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Sample records for propagating low-frequency slow

  1. Universality of Slow Earthquakes in the Very Low Frequency Band

    NASA Astrophysics Data System (ADS)

    Ide, S.; Yabe, S.

    2014-12-01

    Deep tectonic tremors have been observed together with signals in the very low frequency (VLF) band from 0.02 to 0.05 Hz, which have been identified as VLF events in limited regions of subduction zones. By stacking broadband seismograms relative to the timing of tremors, we can detect similar signals in all regions where tremors occur in western Japan. These signals are inverted to obtain the moment tensor, and the fault-normal and slip vectors are generally consistent with the geometry of the plate interface and the direction of plate motion. Therefore, these signals are probably radiated by shear slip on the plate interface. The ratio between the seismic energy rate estimated from the tremors and seismic moment rate in the VLF band is almost proportional, with a proportionality constant (i.e., scaled energy) of around 10-10. The spatial distribution of scaled energy may reflect spatial variations in the frequency-dependent characteristics of slow deformation. This method is broadly applicable if abundant data are available. We demonstrate that focal mechanisms can be determined using VLF signals for Cascadia and Mexican subduction zones.

  2. Low-frequency dilatational wave propagation through unsaturated porous media containing two immiscible fluids

    SciTech Connect

    Lo, W.-C.; Sposito, G.; Majer, E.

    2007-02-01

    An analytical theory is presented for the low-frequency behavior of dilatational waves propagating through a homogeneous elastic porous medium containing two immiscible fluids. The theory is based on the Berryman-Thigpen-Chin (BTC) model, in which capillary pressure effects are neglected. We show that the BTC model equations in the frequency domain can be transformed, at sufficiently low frequencies, into a dissipative wave equation (telegraph equation) and a propagating wave equation in the time domain. These partial differential equations describe two independent modes of dilatational wave motion that are analogous to the Biot fast and slow compressional waves in a single-fluid system. The equations can be solved analytically under a variety of initial and boundary conditions. The stipulation of 'low frequency' underlying the derivation of our equations in the time domain is shown to require that the excitation frequency of wave motions be much smaller than a critical frequency. This frequency is shown to be the inverse of an intrinsic time scale that depends on an effective kinematic shear viscosity of the interstitial fluids and the intrinsic permeability of the porous medium. Numerical calculations indicate that the critical frequency in both unconsolidated and consolidated materials containing water and a nonaqueous phase liquid ranges typically from kHz to MHz. Thus engineering problems involving the dynamic response of an unsaturated porous medium to low excitation frequencies (e.g. seismic wave stimulation) should be accurately modeled by our equations after suitable initial and boundary conditions are imposed.

  3. Low frequency acoustic pulse propagation in temperate forests.

    PubMed

    Albert, Donald G; Swearingen, Michelle E; Perron, Frank E; Carbee, David L

    2015-08-01

    Measurements of acoustic pulse propagation for a 30-m path were conducted in an open field and in seven different forest stands in the northeastern United States consisting of deciduous, evergreen, or mixed tree species. The waveforms recorded in forest generally show the pulse elongation characteristic of propagation over a highly porous ground surface, with high frequency scattered arrivals superimposed on the basic waveform shape. Waveform analysis conducted to determine ground properties resulted in acoustically determined layer thicknesses of 4-8 cm in summer, within 2 cm of the directly measured thickness of the litter layers. In winter the acoustic thicknesses correlated with the site-specific snow cover depths. Effective flow resistivity values of 50-88 kN s m(-4) were derived for the forest sites in summer, while lower values typical for snow were found in winter. Reverberation times (T60) were typically around 2 s, but two stands (deciduous and pruned spruce planted on a square grid) had lower values of about 1.2 s. One site with a very rough ground surface had very low summer flow resistivity value and also had the longest reverberation time of about 3 s. These measurements can provide parameters useful for theoretical predictions of acoustic propagation within forests. PMID:26328690

  4. Low frequency acoustic pulse propagation in temperate forests.

    PubMed

    Albert, Donald G; Swearingen, Michelle E; Perron, Frank E; Carbee, David L

    2015-08-01

    Measurements of acoustic pulse propagation for a 30-m path were conducted in an open field and in seven different forest stands in the northeastern United States consisting of deciduous, evergreen, or mixed tree species. The waveforms recorded in forest generally show the pulse elongation characteristic of propagation over a highly porous ground surface, with high frequency scattered arrivals superimposed on the basic waveform shape. Waveform analysis conducted to determine ground properties resulted in acoustically determined layer thicknesses of 4-8 cm in summer, within 2 cm of the directly measured thickness of the litter layers. In winter the acoustic thicknesses correlated with the site-specific snow cover depths. Effective flow resistivity values of 50-88 kN s m(-4) were derived for the forest sites in summer, while lower values typical for snow were found in winter. Reverberation times (T60) were typically around 2 s, but two stands (deciduous and pruned spruce planted on a square grid) had lower values of about 1.2 s. One site with a very rough ground surface had very low summer flow resistivity value and also had the longest reverberation time of about 3 s. These measurements can provide parameters useful for theoretical predictions of acoustic propagation within forests.

  5. Low-Frequency Acoustic Signals Propagation in Buried Pipelines

    NASA Astrophysics Data System (ADS)

    Ovchinnikov, A. L.; Lapshin, B. M.

    2016-01-01

    The article deals with the issues concerning acoustic signals propagation in the large-diameter oil pipelines caused by mechanical action on the pipe body. Various mechanisms of signals attenuation are discussed. It is shown that the calculation of the attenuation caused only by internal energy loss, i.e, the presence of viscosity, thermal conductivity and liquid pipeline wall friction lead to low results. The results of experimental studies, carried out using the existing pipeline with a diameter of 1200 mm. are shown. It is experimentally proved that the main mechanism of signal attenuation is the energy emission into the environment. The numerical values of attenuation coefficients that are 0,14- 0.18 dB/m for the pipeline of 1200 mm in diameter, in the frequency range from 50 Hz to 500 Hz, are determined.

  6. Using Low Frequency Earthquakes to Examine Slow Slip Beneath the Olympic Peninsula, WA

    NASA Astrophysics Data System (ADS)

    Chestler, S.; Creager, K. C.; Sweet, J. R.

    2014-12-01

    Using data from the Array of Arrays (AofA) and Cascadia Arrays for Earthscope (CAFE) experiments we found 61 families of low frequency earthquakes (LFEs) beneath the Olympic Peninsula, Washington. Detections within each family range from Mw1-2. We cross-correlated 6-second long windows within 99 separate hours of tremor data during the 2010 and 2011 Episodic Tremor and Slip (ETS) events. For each hour, we stacked the autocorrelation functions from a set of 7 three-component base stations chosen for their high signal-to-noise ratios. We extracted windows with correlation coefficients higher than 9 times the median absolute deviation. These time windows contain our preliminary LFE detections. We clustered the time windows and produced template waveforms by stacking the waveforms corresponding to a given cluster. By scanning templates through the entire time period when the AofA network was active (June 2009 - September 2010 and August 2011), we identify bursts of LFE activity lasting 2-10 days during times of known tremor [Wech, 2010], including the August 2010 and 2011 ETS events and three tremor swarms in November 2009, March 2010, and July 2010, each of which is assumed to signify a slow-slip event (SSE). During the larger ETS events, we can identify the passage of the main rupture front, rapid tremor reversals and/or dip-parallel streaks. These alternate propagation modes are less obvious during smaller SSEs. We examine the spatial extent of the SSEs by determining which families were active during each event. While all families were active during the 2010 and 2011 ETS events, fewer families were active during the smaller SSEs. The families active during smaller SSEs are located farther down dip. Finally, we are applying double-difference methods to obtain more robust LFE locations, which will shed light on the patchy structure of the plate interface.

  7. Low frequency sound attenuation in a flow duct using a thin slow sound material.

    PubMed

    Aurégan, Yves; Farooqui, Maaz; Groby, Jean-Philippe

    2016-05-01

    A thin subwavelength material that can be flush mounted in a duct and that gives an attenuation band at low frequencies in air flow channels is presented. To decrease the material thickness, the sound is slowed in the material using folded side branch tubes. The impedance of the material is compared to the optimal value given by the Cremer condition, which can differ greatly from the air characteristic impedance. Grazing flow on this material increases the losses at the interface between the flow and the material.

  8. Scattering resonance of elastic wave and low-frequency equivalent slow wave

    NASA Astrophysics Data System (ADS)

    Meng, X.; Liu, H.; Hu, T.; Yang, L.

    2015-12-01

    Transmitted wave occurs as fast p-wave and slow p-wave in certain conditions when seismic waves travel through inhomogeneous layers. Energy of slow p-waves is strongest at some frequency band, but rather weak at both high frequency band and low frequency band, called scattering resonance. For practical seismic exploration, the frequency of slow p-wave occurs is below 10Hz, which cannot be explained by Biot's theory which predicts existence of the slow p-wave at ultrasonic band in the porous media. The slow p-wave equation have been derived, but which only adapted to explaining slow p-wave in the ultrasonic band. Experimental observations exhibit that slow p-wave also exists in nonporous media but with enormous low-velocity interbeds. When vertical incidence, elastic wave is simplified as compressing wave, the generation of slow waves is independent on shear wave. In the case of flat interbed and gas bubble, Liu (2006) has studied the transmission of acoustic waves, and found that the slow waves below the 10Hz frequency band can be explained. In the case of general elastic anisotropy medium, the tiheoretical research on the generation of slow waves is insufficient. Aiming at this problem, this paper presents an exponential mapping method based on transmitted wave (Magnus 1954), which can successfully explain the generation of the slow wave transmission in that case. Using the prediction operator (Claerbout 1985) to represent the transmission wave, this can be derived as first order partial differential equation. Using expansions in the frequency domain and the wave number domain, we find that the solutions have different expressions in the case of weak scattering and strong scattering. Besides, the method of combining the prediction operator and the exponential map is needed to extend to the elastic wave equation. Using the equation (Frazer and Fryer 1984, 1987), we derive the exponential mapping solution for the prediction operator of the general elastic medium

  9. Multipath propagation of low-frequency radio waves inferred from high-resolution array analysis

    NASA Astrophysics Data System (ADS)

    Füllekrug, Martin; Smith, Nathan; Mezentsev, Andrew; Watson, Robert; Astin, Ivan; Gaffet, Stéphane; Evans, Adrian; Rycroft, Michael

    2015-11-01

    The low-frequency radio sky shows the locations of electromagnetic radio sources with a characteristic dilution of precision. Here we report a thorough high-resolution analysis of radio waves from low-frequency (˜20-150 kHz) radio communication transmitters which are recorded with a small aperture array of radio receivers during the day. It is found that the observed dilution of precision results from the array geometry of the radio receivers, a birefringent wave propagation, and the correlated multipath propagation of low-frequency radio waves. The influence of the array geometry on the dilution of precision is reduced by taking into account the impulse response of the array. This procedure reveals for the very first time the splitting of one single radio source into two distinct source locations separated by ˜0.2°-1.9° which result from a birefringent wave propagation. The two locations are yet more clearly identified by using the polarity of the modulated wave number vectors of the radio waves. This polarity is also used to quantify the dilution of precision arising from correlated multipath propagation which is discriminated against wave number fluctuations arising from the timing accuracy of the radio receivers. It is found that ˜69% of the wave number variability is of natural origin and ˜31% originates from the timing accuracy of the receivers. The wave number variability from correlated multipath propagation results in a standard deviation ˜2-8% relative to the source location. This compact measurement of correlated multipath propagation is used to characterize the uncertainty of source locations in the radio sky. The identification of correlated multipath propagation strongly suggests the existence of very fast processes acting on time scales <1 ms in the D region ionosphere with physically meaningful effects on low-frequency radio wave propagation. This important result has implications for practical applications in that the observed multipath

  10. Modeling of the propagation of low-frequency electromagnetic radiation in the Earth’s magnetosphere

    SciTech Connect

    Lebedev, N. V. Rudenko, V. V.

    2015-06-15

    A numerical algorithm for solving the set of differential equations describing the propagation of low-frequency electromagnetic radiation in the magnetospheric plasma, including in the presence of geomagnetic waveguides in the form of large-scale plasma density inhomogeneities stretched along the Earth’s magnetic field, has been developed. Calculations of three-dimensional ray trajectories in the magnetosphere and geomagnetic waveguide with allowance for radiation polarization have revealed characteristic tendencies in the behavior of electromagnetic parameters along the ray trajectory. The results of calculations can be used for magnetospheric plasma diagnostics.

  11. Sound propagation in and low frequency noise absorption by helium-filled porous material.

    PubMed

    Choy, Y S; Huang, Lixi; Wang, Chunqi

    2009-12-01

    Low-frequency noise is difficult to deal with by traditional porous material due to its inherent high acoustic impedance. This study seeks to extend the effective range of sound absorption to lower frequencies by filling a low density gas, such as helium, in the porous material. Compared with conventional air-filled absorption material, the helium-filled porous material has a much reduced characteristic impedance; hence, a good impedance matching with pure air becomes more feasible at low frequencies. The acoustic properties of a series of helium-filled porous materials are investigated with a specially designed test rig. The characteristic of the sound propagation in a helium-filled porous material is established and validated experimentally. Based on the measured acoustic properties, the sound absorption performance of a helium-filled absorber (HA) of finite thickness is studied numerically as well as experimentally. For a random incidence field, the HA is found to perform much better than the air-filled absorber at low frequencies. The main advantage of HA lies in the middle range of oblique incidence angles where wave refraction in the absorber enhances sound absorption. The advantage of HA as duct lining is demonstrated both numerically and experimentally.

  12. Slow-Slip Propagation Speeds

    NASA Astrophysics Data System (ADS)

    Rubin, A. M.; Ampuero, J.

    2007-12-01

    Combined seismic and geodetic data from subduction zones and the Salton Trough have revealed slow slip events with reasonably well-defined propagation speeds. This in turn is suggestive of a more-or-less well- defined front separating nearly locked regions outside the slipping zone from interior regions that slide much more rapidly. Such crack-like nucleation fronts arise naturally in models of rate-and-state friction for lab-like values of a/b, where a and b are the coefficients of the velocity- and state-dependence of the frictional strength (with the surface being velocity-neutral for a/b=1). If the propagating front has a quasi-steady shape, the propagation and slip speeds are kinematically tied via the local slip gradient. Given a sufficiently sharp front, the slip gradient is given dimensionally by Δτp- r/μ', where Δτp-r is the peak-to-residual stress drop at the front and μ' the effective elastic shear modulus. Rate-and-state simulations indicate that Δτp-r is given reasonably accurately by bσ\\ln(Vmaxθi/Dc), where σ is the effective normal stress, Vmax is the maximum slip speed behind the propagating front, θi is the the value of "state" ahead of the propagating front, and Dc is the characteristic slip distance for state evolution. Except for a coefficient of order unity, Δτp-r is independent of the evolution law. This leads to Vprop/Vmax ~μ'/[bσ\\ln(Vmaxθi/Dc)]. For slip speeds a few orders of magnitude above background, \\ln(Vmaxθi/Dc) can with reasonable accuracy be assigned some representative value (~4-5, for example). Subduction zone transients propagate on the order of 10 km/day or 10-1 m/s. Geodetic data constrain the average slip speed to be a few times smaller than 1 cm/day or 10-7 m/s. However, numerical models indicate that the maximum slip speed at the front may be several times larger than the average, over a length scale that is probably too small to resolve geodetically, so a representative value of Vprop/Vmax may be ~106

  13. Characteristics of slow earthquakes in the very low frequency band: Application to the Cascadia subduction zone

    NASA Astrophysics Data System (ADS)

    Ide, Satoshi

    2016-08-01

    Deep tectonic tremors detected in many subduction zones worldwide are often accompanied by very low frequency (VLF) signals, detectable by broadband seismometers but usually hidden in large ambient noise. By stacking broadband seismograms relative to tremor hypocentral times, we can recover the VLF signals. The stacked signals are then inverted to determine a moment tensor solution, using a procedure previously applied to VLF signals in Japan, Taiwan, and Mexico. Here we apply this method to the Cascadia subduction zone, where tremors and slow slip events are clearly observed. As expected, we successfully recover VLF signals for almost the entire tremor region beneath southern Vancouver Island and northern Washington State. The moment tensors are mostly well determined as low-angle thrust type, but source depths are poorly constrained. The slip direction is slightly rotated counterclockwise with respect to the local plate motion direction, probably due to bending of the subducting plate. The seismic moment measured in VLF band is proportional to the seismic energy of tremors, with a scaled energy of about 3 × 10-9. The widespread observability of VLF signals suggests that the deformation associated with tremors and SSEs is actually a very broadband phenomenon, as suggested by stochastic models.

  14. Low-frequency sound propagation modeling over a locally-reacting boundary using the parabolic approximation

    NASA Technical Reports Server (NTRS)

    Robertson, J. S.; Siegman, W. L.; Jacobson, M. J.

    1989-01-01

    There is substantial interest in the analytical and numerical modeling of low-frequency, long-range atmospheric acoustic propagation. Ray-based models, because of frequency limitations, do not always give an adequate prediction of quantities such as sound pressure or intensity levels. However, the parabolic approximation method, widely used in ocean acoustics, and often more accurate than ray models for lower frequencies of interest, can be applied to acoustic propagation in the atmosphere. Modifications of an existing implicit finite-difference implementation for computing solutions to the parabolic approximation are discussed. A locally-reacting boundary is used together with a one-parameter impedance model. Intensity calculations are performed for a number of flow resistivity values in both quiescent and windy atmospheres. Variations in the value of this parameter are shown to have substantial effects on the spatial variation of the acoustic signal.

  15. Extremely-low-frequency magnetic fields disrupt rhythmic slow activity in rat hippocampal slices.

    PubMed

    Bawin, S M; Satmary, W M; Jones, R A; Adey, W R; Zimmerman, G

    1996-01-01

    Several studies have indicated that weak, extremely-low-frequency (ELF; 1-100 Hz) magnetic fields affect brain electrical activity and memory processes in man and laboratory animals. Our studies sought to determine whether ELF magnetic fields could couple directly with brain tissue and affect neuronal activity in vitro. We used rat hippocampal slices to study field effects on a specific brain activity known as rhythmic slow activity (RSA), or theta rhythm, which occurs in 7-15 s bursts in the hippocampus during memory functions. RSA, which, in vivo, is a cholinergic activity, is induced in hippocampal slices by perfusion of the tissue with carbachol, a stable analog of acetylcholine. We previously demonstrated that the free radical nitric oxide (NO), synthesized in carbachol-treated hippocampal slices, lengthened and destabilized the intervals between successive RSA episodes. Here, we investigate the possibility that sinusoidal ELF magnetic fields could trigger the NO-dependent perturbation of the rate of occurrence of the RSA episodes. Carbachol-treated slices were exposed for 10 min epochs to 1 or 60 Hz magnetic fields with field intensities of 5.6, 56, or 560 microT (rms), or they were sham exposed. All exposures took place in the presence of an ambient DC field of 45 microT, with an angle of -66 degrees from the horizontal plane. Sinusoidal 1 Hz fields at 56 and 560 microT, but not at 5.6 microT, triggered the irreversible destabilization of RSA intervals. Fields at 60 Hz resulted in similar, but not statistically significant, trends. Fields had no effects on RSA when NO synthesis was pharmacologically inhibited. However, field effects could take place when extracellular NO, diffusing from its cell of origin to the extracellular space,was chelated by hemoglobin. These results suggest that ELF magnetic fields exert a strong influence on NO systems in the brain; therefore, they could modulate the functional state of a variety of neuronal ensembles. PMID:8915548

  16. Solvent friction effects propagate over the entire protein molecule through low-frequency collective modes.

    PubMed

    Moritsugu, Kei; Kidera, Akinori; Smith, Jeremy C

    2014-07-24

    Protein solvation dynamics has been investigated using atom-dependent Langevin friction coefficients derived directly from molecular dynamics (MD) simulations. To determine the effect of solvation on the atomic friction coefficients, solution and vacuum MD simulations were performed for lysozyme and staphylococcal nuclease and analyzed by Langevin mode analysis. The coefficients thus derived are roughly correlated with the atomic solvent-accessible surface area (ASA), as expected from the fact that friction occurs as the result of collisions with solvent molecules. However, a considerable number of atoms with higher friction coefficients are found inside the core region. Hence, the influence of solvent friction propagates into the protein core. The internal coefficients have large contributions from the low-frequency modes, yielding a simple picture of the surface-to-core long-range damping via solvation governed by collective low-frequency modes. To make use of these findings in implicit-solvent modeling, we compare the all-atom friction results with those obtained using Langevin dynamics (LD) with two empirical representations: the constant-friction and the ASA-dependent (Pastor-Karplus) friction models. The constant-friction model overestimates the core and underestimates the surface damping whereas the ASA-dependent friction model, which damps protein atoms only on the solvent-accessible surface, reproduces well the friction coefficients for both the surface and core regions observed in the explicit-solvent MD simulations. Therefore, in LD simulation, the solvent friction coefficients should be imposed only on the protein surface. PMID:24999844

  17. Solvent friction effects propagate over the entire protein molecule through low-frequency collective modes.

    PubMed

    Moritsugu, Kei; Kidera, Akinori; Smith, Jeremy C

    2014-07-24

    Protein solvation dynamics has been investigated using atom-dependent Langevin friction coefficients derived directly from molecular dynamics (MD) simulations. To determine the effect of solvation on the atomic friction coefficients, solution and vacuum MD simulations were performed for lysozyme and staphylococcal nuclease and analyzed by Langevin mode analysis. The coefficients thus derived are roughly correlated with the atomic solvent-accessible surface area (ASA), as expected from the fact that friction occurs as the result of collisions with solvent molecules. However, a considerable number of atoms with higher friction coefficients are found inside the core region. Hence, the influence of solvent friction propagates into the protein core. The internal coefficients have large contributions from the low-frequency modes, yielding a simple picture of the surface-to-core long-range damping via solvation governed by collective low-frequency modes. To make use of these findings in implicit-solvent modeling, we compare the all-atom friction results with those obtained using Langevin dynamics (LD) with two empirical representations: the constant-friction and the ASA-dependent (Pastor-Karplus) friction models. The constant-friction model overestimates the core and underestimates the surface damping whereas the ASA-dependent friction model, which damps protein atoms only on the solvent-accessible surface, reproduces well the friction coefficients for both the surface and core regions observed in the explicit-solvent MD simulations. Therefore, in LD simulation, the solvent friction coefficients should be imposed only on the protein surface.

  18. MAVEN observation of an obliquely propagating low-frequency wave upstream of Mars

    NASA Astrophysics Data System (ADS)

    Ruhunusiri, Suranga; Halekas, J. S.; Connerney, J. E. P.; Espley, J. R.; McFadden, J. P.; Mazelle, C.; Brain, D.; Collinson, G.; Harada, Y.; Larson, D. E.; Mitchell, D. L.; Livi, R.; Jakosky, B. M.

    2016-03-01

    We report Mars Atmosphere and Volatile EvolutioN mission observations of a large amplitude low-frequency plasma wave that propagated oblique to the ambient magnetic field upstream of Mars along with a non-solar-wind plasma component that had a flow velocity perpendicular to the magnetic field. We consider nine possibilities for this wave that include various combinations of its propagation direction, polarization in the solar wind frame, and ion source responsible for its generation. Using the observed wave parameters and the measured plasma parameters as constraints, we uniquely identify the wave by systematically discarding these possibilities. We determine that the wave is a right-hand polarized wave that propagated upstream in the solar wind frame. We find two possibilities for the ion source that can be responsible for this wave generation. They are either newly born pickup protons or reflected solar wind protons from the bow shock. We determine that the observed non-solar-wind component is not responsible for the wave generation, and it is likely that the non-solar-wind component was merely perturbed by the passage of the wave.

  19. The propagation of low-frequency whistler waves driven by ion beams in the magnetotail

    NASA Technical Reports Server (NTRS)

    Burinskaia, T.; Schriver, D.; Ashour-Abdalla, M.

    1993-01-01

    The generation and propagation of low-frequency whistler waves excited by ion beams in the plasma sheet boundary layer are followed using standard ray tracing techniques and assuming a Harris-type neutral sheet magnetic field profiles. The density is chosen such that the total pressure remains constant. The wave energy is calculated along the wave path taking into account growth due to the ion beam while the wave is in the plasma sheet boundary layer as well as damping due to resonant interactions with the background plasma. The results show that the electromagnetic waves are guided toward the central plasma sheet by the plasma gradients but are damped out before reaching the neutral plane itself due to Cerenkov resonance with the hot central plasma sheet background ions. The amplitudes and final positions of the waves depend on the temperature of the background plasma, the ion beam drift speed, and the ion beam thermal speed.

  20. Comparison of FFP predictions with measurements of a low-frequency signal propagated in the atmosphere

    NASA Technical Reports Server (NTRS)

    Wilson, K. Keith; Thomson, Dennis W.

    1990-01-01

    An experimental study of low-frequency propagation over a distance of 770 m was previously reported (J. Acoust. Soc. Am. Suppl. 1 86, S120 (1989)). For that study, sound speed profiles were reconstructed entirely from surface-layer micrometeorological data. When the acoustic data were compared with theoretical predictions from a fast field program (FFP), it was found that the FFP underpredicted sound levels measured in a shadow zone. Here, the effect on the predictions of including meteorological data for heights greater than the surface layer, i.e., wind profiles measured by a Doppler sodar, is discussed. Vertical structure of turbulence is simulated by stochastically perturbing the mean profiles, and the agreement between the acoustic data and FFP predictions is improved.

  1. Activated Very Low Frequency Earthquakes By the Slow Slip Events in the Ryukyu Subduction Zone

    NASA Astrophysics Data System (ADS)

    Nakamura, M.; Sunagawa, N.

    2014-12-01

    The Ryukyu Trench (RT), where the Philippine Sea plate is subducting, has had no known thrust earthquakes with a Mw>8.0 in the last 300 years. However, the rupture source of the 1771 tsunami has been proposed as an Mw > 8.0 earthquake in the south RT. Based on the dating of tsunami boulders, it has been estimated that large tsunamis occur at intervals of 150-400 years in the south Ryukyu arc (RA) (Araoka et al., 2013), although they have not occurred for several thousand years in the central and northern Ryukyu areas (Goto et al., 2014). To address the discrepancy between recent low moment releases by earthquakes and occurrence of paleo-tsunamis in the RT, we focus on the long-term activity of the very low frequency earthquakes (VLFEs), which are good indicators of the stress release in the shallow plate interface. VLFEs have been detected along the RT (Ando et al., 2012), which occur on the plate interface or at the accretionary prism. We used broadband data from the F-net of NIED along the RT and from the IRIS network. We applied two filters to all the raw broadband seismograms: a 0.02-0.05 Hz band-pass filter and a 1 Hz high-pass filter. After identification of the low-frequency events from the band-pass-filtered seismograms, the local and teleseismic events were removed. Then we picked the arrival time of the maximum amplitude of the surface wave of the VLFEs and determined the epicenters. VLFEs occurred on the RA side within 100 km from the trench axis along the RT. Distribution of the 6670 VLFEs from 2002 to 2013 could be divided to several clusters. Principal large clusters were located at 27.1°-29.0°N, 25.5°-26.6°N, and 122.1°-122.4°E (YA). We found that the VLFEs of the YA are modulated by repeating slow slip events (SSEs) which occur beneath south RA. The activity of the VLFEs increased to two times of its ordinary rate in 15 days after the onset of the SSEs. Activation of the VLFEs could be generated by low stress change of 0.02-20 kPa increase in

  2. Application of ray theory to propagation of low frequency noise from wind turbines

    NASA Technical Reports Server (NTRS)

    Hawkins, James A.

    1987-01-01

    Ray theory is used to explain data from two experiments (1985 and 1985) on the propagation of low frequency sound generated by the WTS-4 wind turbine. Emphasis is on downwind data, but some upwind measurements taken during the 1985 experiment are also considered. General ray theory for a moving medium is reviewed and ray equations obtained. Restrictions are introduced simplifying the equations and permitting the use of a ray theory program MEDUSA, the computed propagation loss curve of which is compared to the measurements. Good qualitative agreement is obtained with 1984 downwind data. The results indicate that the downwind sound field is that of a near-ground sound channel. Although more scatter is seen in the 1985 data, agreement between theory and data is also good. In particular, the position and magnitude of the jump in the sound levels associated with the beginning of the sound channel is correctly predicted. The theoretical explanation of the upwind data is less successful. Ray theory calculations indicate the formation of a shadow zone that, in fact, does not occur. While no sharp shadow zone is apparent in the data, the general expectation (based on ray theory) that sound levels should be much reduced upwind is confirmed by the data.

  3. Breathing as a low frequency wave propagation in nonlinear elastic permeable medium

    NASA Astrophysics Data System (ADS)

    Kyriakou, Elizabeth; McKenzie, David R.; Suchowerska, Natalka; Fulton, Roger R.

    2007-05-01

    Breathing can be regarded as a type of low frequency wave propagation. Unlike sound propagation in open air, in breathing, the air compressibility is not as important as the flow of air, and to a first approximation the air can be regarded as incompressible. We have developed a one-dimensional analytical description of wave motion in a metamaterial consisting of a porous elastic medium contained within chambers, separated by plates with orifices representing the minor airways. The metamaterial is placed within a cylinder with impermeable sides representing the thorax, driven at one end by a piston representing the diaphragm. The incompressible air is able to escape from the top of the cylinder. The solutions to the wave equation have characteristics that depend on the values of permeability (defined by the size of the orifice in the plates), the Young's modulus of the elastic medium and the density of lung tissue. A ‘normal' regime is identified in which the strain of the medium near the diaphragm is large and the strain at the top of the cylinder near the outlet is small. An ‘abnormal' regime is also identified in which the opposite applies. A rapid transition between the two regimes can be caused by changing the parameters representing the lung tissue. This transition may represent the onset of a disease state such as asthma.

  4. Low-frequency Stoneley wave propagation at the interface of two porous half-spaces

    NASA Astrophysics Data System (ADS)

    Markov, M. G.

    2009-05-01

    The Frenkel-Biot theory is used to study a propagation of Stoneley elastic wave at the boundary of two fluid-saturated porous media. The velocity and attenuation of the Stoneley surface wave are determined. I show that the dispersion equation coincides with the equation for the Stoneley wave at the interface of two elastic half-spaces in the low-frequency range. Numerical examples of calculations are presented for two important cases: two different fluids lying in the same viscoelastic skeleton (gas-water interface) and two poroelastic half-spaces with different porosity and permeability containing the same fluid. To take into account the absorption in the solid matrix, I use well-known Stoll's model. Our calculation results have shown that the Stoneley wave absorption is determined by the energy dissipation in the solid matrix for consolidated rocks. As the frequency is increased, hydrodynamic effects connected with the presence of a movable fluid in the pores begin to play a significant role.

  5. Illuminating the Transition Between Steady Sliding and Episodic Tremor and Slow Slip Using Low Frequency Earthquakes at the Downdip Edge

    NASA Astrophysics Data System (ADS)

    Creager, K. C.; Sweet, J.; Vidale, J. E.; Houston, H.

    2012-12-01

    Using data from the Array of Arrays and CAFE experiments, we have identified eight Low-Frequency Earthquake (LFE) families on the subduction plate interface, under the Olympic Peninsula, Washington State. We analyze the time history of each during the time interval 2007-2012. The updip-most family (LFE1) only lights up during the well-known northern Cascadia Episodic Tremor and Slip (ETS) events that recur every 15 months. The recurrence intervals shorten from updip LFE1 to the downdip-most family (LFE4), which repeats every 14 days; 30 times more frequently. This presentation focuses on the downdip family. See the Sweet presentation, this session, for an analysis of the updip-most LFE family. LFEs from family 4 typically have durations of about one hour, with as many as 100 repeats during that time. Unlike their updip counterparts, they occur as discrete events without other LFEs or tremor visible during that time. They are strongly modulated by tidal shear stress. Twice as many LFEs occur during encouraging shear stress as during discouraging times. In contrast, these same LFEs occur when tidal normal stress is compressive which should inhibit slip. To reconcile LFE occurrence with favorable tidal Coulomb stress requires that the friction coefficient be less than 0.2 .This extreme sensitivity to very small shear stresses also suggests near lithostatic pore fluid pressures. We propose that the bursts of LFEs in this family correspond to discrete slow-slip events that occur with remarkable regularity. To add up to plate rates, each burst would correspond to a little more than 1 mm of slip, and each individual LFE to a little less than 0.1 mm, assuming all the slip occurs in the form of LFE activity and each LFE ruptures the same spot. One of these event sequences was captured by our 1-km aperture 80-element Big Skidder Array in 2008. Careful stacked correlation functions from 32 LFEs relative to a reference event showed S-P times varied only up to 0.02s, which

  6. Unraveling the Intricacies of Cascadia Slow-Slip Rupture Using Repeating Low-Frequency Earthquakes

    NASA Astrophysics Data System (ADS)

    Creager, K. C.; Sweet, J. R.; Chestler, S.; Houston, H.; Vidale, J. E.

    2013-12-01

    Using data from the 2-year Array of Arrays and the 6-year CAFE seismic experiments on the Olympic Peninsula, Washington, we have identified and located nine groups (families) of repeating Low-Frequency Earthquakes (LFEs). Each family locates within a few km of the plate interface as estimated by active-source wide-angle reflections (Preston et al., Science, 2003) and repeats 100s to 10,000 times in intriguing temporal patterns. At the down-dip end they light up every 1-2 weeks, each with 10s to 100s of LFE repeats, during typical time scales of about one hour. Double-difference locations indicate the LFEs are constrained to a linear patch 2 km long, on the plate interface elongated in the direction of relative plate motion. In contrast, the up-dip-most LFE family lights up primarily during the big 14-month Episodic Tremor and Slip (ETS) events. It repeatedly exhibits a pattern of being quiet for 14 months, then lighting up with hundreds of repeats during a few hour period, which we interpret as the main ETS rupture front passing the location of the LFE family. This is followed by a five-day period of quiescence punctuated by about a dozen short-duration episodes of frenzied LFE activity. Monitoring LFE families within 20 km of each other, we find their bursts of activity correlate roughly with each other, but with time lags of 10s of minutes to hours. We interpret this activity as the passage of streaks and Rapid Tremor Reversals that occur during the 5 days after the main rupture front passes. After this time, either the stress is relieved, or the fault has healed and the LFE family is quiet for another 14 months. The magnitudes of the down-dip LFEs, based on S-wave amplitudes, range from -1 to 1. In the limited magnitude range over which our LFE catalog is complete (0.6 magnitude units) they appear to follow a Gutenberg-Richter distribution with a very large b-value of 4. There is a systematic pattern of short-duration LFE activity happening often (every 1

  7. Possible shallow slow slip events in Hyuga-nada, Nankai subduction zone, inferred from migration of very low frequency earthquakes

    NASA Astrophysics Data System (ADS)

    Asano, Youichi; Obara, Kazushige; Matsuzawa, Takanori; Hirose, Hitoshi; Ito, Yoshihiro

    2015-01-01

    investigated the spatiotemporal evolution of a shallow very low frequency earthquake (sVLFE) swarm linked to the 2009/2010 long-term slow slip event (SSE) in the Bungo channel, southwestern Japan. Broadband seismograms were analyzed using a cross-correlation technique to detect sVLFEs having similar waveforms to template sVLFEs, and their relative locations were estimated. The sVLFEs exhibit clear migration over a distance of 150 km along the Nankai trough, similar to nonvolcanic tremors and deep very low frequency earthquakes (dVLFEs) accompanied by short-term SSEs on the downward extension of the seismogenic zone. This similarity between sVLFEs and dVLFEs suggests that SSEs occur in both deeper and shallower extensions of the seismogenic zone. The analyzed sVLFEs were likely caused by a shallow SSE that occurred from January to March 2010 following the initiation and acceleration of the long-term SSE. This temporal evolution may be caused by stress interaction between the shallow SSE and the long-term SSE.

  8. Status report on environment, propagation and system modeling for an elf/vlf/lf(extremely low frequency/very low frequency/low frequency) ionospheric dependent propagation code. Technical report

    SciTech Connect

    Rutherford, R.R.; Knapp, W.S.

    1983-06-28

    This report describes the continuing work on WEDCOM during the 1982 contractual period. Environmental models were updated and efficient propagation computational procedures were implemented to reduce execution time. Procedures were developed to provide the WEDCOM user with an automated method of selecting calculation times and ionization profile locations consistent with nuclear environmental sensitivities. VLF/LF signal processing models were adapted for use in WEDCOM and procedures for including atmospheric noise were developed.

  9. Instabilities of low frequency, parallel propagating electromagnetic waves in the earth's foreshock region

    NASA Technical Reports Server (NTRS)

    Sentman, D. D.; Edmiston, J. P.; Frank, L. A.

    1981-01-01

    An instability analysis is presented for parallel and antiparallel propagating electromagnetic waves generated by reflected and diffuse suprathermal ions upstream of the earth's bow shock. Calculations are performed on the basis of upstream particle observations made by the ISEE 1 Quadrispheric Lepedea instrument and low-energy electron measurements made by the ISEE 1 electron spectrometer for a single period. The electromagnetic dispersion relation is computed and the unstable modes and growth times of the fastest growing waves are determined. It is found that the reflected ions destabilize the plasma most strongly at a wave frequency 0.1 that of the ion gyrofrequency by a resonant ion beam instability for waves propagating upstream and by a nonresonant firehose-like instability for waves propagating downstream. The diffuse ions also destabilize the plasma most strongly at the same frequency by means of resonant instabilities of both right- and left-hand polarized waves propagating away from the bow shock.

  10. Acoustical effects of a large ridge on low-frequency sound propagation in stationary and moving atmospheres

    NASA Technical Reports Server (NTRS)

    Robertson, J. S.; Jacobson, M. J.; Siegmann, W. L.; Santandrea, D. P.

    1989-01-01

    The effects of a ridge on a low-frequency acoustic propagation in quiescent and windy atmospheres are investigated using a parabolic approximation. A logarithmic wind-speed profile, commonly employed to model atmospheric wind currents, is modified and used to model two-dimensional atmospheric flow over a triangularly-shaped hill. The parabolic equation is solved using an implicit finite-difference algorithm. Several examples are examined to determine the combined effects of source-ridge distance, ridge dimensions, wind-speed profile, and CW source frequency on the received acoustic field.

  11. Effect of environmental uncertainty on low frequency sonar propagation in a shallow sea

    NASA Astrophysics Data System (ADS)

    Chen, Feng; Shapiro, Georgy; Thain, Richard

    2013-04-01

    Underwater acoustics is widely used in navigational, scientific and military areas. The technique of coupled ocean-acoustic modelling has been of interest for many years. The predictive capability of acoustic propagation modelling is highly dependent on the marine environment and seabed properties. The direction and intensity of sound propagation is determined by the sound speed gradients in the water column, which in turn are dependent upon variations in temperature and salinity. These variations occur on a range of scales - from climatic (tens of years) to the mesoscale (days and weeks) in time and from hundreds of meters to tens of kilometres in space, especially on the continental shelf. In shallow water, extremely dynamic features such as strong density fronts, intense stratifications, eddies, filaments and other mesoscale features exist persistently. These features described above have significant impacts on underwater sound propagation and therefore must be investigated in order to improve the predictive accuracy of acoustic modelling. Uncertainties in the ocean model simulations are transferred to the acoustic field due to the usage of coupled ocean-acoustic system. The area selected for this study is the Celtic Sea, which is typical European continental shelf shallow water. It is filled with mesoscale eddies which contribute to the formation of the residual (tidally averaged) circulation pattern. The sea is strongly stratified from April to November along with bottom fronts, which adds to the formation of density driven currents. In this paper we employ the ocean model POLCOMS which has been validated for different regions of the world ocean and also been used operationally by the UK Met Office for the European Shelf seas to construct the environmental condition for the acoustic model and the sonar performance model HARCAM, which has been validated formally by the U.K. Ministry of Defence over a variety of frequencies, to generate acoustic propagation data

  12. Study of the propagation characteristics of Very Low Frequency Signal as observed from Indian Permanent station Maitri and Bharati

    NASA Astrophysics Data System (ADS)

    Sasmal, Sudipta; Chakrabarti, Sandip Kumar; Pal, Sujay; Palit, Sourav; Chakraborty, Suman

    2016-07-01

    Propagation of Very Low Frequency (VLF) radio signal through the Earth-ionosphere waveguide strongly depends on the plasma properties of the ionospheric D layer. Solar extreme ultraviolet radiation plays the central role in controlling physical and chemical properties of the lower ionospheric layers and hence determining the quality and propagation characteristics of a VLF signal. The nature of interference among different propagating modes varies widely with the length of the propagation path. For a very long path, exposure of solar radiation and thus the degree of ionization vary by a large amount along the path. Study of radio signal characteristics in the Antarctic region during summer period in the Southern Hemisphere gives us a unique opportunity to explore such a possibility. In addition, there is an extra feature in this path - the presence of solar radiation and hence the D region for the whole day during summer in at least some sections of the path. We present long-distance propagation characteristics of VLF signals transmitted from VTX (18.2 kHz) and NWC (19.8 kHz) transmitters recorded simultaneously at Indian permanent stations Maitri (latitude 70 ^{o}45 ^{'}S, longitude 11 ^{o}40 ^{'}E) and Bharati (69 ^{o}24 ^{'}S, 76 ^{o}10 ^{'}E). A very stable diurnal variation of the signal (both amplitude and phase) has been obtained with no signature of nighttime fluctuation due the presence of 24 h of sunlight for both the stations. We present the attenuation rate of the dominant waveguide modes corresponding to those propagation conditions where the effects of the Antarctic polar ice on the attenuation of different propagating waveguide modes are visible. VLF signals show the effects of high energetic solar events. Using ion production and recombination profiles by solar irradiance and incorporating D region ion chemistry processes, we calculate the electron density profile at different heights. Using this profile in the Long Wavelength Propagation Capability

  13. Migration Episode of Shallow Low-frequency Tremor at the Nankai Trough Subduction Zone: Seismological Evidence for Episodic Slow Slip Event Occurring at the Shallow Transition Zone

    NASA Astrophysics Data System (ADS)

    Yamashita, Y.; Yakiwara, H.; Shimizu, H.; Uchida, K.; Hirano, S.; Miyamachi, H.; Umakoshi, K.; Nakamoto, M.; Fukui, M.; Kamizono, M.; Kanehara, H.; Yamada, T.; Shinohara, M.; Obara, K.

    2014-12-01

    To understand the shallow part of plate interface between megathrust seismogenic zone and trench axis is very important for development of huge earthquake rupture and generation of tsunami. Monitoring of offshore seismicity near the Nankai trough by temporal ocean bottom seismographic observation in 2013 revealed that low-frequency tremor occurred associated with shallow very-low-frequency earthquakes (VLFEs) in the shallow part of plate interface. The shallow tremor episode lasted for approximately 1 month, which is almost consistent with the shallow VLFE activity observed from land broad-band seismic stations [Asano, 2014]. The horizontal location of shallow tremor estimate by envelope correlation method [Obara, 2002] shows a belt-like distribution along trench strike with narrow width than the deep tremor. The most remarkable feature of the shallow tremor activity is migration. There are two migration modes including diffusive slower migration and rapid tremor reversal (RTR), which are very similar to the deep tremor as a part of the ETS. This strongly indicates a possibility of the occurrence of episodic slow slip event in the shallow transition zone. That is to say, the migration of shallow tremor is supposed to be caused by migrating rupture front of SSE. In addition, the migration was detouring around the subducted Kyushu-Palau ridge. This suggests that the occurrence of tremor is sensitive to change in the shape of plate interface and seeks to propagate along almost the same depth range, in other word, a specified temperature and pressure condition. The narrow width distribution of shallow tremor also indicates that the shallow tremor is strongly related to dehydration process of a specified mineral under a narrow limited range of temperature and pressure condition compared to the deep tremor.

  14. A Probe of Magnetosphere-Ionosphere Coupling using the Propagation Characteristics of Very Low Frequency Signal

    NASA Astrophysics Data System (ADS)

    Nwankwo, V. U. J.; Chakrabarti, S. K.; Ogunmodimu, O. A.

    2015-12-01

    The amplitude and phase of VLF/LF radio signal are sensitive to changes in the electrical conductivity of the lower ionosphere when propagated in the Earth-ionosphere waveguide. This unique characteristic makes it useful in studying sudden ionospheric disturbances and/or anomaly especially those related to prompt X-ray flux output from solar flares and gamma ray bursts (GRBs). However, strong geomagnetic disturbances and/or storm conditions are known to produce large and global ionospheric disturbances, which can significantly affect VLF radio propagation in the D region ionosphere. Other than X-ray flux enhancement of amplitude and phase, diurnal VLF signature may convey other important information especially those related to geomagnetic disturbance/storm induced ionospheric changes. In this paper, using the data of three propagation paths (at latitudes 40-54), we performed detail analysis of the trend of variations of aspects VLF diurnal signal under varying solar and/or geomagnetic space environmental conditions for identification of possible geomagnetic footprint on the ionosphere. We found that trend of variations significantly reflected the prevailing space weather conditions of various time scales. The `dipping' of the signal diurnal amplitude have shown noteworthy consistency with significantly geomagnetic perturbed and/or storm conditions in the time scale of 1-2 days. We also found that dipping of most MDP signal occurred irrespective of the time (of the day), which an event happened, while those of MBSR, MASS, SRT and SST appear to largely depend on event occurrence time and/or duration. Pre-sunset event had more influence on the SST and MASS (dusk signal), while pre-sunrise event had more influence on the SRT and MBSR (dawn signal), and depending on the duration of the event, impact could be extended to the neighbouring point/component in succession. The induced dipping varied with geomagnetic activity/event intensity and/or duration, as well as the

  15. Slow crack propagation in heterogeneous materials.

    PubMed

    Kierfeld, J; Vinokur, V M

    2006-05-01

    Statistics and thermally activated dynamics of crack nucleation and propagation in a two-dimensional heterogeneous material containing quenched randomly distributed defects are studied theoretically. Using the generalized Griffith criterion we derive the equation of motion for the crack tip position accounting for dissipation, thermal noise, and the random forces arising from the defects. We find that aggregations of defects generating long-range interaction forces (e.g., clouds of dislocations) lead to anomalously slow creep of the crack tip or even to its complete arrest. We demonstrate that heterogeneous materials with frozen defects contain a large number of arrested microcracks and that their fracture toughness is enhanced to the experimentally accessible time scales.

  16. Difference in Simulated Low-Frequency Sound Propagation in the Various Species of Baleen Whale

    NASA Astrophysics Data System (ADS)

    Tsuchiya, Toshio; Naoi, Jun; Futa, Koji; Kikuchi, Toshiaki

    2004-05-01

    Whales found in the north Pacific are known to migrate over several thousand kilometers, from the Alaskan coast where they heartily feed during the summer to low latitude waters where they breed during the winter. Therefore, it is assumed that whales are using the “deep sound channel” for their long-distance communication. The main objective of this study is to clarify the behaviors of baleen whales from the standpoint of acoustical oceanography. Hence, authors investigated the possibility of long distance communication in various species of baleen whales, by simulating the long-distance propagation of their sound transmission, by applying the mode theory to actual sound speed profiles and by simulating their transmission frequencies. As a result, the possibility of long distance communication among blue whales using the deep sound channel was indicated. It was also indicated that communication among fin whales and blue whales can be made possible by coming close to shore slopes such as the Island of Hawaii.

  17. Inelastic Caterpillar-like Deformational Wave as a Trigger of Tremors, Very-low-frequency Earthquakes and Slow Slip Events

    NASA Astrophysics Data System (ADS)

    Gershenzon, N. I.; Bambakidis, G.; Hauser, E. C.

    2009-12-01

    Deep low-frequency tremors, very-low-frequency earthquakes (VLFE), short-term slow slip events (SSE), and step-like tilt changes are different manifestations of plate motion along faults. It has been observed [Shelly et al, 2007; Ito et al, 2007; Shelly et al, 2009; Obara, 2009] that: 1) tremor sources migrate with speeds from about 1km per minute to 10 km per day - a few orders of magnitude less than the speed of elastic waves (c); 2) the direction of a tremor source in some cases changes periodically in sign; 3) periodic step-like tilt changes coincide with the tremor bursts (the duration of tilt changes is much smaller than the time interval between them). It can be shown that the Frenkel-Kontorova (FK) model, well known from the theory of dislocations in crystalline materials, intrinsically explains these features [Gershenzon et al, 2009]. Remarkably, the FK model predicts that: 1) the steady state shear stress can generate an inelastic caterpillar-like deformational wave along a plate boundary, i.e. the migration of one or more periodic deformational pulse(s)/dislocation(s); 2) a pulse/dislocation has a short spatial extent in the direction of the shear stress (in comparison with the distance between dislocations) and a long extent in the perpendicular direction; 3) there is a strong local positive or negative stress/strain anomaly inside of the dislocation area; 4) dislocations are able to move along a fault with migration velocity v ranging from -c to +c or can even be stationary (v = 0); 5) the magnitude of the migration velocity is a strong, almost exponential function of the averaged accumulated shear stress. In the case of slow slip events, the migration velocity is usually much smaller than the seismic velocity (v << c); 6) under external shear stress, positive and negative dislocations move in opposite directions, resulting in sliding of the plates relative to each other with average plate slip velocity of a few cm/year; 7) measurable parameters such

  18. Observations and transport theory analysis of low frequency, acoustic mode propagation in the Eastern North Pacific Ocean.

    PubMed

    Chandrayadula, Tarun K; Colosi, John A; Worcester, Peter F; Dzieciuch, Matthew A; Mercer, James A; Andrew, Rex K; Howe, Bruce M

    2013-10-01

    Second order mode statistics as a function of range and source depth are presented from the Long Range Ocean Acoustic Propagation EXperiment (LOAPEX). During LOAPEX, low frequency broadband signals were transmitted from a ship-suspended source to a mode-resolving vertical line array. Over a one-month period, the ship occupied seven stations from 50 km to 3200 km distance from the receiver. At each station broadband transmissions were performed at a near-axial depth of 800 m and an off-axial depth of 350 m. Center frequencies at these two depths were 75 Hz and 68 Hz, respectively. Estimates of observed mean mode energy, cross mode coherence, and temporal coherence are compared with predictions from modal transport theory, utilizing the Garrett-Munk internal wave spectrum. In estimating the acoustic observables, there were challenges including low signal to noise ratio, corrections for source motion, and small sample sizes. The experimental observations agree with theoretical predictions within experimental uncertainty.

  19. Enhancement of the low-frequency response of a reflective semiconductor optical amplifier slow light-based microwave phase shifter by forced coherent population oscillations

    NASA Astrophysics Data System (ADS)

    Meehan, Aidan; Connelly, Michael J.

    2014-05-01

    The enhancement of the low frequency gain response of a microwave phase shifter based on slow light in a bulk reflective semiconductor optical amplifier (RSOA), by using forced coherent population oscillations (FCPO), is experimentally demonstrated. FCPO is achieved by simultaneously modulating the input optical power and bias current. The beat signal gain improvement ranges from 45 to 0 dB over a frequency range of 0.5 to 2.5 GHz, thereby improving the noise performance of the phase shifter. Tunable phase shifts of up to 40º are possible over this frequency range.

  20. ON THE SOURCE OF PROPAGATING SLOW MAGNETOACOUSTIC WAVES IN SUNSPOTS

    SciTech Connect

    Prasad, S. Krishna; Jess, D. B.; Khomenko, Elena

    2015-10-10

    Recent high-resolution observations of sunspot oscillations using simultaneously operated ground- and space-based telescopes reveal the intrinsic connection between different layers of the solar atmosphere. However, it is not clear whether these oscillations are externally driven or generated in situ. We address this question by using observations of propagating slow magnetoacoustic waves along a coronal fan loop system. In addition to the generally observed decreases in oscillation amplitudes with distance, the observed wave amplitudes are also found to be modulated with time, with similar variations observed throughout the propagation path of the wave train. Employing multi-wavelength and multi-instrument data, we study the amplitude variations with time as the waves propagate through different layers of the solar atmosphere. By comparing the amplitude modulation period in different layers, we find that slow magnetoacoustic waves observed in sunspots are externally driven by photospheric p-modes, which propagate upward into the corona before becoming dissipated.

  1. Propagated infra-slow intrinsic brain activity reorganizes across wake and slow wave sleep.

    PubMed

    Mitra, Anish; Snyder, Abraham Z; Tagliazucchi, Enzo; Laufs, Helmut; Raichle, Marcus E

    2015-11-09

    Propagation of slow intrinsic brain activity has been widely observed in electrophysiogical studies of slow wave sleep (SWS). However, in human resting state fMRI (rs-fMRI), intrinsic activity has been understood predominantly in terms of zero-lag temporal synchrony (functional connectivity) within systems known as resting state networks (RSNs). Prior rs-fMRI studies have found that RSNs are generally preserved across wake and sleep. Here, we use a recently developed analysis technique to study propagation of infra-slow intrinsic blood oxygen level dependent (BOLD) signals in normal adults during wake and SWS. This analysis reveals marked changes in propagation patterns in SWS vs. wake. Broadly, ordered propagation is preserved within traditionally defined RSNs but lost between RSNs. Additionally, propagation between cerebral cortex and subcortical structures reverses directions, and intra-cortical propagation becomes reorganized, especially in visual and sensorimotor cortices. These findings show that propagated rs-fMRI activity informs theoretical accounts of the neural functions of sleep.

  2. Propagated infra-slow intrinsic brain activity reorganizes across wake and slow wave sleep

    PubMed Central

    Mitra, Anish; Snyder, Abraham Z; Tagliazucchi, Enzo; Laufs, Helmut; Raichle, Marcus E

    2015-01-01

    Propagation of slow intrinsic brain activity has been widely observed in electrophysiogical studies of slow wave sleep (SWS). However, in human resting state fMRI (rs-fMRI), intrinsic activity has been understood predominantly in terms of zero-lag temporal synchrony (functional connectivity) within systems known as resting state networks (RSNs). Prior rs-fMRI studies have found that RSNs are generally preserved across wake and sleep. Here, we use a recently developed analysis technique to study propagation of infra-slow intrinsic blood oxygen level dependent (BOLD) signals in normal adults during wake and SWS. This analysis reveals marked changes in propagation patterns in SWS vs. wake. Broadly, ordered propagation is preserved within traditionally defined RSNs but lost between RSNs. Additionally, propagation between cerebral cortex and subcortical structures reverses directions, and intra-cortical propagation becomes reorganized, especially in visual and sensorimotor cortices. These findings show that propagated rs-fMRI activity informs theoretical accounts of the neural functions of sleep. DOI: http://dx.doi.org/10.7554/eLife.10781.001 PMID:26551562

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

    SciTech Connect

    Liu, DongLin Li, XiaoPing; Xie, Kai; Liu, ZhiWei

    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's 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.

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

    NASA Astrophysics Data System (ADS)

    Liu, DongLin; Li, XiaoPing; Xie, Kai; Liu, ZhiWei

    2015-10-01

    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's 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.

  5. The Propagation of Slow Wave Potentials in Pea Epicotyls.

    PubMed Central

    Stahlberg, R.; Cosgrove, D. J.

    1997-01-01

    Slow wave potentials are considered to be electric long-distance signals specific for plants, although there are conflicting ideas about a chemical, electrical, or hydraulic mode of propagation. These ideas were tested by comparing the propagation of hydraulic and electric signals in epicotyls of pea (Pisum sativum L). A hydraulic signal in the form of a defined step increase in xylem pressure (Px) was applied to the root of intact seedlings and propagated nearly instantly through the epicotyl axis while its amplitude decreased with distance from the pressure chamber. This decremental propagation was caused by a leaky xylem and created an axial Px gradient in the epicotyl. Simultaneously along the epicotyl surface, depolarizations appeared with lag times that increased acropetally with distance from the pressure chamber from 5 s to 3 min. When measured at a constant distance, the lag times increased as the size of the applied pressure steps decreased. We conclude that the Px gradient in the epicotyl caused local depolarizations with acropetally increasing lag times, which have the appearance of an electric signal propagating with a rate of 20 to 30 mm min-1. This static description of the slow wave potentials challenges its traditional classification as a propagating electric signal. PMID:12223601

  6. Slow and fast light propagation in nonlinear Kerr media.

    NASA Astrophysics Data System (ADS)

    Yang, Qiguang; Ma, Seongmin; Wang, Huitian; Jung, S. S.

    2005-04-01

    Sub- and superluminal propagation of light pulse in Kerr materials has been investigated. Group velocities as slow as much less than 1 millimeter per second to as fast as negative several hundreds meters per second can be easily obtained in Kerr medium, which possesses large nonlinear refractive index and long relaxation time, such as Cr doped Alexandrite, Ruby, and GdAlO3. The physical mechanism is the strong highly dispersive coupling between different frequency components of the pulse. The new mechanism of slowing down pulses as well as producing superluminal pulses enlarges the very specific materials to all kinds of nonlinear optical materials.

  7. Effect of pore pressure buildup on slowness of rupture propagation

    NASA Astrophysics Data System (ADS)

    Ougier-Simonin, A.; Zhu, W.

    2015-12-01

    Pore fluid pressure is known to play an important role in brittle fracture initiation and propagation, yet the underlying mechanisms remain unclear. We conducted triaxial experiments on saturated porous sandstones to investigate effects of pore pressure buildup on the slowness of shear rupture propagation at different confining pressures. At low to intermediate confinements, rocks fail by brittle faulting, and pore pressure buildup causes a reduction in rock's shear strength but does not induce measurable differences in slip behavior. When the confinement is high enough to prohibit dynamic faulting, rocks fail in the brittle-ductile transitional regime. In the transitional regime, pore pressure buildup promotes slip instability on an otherwise stably sliding fracture. Compared to those observed in the brittle regime, the slip rate, stress drop, and energy dissipated during rupture propagation with concurrent pore pressure buildup in the transitional regime are distinctively different. When decreasing confining pressure instead, the slip behavior resembles the ones of the brittle regime, emphasizing how the observed slowness is related to excess pore pressure beyond the effective pressure phenomenon. Analysis of the mechanical data using existing theoretical models confirms these observations. Quantitative microstructural analyses reveal that increasing pore pressure lessens the dilatancy hardening during failure, thus enhances slip along the localized zone in the transitional regime. Our experimental results suggest that pore pressure buildup induces slow slip in the transitional regime, and slip rates along a shear fracture may vary considerably depending on effective stress states.

  8. Investigation into the propagation of Omega very low frequency signals and techniques for improvement of navigation accuracy including differential and composite omega

    NASA Technical Reports Server (NTRS)

    1973-01-01

    An analysis of Very Low Frequency propagation in the atmosphere in the 10-14 kHz range leads to a discussion of some of the more significant causes of phase perturbation. The method of generating sky-wave corrections to predict the Omega phase is discussed. Composite Omega is considered as a means of lane identification and of reducing Omega navigation error. A simple technique for generating trapezoidal model (T-model) phase prediction is presented and compared with the Navy predictions and actual phase measurements. The T-model prediction analysis illustrates the ability to account for the major phase shift created by the diurnal effects on the lower ionosphere. An analysis of the Navy sky-wave correction table is used to provide information about spatial and temporal correlation of phase correction relative to the differential mode of operation.

  9. Crowdsourcing a Spatial Temporal Study of Low Frequency (LF) Propagation Effects Due to a Total Solar Eclipse: Engaging Students and Citizens in STEM

    NASA Astrophysics Data System (ADS)

    Lumsden, N. A.; Lukes, L.; Nelson, J.; Liles, W. C.; Kerby, K. C.; Crowov, F.; Rockway, J.

    2015-12-01

    The first experiments to study the effects of a solar eclipse on radio wave propagation were done in 1912 utilizing Low Frequency (LF; 30 - 300 kHz) radio waves at a handful of sites across Europe before any theory of the ionosphere had been confirmed and even before the word "ionosphere" existed. In the 1920s, a large cooperative experiment was promoted in the U.S. by Scientific American magazine. They collected over 2000 reports of AM broadcast stations from throughout the U.S. Unfortunately, many of the submissions were unusable because they lacked critical information such as date, time or location. We propose to use the 2017 solar eclipse over the continental U.S. to conduct the first wide-area LF propagation study. To perform this study, we plan to crowdsource the collection of the data by engaging student groups, citizens, and the scientific community. The tools for the different collection stations will consist of a simple homemade antenna, a simple receiver to convert the radio frequency (RF) signals to audio frequencies and a smart phone app. By using the time, date and location features of the smart phone, the problems experienced in the Scientific American experiment will be minimized. By crowdsourcing the observation sites, a number of different short, medium and long-paths studies can be obtained as the total eclipse crosses the continental U.S. The transmitter for this experiment will be WWVB located near Fort Collins, Colorado on 60.000 kHz. This is a U.S. frequency standard that is operated by NIST and transmits time codes. A second frequency, 55.500 kHz transmitted by a LF station in Dixon, CA is also being considered for this experiment. We will present an overall strategy for recruiting participants/crowdsourcing the RF collections during the 2017 total solar eclipse. Preliminary coverage calculations will be presented for WWVB and Dixon, as well as path loss calculations that can be expected during the solar eclipse condition. We will also

  10. Surface Current Density Mapping for Identification of Gastric Slow Wave Propagation

    PubMed Central

    Bradshaw, L. A.; Cheng, L. K.; Richards, W. O.; Pullan, A. J.

    2009-01-01

    The magnetogastrogram records clinically relevant parameters of the electrical slow wave of the stomach noninvasively. Besides slow wave frequency, gastric slow wave propagation velocity is a potentially useful clinical indicator of the state of health of gastric tissue, but it is a difficult parameter to determine from noninvasive bioelectric or biomagnetic measurements. We present a method for computing the surface current density (SCD) from multichannel magnetogastrogram recordings that allows computation of the propagation velocity of the gastric slow wave. A moving dipole source model with hypothetical as well as realistic biomagnetometer parameters demonstrates that while a relatively sparse array of magnetometer sensors is sufficient to compute a single average propagation velocity, more detailed information about spatial variations in propagation velocity requires higher density magnetometer arrays. Finally, the method is validated with simultaneous MGG and serosal EMG measurements in a porcine subject. PMID:19403355

  11. Propagation and damping of slow MHD waves in a flowing viscous coronal plasma

    NASA Astrophysics Data System (ADS)

    Kumar, Nagendra; Kumar, Anil; Murawski, K.

    2016-04-01

    We investigate the propagation of slow MHD waves in a flowing viscous solar coronal plasma. The compressive viscosity and steady flow along and opposite to the wave propagation are taken into account to study the damping of slow waves. We numerically solve the MHD equations by MacCormack method to examine the effect of steady flow on the damping of slow MHD waves in viscous solar coronal plasma. Amplitude of velocity perturbation and damping time of slow waves decrease with the increase in the value of Mach number. Flow causes a phase shift in the perturbed velocity amplitude and an increase in wave period. The damping of slow waves in flowing viscous plasma is stronger than the damping of waves in viscous plasma. Slow wave in backward flow damps earlier than the wave in forward flow.

  12. Superluminal and Ultra-Slow Light Propagation in Room-Temperature Solids

    NASA Astrophysics Data System (ADS)

    Boyd, Robert W.; Bigelow, Matthew S.; Lepeshkin, Nick N.

    2004-12-01

    We have observed ultra-slow light propagation (57 m s-1) in ruby and superluminal (-800 m s-1) light propagation in alexandrite at room temperature. The modified light speed results from the rapid variation in refractive index associated with spectral holes and antiholes produced by the process of coherent population oscillations.

  13. Observed speed of the slow propagation of an optical discharge

    NASA Astrophysics Data System (ADS)

    Gus'kov, K. G.; Raizer, Iu. P.; Surzhikov, S. T.

    1990-07-01

    The paper examines the discrepancy between the measured speed of the front motion of an optical discharge counter to the laser radiation and the theoreticaly predicted speed of thermoconductive or radiative discharge propagation through the cold gas that is adjacent to the front. The effect is explained by means of a model of dense gas flow around a hot sphere with low gas density. The observed effect is explained by the two-dimensional character of the gas motion near the discharge. Only a small part of the flow enters the discharge, while the main stream flows around the plasma body as if it were a solid.

  14. Wideband slow-light propagation with no distortion in a nanofiber-plane-grating composite waveguide

    NASA Astrophysics Data System (ADS)

    Ma, Chengju; Ren, Liyong; Guo, Wenge; Fu, Haiwei; Xu, Yiping; Liu, Yinggang; Zhang, Xiaozhen

    2016-06-01

    A nanofiber-plane-grating composite slow-light waveguide to achieve wideband slowlight propagation with no distortion is proposed. The waveguide is formed by embedding a tapered nanofiber into a V-groove on a plane-grating surface. By optimizing the waveguide structural parameters, a slow-light effect with bandwidth of about 1453 GHz is obtained. Based on finite-difference time-domain (FDTD) method, we analyze the waveguide's optical properties and slow-light characteristics. Simulation results show that a picosecond optical pulse propagating in the slow-light waveguide can be delayed for about 980 fs and without distortion. The group velocity of the optical pulse can be reduced to about 0.3c (c is the speed of light in vacuum). This study will provide important theoretical basis and innovative ideas for the development of new-type slow-light elements.

  15. Probing geomagnetic storm-driven magnetosphere-ionosphere dynamics in D-region via propagation characteristics of very low frequency radio signals

    NASA Astrophysics Data System (ADS)

    Nwankwo, Victor U. J.; Chakrabarti, Sandip K.; Ogunmodimu, Olugbenga

    2016-07-01

    The amplitude and phase of VLF/LF radio signals are sensitive to changes in electrical conductivity of the lower ionosphere which imprints its signature on the Earth-ionosphere waveguide. This characteristic makes it useful in studying sudden ionospheric disturbances, especially those related to prompt X-ray flux output from solar flares and gamma ray bursts (GRBs). However, strong geomagnetic disturbance and storm conditions are known to produce large and global ionospheric disturbances, which can significantly affect VLF radio propagation in the D region of the ionosphere. In this paper, using the data of three propagation paths at mid-latitudes (40-54°), we analyse the trend in variation of aspects of VLF diurnal signal under varying solar and geomagnetic space environmental conditions in order to identify possible geomagnetic footprints on the D region characteristics. We found that the trend of variations generally reflected the prevailing space weather conditions in various time scales. In particular, the 'dipping' of mid-day signal amplitude peak (MDP) occurs after significant geomagnetic perturbed or storm conditions in the time scale of 1-2 days. The mean signal amplitude before sunrise (MBSR) and mean signal amplitude after sunset (MASS) also exhibit storm-induced dipping, but they appear to be influenced by event's exact occurrence time and the highly variable conditions of dusk-to-dawn ionosphere. We also observed few cases of the signals rise (e.g., MDP, MBSR or MASS) following a significant geomagnetic event. This effect may be related to storms associated phenomena or effects arising from sources other than solar origin. The magnitude of induced dipping (or rise) significantly depends on the intensity and duration of event(s), as well as the propagation path of the signal. The post-storm day signal (following a main event, with lesser or significantly reduced geomagnetic activity) exhibited a tendency of recovery to pre-storm day level. In the

  16. Low-frequency pulse propagation over 510 km in the Philippine Sea: A comparison of observed and theoretical pulse spreading.

    PubMed

    Andrew, Rex K; Ganse, Andrew; White, Andrew W; Mercer, James A; Dzieciuch, Matthew A; Worcester, Peter F; Colosi, John A

    2016-07-01

    Observations of the spread of wander-corrected averaged pulses propagated over 510 km for 54 h in the Philippine Sea are compared to Monte Carlo predictions using a parabolic equation and path-integral predictions. Two simultaneous m-sequence signals are used, one centered at 200 Hz, the other at 300 Hz; both have a bandwidth of 50 Hz. The internal wave field is estimated at slightly less than unity Garrett-Munk strength. The observed spreads in all the early ray-like arrivals are very small, <1 ms (for pulse widths of 17 and 14 ms), which are on the order of the sampling period. Monte Carlo predictions show similar very small spreads. Pulse spread is one consequence of scattering, which is assumed to occur primarily at upper ocean depths where scattering processes are strongest and upward propagating rays refract downward. If scattering effects in early ray-like arrivals accumulate with increasing upper turning points, spread might show a similar dependence. Real and simulation results show no such dependence. Path-integral theory prediction of spread is accurate for the earliest ray-like arrivals, but appears to be increasingly biased high for later ray-like arrivals, which have more upper turning points. PMID:27475148

  17. Low-frequency pulse propagation over 510 km in the Philippine Sea: A comparison of observed and theoretical pulse spreading.

    PubMed

    Andrew, Rex K; Ganse, Andrew; White, Andrew W; Mercer, James A; Dzieciuch, Matthew A; Worcester, Peter F; Colosi, John A

    2016-07-01

    Observations of the spread of wander-corrected averaged pulses propagated over 510 km for 54 h in the Philippine Sea are compared to Monte Carlo predictions using a parabolic equation and path-integral predictions. Two simultaneous m-sequence signals are used, one centered at 200 Hz, the other at 300 Hz; both have a bandwidth of 50 Hz. The internal wave field is estimated at slightly less than unity Garrett-Munk strength. The observed spreads in all the early ray-like arrivals are very small, <1 ms (for pulse widths of 17 and 14 ms), which are on the order of the sampling period. Monte Carlo predictions show similar very small spreads. Pulse spread is one consequence of scattering, which is assumed to occur primarily at upper ocean depths where scattering processes are strongest and upward propagating rays refract downward. If scattering effects in early ray-like arrivals accumulate with increasing upper turning points, spread might show a similar dependence. Real and simulation results show no such dependence. Path-integral theory prediction of spread is accurate for the earliest ray-like arrivals, but appears to be increasingly biased high for later ray-like arrivals, which have more upper turning points.

  18. Energetic Particle Propagation in the Inner Heliosphere as Deduced from Low Frequency (less than 100 kHz) Observations of Type III Radio Bursts

    NASA Technical Reports Server (NTRS)

    Cane, H. V.; Erickson, W. C.

    2003-01-01

    Solar energetic particle (SEP) events are well-associated with solar flares. It is observed that the delay between the time of the flare and the first-arriving particles at a spacecraft increases with increasing difference between the flare longitude and the footpoint of the field line on which the spacecraft is located. This difference we call the "connection angle" and can be as large as approximately 120 deg. Recently it has been found that all SEP events are preceded by type III radio bursts. These bursts are plasma emission caused by the propagation of 2-50 keV flare electrons through the solar corona and into the solar wind. The drift of these type III radio bursts to lower and lower frequencies enables the propagation of the flare electrons to be traced from the Sun to about 1 AU. We have made an extensive analysis of the type III bursts associated with greater than 20 MeV proton events and find that, in most cases, the radio emission extends to the local plasma frequency when the energetic particles arrive within a few hours of the flare. We conclude that this emission at the lowest possible frequency is generated close to the spacecraft. We then use the time from when the burst started at the Sun to when it reached the local plasma frequency to infer the time it took the radio producing electrons to travel to the spacecraft. We find that these delay times are organized by the connection angle and correlate with the proton delay times. We also find that the differences between the radio delays at Wind and Ulysses are matched by differences in the relative arrival times of the energetic particles at the two spacecraft. The consistent timing between the relative arrival times of energetic electrons and protons and the start of the lowest frequency radio emissions suggests that the first arriving particles of both species are accelerated as part of the flare process and that they propagate to the spacecraft along trajectories similar to those of the lower

  19. Low frequency radiation exposure

    SciTech Connect

    Not Available

    1993-05-01

    This article consists of a summarized report of the Committee on Interagency Radiation Research and Policy Coordination (CIRRPC) and critical commentaries on the report by two leading researchers in electric and magnetic field frequency exposure. The report was requested by the U.S. Department of Labor, which was particularly concerned about published information suggesting that cancer results from electrical transmission lines, household appliances, and video display terminals. The commentaries were by David Savitz, University of North Carolina at Chapel Hill and Thomas Tenforde, a biophysicist with Battelle Pacific Northwest Laboratories. In response to the Department of Labor request, CIRRPC asked Oak Ridge Associated Universities to establish a panel to conduct an independent scientific review on the reported health hazards attributed to low frequency electromagnetic fields (ELF-EMF).

  20. Modeling of Reflective Propagating Slow-mode Wave in a Flaring Loop

    NASA Astrophysics Data System (ADS)

    Fang, X.; Yuan, D.; Van Doorsselaere, T.; Keppens, R.; Xia, C.

    2015-11-01

    Quasi-periodic propagating intensity disturbances have been observed in large coronal loops in extreme ultraviolet images over a decade, and are widely accepted to be slow magnetosonic waves. However, spectroscopic observations from Hinode/EIS revealed their association with persistent coronal upflows, making this interpretation debatable. We perform a 2.5D magnetohydrodynamic simulation to imitate the chromospheric evaporation and the following reflected patterns in a flare loop. Our model encompasses the corona, transition region, and chromosphere. We demonstrate that the quasi periodic propagating intensity variations captured by the synthesized Solar Dynamics Observatory/Atmospheric Imaging Assembly 131, 94 Å emission images match the previous observations well. With particle tracers in the simulation, we confirm that these quasi periodic propagating intensity variations consist of reflected slow mode waves and mass flows with an average speed of 310 km s‑1 in an 80 Mm length loop with an average temperature of 9 MK. With the synthesized Doppler shift velocity and intensity maps of the Solar and Heliospheric Observatory/Solar Ultraviolet Measurement of Emitted Radiation Fe xix line emission, we confirm that these reflected slow mode waves are propagating waves.

  1. MODELING OF REFLECTIVE PROPAGATING SLOW-MODE WAVE IN A FLARING LOOP

    SciTech Connect

    Fang, X.; Yuan, D.; Van Doorsselaere, T.; Keppens, R.; Xia, C.

