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Sample records for propagating low-frequency slow

  1. Low frequency sound propagation in activated carbon.

    PubMed

    Bechwati, F; Avis, M R; Bull, D J; Cox, T J; Hargreaves, J A; Moser, D; Ross, D K; Umnova, O; Venegas, R

    2012-07-01

    Activated carbon can adsorb and desorb gas molecules onto and off its surface. Research has examined whether this sorption affects low frequency sound waves, with pressures typical of audible sound, interacting with granular activated carbon. Impedance tube measurements were undertaken examining the resonant frequencies of Helmholtz resonators with different backing materials. It was found that the addition of activated carbon increased the compliance of the backing volume. The effect was observed up to the highest frequency measured (500 Hz), but was most significant at lower frequencies (at higher frequencies another phenomenon can explain the behavior). An apparatus was constructed to measure the effective porosity of the activated carbon as well as the number of moles adsorbed at sound pressures between 104 and 118 dB and low frequencies between 20 and 55 Hz. Whilst the results were consistent with adsorption affecting sound propagation, other phenomena cannot be ruled out. Measurements of sorption isotherms showed that additional energy losses can be caused by water vapor condensing onto and then evaporating from the surface of the material. However, the excess absorption measured for low frequency sound waves is primarily caused by decreases in surface reactance rather than changes in surface resistance.

  2. Low frequency guided plate wave propagation in fiber reinforced composites

    SciTech Connect

    Lih, S.S.; Mal, A.K.; Bar-Cohen, Y.

    1995-12-31

    The behavior of low frequency guided waves in composite laminates was studied theoretically and experimentally. The objective of this study is to develop a contact-coupling ultrasonic method of determining of the stiffness constants of composite materials. The solution for the low frequency guided wave modes was derived from exact and approximate plate theories. A parametric study was curried out to examine the influence of variations in the elastic stiffness constants on the guided wave modes. A comparison was made between the measured and calculated group velocities to corroborate the theoretical calculations. The experimental setup consisted of a contact coupled pair of transmitting and receiving transducers using pulsed waves and a broadband ultrasonic system. Graphite/epoxy laminates were tested by transmitting the wave along various angles of propagation with the fibers. The received signals were analyzed to determine the group velocity of the low frequency wave modes. Test results have shown a very, good agreement of the calculated and measured elastic constants.

  3. The Effects of Sediment Properties on Low Frequency Acoustic Propagation

    DTIC Science & Technology

    2014-09-30

    RI: We have acquired a geophone/hydrophone array under a DURIP grant ( Seafloor Shear Measurement Using Interface Waves, Miller and Potty PIs...low frequency sound absorption, leading to wider spread of low frequency sounds. 6 Figure 4: Left panel shows the absorption (in dB) at 10 km

  4. 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.

  5. Obliquely propagating low frequency electromagnetic shock waves in two dimensional quantum magnetoplasmas

    SciTech Connect

    Masood, W.

    2009-04-15

    Linear and nonlinear propagation characteristics of low frequency magnetoacoustic waves in quantum magnetoplasmas are studied employing the quantum magnetohydrodynamic model. In this regard, a quantum Kadomtsev-Petviashvili-Burgers (KPB) equation is derived using the small amplitude expansion method. The dissipation is introduced by taking into account the kinematic viscosity among the plasma constituents. Furthermore, the solution of KPB equation is presented using the tangent hyperbolic (tanh) method. The variation in the fast and slow magnetoacoustic shock profiles with the quantum Bohm potential via increasing number density, obliqueness angle {theta}, magnetic field, and the resistivity are also investigated. It is observed that the aforementioned plasma parameters significantly modify the propagation characteristics of nonlinear magnetoacoustic shock waves in quantum magnetoplasmas. The relevance of the present investigation with regard to dense astrophysical environments is also pointed out.

  6. Low Frequency Acoustic Intensity Propagation Modeling in Shallow Water Waveguides

    DTIC Science & Technology

    2016-06-01

    examine the acoustic pressure and intensity features present in several environments of interest. Free field propagation and analytically tractable...acoustic pressure and intensity features present in several environments of interest. Free field propagation and analytically tractable planar...is available commercially [1]. While numerous scenarios involve radiation of energy into a quiescent free field , there are similar problems in which

  7. The Effects of Sediment Properties on Low Frequency Acoustic Propagation

    DTIC Science & Technology

    2015-09-30

    Acoustic Propagation James H. Miller and Gopu R. Potty University of Rhode Island Department of Ocean Engineering Narragansett, RI 02881 Phone...for Shear Wave Speed using Scholte Wave Dispersion,” OCEANS 2013, September 23-26, San Diego, USA, (2013). 3. M. K. Broadhead, H. B. Ali, and L. D...crustaceans and groundfish,” in Effects of Noise on Aquatic Life II, eds. Popper, Arthur and Hawkins, Anthony, Springer, 2014 [accepted, Book Chapter]. 6

  8. 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.

  9. Low frequency piezoresonance defined dynamic control of terahertz wave propagation

    NASA Astrophysics Data System (ADS)

    Dutta, Moumita; Betal, Soutik; Peralta, Xomalin G.; Bhalla, Amar S.; Guo, Ruyan

    2016-11-01

    Phase modulators are one of the key components of many applications in electromagnetic and opto-electric wave propagations. Phase-shifters play an integral role in communications, imaging and in coherent material excitations. In order to realize the terahertz (THz) electromagnetic spectrum as a fully-functional bandwidth, the development of a family of efficient THz phase modulators is needed. Although there have been quite a few attempts to implement THz phase modulators based on quantum-well structures, liquid crystals, or meta-materials, significantly improved sensitivity and dynamic control for phase modulation, as we believe can be enabled by piezoelectric-resonance devices, is yet to be investigated. In this article we provide an experimental demonstration of phase modulation of THz beam by operating a ferroelectric single crystal LiNbO3 film device at the piezo-resonance. The piezo-resonance, excited by an external a.c. electric field, develops a coupling between electromagnetic and lattice-wave and this coupling governs the wave propagation of the incident THz beam by modulating its phase transfer function. We report the understanding developed in this work can facilitate the design and fabrication of a family of resonance-defined highly sensitive and extremely low energy sub-millimeter wave sensors and modulators.

  10. Low frequency piezoresonance defined dynamic control of terahertz wave propagation

    PubMed Central

    Dutta, Moumita; Betal, Soutik; Peralta, Xomalin G.; Bhalla, Amar S.; Guo, Ruyan

    2016-01-01

    Phase modulators are one of the key components of many applications in electromagnetic and opto-electric wave propagations. Phase-shifters play an integral role in communications, imaging and in coherent material excitations. In order to realize the terahertz (THz) electromagnetic spectrum as a fully-functional bandwidth, the development of a family of efficient THz phase modulators is needed. Although there have been quite a few attempts to implement THz phase modulators based on quantum-well structures, liquid crystals, or meta-materials, significantly improved sensitivity and dynamic control for phase modulation, as we believe can be enabled by piezoelectric-resonance devices, is yet to be investigated. In this article we provide an experimental demonstration of phase modulation of THz beam by operating a ferroelectric single crystal LiNbO3 film device at the piezo-resonance. The piezo-resonance, excited by an external a.c. electric field, develops a coupling between electromagnetic and lattice-wave and this coupling governs the wave propagation of the incident THz beam by modulating its phase transfer function. We report the understanding developed in this work can facilitate the design and fabrication of a family of resonance-defined highly sensitive and extremely low energy sub-millimeter wave sensors and modulators. PMID:27901070

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. Activation of very low frequency earthquakes by slow slip events in the Ryukyu Trench

    NASA Astrophysics Data System (ADS)

    Nakamura, Mamoru; Sunagawa, Naoya

    2015-02-01

    Long-term activity of shallow very low frequency earthquakes (VLFEs) in the Ryukyu Trench, unassociated with recent large thrust earthquakes, was analyzed using a broadband seismometer network. The distribution of shallow VLFEs was divided into three large clusters. The activity of the VLFEs is modulated by repetitive slow slip events, and the activity of these VLFEs increases to 2-3 times its ordinary rate at 10-20 days after the onset of the slow slip events. The activation of VLFEs could be generated by small increases on the order of approximately 0.1-0.5 kPa in Coulomb failure stress, suggesting that stress in the plate interface where the VLFEs occur is frequently released in small amounts. Moreover, the distribution of VLFEs is complementary to the historical tsunami source area and locked area. The distribution of the VLFEs indicates heterogeneity in interplate coupling along the trench.

  16. Imbricated slip rate processes during slow slip transients imaged by low-frequency earthquakes

    NASA Astrophysics Data System (ADS)

    Lengliné, O.; Frank, W. B.; Marsan, D.; Ampuero, J.-P.

    2017-10-01

    Low Frequency Earthquakes (LFEs) often occur in conjunction with transient strain episodes, or Slow Slip Events (SSEs), in subduction zones. Their focal mechanism and location consistent with shear failure on the plate interface argue for a model where LFEs are discrete dynamic ruptures in an otherwise slowly slipping interface. SSEs are mostly observed by surface geodetic instruments with limited resolution and it is likely that only the largest ones are detected. The time synchronization of LFEs and SSEs suggests that we could use the recorded LFEs to constrain the evolution of SSEs, and notably of the geodetically-undetected small ones. However, inferring slow slip rate from the temporal evolution of LFE activity is complicated by the strong temporal clustering of LFEs. Here we apply dedicated statistical tools to retrieve the temporal evolution of SSE slip rates from the time history of LFE occurrences in two subduction zones, Mexico and Cascadia, and in the deep portion of the San Andreas fault at Parkfield. We find temporal characteristics of LFEs that are similar across these three different regions. The longer term episodic slip transients present in these datasets show a slip rate decay with time after the passage of the SSE front possibly as t - 1 / 4. They are composed of multiple short term transients with steeper slip rate decay as t-α with α between 1.4 and 2. We also find that the maximum slip rate of SSEs has a continuous distribution. Our results indicate that creeping faults host intermittent deformation at various scales resulting from the imbricated occurrence of numerous slow slip events of various amplitudes.

  17. 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.

  18. Three-dimensional parabolic equation model for low frequency sound propagation in irregular urban canyons.

    PubMed

    Doc, Jean-Baptiste; Lihoreau, Bertrand; Félix, Simon; Faure, Cédric; Dubois, Guillaume

    2015-01-01

    A three-dimensional wide-angle parabolic equation (3DPE) is used to model low frequency sound propagation in irregular urban canyons at low computational cost. This one-way wave equation is solved using the Alternating Direction Implicit method. A finite difference scheme adapted to the geometry of the urban environment is then developed. Abrupt variations of the street width are treated as a single scattering problem using the Kirchhoff approximation. Numerical results are compared with experimental data obtained on a scale model of a street. Comparisons show the ability of the 3DPE model to provide reliable transmitted fields even for large irregularities.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

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

    SciTech Connect

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

    2014-06-25

    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. Furthermore, in LD simulation, the solvent friction coefficients should be imposed only on the protein surface.

  4. MAVEN Observation of an Obliquely Propagating Low-Frequency Wave Upstream of Mars

    NASA Technical Reports Server (NTRS)

    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.; hide

    2016-01-01

    We report Mars Atmosphere and Volatile EvolutioN (MAVEN) 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.

  5. MAVEN Observation of an Obliquely Propagating Low-Frequency Wave Upstream of Mars

    NASA Technical Reports Server (NTRS)

    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.

    2016-01-01

    We report Mars Atmosphere and Volatile EvolutioN (MAVEN) 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.

  6. 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.

  7. 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.

  8. Numerical modeling of interaction between shallow very low frequency earthquakes and deep slow slip events

    NASA Astrophysics Data System (ADS)

    Matsuzawa, T.; Shibazaki, B.; Obara, K.; Hirose, H.

    2013-12-01

    We numerically simulate shallow very low frequency earthquakes (SVLFs) and slow slip events (SSEs) in a single model. SSEs in the Nankai subduction zone, Japan, are classified to short- and long-term depending on their duration. Short-term SSEs are found with episodic tremor activity, and recur at the interval of several months. Long-term SSEs are located at shallower part than short-term SSEs, and recur at the interval of 6-7 years at the Bungo Channel in the Nankai subduction zone. Both of long- and short-term SSEs are found at the deeper extent of the major slip region of megathrust earthquakes. On the other hand, SVLFs are found at close to the trench axis, and have a dominant frequency below 0.1 Hz. Hirose et al. (2010) reported that SVLFs became active during periods of long-term SSEs in the Bungo channel. Long- and short-term SSEs are numerically reproduced in a flat plate model, adopting a rate- and state-dependent friction law with cutoff velocities (Matsuzawa et al., 2010). In addition, Shibazaki et al. (2012) successfully reproduced segments of short-term SSEs and nonvolcanic tremor, introducing actual tremor distribution and the configuration of subducting plate. However, occurrence of SVLFs and the interaction with long-term SSEs have not been reproduced in a numerical model. In this study, we numerically reproduce the characteristics of SVLFs in a flat plate model. In the numerical simulations, the rate- and state-dependent friction law (RS-law) with cut-off velocities is adopted to reproduce SSEs. We assume low effective normal stress and negative (a-b) value in the RS-law at the long- and short-term SSE region, as in our previous study (Matsuzawa et al., 2010). Above the depth of 10 km, we pose circular patches for SVLFs with low-effective normal stress. Based on rock experiment, Saito et al. (2013) suggested that frictional property in the SVLF region changes from velocity-weakening to velocity-strengthening with the increase of slip velocity. Thus

  9. Study on degradation of propagation delay time and low-frequency noise of high-speed optocoupler

    NASA Astrophysics Data System (ADS)

    Huang, Jiaoying; Hu, Sicong; Wang, Xiangfen; Hu, Linjiang

    2017-02-01

    CTR (Current transfer ratio) is generally used to characterize the reliability parameters of optocoupler in engineering. However, high-speed optocoupler has a different structure from the common optocoupler, therefore its most important parameter should be propagation delay time. In addition, CTR serving as the macroscopic parameters, its changes can't directly reflect microscopic changes of the internal defects in device. It is discovered that the number of microscopic defects in the device and the level of low-frequency noise shows a positive correlation. In terms of high-speed optocoupler, this paper proposed a method of combining propagation delay time and low-frequency noise to evaluate the storage reliability. The paper demonstrated how to design circuit to test these parameters and obtain their variations trajectory in accelerated degradation test. In this paper, 20 VO2630 devices were divided into four groups, and a accelerated test at 100°C, 125°C, 150°C and 175°C was conducted to monitor propagation delay time and other parameters related with low-frequency noise. These parameters had different degrees of degradation. This paper showed the degradation process of propagation delay time. It was found that the initial value of propagation delay time was nearly identical, but parameters related with low-frequency noise had different initial values. The larger the initial value of low frequency noise is, the faster propagation delay time will degrade. The main cause of degradation of propagation delay time is Schottky clamped transistor degradation. Finally, this paper discussed the advantages and disadvantages about utilizing conventional electrical parameters or low frequency noise to evaluate the reliability.

  10. A causal relationship between the slow slip event and deep low frequency tremor indicated by strain data recorded at Shingu borehole station

    NASA Astrophysics Data System (ADS)

    Fukuda, M.; Sagiya, T.; Asai, Y.

    2008-12-01

    In the southwest Japan, synchronized deep low frequency tremors and short-term slow slip events occur repeatedly in several regions such as Tokai, northern Kii Peninsula and western Shikoku areas, and these activities are partitioned by 'gaps' of tremors. Although concurrent occurrences of slow slips and tremors have been detected at various subducting plate boundary, their physical mechanism is still not well understood. We are monitoring crustal deformation at Shingu city on the southeastern coast of Kii Peninsula, with an integrated multi-component borehole monitoring system developed by Ishii et al. [2002]. The borehole sensor unit consists of 6 strain sensors (4 in horizontal, 2 in vertical), 2 pendulum tilt sensors, magnetic direction finder and a quartz thermometer and installed at 510m depth. Fukuda et al. [2007] reported two types of strain changes, one associated with deep low frequency tremors and the other without tremors from November 2005 to March 2006. We extend the analysis period to 41 months, from January 2004 to September 2007. We identified 11 episodic strain changes. One of them was caused by heavy rainfall but the rest of the changes are considered to be slow slips. Among all the slow slips identified, five events occurred associated with reported tremor events, but the rest 5 changes were not accompanied by tremors. These slow slip events are characterized by N-S compression (0.017 - 0.063 ppm), and E-W extension (0.013 - 0.071 ppm), NW-SE extension (0.008 - 0.097 ppm), and last 4 - 9 days. We estimate a fault model for each event by forward modeling, and find that the all the strain changes can be attributed to reverse faulting on the plate boundary beneath the Kii Peninsula. An interesting strain change occurred from 26 Dec. 2004 to 2 Jan. 2005. In this period, a tremor activity propagated southwestward on central Kii Peninsula and the level of activity remarkably drops when the activity propagated into the tremor gap zone. After that, the

  11. Slow wave propagation in soft adhesive interfaces.

    PubMed

    Viswanathan, Koushik; Sundaram, Narayan K; Chandrasekar, Srinivasan

    2016-11-16

    Stick-slip in sliding of soft adhesive surfaces has long been associated with the propagation of Schallamach waves, a type of slow surface wave. Recently it was demonstrated using in situ experiments that two other kinds of slow waves-separation pulses and slip pulses-also mediate stick-slip (Viswanathan et al., Soft Matter, 2016, 12, 5265-5275). While separation pulses, like Schallamach waves, involve local interface detachment, slip pulses are moving stress fronts with no detachment. Here, we present a theoretical analysis of the propagation of these three waves in a linear elastodynamics framework. Different boundary conditions apply depending on whether or not local interface detachment occurs. It is shown that the interface dynamics accompanying slow waves is governed by a system of integral equations. Closed-form analytical expressions are obtained for the interfacial pressure, shear stress, displacements and velocities. Separation pulses and Schallamach waves emerge naturally as wave solutions of the integral equations, with oppositely oriented directions of propagation. Wave propagation is found to be stable in the stress regime where linearized elasticity is a physically valid approximation. Interestingly, the analysis reveals that slow traveling wave solutions are not possible in a Coulomb friction framework for slip pulses. The theory provides a unified picture of stick-slip dynamics and slow wave propagation in adhesive contacts, consistent with experimental observations.

  12. A numerical study of transcranial focused ultrasound beam propagation at low frequency

    NASA Astrophysics Data System (ADS)

    Yin, Xiangtao; Hynynen, Kullervo

    2005-04-01

    The feasibility of transcranial ultrasound focusing with a non-moving phased array and without skull-specific aberration correction was investigated using computer simulations. Three cadaver skull CT image data sets were incorporated into an acoustic wave transmission model to simulate transskull ultrasound wave propagation. Using a 0.25 MHz hemispherical array (125 mm radius of curvature, 250 mm diameter, 24 255 elements), the simulated beams could be focused and steered with transducer element driving phases and amplitude adjusted for focal beam steering in water (water-path). A total of 82 foci, spanning wide ranges of distance in the three orthogonal dimensions, were simulated to test the focal beam steering capability inside the three skulls. The acoustic pressure distribution in a volume of 20 × 20 × 20 mm3 centred at each focus was calculated with a 0.5 mm spacing in each axis. Clearly defined foci were retained through the skulls (skull-path) in most cases. The skull-path foci were on average 1.6 ± 0.8 mm shifted from their intended locations. The -3 dB skull-path beam width and length were on average 4.3 ± 1.0 mm and 7.7 ± 1.8 mm, respectively. The skull-path sidelobe levels ranged from 25% to 55% of the peak pressure values. The skull-path peak pressure levels were about 10%-40% of their water-path counterparts. Focusing low-frequency beam through skull without skull-specific aberration correction is possible. This method may be useful for applying ultrasound to disrupt the blood-brain barrier for targeted delivery of therapeutic or diagnostic agents, or to induce microbubbles, or for other uses of ultrasound in brain where the required power levels are low and the sharp focusing is not needed.

  13. A numerical study of transcranial focused ultrasound beam propagation at low frequency.

    PubMed

    Yin, Xiangtao; Hynynen, Kullervo

    2005-04-21

    The feasibility of transcranial ultrasound focusing with a non-moving phased array and without skull-specific aberration correction was investigated using computer simulations. Three cadaver skull CT image data sets were incorporated into an acoustic wave transmission model to simulate transskull ultrasound wave propagation. Using a 0.25 MHz hemispherical array (125 mm radius of curvature, 250 mm diameter, 24 255 elements), the simulated beams could be focused and steered with transducer element driving phases and amplitude adjusted for focal beam steering in water (water-path). A total of 82 foci, spanning wide ranges of distance in the three orthogonal dimensions, were simulated to test the focal beam steering capability inside the three skulls. The acoustic pressure distribution in a volume of 20 x 20 x 20 mm(3) centred at each focus was calculated with a 0.5 mm spacing in each axis. Clearly defined foci were retained through the skulls (skull-path) in most cases. The skull-path foci were on average 1.6 +/- 0.8 mm shifted from their intended locations. The -3 dB skull-path beam width and length were on average 4.3 +/- 1.0 mm and 7.7 +/- 1.8 mm, respectively. The skull-path sidelobe levels ranged from 25% to 55% of the peak pressure values. The skull-path peak pressure levels were about 10%-40% of their water-path counterparts. Focusing low-frequency beam through skull without skull-specific aberration correction is possible. This method may be useful for applying ultrasound to disrupt the blood-brain barrier for targeted delivery of therapeutic or diagnostic agents, or to induce microbubbles, or for other uses of ultrasound in brain where the required power levels are low and the sharp focusing is not needed.

  14. Excitation of low-frequency waves via coupling between slow Alfven waves in the GAMMA 10 tandem mirror

    NASA Astrophysics Data System (ADS)

    Ikezoe, R.; Ichimura, M.; Okada, T.; Hirata, M.; Sakamoto, M.; Iwamoto, Y.; Sumida, S.; Jang, S.; Itagaki, J.; Onodera, Y.; Yoshikawa, M.; Kohagura, J.; Shima, Y.; Wang, X.; Nakashima, Y.

    2015-11-01

    In normal discharges of the GAMMA 10 tandem mirror, confined energy is saturated against heating power and unstable slow Alfven wave named as Alfven-Ion-Cyclotron (AIC) wave is observed in the saturated phase. This saturation may be partly related to (1) the decay of ICRF heating power, which is the main power source in GAMMA 10, due to the coupling with the AIC waves to produce difference-frequency waves and (2) the enhancement of axial transport of high-energy ions owing to nonlinearly excited low-frequency waves. To investigate these phenomena precisely, reflectometry is applied, which can provide assessment of nonlinear process at the location where the nonlinear process are taking place without any disturbance. Bispectral analysis applied to the density fluctuations measured at a wide radial region clearly shows the occurrence of various wave-wave couplings among the heating ICRF wave and the AIC waves. Generation of low-frequency waves via the coupling between coexisting AIC waves is found to be significant only near the core region. Details of measured nonlinear couplings are presented along with the observation showing the clear relation of generated low-frequency waves with the axial transport of high-energy ions. This work is partly supported by JSPS, Japan (25400531, 15K17797) and by NIFS, Japan (NIFS15KUGM101).

  15. 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

  16. 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

  17. Relative Slowness Estimates for Locations of Repeating Low-Frequency Earthquakes and Narrow-Band Tremor at Fuego Volcano, Guatemala

    NASA Astrophysics Data System (ADS)

    Waite, G. P.; Lyons, J. J.

    2009-12-01

    Fuego volcano, Guatemala, is an open-vent basaltic stratovolcano characterized by nearly constant, but low-level eruptive activity since 1999. In January 2008, we deployed small antennas of six broadband seismic and five acoustic sensors 0.9 km north of the active vent to investigate the source of explosions and low-frequency seismicity. The seismic array had stations spaced 30 m apart and a total aperture of ~140 m. The infrasound sensors were deployed in a similar array, but with average station spacing of 50 m. There was no lava effusion during the deployment, but explosions were recorded approximately once per hour, with varied amounts of ash, and with durations from 20-150 s. In addition to the explosions, our seismic array recorded narrow band tremor with dominant frequencies of 1.6 and 1.9 Hz and discrete events that were not generally detected by the acoustic array. The dominant class of these events, which repeated approximately 10-15 times per hour, had an impulsive onset with first motion toward the vent, a short duration of <5 s, and dominant frequencies from 1-3 Hz. Their similarity suggests a nondestructive source process. While waveforms are similar from event to event when viewed on the same channel, the large variation in waveforms across the array yields a large uncertainty in slowness parameter estimates. We take advantage of the high degree of similarity between events to determine relative slowness estimates. After determining the best-fit slowness parameters for a master event, we measured the relative slowness parameters for 203 similar events. The results indicate a stationary source, although subtle variations in waveforms suggest that the source mechanism or source location varied slightly with time. The low-frequency events were located by computing slowness parameters from synthetic waveforms for a volume of sources beneath the summit region. The source is ~150 m directly beneath the active vent, but not associated with explosions. Full

  18. Belief Propagation for Probabilistic Slow Feature Analysis

    NASA Astrophysics Data System (ADS)

    Omori, Toshiaki; Sekiguchi, Tomoki; Okada, Masato

    2017-08-01

    Slow feature analysis (SFA) is a time-series analysis method for extracting slowly-varying latent features from multi-dimensional data. A recent study proposed a probabilistic framework of SFA using the Bayesian statistical framework. However, the conventional probabilistic framework of SFA can not accurately extract the slow feature in noisy environments since its marginal likelihood function was approximately derived under the assumption that there exists no observation noise. In this paper, we propose a probabilistic framework of SFA with rigorously derived marginal likelihood function. Here, we rigorously derive the marginal likelihood function of the probabilistic framework of SFA by using belief propagation. We show using numerical data that the proposed probabilistic framework of SFA can accurately extract the slow feature and underlying parameters for the latent dynamics simultaneously even under noisy environments.

  19. 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.

  20. 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.

  1. The Influence of Low-frequency Oscillation Propagation of the Tibetan Plateau Vortex on Rainstorm Downstream

    NASA Astrophysics Data System (ADS)

    Xiao, Tiangui; Wang, Chao; La, Jia; Du, Jun; Zhang, Kairong

    2017-04-01

    Based on Tibetan Plateau vortex data, ERA-Interim and NCEP/NCAR reanalysis data, the characteristics of Tibetan Plateau vortex and the relationship with Low-Frequency Oscillation (LFO) from 2003 to 2012 were investigated. The heavy rainstorm occurred in Sichuan from June 29th to July 2nd in 2013, caused by the LFO, was studied. Besides, the signal of LFO, energy transmission and those influence to rainstorm were also investigate. The main conclusions are as follows: (1)Most of Tibetan Plateau vortex generate in eastern plateau, located at Tanggula Mountains, Zaduo, Dege, Qumalai and Qaidam. The moving-out Tibetan Plateau vortex mainly generate in Qumalai and most vortex occurrences during April to September. There are three directions of moving-out vortex paths: northeast, southeast and east. The areas which plateau vortex moving into are mainly distributed in Gansu, Sichuan, Shaanxi and Ningxia. (2)The zonal wind at 500hPa in plateau key region has a significant main 10-30d oscillation, with the secondly significant oscillation in 30-50d and the third in 70-90d. The relative vorticity at 500hPa in plateau key region has a significant main 30-50d oscillations, with the secondly significant oscillation in 10-30d. The 30-50d oscillation phase zone with weak westerly oscillation zone of 500hPa, and the 10-30d oscillation positive phase zone with weak oscillation zone of 500hPa are benefit to vortex generation. The 30-50d oscillation of zonal wind at 500hPa provides necessary circulation background for generation of plateau vortex, and positive phase region of 10-30d oscillation of relative vorticity at 500hPa provide necessary dynamic background conditions for it. (3) Comparing with the high frequency oscillation vortex, 10-25d low-frequency vortex is not significant at 500hPa before merging into the basin vortex. However, after merging into the basin vortex, there is a significant relationship between low-frequency vortex and the process of development, weakening and

  2. 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.

  3. 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

  4. Slow crack propagation in composite restorative materials.

    PubMed

    Montes-G, G M; Draughn, R A

    1987-05-01

    The double-torsion test technique was used to study slow crack propagation in a set of dental composite resins including two glass-filled and two microfilled materials. The microstructure within each pair was the same but one of the resins was selfcured and the other photocured. The fracture behavior was dependent on the filler concentration and the presence of absorbed water. Wet materials fractured by slow crack growth in the range of crack velocity studied (10(-7) to 10(-3) m/s), and the microfilled composites, which contain a lower concentration of inorganic filler, had lower stress intensity factors (K1c) than the glass-filled composites tested. Dry specimens of the microfilled materials and the selfcured, glass-filled composite also showed unstable, stick-slip fracture behavior indicative of a crack blunting mechanism which leads to an elevation of the stress intensity factor for crack initiation over K1c for stable crack growth. The plasticizing effect of water increased the viscoelastic response of the materials measured by the slope of curves of slow crack growth. Analysis of fracture surfaces showed that cracks propagated at low velocities (10(-7) to 10(-5) m/s) by the apparent failure of the filler/matrix interfacial bond, and absorbed water affected the strength or fracture resistance of the interface. At high crack velocities the properties of the composite depend on the properties of the polymeric matrix, the filler, and the filler volume fraction, but at low velocities the interface is the controlling factor in the durability of these composites exposed to an aqueous environment.

  5. Physical modeling of low-frequency sound propagation through human thoracic tissue.

    PubMed

    Pandia, Keya; Vijayraghavan, Karthik; Kovacs, Gregory T A; Giovangrandi, Laurent

    2010-01-01

    This work aims at modeling, in the presence of simplifying physical and geometrical assumptions, acoustic wave propagation through human thoracic tissue. Presented here are preliminary modeling results that are indicative of dominant lung resonances at specific frequencies. These resonant modes strongly impact pressure distribution in the tissue as well as the pressure and acceleration at the tissue-air interface. Under the modeling conditions, the effect of these lung resonant modes outweighs that of bones on acoustic waves at these frequencies.

  6. 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

  7. 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.

  8. 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.

  9. Technical Note: Remote sensing of sea surface salinity using the propagation of low-frequency navigation signals

    NASA Astrophysics Data System (ADS)

    Astin, I.; Feng, Y.

    2014-12-01

    This paper introduces a potential method for the remote sensing of sea surface salinity (SSS) using measured propagation delay of low-frequency Loran-C signals transmitted over an all-seawater path between the Sylt station in Germany and an integrated Loran-C/GPS receiver located in Harwich, UK. The overall delay variations in Loran-C surface waves along the path may be explained by changes in sea surface properties (especially the temperature and salinity), as well as atmospheric dynamics that determine the refractive index of the atmosphere. After removing the atmospheric and sea surface temperature (SST) effects, the residual delay revealed a temporal variation similar to that of SSS data obtained by the European Space Agency's Soil Moisture and Ocean Salinity (SMOS) satellite.

  10. Technical Note: Remote sensing of sea surface salinity using the propagation of low-frequency navigation signals

    NASA Astrophysics Data System (ADS)

    Astin, I.; Feng, Y.

    2015-09-01

    This paper introduces a potential method for the remote sensing of sea surface salinity (SSS) using the measured propagation delay of low-frequency Loran-C signals transmitted over an all-seawater path between the Sylt station in Germany and an integrated Loran-C/GPS receiver located in Harwich, UK. The overall delay variations in Loran-C surface waves along the path may be explained by changes in sea surface properties (especially the temperature and salinity), as well as atmospheric properties that determine the refractive index of the atmosphere. After removing the atmospheric and sea surface temperature (SST) effects from the measured delay, the residual delay revealed a temporal variation similar to that of SSS data obtained by the European Space Agency's Soil Moisture and Ocean Salinity (SMOS) satellite.

  11. Slip History for Short-Term Slow Slip Events With Low-Frequency Tremor in Southwest Japan

    NASA Astrophysics Data System (ADS)

    Hirose, H.; Obara, K.

    2005-12-01

    Slow slip events (SSE) which coincide with nonvolcanic deep low-frequency tremor have been detected in southwest Japan subduction zone (Obara et al., 2004). This coupling phenomenon has similar characteristics to the similar to the episodic tremor and slip (ETS) in the Cascadia subduction zone (Rogers and Dragert, 2003). The SSEs have been found not only in the western Shikoku region (Obara et al., 2004; Hirose and Obara, 2005), but also in the Tokai area. This activity could happen on the deeper part of a source region of a megathrust earthquake which recurs on the shallower part of the subduction plate interface. Hence the knowledge about the generation history of the activity is of decisive importance in understanding the nature of the megathrust earthquake cycle. In this study, we investigate a spatio-temporal history of moment release by SSEs which are accompanied by the tremor in southwest Japan. We use the NIED Hi-net tiltmeter records for monitoring the crustal deformation due to SSE. Tilt change during the episode of the coupling activity is inverted to find a fault model for a SSE, based on Okada's (1992) expression. In the western Shikoku region, 12 episodes are observed since 2001. We estimate a fault model for each episode. These results are compiled to draw a diagram of spatio-temporal distribution of interplate moment release (Kawasaki et al., 2001) as SSE. We found that the interplate coupling ratio at the source region of SSE with tremor is 30-50% in 2001--02, while from 2003 to the early 2004, most of the strain accumulated by the relative plate motion is released by the SSEs. This temporal change in the coupling ratio is possibly related to the occurrence of the 2003 Bungo channel long-term SSE (Ozawa et al., 2004; Hirose and Obara, 2005). The slip history and the similarity in the spatial pattern of the tilt changes suggest that there may be at least four `SSE patches' in the western Shikoku region. We also found the repeating activity of the

  12. Slow light propagation in a ring erbium-doped fiber.

    PubMed

    Bencheikh, K; Baldit, E; Briaudeau, S; Monnier, P; Levenson, J A; Mélin, G

    2010-12-06

    Slow light propagation is demonstrated by implementing Coherent Population Oscillations in a silica fiber doped with erbium ions in a ring surrounding the single mode core. Though only the wings of the mode interact with erbium ions, group velocities around 1360 m/s are obtained without any spatial distortion of the propagating mode.

  13. 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.

  14. ON THE LOW-FREQUENCY BOUNDARY OF SUN-GENERATED MAGNETOHYDRODYNAMIC TURBULENCE IN THE SLOW SOLAR WIND

    SciTech Connect

    Shergelashvili, Bidzina M.; Fichtner, Horst

    2012-06-20

    New aspects of the slow solar wind turbulent heating and acceleration are investigated. A physical meaning of the lower boundary of the Alfven wave turbulent spectra in the solar atmosphere and the solar wind is studied and the significance of this natural parameter is demonstrated. Via an analytical and quantitative treatment of the problem we show that a truncation of the wave spectra from the lower frequency side, which is a consequence of the solar magnetic field structure and its cyclic changes, results in a significant reduction of the heat production and acceleration rates. An appropriate analysis is presented regarding the link of the considered problem with existing observational data and slow solar wind initiation scenarios.

  15. 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.

  16. Modeling the Slow-Tail of Atmospheric Waves to Approximate the Distance of Propagation

    NASA Astrophysics Data System (ADS)

    Le Cocq, C.; Fraser-Smith, A. C.

    2007-12-01

    A lightning strike emits an electromagnetic wave known as an atmospheric or sferic, which propagates through the earth-ionosphere waveguide. Sferics can be recorded by extremely low and very low frequency, ELF and VLF, receiver systems. The recorded signal is composed of two segments, a pulse containing VLF frequencies, followed by a slow-tail, containing the ELF components. The slow-tail is essentially a single cycle wave, which is delayed with respect to the rest of the sferic due to the dispersive nature of the ionosphere. The recorded time- domain slow-tail varies with the lightning strike's current moment, and the waveguide's media characteristics. It is possible to approximate the location of the lightning source with measurements of the sferic. Many methods require measurements from multiple stations, however the goal of this work is to approximate the distance a sferic propagated with a single station. J.R. Wait developed a mode theory where propagating ELF radio are characterized by the first mode. The research reported here uses the first mode equations to model a slow-tail that propagated a certain distance. We include a comparison to measurements on slow-tails observed at widely variable distances from their causative lightning, and analyze the accuracy of our model. Using the inverse of this method along with sferics from known locations, we approximate the form of the current moment at the source and use an average of this waveform to improve our slow-tail model. With an accurate computed slow-tail we can approximate the distance of propagation by fitting the computed waveform to the observed slow-tail. An analysis is given of the effectiveness of this method. As expected, since this method uses data from only one station, the estimation error from this method are larger than those of the traditional multiple station estimation method. However, in most instances our method was accurate to within hundreds of kilometers. With such accuracy, this method

  17. 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

  18. 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.

  19. 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

  20. An Evaluation of a Numerical Prediction Method for Electric Field Strength of Low Frequency Radio Waves based on Wave-Hop Ionospheric Propagation

    NASA Astrophysics Data System (ADS)

    Kitauchi, H.; Nozaki, K.; Ito, H.; Kondo, T.; Tsuchiya, S.; Imamura, K.; Nagatsuma, T.; Ishii, M.

    2014-12-01

    We present our recent efforts on an evaluation of the numerical prediction method of electric field strength for ionospheric propagation of low frequency (LF) radio waves based on a wave-hop propagation theory described in Section 2.4 of Recommendation ITU-R P.684-6 (2012), "Prediction of field strength at frequencies below about 150 kHz," made by International Telecommunication Union Radiocommunication Sector (ITU-R). As part of the Japanese Antarctic Research Expedition (JARE), we conduct on-board measurements of the electric field strengths and phases of LF 40 kHz and 60 kHz of radio signals (call sign JJY) continuously along both the ways between Tokyo, Japan and Syowa Station, the Japanese Antarctic station, at 69° 00' S, 39° 35' E on East Ongul Island, Lützow-Holm Bay, East Antarctica. The measurements are made by a newly developed, highly sensitive receiving system installed on board the Japanese Antarctic research vessel (RV) Shirase. We obtained new data sets of the electric field strength up to approximately 13,000-14,000 km propagation of LF JJY 40 kHz and 60 kHz radio waves by utilizing a newly developed, highly sensitive receiving system, comprised of an orthogonally crossed double-loop antenna and digital-signal-processing lock-in amplifiers, on board RV Shirase during the 55th JARE from November 2013 to April 2014. We have made comparisons between those on-board measurements and the numerical predictions of field strength for long-range propagation of low frequency radio waves based on a wave-hop propagation theory described in Section 2.4 of Recommendation ITU-R P.684-6 (2012) to show that our results qualitatively support the recommended wave-hop theory for the great-circle paths approximately 7,000-8,000 km and 13,000-14,000 km propagations.

  1. 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.

  2. 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.

  3. Integral Equation Approach to the Propagation of Low-Frequency Groundwaves over Irregular Terrains: II. Two-Dimensional Terrain Features and Elevated Receivers.

    DTIC Science & Technology

    1981-10-01

    E C FIELD, S GAYER, 8 D’AMBR OS IO F19628-78-C-0088 UNCLASSIFIED PSR_ 11 3 RAOC-TR-81-287 NI’ 11111 1.11111.8~ 1111H15 II II .4 i1. -~ * MICROCOPY...GROUNDWAVES OVER IRREGULAR TERRAINS: II . TWO-DIMENSIONAL TERRAIN FEATURES AND ELEVATED RECEIVERS Pa fcific-Sierra Rtarch Cwrp. tl. E. C. Fields. Gay,, 1i...PROPAGATION OF LOW-FREQUENCY GROUNDWAVES Final Technical Report OVER IRREGULAR TERRAIN: II . TWO-DIMENSIONAL Oct 79 - May 81 TERRAIN FEATURES AND ELEVATED

  4. 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.

