frequency harmonic. The model is supported by numerical simulations that show good agreement with the observations. The (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions results and model discussions are complemented by the Kodiak radar, ionograms, and stimulated electromagnetic emission observations.

Single crystal metal wedges for surface acoustic wave propagation

DOEpatents

Fisher, E.S.

1980-05-09

An ultrasonic testing device has been developed to evaluate flaws and inhomogeneities in the near-surface region of a test material. A metal single crystal wedge is used to generate high frequency Rayleigh surface waves in the test material surface by conversion of a slow velocity, bulk acoustic mode in the wedge into a Rayleigh wave at the metal-wedge test material interface. Particular classes of metals have been found to provide the bulk acoustic modes necessary for production of a surface wave with extremely high frequency and angular collimation. The high frequency allows flaws and inhomogeneities to be examined with greater resolution. The high degree of angular collimation for the outgoing ultrasonic beam permits precision angular location of flaws and inhomogeneities in the test material surface.

Single crystal metal wedges for surface acoustic wave propagation

DOEpatents

Fisher, Edward S.

1982-01-01

An ultrasonic testing device has been developed to evaluate flaws and inhomogeneities in the near-surface region of a test material. A metal single crystal wedge is used to generate high frequency Rayleigh surface waves in the test material surface by conversion of a slow velocity, bulk acoustic mode in the wedge into a Rayleigh wave at the metal-wedge test material interface. Particular classes of metals have been found to provide the bulk acoustic modes necessary for production of a surface wave with extremely high frequency and angular collimation. The high frequency allows flaws and inhomogeneities to be examined with greater resolution. The high degree of angular collimation for the outgoing ultrasonic beam permits precision angular location of flaws and inhomogeneities in the test material surface.

Artificial Excitation of Schumann Resonance with HAARP

NASA Astrophysics Data System (ADS)

Streltsov, A. V.; Chang, C. L.

2014-12-01

We report results from the experiment aimed at the artificial excitation of extremely-low-frequency (ELF) electromagnetic waves with frequencies corresponding to the frequency of Schumann resonance (typically, 7.5 - 8.0 Hz frequency range). Electromagnetic waves with these frequencies can form a standing pattern inside the spherical cavity formed by the surface of the earth and the ionosphere. In the experiment the ELF waves were excited by heating the ionosphere with X-mode HF electromagnetic waves generated by the High Frequency Active Auroral Research Program (HAARP) facility in Alaska. The experiment demonstrates that heating of the ionosphere can excite relatively large-amplitude electromagnetic waves with frequencies in the range of the Schumann resonance, when the ionosphere has a strong F-layer and an electric field greater than 5 mV/m is present in the E-region.

High Transparency of Photosphere Plasma for Electromagnetic Waves Polarized Across Strong Magnetic Field on White Dwarfs

NASA Astrophysics Data System (ADS)

Koryagin, S. A.

2015-06-01

We showed that, in the photosphere of a white dwarf with strong magnetic field, the collisional absorption significantly decreases at the frequencies below the electron cyclotron frequency for the electromagnetic waves linearly polarized across the magnetic field lines (for the so-called extraordinary waves in a magnetized plasma). As a result, the extraordinary waves can escape from the deeper and hotter photosphere layers than the ordinary waves and, in this way, can determine the high linear polarization at the infrared and optical continuum.

Topology optimization of two-dimensional elastic wave barriers

NASA Astrophysics Data System (ADS)

Van hoorickx, C.; Sigmund, O.; Schevenels, M.; Lazarov, B. S.; Lombaert, G.

2016-08-01

Topology optimization is a method that optimally distributes material in a given design domain. In this paper, topology optimization is used to design two-dimensional wave barriers embedded in an elastic halfspace. First, harmonic vibration sources are considered, and stiffened material is inserted into a design domain situated between the source and the receiver to minimize wave transmission. At low frequencies, the stiffened material reflects and guides waves away from the surface. At high frequencies, destructive interference is obtained that leads to high values of the insertion loss. To handle harmonic sources at a frequency in a given range, a uniform reduction of the response over a frequency range is pursued. The minimal insertion loss over the frequency range of interest is maximized. The resulting design contains features at depth leading to a reduction of the insertion loss at the lowest frequencies and features close to the surface leading to a reduction at the highest frequencies. For broadband sources, the average insertion loss in a frequency range is optimized. This leads to designs that especially reduce the response at high frequencies. The designs optimized for the frequency averaged insertion loss are found to be sensitive to geometric imperfections. In order to obtain a robust design, a worst case approach is followed.

The P Wave Time-Frequency Variability Reflects Atrial Conduction Defects before Paroxysmal Atrial Fibrillation.

PubMed

Alcaraz, Raúl; Martínez, Arturo; Rieta, José J

2015-09-01

The study of atrial conduction defects associated with the onset of paroxysmal atrial fibrillation (PAF) can be addressed by analyzing the P wave from the surface electrocardiogram (ECG). Traditionally, signal-averaged ECGs have been mostly used for this purpose. However, this alternative hinders the possibility to quantify every single P wave, its variability over time, as well as to obtain complimentary and evolving information about the arrhythmia. This work analyzes the time progression of several time and frequency P wave features as potential indicators of atrial conduction variability several hours preceding the onset of PAF. The longest sinus rhythm interval from 24-hour Holter recordings of 46 PAF patients was selected. Next, the 2 hours before the onset of PAF were extracted and divided into two 1-hour periods. Every single P wave was automatically delineated and characterized by 16 time and frequency metrics, such as its duration, absolute energy in several frequency bands and high-to-low-frequency energy ratios. Finally, the P wave variability over each 1-hour period was estimated from the 16 features making use of a least-squares linear fitting. As a reference, the same parameters were also estimated from a set of 1-hour ECG segments randomly chosen from a control group of 53 healthy subjects age-, gender-, and heart rate-matched. All the analyzed metrics provided an increasing P wave variability trend as the onset of PAF approximated, being P wave duration and P wave high-frequency energy the most significant individual metrics. The linear fitting slope α associated with P wave duration was (2.48 ± 1.98)×10(-2) for healthy subjects, (23.8 ± 14.1)×10(-2) for ECG segments far from PAF and for (81.8 ± 48.7)×10(-2) ECG segments close to PAF p = 6.96×10(-22) . Similarly, the P wave high-frequency energy linear fitting slope was (2.42 ± 4.97)×10(-9) , (54.2 ± 107.1)×10(-9) and (274.2 ± 566.1)×10(-9) , respectively (p = 2.85×10(-20) ). A univariate discriminant analysis provided that both P wave duration and P wave high-frequency energy could discern among the three ECG sets with diagnostic ability around 80%, which was improved up to 88% by combining these metrics in a multivariate discriminant analysis. Alterations in atrial conduction can be successfully quantified several hours before the onset of PAF by estimating variability over time of several time and frequency P wave features. © 2014 Wiley Periodicals, Inc.

Location of high-frequency P wave microseismic noise in the Pacific Ocean using multiple small aperture arrays

DOE PAGES

Pyle, Moira L.; Koper, Keith D.; Euler, Garrett G.; ...

2015-04-20

We investigate source locations of P-wave microseisms within a narrow frequency band (0.67–1.33 Hz) that is significantly higher than the classic microseism band (~0.05–0.3 Hz). Employing a backprojection method, we analyze data recorded during January 2010 from five International Monitoring System arrays that border the Pacific Ocean. We develop a ranking scheme that allows us to combine beam power from multiple arrays to obtain robust locations of the microseisms. Some individual arrays exhibit a strong regional component, but results from the combination of all arrays show high-frequency P wave energy emanating from the North Pacific basin, in general agreement withmore » previous observations in the double-frequency (DF) microseism band (~0.1–0.3 Hz). This suggests that the North Pacific source of ambient P noise covers a broad range of frequencies and that the wave-wave interaction model is likely valid at shorter periods.« less

Quantified Energy Dissipation Rates in the Terrestrial Bow Shock. 2; Waves and Dissipation

NASA Technical Reports Server (NTRS)

Wilson, L. B., III; Sibeck, D. G.; Breneman, A. W.; Le Contel, O.; Cully, C.; Turner, D. L.; Angelopoulos, V.; Malaspina, D. M.

2014-01-01

We present the first quantified measure of the energy dissipation rates, due to wave-particle interactions, in the transition region of the Earth's collision-less bow shock using data from the Time History of Events and Macro-Scale Interactions during Sub-Storms spacecraft. Our results show that wave-particle interactions can regulate the global structure and dominate the energy dissipation of collision-less shocks. In every bow shock crossing examined, we observed both low-frequency (less than 10 hertz) and high-frequency (approximately or greater than10 hertz) electromagnetic waves throughout the entire transition region and into the magnetosheath. The low-frequency waves were consistent with magnetosonic-whistler waves. The high-frequency waves were combinations of ion-acoustic waves, electron cyclotron drift instability driven waves, electrostatic solitary waves, and whistler mode waves. The high-frequency waves had the following: (1) peak amplitudes exceeding delta B approximately equal to 10 nanoteslas and delta E approximately equal to 300 millivolts per meter, though more typical values were delta B approximately equal to 0.1-1.0 nanoteslas and delta E approximately equal to 10-50 millivolts per meter (2) Poynting fluxes in excess of 2000 microWm(sup -2) (micro-waves per square meter) (typical values were approximately 1-10 microWm(sup -2) (micro-waves per square meter); (3) resistivities greater than 9000 omega meters; and (4) associated energy dissipation rates greater than 10 microWm(sup -3) (micro-waves per cubic meter). The dissipation rates due to wave-particle interactions exceeded rates necessary to explain the increase in entropy across the shock ramps for approximately 90 percent of the wave burst durations. For approximately 22 percent of these times, the wave-particle interactions needed to only be less than or equal to 0.1 percent efficient to balance the nonlinear wave steepening that produced the shock waves. These results show that wave-particle interactions have the capacity to regulate the global structure and dominate the energy dissipation of collision-less shocks.

Stimulated Brillouin Scatter in a Magnetized Ionospheric Plasma

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

Bernhardt, P. A.; Selcher, C. A.; Lehmberg, R. H.

2010-04-23

High power electromagnetic waves transmitted from the HAARP facility in Alaska can excite low-frequency electrostatic waves by magnetized stimulated Brillouin scatter. Either an ion-acoustic wave with a frequency less than the ion cyclotron frequency (f{sub CI}) or an electrostatic ion cyclotron (EIC) wave just above f{sub CI} can be produced. The coupled equations describing the magnetized stimulated Brillouin scatter instability show that the production of both ion-acoustic and EIC waves is strongly influenced by the wave propagation relative to the background magnetic field. Experimental observations of stimulated electromagnetic emissions using the HAARP transmitter have confirmed that only ion-acoustic waves aremore » excited for propagation along the magnetic zenith and that EIC waves can only be detected with oblique propagation angles. The ion composition can be obtained from the measured EIC frequency.« less

Source parameters and effects of bandwidth and local geology on high- frequency ground motions observed for aftershocks of the northeastern Ohio earthquake of 31 January 1986

USGS Publications Warehouse

Glassmoyer, G.; Borcherdt, R.D.

1990-01-01

A 10-station array (GEOS) yielded recordings of exceptional bandwidth (400 sps) and resolution (up to 96 dB) for the aftershocks of the moderate (mb???4.9) earthquake that occurred on 31 January 1986 near Painesville, Ohio. Nine aftershocks were recorded with seismic moments ranging between 9 ?? 1016 and 3 ?? 1019 dyne-cm (MW: 0.6 to 2.3). The aftershock recordings at a site underlain by ???8m of lakeshore sediments show significant levels of high-frequency soil amplification of vertical motion at frequencies near 8, 20 and 70 Hz. Viscoelastic models for P and SV waves incident at the base of the sediments yield estimates of vertical P-wave response consistent with the observed high-frequency site resonances, but suggest additional detailed shear-wave logs are needed to account for observed S-wave response. -from Authors

Low and high frequency instabilities in an explosion-generated-plasma and possibility of wave triplet

NASA Astrophysics Data System (ADS)

Malik, O. P.; Singh, Sukhmander; Malik, Hitendra K.; Kumar, A.

2015-01-01

An explosion-generated-plasma is explored for low and high frequency instabilities by taking into account the drift of all the plasma species together with the dust particles which are charged. The possibility of wave triplet is also discussed based on the solution of dispersion equation and synchronism conditions. High frequency instability (HFI) and low frequency instability (LFI) are found to occur in this system. LFI grows faster with the higher concentration of dust particles, whereas its growth rate goes down if the mass of the dust is higher. The ion and electron temperatures affect its growth in opposite manner and the electron temperature causes this instability to grow. In addition to the instabilities, a simple wave is also observed to propagate, whose velocity is larger for larger wave number, smaller mass of the dust and higher ion temperature.

The propagation characteristics of electromagnetic waves through plasma in the near-field region of low-frequency loop antenna

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

Liu, DongLin, E-mail: donglinliu@stu.xidian.edu.cn; Li, XiaoPing; Xie, Kai

2015-10-15

A high-speed vehicle flying through the atmosphere between 100 and 20 km may suffer from a “communication blackout.” In this paper, a low frequency system with an on-board loop antenna to receive signals is presented as a potential blackout mitigation method. Because the plasma sheath is in the near-field region of the loop antenna, the traditional scattering matrix method that is developed for the far-field region may overestimate the electromagnetic (EM) wave's attenuation. To estimate the EM wave's attenuation in the near-field region, EM interference (EMI) shielding theory is introduced. Experiments are conducted, and the results verify the EMI shielding theory'smore » effectiveness. Simulations are also conducted with different plasma parameters, and the results obtained show that the EM wave's attenuation in the near-field region is far below than that in the far-field region. The EM wave's attenuation increases with the increase in electron density and decreases with the increase in collision frequency. The higher the frequency, the larger is the EM wave's attenuation. During the entire re-entry phase of a RAM-C module, the EM wave's attenuations are below 10 dB for EM waves with a frequency of 1 MHz and below 1 dB for EM waves with a frequency of 100 kHz. Therefore, the low frequency systems (e.g., Loran-C) may provide a way to transmit some key information to high-speed vehicles even during the communication “blackout” period.« less

Electron Scattering by High-Frequency Whistler Waves at Earth's Bow Shock

NASA Technical Reports Server (NTRS)

Oka, M.; Wilson, L. B., III; Phan, T. D.; Hull, A. J.; Amano, T.; Hoshino, M.; Argall, M. R.; Le Contel, O.; Agapitov, O.; Gersham, D. J.;

Electron Scattering by High-frequency Whistler Waves at Earth’s Bow Shock

NASA Astrophysics Data System (ADS)

Oka, M.; Wilson, L. B., III; Phan, T. D.; Hull, A. J.; Amano, T.; Hoshino, M.; Argall, M. R.; Le Contel, O.; Agapitov, O.; Gershman, D. J.; Khotyaintsev, Y. V.; Burch, J. L.; Torbert, R. B.; Pollock, C.; Dorelli, J. C.; Giles, B. L.; Moore, T. E.; Saito, Y.; Avanov, L. A.; Paterson, W.; Ergun, R. E.; Strangeway, R. J.; Russell, C. T.; Lindqvist, P. A.

2017-06-01

Electrons are accelerated to non-thermal energies at shocks in space and astrophysical environments. While different mechanisms of electron acceleration have been proposed, it remains unclear how non-thermal electrons are produced out of the thermal plasma pool. Here, we report in situ evidence of pitch-angle scattering of non-thermal electrons by whistler waves at Earth’s bow shock. On 2015 November 4, the Magnetospheric Multiscale (MMS) mission crossed the bow shock with an Alfvén Mach number ˜11 and a shock angle ˜84°. In the ramp and overshoot regions, MMS revealed bursty enhancements of non-thermal (0.5-2 keV) electron flux, correlated with high-frequency (0.2-0.4 {{{Ω }}}{ce}, where {{{Ω }}}{ce} is the cyclotron frequency) parallel-propagating whistler waves. The electron velocity distribution (measured at 30 ms cadence) showed an enhanced gradient of phase-space density at and around the region where the electron velocity component parallel to the magnetic field matched the resonant energy inferred from the wave frequency range. The flux of 0.5 keV electrons (measured at 1 ms cadence) showed fluctuations with the same frequency. These features indicate that non-thermal electrons were pitch-angle scattered by cyclotron resonance with the high-frequency whistler waves. However, the precise role of the pitch-angle scattering by the higher-frequency whistler waves and possible nonlinear effects in the electron acceleration process remains unclear.

Periodically sheared 2D Yukawa systems

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

Kovács, Anikó Zsuzsa; Hartmann, Peter; Center for Astrophysics, Space Physics and Engineering Research

2015-10-15

We present non-equilibrium molecular dynamics simulation studies on the dynamic (complex) shear viscosity of a 2D Yukawa system. We have identified a non-monotonic frequency dependence of the viscosity at high frequencies and shear rates, an energy absorption maximum (local resonance) at the Einstein frequency of the system at medium shear rates, an enhanced collective wave activity, when the excitation is near the plateau frequency of the longitudinal wave dispersion, and the emergence of significant configurational anisotropy at small frequencies and high shear rates.

In Situ Detection of Strong Langmuir Turbulence Processes in Solar Type III Radio Bursts

NASA Technical Reports Server (NTRS)

Golla, Thejappa; Macdowall, Robert J.; Bergamo, M.

2012-01-01

The high time resolution observations obtained by the WAVES experiment of the STEREO spacecraft in solar type III radio bursts show that Langmuir waves often occur as intense localized wave packets. These wave packets are characterized by short durations of only a few ms and peak intensities, which well exceed the supersonic modulational instability (MI) thresholds. These timescales and peak intensities satisfy the criterion of the solitons collapsed to spatial scales of a few hundred Debye lengths. The spectra of these wave packets consist of primary spectral peaks corresponding to beam-resonant Langmuir waves, two or more sidebands corresponding to down-shifted and up-shifted daughter Langmuir waves, and low frequency enhancements below a few hundred Hz corresponding to daughter ion sound waves. The frequencies and wave numbers of these spectral components satisfy the resonance conditions of the modulational instability (MI). Moreover, the tricoherences, computed using trispectral analysis techniques show that these spectral components are coupled to each other with a high degree of coherency as expected of the MI type of four wave interactions. The high intensities, short scale lengths, sideband spectral structures and low frequency spectral enhancements and, high levels of tricoherences amongst the spectral components of these wave packets provide unambiguous evidence for the supersonic MI and related strong turbulence processes in type III radio bursts. The implication of these observations include: (1) the MI and related strong turbulence processes often occur in type III source regions, (2) the strong turbulence processes probably play very important roles in beam stabilization as well as conversion of Langmuir waves into escaping radiation at the fundamental and second harmonic of the electron plasma frequency, fpe, and (3) the Langmuir collapse probably follows the route of MI in type III radio bursts.

Plasma waves downstream of weak collisionless shocks

NASA Technical Reports Server (NTRS)

Coroniti, F. V.; Greenstadt, E. W.; Moses, S. L.; Smith, E. J.; Tsurutani, B. T.

1993-01-01

In September 1983 the International Sun Earth Explorer 3 (ISEE 3) International Cometary Explorer (ICE) spacecraft made a long traversal of the distant dawnside flank region of the Earth's magnetosphere and had many encounters with the low Mach number bow shock. These weak shocks excite plasma wave electric field turbulence with amplitudes comparable to those detected in the much stronger bow shock near the nose region. Downstream of quasi-perpendicular (quasi-parallel) shocks, the E field spectra exhibit a strong peak (plateau) at midfrequencies (1 - 3 kHz); the plateau shape is produced by a low-frequency (100 - 300 Hz) emission which is more intense behind downstream of two quasi-perpendicular shocks show that the low frequency signals are polarized parallel to the magnetic field, whereas the midfrequency emissions are unpolarized or only weakly polarized. A new high frequency (10 - 30 kHz) emission which is above the maximum Doppler shift exhibit a distinct peak at high frequencies; this peak is often blurred by the large amplitude fluctuations of the midfrequency waves. The high-frequency component is strongly polarized along the magnetic field and varies independently of the lower-frequency waves.

Frequency clusters in self-excited dust density waves

NASA Astrophysics Data System (ADS)

Menzel, Kristoffer O.; Arp, Oliver; Piel, Alexander

2010-11-01

Self-excited dust density waves were studied under microgravity conditions. Their non-sinusoidal shape and high degrees of modulation suggests that nonlinear effects play an important role in their spatio-temporal dynamics. The resulting complex wave pattern is analyzed in great detail by means of the Hilbert transform, which provides instantaneous wave attributes, such as the phase and the frequency. Our analysis showed that the spatial frequency distribution of the DDWs is usually not constant over the dust cloud. In contrast, the wave field is divided into regions of different but almost constant frequencies [1]. The boundaries of these so-called frequency clusters coincide with the locations of phase defects in the wave field. It is found that the size of the clusters depends on the strength of spatial gradients in the plasma parameters. We attribute the formation of frequency clusters to synchronization phenomena as a consequence of the nonlinear character of the wave.[1] K. O. Menzel, O. Arp, A.Piel, Phys. Rev. Lett. 104, 235002 (2010)

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

Acousto-optic modulation of a photonic crystal nanocavity with Lamb waves in microwave K band

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

Tadesse, Semere A.; School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455; Li, Huan

2015-11-16

Integrating nanoscale electromechanical transducers and nanophotonic devices potentially can enable acousto-optic devices to reach unprecedented high frequencies and modulation efficiency. Here, we demonstrate acousto-optic modulation of a photonic crystal nanocavity using Lamb waves with frequency up to 19 GHz, reaching the microwave K band. The devices are fabricated in suspended aluminum nitride membrane. Excitation of acoustic waves is achieved with interdigital transducers with period as small as 300 nm. Confining both acoustic wave and optical wave within the thickness of the membrane leads to improved acousto-optic modulation efficiency in these devices than that obtained in previous surface acoustic wave devices. Ourmore » system demonstrates a scalable optomechanical platform where strong acousto-optic coupling between cavity-confined photons and high frequency traveling phonons can be explored.« less

Experimental demonstration of highly localized pulses (X waves) at microwave frequencies

NASA Astrophysics Data System (ADS)

Chiotellis, Nikolaos; Mendez, Victor; Rudolph, Scott M.; Grbic, Anthony

2018-02-01

A device that radiates transverse magnetic Bessel beams in the radiative near field is reported. The cone angle of the emitted radiation remains constant over a wide frequency range (18-30 GHz), allowing highly localized pulses (X waves) to be generated under a broadband excitation. The design process, based on ray optics, is discussed. Both frequency and time domain experimental results for a prototype are presented. The measured fields show close agreement with simulation results, and demonstrate the radiator's ability to emit X waves within its nondiffracting range.

Heterodyne mixing of millimetre electromagnetic waves and sub-THz sound in a semiconductor device

PubMed Central

Heywood, Sarah L.; Glavin, Boris A.; Beardsley, Ryan P.; Akimov, Andrey V.; Carr, Michael W.; Norman, James; Norton, Philip C.; Prime, Brian; Priestley, Nigel; Kent, Anthony J.

2016-01-01

We demonstrate heterodyne mixing of a 94 GHz millimetre wave photonic signal, supplied by a Gunn diode oscillator, with coherent acoustic waves of frequency ~100 GHz, generated by pulsed laser excitation of a semiconductor surface. The mixing takes place in a millimetre wave Schottky diode, and the intermediate frequency electrical signal is in the 1–12 GHz range. The mixing process preserves all the spectral content in the acoustic signal that falls within the intermediate frequency bandwidth. Therefore this technique may find application in high-frequency acoustic spectroscopy measurements, exploiting the nanometre wavelength of sub-THz sound. The result also points the way to exploiting acoustoelectric effects in photonic devices working at sub-THz and THz frequencies, which could provide functionalities at these frequencies, e.g. acoustic wave filtering, that are currently in widespread use at lower (GHz) frequencies. PMID:27477841

S-Wave Normal Mode Propagation in Aluminum Cylinders

USGS Publications Warehouse

Lee, Myung W.; Waite, William F.

2010-01-01

Large amplitude waveform features have been identified in pulse-transmission shear-wave measurements through cylinders that are long relative to the acoustic wavelength. The arrival times and amplitudes of these features do not follow the predicted behavior of well-known bar waves, but instead they appear to propagate with group velocities that increase as the waveform feature's dominant frequency increases. To identify these anomalous features, the wave equation is solved in a cylindrical coordinate system using an infinitely long cylinder with a free surface boundary condition. The solution indicates that large amplitude normal-mode propagations exist. Using the high-frequency approximation of the Bessel function, an approximate dispersion relation is derived. The predicted amplitude and group velocities using the approximate dispersion relation qualitatively agree with measured values at high frequencies, but the exact dispersion relation should be used to analyze normal modes for full ranges of frequency of interest, particularly at lower frequencies.

Multi-Tone Millimeter-Wave Frequency Synthesizer for Atmospheric Propagation Studies

NASA Technical Reports Server (NTRS)

Simons, Rainee N.; Wintucky, Edwin G.

2014-01-01

The design and test results of a multi-tone millimeter-wave frequency synthesizer, based on a solid-state frequency comb generator is presented. The intended applications of the synthesizer is in a space-borne transmitter for radio wave atmospheric studies at Q-band (37 to 43 GHz). These studies would enable the design of robust high data rate space-to-ground satellite communication links.

Multi-Tone Millimeter-Wave Frequency Synthesizer for Atmospheric Propagation Studies

NASA Technical Reports Server (NTRS)

Simons, Rainee N.; Wintucky, Edwin G.

2014-01-01

This paper presents the design and test results of a multi-tone millimeter-wave frequency synthesizer, based on a solid-state frequency comb generator. The intended application of the synthesizer is in a space-borne transmitter for radio wave atmospheric studies at Q-band (37-43 GHz). These studies would enable the design of robust high data rate space-to-ground satellite communication links.

Multi-Tone Millimeter-Wave Frequency Synthesizer for Atmospheric Propagation Studies

NASA Technical Reports Server (NTRS)

Simons, Rainee N.; Wintucky, Edwin G.

2014-01-01

This paper presents the design and test results of a multi-tone millimeter-wave frequency synthesizer, based on a solid-state frequency comb generator. The intended application of the synthesizer is in a space-borne transmitter for radio wave atmospheric studies at Q-band (37 to 43 GHz). These studies would enable the design of robust high data rate space-to-ground satellite communication links.

Gigatron microwave amplifier

DOEpatents

McIntyre, P.M.

1993-07-13

An electron tube for achieving high power at high frequency with high efficiency is described, including an input coupler, a ribbon-shaped electron beam and a traveling wave output coupler. The input coupler is a lumped constant resonant circuit that modulates a field emitter array cathode at microwave frequency. A bunched ribbon electron beam is emitted from the cathode in periodic bursts at the desired frequency. The beam has a ribbon configuration to eliminate limitations inherent in round beam devices. The traveling wave coupler efficiently extracts energy from the electron beam, and includes a waveguide with a slot there through for receiving the electron beam. The ribbon beam is tilted at an angle with respect to the traveling wave coupler so that the electron beam couples in-phase with the traveling wave in the waveguide. The traveling wave coupler thus extracts energy from the electron beam over the entire width of the beam.

Gigatron microwave amplifier

DOEpatents

McIntyre, Peter M.

1993-01-01

An electron tube for achieving high power at high frequency with high efficiency, including an input coupler, a ribbon-shaped electron beam and a traveling wave output coupler. The input coupler is a lumped constant resonant circuit that modulates a field emitter array cathode at microwave frequency. A bunched ribbon electron beam is emitted from the cathode in periodic bursts at the desired frequency. The beam has a ribbon configuration to eliminate limitations inherent in round beam devices. The traveling wave coupler efficiently extracts energy from the electron beam, and includes a waveguide with a slot therethrough for receiving the electron beam. The ribbon beam is tilted at an angle with respect to the traveling wave coupler so that the electron beam couples in-phase with the traveling wave in the waveguide. The traveling wave coupler thus extracts energy from the electron beam over the entire width of the beam.

Nonlinear generation of sum and difference frequency waves by two helicon waves in a semiconductor

NASA Astrophysics Data System (ADS)

Salimullah, M.; Ferdous, T.

1984-05-01

This paper presents a theoretical investigation of the nonlinear generation of electrostatic waves at the sum and the difference frequency when two high amplitude elliptically polarized helicon waves propagate along the direction of the externally applied static magnetic field in an n-type semiconductor. The nonlinearity arises through the ponderomotive force on electrons. It is noticed that the power conversion efficiency of the difference frequency generation is much larger than that of the sum frequency generation. The power conversion efficiency may be easily increased by increasing the density of electrons in the semiconductor.

Periodic nonlinear waves resulting from the contact interaction of a crack

NASA Astrophysics Data System (ADS)

Lee, Sang Eon; Jin, Suyeong; Hong, Jung-Wuk

2017-09-01

When two different inputs of distinct low and high frequencies are applied to a medium, the linear responses are composed of waves of two dominant frequencies. However, microcracks such as fatigue cracks generate nonlinear waves by modulating the characteristics of the incident waves. Although this phenomenon has been observed and used to detect microcracks, the underlying principles have not been thoroughly elucidated. The hysteresis properties were introduced to describe the nonlinear relationship between the stress and strain to explain these phenomena [Van Den Abeele et al., Res. Nondestruct. Eval. 12, 17 (2000) and Nazarov et al., Acoust. Phys. 49, 344 (2003)]. The generation of harmonics was explained by superimposing stress-strain relations that vary with crack width and excitation magnitude. As the crack depth increases, the ratio of magnitudes of the second harmonic to the first harmonic increases, but the increment becomes smaller [Kawashima et al., Ultrasonics 40, 611 (2002)]. Here, we show that the waves affected by the contact motion of the crack surfaces cultivate the nonlinearity in waveforms, resulting in high frequency off-band signals. With the hypothesis that the clapping of cracks might generate nonlinear components close to the high excitation frequency, we prove that the generation of the high frequency off-band peaks is directly affected by the clapping contact interaction of the crack surfaces. The amount of energy transmitted is closely related to the size of the crack width and the magnitudes of low and high frequency excitations.

Experimental study of inertial waves in a spherical shell induced by librations of the inner sphere

NASA Astrophysics Data System (ADS)

Hoff, Michael; Harlander, Uwe; Jahangir, Saad; Egbers, Christoph

2015-04-01

Many planetary bodies do not rotate with a constant velocity but undergo rotations with superposed oscillations called longitudinal librations. This is the case e.g. for the Earth's moon, Mars' moon, Mercury and many other moons of Jupiter and Saturn and some of them have a solid inner core and a molten outer core. It is worth to know the interaction between the libration of the core and the interior of the fluid to understand tidal heating, fluid mixing, and the generation of magnetic fields. Here we present an experimental investigation of inertial waves in a spherical shell. The shell rotates with a mean angular velocity Ω around its vertical axis overlaid by a time periodic oscillation of the inner sphere in the range 0 < ω < 2Ω, in order to excite inertial waves with a known frequency. We want to show the influence of the libration amplitude ɛ on different libration frequencies ω and how efficient libration is, to excite inertial waves in the given frequency range. For low ω and high ɛ instability starts to grow and, beside the excited inertial waves, several low frequency structures can be found. Quantitative PIV analyses of the horizontal plane in the co-rotation frame show clear spiral structures with different wave numbers for high libration amplitudes due to strong shear, similar to differential rotation. Another question, we like to address, is whether high libration amplitudes can also excite very low frequency Rossby wave structures? If the frequency increases, it can be seen from Poincaré plots that large attractor windows for inertial waves appear. We want to show PIV analyses for such flows dominated by wave attractors. It is known that for large excitation frequencies subharmonic parametric instability starts to grow and triads will be excited. Our experimental data show hints for the existence of triads and preliminary results will be discussed.

External control of ion waves in a plasma by high frequency fields

DOEpatents

Kaw, P.K.; Dawson, J.M.

1973-12-18

An apparatus and method are described for stabilizing plasma instabilities, in a magnetically confined plasma column by transmitting into the plasma high frequency electromagnetic waves at a frequency close to the electron plasma frequency. The said frequencies, e.g., are between the plasma frequency and 1.5 times the plasma frequency at a power level below the level for producing parametric instabilities in a plasma having temperatures from below 10 eV to about 10 keV or more, at densities from below 10/sup 13/ to above 10/sup 18/ particles/cm/sup 3/. (Official Gazette)

Interferometry

NASA Technical Reports Server (NTRS)

Ridgway, Stephen; Wilson, Robert W.; Begelman, Mitchell C.; Bender, Peter; Burke, Bernard F.; Cornwell, Tim; Drever, Ronald; Dyck, H. Melvin; Johnston, Kenneth J.; Kibblewhite, Edward

1991-01-01

The following recommended programs are reviewed: (1) infrared and optical interferometry (a ground-based and space programs); (2) compensation for the atmosphere with adaptive optics (a program for development and implementation of adaptive optics); and (3) gravitational waves (high frequency gravitational wave sources (LIGO), low frequency gravitational wave sources (LAGOS), a gravitational wave observatory program, laser gravitational wave observatory in space, and technology development during the 1990's). Prospects for international collaboration and related issues are also discussed.

VLF wave generation by beating of two HF waves in the ionosphere

NASA Astrophysics Data System (ADS)

Kuo, Spencer; Snyder, Arnold; Kossey, Paul; Chang, Chia-Lie; Labenski, John

2011-05-01

Theory of a beat-wave mechanism for very low frequency (VLF) wave generation in the ionosphere is presented. The VLF current is produced by beating two high power HF waves of slightly different frequencies through the nonlinearity and inhomogeneity of the ionospheric plasma. Theory also shows that the density irregularities can enhance the beat-wave generation. An experiment was conducted by transmitting two high power HF waves of 3.2 MHz and 3.2 MHz + f, where f = 5, 8, 13, and 2.02 kHz, from the HAARP transmitter. In the experiment, the ionosphere was underdense to the O-mode heater, i.e., the heater frequency f0 > foF2, and overdense or slightly underdense to the X-mode heater, i.e., f0 < fxF2 or f0 ≥ fxF2. The radiation intensity increased with the VLF wave frequency, was much stronger with the X-mode heaters, and was not sensitive to the electrojet. The strongest VLF radiation of 13 kHz was generated when the reflection layer of the X-mode heater was just slightly below the foF2 layer and the spread of the O-mode sounding echoes had the largest enhancement, suggesting an optimal setting for beat-wave generation of VLF waves by the HF heaters.

Slow wave contraction frequency plateaus in the small intestine are composed of discrete waves of interval increase associated with dislocations.

PubMed

Parsons, Sean P; Huizinga, Jan D

2018-06-03

What is the central question of this study? What is the nature of slow wave driven contraction frequency gradients in the small intestine? What is the main finding and its importance? Frequency plateaus are composed of discrete waves of increased interval, each wave associated with a contraction dislocation. Smooth frequency gradients are generated by localised neural modulation of wave frequency, leading to functionally important wave turbulence. Both patterns are emergent properties of a network of coupled oscillators, the interstitial cells of Cajal. A gut-wide network of interstitial cells of Cajal (ICC) generate electrical oscillations (slow waves) that orchestrate waves of muscle contraction. In the small intestine there is a gradient in slow wave frequency from high at the duodenum to low at the terminal ileum. Time-averaged measurements of frequency have suggested either a smooth or stepped (plateaued) gradient. We measured individual contraction intervals from diameter maps of the mouse small intestine to create interval maps (IMaps). IMaps showed that each frequency plateau was composed of discrete waves of increased interval. Each interval wave originated at a terminating contraction wave, a "dislocation", at the plateau's proximal boundary. In a model chain of coupled phase oscillators, interval wave frequency increased as coupling decreased or as the natural frequency gradient or noise increased. Injuring the intestine at a proximal point to destroy coupling, suppressed distal steps which then reappeared with gap junction block by carbenoxolone. This lent further support to our previous hypothesis that lines of dislocations were fixed by points of low coupling strength. Dislocations induced by electrical field pulses in the intestine and by equivalent phase shift in the model, were associated with interval waves. When the enteric nervous system was active, IMaps showed a chaotic, turbulent pattern of interval change with no frequency steps or plateaus. This probably resulted from local, stochastic release of neurotransmitters. Plateaus, dislocations, interval waves and wave turbulence arise from a dynamic interplay between natural frequency and coupling in the ICC network. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Dynamic response of a riser under excitation of internal waves

NASA Astrophysics Data System (ADS)

Lou, Min; Yu, Chenglong; Chen, Peng

2015-12-01

In this paper, the dynamic response of a marine riser under excitation of internal waves is studied. With the linear approximation, the governing equation of internal waves is given. Based on the rigid-lid boundary condition assumption, the equation is solved by Thompson-Haskell method. Thus the velocity field of internal waves is obtained by the continuity equation. Combined with the modified Morison formula, using finite element method, the motion equation of riser is solved in time domain with Newmark-β method. The computation programs are compiled to solve the differential equations in time domain. Then we get the numerical results, including riser displacement and transfiguration. It is observed that the internal wave will result in circular shear flow, and the first two modes have a dominant effect on dynamic response of the marine riser. In the high mode, the response diminishes rapidly. In different modes of internal waves, the deformation of riser has different shapes, and the location of maximum displacement shifts. Studies on wave parameters indicate that the wave amplitude plays a considerable role in response displacement of riser, while the wave frequency contributes little. Nevertheless, the internal waves of high wave frequency will lead to a high-frequency oscillation of riser; it possibly gives rise to fatigue crack extension and partial fatigue failure.

Experimental Investigation of the Properties of an Acoustic Wave Induced by Laser Ablation of a Solid Target in Water-Confined Plasma Propulsion

NASA Astrophysics Data System (ADS)

Zheng, Zhiyuan; Gao, Hua; Gao, Lu; Xing, Jie

2014-11-01

Acoustic waves generated in nanosecond pulsed-laser ablation of a solid target in both air and water-confined environments were measured experimentally. It was found that the amplitude of the acoustic wave tended to decrease with an increase in water thickness. The waves were analyzed by means of fast Fourier transform. It was shown that there are several frequency components in the acoustic waves with the dominant frequency shifting from high frequency to low frequency as the thickness of the water layer increases. Furthermore, strong acoustic pressure led to enhancement of the coupling of the laser energy to the target in laser plasma propulsion.

Rock physics model-based prediction of shear wave velocity in the Barnett Shale formation

NASA Astrophysics Data System (ADS)

Guo, Zhiqi; Li, Xiang-Yang

2015-06-01

Predicting S-wave velocity is important for reservoir characterization and fluid identification in unconventional resources. A rock physics model-based method is developed for estimating pore aspect ratio and predicting shear wave velocity Vs from the information of P-wave velocity, porosity and mineralogy in a borehole. Statistical distribution of pore geometry is considered in the rock physics models. In the application to the Barnett formation, we compare the high frequency self-consistent approximation (SCA) method that corresponds to isolated pore spaces, and the low frequency SCA-Gassmann method that describes well-connected pore spaces. Inversion results indicate that compared to the surroundings, the Barnett Shale shows less fluctuation in the pore aspect ratio in spite of complex constituents in the shale. The high frequency method provides a more robust and accurate prediction of Vs for all the three intervals in the Barnett formation, while the low frequency method collapses for the Barnett Shale interval. Possible causes for this discrepancy can be explained by the fact that poor in situ pore connectivity and low permeability make well-log sonic frequencies act as high frequencies and thus invalidate the low frequency assumption of the Gassmann theory. In comparison, for the overlying Marble Falls and underlying Ellenburger carbonates, both the high and low frequency methods predict Vs with reasonable accuracy, which may reveal that sonic frequencies are within the transition frequencies zone due to higher pore connectivity in the surroundings.

Generation of a pseudo-2D shear-wave velocity section by inversion of a series of 1D dispersion curves

USGS Publications Warehouse

Luo, Y.; Xia, J.; Liu, J.; Xu, Y.; Liu, Q.

2008-01-01

Multichannel Analysis of Surface Waves utilizes a multichannel recording system to estimate near-surface shear (S)-wave velocities from high-frequency Rayleigh waves. A pseudo-2D S-wave velocity (vS) section is constructed by aligning 1D models at the midpoint of each receiver spread and using a spatial interpolation scheme. The horizontal resolution of the section is therefore most influenced by the receiver spread length and the source interval. The receiver spread length sets the theoretical lower limit and any vS structure with its lateral dimension smaller than this length will not be properly resolved in the final vS section. A source interval smaller than the spread length will not improve the horizontal resolution because spatial smearing has already been introduced by the receiver spread. In this paper, we first analyze the horizontal resolution of a pair of synthetic traces. Resolution analysis shows that (1) a pair of traces with a smaller receiver spacing achieves higher horizontal resolution of inverted S-wave velocities but results in a larger relative error; (2) the relative error of the phase velocity at a high frequency is smaller than at a low frequency; and (3) a relative error of the inverted S-wave velocity is affected by the signal-to-noise ratio of data. These results provide us with a guideline to balance the trade-off between receiver spacing (horizontal resolution) and accuracy of the inverted S-wave velocity. We then present a scheme to generate a pseudo-2D S-wave velocity section with high horizontal resolution using multichannel records by inverting high-frequency surface-wave dispersion curves calculated through cross-correlation combined with a phase-shift scanning method. This method chooses only a pair of consecutive traces within a shot gather to calculate a dispersion curve. We finally invert surface-wave dispersion curves of synthetic and real-world data. Inversion results of both synthetic and real-world data demonstrate that inverting high-frequency surface-wave dispersion curves - by a pair of traces through cross-correlation with phase-shift scanning method and with the damped least-square method and the singular-value decomposition technique - can feasibly achieve a reliable pseudo-2D S-wave velocity section with relatively high horizontal resolution. ?? 2008 Elsevier B.V. All rights reserved.

High-Frequency Gravitational Wave research and application to exoplanet studies

NASA Astrophysics Data System (ADS)

Baker, R. M. L., Jr.

2017-10-01

A discussion of the history of High-Frequency Gravitational Wave (HFGW) research is first presented. Over the years until modern times, starting with the first mention of Gravitational Waves by Poincaré in 1905 and the definition of HFGWs in 1961 by Robert L. Forward, the discussion continues concerning the international research efforts to detect HFGWs. The article highlights the accomplishments of HFGW researchers in China, Russia, Ukraine, England, Australia, Japan, Germany, Spain, Italy, and the United States. Comparisons are made with Low-Frequency Gravitational Wave (LFGW) research, especially concerning the Laser Interferometer Gravitational Observatory or LIGO. In fine, there are presented several interesting perspectives concerning cosmology, the speed of time and, especially, exoplanet applications of HFGWs.

High-energy terahertz wave parametric oscillator with a surface-emitted ring-cavity configuration.

PubMed

Yang, Zhen; Wang, Yuye; Xu, Degang; Xu, Wentao; Duan, Pan; Yan, Chao; Tang, Longhuang; Yao, Jianquan

2016-05-15

A surface-emitted ring-cavity terahertz (THz) wave parametric oscillator has been demonstrated for high-energy THz output and fast frequency tuning in a wide frequency range. Through the special optical design with a galvano-optical scanner and four-mirror ring-cavity structure, the maximum THz wave output energy of 12.9 μJ/pulse is achieved at 1.359 THz under the pump energy of 172.8 mJ. The fast THz frequency tuning in the range of 0.7-2.8 THz can be accessed with the step response of 600 μs. Moreover, the maximum THz wave output energy from this configuration is 3.29 times as large as that obtained from the conventional surface-emitted THz wave parametric oscillator with the same experimental conditions.

Quantified Energy Dissipation Rates in the Terrestrial Bow Shock. 1.; Analysis Techniques and Methodology

NASA Technical Reports Server (NTRS)

Wilson, L. B., III; Sibeck, D. G.; Breneman, A.W.; Le Contel, O.; Cully, C.; Turner, D. L.; Angelopoulos, V.; Malaspina, D. M.

2014-01-01

We present a detailed outline and discussion of the analysis techniques used to compare the relevance of different energy dissipation mechanisms at collisionless shock waves. We show that the low-frequency, quasi-static fields contribute less to ohmic energy dissipation, (-j · E ) (minus current density times measured electric field), than their high-frequency counterparts. In fact, we found that high-frequency, large-amplitude (greater than 100 millivolts per meter and/or greater than 1 nanotesla) waves are ubiquitous in the transition region of collisionless shocks. We quantitatively show that their fields, through wave-particle interactions, cause enough energy dissipation to regulate the global structure of collisionless shocks. The purpose of this paper, part one of two, is to outline and describe in detail the background, analysis techniques, and theoretical motivation for our new results presented in the companion paper. The companion paper presents the results of our quantitative energy dissipation rate estimates and discusses the implications. Together, the two manuscripts present the first study quantifying the contribution that high-frequency waves provide, through wave-particle interactions, to the total energy dissipation budget of collisionless shock waves.

Detectability of primordial gravitational waves produced in bouncing models

NASA Astrophysics Data System (ADS)

Pinto-Neto, Nelson; Scardua, Arthur

2017-06-01

It is widely known that bouncing models with a dust hydrodynamical fluid satisfying cs2=pd/ρd≈0 , where cs , pd , ρd are the sound velocity, pressure, and energy density of the dust fluid, respectively, have almost scale invariant spectrum of scalar perturbations and negligible primordial gravitational waves. We investigate whether adding another fluid with 1 /3

High resolution wavenumber analysis for investigation of arterial pulse wave propagation

NASA Astrophysics Data System (ADS)

Hasegawa, Hideyuki; Sato, Masakazu; Irie, Takasuke

2016-07-01

The propagation of the pulse wave along the artery is relatively fast (several m/s), and a high-temporal resolution is required to measure pulse wave velocity (PWV) in a regional segment of the artery. High-frame-rate ultrasound enables the measurement of the regional PWV. In analyses of wave propagation phenomena, the direction and propagation speed are generally identified in the frequency-wavenumber space using the two-dimensional Fourier transform. However, the wavelength of the pulse wave is very long (1 m at a propagation velocity of 10 m/s and a temporal frequency of 10 Hz) compared with a typical lateral field of view of 40 mm in ultrasound imaging. Therefore, PWV cannot be identified in the frequency-wavenumber space owing to the low resolution of the two-dimensional Fourier transform. In the present study, PWV was visualized in the wavenumber domain using phases of arterial wall acceleration waveforms measured by high-frame-rate ultrasound.

Corrosion monitoring using high-frequency guided waves

NASA Astrophysics Data System (ADS)

Fromme, P.

2016-04-01

Corrosion can develop due to adverse environmental conditions during the life cycle of a range of industrial structures, e.g., offshore oil platforms, ships, and desalination plants. Generalized corrosion leading to wall thickness loss can cause the reduction of the strength and thus degradation of the structural integrity. The monitoring of corrosion damage in difficult to access areas can be achieved using high frequency guided waves propagating along the structure from accessible areas. Using standard ultrasonic wedge transducers with single sided access to the structure, guided wave modes were selectively generated that penetrate through the complete thickness of the structure. The wave propagation and interference of the different guided wave modes depends on the thickness of the structure. Laboratory experiments were conducted for wall thickness reduction due to milling of the steel structure. From the measured signal changes due to the wave mode interference the reduced wall thickness was monitored. Good agreement with theoretical predictions was achieved. The high frequency guided waves have the potential for corrosion damage monitoring at critical and difficult to access locations from a stand-off distance.

Corrosion monitoring using high-frequency guided ultrasonic waves

NASA Astrophysics Data System (ADS)

Fromme, Paul

2014-02-01

Corrosion develops due to adverse environmental conditions during the life cycle of a range of industrial structures, e.g., offshore oil platforms, ships, and desalination plants. Both pitting corrosion and generalized corrosion leading to wall thickness loss can cause the degradation of the structural integrity. The nondestructive detection and monitoring of corrosion damage in difficult to access areas can be achieved using high frequency guided waves propagating along the structure from accessible areas. Using standard ultrasonic transducers with single sided access to the structure, guided wave modes were generated that penetrate through the complete thickness of the structure. The wave propagation and interference of the different guided wave modes depends on the thickness of the structure. Laboratory experiments were conducted and the wall thickness reduced by consecutive milling of the steel structure. Further measurements were conducted using accelerated corrosion in a salt water bath and the damage severity monitored. From the measured signal change due to the wave mode interference the wall thickness reduction was monitored. The high frequency guided waves have the potential for corrosion damage monitoring at critical and difficult to access locations from a stand-off distance.

Nonlinear Interaction of Waves in Rotating Spherical Layers

NASA Astrophysics Data System (ADS)

Zhilenko, D.; Krivonosova, O.; Gritsevich, M.

2018-01-01

Flows of a viscous incompressible fluid in a spherical layer that are due to rotational oscillations of its inner boundary at two frequencies with respect to the state of rest are numerically studied. It is found that an increase in the amplitude of oscillations of the boundary at the higher frequency can result in a significant enhancement of the low-frequency mode in a flow near the outer boundary. The direction of propagation of the low-frequency wave changes from radial to meridional, whereas the high-frequency wave propagates in the radial direction in a limited inner region of the spherical layer. The role of the meridional circulation in the energy exchange between spaced waves is demonstrated.

Compact Tunable Narrowband Terahertz-Wave Source Based on Difference Frequency Generation Pumped by Dual Fiber Lasers in MgO:LiNbO3

NASA Astrophysics Data System (ADS)

Wada, Yoshio; Satoh, Takumi; Higashi, Yasuhiro; Urata, Yoshiharu

2017-12-01

We demonstrate a high-average-power, single longitudinal-mode, and tunable terahertz (THz)-wave source based on difference frequency generation (DFG) in a MgO:LiNbO3 (MgO:LN) crystal. The waves for DFG are generated using a pair of Yb-doped pulsed fiber lasers with a master oscillator power fiber amplifier configuration. The average power of the THz-wave output reaches 450 μW at 1.07 THz (280 μm) at a linewidth of 7.2 GHz, and the tunability ranges from 0.35 to 1.07 THz under the pulse repetition frequency of 500 kHz. A short burn-in test of the THz wave is also carried out, and the output power stability is within ± 5% of the averaged power without any active stabilizing technique. The combination of MgO:LN-DFG and stable and robust fiber laser sources is highly promising for the development of high-average-power THz-wave sources, particularly in the high transmission sub-THz region. This approach may enable new applications of THz-wave spectroscopy in imaging and remote sensing.

Multi-Species Test of Ion Cyclotron Resonance Heating at High Altitudes

NASA Technical Reports Server (NTRS)

Persoon, A. M.; Peterson, W. K.; Andre, M.; Chang, T.; Gurnett, D. A.; Retterer, J. M.; Crew, G. B.

1997-01-01

Observations of ion distributions and plasma waves obtained by the Dynamics Explorer 1 satellite in the high-altitude, nightside auroral zone are used to study ion energization for three ion species. A number of theoretical models have been proposed to account for the transverse heating of these ion populations. One of these, the ion cyclotron resonance heating (ICRH) mechanism, explains ion conic formation through ion cyclotron resonance with broadband electromagnetic wave turbulence in the vicinity of the characteristic ion cyclotron frequency. The cyclotron resonant heating of the ions by low- frequency electromagnetic waves is an important energy source for the transport of ions from the ionosphere to the magnetosphere. In this paper we test the applicability of the ICRH mechanism to three simultaneously heated and accelerated ion species by modelling the ion conic formation in terms of a resonant wave-particle interaction in which the ions extract energy from the portion of the broadband electromagnetic wave spectrum which includes the ion cyclotron frequency. Using a Monte Carlo technique we evaluate the ion heating produced by the electromagnetic turbulence at low frequencies and find that the wave amplitudes near the ion cyclotron frequencies are sufficient to explain the observed ion energies.

Multi-Species Test of Ion Cyclotron Resonance Heating at High Altitudes

NASA Technical Reports Server (NTRS)

Persoon, A. M.; Peterson, W. K.; Andre, M.; Chang, T.; Gurnett, D. A.; Retterer, J. M.; Crew, G. B.

1997-01-01

Observations of ion distributions and plasma waves obtained by the Dynamics Explorer 1 satellite in the high-altitude, nightside auroral zone are used to study ion energization for three ion species. A number of theoretical models have been proposed to account for the transverse heating of these ion populations. One of these, the ion cyclotron resonance heating (ICRH) mechanism, explains ion conic formation through ion cyclotron resonance with broadband electromagnetic wave turbulence in the vicinity of the characteristic ion cyclotron frequency. The cyclotron resonant heating of the ions by low-frequency electromagnetic waves is an important energy source for the transport of ions from the ionosphere to the magnetosphere. In this paper we test the applicability of the ICRH mechanism to three simultaneously heated and accelerated ion species by modelling the ion conic formation in terms of a resonant wave-particle interaction in which the ions extract energy from the portion of the broadband electromagnetic wave spectrum which includes the ion cyclotron frequency. Using a Monte Carlo technique we evaluate the ion heating produced by the electromagnetic turbulence at low frequencies and find that the wave amplitudes near the ion cyclotron frequencies are sufficient to explain the observed ion energies.

Wideband spectrum analysis of ultra-high frequency radio-wave signals due to advanced one-phonon non-collinear anomalous light scattering.

PubMed

Shcherbakov, Alexandre S; Arellanes, Adan Omar

2017-04-20

We present a principally new acousto-optical cell providing an advanced wideband spectrum analysis of ultra-high frequency radio-wave signals. For the first time, we apply a recently developed approach with the tilt angle to a one-phonon non-collinear anomalous light scattering. In contrast to earlier cases, now one can exploit a regime with the fixed optical wavelength for processing a great number of acoustic frequencies simultaneously in the linear regime. The chosen rutile-crystal combines a moderate acoustic velocity with low acoustic attenuation and allows us wide-band data processing within GHz-frequency acoustic waves. We have created and experimentally tested a 6-cm aperture rutile-made acousto-optical cell providing the central frequency 2.0 GHz, frequency bandwidth ∼0.52  GHz with the frequency resolution about 68.3 kHz, and ∼7620 resolvable spots. A similar cell permits designing an advanced ultra-high-frequency arm within a recently developed multi-band radio-wave acousto-optical spectrometer for astrophysical studies. This spectrometer is intended to operate with a few parallel optical arms for processing the multi-frequency data flows within astrophysical observations. Keeping all the instrument's advantages of the previous schematic arrangement, now one can create the highest-frequency arm using the developed rutile-based acousto-optical cell. It permits optimizing the performances inherent in that arm via regulation of both the central frequency and the frequency bandwidth for spectrum analysis.

Finite-difference modeling and dispersion analysis of high-frequency love waves for near-surface applications

USGS Publications Warehouse

Luo, Y.; Xia, J.; Xu, Y.; Zeng, C.; Liu, J.

2010-01-01

Love-wave propagation has been a topic of interest to crustal, earthquake, and engineering seismologists for many years because it is independent of Poisson's ratio and more sensitive to shear (S)-wave velocity changes and layer thickness changes than are Rayleigh waves. It is well known that Love-wave generation requires the existence of a low S-wave velocity layer in a multilayered earth model. In order to study numerically the propagation of Love waves in a layered earth model and dispersion characteristics for near-surface applications, we simulate high-frequency (>5 Hz) Love waves by the staggered-grid finite-difference (FD) method. The air-earth boundary (the shear stress above the free surface) is treated using the stress-imaging technique. We use a two-layer model to demonstrate the accuracy of the staggered-grid modeling scheme. We also simulate four-layer models including a low-velocity layer (LVL) or a high-velocity layer (HVL) to analyze dispersive energy characteristics for near-surface applications. Results demonstrate that: (1) the staggered-grid FD code and stress-imaging technique are suitable for treating the free-surface boundary conditions for Love-wave modeling, (2) Love-wave inversion should be treated with extra care when a LVL exists because of a lack of LVL information in dispersions aggravating uncertainties in the inversion procedure, and (3) energy of high modes in a low-frequency range is very weak, so that it is difficult to estimate the cutoff frequency accurately, and "mode-crossing" occurs between the second higher and third higher modes when a HVL exists. ?? 2010 Birkh??user / Springer Basel AG.

Frequency-dependent Alfvén-wave Propagation in the Solar Wind: Onset and Suppression of Parametric Decay Instability

NASA Astrophysics Data System (ADS)

Shoda, Munehito; Yokoyama, Takaaki; Suzuki, Takeru K.

2018-06-01

Using numerical simulations we investigate the onset and suppression of parametric decay instability (PDI) in the solar wind, focusing on the suppression effect by the wind acceleration and expansion. Wave propagation and dissipation from the coronal base to 1 au is solved numerically in a self-consistent manner; we take into account the feedback of wave energy and pressure in the background. Monochromatic waves with various injection frequencies, f 0, are injected to discuss the suppression of PDI, while broadband waves are applied to compare the numerical results with observation. We find that high-frequency ({f}0≳ {10}-3 {Hz}) Alfvén waves are subject to PDI. Meanwhile, the maximum growth rate of the PDI of low-frequency ({f}0≲ {10}-4 {Hz}) Alfvén waves becomes negative due to acceleration and expansion effects. Medium-frequency ({f}0≈ {10}-3.5 {Hz}) Alfvén waves have a positive growth rate but do not show the signature of PDI up to 1 au because the growth rate is too small. The medium-frequency waves experience neither PDI nor reflection so they propagate through the solar wind most efficiently. The solar wind is shown to possess a frequency-filtering mechanism with respect to Alfvén waves. The simulations with broadband waves indicate that the observed trend of the density fluctuation is well explained by the evolution of PDI while the observed cross-helicity evolution is in agreement with low-frequency wave propagation.

Generalized thermoelastic diffusive waves in heat conducting materials

NASA Astrophysics Data System (ADS)

Sharma, J. N.

2007-04-01

Keeping in view the applications of diffusion processes in geophysics and electronics industry, the aim of the present paper is to give a detail account of the plane harmonic generalized thermoelastic diffusive waves in heat conducting solids. According to the characteristic equation, three longitudinal waves namely, elastodiffusive (ED), mass diffusion (MD-mode) and thermodiffusive (TD-mode), can propagate in such solids in addition to transverse waves. The transverse waves get decoupled from rest of the fields and hence remain unaffected due to temperature change and mass diffusion effects. These waves travel without attenuation and dispersion. The other generalized thermoelastic diffusive waves are significantly influenced by the interacting fields and hence suffer both attenuation and dispersion. At low frequency mass diffusion and thermal waves do not exist but at high-frequency limits these waves propagate with infinite velocity being diffusive in character. Moreover, in the low-frequency regions, the disturbance is mainly dominant by mechanical process of transportation of energy and at high-frequency regions it is significantly dominated by a close to diffusive process (heat conduction or mass diffusion). Therefore, at low-frequency limits the waves like modes are identifiable with small amplitude waves in elastic materials that do not conduct heat. The general complex characteristic equation is solved by using irreducible case of Cardano's method with the help of DeMoivre's theorem in order to obtain phase speeds, attenuation coefficients and specific loss factor of energy dissipation of various modes. The propagation of waves in case of non-heat conducting solids is also discussed. Finally, the numerical solution is carried out for copper (solvent) and zinc (solute) materials and the obtained phase velocities, attenuation coefficients and specific loss factor of various thermoelastic diffusive waves are presented graphically.

A Source Term for Wave Attenuation by Sea Ice in WAVEWATCH III(registered trademark): IC4

DTIC Science & Technology

2017-06-07

energy in the high frequency face of the spectrum, which highlights the fact that frequency dependent attenuation in necessary to replicate the low-pass... frequency space ; M6) and an expanded version of M5 with up to 10 steps. The remainder of this report is structured as follows: a note about the...function period, T = 1/f. Measurements have shown that ice preferentially damps high frequency waves and in this way ice acts as a low pass filter

Generation of uniform large-area very high frequency plasmas by launching two specific standing waves simultaneously

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

Chen, Hsin-Liang, E-mail: hlchen@iner.gov.tw; Tu, Yen-Cheng; Hsieh, Cheng-Chang

2014-09-14

With the characteristics of higher electron density and lower ion bombardment energy, large-area VHF (very high frequency) plasma enhanced chemical vapor deposition has become an essential manufacturing equipment to improve the production throughput and efficiency of thin film silicon solar cell. However, the combination of high frequency and large electrodes leads to the so-called standing wave effect causing a serious problem for the deposition uniformity of silicon thin film. In order to address this issue, a technique based on the idea of simultaneously launching two standing waves that possess similar amplitudes and are out of phase by 90° in timemore » and space is proposed in this study. A linear plasma reactor with discharge length of 54 cm is tested with two different frequencies including 60 and 80 MHz. The experimental results show that the proposed technique could effectively improve the non-uniformity of VHF plasmas from >±60% when only one standing wave is applied to <±10% once two specific standing waves are launched at the same time. Moreover, in terms of the reactor configuration adopted in this study, in which the standing wave effect along the much shorter dimension can be ignored, the proposed technique is applicable to different frequencies without the need to alter the number and arrangement of power feeding points.« less

Optical frequency standards for gravitational wave detection using satellite velocimetry

NASA Astrophysics Data System (ADS)

Vutha, Amar

2015-04-01

Satellite Doppler velocimetry, building on the work of Kaufmann and Estabrook and Wahlquist, is a complementary technique to interferometric methods of gravitational wave detection. This method is based on the fact that the gravitational wave amplitude appears in the apparent Doppler shift of photons propagating from an emitter to a receiver. This apparent Doppler shift can be resolved provided that a frequency standard, capable of quickly averaging down to a high stability, is available. We present a design for a space-capable optical atomic frequency standard, and analyze the sensitivity of satellite Doppler velocimetry for gravitational wave astronomy in the milli-hertz frequency band.

The detectability of high frequency energy at teleseismic and regional distances, 1. Studies of radiation from high-explosive and nuclear cratering events, 2

NASA Astrophysics Data System (ADS)

der, Z. A.; Blandford, R. R.

