WorldWideScience

Sample records for constraining low-frequency alfvenic

  1. Effect of Alfven resonance on low-frequency fast wave current drive

    Energy Technology Data Exchange (ETDEWEB)

    Wang, C.Y.; Batchelor, D.B.; Carter, M.D.; Jaeger, E.F.; Stallings, D.C. [Fusion Energy Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

    1995-07-01

    The Alfven 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 {bold 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. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  2. The effect of toroidal plasma rotation on low-frequency reversed shear Alfven eigenmodes in tokamaks

    NARCIS (Netherlands)

    Haverkort, J. W.

    2012-01-01

    The influence of toroidal plasma rotation on the existence of reversed shear Alfven eigenmodes (RSAEs) near their minimum frequency is investigated analytically. An existence condition is derived showing that a radially decreasing kinetic energy density is unfavourable for the existence of RSAEs. Th

  3. Alfvenic tornadoes

    CERN Document Server

    Shukla, P K

    2012-01-01

    It is shown that a three-dimensional (3D) modified-kinetic Alfv\\'en waves (m-KAWs) can propagate in the form of Alfv\\'enic tornadoes characterized by plasma density whirls or magnetic flux ropes carrying orbital angular momentum (OAM). By using the two fluid model, together with Amp\\`ere's law, we derive the wave equation for a 3D m-KAWs in a magnetoplasma with $m_e/m_i \\ll \\beta \\ll 1$, where $m_e$ $(m_i)$ is the electron (ion) mass, $\\beta =4 \\pi n_0 k_B (T_e + T_i)/B_0^2$, $n_0$ the unperturbed plasma number density, $k_B$ the Boltzmann constant, $T_e (T_e)$ the electron (ion) temperature, and $B_0$ the strength of the ambient magnetic field. The 3D m-KAW equation admits solutions in the form of a Laguerre-Gauss (LG) Alfv\\'enic vortex beam or Alfv\\'enic tornadoes with plasma density whirls that support the dynamics of Alfv\\'en magnetic flux ropes.

  4. Constraining the Rate of Primordial Black-Hole Explosions and Extra Dimension Scale using a Low-Frequency Radio Antenna Array

    CERN Document Server

    Cutchin, Sean E; Ellingson, Steven W; Larracuente, Amanda S; Kavic, Michael J

    2016-01-01

    An exploding primordial black-hole (PBH) may produce a single pulse of electromagnetic radiation detectable at the low-frequency end of the radio spectrum. Furthermore, a radio transient from an exploding PBH could be a signature of an extra spatial dimension. We describe here an approach for searching for PBH explosions using a low-frequency radio antenna array, and as a practical example, the results of a such a search using the Eight-meter-wavelength Transient Array (ETA). No compelling astrophysical signal was detected in $\\approx 4$ hours of data implying an observational upper limit on the rate of exploding PBHs is $2.3 \\times 10^{-7} \\,\\rm{pc}^{-3}\\,\\rm{yr}^{-1}$ for an exploding PBH with a fireball Lorentz factor of $10^{4.3}$ for the standard scenario of Page and Hawking. This rate is an order of magnitude higher than that set using the Arecibo Observatory during $\\sim 300$~hours of observations, but implies a considerably lower limit can be established with more observing time and a larger number of...

  5. Alfvenic tornadoes

    OpenAIRE

    Shukla, P. K.

    2012-01-01

    It is shown that a three-dimensional (3D) modified-kinetic Alfv\\'en waves (m-KAWs) can propagate in the form of Alfv\\'enic tornadoes characterized by plasma density whirls or magnetic flux ropes carrying orbital angular momentum (OAM). By using the two fluid model, together with Amp\\`ere's law, we derive the wave equation for a 3D m-KAWs in a magnetoplasma with $m_e/m_i \\ll \\beta \\ll 1$, where $m_e$ $(m_i)$ is the electron (ion) mass, $\\beta =4 \\pi n_0 k_B (T_e + T_i)/B_0^2$, $n_0$ the unpert...

  6. Alfven Wave Solar Model: Part 1, Coronal Heating

    CERN Document Server

    van der Holst, Bart; Meng, Xing; Jin, Meng; Manchester, Ward B; Toth, Gabor; Gombosi, Tamas I

    2013-01-01

    We present the new Alfven Wave Solar Model (AWSoM), a global model from the upper chromosphere to the corona and the heliosphere. The coronal heating and solar wind acceleration are addressed with low-frequency Alfven wave turbulence. The injection of Alfven wave energy at the inner boundary is such that the Poynting flux is proportional to the magnetic field strength. The three-dimensional magnetic field topology is simulated using data from photospheric magnetic field measurements. This model does not impose open-closed magnetic field boundaries; those develop self-consistently. The physics includes: (1) The model employs three different temperatures, namely the isotropic electron temperature and the parallel and perpendicular ion temperatures. The firehose, mirror, and ion-cyclotron instabilities due to the developing ion temperature anisotropy are accounted for. (2) The Alfven waves are partially reflected by the Alfven speed gradient and the vorticity along the field lines. The resulting counter-propagat...

  7. Interchange Reconnection Alfven Wave Generation

    CERN Document Server

    Lynch, B J; Li, Y

    2014-01-01

    Given recent observational results of interchange reconnection processes in the solar corona and the theoretical development of the S-Web model for the slow solar wind, we present further analysis of the 3D MHD simulation of interchange reconnection by Edmondson et al. (Astrophys. J. 707, 1427, 2009). Specifically, we analyze the consequences of the dynamic streamer belt jump that corresponds to flux opening by interchange reconnection. Information about the magnetic field restructuring by interchange reconnection is carried throughout the system by Alfven waves propagating away from the reconnection region, distributing the shear and twist imparted by the driving flows, including shedding the injected stress-energy and accumulated magnetic helicity along newly-open field lines. We quantify the properties of the reconnection-generated wave activity in the simulation. There is a localized high frequency component associated with the current sheet/reconnection site and an extended low frequency component associ...

  8. Characteristics of Short Wavelength Compressional Alfven Eigenmodes

    Energy Technology Data Exchange (ETDEWEB)

    Fredrickson, E D; Podesta, M; Bortolon, A; Crocker, N A; Gerhardt, S P; Bell, R E; Diallo, A; LeBlanc, B; Levinton, F M

    2012-12-19

    Most Alfvenic activity in the frequency range between Toroidal Alfven Eigenmodes and roughly one half of the ion cyclotron frequency on NSTX [M. Ono, et al., Nucl. Fusion 40 (2000) 557], that is, approximately 0.3 MHz up to ≈ 1.2 MHz, are modes propagating counter to the neutral beam ions. These have been modeled as Compressional and Global Alfven Eigenmodes (CAE and GAE) and are excited through a Doppler-shifted cyclotron resonance with the beam ions. There is also a class of co-propagating modes at higher frequency than the counter-propagating CAE and GAE. These modes have been identified as CAE, and are seen mostly in the company of a low frequency, n=1 kink-like mode. In this paper we present measurements of the spectrum of these high frequency CAE (hfCAE), and their mode structure. We compare those measurements to a simple model of CAE and present evidence of a curious non-linear coupling of the hfCAE and the low frequency kink-like mode.

  9. Low-frequency-noise complaints

    DEFF Research Database (Denmark)

    Pedersen, Christian Sejer; Møller, Henrik; Persson-Waye, Kerstin

    2008-01-01

    From 203 cases of low-frequency complaints a random selection of twenty-one cases were investigated. The main aim of the investigation was to answer the question whether the annoyance is caused by an external physical sound or by a physically non-existing sound, i.e. low-frequency tinnitus. Noise...... of the complainants are annoyed by a physical sound (20-180 Hz), while others suffer from low-frequency tinnitus (perceived frequency 40-100 Hz). Physical sound at frequencies below 20 Hz (infrasound) is not responsible for the annoyance - or at all audible - in any of the investigated cases, and none...... of the complainants has extraordinary hearing sensitivity at low frequencies. For comparable cases of low-frequency noise complaints in general, it is anticipated that physical sound is responsible in a substantial part of the cases, while low-frequency tinnitus is responsible in another substantial part of the cases....