  5. An eigenfunction expansion for low-frequency acoustic propagation in a downward-refracting stratified medium over a complex impedance plane

    NASA Astrophysics Data System (ADS)

    Waxler, Roger

    2002-05-01

    The well-known eigenfunction expansions associated with self-adjoint operators cannot be used to describe sound propagation over a complex impedance plane since, if the impedance has a real part, the resulting impedance boundary condition is not self-adjoint. Instead, a less widely known eigenfunction expansion associated with non-self-adjoint operators can be used. This eigenfunction expansion is applied to a vertically stratified model for downward refraction in the nighttime boundary layer. As in the self-adjoint case the propagation separates into a ducted part, expressed as a sum of modes which decay exponentially with height, and an upwardly propagating part, expressed as an integral over modes which are asymptotically (with height) plane waves. The eigenvalues associated with the ducted modes are complex, the imaginary parts being related to the acoustic attenuation. An efficient method for finding the complex eigenvalues is introduced from which a physically intuitive form of the attenuation coefficients is obtained. For low-frequency propagation (100 Hz or less) the number of modes is small, making this a simple way to model the ducted part of the propagation.

  6. Low-frequency broadband sound source localization using an adaptive normal mode back-propagation approach in a shallow-water ocean.

    PubMed

    Lin, Ying-Tsong; Newhall, Arthur E; Lynch, James F

    2012-02-01

    A variety of localization methods with normal mode theory have been established for localizing low frequency (below a few hundred Hz), broadband signals in a shallow water environment. Gauss-Markov inverse theory is employed in this paper to derive an adaptive normal mode back-propagation approach. Joining with the maximum a posteriori mode filter, this approach is capable of separating signals from noisy data so that the back-propagation will not have significant influence from the noise. Numerical simulations are presented to demonstrate the robustness and accuracy of the approach, along with comparisons to other methods. Applications to real data collected at the edge of the continental shelf off New Jersey, USA are presented, and the effects of water column fluctuations caused by nonlinear internal waves and shelfbreak front variability are discussed.

  7. Solar winds driven by nonlinear low-frequency Alfvén waves from the photosphere: Parametric study for fast/slow winds and disappearance of solar winds

    NASA Astrophysics Data System (ADS)

    Suzuki, Takeru K.; Inutsuka, Shu-Ichiro

    2006-06-01

    We investigate how properties of the corona and solar wind in open coronal holes depend on properties of magnetic fields and their footpoint motions at the surface. We perform one-dimensional magnetohydrodynamical (MHD) simulations for the heating and the acceleration in coronal holes by low-frequency Alfvén waves from the photosphere to 0.3 or 0.1 AU. We impose low-frequency (≲0.05 Hz) transverse fluctuations of the field lines at the photosphere with various amplitude, spectrum, and polarization in the open flux tubes with different photospheric field strength, Br,0, and superradial expansion of the cross section, fmax. We find that transonic solar winds are universal consequences. The atmosphere is also stably heated up to ≳106 K by the dissipation of the Alfvén waves through compressive-wave generation and wave reflection in the cases of the sufficient wave input with photospheric amplitude, ≳ 0.7 km s-1. The density, and accordingly the mass flux, of solar winds show a quite sensitive dependence on because of an unstable aspect of the heating by the nonlinear Alfvén waves. A case with = 0.4 km s-1 gives ≃50 times smaller mass flux than the fiducial case for the fast wind with = 0.7 km s-1; solar wind virtually disappears only if becomes ≃1/2. We also find that the solar wind speed has a positive correlation with Br,0/fmax, which is consistent with recent observations by Kojima et al. On the basis of these findings, we show that both fast and slow solar winds can be explained by the single process, the dissipation of the low-frequency Alfvén waves, with different sets of and Br,0/fmax. Our simulations naturally explain the observed (1) anticorrelation of the solar wind speed and the coronal temperature and (2) larger amplitude of Alfvénic fluctuations in the fast wind. In Appendix A, we also explain our implementation of the outgoing boundary condition of the MHD waves with some

  8. Effect of satellite cell ablation on low-frequency-stimulated fast-to-slow fibre-type transitions in rat skeletal muscle

    PubMed Central

    Martins, Karen J B; Gordon, Tessa; Pette, Dirk; Dixon, Walter T; Foxcroft, George R; MacLean, Ian M; Putman, Charles T

    2006-01-01

    The purpose of this study was to determine whether satellite cell ablation within rat fast-twitch muscles exposed to chronic low-frequency stimulation (CLFS) would limit fast-to-slow fibre-type transitions. Twenty-nine male Wistar rats were randomly assigned to one of three groups. Satellite cells of the left tibialis anterior were ablated by weekly exposure to a 25 Gy dose of γ-irradiation during 21 days of CLFS (IRR-Stim), whilst a second group received only 21 days of CLFS (Stim). A third group received weekly doses of γ-irradiation (IRR). Non-irradiated right legs served as internal controls. Continuous infusion of 5-bromo-2′-deoxyuridine (BrdU) revealed that CLFS induced an 8.0-fold increase in satellite cell proliferation over control (mean ± s.e.m.: 23.9 ± 1.7 versus 3.0 ± 0.5 mm−2, P < 0.0001) that was abolished by γ-irradiation. M-cadherin and myogenin staining were also elevated 7.7- and 3.8-fold (P < 0.0001), respectively, in Stim compared with control, indicating increases in quiescent and terminally differentiating satellite cells; these increases were abolished by γ-irradiation. Myonuclear content was elevated 3.3-fold (P < 0.0001) in Stim, but remained unchanged in IRR-Stim. Immunohistochemical analyses revealed attenuation of fast-to-slow fibre-type transitions in IRR-Stim compared with Stim. Comparable changes were observed at the protein level by SDS-PAGE. It is concluded that although considerable adaptive potential exists within myonuclei, satellite cells play a role in facilitating fast-to-slow fibre-type transitions. PMID:16439424

  9. Low-Frequency Type II Radio Detections and Coronagraph Data to Describe and Forecast the Propagation of 71 CMEs/Shocks

    NASA Astrophysics Data System (ADS)

    St Cyr, O. C.; Cremades, H.; Iglesias, F. A.; Xie, H.; Kaiser, M. L.; Gopalswamy, N.

    2015-12-01

    Motivated by improving predictions of arrival times at Earth of shocks driven by coronal mass ejections (CMEs), we have analyzed 71 Earth-directed events in different stages of their propagation. The study is primarily based on approximated locations of interplanetary (IP) shocks derived from Type-II radio emissions detected by the Wind/WAVES experiment during 1997-2007. Distance-time diagrams resulting from the combination of white-light corona, IP Type-II radio, and in situ data lead to the formulation of descriptive profiles of each CME's journey toward Earth. Furthermore, two different methods to track and predict the location of CME-driven IP shocks are presented. The linear method, solely based on Wind/WAVES data, arises after key modifications to a pre-existing technique that linearly projects the drifting low-frequency Type-II emissions to 1 AU. This upgraded method improves forecasts of shock arrival time by almost 50%. The second predictive method is proposed on the basis of information derived from the descriptive profiles, and relies on a single CME height-time point and on low-frequency Type-II radio emissions to obtain an approximate value of the shock arrival time at Earth. In addition, we discuss results on CME-radio emission associations, characteristics of IP propagation, and the relative success of the forecasting methods.

  10. Low-Frequency Type-II Radio Detections and Coronagraph Data Employed to Describe and Forecast the Propagation of 71 CMEs/Shocks

    NASA Astrophysics Data System (ADS)

    Cremades, H.; Iglesias, F. A.; St. Cyr, O. C.; Xie, H.; Kaiser, M. L.; Gopalswamy, N.

    2015-09-01

    Motivated by improving predictions of arrival times at Earth of shocks driven by coronal mass ejections (CMEs), we have analyzed 71 Earth-directed events in different stages of their propagation. The study is primarily based on approximated locations of interplanetary (IP) shocks derived from Type-II radio emissions detected by the Wind/WAVES experiment during 1997 - 2007. Distance-time diagrams resulting from the combination of white-light corona, IP Type-II radio, and in-situ data lead to the formulation of descriptive profiles of each CME's journey toward Earth. Furthermore, two different methods for tracking and predicting the location of CME-driven IP shocks are presented. The linear method, solely based on Wind/WAVES data, arises after key modifications to a pre-existing technique that linearly projects the drifting low-frequency Type-II emissions to 1 AU. This upgraded method improves forecasts of shock-arrival times by almost 50 %. The second predictive method is proposed on the basis of information derived from the descriptive profiles and relies on a single CME height-time point and on low-frequency Type-II radio emissions to obtain an approximate value of the shock arrival time at Earth. In addition, we discuss results on CME-radio emission associations, characteristics of IP propagation, and the relative success of the forecasting methods.

  11. Low-Frequency Acoustic Propagation Loss in the Arctic Ocean: Results of the Arctic Climate Observations using Underwater Sound Experiment

    DTIC Science & Technology

    2004-03-05

    experiment on the Turpan-SIMI path, but much smaller than those measured on the Turpan- Narwhal path which was almost coincident with the 1000-km section of...the ACOUS path from the Nansen Basin to the Lincoln Sea. The integral propagation loss on the path to Narwhal was about 30 dB for mode 1 and 10-13 dB

  12. Oblique propagation of low frequency nonlinear waves in an electron depleted magnetized plasma with positive and negative dust

    NASA Astrophysics Data System (ADS)

    Mobarak Hossen, M.; Alam, M. S.; Sultana, S.; Mamun, A. A.

    2016-02-01

    A rigorous theoretical investigation has been carried out to study the properties of obliquely propagating dust-acoustic (DA) waves in an electron depleted magnetized dusty plasma system containing nonextensive q-distributed ions and mobile positively charged, as well as negatively charged dust particles. The reductive perturbation technique is employed to derive the modified Korteweg-de Vries (mK-dV) equation to analyze solitary waves (SWs) and the standard Gardner (SG) equation to analyze SWs and double layers (DLs) solution. The basic features (viz., amplitude, polarity, speed, width, etc.) of the DA mK-dV SWs, SG SWs, and DLs are examined. The comparison between mK-dV SWs and SG SWs is also made. It is seen that the amplitude, polarity, speed, width of such DA SWs, and DLs are significantly modified by the presence of nonextensive ions, external magnetic field, and obliquity angle (the angle between the external magnetic field and wave propagation). The results of our present investigation may be useful for understanding the nonlinear wave propagation in various interstellar space plasma environments where positive and negative dust particles are available.

  13. Low-frequency changes in Southern Ocean ventilation quantified using an Atlantic sector model: A boundary-propagator approach

    NASA Astrophysics Data System (ADS)

    Sasse, T.; Holzer, M.

    2016-02-01

    The ventilation of the Southern Ocean, i.e., the exchange between the Southern Ocean surface and the interior, plays a key role in regulating Earth's climate. In recent decades, surface westerly winds have been observed to intensify and shift poleward, resulting in changes to the SO circulation and ventilation. This has important implications for the ocean's capacity to absorb carbon and heat from the atmosphere. While recent inverse modelling of repeat hydrographies has provided some insights into ventilation changes in terms of changes in CFCs, these studies have so far been limited to analyzing differences between two snapshots in time. Here we use an idealized Atlantic sector forward model to quantify inter-annual to decadal variability in fundamental ventilation metrics, such as the water-mass fraction last ventilated some time during the last τ years, as a function of τ. We do this by explicitly computing the boundary-propagator Green function, G, that partitions water locally according to where and when it was last ventilated. The boundary propagators were computed with respect to surface regions that ventilate bottom, intermediate, and mode waters. Suitable integrals of G quantify the timescales and pathways of ventilation, and how these change on interannual to decadal timescales. We also consider the impact of the ocean's changing ventilation on anthropogenic carbon. To investigate the changing interplay between eddies and mean circulation, the calculations were performed for both coarse (1°x1°) and eddy permitting (1/4°x1/4°) resolutions.

  14. Co- and counter-propagating slow light systems

    NASA Astrophysics Data System (ADS)

    Baba, T.; Kondo, K.

    2016-03-01

    We report what we call co- and counter propagating slow-light systems based on the high nonlinearity in Si lattice-shifted photonic crystal waveguides (LSPCWs). The intense slow-light pulse, as a control pulse, efficiently generates two-photon absorption and carrier plasma effects, which tunes the dispersion characteristics of the LSPCWs and spectrum of copropagating or counter-propagating slow-light pulse, as a signal pulse. Using the control pulse, we succeeded in experimentally demonstrating adiabatic wavelength conversion and its enhancement, delay tuning of up to 10 ps with a response time <10 ps, and temporal pulse compression of factor 9.9 in the signal pulse. Furthermore, we discussed theoretically the collision and reflection of the signal pulse counterpropagating against the control pulse through the photonic-bandgap shift, resulting in a large Doppler shift. Considering the detail of these phenomena, we clarified the relation and difference between the adiabatic wavelength conversion, cross-phase modulation, and Doppler shift, which have been unclear so far.

  15. Effects of alcohols on the stability and low-frequency local motions that control the slow changes in structural dynamics of ferrocytochrome c.

    PubMed

    Jain, Rishu; Sharma, Deepak; Kumar, Rajesh

    2013-10-01

    To determine the effects of alcohols on the low-frequency local motions that control slow changes in structural dynamics of native-like compact states of proteins, we have studied the effects of alcohols on structural fluctuation of M80-containing Ω-loop by measuring the rate of thermally driven CO dissociation from a natively folded carbonmonoxycytochrome c under varying concentrations of alcohols (methanol, ethanol, 1-propanol, 2-propanol, 3°-butanol, 2,2,2-trifluoroethanol). As alcohol is increased, the rate coefficient of CO dissociation (k(diss)) first decreases in subdenaturing region and then increases on going from subdenaturing to denaturing milieu. This decrease in k(diss) is more for 2,2,2-trifluroethanol and 1-propanol and least for methanol, indicating that the first phase of motional constraint is due to the hydrophobicity of alcohols and intramolecular protein cross-linking effect of alcohols, which results in conformational entropy loss of protein. The thermal denaturation midpoint for ferrocytochrome c decreases with increase in alcohol, indicating that alcohol decrease the global stability of protein. The stabilization free energy (ΔΔG) in alcohols' solution was calculated from the slope of the Wyman-Tanford plot and water activity. The m-values obtained from the slope of ΔΔG versus alcohols plot were found to be more negative for longer and linear chain alcohols, indicating destabilization of proteins by alcohols through disturbance of hydrophobic interactions and hydrogen bonding.

  16. Elephant low-frequency vocalizations propagate in the ground and seismic playbacks of these vocalizations are detectable by wild African elephants (Loxodonta africana)

    NASA Astrophysics Data System (ADS)

    O'Connell-Rodwell, Caitlin E.; Wood, Jason D.; Gunther, Roland; Klemperer, Simon; Rodwell, Timothy C.; Puria, Sunil; Sapolsky, Robert; Kinzley, Colleen; Arnason, Byron T.; Hart, Lynette A.

    2004-05-01

    Seismic correlates of low-frequency vocalizations in African and Asian elephants propagate in the ground at different velocities, with the potential of traveling farther than their airborne counterparts. A semblance technique applied to linear moveouts on narrow-bandpass-filtered data, coupled with forward modeling, demonstrates that the complex waves observed are the interference of an air wave and a Rayleigh wave traveling at the appropriate velocities. The Rayleigh wave appears to be generated at or close to the elephant, either by coupling through the elephant's body or through the air near the body to the ground. Low-frequency elephant vocalizations were reproduced seismically and played back to both a captive elephant and to elephant breeding herds in the wild, monitoring the elephants' behavioral responses, spacing between herd members and time spent at the water hole as an index of heightened vigilance. Breeding herds detected and responded appropriately to seismically transmitted elephant warning calls. The captive studies promise to elucidate a vibrotactile threshold of sensitivity for the elephant foot. Elephants may benefit from the exploitation of seismic cues as an additional communication modality, thus expanding their signaling repertoire and extending their range of potential communication and eavesdropping beyond that possible with airborne sound.

  17. 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.

  18. Radiation efficiency during slow crack propagation: an experimental study.

    NASA Astrophysics Data System (ADS)

    Jestin, Camille; Lengliné, Olivier; Schmittbuhl, Jean

    2017-04-01

    Creeping faults are known to host a significant aseismic deformation. However, the observations of micro-earthquake activity related to creeping faults (e.g. San Andreas Faults, North Anatolian Fault) suggest the presence of strong lateral variabilities of the energy partitioning between radiated and fracture energies. The seismic over aseismic slip ratio is rather difficult to image over time and at depth because of observational limitations (spatial resolution, sufficiently broad band instruments, etc.). In this study, we aim to capture in great details the energy partitioning during the slow propagation of mode I fracture along a heterogeneous interface, where the toughness is strongly varying in space.We lead experiments at laboratory scale on a rock analog model (PMMA) enabling a precise monitoring of fracture pinning and depinning on local asperities in the brittle-creep regime. Indeed, optical imaging through the transparent material allows the high resolution description of the fracture front position and velocity during its propagation. At the same time, acoustic emissions are also measured by accelerometers positioned around the rupture. Combining acoustic records, measurements of the crack front position and the loading curve, we compute the total radiated energy and the fracture energy. We deduce from them the radiation efficiency, ηR, characterizing the proportion of the available energy that is radiated in form of seismic wave. We show an increase of ηR with the crack rupture speed computed for each of our experiments in the sub-critical crack propagation domain. Our experimental estimates of ηR are larger than the theoretical model proposed by Freund, stating that the radiation efficiency of crack propagation in homogeneous media is proportional to the crack velocity. Our results are demonstrated to be in agreement with existing studies which showed that the distribution of crack front velocity in a heterogeneous medium can be well described by a

  19. Slow crack propagation in glass and creep prediction

    NASA Astrophysics Data System (ADS)

    Mallet, Celine; Fortin, Jerome; Gueguen, Yves

    2013-04-01

    The context of our study is the observation of the time-dependent deformation of cracked glass. The aim of our study is to observe the slow crack propagation, to quantify it and to predict finally the creep behavior. We performed creep experiments in compaction conditions in a triaxial cell, on cracked boro-silicate glass samples. The chemical composition of the investigated glass is very close to the composition of waste vitrified packages. The matrix of the original glass (OG) is perfectly amorphous, without porosity. A few isolated air bubbles are trapped during the glass flow. Cracks are introduced in the OG through thermal shocks. Strain and acoustic emission (AE) are recorded. Several experiments are performed at different confining pressures (15 or 25 MPa), different pore fluid conditions (with argon gas, considered as the dry case, with tap water saturated porosity, or with distilled water) and different temperatures (ambiant temperature, 50oC or 80oC). Linear increase of the volumetric strain is first observed. A dilatancy increase is recorded. Note that dilatancy does not appear in constant strain rate tests. Constant stress tests show that dilatancy develops during a time interval that depends on the stress level. In addition AE rate are recorded. A non zero AE rate is an evidence of crack propagation. We use a micro-mechanical model that gives the stress intensity factor at the crack tips. This factor depends on stress and geometrical parameters (all known). An exponential law describe the rate of crack propagation, as a function of temperature, environment and applied stresses. This model allows us to predict the creep rate in glass. Assuming a constant crack aspect ratio, crack length and volumetric strain are related. The volumetric strain rate is calculated from model and compared to the data.

  20. Low Frequency Sonar Signal Simulation

    DTIC Science & Technology

    2010-04-14

    participating in workshops. Task 3, Assess SST Propagation Accuracy at Low Frequencies: Determine accuracy domain of SST eigenray -based propagation model at... eigenrays ). The new algorithm, which is conceptually similar to the “point scatterer” approach, generates uncorrelated random Gaussian scattering...amplitudes for many cells (smaller than the sonar resolution) covering the bottom. These are combined with eigenray pairs and weighted by the angle

  1. Effects of frequency on the wave form of propagated slow waves in canine gastric antral muscle.

    PubMed Central

    Publicover, N G; Sanders, K M

    1986-01-01

    Experiments were performed to test the effects of frequency on the wave form of electrical slow waves in canine antral circular muscle. At frequencies between 3.0 and 5.6 cycles per minute antral slow waves revealed an alternating wave form pattern. At physiological frequencies antral muscle was incapable of consistently propagating mechanically productive slow waves. Two components of the slow wave were identified on the basis of propagation refractory period. At inter-slow-wave intervals of 3-14 s, the amplitude and duration of the plateau phase wave decreased, but the upstroke phase of the slow wave was minimally affected. Intervals of 2.5-4 s resulted in a normal upstroke event but abolished the plateau. At shorter intervals the upstroke phase of the slow wave was greatly reduced or abolished. The absolute propagation refractory period averaged 2.8 +/- 0.9 s (n = 7) following repolarization of a 'conditioning' slow wave. Slow waves failed to propagate within the absolute propagation refractory period. Acetylcholine decreased the interval required for the plateau phase of the slow wave to recover and permitted conduction of mechanically productive slow waves at or above physiological frequencies. The data presented suggest that gastric motility is modulated by extrinsic and intrinsic factors which regulate slow-wave frequency. PMID:3701649

  2. 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

  3. Slow-wave propagation on monolithic microwave integrated circuits with layered and non-layered structures

    SciTech Connect

    Tzuang, C.K.C.

    1986-01-01

    Various MMIC (monolithic microwave integrated circuit) planar waveguides have shown possible existence of a slow-wave propagation. In many practical applications of these slow-wave circuits, the semiconductor devices have nonuniform material properties that may affect the slow-wave propagation. In the first part of the dissertation, the effects of the nonuniform material properties are studied by a finite-element method. In addition, the transient pulse excitations of these slow-wave circuits also have great theoretical and practical interests. In the second part, the time-domain analysis of a slow-wave coplanar waveguide is presented.

  4. Origin and propagation of individual slow waves along the intact feline small intestine.

    PubMed

    Lammers, Wim J E P; Stephen, Betty

    2008-03-01

    The pattern of propagation of slow waves in the small intestine is not clear. Specifically, it is not known whether propagation is determined by a single dominant ICC-MP (Interstitial cells of Cajal located in the Myenteric Plexus) pacemaker unit or whether there are multiple active pacemakers. To determine this pattern of propagation, waveforms were recorded simultaneously from 240 electrodes distributed along the whole length of the intact isolated feline small intestine. After the experiments, the propagation patterns of successive individual slow waves were analysed. In the intact small intestine, there was only a single slow wave pacemaker unit active, and this was located at or 6-10 cm from the pyloric junction. From this site, slow waves propagated in the aboral direction at gradually decreasing velocities. The majority of slow waves (73%) reached the ileocaecal junction while the remaining waves were blocked. Ligation of the intestine at one to four locations led to: (a) decrease in the distal frequencies; (b) disappearance of distal propagation blocks; (c) increase in velocities; (d) emergence of multiple and unstable pacemaker sites; and (e) propagation from these sites in the aboral and oral directions. In conclusion, in the quiescent feline small intestine a single pacemaker unit dominates the organ, with occasional propagation blocks of the slow waves, thereby producing the well-known frequency gradient.

  5. 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

  6. 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.

  7. Nonlinear light propagation in chalcogenide photonic crystal slow light waveguides.

    PubMed

    Suzuki, Keijiro; Baba, Toshihiko

    2010-12-06

    Optical nonlinearity can be enhanced by the combination of highly nonlinear chalcogenide glass and photonic crystal waveguides (PCWs) providing strong optical confinement and slow-light effects. In a Ag-As(2)Se(3) chalcogenide PCW, the effective nonlinear parameter γeff reaches 6.3 × 10(4) W(-1)m(-1), which is 200 times larger than that in Si photonic wire waveguides. In this paper, we report the detailed design, fabrication process, and the linear and nonlinear characteristics of this waveguide at silica fiber communication wavelengths. We show that the waveguide exhibits negligible two-photon absorption, and also high-efficiency self-phase modulation and four-wave mixing, which are assisted by low-dispersion slow light.

  8. Low frequency cauterization.

    PubMed

    Sawatzky, G; Wiest, P P

    1993-01-01

    Low frequency cauterization is presented in comparison to the related high frequency method. Both methods are defined and compared and their advantages and disadvantages are illustrated. Finally, a promising combination of both methods is described.

  9. 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.

  10. Limits of slow sound propagation and transparency in lossy, locally resonant periodic structures

    NASA Astrophysics Data System (ADS)

    Theocharis, G.; Richoux, O.; Romero García, V.; Merkel, A.; Tournat, V.

    2014-09-01

    We investigate sound propagation in lossy, locally resonant periodic structures by studying an air-filled tube periodically loaded with Helmholtz resonators and taking into account the intrinsic viscothermal losses. In particular, by tuning the resonator with the Bragg gap in this prototypical locally resonant structure, we study the limits and various characteristics of slow sound propagation. While in the lossless case the overlapping of the gaps results in slow-sound-induced transparency of a narrow frequency band surrounded by a strong and broadband gap, the inclusion of the unavoidable losses imposes limits to the slowdown factor and the maximum transmission. Experiments, theory, and finite element simulations have been used for the characterization of acoustic wave propagation by tuning the Helmholtz/Bragg frequencies and the total amount of loss both for infinite and finite lattices. This study contributes to the field of locally resonant acoustic metamaterials and slow sound applications.

  11. 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

  12. Trace observations of propagating slow magneto-acoustic disturbances in coronal loops

    NASA Astrophysics Data System (ADS)

    De Moortel, I.; Ireland, J.; Walsh, R. W.

    2002-06-01

    We study propagating disturbances in 38 coronal loops and give an overview of their properties using high cadence, 171 Å, TRACE data (JOP 83 & JOP 144). The majority of these outward propagating oscillations are found in the footpoints of large diffuse coronal loop structures, close to active regions. The disturbances travel outward with a propagation speed of the order of v ≍ 119+/-39 km/s. The variations in intensity are estimated to be roughly 4.1+/-1.6% of the background brightness and the propagating disturbances are found to be damped very quickly, within 8.6+/-3.8 Mm along the loop. Using a wavelet analysis, periods of the order of 282+/-93 seconds are found and the energy flux was estimated as 346+/-132 ergs/cm2s. It is suggested that these oscillations are slow magneto-acoustic waves propagating along the lower part of large, quiescent, coronal loops.

  13. Low Frequency Acoustics

    DTIC Science & Technology

    2016-06-13

    understanding of very low frequency (VLF) acoustics in the deep ocean as applicable to naval warfare and coexistence with marine mammals. OBJECTIVES The...characteristics in the deep ocean; (3) encourage a cooperative interagency working relationship to investigate acoustic impact on marine mammals; and...with NOAA(NMFS) and other parties has dealt with ocean acoustics related to issues stimulated by the Marine Mammal Protection Act. A focal point has

  14. 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.

  15. Quantum mutual information of an entangled state propagating through slow- and fast-light media

    NASA Astrophysics Data System (ADS)

    Glasser, Ryan T.; Clark, Jeremy B.; Glorieux, Quentin; Vogl, Ulrich; Lett, Paul D.

    2013-03-01

    Due to its vital role in many quantum information and communication protocols, much theoretical and experi- mental work has been conducted in order to investigate the fundamental properties of entanglement. In this work we describe an experimental investigation into the behavior of continuous-variable entanglement and quantum mutual information upon propagation through slow- and fast-light media. A four-wave mixing process in warm atomic vapor is used to generate an entangled two-mode squeezed vacuum state of light. One of the two modes of the resulting state is then sent through a second four-wave mixing process that is tuned to exhibit either slow- or fast-light properties. The cross-correlation and quantum mutual information shared between the resulting modes is quanti ed, and di erences in their behavior after propagation through slow- and fast-light media are discussed.

  16. 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

  17. Analyzing critical propagation in a reaction-diffusion-advection model using unstable slow waves.

    PubMed

    Kneer, Frederike; Obermayer, Klaus; Dahlem, Markus A

    2015-02-01

    The effect of advection on the propagation and in particular on the critical minimal speed of traveling waves in a reaction-diffusion model is studied. Previous theoretical studies estimated this effect on the velocity of stable fast waves and predicted the existence of a critical advection strength below which propagating waves are not supported anymore. In this paper, an analytical expression for the advection-velocity relation of the unstable slow wave is derived. In addition, the critical advection strength is calculated taking into account the unstable slow wave solution. We also analyze a two-variable reaction-diffusion-advection model numerically in a wide parameter range. Due to the new control parameter (advection) we can find stable wave propagation in the otherwise non-excitable parameter regime, if the advection strength exceeds a critical value. Comparing theoretical predictions to numerical results, we find that they are in good agreement. Theory provides an explanation for the observed behaviour.

  18. Alternative source models of very low frequency events

    USGS Publications Warehouse

    Gomberg, Joan S.; Agnew, D.C.; Schwartz, S.Y.

    2016-01-01

    We present alternative source models for very low frequency (VLF) events, previously inferred to be radiation from individual slow earthquakes that partly fill the period range between slow slip events lasting thousands of seconds and low-frequency earthquakes (LFE) with durations of tenths of a second. We show that VLF events may emerge from bandpass filtering a sum of clustered, shorter duration, LFE signals, believed to be the components of tectonic tremor. Most published studies show VLF events occurring concurrently with tremor bursts and LFE signals. Our analysis of continuous data from Costa Rica detected VLF events only when tremor was also occurring, which was only 7% of the total time examined. Using analytic and synthetic models, we show that a cluster of LFE signals produces the distinguishing characteristics of VLF events, which may be determined by the cluster envelope. The envelope may be diagnostic of a single, dynamic, slowly slipping event that propagates coherently over kilometers or represents a narrowly band-passed version of nearly simultaneous arrivals of radiation from slip on multiple higher stress drop and/or faster propagating slip patches with dimensions of tens of meters (i.e., LFE sources). Temporally clustered LFE sources may be triggered by single or multiple distinct aseismic slip events or represent the nearly simultaneous chance occurrence of background LFEs. Given the nonuniqueness in possible source durations, we suggest it is premature to draw conclusions about VLF event sources or how they scale.

  19. Alternative source models of very low frequency events

    NASA Astrophysics Data System (ADS)

    Gomberg, J.; Agnew, D. C.; Schwartz, S. Y.

    2016-09-01

    We present alternative source models for very low frequency (VLF) events, previously inferred to be radiation from individual slow earthquakes that partly fill the period range between slow slip events lasting thousands of seconds and low-frequency earthquakes (LFE) with durations of tenths of a second. We show that VLF events may emerge from bandpass filtering a sum of clustered, shorter duration, LFE signals, believed to be the components of tectonic tremor. Most published studies show VLF events occurring concurrently with tremor bursts and LFE signals. Our analysis of continuous data from Costa Rica detected VLF events only when tremor was also occurring, which was only 7% of the total time examined. Using analytic and synthetic models, we show that a cluster of LFE signals produces the distinguishing characteristics of VLF events, which may be determined by the cluster envelope. The envelope may be diagnostic of a single, dynamic, slowly slipping event that propagates coherently over kilometers or represents a narrowly band-passed version of nearly simultaneous arrivals of radiation from slip on multiple higher stress drop and/or faster propagating slip patches with dimensions of tens of meters (i.e., LFE sources). Temporally clustered LFE sources may be triggered by single or multiple distinct aseismic slip events or represent the nearly simultaneous chance occurrence of background LFEs. Given the nonuniqueness in possible source durations, we suggest it is premature to draw conclusions about VLF event sources or how they scale.

  20. Origin and propagation of human gastric slow-wave activity defined by high-resolution mapping

    PubMed Central

    Du, Peng; Cheng, Leo K.; Egbuji, John U.; Lammers, Wim J. E. P.; Windsor, John A.; Pullan, Andrew J.

    2010-01-01

    Slow waves coordinate gastric motility, and abnormal slow-wave activity is thought to contribute to motility disorders. The current understanding of normal human gastric slow-wave activity is based on extrapolation from data derived from sparse electrode recordings and is therefore potentially incomplete. This study employed high-resolution (HR) mapping to reevaluate human gastric slow-wave activity. HR mapping was performed in 12 patients with normal stomachs undergoing upper abdominal surgery, using flexible printed circuit board (PCB) arrays (interelectrode distance 7.6 mm). Up to six PCBs (192 electrodes; 93 cm2) were used simultaneously. Slow-wave activity was characterized by spatiotemporal mapping, and regional frequencies, amplitudes, and velocities were defined and compared. Slow-wave activity in the pacemaker region (mid to upper corpus, greater curvature) was of greater amplitude (mean 0.57 mV) and higher velocity (8.0 mm/s) than the corpus (0.25 mV, 3.0 mm/s) (P < 0.001) and displayed isotropic propagation. A marked transition to higher amplitude and velocity activity occurred in the antrum (0.52 mV, 5.9 mm/s) (P < 0.001). Multiple (3–4) wavefronts were found to propagate simultaneously in the organoaxial direction. Frequencies were consistent between regions (2.83 ± 0.35 cycles per min). HR mapping has provided a more complete understanding of normal human gastric slow-wave activity. The pacemaker region is associated with high-amplitude, high-velocity activity, and multiple wavefronts propagate simultaneously. These data provide a baseline for future HR mapping studies in disease states and will inform noninvasive diagnostic strategies. PMID:20595620

  1. Slow diffusive fault slip propagation: direct evidences from high-sensitivity strain measurements.

    NASA Astrophysics Data System (ADS)

    Crescentini, L.; Amoruso, A.; Botta, V.

    2012-04-01

    Slow earthquakes preceding following or without ordinary earthquakes may play an important role in the stress redistribution process and seismic hazard assessment. They were firstly observed by high-sensitivity strainmeters; characteristic times ranged tens of seconds to several days and sources were fairly shallow. During the last decades several slow earthquakes have been observed at transcurrent margins, extensional areas and almost all subduction zones. The observation of a swarm of small local slow earthquakes by one laser strainmeter at Gran Sasso (Italy) in 1997 led to the first suggestion of the diffusive character of the slow slip propagation along the fault. This feature was later confirmed on the basis of a large number of events -- mainly recorded at subduction zones -- whose characteristic time spanned many orders of magnitude. The diffusive character of the rupture propagation was mainly deduced from the observed relationship between seismic moment and characteristic time. The first direct observation of the diffusion process occurred after the 2009 L'Aquila (Italy) earthquake, from the temporal evolution of deformation recorded by two laser strainmeter at Gran Sasso. One of the strain signals is monotonic, while the other one shows a marked minimum. Such features suggest fracture propagation crossing a nodal line on the fault plane, which separates areas capable of producing deformation of opposite sign at the observation point. Strain history at both interferometers is fully consistent with diffusive slip propagation, but inconsistent with contant velocity propagation. We have searched for other direct evidences of the diffusive rupture propagation, looking at strain records similar to those recorded after L'Aquila earthquake. In particular here we analyze three different events, recorded by (i) three Sacks-Evertson borehole dilatometers at Izu-Oshima (Japan) in 1978, (ii) two long-base laser strainmeters at Durmid Hill, near the San Andreas fault

  2. 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.

  3. Slow propagation, anomalous absorption, and total external reflection of surface plasmon polaritons in nanolayer systems.

    PubMed

    Stockman, Mark I

    2006-11-01

    I predict that a nanoscopic, high-permittivity layer on the surface of a plasmonic metal can cause total external reflection of surface plasmon polaritons (SPPs). Such a layer can be used as a mirror in nanoplasmonics, in particular for resonators of nanolasers and spasers and can also be used in adiabatic nanooptics. I also show that the earlier predicted slow propagating SPP modes, especially those with negative refraction, are highly damped.

  4. 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.

  5. Voltage-gated Ca2+ currents are necessary for slow-wave propagation in the canine gastric antrum.

    PubMed

    Bayguinov, Orline; Ward, Sean M; Kenyon, James L; Sanders, Kenton M

    2007-11-01

    Electrical slow waves determine the timing and force of peristaltic contractions in the stomach. Slow waves originate from a dominant pacemaker in the orad corpus and propagate actively around and down the stomach to the pylorus. The mechanism of slow-wave propagation is controversial. We tested whether Ca(2+) entry via a voltage-dependent, dihydropyridine-resistant Ca(2+) conductance is necessary for active propagation in canine gastric antral muscles. Muscle strips cut parallel to the circular muscle were studied with intracellular electrophysiological techniques using a partitioned-chamber apparatus. Slow-wave upstroke velocity and plateau amplitude decreased from the greater to the lesser curvature, and this corresponded to a decrease in the density of interstitial cells of Cajal in the lesser curvature. Slow-wave propagation velocity between electrodes impaling cells in two regions of muscle and slow-wave upstroke and plateau were measured in response to experimental conditions that reduce the driving force for Ca(2+) entry or block voltage-dependent Ca(2+) currents. Nicardipine (0.1-1 microM) did not affect slow-wave upstroke or propagation velocities. Upstroke velocity, amplitude, and propagation velocity were reduced in a concentration-dependent manner by Ni(2+) (1-100 microM), mibefradil (10-30 microM), and reduced extracellular Ca(2+) (0.5-1.5 mM). Depolarization (by 10-15 mM K(+)) or hyperpolarization (10 microM pinacidil) also reduced upstroke and propagation velocities. The higher concentrations (or lowest Ca(2+)) of these drugs and ionic conditions tested blocked slow-wave propagation. Treatment with cyclopiazonic acid to empty Ca(2+) stores did not affect propagation. These experiments show that voltage-dependent Ca(2+) entry is obligatory for the upstroke phase of slow waves and active propagation.

  6. 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.

  7. Multi-channel wireless mapping of gastrointestinal serosal slow wave propagation

    PubMed Central

    Paskaranandavadivel, Niranchan; Wang, Rui; Sathar, Shameer; O’Grady, Gregory; Cheng, Leo K; Farajidavar, Aydin

    2015-01-01

    Background High-resolution (HR) extracellular mapping allows accurate profiling of normal and dysrhythmic slow wave patterns. A current limitation is that cables traverse the abdominal wall or a natural orifice, risking discomfort, dislodgement or infection. Wireless approaches offer advantages, but a multi-channel system is required, capable of recording slow waves and mapping propagation with high fidelity. Methods A novel multi-channel (n=7) wireless mapping system was developed and compared to a wired commercial system. Slow wave signals were recorded from the porcine gastric and intestinal serosa in-vivo. Signals were simultaneously acquired using both systems, and were filtered and processed to map activation wavefronts. For validation, the frequency and amplitude of detected events were compared, together with the speed and direction of mapped wavefronts. Key Results The wireless device achieved comparable signal quality to the reference device, and slow wave frequencies were identical. Amplitudes of the acquired gastric and intestinal slow wave signals were consistent between the devices. During normal propagation, spatiotemporal mapping remained accurate in the wireless system, however, during ectopic dysrhythmic pacemaking, the lower sampling resolution of the wireless device led to reduced accuracy in spatiotemporal mapping. Conclusions and Inferences A novel multichannel wireless device is presented for mapping slow wave activity. The device achieved high quality signals, and has the potential to facilitate chronic monitoring studies and clinical translation of spatiotemporal mapping. The current implementation may be applied to detect normal patterns and dysrhythmia onset, but HR mapping with finely spaced arrays currently remains necessary to accurately define dysrhythmic patterns. PMID:25599978

  8. Low frequency cavitation erosion

    NASA Astrophysics Data System (ADS)

    Pardue, Sally J.; Chandekar, Gautam

    2002-11-01

    Damage of diesel engine piston sleeve liners due to cavitation of the coolant fluid can be severe. Coolant fluid additives are used to inhibit cavitation damage, and are evaluated by industry suppliers using ASTM G32-98 Standard Test Method for Cavitation Erosion Using Vibratory Apparatus. The ASTM G32-98 test procedure uses an ultrasonic horn at 20 kHz to vibrate a test button in the coolant. The test button mass loss and surface appearance are studied to sort the performance of new coolant additives. Mismatch between good lab performers and actual engine test runs has raised concerns over the current lab test. The frequency range of the current test has been targeted for investigation. A low frequency, less than 2000 Hz, test rig was built to explore the cavitation damage. The test system did produce cavitation on the surface of the test button for a period of 36 h, with minimal mass loss. The test rig experienced cyclic fatigue when test times were extended. The work is now focusing on designing a better test rig for long duration tests and on developing numerical models in order to explore the effects of cavitation excitation frequency on surface erosion.