    2015-11-01

    Quasi-periodic propagating intensity disturbances have been observed in large coronal loops in extreme ultraviolet images over a decade, and are widely accepted to be slow magnetosonic waves. However, spectroscopic observations from Hinode/EIS revealed their association with persistent coronal upflows, making this interpretation debatable. We perform a 2.5D magnetohydrodynamic simulation to imitate the chromospheric evaporation and the following reflected patterns in a flare loop. Our model encompasses the corona, transition region, and chromosphere. We demonstrate that the quasi periodic propagating intensity variations captured by the synthesized Solar Dynamics Observatory/Atmospheric Imaging Assembly 131, 94 Å emission images match the previous observations well. With particle tracers in the simulation, we confirm that these quasi periodic propagating intensity variations consist of reflected slow mode waves and mass flows with an average speed of 310 km s{sup −1} in an 80 Mm length loop with an average temperature of 9 MK. With the synthesized Doppler shift velocity and intensity maps of the Solar and Heliospheric Observatory/Solar Ultraviolet Measurement of Emitted Radiation Fe xix line emission, we confirm that these reflected slow mode waves are propagating waves.

  2. Measurement of the information velocity in fast- and slow-light optical pulse propagation

    NASA Astrophysics Data System (ADS)

    Stenner, Michael David

    This thesis describes a study of the velocity of information on optical pulses propagating through fast- and slow-light media. In fast- and slow-light media, the group velocity vg is faster than the speed of light in vacuum c (vg > c or vg < 0) or slower than c (0 < vg < c) respectively. While it is largely accepted that optical pulses can travel at these extreme group velocities, the velocity of information encoded on them is still the subject of considerable debate. There are many contradictory theories describing the velocity of information on optical pulses, but no accepted techniques for its experimental measurement. The velocity of information has broad implications for the principle of relativistic causality (which requires that information travels no faster than c) and for modern communications and computation. In this thesis, a new technique for measuring the information velocity vi is described and implemented for fast- and slow-light media. The fast- and slow-light media are generated using modern dispersion-tailoring techniques that use large atomic coherences to generate strong normal and anomalous dispersion. The information velocity in these media can then be measured using information-theoretic concepts by creating an alphabet of two distinct pulse symbols and transmitting the symbols through the media. By performing a detailed statistical analysis of the received information as a function of time, it is possible to calculate vi. This new technique makes it possible for the first time to measure the velocity of information on optical pulses. Applying this technique to fast-light pulses, where vg/c = -0.051 +/- 0.002, it is found that vi /c = 0.4(+0.7--0.2). In the slow-light case, where vg/c = 0.0097 +/- 0.0003, information is found to propagate at vi/c = 0.6. In the slow-light case, the error bars are slightly more complicated. The fast bound is -0.5c (which is faster than positive values) and the slow bound is 0.2c . These results represent the

  3. Propagation of Long-Wavelength Nonlinear Slow Sausage Waves in Stratified Magnetic Flux Tubes

    NASA Astrophysics Data System (ADS)

    Barbulescu, M.; Erdélyi, R.

    2016-05-01

    The propagation of nonlinear, long-wavelength, slow sausage waves in an expanding magnetic flux tube, embedded in a non-magnetic stratified environment, is discussed. The governing equation for surface waves, which is akin to the Leibovich-Roberts equation, is derived using the method of multiple scales. The solitary wave solution of the equation is obtained numerically. The results obtained are illustrative of a solitary wave whose properties are highly dependent on the degree of stratification.

  4. Propagation of quasisolitons in a fiber Bragg grating written in a slow saturable fiber amplifier

    SciTech Connect

    Shapira, Yuval P.; Horowitz, Moshe

    2011-05-15

    We show, by using numerical simulations, that quasisolitons can propagate over a long distance in a fiber Bragg grating that is written in a slow saturable fiber amplifier, such as an erbium-doped fiber amplifier. During the pulse propagation, the front end of the pulse experiences a net gain while the rear end of pulse is attenuated due to the combination of gain saturation and loss. However, the pulse profile almost does not change after propagating over a length of 5 m that is approximately 2500 times larger than the spatial pulse width. The pulse amplitude has an approximately hyperbolic secant profile. We develop a reduced model by using a multiscale analysis to study solitary-wave propagation when nonlinearity and gain are small. When gain saturation also becomes small we find analytically a new family of solitary-wave hyperbolic-secant solutions that approximately solve the reduced model. The solitary waves propagate slightly faster than Bragg solitons that propagate in fiber Bragg gratings without gain and loss.

  5. Low Frequency Radio Experiment (LORE)

    NASA Astrophysics Data System (ADS)

    Manoharan, P. K.; Naidu, Arun; Joshi, B. C.; Roy, Jayashree; Kate, G.; Pethe, Kaiwalya; Galande, Shridhar; Jamadar, Sachin; Mahajan, S. P.; Patil, R. A.

    2016-03-01

    In this paper, we present a case study of Low Frequency Radio Experiment (LORE) payload to probe the corona and the solar disturbances at solar offsets greater than 2 solar radii, i.e., at frequencies below 30 MHz. The LORE can be complimentary to the planned Indian solar mission, “Aditya-L1” and its other payloads as well as synergistic to ground-based interplanetary scintillation (IPS) observations, which are routinely carried out by the Ooty Radio Telescope. We discuss the baseline design and technical details of the proposed LORE and its particular suitability for providing measurements on the detailed time and frequency structure of fast drifting type-III and slow drifting type-II radio bursts with unprecedented time and frequency resolutions. We also brief the gonio-polarimetry, which is possible with better-designed antennas and state-of-the-art electronics, employing FPGAs and an intelligent data management system. These would enable us to make a wide range of studies, such as nonlinear plasma processes in the Sun-Earth distance, in-situ radio emission from coronal mass ejections (CMEs), interplanetary CME driven shocks, nature of ICMEs driving decelerating IP shocks and space weather effects of solar wind interaction regions.

  6. Effect of stress state on slow rupture propagation in synthetic fault gouges

    NASA Astrophysics Data System (ADS)

    Hirauchi, Ken-ichi; Muto, Jun

    2015-02-01

    Slow slip events (SSEs) in subduction zones are known to proceed so sluggishly that the associated slow ruptures do not generate any detectable radiating seismic waves. Moreover, they propagate at speeds at least four orders of magnitude slower than regular earthquakes. However, the underlying physics of slow slip generation has yet to be understood. Here, we carry out laboratory studies of unstable slip along simulated fault zones of lizardite/chrysotile (liz/ctl) and antigorite (i.e., low- and high-temperature serpentine phases, respectively) and olivine, under varying conditions of normal stress, with the aim of better understanding the influence of stress state on the process of slow rupture along the plate interface. During a single unstable slip, we clearly observe a slow rupture phase that is often followed by an unstable, high-speed rupture. We find that lower fault-zone friction coefficients (μ values from 0.7 down to 0.5) lead to increasing degree of the slow rupture mode, and also that the slow rupture velocities ( V r = 0.07 to 5.43 m/s) are largely consistent with those of short-term SSEs observed in nature. Our findings suggest that the generation of SSEs is facilitated by conditions of low normal stress and low fault-zone strength along the plate interface, which may be weakened by metamorphic reactions that result in the production of hydrous phases (e.g., serpentine) and/or the direct involvement of fluid itself, leading to a reduction in effective normal stress.

  7. Relationships among temperature, dehydration of the subducting Philippine Sea plate, and the occurrence of a megathrust earthquake, low-frequency earthquakes, and a slow slip event in the Tokai district, central Japan

    NASA Astrophysics Data System (ADS)

    Suenaga, Nobuaki; Yoshioka, Shoichi; Matsumoto, Takumi

    2016-11-01

    In this study, we performed two-dimensional numerical simulations of temperature distribution associated with subduction of the Philippine Sea (PHS) plate, and estimated the dehydration process of hydrous mid-ocean-ridge basalt (MORB) in the oceanic crust in the Tokai district, central Japan. We discuss the relationship among temperature, dehydration, and a seismogenic zone of an expected megathrust Tokai earthquake, and the occurrence of a slow slip event (SSE) and deep low-frequency earthquakes (LFEs). The depth range of the seismogenic zone for the megathrust earthquake was estimated to be 8-22 km, narrowing toward the east. The most suitable value of the pore pressure ratio on the plate interface was estimated to be 0.97, indicating minimal frictional heating there. The temperatures of the upper surface of the PHS plate, where the Tokai SSE occurred from 2000 to 2005, were estimated to be 350-450 °C. Therefore, the Tokai SSE is considered to have occurred at the transition zone between unstable and stable sliding. In addition, hydrous MORB was transformed from blueschist into greenschist near the region where the Tokai SSE occurred. The temperatures of the upper surface of the PHS plate, where LFEs occur, were estimated to be 450-500 °C. Therefore, LFEs are considered to occur near the down-dip limit of the transition zone. The amount of dehydration from the oceanic crust of the subducting PHS plate near the region where LFEs are distributed in a belt-like form decreases toward the east with deepening of the hypocenters of the LFEs. Thus, the mechanisms of generation of LFEs in the Tokai district might differ from those in southwest and central Japan where LFEs generally occur at depths between 27 and 35 km. In summary, we consider that the occurrence of LFEs is related to both temperature conditions and dehydration process. However, there is an exceptional area in the eastern part of the Tokai district where the occurrence of LFEs is restricted by

  8. Effect of ion concentration on slow light propagation in highly doped erbium fibers

    NASA Astrophysics Data System (ADS)

    Melle, Sonia; Calderón, Oscar G.; Carreño, F.; Cabrera, Eduardo; Antón, M. A.; Jarabo, S.

    2007-11-01

    The effect of ion density on slow light propagation enabled by coherent population oscillations has been experimentally investigated for highly doped erbium fibers at room temperature. We found that fractional delay increases with ion density. A saturation effect in the fractional delay has been observed for doping levels above ˜3150 ppm. Ultra-high ion concentration can simultaneously increase the fractional delay and the bandwidth of the signals. We have studied the propagation of Gaussian pulses along the fibers obtaining fractional delays up to 0.7 for the highest doping levels used. It is shown that pulse power can be used as a control parameter to reduce distortion at different pulse bandwidths.

  9. 'Burst-Like' Slow Slip Propagation on Frictional Faults in the Laboratory

    NASA Astrophysics Data System (ADS)

    Parker, J.; Selvadurai, P. A.; Glaser, S. D.

    2015-12-01

    We present laboratory findings on burst-like premonitory slip propagation that leads to fault rupture. The experiments take place on a PMMA-PMMA interface in a direct shear configuration, where the effective strength heterogeneity is controlled by the non-uniform distribution of asperities throughout the fault. A pressure sensitive film was used to locate, size and measure normal stress on individual asperities. Prior to rapid sliding, we observed slow premonitory slip which accumulated non-uniformly along the fault. Slow displacement was measured using slip sensors placed at seven locations along the fault strike and showed intermittent, 'burst-like' increases in spectral power between the frequencies of 60 to 150 Hz. Each burst event lasted between 5 to 12 seconds, and a local increase in the extended fault slip rate was observed after its cessation. The 'burst-like' features migrated along the fault at speeds between Vprop ~ 1.3 mm/s to 9.3 mm/s. Propagation speed of the 'burst-like' front Vprop was dependent on the normal stress confining the fault σn- increased normal stress caused the rupture to move slower by increasing 'effective fault strength'. Finally, foreshocks were recorded using absolutely calibrated acoustic emission sensors and occurred at the later stages of the slow slip phase. The source radii of the foreshocks [Brune, 1970] ranged from 0.21 to 1.09 mm and their ruptures occurred over timescales ~5-7 orders of magnitude faster than the 'burst-like' slow slip signals. Observations of similar variations in time scales have been made between regular earthquakes and aseismic transients in the field [Ide, 2007]. These results will help develop a mechanistic understanding of the effective fault strength heterogeneity necessary for the development of slow earthquakes and tremor-like shaking. References: Ide, S., D. R. Beroza, G. C. Shelly & T. Uchide (2007), 'A scaling law for slow earthquakes', Nature 447, 76-79. Brune, J. N. (1970), 'Tectonic stress

  10. Local propagation speed constrained estimation of the slowness vector from non-planar array observations.

    PubMed

    Nouvellet, Adrien; Roueff, François; Le Pichon, Alexis; Charbit, Maurice; Vergoz, Julien; Kallel, Mohamed; Mejri, Chourouq

    2016-01-01

    The estimation of the slowness vector of infrasound waves propagating across an array is a critical process leading to the determination of parameters of interest such as the direction of arrival. The sensors of an array are often considered to be located in a horizontal plane. However, due to topography, the altitudes of the sensors are not identical and introduce a bias on the estimate if neglected. However, the unbiased 3D estimation procedure, while suppressing the bias, leads to an increase of the variance. Accounting for an a priori constraint on the slowness vector significantly reduces the variance and could therefore improve the performance of the estimation if the introduced bias by incorrect a priori information remains negligible. This study focuses on measuring the benefits of this approach with a thorough investigation of the bias and variance of the constrained 3D estimator, which is not available in the existing literature. This contribution provides such computations based on an asymptotic Gaussian approximation. Simulations are carried out to assess the theoretical results both with synthetic and real data. Thus, a constrained 3D estimator is proposed yielding the best bias/variance compromise if good knowledge of the propagation wave speed is accessible. PMID:26827049

  11. Frequency-dependent damping in propagating slow magneto-acoustic waves

    SciTech Connect

    Prasad, S. Krishna; Banerjee, D.; Van Doorsselaere, T.

    2014-07-10

    Propagating slow magneto-acoustic waves are often observed in polar plumes and active region fan loops. The observed periodicities of these waves range from a few minutes to a few tens of minutes and their amplitudes were found to decay rapidly as they travel along the supporting structure. Previously, thermal conduction, compressive viscosity, radiation, density stratification, and area divergence were identified to be some of the causes for change in the slow wave amplitude. Our recent studies indicate that the observed damping in these waves is frequency-dependent. We used imaging data from the Solar Dynamics Observatory/Atmospheric Imaging Assembly to study this dependence in detail and for the first time via observations we attempted to deduce a quantitative relation between the damping length and frequency of these oscillations. We developed a new analysis method to obtain this relation. The observed frequency dependence does not seem to agree with the current linear wave theory and it was found that the waves observed in the polar regions show a different dependence from those observed in the on-disk loop structures despite the similarity in their properties.

  12. Effect of Alfvén resonance on low-frequency fast wave current drive

    NASA Astrophysics Data System (ADS)

    Wang, C. Y.; Batchelor, D. B.; Carter, M. D.; Jaeger, E. F.; Stallings, D. C.

    1995-08-01

    The Alfvén resonances may occur on the low- and high-field sides for a low-frequency fast wave current drive scenario proposed for the International Thermonuclear Experimental Reactor (ITER) [Nucl. Fusion 31, 1135 (1991)]. At the resonance on the low-field side, the fast wave may be mode converted into a short-wavelength slow wave, which can be absorbed by electrons at the plasma edge, before the fast wave propagates into the core area of the plasma. Such absorption may cause a significant parasitic power loss.

  13. Low-frequency VLBI in space and interstellar refraction

    SciTech Connect

    Dennison, B.; Booth, R.S.

    1986-08-01

    The proposed orbiting Quasat antenna, equipped with a low-frequency capability (e.g. 327 MHz), would be uniquely suited for studying refractive focusing (slow scintillation) in the interstellar medium, which is suspected of being responsible for at least some apparent low-frequency variability of extragalactic sources. The authors consider in some detail various technical considerations, including the decorrelating effects of the ionosphere and interplanetary medium, and conclude that low-frequency VLBI observations involving Quasat and Earth-based antennas would be feasible, particularly if sources are observed when they are in the anti-solar hemisphere.

  14. Extremely Low Frequency Electromagnetic Investigation on Mars

    NASA Astrophysics Data System (ADS)

    Kozakiewicz, Joanna; Kulak, Andrzej; Kubisz, Jerzy; Zietara, Krzysztof

    2016-07-01

    Natural electromagnetic (EM) signals of extremely low frequencies (ELF, 3 Hz-3 kHz) can be used to study many of the electromagnetic processes and properties occurring in the Martian environment. Sources of these signals, related to electrical activity in the atmosphere, are very significant since they can influence radio wave propagation on the planet, the atmospheric composition, and the ionospheric structure. In addition, such EM signals can be employed in many purposes such as: surveying the subsurface of Mars or studying the impact of the space weather on the Martian ionosphere. As ELF waves propagate on very long distances, it is possible to explore properties of the entire planet using single-station recordings. In this study, we propose an experiment that allows measuring ELF signals from the Martian surface. Such measurements can be used for detection of electric discharges in the atmosphere and water reservoirs in the planetary subsurface.

  15. Experimental evidence of dynamical propagation for solitary waves in ultra slow stochastic non-local Kerr medium.

    PubMed

    Louis, H; Tlidi, M; Louvergneaux, E

    2016-07-11

    We perform a statistical analysis of the optical solitary wave propagation in an ultra-slow stochastic non-local focusing Kerr medium such as liquid crystals. Our experimental results show that the localized beam trajectory presents a dynamical random walk whose beam position versus the propagation distance z depicts two different kind of evolutions A power law is found for the beam position standard deviation during the first stage of propagation. It obeys approximately z3/2 up to ten times the power threshold for solitary wave generation. PMID:27410886

  16. Experimental evidence of dynamical propagation for solitary waves in ultra slow stochastic non-local Kerr medium.

    PubMed

    Louis, H; Tlidi, M; Louvergneaux, E

    2016-07-11

    We perform a statistical analysis of the optical solitary wave propagation in an ultra-slow stochastic non-local focusing Kerr medium such as liquid crystals. Our experimental results show that the localized beam trajectory presents a dynamical random walk whose beam position versus the propagation distance z depicts two different kind of evolutions A power law is found for the beam position standard deviation during the first stage of propagation. It obeys approximately z3/2 up to ten times the power threshold for solitary wave generation. PMID:27410887

  17. Do calcium buffers always slow down the propagation of calcium waves?

    PubMed

    Tsai, Je-Chiang

    2013-12-01

    Calcium buffers are large proteins that act as binding sites for free cytosolic calcium. Since a large fraction of cytosolic calcium is bound to calcium buffers, calcium waves are widely observed under the condition that free cytosolic calcium is heavily buffered. In addition, all physiological buffered excitable systems contain multiple buffers with different affinities. It is thus important to understand the properties of waves in excitable systems with the inclusion of buffers. There is an ongoing controversy about whether or not the addition of calcium buffers into the system always slows down the propagation of calcium waves. To solve this controversy, we incorporate the buffering effect into the generic excitable system, the FitzHugh-Nagumo model, to get the buffered FitzHugh-Nagumo model, and then to study the effect of the added buffer with large diffusivity on traveling waves of such a model in one spatial dimension. We can find a critical dissociation constant (K = K(a)) characterized by system excitability parameter a such that calcium buffers can be classified into two types: weak buffers (K ∈ (K(a), ∞)) and strong buffers (K ∈ (0, K(a))). We analytically show that the addition of weak buffers or strong buffers but with its total concentration b(0)(1) below some critical total concentration b(0,c)(1) into the system can generate a traveling wave of the resulting system which propagates faster than that of the origin system, provided that the diffusivity D1 of the added buffers is sufficiently large. Further, the magnitude of the wave speed of traveling waves of the resulting system is proportional to √D1 as D1 --> ∞. In contrast, the addition of strong buffers with the total concentration b(0)(1) > b(0,c)(1) into the system may not be able to support the formation of a biologically acceptable wave provided that the diffusivity D1 of the added buffers is sufficiently large.

  18. PROPAGATING SLOW MAGNETOACOUSTIC WAVES IN CORONAL LOOPS OBSERVED BY HINODE/EIS

    SciTech Connect

    Wang, T. J.; Ofman, L.; Davila, J. M.

    2009-05-10

    We present the first Hinode/EUV Imaging Spectrometer observations of 5 minute quasi-periodic oscillations detected in a transition-region line (He II) and five coronal lines (Fe X, Fe XII, Fe XIII, Fe XIV, and Fe XV) at the footpoint of a coronal loop. The oscillations exist throughout the whole observation, characterized by a series of wave packets with nearly constant period, typically persisting for 4-6 cycles with a lifetime of 20-30 minutes. There is an approximate in-phase relation between Doppler shift and intensity oscillations. This provides evidence for slow magnetoacoustic waves propagating upward from the transition region into the corona. We find that the oscillations detected in the five coronal lines are highly correlated, and the amplitude decreases with increasing temperature. The amplitude of Doppler shift oscillations decrease by a factor of about 3, while that of relative intensity decreases by a factor of about 4 from Fe X to Fe XV. These oscillations may be caused by the leakage of the photospheric p-modes through the chromosphere and transition region into the corona, which has been suggested as the source for intensity oscillations previously observed by Transition Region and Coronal Explorer. The temperature dependence of the oscillation amplitudes can be explained by damping of the waves traveling along the loop with multithread structure near the footpoint. Thus, this property may have potential value for coronal seismology in diagnostic of temperature structure in a coronal loop.

  19. Low-frequency electrical properties.

    USGS Publications Warehouse

    Olhoeft, G.R.

    1985-01-01

    In the interpretation of induced polarization data, it is commonly assumed that metallic mineral polarization dominantly or solely causes the observed response. However, at low frequencies, there is a variety of active chemical processes which involve the movement or transfer of electrical charge. Measurements of electrical properties at low frequencies (such as induced polarization) observe such movement of charge and thus monitor many geochemical processes at a distance. Examples in which this has been done include oxidation-reduction of metallic minerals such as sulfides, cation exchange on clays, and a variety of clay-organic reactions relevant to problems in toxic waste disposal and petroleum exploration. By using both the frequency dependence and nonlinear character of the complex resistivity spectrum, these reactions may be distinguished from each other and from barren or reactionless materials.-Author

  20. SLOW PATCHY EXTREME-ULTRAVIOLET PROPAGATING FRONTS ASSOCIATED WITH FAST CORONAL MAGNETO-ACOUSTIC WAVES IN SOLAR ERUPTIONS

    SciTech Connect

    Guo, Y.; Ding, M. D.; Chen, P. F.

    2015-08-15

    Using the high spatiotemporal resolution extreme ultraviolet (EUV) observations of the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we conduct a statistical study of the observational properties of the coronal EUV propagating fronts. We find that it might be a universal phenomenon for two types of fronts to coexist in a large solar eruptive event. It is consistent with the hybrid model of EUV propagating fronts, which predicts that coronal EUV propagating fronts consist of both a fast magneto-acoustic wave and a nonwave component. We find that the morphologies, propagation behaviors, and kinematic features of the two EUV propagating fronts are completely different from each other. The fast magneto-acoustic wave fronts are almost isotropic. They travel continuously from the flaring region across multiple magnetic polarities to global distances. On the other hand, the slow nonwave fronts appear as anisotropic and sequential patches of EUV brightening. Each patch propagates locally in the magnetic domains where the magnetic field lines connect to the bottom boundary and stops at the magnetic domain boundaries. Within each magnetic domain, the velocities of the slow patchy nonwave component are an order of magnitude lower than that of the fast-wave component. However, the patches of the slow EUV propagating front can jump from one magnetic domain to a remote one. The velocities of such a transit between different magnetic domains are about one-third to one-half of those of the fast-wave component. The results show that the velocities of the nonwave component, both within one magnetic domain and between different magnetic domains, are highly nonuniform due to the inhomogeneity of the magnetic field in the lower atmosphere.

  1. Earthquake triggering by slow earthquake propagation: the case of the large 2014 slow slip event in Guerrero, Mexico.

    NASA Astrophysics Data System (ADS)

    Radiguet, M.; Perfettini, H.; Cotte, N.; Gualandi, A.; Kostoglodov, V.; Lhomme, T.; Walpersdorf, A.; Campillo, M.; Valette, B.

    2015-12-01

    Since their discovery nearly two decades ago, the importance of slow slip events (SSEs) in the processes of strain accommodation in subduction zones has been revealed. Nevertheless, the influence of slow aseismic slip on the nucleation of large earthquakes remains unclear. In this study, we focus on the Guerrero region of the Central American subduction zone in Mexico, where large SSEs have been observed since 1998, with a recurrence period of about 4 years, and produce aseismic slip in the Guerrero seismic gap. We investigate the large 2014 SSE (equivalent Mw=7.7), which initiated in early 2014 and lasted until the end of October 2014. During this time period, the 18 April Papanoa earthquake (Mw7.2) occurred on the western limit of the Guerrero gap. We invert the continuous GPS time series using the PCAIM (Principal Component Analysis Inversion Method) to assess the space and time evolution of slip on the subduction. To focus on the aseismic processes, we correct the cGPS time series from the co-seismic offsets. Our results show that the slow slip event initiated in the Guerrero gap region, as already observed during the previous SSEs. The Mw7.2 Papanoa earthquake occurred on the western limit of the region that was slipping aseismically before the earthquake. After the Papanoa earthquake, the aseismic slip rate increases. This geodetic signal consists of both the ongoing SSE and the postseismic (afterslip) response due to the Papanoa earthquake. The majority of the post-earthquake aseismic slip is concentrated downdip from the main earthquake asperity, but significant slip is also observed in the Guerrero gap region. Compared to previous SSEs in that region, the 2014 SSE produced a larger aseismic slip and the maximum slip is located downdip from the main brittle asperity corresponding to the Papanoa earthquake, a region that was not identified as active during the previous SSEs. Since the Mw 7.2 Papanoa earthquake occurred about 2 months after the onset of the

  2. Low Frequency Interstellar Scattering and Pulsar Observations

    NASA Technical Reports Server (NTRS)

    Cordes, James M.

    1992-01-01

    Radio astronomy at frequencies from 2 to 30 MHz challenges time tested methods for extracting usable information from observations. One fundamental reason for this is that propagation effects due to the magnetoionic ionosphere, interplanetary medium, and interstellar matter (ISM) increase strongly with wavelength. The problems associated with interstellar scattering off of small scale irregularities in the electron density are addressed. What is known about interstellar scattering is summarized on the basis of high frequency observations, including scintillation and temporal broadening of pulsars and angular broadening of various galactic and extragalactic radio sources. Then those high frequency phenomena are addressed that are important or detectable at low frequencies. The radio sky becomes much simpler at low frequencies, most pulsars will not be seen as time varying sources, intensity variations will be quenched or will occur on time scales much longer than a human lifetime, and many sources will be angularly broadened and/or absorbed into the noise. Angular broadening measurements will help delineate the galactic distribution and power spectrum of small scale electron density irregularities.

  3. Low-Frequency Waves in Space Plasmas

    NASA Astrophysics Data System (ADS)

    Keiling, Andreas; Lee, Dong-Hun; Nakariakov, Valery

    2016-02-01

    Low-frequency waves in space plasmas have been studied for several decades, and our knowledge gain has been incremental with several paradigm-changing leaps forward. In our solar system, such waves occur in the ionospheres and magnetospheres of planets, and around our Moon. They occur in the solar wind, and more recently, they have been confirmed in the Sun's atmosphere as well. The goal of wave research is to understand their generation, their propagation, and their interaction with the surrounding plasma. Low-frequency Waves in Space Plasmas presents a concise and authoritative up-to-date look on where wave research stands: What have we learned in the last decade? What are unanswered questions? While in the past waves in different astrophysical plasmas have been largely treated in separate books, the unique feature of this monograph is that it covers waves in many plasma regions, including: Waves in geospace, including ionosphere and magnetosphere Waves in planetary magnetospheres Waves at the Moon Waves in the solar wind Waves in the solar atmosphere Because of the breadth of topics covered, this volume should appeal to a broad community of space scientists and students, and it should also be of interest to astronomers/astrophysicists who are studying space plasmas beyond our Solar System.

  4. Quantitative analysis of seismic wave propagation anomalies in azimuth and apparent slowness at Deception Island volcano (Antarctica) using seismic arrays

    NASA Astrophysics Data System (ADS)

    Yeguas, A. García.; Almendros, J.; Abella, R.; Ibáñez, J. M.

    2011-02-01

    We analyse shot data recorded by eight seismic arrays during an active-source seismic experiment carried out at Deception Island (Antarctica) in 2005 January. For each source we estimate the apparent slowness and propagation azimuth of the first wave arrival. Since both source and receiver positions are accurately known, we are able to interpret the results in terms of the effect of the heterogeneities of the medium on wave propagation. The results show the presence of significant propagation anomalies. Nearby shots produce large apparent slowness values above 0.6 s km-1, while distant shots produce small values, down to about 0.15-0.20 s km-1. These values are different for each array, which shows the importance of the local structure under the receiver. The spatial distributions of apparent slowness are not radial as we would expect in a flat-layered medium. And again, these distributions are different for each array. The azimuth anomalies defined as the difference between the empirical estimates and the values expected in a 1-D model (i.e. the source-array directions) suggest ubiquitous wave front distortions. We have detected both positive and negative anomalies. For some shot-array geometries, azimuth anomalies are quite large with values up to 60°. The distribution of the anomalies depends on the position of the array. Some of these features can be interpreted in terms of a shallow magma chamber and shallow rigid bodies imaged by high-resolution seismic tomography. However several details remain unexplained. Further work is required, including modelling of synthetic wavefields on realistic models of Deception Island and/or apparent slowness vector tomography.

  5. Low frequency ac waveform generator

    DOEpatents

    Bilharz, O.W.

    1983-11-22

    Low frequency sine, cosine, triangle and square waves are synthesized in circuitry which allows variation in the waveform amplitude and frequency while exhibiting good stability and without requiring significant stablization time. A triangle waveform is formed by a ramped integration process controlled by a saturation amplifier circuit which produces the necessary hysteresis for the triangle waveform. The output of the saturation circuit is tapped to produce the square waveform. The sine waveform is synthesized by taking the absolute value of the triangular waveform, raising this absolute value to a predetermined power, multiplying the raised absolute value of the triangle wave with the triangle wave itself and properly scaling the resultant waveform and subtracting it from the triangular waveform to a predetermined power and adding the squared waveform raised to the predetermined power with a DC reference and subtracting the squared waveform therefrom, with all waveforms properly scaled. The resultant waveform is then multiplied with a square wave in order to correct the polarity and produce the resultant cosine waveform.

  6. Low frequency AC waveform generator

    DOEpatents

    Bilharz, Oscar W.

    1986-01-01

    Low frequency sine, cosine, triangle and square waves are synthesized in circuitry which allows variation in the waveform amplitude and frequency while exhibiting good stability and without requiring significant stabilization time. A triangle waveform is formed by a ramped integration process controlled by a saturation amplifier circuit which produces the necessary hysteresis for the triangle waveform. The output of the saturation circuit is tapped to produce the square waveform. The sine waveform is synthesized by taking the absolute value of the triangular waveform, raising this absolute value to a predetermined power, multiplying the raised absolute value of the triangle wave with the triangle wave itself and properly scaling the resultant waveform and subtracting it from the triangular waveform itself. The cosine is synthesized by squaring the triangular waveform, raising the triangular waveform to a predetermined power and adding the squared waveform raised to the predetermined power with a DC reference and subtracting the squared waveform therefrom, with all waveforms properly scaled. The resultant waveform is then multiplied with a square wave in order to correct the polarity and produce the resultant cosine waveform.

  7. Reflection of Propagating Slow Magneto-acoustic Waves in Hot Coronal Loops: Multi-instrument Observations and Numerical Modeling

    NASA Astrophysics Data System (ADS)

    Mandal, Sudip; Yuan, Ding; Fang, Xia; Banerjee, Dipankar; Pant, Vaibhav; Van Doorsselaere, Tom

    2016-09-01

    Slow MHD waves are important tools for understanding coronal structures and dynamics. In this paper, we report a number of observations from the X-Ray Telescope (XRT) on board HINODE and Solar Dynamic Observatory/Atmospheric Imaging Assembly (AIA) of reflecting longitudinal waves in hot coronal loops. To our knowledge, this is the first report of this kind as seen from the XRT and simultaneously with the AIA. The wave appears after a micro-flare occurs at one of the footpoints. We estimate the density and temperature of the loop plasma by performing differential emission measure (DEM) analysis on the AIA image sequence. The estimated speed of propagation is comparable to or lower than the local sound speed, suggesting it to be a propagating slow wave. The intensity perturbation amplitude, in every case, falls very rapidly as the perturbation moves along the loop and eventually vanishes after one or more reflections. To check the consistency of such reflection signatures with the obtained loop parameters, we perform a 2.5D MHD simulation, which uses the parameters obtained from our observation as inputs, and perform forward modeling to synthesize AIA 94 Å images. Analyzing the synthesized images, we obtain the same properties of the observables as for the real observation. From the analysis we conclude that a footpoint heating can generate a slow wave which then reflects back and forth in the coronal loop before fading. Our analysis of the simulated data shows that the main agent for this damping is anisotropic thermal conduction.

  8. Ionospheric very low frequency transmitter

    SciTech Connect

    Kuo, Spencer P.

    2015-02-15

    The theme of this paper is to establish a reliable ionospheric very low frequency (VLF) transmitter, which is also broad band. Two approaches are studied that generate VLF waves in the ionosphere. The first, classic approach employs a ground-based HF heater to directly modulate the high latitude ionospheric, or auroral electrojet. In the classic approach, the intensity-modulated HF heater induces an alternating current in the electrojet, which serves as a virtual antenna to transmit VLF waves. The spatial and temporal variations of the electrojet impact the reliability of the classic approach. The second, beat-wave approach also employs a ground-based HF heater; however, in this approach, the heater operates in a continuous wave mode at two HF frequencies separated by the desired VLF frequency. Theories for both approaches are formulated, calculations performed with numerical model simulations, and the calculations are compared to experimental results. Theory for the classic approach shows that an HF heater wave, intensity-modulated at VLF, modulates the electron temperature dependent electrical conductivity of the ionospheric electrojet, which, in turn, induces an ac electrojet current. Thus, the electrojet becomes a virtual VLF antenna. The numerical results show that the radiation intensity of the modulated electrojet decreases with an increase in VLF radiation frequency. Theory for the beat wave approach shows that the VLF radiation intensity depends upon the HF heater intensity rather than the electrojet strength, and yet this approach can also modulate the electrojet when present. HF heater experiments were conducted for both the intensity modulated and beat wave approaches. VLF radiations were generated and the experimental results confirm the numerical simulations. Theory and experimental results both show that in the absence of the electrojet, VLF radiation from the F-region is generated via the beat wave approach. Additionally, the beat wave approach

  9. Low-frequency creep in CoNiFe films.

    NASA Technical Reports Server (NTRS)

    Bartran, D. S.; Bourne, H. C., Jr.; Chow, L. G.

    1972-01-01

    Domain wall motion excited by slow rise-time, bipolar, hard-axis pulses in vacuum deposited CoNiFe films from 1500 to 2000 A thick is studied. The results are consistent with those of comparable NiFe films. Furthermore, the wall coercivity is found to be the most significant sample property correlated to the low-frequency creep properties of all the samples.

  10. Slow-light propagation using mode locking of spin precession in quantum dots

    SciTech Connect

    Shabaev, A.; Dutton, Z.; Kennedy, T. A.; Efros, Al. L.

    2010-11-15

    We propose using mode locking to enable coherent nonlinear optical effects in inhomogenously broadened spin ensembles. We carry out detailed calculations for quantum dot systems in which increased spin coherence via mode locking has been recently observed [A. Greilich et al., Science 313, 341 (2006); 317, 1896 (2007)]. We show how, in the presence of spin locking, a strong pulse-matching effect occurs, providing a powerful tool for high-bandwidth linear optical processing. We then go on to study 'slow light' in this system and show that high-bandwidth pulses can be controllably delayed by a time comparable to the pulse width.

  11. Low frequency hybrid instability in quantum magneto semiconductor plasmas

    NASA Astrophysics Data System (ADS)

    Rasheed, A.; Jamil, M.; Areeb, F.; Siddique, M.; Salimullah, M.

    2016-05-01

    The excitation of electrostatic, comparatively low frequency, lower-hybrid waves (LHWs) induced by electron beam in semiconductor plasma is examined using a quantum hydrodynamic model. Various quantum effects are taken into account including the recoil effect, Fermi degenerate pressure, and exchange-correlation potential. The effects of different parameters like the electron-to-hole number density ratio, scaled electron beam temperature and streaming speed, propagation angle and cyclotron frequency over the growth, and phase speed of LHWs are investigated. It is noticed that an increase in the electron number density and streaming speed enhance the instability. Similar effects are observed on decreasing the propagation angle with magnetic field.

  12. Achilles tendon loading patterns during barefoot walking and slow running on a treadmill: An ultrasonic propagation study.

    PubMed

    Wulf, M; Wearing, S C; Hooper, S L; Smeathers, J E; Horstmann, T; Brauner, T

    2015-12-01

    Measurement of tendon loading patterns during gait is important for understanding the pathogenesis of tendon "overuse" injury. Given that the speed of propagation of ultrasound in tendon is proportional to the applied load, this study used a noninvasive ultrasonic transmission technique to measure axial ultrasonic velocity in the right Achilles tendon of 27 healthy adults (11 females and 16 males; age, 26 ± 9 years; height, 1.73 ± 0.07 m; weight, 70.6 ± 21.2 kg), walking at self-selected speed (1.1 ± 0.1 m/s), and running at fixed slow speed (2 m/s) on a treadmill. Synchronous measures of ankle kinematics, spatiotemporal gait parameters, and vertical ground reaction forces were simultaneously measured. Slow running was associated with significantly higher cadence, shorter step length, but greater range of ankle movement, higher magnitude and rate of vertical ground reaction force, and higher ultrasonic velocity in the tendon than walking (P < 0.05). Ultrasonic velocity in the Achilles tendon was highly reproducible during walking and slow running (mean within-subject coefficient of variation < 2%). Ultrasonic maxima (P1, P2) and minima (M1, M2) were significantly higher and occurred earlier in the gait cycle (P1, M1, and M2) during running than walking (P < 0.05). Slow running was associated with higher and earlier peaks in loading of the Achilles tendon than walking.

  13. Achilles tendon loading patterns during barefoot walking and slow running on a treadmill: An ultrasonic propagation study.

    PubMed

    Wulf, M; Wearing, S C; Hooper, S L; Smeathers, J E; Horstmann, T; Brauner, T

    2015-12-01

    Measurement of tendon loading patterns during gait is important for understanding the pathogenesis of tendon "overuse" injury. Given that the speed of propagation of ultrasound in tendon is proportional to the applied load, this study used a noninvasive ultrasonic transmission technique to measure axial ultrasonic velocity in the right Achilles tendon of 27 healthy adults (11 females and 16 males; age, 26 ± 9 years; height, 1.73 ± 0.07 m; weight, 70.6 ± 21.2 kg), walking at self-selected speed (1.1 ± 0.1 m/s), and running at fixed slow speed (2 m/s) on a treadmill. Synchronous measures of ankle kinematics, spatiotemporal gait parameters, and vertical ground reaction forces were simultaneously measured. Slow running was associated with significantly higher cadence, shorter step length, but greater range of ankle movement, higher magnitude and rate of vertical ground reaction force, and higher ultrasonic velocity in the tendon than walking (P < 0.05). Ultrasonic velocity in the Achilles tendon was highly reproducible during walking and slow running (mean within-subject coefficient of variation < 2%). Ultrasonic maxima (P1, P2) and minima (M1, M2) were significantly higher and occurred earlier in the gait cycle (P1, M1, and M2) during running than walking (P < 0.05). Slow running was associated with higher and earlier peaks in loading of the Achilles tendon than walking. PMID:25913324

  14. Dispersion relations and polarizations of low-frequency waves in two-fluid plasmas

    SciTech Connect

    Zhao, Jinsong

    2015-04-15

    Analytical expressions for the dispersion relations and polarizations of low-frequency waves in magnetized plasmas based on two-fluid model are obtained. The properties of waves propagating at different angles (to the ambient magnetic field B{sub 0}) and β (the ratio of the plasma to magnetic pressures) values are investigated. It is shown that two linearly polarized waves—namely, the fast and Alfvén modes in the low-β (β≪1) plasmas, the fast and slow modes in the β∼1 plasmas, and the Alfvén and slow modes in the high-β (β≫1) plasmas—become circularly polarized at the near-parallel (to B{sub 0}) propagation. The negative magnetic-helicity of the Alfvén mode occurs only at small or moderate angles in the low-β plasmas, and the ion cross-helicity of the slow mode is nearly the same as that of the Alfvén mode in the high-β plasmas. It is also shown that the electric polarization δE{sub z}/δE{sub y} decreases with the temperature ratio T{sub e}/T{sub i} for the long-wavelength waves, and the transition between left- and right-hand polarizations of the Alfvén mode in T{sub e}/T{sub i}≠0 plasmas can disappear when T{sub e}/T{sub i}=0. The approximate dispersion relations in the near-perpendicular propagation, low-β, and high-β limits can quite accurately describe the three modes.

  15. Low Frequency Radio Signals from Sprite Streamers

    NASA Astrophysics Data System (ADS)

    Qin, J.; Celestin, S. J.; Pasko, V. P.

    2013-12-01

    Sprites are mesospheric discharges that carry significant electrical currents and produce radio signals observed typically in the extremely low (ELF) to very low (VLF) frequency bands [Cummer et al., GRL, 25, 1281, 1998]. Recently, Low-Frequency (LF) radio observations of sprite-producing lightning discharges have shown the existence of consecutive broadband pulses exhibiting EM radiation that spans in the LF range, and it has been suggested that this LF radio signals may stem from non-luminous relativistic electron beams above thunderstorms [Fullekrug et al., JGR, 115, A00E09, 2010]. In this talk, we present the first theoretical estimates of the radio signals produced by individual sprite streamers using simulation results from a plasma fluid model. It is demonstrated that the spectral content of the radiation produced by sprite streamers is a function of the air density N and the lightning-induced quasi-static ambient electric field E in the regions of space where the sprite streamers are propagating. We demonstrate that the exponential growth of the current in sprite streamers at 75 km would be preferentially associated with electromagnetic radiation in the frequency range from 0 and up to ˜3 kHz, whereas the growth of the streamer current at 40 km could produce radiation with frequencies up to ˜300 kHz, consistently with the scaling of atmospheric air density [Kosar et al., JGR, 117, A08328, 2012]. We further conjecture that the periodic branching of streamers may lead to a radiation spectrum enhancement in the VLF to LF range. The present study shows that sprite streamers could be responsible for at least part of the LF radiation associated with sprite-producing lightning discharges that was detected recently by Fullekrug et al. [2010].

  16. Investigating Low-Frequency Earthquake Properties

    NASA Astrophysics Data System (ADS)

    Sweet, J. R.; Creager, K. C.

    2013-12-01

    Low-frequency earthquakes (LFEs) have been associated with tectonic tremor and slow slip on the deep extension of subduction zones faults and major strike-slip faults. These tiny earthquakes are thought to represent small amounts of slip on the plate interface in places with high pore fluid pressure and low effective stress. Some tectonic tremor has been shown to consist of the superposition of many LFEs occurring at nearly the same time [Shelly et al., 2007]. In northern Cascadia, we use data from the Array of Arrays and CAFE experiments to detect and study properties of a curious LFE family on the downdip extension of the transition zone. This family--the deepest we've yet discovered in Cascadia--occurs in small swarms of ~1 hour duration every 1 to 2 weeks. Over our 6-year dataset we have identified ~9000 individual repeats of this LFE. Using double-difference techniques on one swarm, we have found that the LFEs lie on a dipping plane (<300m thick) that locates on the inferred plate interface [McCrory et al., 2012; Preston et al., 2003]. Individual LFE locations have errors of order 100m. Interestingly, we also find that over the course of an hour the LFEs migrate updip over a distance of ~2km in a narrow channel parallel to the plate convergence direction. We suggest this migration represents the movement of a slow slip front, and may be similar to previously described tremor streaks, also seen in Cascadia [Ghosh et al., 2010]; however our migration velocity of 2km/hr would be intermediate between the slower reported velocities of rapid tremor reversals [Houston et al., 2010] and the much faster tremor streaks. We find that amplitudes for this LFE family occupy a relatively narrow range, with louder events equally likely to occur at the beginning, middle, or end of a swarm of LFEs. We estimate LFE magnitudes of -0.8 to +0.8 by comparing peak-to-peak amplitudes and PNSN assigned magnitudes for 8 small earthquakes within 10km of the LFEs. Amplitudes below about

  17. Slow and fast light propagation in a triple quantum well nanostructure

    NASA Astrophysics Data System (ADS)

    Solookinejad, Ghahraman; Panahi, Mohsen; Ahmadi Sangachin, Elnaz; Asadpour, Seyyed Hossein

    2016-02-01

    In this paper, we investigate the absorption and dispersion properties of a weak probe field in a triple quantum well nanostructure by using the incoherent pumping fields. A deep 7.1 nm-thick GaAs well is coupled, on one side, to two shallow 6.8 nm-thick Al0.2Ga0.8As wells by a 2.5 nm-thick Al0.4Ga0.6As barrier. The two shallow wells are separated by a 2.0 nm-thick Al0.4Ga0.8As barrier. Both sides of quantum well contact with 36 nm Al0.4Ga0.6As. Therefore, this type of triple quantum well nanostructure can be used as a suitable medium for studying the effect of spontaneously generated coherence (SGC) and interference between incoherent pumping fields on absorption and dispersion properties of weak probe light. We find that the interferences from spontaneous emission and incoherent pumping processes can change the slope of dispersion and group velocity of the probe light from slow to fast or vice versa. Moreover, it is demonstrated that the group velocity of the light pulse can be controlled with the rates of incoherent pumping fields.

  18. Implementation of dispersion-free slow acoustic wave propagation and phase engineering with helical-structured metamaterials

    PubMed Central

    Zhu, Xuefeng; Li, Kun; Zhang, Peng; Zhu, Jie; Zhang, Jintao; Tian, Chao; Liu, Shengchun

    2016-01-01

    The ability to slow down wave propagation in materials has attracted significant research interest. A successful solution will give rise to manageable enhanced wave–matter interaction, freewheeling phase engineering and spatial compression of wave signals. The existing methods are typically associated with constructing dispersive materials or structures with local resonators, thus resulting in unavoidable distortion of waveforms. Here we show that, with helical-structured acoustic metamaterials, it is now possible to implement dispersion-free sound deceleration. The helical-structured metamaterials present a non-dispersive high effective refractive index that is tunable through adjusting the helicity of structures, while the wavefront revolution plays a dominant role in reducing the group velocity. Finally, we numerically and experimentally demonstrate that the helical-structured metamaterials with designed inhomogeneous unit cells can turn a normally incident plane wave into a self-accelerating beam on the prescribed parabolic trajectory. The helical-structured metamaterials will have profound impact to applications in explorations of slow wave physics. PMID:27198887

  19. Implementation of dispersion-free slow acoustic wave propagation and phase engineering with helical-structured metamaterials.

    PubMed

    Zhu, Xuefeng; Li, Kun; Zhang, Peng; Zhu, Jie; Zhang, Jintao; Tian, Chao; Liu, Shengchun

    2016-05-20

    The ability to slow down wave propagation in materials has attracted significant research interest. A successful solution will give rise to manageable enhanced wave-matter interaction, freewheeling phase engineering and spatial compression of wave signals. The existing methods are typically associated with constructing dispersive materials or structures with local resonators, thus resulting in unavoidable distortion of waveforms. Here we show that, with helical-structured acoustic metamaterials, it is now possible to implement dispersion-free sound deceleration. The helical-structured metamaterials present a non-dispersive high effective refractive index that is tunable through adjusting the helicity of structures, while the wavefront revolution plays a dominant role in reducing the group velocity. Finally, we numerically and experimentally demonstrate that the helical-structured metamaterials with designed inhomogeneous unit cells can turn a normally incident plane wave into a self-accelerating beam on the prescribed parabolic trajectory. The helical-structured metamaterials will have profound impact to applications in explorations of slow wave physics.

  20. Implementation of dispersion-free slow acoustic wave propagation and phase engineering with helical-structured metamaterials

    NASA Astrophysics Data System (ADS)

    Zhu, Xuefeng; Li, Kun; Zhang, Peng; Zhu, Jie; Zhang, Jintao; Tian, Chao; Liu, Shengchun

    2016-05-01

    The ability to slow down wave propagation in materials has attracted significant research interest. A successful solution will give rise to manageable enhanced wave-matter interaction, freewheeling phase engineering and spatial compression of wave signals. The existing methods are typically associated with constructing dispersive materials or structures with local resonators, thus resulting in unavoidable distortion of waveforms. Here we show that, with helical-structured acoustic metamaterials, it is now possible to implement dispersion-free sound deceleration. The helical-structured metamaterials present a non-dispersive high effective refractive index that is tunable through adjusting the helicity of structures, while the wavefront revolution plays a dominant role in reducing the group velocity. Finally, we numerically and experimentally demonstrate that the helical-structured metamaterials with designed inhomogeneous unit cells can turn a normally incident plane wave into a self-accelerating beam on the prescribed parabolic trajectory. The helical-structured metamaterials will have profound impact to applications in explorations of slow wave physics.

  1. Implementation of dispersion-free slow acoustic wave propagation and phase engineering with helical-structured metamaterials.

    PubMed

    Zhu, Xuefeng; Li, Kun; Zhang, Peng; Zhu, Jie; Zhang, Jintao; Tian, Chao; Liu, Shengchun

    2016-01-01

    The ability to slow down wave propagation in materials has attracted significant research interest. A successful solution will give rise to manageable enhanced wave-matter interaction, freewheeling phase engineering and spatial compression of wave signals. The existing methods are typically associated with constructing dispersive materials or structures with local resonators, thus resulting in unavoidable distortion of waveforms. Here we show that, with helical-structured acoustic metamaterials, it is now possible to implement dispersion-free sound deceleration. The helical-structured metamaterials present a non-dispersive high effective refractive index that is tunable through adjusting the helicity of structures, while the wavefront revolution plays a dominant role in reducing the group velocity. Finally, we numerically and experimentally demonstrate that the helical-structured metamaterials with designed inhomogeneous unit cells can turn a normally incident plane wave into a self-accelerating beam on the prescribed parabolic trajectory. The helical-structured metamaterials will have profound impact to applications in explorations of slow wave physics. PMID:27198887

  2. GPS detection of ultra-low-frequency crustal resonance caused by Hurricane Sandy

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Holt, W. E.; Blewitt, G.

    2013-12-01

    Using 5-minute solutions of vertical component GPS, processed from the CORS network, we observe spatially correlated displacements that appear to propagate for several hundreds of kilometers within the Northeastern U.S., just after the landfall of Hurricane Sandy. This displacement field lasts for about 4.5 hours and shows great attenuation when propagating from the coast into the mainland. Its amplitude is about 10 times bigger than that predicted by a static loading using traditional theory and models. We interpret the propagation of the time-dependent vertical displacement field as a Biot slow wave associated with a medium containing abundant water-filled fractures in the crust. This ultra-long period wave appears to have been excited by the large storm surge that impacted the coastal region during, and just prior to, the Sandy landfall. Our interpretation predicts three key features simultaneously: strong attenuation, low wave speed (no more than 100 m/s) and high displacement amplification (about 10 times). The observations may suggest that poroelastic behavior plays an important role in elastodynamics for the crust, especially for ultra low frequency loading.

  3. 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.

  4. Very low frequency earthquakes in Cascadia migrate with tremor

    NASA Astrophysics Data System (ADS)

    Ghosh, Abhijit; Huesca-Pérez, Eduardo; Brodsky, Emily; Ito, Yoshihiro

    2015-05-01

    We find very low frequency earthquakes (VLFEs) in Cascadia under northern Washington during 2011 episodic tremor and slip event. VLFEs are rich in low-frequency energy (20-50 s) and depleted in higher frequencies (higher than 1 Hz) compared to local earthquakes. Based on a grid search centroid moment tensor inversion, we find that VLFEs are located near the plate interface in the zone where tremor and slow slip are observed. In addition, they migrate along strike with tremor activity. Their moment tensor solutions show double-couple sources with shallow thrust mechanisms, consistent with shear slip at the plate interface. Their magnitude ranges between Mw 3.3 and 3.7. Seismic moment released by a single VLFE is comparable to the total cumulative moment released by tremor activity during an entire episodic tremor and slip event. The VLFEs contribute more seismic moment to this episodic tremor and slip event than cumulative tremor activity and indicate a higher seismic efficiency of slow earthquakes in Cascadia than previously thought. Spatiotemporal correlation of VLFE and tremor activity suggests that they are the results of the same physical processes governing slow earthquakes.

  5. On apparent temperature in low-frequency Alfvenic turbulence

    SciTech Connect

    Nariyuki, Yasuhiro

    2012-08-15

    Low-frequency, parallel propagating Alfvenic turbulence in collisionless plasmas is theoretically studied. Alfvenic turbulence is derived as an equilibrium state (Beltrami field) in the magnetohydrodynamic equations with the pressure anisotropy and multi-species of ions. It is shown that the conservation of the total 'apparent temperature' corresponds to the Bernoulli law. A simple model of the radially expanding solar wind including Alfvenic turbulence is also discussed. The conversion of the wave energy in the 'apparent temperature' into the 'real temperature' is facilitated with increasing radial distance.

  6. Improved low frequency stability of bolometric detectors

    SciTech Connect

    Wilbanks, T.; Devlin, M.; Lange, A.E. . Dept. of Physics); Sato, S. . Dept. of Physics); Beeman, J.W.; Haller, E.E. . Center for Advanced Materials)

    1990-04-01

    The authors have developed an AC bridge readout system that greatly improves the low-frequency stability of bolometric detectors. The readout can be implemented with a simple circuit appropriate for use in space applications. Using a matched pair of detectors in the readout, the authors have achieved system noise within a factor of two of the fundamental noise limit of the detectors at frequencies as low as 10 mHz. The low frequency stability of the readout system allows slower, more sensitive detectors to be used in many applications, and facilitates observing strategies that are well-suited to space-borne observations.

  7. Low frequency acoustic and electromagnetic scattering

    NASA Technical Reports Server (NTRS)

    Hariharan, S. I.; Maccamy, R. C.

    1986-01-01

    This paper deals with two classes of problems arising from acoustics and electromagnetics scattering in the low frequency stations. The first class of problem is solving Helmholtz equation with Dirichlet boundary conditions on an arbitrary two dimensional body while the second one is an interior-exterior interface problem with Helmholtz equation in the exterior. Low frequency analysis show that there are two intermediate problems which solve the above problems accurate to 0(k/2/ log k) where k is the frequency. These solutions greatly differ from the zero frequency approximations. For the Dirichlet problem numerical examples are shown to verify the theoretical estimates.

  8. Low frequency acoustic and electromagnetic scattering

    NASA Technical Reports Server (NTRS)

    Hariharan, S. I.; Maccamy, R. C.

    1983-01-01

    This paper deals with two classes of problems arising from acoustics and electromagnetics scattering in the low frequency stations. The first class of problem is solving Helmholtz equation with Dirichlet boundary conditions on an arbitrary two dimensional body while the second one is an interior-exterior interface problem with Helmholtz equation in the exterior. Low frequency analysis show that there are two intermediate problems which solve the above problems accurate to 0(k(2) log k) where k is the frequency. These solutions greatly differ from the zero frequency approximations. For the Dirichlet problem numerical examples are shown to verify the theoretical estimates.

  9. Non-volcanic tremor and low-frequency earthquake swarms.

    PubMed

    Shelly, David R; Beroza, Gregory C; Ide, Satoshi

    2007-03-15

    Non-volcanic tremor is a weak, extended duration seismic signal observed episodically on some major faults, often in conjunction with slow slip events. Such tremor may hold the key to understanding fundamental processes at the deep roots of faults, and could signal times of accelerated slip and hence increased seismic hazard. The mechanism underlying the generation of tremor and its relationship to aseismic slip are, however, as yet unresolved. Here we demonstrate that tremor beneath Shikoku, Japan, can be explained as a swarm of small, low-frequency earthquakes, each of which occurs as shear faulting on the subduction-zone plate interface. This suggests that tremor and slow slip are different manifestations of a single process.

  10. Low frequency dielectric relaxation in boracites

    NASA Technical Reports Server (NTRS)

    Kim, Q.; Somoano, R.

    1983-01-01

    In order to elucidate the nature of the imperfections which adversely affect pyroelectric processes in boracites, the thermal and dispersive characteristics of the low frequency dielectric response in iron-iodide boracite (Fe3B7O13I) and copper-chloride boracite (Cu3B7O13Cl) have been investigated. These characteristics were measured as a function of crystallographic orientation and applied field in both the ferroelectric and paraelectric states. The low frequency dielectric relaxation of 100 line oriented multi-domain copper-chloride boracite clearly indicates the dipole nature of the lattice imperfections. The activation energies calculated from a noninteracting Debye model, are 0.53 eV in the ferroelectric phase and 0.10 eV in the paraelectric phase.

  11. Extreme low frequency acoustic measurement system

    NASA Technical Reports Server (NTRS)

    Shams, Qamar A. (Inventor); Zuckerwar, Allan J. (Inventor)

    2013-01-01

    The present invention is an extremely low frequency (ELF) microphone and acoustic measurement system capable of infrasound detection in a portable and easily deployable form factor. In one embodiment of the invention, an extremely low frequency electret microphone comprises a membrane, a backplate, and a backchamber. The backchamber is sealed to allow substantially no air exchange between the backchamber and outside the microphone. Compliance of the membrane may be less than ambient air compliance. The backplate may define a plurality of holes and a slot may be defined between an outer diameter of the backplate and an inner wall of the microphone. The locations and sizes of the holes, the size of the slot, and the volume of the backchamber may be selected such that membrane motion is substantially critically damped.

  12. A variable passive low-frequency absorber

    NASA Astrophysics Data System (ADS)

    Larsen, Niels Werner; Thompson, Eric R.; Gade, Anders Christian

    2005-04-01

    Multi-purpose concert halls face a dilemma. They can host classical music concerts, rock concerts and spoken word performances in a matter of a short period. These different performance types require significantly different acoustic conditions in order to provide the best sound quality to both the performers and the audience. A recommended reverberation time for classical music may be in the range of 1.5-2 s for empty halls, where rock music sounds best with a reverberation time around 0.8-1 s. Modern rhythmic music often contains high levels of sound energy in the low frequency bands but still requires a high definition for good sound quality. Ideally, the absorption of the hall should be adjustable in all frequency bands in order to provide good sound quality for all types of performances. The mid and high frequency absorption is easily regulated, but adjusting the low-frequency absorption has typically been too expensive or requires too much space to be practical for multi-purpose halls. Measurements were made on a variable low-frequency absorber to develop a practical solution to the dilemma. The paper will present the results of the measurements as well as a possible design.

  13. LOFAR: The LOw-Frequency ARray

    NASA Astrophysics Data System (ADS)

    van Haarlem, M. P.; Wise, M. W.; Gunst, A. W.; Heald, G.; McKean, J. P.; Hessels, J. W. T.; de Bruyn, A. G.; Nijboer, R.; Swinbank, J.; Fallows, R.; Brentjens, M.; Nelles, A.; Beck, R.; Falcke, H.; Fender, R.; Hörandel, J.; Koopmans, L. V. E.; Mann, G.; Miley, G.; Röttgering, H.; Stappers, B. W.; Wijers, R. A. M. J.; Zaroubi, S.; van den Akker, M.; Alexov, A.; Anderson, J.; Anderson, K.; van Ardenne, A.; Arts, M.; Asgekar, A.; Avruch, I. M.; Batejat, F.; Bähren, L.; Bell, M. E.; Bell, M. R.; van Bemmel, I.; Bennema, P.; Bentum, M. J.; Bernardi, G.; Best, P.; Bîrzan, L.; Bonafede, A.; Boonstra, A.-J.; Braun, R.; Bregman, J.; Breitling, F.; van de Brink, R. H.; Broderick, J.; Broekema, P. C.; Brouw, W. N.; Brüggen, M.; Butcher, H. R.; van Cappellen, W.; Ciardi, B.; Coenen, T.; Conway, J.; Coolen, A.; Corstanje, A.; Damstra, S.; Davies, O.; Deller, A. T.; Dettmar, R.-J.; van Diepen, G.; Dijkstra, K.; Donker, P.; Doorduin, A.; Dromer, J.; Drost, M.; van Duin, A.; Eislöffel, J.; van Enst, J.; Ferrari, C.; Frieswijk, W.; Gankema, H.; Garrett, M. A.; de Gasperin, F.; Gerbers, M.; de Geus, E.; Grießmeier, J.-M.; Grit, T.; Gruppen, P.; Hamaker, J. P.; Hassall, T.; Hoeft, M.; Holties, H. A.; Horneffer, A.; van der Horst, A.; van Houwelingen, A.; Huijgen, A.; Iacobelli, M.; Intema, H.; Jackson, N.; Jelic, V.; de Jong, A.; Juette, E.; Kant, D.; Karastergiou, A.; Koers, A.; Kollen, H.; Kondratiev, V. I.; Kooistra, E.; Koopman, Y.; Koster, A.; Kuniyoshi, M.; Kramer, M.; Kuper, G.; Lambropoulos, P.; Law, C.; van Leeuwen, J.; Lemaitre, J.; Loose, M.; Maat, P.; Macario, G.; Markoff, S.; Masters, J.; McFadden, R. A.; McKay-Bukowski, D.; Meijering, H.; Meulman, H.; Mevius, M.; Middelberg, E.; Millenaar, R.; Miller-Jones, J. C. A.; Mohan, R. N.; Mol, J. D.; Morawietz, J.; Morganti, R.; Mulcahy, D. D.; Mulder, E.; Munk, H.; Nieuwenhuis, L.; van Nieuwpoort, R.; Noordam, J. E.; Norden, M.; Noutsos, A.; Offringa, A. R.; Olofsson, H.; Omar, A.; Orrú, E.; Overeem, R.; Paas, H.; Pandey-Pommier, M.; Pandey, V. N.; Pizzo, R.; Polatidis, A.; Rafferty, D.; Rawlings, S.; Reich, W.; de Reijer, J.-P.; Reitsma, J.; Renting, G. A.; Riemers, P.; Rol, E.; Romein, J. W.; Roosjen, J.; Ruiter, M.; Scaife, A.; van der Schaaf, K.; Scheers, B.; Schellart, P.; Schoenmakers, A.; Schoonderbeek, G.; Serylak, M.; Shulevski, A.; Sluman, J.; Smirnov, O.; Sobey, C.; Spreeuw, H.; Steinmetz, M.; Sterks, C. G. M.; Stiepel, H.-J.; Stuurwold, K.; Tagger, M.; Tang, Y.; Tasse, C.; Thomas, I.; Thoudam, S.; Toribio, M. C.; van der Tol, B.; Usov, O.; van Veelen, M.; van der Veen, A.-J.; ter Veen, S.; Verbiest, J. P. W.; Vermeulen, R.; Vermaas, N.; Vocks, C.; Vogt, C.; de Vos, M.; van der Wal, E.; van Weeren, R.; Weggemans, H.; Weltevrede, P.; White, S.; Wijnholds, S. J.; Wilhelmsson, T.; Wucknitz, O.; Yatawatta, S.; Zarka, P.; Zensus, A.; van Zwieten, J.

    2013-08-01

    LOFAR, the LOw-Frequency ARray, is a new-generation radio interferometer constructed in the north of the Netherlands and across europe. Utilizing a novel phased-array design, LOFAR covers the largely unexplored low-frequency range from 10-240 MHz and provides a number of unique observing capabilities. Spreading out from a core located near the village of Exloo in the northeast of the Netherlands, a total of 40 LOFAR stations are nearing completion. A further five stations have been deployed throughout Germany, and one station has been built in each of France, Sweden, and the UK. Digital beam-forming techniques make the LOFAR system agile and allow for rapid repointing of the telescope as well as the potential for multiple simultaneous observations. With its dense core array and long interferometric baselines, LOFAR achieves unparalleled sensitivity and angular resolution in the low-frequency radio regime. The LOFAR facilities are jointly operated by the International LOFAR Telescope (ILT) foundation, as an observatory open to the global astronomical community. LOFAR is one of the first radio observatories to feature automated processing pipelines to deliver fully calibrated science products to its user community. LOFAR's new capabilities, techniques and modus operandi make it an important pathfinder for the Square Kilometre Array (SKA). We give an overview of the LOFAR instrument, its major hardware and software components, and the core science objectives that have driven its design. In addition, we present a selection of new results from the commissioning phase of this new radio observatory.

  14. FR II radio galaxies at low frequencies

    NASA Astrophysics Data System (ADS)

    Harwood, Jeremy

    2016-08-01

    Due to their steep spectra, low-frequency observations of FR II radio galaxies potentially provide key insights in to the morphology, energetics and underlying physics of these powerful radio sources. However, limitations imposed by the previous generation of radio interferometers at metre wavelengths have meant that this region of parameter space remains largely unexplored.In this talk, we present our latest results using LOFAR and the JVLA at frequencies between 50 and 460 MHz which, along with complementary archival radio and X-ray data, now allows us to undertake well resolved, detailed studies of nearby FR II radio galaxies at low frequencies. We discuss how our improved knowledge of the low-energy electron distribution, magnetic field strength and total energy content of the lobes impacts upon our understanding of the dynamics and energetics of nearby FR II radio galaxies and, for the first time, present the spectral structure of these sources on small spatial scales at low frequencies. We conclude by discussing how these findings change our current understanding of the underlying physics of FR II radio galaxies and, ultimately, their impact on the environment and galaxy evolution as a whole.

  15. Low-Frequency Waves in Cold Three-Component Plasmas

    NASA Astrophysics Data System (ADS)

    Fu, Qiang; Tang, Ying; Zhao, Jinsong; Lu, Jianyong

    2016-09-01

    The dispersion relation and electromagnetic polarization of the plasma waves are comprehensively studied in cold electron, proton, and heavy charged particle plasmas. Three modes are classified as the fast, intermediate, and slow mode waves according to different phase velocities. When plasmas contain positively-charged particles, the fast and intermediate modes can interact at the small propagating angles, whereas the two modes are separate at the large propagating angles. The near-parallel intermediate and slow waves experience the linear polarization, circular polarization, and linear polarization again, with the increasing wave number. The wave number regime corresponding to the above circular polarization shrinks as the propagating angle increases. Moreover, the fast and intermediate modes cause the reverse change of the electromagnetic polarization at the special wave number. While the heavy particles carry the negative charges, the dispersion relations of the fast and intermediate modes are always separate, being independent of the propagating angles. Furthermore, this study gives new expressions of the three resonance frequencies corresponding to the highly-oblique propagation waves in the general three-component plasmas, and shows the dependence of the resonance frequencies on the propagating angle, the concentration of the heavy particle, and the mass ratio among different kinds of particles. supported by National Natural Science Foundation of China (Nos. 11303099, 41531071 and 41574158), and the Youth Innovation Promotion Association CAS

  16. Ultra low frequency electromagnetic fire alarm system for underground mines

    SciTech Connect

    Not Available

    1991-01-01

    During an underground mine fire, air can be rapidly depleted of oxygen and contaminated with smoke and toxic fire gases. Any delay in warning miners could have disastrous consequences. Unfortunately, present mine fire alarm systems, such as stench, audible or visual alarms, telephones, and messengers, are often slow, unreliable, and limited in mine area coverage. Recent research by the U.S. Bureau of Mines has demonstrated that ultra-low-frequency electromagnetic signaling can be used for an underground mine fire alarm. In field tests of prototype equipment at five mines, electromagnetic signals from 630 to 2,000 Hz were transmitted through mine rock for distances as great as 1,645 m to an intrinsically safe receiver. The prototype system uses off-the-shelf components and state-of-the-art technology to ensure high reliability and low cost. When utilized, this technology would enable simultaneous and instantaneous warning of all underground personnel, regardless of their location or work activity, thereby increasing the likelihood of their successfully escaping a mine disaster. This paper presents the theoretical basis for through-the-rock ultra-low-frequency electromagnetic transmission, design of the prototype transmitter and receiver, and the results of in-mine tests of the prototype system.

  17. Generation of low-frequency components in ultrasonic waves penetrating the interface between contacting solids

    NASA Astrophysics Data System (ADS)

    Tanaka, H.; Okamoto, T.; Kurihara, K.; Sugiura, T.

    2014-02-01

    It is difficult to detect a closed crack by conventional ultrasonic testing. However, nonlinear ultrasonics may be useful for detection of a closed crack in structures. This study experimentally examined propagation of ultrasonic waves through the interface between contacting solids. We simulated a closed crack by compressing two aluminum blocks. The input frequency was changed in the range of 1.0-2.0MHz and two different types of surface roughness of specimens were used. As a result, generation of low-frequency components at about 600 kHz was found regardless of the input frequency. Such a feature of low-frequency components is different from that of subharmonics. Additionally, this phenomenon was not confirmed in specimens with smoother surface. Therefore, surface roughness can be one of important factors of generating low-frequency components. The results suggest that these low-frequency components can be useful for detecting a closed crack.

  18. Low-frequency vibrational modes of glutamine

    NASA Astrophysics Data System (ADS)

    Wang, Wei-Ning; Wang, Guo; Zhang, Yan

    2011-12-01

    High-resolution terahertz absorption and Raman spectra of glutamine in the frequency region 0.2 THz-2.8 THz are obtained by using THz time domain spectroscopy and low-frequency Raman spectroscopy. Based on the experimental and the computational results, the vibration modes corresponding to the terahertz absorption and Raman scatting peaks are assigned and further verified by the theoretical calculations. Spectral investigation of the periodic structure of glutamine based on the sophisticated hybrid density functional B3LYP indicates that the vibrational modes come mainly from the inter-molecular hydrogen bond in this frequency region.

  19. Low frequency ionic conduction across liquid interfaces

    NASA Astrophysics Data System (ADS)

    Solis, Francisco J.; Guerrero, Guillermo Ivan; Olvera de La Cruz, Monica

    Ionic conduction in liquid media is a central component of many recently proposed technologies. As in the case of solid state systems, the presence of heterogeneous media gives rise to interesting nonlinear phenomena. We present simulations and theoretical analysis of the low frequency ionic conduction in a two-liquid system. In the case analyzed, the conduction is driven by an electric field perpendicular to the liquid-liquid interface. We show that the dielectric contrast between the liquids produces non-linear effects in the effective conductivity of the system and discuss the effects of the ion solubility in the media.

  20. Minimization of nanosatellite low frequency magnetic fields

    NASA Astrophysics Data System (ADS)

    Belyayev, S. M.; Dudkin, F. L.

    2016-03-01

    Small weight and dimensions of the micro- and nanosatellites constrain researchers to place electromagnetic sensors on short booms or on the satellite body. Therefore the electromagnetic cleanliness of such satellites becomes a central question. This paper describes the theoretical base and practical techniques for determining the parameters of DC and very low frequency magnetic interference sources. One of such sources is satellite magnetization, the reduction of which improves the accuracy and stability of the attitude control system. We present design solutions for magnetically clean spacecraft, testing equipment, and technology for magnetic moment measurements, which are more convenient, efficient, and accurate than the conventional ones.

  1. Minimization of nanosatellite low frequency magnetic fields.

    PubMed

    Belyayev, S M; Dudkin, F L

    2016-03-01

    Small weight and dimensions of the micro- and nanosatellites constrain researchers to place electromagnetic sensors on short booms or on the satellite body. Therefore the electromagnetic cleanliness of such satellites becomes a central question. This paper describes the theoretical base and practical techniques for determining the parameters of DC and very low frequency magnetic interference sources. One of such sources is satellite magnetization, the reduction of which improves the accuracy and stability of the attitude control system. We present design solutions for magnetically clean spacecraft, testing equipment, and technology for magnetic moment measurements, which are more convenient, efficient, and accurate than the conventional ones. PMID:27036801

  2. Low frequency pressure modulation of indium antimonide

    SciTech Connect

    Hallock, Gary A.; Meier, Mark A.

    2012-07-15

    A lumped parameter resonator capable of generating megapascal pressures at low frequency (kilohertz) is described. Accelerometers are used to determine the applied pressure, and are calibrated with a piezoelectric sample. A laser diagnostic was also developed to measure the pressure in semiconductor samples through the band gap pressure dependence. In addition, the laser diagnostic has been used to measure the attenuation coefficient {alpha} of commercially available indium antimonide (InSb) wafers. The resonator and laser diagnostic have been used with InSb samples to verify the pressure response.

  3. Low frequency variability of Southern Ocean jets

    NASA Astrophysics Data System (ADS)

    Thompson, A. F.; Richards, K. J.

    2011-12-01

    Both observations and high resolution numerical models show that the Southern Ocean circumpolar flow is concentrated in a large number (approximately 8 to 12) of narrow filamentary jets. It is shown here that coherent jets exhibit a range of low frequency variability, on time scales of months to years, that can lead to displacement and to intermittent formation and dissipation of jets. Using output from an eddy-resolving ocean general circulation model in local regions near topographic features, the impact of energy exchange between eddy and mean flow components on jet persistence and variability is examined. A novel approach that uses a time-dependent definition of the mean flow provides a clearer picture of eddy-mean flow interactions in regions with spatially and temporally varying flow structure. The dynamics are largely consistent with those in idealized quasi-geostrophic models, including topographically-organized and surface-enhanced Reynolds stress forcing of the mean flow. Jets form during periods of enhanced eddy activity, but may persist long after the eddy activity has decayed. Similarly, jets may evolve in a downstream sense, with jet formation localized near topography and undergoing modification in response to changing bathymetry. The evolution of both temperature and potential vorticity is used to show that the low-frequency variability of the jets impacts water mass structure and tracer transport. This study highlights various examples of Southern Ocean dynamics that will prove difficult to capture through existing parameterizations in coarser climate models.

  4. Low frequency variability of Southern Ocean jets

    NASA Astrophysics Data System (ADS)

    Thompson, Andrew F.; Richards, Kelvin J.

    2011-09-01

    Both observations and high resolution numerical models show that the Southern Ocean circumpolar flow is concentrated in a large number (approximately 8 to 12) of narrow filamentary jets. It is shown here that coherent jets exhibit a range of low frequency variability, on timescales of months to years, that can lead to displacement and to intermittent formation and dissipation of jets. Using output from an eddy-resolving ocean general circulation model in local regions near topographic features, the impact of energy exchange between eddy and mean flow components on jet persistence and variability is examined. A novel approach that uses a time-dependent definition of the mean flow provides a clearer picture of eddy-mean flow interactions in regions with spatially and temporally varying flow structure. The dynamics are largely consistent with those in idealized quasi-geostrophic models, including topographically-organized and surface-enhanced Reynolds stress forcing of the mean flow. Jets form during periods of enhanced eddy activity, but may persist long after the eddy activity has decayed. Similarly, jets may evolve in a downstream sense, with jet formation localized near topography and undergoing modification in response to changing bathymetry. The evolution of both temperature and potential vorticity is used to show that the low-frequency variability of the jets impacts water mass structure and tracer transport. This study highlights various examples of Southern Ocean dynamics that will prove difficult to capture through parameterizations in coarser climate models.