1981-03-01

A survey of the literature on short period seismic studies showed that seismic waves of high frequency in the 3-10 Hz range can be observed regularly at both regional and teleseismic distances. These observations show that the low Q values proposed for the long period seismic waves cannot be valid in the short period band. The data indicate that, in the mantle, Q increases with frequency and may be as much as five times higher at 5-10 Hz than in the long period band. Even with the most conservative assumptions, the level of high frequency amplitudes in the teleseismic P waves exceeds that predicted with a constant t*p = 1 sec by a factor of at least 100,000 at and beyond 5 Hz. The apparent Q beta of the lithosphere, which may be largely due to scattering by the small scale inhomogeneities in the crust, also shows an increase with frequency by as much as a factor of four within the 1-10 Hz band. This parameter controls the attenuation and the detectability of seismic waves at regional distances such as Pn, Pg, Su and Lg.

Detecting Gravitational Wave Memory without Parent Signals

NASA Astrophysics Data System (ADS)

McNeill, Lucy O.; Thrane, Eric; Lasky, Paul D.

2017-05-01

Gravitational-wave memory manifests as a permanent distortion of an idealized gravitational-wave detector and arises generically from energetic astrophysical events. For example, binary black hole mergers are expected to emit memory bursts a little more than an order of magnitude smaller in strain than the oscillatory parent waves. We introduce the concept of "orphan memory": gravitational-wave memory for which there is no detectable parent signal. In particular, high-frequency gravitational-wave bursts (≳kHz ) produce orphan memory in the LIGO/Virgo band. We show that Advanced LIGO measurements can place stringent limits on the existence of high-frequency gravitational waves, effectively increasing the LIGO bandwidth by orders of magnitude. We investigate the prospects for and implications of future searches for orphan memory.

Extremely high frequency RF effects on electronics.

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

Loubriel, Guillermo Manuel; Vigliano, David; Coleman, Phillip Dale

The objective of this work was to understand the fundamental physics of extremely high frequency RF effects on electronics. To accomplish this objective, we produced models, conducted simulations, and performed measurements to identify the mechanisms of effects as frequency increases into the millimeter-wave regime. Our purpose was to answer the questions, 'What are the tradeoffs between coupling, transmission losses, and device responses as frequency increases?', and, 'How high in frequency do effects on electronic systems continue to occur?' Using full wave electromagnetics codes and a transmission-line/circuit code, we investigated how extremely high-frequency RF propagates on wires and printed circuit boardmore » traces. We investigated both field-to-wire coupling and direct illumination of printed circuit boards to determine the significant mechanisms for inducing currents at device terminals. We measured coupling to wires and attenuation along wires for comparison to the simulations, looking at plane-wave coupling as it launches modes onto single and multiconductor structures. We simulated the response of discrete and integrated circuit semiconductor devices to those high-frequency currents and voltages, using SGFramework, the open-source General-purpose Semiconductor Simulator (gss), and Sandia's Charon semiconductor device physics codes. This report documents our findings.« less

Laser-Generated Rayleigh Waves Propagating in Transparent Viscoelastic Adhesive Coating/Metal Substrate Systems

NASA Astrophysics Data System (ADS)

Guan, Yi-jun; Sun, Hong-xiang; Yuan, Shou-qi; Zhang, Shu-yi; Ge, Yong

2016-10-01

We have established numerical models for simulating laser-generated Rayleigh waves in coating/substrate systems by a finite element method and investigated the propagation characteristics of Rayleigh waves in systems concerning the viscoelasticity and transparency of adhesive coatings. In this way, we have studied the influence of the mechanical properties of the coating, such as the elastic moduli, viscoelastic moduli, coating thickness, transparency, and coating material, on the propagation characteristics of the Rayleigh waves. The results show that the propagation characteristics of the Rayleigh waves can be divided into low- and high-frequency parts. The high-frequency propagation characteristics of the Rayleigh wave are closely related to the properties of the adhesive coating.

Evidence for a continuous spectrum of equatorial waves in the Indian Ocean

NASA Astrophysics Data System (ADS)

Eriksen, Charles C.

1980-06-01

Seven-month records of current and temperature measurements from a moored array centered at 53°E on the equator in the Indian Ocean are consistent with a continuous spectrum of equatorially trapped internal inertial-gravity, mixed Rossby-gravity, and Kelvin waves. A model spectrum of free linear waves analogous to those for mid-latitude internal gravity waves is used to compute spectra of observed quantities at depths greater than about 2000 m. Model parameters are adjusted to fit general patterns in the observed spectra over periods from roughly 2 days to 1 month. Measurements at shallower depths presumably include forced motions which we have not attempted to model. This `straw-person' spectrum is consistent with the limited data available. The model spectru Ē (n, m, ω) = K · B(m) · C(n, ω), where Ē is an average local energy density in the equatorial wave guide which has amplitude K, wave number shape B(m) ∝ (1 + m/m*)-3, where m is vertical mode number and the bandwidth parameter m* is between 4 and 8, and frequency shape C(n, ω) ∝ [(2n + 1 + s2)½ · σ3]-1 where n is meridional mode number, and s and σ are dimensionless zonal wave number and frequency related by the usual dispersion relation. The scales are (β/cm)½ and (β · cm)½ for horizontal wave number and frequency, where cm is the Kelvin wave speed of the vertical mode m. At each frequency and vertical wave number, energy is partitioned equally among the available inertial gravity modes so that the field tends toward horizontal isotropy at high frequency. The transition between Kelvin and mixed Rossby-gravity motion at low frequency and inertial-gravity motion at high frequency occurs at a period of roughly 1 week. At periods in the range 1-3 weeks, the model spectrum which fits the observations suggests that mixed Rossby-gravity motion dominates; at shorter periods gravity motion dominates. The model results are consistent with the low vertical coherence lengths observed (roughly 80 m). Horizontal coherence over 2 km is consistent with isotropic energy flux. Evidence for net zontal energy flux is not found in this data, and the presence of a red wave number shape suggests that net flux will be difficult to observe from modest moored arrays. The equatorial wave spectrum does not match across the diurnal and semidiurnal tides to the high-frequency internal wave spectrum (the latter is roughly 1 decade higher).

Traveling-Wave Tubes

NASA Technical Reports Server (NTRS)

Kory, Carol L.

1998-01-01

The traveling-wave tube (TWT) is a vacuum device invented in the early 1940's used for amplification at microwave frequencies. Amplification is attained by surrendering kinetic energy from an electron beam to a radio frequency (RF) electromagnetic wave. The demand for vacuum devices has been decreased largely by the advent of solid-state devices. However, although solid state devices have replaced vacuum devices in many areas, there are still many applications such as radar, electronic countermeasures and satellite communications, that require operating characteristics such as high power (Watts to Megawatts), high frequency (below 1 GHz to over 100 GHz) and large bandwidth that only vacuum devices can provide. Vacuum devices are also deemed irreplaceable in the music industry where musicians treasure their tube-based amplifiers claiming that the solid-state and digital counterparts could never provide the same "warmth" (3). The term traveling-wave tube includes both fast-wave and slow-wave devices. This article will concentrate on slow-wave devices as the vast majority of TWTs in operation fall into this category.

InP HEMT Integrated Circuits for Submillimeter Wave Radiometers in Earth Remote Sensing

NASA Technical Reports Server (NTRS)

Deal, William R.; Chattopadhyay, Goutam

2012-01-01

The operating frequency of InP integrated circuits has pushed well into the Submillimeter Wave frequency band, with amplification reported as high as 670 GHz. This paper provides an overview of current performance and potential application of InP HEMT to Submillimeter Wave radiometers for earth remote sensing.

Results of an all-sky high-frequency Einstein@Home search for continuous gravitational waves in LIGO's fifth science run

NASA Astrophysics Data System (ADS)

Singh, Avneet; Papa, Maria Alessandra; Eggenstein, Heinz-Bernd; Zhu, Sylvia; Pletsch, Holger; Allen, Bruce; Bock, Oliver; Maschenchalk, Bernd; Prix, Reinhard; Siemens, Xavier

2016-09-01

We present results of a high-frequency all-sky search for continuous gravitational waves from isolated compact objects in LIGO's fifth science run (S5) data, using the computing power of the Einstein@Home volunteer computing project. This is the only dedicated continuous gravitational wave search that probes this high-frequency range on S5 data. We find no significant candidate signal, so we set 90% confidence level upper limits on continuous gravitational wave strain amplitudes. At the lower end of the search frequency range, around 1250 Hz, the most constraining upper limit is 5.0 ×10-24, while at the higher end, around 1500 Hz, it is 6.2 ×10-24. Based on these upper limits, and assuming a fiducial value of the principal moment of inertia of 1038 kg m2 , we can exclude objects with ellipticities higher than roughly 2.8 ×10-7 within 100 pc of Earth with rotation periods between 1.3 and 1.6 milliseconds.

Scattering of plane evanescent waves by cylindrical shells and wave vector coupling conditions for exciting flexural waves

NASA Astrophysics Data System (ADS)

Marston, Philip L.

2002-05-01

The coupling of sound to buried targets can be associated with acoustic evanescent waves when the sea bottom is smooth. To understand the excitation of flexural waves on buried shells by acoustic evanescent waves, the partial wave series for the scattering is found for cylindrical shells at normal incidence in an unbounded medium. The formulation uses the simplifications of thin-shell dynamics. In the case of ordinary waves incident on a shell, a ray formulation is available to describe the coupling to subsonic flexural waves [P. L. Marston and N. H. Sun, J. Acoust. Soc. Am. 97, 777-783 (1995)]. When the incident wave is evanescent, the distance between propagating plane wavefronts is smaller than the ordinary acoustical wavelength at the same frequency and the coupling condition for the excitation of flexural waves on shells or plates is modified. Instead of matching the flexural wave number with the propagating part of the acoustic wave number only at the coincidence frequency, a second low-frequency wave number matching condition is found for highly evanescent waves. Numerical evaluation of the modified partial-wave-series appropriate for an evanescent wave is used to investigate the low-frequency coupling of evanescent waves with flexural wave resonances of shells.

Estimation of pseudo-2D shear-velocity section by inversion of high frequency surface waves

USGS Publications Warehouse

Luo, Y.; Liu, J.; Xia, J.; Xu, Y.; Liu, Q.

2006-01-01

A scheme to generate pseudo-2D shear-velocity sections with high horizontal resolution and low field cost by inversion of high frequency surface waves is presented. It contains six steps. The key step is the joint method of crossed correlation and phase shift scanning. This joint method chooses only two traces to generate image of dispersion curve. For Rayleigh-wave dispersion is most important for estimation of near-surface shear-wave velocity, it can effectively obtain reliable images of dispersion curves with a couple of traces. The result of a synthetic example shows the feasibility of this scheme. ?? 2005 Society of Exploration Geophysicists.

Analysis of Meniscus Fluctuation in a Continuous Casting Slab Mold

NASA Astrophysics Data System (ADS)

Zhang, Kaitian; Liu, Jianhua; Cui, Heng; Xiao, Chao

2018-06-01

A water model of slab mold was established to analyze the microscopic and macroscopic fluctuation of meniscus. The fast Fourier transform and wavelet entropy were adopted to analyze the wave amplitude, frequency, and components of fluctuation. The flow patterns under the meniscus were measured by using particle image velocimetry measurement and then the mechanisms of meniscus fluctuation were discussed. The results reflected that wavelet entropy had multi-scale and statistical properties, and it was suitable for the study of meniscus fluctuation details both in time and frequency domain. The basic wave, frequency of which exceeding 1 Hz in the condition of no mold oscillation, was demonstrated in this work. In fact, three basic waves were found: long-wave with low frequency, middle-wave with middle frequency, and short-wave with high frequency. In addition, the upper roll flow in mold had significant effect on meniscus fluctuation. When the position of flow impinged was far from the meniscus, long-wave dominated the fluctuation and the stability of meniscus was enhanced. However, when the velocity of flow was increased, the short-wave dominated the meniscus fluctuation and the meniscus stability was decreased.

Variable dual-frequency electrostatic wave launcher for plasma applications.

PubMed

Jorns, Benjamin; Sorenson, Robert; Choueiri, Edgar

2011-12-01

A variable tuning system is presented for launching two electrostatic waves concurrently in a magnetized plasma. The purpose of this system is to satisfy the wave launching requirements for plasma applications where maximal power must be coupled into two carefully tuned electrostatic waves while minimizing erosion to the launching antenna. Two parallel LC traps with fixed inductors and variable capacitors are used to provide an impedance match between a two-wave source and a loop antenna placed outside the plasma. Equivalent circuit analysis is then employed to derive an analytical expression for the normalized, average magnetic flux density produced by the antenna in this system as a function of capacitance and frequency. It is found with this metric that the wave launcher can couple to electrostatic modes at two variable frequencies concurrently while attenuating noise from the source signal at undesired frequencies. An example based on an experiment for plasma heating with two electrostatic waves is used to demonstrate a procedure for tailoring the wave launcher to accommodate the frequency range and flux densities of a specific two-wave application. This example is also used to illustrate a method based on averaging over wave frequencies for evaluating the overall efficacy of the system. The wave launcher is shown to be particularly effective for the illustrative example--generating magnetic flux densities in excess of 50% of the ideal case at two variable frequencies concurrently--with a high adaptability to a number of plasma dynamics and heating applications.

40 MHz high-frequency ultrafast ultrasound imaging.

PubMed

Huang, Chih-Chung; Chen, Pei-Yu; Peng, Po-Hsun; Lee, Po-Yang

2017-06-01

Ultrafast high-frame-rate ultrasound imaging based on coherent-plane-wave compounding has been developed for many biomedical applications. Most coherent-plane-wave compounding systems typically operate at 3-15 MHz, and the image resolution for this frequency range is not sufficient for visualizing microstructure tissues. Therefore, the purpose of this study was to implement a high-frequency ultrafast ultrasound imaging operating at 40 MHz. The plane-wave compounding imaging and conventional multifocus B-mode imaging were performed using the Field II toolbox of MATLAB in simulation study. In experiments, plane-wave compounding images were obtained from a 256 channel ultrasound research platform with a 40 MHz array transducer. All images were produced by point-spread functions and cyst phantoms. The in vivo experiment was performed from zebrafish. Since high-frequency ultrasound exhibits a lower penetration, chirp excitation was applied to increase the imaging depth in simulation. The simulation results showed that a lateral resolution of up to 66.93 μm and a contrast of up to 56.41 dB were achieved when using 75-angles plane waves in compounding imaging. The experimental results showed that a lateral resolution of up to 74.83 μm and a contrast of up to 44.62 dB were achieved when using 75-angles plane waves in compounding imaging. The dead zone and compounding noise are about 1.2 mm and 2.0 mm in depth for experimental compounding imaging, respectively. The structure of zebrafish heart was observed clearly using plane-wave compounding imaging. The use of fewer than 23 angles for compounding allowed a frame rate higher than 1000 frames per second. However, the compounding imaging exhibits a similar lateral resolution of about 72 μm as the angle of plane wave is higher than 10 angles. This study shows the highest operational frequency for ultrafast high-frame-rate ultrasound imaging. © 2017 American Association of Physicists in Medicine.

Imaging a soil fragipans using a high-frequency MASW method

USDA-ARS?s Scientific Manuscript database

The objective of this study was to noninvasively image a fragipan layer, a naturally occurring dense soil layer, using a high-frequency (HF) multi-channel analysis of surface wave (MASW) method. The HF-MASW is developed to measure the soil profile in terms of the shear (S) wave velocity at depths up...

Atmospheric-radiation boundary conditions for high-frequency waves in time-distance helioseismology

NASA Astrophysics Data System (ADS)

Fournier, D.; Leguèbe, M.; Hanson, C. S.; Gizon, L.; Barucq, H.; Chabassier, J.; Duruflé, M.

2017-12-01

The temporal covariance between seismic waves measured at two locations on the solar surface is the fundamental observable in time-distance helioseismology. Above the acoustic cut-off frequency ( 5.3 mHz), waves are not trapped in the solar interior and the covariance function can be used to probe the upper atmosphere. We wish to implement appropriate radiative boundary conditions for computing the propagation of high-frequency waves in the solar atmosphere. We consider recently developed and published radiative boundary conditions for atmospheres in which sound-speed is constant and density decreases exponentially with radius. We compute the cross-covariance function using a finite element method in spherical geometry and in the frequency domain. The ratio between first- and second-skip amplitudes in the time-distance diagram is used as a diagnostic to compare boundary conditions and to compare with observations. We find that a boundary condition applied 500 km above the photosphere and derived under the approximation of small angles of incidence accurately reproduces the "infinite atmosphere" solution for high-frequency waves. When the radiative boundary condition is applied 2 Mm above the photosphere, we find that the choice of atmospheric model affects the time-distance diagram. In particular, the time-distance diagram exhibits double-ridge structure when using a Vernazza Avrett Loeser atmospheric model.

First On-Wafer Power Characterization of MMIC Amplifiers at Sub-Millimeter Wave Frequencies

NASA Technical Reports Server (NTRS)

Fung, A. K.; Gaier, T.; Samoska, L.; Deal, W. R.; Radisic, V.; Mei, X. B.; Yoshida, W.; Liu, P. S.; Uyeda, J.; Barsky, M.;

Tunable ferromagnetic resonance in La-Co substituted barium hexaferrites at millimeter wave frequencies

NASA Astrophysics Data System (ADS)

Korolev, Konstantin A.; Wu, Chuanjian; Yu, Zhong; Sun, Ke; Afsar, Mohammed N.; Harris, Vincent G.

2018-05-01

Transmittance measurements have been performed on La-Co substituted barium hexaferrites in millimeter waves. Broadband millimeter-wave measurements have been carried out using the free space quasi-optical spectrometer, equipped with a set of high power backward wave oscillators covering the frequency range of 30 - 120 GHz. Strong absorption zones have been observed in the millimeter-wave transmittance spectra of all La-Co substituted barium hexaferrites due to the ferromagnetic resonance. Linear shift of ferromagnetic resonance frequency as functions of La-Co substitutions have been found. Real and imaginary parts of dielectric permittivity of La-Co substituted barium hexaferrites have been calculated using the analysis of recorded high precision transmittance spectra. Frequency dependences of magnetic permeability of La-Co substituted barium hexaferrites, as well as saturation magnetization and anisotropy field have been determined based on Schlömann's theory for partially magnetized ferrites. La-Co substituted barium hexaferrites have been further investigated by DC magnetization to assess magnetic behavior and compare with millimeter wave data. Consistency of saturation magnetization determined independently by both millimeter wave absorption and DC magnetization have been found for all La-Co substituted barium hexaferrites. These materials seem to be quite promising as tunable millimeter wave absorbers, filters, circulators, based on the adjusting of their substitution parameters.

High-power free-electron maser with frequency multiplication operating in a shortwave part of the millimeter wave range

NASA Astrophysics Data System (ADS)

Bandurkin, I. V.; Kaminsky, A. K.; Perelstein, E. A.; Peskov, N. Yu.; Savilov, A. V.; Sedykh, S. N.

2012-08-01

The possibility of using frequency multiplication in order to obtain high-power short-wavelength radiation from a free-electron maser (FEM) with a Bragg resonator has been studied. Preliminary experiments with an LIU-3000 (JINR) linear induction accelerator demonstrate the operation of a frequency-multiplying FEM at megawatt power in the 6- and 4-mm wave bands on the second and third harmonic, respectively.

Multifrequency synthesis and extraction using square wave projection patterns for quantitative tissue imaging.

PubMed

Nadeau, Kyle P; Rice, Tyler B; Durkin, Anthony J; Tromberg, Bruce J

2015-11-01

We present a method for spatial frequency domain data acquisition utilizing a multifrequency synthesis and extraction (MSE) method and binary square wave projection patterns. By illuminating a sample with square wave patterns, multiple spatial frequency components are simultaneously attenuated and can be extracted to determine optical property and depth information. Additionally, binary patterns are projected faster than sinusoids typically used in spatial frequency domain imaging (SFDI), allowing for short (millisecond or less) camera exposure times, and data acquisition speeds an order of magnitude or more greater than conventional SFDI. In cases where sensitivity to superficial layers or scattering is important, the fundamental component from higher frequency square wave patterns can be used. When probing deeper layers, the fundamental and harmonic components from lower frequency square wave patterns can be used. We compared optical property and depth penetration results extracted using square waves to those obtained using sinusoidal patterns on an in vivo human forearm and absorbing tube phantom, respectively. Absorption and reduced scattering coefficient values agree with conventional SFDI to within 1% using both high frequency (fundamental) and low frequency (fundamental and harmonic) spatial frequencies. Depth penetration reflectance values also agree to within 1% of conventional SFDI.

Multifrequency synthesis and extraction using square wave projection patterns for quantitative tissue imaging

PubMed Central

Nadeau, Kyle P.; Rice, Tyler B.; Durkin, Anthony J.; Tromberg, Bruce J.

2015-01-01

Abstract. We present a method for spatial frequency domain data acquisition utilizing a multifrequency synthesis and extraction (MSE) method and binary square wave projection patterns. By illuminating a sample with square wave patterns, multiple spatial frequency components are simultaneously attenuated and can be extracted to determine optical property and depth information. Additionally, binary patterns are projected faster than sinusoids typically used in spatial frequency domain imaging (SFDI), allowing for short (millisecond or less) camera exposure times, and data acquisition speeds an order of magnitude or more greater than conventional SFDI. In cases where sensitivity to superficial layers or scattering is important, the fundamental component from higher frequency square wave patterns can be used. When probing deeper layers, the fundamental and harmonic components from lower frequency square wave patterns can be used. We compared optical property and depth penetration results extracted using square waves to those obtained using sinusoidal patterns on an in vivo human forearm and absorbing tube phantom, respectively. Absorption and reduced scattering coefficient values agree with conventional SFDI to within 1% using both high frequency (fundamental) and low frequency (fundamental and harmonic) spatial frequencies. Depth penetration reflectance values also agree to within 1% of conventional SFDI. PMID:26524682

Multi-point measurement using two-channel reflectometer with antenna switching for study of high-frequency fluctuations in GAMMA 10

NASA Astrophysics Data System (ADS)

Ikezoe, R.; Ichimura, M.; Okada, T.; Itagaki, J.; Hirata, M.; Sumida, S.; Jang, S.; Izumi, K.; Tanaka, A.; Yoshikawa, M.; Kohagura, J.; Sakamoto, M.; Nakashima, Y.

2017-03-01

A two-channel microwave reflectometer system with fast microwave antenna switching capability was developed and applied to the GAMMA 10 tandem mirror device to study high-frequency small-amplitude fluctuations in a hot mirror plasma. The fast switching of the antennas is controlled using PIN diode switches, which offers the significant advantage of reducing the number of high-cost microwave components and digitizers with high bandwidths and large memory that are required to measure the spatiotemporal behavior of the high-frequency fluctuations. The use of two channels rather than one adds the important function of a simultaneous two-point measurement in either the radial direction or the direction of the antenna array to measure the phase profile of the fluctuations along with the normal amplitude profile. The density fluctuations measured using this system clearly showed the high-frequency coherent fluctuations that are associated with Alfvén-ion-cyclotron (AIC) waves in GAMMA 10. A correlation analysis applied to simultaneously measured density fluctuations showed that the phase component that was included in a reflected microwave provided both high coherence and a clear phase difference for the AIC waves, while the amplitude component showed neither significant coherence nor clear phase difference. The axial phase differences of the AIC waves measured inside the hot plasma confirmed the formation of a standing wave structure. The axial variation of the radial profiles was evaluated and a clear difference was found among the AIC waves for the first time, which would be a key to clarify the unknown boundary conditions of the AIC waves.

Dual-band and high-efficiency polarization converter based on metasurfaces at microwave frequencies

NASA Astrophysics Data System (ADS)

Liu, Yajun; Xia, Song; Shi, Hongyu; Zhang, Anxue; Xu, Zhuo

2016-06-01

We present a dual-band and high-efficiency polarization converter in microwave regime. The proposed converter can convert a linearly polarized wave to its cross-polarized wave for two distinct bands: Ku (11.5-20.0 GHz) and Ka (28.8-34.0 GHz). It can also convert the linearly polarized wave to a circularly polarized wave at four other frequencies. The experimental results are in good agreement with simulation results for both frequency bands. The polarization conversion ratio is above 0.94 for the Ku-band and 0.90 for the Ka-band. Furthermore, the converter can achieve dual-band and high-efficiency polarization conversion over angles of incidence up to 45°. The converter is also polarization-selective in that only the x- and y-polarized waves can be converted. The physical mechanism of the dual-band polarization conversion effect is interpreted via decomposed electric field components that couple with different plasmon resonance modes of the structure.

Current drive with combined electron cyclotron wave and high harmonic fast wave in tokamak plasmas

NASA Astrophysics Data System (ADS)

Li, J. C.; Gong, X. Y.; Dong, J. Q.; Wang, J.; Zhang, N.; Zheng, P. W.; Yin, C. Y.

2016-12-01

The current driven by combined electron cyclotron wave (ECW) and high harmonic fast wave is investigated using the GENRAY/CQL3D package. It is shown that no significant synergetic current is found in a range of cases with a combined ECW and fast wave (FW). This result is consistent with a previous study [Harvey et al., in Proceedings of IAEA TCM on Fast Wave Current Drive in Reactor Scale Tokamaks (Synergy and Complimentarily with LHCD and ECRH), Arles, France, IAEA, Vienna, 1991]. However, a positive synergy effect does appear with the FW in the lower hybrid range of frequencies. This positive synergy effect can be explained using a picture of the electron distribution function induced by the ECW and a very high harmonic fast wave (helicon). The dependence of the synergy effect on the radial position of the power deposition, the wave power, the wave frequency, and the parallel refractive index is also analyzed, both numerically and physically.

High power broadband millimeter wave TWTs

NASA Astrophysics Data System (ADS)

James, Bill G.

1999-05-01

In the early 1980's the requirement for high power broadband millimeter wave sources encouraged the development of microwave vacuum device amplifiers for radar and communication systems. Many government funded programs were implemented for the development of high power broadband millimeter wave amplifiers that would meet the needs of the high power community. The tube design capable of meeting these goals was the slow wave coupled cavity traveling wave device, which had a proven technology base at the lower frequencies (X Band). However scaling this technology to the millimeter frequencies had severe shortcomings in both thermal and manufacturing design. These shortcomings were overcome with the development of the Ladder Circuit technology. In conjunction with the circuit development high power electron beam systems had to be developed for the generation of high rf powers. These beam systems had to be capable of many megawatts of beam power density and high current densities. The cathode technology required to be capable of operating at current densities of 10 amperes per square centimeter at long pulse lengths and high duty cycle. Since the introduction of the Ladder Circuit technology a number of high power broadband millimeter wave amplifiers have been developed using this technology, and have been deployed in operating radar and communication systems. Broadband millimeter wave sources have been manufactured in the frequency range from 27 GHz to 100 GHz with power levels ranging from 100 watts to 50 kilowatts. Today the power levels achieved by these devices are nearing the limits of this technology; therefore to gain a significant increase in power at the millimeter wave frequencies other technologies will have to be considered particularly fast wave devices. This paper will briefly review the ladder circuit technology and present the designs of a number of broadband high power devices developed at Ka and W band. The discussion will include the beam systems employed in these devices which are the highest power density linear beams generated to date. In conclusion the limits of the power generating capability of this technology will be presented.

High Power Broadband Millimeter Wave TWTs

NASA Astrophysics Data System (ADS)

James, Bill G.

1998-04-01

In the early 1980's the requirement for high power broadband millimeter wave sources encouraged the development of microwave vacuum device amplifiers for radar and communication systems. Many government funded programs were implemented for the development of high power broadband millimeter wave amplifiers that would meet the needs of the high power community. The tube design capable of meeting these goals was the slow wave coupled cavity traveling wave device, which had a proven technology base at the lower frequencies (X Band). However scaling this technology to the millimeter frequencies had severe shortcomings in both thermal and manufacturing design. These shortcomings were overcome with the development of the Ladder Circuit technology. In conjunction with the circuit development high power electron beam systems had to be developed for the generation of high rf powers. These beam systems had to be capable of many megawatts of beam power density and high current densities. The cathode technology required to be capable of operating at current densities of 10 amperes per square centimeter at long pulse lengths and high duty cycle. Since the introduction of the Ladder Circuit technology a number of high power broadband millimeter wave amplifiers have been developed and deployed in operating radar and communication systems. Broadband millimeter wave sources have been manufactured in the frequency range from 27 GHz to 100 GHz with power levels ranging from 100 watts CW to 10 kilowatts Peak at W band over a 2 GHz bandwidth. Also a 50 kW peak power and 10 kW average power device at Ka band with 2 GHz bandwidth has been developed. Today the power levels achieved by these devices are nearing the limits of this technology; therefore to gain a significant increase in power at the millimeter wave frequencies, other technologies will have to be considered, particularly fast wave devices. This paper will briefly review the ladder circuit technology and present the designs of a number of broadband high power devices developed at Ka and W band. The discussion will include the beam systems employed in these devices which are the highest power density linear beams generated to date. In conclusion the limits of the power generating capability of this technology will be presented.

An analysis of short pulse and dual frequency radar techniques for measuring ocean wave spectra from satellites

NASA Technical Reports Server (NTRS)

Jackson, F. C.

1980-01-01

Scanning beam microwave radars were used to measure ocean wave directional spectra from satellites. In principle, surface wave spectral resolution in wave number can be obtained using either short pulse (SP) or dual frequency (DF) techniques; in either case, directional resolution obtains naturally as a consequence of a Bragg-like wave front matching. A four frequency moment characterization of backscatter from the near vertical using physical optics in the high frequency limit was applied to an analysis of the SP and DF measurement techniques. The intrinsic electromagnetic modulation spectrum was to the first order in wave steepness proportional to the large wave directional slope spectrum. Harmonic distortion was small and was a minimum near 10 deg incidence. NonGaussian wave statistics can have an effect comparable to that in the second order of scattering from a normally distributed sea surface. The SP technique is superior to the DF technique in terms of measurement signal to noise ratio and contrast ratio.

Generation of Artificial Ionospheric Irregularities in the Midlatitude Ionosphere Modified by High-Power High-Frequency X-Mode Radio Waves

NASA Astrophysics Data System (ADS)

Frolov, V. L.; Bolotin, I. A.; Komrakov, G. P.; Pershin, A. V.; Vertogradov, G. G.; Vertogradov, V. G.; Vertogradova, E. G.; Kunitsyn, V. E.; Padokhin, A. M.; Kurbatov, G. A.; Akchurin, A. D.; Zykov, E. Yu.

2014-11-01

We consider the properties of the artificial ionospheric irregularities excited in the ionospheric F 2 region modified by high-power high-frequency X-mode radio waves. It is shown that small-scale (decameter) irregularities are not generated in the midlatitude ionosphere. The intensity of irregularities with the scales l ⊥ ≈50 m to 3 km is severalfold weaker compared with the case where the irregularities are excited by high-power O-mode radio waves. The intensity of the larger-scale irregularities is even stronger attenuated. It is found that the generation of large-scale ( l ⊥ ≈5-10 km) artificial ionospheric irregularities is enhanced at the edge of the directivity pattern of a beam of high-power radio waves.

Frequency domain finite-element and spectral-element acoustic wave modeling using absorbing boundaries and perfectly matched layer

NASA Astrophysics Data System (ADS)

Rahimi Dalkhani, Amin; Javaherian, Abdolrahim; Mahdavi Basir, Hadi

2018-04-01

Wave propagation modeling as a vital tool in seismology can be done via several different numerical methods among them are finite-difference, finite-element, and spectral-element methods (FDM, FEM and SEM). Some advanced applications in seismic exploration benefit the frequency domain modeling. Regarding flexibility in complex geological models and dealing with the free surface boundary condition, we studied the frequency domain acoustic wave equation using FEM and SEM. The results demonstrated that the frequency domain FEM and SEM have a good accuracy and numerical efficiency with the second order interpolation polynomials. Furthermore, we developed the second order Clayton and Engquist absorbing boundary condition (CE-ABC2) and compared it with the perfectly matched layer (PML) for the frequency domain FEM and SEM. In spite of PML method, CE-ABC2 does not add any additional computational cost to the modeling except assembling boundary matrices. As a result, considering CE-ABC2 is more efficient than PML for the frequency domain acoustic wave propagation modeling especially when computational cost is high and high-level absorbing performance is unnecessary.

Statistical analysis of dispersion relations in turbulent solar wind fluctuations using Cluster data

NASA Astrophysics Data System (ADS)

Perschke, C.; Narita, Y.

2012-12-01

Multi-spacecraft measurements enable us to resolve three-dimensional spatial structures without assuming Taylor's frozen-in-flow hypothesis. This is very useful to study frequency-wave vector diagram in solar wind turbulence through direct determination of three-dimensional wave vectors. The existence and evolution of dispersion relation and its role in fully-developed plasma turbulence have been drawing attention of physicists, in particular, if solar wind turbulence represents kinetic Alfvén or whistler mode as the carrier of spectral energy among different scales through wave-wave interactions. We investigate solar wind intervals of Cluster data for various flow velocities with a high-resolution wave vector analysis method, Multi-point Signal Resonator technique, at the tetrahedral separation about 100 km. Magnetic field data and ion data are used to determine the frequency- wave vector diagrams in the co-moving frame of the solar wind. We find primarily perpendicular wave vectors in solar wind turbulence which justify the earlier discussions about kinetic Alfvén or whistler wave. The frequency- wave vector diagrams confirm (a) wave vector anisotropy and (b) scattering in frequencies.

Coherence Volume of an Optical Wave Field with Broad Frequency and Angular Spectra

NASA Astrophysics Data System (ADS)

Lyakin, D. V.; Mysina, N. Yu.; Ryabukho, V. P.

2018-03-01

We consider the sizes of a region in a three-dimensional space in which an optical wave field excites mutually coherent perturbations. We discuss the conditions under which the length of this region along the direction of propagation of the wave field and, correspondingly, its volume are determined either by the width of the frequency spectrum of the field or by the width of its angular spectrum, or by the parameters of these spectra simultaneously. We obtain expressions for estimating extremely small values of the coherence volume of the fields with a broad frequency spectrum and an extremely broad angular spectrum. Using the notion of instantaneous speckle-modulation of the wave field, we give a physical interpretation to the occurrence of a limited coherence volume of the field. The length of the spatiotemporal coherence region in which mutually coherent perturbations occur at different times is determined. The coherence volume of a wave field that illuminates an object in high-resolution microscopy with frequency broadband light is considered. The conditions for the dominant influence of the angular or frequency spectra on the longitudinal length of the coherence region are given, and the conditions for the influence of the frequency spectrum width on the transverse coherence of the wave field are examined. We show that, when using fields with broad and ultrabroad spectra in high-resolution microscopy, this influence should be taken into account.

Estimation of near-surface shear-wave velocity by inversion of Rayleigh waves

USGS Publications Warehouse

Xia, J.; Miller, R.D.; Park, C.B.

1999-01-01

The shear-wave (S-wave) velocity of near-surface materials (soil, rocks, pavement) and its effect on seismic-wave propagation are of fundamental interest in many groundwater, engineering, and environmental studies. Rayleigh-wave phase velocity of a layered-earth model is a function of frequency and four groups of earth properties: P-wave velocity, S-wave velocity, density, and thickness of layers. Analysis of the Jacobian matrix provides a measure of dispersion-curve sensitivity to earth properties. S-wave velocities are the dominant influence on a dispersion curve in a high-frequency range (>5 Hz) followed by layer thickness. An iterative solution technique to the weighted equation proved very effective in the high-frequency range when using the Levenberg-Marquardt and singular-value decomposition techniques. Convergence of the weighted solution is guaranteed through selection of the damping factor using the Levenberg-Marquardt method. Synthetic examples demonstrated calculation efficiency and stability of inverse procedures. We verify our method using borehole S-wave velocity measurements.Iterative solutions to the weighted equation by the Levenberg-Marquardt and singular-value decomposition techniques are derived to estimate near-surface shear-wave velocity. Synthetic and real examples demonstrate the calculation efficiency and stability of the inverse procedure. The inverse results of the real example are verified by borehole S-wave velocity measurements.

Dynamics of liquid films exposed to high-frequency surface vibration

NASA Astrophysics Data System (ADS)

Manor, Ofer; Rezk, Amgad R.; Friend, James R.; Yeo, Leslie Y.

2015-05-01

We derive a generalized equation that governs the spreading of liquid films under high-frequency (MHz-order) substrate vibration in the form of propagating surface waves and show that this single relationship is universally sufficient to collectively describe the rich and diverse dynamic phenomena recently observed for the transport of oil films under such substrate excitation, in particular, Rayleigh surface acoustic waves. In contrast to low-frequency (Hz- to kHz-order) vibration-induced wetting phenomena, film spreading at such high frequencies arises from convective drift generated by the viscous periodic flow localized in a region characterized by the viscous penetration depth β-1≡(2μ /ρ ω ) 1 /2 adjacent to the substrate that is invoked directly by its vibration; μ and ρ are the viscosity and the density of the liquid, respectively, and ω is the excitation frequency. This convective drift is responsible for driving the spreading of thin films of thickness h ≪kl-1 , which spread self-similarly as t1 /4 along the direction of the drift corresponding to the propagation direction of the surface wave, kl being the wave number of the compressional acoustic wave that forms in the liquid due to leakage of the surface wave energy from the substrate into the liquid and t the time. Films of greater thicknesses h ˜kl-1≫β-1 , in contrast, are observed to spread with constant velocity but in a direction that opposes the drift and surface wave propagation due to the attenuation of the acoustic wave in the liquid. The universal equation derived allows for the collective prediction of the spreading of these thin and thick films in opposing directions.

Multi-Band (K- Q- and E-Band) Multi-Tone Millimeter-Wave Frequency Synthesizer for Radio Wave Propagation Studies

NASA Technical Reports Server (NTRS)

Simons, Rainee N.; Wintucky, Edwin G.

2014-01-01

This paper presents the design and test results of a multi-band multi-tone millimeter-wave frequency synthesizer, based on a solid-state frequency comb generator. The intended application of the synthesizer is in a space-borne transmitter for radio wave atmospheric studies at K-band (18 to 26.5 GHz), Q-band (37 to 42 GHz), and E-band (71 to 76 GHz). These studies would enable the design of robust multi-Gbps data rate space-to-ground satellite communication links. Lastly, the architecture for a compact multi-tone beacon transmitter, which includes a high frequency synthesizer, a polarizer, and a conical horn antenna, has been investigated for a notional CubeSat based space-to-ground radio wave propagation experiment.

Interface waves in multilayered plates.

PubMed

Li, Bing; Li, Ming-Hang; Lu, Tong

2018-04-01

In this paper, the characteristic equation of interface waves in multilayered plates is derived. With a reasonable assumption undertaken for the potential functions of longitudinal and shear waves in the nth layer medium, the characteristic equation of interface waves in the N-layered plate is derived and presented in a determinant form. The particle displacement and stress components are further presented in explicit forms. The dispersion curves and wave structures of interface waves in both a three-layered Al-Steel-Ti and a four-layered Steel-Al-Steel-Ti plate are displayed subsequently. It is observed in dispersion curves that obvious dispersion occurs on the low frequency band, whereas the phase velocities converge to the corresponding true Stoneley wave mode velocities at high frequency, and the number of interface wave modes equals the number of interfaces in multilayered plates (if all individual interfaces satisfy the existence condition of Stoneley waves). The wave structures reveal that the displacement components of interface waves are relatively high at interfaces, and the amplitude distribution varies from frequency to frequency. In the end, a similarly structured three-layered Al-Steel-Ti plate is tested. In this experiment, theoretical group velocity and experimental group velocity are compared. According to the discussion and comparison, the predicted group velocities are in good agreement with the experimental results. Thus, the theory of interface wave in multilayered plates is proved. As a result, the proposed theoretical approach represents a leap forward in the understanding of how to promote the characteristic study and practical applications of interface waves in multilayered structures.

Magnetospheric filter effect for Pc 3 Alfven mode waves

NASA Technical Reports Server (NTRS)

Zhang, X.; Comfort, R. H.; Gallagher, D. L.; Green, J. L.; Musielak, Z. E.; Moore, T. E.

1995-01-01

We present a ray-tracing study of the propagation of Pc 3 Alfven mode waves originating at the dayside magnetopause. This study reveals interesting features of magnetospheric filter effect for these waves. Pc 3 Alfven mode waves cannot penetrate to low Earth altitudes unless the wave frequency is below approximately 30 mHz. Configurations of the dispersion curves and the refractive index show that the gyroresonance and pseudo-cutoff introduced by the heavy ion O(+) block the waves. When the O(+) concentration is removed from the plasma composition, the barriers caused by the O(+) no longer exist, and waves with much higher frequencies than 30 mHz can penetrate to low altitudes. The result that the 30 mHz or lower frequency Alfven waves can be guided to low altitudes agrees with ground-based power spectrum observation at high altitudes.

Magnetospheric filter effect for Pc 3 Alfven mode waves

NASA Technical Reports Server (NTRS)

Zhang, X.; Comfort, R. H.; Gallagher, D. L.; Green, J. L.; Musielak, Z. E.; Moore, T. E.

1994-01-01

We present a ray-tracing study of the propagation of Pc 3 Alfven mode waves originating at the dayside magnetopause. This study reveals interesting features of a magnetospheric filter effect for these waves. Pc 3 Alfven mode waves cannot penetrate to low Earth altitudes unless the wave frequency is below approximately 30 mHz. Configurations of the dispersion curves and the refractive index show that the gyroresonance and pseudo-cutoff introduced by the heavy ion O(+) block the waves. When the O(+) concentration is removed from the plasma composition, the barriers caused by the O(+) no longer exist, and waves with much higher frequencies than 30 mHz can penetrate to low altitudes. The result that the 30 mHz or lower frequency Alfven waves can be guided to low altitudes agrees with ground-based power spectrum observations at high latitudes.

Transition From High Harmonic Fast Wave to Whistler/Helicon Regime in Tokamaks

NASA Astrophysics Data System (ADS)

Harris, S. P.; Pinsker, R. I.; Porkolab, M.

2014-10-01

Experiments are being prepared1 on DIII-D in which fast waves (FWs) at 0.5 GHz will be used to drive current noninductively in the mid-radius region. Previous DIII-D experiments used FWs at ~0.1 GHz to drive central current; in this work we examine the frequency dependence of wave propagation and damping in the 0.1-1.0 GHz range with the goal of identifying the optimum frequency range for a particular application. Strongly enhanced electron damping and reduced ion damping at higher frequencies must be weighed against increasing coupling difficulties at higher frequencies and more restrictive wave accessibility at low toroidal field. Wave propagation and accessibility is studied with ray tracing models in slab, cylindrical, and fully toroidal geometries. Analytic expressions for electron and ion damping will be derived with an emphasis on understanding the transition from the moderate-to-high ion cyclotron harmonic regime to the very high harmonic or ``whistler''/``helicon''/lower hybrid FW regime. Work supported in part by the National Undergraduate Fellowship Program in Plasma Physics and Fusion Energy Sciences and the US Department of Energy under DE-FC02-04ER54698.

High-frequency waves following PKP-CDIFF at distances greater than 155°

NASA Astrophysics Data System (ADS)

Nakanishi, Ichiro

1990-04-01

Using a seismic network in Hokkaido-Tohoku region, Japan we observe PKP waves in the distance range 152 to 157°from a deep earthquake in Argentina. The seismic network consists of 26 stations and provides us with a data set of dense distance sampling. The examination of amplitude variation of PKP-BC and PKP-Cdiff with distance locates the C-cusp at about 155.5° for a surface source for the path from Argentina to Japan. This C-cusp position suggests a P velocity of 10.27 km/s at the bottom of the outer core. The bandpass filtering of the data shows that high-frequency waves are observed following PKP-Cdiff at distances beyond the C-cusp. The waves are characterized by a dominant frequency of about 2 to 3 Hz, a long duration of oscillation until the arrival of PKP-AB, and an apparent onset slowness of about 4 s/deg, which is approximately equal to that of PKP-AB in the distance range. The onset time of the high-frequency waves seems to be consistent with the least time of the scattering of PKP-BC on the receiver side near the bottom of the upper mantle.

Simple surgical approach with high-frequency radio-wave electrosurgery for conjunctivochalasis.

PubMed

Youm, Dong Ju; Kim, Joon Mo; Choi, Chul Young

2010-11-01

To introduce a new simple surgical approach with high-frequency radio-wave electrosurgery to reduce conjunctivochalasis (CCh). Prospective, noncomparative, interventional case series analysis. Twelve patients (20 eyes) with CCh were recruited from the outpatient service of the Department of Ophthalmology, Kangbuk Samsung Hospital, Seoul, Korea. On the inferior bulbar conjunctiva, subconjunctival coagulation was performed with a fine-needle electrode using a high-frequency radio-wave electrosurgical unit (Ellman Surgitron; Ellman International, Inc., Hewlett, NY) in coagulation mode. Conjunctivochalasis grade; epiphora and dry eye symptoms (the Ocular Surface Disease Index [OSDI]; Allergan Inc., Irvine, CA, holds the copyright); and intraoperative and postoperative complications. Eighteen eyes (90%) recovered a smooth, wet, and noninflamed conjunctival surface within 1 month and remained stable for a follow-up period of 3 months. At 3 months postoperatively, 18 eyes (90%) had grade 0 CCh. There was a statistically significant decrease of the OSDI score at 3 months postoperatively (P < 0.001). A surgical approach with high-frequency radio-wave electrosurgery produced a significant reduction in CCh and an improvement in symptoms. Radio-wave surgical techniques represent a favorable alternative to surgical treatment of CCh. The author(s) have no proprietary or commercial interest in any materials discussed in this article. Copyright © 2010 American Academy of Ophthalmology. Published by Elsevier Inc. All rights reserved.

Low Frequency Turbulence as the Source of High Frequency Waves in Multi-Component Space Plasmas

NASA Technical Reports Server (NTRS)

Khazanov, George V.; Krivorutsky, Emmanuel N.; Uritsky, Vadim M.

2011-01-01

Space plasmas support a wide variety of waves, and wave-particle interactions as well as wavewave interactions are of crucial importance to magnetospheric and ionospheric plasma behavior. High frequency wave turbulence generation by the low frequency (LF) turbulence is restricted by two interconnected requirements: the turbulence should be strong enough and/or the coherent wave trains should have the appropriate length. These requirements are strongly relaxed in the multi-component plasmas, due to the heavy ions large drift velocity in the field of LF wave. The excitation of lower hybrid waves (LHWs), in particular, is a widely discussed mechanism of interaction between plasma species in space and is one of the unresolved questions of magnetospheric multi-ion plasmas. It is demonstrated that large-amplitude Alfven waves, in particular those associated with LF turbulence, may generate LHW s in the auroral zone and ring current region and in some cases (particularly in the inner magnetosphere) this serves as the Alfven wave saturation mechanism. We also argue that the described scenario can playa vital role in various parts of the outer magnetosphere featuring strong LF turbulence accompanied by LHW activity. Using the data from THEMIS spacecraft, we validate the conditions for such cross-scale coupling in the near-Earth "flow-braking" magnetotail region during the passage of sharp injection/dipolarization fronts, as well as in the turbulent outflow region of the midtail reconnection site.

Multi-dynamic range compressional wave detection using optical-frequency comb

NASA Astrophysics Data System (ADS)

Minamikawa, Takeo; Masuoka, Takashi; Oe, Ryo; Nakajima, Yoshiaki; Yamaoka, Yoshihisa; Minoshima, Kaoru; Yasui, Takeshi

2018-02-01

Compressional wave detection is useful means for health monitoring of building, detection of abnormal vibration of moving objects, defect evaluation, and biomedical imaging such as echography and photoacoustic imaging. The frequency of the compressional wave is varied from quasi-static to a few tens of megahertz depending on applications. Since the dynamic range of general compressional wave detectors is limited, we need to choose a proper compressional wave detector depending on applications. For the compressional wave detection with wide dynamic range, two or more detectors with different detection ranges is required. However, these detectors with different detection ranges generally has different accuracy and precision, disabling the seamless detection over these detection ranges. In this study, we proposed a compressional wave detector employing optical frequency comb (OFC). The compressional wave was sensed with a part of an OFC cavity, being encoded into OFC. The spectrally encoded OFC was converted to radio-frequency by the frequency link nature of OFC. The compressional wave-encoded radio-frequency can therefore be directly measured with a high-speed photodetector. To enhance the dynamic range of the compressional wave detection, we developed a cavityfeedback-based system and a phase-sensitive detection system, both of which the accuracy and precision are coherently linked to these of the OFC. We provided a proof-of-principle demonstration of the detection of compressional wave from quasi-static to ultrasound wave by using the OFC-based compressional wave sensor. Our proposed approach will serve as a unique and powerful tool for detecting compressional wave versatile applications in the future.

A Millimeter-Wave Cavity-Backed Suspended Substrate Stripline Antenna

NASA Technical Reports Server (NTRS)

Simons, Rainee N.

1999-01-01

Future generation satellite communication systems in near-Earth orbit will operate at frequencies in the higher mm-wave frequency bands. These satellite systems require low-profile, high gain, light weight and low cost antennas for communications to and from Earth as well as for inter-satellite links (ISL). At higher mm-wave frequencies, the conductor loss of conventional microstrip line is high and consequently the feed network loss of patch antenna arrays is also high. The high loss lowers the array efficiency, and in addition lowers the G/T ratio in a receiving array. Recently a radial line slot antenna array has been demonstrated to have high gain and efficiency at 60 GHz. In this paper, the design, fabrication and characterization of a V-Band (50-75 GHz), cavity backed, circular aperture antenna with suspended substrate stripline (SSS) feed is presented.

Sensitivity of high-frequency Rayleigh-wave data revisited

USGS Publications Warehouse

Xia, J.; Miller, R.D.; Ivanov, J.

2007-01-01

Rayleigh-wave phase velocity of a layered earth model is a function of frequency and four groups of earth properties: P-wave velocity, S-wave velocity (Vs), density, and thickness of layers. Analysis of the Jacobian matrix (or the difference method) provides a measure of dispersion curve sensitivity to earth properties. Vs is the dominant influence for the fundamental mode (Xia et al., 1999) and higher modes (Xia et al., 2003) of dispersion curves in a high frequency range (>2 Hz) followed by layer thickness. These characteristics are the foundation of determining S-wave velocities by inversion of Rayleigh-wave data. More applications of surface-wave techniques show an anomalous velocity layer such as a high-velocity layer (HVL) or a low-velocity layer (LVL) commonly exists in near-surface materials. Spatial location (depth) of an anomalous layer is usually the most important information that surface-wave techniques are asked to provide. Understanding and correctly defining the sensitivity of high-frequency Rayleigh-wave data due to depth of an anomalous velocity layer are crucial in applying surface-wave techniques to obtain a Vs profile and/or determine the depth of an anomalous layer. Because depth is not a direct earth property of a layered model, changes in depth will result in changes in other properties. Modeling results show that sensitivity at a given depth calculated by the difference method is dependent on the Vs difference (contrast) between an anomalous layer and surrounding layers. The larger the contrast is, the higher the sensitivity due to depth of the layer. Therefore, the Vs contrast is a dominant contributor to sensitivity of Rayleigh-wave data due to depth of an anomalous layer. Modeling results also suggest that the most sensitive depth for an HVL is at about the middle of the depth to the half-space, but for an LVL it is near the ground surface. ?? 2007 Society of Exploration Geophysicists.

Electromagnetic radiation by parametric decay of upper hybrid waves in ionospheric modification experiments

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

Leyser, T.B.

1994-06-01

A nonlinear dispersion relation for the parametric decay of an electrostatic upper hybrid wave into an ordinary mode electromagnetic wave, propagating parallel to the ambient magnetic field, and an electrostatic low frequency wave, being either a lower hybrid wave or a high harmonic ion Bernstein wave, is derived. The coherent and resonant wave interaction is considered to take place in a weakly magnetized and collisionless Vlasov plasma. The instability growth rate is computed for parameter values typical of ionospheric modification experiments, in which a powerful high frequency electromagnetic pump wave is injected into the ionospheric F-region from ground-based transmitters. Themore » electromagnetic radiation which is excited by the decaying upper hybrid wave is found to be consistent with the prominent and commonly observed downshifted maximum (DM) emission in the spectrum of stimulated electromagnetic emission.« less

Acoustic response characteristics of unsaturated porous media

NASA Astrophysics Data System (ADS)

Zhao, Haibo; Wang, Xiuming; Chen, Shumin; Li, Lailin

2010-08-01

By employing the plane wave analysis method, the dispersion equations associated with compressional and shear waves using Santos’s three-phase poroelastic theory were driven. Considering the reservoir pressure, the high frequency corrections and the coupling drag of two fluids in pores, the influences of frequency and gas saturation on the phase velocities and the inverse quality factors of four body waves predicted by Santos’s theory were discussed in detail. The theoretical velocities of the fast compressional and shear waves were compared with the results of the low and high frequency experiments from open publications, respectively. The results showed that they are in good agreement in the low frequency case rather than in the high frequency case. In the latter case, several popular poroelastic models were considered and compared with the experimental data. In the models, the results of White’s theory fit the experimental data, but the parameter b in White’s model has a significant impact on the results. Under the framework of the linear viscoelasticity theory, the attenuation mechanism of Santos’s model was extended, and the comparisons between the experimental and theoretical results were also made with respect to attenuation. For the case of water saturation less than 90%, the extended model makes good predictions of the inverse quality factor of shear wave. There is a significant difference between the experimental and theoretical results for the compressional wave, but the difference can be explained by the experimental data available.

LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Mechanism for shock wave merging in magnetised plasma: criteria and efficiency of formation of low-frequency magnetosonic waves

NASA Astrophysics Data System (ADS)

Tishchenko, V. N.; Shaikhislamov, I. F.

2010-08-01

The mechanism of merging of shock waves produced by a pulsating energy source is considered for magnetised plasma. The criteria for the emergence of this mechanism are found and its high efficiency for producing low-frequency magnetosonic waves, which have the form of a jet and propagate at large distances without attenuation, is shown.

Global observations of magnetospheric high‐m poloidal waves during the 22 June 2015 magnetic storm

PubMed Central

Chi, P. J.; Strangeway, R. J.; Russell, C. T.; Slavin, J. A.; Takahashi, K.; Singer, H. J.; Anderson, B. J.; Bromund, K.; Fischer, D.; Kepko, E. L.; Magnes, W.; Nakamura, R.; Plaschke, F.; Torbert, R. B.

2017-01-01

Abstract We report global observations of high‐m poloidal waves during the recovery phase of the 22 June 2015 magnetic storm from a constellation of widely spaced satellites of five missions including Magnetospheric Multiscale (MMS), Van Allen Probes, Time History of Events and Macroscale Interactions during Substorm (THEMIS), Cluster, and Geostationary Operational Environmental Satellites (GOES). The combined observations demonstrate the global spatial extent of storm time poloidal waves. MMS observations confirm high azimuthal wave numbers (m ~ 100). Mode identification indicates the waves are associated with the second harmonic of field line resonances. The wave frequencies exhibit a decreasing trend as L increases, distinguishing them from the single‐frequency global poloidal modes normally observed during quiet times. Detailed examination of the instantaneous frequency reveals discrete spatial structures with step‐like frequency changes along L. Each discrete L shell has a steady wave frequency and spans about 1 R E, suggesting that there exist a discrete number of drift‐bounce resonance regions across L shells during storm times. PMID:28713180

Three-dimensional instability of standing waves

NASA Astrophysics Data System (ADS)

Zhu, Qiang; Liu, Yuming; Yue, Dick K. P.

2003-12-01

We investigate the three-dimensional instability of finite-amplitude standing surface waves under the influence of gravity. The analysis employs the transition matrix (TM) approach and uses a new high-order spectral element (HOSE) method for computation of the nonlinear wave dynamics. HOSE is an extension of the original high-order spectral method (HOS) wherein nonlinear wave wave and wave body interactions are retained up to high order in wave steepness. Instead of global basis functions in HOS, however, HOSE employs spectral elements to allow for complex free-surface geometries and surface-piercing bodies. Exponential convergence of HOS with respect to the total number of spectral modes (for a fixed number of elements) and interaction order is retained in HOSE. In this study, we use TM-HOSE to obtain the stability of general three-dimensional perturbations (on a two-dimensional surface) on two classes of standing waves: plane standing waves in a rectangular tank; and radial/azimuthal standing waves in a circular basin. For plane standing waves, we confirm the known result of two-dimensional side-bandlike instability. In addition, we find a novel three-dimensional instability for base flow of any amplitude. The dominant component of the unstable disturbance is an oblique (standing) wave oriented at an arbitrary angle whose frequency is close to the (nonlinear) frequency of the original standing wave. This finding is confirmed by direct long-time simulations using HOSE which show that the nonlinear evolution leads to classical Fermi Pasta Ulam recurrence. For the circular basin, we find that, beyond a threshold wave steepness, a standing wave (of nonlinear frequency Omega) is unstable to three-dimensional perturbations. The unstable perturbation contains two dominant (standing-wave) components, the sum of whose frequencies is close to 2Omega. From the cases we consider, the critical wave steepness is found to generally decrease/increase with increasing radial/azimuthal mode number of the base standing wave. Finally, we show that the instability we find for both two- and three-dimensional standing waves is a result of third-order (quartet) resonance.

Gravitational Waves and Time Domain Astronomy

NASA Technical Reports Server (NTRS)

Centrella, Joan; Nissanke, Samaya; Williams, Roy

2012-01-01

The gravitational wave window onto the universe will open in roughly five years, when Advanced LIGO and Virgo achieve the first detections of high frequency gravitational waves, most likely coming from compact binary mergers. Electromagnetic follow-up of these triggers, using radio, optical, and high energy telescopes, promises exciting opportunities in multi-messenger time domain astronomy. In the decade, space-based observations of low frequency gravitational waves from massive black hole mergers, and their electromagnetic counterparts, will open up further vistas for discovery. This two-part workshop featured brief presentations and stimulating discussions on the challenges and opportunities presented by gravitational wave astronomy. Highlights from the workshop, with the emphasis on strategies for electromagnetic follow-up, are presented in this report.

Spin-wave-driven high-speed domain-wall motions in soft magnetic nanotubes

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

Yang, Jaehak; Yoo, Myoung-Woo; Kim, Sang-Koog, E-mail: sangkoog@snu.ac.kr

We report on a micromagnetic simulation study of interactions between propagating spin waves and a head-to-head domain wall in geometrically confined magnetic nanotubes. We found that incident spin waves of specific frequencies can lead to sufficiently high-speed (on the order of a few hundreds of m/s or higher) domain-wall motions in the same direction as that of the incident spin-waves. The domain-wall motions and their speed vary remarkably with the frequency and the amplitude of the incident spin-waves. High-speed domain-wall motions originate from the transfer torque of spin waves' linear momentum to the domain wall, through the partial or completemore » reflection of the incident spin waves from the domain wall. This work provides a fundamental understanding of the interaction of the spin waves with a domain wall in the magnetic nanotubes as well as a route to all-magnetic control of domain-wall motions in the magnetic nanoelements.« less

Interharmonic modulation products as a means to quantify nonlinear D-region interactions

NASA Astrophysics Data System (ADS)

Moore, Robert

Experimental observations performed during dual beam ionospheric HF heating experiments at the High frequency Active Auroral Research Program (HAARP) HF transmitter in Gakona, Alaska are used to quantify the relative importance of specific nonlinear interactions that occur within the D region ionosphere. During these experiments, HAARP broadcast two amplitude modulated HF beams whose center frequencies were separated by less than 20 kHz. One beam was sinusoidally modulated at 500 Hz while the second beam was sinusoidally modulated using a 1-7 kHz linear frequency-time chirp. ELF/VLF observations performed at two different locations (3 and 98 km from HAARP) provide clear evidence of strong interactions between all field components of the two HF beams in the form of low and high order interharmonic modulation products. From a theoretical standpoint, the observed interharmonic modulation products could be produced by several different nonlinearities. The two primary nonlinearities take the form of wave-medium interactions (i.e., cross modulation), wherein the ionospheric conductivity modulation produced by one signal crosses onto the other signal via collision frequency modification, and wave-wave interactions, wherein the conduction current associated with one wave mixes with the electric field of the other wave to produce electron temperature oscillations. We are able to separate and quantify these two different nonlinearities, and we conclude that the wave-wave interactions dominate the wave-medium interactions by a factor of two. These results are of great importance for the modeling of transioinospheric radio wave propagation, in that both the wave-wave and the wave-medium interactions could be responsible for a significant amount of anomalous absorption.

The effect of stratification and topography on high-frequency internal waves in a continental shelf sea

NASA Astrophysics Data System (ADS)

Domina, Anastasiia; Palmer, Matthew; Vlasenko, Vasil; Sharples, Jonathan; Green, Mattias; Stashchuk, Nataliya

2017-04-01

Internal gravity waves (IWs) have been recognised as one of the main drivers of climate controlling circulation, sustaining fisheries in shelf seas and CO2-pump system. High frequency IWs are particularly important to internal mixing in the shelf seas, where they contain an enhanced fraction of the available baroclinic energy. The origin, generation mechanism, propagation and spatial distribution of these waves are unfortunately still poorly understood since they are difficult to measure and simulate, and are therefore not represented in the vast majority of ocean and climate models. In this study we aim to increase our understanding of high frequency IWs dynamics in shelf seas through a combination of observational (from moorings and ocean gliders) and modelling methods (MITgcm), and test the hypothesis that "Solitary waves are responsible for driving a large fraction of the vertical diffusivity at the shelf edge and adjacent shelf region". A new high-resolution (50m horizontal) MITgcm configuration is employed to identify the generation and propagation of IWs in a regional shelf sea and subsequently identify internal wave generation hotspots by using calculated Froude number and body force maps. We assess the likely impact of changing seasonal and climate forcing on IWs with a range of different density structures. Our model suggests that under increasing stratification, the IW field becomes more energetic at all frequencies, however the increase in energy is not evenly distributed. While energy in the dominant low frequency IWs increase by 20-40%, energy associated with high frequency waves increases by as much as 90%. These model results are compared to varying stratification scenarios from observations made during 2012 and 2013 to interpret the impact on continental shelf sea IW generation and propagation. We use the results from a turbulence enabled ocean glider to assess the impact that this varying wavefield has on internal mixing, and discuss the implications this might have on future climate scenarios.