  9. Transequatorial Propagation of Very Low Frequency Radiowaves

    DTIC Science & Technology

    1981-04-15

    sources. However, Svennesson and Westerlund (1979), using waveguide mode theory combined with nighttime profiles given by ionospheric theory, claim results...lower substrata ( Westerlund , 1974). The detailed geometrical characteristics of the surface are not very important for VLF waves because the...characteristics car, be quite important (Galels, 1972). (.)uite the opposite, however, is true concerning the conduc- tivity ( Westerlund , 1974). The upper

  10. Propagation of slow waves in the guinea-pig gastric antrum.

    PubMed

    Hirst, G David S; Garcia-Londoño, A Pilar; Edwards, Frank R

    2006-02-15

    Intracellular recordings were made from the circular layer of the intact muscular wall of the guinea-pig gastric antrum in preparations where much of the corpus remained attached. When two electrodes were positioned parallel to and near to the greater curvature, slow waves were first detected at the oral site and subsequently at the anal site: the oro-anal conduction velocity was found to be 2.5 mm s(-1). When one electrode was positioned near the greater curvature and the other at a circumferential location, slow waves were first detected near the greater curvature and subsequently at the circumferential site: the circumferential conduction velocity was 13.9 mm s(-1). When recordings were made from preparations in which the circular muscle layer had been removed, the oro-anal and the circumferential conduction velocities were both about 3.5 mm s(-1). When slow waves were recorded from preparations in which much of the myenteric network of antral interstitial cells (ICC(MY)) had been dissected away, slow waves were first detected near the region of intact ICC(MY) and subsequently at a circumferential location: the circumferential conduction velocity of slow waves in regions devoid of ICC(MY) was 14.7 mm s(-1). When the electrical properties of isolated single bundles of circular muscle were determined, their length constants were about 3 mm and their time constant about 230 ms, giving an asymptotic electrotonic propagation velocity of 25 mm s(-1). Oro-anal electrical coupling between adjacent bundles of circular muscle was found to vary widely: some bundles were well connected to neighbouring bundles whereas others were not. Together the observations suggest that the slow oro-anal progression of slow waves results from a slow conduction velocity of pacemaker potentials in the myenteric network of interstitial cells. The rapid circumferential conduction of slow waves results from the electrical properties of the circular muscle layer which allow intramuscular ICC

  11. Propagation of the Slow Magnetoacoustic Waves in Coronal Loops above the Sunspot

    NASA Astrophysics Data System (ADS)

    Li, H. D.; Zhao, L.; Liang, H. F.; Bi, Y.; Hong, J., C.; Zheng, R. S.

    2013-01-01

    The observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) reveal the weak propagating disturbances (PDs) in the fan-like coronal loops of the active region (AR 11092) in 171 Å, 193 Å, and 211 Å. These PDs seem to be a common phenomenon in this part of the active region. The disturbances originate from small-scale brightenings at the footpoints of the loops and propagate along the loops. The observed propagation speeds decreased when the PDs were propagating in hotter plasmas. It roughly varies between 40 km/s and 121 km/s for three bandpasses, which is close to and below the expected sound speed in the coronal loops. Considering the projection effect and different angles to our line of sight, it is exactly what the slow-wave model expects. The wavelet analysis does not show a significant difference among the periods of the PDs observed in different bandpasses. The periodic patterns of two distinct periods, 3 min and more than 10 min, are detected in three bandpasses. Not only the coronal loops but also the sunspot regions on the chromosphere display intensity oscillations with a period of the order of 3 min. This result suggests that the sunspot oscillations can propagate into the corona through the chromospheres and the transition region.

  12. 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.

  13. Propagation of Biot slow waves in heterogeneous pipe networks: Effect of the pipe radius distribution on the effective wave velocity and attenuation

    NASA Astrophysics Data System (ADS)

    Bernabé, Y.

    2009-11-01

    This paper extends a previous study of the harmonic (or AC) flow of a compressible fluid through a single, elastic, thick-wall pipe. The model previously developed is used to investigate propagation of pore-scale Biot slow waves through heterogeneous one-, two- and three-dimensional networks of pipes. A novel method is applied to the results of the network simulations to numerically determine the dispersion equation of the upscaled Biot slow waves and investigate its dependence on pore-scale heterogeneity. As a function of frequency, the phase velocity of the macroscale Biot slow waves displays an S-shaped curve, increasing from zero at low frequencies (i.e., nonpropagative regime) to C? at high frequencies (i.e., propagative regime with C? lower than the sound velocity in the fluid). The transition between these two regimes is marked by the inflection point at the frequency ωB (where ωB is inversely proportional to the length scale Λ characteristic of fluid flow and permeability). The high-frequency phase velocity C? depends on the dimensionality of the network considered and decreases with increasing heterogeneity. The wave attenuation (as measured by the inverse quality factor) also presents an S-shaped curve, decreasing from 2 (i.e., critical damping) to zero, with the same inflection point at ωB. This behavior is approximately independent on the pore radius distribution, provided that ωB (or the corresponding fluid flow length scale Λ) is held constant. A mechanism based on wave scattering and interferences of forward and backward traveling (pore-scale) Biot slow waves is proposed to explain the observations.

  14. 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

  15. 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.

  16. Oscillatory instability in slow crack propagation in rubber under large deformation

    NASA Astrophysics Data System (ADS)

    Endo, Daiki; Sato, Katsuhiko; Hayakawa, Yoshinori

    2012-07-01

    We performed experiments to investigate slow fracture in thin rubber films under uniaxial tension using high-viscosity oils. In this system we observed an oscillating instability in slowly propagating cracks for small applied strains. The transition between oscillatory and straight patterns occurred near the characteristic strain at which rubber exhibits a nonlinear stress-strain relation. This suggests that nonlinear elasticity plays an important role in the formation of the observed pattern. This was confirmed by numerical simulation for neo-Hookean and linear elasticity models.

  17. Propagation of the Slow Magnetoacoustic Waves in Coronal Loops Above Sunspots

    NASA Astrophysics Data System (ADS)

    Li, Hai-dong; Zhao, Li; Liang, Hong-fei; Bi, Yi; Hong, Jun-chao; Zheng, Rui-sheng

    2013-07-01

    The observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) have revealed the weak dis- turbances (WDs) propagating in the fan-like coronal loops of the active region (AR 11092) at 171 ˚A, 193 ˚A, and 211 ˚A. These WDs seem to be a common phenomenon in this part of the active region. The disturbances originate from the bright loop foot, and propagate along the loops. The observed propagation speed decreases with the increasing temperature, and varies between 40 km/s and 121 km/s, close to and less than the sound speed in coronal loops. Consid- ering the projection effect and the different angles of the loops with respect to the line of sight, this is exactly what the slow-wave model expects. The wavelet analysis shows that the periods of the WDs observed in different wavebands have no significant difference, the two distinct periods, 3 min and more than 10 min, are all detected in the three EUV wavebands. Not only the coronal loops but also the sunspot region in the chromosphere exhibit intensity oscillations with a period of the order of 3 min. This result suggests that the sunspot oscillations can propagate into the corona through the chromosphere and transition region.

  18. '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

  19. Anti-aging treatments slow propagation of synucleinopathy by restoring lysosomal function.

    PubMed

    Kim, Dong-Kyu; Lim, Hee-Sun; Kawasaki, Ichiro; Shim, Yhong-Hee; Vaikath, Nishant N; El-Agnaf, Omar M A; Lee, He-Jin; Lee, Seung-Jae

    2016-10-02

    Aging is the major risk factor for neurodegenerative diseases that are also associated with impaired proteostasis, resulting in abnormal accumulation of protein aggregates. However, the role of aging in development and progression of disease remains elusive. Here, we used Caenorhabditis elegans models to show that aging-promoting genetic variations accelerated the rate of cell-to-cell transmission of SNCA/α-synuclein aggregates, hallmarks of Parkinson disease, and the progression of disease phenotypes, such as nerve degeneration, behavioral deficits, and reduced life span. Genetic and pharmacological anti-aging manipulations slowed the spread of aggregates and the associated phenotypes. Lysosomal degradation was significantly impaired in aging models, while anti-aging treatments reduced the impairment. Transgenic expression of hlh-30p::hlh-30, the master controller of lysosomal biogenesis, alleviated intercellular transmission of aggregates in the aging model. Our results demonstrate that the rate of aging closely correlates with the rate of aggregate propagation and that general anti-aging treatments can slow aggregate propagation and associated disease progression by restoring lysosomal function.

  20. Anti-aging treatments slow propagation of synucleinopathy by restoring lysosomal function

    PubMed Central

    Kim, Dong-Kyu; Lim, Hee-Sun; Kawasaki, Ichiro; Shim, Yhong-Hee; Vaikath, Nishant N.; El-Agnaf, Omar M. A.; Lee, He-Jin; Lee, Seung-Jae

    2016-01-01

    ABSTRACT Aging is the major risk factor for neurodegenerative diseases that are also associated with impaired proteostasis, resulting in abnormal accumulation of protein aggregates. However, the role of aging in development and progression of disease remains elusive. Here, we used Caenorhabditis elegans models to show that aging-promoting genetic variations accelerated the rate of cell-to-cell transmission of SNCA/α-synuclein aggregates, hallmarks of Parkinson disease, and the progression of disease phenotypes, such as nerve degeneration, behavioral deficits, and reduced life span. Genetic and pharmacological anti-aging manipulations slowed the spread of aggregates and the associated phenotypes. Lysosomal degradation was significantly impaired in aging models, while anti-aging treatments reduced the impairment. Transgenic expression of hlh-30p::hlh-30, the master controller of lysosomal biogenesis, alleviated intercellular transmission of aggregates in the aging model. Our results demonstrate that the rate of aging closely correlates with the rate of aggregate propagation and that general anti-aging treatments can slow aggregate propagation and associated disease progression by restoring lysosomal function. PMID:27485532

  1. A model of slow wave propagation and entrainment along the stomach.

    PubMed

    Buist, Martin L; Corrias, Alberto; Poh, Yong Cheng

    2010-09-01

    Interstitial cells of Cajal (ICC) isolated from different regions of the stomach generate spontaneous electrical slow wave activity at different frequencies, with cells from the proximal stomach pacing faster than their distal counterparts. However, in vivo there exists a uniform pacing frequency; slow waves propagate aborally from the proximal stomach and subsequently entrain distal tissues. Significant resting membrane potential (RMP) gradients also exist within the stomach whereby membrane polarization generally increases from the fundus to the antrum. Both of these factors play a major role in the macroscopic electrical behavior of the stomach and as such, any tissue or organ level model of gastric electrophysiology should ensure that these phenomena are properly described. This study details a dual-cable model of gastric electrical activity that incorporates biophysically detailed single-cell models of the two predominant cell types, the ICC and smooth muscle cells. Mechanisms for the entrainment of the intrinsic pacing frequency gradient and for the establishment of the RMP gradient are presented. The resulting construct is able to reproduce experimentally recorded slow wave activity and provides a platform on which our understanding of gastric electrical activity can advance.

  2. FORWARD MODELING OF PROPAGATING SLOW WAVES IN CORONAL LOOPS AND THEIR FREQUENCY-DEPENDENT DAMPING

    SciTech Connect

    Mandal, Sudip; Banerjee, Dipankar; Magyar, Norbert; Yuan, Ding; Doorsselaere, Tom Van

    2016-03-20

    Propagating slow waves in coronal loops exhibit a damping that depends upon the frequency of the waves. In this study we aim to investigate the relationship of the damping length (L{sub d}) with the frequency of the propagating wave. We present a 3D coronal loop model with uniform density and temperature and investigate the frequency-dependent damping mechanism for the four chosen wave periods. We include the thermal conduction to damp the waves as they propagate through the loop. The numerical model output has been forward modeled to generate synthetic images of SDO/AIA 171 and 193 Å channels. The use of forward modeling, which incorporates the atomic emission properties into the intensity images, allows us to directly compare our results with the real observations. The results show that the damping lengths vary linearly with the periods. We also measure the contributions of the emission properties on the damping lengths by using density values from the simulation. In addition to that we have also calculated the theoretical dependence of L{sub d} with wave periods and showed that it is consistent with the results we obtained from the numerical modeling and earlier observations.

  3. Low Frequency Radio Experiment (LORE)

    NASA Astrophysics Data System (ADS)

    Manoharan, Periasamy K.; Joshi, Bhal Chandra; Naidu, Arun Kumar

    High temporal and frequency resolution observations of solar generated disturbances below 15 MHz in the near-Sun region and at Sun-Earth distances in conjunction with optical and high energy observations of Sun are essential to understand the structure and evolution of eruptions, such as, flares, coronal mass ejections (CMEs), and their associated solar wind disturbances at heights above the photosphere and their consequences in the interplanetary medium. This talk presents 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 below 30 MHz. The LORE, although not part of Aditya-L1 mission, can be complimentary to planned Aditya-L1 coronagraph and its other on-board payloads as well as synergistic to ground based observations, which are routinely carried out by Ooty Radio Telescope. We discuss the baseline design and technical details of the proposed LORE and it is particularly suitable for providing data on the detailed time and frequency structure of fast drifting Type-III and slow drifting Type-II radio bursts with unprecedented time and frequency resolution as well as goniopolarimetry, made possible with better designed antennas and state-of-art electronics, employing FPGAs and an intelligent data management system. This would enable wide ranging studies such as studies of nonlinear plasma processes, CME in-situ radio emission, CME driven phenomena, interplanetary CME driven shocks, ICMEs driven by decelerating IP shocks and space weather effects of Solar Wind interaction regions. The talk will highlight the science objectives as well as the proposed technical design features.

  4. Deformation rates in northern Cascadia consistent with slow updip propagation of deep interseismic creep

    NASA Astrophysics Data System (ADS)

    Bruhat, Lucile; Segall, Paul

    2017-10-01

    Interpretations of interseismic slip deficit on the northern Cascadia megathrust are complicated by an enigmatic `gap' between the downdip limit of the locked region, inferred from kinematic inversions of deformation rates, and the top of the episodic tremor and slip (ETS) zone. Recent inversions of global positioning system (GPS) and tide gauge/leveling data for shear stress rates acting on the megathrust found a ˜21 km locking depth with a steep slip-rate gradient at its base is required to fit the data. Previous studies have assumed the depth distribution of interseismic slip rate to be time invariant; however, steep slip-rate gradients could also result from the updip propagation of slip into the locked region. This study explores models where interseismic slip penetrates up into the locked zone. We consider the creeping region, corresponding to the gap and the ETS zone, as a quasi-static crack driven by the plate velocity at its downdip end. We derive a simple model that allows for crack propagation over time, and provides analytical expressions for stress drop within the crack, slip and slip rate on the fault. It is convenient to expand the non-singular slip-rate distribution in a sum of Chebyshev polynomials. Estimation of the polynomial coefficients is underdetermined, yet provides a useful way of testing particular solutions and provides bounds on the updip propagation rate. When applied to the deformation rates in northern Cascadia, best-fitting models reveal that a very slow updip propagation, between 30 and 120 m yr-1 along the fault, could explain the steep slip-rate profile, needed to fit the data. This work provides a new tool for estimating interseismic slip rates, between purely kinematic inversions and full physics-based modeling, allowing for the possibility for updip expansion of the creeping zone.

  5. Causal information velocity in fast and slow pulse propagation in an optical ring resonator

    SciTech Connect

    Tomita, Makoto; Uesugi, Hiroyuki; Sultana, Parvin; Oishi, Tohru

    2011-10-15

    We examined the propagation of nonanalytical points encoded on temporally Gaussian-shaped optical pulses in fast and slow light in an optical ring resonator at {lambda} = 1.5 {mu}m. The temporal peak of the Gaussian pulse was either advanced or delayed, reflecting anomalous or normal dispersions in the ring resonator, relevant to under- or overcoupling conditions, respectively. The nonanalytical points were neither advanced nor delayed but appeared as they entered the ring resonator. The nonanalytical points could be interpreted as information; therefore, the experimental results suggested that information velocity is equal to the light velocity in vacuum or the background medium, independent of the group velocity. The transient behaviors at the leading and trailing edges of the nonanalytical points are discussed in terms of optical precursors.

  6. Analysis of Jovian low frequency radio emissions

    NASA Technical Reports Server (NTRS)

    Gurnett, D. A.

    1985-01-01

    The density of ions in the Io plasma torus and the scattering of these ions by low frequency electromagnetic emissions detected by Voyager 1 were studied. The ion density profile was investigated using whistler dispersion measurements provided by the Voyager plasma instrument. The scale height and absolute density of H+ ions in the vicinity of the plasma torus were determined by combining the measured plasma densities with the whistler dispersion measurements. A theoretical analysis of the modes of propagation of low frequency electromagnetic emissions in the torus was undertaken. Polarization reversal effects and rough estimates of the ion diffusion coefficient were utilized. Numerical evaluation of the ion diffusion coefficients in the torus were made using the observed Voyager 1 wave intensities. Results show that the observed wave intensities produce significant ion diffusion effects in the ion torus.

  7. 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.

  8. Zero-broadening SBS slow light propagation in an optical fiber using two broadband pump beams.

    PubMed

    Wang, Shihe; Ren, Liyong; Liu, Yu; Tomita, Yasuo

    2008-05-26

    A new method of tailoring stimulated Brillouin scattering (SBS) gain spectrum for slow light propagation is proposed by use of two Gaussian-shaped broadband pump beams with different powers and spectral widths. The central frequency interval between the two pump beams are carefully set to be two inherent Brillouin frequency shift, ensuring that the gain spectrum of one pump has the same central frequency with the loss spectrum of the other one. Different gain profiles are obtained and analyzed. Among them a special gain profile is found that ensures a zero-broadening of the signal pulse independent of the Brillouin gain. This is owing to the compensation between the positive gain-dependent broadening and the negative GVD (group velocity dispersion) dependent broadening. The relationship of two pump beams is also found for constructing such a gain profile. It provides us a new idea of managing the broadening of SBS-based slow pulse by artificially constructing and optimizing the profile of gain spectrum.

  9. Reverse cochlear propagation in the intact cochlea of the gerbil: evidence for slow traveling waves.

    PubMed

    Meenderink, Sebastiaan W F; van der Heijden, Marcel

    2010-03-01

    The inner ear can produce sounds, but how these otoacoustic emissions back-propagate through the cochlea is currently debated. Two opposing views exist: fast pressure waves in the cochlear fluids and slow traveling waves involving the basilar membrane. Resolving this issue requires measuring the travel times of emissions from their cochlear origin to the ear canal. This is problematic because the exact intracochlear location of emission generation is unknown and because the cochlea is vulnerable to invasive measurements. We employed a multi-tone stimulus optimized to measure reverse travel times. By exploiting the dispersive nature of the cochlea and by combining acoustic measurements in the ear canal with recordings of the cochlear-microphonic potential, we were able to determine the group delay between intracochlear emission-generation and their recording in the ear canal. These delays remained significant after compensating for middle-ear delay. The results contradict the hypothesis that the reverse propagation of emissions is exclusively by direct pressure waves.

  10. The effect of higher-order dispersion on slow light propagation in photonic crystal waveguides.

    PubMed

    Engelen, R J P; Sugimoto, Y; Watanabe, Y; Korterik, J P; Ikeda, N; van Hulst, N F; Asakawa, K; Kuipers, L

    2006-02-20

    We have studied the dispersion of ultrafast pulses in a photonic crystal waveguide as a function of optical frequency, in both experiment and theory. With phase-sensitive and time-resolved near-field microscopy, the light was probed inside the waveguide in a non-invasive manner. The effect of dispersion on the shape of the pulses was determined. As the optical frequency decreased, the group velocity decreased. Simultaneously, the measured pulses were broadened during propagation, due to an increase in group velocity dispersion. On top of that, the pulses exhibited a strong asymmetric distortion as the propagation distance increased. The asymmetry increased as the group velocity decreased. The asymmetry of the pulses is caused by a strong increase of higher order dispersion. As the group velocity was reduced to 0.116(9) .c, we found group velocity dispersion of -1.1(3) .10(6) ps(2)/km and third order dispersion of up to 1.1(4) .10(5) ps(3)/km. We have modelled our interferometric measurements and included the full dispersion of the photonic crystal waveguide. Our mathematical model and the experimental findings showed a good correspondence. Our findings show that if the most commonly used slow light regime in photonic crystals is to be exploited, great care has to be taken about higher-order dispersion.

  11. Theory for accelerated slow crack propagation in polyethylene fuel pipes. Annual report 1984-1985

    SciTech Connect

    Moet, A.; Chudnovsky, A.; Sehanobish, K.; Kasakevich, M.L.; Chaoui, K.

    1985-04-01

    Studies of field failure indicate that polyethylene fuel pipe fails by brittle crack propagation. To reproduce this type of failure in accelerated laboratory testing requires a similarity criterion. Quantitative fractographic analysis of field failure in MDPE pipe suggests that the number of ligaments broken per unit brittle crack excursion could probably serve as a similarity parameter. Efforts to accelerate brittle fracture in polyethylene has been successful under fatigue loading in 4'' MDPE pipe and in HDPE. The latter, used as a model material, displayed significant damage evolution that enabled the authors to apply concepts of the crack layer theory to describe entire slow crack-propagation regime. It is found that rate of crack extension is controlled by the rate of expansion and distortion (shape changes) of the damage zone preceding the crack. A method was developed to quantify this phenomena. It is also found that the observed energy release rate is significantly less than the theoretical predictions, for large cracks. Research is continued to develop quantitative account of this phenomena within the framework of the crack-layer theory.

  12. Slow fault propagation in serpentinite under conditions of high pore fluid pressure

    NASA Astrophysics Data System (ADS)

    French, Melodie E.; Zhu, Wenlu

    2017-09-01

    The rupture, localization, and slip of faults in serpentinite were studied under varying pore fluid pressure conditions to understand deformation mechanisms potentially responsible for slow slip in fault zones. Experiments were conducted at a constant effective confining pressure of 10 MPa and under pore fluid pressures from 0 to 120 MPa and at temperatures from 23 to 110 °C. With no fluid pressure, faulting occurs rapidly and audibly, and the duration of failure increases monotonically with increasing fluid pressure and temperature. Although non-dilatant during initial strain hardening, the serpentinite dilates during strain weakening concomitant with fault rupture and slip. Non-dilatant strain hardening occurs by microcracking along serpentine basal planes and grain boundaries and rarely in mode I orientations, consistent with previous studies. Dilatant fault rupture produces a network of transgranular shear fractures in conjugate orientations, generally with one dominant fracture. Structural observations show that as fluid pressure increases, the number of transgranular fractures increases. We propose that when faulting occurs over a distributed zone rather than a pre-existing principal slip surface, dilatant hardening causes deformation to migrate. This process causes an increase in slip weakening distance and fracture energy at elevated fluid pressures that can lead to more stable failure. Further, thermally-activated processes caused deformation at propagating crack tips, which also increases the slip weakening distance and the effective fracture energy with increasing temperature. Given the geologic settings for slow slip, our results indicate that high fluid pressure, distributed deformation, and thermally-activated processes may all contribute to slow fault rupture and slip.

  13. Low-frequency electromagnetic instabilities caused by a rotating dust flow

    SciTech Connect

    Prudskikh, V. V.

    2010-12-15

    Low-frequency electromagnetic waves propagating obliquely to an external magnetic field in a plasma with an anisotropic dust component are considered. The cold dust is assumed to have considerable longitudinal and transverse velocity components with respect to the magnetic field. A dispersion relation demonstrating that both fast and slow waves can be unstable is derived in the framework of kinetic theory. Mechanisms and consequences of these instabilities are discussed in the context of the problem of plasma transition into a turbulent state behind the shock front of a supernova.

  14. 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.

  15. 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.

  16. Identification of low-frequency fluctuations in the terrestrial magnetosheath

    NASA Technical Reports Server (NTRS)

    Song, P.; Russell, C. T.; Gary, S. P.

    1994-01-01

    On the basis of magnetohydrodynamic (MHD) theory we develop a scheme for distinguishing among the four low-frequency modes which may propagate in a high-beta anisotropic plasma such as the magnetosheath: the fast and slow magnetosonic, the Alfven, and mirror modes. We use four parameters: the ratio of transverse to compressional powers in the magnetic field, the ratio of the wave powers in the thermal pressure and in the magnetic field, the ratio of the perturbations in the thermal and magnetic pressures, and the ratio of the wave powers in the velocity and in the magnetic field. In the test case of an Active Magnetospheric Particle Tracer Explorers/Ion Release Module (AMPTE/IRM) magnetosheath pass near the Sun-Earth line downstream of a quasi-perpendicular shock, the four modes can be clearly distinguished both spatially and spectrally. Near the bow shock, the waves are Alfvenic in a large frequency range, 1 to 100 mHz. In the middle and inner magnetosheath, the waves below 10 mHz are Alfvenic. The fast mode waves occur in the higher-frequency end of the enhanced spectrum, 80 mHz for the middle magnetosheath and 55 mHz for the inner sheath. The wave enhancement in the intermediate frequencies is slow modes in the inner sheath and mirror modes in the middle sheath. This confirms the earlier report of the existence of the slow mode waves near the magnetopause. These slow waves provide evidence that the magnetopause is an active source of the waves in the sheath. We also show that the measured frequency of a wave is close to an invariant if the magnetosheath flow is in a steady state. Therefore changes in the frequencies of enhanced waves indicate emergence, or damping, or mode conversion of the waves.

  17. Extremely Low Frequency Electromagnetic Investigation on Mars

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

    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.

  18. On Sun-to-Earth Propagation of Coronal Mass Ejections: II. Slow Events and Comparison with Others

    NASA Astrophysics Data System (ADS)

    Liu, Y. D.; Hu, H.; Wang, C.; Luhmann, J. G.; Richardson, J. D.; Yang, Z.; Wang, R.

    2016-12-01

    As a follow-up study on Sun-to-Earth propagation of fast coronal mass ejections (CMEs), we examine the Sun-to-Earth characteristics of slow CMEs combining heliospheric imaging and in situ observations. Three events of particular interest, the 2010 June 16, 2011 March 25 and 2012 September 25 CMEs, are selected for this study. We compare slow CMEs with fast and intermediate-speed events, and obtain key results complementing the attempt of tet{liu13} to create a general picture of CME Sun-to-Earth propagation: (1) the Sun-to-Earth propagation of a typical slow CME can be approximately described by two phases, a gradual acceleration out to about 20-30 solar radii, followed by a nearly invariant speed around the average solar wind level; (2) comparison between different types of CMEs indicates that faster CMEs tend to accelerate and decelerate more rapidly and have shorter cessation distances for the acceleration and deceleration; (3) both intermediate-speed and slow CMEs would have a speed comparable to the average solar wind level before reaching 1 AU; (4) slow CMEs have a high potential to interact with other solar wind structures in the Sun-Earth space due to their slow motion, providing critical ingredients to enhance space weather; and (5) the slow CMEs studied here lack strong magnetic fields at the Earth but tend to preserve a flux-rope structure with axis generally perpendicular to the radial direction from the Sun. We also suggest a ``best" strategy for the application of a triangulation concept in determining CME Sun-to-Earth kinematics, which helps to clarify confusions about CME geometry assumptions in the triangulation and to improve CME analysis and observations.

  19. ON SUN-TO-EARTH PROPAGATION OF CORONAL MASS EJECTIONS: II. SLOW EVENTS AND COMPARISON WITH OTHERS

    SciTech Connect

    Liu, Ying D.; Hu, Huidong; Wang, Chi; Yang, Zhongwei; Wang, Rui; Luhmann, Janet G.; Richardson, John D.

    2016-02-15

    As a follow-up study on Sun-to-Earth propagation of fast coronal mass ejections (CMEs), we examine the Sun-to-Earth characteristics of slow CMEs combining heliospheric imaging and in situ observations. Three events of particular interest, the 2010 June 16, 2011 March 25, and 2012 September 25 CMEs, are selected for this study. We compare slow CMEs with fast and intermediate-speed events, and obtain key results complementing the attempt of Liu et al. to create a general picture of CME Sun-to-Earth propagation: (1) the Sun-to-Earth propagation of a typical slow CME can be approximately described by two phases, a gradual acceleration out to about 20–30 solar radii, followed by a nearly invariant speed around the average solar wind level; (2) comparison between different types of CMEs indicates that faster CMEs tend to accelerate and decelerate more rapidly and have shorter cessation distances for the acceleration and deceleration; (3) both intermediate-speed and slow CMEs would have speeds comparable to the average solar wind level before reaching 1 au; (4) slow CMEs have a high potential to interact with other solar wind structures in the Sun–Earth space due to their slow motion, providing critical ingredients to enhance space weather; and (5) the slow CMEs studied here lack strong magnetic fields at the Earth but tend to preserve a flux-rope structure with an axis generally perpendicular to the radial direction from the Sun. We also suggest a “best” strategy for the application of a triangulation concept in determining CME Sun-to-Earth kinematics, which helps to clarify confusions about CME geometry assumptions in the triangulation and to improve CME analysis and observations.

  20. Slow Patchy Extreme-ultraviolet Propagating Fronts Associated with Fast Coronal Magneto-acoustic Waves in Solar Eruptions

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    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. 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.

  2. Sources and effects of low-frequency noise.

    PubMed

    Berglund, B; Hassmén, P; Job, R F

    1996-05-01

    The sources of human exposure to low-frequency noise and its effects are reviewed. Low-frequency noise is common as background noise in urban environments, and as an emission from many artificial sources: road vehicles, aircraft, industrial machinery, artillery and mining explosions, and air movement machinery including wind turbines, compressors, and ventilation or air-conditioning units. The effects of low-frequency noise are of particular concern because of its pervasiveness due to numerous sources, efficient propagation, and reduced efficacy of many structures (dwellings, walls, and hearing protection) in attenuating low-frequency noise compared with other noise. Intense low-frequency noise appears to produce clear symptoms including respiratory impairment and aural pain. Although the effects of lower intensities of low-frequency noise are difficult to establish for methodological reasons, evidence suggests that a number of adverse effects of noise in general arise from exposure to low-frequency noise: Loudness judgments and annoyance reactions are sometimes reported to be greater for low-frequency noise than other noises for equal sound-pressure level; annoyance is exacerbated by rattle or vibration induced by low-frequency noise; speech intelligibility may be reduced more by low-frequency noise than other noises except those in the frequency range of speech itself, because of the upward spread of masking. On the other hand, it is also possible that low-frequency noise provides some protection against the effects of simultaneous higher frequency noise on hearing. Research needs and policy decisions, based on what is currently known, are considered.

  3. The Low Frequency Space Array

    NASA Technical Reports Server (NTRS)

    Dennison, Brian; Weiler, K. W.; Johnston, K. J.; Simon, R. S.; Spencer, J. H.; Hammarstrom, L. M.; Wilhelm, P. G.; Kaiser, M. L.; Desch, M. D.; Fainberg, J.

    1987-01-01

    The Low Frequency Space Array (LFSA) is a conceptual mission to survey the entire sky and to image individual sources at frequencies between 1.5 and 26 MHz, a frequency range over which the earth's ionosphere transmits poorly or not at all. With high resolution, high sensitivity observations, a new window will be opened in the electromagnetic spectrum for astronomical investigation. Also, extending observations down to such low frequencies will bring astronomy to the fundamental limit below which the galaxy becomes optically thick due to free-free absorption. A number of major scientific goals can be pursued with such a mission, including mapping galactic emission and absorption, studies of individual source spectra in a frequency range where a number of important processes may play a role, high resolution imaging of extended sources, localization of the impulsive emission from Jupiter, and a search for coherent emission processes.

  4. 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

  5. Low Frequency Geoacoustic Inversion Method

    DTIC Science & Technology

    2011-09-01

    DISTRIBUTION STATEMENT A: Distribution approved for public release, distribution is unlimited Low Frequency Geoacoustic Inversion Method A. Tolstoy ... Tolstoy , ’10), particularly the investigation of a new broadband method (the minimization method; see Tolstoy , ’12); � to apply the LF G.I. method...ADDRESS(ES) A. Tolstoy ,1538 Hampton Hill Circle,McLean,VA,22101 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND

  6. Low Frequency Geoacoustic Inversion Method

    DTIC Science & Technology

    2012-09-30

    DISTRIBUTION STATEMENT A: Distribution approved for public release, distribution is unlimited Low Frequency Geoacoustic Inversion Method A. Tolstoy ...recently featuring the minimization processor ( Tolstoy , ’10 and ’12); demonstration that horizontal arrays can be successfully used for G.I. with the...over twenty years, particularly for the suppression of sidelobes ( Tolstoy , ’93). For each the MFP values at sidelobes (non-true parameter values

  7. LOFAR, the low frequency array

    NASA Astrophysics Data System (ADS)

    Vermeulen, R. C.

    2012-09-01

    LOFAR, the Low Frequency Array, is a next-generation radio telescope designed by ASTRON, with antenna stations concentrated in the north of the Netherlands and currently spread into Germany, France, Sweden and the United Kingdom; plans for more LOFAR stations exist in several other countries. Utilizing a novel, phased-array design, LOFAR is optimized for the largely unexplored low frequency range between 30 and 240 MHz. Digital beam-forming techniques make the LOFAR system agile and allow for rapid re-pointing of the telescopes as well as the potential for multiple simultaneous observations. Processing (e.g. cross-correlation) takes place in the LOFAR BlueGene/P supercomputer, and associated post-processing facilities. With its dense core (inner few km) array and long (more than 1000 km) interferometric baselines, LOFAR reaches unparalleled sensitivity and resolution in the low frequency radio regime. The International LOFAR Telescope (ILT) is now issuing its first call for observing projects that will be peer reviewed and selected for observing starting in December. Part of the allocations will be made on the basis of a fully Open Skies policy; there are also reserved fractions assigned by national consortia in return for contributions from their country to the ILT. In this invited talk, the gradually expanding complement of operationally verified observing modes and capabilities are reviewed, and some of the exciting first astronomical results are presented.

  8. 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

  9. Slow Surface Wave Propagation in an Azimuthally-Magnetized Millimeter-Wave Solid-Plasma Coaxial Waveguide

    NASA Astrophysics Data System (ADS)

    Obunai, Tetsuo; Hakamada, Katsuhiro

    1984-08-01

    The propagation characteristics in an azimuthally-magnetized partially-filled solid-plasma coaxial waveguide using n-type InSb at 77 K as the plasma material have been analyzed theoretically and calculated numerically. The results are compared with those for parallel-plate plasma waveguide studied previously. When the proper cross-sectional configuration and field parameters are employed, slow surface wave resonance takes place in the waveguide and a much slower wave propagation velocity at a reduced resonant magnetic field is obtained.

  10. 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.

  11. 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.

  12. Low-frequency hippocampal–cortical activity drives brain-wide resting-state functional MRI connectivity

    PubMed Central

    Chan, Russell W.; Leong, Alex T. L.; Ho, Leon C.; Gao, Patrick P.; Wong, Eddie C.; Dong, Celia M.; Wang, Xunda; He, Jufang; Chan, Ying-Shing; Lim, Lee Wei; Wu, Ed X.

    2017-01-01

    The hippocampus, including the dorsal dentate gyrus (dDG), and cortex engage in bidirectional communication. We propose that low-frequency activity in hippocampal–cortical pathways contributes to brain-wide resting-state connectivity to integrate sensory information. Using optogenetic stimulation and brain-wide fMRI and resting-state fMRI (rsfMRI), we determined the large-scale effects of spatiotemporal-specific downstream propagation of hippocampal activity. Low-frequency (1 Hz), but not high-frequency (40 Hz), stimulation of dDG excitatory neurons evoked robust cortical and subcortical brain-wide fMRI responses. More importantly, it enhanced interhemispheric rsfMRI connectivity in various cortices and hippocampus. Subsequent local field potential recordings revealed an increase in slow oscillations in dorsal hippocampus and visual cortex, interhemispheric visual cortical connectivity, and hippocampal–cortical connectivity. Meanwhile, pharmacological inactivation of dDG neurons decreased interhemispheric rsfMRI connectivity. Functionally, visually evoked fMRI responses in visual regions also increased during and after low-frequency dDG stimulation. Together, our results indicate that low-frequency activity robustly propagates in the dorsal hippocampal–cortical pathway, drives interhemispheric cortical rsfMRI connectivity, and mediates visual processing. PMID:28760982

  13. Slow group velocity propagation of sound via defect coupling in a one-dimensional acoustic band gap array

    NASA Astrophysics Data System (ADS)

    Robertson, W. M.; Baker, C.; Bennett, C. Brad

    2004-02-01

    A simple experimental system is presented in which the group velocity of acoustic wave packets traveling in an air-filled waveguide can be slowed to values much smaller than the speed of sound in air. The experiment is an acoustic analog of the much-studied optical phenomenon of slow light propagation. Slow (or even stopped) light propagation has been observed in atomic vapors in the vicinity of strong dispersion, typically associated with electromagnetically induced transparency. In the acoustic experiment described here, strong dispersion is produced by the introduction of a defect in an otherwise perfectly periodic one-dimensional acoustic band gap array. The defect produces a narrow transmission band within the forbidden acoustic band gap region resulting in strong dispersion. By tuning the carrier frequency of the acoustic wave packet to the peak transmission of the defect, the group velocity can be slowed to 0.24vs, where vs is the speed of sound in air. These results are shown to be consistent with theoretical calculations.

  14. Low frequency acoustic resonances in urban courtyards.

    PubMed

    Molerón, Miguel; Félix, Simon; Pagneux, Vincent; Richoux, Olivier

    2014-01-01

    Urban courtyards can be regarded as open cavities in the urban area, in which resonances can be excited by waves generated in the neighboring streets. The aim of the present work is to experimentally and numerically investigate low frequency resonance phenomena in these configurations. Experiments are carried out in a scale model and a numerical study is performed with a coupled modal-finite elements method. The method enables the three-dimensional modeling of the acoustic field and thus to take into account the interactions between the courtyard and the street canyon that occur above the roof level, a particular characteristic of wave propagation in urban areas. The attention is focused on two aspects, the amplification of the sound level inside the courtyard and the acoustic attenuation in the street due to resonances. Experimental and numerical results are in good agreement and show a strong resonant behavior of these configurations.

  15. Characterization and Impact of Low Frequency Wind Turbine Noise Emissions

    NASA Astrophysics Data System (ADS)

    Finch, James

    Wind turbine noise is a complex issue that requires due diligence to minimize any potential impact on quality of life. This study enhances existing knowledge of wind turbine noise through focused analyses of downwind sound propagation, directionality, and the low frequency component of the noise. Measurements were conducted at four wind speeds according to a design of experiments at incremental distances and angles. Wind turbine noise is shown to be highly directional, while downwind sound propagation is spherical with limited ground absorption. The noise is found to have a significant low frequency component that is largely independent of wind speed over the 20-250 Hz range. The generated low frequency noise is shown to be audible above 40 Hz at the MOE setback distance of 550 m. Infrasound levels exhibit higher dependency on wind speed, but remain below audible levels up to 15 m/s.

  16. 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.

  17. 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.

  18. 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.

  19. Low-frequency sonophoresis: a review.

    PubMed

    Mitragotri, Samir; Kost, Joseph

    2004-03-27

    Application of ultrasound enhances skin permeability to a variety of molecules (sonophoresis). The enhancement induced by ultrasound is particularly significant at low-frequencies (f<100 kHz, low-frequency sonophoresis). This review summarizes mechanisms and applications of low-frequency sonophoresis. In vitro, in vivo, as well as clinical studies demonstrating the effect of low-frequency ultrasound on transdermal drug delivery and glucose extraction are summarized. Mechanistic insights gained through a number of investigations are also reviewed. Finally, reports on the synergistic effect of low-frequency ultrasound with other enhancers including chemicals and iontophoresis are summarized.

  20. 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

  1. Low frequency nonlinear waves in electron depleted magnetized nonthermal plasmas

    NASA Astrophysics Data System (ADS)

    Mobarak Hossen, Md.; Sahadat Alam, Md.; Sultana, Sharmin; Mamun, A. A.