  10. Minimization of nanosatellite low frequency magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Belyayev, S. M., E-mail: belyayev@isr.lviv.ua [Lviv Centre of Institute for Space Research, Lviv 79060 (Ukraine); Royal Institute of Technology, Stockholm 11428 (Sweden); Dudkin, F. L. [Lviv Centre of Institute for Space Research, Lviv 79060 (Ukraine)

    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.

  11. Low-frequency noise complaints

    DEFF Research Database (Denmark)

    Pedersen, Christian Sejer; Møller, Henrik; Persson-Waye, Kerstin

    2006-01-01

    In Denmark and in other industrialized countries there are cases where people complain about annoying low-frequency or infrasonic noise in their homes. Besides noise annoyance people often report other adverse effects such as insomnia, headache, lack of concentration etc. In many cases the noise...

  12. Harvesting Low-Frequency (Nanogenerator.

    Science.gov (United States)

    Zi, Yunlong; Guo, Hengyu; Wen, Zhen; Yeh, Min-Hsin; Hu, Chenguo; Wang, Zhong Lin

    2016-04-26

    Electromagnetic generators (EMGs) and triboelectric nanogenerators (TENGs) are the two most powerful approaches for harvesting ambient mechanical energy, but the effectiveness of each depends on the triggering frequency. Here, after systematically comparing the performances of EMGs and TENGs under low-frequency motion (10-100 V) and independent of frequency so that most of the generated power can be effectively used to power the devices. Furthermore, a TENG also has advantages of light weight, low cost, and easy scale up through advanced structure designs. All these merits verify the possible killer application of a TENG for harvesting energy at low frequency from motions such as human motions for powering small electronics and possibly ocean waves for large-scale blue energy.

  13. Low Frequency Radio Experiment (LORE)

    Science.gov (United States)

    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.

  14. Non-linear modulation of short wavelength compressional Alfven eigenmodes

    Energy Technology Data Exchange (ETDEWEB)

    Fredrickson, E. D.; Gorelenkov, N. N.; Podesta, M.; Gerhardt, S. P.; Bell, R. E.; Diallo, A.; LeBlanc, B. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States); Bortolon, A. [University of California, Irvine, California 92697 (United States); Crocker, N. A. [University of California, Los Angeles, California 90095 (United States); Levinton, F. M.; Yuh, H. [Nova Photonics, Princeton, New Jersey 08543 (United States)

    2013-04-15

    Most Alfvenic activity in the frequency range between toroidal Alfven eigenmodes and roughly one half of the ion cyclotron frequency on National Spherical Torus eXperiment [Ono et al., Nucl. Fusion 40, 557 (2000)], that is, approximately 0.3 MHz up to Almost-Equal-To 1.2 MHz, are modes propagating counter to the neutral beam ions. These have been modeled as Compressional and Global Alfven Eigenmodes (CAE and GAE) and are excited through a Doppler-shifted cyclotron resonance with the beam ions. There is also a class of co-propagating modes at higher frequency than the counter-propagating CAE and GAE. These modes have been identified as CAE, and are seen mostly in the company of a low frequency, n = 1 kink-like mode. In this paper, we present measurements of the spectrum of these high frequency CAE (hfCAE) and their mode structure. We compare those measurements to a simple model of CAE and present a predator-prey type model of the curious non-linear coupling of the hfCAE and the low frequency kink-like mode.

  15. Auditory filters at low-frequencies

    DEFF Research Database (Denmark)

    Orellana, Carlos Andrés Jurado; Pedersen, Christian Sejer; Møller, Henrik

    2009-01-01

    Prediction and assessment of low-frequency noise problems requires information about the auditory filter characteristics at low-frequencies. Unfortunately, data at low-frequencies is scarce and practically no results have been published for frequencies below 100 Hz. Extrapolation of ERB results......-ear transfer function), the asymmetry of the auditory filter changed from steeper high-frequency slopes at 1000 Hz to steeper low-frequency slopes below 100 Hz. Increasing steepness at low-frequencies of the middle-ear high-pass filter is thought to cause this effect. The dynamic range of the auditory filter...

  16. Dispersion Relations and Polarizations of Low-frequency Waves in Two-fluid Plasmas

    CERN Document Server

    Zhao, Jinsong

    2015-01-01

    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 $\\mathbf{B}_{0}$) and \\beta (the ratio of the plasma to magnetic pressures) values are investigated. It is shown that two linearly polarized waves, namely the fast and Alfv\\'{e}n modes in the low-\\beta $\\left( \\beta \\ll 1\\right)$ plasmas, the fast and slow modes in the \\beta \\sim 1 plasmas, and the Alfv\\'{e}n and slow modes in the high-\\beta $\\left( \\beta \\gg 1\\right)$ plasmas, become circularly polarized at the near-parallel (to $\\mathbf{B}_{0}$) propagation. The negative magnetic-helicity of the Alfv\\'{e}n mode occurs only at small or moderate angles in the low-\\beta plasmas, and the ion cross-helicity of the slow mode is nearly the same as that of the Alfv\\'{e}n mode in the high-\\beta plasmas. It also shown the electric polarization $\\delta E_{z}/\\delta E_{y}$ decreases...

  17. Demodulated low frequency currents from electrosurgical procedures.

    Science.gov (United States)

    Tucker, R D; Schmitt, O H; Sievert, C E; Silvis, S E

    1984-07-01

    Low frequency currents produced incidental to electrosurgical procedures are usually only a minor threat unless they are coupled directly into the heart through a catheter or a thoracic surgical procedure. However, should the low frequency blocking capacitors in the electrosurgical generator fail in the conducting state, extremely dangerous low frequency currents of many milliamperes may flow into the patient. Even with properly functioning capacitors, low frequencies up to several milliamperes may be produced by some generators. The results of this study show that the coagulation mode of operation produces greater amounts of low frequency currents than the "pure cutting" mode at the same power setting. These results also demonstrate that the higher the generator power output, the higher the magnitude of the low frequency currents.

  18. Low-frequency sonophoresis: a review.

    Science.gov (United States)

    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 (feffect 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.

  19. Disperson relation of finite amplitude Alfven wave in a relativistic electron- positron plasma

    CERN Document Server

    Hada, T; Muñoz, V; Hada, Tohru; Matsukiyo, Shuichi; Munoz, Victor

    2004-01-01

    The linear dispersion relation of a finite amplitude, parallel, circularly polarized Alfv\\'en wave in a relativistic electron-positron plasma is derived. In the nonrelativistic regime, the dispersion relation has two branches, one electromagnetic wave, with a low frequency cutoff at $\\sqrt{1+2\\omega_p^2/\\Omega_p^2}$ (where $\\omega_p=(4\\pi n e^2/m)^{1/2}$ is the electron/positron plasma frequency), and an Alfv\\'en wave, with high frequency cutoff at the positron gyrofrequency $\\Omega_p$. There is only one forward propagating mode for a given frequency. However, due to relativistic effects, there is no low frequency cutoff for the electromagnetic branch, and there appears a critical wave number above which the Alfv\\'en wave ceases to exist. This critical wave number is given by $ck_c/\\Omega_p=a/\\eta$, where $a=\\omega_p^2/\\Omega_p^2$ and $\\eta$ is the ratio between the Alfv\\'en wave magnetic field amplitude and the background magnetic field. In this case, for each frequency in the Alfv\\'en branch, two additional...