Fluctuation spectra in the NASA Lewis bumpy-torus plasma

NASA Technical Reports Server (NTRS)

Singh, C. M.; Krawczonek, W. M.; Roth, J. R.; Hong, J. Y.; Powers, E. J.

1978-01-01

The electrostatic potential fluctuation spectrum in the NASA Lewis bumpy-torus plasma was studied with capacitive probes in the low pressure (high impedance) mode and in the high pressure (low impedance) mode. Under different operating conditions, the plasma exhibited electrostatic potential fluctuations (1) at a set of discrete frequencies, (2) at a continuum of frequencies, and (3) as incoherent high-frequency turbulence. The frequencies and azimuthal wave numbers were determined from digitally implemented autopower and cross-power spectra. The azimuthal dispersion characteristics of the unstable waves were examined by varying the electrode voltage, the polarity of the voltage, and the neutral background density at a constant magnetic field strength.

Large-Amplitude High-Frequency Waves at Earth's Magnetopause

NASA Astrophysics Data System (ADS)

Graham, D. B.; Vaivads, A.; Khotyaintsev, Yu. V.; André, M.; Le Contel, O.; Malaspina, D. M.; Lindqvist, P.-A.; Wilder, F. D.; Ergun, R. E.; Gershman, D. J.; Giles, B. L.; Magnes, W.; Russell, C. T.; Burch, J. L.; Torbert, R. B.

2018-04-01

Large-amplitude waves near the electron plasma frequency are found by the Magnetospheric Multiscale (MMS) mission near Earth's magnetopause. The waves are identified as Langmuir and upper hybrid (UH) waves, with wave vectors either close to parallel or close to perpendicular to the background magnetic field. The waves are found all along the magnetopause equatorial plane, including both flanks and close to the subsolar point. The waves reach very large amplitudes, up to 1 V m-1, and are thus among the most intense electric fields observed at Earth's magnetopause. In the magnetosphere and on the magnetospheric side of the magnetopause the waves are predominantly UH waves although Langmuir waves are also found. When the plasma is very weakly magnetized only Langmuir waves are likely to be found. Both Langmuir and UH waves are shown to have electromagnetic components, which are consistent with predictions from kinetic wave theory. These results show that the magnetopause and magnetosphere are often unstable to intense wave activity near the electron plasma frequency. These waves provide a possible source of radio emission at the magnetopause.

Millimeter Wave Systems for Airports and Short-Range Aviation Communications: A Survey of the Current Channel Models at mmWave Frequencies

NASA Technical Reports Server (NTRS)

Khatun, Mahfuza; Mehrpouyan, Hani; Matolak, David; Guvenc, Ismail

2017-01-01

Millimeter-wave (mmWave) communications will play a key role in enhancing the throughput, reliability, and security of next generation wireless networks. These advancements are achieved through the large bandwidth available in this band and through the use of highly directional links that will be used to overcome the large pathloss at these frequencies. Although the terrestrial application of mmWave systems is advancing at a rapid pace, the use of mmWave communication systems in aviation systems or airports is still in its infancy. This can be attributed to the challenges related to radio technology and lack of development, and characterization of mmWave wireless channels for the aviation field and the airport environment. Consequently, one of our goals is to develop methodologies that support mmWave air to ground links, and various links at airports, by applying new localization schemes that allow for application of highly directional links that can be deployed over longer distances despite the high path loss at mmWave frequencies. However, a very thorough understanding of the mmWave channel models are needed to enable such new applications. To this end, in this paper, we present a survey of the current channel models in the mmWave band. The 3-dimensional statistical channel model is also reviewed and its parameters and typical characteristics for this model are identified and computed through simulation for the Boise metropolitan area.

Square or sine: finding a waveform with high success rate of eliciting SSVEP.

PubMed

Teng, Fei; Chen, Yixin; Choong, Aik Min; Gustafson, Scott; Reichley, Christopher; Lawhead, Pamela; Waddell, Dwight

2011-01-01

Steady state visual evoked potential (SSVEP) is the brain's natural electrical potential response for visual stimuli at specific frequencies. Using a visual stimulus flashing at some given frequency will entrain the SSVEP at the same frequency, thereby allowing determination of the subject's visual focus. The faster an SSVEP is identified, the higher information transmission rate the system achieves. Thus, an effective stimulus, defined as one with high success rate of eliciting SSVEP and high signal-noise ratio, is desired. Also, researchers observed that harmonic frequencies often appear in the SSVEP at a reduced magnitude. Are the harmonics in the SSVEP elicited by the fundamental stimulating frequency or by the artifacts of the stimuli? In this paper, we compare the SSVEP responses of three periodic stimuli: square wave (with different duty cycles), triangle wave, and sine wave to find an effective stimulus. We also demonstrate the connection between the strength of the harmonics in SSVEP and the type of stimulus.

Multiple-frequency continuous wave ultrasonic system for accurate distance measurement

NASA Astrophysics Data System (ADS)

Huang, C. F.; Young, M. S.; Li, Y. C.

1999-02-01

A highly accurate multiple-frequency continuous wave ultrasonic range-measuring system for use in air is described. The proposed system uses a method heretofore applied to radio frequency distance measurement but not to air-based ultrasonic systems. The method presented here is based upon the comparative phase shifts generated by three continuous ultrasonic waves of different but closely spaced frequencies. In the test embodiment to confirm concept feasibility, two low cost 40 kHz ultrasonic transducers are set face to face and used to transmit and receive ultrasound. Individual frequencies are transmitted serially, each generating its own phase shift. For any given frequency, the transmitter/receiver distance modulates the phase shift between the transmitted and received signals. Comparison of the phase shifts allows a highly accurate evaluation of target distance. A single-chip microcomputer-based multiple-frequency continuous wave generator and phase detector was designed to record and compute the phase shift information and the resulting distance, which is then sent to either a LCD or a PC. The PC is necessary only for calibration of the system, which can be run independently after calibration. Experiments were conducted to test the performance of the whole system. Experimentally, ranging accuracy was found to be within ±0.05 mm, with a range of over 1.5 m. The main advantages of this ultrasonic range measurement system are high resolution, low cost, narrow bandwidth requirements, and ease of implementation.

Rogue wave triggered at a critical frequency of a nonlinear resonant medium.

PubMed

He, Jingsong; Xu, Shuwei; Porsezian, K; Cheng, Yi; Dinda, P Tchofo

2016-06-01

We consider a two-level atomic system interacting with an electromagnetic field controlled in amplitude and frequency by a high intensity laser. We show that the amplitude of the induced electric field admits an envelope profile corresponding to a breather soliton. We demonstrate that this soliton can propagate with any frequency shift with respect to that of the control laser, except a critical frequency, at which the system undergoes a structural discontinuity that transforms the breather in a rogue wave. A mechanism of generation of rogue waves by means of an intense laser field is thus revealed.

Study of guided modes in three-dimensional composites

NASA Astrophysics Data System (ADS)

Baste, S.; Gerard, A.

The propagation of elastic waves in a three-dimensional carbon-carbon composite is modeled with a mixed variational method, using the Bloch or Floquet theories and the Hellinger-Reissner function for two independent fields. The model of the equivalent homogeneous material only exists below a cut-off frequency of about 600 kHz. The existence below the cut-off frequency of two guided waves can account for the presence of a slow guided wave on either side of the cut-off frequency. Optical modes are generated at low frequencies, and can attain high velocites (rapid guided modes of 15,000 m/sec).

Transition region, coronal heating and the fast solar wind

NASA Astrophysics Data System (ADS)

Li, Xing

2003-07-01

It is assumed that magnetic flux tubes are strongly concentrated at the boundaries of supergranule convection cells. A power law spectrum of high frequency Alfvén waves with a spectral index -1 originating from the sun is assumed to supply all the energy needed to energize the plasma flowing in such magnetic flux tubes. At the high frequency end, the waves are eroded by ions due to ion cyclotron resonance. The magnetic flux concentration is essential since it allows a sufficiently strong energy flux to be carried by high frequency ion cyclotron waves and these waves can be readily released at the coronal base by cyclotron resonance. The main results are: 1. The waves are capable of creating a steep transition region, a hot corona and a fast solar wind if both the wave frequency is high enough and the magnetic flux concentration is sufficiently strong in the boundaries of the supergranule convection zone. 2. By primarily heating alpha particles only, it is possible to produce a steep transition region, a hot corona and a fast solar wind. Coulomb coupling plays a key role in transferring the thermal energy of alpha particles to protons and electrons at the corona base. The electron thermal conduction then does the remaining job to create a sharp transition region. 3. Plasma species (even ions) may already partially lose thermal equilibrium in the transition region, and minor ions may already be faster than protons at the very base of the corona. 4. The model predicts high temperature alpha particles (Talpha ~ 2 x 107 K) and low proton temperatures (Tp < 106 K) between 2 and 4 solar radii, suggesting that hydrogen Lyman lines observed by UVCS above coronal holes may be primarily broadened by Alfvén waves in this range.

Brain stem auditory potentials evoked by clicks in the presence of high-pass filtered noise in dogs.

PubMed

Poncelet, L; Deltenre, P; Coppens, A; Michaux, C; Coussart, E

2006-04-01

This study evaluates the effects of a high-frequency hearing loss simulated by the high-pass-noise masking method, on the click-evoked brain stem-evoked potentials (BAEP) characteristics in dogs. BAEP were obtained in response to rarefaction and condensation click stimuli from 60 dB normal hearing level (NHL, corresponding to 89 dB sound pressure level) to wave V threshold, using steps of 5 dB in eleven 58 to 80-day-old Beagle puppies. Responses were added, providing an equivalent to alternate polarity clicks, and subtracted, providing the rarefaction-condensation potential (RCDP). The procedure was repeated while constant level, high-pass filtered (HPF) noise was superposed to the click. Cut-off frequencies of the successively used filters were 8, 4, 2 and 1 kHz. For each condition, wave V and RCDP thresholds, and slope of the wave V latency-intensity curve (LIC) were collected. The intensity range at which RCDP could not be recorded (pre-RCDP range) was calculated. Compared with the no noise condition, the pre-RCDP range significantly diminished and the wave V threshold significantly increased when the superposed HPF noise reached the 4 kHz area. Wave V LIC slope became significantly steeper with the 2 kHz HPF noise. In this non-invasive model of high-frequency hearing loss, impaired hearing of frequencies from 8 kHz and above escaped detection through click BAEP study in dogs. Frequencies above 13 kHz were however not specifically addressed in this study.

Low-Temperature Variation of Acoustic Velocity in PDMS for High-Frequency Applications.

PubMed

Streque, Jeremy; Rouxel, Didier; Talbi, Abdelkrim; Thomassey, Matthieu; Vincent, Brice

2018-05-01

Polydimethylsiloxane (PDMS) and other related silicon-based polymers are among the most widely employed elastomeric materials in microsystems, owing to their physical and chemical properties. Meanwhile, surface acoustic wave (SAW) and bulk acoustic wave (BAW) sensors and filters have been vastly explored for sensing and wireless applications. Many fields could benefit from the combined use of acoustic wave devices, and polydimethylsiloxane-based soft-substrates, microsystems, or packaging elements. The mechanical constants of PDMS strongly depend on frequency, similar to rubber materials. This brings to the exploration of the specific mechanical properties of PDMS encountered at high frequency, required for its exploitation in SAW or BAW devices. First, low-frequency mechanical behavior is confirmed from stress strain measurements, remaining useful for the exploitation of PDMS as a soft substrate or packaging material. The study, then, proposes a temperature-dependent, high-frequency mechanical study of PDMS based on Brillouin spectroscopy to determine the evolution of the longitudinal acoustic velocity in this material, which constitutes the main mechanical parameter for the design of acoustic wave devices. The PDMS glass transition is then retrieved by differential scanning calorimetry in order to confirm the observations made by Brillouin spectroscopy. This paper validates Brillouin spectroscopy as a very suitable characterization technique for the retrieval of longitudinal mechanical properties at low temperature, as a preliminary investigation for the design of acoustic wave devices coupled with soft materials.

Micro-seismic measurements of cliff motion under wave impact and implications for the development of near-horizontal shore platforms

NASA Astrophysics Data System (ADS)

Dickson, Mark E.; Pentney, Rachael

2012-05-01

Few high-resolution measurements of process-form interactions have been taken on rock coasts, but recent studies in California have shown that portable seismometers enable useful proxy measurements of wave-energy delivery to cliffs. Here we describe measurements over 20 days of high frequency ground motion of cliffs formed in sedimentary (flysch) rocks at Okakari Point, north of Auckland, New Zealand. Three sensors were located in a shore-normal array inland from the cliff top and a fourth sensor was bolted to a ledge 2 m above the cliff toe. The nearshore wave field in front of the cliff and shore platform was monitored using a shore-normal array of 5 wave gauges. The instrumentation provided measurements of wave-energy delivery and consequent ground motion, including the first observations of motion at the top and bottom of cliffs. Results showed that horizontal ground motion is dominant at the cliff top, whereas vertical motion is dominant at the cliff toe. Power spectra show that several high frequency peaks occur in data from the cliff toe, whereas a single, broader peak frequency occurs at the cliff top resulting from signal modification as seismic waves pass through tens of metres of cliff rock. A 100 m wide shore platform at the cliff toe fundamentally controls the patterns of observed energy delivery. The shore platform is nearly horizontal, elevated close to high water level, and abruptly plunges into water > 10 m deep at its seaward edge. As expected, the magnitude of ground motion at all sensors is greatest during larger waves. Measurements further show that ground motion, both at the bottom and top of the cliff, is strongest at low tide and weakest at high tide. This observation is opposite to that noted at Santa Cruz, where ground motion was greatest at high tide. At Okakari Point the most significant high frequency ground motions occur at low tide when waves are forced to break (sometimes violently) against the seaward edge of the shore platform. Four distinctive frequency peaks between 1 and 50 Hz increase in magnitude as tidal stage drops, implying that wave breaking against the outside edge of the shore platform represents an important source of vibration. A detailed understanding of the energy source (e.g. short duration shock pressures) and rock resonance is not provided by this study. However, quantifying the spatial and temporal patterns of energy delivery places strong emphasis on the important role of shore platform geometry in filtering wave-energy delivery to the cliff. During the 20-day experiment most wave energy was delivered to the outside edge of the shore platform, not the cliff toe. The geomorphic role of high-frequency shaking from wave impacts remains to be clearly demonstrated, but if wave impacts are capable of eroding rock then the data from this study imply that under present conditions the outside edge of the shore platform may be subject to higher erosion rates than the cliff toe. It is possible that the shore platform is currently being destroyed rather than created, but a longer programme of measurements is required to test this notion.

Measurement of the electron beam mode in earth's foreshock

NASA Technical Reports Server (NTRS)

Onsager, T. G.; Holzworth, R. H.

1990-01-01

High frequency electric field measurements from the AMPTE IRM plasma wave receiver are used to identify three simultaneously excited electrostatic wave modes in the earth's foreshock region: the electron beam mode, the Langmuir mode, and the ion acoustic mode. A technique is developed which allows the rest frame frequecy and wave number of the electron beam waves to be determined. It is shown that the experimentally determined rest frame frequency and wave number agree well with the most unstable frequency and wave number predicted by linear homogeneous Vlasov theory for a plasma with Maxwellian background electrons and a Lorentzian electron beam. From a comparison of the experimentally determined and theoretical values, approximate limits are put on the electron foreshock beam temperatures. A possible generation mechanism for ion acoustic waves involving mode coupling between the electron beam and Langmuir modes is also discussed.

Wafer scale millimeter-wave integrated circuits based on epitaxial graphene in high data rate communication.

PubMed

Habibpour, Omid; He, Zhongxia Simon; Strupinski, Wlodek; Rorsman, Niklas; Zirath, Herbert

2017-02-01

In recent years, the demand for high data rate wireless communications has increased dramatically, which requires larger bandwidth to sustain multi-user accessibility and quality of services. This can be achieved at millimeter wave frequencies. Graphene is a promising material for the development of millimeter-wave electronics because of its outstanding electron transport properties. Up to now, due to the lack of high quality material and process technology, the operating frequency of demonstrated circuits has been far below the potential of graphene. Here, we present monolithic integrated circuits based on epitaxial graphene operating at unprecedented high frequencies (80-100 GHz). The demonstrated circuits are capable of encoding/decoding of multi-gigabit-per-second information into/from the amplitude or phase of the carrier signal. The developed fabrication process is scalable to large wafer sizes.

New Observation of Wave Excitation and Inverse Cascade in the Foreshock Region

NASA Astrophysics Data System (ADS)

He, Jiansen; Duan, Die; Yan, Limei; Huang, Shiyong; Tu, Chuanyi; Marsch, Eckart; Wang, Linghua; Tian, Hui

2016-04-01

Foreshock with nascent plasma turbulence is regarded as a fascinating region to understand the basic plasma physical processes, e.g., wave-particle interactions as well as wave-wave couplings. Although there have been a bunch of intensive studies on this topic, some key clues about the chain of the physical processes still lacks from observations, e.g., the co-existence of upstream energetic particles as the free energy source, excited pump waves as the wave seed, inverse cascaded daughter waves, and scattered energetic particles as the end of nonlinear processes. A relatively comprehensive case study with some new observations is presented in this work. In our case, upstream energetic protons drifting at tens of Alfvén speed with respect to the background plasma protons is observed from 3DP/PESA-High onboard the WIND spacecraft. When looking at the wave magnetic activities, we are surprised to find the co-existence of high-frequency (0.1-0.5 Hz) large-amplitude right-hand polarized (RHP) waves and low-frequency (0.02-0.1 Hz) small-amplitude left-hand polarized (LHP) waves in the spacecraft (SC) frame. The anti-correlation between magnetic and velocity fluctuations along with the sunward magnetic field direction indicates the low-frequency LHP waves in the SC frame is in fact the sunward upstream RHP waves in the solar wind frame. This new observation lays solid foundation for the applicability of plasma non-resonance instability theory and inverse cascade theory to the foreshock region, in which the downstream high-frequency RHP pump waves are excited by the upstream reflected energetic protons through non-resonance instability and low-frequency RHP daughter waves are generated by the pump waves due to nonlinear parametric decay. The weak signal of alpha particle flux in the foreshock region concerned is also favorable to the occurrence of nonlinear decay process. Furthermore, enhanced downstream energetic proton fluxes are found and inferred to be scattered by the nascent turbulent fluctuations. Therefore, some key clues about the newborn turbulence in the foreshock are supplemented in this work. Nevertheless, the more complete scenario about the fundamental plasma physical processes in the foreshock is left for the newly launched MMS project and the proposed THOR mission.

High-efficiency and multi-frequency polarization converters based on graphene metasurface with twisting double L-shaped unit structure array

NASA Astrophysics Data System (ADS)

Chen, Ming; Xiao, Xiaofei; Chang, Linzi; Wang, Congyun; Zhao, Deping

2017-07-01

In this work, a high-efficiency and tunable dual-frequency reflective polarization converter composed of graphene metasurface with twisting double L-shaped unit is firstly realized. Numerical results demonstrate that the device can convert a linearly polarized wave to its cross-polarized wave, and meantime it can also convert to a circularly polarized wave. Subsequently, one thickness of 500 nm SiO2 layer sandwiched by two graphene metasurfaces with similar pattern is stacked on the top of the two-layered structure, a four-frequency efficient reflective polarization converters is realized. Above all, those working frequencies can also be dynamically tuned within a large frequency range by adjusting the Fermi energy of the graphene, without reoptimizing and refabricating the nanostructures, which paves a novel way toward developing a controllable polarization converter for mid-infrared applications.

Shear Wave Imaging of Breast Tissue by Color Doppler Shear Wave Elastography.

PubMed

Yamakoshi, Yoshiki; Nakajima, Takahito; Kasahara, Toshihiro; Yamazaki, Mayuko; Koda, Ren; Sunaguchi, Naoki

2017-02-01

Shear wave elastography is a distinctive method to access the viscoelastic characteristic of the soft tissue that is difficult to obtain by other imaging modalities. This paper proposes a novel shear wave elastography [color Doppler shear wave imaging (CD SWI)] for breast tissue. Continuous shear wave is produced by a small lightweight actuator, which is attached to the tissue surface. Shear wave wavefront that propagates in tissue is reconstructed as a binary pattern that consists of zero and the maximum flow velocities on color flow image (CFI). Neither any modifications of the ultrasound color flow imaging instrument nor a high frame rate ultrasound imaging instrument is required to obtain the shear wave wavefront map. However, two conditions of shear wave displacement amplitude and shear wave frequency are needed to obtain the map. However, these conditions are not severe restrictions in breast imaging. This is because the minimum displacement amplitude is [Formula: see text] for an ultrasonic wave frequency of 12 MHz and the shear wave frequency is available from several frequencies suited for breast imaging. Fourier analysis along time axis suppresses clutter noise in CFI. A directional filter extracts shear wave, which propagates in the forward direction. Several maps, such as shear wave phase, velocity, and propagation maps, are reconstructed by CD SWI. The accuracy of shear wave velocity measurement is evaluated for homogeneous agar gel phantom by comparing with the acoustic radiation force impulse method. The experimental results for breast tissue are shown for a shear wave frequency of 296.6 Hz.

Millimeter-wave generation and characterization of a GaAs FET by optical mixing

NASA Technical Reports Server (NTRS)

Ni, David C.; Fetterman, Harold R.; Chew, Wilbert

1990-01-01

Coherent mixing of optical radiation from a tunable continuous-wave dye laser and a stabilized He-Ne laser was used to generate millimeter-wave signals in GaAs FETs attached to printed-circuit millimeter-wave antennas. The generated signal was further down-converted to a 2-GHz IF by an antenna-coupled millimeter-wave local oscillator at 62 GHz. Detailed characterizations of power and S/N under different bias conditions have been performed. This technique is expected to allow signal generation and frequency-response evaluation of millimeter-wave devices at frequencies as high as 100 GHz.

Spatial Variations of Poloidal and Toroidal Mode Field Line Resonances Observed by MMS

NASA Astrophysics Data System (ADS)

Le, G.; Chi, P. J.; Strangeway, R. J.; Russell, C. T.; Slavin, J. A.; Anderson, B. J.; Kepko, L.; Nakamura, R.; Plaschke, F.; Torbert, R. B.

2017-12-01

Field line resonances (FLRs) are magnetosphere's responses to solar wind forcing and internal instabilities generated by solar wind-magnetospheric interactions. They are standing waves along the Earth's magnetic field lines oscillating in either poloidal or toroidal modes. The two types of waves have their unique frequency characteristics. The eigenfrequency of FLRs is determined by the length of the field line and the plasma density, and thus gradually changes with L. For toroidal mode oscillations with magnetic field perturbations in the azimuthal direction, ideal MHD predicts that each field line oscillates independently with its own eigenfrequency. For poloidal mode waves with field lines oscillating radially, their frequency cannot change with L easily as L shells need to oscillate in sync to avoid efficient damping due to phase mixing. Observations, mainly during quiet times, indeed show that poloidal mode waves often exhibit nearly constant frequency across L shells. Our recent observations, on the other hand, reveal a clear L-dependent frequency trend for a long lasting storm-time poloidal wave event, indicating the wave can maintain its power with changing frequencies for an extended period [Le et al., 2017]. The spatial variation of the frequency shows discrete spatial structures. The frequency remains constant within each discrete structure that spans about 1 REalong L, and changes discretely. We present a follow-up study to investigate spatial variations of wave frequencies using the Wigner-Ville distribution. We examine both poloidal and toroidal waves under different geomagnetic conditions using multipoint observations from MMS, and compare their frequency and occurrence characteristics for insights into their generation mechanisms. Reference: Le, G., et al. (2017), Global observations of magnetospheric high-m poloidal waves during the 22 June 2015 magnetic storm, Geophys. Res. Lett., 44, 3456-3464, doi:10.1002/2017GL073048.

Examining P-Wave Arrivals of Low-Frequency Earthquakes for Evidence of Attenuation and its Effects on Moment-Duration Scaling

NASA Astrophysics Data System (ADS)

Gerzina, J.; Rubin, A. M.

2017-12-01

Bostock et. al. (2015) found that low-frequency earthquake (LFE) duration is nearly independent of moment, a result that is surprising enough to warrant investigating whether it might be an artifact of attenuation. Bostock et. al. (2017) found that bulk crustal attenuation could not be the culprit, but suggested that near-source attenuation might cause pronounced depletion of high frequency S-waves. Despite their lower signal-to noise ratio, looking at the P-waves might be enlightening because they aren't expected to attenuate as much as S-waves in the high Vp/Vs region near the tremor source. We have examined P-wave arrivals of LFEs that occurred during episodic tremor in the Cascadia subduction zone with the goal of refining the relationship between LFE magnitude and duration.Bostock et. al's duration measurements were made on stacked templates rather than individual arrivals. Because members of Bostock's LFE families vary in location, and therefore in P-S delay time, aligning the stacks primarily on the S arrival may artificially widen the P pulse. To circumvent this, we used cross-station cross correlations on Bostock's detections to identify and stack events with similar locations and therefore similar P-S delay times, until P arrivals became visible. We then stacked these stacks based on cross-correlating the optimal P component in a small window surrounding the P arrival. Although this procedure narrowed both the P and S pulse widths, it did not dramatically narrow P in relation to S, nor did we observe different P pulse widths for small and large events.We also compared the frequency spectra of small windows around the expected P and S arrivals for each amplitude bin. Although there is more high-frequency content in P-waves than S-waves, we have not yet been able to resolve a difference in P-wave corner frequency for different event sizes. Thus our preliminary results support the notion that LFEs are intrinsically low frequency.

Geophysical Remote Sensing Using the HF Pumped Stimulated Brillouin Scatter (SBS) Emission Lines Produced by HAARP

NASA Astrophysics Data System (ADS)

Bernhardt, P. A.; Selcher, C. A.

2009-12-01

An ordinary or extraordinary mode electromagnetic wave can decay into a low frequency electrostatic wave and a scattered electromagnetic wave by a process called stimulated Brillouin scatter (SBS). The low frequency wave can be either an ion acoustic wave (IA) or an electrostatic ion cyclotron (EIC) wave. The first detection ion acoustic waves by this process during ionospheric modification with high power radio waves was reported by Norin et al. (2009) using the HAARP transmitter in Alaska. The first detection of the electrostatic ion cyclotron waves is reported here using HAARP during the March 2009 campaign. Subsequent experiments have provided additional verification of the SBS process and quantitative interpretation of the scattered wave frequency offsets to yield measurements of the electron temperatures in the heated ionosphere by Bernhardt et al. (2009). Using the SBS technique to generate ion acoustic waves, electron temperatures between 3000 and 4000 K were measured over the HAARP facility. The matching conditions for decay of the high frequency pump wave show that in addition to the production of an ion-acoustic wave, an electrostatic ion cyclotron wave can produced by the generalized SBS processes only if the pump waves makes a large angle with the magnetic field. When the EIC mode is produced, it is seen as a narrow of stimulated electromagnetic emissions at the ion cyclotron frequency. Occasionally, multiple lines are seen and analyzed to yield the relative abundance of oxygen, and molecular ions in the lower ionosphere. This ion mass spectrometer interpretation of the SBS data is new to the field of ionosphere remote sensing. In addition, based on the matching condition theory, the first profiles of the scattered wave amplitude are produced using the stimulated Brillouin scatter (SBS) matching conditions. These profiles are consistent with maximum ionospheric interactions at the upper-hybrid resonance height and at a region just below the plasma resonance altitude where the pump wave electric fields reach their maximum values. All of these measurements of the HF modified ionosphere are made possible at HAARP because of (1) the recently increased transmitter power to 3.6 MW into the large antenna array and (2) the new digital receiver diagnostics that allow up to 100 dB dynamic range in the stimulated electromagnetic emission measurements. Paul A. Bernhardt, Craig A. Selcher, Robert H. Lehmberg, Serafin Rodriguez, Joe Thomason, Mike McCarrick, Gordon Frazer, Determination of the Electron Temperature in the Modified Ionosphere over HAARP Using the HF Pumped Stimulated Brillouin Scatter (SBS) Emission Lines, Annales Geophysicae, in press, 2009. Norin, L., Leyser, T. B., Nordblad, E., Thidé, B., and McCarrick, M., Unprecedentedly strong and narrow electromagnetic emissions stimulated by high-frequency radio waves in the ionosphere, Phys. Rev. Lett., 102, 065003, 2009.

Electromagnetic properties of polycrystalline diamond from 35 K to room temperature and microwave to terahertz frequencies

NASA Astrophysics Data System (ADS)

Floch, Jean-Michel Le; Bara, Romain; Hartnett, John G.; Tobar, Michael E.; Mouneyrac, David; Passerieux, Damien; Cros, Dominique; Krupka, Jerzy; Goy, Philippe; Caroopen, Sylvain

2011-05-01

Dielectric resonators are key components for many microwave and millimeter wave applications, including high-Q filters and frequency-determining elements for precision frequency synthesis. These often depend on the quality of the dielectric material. The commonly used material for building the best cryogenic microwave oscillators is sapphire. However, sapphire is becoming a limiting factor for higher frequency designs. It is, then, important to find new candidates that can fulfill the requirements for millimeter wave low noise oscillators at room and cryogenic temperatures. These clocks are used as a reference in many fields, such as modern telecommunication systems, radio astronomy (very-long-baseline interferometry), and precision measurements at the quantum limit. High resolution measurements were taken of the temperature-dependence of the electromagnetic properties of a polycrystalline diamond disk at temperatures between 35 and 330 K at microwave to submillimeter wave frequencies. The cryogenic measurements were made using a TE01δ dielectric mode resonator placed inside a vacuum chamber connected to a single-stage pulse-tube cryocooler. The high frequency characterization was performed at room temperature using a combination of a quasi-optical two-lens transmission setup, a Fabry-Perot cavity, and a whispering gallery mode resonator excited with waveguides. Our CVD diamond sample exhibits a decreasing loss tangent with increasing frequencies. We compare the results with well known crystals. This comparison makes it clear that polycrystalline diamond could be an important material for generating stable frequencies at millimeter waves.

The origin of SH-wave resonance frequencies in sedimentary layers

NASA Astrophysics Data System (ADS)

van der Baan, Mirko

2009-09-01

Resonance frequencies are often analysed in geo-engineering studies to evaluate seismic risk and microzonation in urban areas. The Nakamura technique constitutes a popular approach that computes the spectral ratio of horizontal-to-vertical ground motion in ambient noise recordings to reveal the existence of any site resonance frequencies. Its theoretical basis remains however unclear with some authors arguing that the method de-emphasizes any Rayleigh-wave contributions and that the resonance frequencies are solely caused by vertically incident SH waves. Other authors explain the same resonance frequencies by the ellipticity of the fundamental Rayleigh wave. Recent numerical simulations reveal that the magnitude of the peak frequency is proportional to the relative portion of Love waves present. This study demonstrates that Love waves alone can be responsible for any observed resonance frequencies in sedimentary layers. Yet sharp SH-wave resonance frequencies are only excited by a source in the bedrock. These resonance frequencies are caused by inhomogeneous waves excited by the bedrock source that tunnel through the high-velocity bedrock to emerge in the low-velocity sediments with a very reduced range of slownesses. The resulting SH waves are then free to interfere constructively thereby creating the observed resonance frequencies. This general trigger mechanism leads to resonances that are almost offset independent. The resulting resonance frequencies map onto points of maximum curvature in the Love-wave phase-velocity dispersion curves at or just beyond the critical horizontal slowness. They can be analysed with the quarter-wavelength law if a large velocity contrast exists between the unconsolidated sediments and the bedrock. A minor modification of the quarter-wavelength law provides more accurate predictions, also for smaller velocity contrasts. Multisource simulations show that site amplification factors as determined by horizontal-over-vertical (H/V) spectral ratios would not only depend on the relative portion of Love waves in the total wavefield but also on the depth distribution and the relative strength of the SH sources inside the bedrock compared with those in the sediments. An accurate interpretation of site amplification factors by means of H/V peak frequencies would thus require in-depth knowledge of the causes and origins of the local microseismic noise field.

A Millimeter-wave Cavity-backed Suspended Substrate Stripline Antenna

NASA Technical Reports Server (NTRS)

Simons, Rainee N.

1999-01-01

Future generation satellite communication systems in near-Earth orbit will operate at frequencies in the higher mm-wave frequency hands. These satellite systems require low-profile, high gain, light weight and low cost antennas for communications to and from Earth as well as for inter-satellite links (ISL). At higher mm-wave frequencies, the conductor loss of conventional microstrip line is high and consequently the feed network loss of patch antenna arrays is also high. The high loss lowers the array efficiency and in addition lowers the G/T ratio in a receiving array. Recently a radial line slot antenna array has been demonstrated to have high gain and efficiency at 60 GHz. In this paper, the design, fabrication and characterization of a V-Band (50-75 GHz) 4 x 4 planar array of cavity backed circular aperture antennas with suspended substrate stripline (SSS) corporate feed is presented.

Frequency-tunable continuous-wave terahertz sources based on GaAs plasmonic photomixers

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

Yang, Shang-Hua; Jarrahi, Mona; Electrical Engineering Department, University of California Los Angeles, Los Angeles, California 90095

2015-09-28

We present frequency-tunable, continuous-wave terahertz sources based on GaAs plasmonic photomixers, which offer high terahertz radiation power levels at 50% radiation duty cycle. The use of plasmonic contact electrodes enhances photomixer quantum efficiency while maintaining its ultrafast operation by concentrating a large number of photocarriers in close proximity to the device contact electrodes. Additionally, the relatively high thermal conductivity and high resistivity of GaAs allow operation under high optical pump power levels and long duty cycles without reaching the thermal breakdown limit of the photomixer. We experimentally demonstrate continuous-wave terahertz radiation with a radiation frequency tuning range of more thanmore » 2 THz and a record-high radiation power of 17 μW at 1 THz through plasmonic photomixers fabricated on a low temperature grown GaAs substrate at 50% radiation duty cycle.« less

A Statistical Analysis of Langmuir Wave-Electron Correlations Observed by the CHARM II Auroral Sounding Rocket

NASA Astrophysics Data System (ADS)

Dombrowski, M. P.; Labelle, J. W.; Kletzing, C.; Bounds, S. R.; Kaeppler, S. R.

2014-12-01

Langmuir-mode electron plasma waves are frequently observed by spacecraft in active plasma environments such as the ionosphere. Ionospheric Langmuir waves may be excited by the bump-on-tail instability generated by impinging beams of electrons traveling parallel to the background magnetic field (B). The Correlation of High-frequencies and Auroral Roar Measurement (CHARM II) sounding rocket was launched into a substorm at 9:49 UT on 17 February 2010, from the Poker Flat Research Range in Alaska. The primary instruments included the University of Iowa Wave-Particle Correlator (WPC), the Dartmouth High-Frequency Experiment (HFE), several charged particle detectors, low-frequency wave instruments, and a magnetometer. The HFE is a receiver system which effectively yields continuous (100% duty cycle) electric-field waveform measurements from 100 kHz to 5 MHz, and which had its detection axis aligned nominally parallel to B. The HFE output was fed on-payload to the WPC, which uses a phase-locked loop to track the incoming wave frequency with the most power, then sorting incoming electrons at eight energy levels into sixteen wave-phase bins. CHARM II encountered several regions of strong Langmuir wave activity throughout its 15-minute flight, and the WPC showed wave-lock and statistically significant particle correlation distributions during several time periods. We show results of an in-depth analysis of the CHARM II WPC data for the entire flight, including statistical analysis of correlations which show evidence of direct interaction with the Langmuir waves, indicating (at various times) trapping of particles and both driving and damping of Langmuir waves by particles. In particular, the sign of the gradient in particle flux appears to correlate with the phase relation between the electrons and the wave field, with possible implications for the wave physics.

High-frequency homogenization for travelling waves in periodic media.

PubMed

Harutyunyan, Davit; Milton, Graeme W; Craster, Richard V

2016-07-01

We consider high-frequency homogenization in periodic media for travelling waves of several different equations: the wave equation for scalar-valued waves such as acoustics; the wave equation for vector-valued waves such as electromagnetism and elasticity; and a system that encompasses the Schrödinger equation. This homogenization applies when the wavelength is of the order of the size of the medium periodicity cell. The travelling wave is assumed to be the sum of two waves: a modulated Bloch carrier wave having crystal wavevector [Formula: see text] and frequency ω 1 plus a modulated Bloch carrier wave having crystal wavevector [Formula: see text] and frequency ω 2 . We derive effective equations for the modulating functions, and then prove that there is no coupling in the effective equations between the two different waves both in the scalar and the system cases. To be precise, we prove that there is no coupling unless ω 1 = ω 2 and [Formula: see text] where Λ =(λ 1 λ 2 …λ d ) is the periodicity cell of the medium and for any two vectors [Formula: see text] the product a ⊙ b is defined to be the vector ( a 1 b 1 , a 2 b 2 ,…, a d b d ). This last condition forces the carrier waves to be equivalent Bloch waves meaning that the coupling constants in the system of effective equations vanish. We use two-scale analysis and some new weak-convergence type lemmas. The analysis is not at the same level of rigour as that of Allaire and co-workers who use two-scale convergence theory to treat the problem, but has the advantage of simplicity which will allow it to be easily extended to the case where there is degeneracy of the Bloch eigenvalue.

Large scale modulation of high frequency acoustic waves in periodic porous media.

PubMed

Boutin, Claude; Rallu, Antoine; Hans, Stephane

2012-12-01

This paper deals with the description of the modulation at large scale of high frequency acoustic waves in gas saturated periodic porous media. High frequencies mean local dynamics at the pore scale and therefore absence of scale separation in the usual sense of homogenization. However, although the pressure is spatially varying in the pores (according to periodic eigenmodes), the mode amplitude can present a large scale modulation, thereby introducing another type of scale separation to which the asymptotic multi-scale procedure applies. The approach is first presented on a periodic network of inter-connected Helmholtz resonators. The equations governing the modulations carried by periodic eigenmodes, at frequencies close to their eigenfrequency, are derived. The number of cells on which the carrying periodic mode is defined is therefore a parameter of the modeling. In a second part, the asymptotic approach is developed for periodic porous media saturated by a perfect gas. Using the "multicells" periodic condition, one obtains the family of equations governing the amplitude modulation at large scale of high frequency waves. The significant difference between modulations of simple and multiple mode are evidenced and discussed. The features of the modulation (anisotropy, width of frequency band) are also analyzed.

Phase-locking and coherent power combining of broadband linearly chirped optical waves.

PubMed

Satyan, Naresh; Vasilyev, Arseny; Rakuljic, George; White, Jeffrey O; Yariv, Amnon

2012-11-05

We propose, analyze and demonstrate the optoelectronic phase-locking of optical waves whose frequencies are chirped continuously and rapidly with time. The optical waves are derived from a common optoelectronic swept-frequency laser based on a semiconductor laser in a negative feedback loop, with a precisely linear frequency chirp of 400 GHz in 2 ms. In contrast to monochromatic waves, a differential delay between two linearly chirped optical waves results in a mutual frequency difference, and an acoustooptic frequency shifter is therefore used to phase-lock the two waves. We demonstrate and characterize homodyne and heterodyne optical phase-locked loops with rapidly chirped waves, and show the ability to precisely control the phase of the chirped optical waveform using a digital electronic oscillator. A loop bandwidth of ~ 60 kHz, and a residual phase error variance of < 0.01 rad(2) between the chirped waves is obtained. Further, we demonstrate the simultaneous phase-locking of two optical paths to a common master waveform, and the ability to electronically control the resultant two-element optical phased array. The results of this work enable coherent power combining of high-power fiber amplifiers-where a rapidly chirping seed laser reduces stimulated Brillouin scattering-and electronic beam steering of chirped optical waves.

ELF/VLF Waves Generated by an Artificially-Modulated Auroral Electrojet Above the HAARP HF Transmitter

NASA Astrophysics Data System (ADS)

Moore, R. C.; Inan, U. S.; Bell, T. F.

2004-12-01

Naturally-forming, global-scale currents, such as the polar electrojet current and the mid-latitude dynamo, have been used as current sources to generate electromagnetic waves in the Extremely Low Frequency (ELF) and Very Low Frequency (VLF) bands since the 1970's. While many short-duration experiments have been performed, no continuous multi-week campaign data sets have been published providing reliable statistics for ELF/VLF wave generation. In this paper, we summarize the experimental data resulting from multiple ELF/VLF wave generation campaigns conducted at the High-frequency Active Auroral Research Project (HAARP) HF transmitter in Gakona, Alaska. For one 14-day period in March, 2002, and one 24-day period in November, 2002, the HAARP HF transmitter broadcast ELF/VLF wave generation sequences for 10 hours per day, between 0400 and 1400 UT. Five different modulation frequencies broadcast separately using two HF carrier frequencies are examined at receivers located 36, 44, 147, and 155 km from the HAARP facility. Additionally, a continuous 24-hour transmission period is analyzed to compare day-time wave generation to night-time wave generation. Lastly, a power-ramping scheme was employed to investigate possible thresholding effects at the wave-generating altitude. Wave generation statistics are presented along with source-region property calculations performed using a simple model.

Jupiter plasma wave observations: an initial voyager 1 overview.

PubMed

Scarf, F L; Gurnett, D A; Kurth, W S

1979-06-01

The Voyager I plasma wave instrument detected low-frequency radio emissions, ion acoustic waves, and electron plasma oscillations for a period of months before encountering Jupiter's bow shock. In the outer magnetosphere, measurements of trapped radio waves were used to derive an electron density profile. Near and within the Io plasma torus the instrument detected high-frequency electrostatic waves, strong whistler mode turbulence, and discrete whistlers, apparently associated with lightning. Some strong emissions in the tail region and some impulsive signals have not yet been positively identified.

Current-induced modulation of backward spin-waves in metallic microstructures

NASA Astrophysics Data System (ADS)

Sato, Nana; Lee, Seo-Won; Lee, Kyung-Jin; Sekiguchi, Koji

2017-03-01

We performed a propagating spin-wave spectroscopy for backward spin-waves in ferromagnetic metallic microstructures in the presence of electric-current. Even with the smaller current injection of 5× {{10}10} A m-2 into ferromagnetic microwires, the backward spin-waves exhibit a gigantic 200 MHz frequency shift and a 15% amplitude change, showing 60 times larger modulation compared to previous reports. Systematic experiments by measuring dependences on a film thickness of mirowire, on the wave-vector of spin-wave, and on the magnitude of bias field, we revealed that for the backward spin-waves a distribution of internal magnetic field generated by electric-current efficiently modulates the frequency and amplitude of spin-waves. The gigantic frequency and amplitude changes were reproduced by a micromagnetics simulation, predicting that the current-injection of 5× {{10}11} A m-2 allows 3 GHz frequency shift. The effective coupling between electric-current and backward spin-waves has a potential to build up a logic control method which encodes signals into the phase and amplitude of spin-waves. The metallic magnonics cooperating with electronics could suggest highly integrated magnonic circuits both in Boolean and non-Boolean principles.

Relativistic Tennis with Photons: Frequency Up-Shifting, Light Intensification and Ion Acceleration with Flying Mirrors

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

Bulanov, S. V.; Esirkepov, T. Zh.; Kando, M.

2011-01-04

We formulate the Flying Mirror Concept for relativistic interaction of ultra-intense electromagnetic waves with plasmas, present its theoretical description and the results of computer simulations and laboratory experiments. In collisionless plasmas, the relativistic flying mirrors are thin and dense electron or electron-ion layers accelerated by the high intensity electromagnetic waves up to velocity close to the speed of light in vacuum; in nonlinear-media and in nonlinear vacuum they are the ionization fronts and the refraction index modulations induced by a strong electromagnetic wave. The reflection of the electromagnetic wave at the relativistic mirror results in its energy and frequency changemore » due to the double Doppler effect. In the co-propagating configuration, in the radiation pressure dominant regime, the energy of the electromagnetic wave is transferred to the ion energy providing a highly efficient acceleration mechanism. In the counter-propagation configuration the frequency of the reflected wave is multiplied by the factor proportional to the gamma-factor squared. If the relativistic mirror performs an oscillatory motion as in the case of the electron motion at the plasma-vacuum interface, the reflected light spectrum is enriched with high order harmonics.« less

Survey of Ionospheric Pc3-5 ULF Wave Signatures in SuperDARN High Time Resolution Data

NASA Astrophysics Data System (ADS)

Shi, X.; Ruohoniemi, J. M.; Baker, J. B. H.; Lin, D.; Bland, E. C.; Hartinger, M. D.; Scales, W. A.

2018-05-01

Ionospheric signatures of ultralow frequency (ULF) wave in the Pc3-5 band (1.7-40.0 mHz) were surveyed using ˜6-s resolution data from Super Dual Auroral Radar Network (SuperDARN) radars in the Northern Hemisphere from 2010 to 2016. Numerical experiments were conducted to derive wave period-dependent thresholds for automated detection of ULF waves using the Lomb-Scargle periodogram technique. The spatial occurrence distribution, frequency characteristics, seasonal effects, solar wind condition, and geomagnetic activity level dependence have been studied. Pc5 wave events were found to dominate at high and polar latitudes with a most probable frequency of 2.08 ± 0.07 mHz, while Pc3-4 waves were relatively more common at midlatitudes on the nightside with a most probable frequency of 11.39 ± 0.14 mHz. At high latitudes, the occurrence rate of Pc4-5 waves maximizes in the dusk sector and during winter. These events tend to occur during low geomagnetic activity and northward interplanetary magnetic field. For the category of radially bounded but longitudinally extended Pc4 events in the duskside ionosphere, an internal driving source is suggested. At midlatitudes, the poloidal Pc3-4 occurrence rate maximizes premidnight and during equinox. This tendency becomes more prominent with increasing auroral electrojet (AE) index and during southward interplanetary magnetic field, which suggests that many of these events are Pi2 and Pc3-4 pulsations associated with magnetotail dynamics during active geomagnetic intervals. The overall occurrence rate of Pc3-5 wave events is lowest in summer, which suggests that the ionospheric conductivity plays a role in controlling ULF wave occurrence.

Whistlers, Helicons, Lower Hybrid Waves: the Physics of RF Wave Absorption Without Cyclotron Resonances

NASA Astrophysics Data System (ADS)

Pinsker, R. I.

2014-10-01

In hot magnetized plasmas, two types of linear collisionless absorption processes are used to heat and drive noninductive current: absorption at ion or electron cyclotron resonances and their harmonics, and absorption by Landau damping and the transit-time-magnetic-pumping (TTMP) interactions. This tutorial discusses the latter process, i.e., parallel interactions between rf waves and electrons in which cyclotron resonance is not involved. Electron damping by the parallel interactions can be important in the ICRF, particularly in the higher harmonic region where competing ion cyclotron damping is weak, as well as in the Lower Hybrid Range of Frequencies (LHRF), which is in the neighborhood of the geometric mean of the ion and electron cyclotron frequencies. On the other hand, absorption by parallel processes is not significant in conventional ECRF schemes. Parallel interactions are especially important for the realization of high current drive efficiency with rf waves, and an application of particular recent interest is current drive with the whistler or helicon wave at high to very high (i.e., the LHRF) ion cyclotron harmonics. The scaling of absorption by parallel interactions with wave frequency is examined and the advantages and disadvantages of fast (helicons/whistlers) and slow (lower hybrid) waves in the LHRF in the context of reactor-grade tokamak plasmas are compared. In this frequency range, both wave modes can propagate in a significant fraction of the discharge volume; the ways in which the two waves can interact with each other are considered. The use of parallel interactions to heat and drive current in practice will be illustrated with examples from past experiments; also looking forward, this tutorial will provide an overview of potential applications in tokamak reactors. Supported by the US Department of Energy under DE-FC02-04ER54698.

High-frequency guided ultrasonic waves to monitor corrosion thickness loss

NASA Astrophysics Data System (ADS)

Fromme, Paul; Bernhard, Fabian; Masserey, Bernard

2017-02-01

Corrosion due to adverse environmental conditions can occur for a range of industrial structures, e.g., ships and offshore oil platforms. Pitting corrosion and generalized corrosion can lead to the reduction of the strength and thus degradation of the structural integrity. The nondestructive detection and monitoring of corrosion damage in difficult to access areas can be achieved using high frequency guided ultrasonic waves propagating along the structure. Using standard ultrasonic transducers with single sided access to the structure, the two fundamental Lamb wave modes were selectively generated simultaneously, penetrating through the complete thickness of the structure. The wave propagation and interference of the guided wave modes depends on the thickness of the structure. Numerical simulations were performed using a 2D Finite Difference Method (FDM) algorithm in order to visualize the guided wave propagation and energy transfer across the plate thickness. Laboratory experiments were conducted and the wall thickness reduced initially uniformly by milling of the steel structure. Further measurements were conducted using accelerated corrosion in salt water. From the measured signal change due to the wave mode interference, the wall thickness reduction was monitored and good agreement with theoretical predictions was achieved. Corrosion can lead to non-uniform thickness reduction and the influence of this on the propagation of the high frequency guided ultrasonic waves was investigated. The wave propagation in a steel specimen with varying thickness was measured experimentally and the influence on the wave propagation characteristics quantified.

Signal photon flux generated by high-frequency relic gravitational waves

NASA Astrophysics Data System (ADS)

Li, Xin; Wang, Sai; Wen, Hao

2016-08-01

The power spectrum of primordial tensor perturbations increases rapidly in the high frequency region if the spectral index n t > 0. It is shown that the amplitude of relic gravitational waves h t(5 × 109 Hz) varies from 10-36 to 10-25 while n t varies from -6.25 × 10-3 to 0.87. A high frequency gravitational wave detector proposed by F.-Y. Li detects gravitational waves through observing the perturbed photon flux that is generated by interaction between relic gravitational waves and electromagnetic field. It is shown that the perturbative photon flux (5 × 109 Hz) varies from 1.40 × 10-4 s-1 to 2.85 × 107 s-1 while n t varies from -6.25 × 10-3 to 0.87. Correspondingly, the ratio of the transverse perturbative photon flux to the background photon flux varies from 10-28 to 10-16. Supported by National Natural Science Foundation of China (11305181,11322545,11335012) and Open Project Program of State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, China (Y5KF181CJ1)

Detecting high-frequency gravitational waves with optically levitated sensors.

PubMed

Arvanitaki, Asimina; Geraci, Andrew A

2013-02-15

We propose a tunable resonant sensor to detect gravitational waves in the frequency range of 50-300 kHz using optically trapped and cooled dielectric microspheres or microdisks. The technique we describe can exceed the sensitivity of laser-based gravitational wave observatories in this frequency range, using an instrument of only a few percent of their size. Such a device extends the search volume for gravitational wave sources above 100 kHz by 1 to 3 orders of magnitude, and could detect monochromatic gravitational radiation from the annihilation of QCD axions in the cloud they form around stellar mass black holes within our galaxy due to the superradiance effect.

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

Gunawan, H.; Puspito, N. T.; Ibrahim, G.

The new approach method to determine the magnitude by using amplitude displacement relationship (A), epicenter distance ({Delta}) and duration of high frequency radiation (t) has been investigated for Tasikmalaya earthquake, on September 2, 2009, and their aftershock. Moment magnitude scale commonly used seismic surface waves with the teleseismic range of the period is greater than 200 seconds or a moment magnitude of the P wave using teleseismic seismogram data and the range of 10-60 seconds. In this research techniques have been developed a new approach to determine the displacement amplitude and duration of high frequency radiation using near earthquake. Determinationmore » of the duration of high frequency using half of period of P waves on the seismograms displacement. This is due tothe very complex rupture process in the near earthquake. Seismic data of the P wave mixing with other wave (S wave) before the duration runs out, so it is difficult to separate or determined the final of P-wave. Application of the 68 earthquakes recorded by station of CISI, Garut West Java, the following relationship is obtained: Mw = 0.78 log (A) + 0.83 log {Delta}+ 0.69 log (t) + 6.46 with: A (m), d (km) and t (second). Moment magnitude of this new approach is quite reliable, time processing faster so useful for early warning.« less

[The extraction and analysis of a- and b- wave from electroretinogram in human].

PubMed

Chen, Zi-he; Zheng, Chang-wei; Lei, Bo

2013-12-01

To determine the frequency range of a-b wave complex in the dark- and light-adapted electroretinogram (ERG) and to isolate the pure a- and b- waves. Case series study. Full-field ERGs were recorded in 16 eyes of 8 normal volunteers from October to November 2011. Digital filtering technique was used to extract the a- and b-waves from dark- and light-adapted ERG responses. The timings of a- and b-wave were measured to determine the frequency range of a-b wave complex. Major frequency components were determined from power spectra using fast Fourier transform (FFT). The effect of different order settings in the digital filter were compared to investigate the optimum condition, where the oscillatory potential (OP) was completely removed while the amplitudes and phases of the a- and b- waves were less affected. The Student-t test was used to compare the frequency range of a-b wave complex in dark- and light-adapted ERG. The averaged frequency range of the dark-adapted a-b wave complex was from (14.99 ± 2.39) to (25.35 ± 3.77) Hz, compared with (25.22 ± 6.56) to (32.47 ± 3.68) Hz for the light-adapted a-b wave complex, respectively, indicating the frequency range of the dark-adapted a-b wave complex was significantly less than the light-adapted a-b wave complex (t = 7.910, 7.693; both P < 0.01). The third order of the digital filter and a passband of 1 to 45 Hz was the best choice in term of removing the high frequency OP from the waveform of ERG and keeping the amplitude and phase of the a- and b- waves. The frequency of a-b wave complex is lower than that of OP. Therefore the a- and b- waves can be isolated from OP using different digital filter settings in human ERG. A third order and a passband of 1 to 45 Hz is the best choice to extract pure a- and b- waves from the original ERG.

The Exponent of High-frequency Source Spectral Falloff and Contribution to Source Parameter Estimates

NASA Astrophysics Data System (ADS)

Kiuchi, R.; Mori, J. J.

2015-12-01

As a way to understand the characteristics of the earthquake source, studies of source parameters (such as radiated energy and stress drop) and their scaling are important. In order to estimate source parameters reliably, often we must use appropriate source spectrum models and the omega-square model is most frequently used. In this model, the spectrum is flat in lower frequencies and the falloff is proportional to the angular frequency squared. However, Some studies (e.g. Allmann and Shearer, 2009; Yagi et al., 2012) reported that the exponent of the high frequency falloff is other than -2. Therefore, in this study we estimate the source parameters using a spectral model for which the falloff exponent is not fixed. We analyze the mainshock and larger aftershocks of the 2008 Iwate-Miyagi Nairiku earthquake. Firstly, we calculate the P wave and SH wave spectra using empirical Green functions (EGF) to remove the path effect (such as attenuation) and site effect. For the EGF event, we select a smaller earthquake that is highly-correlated with the target event. In order to obtain the stable results, we calculate the spectral ratios using a multitaper spectrum analysis (Prieto et al., 2009). Then we take a geometric mean from multiple stations. Finally, using the obtained spectra ratios, we perform a grid search to determine the high frequency falloffs, as well as corner frequency of both of events. Our results indicate the high frequency falloff exponent is often less than 2.0. We do not observe any regional, focal mechanism, or depth dependencies for the falloff exponent. In addition, our estimated corner frequencies and falloff exponents are consistent between the P wave and SH wave analysis. In our presentation, we show differences in estimated source parameters using a fixed omega-square model and a model allowing variable high-frequency falloff.

Instantaneous Frequency Analysis on Nonlinear EMIC Emissions: Arase Observation

NASA Astrophysics Data System (ADS)

Shoji, M.; Yoshizumi, M.; Omura, Y.; Kasaba, Y.; Ishisaka, K.; Matsuda, S.; Kasahara, Y.; Yagitani, S.; Matsuoka, A.; Teramoto, M.; Takashima, T.; Shinohara, I.

2017-12-01

In the inner magnetosphere, electromagnetic ion cyclotron (EMIC) waves cause nonlinear interactions with energetic protons. The waves drastically modify the proton distribution function, resulting in the particle loss in the radiation belt. Arase spacecraft, launched in late 2016, observed a nonlinear EMIC falling tone emission in the high magnetic latitude (MLAT) region of the inner magnetosphere. The wave growth with sub-packet structures of the falling tone emission is found by waveform data from PWE/EFD instrument. The evolution of the instantaneous frequency of the electric field of the EMIC falling tone emission is analyzed by Hilbert-Huang transform (HHT). We find several sub-packets with rising frequency in the falling tone wave. A self-consistent hybrid simulation suggested the complicate frequency evolution of the EMIC sub-packet emissions in the generation region. The intrinsic mode functions of Arase data derived from HHT are compared with the simulation data. The origin of the falling tone emission in the high MLAT region is also discussed.

Four-amplitude shift keying-single sideband millimeter-wave signal generation with frequency sextupling based on optical phase modulation

NASA Astrophysics Data System (ADS)

Wu, Peng; Ma, Jianxin

2017-03-01

We have proposed and demonstrated a scheme to generate a frequency-sextupling amplitude shift keying (ASK)-single sideband optical millimeter (mm)-wave signal with high dispersion tolerance based on an optical phase modulator (PM) by ably using the-4th-order and +2nd-order sidebands of the optical modulation. The ASK radio frequency signal, superposed by a local oscillator with the same frequency, modulates the lightwave via an optical PM with proper voltage amplitudes, the +2nd-order sideband carries the ASK signal with a constant slope while the -4th-order sideband maintains constant amplitude. These two sidebands can be abstracted by a wavelength selective switch to form a dual-tone optical mm-wave with only one tone carrying the ASK signal. As only one tone bears the ASK signal while the other tone is unmodulated, the generated dual-tone optical mm-wave signal has high dispersion tolerance.

Direct ambient noise tomography for 3-D near surface shear velocity structure: methodology and applications

NASA Astrophysics Data System (ADS)

Yao, H.; Fang, H.; Li, C.; Liu, Y.; Zhang, H.; van der Hilst, R. D.; Huang, Y. C.

2014-12-01

Ambient noise tomography has provided essential constraints on crustal and uppermost mantle shear velocity structure in global seismology. Recent studies demonstrate that high frequency (e.g., ~ 1 Hz) surface waves between receivers at short distances can be successfully retrieved from ambient noise cross-correlation and then be used for imaging near surface or shallow crustal shear velocity structures. This approach provides important information for strong ground motion prediction in seismically active area and overburden structure characterization in oil and gas fields. Here we propose a new tomographic method to invert all surface wave dispersion data for 3-D variations of shear wavespeed without the intermediate step of phase or group velocity maps.The method uses frequency-dependent propagation paths and a wavelet-based sparsity-constrained tomographic inversion. A fast marching method is used to compute, at each period, surface wave traveltimes and ray paths between sources and receivers. This avoids the assumption of great-circle propagation that is used in most surface wave tomographic studies, but which is not appropriate in complex media. The wavelet coefficients of the velocity model are estimated with an iteratively reweighted least squares (IRLS) algorithm, and upon iterations the surface wave ray paths and the data sensitivity matrix are updated from the newly obtained velocity model. We apply this new method to determine the 3-D near surface wavespeed variations in the Taipei basin of Taiwan, Hefei urban area and a shale and gas production field in China using the high-frequency interstation Rayleigh wave dispersion data extracted from ambient noisecross-correlation. The results reveal strong effects of off-great-circle propagation of high-frequency surface waves in these regions with above 30% shear wavespeed variations. The proposed approach is more efficient and robust than the traditional two-step surface wave tomography for imaging complex structures. In the future, approximate 3-D sensitivity kernels for dispersion data will be incorporated to account for finite-frequency effect of surface wave propagation. In addition, our approach provides a consistent framework for joint inversion of surface wave dispersion and body wave traveltime data for 3-D Vp and Vs structures.

Quantum-limited detection of millimeter waves using superconducting tunnel junctions

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

Mears, Carl Atherton

1991-09-01

The quasiparticle tunneling current in a superconductor-insulator- superconductor (SIS) tunnel junction is highly nonlinear. Such a nonlinearity can be used to mix two millimeter wave signals to produce a signal at a much lower intermediate frequency. We have constructed several millimeter and sub-millimeter wave SIS mixers in order to study high frequency response of the quasiparticle tunneling current and the physics of high frequency mixing. We have made the first measurement of the out-of-phase tunneling currents in an SIS tunnel junction. We have developed a method that allows us to determine the parameters of the high frequency embedding circuit bymore » studying the details of the pumped I-V curve. We have constructed a 80--110 GHz waveguide-based mixer test apparatus that allows us to accurately measure the gain and added noise of the SIS mixer under test. Using extremely high quality tunnel junctions, we have measured an added mixer noise of 0.61 ± 0.36 quanta, which is within 25 percent of the quantum limit imposed by the Heisenberg uncertainty principle. This measured performance is in excellent agreement with that predicted by Tucker`s theory of quantum mixing. We have also studied quasioptically coupled millimeter- and submillimeter-wave mixers using several types of integrated tuning elements. 83 refs.« less

Quantum-limited detection of millimeter waves using superconducting tunnel junctions

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

Mears, C.A.

1991-09-01

The quasiparticle tunneling current in a superconductor-insulator- superconductor (SIS) tunnel junction is highly nonlinear. Such a nonlinearity can be used to mix two millimeter wave signals to produce a signal at a much lower intermediate frequency. We have constructed several millimeter and sub-millimeter wave SIS mixers in order to study high frequency response of the quasiparticle tunneling current and the physics of high frequency mixing. We have made the first measurement of the out-of-phase tunneling currents in an SIS tunnel junction. We have developed a method that allows us to determine the parameters of the high frequency embedding circuit bymore » studying the details of the pumped I-V curve. We have constructed a 80--110 GHz waveguide-based mixer test apparatus that allows us to accurately measure the gain and added noise of the SIS mixer under test. Using extremely high quality tunnel junctions, we have measured an added mixer noise of 0.61 {plus minus} 0.36 quanta, which is within 25 percent of the quantum limit imposed by the Heisenberg uncertainty principle. This measured performance is in excellent agreement with that predicted by Tucker's theory of quantum mixing. We have also studied quasioptically coupled millimeter- and submillimeter-wave mixers using several types of integrated tuning elements. 83 refs.« less

Nonlinear extraordinary wave in dense plasma

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

Krasovitskiy, V. B., E-mail: krasovit@mail.ru; Turikov, V. A.