  5. Moonquakes and Low Frequencies of Earthquakes

    NASA Astrophysics Data System (ADS)

    Patitsas, T. A.

    2004-05-01

    Some new results concerning moonquakes are included in this study. According to F. Duennebier and G. H. Sutton, 'Thermal moonquakes', J. of Geophysical Res., 79, 4351-4363, 1974, the moonquakes occur primarily during the early hours of the moon day. The frequency of these acoustic emissions is about 5 Hz and their duration is more than 60 s. There are interruptions in the emissions about every 10 cycles, similar to those seen in the acoustic emissions from granular media when they are forced to flow between the walls of the plunger and the container. The latter can be seen in a paper by H. Takahara, 'Sounding mechanism of singing sand', J. Acoustical Soc. Am., 53, 634-639, 1973. In a recent paper by A. J. Patitsas, 'Booming and singing acoustic emissions', J. of Fluids and Structures, 17, 287-315, 2003, the origin of the moonquakes is sought in the granular flow in the crevices of the craters during the early hours of the moon day when the rock masses tend to expand due to the relatively steep rise in the temperature on the surface of the moon. In order to render credibility to such a scenario, several simple experiments were done involving the squeezing and shearing of granular media between stone plates. The results of these experiments and the mechanism responsible for the low frequencies of the moonquakes and also for the very low frequencies associated with earthquakes will be discussed.

  6. Simple Low-Frequency Beam Pickup

    SciTech Connect

    Novokhatski, A.; Heifets, S.; Aleksandrov, A.; /Oak Ridge

    2011-10-12

    Detection of the field induced by a beam outside of the beam pipe can be used as a beam diagnostic. Wires placed in longitudinal slots in the outside wall of the beam pipe can be used as a beam pickup. This has a very small beam-coupling impedance and avoids complications of having a feedthrough. The signal can be reasonably high at low frequencies. We present a field waveform at the outer side of a beam pipe, obtained as a result of calculations and measurements. We calculate the beam-coupling impedance due to a long longitudinal slot in the resistive wall and the signal induced in a wire placed in such a slot and shielded by a thin screen from the beam. These results should be relevant for impedance calculations of the slot in an antechamber and for slots in the PEP-II distributed ion pump screens. The design of the low-frequency beam position monitor is very simple. It can be used in storage rings, synchrotron light sources, and free electron lasers, like LINAC coherent light source.

  7. Pulsar timing sensitivity to very-low-frequency gravitational waves

    SciTech Connect

    Jenet, Fredrick A.; Armstrong, J. W.; Tinto, Massimo

    2011-04-15

    We compute the sensitivity, constrained by instrumental, propagation, and other fundamental noises, of pulsar timing to very-low-frequency gravitational waves (GWs). Reaching predicted GW signal strengths will require suppression of time-of-arrival fluctuations caused by interstellar plasma turbulence and a reduction of white rms timing noise to < or approx. 100 ns. Assuming negligible intrinsic pulsar rotational noise, perfect time transfer from time standard to observatory, and stable pulse profiles, the resulting single-pulsar signal-to-noise ratio=1 sensitivity is limited by terrestrial time standards at h{sub rms}{approx}2x10{sup -16} [f/ (1 cycle/year)]-1/2 for f<3x10{sup -8} Hz, where f is the Fourier frequency and a bandwidth of 1 cycle/(10 years) is assumed. Since this sensitivity is comparable to predicted GW signal levels, a reliable detection will require substantial signal-to-noise ratio improvement via pulsar timing array.

  8. Low frequency wave modes of liquid-filled flexible tubes

    NASA Astrophysics Data System (ADS)

    Chou, Yuan-Fang; Peng, Tzu-Huan

    2015-09-01

    Many canals in the human body are liquid-filled thin wall flexible tubes. In general the P-wave and S-wave velocities of tube material are much slower than the sound velocity of the liquid. It is interested to study the dynamic deformation of the wall caused by pressure fluctuation of liquid. In the low frequency range, the liquid pressure is essentially axial symmetric. Therefore, axial symmetric wave propagation modes are investigated. The calculated spectrum shows there are two modes with zero frequency limit. Phase velocities of these two modes are much smaller than the sound velocity of the liquid. They are also slower than the P-wave velocity of the tube material. At very low wave number, radial displacements of both liquid particles and tube are very small compared to their axial counter parts. As the frequency goes higher, boundary waves are observed.

  9. Low-Frequency Radio Bursts and Space Weather

    NASA Technical Reports Server (NTRS)

    Gopalswamy, N.

    2016-01-01

    Low-frequency radio phenomena are due to the presence of nonthermal electrons in the interplanetary (IP) medium. Understanding these phenomena is important in characterizing the space environment near Earth and other destinations in the solar system. Substantial progress has been made in the past two decades, because of the continuous and uniform data sets available from space-based radio and white-light instrumentation. This paper highlights some recent results obtained on IP radio phenomena. In particular, the source of type IV radio bursts, the behavior of type III storms, shock propagation in the IP medium, and the solar-cycle variation of type II radio bursts are considered. All these phenomena are closely related to solar eruptions and active region evolution. The results presented were obtained by combining data from the Wind and SOHO missions.

  10. Resonant interactions between cometary ions and low frequency electromagnetic waves

    NASA Technical Reports Server (NTRS)

    Thorne, Richard M.; Tsurutani, Bruce T.

    1987-01-01

    The conditions for resonant wave amplification in a plasma with a ring-beam distribution which is intended to model pick-up ions in a cometary environment are investigated. The inclination between the interplanetary field and the solar wind is found to play a crucial role in governing both the resonant frequency and the growth rate of any unstable mode. It is suggested that the low-frequency MHD mode should experience the most rapid amplification for intermediate inclination. In the frame of the solar wind, such waves should propagate along the field in the direction upstream toward the sun with a phase speed lower than the beaming velocity of the pick-up ions. This mechanism may account for the presence of the interior MHD waves noted by satellites over a region surrounding comets Giacobini-Zinner and Halley.

  11. Ultra-Low-Frequency Waves at Venus and Mars

    NASA Astrophysics Data System (ADS)

    Dubinin, E.; Fraenz, M.

    2016-02-01

    Mars and Venus have no global magnetic field. The solar wind interacts directly with their ionospheres and atmospheres, inducing magnetospheres by a pileup of the interplanetary magnetic field. The first measurements of the ultra-low-frequency activity on Mars were made by the Phobos-2 spacecraft. This chapter investigates the wave observations recently supplied by the Mars Global Surveyor, Venus Express, and Mars Express. Coherent wave structures are a typical feature of the Martian magnetosheath. It is likely that the periodic compressional waves generated upstream of the bow shock are transported to the magnetosheath. At Venus, there has often been observed a penetration of the field oscillations downward to the ionosphere. Periodic oscillations of the escaping oxygen ions were typically observed in the Martian tail by MEX. It seems reasonable to suggest that the observed oscillations take their origin in the foreshock/magnetosheath and then propagate to the ionosphere and further to the tail.

  12. A new low-frequency backward mode in inhomogeneous plasmas

    SciTech Connect

    Vranjes, J.

    2014-07-15

    When an electromagnetic transverse wave propagates through an inhomogeneous plasma so that its electric field has a component in the direction of the background density gradient, there appears a disbalance of charge in every plasma layer, caused by the density gradient. Due to this, some additional longitudinal electric field component appears in the direction of the wave vector. This longitudinal field may couple with the usual electrostatic longitudinal perturbations like the ion acoustic, electron Langmuir, and ion plasma waves. As a result, these standard electrostatic waves are modified and in addition to this a completely new low-frequency mode appears. Some basic features of the coupling and modification of the ion acoustic wave, and properties of the new mode are discussed here, in ordinary electron-ion and in pair plasmas.

  13. Alternative theories of atmospheric telecommunications and low-frequency fluctuations

    NASA Astrophysics Data System (ADS)

    Frederiksen, Jorgen S.; Webster, Peter J.

    1988-08-01

    for the formation of quasi-stationary low-frequency fluctuations. One of these is the baroclinic-barotropic dipole instability mechanism in which the formation of quasi-stationary mature anomalies is initiated by the upstream development of mid-latitude eastward propagating dipole wave trains which arise through the combined baroclinic-barotropic instability of the three-dimensional atmospheric flow. The other is the westerly duct mechanism in which the initiation of low-frequency variability is caused by tropical disturbances. According to this hypothesis, the longitudinal variation of the basic state flow near the equator causes a ducting of wave energy generated in the tropics to specific zones in the upper tropospheric westerlies; these zones then act as source regions for the emanation of waves into the extratropics. Furthermore, this duct also acts as a waveguide for extratropical modes propagating into or through the tropics.

  14. Low-frequency electrostatic waves in the solar wind

    NASA Astrophysics Data System (ADS)

    Sreeraj, T.; Singh, Satyavir; Singh Lakhina, Gurbax

    2016-07-01

    Electrostatic ion cyclotron waves are one of the ubiquitous features in space and laboratory plasmas. Here we present a linear study of electrostatic ion cyclotron waves in the solar wind. We model the solar wind by three-component magnetised plasma consisting of hot electrons with kappa distribution and fluid cold protons and doubly charged Helium ions. A numerical analysis of the linear electrostatic dispersion relation has been carried out for slow solar wind parameters and for -oblique wave propagation. The system supports four different modes i.e., fast and slow acoustic modes, and proton and Helium cyclotron modes. It has to be emphasised that for parallel propagation, physically acceptable solution to the dispersion relation are those of fast and slow acoustic modes. For oblique propagation, the coupling between various modes can be seen. Moreover, when the angle of propagation is increased the separation between acoustic modes and cyclotron modes increases and at perpendicular propagation, only proton and Helium-cyclotron modes can exist. The effect of various parameters like number density and temperature of Helium ions and kappa index on the dispersive properties has also been investigated. As the number density of helium ions increases, frequency of proton cyclotron mode decreases and frequency of Helium cyclotron mode increases at a fixed wave number. When the value of kappa increases, the frequency of the proton cyclotron mode increases but it does not have significant effect on the frequency of the Helium cyclotron mode. Likewise, when the temperature of Helium ions increases, the frequency of Helium cyclotron mode increases, however, the frequency of proton cyclotron mode remains more or less unchanged.

  15. Low-frequency electromagnetic plasma waves at comet P/Grigg-Skjellerup: Analysis and interpretation

    NASA Technical Reports Server (NTRS)

    Neubauer, Fritz M.; Glassmeier, Karl-Heinz; Coates, A. J.; Johnstone, A. D.

    1993-01-01

    The propagation and polarization characteristic of low-frequency electromagnetic wave fields near comet P/Grigg-Skjellerup (P/GS) are analyzed using magnetic field and plasma observations obtained by the Giotto magnetometer experiment and the Johnstone plasma analyzer during the encounter at the comet on July 10, 1992. The results have been physically interpreted.

  16. Low-frequency radio navigation system

    NASA Technical Reports Server (NTRS)

    Wallis, D. E. (Inventor)

    1983-01-01

    A method of continuous wave navigation using four transmitters operating at sufficiently low frequencies to assure essentially pure groundwave operation is described. The transmitters are keyed to transmit constant bursts (1/4 sec) in a time-multiplexed pattern with phase modulation of at least one transmitter for identification of the transmitters and with the ability to identify the absolute phase of the modulated transmitter and the ability to modulate low rate data for transmission. The transmitters are optimally positioned to provide groundwave coverage over a service region of about 50 by 50 km for the frequencies selected in the range of 200 to 500 kHz, but their locations are not critical because of the beneficial effect of overdetermination of position of a receiver made possible by the fourth transmitter. Four frequencies are used, at least two of which are selected to provide optimal resolution. All transmitters are synchronized to an average phase as received by a monitor receiver.

  17. Low Frequency Electromagnetic Pulse and Explosions

    SciTech Connect

    Sweeney, J J

    2011-02-01

    This paper reviews and summarizes prior work related to low frequency (< 100 Hz) EMP (ElectroMagnetic Pulse) observed from explosions. It focuses on how EMP signals might, or might not, be useful in monitoring underground nuclear tests, based on the limits of detection, and physical understanding of these signals. In summary: (1) Both chemical and nuclear explosions produce an EMP. (2) The amplitude of the EMP from underground explosions is at least two orders of magnitude lower than from above ground explosions and higher frequency components of the signal are rapidly attenuated due to ground conductivity. (3) In general, in the near field, that is distances (r) of less than 10s of kilometers from the source, the amplitude of the EMP decays approximately as 1/r{sup 3}, which practically limits EMP applications to very close (<{approx}1km) distances. (4) One computational model suggests that the EMP from a decoupled nuclear explosion may be enhanced over the fully coupled case. This has not been validated with laboratory or field data. (5) The magnitude of the EMP from an underground nuclear explosion is about two orders of magnitude larger than that from a chemical explosion, and has a larger component of higher frequencies. In principle these differences might be used to discriminate a nuclear from a chemical explosion using sensors at very close (<{approx}1 km) distances. (6) Arming and firing systems (e.g. detonators, exploding bridge wires) can also produce an EMP from any type of explosion. (7) To develop the understanding needed to apply low frequency EMP to nuclear explosion monitoring, it is recommended to carry out a series of controlled underground chemical explosions with a variety of sizes, emplacements (e.g. fully coupled and decoupled), and arming and firing systems.

  18. Imaging Jupiter Radiation Belts At Low Frequencies

    NASA Astrophysics Data System (ADS)

    Girard, J. N.; de Pater, I.; Zarka, P.; Santos-Costa, D.; Sault, R.; Hess, S.; Cecconi, B.; Fender, R.; Pewg, Lofar

    2014-04-01

    , at different epochs only provided, each time, glimpses of the spectral content in different observational configurations. As the synchrotron emission frequency peaks at Vmax / E2B (with Vmax in MHz, E, the electron energy in MeV and B, the magnetic field in Gauss), the low frequency content of this emission is associated with low energy electron populations inside the inner belt and the energetic electrons located in regions of weaker magnetic field (at few jovian radii). Therefore, there is much interest in extending and completing the current knowledge of the synchrotron emission from the belts, with low frequency resolved observations. LOFAR, the LOw Frequency ARray (LOFAR) [6], is a giant flexible and digital ground-based radio interferometer operating in the 30-250 MHz band. It brings very high time (~ μs), frequency (~ kHz) and angular resolutions (~1") and huge sensitivity (mJy). In November 2011, a single 10-hour track enabled to cover an entire planetary rotation and led to the first resolved image of the radiation belts between 127- 172 MHz [7,8]. In Feb 2013, an 2×5h30 joint LOFAR/ WSRT observing campaign seized the state of the radiation belts from 45 MHz up to 5 GHz. We will present the current state of the study (imaging, reconstruction method and modeling) of the radiation belts dynamic with this current set of observations. LOFAR can contribute to the understanding of the physics taking place in the inner belt as well as possibly providing a fast and a systematic "diagnostic" of the state of the belts. The latter represents an opportunity to give context and ground-based support for the arrival of JUNO (NASA) scheduled in July 2016 and also for future missions, such as JUICE (ESA), at the vicinity of Jupiter by the exploration of its icy satellites.

  19. The LWA1 Low Frequency Sky Survey

    NASA Astrophysics Data System (ADS)

    Dowell, Jayce; Taylor, Gregory B.; LWA Collaboration

    2015-01-01

    The LWA1 Low Frequency Sky Survey is a survey of the sky visible from the first station of the Long Wavelength Array (LWA1) across the frequency range of 35 to 80 MHz. The primary motivation behind this effort is to improve our understanding of the sky at these frequencies. In particular, an understanding of the low frequency foreground emission is necessary for work on detecting the epoch of reionization and the cosmic dark ages where the foreground signal dwarfs the expected redshifted HI signal by many orders of magnitude (Pritchard & Loeb 2012, Rep. Prog. Phys., 75, 086901). The leading model for the sky in the frequency range of 20 to 200 MHz is the Global Sky Model (GSM) by de Oliveria-Costas et al. (2008, MNRAS, 288, 247). This model is based upon a principle component analysis of 11 sky maps ranging in frequency from 10 MHz to 94 GHz. Of these 11 maps, only four are below 1 GHz; 10 MHz from Caswell (1976, MNRAS, 177, 601), 22 MHz from Roger et al. (1999, A&AS, 137, 7), 45 MHz from Alvarez et al. (1997, A&AS, 124, 315) and Maeda et al. (1999, A&AS, 140, 145), and 408 MHz from Haslam et al. (1982, A&AS, 47, 1). Thus, within this model, the region of interest to both cosmic dawn and the epoch of reionization is largely unconstrained based on the available survey data, and are also limited in terms of the spatial coverage and calibration. A self-consistent collection of maps is necessary for both our understanding of the sky and the removal of the foregrounds that mask the redshifted 21-cm signal.We present the current state of the survey and discuss the imaging and calibration challenges faced by dipole arrays that are capable of imaging nearly 2π steradians of sky simultaneously over a large fractional bandwidth.Construction of the LWA has been supported by the Office of Naval Research under Contract N00014-07-C-0147. Support for operations and continuing development of the LWA1 is provided by the National Science Foundation under grants AST-1139963 and AST

  20. An autocorrelation method to detect low frequency earthquakes within tremor

    USGS Publications Warehouse

    Brown, J.R.; Beroza, G.C.; Shelly, D.R.

    2008-01-01

    Recent studies have shown that deep tremor in the Nankai Trough under western Shikoku consists of a swarm of low frequency earthquakes (LFEs) that occur as slow shear slip on the down-dip extension of the primary seismogenic zone of the plate interface. The similarity of tremor in other locations suggests a similar mechanism, but the absence of cataloged low frequency earthquakes prevents a similar analysis. In this study, we develop a method for identifying LFEs within tremor. The method employs a matched-filter algorithm, similar to the technique used to infer that tremor in parts of Shikoku is comprised of LFEs; however, in this case we do not assume the origin times or locations of any LFEs a priori. We search for LFEs using the running autocorrelation of tremor waveforms for 6 Hi-Net stations in the vicinity of the tremor source. Time lags showing strong similarity in the autocorrelation represent either repeats, or near repeats, of LFEs within the tremor. We test the method on an hour of Hi-Net recordings of tremor and demonstrates that it extracts both known and previously unidentified LFEs. Once identified, we cross correlate waveforms to measure relative arrival times and locate the LFEs. The results are able to explain most of the tremor as a swarm of LFEs and the locations of newly identified events appear to fill a gap in the spatial distribution of known LFEs. This method should allow us to extend the analysis of Shelly et al. (2007a) to parts of the Nankai Trough in Shikoku that have sparse LFE coverage, and may also allow us to extend our analysis to other regions that experience deep tremor, but where LFEs have not yet been identified. Copyright 2008 by the American Geophysical Union.

  1. Very low frequency earthquakes spatiotemporally asynchronous with strong tremor during the 2014 episodic tremor and slip event in Cascadia

    NASA Astrophysics Data System (ADS)

    Hutchison, Alexandra A.; Ghosh, Abhijit

    2016-07-01

    We find very low frequency earthquakes (VLFEs) in Cascadia during the 2014 episodic tremor and slip event under Washington and Vancouver Island using a grid search centroid moment tensor inversion method. The very low frequency earthquakes occur when and where there is no strong tremor detected, contrasting with previous findings where tremor and very low frequency earthquakes have a clear spatiotemporal relationship. This challenges our current understanding of the dynamic relationship between the different types of slow earthquakes and their relationship to slow slip. We interpret these findings to suggest that VLFEs and tremor may have their own "seismic cycles," resulting from asperities of different sizes or characteristics that respond pseudo-independently to stress loading. We propose that very low frequency earthquakes and tremor are subject to asynchronous seismic cycles.

  2. Human Hippocampal Increases in Low-Frequency Power during Associative Prediction Violations

    PubMed Central

    Chen, Janice; Dastjerdi, Mohammad; Foster, Brett L.; LaRocque, Karen F.; Rauschecker, Andreas M.; Parvizi, Josef; Wagner, Anthony D.

    2013-01-01

    Environmental cues often trigger memories of past events (associative retrieval), and these memories are a form of prediction about imminent experience. Learning is driven by the detection of prediction violations, when the past and present diverge. Using intracranial electroencephalography (iEEG), we show that associative prediction violations elicit increased low-frequency power (in the slow-theta range) in human hippocampus, that this low-frequency power increase is modulated by whether conditions allow predictions to be generated, that the increase rapidly onsets after the moment of violation, and that changes in low-frequency power are not present in adjacent perirhinal cortex. These data suggest that associative mismatch is computed within hippocampus when cues trigger predictions that are violated by imminent experience. PMID:23571081

  3. Low-Frequency Earthquakes in Cascadia

    NASA Astrophysics Data System (ADS)

    Sweet, J. R.; Creager, K. C.; Ghosh, A.; Vidale, J. E.

    2009-12-01

    Low-frequency earthquakes (LFEs) are a recently identified class of earthquakes that have been observed to occur coincidentally with non-volcanic tremor in time and space. These LFEs also have a frequency spectra that is nearly identical to that of tremor—implying a common source for these two phenomena. Indeed, it has been proposed that tremor may simply be a superposition of many individual LFEs (Shelly et al., 2006, 2007, Nature). As such, LFEs have been used to constrain the location of tremor. We first reported LFEs in Cascadia last year, following the deployment of an 80-station, 1-km aperture seismic array on the Olympic Peninsula of western Washington State. This past year we have deployed 8 small aperture, 3-component seismic arrays across the northern Olympic Peninsula in the hopes of recording and locating additional tremor and LFEs. These arrays are composed of 10 3-component and 10 vertical component EarthScope seismometers. We use a combination of methods to identify and locate LFEs in our new, expanded dataset. Potential LFEs are first flagged by searching for peaks in the cross correlation of vertical and horizontal components that correspond to S minus P times of arriving energy (La Rocca, 2009, Science). These targets are then used as template events and are cross correlated with several hours of continuous data to find matching events. Using stacking and correlation we obtain accurate S minus P times for some arrays, and differential S and P times between arrays. We use these times to obtain robust estimates of LFE hypocenters. Unfortunately none of the 2009 data from the array of arrays covers a period of Episodic Tremor and Slip (ETS), but several smaller tremor bursts were recorded.

  4. Ray tracing of Jovian low frequency radiation

    NASA Technical Reports Server (NTRS)

    Six, N. Frank

    1987-01-01

    The radio emission from Jupiter in the decametric range (2 to 40 MHz) has been studied for three decades. It is known that this emission is correlated with particular longitude regions on the planet and with the position of the satellite Io. The Planetary Radio Astronomy experiment on the Voyager 1 and 2 spacecraft observed this emission, obtaining valuable new information. The objectives of this study are as follows: (1) calculate raypaths for decametric wavelength radiation in Jupiter's magnetosphere; (2) compare the model-dependent raypaths with the Voyager observations; and (3) deduce characteristics of the source regions and the influence of propagation effects.

  5. Undulations from amplified low frequency surface waves

    SciTech Connect

    Coutant, Antonin; Parentani, Renaud

    2014-04-15

    We study the linear scattering of gravity waves in longitudinal inhomogeneous stationary flows. When the flow becomes supercritical, it is known that counterflow propagating shallow waves are blocked and converted into deep waves. Here we show that in the zero-frequency limit, the reflected waves are amplified in such a way that the free surface develops an undulation, i.e., a zero-frequency wave of large amplitude with nodes located at specific places. This amplification involves negative energy waves and implies that flat surfaces are unstable against incoming perturbations of arbitrary small amplitude. The relation between this instability and black hole radiation (the Hawking effect) is established.

  6. Mode properties of low-frequency waves: Kinetic theory versus Hall-MHD

    NASA Technical Reports Server (NTRS)

    Krauss-Varban, D.; Omidi, N.; Quest, K. B.

    1994-01-01

    In fluid theory, the ordering of low-frequency modes in a homogeneous plasma is based on the phase velocity, since modes do not intersect each other in dispersion diagrams as a function of wavenumber or other parameters. In linear kinetic theory, modes cross each other. Thus a consistent and useful classification should be based on the physical properties of the modes instead. This paper attempts such a classification by documeting the dispersion and general mode properties of the low-frequency waves (omega much less than (OMEGA(sub ci) OMEGA(sub ce) (exp 1/2)), where OMEGA(sub ci), OMEGA(sub ce) are the cyclotron frequencies of the ions and electrons, respectively) in kinetic theory, and by comparing them to the results of two-fluid theory. Kinetic theory gives a seperate Alfven/ion-cyclotron (A/IC) wave with phase speed Omega/k approximately = v(sub A) cos theta for omega much less than OMEGA(sub ci), where v(sub A) is the Alfven velocity and theta the angle of propagation between wave vector k and background magnetic field B(sub o). For a given wavenumber, the magnetosonic mode is a double-valued solution with a singular point in theta, beta parameter space, where beta is the ratio of thermal pressure to magnetic pressure. It is shown that a branch cut starting at the singular point theta approximately 30 deg, beta approximately 3 and leading to larger beta gives a practical and consitent seperation of this double-valued magnetosonic solution. Selection of this branch cut results in a moderately damped fast/magnetos onic and a heavily damped slow/sound wave. A comprehensive review of the polarization, compressibility and other mode properties is given and shown to be consistent with the selected branch cut. At small wavenumbers, the kinetic mode properties typically start to deviate significantly from their fluid counterparts at beta approximately 0.5. At larger beta, there is no longer a consistent correspondence between the fluid and kinetic modes. Kinetic

  7. New families of low frequency earthquakes beneath the Olympic Peninsula, Washington

    NASA Astrophysics Data System (ADS)

    Chestler, S.; Creager, K. C.; Sweet, J. R.

    2013-12-01

    Using data from the Array of Arrays (AofA) and Cascadia Arrays for Earthscope (CAFÉ) experiments we search for new families of low frequency earthquakes (LFEs) beneath the Olympic Peninsula, Washington. LFE families are clusters of repeating LFEs that occur in approximately the same location. Following methodology similar to Bostock et al. [2012, G3], we cross correlate 6-second long windows within an hour of data during the 2010 and 2011 ETS events. We apply this to 99 hours of tremor data. For each hour, we stack the autocorrelation functions from a set of 7 3-component base stations chosen for their high signal-to-noise ratios (SNRs). We extract a maximum of 10 windows per hour with correlation coefficients higher than 9 times the median absolute deviation (MAD). These time windows contain our preliminary LFE detections. We then cross correlate these data and group them using a hierarchical clustering algorithm. We produce template waveforms by stacking the waveforms corresponding to a given cluster. To strengthen the templates we scan them through on day of tremor and stack all waveforms that correlate with the original template. Our efforts have yielded dozens of new families scattered beneath the AofA stations. These additional LFE families add to the 9 known families beneath the Olympic Peninsula [Sweet et al., AGU fall meeting, 2012]. The detection of more LFE families will allow us to (1) interpolate the pattern of stress transfer through the transition zone [Wech et al., Nature Geoscie., 2011], (2) gain insight into the distribution of asperities, or sticky spots, on the plate interface [Ghosh et al., JGR, 2012], and (3) track slow slip rupture propagation with unprecedented spatial and temporal accuracy.

  8. Low-frequency earthquakes in Shikoku, Japan, and their relationship to episodic tremor and slip.

    PubMed

    Shelly, David R; Beroza, Gregory C; Ide, Satoshi; Nakamula, Sho

    2006-07-13

    Non-volcanic seismic tremor was discovered in the Nankai trough subduction zone in southwest Japan and subsequently identified in the Cascadia subduction zone. In both locations, tremor is observed to coincide temporally with large, slow slip events on the plate interface downdip of the seismogenic zone. The relationship between tremor and aseismic slip remains uncertain, however, largely owing to difficulty in constraining the source depth of tremor. In southwest Japan, a high quality borehole seismic network allows identification of coherent S-wave (and sometimes P-wave) arrivals within the tremor, whose sources are classified as low-frequency earthquakes. As low-frequency earthquakes comprise at least a portion of tremor, understanding their mechanism is critical to understanding tremor as a whole. Here, we provide strong evidence that these earthquakes occur on the plate interface, coincident with the inferred zone of slow slip. The locations and characteristics of these events suggest that they are generated by shear slip during otherwise aseismic transients, rather than by fluid flow. High pore-fluid pressure in the immediate vicinity, as implied by our estimates of seismic P- and S-wave speeds, may act to promote this transient mode of failure. Low-frequency earthquakes could potentially contribute to seismic hazard forecasting by providing a new means to monitor slow slip at depth.

  9. Low-frequency surface waves on semi-bounded magnetized quantum plasma

    NASA Astrophysics Data System (ADS)

    Moradi, Afshin

    2016-08-01

    The propagation of low-frequency electrostatic surface waves on the interface between a vacuum and an electron-ion quantum plasma is studied in the direction perpendicular to an external static magnetic field which is parallel to the interface. A new dispersion equation is derived by employing both the quantum magnetohydrodynamic and Poisson equations. It is shown that the dispersion equations for forward and backward-going surface waves are different from each other.

  10. High energy, low frequency, ultrasonic transducer

    SciTech Connect

    Brown, Albert E.

    2000-01-01

    A wide bandwidth, ultrasonic transducer to generate nondispersive, extensional, pulsed acoustic pressure waves into concrete reinforced rods and tendons. The wave propagation distance is limited to double the length of the rod. The transducer acoustic impedance is matched to the rod impedance for maximum transfer of acoustic energy. The efficiency of the transducer is approximately 60 percent, depending upon the type of active elements used in the transducer. The transducer input energy is, for example, approximately 1 mJ. Ultrasonic reflections will occur at points along the rod where there are changes of one percent of a wavelength in the rod diameter. A reduction in the rod diameter will reflect a phase reversed echo, as compared with the reflection from an incremental increase in diameter. Echo signal processing of the stored waveform permits a reconstruction of those echoes into an image of the rod. The ultrasonic transducer has use in the acoustic inspection of long (40+foot) architectural reinforcements and structural supporting members, such as in bridges and dams.

  11. Subsurface Ice Detection via Low Frequency Surface Electromagnetic Method

    NASA Astrophysics Data System (ADS)

    Stillman, D. E.; Grimm, R. E.; Mcginnis, R. N.

    2014-12-01

    The geophysical detection of ice in the Cryosphere is typically conducted by measuring the absence of water. These interpretations can become non-unique in dry soils or in clay- and silt-rich soils that contain significant quantities of unfrozen water. Extensive laboratory measurements of electrical properties were made on permafrost samples as a function of frequency, temperature, and water content. These laboratory measurements show that the amount of ice can be uniquely obtained by measuring a frequency dependence of the electrical properties over a large frequency range (20 kHz - 10 Hz). In addition, the electrical properties of permafrost are temperature dependent, which can allow for an estimate of subsurface temperature. In order to test this approach in the field, we performed field surveys at four locations in Alaska. We used three low frequency electromagnetic methods: Spectral Induced Polarization (SIP: 20 kHz - 10 Hz), Capacively Coupled Resistivity (CCR: OhmMapper - 16.5 kHz), and DC Resistivity (Syscal ~ 8 Hz). At the Cold Regions Research and Engineering Laboratory permafrost tunnel near Fox, AK, we used SIP to measure the average ice concentration of 80 v% and determined the temperature to be -3±1°C by matching survey results to lab data. SIP data acquisition is very slow; therefore, at three sites near Tok, AK, we used CCR to perform reconnaissance of the area. Then SIP and DC resistivity were performed at anomalous areas. The three survey types give very similar absolute resistivity values. We found that while SIP gives the most quantitative results, the frequency dependence from the CCR and DC resistivity surveys is all that are needed to determine ice content in permafrost.

  12. Low-frequency radio observations of SN 2011dh and the evolution of its post-shock plasma properties

    NASA Astrophysics Data System (ADS)

    Yadav, Naveen; Ray, Alak; Chakraborti, Sayan

    2016-06-01

    We present late time, low-frequency observations of SN 2011dh made using the Giant Metrewave Radio Telescope (GMRT). Our observations at 325, 610 and 1280 MHz conducted between 93 and 421 d after the explosion supplement the millimeter and centimetre wave observations conducted between 4 and 15 d after explosion using the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and extensive radio observations (1.0-36.5 GHz) conducted between 16 and 93 d after explosion using Jansky Very Large Array (JVLA). We fit a synchrotron self absorption model (SSA) to the 610 and 1280 MHz radio light curves. We use it to determine the radius (Rp) and magnetic field (Bp) at 173 and 323 d after the explosion. A comparison of the peak radio luminosity Lop with the product of the peak frequency νp and time to peak tp shows that the supernova evolves between the epochs of CARMA, JVLA and GMRT observations. It shows a general slowing down of the expansion speed of the radio emitting region on a time-scale of several hundred days during which the shock is propagating through a circumstellar medium set up by a wind with a constant mass-loss parameter, dot{M}/{v}_w. We derive the mass-loss parameter (A⋆) based on 610 and 1280 MHz radio light curves, which are found to be consistent with each other within error limits.

  13. Low-frequency otolith and semicircular canal interactions after canal inactivation

    NASA Technical Reports Server (NTRS)

    Angelaki, D. E.; Merfeld, D. M.; Hess, B. J.

    2000-01-01

    During sustained constant velocity and low-frequency off-vertical axis rotations (OVAR), otolith signals contribute significantly to slow-phase eye velocity. The adaptive plasticity of these responses was investigated here after semicircular canal plugging. Inactivation of semicircular canals results in a highly compromised and deficient vestibulo-ocular reflex (VOR). Based on the VOR enhancement hypothesis, one could expect an adaptive increase of otolith-borne angular velocity signals due to combined otolith/canal inputs after inactivation of the semicircular canals. Contrary to expectations, however, the steady-state slow-phase velocity during constant velocity OVAR decreased in amplitude over time. A similar progressive decrease in VOR gain was also observed during low-frequency off-vertical axis oscillations. This response deterioration was present in animals with either lateral or vertical semicircular canals inactivated and was limited to the plane(s) of the plugged canals. The results are consistent with the idea that the low-frequency otolith signals do not simply enhance VOR responses. Rather, the nervous system appears to correlate vestibular sensory information from the otoliths and the semicircular canals to generate an integral response to head motion.

  14. Low frequency oscillatory flow in a rotating curved pipe.

    PubMed

    Chen, Hua-Jun; Zhang, Ben-Zhao; Su, Xiao-Yan

    2003-01-01

    The low frequency oscillatory flow in a rotating curved pipe was studied by using the method of biparameter perturbation. Perturbation solutions up to the second order were obtained and the effects of rotation on the low frequency oscillatory flow were examined in detail. The results indicated that there exists evident difference between the low frequency oscillatory flow in a rotating curved pipe and in a curved pipe without rotation. During a period, four secondary vortexes may exist on the circular cross-section and the distribution of axial velocity and wall shear stress are related to the ratio of the Coriolis force to centrifugal force and the axial pressure gradient. PMID:12861615

  15. Geophysics. Migrating tremor off southern Kyushu as evidence for slow slip of a shallow subduction interface.

    PubMed

    Yamashita, Y; Yakiwara, H; Asano, Y; Shimizu, H; Uchida, K; Hirano, S; Umakoshi, K; Miyamachi, H; Nakamoto, M; Fukui, M; Kamizono, M; Kanehara, H; Yamada, T; Shinohara, M; Obara, K

    2015-05-01

    Detection of shallow slow earthquakes offers insight into the near-trench part of the subduction interface, an important region in the development of great earthquake ruptures and tsunami generation. Ocean-bottom monitoring of offshore seismicity off southern Kyushu, Japan, recorded a complete episode of low-frequency tremor, lasting for 1 month, that was associated with very-low-frequency earthquake (VLFE) activity in the shallow plate interface. The shallow tremor episode exhibited two migration modes reminiscent of deep tremor down-dip of the seismogenic zone in some other subduction zones: a large-scale slower propagation mode and a rapid reversal mode. These similarities in migration properties and the association with VLFEs strongly suggest that both the shallow and deep tremor and VLFE may be triggered by the migration of episodic slow slip events. PMID:25954006

  16. Long term estimations of low frequency noise levels over water from an off-shore wind farm.

    PubMed

    Bolin, Karl; Almgren, Martin; Ohlsson, Esbjörn; Karasalo, Ilkka

    2014-03-01

    This article focuses on computations of low frequency sound propagation from an off-shore wind farm. Two different methods for sound propagation calculations are combined with meteorological data for every 3 hours in the year 2010 to examine the varying noise levels at a reception point at 13 km distance. It is shown that sound propagation conditions play a vital role in the noise impact from the off-shore wind farm and ordinary assessment methods can become inaccurate at longer propagation distances over water. Therefore, this paper suggests that methodologies to calculate noise immission with realistic sound speed profiles need to be combined with meteorological data over extended time periods to evaluate the impact of low frequency noise from modern off-shore wind farms.

  17. Long term estimations of low frequency noise levels over water from an off-shore wind farm.

    PubMed

    Bolin, Karl; Almgren, Martin; Ohlsson, Esbjörn; Karasalo, Ilkka

    2014-03-01

    This article focuses on computations of low frequency sound propagation from an off-shore wind farm. Two different methods for sound propagation calculations are combined with meteorological data for every 3 hours in the year 2010 to examine the varying noise levels at a reception point at 13 km distance. It is shown that sound propagation conditions play a vital role in the noise impact from the off-shore wind farm and ordinary assessment methods can become inaccurate at longer propagation distances over water. Therefore, this paper suggests that methodologies to calculate noise immission with realistic sound speed profiles need to be combined with meteorological data over extended time periods to evaluate the impact of low frequency noise from modern off-shore wind farms. PMID:24606254

  18. 7. Survivable low frequency communication system pathway, looking east ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    7. Survivable low frequency communication system pathway, looking east - Ellsworth Air Force Base, Delta Flight, Launch Control Facility, County Road CS23A, North of Exit 127, Interior, Jackson County, SD

  19. Searching for Low-Frequency Radio Transients from Supernovae

    NASA Astrophysics Data System (ADS)

    Tsai-Wei, Jr.; Cutchin, Sean; Kothari, Manthan; Schmitt, Christian; Kavic, Michael; Simonetti, John

    2011-10-01

    Supernovae events may be accompanied by prompt emission of a low-frequency electromagnetic transient. These transient events are created by the interaction of a shock wave of charged particles created by SN core-collapse with a stars ambient magnetic field. Such events can be detected in low-frequency radio array. Here we discuss an ongoing search for such events using two radio arrays: the Long Wavelength Array (LWA) and Eight-meter-wavelength Transient Array (ETA).

  20. Compensation Low-Frequency Errors in TH-1 Satellite

    NASA Astrophysics Data System (ADS)

    Wang, Jianrong; Wang, Renxiang; Hu, Xin

    2016-06-01

    The topographic mapping products at 1:50,000 scale can be realized using satellite photogrammetry without ground control points (GCPs), which requires the high accuracy of exterior orientation elements. Usually, the attitudes of exterior orientation elements are obtained from the attitude determination system on the satellite. Based on the theoretical analysis and practice, the attitude determination system exists not only the high-frequency errors, but also the low-frequency errors related to the latitude of satellite orbit and the time. The low-frequency errors would affect the location accuracy without GCPs, especially to the horizontal accuracy. In SPOT5 satellite, the latitudinal model was proposed to correct attitudes using approximately 20 calibration sites data, and the location accuracy was improved. The low-frequency errors are also found in Tian Hui 1 (TH-1) satellite. Then, the method of compensation low-frequency errors is proposed in ground image processing of TH-1, which can detect and compensate the low-frequency errors automatically without using GCPs. This paper deal with the low-frequency errors in TH-1: First, the analysis about low-frequency errors of the attitude determination system is performed. Second, the compensation models are proposed in bundle adjustment. Finally, the verification is tested using data of TH-1. The testing results show: the low-frequency errors of attitude determination system can be compensated during bundle adjustment, which can improve the location accuracy without GCPs and has played an important role in the consistency of global location accuracy.

  1. Low frequency magnetic signals associated with Langmuir waves

    NASA Technical Reports Server (NTRS)

    Kellogg, Paul J.; Goetz, K.; Lin, N.; Monson, S. J.; Balogh, A.; Forsyth, R. J.; Stone, R. G.

    1992-01-01

    With the URAP experiment on Ulysses, low frequency signals with a magnetic component in close time correlation with electrostatic Langmuir waves at the plasma frequency are observed. In most, if not all, of these cases, the Langmuir waves are part of a Type III solar burst. This effect is investigated and it is shown that the low frequency waves are in the whistler mode and are most likely due to nonlinear effects involving Langmuir waves.

  2. Parametric excitation of coupled fast and slow upper hybrid waves by counter-propagating circularly polarized lasers in a magnetized plasma

    NASA Astrophysics Data System (ADS)

    Verma, Kanika; Baliyan, Sweta; Sajal, Vivek; Kumar, Ravindra; Sharma, Navneet K.

    2016-07-01

    The parametric decay of large amplitude non-resonant beating mode of counter-propagating lasers (having a frequency difference ≥ 2 ω p ) into a pair of upper hybrid waves is studied in magnetized plasma. One of the excited upper hybrid waves (known as fast wave) having phase velocity close to c , can be utilized for electron acceleration. The coupled mode equations of fast and slow upper hybrid waves are modelled by solving equation of motion and continuity equation simultaneously (using the density perturbation technique) to derive the dispersion relation for two plasmon decay process. The growth rate of the present excitation process using right circularly polarized beating lasers is higher as compared with the growth rates of the excitation processes using ordinary and extraordinary beating lasers. However, the growth rate is not significant in the case of left circularly polarized beating lasers. The growth rate ˜ 0.15 ω p s - 1 is achieved for right circularly polarized beating lasers having v 1 , 2 / c = 0.1 for scattering angle θ s ˜ 160 ° and applied magnetic field ˜ 90 T. The growth rate of fast upper hybrid wave was reduced with the applied axial magnetic field in the present case. The present work is not only significant for the electron acceleration by fast upper hybrid wave but also for diagnostic purpose.

  3. Structure of the tsunamigenic plate boundary and low-frequency earthquakes in the southern Ryukyu Trench

    PubMed Central

    Arai, Ryuta; Takahashi, Tsutomu; Kodaira, Shuichi; Kaiho, Yuka; Nakanishi, Ayako; Fujie, Gou; Nakamura, Yasuyuki; Yamamoto, Yojiro; Ishihara, Yasushi; Miura, Seiichi; Kaneda, Yoshiyuki

    2016-01-01

    It has been recognized that even weakly coupled subduction zones may cause large interplate earthquakes leading to destructive tsunamis. The Ryukyu Trench is one of the best fields to study this phenomenon, since various slow earthquakes and tsunamis have occurred; yet the fault structure and seismic activity there are poorly constrained. Here we present seismological evidence from marine observation for megathrust faults and low-frequency earthquakes (LFEs). On the basis of passive observation we find LFEs occur at 15–18 km depths along the plate interface and their distribution seems to bridge the gap between the shallow tsunamigenic zone and the deep slow slip region. This suggests that the southern Ryukyu Trench is dominated by slow earthquakes at any depths and lacks a typical locked zone. The plate interface is overlaid by a low-velocity wedge and is accompanied by polarity reversals of seismic reflections, indicating fluids exist at various depths along the plate interface. PMID:27447546

  4. Structure of the tsunamigenic plate boundary and low-frequency earthquakes in the southern Ryukyu Trench

    NASA Astrophysics Data System (ADS)

    Arai, Ryuta; Takahashi, Tsutomu; Kodaira, Shuichi; Kaiho, Yuka; Nakanishi, Ayako; Fujie, Gou; Nakamura, Yasuyuki; Yamamoto, Yojiro; Ishihara, Yasushi; Miura, Seiichi; Kaneda, Yoshiyuki

    2016-07-01

    It has been recognized that even weakly coupled subduction zones may cause large interplate earthquakes leading to destructive tsunamis. The Ryukyu Trench is one of the best fields to study this phenomenon, since various slow earthquakes and tsunamis have occurred; yet the fault structure and seismic activity there are poorly constrained. Here we present seismological evidence from marine observation for megathrust faults and low-frequency earthquakes (LFEs). On the basis of passive observation we find LFEs occur at 15-18 km depths along the plate interface and their distribution seems to bridge the gap between the shallow tsunamigenic zone and the deep slow slip region. This suggests that the southern Ryukyu Trench is dominated by slow earthquakes at any depths and lacks a typical locked zone. The plate interface is overlaid by a low-velocity wedge and is accompanied by polarity reversals of seismic reflections, indicating fluids exist at various depths along the plate interface.

  5. Structure of the tsunamigenic plate boundary and low-frequency earthquakes in the southern Ryukyu Trench.

    PubMed

    Arai, Ryuta; Takahashi, Tsutomu; Kodaira, Shuichi; Kaiho, Yuka; Nakanishi, Ayako; Fujie, Gou; Nakamura, Yasuyuki; Yamamoto, Yojiro; Ishihara, Yasushi; Miura, Seiichi; Kaneda, Yoshiyuki

    2016-01-01

    It has been recognized that even weakly coupled subduction zones may cause large interplate earthquakes leading to destructive tsunamis. The Ryukyu Trench is one of the best fields to study this phenomenon, since various slow earthquakes and tsunamis have occurred; yet the fault structure and seismic activity there are poorly constrained. Here we present seismological evidence from marine observation for megathrust faults and low-frequency earthquakes (LFEs). On the basis of passive observation we find LFEs occur at 15-18 km depths along the plate interface and their distribution seems to bridge the gap between the shallow tsunamigenic zone and the deep slow slip region. This suggests that the southern Ryukyu Trench is dominated by slow earthquakes at any depths and lacks a typical locked zone. The plate interface is overlaid by a low-velocity wedge and is accompanied by polarity reversals of seismic reflections, indicating fluids exist at various depths along the plate interface. PMID:27447546

  6. Structure of the tsunamigenic plate boundary and low-frequency earthquakes in the southern Ryukyu Trench.

    PubMed

    Arai, Ryuta; Takahashi, Tsutomu; Kodaira, Shuichi; Kaiho, Yuka; Nakanishi, Ayako; Fujie, Gou; Nakamura, Yasuyuki; Yamamoto, Yojiro; Ishihara, Yasushi; Miura, Seiichi; Kaneda, Yoshiyuki

    2016-07-22

    It has been recognized that even weakly coupled subduction zones may cause large interplate earthquakes leading to destructive tsunamis. The Ryukyu Trench is one of the best fields to study this phenomenon, since various slow earthquakes and tsunamis have occurred; yet the fault structure and seismic activity there are poorly constrained. Here we present seismological evidence from marine observation for megathrust faults and low-frequency earthquakes (LFEs). On the basis of passive observation we find LFEs occur at 15-18 km depths along the plate interface and their distribution seems to bridge the gap between the shallow tsunamigenic zone and the deep slow slip region. This suggests that the southern Ryukyu Trench is dominated by slow earthquakes at any depths and lacks a typical locked zone. The plate interface is overlaid by a low-velocity wedge and is accompanied by polarity reversals of seismic reflections, indicating fluids exist at various depths along the plate interface.

  7. The isolation of low frequency impact sounds in hotel construction

    NASA Astrophysics Data System (ADS)

    LoVerde, John J.; Dong, David W.

    2002-11-01

    One of the design challenges in the acoustical design of hotels is reducing low frequency sounds from footfalls occurring on both carpeted and hard-surfaced floors. Research on low frequency impact noise [W. Blazier and R. DuPree, J. Acoust. Soc. Am. 96, 1521-1532 (1994)] resulted in a conclusion that in wood construction low frequency impact sounds were clearly audible and that feasible control methods were not available. The results of numerous FIIC (Field Impact Insulation Class) measurements performed in accordance with ASTM E1007 indicate the lack of correlation between FIIC ratings and the reaction of occupants in the room below. The measurements presented include FIIC ratings and sound pressure level measurements below the ASTM E1007 low frequency limit of 100 Hertz, and reveal that excessive sound levels in the frequency range of 63 to 100 Hertz correlate with occupant complaints. Based upon this history, a tentative criterion for maximum impact sound level in the low frequency range is presented. The results presented of modifying existing constructions to reduce the transmission of impact sounds at low frequencies indicate that there may be practical solutions to this longstanding problem.

  8. Testing General Relativity with Low-Frequency, Space-Based Gravitational-Wave Detectors

    NASA Astrophysics Data System (ADS)

    Gair, Jonathan R.; Vallisneri, Michele; Larson, Shane L.; Baker, John G.

    2013-09-01

    We review the tests of general relativity that will become possible with space-based gravitational-wave detectors operating in the ˜ 10(-5) - 1 Hz low-frequency band. The fundamental aspects of gravitation that can be tested include the presence of additional gravitational fields other than the metric; the number and tensorial nature of gravitational-wave polarization states; the velocity of propagation of gravitational waves; the binding energy and gravitational-wave radiation of binaries, and therefore the time evolution of binary inspirals; the strength and shape of the waves emitted from binary mergers and ringdowns; the true nature of astrophysical black holes; and much more. The strength of this science alone calls for the swift implementation of a space-based detector; the remarkable richness of astrophysics, astronomy, and cosmology in the low-frequency gravitational-wave band make the case even stronger.

  9. The oblique behavior of low-frequency electromagnetic waves excited by newborn cometary ions

    NASA Technical Reports Server (NTRS)

    Brinca, Armando L.; Tsurutani, Bruce T.

    1989-01-01

    The free energy in oxygen or hydrogen ions freshly created in the solar wind stimulates low-frequency electromagnetic waves whose growth does not always maximize at parallel propagation. Exploration of the wave vector plane discloses the frequent occurrence of islets of oblique growth unconnected to the unstable parallel modes. Contour plots of the growth rate, real frequency, polarization, and magnetic compression characterize the oblique wave behavior for large values of the initial pitch angle of the cometary particles. Although wave-particle (Landau and cyclotron) resonances feed most of the surveyed oblique instabilities, some are seemingly fluidlike. The results, obtained from the numerical solution of the kinetic dispersion and wave equations, imply that newborn ions can easily excite significant oblique hydromagnetic wave activity. Cometary environments provide the adopted plasma model, but the study is helpful in the interpretation of other low-frequency wave observations in space.

  10. Low-frequency flute instabilities of self-pinched ion beams

    SciTech Connect

    Uhm, Han S.; Davidson, Ronald C.

    2005-12-15

    The stability properties of the low-frequency flute instabilities in a self-pinched ion beam propagating through a preformed plasma channel are investigated for long-wavelength and low-frequency perturbations. Consistent with the flute instabilities, the stability analysis is restricted to the surface perturbations on the ion beam. A closed algebraic dispersion relation of the flute instabilities for Bennett [Phys. Rev. 45, 890 (1934)] density profile is obtained, by making use of the energy group model. From the analytical and numerical calculations of the dispersion relation for highly collisional plasma, we find the necessary condition for instability in terms of the fractional current neutralization f. Threshold values of the fractional current neutralization for instability are tabulated for each azimuthal mode number l.

  11. Manipulating neuronal activity with low frequency transcranial ultrasound

    NASA Astrophysics Data System (ADS)

    Moore, Michele Elizabeth

    neurons impose temporal constraints on their response to stimulation. If ultrasound-mediated responses are, in fact, ion channel mediated responses, ultrasound-induced responses should exhibit time-dependence characteristics similar to those of optogenetically-triggered responses. Minimal stimulus duration thresholds and the temporal limits of paired pulse facilitation for ultrasound stimulation were identical to those of optogenetic stimulation. Collectively, these experiments demonstrate an electrophysiological basis for low-frequency transcranial ultrasound stimulation of cerebral cortical neuronal activity.

  12. Activity of Very-low-frequency Earthquakes in Japan Monitored by a Sensitive Accelerometer Network

    NASA Astrophysics Data System (ADS)

    Asano, Y.; Ito, Y.; Obara, K.

    2006-12-01

    We developed automatically detection method of very-low-frequency (VLF) earthquakes based on semblance analysis in order to spatio-tempotal distribution of VLF earthquakes in Japan. Seismograms observed by a sensitive accelerometer network (Hi-net Tilt) with a station separation of about 20 km were analyzed in this study. Band-pass filter with a pass-band of 0.02-0.05 Hz was applied to the original seismograms; and the filtered seismograms were re-sampled with a sampling frequency of 1 Hz. We composed 110 arrays with an aperture of about 50-100 km in all over Japan. Re-sampled seismograms observed at these stations in each array were analyzed to evaluate semblance coefficient and to estimate azimuths and apparent slownesses of propagating seismic waves in plain wave approximation. Window length and time step of the moving time windows to evaluate semblance coefficient were selected to be 30 s and 15 s, respectively. An azimuth and an apparent slowness corresponding to the maximum semblance coefficient in each time step can be estimated by a grid search algorism for each array. If the propagating seismic waves are radiated from a hypocenter, it is expected that the azimuths observed at each array are consistent with the epicenter location. Therefore we can estimate the epicenter location which explains these azimuths at each array. Inner products of observed and model predicted unit vectors corresponding to the azimuths of the incident wave are averaged over all arrays with weighting factors; and an epicenter location is estimated to maximumize the averaged value. We estimated epicenters for coherent wave arrivals detected by semblance analysis. After detection and epicenter determination for coherent events, events which are corresponding to ordinary earthquakes described in the event catalogue of Hi-net routine were excluded; and the rest is identified as VLF earthquake which have no distinct high-frequency radiation. We analyzed continuous waveform data from 2003

  13. EDITORIAL: Slow light Slow light

    NASA Astrophysics Data System (ADS)

    Boyd, Robert; Hess, Ortwin; Denz, Cornelia; Paspalakis, Emmanuel

    2010-10-01

    storage, optical memories, quantum information devices, and optical communication systems in which the use of slow light will allow all-optical processing with less wasted heat. To implement these applications, devices such as buffers, memories, interferometers and switches that utilize slow light need to be developed. Future challenges include the need for improved coupling of light into slow light modes, overcoming propagation losses, and mitigating the influence of large dispersion of the group velocity. The collection of papers in this special issue of Journal of Optics features a broad spectrum of articles that highlight actual developments in many of the material types and schemes described above. It represents therefore an excellent up to date snapshot of the current state of the field of slow light research. References [1] Lorentz H A 1880 Uber die Beziehung zwischen der Fortpflanzung des Lichtes und der Körperdichte Wiedemann Ann. 9 641-64 [2] McCall S L and Hahn E L 1967 Self-induced transparency by pulsed coherent light Phys. Rev. Lett. 18 908-11 [3] Vestergaard Hau L, Harris S E, Dutton Z and Behroozi C H 1999 Nature 397 594 [4] Philips D F, Fleischhauer A, Mair A, Walsworth R L and Lukin M D 2001 Storage of light in atomic vapor Phys. Rev. Lett. 86 783-6

  14. A Review of Low Frequency Electromagnetic Wave Phenomena Related to Tropospheric-Ionospheric Coupling Mechanisms

    NASA Technical Reports Server (NTRS)

    Simoes, Fernando; Pfaff, Robert; Berthelier, Jean-Jacques; Klenzing, Jeffrey

    2012-01-01

    Investigation of coupling mechanisms between the troposphere and the ionosphere requires a multidisciplinary approach involving several branches of atmospheric sciences, from meteorology, atmospheric chemistry, and fulminology to aeronomy, plasma physics, and space weather. In this work, we review low frequency electromagnetic wave propagation in the Earth-ionosphere cavity from a troposphere-ionosphere coupling perspective. We discuss electromagnetic wave generation, propagation, and resonance phenomena, considering atmospheric, ionospheric and magnetospheric sources, from lightning and transient luminous events at low altitude to Alfven waves and particle precipitation related to solar and magnetospheric processes. We review in situ ionospheric processes as well as surface and space weather phenomena that drive troposphere-ionosphere dynamics. Effects of aerosols, water vapor distribution, thermodynamic parameters, and cloud charge separation and electrification processes on atmospheric electricity and electromagnetic waves are reviewed. We also briefly revisit ionospheric irregularities such as spread-F and explosive spread-F, sporadic-E, traveling ionospheric disturbances, Trimpi effect, and hiss and plasma turbulence. Regarding the role of the lower boundary of the cavity, we review transient surface phenomena, including seismic activity, earthquakes, volcanic processes and dust electrification. The role of surface and atmospheric gravity waves in ionospheric dynamics is also briefly addressed. We summarize analytical and numerical tools and techniques to model low frequency electromagnetic wave propagation and solving inverse problems and summarize in a final section a few challenging subjects that are important for a better understanding of tropospheric-ionospheric coupling mechanisms.

  15. Low-frequency noise from large wind turbines.

    PubMed

    Møller, Henrik; Pedersen, Christian Sejer

    2011-06-01

    As wind turbines get larger, worries have emerged that the turbine noise would move down in frequency and that the low-frequency noise would cause annoyance for the neighbors. The noise emission from 48 wind turbines with nominal electric power up to 3.6 MW is analyzed and discussed. The relative amount of low-frequency noise is higher for large turbines (2.3-3.6 MW) than for small turbines (≤ 2 MW), and the difference is statistically significant. The difference can also be expressed as a downward shift of the spectrum of approximately one-third of an octave. A further shift of similar size is suggested for future turbines in the 10-MW range. Due to the air absorption, the higher low-frequency content becomes even more pronounced, when sound pressure levels in relevant neighbor distances are considered. Even when A-weighted levels are considered, a substantial part of the noise is at low frequencies, and for several of the investigated large turbines, the one-third-octave band with the highest level is at or below 250 Hz. It is thus beyond any doubt that the low-frequency part of the spectrum plays an important role in the noise at the neighbors. PMID:21682397

  16. Low-frequency noise from large wind turbines.

    PubMed

    Møller, Henrik; Pedersen, Christian Sejer

    2011-06-01

    As wind turbines get larger, worries have emerged that the turbine noise would move down in frequency and that the low-frequency noise would cause annoyance for the neighbors. The noise emission from 48 wind turbines with nominal electric power up to 3.6 MW is analyzed and discussed. The relative amount of low-frequency noise is higher for large turbines (2.3-3.6 MW) than for small turbines (≤ 2 MW), and the difference is statistically significant. The difference can also be expressed as a downward shift of the spectrum of approximately one-third of an octave. A further shift of similar size is suggested for future turbines in the 10-MW range. Due to the air absorption, the higher low-frequency content becomes even more pronounced, when sound pressure levels in relevant neighbor distances are considered. Even when A-weighted levels are considered, a substantial part of the noise is at low frequencies, and for several of the investigated large turbines, the one-third-octave band with the highest level is at or below 250 Hz. It is thus beyond any doubt that the low-frequency part of the spectrum plays an important role in the noise at the neighbors.

  17. Nonlinear low-frequency electrostatic wave dynamics in a two-dimensional quantum plasma

    NASA Astrophysics Data System (ADS)

    Ghosh, Samiran; Chakrabarti, Nikhil

    2016-08-01

    The problem of two-dimensional arbitrary amplitude low-frequency electrostatic oscillation in a quasi-neutral quantum plasma is solved exactly by elementary means. In such quantum plasmas we have treated electrons quantum mechanically and ions classically. The exact analytical solution of the nonlinear system exhibits the formation of dark and black solitons. Numerical simulation also predicts the possible periodic solution of the nonlinear system. Nonlinear analysis reveals that the system does have a bifurcation at a critical Mach number that depends on the angle of propagation of the wave. The small-amplitude limit leads to the formation of weakly nonlinear Kadomstev-Petviashvili solitons.

  18. Internal Rot Detection with the Use of Low-Frequency Flaw Detector

    NASA Astrophysics Data System (ADS)

    Proskórnicki, Marek; Ligus, Grzegorz

    2014-12-01

    The issue of rot detection in standing timber or stocked wood is very important in forest management. Rot flaw detection used for that purpose is represented by invasive and non-invasive devices. Non-invasive devices are very accurate, but due to the cost and complicated operation they have not been applied on a large scale in forest management. Taking into account the practical needs of foresters a prototype of low-frequency flaw was developed. The principle of its operation is based on the difference in acoustic wave propagation in sound wood and wood with rot.

  19. Minimal basilar membrane motion in low-frequency hearing.

    PubMed

    Warren, Rebecca L; Ramamoorthy, Sripriya; Ciganović, Nikola; Zhang, Yuan; Wilson, Teresa M; Petrie, Tracy; Wang, Ruikang K; Jacques, Steven L; Reichenbach, Tobias; Nuttall, Alfred L; Fridberger, Anders

    2016-07-26

    Low-frequency hearing is critically important for speech and music perception, but no mechanical measurements have previously been available from inner ears with intact low-frequency parts. These regions of the cochlea may function in ways different from the extensively studied high-frequency regions, where the sensory outer hair cells produce force that greatly increases the sound-evoked vibrations of the basilar membrane. We used laser interferometry in vitro and optical coherence tomography in vivo to study the low-frequency part of the guinea pig cochlea, and found that sound stimulation caused motion of a minimal portion of the basilar membrane. Outside the region of peak movement, an exponential decline in motion amplitude occurred across the basilar membrane. The moving region had different dependence on stimulus frequency than the vibrations measured near the mechanosensitive stereocilia. This behavior differs substantially from the behavior found in the extensively studied high-frequency regions of the cochlea. PMID:27407145

  20. Atomic Oxygen Energy in Low Frequency Hyperthermal Plasma Ashers

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Miller, Sharon K R.; Kneubel, Christian A.

    2014-01-01

    Experimental and analytical analysis of the atomic oxygen erosion of pyrolytic graphite as well as Monte Carlo computational modeling of the erosion of Kapton H (DuPont, Wilmington, DE) polyimide was performed to determine the hyperthermal energy of low frequency (30 to 35 kHz) plasma ashers operating on air. It was concluded that hyperthermal energies in the range of 0.3 to 0.9 eV are produced in the low frequency air plasmas which results in texturing similar to that in low Earth orbit (LEO). Monte Carlo computational modeling also indicated that such low energy directed ions are fully capable of producing the experimentally observed textured surfaces in low frequency plasmas.

  1. Minimal basilar membrane motion in low-frequency hearing

    PubMed Central

    Warren, Rebecca L.; Ramamoorthy, Sripriya; Ciganović, Nikola; Zhang, Yuan; Wilson, Teresa M.; Petrie, Tracy; Wang, Ruikang K.; Jacques, Steven L.; Reichenbach, Tobias; Nuttall, Alfred L.; Fridberger, Anders

    2016-01-01

    Low-frequency hearing is critically important for speech and music perception, but no mechanical measurements have previously been available from inner ears with intact low-frequency parts. These regions of the cochlea may function in ways different from the extensively studied high-frequency regions, where the sensory outer hair cells produce force that greatly increases the sound-evoked vibrations of the basilar membrane. We used laser interferometry in vitro and optical coherence tomography in vivo to study the low-frequency part of the guinea pig cochlea, and found that sound stimulation caused motion of a minimal portion of the basilar membrane. Outside the region of peak movement, an exponential decline in motion amplitude occurred across the basilar membrane. The moving region had different dependence on stimulus frequency than the vibrations measured near the mechanosensitive stereocilia. This behavior differs substantially from the behavior found in the extensively studied high-frequency regions of the cochlea. PMID:27407145

  2. Present and Future Modes of Low Frequency Climate Variability

    SciTech Connect

    Cane, Mark A.

    2014-02-20

    This project addressed area (1) of the FOA, “Interaction of Climate Change and Low Frequency Modes of Natural Climate Variability”. Our overarching objective is to detect, describe and understand the changes in low frequency variability between model simulations of the preindustrial climate and simulations of a doubled CO2 climate. The deliverables are a set of papers providing a dynamical characterization of interannual, decadal, and multidecadal variability in coupled models with attention to the changes in this low frequency variability between pre-industrial concentrations of greenhouse gases and a doubling of atmospheric concentrations of CO2. The principle mode of analysis, singular vector decomposition, is designed to advance our physical, mechanistic understanding. This study will include external natural variability due to solar and volcanic aerosol variations as well as variability internal to the climate system. An important byproduct is a set of analysis tools for estimating global singular vector structures from the archived output of model simulations.

  3. Low-frequency sound affects active micromechanics in the human inner ear

    PubMed Central

    Kugler, Kathrin; Wiegrebe, Lutz; Grothe, Benedikt; Kössl, Manfred; Gürkov, Robert; Krause, Eike; Drexl, Markus

    2014-01-01

    Noise-induced hearing loss is one of the most common auditory pathologies, resulting from overstimulation of the human cochlea, an exquisitely sensitive micromechanical device. At very low frequencies (less than 250 Hz), however, the sensitivity of human hearing, and therefore the perceived loudness is poor. The perceived loudness is mediated by the inner hair cells of the cochlea which are driven very inadequately at low frequencies. To assess the impact of low-frequency (LF) sound, we exploited a by-product of the active amplification of sound outer hair cells (OHCs) perform, so-called spontaneous otoacoustic emissions. These are faint sounds produced by the inner ear that can be used to detect changes of cochlear physiology. We show that a short exposure to perceptually unobtrusive, LF sounds significantly affects OHCs: a 90 s, 80 dB(A) LF sound induced slow, concordant and positively correlated frequency and level oscillations of spontaneous otoacoustic emissions that lasted for about 2 min after LF sound offset. LF sounds, contrary to their unobtrusive perception, strongly stimulate the human cochlea and affect amplification processes in the most sensitive and important frequency range of human hearing. PMID:26064536

  4. Hemodynamic responses can modulate the brain oscillations in low frequency

    NASA Astrophysics Data System (ADS)

    Lu, Feng-Mei; Wang, Yi-Feng; Yuan, Zhen

    2016-03-01

    Previous studies have showed that the steady-state responses were able to be used as an effective index for modulating the neural oscillations in the high frequency ranges (> 1 Hz). However, the neural oscillations in low frequency ranges (<1 Hz) remain unknown. In this study, a series of fNIRS experimental tests were conducted to validate if the low frequency bands (0.1 Hz - 0.8 Hz) steady-state hemoglobin responses (SSHbRs) could be evoked and modulate the neural oscillation during a serial reaction time (SRT) task.

  5. Improvement of Space Shuttle Main Engine Low Frequency Acceleration Measurements

    NASA Technical Reports Server (NTRS)

    Stec, Robert C.

    1999-01-01

    The noise floor of low frequency acceleration data acquired on the Space Shuttle Main Engines is higher than desirable. Difficulties of acquiring high quality acceleration data on this engine are discussed. The approach presented in this paper for reducing the acceleration noise floor focuses on a search for an accelerometer more capable of measuring low frequency accelerations. An overview is given of the current measurement system used to acquire engine vibratory data. The severity of vibration, temperature, and moisture environments are considered. Vibratory measurements from both laboratory and rocket engine tests are presented.

  6. Low-frequency oscillations of forced barotropic flow

    NASA Technical Reports Server (NTRS)

    Nathan, Terrence R.; Barcilon, Albert

    1994-01-01

    Jin and Ghil demonstrate that for topographically resonant flow, low-frequency finite-amplitude oscillations may arise from wave -- wave interactions and topographic form drag. Their model is extended to include a zonally asymmetric vorticity source, which is shown to interact with the perturbation field to produce zonally rectified wave fluxes that dramatically alter the Hopf bifurcation from stationary solutions to low-frequency oscillations. The frequency, intensity, and general character of these oscillations are shown to depend crucially upon the phasing and relative strength of the forcings.

  7. Low-frequency oscillations of forced barotropic flow

    SciTech Connect

    Nathan, T.R.; Barcilon, A. The Florida State Univ., Tallahassee, FL )

    1994-02-01

    Jin and Ghil demonstrate that for topographically resonant flow, low-frequency finite-amplitude oscillations may arise from wave -- wave interactions and topographic form drag. Their model is extended to include a zonally asymmetric vorticity source, which is shown to interact with the perturbation field to produce zonally rectified wave fluxes that dramatically alter the Hopf bifurcation from stationary solutions to low-frequency oscillations. The frequency, intensity, and general character of these oscillations are shown to depend crucially upon the phasing and relative strength of the forcings.

  8. Improvement of the low frequency oscillation model for Hall thrusters

    NASA Astrophysics Data System (ADS)

    Wang, Chunsheng; Wang, Huashan

    2016-08-01

    The low frequency oscillation of the discharge current in Hall thrusters is a major aspect of these devices that requires further study. While the existing model captures the ionization mechanism of the low frequency oscillation, it unfortunately fails to express the dynamic characteristics of the ion acceleration. The analysis in this paper shows this is because of the simplification of the electron equation, which affects both the electric field distribution and the ion acceleration process. Additionally, the electron density equation is revised and a new model that is based on the physical properties of ion movement is proposed.

  9. The global atmospheric response to low-frequency tropical forcing: Zonally averaged basic states

    NASA Technical Reports Server (NTRS)

    Li, Long; Nathan, Terrence R.

    1994-01-01

    The extratropical response to localized, low-frequency tropical forcing is examined using a linearized, non-divergent barotropic model on a sphere. Zonal-mean basic states characterized by solid-body rotation or critical latitudes are considered. An analytical analysis based on WKB and ray tracing methods shows that, in contrast to stationary Rossby waves, westward moving, low-frequency Rossby waves can propagate through the tropical easterlies into the extratropics. It is shown analytically that the difference between the stationary and low-frequency ray paths is proportional to the forcing frequency and inversely proportional to the zonal wavenumber cubed. An expression for the disturbance amplitude is derived that shows the ability of the forced waves to maintain their strength well into middle latitudes depends on their meridional wave scale and northward group velocity, both of which are functions of the slowly varying background flow. A local energetics analysis shows that the combination of energy dispersion from the forcing region and energy extraction from the equatorward flank of the midlatitude jet produces disturbances that have the greatest impact on the extratropical circulation. Under the assumption that the forcing amplitude is independent of frequency, this impact is largest when the tropical forcing period is in the range 10-20 days.

  10. A forward model and conjugate gradient inversion technique for low-frequency ultrasonic imaging.

    PubMed

    van Dongen, Koen W A; Wright, William M D

    2006-10-01

    Emerging methods of hyperthermia cancer treatment require noninvasive temperature monitoring, and ultrasonic techniques show promise in this regard. Various tomographic algorithms are available that reconstruct sound speed or contrast profiles, which can be related to temperature distribution. The requirement of a high enough frequency for adequate spatial resolution and a low enough frequency for adequate tissue penetration is a difficult compromise. In this study, the feasibility of using low frequency ultrasound for imaging and temperature monitoring was investigated. The transient probing wave field had a bandwidth spanning the frequency range 2.5-320.5 kHz. The results from a forward model which computed the propagation and scattering of low-frequency acoustic pressure and velocity wave fields were used to compare three imaging methods formulated within the Born approximation, representing two main types of reconstruction. The first uses Fourier techniques to reconstruct sound-speed profiles from projection or Radon data based on optical ray theory, seen as an asymptotical limit for comparison. The second uses backpropagation and conjugate gradient inversion methods based on acoustical wave theory. The results show that the accuracy in localization was 2.5 mm or better when using low frequencies and the conjugate gradient inversion scheme, which could be used for temperature monitoring.

  11. Detection and Analysis of Low-Frequency Sperm Whale Vocalizations with a Towed Array

    NASA Astrophysics Data System (ADS)

    Bohn, Alexander

    Sperm whale vocalizations recorded during a sea test and calibration experiment in the Gulf of Maine on a single towed, horizontal, densely sampled, low-frequency (< 2500 Hz), coherent hydrophone array system are detected and analyzed for signal energy level and other characteristics. The vocalizing individuals are localized in bearing, range, and depth. An algorithm is developed to achieve automatic detection of vocalizations. This analysis is shown to have potential utility despite restriction to only the low-frequency component of the vocalizations by sampling theory. In addition, transmission loss in the New England continental shelf and slope environment is accounted for with an ocean waveguide-acoustic propagation model. Multiple averaged realizations of this model are used to estimate transmission loss as a function of range and depth for transects between the receiver array and vocalizing whales. Comparison of the vocalizations and background noise levels and the estimated transmission loss suggests the sperm whale detection range after coherent array processing exceeds 60 km in low-to-moderate sea states. Low-frequency source levels of vocalizations are estimated using the received levels and the estimated transmission loss, and applications of both this estimate and the receiver-side statistics are discussed.

  12. Constraints on the source parameters of low-frequency earthquakes on the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Thomas, Amanda M.; Beroza, Gregory C.; Shelly, David R.

    2016-02-01

    Low-frequency earthquakes (LFEs) are small repeating earthquakes that occur in conjunction with deep slow slip. Like typical earthquakes, LFEs are thought to represent shear slip on crustal faults, but when compared to earthquakes of the same magnitude, LFEs are depleted in high-frequency content and have lower corner frequencies, implying longer duration. Here we exploit this difference to estimate the duration of LFEs on the deep San Andreas Fault (SAF). We find that the M ~ 1 LFEs have typical durations of ~0.2 s. Using the annual slip rate of the deep SAF and the average number of LFEs per year, we estimate average LFE slip rates of ~0.24 mm/s. When combined with the LFE magnitude, this number implies a stress drop of ~104 Pa, 2 to 3 orders of magnitude lower than ordinary earthquakes, and a rupture velocity of 0.7 km/s, 20% of the shear wave speed. Typical earthquakes are thought to have rupture velocities of ~80-90% of the shear wave speed. Together, the slow rupture velocity, low stress drops, and slow slip velocity explain why LFEs are depleted in high-frequency content relative to ordinary earthquakes and suggest that LFE sources represent areas capable of relatively higher slip speed in deep fault zones. Additionally, changes in rheology may not be required to explain both LFEs and slow slip; the same process that governs the slip speed during slow earthquakes may also limit the rupture velocity of LFEs.