    2016-11-01

    A theoretical study on the ultra-low frequency small but finite amplitude solitary waves has been carried out in an electron depleted magnetized nonthermal dusty plasma consisting of both polarity (positively charged as well as negatively charged) inertial massive dust particles and nonextensive q distributed ions. The reductive perturbation technique is employed to derive the ZakharovKuznetsov (ZK) equation. The basic features of low frequency solitary wave are analyzed via the solution of ZK equation. It is observed that the intrinsic properties (e.g., polarity, amplitude, width, etc.) of dust-acoustic (DA) solitary waves (SWs) are significantly influenced by the effects external magnetic field, obliqueness, nonextensivity of ions, and the ratio of ion number density to the product of electron and negative dust number density. The findings of our results may be useful to explain the low frequency nonlinear wave propagation in some plasma environments like cometary tails, the earth polar mesosphere, Jupiter's magnetosphere, etc.

  2. Propagation of phase nonanalytical points in fast- and slow-light media

    NASA Astrophysics Data System (ADS)

    Morita, Yuma; Tomita, Makoto

    2017-08-01

    We performed a series of experiments to examine the arrival of phase nonanalytical points in fast- and slow-light media, using a Gaussian-shaped temporal pulse and encoding phase nonanalytical points at various positions within the pulse envelope. For the phase nonanalytical points, the amplitude of the slowly varying pulse envelope, as well as any order of the derivatives, is continuous, but the phase of the carrier wave is discontinuous. The phase nonanalytical points were neither advanced nor delayed, but appeared at the same instance as they entered the fast- and slow-light media, in good accordance with the idea that the information velocity was equal to the velocity of light in a vacuum, c , or in the background medium.

  3. Low frequency gravitational wave astrophysics

    NASA Astrophysics Data System (ADS)

    Larson, Shane

    The field of low-frequency gravitational wave astronomy is evolving as the design of the Laser Interferometer Space Antenna (LISA) is in flux. Changing mission architectures naturally has an impact on the science goals and science capabilities in gravitational wave astronomy, requiring astrophysicists to pursue a deeper understanding on three fronts. (1) What astrophysical knowledge can be extracted from populations of sources based on their relative strengths in the data streams? (2) How are the science returns maximized as detector capabilities evolve? (3) How do evolving detector performance expectations alter the science that is possible with space- based gravitational wave detectors? This work proposes a series of investigations that address these questions along two broad avenues of inquiry. The first thrust of this effort is designed to examine how the population of ultra-compact galactic binaries can be better characterized by multi-messenger observations and statistical population analyses. While these investigations are astrophysical interesting in and of themselves, they are particularly relevant as detector designs evolve because the binaries are a limiting source of astrophysical noise that must be mitigated in order to maximize the science return for other sources, such as massive binary black hole inspirals and extreme mass ratio inspirals. The second thrust of this effort is geared toward characterization of the detector itself, since this ultimately fixes our ability to answer astrophysical questions. While many high-fidelity simulators exist for the original LISA mission architecture, the work proposed here will develop a new, flexible suite of prototyping tools analogous to the "Online Sensitivity Curve Generator" (which the PI authored). These tools will allow astrophysicists and data analysts alike to rapidly assess whether new proposed architectures for a space-based gravitational wave observatory will enhance or adversely impact the science

  4. Propagating slow magneto-acoustic waves in coronal loops as seen from trace and cds

    NASA Astrophysics Data System (ADS)

    Prasad Samayamanthula, Krishna; Banerjee, Dipankar; Gupta, Girjesh R.

    Propagating intensity disturbances along various Active region loop structures with projected speeds less than and close to acoustic speeds, now commonly called magneto-acoustic waves, are proposed to be photospheric p-modes leaking into solar atmosphere. Though there is a wide range of periodicities observed, the 3 min. and 5 min. periodicities, which are character-istic of sunspot umbral and penumbral regions lifted their importance of study. Simultaneous observations of these waves at different heights from photosphere, through transition region to corona will give us direct evidence for their involvement and contribution to coronal heating. AR 10457 had been extensively studied for the presence of such propagating oscillations, when it is on-disk, on 11th September 2003, using the CDS/SoHO, TRACE, and MDI data of JOP 165 campaign. Different periodicities are found and the resonance feature in the periodicity is observed in few locations, but the speeds are found to be quite low(< 20 km/s). Comparison will be made between sunspot and non-sunspot linked open structures. There is also a signature of decelerating propagation in a structure. Significance of the results in the context of coronal heating and future observations with SDO will be discussed.

  5. Distribution of low-frequency earthquakes accompanying the very low frequency earthquakes along the Ryukyu Trench

    NASA Astrophysics Data System (ADS)

    Nakamura, Mamoru

    2017-04-01

    This study investigated the activity and distribution of low-frequency earthquakes (LFEs) accompanying the very low frequency earthquakes (VLFEs) in the central and southern Ryukyu Trench. This investigation was based on short-period seismometer waveforms obtained by the Japan Meteorological Agency from April 2004 to December 2015. The LFEs were detected using the Envelope Correlation Method, and the hypocenter locations were established using the arrival time difference of the envelope. The arrival times of the P- and S-phases were selected for events in which conspicuous P and S arrivals were observed and their hypocenters were determined. The results showed that LFEs are distributed 30-50 km from the trench axis in the Okinawa and Yaeyama areas. These areas correspond to a slab depth of 12-25 km. The LFEs and VLFEs occurred in association with slow slip events (SSEs) in the Okinawa and Yaeyama areas, indicating that they are induced by SSEs in the Ryukyu Trench. Moreover, the SSEs, LFE-VLFEs, and thrust-type ordinary earthquakes exhibit separate distributions. This suggests change in the frictional condition at the slab depth of 12-25 km along the trench axis in the Ryukyu subduction zone. In the southern Ryukyu Trench, LFEs occur approximately 50 km from the SSE faults, suggesting that SSEs trigger the LFEs near the southern Ryukyu Trench.[Figure not available: see fulltext.

  6. 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.

  7. Ultra-slow light propagation by self-induced transparency in ruby in the superhyperfine limit.

    PubMed

    Riesen, Hans; Rebane, Aleksander; Rajan, Rajitha Papakutty; Hutchison, Wayne; Ganschow, Steffen; Szabo, Alex

    2017-05-15

    Self-induced transparency is reported for circularly polarized light in the R1(-3/2) line of a 30 ppm ruby (α-Al2O3:Cr3+) at 1.7 K in a magnetic field of B‖c=4.5  T. In such a field and temperature, a 30 ppm ruby is in the so-called superhyperfine limit resulting in a long phase memory time, TM=50  μs, and a thousand-fold slower pulse propagation velocity of ∼300  m/s was observed, compared to the ∼300  km/s measured in the first observation of self-induced transparency (SIT) ∼50 years ago, that employed a ruby with a 500 ppm chromium concentration in zero field and at 4.2 K. To date, this is the slowest pulse propagation ever observed in a SIT experiment.

  8. Demonstration of slow sound propagation and acoustic transparency with a series of detuned resonators

    NASA Astrophysics Data System (ADS)

    Santillán, Arturo; Bozhevolnyi, Sergey I.

    2014-05-01

    We present experimental results demonstrating the phenomenon of acoustic transparency with a significant slowdown of sound propagation realized with a series of paired detuned acoustic resonators (DAR) side-attached to a waveguide. The phenomenon mimics the electromagnetically induced transparency in atomic physics. By arranging four identical DAR pairs along the waveguide with an equal subwavelength separation between adjacent pairs, we show that this arrangement features unique properties of narrow-band transmission and strong dispersion. In particular, we demonstrate side-lobe suppression of more than 20 dB on both sides of the transparency window, and we quantify directly (using a pulse propagation) the acoustic slowdown effect, resulting in the sound group velocity of ˜9.8 m/s (i.e. in the group refractive index of 35). We find very similar values of the group refractive index by using measurements of the phase of the transmitted wave. It is also shown that a direct coupling exists between the DAR in each pair, which cannot be explained by the interference of waves radiated from those resonators. This detrimental coupling becomes noticeable for small values of detuning and also if the cross-sectional area of the neck of the resonators is increased.

  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. 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.

  11. Low-frequency collective modes in dry and hydrated proteins.

    PubMed Central

    Bellissent-Funel, M C; Teixeira, J; Chen, S H; Dorner, B; Middendorf, H D; Crespi, H L

    1989-01-01

    We have observed Brillouin-like low frequency collective modes in the scattering of 1 A neutrons from a fully in vivo deuterated protein. These modes are tentatively interpreted as due to short-lived coherent excitations propagating with velocities between 2,000 and 4,000 m/s in elements of the secondary structure and patches of closely associated water. PMID:2554989

  12. Spatial structure of low-frequency wind noise.

    PubMed

    Wilson, D Keith; Greenfield, Roy J; White, Michael J

    2007-12-01

    The distinguishing spatial properties of low-frequency microphone wind noise (turbulent pressure disturbances) are examined with a planar, 49-element array. Individual, propagating transient pressure disturbances are imaged by wavelet processing to the array data. Within a given frequency range, the wind disturbances are much smaller and less spatially coherent than sound waves. Conventional array processing techniques are particularly sensitive to wind noise when sensor separations are small compared to the acoustic wavelengths of interest.

  13. Possible feedback path for low-frequency atmospheric oscillations

    NASA Technical Reports Server (NTRS)

    Gao, X. H.; Stanford, J. L.

    1988-01-01

    Four years of satellite-derived microwave radiance data have been analyzed, providing evidence for the possiblity of a feedback route in the Southern Hemisphere. The present propagation path extends from the central equatorial Pacific across lower South America, heads equatorward after passing south of Africa, and finally reenters the equatorial Indian Ocean with correct phase to enhance the primary equatorial dipole structure. The Southern Hemisphere propagation path migrates northward in April-September and southward in October-March, and it may constitute a feedback mechanism which could stabilize the low frequency oscillations.

  14. 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

  15. 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.

  16. Phase-resolved pulse propagation through metallic photonic crystal slabs: plasmonic slow light

    NASA Astrophysics Data System (ADS)

    Schönhardt, Anja; Nau, Dietmar; Bauer, Christina; Christ, André; Gräbeldinger, Hedi; Giessen, Harald

    2017-03-01

    We characterized the electromagnetic field of ultra-short laser pulses after propagation through metallic photonic crystal structures featuring photonic and plasmonic resonances. The complete pulse information, i.e. the envelope and phase of the electromagnetic field, was measured using the technique of cross-correlation frequency resolved optical gating. In good agreement, measurements and scattering matrix simulations show a dispersive behaviour of the spectral phase at the position of the resonances. Asymmetric Fano-type resonances go along with asymmetric phase characteristics. Furthermore, the spectral phase is used to calculate the dispersion of the sample and possible applications in dispersion compensation are investigated. Group refractive indices of 700 and 70 and group delay dispersion values of 90 000 fs2 and 5000 fs2 are achieved in transverse electric and transverse magnetic polarization, respectively. The behaviour of extinction and spectral phase can be understood from an intuitive model using the complex transmission amplitude. An associated depiction in the complex plane is a useful approach in this context. This method promises to be valuable also in photonic crystal and filter design, for example, with regards to the symmetrization of the resonances. This article is part of the themed issue 'New horizons for nanophotonics'.

  17. Phase-resolved pulse propagation through metallic photonic crystal slabs: plasmonic slow light.

    PubMed

    Schönhardt, Anja; Nau, Dietmar; Bauer, Christina; Christ, André; Gräbeldinger, Hedi; Giessen, Harald

    2017-03-28

    We characterized the electromagnetic field of ultra-short laser pulses after propagation through metallic photonic crystal structures featuring photonic and plasmonic resonances. The complete pulse information, i.e. the envelope and phase of the electromagnetic field, was measured using the technique of cross-correlation frequency resolved optical gating. In good agreement, measurements and scattering matrix simulations show a dispersive behaviour of the spectral phase at the position of the resonances. Asymmetric Fano-type resonances go along with asymmetric phase characteristics. Furthermore, the spectral phase is used to calculate the dispersion of the sample and possible applications in dispersion compensation are investigated. Group refractive indices of 700 and 70 and group delay dispersion values of 90 000 fs(2) and 5000 fs(2) are achieved in transverse electric and transverse magnetic polarization, respectively. The behaviour of extinction and spectral phase can be understood from an intuitive model using the complex transmission amplitude. An associated depiction in the complex plane is a useful approach in this context. This method promises to be valuable also in photonic crystal and filter design, for example, with regards to the symmetrization of the resonances.This article is part of the themed issue 'New horizons for nanophotonics'. © 2017 The Author(s).

  18. Comparison of optical and acoustical monitoring during a crack propagation, implication for slow earthquake dynamics

    NASA Astrophysics Data System (ADS)

    Lengliné, Olivier; Schmittbuhl, Jean; Elkhoury, Jean; Toussaint, Renaud; Daniel, Guillaume; Maloy, Knut Jurgen

    2010-05-01

    Observations of aseismic transients in several tectonic context suggest that they might be linked to seismicity. However a clear observation and description of these phenomena and their interaction is lacking. This owes to the difficulty of characterizing with a sufficient resolution processes taking place at depth. Here we aim to study these interactions between aseismic and seismic slip taking advantage of an unique experimental setup. We conducted a series of mode I crack propagation experiments on transparent materials (PMMA). The crack advance is trapped in a weakness plane which is the interface between two previously sandblasted and annealed plexiglass plates. A fast video camera taking up to 500 frames per second ensures the tracking of the front rupture. The acoustic system is composed of a maximum of 44 channels continuously recording at 5 MHz for a few tens of seconds. Piezo-electric sensors are composed of a 32 elements linear array and individual sensors surrounding the crack front. An automatic detection and localization procedure allows us to obtain the position of acoustic emission (A.E.) that occurred during the crack advance. Crack front image processing reveals an intermittent opening which might be linked to the time and space clustering of the AE. An analogy between the mode I (opening) and the mode III (antiplane slip) allows us to interpret our results in term of slip on faults. Our experiment thus helps to reveal the interplay between seismic and aseismic slip on faults.

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. The Effects of Sediment Properties on Low Frequency Acoustic Propagation

    DTIC Science & Technology

    2013-09-30

    interface/ Scholte wave-based inversions for shear properties. • Adapt our long range sediment tomography technique for compressional and shear wave...used a simple model developed by Chapman and Godin3 to predict the Scholte wave arrivals for an ocean bottom assuming power-law variation of shear...estimation using Scholte wave data will be pursued. The tasks associated with this objective are summarized as follows: a. Develop inversion

  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. Upgrading Emma to Use Low-Frequency RF Cavities

    NASA Astrophysics Data System (ADS)

    Ohmori, Chihiro; Berg, J. Scott

    EMMA is an experiment to study beam dynamics in fixed field alternating gradient accelerators (FFAGs). It accelerates the beam in about 10 turns using 1.3 GHz cavities in a mode like that used for muon accelerators. Many applications of FFAGs prefer to have slower acceleration, typically thousands of turns. To do so in EMMA would require the RF system to be replaced with a low-frequency, high-gradient system. This paper describes the motivation for studying slow acceleration in EMMA and the required parameters for an RF system to do that. It then describes the technology needed for the RF system.

  6. Effects of low-frequency noise in driven coherent nanodevices

    NASA Astrophysics Data System (ADS)

    Falci, G.; Berritta, M.; Russo, A.; D'Arrigo, A.; Paladino, E.

    2012-11-01

    We study the effect of low-frequency noise in ac-driven two- or many-level coherent nanodevices. Fluctuations in the properties of the device are translated into equivalent fluctuations of the driving fields. The impact on Rabi oscillations can be modulated with the detuning and minimized at resonance. In three-level atoms slow noise produces qualitative changes for protocols as coherent population transfer. We propose a strategy allowing us to operate at parity symmetry points, where the device is well protected against noise, despite selection rules preventing direct couplings to external fields of involved transitions.

  7. New nonlinear mechanisms of midlatitude atmospheric low-frequency variability

    NASA Astrophysics Data System (ADS)

    Sterk, Alef; Vitolo, Renato; Broer, Henk; Simo, Carles; Dijkstra, Henk

    2010-05-01

    We investigate the dynamical mechanisms potentially involved in the so-called atmospheric low-frequency variability, occurring at midlatitudes in the Northern Hemisphere. This phenomenon is characterised by recurrent non-propagating and temporally persistent flow patterns, with typical spatial and temporal scales of 6000-10000 km and 10-50 days, respectively. We study a low-order model derived from the 2-layer shallow-water equations on a β-plane channel. The main ingredients of the low-order model are a zonal flow, a planetary scale wave, orography, and a baroclinic-like forcing. A systematic analysis of the dynamics of the low-order model is performed using techniques and concepts from dynamical systems theory. Orography height (h0) and magnitude of zonal wind forcing (U0) are used as control parameters to study the bifurcations of equilibria and periodic orbits. An equilibrium loses stability (U0 ≥ 12.5 m/s) along two curves of Hopf bifurcations and gives birth to two distinct families of periodic orbits. These periodic orbits bifurcate into strange attractors along three routes to chaos: period doubling cascades, breakdown of 2-tori by homo- and heteroclinic bifurcations, and intermittency (U0 ≥ 14.5 m/s and h0 ≥ 800 m). The observed attractors exhibit spatial and temporal low-frequency patterns comparing well with those observed in the atmosphere. For h0 ≤ 800 m the periodic orbits have a period of about 10 days and patterns in the vorticity field propagate eastward. For h0 ≥ 800 m, the period is longer (30-60 days) and patterns in the vorticity field are non-propagating. The dynamics on the strange attractors are associated with low-frequency variability: the vorticity fields show weakening and strengthening of non-propagating planetary waves on time scales of 10-200 days. The spatio-temporal characteristics are 'inherited' (by intermittency) from the two families of periodic orbits and are detected in a relatively large region of the parameter

  8. New nonlinear mechanisms of midlatitude atmospheric low-frequency variability

    NASA Astrophysics Data System (ADS)

    Sterk, A. E.; Vitolo, R.; Broer, H. W.; Simó, C.; Dijkstra, H. A.

    2010-05-01

    This paper studies the dynamical mechanisms potentially involved in the so-called atmospheric low-frequency variability, occurring at midlatitudes in the Northern Hemisphere. This phenomenon is characterised by recurrent non-propagating and temporally persistent flow patterns, with typical spatial and temporal scales of 6000-10 000 km and 10-50 days, respectively. We study a low-order model derived from the 2-layer shallow-water equations on a β-plane channel. The main ingredients of the low-order model are a zonal flow, a planetary scale wave, orography, and a baroclinic-like forcing. A systematic analysis of the dynamics of the low-order model is performed using techniques and concepts from dynamical systems theory. Orography height ( h0) and magnitude of zonal wind forcing ( U0) are used as control parameters to study the bifurcations of equilibria and periodic orbits. Along two curves of Hopf bifurcations an equilibrium loses stability ( U0≥12.5 m/s) and gives birth to two distinct families of periodic orbits. These periodic orbits bifurcate into strange attractors along three routes to chaos: period doubling cascades, breakdown of 2-tori by homo- and heteroclinic bifurcations, or intermittency ( U0≥14.5 m/s and h0≥800 m). The observed attractors exhibit spatial and temporal low-frequency patterns comparing well with those observed in the atmosphere. For h0≤800 m the periodic orbits have a period of about 10 days and patterns in the vorticity field propagate eastward. For h0≥800 m, the period is longer (30-60 days) and patterns in the vorticity field are non-propagating. The dynamics on the strange attractors are associated with low-frequency variability: the vorticity fields show weakening and strengthening of non-propagating planetary waves on time scales of 10-200 days. The spatio-temporal characteristics are “inherited” (by intermittency) from the two families of periodic orbits and are detected in a relatively large region of the parameter

  9. The LWA1 Low Frequency Sky Survey

    NASA Astrophysics Data System (ADS)

    Dowell, Jayce; Taylor, Gregory B.; Schinzel, Frank K.; Kassim, Namir E.; Stovall, Kevin

    2017-08-01

    We present a survey of the radio sky accessible from the first station of the Long Wavelength Array. Images are presented at nine frequencies between 35 and 80 MHz with spatial resolutions ranging from 4.7° to 2.0°, respectively. The maps cover the sky north of a declination of -40° and represent the most modern systematic survey of the diffuse Galactic emission within this frequency range. We also combine our survey with other low-frequency sky maps to create an updated model of the low-frequency sky. Due to the low frequencies probed by our survey, the updated model better accounts for the effects of free-free absorption from Galactic-ionized hydrogen. A longer term motivation behind this survey is to understand the foreground emission that obscures the redshifted 21-cm transition of neutral hydrogen from the cosmic dark ages (z >10) and, at higher frequencies, the epoch of reionization (z >6).

  10. Kinetic Scale Structure of Low-frequency Waves and Fluctuations

    NASA Astrophysics Data System (ADS)

    López, Rodrigo A.; Viñas, Adolfo F.; Araneda, Jaime A.; Yoon, Peter H.

    2017-08-01

    The dissipation of solar wind turbulence at kinetic scales is believed to be important for the heating of the corona and for accelerating the wind. The linear Vlasov kinetic theory is a useful tool for identifying various wave modes, including kinetic Alfvén, fast magnetosonic/whistler, and ion-acoustic (or kinetic slow), and their possible roles in the dissipation. However, the kinetic mode structure in the vicinity of ion-cyclotron modes is not clearly understood. The present paper aims to further elucidate the structure of these low-frequency waves by introducing discrete particle effects through hybrid simulations and Klimontovich formalism of spontaneous emission theory. The theory and simulation of spontaneously emitted low-frequency fluctuations are employed to identify and distinguish the detailed mode structures associated with ion-Bernstein modes versus quasi-modes. The spontaneous emission theory and simulation also confirm the findings of the Vlasov theory in that the kinetic Alfvén waves can be defined over a wide range of frequencies, including the proton cyclotron frequency and its harmonics, especially for high-beta plasmas. This implies that these low-frequency modes may play predominant roles even in the fully kinetic description of kinetic scale turbulence and dissipation despite the fact that cyclotron harmonic and Bernstein modes may also play important roles in wave-particle interactions.

  11. 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.

  12. 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.

  13. Low frequency Raman study of the nucleosides

    NASA Astrophysics Data System (ADS)

    Koontz, Craig; Lee, Scott

    2011-03-01

    In both transcription and replication, the two helices of the DNA molecule move apart. Consequently, vibrations involving the relative motions of large portions of the molecule with respect to one another are of intrinsic interest. Such vibrations have relatively low frequencies because they involve weak bonds and large masses. Low frequency modes are difficult to observe in Raman spectroscopy because they are very close to the signal from the Rayleigh scattered light (which is very intense). In this poster, we will describe our results for the eight nucleosides: adenosine, deoxyadenosine, guanosine, deoxyguanosine, cytidine, deoxycytidine, uracil and deoxythymidine.

  14. Low frequency Raman study of the nucleosides

    NASA Astrophysics Data System (ADS)

    Koontz, Craig; Lee, Scott

    2010-10-01

    In both transcription and replication, the two helices of the DNA molecule move apart. Consequently, vibrations involving the relative motions of large portions of the molecule with respect to one another are of intrinsic interest. Such vibrations have relatively low frequencies because they involve weak bonds and large masses. Low frequency modes are difficult to observe in Raman spectroscopy because they are very close to the signal from the Rayleigh scattered light (which is very intense). In this poster, we will describe our results for the eight nucleosides: adenosine, deoxyadenosine, guanosine, deoxyguanosine, cytidine, deoxycytidine, uracil and deoxythymidine.

  15. Low frequency Raman study of the nucleosides

    NASA Astrophysics Data System (ADS)

    Koontz, Craig; Lee, Scott

    2011-04-01

    In both transcription and replication, the two helices of the DNA molecule move apart. Consequently, vibrations involving the relative motions of large portions of the molecule with respect to one another are of intrinsic interest. Such vibrations have relatively low frequencies because they involve weak bonds and large masses. Low frequency modes are difficult to observe in Raman spectroscopy because they are very close to the signal from the Rayleigh scattered light (which is very intense). In this poster, we will describe our results for the eight nucleosides: adenosine, deoxyadenosine, guanosine, deoxyguanosine, cytidine, deoxycytidine, uracil and deoxythymidine.

  16. Hearing Foreign Languages through Low Frequencies.

    ERIC Educational Resources Information Center

    Roberge, Claude

    A study to assess the feasibility of the use of low frequencies for teaching foreign language to the hearing impaired is described. The subjects were unimpaired Japanese students, aged 18 and 19, in beginning French language study. Recorded sentences translated into English, French, and Mandarin Chinese were combined in various ways and presented…

  17. Low Frequency Rada Sounding Through Martian Ionosphere

    NASA Technical Reports Server (NTRS)

    Safaeinili, A.; Jordan, R.

    2000-01-01

    In remote radar sounding, it is highly desirable to operate at low frequencies to improve depth of penetration. For spaceborne sounders, the lowest operating frequency is limited by the effect of the ionosphere due to significant dispersion of the radar waves at near plasma frequency.

  18. Is low frequency ocean sound increasing globally?

    PubMed

    Miksis-Olds, Jennifer L; Nichols, Stephen M

    2016-01-01

    Low frequency sound has increased in the Northeast Pacific Ocean over the past 60 yr [Ross (1993) Acoust. Bull. 18, 5-8; (2005) IEEE J. Ocean. Eng. 30, 257-261; Andrew, Howe, Mercer, and Dzieciuch (2002) J. Acoust. Soc. Am. 129, 642-651; McDonald, Hildebrand, and Wiggins (2006) J. Acoust. Soc. Am. 120, 711-717; Chapman and Price (2011) J. Acoust. Soc. Am. 129, EL161-EL165] and in the Indian Ocean over the past decade, [Miksis-Olds, Bradley, and Niu (2013) J. Acoust. Soc. Am. 134, 3464-3475]. More recently, Andrew, Howe, and Mercer's [(2011) J. Acoust. Soc. Am. 129, 642-651] observations in the Northeast Pacific show a level or slightly decreasing trend in low frequency noise. It remains unclear what the low frequency trends are in other regions of the world. In this work, data from the Comprehensive Nuclear-Test Ban Treaty Organization International Monitoring System was used to examine the rate and magnitude of change in low frequency sound (5-115 Hz) over the past decade in the South Atlantic and Equatorial Pacific Oceans. The dominant source observed in the South Atlantic was seismic air gun signals, while shipping and biologic sources contributed more to the acoustic environment at the Equatorial Pacific location. Sound levels over the past 5-6 yr in the Equatorial Pacific have decreased. Decreases were also observed in the ambient sound floor in the South Atlantic Ocean. Based on these observations, it does not appear that low frequency sound levels are increasing globally.

  19. Low frequency signal spectrum analysis for strong earthquakes

    NASA Astrophysics Data System (ADS)

    Rozhnoi, Alexander; Solovieva, Maria; Biagi, Pier Francesco; Schwingenschuh, Konrad; Hayakawa, Masashi

    2012-04-01

    We examined changes in the spectral composition of the low frequency (LF) subionospheric signals from the NRK transmitter (37.5 kHz) in Iceland that were received in Bari (Italy) relative to the earthquake that occurred in L'Aquila on April 6, 2009. In our previous studies, we have reported the occurrence of preseismic night-time anomalies using observations from three receivers located in Bari, Graz (Austria) and Moscow (Russia). The strongest anomalies in the signals were observed in the NRK-Bari propagation path during the period 5-6 days before the L'Aquila earthquake, as well as during the series of aftershocks. During this period, similar very low frequency (VLF)/LF amplitude anomalies were also observed along several other propagation paths that crossed the L'Aquila seismogenic zone. Spectral analysis of the LF signals filtered in the frequency range 0.28 mHz to 15 mHz shows differences in the spectra for seismo-disturbed days when compared to those for either quiet or geomagnetically disturbed days. These spectral anomalies, which are only observed in the propagation path between NRK and Bari, contain signals with periods of about 10 min to 20 min. These periodic signals are absent both in the spectra of the undisturbed signals for the control paths, and in the spectra of the signals received during geomagnetic storms. The same changes in the spectral composition were observed in the analysis of LF (40 kHz) signals from the JJY transmitter in Japan that were received in Petropavlovsk-Kamchatsky (Russia) during the occurrence of three strong earthquakes with M ≥7.0. The results of this study support the theoretical prediction that the possible mechanism for energy penetration from the origin of an earthquake through the atmosphere and into the ionosphere is based on the excitation and upward propagation of internal gravity waves.

  20. Low-frequency sound exposure causes reversible long-term changes of cochlear transfer characteristics.

    PubMed

    Drexl, Markus; Otto, Larissa; Wiegrebe, Lutz; Marquardt, Torsten; Gürkov, Robert; Krause, Eike

    2016-02-01

    Intense, low-frequency sound presented to the mammalian cochlea induces temporary changes of cochlear sensitivity, for which the term 'Bounce' phenomenon has been coined. Typical manifestations are slow oscillations of hearing thresholds or the level of otoacoustic emissions. It has been suggested that these alterations are caused by changes of the mechano-electrical transducer transfer function of outer hair cells (OHCs). Shape estimates of this transfer function can be derived from low-frequency-biased distortion product otoacoustic emissions (DPOAE). Here, we tracked the transfer function estimates before and after triggering a cochlear Bounce. Specifically, cubic DPOAEs, modulated by a low-frequency biasing tone, were followed over time before and after induction of the cochlear Bounce. Most subjects showed slow, biphasic changes of the transfer function estimates after low-frequency sound exposure relative to the preceding control period. Our data show that the operating point changes biphasically on the transfer function with an initial shift away from the inflection point followed by a shift towards the inflection point before returning to baseline values. Changes in transfer function and operating point lasted for about 180 s. Our results are consistent with the hypothesis that intense, low-frequency sound disturbs regulatory mechanisms in OHCs. The homeostatic readjustment of these mechanisms after low-frequency offset is reflected in slow oscillations of the estimated transfer functions.

  1. 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

  2. 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.

  3. Extreme Low Frequency Acoustic Measurement System

    NASA Technical Reports Server (NTRS)

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

    2017-01-01

    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.

  4. 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.

  5. Seabed Scattering from Low Frequency Reverberation Measurements

    DTIC Science & Technology

    2015-09-30

    X.Z. Zhang, " Low frequency seabed scattering at low grazing angles," Journal of the Acoustical Society of America, 131 (4), 261 1-2621 (Apr 2012). 2...13). 15. SUBJECT TERMS ocean reverberation, modeling and inversion, seabed scattering , seabottom acoustic model, the energy flux method for...reverberation, shallow water acoustics , low grazing angles scattering , shear waves 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF a . REPORT b

  6. An Overview of Low Frequency Communications

    DTIC Science & Technology

    1992-06-01

    could be used for signalling was Guglielmo Marconi . a young Italian elecrncity buff. He used real and error to develop his idea, and on 2 June 1896...vol. 17, no. 9, p. 1465, August, 1990. - Morgan, Nina, Guglielmo Marconi , New York. The Bookwnght Press, 1991 - T. L. Simpson. J. C. Logan, J. W...overcome these challenges every since the das of Marconi . HISTORY OF LOW FREQUENCY CONLMUNICATIONS Early transmissions used spark gap transmitters, which

  7. Slow earthquakes coincident with episodic tremors and slow slip events.

    PubMed

    Ito, Yoshihiro; Obara, Kazushige; Shiomi, Katsuhiko; Sekine, Shutaro; Hirose, Hitoshi

    2007-01-26

    We report on the very-low-frequency earthquakes occurring in the transition zone of the subducting plate interface along the Nankai subduction zone in southwest Japan. Seismic waves generated by very-low-frequency earthquakes with seismic moment magnitudes of 3.1 to 3.5 predominantly show a long period of about 20 seconds. The seismicity of very-low-frequency earthquakes accompanies and migrates with the activity of deep low-frequency tremors and slow slip events. The coincidence of these three phenomena improves the detection and characterization of slow earthquakes, which are thought to increase the stress on updip megathrust earthquake rupture zones.

  8. 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.

  9. 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.

  10. Low Frequency Variability and the Eastern Mediterranean Teleconnection Pattern

    NASA Astrophysics Data System (ADS)

    Hatzaki, M.; Flocas, H. A.

    2007-12-01

    The long time series analysis of the atmospheric circulation has revealed large scale correlations between the flow at remote locations. These fluctuations belong in the low frequency range of timescale and referred to as teleconnections patterns. They are located in particular places and appear as preferred modes of low-frequency natural variability of the atmospheric circulation with fixed oscillating nodes and antinodes, called poles. These teleconnection patterns describe standing waves oscillating with time scales of a month or longer. It has been recognized that the large scale eddies and their feedback onto the mean flow, the propagation of Rossby waves in the midlatitudes and the stratosphere-troposphere interaction play an important role in understanding low frequency general circulation and variability. In previous studies, the Eastern Mediterranean Teleconnection pattern (EMP) was found with its two poles located in North-eastern Europe and Eastern Mediterranean, and it was predominantly identified at the upper troposphere during winter. An index was defined, based on the exact position of the two poles of the pattern, to represent the strength of the teleconnection pattern and to discriminate its positive and negative phase. The objective of this study is to investigate the large scale dynamics related to the development of EMP. For this purpose, datasets of daily geopotential height, temperature and horizontal wind components at several isobaric levels are employed, as obtained from the NCEP/NCAR and from the ECMWF centres, for the calculation of transient eddy kinetic energy, E-vectors, Rossby wave source and potential vorticity. It was found that the role of the eddy driven mid-latitude jet is important. It is likely that the subtropical jet is passive and that the transient eddies remove much more momentum in the negative phase, when the storm- track comes charging into Europe. Rossby wave propagation seems to determine the differing wave

  11. Low frequency electric and magnetic fields

    NASA Technical Reports Server (NTRS)

    Spaniol, Craig

    1989-01-01

    Following preliminary investigations of the low frequency electric and magnetic fields that may exists in the Earth-ionospheric cavity, measurements were taken with state-of-the art spectrum analyzers. As a follow up to this activity, an investigation was initiated to determine sources and values for possible low frequency signal that would appear in the cavity. The lowest cavity resonance is estimated at about 8 Hz, but lower frequencies may be an important component of our electromagnetic environment. The potential field frequencies produced by the electron were investigated by a classical model that included possible cross coupling of the electric and gravitation fields. During this work, an interesting relationship was found that related the high frequency charge field with the extremely low frequency of the gravitation field. The results of numerical calculations were surprisingly accurate and this area of investigation is continuing. The work toward continued development of a standardized monitoring facility is continuing with the potential of installing the prototype at West Virginia State College early in 1990. This installation would be capable of real time monitoring of ELF signals in the Earth-ionoshpere cavity and would provide some directional information. A high gain, low noise, 1/f frequency corrected preamplifier was designed and tested for the ferrite core magnetic sensor. The potential application of a super conducting sensor for the ELF magnetic field detection is under investigation. It is hoped that a fully operational monitoring network could pinpoint the location of ELF signal sources and provide new information on where these signals originate and what causes them, assuming that they are natural in origin.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Minimization of nanosatellite low frequency magnetic fields

    SciTech Connect

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

    2016-03-15

    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.

  17. 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.

  18. 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.

  19. Low-frequency macroscopic instabilities of fully ionized magnetoplasma

    NASA Technical Reports Server (NTRS)

    Rognlien, T. D.

    1972-01-01

    Studies are described of low-frequency quasi-static instabilities in a fully ionized plasma. The plasma is assumed to be immersed in a uniform magnetic field, and is either uniform or has a number density gradient perpendicular to the magnetic field. A moment equation description of the ion and electron dynamics is used; collisions are assumed to have a strong effect on electron motion along the magnetic field. Before considering specific modes, a stability analysis is developed which allows a classification of wave growth characteristics to be made for a bounded system from solutions to the dispersion relation for an infinite system. Also, a method is given for calculating the normal mode frequencies and wave profiles by using the reflection coefficients at the boundaries. For wave propagation perpendicular to the magnetic field, the flute wave is studied in cylindrical geometry. The destabilizing effect of a radial electric field is considered by solving a differential equation.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Low Frequency Observations of Galactic Supernova Remnants

    NASA Astrophysics Data System (ADS)

    Brogan, C. L.; Kassim, N.; Lacey, C.; Nord, M.; Lazio, J.

    2001-12-01

    We present VLA multi-configuration 330 MHz and 74 MHz observations of three fields centered on the locations of the Galactic supernova remnants (SNRs): G29.7-0.3, G11.2-0.3, and G349.7+0.2. The wide fields of view afforded by the VLA at these frequencies, 4o at 330 MHz and 11o at 74 MHz, allow us to simultaneously study the low frequency properties of a wide range of objects. Our primary goal is to study the SNRs in these fields to accurately characterize their low frequency spectra and to look for foreground or interior thermal free-free absorption, as well as spectral signatures of diffusive shock acceleration of cosmic rays. Additionally, a few Galactic HII regions and extragalactic sources will be discussed. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Basic research in radio astronomy at the Naval Research Laboratory is supported by the Office of Naval Research.

  6. LOFAR: A LOw Frequency radio ARray

    NASA Astrophysics Data System (ADS)

    Hewitt, Jacqueline

    2001-04-01

    Recent advances in calibration and imaging algorithms at low radio frequencies, combined with advances in digital signal processing, have led to the realization that a large low-frequency radio array is now technically feasible and affordable. Improvements of one to two orders of magnitude (depending on frequency) in both sensitivity and resolution would make possible new approaches to the study of many astrophysics problems. In particular, key science areas that would be revolutionized by such an array are the high redshift universe, the epoch of reionization, the distribution of galactic cosmic rays, the bursting and transient universe, ionospheric structure, and the solar-terrestrial relationship. An ASTRON-NRL-MIT collaboration has proposed the design and construction of a low frequency array (LOFAR) made up of over 13,000 fixed dipole and dipole-array antennas that would operate in the 15-240 MHz range. The goals are to achieve a collecting area of one square kilometer at 15 MHz, arc-second angular resolution, high dynamic range, and wide-field imaging capabilities.

  7. A low frequency RFI monitoring system

    NASA Astrophysics Data System (ADS)

    Amiri, Shahram; Shankar, N. Udaya; Girish, B. S.; Somashekar, R.

    Radio frequency interference (RFI) is a growing problem for research in radio astronomy particularly at wavelengths longer than 2m. For satisfactory operation of a radio telescope, several bands have been protected for radio astronomy observations by the International Telecommunication Union. Since the radiation from cosmic sources are typically 40 to 100 dB below the emission from services operating in unprotected bands, often the out-of-band emission limits the sensitivity of astronomical observations. Moreover, several radio spectral emissions from cosmic sources are present in the frequency range outside the allocated band for radio astronomy. Thus monitoring of RFI is essential before building a receiver system for low frequency radio astronomy. We describe the design and development of an RFI monitoring system operating in the frequency band 30 to 100 MHz. This was designed keeping in view our proposal to extend the frequency of operation of GMRT down to 40 MHz. The monitor is a PC based spectrometer recording the voltage output of a receiver connected to an antenna, capable of digitizing the low frequency RF directly with an 8 bit ADC and sampling bandwidths up to 16 MHz. The system can operate continuously in almost real-time with a loss of only 2% of data. Here we will present the systems design aspects and the results of RFI monitoring carried out at the Raman Research Institute, Bangalore and at the GMRT site in Khodad.

  8. Multiple seismic array analysis of low frequency tremors in western Shikoku, Japan

    NASA Astrophysics Data System (ADS)

    Ueno, T.; Maeda, T.; Obara, K.; Asano, Y.; Takeda, T.

    2007-12-01

    In southwest Japan, low frequency tremors (LFTs) have been detected at deeper part of the seismogenic zone on the subducting Philippine Sea plate interface by high sensitivity seismograph network Hi-net operated by NIED. The tremor source area migrates during each episode along the strike of the subducting plate with a migration velocity of roughly 10 km/day, which was referred from source locations obtained by the envelope correlation method. In order to investigate the wave field propagation from the tremors in detail, we carried out a seismic observation campaign in western Shikoku, where the active tremor associated with the short-term slow slip event occurs with a recurrence interval of around six months. In this campaign, we deployed three seismic arrays above the belt-like LFT area with a spacing of about 20 km among arrays, during the period from February to May in 2007 because we anticipated the coming LFT episode to occur on March or April, 2007. Each array was composed of 32-channel receivers which mainly consist of vertical-component with natural frequency of 2 Hz. The receivers were placed with an average spacing of 30 m. Waveform data were recorded continuously with a sampling interval of 0.01 s. Since the active tremor episode with the short-term slow slip event occurred from 13 to 15 on March 2007 as expected, we performed frequency-wave number power spectrum analysis for each array recordings by the MUltiple SIgnal Classification (MUSIC) method in the period. At two seismic arrays, the apparent slowness were continuously low during the tremor episode. At the other array, the slowness was relatively high, and the arrival direction of the waves slightly changed with increasing time. In order to ascertain the change to be migration of the tremors, we located the sources of tremors by grid search method by using backazimuth and apparent slowness estimated at each array. We successfully located the sources of tremors, and detected the migration of the

  9. 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.