2013-10-15

Conditions for the propagation of a slow extraordinary wave in dense magnetized plasma are found. A solution to the set of relativistic hydrodynamic equations and Maxwell’s equations under the plasma resonance conditions, when the phase velocity of the nonlinear wave is equal to the speed of light, is obtained. The deviation of the wave frequency from the resonance frequency is accompanied by nonlinear longitudinal-transverse oscillations. It is shown that, in this case, the solution to the set of self-consistent equations obtained by averaging the initial equations over the period of high-frequency oscillations has the form of an envelope soliton. Themore » possibility of excitation of a nonlinear wave in plasma by an external electromagnetic pulse is confirmed by numerical simulations.« less

High-frequency waves following PKP-C sub diff at distances greater than 155 degree

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

Nakanishi, Ichiro

Using a seismic network in Hokkaido-Tohoku region, Japan the author observes PKP waves in the distance range 152 to 157{degree} from a deep earthquake in Argentina. The seismic network consists of 26 stations and provides a data set of dense distance sampling. The examination of amplitude variation of PKP-BC and PKP-C{sub diff} with distance locates the C-cusp at about 155.5{degree} for a surface source for the path from Argentina to Japan. This C-cusp position suggests a P velocity of 10.27 km/s at the bottom of the outer core. The bandpass filtering of the data shows that high-frequency waves are observedmore » following PKP-C{sub diff} at distances beyond the C-cusp. The waves are characterized by a dominant frequency of about 29 to 3 Hz, a long duration of oscillation until the arrival of PKP-AB, and an apparent onset slowness of about 4 s/deg, which is approximately equal to that of PKP-AB in the distance range. The onset time of the high-frequency waves seems to be consistent with the least time of the scattering of PKP-BC on the receiver side near the bottom of the upper mantle.« less

Wideband and high-gain frequency stabilization of a 100-W injection-locked Nd:YAG laser for second-generation gravitational wave detectors.

PubMed

Ohmae, Noriaki; Moriwaki, Shigenori; Mio, Norikatsu

2010-07-01

Second-generation gravitational wave detectors require a highly stable laser with an output power greater than 100 W to attain their target sensitivity. We have developed a frequency stabilization system for a 100-W injection-locked Nd:YAG (yttrium aluminum garnet) laser. By placing an external wideband electro-optic modulator used as a fast-frequency actuator in the optical path of the slave output, we can circumvent a phase delay in the frequency control loop originating from the pole of an injection-locked slave cavity. Thus, we have developed an electro-optic modulator made of a MgO-doped stoichiometric LiNbO(3) crystal. Using this modulator, we achieve a frequency control bandwidth of 800 kHz and a control gain of 180 dB at 1 kHz. These values satisfy the requirement for a laser frequency control loop in second-generation gravitational wave detectors.

Demonstration of a Sub-Millimeter Wave Integrated Circuit (S-MMIC) using InP HEMT with a 35-nm Gate

NASA Technical Reports Server (NTRS)

Deal, W. R.; Din, S.; Padilla, J.; Radisic, V.; Mei, G.; Yoshida, W.; Liu, P. S.; Uyeda, J.; Barsky, M.; Gaier, T.;

Spectral modification of seismic waves propagating through solids exhibiting a resonance frequency: a 1-D coupled wave propagation-oscillation model

NASA Astrophysics Data System (ADS)

Frehner, Marcel; Schmalholz, Stefan M.; Podladchikov, Yuri

2009-02-01

A 1-D model is presented that couples the microscale oscillations of non-wetting fluid blobs in a partially saturated poroelastic medium with the macroscale wave propagation through the elastic skeleton. The fluid oscillations are caused by surface tension forces that act as the restoring forces driving the oscillations. The oscillations are described mathematically with the equation for a linear oscillator and the wave propagation is described with the 1-D elastic wave equation. Coupling is done using Hamilton's variational principle for continuous systems. The resulting linear system of two partial differential equations is solved numerically with explicit finite differences. Numerical simulations are used to analyse the effect of solids exhibiting internal oscillations, and consequently a resonance frequency, on seismic waves propagating through such media. The phase velocity dispersion relation shows a higher phase velocity in the high-frequency limit and a lower phase velocity in the low-frequency limit. At the resonance frequency a singularity in the dispersion relation occurs. Seismic waves can initiate oscillations of the fluid by transferring energy from solid to fluid at the resonance frequency. Due to this transfer, the spectral amplitude of the solid particle velocity decreases at the resonance frequency. After initiation, the oscillatory movement of the fluid continuously transfers energy at the resonance frequency back to the solid. Therefore, the spectral amplitude of the solid particle velocity is increased at the resonance frequency. Once initiated, fluid oscillations decrease in amplitude with increasing time. Consequently, the spectral peak of the solid particle velocity at the resonance frequency decreases with time.

Holographic leaky-wave metasurfaces for dual-sensor imaging.

PubMed

Li, Yun Bo; Li, Lian Lin; Cai, Ben Geng; Cheng, Qiang; Cui, Tie Jun

2015-12-10

Metasurfaces have huge potentials to develop new type imaging systems due to their abilities of controlling electromagnetic waves. Here, we propose a new method for dual-sensor imaging based on cross-like holographic leaky-wave metasurfaces which are composed of hybrid isotropic and anisotropic surface impedance textures. The holographic leaky-wave radiations are generated by special impedance modulations of surface waves excited by the sensor ports. For one independent sensor, the main leaky-wave radiation beam can be scanned by frequency in one-dimensional space, while the frequency scanning in the orthogonal spatial dimension is accomplished by the other sensor. Thus, for a probed object, the imaging plane can be illuminated adequately to obtain the two-dimensional backward scattered fields by the dual-sensor for reconstructing the object. The relativity of beams under different frequencies is very low due to the frequency-scanning beam performance rather than the random beam radiations operated by frequency, and the multi-illuminations with low relativity are very appropriate for multi-mode imaging method with high resolution and anti- noise. Good reconstruction results are given to validate the proposed imaging method.

Proofs for the Wave Theory of Plants

NASA Astrophysics Data System (ADS)

Wagner, Orvin E.

1997-03-01

Oscillatory behavior in plants. (2)Standing waves observed coming from probes equally spaced up tree trunks and freshly cut live wood samples. (3)Beat frequencies observed while applying AC voltages to plants. (4)Plant length quantization. (5)Plant growth angle and voltage quantization with respect to the gravitational field. (6)The measurement of plant frequences with a low frequency spectrum analyzer which correlate with the frequencies observed by other means such as by measuring plant lengths, considered as half wavelengths, and beat frequencies. (7)Voltages obtained from insulated, isolated from light, diode dies placed in slits in tree trunks. Diodes become relatively low impedance sources for voltages as high as eight volts. Diodes indicate charge separating longitudinal standing waves sweeping up and down a tree trunk. Longitudinal waves also indicated by plant structure. (8)The measured discrete wave velocities appear to be dependent on their direction of travel with respect to the gravitational field. These provide growth references for the plant and a wave guide affect. For references see Wagner Research Laboratory Web Page.

Explosion source strong ground motions in the Mississippi embayment

USGS Publications Warehouse

Langston, C.A.; Bodin, P.; Powell, C.; Withers, M.; Horton, S.; Mooney, W.

2006-01-01

Two strong-motion arrays were deployed for the October 2002 Embayment Seismic Excitation Experiment to study the spatial variation of strong ground motions in the deep, unconsolidated sediments of the Mississippi embayment because there are no comparable strong-motion data from natural earthquakes in the area. Each linear array consisted of eight three-component K2 accelerographs spaced 15 m apart situated 1.2 and 2.5 kin from 2268-kg and 1134-kg borehole explosion sources, respectively. The array data show distinct body-wave and surface-wave arrivals that propagate within the thick, unconsolidated sedimentary column, the high-velocity basement rocks, and small-scale structure near the surface. Time-domain coherence of body-wave and surface-wave arrivals is computed for acceleration, velocity, and displacement time windows. Coherence is high for relatively low-frequency verticalcomponent Rayleigh waves and high-frequency P waves propagating across the array. Prominent high-frequency PS conversions seen on radial components, a proxy for the direct S wave from earthquake sources, lose coherence quickly over the 105-m length of the array. Transverse component signals are least coherent for any ground motion and appear to be highly scattered. Horizontal phase velocity is computed by using the ratio of particle velocity to estimates of the strain based on a plane-wave-propagation model. The resulting time-dependent phase-velocity map is a useful way to infer the propagation mechanisms of individual seismic phases and time windows of three-component waveforms. Displacement gradient analysis is a complementary technique for processing general spatial-array data to obtain horizontal slowness information.

Effects of Second-Order Sum- and Difference-Frequency Wave Forces on the Motion Response of a Tension-Leg Platform Considering the Set-down Motion

NASA Astrophysics Data System (ADS)

Wang, Bin; Tang, Yougang; Li, Yan; Cai, Runbo

2018-04-01

This paper presents a study on the motion response of a tension-leg platform (TLP) under first- and second-order wave forces, including the mean-drift force, difference and sum-frequency forces. The second-order wave force is calculated using the full-field quadratic transfer function (QTF). The coupled effect of the horizontal motions, such as surge, sway and yaw motions, and the set-down motion are taken into consideration by the nonlinear restoring matrix. The time-domain analysis with 50-yr random sea state is performed. A comparison of the results of different case studies is made to assess the influence of second-order wave force on the motions of the platform. The analysis shows that the second-order wave force has a major impact on motions of the TLP. The second-order difference-frequency wave force has an obvious influence on the low-frequency motions of surge and sway, and also will induce a large set-down motion which is an important part of heave motion. Besides, the second-order sum-frequency force will induce a set of high-frequency motions of roll and pitch. However, little influence of second-order wave force is found on the yaw motion.

Mode perturbation method for optimal guided wave mode and frequency selection.

PubMed

Philtron, J H; Rose, J L

2014-09-01

With a thorough understanding of guided wave mechanics, researchers can predict which guided wave modes will have a high probability of success in a particular nondestructive evaluation application. However, work continues to find optimal mode and frequency selection for a given application. This "optimal" mode could give the highest sensitivity to defects or the greatest penetration power, increasing inspection efficiency. Since material properties used for modeling work may be estimates, in many cases guided wave mode and frequency selection can be adjusted for increased inspection efficiency in the field. In this paper, a novel mode and frequency perturbation method is described and used to identify optimal mode points based on quantifiable wave characteristics. The technique uses an ultrasonic phased array comb transducer to sweep in phase velocity and frequency space. It is demonstrated using guided interface waves for bond evaluation. After searching nearby mode points, an optimal mode and frequency can be selected which has the highest sensitivity to a defect, or gives the greatest penetration power. The optimal mode choice for a given application depends on the requirements of the inspection. Copyright © 2014 Elsevier B.V. All rights reserved.

Scattering of waves by impurities in precompressed granular chains.

PubMed

Martínez, Alejandro J; Yasuda, Hiromi; Kim, Eunho; Kevrekidis, P G; Porter, Mason A; Yang, Jinkyu

2016-05-01

We study scattering of waves by impurities in strongly precompressed granular chains. We explore the linear scattering of plane waves and identify a closed-form expression for the reflection and transmission coefficients for the scattering of the waves from both a single impurity and a double impurity. For single-impurity chains, we show that, within the transmission band of the host granular chain, high-frequency waves are strongly attenuated (such that the transmission coefficient vanishes as the wavenumber k→±π), whereas low-frequency waves are well-transmitted through the impurity. For double-impurity chains, we identify a resonance-enabling full transmission at a particular frequency-in a manner that is analogous to the Ramsauer-Townsend (RT) resonance from quantum physics. We also demonstrate that one can tune the frequency of the RT resonance to any value in the pass band of the host chain. We corroborate our theoretical predictions both numerically and experimentally, and we directly observe almost complete transmission for frequencies close to the RT resonance frequency. Finally, we show how this RT resonance can lead to the existence of reflectionless modes in granular chains (including disordered ones) with multiple double impurities.

High-frequency Lamb wave device composed of MEMS structure using LiNbO3 thin film and air gap.

PubMed

Kadota, Michio; Ogami, Takashi; Yamamoto, Kansho; Tochishita, Hikari; Negoro, Yasuhiro

2010-11-01

High-frequency devices operating at 3 GHz or higher are required, for instance, for future 4th generation mobile phone systems in Japan. Using a substrate with a high acoustic velocity is one method to realize a high-frequency acoustic or elastic device. A Lamb wave has a high velocity when the substrate thickness is thin. To realize a high-frequency device operating at 3 GHz or higher using a Lamb wave, a very thin (less than 0.5 μm thick) single-crystal plate must be used. It is difficult to fabricate such a very thin single crystal plate. The authors have attempted to use a c-axis orientated epitaxial LiNbO(3) thin film deposited by a chemical vapor deposition system (CVD) instead of using a thin LiNbO(3) single crystal plate. Lamb wave resonators composed of a interdigital transducer (IDT)/the LiNbO(3) film/air gap/base substrate structure like micro-electromechanical system (MEMS) transducers were fabricated. These resonators have shown a high frequency of 4.5 and 6.3 GHz, which correspond to very high acoustic velocities of 14,000 and 12,500 m/s, respectively, have excellent characteristics such as a ratio of resonant and antiresonant impedance of 52 and 38 dB and a wide band of 7.2% and 3.7%, respectively, and do not have spurious responses caused by the 0th modes of shear horizontal (SH(0)) and symmetric (S(0)) modes.

Resonant scattering of energetic electrons in the outer radiation belt by HAARP-induced ELF/VLF waves

NASA Astrophysics Data System (ADS)

Chang, Shanshan; Zhu, Zhengping; Ni, Binbin; Cao, Xing; Luo, Weihua

2016-10-01

Several extremely low-frequency (ELF)/very low-frequency (VLF) wave generation experiments have been performed successfully at High-Frequency Active Auroral Research Program (HAARP) heating facility and the artificial ELF/VLF signals can leak into the outer radiation belt and contribute to resonant interactions with energetic electrons. Based on the artificial wave properties revealed by many of in situ observations, we implement test particle simulations to evaluate the effects of energetic electron resonant scattering driven by the HAARP-induced ELF/VLF waves. The results indicate that for both single-frequency/monotonic wave and multi-frequency/broadband waves, the behavior of each electron is stochastic while the averaged diffusion effect exhibits temporal linearity in the wave-particle interaction process. The computed local diffusion coefficients show that, the local pitch-angle scattering due to HARRP-induced single-frequency ELF/VLF whistlers with an amplitude of ∼10 pT can be intense near the loss cone with a rate of ∼10-2 rad2 s-1, suggesting the feasibility of HAARP-induced ELF/VLF waves for removal of outer radiation belt energetic electrons. In contrast, the energy diffusion of energetic electrons is relatively weak, which confirms that pitch-angle scattering by artificial ELF/VLF waves can dominantly lead to the precipitation of energetic electrons. Moreover, diffusion rates of the discrete, broadband waves, with the same amplitude of each discrete frequency as the monotonic waves, can be much larger, which suggests that it is feasible to trigger a reasonable broadband wave instead of the monotonic wave to achieve better performance of controlled precipitation of energetic electrons. Moreover, our test particle scattering simulation show good agreement with the predictions of the quasi-linear theory, confirming that both methods are applied to evaluate the effects of resonant interactions between radiation belt electrons and artificially generated discrete ELF/VLF waves.

Antenna design for propagating spin wave spectroscopy in ferromagnetic thin films

NASA Astrophysics Data System (ADS)

Zhang, Yan; Yu, Ting; Chen, Ji-lei; Zhang, You-guang; Feng, Jian; Tu, Sa; Yu, Haiming

2018-03-01

In this paper, we investigate the characteristics of antenna for propagating-spin-wave-spectroscopy (PSWS) experiment in ferromagnetic thin films. Firstly, we simulate the amplitude and phase distribution of the high-frequency magnetic field around antenna by high frequency structure simulator (HFSS). And then k distribution of the antenna is obtained by fast Fourier transformation (FFT). Furthermore, three kinds of antenna designs, i.e. micro-strip line, coplanar waveguide (CPW), loop, are studied and compared. How the dimension parameter of antenna influence the corresponding high-frequency magnetic field amplitude and k distribution are investigated in details.

Wave-induced fluid flow in random porous media: Attenuation and dispersion of elastic waves

NASA Astrophysics Data System (ADS)

Müller, Tobias M.; Gurevich, Boris

2005-05-01

A detailed analysis of the relationship between elastic waves in inhomogeneous, porous media and the effect of wave-induced fluid flow is presented. Based on the results of the poroelastic first-order statistical smoothing approximation applied to Biot's equations of poroelasticity, a model for elastic wave attenuation and dispersion due to wave-induced fluid flow in 3-D randomly inhomogeneous poroelastic media is developed. Attenuation and dispersion depend on linear combinations of the spatial correlations of the fluctuating poroelastic parameters. The observed frequency dependence is typical for a relaxation phenomenon. Further, the analytic properties of attenuation and dispersion are analyzed. It is shown that the low-frequency asymptote of the attenuation coefficient of a plane compressional wave is proportional to the square of frequency. At high frequencies the attenuation coefficient becomes proportional to the square root of frequency. A comparison with the 1-D theory shows that attenuation is of the same order but slightly larger in 3-D random media. Several modeling choices of the approach including the effect of cross correlations between fluid and solid phase properties are demonstrated. The potential application of the results to real porous materials is discussed. .

Forecasting and Hindcasting Waves In and Near the Marginal Ice Zone: Wave Modeling and the ONR Sea State Field Experiment

DTIC Science & Technology

2018-04-12

non-directional) wave spectra, but we consider the energy at high frequencies to be unreliable, so we only use significant waveheight Hs and dominant...spectral density, N=E/s), which is a function of wavenumber or frequency (k or s), direction (θ), space (x,y), and time (t), with spectral density...Elgar 1987). As the spectra are now co-located in time, space , and frequency , the inversion is simply a minimization process for |logVR(6jvH>w(9

Traveling-Wave Membrane Photomixers

NASA Technical Reports Server (NTRS)

Wyss, R. A.; Martin, S. C.; Nakamura, B. J.; Neto, A.; Pasqualini, D.; Siegel, P. H.; Kadow, C.; Gossard, A. C.

2001-01-01

Traveling-wave photomixers have superior performance when compared with lumped area photomixers in the 1 to 3 THz frequency range. Their large active area and distributed gain mechanism assure high thermal damage threshold and elimination of the capacitive frequency roll-off. However, the losses experienced by the radio frequency wave traveling along the coplanar strips waveguide (due to underlying semi-infinite GaAs substrate) were a serious drawback. In this paper we present device designs and an experimental setup that make possible the realization of photomixers on membranes which eliminate the losses.

Wave activity in the neighborhood of the bowshock of Mars

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

Sagdeev, R.Z.; Shapiro, V.D.; Shevchenko, V.I.

Plasma wave activity in the neighborhood of the Martial bow shock were measured for the first time by the Soviet spacecraft Phobos-2 in a wide frequency range from dc to 150 kHz. The wave activity varied in character as the spacecraft moved across different plasma regions: in the neighborhood of the Martian bow shock, inside the magnetosheath and in the tail region. In this paper the authors provide suggestions for the processes responsible for these plasma waves. The most interesting peculiarities of the wave activity around Mars is the sharp increase of wave intensity in the magnetosheath region. This increasemore » is attributed to two different physical mechanisms. High frequency waves are excited at the shock front due to currents flowing along the front; these ion acoustic waves are convected inside by the solar wind. The low frequency waves ({approximately}100 Hz) close to the inside boundary were, they believe, generated by heavy Martian ions diffusing through the planetopause into the magnetosheath.« less

The 2011 Tohoku Tsunami on the Coast of Mexico: A Case Study

NASA Astrophysics Data System (ADS)

Zaytsev, Oleg; Rabinovich, Alexander B.; Thomson, Richard E.

2017-08-01

The Tohoku (East Japan) earthquake of 11 March 2011 ( M w 9.0) generated a great trans-oceanic tsunami that spread throughout the Pacific Ocean, where it was measured by numerous coastal tide gauges and open-ocean DART (Deep-ocean Assessment and Reporting of Tsunamis) stations. Statistical and spectral analyses of the tsunami waves recorded along the Pacific coast of Mexico have enabled us to estimate the principal parameters of the waves along the coast and to compare statistical features of the tsunami with other tsunamis recorded on this coast. We identify coastal "hot spots"—Manzanillo, Zihuatanejo, Acapulco, and Ensenada—corresponding to sites having highest tsunami hazard potential, where wave heights during the 2011 event exceeded 1.5-2 m and tsunami-induced currents were strong enough to close port operations. Based on a joint spectral analysis of the tsunamis and background noise, we reconstructed the spectra of tsunami waves in the deep ocean and found that, with the exception of the high-frequency spectral band (>5 cph), the spectra are in close agreement with the "true" tsunami spectra determined from DART bottom pressure records. The departure of the high-frequency spectra in the coastal region from the deep-sea spectra is shown to be related to background infragravity waves generated in the coastal zone. The total energy and frequency content of the Tohoku tsunami is compared with the corresponding results for the 2010 Chilean tsunami. Our findings show that the integral open-ocean tsunami energy, I 0, was 2.30 cm2, or approximately 1.7 times larger than for the 2010 event. Comparison of this parameter with the mean coastal tsunami variance (451 cm2) indicates that tsunami waves propagating onshore from the open ocean amplified by 14 times; the same was observed for the 2010 tsunami. The "tsunami colour" (frequency content) for the 2011 Tohoku tsunami was "red", with about 65% of the total energy associated with low-frequency waves at frequencies <1.7 cph (periods >35 min). The "red colour" (i.e., the prevalence of low-frequency waves) in the 2011 Tohoku, as well as in the 2010 Chile tsunamis, is explained by the large extension of the source areas. In contrast, the 2014 and 2015 Chilean earthquakes had much smaller source areas and, consequently, induced "bluish" (high-frequency) tsunamis.

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.

Longitudinal spread of mechanical excitation through tectorial membrane traveling waves

PubMed Central

Sellon, Jonathan B.; Farrahi, Shirin; Ghaffari, Roozbeh; Freeman, Dennis M.

2015-01-01

The mammalian inner ear separates sounds by their frequency content, and this separation underlies important properties of human hearing, including our ability to understand speech in noisy environments. Studies of genetic disorders of hearing have demonstrated a link between frequency selectivity and wave properties of the tectorial membrane (TM). To understand these wave properties better, we developed chemical manipulations that systematically and reversibly alter TM stiffness and viscosity. Using microfabricated shear probes, we show that (i) reducing pH reduces TM stiffness with little change in TM viscosity and (ii) adding PEG increases TM viscosity with little change in TM stiffness. By applying these manipulations in measurements of TM waves, we show that TM wave speed is determined primarily by stiffness at low frequencies and by viscosity at high frequencies. Both TM viscosity and stiffness affect the longitudinal spread of mechanical excitation through the TM over a broad range of frequencies. Increasing TM viscosity or decreasing stiffness reduces longitudinal spread of mechanical excitation, thereby coupling a smaller range of best frequencies and sharpening tuning. In contrast, increasing viscous loss or decreasing stiffness would tend to broaden tuning in resonance-based TM models. Thus, TM wave and resonance mechanisms are fundamentally different in the way they control frequency selectivity. PMID:26438861

Filterless frequency 12-tupling optical millimeter-wave generation using two cascaded dual-parallel Mach-Zehnder modulators.

PubMed

Zhu, Zihang; Zhao, Shanghong; Zheng, Wanze; Wang, Wei; Lin, Baoqin

2015-11-10

A novel frequency 12-tupling optical millimeter-wave (mm-wave) generation using two cascaded dual-parallel Mach-Zehnder modulators (DP-MZMs) without an optical filter is proposed and demonstrated by computer simulation. By properly adjusting the amplitude and phase of radio frequency (RF) driving signal and the direct current (DC) bias points of two DP-MZMs, a 120 GHz mm-wave with an optical sideband suppression ratio (OSSR) of 25.1 dB and a radio frequency spurious suppression ratio (RFSSR) of 19.1 dB is shown to be generated from a 10 GHz RF driving signal, which largely reduces the response frequency of electronic devices. Furthermore, it is also proved to be valid that even if the phase difference of RF driving signals, the RF driving voltage, and the DC bias voltage deviate from the ideal values to a certain degree, the performance is still acceptable. Since no optical filter is employed to suppress the undesired optical sidebands, a high-spectral-purity mm-wave signal tunable from 48 to 216 GHz can be obtained theoretically when a RF driving signal from 4 to 18 GHz is applied to the DP-MZMs, and the system can be readily implemented in wavelength-division-multiplexing upconversion systems to provide high-quality optical local oscillator signal.

Radial localization of magnetospheric guided poloidal Pc 4-5 waves

NASA Astrophysics Data System (ADS)

Denton, R. E.; Lessard, M. R.; Kistler, L. M.

2003-03-01

The toroidal Alfvén wave, with magnetic field oscillations in the azimuthal direction, exhibits a singularity in the vicinity of the toroidal resonant frequency (field line resonance), so it is not surprising that this wave often exhibits varying frequency as a function of L shell. It is less clear why the poloidal Alfvén wave, with magnetic field oscillations in the radial direction, often exhibits a relatively constant frequency over a range of L shells. So far, the most promising proposal to explain this phenomenon is the theory of [1994, 1996], who showed that an energetically trapped global poloidal mode can exist in a region where the poloidal Alfvén frequency is lower than the toroidal frequency and where it exhibits a dip (minimum) with respect to L. While this theory is mathematically plausible, it has never been shown that poloidal Alfvén waves actually occur in association with such a dip in poloidal frequency. Here we examine poloidal wave events observed by the AMPTE/IRM spacecraft and calculate the theoretical poloidal frequency as a function of L using the equilibrium parameters obtained from the spacecraft observations. We find that the poloidal Alfvén wave does occur in association with such a dip (or at least a flattening) in poloidal frequency. While Vetoulis and Chen hypothesized that such a dip would occur because of a sharp gradient in plasma pressure, we find that the dip in poloidal frequency may result from the L dependence of the equilibrium density or magnetic field. The observed frequencies are in rough agreement with the theoretical frequencies, though in some cases we must assume that the observed oscillations result from a high harmonic (third or fourth harmonic structure along the magnetic field). We also apply the same analysis to compressional wave events (with oscillations in the direction of the equilibrium magnetic field). Such oscillations may be on the poloidal wave branch or the mirror mode branch. Here also, the observed fluctuations occur in the region of a dip in poloidal frequency. In one case the observed frequency is consistent with the theoretical poloidal frequency, whereas in another case it is not.

Towards 5G: A Photonic Based Millimeter Wave Signal Generation for Applying in 5G Access Fronthaul.

PubMed

Alavi, S E; Soltanian, M R K; Amiri, I S; Khalily, M; Supa'at, A S M; Ahmad, H

2016-01-27

5G communications require a multi Gb/s data transmission in its small cells. For this purpose millimeter wave (mm-wave) RF signals are the best solutions to be utilized for high speed data transmission. Generation of these high frequency RF signals is challenging in electrical domain therefore photonic generation of these signals is more studied. In this work, a photonic based simple and robust method for generating millimeter waves applicable in 5G access fronthaul is presented. Besides generating of the mm-wave signal in the 60 GHz frequency band the radio over fiber (RoF) system for transmission of orthogonal frequency division multiplexing (OFDM) with 5 GHz bandwidth is presented. For the purpose of wireless transmission for 5G application the required antenna is designed and developed. The total system performance in one small cell was studied and the error vector magnitude (EVM) of the system was evaluated.

Towards 5G: A Photonic Based Millimeter Wave Signal Generation for Applying in 5G Access Fronthaul

PubMed Central

Alavi, S. E.; Soltanian, M. R. K.; Amiri, I. S.; Khalily, M.; Supa’at, A. S. M.; Ahmad, H.

2016-01-01

5G communications require a multi Gb/s data transmission in its small cells. For this purpose millimeter wave (mm-wave) RF signals are the best solutions to be utilized for high speed data transmission. Generation of these high frequency RF signals is challenging in electrical domain therefore photonic generation of these signals is more studied. In this work, a photonic based simple and robust method for generating millimeter waves applicable in 5G access fronthaul is presented. Besides generating of the mm-wave signal in the 60 GHz frequency band the radio over fiber (RoF) system for transmission of orthogonal frequency division multiplexing (OFDM) with 5 GHz bandwidth is presented. For the purpose of wireless transmission for 5G application the required antenna is designed and developed. The total system performance in one small cell was studied and the error vector magnitude (EVM) of the system was evaluated. PMID:26814621

Towards 5G: A Photonic Based Millimeter Wave Signal Generation for Applying in 5G Access Fronthaul

NASA Astrophysics Data System (ADS)

Alavi, S. E.; Soltanian, M. R. K.; Amiri, I. S.; Khalily, M.; Supa'At, A. S. M.; Ahmad, H.

2016-01-01

5G communications require a multi Gb/s data transmission in its small cells. For this purpose millimeter wave (mm-wave) RF signals are the best solutions to be utilized for high speed data transmission. Generation of these high frequency RF signals is challenging in electrical domain therefore photonic generation of these signals is more studied. In this work, a photonic based simple and robust method for generating millimeter waves applicable in 5G access fronthaul is presented. Besides generating of the mm-wave signal in the 60 GHz frequency band the radio over fiber (RoF) system for transmission of orthogonal frequency division multiplexing (OFDM) with 5 GHz bandwidth is presented. For the purpose of wireless transmission for 5G application the required antenna is designed and developed. The total system performance in one small cell was studied and the error vector magnitude (EVM) of the system was evaluated.

Room temperature continuous wave, monolithic tunable THz sources based on highly efficient mid-infrared quantum cascade lasers

PubMed Central

Lu, Quanyong; Wu, Donghai; Sengupta, Saumya; Slivken, Steven; Razeghi, Manijeh

2016-01-01

A compact, high power, room temperature continuous wave terahertz source emitting in a wide frequency range (ν ~ 1–5 THz) is of great importance to terahertz system development for applications in spectroscopy, communication, sensing, and imaging. Here, we present a strong-coupled strain-balanced quantum cascade laser design for efficient THz generation based on intracavity difference frequency generation. Room temperature continuous wave emission at 3.41 THz with a side-mode suppression ratio of 30 dB and output power up to 14 μW is achieved with a wall-plug efficiency about one order of magnitude higher than previous demonstrations. With this highly efficient design, continuous wave, single mode THz emissions with a wide frequency tuning range of 2.06–4.35 THz and an output power up to 4.2 μW are demonstrated at room temperature from two monolithic three-section sampled grating distributed feedback-distributed Bragg reflector lasers. PMID:27009375

Room temperature continuous wave, monolithic tunable THz sources based on highly efficient mid-infrared quantum cascade lasers.

PubMed

Lu, Quanyong; Wu, Donghai; Sengupta, Saumya; Slivken, Steven; Razeghi, Manijeh

2016-03-24

A compact, high power, room temperature continuous wave terahertz source emitting in a wide frequency range (ν~1-5 THz) is of great importance to terahertz system development for applications in spectroscopy, communication, sensing, and imaging. Here, we present a strong-coupled strain-balanced quantum cascade laser design for efficient THz generation based on intracavity difference frequency generation. Room temperature continuous wave emission at 3.41 THz with a side-mode suppression ratio of 30 dB and output power up to 14 μW is achieved with a wall-plug efficiency about one order of magnitude higher than previous demonstrations. With this highly efficient design, continuous wave, single mode THz emissions with a wide frequency tuning range of 2.06-4.35 THz and an output power up to 4.2 μW are demonstrated at room temperature from two monolithic three-section sampled grating distributed feedback-distributed Bragg reflector lasers.

Generation of Z mode radiation by diffuse auroral electron precipitation

NASA Astrophysics Data System (ADS)

Dusenbery, P. B.; Lyons, L. R.

1985-03-01

The generation of Z mode waves by diffuse auroral electron precipitation is investigated assuming that a loss cone exists in the upgoing portion of the distribution due to electron interactions with the atmosphere. The waves are generated at frequencies above, but very near, the local electron cyclotron frequency omega(e) and at wave normal angles larger than 90 deg. In agreement with Hewitt et al. (1983), the group velocity is directed downward in regions where the ratio of the upper hybrid frequency omega(pe) to Omega(e) is less than 0.5, so that Z mode waves excited above a satellite propagate toward it and away from the upper hybrid resonance. Z mode waves are excited in a frequency band between Omega(e) and about 1.02 Omega(e), and with maximum growth rates of about 0.001 Omega(e). The amplification length is about 100 km, which allows Z mode waves to grow to the intensities observed by high-altitude satellites.

Generation of Z mode radiation by diffuse auroral electron precipitation

NASA Technical Reports Server (NTRS)

Dusenbery, P. B.; Lyons, L. R.

1985-01-01

The generation of Z mode waves by diffuse auroral electron precipitation is investigated assuming that a loss cone exists in the upgoing portion of the distribution due to electron interactions with the atmosphere. The waves are generated at frequencies above, but very near, the local electron cyclotron frequency omega(e) and at wave normal angles larger than 90 deg. In agreement with Hewitt et al. (1983), the group velocity is directed downward in regions where the ratio of the upper hybrid frequency omega(pe) to Omega(e) is less than 0.5, so that Z mode waves excited above a satellite propagate toward it and away from the upper hybrid resonance. Z mode waves are excited in a frequency band between Omega(e) and about 1.02 Omega(e), and with maximum growth rates of about 0.001 Omega(e). The amplification length is about 100 km, which allows Z mode waves to grow to the intensities observed by high-altitude satellites.

Magnetostatic wave tunable resonators

NASA Astrophysics Data System (ADS)

Castera, J.-P.; Hartemann, P.

1983-06-01

Theoretical principles and techniques for the implementation of magnetostatic surface wave and volume wave resonators in high frequency oscillators are discussed. Magnetostatic waves are magnetic waves that propagate in materials exposed to a polarized magnetic field. The propagation speed ranges from 3-300 km/sec for wavelengths between 1 micron and 10 mm, in the presence of lags from 10-1000 nsec/ cm. Tunable resonators in the 1-20 GHz frequency range have been manufactured with YIG using liquid phase epitaxy for deposition on gadolinium and gallium substrates. Distributed-mirror Fabry-Perot cavity resonators are described and performance tests results are reported, including losses of 8 dB, a quality coefficient under voltage of 450, and frequency rejection outside of resonance better than 10 dB. However, saturation occurs at low power levels at frequencies lower than 4.2 GHz, a feature overcome with forward volume magnetostatic wave generators, which have a quality factor of 500, an insertion loss of 22 dB, and rejection around 15 dB.

Transferred substrate heterojunction bipolar transistors for submillimeter wave applications

NASA Technical Reports Server (NTRS)

Fung, A.; Samoska, L.; Siegel, P.; Rodwell, M.; Urteaga, M.; Paidi, V.

2003-01-01

We present ongoing work towards the development of submillimeter wave transistors with goals of realizing advanced high frequency amplifiers, voltage controlled oscillators, active multipliers, and traditional high-speed digital circuits.

Wafer scale millimeter-wave integrated circuits based on epitaxial graphene in high data rate communication

PubMed Central

Habibpour, Omid; He, Zhongxia Simon; Strupinski, Wlodek; Rorsman, Niklas; Zirath, Herbert

2017-01-01

In recent years, the demand for high data rate wireless communications has increased dramatically, which requires larger bandwidth to sustain multi-user accessibility and quality of services. This can be achieved at millimeter wave frequencies. Graphene is a promising material for the development of millimeter-wave electronics because of its outstanding electron transport properties. Up to now, due to the lack of high quality material and process technology, the operating frequency of demonstrated circuits has been far below the potential of graphene. Here, we present monolithic integrated circuits based on epitaxial graphene operating at unprecedented high frequencies (80–100 GHz). The demonstrated circuits are capable of encoding/decoding of multi-gigabit-per-second information into/from the amplitude or phase of the carrier signal. The developed fabrication process is scalable to large wafer sizes. PMID:28145513

Current drive at plasma densities required for thermonuclear reactors.

PubMed

Cesario, R; Amicucci, L; Cardinali, A; Castaldo, C; Marinucci, M; Panaccione, L; Santini, F; Tudisco, O; Apicella, M L; Calabrò, G; Cianfarani, C; Frigione, D; Galli, A; Mazzitelli, G; Mazzotta, C; Pericoli, V; Schettini, G; Tuccillo, A A

2010-08-10

Progress in thermonuclear fusion energy research based on deuterium plasmas magnetically confined in toroidal tokamak devices requires the development of efficient current drive methods. Previous experiments have shown that plasma current can be driven effectively by externally launched radio frequency power coupled to lower hybrid plasma waves. However, at the high plasma densities required for fusion power plants, the coupled radio frequency power does not penetrate into the plasma core, possibly because of strong wave interactions with the plasma edge. Here we show experiments performed on FTU (Frascati Tokamak Upgrade) based on theoretical predictions that nonlinear interactions diminish when the peripheral plasma electron temperature is high, allowing significant wave penetration at high density. The results show that the coupled radio frequency power can penetrate into high-density plasmas due to weaker plasma edge effects, thus extending the effective range of lower hybrid current drive towards the domain relevant for fusion reactors.

Atmospheric and Fog Effects on Ultra-Wide Band Radar Operating at Extremely High Frequencies.

PubMed

Balal, Nezah; Pinhasi, Gad A; Pinhasi, Yosef

2016-05-23

The wide band at extremely high frequencies (EHF) above 30 GHz is applicable for high resolution directive radars, resolving the lack of free frequency bands within the lower part of the electromagnetic spectrum. Utilization of ultra-wideband signals in this EHF band is of interest, since it covers a relatively large spectrum, which is free of users, resulting in better resolution in both the longitudinal and transverse dimensions. Noting that frequencies in the millimeter band are subjected to high atmospheric attenuation and dispersion effects, a study of the degradation in the accuracy and resolution is presented. The fact that solid-state millimeter and sub-millimeter radiation sources are producing low power, the method of continuous-wave wideband frequency modulation becomes the natural technique for remote sensing and detection. Millimeter wave radars are used as complementary sensors for the detection of small radar cross-section objects under bad weather conditions, when small objects cannot be seen by optical cameras and infrared detectors. Theoretical analysis for the propagation of a wide "chirped" Frequency-Modulated Continuous-Wave (FMCW) radar signal in a dielectric medium is presented. It is shown that the frequency-dependent (complex) refractivity of the atmospheric medium causes distortions in the phase of the reflected signal, introducing noticeable errors in the longitudinal distance estimations, and at some frequencies may also degrade the resolution.

Atmospheric and Fog Effects on Ultra-Wide Band Radar Operating at Extremely High Frequencies

PubMed Central

Balal, Nezah; Pinhasi, Gad A.; Pinhasi, Yosef

2016-01-01

The wide band at extremely high frequencies (EHF) above 30 GHz is applicable for high resolution directive radars, resolving the lack of free frequency bands within the lower part of the electromagnetic spectrum. Utilization of ultra-wideband signals in this EHF band is of interest, since it covers a relatively large spectrum, which is free of users, resulting in better resolution in both the longitudinal and transverse dimensions. Noting that frequencies in the millimeter band are subjected to high atmospheric attenuation and dispersion effects, a study of the degradation in the accuracy and resolution is presented. The fact that solid-state millimeter and sub-millimeter radiation sources are producing low power, the method of continuous-wave wideband frequency modulation becomes the natural technique for remote sensing and detection. Millimeter wave radars are used as complementary sensors for the detection of small radar cross-section objects under bad weather conditions, when small objects cannot be seen by optical cameras and infrared detectors. Theoretical analysis for the propagation of a wide “chirped” Frequency-Modulated Continuous-Wave (FMCW) radar signal in a dielectric medium is presented. It is shown that the frequency-dependent (complex) refractivity of the atmospheric medium causes distortions in the phase of the reflected signal, introducing noticeable errors in the longitudinal distance estimations, and at some frequencies may also degrade the resolution. PMID:27223286

Stabilized soliton self-frequency shift and 0.1- PHz sideband generation in a photonic-crystal fiber with an air-hole-modified core.

PubMed

Liu, Bo-Wen; Hu, Ming-Lie; Fang, Xiao-Hui; Li, Yan-Feng; Chai, Lu; Wang, Ching-Yue; Tong, Weijun; Luo, Jie; Voronin, Aleksandr A; Zheltikov, Aleksei M

2008-09-15

Fiber dispersion and nonlinearity management strategy based on a modification of a photonic-crystal fiber (PCF) core with an air hole is shown to facilitate optimization of PCF components for a stable soliton frequency shift and subpetahertz sideband generation through four-wave mixing. Spectral recoil of an optical soliton by a red-shifted dispersive wave, generated through a soliton instability induced by high-order fiber dispersion, is shown to stabilize the soliton self-frequency shift in a highly nonlinear PCF with an air-hole-modified core relative to pump power variations. A fiber with a 2.3-microm-diameter core modified with a 0.9-microm-diameter air hole is used to demonstrate a robust soliton self-frequency shift of unamplified 50-fs Ti: sapphire laser pulses to a central wavelength of about 960 nm, which remains insensitive to variations in the pump pulse energy within the range from 60 to at least 100 pJ. In this regime of frequency shifting, intense high- and low-frequency branches of dispersive wave radiation are simultaneously observed in the spectrum of PCF output. An air-hole-modified-core PCF with appropriate dispersion and nonlinearity parameters is shown to provide efficient four-wave mixing, giving rise to Stokes and anti-Stokes sidebands whose frequency shift relative to the pump wavelength falls within the subpetahertz range, thus offering an attractive source for nonlinear Raman microspectroscopy.

Mechanism of travelling-wave transport of particles

NASA Astrophysics Data System (ADS)

Kawamoto, Hiroyuki; Seki, Kyogo; Kuromiya, Naoyuki

2006-03-01

Numerical and experimental investigations have been carried out on transport of particles in an electrostatic travelling field. A three-dimensional hard-sphere model of the distinct element method was developed to simulate the dynamics of particles. Forces applied to particles in the model were the Coulomb force, the dielectrophoresis force on polarized dipole particles in a non-uniform field, the image force, gravity and the air drag. Friction and repulsion between particle-particle and particle-conveyer were included in the model to replace initial conditions after mechanical contacts. Two kinds of experiments were performed to confirm the model. One was the measurement of charge of particles that is indispensable to determine the Coulomb force. Charge distribution was measured from the locus of free-fallen particles in a parallel electrostatic field. The averaged charge of the bulk particle was confirmed by measurement with a Faraday cage. The other experiment was measurements of the differential dynamics of particles on a conveyer consisting of parallel electrodes to which a four-phase travelling electrostatic wave was applied. Calculated results agreed with measurements, and the following characteristics were clarified. (1) The Coulomb force is the predominant force to drive particles compared with the other kinds of forces, (2) the direction of particle transport did not always coincide with that of the travelling wave but changed partially. It depended on the frequency of the travelling wave, the particle diameter and the electric field, (3) although some particles overtook the travelling wave at a very low frequency, the motion of particles was almost synchronized with the wave at the low frequency and (4) the transport of some particles was delayed to the wave at medium frequency; the majority of particles were transported backwards at high frequency and particles were not transported but only vibrated at very high frequency.

Electromechanical Frequency Filters

NASA Astrophysics Data System (ADS)

Wersing, W.; Lubitz, K.

Frequency filters select signals with a frequency inside a definite frequency range or band from signals outside this band, traditionally afforded by a combination of L-C-resonators. The fundamental principle of all modern frequency filters is the constructive interference of travelling waves. If a filter is set up of coupled resonators, this interference occurs as a result of the successive wave reflection at the resonators' ends. In this case, the center frequency f c of a filter, e.g., set up of symmetrical λ/2-resonators of length 1, is given by f_c = f_r = v_{ph}/λ = v_{ph}/2l , where v ph is the phase velocity of the wave. This clearly shows the big advantage of acoustic waves for filter applications in comparison to electro-magnetic waves. Because v ph of acoustic waves in solids is about 104-105 smaller than that of electro-magnetic waves, much smaller filters can be realised. Today, piezoelectric materials and processing technologies exist that electromechanical resonators and filters can be produced in the frequency range from 1 kHz up to 10 GHz. Further requirements for frequency filters such as low losses (high resonator Q) and low temperature coefficients of frequency constants can also be fulfilled with these filters. Important examples are quartz-crystal resonators and filters (1 kHz-200 MHz) as discussed in Chap. 2, electromechanical channel filters (50 kHz and 130 kHz) for long-haul communication systems as discussed in this section, surface acoustic wave (SAW) filters (20 MHz-5 GHz), as discussed in Chap. 14, and thin film bulk acoustic resonators (FBAR) and filters (500 MHz-10 GHz), as discussed in Chap. 15.

Exciting Alfven Waves using Modulated Electron Heating by High Power Microwaves

NASA Astrophysics Data System (ADS)

Wang, Yuhou; Gekelman, Walter; Pribyl, Patrick; van Compernolle, Bart; Papadopoulos, Konstantinos

2014-10-01

Experiments exploring the physics of ionospheric modification with intense perpendicular propagating waves (k-> ⊥B->0) on the Large Plasma Device (LaPD) at UCLA have been upgraded with the addition of a high power rapidly pulsed microwave source. The plasma is irradiated with ten pulses (250 kW X-band) near the upper-hybrid frequency. The pulses are modulated at a frequency of a fraction (0.1-1.0) of fci (ion cyclotron frequency). Based on a previous single-pulse experiment, the modulated electron heating may drive a large amplitude shear Alfvén wave (f

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

Silin, D.; Goloshubin, G.

Analysis of compression wave propagation in a poroelastic medium predicts a peak of reflection from a high-permeability layer in the low-frequency end of the spectrum. An explicit formula expresses the resonant frequency through the elastic moduli of the solid skeleton, the permeability of the reservoir rock, the fluid viscosity and compressibility, and the reservoir thickness. This result is obtained through a low-frequency asymptotic analysis of Biot's model of poroelasticity. A review of the derivation of the main equations from the Hooke's law, momentum and mass balance equations, and Darcy's law suggests an alternative new physical interpretation of some coefficients ofmore » the classical poroelasticity. The velocity of wave propagation, the attenuation factor, and the wave number, are expressed in the form of power series with respect to a small dimensionless parameter. The absolute value of this parameter is equal to the product of the kinematic reservoir fluid mobility and the wave frequency. Retaining only the leading terms of the series leads to explicit and relatively simple expressions for the reflection and transmission coefficients for a planar wave crossing an interface between two permeable media, as well as wave reflection from a thin highly-permeable layer (a lens). Practical applications of the obtained asymptotic formulae are seismic modeling, inversion, and at-tribute analysis.« less

Controlling of the electromagnetic solitary waves generation in the wake of a two-color laser

NASA Astrophysics Data System (ADS)

Pan, K. Q.; Li, S. W.; Guo, L.; Yang, D.; Li, Z. C.; Zheng, C. Y.; Jiang, S. E.; Zhang, B. H.; He, X. T.

2018-05-01

Electromagnetic solitary waves generated by a two-color laser interaction with an underdense plasma are investigated. It is shown that, when the former wave packet of the two-color laser is intense enough, it will excite nonlinear wakefields and generate electron density cavities. The latter wave packets will beat with the nonlinear wakefield and generate both high-frequency and low-frequency components. When the peak density of the cavities exceeds the critical density of the low-frequency component, this part of the electromagnetic field will be trapped to generate electromagnetic solitary waves. By changing the laser and plasma parameters, we can control the wakefield generation, which will also control the generation of the solitary waves. One-dimensional particle-in-cell simulations are performed to prove the controlling of the solitary waves. The simulation results also show that solitary waves generated by higher laser intensities will become moving solitary waves. The two-dimensional particle-in-cell also shows the generation of the solitary waves. In the two-dimensional case, solitary waves are distributed in the transverse directions because of the filamentation instability.

High-frequency solitons in media with induced scattering from damped low-frequency waves with nonuniform dispersion and nonlinearity

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

Aseeva, N. V., E-mail: vtyutin@hse.ru; Gromov, E. M.; Tyutin, V. V.

2015-12-15

The dynamics of high-frequency field solitons is considered using the extended nonhomogeneous nonlinear Schrödinger equation with induced scattering from damped low-frequency waves (pseudoinduced scattering). This scattering is a 3D analog of the stimulated Raman scattering from temporal spatially homogeneous damped low-frequency modes, which is well known in optics. Spatial inhomogeneities of secondorder linear dispersion and cubic nonlinearity are also taken into account. It is shown that the shift in the 3D spectrum of soliton wavenumbers toward the short-wavelength region is due to nonlinearity increasing in coordinate and to decreasing dispersion. Analytic results are confirmed by numerical calculations.

Implementation of acoustic demultiplexing with membrane-type metasurface in low frequency range

NASA Astrophysics Data System (ADS)

Chen, Xing; Liu, Peng; Hou, Zewei; Pei, Yongmao

2017-04-01

Wavelength division multiplexing technology, adopted to increase the information density, plays a significant role in optical communication. However, in acoustics, a similar function can be hardly implemented due to the weak dispersion in natural acoustic materials. Here, an acoustic demultiplexer, based on the concept of metasurfaces, is proposed for splitting acoustic waves and propagating along different trajectories in a low frequency range. An acoustic metasurface, containing multiple resonant units, is designed with various phase profiles for different frequencies. Originating from the highly dispersive properties, the resonant units are independent and merely work in the vicinity of their resonant frequencies. Therefore, by combing multiple resonant units appropriately, the phenomena of anomalous reflection, acoustic focusing, and acoustic wave bending can occur in different frequencies. The proposed acoustic demultiplexer has advantages on the subwavelength scale and the versatility in wave control, providing a strategy for separating acoustic waves with different Fourier components.

Investigation of hydroelastic ship responses of an ULOC in head seas

NASA Astrophysics Data System (ADS)

Wang, Xue-liang; Temarel, Pandeli; Hu, Jia-jun; Gu, Xue-kang

2016-10-01

Investigation of hydroelastic ship responses has been brought to the attention of the scientific and engineering world for several decades. There are two kinds of high-frequency vibrations in general ship responses to a large ocean-going ship in its shipping line, so-called springing and whipping, which are important for the determination of design wave load and fatigue damage as well. Because of the huge scale of an ultra large ore carrier (ULOC), it will suffer seldom slamming events in the ocean. The resonance vibration with high frequency is springing, which is caused by continuous wave excitation. In this paper, the wave-induced vibrations of the ULOC are addressed by experimental and numerical methods according to 2D and 3D hydroelasticity theories and an elastic model under full-load and ballast conditions. The influence of loading conditions on high-frequency vibration is studied both by numerical and experimental results. Wave-induced vibrations are higher under ballast condition including the wave frequency part, the multiple frequencies part, the 2-node and the 3-node vertical bending parts of the hydroelastic responses. The predicted results from the 2D method have less accuracy than the 3D method especially under ballast condition because of the slender-body assumption in the former method. The applicability of the 2D method and the further development of nonlinear effects to 3D method in the prediction of hydroelastic responses of the ULOC are discussed.

Slab anisotropy from subduction zone guided waves in Taiwan

NASA Astrophysics Data System (ADS)

Chen, K. H.; Tseng, Y. L.; Hu, J. C.

2014-12-01

Frozen-in anisotropic structure in the oceanic lithosphere and faulting/hydration in the upper layer of the slab are expected to play an important role in anisotropic signature of the subducted slab. Over the past several decades, despite the advances in characterizing anisotropy using shear wave splitting method and its developments, the character of slab anisotropy remains poorly understood. In this study we investigate the slab anisotropy using subduction zone guided waves characterized by long path length in the slab. In the southernmost Ryukyu subduction zone, seismic waves from events deeper than 100 km offshore northern Taiwan reveal wave guide behavior: (1) a low-frequency (< 1 Hz) first arrival recognized on vertical and radial components but not transverse component (2) large, sustained high-frequency (3-10 Hz) signal in P and S wave trains. The depth dependent high-frequency content (3-10Hz) confirms the association with a waveguide effect in the subducting slab rather than localized site amplification effects. Using the selected subduction zone guided wave events, we further analyzed the shear wave splitting for intermediate-depth earthquakes in different frequency bands, to provide the statistically meaningful shear wave splitting parameters. We determine shear wave splitting parameters from the 34 PSP guided events that are deeper than 100 km with ray path traveling along the subducted slab. From shear wave splitting analysis, the slab and crust effects reveal consistent polarization pattern of fast directions of EN-WS and delay time of 0.13 - 0.27 sec. This implies that slab anisotropy is stronger than the crust effect (<0.1 s) but weaker than the mantle wedge and sub-slab mantle effect (0.3-1.3 s) in Taiwan.

A unifying fractional wave equation for compressional and shear waves.

PubMed

Holm, Sverre; Sinkus, Ralph

2010-01-01

This study has been motivated by the observed difference in the range of the power-law attenuation exponent for compressional and shear waves. Usually compressional attenuation increases with frequency to a power between 1 and 2, while shear wave attenuation often is described with powers less than 1. Another motivation is the apparent lack of partial differential equations with desirable properties such as causality that describe such wave propagation. Starting with a constitutive equation which is a generalized Hooke's law with a loss term containing a fractional derivative, one can derive a causal fractional wave equation previously given by Caputo [Geophys J. R. Astron. Soc. 13, 529-539 (1967)] and Wismer [J. Acoust. Soc. Am. 120, 3493-3502 (2006)]. In the low omegatau (low-frequency) case, this equation has an attenuation with a power-law in the range from 1 to 2. This is consistent with, e.g., attenuation in tissue. In the often neglected high omegatau (high-frequency) case, it describes attenuation with a power-law between 0 and 1, consistent with what is observed in, e.g., dynamic elastography. Thus a unifying wave equation derived properly from constitutive equations can describe both cases.

Multichannel analysis of surface waves

USGS Publications Warehouse

Park, C.B.; Miller, R.D.; Xia, J.

1999-01-01

The frequency-dependent properties of Rayleigh-type surface waves can be utilized for imaging and characterizing the shallow subsurface. Most surface-wave analysis relies on the accurate calculation of phase velocities for the horizontally traveling fundamental-mode Rayleigh wave acquired by stepping out a pair of receivers at intervals based on calculated ground roll wavelengths. Interference by coherent source-generated noise inhibits the reliability of shear-wave velocities determined through inversion of the whole wave field. Among these nonplanar, nonfundamental-mode Rayleigh waves (noise) are body waves, scattered and nonsource-generated surface waves, and higher-mode surface waves. The degree to which each of these types of noise contaminates the dispersion curve and, ultimately, the inverted shear-wave velocity profile is dependent on frequency as well as distance from the source. Multichannel recording permits effective identification and isolation of noise according to distinctive trace-to-trace coherency in arrival time and amplitude. An added advantage is the speed and redundancy of the measurement process. Decomposition of a multichannel record into a time variable-frequency format, similar to an uncorrelated Vibroseis record, permits analysis and display of each frequency component in a unique and continuous format. Coherent noise contamination can then be examined and its effects appraised in both frequency and offset space. Separation of frequency components permits real-time maximization of the S/N ratio during acquisition and subsequent processing steps. Linear separation of each ground roll frequency component allows calculation of phase velocities by simply measuring the linear slope of each frequency component. Breaks in coherent surface-wave arrivals, observable on the decomposed record, can be compensated for during acquisition and processing. Multichannel recording permits single-measurement surveying of a broad depth range, high levels of redundancy with a single field configuration, and the ability to adjust the offset, effectively reducing random or nonlinear noise introduced during recording. A multichannel shot gather decomposed into a swept-frequency record allows the fast generation of an accurate dispersion curve. The accuracy of dispersion curves determined using this method is proven through field comparisons of the inverted shear-wave velocity (??(s)) profile with a downhole ??(s) profile.Multichannel recording is an efficient method of acquiring ground roll. By displaying the obtained information in a swept-frequency format, different frequency components of Rayleigh waves can be identified by distinctive and simple coherency. In turn, a seismic surface-wave method is derived that provides a useful noninvasive tool, where information about elastic properties of near-surface materials can be effectively obtained.

Time-Delay Interferometry for Space-based Gravitational Wave Searches

NASA Technical Reports Server (NTRS)

Armstrong, J.; Estabrook, F.; Tinto, M.

1999-01-01

Ground-based, equal-arm-length laser interferometers are being built to measure high-frequency astrophysical graviatational waves. Because of the arm-length equality, laser light experiences the same delay in each arm and thus phase or frequency noise from the laser itself precisely cancels at the photodetector.

Frequency correlation of probe waves backscattered from small scale ionospheric irregularities generated by high power HF radio waves

NASA Astrophysics Data System (ADS)

Puchkov, V. A.

2016-09-01

Aspect sensitive scattering of multi-frequency probe signals by artificial, magnetic field aligned density irregularities (with transverse size ∼ 1- 10 m) generated in the ionosphere by powerful radio waves is considered. Fluctuations of received signals depending on stochastic properties of the irregularities are calculated. It is shown that in the case of HF probe waves two mechanisms may contribute to the scattered signal fluctuations. The first one is due to the propagation of probe waves in the ionospheric plasma as in a randomly inhomogeneous medium. The second one lies in non-stationary stochastic behavior of irregularities which satisfy the Bragg conditions for the scattering geometry and therefore constitute centers of scattering. In the probe wave frequency band of the order of 10-100 MHz the second mechanism dominates which delivers opportunity to recover some properties of artificial irregularities from received signals. Correlation function of backscattered probe waves with close frequencies is calculated, and it is shown that detailed spatial distribution of irregularities along the scattering vector can be found experimentally from observations of this correlation function.

High Speed Terahertz Modulator on the Chip Based on Tunable Terahertz Slot Waveguide

PubMed Central

Singh, P. K.; Sonkusale, S.

2017-01-01

This paper presents an on-chip device that can perform gigahertz-rate amplitude modulation and switching of broadband terahertz electromagnetic waves. The operation of the device is based on the interaction of confined THz waves in a novel slot waveguide with an electronically tunable two dimensional electron gas (2DEG) that controls the loss of the THz wave propagating through this waveguide. A prototype device is fabricated which shows THz intensity modulation of 96% at 0.25 THz carrier frequency with low insertion loss and device length as small as 100 microns. The demonstrated modulation cutoff frequency exceeds 14 GHz indicating potential for the high-speed modulation of terahertz waves. The entire device operates at room temperature with low drive voltage (<2 V) and zero DC power consumption. The device architecture has potential for realization of the next generation of on-chip modulators and switches at THz frequencies. PMID:28102306

Amplification of a high-frequency electromagnetic wave by a relativistic plasma

NASA Technical Reports Server (NTRS)

Yoon, Peter H.

1990-01-01

The amplification of a high-frequency transverse electromagnetic wave by a relativistic plasma component, via the synchrotron maser process, is studied. The background plasma that supports the transverse wave is considered to be cold, and the energetic component whose density is much smaller than that of the background component has a loss-cone feature in the perpendicular momentum space and a finite field-aligned drift speed. The ratio of the background plasma frequency squared to the electron gyrofrequency squared is taken to be sufficiently larger than unity. Such a parameter regime is relevant to many space and astrophysical situations. A detailed study of the amplification process is carried out over a wide range of physical parameters including the loss-cone index, the ratio of the electron mass energy to the temperature of the energetic component, the field-aligned drift speed, the normalized density, and the wave propagation angle.

Statistical Analysis of Bursty Langmuir Waves, Alfvén and Whistler Waves, and Precipitating Electrons Seen by the CHARM II Nightside Sounding Rocket

NASA Astrophysics Data System (ADS)

Dombrowski, M. P.; Labelle, J. W.; Kletzing, C.; Bounds, S. R.; Kaeppler, S. R.

2013-12-01

Bursty Langmuir waves have been interpreted as the result of the superposition of multiple Langmuir normal-mode waves, with the resultant modulation being the beat pattern between waves with e.g. 10 kHz frequency differences. The normal-mode waves could be generated either through wave-wave interactions with VLF waves, or through independent linear processes. The CHARM II sounding rocket was launched into a substorm at 9:49 UT on 15 February 2010, from the Poker Flat Research Range in Alaska. The primary instruments included the Dartmouth High-Frequency Experiment (HFE), a receiver system which effectively yields continuous (100% duty cycle) E-field waveform measurements up to 5 MHz, as well as a number of charged particle detectors, including a wave-particle correlator. The payload also included a magnetometer and several low-frequency wave instruments. CHARM II encountered several regions of strong Langmuir wave activity throughout its 15-minute flight, including several hundred discrete Langmuir-wave bursts. We show results of a statistical analysis of CHARM II data for the entire flight, comparing HFE data with the other payload instruments, specifically looking at timings and correlations between bursty Langmuir waves, Alfvén and whistler-mode waves, and electrons precipitating parallel to the magnetic field. Following a similar analysis on TRICE dayside sounding rocket data, we also calculate the fraction of correlated waves with VLF waves at appropriate frequencies to support the wave-wave interaction bursty Langmuir wave generation mechanism, and compare to results from CHARM II nightside data.

Single frequency thermal wave radar: A next-generation dynamic thermography for quantitative non-destructive imaging over wide modulation frequency ranges.