  20. Low-frequency cosmology from the moon

    NARCIS (Netherlands)

    Klein Wolt, M.; Aminaei, A.; Pourshaghaghi, H.; Koopmans, L.; Falcke, H.

    2013-01-01

    From a low-frequency point of view, the moon provides excess to the virtually unexplored radio frequency domain below 30 MHz that is not accessible from Earth due to the atmospheric cutoff and interference from man-made RFI. We show that with a single low-frequency radio antenna the detection of the

  1. ALFVEN WAVES IN A PARTIALLY IONIZED TWO-FLUID PLASMA

    Energy Technology Data Exchange (ETDEWEB)

    Soler, R.; Ballester, J. L.; Terradas, J. [Departament de Fisica, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain); Carbonell, M., E-mail: roberto.soler@uib.es, E-mail: joseluis.ballester@uib.es, E-mail: jaume.terradas@uib.es, E-mail: marc.carbonell@uib.es [Departament de Matematiques i Informatica, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain)

    2013-04-20

    Alfven waves are a particular class of magnetohydrodynamic waves relevant in many astrophysical and laboratory plasmas. In partially ionized plasmas the dynamics of Alfven waves is affected by the interaction between ionized and neutral species. Here we study Alfven waves in a partially ionized plasma from the theoretical point of view using the two-fluid description. We consider that the plasma is composed of an ion-electron fluid and a neutral fluid, which interact by means of particle collisions. To keep our investigation as general as possible, we take the neutral-ion collision frequency and the ionization degree as free parameters. First, we perform a normal mode analysis. We find the modification due to neutral-ion collisions of the wave frequencies and study the temporal and spatial attenuation of the waves. In addition, we discuss the presence of cutoff values of the wavelength that constrain the existence of oscillatory standing waves in weakly ionized plasmas. Later, we go beyond the normal mode approach and solve the initial-value problem in order to study the time-dependent evolution of the wave perturbations in the two fluids. An application to Alfven waves in the low solar atmospheric plasma is performed and the implication of partial ionization for the energy flux is discussed.

  2. Formation of quasiparallel Alfven solitons

    Science.gov (United States)

    Hamilton, R. L.; Kennel, C. F.; Mjolhus, E.

    1992-01-01

    The formation of quasi-parallel Alfven solitons is investigated through the inverse scattering transformation (IST) for the derivative nonlinear Schroedinger (DNLS) equation. The DNLS has a rich complement of soliton solutions consisting of a two-parameter soliton family and a one-parameter bright/dark soliton family. In this paper, the physical roles and origins of these soliton families are inferred through an analytic study of the scattering data generated by the IST for a set of initial profiles. The DNLS equation has as limiting forms the nonlinear Schroedinger (NLS), Korteweg-de-Vries (KdV) and modified Korteweg-de-Vries (MKdV) equations. Each of these limits is briefly reviewed in the physical context of quasi-parallel Alfven waves. The existence of these limiting forms serves as a natural framework for discussing the formation of Alfven solitons.

  3. Observation of an Alfv\\'en Wave Parametric Instability in a Laboratory Plasma

    CERN Document Server

    Dorfman, S

    2016-01-01

    A shear Alfv\\'en wave parametric instability is observed for the first time in the laboratory. When a single finite $\\omega/\\Omega_i$ kinetic Alfv\\'en wave (KAW) is launched in the Large Plasma Device above a threshold amplitude, three daughter modes are produced. These daughter modes have frequencies and parallel wave numbers that are consistent with copropagating KAW sidebands and a low frequency nonresonant mode. The observed process is parametric in nature, with the frequency of the daughter modes varying as a function of pump wave amplitude. The daughter modes are spatially localized on a gradient of the pump wave magnetic field amplitude in the plane perpendicular to the background field, suggesting that perpendicular nonlinear forces (and therefore $k_{\\perp}$ of the pump wave) play an important role in the instability process. Despite this, modulational instability theory with $k_{\\perp}=0$ has several features in common with the observed nonresonant mode and Alfv\\'en wave sidebands.

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

    Energy Technology Data Exchange (ETDEWEB)

    Prajapati, R. P., E-mail: prajapati-iter@yahoo.co.in [Department of Pure and Applied Physics, Guru Ghasidas Central University, Bilaspur-495009 (C.G.) (India)

    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.

  5. Gravity and low-frequency geodynamics

    CERN Document Server

    Teisseyre, Roman

    1989-01-01

    This fourth volume in the series Physics and Evolution of the Earth's Interior, provides a comprehensive review of the geophysical and geodetical aspects related to gravity and low-frequency geodynamics. Such aspects include the Earth's gravity field, geoid shape theory, and low-frequency phenomena like rotation, oscillations and tides.Global-scale phenomena are treated as a response to source excitation in spherical Earth models consisting of several shells: lithosphere, mantle, core and sometimes also the inner solid core. The effect of gravitation and rotation on the Earth's shape is anal

  6. Integral methods in low-frequency electromagnetics

    CERN Document Server

    Solin, Pavel; Karban, Pavel; Ulrych, Bohus

    2009-01-01

    A modern presentation of integral methods in low-frequency electromagnetics This book provides state-of-the-art knowledge on integral methods in low-frequency electromagnetics. Blending theory with numerous examples, it introduces key aspects of the integral methods used in engineering as a powerful alternative to PDE-based models. Readers will get complete coverage of: The electromagnetic field and its basic characteristics An overview of solution methods Solutions of electromagnetic fields by integral expressions Integral and integrodifferential methods

  7. Auditory filters at low-frequencies

    DEFF Research Database (Denmark)

    Orellana, Carlos Andrés Jurado; Pedersen, Christian Sejer; Møller, Henrik

    2009-01-01

    -ear transfer function), the asymmetry of the auditory filter changed from steeper high-frequency slopes at 1000 Hz to steeper low-frequency slopes below 100 Hz. Increasing steepness at low-frequencies of the middle-ear high-pass filter is thought to cause this effect. The dynamic range of the auditory filter...... was found to steadily decrease with decreasing center frequency. Although the observed decrease in filter bandwidth with decreasing center frequency was only approximately monotonic, the preliminary data indicates the filter bandwidth does not stabilize around 100 Hz, e.g. it still decreases below...

  8. Hearing Foreign Languages through Low Frequencies.

    Science.gov (United States)

    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…

  9. Digital Filters for Low Frequency Equalization

    DEFF Research Database (Denmark)

    Tyril, Marni; Abildgaard, J.; Rubak, Per

    2001-01-01

    Digital filters with high resolution in the low-frequency range are studied. Specifically, for a given computational power, traditional IIR filters are compared with warped FIR filters, warped IIR filters, and modified warped FIR filters termed warped individual z FIR filters (WizFIR). The results...... indicate that IIR filters are the most effective in a number of situations....

  10. Orbiting low frequency array for radio astronomy

    NARCIS (Netherlands)

    Rajan, Rai Thilak; Rajan, Raj; Engelen, Steven; Bentum, Marinus Jan; Verhoeven, Chris

    2011-01-01

    Recently new and interesting science drivers have emerged for very low frequency radio astronomy from 0.3 MHz to 30 MHz. However Earth bound radio observations at these wavelengths are severely hampered by ionospheric distortions, man made interference, solar flares and even complete reflection belo

  11. Orbiting low frequency array for radio astronomy

    NARCIS (Netherlands)

    Rajan, Rai Thilak; Engelen, Steven; Bentum, Mark; Verhoeven, Chris

    2011-01-01

    Recently new and interesting science drivers have emerged for very low frequency radio astronomy from 0.3 MHz to 30 MHz. However Earth bound radio observations at these wavelengths are severely hampered by ionospheric distortions, man made interference, solar flares and even complete reflection belo

  12. Digital Filters for Low Frequency Equalization

    DEFF Research Database (Denmark)

    Tyril, Marni; Abildgaard, J.; Rubak, Per

    2001-01-01

    Digital filters with high resolution in the low-frequency range are studied. Specifically, for a given computational power, traditional IIR filters are compared with warped FIR filters, warped IIR filters, and modified warped FIR filters termed warped individual z FIR filters (WizFIR). The results...