  10. A Dynamic Closure of Synoptic Eddy and Low-frequency Flow (SELF) Interaction and the Self-organization of Low-frequency Modes

    NASA Astrophysics Data System (ADS)

    Jin, F.; Pan, L.; Watanabe, M.

    2005-05-01

    The two-way interaction between synoptic eddy and low-frequency flow (SELF), which we will refer to as the SELF interaction, has been recognized for decades to play an important role in the dynamics of the low-frequency variability of the atmospheric circulation. We propose a new framework for studying the dynamics of the SELF interaction and the low-frequency variability in a stormy background flow. By considering a Gaussian flow as a surrogate for the stormy background flow, we expand the traditional climatological basic flow to a synthetic stochastic basic flow. Its ensemble mean is the observed climatological mean flow while its prescribed variance/covariance fields represent the climatological variance/covariance fields of the observed synoptic eddies. Low-frequency anomalies in the traditional month-to-seasonal mean flow and in the variance/covariance fields of the transient eddy flow are viewed as equivalent to the anomalies in the first and second moments of the quasi-stationary stochastic flow ensemble. The linear dynamics of SELF interaction are described by the coupling among the anomalies in first and second moments. Under the assumption that slow changes in the second moments are in quasi-equilibrium with the anomalies in the first moment, an analytical non-local dynamical closure for SELF interaction is obtained. Using this framework, we show that leading low-frequency modes earn their dominance because they can effective organizing the turbulent synoptic flow such that they get reinforced by positive SELF interaction.

  11. 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.

  12. Sporadically Emitting Pulsars at Low Frequencies

    NASA Astrophysics Data System (ADS)

    Meyers, B. W.; Tremblay, S. E.; Bhat, N. D. R.; Shannon, R. M.

    2017-01-01

    Sporadic emission from pulsars has long been observed, however, the mechanism which causes the intermittency is still a mystery. The proposed observations of three nulling pulsars (J0659+1414, J2048-1616 and J1456-6843), two Rotating Radio Transients (J0410-31 and J1423-56) and one intermittent pulsar (J1107-5907) will provide information on pulsar emission over a variety of time scales. Studying these objects at low frequencies allows us to explore the links between the different populations and how the sporadic emission evolves with frequency. Ultimately, studying these extraordinary pulsars gives us new insight into the dynamic nature of the emission processes and pulsar magnetosphere. This information is imperative for linking models and theories regarding pulsar radio emission physics to the myriad sporadic emission phenomena we observe.

  13. Time evolution of low frequency plasma modes

    NASA Astrophysics Data System (ADS)

    Gratton, Fausto T.; Gnavi, Graciela; Biernat, Helfried K.; Heyn, Martin F.; Rijnbeek, Richard P.

    The time evolution of linear, low frequency, plasma waves in the emission region is studied via theoretical properties and numerical solutions of Volterra integral equations of the second kind. Bounds for the growth rates of unstable plasmas, with arbitrary distribution functions, are established. The asymptotic value of the electric field E(infinity) is found by means of the Paley-Wiener theorem for stable plasmas. For initial perturbations of the distribution function f1(0) which are square integrable, E(infinity) = 0 (Landau damping). When f1(0) contains beams of particles (it is not square integrable) E(infinity) does not equal O. The arbitrariness of the time decay of the electric field is obtained straightforwardly. Some examples of numerical solutions for electron plasma waves and electron Bernstein modes are given.

  14. 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.

  15. Low-frequency Stoneley energy for stratigraphic evaluation

    SciTech Connect

    Hlaing, K.K.; Lemoy, C.; Maret, J.P.; Kremer, Y.; Borland, W.H.; Maw, M.

    1994-07-01

    Conventional sonic measurements of shear and compressional slowness are body waves that travel within the formation and are commonly used for petrophysical analysis of a well. Low-frequency Stoneley waves travel within the well bore and are traditionally used to interpret fractures and formation permeability, usually by analyzing the energy losses and, to a lesser extent, the slowness. The authors have found that Stoneley energy has been very useful in the identification of vuggy carbonate facies linked to paleokarstic surfaces in the Upper Burman limestone reservoir of Miocene age, in the YADANA gas deposit, offshore Myanmar. One good example is seen in well YAD-1 where the carbonate reservoir has been cored, allowing precise facies and porosity type determination. Matching Stoneley energy and core description show a striking correlation between loss of energy and vuggy carbonate facies due to karstic diagenetic processes, always in relation with reefal or near reefal facies. Accordingly, facies interpretation has tentatively been done in the deeper, noncored reservoir zone, where losses of energy are important and considered as indicating karstic influence and the specific environment.

  16. 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.

  17. Interim prediction method for low frequency core engine noise

    NASA Technical Reports Server (NTRS)

    Huff, R. G.; Clark, B. J.; Dorsch, R. G.

    1974-01-01

    A literature survey on low-frequency core engine noise is presented. Possible sources of low frequency internally generated noise in core engines are discussed with emphasis on combustion and component scrubbing noise. An interim method is recommended for predicting low frequency core engine noise that is dominant when jet velocities are low. Suggestions are made for future research on low frequency core engine noise that will aid in improving the prediction method and help define possible additional internal noise sources.

  18. 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

  19. HERO: a space based low frequency interferometric observatory for heliophysicsenabled by novel vector sensor technology

    DTIC Science & Technology

    2017-04-07

    HERO: A SPACE -BASED LOW FREQUENCY1 INTERFEROMETRIC OBSERVATORY FOR2 HELIOPHYSICS ENABLED BY NOVEL VECTOR3 SENSOR TECHNOLOGY4 M. Knapp∗, D. Gary†, M...hybrid ground and space7 interferometric instrument. The space segment (HeRO-S) covers low frequencies,8 100 kHz – 20 MHz, and is composed of 6 free...Heliophysics Radio Observer), a hybrid ground and space in-29 strument to map and track type II and III solar radio bursts as they propagate from the30 solar

  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. A synthetic low-frequency mammalian oscillator

    PubMed Central

    Tigges, Marcel; Dénervaud, Nicolas; Greber, David; Stelling, Joerg; Fussenegger, Martin

    2010-01-01

    Circadian clocks have long been known to be essential for the maintenance of physiological and behavioral processes in a variety of organisms ranging from plants to humans. Dysfunctions that subvert gene expression of oscillatory circadian-clock components may result in severe pathologies, including tumors and metabolic disorders. While the underlying molecular mechanisms and dynamics of complex gene behavior are not fully understood, synthetic approaches have provided substantial insight into the operation of complex control circuits, including that of oscillatory networks. Using iterative cycles of mathematical model-guided design and experimental analyses, we have developed a novel low-frequency mammalian oscillator. It incorporates intronically encoded siRNA-based silencing of the tetracycline-dependent transactivator to enable the autonomous and robust expression of a fluorescent transgene with periods of 26 h, a circadian clock-like oscillatory behavior. Using fluorescence-based time-lapse microscopy of engineered CHO-K1 cells, we profiled expression dynamics of a destabilized yellow fluorescent protein variant in single cells and real time. The novel oscillator design may enable further insights into the system dynamics of natural periodic processes as well as into siRNA-mediated transcription silencing. It may foster advances in design, analysis and application of complex synthetic systems in future gene therapy initiatives. PMID:20197318

  2. Low frequency earthquakes below southern Vancouver Island

    NASA Astrophysics Data System (ADS)

    Bostock, M. G.; Royer, A. A.; Hearn, E. H.; Peacock, S. M.

    2012-11-01

    The nature and distribution of low frequency earthquakes (LFEs) in subduction zones provide insight into plate boundary deformation downdip of the locked seismogenic zone. We employ network autocorrelation detection to identify LFE families beneath southern Vancouver Island and environs. An initial suite of 5775 LFEs detected in 2004 and 2005 at a select set of 7 stations is grouped into 140 families using waveform cluster analysis. These families are used as templates within an iterative network cross correlation scheme to detect LFEs across different tremor episodes, incorporate new stations, and improve LFE template signal-to-noise ratio. As in southwest Japan, representative LFE locations define a relatively tight, dipping surface several km above the locus of intraslab seismicity, within a prominent, dipping low-velocity zone (LVZ). LFE polarizations for near-vertical source-receiver geometries possess a remarkably uniform dipolar signature indicative of point-source, double-couple excitation. Focal mechanisms determined fromP-wave first motions are characterized by a combination of strike-slip and thrust faulting. We suggest that LFEs and regular intraslab seismicity occur in distinct structural and stress regimes. The LVZ, inferred to represent weak, overpressured, porous and mylonitized metabasalts of oceanic crustal Layer 2, separates LFEs manifesting deformation within a plate boundary shear zone from intraslab earthquakes generated by tensional stresses and dehydration embrittlement within a more competent lower oceanic crustal Layer 3 and underlying mantle.

  3. Low frequency electromagnetic radiation and hearing.

    PubMed

    Morales, J; Garcia, M; Perez, C; Valverde, J V; Lopez-Sanchez, C; Garcia-Martinez, V; Quesada, J L

    2009-11-01

    To analyse the possible impact of low and extremely low frequency electromagnetic fields on the outer hairs cells of the organ of Corti, in a guinea pig model. Electromagnetic fields of 50, 500, 1000, 2000, 4000 and 5000 Hz frequencies and 1.5 microT intensity were generated using a transverse electromagnetic wave guide. Guinea pigs of both sexes, weighing 100-150 g, were used, with no abnormalities on general and otic examination. Total exposure times were: 360 hours for 50, 500 and 1000 Hz; 3300 hours for 2000 Hz; 4820 hours for 4000 Hz; and 6420 hours for 5000 Hz. One control animal was used in each frequency group. The parameters measured by electric response audiometer included: hearing level; waves I-IV latencies; wave I-III interpeak latency; and percentage appearance of waves I-III at 90 and 50 dB sound pressure level intensity. Values for the above parameters did not differ significantly, comparing the control animal and the rest of each group. In addition, no significant differences were found between our findings and those of previous studies of normal guinea pigs. Prolonged exposure to electromagnetic fields of 50 Hz to 5 KHz frequencies and 1.5 microT intensity, produced no functional or morphological alteration in the outer hair cells of the guinea pig organ of Corti.

  4. Seismic moment tensor recovery at low frequencies

    NASA Astrophysics Data System (ADS)

    Riedesel, M. A.

    A low-frequency, normal mode technique which provides estimates of the seismic moment tensor in as many as ten separate 1 mHz bands is described. The basic data kernels are integrals of the complex spectra of the untaped seismograms with a bandwidth of .1 mHz, centered on the model frequencies of the fundamental modes. The frequency-domain integration process reduces the sensitivity of the solutions to attenuation and splitting. Adjustments in the phase of the integrals are computed to compensate for the effects of latteral heterogeneity, station timing errors, and centroid time shifts. Estimates of the covariance of the solutions are used to provide uncertainties for the source mechanism and the principle stress axes. A graphical method is developed which allows a rapid visual assessment of the significance of nondouble-couple and isotropic components of the solutions. The method was applied to 57 earthquakes recorded on the IDA network between 1977 and 1984. The moment rate tensor and its uncertainty was investigated in 1 mHz bands over the 1 to 11 mHz frequency range.

  5. A low frequency rotational energy harvesting system

    NASA Astrophysics Data System (ADS)

    Febbo, M.; Machado, S. P.; Ramirez, J. M.; Gatti, C. D.

    2016-11-01

    This paper presents a rotary power scavenging unit comprised of two systems of flexible beams connected by two masses which are joined by means of a spring, considering a PZT (QP16N, Midé Corporation) piezoelectric sheet mounted on one of the beams. The energy harvesting (EH) system is mounted rigidly on a rotating hub. The gravitational force on the masses causes sustained oscillatory motion in the flexible beams as long as there is rotary motion. The intention is to use the EH system in the wireless autonomous monitoring of wind turbines under different wind conditions. Specifically, the development is oriented to monitor the dynamic state of the blades of a wind generator of 30 KW which rotates between 50 and 150 rpm. The paper shows a complete set of experimental results on three devices, modifying the amount of beams in the frame supporting the system. The results show an acceptable sustained voltage generation for the expected range, in the three proposed cases. Therefore, it is possible to use this system for generating energy in a low-frequency rotating environment. As an alternative, the system can be easily adapted to include an array of piezoelectric sheets to each of the beams, to provide more power generation.

  6. 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.

  7. 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.

  8. 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

  9. MultiView High Precision VLBI Astrometry at Low Frequencies

    NASA Astrophysics Data System (ADS)

    Rioja, María J.; Dodson, Richard; Orosz, Gabor; Imai, Hiroshi; Frey, Sandor

    2017-03-01

    The arrival of the Square Kilometer Array (SKA) will revitalize all aspects of Very Long Baseline Interferometry (VLBI) astronomy at lower frequencies. In the last decade, there have been huge strides toward routinely achieving high precision VLBI astrometry at frequencies dominated by tropospheric contributions, most notably at 22 GHz, using advanced phase-referencing techniques. Nevertheless, to increase the capability for high precision astrometric measurements at low radio frequencies (<8 GHz), an effective calibration strategy of the systematic ionospheric propagation effects that is widely applicable is required. Observations at low frequencies are dominated by distinct direction-dependent ionospheric propagation errors, which place a very tight limit on the angular separation of a suitable phase-referencing calibrator. The MultiView technique holds the key to compensating for atmospheric spatial-structure errors, by using observations of multiple calibrators and two-dimensional interpolation in the visibility domain. In this paper we present the first demonstration of the power of MultiView using three calibrators, several degrees from the target, along with a comparative study of the astrometric accuracy between MultiView and phase-referencing techniques. MultiView calibration provides an order of magnitude improvement in astrometry with respect to conventional phase referencing, achieving ∼100 μas astrometry errors in a single epoch of observations, effectively reaching the thermal noise limit. MultiView will achieve its full potential with the enhanced sensitivity and multibeam capabilities of SKA and the pathfinders, which will enable simultaneous observations of the target and calibrators. Our demonstration indicates that the 10 μas goal of astrometry at ∼1.6 GHz using VLBI with SKA is feasible using the MultiView technique.

  10. The Low-Frequency Variability of the Tropical Atlantic Ocean

    NASA Technical Reports Server (NTRS)

    Haekkinen, Sirpa; Mo, Kingtse C.; Koblinsky, Chester J. (Technical Monitor)

    2001-01-01

    Upper ocean temperature variability in the tropical Atlantic is examined from the Comprehensive Ocean Atmosphere Data Set (COADS) as well as from an ocean model simulation forced by COADS anomalies appended to a monthly climatology. Our findings are as follows: Only the sea surface temperatures (SST) in the northern tropics are driven by heat fluxes, while the southern tropical variability arises from wind driven ocean circulation changes. The subsurface temperatures in the northern and southern tropics are found to have a strong linkage to buoyancy forcing changes in the northern North Atlantic. Evidence for Kelvin-like boundary wave propagation from the high latitudes is presented from the model simulation. This extratropical influence is associated with wintertime North Atlantic Oscillation (NAO) forcing and manifests itself in the northern and southern tropical temperature anomalies of the same sign at depth of 100-200 meters as result of a Rossby wave propagation away from the eastern boundary in the wake of the boundary wave passage. The most apparent association of the southern tropical sea surface temperature anomalies (STA) arises with the anomalous cross-equatorial winds which can be related to both NAO and the remote influence from the Pacific equatorial region. These teleconnections are seasonal so that the NAO impact on the tropical SST is the largest it mid-winter but in spring and early summer the Pacific remote influence competes with NAO. However, NAO appears to have a more substantial role than the Pacific influence at low frequencies during the last 50 years. The dynamic origin of STA is indirectly confirmed from the SST-heat flux relationship using ocean model experiments which remove either anomalous wind stress forcing or atmospheric forcing anomalies contributing to heat exchange.

  11. New observations of the low frequency interplanetary radio emissions

    NASA Technical Reports Server (NTRS)

    Kurth, W. S.; Gurnett, D. A.

    1991-01-01

    Recent Voyager 1 observations reveal reoccurrences of the low frequency interplanetary radio emissions. Three of the new events are weak transient events which rise in frequency from the range of 2-2.5 kHz to about 3 kHz with drift rates of approximately 1.5 kHz/year. The first of the transient events begins in mid-1989 and the more recent pair of events both were first detected in late 1991. In addition, there is an apparent onset of a 2-kHz component of the emission beginning near day 70 of 1991. The new transient emissions are barely detectable on Voyager 1 and are below the threshold of detectability on Voyager 2, which is less sensitive than Voyager 1. The new activity provides new opportunities to test various theories of the triggering, generation, and propagation of the outer heliospheric radio emissions and may signal a response of the source of the radio emissions to the increased solar activity associated with the recent peak in the solar cycle.

  12. Low-frequency evolution of pulsar profiles with LOFAR

    NASA Astrophysics Data System (ADS)

    Pilia, Maura

    We present a LOFAR census of the low-frequency pulse profiles of 100 pulsars. We produced the cumulative pulse profiles of 100 pulsars in the 120-167 MHz range as well as the 15-63 MHz profiles for 25 of these pulsars. These are compared with higher-frequency archival profiles from Westerbork and Jodrell Bank. We studied the relationship between the profile evolution with frequency and the emission geometry, and/or evolution due to propagation effects, prominent at lower frequencies. In particular, we present the evolution of the full profile width and that of its single components, in the case of multiple peaks; also, in the case of multiple peaks, we traced the evolution of the ratio of the amplitudes of the two most prominent peaks. In this work we show that the evolution of the profile width with frequency generally follows radius-to-frequency mapping. We find good agreement of our data with the empirical core-plus-cone models from Rankin (1983+) and the phenomenological model from Karastergiou and Johnston (2007).

  13. Low-frequency fluctuations in the magnetosheath near the magnetopause

    NASA Technical Reports Server (NTRS)

    Denton, Richard E.; Gary, S. Peter; Li, Xinlin; Anderson, Brian J.; Labelle, James W.; Lessard, Marc

    1995-01-01

    There are four low-frequency modes which may propagate in a high-beta nearly bi-Maxwellian plasma. These are the magnetosonic, Alfven, ion acoustic, and mirror modes. This manuscript defines a procedure based on linear Vlasov theory for the unique identification of these modes by use of transport ratios, dimensionless ratios of the fluctuating field and plasma quantities. A single parameter, the mode deviation is calculated using the plasma and magnetic field data gathered by the Active Magnetospheric Particle Tracer Explorers/Ion Release Module (AMPTE/IRM) spacecraft to identify the modes observed in the terrestial magnetosheath near the magnetopause. As well as determining the mode which best describes the observed fluctuations, it gives us a measure of whether or not the resulting identification is unique. Using 17 time periods temporally close to a magnetopause crossing, and confining our study to the frequency range from 0.01 to 0.04 Hz, we find that the only clearly identified mode in this frequency range is the mirror mode. Most commonly, the quasi-perpendicular mirror mode (with wave vector k roughly perpendicular to the background magnetic field B(sub zero) is observed. In two events the quasi-parallel mirror mode k parallel B(sub zero) was identified.

  14. 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.

  15. Twofluid Simulations of Propagation of Slow and ALFVÉN Waves in the Partially Ionized Solar Chromosphere

    NASA Astrophysics Data System (ADS)

    Maneva, Y. G.; Poedts, S.; Alvarez Laguna, A.; Lani, A.

    2016-12-01

    Ion-neutral interactions play crucial role in the energetics and dynamics of the partially ionized solar chromosphere. To study the effect of neutrals for the evolution of the chromospheric plasma, including the transport coefficients, chemical reactions and possible contribution to wave damping and absorption, we have developed a multi-fluid simulation tool, which considers ionization and recombination processes in gravitationally stratified magnetized collisional media. Recent works have suggested that the vastly dominant neutrals might over-damp Alfvén waves in the chromosphere, thus absorbing their energy closer to the solar surface and reducing the contribution of Alfvén waves generated by the photospheric drivers to the coronal heating problem. In this study we have driven slow magnetosonic and Alfvén waves at the photosphere and have followed their evolution through the chromosphere towards the transition region. We have investigated the wave energy transfer related to shock formation, wave absorption and mode conversion in the gravitationally stratified media, as well as have the distribution of Poynting flux. Our two-fluid model consists of resistive MHD electrons and ions, which are chemically and collisionally coupled to a separate fluid population of neutral hydrogen. The model takes into account Coulomb collisions, anisotropic heat flux determined by Braginskii's transport coefficients, as well as impact ionization and radiative recombination. The initial state represents gravitationally stratified temperature and density profiles, which satisfy hydrostatic chemical equilibrium, except for the Lorentz force associated with the external magnetic field. We study the effects of the initial driver's amplitude and period on the related plasma energization, as well as the wave-induced changes in ionization and recombination.

  16. Low-frequency sonophoresis: current status and future prospects.

    PubMed

    Ogura, Makoto; Paliwal, Sumit; Mitragotri, Samir

    2008-06-30

    Application of ultrasound enhances skin permeability to drugs, a phenomenon referred to as sonophoresis. Significant strides have been made in sonophoresis research in recent years, especially under low-frequency conditions (20 kHzlow-frequency conditions. Several therapeutic macromolecules including insulin, low-molecular weight heparin, and vaccines have been delivered using low-frequency sonophoresis in vivo. Clinical trials have been performed with several drugs including lidocaine and cyclosporin. Novel theoretical and experimental approaches have provided insights into the mechanisms of low-frequency sonophoresis. Current understanding of these mechanisms is presented.

  17. High energy, low frequency, ultrasonic transducer

    DOEpatents

    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.

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

    SciTech Connect

    Moradi, Afshin

    2016-08-15

    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.

  19. Generation of Weak Double Layers and Low-Frequency Electrostatic Waves in the Solar Wind

    NASA Astrophysics Data System (ADS)

    Lakhina, G. S.; Singh, S. V.

    2015-10-01

    We propose that the mechanism for the generation of weak double layers (WDLs) and low-frequency coherent electrostatic waves, observed by Wind in the solar wind at 1 AU, might be slow and fast ion-acoustic solitons and double layers. The solar wind plasma is modelled as a fluid of hot protons and hot α particles streaming with respect to protons, and suprathermal electrons having a κ-distribution. The fast ion-acoustic mode is similar to the ion-acoustic mode of a 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 α particles. This mode can support both positive and negative solitons and double layers. The slow ion-acoustic mode can exist even when the relative streaming, U0, between α particles and protons is zero, provided that the α temperature, Ti, is not exactly equal to four times the proton temperature, Tp. 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 the shapes, of the observed WDLs 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 an electric field in the range of E = (0.01 - 0.7) mV m^{-1}, in excellent agreement with the observed low-frequency electrostatic wave activity in the solar wind at 1 AU.

  20. 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.

  1. Ultra-low-frequency broadband of a new-type acoustic metamaterial beams with stiffness array

    NASA Astrophysics Data System (ADS)

    Yan, Zhang Yong; Wu, Jiu Hui

    2017-09-01

    Periodic structures are effective in attenuating waves in a low frequency range at local resonance (LR) conditions, but it is still a challenge to achieve this in a very low frequency range, because the system stability can be damaged due to the excessive quality or the deduction of stiffness. However, the structural stability theory shows that the structural stability is closely related to the support surface; the larger the support surface, the more stable the structure, and thereby the array structure has the feature of maintaining the stability of the system through expanding the support surface. Based on the theoretical principle, a new type of local resonator with stiffness arrays is presented to further lower the band gaps of flexural wave propagation in LR beams, in which the traditional stiffness is equally divided into an array form. Due to the stiffness array connections, the system stiffness is not only reduced to a very low value, but also the stability is still better maintained through expanding the support surface. Meanwhile, the band structures of the LR beams with stiffness array connections, obtained by the finite element method, demonstrate that the lower bound of the band-gap can be successfully decreased more times than that of conventional LR beams under the premise of maintaining the stability of the system, and an ultra-low-frequency broadband of 25-395 Hz is realized. Clearly, the strategy of dividing the traditional stiffness into the stiffness array can successfully realize the low frequency band gap and overcome the shortcomings of the system instability in the traditional method. Therefore, two puzzles of realizing the ultra-low-frequency broadband and simultaneously maintaining the system stability may be successfully resolved through introducing the stiffness arrays into the local resonance system, and the new structures with stiffness arrays could have potential applications for ultra-low-frequency vibration and noise attenuation.

  2. Low-frequency gain compensation in directional hearing aids.

    PubMed

    Ricketts, Todd; Henry, Paula

    2002-06-01

    Hearing aids currently available on the market with both omnidirectional and directional microphone modes often have reduced amplification in the low frequencies when in directional microphone mode due to better phase matching. The effects of this low-frequency gain reduction for individuals with hearing loss in the low frequencies was of primary interest. Changes in sound quality for quiet listening environments following gain compensation in the low frequencies was of secondary interest. Thirty participants were fit with bilateral in-the-ear hearing aids, which were programmed in three ways while in directional microphone mode: no-gain compensation, adaptive-gain compensation, and full-gain compensation. All participants were tested with speech in noise tasks. Participants also made sound quality judgments based on monaural recordings made from the hearing aid. Results support a need for gain compensation for individuals with low-frequency hearing loss of greater than 40 dB HL.

  3. Low Frequency Radioastronomy at Moon: possible approach and architecture

    NASA Astrophysics Data System (ADS)

    Skalsky, A.; Mogilevsky, M.; Nazarov, V.; Nazirov, R.; Batanov, O.; Sadovski, A.

    2009-04-01

    The Moon, the Earth's neighbor, attracts an attention as a celestial body, as a source for mineral and other resources and as a possible base for fundamental scientific researches. The conducting ionosphere of Earth completely shields radioemissions coming from outer space and propagating at frequencies below a few MHz. In contrary, the Moon possessing a week atmosphereionosphere around its surface seems to be a perfect base for carrying out measurements of low frequency radio emissions originated from the space. The radio facility deployed at Moon's surface seems to be a powerful tool for various fundamental space researches related to astrophysics, solar system and magnetospheric investigations. The most intriguing objective is a search of terrestrial-like planets in the exosolar system, i.e. planets possessing the intrinsic magnetic fields and developed magnetospheres which interaction with the star wind results in generation of radioemissions (similar to AKR radiation of the terrestrial magnetosphere). Creating the infrastructure of antennas (sensors) on Moon's surface is planned for reaching the described goals. Ideology of such infrastructure (which may be treated as macro-instrument) is closely to SensorWeb approach. The different sensors are collected to unified platforms (PODs in terms of SensorWeb) which provide omni-and bidirectional information flows between PODs. Thus a set of sensors is integrated self-organizing amorphous organism on the base of wireless network. It increases reliability of the research complex and allows quick reconfiguring and adopting it for different investigation tasks. For additional redundancy and openness of the complex at least some PODs will support not only inter-PODs protocol but IEEE 802.16 Wireless LAN standard used in NASA Lunar Communication and Navigation Architecture also. The paper presents a possible approach to the development of the radio facility deployed at Moon's surface, its implementation for various

  4. Near-continuous tremor and low-frequency earthquake activities in the Alaska-Aleutian subduction zone revealed by a mini seismic array

    NASA Astrophysics Data System (ADS)

    Li, Bo; Ghosh, Abhijit

    2017-06-01

    Tectonic tremor and low-frequency earthquakes (LFEs) are relatively poorly studied in the Alaska-Aleutian subduction zone due to the limited data availability, difficult logistics, and rugged terrain. Using 2 months of continuous data recorded by a mini seismic array in the Akutan Island, we detect near-continuous tremor activity with an average of 1.3 h of tectonic tremor per day using a beam backprojection method. Tremor sources are clustered in two patches with an 25 km gap in between them. In addition, we visually identify three low-frequency earthquakes, and using them as templates, we detect 1300 additional LFEs applying a matched-filter method. Tremor and LFE activities agree well in space and time, and LFEs show a much smaller recurrence interval during tremor than during non-tremor time periods. Tremor sources propagate both along the strike and dip directions of the subduction fault with velocities ranging between 13 and 110 km/h. Prolific patchy tremor and LFE activities suggest lateral heterogeneity in the locked to freely slipping transition zone, indicating that slow earthquakes may play an important role in the earthquake cycles in this subduction zone.

  5. 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.

  6. 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.

  7. 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

    2015-05-08

    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. Copyright © 2015, American Association for the Advancement of Science.

  8. 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.

  9. Frequency-specific alternations in the amplitude of low-frequency fluctuations in schizophrenia.

    PubMed

    Yu, Rongjun; Chien, Yi-Ling; Wang, Hsiao-Lan Sharon; Liu, Chih-Min; Liu, Chen-Chung; Hwang, Tzung-Jeng; Hsieh, Ming H; Hwu, Hai-Gwo; Tseng, Wen-Yih Isaac

    2014-02-01

    Schizophrenia has been associated with abnormal task-related brain activation in sensory and motor regions as well as social cognition network. Recently, two studies investigated temporal correlation between resting-state functional magnetic resonance imaging (R-fMRI) low-frequency oscillations (LFOs) in schizophrenia but reported mixed results. This may be due to the different frequency bands used in these studies. Here we utilized R-fMRI to measure the amplitude of low-frequency fluctuations (ALFF) and fractional ALFF (fALFF) in three different frequency bands (slow-5: 0.01-0.027 Hz; slow-4: 0.027-0.08 Hz; and typical band: 0.01-0.08 Hz) in 69 patients with schizophrenia and 62 healthy controls. We showed that there were significant differences in ALFF/fALFF between the two bands (slow-5 and slow-4) in regions including basal ganglia, midbrain, and ventromedial prefrontal cortex. Importantly, we also identified significant interaction between frequency bands and groups in inferior occipital gyrus, precuneus, and thalamus. The results suggest that the abnormalities of LFOs in schizophrenia is dependent on the frequency band and suggest that future studies should take the different frequency bands into account when measure intrinsic brain activity.

  10. Modality-Dependent Impact of Hallucinations on Low-Frequency Fluctuations in Schizophrenia.

    PubMed

    Hare, Stephanie M; Ford, Judith M; Ahmadi, Aral; Damaraju, Eswar; Belger, Aysenil; Bustillo, Juan; Lee, Hyo Jong; Mathalon, Daniel H; Mueller, Bryon A; Preda, Adrian; van Erp, Theo G M; Potkin, Steven G; Calhoun, Vince D; Turner, Jessica A

    2017-03-01

    Prior resting-state functional magnetic resonance imaging (fMRI) analyses have identified patterns of functional connectivity associated with hallucinations in schizophrenia (Sz). In this study, we performed an analysis of the mean amplitude of low-frequency fluctuations (ALFF) to compare resting state spontaneous low-frequency fluctuations in patients with Sz who report experiencing hallucinations impacting different sensory modalities. By exploring dynamics across 2 low-frequency passbands (slow-4 and slow-5), we assessed the impact of hallucination modality and frequency range on spatial ALFF variation. Drawing from a sample of Sz and healthy controls studied as part of the Functional Imaging Biomedical Informatics Research Network (FBIRN), we replicated prior findings showing that patients with Sz have decreased ALFF in the posterior brain in comparison to controls. Remarkably, we found that patients that endorsed visual hallucinations did not show this pattern of reduced ALFF in the back of the brain. These patients also had elevated ALFF in the left hippocampus in comparison to patients that endorsed auditory (but not visual) hallucinations. Moreover, left hippocampal ALFF across all the cases was related to reported hallucination severity in both the auditory and visual domains, and not overall positive symptoms. This supports the hypothesis that dynamic changes in the ALFF in the hippocampus underlie severity of hallucinations that impact different sensory modalities. Published by Oxford University Press on behalf of the Maryland Psychiatric Research Center 2016.

  11. 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.

  12. Frequency-specific alternations in the amplitude of low-frequency fluctuations in chronic tinnitus.

    PubMed

    Chen, Yu-Chen; Xia, Wenqing; Luo, Bin; Muthaiah, Vijaya P K; Xiong, Zhenyu; Zhang, Jian; Wang, Jian; Salvi, Richard; Teng, Gao-Jun

    2015-01-01

    Tinnitus, a phantom ringing, buzzing, or hissing sensation with potentially debilitating consequences, is thought to arise from aberrant spontaneous neural activity at one or more sites within the central nervous system; however, the location and specific features of these oscillations are poorly understood with respect to specific tinnitus features. Recent resting-state functional magnetic resonance imaging (fMRI) studies suggest that aberrant fluctuations in spontaneous low-frequency oscillations (LFO) of the blood oxygen level-dependent (BOLD) signal may be an important factor in chronic tinnitus; however, the role that frequency-specific components of LFO play in subjective tinnitus remains unclear. A total of 39 chronic tinnitus patients and 41 well-matched healthy controls participated in the resting-state fMRI scans. The LFO amplitudes were investigated using the amplitude of low-frequency fluctuation (ALFF) and fractional ALFF (fALFF) in two different frequency bands (slow-4: 0.027-0.073 Hz and slow-5: 0.01-0.027 Hz). We observed significant differences between tinnitus patients and normal controls in ALFF/fALFF in the two bands (slow-4 and slow-5) in several brain regions including the superior frontal gyrus (SFG), inferior frontal gyrus, middle temporal gyrus, angular gyrus, supramarginal gyrus, and middle occipital gyrus. Across the entire subject pool, significant differences in ALFF/fALFF between the two bands were found in the midbrain, basal ganglia, hippocampus and cerebellum (Slow 4 > Slow 5), and in the middle frontal gyrus, supramarginal gyrus, posterior cingulate cortex, and precuneus (Slow 5 > Slow 4). We also observed significant interaction between frequency bands and patient groups in the orbitofrontal gyrus. Furthermore, tinnitus distress was positively correlated with the magnitude of ALFF in right SFG and the magnitude of fALFF slow-4 band in left SFG, whereas tinnitus duration was positively correlated with the magnitude of ALFF in right

  13. Low-Frequency Oscillations and Control of the Motor Output

    PubMed Central

    Lodha, Neha; Christou, Evangelos A.

    2017-01-01

    A less precise force output impairs our ability to perform movements, learn new motor tasks, and use tools. Here we show that low-frequency oscillations in force are detrimental to force precision. We summarize the recent evidence that low-frequency oscillations in force output represent oscillations of the spinal motor neuron pool from the voluntary drive, and can be modulated by shifting power to higher frequencies. Further, force oscillations below 0.5 Hz impair force precision with increased voluntary drive, aging, and neurological disease. We argue that the low-frequency oscillations are (1) embedded in the descending drive as shown by the activation of multiple spinal motor neurons, (2) are altered with force intensity and brain pathology, and (3) can be modulated by visual feedback and motor training to enhance force precision. Thus, low-frequency oscillations in force provide insight into how the human brain regulates force precision. PMID:28261107

  14. 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

  15. 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).

  16. 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.

  17. 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.

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

    PubMed

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

    2013-01-01

    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.

  19. Low-frequency absorption using a two-layer system with active control of input impedance.

    PubMed

    Cobo, Pedro; Fernández, Alejandro; Doutres, Olivier

    2003-12-01

    Broadband noise absorption, including low frequencies, may be obtained by a hybrid passive-active two-layer system. A porous layer in front of an air layer provides passive absorption, at medium and high frequencies. Active control of the input impedance of the two-layer system yields absorption at low frequencies. The active control system can implement either pressure-release or impedance-matching conditions. A simple analytical model based upon plane waves propagating in a tube permits the comparison of both control strategies. The results of this simple model show that the pressure-release condition affords higher absorption than the impedance-matching condition for some combinations of geometrical and material parameters. Experimental results corroborate the good performance of the pressure-release condition under the prescribed geometrical setup.

  20. 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.

  1. 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.

  2. 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.

  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. 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.

  5. High vs low frequency neural oscillations in schizophrenia.

    PubMed

    Moran, Lauren V; Hong, L Elliot

    2011-07-01

    There is growing recognition that neural oscillations are important in a wide range of perceptual and cognitive functions. One of the key issues in electrophysiological studies of schizophrenia is whether high or low frequency oscillations, or both, are related to schizophrenia because many brain functions are modulated with frequency specificities. Many recent electrophysiological studies of schizophrenia have focused on high frequency oscillations at gamma band and in general support gamma band dysfunction in schizophrenia. We discuss the concept that gamma oscillation abnormalities in schizophrenia often occur in the background of oscillation abnormalities of lower frequencies. The review discusses the basic neurobiology for the emergence of oscillations of all frequency bands in association with networks of inhibitory interneurons and the convergence and divergence of such mechanisms in generating high vs low frequency oscillations. We then review the literature of oscillatory frequency abnormalities identified in each frequency band in schizophrenia. By describing some of the key functional roles exerted by gamma, low frequencies, and their cross-frequency coupling, we conceptualize that even isolated alterations in gamma or low frequency oscillations may impact the interactions of high and low frequency bands that are involved in key cognitive functions. The review concludes that studying the full spectrum and the interaction of gamma and low frequency oscillations may be critical for deciphering the complex electrophysiological abnormalities observed in schizophrenia patients.

  6. Prediction of long-term properties in polymeric systems: I. Slow crack propagation in poly(vinyl chloride). II. Aging of poly(lactide)/poly(ethylene glycol) blends

    NASA Astrophysics Data System (ADS)

    Hu, Yu

    Slow crack growth in PVC pipe was studied in order to develop a methodology for predicting long-term creep fracture from short-term tension-tension fatigue tests. In all cases, the crack propagated continuously through a crack-tip craze. In fatigue, the density of drawn craze fibrils gradually increased with decreased frequency and increased temperature. At the lowest frequency, 0.01 Hz, the fibril density in fatigue approached that in creep. The kinetics of fatigue and creep crack growth followed the conventional Paris law formulations with the same power 2.7, da/dt = AfDK2.7I , da/dt = BK2.7I , respectively. The effects of frequency, temperature and R-ratio (the ratio of minimum to maximum stress intensity factor in the fatigue loading cycle) on the Paris law prefactors were characterized. A linear correlation allowed extrapolation of the creep prefactor ( B) from fatigue data. The extrapolated values were systematically higher than the values measured directly from creep and only converged at Tg. The difference was attributed to damage of the craze fibrils during crack closure upon unloading in the fatigue cycle. Blending poly(ethylene glycol) (PEG) with poly(lactide) (PLA) decreases the Tg and improves the mechanical properties. It was demonstrated that a PLA of lower stereoregularity was miscible with up to 30 wt% PEG. Aging was due to slow crystallization of PEG from the homogeneous amorphous blend. Crystallization of PEG depleted the amorphous phase of PEG and gradually increased the Tg until aging essentially ceased when Tg of the amorphous phase reached the aging temperature. Different aging mechanism was found with a crystallizable PLA of higher stereoregularity. The effect of cooling rate on crystallization and subsequent aging of high stereoregular PLA blended PEG was studied by thermal analysis and by direct observation of the solid state structure with atomic force microscopy (AFM). The partially crystallized blend obtained with a cooling rate of 30

  7. A stochastic model with a low-frequency amplification feedback for the stratospheric northern annular mode

    NASA Astrophysics Data System (ADS)

    Yu, Yueyue; Cai, Ming; Ren, Rongcai

    2017-08-01

    We consider three indices to measure the polar stratospheric mass and stratospheric meridional mass circulation variability: anomalies of (1) total mass in the polar stratospheric cap (60-90°N, above the isentropic surface 400 K, PSM), (2) total adiabatic mass transport across 60°N into the polar stratosphere cap (AMT), (3) and total diabetic mass transport across 400 K from the polar stratosphere into the troposphere below (DMT). It is confirmed that the negative stratospheric Northern Annular Mode (NAM) and PSM indices have a nearly indistinguishable temporal evolution and a similar red-noise-like spectrum with a de-correlation timescale of 4 weeks. This enables us to examine the low-frequency nature of the NAM in the framework of mass circulation, namely, d/{dt}{PSM}={AMT} - {DMT} . The DMT index tends to be positively correlated with the PSM with a red-noise-like spectrum, representing slow radiative cooling processes giving rise to a de-correlation timescale of 3-4 weeks. The AMT is nearly perfectly correlated with the day-to-day tendency of PSM, reflecting a robust quasi 90° out-of-phase relation between the AMT and PSM at all frequency bands. Variations of vertically westward tilting of planetary waves contribute mainly to the high-frequency portion of AMT. It is the wave amplitude's slow vacillation that plays the leading role in the quasi 90° out-of-phase relation between the AMT and PSM. Based on this, we put forward a linear stochastic model with a low-frequency amplification feedback from low-frequency amplitude vacillations of planetary waves to explain the amplified low-frequency response of PSM/NAM to a stochastic forcing from the westward tilting variability.