PubMed

Melnikov, Alexander; Chen, Liangjie; Ramirez Venegas, Diego; Sivagurunathan, Koneswaran; Sun, Qiming; Mandelis, Andreas; Rodriguez, Ignacio Rojas

2018-04-01

Single-Frequency Thermal Wave Radar Imaging (SF-TWRI) was introduced and used to obtain quantitative thickness images of coatings on an aluminum block and on polyetherketone, and to image blind subsurface holes in a steel block. In SF-TWR, the starting and ending frequencies of a linear frequency modulation sweep are chosen to coincide. Using the highest available camera frame rate, SF-TWRI leads to a higher number of sampled points along the modulation waveform than conventional lock-in thermography imaging because it is not limited by conventional undersampling at high frequencies due to camera frame-rate limitations. This property leads to large reduction in measurement time, better quality of images, and higher signal-noise-ratio across wide frequency ranges. For quantitative thin-coating imaging applications, a two-layer photothermal model with lumped parameters was used to reconstruct the layer thickness from multi-frequency SF-TWR images. SF-TWRI represents a next-generation thermography method with superior features for imaging important classes of thin layers, materials, and components that require high-frequency thermal-wave probing well above today's available infrared camera technology frame rates.

Single frequency thermal wave radar: A next-generation dynamic thermography for quantitative non-destructive imaging over wide modulation frequency ranges

NASA Astrophysics Data System (ADS)

Melnikov, Alexander; Chen, Liangjie; Ramirez Venegas, Diego; Sivagurunathan, Koneswaran; Sun, Qiming; Mandelis, Andreas; Rodriguez, Ignacio Rojas

2018-04-01

Single-Frequency Thermal Wave Radar Imaging (SF-TWRI) was introduced and used to obtain quantitative thickness images of coatings on an aluminum block and on polyetherketone, and to image blind subsurface holes in a steel block. In SF-TWR, the starting and ending frequencies of a linear frequency modulation sweep are chosen to coincide. Using the highest available camera frame rate, SF-TWRI leads to a higher number of sampled points along the modulation waveform than conventional lock-in thermography imaging because it is not limited by conventional undersampling at high frequencies due to camera frame-rate limitations. This property leads to large reduction in measurement time, better quality of images, and higher signal-noise-ratio across wide frequency ranges. For quantitative thin-coating imaging applications, a two-layer photothermal model with lumped parameters was used to reconstruct the layer thickness from multi-frequency SF-TWR images. SF-TWRI represents a next-generation thermography method with superior features for imaging important classes of thin layers, materials, and components that require high-frequency thermal-wave probing well above today's available infrared camera technology frame rates.

High-precision terahertz frequency modulated continuous wave imaging method using continuous wavelet transform

NASA Astrophysics Data System (ADS)

Zhou, Yu; Wang, Tianyi; Dai, Bing; Li, Wenjun; Wang, Wei; You, Chengwu; Wang, Kejia; Liu, Jinsong; Wang, Shenglie; Yang, Zhengang

2018-02-01

Inspired by the extensive application of terahertz (THz) imaging technologies in the field of aerospace, we exploit a THz frequency modulated continuous-wave imaging method with continuous wavelet transform (CWT) algorithm to detect a multilayer heat shield made of special materials. This method uses the frequency modulation continuous-wave system to catch the reflected THz signal and then process the image data by the CWT with different basis functions. By calculating the sizes of the defects area in the final images and then comparing the results with real samples, a practical high-precision THz imaging method is demonstrated. Our method can be an effective tool for the THz nondestructive testing of composites, drugs, and some cultural heritages.

Plasma Waves Observed in the Cusp Turbulent Boundary Layer: An Analysis of High Time Resolution Wave and Particle Measurements from the Polar Spacecraft

NASA Technical Reports Server (NTRS)

Pickett, J. S.; Franz, J. R.; Scudder, J. D.; Menietti, J. D.; Gurnett, D. A.; Hospodarsky, G. B.; Braunger, R. M.; Kintner, P. M.; Kurth, W. S.

2001-01-01

The boundary layer located in the cusp and adjacent to the magnetopause is a region that is quite turbulent and abundant with waves. The Polar spacecraft's orbit and sophisticated instrumentation are ideal for studying this region of space. Our analysis of the waveform data obtained in this turbulent boundary layer shows broadband magnetic noise extending up to a few kilohertz (but less than the electron cyclotron frequency); sinusoidal bursts (a few tenths of a second) of whistler mode waves at around a few tens of hertz, a few hundreds of hertz, and just below the electron cyclotron frequency; and bipolar pulses, interpreted as electron phase-space holes. In addition, bursts of electron cyclotron harmonic waves are occasionally observed with magnetic components. We show evidence of broadband electrostatic bursts covering a range of approx. 3 to approx. 25 kHz (near but less than the plasma frequency) occurring in packets modulated at the frequency of some of the whistler mode waves. On the basis of high time resolution particle data from the Polar HYDRA instrument, we show that these bursts are consistent with generation by the resistive medium instability. The most likely source of the whistler mode waves is the magnetic reconnection site closest to the spacecraft, since the waves are observed propagating both toward and away from the Earth, are bursty, which is often the case with reconnection, and do not fit on the theoretical cold plasma dispersion relation curve.

Design parameters of stainless steel plates for maximizing high frequency ultrasound wave transmission.

PubMed

Michaud, Mark; Leong, Thomas; Swiergon, Piotr; Juliano, Pablo; Knoerzer, Kai

2015-09-01

This work validated, in a higher frequency range, the theoretical predictions made by Boyle around 1930, which state that the optimal transmission of sound pressure through a metal plate occurs when the plate thickness equals a multiple of half the wavelength of the sound wave. Several reactor design parameters influencing the transmission of high frequency ultrasonic waves through a stainless steel plate were examined. The transmission properties of steel plates of various thicknesses (1-7 mm) were studied for frequencies ranging from 400 kHz to 2 MHz and at different distances between plates and transducers. It was shown that transmission of sound pressure through a steel plate showed high dependence of the thickness of the plate to the frequency of the sound wave (thickness ratio). Maximum sound pressure transmission of ∼ 60% of the incident pressure was observed when the ratio of the plate thickness to the applied frequency was a multiple of a half wavelength (2 MHz, 6mm stainless steel plate). In contrast, minimal sound pressure transmission (∼ 10-20%) was measured for thickness ratios that were not a multiple of a half wavelength. Furthermore, the attenuation of the sound pressure in the transmission region was also investigated. As expected, it was confirmed that higher frequencies have more pronounced sound pressure attenuation than lower frequencies. The spatial distribution of the sound pressure transmitted through the plate characterized by sonochemiluminescence measurements using luminol emission, supports the validity of the pressure measurements in this study. Copyright © 2015 Elsevier B.V. All rights reserved.

Fiber optic sensing system

NASA Technical Reports Server (NTRS)

Adamovsky, Grigory (Inventor)

1991-01-01

A fiber optic interferometer utilizes a low coherence light emitting diode (LED) laser as a light source which is filtered and driven at two RF frequencies, high and low, that are specific to the initial length of the resonator chamber. A displacement of a reflecting mirror changes the length traveled by the nonreferencing signal. The low frequency light undergoes destructive interference which reduces the average intensity of the wave while the high frequency light undergoes constructive interference which increases the average intensity of the wave. The ratio of these two intensity measurements is proportional to the displacement incurred.

Analysis of group-velocity dispersion of high-frequency Rayleigh waves for near-surface applications

USGS Publications Warehouse

Luo, Y.; Xia, J.; Xu, Y.; Zeng, C.

2011-01-01

The Multichannel Analysis of Surface Waves (MASW) method is an efficient tool to obtain the vertical shear (S)-wave velocity profile using the dispersive characteristic of Rayleigh waves. Most MASW researchers mainly apply Rayleigh-wave phase-velocity dispersion for S-wave velocity estimation with a few exceptions applying Rayleigh-wave group-velocity dispersion. Herein, we first compare sensitivities of fundamental surface-wave phase velocities with group velocities with three four-layer models including a low-velocity layer or a high-velocity layer. Then synthetic data are simulated by a finite difference method. Images of group-velocity dispersive energy of the synthetic data are generated using the Multiple Filter Analysis (MFA) method. Finally we invert a high-frequency surface-wave group-velocity dispersion curve of a real-world example. Results demonstrate that (1) the sensitivities of group velocities are higher than those of phase velocities and usable frequency ranges are wider than that of phase velocities, which is very helpful in improving inversion stability because for a stable inversion system, small changes in phase velocities do not result in a large fluctuation in inverted S-wave velocities; (2) group-velocity dispersive energy can be measured using single-trace data if Rayleigh-wave fundamental-mode energy is dominant, which suggests that the number of shots required in data acquisition can be dramatically reduced and the horizontal resolution can be greatly improved using analysis of group-velocity dispersion; and (3) the suspension logging results of the real-world example demonstrate that inversion of group velocities generated by the MFA method can successfully estimate near-surface S-wave velocities. ?? 2011 Elsevier B.V.

Monitoring corrosion of rebar embedded in mortar using guided ultrasonic waves

NASA Astrophysics Data System (ADS)

Ervin, Benjamin Lee

This thesis investigates the use of guided mechanical waves for monitoring uniform and localized corrosion in steel reinforcing bars embedded in concrete. The main forms of structural deterioration from uniform corrosion in reinforced concrete are the destruction of the bond between steel and concrete, the loss of steel cross-sectional area, and the loss of concrete cross-sectional area from cracking and spalling. Localized corrosion, or pitting, leads to severe loss of steel cross-sectional area, creating a high risk of bar tensile failure and unintended transfer of loads to the surrounding concrete. Reinforcing bars were used to guide the waves, rather than bulk concrete, allowing for longer inspection distances due to lower material absorption, scattering, and divergence. Guided mechanical waves in low frequency ranges (50-200 kHz) and higher frequency ranges (2-8 MHz) were monitored in reinforced mortar specimens undergoing accelerated uniform corrosion. The frequency ranges chosen contain wave modes with varying amounts of interaction, i.e. displacement profile, at the material interface. Lower frequency modes were shown to be sensitive to the accumulation of corrosion product and the level of bond between the surrounding mortar and rebar. This allows for the onset of corrosion and bond deterioration to be monitored. Higher frequency modes were shown to be sensitive to changes in the bar profile surface, allowing for the loss of cross-sectional area to be monitored. Guided mechanical waves in the higher frequency range were also used to monitor reinforced mortar specimens undergoing accelerated localized corrosion. The high frequency modes were sensitive to the localized attack. Also promising was the unique frequency spectrum response for both uniform and localized corrosion, allowing the two corrosion types to be differentiated from through-transmission evaluation. The isolated effects of the reinforcing ribs, simulated debonding, simulated pitting, water surrounding, and mortar surrounding were also investigated using guided mechanical waves. Results are presented and discussed within the framework of a corrosion process degradation model and service life. A thorough review and discussion of the corrosion process, modeling the propagation of corrosion, nondestructive methods for monitoring corrosion in reinforced concrete, and guided mechanical waves have also been presented.

Synthetic Pn and Sn phases and the frequency dependence of Q of oceanic lithosphere

NASA Astrophysics Data System (ADS)

Sereno, Thomas J., Jr.; Orcutt, John A.

1987-04-01

The oceanic lithosphere is an extremely efficient waveguide for high-frequency seismic energy. In particular, the propagation of the regional to teleseismic oceanic Pn and Sn phases is largely controlled by properties of the oceanic plates. The shallow velocity gradient in the sub-Moho lithosphere results in a nearly linear travel time curve for these oceanic phases and an onset velocity near the material velocity of the uppermost mantle. The confinement of Pn/Sn to the lithosphere imposes a constraint on the maximum range that a normally refracted wave can be observed. The rapid disappearance of Sn and the discontinuous drop in Pn/Sn group velocity beyond a critical distance, dependent upon the local thickness of the lithosphere, are interpreted as a shadowing effect of the low Q asthenosphere. Wave number integration was used to compute complete synthetic seismograms for a model of oceanic lithosphere. The results were compared to data collected during the 1983 Ngendei Seismic Experiment in the southwest Pacific. The Pn/Sn coda is successfully modeled as a sum of leaky organ-pipe modes in the sediment layer and oceanic water column. While scattering is present to some degree, it is not required to explain the long duration and complicated nature of the Pn/Sn wave trains. The presence of extremely high frequencies in Pn/Sn phases and the greater efficiency of Sn than Pn propagation are interpreted in terms of an absorption band rheology. A shorter high-frequency relaxation time for P waves than for S waves results in a rheology with the property that Qα > Qβ at low frequency while Qβ > Qα at high frequency, consistent with the teleseismic Pn/Sn observations. The absorption band model is to viewed as only an approximation to the true frequency dependence of Q in the oceanic lithosphere for which analytic expressions for the material dispersion have been developed.

Simultaneous quarter-wave plate and half-mirror operation through a highly flexible single layer anisotropic metasurface.

PubMed

Khan, M Ismail; Tahir, Farooq A

2017-11-22

A highly flexible single-layer metasurface manifesting quarter-wave plate as well as half-mirror (1:1 beam-splitter) operation in the microwave frequency regime is being presented in this research. The designed metasurface reflects half power of the impinging linearly polarized electromagnetic wave as circularly polarized wave while the remaining half power is transmitted as circularly polarized wave at resonance frequency. Similarly, a circularly polarized incident wave is reflected and transmitted as linearly polarized wave with equal half powers. Moreover, the response of the metasurface is quite stable against the variations in the incidence angle up to 45°. The measurements performed on the fabricated prototype exhibit a good agreement with the simulation results. The compact size, flexible structure, angular stability and two in one operation (operating as a quarter-wave plate and beam-splitter at the same time) are the main characteristics of the subject metasurface that makes it a potential candidate for numerous applications in communication and miniaturized and conformal polarization control devices.

High speed all optical shear wave imaging optical coherence elastography (Conference Presentation)

NASA Astrophysics Data System (ADS)

Song, Shaozhen; Hsieh, Bao-Yu; Wei, Wei; Shen, Tueng; O'Donnell, Matthew; Wang, Ruikang K.

2016-03-01

Optical Coherence Elastography (OCE) is a non-invasive testing modality that maps the mechanical property of soft tissues with high sensitivity and spatial resolution using phase-sensitive optical coherence tomography (PhS-OCT). Shear wave OCE (SW-OCE) is a leading technique that relies on the speed of propagating shear waves to provide a quantitative elastography. Previous shear wave imaging OCT techniques are based on repeated M-B scans, which have several drawbacks such as long acquisition time and repeated wave stimulations. Recent developments of Fourier domain mode-locked high-speed swept-source OCT system has enabled enough speed to perform KHz B-scan rate OCT imaging. Here we propose ultra-high speed, single shot shear wave imaging to capture single-shot transient shear wave propagation to perform SW-OCE. The frame rate of shear wave imaging is 16 kHz, at A-line rate of ~1.62 MHz, which allows the detection of high-frequency shear wave of up to 8 kHz. The shear wave is generated photothermal-acoustically, by ultra-violet pulsed laser, which requires no contact to OCE subjects, while launching high frequency shear waves that carries rich localized elasticity information. The image acquisition and processing can be performed at video-rate, which enables real-time 3D elastography. SW-OCE measurements are demonstrated on tissue-mimicking phantoms and porcine ocular tissue. This approach opens up the feasibility to perform real-time 3D SW-OCE in clinical applications, to obtain high-resolution localized quantitative measurement of tissue biomechanical property.

Experimental study of sound propagation in a flexible duct

PubMed

Huang; Choy; So; Chong

2000-08-01

Propagation of sound in a flexible duct is investigated both theoretically and experimentally. Strong coupling of sound and flexural waves on the duct wall is found when the wall-to-air mass ratio is of the order of unity. The axial phase speed of sound approaches the in vacuo speed of flexural waves (subsonic in this case) at low frequencies. However, a speed higher than the isentropic sound speed in free space (340 m/s) is found beyond a critical frequency which is a function of the mass ratio. Experiments using a duct with a finite section of tensioned membrane are compared with the propagating modes pertaining to the infinite membrane model. Satisfactory quantitative agreement is obtained and the measured phase speed ranges from 8.3 to 1348 m/s. In the moderate frequency range, the theory predicts high spatial damping rate for the subsonic waves, which is consistent with the experimental observation that subsonic waves become increasingly undetectable as the frequency increases. Substantial sound reflection is observed at the interface between the rigid and the flexible segments of the duct without cross-section discontinuity, which, together with the high spatial damping, could form a basis for passive control of low-frequency duct noise.

Magnetic Search Coil (MSC) of Plasma Wave Experiment (PWE) aboard the Arase (ERG) satellite

NASA Astrophysics Data System (ADS)

Ozaki, Mitsunori; Yagitani, Satoshi; Kasahara, Yoshiya; Kojima, Hirotsugu; Kasaba, Yasumasa; Kumamoto, Atsushi; Tsuchiya, Fuminori; Matsuda, Shoya; Matsuoka, Ayako; Sasaki, Takashi; Yumoto, Takahiro

2018-05-01

This paper presents detailed performance values of the Magnetic Search Coil (MSC) that is part of the Plasma Wave Experiment on board the Arase (ERG) satellite. The MSC consists of a three-axis search coil magnetometer with a 200-mm-long magnetic core. The MSC plays a central role in the magnetic field observations, particularly for whistler mode chorus and hiss waves in a few kHz frequency range, which may cause local acceleration and/or rapid loss of radiation belt electrons. Accordingly, the MSC was carefully designed and developed to operate well in harsh radiation environments. To ascertain the wave-normal vectors, polarizations, and refractive indices of the plasma waves in a wide frequency band, the output signals detected by the MSC are fed into the two different wave receivers: one is the WaveForm Capture/Onboard Frequency Analyzer for waveform and spectrum observations in the frequency range from a few Hz up to 20 kHz, and the other is the High Frequency Analyzer for spectrum observations in the frequency range from 10 to 100 kHz. The noise equivalent magnetic induction of the MSC is 20 {fT/Hz}^{1/2} at a frequency of 2 kHz, and the null depth of directionality is - 40 dB, which is equivalent to an angular error less than 1°. The MSC on board the Arase satellite is the first experiment using a current-sensitive preamplifier for probing the plasma waves in the radiation belts.[Figure not available: see fulltext.

Rayleigh-wave dispersive energy imaging using a high-resolution linear radon transform

USGS Publications Warehouse

Luo, Y.; Xia, J.; Miller, R.D.; Xu, Y.; Liu, J.; Liu, Q.

2008-01-01

Multichannel Analysis of Surface Waves (MASW) analysis is an efficient tool to obtain the vertical shear-wave profile. One of the key steps in the MASW method is to generate an image of dispersive energy in the frequency-velocity domain, so dispersion curves can be determined by picking peaks of dispersion energy. In this paper, we propose to image Rayleigh-wave dispersive energy by high-resolution linear Radon transform (LRT). The shot gather is first transformed along the time direction to the frequency domain and then the Rayleigh-wave dispersive energy can be imaged by high-resolution LRT using a weighted preconditioned conjugate gradient algorithm. Synthetic data with a set of linear events are presented to show the process of generating dispersive energy. Results of synthetic and real-world examples demonstrate that, compared with the slant stacking algorithm, high-resolution LRT can improve the resolution of images of dispersion energy by more than 50%. ?? Birkhaueser 2008.

A self-mixing based ring-type fiber-optic acoustic sensor

NASA Astrophysics Data System (ADS)

Wang, Lutang; Wu, Chunxu; Fang, Nian

2014-07-01

A novel, simple fiber-optic acoustic sensor consisting of a self-mixing effect based laser source and a ring-type interferometer is presented. With weak external optical feedbacks, the acoustic wave signals can be detected by measuring the changes of oscillating frequency of the laser diode, induced by the disturbances of sensing fiber, with the ring-type interferometer. The operation principles of the sensor system are explored in-depth and the experimental researches are carried out. The acoustic wave signals produced by various actions, such as by pencil broken, mental pin free falling and PZT are detected for evaluating the sensing performances of the experimental system. The investigation items include the sensitivity as well as frequency responses of the sensor system. An experiment for the detection of corona discharges is carried out, which occur in a high-voltage environment between two parallel copper electrodes, under different humidity levels. The satisfied experimental results are obtained. These experimental results well prove that our proposed sensing system has very high sensitivity and excellent high frequency responses characteristics in the detections of weak, high-frequency acoustic wave signals.

The gyrotron - a natural source of high-power orbital angular momentum millimeter-wave beams

NASA Astrophysics Data System (ADS)

Thumm, M.; Sawant, A.; Choe, M. S.; Choi, E. M.

2017-08-01

Orbital angular momentum (OAM) of electromagnetic-wave beams provides further diversity to multiplexing in wireless communication. The present report shows that higher-order mode gyrotrons are natural sources of high-power OAM millimeter (mm) wave beams. The well-defined OAM of their rotating cavity modes operating at near cutoff frequency has been derived by photonic and electromagnetic wave approaches.

Generation of continuous-wave single-frequency 1.5 W 378 nm radiation by frequency doubling of a Ti:sapphire laser.

PubMed

Cha, Yong-Ho; Ko, Kwang-Hoon; Lim, Gwon; Han, Jae-Min; Park, Hyun-Min; Kim, Taek-Soo; Jeong, Do-Young

2010-03-20

We have generated continuous-wave single-frequency 1.5 W 378 nm radiation by frequency doubling a high-power Ti:sapphire laser in an external enhancement cavity. An LBO crystal that is Brewster-cut and antireflection coated on both ends is used for a long-term stable frequency doubling. By optimizing the input coupler's reflectivity, we could generate 1.5 W 378 nm radiation from a 5 W 756 nm Ti:sapphire laser. According to our knowledge, this is the highest CW frequency-doubled power of a Ti:sapphire laser.

Transmission of 100-MHz-range ultrasound through a fused quartz fiber.

PubMed

Irie, Takasuke; Tagawa, Norio; Tanabe, Masayuki; Moriya, Tadashi; Yoshizawa, Masasumi; Iijima, Takashi; Itoh, Kouichi; Yokoyama, Taku; Kumagai, Hideki; Taniguchi, Nobuyuki

2011-07-01

This paper describes an investigation into direct observation of microscopic images of tissue using a thin acoustic wave guide. First, the characteristics of the ultrasonic wave propagated in a fused quartz fiber were measured using the reflection method in order to study the insertion loss and the frequency shift of the ultrasonic wave transmitted from the transducer. Next, a receiving transducer was placed close to the end of the fiber, and the characteristics of the ultrasonic waves propagated through the acoustic coupling medium were measured using the penetration method in order to study the insertion loss and the frequency-dependent attenuation of the penetrated waves. Finally, a C-mode image was obtained by optimizing the measuring conditions using the results of the above measurements and scanning the ultrasonic beams on a target (coin) in water. A reflected wave with a peak frequency of approximately 220 MHz was obtained from the end of the fiber. The transmitted ultrasonic waves propagated through the acoustic coupling medium were detected with a frequency range of approximately 125-170 MHz, and the maximum detectable distance of the waves was approximately 1.2 mm within the 100-MHz frequency range. Finally, a high-frequency C-mode image of a coin in water was obtained using a tapered fused quartz fiber. The results suggest that it is necessary to improve the signal-to-noise ratio and reduce the insertion loss in the experimental system in order to make it possible to obtain microscopic images of tissue.

Efficient energy transmission and amplification in the cochlea relies on frequency-dependent material properties of the tectorial membrane

NASA Astrophysics Data System (ADS)

Jones, Gareth P.; Lukashkina, Victoria A.; Russell, Ian J.; Elliott, Stephen J.; Lukashkin, Andrei N.

2015-12-01

The remarkable sensitivity, frequency selectivity, and dynamic range of the mammalian cochlea relies on longitudinal transmission of minuscule amounts of energy as passive, pressure-driven, basilar membrane (BM) traveling waves which are actively amplified at frequency-specific locations. Transmission of passive waves through viscous tissue situated in a viscous media is not an easy task. Here we describe mechanical properties of the tectorial membrane (TM) which facilitate this transmission. From mechanical measurements of isolated segments of the TM, we discovered that the stiffness of the TM is reduced when it is mechanically stimulated at physiologically relevant magnitudes and at frequencies below their frequency place in the cochlea. The reduction in stiffness functionally uncouples the TM from the organ of Corti, thereby minimizing energy losses during passive traveling wave propagation. Stiffening and decreased viscosity of the TM at high stimulus frequencies can potentially facilitate active amplification, especially in the high-frequency, basal turn, where energy loss due to internal friction within the TM is less than in the apex. This prediction is confirmed by neural recordings from several frequency regions of the cochlea.

STEREO observations of insitu waves in the vicinity of interplanetary shocks

NASA Astrophysics Data System (ADS)

Golla, T.; MacDowall, R. J.

2017-12-01

We present the high time resolution observations of the in situ waves obtained by the time domain sampler (TDS) of the WAVES experiment on the STEREO spacecraft in the vicinity of typical quasi-perpendicular super-critical interplanetary shocks. We show that often Langmuir waves occur as coherent one dimensional magnetic field aligned wave packets in the upstream regions and persist over large distances. The characteristics of these wave packets are consistent with those of Langmuir solitons formed as a result of oscillatting two stream instability (OTSI). Very intense high frequency waves which are completely different from Langmuir waves occur in the transition regions. These waves occur as very incoherent emissions and exhibit broad fundamental and second harmonic spectral peaks. We identify these waves as electron acoustic waves excited by the electron beams in the transition regions. We also show that very intense low frequency ion sound waves occur in the downstream regions. We discuss the implications of these observations on the theories of (1) strong Langmuir turbulence, (2) beam stabilization, (3) emission mechanisms of solar type II radio bursts, (4) wave-particle interactions responsible for collisionless dissipation, and (5) heating of the downstream plasmas.

On wind-wave-current interactions during the Shoaling Waves Experiment

NASA Astrophysics Data System (ADS)

Zhang, Fei W.; Drennan, William M.; Haus, Brian K.; Graber, Hans C.

2009-01-01

This paper presents a case study of wind-wave-current interaction during the Shoaling Waves Experiment (SHOWEX). Surface current fields off Duck, North Carolina, were measured by a high-frequency Ocean Surface Current Radar (OSCR). Wind, wind stress, and directional wave data were obtained from several Air Sea Interaction Spar (ASIS) buoys moored in the OSCR scanning domain. At several times during the experiment, significant coastal currents entered the experimental area. High horizontal shears at the current edge resulted in the waves at the peak of wind-sea spectra (but not those in the higher-frequency equilibrium range) being shifted away from the mean wind direction. This led to a significant turning of the wind stress vector away from the mean wind direction. The interactions presented here have important applications in radar remote sensing and are discussed in the context of recent radar imaging models of the ocean surface.

Rayleigh-wave mode separation by high-resolution linear radon transform

USGS Publications Warehouse

Luo, Y.; Xia, J.; Miller, R.D.; Xu, Y.; Liu, J.; Liu, Q.

2009-01-01

Multichannel analysis of surface waves (MASW) method is an effective tool for obtaining vertical shear wave profiles from a single non-invasive measurement. One key step of the MASW method is generation of a dispersion image and extraction of a reliable dispersion curve from raw multichannel shot records. Because different Rayleigh-wave modes normally interfere with each other in the time and space domain, it is necessary to perform mode separation and reconstruction to increase the accuracy of phase velocities determined from a dispersion image. In this paper, we demonstrate the effectiveness of high-resolution linear Radon transform (LRT) as a means of separating and reconstructing multimode, dispersive Rayleigh-wave energy. We first introduce high-resolution LRT methods and Rayleigh-wave mode separation using high-resolution LRT. Next, we use synthetic data and a real-world example to demonstrate the effectiveness of Rayleigh-wave mode separation using high-resolution LRT. Our synthetic and real-world results demonstrate that (1) high-resolution LRT successfully separates and reconstructs multimode dispersive Rayleigh-wave energy with high resolution allowing the multimode energy to be more accurately determined. The horizontal resolution of the Rayleigh-wave method can be increased by extraction of dispersion curves from a pair of traces in the mode-separated shot gather and (2) multimode separation and reconstruction expand the usable frequency range of higher mode dispersive energy, which increases the depth of investigation and provides a means for accurately determining cut-off frequencies. ?? 2009 The Authors Journal compilation ?? 2009 RAS.

Constraining the source location of the 30 May 2015 (Mw 7.9) Bonin deep-focus earthquake using seismogram envelopes of high-frequency P waveforms: Occurrence of deep-focus earthquake at the bottom of a subducting slab

NASA Astrophysics Data System (ADS)

Takemura, Shunsuke; Maeda, Takuto; Furumura, Takashi; Obara, Kazushige

2016-05-01

In this study, the source location of the 30 May 2015 (Mw 7.9) deep-focus Bonin earthquake was constrained using P wave seismograms recorded across Japan. We focus on propagation characteristics of high-frequency P wave. Deep-focus intraslab earthquakes typically show spindle-shaped seismogram envelopes with peak delays of several seconds and subsequent long-duration coda waves; however, both the main shock and aftershock of the 2015 Bonin event exhibited pulse-like P wave propagations with high apparent velocities (~12.2 km/s). Such P wave propagation features were reproduced by finite-difference method simulations of seismic wave propagation in the case of slab-bottom source. The pulse-like P wave seismogram envelopes observed from the 2015 Bonin earthquake show that its source was located at the bottom of the Pacific slab at a depth of ~680 km, rather than within its middle or upper regions.

Temporal and Spatial Evolution Characteristics of Disturbance Wave in a Hypersonic Boundary Layer due to Single-Frequency Entropy Disturbance

PubMed Central

Lv, Hongqing; Shi, Jianqiang

2014-01-01

By using a high-order accurate finite difference scheme, direct numerical simulation of hypersonic flow over an 8° half-wedge-angle blunt wedge under freestream single-frequency entropy disturbance is conducted; the generation and the temporal and spatial nonlinear evolution of boundary layer disturbance waves are investigated. Results show that, under the freestream single-frequency entropy disturbance, the entropy state of boundary layer is changed sharply and the disturbance waves within a certain frequency range are induced in the boundary layer. Furthermore, the amplitudes of disturbance waves in the period phase are larger than that in the response phase and ablation phase and the frequency range in the boundary layer in the period phase is narrower than that in these two phases. In addition, the mode competition, dominant mode transformation, and disturbance energy transfer exist among different modes both in temporal and in spatial evolution. The mode competition changes the characteristics of nonlinear evolution of the unstable waves in the boundary layer. The development of the most unstable mode along streamwise relies more on the motivation of disturbance waves in the upstream than that of other modes on this motivation. PMID:25143983

Temporal and spatial evolution characteristics of disturbance wave in a hypersonic boundary layer due to single-frequency entropy disturbance.

PubMed

Wang, Zhenqing; Tang, Xiaojun; Lv, Hongqing; Shi, Jianqiang

2014-01-01

By using a high-order accurate finite difference scheme, direct numerical simulation of hypersonic flow over an 8° half-wedge-angle blunt wedge under freestream single-frequency entropy disturbance is conducted; the generation and the temporal and spatial nonlinear evolution of boundary layer disturbance waves are investigated. Results show that, under the freestream single-frequency entropy disturbance, the entropy state of boundary layer is changed sharply and the disturbance waves within a certain frequency range are induced in the boundary layer. Furthermore, the amplitudes of disturbance waves in the period phase are larger than that in the response phase and ablation phase and the frequency range in the boundary layer in the period phase is narrower than that in these two phases. In addition, the mode competition, dominant mode transformation, and disturbance energy transfer exist among different modes both in temporal and in spatial evolution. The mode competition changes the characteristics of nonlinear evolution of the unstable waves in the boundary layer. The development of the most unstable mode along streamwise relies more on the motivation of disturbance waves in the upstream than that of other modes on this motivation.

Proposed Ultra-High Sensitivity High-Frequency Gravitational Wave Detector

NASA Astrophysics Data System (ADS)

Baker, Robert M. L.; Stephenson, Gary V.; Li, Fangyu

2008-01-01

The paper discusses the proposed improvement of a High-Frequency Relic Gravitational Wave (HFRGW) detector designed by Li, Baker, Fang, Stephenson and Chen in order to greatly improve its sensitivity. The improved detector is inspired by the Laser Interferometer Gravitational Observatory or LIGO, but is sensitive to the high-frequency end of the gravitational-wave spectrum. As described in prior papers it utilizes the Gertsenshtein effect, which introduces the conversion of gravitational waves to electromagnetic (EM) waves in the presence of a static magnetic field. Such a conversion, if it leads to photons moving in a direction perpendicular to the plane of the EM waves and the magnetic field, will allow for ultra-high sensitivity HFRGW detection. The use of sensitive microwave, single photon detectors such as a circuit QED and/or the Rydberg Atom Cavity Detector, or off-the-shelf detectors, could lead to such detection. When the EM-detection photons are focused at the microwave detectors by fractal-membrane reflectors sensitivity is also improved. Noise sources external to the HFRGW detector will be eliminated by placing a tight mosaic of superconducting tiles (e.g., YBCO) and/or fractal membranes on the interior surface of the detector's cryogenic containment vessel in order to provide a perfect Faraday cage. Internal thermal noise will be eliminated by means of a microwave absorbing (or reflecting) interior enclosure shaped to conform to a high-intensity continuous microwave Gaussian beam (GB), will reduce any background photon flux (BPF) noise radiated normal to the GB's axis. Such BPF will be further attenuated by a series of microwave absorbing baffles forming tunnels to the sensitive microwave detectors on each side of the GB and at right angles to the static magnetic field. A HFGW detector of bandwidth of 1 KHz to 10 KHz or less in the GHz band has been selected. It is concluded that the utilization of the new ultra-high-sensitivity microwave detectors, together with the increased microwave power and magnet intensity will allow for a detection of high-frequency gravitational waves (HFGWs) exhibiting amplitudes, A, of the time-varying spacetime strains on the order of 10-30 to 10-34.

Inhibition of Salmonella typhi growth using extremely low frequency electromagnetic (ELF-EM) waves at resonance frequency.

PubMed

Fadel, M A; Mohamed, S A; Abdelbacki, A M; El-Sharkawy, A H

2014-08-01

Typhoid is a serious disease difficult to be treated with conventional drugs. The aim of this study was to demonstrate a new method for the control of Salmonella typhi growth, through the interference with the bioelectric signals generated from the microbe during cell division by extremely low frequency electromagnetic waves (ELF-EMW-ELF-EM) at resonance frequency. Isolated Salmonella typhi was subjected to square amplitude modulated waves (QAMW) with different modulation frequencies from two generators with constant carrier frequency of 10 MHz, amplitude of 10 Vpp, modulating depth ± 2 Vpp and constant field strength of 200 V m(-1) at 37°C. Both the control and exposed samples were incubated at the same conditions during the experiment. The results showed that there was highly significant inhibition effect for Salm. typhi exposed to 0·8 Hz QAMW for a single exposure for 75 min. Dielectric relaxation, TEM and DNA results indicated highly significant changes in the molecular structure of the DNA and cellular membrane resulting from the exposure to the inhibiting EM waves. It was concluded that finding out the inhibiting resonance frequency of ELF-EM waves that deteriorates Salm. typhi growth will be promising method for the treatment of Salm. typhi infection either in vivo or in vitro. This new non-invasive technique for treatment of bacterial infections is of considerable interest for the use in medical and biotechnological applications. © 2014 The Society for Applied Microbiology.

Giant frequency down-conversion of the dancing acoustic bubble

PubMed Central

Deymier, P. A.; Keswani, M.; Jenkins, N.; Tang, C.; Runge, K.

2016-01-01

We have demonstrated experimentally the existence of a giant frequency down-conversion of the translational oscillatory motion of individual submillimeter acoustic bubbles in water in the presence of a high frequency (500 kHz) ultrasonic standing wave. The frequency of the translational oscillations (~170 Hz) is more than three orders of magnitude smaller than that of the driving acoustic wave. We elucidate the mechanism of this very slow oscillation with an analytical model leading to an equation of translational motion of a bubble taking the form of Mathieu’s equation. This equation illuminates the origin of the giant down conversion in frequency as arising from an unstable equilibrium. We also show that bubbles that form chains along the direction of the acoustic standing wave due to radiation interaction forces exhibit also translation oscillations that form a spectral band. This band extends approximately from 130 Hz up to nearly 370 Hz, a frequency range that is still at least three orders of magnitude lower than the frequency of the driving acoustic wave. PMID:27857217

Giant frequency down-conversion of the dancing acoustic bubble

NASA Astrophysics Data System (ADS)

Deymier, P. A.; Keswani, M.; Jenkins, N.; Tang, C.; Runge, K.

2016-11-01

We have demonstrated experimentally the existence of a giant frequency down-conversion of the translational oscillatory motion of individual submillimeter acoustic bubbles in water in the presence of a high frequency (500 kHz) ultrasonic standing wave. The frequency of the translational oscillations (~170 Hz) is more than three orders of magnitude smaller than that of the driving acoustic wave. We elucidate the mechanism of this very slow oscillation with an analytical model leading to an equation of translational motion of a bubble taking the form of Mathieu’s equation. This equation illuminates the origin of the giant down conversion in frequency as arising from an unstable equilibrium. We also show that bubbles that form chains along the direction of the acoustic standing wave due to radiation interaction forces exhibit also translation oscillations that form a spectral band. This band extends approximately from 130 Hz up to nearly 370 Hz, a frequency range that is still at least three orders of magnitude lower than the frequency of the driving acoustic wave.

Microphysics of Waves and Instabilities in the Solar Wind and their Macro Manifestations in the Corona and Interplanetary Space

NASA Technical Reports Server (NTRS)

Habbal, Shadia R.; Gurman, Joseph (Technical Monitor)

2003-01-01

Investigations of the physical processes responsible for the acceleration of the solar wind were pursued with the development of two new solar wind codes: a hybrid code and a 2-D MHD code. Hybrid simulations were performed to investigate the interaction between ions and parallel propagating low frequency ion cyclotron waves in a homogeneous plasma. In a low-beta plasma such as the solar wind plasma in the inner corona, the proton thermal speed is much smaller than the Alfven speed. Vlasov linear theory predicts that protons are not in resonance with low frequency ion cyclotron waves. However, non-linear effect makes it possible that these waves can strongly heat and accelerate protons. This study has important implications for study of the corona and the solar wind. Low frequency ion cyclotron waves or Alfven waves are commonly observed in the solar wind. Until now, it is believed that these waves are not able to heat the solar wind plasma unless some cascading processes transfer the energy of these waves to high frequency part. However, this study shows that these waves may directly heat and accelerate protons non-linearly. This process may play an important role in the coronal heating and the solar wind acceleration, at least in some parameter space.

Initial report of the High Frequency Analyzer (HFA) onboard the ARASE (ERG) Satellite: Observations of the plasmasphere evolution and auroral kilometric radiation from the both hemisphere

NASA Astrophysics Data System (ADS)

Kumamoto, A.; Tsuchiya, F.; Kasahara, Y.; Kasaba, Y.; Kojima, H.; Yagitani, S.; Ishisaka, K.; Imachi, T.; Ozaki, M.; Matsuda, S.; Shoji, M.; Matsuoka, A.; Katoh, Y.; Miyoshi, Y.; Shinohara, I.; Obara, T.

2017-12-01

High Frequency Analyzer (HFA) is a subsystem of the Plasma Wave Experiment (PWE) onboard the ARASE (ERG, Exploration of energization and Radiation in Geospace) spacecraft for observation of radio and plasma waves in a frequency range from 0.01 to 10 MHz. In ARASE mission, HFA is expected to perform the following observations: (1) Upper hybrid resonance (UHR) waves in order to determine the electron number density around the spacecraft. (2) Magnetic field component of the chorus waves in a frequency range from 20 kHz to 100 kHz. (3) Radio and plasma waves excited via wave particle interactions and mode conversion processes in storm-time magnetosphere.HFA is operated in the following three observation modes: EE-mode, EB-mode, and PP-mode. In far-Earth region, HFA is operated in EE-mode. Spectrogram of two orthogonal or right and left-handed components of electric field in perpendicular directions to the spin axis of the spacecraft are obtained. In the near-Earth region, HFA is operated in EB-mode. Spectrogram of one components of electric field in perpendicular direction to the spin plane, and one component of the magnetic field in parallel direction to the spin axis are obtained. In EE and EB-modes, the frequency range from 0.01 to 10 MHz are covered with 480 frequency steps. The time resolution is 8 sec. We also prepared PP mode to measure the locations and structures of the plasmapause at higher resolution. In PP-mode, spectrogram of one electric field component in a frequency range from 0.01-0.4 MHz (PP1) or 0.1-1 MHz (PP2) can be obtained at time resolution of 1 sec.After the successful deployment of the wire antenna and search coils mast and initial checks, we could start routine observations and detect various radio and plasma wave phenomena such as upper hybrid resonance (UHR) waves, electrostatic electron cyclotron harmonic (ESCH) waves, auroral kilometric radiation (AKR), kilometric continuum (KC) and Type-III solar radio bursts. In the presentation, we will report the initial results based on the datasets obtained since January 2017 focusing on the analyses of plasmasphere evolution by semi-automatic identification of UHR frequency, and AKR from the both hemisphere based on polarization measurement.

Modeling electromagnetic ion cyclotron waves in the inner magnetosphere

NASA Astrophysics Data System (ADS)

Gamayunov, Konstantin; Engebretson, Mark; Zhang, Ming; Rassoul, Hamid

The evolution of He+-mode electromagnetic ion cyclotron (EMIC) waves is studied inside the geostationary orbit using our global model of ring current (RC) ions, electric field, plasmasphere, and EMIC waves. In contrast to the approach previously used by Gamayunov et al. [2009], however, we do not use the bounce-averaged wave kinetic equation but instead use a complete, non bounce-averaged, equation to model the evolution of EMIC wave power spectral density, including off-equatorial wave dynamics. The major results of our study can be summarized as follows. (1) The thermal background level for EMIC waves is too low to allow waves to grow up to the observable level during one pass between the “bi-ion latitudes” (the latitudes where the given wave frequency is equal to the O+-He+ bi-ion frequency) in conjugate hemispheres. As a consequence, quasi-field-aligned EMIC waves are not typically produced in the model if the thermal background level is used, but routinely observed in the Earth’s magnetosphere. To overcome this model-observation discrepancy we suggest a nonlinear energy cascade from the lower frequency range of ultra low frequency waves into the frequency range of EMIC wave generation as a possible mechanism supplying the needed level of seed fluctuations that guarantees growth of EMIC waves during one pass through the near equatorial region. The EMIC wave development from a suprathermal background level shows that EMIC waves are quasi-field-aligned near the equator, while they are oblique at high latitudes, and the Poynting flux is predominantly directed away from the near equatorial source region in agreement with observations. (2) An abundance of O+ strongly controls the energy of oblique He+-mode EMIC waves that propagate to the equator after their reflection at “bi-ion latitudes”, and so it controls a fraction of wave energy in the oblique normals. (3) The RC O+ not only causes damping of the He+-mode EMIC waves but also causes wave generation in the region of highly oblique wave normal angles, typically for theta > 82deg, where a growth rate gamma > 0.01 rad/s is frequently observed. The instability is driven by the loss-cone feature in the RC O+ distribution function. (4) The oblique and intense He+-mode EMIC waves generated by RC O+ in the region L ˜ 2-3 may have an implication to the energetic particle loss in the inner radiation belt. Acknowledgments: This paper is based upon work supported by the National Science Foundation under Grant Number AGS-1203516.

Resonant triad in boundary-layer stability. Part 1: Fully nonlinear interaction

NASA Technical Reports Server (NTRS)

Mankbadi, Reda R.

1991-01-01

A first principles theory is developed to study the nonlinear spatial evolution of a near-resonance triad of instability waves in boundary layer transition. This triad consists of a plane wave at fundamental frequency and a pair of symmetrical, oblique waves at the subharmonic frequency. A low frequency, high Reynolds number asymptotic scaling leads to a distinct critical layer where nonlinearity first becomes important; the development of the triad's waves is determined by the critical layer's nonlinear, viscous dynamics. The resulting theory is fully nonlinear in that all nonlinearly generated oscillatory and nonoscillatory components are accounted for. The presence of the plane wave initially causes exponential of exponential growth of the oblique waves. However, the plane wave continues to follow the linear theory, even when the oblique waves' amplitude attains the same order of magnitude as that of the plane wave. A fully interactive stage then comes into effect when the oblique waves exceed a certain level compared to that of the plane wave. The oblique waves react back on the fundamental, slowing its growth rate. The oblique waves' saturation results from their self-interaction - a mechanism that does not require the presence of the plane wave. The oblique waves' saturation level is independent of their initial level, but decreases as the obliqueness angle increases.

Tunable infrared source employing Raman mixing

DOEpatents

Byer, Robert L.; Herbst, Richard L.

1980-01-01

A tunable source of infrared radiation is obtained by irradiating an assemblage of Raman active gaseous atoms or molecules with a high intensity pumping beam of coherent radiation at a pump frequency .omega..sub.p to stimulate the generation of Stokes wave energy at a Stokes frequency .omega..sub.s and to stimulate the Raman resonant mode at the Raman mode frequency .omega..sub.R within the irradiated assemblage where the pump frequency .omega..sub.p minus the Stokes frequency .omega..sub.s is equal to the Raman mode frequency .omega..sub.R. The stimulated assemblage is irradiated with a tunable source of coherent radiation at a frequency .omega..sub.i to generate the output infrared radiation of the frequency .omega..sub.0 which is related to the Raman mode frequency .omega..sub.R and the input wave .omega..sub.i by the relation .omega..sub.0 =.omega..sub.i .+-..omega..sub.R. In one embodiment the interaction between the pump wave energy .omega..sub.p and the tunable input wave energy .omega..sub.i is collinear and the ratio of the phase velocity mismatch factor .DELTA.k to the electric field exponential gain coefficient T is within the range of 0.1 to 5. In another embodiment the pump wave energy .omega..sub.p and the tunable input wave energy .omega..sub.i have velocity vectors k.sub.p and k.sub.i which cross at an angle to each other to compensate for phase velocity mismatches in the medium. In another embodiment, the Stokes wave energy .omega..sub.s is generated by pump energy .omega..sub.p in a first Raman cell and .omega..sub.s, .omega..sub.i and .omega..sub.p are combined in a second Raman mixing cell to produce the output at .omega..sub.i.

A practical double-sided frequency selective surface for millimeter-wave applications

NASA Astrophysics Data System (ADS)

Mohyuddin, Wahab; Woo, Dong Sik; Choi, Hyun Chul; Kim, Kang Wook

2018-02-01

Analysis, design, and implementation of a practical, high-rejection frequency selective surface (FSS) are presented in this paper. An equivalent circuit model is introduced for predicting the frequency response of the FSS. The FSS consists of periodic square loop structures fabricated on both sides of the thin dielectric substrate by using the low-cost chemical etching technique. The proposed FSS possesses band-stop characteristics and is implemented to suppress the 170 GHz signal with attenuation of more than 45 dB with insensitivity to an angle of incident plane wave over 20°. Good agreement is observed among calculated, simulated, and measured results. The proposed FSS filter can be used in various millimeter-wave applications such as the protection of imaging diagnostic systems from high spurious input power.

Recent Observations and Modeling of Narrowband Stimulated Electromagnetic Emissions SEEs at the HAARP Facility

NASA Astrophysics Data System (ADS)

Scales, Wayne; Bernhardt, Paul; McCarrick, Michael; Briczinski, Stanley; Mahmoudian, Alireza; Fu, Haiyang; Ranade Bordikar, Maitrayee; Samimi, Alireza

There has been significant interest in so-called narrowband Stimulated Electromagnetic Emission SEE over the past several years due to recent discoveries at the High Frequency Active Auroral Research Program HAARP facility near Gakone, Alaska. Narrowband SEE (NSEE) has been defined as spectral features in the SEE spectrum typically within 1 kHz of the transmitter (or pump) frequency. SEE is due to nonlinear processes leading to re-radiation at frequencies other than the pump wave frequency during heating the ionospheric plasma with high power HF radio waves. Although NSEE exhibits a richly complex structure, it has now been shown after a substantial number of observations at HAARP, that NSEE can be grouped into two basic classes. The first are those spectral features, associated with Stimulated Brillouin Scatter SBS, which typically occur when the pump frequency is not close to electron gyro-harmonic frequencies. Typically, these spectral features are within roughly 50 Hz of the pump wave frequency where it is to be noted that the O+ ion gyro-frequency is roughly 50 Hz. The second class of spectral features corresponds to the case when the pump wave frequency is typically within roughly 10 kHz of electron gyro-harmonic frequencies. In this case, spectral features ordered by harmonics of ion gyro-frequencies are typically observed, and termed Stimulated Ion Bernstein Scatter SIBS. There is also important parametric behavior on both classes of NSEE depending on the pump wave parameters including the field strength, antenna beam angle, and electron gyro-harmonic number. This presentation will first provide an overview of the recent NSEE experimental observations at HAARP. Both Stimulated Brillouin Scatter SBS and Stimulated Ion Bernstein Scatter SIBS observations will be discussed as well as their relationship to each other. Possible theoretical formulation in terms of parametric decay instabilities will be provided. Computer simulation model results will be presented to provide insight into associated higher order nonlinear effects including particle acceleration and wave-wave processes. Both theory and model results will be put into the context of the experimental observations. Finally, possible applications of NSEE will be pointed out including triggering diagnostics for artificial ionization layer formation, proton precipitation event diagnostics, and electron temperature measurements in the heated volume.

Interference effects in phased beam tracing using exact half-space solutions.

PubMed

Boucher, Matthew A; Pluymers, Bert; Desmet, Wim

2016-12-01

Geometrical acoustics provides a correct solution to the wave equation for rectangular rooms with rigid boundaries and is an accurate approximation at high frequencies with nearly hard walls. When interference effects are important, phased geometrical acoustics is employed in order to account for phase shifts due to propagation and reflection. Error increases, however, with more absorption, complex impedance values, grazing incidence, smaller volumes and lower frequencies. Replacing the plane wave reflection coefficient with a spherical one reduces the error but results in slower convergence. Frequency-dependent stopping criteria are then applied to avoid calculating higher order reflections for frequencies that have already converged. Exact half-space solutions are used to derive two additional spherical wave reflection coefficients: (i) the Sommerfeld integral, consisting of a plane wave decomposition of a point source and (ii) a line of image sources located at complex coordinates. Phased beam tracing using exact half-space solutions agrees well with the finite element method for rectangular rooms with absorbing boundaries, at low frequencies and for rooms with different aspect ratios. Results are accurate even for long source-to-receiver distances. Finally, the crossover frequency between the plane and spherical wave reflection coefficients is discussed.

Unusual whistler with very large dispersion near the magnetopause: Geotail observation and ray-tracing modeling

NASA Astrophysics Data System (ADS)

Nagano, I.; Wu, X.-Y.; Yagitani, S.; Miyamura, K.; Matsumoto, H.

1998-06-01

A case of highly dispersed (~860 s1/2) whistler-like ELF (700-960 Hz) wave was detected with the waveform capture (WFC) receiver aboard the Geotail satellite during a dayside magnetopause skimming. Features of the single event distinguish it from the usual falling tone discrete emissions. By ray-tracing and full-wave calculation, the accessibility of the waves from a ground source of a distorted model magnetosphere were investigated. We propose that a lightning discharge at high latitudes is the most plausible source of the event via a special propagation effect revealed by the ray tracing. We demonstrate that the observed large wavenormal angle with respect to the geomagnetic field, the unusually large level of dispersion, and the lack of the expected nose frequency might be attributable to the frequency-dependent nonducted paths to the satellite. The rare occurrence may partly be caused by the Landau damping by the convecting suprathermal electron beams of several hundred eV. It is also shown that the multiple-hop magnetospherically reflected (MR) whistlers from middle latitudes, though being refracted to higher L shells by the plasmapause, are unable to reach the outer magnetosphere. Interhemisphere ducted propagation is possible for ELF waves along a narrow, modestly (15% or more) enhanced flux tube and shows an upper cutoff frequency governed by the high-latitude minimum-magnetic field ``horns'' regions and the duct enhancement and diameter. A full-wave calculation also implies no lower-frequency cutoff in the upward ionospheric transmission of lightning radiation down to 200 Hz. Because of the complexity of the various effects that influence the propagation from a ground source and the very low occurrence, effective whistler mode waves diagnostics of the highly variable outer magnetosphere are at present beyond our reach.

Excitation of Plasma Waves in Aurora by Electron Beams

NASA Technical Reports Server (NTRS)

daSilva, C. E.; Vinas, A. F.; deAssis, A. S.; deAzevedo, C. A.

1996-01-01

In this paper, we study numerically the excitation of plasma waves by electron beams, in the auroral region above 2000 km of altitude. We have solved the fully kinetic dispersion relation, using numerical method and found the real frequency and the growth rate of the plasma wave modes. We have examined the instability properties of low-frequency waves such as the Electromagnetic Ion Cyclotron (EMIC) wave as well as Lower-Hybrid (LH) wave in the range of high-frequency. In all cases, the source of free energy are electron beams propagating parallel to the geomagnetic field. We present some features of the growth rate modes, when the cold plasma parameters are changed, such as background electrons and ions species (H(+) and O(+)) temperature, density or the electron beam density and/or drift velocity. These results can be used in a test-particle simulation code, to investigate the ion acceleration and their implication in the auroral acceleration processes, by wave-particle interaction.

On the Convection of a Binary Mixture in a Horizontal Layer Under High-frequency Vibrations

NASA Astrophysics Data System (ADS)

Smorodin, B. L.; Ishutov, S. M.; Myznikova, B. I.

2018-02-01

The convective instability and non-linear flows are considered in a horizontal, binary-mixture layer with negative Soret coupling, subjected to the high-frequency vibration whose axis is directed at an arbitrary angle to the layer boundaries. The limiting case of long-wave disturbances is studied using the perturbation method. The influence of the intensity and direction of vibration on the spatially-periodic traveling wave solution is analyzed. It is shown that the shift in the Rayleigh number range, in which the traveling wave regime exists, toward higher values is a response to a horizontal-to-vertical transition in the vibration axis orientation. The characteristics of amplitude- and phase-modulated traveling waves are obtained and discussed.

Rogue waves in a multistable system.

PubMed

Pisarchik, Alexander N; Jaimes-Reátegui, Rider; Sevilla-Escoboza, Ricardo; Huerta-Cuellar, G; Taki, Majid

2011-12-30

Clear evidence of rogue waves in a multistable system is revealed by experiments with an erbium-doped fiber laser driven by harmonic pump modulation. The mechanism for the rogue wave formation lies in the interplay of stochastic processes with multistable deterministic dynamics. Low-frequency noise applied to a diode pump current induces rare jumps to coexisting subharmonic states with high-amplitude pulses perceived as rogue waves. The probability of these events depends on the noise filtered frequency and grows up when the noise amplitude increases. The probability distribution of spike amplitudes confirms the rogue wave character of the observed phenomenon. The results of numerical simulations are in good agreement with experiments.

Wide-range lock-in amplifier

DOEpatents

McNeilly, D.R.

1984-01-01

A lock-in amplifier is provided which allows detection of a signal buried in noise without preprocessing of the input signal. An analog signal multiplier is used to obtain a dc output which is the product of the signal being detected and a high-purity sine wave signal. A reference signal of a known selectable frequency is applied to a sine-wave generator to generate the sine wave of the same frequency. The sine wave is applied to a multiplier through a phase shift arrangement to allow the detection of both amplitude of the detected signal and the phases relative to the reference signal. The multiplier output is filtered by a low-pass filter to eliminate unwanted frequency components from the output signal.

Wide-range lock-in amplifier

DOEpatents

McNeilly, David R.

1985-01-01

A lock-in amplifier is provided which allows detection of a signal buried in noise without preprocessing of the input signal. An analog signal multiplier is used to obtain a dc output which is the product of the signal being detected and a high-purity sine wave signal. A reference signal of a known selectable frequency is applied to a sine-wave generator to generate the sine wave of the same frequency. The sine wave is applied to a multiplier through a phase shift arrangement to allow the detection of both amplitude of the detected signal and the phases relative to the reference signal. The multiplier output is filtered by a low-pass filter to eliminate unwanted frequency components from the output signal.

Electromagnetic wave absorption properties of cement based composites using helical carbon fibers as absorbent

NASA Astrophysics Data System (ADS)

Xie, Shuai; Wang, Jing; Wang, Wufeng; Hou, Guoyan; Li, Bin; Shui, Zhonghe; Ji, Zhijiang

2018-02-01

In order to develop a cement based composites with high electromagnetic (EM) wave absorbing performance, helical carbon fibers (HCFs) were added into the cement matrix as an absorbent. The reflection loss (RL) of the prepared HCFs/cement based composites was studied by arched testing method in the frequency ranges of 1-8 GHz and 8-18 GHz. The results show that the EM wave absorption properties of the cement based composites can be evidently enhanced by the addition of HCFs. The composites with 1.5% HCFs exhibits optimum EM wave absorption performance in the frequency range of 1-8 GHz. However, in 8-18 GHz frequency range, the EM wave absorption performance of the cement composites with 1% HCFs is much better than others. The RL values of the prepared HCFs/cement based composites are less than -5 dB in the whole testing frequency regions, which can be attributed to the strong dielectric loss ability and unique chiral structure of HCFs.

Human Pulse Wave Measurement by MEMS Electret Condenser Microphone

NASA Astrophysics Data System (ADS)

Nomura, Shusaku; Hanasaka, Yasushi; Ishiguro, Tadashi; Ogawa, Hiroshi

A micro Electret Condenser Microphone (ECM) fabricated by Micro Electro Mechanical System (MEMS) technology was employed as a novel apparatus for human pulse wave measurement. Since ECM frequency response characteristic, i.e. sensitivity, logically maintains a constant level at lower than the resonance frequency (stiffness control), the slightest pressure difference at around 1.0Hz generated by human pulse wave is expected to detect by MEMS-ECM. As a result of the verification of frequency response of MEMS-ECM, it was found that -20dB/dec of reduction in the sensitivity around 1.0Hz was engendered by a high input-impedance amplifier, i.e. the field effect transistor (FET), mounted near MEMS chip for amplifying tiny ECM signal. Therefore, MEMS-ECM is assumed to be equivalent with a differentiation circuit at around human pulse frequency. Introducing compensation circuit, human pulse wave was successfully obtained. In addition, the radial and ulnar artery tracing, and pulse wave velocity measurement at forearm were demonstrated; as illustrating a possible application of this micro device.

A Low Cost Traveling Wave Tube for Wireless Communications

NASA Technical Reports Server (NTRS)

Vancil, Bernard Kenneth; Wintucky, Edwin G.; Williams, W. D. (Technical Monitor)

2002-01-01

Demand for high data rate wireless communications is pushing up amplifier power, bandwidth and frequency requirements. Some systems are using vacuum electron devices again because solid-state power amplifiers are not able to efficiently meet the new requirements. The traveling wave tube is the VED of choice because of its excellent broadband capability as well as high power efficiency and frequency. But TWTs are very expensive on a per watt basis below about 200 watts of output power. We propose a new traveling wave tube that utilizes cathode ray tube construction technology and electrostatic focusing. We believe the tube can be built in quantity for under $1,000 each. We discuss several traveling wave tube slow wave circuits that lend themselves to the new construction. We will present modeling results and data on prototype devices.

Generation of Shear Alfvén Waves by Repetitive High Power Microwave Pulses Near the Electron Plasma Frequency - A laboratory study of a ``Virtual Antenna''

NASA Astrophysics Data System (ADS)

Wang, Yuhou; Gekelman, Walter; Pribyl, Patrick; van Compernolle, Bart; Papadopoulos, Konstantinos

2015-11-01

ELF / ULF waves are important in terrestrial radio communications but difficult to launch using ground-based structures due to their enormous wavelengths. In spite of this generation of such waves by field-aligned ionospheric heating modulation was first demonstrated using the HAARP facility. In the future heaters near the equator will be constructed and laboratory experiments on cross-field wave propagation could be key to the program's success. Here we report a detailed laboratory study conducted on the Large Plasma Device (LaPD) at UCLA. In this experiment, ten rapid pulses of high power microwaves (250 kW X-band) near the plasma frequency were launched transverse to the background field, and were modulated at a variable fraction (0.1-1.0) of fci. Along with bulk electron heating and density modification, the microwave pulses generated a population of fast electrons. The field-aligned current carried by the fast electrons acted as an antenna that radiated shear Alfvén waves. It was demonstrated that a controllable arbitrary frequency (f

Accelerated ions and self-excited Alfvén waves at the Earth's bow shock

NASA Astrophysics Data System (ADS)

Berezhko, E. G.; Taneev, S. N.; Trattner, K. J.

2011-07-01

The diffuse energetic ion event and related Alfvén waves upstream of the Earth's bow shock, measured by AMPTE/IRM satellite on 29 September 1984, 06:42-07:22 UT, was studied using a self-consistent quasi-linear theory of ion diffusive shock acceleration and associated Alfvén wave generation. The wave energy density satisfies a wave kinetic equation, and the ion distribution function satisfies the diffusive transport equation. These coupled equations are solved numerically, and calculated ion and wave spectra are compared with observations. It is shown that calculated steady state ion and Alfvén wave spectra are established during the time period of about 1000 s. Alfvén waves excited by accelerated ions are confined within the frequency range (10-2 to 1) Hz, and their spectral peak with the wave amplitude δB ≈ B comparable to the interplanetary magnetic field value B corresponds to the frequency 2 × 10-2 Hz. The high-frequency part of the wave spectrum undergoes absorption by thermal protons. It is shown that the observed ion spectra and the associated Alfvén wave spectra are consistent with the theoretical prediction.

Acoustic Wave Filter Technology-A Review.

PubMed

Ruppel, Clemens C W

2017-09-01

Today, acoustic filters are the filter technology to meet the requirements with respect to performance dictated by the cellular phone standards and their form factor. Around two billion cellular phones are sold every year, and smart phones are of a very high percentage of approximately two-thirds. Smart phones require a very high number of filter functions ranging from the low double-digit range up to almost triple digit numbers in the near future. In the frequency range up to 1 GHz, surface acoustic wave (SAW) filters are almost exclusively employed, while in the higher frequency range, bulk acoustic wave (BAW) and SAW filters are competing for their shares. Prerequisites for the success of acoustic filters were the availability of high-quality substrates, advanced and highly reproducible fabrication technologies, optimum filter techniques, precise simulation software, and advanced design tools that allow the fast and efficient design according to customer specifications. This paper will try to focus on innovations leading to high volume applications of intermediate frequency (IF) and radio frequency (RF) acoustic filters, e.g., TV IF filters, IF filters for cellular phones, and SAW/BAW RF filters for the RF front-end of cellular phones.