  13. Highly Alfvenic Slow Solar Wind

    Science.gov (United States)

    Roberts, D. Aaron

    2010-01-01

    It is commonly thought that fast solar wind tends to be highly Alfvenic, with strong correlations between velocity and magnetic fluctuations, but examples have been known for over 20 years in which slow wind is both Alfvenic and has many other properties more typically expected of fast solar wind. This paper will present a search for examples of such flows from more recent data, and will begin to characterize the general characteristics of them. A very preliminary search suggests that such intervals are more common in the rising phase of the solar cycle. These intervals are important for providing constraints on models of solar wind acceleration, and in particular the role waves might or might not play in that process.

  14. Ion kinetic energy conservation and magnetic field strength constancy in multi-fluid solar wind Alfv\\'enic turbulence

    CERN Document Server

    Matteini, L; Pantellini, F; Velli, M; Schwartz, S J

    2015-01-01

    We investigate properties of the plasma fluid motion in the large amplitude low frequency fluctuations of highly Alfv\\'enic fast solar wind. We show that protons locally conserve total kinetic energy when observed from an effective frame of reference comoving with the fluctuations. For typical properties of the fast wind, this frame can be reasonably identified by alpha particles, which, owing to their drift with respect to protons at about the Alfv\\'en speed along the magnetic field, do not partake in the fluid low frequency fluctuations. Using their velocity to transform proton velocity into the frame of Alfv\\'enic turbulence, we demonstrate that the resulting plasma motion is characterized by a constant absolute value of the velocity, zero electric fields, and aligned velocity and magnetic field vectors as expected for unidirectional Alfv\\'enic fluctuations in equilibrium. We propose that this constraint, via the correlation between velocity and magnetic field in Alfv\\'enic turbulence, is at the origin of ...

  15. Alfven waves in a partially ionized two-fluid plasma

    CERN Document Server

    Soler, R; Ballester, J L; Terradas, J

    2013-01-01

    Alfv\\'en waves are a particular class of magnetohydrodynamic waves relevant in many astrophysical and laboratory plasmas. In partially ionized plasmas the dynamics of Alfv\\'en waves is affected by the interaction between ionized and neutral species. Here we study Alfv\\'en waves in a partially ionized plasma from the theoretical point of view using the two-fluid description. We consider that the plasma is composed of an ion-electron fluid and a neutral fluid, which interact by means of particle collisions. To keep our investigation as general as possible we take the neutral-ion collision frequency and the ionization degree as free parameters. First, we perform a normal mode analysis. We find the modification due to neutral-ion collisions of the wave frequencies and study the temporal and spatial attenuation of the waves. In addition, we discuss the presence of cut-off values of the wavelength that constrain the existence of oscillatory standing waves in weakly ionized plasmas. Later, we go beyond the normal mo...

  16. Nonlinear Modelling of Low Frequency Loudspeakers

    DEFF Research Database (Denmark)

    Olsen, Erling Sandermann

    1997-01-01

    In the Danish LoDist project on distortion from dynamic low-frequency loudspeakers, a detailed nonlinear model of loudspeakers has been developed. The model has been implemented in a PC program so that it can be used to create signals for listening tests and analysis. Also, different methods...... for describing the nonlinearities have been developed. Different aspects of modelling loudspeaker nonlinearities are discussed, and the program is briefly described....

  17. Nonlinear Modelling of Low Frequency Loudspeakers

    DEFF Research Database (Denmark)

    Olsen, Erling Sandermann

    1997-01-01

    In the Danish LoDist project on distortion from dynamic low frequency loudspeakers a detailed nonlinear model of loudspeakers has been developed. The model has been implemented in a PC program so that it can be used to create signals for listening tests and analysis. Also, different methods...... for describing the nonlinearities have been developed. Different aspects of modelling loudspeaker nonlinearities are discussed and the program is briefly demonstrated....

  18. Low-Frequency Electromagnetic Backscattering from Tunnels

    Energy Technology Data Exchange (ETDEWEB)

    Casey, K; Pao, H

    2007-01-16

    Low-frequency electromagnetic scattering from one or more tunnels in a lossy dielectric half-space is considered. The tunnel radii are assumed small compared to the wavelength of the electromagnetic field in the surrounding medium; a tunnel can thus be modeled as a thin scatterer, described by an equivalent impedance per unit length. We examine the normalized backscattering width for cases in which the air-ground interface is either smooth or rough.

  19. LOFAR: The LOw-Frequency ARray

    CERN Document Server

    van Haarlem, M P; 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; Mann, L V E Koopmans G; Miley, G; Röttgering, H; Stappers, B W; Wijers, R A M J; Zaroubi, S; Akker, M van den; 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 Gasparin, F; Gerbers, M; de Geus, E; Grießmeier, J -M; Grit, T; Gruppen, P; Hamaker, J P; Hassall, T; Hoeft, M; Holties, H; Horneffer, A; van der Horst, A; van Houwelingen, A; Huijgen, A; Iacobelli, M; Intema, H; Jackson, N; Jelic, V; de Jong, A; 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; McKay-Bukowski, D; Meijering, H; Meulman, H; Mevius, M; 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, 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

    2013-01-01

    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 ob...

  20. A variable passive low-frequency absorber

    Science.gov (United States)

    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.

  1. Plasma heating inside ICMEs by Alfvenic fluctuations dissipation

    CERN Document Server

    Li, Hui; He, Jiansen; Zhang, Lingqian; Richardson, John D; Belcher, John W; Tu, Cui

    2016-01-01

    Nonlinear cascade of low-frequency Alfvenic fluctuations (AFs) is regarded as one candidate of the energy sources to heat plasma during the non-adiabatic expansion of interplanetary coronal mass ejections (ICMEs). However, AFs inside ICMEs were seldom reported in the literature. In this study, we investigate AFs inside ICMEs using observations from Voyager 2 between 1 and 6 au. It is found that AFs with high degree of Alfvenicity frequently occurred inside ICMEs, for almost all the identified ICMEs (30 out of 33 ICMEs), and 12.6% of ICME time interval. As ICMEs expand and move outward, the percentage of AF duration decays linearly in general. The occurrence rate of AFs inside ICMEs is much less than that in ambient solar wind, especially within 4 au. AFs inside ICMEs are more frequently presented in the center and at the boundaries of ICMEs. In addition, the proton temperature inside ICME has a similar distribution. These findings suggest significant contribution of AFs on local plasma heating inside ICMEs.

  2. Measuring low-frequency noise indoors

    DEFF Research Database (Denmark)

    Pedersen, Steffen; Møller, Henrik; Persson-Waye, Kerstin

    2008-01-01

    that is exceeded in 10% of the volume of a room (L10) is proposed as a rational and objective target for a measurement method. In Sweden and Denmark rules exist for measuring low-frequency noise indoors. The performance of these procedures was investigated in three rooms. The results from the Swedish method were...... close to the L10 target, but, due to a doubtful use of C-weighting in the scanning, it may give too low results in case of complex sounds. The Danish method was found to have a high risk of giving results substantially below the target, unless complainants can precisely appoint measurement positions...

  3. LOFAR, a new low frequency radio telescope

    CERN Document Server

    Röttgering, H J A

    2003-01-01

    LOFAR, the Low Frequency Array, is a large radio telescope consisting of approximately 100 soccer-field sized antenna stations spread over a region of 400 km in diameter. It will operate at frequencies from ~10 to 240 MHz, with a resolution at 240 MHz of better than an arcsecond. Its superb sensitivity will allow for studies of a broad range of astrophysical topics, including reionisation, transient radio sources and cosmic rays, distant galaxies and AGNs. In this contribution a status rapport of the LOFAR project and an overview of the science case is presented.