  8. 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

  9. 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.

  10. Phase Measurements of Very Low Frequency Signals from the Magnetosphere.

    NASA Astrophysics Data System (ADS)

    Paschal, Evans Wayne

    1988-12-01

    The usual methods of spectrum analysis applied to analog tape recordings of very low frequency (VLF) signals extract only magnitude information and ignore phase information. A digital signal processing system using a recorded constant -frequency pilot tone has been developed which can correct tape errors due to wow and flutter, and reconstruct the signal phases. Frequency shifts are corrected during analysis by interpolating between spectral points in the windowed Fourier transform, and the output phases of the synthesized filters are corrected for timing errors. Having signal component phases as well as magnitudes doubles the available information. Whistler-mode signals from the VLF transmitter at Siple Station, Antarctica, are analyzed as received at Roberval, Quebec. The phase of a non-growing signal is found to give a less-noisy measure of duct motion than Doppler frequency shift, with improved time resolution. Correlations are seen between variations in the whistler-mode phase delay and the earth's magnetic field component D. They are interpreted as Pc 2 micropulsation transients, short compared to the length of the field line, which propagate from equator to ground as Alfven waves. Pulses with temporal growth show an advance in relative phase with time, indicating a positive frequency offset from the transmitted signal. This offset is sometimes seen even at the beginning of a received pulse, an effect not explained by any current model of cyclotron-resonant wave-particle interactions. Pre-termination triggering of an emission always occurs after a phase advance of 1.5 -3 revolutions. Instantaneous frequency measurements show that all emissions, even termination fallers, begin above the frequency of the triggering signal, and that the transition from a signal to a termination emission 100 Hz higher may occur in less than 5 ms. Other phase effects give clues to the mechanisms of sideband generation, suppression, entrainment, and whistler precursors

  11. I. S. Shklovsky and Low-Frequency Radio Astronomy

    NASA Astrophysics Data System (ADS)

    Konovalenko, A. A.

    2017-03-01

    Purpose: Proving of the high astrophysical significance of the low-frequency radio astronomy (decameter and adjacent hectometer and meter wavelengths), demonstration of the priority results of the Ukrainian low-frequency radio astronomy as well as significant contribution of I. S. Shklovsky to its development. Design/methodology/approach: The requirements to characteristics of high efficiency radio telescopes UTR-2, URAN, GURT and to sensitive and interference immune observational methods at low frequencies are formulated by using the theoretical analysis and astrophysical predictions including those I. S. Shklovsky’s. Findings: New generation radio telescopes UTR-2, URAN, GURT are created and modernized. New observational methods at low frequencies are introduced. Large-scale investigations of the Solar system, Galaxy and Methagalaxy are carried out. They have allowed to detect new objects and phenomena for the continuum, monochromatic, pulse and sporadic cosmic radio emission. The role of I. S. Shklovsky in the development of many low-frequency radio astronomy directions is noted, too. Conclusions: The unique possibilities of the low-frequency radio astronomy which gives new information about the Universe, inaccessible with the other astrophysical methods, are shown. The progress of the low-frequency radio astronomy opens the impressive possibilities for the future. It includes modernization of the largest radio telescopes UTR-2, URAN, NDA and creation of new instruments GURT, NenuFAR, LOFAR, LWA, MWA, SKA as well as making multi-antenna and ground-space experiments. The contribution of outstanding astrophysicist of the XX century I. S. Shklovsky to this part of actual astronomical science is evident, claiming for attention and will never be forgotten.

  12. Frequency-dependent alterations in the amplitude of low-frequency fluctuations in social anxiety disorder.

    PubMed

    Zhang, Youxue; Zhu, Chunyan; Chen, Heng; Duan, Xujun; Lu, Fengmei; Li, Meiling; Liu, Feng; Ma, Xujing; Wang, Yifeng; Zeng, Ling; Zhang, Wei; Chen, Huafu

    2015-03-15

    Recent studies on resting-state functional magnetic resonance imaging (fMRI) have found an abnormal temporal correlation between low-frequency oscillations (LFO) in social anxiety disorder (SAD). However, alterations in the amplitudes of these LFO remain unclear. This study included 20 SAD patients and 20 age-, gender-, and education-matched healthy controls. Resting-state fMRI data were acquired using a gradient-echo echo-planar imaging sequence, and the amplitudes of LFO were investigated using the amplitude of low-frequency fluctuation (ALFF) approach. Two frequency bands (slow-5: 0.01-0.027Hz; slow-4: 0.027-0.073Hz) were analyzed. Significant differences in ALFF were observed between the two bands in widespread regions including the postcentral gyrus, precentral gyrus, medial prefrontal cortex (MPFC), orbitofrontal cortex, hippocampus, thalamus, caudate, putamen, and insula. Compared with the healthy controls, the SAD patients showed lower ALFF in the dorsolateral prefrontal cortex (DLPFC), MPFC, superior temporal gyrus, and insula but higher ALFF in the middle occipital gyrus. Furthermore, we found that the SAD patients had reduced ALFF in the MPFC in the slow-5 band. The small sample size may decrease the statistical power of the results. SAD patients had frequency-dependent alteration in intrinsic brain activity. This finding may provide insights into the understanding of the pathophysiology of SAD. Copyright © 2014 Elsevier B.V. All rights reserved.

  13. 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.

  14. High Power HF Excitation of Low Frequency Stimulated Electrostatic Waves in the Ionospheric Plasma over HAARP

    NASA Astrophysics Data System (ADS)

    Bernhardt, Paul; Selcher, Craig A.

    High Power electromagnetic (EM) waves transmitted from the HAARP facility in Alaska can excite low frequency electrostatic waves by several processes including (1) direct magnetized stimulated Brillouin scatter (MSBS) and (2) parametric decay of high frequency electrostatic waves into electron and ion Bernstein waves. Either an ion acoustic (IA) wave with a frequency less than the ion cyclotron frequency (fCI) or an electrostatic ion cyclotron (EIC) wave just above fCI can be produced by MSBS. The coupled equations describing the MSBS instabil-ity show that the production of both IA and EIC waves is strongly influenced by the wave propagation direction relative to the background magnetic field. Experimental observations of stimulated electromagnetic emissions (SEE) using the HAARP transmitter in Alaska have confirmed the theoretical predictions that only IA waves are excited for propagation along the magnetic zenith and that EIC waves can only be detected with oblique propagation angles. The electron temperature in the heated plasma is obtained from the IA spectrum offsets from the pump frequency. The ion composition can be determined from the measured EIC frequency. Near the second harmonic of the electron cyclotron frequency, the EM pump wave is converted into an electron Bernstein (EB) wave that decays into another EB wave and an ion Bernstein (IB) wave. Strong cyclotron resonance with the EB wave leads to acceleration of the electrons. Ground based SEE observations are related to the theory of low-frequency electrostatic wave generation.

  15. Reduced models of extratropical low-frequency variability

    NASA Astrophysics Data System (ADS)

    Strounine, Kirill

    -model's linearized propagator, to rotate the EOF basis in a way that emphasizes the low-frequency modes. The reduced model's performance for a given basis was judged by how well that model reproduces statistical properties of the leading LFV modes of the full model, in the same basis. The statistical properties considered included one dimensional probability density functions (PDFs) and autocorrelation functions. We also used Gaussian mixtures to estimate a multi-dimensional PDF in a subspace of leading EOFs to study the regime behavior of the full and reduced models considered. Overall, the reduced models perform better when more statistical information is used in model construction. Thus, the purely empirical stochastic models with quadratic nonlinearity and additive noise reproduce very well the linear properties of the full QG3 model's LFV, i.e. its autocorrelations and spectra, as well as the nonlinear properties, i.e. the persistent flow regimes that induce non-Gaussian features in the model's PDF. The empirical-dynamical models capture the basic statistical properties of the full model's LFV, such as the variance and integral correlation time scales of the leading LFV modes, as well as some of the regime-behavior features, but fail to reproduce the detailed structure of autocorrelations and distort the statistics of the regimes. Dynamical models that use data-assimilation corrections do capture the linear statistics to a degree comparable with that of empirical-dynamical models, but do much less well on the full QG3 model's nonlinear dynamics. There is no appreciable difference between the performance of the models constructed using the energy norm or the potential-vorticity norm in defining the EOFs. The rotated bases were shown to emphasize the system's linear dynamics, which makes them unsuitable for studies of nonlinear behavior of mid-latitude LFV. The analysis of and comparisons between all the reduced models showed that the cubic nonlinear corrections suggested by the

  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

    SciTech Connect

    Ghosh, Samiran; Chakrabarti, Nikhil

    2016-08-15

    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. Generation of Low-Frequency Electromagnetic Waves by Spectrally Broad Intense Laser Pulses in a Plasma

    NASA Astrophysics Data System (ADS)

    Tsintsadze, L. N.; Tajima, T.; Nishikawa, K.; Koga, J. K.; Nakagawa, K.; Kishimoto, Y.

    A new mechanism for the emission of low-frequency electromagnetic (EM) waves, including the generation of a quasistatic magnetic field, by a relativistically intense laser pulse with a wide spectrum is presented. The emission is due to modulational and filamentational instabilities of the photon gas in a plasma. The generation of the magnetic field is associated with a significant change in the laser pulse shape during the propagation. This process is identified in our 2D particle-in-cell (PIC) simulations with a high intensity (1019

  19. On the coherent components of low-frequency ambient noise in the Indian Ocean.

    PubMed

    Sabra, Karim G; Fried, Stephanie; Kuperman, W A; Prior, Mark

    2013-01-01

    This letter demonstrates that the dominant coherent component of low-frequency (1 Hz < f < 20 Hz) ambient noise propagating between hydrophone pairs of the same hydroacoustic station, deployed in the deep sound channel of the Indian Ocean, is directional and mainly originates from Antarctica. However, the amplitude of the peak coherent noise arrivals, obtained using a 4-month-long averaging interval, was relatively low given the small hydrophones spacing hydrophones (<2 km). Hence, extracting similar coherent arrivals between two distinct hydroacoustic stations separated instead by thousands of kilometers for noise-based acoustic thermometry purposes seems unlikely, even using a year-long averaging.

  20. Low frequency electric field variations during HF transmissions on a mother-daughter rocket

    NASA Technical Reports Server (NTRS)

    Rosenberg, T. J.; Maynard, M. C.; Holtet, J. A.; Karlsen, N. O.; Egeland, A.; Moe, T. E.; Troim, J.

    1977-01-01

    HF wave propagation experiments were conducted on Mother-Daughter rockets in the polar ionosphere. Swept frequency transmissions from the Mother, nominally covering the range from 0.5 to 5 MHz in both CW and pulse modes, are received by the Daughter. In the most recent rocket of the series, the Mother also contained an AC electric field spectrometer covering the frequency range from 10 Hz to 100 kHz in four decade bands. The low frequency response of the ionosphere with respect to waves emitted from the onboard HF transmitter is examined.

  1. A low-frequency sound absorbing material with subwavelength thickness

    NASA Astrophysics Data System (ADS)

    Chen, Changru; Du, Zhibo; Hu, Gengkai; Yang, Jun

    2017-05-01

    We propose a sound absorbing material efficient for low frequency. This material is mainly composed of two axially coupled tubes in series, which are co-planarly coiled in a plane perpendicular to incident waves. By carefully designing the geometric parameters of the coupled tubes, we can overlap the absorption coefficient curves of each individual tube and are therefore able to broaden the frequency bandwidth within which the absorption coefficient is larger than a designed value. A material with an absorption coefficient greater than 0.8 over a frequency bandwidth of 36 Hz for a low frequency of around 100 Hz can be designed, and the wavelength to thickness ratio reaches as high as 38.5. The experiment measurement with the sample made by the 3D printing technique is also conducted to validate the proposed design method. This work may stimulate the research studies on and applications for low frequency sound absorption.

  2. 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.

  3. Low-Frequency Vibration Drilling of Titanium Alloy

    NASA Astrophysics Data System (ADS)

    Okamura, Kiyoshi; Sasahara, Hiroyuki; Segawa, Toshiaki; Tsutsumi, Masaomi

    Dry drilling of composite/metallic stacks for aircraft components is extremely difficult to keep sufficient hole quality and efficiency of drilling process. Problems of the dry drilling of those kinds of stacks are chip ejection, chip formation and high temperature especially for titanium alloy. To clear these problems, low-frequency vibration (10-50Hz) drilling is proposed in this study. Controlled sinusoidal vibration was given in drill axis direction with constant feed motion. The relationship between vibration conditions, such as vibration amplitude, frequency and drill feed rate, and chip formation and drilling temperature were investigated. As a result, low-frequency vibration drilling can control chip formation to reduce chip jamming and can reduce drilling temperature. Temperature measured at the cap burr decreased by 300 degrees C or more when low-frequency vibration was applied compared with the conventional drilling. Also the wear rate of the drill is decreased when the vibration is applied.

  4. 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.

  5. 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.

  6. 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

  7. Reducing low-frequency noise during reversible fluctuations

    NASA Astrophysics Data System (ADS)

    Chamberlin, Ralph V.

    2017-02-01

    The noise from most materials exhibits a power-spectral density that tends to diverge as S(f) ∝ 1/f at low frequencies, f. A fundamental mechanism for this 1/f noise comes from the thermodynamics of small systems applied to reversible fluctuations of nanometer-sized regions inside bulk samples. Here this "nanothermodynamics" is used to derive a nonlinear correction to Boltzmann's factor. Specifically: Boltzmann's factor comes from the first-order (linear) derivative of entropy with respect to energy, whereas the nonlinear correction comes from higher-order terms. The nonlinear correction is applied to Monte Carlo simulations of small regions in the Ising model, yielding a low-frequency crossover to white noise that keeps the power-spectral density finite as f → 0. It is shown that the low-frequency noise in the model is reduced by reducing the size of the regions.

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

    PubMed

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

    2014-10-01

    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.

  9. 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.

  10. 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.

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

    SciTech Connect

    Wang, Chunsheng Wang, Huashan

    2016-08-15

    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.

  12. Listening to the low-frequency gravitational-wave band

    NASA Astrophysics Data System (ADS)

    Hughes, Scott

    2016-03-01

    Ground-based gravitational-wave detectors are beginning to explore the high-frequency band of roughly 10 to 1000 Hz. These three decades in frequency represent one of several astrophysically important wavebands. In this talk, I will focus on the astrophysics of the low-frequency band, from roughly 30 microhertz to 0.1 Hz. This band is expected to be particularly rich with very loud sources. I will survey what we expect to be important sources of low-frequency gravitational waves, and review the scientific payoff that would come from measuring them.

  13. Planetary and exoplanetary low frequency radio observations from the Moon

    NASA Astrophysics Data System (ADS)

    Zarka, P.; Bougeret, J.-L.; Briand, C.; Cecconi, B.; Falcke, H.; Girard, J.; Grießmeier, J.-M.; Hess, S.; Klein-Wolt, M.; Konovalenko, A.; Lamy, L.; Mimoun, D.; Aminaei, A.

    2012-12-01

    We analyze the planetary and exoplanetary science that can be carried out with precursor as well as future low frequency radio instruments on the Moon, assessing the limiting noise sources, comparing them to the average and peak spectra of all planetary radio components as they will be seen from the Lunar surface or orbit. We identify which objectives will be accessible with each class of instrument, and discuss the interest of these observations compared to observations by planetary probes and to ground-based observations by large low-frequency radio arrays. The interest of goniopolarimetry is emphasized for pathfinder missions.

  14. 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.

  15. Multi-large low-frequency band gaps in a periodic hybrid structure

    NASA Astrophysics Data System (ADS)

    Wang, T.; Sheng, M. P.; Guo, H. B.

    2016-03-01

    A hybrid structure composed of a local resonance mass and an external oscillator is proposed in this paper for restraining the elastic longitudinal wave propagation. Theoretical model has been established to investigate the dispersion relation and band gaps of the structure. The results show that the hybrid structure can produce multi-band gaps wider than the multi-resonator acoustic metamaterials. It is much easier for the hybrid structure to yield wide and low band gaps by adjusting the mass and stiffness of the external oscillator. Small series spring constant ratio results in low-frequency band gaps, in which the external oscillator acts as a resonator and replaces the original local resonator to hold the band gaps in low frequency range. Compared with the one-dimensional phononic crystal (PC) lattice, a new band gap emerges in lower frequency range in the hybrid structure because of the added local resonance, which will be a significant assistance in low-frequency vibration and noise reduction. Further, harmonic response analysis using finite element method (FEM) has been performed, and results show that elastic longitudinal waves are efficiently forbidden within the band gaps.

  16. 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.

  17. 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.

  18. Generation mechanism of slow earthquakes: Numerical analysis based on a dynamic model with brittle-ductile mixed fault heterogeneity

    NASA Astrophysics Data System (ADS)

    Nakata, Ryoko; Ando, Ryosuke; Hori, Takane; Ide, Satoshi

    2011-08-01

    Various characteristics have been discovered for small, slow earthquakes occurring along subduction zones, which are deep nonvolcanic tremor, low-frequency earthquakes (LFEs), and very low frequency earthquakes (VLFs). In this study, we model these slow earthquakes using a dynamic model consisting of a cluster of frictionally unstable patches on a stable background. The controlling parameters in our model are related to the patch distribution and the viscosity of both the patches and the background. By decreasing patch density or increasing viscosity, we observed the transition in rupture propagation mechanism, that is, from fast elastodynamic interactions characterized by an elastic wave propagation to slow diffusion limited by viscous relaxation times of traction on fault patches and/or background. Some sets of these geometrical and frictional parameters collectively explain the moment rate functions, source spectra, and scaled energy of observed slow earthquakes. In addition, we successfully explain both parabolic and constant velocity migrations in the case of the diffusion-limited rupture. Therefore, the observed various characteristics of tremor, LFEs, VLFs, and, potentially, slow slip events, may be essentially explained by our simple model with a few parameters describing source structures and frictional properties of brittle-ductile transition zones along plate boundaries.

  19. 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.

  20. Subgrid-scale parameterization and low-frequency variability: a response theory approach

    NASA Astrophysics Data System (ADS)

    Demaeyer, Jonathan; Vannitsem, Stéphane

    2016-04-01

    Weather and climate models are limited in the possible range of resolved spatial and temporal scales. However, due to the huge space- and time-scale ranges involved in the Earth System dynamics, the effects of many sub-grid processes should be parameterized. These parameterizations have an impact on the forecasts or projections. It could also affect the low-frequency variability present in the system (such as the one associated to ENSO or NAO). An important question is therefore to know what is the impact of stochastic parameterizations on the Low-Frequency Variability generated by the system and its model representation. In this context, we consider a stochastic subgrid-scale parameterization based on the Ruelle's response theory and proposed in Wouters and Lucarini (2012). We test this approach in the context of a low-order coupled ocean-atmosphere model, detailed in Vannitsem et al. (2015), for which a part of the atmospheric modes is considered as unresolved. A natural separation of the phase-space into a slow invariant set and its fast complement allows for an analytical derivation of the different terms involved in the parameterization, namely the average, the fluctuation and the long memory terms. Its application to the low-order system reveals that a considerable correction of the low-frequency variability along the invariant subset can be obtained. This new approach of scale separation opens new avenues of subgrid-scale parameterizations in multiscale systems used for climate forecasts. References: Vannitsem S, Demaeyer J, De Cruz L, Ghil M. 2015. Low-frequency variability and heat transport in a low-order nonlinear coupled ocean-atmosphere model. Physica D: Nonlinear Phenomena 309: 71-85. Wouters J, Lucarini V. 2012. Disentangling multi-level systems: averaging, correlations and memory. Journal of Statistical Mechanics: Theory and Experiment 2012(03): P03 003.

  1. 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.

  2. 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

  3. 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…

  4. Intrinsic low-frequency variability of the Gulf Stream

    NASA Astrophysics Data System (ADS)

    Quattrocchi, G.; Pierini, S.; Dijkstra, H. A.

    2012-03-01

    In this paper a process study aimed at analyzing the low-frequency variability of intrinsically oceanic origin of the Gulf Stream (GS) and GS extension (GSE) is presented. An eddy-permitting reduced-gravity nonlinear shallow water model is implemented in an idealized North Atlantic Ocean, with schematic boundaries including the essential geometric features of the coastline and a realistic zonal basin width at all latitudes. The forcing is provided by a time-independent climatological surface wind stress obtained from 41 years of monthly ECMWF fields. The model response yields strong intrinsic low-frequency fluctuations on the interannual to decadal time scales. The modelled time-averaged GS/GSE flows are found to exhibit several features that can also be deduced from satellite altimeter data, such as the Florida Current seaward deflection, the GS separation at Cape Hatteras, and the overall structure of the GSE. The intrinsic low-frequency variability yields two preferred states of the GSE differing in latitudinal location that also have their counterpart in the altimeter data. A preliminary analysis of the variability in terms of dynamical systems theory is carried out by using the lateral eddy viscosity as the control parameter. A complex transition sequence from a steady state to irregular low-frequency variability emerges, in which Hopf and global bifurcations can be identified.

  5. 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…

  6. 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.

  7. Low-Frequency Microaccelerations onboard the Foton-11 Satellite

    NASA Astrophysics Data System (ADS)

    Sazonov, V. V.; Chebukov, S. Yu.; Abrashkin, V. I.; Kazakova, A. E.; Zaitsev, A. S.

    2004-03-01

    We analyze the microacceleration measurements carried out onboard the Foton-11 satellite with the three-component accelerometer BETA. The microaccelerations were recorded virtually throughout the entire orbital flight of the Foton-11 satellite. The data obtained were analyzed in the following way. First they were used to determine the actual rotational motion of the satellite for several arbitrarily selected time intervals 4 h long. This problem was solved by constructing the approximation of the microacceleretation low-frequency component (previously determined from the data) by its calculated analog computed along the solutions to differential equations of rotational motion of the satellite. The approximation was made by the least squares method. As a result, those mathematical model parameters and the solutions to equations of motion were found that gave the best consistency of the microacceleretation low-frequency component and its calculated analog. Then the spectral analysis of the low-frequency component and its calculated analog was made. It was shown that, although basic harmonics of these functions coincided sufficiently well, some harmonics of the low-frequency component failed to be interpreted in terms of the satellite's rotational motion.

  8. Low-frequency oscillations of vortices in rotating He II

    SciTech Connect

    Sonin, E.B.

    1983-01-20

    The low-frequency branch of the spectrum of oscillations of a stack of disks in rotating He II with large angular velocities corresponds to excitation of an inertial wave, a well known phenomenon in hydrodynamics of rotating classical fluids, in the volume between the disks. This agrees with the results of experiments by Andereck, Chalupa, and Glaberson.

  9. UXO Detector for Underwater Surveys Using Low-Frequency Sonar

    DTIC Science & Technology

    2015-06-01

    ABSTRACT Locating and surveying underwater dumping sites of unexploded ordnance (UXO) is challenging, particularly when they are buried beneath the...seafloor sediment. Low-frequency (LF) sonars have a demonstrated capability for detecting buried objects. However, high clutter densities observed in...vi Acronyms APL Applied Physics Laboratory BOSS Buried Object Scanning Sonar CMRE Centre for Maritime Research and

  10. 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.

  11. 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.

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

    DOE PAGES

    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

  13. 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.

  14. Salbutamol and chronic low-frequency stimulation of canine skeletal muscle.

    PubMed Central

    Hu, P; Zhang, K M; Feher, J J; Wang, S W; Wright, L D; Wechsler, A S; Spratt, J A; Briggs, F N

    1996-01-01

    1. The effect of simultaneous application of chronic muscle stimulation and salbutamol on the expression of mRNAs and proteins normally expressed by fast- or slow-twitch fibres was followed and the effects of changes in protein expression on mechanical performance were evaluated. Chronic low-frequency stimulation increased the myosin heavy chain (HC)-I level in the canine latissimus dorsi muscle and simultaneous administration of salbutamol partially blocked this change. Associated with the increase in HC-I level was a decrease in the velocity of shortening at zero load, VMAX. The change in VMAX was partially blocked by salbutamol. 2. Chronic low-frequency stimulation increased the levels of slow-twitch cardiac isoform sarco-/endoplasmic reticulum Ca(2+)-ATPase (SERCA2a) and phospholamban mRNA, and SERCA2a and phospholamban protein expression. These changes were associated with an increase in time-to-peak tension and a decrease in fusion frequency. Simultaneous administration of salbutamol blocked these changes in protein expression and muscle mechanics. Chronic stimulation of latissimus dorsi decreased the levels of the fast-twitch isoform of sarco-/endoplasmic reticulum Ca(2+)-ATPase (SERCA1a) and increased SERCA2a protein expression and decreased calcium uptake rate by muscle homogenates. These changes were blocked by salbutamol. 3. The loss of latissimus dorsi muscle weight by chronic stimulation was partially blocked by salbutamol. Images Figure 1 Figure 4 PMID:8910210

  15. Effects of continuous low-frequency pacing on immature canine diaphragm.

    PubMed

    Marzocchi, M; Brouillette, R T; Klemka-Walden, L M; Heller, S L; Weese-Mayer, D E; Brozanski, B S; Caliendo, J; Daood, M; Ilbawi, M N; Hunt, C E

    1990-09-01

    Although diaphragm pacing has been shown to be a practical method of supporting ventilation in children, its usefulness has been limited because of concern that continuous (24 h/day) diaphragm pacing would fatigue and damage the diaphragm. We examined the functional and structural effects of continuous low-frequency diaphragm pacing on the left hemidiaphragm of five immature dogs aged 65 +/- 2 (SD) days at onset of pacing. Stimulus parameters approximated those required to pace infants: frequency 11.1 Hz, inspiratory time 810 ms, and respiratory rate 20 breaths/min. Animals were paced 24 h/day for 24-28 days. Paced tidal volumes and airway occlusion pressures were unchanged at low (less than 15 Hz) stimulus frequencies but were reduced at high (greater than 20 Hz) stimulus frequencies. Although histologically the paced hemidiaphragms appeared normal, histochemical studies showed a conversion from a mixture of type I (54%) and type II (46%) fibers to a uniform population of type I fibers with high oxidative enzyme activity. Transformation of muscle type was also demonstrated by pyrophosphate gel electrophoresis; fast and slow isomyosin bands were noted in control specimens, whereas only slow isomyosin was identified in paced specimens. Thus, in immature dogs, continuous low-frequency pacing affects both function and structure of the diaphragm.

  16. 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.

  17. Pseudochaos and low-frequency percolation scaling for turbulent diffusion in magnetized plasma.

    PubMed

    Milovanov, Alexander V

    2009-04-01

    The basic physics properties and simplified model descriptions of the paradigmatic "percolation" transport in low-frequency electrostatic (anisotropic magnetic) turbulence are theoretically analyzed. The key problem being addressed is the scaling of the turbulent diffusion coefficient with the fluctuation strength in the limit of slow fluctuation frequencies (large Kubo numbers). In this limit, the transport is found to exhibit pseudochaotic, rather than simply chaotic, properties associated with the vanishing Kolmogorov-Sinai entropy and anomalously slow mixing of phase-space trajectories. Based on a simple random-walk model, we find the low-frequency percolation scaling of the turbulent diffusion coefficient to be given by D/omega proportional, variantQ;{2/3} (here Q1 is the Kubo number and omega is the characteristic fluctuation frequency). When the pseudochaotic property is relaxed, the percolation scaling is shown to cross over to Bohm scaling. The features of turbulent transport in the pseudochaotic regime are described statistically in terms of a time fractional diffusion equation with the fractional derivative in the Caputo sense. Additional physics effects associated with finite particle inertia are considered.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

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

    PubMed Central

    Bauhofer, Anton; Krödel, Sebastian; Palermo, Antonio; Daraio, Chiara

    2016-01-01

    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. PMID:27410042

  3. 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.

  4. 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.

  5. 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

  6. 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

  7. Shallow-Water Propagation

    DTIC Science & Technology

    2016-06-07

    efficient performance of our propagation model for low frequency range-dependent problems in elastic media. A new PE solution [22] for gravity wave...21] J. Bruch, M. D. Collins, D. K. Dacol, J. F. Lingevitch, and W. L. Siegmann, “A parabolic equation for advected acousto- gravity waves,” (A

  8. A method for sputtering with low frequency alternating current

    SciTech Connect

    Timberlake, J.R.

    1993-12-31

    Low frequency alternating current sputtering is provided by connecting a low frequency alternating current to a high voltage transformer having outer taps and a center tap for stepping up the voltage of the alternating currentThe center tap of the tmsformer 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 ftwsformer. 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.

  9. Observations of Fast Radio Bursts and perspectives at low frequencies

    NASA Astrophysics Data System (ADS)

    Zarka, P.; Mottez, F.

    2016-12-01

    We briefly summarize the characteristics of the elusive Fast Radio Bursts from existing observations. Then we emphasize the interest of low-frequency observations, e.g. with NenuFAR. In order to define the best observing parameters and detection scheme, we have built a simulation program of FRB at low-frequencies, that proceeds in 2 steps: (i) FRB generation and dilution in a dynamic spectrum with given characteristics, and (ii) definition of the FRB spectrum, and detection on the galactic radio background by means of parametric dedispersion. We carry on a preliminary simulation study, that allows us to draw first conclusions, among which the possibility to detect Lorimer-like FRB with NenuFAR.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. A procedure for the assessment of low frequency noise complaints.

    PubMed

    Moorhouse, Andy T; Waddington, David C; Adams, Mags D

    2009-09-01

    The development and application of a procedure for the assessment of low frequency noise (LFN) complaints are described. The development of the assessment method included laboratory tests addressing low frequency hearing threshold and the effect on acceptability of fluctuation, and field measurements complemented with interview-based questionnaires. Environmental health departments then conducted a series of six trials with genuine "live" LFN complaints to test the workability and usefulness of the procedure. The procedure includes guidance notes and a pro-forma report with step-by-step instructions. It does not provide a prescriptive indicator of nuisance but rather gives a systematic procedure to help environmental health practitioners to form their own opinion. Examples of field measurements and application of the procedure are presented. The procedure and examples are likely to be of particular interest to environmental health practitioners involved in the assessment of LFN complaints.

  17. Low-frequency Flux Noise in SQUIDs and Superconducting Qubits

    NASA Astrophysics Data System (ADS)

    Sendelbach, Steven; Hover, David; Kittel, Achim; Mueck, Michael; McDermott, Robert

    2008-03-01

    Superconducting qubits are a leading candidate for scalable quantum information processing. In order to realize the full potential of these qubits, it is necessary to develop a more complete understanding of the microscopic physics that governs dissipation and dephasing of the quantum state. In the case of the Josephson phase and flux qubits, the dominant dephasing mechanism is an apparent low-frequency magnetic flux noise with a 1/f spectrum. The origin of this excess noise is not understood. We report the results of SQUID measurements that explore the dependence of the excess low-frequency flux noise on SQUID inductance, geometry, materials, and temperature. We discuss contributions to the measured noise from temperature fluctuations, trapped vortices in the superconducting films, and surface magnetic states in the native oxides of the superconductors. We discuss implications of our measurements for qubit dephasing.

  18. 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.

  19. Dielectric behavior of some ferrofluids in low-frequency fields.

    PubMed

    Malaescu, I; Marin, C N

    2002-07-01

    The dielectric behavior of a ferrofluid with magnetite particles dispersed in kerosene was analyzed taking into account the Schwarz model, concerning the low-frequency dielectric behavior in systems consisting of colloidal particles suspended in electrolytes. For this reason, the complex dielectric permittivity and dielectric loss factor, in the frequency range of 10 Hz-500 kHz, at different temperatures between 20 degrees C and 100 degrees C were measured. Based on these experimental results, the experimental dependencies on both temperature of the relaxation time and activation energy of the relaxation process were analyzed. The obtained results show that the Schwarz model can be applied, in order to explain the low-frequency dielectric behavior of a ferrofluid with magnetite particles in kerosene, if the change of counterion concentration at the surface of colloidal particles is taken into account. Consequently, it is shown that the dielectric spectroscopy can be used in order to analyze the presence of particle agglomerations within ferrofluids.

  20. Determining low-frequency source location from acoustic phase measurements

    NASA Astrophysics Data System (ADS)

    Poole, Travis L.; Frisk, George V.

    2002-11-01

    For low-frequency cw sound sources in shallow water, the time rate-of-change of the measured acoustic phase is well approximated by the time rate-of-change of the source-receiver separation distance. An algorithm for determining a locus of possible source locations based on this idea has been developed. The locus has the general form of a hyperbola, which can be used to provide a bearing estimation at long ranges, and an estimate of source location at short ranges. The algorithm uses only acoustic phase data and receiver geometry as input, and can be used even when the source frequency is slightly unstable and/or imprecisely known. The algorithm has been applied to data from low-frequency experiments (20-300 Hz), both for stable and unstable source frequencies, and shown to perform well. [Work supported by ONR and WHOI Academic Programs Office.

  1. 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.

  2. Low frequency electrorotation of fixed red blood cells.

    PubMed Central

    Georgieva, R; Neu, B; Shilov, V M; Knippel, E; Budde, A; Latza, R; Donath, E; Kiesewetter, H; Bäumler, H

    1998-01-01

    Electrorotation of fixed red blood cells has been investigated in the frequency range between 16 Hz and 30 MHz. The rotation was studied as a function of electrolyte conductivity and surface charge density. Between 16 Hz and 1 kHz, fixed red blood cells undergo cofield rotation. The maximum of cofield rotation occurs between 30 and 70 Hz. The position of the maximum depends weakly on the bulk electrolyte conductivity and surface charge density. Below 3.5 mS/m, the cofield rotation peak is broadened and shifted to higher frequencies accompanied by a decrease of the rotation speed. Surface charge reduction leads to a decrease of the rotation speed in the low frequency range. These observations are consistent with the recently developed electroosmotic theory of low frequency electrorotation. PMID:9545070

  3. Low-frequency shift Raman spectroscopy using atomic filters.

    PubMed

    Xue, Xiaobo; Janisch, Corey; Chen, Yizhu; Liu, Zhiwen; Chen, Jingbiao

    2016-11-15

    A Faraday anomalous dispersion optical filter (FADOF) and an atomic resonant absorption filter are used in tandem to demonstrate a low-frequency shift Raman measurement down to few cm-1. The FADOF, with an ultralow bandwidth of 0.08  cm-1 at 780 nm, serves as a bandpass filter, while the rubidium atomic cell acts as a notch filter which has a bandwidth of 0.3  cm-1. A proof-of-concept study to measure a Raman signal generated from a silica optical fiber is performed, demonstrating a low-frequency measurement of both the Stokes and the anti-Stokes shift down to 3  cm-1 at an equivalent signal level. These results indicate the prospect for gigahertz-terahertz low-energy Raman spectroscopy based on atomic filters.

  4. Detecting topological superconductivity using low-frequency doubled Shapiro steps

    NASA Astrophysics Data System (ADS)

    Sau, Jay D.; Setiawan, F.

    2017-02-01

    The fractional Josephson effect has been observed in many instances as a signature of a topological superconducting state containing zero-energy Majorana modes. We present a nontopological scenario which can produce a fractional Josephson effect generically in semiconductor-based Josephson junctions, namely, a resonant impurity bound state weakly coupled to a highly transparent channel. We show that the fractional ac Josephson effect can be generated by the Landau-Zener processes which flip the electron occupancy of the impurity bound state. The Josephson effect signature for Majorana modes become distinct from this nontopological scenario only at low frequency. We prove that a variant of the fractional ac Josephson effect, namely, the low-frequency doubled Shapiro steps, can provide a more reliable signature of the topological superconducting state.

  5. A PVDF transducer for low-frequency acceleration measurements.

    PubMed

    Daku, Brian L F; Mohamed, Enas M A; Prugger, Arnfinn F

    2004-07-01

    A unique acceleration transducer, using piezoelectric PVDF, has been developed for low-frequency vibration monitoring. The paper develops the theoretical model for this low-cost, robust sensor. The theoretical model is validated using experimental results from laboratory tests. The sensor was also installed in an underground potash mine alongside a commercial geophone for a three-month in-mine test producing results that show a close correspondence between the two transducers.

  6. 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

  7. 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.

  8. 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.

  9. Zinc oxide piezoelectric nano-generators for low frequency applications

    NASA Astrophysics Data System (ADS)

    Nour, E. S.; Nur, O.; Willander, M.

    2017-06-01

    Piezoelectric Zinc Oxide (ZnO) nanogenerators (NGs) have been fabricated for low frequency (<100 Hz) energy harvesting applications. Different types of NGs based on ZnO nanostructures have been carefully developed, and studied for testing under different kinds of low frequency mechanical deformations. Well aligned ZnO nanowires (NWs) possessing high piezoelectric coefficient were synthesized on flexible substrates using the low temperature hydrothermal route. These ZnO NWs were then used in different configurations to demonstrate different low frequency energy harvesting devices. Using piezoelectric ZnO NWs, we started with the fabrication of a sandwiched NG for a handwriting enabled energy harvesting device based on a thin silver layer coated paper substrate. Such device configurations can be used for the development of electronic programmable smart paper. Further, we developed this NG to work as a triggered sensor for a wireless system using footstep pressure. These studies demonstrate the feasibility of using a ZnO NWs piezoelectric NG as a low-frequency self- powered sensor, with potential applications in wireless sensor networks. After that, we investigated and fabricated a sensor on a PEDOT: PSS plastic substrate using a one-sided growth and double-sided growth technique. For the first growth technique, the fabricated NG has been used as a sensor for an acceleration system; while the fabricated NG by the second technique works as an anisotropic direction sensor. This fabricated configuration showed stability for sensing and can be used in surveillance, security, and auto-Mobil applications. In addition to that, we investigated the fabrication of a sandwiched NG on plastic substrates. Finally, we demonstrated that doping ZnO NWs with extrinsic elements (such as Ag) will lead to the reduction of the piezoelectric effect due to the loss of crystal symmetry. A brief summary into future opportunities and challenges is also presented.

  10. 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.

  11. Low-Frequency Scattering from Two-Dimensional Perfect Conductors

    DTIC Science & Technology

    1991-04-01

    jkr ! G(f, f’)K.(f’)ds’, f E S (2.6) where the bar on the integral sign indicates that the singularity at f = f’ is excluded. From the small...2.17) is O~n’ 𔃼 7 The bar on the integral sign indicates that this is a Cauchy principal value integration. To determine the low-frequency expansion

  12. A kinetic-MHD model for low frequency phenomena

    SciTech Connect

    Cheng, C.Z.