  13. Specific frequency bands of amplitude low-frequency oscillation encodes personality.

    PubMed

    Wei, Luqing; Duan, Xujun; Zheng, Chunyan; Wang, Shanshan; Gao, Qing; Zhang, Zhiqiang; Lu, Guangming; Chen, Huafu

    2014-01-01

    The biological model of extraversion and neuroticism identified by Eysenck has stimulated increasing interest in uncovering neurobiological substrate of the two fundamental dimensions. Here we aim to explore brain disturbances underlying extraversion and neuroticism in 87 healthy individuals using fractional amplitude of low-frequency fluctuations (LFF) on resting-state functional magnetic resonance imaging. Two different frequency bands, Slow-5 (0.01-0.027 Hz) exhibiting higher power and involving larger brain regions, and Slow-4 (0.027-0.073 Hz) exhibiting less power and emerging locally, were analyzed. Our results showed a positive correlation between LFF amplitude at Slow-5 and extraversion in medial prefrontal cortex and precuneus, important portions of the default mode network, thus suggesting a link between default network activity and personality traits. LFF amplitude at Slow-5 was correlated positively with neuroticism in right posterior portion of the frontal lobe, further validating neuroticism with frontal lateralization. In addition, LFF amplitude at Slow-4 was negatively associated with extraversion and neuroticism in left hippocampus (HIP) and bilateral superior temporal cortex (STC) respectively, supporting the hypothesized (inverse) relationship between extraversion and resting arousal, also implying neural circuit underlying emotional process influencing on personality. Overall, these findings suggest the important relationships, between personality and LFF amplitude dynamic, depend on specific frequency bands.

  14. The evolving interaction of low-frequency earthquakes during transient slip.

    PubMed

    Frank, William B; Shapiro, Nikolaï M; Husker, Allen L; Kostoglodov, Vladimir; Gusev, Alexander A; Campillo, Michel

    2016-04-01

    Observed along the roots of seismogenic faults where the locked interface transitions to a stably sliding one, low-frequency earthquakes (LFEs) primarily occur as event bursts during slow slip. Using an event catalog from Guerrero, Mexico, we employ a statistical analysis to consider the sequence of LFEs at a single asperity as a point process, and deduce the level of time clustering from the shape of its autocorrelation function. We show that while the plate interface remains locked, LFEs behave as a simple Poisson process, whereas they become strongly clustered in time during even the smallest slow slip, consistent with interaction between different LFE sources. Our results demonstrate that bursts of LFEs can result from the collective behavior of asperities whose interaction depends on the state of the fault interface. PMID:27152345

  15. The evolving interaction of low-frequency earthquakes during transient slip

    PubMed Central

    Frank, William B.; Shapiro, Nikolaï M.; Husker, Allen L.; Kostoglodov, Vladimir; Gusev, Alexander A.; Campillo, Michel

    2016-01-01

    Observed along the roots of seismogenic faults where the locked interface transitions to a stably sliding one, low-frequency earthquakes (LFEs) primarily occur as event bursts during slow slip. Using an event catalog from Guerrero, Mexico, we employ a statistical analysis to consider the sequence of LFEs at a single asperity as a point process, and deduce the level of time clustering from the shape of its autocorrelation function. We show that while the plate interface remains locked, LFEs behave as a simple Poisson process, whereas they become strongly clustered in time during even the smallest slow slip, consistent with interaction between different LFE sources. Our results demonstrate that bursts of LFEs can result from the collective behavior of asperities whose interaction depends on the state of the fault interface. PMID:27152345

  16. The evolving interaction of low-frequency earthquakes during transient slip.

    PubMed

    Frank, William B; Shapiro, Nikolaï M; Husker, Allen L; Kostoglodov, Vladimir; Gusev, Alexander A; Campillo, Michel

    2016-04-01

    Observed along the roots of seismogenic faults where the locked interface transitions to a stably sliding one, low-frequency earthquakes (LFEs) primarily occur as event bursts during slow slip. Using an event catalog from Guerrero, Mexico, we employ a statistical analysis to consider the sequence of LFEs at a single asperity as a point process, and deduce the level of time clustering from the shape of its autocorrelation function. We show that while the plate interface remains locked, LFEs behave as a simple Poisson process, whereas they become strongly clustered in time during even the smallest slow slip, consistent with interaction between different LFE sources. Our results demonstrate that bursts of LFEs can result from the collective behavior of asperities whose interaction depends on the state of the fault interface.

  17. Low-frequency switching voltage regulators for terrestrial photovoltaic systems

    NASA Technical Reports Server (NTRS)

    Delombard, R.

    1984-01-01

    The photovoltaic technology project and the stand alone applications project are discussed. Two types of low frequency switching type regulators were investigated. The design, operating characteristics and field application of these regulators is described. The regulators are small in size, low in cost, very low in power dissipation, reliable and allow considerable flexibility in system design.

  18. An impedance technique for determining low-frequency payload environments

    NASA Technical Reports Server (NTRS)

    Payne, K. R.

    1979-01-01

    The technique presented is based on frequency domain analysis and eliminates the necessity of final eigen solution for coupled payload/booster systems. A demonstration of the technique using Titan flight data and a low frequency environment prediction for a Shuttle payload are included. Criteria and philosophy for the technique for future payloads is discussed.

  19. Is Reaction Time Variability in ADHD Mainly at Low Frequencies?

    ERIC Educational Resources Information Center

    Karalunas, Sarah L.; Huang-Pollock, Cynthia L.; Nigg, Joel T.

    2013-01-01

    Background: Intraindividual variability in reaction times (RT variability) has garnered increasing interest as an indicator of cognitive and neurobiological dysfunction in children with attention deficit hyperactivity disorder (ADHD). Recent theory and research has emphasized specific low-frequency patterns of RT variability. However, whether…

  20. Modelling broad-band poroelastic propagation using an asymptotic approach

    NASA Astrophysics Data System (ADS)

    Vasco, D. W.

    2009-10-01

    An asymptotic method, valid in the presence of smoothly varying heterogeneity, is used to derive a semi-analytic solution to the equations for fluid and solid displacements in a poroelastic medium. The solution is defined along trajectories through the porous medium model, in the manner of ray theory. The lowest order expression in the asymptotic expansion provides an eikonal equation for the phase. There are three modes of propagation, two modes of longitudinal displacement and a single mode of transverse displacement. The two longitudinal modes define the Biot fast and slow waves which have very different propagation characteristics. In the limit of low frequency, the Biot slow wave propagates as a diffusive disturbance, in essence a transient pressure pulse. Conversely, at low frequencies the Biot fast wave and the transverse mode are modified elastic waves. At intermediate frequencies the wave characteristics of the longitudinal modes are mixed. A comparison of the asymptotic solution with analytic and numerical solutions shows reasonably good agreement for both homogeneous and heterogeneous earth models.

  1. Modeling broadband poroelastic propagation using an asymptotic approach

    SciTech Connect

    Vasco, Donald W.

    2009-05-01

    An asymptotic method, valid in the presence of smoothly-varying heterogeneity, is used to derive a semi-analytic solution to the equations for fluid and solid displacements in a poroelastic medium. The solution is defined along trajectories through the porous medium model, in the manner of ray theory. The lowest order expression in the asymptotic expansion provides an eikonal equation for the phase. There are three modes of propagation, two modes of longitudinal displacement and a single mode of transverse displacement. The two longitudinal modes define the Biot fast and slow waves which have very different propagation characteristics. In the limit of low frequency, the Biot slow wave propagates as a diffusive disturbance, in essence a transient pressure pulse. Conversely, at low frequencies the Biot fast wave and the transverse mode are modified elastic waves. At intermediate frequencies the wave characteristics of the longitudinal modes are mixed. A comparison of the asymptotic solution with analytic and numerical solutions shows reasonably good agreement for both homogeneous and heterogeneous Earth models.

  2. Very Low Frequency Earthquakes (VLFEs) in Cascadia and Their Interactions with Tremor

    NASA Astrophysics Data System (ADS)

    Ghosh, A.

    2014-12-01

    Very low frequency earthquakes (VLFEs) are discrete seismic events rich in low frequencies (20 - 50 sec) and depleted in high frequencies compared to similar size local events. They are associated with slow earthquakes and so far found in only a handful of subduction zones worldwide. I systematically search and find VLFEs in the Cascadia subduction zone. I use a grid-search moment tensor inversion method to scan for VLFEs in 3-D space and time, locate them and determine their source parameters. They are located downdip of the locked zone, where non-volcanic tremor occurs (Fig. 1). The best estimates of VLFE depths put them near the plate interface. Their focal mechanisms indicate double couple sources and are consistent with shallow dipping thrust movement. Their moment magnitude ranges between 3.3 and 3.5 suggesting that a significant part of seismic moment may be released by such VLFEs during slow earthquakes. Interestingly, most of the VLFEs are located where the slip is the largest in an ETS event. Generally, VLFEs correlates with tremor quite well in space and time. They slowly migrate alongstrike form south to north with tremor. In detail, VLFEs appear to be tracking tremor even during tremor migration of shorter time scales. I am currently expanding the VLFE catalog in space and time to better characterize their spatiotemporal distribution, moment release, and their role in slow earthquakes. VLFEs and their interaction with tremor is providing new insights to the physics of slow earthquakes, underlying processes governing them and fault properties in Cascadia.

  3. Tectonic Tremor and the Collective Behavior of Low-Frequency Earthquakes

    NASA Astrophysics Data System (ADS)

    Frank, W.; Shapiro, N.; Husker, A. L.; Kostoglodov, V.; Campillo, M.; Gusev, A. A.

    2015-12-01

    Tectonic tremor, a long duration, emergent seismic signal observed along the deep roots of plate interfaces, is thought to be the superposition of repetitive shear events called low-frequency earthquakes (LFE) [e.g. Shelly et al., Nature, 2007]. We use a catalog of more than 1.8 million LFEs regrouped into more than 1000 families observed over 2 years in the Guerrero subduction zone in Mexico, considering each family as an individual repetitive source or asperity. We develop a statistical analysis to determine whether the subcatalogs corresponding to different sources represent random Poisson processes or if they exhibit scale-invariant clustering in time, which we interpret as a manifestation of collective behavior. For each individual LFE source, we compare their level of collective behavior during two time periods: during the six-month-long 2006 Mw 7.5 slow-slip event and during a calm period with no observed slow slip. We find that the collective behavior of LFEs depends on distance from the trench and increases when the subduction interface is slowly slipping. Our results suggest that the occurrence of strong episodes of tectonic tremors cannot be simply explained by increased rates of low frequency earthquakes at every individual LFE source but correspond to an enhanced collective behavior of the ensemble of LFE asperities.

  4. Implicit approximate-factorization schemes for the low-frequency transonic equation

    NASA Technical Reports Server (NTRS)

    Ballhaus, W. F.; Steger, J. L.

    1975-01-01

    Two- and three-level implicit finite-difference algorithms for the low-frequency transonic small disturbance-equation are constructed using approximate factorization techniques. The schemes are unconditionally stable for the model linear problem. For nonlinear mixed flows, the schemes maintain stability by the use of conservatively switched difference operators for which stability is maintained only if shock propagation is restricted to be less than one spatial grid point per time step. The shock-capturing properties of the schemes were studied for various shock motions that might be encountered in problems of engineering interest. Computed results for a model airfoil problem that produces a flow field similar to that about a helicopter rotor in forward flight show the development of a shock wave and its subsequent propagation upstream off the front of the airfoil.

  5. Localization of ultra-low frequency waves in multi-ion plasmas of the planetary magnetosphere

    SciTech Connect

    Kim, Eun -Hwa; Johnson, Jay R.; Lee, Dong -Hun

    2015-01-01

    By adopting a 2D time-dependent wave code, we investigate how mode-converted waves at the Ion-Ion Hybrid (IIH) resonance and compressional waves propagate in 2D density structures with a wide range of field-aligned wavenumbers to background magnetic fields. The simulation results show that the mode-converted waves have continuous bands across the field line consistent with previous numerical studies. These waves also have harmonic structures in frequency domain and are localized in the field-aligned heavy ion density well. Lastly, our results thus emphasize the importance of a field-aligned heavy ion density structure for ultra-low frequency wave propagation, and suggest that IIH waves can be localized in different locations along the field line.

  6. Localization of ultra-low frequency waves in multi-ion plasmas of the planetary magnetosphere

    DOE PAGESBeta

    Kim, Eun -Hwa; Johnson, Jay R.; Lee, Dong -Hun

    2015-01-01

    By adopting a 2D time-dependent wave code, we investigate how mode-converted waves at the Ion-Ion Hybrid (IIH) resonance and compressional waves propagate in 2D density structures with a wide range of field-aligned wavenumbers to background magnetic fields. The simulation results show that the mode-converted waves have continuous bands across the field line consistent with previous numerical studies. These waves also have harmonic structures in frequency domain and are localized in the field-aligned heavy ion density well. Lastly, our results thus emphasize the importance of a field-aligned heavy ion density structure for ultra-low frequency wave propagation, and suggest that IIH wavesmore » can be localized in different locations along the field line.« less

  7. Global model of low-frequency chorus (fLHR

    PubMed Central

    Meredith, Nigel P; Horne, Richard B; Li, Wen; Thorne, Richard M; Sicard-Piet, Angélica

    2014-01-01

    Whistler mode chorus is an important magnetospheric emission, playing a dual role in the acceleration and loss of relativistic electrons in the Earth's outer radiation belt. Chorus is typically generated in the equatorial region in the frequency range 0.1–0.8 fce, where fce is the local electron gyrofrequency. However, as the waves propagate to higher latitudes, significant wave power can occur at frequencies below 0.1fce. Since this wave power is largely omitted in current radiation belt models, we construct a global model of low-frequency chorus, fLHRlow-frequency chorus is strongest, with an average intensity of 200 pT2, in the prenoon sector during active conditions at midlatitudes (20°<|λm|<50°) from 4low-frequency chorus wave power will contribute to the acceleration and loss of relativistic electrons and should be taken into account in radiation belt models. Key Points Strong chorus waves can extend below 0.1 times local electron gyrofrequency Low frequency chorus strongest at mid-latitudes in pre-noon sector for L*=4 to 8 Low frequency chorus should be included in radiation belt models PMID:25821274

  8. Composite 3D-printed metastructures for low-frequency and broadband vibration absorption.

    PubMed

    Matlack, Kathryn H; Bauhofer, Anton; Krödel, Sebastian; Palermo, Antonio; Daraio, Chiara

    2016-07-26

    Architected materials that control elastic wave propagation are essential in vibration mitigation and sound attenuation. Phononic crystals and acoustic metamaterials use band-gap engineering to forbid certain frequencies from propagating through a material. However, existing solutions are limited in the low-frequency regimes and in their bandwidth of operation because they require impractical sizes and masses. Here, we present a class of materials (labeled elastic metastructures) that supports the formation of wide and low-frequency band gaps, while simultaneously reducing their global mass. To achieve these properties, the metastructures combine local resonances with structural modes of a periodic architected lattice. Whereas the band gaps in these metastructures are induced by Bragg scattering mechanisms, their key feature is that the band-gap size and frequency range can be controlled and broadened through local resonances, which are linked to changes in the lattice geometry. We demonstrate these principles experimentally, using advanced additive manufacturing methods, and inform our designs using finite-element simulations. This design strategy has a broad range of applications, including control of structural vibrations, noise, and shock mitigation. PMID:27410042

  9. Composite 3D-printed metastructures for low-frequency and broadband vibration absorption.

    PubMed

    Matlack, Kathryn H; Bauhofer, Anton; Krödel, Sebastian; Palermo, Antonio; Daraio, Chiara

    2016-07-26

    Architected materials that control elastic wave propagation are essential in vibration mitigation and sound attenuation. Phononic crystals and acoustic metamaterials use band-gap engineering to forbid certain frequencies from propagating through a material. However, existing solutions are limited in the low-frequency regimes and in their bandwidth of operation because they require impractical sizes and masses. Here, we present a class of materials (labeled elastic metastructures) that supports the formation of wide and low-frequency band gaps, while simultaneously reducing their global mass. To achieve these properties, the metastructures combine local resonances with structural modes of a periodic architected lattice. Whereas the band gaps in these metastructures are induced by Bragg scattering mechanisms, their key feature is that the band-gap size and frequency range can be controlled and broadened through local resonances, which are linked to changes in the lattice geometry. We demonstrate these principles experimentally, using advanced additive manufacturing methods, and inform our designs using finite-element simulations. This design strategy has a broad range of applications, including control of structural vibrations, noise, and shock mitigation.

  10. Low-frequency thermohaline variability in the Subtropical South Atlantic pycnocline during 2002-2013

    NASA Astrophysics Data System (ADS)

    Kolodziejczyk, Nicolas; Reverdin, Gilles; Gaillard, Fabienne; Lazar, Alban

    2015-04-01

    Low-frequency variability of spiciness is observed in the Subtropical South Atlantic over the period 2002-2013 with the Argo gridded product ISAS. Within the pycnocline, spiciness anomalies propagate at a mean speed of 0.04±0.02 m.s-1, the same speed as the gyre mean circulation, from the Agulhas Retroflection region off South Africa (~35°S-20°E) towards the South American coast (~18°S-35°W). After 2010, propagation is still found, but stationary local spiciness generation is also found over the Subtropical South Atlantic. This spiciness increase is associated with high values of vertical Turner angle below the mixed layer base during late winter. This suggests spice injection resulting from penetrative convective mixing due to air-sea buoyancy loss. These features may have an impact on the low-frequency warm and salty signal produced by the Agulhas leakage in Subtropical South Atlantic and the upper branch of the Atlantic Meridional Overturning Circulation.

  11. Composite 3D-printed metastructures for low-frequency and broadband vibration absorption

    NASA Astrophysics Data System (ADS)

    Matlack, Kathryn H.; Bauhofer, Anton; Krödel, Sebastian; Palermo, Antonio; Daraio, Chiara

    2016-07-01

    Architected materials that control elastic wave propagation are essential in vibration mitigation and sound attenuation. Phononic crystals and acoustic metamaterials use band-gap engineering to forbid certain frequencies from propagating through a material. However, existing solutions are limited in the low-frequency regimes and in their bandwidth of operation because they require impractical sizes and masses. Here, we present a class of materials (labeled elastic metastructures) that supports the formation of wide and low-frequency band gaps, while simultaneously reducing their global mass. To achieve these properties, the metastructures combine local resonances with structural modes of a periodic architected lattice. Whereas the band gaps in these metastructures are induced by Bragg scattering mechanisms, their key feature is that the band-gap size and frequency range can be controlled and broadened through local resonances, which are linked to changes in the lattice geometry. We demonstrate these principles experimentally, using advanced additive manufacturing methods, and inform our designs using finite-element simulations. This design strategy has a broad range of applications, including control of structural vibrations, noise, and shock mitigation.

  12. A low-frequency asymptotic model of seismic reflection from a high-permeability layer

    SciTech Connect

    Silin, Dmitriy; Goloshubin, Gennady

    2009-03-01

    Analysis of compression wave propagation through a high-permeability layer in a homogeneous poroelastic medium predicts a peak of reflection 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 the Biot's model of poroelasticity. A new physical interpretation of some coefficients of the classical poroelasticity is a result of the derivation of the main equations from the Hooke's law, momentum and mass balance equations, and the Darcy's law. 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 latter is equal to the product of the kinematic reservoir fluid mobility, an imaginary unit, and the frequency of the signal. 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). The practical implications of the theory developed here are seismic modeling, inversion, and attribute analysis.

  13. Low frequency electrostatic instabilities excited by injection of an electron beam in space

    SciTech Connect

    Hwang, Y.S.; Okuda, H.

    1989-02-01

    One-dimensional particle simulations have been carried out to study the low frequency broadband electrostatic noise that propagates almost perpendicularly from the magnetic field line when a nonrelativistic electron beam is injected into space from a spacecraft. For T/sub e/ = T/sub i/ the electrostatic ion cyclotron waves appear as well as the waves near the lower hybrid frequency. When the magnetic field is reduced so that ..cap omega../sub e/ << ..omega../sub pe/ in a non-isothermal plasma, T/sub e/ > T/sub i/, oblique ion acoustic instabilities appear to propagate almost perpendicular to the magnetic field. In addition, a very low frequency mode at ..omega.. << ..cap omega../sub i/ is found to be generated by the electrons flowing into the conductor. Both the ion injected beam electrons as well as the ambient electrons flowing into the spacecraft are responsible for generating those instabilities, which accelerate ions perpendicular to the magnetic field. 11 refs., 9 figs.

  14. Low-frequency spatial wave manipulation via phononic crystals with relaxed cell symmetry

    SciTech Connect

    Celli, Paolo; Gonella, Stefano

    2014-03-14

    Phononic crystals enjoy unique wave manipulation capabilities enabled by their periodic topologies. On one hand, they feature frequency-dependent directivity, which allows directional propagation of selected modes even at low frequencies. However, the stellar nature of the propagation patterns and the inability to induce single-beam focusing represent significant limitations of this functionality. On the other hand, one can realize waveguides by defecting the periodic structure of a crystal operating in bandgap mode along some desired path. Waveguides of this type are only activated in the relatively high and narrow frequency bands corresponding to total bandgaps, which limits their potential technological applications. In this work, we introduce a class of phononic crystals with relaxed cell symmetry and we exploit symmetry relaxation of a population of auxiliary microstructural elements to achieve spatial manipulation of elastic waves at very low frequencies, in the range of existence of the acoustic modes. By this approach, we achieve focusing without modifying the default static properties of the medium and by invoking mechanisms that are well suited to envision adaptive configurations for semi-active wave control.

  15. Detection and location of shallow very low frequency earthquakes along the Nankai trough and the Ryukyu trench

    NASA Astrophysics Data System (ADS)

    Asano, Y.; Matsuzawa, T.; Obara, K.

    2013-12-01

    We have investigated spatiotemporal distribution of shallow very low frequency earthquakes (VLFEs) along the Nankai trough and the Ryukyu trench. Three component seismograms recorded at broadband stations of the NIED F-net were analyzed by using waveform-correlation and back-projection techniques after processing a band-pass filter (0.02 to 0.05 Hz). Here we used known VLFEs and regular interplate earthquakes near the trench axis as template events. Time series of cross-correlation function (CC) at each station was calculated from continuous waveform data and triggered seismograms of template events with a length of 180 s. Assuming surface wave propagation with a velocity of 3.8 km/s, CCs are back-propagated onto possible origin times and horizontal locations. We obtained VLFE epicenters by performing a grid search in time and space domains with spacing of 1 s and 0.025 degrees, respectively, to maximize the averaged CCs from all stations. At first, we choose grid points with averaged CCs larger than 0.5. If these grid points have similar origin times within 180 s, we assume that these grid points reflect a same event and choose the VLFE candidate having the largest averaged CC. If some grid points are detected in the same time window from different template events, we choose the VLFE candidate with the largest averaged CC from grid points located within 100 km from the template event. VLFEs were finally identified by removing regular earthquakes listed in the JMA catalogue from all candidates. As a result of the analysis for data from October, 2009 to February, 2010, two episodes of VLFE activity were detected. One episode was located east of the M6.8 interplate earthquake which occurred on October 30, 2009 along the Ryukyu trench. The VLFE seismicity was quite active just after the M6.8 earthquake and had been smoothly decreasing with the elapsed time. Such time dependent seismicity may be related to the post-seismic slip following the M6.8 earthquake. Another

  16. Boreal Low Frequency Variability in CMIP5 models

    NASA Astrophysics Data System (ADS)

    Lee, Y.; Black, R. X.

    2012-12-01

    Monthly variability in the boreal extratropical tropospheric circulation is organized by several recurring natural modes of low frequency variability [Wallace and Gutzler, 1981; Barnston and Livezey, 1987; Thompson and Wallace, 1998]. The phase and amplitude of those low frequency modes strongly influence regional weather conditions [Notaro et al., 2006; Archambault et al., 2008].The new suite of model simulations now available in association with phase 5 of CMIP (CMIP5, Taylor et al. [2007]) provides an ideal opportunity to assess the capabilities of state-of-the-science AOGCMs in representing the structure and regional impact of the main extratropical low frequency modes occurring during boreal winter. The primary goal of this study is to assess how the nature of simulated low frequency variability is represented in CMIP5 simulations of historical and future climate. Principal component analysis is applied to monthly-mean data of 15 models' historical simulations and NCEP-NCAR reanalyses (NNR) to isolate the leading patterns of variability in sea level pressure and 500 hPa height (with the latter field rotated). The first empirical orthogonal function in sea level pressure is considered the Arctic Oscillation (AO). For each model dataset, NAO-like and PNA-like patterns are identified using pattern correlation analysis (against NNR patterns). The relative pattern correspondence is further quantified via separate cluster analyses of AO, NAO-like and PNA-like patterns, respectively. Preliminary results find that 40% (33% and 20%) of the model patterns lie within the same cluster as NNR for the AO (NAO-like and PNA-like) analyses. Composite differences among clusters chiefly consist of (a) longitudinal displacements of or (b) regional magnitude disparities in the main anomaly features. While all models replicate the basic aspects of PNA-like variability, a small minority of models fails to replicate the main characteristics of either the AO or NAO. Overall, the best

  17. Parametric study of a Schamel equation for low-frequency dust acoustic waves in dusty electronegative plasmas

    NASA Astrophysics Data System (ADS)

    Sabetkar, Akbar; Dorranian, Davoud

    2015-08-01

    In this paper, our attention is first concentrated on obliquely propagating properties of low-frequency (ω ≪ ωcd) "fast" and "slow" dust acoustic waves, in the linear regime, in dusty electronegative plasmas with Maxwellian electrons, kappa distributed positive ions, negative ions (following the combination of kappa-Schamel distribution), and negatively charged dust particles. So, an explicit expression for dispersion relation is derived by linearizing a set of dust-fluid equations. The results show that wave frequency ω in long and short-wavelengths limit is conspicuously affected by physical parameters, namely, positive to negative temperature ion ratio (βp), trapping parameter of negative ions (μ), magnitude of the magnetic field B0 (via ωcd), superthermal index ( κn,κp ), and positive ion to dust density ratio (δp). The signature of the penultimate parameter (i.e., κn) on wave frequency reveals that the frequency gap between the modes reduces (escalates) for k kc r ), where kcr is critical wave number. Alternatively, for weakly nonlinear analysis, reductive perturbation theory has been used to construct 1D and 3D Schamel Korteweg-de Vries (S-KdV) equations, whose nonlinearity coefficient prescribes only compressive soliton for all parameter values of interest. The survey manifests that deviation of ions from Maxwellian behavior leads intrinsic properties of solitary waves to be evolved in opposite trend. Additionally, at lower proportion of trapped negative ions, solitary wave amplitude mitigates, whilst the trapping parameter has no effect on both spatial width and the linear wave. The results are discussed in the context of the Earth's mesosphere of dusty electronegative plasma.

  18. Low Frequency Waves at and Upstream of Collisionless Shocks

    NASA Astrophysics Data System (ADS)

    Wilson, L. B.

    2016-02-01

    This chapter focuses on the range of low frequency electromagnetic modes observed at and upstream of collisionless shocks in the heliosphere. It discusses a specific class of whistler mode wave observed immediately upstream of collisionless shock ramps, called a whistler precursor. Though these modes have been (and are often) observed upstream of quasi-parallel shocks, the authors limit their discussion to those observed upstream of quasi-perpendicular shocks. The chapter discusses the various ion velocity distributions observed at and upstream of collisionless shocks. It also introduces some terminology and relevant instabilities for ion foreshock waves. The chapter discusses the most common ultra-low frequency (ULF) wave types, their properties, and their free energy sources. It discusses modes that are mostly Alfvénic (i.e., mostly transverse but can be compressive) in nature.

  19. A lunar far-side very low frequency array

    NASA Technical Reports Server (NTRS)

    Burns, Jack O. (Editor); Duric, Nebojsa (Editor); Johnson, Stewart (Editor); Taylor, G. Jeffrey (Editor)

    1989-01-01

    Papers were presented to consider very low frequency (VLF) radio astronomical observations from the moon. In part 1, the environment in which a lunar VLF radio array would function is described. Part 2 is a review of previous and proposed low-frequency observatories. The science that could be conducted with a lunar VLF array is described in part 3. The design of a lunar VLF array and site selection criteria are considered, respectively, in parts 4 and 5. Part 6 is a proposal for precursor lunar VLF observations. Finally, part 7 is a summary and statement of conclusions, with suggestions for future science and engineering studies. The workshop concluded with a general consensus on the scientific goals and preliminary design for a lunar VLF array.

  20. Low-frequency computational electromagnetics for antenna analysis

    SciTech Connect

    Miller, E.K. ); Burke, G.J. )

    1991-01-01

    An overview of low-frequency, computational methods for modeling the electromagnetic characteristics of antennas is presented here. The article presents a brief analytical background, and summarizes the essential ingredients of the method of moments, for numerically solving low-frequency antenna problems. Some extensions to the basic models of perfectly conducting objects in free space are also summarized, followed by a consideration of some of the same computational issues that affect model accuracy, efficiency and utility. A variety of representative computations are then presented to illustrate various modeling aspects and capabilities that are currently available. A fairly extensive bibliography is included to suggest further reference material to the reader. 90 refs., 27 figs.

  1. An evolutionary sequence of low frequency radio astronomy missions

    NASA Technical Reports Server (NTRS)

    Jones, Dayton L.

    1990-01-01

    Many concepts for space-based low frequency radio astronomy missions are being developed, ranging from simple single-satellite experiments to large arrays on the far side of the moon. Each concept involves a different tradeoff between the range of scientific questions it can answer and the technical complexity of the experiment. Since complexity largely determines the development time, risk, launch vehicle requirements, cost, and probability of approval, it is important to see where the ability to expand the scientific return justifies a major increase in complexity. An evolutionary series of increasingly capable missions, similar to the series of missions for infrared or X-ray astronomy, is advocated. These would range from inexpensive 'piggy-back' experiments on near-future missions to a dedicated low frequency array in earth orbit (or possibly on the lunar nearside) and eventually to an array on the lunar farside.

  2. Theory of low frequency noise transmission through turbines

    NASA Technical Reports Server (NTRS)

    Matta, R. K.; Mani, R.

    1979-01-01

    Improvements of the existing theory of low frequency noise transmission through turbines and development of a working prediction tool are described. The existing actuator-disk model and a new finite-chord model were utilized in an analytical study. The interactive effect of adjacent blade rows, higher order spinning modes, blade-passage shocks, and duct area variations were considered separately. The improved theory was validated using the data acquired in an earlier NASA program. Computer programs incorporating the improved theory were produced for transmission loss prediction purposes. The programs were exercised parametrically and charts constructed to define approximately the low frequency noise transfer through turbines. The loss through the exhaust nozzle and flow(s) was also considered.

  3. Method for sputtering with low frequency alternating current

    DOEpatents

    Timberlake, J.R.

    1996-04-30

    Low frequency alternating current sputtering is provided by connecting a low frequency alternating current source to a high voltage transformer having outer taps and a center tap for stepping up the voltage of the alternating current. The center tap of the transformer is connected to a vacuum vessel containing argon or helium gas. Target electrodes, in close proximity to each other, and containing material with which the substrates will be coated, are connected to the outer taps of the transformer. With an applied potential, the gas will ionize and sputtering from the target electrodes onto the substrate will then result. The target electrodes can be copper or boron, and the substrate can be stainless steel, aluminum, or titanium. Copper coatings produced are used in place of nickel and/or copper striking. 6 figs.

  4. Method for sputtering with low frequency alternating current

    DOEpatents

    Timberlake, John R.

    1996-01-01

    Low frequency alternating current sputtering is provided by connecting a low frequency alternating current source to a high voltage transformer having outer taps and a center tap for stepping up the voltage of the alternating current. The center tap of the transformer is connected to a vacuum vessel containing argon or helium gas. Target electrodes, in close proximity to each other, and containing material with which the substrates will be coated, are connected to the outer taps of the transformer. With an applied potential, the gas will ionize and sputtering from the target electrodes onto the substrate will then result. The target electrodes can be copper or boron, and the substrate can be stainless steel, aluminum, or titanium. Copper coatings produced are used in place of nickel and/or copper striking.

  5. TorPeDO: A Low Frequency Gravitational Force Sensor

    NASA Astrophysics Data System (ADS)

    McManus, D. J.; Yap, M. J.; Ward, R. L.; Shaddock, D. A.; McClelland, D. E.; Slagmolen, B. J. J.

    2016-05-01

    Second generation gravitational wave detectors are likely to be limited by Newtonian Noise at low frequencies. A dual torsion pendulum sensor aimed at exploring low- frequency gravitational-force noise is being studied at the ANU. This sensor is designed to measure local gravitational forces to high precision and will be limited by Newtonian noise. We report on a controls prototype which has been constructed and suspended, along with initial characterisation and testing of the two torsion pendulums. Large weights at the end of each bar reposition the centres of mass to the same point in space external to both bars. Since both bars have a common suspension point, resonant frequency (≈33.4 mHz), and centre of mass, mechanical disturbances and other noise will affect both bars in the same manner, providing a large mechanical common mode rejection.

  6. Low-frequency noise reduction of lightweight airframe structures

    NASA Technical Reports Server (NTRS)

    Getline, G. L.

    1976-01-01

    The results of an experimental study to determine the noise attenuation characteristics of aircraft type fuselage structural panels were presented. Of particular interest was noise attenuation at low frequencies, below the fundamental resonances of the panels. All panels were flightweight structures for transport type aircraft in the 34,050 to 45,400 kg (75,000 to 100,000 pounds) gross weight range. Test data include the results of vibration and acoustic transmission loss tests on seven types of isotropic and orthotropically stiffened, flat and curved panels. The results show that stiffness controlled acoustically integrated structures can provide very high noise reductions at low frequencies without significantly affecting their high frequency noise reduction capabilities.

  7. Computer simulation of low-frequency electromagnetic data acquisition

    SciTech Connect

    SanFilipo, W.A.; Hohmann, G.W.

    1982-02-01

    Computer simulation of low frequency electromagnetic (LFEM) digital data acquisition in the presence of natural field noise demonstrates several important limitations and considerations. Without the use of a remote reference noise removal scheme it is difficult to obtain an adequate ratio of signal to noise below 0.1 Hz for frequency domain processing and below 0.3 Hz base frequency for time domain processing for a typical source-receiver configuration. A digital high-pass filter substantially facilitates rejection of natural field noise above these frequencies but, at lower frequencies where much longer stacking times are required, it becomes ineffective. Use of a remote reference to subtract natural field noise extends these low-frequency limits a decade, but this technique is limited by the resolution and dynamic range of the instrumentation. Gathering data in short segments so that natural field drift can be offset for each segment allows a higher gain setting to minimize dynamic range problems.

  8. Diatom response to extremely low-frequency magnetic fields

    SciTech Connect

    Parkinson, W.C.; Sulik, G.L. )

    1992-06-01

    Reports that extremely low-frequency magnetic fields can interfere with normal biological cell function continue to stimulate experimental activity as well as investigations into the possible mechanism of the interaction. The cyclotron resonance' model of Liboff has been tested by Smith et al. using as the biological test system the diatom Amphora coffeiformis. They report enhanced motility of the diatom in response to a low-frequency electromagnetic field tuned to the cyclotron resonance condition for calcium ions. We report here an attempt to reproduce their results. Following their protocol diatoms were seeded onto agar plates containing varying amounts of calcium and exposed to colinear DC and AC magnetic fields tuned to the cyclotron resonant condition for frequencies of 16, 30, and 60 Hz. The fractional motility was compared with that of control plates seeded at the same time from the same culture. We find no evidence of a cyclotron resonance effect.

  9. Characterization of low frequency plasma waves and their energy deposition in the Martian magnetosphere with MAVEN

    NASA Astrophysics Data System (ADS)

    Ruhunusiri, S.; Halekas, J. S.; Connerney, J. E. P.; Espley, J. R.; McFadden, J. P.; Larson, D. E.; Mitchell, D. L.; Mazelle, C. X.; Jakosky, B. M.; Brain, D. A.; Harada, Y.; Livi, R.

    2015-12-01

    Mars has one of the unique environments in the solar system for the exploration of plasma waves. Mars does not have an intrinsic magnetosphere, but it has an induced magnetosphere due to the interaction of the solar wind with its ionosphere. Mars also possesses an extended exosphere, which spans beyond its bow shock. The interaction of the solar wind with the magnetosphere and the exosphere leads to excitation of low frequency waves that have frequencies near or below the proton gyro-frequency. MAVEN has been orbiting Mars since the late September of 2014, traversing through various regions of the Martian magnetosphere and the upstream region. MAVEN has a number of particle and field instruments for performing plasma diagnostics. Thus, for the first time at Mars, we have a complete set of plasma instruments for characterizing these low frequency plasma waves. The goal of this work is to distinguish the observed waves as one of the four low frequency wave modes (Alfven, fast, slow, and mirror) and to characterize their occurrence ratios and energy deposition in the various regions of the Martian magnetosphere and in the upstream region. To identify these waves, we use ratios and phase differences among the ion moment fluctuations and magnetic field fluctuations. To measure the ion moment fluctuations, in particular, we use two of the MAVEN ion instruments, solar wind ion analyzer (SWIA) and suprathermal and thermal ion composition instrument (STATIC). We use the MAVEN magnetometer for obtaining the magnetic field fluctuations. SWIA and STATIC have sampling cadence of 4s, much higher than that of their predecessors flown to Mars, and this is often adequate to detect the low frequency waves at Mars. We find that the Alfven waves are the most dominant waves in the upstream region and in the Martian magnetosphere. Fast waves, on the other hand, have the second highest occurrence ratio and they are found frequently near the bow shock and near the magnetic pileup boundary

  10. An ultralow noise preamplifier for low frequency noise measurements.

    PubMed

    Cannatà, Gianluca; Scandurra, Graziella; Ciofi, Carmine

    2009-11-01

    Low frequency noise measurements are among the most sensitive tools for the investigation of the quality and of the reliability of semiconductor devices. The sensitivity that can be obtained depends on the background noise of the low noise preamplifier coupled to the device under test (DUT) that, at very low frequencies, is dominated by flicker noise. The low frequency noise produced by the DUT, on the other end, is very often the most interesting signal to be detected and analyzed. In this work we propose a very simple topology for the realization of a general purpose low noise preamplifier whose noise performances, at very low frequencies (below 10 Hz), are significantly better than those that can be obtained by the most popular commercial instrumentation. Indeed, a gain of 80 dB with a pass band extending from a few tens of mHz up to a few kHz with an equivalent input voltage noise as low as 14 nV/square root(Hz) (100 mHz), 1.4 nV/square root(Hz) (1 Hz), 1.0 nV/square root(Hz) (10 Hz), and 0.8 nV/square root(Hz) (1 kHz) are consistently obtained by using quite standard electronic components and with no need for trimming and/or calibration steps. Moreover, the junction field-effect transistor input stage of the amplifier is characterized by an equivalent input current noise below 4 fA/square root(Hz) in the entire bandwidth, resulting in negligible background noise degradation for DUT impedances in excess of 100 kohms. PMID:19947746

  11. Low Frequency Electromagnetic Background Radiation From Electron Acceleration Above Thunderclouds

    NASA Astrophysics Data System (ADS)

    Fullekrug, Martin; Mezentsev, Andrew; Soula, Serge; van der Velde, Oscar; Farges, Thomas

    2013-04-01

    It was recently proposed that the acceleration of electrons during the growth and branching of streamers above thunderclouds initiated by intense lightning discharges could result in detectable low frequency electromagnetic radiation from several tens of kHz up to several hundreds of kHz (Qin et al., GRL, 2012). The intensity of the predicted radiation scales with the streamer density which is particularly large during spectacular sprite occurrences such as jellyfish sprites and/or dancing sprites. Dancing sprites are up to one second long sequences of consecutive sprites or sprite groups which are typically separated by some hundreds of milliseconds and which tend to follow the spatial development of large scale intracloud lightning discharges. A particularly spectacular series of 10 dancing sprite events over a Mediterranean mesoscale convective system was recorded with a low light video camera in south-eastern France during the early morning hours of August 31, 2012. Each dancing sprite event was composed of ~3-4 consecutive sprites or groups of sprites. All of these sprite occurrences were associated with a sudden enhancement ~2 uV/m/Hz-1/2 of the low frequency electromagnetic background radiation as measured with a radio receiver in south-west England. It is estimated that ~1000 streamers at a height of ~40 km are necessary to epxlain the observed electric field strengths. These sudden enhancements are superimposed on a more continuous low frequency electromagnetic background radiation which accompanies each dancing sprite event. It is speculated that this low frequency 'radio glow' results from filamentary streamers near the cloud top as a result of the large scale electrostatic charging of the thundercloud and that it may be used as an indicator for sprite occurrences in future studies.

  12. Free electron maser experiments in the low-frequency limit

    SciTech Connect

    Drori, R.; Jerby, E.; Shahadi, A.

    1995-12-31

    Table-top free-electron maser (FEM) experiments operating in the low-frequency (< 1 GHz) low-energy ({approximately} 1 keV) limit are reported. These FEM devices employ parallel-stripline non-dispersive waveguides (which support TEM-modes), and planar folded-foil wigglers. Thermionic cathodes and carbon-fiber cold-cathodes are used in these experiments. Results of oscillator and amplifier experiments are presented and compared with theory.

  13. The reduction of low frequency fluctuations in RFP experiments

    SciTech Connect

    Phillips, J.A.; Baker, D.A.; Gribble, R.F.

    1998-09-01

    The low frequency fluctuations seen in RFP experiments are found to be correlated with changes in the toroidal flux measured by diamagnetic loops surrounding the discharge. The correlation of the onset of impurity radiation and x-rays with the crash seen in experiments is caused by plasma bombarding the metal liner associated with this loss of flux. Efforts should be made to design improved stabilizing shells that will reduce the loss of flux and give improved RFP energy confinement times.

  14. Large-N correlator systems for low frequency radio astronomy

    NASA Astrophysics Data System (ADS)

    Foster, Griffin

    Low frequency radio astronomy has entered a second golden age driven by the development of a new class of large-N interferometric arrays. The low frequency array (LOFAR) and a number of redshifted HI Epoch of Reionization (EoR) arrays are currently undergoing commission and regularly observing. Future arrays of unprecedented sensitivity and resolutions at low frequencies, such as the square kilometer array (SKA) and the hydrogen epoch of reionization array (HERA), are in development. The combination of advancements in specialized field programmable gate array (FPGA) hardware for signal processing, computing and graphics processing unit (GPU) resources, and new imaging and calibration algorithms has opened up the oft underused radio band below 300 MHz. These interferometric arrays require efficient implementation of digital signal processing (DSP) hardware to compute the baseline correlations. FPGA technology provides an optimal platform to develop new correlators. The significant growth in data rates from these systems requires automated software to reduce the correlations in real time before storing the data products to disk. Low frequency, widefield observations introduce a number of unique calibration and imaging challenges. The efficient implementation of FX correlators using FPGA hardware is presented. Two correlators have been developed, one for the 32 element BEST-2 array at Medicina Observatory and the other for the 96 element LOFAR station at Chilbolton Observatory. In addition, calibration and imaging software has been developed for each system which makes use of the radio interferometry measurement equation (RIME) to derive calibrations. A process for generating sky maps from widefield LOFAR station observations is presented. Shapelets, a method of modelling extended structures such as resolved sources and beam patterns has been adapted for radio astronomy use to further improve system calibration. Scaling of computing technology allows for the

  15. Length sensing and control for Einstein Telescope Low Frequency

    NASA Astrophysics Data System (ADS)

    Adya, Vaishali; Leavey, Sean; Lück, Harald; Gräf, Christian; Hild, Stefan

    2016-05-01

    In this paper we describe a feasible length sensing and control scheme for the low frequency interferometers of the Einstein Telescope (ET-LF) along with the techniques used to optimise several optical parameters, including the length of the recycling cavities and the modulation frequencies, using two numerical interferometer simulation packages: Optickle and Finesse. The investigations have suggested the use of certain combinations of sidebands to obtain independent information about the different degrees of freedom.

  16. Low-frequency electromagnetic field in a Wigner crystal

    SciTech Connect

    Stupka, Anton

    2013-03-15

    Long-wave low-frequency oscillations are described in a Wigner crystal by generalization of the reverse continuum model for the case of electronic lattice. The internal self-consistent long-wave electromagnetic field is used to describe the collective motions in the system. The eigenvectors and eigenvalues of the obtained system of equations are derived. The velocities of longitudinal and transversal sound waves are found.

  17. Double streamer phenomena in atmospheric pressure low frequency corona plasma

    SciTech Connect

    Kim, Dan Bee; Jung, H.; Gweon, B.; Choe, Wonho

    2010-07-15

    Time-resolved images of an atmospheric pressure corona discharge, generated at 50 kHz in a single pin electrode source, show unique positive and negative corona discharge features: a streamer for the positive period and a glow for the negative period. However, unlike in previous reports of dc pulse and low frequency corona discharges, multistreamers were observed at the initial time stage of the positive corona. A possible physical mechanism for the multistreamers is suggested.

  18. Anomalous low-frequency grain-boundary capacitance in silicon

    NASA Astrophysics Data System (ADS)

    Seager, C. H.; Pike, G. E.

    1980-10-01

    The admittance of silicon bicrystals has been measured as a function of temperature, frequency, and dc voltage. In some cases the low-frequency capacitance is anomalously large. The ac response of a simple double depletion layer structure is calculated. The anomalous capacitive currents are due to an out-of-phase modulation of the barrier height caused by charge injected into grain-boundary traps.

  19. Relativistic runaway breakdown in low-frequency radio

    NASA Astrophysics Data System (ADS)

    Füllekrug, Martin; Roussel-Dupré, Robert; Symbalisty, Eugene M. D.; Chanrion, Olivier; Odzimek, Anna; van der Velde, Oscar; Neubert, Torsten

    2010-01-01

    The electromagnetic radiation emitted by an electron avalanche beam resulting from relativistic runaway breakdown within the Earth's atmosphere is investigated. It is found from theoretical modeling with a computer simulation that the electron beam emits electromagnetic radiation which is characterized by consecutive broadband pulses in the low-frequency radio range from ˜10 to 300 kHz at a distance of ˜800 km. Experimental evidence for the existence of consecutive broadband pulses is provided by low-frequency radio observations of sprite-producing lightning discharges at a distance of ˜550 km. The measured broadband pulses occur ˜4-9 ms after the sprite-producing lightning discharge, they exhibit electromagnetic radiation which mainly spans the frequency range from ˜50 to 350 kHz, and they exhibit complex waveforms without the typical ionospheric reflection of the first hop sky wave. Two consecutive pulses occur ˜4.5 ms and ˜3 ms after the causative lightning discharge and coincide with the sprite luminosity. It is concluded that relativistic runaway breakdown within the Earth's atmosphere can emit broadband electromagnetic pulses and possibly generates sprites. The source location of the broadband pulses can be determined with an interferometric network of wideband low-frequency radio receivers to lend further experimental support to the relativistic runaway breakdown theory.

  20. Measurement of Flux Density of Cas A at Low Frequencies

    NASA Astrophysics Data System (ADS)

    Patil, Ajinkya; Fisher, R.

    2012-01-01

    Cas A is used as a flux calibrator throughout the radio spectrum. Therefore it is important to know the spectral and secular variations in its flux density. Earlier observations by Scott et. al. (1969) and Baars et. al. (1972) suggested a secular decrease in flux density of Cas A at a rate of about 1% per year at all frequencies. However later observations by Erickson & Perley (1975) and Read (1977) indicated anomalously high flux from Cas A at 38 MHz. Also, these observations suggested that the original idea of faster decay of the flux density rate at low frequencies may be in error or that something more complex than simple decay is affecting the flux density at low frequencies. The source changes at 38 MHz still remains a mystery. We intend to present the results of follow up observations made from 1995 to 1998 with a three element interferometer in Green Bank operating in frequency range 30 to 120 MHz. We will discuss the problems at such low frequencies due to large beamwidth and unstable ionosphere. We will also discuss the strategies we have used so far to to find the flux density of Cas A by calculating the ratio of flux density of Cas A to that of Cyg A, assuming flux density of Cyg A to be constant. Above mentioned work was performed in summer student program sponsored by National Radio Astronomy Observatory.

  1. Solar observations with a low frequency radio telescope

    NASA Astrophysics Data System (ADS)

    Myserlis, I.; Seiradakis, J.; Dogramatzidis, M.

    2012-01-01

    We have set up a low frequency radio monitoring station for solar bursts at the Observatory of the Aristotle University in Thessaloniki. The station consists of a dual dipole phased array, a radio receiver and a dedicated computer with the necessary software installed. The constructed radio receiver is based on NASA's Radio Jove project. It operates continuously, since July 2010, at 20.1 MHz (close to the long-wavelength ionospheric cut-off of the radio window) with a narrow bandwidth (~5 kHz). The system is properly calibrated, so that the recorded data are expressed in antenna temperature. Despite the high interference level of an urban region like Thessaloniki (strong broadcasting shortwave radio stations, periodic experimental signals, CBs, etc), we have detected several low frequency solar radio bursts and correlated them with solar flares, X-ray events and other low frequency solar observations. The received signal is monitored in ordinary ASCII format and as audio signal, in order to investigate and exclude man-made radio interference. In order to exclude narrow band interference and calculate the spectral indices of the observed events, a second monitoring station, working at 36 MHz, is under construction at the village of Nikiforos near the town of Drama, about 130 km away of Thessaloniki. Finally, we plan to construct a third monitoring station at 58 MHz, in Thessaloniki. This frequency was revealed to be relatively free of interference, after a thorough investigation of the region.

  2. Low frequency waves and gravitational instability in homogeneous magnetized gyrotropic quantum plasma

    SciTech Connect

    Prajapati, R. P.

    2014-11-15

    In this work, the low frequency waves and gravitational (Jeans) instability of a homogeneous gyrotropic, magnetized, quantum plasma is investigated using the quantum magnetohydrodynamic and Chew-Goldberger-Low fluid models. An analytical dispersion relation for the considered system is obtained solving the linearized perturbations equations employing the Fourier transformation. The onset criterion of the “firehose” instability is retained in parallel propagation, which is unaffected due to the presence of quantum corrections. The gravitational mode modified by the quantum corrections is obtained separately along with the “firehose” mode. In perpendicular propagation, the quantum diffraction term is coupled with the Jeans and Alfven modes whereas in parallel propagation, the Alfven mode does not contribute to the dispersion characteristics as it leads to the “firehose” instability criterion in terms of quantum pressure anisotropy. The stabilizing influences of the quantum diffraction parameter and magnetic field on the growth rates of Jeans instability are examined. It is observed that the growth rate stabilizes much faster in transverse mode due to Alfven stabilization as compared to the longitudinal mode of propagation.

  3. Low frequency signals analysis from broadband seismometers records

    NASA Astrophysics Data System (ADS)

    Hsu, Po-Chin

    2016-04-01

    Broadband seismometers record signals over a wide frequency band, in which the high-frequency background noise is usually associated with human activities, such as cars, trains and factory-related activities. Meanwhile, the low-frequency signals are generally linked to the microseisms, atmospheric phenomena and oceanic wave movement. In this study, we selected the broadband seismometer data recorded during the pass of the typhoons with different moving paths, such as Doksuri in 2012, Trami and Kong-Rey in 2013, Hagibis and Matmo in 2014. By comparing the broadband seismic data, the meteorological information, and the marine conditions, we attempt to understand the effect of the meteorological conditions on the low-frequency noise. The result shows that the broadband station located along the southwestern coast of Taiwan usually have relatively higher background noise value, while the inland stations were characterized by lower noise energy. This rapid decay of the noise energy with distance from the coastline suggest that the low frequency noise could be correlated with the oceanic waves. In addition, the noise energy level increases when the distance from the typhoon and the station decreases. The enhanced frequency range is between 0.1~0.3 Hz, which is consistent with the effect caused by the interference of oceanic waves as suggested by the previous studies. This observation indicates that when the pass of typhoon may reinforce the interaction of oceanic waves and caused some influence on the seismic records. The positive correlation between the significant wave height and the noise energy could also give evidence to this observation. However, we found that the noise energy is not necessarily the strongest when the distance from typhoon and the station is the shortest. This phenomenon seems to be related to the typhoon path. When the typhoon track is perpendicular to the coastline, the change of noise energy is generally more significantly; whereas less energy

  4. PolInSAR at Low Frequency and Ionospheric Effects

    NASA Astrophysics Data System (ADS)

    Dubois-Fernandez, P.; Angelliaume, S.; Truong-Loi, M.-L.; Freeman, A.; Pottier, E.

    2009-04-01

    Global warning is now known to be the major environmental issue mankind will have to face in the next decade. Monitoring of vegetation and biomass is clearly an essential piece of information required at all levels ranging from the scientific studies to understand and forecast, to the political actors and government leaders responsible for drafting remediation policies and evaluating their impact. Microwave remote sensing with the low-frequency SAR technique can provide a useful characterization of forest (spatial coverage, species, density, height...) at a global scale, relying on the all-weather imaging capabilities of SAR linked with the significant penetration of the low-frequency EM wave in the canopy. The published techniques for forest characterization from low frequency SAR data include radiometry inversion, polarimetric inversion based on the anisotropy parameters and PolInSAR Random Volume Over Ground inversion [1]. In this paper, we will more specifically concentrate on the PolInSAR technique and the impact of ionospheric effect on this inversion. PolInSAR at low frequency can be envisioned with two radar platforms flying in formation or as a repeat pass mission. The second alternative is more plausible given the cost and the size of a low frequency SAR instrument. However the two cases will be discussed in the paper. Among the challenges, the following questions need to be addressed: · What is the impact of ionosphere and Faraday rotation on the PolInSAR inversion results? · Is it necessary to correct the data prior to applying the inversion and what is the highest Faraday rotation for which a correction is not necessary? · What is the effect of loss of interferometric coherence and could this be compensated for? · Can the technique provide an estimation of the Faraday rotation or the differential Faraday rotation? · How does ionospheric and calibration effects interact? · What are the implications on a compact polarimetry mode of operation?

  5. A mechanism for weak double layers and coherent low-frequency electrostatic wave activity in the solar wind

    NASA Astrophysics Data System (ADS)

    Singh Lakhina, Gurbax; Singh, Satyavir

    2016-07-01

    A mechanism for the weak double layers and coherent low-frequency electrostatic wave activity observed by Wind spacecraft in the solar wind at 1 AU is proposed in terms of ion-acoustic solitons and double layers. The solar wind plasma is modelled by a three component plasma consisting of fluid hot protons, hot alpha particles streaming with respect to protons, and suprathermal electrons having κ- distribution. This system supports two types of, slow and fast, ion-acoustic solitary waves. The fast ion-acoustic mode is similar to the ion-acoustic mode of proton-electron plasma, and can support only positive potential solitons. The slow ion-acoustic mode is a new mode that occurs due to the presence of alpha particles. This mode can support both positive and negative solitons and double layers. An increase of the κ- index leads to an increase in the critical Mach number, maximum Mach number and the maximum amplitude of both slow and fast ion-acoustic solitons. The slow ion-acoustic double layer can explain the amplitudes and widths, but not shapes, of the weak double layers (WDLs) observed in the solar wind at 1 AU by Wind spacecraft. The Fourier transform of the slow ion-acoustic solitons/double layers would produce broadband low-frequency electrostatic waves having main peaks between 0.35 kHz to 1.6 kHz, with electric field in the range of E = (0.01 - 0.7 ) mV/m, in excellent agreement with the observed low-frequency electrostatic wave activity in the solar wind at 1 AU.

  6. Wide-band, low-frequency pulse profiles of 100 radio pulsars with LOFAR

    NASA Astrophysics Data System (ADS)

    Pilia, M.; Hessels, J. W. T.; Stappers, B. W.; Kondratiev, V. I.; Kramer, M.; van Leeuwen, J.; Weltevrede, P.; Lyne, A. G.; Zagkouris, K.; Hassall, T. E.; Bilous, A. V.; Breton, R. P.; Falcke, H.; Grießmeier, J.-M.; Keane, E.; Karastergiou, A.; Kuniyoshi, M.; Noutsos, A.; Osłowski, S.; Serylak, M.; Sobey, C.; ter Veen, S.; Alexov, A.; Anderson, J.; Asgekar, A.; Avruch, I. M.; Bell, M. E.; Bentum, M. J.; Bernardi, G.; Bîrzan, L.; Bonafede, A.; Breitling, F.; Broderick, J. W.; Brüggen, M.; Ciardi, B.; Corbel, S.; de Geus, E.; de Jong, A.; Deller, A.; Duscha, S.; Eislöffel, J.; Fallows, R. A.; Fender, R.; Ferrari, C.; Frieswijk, W.; Garrett, M. A.; Gunst, A. W.; Hamaker, J. P.; Heald, G.; Horneffer, A.; Jonker, P.; Juette, E.; Kuper, G.; Maat, P.; Mann, G.; Markoff, S.; McFadden, R.; McKay-Bukowski, D.; Miller-Jones, J. C. A.; Nelles, A.; Paas, H.; Pandey-Pommier, M.; Pietka, M.; Pizzo, R.; Polatidis, A. G.; Reich, W.; Röttgering, H.; Rowlinson, A.; Schwarz, D.; Smirnov, O.; Steinmetz, M.; Stewart, A.; Swinbank, J. D.; Tagger, M.; Tang, Y.; Tasse, C.; Thoudam, S.; Toribio, M. C.; van der Horst, A. J.; Vermeulen, R.; Vocks, C.; van Weeren, R. J.; Wijers, R. A. M. J.; Wijnands, R.; Wijnholds, S. J.; Wucknitz, O.; Zarka, P.

    2016-02-01

    Context. LOFAR offers the unique capability of observing pulsars across the 10-240 MHz frequency range with a fractional bandwidth of roughly 50%. This spectral range is well suited for studying the frequency evolution of pulse profile morphology caused by both intrinsic and extrinsic effects such as changing emission altitude in the pulsar magnetosphere or scatter broadening by the interstellar medium, respectively. Aims: The magnitude of most of these effects increases rapidly towards low frequencies. LOFAR can thus address a number of open questions about the nature of radio pulsar emission and its propagation through the interstellar medium. Methods: We present the average pulse profiles of 100 pulsars observed in the two LOFAR frequency bands: high band (120-167 MHz, 100 profiles) and low band (15-62 MHz, 26 profiles). We compare them with Westerbork Synthesis Radio Telescope (WSRT) and Lovell Telescope observations at higher frequencies (350 and 1400 MHz) to study the profile evolution. The profiles were aligned in absolute phase by folding with a new set of timing solutions from the Lovell Telescope, which we present along with precise dispersion measures obtained with LOFAR. Results: We find that the profile evolution with decreasing radio frequency does not follow a specific trend; depending on the geometry of the pulsar, new components can enter into or be hidden from view. Nonetheless, in general our observations confirm the widening of pulsar profiles at low frequencies, as expected from radius-to-frequency mapping or birefringence theories. We offer this catalogue of low-frequency pulsar profiles in a user friendly way via the EPN Database of Pulsar Profiles, http://www.epta.eu.org/epndb/

  7. The mechanism of growth of the low-frequency East Asia-Pacific teleconnection and the triggering role of tropical intraseasonal oscillation

    NASA Astrophysics Data System (ADS)

    Wang, Jiabao; Wen, Zhiping; Wu, Renguang; Guo, Yuanyuan; Chen, Zesheng

    2016-06-01

    The East Asia-Pacific (EAP) pattern is a well-known meridional teleconnection over East Asia during boreal summer. In this study, the mechanism for growth of the EAP on intraseasonal timescale is investigated through a vorticity budget. It is found that the beta-effect and high-frequency transient eddies have primary contributions to the growth of the low-frequency EAP. The former leads to a westward shift of disturbances associated with the low-frequency EAP and the latter favors an amplification of disturbances, respectively. The interaction between low-frequency disturbances and zonal flow has a damping effect by dragging disturbances eastward. The impact of boreal summer intraseasonal oscillation (BSISO) on the triggering of the low-frequency EAP is also examined in this study based on observational analysis and a linear model experiment. It is shown that an elongated anomalous convection band located in the vicinity of Philippines associated with the dominant mode of BSISO has a significant impact on the initiation of low-frequency EAP via Rossby wave propagation, whereas anomalous convection located over the North Indian Ocean has a limited impact. Based on the results of present study, the low-frequency EAP could be a self-sustained mode, and the BSISO plays a substantial role in triggering the low-frequency EAP.

  8. Low-Frequency Electromagnetic Exploration for Groundwater on Mars

    NASA Technical Reports Server (NTRS)

    Grimm, Robert E.

    2002-01-01

    Water with even a small amount of dissolved solids has an electrical conductivity orders of magnitude higher than dry rock and is therefore a near-ideal exploration target on Mars for low frequency, diffusive electromagnetic methods. Models of the temperature- and frequency-dependent electrical properties of rock-ice-water mixtures are used to predict the electromagnetic response of the Martian subsurface. Detection of ice is difficult unless it is massively segregated. In contrast, liquid water profoundly affects soundings, and even a small amount of adsorbed water in the cryosphere can be detected. Subcryospheric water is readily distinguishable at frequencies as low as 100 Hz for fresh water to 10 mHz for brines. These responses can be measured using either natural or artificial sources. Ultra low frequency signals from solar wind and diurnal-heating perturbations of the ionosphere are likely, and disturbances of regional crustal magnetic fields may also be observable. Spherics, or extremely to very low frequency signals from lightning discharge, would provide optimal soundings; however, lightning may be the least likely of the possible natural sources. Among the active techniques, only the time-domain electromagnetic (TDEM) method can accommodate a closely spaced transmitter and receiver and sound to depths of hundreds of meters or more. A ground- or aircraft-based TDEM system of several kilograms can detect water to a depth of several hundred meters, and a system of tens of kilograms featuring a large, fixed, rover- or ballistically deployed loop can detect water to several kilometers depth.

  9. Boreal winter low-frequency variability in CMIP5 models

    NASA Astrophysics Data System (ADS)

    Lee, Yun-Young; Black, Robert X.

    2013-07-01

    study assesses the capability of CMIP5 models in representing primary modes of boreal winter extratropical low-frequency variability. Rotated principal component analysis is applied to monthly mean output from historical simulations of 14 plus two variants models and National Centers for Environmental Prediction-National Center for Atmospheric Research reanalyses (NNR) to isolate the leading patterns of variability in 500 hPa height. For each model data set, North Atlantic Oscillation (NAO)-like and Pacific-North American (PNA)-like patterns are identified using pattern correlation analysis (against NNR patterns). The relative pattern correspondence among CMIP5 models and reanalyses is further quantified via cluster analyses of the rotated empirical orthogonal function, NAO-like, and PNA-like patterns, respectively. For both NAO and PNA, 18.8% of the model patterns lie within the same cluster as NNR. Composite structural differences among clusters chiefly consist of (a) spatial displacements of or (b) regional magnitude disparities in the primary anomaly features. While all models replicate the basic aspects of PNA, a small minority of models fails to replicate NAO pattern. Overall, the best performing model is the "GFDL-ESM2G." Interestingly, models having a well-resolved stratosphere generally perform more poorly than those without. Model biases in low-frequency mode structure have important consequences for the representation of associated regional anomalies in surface air temperature and storm track behavior. Those differences among clusters are linked to variations in dynamical structures and their relation to the climatological-mean flow. It is concluded that some state-of-the-art models have important deficiencies in representing low-frequency variability and some of these deficiencies are associated with the failure of models to adequately replicate the observed climatological stationary waves.

  10. Low-frequency source parameters of twelve large earthquakes

    NASA Astrophysics Data System (ADS)

    Harabaglia, Paolo

    1993-06-01

    A global survey of the low-frequency (1-21 mHz) source characteristics of large events are studied. We are particularly interested in events unusually enriched in low-frequency and in events with a short-term precursor. We model the source time function of 12 large earthquakes using teleseismic data at low frequency. For each event we retrieve the source amplitude spectrum in the frequency range between 1 and 21 mHz with the Silver and Jordan method and the phase-shift spectrum in the frequency range between 1 and 11 mHz with the Riedesel and Jordan method. We then model the source time function by fitting the two spectra. Two of these events, the 1980 Irpinia, Italy, and the 1983 Akita-Oki, Japan, are shallow-depth complex events that took place on multiple faults. In both cases the source time function has a length of about 100 seconds. By comparison Westaway and Jackson find 45 seconds for the Irpinia event and Houston and Kanamori about 50 seconds for the Akita-Oki earthquake. The three deep events and four of the seven intermediate-depth events are fast rupturing earthquakes. A single pulse is sufficient to model the source spectra in the frequency range of our interest. Two other intermediate-depth events have slower rupturing processes, characterized by a continuous energy release lasting for about 40 seconds. The last event is the intermediate-depth 1983 Peru-Ecuador earthquake. It was first recognized as a precursive event by Jordan. We model it with a smooth rupturing process starting about 2 minutes before the high frequency origin time superimposed to an impulsive source.

  11. Biological Effects of Low-Frequency Shear Strain: Physical Descriptors.

    PubMed

    Carstensen, Edwin L; Parker, Kevin J; Dalecki, Diane; Hocking, Denise C

    2016-01-01

    Biological effects of megahertz-frequency diagnostic ultrasound are thoroughly monitored by professional societies throughout the world. A corresponding, thorough, quantitative evaluation of the archival literature on the biological effects of low-frequency vibration is needed. Biological effects, of course, are related directly to what those exposures do physically to the tissue-specifically, to the shear strains that those sources produce in the tissues. Instead of the simple compressional strains produced by diagnostic ultrasound, realistic sources of low-frequency vibration produce both fast (∼1,500 m/s) and slow (1-10 m/s) waves, each of which may have longitudinal and transverse shear components. Part 1 of this series illustrates the resulting strains, starting with those produced by longitudinally and transversely oscillating planes, through monopole and dipole sources of fast waves and, finally, to the case of a sphere moving in translation-the simplest model of the fields produced by realistic sources. PMID:26458790

  12. Chronic effects of low-frequency low-intensity electrical stimulation of stretched human muscle

    NASA Astrophysics Data System (ADS)

    Shenkman, Boris S.; Lyubaeva, Ekaterina V.; Popov, Daniil V.; Netreba, Aleksey I.; Bravy, Yan R.; Tarakin, Pavel P.; Lemesheva, Yulia S.; Vinogradova, Olga L.

    2007-02-01

    Effects of low-frequency electrical stimulation, which is currently considered to be a possible countermeasure for long-duration spaceflights, with and without stretch were evaluated. Twelve young male volunteers were randomly distributed into two groups. In one group anterior thigh muscles—knee extensors of both legs were stimulated with frequency of 15 Hz for 4.5 wks, six times a week; each session was 6-h long. In the other group, electrical stimulation with the same parameters was applied to stretched knee extensors. Following stimulation the subjects exhibited an increase in fatigue resistance, and in the succinate dehydrogenase activity and a 10% gain in the percentage of muscle fibers with slow myosin heavy chain isoforms. In a stimulated group the peak voluntary strength went down significantly, the CSA of fast muscle fibers in m. quadriceps femoris became slightly less in size (10%). Electrical stimulation of the stretched muscles induced an insignificant decline in their strength and an increase of cross-sectional area of muscle fibers of both types. Thus chronic low-frequency electrical stimulation may be proposed as a candidate countermeasure against muscle strength and mass loss if it is combined with stretch.

  13. Nonlinear behavior of electrodynamic loudspeaker suspension at low frequencies

    NASA Astrophysics Data System (ADS)

    Feng, ZiXin; Shen, Yong; Heng, Wei; Liu, YunFeng

    2013-07-01

    The suspension of electrodynamic loudspeakers includes a surround of the cone and a spider, and it is characterized by the mechanic stiffness in the lumped-parameter model. By solving the nonlinear differential equation of motion which considers the nonlinearity of suspension at low frequencies numerically and measuring different kinds of surrounds and spiders, the nonlinear behavior of suspension is theoretically and experimentally studied. Since the nonlinear stiffness of spiders and surrounds can be measured and fitted respectively before assembled into loudspeakers, which spider works best with which surround is studied. The performance of loudspeakers such as harmonic distortion based on the nonlinear parameters can be predicted.

  14. Low-Frequency Measurements of the CMB Spectrum

    SciTech Connect

    Kogut, A.; Bensadoun, M.; De Amici, Giovanni; Levin, S.; Limon,M.; Smoot, George F.; Sironi, G.; Bersanelli, M.; Bonelli, G.

    1989-10-01

    As part of an extended program to characterize the spectrum of the cosmic microwave background (CMB) at low frequencies, we have performed multiple measurements from a high-altitude site in California. On average, these measurements suggest a CMB temperature slightly lower than measurements at higher frequencies. Atmospheric conditions and the encroachment of civilization are now significant limitations from our present observing site. In November 1989, we will make new measurements from the South Pole Amundsen-Scott Station at frequencies 0.82, 1.5, 2.5, 3.8, 7.5, and 90 GHz. We discuss recent measurements and indicate improvements possible from a polar observing site.

  15. Low-frequency fluid waves in fractures and pipes

    SciTech Connect

    Korneev, Valeri

    2010-09-01

    Low-frequency analytical solutions have been obtained for phase velocities of symmetrical fluid waves within both an infinite fracture and a pipe filled with a viscous fluid. Three different fluid wave regimes can exist in such objects, depending on the various combinations of parameters, such as fluid density, fluid viscosity, walls shear modulus, channel thickness, and frequency. Equations for velocities of all these regimes have explicit forms and are verified by comparisons with the exact solutions. The dominant role of fractures in rock permeability at field scales and the strong amplitude and frequency effects of Stoneley guided waves suggest the importance of including these wave effects into poroelastic theories.

  16. On the Origin of Low Frequency Oscillations in Hall Thrusters

    SciTech Connect

    Barral, S.; Ahedo, E.

    2008-03-19

    The breathing mode is a low frequency, longitudinal bulk instability observed in a majority of Hall thrusters. Its occurrence is accompanied by wide, regular discharge current oscillations in the 10-30 kHz range. A concise outline of the prevailing interpretations of this mode is provided, followed by an overview of a recently proposed theory. It is eventually shown that this ionization instability is not related to the motion of the ionization front but to an ionization predator-prey cycle, the former phenomenon being rather a consequence of the latter.

  17. Fetal exposure to low frequency electric and magnetic fields

    NASA Astrophysics Data System (ADS)

    Cech, R.; Leitgeb, N.; Pediaditis, M.

    2007-02-01

    To investigate the interaction of low frequency electric and magnetic fields with pregnant women and in particular with the fetus, an anatomical voxel model of an 89 kg woman at week 30 of pregnancy was developed. Intracorporal electric current density distributions due to exposure to homogeneous 50 Hz electric and magnetic fields were calculated and results were compared with basic restrictions recommended by ICNIRP guidelines. It could be shown that the basic restriction is met within the central nervous system (CNS) of the mother at exposure to reference level of either electric or magnetic fields. However, within the fetus the basic restriction is considerably exceeded. Revision of reference levels might be necessary.

  18. Enhanced sound transmission from water to air at low frequencies.

    PubMed

    McDonald, B Edward; Calvo, David C

    2007-12-01

    Excitation of acoustic radiation into the air from a low-frequency point source under water is investigated using plane wave expansion of the source spectrum and Rayleigh reflection/transmission coefficients. Expressions are derived for the acoustic power radiated into air and water as a function of source depth and given to lowest order in the air/water density ratio. Near zero source depth, the radiation into the water is quenched by the source's acoustic image, while the power radiated into air reaches about 1% of the power that would be radiated into unbounded water.

  19. Low-frequency instabilities of collisionless plasma and the 16-moment approximation

    SciTech Connect

    Dzhalilov, N. S. Kuznetsov, V. D.

    2013-12-15

    Using the 16-moment equations that take into account heat fluxes in anisotropic collisionless plasma, the properties of magnetohydrodynamic (MHD) instabilities are investigated. For all instabilities occurring in the MHD approach (the normal incompressible firehose instability, the second compressible almost longitudinal firehose instability, and the almost transverse mirror instability of slow magnetosonic modes, as well as thermal instability caused by the heat flux directed along the magnetic field), their kinetic analogs are considered. The kinetic dispersion relation in the low-frequency range in the vicinity of the ion thermal velocity is analyzed. The flow of plasma ions along the magnetic field is taken into account. The thresholds and instability growth rates obtained in the MHD and kinetic approaches are found to be in good agreement. This indicates that the 16-moment MHD equations adequately describe the dynamics of collisionless plasma.

  20. Near-field Observations of Very-low-frequency Earthquakes on the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Peña-Castro, A. F.; Harrington, R. M.; Cochran, E. S.

    2015-12-01

    Fault rupture at varying time scales has been detected in multiple subduction zones, e.g., in slow-slip events (SSEs), very-low-frequency earthquakes (VLFEs), and low-frequency earthquakes (LFEs) or tectonic tremor. However, only LFEs or tremor have been identified and studied in detail along strike-slip faults, like the San Andreas Fault (SAF). Here, we present evidence for VLFEs on the SAF near Parkfield, California. Using data from permanent broadband stations and a temporary deployment of 13 broadband stations installed in 2010-2011 near Cholame, California, we detect 5 VLFEs, with 1 VLFE occurring unambiguosly when there is visible tremor activity. We check that the signals we detect are local by confirming that they appear only on stations within a 70 km radius, and removing time periods when teleseismic events occur, as identified in the global Centroid Moment Tensor (CMT) and the Northern California Seismic Network (NCSN) catalogs. VLFEs have to-date been observed to only occur simultaneously in time and space with tremor activity, but our detections suggests that VLFEs can occur independent of tremor along strike-slip faults. This may indicate that the slipping patches that produce slow earthquakes in transform faults have different mechanical properties than the patches in subducting plates, althought it does not rule out that VLFEs are only observed with tremor in subduction zones simply due to detection methods. An approximate estimation of the apparent velocity, based on a grid-search location using variance reduction, suggests that the observed phase velocity of the VLFEs is ~ 3km/s, corresponding to surface waves. We perform a focal mechanism inversion with a grid search to find a more precise location, depth and orientation of the VLFEs. These results provide new insight into the behavior of the SAF and more generally contribute to an improved understanding of transform fault systems.