Multi-fluid Approach to High-frequency Waves in Plasmas. III. Nonlinear Regime and Plasma Heating

NASA Astrophysics Data System (ADS)

Martínez-Gómez, David; Soler, Roberto; Terradas, Jaume

2018-03-01

The multi-fluid modeling of high-frequency waves in partially ionized plasmas has shown that the behavior of magnetohydrodynamic waves in the linear regime is heavily influenced by the collisional interaction between the different species that form the plasma. Here, we go beyond linear theory and study large-amplitude waves in partially ionized plasmas using a nonlinear multi-fluid code. It is known that in fully ionized plasmas, nonlinear Alfvén waves generate density and pressure perturbations. Those nonlinear effects are more pronounced for standing oscillations than for propagating waves. By means of numerical simulations and analytical approximations, we examine how the collisional interaction between ions and neutrals affects the nonlinear evolution. The friction due to collisions dissipates a fraction of the wave energy, which is transformed into heat and consequently raises the temperature of the plasma. As an application, we investigate frictional heating in a plasma with physical conditions akin to those in a quiescent solar prominence.

Improving the accurate assessment of a layered shear-wave velocity model using joint inversion of the effective Rayleigh wave and Love wave dispersion curves

NASA Astrophysics Data System (ADS)

Yin, X.; Xia, J.; Xu, H.

2016-12-01

Rayleigh and Love waves are two types of surface waves that travel along a free surface.Based on the assumption of horizontal layered homogenous media, Rayleigh-wave phase velocity can be defined as a function of frequency and four groups of earth parameters: P-wave velocity, SV-wave velocity, density and thickness of each layer. Unlike Rayleigh waves, Love-wave phase velocities of a layered homogenous earth model could be calculated using frequency and three groups of earth properties: SH-wave velocity, density, and thickness of each layer. Because the dispersion of Love waves is independent of P-wave velocities, Love-wave dispersion curves are much simpler than Rayleigh wave. The research of joint inversion methods of Rayleigh and Love dispersion curves is necessary. (1) This dissertation adopts the combinations of theoretical analysis and practical applications. In both lateral homogenous media and radial anisotropic media, joint inversion approaches of Rayleigh and Love waves are proposed to improve the accuracy of S-wave velocities.A 10% random white noise and a 20% random white noise are added to the synthetic dispersion curves to check out anti-noise ability of the proposed joint inversion method.Considering the influences of the anomalous layer, Rayleigh and Love waves are insensitive to those layers beneath the high-velocity layer or low-velocity layer and the high-velocity layer itself. Low sensitivities will give rise to high degree of uncertainties of the inverted S-wave velocities of these layers. Considering that sensitivity peaks of Rayleigh and Love waves separate at different frequency ranges, the theoretical analyses have demonstrated that joint inversion of these two types of waves would probably ameliorate the inverted model.The lack of surface-wave (Rayleigh or Love waves) dispersion data may lead to inaccuracy S-wave velocities through the single inversion of Rayleigh or Love waves, so this dissertation presents the joint inversion method of Rayleigh and Love waves which will improve the accuracy of S-wave velocities. Finally, a real-world example is applied to verify the accuracy and stability of the proposed joint inversion method. Keywords: Rayleigh wave; Love wave; Sensitivity analysis; Joint inversion method.

Spread-Spectrum Beamforming and Clutter Filtering for Plane-Wave Color Doppler Imaging.

PubMed

Mansour, Omar; Poepping, Tamie L; Lacefield, James C

2016-07-21

Plane-wave imaging is desirable for its ability to achieve high frame rates, allowing the capture of fast dynamic events and continuous Doppler data. In most implementations of plane-wave imaging, multiple low-resolution images from different plane wave tilt angles are compounded to form a single high-resolution image, thereby reducing the frame rate. Compounding improves the lateral beam profile in the high-resolution image, but it also acts as a low-pass filter in slow time that causes attenuation and aliasing of signals with high Doppler shifts. This paper introduces a spread-spectrum color Doppler imaging method that produces high-resolution images without the use of compounding, thereby eliminating the tradeoff between beam quality, maximum unaliased Doppler frequency, and frame rate. The method uses a long, random sequence of transmit angles rather than a linear sweep of plane wave directions. The random angle sequence randomizes the phase of off-focus (clutter) signals, thereby spreading the clutter power in the Doppler spectrum, while keeping the spectrum of the in-focus signal intact. The ensemble of randomly tilted low-resolution frames also acts as the Doppler ensemble, so it can be much longer than a conventional linear sweep, thereby improving beam formation while also making the slow-time Doppler sampling frequency equal to the pulse repetition frequency. Experiments performed using a carotid artery phantom with constant flow demonstrate that the spread-spectrum method more accurately measures the parabolic flow profile of the vessel and outperforms conventional plane-wave Doppler in both contrast resolution and estimation of high flow velocities. The spread-spectrum method is expected to be valuable for Doppler applications that require measurement of high velocities at high frame rates.

Neurological Diagnostic Tests and Procedures

MedlinePlus

... stem auditory evoked response ) are used to assess high-frequency hearing loss, diagnose any damage to the acoustic ... imaging , also called ultrasound scanning or sonography, uses high-frequency sound waves to obtain images inside the body. ...

Design of a LiNbO(3) ribbon waveguide for efficient difference-frequency generation of terahertz wave in the collinear configuration.

PubMed

Takushima, Y; Shin, S Y; Chung, Y C

2007-10-29

We propose and investigate a ribbon waveguide for difference-frequency generation of terahertz (THz) wave from infrared light sources. The proposed ribbon waveguide is composed of a nonlinear optic crystal and has a thickness less than the wavelength of the THz wave to support the surface-wave mode in the THz region. By utilizing the waveguide dispersion of the surface-wave mode, the phase matching condition between infrared pump, idler and THz waves can be realized in the collinear configuration. Owing to the weak mode confinement of the THz wave, the absorption coefficient can also be reduced. We design the ribbon waveguide which uses LiNbO(3) crystal and discuss the phase-matching condition for DFG of THz wave. Highly efficient THz-wave generation is confirmed by numerical simulations.

Every slow-wave impulse is associated with motor activity of the human stomach.

PubMed

Hocke, Michael; Schöne, Ulrike; Richert, Hendryk; Görnert, Peter; Keller, Jutta; Layer, Peter; Stallmach, Andreas

2009-04-01

Using a newly developed high-resolution three-dimensional magnetic detector system (3D-MAGMA), we observed periodical movements of a small magnetic marker in the human stomach at the typical gastric slow-wave frequency, that is 3 min(-1). Thus we hypothesized that each gastric slow wave induces a motor response that is not strong enough to be detected by conventional methods. Electrogastrographies (EGG, Medtronic, Minneapolis, MN) for measurement of gastric slow waves and 3D-MAGMA (Innovent, Jena, Germany) measurements were simultaneously performed in 21 healthy volunteers (10 men, 40.4+/-13.6 yr; 11 women, 35.8+/-11.6 yr). The 3D-MAGMA system contains 27 highly sensitive magnetic field sensors that are able to locate a magnetic pill inside a human body with an accuracy of +/-5 mm or less in position and +/-2 degrees in orientation at a frequency of 50 Hz. Gastric transit time of the magnetic marker ranged from 19 to 154 min. The mean dominant EGG frequency while the marker was in the stomach was 2.87+/-0.15 cpm. The mean dominant 3D-MAGMA frequency during this interval was nearly identical; that is, 2.85+/-0.15 movements per minute. We observed a strong linear correlation between individual dominant EGG and 3D-MAGMA frequency (R=0.66, P=0.0011). Our findings suggest that each gastric slow wave induces a minute contraction that is too small to be detected by conventional motility investigations but can be recorded by the 3D-MAGMA system. The present slow-wave theory that assumes that the slow wave is a pure electrical signal should be reconsidered.

Lamb wave extraction of dispersion curves in micro/nano-plates using couple stress theories

NASA Astrophysics Data System (ADS)

Ghodrati, Behnam; Yaghootian, Amin; Ghanbar Zadeh, Afshin; Mohammad-Sedighi, Hamid

2018-01-01

In this paper, Lamb wave propagation in a homogeneous and isotropic non-classical micro/nano-plates is investigated. To consider the effect of material microstructure on the wave propagation, three size-dependent models namely indeterminate-, modified- and consistent couple stress theories are used to extract the dispersion equations. In the mentioned theories, a parameter called 'characteristic length' is used to consider the size of material microstructure in the governing equations. To generalize the parametric studies and examine the effect of thickness, propagation wavelength, and characteristic length on the behavior of miniature plate structures, the governing equations are nondimensionalized by defining appropriate dimensionless parameters. Then the dispersion curves for phase and group velocities are plotted in terms of a wide frequency-thickness range to study the lamb waves propagation considering microstructure effects in very high frequencies. According to the illustrated results, it was observed that the couple stress theories in the Cosserat type material predict more rigidity than the classical theory; so that in a plate with constant thickness, by increasing the thickness to characteristic length ratio, the results approach to the classical theory, and by reducing this ratio, wave propagation speed in the plate is significantly increased. In addition, it is demonstrated that for high-frequency Lamb waves, it converges to dispersive Rayleigh wave velocity.

Fault Zone Imaging from Correlations of Aftershock Waveforms

NASA Astrophysics Data System (ADS)

Hillers, Gregor; Campillo, Michel

2018-03-01

We image an active fault zone environment using cross correlations of 154 15 s long 1992 Landers earthquake aftershock seismograms recorded along a line array. A group velocity and phase velocity dispersion analysis of the reconstructed Rayleigh waves and Love waves yields shear wave velocity images of the top 100 m along the 800 m long array that consists of 22 three component stations. Estimates of the position, width, and seismic velocity of a low-velocity zone are in good agreement with the findings of previous fault zone trapped waves studies. Our preferred solution indicates the zone is offset from the surface break to the east, 100-200 m wide, and characterized by a 30% velocity reduction. Imaging in the 2-6 Hz range resolves further a high-velocity body of similar width to the west of the fault break. Symmetry and shape of zero-lag correlation fields or focal spots indicate a frequency and position dependent wavefield composition. At frequencies greater than 4 Hz surface wave propagation dominates, whereas at lower frequencies the correlation field also exhibits signatures of body waves that likely interact with the high-velocity zone. The polarization and late arrival times of coherent wavefronts observed above the low-velocity zone indicate reflections associated with velocity contrasts in the fault zone environment. Our study highlights the utility of the high-frequency correlation wavefield obtained from records of local and regional seismicity. The approach does not depend on knowledge of earthquake source parameters, which suggests the method can return images quickly during aftershock campaigns to guide network updates for optimal coverage of interesting geological features.

Unveiling Extreme Anisotropy in Elastic Structured Media

NASA Astrophysics Data System (ADS)

Lefebvre, G.; Antonakakis, T.; Achaoui, Y.; Craster, R. V.; Guenneau, S.; Sebbah, P.

2017-06-01

Periodic structures can be engineered to exhibit unique properties observed at symmetry points, such as zero group velocity, Dirac cones, and saddle points; identifying these and the nature of the associated modes from a direct reading of the dispersion surfaces is not straightforward, especially in three dimensions or at high frequencies when several dispersion surfaces fold back in the Brillouin zone. A recently proposed asymptotic high-frequency homogenization theory is applied to a challenging time-domain experiment with elastic waves in a pinned metallic plate. The prediction of a narrow high-frequency spectral region where the effective medium tensor dramatically switches from positive definite to indefinite is confirmed experimentally; a small frequency shift of the pulse carrier results in two distinct types of highly anisotropic modes. The underlying effective equation mirrors this behavior with a change in form from elliptic to hyperbolic exemplifying the high degree of wave control available and the importance of a simple and effective predictive model.

Lower Hybrid Frequency Range Waves Generated by Ion Polarization Drift Due to Electromagnetic Ion Cyclotron Waves: Analysis of an Event Observed by the Van Allen Probe B

NASA Technical Reports Server (NTRS)

Khazanov, G. V.; Boardsen, S.; Krivorutsky, E. N.; Engebretson, M. J.; Sibeck, D.; Chen, S.; Breneman, A.

2017-01-01

We analyze a wave event that occurred near noon between 07:03 and 07:08 UT on 23 February 2014 detected by the Van Allen Probes B spacecraft, where waves in the lower hybrid frequency range (LHFR) and electromagnetic ion cyclotron (EMIC) waves are observed to be highly correlated, with Pearson correlation coefficient of approximately 0.86. We assume that the correlation is the result of LHFR wave generation by the ions polarization drift in the electric field of the EMIC waves. To check this assumption the drift velocities of electrons and H+, He+, and O+ ions in the measured EMIC wave electric field were modeled. Then the LHFR wave linear instantaneous growth rates for plasma with these changing drift velocities and different plasma compositions were calculated. The time distribution of these growth rates, their frequency distribution, and the frequency dependence of the ratio of the LHFR wave power spectral density (PSD)parallel and perpendicular to the ambient magnetic eld to the total PSD were found. These characteristics of the growth rates were compared with the corresponding characteristics of the observed LHFR activity. Reasonable agreement between these features and the strong correlation between EMIC and LHFR energy densities support the assumption that the LHFR wave generation can be caused by the ions polarization drift in the electric field of an EMIC wave.

The influence of spatially and temporally high-resolution wind forcing on the power input to near-inertial waves in the ocean

NASA Astrophysics Data System (ADS)

Rimac, A.; Eden, C.; von Storch, J.

2012-12-01

Coexistence of stable stratification, the meridional overturning circulation and meso-scale eddies and their influence on the ocean's circulation still raise complex questions concerning the ocean energetics. Oceanic general circulation is mainly forced by the wind field and deep water tides. Its essential energetics are the conversion of kinetic energy of the winds and tides into oceanic potential and kinetic energy. Energy needed for the circulation is bound to internal wave fields. Direct internal wave generation by the wind at the sea surface is one of the sources of this energy. Previous studies using mixed-layer type of models and low frequency wind forcings (six-hourly and daily) left room for improvement. Using mixed-layer models it is not possible to assess the distribution of near-inertial energy into the deep ocean. Also, coarse temporal resolution of wind forcing strongly underestimates the near-inertial wave energy. To overcome this difficulty we use a high resolution ocean model with high frequency wind forcings. We establish the following model setup: We use the Max Planck Institute Ocean Model (MPIOM) on a tripolar grid with 45km horizontal resolution and 40 vertical levels. We run the model with wind forcings that vary in horizontal (250km versus 40km) and temporal resolution (six versus one-hourly). In our study we answer the following questions: How big is the wind kinetic energy input to the near-inertial waves? Is the kinetic energy of the near-inertial waves enhanced when high-frequency wind forcings are used? If so, by how much and why, due to higher level of temporal wind variability or due to better spatial representation of the near-inertial waves? How big is the total power of near-inertial waves generated by the wind at the surface of the ocean? We run the model for one year. Our model results show that the near-inertial waves are excited both using wind forcings of high and low horizontal and temporal resolution. Near-inertial energy is almost two times higher when we force the model with high frequency wind forcings. The influence on the energy mostly depends on the time difference between two forcing fields while the spatial difference has little influence.

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.

Probing Thermomechanics at the Nanoscale: Impulsively Excited Pseudosurface Acoustic Waves in Hypersonic Phononic Crystals

PubMed Central

2011-01-01

High-frequency surface acoustic waves can be generated by ultrafast laser excitation of nanoscale patterned surfaces. Here we study this phenomenon in the hypersonic frequency limit. By modeling the thermomechanics from first-principles, we calculate the system’s initial heat-driven impulsive response and follow its time evolution. A scheme is introduced to quantitatively access frequencies and lifetimes of the composite system’s excited eigenmodes. A spectral decomposition of the calculated response on the eigemodes of the system reveals asymmetric resonances that result from the coupling between surface and bulk acoustic modes. This finding allows evaluation of impulsively excited pseudosurface acoustic wave frequencies and lifetimes and expands our understanding of the scattering of surface waves in mesoscale metamaterials. The model is successfully benchmarked against time-resolved optical diffraction measurements performed on one-dimensional and two-dimensional surface phononic crystals, probed using light at extreme ultraviolet and near-infrared wavelengths. PMID:21910426

Amplitudes and frequency sweep rates of wave packets of whistler-mode chorus observed by the Cluster spacecraft

NASA Astrophysics Data System (ADS)

Macusova, E.; Santolik, O.; Pickett, J. S.; Gurnett, D. A.; Cornilleau-Wehrlin, N.; Demekhov, A. G.; Titova, E. E.

2013-12-01

Whistler-mode chorus is one of the most intense electromagnetic wave emissions observed in the inner magnetosphere, usually outside the plasmasphere. These waves play an important role in wave-particle interactions. They are usually generated close to the geomagnetic equator in a wide range of L-shells, and they propagate toward larger magnetic latitudes. Whistler-mode chorus is sometimes composed of two frequency bands separated by a gap at one half of the electron cyclotron frequency. At short time scales (on the order of hundreds of milliseconds) chorus consist of different discrete spectral shapes: rising tones, falling tones, constant frequency tones, and hooks. Our survey is based on high time resolution measurements collected by the WBD instrument onboard four Cluster spacecraft. We analyze time intervals containing different types of spectral shapes occurring at different L-shells, and at different latitudes relative to the chorus source region, as it is determined from measurements of the STAFF-SA instrument. Each of these events includes a large number of individual wave packets (between a few hundreds to a few thousands). For each individual wave packet we determine the frequency sweep rate and the average amplitude. Our results confirm previous conclusions of numerical simulations, theoretical predictions, and case studies showing that the amplitude of chorus wave packets increases with an increasing frequency sweep rate. The amplitude also increases as the wave forming chorus propagate away from the equator. The scatter of obtained values of frequency sweep rates and amplitudes is much larger closer to the Earth than at larger radial distances. This work receives EU support through the FP7-Space grant agreement no 284520 for the MAARBLE collaborative research project.

High-speed noncontact acoustic inspection method for civil engineering structure using multitone burst wave

NASA Astrophysics Data System (ADS)

Sugimoto, Tsuneyoshi; Sugimoto, Kazuko; Kosuge, Nobuaki; Utagawa, Noriyuki; Katakura, Kageyoshi

2017-07-01

The noncontact acoustic inspection method focuses on the resonance phenomenon, and the target surface is measured by being vibrated with an airborne sound. It is possible to detect internal defects near the surface layer of a concrete structure from a long distance. However, it requires a fairly long measurement time to achieve the signal-to-noise (S/N) ratio just to find some resonance frequencies. In our method using the conventional waveform “single-tone burst wave”, only one frequency was used for one-sound-wave emission to achieve a high S/N ratio using a laser Doppler vibrometer (LDV) at a safe low power (e.g., He-Ne 1 mW). On the other hand, in terms of the difference in propagation velocity between laser light and sound waves, the waveform that can be used for high-speed measurement was devised using plural frequencies for one-sound-wave emission (“multitone burst wave”). The measurement time at 35 measurement points has been dramatically decreased from 210 to 28 s when using this waveform. Accordingly, 7.5-fold high-speed measurement became possible. By some demonstration experiments, we confirmed the effectiveness of our measurement technique.

Characterization of Acoustic Streaming Beyond 100 MHz

NASA Astrophysics Data System (ADS)

Eisener, J.; Lippert, A.; Nowak, T.; Cairós, C.; Reuter, F.; Mettin, R.

The aim of this study is to investigate acoustic streaming in water at very high ultrasonic frequencies, namely beyond 100 MHz. At such high frequencies, the dissipation length of acoustic waves shrinks considerably, and the acoustic streaming transforms from the well-known Eckart type into a Stuart-Lighthill type: While Eckart streaming is driven by a small momentum transfer along the path of a weakly damped travelling sound wave, Stuart-Lighthill streaming is generated by rather local and strong momentum transfer of a highly damped and therefore rapidly decaying wave. Then the inertia of the induced flow cannot be neglected anymore, and a potentially turbulent jet flow emerges. Here we report on streaming velocity measurements for the case where the sound is completely absorbed within a region much smaller than the generated jet. In contrast to previous work in this frequency range, where mainly surface acoustic wave transducers have been employed, we use piston-type transducers that emit vertically to the transducer surface. The acoustic streaming effects are characterized by ink front tracking and particle tracking velocimetry, and by numerical studies. The results show narrow high-speed jet flows that extend much farther into the liquid than the acoustic field. Velocities of several m/s are observed.

Quasi-Rayleigh waves in butt-welded thick steel plate

NASA Astrophysics Data System (ADS)

Kamas, Tuncay; Giurgiutiu, Victor; Lin, Bin

2015-03-01

This paper discusses theoretical and experimental analyses of weld guided surface acoustic waves (SAW) through the guided wave propagation (GWP) analyses. The GWP analyses have been carried out by utilizing piezoelectric wafer active sensors (PWAS) for in situ structural inspection of a thick steel plate with butt weld as the weld bead is ground flush. Ultrasonic techniques are commonly used for validation of welded structures in many in-situ monitoring applications, e.g. in off-shore structures, in nuclear and pressure vessel industries and in a range of naval applications. PWAS is recently employed in such ultrasonic applications as a resonator as well as a transducer. Quasi-Rayleigh waves a.k.a. SAW can be generated in relatively thick isotropic elastic plate having the same phase velocity as Rayleigh waves whereas Rayleigh waves are a high frequency approximation of the first symmetric (S0) and anti-symmetric (A0) Lamb wave modes. As the frequency becomes very high the S0 and the A0 wave speeds coalesce, and both have the same value. This value is exactly the Rayleigh wave speed and becomes constant along the frequency i.e. Rayleigh waves are non-dispersive guided surface acoustic waves. The study is followed with weld-GWP tests through the pitch-catch method along the butt weld line. The tuning curves of quasi-Rayleigh wave are determined to show the tuning and trapping effect of the weld bead that has higher thickness than the adjacent plates on producing a dominant quasi-Rayleigh wave mode. The significant usage of the weld tuned and guided quasi-Rayleigh wave mode is essentially discussed for the applications in the in-situ inspection of relatively thick structures with butt weld such as naval offshore structures. The paper ends with summary, conclusions and suggestions for future work.

Exploring properties of high-density matter through remnants of neutron-star mergers

NASA Astrophysics Data System (ADS)

Bauswein, Andreas; Stergioulas, Nikolaos; Janka, Hans-Thomas

2016-03-01

Remnants of neutron-star mergers are essentially massive, hot, differentially rotating neutron stars, which are initially strongly oscillating. As such they represent a unique probe for high-density matter because the oscillations are detectable via gravitational-wave measurements and are strongly dependent on the equation of state. The impact of the equation of state for instance is apparent in the frequency of the dominant oscillation mode of the remnant. For a fixed total binary mass a tight relation between the dominant postmerger oscillation frequency and the radii of nonrotating neutron stars exists. Inferring observationally the dominant postmerger frequency thus determines neutron star radii with high accuracy of the order of a few hundred meters. By considering symmetric and asymmetric binaries of the same chirp mass, we show that the knowledge of the binary mass ratio is not critical for this kind of radius measurements. We perform simulations which show that initial intrinsic neutron star rotation is unlikely to affect this method of constraining the high-density equation of state. We also summarize different possibilities about how the postmerger gravitational-wave emission can be employed to deduce the maximum mass of nonrotating neutron stars. We clarify the nature of the three most prominent features of the postmerger gravitational-wave spectrum and argue that the merger remnant can be considered to be a single, isolated, self-gravitating object that can be described by concepts of asteroseismology. We sketch how the consideration of the strength of secondary gravitational-wave peaks leads to a classification scheme of the gravitational-wave emission and postmerger dynamics. The understanding of the different mechanisms shaping the gravitational-wave signal yields a physically motivated analytic model of the gravitational-wave emission, which may form the basis for template-based gravitational-wave data analysis. We explore the observational consequences of a scenario of two families of compact stars including hadronic and quark matter stars. We find that this scenario leaves a distinctive imprint on the postmerger gravitational-wave signal. In particular, a strong discontinuity in the dominant postmerger frequency as function of the total mass will be a strong indication for two families of compact stars.

Influence of the parameters of a high-frequency acoustic wave on the structure, properties, and plastic flow of metal in the zone of a joint of materials welded by ultrasound-assisted explosive welding

NASA Astrophysics Data System (ADS)

Peev, A. P.; Kuz'min, S. V.; Lysak, V. I.; Kuz'min, E. V.; Dorodnikov, A. N.

2017-05-01

The results of an investigation of the influence of the parameters of high-frequency acoustic wave on the structure and properties of the zone of joint of homogeneous metals bonded by explosive welding under the action of ultrasound have been presented. The influence of the frequency and amplitude of ultrasonic vibrations on the structure and properties of the explosively welded joints compared with the samples welded without the application of ultrasound has been established. The action of high-frequency acoustic waves on the metal leads to a reduction in the dynamic yield stress, which changes the properties of the surface layers of the metal and the conditions of the formation of the joint of the colliding plates upon the explosive welding. It has been shown that the changes in the length and amplitude of waves that arise in the weld joint upon the explosive welding with the simultaneous action of ultrasonic vibrations are connected with a decrease in the magnitude of the deforming pulse and time of action of the compressive stresses that exceed the dynamic yield stress beyond the point of contact.

Optimization of VLf/ELF Wave Generation using Beam Painting

NASA Astrophysics Data System (ADS)

Robinson, A.; Moore, R. C.

2017-12-01

A novel optimized beam painting algorithm (OBP) is used to generate high amplitude very low frequency (VLF) and extremely low frequency (ELF) waves in the D-region of the ionosphere above the High-frequency Active Auroral Research Program (HAARP) observatory. The OBP method creates a phased array of sources in the ionosphere by varying the azimuth and zenith angles of the high frequency (HF) transmitter to capitalize on the constructive interference of propagating VLF/ELF waves. OBP generates higher amplitude VLF/ELF signals than any other previously proposed method. From April through June during 2014, OBP was performed at HAARP over 1200 times. We compare the BP generated signals against vertical amplitude modulated transmissions at 50 % duty cycle (V), oblique amplitude modulated transmissions at 15 degrees zenith and 81 degrees azimuth at 50 % duty cycle (O), and geometric (circle-sweep) modulation at 15 degrees off-zenith angle at 1562.5 Hz, 3125 Hz, and 5000 Hz. We present an analysis of the directional dependence of each signal, its polarization, and its dependence on the properties of the different source region elements. We find that BP increases the received signal amplitudes of VLF and ELF waves when compared to V, O, and GM methods over a statistically significant number of trials.

Three-dimensional propagation and absorption of high frequency Gaussian beams in magnetoactive plasmas

NASA Astrophysics Data System (ADS)

Nowak, S.; Orefice, A.

1994-05-01

In today's high frequency systems employed for plasma diagnostics, power heating, and current drive the behavior of the wave beams is appreciably affected by the self-diffraction phenomena due to their narrow collimation. In the present article the three-dimensional propagation of Gaussian beams in inhomogeneous and anisotropic media is analyzed, starting from a properly formulated dispersion relation. Particular attention is paid, in the case of electromagnetic electron cyclotron (EC) waves, to the toroidal geometry characterizing tokamak plasmas, to the power density evolution on the advancing wave fronts, and to the absorption features occurring when a beam crosses an EC resonant layer.

Relations among low ionosphere parameters and high frequency radio wave absorption

NASA Technical Reports Server (NTRS)

Cipriano, J. P.

1973-01-01

Charged particle conductivities measured in the very low ionosphere at White Sands Missile Range, New Mexico, and Wallops Island, Virginia, are compared with atmospheric parameters and high frequency radio wave absorption measurements. Charged particle densities are derived from the conductivity data. Between 33 and 58 km, positive conductivity correlated well with neutral atmospheric temperature, with temperature coefficients as large as 4.6%/deg K. Good correlations were also found between HF radio wave absorption and negative conductivity at altitudes as low as 53 km, indicating that the day-to-day absorption variations were principally due to variations in electron loss rate.

Characteristics of enhanced-mode AlGaN/GaN MIS HEMTs for millimeter wave applications

NASA Astrophysics Data System (ADS)

Lee, Jong-Min; Ahn, Ho-Kyun; Jung, Hyun-Wook; Shin, Min Jeong; Lim, Jong-Won

2017-09-01

In this paper, an enhanced-mode (E-mode) AlGaN/GaN high electron mobility transistor (HEMT) was developed by using 4-inch GaN HEMT process. We designed and fabricated Emode HEMTs and characterized device performance. To estimate the possibility of application for millimeter wave applications, we focused on the high frequency performance and power characteristics. To shift the threshold voltage of HEMTs we applied the Al2O3 insulator to the gate structure and adopted the gate recess technique. To increase the frequency performance the e-beam lithography technique was used to define the 0.15 um gate length. To evaluate the dc and high frequency performance, electrical characterization was performed. The threshold voltage was measured to be positive value by linear extrapolation from the transfer curve. The device leakage current is comparable to that of the depletion mode device. The current gain cut-off frequency and the maximum oscillation frequency of the E-mode device with a total gate width of 150 um were 55 GHz and 168 GHz, respectively. To confirm the power performance for mm-wave applications the load-pull test was performed. The measured power density of 2.32 W/mm was achieved at frequencies of 28 and 30 GHz.

Developments of high frequency and intensity stabilized lasers for space gravitational wave detector DECIGO/B-DECIGO

NASA Astrophysics Data System (ADS)

Suemasa, Aru; Shimo-oku, Ayumi; Nakagawa, Ken'ichi; Musha, Mitsuru

2017-12-01

In Japan, not only the ground-based gravitational wave (GW) detector mission KAGRA but also the space GW detector mission DECIGO (DECi-hertz Interferometer Gravitational wave Observatory) and its milestone mission B-DECIGO have been promoted. The designed strain sensitivity of DECIGO and B-DECIGO are δL/ L < 10-23. Since the GW detector requires high power and highly-stable light source, we have developed the light source with high frequency and intensity stability for DECIGO and B-DECIGO. The frequency of the Yb-doped fiber DFB lasers are stabilized to the iodine saturated absorption at 515 nm, and the intensity of the laser at 1 Hz (observation band) is stabilized by controlling the pump source of an Yb-doped fiber amplifier. The intensity of the laser at 200 kHz (modulation band) is also stabilized using an acousto-optic modulator to improve the frequency stability of the laser. In the consequences, we obtain the frequency stability of δf = 0.4 Hz/√Hz (in-loop) at 1 Hz, and the intensity stability of δI/ I = 1.2 × 10-7/√Hz (out-of-loop) and δI/I = 1.5 × 10-7/√Hz (in-loop) at 1 Hz and 200 kHz, respectively.

High-frequency internal waves and thick bottom mixed layers observed by gliders in the Gulf Stream

NASA Astrophysics Data System (ADS)

Todd, Robert E.

2017-06-01

Autonomous underwater gliders are conducting high-resolution surveys within the Gulf Stream along the U.S. East Coast. Glider surveys reveal two mechanisms by which energy is extracted from the Gulf Stream as it flows over the Blake Plateau, a portion of the outer continental shelf between Florida and North Carolina where bottom depths are less than 1000 m. Internal waves with vertical velocities exceeding 0.1 m s-1 and frequencies just below the local buoyancy frequency are routinely found over the Blake Plateau, particularly near the Charleston Bump, a prominent topographic feature. These waves are likely internal lee waves generated by the subinertial Gulf Stream flow over the irregular bathymetry of the outer continental shelf. Bottom mixed layers with O(100) m thickness are also frequently encountered; these thick bottom mixed layers likely form in the lee of topography due to enhanced turbulence generated by O(1) m s-1 near-bottom flows.

Imaging the 2016 Mw 7.8 Kaikoura, New Zealand, earthquake with teleseismic P waves: A cascading rupture across multiple faults

NASA Astrophysics Data System (ADS)

Zhang, Hao; Koper, Keith D.; Pankow, Kristine; Ge, Zengxi

2017-05-01

The 13 November 2016 Mw 7.8 Kaikoura, New Zealand, earthquake was investigated using teleseismic P waves. Backprojection of high-frequency P waves from two regional arrays shows unilateral rupture of at least two southwest-northeast striking faults with an average rupture speed of 1.4-1.6 km/s and total duration of 100 s. Guided by these backprojection results, 33 globally distributed low-frequency P waves were inverted for a finite fault model (FFM) of slip. The FFM showed evidence of several subevents; however, it lacked significant moment release near the epicenter, where a large burst of high-frequency energy was observed. A local strong-motion network recorded strong shaking near the epicenter; hence, for this earthquake the distribution of backprojection energy is superior to the FFM as a guide of strong shaking. For future large earthquakes that occur in regions without strong-motion networks, initial shaking estimates could benefit from backprojection constraints.

INSPIRE

NASA Technical Reports Server (NTRS)

Taylor, Bill; Pine, Bill

2003-01-01

INSPIRE (Interactive NASA Space Physics Ionosphere Radio Experiment - http://image.gsfc.nasa.gov/poetry/inspire) is a non-profit scientific, educational organization whose objective is to bring the excitement of observing natural and manmade radio waves in the audio region to high school students and others. The project consists of building an audio frequency radio receiver kit, making observations of natural and manmade radio waves and analyzing the data. Students also learn about NASA and our natural environment through the study of lightning, the source of many of the audio frequency waves, the atmosphere, the ionosphere, and the magnetosphere where the waves travel.

Rarefaction shock waves and Hugoniot curve in the presence of free and trapped particles

NASA Astrophysics Data System (ADS)

Niknam, A. R.; Hashemzadeh, M.; Shokri, B.; Rouhani, M. R.

2009-12-01

The effects of the relativistic ponderomotive force and trapped particles in the presence of ponderomotive force on the rarefaction shock waves are investigated. The ponderomotive force alters the electron density distribution. This force and relativistic mass affect the plasma frequency. These physical parameters modify the total pressure and the existence condition of the rarefaction shock wave. Furthermore, the trapping of particles by the high frequency electromagnetic field considerably changes the existence condition of the rarefaction shock wave. The total pressure and Hugoniot curve are obtained by considering the relativistic ponderomotive force and trapped particles.

Imaging of conductivity distributions using audio-frequency electromagnetic data

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

Lee, Ki Ha; Morrison, H.F.

1990-10-01

The objective of this study has been to develop mathematical methods for mapping conductivity distributions between boreholes using low frequency electromagnetic (em) data. In relation to this objective this paper presents two recent developments in high-resolution crosshole em imaging techniques. These are (1) audio-frequency diffusion tomography, and (2) a transform method in which low frequency data is first transformed into a wave-like field. The idea in the second approach is that we can then treat the transformed field using conventional techniques designed for wave field analysis.

Chirped-Pulse Millimeter-Wave Spectroscopy of Rydberg-Rydberg Transitions

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

Prozument, Kirill; Colombo, Anthony P.; Zhou Yan

2011-09-30

Transitions between Rydberg states of Ca atoms, in a pulsed, supersonic atomic beam, are directly detected by chirped-pulse millimeter-wave spectroscopy. Broadband, high-resolution spectra with accurate relative intensities are recorded instantly. Free induction decay (FID) of atoms, polarized by the chirped pulse, at their Rydberg-Rydberg transition frequencies, is heterodyne detected, averaged in the time domain, and Fourier transformed into the frequency domain. Millimeter-wave transient nutations are observed, and the possibility of FID evolving to superradiance is discussed.

Subduction zone guided waves in Northern Chile

NASA Astrophysics Data System (ADS)

Garth, Thomas; Rietbrock, Andreas

2016-04-01

Guided wave dispersion is observed in subduction zones as high frequency energy is retained and delayed by low velocity structure in the subducting slab, while lower frequency energy is able to travel at the faster velocities associated with the surrounding mantle material. As subduction zone guided waves spend longer interacting with the low velocity structure of the slab than any other seismic phase, they have a unique capability to resolve these low velocity structures. In Northern Chile, guided wave arrivals are clearly observed on two stations in the Chilean fore-arc on permanent stations of the IPOC network. High frequency (> 5 Hz) P-wave arrivals are delayed by approximately 2 seconds compared to the low frequency (< 2 Hz) P-wave arrivals. Full waveform finite difference modelling is used to test the low velocity slab structure that cause this P-wave dispersion. The synthetic waveforms produced by these models are compared to the recorded waveforms. Spectrograms are used to compare the relative arrival times of different frequencies, while the velocity spectra is used to constrain the relative amplitude of the arrivals. Constraining the waveform in these two ways means that the full waveform is also matched, and the low pass filtered observed and synthetic waveforms can be compared. A combined misfit between synthetic and observed waveforms is then calculated following Garth & Rietbrock (2014). Based on this misfit criterion we constrain the velocity model by using a grid search approach. Modelling the guided wave arrivals suggest that the observed dispersion cannot be solely accounted for by a single low velocity layer as suggested by previous guided wave studies. Including dipping low velocity normal fault structures in the synthetic model not only accounts for the observed strong P-wave coda, but also produces a clear first motion dispersion. We therefore propose that the lithospheric mantle of the subducting Nazca plate is highly hydrated at intermediate depths by dipping low velocity normal faults. Additionally, we show that the low velocity oceanic crust persists to depths of up to 200 km, well beyond the depth range where the eclogite transition is expected to have occurred. Our results suggest that young subducting lithosphere also has the potential to carry much larger amounts of water to the mantle than has previously been appreciated.

Processing of simple and complex acoustic signals in a tonotopically organized ear

PubMed Central

Hummel, Jennifer; Wolf, Konstantin; Kössl, Manfred; Nowotny, Manuela

2014-01-01

Processing of complex signals in the hearing organ remains poorly understood. This paper aims to contribute to this topic by presenting investigations on the mechanical and neuronal response of the hearing organ of the tropical bushcricket species Mecopoda elongata to simple pure tone signals as well as to the conspecific song as a complex acoustic signal. The high-frequency hearing organ of bushcrickets, the crista acustica (CA), is tonotopically tuned to frequencies between about 4 and 70 kHz. Laser Doppler vibrometer measurements revealed a strong and dominant low-frequency-induced motion of the CA when stimulated with either pure tone or complex stimuli. Consequently, the high-frequency distal area of the CA is more strongly deflected by low-frequency-induced waves than by high-frequency-induced waves. This low-frequency dominance will have strong effects on the processing of complex signals. Therefore, we additionally studied the neuronal response of the CA to native and frequency-manipulated chirps. Again, we found a dominant influence of low-frequency components within the conspecific song, indicating that the mechanical vibration pattern highly determines the neuronal response of the sensory cells. Thus, we conclude that the encoding of communication signals is modulated by ear mechanics. PMID:25339727

The role of stress waves in thoracic visceral injury from blast loading: modification of stress transmission by foams and high-density materials.

PubMed

Cooper, G J; Townend, D J; Cater, S R; Pearce, B P

1991-01-01

Materials have been applied to the thoracic wall of anaesthetised experimental animals exposed to blast overpressure to investigate the coupling of direct stress waves into the thorax and the relative contribution of compressive stress waves and gross thoracic compression to lung injury. The ultimate purpose of the work is to develop effective personal protection from the primary effects of blast overpressure--efficient protection can only be achieved if the injury mechanism is identified and characterized. Foam materials acted as acoustic couplers and resulted in a significant augmentation of the visceral injury; decoupling and elimination of injury were achieved by application of a high acoustic impedance layer on top of the foam. In vitro experiments studying stress wave transmission from air through various layers into an anechoic water chamber showed a significant increase in power transmitted by the foams, principally at high frequencies. Material such as copper or resin bonded Kevlar incorporated as a facing upon the foam achieved substantial decoupling at high frequencies--low frequency transmission was largely unaffected. An acoustic transmission model replicated the coupling of the blast waves into the anechoic water chamber. The studies suggest that direct transmission of stress waves plays a dominant role in lung parenchymal injury from blast loading and that gross thoracic compression is not the primary injury mechanism. Acoustic decoupling principles may therefore be employed to reduce the direct stress coupled into the body and thus reduce the severity of lung injury--the most simple decoupler is a high acoustic impedance material as a facing upon a foam, but decoupling layers may be optimized using acoustic transmission models. Conventional impacts producing high body wall velocities will also lead to stress wave generation and transmission--stress wave effects may dominate the visceral response to the impact with direct compression and shear contributing little to the aetiology of the injury.

Comparative study of ion cyclotron waves at Mars, Venus and Earth

NASA Astrophysics Data System (ADS)

Wei, H. Y.; Russell, C. T.; Zhang, T. L.; Blanco-Cano, X.

2011-08-01

Ion cyclotron waves are generated in the solar wind when it picks up freshly ionized planetary exospheric ions. These waves grow from the free energy of the highly anisotropic distribution of fresh pickup ions, and are observed in the spacecraft frame with left-handed polarization and a wave frequency near the ion's gyrofrequency. At Mars and Venus and in the Earth's polar cusp, the solar wind directly interacts with the planetary exospheres. Ion cyclotron waves with many similar properties are observed in these diverse plasma environments. The ion cyclotron waves at Mars indicate its hydrogen exosphere to be extensive and asymmetric in the direction of the interplanetary electric field. The production of fast neutrals plays an important role in forming an extended exosphere in the shape and size observed. At Venus, the region of exospheric proton cyclotron wave production may be restricted to the magnetosheath. The waves observed in the solar wind at Venus appear to be largely produced by the solar-wind-Venus interaction, with some waves at higher frequencies formed near the Sun and carried outward by the solar wind to Venus. These waves have some similarity to the expected properties of exospherically produced proton pickup waves but are characterized by magnetic connection to the bow shock or by a lack of correlation with local solar wind properties respectively. Any confusion of solar derived waves with exospherically derived ion pickup waves is not an issue at Mars because the solar-produced waves are generally at much higher frequencies than the local pickup waves and the solar waves should be mostly absorbed when convected to Mars distance as the proton cyclotron frequency in the plasma frame approaches the frequency of the solar-produced waves. In the Earth's polar cusp, the wave properties of ion cyclotron waves are quite variable. Spatial gradients in the magnetic field may cause this variation as the background field changes between the regions in which the fast neutrals are produced and where they are re-ionized and picked up. While these waves were discovered early in the magnetospheric exploration, their generation was not understood until after we had observed similar waves in the exospheres of Mars and Venus.

Hybridizing Gravitationl Waveforms of Inspiralling Binary Neutron Star Systems

NASA Astrophysics Data System (ADS)

Cullen, Torrey; LIGO Collaboration

2016-03-01

Gravitational waves are ripples in space and time and were predicted to be produced by astrophysical systems such as binary neutron stars by Albert Einstein. These are key targets for Laser Interferometer and Gravitational Wave Observatory (LIGO), which uses template waveforms to find weak signals. The simplified template models are known to break down at high frequency, so I wrote code that constructs hybrid waveforms from numerical simulations to accurately cover a large range of frequencies. These hybrid waveforms use Post Newtonian template models at low frequencies and numerical data from simulations at high frequencies. They are constructed by reading in existing Post Newtonian models with the same masses as simulated stars, reading in the numerical data from simulations, and finding the ideal frequency and alignment to ``stitch'' these waveforms together.

Self-adaptive method for high-frequency dispersion curve determination

USDA-ARS?s Scientific Manuscript database

When high-frequency (from 50 to 500 Hz) MASW is conducted to explore soil profile in the vadose zone, existing rules for selecting near offset and receiver spread length cannot satisfy the requirements of planar and dominant Rayleigh waves for all frequencies and will inevitably introduce near and f...

Success of spiral wave unpinning from heterogeneity in a cardiac tissue depends on its boundary conditions

NASA Astrophysics Data System (ADS)

Kachalov, V. N.; Tsvelaya, V. A.; Kudryashova, N. N.; Agladze, K. I.

2017-11-01

The mechanism of the low voltage defibrillation is based on the drift of the spiral wave induced by a high frequency wave train. In the process, it is first necessary to unpin the wave from the stabilizing obstacle. We study the conditions of unpinning of a rotating wave anchored to the defect by posing the main accent on the boundary conditions of it. The computer simulations performed using the Korhonen model showed that the fluxes through the border of the defect in the cardiac tissue can significantly modify the excitation pattern, and the working frequency gap for the unpinning of reentry waves could be substantially reduced, making overdrive pacing procedure less effective or practically inapplicable.

Nonlinear equations of motion for Landau resonance interactions with a whistler mode wave

NASA Technical Reports Server (NTRS)

Inan, U. S.; Tkalcevic, S.

1982-01-01

A simple set of equations is presented for the description of the cyclotron averaged motion of Landau resonant particles in a whistler mode wave propagating at an angle to the static magnetic field. A comparison is conducted of the wave magnetic field and electric field effects for the parameters of the magnetosphere, and the parameter ranges for which the wave magnetic field effects would be negligible are determined. It is shown that the effect of the wave magnetic field can be neglected for low pitch angles, high normal wave angles, and/or high normalized wave frequencies.

Towards a better understanding of high-energy electron pitch-angle scattering by electromagnetic ion cyclotron waves

NASA Astrophysics Data System (ADS)

Vincena, S.; Gekelman, W.; Pribyl, P.; Tang, S., W.,; Papadopoulos, K.

2017-10-01

Shear Alfven waves are a fundamental mode in magnetized plasmas. Propagating near the ion cyclotron frequency, these waves are often termed electromagnetic ion cyclotron (EMIC) waves and can involve multiple ion species. Near the earth, for example, the wave may interact resonantly with oxygen ions at altitudes ranging from 1000 to 2000 km. The waves may either propagate from space towards the earth (possibly involving mode conversion), or be generated by RF transmitters on the ground. These preliminary experiments are motivated by theoretical predictions that such waves can pitch-angle scatter relativistic electrons trapped in the earth's dipole field. EMIC waves are launched in the Large Plasma Device at UCLA's Basic Plasma Science Facility in plasmas with single and multiple ion species into magnetic field gradients where ion cyclotron resonance is satisfied. We report here on the frequency and k-spectra in the critical layer and how they compare with theoretical predictions in computing an effective diffusion coefficient for high-energy electrons. Funding is provided by the NSF, DoE, and AFSOR.

Anomalous high-frequency wave activity flux preceding anomalous changes in the Northern polar jet

NASA Astrophysics Data System (ADS)

Nakamura, Mototaka; Kadota, Minoru; Yamane, Shozo

2010-05-01

Anomalous forcing by quasi-geostrophic (QG) waves has been reported as an important forcing factor in the Northern Annular Mode (NAM) in recent literatures. In order to shed a light on the dynamics of the NAM from a different angle, we have examined anomalous behavior of the winter jets in the upper troposphere and stratosphere by focusing our diagnosis on not the anomalous geopotential height (Z) itself, but on the anomalous change in the Z (dZ) between two successive months and preceding transient QG wave activity flux during the cold season. We calculated EOFs of dZ between two successive months at 150hPa for a 46-year period, from 1958 to 2003, using the monthly mean NCEP reanalysis data. We then formed anomaly composites of changes in Z and the zonal velocity (U), as well as the preceding and following wave activity flux, Z, U, and temperature at various heights, for both positive and negative phases of the first EOF. For the wave forcing fields, we adopted the diagnostic system for the three-dimensional QG transient wave activity flux in the zonally-varying three-dimensional mean flow developed by Plumb (1986) with a slight modification in its application to the data. Our choice of the Plumb86 is based on the fact that the winter mean flow in the Northern Hemisphere is characterized by noticeable zonal asymmetry, and has a symbiotic relationship with waves in the extra-tropics. The Plumb86 flux was calculated for high-frequency (period of 2 to 7 days) and low-frequency (period of 10 to 20 days) waves with the ultra-low-frequency (period of 30 days or longer) flow as the reference state for each time frame of the 6 hourly NCEP reanalysis data from 1958 to 2003. By replacing the mean flow with the ultra-low-frequency flow in the application of the Plumb86 formula, the flux fields were calculated as time series at 6 hour intervals. The time series of the wave activity flux was then averaged for each month. The patterns of composited anomalous dZ and dU clearly show anomalous acceleration or deceleration of U in the polar region, accompanied by anomalies of the opposite sign in the subtropics throughout the troposphere and stratosphere. The anomalies are conspicuously large in the polar stratosphere. The composited anomalous Z and U in the preceding and following months indicate that these large anomalies in dZ and dU occur when the polar troposphere and stratosphere are relaxing back toward the climatology from strongly anomalous states that closely resemble the positive and negative phases of the NAM. In this process of relaxation, the atmosphere actually overshoots the climatology and develops anomalies of the sign opposite to those existed initially. The anomalous wave activity flux exhibit strong signals of anomalous upward (downward) propagation of high-frequency waves in the North Atlantic storm track from the bottom of the atmosphere, penetrating up to the stratosphere, when the polar jet is anomalously strong (weak) in the preceding month. The anomalous horizontal wave activity flux shows anomalous eastward (westward) flux emanating from the North Atlantic storm track when the polar jet is anomalously strong (weak) in the preceding month. These patterns suggest that anomalous high-frequency waves originating from the North Atlantic storm track in the lower troposphere contribute to the destruction of both phases of the NAM. However, the anomalous flux divergence is very noisy everywhere due to the noisiness of the advective horizontal flux, making it difficult to ascertain the role of the high-frequency transients in the destruction of the NAM.

A New Approach for Very Large Broadband Geophysical Monitoring of rock Deformations Into Deep Boreholes: The "High-Pulse Poroelasticity Protocol" (HPPP)

NASA Astrophysics Data System (ADS)

Guglielmi, Y.; Cappa, F.; Virieux, J.; Rutqvist, J.; Tsang, C.

2007-12-01

We present a new approach, called the "High-Pulse Poroelasticity Protocol" (HPPP), for a very large broadband geophysical monitoring of rock deformations into deep boreholes (from 200 m to 1 km depth). The HPPP consists in developing an innovative probe that allows the hydromechanical loading of rocks with synchronous fluid pressure - 3D deformations (translational components along and in the orthogonal plan of the borehole axis, and rotational components along the longitudinal axis) - seismic wave measurements over a broadband of frequencies (from static to dynamic [1-1,000 Hz]). In this protocol, the rock is subjected to a controlled source corresponding to a fast (few seconds) hydraulic pressure pulse (pressure wave) localized into a short injection chamber (from 1 to 3 m) which is isolated between two inflatable packers in a borehole. In the chamber, measurements are done with fibre-optic and acoustic sensors that makes possible to use a wide range of frequencies (1-1,000 Hz) and high accuracy (10-7) sampling of fluid pressure and 3D deformations. When the pressure wave is applied, several poroelastic effects are measured: (i) a static poroelastic response that is linked to the fluid diffusion in phase with mechanical deformation of the porous rock; (ii) a low-frequency slow Biot wave (P2 wave) associated with the motion out of phase of solid and fluid phases; (iii) a high-frequency pressure wave that is generated and converted to seismic waves (P1 and S waves) at the borehole wall. This new approach aims at determining the infinitesimal shear and axial components of the strain tensor within the rock crossed by a borehole. The HPPP also allows studying the relationships between elastic waves propagation and rock hydromechanical properties and state at an intermediate scale (mesoscopic scale), between the laboratory and crustal scales, in a volume of one to a few tens of meters around the borehole. This new approach was designed from previous pulse testing done in a fault zone with a first prototype of the HPPP probe capable of simultaneously measuring changes (with a high frequency [120 Hz] and high accuracy) in fluid pressure (± 1 kPa) and displacement normal to the fault (± 10-7 m). This prototype consisted of a fibre-optic fluid pressure and a fibre-optic normal displacement sensor fixed to the borehole walls by two anchors located on both sides of the fault which was isolated with two packers to create a 0.4 m injection chamber. Results indicated that fiber-optic measurements allow good capturing of all the high-frequency changes during the hydraulic pulse. The method appears useful for accurately measuring time discrepancies between pressure and deformation signals as small as a few milliseconds. Moreover, high-frequency measurement of the fault "pressure-deformation" poroelastic response allows highlighting of a loop-shaped evolution that is not observed in conventional laboratory or in situ experiments. Consequently, the HPPP approach will provide new data with axial and shear components of the strain tensor which will give us additional information for determination of the rock seismic and hydromechanical properties at various depths in the crust. Moreover, the HPPP will be adapted to study seismic and mechanical instability of fault zones under controlled hydraulic loading and localized in a point source.

Numerical study of the generation and propagation of ultralow-frequency waves by artificial ionospheric F region modulation at different latitudes

NASA Astrophysics Data System (ADS)

Xu, Xiang; Zhou, Chen; Shi, Run; Ni, Binbin; Zhao, Zhengyu; Zhang, Yuannong

2016-09-01

Powerful high-frequency (HF) radio waves can be used to efficiently modify the upper-ionospheric plasmas of the F region. The pressure gradient induced by modulated electron heating at ultralow-frequency (ULF) drives a local oscillating diamagnetic ring current source perpendicular to the ambient magnetic field, which can act as an antenna radiating ULF waves. In this paper, utilizing the HF heating model and the model of ULF wave generation and propagation, we investigate the effects of both the background ionospheric profiles at different latitudes in the daytime and nighttime ionosphere and the modulation frequency on the process of the HF modulated heating and the subsequent generation and propagation of artificial ULF waves. Firstly, based on a relation among the radiation efficiency of the ring current source, the size of the spatial distribution of the modulated electron temperature and the wavelength of ULF waves, we discuss the possibility of the effects of the background ionospheric parameters and the modulation frequency. Then the numerical simulations with both models are performed to demonstrate the prediction. Six different background parameters are used in the simulation, and they are from the International Reference Ionosphere (IRI-2012) model and the neutral atmosphere model (NRLMSISE-00), including the High Frequency Active Auroral Research Program (HAARP; 62.39° N, 145.15° W), Wuhan (30.52° N, 114.32° E) and Jicamarca (11.95° S, 76.87° W) at 02:00 and 14:00 LT. A modulation frequency sweep is also used in the simulation. Finally, by analyzing the numerical results, we come to the following conclusions: in the nighttime ionosphere, the size of the spatial distribution of the modulated electron temperature and the ground magnitude of the magnetic field of ULF wave are larger, while the propagation loss due to Joule heating is smaller compared to the daytime ionosphere; the amplitude of the electron temperature oscillation decreases with latitude in the daytime ionosphere, while it increases with latitude in the nighttime ionosphere; both the electron temperature oscillation amplitude and the ground ULF wave magnitude decreases as the modulation frequency increases; when the electron temperature oscillation is fixed as input, the radiation efficiency of the ring current source is higher in the nighttime ionosphere than in the daytime ionosphere.

Fast focus-scanning head in two-photon photoacoustic microscopy with electrically controlled liquid lens

NASA Astrophysics Data System (ADS)

Yamaoka, Yoshihisa; Kimura, Yuka; Harada, Yoshinori; Takamatsu, Tetsuro; Takahashi, Eiji

2018-02-01

Conventional one-photon photoacoustic microscopy (PAM) utilizes high-frequency components of generated photoacoustic waves to improve the depth resolution. However, to obtain optically-high resolution in PAM in the depth direction, the use of high-frequency ultrasonic waves is to be avoided. It is because that the propagation distance is shortened as the frequency of ultrasonic waves becomes high. To overcome this drawback, we have proposed and developed two-photon photoacoustic microscopy (TP-PAM). Two-photon absorption occurs only at the focus point. TPPAM does not need to use the high-frequency components of photoacoustic waves. Thus, TP-PAM can improve the penetration depth while preserving the spatial resolution. However, the image acquisition time of TP-PAM is longer than that of conventional PAM, because TP-PAM needs to scan the laser spot both in the depth and transverse directions to obtain cross-sectional images. In this paper, we have introduced a focus-tunable electrically-controlled liquid lens in TP-PAM. Instead of a mechanical stepping-motor stage, we employed electrically-controlled liquid lens so that the depth of the focus spot can be quickly changed. In our system, the imaging speed of TP-PAM using the liquid lens and one-axis stepping-motor stage was 10 times faster than that using a two-axis stepping-motor stage only. TP-PAM with focus-scanning head consisting of the liquid lens and stepping-motor stage will be a promising method to investigate the inside of living tissues.

[Comparative evaluation of the efficiency of the effect of very high frequency electromagnetic waves on platelet functional activity].

PubMed

Kirichuk, V F; Maĭborodin, A V; Volin, M V; Krenitskiĭ, A P; Tupikin, V D

2001-01-01

A comparative analysis was made of the effect of two kinds of EMI MMD-radiation: EMI MMD-waves, generated by a vehicle "Jav-1 M" (42.2 and 53.5 HHz), and EMI MMD-waves exerting influence with frequencies of molecular spectrum of radiation and nitric oxide absorption (150.176-150.644 HHz), obtained with a specially created generator, with respect to their influence on the functional ability of platelets of unstable angina pectoris patients. It was shown that in vitro EMI MMD-fluctuations with frequencies of molecular spectrum of radiation and nitric oxide absorption exert a stronger inhibiting influence on the functional activity of platelets of unstable angina pectoris patients. Features of the action of various kinds of EMI MMD-effect on the activative-high-speed characteristics of platelet aggregation are shown.

Micro and nano devices in passive millimetre wave imaging systems

NASA Astrophysics Data System (ADS)

Appleby, R.

2013-06-01

The impact of micro and nano technology on millimetre wave imaging from the post war years to the present day is reviewed. In the 1950s whisker contacted diodes in mixers and vacuum tubes were used to realise both radiometers and radars but required considerable skill to realise the performance needed. Development of planar semiconductor devices such as Gunn and Schottky diodes revolutionised mixer performance and provided considerable improvement. The next major breakthrough was high frequency transistors based on gallium arsenide which were initially used at intermediate frequencies but later after further development at millimeter wave frequencies. More recently Monolithic Microwave Integrated circuits(MMICs) offer exceptional performance and the opportunity for innovative design in passive imaging systems. In the future the use of micro and nano technology will continue to drive system performance and we can expect to see integration of antennae, millimetre wave and sub millimetre wave circuits and signal processing.

The Frequency-dependent Damping of Slow Magnetoacoustic Waves in a Sunspot Umbral Atmosphere

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

Prasad, S. Krishna; Jess, D. B.; Doorsselaere, T. Van

High spatial and temporal resolution images of a sunspot, obtained simultaneously in multiple optical and UV wavelengths, are employed to study the propagation and damping characteristics of slow magnetoacoustic waves up to transition region heights. Power spectra are generated from intensity oscillations in sunspot umbra, across multiple atmospheric heights, for frequencies up to a few hundred mHz. It is observed that the power spectra display a power-law dependence over the entire frequency range, with a significant enhancement around 5.5 mHz found for the chromospheric channels. The phase difference spectra reveal a cutoff frequency near 3 mHz, up to which themore » oscillations are evanescent, while those with higher frequencies propagate upward. The power-law index appears to increase with atmospheric height. Also, shorter damping lengths are observed for oscillations with higher frequencies suggesting frequency-dependent damping. Using the relative amplitudes of the 5.5 mHz (3 minute) oscillations, we estimate the energy flux at different heights, which seems to decay gradually from the photosphere, in agreement with recent numerical simulations. Furthermore, a comparison of power spectra across the umbral radius highlights an enhancement of high-frequency waves near the umbral center, which does not seem to be related to magnetic field inclination angle effects.« less

Qualitative numerical studies of the modification of the pitch angle distribution of test particles by alfvènic wave activity

NASA Astrophysics Data System (ADS)

Keilbach, D.; Drews, C.; Berger, L.; Marsch, E.; Wimmer-Schweingruber, R. F.

2017-12-01

Using a test particle approach we have investigated, how an oxygen pickup ion torus velocity distribution is modified by continuous and intermittent alfvènic waves on timescales, where the gyro trajectory of each particle can be traced.We have therefore exposed the test particles to mono frequent waves, which expanded through the whole simulation in time and space. The general behavior of the pitch angle distribution is found to be stationary and a nonlinear function of the wave frequency, amplitude and the initial angle between wave elongation and field-perpendicular particle velocity vector. The figure shows the time-averaged pitch angle distributions as a function of the Doppler shifted wave frequency (where the Doppler shift was calculated with respect to the particles initial velocity) for three different wave amplitudes (labeled in each panel). The background field is chosen to be 5 nT and the 500 test particles were initially distributed on a torus with 120° pitch angle at a solar wind velocity of 450 km/s. Each y-slice of the histogram (which has been normalized to it's respective maximum) represents an individual run of the simulation.The frequency-dependent behavior of the test particles is found to be classifiable into the regimes of very low/high frequencies and frequencies close to first order resonance. We have found, that only in the latter regime the particles interact strongly with the wave, where in the time averaged histograms a branch structure is found, which was identified as a trace of particles co-moving with the wave phase. The magnitude of pitch angle change of these particles is as well as the frequency margin, where the branch structure is found, an increasing function with the wave amplitude.We have also investigated the interaction with mono frequent intermittent waves. Exposed to such waves a torus distribution is scattered in pitch angle space, whereas the pitch angle distribution is broadened systematically over time similar to pitch angle diffusion.The framework of our simulations is a first step toward understanding wave particle interactions at the most basic level and is readily expandable to e.g. the inclusion of multiple wave frequencies, intermittent wave activity, gradients in the background magnetic field or collisions with solar wind particles.

Rayleigh wave nonlinear inversion based on the Firefly algorithm

NASA Astrophysics Data System (ADS)

Zhou, Teng-Fei; Peng, Geng-Xin; Hu, Tian-Yue; Duan, Wen-Sheng; Yao, Feng-Chang; Liu, Yi-Mou

2014-06-01

Rayleigh waves have high amplitude, low frequency, and low velocity, which are treated as strong noise to be attenuated in reflected seismic surveys. This study addresses how to identify useful shear wave velocity profile and stratigraphic information from Rayleigh waves. We choose the Firefly algorithm for inversion of surface waves. The Firefly algorithm, a new type of particle swarm optimization, has the advantages of being robust, highly effective, and allows global searching. This algorithm is feasible and has advantages for use in Rayleigh wave inversion with both synthetic models and field data. The results show that the Firefly algorithm, which is a robust and practical method, can achieve nonlinear inversion of surface waves with high resolution.