  4. A variable passive low-frequency absorber

    DEFF Research Database (Denmark)

    Larsen, Niels Werner; Thompson, Eric Robert; Gade, Anders

    2005-01-01

    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.......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...

  5. Analysis of the Interaction between Low-Frequency Waves and Ions in the High-Altitude Cusp Region Observed by Satellite Cluster

    Institute of Scientific and Technical Information of China (English)

    DUAN Su-Ping; A. Balogh; M. Andre; LIU Zhen-Xing; CAO Jin-Bin; SHI Jian-Kui; LU Li; LI Zhong-Yuan; Q. G. Zong; H. Reme; N. Cornilleau-Wehrlin

    2006-01-01

    @@ The energy transfer between ions (protons) and low frequency waves (LFWs) in the frequency range f1 from 0.3to 10 Hz is observed by Cluster crossing the high-altitude polar cusp. The energy transfer between low frequency waves and ions has two means. One is that the energy is transferred from low frequency waves to ions and ions energy increases. The other is that the energy is transferred from ions to low frequency waves and the ion energy decreases. Ion gyratory motion plays an important role in the energy transfer processes. The electromagnetic field of f1 LFWs can accelerate or decelerate protons along the direction of ambient magneticfield and warm or refrigerate protons in the parallel and perpendicular directions of ambient magnetic field. The peak values of proton number densities have the corresponding peak values of electromagnetic energy of low-frequency waves.This implies that the kinetic Alfven waves and solitary kinetic Alfven waves possibly exist in the high-altitude cusp region.

  6. Predictions and observations of global beta-induced Alfven-acoustic modes in JET and NSTX

    Energy Technology Data Exchange (ETDEWEB)

    Gorelenkov, N N [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Berk, H L [Institute for Fusion Studies, University of Texas, Austin, TX 78712 (United States); Crocker, N A [Institute of Plasma and Fusion Research, University of California, Los Angeles, CA 90095-1354 (United States); Fredrickson, E D [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Kaye, S [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Kubota, S [Institute of Plasma and Fusion Research, University of California, Los Angeles, CA 90095-1354 (United States); Park, H [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Peebles, W [Institute of Plasma and Fusion Research, University of California, Los Angeles, CA 90095-1354 (United States); Sabbagh, S A [Department of Applied Physics, Columbia University, New York, NY 10027-6902 (United States); Sharapov, S E [Euroatom/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB (United Kingdom); Stutmat, D [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Tritz, K [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Levinton, F M [Nova Photonics, One Oak Place, Princeton, NJ 08540 (United States); Yuh, H [Nova Photonics, One Oak Place, Princeton, NJ 08540 (United States)

    2007-12-15

    In this paper we report on observations and interpretations of a new class of global MHD eigenmode solutions arising in gaps in the low frequency Alfven-acoustic continuum below the geodesic acoustic mode frequency. These modes have been just reported (Gorelenkov et al 2007 Phys. Lett. 370 70-7) where preliminary comparisons indicate qualitative agreement between theory and experiment. Here we show a more quantitative comparison emphasizing recent NSTX experiments on the observations of the global eigenmodes, referred to as beta-induced Alfven-acoustic eigenmodes (BAAEs), which exist near the extrema of the Alfven-acoustic continuum. In accordance to the linear dispersion relations, the frequency of these modes may shift as the safety factor, q, profile relaxes. We show that BAAEs can be responsible for observations in JET plasmas at relatively low beta <2% as well as in NSTX plasmas at relatively high beta >20%. In NSTX plasma observed magnetic activity has the same properties as predicted by theory for the mode structure and the frequency. Found numerically in NOVA simulations BAAEs are used to explain the observed properties of relatively low frequency experimental signals seen in NSTX and JET tokamaks.

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

    Science.gov (United States)

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

    2011-01-01

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

  8. Low-frequency wiggler modes in the free-electron laser with a dusty magnetoplasma medium

    Science.gov (United States)

    Jafari, S.

    2015-07-01

    An advanced incremental scheme for generating tunable coherent radiation in a free-electron laser has been presented: the basic concept is the use of a relativistic electron beam propagating through a magnetized dusty plasma channel where dust helicon, dust Alfven and coupled dust cyclotron-Alfven waves can play a role as a low-frequency wiggler, triggering coherent emissions. The wiggler wavelength at the sub-mm level allows one to reach the wavelength range from a few nm down to a few Å with moderately relativistic electrons of kinetic energies of a few tens/hundreds of MeV. The laser gain and the effects of beam self-electric and self-magnetic fields on the gain have been estimated and compared with findings of the helical magnetic and electromagnetic wigglers in vacuum. To study the chaotic regions of the electron motion in the dusty plasma wave wiggler, a time independent Hamiltonian has been obtained. The Poincare surface of a section map has been used numerically to analyze the nonintegrable system where chaotic regions in phase-space emerge. This concept opens a path toward a new generation of synchrotron sources based on compact plasma structures.

  9. The VLA Low-frequency Sky Survey

    CERN Document Server

    Cohen, A S; Cotton, W D; Kassim, N E; Lazio, T J W; Perley, R A; Condon, J J; Erickson, W C

    2007-01-01

    The Very Large Array (VLA) Low-frequency Sky Survey (VLSS) has imaged 95% of the 3*pi sr of sky north of declination = -30 degrees at a frequency of 74 MHz (4 meter wavelength). The resolution is 80" (FWHM) throughout, and the typical RMS noise level is ~0.1 Jy/beam. The typical point-source detection limit is 0.7 Jy/beam and so far nearly 70,000 sources have been catalogued. This survey used the 74 MHz system added to the VLA in 1998. It required new imaging algorithms to remove the large ionospheric distortions at this very low frequency throughout the entire ~11.9 degree field of view. This paper describes the observation and data reduction methods used for the VLSS and presents the survey images and source catalog. All of the calibrated images and the source catalog are available online (http://lwa.nrl.navy.mil/VLSS) for use by the astronomical community.

  10. Low frequency variability of Southern Ocean jets

    Science.gov (United States)

    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.

  11. Simple Low-Frequency Beam Pickup

    Energy Technology Data Exchange (ETDEWEB)

    Novokhatski, A.; Heifets, S.; /SLAC; 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.

  12. Low-Frequency Waves in Space Plasmas

    Science.gov (United States)

    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.

  13. Alfven Wave Tomography for Cold MHD Plasmas

    Energy Technology Data Exchange (ETDEWEB)

    I.Y. Dodin; N.J. Fisch

    2001-09-07

    Alfven waves propagation in slightly nonuniform cold plasmas is studied by means of ideal magnetohydrodynamics (MHD) nonlinear equations. The evolution of the MHD spectrum is shown to be governed by a matrix linear differential equation with constant coefficients determined by the spectrum of quasi-static plasma density perturbations. The Alfven waves are shown not to affect the plasma density inhomogeneities, as they scatter off of them. The application of the MHD spectrum evolution equation to the inverse scattering problem allows tomographic measurements of the plasma density profile by scanning the plasma volume with Alfven radiation.

  14. Bench Measurements of Low Frequency Transverse Impedance

    CERN Document Server

    Caspers, Friedhelm; Mostacci, A

    2003-01-01

    For frequencies below 10 MHz the classical two wire transmission line method is subject to difficulties in sensitivity and measurement uncertainties. Thus for evaluation of the low frequency transverse impedance properties of the LHC dump kicker a modified version of the two wire transmission line has been used. It consists, in the present case, of a 10 turn loop of approximately 1 meter length and 2 cm width. The change of input impedance of the loop is measured as a function of the surroundings and by using a proper reference (metallic beampipe) these changes are converted into a meaningful transverse beam coupling impedance. Measurements of several calibration objects have shown close agreement with theoretical results.