  1. A new approach to imaging with low-frequency electromagnetic fields

    SciTech Connect

    Ki Ha Lee; Ganquan Xie )

    1993-06-01

    The authors present a new method for interpreting electromagnetic (EM) data using ray tomography. Direct application of ray tomography to low-frequency EM data is difficult because of the diffusive nature of the field. Diffusive EM fields can, however, be mathematically transformed to wavefields defined in a time-like variable. The transform uniquely relates a field satisfying a diffusion equation in time, or in frequency, to an integral of the corresponding wavefield. If the corresponding wavefields can be computed from low-frequency EM data, one should be able to interpret these data using techniques developed for the wavefields. To test the idea, numerically calculated transient magnetic fields were first transformed to wavefields. The typical window of the time-domain data required for the transform is 1.5 decades. Traveltimes from a source to the receivers were estimated from the reconstructed wavefields. Time-domain data with a Gaussian noise of 3 percent gave a traveltime resolution of better than one percent. For the tomographic inversion, the cross-section between the transmitter and receiver boreholes is divided into a number of rectangular elements, and a continuous slowness is assigned to each of these elements. A functional is formulated by invoking Fermat's principle for the traveltime data. Imposing a stationary condition on the functional gives an iterative procedure for the slowness model. Rays are allowed to bend smoothly within each cell. Incorporating smoothly bending rays is extremely important when the velocity contrast is large. A model with a conductivity contrast of ten (10) has been successfully imaged in 120 iterations with 5 CPU hours on a SUN SPARCstation 2.

  2. Technologies for Low Frequency Radio Observations of the Cosmic Dawn

    NASA Technical Reports Server (NTRS)

    Jones, Dayton L.

    2014-01-01

    The Jet Propulsion Laboratory (JPL) is developing concepts and technologies for low frequency radio astronomy space missions aimed at observing highly redshifted neutral Hydrogen from the Dark Ages. This is the period of cosmic history between the recombination epoch when the microwave background radiation was produced and the re-ionization of the intergalactic medium by the first generation of stars (Cosmic Dawn). This period, at redshifts greater than about 20, is a critical epoch for the formation and evolution of large-scale structure in the universe. The 21-cm spectral line of Hydrogen provides the most promising method for directly studying the Dark Ages, but the corresponding frequencies at such large redshifts are only tens of MHz and thus require space-based observations to avoid terrestrial RFI and ionospheric absorption and refraction. This paper reports on the status of several low frequency technology development activities at JPL, including deployable bi-conical dipoles for a planned lunar-orbiting mission, and both rover-deployed and inflation-deployed long dipole antennas for use on the lunar surface.

  3. Low-frequency 1/f noise in graphene devices

    NASA Astrophysics Data System (ADS)

    Balandin, Alexander A.

    2013-08-01

    Low-frequency noise with a spectral density that depends inversely on frequency has been observed in a wide variety of systems including current fluctuations in resistors, intensity fluctuations in music and signals in human cognition. In electronics, the phenomenon, which is known as 1/f noise, flicker noise or excess noise, hampers the operation of numerous devices and circuits, and can be a significant impediment to the development of practical applications from new materials. Graphene offers unique opportunities for studying 1/f noise because of its two-dimensional structure and widely tunable two-dimensional carrier concentration. The creation of practical graphene-based devices will also depend on our ability to understand and control the low-frequency noise in this material system. Here, the characteristic features of 1/f noise in graphene and few-layer graphene are reviewed, and the implications of such noise for the development of graphene-based electronics including high-frequency devices and sensors are examined.

  4. Online detection of low-frequency functional connectivity

    NASA Astrophysics Data System (ADS)

    Peltier, Scott J.; LaConte, Stephen M.; Hu, Xiaoping

    2004-04-01

    Synchronized oscillations in resting state timecourses have been detected in recent fMRI studies. These oscillations are low frequency in nature (<0.08 Hz), and seem to be a property of symmetric cortices. These fluctuations are important as a pontential signal of interest, which could indicate connectivity between functionally related areas of the brain. It has also been shown that the synchronized oscillations decrease in some spontaneous pathological states (such as cocaine injection). Thus, detection of these functional connectivity patterns may help to serve as a guage of normal brain activity. Currently, functional connectivity detection is applied only in offline post-processing analysis. Online detection methods have been applied to detect task activation in functional MRI. This allows real-time analysis of fMRI results, and could be important in detecting short-term changes in functional states. In this work, we develop an outline algorithm to detect low frequency resting state functional connectivity in real time. This will extend connectivity analysis to allow online detection of changes in "resting state" brain networks.

  5. A Digital Backend for the Low Frequency All Sky Monitor

    NASA Astrophysics Data System (ADS)

    Dartez, L. P.

    2014-04-01

    The Low Frequency All Sky Monitor (LoFASM) is a distributed array of dipole antennas that are sensitive to radio frequencies from 10 to 88 MHz. The primary science goals of LoFASM are the detection and study of low-frequency radio transients, a high priority science goal as deemed by the National Research Council's decadal survey. LoFASM consists of antennas and front-end electronics that were originally developed for the Long Wavelength Array (LWA) by the U.S. Naval Research Lab, the University of New Mexico, Virginia Tech, and the Jet Propulsion Laboratory. LoFASM, funded by the U.S. Department of Defense, will initially consist of four stations, each consisting of 12 dual-polarization dipole antennas. In a single station, RF signals from each of the individual LoFASM dipoles are combined in phase in order to synthesize LoFASM's beam. The LoFASM RF signals are phased up so that the resulting beam is sensitive to radio emission that originates from the zenith and RF signals approaching from the horizon are attenuated. Digitally, this is achieved using a full Stokes 100MHz correlating spectrometer constructed using field programmable gate array (FPGA) technology. In this thesis I will describe the design and usage of the LoFASM Correlator.

  6. Characterizing low frequency plasma waves at Mars with MAVEN

    NASA Astrophysics Data System (ADS)

    Ruhunusiri, Suranga; Halekas, Jasper; Connerney, Jack; Espley, Jared; Larson, Davin; Mitchell, David L.

    2015-04-01

    We use the measurements from the Solar Wind Ion Analyzer (SWIA) and the magnetometer (MAG) instruments aboard the MAVEN spacecraft to characterize plasma waves in the Martian magnetosphere. SWIA is a toroidal energy analyzer that measures 3-d ion velocity distributions, and we use it for measuring ion moment fluctuations. MAG instrument, on the other hand, is a fluxgate magnetometer, and we use it for measuring magnetic field fluctuations. Mars is unique in the solar system because of two characteristics: it only has an induced magnetosphere with strong crustal fields at low altitudes, and it has an extended atmosphere due to its lower gravity. Due to these two characteristics, Mars presents a unique environment to study the interaction of a planetary magnetosphere and an exosphere with the solar wind. One consequence of this interaction is the excitation of low frequency plasma waves which have highest power near and below the proton gyrofrequency. Studying these waves is of interest because they can play a vital role in the mass and energy transport in the Martian magnetosphere. In this investigation, we use both ion moment fluctuations (density and velocity) and the magnetic field fluctuations to characterize these low frequency plasma waves.

  7. Low frequency motion measurement and control of spacecrafts and satellites

    NASA Astrophysics Data System (ADS)

    Acernese, F.; Giordano, G.; Romano, R.; Barone, F.

    2015-04-01

    This paper describes a new mechanical application of the Watt-linkage for the development and implementation of mono-axial sensors aimed to low frequency motion measurement and control of spacecrafts and satellites. The basic component of these sensors is the one dimensional UNISA Folded Pendulum mechanical sensor, developed for ground-based applications, whose unique features are due to a very effective optimization of the effects of gravitational force on the folded pendulum mechanical components, that allowed the design and implementation of FP sensors compact (< 20 cm), light (< 300 g), scalable, tunable resonance frequency < 200mHz), with large band (10-6 Hz - 100Hz), high quality factor (Q > 15000 in vacuum at 1Hz), with good immunity to environmental noises and sensitivity, guaranteed by an integrated laser optical readout, and fully adaptable to the specific requirements of the application. In this paper we show how to extend the application of ground-based FP also to space, in absence of gravity, still keeping all the above interesting features and characteristics that make this class of sensors very effective in terms of large band, especially in the low frequency, sensitivity and long term reliability. Preliminary measurements on a prototype confirm the feasibility, showing also that very good performances can be relatively easily obtained.

  8. Low-frequency sounds and amphibious communication in Hippopotamus amphibious

    NASA Astrophysics Data System (ADS)

    Barklow, William E.

    2001-05-01

    Hippos make sounds in both air and underwater, and, with their heads in an amphibious position (eyes and nostrils above water but mouth and throat below), are able to transmit sounds to both media simultaneously. Hippos on the surface respond to the surface component by calling. Hippos underwater consistently surface and call in a chorus that can spread in air from one territory to the next for many kilometers. They produce several low-frequency, high-amplitude (100 dB re: 20 μPa) sounds. The grunt, their most common call, has a 30- to 60-Hz fundamental, and the huff and some tonal sounds end with an abrupt drop in frequency to 20- to 30-Hz. These sounds are usually given amphibiously, but the high-pass filter characteristics of shallow water attenuates the low frequencies of the underwater component. Hippos also emit these and other sounds when they are completely submerged. These are inaudible in air, but they produce a fountain on the surface accompanied by a 10- to 20-Hz sound. They also produce this effect with plosive blows underwater without other sounds. Similar ``bubble blasts'' have been reported in gray whales. The function of these sounds is not clear, but they may facilitate long-distance ``chain chorusing.''

  9. Low-frequency terrestrial tensor gravitational-wave detector

    NASA Astrophysics Data System (ADS)

    Paik, Ho Jung; Griggs, Cornelius E.; Vol Moody, M.; Venkateswara, Krishna; Lee, Hyung Mok; Nielsen, Alex B.; Majorana, Ettore; Harms, Jan

    2016-04-01

    Terrestrial gravitational-wave (GW) detectors are mostly based on Michelson-type laser interferometers with arm lengths of a few km and signal bandwidths of tens of Hz to a few kHz. Many conceivable sources would emit GWs below 10 Hz. A low-frequency tensor GW detector can be constructed by combining six magnetically levitated superconducting test masses. Seismic noise and Newtonian gravity noise are serious obstacles in constructing terrestrial GW detectors at such low frequencies. By using the transverse nature of GWs, a full tensor detector, which can in principle distinguish GWs from near-field Newtonian gravity, can be constructed. Such a tensor detector is sensitive to GWs coming from any direction with any polarization; thus a single antenna is capable of resolving the source direction and polarization. We present a design concept of a tensor GW detector that could reach a strain sensitivity of 10-19-10-20 Hz-1/2 at 0.2-10 Hz, compute its intrinsic detector noise, and discuss procedures of mitigating the seismic and Newtonian noise.

  10. Sintering of ceramics using low frequency rf power

    SciTech Connect

    Caughman, J.B.O.; Hoffman, D.J.; Baity, F.W.; Akerman, M.A.; Forrester, S.C.; Kass, M.D.

    1995-07-01

    Sintering with low frequency rf power ({approximately}50 MHz) is a new technique with unique capabilities that has been used to sinter a variety of ceramic materials, including zirconia-toughened alumina, alumina, silicon carbide, and boron carbide. Processing with low frequencies offers many advantages compared to processing with conventional microwave frequencies (915 MHz and 2.45 GHz). Because of the longer wavelength, the rf electric field penetrates materials more than microwaves. This effect allows the processing of a wider variety of materials and allows for an increase in the physical size of the material being processed. In addition, the material is heated in a single mode cavity with a uniform electric field, which reduces the occurrence of hot-spot generation and thermal runaway effects. This technique has been used to sinter large crack-free alumina samples (3 inch square) to > 97% density. The sintering and/or annealing of a number of carbide materials has been demonstrated as well, including silicon carbide, boron carbide, tungsten carbide, and titanium carbide.

  11. A new era for low frequency Galactic center transient monitoring

    NASA Astrophysics Data System (ADS)

    Kassim, N. E.; Hyman, S. D.; Intema, H.; Lazio, T. J. W.

    2014-05-01

    An upgrade of the low frequency observing system of the VLA developed by NRL and NRAO, called low band (LB), will open a new era of Galactic center (GC) transient monitoring. Our previous searches using the VLA and GMRT have revealed a modest number of radio-selected transients, but have been severely sensitivity and observing time limited. The new LB system, currently accessing the 236--492 MHz frequency range, promises ≥5 × improved sensitivity over the legacy VLA system. The new system is emerging from commissioning in time to catch any enhanced sub-GHz emission from the G2 cloud event, and we review existing limits based on recent observations. We also describe a proposed 24/7 commensal system, called the LOw Band Observatory (LOBO). LOBO offers over 100 VLA GC monitoring hours per year, possibly revealing new transients and helping validate ASTRO2010's anticipation of a new era of transient radio astronomy. A funded LOBO pathfinder called the VLA Low Frequency Ionosphere and Transient Experiment (VLITE) is under development. Finally, we consider the impact of LB and LOBO on our GC monitoring program.

  12. Gravitational dynamos and the low-frequency geomagnetic secular variation.

    PubMed

    Olson, P

    2007-12-18

    Self-sustaining numerical dynamos are used to infer the sources of low-frequency secular variation of the geomagnetic field. Gravitational dynamo models powered by compositional convection in an electrically conducting, rotating fluid shell exhibit several regimes of magnetic field behavior with an increasing Rayleigh number of the convection, including nearly steady dipoles, chaotic nonreversing dipoles, and chaotic reversing dipoles. The time average dipole strength and dipolarity of the magnetic field decrease, whereas the dipole variability, average dipole tilt angle, and frequency of polarity reversals increase with Rayleigh number. Chaotic gravitational dynamos have large-amplitude dipole secular variation with maximum power at frequencies corresponding to a few cycles per million years on Earth. Their external magnetic field structure, dipole statistics, low-frequency power spectra, and polarity reversal frequency are comparable to the geomagnetic field. The magnetic variability is driven by the Lorentz force and is characterized by an inverse correlation between dynamo magnetic and kinetic energy fluctuations. A constant energy dissipation theory accounts for this inverse energy correlation, which is shown to produce conditions favorable for dipole drift, polarity reversals, and excursions. PMID:18048345

  13. Micromachined low frequency rocking accelerometer with capacitive pickoff

    DOEpatents

    Lee, Abraham P.; Simon, Jonathon N.; McConaghy, Charles F.

    2001-01-01

    A micro electro mechanical sensor that uses capacitive readout electronics. The sensor involves a micromachined low frequency rocking accelerometer with capacitive pickoff fabricated by deep reactive ion etching. The accelerometer includes a central silicon proof mass, is suspended by a thin polysilicon tether, and has a moving electrode (capacitor plate or interdigitated fingers) located at each end the proof mass. During movement (acceleration), the tethered mass moves relative to the surrounding packaging, for example, and this defection is measured capacitively by a plate capacitor or interdigitated finger capacitor, having the cooperating fixed electrode (capacitor plate or interdigitated fingers) positioned on the packaging, for example. The micromachined rocking accelerometer has a low frequency (<500 Hz), high sensitivity (.mu.G), with minimal power usage. The capacitors are connected to a power supply (battery) and to sensor interface electronics, which may include an analog to digital (A/D) converter, logic, RF communication link, antenna, etc. The sensor (accelerometer) may be, for example, packaged along with the interface electronics and a communication system in a 2".times.2".times.2" cube. The proof mass may be asymmetric or symmetric. Additional actuating capacitive plates may be used for feedback control which gives a greater dynamic range.

  14. Excitations of low-frequency hydromagnetic waves by freshly created ions in the solar wind

    SciTech Connect

    Price, C.P.; Gaffey J.D. Jr.; Dong, J.Q.

    1988-02-01

    Low-frequency hydromagnetic waves excited by newborn ions in the solar wind plasma are studied. The freshly created ions appear in the solar wind frame with a ring beam distribution. Both Alfven and fast magentosonic waves are made unstable by the presence of the newborn ions. The dependence of the growth rate of both waves on the newborn ion density, the angle between the interplanetary magnetic field (IMF) and solar wind flow, and the angle of wave propagation relative to the IMF is investigated. Analytic approximations for the growth rates are presented, and numerical solutions of the dispersion equation are shown. The approximations are quite close to the numerically determined growth rates. We find that the waves grow preferentially in the direction parallel to the IMF and that the growth rates increase with both newborn ion density and the angle between the IMF and the solar wind flow. copyright American Geophysical Union 1988

  15. Low-frequency electromagnetic waves driven by gyrotropic gyrating ion beams

    NASA Technical Reports Server (NTRS)

    Sharma, O. P.; Patel, V. L.

    1986-01-01

    The origin of left- and right-hand-polarized low-frequency waves in space plasmas is analyzed. It has been shown that a gyrotropic gyrating ion beam, a ring in velocity space, can excite electromagnetic modes in the plasma near the beam gyrofrequency. It excites left-hand-polarized shear Alfven waves and their harmonics via the coupling of Alfven modes with the beam modes. It can also excite right-hand-polarized fast-mode magnetosonic waves and their harmonics as well. The excitation is possible for beam ions heavier than the plasma ions. The growth rate varies as one-third power of the beam density and decreases with the angle of wave propagation with respect to the ambient magnetic field. The nonlocality has a stabilizing effect on the instability. The predicted values of the wave frequencies compare reasonably well with those observed in satellite data.

  16. Generation of infrasonic waves by low-frequency dust acoustic perturbations in the Earth's lower ionosphere

    NASA Astrophysics Data System (ADS)

    Kopnin, S. I.; Popel, S. I.

    2008-06-01

    It is shown that, during Perseid, Geminid, Orionid, and Leonid meteor showers, the excitation of low-frequency dust acoustic perturbations by modulational instability in the Earth’s ionosphere can lead to the generation of infrasonic waves. The processes accompanying the propagation of these waves are considered, and the possibility of observing the waves from the Earth’s surface is discussed, as well as the possible onset of acoustic gravitational vortex structures in the region of dust acoustic perturbations. The generation of such structures during Perseid, Geminid, Orionid, and Leonid meteor showers can show up as an increase in the intensity of green nightglow by an amount on the order of 10% and can be attributed to the formation of nonlinear (vortex) structures at altitudes of 110-120 km.

  17. High- and low-frequency phonon modes in dipolar quantum gases trapped in deep lattices

    NASA Astrophysics Data System (ADS)

    Maluckov, Aleksandra; Gligorić, Goran; Hadžievski, Ljupčo; Malomed, Boris A.; Pfau, Tilman

    2013-02-01

    We study normal modes propagating on top of the stable uniform background in arrays of dipolar Bose-Einstein condensate (BEC) droplets trapped in a deep optical lattice. Both the on-site mean-field dynamics of the droplets and their displacement due to the repulsive dipole-dipole interactions (DDIs) are taken into account. Dispersion relations for two modes, viz., high- and low- frequency counterparts of optical and acoustic phonon modes in condensed matter, are derived analytically and verified by direct simulations, for both cases of the repulsive and attractive contact interactions. The (counterpart of the) optical-phonon branch does not exist without the DDIs. These results are relevant in the connection to emerging experimental techniques enabling real-time imaging of the condensate dynamics and direct experimental measurement of phonon dispersion relations in BECs.

  18. Low frequency components of the body's center of gravity and blood circulation.

    PubMed

    Inamura, K; Mano, T; Iwase, S; Amagishi, Y; Aoki, K

    1991-01-01

    The purpose of this study was to clarify how low frequency components of the body's center of gravity, mainly 1 minute waves (1-MWs), are related to the mechanism of compensation for the venous blood pooling in the legs during static standing in humans. The 1-MWs of foot pressure center, oscillations of body circumferences and other parameters were analyzed with cross-power spectral analysis. The 1-MW of the calf's blood volume propagated to the chest via the venous system. This was inversely synchronized with the 1-MW of the body's center of gravity. It was speculated that muscular pumping of the calf related to the 1-MW of the body's center of gravity might be compensating for the venous blood pooling in the legs.

  19. Generation of infrasonic waves by low-frequency dust acoustic perturbations in the Earth's lower ionosphere

    SciTech Connect

    Kopnin, S. I.; Popel, S. I.

    2008-06-15

    It is shown that, during Perseid, Geminid, Orionid, and Leonid meteor showers, the excitation of low-frequency dust acoustic perturbations by modulational instability in the Earth's ionosphere can lead to the generation of infrasonic waves. The processes accompanying the propagation of these waves are considered, and the possibility of observing the waves from the Earth's surface is discussed, as well as the possible onset of acoustic gravitational vortex structures in the region of dust acoustic perturbations. The generation of such structures during Perseid, Geminid, Orionid, and Leonid meteor showers can show up as an increase in the intensity of green nightglow by an amount on the order of 10% and can be attributed to the formation of nonlinear (vortex) structures at altitudes of 110-120 km.

  20. A test of two theories for the low-frequency cutoffs of nonthermal continuum radiation

    NASA Technical Reports Server (NTRS)

    Shaw, R. R.; Gurnett, D. A.

    1980-01-01

    A discussion and analysis of two theories that differently identify the low-frequency cutoffs of nonthermal continuum radiation are presented. The cold plasma theory and an alternate one proposed by Jones (1976) are compared experimentally with the use of continuum radiation data obtained in the outer magnetosphere by the Imp 6 and ISEE 1 spacecraft. It is found that the characteristics of this specific radiation are consistent with those expected of ordinary and extraordinary mode waves described by the cold plasma theory and it is shown that the cutoff frequencies occur at the local plasma frequency and R = 0 cutoff frequency as proposed by the same theory. The inconsistencies which were found between the Jones theory (1976) and observation are presented, and in addition no evidence is found for a component of continuum radiation propagating in the Z mode in the outer magnetosphere.

  1. Low Frequency Vibration Energy Harvesting using Diamagnetically Stabilized Magnet Levitation

    NASA Astrophysics Data System (ADS)

    Palagummi, Sri Vikram

    Over the last decade, vibration-based energy harvesting has provided a technology push on the feasibility of self-powered portable small electronic devices and wireless sensor nodes. Vibration energy harvesters in general transduce energy by damping out the environmentally induced relative emotion through either a cantilever beam or an equivalent suspension mechanism with one of the transduction mechanisms, like, piezoelectric, electrostatic, electromagnetic or magnetostrictive. Two major challenges face the present harvesters in literature, one, they suffer from the unavoidable mechanical damping due to internal friction present in the systems, second, they cannot operate efficiently in the low frequency range (< 10 Hz), when most of the ambient vibrational energy is in this low frequency broadband range. Passive and friction free diamagnetically stabilized magnet levitation mechanisms which can work efficiently as a vibration energy harvester in the low frequency range are discussed in this work. First, a mono-stable vertical diamagnetic levitation (VDL) based vibration energy harvester (VEH) is discussed. The harvester consists of a lifting magnet (LM), a floating magnet (FM) and two diamagnetic plates (DPs). The LM balances out the weight of the FM and stability is brought about by the repulsive effect of the DPs, made of pyrolytic graphite. Two thick cylindrical coils, placed in grooves which are engraved in the DPs, are used to convert the mechanical energy into electrical energy. Experimental frequency response of the system is validated by the theoretical analysis which showed that the VEH works in a low frequency range but sufficient levitation gap was not achieved and the frequency response characteristic of the system was effectively linear. To overcome these challenges, the influence of the geometry of the FM, the LM, and the DP were parametrically studied to assess their effects on the levitation gap, size of the system and the natural frequency. For

  2. Role of low-frequency vibrations on sound propagation in glasses at intermediate temperature.

    SciTech Connect

    Criado, A.; Jimenez-Ruiz, M.; Cabrillo, C.; Bermejo, F. J.; Grimsditch, M.; Fischer, H. E.; Bennington, S. M.; Eccleston, R. S.; Materials Science Division; Conesjo Superior de Investigaciones Cientificas; Univ. de Sevilla; Inst. Laue Langevin; Rutherford Appleton Lab.

    2000-04-01

    We report measurements of the temperature dependence of the sound attenuation and the fractional change in sound velocity for the glass (G) and orientational-glass (OG) phases of polymorphic ethanol. Strikingly similar behaviors are found for both phases despite the OG's underlying crystal (bcc) lattice. Such similarity, which is also revealed in dielectric spectroscopy and inelastic neutron scattering measurements, suggests whole molecule small-angle librations as a common microscopic origin for a wide variety of 'glassy' phenomena.

  3. Low Frequency-SAFT Inspection Methodology for Coarse-Grained Steel Rail Components (Manganese Steel Frogs)

    SciTech Connect

    Diaz, Aaron A.; Andersen, Eric S.; Samuel, Todd J.

    2004-11-01

    In the rail industry, sections of high strength Manganese steel are employed at critical locations in railroad networks. Ultrasonic inspections of Manganese steel microstructures are difficult to inspect with conventional means, as the propagation medium is highly attenuative, coarse-grained, anisotropic and nonhomogeneous in nature. Current in-service inspection methods are ineffective while pre-service X-ray methods (used for full-volumetric examinations of components prior to shipment) are time-consuming, costly, require special facilities and highly trained personnel for safe operations, and preclude manufacturers from inspecting statistically meaningful numbers of frogs for effective quality assurance. In-service examinations consist of visual inspections only and by the time a defect or flaw is visually detected, the structural integrity of the component may already be compromised, and immediate repair or replacement is required. A novel ultrasonic inspection technique utilizing low frequency ultrasound (100 to 500 kHz) combined with a synthetic aperture focusing technique (SAFT) for effective reduction of signal clutter and noise, and extraction of important features in the data, has proven to be effective for these coarse grained steel components. Results from proof-of-principal tests in the laboratory demonstrate an effective means to detect and localize reflectors introduced as a function of size and depth from the top of the frog rail. Using non-optimal, commercially available transducers coupled with the low-frequency/SAFT approach, preliminary evaluations were conducted to study the effects of the material microstructure on ultrasonic propagation, sensitivity and resolution in thick section frog components with machined side-drilled holes. Results from this study will be presented and discussed.

  4. Low-frequency waves at comet 67P/Churyumov-Gerasimenko. Observations compared to numerical simulations

    NASA Astrophysics Data System (ADS)

    Koenders, C.; Perschke, C.; Goetz, C.; Richter, I.; Motschmann, U.; Glassmeier, K. H.

    2016-10-01

    Context. A new type of low-frequency wave was detected by the magnetometer of the Rosetta Plasma Consortium at the comet during the initial months after the arrival of the Rosetta spacecraft at comet 67P/Churyumov-Gerasimenko. This large-amplitude, nearly continuous wave activity is observed in the frequency range from 30 mHz to 80 mHz where 40 mHz to 50 mHz is the dominant frequency. This type of low frequency is not closely related to the gyrofrequency of newborn cometary ions, which differs from previous wave activity observed in the interaction region of comets with the solar wind. Aims: This work aims to reveal a global view on the wave activity region using simulations of the comet-solar wind interaction region. Parameters, such as wavelength, propagation direction, and propagation patterns, are within the focus of this study. While the Rosetta observations only provide local information, numerical simulations provide further information on the global wave properties. Methods: Standard hybrid simulations were applied to the comet-solar wind interaction scenario. In the model, the ions were described as particles, which allows us to describe kinetic processes of the ions. The electrons were described as a fluid. Results: The simulations exhibit a threefold wave structure of the interaction region. A Mach cone and a Whistler wing are observed downstream of the comet. The third kind of wave activity found are low-frequency waves at 97 mHz, which corresponds to the waves observed by Richter et al. (2015, Ann. Geophys., 33, 1031). These waves are caused by the initial pick-up of the cometary ions that are perpendicular to the solar wind flow and in the interplanetary magnetic field direction. The associated electric current becomes unstable. The simulations show that wave activity is only detectable in the + E hemisphere and that the Mach cone and whistler wings need to be distinguished from the newly found instability driven wave activity. The movie associated to

  5. Low-Frequency Electromagnetic Sounding for Planetary Volatiles (Invited)

    NASA Astrophysics Data System (ADS)

    Grimm, R. E.

    2013-12-01

    EM sounding is divided by loss tangent << 1 (surface-penetrating radars) and >> 1 (inductive methods). The former have high resolution and responses dominated by dielectric permittivity. They have been useful for sounding the polar caps of Mars and are very promising to image the shells of icy satellites as well as the uppermost crusts of silicate bodies. The latter have poorer resolution but greater penetration depth, responses dominated by electrical conductivity, and are the subject of this talk. Low-frequency inductive methods are further divided by comparing the source-receiver separation to the skin depth. Large separations are parametric in frequency so that the variation of EM response with frequency is translated to change in conductivity with depth. Parametric soundings can exploit natural sources from the solar wind, magnetosphere, ionosphere, or atmosphere. Small source-sensor separations are geometric with transmitter-receiver positions: both conductivity and permittivity can be recovered as a function of frequency (a dielectric spectrum), but at greater resource requirements. Subsurface liquid water is an optimal low-frequency EM target because even small quantities of dissolved ions make it a powerful electrical conductor compared to dry, resistive, silicate crusts. Water at kms or even tens of kms can be detected using the magnetotelluric, geomagnetic-depth sounding, or wave-tilt methods: these are all natural-source soundings using different combinations of field components and receiver geometries. If natural sources are weak or absent, a transmitter can be used to obtain high SNR; the time-domain EM (TDEM) method has been used extensively for terrestrial groundwater exploration. Using a ballistically deployed 200-m diameter transmitter loop, TDEM can detect groundwater at depths of several km. If landed in a region of strong local crustal magnetism, the characteristic Larmor frequency of liquid water can be detected with a TDEM-like setup using

  6. Electrojet-independent ionospheric extremely low frequency/very low frequency wave generation by powerful high frequency waves

    SciTech Connect

    Kuo, Spencer; Snyder, Arnold; Chang, Chia-Lie

    2010-08-15

    Results of extremely low frequency/very low frequency (ELF/VLF) wave generation by intensity-modulated high frequency (HF) heaters of 3.2 MHz in Gakona, Alaska, near local solar noon during a geomagnetic quiet time, are presented to support an electrojet-independent ELF/VLF wave generation mechanism. The modulation was set by splitting the HF transmitter array into two subarrays; one was run at cw full power and the other run alternatively at 50% and 100% power modulation by rectangular waves of 2.02, 5, 8, and 13 kHz. The most effective generation was from the X-mode heater with 100% modulation. While the 8 kHz radiation has the largest wave amplitude, the spectral intensity of the radiation increases with the modulation frequency, i.e., 13 kHz line is the strongest. Ionograms recorded significant virtual height spread of the O-mode sounding echoes. The patterns of the spreads and the changes of the second and third hop virtual height traces caused by the O/X-mode heaters are distinctively different, evidencing that it is due to differently polarized density irregularities generated by the filamentation instability of the O/X-mode HF heaters.

  7. Physiological and content considerations for a second low frequency channel for bass management, subwoofers, and low frequency enhancement (LFE)

    NASA Astrophysics Data System (ADS)

    Miller, Robert E. (Robin)

    2005-04-01

    Perception of very low frequencies (VLF) below 125 Hz reproduced by large woofers and subwoofers (SW), encompassing 3 octaves of the 10 regarded as audible, has physiological and content aspects. Large room acoustics and vibrato add VLF fluctuations, modulating audible carrier frequencies to >1 Hz. By convention, sounds below 90 Hz produce no interaural cues useful for spatial perception or localization, therefore bass management redirects the VLF range from main channels to a single (monaural) subwoofer channel, even if to more than one subwoofer. Yet subjects claim they hear a difference between a single subwoofer channel and two (stereo bass). If recordings contain spatial VLF content, is it possible physiologically to perceive interaural time/phase difference (ITD/IPD) between 16 and 125 Hz? To what extent does this perception have a lifelike quality; to what extent is it localization? If a first approximation of localization, would binaural SWs allow a higher crossover frequency (smaller satellite speakers)? Reported research supports the Jeffress model of ITD determination in brain structures, and extending the accepted lower frequency limit of IPD. Meanwhile, uncorrelated very low frequencies exist in all tested multi-channel music and movie content. The audibility, recording, and reproduction of uncorrelated VLF are explored in theory and experiments.

  8. Characterisation of wind farm infrasound and low-frequency noise

    NASA Astrophysics Data System (ADS)

    Zajamšek, Branko; Hansen, Kristy L.; Doolan, Con J.; Hansen, Colin H.

    2016-05-01

    This paper seeks to characterise infrasound and low-frequency noise (ILFN) from a wind farm, which contains distinct tonal components with distinguishable blade-pass frequency and higher harmonics. Acoustic measurements were conducted at dwellings in the vicinity of the wind farm and meteorological measurements were taken at the wind farm location and dwellings. Wind farm ILFN was measured frequently under stable and very stable atmospheric conditions and was also found to be dependent on the time of year. For noise character assessment, wind farm ILFN was compared with several hearing thresholds and also with the spectra obtained when the wind farm was not operating. Wind farm ILFN was found to exceed the audibility threshold at distances up to 4 km from the wind farm and to undergo large variations in magnitude with time.

  9. Membrane-constrained acoustic metamaterials for low frequency sound insulation

    NASA Astrophysics Data System (ADS)

    Wang, Xiaole; Zhao, Hui; Luo, Xudong; Huang, Zhenyu

    2016-01-01

    We present a constrained membrane-type acoustic metamaterial (CMAM) that employs constraint sticks to add out-of-plane dimensions in the design space of MAM. A CMAM sample, which adopts constraint sticks to suppress vibrations at the membrane center, was fabricated to achieve a sound transmission loss (STL) peak of 26 dB at 140 Hz, with the static areal density of 6.0 kg/m2. The working mechanism of the CMAM as an acoustic metamaterial is elucidated by calculating the averaged normal displacement, the equivalent areal density, and the effective dynamic mass of a unit cell through finite element simulations. Furthermore, the vibration modes of the CMAM indicate that the eigenmodes related to STL dips are shifted into high frequencies, thus broadening its effective bandwidth significantly. Three samples possessing the same geometry and material but different constraint areas were fabricated to illustrate the tunability of STL peaks at low frequencies.

  10. Multifrequency light curves of low-frequency variable radio sources

    NASA Technical Reports Server (NTRS)

    Altschuler, D. R.; Broderick, J. J.; Dennison, B.; Mitchell, K. J.; Odell, S. L.; Condon, J. J.; Payne, H. E.

    1984-01-01

    Light curves for the low-frequency variable sources AO 0235 + 16, NRAO 140, PKS 1117 + 14, DA 406, CTA 102, and 3C 454.3, obtained in monthly observations at 318, 430, and 606 MHz using the 305-m telescope at Arecibo and in bimonthly observations at 880 MHz and 1.4 GHz using the 91-m Green Bank transit telescope during 1980-1983, are presented and analyzed. AO 0235 + 16 is found to have basically canonical variability which is attributed to relativistically moving evolving synchrotron components; but in the other sources, strong simultaneous variations at 318, 430, and 606 MHz are observed to be greatly diminished in amplitude at 880 MHz and 1.4 GHz, confirming the existence of the intermediate-frequency gap at about 1 GHz proposed by Spangler and Cotton (1981). The possibility that a second variability mechanism is active in these sources is explored.

  11. Planck 2015 results. II. Low Frequency Instrument data processings

    NASA Astrophysics Data System (ADS)

    Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Ballardini, M.; Banday, A. J.; Barreiro, R. B.; Bartolo, N.; Basak, S.; Battaglia, P.; Battaner, E.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bock, J. J.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Bucher, M.; Burigana, C.; Butler, R. C.; Calabrese, E.; Cardoso, J.-F.; Castex, G.; Catalano, A.; Chamballu, A.; Christensen, P. R.; Colombi, S.; Colombo, L. P. L.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Dickinson, C.; Diego, J. M.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Ducout, A.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Fergusson, J.; Finelli, F.; Forni, O.; Frailis, M.; Franceschet, C.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Giard, M.; Giraud-Héraud, Y.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Hansen, F. K.; Hanson, D.; Harrison, D. L.; Henrot-Versillé, S.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kiiveri, K.; Kisner, T. S.; Knoche, J.; Krachmalnicoff, N.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lähteenmäki, A.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Leahy, J. P.; Leonardi, R.; Lesgourgues, J.; Levrier, F.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; Lindholm, V.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maggio, G.; Maino, D.; Mandolesi, N.; Mangilli, A.; Maris, M.; Martin, P. G.; Martínez-González, E.; Masi, S.; Matarrese, S.; Mazzotta, P.; McGehee, P.; Meinhold, P. R.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Montier, L.; Morgante, G.; Morisset, N.; Mortlock, D.; Moss, A.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Novikov, D.; Novikov, I.; Oppermann, N.; Paci, F.; Pagano, L.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Pearson, T. J.; Peel, M.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Pierpaoli, E.; Pietrobon, D.; Pointecouteau, E.; Polenta, G.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renzi, A.; Rocha, G.; Romelli, E.; Rosset, C.; Rossetti, M.; Roudier, G.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savelainen, M.; Scott, D.; Seiffert, M. D.; Shellard, E. P. S.; Spencer, L. D.; Stolyarov, V.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Tavagnacco, D.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Türler, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vassallo, T.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Watson, R.; Wehus, I. K.; Wilkinson, A.; Yvon, D.; Zacchei, A.; Zonca, A.

    2016-09-01

    We present an updated description of the Planck Low Frequency Instrument (LFI) data processing pipeline, associated with the 2015 data release. We point out the places where our results and methods have remained unchanged since the 2013 paper and we highlight the changes made for the 2015 release, describing the products (especially timelines) and the ways in which they were obtained. We demonstrate that the pipeline is self-consistent (principally based on simulations) and report all null tests. For the first time, we present LFI maps in Stokes Q and U polarization. We refer to other related papers where more detailed descriptions of the LFI data processing pipeline may be found if needed.

  12. Conformational heterogeneity and low-frequency vibrational modes of proteins

    SciTech Connect

    Balog, E; Smith, Jeremy C; Perahia, David

    2006-12-01

    Molecular dynamics simulation and normal mode analysis are used to calculate the vibrational density of states of dihydrofolate reductase complexed with nicotinamide adenine dinucleotide phosphate at 120 K and the results are compared with the experimental spectrum derived from inelastic neutron scattering. The simulation results indicate that the experimental spectrum arises from an average over proteins trapped in different conformations with structural differences mainly in the loop regions, and that these conformations have significantly different low-frequency (<20 cm-1) spectra. Thus, the experimentally measured spectrum is an average over the vibrational modes of different protein conformations and is thus inhomogeneously broadened. The implications of this broadening for future neutron scattering experiments and ligand binding calculations are discussed.

  13. Low-frequency Electrical Response to Microbial Induced Sulfide Precipitation

    SciTech Connect

    Ntarlagiannis, Dimitrios; Williams, Kenneth H.; Slater, Lee D.; Hubbard, Susan S.

    2005-11-19

    We investigated the sensitivity of low-frequency electrical measurements to microbeinduced metal sulfide precipitation. Three identical sand-packed monitoring columns were used; a geochemical column, an electrical column and a control column. In the first experiment, continuous upward flow of nutrients and metals in solution was established in each column. Cells of Desulfovibrio vulgaris (D. vulgaris) were injected into the center of the geochemical and electrical columns. Geochemical sampling and post-experiment destructive analysis showed that microbial induced sulfate reduction led to metal precipitation on bacteria cells, forming motile biominerals. Precipitation initially occurred in the injection zone, followed by chemotactic migration of D. vulgaris and ultimate accumulation around the nutrient source at the column base.

  14. A very low frequency radio astronomy observatory on the Moon

    NASA Technical Reports Server (NTRS)

    Douglas, James N.; Smith, Harlan J.

    1988-01-01

    Because of terrestrial ionospheric absorption, very little is known of the radio sky beyond 10 m wavelength. An extremely simple, low cost very low frequency radio telescope is proposed, consisting of a large array of short wires laid on the lunar surface, each wire equipped with an amplifier and a digitizer, and connected to a common computer. The telescope could do simultaneous multifrequency observations of much of the visible sky with high resolution in the 10 to 100 m wavelength range, and with lower resolution in the 100 to 1000 m range. It would explore structure and spectra of galactic and extragalactic point sources, objects, and clouds, and would produce detailed quasi-three-dimensional mapping of interstellar matter within several thousand parsecs of the Sun.

  15. Space applications of superconductivity - Low frequency superconducting sensors

    NASA Technical Reports Server (NTRS)

    Zimmerman, J. E.

    1980-01-01

    Although this paper deals with several low-frequency instruments and devices, most of the discussion relates to SQUID (Superconducting QUantum Interference Device) magnetometers and gradiometers, since these are perceived as the instruments with the greatest potential for space applications. The discussion covers SQUID for magnetic field measurements; present state of the art of SQUID technology; ultimate potential performance; applications to magnetic measurements in space; SQUID galvanometers, voltage and current sensors, and wide-band amplifiers; magnetic shielding, and superconducting dc transformer. SQUIDS are superior to all other magnetic sensors in sensitivity, frequency response, range, and linearity. It is suggested that SQUID instruments, both magnetometers and gradiometers, would be valuable in studies of the dynamics of interplanetary and planetary fields. SQUID gradiometers are useful for detection and mapping of magnetic anomalies at short to moderate ranges.

  16. Stochastic regimes in very-low-frequency fluidic oscillator

    NASA Astrophysics Data System (ADS)

    Tesař, Václav

    2016-03-01

    Paper discusses interesting unexpected stochastic regimes discovered in a fluidic oscillator designed for operation at very low oscillation frequencies - without the inconvenience of the long feedback loops needed in standard low-frequency oscillator designs. The new oscillator contains a pair of bistable turn-down active valves operating in anti-parallel — essentially analogous to Abraham & Bloch electric "multibrateur" invented in 1919. Three different self-excited oscillation regimes were found. In the order of increasing supplied flow rate, these regimes are characterised by: (A) generation of stochastic-duration multi-pulse packs, (B) generation of individual pulses with a degree of periodicity, and (C) regime with randomly appearing flow pulses separated by intervals of the order of seconds.

  17. Method for imaging with low frequency electromagnetic fields

    DOEpatents

    Lee, K.H.; Xie, G.Q.

    1994-12-13

    A method is described for imaging with low frequency electromagnetic fields, and for interpreting the electromagnetic data using ray tomography, in order to determine the earth conductivity with high accuracy and resolution. The imaging method includes the steps of placing one or more transmitters, at various positions in a plurality of transmitter holes, and placing a plurality of receivers in a plurality of receiver holes. The transmitters generate electromagnetic signals which diffuse through a medium, such as earth, toward the receivers. The measured diffusion field data H is then transformed into wavefield data U. The travel times corresponding to the wavefield data U, are then obtained, by charting the wavefield data U, using a different regularization parameter [alpha] for each transform. The desired property of the medium, such as conductivity, is then derived from the velocity, which in turn is constructed from the wavefield data U using ray tomography. 13 figures.

  18. Method for imaging with low frequency electromagnetic fields

    DOEpatents

    Lee, Ki H.; Xie, Gan Q.

    1994-01-01

    A method for imaging with low frequency electromagnetic fields, and for interpreting the electromagnetic data using ray tomography, in order to determine the earth conductivity with high accuracy and resolution. The imaging method includes the steps of placing one or more transmitters, at various positions in a plurality of transmitter holes, and placing a plurality of receivers in a plurality of receiver holes. The transmitters generate electromagnetic signals which diffuse through a medium, such as earth, toward the receivers. The measured diffusion field data H is then transformed into wavefield data U. The traveltimes corresponding to the wavefield data U, are then obtained, by charting the wavefield data U, using a different regularization parameter .alpha. for each transform. The desired property of the medium, such as conductivity, is then derived from the velocity, which in turn is constructed from the wavefield data U using ray tomography.

  19. Analysis of Low Frequency Oscillations in Magnetron Injection Guns

    NASA Astrophysics Data System (ADS)

    Pu, Youlei; Luo, Yong; Yan, Ran; Liu, Guo; Jiang, Wei

    2012-02-01

    In our gyro-TWT experiments, low-frequency oscillations (LFOs) had been observed. LFOs is a physical phenomenon usually caused by the electrons trapped between the magnetron injection guns (MIGs) and the interaction region. In this paper, the formation procedure and physical mechanism of LFOs are reported. Available methods including optimizing the magnetic field distribution in the beam compression region and loading bevel cuts on the second anode are involved to capture the trapped electrons, suppress the LFOs and improve the helical electron beam quality. Simulations and experimental results are in good agreement with each other and also reveal the reasonableness of this means. Finally, the influence of current capture ratio on LFOs and the beam quality are studied. With the current capture ratio increasing, the amplitude of LFOs decreases, the pitch factor maintains a constant about 1.2 and we also demonstrate a low transverse velocity spread about 3%.

  20. Thermocapillary Flows with Low Frequency g-Jitter

    NASA Technical Reports Server (NTRS)

    Grassia, P.; Homsy, G. M.

    1999-01-01

    A thermocapillary parallel flow is established in a fluid filled slot with an applied temperature gradient. Low frequency jitter is imposed in arbitrary directions. Vertical jitter proves to be relatively uninteresting, merely augmenting or opposing the basic thermocapillary flow. Streamwise jitter still produces parallel flows, but these now exhibit boundary layers or layered cellular structures for large Rayleigh number as the applied stratification alternates between stable and unstable. Runaways are possible for unstable stratification and these correspond to resonant excitation of stationary long wave Rayleigh-Benard modes. Spanwise jitter produces fully three dimensional motion. A spanwise-streamwise circulation results for weak spanwise jitter, which advects the interfacial temperature establishing a subsidiary spanwise thermocapillary flow. This flow is strong at small Biot number when advected temperature is trapped in the slot, and has a counter-intuitive dependence on the spanwise-streamwise aspect ratio.

  1. Characterization of microstructure with low frequency electromagnetic techniques

    SciTech Connect

    Cherry, Matthew R.; Sathish, Shamachary; Pilchak, Adam L.; Blodgett, Mark P.; Cherry, Aaron J.

    2014-02-18

    A new computational method for characterizing the relationship between surface crystallography and electrical conductivity in anisotropic materials with low frequency electromagnetic techniques is presented. The method is discussed from the standpoint of characterizing the orientation of a single grain, as well as characterizing statistical information about grain ensembles in the microstructure. Large-area electron backscatter diffraction (EBSD) data was obtained and used in conjunction with a synthetic aperture approach to simulate the eddy current response of beta annealed Ti-6Al-4V. Experimental eddy current results are compared to the computed eddy current approximations based on electron backscatter diffraction (EBSD) data, demonstrating good agreement. The detectability of notches in the presence of noise from microstructure is analyzed with the described simulation method and advantages and limitations of this method are discussed relative to other NDE techniques for such analysis.

  2. Broadband fractal acoustic metamaterials for low-frequency sound attenuation

    NASA Astrophysics Data System (ADS)

    Song, Gang Yong; Cheng, Qiang; Huang, Bei; Dong, Hui Yuan; Cui, Tie Jun

    2016-09-01

    We fabricate and experimentally characterize a broadband fractal acoustic metamaterial that can serve to attenuate the low-frequency sounds at selective frequencies ranging from 225 to 1175 Hz. The proposed metamaterials are constructed by the periodic Hilbert fractal elements made of photosensitive resin via 3D printing. In analogy to electromagnetic fractal structures, it is shown that multiple resonances can also be excited in the acoustic counterpart due to their self-similar properties, which help to attenuate the acoustic energy in a wide spectrum. The confinement of sound waves in such subwavelength element is evidenced by both numerical and experimental results. The proposed metamaterial may provide possible alternative for various applications such as the noise attenuation and the anechoic materials.

  3. Low frequency drift instabilities in a dusty plasma

    SciTech Connect

    Rosenberg, M.; Krall, N.A.

    1996-02-01

    Low frequency drift instabilities are investigated in a dusty magnetized plasma with negatively charged grains in which locally there is an electron density gradient which is opposite in sign to a dust density gradient. Frequencies less than the ion gyrofrequency but much larger than the dust gyrofrequency are considered. Two different equilibria are considered that are characterized by {rho}{sub {ital d}}{lt_or_gt}{ital L}{sub {ital nd}}, where {rho}{sub {ital d}} is the dust gyroradius and {ital L}{sub {ital nd}} is the dust density scale length. Instabilities analogous to the universal instability and to the lower-hybrid-drift instability (with the lower-hybrid frequency in this case associated with the dust) are investigated. Possible applications to dusty space plasmas such as the spoke regions of Saturn{close_quote}s B-ring are discussed. {copyright} {ital 1996 American Institute of Physics.}

  4. Extremely low frequency electromagnetic fields and cancer: The epidemiologic evidence

    SciTech Connect

    Bates, M.N. )

    1991-11-01

    This paper reviews the epidemiologic evidence that low frequency electromagnetic fields generated by alternating current may be cause of cancer. Studies examining residential exposures of children and adults and studies of electrical and electronics workers are reviewed. Using conventional epidemiologic criteria for inferring causal associations, including strength and consistency of the relationship, biological plausibility, and the possibility of bias as an explanation, it is concluded that the evidence is strongly suggestive that such radiation is carcinogenic. The evidence is strongest for brain and central nervous system cancers in electrical workers and children. Weaker evidence supports an association with leukemia in electrical workers. Some evidence also exists for an association with melanoma in electrical workers. Failure to find consistent evidence of a link between residential exposures and adult cancers may be attributable to exposure misclassification. Studies so far have used imperfect surrogates for any true biologically effective magnetic field exposure. The resulting exposure misclassification has produced relative risk estimates that understate any true risk.

  5. Extremely low frequency electromagnetic fields prevent chemotherapy induced myelotoxicity.

    PubMed

    Rossi, Edoardo; Corsetti, Maria Teresa; Sukkar, Samir; Poggi, Claudio

    2007-01-01

    Side effects of chemo-radiotherapy reduce the quality and also the survivability of patients. The consequent fatigue and infections, related to myelodepression, act to reduce the dose-intensity of the protocol. Late side effects of chemo-radiotherapy include secondary tumours, acute myeloid leukemias and cardiotoxicity. Side effects of chemotherapy are related to oxidative stress produced by the treatment. Oxidative stress also reduces the efficacy of the treatment. Antioxidative treatment with natural (dietetic) or chemical agents has been reported to reduce the toxicity of chemo-radiotherapy and improve the efficacy of treatment. We here report our experience with SEQEX, an electromedical device that generates Extremely Low Frequency ElectroMagnetic Fields (ELF-EMF) to produce endogenic cyclotronic ionic resonance, to reduce myelotoxicity consequent to ABVD protocol in patients with Hodgkin's lymphoma.

  6. Early experience using low-frequency ultrasound in chronic wounds.

    PubMed

    Breuing, Karl H; Bayer, Lauren; Neuwalder, Jennifer; Orgill, Dennis P

    2005-08-01

    Periodic wound debridement promotes healing in chronic wounds. Low-frequency ultrasonic debridement (LFUD) is a promising adjunct to wound care, which offers relatively painless debridement and bacterial biofilm destruction. We performed LFUD on 17 patients over 8 months, with a minimum follow-up of 3 months. Nine of the wounds (53%) healed primarily or with the aid of a skin graft. Six additional patients (35%) experienced a wound-size reduction of at least 50%. The remaining 2 patients (12%), one with sickle cell anemia and one with a venous stasis ulcer, had reductions in wound area of 20%-30%. None of the patients required initiation of antibiotic treatment after starting LFUD. LFUD has had an early favorable experience in our institution. Further randomized clinical studies are required to better define the mechanism of action and the patient populations most appropriate for this modality.

  7. Low frequency mechanical modes of viruses with atomic detail

    NASA Astrophysics Data System (ADS)

    Dykeman, Eric; Sankey, Otto

    2008-03-01

    The low frequency mechanical modes of viruses can provide important insights into the large global motions that a virus may exhibit. Recently it has been proposed that these large global motions may be excited using impulsive stimulated Raman scattering producing permanent damage to the virus. In order to understand the coupling of external probes to the capsid, vibrational modes with atomic detail are essential. The standard approach to find the atomic modes of a molecule with N atoms requires the formation and diagonlization of a 3Nx3N matrix. As viruses have 10^5 or more atoms, the standard approach is difficult. Using ideas from electronic structure theory, we have developed a method to construct the mechanical modes of large molecules such as viruses with atomic detail. Application to viruses such as the cowpea chlorotic mottle virus, satellite tobacco necrosis virus, and M13 bacteriophage show a fairly complicated picture of the mechanical modes.

  8. The effect of islands on low frequency equatorial motions

    NASA Technical Reports Server (NTRS)

    Cane, M. A.; Du Penhoat, Y.

    1982-01-01

    A complete analytic solution is presented for the influence of equatorial islands on steady low-frequency waves. If the island is small (the meridional extent is much less than the equatorial radius of deformation, R), the waves pass it almost undisturbed, with the mass flux incident on the upstream side flowing around it nearly equally to the north and to the south and continuing on downstream in the lee of the island. For large islands (comparable in extent with R or larger), the principal response is organized as it would be if the island barrier were meridionally infinite. An incident Kelvin wave is largely reflected as long Rossby waves; symmetric long Rossby waves are reflected as equatorial Kelvin waves, while antisymmetric ones stop at the island barrier. In all cases, a boundary current composed of short Rossby waves forms at the eastern side of the island and accomplishes the required meridional redistribution of the zonal mass flux.

  9. Dielectric dispersion of Y-type hexaferrites at low frequencies

    NASA Astrophysics Data System (ADS)

    Abo El Ata, A. M.; Attia, S. M.

    2003-02-01

    A series of polycrystalline Y-type hexaferrites with composition Ba 2Ni 2- xZn xFe 12O 22 (where 0.0⩽ x⩽2.0) were prepared by the standard ceramic method to study the effect of the frequency, temperature and composition on their AC electrical conductivity σ' AC, and dielectric properties. It was found that, the AC conductivity shows dispersion at high frequencies. This dispersion was attributed to the interfacial polarization arising from the inhomogeneous structure of the material. At low frequencies the dielectric constant, ɛ', is abnormally high and decreases rapidly with increasing frequency. Dielectric relaxation peaks were observed on the tan δ( F) curves. The results of the dielectric constant and dielectric loss were explained on the basis of the assumption that the mechanism of dielectric polarization is similar to that of the conduction process.

  10. Theory for low-frequency modulated Langmuir wave packets

    NASA Technical Reports Server (NTRS)

    Cairns, Iver H.; Robinson, P. A.

    1992-01-01

    Langmuir wave packets with low frequency modulations (or beats) observed in the Jovian foreshock are argued to be direct evidence for the Langmuir wave decay L yields L-prime + S. In this decay, 'pump' Langmuir waves L, driven by an electron beam, produce backscattered product Langmuir waves L-prime and ion sound waves S. The L and L-prime waves beat at the frequency and wavevector of the S waves, thereby modulating the wave packets. Beam speeds calculated using the modulated Jovian wave packets (1) are reasonable, at 4-10 times the electron thermal speed, (2) are consistent with theoretical limits on the decay process, and (3) decrease with increasing foreshock depth, as expected theoretically. These results strongly support the theory. The modulation depth of some wave packets suggests saturation by the decay L yields L-prime + S. Applications to modulated Langmuir packets in the Venusian and terrestrial foreshocks and in a type III radio source are proposed.

  11. Low frequency, high sensitive tunable mechanical monolithic horizontal sensors

    NASA Astrophysics Data System (ADS)

    Acernese, Fausto; De Rosa, Rosario; Giordano, Gerardo; Romano, Rocco; Vilasi, Silvia; Barone, Fabrizio

    2011-04-01

    This paper describes an optimized version of the mechanical version of the monolithic tunable folded pendulum, developed at the University of Salerno, configurable both as seismometer and, in a force-feedback configuration, as accelerometer. Typical application of the sensors are in the field of geophysics, including the study of seismic and newtonian noise for characterization of suitable sites for underground interferometer for gravitational waves detection. The sensor, shaped with precision machining and electric-discharge-machining, like the previous version, is a very compact instrument, very sensitive in the low-frequency seismic noise band, with a very good immunity to environmental noises. Important characteristics are the tunability of the resonance frequency and the integrated laser optical readout, consisting of an optical lever and an interferometer. The theoretical sensitivity curves, largely improved due to a new design of the pendulum arms and of the electronics, are in a very good agreement with the measurements. The very large measurement band (10-6 +/- 10Hz) is couple to a very good sensitivity (10-12 m/√Hz in the band 0.1 +/- 10Hz), as seismometer. Prototypes of monolithic seismometers are already operational in selected sites around the world both to acquire seismic data for scientific analysis of seismic noise and to collect all the useful information to understand their performances in the very low frequency band (f < 1mHz). The results of the monolithic sensor as accelerometer (force feed-back configuration) are also presented and discussed. Particular relevance has their sensitivity that is better than 10-11 m/s2/√Hz in the band 0.1 +/- 10Hz. Finally, hypotheses are made on further developments and improvements of monolithic sensors.

  12. Kinetics of neuromuscular changes during low-frequency electrical stimulation.

    PubMed

    Papaiordanidou, Maria; Guiraud, David; Varray, Alain

    2010-01-01

    The purpose of the study was to examine the time course of neuromuscular fatigue components during a low-frequency electrostimulation (ES) session. Three bouts of 17 trains of stimulation at 30 HZ (4 s on, 6 s off) were used to electrically induce fatigue in the plantar flexor muscles. Before and after every 17-train bout, torque, electromyographic activity [expressed as root mean square (RMS) and median frequency (MF) values], evoked potentials (M-wave and H-reflex), and the level of voluntary activation (LOA, using twitch interpolation technique) were assessed. Torque during maximal voluntary contraction decreased significantly from the very first stimulation bout (-6.6 +/- 1.11%, P < 0.001) and throughout the session (-10.32 +/- 1.68% and -11.53 +/- 1.27%, for the second and third bouts, respectively). The LOA and RMS/Mmax values were significantly decreased during the ES session (-2.9 +/- 1.07% and -17.5 +/- 6.14%, P < 0.01 and P< 0.001, respectively, at the end of the protocol), while MF showed no changes. The Hmax/Mmax ratio and Mmax were not significantly modified during the session. All twitch parameters were significantly potentiated after the first bout and throughout the session (P < 0.001). The maximal torque decrease was evident from the early phase of a low-frequency ES protocol, with no concomitant inhibition of motoneuron excitability or depression of muscle contractile properties. These results are consistent with an early failure of the central drive to the muscle. PMID:19882645

  13. Low-Frequency Waves in the Outer Heliosphere

    NASA Astrophysics Data System (ADS)

    Zank, G. P.; Hunana, P.; Goldstein, M. L.

    2013-12-01

    The outer heliosphere beyond some 10 AU is dominated by mass by interstellar neutral Hydrogen (H). Neutral H is coupled to the background solar wind plasma by charge exchange processes, which leads to the creation of a suprathermal pickup ion (PUI) population. The initially unstable ring beam PUI distribution is isotropized to form a filled shell distribution. The PUI contribution to the thermal solar wind pressure/temperature is sizable and in fact can dominate that of the colder thermal solar wind protons. Furthermore, the PUI distribution does not equilibrate or thermalize with the background solar wind plasma, and should therefore be regarded as a distinct distribution. Based on an elaboration of a three-fluid model, we investigate the effect of PUIs on the low-frequency wave properties of the outer heliosphere. To maintain tractability initially, we neglect the electron mass and obtain a 10th-order dispersion relation (compared to the 6th-order two-fluid dispersion relation). Our analysis reveals the existence of several wave modes that do not have a standard solar wind two-fluid plasma counterpart. For the zero angle case, of the 10 solutions, it is possible to obtain 6 analytic solutions for a general value of the ratio of electron number density to the thermal proton number density, four of which are dispersive Alfven waves (left and right polarized, two forward and two backward). Two other solutions are finite frequency modes, and the remaining four modes are magnetoacoustic modes (2 forward, 2 backward). One solution is a (magneto)acoustic wave with the usual 2-fluid sound speed, and the second is a (magneto)acoustic mode with a sound speed associated with the PUI distribution. Both (magneto)acoustic modes couple to the 'other fluids.' We present an analysis of the full dispersion relation for wave modes in the outer heliosphere, clarifying the role of PUIs in determining the properties of low-frequency fluctuations.

  14. X-ray Thomson scattering in warm dense matter at low frequencies

    SciTech Connect

    Murillo, Michael S.

    2010-03-15

    The low-frequency portion of the x-ray Thomson scattering spectrum is determined by electrons that follow the slow ion motion. This ion motion is characterized by the ion-ion dynamic structure factor, which contains a wealth of information about the ions, including structure and collective modes. The frequency-integrated (diffraction) contribution is considered first. An effective dressed-particle description of warm dense matter is derived from the quantum Ornstein-Zernike equations, and this is used to identify a Yukawa model for warm dense matter. The efficacy of this approach is validated by comparing a predicted structure with data from the extreme case of a liquid metal; good agreement is found. A Thomas-Fermi model is then introduced to allow the separation of bound and free states at finite temperatures, and issues with the definition of the ionization state in warm dense matter are discussed. For applications, analytic structure factors are given on either side of the Kirkwood line. Finally, several models are constructed for describing the slow dynamics of warm dense matter. Two classes of models are introduced that both satisfy the basic sum rules. One class of models is the 'plasmon-pole'-like class, which yields the dispersion of ion-acoustic waves. Damping is then included via generalized hydrodynamics models that incorporate viscous contributions.

  15. Scaled energy of deep low-frequency tremor in southwest Japan

    NASA Astrophysics Data System (ADS)

    Horino, K.; Hiramatsu, Y.; Mizukami, T.; Obara, K.; Matsuzawa, T.

    2014-12-01

    In southwestern Japan, deep low-frequency tremor occurs along the subduction zone of Philippine Sea plate. Sources of the tremor show a belt-like distribution of about 30-40 km in depth [Obara, 2002], where the transition from unstable to stable slip occurs at the plate interface. The ratio of radiated energy and seismic moment is called the scaled energy, and it has been often used for comparing the dynamic characteristics of small and large earthquakes. The scaled energy of slow earthquake is in the order of 10-11-10-9 [e.g. Ide et al., 2008; Maeda and Obara, 2009]. This value is about 5 orders smaller than regular earthquakes, indicating that the source process of slow earthquakes is different from that of regular earthquakes. We investigate here the scaled energy of tremor in southwestern Japan to understand the source process of the tremor. We analyze tremor recorded by NIED Hi-net, with Hybrid catalog [Maeda and Obara, 2009] and Hybrid Clustering catalog [Obara et al., 2010], from January 2001 to June 2011 in southwest Japan. We follow the procedure of Maeda and Obara [2009] to estimate the radiated energy of tremor. The values of the scaled energy of tremor are in the range of 10-8-10-6 and are smaller than those of regular earthquakes by order of 2. Multiplying the scaled energy by the rigidity provides that the apparent stress drop of tremor is lower than that of regular earthquakes. This result indicates that tremor occurs in the condition of lower-stress and strain than regular earthquake. Furthermore, the obtained value is 2 orders larger than the scaled energy of very low-frequency earthquake [Maeda and Obara, 2009]. These comparisons imply that each slip phenomenon of slow earthquake family has different dynamic characteristics. We recognize heterogeneous distribution of the scaled energy along the strike and the dip directions of the plate. Shallower events show larger value of the scaled energy. This indicates that the source process of the tremor

  16. Recreational scuba divers' aversion to low-frequency underwater sound.

    PubMed

    Fothergill, D M; Sims, J R; Curley, M D

    2001-01-01

    Increasing use of active low-frequency sonar by submarines and ships raises the risk of accidental exposure of recreational divers to low-frequency underwater sound (LFS). This study aimed to characterize the subjective responses of recreational scuba divers to LFS to ascertain the extent to which LFS may impact their enjoyment, comfort, or time spent underwater. Seventeen male and nine female recreational scuba divers participated. Diving was conducted in an acoustically transparent tank located within a larger anechoic pool. Subjects wore scuba gear and were positioned I m below the surface in a prone position. The sound transducer was located 4 m directly below the diver's head. Sound exposures consisted of three signal types (pure tone, 30 Hz hyperbolic sweep up, and 30 Hz hyperbolic sweep down) each presented at six center frequencies from 100 to 500 Hz and six sound pressure levels(SPL) ranging from 130 to 157 dB re 1 microPa. The duration of each sound exposure was 7 s. Subjects responded via an underwater console to rate aversion to LFS on a category-ratio scale, and to indicate the presence or absence of vibration of any body part. Aversion to LFS and the percent incidence of vibration increased as the SPL increased. The percent incidence of vibration decreased linearly with increasing frequency. At the highest SPL the probability that an aversion rating would exceed Very Severe (7 on the category-ratio scale) was predicted to be 19%. There was no significant difference in aversion among signal types. The 100 Hz frequency was the most aversive frequency (P < 0.05). A plot of aversion vs. frequency showed a U-shaped function with minimum aversion at 250 Hz. In conclusion, diver aversion to LFS is dependent upon SPL and center frequency. The highest aversion rating was given for 100 Hz, this frequency corresponded with the greatest probability of detecting vibration. Factors other than vibration seem to account for aversion to the highest frequencies. Our

  17. The application of low frequency longitudinal guided wave mode for the inspection of multi-hole steel floral pipes

    NASA Astrophysics Data System (ADS)

    Liu, Z. H.; Xie, X. D.; Wu, B.; Li, Y. H.; He, C. F.

    2012-03-01

    Shed-pipe grouting technology, an effective advanced supporting method, is often used in the excavation of soft strata. Steel floral pipes are one of the key load-carrying components of shed-pipe grouting supporting structures. Guided waves are a very attractive methodology to inspect multi-hole steel floral pipes as they offer long range inspection capability, mode and frequency tuning, and cost effectiveness. In this contribution, preliminary experiments are described for the inspection of steel floral pipes using a low frequency longitudinal guided wave mode, L(0,2). The relation between the number of grouting holes and the peak-to-peak amplitude of the first end-reflected signal was obtained. The effect of the grouting holes in steel floral pipes on the propagation velocity of the L(0,2) mode at 30 kHz was analyzed. Experimental results indicate that the typical grouting holes in steel floral pipe have no significant effect on the propagation of this mode. As a result, low frequency longitudinal guided wave modes have potential for the non-destructive long range inspection of multi-hole steel floral pipes. Furthermore, the propagation velocity of the investigated L(0,2) mode at 30 kHz decreases linearly with the increase of the number of grouting holes in a steel floral pipe. It is also noticeable that the effect of the grouting holes cumulates along with the increase in the number of grouting holes and subsequent increase in reflection times of longitudinal guided waves in the steel floral pipe. The application potential of the low frequency longitudinal guided wave technique for the inspection of embedded steel floral pipes is discussed.

  18. Planck early results. V. The Low Frequency Instrument data processing

    NASA Astrophysics Data System (ADS)

    Zacchei, A.; Maino, D.; Baccigalupi, C.; Bersanelli, M.; Bonaldi, A.; Bonavera, L.; Burigana, C.; Butler, R. C.; Cuttaia, F.; de Zotti, G.; Dick, J.; Frailis, M.; Galeotta, S.; González-Nuevo, J.; Górski, K. M.; Gregorio, A.; Keihänen, E.; Keskitalo, R.; Knoche, J.; Kurki-Suonio, H.; Lawrence, C. R.; Leach, S.; Leahy, J. P.; López-Caniego, M.; Mandolesi, N.; Maris, M.; Matthai, F.; Meinhold, P. R.; Mennella, A.; Morgante, G.; Morisset, N.; Natoli, P.; Pasian, F.; Perrotta, F.; Polenta, G.; Poutanen, T.; Reinecke, M.; Ricciardi, S.; Rohlfs, R.; Sandri, M.; Suur-Uski, A.-S.; Tauber, J. A.; Tavagnacco, D.; Terenzi, L.; Tomasi, M.; Valiviita, J.; Villa, F.; Zonca, A.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Bartolo, N.; Bedini, L.; Bennett, K.; Binko, P.; Borrill, J.; Bouchet, F. R.; Bremer, M.; Cabella, P.; Cappellini, B.; Chen, X.; Colombo, L.; Cruz, M.; Curto, A.; Danese, L.; Davies, R. D.; Davis, R. J.; de Gasperis, G.; de Rosa, A.; de Troia, G.; Dickinson, C.; Diego, J. M.; Donzelli, S.; Dörl, U.; Efstathiou, G.; Enßlin, T. A.; Eriksen, H. K.; Falvella, M. C.; Finelli, F.; Franceschi, E.; Gaier, T. C.; Gasparo, F.; Génova-Santos, R. T.; Giardino, G.; Gómez, F.; Gruppuso, A.; Hansen, F. K.; Hell, R.; Herranz, D.; Hovest, W.; Huynh, M.; Jewell, J.; Juvela, M.; Kisner, T. S.; Knox, L.; Lähteenmäki, A.; Lamarre, J.-M.; Leonardi, R.; León-Tavares, J.; Lilje, P. B.; Lubin, P. M.; Maggio, G.; Marinucci, D.; Martínez-González, E.; Massardi, M.; Matarrese, S.; Meharga, M. T.; Melchiorri, A.; Migliaccio, M.; Mitra, S.; Moss, A.; Nørgaard-Nielsen, H. U.; Pagano, L.; Paladini, R.; Paoletti, D.; Partridge, B.; Pearson, D.; Pettorino, V.; Pietrobon, D.; Prézeau, G.; Procopio, P.; Puget, J.-L.; Quercellini, C.; Rachen, J. P.; Rebolo, R.; Robbers, G.; Rocha, G.; Rubiño-Martín, J. A.; Salerno, E.; Savelainen, M.; Scott, D.; Seiffert, M. D.; Silk, J. I.; Smoot, G. F.; Sternberg, J.; Stivoli, F.; Stompor, R.; Tofani, G.; Toffolatti, L.; Tuovinen, J.; Türler, M.; Umana, G.; Vielva, P.; Vittorio, N.; Vuerli, C.; Wade, L. A.; Watson, R.; White, S. D. M.; Wilkinson, A.

    2011-12-01

    We describe the processing of data from the Low Frequency Instrument (LFI) used in production of the Planck Early Release Compact Source Catalogue (ERCSC). In particular, we discuss the steps involved in reducing the data from telemetry packets to cleaned, calibrated, time-ordered data (TOD) and frequency maps. Data are continuously calibrated using the modulation of the temperature of the cosmic microwave background radiation induced by the motion of the spacecraft. Noise properties are estimated from TOD from which the sky signal has been removed using a generalized least square map-making algorithm. Measured 1/f noise knee-frequencies range from ~100 mHz at 30 GHz to a few tens of mHz at 70GHz. A destriping code (Madam) is employed to combine radiometric data and pointing information into sky maps, minimizing the variance of correlated noise. Noise covariance matrices required to compute statistical uncertainties on LFI and Planck products are also produced. Main beams are estimated down to the ≈-10dB level using Jupiter transits, which are also used for geometrical calibration of the focal plane. Corresponding author: A. Zacchei, e-mail: zacchei@oats.inaf.it

  19. Low-Frequency Electromagnetic Methods for Plasmas and Materials

    NASA Astrophysics Data System (ADS)

    Gibbons, Matthew

    1996-05-01

    The pervasive need for rapid, accurate calculations of various electromagnetic phenomena require robust, flexible algorithms with general applicability. An example of such a successful technique is the Coupled Equation Dynamic ADI algorithm. Originally introduced to solve electromagnetic, plasma field equations, it has found an interesting new application regime in the field of micromagnetic simulation. Typical plasma applications include plasma etching/depositions chambers where issues such as uniformity, chemical composition, and etching/deposition rates depend critically on chamber and antenna geometry. Since these antennas are typically driven at 13.56 MHz, low-frequency approximations that neglect purely electromagnetic modes are appropriate. We have developed algorithms that neglect just the solenoidal part of the displacement current, the Darwin model, that can now be solved routinely and rapidly. Typical micromagnetic calculations address the formation and equilibrium properties of magnetic domain walls that provide insight into the practical operating regime of magnetic thin films and magneto-resistive read-write heads. These calculations are computationally intensive and the Coupled Equation DADI component of our earlier work offers new prospects for substantially reducing the numerical effort. Examples that demonstrate the power of our new methods will be given. Collaborators include: Charles Cerjan, Dennis W. Hewett

  20. Mechanical monolithic sensor for low frequency seismic noise measurement

    NASA Astrophysics Data System (ADS)

    Acernese, Fausto; De Rosa, Rosario; Giordano, Gerardo; Romano, Rocco; Barone, Fabrizio

    2007-10-01

    This paper describes a mechanical monolithic sensor for geophysical applications developed at the University of Salerno. The instrument is basically a monolithic tunable folded pendulum, shaped with precision machining and electric-discharge-machining, that can be used both as seismometer and, in a force-feedback configuration, as accelerometer. The monolithic mechanical design and the introduction of laser interferometric techniques for the readout implementation make it a very compact instrument, very sensitive in the low-frequency seismic noise band, with a very good immunity to environmental noises. Many changes have been produced since last version (2006), mainly aimed to the improvement of the mechanics and of the optical readout of the instrument. In fact, we have developed and tested a prototype with elliptical hinges and mechanical tuning of the resonance frequency together with a new laser optical lever and laser interferometer readout system. The theoretical sensitivity curve for both laser optical lever and laser interferometric readouts, calculated on the basis of suitable theoretical models, shows a very good agreement with the experimental measurements. Very interesting scientific result is that the measured natural resonance frequency of the instrument is ~ 70mHz with a Q ~ 140 in air without thermal stabilization, demonstrating the feasibility of a monolithic FP sensor with a natural resonance frequency of the order of 5 mHz with a more refined mechanical tuning.

  1. Mechanical monolithic horizontal sensor for low frequency seismic noise measurement

    NASA Astrophysics Data System (ADS)

    Acernese, Fausto; Giordano, Gerardo; Romano, Rocco; De Rosa, Rosario; Barone, Fabrizio

    2008-07-01

    This paper describes a mechanical monolithic horizontal sensor for geophysical applications developed at the University of Salerno. The instrument is basically a monolithic tunable folded pendulum, shaped with precision machining and electric discharge machining, that can be used both as seismometer and, in a force-feedback configuration, as accelerometer. The monolithic mechanical design and the introduction of laser interferometric techniques for the readout implementation makes it a very compact instrument, very sensitive in the low frequency seismic noise band, with a very good immunity to environmental noises. Many changes have been produced since last version (2007), mainly aimed to the improvement of the mechanics and of the optical readout of the instrument. In fact, we have developed and tested a prototype with elliptical hinges and mechanical tuning of the resonance frequency together with a laser optical lever and a new laser interferometer readout system. The theoretical sensitivity curve for both laser optical lever and laser interferometric readouts, evaluated on the basis of suitable theoretical models, shows a very good agreement with the experimental measurements. Very interesting scientific result is the measured natural resonance frequency of the instrument of 70mHz with a Q =140 in air without thermal stabilization. This result demonstrates the feasibility of a monolithic folded pendulum sensor with a natural resonance frequency of the order of millihertz with a more refined mechanical tuning.