    1991-07-01

    A hybrid kinetic-MHD model for describing low-frequency phenomena in high beta anisotropic plasmas that consist of two components: a low energy core component and an energetic component with low density. The kinetic-MHD model treats the low energy core component by magnetohydrodynamic (MHD) description, the energetic component by kinetic approach such as the gyrokinetic equation, and the coupling between the dynamics of these two components through plasma pressure in the momentum equation. The kinetic-MHD model optimizes both the physics contents and the theoretical efforts in studying low frequency MHD waves and transport phenomena in general magnetic field geometries, and can be easily modified to include the core plasma kinetic effects if necessary. It is applicable to any magnetized collisionless plasma system where the parallel electric field effects are negligibly small. In the linearized limit two coupled eigenmode equations for describing the coupling between the transverse Alfven type and the compressional Alfven type waves are derived. The eigenmode equations are identical to those derived from the full gyrokinetic equation in the low frequency limit and were previously analyzed both analytically nd numerically to obtain the eigenmode structure of the drift mirror instability which explains successfully the multi-satellite observation of antisymmetric field-aligned structure of the compressional magnetic field of Pc 5 waves in the magnetospheric ring current plasma. Finally, a quadratic form is derived to demonstrate the stability of the low-frequency transverse and compressional Alfven type instabilities in terms of the pressure anisotropy parameter {tau} and the magnetic field curvature-pressure gradient parameter. A procedure for determining the stability of a marginally stable MHD wave due to wave-particle resonances is also presented.

  13. 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.

  14. Parallel-Flow-Shear Driven Low-Frequency Plasma Instability

    SciTech Connect

    Ishiguro, Seiji; Matsumoto, Noriaki; Kaneko, Toshiro; Hatakeyama, Rikizo

    2004-12-01

    Full three dimensional Particle-in-Cell (PIC) simulations are performed in order to investigate effects of field-aligned (parallel) ion flow shears on low-frequency plasma instabilities. It is shown that the parallel ion flow velocity shear can induce the ion-acoustic instability, even when the ion flow velocity is so small that the instability can not take place. Simulation results are consistent with the analysis based on the local theory.

  15. Ultra-low frequency shock dynamics in degenerate relativistic plasmas

    NASA Astrophysics Data System (ADS)

    Islam, S.; Sultana, S.; Mamun, A. A.

    2017-09-01

    A degenerate relativistic three-component plasma model is proposed for ultra-low frequency shock dynamics. A reductive perturbation technique is adopted, leading to Burgers' nonlinear partial differential equation. The properties of the shock waves are analyzed via the stationary shock wave solution for different plasma configuration parameters. The role of different intrinsic plasma parameters, especially the relativistic effects on the linear wave properties and also on the shock dynamics, is briefly discussed.

  16. A Low Frequency Electromagnetic Sensor for Underwater Geo-Location

    DTIC Science & Technology

    2011-05-01

    using the magnetic field. Mrs. Irma Shamatava of Sky Research, who is an expert in the MAS, conducted detailed EMI noise estimation studies...Underwater Geo-location Technical publications produced under this project: F. Shubitidze, A. Bijamov, Irma Shamatava, John Miller, G...Shubitidze, Irma Shamatava, John Miller, G. Schultz, "A low frequency magentic field sensor for underwater geo-location.” Partners in Environmental

  17. How non-parallel flow affects the low frequency sound of supersonic heated jets

    NASA Astrophysics Data System (ADS)

    Afsar, Mohammed; Sescu, Adrian

    2015-11-01

    Experiements show that the peak noise of heated supersonic jets is lower than the peak noise associated with isothermal jets at all observation angles. Attempts to explain this reduction via acoustic analogy approaches were based on theories in which the enthalpy or momentum flux co-variance (coupling term) reduces the acoustic spectrum at small observation angles. These results, that were derived using a parallel flow assumption and determined using a low frequency asymptotic analysis, indicate that the propagator in the coupling term possesses an odd power of inverse Doppler factors that change sign at small observation angles to the jet axis for supersonic jets. This result, however, does not take into account mean flow spreading. In this study, we extend a previously developed asymptotic theory for the propagator in non-parallel flows, to heated jets. Our calculations show that, non-parallelism re-distributes the spatial structure of the propagator at small observation angles for supersonic jets. Rather than introducing cancellation in the acoustic spectrum, as parallel flow asymptotics predict, the non-parallel flow asymptotic analysis suggests that heating shifts the propagator's peak much further downstream, into regions where turbulence becomes weak.

  18. 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.

  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. Interaction between respiratory and RR interval oscillations at low frequencies.

    PubMed

    Aguirre, A; Wodicka, G R; Maayan, C; Shannon, D C

    1990-03-01

    Oscillations in RR interval between 0.02 and 1.00 cycles per second (Hz) have been related to the action of the autonomic nervous system. Respiration has been shown to influence RR interval at normal breathing frequencies between approximately 0.16 and 0.5 Hz in children and adults--a phenomenon known as respiratory sinus arrhythmia. In this study we investigated the effect of respiration on RR interval in a lower frequency range between 0.02 and 0.12 Hz. Low frequency oscillations in respiration were induced in healthy sleeping adult subjects via the administration of a bolus of CO2 during inhalation. Power spectra of RR interval and respiration were obtained before and after the CO2 pulse, and the frequency content in the low frequency range was quantitatively compared. An increase in the spectral energy in both respiration and RR interval was observed for the group. However, this increase was accounted for by six of 29 epochs. We conclude that respiration (tidal volume) can influence RR interval at frequencies below those usually associated with respiratory sinus arrhythmia. This influence may be mediated through a sympathetic reflex. This result is applicable to the measurement and interpretation of heart rate variability and to autonomic influences of low frequency fluctuations in RR interval.

  1. Tectonic tremor locations using template matching of low frequency earthquakes

    NASA Astrophysics Data System (ADS)

    Skoumal, R.; Colella, H. V.; Holtkamp, S. G.; Brudzinski, M. R.; Schlanser, K. M.; Shelly, D. R.; Cabral-Cano, E.; Arciniega-Ceballos, A.

    2012-12-01

    Tectonic (non-volcanic) tremor is difficult to locate due to its emergent nature, but critical to assess what impact it has on the plate interface slip budget. Recent studies have found that tectonic tremor is primarily composed of a swarm of low frequency earthquakes, such that identifying individual low frequency earthquakes can provide opportunities to improve source characterizations. This study seeks to refine the tremor source locations by stacking families of similar low frequency earthquakes to enhance the signal to noise ratio and clarify P- and S-wave arrivals, and to better characterize the time history of specific "famlies" of tremor events. Short, well-defined tremor bursts identified from previous source location analysis are used to define template waveforms that are cross-correlated over several years of recording. Since multi-station template matching algorithms are particularly sensitive to source location, accurate time histories of event families can be produced. These time histories provide an important additional constraint on episodic tremor and slip events (and an independent test of both procedures) since they do not depend on station amplitudes as more traditional techniques do, which may impart a detection bias. Stacking similar events clarifies arrival times that are then used to refine the source locations. This approach is being applied to the Oaxaca region of Mexico and southern Cascadia, where lower network density has limited detailed tremor source location analysis.

  2. Low-frequency and common genetic variation in ischemic stroke

    PubMed Central

    Malik, Rainer; Traylor, Matthew; Pulit, Sara L.; Bevan, Steve; Hopewell, Jemma C.; Holliday, Elizabeth G.; Zhao, Wei; Abrantes, Patricia; Amouyel, Philippe; Attia, John R.; Battey, Thomas W.K.; Berger, Klaus; Boncoraglio, Giorgio B.; Chauhan, Ganesh; Cheng, Yu-Ching; Chen, Wei-Min; Clarke, Robert; Cotlarciuc, Ioana; Debette, Stephanie; Falcone, Guido J.; Ferro, Jose M.; Gamble, Dale M.; Ilinca, Andreea; Kittner, Steven J.; Kourkoulis, Christina E.; Lemmens, Robin; Levi, Christopher R.; Lichtner, Peter; Lindgren, Arne; Liu, Jingmin; Meschia, James F.; Mitchell, Braxton D.; Oliveira, Sofia A.; Pera, Joana; Reiner, Alex P.; Rothwell, Peter M.; Sharma, Pankaj; Slowik, Agnieszka; Sudlow, Cathie L.M.; Tatlisumak, Turgut; Thijs, Vincent; Vicente, Astrid M.; Woo, Daniel; Seshadri, Sudha; Saleheen, Danish; Rosand, Jonathan; Markus, Hugh S.; Worrall, Bradford B.

    2016-01-01

    Objective: To investigate the influence of common and low-frequency genetic variants on the risk of ischemic stroke (all IS) and etiologic stroke subtypes. Methods: We meta-analyzed 12 individual genome-wide association studies comprising 10,307 cases and 19,326 controls imputed to the 1000 Genomes (1 KG) phase I reference panel. We selected variants showing the highest degree of association (p < 1E-5) in the discovery phase for replication in Caucasian (13,435 cases and 29,269 controls) and South Asian (2,385 cases and 5,193 controls) samples followed by a transethnic meta-analysis. We further investigated the p value distribution for different bins of allele frequencies for all IS and stroke subtypes. Results: We showed genome-wide significance for 4 loci: ABO for all IS, HDAC9 for large vessel disease (LVD), and both PITX2 and ZFHX3 for cardioembolic stroke (CE). We further refined the association peaks for ABO and PITX2. Analyzing different allele frequency bins, we showed significant enrichment in low-frequency variants (allele frequency <5%) for both LVD and small vessel disease, and an enrichment of higher frequency variants (allele frequency 10% and 30%) for CE (all p < 1E-5). Conclusions: Our findings suggest that the missing heritability in IS subtypes can in part be attributed to low-frequency and rare variants. Larger sample sizes are needed to identify the variants associated with all IS and stroke subtypes. PMID:26935894

  3. 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.

  4. Impact of low-frequency sound on historic structures

    NASA Astrophysics Data System (ADS)

    Sutherland, Louis C.; Horonjeff, Richard D.

    2005-09-01

    In common usage, the term soundscape usually refers to portions of the sound spectrum audible to human observers, and perhaps more broadly other members of the animal kingdom. There is, however, a soundscape regime at the low end of the frequency spectrum (e.g., 10-25 Hz), which is inaudible to humans, where nonindigenous sound energy may cause noise-induced vibrations in structures. Such low frequency components may be of sufficient magnitude to pose damage risk potential to historic structures and cultural resources. Examples include Anasazi cliff and cave dwellings, and pueblo structures of vega type roof construction. Both are susceptible to noise induced vibration from low-frequency sound pressures that excite resonant frequencies in these structures. The initial damage mechanism is usually fatigue cracking. Many mechanisms are subtle, temporally multiphased, and not initially evident to the naked eye. This paper reviews the types of sources posing the greatest potential threat, their low-frequency spectral characteristics, typical structural responses, and the damage risk mechanisms involved. Measured sound and vibration levels, case history studies, and conditions favorable to damage risk are presented. The paper concludes with recommendations for increasing the damage risk knowledge base to better protect these resources.

  5. 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.

  6. Low-frequency sea waves generated by atmospheric convection cells

    NASA Astrophysics Data System (ADS)

    de Jong, M. P. C.; Battjes, J. A.

    2004-01-01

    The atmospheric origin of low-frequency sea waves that cause seiches in the Port of Rotterdam is investigated using hydrological and meteorological observations. These observations, combined with weather charts, show that all significant seiche events coincide with the passage of a low-pressure area and a cold front. Following these front passages, increased wind speed fluctuations occur with periods on the order of 1 hour. The records show that enhanced low-frequency wave energy at sea and the seiche events in the harbor occur more or less simultaneously with these strong wind speed fluctuations. These oscillatory wind speed changes are due to convection cells that arise in an unstable lower atmosphere in the area behind a cold front, where cold air moves over the relatively warm sea surface. It is shown that the moving system of a cold front and trailing convection cells generates forced low-frequency waves at sea that can cause seiche events inside the harbor. The occurrence of such events may be predictable operationally on the basis of a criterion for the difference in temperature between the air in the upper atmosphere and the water at the sea surface.

  7. 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

  8. Theoretical and experimental investigation into structural and fluid motions at low frequencies in water distribution pipes

    NASA Astrophysics Data System (ADS)

    Gao, Yan; Liu, Yuyou

    2017-06-01

    Vibrational energy is transmitted in buried fluid-filled pipes in a variety of wave types. Axisymmetric (n = 0) waves are of practical interest in the application of acoustic techniques for the detection of leaks in underground pipelines. At low frequencies n = 0 waves propagate longitudinally as fluid-dominated (s = 1) and shell-dominated (s = 2) waves. Whilst sensors such as hydrophones and accelerometers are commonly used to detect leaks in water distribution pipes, the mechanism governing the structural and fluid motions is not well documented. In this paper, the low-frequency behaviour of the pipe wall and the contained fluid is investigated. For most practical pipework systems, these two waves are strongly coupled; in this circumstance the ratios of the radial pipe wall displacements along with the internal pressures associated with these two wave types are obtained. Numerical examples show the relative insensitivity of the structural and fluid motions to the s = 2 wave for both metallic and plastic pipes buried in two typical soils. It is also demonstrated that although both acoustic and vibration sensors at the same location provide the identical phase information of the transmitted signals, pressure responses have significantly higher levels than acceleration responses, and thus hydrophones are better suited in a low signal-to-noise ratio (SNR) environment. This is supported by experimental work carried out at a leak detection facility. Additional pressure measurements involved excitation of the fluid and the pipe fitting (hydrant) on a dedicated water pipe. This work demonstrates that the s = 1 wave is mainly responsible for the structural and fluid motions at low frequencies in water distribution pipes as a result of water leakage and direct pipe excitation.

  9. 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.

  10. Very-low-frequency oscillations of cerebral hemodynamics and blood pressure are affected by aging and cognitive load.

    PubMed

    Vermeij, Anouk; Meel-van den Abeelen, Aisha S S; Kessels, Roy P C; van Beek, Arenda H E A; Claassen, Jurgen A H R

    2014-01-15

    Spontaneous slow oscillations occur in cerebral hemodynamics and blood pressure (BP), and may reflect neurogenic, metabolic or myogenic control of the cerebral vasculature. Aging is accompanied by a degeneration of the vascular system, which may have consequences for regional cerebral blood flow and cognitive performance. This degeneration may be reflected in a reduction of spontaneous slow oscillations of cerebral hemodynamics and BP. Therefore, we aimed to establish the dependency of slow oscillations of cerebral hemodynamics and BP on the factors age and cognitive load, by using functional near-infrared spectroscopy (fNIRS). Fourteen healthy young (23-32 years) and 14 healthy older adults (64-78 years) performed a verbal n-back working-memory task. Oxygenated and deoxygenated hemoglobin concentration changes were registered by two fNIRS channels located over left and right prefrontal cortex. BP was measured in the finger by photoplethysmography. We found that very-low-frequency oscillations (0.02-0.07 Hz) and low-frequency oscillations (0.07-0.2 Hz) of cerebral hemodynamics and BP were reduced in the older adults compared to the young during task performance. In young adults, very-low-frequency oscillations of cerebral hemodynamics and BP reduced with increased cognitive load. Cognitive load did not affect low-frequency oscillations of the cerebral hemodynamics and BP. Transfer function analysis indicated that the relationship between BP and cerebral hemodynamic oscillations does not change under influence of age and cognitive load. Our results suggest aging-related changes in the microvasculature such as declined spontaneous activity in microvascular smooth muscle cells and vessel stiffness. Moreover, our results indicate that in addition to local vasoregulatory processes, systemic processes also influence cerebral hemodynamic signals. It is therefore crucial to take the factors age and BP into consideration for the analysis and interpretation of hemodynamic

  11. 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.

  12. Low Frequency Radio Astronomical Antennas for the Lunar Environment

    NASA Astrophysics Data System (ADS)

    Burns, Jack O.; Lazio, J.; ROLSS DALI Teams

    2009-01-01

    Low radio frequencies ( MHz) represent the last of the relatively unexplored wavebands in the electromagnetic spectrum for astrophysics. Such observations are very challenging from the surface of the Earth because of an abundance of human-made radio interference (e.g., FM bands, TV channels) and because of ionospheric refraction. The lunar farside presents a unique opportunity to fully open this cosmic window because of the demonstrated radio-quiet environment. The ultimate science goal of a lunar farside low frequency telescope is to explore a new frontier in cosmology, the so-called Dark Ages. This era occurs between Recombination (at z 1100) when the universe first becomes transparent (producing what we observe today as the CMB) and Reionization when the first stars and galaxies form (at z 10-20). During the Dark Ages, the universe was unlit by any star and the only detectable signal is likely to arise from neutral hydrogen absorption against the CMB (from the collapse of the first structures). Observing this absorption signal would be a powerful probe of fundamental cosmology. During the Dark Ages (z 20 - 150), when the 21-cm (1.4 GHz) neutral hydrogen line is redshifted into the low frequency radio band (10-30 MHz, 10-30 m), the absorption signal has the potential to be the richest of all cosmological data sets. In this poster, we will discuss the opportunities and options for low frequency radio antennas in both lunar orbit and on the lunar surface. We are investigating a novel concept to deploy a large number of low-mass antennas deposited on sheets of polyimide film. We will also describe results of laboratory vacuum testing at U. Colorado on polyimide film cycled between -150 C and 100 C, and exposed to far-ultraviolet light, with conditions like those on the lunar surface.

  13. Mismatch negativity and low frequency oscillations in schizophrenia families.

    PubMed

    Hong, L Elliot; Moran, Lauren V; Du, Xiaoming; O'Donnell, Patricio; Summerfelt, Ann

    2012-10-01

    Theta-alpha range oscillations have been associated with MMN in healthy controls. Our previous studies showed that theta-alpha activities are highly heritable in schizophrenia patients' families. We aimed to test the hypothesis that theta-alpha activities may contribute to MMN in schizophrenia patients and their family members. We compared MMN and single trial oscillations during MMN in 95 patients, 75 first-degree relatives, 87 controls, and 34 community subjects with schizophrenia spectrum personality (SSP) traits. We found that (1) MMN was reduced in patients (p<0.001) and SSP subjects (p=0.047) but not in relatives (p=0.42); (2) there were augmented 1-20 Hz oscillations in patients (p=0.02 to <0.001) during standard and deviant stimuli; (3) theta-alpha (5-12 Hz) oscillations had the strongest correlation to MMN in controls and relatives (ΔR(2)=21.4-23.9%, all p<0.001), while delta (<5 Hz) showed the strongest correlation to MMN in schizophrenia and SSP trait subjects; and, (4) MMN (h(2)=0.56, p=0.002) and theta-alpha (h(2)=0.55, p=0.004) were heritable traits. Low frequency oscillations have a robust relationship with MMN and the relationship appears altered by schizophrenia; and schizophrenia patients showed augmented low frequency activities during the MMN paradigm. The results encourage investigation of low frequency oscillations to elucidate the neurophysiological pathology underlying MMN abnormalities in schizophrenia. Copyright © 2012 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

  14. 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.

  15. Locally resonant periodic structures with low-frequency band gaps

    NASA Astrophysics Data System (ADS)

    Cheng, Zhibao; Shi, Zhifei; Mo, Y. L.; Xiang, Hongjun

    2013-07-01

    Presented in this paper are study results of dispersion relationships of periodic structures composited of concrete and rubber, from which the frequency band gap can be found. Two models with fixed or free boundary conditions are proposed to approximate the bound frequencies of the first band gap. Studies are conducted to investigate the low-frequency and directional frequency band gaps for their application to engineering. The study finds that civil engineering structures can be designed to block harmful waves, such as earthquake disturbance.

  16. Is VHF Fresnel reflectivity due to low frequency buoyancy waves?

    NASA Technical Reports Server (NTRS)

    Vanzandt, T. E.; Vincent, R. A.

    1983-01-01

    VHF radar echoes are greatly enhanced near the zenith relative to other directions. This enhancement must be due to reflection from horizontally stratified laminate of refractive index. The refractivity laminate are due to the displacements of low frequency buoyancy (internal gravity) waves acting on the background vertical gradient of refractivity. VANZANDT (1982) has shown that the observed spectra of mesoscale wind fluctuations in the troposphere and lower stratosphere are modeled by a universal spectrum of buoyancy (internal gravity) waves. Since the observed frequency spectrum is red, the buoyancy wave model of the vertical displacement spectrum is strongly enhanced near the zenith. In other terms, the resulting refractivity irregularities are strongly stratified.

  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. 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.

  19. 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.

  20. Low frequency mechanical modes of viral capsids: an atomistic approach.

    PubMed

    Dykeman, Eric C; Sankey, Otto F

    2008-01-18

    We present a method for the calculation of the low frequency vibrational modes and frequencies of viral capsids, or other large molecules, where the modes are modeled with atomic detail. Extending ideas from electronic structure theory, an energy functional is used to find modes of a classical dynamical matrix below a fixed (pseudo-Fermi) level. The icosahedral satellite tobacco necrosis virus is modeled as an example. We find that atoms around the C5 and C3 axis have small relative displacement while the beta sheet body shows gliding motion.

  1. Sensitivity of the Low Frequency Facility experiment around 10 Hz

    NASA Astrophysics Data System (ADS)

    Di Virgilio, A.; Braccini, S.; Ballardin, G.; Bradaschia, C.; Cella, G.; Cuoco, E.; Dattilo, V.; Ferrante, I.; Fidecaro, F.; Frasconi, F.; Giazotto, A.; Gennai, A.; Holloway, L. H.; La Penna, P.; Losurdo, G.; Paoletti, F.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Porzio, A.; Puppo, P.; Raffaelli, F.; Rapagnani, P.; Ricci, F.; Ricciardi, J.; Solimeno, S.; Stanga, R.; Vetrano, F.; Zhang, Z.

    2004-02-01

    The reduction of thermal noise is a fundamental issue for the improvement of future gravitational wave antennas. The main purpose of the Low Frequency Facility (LFF) is to study pendulum thermal noise in the region of 10 Hz. Data at the LFF has been taking since the beginning of 2003 and has been analyzed in order to thoroughly understand the region around 10 Hz. Above 7 Hz, the displacement noise floor is at the level of 10 -14 m/ Hz, decreasing with frequency approximately as 1/ ν. Seismic noise contamination is not observed above a few Hz.

  2. Angular structure of extragalactic radio sources at low frequencies

    NASA Astrophysics Data System (ADS)

    Brazhenko, A. I.; Koshovy, V. V.; Lozynsky, A. R.; Megn, A. V.; Rashkovsky, S. L.; Shepelev, V. A.

    2005-06-01

    The low frequency VLBI of URAN network operated in the decameter range has been designed in Ukraine to study cosmic radio sources. The network consists of five radio telescopes making up of four interferometers with baselines range from 42 to 913 km with UTR-2 radio telescope operated as the main antenna of the interferometers. The angular resolution of the network amount to 1 arcsec at the highest frequency of the range, and its sensitivity is about 20 Jy. Regular observations of galactic and extragalactic radio sources are performed with the network. Some results of studies are presented here.

  3. 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.

  4. Low-frequency measurements of the CMB spectrum

    SciTech Connect

    Kogut, A.; Bensadoun, M.; Amici, G.D.; Levin, S.; Limon, M.; Smoot, G. Lawrence Berkeley Laboratory, Berkeley, CA Space Sciences Laboratory, Berkeley, CA ); Sironi, G. ); Bersanelli, M.; Bonelli, G. )

    1990-01-15

    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 Calfornia. On average, these measurements suggests 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.

  5. Weak low-frequency electromagnetic oscillations in water.

    PubMed

    Liboff, A R; Poggi, Claudio; Pratesi, Piero

    2017-01-01

    Recent observations of low-frequency electromagnetic oscillations in water suggest an inductive structural component. Accordingly, we assume a helical basis enabling us to model water as an LC tuned oscillator. A proposed tetrahedral structure consisting of three water molecules and one hydronium ion is incorporated into the Boerdijk-Coxeter tetrahelix to form long water chains that are shown to have resonance frequencies consistent with observation. This model also serves to explain separately reported claims of ion cyclotron resonance of hydronium ions, in that the tetrahelix provides a built-in path for helical proton-hopping.

  6. Low-frequency quadrupole impedance of undulators and wigglers

    NASA Astrophysics Data System (ADS)

    Blednykh, A.; Bassi, G.; Hidaka, Y.; Smaluk, V.; Stupakov, G.

    2016-10-01

    An analytical expression of the low-frequency quadrupole impedance for undulators and wigglers is derived and benchmarked against beam-based impedance measurements done at the 3 GeV NSLS-II storage ring. The adopted theoretical model, valid for an arbitrary number of electromagnetic layers with parallel geometry, allows to calculate the quadrupole impedance for arbitrary values of the magnetic permeability μr . In the comparison of the analytical results with the measurements for variable magnet gaps, two limit cases of the permeability have been studied: the case of perfect magnets (μr→∞ ), and the case in which the magnets are fully saturated (μr=1 ).

  7. Low frequency acoustic properties of Posidonia oceanica seagrass leaf blades

    PubMed Central

    Johnson, Jay R.; Venegas, Gabriel R.; Wilson, Preston S.; Hermand, Jean-Pierre

    2017-01-01

    The acoustics of seagrass meadows impacts naval and oceanographic sonar applications. To study this environment, a one-dimensional resonator was used to assess the low-frequency (1–5 kHz) acoustic response of the leaf blades of the Mediterranean seagrass Posidonia oceanica in water. Three separate collections of plants from Crete, Greece, and Sicily, Italy were investigated. A high consistency in effective sound speed was observed within each collection while a strong variability was observed between different collections. Average size, mass, and epiphytic coverage within each collection were quantified, and discoloration and stiffness are discussed qualitatively with respect to the observed acoustic variability. PMID:28618796

  8. Receiving antenna array element with extended bandwidth toward low frequencies

    NASA Astrophysics Data System (ADS)

    Balzovsky, E. V.; Buyanov, Yu I.; Koshelev, V. I.; Nekrasov, E. S.

    2017-08-01

    An ultrawideband antenna based on a short dielectric dipole has been developed to sound dielectric layered media and to search objects including those hidden behind a dielectric barrier. In contrast to the previously presented antennas, the new one has an unbalanced output and contains a built-in balanced-to-unbalanced unit. As a result of optimization of the antenna geometry and topology of active elements, the lower frequency boundary was shifted toward low frequencies. The antenna records short nanosecond pulses with the spectrum ranging from 150 MHz to 2 GHz with small waveform distortions.

  9. Infrasonic and low-frequency insert earphone hearing threshold.

    PubMed

    Kuehler, Robert; Fedtke, Thomas; Hensel, Johannes

    2015-04-01

    Low-frequency and infrasonic pure-tone monaural hearing threshold data down to 2.5 Hz are presented. These measurements were made by means of a newly developed insert-earphone source. The source is able to generate pure-tone sound pressure levels up to 130 dB between 2 and 250 Hz with very low harmonic distortions. Behavioral hearing thresholds were determined in the frequency range from 2.5 to 125 Hz for 18 otologically normal test persons. The median hearing thresholds are comparable to values given in the literature. They are intended for stimulus calibration in subsequent brain imaging investigations.

  10. A new hybrid phononic crystal in low frequencies

    NASA Astrophysics Data System (ADS)

    Zhang, Z.; Han, X. K.

    2016-11-01

    A novel hybrid phononic crystal is designed to obtain wider band gaps in low frequency range. The hybrid phononic crystal consists of rubber slab with periodic holes and plumbum stubs. In comparison with the phononic crystal without periodic holes, the new designed phononic crystal can obtain wider band gaps and better vibration damping characteristics. The wider band gap can be attributed to the interaction of local resonance and Bragg scattering. The controlling of the BG is explained by the strain energy of the hybrid PC and the introduced effective mass. The effects of the geometrical parameters and the shapes of the stubs and holes on the controlling of waves are further studied.

  11. 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.

  12. Possible role of ELF (extremely low frequency) fields in leukemogenesis

    SciTech Connect

    Stevens, R.G.

    1988-12-01

    This report presents a biological rationale for a possible role of ELF (extremely low frequency electric and/or magnetic) fields in the etiology of leukemia. The hypothesis is based on three lines of evidence: ELF fields may increase calcium efflux from cells, the intracellular concentration of oxygen radicals may increase as a result of increased calcium efflux, and certain leukocytes may be at exaggerated risk of oxidative damage resulting from increased calcium efflux because they produce oxygen radicals to do their job. An increase in the concentration of oxygen radicals may increase mutation to DNA and thereby increase risk of transformation. 23 refs.

  13. 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.

  14. 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.

  15. Characteristics of secondary slip fronts associated with slow earthquakes in Cascadia

    NASA Astrophysics Data System (ADS)

    Bletery, Quentin; Thomas, Amanda M.; Hawthorne, Jessica C.; Skarbek, Robert M.; Rempel, Alan W.; Krogstad, Randy D.

    2017-04-01

    We implement an algorithm to automatically detect migrations of low frequency earthquakes at time scales between 30 min and 32 h during the 2003, 2004 and 2005 slow slip events in Cascadia. We interpret these migrations of seismicity as a passive manifestation of secondary slip fronts (SSFs) that propagate faster than the main front. We identify the dominant features of 383 SSFs, including time, location, duration, area, propagation velocity and estimate: their moment, stress drop, slip, and slip rate. We apply the same algorithm to continuous tremor detection in Cascadia between 2009 and 2015 and characterize 693 SSFs at time scales between 4 h and 32 h. We identify - to our knowledge for the first time - numerous 11-22.5 h long SSFs that propagate at velocities intermediate between slow slip events and previously reported SSFs. The systematic detection of SSFs fills a gap between seismically and geodetically detectable slow earthquake processes. Analysis of SSF basic features indicates a wide range of stress drops and slip rates (with medians of 5.8 kPa and 1.1 mm/h) as well as an intriguing relationship between SSF direction and duration that was observed in other contexts and could potentially help discriminate between the different physical models proposed to explain slow slip phenomena.

  16. Long-period dynamic spectrograms of low-frequency interplanetary radio emissions

    NASA Technical Reports Server (NTRS)

    Kurth, W. S.; Gurnett, D. A.; Scarf, F. L.; Poynter, R. L.

    1987-01-01

    Dynamic spectrograms of the low-frequency interplanetary radio emissions as observed by Voyagers 1 and 2 from 1983 through mid-1986 are reported. The radio emissions were observed to be most intense in the latter portion of 1983 at 3 kHz but have also been detected at 2 kHz. The emission has been present almost continuously at either 2 or 3 kHz since late 1983. The spectrograms presented herein show that the phenomenon appears almost identically as observed by the two spacecraft separated by more than 10 AU, at least at the higher frequency. One feature revealed by the dynamic spectrograms which had not been noticed previously is a gradual rise in frequency of the 3-kHz component following the onset of the late 1983 event. These new observations reinforce the conclusion that the low-frequency emissions are freely propagating radio waves, but the two-component spectral structure implies that the previous model of emission at twice the plasma frequency at the inner heliosphere shock is inadequate to fully account for the observations. Either an additional source region or an additional source mechanism is suggested.

  17. A mathematical model of extremely low frequency ocean induced electromagnetic noise

    NASA Astrophysics Data System (ADS)

    Dautta, Manik; Faruque, Rumana Binte; Islam, Rakibul

    2016-07-01

    Magnetic Anomaly Detection (MAD) system uses the principle that ferromagnetic objects disturb the magnetic lines of force of the earth. These lines of force are able to pass through both water and air in similar manners. A MAD system, usually mounted on an aerial vehicle, is thus often employed to confirm the detection and accomplish localization of large ferromagnetic objects submerged in a sea-water environment. However, the total magnetic signal encountered by a MAD system includes contributions from a myriad of low to Extremely Low Frequency (ELF) sources. The goal of the MAD system is to detect small anomaly signals in the midst of these low-frequency interfering signals. Both the Range of Detection (Rd) and the Probability of Detection (Pd) are limited by the ratio of anomaly signal strength to the interfering magnetic noise. In this paper, we report a generic mathematical model to estimate the signal-to-noise ratio or SNR. Since time-variant electro-magnetic signals are affected by conduction losses due to sea-water conductivity and the presence of air-water interface, we employ the general formulation of dipole induced electromagnetic field propagation in stratified media [1]. As a first step we employ a volumetric distribution of isolated elementary magnetic dipoles, each having its own dipole strength and orientation, to estimate the magnetic noise observed by a MAD system. Numerical results are presented for a few realizations out of an ensemble of possible realizations of elementary dipole source distributions.

  18. Unfolding the damping behavior of multilayer graphene membrane in the low-frequency regime.

    PubMed

    Lahiri, Debrupa; Das, Santanu; Choi, Wonbong; Agarwal, Arvind

    2012-05-22

    The damping behavior of few-layered graphene membrane in the low-frequency regime of mechanical loading is investigated in the present study. Damping of graphene has significant applications in micro/nanoscale devices and macroscale dynamic systems for absorbing shock-generated energies. Damping behavior of graphene is experimentally evaluated, for the first time, by dynamic mechanical analysis at the nanoscale with cyclic mechanical loading in the range 0.1-50 μN applied at a frequency range of 10-250 Hz. This study reveals 260% higher damping on graphene membranes than a silicon surface. The damping shows excellent reproducibility and remains steady even after 100,000 cycles. The damping of multilayer graphene membrane, supported on a Si/SiO(2) substrate, shows a strong dependence on the frequency of cyclic loading. The mechanism governing impressive damping of a graphene membrane is elucidated by structural changes such as ripple formation, ripple wave propagation, and z-axis compression. Damping behavior of a graphene membrane in this low-frequency regime is also found to depend on the number of graphene layers and is explained as the interplay between in-plane sp(2) and out-of-plane van der Waals forces. These findings are important for establishing the potential of graphene for applications in macro- to nanoscale structures that require continuous absorption of shock waves without destruction/failure.

  19. Lattice Dynamics at Low Frequency: Resonant and Excess Modes in Amorphous Silicon

    NASA Astrophysics Data System (ADS)

    Feldman, J. L.; Allen, Philip B.; Bickham, S. R.

    1998-03-01

    We study lattice vibrations in amorphous silicon by simulations and exact diagonalizations on finite-size models (216, 1000, and 4096 atoms) built by Wooten using the algorithm of Wooten, Winer, and Weaire. The lowest energy vibrations are at (9.1, 5.4, and 3.4meV) respectively, close to the relevant energy range where ``excess modes'' (``Excess modes'' appear in what is sometimes called the ``Boson peak.'') are found in many glasses. The finite size causes a discrete spectrum rather than the continuous spectrum of a macroscopic sample. Because Q is an approximate quantum number at low frequency, modes tend to bunch into quasi-degenerate groups corresponding to the degeneracies of the small size-quantized Q's. However, approximately 10--20% of low energy modes have frequencies split off from quasi-degenerate groups, and eigenvectors with no good Q, but instead ``quasilocalized'' or ``resonant.'' There is a possible connection with the ``excess vibrations'' and also with anomalously big Grüneisen constants deduced from thermal expansion. Here we report our efforts to extrapolate macroscopic information about low frequency modes. We find a satisfactory fit using an extrapolation which yields only propagating damped acoustic waves with no ``excess modes.'' Therefore we suggest that either amorphous silicon has no excess vibrations or else that excess vibrations are associated with mesoscopic defects such as voids which are absent in our model.

  20. Imaging of the interaction of low frequency electric fields with biological tissues by optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Peña, Adrian F.; Devine, Jack; Doronin, Alexander; Meglinski, Igor

    2014-03-01

    We report the use of conventional Optical Coherence Tomography (OCT) for visualization of propagation of low frequency electric field in soft biological tissues ex vivo. To increase the overall quality of the experimental images an adaptive Wiener filtering technique has been employed. Fourier domain correlation has been subsequently applied to enhance spatial resolution of images of biological tissues influenced by low frequency electric field. Image processing has been performed on Graphics Processing Units (GPUs) utilizing Compute Unified Device Architecture (CUDA) framework in the frequencydomain. The results show that variation in voltage and frequency of the applied electric field relates exponentially to the magnitude of its influence on biological tissue. The magnitude of influence is about twice more for fresh tissue samples in comparison to non-fresh ones. The obtained results suggest that OCT can be used for observation and quantitative evaluation of the electro-kinetic changes in biological tissues under different physiological conditions, functional electrical stimulation, and potentially can be used non-invasively for food quality control.

  1. Effect of low frequency transcutaneous magnetic stimulation on sensory and motor transmission.

    PubMed

    Leung, Albert; Shukla, Shivshil; Lee, Jacquelyn; Metzger-Smith, Valerie; He, Yifan; Chen, Jeffrey; Golshan, Shahrokh

    2015-09-01

    Peripheral nerve injury diminishes fast conducting large myelinated afferent fibers transmission but enhances smaller pain transmitting fibers firing. This aberrant afferent neuronal behavior contributes to development of chronic post-traumatic peripheral neuropathic pain (PTP-NP). Non-invasive dynamic magnetic flux stimulation has been implicated in treating PTP-NP, a condition currently not adequately addressed by other therapies including transcutaneous electrical nerve stimulation (TENS). The current study assessed the effect of low frequency transcutaneous magnetic stimulation (LFTMS) on peripheral sensory thresholds, nerve conduction properties, and TENS induced fast afferent slowing effect as measured by motor and sensory conduction studies in the ulnar nerve. Results indicated sham LFTMS with TENS (Sham + TENS) significantly (P = 0.02 and 0.007, respectively) reduces sensory conduction velocity (CV) and increases sensory onset latency (OL), and motor peak latency (PL) whereas, real LFTMS with TENS (Real + TENS) reverses effects of TENS on sensory CV and OL, and significantly (P = 0.036) increases the sensory PL. LFTMS alone significantly (P < 0.05) elevates sensory PL and onset-to-peak latency. LFTMS appears to reverse TENS slowing effect on fast conducting fibers and casts a selective peripheral modulatory effect on slow conducting pain afferent fibers.

  2. Low Frequency Seismo-Acoustic Propagation in a Sloping Ocean Environment: Measured Results and Numerical Predictions

    DTIC Science & Technology

    1987-11-01

    15407 - 1525,1 m/s Cp = 1900 m/ s , op = 0,2, p= 1.8 L . Cp = 2340 m/ s . Op = 02, p= 1,9 Cp = 3000 m/ s . Op = 02, P = 2,2 Cj = 1500 m/s, oj = 02 Cp...4300 m/ s , op = 005, p = 24 Cc = 2150 m/s, o^ = 01 20 Figure 5. Geoacoustic input parameters for SAFARI model. 0.0 10.0 30.0 30.0 RANGE IKM

  3. ELF (Extremely Low Frequency) PVS (Propagation Validation System) Field Strength Measurements, January 1977.

    DTIC Science & Technology

    1983-03-21

    in the North-Atlantic/Norwegian- Sea area at a range of approximately 5 Mm from WTF. Signal-strength data (both amplitude and relative phase) were...measured on all three submarines is plotted in figure 1* versus GMT. Previous January effective-noise measure- ments in the Norwegian- Sea area (Tromso...Inc., 404 Tasman Dr. Sunnyvale, CA 94086 1 Dr. Eivind Trane, NDRE, P.O. Box 25, 2007 Kjeller, Norway 1 RCA David Sarnoff Research Center (K. Powers

  4. ELF (Extremely Low Frequency) PVS (Propagation Validation System) Field Strength Measurements, March 1977.

    DTIC Science & Technology

    1983-02-03

    field-strength measurements were taken in Connecticut and aboard three submarines located in the North-Atlantic/Norwegian- Sea area. The daytime...Develco, Inc., 404 Tasman Dr. Sunnyvale, CA 94086 Dr. Eivind Trane, NDRE, P.O. Box 25, 2007 Kjeller, Norway RCA David Sarnoff Research Center (K

  5. Low-Frequency Sound Propagation in a Fluctuating Infinite Ocean. II

    DTIC Science & Technology

    1975-06-01

    Darre 11 Director, Undersea Warfare Technology Office of Naval Research (Code 412) Arlington, Virginia 22217 Dr. Roger F. Da alien...D. A. Rogers (NSP) SP2018 Department of the Navy Washington, D.C. 20390 32 Mr. Benjamin Rosenberg (OHNAV) Room 4B513 The Pentagon

  6. 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.

  7. Teleseismic search for slow precursors to large earthquakes.

    PubMed

    Ihmlé, P F; Jordan, T H

    1994-12-02

    Some large earthquakes display low-frequency seismic anomalies that are best explained by episodes of slow, smooth deformation immediately before their high-frequency origin times. Analysis of the low-frequency spectra of 107 shallow-focus earthquakes revealed 20 events that had slow precursors (95 percent confidence level); 19 were slow earthquakes associated with the ocean ridge-transform system, and 1 was a slow earthquake on an intracontinental transform fault in the East African Rift system. These anomalous earthquakes appear to be compound events, each comprising one or more ordinary (fast) ruptures in the shallow seismogenic zone initiated by a precursory slow event in the adjacent or subjacent lithosphere.