  15. Low frequency signal in the GOLF measurements

    Energy Technology Data Exchange (ETDEWEB)

    Grec, G; Provost, J; Renaud, C, E-mail: grec@obs-nice.fr [Universite de Nice-Sophia Antipolis, CNRS UMR 6202 Cassiopee, OCA (France)

    2011-01-01

    This paper shows the results obtained using a revisited method to normalize the velocity evaluation extracted from the measurements, for roughly 14 years of GOLF data. For the search of g modes, we calculate the low frequency power spectrum of the signal with 2 different approaches: - . The classical calculation of the power spectrum of the velocity signal. - . An alternative calculation, extracting first the variations along the time of the p-mode; frequencies, then calculating the power spectrum of those frequency modulation. Both spectra are compared to the g-mode frequency spectrum calculated for a solar model. Several observed frequencies are in close agreement with the calculated g modes. A careful statistical analysis of this result should now follow.

  16. Predictions and observations of low-shear beta-induced shear Alfven-acoustic eigenmodes in toroidal plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Gorelenkov, N.N. [Princeton Plasma Physics Laboratory, Princeton University (United States)], E-mail: ngorelen@pppl.gov; Berk, H.L. [IFS, Austin, Texas (United States); Fredrickson, E. [Princeton Plasma Physics Laboratory, Princeton University (United States); Sharapov, S.E. [Euroatom/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire (United States)

    2007-10-08

    New global MHD eigenmode solutions arising in gaps in the low frequency Alfven-acoustic continuum below the geodesic acoustic mode (GAM) frequency have been found numerically and have been used to explain relatively low frequency experimental signals seen in NSTX and JET tokamaks. These global eigenmodes, referred to here as Beta-induced Alfven-Acoustic Eigenmodes (BAAE), exist in the low magnetic safety factor region near the extrema of the Alfven-acoustic continuum. In accordance to the linear dispersion relations, the frequency of these modes shifts as the safety factor, q, decreases. We show that BAAEs can be responsible for observations in JET plasmas at relatively low beta <2% as well as in NSTX plasmas at relatively high-beta >20%. In contrast to the mostly electrostatic character of GAMs the new global modes also contain an electromagnetic (magnetic field line bending) component due to the Alfven coupling, leading to wave phase velocities along the field line that are large compared to the sonic speed. Qualitative agreement between theoretical predictions and observations are found.

  17. 2D continuous spectrum of shear Alfven waves in the presence of a magnetic island

    CERN Document Server

    Biancalani, Alessandro; Pegoraro, Francesco; Zonca, Fulvio

    2010-01-01

    The radial structure of the continuous spectrum of shear Alfven modes is calculated in the presence of a magnetic island in tokamak plasmas. Modes with the same helicity of the magnetic island are considered in a slab model approximation. In this framework, with an appropriate rotation of the coordinates the problem reduces to 2 dimensions. Geometrical effects due to the shape of the flux surface’s cross section are retained to all orders. On the other hand, we keep only curvature effects responsible of the beta induced gap in the low-frequency part of the continuous spectrum. New continuum accumulation points are found at the O-point of the magnetic island. The beta-induced Alfven Eigenmodes (BAE) continuum accumulation point is found to be positioned at the separatrix flux surface. The most remarkable result is the nonlinear modification of the BAE continuum accumulation point frequency.

  18. Imaging Jupiter Radiation Belts At Low Frequencies

    Science.gov (United States)

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

    2014-04-01

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

  19. Low-frequency characteristics extension for vibration sensors

    Institute of Scientific and Technical Information of China (English)

    杨学山; 高峰; 候兴民

    2004-01-01

    Traditional magneto-electric vibration sensors and servo accelerometers have severe shortcomings when used to measure vibration where low frequency components predominate. A low frequency characteristic extension for velocity vibration sensors is presented in this paper. The passive circuit technology, active compensation technology and the closedcycle pole compensation technology are used to extend the measurable range and to improve low frequency characteristics of sensors. Thses three types of low frequency velocity vibration sensors have been developed and widely adopted in China.

  20. Nonlinear Landau damping and Alfven wave dissipation

    Science.gov (United States)

    Vinas, Adolfo F.; Miller, James A.

    1995-01-01

    Nonlinear Landau damping has been often suggested to be the cause of the dissipation of Alfven waves in the solar wind as well as the mechanism for ion heating and selective preacceleration in solar flares. We discuss the viability of these processes in light of our theoretical and numerical results. We present one-dimensional hybrid plasma simulations of the nonlinear Landau damping of parallel Alfven waves. In this scenario, two Alfven waves nonresonantly combine to create second-order magnetic field pressure gradients, which then drive density fluctuations, which in turn drive a second-order longitudinal electric field. Under certain conditions, this electric field strongly interacts with the ambient ions via the Landau resonance which leads to a rapid dissipation of the Alfven wave energy. While there is a net flux of energy from the waves to the ions, one of the Alfven waves will grow if both have the same polarization. We compare damping and growth rates from plasma simulations with those predicted by Lee and Volk (1973), and also discuss the evolution of the ambient ion distribution. We then consider this nonlinear interaction in the presence of a spectrum of Alfven waves, and discuss the spectrum's influence on the growth or damping of a single wave. We also discuss the implications for wave dissipation and ion heating in the solar wind.

  1. A low frequency rotational energy harvesting system

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  3. Fine Structure Zonal Flow Excitation by Beta-induced Alfven Eigenmode

    CERN Document Server

    Qiu, Zhiyong; Zonca, Fulvio

    2016-01-01

    Nonlinear excitation of low frequency zonal structure (LFZS) by beta-induced Alfven eigenmode (BAE) is investigated using nonlinear gyrokinetic theory. It is found that electrostatic zonal flow (ZF), rather than zonal current, is preferentially excited by finite amplitude BAE. In addition to the well-known meso-scale radial envelope structure, ZF is also found to exhibit fine radial structure due to the localization of BAE with respect to mode rational surfaces. Specifically, the zonal electric field has an even mode structure at the rational surface where radial envelope peaks.

  4. Alfven Wave-Driven Supernova Explosion

    CERN Document Server

    Suzuki, T K; Yamada, S

    2007-01-01

    We investigate the role of Alfven waves in the core-collapse supernova (SN) explosion. We assume that Alfven waves are generated by convections inside a proto-neutron star (PNS) and emitted from its surface. Then these waves propagate outwards and dissipate via nonlinear processes and heat up matter around a stalled prompt shock. To quantitatively assess the importance of this process for revival of the stalled shock, we perform 1D time-dependent hydrodynamical simulations, taking into account the heating via the dissipation of Alfven waves. We show that the shock revival occurs if the surface field strength is larger than ~2x10^{15}G and if the amplitude of velocity fluctuation at the PNS surface is larger than ~ 20% of the local sound speed. Interestingly, the Alfven wave mechanism is self-regulating in the sense that the explosion energy is not very sensitive to the surface field strength and initial amplitude of Alfven waves as long as they are larger than the threshold values given above. It should be em...

  5. Sub-Alfvenic reduced equations in a tokamak

    Science.gov (United States)

    Sengupta, Wrick

    Magnetized fusion experiments generally perform under conditions where ideal Alfvenic modes are stable. It is therefore desirable to develop a reduced formalism which would order out Alfvenic frequencies. This is challenging because sub-Alfvenic phenomena are sensitive to magnetic geometries. In this work an attempt has been made to develop a formalism to study plasma phenomena on time scales much longer than the Alfvenic time scales. (Abstract shortened by ProQuest.).