  2. Progress on the Low Frequency All Sky Monitor

    NASA Astrophysics Data System (ADS)

    Murray, James; Jenet, Fredrick; Craig, Joseph; Creighton, Teviet David; Percy Dartez, Louis; Ford, Anthony J.; Hernandez, Andrés; Hicks, Brian; Hinojosa, Jesus; Jaramillo, Ricardo; Kassim, Namir E.; Lazio, Joseph; Lunsford, Grady; Miller, Rossina B.; Ray, Paul S.; Rivera, Jesus; Taylor, Gregory B.; Teitelbaum, Lawrence; CenterAdvanced Radio Astronomy, University of Texas at Brownsville, University of New Mexico, Naval Research Laboratory, Jet Propulsion Laborator

    2015-01-01

    The Low Frequency All Sky Monitor (LoFASM) is a system of geographically separated radio arrays dedicated to the study of radio transients. LoFASM consists of four stations, each comprised of 12 cross-dipole antennas designed to operate between 10-88MHz. The antennas and front end electronics for LoFASM were designed by the Naval Research Laboratory for the Long Wavelength Array (LWA) project (cf. Hicks et al. PASP 124, 1090 (2012)). All four stations are currently operational and in the commissioning stage . Over the last 3 years, undergraduate and graduate students from the University of Texas at Brownsville's Center for Advanced Radio Astronomy have been establishing these stations around the continental US, consisting of sites located in Port Mansfield, Texas, the LWA North Arm site of the LWA1 Radio Observatory in New Mexico, adjacent to the North Arm of the Very Large Array, the Green Bank Radio Observatory, West Virginia, and the Goldstone Deep Space Communications Complex, California. In combination with the establishment of these sites was the development of the analog hardware, which consists of custom RF splitter/combiners and a custom amplifier and filter chain designed at Center for Advanced Radio Astronomy (CARA). This poster will expound on progress in site installation and the development of the analog signal chain, specifically the redesigned analog receiving system.

  3. Energy harvesting from low frequency applications using piezoelectric materials

    SciTech Connect

    Li, Huidong; Tian, Chuan; Deng, Z. Daniel

    2014-12-15

    In an effort to eliminate the replacement of the batteries of electronic devices that are difficult or impractical to service once deployed, harvesting energy from mechanical vibrations or impacts using piezoelectric materials has been researched over the last several decades. However, a majority of these applications have very low input frequencies. This presents a challenge for the researchers to optimize the energy output of piezoelectric energy harvesters, due to the relatively high elastic moduli of piezoelectric materials used to date. This paper reviews the current state of research on piezoelectric energy harvesting devices for low frequency (0–100 Hz) applications and the methods that have been developed to improve the power outputs of the piezoelectric energy harvesters. Various key aspects that contribute to the overall performance of a piezoelectric energy harvester are discussed, including geometries of the piezoelectric element, types of piezoelectric material used, techniques employed to match the resonance frequency of the piezoelectric element to input frequency of the host structure, and electronic circuits specifically designed for energy harvesters.

  4. Low-frequency earthquakes in the Mexican Sweet Spot

    NASA Astrophysics Data System (ADS)

    Frank, William B.; Shapiro, Nikolaï M.; Kostoglodov, Vladimir; Husker, Allen L.; Campillo, Michel; Payero, Juan S.; Prieto, GermáN. A.

    2013-06-01

    We use data from the Meso-America Subduction Experiment to detect and locate low-frequency earthquakes (LFEs) in the Mexican subduction zone. We use visually-identified templates to perform a network waveform correlation search that produced ~17,000 robustly detected LFEs that form 15 distinct families. Stacking an LFE family's corresponding detections results in seismograms with high signal-to-noise ratios and clear P and S wave arrivals; we use these travel times to locate the sources. The resulting locations superpose a previously identified region of permanent non-volcanic tremor (NVT) activity. Husker et al. (2012) called this region a Sweet Spot, suggesting that the local conditions are adequate to continuously generate NVT. The LFE hypocenters have been located at a depth of 40-45 km in an area that is surrounding the upper slab-plate interface. We characterize their focal mechanisms by comparing their stacked seismograms to synthetic seismograms. This analysis reveals a common low-dipping focal mechanism.

  5. A Study of Low Frequency Earthquakes in Washington State

    NASA Astrophysics Data System (ADS)

    Royer, A. A.; Bostock, M. G.

    2012-12-01

    In the past decade, studies have shown that non-volcanic tremor in southwest Japan can be explained by swarms of low frequency earthquakes (LFEs). More recently LFEs have been identified and documented in southern Vancouver Island. Here we extend study of LFEs to Washington state by exploiting data from the IRIS-PASCAL CAFE experiment. We use network autocorrelation to detect LFEs within 4 different tremor episodes (2007,2008,2010 and 2011). We separate the dataset into 2 components, one involving stations between the Olympic Peninsula and Puget Sound (North Group) and the other involving stations to the south of Puget Sound (South Group). For the South Group, only the 2007 and 2008 tremor episodes are available. From an initial 4915 (North Group) and 3306 (South Group) detections of LFEs using a set of 7 3-components stations, we use iterative network cross-correlation to register further detections and stack to improve signal-to-noise ratio of LFE family templates. On the basis of progress to date, we anticipate the assembly of ~150 and ~50 LFE family templates for the North and South Groups, respectively. We plan to locate these LFE family templates, determine representative focal mechanisms and investigate LFE occurrence relative to regular seismicity for comparison with previous results from southern Vancouver Island and southwest Japan.

  6. Modeling low frequency vibrational modes of large biomolecules

    NASA Astrophysics Data System (ADS)

    Sankey, Otto; Dykeman, Eric

    2008-03-01

    Mechanical oscillations of proteins in their native state are relevant to understanding the flexibility of the protein assembly, the binding of substrates, the mechanical action involved in enzymatic activity, and the vibrational response to light scattering. Often, only the low frequency modes are of interest and coarse grained methods or other approximations are used due to the large size of the dynamical matrix. We introduce a computational approach, which exploits the methodology from electronic structure Order N methods, to find the vibrational modes below some frequency threshold (analogous to a Fermi-level in electronic structure theory). The approach allows systems to be described in atomistic detail. We use a generalized Born force field to model the interactions. Examples of normal modes for icosahedral viruses (e.g. satellite tobacco necrosis virus), tubular viruses (e.g. M13), and enzymes (e.g. lysozyme, HIV-protease, alpha-lytic protease) will be discussed. This effort is motivated by recent experimental work to produce high amplitude vibrations of viruses from impulsive stimulated Raman scattering.

  7. Transient Modeling of Hybrid Rocket Low Frequency Instabilities

    NASA Technical Reports Server (NTRS)

    Karabeyoglu, M. Arif; DeZilwa, Shane; Cantwell, Brian; Zilliac, Greg

    2003-01-01

    A comprehensive dynamic model of a hybrid rocket has been developed in order to understand and predict the transient behavior including instabilities. A linearized version of the transient model predicted the low-frequency chamber pressure oscillations that are commonly observed in hybrids. The source of the instabilities is based on a complex coupling of thermal transients in the solid fuel, wall heat transfer blocking due to fuel regression rate and the transients in the boundary layer that forms on the fuel surface. The oscillation frequencies predicted by the linearized theory are in very good agreement with 43 motor test results obtained from the hybrid propulsion literature. The motor test results used in the comparison cover a very wide spectrum of parameters including: 1) four separate research and development programs, 2) three different oxidizers (LOX, GOX, N2O), 3) a wide range of motor dimensions (i.e. from 5 inch diameter to 72 inch diameter) and operating conditions and 4) several fuel formulations. A simple universal scaling formula for the frequency of the primary oscillation mode is suggested.

  8. Low-frequency dielectric dispersion of bacterial cell suspensions.

    PubMed

    Asami, Koji

    2014-07-01

    Dielectric spectra of Escherichia coli cells suspended in 0.1-10 mM NaCl were measured over a frequency range of 10 Hz to 10 MHz. Low-frequency dielectric dispersion, so-called the α-dispersion, was found below 10 kHz in addition to the β-dispersion, due to interfacial polarization, appearing above 100 kHz. When the cells were killed by heating at 60°C for 30 min, the β-dispersion disappeared completely, whereas the α-dispersion was little influenced. This suggests that the plasma (or inner) membranes of the dead cells are no longer the permeability barrier to small ions, and that the α-dispersion is not related to the membrane potential due to selective membrane permeability of ions. The intensity of the α-dispersion depended on both of the pH and ionic strength of the external medium, supporting the model that the α-dispersion results from the deformation of the ion clouds formed outside and inside the cell wall containing charged residues.

  9. Suppression of Leidenfrost effect via low frequency vibrations

    NASA Astrophysics Data System (ADS)

    Ng, Boon Thiam; Hung, Yew Mun; Tan, Ming Kwang

    2015-11-01

    Leidenfrost effect occurs when vapor layer forms in between the coolant and the hot surface above Leidenfrost point, which dramatically reduces the cooling efficiency due to low thermal conductivity of the vapor layer. To prevent surface overheating, there have been number of reported methods to suppress the Leidenfrost effect that were mainly based on functionalization of the substrate surface and application of electric field across the droplet and substrate. In this work, we induce low frequency vibrations (f ~ 100 Hz) to the heated substrate to suppress the Leidenfrost effect. Three distinct impact dynamics are observed based on different magnitudes of surface acceleration and surface temperature. In gentle film boiling regime, formation of thin spreading lamella around the periphery of the impinged droplet is observed; in film boiling regime, due to thicker vapor cushion, rebound of the impinged droplet is observed; in contact boiling regime, due to the direct contact between the impinged droplet and heated substrate, ejection of the tiny droplet is observed. Also, estimated cooling enhancement ratio for contact boiling regime shows an improvement from 95% to 105%.

  10. Low Frequency Waves in the Plasma Environment Around the Shuttle

    NASA Technical Reports Server (NTRS)

    Vayner, Boris V.; Ferguson, Dale C.

    1996-01-01

    As a part of the SAMPIE (The Solar Array Module Plasma Interaction Experiment) program, the Langmuir probe (LP) was employed to measure plasma characteristics during the flight of STS-62. The whole set of data could be divided into two parts: (1) low frequency sweeps to determine voltage-current characteristics and to find the electron temperature and number density; (2) high frequency turbulence (HFT) data caused by electromagnetic noise around the Shuttle. Broadband noise was observed at 250-20,000 Hz frequencies. Measurements were performed in ram conditions; thus, it seems reasonable to believe that the influence of spacecraft operations on plasma parameters was minimized. It is shown that ion acoustic waves were observed, and two kinds of instabilities are suggested for explanation of the origin of these waves. According to the purposes of SAMPIE, samples of solar cells were placed in the cargo bay of the Shuttle, and high negative bias voltages were applied to them to initiate arcing between these cells and the surrounding plasma. The arcing onset was registered by special counters, and data were obtained that included the amplitudes of current, duration of each arc, and the number of arcs per one experiment. The LP data were analyzed for two different situations: with arcing and without arcing. Electrostatic noise spectra for both situations and a theoretical explanation of the observed features are presented in this paper.

  11. Endogenous modulation of low frequency oscillations by temporal expectations

    PubMed Central

    Cravo, Andre M.; Rohenkohl, Gustavo; Wyart, Valentin

    2011-01-01

    Recent studies have associated increasing temporal expectations with synchronization of higher frequency oscillations and suppression of lower frequencies. In this experiment, we explore a proposal that low-frequency oscillations provide a mechanism for regulating temporal expectations. We used a speeded Go/No-go task and manipulated temporal expectations by changing the probability of target presentation after certain intervals. Across two conditions, the temporal conditional probability of target events differed substantially at the first of three possible intervals. We found that reactions times differed significantly at this first interval across conditions, decreasing with higher temporal expectations. Interestingly, the power of theta activity (4–8 Hz), distributed over central midline sites, also differed significantly across conditions at this first interval. Furthermore, we found a transient coupling between theta phase and beta power after the first interval in the condition with high temporal expectation for targets at this time point. Our results suggest that the adjustments in theta power and the phase-power coupling between theta and beta contribute to a central mechanism for controlling neural excitability according to temporal expectations. PMID:21900508

  12. Low-frequency sound level in the Southern Indian Ocean.

    PubMed

    Tsang-Hin-Sun, Eve; Royer, Jean-Yves; Leroy, Emmanuelle C

    2015-12-01

    This study presents long-term statistics on the ambient sound in the Southern Indian Ocean basin based on 2 years of data collected on six widely distributed autonomous hydrophones from 47°S to 4°S and 53°E to 83°E. Daily mean power spectra (10-100 Hz) were analyzed in order to identify the main sound sources and their space and time variability. Periodic signals are principally associated with the seasonal presence of three types of blue whales and fin whales whose signatures are easily identified at specific frequencies. In the low frequencies, occurrence of winter lows and summer highs in the ambient noise levels are well correlated with iceberg volume variations at the southern latitudes, suggesting that icebergs are a major sound source, seasonally contributing to the ambient noise, even at tropical latitudes (26°S). The anthropogenic contribution to the noise spectrum is limited. Shipping sounds are only present north and west of the study area in the vicinity of major traffic lanes. Acoustic recordings from the southern sites may thus be representative of the pristine ambient noise in the Indian Ocean. PMID:26723301

  13. Pore Structure and the Low Frequency Permittivity of Sea Ice

    NASA Astrophysics Data System (ADS)

    O'Sadnick, M.; Ingham, M.; Eicken, H.

    2014-12-01

    Field and laboratory measurements of the dielectric permittivity of first-year sea ice both show that below a frequency of about 10 Hz the real part of the relative permittivity (ɛ') increases with decreasing frequency. Field measurements in Barrow, Alaska and McMurdo Sound suggest that this rise in low frequency ɛ' steepens as the ice warms, and is confined primarily to the upper 0.50m of the ice cover as it approaches maximum thickness. We propose that this behaviour may be related to membrane polarization occurring in the pore structure within the ice. With ice-liquid interfaces carrying a net charge, an electric double layer forms within the brine filled pores. Polarization occurs at grain boundaries, intragranular films and "necks" in the pore structure where the effective thickness of the double layer approaches the width of the pore resulting in differential transport of ions. This process is dependent on both the characteristic lengths and radii of pores relative to the length and radii of the "necks" or the geometry of inter/intragranular brine layers. By representing the measured dielectric permittivity in terms of a Cole-Cole model it is possible to show that the distribution of pore sizes evolves with temperature. Derived values of complex conductivity are also examined in relationship to the temporal evolution of pore geometry including smoothness of the pore-ice interface.

  14. Extremely Low Frequency Magnetic Field Modulates the Level of Neurotransmitters

    PubMed Central

    Chung, Yoon Hee; Lee, Young Joo; Lee, Ho Sung; Chung, Su Jin; Lim, Cheol Hee; Oh, Keon Woong; Sohn, Uy Dong

    2015-01-01

    This study was aimed to observe that extremely low frequency magnetic field (ELF-MF) may be relevant to changes of major neurotransmitters in rat brain. After the exposure to ELF-MF (60 Hz, 2.0 mT) for 2 or 5 days, we measured the levels of biogenic amines and their metabolites, amino acid neurotransmitters and nitric oxide (NO) in the cortex, striatum, thalamus, cerebellum and hippocampus. The exposure of ELF-MF for 2 or 5 days produced significant differences in norepinephrine and vanillyl mandelic acid in the striatum, thalamus, cerebellum and hippocampus. Significant increases in the levels of serotonin and 5-hydroxyindoleacetic acid were also observed in the striatum, thalamus or hippocampus. ELF-MF significantly increased the concentration of dopamine in the thalamus. ELF-MF tended to increase the levels of amino acid neurotransmitters such as glutamine, glycine and γ -aminobutyric acid in the striatum and thalamus, whereas it decreased the levels in the cortex, cerebellum and hippocampus. ELF-MF significantly increased NO concentration in the striatum, thalamus and hippocampus. The present study has demonstrated that exposure to ELF-MFs may evoke the changes in the levels of biogenic amines, amino acid and NO in the brain although the extent and property vary with the brain areas. However, the mechanisms remain further to be characterized. PMID:25605992

  15. A perceived low-frequency sound in Taos, New Mexico

    SciTech Connect

    Mullins, J.H. ); Poteet, H. )

    1994-11-01

    Persistent complaints of an annoying low-frequency sound in Northern New Mexico, particularly in the vicinity of Taos, led to a request by members of the Congressional delegation of NM for an investigation. During the summer of 1993, in Taos, extensive simultaneous measurements were carried out of acoustic, seismic, electric, magnetic, and electromagnetic signals by a team from Sandia and Los Alamos National Laboratories, the Air Force Phillips Laboratory, and the University of New Mexico. Since anecdotal evidence and signal matching tests by the hearers implicated the frequencies between 30 to 100 Hz, special attention was given to that range. However, no signals were found matching the description, and in particular no airborne audio signals in this range were found other than background, even though the acoustical detector was capable of measuring signals less than [minus]50 dB SPL. Subsequent complaints of similar sounds from widely distributed areas in the U.S., and a long history of these in the U.K. [R. N. Vasudevan and C. G. Gordon, Appl. Acoust. [bold 10], 57--69 (1977)] have focused attention on human hearing in the 20--100 Hz range. New instruments are being developed and controlled clinical tests are planned with hearers and nonhearers in the Taos area.

  16. Low-frequency sound level in the Southern Indian Ocean.

    PubMed

    Tsang-Hin-Sun, Eve; Royer, Jean-Yves; Leroy, Emmanuelle C

    2015-12-01

    This study presents long-term statistics on the ambient sound in the Southern Indian Ocean basin based on 2 years of data collected on six widely distributed autonomous hydrophones from 47°S to 4°S and 53°E to 83°E. Daily mean power spectra (10-100 Hz) were analyzed in order to identify the main sound sources and their space and time variability. Periodic signals are principally associated with the seasonal presence of three types of blue whales and fin whales whose signatures are easily identified at specific frequencies. In the low frequencies, occurrence of winter lows and summer highs in the ambient noise levels are well correlated with iceberg volume variations at the southern latitudes, suggesting that icebergs are a major sound source, seasonally contributing to the ambient noise, even at tropical latitudes (26°S). The anthropogenic contribution to the noise spectrum is limited. Shipping sounds are only present north and west of the study area in the vicinity of major traffic lanes. Acoustic recordings from the southern sites may thus be representative of the pristine ambient noise in the Indian Ocean.

  17. Progress on the Low Frequency All Sky Monitor

    NASA Astrophysics Data System (ADS)

    Ford, Anthony; Jenet, F.; Craig, J.; Creighton, T. D.; Dartez, L. P.; Hicks, B.; Hinojosa, J.; Jaramillo, R.; Kassim, N. E.; Lunsford, G.; Miller, R. B.; Murray, J.; Ray, P. S.; Rivera, J.; Taylor, G. B.

    2013-01-01

    The Low Frequency All Sky Monitor is a system of geographically separated radio arrays dedicated to the study of radio transients. LoFASM consists of four stations, each comprised of 12 cross-dipole antennas designed to operate between 5-88MHz. The antennas and front end electronics for LoFASM were designed by the Naval Research Laboratory for the Long Wavelength Array project. Over the last year, undergraduate students from the University of Texas at Brownsville’s Center for Advanced Radio Astronomy have been establishing these stations around the continental US, consisting of sites located in Port Mansfield, Texas, the LWA North Arm site of the LWA1 Radio Observatory in New Mexico, adjacent to the North Arm of the Very Large Array, the Green Bank Radio Observatory, West Virginia, and NASA’s Goldstone tracking complex in California. In combination with the establishment of these sites was the development of the analog hardware, which consists of commercial off-the-shelf RF splitter/combiners and a custom amplifier and filter chain designed by colleagues at the University of New Mexico. This poster will expound on progress in site installation and development of the analog signal chain.

  18. Very Low Frequency Remote Sensing of the Ionosphere and Magnetosphere

    NASA Astrophysics Data System (ADS)

    Cohen, M.

    2013-05-01

    This review talk will explore the technique of Very Low Frequency (VLF, 3-30 kHz) remote sensing of the ionosphere and magnetosphere, in which ground-based transmitter beacons (nominally for submarine communications) are used as a probe wave to study the D-region of the ionosphere (60-90 km), a layer is too low for satellites and too high for balloons. Guided efficiently by the Earth-ionosphere waveguide, VLF waves can be used on a global level, to sensitively quantify any ionospheric disturbance in the D-region. These include the impacts of solar flares, lightning heating (both the EMP and the quasi-static field changes), electron precipitation from lightning, and cosmic gamma-ray bursts. We will review many experimental and modeling efforts that have been made over the past several decades, including recent work on the transionospheric absorption of VLF waves from transmitters and lightning radio emissions. We will also review recent international efforts to build a global network of VLF receivers under the umbrella of the United Nations Basic Space Science Initiative.

  19. Office worker exposure to extremely low frequency magnetic fields

    SciTech Connect

    Hiebert, D.G.

    1994-05-01

    A study of office worker exposure to extremely low frequency magnetic fields (ELF MF) was conducted at Los Alamos National Laboratory. The main purpose of this study was to quantitatively assess ELF MF exposures. A secondary objective was to determine whether or not exposures to ELF MF can be reduced by implementing administrative controls and educating workers on the sources of such fields. EMDEX dosimeters were used to determine full shift personal exposures for 12 volunteers from two personnel sections and one training section. In addition, using the EMDEX meter in survey mode, office area evaluations were conducted. Administrative controls and training were implemented in an attempt to reduce exposures. Post control monitoring was conducted to determine if a reduction in ELF MF occurred among the workers. On average, baseline office worker exposures to ELF MF were 2.3 mG, ranging from 0.6 to 9.7 mG. The post control exposures averaged 1.1 mG with a range from 0.5 to 2.2 mG. A reduction of 53% overall was seen after implementation of administrative controls and training. The office area survey indicated that many sources of ELF MF influence exposure and that magnetic field strengths vary not only from one type of equipment to another, but also vary between two similar pieces of equipment.

  20. Extremely Low Frequency Signal Acquisition, Recording and Analysis

    NASA Astrophysics Data System (ADS)

    Zantis, Franz P.; Hribik, Ján; Ďuračková, Daniela

    2016-05-01

    Our environment is permeated by electrical and magnetic alternating waves in the frequency range above the AC voltage of 50 Hz and also in the radio frequency range. Much attention from the public is given to these waves. Through numerous studies and publications about this type of oscillations and waves it is largely known from which sources they occur and which impact they have. However, very little information could be found about electrical and magnetic alternating waves in the frequency range below 50 Hz. The aim of this research is to demonstrate that these signals exist and also to show how the signals look like and where and when they occur. This article gives an overview of the occurrence of these ELF (Extremely Low Frequencies) signals, their specific properties in view of the time domain and in view of the frequency domain and of the possible sources of these waves. Precise knowledge of the structures of the ELF signals allows conclusions about their potential to cause electromagnetic interference in electronic systems. Also other effects in our environment, eg on flora and fauna could be explained.

  1. Recent developments in thermoacoustically-driven low-frequency projectors

    SciTech Connect

    Ward, W.C.; Merrigan, M.A.

    1992-05-01

    Thermoacoustic engines are a recent class of devices that can efficiently convert heat to acoustic energy without moving parts or intervening mechanisms. These engines have a natural potential for powering low-frequency sonar projectors with high reliability and efficiencies that cannot be matched by conventional technologies. A recent design study has produced thermoacoustic projector configurations that can execute standard projector performance requirements such as FM sweep and velocity magnitude and phase control in array environments for a wide range of positive and negative radiation resistances. The thermoacoustic driver is a vertically oriented, helium-filled resonator that contains a movable tuning element to vary the resonator frequency. It is coupled to a variable length water column that is tunable by a similar means to adjust the effective source impedance of the device. Modeling results indicate a sweep range of at least an octave for a single device, and maximum overall (heat-to-acoustic) conversion efficiencies of 25% at 50 Hz. Efficiency increases slightly at lower frequencies, and the lowest operational frequency is limited only by the size of the projector. Output power increases linearly with mean pressure, and at depths of 200 m or more, power densities in excess of 500 kW/m{sup 2} are achievable. Control aspects have been investigated, including rapid startup and shutdown that can be performed by manipulating the water tuning column. Future trends and development prospects are discussed. 4 refs.

  2. Recent developments in thermoacoustically-driven low-frequency projectors

    SciTech Connect

    Ward, W.C.; Merrigan, M.A.

    1992-01-01

    Thermoacoustic engines are a recent class of devices that can efficiently convert heat to acoustic energy without moving parts or intervening mechanisms. These engines have a natural potential for powering low-frequency sonar projectors with high reliability and efficiencies that cannot be matched by conventional technologies. A recent design study has produced thermoacoustic projector configurations that can execute standard projector performance requirements such as FM sweep and velocity magnitude and phase control in array environments for a wide range of positive and negative radiation resistances. The thermoacoustic driver is a vertically oriented, helium-filled resonator that contains a movable tuning element to vary the resonator frequency. It is coupled to a variable length water column that is tunable by a similar means to adjust the effective source impedance of the device. Modeling results indicate a sweep range of at least an octave for a single device, and maximum overall (heat-to-acoustic) conversion efficiencies of 25% at 50 Hz. Efficiency increases slightly at lower frequencies, and the lowest operational frequency is limited only by the size of the projector. Output power increases linearly with mean pressure, and at depths of 200 m or more, power densities in excess of 500 kW/m{sup 2} are achievable. Control aspects have been investigated, including rapid startup and shutdown that can be performed by manipulating the water tuning column. Future trends and development prospects are discussed. 4 refs.

  3. Low-frequency nuclear quadrupole resonance with a dc SQUID

    SciTech Connect

    Chang, J.W.

    1991-07-01

    Conventional pure nuclear quadrupole resonance (NQR) is a technique well suited for the study of very large quadrupolar interactions. Numerous nuclear magnetic resonance (NMR) techniques have been developed for the study of smaller quadrupolar interactions. However, there are many nuclei which have quadrupolar interactions of intermediate strength. Quadrupolar interactions in this region have traditionally been difficult or unfeasible to detect. This work describes the development and application of a SQUID NQR technique which is capable of measuring intermediate strength quadrupolar interactions, in the range of a few hundred kilohertz to several megahertz. In this technique, a dc SQUID (Superconducting QUantum Interference Device) is used to monitor the longitudinal sample magnetization, as opposed to the transverse magnetization, as a rf field is swept in frequency. This allows the detection of low-frequency nuclear quadrupole resonances over a very wide frequency range with high sensitivity. The theory of this NQR technique is discussed and a description of the dc SQUID system is given. In the following chapters, the spectrometer is discussed along with its application to the study of samples containing half-odd-integer spin quadrupolar nuclei, in particular boron-11 and aluminum-27. The feasibility of applying this NQR technique in the study of samples containing integer spin nuclei is discussed in the last chapter. 140 refs., 46 figs., 6 tabs.

  4. Low-frequency meandering piezoelectric vibration energy harvester.

    PubMed

    Berdy, David F; Srisungsitthisunti, Pornsak; Jung, Byunghoo; Xu, Xianfan; Rhoads, Jeffrey F; Peroulis, Dimitrios

    2012-05-01

    The design, fabrication, and characterization of a novel low-frequency meandering piezoelectric vibration energy harvester is presented. The energy harvester is designed for sensor node applications where the node targets a width-to-length aspect ratio close to 1:1 while simultaneously achieving a low resonant frequency. The measured power output and normalized power density are 118 μW and 5.02 μW/mm(3)/g(2), respectively, when excited by an acceleration magnitude of 0.2 g at 49.7 Hz. The energy harvester consists of a laser-machined meandering PZT bimorph. Two methods, strain-matched electrode (SME) and strain-matched polarization (SMP), are utilized to mitigate the voltage cancellation caused by having both positive and negative strains in the piezoelectric layer during operation at the meander's first resonant frequency. We have performed finite element analysis and experimentally demonstrated a prototype harvester with a footprint of 27 x 23 mm and a height of 6.5 mm including the tip mass. The device achieves a low resonant frequency while maintaining a form factor suitable for sensor node applications. The meandering design enables energy harvesters to harvest energy from vibration sources with frequencies less than 100 Hz within a compact footprint.

  5. Unusual Low-frequency Magnetic Perturbations in TFTR

    SciTech Connect

    H. Takahashi; E.D. Fredrickson; M.S. Chance

    2001-02-12

    Low-frequency magnetic perturbations (less than or equal to 30 kHz) observed in the Tokamak Fusion Test Reactor (TFTR) tokamak do not always conform to expectations from Magneto-Hydro-Dynamic (MHD) modes. The discrepancy between observations and expectations arises from the existence of three classes of magnetic perturbations in TFTR: (1) 'Edge Originated Magnetic Perturbations' (EOMP's), (2) 'Kink-like Modes' (KLM's), and (3) Tearing Modes (TM's). The EOMP class has unusual magnetic phenomenon including up/down asymmetry in poloidal intensity variation that MHD modes alone cannot generate. The contributions of MHD modes in plasma edge regions are too small to explain the magnitude of observed EOMP perturbations. At least two-thirds, possibly nearly all, of magnetic perturbations in a typical EOMP originate from sources other than MHD modes. An EOMP has a unity toroidal harmonic number and a poloidal harmonic number close to a discharge's edge q-value. It produces little temperature fluctuations, except possibly in edge regions. The KLM class produces temperature fluctuations, mostly confined within the q=1 surface with an ideal-mode-like structure, but generates little external magnetic perturbations. The TM class conforms generally to expectations from MHD modes. We propose that current flowing in the Scrape-off-layer (SOL) plasma is a possible origin of EOMP's.

  6. The VLA Low Frequency Sky Survey Redux (VLSSr)

    NASA Astrophysics Data System (ADS)

    Peters, Wendy M.; Cotton, W. D.; Kassim, N. E.

    2014-01-01

    We present the Very Large Array (VLA) Low-frequency Sky Survey Redux (VLSSr), which covers the sky above declinations δ > -30 degrees at a frequency of 74 MHz with 75" resolution and an average RMS noise of 0.1 Jy/beam. The theoretical largest angular size imaged is 36', and there are approximately 95,000 cataloged sources. We have completely re-imaged all data from the original VLSS survey leading to improvements in a number of areas. These include the application of a more accurate primary beam correction which removes substantial radially dependent flux errors present in the VLSS, and smart-windowing to reduce the clean bias by half. We look ahead to the possibility of an expanded, "VLSS generation 2", made by piggybacking observations of the planned VLA Sky Survey (VLASS) using a proposed 24/7 commensal system, called the LOw Band Observatory (LOBO). Catalogs and images for the VLSSr are available at .

  7. Extremely low frequency magnetic field modulates the level of neurotransmitters.

    PubMed

    Chung, Yoon Hee; Lee, Young Joo; Lee, Ho Sung; Chung, Su Jin; Lim, Cheol Hee; Oh, Keon Woong; Sohn, Uy Dong; Park, Eon Sub; Jeong, Ji Hoon

    2015-01-01

    This study was aimed to observe that extremely low frequency magnetic field (ELF-MF) may be relevant to changes of major neurotransmitters in rat brain. After the exposure to ELF-MF (60 Hz, 2.0 mT) for 2 or 5 days, we measured the levels of biogenic amines and their metabolites, amino acid neurotransmitters and nitric oxide (NO) in the cortex, striatum, thalamus, cerebellum and hippocampus. The exposure of ELF-MF for 2 or 5 days produced significant differences in norepinephrine and vanillyl mandelic acid in the striatum, thalamus, cerebellum and hippocampus. Significant increases in the levels of serotonin and 5-hydroxyindoleacetic acid were also observed in the striatum, thalamus or hippocampus. ELF-MF significantly increased the concentration of dopamine in the thalamus. ELF-MF tended to increase the levels of amino acid neurotransmitters such as glutamine, glycine and γ -aminobutyric acid in the striatum and thalamus, whereas it decreased the levels in the cortex, cerebellum and hippocampus. ELF-MF significantly increased NO concentration in the striatum, thalamus and hippocampus. The present study has demonstrated that exposure to ELF-MFs may evoke the changes in the levels of biogenic amines, amino acid and NO in the brain although the extent and property vary with the brain areas. However, the mechanisms remain further to be characterized.

  8. Amplitude of Low-Frequency Fluctuations in Multiple-Frequency Bands in Acute Mild Traumatic Brain Injury.

    PubMed

    Zhan, Jie; Gao, Lei; Zhou, Fuqing; Bai, Lijun; Kuang, Hongmei; He, Laichang; Zeng, Xianjun; Gong, Honghan

    2016-01-01

    Functional disconnectivity during the resting state has been observed in mild traumatic brain injury (mTBI) patients during the acute stage. However, it remains largely unknown whether the abnormalities are related to specific frequency bands of the low-frequency oscillations (LFO). Here, we used the amplitude of low-frequency fluctuations (ALFF) to examine the amplitudes of LFO in different frequency bands (slow-5: 0.01-0.027 Hz; slow-4: 0.027-0.073 Hz; and typical: 0.01-0.08 Hz) in patients with acute mTBI. A total of 24 acute mTBI patients and 24 age-, sex-, and education-matched healthy controls participated in this study. In the typical band, acute mTBI patients showed lower standardized ALFF in the right middle frontal gyrus and higher standardized ALFF in the right lingual/fusiform gyrus and left middle occipital gyrus. Further analyses showed that the difference between groups was concentrated in a narrower (slow-4) frequency band. In the slow-5 band, mTBI patients only exhibited higher standardized ALFF in the occipital areas. No significant correlation between the mini-mental state examination score and the standardized ALFF value was found in any brain region in the three frequency bands. Finally, no significant interaction between frequency bands and groups was found in any brain region. We concluded that the abnormality of spontaneous brain activity in acute mTBI patients existed in the frontal lobe as well as in distributed brain regions associated with integrative, sensory, and emotional roles, and the abnormal spontaneous neuronal activity in different brain regions could be better detected by the slow-4 band. These findings might contribute to a better understanding of local neural psychopathology of acute mTBI. Future studies should take the frequency bands into account when measuring intrinsic brain activity of mTBI patients. PMID:26869907

  9. Mobilization of colloidal particles by low-frequency dynamic stress stimulation.

    PubMed

    Beckham, Richard E; Abdel-Fattah, Amr I; Roberts, Peter M; Ibrahim, Reem; Tarimala, Sowmitri

    2010-01-01

    Naturally occurring seismic events and artificially generated low-frequency (1 to 500 Hz) elastic waves have been observed to alter the production rates of oil and water wells, sometimes increasing and sometimes decreasing production, and to influence the turbidity of surface and well water. The decreases in production are of particular concern, especially when artificially generated elastic waves are applied as a method for enhanced oil recovery. The exact conditions that result in a decrease in production remain unknown. Although the underlying environment is certainly complex, the observed increase in water well turbidity after natural seismic events suggests the existence of a mechanism that can affect both the subsurface flow paths and the mobilization of in situ colloidal particles. This article explores the macroscopic and microscopic effects of low-frequency dynamic stress stimulations on the release of colloidal particles from an analog core representing an infinitesimal section along the propagation paths of an elastic wave. Experiments on a column packed with 1 mm borosilicate beads and loaded with polystyrene microparticles demonstrate that axial mechanical stress oscillations enhance the mobilization of captured microparticles. Increasing the amplitude of the oscillations increases the number of microparticles released and can also result in cyclical spikes in effluent microparticle concentration during stimulation. Under a prolonged period of stimulation, the cyclical effluent spikes coincided with fluctuations in the column pressure data and continued at a diminished level after stimulation. This behavior can be attributed to rearrangements of the beads in the column, resulting in possible changes in the void space and/or tortuosity of the packing. Optical microscopy observations of the beads during low-frequency oscillations reveal that individual beads rotate, thereby rubbing against each other and scraping away portions of the adsorbed

  10. Identification of Mining Blasts at Mid- to Far-regional Distances Using Low Frequency Seismic Signals

    NASA Astrophysics Data System (ADS)

    Hedlin, M. A. H.; Stump, B. W.; Pearson, D. C.; Yang, X.

    - This paper reports results from two recent monitoring experiments in Wyoming. Broadband seismic recordings of kiloton class delay-fired cast blasts and instantaneous calibration shots in the Black Thunder coal mine were made at four azimuths at ranges from 1° to 2°. The primary focus of this experiment was to observe and to explain low-frequency signals that can be seen at all azimuths and should routinely propagate above noise to mid-regional distances where most events will be recorded by International Monitoring System (IMS) stations.The recordings clearly demonstrate that large millisecond delay-fired cast blasts routinely produce seismic signals that have significant spectral modulations below 10Hz. These modulations are independent of time, the azimuth from the source and the orientation of the sensor. Low-frequency modulations below 5Hz are seen beyond 9°. The modulations are not due to resonance as they are not produced by the calibration shots. Linear elastic modeling of the blasts that is guided by mine-blast reports fails to reproduce the fine detail of these modulations but clearly indicates that the enhanced ``spectral roughness'' is due to long interrow delays and source finiteness. The mismatch between the data and the synthetics is likely due to source processes, such as nonlinear interactions between shots, that are poorly understood and to other effects, such as variations of shot time and yield from planned values, that are known to be omnipresent but cannot be described accurately. A variant of the Automated Time-Frequency Discriminant (Hedlin, 1998b), which uses low-frequency spectral modulations, effectively separates these events from the calibration shots.The experiment also provided evidence that kiloton class cast blasts consistently yield energetic 2-10 second surface waves. The surface waves are strongly dependent on azimuth but are seen beyond 9°. Physical modeling of these events indicates that the surface waves are due mainly to

  11. Mobilization of colloidal particles by low-frequency dynamic stress stimulation

    SciTech Connect

    Beckham, Richard Edward; Amr, Abdel - Fattah I; Peter, Roberts M; Reem, Ibrahim; Tarimala, Sowmitri

    2009-01-01

    Naturally occurring seismic events and artificially generated low-frequency (1 to 500 Hertz) elastic waves have been observed to alter the production rates of oil and water wells, sometimes increasing and sometimes decreasing production, and to influence the turbidity of surface and well water. The decreases in production are of particular concern - especially when artificially generated elastic waves are applied as a method for enhanced oil recovery. The exact conditions that result in a decrease in production remain unknown. While the underlying environment is certainly complex, the observed increase in water well turbidity after natural seismic events suggests the existence of a mechanism that can affect both the subsurface flow paths and mobilization of in-situ colloidal particles. This paper explores the macroscopic and microscopic effects of low-frequency dynamic stress stimulations on the release of colloidal particles from an analog core representing an infinitesimal section along the propagation paths of an elastic wave. Experiments on a column packed with 1-mm borosilicate beads and loaded with polystyrene microspheres demonstrate that axial mechanical stress oscillations enhance the mobilization of captured microspheres. Increasing the amplitude of the oscillations increases the number of microspheres released and can also result in cyclical spikes in effluent microsphere concentration during stimulation. Under a prolonged period of stimulation, the cyclical effluent spikes coincided with fluctuations in the column pressure data, and continue at a diminished level after stimulation. This behavior can be attributed to rearrangements of the beads in the column, resulting in possible changes to the void space and/or tortuosity of the packing. Optical microscopy observations of the beads during low frequency oscillations reveal that individual beads rotate, thereby rubbing against each other and scraping away portions of the adsorbed microspheres. These

  12. Analysis of waves in the plasma guided by a periodical vane-type slow wave structure

    SciTech Connect

    Wu, T.J.; Kou, C.S.

    2005-10-01

    In this study, the dispersion relation has been derived to characterize the propagation of the waves in the plasma guided by a periodical vane-type slow wave structure. The plasma is confined by a quartz plate. Results indicate that there are two different waves in this structure. One is the plasma mode that originates from the plasma surface wave propagating along the interface between the plasma and the quartz plate, and the other is the guide mode that originally travels along the vane-type slow wave structure. In contrast to its original slow wave characteristics, the guide mode becomes a fast wave in the low-frequency portion of the passband, and there exists a cut-off frequency for the guide mode. The vane-type guiding structure has been shown to limit the upper frequency of the passband of the plasma mode, compared with that of the plasma surface wave. In addition, the passband of the plasma mode increases with the plasma density while it becomes narrower for the guide mode. The influences of the parameters of the guiding structure and plasma density on the propagation of waves are also presented.

  13. Experimental observation of stimulated low-frequency Raman scattering in water suspensions of silver and gold nanoparticles.

    PubMed

    Tcherniega, N V; Zemskov, K I; Savranskii, V V; Kudryavtseva, A D; Olenin, A Y; Lisichkin, G V

    2013-03-15

    In this Letter we report on experimental observation of stimulated low-frequency Raman scattering (SLFRS) in gold and silver nanoparticle suspensions excited by 20 ns ruby laser pulses, SLFRS propagated in forward and backward directions with a maximum conversion efficiency up to 20%. Frequency shift for silver nanoparticle suspension was found to be 0.33 THz and for gold nanoparticle suspension 0.435 THz. This type of stimulated scattering of light can be used as an effective source of biharmonic pumping for solving a large number of practical tasks.

  14. Low-frequency resonances of the refractive index in weakly ionized plasma with an admixture of dust

    SciTech Connect

    Prudskikh, V. V.

    2013-12-15

    The propagation of low-frequency electromagnetic waves along the magnetic field in weakly ionized plasma with an admixture of dust is studied in the framework of the Hall magnetohydrodynamics. Explicit expressions for the coefficients of magnetic field diffusion in plasma are derived. The resonance of the refractive index is found to occur for either right- or left-hand polarized waves. A quantitative criterion is obtained that allows one to determine the polarization of waves that experience resonance at given plasma parameters. The physical mechanism of the resonance is discussed, and the obtained results are compared with the available literature data.

  15. Low-frequency intraseasonal variability in a zonally symmetric aquaplanet model

    NASA Astrophysics Data System (ADS)

    Das, Surajit; Sengupta, Debasis; Chakraborty, A.; Sukhatme, Jai; Murtugudde, Raghu

    2016-04-01

    We use the aquaplanet version of the community atmospheric model, with perpetual spring equinox forcing and zonally symmetric sea surface temperature (SST), to study tropical intraseasonal oscillations (ISOs). In the first two experiments, we specify zonally symmetric SST profiles that mimic observed climatological July and January SSTs as surface boundary conditions. In the January SST simulation, we find a zonal wavenumber 1 mode with dominant period of 60 days, moving east at about 6 m s-1. This mode, which resembles the Madden-Julian oscillation (MJO), is absent in the July SST case, although convectively coupled Kelvin waves are prominent in both experiments. To further investigate the influence of tropical SST on ISO and convectively coupled equatorial waves, we conduct experiments with idealised symmetric SST profiles having different widths of warm ocean centered at the equator. In the narrowest SST experiment, the variance of moist activity is predominantly in weather-scale Kelvin waves. When the latitudinal extent of warm SST is comparable to or larger than the equatorial Rossby radius, we find a dominant low frequency (50-80 days) eastward mode that resembles the MJO, as in the January SST experiment. We also find westward propagating waves with intraseasonal (30-120 days) periods and zonal wavenumber 1-3; the structure of these signals projects onto equatorially trapped Rossby waves with meridional mode numbers 1, 3 and 5, associated with convection that is symmetric about the equator. In addition, the model generates 30-80 days westward moving signals with zonal wavenumber 4-7, particularly in the narrow SST experiment. Although these waves are seen in the wavenumber-frequency spectra in the equatorial region, they have largest amplitude in the middle and high latitudes. Thus, our study shows that wider, meridionally symmetric SST profiles support a strong MJO-like eastward propagation, and even in an aquaplanet setting, westward propagating Rossby

  16. Plasma filamentation and shock wave enhancement in microwave rockets by combining low-frequency microwaves with external magnetic field

    NASA Astrophysics Data System (ADS)

    Takahashi, Masayuki; Ohnishi, Naofumi

    2016-08-01

    A filamentary plasma is reproduced based on a fully kinetic model of electron and ion transports coupled with electromagnetic wave propagation. The discharge plasma transits from discrete to diffusive patterns at a 110-GHz breakdown, with decrease in the ambient pressure, because of the rapid electron diffusion that occurs during an increase in the propagation speed of the ionization front. A discrete plasma is obtained at low pressures when a low-frequency microwave is irradiated because the ionization process becomes more dominant than the electron diffusion, when the electrons are effectively heated by the low-frequency microwave. The propagation speed of the plasma increases with decrease in the incident microwave frequency because of the higher ionization frequency and faster plasma diffusion resulting from the increase in the energy-absorption rate. An external magnetic field is applied to the breakdown volume, which induces plasma filamentation at lower pressures because the electron diffusion is suppressed by the magnetic field. The thrust performance of a microwave rocket is improved by the magnetic fields corresponding to the electron cyclotron resonance (ECR) and its higher-harmonic heating, because slower propagation of the ionization front and larger energy-absorption rates are obtained at lower pressures. It would be advantageous if the fundamental mode of ECR heating is coupled with a lower frequency microwave instead of combining the higher-harmonic ECR heating with the higher frequency microwave. This can improve the thrust performance with smaller magnetic fields even if the propagation speed increases because of the decrease in the incident microwave frequency.

  17. Linking Sleep Slow Oscillations with consciousness theories: new vistas on Slow Wave Sleep unconsciousness.

    PubMed

    Gemignani, Angelo; Menicucci, Danilo; Laurino, Marco; Piarulli, Andrea; Mastorci, Francesca; Sebastiani, Laura; Allegrini, Paolo

    2015-01-01

    We review current models of consciousness in the context of wakefulness and sleep. We show that recent results on Slow Wave Sleep, including our own works, naturally fit within consciousness models. In particular, Sleep Slow Oscillations, namely low-frequency (<1Hz) oscillations, contain electrophysiological properties (up and down states) able to elicit and quench neural integration during Slow Wave Sleep. The physiological unconsciousness related to the Sleep Slow Oscillation derives from the interplay between spontaneous or evoked wake-like activities (up states) and half-a-second's electrical silences (down states). Sleep Slow Oscillation induces unconsciousness via the formation of parallel and segregated neural activities. PMID:26742667

  18. Intense low-frequency chorus waves observed by Van Allen Probes: Fine structures and potential effect on radiation belt electrons

    NASA Astrophysics Data System (ADS)

    Gao, Zhonglei; Su, Zhenpeng; Zhu, Hui; Xiao, Fuliang; Zheng, Huinan; Wang, Yuming; Shen, Chao; Wang, Shui

    2016-02-01

    Frequency distribution is a vital factor in determining the contribution of whistler mode chorus to radiation belt electron dynamics. Chorus is usually considered to occur in the frequency range 0.1-0.8fce_eq (with the equatorial electron gyrofrequency fce_eq). We here report an event of intense low-frequency chorus with nearly half of wave power distributed below 0.1fce_eq observed by Van Allen Probe A on 27 August 2014. This emission propagated quasi-parallel to the magnetic field and exhibited hiss-like signatures most of the time. The low-frequency chorus can produce the rapid loss of low-energy (˜0.1 MeV) electrons, different from the normal chorus. For high-energy (≥0.5 MeV) electrons, the low-frequency chorus can yield comparable momentum diffusion to that of the normal chorus but much stronger (up to 2 orders of magnitude) pitch angle diffusion near the loss cone.

  19. Intense Low-frequency Chorus Waves Observed by Van Allen Probes: Fine Structures and Potential Effect on Radiation Belt Electrons

    NASA Astrophysics Data System (ADS)

    Gao, Z.; Su, Z.; Zhu, H.

    2015-12-01

    Whistler-mode chorus emission in the low-density plasmatrough contributes significantly to the radiation belt electron dynamics. Chorus was usually considered to occur in the frequency range 0.1-0.8 fce (with the equatorial electron gyrofrequency fce ). We here report an event of intense low-frequency chorus with nearly half of wave power distributed below 0.1 fce observed by the Van Allen Probes on 27 August 2014. This emission exhibited little discrete rising tones but mainly the hiss-like signatures, had the high ellipticity of ˜1 and propagated quasi-parallel to the magnetic field. Compared with the typical chorus, the low-frequency chorus can produce weaker (2 times at ~ MeV and even up to several orders of magnitude at ~0.1MeV) momentum diffusion of the near-equatorially trapped electrons, but much stronger (1-2 orders of magnitude) pitch-angle diffusion near the loss cone. The acceleration and particularly loss effect of such intense low-frequency chorus may need to be taken into account in future radiation belt models.

  20. Low frequency noise sources and mechanisms in semiconductor nanowire transistors

    NASA Astrophysics Data System (ADS)

    Delker, Collin James

    Semiconductor nanowires are attractive candidates for use in future high-speed electronics, transparent/flexible devices, and chemical sensors. Among other materials, III-V semiconductors have gained considerable interest for their high bulk mobility and low band gap, making them promising for high-speed nanoscale devices. However, nanowire devices also exhibit high levels of low-frequency noise due to their low band gap and high surface-to-volume ratio. The sources and mechanisms of this noise must be understood and controlled in order to realize practical applications of nanowire electronics. This work seeks to understand the underlying noise mechanisms of nanowire transistors in order discover ways to reduce noise levels. It also demonstrates how noise can provide a spectroscopy for analyzing device quality. Most traditional noise studies tend to apply standard MOSFET models to nanowire noise and transport, which lump together all possible independent noise sources in a nanowire, ignoring effects of the contacts or multiple gates, and could lead to misestimation of the noise figures for a device. This work demonstrates how noise in a nanowire transistor can stem from the channel, ungated access regions, metal- semiconductor contacts, and tunnel barriers, all independently adding to the total noise. Each source of noise can contribute and may dominate the overall noise behavior under certain bias regimes and temperatures, as demonstrated in this work through various device structures and measurements. For example, the contacts can influence noise even below the threshold voltage under certain conditions, emphasizing the need for high-quality metal-semiconductor interface technology.

  1. Low-frequency electrical response to microbial induced sulfide precipitation

    NASA Astrophysics Data System (ADS)

    Ntarlagiannis, Dimitrios; Williams, Kenneth Hurst; Slater, Lee; Hubbard, Susan

    2005-12-01

    We investigated the sensitivity of low-frequency electrical measurements to microbe-induced metal sulfide precipitation. Three identical sand-packed monitoring columns were used; a geochemical column, an electrical column and a control column. In the first experiment, continuous upward flow of nutrients and metals in solution was established in each column. Cells of Desulfovibrio vulgaris (D. vulgaris) were injected into the center of the geochemical and electrical columns. Geochemical sampling and post-experiment destructive analysis showed that microbial induced sulfate reduction led to metal precipitation on bacteria cells, forming motile biominerals. Precipitation initially occurred in the injection zone, followed by chemotactic migration of D. vulgaris and ultimate accumulation around the nutrient source at the column base. Results from this experiment conducted with metals show (1) polarization anomalies, up to 14 mrad, develop at the bacteria injection and final accumulation areas, (2) the onset of polarization increase occurs concurrently with the onset of lactate consumption, (3) polarization profiles are similar to calculated profiles of the rate of lactate consumption, and (4) temporal changes in polarization and conduction correlate with a geometrical rearrangement of metal-coated bacterial cells. In a second experiment, the same biogeochemical conditions were established except that no metals were added to the flow solution. Polarization anomalies were absent when the experiment was replicated without metals in solution. We therefore attribute the polarization increase observed in the first experiment to a metal-fluid interfacial mechanism that develops as metal sulfides precipitate onto microbial cells and form biominerals. Temporal changes in polarization and conductivity reflect changes in (1) the amount of metal-fluid interfacial area, and (2) the amount of electronic conduction resulting from microbial growth, chemotactic movement and final

  2. Giant Crab pulses at low frequency: statistics, scattering, polarization

    SciTech Connect

    Smirnova, T. V.

    2010-01-01

    We carried out observations of Crab giant pulses at frequency 112 MHz from 2005 till 2008 on the Large Phased Array of the Pushchino Radio Astronomy Observatory. The scattering of pulses observed in various series varies by a factor of 3: from 11 ms in November 2005 till 34 ms in September 2008. The cumulative probability distribution for the peak intensities of the giant pulses for each of these series shows that the distribution is stable and is a power law with a single slope (n = -2.3). This testifies to stability of the mechanism generating the giant pulses. The energy in the pulses is conserved; i.e., the increase in the pulse intensity is proportional to the decrease in the scattering. Refractive scintillations at low frequencies in measurements with large time separation lead to variations in the relative number of giant pulses exceeding a given amplitude, proportional to the ratio of the mean flux densities of the pulsar in the corresponding observational series. The maximum energy of the recorded giant pulses is 2.5x10{sup 7} Jy mus. Analysis of the giant pulses observed at other frequencies shows that the frequency dependence of the maximum energy of the giant pulses in the range of 23 MHz-9 GHz is a power-law with index -2.2+-0.2. We measured the rotation measure using GP which is RM (-47.5+-0.4) rad/m{sup 2}, and the degree of linear polarization for pulses with measured frequency modulation was 9% divide 17% for November 2005.

  3. Tremor entrainment by patterned low-frequency stimulation.

    PubMed

    Barnikol, Utako B; Popovych, Oleksandr V; Hauptmann, Christian; Sturm, Volker; Freund, Hans-Joachim; Tass, Peter A

    2008-10-13

    High-frequency test stimulation for tremor suppression is a standard procedure for functional target localization during deep brain stimulation. This method does not work in cases where tremor vanishes intraoperatively, for example, due to general anaesthesia or due to an insertional effect. To overcome this difficulty, we developed a stimulation technique that effectively evokes tremor in a well-defined and quantifiable manner. For this, we used patterned low-frequency stimulation (PLFS), i.e. brief high-frequency pulse trains administered at pulse rates similar to neurons' preferred burst frequency. Unlike periodic single-pulse stimulation, PLFS enables one to convey effective and considerably greater integral charge densities without violation of safety requirements. In a computational investigation of an oscillatory neuronal network temporarily rendered inactive, we found that PLFS evokes synchronized activity, phase locked to the stimulus. While a stronger increase in the amount of synchrony in the neuronal population requires higher stimulus intensities, the portion of synchronously active neurons nevertheless becomes strongly phase locked to PLFS already at weak stimulus intensities. The phase entrainment effect of PLFS turned out to be robust against variations in the stimulation frequency, whereas enhancement of synchrony required precisely tuned stimulation frequencies. We applied PLFS to a patient with spinocerebellar ataxia type 2 (SCA2) with pronounced tremor that disappeared intraoperatively under general anaesthesia. In accordance with our computational results, PLFS evoked tremor, phase locked to the stimulus. In particular, weak PLFS caused low-amplitude, but strongly phase-locked tremor. PLFS test stimulations provided the only functional information about target localization. Optimal target point selection was confirmed by excellent post-operative tremor suppression. PMID:18632457

  4. Low-frequency fluctuations in plasma magnetic fields

    SciTech Connect

    Cable, S.; Tajima, T.

    1992-02-01

    It is shown that even a non-magnetized plasma with temperature T sustains zero-frequency magnetic fluctuations in thermal equilibrium. Fluctuations in electric and magnetic fields, as well as in densities, are computed. Four cases are studied: a cold, gaseous, isotropic, non-magnetized plasma; a cold, gaseous plasma in a uniform magnetic field; a warm, gaseous plasma described by kinetic theory; and a degenerate electron plasma. For the simple gaseous plasma, the fluctuation strength of the magnetic field as a function of frequency and wavenumber is calculated with the aid of the fluctuation-dissipation theorem. This calculation is done for both collisional and collisionless plasmas. The magnetic field fluctuation spectrum of each plasma has a large zero-frequency peak. The peak is a Dirac {delta}-function in the collisionless plasma; it is broadened into a Lorentzian curve in the collisional plasma. The plasma causes a low frequency cutoff in the typical black-body radiation spectrum, and the energy under the discovered peak approximates the energy lost in this cutoff. When the imposed magnetic field is weak, the magnetic field were vector fluctuation spectra of the two lowest modes are independent of the strength of the imposed field. Further, these modes contain finite energy even when the imposed field is zero. It is the energy of these modes which forms the non-magnetized zero-frequency peak of the isotropic plasma. In deriving these results, a simple relationship between the dispersion relation and the fluctuation power spectrum of electromagnetic waves if found. The warm plasma is shown, by kinetic theory, to exhibit a zero-frequency peak in its magnetic field fluctuation spectrum as well. For the degenerate plasma, we find that electric field fluctuations and number density fluctuations vanish at zero frequency; however, the magnetic field power spectrum diverges at zero frequency.

  5. Natural very-low-frequency sferics and headache

    NASA Astrophysics Data System (ADS)

    Vaitl, D.; Propson, N.; Stark, R.; Schienle, A.

      Very-low-frequency (VLF) atmospherics or sferics are pulse-shaped alternating electric and magnetic fields which originate from atmospheric discharges (lightning). The objective of the study was threefold: (i) to analyse numerous parameters characterizing the sferics activity with regard to their suitability for field studies, (ii) to identify meteorological processes related to the sferics activity and (iii) to investigate the possible association of sferics with pain processes in patients suffering from migraine- and tension-type headaches. Over a period of 6 months (July through December) the sferics activity in the area of Giessen (Germany) was recorded. Three sferics parameters were chosen. The number of sferics impulses per day, the variability of the impulse rate during a day and the variability in comparison to the preceding day were correlated with weather processes (thunderstorm, temperature, vapour pressure, barometric pressure, humidity, wind velocity, warm sector). Significant correlations were obtained during the summer months (July, August) but not during the autumn months (October, November, December). During autumn, however, the sferics activity was correlated with the occurrence of migraine-type headaches (r=0.33, P<0.01) recorded by 37 women who had filled out a headache diary over a period of 6 months (July-December). While the thunderstorm activity was very intense during July and August, no relationship between sferics and migraine was found. In summer, tension-type headaches were associated with meteorological parameters such as temperature (r=0.42, P<0.01) and vapour pressure (r=0.28, P<0.05). Although the sferics activity can explain a small percentage of the variation in migraine occurrence, a direct influence was more likely exerted by visible or otherwise perceptible weather conditions (thunderstorms, humidity, vapour pressure, warm sector, etc.) than by the sferics activity itself.

  6. Natural very-low-frequency sferics and headache.

    PubMed

    Vaitl, D; Propson, N; Stark, R; Schienle, A

    2001-09-01

    Very-low-frequency (VLF) atmospherics or sferics are pulse-shaped alternating electric and magnetic fields which originate from atmospheric discharges (lightning). The objective of the study was threefold: (i) to analyse numerous parameters characterizing the sferics activity with regard to their suitability for field studies, (ii) to identify meteorological processes related to the sferics activity and (iii) to investigate the possible association of sferics with pain processes in patients suffering from migraine- and tension-type headaches. Over a period of 6 months (July through December) the sferics activity in the area of Giessen (Germany) was recorded. Three sferics parameters were chosen. The number of sferics impulses per day, the variability of the impulse rate during a day and the variability in comparison to the preceding day were correlated with weather processes (thunderstorm, temperature, vapour pressure, barometric pressure, humidity, wind velocity, warm sector). Significant correlations were obtained during the summer months (July, August) but not during the autumn months (October, November, December). During autumn, however, the sferics activity was correlated with the occurrence of migraine-type headaches (r=0.33, P<0.01) recorded by 37 women who had filled out a headache diary over a period of 6 months (July-December). While the thunderstorm activity was very intense during July and August, no relationship between sferics and migraine was found. In summer, tension-type headaches were associated with meteorological parameters such as temperature (r=0.42, P<0.01) and vapour pressure (r=0.28, P<0.05). Although the sferics activity can explain a small percentage of the variation in migraine occurrence, a direct influence was more likely exerted by visible or otherwise perceptible weather conditions (thunderstorms, humidity, vapour pressure, warm sector, etc.) than by the sferics activity itself. PMID:11594631

  7. Natural very-low-frequency sferics and headache.

    PubMed

    Vaitl, D; Propson, N; Stark, R; Schienle, A

    2001-09-01

    Very-low-frequency (VLF) atmospherics or sferics are pulse-shaped alternating electric and magnetic fields which originate from atmospheric discharges (lightning). The objective of the study was threefold: (i) to analyse numerous parameters characterizing the sferics activity with regard to their suitability for field studies, (ii) to identify meteorological processes related to the sferics activity and (iii) to investigate the possible association of sferics with pain processes in patients suffering from migraine- and tension-type headaches. Over a period of 6 months (July through December) the sferics activity in the area of Giessen (Germany) was recorded. Three sferics parameters were chosen. The number of sferics impulses per day, the variability of the impulse rate during a day and the variability in comparison to the preceding day were correlated with weather processes (thunderstorm, temperature, vapour pressure, barometric pressure, humidity, wind velocity, warm sector). Significant correlations were obtained during the summer months (July, August) but not during the autumn months (October, November, December). During autumn, however, the sferics activity was correlated with the occurrence of migraine-type headaches (r=0.33, P<0.01) recorded by 37 women who had filled out a headache diary over a period of 6 months (July-December). While the thunderstorm activity was very intense during July and August, no relationship between sferics and migraine was found. In summer, tension-type headaches were associated with meteorological parameters such as temperature (r=0.42, P<0.01) and vapour pressure (r=0.28, P<0.05). Although the sferics activity can explain a small percentage of the variation in migraine occurrence, a direct influence was more likely exerted by visible or otherwise perceptible weather conditions (thunderstorms, humidity, vapour pressure, warm sector, etc.) than by the sferics activity itself.

  8. Characterization of Indoor Extremely Low Frequency and Low Frequency Electromagnetic Fields in the INMA-Granada Cohort

    PubMed Central

    Calvente, Irene; Dávila-Arias, Cristina; Ocón-Hernández, Olga; Pérez-Lobato, Rocío; Ramos, Rosa; Artacho-Cordón, Francisco; Olea, Nicolás; Núñez, María Isabel; Fernández, Mariana F.

    2014-01-01

    Objective To characterize the exposure to electric fields and magnetic fields of non-ionizing radiation in the electromagnetic spectrum (15 Hz to 100 kHz) in the dwellings of children from the Spanish Environment and Childhood-“INMA” population-based birth cohort. Methodology The study sample was drawn from the INMA-Granada cohort. Out of 300 boys participating in the 9–10 year follow-up, 123 families agreed to the exposure assessment at home and completed a specific ad hoc questionnaire gathering information on sources of non-ionizing radiation electric and magnetic fields inside the homes and on patterns of use. Long-term indoor measurements were carried out in the living room and bedroom. Results Survey data showed a low exposure in the children's homes according to reference levels of the International Commission on Non-Ionizing Radiation Protection but with large differences among homes in mean and maximum values. Daytime electrostatic and magnetic fields were below the quantification limit in 78.6% (92 dwellings) and 92.3% (108 dwellings) of houses, with an arithmetic mean value (± standard deviation) of 7.31±9.32 V/m and 162.30±91.16 nT, respectively. Mean magnetic field values were 1.6 lower during the night than the day. Nocturnal electrostatic values were not measured. Exposure levels were influenced by the area of residence (higher values in urban/semi-urban versus rural areas), type of dwelling, age of dwelling, floor of the dwelling, and season. Conclusion Given the greater sensitivity to extremely low-frequency electromagnetic fields of children and following the precautionary principle, preventive measures are warranted to reduce their exposure. PMID:25192253

  9. Low-Frequency Earthquakes in Cascadia Using Texan Array

    NASA Astrophysics Data System (ADS)

    Sweet, J. R.; Creager, K. C.; Vidale, J. E.; Ghosh, A.; Nichols, M. L.; Pratt, T. L.

    2008-12-01

    Low-frequency earthquakes (LFEs) were first reported in Japan and have been observed to occur coincidently with non-volcanic tremor in both space and time. Compared to similarly-sized ordinary earthquakes, LFEs are deficient in frequencies above 5 Hz. The frequency spectrum of LFEs mirrors the spectrum of tremor. Indeed Shelly et al. (2006, 2007, Nature) have suggested that tremor is simply the superposition of many individual LFEs. Accordingly, LFEs have been used to constrain the location of tremor. In Japan, LFEs are routinely identified by their S-waves, while their P-waves are typically below noise levels. In March 2008 we deployed a 1km aperture array on the Olympic Peninsula of Washington State that recorded a small tremor swarm prior to the main episodic tremor and slip event in May. Our array consisted of approximately 80 geophones paired with Texan recorders and was laid out on a 100m spaced grid. Initial analysis of one hour of data reveals many LFE-like events with similar spectra to locally observed tremor. Unlike LFEs in Japan, P-waves are clearly seen on many individual stations. Using a clear LFE as a template event, nearly 100 matching events have been found with S minus P times that differ by less than a few hundredths of a second from event to event suggesting that they are all within a few hundred meters of each other. Preliminary locations of this cluster indicate that the LFEs are near the plate interface east of our array. For many of the LFEs, stacks of the P-wave are very similar to stacks of the S-wave, suggesting that these stacks are reasonably good approximations of source time functions. These source time functions vary in complexity from one LFE to another. Synthetic waveform modeling suggests a source focal mechanism consistent with thrust faulting on the plate interface. The location and focal mechanism of these LFEs support the notion that tremor is associated with slip on the plate interface. This LFE cluster provides a promising

  10. A Sub-Hertz, Low-Frequency Vibration Isolation Platform

    NASA Technical Reports Server (NTRS)

    Ortiz, Gerardo, G.; Farr, William H.; Sannibale, Virginio

    2011-01-01

    One of the major technical problems deep-space optical communication (DSOC) systems need to solve is the isolation of the optical terminal from vibrations produced by the spacecraft navigational control system and by the moving parts of onboard instruments. Even under these vibration perturbations, the DSOC transceivers (telescopes) need to be pointed l000 fs of times more accurately than an RF communication system (parabolic antennas). Mechanical resonators have been extensively used to provide vibration isolation for groundbased, airborne, and spaceborne payloads. The effectiveness of these isolation systems is determined mainly by the ability of designing a mechanical oscillator with the lowest possible resonant frequency. The Low-Frequency Vibration Isolation Platform (LFVIP), developed during this effort, aims to reduce the resonant frequency of the mechanical oscillators into the sub-Hertz region in order to maximize the passive isolation afforded by the 40 dB/decade roll-off response of the resonator. The LFVIP also provides tip/tilt functionality for acquisition and tracking of a beacon signal. An active control system is used for platform positioning and for dampening of the mechanical oscillator. The basic idea in the design of the isolation platform is to use a passive isolation strut with an approximately equal to 100-mHz resonance frequency. This will extend the isolation range to lower frequencies. The harmonic oscillator is a second-order lowpass filter for mechanical disturbances. The resonance quality depends on the dissipation mechanisms, which are mainly hysteretic because of the low resonant frequency and the absence of any viscous medium. The LFVIP system is configured using the well-established Stewart Platform, which consists of a top platform connected to a base with six extensible struts (see figure). The struts are attached to the base and to the platform via universal joints, which permit the extension and contraction of the struts. The

  11. Low Frequency Radio-wave System for subsurface investigation

    NASA Astrophysics Data System (ADS)

    Soldovieri, Francesco; Gennarelli, Gianluca; Kudelya, Anatoliy; Denisov, Alexander

    2015-04-01

    Low frequency radio-wave methods (RWM) allow subsurface investigations in terms of lithological structure characterization, detection of filtration flows of ground water, anthropogenic and natural cavities. In this contribution, we present a RWM that exploits two coils working at frequencies of few MHz as transmitting and receiving antennas. The basic principle of this inductive method is as follows. The primary alternating electromagnetic field radiated by the transmitting coil induces eddy currents in the subsurface mainly due to the conductivity anomalies. These eddy currents generate a secondary (scattered) magnetic field which overlaps to the incident magnetic field and is detected by the receiving coil. Despite the simple operation of the system, the complexity of the electromagnetic scattering phenomenon at hand must be properly modeled to achieve adequate performance. Therefore, an advanced data processing technique, belonging to the class of the inverse scattering approaches, has been developed by the authors in a full 3D geometry. The proposed method allows to deal with data collected on a scanning surface under a dipole inductive profiling (DIP) modality, where the transmitting/receiving coils are moved simultaneously with fixed offset (multi-bistatic configuration). The hardware, called Dipole Inductive Radio-wave System (DIRS), is composed by an electronic unit and transmitting and receiving loop antennas radiating at frequencies of few MHz (2-4 MHz), which are installed on theodolite supports. The compactness of DIRS and its robustness to external electromagnetic interference offers the possibility to perform geophysical research up to the depth of some tens of meters and under several types of ground and water surfaces, vegetation, and weather conditions. The light weight and small size of system (the single antenna with support weights about 5 kg and has a diameter of 0.5m) allows two operators to perform geophysical research without disturbing the

  12. Experimental investigation on the effects of normal stress on fracture propagation and slip instability

    NASA Astrophysics Data System (ADS)

    Ougier-Simonin, A.; Zhu, W.

    2011-12-01

    Recent discoveries of slow slip phenomena, from low frequency earthquakes to episodic tremor and slip events, create new challenges to our understanding of source processes. High pore pressure is often cited as the likely cause for these slow slip events. The working hypothesis is that pore pressure excess reduces effective normal stress on the fault plane thus generates slip instability. However, experimental evidence on whether and how different slip instabilities results from high pore pressure is still missing. In this study, we conducted triaxial deformation experiments to investigate how the reduction of effective normal stress affects slip instability and fracture propagation. Porous sedimentary rocks were deformed at constant strain rates and under fully drained conditions. We designed loading configurations so that brittle failure and frictional instability in samples deformed under decreasing effective stress can be compared to those under increasing effective stress. Our experimental results indicate that, 1) effects of loading configuration and strain rate on the brittle strength is negligible; 2) the slip distance during fracture nucleation is sensitive to strain rate and loading path; 3) shear fracture energy released during fracture propagation is a function of slip. However, fracture propagation in samples deformed under decreasing effective normal stress tend to be more stable, which bears similar characteristics with slow slip events. The observed slip instability under decreasing normal stress can be modeled using a theoretical framework proposed by Dieterich and Linker [1992]. Quantitative microstructural analysis was performed on samples undergone different stages of failure to characterize the progressive damage during fracture propagation.

  13. Frequency-dependent moment release of very low frequency earthquakes in the Cascadia subduction zone

    NASA Astrophysics Data System (ADS)

    Takeo, A.; Houston, H.

    2014-12-01

    Episodic tremor and slip (ETS) has been observed in Cascadia subduction zone at two different time scales: tremor at a high-frequency range of 2-8 Hz and slow slip events at a geodetic time-scale of days-months. The intermediate time scale is needed to understand the source spectrum of slow earthquakes. Ghosh et al. (2014, IRIS abs) recently reported the presence of very low frequency earthquakes (VLFEs) in Cascadia. In southwest Japan, VLFEs are usually observed at a period range around 20-50 s, and coincide with tremors (e.g., Ito et al. 2007). In this study, we analyzed VLFEs in and around the Olympic Peninsula to confirm their presence and estimate their moment release. We first detected VLFE events by using broadband seismograms with a band-pass filter of 20-50 s. The preliminary result shows that there are at least 16 VLFE events with moment magnitudes of 3.2-3.7 during the M6.8 2010 ETS. The focal mechanisms are consistent with the thrust earthquakes at the subducting plate interface. To detect signals of VLFEs below noise level, we further stacked long-period waveforms at the peak timings of tremor amplitudes for tremors within a 10-15 km radius by using tremor catalogs in 2006-2010, and estimated the focal mechanisms for each tremor source region as done in southwest Japan (Takeo et al. 2010 GRL). As a result, VLFEs could be detected for almost the entire tremor source region at a period range of 20-50 s with average moment magnitudes in each 5-min tremor window of 2.4-2.8. Although the region is limited, we could also detect VLFEs at a period range of 50-100 s with average moment magnitudes of 3.0-3.2. The moment release at 50-100 s is 4-8 times larger than that at 20-50 s, roughly consistent with an omega-squared spectral model. Further study including tremor, slow slip events and characteristic activities, such as rapid tremor reversal and tremor streaks, will reveal the source spectrum of slow earthquakes in a broader time scale from 0.1 s to days.

  14. Low-frequency connectivity is associated with mild traumatic brain injury

    PubMed Central

    Dunkley, B.T.; Da Costa, L.; Bethune, A.; Jetly, R.; Pang, E.W.; Taylor, M.J.; Doesburg, S.M.

    2015-01-01

    Mild traumatic brain injury (mTBI) occurs from a closed-head impact. Often referred to as concussion, about 20% of cases complain of secondary psychological sequelae, such as disorders of attention and memory. Known as post-concussive symptoms (PCS), these problems can severely disrupt the patient's quality of life. Changes in local spectral power, particularly low-frequency amplitude increases and/or peak alpha slowing have been reported in mTBI, but large-scale connectivity metrics based on inter-regional amplitude correlations relevant for integration and segregation in functional brain networks, and their association with disorders in cognition and behaviour, remain relatively unexplored. Here, we used non-invasive neuroimaging with magnetoencephalography to examine functional connectivity in a resting-state protocol in a group with mTBI (n = 20), and a control group (n = 21). We observed a trend for atypical slow-wave power changes in subcortical, temporal and parietal regions in mTBI, as well as significant long-range increases in amplitude envelope correlations among deep-source, temporal, and frontal regions in the delta, theta, and alpha bands. Subsequently, we conducted an exploratory analysis of patterns of connectivity most associated with variability in secondary symptoms of mTBI, including inattention, anxiety, and depression. Differential patterns of altered resting state neurophysiological network connectivity were found across frequency bands. This indicated that multiple network and frequency specific alterations in large scale brain connectivity may contribute to overlapping cognitive sequelae in mTBI. In conclusion, we show that local spectral power content can be supplemented with measures of correlations in amplitude to define general networks that are atypical in mTBI, and suggest that certain cognitive difficulties are mediated by disturbances in a variety of alterations in network interactions which are differentially expressed across

  15. Monitoring the Low Frequency Sky with the LWA1 and the Prototype All-Sky Imager

    NASA Astrophysics Data System (ADS)

    Obenberger, Kenneth Steven; LWA Collaboration

    2015-01-01

    We present findings from the Prototype All-Sky Imager (PASI), a backend correlator of the first station of the Long Wavelength Array (LWA1). PASI cross-correlates a live stream of all 260 dual-polarization dipole antennas of the LWA1, creates all-sky images, and uploads them to the LWA-TV website in near real-time. PASI has recorded over 14,000 hours of all-sky images at frequencies between 10 and 88 MHz. These data have resulted in the discovery of radio emission from large meteors (Fireballs), and has been used to set improved limits on slow transients at 38, 52, and 74 MHz. PASI is also being used to characterize how the ionosphere affects low frequency transient astronomy. Construction of the LWA has been supported by the Office of Naval Research under Contract N00014-07-C-0147. Support for operations and continuing development of the LWA1 is provided by the National Science Foundation under grants AST-1139963 and AST-1139974 of the University Radio Observatory program.