High power water load for microwave and millimeter-wave radio frequency sources

DOEpatents

Ives, R. Lawrence; Mizuhara, Yosuke M.; Schumacher, Richard V.; Pendleton, Rand P.

1999-01-01

A high power water load for microwave and millimeter wave radio frequency sources has a front wall including an input port for the application of RF power, a cylindrical dissipation cavity lined with a dissipating material having a thickness which varies with depth, and a rear wall including a rotating reflector for the reflection of wave energy inside the cylindrical cavity. The dissipation cavity includes a water jacket for removal of heat generated by the absorptive material coating the dissipation cavity, and this absorptive material has a thickness which is greater near the front wall than near the rear wall. Waves entering the cavity reflect from the rotating reflector, impinging and reflecting multiple times on the absorptive coating of the dissipation cavity, dissipating equal amounts of power on each internal reflection.

Non-contact feature detection using ultrasonic Lamb waves

DOEpatents

Sinha, Dipen N [Los Alamos, NM

2011-06-28

Apparatus and method for non-contact ultrasonic detection of features on or within the walls of hollow pipes are described. An air-coupled, high-power ultrasonic transducer for generating guided waves in the pipe wall, and a high-sensitivity, air-coupled transducer for detecting these waves, are disposed at a distance apart and at chosen angle with respect to the surface of the pipe, either inside of or outside of the pipe. Measurements may be made in reflection or transmission modes depending on the relative position of the transducers and the pipe. Data are taken by sweeping the frequency of the incident ultrasonic waves, using a tracking narrow-band filter to reduce detected noise, and transforming the frequency domain data into the time domain using fast Fourier transformation, if required.

Multi-Band Multi-Tone Tunable Millimeter-Wave Frequency Synthesizer For Satellite Beacon Transmitter

NASA Technical Reports Server (NTRS)

Simons, Rainee N.; Wintucky, Edwin G.

2016-01-01

This paper presents the design and test results of a multi-band multi-tone tunable millimeter-wave frequency synthesizer, based on a solid-state frequency comb generator. The intended application of the synthesizer is in a satellite beacon transmitter for radio wave propagation studies at K-band (18 to 26.5 GHz), Q-band (37 to 42 GHz), and E-band (71 to 76 GHz). In addition, the architecture for a compact beacon transmitter, which includes the multi-tone synthesizer, polarizer, horn antenna, and power/control electronics, has been investigated for a notional space-to-ground radio wave propagation experiment payload on a small satellite. The above studies would enable the design of robust high throughput multi-Gbps data rate future space-to-ground satellite communication links.

Observation of Bernstein Waves Excited by Newborn Interstellar Pickup Ions in the Solar Wind

NASA Technical Reports Server (NTRS)

Joyce, Colin J.; Smith, Charles W.; Isenberg, Philip A.; Gary, S. Peter; Murphy, Neil; Gray, Perry C.; Burlaga, Leonard F.

2012-01-01

A recent examination of 1.9 s magnetic field data recorded by the Voyager 2 spacecraft in transit to Jupiter revealed several instances of strongly aliased spectra suggestive of unresolved high-frequency magnetic fluctuations at 4.4 AU. A closer examination of these intervals using the highest resolution data available revealed one clear instance of wave activity at spacecraft frame frequencies from 0.2 to 1 Hz. Using various analysis techniques, we have characterized these fluctuations as Bernstein mode waves excited by newborn interstellar pickup ions. We can find no other interpretation or source consistent with the observations, but this interpretation is not without questions. In this paper, we report a detailed analysis of the waves, including their frequency and polarization, that supports our interpretation.

Breathing Bright Solitons in a Bose Einstein Condensate

NASA Astrophysics Data System (ADS)

Chong, Gui-Shu; Hai, Wen-Hua; Xie, Qiong-Tao

2003-12-01

A Bose-Einstein condensate with time varying scattering length in time-dependent harmonic trap is analytically investigated and soliton-like solutions of the Gross-Pitaeviskii equation are obtained to describe single soliton, bisoliton and N-soliton properties of the matter wave. The influences of the geometrical property and modulate frequency of trapping potential on soliton behaviour are discussed. When the trap potential has a very small trap aspect ratio or oscillates with a high frequency, the matter wave preserves its shape nearly like a soliton train in propagation, while the breathing behaviour, which displays the periodic collapse and revival of the matter wave, is found for a relatively large aspect ratio or slow varying potential. Meanwhile mass centre of the matter wave translates and/or oscillates for different trap aspect ratio and trap frequencies.

Mechanics of the Mammalian Cochlea

PubMed Central

Robles, Luis; Ruggero, Mario A.

2013-01-01

In mammals, environmental sounds stimulate the auditory receptor, the cochlea, via vibrations of the stapes, the innermost of the middle ear ossicles. These vibrations produce displacement waves that travel on the elongated and spirally wound basilar membrane (BM). As they travel, waves grow in amplitude, reaching a maximum and then dying out. The location of maximum BM motion is a function of stimulus frequency, with high-frequency waves being localized to the “base” of the cochlea (near the stapes) and low-frequency waves approaching the “apex” of the cochlea. Thus each cochlear site has a characteristic frequency (CF), to which it responds maximally. BM vibrations produce motion of hair cell stereocilia, which gates stereociliar transduction channels leading to the generation of hair cell receptor potentials and the excitation of afferent auditory nerve fibers. At the base of the cochlea, BM motion exhibits a CF-specific and level-dependent compressive nonlinearity such that responses to low-level, near-CF stimuli are sensitive and sharply frequency-tuned and responses to intense stimuli are insensitive and poorly tuned. The high sensitivity and sharp-frequency tuning, as well as compression and other nonlinearities (two-tone suppression and intermodulation distortion), are highly labile, indicating the presence in normal cochleae of a positive feedback from the organ of Corti, the “cochlear amplifier.” This mechanism involves forces generated by the outer hair cells and controlled, directly or indirectly, by their transduction currents. At the apex of the cochlea, nonlinearities appear to be less prominent than at the base, perhaps implying that the cochlear amplifier plays a lesser role in determining apical mechanical responses to sound. Whether at the base or the apex, the properties of BM vibration adequately account for most frequency-specific properties of the responses to sound of auditory nerve fibers. PMID:11427697

Generation of dark and bright spin wave envelope soliton trains through self-modulational instability in magnetic films.

PubMed

Wu, Mingzhong; Kalinikos, Boris A; Patton, Carl E

2004-10-08

The generation of dark spin wave envelope soliton trains from a continuous wave input signal due to spontaneous modulational instability has been observed for the first time. The dark soliton trains were formed from high dispersion dipole-exchange spin waves propagated in a thin yttrium iron garnet film with pinned surface spins at frequencies situated near the dipole gaps in the dipole-exchange spin wave spectrum. Dark and bright soliton trains were generated for one and the same film through placement of the input carrier frequency in regions of negative and positive dispersion, respectively. Two unreported effects in soliton dynamics, hysteresis and period doubling, were also observed.

Frequency mode excitations in two-dimensional Hindmarsh-Rose neural networks

NASA Astrophysics Data System (ADS)

Tabi, Conrad Bertrand; Etémé, Armand Sylvin; Mohamadou, Alidou

2017-05-01

In this work, we explicitly show the existence of two frequency regimes in a two-dimensional Hindmarsh-Rose neural network. Each of the regimes, through the semi-discrete approximation, is shown to be described by a two-dimensional complex Ginzburg-Landau equation. The modulational instability phenomenon for the two regimes is studied, with consideration given to the coupling intensities among neighboring neurons. Analytical solutions are also investigated, along with their propagation in the two frequency regimes. These waves, depending on the coupling strength, are identified as breathers, impulses and trains of soliton-like structures. Although the waves in two regimes appear in some common regions of parameters, some phase differences are noticed and the global dynamics of the system is highly influenced by the values of the coupling terms. For some values of such parameters, the high-frequency regime displays modulated trains of waves, while the low-frequency dynamics keeps the original asymmetric character of action potentials. We argue that in a wide range of pathological situations, strong interactions among neurons can be responsible for some pathological states, including schizophrenia and epilepsy.

Controlling runaway vortex via externally injected high-frequency electromagnetic waves

NASA Astrophysics Data System (ADS)

Guo, Zehua; McDevitt, Chris; Tang, Xianzhu

2017-10-01

One way of mitigating runaway damage of the plasma-facing components in a tokamak fusion reactor is by limiting the runaway electron energy under a few MeV, while not necessarily reducing the runaway current appreciably. Here we describe a physics mechanism by which such momentum space engineering of the runaway distribution can be facilitated by externally injected high-frequency electromagnetic waves such as the whistler waves. The drastic impact that wave-induced scattering can have on the runaway energy distribution is fundamentally the result of its ability to control the runaway vortex in the momentum space. The runaway vortex, which is a local circulation of runaways in momentum space, is the outcome of the competition between Coulomb collisions, synchrotron radiation damping, and runaway acceleration by parallel electric field. By introducing a wave that resonantly interacts with runaways at a particular range of energy that is mildly relativistic, the enhanced scattering would reshape the vortex by cutting off the part that is highly relativistic. The efficiency of resonant scattering accentuates the requirement that the wave amplitude can be small so the power requirement from external wave injection is practical for the mitigation scheme.

Slip-pulse rupture behavior on a 2 meter granite fault

USGS Publications Warehouse

McLaskey, Gregory C.; Kilgore, Brian D.; Beeler, Nicholas M.

2015-01-01

We describe observations of dynamic rupture events that spontaneously arise on meter-scale laboratory earthquake experiments. While low-frequency slip of the granite sample occurs in a relatively uniform and crack-like manner, instruments capable of detecting high frequency motions show that some parts of the fault slip abruptly (velocity >100 mm∙s-1, acceleration >20 km∙s-2) while the majority of the fault slips more slowly. Abruptly slipping regions propagate along the fault at nearly the shear wave speed. We propose that the dramatic reduction in frictional strength implied by this pulse-like rupture behavior has a common mechanism to the weakening reported in high velocity friction experiments performed on rotary machines. The slip pulses can also be identified as migrating sources of high frequency seismic waves. As observations from large earthquakes show similar propagating high frequency sources, the pulses described here may have relevance to the mechanics of larger earthquakes.

Nonlinear Whistler Wave Physics in the Radiation Belts

NASA Astrophysics Data System (ADS)

Crabtree, Chris

2016-10-01

Wave particle interactions between electrons and whistler waves are a dominant mechanism for controlling the dynamics of energetic electrons in the radiation belts. They are responsible for loss, via pitch-angle scattering of electrons into the loss cone, and energization to millions of electron volts. It has previously been theorized that large amplitude waves on the whistler branch may scatter their wave-vector nonlinearly via nonlinear Landau damping leading to important consequences for the global distribution of whistler wave energy density and hence the energetic electrons. It can dramatically reduce the lifetime of energetic electrons in the radiation belts by increasing the pitch angle scattering rate. The fundamental building block of this theory has now been confirmed through laboratory experiments. Here we report on in situ observations of wave electro-magnetic fields from the EMFISIS instrument on board NASA's Van Allen Probes that show the signatures of nonlinear scattering of whistler waves in the inner radiation belts. In the outer radiation belts, whistler mode chorus is believed to be responsible for the energization of electrons from 10s of Kev to MeV energies. Chorus is characterized by bursty large amplitude whistler mode waves with frequencies that change as a function of time on timescales corresponding to their growth. Theories explaining the chirping have been developed for decades based on electron trapping dynamics in a coherent wave. New high time resolution wave data from the Van Allen probes and advanced spectral techniques are revealing that the wave dynamics is highly structured, with sub-elements consisting of multiple chirping waves with discrete frequency hops between sub-elements. Laboratory experiments with energetic electron beams are currently reproducing the complex frequency vs time dynamics of whistler waves and in addition revealing signatures of wave-wave and beat-wave nonlinear wave-particle interactions. These new data suggest that these weak turbulence processes may be playing a role in saturating the nonlinear instability.

Modification of wave propagation and wave travel-time by the presence of magnetic fields in the solar network atmosphere

NASA Astrophysics Data System (ADS)

Nutto, C.; Steiner, O.; Schaffenberger, W.; Roth, M.

2012-02-01

Context. Observations of waves at frequencies above the acoustic cut-off frequency have revealed vanishing wave travel-times in the vicinity of strong magnetic fields. This detection of apparently evanescent waves, instead of the expected propagating waves, has remained a riddle. Aims: We investigate the influence of a strong magnetic field on the propagation of magneto-acoustic waves in the atmosphere of the solar network. We test whether mode conversion effects can account for the shortening in wave travel-times between different heights in the solar atmosphere. Methods: We carry out numerical simulations of the complex magneto-atmosphere representing the solar magnetic network. In the simulation domain, we artificially excite high frequency waves whose wave travel-times between different height levels we then analyze. Results: The simulations demonstrate that the wave travel-time in the solar magneto-atmosphere is strongly influenced by mode conversion. In a layer enclosing the surface sheet defined by the set of points where the Alfvén speed and the sound speed are equal, called the equipartition level, energy is partially transferred from the fast acoustic mode to the fast magnetic mode. Above the equipartition level, the fast magnetic mode is refracted due to the large gradient of the Alfvén speed. The refractive wave path and the increasing phase speed of the fast mode inside the magnetic canopy significantly reduce the wave travel-time, provided that both observing levels are above the equipartition level. Conclusions: Mode conversion and the resulting excitation and propagation of fast magneto-acoustic waves is responsible for the observation of vanishing wave travel-times in the vicinity of strong magnetic fields. In particular, the wave propagation behavior of the fast mode above the equipartition level may mimic evanescent behavior. The present wave propagation experiments provide an explanation of vanishing wave travel-times as observed with multi-line high-cadence instruments. Movies are available in electronic form at http://www.aanda.org

Relationship between delta power and the electrocardiogram-derived cardiopulmonary spectrogram: possible implications for assessing the effectiveness of sleep.

PubMed

Thomas, Robert Joseph; Mietus, Joseph E; Peng, Chung-Kang; Guo, Dan; Gozal, David; Montgomery-Downs, Hawley; Gottlieb, Daniel J; Wang, Cheng-Yen; Goldberger, Ary L

2014-01-01

The physiologic relationship between slow-wave activity (SWA) (0-4 Hz) on the electroencephalogram (EEG) and high-frequency (0.1-0.4 Hz) cardiopulmonary coupling (CPC) derived from electrocardiogram (ECG) sleep spectrograms is not known. Because high-frequency CPC appears to be a biomarker of stable sleep, we tested the hypothesis that that slow-wave EEG power would show a relatively fixed-time relationship to periods of high-frequency CPC. Furthermore, we speculated that this correlation would be independent of conventional nonrapid eye movement (NREM) sleep stages. We analyzed selected datasets from an archived polysomnography (PSG) database, the Sleep Heart Health Study I (SHHS-I). We employed the cross-correlation technique to measure the degree of which 2 signals are correlated as a function of a time lag between them. Correlation analyses between high-frequency CPC and delta power (computed both as absolute and normalized values) from 3150 subjects with an apnea-hypopnea index (AHI) of ≤5 events per hour of sleep were performed. The overall correlation (r) between delta power and high-frequency coupling (HFC) power was 0.40±0.18 (P=.001). Normalized delta power provided improved correlation relative to absolute delta power. Correlations were somewhat reduced in the second half relative to the first half of the night (r=0.45±0.20 vs r=0.34±0.23). Correlations were only affected by age in the eighth decade. There were no sex differences and only small racial or ethnic differences were noted. These results support a tight temporal relationship between slow wave power, both within and outside conventional slow wave sleep periods, and high frequency cardiopulmonary coupling, an ECG-derived biomarker of "stable" sleep. These findings raise mechanistic questions regarding the cross-system integration of neural and cardiopulmonary control during sleep. Copyright © 2013 Elsevier B.V. All rights reserved.

Stability of an ion-ring distribution in a multi-ion component plasma

NASA Astrophysics Data System (ADS)

Mithaiwala, Manish; Rudakov, Leonid; Ganguli, Gurudas

2010-04-01

The stability of a cold ion-ring velocity distribution in a thermal plasma is analyzed. In particular, the effect of plasma temperature and density on the instability is considered. A high ring density (compared to the background plasma) neutralizes the stabilizing effect of the warm background plasma and the ring is unstable to the generation of waves below the lower-hybrid frequency even for a very high temperature plasma. For ring densities lower than the background plasma density, there is a slow instability where the growth rate is less than the background-ion cyclotron frequency and, consequently, the background-ion response is magnetized. This is in addition to the widely discussed fast instability where the wave growth rate exceeds the background-ion cyclotron frequency and hence the background ions are effectively unmagnetized. Thus, even a low density ring is unstable to waves around the lower-hybrid frequency range for any ring speed. This implies that effectively there is no velocity threshold for a sufficiently cold ring.

Dielectric permeability tensor and linear waves in spin-1/2 quantum kinetics with non-trivial equilibrium spin-distribution functions

NASA Astrophysics Data System (ADS)

Andreev, Pavel A.; Kuz'menkov, L. S.

2017-11-01

A consideration of waves propagating parallel to the external magnetic field is presented. The dielectric permeability tensor is derived from the quantum kinetic equations with non-trivial equilibrium spin-distribution functions in the linear approximation on the amplitude of wave perturbations. It is possible to consider the equilibrium spin-distribution functions with nonzero z-projection proportional to the difference of the Fermi steps of electrons with the chosen spin direction, while x- and y-projections are equal to zero. It is called the trivial equilibrium spin-distribution functions. In the general case, x- and y-projections of the spin-distribution functions are nonzero which is called the non-trivial regime. A corresponding equilibrium solution is found in Andreev [Phys. Plasmas 23, 062103 (2016)]. The contribution of the nontrivial part of the spin-distribution function appears in the dielectric permeability tensor in the additive form. It is explicitly found here. A corresponding modification in the dispersion equation for the transverse waves is derived. The contribution of the nontrivial part of the spin-distribution function in the spectrum of transverse waves is calculated numerically. It is found that the term caused by the nontrivial part of the spin-distribution function can be comparable with the classic terms for the relatively small wave vectors and frequencies above the cyclotron frequency. In a majority of regimes, the extra spin caused term dominates over the spin term found earlier, except the small frequency regime, where their contributions in the whistler spectrum are comparable. A decrease of the left-hand circularly polarized wave frequency, an increase of the high-frequency right-hand circularly polarized wave frequency, and a decrease of frequency changing by an increase of frequency at the growth of the wave vector for the whistler are found. A considerable decrease of the spin wave frequency is found either. It results in an increase of module of the negative group velocity of the spin wave. The found dispersion equations are used for obtaining of an effective quantum hydrodynamics reproducing these results. This generalization requires the introduction of the corresponding equation of state for the thermal part of the spin current in the spin evolution equation.

Long-range parametric amplification of THz wave with absorption loss exceeding parametric gain.

PubMed

Wang, Tsong-Dong; Huang, Yen-Chieh; Chuang, Ming-Yun; Lin, Yen-Hou; Lee, Ching-Han; Lin, Yen-Yin; Lin, Fan-Yi; Kitaeva, Galiya Kh

2013-01-28

Optical parametric mixing is a popular scheme to generate an idler wave at THz frequencies, although the THz wave is often absorbing in the nonlinear optical material. It is widely suggested that the useful material length for co-directional parametric mixing with strong THz-wave absorption is comparable to the THz-wave absorption length in the material. Here we show that, even in the limit of the absorption loss exceeding parametric gain, the THz idler wave can grows monotonically from optical parametric amplification over a much longer distance in a nonlinear optical material until pump depletion. The coherent production of the non-absorbing signal wave can assist the growth of the highly absorbing idler wave. We also show that, for the case of an equal input pump and signal in difference frequency generation, the quick saturation of the THz idler wave predicted from a much simplified and yet popular plane-wave model fails when fast diffraction of the THz wave from the co-propagating optical mixing waves is considered.

Highly selective surface-wave resonators for terahertz frequency range formed by metallic Bragg gratings

NASA Astrophysics Data System (ADS)

Ginzburg, N. S.; Malkin, A. M.; Sergeev, A. S.; Fil'chenkov, S. E.; Zaslavsky, V. Yu.

2018-04-01

In the frame of the quasi-optical approach we solve the diffraction problem and describe surface modes confined at a metallic plate with a shallow grating of finite length. We prove that such planar grating can form a highly selective surface-wave Bragg resonator. For a given material conductivity and grating length, we find the optimum corrugation depth that provides the maximum value of Q factor. These results are applicable for developing resonators for terahertz frequency bands.

Anomalous resistivity due to low-frequency turbulence. [of collisionless plasma with limited acceleration of high velocity runaway electrons

NASA Technical Reports Server (NTRS)

Rowland, H. L.; Palmadesso, P. J.

1983-01-01

Large amplitude ion cyclotron waves have been observed on auroral field lines. In the presence of an electric field parallel to the ambient magnetic field these waves prevent the acceleration of the bulk of the plasma electrons leading to the formation of a runaway tail. It is shown that low-frequency turbulence can also limit the acceleration of high-velocity runaway electrons via pitch angle scattering at the anomalous Doppler resonance.

Spectral decomposition of internal gravity wave sea surface height in global models

NASA Astrophysics Data System (ADS)

Savage, Anna C.; Arbic, Brian K.; Alford, Matthew H.; Ansong, Joseph K.; Farrar, J. Thomas; Menemenlis, Dimitris; O'Rourke, Amanda K.; Richman, James G.; Shriver, Jay F.; Voet, Gunnar; Wallcraft, Alan J.; Zamudio, Luis

2017-10-01

Two global ocean models ranging in horizontal resolution from 1/12° to 1/48° are used to study the space and time scales of sea surface height (SSH) signals associated with internal gravity waves (IGWs). Frequency-horizontal wavenumber SSH spectral densities are computed over seven regions of the world ocean from two simulations of the HYbrid Coordinate Ocean Model (HYCOM) and three simulations of the Massachusetts Institute of Technology general circulation model (MITgcm). High wavenumber, high-frequency SSH variance follows the predicted IGW linear dispersion curves. The realism of high-frequency motions (>0.87 cpd) in the models is tested through comparison of the frequency spectral density of dynamic height variance computed from the highest-resolution runs of each model (1/25° HYCOM and 1/48° MITgcm) with dynamic height variance frequency spectral density computed from nine in situ profiling instruments. These high-frequency motions are of particular interest because of their contributions to the small-scale SSH variability that will be observed on a global scale in the upcoming Surface Water and Ocean Topography (SWOT) satellite altimetry mission. The variance at supertidal frequencies can be comparable to the tidal and low-frequency variance for high wavenumbers (length scales smaller than ˜50 km), especially in the higher-resolution simulations. In the highest-resolution simulations, the high-frequency variance can be greater than the low-frequency variance at these scales.

Application of Excitation from Multiple Locations on a Simplified High-Lift System

NASA Technical Reports Server (NTRS)

Melton, LaTunia Pack; Yao, Chung-Sheng; Seifert, Avi

2004-01-01

A series of active flow control experiments were recently conducted on a simplified high-lift system. The purpose of the experiments was to explore the prospects of eliminating all but simply hinged leading and trailing edge flaps, while controlling separation on the supercritical airfoil using multiple periodic excitation slots. Excitation was provided by three. independently controlled, self-contained, piezoelectric actuators. Low frequency excitation was generated through amplitude modulation of the high frequency carrier wave, the actuators' resonant frequencies. It was demonstrated, for the first time, that pulsed modulated signal from two neighboring slots interact favorably to increase lift. Phase sensitivity at the low frequency was measured, even though the excitation was synthesized from the high-frequency carrier wave. The measurements were performed at low Reynolds numbers and included mean and unsteady surface pressures, surface hot-films, wake pressures and particle image velocimetry. A modest (6%) increase in maximum lift (compared to the optimal baseline) was obtained due t o the activation of two of the three actuators.

Millimeter wave propagation measurements using the ATS 5 satellite

NASA Technical Reports Server (NTRS)

Ippolito, L. J.

1972-01-01

The ATS 5 millimeter wave propagation experiment determines long- and short-term attenuation statistics of operational millimeter wavelength earthspace links as functions of defined meteorological conditions. A preliminary analysis of results with 15 GHz downlink and 32 GHz uplink frequency bands indicates that both frequency bands exhibit an excellent potential for utilization in reliable high data rate earth-space communications systems.

Non-linear Evolution of Velocity Ring Distributions: Generation of Whistler Waves

NASA Astrophysics Data System (ADS)

Mithaiwala, M.; Rudakov, L.; Ganguli, G.

2010-12-01

Although it is typically believed that an ion ring velocity distribution has a stability threshold, we find that they are universally unstable. This can substantially impact the understanding of dynamics in both laboratory and space plasmas. A high ring density neutralizes the stabilizing effect of ion Landau damping in a warm plasma and the ring is unstable to the generation of waves below the lower hybrid frequency- even for a very high temperature plasma. For ring densities lower than the background plasma density there is a slow instability with growth rate less than the background ion cyclotron frequency and consequently the background ion response is magnetized. This is in addition to the widely discussed fast instability where the wave growth rate exceeds the background ion cyclotron frequency and hence the background ions are effectively unmagnetized. Thus, even a low density ring is unstable to waves around the lower hybrid frequency range for any ring speed. This implies that effectively there is no velocity threshold for a sufficiently cold ring. The importance of these conclusions on the nonlinear evolution of space plasmas, in particular to solar wind-comet interaction, post-magnetospheric storm conditions, and chemical release experiments in the ionosphere will be discussed.

Kinetic scale structure of low-frequency waves and fluctuations

NASA Astrophysics Data System (ADS)

Lopez Herrera, R. A.; Figueroa-Vinas, A.; Araneda, J. A.; Yoon, P. H.

2017-12-01

The dissipation of solar wind turbulence at kinetic scales is believed to be important for heating the corona and accelerating the wind. Linear Vlasov kinetic theory is a useful tool in identifying various wave modes, including kinetic Alfvén, fast magnetosonic/whistler, ion-acoustic (or kinetic slow mode), and their possible roles in the dissipation. However, kinetic mode structure near the vicinity of ion cyclotron modes is not clearly understood. The present poster aims to further elucidate the structure of these low-frequency waves by introducing discrete particle effects through hybrid simulations and Klimontovich formalism of spontaneous emission theory. The theory and simulation of spontaneously emitted low-frequency fluctuations are employed to identify and distinguish the detailed mode structures associated with ion Bernstein versus quasi modes. The spontaneous emission theory and simulation also confirm the findings of Vlasov theory in that the kinetic Alfvén wave can be defined over a wide range of frequencies, including the proton cyclotron frequency and its harmonics, especially for high beta plasmas. This implies that these low-frequency modes may play predominant roles even in the fully kinetic description of kinetic scale turbulence and dissipation despite the fact that cyclotron harmonic and Bernstein modes may also play important roles in wave-particle interactions.

Dynamic interaction of twin vertically overlapping lined tunnels in an elastic half space subjected to incident plane waves

NASA Astrophysics Data System (ADS)

Liu, Zhongxian; Wang, Yirui; Liang, Jianwen

2016-06-01

The scattering of plane harmonic P and SV waves by a pair of vertically overlapping lined tunnels buried in an elastic half space is solved using a semi-analytic indirect boundary integration equation method. Then the effect of the distance between the two tunnels, the stiffness and density of the lining material, and the incident frequency on the seismic response of the tunnels is investigated. Numerical results demonstrate that the dynamic interaction between the twin tunnels cannot be ignored and the lower tunnel has a significant shielding effect on the upper tunnel for high-frequency incident waves, resulting in great decrease of the dynamic hoop stress in the upper tunnel; for the low-frequency incident waves, in contrast, the lower tunnel can lead to amplification effect on the upper tunnel. It also reveals that the frequency-spectrum characteristics of dynamic stress of the lower tunnel are significantly different from those of the upper tunnel. In addition, for incident P waves in low-frequency region, the soft lining tunnels have significant amplification effect on the surface displacement amplitude, which is slightly larger than that of the corresponding single tunnel.

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.

A hybrid single-end-access MZI and Φ-OTDR vibration sensing system with high frequency response

NASA Astrophysics Data System (ADS)

Zhang, Yixin; Xia, Lan; Cao, Chunqi; Sun, Zhenhong; Li, Yanting; Zhang, Xuping

2017-01-01

A hybrid single-end-access Mach-Zehnder interferometer (MZI) and phase sensitive OTDR (Φ-OTDR) vibration sensing system is proposed and demonstrated experimentally. In our system, the narrow optical pulses and the continuous wave are injected into the fiber through the front end of the fiber at the same time. And at the rear end of the fiber, a frequency-shift-mirror (FSM) is designed to back propagate the continuous wave modulated by the external vibration. Thus the Rayleigh backscattering signals (RBS) and the back propagated continuous wave interfere with the reference light at the same end of the sensing fiber and a single-end-access configuration is achieved. The RBS can be successfully separated from the interference signal (IS) through digital signal process due to their different intermediate frequency based on frequency division multiplexing technique. There is no influence between these two schemes. The experimental results show 10 m spatial resolution and up to 1.2 MHz frequency response along a 6.35 km long fiber. This newly designed single-end-access setup can achieve vibration events locating and high frequency events response, which can be widely used in health monitoring for civil infrastructures and transportation.

A Census of Plasma Waves and Structures Associated With an Injection Front in the Inner Magnetosphere

NASA Astrophysics Data System (ADS)

Malaspina, David M.; Ukhorskiy, Aleksandr; Chu, Xiangning; Wygant, John

2018-04-01

Now that observations have conclusively established that the inner magnetosphere is abundantly populated with kinetic electric field structures and nonlinear waves, attention has turned to quantifying the ability of these structures and waves to scatter and accelerate inner magnetospheric plasma populations. A necessary step in that quantification is determining the distribution of observed structure and wave properties (e.g., occurrence rates, amplitudes, and spatial scales). Kinetic structures and nonlinear waves have broadband signatures in frequency space, and consequently, high-resolution time domain electric and magnetic field data are required to uniquely identify such structures and waves as well as determine their properties. However, most high-resolution fields data are collected with a strong bias toward high-amplitude signals in a preselected frequency range, strongly biasing observations of structure and wave properties. In this study, an ˜45 min unbroken interval of 16,384 samples/s field burst data, encompassing an electron injection event, is examined. This data set enables an unbiased census of the kinetic structures and nonlinear waves driven by this electron injection, as well as determination of their "typical" properties. It is found that the properties determined using this unbiased burst data are considerably different than those inferred from amplitude-biased burst data, with significant implications for wave-particle interactions due to kinetic structures and nonlinear waves in the inner magnetosphere.

Interaction between spiral and paced waves in cardiac tissue

PubMed Central

Agladze, Konstantin; Kay, Matthew W.; Krinsky, Valentin; Sarvazyan, Narine

2010-01-01

For prevention of lethal arrhythmias, patients at risk receive implantable cardioverter-defibrillators, which use high-frequency antitachycardia pacing (ATP) to convert tachycardias to a normal rhythm. One of the suggested ATP mechanisms involves paced-induced drift of rotating waves followed by their collision with the boundary of excitable tissue. This study provides direct experimental evidence of this mechanism. In monolayers of neonatal rat cardiomyocytes in which rotating waves of activity were initiated by premature stimuli, we used the Ca2+-sensitive indicator fluo 4 to observe propagating wave patterns. The interaction of the spiral tip with a paced wave was then monitored at a high spatial resolution. In the course of the experiments, we observed spiral wave pinning to local heterogeneities within the myocyte layer. High-frequency pacing led, in a majority of cases, to successful termination of spiral activity. Our data show that 1) stable spiral waves in cardiac monolayers tend to be pinned to local heterogeneities or areas of altered conduction, 2) overdrive pacing can shift a rotating wave from its original site, and 3) the wave break, formed as a result of interaction between the spiral tip and a paced wave front, moves by a paced-induced drift mechanism to an area where it may become unstable or collide with a boundary. The data were complemented by numerical simulations, which was used to further analyze experimentally observed behavior. PMID:17384124

On possible plume-guided seismic waves

USGS Publications Warehouse

Julian, B.R.; Evans, J.R.

2010-01-01

Hypothetical thermal plumes in the Earth's mantle are expected to have low seismic-wave speeds and thus would support the propagation of guided elastic waves analogous to fault-zone guided seismic waves, fiber-optic waves, and acoustic waves in the oceanic SOund Fixing And Ranging channel. Plume-guided waves would be insensitive to geometric complexities in the wave guide, and their dispersion would make them distinctive on seismograms and would provide information about wave-guide structure that would complement seismic tomography. Detecting such waves would constitute strong evidence of a new kind for the existence of plumes. A cylindrical channel embedded in an infinite medium supports two classes of axially symmetric elastic-wave modes, torsional and longitudinal-radial. Torsional modes have rectilinear particle motion tangent to the cylinder surface. Longitudinal-radial modes have elliptical particle motion in planes that include the cylinder axis, with retrograde motion near the axis. The direction of elliptical particle motion reverses with distance from the axis: once for the fundamental mode, twice for the first overtone, and so on. Each mode exists only above its cut-off frequency, where the phase and group speeds equal the shear-wave speed in the infinite medium. At high frequencies, both speeds approach the shear-wave speed in the channel. All modes have minima in their group speeds, which produce Airy phases on seismograms. For shear wave-speed contrasts of a few percent, thought to be realistic for thermal plumes in the Earth, the largest signals are inversely dispersed and have dominant frequencies of about 0.1-1 Hz and durations of 15-30 sec. There are at least two possible sources of observable plume waves: (1) the intersection of mantle plumes with high-amplitude core-phase caustics in the deep mantle; and (2) ScS-like reflection at the core-mantle boundary of downward-propagating guided waves. The widespread recent deployment of broadband seismometers makes searching for these waves possible.

High-frequency Oscillations in the Atmosphere above a Sunspot Umbra

NASA Astrophysics Data System (ADS)

Wang, Feng; Deng, Hui; Li, Bo; Feng, Song; Bai, Xianyong; Deng, Linhua; Yang, Yunfei; Xue, Zhike; Wang, Rui

2018-03-01

We use high spatial and temporal resolution observations, simultaneously obtained with the New Vacuum Solar Telescope and Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, to investigate the high-frequency oscillations above a sunspot umbra. A novel time–frequency analysis method, namely, the synchrosqueezing transform (SST), is employed to represent their power spectra and to reconstruct the high-frequency signals at different solar atmospheric layers. A validation study with synthetic signals demonstrates that SST is capable of resolving weak signals even when their strength is comparable to the high-frequency noise. The power spectra, obtained from both SST and the Fourier transform, of the entire umbral region indicate that there are significant enhancements between 10 and 14 mHz (labeled as 12 mHz) at different atmospheric layers. Analyzing the spectrum of a photospheric region far away from the umbra demonstrates that this 12 mHz component exists only inside the umbra. The animation based on the reconstructed 12 mHz component in AIA 171 Å illustrates that an intermittently propagating wave first emerges near the footpoints of coronal fan structures, and then propagates outward along the structures. A time–distance diagram, coupled with a subsonic wave speed (∼49 km s‑1), highlights the fact that these coronal perturbations are best described as upwardly propagating magnetoacoustic slow waves. Thus, we first reveal the high-frequency oscillations with a period around one minute in imaging observations at different height above an umbra, and these oscillations seem to be related to the umbral perturbations in the photosphere.

A High Efficiency, Miniaturized Ka Band Traveling Wave Tube Based on a Novel Finned Ladder RF Circuit Design

NASA Technical Reports Server (NTRS)

Wintucky, E. G.; Wilson, J. D.; Vaden, K. R.; Force, D. A.; Freeman, J. C.; Lesny, G. G.; Kory, C. L.; Chevalier, C. T.; Ebihara, B.; Dayton, J. A.;

Initial Steps Toward Next-Generation, Waveform-Based, Three-Dimensional Models and Metrics to Improve Nuclear Explosion Monitoring in the Middle East

DTIC Science & Technology

2008-09-30

propagation effects by splitting apart the longer period surface waves from the shorter period, depth-sensitive Pnl waves. Problematic, or high-error... Pnl waves. Problematic, or high-error, stations and paths were further analyzed to identify systematic errors with unknown sensor responses and...frequency Pnl components and slower, longer period surface waves. All cut windows are fit simultaneously, allowing equal weighting of phases that may be

Experimental Validation of a Theory for a Variable Resonant Frequency Wave Energy Converter (VRFWEC)

NASA Astrophysics Data System (ADS)

Park, Minok; Virey, Louis; Chen, Zhongfei; Mäkiharju, Simo

2016-11-01

A point absorber wave energy converter designed to adapt to changes in wave frequency and be highly resilient to harsh conditions, was tested in a wave tank for wave periods from 0.8 s to 2.5 s. The VRFWEC consists of a closed cylindrical floater containing an internal mass moving vertically and connected to the floater through a spring system. The internal mass and equivalent spring constant are adjustable and enable to match the resonance frequency of the device to the exciting wave frequency, hence optimizing the performance. In a full scale device, a Permanent Magnet Linear Generator will convert the relative motion between the internal mass and the floater into electricity. For a PMLG as described in Yeung et al. (OMAE2012), the electromagnetic force proved to cause dominantly linear damping. Thus, for the present preliminary study it was possible to replace the generator with a linear damper. While the full scale device with 2.2 m diameter is expected to generate O(50 kW), the prototype could generate O(1 W). For the initial experiments the prototype was restricted to heave motion and data compared to predictions from a newly developed theoretical model (Chen, 2016).

The influence of spatially and temporally high-resolution wind forcing on the power input to near-inertial waves in the ocean

NASA Astrophysics Data System (ADS)

Rimac, Antonija; von Storch, Jin-Song; Eden, Carsten

2013-04-01

The estimated power required to sustain global general circulation in the ocean is about 2 TW. This power is supplied with wind stress and tides. Energy spectrum shows pronounced maxima at near-inertial frequency. Near-inertial waves excited by high-frequency winds represent an important source for deep ocean mixing since they can propagate into the deep ocean and dissipate far away from the generation sites. The energy input by winds to near-inertial waves has been studied mostly using slab ocean models and wind stress forcing with coarse temporal resolution (e.g. 6-hourly). Slab ocean models lack the ability to reproduce fundamental aspects of kinetic energy balance and systematically overestimate the wind work. Also, slab ocean models do not account the energy used for the mixed layer deepening or the energy radiating downward into the deep ocean. Coarse temporal resolution of the wind forcing strongly underestimates the near-inertial energy. To overcome this difficulty we use an eddy permitting ocean model with high-frequency wind forcing. We establish the following model setup: We use the Max Planck Institute Ocean Model (MPIOM) on a tripolar grid with 45 km horizontal resolution and 40 vertical levels. We run the model with wind forcings that vary in horizontal and temporal resolution. We use high-resolution (1-hourly with 35 km horizontal resolution) and low-resolution winds (6-hourly with 250 km horizontal resolution). We address the following questions: Is the kinetic energy of near-inertial waves enhanced when high-resolution wind forcings are used? If so, is this due to higher level of overall wind variability or higher spatial or temporal resolution of wind forcing? How large is the power of near-inertial waves generated by winds? Our results show that near-inertial waves are enhanced and the near-inertial kinetic energy is two times higher (in the storm track regions 3.5 times higher) when high-resolution winds are used. Filtering high-resolution winds in space and time, the near-inertial kinetic energy reduces. The reduction is faster when a temporal filter is used suggesting that the high-frequency wind forcing is more efficient in generating near-inertial wave energy than the small-scale wind forcing. Using low-resolution wind forcing the wind generated power to near-inertial waves is 0.55 TW. When we use high-resolution wind forcing the result is 1.6 TW meaning that the result increases by 300%.

Resonant scattering of energetic electrons in the plasmasphere by monotonic whistler-mode waves artificially generated by ionospheric modification

NASA Astrophysics Data System (ADS)

Chang, S. S.; Ni, B. B.; Bortnik, J.; Zhou, C.; Zhao, Z. Y.; Li, J. X.; Gu, X. D.

2014-05-01

Modulated high-frequency (HF) heating of the ionosphere provides a feasible means of artificially generating extremely low-frequency (ELF)/very low-frequency (VLF) whistler waves, which can leak into the inner magnetosphere and contribute to resonant interactions with high-energy electrons in the plasmasphere. By ray tracing the magnetospheric propagation of ELF/VLF emissions artificially generated at low-invariant latitudes, we evaluate the relativistic electron resonant energies along the ray paths and show that propagating artificial ELF/VLF waves can resonate with electrons from ~ 100 keV to ~ 10 MeV. We further implement test particle simulations to investigate the effects of resonant scattering of energetic electrons due to triggered monotonic/single-frequency ELF/VLF waves. The results indicate that within the period of a resonance timescale, changes in electron pitch angle and kinetic energy are stochastic, and the overall effect is cumulative, that is, the changes averaged over all test electrons increase monotonically with time. The localized rates of wave-induced pitch-angle scattering and momentum diffusion in the plasmasphere are analyzed in detail for artificially generated ELF/VLF whistlers with an observable in situ amplitude of ~ 10 pT. While the local momentum diffusion of relativistic electrons is small, with a rate of < 10-7 s-1, the local pitch-angle scattering can be intense near the loss cone with a rate of ~ 10-4 s-1. Our investigation further supports the feasibility of artificial triggering of ELF/VLF whistler waves for removal of high-energy electrons at lower L shells within the plasmasphere. Moreover, our test particle simulation results show quantitatively good agreement with quasi-linear diffusion coefficients, confirming the applicability of both methods to evaluate the resonant diffusion effect of artificial generated ELF/VLF whistlers.

Water Surface Currents, Short Gravity-Capillary Waves and Radar Backscatter

NASA Technical Reports Server (NTRS)

Atakturk, Serhad S.; Katsaros, Kristina B.

1993-01-01

Despite their importance for air-sea interaction and microwave remote sensing of the ocean surface, intrinsic properties of short gravity-capillary waves are not well established. This is largely due to water surface currents and their effects on the direct measurements of wave parameters conducted at a fixed point. Frequencies of small scale waves propagating on a surface which itself is in motion, are subject to Doppler shifts. Hence, the high frequency tail of the wave spectra obtained from such temporal observations is smeared. Conversion of this smeared measured-frequency spectra to intrinsic-frequency (or wavenumber) spectra requires corrections for the Doppler shifts. Such attempts in the past have not been very successful in particular when field data were used. This becomes evident if the amplitude modulation of short waves by underlying long waves is considered. Microwave radar studies show that the amplitude of a short wave component attains its maximum value near the crests and its minimum in the troughs of the long waves. Doppler-shifted wave data yield similar results but much larger in modulation magnitude, as expected. In general, Doppler shift corrections reduce the modulation magnitude. Overcorrection may result in a negligible modulation or even in a strong modulation with the maximum amplitude in the wave troughs. The latter situation is clearly contradictory to our visual observations as well as the radar results and imply that the advection by currents is overestimated. In this study, a differential-advection approach is used in which small scale waves are advected by the currents evaluated not at the free surface, but at a depth proportional to their wavelengths. Applicability of this approach is verified by the excellent agreement in phase and magnitude of short-wave modulation between results based on radar and on wave-gauge measurements conducted on a lake.

Broadband reflective multi-polarization converter based on single-layer double-L-shaped metasurface

NASA Astrophysics Data System (ADS)

Mao, Chenyang; Yang, Yang; He, Xiaoxiang; Zheng, Jingming; Zhou, Chun

2017-12-01

In this paper, a broadband reflective multi-polarization converter based on single-layer double-L-shaped metasurface is proposed. The proposed metasurface can effectively convert linear-polarized (TE/TM) incident wave into the reflected wave with three different polarizations within the frequency bands of 5.5-22.75 GHz. Based on the electric and magnetic resonant features of the double-L-shaped structure, the proposed metasurface can convert linearly polarized waves into cross-polarized waves at three resonant frequency bands. Furthermore, the incident linearly polarized waves can be effectively converted into left/right handed circular-polarized (LHCP and RHCP) waves at other four non-resonance frequency bands. Thus, the proposed metasurface can be regarded as a seven-band multi-polarization converter. The prototype of the proposed polarization converter is analyzed and measured. Both simulated and measured results show the 3-dB axis ratio bandwidth of circular polarization bands and the high polarization conversion efficiency of cross-polarization bands when the incident wave changes from 0° to 30° at both TE and TM modes.

Elastic wave manipulation by using a phase-controlling meta-layer

NASA Astrophysics Data System (ADS)

Shen, Xiaohui; Sun, Chin-Teh; Barnhart, Miles V.; Huang, Guoliang

2018-03-01

In this work, a high pass meta-layer for elastic waves is proposed. An elastic phase-controlling meta-layer is theoretically realized using parallel and periodically arranged metamaterial sections based on the generalized Snell's law. The elastic meta-layer is composed of periodically repeated supercells, in which the frequency dependent elastic properties of the metamaterial are used to control a phase gradient at the interface between the meta-layer and conventional medium. It is analytically and numerically demonstrated that with a normal incident longitudinal wave, the wave propagation characteristics can be directly manipulated by the periodic length of the meta-layer element at the sub-wavelength scale. It is found that propagation of the incident wave through the interface is dependent on whether the working wavelength is longer or shorter than the periodic length of the meta-layer element. Specifically, a mode conversion of the P-wave to an SV-wave is investigated as the incident wave passes through the meta-layer region. Since the most common and damaging elastic waves in civil and mechanical industries are in the low frequency region, the work in this paper has great potential in the seismic shielding, engine vibration isolation, and other highly dynamic fields.

Role of the P-wave high frequency energy and duration as noninvasive cardiovascular predictors of paroxysmal atrial fibrillation.

PubMed

Alcaraz, Raúl; Martínez, Arturo; Rieta, José J

2015-04-01

A normal cardiac activation starts in the sinoatrial node and then spreads throughout the atrial myocardium, thus defining the P-wave of the electrocardiogram. However, when the onset of paroxysmal atrial fibrillation (PAF) approximates, a highly disturbed electrical activity occurs within the atria, thus provoking fragmented and eventually longer P-waves. Although this altered atrial conduction has been successfully quantified just before PAF onset from the signal-averaged P-wave spectral analysis, its evolution during the hours preceding the arrhythmia has not been assessed yet. This work focuses on quantifying the P-wave spectral content variability over the 2h preceding PAF onset with the aim of anticipating as much as possible the arrhythmic episode envision. For that purpose, the time course of several metrics estimating absolute energy and ratios of high- to low-frequency power in different bands between 20 and 200Hz has been computed from the P-wave autoregressive spectral estimation. All the analyzed metrics showed an increasing variability trend as PAF onset approximated, providing the P-wave high-frequency energy (between 80 and 150Hz) a diagnostic accuracy around 80% to discern between healthy subjects, patients far from PAF and patients less than 1h close to a PAF episode. This discriminant power was similar to that provided by the most classical time-domain approach, i.e., the P-wave duration. Furthermore, the linear combination of both metrics improved the diagnostic accuracy up to 88.07%, thus constituting a reliable noninvasive harbinger of PAF onset with a reasonable anticipation. The information provided by this methodology could be very useful in clinical practice either to optimize the antiarrhythmic treatment in patients at high-risk of PAF onset and to limit drug administration in low risk patients. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Radiowaves and Tectonic Dichotomy: Two Sides of One Coin

NASA Astrophysics Data System (ADS)

Kochemasov, G.

The first theorem of the wave planetology states that "Celestial bodies are di- chotomic"[1]. This notion is best demonstrated by modulation of the high frequency orbiting in the Solar system (SS) by the low frequency orbiting the SS in Galaxy. Or- biting frequencies of all bodies in the SS -from 1/8 hours for Phobos to 1/248 years for Pluto - are high comparative to the SS orbiting in Galaxy -about 1/200 000 000 years. Modulation of a high frequency by a low frequency brings about side frequencies at both sides of a high frequency. Earlier we considered only one side of the modula- tion stressing that the lower side frequency in any celestial body can achieve only the fundamental wave and produce related to it inevitable tectonic dichotomy [2]. Now we consider the higher side frequencies and find that they are in the limits of the ra- dio frequencies. Dividing all possible orbiting frequencies of bodies in the SS by the SS orbiting frequency in Galaxy one comes to a range of side frequencies from mi- crowaves to kilometer waves. This finding is rather important as it is well known that all bodies of the SS emit often enigmatic radiowaves. Figuratively, the SS is wrapped by a cloud of crossing radiowaves of various frequencies. Some calculations below show modulation of tectonic granula sizes of some celestial bodies. A granula size is a half of a wavelength which is tied to an orbiting frequency. A scale is the Earth's orbiting period 1 year and the granula size pR/4. The tectonic granula sizes of bodies are proportional to their orbital periods (Theorem 3 [1[). The modulating frequency is 1/200 000 000 years. Jupiter (12 y : 200 000 000 y) pR= (12 : 200 000 000) 3.14°u 71400 km=13.4 m tectonic granula or 26.8 m wavelength. Varying orbital periods and bodies'radia one comes to the following wavelengths. Jupiter-26.8 m, Saturn-56.4 m, Uranus-67 m, Neptune-124 m, Pluto-10.9 m, Sun-1.46 m, Triton-11.4 m (for the cir- cumsolar frequency), 1.84 mm (circumneptunian fr.), Amalthea-4.88 cm (circumsolar fr.), 0.0028 mm (circumjovian fr.), the Moon-5.46 cm (circumsolar fr.), 0.46 cm (cir- cumterrestrial fr.) [3]. This range of frequencies (infrared-kilometer waves) is typical for the SS. Within it surely there are waves of other modulations, harmonics, reso- nances. Extra heat emissions of Amalthea, Io, Triton could be related to microwave and infrared emissions (oscillations). References. [1] Kochemasov G.G.(1999) Geophys. Res. Abstr., v.1, #3.700; [2]Kochemasov G.G. (2000) 32nd Vernadsky-Brown microsymp. on comparative planetology, Abstr.,Moscow, 88-89; [3]Kochemasov G.G. (2001) 34th Vernadsky-Brown microsymp. Topics in comparative planetology, Ab- str., Moscow,(CD-ROM).

Analysis and measurement of the modulation transfer function of harmonic shear wave induced phase encoding imaging.

PubMed

McAleavey, Stephen A

2014-05-01

Shear wave induced phase encoding (SWIPE) imaging generates ultrasound backscatter images of tissue-like elastic materials by using traveling shear waves to encode the lateral position of the scatters in the phase of the received echo. In contrast to conventional ultrasound B-scan imaging, SWIPE offers the potential advantages of image formation without beam focusing or steering from a single transducer element, lateral resolution independent of aperture size, and the potential to achieve relatively high lateral resolution with low frequency ultrasound. Here a Fourier series description of the phase modulated echo signal is developed, demonstrating that echo harmonics at multiples of the shear wave frequency reveal target k-space data at identical multiples of the shear wavenumber. Modulation transfer functions of SWIPE imaging systems are calculated for maximum shear wave acceleration and maximum shear constraints, and compared with a conventionally focused aperture. The relative signal-to-noise ratio of the SWIPE method versus a conventionally focused aperture is found through these calculations. Reconstructions of wire targets in a gelatin phantom using 1 and 3.5 MHz ultrasound and a cylindrical shear wave source are presented, generated from the fundamental and second harmonic of the shear wave modulation frequency, demonstrating weak dependence of lateral resolution with ultrasound frequency.

Novel high-gain, improved-bandwidth, finned-ladder V-band Traveling-Wave Tube slow-wave circuit design

NASA Technical Reports Server (NTRS)

Kory, Carol L.; Wilson, Jeffrey D.

1994-01-01

The V-band frequency range of 59-64 GHz is a region of the millimeter-wave spectrum that has been designated for inter-satellite communications. As a first effort to develop a high-efficiency V-band Traveling-Wave Tube (TWT), variations on a ring-plane slow-wave circuit were computationally investigated to develop an alternative to the more conventional ferruled coupled-cavity circuit. The ring-plane circuit was chosen because of its high interaction impedance, large beam aperture, and excellent thermal dissipation properties. Despite these advantages, however, low bandwidth and high voltage requirements have, until now, prevented its acceptance outside the laboratory. In this paper, the three-dimensional electrodynamic simulation code MAFIA (solution of MAxwell's Equation by the Finite-Integration-Algorithm) is used to investigate methods of increasing the bandwidth and lowering the operating voltage of the ring-plane circuit. Calculations of frequency-phase dispersion, beam on-axis interaction impedance, attenuation and small-signal gain per wavelength were performed for various geometric variations and loading distributions of the ring-plane TWT slow-wave circuit. Based on the results of the variations, a circuit termed the finned-ladder TWT slow-wave circuit was designed and is compared here to the scaled prototype ring-plane and a conventional ferruled coupled-cavity TWT circuit over the V-band frequency range. The simulation results indicate that this circuit has a much higher gain, significantly wider bandwidth, and a much lower voltage requirement than the scaled ring-plane prototype circuit, while retaining its excellent thermal dissipation properties. The finned-ladder circuit has a much larger small-signal gain per wavelength than the ferruled coupled-cavity circuit, but with a moderate sacrifice in bandwidth.

Microwave dynamics of high aspect ratio superconducting nanowires studied using self-resonance

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

Santavicca, Daniel F., E-mail: daniel.santavicca@unf.edu; Adams, Jesse K.; Grant, Lierd E.

2016-06-21

We study the microwave impedance of extremely high aspect ratio (length/width ≈ 5000) superconducting niobium nitride nanowires. The nanowires are fabricated in a compact meander geometry that is in series with the center conductor of a 50 Ω coplanar waveguide transmission line. The transmission coefficient of the sample is measured up to 20 GHz. At high frequency, a peak in the transmission coefficient is seen. Numerical simulations show that this is a half-wave resonance along the length of the nanowire, where the nanowire acts as a high impedance, slow wave transmission line. This resonance sets the upper frequency limit for these nanowires asmore » inductive elements. Fitting simulations to the measured resonance enables a precise determination of the nanowire's complex sheet impedance at the resonance frequency. The real part is a measure of dissipation, while the imaginary part is dominated by kinetic inductance. We characterize the dependence of the sheet resistance and sheet inductance on both temperature and current and compare the results to recent theoretical predictions for disordered superconductors. These results can aid in the understanding of high frequency devices based on superconducting nanowires. They may also lead to the development of novel superconducting devices such as ultra-compact resonators and slow-wave structures.« less

Very high-frequency gravitational waves from magnetars and gamma-ray bursts

NASA Astrophysics Data System (ADS)

Wen, Hao; Li, Fang-Yu; Li, Jin; Fang, Zhen-Yun; Beckwith, Andrew

2017-12-01

Extremely powerful astrophysical electromagnetic (EM) systems could be possible sources of high-frequency gravitational waves (HFGWs). Here, based on properties of magnetars and gamma-ray bursts (GRBs), we address “Gamma-HFGWs” (with very high-frequency around 1020 Hz) caused by ultra-strong EM radiation (in the radiation-dominated phase of GRB fireballs) interacting with super-high magnetar surface magnetic fields (˜1011 T). By certain parameters of distance and power, the Gamma-HFGWs would have far field energy density Ω gw around 10-6, and they would cause perturbed signal EM waves of ˜10-20 W/m2 in a proposed HFGW detection system based on the EM response to GWs. Specially, Gamma-HFGWs would possess distinctive envelopes with characteristic shapes depending on the particular structures of surface magnetic fields of magnetars, which could be exclusive features helpful to distinguish them from background noise. Results obtained suggest that magnetars could be involved in possible astrophysical EM sources of GWs in the very high-frequency band, and Gamma-HFGWs could be potential targets for observations in the future. Supported by National Natural Science Foundation of China (11605015, 11375279, 11205254, 11647307) and the Fundamental Research Funds for the Central Universities (106112017CDJXY300003, 106112017CDJXFLX0014)

Autonomous bed-sediment imaging-systems for revealing temporal variability of grain size

USGS Publications Warehouse

Buscombe, Daniel; Rubin, David M.; Lacy, Jessica R.; Storlazzi, Curt D.; Hatcher, Gerald; Chezar, Henry; Wyland, Robert; Sherwood, Christopher R.

2014-01-01

We describe a remotely operated video microscope system, designed to provide high-resolution images of seabed sediments. Two versions were developed, which differ in how they raise the camera from the seabed. The first used hydraulics and the second used the energy associated with wave orbital motion. Images were analyzed using automated frequency-domain methods, which following a rigorous partially supervised quality control procedure, yielded estimates to within 20% of the true size as determined by on-screen manual measurements of grains. Long-term grain-size variability at a sandy inner shelf site offshore of Santa Cruz, California, USA, was investigated using the hydraulic system. Eighteen months of high frequency (min to h), high-resolution (μm) images were collected, and grain size distributions compiled. The data constitutes the longest known high-frequency record of seabed-grain size at this sample frequency, at any location. Short-term grain-size variability of sand in an energetic surf zone at Praa Sands, Cornwall, UK was investigated using the ‘wave-powered’ system. The data are the first high-frequency record of grain size at a single location of a highly mobile and evolving bed in a natural surf zone. Using this technology, it is now possible to measure bed-sediment-grain size at a time-scale comparable with flow conditions. Results suggest models of sediment transport at sandy, wave-dominated, nearshore locations should allow for substantial changes in grain-size distribution over time-scales as short as a few hours.

Comparison of Focused and Near-Field Imaging of Spray on Foam Insulation (SOFI) at Millimeter Wave Frequencies

NASA Technical Reports Server (NTRS)

Kharkovshy, S.; Zoughi, R.; Hepburn, F. L.

2007-01-01

Millimeter wave imaging techniques can provide high spatial-resolution images of various composites. Lens antennas may be incorporated into the imaging system to provide a small incident beam footprint. Another approach may involve the use of horn antennas, which if operating in their near-fields, images with reasonably high spatial-resolutions may also be obtained. This paper gives a comparison between such near-field and focused far-field imaging of the Space Shuttle Spray on Foam Insulation (SOFI) used in its external fuel tank at millimeter wave frequencies. Small horn antennas and lens antennas with relatively long depth of focus were used in this investigation.

Hydrodynamic influences on acoustical and optical backscatter in a fringing reef environment

NASA Astrophysics Data System (ADS)

Pawlak, Geno; Moline, Mark A.; Terrill, Eric J.; Colin, Patrick L.

2017-01-01

Observations of hydrodynamics along with optical and acoustical water characteristics in a tropical fringing reef environment reveal a distinct signature associated with flow characteristics and tidal conditions. Flow conditions are dominated by tidal forcing with an offshore component from the reef flat during ebb. Measurements span variable wave conditions enabling identification of wave effects on optical and acoustical water properties. High-frequency acoustic backscatter (6 MHz) is strongly correlated with tidal forcing increasing with offshore directed flow and modulated by wave height, indicating dominant hydrodynamic influence. Backscatter at 300 and 1200 kHz is predominantly diurnal suggesting a biological component. Optical backscatter is closely correlated with high-frequency acoustic backscatter across the range of study conditions. Acoustic backscatter frequency dependence is used along with changes in optical properties to interpret particle-size variations. Changes across wave heights suggest shifts in particle-size distributions with increases in relative concentrations of smaller particles for larger wave conditions. Establishing a connection between the physical processes of a fringing tropical reef and the resulting acoustical and optical signals allows for interpretation and forecasting of the remote sensing response of these phenomena over larger scales.

Photonic Crystal-Based High-Power Backward Wave Oscillator

DOE PAGES

Poole, Brian R.; Harris, John R.

2017-12-01

An electron beam traversing a slow wave structure can be used to either generate or amplify electromagnetic radiation through the interaction of the slow space charge wave on the beam with the slow wave structure modes. Here, a cylindrical waveguide with a periodic array of conducting loops is used for the slow wave structure. This paper considers operation as a backward wave oscillator. The dispersion properties of the structure are determined using a frequency-domain eigenmode solver. The interaction of the electron beam with the structure modes is investigated using a 2-D particle-in-cell (PIC) code. In conclusion, the operating frequency andmore » growth rate dependence on beam energy and beam current are investigated using the PIC code and compared with analytic and scaling estimates where possible.« less

Photonic Crystal-Based High-Power Backward Wave Oscillator

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

Poole, Brian R.; Harris, John R.

An electron beam traversing a slow wave structure can be used to either generate or amplify electromagnetic radiation through the interaction of the slow space charge wave on the beam with the slow wave structure modes. Here, a cylindrical waveguide with a periodic array of conducting loops is used for the slow wave structure. This paper considers operation as a backward wave oscillator. The dispersion properties of the structure are determined using a frequency-domain eigenmode solver. The interaction of the electron beam with the structure modes is investigated using a 2-D particle-in-cell (PIC) code. In conclusion, the operating frequency andmore » growth rate dependence on beam energy and beam current are investigated using the PIC code and compared with analytic and scaling estimates where possible.« less

Space-time properties of wind-waves: a new look at directional wave distributions

NASA Astrophysics Data System (ADS)

Leckler, Fabien; Ardhuin, Fabrice; Benetazzo, Alvise; Fedele, Francesco; Bergamasco, Filippo; Dulov, Vladimir

2014-05-01

Few accurate observed directional wave spectra are available in the literature at spatial scales ranging between 0.5 and 5.0 m. These intermediate wave scales, relevant for air-sea fluxes and remote sensing are also expected to feed back on the dominant wave properties through wave generation. These wave scales can be prolifically investigated using the well-known optical stereo methods that provides, from a couple of synchronized images, instantaneous representation of wave elevations over a given sea surface. Thus, two stereo systems (the so-called Wave Acquisition Stereo Systems, WASS) were deployed on top of the deep-water platform at Katsiveli, in the Black Sea, in September 2011 and 2013. From image pairs taken by the couple of synchronized high-resolution cameras, ocean surfaces have been reconstructed by stereo-triangulation. Here we analyze sea states corresponding to mean wind speeds of 11 to 14 m/s, and young wave ages of 0.35 to 0.42, associated to significant wave heights of 0.3 to 0.55m. As a result, four 12 Hz time evolutions of sea surface elevation maps with areas about 10 x 10 m2 have been obtained for sequence durations ranging between 15 and 30 minutes, and carefully validated with nearby capacitance wave gauges. The evolving free surfaces elevations were processed into frequency-wavenumber-direction 3D spectra. We found that wave energy chiefly follows the dispersion relation up to frequency of 1.6Hz and wavenumber of 10 rad/m, corresponding to wavelength of about 0.5 m. These spectra also depict well the energy contribution from non-linear waves, which is quantified and compared to theory. A strong bi-modality of the linear spectra was also observed, with the angle of the two maxima separated by about 160 degrees. Furthermore, spectra also exhibit the bimodality of the non-linear part. Integrated over positive frequencies to obtain wavenumber spectra unambiguous in direction, the bimodality of the spectra is partially hidden by the energy from second order waves, in particular from wave harmonics of the peak waves. However, the obtained spreading functions and integrals question the isotropy of the spectrum at high frequencies, generally assumed to explain deep water pressure measurement.