  6. Elastic envelope inversion using multicomponent seismic data without low frequency

    OpenAIRE

    2014-01-01

    Low frequency is a key issue to reduce the nonlinearity of elastic full waveform inversion. Hence, the lack of low frequency in recorded seismic data is one of the most challenging problems in elastic full waveform inversion. Theoretical derivations and numerical analysis are presented in this paper to show that envelope operator can retrieve strong low frequency modulation signal demodulated in multicomponent data, no matter what the frequency bands of the data is. With the be...

  7. Kinetic Alfven wave turbulence in space plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, R.P. [Plasma Simulation Laboratory, Centre for Energy Studies, Indian Institute of Technology, Delhi-110016, New Delhi (India); Kumar, Sachin, E-mail: dynamicalfven@gmail.co [Plasma Simulation Laboratory, Centre for Energy Studies, Indian Institute of Technology, Delhi-110016, New Delhi (India)

    2010-07-26

    This work presents the derivation of nonlinear coupled equations for the evolution of solar wind turbulence. These equations are governing the coupled dynamics of kinetic Alfven wave and ion acoustic wave. Numerical simulation of these equations is also presented. The ponderomotive nonlinearity is incorporated in the wave dynamics. Filamentation of kinetic Alfven wave and the turbulent spectra are presented in intermediate-{beta} plasmas at heliocentric distances (0.3 AU{<=}r<1.0 AU). The growing filaments and steeper turbulent spectra (of power law k{sup -S}, 5/3{<=}S{<=}3) can be responsible for plasma heating and particle acceleration in solar wind.

  8. Nonlinear Landau damping of Alfven waves.

    Science.gov (United States)

    Hollweg, J. V.

    1971-01-01

    Demonstration that large-amplitude linearly or elliptically polarized Alfven waves propagating parallel to the average magnetic field can be dissipated by nonlinear Landau damping. The damping is due to the longitudinal electric field associated with the ion sound wave which is driven (in second order) by the Alfven wave. The damping rate can be large even in a cold plasma (beta much less than 1, but not zero), and the mechanism proposed may be the dominant one in many plasmas of astrophysical interest.

  9. Beam Distribution Modification By Alfven Modes

    Energy Technology Data Exchange (ETDEWEB)

    White, R. B.; Gorelenkov, N.; Heidbrink, W. W.; Van Zeeland, M. A.

    2010-01-25

    Modification of a deuterium beam distribution in the presence of low amplitude Toroidal Alfven (TAE) eigenmodes and Reversed Shear Alfven (RSAE) eigenmodes in a toroidal magnetic confinement device is examined. Comparison with experimental data shows that multiple low amplitude modes can account for significant modification of high energy beam particle distributions. It is found that there is a stochastic threshold for beam transport, and that the experimental amplitudes are only slightly above this threshold. The modes produce a substantial central flattening of the beam distribution.

  10. Beam Distribution Modification by Alfven Modes

    Energy Technology Data Exchange (ETDEWEB)

    White, R. B.; Gorelenkov, N.; Heidbrink, W. W.; Van Zeeland, M. A.

    2010-04-03

    Modification of a deuterium beam distribution in the presence of low amplitude Toroidal Alfven (TAE) eigenmodes and Reversed Shear Alfven (RSAE) eigenmodes in a toroidal magnetic confinement device is examined. Comparison with experimental data shows that multiple low amplitude modes can account for significant modification of high energy beam particle distributions. It is found that there is a stochastic threshold for beam transport, and that the experimental amplitudes are only slightly above this threshold. The modes produce a substantial central flattening of the beam distribution.

  11. Analysis of Magnetic Fields in Inertial Alfven Wave Collisions

    CERN Document Server

    Drake, Dereth J; Shanken, Brian C; Howes, Gregory G; Skiff, Frederick; Kletzing, Craig A; Carter, Troy A; Dorfman, Seth

    2014-01-01

    Turbulence in astrophysical and space plasmas is dominated by the nonlinear interaction of counterpropagating Alfven waves. Most Alfven wave turbulence theories have been based on ideal plasma models, such as incompressible MHD, for Alfven waves at large scales. However, in the inertial Alfven wave regime (vA > vthe), relevant to magnetospheric plasmas, how the turbulent nonlinear interactions are modified by the dispersive nature of the waves remains to be explored. Here we present the first laboratory evidence of the nonlinear interaction in the inertial regime. A comparison is made with the theory for MHD Alfven waves.

  12. Annoyance of low frequency noise and traffic noise

    DEFF Research Database (Denmark)

    Mortensen, F.R.; Poulsen, Torben

    2001-01-01

    The annoyance of different low frequency noise sources was determined and compared to the annoyance from traffic noise. Twenty-two subjects participated in laboratory listening tests. The sounds were presented by loudspeakers in a listening room and the spectra of the low frequency noises were...

  13. Nonlinear Evolution of Alfvenic Wave Packets

    Science.gov (United States)

    Buti, B.; Jayanti, V.; Vinas, A. F.; Ghosh, S.; Goldstein, M. L.; Roberts, D. A.; Lakhina, G. S.; Tsurutani, B. T.

    1998-01-01

    Alfven waves are a ubiquitous feature of the solar wind. One approach to studying the evolution of such waves has been to study exact solutions to approximate evolution equations. Here we compare soliton solutions of the Derivative Nonlinear Schrodinger evolution equation (DNLS) to solutions of the compressible MHD equations.

  14. Spectral stability of Alfven filament chains

    NARCIS (Netherlands)

    Bergmans, J.; Kuvshinov, B. N.; Lakhin, V. P.; Schep, T. J.

    2000-01-01

    The two-fluid model of nonlinear Alfven perturbations has singular solutions in the form of current-vortex filaments. We investigate analytically and numerically the spectral stability of single and double rows of filaments. Staggered and non-staggered double rows (von Karman streets) are studied. I

  15. Spectral stability of Alfven filament configurations

    NARCIS (Netherlands)

    Bergmans, J.; Kuvshinov, B. N.; Lakhin, V. P.; Schep, T. J.

    2000-01-01

    The two-fluid plasma equations that describe nonlinear Alfven perturbations have singular solutions in the form of current-vortex filaments. These filaments are analogous to point vortices in ideal hydrodynamics and geostrophic fluids. In this work the spectral (linear) stability of current-vortex f

  16. The influences of low frequency noise on mental performance

    Directory of Open Access Journals (Sweden)

    J. Hatami

    2008-01-01

    Full Text Available AbstractBackground and Purpose: Although the evolution of industrial systems toward digital technologies decreased the exposure to high levels of noise, it has created some problems encountered with low level and provoking noise (low frequency noise. In the present work, the mental performance of students exposed to low frequency and reference noises at low and high levels (45 & 65 dB were studied. Additionally, other factors such as annoyance, sensitivity to low frequency noise and hearing status of participants were considered.Materials and Methods: After generating low frequency and reference noises required for the study, a pilot study was conducted. Then, 54 students participated in the main study after preliminary tests. Their mental performances were evaluated with standard psychological tests while they were exposed to low frequency and reference noises at 45 and 65 dBA.Results: The results showed that noise annoyance and low frequency noise sensitivity do not have a significant correlation with age and sex. The results also revealed that, low frequency noise at 65 dB can decrease concentration (P=0.003 and increase response time (P=0.039 of performance in comparison with low frequency noise at 45 dB. On the other hand, reference noise at 65 dB can increase speed (P<0.001 of performance in comparison with reference noise at 45 dB.Conclusion: Low frequency noise can reduce the mental performance and increase its response time.Key words: Low Frequency Noise, Reference Noise, Noise Annoyance, Mental PerformanceJ Mazand Univ Med Sci 2008; 18(63: 55-65(Persian

  17. Low Frequency Scattering Resonance Wave in Strong Heterogeneity

    CERN Document Server

    Liu, Yinbin

    2015-01-01

    Multiple scattering of wave in strong heterogeneity can cause resonance-like wave phenomenon where signal exhibits low frequency, high intensity, and slowly propagating velocity. For example, long period event in volcanic seismology and surface plasmon wave and quantum Hall effect in wave-particle interactions. Collective behaviour in a many-body system is usually thought to be the source for generating the anomaly. However, the detail physical mechanism is not fully understood. Here I show by wave field modeling for microscopic bubble cloud model and 1D heterogeneity that the anomaly is related to low frequency scattering resonance happened in transient regime. This low frequency resonance is a kind of wave coherent scattering enhancement phenomenon in strongly-scattered small-scale heterogeneity. Its resonance frequency is inversely proportional to heterogeneous scale and contrast and will further shift toward lower frequency with random heterogeneous scale and velocity fluctuations. Low frequency scatterin...