  16. Empirical mode decomposition: a method to reduce low frequency interferences from surface electroenterogram.

    PubMed

    Ye, Y; Garcia-Casado, J; Martinez-de-Juan, J L; Ponce, J L

    2007-06-01

    The surface electroenterogram (EEnG) is a non-invasive method of studying myoelectrical bowel activity. However, surface EEnG recordings are contaminated by cardiac activity, respiratory and motion artifacts, and other sources of interference. The aim of this work is to remove the respiration artifact and the very low frequency components from surface EEnG by means of empirical mode decomposition (EMD). Eleven recording sessions were carried out on canine model. Several parameters were calculated before and after the application of the method: signal-to-interference ratio (S/I ratio) and the attenuation level of the signal and of interference. The results show that the S/I ratio was significantly higher after the application of the method (3.68+/-5.54 dB vs. 10.45+/-3.65 dB), the attenuation level of signal and of interference is -0.49+/-0.80 dB versus -7.26+/-5.42 dB, respectively. Therefore, EMD could be a useful aid in identifying the intestinal slow wave and in removing interferences from EEnG recordings.

  17. Maximization of the effective impulse delivered by a high-frequency/low-frequency planetary drill tool.

    PubMed

    Harkness, Patrick; Lucas, Margaret; Cardoni, Andrea

    2011-11-01

    Ultrasonic tools are used for a variety of cutting applications in surgery and the food industry, but when they are applied to harder materials, such as rock, their cutting performance declines because of the low effective impulse delivered by each vibration cycle. To overcome this problem, a technique known as high-frequency/low-frequency (or alternatively, ultrasonic/sonic) drilling is employed. In this approach, an ultrasonic step-horn is used to deliver an impulse to a free mass which subsequently moves toward a drilling bit, delivering the impulse on contact. The free mass then rebounds to complete the cycle. The horn has time between impacts to build significant vibration amplitude and thus delivers a much larger impulse to the free mass than could be delivered if it were applied directly to the target. To maximize the impulse delivered to the target by the cutting bit, both the momentum transfer from the ultrasonic horn to the free mass and the dynamics of the horn/free mass/cutting bit stack must be optimized. This paper uses finite element techniques to optimize the ultrasonic horns and numerical propagation of the stack dynamics to maximize the delivered effective impulse, validated in both cases by extensive experimental analysis.

  18. Simulation study of the role of ion kinetics in low-frequency wave train evolution

    NASA Technical Reports Server (NTRS)

    Vasquez, Bernard J.

    1995-01-01

    The evolution of uniform, parallel propagating, low-frequency (less than or approx. ion cyclotron) wave trains is followed with a one-dimensional hybrid numerical code with fluid electrons and particle ions. We show that moderate amplitude (delta B/B less than 1/2) wave trains give instabilities and saturated states which differ completely from pure fluid evolution. This is most clearly seen when beta greater than 1 and instability exists for wavenumbers both below and above the wavenumber of an inital, left-handed wave train or pump wave. For corresponding parameters a fluid theory gives only a narrow range of instability above the pump wavenumber where decay and beat instabilities can occur. in simulations wave energy inverse cascades to smaller wavenumbers and into a greater number of forward than backward going waves. In fluids energy by decay goes mostly to backward ones of smaller wavenumber, and energy by beat goes mostly to forward ones of larger wavenumber. Neither fluid instability explains simulation results. The instability is saturated by thermalizing ions and sometimes exciting small wavenumber electrostatic or acoustic modes. In contrast, saturation in fluids first occurs by generating the harmonics of the growing linear modes. Harmonic generation is mostly absent in simulations. Simulations are carried out to long times and mostly reach a limit beyond which no further significant evolution can occur. Application to Alfvenic fluctuations in the solar wind is discussed.

  19. Radial evolution of the high/low frequency breakpoint in magnetic field spectra

    NASA Technical Reports Server (NTRS)

    Feynman, J.; Ruzmaikin, A.; Smith, E. J.

    1995-01-01

    The spectra of magnetic field variations in the solar wind show different behavior in two frequency regions; a high frequency region in which the spectral exponent is about -5/3 and a low frequency region in which it is typically -1. The two types of variations must arise from different processes and a clue to the relationship between the spectral regions lies in understanding the behavior of the breakpoint between the spectral regions. Studies of the average behavior of spectra have shown that the break point occurs at about 3.5 hours at 1 AU. It is also known that, on average, the breakpoint occurs at lower frequencies with larger heliocentric distances. Ideally however, instead of the average properties of the spectra, we would like to know how the breakpoint evolves in particular samples of the solar wind as they propagate to larger heliocentric distances. In the study reported here we take advantage of the fact that, in 1974, Pioneer 10 (4.4 AU) and Pioneer 11 (5.6 AU) were close to being co-aligned and being aligned with the Earth. Solar wind observed at Earth can be closely matched with solar wind later observed at P10 and P11. We here compare the breakpoint observed at Earth with that observed at Pioneers 10 and 11 for matched samples of the wind.

  20. Low-frequency sound transmission through a gas-liquid interface.

    PubMed

    Godin, Oleg A

    2008-04-01

    Typically, sound speed in gases is smaller and mass density is much smaller than in liquids, resulting in a very strong acoustic impedance contrast at a gas-liquid interface. Sound transmission through a boundary with a strong impedance contrast is normally very weak. This paper studies the power output of localized sound sources and acoustic power fluxes through a plane gas-liquid interface in a layered medium. It is shown that, for low-frequency sound, a phenomenon of anomalous transparency can occur where most of the acoustic power generated by a source in a liquid half-space can be radiated into a gas half-space. The main physical mechanism responsible for anomalous transparency is found to be an acoustic power transfer by inhomogeneous (evanescent) waves in the plane-wave decomposition of the acoustic field in the liquid. The effects of a liquid's stratification and of guided sound propagation in the liquid on the anomalous transparency of the gas-liquid interface are considered. Geophysical and biological implications of anomalous transparency of water-air interface to infrasound are indicated.

  1. The Cubesat Radio Experiment (CURE) and Beyond: Cubesat-based Low Frequency Radio Interferometry

    NASA Astrophysics Data System (ADS)

    Saint-Hilaire, P.; Sundkvist, D. J.; Martinez Oliveros, J. C.; Sample, J. G.; Pulupa, M.; Maruca, B.; Bale, S. D.; Bonnell, J. W.; Mozer, F.; Hurford, G. J.

    2014-12-01

    We have proposed a 3U cubesat, to carry a low-frequency radio receiver into low-Earth orbit to study solar radio bursts induced by solar flares and Coronal Mass Ejections. Because of the reflective properties of the Earth's ionosphere, observations of radio waves around and below 10 MHz must be made from space. The measurements will allow continuous tracking of radio bursts and associated CMEs through the inner heliosphere. These observations are important since such events are the main cause for space weather disturbances. Data products from the mission will primarily be spectra and waveforms of solar radio type II and III bursts, and the direction to the radio source as it propagates through the inner heliosphere. These data products will be available to the community through an automated pipeline nominally within a few hours of downlink. Additional science data products will be sizes of radio sources obtained via lunar occultations, and local ionospheric plasma density and electron temperature. As a first cubesat with a scientific radio instrument at these frequencies, this project is also intended as a path-finder: the instrument and sub-systems can immediately be duplicated in other cubesats, with the goal of providing the first radio interferometric measurements below the ionospheric cutoff.

  2. Low-frequency wiggler modes in the free-electron laser with a dusty magnetoplasma medium

    NASA Astrophysics Data System (ADS)

    Jafari, S.

    2015-07-01

    An advanced incremental scheme for generating tunable coherent radiation in a free-electron laser has been presented: the basic concept is the use of a relativistic electron beam propagating through a magnetized dusty plasma channel where dust helicon, dust Alfven and coupled dust cyclotron-Alfven waves can play a role as a low-frequency wiggler, triggering coherent emissions. The wiggler wavelength at the sub-mm level allows one to reach the wavelength range from a few nm down to a few Å with moderately relativistic electrons of kinetic energies of a few tens/hundreds of MeV. The laser gain and the effects of beam self-electric and self-magnetic fields on the gain have been estimated and compared with findings of the helical magnetic and electromagnetic wigglers in vacuum. To study the chaotic regions of the electron motion in the dusty plasma wave wiggler, a time independent Hamiltonian has been obtained. The Poincare surface of a section map has been used numerically to analyze the nonintegrable system where chaotic regions in phase-space emerge. This concept opens a path toward a new generation of synchrotron sources based on compact plasma structures.

  3. Experimental verification of enhanced sound transmission from water to air at low frequencies.

    PubMed

    Calvo, David C; Nicholas, Michael; Orris, Gregory J

    2013-11-01

    Laboratory measurements of enhanced sound transmission from water to air at low frequencies are presented. The pressure at a monitoring hydrophone is found to decrease for shallow source depths in agreement with the classical theory of a monopole source in proximity to a pressure release interface. On the other hand, for source depths below 1/10 of an acoustic wavelength in water, the radiation pattern in the air measured by two microphones becomes progressively omnidirectional in contrast to the classical geometrical acoustics picture in which sound is contained within a cone of 13.4° half angle. The measured directivities agree with wavenumber integration results for a point source over a range of frequencies and source depths. The wider radiation pattern owes itself to the conversion of evanescent waves in the water into propagating waves in the air that fill the angular space outside the cone. A ratio of pressure measurements made using an on-axis microphone and a near-axis hydrophone are also reported and compared with theory. Collectively, these pressure measurements are consistent with the theory of anomalous transparency of the water-air interface in which a large fraction of acoustic power emitted by a shallow source is radiated into the air.

  4. Low-frequency ultrawideband synthetic aperture radar: frequency subbanding for targets obscured by the ground

    NASA Astrophysics Data System (ADS)

    Happ, Lynn; Le, Francis; Ressler, Marc A.; Kappra, Karl A.

    1996-06-01

    The Army Research Laboratory (ARL) has been investigating the potential of ultra-wideband synthetic aperture radar (UWB SAR) technology to detect and classify targets concealed by subsurface targets and foliage. Our investigative approach is to collect high-quality precision data to support phenomenological investigations of electromagnetic wave propagation through dielectric media. These investigations, in turn, support the development of algorithms for automatic target recognition. In order to achieve these goals, ARL designed and built an impulse (very short pulse) radar to collect data at a variety of test sites to measure and analyze the responses from targets, clutter, and targets embedded in clutter. The UWB BoomSAR, mounted on a 150-foot-high mobile boom lift, collects the high-quality, precision data sets needed for understanding UWB SAR system requirements and foliage penetration and ground penetration phenomenology. The BoomSAR operates with over 1 gigahertz of bandwidth covering a spectrum from 40 MHz to 1 GHz and is fully polarimetric. This bandwidth contains low frequencies needed for ground penetration while also maintaining higher frequency coverage for high resolution imagery. This paper shows a GPEN target area from data collected at Yuma Proving Grounds, AZ in low- and high- frequency subbands.

  5. Low Frequency Phased Array Techniques for Crack Detection in Cast Austenitic Piping Welds: A Feasibility Study

    SciTech Connect

    Anderson, Michael T.; Cumblidge, Stephen E.; Doctor, Steven R.

    2007-01-01

    Studies conducted at the Pacific Northwest National Laboratory (PNNL) in Richland, Washington have focused on developing and evaluating the reliability of nondestructive testing (NDT) approaches for coarse-grained stainless steel reactor components. The objective of this work is to provide information to the United States Nuclear Regulatory Commission (NRC) on the utility, effectiveness and limitation of NDT techniques as related to inservice testing of primary system piping components in pressurized water reactors. We examined cast stainless steel pipe specimens containing thermal and mechanical fatigue cracks located close to the weld roots and having inner and outer diameter surface geometrical conditions that simulate several water reactor primary piping configurations. In addition, segments of vintage centrifugally cast piping were examined to characterize the inherent acoustic noise and scattering caused by grain structures and to determine the consistency of ultrasonic responses when propagating through differing microstructures. Advanced ultrasonic phased array techniques were applied from the outside surface of these specimens using automated scanning devices and water coupling. The phased array approach was implemented with a modified instrument operating at low frequencies, and composite volumetric images of the specimens were generated. Results from laboratory studies for assessing crack detection effectiveness in cast stainless steel as a function of frequency are discussed in this paper.

  6. Low-frequency sound transmission through a gas-liquid interface.

    PubMed

    Godin, Oleg A

    2008-04-01

    Typically, sound speed in gases is smaller and mass density is much smaller than in liquids, resulting in a very strong acoustic impedance contrast at a gas-liquid interface. Sound transmission through a boundary with a strong impedance contrast is normally very weak. This paper studies the power output of localized sound sources and acoustic power fluxes through a plane gas-liquid interface in a layered medium. It is shown that, for low-frequency sound, a phenomenon of anomalous transparency can occur where most of the acoustic power generated by a source in a liquid half-space can be radiated into a gas half-space. The main physical mechanism responsible for anomalous transparency is found to be an acoustic power transfer by inhomogeneous (evanescent) waves in the plane-wave decomposition of the acoustic field in the liquid. The effects of a liquid's stratification and of guided sound propagation in the liquid on the anomalous transparency of the gas-liquid interface are considered. Geophysical and biological implications of anomalous transparency of water-air interface to infrasound are indicated. PMID:18396996

  7. Source implementation to eliminate low-frequency artifacts in finite difference time domain room acoustic simulation.

    PubMed

    Jeong, Hyok; Lam, Yiu Wai

    2012-01-01

    The finite difference time domain (FDTD) method is a numerical technique that is straight forward to implement for the simulation of acoustic propagation. For room acoustics applications, the implementation of efficient source excitation and frequency dependent boundary conditions on arbitrary geometry can be seen as two of the most significant problems. This paper deals with the source implementation problem. Among existing source implementation methods, the hard source implementation is the simplest and computationally most efficient. Unfortunately, it generates a large low-frequency modulation in the measured time response. This paper presents a detailed investigation into these side effects. Surprisingly, some of these side effects are found to exist even if a transparent source implementation is used. By combing a time limited approach with a class of more natural source pulse function, this paper develops a source implementation method in FDTD that is as simple and computationally as efficient as a hard source implementation and yet capable of producing results that are virtually the same as a true transparent source. It is believed that the source implementation method developed in this paper will provide an improvement to the practical usability of the FDTD method for room acoustic simulation. PMID:22280589

  8. Mechanical and Acoustic Signature of Slow Earthquakes on Laboratory Faults

    NASA Astrophysics Data System (ADS)

    Scuderi, Marco Maria; Marone, Chris; Tinti, Elisa; Scognamiglio, Laura; Di Stefano, Giuseppe; Collettini, Cristiano

    2015-04-01

    Recent seismic and geodetic observations show that fault slip occurs via a spectrum of behaviors that range from seismic (fast dynamic) to aseismic (creep). Indeed faults can slip via a variety of quasi-dynamic processes such as Slow-Slip, Low Frequency Earthquakes (LFE), and Tremor. These transient modes of slip represent slow, but self-propagating acceleration of slip along fault zones. These phenomena have been observed worldwide in a variety of active tectonic environments, however the physics of quasi-dynamic rupture and the underlying fault zone processes are still poorly understood. Rate- and State- frictional constitutive equations predict that fast dynamic slip will occur when the stiffness of the loading system (k) is less than a critical stiffness (kc) characterizing the fault gouge. In order to investigate quasi-dynamic transients, we performed laboratory experiments on simulated fault gouge (silica powders) in the double direct shear configuration with a compliant central block allowing boundary conditions where k≈kc. In addition, PZTs were used to measure acoustical properties of the gouge layers during shear. We document an evolution of the fault mechanical properties as the σn is increased. For σn < 10 MPa we observe a steady state frictional type of shear. When σn ≥ 15 MPa we observe emergent slow-slip events from steady state shear with accumulated shear displacement of about 10 mm. The typical values of stress drop (Δτ) vary between 0.2 and 0.8 MPa, and have typical duration from 0.5 up to 3 seconds giving the characteristics of slow stick-slip. As σn is varied we observe different characteristics of slow slip. For σn = 15MPa a repetitive double period oscillation is observed with slow slip growing until a maximum stress drop and then self attenuating. When σn is increased to 20 and 25 MPa slow slip are characterized by larger Δτ with constant τmax and τmin, however still showing a co-seismic duration of ~2 seconds. Our results

  9. Cellular studies and interaction mechanisms of extremely low frequency fields

    NASA Astrophysics Data System (ADS)

    Liburdy, Robert P.

    1995-01-01

    Worldwide interest in the biological effects of ELF (extremely low frequency, <1 kHz) electromagnetic fields has grown significantly. Health professionals and government administrators and regulators, scientists and engineers, and, importantly, an increasing number of individuals in the general public are interested in this health issue. The goal of research at the cellular level is to identify cellular responses to ELF fields, to develop a dose threshold for such interactions, and with such information to formulate and test appropriate interaction mechanisms. This review is selective and will discuss the most recent cellular studies directed at these goals which relate to power line, sinusoidal ELF fields. In these studies an interaction site at the cell membrane is by consensus a likely candidate, since changes in ion transport, ligand-receptor events such as antibody binding, and G protein activation have been reported. These changes strongly indicate that signal transduction (ST) can be influenced. Also, ELF fields are reported to influence enzyme activation, gene expression, protein synthesis, and cell proliferation, which are triggered by earlier ST events at the cell membrane. The concept of ELF fields altering early cell membrane events and thereby influencing intracellular cell function via the ST cascade is perhaps the most plausible biological framework currently being investigated for understanding ELF effects on cells. For example, the consequence of an increase due to ELF fields in mitogenesis, the final endpoint of the ST cascade, is an overall increase in the probability of mutagenesis and consequently cancer, according to the Ames epigenetic model of carcinogenesis. Consistent with this epigenetic mechanism and the ST pathway to carcinogenesis is recent evidence that ELF fields can alter breast cancer cell proliferation and can act as a copromoter in vitro. The most important dosimetric question being addressed currently is whether the electric (E

  10. Low-frequency vibrational modes in blue opsin: A computational study

    NASA Astrophysics Data System (ADS)

    Thirumuruganandham, Saravana Prakash; Urbassek, Herbert M.

    Vibrational excitations of low-frequency collective modes are essential for functionally important conformational transitions in proteins. We have carried out an analysis of the low-frequency modes in blue opsin based on both normal-mode analysis and molecular dynamics simulations. Power spectra obtained by molecular dynamics agree well with the normal modes. A representative set of low-frequency modes is discussed with the help of vector-field representation. We thus demonstrate that terahertz spectroscopy of low-frequency modes might be relevant for identifying those vibrational degrees of freedom that correlate to known conformational changes in opsins.

  11. Modulating action of low frequency oscillations on high frequency instabilities in Hall thrusters

    SciTech Connect

    Liqiu, Wei E-mail: weiliqiu@hit.edu.cn; Liang, Han; Ziyi, Yang; Jing, Li; Yong, Cao; Daren, Yu; Jianhua, Du

    2015-02-07

    It is found that the low frequency oscillations have modulating action on high frequency instabilities in Hall thrusters. The physical mechanism of this modulation is discussed and verified by numerical simulations. Theoretical analyses indicate that the wide-range fluctuations of plasma density and electric field associated with the low frequency oscillations affect the electron drift velocity and anomalous electron transport across the magnetic field. The amplitude and frequency of high frequency oscillations are modulated by low frequency oscillations, which show the periodic variation in the time scale of low frequency oscillations.

  12. SCALAR AND VECTOR NONLINEAR DECAYS OF LOW-FREQUENCY ALFVÉN WAVES

    SciTech Connect

    Zhao, J. S.; Wu, D. J.; Voitenko, Y.; De Keyser, J.

    2015-02-01

    We found several efficient nonlinear decays for Alfvén waves in the solar wind conditions. Depending on the wavelength, the dominant decay is controlled by the nonlinearities proportional to either scalar or vector products of wavevectors. The two-mode decays of the pump MHD Alfvén wave into co- and counter-propagating product Alfvén and slow waves are controlled by the scalar nonlinearities at long wavelengths ρ{sub i}{sup 2}k{sub 0⊥}{sup 2}<ω{sub 0}/ω{sub ci} (k {sub 0} is wavenumber perpendicular to the background magnetic field, ω{sub 0} is frequency of the pump Alfvén wave, ρ {sub i} is ion gyroradius, and ω {sub ci} is ion-cyclotron frequency). The scalar decays exhibit both local and nonlocal properties and can generate not only MHD-scale but also kinetic-scale Alfvén and slow waves, which can strongly accelerate spectral transport. All waves in the scalar decays propagate in the same plane, hence these decays are two-dimensional. At shorter wavelengths, ρ{sub i}{sup 2}k{sub 0⊥}{sup 2}>ω{sub 0}/ω{sub ci}, three-dimensional vector decays dominate generating out-of-plane product waves. The two-mode decays dominate from MHD up to ion scales ρ {sub i} k {sub 0} ≅ 0.3; at shorter scales the one-mode vector decays become stronger and generate only Alfvén product waves. In the solar wind the two-mode decays have high growth rates >0.1ω{sub 0} and can explain the origin of slow waves observed at kinetic scales.

  13. Low-frequency variability of Western Boundary Currents in the turbulent ocean: intrinsic modes and atmospheric forcing

    NASA Astrophysics Data System (ADS)

    Sérazin, Guillaume; Penduff, Thierry; Terray, Laurent; Grégorio, Sandy; Barnier, Bernard; Molines, Jean-Marc

    2015-04-01

    Ocean-atmosphere heat fluxes are particularly strong in Western Boundary Current (WBC) regions where SST front variations influence basin-scale climate variability. Observed low-frequency fluctuations in latitude and strength of these oceanic jets are classically thought to be essentially atmospherically-driven by wind stress curl variability via the oceanic Rossby wave adjustment. Yet academic eddy-resolving process-oriented models with double-gyre configurations have revealed that an idealized WBC may exhibit low-frequency intrinsic fluctuations without low-frequency external forcing (e.g. Berloff et al., 2007, Dijkstra and Ghil, 2005, etc). Experiments with eddying Ocean General Circulation Models (OGCMs) have also shown that the amount of low-frequency Sea Level Anomaly (SLA) variability is largely intrinsic in WBCs (Penduff et al. 2011; Sérazin et al 2014) and that the frontal-scale (<10°) pattern of the Kuroshio Extension (KE) variability is similar to intrinsic modes (Taguchi et al. 2010). Based on a pair of atmospherically-forced 1/12° OGCM experiments that simulate with accuracy either the intrinsic variability (seasonally-forced) or the observed total variability (forced with the full range of atmospheric timescales), Empirical Orthogonal Function analysis is performed on zonally-averaged SLA fields of four main WBCs (e.g. Gulf Stream, Kuroshio Extension, Agulhas Current and East Australian Current). The first two modes of the KE and GS exhibit a similar spatial structure that is shaped by oceanic intrinsic processes. The frequency content is however different between the intrinsic and total Principal Components, the former containing a wide range of timescales similar to a red noise and the latter being more autocorrelated at interannual-to-decadal timescales. These modes are compared with those obtained from the 20 years of altimetry observation and relationships with low-frequency westward propagative features in the respective oceanic basin are

  14. Low frequency spectra of type III solar radio bursts

    NASA Technical Reports Server (NTRS)

    Weber, R. R.

    1978-01-01

    Flux density spectra have been determined for 91 simple type III solar bursts observed by the Goddard Space Flight Center radio astronomy experiment on the IMP-6 spacecraft during 1971 and 1972. Spectral peaks were found to occur at frequencies ranging from 44 kHz up to 2500 kHz. Half of the bursts peaked between 250 kHz and 900 kHz, corresponding to emission at solar distances of about 0.3 to 0.1 AU. Maximum burst flux density sometimes exceeds 10 to the -14th W/sq m/Hz. The primary factor controlling the spectral peak frequency of these bursts appears to be a variation in intrinsic power radiated by the source as the exciter moves outward from the sun, rather than radio propagation effects between the source and IMP-6. Thus, a burst spectrum strongly reflects the evolution of the properties of the exciting electron beam, and according to current theory, beam deceleration could help account for the observations.

  15. Time History of Repeating Low-Frequency Earthquakes Spanning 5 Years

    NASA Astrophysics Data System (ADS)

    Sweet, J. R.; Creager, K. C.

    2011-12-01

    Low-frequency earthquakes (LFEs) are a recently identified class of earthquakes that occur coincidentally with tectonic tremor in time and space. LFEs comprise much of the tectonic tremor in Japan, and LFE locations have been used to pin down the location of tremor bursts within subduction zones around the world (Brown et al., 2009, GRL), as well as on deep segments of the San Andreas Fault (Shelly et al., 2009, GRL). While prior LFE studies have allowed us to see where and when various fault patches are radiating seismic energy with unprecedented detail, the time history of repeating LFEs has received less attention. Using well-recorded LFEs as templates, we employ a cross-correlation filter to find matching events. We have identified several locations in the northern Cascadia subduction zone which produce LFEs that repeated several hundred times during the past five years. The LFEs are active during multiple Episodic Tremor and Slip (ETS) events. In each case, the matching events first appear rather suddenly and at a feverish pace. Following this initial burst of several hours, the events exhibit a much more discrete pattern of recurrence that starts out as frequent pops that become less and less frequent over a period of several days. We suggest that the initial burst is associated with the passage of a slip front on the fault surface at the location of the template event. Later pops may be attributed to resurgent slow slip that briefly generates seismic energy during the days following the passage of the initial slip front. One LFE template was also active during an inter-ETS event. Its time history was similar to the initial bursts during the ETS events, but it was not followed by the later pops-perhaps due to the absence of resurgent slow slip during the small inter-ETS event. We have previously identified several additional LFE templates that occurred during smaller inter-ETS episodes farther downdip of the main ETS zone. Using these additional templates, we

  16. Low-frequency Intensity Variation of the South Asian High and its relationship to Boreal Summer Intraseasonal Oscillation

    NASA Astrophysics Data System (ADS)

    Shang, Wei; Ren, Xuejuan

    2016-04-01

    and northwest from day -12 to day 0 is associated with the Boreal Summer Intraseasonal Oscillation 2 (BSISO 2) of 10 - 30 days in the Asian monsoon areas. When BSISO2 propagates from subtropics to Asian continents , more anomalous rainfall appear in the Asian monsoon areas, which correspond more anomalous condensation heat release. The anomalous heating stimulate positive height anomalies with an anomalous anticyclonic circulation to its northwest in the upper troposphere, causing the strengthening of the SAH intensity. In addition, the strengthening of the west part of SAH may result from an anomalous low-frequency anticyclonic in the upper troposphere propagating northward from Arabian Sea to Iranian plateau.

  17. Low frequency waves associated with PSBL ion beams. Cluster observations.

    NASA Astrophysics Data System (ADS)

    Grigorenko, Elena; Sauvaud, Jean-Andre; Zeleniy, Lev; Burinskaya, T.

    The processes of non-adiabatic ion acceleration occurring in the Current Sheet of the Earth's magnetotail produce highly accelerated (up to 2500km/s) field-aligned ion beams (beamlets) with transient appearance streaming earthward in the Plasma Sheet Boundary Layer (PSBL). Multipoint Cluster observations have led to a new understanding of these phenomena with a spatial rather than a temporal structure. Comparison of data from different Cluster spacecraft allows to evaluate the duration of beamlets to be, at least, 5-15 min and confirms their welldefined localization along Y and/or Z directions, i.e. across the lobe magnetic field. Earlier results reporting shorter duration of beamlet observations could be understood by the invoking of an additional effect revealed by Cluster: earthward propagation of magnetic perturbations along the beamlet filaments. Phase velocity of these perturbations is of the order of the local Alfven velocity (V 600-1000km/s) and related fast flappings of localized beamlet structures in Y-Z direction significantly decreases the time of their observation at a given spacecraft. Statistical studies of 90 beamlets have shown that the typical wave length of the related disturbances is about tens RE and typical period is about several minutes. Such Alfvenic-type disturbances may be caused by Kelvin-Helmholtz instability triggered by a flow shear between the highvelocity plasma beam streaming at the PSBL boundary and the slowly moving plasma of the outer lobe. Our analysis revealed that for the majority of accelerated ion beams observed in the PSBL of magnetotail the conditions for the development of Kelvin-Helmholtz instability are satisfied. This work was supported by RFBR grants 07-02-00319; 06-02-72561

  18. Slow Pseudotachylites

    NASA Astrophysics Data System (ADS)

    Pec, M.; Stunitz, H.; Heilbronner, R.

    2011-12-01

    Tectonic pseudotachylites as solidified, friction induced melts are believed to be the only unequivocal evidence for paleo-earthquakes. Earthquakes occur when fast slip (1 - 3 m/s) propagates on a localized failure plane and are always related with stress drops. The mechanical work expended, together with the rock composition and the efficiency of thermal dissipation, controls whether the temperature increase on a localized slip plane will be sufficient to induce fusion. We report the formation of pseudotachylites during steady-state plastic flow at slow bulk shear strain rates (~10^-3 to ~10^-5 /s corresponding to slip rates of ~10^-6 to ~10^-8 m/s) in experiments performed at high confining pressures (500 MPa) and temperatures (300°C) corresponding to a depth of ~15 km. Crushed granitioid rock (Verzasca gneiss), grain size ≤ 200 μm, with 0.2 wt% water added was placed between alumina forcing blocks pre-cut at 45°, weld-sealed in platinum jackets and deformed with a constant displacement rate in a solid medium deformation apparatus (modified Griggs rig). Microstructural observations show the development of a S-C-C' fabric with C' slip zones being the dominant feature. Strain hardening in the beginning of the experiment is accompanied with compaction which is achieved by closely spaced R1 shears pervasively cutting the whole gouge zone and containing fine-grained material (d < 100 nm). The peak strength is achieved at γ ~ 2 at shear stress levels of 1350-1450 MPa when compaction ceases. During further deformation, large local displacements (γ > 10) are localized in less densely spaced, ~10 μm thick C'-C slip zones which develop predominantly in feldspars and often contain micas. In TEM, they appear to have no porosity consisting of partly amorphous material and small crystalline fragments with the average grain size of 20 nm. After the peak strength, the samples weaken by ~20 MPa and continue deforming up to γ ~ 4 without any stress drops. Strain

  19. The Effectiveness of Low-Frequency Amplification and Filtered-Speech Testing for Preschool Deaf Children.

    ERIC Educational Resources Information Center

    Asp, Carl W.

    In order to study effectiveness of low-frequency amplification and filtered-speech testing for preschool deaf children, an experimental design permitting the teacher to speak simultaneously through two different amplifying systems, a low-frequency auditory training unit (Suvag I) and a conventional auditory training unit (Warren T-2), was used…

  20. 77 FR 52317 - Record of Decision for Surveillance Towed Array Sensor System Low Frequency Active Sonar

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-08-29

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF DEFENSE Department of the Navy Record of Decision for Surveillance Towed Array Sensor System Low Frequency Active... Array Sensor System Low Frequency Active (SURTASS LFA) sonar systems with certain...

  1. THE USE OF LOW FREQUENCY RESIDUAL HEARING IN PROFOUNDLY DEAF CHILDREN.

    ERIC Educational Resources Information Center

    LING, DANIEL

    IN ORDER TO TEST THE HYPOTHESIS THAT ADDITIONAL LOW FREQUENCY AMPLIFICATION WOULD CONTRIBUTE SIGNIFICANTLY TO THE AUDITION OF SPEECH, 12 CHILDREN WITH LOW FREQUENCY RESIDUAL HEARING WERE STUDIED, USING TWO INDIVIDUAL HEARING AIDS--AN EXPERIMENTAL MODEL WITH A FREQUENCY RANGE OF 80-3500 CYCLES PER SECOND (CPS) AND A STANDARD MODEL WITH A FREQUENCY…

  2. Effect of low frequency noise on the echocardiographic parameter E/A ratio.

    PubMed

    Chao, Pao-Chiang; Yeh, Ching-Ying; Juang, Yow-Jer; Hu, Ching-Yao; Chen, Chiou-Jong

    2012-01-01

    The hearing condition of the Taiwanese aerospace maintenance workers affected by the low frequency noise had not been reported. The purpose of this research is to clarify the maintenance workers' health effect when exposed to low frequency and/or general noises and to understand the relationship between the variations of the worker's echocardiographic E/A ratio and the low frequency noise. The low frequency noise monitoring and echocardiographic E/A ratio results obtained for 213 aerospace maintenance workers indicated that the workers' hearing loss was more serious at high frequency 4k and 6k when exposed to the low frequency noise and could be more than 40 dB. The abnormality of echocardiographic E/A ratio was also higher than that of control group. PMID:22918145

  3. Assessment of Crack Detection in Heavy-Walled Cast Stainless Steel Piping Welds Using Advanced Low-Frequency Ultrasonic Methods

    SciTech Connect

    Anderson, Michael T.; Crawford, Susan L.; Cumblidge, Stephen E.; Denslow, Kayte M.; Diaz, Aaron A.; Doctor, Steven R.

    2007-03-01

    Studies conducted at the Pacific Northwest National Laboratory in Richland, Washington, have focused on assessing the effectiveness and reliability of novel approaches to nondestructive examination (NDE) for inspecting coarse-grained, cast stainless steel reactor components. The primary objective of this work is to provide information to the U.S. Nuclear Regulatory Commission on the effectiveness and reliability of advanced NDE methods as related to the inservice inspection of safety-related components in pressurized water reactors (PWRs). This report provides progress, recent developments, and results from an assessment of low frequency ultrasonic testing (UT) for detection of inside surface-breaking cracks in cast stainless steel reactor piping weldments as applied from the outside surface of the components. Vintage centrifugally cast stainless steel piping segments were examined to assess the capability of low-frequency UT to adequately penetrate challenging microstructures and determine acoustic propagation limitations or conditions that may interfere with reliable flaw detection. In addition, welded specimens containing mechanical and thermal fatigue cracks were examined. The specimens were fabricated using vintage centrifugally cast and statically cast stainless steel materials, which are typical of configurations installed in PWR primary coolant circuits. Ultrasonic studies on the vintage centrifugally cast stainless steel piping segments were conducted with a 400-kHz synthetic aperture focusing technique and phased array technology applied at 500 kHz, 750 kHz, and 1.0 MHz. Flaw detection and characterization on the welded specimens was performed with the phased array method operating at the frequencies stated above. This report documents the methodologies used and provides results from laboratory studies to assess baseline material noise, crack detection, and length-sizing capability for low-frequency UT in cast stainless steel piping.

  4. Ponderomotive Force and Lower Hybrid Turbulence Effects in Space Plasmas Subjected to Large-Amplitude Low-Frequency Waves

    NASA Technical Reports Server (NTRS)

    Khazanov, G. V.; Khazanov, George; Liemohn, M. W.; Stone, N. H.; Coffey, V. N.

    1997-01-01

    In the auroral region, simultaneous occurrences of upward-flowing ions and field-aligned electrons have been observed by the Viking satellite. The occurrence is strongly correlated with large amplitude low frequency fluctuations of the electric field. Large-amplitude shear Alfven waves have also been observed by sounding rockets in the auroral ionosphere. When such LF waves are propagating in a plasma, a ponderomotive force and other types of waves are produced which may lead to significant effects on the plasma. This force is directed toward decreasing density, providing the electromagnetic lift of the background plasma and an increase of collisionless plasma expansion. We find that even for modest wave strengths, the influence on the outflowing oxygen ions can be dramatic, increasing the high-altitude density by orders of magnitude. It is also demonstrated that large-amplitude low-frequency waves (LFW) may generate lower hybrid waves (LHW) in the auroral zone. The excitation of LHW by a LF wave may lead to the appearance of an additional channel of energy transfer from, for example, Alfven or fast magnetosonic waves, to particles. This process then influences the formation of the plasma distribution function at the expense of acceleration in the tail of the distribution during the collapse of the LHW. The ion energization due to the LHW can be comparable with that produced by the ponderomotive force of the LFW. It is shown that the LH turbulence leads to equalization of the ponderomotive acceleration of the different ion species. The mechanism of LHW excitation due to the oxygen ion relative drift in a plasma subjected to low-frequency waves is used for analysis of Viking satellite data for events in the cusp/cleft region. It is found that, in some cases, such a mechanism leads to LHW energy densities and ion distribution functions close to those observed.

  5. Source modeling sleep slow waves

    PubMed Central

    Murphy, Michael; Riedner, Brady A.; Huber, Reto; Massimini, Marcello; Ferrarelli, Fabio; Tononi, Giulio

    2009-01-01

    Slow waves are the most prominent electroencephalographic (EEG) feature of sleep. These waves arise from the synchronization of slow oscillations in the membrane potentials of millions of neurons. Scalp-level studies have indicated that slow waves are not instantaneous events, but rather they travel across the brain. Previous studies of EEG slow waves were limited by the poor spatial resolution of EEGs and by the difficulty of relating scalp potentials to the activity of the underlying cortex. Here we use high-density EEG (hd-EEG) source modeling to show that individual spontaneous slow waves have distinct cortical origins, propagate uniquely across the cortex, and involve unique subsets of cortical structures. However, when the waves are examined en masse, we find that there are diffuse hot spots of slow wave origins centered on the lateral sulci. Furthermore, slow wave propagation along the anterior−posterior axis of the brain is largely mediated by a cingulate highway. As a group, slow waves are associated with large currents in the medial frontal gyrus, the middle frontal gyrus, the inferior frontal gyrus, the anterior cingulate, the precuneus, and the posterior cingulate. These areas overlap with the major connectional backbone of the cortex and with many parts of the default network. PMID:19164756

  6. Abnormal functional integration of thalamic low frequency oscillation in the BOLD signal after acute heroin treatment.

    PubMed

    Denier, Niklaus; Schmidt, André; Gerber, Hana; Vogel, Marc; Huber, Christian G; Lang, Undine E; Riecher-Rossler, Anita; Wiesbeck, Gerhard A; Radue, Ernst-Wilhelm; Walter, Marc; Borgwardt, Stefan

    2015-12-01

    Heroin addiction is a severe relapsing brain disorder associated with impaired cognitive control, including deficits in attention allocation. The thalamus has a high density of opiate receptors and is critically involved in orchestrating cortical activity during cognitive control. However, there have been no studies on how acute heroin treatment modulates thalamic activity. In a cross-over, double-blind, vehicle-controlled study, 29 heroin-maintained outpatients were studied after heroin and placebo administration, while 20 healthy controls were included for the placebo condition only. Resting-state functional magnetic resonance imaging was used to analyze functional integration of the thalamus by three different resting state analysis techniques. Thalamocortical functional connectivity (FC) was analyzed by seed-based correlation, while intrinsic thalamic oscillation was assessed by analysis of regional homogeneity (ReHo) and the fractional amplitude of low frequency fluctuations (fALFF). Relative to the placebo treatment and healthy controls, acute heroin administration reduced thalamocortical FC to cortical regions, including the frontal cortex, while the reductions in FC to the mediofrontal cortex, orbitofrontal cortex, and frontal pole were positively correlated with the plasma level of morphine, the main psychoactive metabolite of heroin. Furthermore, heroin treatment was associated with increased thalamic ReHo and fALFF values, whereas fALFF following heroin exposure correlated negatively with scores of attentional control. The heroin-associated increase in fALFF was mainly dominated by slow-4 (0.027-0.073 Hz) oscillations. Our findings show that there are acute effects of heroin within the thalamocortical system and may shed new light on the role of the thalamus in cognitive control in heroin addiction. Future research is needed to determine the underlying physiological mechanisms and their role in heroin addiction.

  7. Magnitudes and moment-duration scaling of low-frequency earthquakes beneath southern Vancouver Island

    NASA Astrophysics Data System (ADS)

    Bostock, M. G.; Thomas, A. M.; Savard, G.; Chuang, L.; Rubin, A. M.

    2015-09-01

    We employ 130 low-frequency earthquake (LFE) templates representing tremor sources on the plate boundary below southern Vancouver Island to examine LFE magnitudes. Each template is assembled from hundreds to thousands of individual LFEs, representing over 269,000 independent detections from major episodic-tremor-and-slip (ETS) events between 2003 and 2013. Template displacement waveforms for direct P and S waves at near epicentral distances are remarkably simple at many stations, approaching the zero-phase, single pulse expected for a point dislocation source in a homogeneous medium. High spatiotemporal precision of template match-filtered detections facilitates precise alignment of individual LFE detections and analysis of waveforms. Upon correction for 1-D geometrical spreading, attenuation, free surface magnification and radiation pattern, we solve a large, sparse linear system for 3-D path corrections and LFE magnitudes for all detections corresponding to a single-ETS template. The spatiotemporal distribution of magnitudes indicates that typically half the total moment release occurs within the first 12-24 h of LFE activity during an ETS episode when tidal sensitivity is low. The remainder is released in bursts over several days, particularly as spatially extensive rapid tremor reversals (RTRs), during which tidal sensitivity is high. RTRs are characterized by large-magnitude LFEs and are most strongly expressed in the updip portions of the ETS transition zone and less organized at downdip levels. LFE magnitude-frequency relations are better described by power law than exponential distributions although they exhibit very high b values ≥˜5. We examine LFE moment-duration scaling by generating templates using detections for limiting magnitude ranges (MW<1.5, MW≥2.0). LFE duration displays a weaker dependence upon moment than expected for self-similarity, suggesting that LFE asperities are limited in fault dimension and that moment variation is dominated by

  8. Abnormal functional integration of thalamic low frequency oscillation in the BOLD signal after acute heroin treatment.

    PubMed

    Denier, Niklaus; Schmidt, André; Gerber, Hana; Vogel, Marc; Huber, Christian G; Lang, Undine E; Riecher-Rossler, Anita; Wiesbeck, Gerhard A; Radue, Ernst-Wilhelm; Walter, Marc; Borgwardt, Stefan

    2015-12-01

    Heroin addiction is a severe relapsing brain disorder associated with impaired cognitive control, including deficits in attention allocation. The thalamus has a high density of opiate receptors and is critically involved in orchestrating cortical activity during cognitive control. However, there have been no studies on how acute heroin treatment modulates thalamic activity. In a cross-over, double-blind, vehicle-controlled study, 29 heroin-maintained outpatients were studied after heroin and placebo administration, while 20 healthy controls were included for the placebo condition only. Resting-state functional magnetic resonance imaging was used to analyze functional integration of the thalamus by three different resting state analysis techniques. Thalamocortical functional connectivity (FC) was analyzed by seed-based correlation, while intrinsic thalamic oscillation was assessed by analysis of regional homogeneity (ReHo) and the fractional amplitude of low frequency fluctuations (fALFF). Relative to the placebo treatment and healthy controls, acute heroin administration reduced thalamocortical FC to cortical regions, including the frontal cortex, while the reductions in FC to the mediofrontal cortex, orbitofrontal cortex, and frontal pole were positively correlated with the plasma level of morphine, the main psychoactive metabolite of heroin. Furthermore, heroin treatment was associated with increased thalamic ReHo and fALFF values, whereas fALFF following heroin exposure correlated negatively with scores of attentional control. The heroin-associated increase in fALFF was mainly dominated by slow-4 (0.027-0.073 Hz) oscillations. Our findings show that there are acute effects of heroin within the thalamocortical system and may shed new light on the role of the thalamus in cognitive control in heroin addiction. Future research is needed to determine the underlying physiological mechanisms and their role in heroin addiction. PMID:26441146

  9. Shallow Low-frequency Tremor in the Hyuga-nada region, western Nankai Trough subduction zone, observed by ocean bottom seismographic experiment

    NASA Astrophysics Data System (ADS)

    Yamashita, Y.; Yakiwara, H.; Shimizu, H.; Uchida, K.; Kamizono, M.; Nakamoto, M.; Fukui, M.; Fujita, S.; Aizawa, K.; Miyamachi, H.; Hirano, S.; Umakoshi, K.; Yamada, T.; Kanehara, H.; Aoshima, T.

    2013-12-01

    event, the source location changed during tremor activity, which may migrate from south to north. In addition, the tremor source area roughly overlapped with the source area of the shallow very-low-frequency earthquake. During tremor activity was found, shallow very-low-frequency earthquake activity was also found [Y. Asano, personal communication]. Therefore, these low-frequency events probably synchronized in spatially and temporally. These spatial and temporal correlation of low-frequency events including slow-slip event were already found in the transient zone of deeper part of the Cascadia and Nankai subduction zones. We suggest that undetected low-frequency event with longer duration such as short or long-term slow-slip events may have occurred at the same time in the shallow part of the Hyuga-nada region. Acknowledgements: We thank the crews of T/S Nagasakimaru (Nagasaki University) for OBS experiment. We also thank Dr. Y. Asano (NIED) for providing us with the catalog of shallow very-low-frequency earthquake in the Hyuga-nada region.

  10. Ultra-Narrow Bandwidth Optical Resonators for Integrated Low Frequency Noise Lasers

    NASA Astrophysics Data System (ADS)

    Spencer, Daryl T.

    The development of narrowband resonators has far reaching applications in integrated optics. As a precise reference of wavelength, filters can be used in sensors, metrology, nonlinear optics, microwave photonics, and laser stabilization. In this work, we develop record high quality factor (Q) Si 3N4 waveguide resonators, and utilize them to stabilize a heterogeneously integrated Si/III V laser. To increase the Q factor of waveguide resonators, particular attention is given to loss mechanisms. Propagation loss of <0.1 dB/m is demonstrated on the ultra low loss waveguide platform, a low index contrast, high aspect ratio Si3N4 waveguide geometry fabricated with high quality materials and high temperature anneals. Ideality in the directional couplers used for coupling to the resonators is studied and losses are reduced such that 81 million intrinsic Q factor is achieved. Additional results include 1x16 resonant splitters, low ? narrowband gratings, and a dual layer waveguide technology for low loss and low bend radius in separate regions of the same device layer. We then combine an ultra high Q resonator and a heterogeneous Si/III V laser in a Pound Drever Hall (PDH) frequency stabilization system to yield narrow linewidth characteristics for a stable on chip laser reference. The high frequency noise filtering is performed with Si resonant mirrors in the laser cavity. A 30 million Q factor Si3N4 resonator is used with electrical feedback to reduce close in noise and frequency walk off. The laser shows high frequency noise levels of 60x103 Hz2/Hz corresponding to 160 kHz linewidth, and the low frequency noise is suppressed 33 dB to 103 Hz2/Hz with the PDH system.

  11. Sapce based low frequency interferometric radioastronomy: the path towards the imaging of the inner heliosphere.

    NASA Astrophysics Data System (ADS)

    Cecconi, B.; Zarka, P. M.; Girard, J. N.; Klein Wolt, M.; Boonstra, A. J.; Baan, W.; Briand, C.; Maksimovic, M.; Segret, B.

    2014-12-01

    Low frequency radioastronomy observatories for the heliosphere have been using similar instrumentation for decades. The Cassini, STEREO, and the future Solar Orbiter mission are embarking goniopolarmetric radio receiver connected to 3 electric wire antennas. Such instrument provides the spectral matrix (or part of it) from which the wave parameters can be derived. They require a point source assumption (plane wave) to derive the direction of arrival of the wave, the polarization and the flux density. In case of a spatially extended source (disk shaped, with a given radial profile), the source centroid direction and the apparent source size can also be derived. This type of instrumentation cannot provide much more parameters, as there is a maximum of to 9 independent measurements for each time-frequency step (i.e. an instantaneous set of measurements). Radio maps can be produced a posteriori combining consecutive data at the cost of averaging out small scale temporal variations. Furthermore, these inversion do not allow solving for several sources, or for complex source geometry. We present a concept of radioastronomy instrumentation using a swarm of small satellites (possibly cubesats) with sensitive radio receivers measuring the wave front and phase of the radio waves on each spacecraft. This instrument will also provide 3-dimensional interferometric measurement from which real imaging capabilities will arise, as it is now occurring on ground at frequencies above 15 MHz, with the LOFAR interferometer in Europe, or the LWA in teh USA. The proposed concept will be very complementary to these instruments, as they will be orepating from a few kHz to a few 10 Mhz from space, and thus not affected by the ionospheric cutoff at 10 MHz. Such resolved imaging capabilities of the inner heliosphere would be a real step forward to better understand the radio emissions mechanisms and the energetic at the orgin of the radio sources, as well as the propagation processes. We will

  12. NONRESONANT INTERACTION OF CHARGED ENERGETIC PARTICLES WITH LOW-FREQUENCY NONCOMPRESSIVE TURBULENCE: NUMERICAL SIMULATION

    SciTech Connect

    Ragot, B. R.

    2012-10-20

    A new method for simulating the three-dimensional dynamics of charged energetic particles in very broadband noncompressive magnetic turbulence is introduced. All scales within the primary inertial range of the turbulence observed in the solar wind near 1 AU are now included for the independent computations of both the particle dynamics and the turbulent magnetic field lines (MFLs). While previous theories of resonant particle pitch-angle (PA) scattering and transport in interplanetary magnetic fields had favored interpreting the observed depletions in the electron PA distributions (PADs) around 90 Degree-Sign PA as evidence of poor scattering at low PA cosines, the computed particle dynamics reveal a very different reality. The MFL directions now vary on many scales, and the PADs are depleted around 90 Degree-Sign PA due to nonresonant filtering of the particles that propagate at too large an angle to the local magnetic field. Rather than being too weak, the scattering through 90 Degree-Sign PA is actually so strong that the particles (electrons and protons/ions) are reflected and trapped in the turbulent magnetic fields. While the low-frequency nonresonant turbulence produces ubiquitous magnetic traps that only let through particles with the most field-aligned velocities, higher-frequency near-gyroscale turbulence, when present, enhances particle transport by allowing the particles to navigate between magnetic traps. Finally, visualizing both particle trajectories and MFLs in the very same turbulence reveals a powerful tool for understanding the effects of the turbulent fields on the particle dynamics and cross-field transport. Some cross-field-line scattering, strongly amplified by MFL dispersal, results in a strong cross-field scattering of the particles. From this visualization, it also appears that near-gyroscale turbulence, previously known as gyroresonant turbulence, does not resonantly interact with the particles. The interaction between particles and

  13. Low-frequency waves within isolated magnetic clouds and complex structures: STEREO observations

    NASA Astrophysics Data System (ADS)

    Siu-Tapia, A.; Blanco-Cano, X.; Kajdic, P.; Aguilar-Rodriguez, E.; Russell, C. T.; Jian, L. K.; Luhmann, J. G.

    2015-04-01

    Complex Structures (CSs) formed by the interaction of magnetic cloud (MC)-like structures with other transients (e.g., another MC, a stream interaction region, or a fast stream of solar wind) were frequently observed in the interplanetary space by STEREO spacecraft during the solar minimum 23 and the rising phase of the solar cycle 24. Here we report the presence of low-frequency waves (LFWs) inside some isolated MCs (IMCs) and inside the CSs observed by STEREO during such period (2007-2011). It is important to study in detail the properties of waves in space plasmas since particle distribution functions can be modified by wave-particle interactions. We compare wave characteristics within IMCs with those waves observed inside CSs. Both left-handed (LH) and right-handed (RH), near-circularly polarized, transverse and almost parallel-propagating LFWs (around the proton cyclotron frequency) were sporadically observed inside both IMCs and CSs. In contrast, compressive mirror-mode waves (MMs) were observed only within CSs. We studied local plasma conditions inside the IMCs and CSs to gain insight about wave origin: most of the MMs within CSs were observed in regions with enhanced plasma beta (β>1) the majority of the LH waves were found in low beta plasmas (β<1), and the RH waves were predominantly observed at moderate betas (0.4<β≤2). These observations are in agreement with linear kinetic theory predictions for the growth of the mirror, the LH ion cyclotron, and the RH ion firehose instability, respectively. It is possible that the waves were generated locally inside the IMCs and CSs via temperature anisotropies. The plasma beta enhancements that were frequently observed inside the CSs may be the result of compressions and heating taking place inside the interacting structures.

  14. Low Frequency Error Analysis and Calibration for High-Resolution Optical Satellite's Uncontrolled Geometric Positioning

    NASA Astrophysics Data System (ADS)

    Wang, Mi; Fang, Chengcheng; Yang, Bo; Cheng, Yufeng

    2016-06-01

    The low frequency error is a key factor which has affected uncontrolled geometry processing accuracy of the high-resolution optical image. To guarantee the geometric quality of imagery, this paper presents an on-orbit calibration method for the low frequency error based on geometric calibration field. Firstly, we introduce the overall flow of low frequency error on-orbit analysis and calibration, which includes optical axis angle variation detection of star sensor, relative calibration among star sensors, multi-star sensor information fusion, low frequency error model construction and verification. Secondly, we use optical axis angle change detection method to analyze the law of low frequency error variation. Thirdly, we respectively use the method of relative calibration and information fusion among star sensors to realize the datum unity and high precision attitude output. Finally, we realize the low frequency error model construction and optimal estimation of model parameters based on DEM/DOM of geometric calibration field. To evaluate the performance of the proposed calibration method, a certain type satellite's real data is used. Test results demonstrate that the calibration model in this paper can well describe the law of the low frequency error variation. The uncontrolled geometric positioning accuracy of the high-resolution optical image in the WGS-84 Coordinate Systems is obviously improved after the step-wise calibration.

  15. Understanding the low-frequency variability in hydroclimatic attributes over the southeastern US

    NASA Astrophysics Data System (ADS)

    Wang, Hui; Sankarasubramanian, A.; Ranjithan, R. S.

    2015-02-01

    Most studies on evaluating the potential in developing seasonal to interannual hydroclimatic forecasts have focused on associating low-frequency climatic conditions with basin-level precipitation/streamflow. The motivation of this study is to provide an understanding on how land surface characteristics modulate the low-frequency (interannual to decadal) variability in precipitation to develop low-frequency signal in streamflow. For this purpose, we consider basins with minimum anthropogenic impacts over southeastern United States and apply Singular Spectrum Analysis (SSA), a data-driven spectrum analysis tool, on annual precipitation and streamflow time series for detecting the dominant frequencies and for estimating the associated variability with them. Hypothesis test against an AR(1) process is carried out via Monte Carlo SSA for detecting significant (at 90% confidence level) low-frequency oscillations. Thus, the study investigates how the observed low-frequency oscillations in precipitation/streamflow vary over the southeastern United States and also their associations with climatic conditions. For most study basins, precipitation exhibits higher low-frequency oscillations than that of streamflow primarily due to reduction in variability by basin storage. Investigating this further, we found that the percentage variance accounted by low-frequency oscillations in streamflow being higher for larger basins which primarily indicates the increased role of climate and basin storage. To develop a fundamental understanding on how basin storage controls the low-frequency oscillations in streamflow, a simple annual hydrological model is employed to explore how the given low-frequency signal in precipitation being modified under different baseflow index conditions and groundwater residence time. Implications of these analyses relating to streamflow predictions and model calibration are also discussed.

  16. A lightweight low-frequency sound insulation membrane-type acoustic metamaterial

    NASA Astrophysics Data System (ADS)

    Lu, Kuan; Wu, Jiu Hui; Guan, Dong; Gao, Nansha; Jing, Li

    2016-02-01

    A novel membrane-type acoustic metamaterial with a high sound transmission loss (STL) at low frequencies (⩽500Hz) was designed and the mechanisms were investigated by using negative mass density theory. This metamaterial's structure is like a sandwich with a thin (thickness=0.25mm) lightweight flexible rubber material within two layers of honeycomb cell plates. Negative mass density was demonstrated at frequencies below the first natural frequency, which results in the excellent low-frequency sound insulation. The effects of different structural parameters of the membrane on the sound-proofed performance at low frequencies were investigated by using finite element method (FEM). The numerical results show that, the STL can be modulated to higher value by changing the structural parameters, such as the membrane surface density, the unite cell film shape, and the membrane tension. The acoustic metamaterial proposed in this study could provide a potential application in the low-frequency noise insulation.

  17. Direct CFD Predictions of Low Frequency Sounds Generated by Helicopter Main Rotors

    NASA Technical Reports Server (NTRS)

    Sim, Ben W.; Potsdam, Mark; Conner, Dave; Watts, Michael E.

    2010-01-01

    This proposed paper will highlight the application of a CSD/CFD methodology currently inuse by the US Army Aerfolightdynamics Directorate (AFDD) to assess the feasibility and fidelity of directly predicting low frequency sounds of helicopter rotors.

  18. Impact to Space Shuttle Vehicle Trajectory on Day of Launch from change in Low Frequency Winds

    NASA Technical Reports Server (NTRS)

    Decker, Ryan K.; Puperi, Daniel; Leach, Richard

    2007-01-01

    The National Aeronautics and Space Administration's (NASA) Space Shuttle utilizes atmospheric winds on day of launch to develop throttle and steering commands to best optimize vehicle performance while keeping structural loading on the vehicle within limits. The steering commands and resultant trajectory are influenced by both the high and low frequency component of the wind. However, the low frequency component has a greater effect on the ascent design. Change in the low frequency wind content from the time of trajectory design until launch can induce excessive loading on the vehicle. Wind change limits have been derived to protect from launching in an environment where these temporal changes occur. Process of developing wind change limits are discussed followed by an observational study of temporal wind change in low frequency wind profiles at the NASA's Kennedy Space Center area are presented.

  19. Low frequency band gaps below 10 Hz in radial flexible elastic metamaterial plate

    NASA Astrophysics Data System (ADS)

    Gao, Nansha; Hou, Hong; Wu, Jiu Hui; Cheng, Baozhu

    2016-11-01

    This paper presents the low frequency acoustic properties of a new proposed elastic metamaterial, which is arranged in the axial coordinate. The band structures, transmission spectra, and eigenmode displacement fields of this metamaterial are different from previous elastic metamaterial structures. Numerical calculation results show that the first order band gap of the radial flexible elastic metamaterial plate is below 10 Hz. A multiple-vibration coupling mechanism is proposed to explain the low frequency band gaps. By changing the geometrical dimensions h 1, h 2, b 1, and b 1 of the centre part, the location and width of the low frequency band gaps can be varied easily. The effects of density and Young’s modulus are also discussed in detail. In summary, the radial flexible elastic metamaterial plate can restrain low frequency vibration, owing to which it can potentially be used to protect infrasound, generate filters, and design acoustic devices.

  20. Low Frequency Activity of Cortical Networks on Microelectrode Arrays is Differentially Altered by Bicuculline and Carbaryl

    EPA Science Inventory

    Thousands of chemicals need to be characterized for their neurotoxicity potential. Neurons grown on microelectrode arrays (MEAs) are an in vitro model used to screen chemicals for functional effects on neuronal networks. Typically, after removal of low frequency components, effec...

  1. Small foamed polystyrene shield protects low-frequency microphones from wind noise

    NASA Technical Reports Server (NTRS)

    Tedrick, R. N.

    1964-01-01

    A foamed polystyrene noise shield for microphones has been designed in teardrop shape to minimize air turbulence. The shield slips on and off the microphone head easily and is very effective in low-frequency sound intensity measurements.

  2. Low-frequency waves associated with Langmuir waves in solar wind

    NASA Technical Reports Server (NTRS)

    Thejappa, G.; Wentzel, Donat G.; Stone, R. G.

    1995-01-01

    The Ulysses spacecraft has detected several events of low-frequency electromagnetic waves in association with Langmuir waves in the solar wind. The high time resolution observations show that the Langmuir waves are very intense and occur as broad peaks superposed by collapsing millisecond spikes. The low-frequency waves are identified as electromagnetic lower hybrid waves. The observed energy densities of these waves often exceed the strong turbulence thresholds. It is shown that none of the parametric decay instabilities involving Langmuir and low-frequency waves are energetically favorable to explain the present observations. The low-frequency waves are proposed to arise from currents associated with gradients in the electron beam originating at sites where Langmuir waves scatter the beam electrons.

  3. The transmission of low frequency medical data using delta modulation techniques.

    NASA Technical Reports Server (NTRS)

    Arndt, G. D.; Dawson, C. T.

    1972-01-01

    The transmission of low-frequency medical data using delta modulation techniques is described. The delta modulators are used to distribute the low-frequency data into the passband of the telephone lines. Both adaptive and linear delta modulators are considered. Optimum bit rates to minimize distortion and intersymbol interference are discussed. Vibrocardiographic waves are analyzed as a function of bit rate and delta modulator configuration to determine their reproducibility for medical evaluation.

  4. Destabilization kinetics of polyvinylpyrrolidone-iodine in a field of low frequency impacts

    NASA Astrophysics Data System (ADS)

    Fadeev, G. N.; Ermolaeva, V. I.; Boldyrev, V. S.; Sinkevich, V. V.

    2016-09-01

    Experimental results on the destabilization kinetics of compounds with chelate structure (polyvinylpyrrolidone-iodine) in the field of the impact of low-frequency vibrations (from 2 to 45 Hz) are presented. The optimum frequencies at which the process rate is greatest are found for different impact modes. Based on the experimental data, conclusions are drawn as to the effect the energy of low-frequency impacts has on the studied clathrate and chelate structures.

  5. A piezoelectric spring-mass system as a low-frequency energy harvester.

    PubMed

    Hu, Hongping; Hu, Lin; Yang, Jiashi; Wang, Hairen; Chen, Xuedong

    2013-04-01

    We propose a new structure consisting of a piezoelectric spring-mass system as a low-frequency piezoelectric energy harvester. A theoretical model is developed for the system from the theory of piezoelectricity. An analysis is performed to demonstrate the low-frequency nature of the system. Other basic characteristics of the energy harvester, including the output power, voltage, and efficiency, are also calculated and examined.

  6. High Accuracy Tiny Crack Detection in Metal by Low Frequency Electromagnetic Technique

    NASA Astrophysics Data System (ADS)

    Lou, Weimin; Shen, Changyu; Shentu, Fengying; Li, Guanghai; Chang, Yu; Lu, Xinyuan

    2016-01-01

    A low frequency testing technology based on eddy current technique is proposed for detecting defects in some special equipment surface. A two-dimension model is built to simulate the distribution of low frequency (10 Hz) magnetic flux density nearby the surface of a metal plate. The influence of lift-off effect, coil diameter, crack shape on the measurement are discussed. And the crack measurement sensitivity of 0.6 pm was obtained.

  7. The Prevalence of Annoyance and Effects after Long-Term Exposure to Low-Frequency Noise

    NASA Astrophysics Data System (ADS)

    PERSSON WAYE, K.; RYLANDER, R.

    2001-02-01

    A cross-sectional questionnaire and noise measurement survey was undertaken among 279 randomly chosen persons exposed to noise from heat pump/ventilation installations in their homes. The aim was to evaluate the prevalence of annoyance, disturbance of rest and concentration and the presence of psycho-social and medical symptoms in relation to noise exposure. Of the sample, 108 persons were exposed to a noise classified as of a low-frequency character (low-frequency noise exposed). As controls were chosen 171 persons living in similar residential areas, but exposed to a noise classified as of a mid-frequency character. The results showed that the prevalence of annoyance and disturbed concentration and rest was significantly higher among the persons exposed to low-frequency noise as compared to controls. Annoyance was suggested to be related to the sound pressure levels of the dominant low frequencies. The dB (A) noise levels did not predict annoyance. No significant differences in medical or psycho-social symptoms were found between the low-frequency noise exposed persons and controls. Among persons reporting themselves to be “rather” or “very” annoyed by low-frequency noise due to the heat pump/ventilation installations, a higher extent of psycho-social symptoms, sleep disturbance and headaches was found.

  8. Non-Gaussian Dyadic and Triadic Mutual Information among Atmospheric-Oceanic Low Frequency Variability Modes

    NASA Astrophysics Data System (ADS)

    Pires, C. L.

    2013-12-01

    Principal components (PCs) of the low-frequency variability have zero cross correlation by construction but they are not statistically independent. Their degree of dependency is assessed through the Shannon mutual information (MI). PCs were computed here both for: 1) the monthly running means of the stream functions of a one million days run of a T63, 3level, perpetual winter forced, quasi-geostrophic (QG3) model and 2) the annual running means of the SST from GISS 1880-2012 data. One computes both the dyadic MI: I(X,Y) and triadic MI: I(X,Y,Z) among arbitrary PCs X,Y,Z (rotated or not) by using a kernel-based MI estimation method applied to previously Gaussianized marginal variables obtained by Gaussian anamorphosis thus making estimation more resistant to outliers. Non-vanishing MI comes from the non-Gaussianity of the full PDF of the state-vector of retained PCs. Statistically significant non-Gaussian dyadic MI appears between leading PC-pairs, both for the QG3 model run (projecting on planetary-slow scales) and for GISS data where some nonlinear correlations are emphasized between Pacific and Atlantic SST modes. We propose an iterative optimization algorithm looking for uncorrelated variables X, Y, Z, (obtained from orthogonal projections), taken from a multivariate space of N PCs (N≥3), which maximize I(X,Y,Z), i.e. their triadic non-Gaussian interaction. It also maximizes the joint negentropy leading to the presence of relevant non-linear correlations across the three linearly uncorrelated variables. This is solved through an iterative optimization method by maximizing a positive contrast function (e.g. the squared expectation E(XYZ)2 ), vanishing under Gaussian conditions. In order to understand the origin of a statistically significant positive mutual information I(X,Y,Z)>0, one decomposes it into a dyadic term: I2(X,Y,Z)≡I(X,Y)+I(X,Z)+I(Y,Z), vanishing iff X,Y,Z are pair-wised independent and into a triadic term, the so called interactivity term: It(X

  9. Deep low-frequency earthquakes beneath the Japan arc - The characteristics and the mechanisms of DLFs -

    NASA Astrophysics Data System (ADS)

    Ueda, H.; Takeo, M.; Hagiwara, H.; Hashimoto, T.; Funasaki, J.

    2002-12-01

    Under the Japan arc, ¤Deep Low Frequency earthquakesŒ are occurring. We call ¤Deep Low Frequency earthquakes (DLF)Œ because such events have very low dominant frequency against other shallow microearthquakes having almost the same magnitude. DLFs occur at the depth around the Moho boundary. The focal area is much deeper than the ordinal seismogenic zone. These events sometimes have large and long tailing coda parts of S-wave. Such events have been reported mainly beneath the volcanic front. These characters led us to the qualitative argument suggesting the relationship between the source process and the magma movement. But now we have some reports that such events are occurring other area. This means that to elucidate the source dynamics of DLF will be the key for deeper understanding of the lower crust dynamics. We report the first step for trying to construct the quantitative physical model of DLFIs source dynamics. We use two processes to make it. First, to estimate the physical environment of the field where DLF are occurring, we investigate the hypocenters of these events, and compare with the Curie point depth contour in the Japan arc. The result is that we find that the hypocenters are almost all within the Moho boundary to lower crust. As an exception, in the Kii peninsula, DLF events are occurring within the upper boundary of the subducting slab to the mantle wedge. There is a positive correlation between the depths of DLF hypocenter and the Curie point depths. This result suggests that the temperature highly affects to the occurring mechanism of DLF. Second, to estimate the source dynamics of DLF, we elucidate the source mechanism for some events. DLF has the characteristics that later phase which has large amplitude longs. It means that forcal mechanism cannot explain the waveform completely. But the forcal mechanism represents the force couple, then important information such as relationship between the mechanism and regional stress field, geometry

  10. New Astronomy from the Moon: a Lunar Based Very-Low Frequency Radio Array

    NASA Astrophysics Data System (ADS)

    Takahashi, Yuki D.

    2002-01-01

    Setting up an observatory on the Moon could not only give us new views of the universe, but also inspire the billions of people who look at the Moon. Such a project will utilize the same transportation, communication, and power systems required for further exploration of the Moon. The lunar surface provides unique advantages for astronomy, even compared to orbits or Lagrange points. It is a large and stable platform that can shield unwanted radiation and that will be easily accessible once a lunar base is established. Astronomy from the Moon has been advocated since at least the mid-1960s. The most seriously investigated concept has always been a very-low- frequency (VLF) array on the lunar far side for mainly three reasons. First, the very low frequencies below ~30 MHz is the last window in the electromagnetic spectrum yet to be explored in astronomy, giving us good reasons to anticipate unexpected discoveries. Second, because of E a r t h ' s significant radio interference, the lunar far side may well be the only site accessible that enables sensitive galactic / extra-galactic VLF observations. Finally, an array of short dipole antennas is one the most technologically feasible observatories to be placed and operated on the Moon. The motivations for a lunar based VLF array is detailed in the first section. The second section provides a review of the foregoing effort and a summary of the consensus to date. To make this dream into a reality, we identify the next required steps in the third section. We must f i r s t address any unresolved issues, especially concerning the lunar environmental factors like the ionosphere density. We should make the most out of the upcoming lunar missions by proposing relevant measurements. Most importantly, we should begin proposing our first array now. C o n s i d e r i n g the limited budget, the first realistic surface array will be deployed as a piggyback payload to early landers on the lunar south pole. The side of the Malapert

  11. The Transport of Low-Frequency Turbulence in Astrophysical Flows. II. Solutions for the Super-Alfvenic Solar Wind

    NASA Astrophysics Data System (ADS)

    Adhikari, L.; Zank, G. P.; Bruno, R.; Telloni, D.; Hunana, P.; Marino, R.; Hu, Q.

    2015-12-01

    Zank et al. 2012 developed a low-frequency turbulence transport model for any magnetized inhomogeneous flow. The model describes the energy corresponding to forward and backward propagating modes, the residual energy, and the correlation lengths corresponding to forward and backward propagating modes and the residual energy. We apply the Zank et al. model to the super-Alfvénic solar wind, considering i) the heliosphere from 0.29 to 5 AU with and without the Alfvén velocity, and ii) the entire heliosphere from 0.29 to 100 AU in the absence of the Alfvén velocity. The model shows that (1) shear driving is responsible for the in situ generation of backward propagating modes, (2) the inclusion of the background magnetic field modifies the transport of turbulence in the inner heliosphere, (3) the correlation lengths of forward and backward propagating modes are almost equal beyond ˜30 AU, and (4) the fluctuating magnetic and kinetic energies in MHD turbulence are in approximate equipartition beyond ˜30 AU. Model results for each case are compared to observations, using Helios 2 and Ulysses observations for the first case, and Voyager 2 data for the second case. For the Voyager 2 observations, we calculate the turbulent quantities corresponding to a positive and negative sign of B_r and B_t, and the azimuthal angle φ=tan-1(B_t /B_r ). The model reproduces the observations quite well from 0.29 to 5 AU. The outer heliosphere (>1 AU) observations are well described by the model. The temporal and latitudinal dependence of the observations makes a detailed comparison difficult but the overall trends are well captured by the models. We conclude that the results reasonably validate the Zank et al. model for the super-Alfvénic solar wind.

  12. Hydro-mechanical modelling of slow slip phenomena in subduction channels

    NASA Astrophysics Data System (ADS)

    Petrini, Claudio; Gerya, Taras; Madonna, Claudio; van Dinther, Ylona

    2016-04-01

    Subduction zone seismicity is widely variable in origin and also includes more recently discovered families of "slow earthquakes", such as low- and very-low-frequency earthquakes, slow slip events and tremor. Several lines of evidence suggest that both regular and slow slip phenomena in subduction zones are intrinsically related to and controlled by fluid-related processes. It is therefore important to investigate and better understand the role that fluids play for the different events and processes in subduction zones. A finite difference fully coupled visco-elasto-plastic hydro-mechanical numerical code with marker-in-cell technique was developed to investigate how the presence of fluids in the pore space of a (de)compacting rock matrix affects shear band formation in subduction channels. Good correlations between shear band and fluid related parameters, such as porosity, permeability and fluid pressure factor have been observed. Tensile shear bands are present when no gravity is taken into account in the model, showing higher porosity and permeability than outside the shear zones. Gravity, however, plays an important role in stabilizing the model; confined shearbands (lower porosity and permeability than outside the shearbands) are observed in the presence of gravity. The model also spontaneously produces periodic slow slip events along plastic shear zones, which could be comparable to slow earthquakes observed in subduction zones. Slow-slip-like events develop in response to the process of propagation of individual fault zones through the subduction channel medium. This process is associated with lowering of total pressure along these zones at nearly constant fluid pressure, which notably reduces brittle/plastic strength of deforming fault rocks. Providing in this way a dynamic feedback for the accumulated elastic stress release in the channel.

  13. Low-Frequency Earthquakes in Cascadia: Results from Array of Arrays

    NASA Astrophysics Data System (ADS)

    Sweet, J. R.; Creager, K. C.; Ghosh, A.; Vidale, J. E.

    2010-12-01

    Low-frequency earthquakes (LFEs) are a recently identified class of earthquakes that have been observed to occur coincidentally with tectonic tremor in time and space. These LFEs also have a frequency spectra that is nearly identical to that of tectonic tremor—implying a common source for these two phenomena. As demonstrated by Shelly et al. (2006, 2007, Nature), tremor in Japan can be thought of as a superposition of many individual LFEs. Accordingly, LFEs have been used to constrain the location and focal mechanism of tremor. LFEs have been identified within tectonic tremor at several subduction zones around the world (Brown et al., 2009, GRL), including Cascadia, as well as strike-slip faults like the San Andreas Fault. In 2008 we identified two LFE clusters in Cascadia using a single dense seismic array. These clusters each contained approximately 100 repeating LFEs over the course of about an hour. The clusters were located on the plate interface and individual LFE locations within the clusters varied by no more than ~200m. Here we show the detection of LFEs in northern Cascadia using newly collected data from the Array of Arrays (AOA) experiment. The AOA consists of 8 dense seismic arrays—containing 10 3-component and 10 single-component instruments each—deployed along the northern Olympic Peninsula of western Washington State. These arrays are situated above the portion of the Cascadia subduction zone that sees regular episodic tremor and slip (ETS) events—approximately between the surface projections of the 30-45km depth contours of the subduction interface. The AOA recorded the August 2010 ETS event that began in southern Puget Sound and migrated along strike directly underneath our arrays—and is continuing as we write this abstract. We will use slowness values calculated using a beam-forming technique to slant stack the array data and enhance the tremor/LFE signal to noise. Identified LFEs will be used as templates that can be cross

  14. Magnitudes and Moment-Duration Scaling of Low-Frequency Earthquakes Beneath Southern Vancouver Island

    NASA Astrophysics Data System (ADS)

    Bostock, M. G.; Thomas, A.; Rubin, A. M.; Savard, G.; Chuang, L. Y.