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

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

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

  9. 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.

  10. 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.

  11. Excitation of low frequency waves by streaming ions via anomalous cyclotron resonance

    NASA Technical Reports Server (NTRS)

    Wu, C. S.; Dillenburg, D.; Gaffey, J. D., Jr.; Ziebell, L. F.; Goedert, J.; Freund, H. P.

    1978-01-01

    The effect of a small population of streaming ions on low-frequency waves with frequencies below the ion cyclotron frequency is analyzed for three modes of interest: Alfven waves, magnetosonic waves, and ion-cyclotron waves. The instability mechanism is the anomalous cyclotron resonance of the waves with the streaming ions. Conditions for excitation of the three types of waves are derived and expressions for the growth rates are obtained. Excitation of Alfven waves is possible even if the ratio of the densities of the streaming ions to the thermal ions is very small. For magnetosonic waves, excitation can easily occur if waves are propagating parallel or nearly parallel to the ambient magnetic field. As for ion-cyclotron waves, it is found that for the ion-whistler branch the excitation is suppressed over a broader range of wave frequencies than for the fast magnetosonic branch.

  12. Variable low-frequency radio emission of the solar system and galactic objects

    NASA Astrophysics Data System (ADS)

    Konovalenko, Alexander; Kolyadin, Vladimir; Rucker, Helmut; Zakharenko, Vyacheslav; Zarka, Philippe; Griessmeier, Jean-M.; Denis, Loran; Melnik, Valentin; Litvinenko, Galina; Zaitsev, Valerij; Falkovich, Igor; Ulyanov, Oleg; Sidorchuk, Mikhail; Stepkin, Sergej; Stanislavskij, Alexander; Kalinichenko, Nikolaj; Boiko, Nastja; Vasiljiva, Iaroslavna; Mukha, Dmytro; Koval, Artem

    2013-04-01

    There are many physical processes and propagation effects for the producing the time variable radio emission just at the low frequencies (at the decameter wavelength). The study of this radio emission is the important part of the modern radio astronomy. Strong progress in the development of the radio telescopes, methods and instrumentation allowed to start the corresponding investigations at new quality and quantity levels. It related to the implementation of the world largest UTR-2 radio telescope (effective area is more than 100 000 sq.m) more high sensitive at frequencies less than 30 MHz. During last years many new observations were carried out with this radio telescope and many new effects have been detected for the Sun, planets, interplanetary medium, exoplanets as well as various kinds of the stars.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

    Barklow, William E.

    2004-05-01

    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.''

  15. 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.''

  16. Low-frequency Raman scattering from silicon nanostructures

    NASA Astrophysics Data System (ADS)

    Shukla, A. K.; Kumar, Vivek

    2011-09-01

    Low-frequency Raman scattering due to acoustic phonons is studied for silicon nanostructures. The lineshapes of the first-order Raman active modes exhibit asymmetry. A tail is observed toward low frequency and high frequency for the optic mode and acoustic mode, respectively. The Raman lineshapes of these modes are determined by a Gaussian envelope function convoluted with the vibrational density of states. The observed blueshift of the acoustic mode with reducing size of the nanostructures can be explained by the relaxation of the wavevector selection rule (q = 0), which is used in the phonon confinement model for positive-slope (dω/dq > 0) phonon dispersion. Because the acoustic and optical phonon branches have high positive and moderate negative slopes, respectively, around the "Gamma"-point in the phonon dispersion, a larger Raman shift of the acoustic mode to a higher frequency is observed in comparison with the shift to a lower frequency of the optic mode for a given nanostructure size.

  17. Low frequency sonophoresis mediated transdermal and intradermal delivery of ketoprofen.

    PubMed

    Herwadkar, Anushree; Sachdeva, Vishal; Taylor, Leslie F; Silver, Herb; Banga, Ajay K

    2012-02-28

    The objective of this study was to test low frequency sonophoresis at 20 kHz for delivery of ketoprofen into and across the skin. Permeation studies were carried out in vitro on excised hairless rat skin over a period of 24h using Franz diffusion cells after which, skin samples were subjected to skin extraction to quantify the amount of drug present in skin. Parameters like ultrasound application time, duty cycle coupling medium and distance of ultrasound horn from skin were optimized. Transepidermal water loss (TEWL) was measured to indicate the extent of barrier disruption following sonophoresis. Confocal microscopy was used to visualize dye penetration through sonophoresis treated skin. Application of ultrasound significantly enhanced permeation of ketoprofen from 74.87 ± 5.27 μg/cm(2) for passive delivery to 491.37 ± 48.78 μg/cm(2) for sonophoresis. Drug levels in skin layers increased from 34.69 ± 7.25 μg following passive permeation to 212.62 ± 45.69 μg following sonophoresis. TEWL increased from 31.6 ± 0.02 (passive) to 69.5 ± 12.60 (sonophoresis) indicating disruption of barrier properties. Confocal microscopy images depicted enhanced dye penetration through sonophoresis treated skin confirming barrier disruption. Low frequency sonophoresis with optimized ultrasound parameters can be effectively used to actively enhance transdermal and topical delivery of ketoprofen.

  18. Functional subdivisions in low-frequency primary auditory cortex (AI).

    PubMed

    Wallace, M N; Palmer, A R

    2009-04-01

    We wished to test the hypothesis that there are modules in low-frequency AI that can be identified by their responsiveness to communication calls or particular regions of space. Units were recorded in anaesthetised guinea pig AI and stimulated with conspecific vocalizations and a virtual motion stimulus (binaural beats) presented via a closed sound system. Recording tracks were mainly oriented orthogonally to the cortical surface. Some of these contained units that were all time-locked to the structure of the chutter call (14/22 tracks) and/or the purr call (12/22 tracks) and/or that had a preference for stimuli from a particular region of space (8/20 tracks with four contralateral, two ipsilateral and two midline), or where there was a strong asymmetry in the response to beats of different direction (two tracks). We conclude that about half of low-frequency AI is organized into modules that are consistent with separate "what" and "where" pathways.

  19. Low frequency vocalizations attributed to sei whales (Balaenoptera borealis).

    PubMed

    Baumgartner, Mark F; Van Parijs, Sofie M; Wenzel, Frederick W; Tremblay, Christopher J; Carter Esch, H; Warde, Ann M

    2008-08-01

    Low frequency (<100 Hz) downsweep vocalizations were repeatedly recorded from ocean gliders east of Cape Cod, MA in May 2005. To identify the species responsible for this call, arrays of acoustic recorders were deployed in this same area during 2006 and 2007. 70 h of collocated visual observations at the center of each array were used to compare the localized occurrence of this call to the occurrence of three baleen whale species: right, humpback, and sei whales. The low frequency call was significantly associated only with the occurrence of sei whales. On average, the call swept from 82 to 34 Hz over 1.4 s and was most often produced as a single call, although pairs and (more rarely) triplets were occasionally detected. Individual calls comprising the pairs were localized to within tens of meters of one another and were more similar to one another than to contemporaneous calls by other whales, suggesting that paired calls may be produced by the same animal. A synthetic kernel was developed to facilitate automatic detection of this call using spectrogram-correlation methods. The optimal kernel missed 14% of calls, and of all the calls that were automatically detected, 15% were false positives.

  20. 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.

  1. Low-Frequency Gravitational Wave Searches Using Spacecraft Doppler Tracking.

    PubMed

    Armstrong, J W

    2006-01-01

    This paper discusses spacecraft Doppler tracking, the current-generation detector technology used in the low-frequency (∼millihertz) gravitational wave band. In the Doppler method the earth and a distant spacecraft act as free test masses with a ground-based precision Doppler tracking system continuously monitoring the earth-spacecraft relative dimensionless velocity 2Δv/c = Δν/ν0, where Δν is the Doppler shift and ν0 is the radio link carrier frequency. A gravitational wave having strain amplitude h incident on the earth-spacecraft system causes perturbations of order h in the time series of Δν/ν0. Unlike other detectors, the ∼ 1-10 AU earth-spacecraft separation makes the detector large compared with millihertz-band gravitational wavelengths, and thus times-of-flight of signals and radio waves through the apparatus are important. A burst signal, for example, is time-resolved into a characteristic signature: three discrete events in the Doppler time series. I discuss here the principles of operation of this detector (emphasizing transfer functions of gravitational wave signals and the principal noises to the Doppler time series), some data analysis techniques, experiments to date, and illustrations of sensitivity and current detector performance. I conclude with a discussion of how gravitational wave sensitivity can be improved in the low-frequency band.

  2. Low-frequency gravitational-wave science frontiers

    NASA Astrophysics Data System (ADS)

    Hughes, Scott

    2017-01-01

    With LIGO detecting stellar mass black holes and (soon) other stellar mass compact objects, and with LISA Pathfinder demonstrating important elements of the technology needed to fly a gravitational-wave antenna in space, the case for a low-frequency, space-based gravitational-wave detector - LISA - is stronger than ever. In this talk, I will survey the landscape of low-frequency gravitational-wave astronomy. The LISA frequency band from afew ×10-5 Hz to about 1 Hz is one which is rich with known sources whose measurement will enable new astronomical and physical measurements of important systems. It is also a band with great potential discovery space. In this talk, I will survey the known knowns and known unknowns in the LISA band, describing the frontiers that we can study in advance of the mission, and the frontiers that LISA measurements will unveil. I will also talk about the possible unknown unknowns where surprising discoveries may lurk.

  3. Low-frequency electromagnetic technique for nondestructive evaluation

    NASA Astrophysics Data System (ADS)

    Dalichaouch, Yacine; Singsaas, Alan L.; Putris, Firas; Perry, Alexander R.; Czipott, Peter V.

    2000-05-01

    We have developed a low frequency electromagnetic technique using sensitive room temperature magnetoresistive (MR) sensors for a variety of nondestructive evaluation (NDE) applications. These applications include the NDE of medical implants and aircraft structures, the detection of cracks and corrosion in metals, the detection of ferromagnetic foreign objects in the eye and the brain, and the noninvasive determination of iron content in the liver. Our technique consists of applying a low frequency ac magnetic field to the sample and detecting the sample response. The low excitation frequency enables us to probe deep into metal structures; the sensitivity of the MR sensor allows us to detect weak responses from the sample without applying too large an excitation field, particularly in the case of human tissue. The MR sensors are small and relatively inexpensive compared to other sensitive magnetic field sensors such as fluxgates and superconducting quantum interference devices or SQUIDs; hence the resulting NDE instrument will be compact and cost-efficient, enabling its commercialization for practical applications. In this paper, we focus primarily on NDE of orthopedic implants.

  4. 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.

  5. Wideband, low-frequency springless vibration energy harvesters: part I

    NASA Astrophysics Data System (ADS)

    Bendame, Mohamed; Abdel-Rahman, Eihab; Soliman, Mostafa

    2016-11-01

    We present a novel architecture for wideband and low-frequency vibration energy harvesting (VEH). Springless vibration energy harvesters (SVEH) employ impact oscillators as energy harvesting elements. A seismic mass moves along a linear guide limited by stoppers at both ends of the track. An electromagnetic transducer converts the kinetic energy captured by the mass into electrical energy. Experiments using prototypes of the horizontal SVEH demonstrated low frequency harvesting (<20 Hz), wideband harvesting (up to 6.0 Hz), and an optimal rectified output power of P  =  12 mW for a base acceleration amplitude of 0.5 g. A model of the electromagnetic SVEH was developed and validated experimentally. A figure of merit was defined to quantify realizable output power in linear and nonlinear VEHs. Comparison using this figure of merit shows that electromagnetic SVEHs outperform their linear counterparts by 92%-232% for acceleration amplitudes in the range of 0.4-0.6 g.

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

    PubMed Central

    Olson, P.

    2007-01-01

    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

  7. Passive Super-Low Frequency electromagnetic prospecting technique

    NASA Astrophysics Data System (ADS)

    Wang, Nan; Zhao, Shanshan; Hui, Jian; Qin, Qiming

    2017-03-01

    The Super-Low Frequency (SLF) electromagnetic prospecting technique, adopted as a non-imaging remote sensing tool for depth sounding, is systematically proposed for subsurface geological survey. In this paper, we propose and theoretically illustrate natural source magnetic amplitudes as SLF responses for the first step. In order to directly calculate multi-dimensional theoretical SLF responses, modeling algorithms were developed and evaluated using the finite difference method. The theoretical results of three-dimensional (3-D) models show that the average normalized SLF magnetic amplitude responses were numerically stable and appropriate for practical interpretation. To explore the depth resolution, three-layer models were configured. The modeling results prove that the SLF technique is more sensitive to conductive objective layers than high resistive ones, with the SLF responses of conductive objective layers obviously showing uprising amplitudes in the low frequency range. Afterwards, we proposed an improved Frequency-Depth transformation based on Bostick inversion to realize the depth sounding by empirically adjusting two parameters. The SLF technique has already been successfully applied in geothermal exploration and coalbed methane (CBM) reservoir interpretation, which demonstrates that the proposed methodology is effective in revealing low resistive distributions. Furthermore, it siginificantly contributes to reservoir identification with electromagnetic radiation anomaly extraction. Meanwhile, the SLF interpretation results are in accordance with dynamic production status of CBM reservoirs, which means it could provide an economical, convenient and promising method for exploring and monitoring subsurface geo-objects.

  8. 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.

  9. The low frequency vibrational modes of green fluorescent proteins

    NASA Astrophysics Data System (ADS)

    Tozzini, V.; Bizzarri, A. R.; Pellegrini, V.; Nifosı̀, R.; Giannozzi, P.; Iuliano, A.; Cannistraro, S.; Beltram, F.

    2003-02-01

    We report the observation and analysis of the low frequency vibrational modes of green fluorescent proteins (GFPs). Our study exploits the surface enhanced Raman scattering technique, which allowed the analysis of the vibrational modes of the proteins down to 300 cm -1. Here we present results on two GFP mutants, namely S65T/F64L GFP (EGFP) and S65T/F64L/T203Y GFP (E 2GFP). These particularly bright mutants display almost inverted population ratio of anionic (B) to neutral (A) forms of the chromophore. By comparing the vibrational spectrum of the proteins with that of a synthetic model chromophore in solution and with the aid of first principle calculations based on density functional theory, we identify the Raman active bands in this region of frequencies. A dominant collective mode at 720 cm -1 is found and assigned to a collective planar deformation of the chromophore. Low frequency vibrational modes belonging specifically to A and/or B structural configurations are also identified. This work demonstrates the possibility of monitoring the structural sub-states of GFPs through vibrational spectroscopy in a range of frequencies where collective modes peculiar of the double ring structure of the chromophore lie.

  10. 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.

  11. Sensitive ultrasonic vibrometer for very low frequency applications.

    PubMed

    Cretin, B; Vairac, P; Jachez, N; Pergaud, J

    2007-08-01

    Ultrasonic measurement of distance is a well-known low cost method but only a few vibrometers have been developed because sensitivity, spatial resolution, and bandwidth are not high or wide enough for standard laboratory applications. Nevertheless, compared to optical vibrometers, two interesting properties should be considered: very low frequency noise (0.1 Hz to 1 kHz) is reduced and the long wavelength enables rough surfaces to be investigated. Moreover, the ultrasonic probe is a differential sensor, without being a mechanical load for the vibrating structure as usual accelerometers based on contacting transducers are. The main specificity of the presented probe is its ultralow noise electronics including a 3/2 order phase locked loop which extracts the phase modulation related to the amplitude of the detected vibration. This article presents the main useful physical aspects and details of the actual probe. The given application is the measurement of the vibration of an isolated optical bench excited at very low frequency with an electromagnetic transducer.

  12. 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.

  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. 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.

  15. 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.

  16. On Corner Frequencies, Attenuation and Low-Frequency Earthquakes

    NASA Astrophysics Data System (ADS)

    Bostock, M. G.; Thomas, A.; Rubin, A. M.; Christensen, N. I.

    2016-12-01

    Characterization of earthquake sources is often performed by parametric modelling of particle displacement seismograms in the log-log spectral domain where the low-frequency, horizontal asymptote yields seismic moment and the intersection of low- and high-frequency asymptotes defines corner frequency, a measure of rupture duration from which source dimension and stress drop can be inferred. The latter definition of corner frequency, though practical and in widespread use, is less convenient for analytic purposes. We employ an alternate definition of corner frequency in the context of standard parametric models as the frequency at which the particle velocity spectrum attains its maximum, to examine the effect of attenuation in biassing corner frequency measurements. This approach indicates that, for a given path and attenuation model, there exists a maximum ``saturation'' frequency that can be observed, as true corner frequency tends to infinity. Equivalently, one may set a minimum bound on path averaged Q from an observed apparent corner frequency. We apply these relations to deep crustal and intraplate seismicity beneath Vancouver Island to estimate bulk crustal attenuation parameters that are subsequently used to correct apparent corner frequency measurements of low frequency earthquakes reported in a previous study. The attenuation bias due to bulk crustal structure is shown to be small, with negligible effect on the principal conclusions of that study. However, evidence for high P-to-S LFE corner frequency ratios raises the possibility that strong, localized, near-source attenuation accompanying high pore-fluid pressures governs the peculiar spectral properties of LFEs.

  17. 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.

  18. 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

  19. 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.

  20. 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

  1. INTERACTION OF LASER RADIATION WITH MATTER: Generation of a low-frequency wave by an optical discharge moving in a gas at a subsonic speed

    NASA Astrophysics Data System (ADS)

    Tishchenko, V. N.

    2003-09-01

    A pulsating optical discharge moving in air at a subsonic speed (~250 — 300 m s-1) and creating in front of it a high-intensity low-frequency wave propagating in the same direction is considered. The range of dimensionless parameters in which this effect is manifested is determined.

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

    NASA Astrophysics Data System (ADS)

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

    2010-08-01

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

  3. 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

  4. 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.

  5. 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.

  6. Biophysical characterization of low-frequency ultrasound interaction with dental pulp stem cells

    PubMed Central

    2013-01-01

    Background Low-intensity ultrasound is considered an effective non-invasive therapy to stimulate hard tissue repair, in particular to accelerate delayed non-union bone fracture healing. More recently, ultrasound has been proposed as a therapeutic tool to repair and regenerate dental tissues. Our recent work suggested that low-frequency kilohertz-range ultrasound is able to interact with dental pulp cells which could have potential to stimulate dentine reparative processes and hence promote the viability and longevity of teeth. Methods In this study, the biophysical characteristics of low-frequency ultrasound transmission through teeth towards the dental pulp were explored. We conducted cell culture studies using an odontoblast-like/dental pulp cell line, MDPC-23. Half of the samples underwent ultrasound exposure while the other half underwent ‘sham treatment’ where the transducer was submerged into the medium but no ultrasound was generated. Ultrasound was applied directly to the cell cultures using a therapeutic ultrasound device at a frequency of 45 kHz with intensity settings of 10, 25 and 75 mW/cm2 for 5 min. Following ultrasound treatment, the odontoblast-like cells were detached from the culture using a 0.25% Trypsin/EDTA solution, and viable cell numbers were counted. Two-dimensional tooth models based on μ-CT 2D images of the teeth were analyzed using COMSOL as the finite element analysis platform. This was used to confirm experimental results and to demonstrate the potential theory that with the correct combination of frequency and intensity, a tooth can be repaired using small doses of ultrasound. Frequencies in the 30 kHz–1 MHz range were analyzed. For each frequency, pressure/intensity plots provided information on how the intensity changes at each point throughout the propagation path. Spatial peak temporal average (SPTA) intensity was calculated and related to existing optimal spatial average temporal average (SATA) intensity deemed effective

  7. 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.

  8. The Noisiness of Low Frequency Bands of Noise

    NASA Technical Reports Server (NTRS)

    Lawton, B. W.

    1975-01-01

    The relative noisiness of low frequency 1/3-octave bands of noise was examined. The frequency range investigated was bounded by the bands centered at 25 and 200 Hz, with intensities ranging from 50 to 95 db (SPL). Thirty-two subjects used a method of adjustment technique, producing comparison band intensities as noisy as 100 and 200 Hz standard bands at 60 and 72 db. The work resulted in contours of equal noisiness for 1/3-octave bands, ranging in intensity from approximately 58 to 86 db (SPL). These contours were compared with the standard equal noisiness contours; in the region of overlap, between 50 and 200 Hz, the agreement was good.

  9. Planck 2015 results: II. Low Frequency Instrument data processings

    DOE PAGES

    Ade, P. A. R.; Aghanim, N.; Ashdown, M.; ...

    2016-09-20

    In this paper, 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. Finally, we refer to other relatedmore » papers where more detailed descriptions of the LFI data processing pipeline may be found if needed.« less

  10. Low Frequency NQR using Double Contact Cross-relaxation

    NASA Astrophysics Data System (ADS)

    Stephenson, David; Smith, John A. S.

    2000-02-01

    A cross-relaxation technique is described which involves two spin contacts per double reso-nance cycle. The result is an improvement in signal to noise ratio particularly at low frequencies. Experimental spectra and analyses are presented: 14N in ammonium sulphate showing that the tech-nique gives essentially the same information as previous studies; 14N in ammonium dichromate determining e2Qq/h as (76±3) kHz and η = 0.84±.04; 7Li in lithium acetylacetonate for which the spectrum (corrected for Zeeman distortion) yields e2Qq/h = (152 ±5) kHz and η=.5 ±.2. Calculated spectra are presented to demonstrate the η dependence of the line shapes for 7Li.

  11. 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.

  12. Low frequency/high sensitivity triaxial monolithic sensor

    NASA Astrophysics Data System (ADS)

    Acernese, F.; Canonico, R.; De Rosa, R.; Giordano, G.; Romano, R.; Barone, F.

    2013-04-01

    This paper describes a new mechanical implementation of a triaxial sensor, configurable as seismometer and/or as accelerometer, consisting of three one-dimensional monolithic FP sensors, suitably geometrically positioned. The triaxial sensor is, therefore, compact, light, scalable, tunable instrument (frequency < 100 mHz with large band (10-7 Hz - 10 Hz), high quality factor (Q < 1500 in air) with good immunity to environmental noises, guaranteed by an integrated laser optical readout. The measured sensitivity curve is in very good agreement with the theoretical ones (10-12m/√Hz) in the band (0.1 ÷ 10Hz). Typical applications are in the field of earthquake engineering, geophysics, civil engineering and in all applications requiring large band-low frequency performances coupled with high sensitivities.

  13. Very low frequency/high sensitivity triaxial monolithic inertial sensor

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    This paper describes a new mechanical implementation of a triaxial sensor, configurable as seismometer and/or as accelerometer, consisting of three one-dimensional monolithic FP sensors, suitably geometrically positioned. The triaxial sensor is, therefore, compact, light, scalable, tunable instrument (frequency < 100mHz), with large band (10-7 Hz - 10Hz), high quality factor (Q > 2500 in air) with good immunity to environmental noises, guaranteed by an integrated laser optical readout. The measured sensitivity curve is in very good agreement with the theoretical ones (10-12m/√Hz) in the band (0.1 ÷ 10Hz). Typical applications are in the field of earthquake engineering, geophysics, civil engineering and in all applications requiring large band-low frequency performances coupled with high sensitivities.

  14. Low frequency/high sensitivity triaxial monolithic inertial sensor

    NASA Astrophysics Data System (ADS)

    Acernese, F.; De Rosa, R.; Giordano, G.; Romano, Rocco; Barone, F.

    2013-10-01

    This paper describes a new mechanical implementation of a triaxial sensor, configurable as seismometer and/or as accelerometer, consisting of three one-dimensional monolithic FP sensors, suitably geometrically positioned. The triaxial sensor is, therefore, compact, light, scalable, tunable instrument (frequency < 100mHz), with large band (10-7 Hz - 10Hz), high quality factor (Q < 2500 in air) with good immunity to environmental noises, guaranteed by an integrated laser optical readout. The measured sensitivity curve is in very good agreement with the theoretical ones (10-12m/pHz) in the band (0.1 ÷ 10Hz). Typical applications are in the field of earthquake engineering, geophysics, civil engineering and in all applications requiring large band-low frequency performances coupled with high sensitivities.

  15. Raman spectra of ammonia borane: low frequency lattice modes.

    PubMed

    Ziparo, C; Colognesi, D; Giannasi, A; Zoppi, M

    2012-09-06

    We have measured the Raman spectrum of ammonia borane at low temperature (T = 15 K) and across the orthorhombic-to-tetragonal phase transition at T = 225 K. A comprehensive study of the low frequency lattice modes using Raman spectroscopy has been carried out. Data analysis has been complemented by a density functional theory calculation of which the results have been used for a detailed assignment of the Raman active modes. The analysis of the spectroscopic measurements taken across the phase transition seems to be consistent with the increasing orientational disorder of the molecular components and seems to be compatible with the equalization of the a and b lattice constants characteristic of the tetragonal phase.

  16. Low-Frequency Waves in a Hall-effect Discharge

    NASA Astrophysics Data System (ADS)

    Gascon, Nicolas; Cappelli, Mark

    2001-10-01

    The growth and dispersion of low-frequency (below 200kHz) waves in a Hall-effect coaxial discharge is presented. These low-pressure, cross-field discharges are being developed for use as ion thrusters for space propulsion, and are well known for exhibiting many different kinds of transient phenomena, some of them suspected to contribute to the observed anomalous cross-field electron conductivity. In the studies reported here, multiple electrostatic probes located at distributed positions along the azimuth and axis of the discharge are used to detect correlated plasma density fluctuations. These fluctuations are shown to be associated primarily with ionization processes, through a comparison to a multi-fluid linear stability analysis. Using both conditional sampling, and wavelet analysis of the multiple probe signals, we show that the behavior of the ionization instabilities depend strongly on the position and operating conditions in the discharge.

  17. Low-frequency spectroscopic analysis of monomeric and fibrillar lysozyme.

    PubMed

    Zakaria, Hidayatul A; Fischer, Bernd M; Bradley, Andrew P; Jones, Inke; Abbott, Derek; Middelberg, Anton P J; Falconer, Robert J

    2011-03-01

    Terahertz time-domain spectroscopy (THz-TDS) and Fourier transform infrared (FT-IR) spectroscopy were used to generate far-infrared and low-frequency spectral measurements of monomeric lysozyme and lysozyme fibrils. The formation of lysozyme fibrils was verified by the Thioflavin T assay and transmission electron microscopy (TEM). It was evident in the FT-IR spectra that between 150 and 350 cm(-1) the two spectra diverge, with the lysozyme fibrils showing higher absorbance intensity than the monomeric form. The broad absorption phenomenon is likely due to light scattered from the fibrillar architecture of lysozyme fibrils as supported by simulation of Rayleigh light scattering. The lack of discrete phonon-like peaks suggest that far-infrared spectroscopy cannot detect vibrational modes between the highly ordered hydrogen-bonded beta-pleated sheets of the lysozyme subunit.

  18. 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.

  19. The Signal Processing Firmware for the Low Frequency Aperture Array

    NASA Astrophysics Data System (ADS)

    Comoretto, Gianni; Chiello, Riccardo; Roberts, Matt; Halsall, Rob; Adami, Kristian Zarb; Alderighi, Monica; Aminaei, Amin; Baker, Jeremy; Belli, Carolina; Chiarucci, Simone; D’Angelo, Sergio; De Marco, Andrea; Mura, Gabriele Dalle; Magro, Alessio; Mattana, Andrea; Monari, Jader; Naldi, Giovanni; Pastore, Sandro; Perini, Federico; Poloni, Marco; Pupillo, Giuseppe; Rusticelli, Simone; Schiaffino, Marco; Schillirò, Francesco; Zaccaro, Emanuele

    The signal processing firmware that has been developed for the Low Frequency Aperture Array component of the Square Kilometre Array (SKA) is described. The firmware is implemented on a dual FPGA board, that is capable of processing the streams from 16 dual polarization antennas. Data processing includes channelization of the sampled data for each antenna, correction for instrumental response and for geometric delays and formation of one or more beams by combining the aligned streams. The channelizer uses an oversampling polyphase filterbank architecture, allowing a frequency continuous processing of the input signal without discontinuities between spectral channels. Each board processes the streams from 16 antennas, as part of larger beamforming system, linked by standard Ethernet interconnections. These are envisaged to be 8192 of these signal processing platforms in the first phase of the SKA so particular attention has been devoted to ensure the design is low cost and low power.

  20. 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.

  1. A Low Frequency FBG Accelerometer with Symmetrical Bended Spring Plates

    PubMed Central

    Liu, Fufei; Dai, Yutang; Karanja, Joseph Muna; Yang, Minghong

    2017-01-01

    To meet the requirements for low-frequency vibration monitoring, a new type of FBG (fiber Bragg grating) accelerometer with a bended spring plate is proposed. Two symmetrical bended spring plates are used as elastic elements, which drive the FBG to produce axial strains equal in magnitude but opposite in direction when exciting vibrations exist, leading to doubling the wavelength shift of the FBG. The mechanics model and a numerical method are presented in this paper, with which the influence of the structural parameters on the sensitivity and the eigenfrequency are discussed. The test results show that the sensitivity of the accelerometer is more than 1000 pm/g when the frequency is within the 0.7–20 Hz range. PMID:28117740

  2. Moving toward low frequencies active vibration control with inertial actuators

    NASA Astrophysics Data System (ADS)

    Cinquemani, S.; Costa, A.; Resta, F.

    2017-04-01

    In applications of vibration suppression, control forces ideally act on the structure increasing its damping. While the frequency response of the structure is guaranteed to have a positive real part under ideal conditions, in practice a stability limit exists when inertial actuators are used. In this case the system response is no longer guaranteed to be positive real and so the control system may become unstable at high gains. Moreover, traditional approaches suggest the use of inertial actuators only if its natural frequency is well below the natural frequency of the structure, thus preventing their use at low frequencies. This paper proposes an interesting technique to enlarge the operational range to lower frequencies and to allow the use of inertial actuators. The approach is numerically tested and experimentally validated on a test rig.

  3. Robust Audio Watermarking by Using Low-Frequency Histogram

    NASA Astrophysics Data System (ADS)

    Xiang, Shijun

    In continuation to earlier work where the problem of time-scale modification (TSM) has been studied [1] by modifying the shape of audio time domain histogram, here we consider the additional ingredient of resisting additive noise-like operations, such as Gaussian noise, lossy compression and low-pass filtering. In other words, we study the problem of the watermark against both TSM and additive noises. To this end, in this paper we extract the histogram from a Gaussian-filtered low-frequency component for audio watermarking. The watermark is inserted by shaping the histogram in a way that the use of two consecutive bins as a group is exploited for hiding a bit by reassigning their population. The watermarked signals are perceptibly similar to the original one. Comparing with the previous time-domain watermarking scheme [1], the proposed watermarking method is more robust against additive noise, MP3 compression, low-pass filtering, etc.

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

    NASA Astrophysics Data System (ADS)

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

    1984-12-01

    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.

  5. 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.

  6. Multimode guidance project low frequency ECM simulator: Hardware description

    NASA Astrophysics Data System (ADS)

    Kaye, H. M.

    1982-10-01

    The Multimode Guidance(MMG) Project, part of the Army/Navy Area Defense SAM Technology Prototyping Program, was established to conduct a feasibility demonstration of multimode guidance concepts. Prototype guidance units for advanced, long range missiles are being built and tested under MMG Project sponsorship. The Johns Hopkins University Applied Physics Laboratory has been designated as Government Agent for countermeasures for this project. In support of this effort, a family of computer-controlled ECM simulators is being developed for validation of contractor's multimode guidance prototype designs. The design of the Low Frequency ECM Simulator is documented in two volumes. This report, Volume A, describes the hardware design of the simulator; Volume B describes the software design. This computer-controlled simulator can simulate up to six surveillance frequency jammers in B through F bands and will be used to evaluate the performance of home-on-jamming guidance modes in multiple jammer environments.

  7. Low-frequency switching in a transistor amplifier.

    PubMed

    Carroll, T L

    2003-04-01

    It is known from extensive work with the diode resonator that the nonlinear properties of a P-N junction can lead to period doubling, chaos, and other complicated behaviors in a driven circuit. There has been very little work on what happens when more than one P-N junction is present. In this work, the first step towards multiple P-N junction circuits is taken by doing both experiments and simulations with a single-transistor amplifier using a bipolar transistor. Period doubling and chaos are seen when the amplifier is driven with signals between 100 kHz and 1 MHz, and they coincide with a very low frequency switching between different period doubled (or chaotic) wave forms. The switching frequencies are between 5 and 10 Hz. The switching behavior was confirmed in a simplified model of the transistor amplifier.

  8. Modeling and investigative studies of Jovian low frequency emissions

    NASA Technical Reports Server (NTRS)

    Menietti, J. D.; Green, James L.; Six, N. Frank; Gulkis, S.

    1986-01-01

    Jovian decametric (DAM) and hectometric (HOM) emissions were first observed over the entire spectrum by the Voyager 1 and 2 flybys of the planet. They display unusual arc-like structures on frequency-versus-time spectrograms. Software for the modeling of the Jovian plasma and magnetic field environment was performed. In addition, an extensive library of programs was developed for the retrieval of Voyager Planetary Radio Astronomy (PRA) data in both the high and low frequency bands from new noise-free, recalibrated data tapes. This software allows the option of retrieving data sorted with respect to particular sub-Io longitudes. This has proven to be invaluable in the analyses of the data. Graphics routines were also developed to display the data on color spectrograms.

  9. High Sensitive Scintillation Observations At Very Low Frequencies

    NASA Astrophysics Data System (ADS)

    Konovalenko, A. A.; Falkovich, I. S.; Kalinichenko, N. N.; Olyak, M. R.; Lecacheux, A.; Rosolen, C.; Bougeret, J.-L.; Rucker, H. O.; Tokarev, Yu.

    The observation of interplanetary scintillations of compact radio sources is powerful method of solar wind diagnostics. This method is developed mainly at decimeter- meter wavelengths. New possibilities are opened at extremely low frequencies (decameter waves) especially at large elongations. Now this approach is being actively developed using high effective decameter antennas UTR-2, URAN and Nancay Decameter Array. New class of back-end facility like high dynamic range, high resolution digital spectral processors, as well as dynamic spectra determination ideology give us new opportunities for distinguishing of the ionospheric and interplanetary scintillations and for observations of large number of radio sources, whith different angular sizes and elongations, even for the cases of rather weak objects.

  10. Low frequency sounds from sustained contraction of human skeletal muscle.

    PubMed Central

    Oster, G; Jaffe, J S

    1980-01-01

    Low frequency audible vibrations are produced by human skeletal muscles undergoing sustained contraction. The effect is easily demonstrable with an electronic stethoscope which amplifies sound below 50 Hz. Autocorrelation analysis of the signal shows that it is periodic with a frequency 25 +/- 2.5 Hz. The quality of the sound is the same for all the skeletal muscles tested and is unaffected by changes in tension, ambient temperature, and blood flow. Electrically-stimulated contraction produces a sound which is indistinguishable from voluntary contraction. The amplitude of the sound increases linearly with tension. The sound signals are uncorrelated both in frequency and phase with electromyographic signals obtained simultaneously while the muscle is contacted. Arguments are presented to show that the sounds may be an intrinsic property of muscle contraction. PMID:7260260

  11. [Low frequency electro-stimulation and ultrasonic therapy (author's transl)].

    PubMed

    Bernau, A; Kruppa, G

    1981-02-01

    In a prospective study 1200 sequences of low frequency electrostimulation and ultrasonic therapy have been examined. The basics of the type of currents applied, the therapy scheme and the indication routine are presented. These parameters were kept constant in the course of the 2 years' study. For the treatment 8 different apparatuses were available. The actual current shapes of the generators were measured, the influence of constant-current and constant-voltage output circuits were tested and were discussed in relation to the electrode types.--Advantages and disadvantages of disposable-type, sponge-type, lead-type and vacuum-type electrodes are reported. Treatments were carried out with the current types DF and CP of the diadynamic currents alone, as combined therapy together with ultrasound, as mere ultrasound treatment, as ultrastimulation current, as iontophoresis and galvanic current. The results are compared with comparable examinations by other authors and they are discussed with respect to different influencing factors.

  12. 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.

  13. 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.

  14. Do GCM's predict the climate.... Or the low frequency weather?

    NASA Astrophysics Data System (ADS)

    Lovejoy, S.; Schertzer, D.; Varon, D.

    2012-04-01

    Over twenty-five years ago, a three-regime scaling model was proposed describing the statistical variability of the atmosphere over time scales ranging from weather scales out to ≈ 100 kyrs. Using modern in situ data reanalyses, monthly surface series (at 5ox5o), 8 "multiproxy" (yearly) series of the Northern hemisphere from 1500 - 1980, and GRIP and Vostok paleotemperatures at 5.2 and ≈ 100 year resolutions (over the past 91-420 kyrs), we refine the model and show how it can be understood with the help of new developments in nonlinear dynamics, especially multifractals and cascades. In a scaling range, mean fluctuations in state variables such as temperature ΔT vary in power law manners ≈ Δt**H the where Δt is the duration. At small (weather) scales the fluctuation exponents are generally H>0; they grow with scale (Δt). At longer scales Δt >τw (≈ 10 days) H changes sign, the fluctuations decrease with scale; this is the low variability, "low frequency weather" regime. In this regime, the spectrum is a relatively flat "plateau", it's variability is low, stable, corresponding to our usual idea of "long term weather statistics". Finally for longer times, Δt>τc ≈ 10 - 100 years, once again H>0, so that the variability increases with scale: the true climate regime. These scaling regimes allow us to objectively define the weather as fluctuations over periods <τw, to define "climate states" as fluctuations at scale τc and then "climate change" as the fluctuations at longer periods (Δt>τc). We show that the intermediate low frequency weather regime is the result of the weather regime undergoing a "dimensional transition": at temporal scales longer than the typical lifetime of planetary structures (τw), the spatial degrees of freedom are rapidly quenched so that only the temporal degrees of freedom are important. This low frequency weather regime has statistical properties well reproduced not only by stochastic cascade models of weather, but also by

  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. 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.

  17. 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.

  18. 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.

  19. Wideband, low-frequency springless vibration energy harvesters: part II

    NASA Astrophysics Data System (ADS)

    Bendame, Mohamed; Abdel-Rahman, Eihab; Soliman, Mostafa

    2016-11-01

    This paper concludes a two-part investigation of a novel architecture for vibration energy harvesting (VEH), the springless VEH. In this part, we study vertical springless electromagnetic VEHs where the direction of motion is aligned with the gravitational field. Experimental results show the existence of three topologies in the response of vertical springless VEHs; linear, single-impact, and double-impact. A model, encompassing all three topologies, was developed and validated by comparison to experimental results. We found that vertical springless VEHs demonstrate low frequency harvesting (<20 Hz), widebeand harvesting (bandwidths up to \\text{BW}=11.2 Hz), and an optimal output power of P  =  7.52 mW at a base acceleration of 0.6 g. While horizontal springless VEHs typically offer more output power, the single-impact regime of the vertical springless VEHs offers the simultaneous advantages of wider harvesting bandwidths at lower operating frequencies.

  20. Interaction of extremely-low-frequency electromagnetic fields with humans

    SciTech Connect

    Tenforde, T.S.

    1991-07-01

    At a macroscopic level, the effects of extremely low frequency (ELF) electromagnetic fields on humans are well understood based on fundamental physical principles, but far less is known about the nature of the interactions at a cellular or molecular level. Current evidence suggests the effects of ELF on cellular biochemistry are due to interactions with the cell membrane. Elucidation of the mechanism that underlies this transmembrane signaling is critical for a molecular-level understanding of ELF field effects. Further research is also required to clarify a possible link between ELF exposure and increased cancer risk, since estimated ELF exposure in occupational or residential settings is much lower that the levels used in laboratory studies. There is a clear need for additional epidemiological research in which qualitative dosimetry is used to characterize ELF exposure and careful attention is given to possible effects of confounding variables. 24 refs.