High-order modes of spoof surface plasmonic wave transmission on thin metal film structure.

PubMed

Liu, Xiaoyong; Feng, Yijun; Zhu, Bo; Zhao, Junming; Jiang, Tian

2013-12-16

Recently, conformal surface plasmon (CSP) structure has been successfully proposed that could support spoof surface plasmon polaritons (SPPs) on corrugated metallic strip with ultrathin thickness [Proc. Natl. Acad. Sci. U.S.A. 110, 40-45 (2013)]. Such concept provides a flexible, conformal, and ultrathin wave-guiding element, very promising for application of plasmonic devices, and circuits in the frequency ranging from microwave to mid-infrared. In this work, we investigated the dispersions and field patterns of high-order modes of spoof SPPs along CSP structure of thin metal film with corrugated edge of periodic array of grooves, and carried out direct measurement on the transmission spectrum of multi-band of surface wave propagation at microwave frequency. It is found that the mode number and mode bands are mainly determined by the depth of the grooves, providing a way to control the multi-band transmission spectrum. We have also experimentally verified the high-order mode spoof SPPs propagation on curved CSP structure with acceptable bending loss. The multi-band propagation of spoof surface wave is believed to be applicable for further design of novel planar devices such as filters, resonators, and couplers, and the concept can be extended to terahertz frequency range.

Real-time terahertz wave imaging by nonlinear optical frequency up-conversion in a 4-dimethylamino-N'-methyl-4'-stilbazolium tosylate crystal

NASA Astrophysics Data System (ADS)

Fan, Shuzhen; Qi, Feng; Notake, Takashi; Nawata, Kouji; Matsukawa, Takeshi; Takida, Yuma; Minamide, Hiroaki

2014-03-01

Real-time terahertz (THz) wave imaging has wide applications in areas such as security, industry, biology, medicine, pharmacy, and arts. In this letter, we report on real-time room-temperature THz imaging by nonlinear optical frequency up-conversion in organic 4-dimethylamino-N'-methyl-4'-stilbazolium tosylate crystal. The active projection-imaging system consisted of (1) THz wave generation, (2) THz-near-infrared hybrid optics, (3) THz wave up-conversion, and (4) an InGaAs camera working at 60 frames per second. The pumping laser system consisted of two optical parametric oscillators pumped by a nano-second frequency-doubled Nd:YAG laser. THz-wave images of handmade samples at 19.3 THz were taken, and videos of a sample moving and a ruler stuck with a black polyethylene film moving were supplied online to show real-time ability. Thanks to the high speed and high responsivity of this technology, real-time THz imaging with a higher signal-to-noise ratio than a commercially available THz micro-bolometer camera was proven to be feasible. By changing the phase-matching condition, i.e., by changing the wavelength of the pumping laser, we suggest THz imaging with a narrow THz frequency band of interest in a wide range from approximately 2 to 30 THz is possible.

Patterns in the Waves

NASA Astrophysics Data System (ADS)

Coco, G.; Guza, R. T.; Garnier, R.; Lomonaco, P.; Lopez De San Roman Blanco, B.; Dalrymple, R. A.; Xu, M.

2014-12-01

Edge waves, gravity waves trapped close to the shoreline by refraction, can in some cases form a standing wave pattern with alongshore periodic sequence of high and low runup. Nonlinear mechanisms for generation of edge waves by monochromatic waves incident on a planar beach from deep water have been elaborated theoretically and in the lab. Edge waves have been long considered a potential source for alongshore periodic morphological patterns in the swash (e.g., beach cusps), and edge-wave based predictions of cusp spacing compare qualitatively well with many field observations. We will discuss the extension of lab observations and numerical modeling to include incident waves with significant frequency and directional bandwidth. Laboratory experiments were performed at the Cantabria Coastal and Ocean Basin. The large rectangular basin (25 m cross-shore by 32 m alongshore) was heavily instrumented, had reflective sidewalls, and a steep concrete beach (slope 1:5) with a constant depth (1m) section between the wavemaker and beach. With monochromatic, normally incident waves we observed the expected, previously described subharmonic observations. Edge wave vertical heights at the shoreline reached 80cm, and edge wave uprushes exceeded the sloping beach freeboard. When frequency and frequency-directional spread are increased, the excited edge wave character changes substantially. In some cases, subharmonic excitation is suppressed completely. In other cases, edge waves are excited intermittently and unpredictably. The spatially and temporally steady forcing required for strong, persistent subharmonic instability is lacking with even modestly spread (direction and frequency) incident waves. An SPH numerical model is capable of reproducing aspects of the observations. It seems unlikely to us that subhamonic edge waves alone are responsible for most cusp formation on natural beaches. The steady incident wave forcing needed to initiate subharmonic growth, and to maintain subharmonics long enough to build cups, are abundantly present with an incident plane wave, but lacking in many natural settings. Although subharmonic edge waves can potentially start the initial spacing, positive feedback between flow and morphology are likely critical to cusp growth.

Dispersion Energy Analysis of Rayleigh and Love Waves in the Presence of Low-Velocity Layers in Near-Surface Seismic Surveys

NASA Astrophysics Data System (ADS)

Mi, Binbin; Xia, Jianghai; Shen, Chao; Wang, Limin

2018-03-01

High-frequency surface-wave analysis methods have been effectively and widely used to determine near-surface shear (S) wave velocity. To image the dispersion energy and identify different dispersive modes of surface waves accurately is one of key steps of using surface-wave methods. We analyzed the dispersion energy characteristics of Rayleigh and Love waves in near-surface layered models based on numerical simulations. It has been found that if there is a low-velocity layer (LVL) in the half-space, the dispersion energy of Rayleigh or Love waves is discontinuous and ``jumping'' appears from the fundamental mode to higher modes on dispersive images. We introduce the guided waves generated in an LVL (LVL-guided waves, a trapped wave mode) to clarify the complexity of the dispersion energy. We confirm the LVL-guided waves by analyzing the snapshots of SH and P-SV wavefield and comparing the dispersive energy with theoretical values of phase velocities. Results demonstrate that LVL-guided waves possess energy on dispersive images, which can interfere with the normal dispersion energy of Rayleigh or Love waves. Each mode of LVL-guided waves having lack of energy at the free surface in some high frequency range causes the discontinuity of dispersive energy on dispersive images, which is because shorter wavelengths (generally with lower phase velocities and higher frequencies) of LVL-guided waves cannot penetrate to the free surface. If the S wave velocity of the LVL is higher than that of the surface layer, the energy of LVL-guided waves only contaminates higher mode energy of surface waves and there is no interlacement with the fundamental mode of surface waves, while if the S wave velocity of the LVL is lower than that of the surface layer, the energy of LVL-guided waves may interlace with the fundamental mode of surface waves. Both of the interlacements with the fundamental mode or higher mode energy may cause misidentification for the dispersion curves of surface waves.

Non-reciprocal optical mirrors based on spatio-temporal acousto-optic modulation

NASA Astrophysics Data System (ADS)

Fleury, R.; Sounas, D. L.; Alù, A.

2018-03-01

Here, we investigate a scheme to realize free-space isolators and highly non-reciprocal mirrors with weak modulation imparted by an acoustic wave. We propose a strategy to dramatically break time-reversal symmetry by exploiting resonant interactions between a travelling acoustic wave and highly resonant Fabry-Pérot modes, inducing total reflection of an optical beam at a given angle, and no reflection at the negative angle. Different from conventional acousto-optic isolators, which are based on non-resonant frequency conversion and filtering, our proposal operates at the frequency of the optical signal by tailoring the resonant properties of the structure as well as the acoustic wave frequency and intensity, enabling 50 dB isolation with modest modulation requirements. Operation in the reflection mode allows for close-to-zero insertion loss, enabling disruptive opportunities in our ability to control and manipulate photons.

Invited article: Dielectric material characterization techniques and designs of high-Q resonators for applications from micro to millimeter-waves frequencies applicable at room and cryogenic temperatures.

PubMed

Le Floch, Jean-Michel; Fan, Y; Humbert, Georges; Shan, Qingxiao; Férachou, Denis; Bara-Maillet, Romain; Aubourg, Michel; Hartnett, John G; Madrangeas, Valerie; Cros, Dominique; Blondy, Jean-Marc; Krupka, Jerzy; Tobar, Michael E

2014-03-01

Dielectric resonators are key elements in many applications in micro to millimeter wave circuits, including ultra-narrow band filters and frequency-determining components for precision frequency synthesis. Distributed-layered and bulk low-loss crystalline and polycrystalline dielectric structures have become very important for building these devices. Proper design requires careful electromagnetic characterization of low-loss material properties. This includes exact simulation with precision numerical software and precise measurements of resonant modes. For example, we have developed the Whispering Gallery mode technique for microwave applications, which has now become the standard for characterizing low-loss structures. This paper will give some of the most common characterization techniques used in the micro to millimeter wave regime at room and cryogenic temperatures for designing high-Q dielectric loaded cavities.

Digital core based transmitted ultrasonic wave simulation and velocity accuracy analysis

NASA Astrophysics Data System (ADS)

Zhu, Wei; Shan, Rui

2016-06-01

Transmitted ultrasonic wave simulation (TUWS) in a digital core is one of the important elements of digital rock physics and is used to study wave propagation in porous cores and calculate equivalent velocity. When simulating wave propagates in a 3D digital core, two additional layers are attached to its two surfaces vertical to the wave-direction and one planar wave source and two receiver-arrays are properly installed. After source excitation, the two receivers then record incident and transmitted waves of the digital rock. Wave propagating velocity, which is the velocity of the digital core, is computed by the picked peak-time difference between the two recorded waves. To evaluate the accuracy of TUWS, a digital core is fully saturated with gas, oil, and water to calculate the corresponding velocities. The velocities increase with decreasing wave frequencies in the simulation frequency band, and this is considered to be the result of scattering. When the pore fluids are varied from gas to oil and finally to water, the velocity-variation characteristics between the different frequencies are similar, thereby approximately following the variation law of velocities obtained from linear elastic statics simulation (LESS), although their absolute values are different. However, LESS has been widely used. The results of this paper show that the transmission ultrasonic simulation has high relative precision.

MESSENGER Magnetic Field Observations of Upstream Ultra-Low Frequency Waves at Mercury

NASA Technical Reports Server (NTRS)

Le, G.; Chi, P. J.; Boardsen, S.; Blanco-Cano, X.; Anderosn, B. J.; Korth, H.

2012-01-01

The region upstream from a planetary bow shock is a natural plasma laboratory containing a variety of wave particle phenomena. The study of foreshocks other than the Earth's is important for extending our understanding of collisionless shocks and foreshock physics since the bow shock strength varies with heliocentric distance from the Sun, and the sizes of the bow shocks are different at different planets. The Mercury's bow shock is unique in our solar system as it is produced by low Mach number solar wind blowing over a small magnetized body with a predominately radial interplanetary magnetic field. Previous observations of Mercury upstream ultra-low frequency (ULF) waves came exclusively from two Mercury flybys of Mariner 10. The MESSENGER orbiter data enable us to study of upstream waves in the Mercury's foreshock in depth. This paper reports an overview of upstream ULF waves in the Mercury's foreshock using high-time resolution magnetic field data, 20 samples per second, from the MESSENGER spacecraft. The most common foreshock waves have frequencies near 2 Hz, with properties similar to the I-Hz waves in the Earth's foreshock. They are present in both the flyby data and in every orbit of the orbital data we have surveyed. The most common wave phenomenon in the Earth's foreshock is the large-amplitude 30-s waves, but similar waves at Mercury have frequencies at near 0.1 Hz and occur only sporadically with short durations (a few wave cycles). Superposed on the "30-s" waves, there are spectral peaks at near 0.6 Hz, not reported previously in Mariner 10 data. We will discuss wave properties and their occurrence characteristics in this paper.

Low-frequency gravitational wave detection via double optical clocks in space

NASA Astrophysics Data System (ADS)

Su, Jianfeng; Wang, Qiang; Wang, Qinghua; Jetzer, Philippe

2018-04-01

We propose a Doppler tracking system for gravitational wave detection via double optical clocks in space (DOCS). In this configuration two spacecrafts (each containing an optical clock) are launched to space for Doppler shift observations. Compared to the similar attempt of gravitational wave detection in the Cassini mission, the radio signal of DOCS that contains the relative frequency changes avoids completely noise effects due for instance to troposphere, ionosphere, ground-based antenna and transponder. Given the high stabilities of the two optical clocks (Allan deviation  ∼ 4.1× 10-17 @ 1000 s), an overall estimated sensitivity of 5 × 10-19 could be achieved with an observation time of 2 yr, and would allow to detect gravitational waves in the frequency range from  ∼10‑4 Hz to  ∼10‑2 Hz.

Multichannel analysis of surface waves (MASW) - Active and passive methods

USGS Publications Warehouse

Park, C.B.; Miller, R.D.; Xia, J.; Ivanov, J.

2007-01-01

The conventional seismic approaches for near-surface investigation have usually been either high-resolution reflection or refraction surveys that deal with a depth range of a few tens to hundreds meters. Seismic signals from these surveys consist of wavelets with frequencies higher than 50 Hz. The multichannel analysis of surface waves (MASW) method deals with surface waves in the lower frequencies (e.g., 1-30 Hz) and uses a much shallower depth range of investigation (e.g., a few to a few tens of meters). ?? 2007 Society of Exploration Geophysicists.

Escape of gravitational radiation from the field of massive bodies

NASA Technical Reports Server (NTRS)

Price, Richard H.; Pullin, Jorge; Kundu, Prasun K.

1993-01-01

We consider a compact source of gravitational waves of frequency omega in or near a massive spherically symmetric distribution of matter or a black hole. Recent calculations have led to apparently contradictory results for the influence of the massive body on the propagation of the waves. We show here that the results are in fact consistent and in agreement with the 'standard' viewpoint in which the high-frequency compact source produces the radiation as if in a flat background, and the background curvature affects the propagation of these waves.

Self-reflection of extremely short light pulses in nonlinear optical waveguides

NASA Astrophysics Data System (ADS)

Kurasov, Alexander E.; Kozlov, Sergei A.

2004-07-01

An equation describing the generation of reflected radiation during the propagation of high-intensity extremely short pulses in a nonlinear optical waveguide is derived. The phenomena taking place during the strong self-inducted changes of the temporal structure of the forward wave are studied. It is shown that the duration of the backward pulse is much greater than the duration of the forward pulse and that the main part of the energy of the backward wave is carried by lower frequencies than the central frequency of the forward wave.

21 CFR 892.1540 - Nonfetal ultrasonic monitor.

Code of Federal Regulations, 2012 CFR

2012-04-01

...) Identification. A nonfetal ultrasonic monitor is a device that projects a continuous high-frequency sound wave... wave and is intended for use in the investigation of nonfetal blood flow and other nonfetal body...

21 CFR 892.1540 - Nonfetal ultrasonic monitor.

Code of Federal Regulations, 2013 CFR

2013-04-01

...) Identification. A nonfetal ultrasonic monitor is a device that projects a continuous high-frequency sound wave... wave and is intended for use in the investigation of nonfetal blood flow and other nonfetal body...

Detection of changes of high-frequency activity by statistical time-frequency analysis in epileptic spikes

PubMed Central

Kobayashi, Katsuhiro; Jacobs, Julia; Gotman, Jean

2013-01-01

Objective A novel type of statistical time-frequency analysis was developed to elucidate changes of high-frequency EEG activity associated with epileptic spikes. Methods The method uses the Gabor Transform and detects changes of power in comparison to background activity using t-statistics that are controlled by the false discovery rate (FDR) to correct type I error of multiple testing. The analysis was applied to EEGs recorded at 2000 Hz from three patients with mesial temporal lobe epilepsy. Results Spike-related increase of high-frequency oscillations (HFOs) was clearly shown in the FDR-controlled t-spectra: it was most dramatic in spikes recorded from the hippocampus when the hippocampus was the seizure onset zone (SOZ). Depression of fast activity was observed immediately after the spikes, especially consistently in the discharges from the hippocampal SOZ. It corresponded to the slow wave part in case of spike-and-slow-wave complexes, but it was noted even in spikes without apparent slow waves. In one patient, a gradual increase of power above 200 Hz preceded spikes. Conclusions FDR-controlled t-spectra clearly detected the spike-related changes of HFOs that were unclear in standard power spectra. Significance We developed a promising tool to study the HFOs that may be closely linked to the pathophysiology of epileptogenesis. PMID:19394892

The detection and characterization of high frequency and high wavenumber solar oscillations. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Fernandes, David Neil

1992-01-01

Doppler shift measurements of the Na D(sub 1) absorption line have revealed solar oscillations in a new regime of frequency and wavenumber. Oscillations of vertical velocities in the temperature minimum and low chromosphere of the Sun are observed with frequencies ranging up to 9.5 mHz. There is no evidence for chromospheric modes of 3 minute period. This indicates that the chromosphere does not form a good cavity for acoustic waves. The fundamental-modes appear with wavenumbers up to 5.57 M per m (equivalent spherical harmonic degree, 3877). The frequencies lie below the predicted values at wavenumbers above 1 M per m. The values are in agreement with previous measurements that exist for wavenumbers up to 2.67 M per m. Spatial maps of velocity power show that high wavenumber oscillations are suppressed in active regions. The shape of the power depression indicates that wave motion is affected in the layer of atmosphere where the measurement is made. The f-modes are suppressed in the same way as p-modes, indicating that the mechanism for wave suppression affects velocity fluctuations. Mode frequencies are not affected by the magnetic fields by more than 50 micro Hz, the precision of the measurement.

High Frequency Analyzer (HFA) of Plasma Wave Experiment (PWE) onboard the Arase spacecraft

NASA Astrophysics Data System (ADS)

Kumamoto, Atsushi; Tsuchiya, Fuminori; Kasahara, Yoshiya; Kasaba, Yasumasa; Kojima, Hirotsugu; Yagitani, Satoshi; Ishisaka, Keigo; Imachi, Tomohiko; Ozaki, Mitsunori; Matsuda, Shoya; Shoji, Masafumi; Matsuoka, Aayako; Katoh, Yuto; Miyoshi, Yoshizumi; Obara, Takahiro

2018-05-01

The High Frequency Analyzer (HFA) is a subsystem of the Plasma Wave Experiment onboard the Arase (ERG) spacecraft. The main purposes of the HFA include (1) determining the electron number density around the spacecraft from observations of upper hybrid resonance (UHR) waves, (2) measuring the electromagnetic field component of whistler-mode chorus in a frequency range above 20 kHz, and (3) observing radio and plasma waves excited in the storm-time magnetosphere. Two components of AC electric fields detected by Wire Probe Antenna and one component of AC magnetic fields detected by Magnetic Search Coils are fed to the HFA. By applying analog and digital signal processing in the HFA, the spectrograms of two electric fields (EE mode) or one electric field and one magnetic field (EB mode) in a frequency range from 10 kHz to 10 MHz are obtained at an interval of 8 s. For the observation of plasmapause, the HFA can also be operated in PP (plasmapause) mode, in which spectrograms of one electric field component below 1 MHz are obtained at an interval of 1 s. In the initial HFA operations from January to July, 2017, the following results are obtained: (1) UHR waves, auroral kilometric radiation (AKR), whistler-mode chorus, electrostatic electron cyclotron harmonic waves, and nonthermal terrestrial continuum radiation were observed by the HFA in geomagnetically quiet and disturbed conditions. (2) In the test operations of the polarization observations on June 10, 2017, the fundamental R-X and L-O mode AKR and the second-harmonic R-X mode AKR from different sources in the northern polar region were observed. (3) The semiautomatic UHR frequency identification by the computer and a human operator was applied to the HFA spectrograms. In the identification by the computer, we used an algorithm for narrowing down the candidates of UHR frequency by checking intensity and bandwidth. Then, the identified UHR frequency by the computer was checked and corrected if needed by the human operator. Electron number density derived from the determined UHR frequency will be useful for the investigation of the storm-time evolution of the plasmasphere and topside ionosphere.[Figure not available: see fulltext.

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.

Interference patterns in the Spacelab 2 plasma wave data - Oblique electrostatic waves generated by the electron beam

NASA Technical Reports Server (NTRS)

Feng, Wei; Gurnett, Donald A.; Cairns, Iver H.

1992-01-01

During the Spacelab 2 mission the University of Iowa's Plasma Diagnostics Package (PDP) explored the plasma environment around the shuttle. Wideband spectrograms of plasma waves were obtained from the PDP at frequencies of 0-30 kHz and at distances up to 400 m from the shuttle. Strong low-frequency (below 10 kHz) electric field noise was observed in the wideband data during two periods in which an electron beam was ejected from the shuttle. This noise shows clear evidence of interference patterns caused by the finite (3.89 m) antenna length. The low-frequency noise was the most dominant type of noise produced by the ejected electron beam. Analysis of antenna interference patterns generated by these waves permits a determination of the wavelength, the direction of propagation, and the location of the source region. The observed waves have a linear dispersion relation very similar to that of ion acoustic waves. The waves are believed to be oblique ion acoustic or high-order ion cyclotron waves generated by a current of ambient electrons returning to the shuttle in response to the ejected electron beam.

Why Is White Light Dispersed by a Prism?

ERIC Educational Resources Information Center

Crawford, Frank S.

1979-01-01

Presents the answer to a question, which is intended for high school students, about the dispersion of white light by a glass prism. Why the high frequency waves travel slower than the lower frequencies in glass is also presented. (HM)

Numerical Investigation of Three-dimensional Instability of Standing Waves

NASA Astrophysics Data System (ADS)

Zhu, Qiang; Liu, Yuming; Yue, Dick K. P.

2002-11-01

We study the three-dimensional instability of finite-amplitude standing waves under the influence of gravity using the transition matrix method. For accurate calculation of the transition matrices, we apply an efficient high-order spectral element method for nonlinear wave dynamics in complex domain. We consider two types of standing waves: (a) plane standing waves; and (b) standing waves in a circular tank. For the former, in addition to the confirmation of the side-band-like instability, we find a new three-dimensional instability for arbitrary base standing waves. The dominant component of the unstable disturbance is an oblique standing wave, with an arbitrary angle relative to the base flow, whose frequency is approximately equal to that of the base standing wave. Based on direct simulations, we confirm such a three-dimensional instability and show the occurrence of the Fermi-Pasta-Ulam recurrence phenomenon during nonlinear evolution. For the latter, we find that beyond a threshold wave steepness, the standing wave with frequency Ω becomes unstable to a small three-dimensional disturbance, which contains two dominant standing-wave components with frequencies ω1 and ω_2, provided that 2Ω ω1 + ω_2. The threshold wave steepness is found to decrease/increase as the radial/azimuthal wavenumber of the base standing wave increases. We show that the instability of standing waves in rectangular and circular tanks is caused by third-order quartet resonances between base flow and disturbance.

Role of Shape and Numbers of Ridges and Valleys in the Insulating Effects of Topography on the Rayleigh Wave Characteristics

NASA Astrophysics Data System (ADS)

Narayan, J. P.; Kumar, Neeraj; Chauhan, Ranu

2018-03-01

This research work is inspired by the recently accepted concept that high frequency Rayleigh waves are generated in the epicentral zone of shallow earthquakes. Such high frequency Rayleigh waves with large amplitude may develop much of spatial variability in ground motion which in turn may cause unexpected damage to long-span structures like bridges, underground pipelines, dams, etc., in the hilly regions. Further, it has been reported that topography acts as an insulator for the Rayleigh waves (Ma et al. BSSA 97:2066-2079, 2007). The above mentioned scientific developments stimulated to quantify the role of shape and number of ridges and valleys falling in the path of Rayleigh wave in the insulating effect of topography on the Rayleigh waves. The simulated results reveals very large amplification of the horizontal component of Rayleigh wave near the top of a triangular ridge which may cause intensive landslides under favorable condition. The computed snapshots of the wave-field of Rayleigh wave reveals that the interaction of Rayleigh wave with the topography causes reflection, splitting, and diffraction of Rayleigh wave in the form of body waves which in turn provides the insulating capacity to the topography. Insulating effects of single valley is more than that of single ridge. Further this effect was more in case of elliptical ridge/valley than triangular ridge/valley. The insulating effect of topography was proportional to the frequency of Rayleigh wave and the number of ridges and valleys in the string. The obtained level of insulation effects of topography on the Rayleigh wave (energy of Rayleigh wave reduced to less than 4% after crossing a topography of span 4.5 km) calls for the consideration of role of hills and valleys in seismic hazard prediction, particularly in case of shallow earthquakes.

Nonlinear modulation of an extraordinary wave under the conditions of parametric decay

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

Dorofeenko, V. G.; Krasovitskiy, V. B.; Turikov, V. A.

2012-06-15

A self-consistent set of Hamilton equations describing nonlinear saturation of the amplitude of oscillations excited under the conditions of parametric decay of an elliptically polarized extraordinary wave in cold plasma is solved analytically and numerically. It is shown that the exponential increase in the amplitude of the secondary wave excited at the half-frequency of the primary wave changes into a reverse process in which energy is returned to the primary wave and nonlinear oscillations propagating across the external magnetic field are generated. The system of 'slow' equations for the amplitudes, obtained by averaging the initial equations over the high-frequency period,more » is used to describe steady-state nonlinear oscillations in plasma.« less

Experimental observation of sub-terahertz backward-wave amplification in a multi-level microfabricated slow-wave circuit

NASA Astrophysics Data System (ADS)

Baik, Chan-Wook; Ahn, Ho Young; Kim, Yongsung; Lee, Jooho; Hong, Seogwoo; Lee, Sang Hun; Choi, Jun Hee; Kim, Sunil; Jeon, So-Yeon; Yu, SeGi; Collins, George; Read, Michael E.; Lawrence Ives, R.; Kim, Jong Min; Hwang, Sungwoo

2015-11-01

In our earlier paper dealing with dispersion retrieval from ultra-deep, reactive-ion-etched, slow-wave circuits on silicon substrates, it was proposed that splitting high-aspect-ratio circuits into multilevels enabled precise characterization in sub-terahertz frequency regime. This achievement prompted us to investigate beam-wave interaction through a vacuum-sealed integration with a 15-kV, 85-mA, thermionic, electron gun. Our experimental study demonstrates sub-terahertz, backward-wave amplification driven by an external oscillator. The measured output shows a frequency downshift, as well as power amplification, from beam loading even with low beam perveance. This offers a promising opportunity for the development of terahertz radiation sources, based on silicon technologies.

Experimental observation of sub-terahertz backward-wave amplification in a multi-level microfabricated slow-wave circuit

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

Baik, Chan-Wook, E-mail: cw.baik@samsung.com; Ahn, Ho Young; Kim, Yongsung

2015-11-09

In our earlier paper dealing with dispersion retrieval from ultra-deep, reactive-ion-etched, slow-wave circuits on silicon substrates, it was proposed that splitting high-aspect-ratio circuits into multilevels enabled precise characterization in sub-terahertz frequency regime. This achievement prompted us to investigate beam-wave interaction through a vacuum-sealed integration with a 15-kV, 85-mA, thermionic, electron gun. Our experimental study demonstrates sub-terahertz, backward-wave amplification driven by an external oscillator. The measured output shows a frequency downshift, as well as power amplification, from beam loading even with low beam perveance. This offers a promising opportunity for the development of terahertz radiation sources, based on silicon technologies.

Modelling guided waves in the Alaskan-Aleutian subduction zone

NASA Astrophysics Data System (ADS)

Coulson, Sophie; Garth, Thomas; Reitbrock, Andreas

2016-04-01

Subduction zone guided wave arrivals from intermediate depth earthquakes (70-300 km depth) have a huge potential to tell us about the velocity structure of the subducting oceanic crust as it dehydrates at these depths. We see guided waves as the oceanic crust has a slower seismic velocity than the surrounding material, and so high frequency energy is retained and delayed in the crustal material. Lower frequency energy is not retained in this crustal waveguide and so travels at faster velocities of the surrounding material. This gives a unique observation at the surface with low frequency energy arriving before the higher frequencies. We constrain this guided wave dispersion by comparing the waveforms recorded in real subduction zones with simulated waveforms, produced using finite difference full waveform modelling techniques. This method has been used to show that hydrated minerals in the oceanic crust persist to much greater depths than accepted thermal petrological subduction zone models would suggest in Northern Japan (Garth & Rietbrock, 2014a), and South America (Garth & Rietbrock, in prep). These observations also suggest that the subducting oceanic mantle may be highly hydrated at intermediate depth by dipping normal faults (Garth & Rietbrock 2014b). We use this guided wave analysis technique to constrain the velocity structure of the down going ~45 Ma Pacific plate beneath Alaska. Dispersion analysis is primarily carried out on guided wave arrivals recorded on the Alaskan regional seismic network. Earthquake locations from global earthquake catalogues (ISC and PDE) and regional earthquake locations from the AEIC (Alaskan Earthquake Information Centre) catalogue are used to constrain the slab geometry and to identify potentially dispersive events. Dispersed arrivals are seen at stations close to the trench, with high frequency (>2 Hz) arrivals delayed by 2 - 4 seconds. This dispersion is analysed to constrain the velocity and width of the proposed waveguide. The velocity structure of this relatively young subducting plate is compared to the velocity structure resolved in the older oceanic lithosphere subducted beneath Northern Japan. We also use guided wave observations to investigate the thickness and low velocity structure of the subducting Yakutat terrain. Additionally we discuss the dependence of the inferred slab geometry on the earthquake catalogues that are used.

cBathy: A robust algorithm for estimating nearshore bathymetry

USGS Publications Warehouse

Plant, Nathaniel G.; Holman, Rob; Holland, K. Todd

2013-01-01

A three-part algorithm is described and tested to provide robust bathymetry maps based solely on long time series observations of surface wave motions. The first phase consists of frequency-dependent characterization of the wave field in which dominant frequencies are estimated by Fourier transform while corresponding wave numbers are derived from spatial gradients in cross-spectral phase over analysis tiles that can be small, allowing high-spatial resolution. Coherent spatial structures at each frequency are extracted by frequency-dependent empirical orthogonal function (EOF). In phase two, depths are found that best fit weighted sets of frequency-wave number pairs. These are subsequently smoothed in time in phase 3 using a Kalman filter that fills gaps in coverage and objectively averages new estimates of variable quality with prior estimates. Objective confidence intervals are returned. Tests at Duck, NC, using 16 surveys collected over 2 years showed a bias and root-mean-square (RMS) error of 0.19 and 0.51 m, respectively but were largest near the offshore limits of analysis (roughly 500 m from the camera) and near the steep shoreline where analysis tiles mix information from waves, swash and static dry sand. Performance was excellent for small waves but degraded somewhat with increasing wave height. Sand bars and their small-scale alongshore variability were well resolved. A single ground truth survey from a dissipative, low-sloping beach (Agate Beach, OR) showed similar errors over a region that extended several kilometers from the camera and reached depths of 14 m. Vector wave number estimates can also be incorporated into data assimilation models of nearshore dynamics.

Multiband coherent perfect absorption in a water-based metasurface.

PubMed

Zhu, Weiren; Rukhlenko, Ivan D; Xiao, Fajun; He, Chong; Geng, Junping; Liang, Xianling; Premaratne, Malin; Jin, Ronghong

2017-07-10

We design an ultrathin water-based metasurface capable of coherent perfect absorption (CPA) at radio frequencies. It is demonstrated that such a metasurface can almost completely absorb two symmetrically incident waves within four frequency bands, each having its own modulation depth of metasurface absorptivity. Specifically, the absorptivity at 557.2 MHz can be changed between 0.59% and 99.99% via the adjustment of the phase difference between the waves. The high angular tolerance of our metasurface is shown to enable strong CPA at oblique incidence, with the CPA frequency almost independent of the incident angle for TE waves and varying from 557.2 up to 584.2 MHz for TM waves. One can also reduce this frequency from 712.0 to 493.3 MHz while retaining strong coherent absorption by varying the water layer thickness. It is also show that the coherent absorption performance can be flexibly controlled by adjusting the temperature of water. The proposed metasurface is low-cost, biocompatible, and useful for electromagnetic modulation and switching.

Rayleigh-wave dispersive energy imaging and mode separating by high-resolution linear Radon transform

USGS Publications Warehouse

Luo, Y.; Xu, Y.; Liu, Q.; Xia, J.

2008-01-01

In recent years, multichannel analysis of surface waves (MASW) has been increasingly used for obtaining vertical shear-wave velocity profiles within near-surface materials. MASW uses a multichannel recording approach to capture the time-variant, full-seismic wavefield where dispersive surface waves can be used to estimate near-surface S-wave velocity. The technique consists of (1) acquisition of broadband, high-frequency ground roll using a multichannel recording system; (2) efficient and accurate algorithms that allow the extraction and analysis of 1D Rayleigh-wave dispersion curves; (3) stable and efficient inversion algorithms for estimating S-wave velocity profiles; and (4) construction of the 2D S-wave velocity field map.

Plasma waves near the magnetopause

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

Anderson, R.R.; Haravey, C.C.; Hoppe, M.M.

1982-04-01

Plasma waves associated with the magnetopause, from the magnetosheath to the outer magnetosphere, are examined with an emphasis on high time resolution data and the comparison between measurements by using different antenna systems. An early ISEE crossing of the magnetopause region, including passage through two well-defined flux transfer events, the magentopause current layer, and boundary plasma, is studied in detail. The waves in these regions are compared and contrasted with the waves in the adjoining magnetosheath and outer magnetosphere. Four types of plamsa wave emissions are characteristic of the nominal magnetosheat: (1) a very low frequency continuum, (2) short wavelengthmore » spikes, (3) 'festoon-shaped' emissions below about 2 kHz, and (4) 'lion roars'. The latter two emissions are well correlated with ultra-low frequency magnetic field fluctuations. The dominant plasma wave features during flux transfer events are (1) an intense low-frequency continuum, which includes a substantial electromagnetic component, (2) a dramatic increase in the frequency of occurrence of the spikes, (3) quasi-periodic electron cyclotron harmonics correlated with approx.1-Hz magnetic field fluctuations, and (4) enhanced electron plasma oscillations. The plasma wave characteristics in the current layer and in the boundary layer are quite similar to the features in the flux transfer events. Upon entry into the outer magnetosphere, the plasma wave spectra are dominated by intense electromagnetic chorus bursts and electrosatic (n+1/2)f/sup -//sub g/ emissions. Wavelength determinations made by comparing the various antenna responses and polarization measurements for the different waves are also presented.« less

Vlasov simulations of electron acceleration by radio frequency heating near the upper hybrid layer

NASA Astrophysics Data System (ADS)

Najmi, A.; Eliasson, B.; Shao, X.; Milikh, G.; Sharma, A. S.; Papadopoulos, K.

2017-10-01

It is shown by using a combination of Vlasov and test particles simulations that the electron distribution function resulting from energization due to Upper Hybrid (UH) plasma turbulence depends critically on the closeness of the pump wave to the double resonance, defined as ω ≈ ωUH ≈ nωce, where n is an integer. For pump frequencies, away from the double resonance, the electron distribution function is very close to Maxwellian, while as the pump frequency approaches the double resonance, it develops a high energy tail. The simulations show turbulence involving coupling between Lower Hybrid (LH) and UH waves, followed by excitation of Electron Bernstein (EB) modes. For the particular case of a pump with frequency between n = 3 and n = 4, the EB modes cover the range from the first to the 5th mode. The simulations show that when the injected wave frequency is between the 3rd and 4th harmonics of the electron cyclotron frequency, bulk electron heating occurs due to the interaction between the electrons and large amplitude EB waves, primarily on the first EB branch leading to an essentially thermal distribution. On the other hand, when the frequency is slightly above the 4th electron cyclotron harmonic, the resonant interaction is predominantly due to the UH branch and leads to a further acceleration of high-velocity electrons and a distribution function with a suprathermal tail of energetic electrons. The results are consistent with ionospheric experiments and relevant to the production of Artificial Ionospheric Plasma Layers.

Millimeter Wave Holographical Inspection of Honeycomb Composites

NASA Technical Reports Server (NTRS)

Case, J. T.; Kharkovsky, S.; Zoughi, R.; Stefes, G.; Hepburn, Frank L.; Hepburn, Frank L.

2007-01-01

Multi-layered composite structures manufactured with honeycomb, foam or balsa wood cores are finding increasing utility in a variety of aerospace, transportation, and infrastructure applications. Due to the low conductivity and inhomogeneity associated with these composites standard nondestructive testing (NDT) methods are not always capable of inspecting their interior for various defects caused during the manufacturing process or as a result of in-service loading. On the contrary, microwave and millimeter wave NDT methods are well-suited for inspecting these structures since signals at these frequencies readily penetrate through these structures and reflect from different interior boundaries revealing the presence of a wide range of defects such as disbond, delamination, moisture and oil intrusion, impact damage, etc. Millimeter wave frequency spectrum spans 30 GHz - 300 GHz with corresponding wavelengths of 10 - 1 mm. Due to the inherent short wavelengths at these frequencies, one can produce high spatial resolution images of these composites either using real-antenna focused or synthetic-aperture focused methods. In addition, incorporation of swept-frequency in the latter method (i.e., holography) results in high-resolution three-dimensional images. This paper presents the basic steps behind producing such images at millimeter wave frequencies and the results of two honeycomb composite panels are demonstrated at Q-band (33-50 GHz). In addition, these results are compared to previous results using X-ray computed tomography.

Millimeter Wave Holographical Inspection of Honeycomb Composites

NASA Astrophysics Data System (ADS)

Case, J. T.; Kharkovsky, S.; Zoughi, R.; Steffes, G.; Hepburn, F. L.

2008-02-01

Multi-layered composite structures manufactured with honeycomb, foam, or balsa wood cores are finding increasing utility in a variety of aerospace, transportation, and infrastructure applications. Due to the low conductivity and inhomogeneity associated with these composites, standard nondestructive testing (NDT) methods are not always capable of inspecting their interior for various defects caused during the manufacturing process or as a result of in-service loading. On the contrary, microwave and millimeter wave NDT methods are well-suited for inspecting these structures since signals at these frequencies readily penetrate through these structures and reflect from different interior boundaries revealing the presence of a wide range of defects such as isband, delamination, moisture and oil intrusion, impact damage, etc. Millimeter wave frequency spectrum spans 30 GHz-300 GHz with corresponding wavelengths of 10-1 mm. Due to the inherent short wavelengths at these frequencies, one can produce high spatial resolution images of these composites either using real-antenna focused or synthetic-aperture focused methods. In addition, incorporation of swept-frequency in the latter method (i.e., holography) results in high-resolution three-dimensional images. This paper presents the basic steps behind producing such images at millimeter wave frequencies and the results of two honeycomb composite panels are demonstrated at Q-band (33-50 GHz). In addition, these results are compared to previous results using X-ray computed tomography.

Demonstration of a Submillimeter-Wave HEMT Oscillator Module at 330 GHz

NASA Technical Reports Server (NTRS)

Radisic, Vesna; Deal, W. R.; Mei, X. B.; Yoshida, Wayne; Liu, P. H.; Uyeda, Jansen; Lai, Richard; Samoska, Lorene; Fung, King Man; Gaier, Todd;

Matrix basis for plane and modal waves in a Timoshenko beam.

PubMed

Claeyssen, Julio Cesar Ruiz; Tolfo, Daniela de Rosso; Tonetto, Leticia

2016-11-01

Plane waves and modal waves of the Timoshenko beam model are characterized in closed form by introducing robust matrix basis that behave according to the nature of frequency and wave or modal numbers. These new characterizations are given in terms of a finite number of coupling matrices and closed form generating scalar functions. Through Liouville's technique, these latter are well behaved at critical or static situations. Eigenanalysis is formulated for exponential and modal waves. Modal waves are superposition of four plane waves, but there are plane waves that cannot be modal waves. Reflected and transmitted waves at an interface point are formulated in matrix terms, regardless of having a conservative or a dissipative situation. The matrix representation of modal waves is used in a crack problem for determining the reflected and transmitted matrices. Their euclidean norms are seen to be dominated by certain components at low and high frequencies. The matrix basis technique is also used with a non-local Timoshenko model and with the wave interaction with a boundary. The matrix basis allows to characterize reflected and transmitted waves in spectral and non-spectral form.

Projections of extreme water level events for atolls in the western Tropical Pacific

NASA Astrophysics Data System (ADS)

Merrifield, M. A.; Becker, J. M.; Ford, M.; Yao, Y.

2014-12-01

Conditions that lead to extreme water levels and coastal flooding are examined for atolls in the Republic of the Marshall Islands based on a recent field study of wave transformations over fringing reefs, tide gauge observations, and wave model hindcasts. Wave-driven water level extremes pose the largest threat to atoll shorelines, with coastal levels scaling as approximately one-third of the incident breaking wave height. The wave-driven coastal water level is partitioned into a mean setup, low frequency oscillations associated with cross-reef quasi-standing modes, and wind waves that reach the shore after undergoing high dissipation due to breaking and bottom friction. All three components depend on the water level over the reef; however, the sum of the components is independent of water level due to cancelling effects. Wave hindcasts suggest that wave-driven water level extremes capable of coastal flooding are infrequent events that require a peak wave event to coincide with mid- to high-tide conditions. Interannual and decadal variations in sea level do not change the frequency of these events appreciably. Future sea-level rise scenarios significantly increase the flooding threat associated with wave events, with a nearly exponential increase in flooding days per year as sea level exceeds 0.3 to 1.0 m above current levels.

Magnetosheath electrostatic turbulence

NASA Technical Reports Server (NTRS)

Rodriquez, P.

1977-01-01

The spectrum of electrostatic plasma waves in the terrestrial magnetosheath was studied using the plasma wave experiment on the IMP-6 satellite. Electrostatic plasma wave turbulence is almost continuously present throughout the magnetosheath with broadband (20 Hz- 70 kHz) r.m.s. field intensities typically 0.01 - 1.0 millivolts/m. Peak intensities of about 1.0 millivolts/m near the electron plasma frequency (30 - 60 kHz) were detected occasionally. The components usually identified in the spectrum of magnetosheath electrostatic turbulence include a high frequency ( or = 30 kHz) component peaking at the electron plasma frequency f sub pe, a low frequency component with a broad intensity maximum below the nominal ion plasma frequency f sub pi (approximately f sub pe/43), and a less well defined intermediate component in the range f sub pi f f sub pe. The intensity distribution of magnetosheath electrostatic turbulence clearly shows that the low frequency component is associated with the bow shock, suggesting that the ion heating begun at the shock continues into the downstream magnetosheath.

The information content of high-frequency seismograms and the near-surface geologic structure of "hard rock" recording sites

USGS Publications Warehouse

Cranswick, E.

1988-01-01

Due to hardware developments in the last decade, the high-frequency end of the frequency band of seismic waves analyzed for source mechanisms has been extended into the audio-frequency range (>20 Hz). In principle, the short wavelengths corresponding to these frequencies can provide information about the details of seismic sources, but in fact, much of the "signal" is the site response of the nearsurface. Several examples of waveform data recorded at "hard rock" sites, which are generally assumed to have a "flat" transfer function, are presented to demonstrate the severe signal distortions, including fmax, produced by near-surface structures. Analysis of the geology of a number of sites indicates that the overall attenuation of high-frequency (>1 Hz) seismic waves is controlled by the whole-path-Q between source and receiver but the presence of distinct fmax site resonance peaks is controlled by the nature of the surface layer and the underlying near-surface structure. Models of vertical decoupling of the surface and nearsurface and horizontal decoupling of adjacent sites on hard rock outcrops are proposed and their behaviour is compared to the observations of hard rock site response. The upper bound to the frequency band of the seismic waves that contain significant source information which can be deconvolved from a site response or an array response is discussed in terms of fmax and the correlation of waveform distortion with the outcrop-scale geologic structure of hard rock sites. It is concluded that although the velocity structures of hard rock sites, unlike those of alluvium sites, allow some audio-frequency seismic energy to propagate to the surface, the resulting signals are a highly distorted, limited subset of the source spectra. ?? 1988 Birkha??user Verlag.

Explaining the dynamics of the ultra-relativistic third Van Allen radiation belt

DOE PAGES

Mann, I. R.; Ozeke, L. G.; Murphy, K. R.; ...

2016-06-20

Since the discovery of the Van Allen radiation belts over 50 years ago, an explanation for their complete dynamics has remained elusive. Especially challenging is understanding the recently discovered ultra-relativistic third electron radiation belt. Current theory asserts that loss in the heart of the outer belt, essential to the formation of the third belt, must be controlled by high-frequency plasma wave–particle scattering into the atmosphere, via whistler mode chorus, plasmaspheric hiss, or electromagnetic ion cyclotron waves. However, this has failed to accurately reproduce the third belt. In this paper, using a data-driven, time-dependent specification of ultra-low-frequency (ULF) waves we showmore » for the first time how the third radiation belt is established as a simple, elegant consequence of storm-time extremely fast outward ULF wave transport. High-frequency wave–particle scattering loss into the atmosphere is not needed in this case. Finally, when rapid ULF wave transport coupled to a dynamic boundary is accurately specified, the sensitive dynamics controlling the enigmatic ultra-relativistic third radiation belt are naturally explained.« less

Explaining the dynamics of the ultra-relativistic third Van Allen radiation belt

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

Mann, I. R.; Ozeke, L. G.; Murphy, K. R.

Since the discovery of the Van Allen radiation belts over 50 years ago, an explanation for their complete dynamics has remained elusive. Especially challenging is understanding the recently discovered ultra-relativistic third electron radiation belt. Current theory asserts that loss in the heart of the outer belt, essential to the formation of the third belt, must be controlled by high-frequency plasma wave–particle scattering into the atmosphere, via whistler mode chorus, plasmaspheric hiss, or electromagnetic ion cyclotron waves. However, this has failed to accurately reproduce the third belt. In this paper, using a data-driven, time-dependent specification of ultra-low-frequency (ULF) waves we showmore » for the first time how the third radiation belt is established as a simple, elegant consequence of storm-time extremely fast outward ULF wave transport. High-frequency wave–particle scattering loss into the atmosphere is not needed in this case. Finally, when rapid ULF wave transport coupled to a dynamic boundary is accurately specified, the sensitive dynamics controlling the enigmatic ultra-relativistic third radiation belt are naturally explained.« less

High frequency poroelastic waves in hydrogels.

PubMed

Chiarelli, Piero; Lanatà, Antonio; Carbone, Marina; Domenici, Claudio

2010-03-01

In this work a continuum model for high frequency poroelastic longitudinal waves in hydrogels is presented. A viscoelastic force describing the interaction between the polymer network and the bounded water present in such materials is introduced. The model is tested by means of ultrasound wave speed and attenuation measurements in polyvinylalcohol hydrogel samples. The theory and experiments show that ultrasound attenuation decreases linearly with the increase in the water volume fraction beta of the hydrogel. The introduction of the viscoelastic force between the bounded water and the polymer network leads to a bi-phasic theory, showing an ultrasonic fast wave attenuation that can vary as a function of the frequency with a non-integer exponent in agreement with the experimental data in literature. When beta tends to 1 (100% of interstitial water) due to the presence of bounded water in the hydrogel, the ultrasound phase velocity acquires higher value than that of pure water. The ultrasound speed gap at beta=1 is confirmed by the experimental results, showing that it increases in less cross-linked gel samples which own a higher concentration of bounded water.

High frequency guided wave propagation in monocrystalline silicon wafers

NASA Astrophysics Data System (ADS)

Pizzolato, Marco; Masserey, Bernard; Robyr, Jean-Luc; Fromme, Paul

2017-04-01

Monocrystalline silicon wafers are widely used in the photovoltaic industry for solar panels with high conversion efficiency. The cutting process can introduce micro-cracks in the thin wafers and lead to varying thickness. High frequency guided ultrasonic waves are considered for the structural monitoring of the wafers. The anisotropy of the monocrystalline silicon leads to variations of the wave characteristics, depending on the propagation direction relative to the crystal orientation. Full three-dimensional Finite Element simulations of the guided wave propagation were conducted to visualize and quantify these effects for a line source. The phase velocity (slowness) and skew angle of the two fundamental Lamb wave modes (first anti-symmetric mode A0 and first symmetric mode S0) for varying propagation directions relative to the crystal orientation were measured experimentally. Selective mode excitation was achieved using a contact piezoelectric transducer with a custom-made wedge and holder to achieve a controlled contact pressure. The out-of-plane component of the guided wave propagation was measured using a noncontact laser interferometer. Good agreement was found with the simulation results and theoretical predictions based on nominal material properties of the silicon wafer.

Ex vivo optimisation of a heterogeneous speed of sound model of the human skull for non-invasive transcranial focused ultrasound at 1 MHz.

PubMed

Marsac, L; Chauvet, D; La Greca, R; Boch, A-L; Chaumoitre, K; Tanter, M; Aubry, J-F

2017-09-01

Transcranial brain therapy has recently emerged as a non-invasive strategy for the treatment of various neurological diseases, such as essential tremor or neurogenic pain. However, treatments require millimetre-scale accuracy. The use of high frequencies (typically ≥1 MHz) decreases the ultrasonic wavelength to the millimetre scale, thereby increasing the clinical accuracy and lowering the probability of cavitation, which improves the safety of the technique compared with the use of low-frequency devices that operate at 220 kHz. Nevertheless, the skull produces greater distortions of high-frequency waves relative to low-frequency waves. High-frequency waves require high-performance adaptive focusing techniques, based on modelling the wave propagation through the skull. This study sought to optimise the acoustical modelling of the skull based on computed tomography (CT) for a 1 MHz clinical brain therapy system. The best model tested in this article corresponded to a maximum speed of sound of 4000 m.s -1 in the skull bone, and it restored 86% of the optimal pressure amplitude on average in a collection of six human skulls. Compared with uncorrected focusing, the optimised non-invasive correction led to an average increase of 99% in the maximum pressure amplitude around the target and an average decrease of 48% in the distance between the peak pressure and the selected target. The attenuation through the skulls was also assessed within the bandwidth of the transducers, and it was found to vary in the range of 10 ± 3 dB at 800 kHz and 16 ± 3 dB at 1.3 MHz.

Frequency selection for coda wave interferometry in concrete structures.

PubMed

Fröjd, Patrik; Ulriksen, Peter

2017-09-01

This study contributes to the establishment of frequency recommendations for use in coda wave interferometry structural health monitoring (SHM) systems for concrete structures. To this end, codas with widely different central frequencies were used to detect boreholes with different diameters in a large concrete floor slab, and to track increasing damage in a small concrete beam subjected to bending loads. SHM results were obtained for damage that can be simulated by drilled holes on the scale of a few mm or microcracks due to bending. These results suggest that signals in the range of 50-150kHz are suitable in large concrete structures where it is necessary to account for the high attenuation of high-frequency signals. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

One-shot and aberration-tolerable homodyne detection for holographic storage readout through double-frequency grating-based lateral shearing interferometry.

PubMed

Yu, Yeh-Wei; Xiao, Shuai; Cheng, Chih-Yuan; Sun, Ching-Cherng

2016-05-16

A simple method to decode the stored phase signal of volume holographic data storage with adequate wave aberration tolerance is highly demanded. We proposed and demonstrated a one-shot scheme to decode a binary-phase encoding signal through double-frequency-grating based shearing interferometry (DFGSI). The lateral shearing amount is dependent on the focal length of the collimated lens and the frequency difference between the gratings. Diffracted waves with phase encoding were successfully decoded through experimentation. An optical model for the DFGSI was built to analyze phase-error induction and phase-difference control by shifting the double-frequency grating longitudinally and laterally, respectively. The optical model was demonstrated experimentally. Finally, a high aberration tolerance of the DFGSI was demonstrated using the optical model.

High-frequency electrostatic waves in the magnetosphere.

NASA Technical Reports Server (NTRS)

Young, T. S. T.

1973-01-01

High-frequency electrostatic microinstabilities in magnetospheric plasmas are considered in detail. Rather special plasma parameters are found to be required to match the theoretical wave spectrum with satellite observations in the magnetosphere. In particular, it is necessary to have a cold and a warm species of electrons such that (1) the warm component has an anomalous velocity distribution function that is nonmonotonic in the perpendicular component of velocity and is the source of free energy driving the instabilities, (2) the density ratio of the cold component to the hot component is greater than about 0.01, and (3) the temperature ratio of the two components for cases of high particle density is no less than 0.1. These requirements and the corresponding instability criteria are satisfied only in the trapping region; this is also the region in which the waves are most frequently observed. The range of unstable wavelengths and an estimate of the diffusion coefficient are also obtained. The wave are found to induce strong diffusion in velocity space for low-energy electrons during periods of moderate wave amplitude.

Acceleration of the Fast Solar Wind through Minor Ions

NASA Astrophysics Data System (ADS)

Li, X.

2004-01-01

It is assumed that the magnetic flux tubes are strongly concentrated at the boundaries of the supergranule convection cells. A power law spectrum of high frequency Alfvén waves with a spectral index -1 originating from the sun is assumed to supply all the energy needed to energize the plasma flowing in such magnetic flux tubes. At the high frequency end, the waves are eroded by ions due to ion cyclotron resonance. The magnetic flux concentration is essential since it allows a sufficiently strong energy flux to be carried by high frequency ion cyclotron waves and these waves can be readily released at the coronal base by cyclotron resonance. The main results are: 1. By primarily heating alpha particles only, it is possible to produce a steep transition region, a hot corona and a fast solar wind. Coulomb coupling plays a key role in transferring the thermal energy of alpha particles to protons and electrons at the corona base. The electron thermal conduction then does the remaining job to create a sharp transition region. 2. Plasma species may already partially lose thermal equilibrium in the transition region, minor ions may already be faster than protons at the very bottom of the corona. 3. The model predicts high temperature alpha particles (T 2 × 107 K) and low proton temperatures (Tp < 106 K) between 2 and 4 solar radii, suggests that hydrogen Lyman lines observed by UVCS above coronal holes may be primarily broadened by Alfvén waves in this range.

Multi-frequency ICRF diagnostic of Tokamak plasmas

NASA Astrophysics Data System (ADS)

Lafonteese, David James

This thesis explores the diagnostic possibilities of a fast wave-based method for measuring the ion density and temperature profiles of tokamak plasmas. In these studies fast waves are coupled to the plasma at frequencies at the second harmonic of the ion gyrofrequency, at which wave energy is absorbed by the finite-temperature ions. As the ion gyrofrequency is dependent upon the local magnetic field, which varies as l/R in a tokamak, this power absorption is radially localized. The simultaneous launching of multiple frequencies, all resonating at different plasma positions, allows local measurements of the ion density and temperature. To investigate the profile applications of wave damping measurements in a simulated tokamak, an inhouse slab-model ICRF code is developed. A variety of analysis methods are presented, and ion density and temperature profiles are reconstructed for hydrogen plasmas for the Electric Tokamak (ET) and ITER parameter spaces. These methods achieve promising results in simulated plasmas featuring bulk ion heating, off-axis RF heating, and density ramps. The experimental results of similar studies on the Electric Tokamak, a high aspect ratio (R/a = 5), low toroidal field (2.2 kG) device are then presented. In these studies, six fast wave frequencies were coupled using a single-strap, low-field-side antenna to ET plasmas. The frequencies were variable, and could be tuned to resonate at different radii for different experiments. Four magnetic pickup loops were used to measure of the toroidal component of the wave magnetic field. The expected greater eigenmode damping of center-resonant frequencies versus edge-resonant frequencies is consistently observed. Comparison of measured aspects of fast wave behavior in ET is made with the slab code predictions, which validate the code simulations under weakly-damped conditions. A density profile is measured for an ET discharge through analysis of the fast wave measurements, and is compared to an electron density profile derived from Thomson scattering data. The methodology behind a similar measurement of the ion temperature profile is also presented.

Pseudo-One-Dimensional Magnonic Crystals for High-Frequency Nanoscale Devices

NASA Astrophysics Data System (ADS)

Banerjee, Chandrima; Choudhury, Samiran; Sinha, Jaivardhan; Barman, Anjan

2017-07-01

The synthetic magnonic crystals (i.e., periodic composites consisting of different magnetic materials) form one fascinating class of emerging research field, which aims to command the process and flow of information by means of spin waves, such as in magnonic waveguides. One of the intriguing features of magnonic crystals is the presence and tunability of band gaps in the spin-wave spectrum, where the high attenuation of the frequency bands can be utilized for frequency-dependent control on the spin waves. However, to find a feasible way of band tuning in terms of a realistic integrated device is still a challenge. Here, we introduce an array of asymmetric saw-tooth-shaped width-modulated nanoscale ferromagnetic waveguides forming a pseudo-one-dimensional magnonic crystal. The frequency dispersion of collective modes measured by the Brillouin light-scattering technique is compared with the band diagram obtained by numerically solving the eigenvalue problem derived from the linearized Landau-Lifshitz magnetic torque equation. We find that the magnonic band-gap width, position, and the slope of dispersion curves are controllable by changing the angle between the spin-wave propagation channel and the magnetic field. The calculated profiles of the dynamic magnetization reveal that the corrugation at the lateral boundary of the waveguide effectively engineers the edge modes, which forms the basis of the interactive control in magnonic circuits. The results represent a prospective direction towards managing the internal field distribution as well as the dispersion properties, which find potential applications in dynamic spin-wave filters and magnonic waveguides in the gigahertz frequency range.

Computer-assisted time-averaged holograms of the motion of the surface of the mammalian tympanic membrane with sound stimuli of 0.4 to 25 kHz

PubMed Central

Rosowski, John J.; Cheng, Jeffrey Tao; Ravicz, Michael E.; Hulli, Nesim; Hernandez-Montes, Maria; Harrington, Ellery; Furlong, Cosme

2009-01-01

Time-averaged holograms describing the sound-induced motion of the tympanic membrane (TM) in cadaveric preparations from three mammalian species and one live ear were measured using opto-electronic holography. This technique allows rapid measurements of the magnitude of motion of the tympanic membrane surface at frequencies as high as 25 kHz. The holograms measured in response to low and middle-frequency sound stimuli are similar to previously reported time-averaged holograms. However, at higher frequencies (f > 4 kHz), our holograms reveal unique TM surface displacement patterns that consist of highly-ordered arrangements of multiple local displacement magnitude maxima, each of which is surrounded by nodal areas of low displacement magnitude. These patterns are similar to modal patterns (two-dimensional standing waves) produced by either the interaction of surface waves traveling in multiple directions or the uniform stimulation of modes of motion that are determined by the structural properties and boundary conditions of the TM. From the ratio of the displacement magnitude peaks to nodal valleys in these apparent surface waves, we estimate a Standing Wave Ratio of at least 4 that is consistent with energy reflection coefficients at the TM boundaries of at least 0.35. It is also consistent with small losses within the uniformly stimulated modal surface waves. We also estimate possible TM surface wave speeds that vary with frequency and species from 20 to 65 m/s, consistent with other estimates in the literature. The presence of standing wave or modal phenomena has previously been intuited from measurements of TM function, but is ignored in some models of tympanic membrane function. Whether these standing waves result either from the interactions of multiple surface waves that travel along the membrane, or by uniformly excited modal displacement patterns of the entire TM surface is still to be determined. PMID:19328841

Computer-assisted time-averaged holograms of the motion of the surface of the mammalian tympanic membrane with sound stimuli of 0.4-25 kHz.

PubMed

Rosowski, John J; Cheng, Jeffrey Tao; Ravicz, Michael E; Hulli, Nesim; Hernandez-Montes, Maria; Harrington, Ellery; Furlong, Cosme

2009-07-01

Time-averaged holograms describing the sound-induced motion of the tympanic membrane (TM) in cadaveric preparations from three mammalian species and one live ear were measured using opto-electronic holography. This technique allows rapid measurements of the magnitude of motion of the tympanic membrane surface at frequencies as high as 25 kHz. The holograms measured in response to low and middle-frequency sound stimuli are similar to previously reported time-averaged holograms. However, at higher frequencies (f>4 kHz), our holograms reveal unique TM surface displacement patterns that consist of highly-ordered arrangements of multiple local displacement magnitude maxima, each of which is surrounded by nodal areas of low displacement magnitude. These patterns are similar to modal patterns (two-dimensional standing waves) produced by either the interaction of surface waves traveling in multiple directions or the uniform stimulation of modes of motion that are determined by the structural properties and boundary conditions of the TM. From the ratio of the displacement magnitude peaks to nodal valleys in these apparent surface waves, we estimate a Standing Wave Ratio of at least 4 that is consistent with energy reflection coefficients at the TM boundaries of at least 0.35. It is also consistent with small losses within the uniformly stimulated modal surface waves. We also estimate possible TM surface wave speeds that vary with frequency and species from 20 to 65 m/s, consistent with other estimates in the literature. The presence of standing wave or modal phenomena has previously been intuited from measurements of TM function, but is ignored in some models of tympanic membrane function. Whether these standing waves result either from the interactions of multiple surface waves that travel along the membrane, or by uniformly excited modal displacement patterns of the entire TM surface is still to be determined.

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