    2015-12-01

    We employ 130 low-frequency-earthquake (LFE) templates representing tremor sources on the plate boundary below southern Vancouver Island to examine LFE magnitudes. Each template is assembled from 100's to 1000's of individual LFEs, representing over 300,000 independent detections from major episodic-tremor-and- slip (ETS) events between 2003 and 2013. Template displacement waveforms for direct P- and S-waves at near epicentral distances are remarkably simple at many stations, approaching the zero-phase, single pulse expected for a point dislocation source in a homogeneous medium. High spatio-temporal precision of template match-filtered detections facilitates precise alignment of individual LFE detections and analysis of waveforms. Upon correction for 1-D geometrical spreading, attenuation, free-surface magnification and radiation pattern, we solve a large, sparse linear system for 3-D path corrections and LFE magnitudes for all detections corresponding to a single ETS template. The spatio-temporal distribution of magnitudes indicates that typically half the total moment release occurs within the first 12-24 hours of LFE activity during an ETS episode when tidal sensitity is low. The remainder is released in bursts over several days, particularly as spatially extensive RTRs, during which tidal sensitivity is high. RTR's are characterized by large magnitude LFEs, and are most strongly expressed in the updip portions of the ETS transition zone and less organized at downdip levels. LFE magnitude-frequency relations are better described by power-law than exponential distributions although they exhibit very high b-values ≥ 6. We examine LFE moment-duration scaling by generating templates using detections for limiting magnitude ranges MW<1.5, MW≥ 2.0. LFE duration displays a weaker dependence upon moment than expected for self-similarity, suggesting that LFE asperities are limited in dimension and that moment variation is dominated by slip. This behaviour implies

  15. The role of low-frequency variation in the manifestation of warming trend and ENSO amplitude

    NASA Astrophysics Data System (ADS)

    Yeo, Sae-Rim; Yeh, Sang-Wook; Kim, Kwang-Yul; Kim, WonMoo

    2016-10-01

    Despite the increase in greenhouse gas concentration, the sea surface temperature (SST) over the tropical eastern Pacific during the period of 1999-2014 exhibits less warming trend compared to the earlier decades. It has been noted that this warming hiatus is accompanied by a negative phase of the Pacific Decadal Oscillation (PDO), which represents low-frequency variability over the Pacific. On the other hand, the 2015/2016 El Niño is among the strongest comparable to the 1997/1998 event, which coincides with the recently altered PDO phase from negative to positive. These observational evidences have generated substantial interest in the role of low-frequency variations in modulating El Niño-Southern Oscillation amplitude as well as manifestation of warming signal in the tropical Pacific. Therefore, it is necessary to appropriately separate low-frequency variability and global warming signal from SST records. Here, we present three primary modes of global SST that include secular warming trend, low-frequency variability, and biennial oscillation. Based on the independent behavior of these three modes, global warming is clearly continuing but its manifestation is enhanced (depressed) when the low-frequency variation is in the positive (negative) phase. Further, possibility of strong El Niño increases under the positive phase of the low-frequency mode, which amplifies warming over the tropical eastern Pacific. Indeed, the strong 2015/2016 El Niño is largely attributed to the positive phase of the low-frequency mode. In order to examine the climate models' ability to simulate the three SST modes as obtained in the observational record, the Coupled Model Intercomparison Project phase 5 (CMIP5) datasets are also analyzed. The spatial and temporal characteristics of the three modes have been replicated closely by the selected CMIP5 models forced by the historical condition, which provides an analogy of the interplay of three modes in the observed tropical Pacific SST.

  16. Slow Antihydrogen

    SciTech Connect

    Gabrielse, G.; Speck, A.; Storry, C.H.; Le Sage, D.; Guise, N.; Larochelle, P.C.; Grzonka, D.; Oelert, W.; Schepers, G.; Sefzick, T.; Pittner, H.; Herrmann, M.; Walz, J.; Haensch, T.W.

    2004-10-20

    Slow antihydrogen is now produced by two different production methods. In Method I, large numbers of H atoms are produced during positron-cooling of antiprotons within a nested Penning trap. In a just-demonstrated Method II, lasers control the production of antihydrogen atoms via charge exchange collisions. Field ionization detection makes it possible to probe the internal structure of the antihydrogen atoms being produced - most recently revealing atoms that are too tightly bound to be well described by the guiding center atom approximation. The speed of antihydrogen atoms has recently been measured for the first time. After the requested overview, the recent developments are surveyed.

  17. On nonlinear evolution of low-frequency Alfvén waves in weakly-expanding solar wind plasmas

    SciTech Connect

    Nariyuki, Y.

    2015-02-15

    A multi-dimensional nonlinear evolution equation for Alfvén waves in weakly-expanding solar wind plasmas is derived by using the reductive perturbation method. The expansion of solar wind plasma parcels is modeled by an expanding box model, which includes the accelerating expansion. It is shown that the resultant equation agrees with the Wentzel-Kramers-Brillouin prediction of the low-frequency Alfvén waves in the linear limit. In the cold and one-dimensional limit, a modified derivative nonlinear Schrodinger equation is obtained. Direct numerical simulations are carried out to discuss the effect of the expansion on the modulational instability of monochromatic Alfvén waves and the propagation of Alfvén solitons. By using the instantaneous frequency, it is quantitatively shown that as far as the expansion rate is much smaller than wave frequencies, effects of the expansion are almost adiabatic. It is also confirmed that while shapes of Alfvén solitons temporally change due to the expansion, some of them can stably propagate after their collision in weakly-expanding plasmas.

  18. A test of the Hall-MHD model: Application to low-frequency upstream waves at Venus

    NASA Technical Reports Server (NTRS)

    Orlowski, D. S.; Russell, C. T.; Krauss-Varban, D.; Omidi, N.

    1994-01-01

    Early studies suggested that in the range of parameter space where the wave angular frequency is less than the proton gyrofrequency and the plasma beta, the ratio of the thermal to magnetic pressure, is less than 1 magnetohydrodynamics provides an adequate description of the propagating modes in a plasma. However, recently, Lacombe et al. (1992) have reported significant differences between basic wave characteristics of the specific propagation modes derived from linear Vlasov and Hall-magnetohydrodynamic (MHD) theories even when the waves are only weakly damped. In this paper we compare the magnetic polarization and normalization magnetic compression ratio of ultra low frequency (ULF) upstream waves at Venus with magnetic polarization and normalized magnetic compression ratio derived from both theories. We find that while the 'kinetic' approach gives magnetic polarization and normalized magnetic compression ratio consistent with the data in the analyzed range of beta (0.5 less than beta less than 5) for the fast magnetosonic mode, the same wave characteristics derived from the Hall-MHD model strongly depend on beta and are consistent with the data only at low beta for the fast mode and at high beta for the intermediate mode.

  19. Very low frequency radio events with a reduced intensity observed by the low-altitude DEMETER spacecraft

    NASA Astrophysics Data System (ADS)

    Záhlava, J.; Němec, F.; Santolík, O.; Kolmašová, I.; Parrot, M.; Rodger, C. J.

    2015-11-01

    We present results of a systematic study of unusual very low frequency (VLF) radio events with a reduced intensity observed in the frequency-time spectrograms measured by the low-orbiting Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) spacecraft. They occur exclusively on the nightside. During these events, the intensity of fractional hop whistlers at specific frequencies is significantly reduced. These frequencies are usually above about 3.4 kHz (second Earth-ionosphere waveguide cutoff frequency), but about 20% of events extend down to about 1.7 kHz (first Earth-ionosphere waveguide cutoff frequency). The frequencies of a reduced intensity vary smoothly with time. We have inspected 6.5 years of DEMETER data, and we identified in total 1601 such events. We present a simple model of the event formation based on the wave propagation in the Earth-ionosphere waveguide. We apply the model to two selected events, and we demonstrate that the model is able to reproduce both the minimum frequencies of the events and their approximate frequency-time shapes. The overall geographic distribution of the events is shifted by about 3000 km westward and slightly southward with respect to the areas with high long-term average lightning activity. We demonstrate that this shift is related to the specific DEMETER orbit, and we suggest its qualitative explanation by the east-west asymmetry of the wave propagation in the Earth-ionosphere waveguide.

  20. Slow magnetohydrodynamic waves in the solar atmosphere.

    PubMed

    Roberts, B

    2006-02-15

    There is increasingly strong observational evidence that slow magnetoacoustic modes arise in the solar atmosphere, either as propagating or standing waves. Sunspots, coronal plumes and coronal loops all appear to support slow modes. Here we examine theoretically how the slow mode may be extracted from the magnetohydrodynamic equations, considering the special case of a vertical magnetic field in a stratified medium: the slow mode is described by the Klein-Gordon equation. We consider its application to recent observations of slow waves in coronal loops. PMID:16414890

  1. An automatic MEG low-frequency source imaging approach for detecting injuries in mild and moderate TBI patients with blast and non-blast causes.

    PubMed

    Huang, Ming-Xiong; Nichols, Sharon; Robb, Ashley; Angeles, Annemarie; Drake, Angela; Holland, Martin; Asmussen, Sarah; D'Andrea, John; Chun, Won; Levy, Michael; Cui, Li; Song, Tao; Baker, Dewleen G; Hammer, Paul; McLay, Robert; Theilmann, Rebecca J; Coimbra, Raul; Diwakar, Mithun; Boyd, Cynthia; Neff, John; Liu, Thomas T; Webb-Murphy, Jennifer; Farinpour, Roxanna; Cheung, Catherine; Harrington, Deborah L; Heister, David; Lee, Roland R

    2012-07-16

    Traumatic brain injury (TBI) is a leading cause of sustained impairment in military and civilian populations. However, mild (and some moderate) TBI can be difficult to diagnose because the injuries are often not detectable on conventional MRI or CT. Injured brain tissues in TBI patients generate abnormal low-frequency magnetic activity (ALFMA, peaked at 1-4 Hz) that can be measured and localized by magnetoencephalography (MEG). We developed a new automated MEG low-frequency source imaging method and applied this method in 45 mild TBI (23 from combat-related blasts, and 22 from non-blast causes) and 10 moderate TBI patients (non-blast causes). Seventeen of the patients with mild TBI from blasts had tertiary injuries resulting from the blast. The results show our method detected abnormalities at the rates of 87% for the mild TBI group (blast-induced plus non-blast causes) and 100% for the moderate group. Among the mild TBI patients, the rates of abnormalities were 96% and 77% for the blast and non-blast TBI groups, respectively. The spatial characteristics of abnormal slow-wave generation measured by Z scores in the mild blast TBI group significantly correlated with those in non-blast mild TBI group. Among 96 cortical regions, the likelihood of abnormal slow-wave generation was less in the mild TBI patients with blast than in the mild non-blast TBI patients, suggesting possible protective effects due to the military helmet and armor. Finally, the number of cortical regions that generated abnormal slow-waves correlated significantly with the total post-concussive symptom scores in TBI patients. This study provides a foundation for using MEG low-frequency source imaging to support the clinical diagnosis of TBI. PMID:22542638

  2. Use of slow sound to design perfect and broadband passive sound absorbing materials.

    PubMed

    Groby, J-P; Pommier, R; Aurégan, Y

    2016-04-01

    Perfect (100%) absorption by thin structures consisting of a periodic arrangement of rectangular quarter-wavelength channels with side detuned quarter-wavelength resonators is demonstrated. The thickness of these structures is 13-17 times thinner than the acoustic wavelength. This low frequency absorption is due to a slow sound wave propagating in the main rectangular channel. A theoretical model is proposed to predict the complex wavenumber in this channel. It is shown that the speed of sound in the channel is much lower than in the air, almost independent of the frequency in the low frequency range, and it is dispersive inside the induced transparency band which is observed. The perfect absorption condition is found to be caused by a critical coupling between the rectangular channel (sub-wavelength resonators) and the incoming wave. It is shown that the width of a large absorption peak in the frequency spectrum can be broadened if several rectangular channels in the unit cell are detuned. The detuning is achieved by varying the length of the side resonators for each channel. The predicted absorption coefficients are validated experimentally. Two resonant cells were produced with stereolithography which enabled the authors to incorporate curved side resonators. PMID:27106313

  3. Low-frequency vocalizations in the Florida manatee (Trichechus manatus latirostris)

    NASA Astrophysics Data System (ADS)

    Frisch, Katherine; Frisch, Stefan

    2003-10-01

    Vocalizations produced by Florida manatees (Trichechus manatus latirostris) have been characterized as being of relatively high frequency, with fundamental tones ranging from 2500-5000 Hz. These sounds have been variously described as squeaks, squeals, and chirps. Vocalizations below 500 Hz have not been previously reported. Two captive-born Florida manatees were recorded at Mote Marine Laboratory in Sarasota, Florida. The analysis of these vocalizations provides evidence of a new category of low-frequency sounds produced by manatees. These sounds are often heard in conjunction with higher-frequency vocalizations. The low-frequency vocalizations are relatively brief and of low amplitude. These vocalizations are perceived as a series of impulses rather than a low-frequency periodic tone. Knowledge of these low-frequency vocalizations could be useful to those developing future management strategies. Interest has recently increased in the development of acoustic detection and deterrence devices to reduce the number of manatee watercraft interactions. The design of appropriate devices must take into account the apparent ability of manatees to perceive and produce sounds of both high and low frequency. It is also important to consider the possibility that acoustic deterrence devices may disrupt the potentially communicative frequencies of manatee vocalizations.

  4. Stress Recovery Effects of High- and Low-Frequency Amplified Music on Heart Rate Variability

    PubMed Central

    2016-01-01

    Sounds can induce autonomic responses in listeners. However, the modulatory effect of specific frequency components of music is not fully understood. Here, we examined the role of the frequency component of music on autonomic responses. Specifically, we presented music that had been amplified in the high- or low-frequency domains. Twelve healthy women listened to white noise, a stress-inducing noise, and then one of three versions of a piece of music: original, low-, or high-frequency amplified. To measure autonomic response, we calculated the high-frequency normalized unit (HFnu), low-frequency normalized unit, and the LF/HF ratio from the heart rate using electrocardiography. We defined the stress recovery ratio as the value obtained after participants listened to music following scratching noise, normalized by the value obtained after participants listened to white noise after the stress noise, in terms of the HFnu, low-frequency normalized unit, LF/HF ratio, and heart rate. Results indicated that high-frequency amplified music had the highest HFnu of the three versions. The stress recovery ratio of HFnu under the high-frequency amplified stimulus was significantly larger than that under the low-frequency stimulus. Our results suggest that the high-frequency component of music plays a greater role in stress relief than low-frequency components. PMID:27660396

  5. Stress Recovery Effects of High- and Low-Frequency Amplified Music on Heart Rate Variability

    PubMed Central

    2016-01-01

    Sounds can induce autonomic responses in listeners. However, the modulatory effect of specific frequency components of music is not fully understood. Here, we examined the role of the frequency component of music on autonomic responses. Specifically, we presented music that had been amplified in the high- or low-frequency domains. Twelve healthy women listened to white noise, a stress-inducing noise, and then one of three versions of a piece of music: original, low-, or high-frequency amplified. To measure autonomic response, we calculated the high-frequency normalized unit (HFnu), low-frequency normalized unit, and the LF/HF ratio from the heart rate using electrocardiography. We defined the stress recovery ratio as the value obtained after participants listened to music following scratching noise, normalized by the value obtained after participants listened to white noise after the stress noise, in terms of the HFnu, low-frequency normalized unit, LF/HF ratio, and heart rate. Results indicated that high-frequency amplified music had the highest HFnu of the three versions. The stress recovery ratio of HFnu under the high-frequency amplified stimulus was significantly larger than that under the low-frequency stimulus. Our results suggest that the high-frequency component of music plays a greater role in stress relief than low-frequency components.

  6. A hybrid method for strong low-frequency noise suppression in prestack seismic data

    NASA Astrophysics Data System (ADS)

    Hu, Chunhua; Lu, Wenkai

    2014-09-01

    Low-frequency components are important portion of seismic data in exploration geophysics, and have great effects on seismic imaging of deep subsurface and full waveform inversion. Unfortunately, seismic data usually suffers from various kinds of noises and has low signal to noise ratio (SNR) in low-frequency band, although this situation has been improved by developments of acquisition technology. In this paper, we propose a low-frequency cascade filter (LFCF) in Fourier domain for strong low-frequency noise suppression in prestack gathers. LFCF includes a 1D adaptive median filter in f-x domain and a 2D notch filter in f-k domain, which is able to process high-amplitude swell noise, random noise, and seismic interference noise. We employ traces rearrangement and spike-detection mechanisms in adaptive f-x median filter, which can handle strong noise specifically, such as wide-spreading swell noise and tug noise. And a notch filter in f-k domain is designed to separate reflection signal and random noise by different apparent velocities. Through these means, our method can effectively attenuate low-frequency random and coherent noise while simultaneously protect the signal. Experiments on synthetic example and field data are conducted, and the results demonstrate that our method is practical and effective and can preserve signal down to 2 Hz.

  7. Examining the Causes of Low-frequency Hybrid Earthquakes During Dike Intrusions in the Afar Rift, Ethiopia

    NASA Astrophysics Data System (ADS)

    Tepp, G.; Ebinger, C. J.; Belachew, M.

    2014-12-01

    Between 2005 and 2012, there were 14 large dike intrusions into the Dabbahu rift segment in the Afar rift, Ethiopia. Swarms of earthquakes with local magnitudes between 1.45low-frequency content and longer codas than expected for typical volcano-tectonic events. These unusual earthquakes were classified as low-frequency hybrid events based on peak frequency and percent of energy below 2 Hz. Previous studies in other volcanic regions have found similar events, which has led to debate about what causes these events and how best to classify them. Explanations for hybrid events include both source and path effects, though the results from previous work and this study suggest that the Afar hybrids are largely a result of path effects based on high attenuation (Q ~ 200) and azimuthal dependence of spectral content. However, large (~3m) surface displacements on short faults indicate that unusual source processes, such as slow rupture times, may also be a factor in these hybrid events. The aims of this study are to distinguish between path and source effects, to characterize the source processes of these events, and to explore the relation between hybrid and normal tectonic events in the region - are the differences in the source or only in the path? For closely located earthquakes, an Empirical Green's Function approach is a great method to isolate the source-time function. Spectral analysis of the source-time function can be used to provide insights into the rupture time, stress drop, and scaling relations of the earthquakes. These results will be used to further refine earthquake classifications and determine if there are any defining characteristics of the classes that associate them with specific faulting processes, such as surface

  8. Analysis of extremely low frequency brain magnetic fields associated with short-term memory and recognition processes (abstract)

    NASA Astrophysics Data System (ADS)

    Yoshida, Hideki; Ueno, Shoogo; Cheyne, Douglas; Weinberg, Harold

    1996-04-01

    One of the advantages of neural magnetic measurement using a dc-SQUID machine is to measure magnetic fields associated with the direct current or the extremely low frequencial components of neural electric activities. In this study, the order of four tones is memorized by the subject and compared with that of another four tones. The extremely slow magnetic fields were observed by using this paradigm. Two kinds of tones (two octaves apart: the 1046.5 Hz tone and the 261.6 Hz tone) were used. A male subject memorized the order of four tones chosen randomly. After 1.4 s rest, the other four tones were presented. The subject discriminated the order of the first tones from that of the last tones in the forward order. When another long (1 s) tone was presented 2.4 s later, the subject was to push either a true or a false button. Pushing the true button meant the order of the first four tones was the same as that of the last in the forward order. Pushing the false button meant the order was not the same. The whole-cortex 64 channels of MEG data were digitized with a sampling frequency of 125 Hz, and filtered (zero phase shift, low pass digital filter with a cutoff at 20 Hz). In comparison with the control wave, the wave during memorizing clearly includes very low frequency components. We observed that the intensities of the power spectral components at 0.5 Hz during memorizing and recognition is higher than that of the control power spectral components, and tried to make the topographies using the differences between the power spectral components at 0.5 Hz during memory and recognition and the control power spectral components. Because the memory processes affect the very low frequency components of MEG, the current dipole source models are made from the data filtered below 0.5 Hz. We observed that the memory processes affected the very low frequency components of MEG. We estimated the current dipole sources using MEG data below 0.5 Hz.

  9. Slow earthquakes linked along dip in the Nankai subduction zone.

    PubMed

    Hirose, Hitoshi; Asano, Youichi; Obara, Kazushige; Kimura, Takeshi; Matsuzawa, Takanori; Tanaka, Sachiko; Maeda, Takuto

    2010-12-10

    We identified a strong temporal correlation between three distinct types of slow earthquakes distributed over 100 kilometers along the dip of the subducting oceanic plate at the western margin of the Nankai megathrust rupture zone, southwest Japan. In 2003 and 2010, shallow very-low-frequency earthquakes near the Nankai trough as well as nonvolcanic tremor at depths of 30 to 40 kilometers were triggered by the acceleration of a long-term slow slip event in between. This correlation suggests that the slow slip might extend along-dip between the source areas of deeper and shallower slow earthquakes and thus could modulate the stress buildup on the adjacent megathrust rupture zone.

  10. Effects of core position of locally resonant scatterers on low-frequency acoustic absorption in viscoelastic panel

    NASA Astrophysics Data System (ADS)

    Zhong, Jie; Wen, Ji-Hong; Zhao, Hong-Gang; Yin, Jian-Fei; Yang, Hai-Bin

    2015-08-01

    Locally resonant sonic materials, due to their ability to control the propagation of low-frequency elastic waves, have become a promising option for underwater sound absorption materials. In this paper, the finite element method is used to investigate the absorption characteristics of a viscoelastic panel periodically embedded with a type of infinite-long non-coaxially cylindrical locally resonant scatterers (LRSs). The effect of the core position in the coating layer of the LRS on the low-frequency (500 Hz-3000 Hz) sound absorption property is investigated. With increasing the longitudinal core eccentricity e, there occur few changes in the absorptance at the frequencies below 1500 Hz, however, the absorptance above 1500 Hz becomes gradually better and the valid absorption (with absorptance above 0.8) frequency band (VAFB) of the viscoelastic panel becomes accordingly broader. The absorption mechanism is revealed by using the displacement field maps of the viscoelastic panel and the steel slab. The results show two typical resonance modes. One is the overall resonance mode (ORM) caused by steel backing, and the other is the core resonance mode (CRM) caused by LRS. The absorptance of the viscoelastic panel by ORM is induced mainly by the vibration of the steel slab and affected little by core position. On the contrary, with increasing the core eccentricity, the CRM shifts toward high frequency band and decouples with the ORM, leading to two separate absorption peaks and the broadened VAFB of the panel. Project supported by the National Natural Science Foundation of China (Grant No. 51275519).

  11. Dual-Beam Histotripsy: A Low-Frequency Pump Enabling a High-Frequency Probe for Precise Lesion Formation

    PubMed Central

    Lin, Kuang-Wei; Duryea, Alexander P.; Kim, Yohan; Hall, Timothy L.; Xu, Zhen; Cain, Charles A.

    2014-01-01

    Histotripsy produces tissue fractionation through dense energetic bubble clouds generated by short, high-pressure, ultrasound pulses. When using pulses shorter than 2 cycles, the generation of these energetic bubble clouds only depends on where the peak negative pressure (P–) exceeds an intrinsic threshold of a medium (26 – 30 MPa in soft tissue with high water content). This paper investigates a strategic method for precise lesion generation in which a low-frequency pump pulse is applied to enable a sub-threshold high-frequency probe pulse to exceed the intrinsic threshold. This pump-probe method of controlling a supra-threshold volume can be called “dual-beam histotripsy.” A 20-element dual-frequency (500 kHz and 3 MHz elements confocally aligned) array transducer was used to generate dual-beam histotripsy pulses in RBC phantoms and porcine hepatic tissue specimens. The results showed that, when sub-intrinsic-threshold pump (500 kHz) and probe (3 MHz) pulses were applied together, dense bubble clouds (and resulting lesions) were only generated when their peak negative pressures combined constructively to exceed the intrinsic threshold. The smallest reproducible lesion varied with the relative amplitude between the pump and probe pulses, and, with a higher proportion of the probe pulse, smaller lesions could be generated. When the propagation direction of the probe pulse relative to the pump pulse was altered, the shape of the produced lesion changed based on the region that exceeded intrinsic threshold. Since the low-frequency pump pulse is more immune to attenuation and aberrations, and the high-frequency probe pulse can provide precision in lesion formation, this dual-beam histotripsy approach would be very useful in situations where precise lesion formation is required through a highly attenuative and aberrative medium, such as transcranial therapy. This is particularly true if a small low-attenuation acoustic window is available for the high

  12. Dual-beam histotripsy: a low-frequency pump enabling a high-frequency probe for precise lesion formation.

    PubMed

    Lin, Kuang-Wei; Duryea, Alexander P; Kim, Yohan; Hall, Timothy L; Xu, Zhen; Cain, Charles A

    2014-02-01

    Histotripsy produces tissue fractionation through dense energetic bubble clouds generated by short, high-pressure, ultrasound pulses. When using pulses shorter than 2 cycles, the generation of these energetic bubble clouds only depends on where the peak negative pressure (P-) exceeds the intrinsic threshold of the medium (26 to 30 MPa in soft tissue with high water content). This paper investigates a strategic method for precise lesion generation in which a low-frequency pump pulse is applied to enable a sub-threshold high-frequency probe pulse to exceed the intrinsic threshold. This pump-probe method of controlling a supra-threshold volume can be called dual-beam histotripsy. A 20-element dual-frequency (500-kHz and 3-MHz elements confocally aligned) array transducer was used to generate dual-beam histotripsy pulses in red blood cell phantoms and porcine hepatic tissue specimens. The results showed that when sub-intrinsic-threshold pump (500-kHz) and probe (3-MHz) pulses were applied together, dense bubble clouds (and resulting lesions) were only generated when their peak negative pressures combined constructively to exceed the intrinsic threshold. The smallest reproducible lesion varied with the relative amplitude between the pump and probe pulses, and, with a higher proportion of the probe pulse, smaller lesions could be generated. When the propagation direction of the probe pulse relative to the pump pulse was altered, the shape of the produced lesion changed based on the region that exceeded intrinsic threshold. Because the low-frequency pump pulse is more immune to attenuation and aberrations, and the high-frequency probe pulse can provide precision in lesion formation, this dual-beam histotripsy approach would be very useful in situations in which precise lesion formation is required through a highly attenuative and aberrative medium, such as transcranial therapy. This is particularly true if a small low-attenuation acoustic window is available for the high

  13. Low frequency, electrodynamic simulation of kinetic plasmas with the DArwin Direct Implicit Particle-In-Cell (DADIPIC) method

    SciTech Connect

    Gibbons, M.R.

    1995-06-01

    This dissertation describes a new algorithm for simulating low frequency, kinetic phenomena in plasmas. DArwin Direct Implicit Particle-in-Cell (DADIPIC), as its name implies, is a combination of the Darwin and direct implicit methods. One of the difficulties in simulating plasmas lies in the enormous disparity between the fundamental scale lengths of a plasma and the scale lengths of the phenomena of interest. The objective is to create models which can ignore the fundamental constraints without eliminating relevant plasma properties. Over the past twenty years several PIC methods have been investigated for overcoming the constraints on explicit electrodynamic PIC. These models eliminate selected high frequency plasma phenomena while retaining kinetic phenomena at low frequency. This dissertation shows that the combination of Darwin and Direct Implicit allows them to operate better than they have been shown to operate in the past. Through the Darwin method the hyperbolic Maxwell`s equations are reformulated into a set of elliptic equations. Propagating light waves do not exist in the formulation so the Courant constraint on the time step is eliminated. The Direct Implicit method is applied only to the electrostatic field with the result that electrostatic plasma oscillations do not have to be resolved for stability. With the elimination of these constraints spatial and temporal discretization can be much larger than that possible with explicit, electrodynamic PIC. The code functions in a two dimensional Cartesian region and has been implemented with all components of the particle velocities, the E-field, and the B-field. Internal structures, conductors or dielectrics, may be placed in the simulation region, can be set at desired potentials, and driven with specified currents.

  14. Dual-beam histotripsy: a low-frequency pump enabling a high-frequency probe for precise lesion formation.

    PubMed

    Lin, Kuang-Wei; Duryea, Alexander P; Kim, Yohan; Hall, Timothy L; Xu, Zhen; Cain, Charles A

    2014-02-01

    Histotripsy produces tissue fractionation through dense energetic bubble clouds generated by short, high-pressure, ultrasound pulses. When using pulses shorter than 2 cycles, the generation of these energetic bubble clouds only depends on where the peak negative pressure (P-) exceeds the intrinsic threshold of the medium (26 to 30 MPa in soft tissue with high water content). This paper investigates a strategic method for precise lesion generation in which a low-frequency pump pulse is applied to enable a sub-threshold high-frequency probe pulse to exceed the intrinsic threshold. This pump-probe method of controlling a supra-threshold volume can be called dual-beam histotripsy. A 20-element dual-frequency (500-kHz and 3-MHz elements confocally aligned) array transducer was used to generate dual-beam histotripsy pulses in red blood cell phantoms and porcine hepatic tissue specimens. The results showed that when sub-intrinsic-threshold pump (500-kHz) and probe (3-MHz) pulses were applied together, dense bubble clouds (and resulting lesions) were only generated when their peak negative pressures combined constructively to exceed the intrinsic threshold. The smallest reproducible lesion varied with the relative amplitude between the pump and probe pulses, and, with a higher proportion of the probe pulse, smaller lesions could be generated. When the propagation direction of the probe pulse relative to the pump pulse was altered, the shape of the produced lesion changed based on the region that exceeded intrinsic threshold. Because the low-frequency pump pulse is more immune to attenuation and aberrations, and the high-frequency probe pulse can provide precision in lesion formation, this dual-beam histotripsy approach would be very useful in situations in which precise lesion formation is required through a highly attenuative and aberrative medium, such as transcranial therapy. This is particularly true if a small low-attenuation acoustic window is available for the high

  15. Evidence of low frequency waves penetration in the ionosphere observed by Chibis-M satellite

    NASA Astrophysics Data System (ADS)

    Pronenko, Vira; Dudkin, Fedir; Korepanov, Valery

    2016-07-01

    Chibis-M microsatellite (MS) was launched using ISS infrastructure to the 500 km circular orbit with inclination 52° and successfully operated during the years 2012-2014. One of the main tasks of this experiment was the study of how powerful natural and technogenic processes are reflected in the ionosphere. For this study, the magnetic wave complex (MWC) was used which measured one electrical component and three components of the magnetic vector in the frequency range 0.1 Hz-40 kHz. Due to the proximity of the magnetic sensors and the satellite control system, their high sensitivity (up to 0.02 pT/sqrt(Hz)) was not used in full because the level of magnetic noise was about 10 pT/sqrt(Hz) in the low-frequency range. Nevertheless, owing to the symmetric fixation of the electric probes relative to the satellite body, the electrical sensor provided high accuracy measurements (about 0.8-0.04 (µV/m)/sqrt(Hz)) in the frequency range of 0.1-40 000 Hz, despite the very small measurement base of 0.42 m. This allowed us to collect valuable information which revealed a number of interesting physical effects, especially in ultralow frequency (ULF) range. In ULF range the ionospheric emissions with a central frequency of 50 (60) Hz - power line emissions (PLE) and the Schumann resonance harmonics (SR) were detected, though, according to the present model of the ionosphere, they have not penetrate there. A detailed study of the obtained data revealed the features of PLE and SR. The spatial distribution of PLE and their connection with the power lines location on the ground were analyzed. It was found that the intensity of PLE depends on the load characteristics of the power line and usually has a minimum in the morning. The cases of an extra long distance of PLE propagation in the Earth's ionosphere over oceans in the equatorial region have been also observed. Further, it was detected that PLE has been recorded both in the shaded and sunlit parts of the orbits and their

  16. The impact of low-frequency and rare variants on lipid levels

    PubMed Central

    Surakka, Ida; Horikoshi, Momoko; Mägi, Reedik; Sarin, Antti-Pekka; Mahajan, Anubha; Lagou, Vasiliki; Marullo, Letizia; Ferreira, Teresa; Miraglio, Benjamin; Timonen, Sanna; Kettunen, Johannes; Pirinen, Matti; Karjalainen, Juha; Thorleifsson, Gudmar; Hägg, Sara; Hottenga, Jouke-Jan; Isaacs, Aaron; Ladenvall, Claes; Beekman, Marian; Esko, Tõnu; Ried, Janina S; Nelson, Christopher P; Willenborg, Christina; Gustafsson, Stefan; Westra, Harm-Jan; Blades, Matthew; de Craen, Anton JM; de Geus, Eco J; Deelen, Joris; Grallert, Harald; Hamsten, Anders; Havulinna, Aki S.; Hengstenberg, Christian; Houwing-Duistermaat, Jeanine J; Hyppönen, Elina; Karssen, Lennart C; Lehtimäki, Terho; Lyssenko, Valeriya; Magnusson, Patrik KE; Mihailov, Evelin; Müller-Nurasyid, Martina; Mpindi, John-Patrick; Pedersen, Nancy L; Penninx, Brenda WJH; Perola, Markus; Pers, Tune H; Peters, Annette; Rung, Johan; Smit, Johannes H; Steinthorsdottir, Valgerdur; Tobin, Martin D; Tsernikova, Natalia; van Leeuwen, Elisabeth M; Viikari, Jorma S; Willems, Sara M; Willemsen, Gonneke; Schunkert, Heribert; Erdmann, Jeanette; Samani, Nilesh J; Kaprio, Jaakko; Lind, Lars; Gieger, Christian; Metspalu, Andres; Slagboom, P Eline; Groop, Leif; van Duijn, Cornelia M; Eriksson, Johan G; Jula, Antti; Salomaa, Veikko; Boomsma, Dorret I; Power, Christine; Raitakari, Olli T; Ingelsson, Erik; Järvelin, Marjo-Riitta; Stefansson, Kari; Franke, Lude; Ikonen, Elina; Kallioniemi, Olli; Pietiäinen, Vilja; Lindgren, Cecilia M; Thorsteinsdottir, Unnur; Palotie, Aarno; McCarthy, Mark I; Morris, Andrew P; Prokopenko, Inga; Ripatti, Samuli

    2016-01-01

    Using a genome-wide screen of 9.6 million genetic variants achieved through 1000 Genomes imputation in 62,166 samples, we identify association to lipids in 93 loci including 79 previously identified loci with new lead-SNPs, 10 new loci, 15 loci with a low-frequency and 10 loci with missense lead-SNPs, and, 2 loci with an accumulation of rare variants. In six loci, SNPs with established function in lipid genetics (CELSR2, GCKR, LIPC, and APOE), or candidate missense mutations with predicted damaging function (CD300LG and TM6SF2), explained the locus associations. The low-frequency variants increased the proportion of variance explained, particularly for LDL-C and TC. Altogether, our results highlight the impact of low-frequency variants in complex traits and show that imputation offers a cost-effective alternative to re-sequencing. PMID:25961943

  17. Application of a finite-element model to low-frequency sound insulation in dwellings.

    PubMed

    Maluski, S P; Gibbs, B M

    2000-10-01

    The sound transmission between adjacent rooms has been modeled using a finite-element method. Predicted sound-level difference gave good agreement with experimental data using a full-scale and a quarter-scale model. Results show that the sound insulation characteristics of a party wall at low frequencies strongly depend on the modal characteristics of the sound field of both rooms and of the partition. The effect of three edge conditions of the separating wall on the sound-level difference at low frequencies was examined: simply supported, clamped, and a combination of clamped and simply supported. It is demonstrated that a clamped partition provides greater sound-level difference at low frequencies than a simply supported. It also is confirmed that the sound-pressure level difference is lower in equal room than in unequal room configurations. PMID:11051501

  18. A system for tranmitting low frequency analog signals over ac power lines

    DOEpatents

    Baker, S.P.; Durall, R.L.; Haynes, H.D.

    1987-07-30

    A system for transmitting low frequency analog signals over ac power lines using FM modulation. A low frequency analog signal to be transmitted is first applied to a voltage-to-frequency converter where it is converted to a signal whose frequency varies in proportion to the analog signal amplitude. This signal is then used to modulate the carrier frequency of an FM transmitter coupled to an ac power line. The modulation signal frequency range is selected to be within the response band of the FM transmitter. The FM modulated carrier signal is received by an FM receiver coupled to the ac power line, demodulated and the demodulated signal frequency is converted by a frequency-to-voltage converter back to the form of the original low frequency analog input signal. 4 figs.

  19. System for transmitting low frequency analog signals over AC power lines

    DOEpatents

    Baker, Steven P.; Durall, Robert L.; Haynes, Howard D.

    1989-09-05

    A system for transmitting low frequency analog signals over AC power lines using FM modulation. A low frequency analog signal to be transmitted is first applied to a voltage-to-frequency converter where it is converted to a signal whose frequency varies in proportion to the analog signal amplitude. This signal is then used to modulate the carrier frequency of an FM transmitter coupled to an AC power line. The modulation signal frequency range in selected to be within the response band of the FM transmitter. The FM modulated carrier signal is received by an FM receiver coupled to the AC power line, demodulated and the demodulated signal frequency is converted by a frequency-to-voltage converter back to the form of the original low frequency analog input signal.

  20. System for transmitting low frequency analog signals over AC power lines

    DOEpatents

    Baker, Steven P.; Durall, Robert L.; Haynes, Howard D.

    1989-01-01

    A system for transmitting low frequency analog signals over AC power lines using FM modulation. A low frequency analog signal to be transmitted is first applied to a voltage-to-frequency converter where it is converted to a signal whose frequency varies in proportion to the analog signal amplitude. This signal is then used to modulate the carrier frequency of an FM transmitter coupled to an AC power line. The modulation signal frequency range in selected to be within the response band of the FM transmitter. The FM modulated carrier signal is received by an FM receiver coupled to the AC power line, demodulated and the demodulated signal frequency is converted by a frequency-to-voltage converter back to the form of the original low frequency analog input signal.

  1. Design and initial characterization of a compact, ultra high vacuum compatible, low frequency, tilt accelerometer

    SciTech Connect

    O’Toole, A. E-mail: riccardo.desalvo@gmail.com; Peña Arellano, F. E.; Rodionov, A. V.; Kim, C.; Shaner, M.; Asadoor, M.; Sobacchi, E.; Dergachev, V.; DeSalvo, R. E-mail: riccardo.desalvo@gmail.com; Bhawal, A.; Gong, P.; Lottarini, A.; Minenkov, Y.; Murphy, C.

    2014-07-15

    A compact tilt accelerometer with high sensitivity at low frequency was designed to provide low frequency corrections for the feedback signal of the Advanced Laser Interferometer Gravitational Wave Observatory active seismic attenuation system. It has been developed using a Tungsten Carbide ceramic knife-edge hinge designed to avoid the mechanical 1/f noise believed to be intrinsic in polycrystalline metallic flexures. Design and construction details are presented; prototype data acquisition and control limitations are discussed. The instrument's characterization reported here shows that the hinge is compatible with being metal-hysteresis-free, and therefore also free of the 1/f noise generated by the dislocation Self-Organized Criticality in the metal. A tiltmeter of this kind will be effective to separate the ground tilt component from the signal of horizontal low frequency seismometers, and to correct the ill effects of microseismic tilt in advanced seismic attenuation systems.

  2. Method for Estimating Low-Frequency Return Current of DC Electric Railcar

    NASA Astrophysics Data System (ADS)

    Hatsukade, Satoru

    The Estimation of the harmonic current of railcars is necessary for achieving compatibility between train signaling systems and railcar equipment. However, although several theoretical analyses methods for estimating the harmonic current of railcars using switching functions exist, there are no theoretical analysis methods estimating a low-frequency current at a frequency less than the power converter's carrier frequency. This paper describes a method for estimating the spectrum (frequency and amplitude) of the low-frequency return current of DC electric railcars. First, relationships between the return current and characteristics of the DC electric railcars, such as mass and acceleration, are determined. Then, the mathematical (not numerical) calculation results for low-frequency current are obtained from the time-current curve for a DC electric railcar by using Fourier series expansions. Finally, the measurement results clearly show the effectiveness of the estimation method development in this study.

  3. Low-frequency quasi-periodic oscillations in black hole and neutron star LMXBs

    NASA Astrophysics Data System (ADS)

    Ingram, Adam

    2016-07-01

    Low-frequency quasi-periodic oscillations (QPOs) are routinely seen in the X-ray flux of accreting black holes and neutron stars. Since the QPO frequency correlates with the low frequency power spectral break in the same manner for both object classes, it is reasonable to believe that these oscillations have the same physical origin in neutron stars as they do in black holes. However, recent successes in modelling black hole low frequency QPOs as Lense-Thirring precession contrast sharply with failures of the same model in neutron stars. This could be attributable to the significant extra complexity, both in the physics and in the observed power spectra, of accreting neutron stars when compared with black holes. Alternatively, the QPO mechanism really is the same for the two object classes, but in that case, why does the Lense-Thirring model work so well for black holes? I will review the current state of this field.

  4. Design and initial characterization of a compact, ultra high vacuum compatible, low frequency, tilt accelerometer.

    PubMed

    O'Toole, A; Peña Arellano, F E; Rodionov, A V; Shaner, M; Sobacchi, E; Dergachev, V; DeSalvo, R; Asadoor, M; Bhawal, A; Gong, P; Kim, C; Lottarini, A; Minenkov, Y; Murphy, C

    2014-07-01

    A compact tilt accelerometer with high sensitivity at low frequency was designed to provide low frequency corrections for the feedback signal of the Advanced Laser Interferometer Gravitational Wave Observatory active seismic attenuation system. It has been developed using a Tungsten Carbide ceramic knife-edge hinge designed to avoid the mechanical 1/f noise believed to be intrinsic in polycrystalline metallic flexures. Design and construction details are presented; prototype data acquisition and control limitations are discussed. The instrument's characterization reported here shows that the hinge is compatible with being metal-hysteresis-free, and therefore also free of the 1/f noise generated by the dislocation Self-Organized Criticality in the metal. A tiltmeter of this kind will be effective to separate the ground tilt component from the signal of horizontal low frequency seismometers, and to correct the ill effects of microseismic tilt in advanced seismic attenuation systems. PMID:25085166

  5. Inductive phenomena at low frequencies in impedance spectra of proton exchange membrane fuel cells - A review

    NASA Astrophysics Data System (ADS)

    Pivac, Ivan; Barbir, Frano

    2016-09-01

    The results of electrochemical impedance spectroscopy of proton exchange membrane (PEM) fuel cells may exhibit inductive phenomena at low frequencies. The occurrence of inductive features at high frequencies is explained by the cables and wires of the test system. However, explanation of inductive loop at low frequencies requires a more detailed study. This review paper discusses several possible causes of such inductive behavior in PEM fuel cells, such as side reactions with intermediate species, carbon monoxide poisoning, and water transport, also as their equivalent circuit representations. It may be concluded that interpretation of impedance spectra at low frequencies is still ambiguous, and that better equivalent circuit models are needed with clearly defined physical meaning of each of the circuit elements.

  6. Statistics and Properties of Low-Frequency Vibrational Modes in Structural Glasses

    NASA Astrophysics Data System (ADS)

    Lerner, Edan; Düring, Gustavo; Bouchbinder, Eran

    2016-07-01

    Low-frequency vibrational modes play a central role in determining various basic properties of glasses, yet their statistical and mechanical properties are not fully understood. Using extensive numerical simulations of several model glasses in three dimensions, we show that in systems of linear size L sufficiently smaller than a crossover size LD, the low-frequency tail of the density of states follows D (ω )˜ω4 up to the vicinity of the lowest Goldstone mode frequency. We find that the sample-to-sample statistics of the minimal vibrational frequency in systems of size L low-frequency modes is elucidated, and a number of glassy length scales are briefly discussed.

  7. Atomic scattering in the presence of a low-frequency laser

    SciTech Connect

    Banerji, J.

    1982-01-01

    In the first four chapters of this thesis previous work on non-resonant potential scattering, resonant potential scattering and non-resonant electron-atom scattering in the presence of a low-frequency laser has been discussed and extended. Chapter 6 deals with the experimental aspects of laser-modified atomic scattering. In chapter 7, the problem of electron-atom ionizing collisions (both resonant and non-resonant) in the presence of a low-frequency laser is discussed. In the next chapter the cut-off Coulomb potential scattering in the presence of a low-frequency laser has been considered. Because of the long range of the Coulomb potential, the result deviates sharply from that obtained for short range potentials unless, of course, the collision energy is very high. Moreover, it has been suggested that the experiments are not reproducible unless the details of the cut-off Coulomb potential are spelled out.

  8. Analytical theory of low-frequency space charge oscillations in gyrotrons

    SciTech Connect

    Yan Ran; Antonsen, T. M. Jr.; Nusinovich, G. S.

    2008-10-15

    Low-frequency oscillations attributed to reflected electrons bouncing adiabatically between the electron gun and the interaction space have been observed in many gyrotrons. An analytical model is considered which allows one to apply space-charge wave theory to the analysis of these oscillations. In the framework of the small-signal theory, the regions of low-frequency oscillations, the oscillation frequency and the temporal and spatial growth rates of low-frequency oscillations are determined in the relevant parameter space. The mode frequency is determined not only by the particle travel time, but by the travel time of charge waves on the reflected electron beam. This explains the existence of modes with noncommensurate frequencies.

  9. Design and initial characterization of a compact, ultra high vacuum compatible, low frequency, tilt accelerometer

    NASA Astrophysics Data System (ADS)

    O'Toole, A.; Peña Arellano, F. E.; Rodionov, A. V.; Shaner, M.; Sobacchi, E.; Dergachev, V.; DeSalvo, R.; Asadoor, M.; Bhawal, A.; Gong, P.; Kim, C.; Lottarini, A.; Minenkov, Y.; Murphy, C.

    2014-07-01

    A compact tilt accelerometer with high sensitivity at low frequency was designed to provide low frequency corrections for the feedback signal of the Advanced Laser Interferometer Gravitational Wave Observatory active seismic attenuation system. It has been developed using a Tungsten Carbide ceramic knife-edge hinge designed to avoid the mechanical 1/f noise believed to be intrinsic in polycrystalline metallic flexures. Design and construction details are presented; prototype data acquisition and control limitations are discussed. The instrument's characterization reported here shows that the hinge is compatible with being metal-hysteresis-free, and therefore also free of the 1/f noise generated by the dislocation Self-Organized Criticality in the metal. A tiltmeter of this kind will be effective to separate the ground tilt component from the signal of horizontal low frequency seismometers, and to correct the ill effects of microseismic tilt in advanced seismic attenuation systems.

  10. Balloon observations of ultra-low-frequency waves in the electric field above the South Pole

    SciTech Connect

    Liao, B.; Benbrrook, J.R.; Bering E.A. III; Byrne, G.J.; Theall, J.R. )

    1988-01-01

    The physics of ultra-low-frequency waves in the magnetosphere, near the cusp and in the polar cap, is important because this region is one where ultra-low-frequency wave energy from the magnetopause can most easily enter the magnetosphere. During the 1985-1986 South Pole balloon campaign, eight stratospheric balloon payloads were launched from Amundsen-Scott Station, South Geographic Pole, Antarctica, to record data on ultra-low-frequency waves. The payloads were instrumented with three-axis double-probe electric field detectors and X-ray scintillation counters. This paper concentrates on the third flight of this series, which was launched at 2205 universal time on 21 December 1985. Good data were received from the payload until the transmitter failed at 0342 universal time on 22 December. During most of the four hours that the balloon was afloat, an intense ultra-low-frequency wave event was in progress. The electric-field data from this period have been examined in detail and compared with magnetic field data, obtained with ground-based fluxgate and induction magnetometers to determine the characteristics of the waves. After float was reached, the electric-field data in figure 1 show large-amplitude, quasi-periodic fluctuations suggesting the presence of intense ultra-low-frequency wave activity. In conclusion, the electric-field signature observed from flight 3 appears to have been essentially an electrostatic event or possibly a short-wavelength hydromagnetic wave with a varying and interesting polarization character. The authors are continuing the analysis of the data to determine the source of the observed ultra-low-frequency waves.

  11. Acoustic properties of pistonphones at low frequencies in the presence of pressure leakage and heat conduction

    NASA Astrophysics Data System (ADS)

    Zhang, Fan; He, Wen; He, Longbiao; Rong, Zuochao

    2015-12-01

    The wide concern on absolute pressure calibration of acoustic transducers at low frequencies prompts the development of the pistonphone method. At low frequencies, the acoustic properties of pistonphones are governed by the pressure leakage and the heat conduction effects. However, the traditional theory for these two effects applies a linear superposition of two independent correction models, which differs somewhat from their coupled effect at low frequencies. In this paper, acoustic properties of pistonphones at low frequencies in full consideration of the pressure leakage and heat conduction effects have been quantitatively studied, and the explicit expression for the generated sound pressure has been derived. With more practical significance, a coupled correction expression for these two effects of pistonphones has been derived. In allusion to two typical pistonphones, the NPL pistonphone and our developed infrasonic pistonphone, comparisons were done for the coupled correction expression and the traditional one, whose results reveal that the traditional one produces maximum insufficient errors of about 0.1 dB above the lower limiting frequencies of two pistonphones, while at lower frequencies, excessive correction errors with an explicit limit of about 3 dB are produced by the traditional expression. The coupled correction expression should be adopted in the absolute pressure calibration of acoustic transducers at low frequencies. Furthermore, it is found that the heat conduction effect takes a limiting deviation of about 3 dB for the pressure amplitude and a small phase difference as frequency decreases, while the pressure leakage effect remarkably drives the pressure amplitude to attenuate and the phase difference tends to be 90° as the frequency decreases. The pressure leakage effect plays a more important role on the low frequency property of pistonphones.

  12. The assessment and evaluation of low-frequency noise near the region of infrasound.

    PubMed

    Ziaran, Stanislav

    2014-01-01

    The main aim of this paper is to present recent knowledge about the assessment and evaluation of low-frequency sounds (noise) and infrasound, close to the threshold of hearing, and identify their potential effect on human health and annoyance. Low-frequency noise generated by air flowing over a moving car with an open window was chosen as a typical scenario which can be subjectively assessed by people traveling by automobile. The principle of noise generated within the interior of the car and its effects on the comfort of the driver and passengers are analyzed at different velocities. An open window of a car at high velocity behaves as a source of specifically strong tonal low-frequency noise which is generally perceived as annoying. The interior noise generated by an open window of a passenger car was measured under different conditions: Driving on a highway and driving on a typical roadway. First, an octave-band analysis was used to assess the noise level and its impact on the driver's comfort. Second, a fast Fourier transform (FFT) analysis and one-third octave-band analysis were used for the detection of tonal low-frequency noise. Comparison between two different car makers was also done. Finally, the paper suggests some possibilities for scientifically assessing and evaluating low-frequency sounds in general, and some recommendations are introduced for scientific discussion, since sounds with strong low-frequency content (but not only strong) engender greater annoyance than is predicted by an A-weighted sound pressure level. PMID:24583675

  13. Low-frequency oscillations in radiative-convective systems. Part II: An idealized model

    SciTech Connect

    Hu, Q. |; Randall, D.A.

    1995-02-15

    A simple model is used to examine the hypothesis that nonlinear interactions among atmospheric radiation, cumulus convection, and the surface moisture flux can result in a stationary, low-frequency (30-60 day period) oscillating heat source in the tropical atmosphere. The model produces low-frequency oscillations of temperature, moisture, and precipitation. The mechanism that produces these oscillations is identified through analyses of the model and its results. The relevance of this mechanism to understanding the observed Madden-Julian oscillation in the tropical atmosphere over the Indian and western Pacific Oceans is discussed. 17 refs., 12 figs., 2 tabs.

  14. Model of m-level low-frequency current fluctuations in metal thermionic cathodes

    NASA Astrophysics Data System (ADS)

    Ghots, S. S.; Bakhtizin, R. Z.

    2003-06-01

    A new model of low-frequency fluctuations, based on the thermionic current model [Mathematical Handbook for Scientists and Engineers, New York, 1961; Introduction to Statistical Radio-Physic. Part 1: Random Processes, Moscow, 1976 (in Russian)], has been designed. The proposed model provides calculation of realization, auto-correlation function (ACF) and power spectral density (PSD) of an m-level quantum signal. This model has allowed to explain the reason of very small magnitude of low-frequency (LF) boundary (10 -4 to 10 -2 Hz) on experimental spectra of LF current fluctuations in a metal thermionic cathodes.

  15. Alternative low frequency magnetic field theranostics: recent advances, safety and hazards

    NASA Astrophysics Data System (ADS)

    Golovin, Y.; Klyachko, N.; Majouga, A.; Golovin, D.; Gribanovsky, S.

    2015-11-01

    The paper presents a brief review and comparative analysis of low frequency (nonheating) and radio-frequency electromagnetic nanomedicine technologies. The former are shown to have a considerable advantage over the latter ones: a higher flexibility and penetrating ability, easier to dose and control, easier to localize, as well as safer and less costly. This makes their employment promising for building a new technological platform for low frequency magnetic theranostics with a wider range of options, i.e. possessing a wider multimodality than traditional radio-frequency methods.

  16. Synchronization of low-frequency oscillations in the human cardiovascular system

    NASA Astrophysics Data System (ADS)

    Karavaev, A. S.; Prokhorov, M. D.; Ponomarenko, V. I.; Kiselev, A. R.; Gridnev, V. I.; Ruban, E. I.; Bezruchko, B. P.

    2009-09-01

    We investigate synchronization between the low-frequency oscillations of heart rate and blood pressure having in humans a basic frequency close to 0.1 Hz. A method is proposed for quantitative estimation of synchronization between these oscillating processes based on calculation of relative time of phase synchronization of oscillations. It is shown that healthy subjects exhibit on average substantially longer epochs of internal synchronization between the low-frequency oscillations in heart rate and blood pressure than patients after acute myocardial infarction.

  17. High efficiency, low frequency linear compressor proposed for Gifford-McMahon and pulse tube cryocoolers

    SciTech Connect

    Höhne, Jens

    2014-01-29

    In order to reduce the amount of greenhouse gas emissions, which are most likely the cause of substantial global warming, a reduction of overall energy consumption is crucial. Low frequency Gifford-McMahon and pulse tube cryocoolers are usually powered by a scroll compressor together with a rotary valve. It has been theoretically shown that the efficiency losses within the rotary valve can be close to 50%{sup 1}. In order to eliminate these losses we propose to use a low frequency linear compressor, which directly generates the pressure wave without using a rotary valve. First results of this development will be presented.

  18. Numerical and experimental investigation of nonlinear ultrasonic Lamb waves at low frequency

    NASA Astrophysics Data System (ADS)

    Zuo, Peng; Zhou, Yu; Fan, Zheng

    2016-07-01

    Nonlinear ultrasonic Lamb waves are popular to characterize the nonlinearity of materials. However, the widely used nonlinear Lamb mode suffers from two associated complications: inherent dispersive and multimode natures. To overcome these, the symmetric Lamb mode (S0) at low frequency region is explored. At the low frequency region, the S0 mode is little dispersive and easy to generate. However, the secondary mode still exists, and increases linearly for significant distance. Numerical simulations and experiments are used to validate the nonlinear features and therefore demonstrate an easy alternative for nonlinear Lamb wave applications.

  19. Impact of LISA's Low Frequency Sensitivity on Observations of Massive Black Hole Mergers

    NASA Technical Reports Server (NTRS)

    Baker, J.; Centrella, J.

    2005-01-01

    LISA will be able to detect gravitational waves from inspiralling massive black hole (MBH) binaries out to redshifts z > 10. If the binary masses and luminosity distances can be extracted from the Laser Interferometer Space Antenna (LISA) data stream, this information can be used to reveal the merger history of MBH binaries and their host galaxies in the evolving universe. Since this parameter extraction generally requires that LISA observe the inspiral for a significant fraction of its yearly orbit, carrying out this program requires adequate sensitivity at low frequencies, f < 10(exp -4) Hz. Using several candidate low frequency sensitivities, we examine LISA's potential for characterizing MBH binary coalescences at redshifts z > 1.

  20. Measurement of Integrated Low Frequency Flux Noise in Superconducting Flux/Phase Qubits

    SciTech Connect

    Mao Bo; Qiu Wei; Han Siyuan

    2008-11-07

    We measured the integrated low frequency flux noise ({approx}1 m{phi}{sub 0}) of an rf SQUID as a flux qubit by fitting the resonant peaks from photon assistant tunneling (PAT). The energy relaxation time Tl between the ground and first excited states in the same potential well, measured directly in time domain, is 3 ns. From these results we identified low frequency flux noise as the dominant source of decoherence. In addition, we found that the measured values of integrated flux noise in three qubits of various sizes differ more than an order of magnitude.

  1. Correction of shaker flatness deviations in very low frequency primary accelerometer calibration

    NASA Astrophysics Data System (ADS)

    Bruns, Th; Gazioch, S.

    2016-06-01

    This paper describes the influence of a constant curvature of the shaker’s air bearing guidance on a low frequency primary accelerometer calibration. Based on the mathematical model, three different methods are developed that allow a quantitative evaluation of this disturbing effect and thus the correction of the resulting systematic deviation. All three methods are applied to the example of a primary low frequency accelerometer calibration performed at PTB, and the results are given in comparison to the original uncorrected magnitude of sensitivity results.

  2. Damping of lower hybrid waves by low-frequency drift waves

    NASA Astrophysics Data System (ADS)

    Krall, Nicholas A.

    1989-11-01

    The conditions under which a spectrum of lower hybrid drift waves will decay into low-frequency drift waves (LFD) are calculated. The purpose is to help understand why lower hybrid drift waves are not seen in all field-reversed configuration (FRC) experiments in which they are predicted. It is concluded that if there is in the plasma a LFD wave amplitude above a critical level, lower hybrid waves will decay into low-frequency drift waves. The critical level required to stabilize TRX-2 [Phys. Fluids 30, 1497 (1987)] is calculated and found to be reasonably consistent with theoretical estimates.

  3. [Modulation of Ca(2+)-Dependent Proteiolysis under the Action of Weak Low-Frequency Magnetic Fields].

    PubMed

    Kantserova, N P; Lysenko, L A; Ushakova, N V; Krylov, V V; Nemova, N N

    2015-01-01

    The study aimed to determine the molecular targets of magnetic fields in living objects. Time-dependent effects of weak low-frequency magnetic field tuned to the parametric resonance for calcium ions were studied on model organisms (fish, whelk). The dynamics of Ca(2+)-dependent proteinase activity under the exposure to magnetic fields with given parameters was determined and minimal time of exposure in order to achieve inactivation of these proteinases was find out as well. As hyperactivation of Ca(2+)-dependent proteinases is a basis of degenerative pathology development the therapeutic potential of weak low-frequency magnetic fields enabling to modulate Ca(2+)-dependent proteinase activity is supported. PMID:27125027

  4. Rescaling effects on a low-frequency drift wave in dusty plasmas

    NASA Astrophysics Data System (ADS)

    Qiu, Xin; Liu, Sanqiu

    2015-03-01

    The effect of dust on the low-frequency drift wave in inhomogeneous magnetized dusty plasmas is investigated. It is shown that a low-frequency drift wave can be modeled by the Hasegawa-Mima equation (HME) both in mobile and immobile dusty plasmas, which are dust-modified HME and HME in dusty background, respectively. The former is rescaled significantly by the presence of the dust and the space-time scale greatly increases with the increasing density and mass of dust, while the latter is not rescaled, but an additional driving force appears to drive the drift waves.

  5. Terrestrial detector for low-frequency gravitational waves based on full tensor measurement

    NASA Astrophysics Data System (ADS)

    Paik, H. J.; Moody, M. V.; Griggs, C. E.; Lee, H. M.; Majorana, E.

    2016-05-01

    Two serious obstacles in constructing terrestrial gravitational wave (GW) detectors that can resolve low-frequency signals (≤ 10 Hz) are seismic and Newtonian noises. Here we describe a new detector concept by adopting new measurement techniques and configurations to overcome the present low-frequency barrier due to these noises. Six magnetically levitated superconducting test masses, widely separated along three orthogonal axes, each with three degrees of freedom, constitute a tensor GW detector. The tensor outputs could be combined to better reject the Newtonian noise. Unlike current two-dimensional detectors, a single tensor detector is able to determine the polarization of GWs and the direction to sources on its own.

  6. Wide-Area Soil Moisture Estimation Using the Propagation of Lightning Generated Low-Frequency Electromagnetic Signals 1977

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Land surface moisture measurements are central to our understanding of the earth’s water system, and are needed to produce accurate model-based weather/climate predictions. Currently, there exists no in-situ network capable of estimating wide-area soil moisture. In this paper, we explore an alterna...

  7. Uniform silicon slow light waveguide

    NASA Astrophysics Data System (ADS)

    Jiang, C.

    2011-01-01

    An uniform silicon waveguide is proposed featuring ultralow-dispersion slow light. The core of the waveguide consists of one silicon trip and two pairs of air/silicon strip and the cladding is composed of several alternative silicon and air strips, which form a transverse band gap to confine propagating light in the core. The waveguide has several nearly linear photonic bands in a large frequency range, which can support broadband slow modes with a group velocity of 0.03-0.08 c and tolerable group velocity dispersion.

  8. Harvesting Low-Frequency (<5 Hz) Irregular Mechanical Energy: A Possible Killer Application of Triboelectric Nanogenerator.

    PubMed

    Zi, Yunlong; Guo, Hengyu; Wen, Zhen; Yeh, Min-Hsin; Hu, Chenguo; Wang, Zhong Lin

    2016-04-26

    Electromagnetic generators (EMGs) and triboelectric nanogenerators (TENGs) are the two most powerful approaches for harvesting ambient mechanical energy, but the effectiveness of each depends on the triggering frequency. Here, after systematically comparing the performances of EMGs and TENGs under low-frequency motion (<5 Hz), we demonstrated that the output performance of EMGs is proportional to the square of the frequency, while that of TENGs is approximately in proportion to the frequency. Therefore, the TENG has a much better performance than that of the EMG at low frequency (typically 0.1-3 Hz). Importantly, the extremely small output voltage of the EMG at low frequency makes it almost inapplicable to drive any electronic unit that requires a certain threshold voltage (∼0.2-4 V), so that most of the harvested energy is wasted. In contrast, a TENG has an output voltage that is usually high enough (>10-100 V) and independent of frequency so that most of the generated power can be effectively used to power the devices. Furthermore, a TENG also has advantages of light weight, low cost, and easy scale up through advanced structure designs. All these merits verify the possible killer application of a TENG for harvesting energy at low frequency from motions such as human motions for powering small electronics and possibly ocean waves for large-scale blue energy. PMID:27077467

  9. Characterization of Low-Frequency Combustion Stability of the Fastrac Engine

    NASA Technical Reports Server (NTRS)

    Rocker, Marvin; Jones, Preston (Technical Monitor)

    2002-01-01

    A series of tests were conducted to measure the combustion performance of the Fastrac engine thrust chamber. During mainstage, the thrust chamber exhibited no large-amplitude chamber pressure oscillations that could be identified as low-frequency combustion instability or 'chug'. However, during start-up and shutdown, the thrust chamber very briefly exhibited large-amplitude chamber pressure oscillations that were identified as chug. These instabilities during start-up and shutdown were regarded as benign due to their brevity. Linear models of the thrust chamber and the propellant feed systems were formulated for both the thrust chamber component tests and the flight engine tests. These linear models determined the frequency and decay rate of chamber pressure oscillations given the design and operating conditions of the thrust chamber and feed system. The frequency of chamber pressure oscillations determined from the model closely matched the frequency of low-amplitude, low-frequency chamber pressure oscillations exhibited in some of the later thrust chamber mainstage tests. The decay rate of the chamber pressure oscillations determined from the models indicated that these low-frequency oscillations were stable. Likewise, the decay rate, determined from the model of the flight engine tests indicated that the low-frequency chamber pressure oscillations would be stable.

  10. S-shape spring sensor: Sensing specific low-frequency vibration by energy harvesting

    NASA Astrophysics Data System (ADS)

    Zhang, Lan; Lu, Jian; Takei, Ryohei; Makimoto, Natsumi; Itoh, Toshihiro; Kobayashi, Takeshi

    2016-08-01

    We have developed a Si-based microelectromechanical systems sensor with high sensitivity for specific low-frequency vibration-sensing and energy-harvesting applications. The low-frequency vibration sensor contains a disk proof mass attached to two or three lead zirconate titanate (PZT) S-shape spring flexures. To obtain a faster and less expensive prototype, the design and optimization of the sensor structure are studied via finite-element method analysis. To validate the sensor structure to detect low-frequency vibration, the effects of geometrical dimensions, including the width and diameter of the S-shape spring of the proof mass, were analyzed and measured. The functional features, including the mechanical property and electrical performance of the vibration sensor, were evaluated. The results demonstrated that a very low resonant frequency of <11 Hz and a reasonably high voltage output of 7.5 mV at acceleration of >0.2g can be typically achieved. Given a low-frequency vibration sensor with ideal performance and mass fabrication, many advanced civilian and industrial applications can be possibly realized.

  11. Visual and Auditory Priming Influences the Production of Low-Frequency Spellings

    ERIC Educational Resources Information Center

    Abrams, Lise; Trunk, Dunja L.; White, Katherine K.

    2008-01-01

    Three experiments investigated whether production of low-frequency spellings could be influenced by other words containing those spellings. Participants saw visually-presented primes (Experiment 1) or heard primes presented auditorily and produced their spelling (Experiments 2 and 3). Primes either shared both orthography and phonology (e.g.,…

  12. Low Frequency Noise Measurement and Analysis of Capacitive Micro-Accelerometers: Temperature Effect

    NASA Astrophysics Data System (ADS)

    Mohd-Yasin, Faisal; Nagel, David J.; Ong, D. S.; Korman, Can E.; Chuah, H. T.

    2008-06-01

    A noise measurements of micro-accelerometers were performed using a special measurement system. A common spectral behavior of noise is found, with 1/ f noise dominating at low frequencies and white thermal noise being the limiting factor at higher frequencies. A temperature dependent and an acceleration dependant of the noise are found in the accelerometers, in agreement and contract of the theories, respectively.

  13. Low-frequency signals produced by Northeast Atlantic killer whales (Orcinus orca).

    PubMed

    Samarra, Filipa I P; Deecke, Volker B; Miller, Patrick J O

    2016-03-01

    Killer whale acoustic behavior has been extensively investigated; however, most studies have focused on pulsed calls and whistles. This study reports the production of low-frequency signals by killer whales at frequencies below 300 Hz. Recordings were made in Iceland and Norway when killer whales were observed feeding on herring and no other marine mammal species were nearby. Low-frequency sounds were identified in Iceland and ranged in duration between 0.14 and 2.77 s and in frequency between 50 and 270 Hz, well below the previously reported lower limit for killer whale tonal sounds of 500 Hz. Low-frequency sounds appeared to be produced close in time to tail slaps, which are indicative of feeding attempts, suggesting that these sounds may be related to a feeding context. However, their precise function is unknown, and they could be the by-product of a non-vocal behavior rather than a vocal signal deliberately produced by the whales. Although killer whales in Norway exhibit similar feeding behavior, this sound has not been detected in recordings from Norway to date. This study suggests that, like other delphinids, killer whales produce low-frequency sounds, but further studies will be required to understand whether similar sounds exist in other killer whale populations. PMID:27036251

  14. Three dimensional ray tracing of the Jovian magnetosphere in the low frequency range

    NASA Technical Reports Server (NTRS)

    Menietti, J. D.

    1984-01-01

    Ray tracing studies of Jovian low frequency emissions were studied. A comprehensive three-dimensional ray tracing computer code for examination of model Jovian decametric (DAM) emission was developed. The improvements to the computer code are outlined and described. The results of the ray tracings of Jovian emissions will be presented in summary form.

  15. Low-frequency signals produced by Northeast Atlantic killer whales (Orcinus orca).

    PubMed

    Samarra, Filipa I P; Deecke, Volker B; Miller, Patrick J O

    2016-03-01

    Killer whale acoustic behavior has been extensively investigated; however, most studies have focused on pulsed calls and whistles. This study reports the production of low-frequency signals by killer whales at frequencies below 300 Hz. Recordings were made in Iceland and Norway when killer whales were observed feeding on herring and no other marine mammal species were nearby. Low-frequency sounds were identified in Iceland and ranged in duration between 0.14 and 2.77 s and in frequency between 50 and 270 Hz, well below the previously reported lower limit for killer whale tonal sounds of 500 Hz. Low-frequency sounds appeared to be produced close in time to tail slaps, which are indicative of feeding attempts, suggesting that these sounds may be related to a feeding context. However, their precise function is unknown, and they could be the by-product of a non-vocal behavior rather than a vocal signal deliberately produced by the whales. Although killer whales in Norway exhibit similar feeding behavior, this sound has not been detected in recordings from Norway to date. This study suggests that, like other delphinids, killer whales produce low-frequency sounds, but further studies will be required to understand whether similar sounds exist in other killer whale populations.

  16. A dedicated pistonphone for absolute calibration of infrasound sensors at very low frequencies

    NASA Astrophysics Data System (ADS)

    He, Wen; He, Longbiao; Zhang, Fan; Rong, Zuochao; Jia, Shushi

    2016-02-01

    Aimed at the absolute calibration of infrasound sensors at very low frequencies, an upgraded and improved infrasonic pistonphone has been developed. The pistonphone was designed such that a very narrow clearance between the piston and its guide was realized based on an automatically-centered clearance-sealing structure, and a large volume rigid-walled chamber was also adopted, which improved the leakage time-constant of the chamber. A composite feedback control system was applied to the electromagnetic vibrator to control the precise motion of the piston. Performance tests and uncertainty analysis show that the leakage time-constant is so large, and the distortion of the sound pressure is so small, that the pistonphone can be used as a standard infrasound source in the frequency range from 0.001 Hz to 20 Hz. The low frequency property of the pistonphone has been verified through calibrating low frequency microphones. Comparison tests with the reciprocity method have shown that the pressure sensitivities from the pistonphone are not only reliable at common frequencies but also have smaller uncertainties at low frequencies.

  17. The Event-Related Low-Frequency Activity of Highly and Average Intelligent Children

    ERIC Educational Resources Information Center

    Liu, Tongran; Shi, Jiannong; Zhao, Daheng; Yang, Jie

    2008-01-01

    Using time-frequency analysis techniques to investigate the event-related low-frequency (delta: 0.5-4 Hz; theta: 4-8 Hz) activity of auditory event-related potentials (ERPs) data of highly and average intelligent children, 18 intellectually gifted children, and 18 intellectually average children participated the present study. Present findings…

  18. Effects of Removing Low-Frequency Electric Information on Speech Perception with Bimodal Hearing

    ERIC Educational Resources Information Center

    Fowler, Jennifer R.; Eggleston, Jessica L.; Reavis, Kelly M.; McMillan, Garnett P.; Reiss, Lina A. J.

    2016-01-01

    Purpose: The objective was to determine whether speech perception could be improved for bimodal listeners (those using a cochlear implant [CI] in one ear and hearing aid in the contralateral ear) by removing low-frequency information provided by the CI, thereby reducing acoustic-electric overlap. Method: Subjects were adult CI subjects with at…

  19. Low-Frequency Interlayer Raman Modes to Probe Interface of Twisted Bilayer MoS2.

    PubMed

    Huang, Shengxi; Liang, Liangbo; Ling, Xi; Puretzky, Alexander A; Geohegan, David B; Sumpter, Bobby G; Kong, Jing; Meunier, Vincent; Dresselhaus, Mildred S

    2016-02-10

    van der Waals homo- and heterostructures assembled by stamping monolayers together present optoelectronic properties suitable for diverse applications. Understanding the details of the interlayer stacking and resulting coupling is crucial for tuning these properties. We investigated the low-frequency interlayer shear and breathing Raman modes (<50 cm(-1)) in twisted bilayer MoS2 by Raman spectroscopy and first-principles modeling. Twisting significantly alters the interlayer stacking and coupling, leading to notable frequency and intensity changes of low-frequency modes. The frequency variation can be up to 8 cm(-1) and the intensity can vary by a factor of ∼5 for twisting angles near 0° and 60°, where the stacking is a mixture of high-symmetry stacking patterns and is thus sensitive to twisting. For twisting angles between 20° and 40°, the interlayer coupling is nearly constant because the stacking results in mismatched lattices over the entire sample. It follows that the Raman signature is relatively uniform. Note that for some samples, multiple breathing mode peaks appear, indicating nonuniform coupling across the interface. In contrast to the low-frequency interlayer modes, high-frequency intralayer Raman modes are much less sensitive to interlayer stacking and coupling. This research demonstrates the effectiveness of low-frequency Raman modes for probing the interfacial coupling and environment of twisted bilayer MoS2 and potentially other two-dimensional materials and heterostructures. PMID:26797083

  20. A natural low frequency oscillation in the wake of an airfoil near stalling conditions

    NASA Technical Reports Server (NTRS)

    Zaman, K. B. M. Q.; Mckinzie, D. J.

    1988-01-01

    An unusually low frequency oscillation in the flow over an airfoil was explored experimentally. Wind tunnel measurements were carried out with a two dimensional airfoil model at a chord Reynolds number of 100,000. During deep stall the usual bluff-body shedding occurred at a Strouhal number. But at the onset of stall a low frequency periodic oscillation occurred, the corresponding Strouhal number being an order of magnitude lower. The phenomenon occurred in relatively unclean flow when the freestream turbulence was raised to 0.4 percent, but did not in the cleaner flow with turbulence intensity of 0.1 percent. It could also be produced by certain high frequency acoustic excitation. Details of the flow field are compared between a case of low frequency oscillation at alpha = 15 deg and a case of bluff-body shedding at alpha = 22.5 deg. The origin of the low frequency oscillation traces to the upper surface of the airfoil and is seemingly associated with the periodic formation and breakdown of a large separation bubble. The intense flow fluctuations impart significant unsteady forces to the airfoil but diminish rapidly within a distance of one chord from the trailing edge.