  18. Distortion-product otoacoustic emission at low frequencies in humans

    DEFF Research Database (Denmark)

    Christensen, Anders Tornvig

    The sensory organ of hearing, the cochlea, emits faint sound as it processes incoming sound. Measurement of such "otoacoustic emission" in the ear canal provides evidence for how the live, healthy ear works. Emissions at mid frequencies associated with speech is usually of prime interest. Low......-frequency hearing has not yet been characterized by measurement of low-frequency emissions from the cochlea. Low-frequency emissions are expected to be covered in sounds of breathing, blood circulation, and so on, if they exist at all at measurable levels. The present study shows, in essence, that the human ear...... emits distortion at least 1-2 octaves lower in frequency than has previously been shown. The emission is promising for further exploratory and clinical assessment of cochlear activity associated with low-frequency hearing. Anders received his M.Sc. degree in acoustics in 2012 from Aalborg University...

  19. Oscillographic Chronopotentiometry with High and Low Frequency Current

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    A novel electroanalytical method, oscillographic chronopotentiometry with high and low frequency current, is presented in this paper. With this method, the sensitivity of almost all kinds of oscillographic chronopotentiometry can be enhanced about one order.

  20. Challenges and limitations in retrofitting facilities for low frequency noise

    Energy Technology Data Exchange (ETDEWEB)

    Wierzba, P. [ATCO Noise Management, Calgary, AB (Canada)

    2007-07-01

    The trend to revise and increase environmental regulations regarding low frequency noise emissions from oil and gas facilities was discussed. Noise related complaints can often be traced to low frequency noise, which is the unwanted sound with a frequency range falling within 31.5-Hz, 63-Hz, and 125-Hz octave bands. This paper also discussed the challenges and limitations of field retrofits of the facilities aimed at reducing low frequency noise. The main sources of low frequency noise associated with a compression facility are the radiator cooler, engine exhaust and the building envelope. Regulators are paying close attention not only to the overall noise exposure as measured by the A-weighted levels, but also to the quality of noise emitted by the particular frequency spectrum. The Alberta Energy and Utilities Board recently issued Noise Control Directive 38 and made it a requirement to perform low frequency noise impact assessment for permitting of all new energy facilities. Under Directive 38, the low frequency noise assessment is to be performed using the C-weighted scale as a measure in addition to the previously used A-weighted scale. Directive 38 recommends that in order to avoid low frequency noise problems the difference between the C-weighted and A-weighted levels at the residential locations should be lower than 20 dB. This implies that noise should be limited to 60 dBC for Category 1 residences of low dwelling density. Small upgrades and changes can be made to lower low frequency noise emissions. These may include upgrading building wall insulation, providing wall-to-skid isolation system, upgrading the fan blades, or reducing the rpm of the fans. It was concluded that these upgrades should be considered for facilities in close proximity to residential areas. 3 refs., 2 tabs., 7 figs.

  1. Low frequency magnetic signals associated with Langmuir waves

    Science.gov (United States)

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

    1992-01-01

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

  2. Phase-dependent audiometry with low-frequency masking revisited.

    Science.gov (United States)

    Rahne, Torsten; Rasinski, Christine; Neumann, Kerstin

    2010-05-15

    Low-frequency masking is a psychoacoustical phenomenon, describing the modulation of a high-frequency probe tone burst by a low-frequency masker tone. The probe tone threshold is increased, if the probe tone is presented at a low-frequency phases around 90 degrees and 270 degrees . At these phases, the low-frequency masker tone induces a displacement of the basilar membrane of the inner ear which modulates the sensitivity of the inner hair cells. Measuring the modulation depth is partially applied in clinical routine to diagnose the endolymphatic hydrops. Although the modulation depth differs between normal ears and those which reveal an endolymphatic hydrops, the significance of these tests seems debatable. Here, we describe a new experimental setup, completely consisting of commercially available devices. Further, a user interface was developed to enable the application in the clinical routine. The experimental setup was approved with ten normal hearing listeners. All reveal a modulation of the probe stimulus threshold by different phases of the low-frequency masker stimulus. With this experimental setup, custom-made modifications of the essential parameters are feasible. This would be a contribution to solve open questions on the clinical relevance of the low-frequency masking phenomenon.

  3. Global Alfven Waves in Solar Physics: Coronal Heating

    Science.gov (United States)

    de Azevedo, C. A.; de Assis, A. S.

    1990-11-01

    RESUMEN. Se ha demostrado que Ia onda discreta de Alfven puede generar por lo memos un 20% de la energia coronal requerida con densidad de flujo de lO- erg 5 . Las ondas discretas de Alfven son una nueva clase `de ondas de Alfven las cuales pueden describirse por el modelo con que incluye un i6n finito, con frecuencia ciclotr6nica ( /uci # 0) y los efectos del equilibrio de plasma mostrados por Appert, Vaclavik and Villar 1984. ABSTRACT. It has been shown that the Discrete Alfven wave can power at least 20% of the required coronal energy flux density iO- Discrete Alfven waves are a new class of Alfven waves wich can be described by the model with the inclusion of finite ion cyclotron frequency (w/wci 0) and the equilibrium plasma current effects as shown by Appert, Vaclavik and Villar 1984. o,t :, HYDROMAGNETICS - SUN-CORONA

  4. Torsional Alfven waves in stratified and expanding magnetic flux tubes

    OpenAIRE

    2011-01-01

    The effects of both density stratification and magnetic field expansion on torsional Alfven waves in magnetic flux tubes are studied. The frequencies, the period ratio P1/P2 of the fundamental and its first-overtone, and eigenfunctions of torsional Alfven modes are obtained. Our numerical results show that the density stratification and magnetic field expansion have opposite effects on the oscillating properties of torsional Alfven waves.

  5. Adiabatic trapping in coupled kinetic Alfven-acoustic waves

    Energy Technology Data Exchange (ETDEWEB)

    Shah, H. A.; Ali, Z. [Department of Physics, G.C. University, 54000 Lahore (Pakistan); Masood, W. [COMSATS, Institute of Information Technology, Park Road, Chak Shahzad, Islamabad 44000 (Pakistan); National Centre for Physics (NCP), Shahdara Valley Road, 44000 Islamabad (Pakistan); Theoretical Plasma Physics Division, P. O. Nilore, Islamabad (Pakistan)

    2013-03-15

    In the present work, we have discussed the effects of adiabatic trapping of electrons on obliquely propagating Alfven waves in a low {beta} plasma. Using the two potential theory and employing the Sagdeev potential approach, we have investigated the existence of arbitrary amplitude coupled kinetic Alfven-acoustic solitary waves in both the sub and super Alfvenic cases. The results obtained have been analyzed and presented graphically and can be applied to regions of space where the low {beta} assumption holds true.

  6. Low-n shear Alfven spectra in axisymmetric toroidal plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, C.Z.; Chance, M.S.

    1985-11-01

    In toroidal plasmas, the toroidal magnetic field is nonuniform over a magnetic surface and causes coupling of different poloidal harmonics. It is shown both analytically and numerically that the toroidicity not only breaks up the shear Alfven continuous spectrum, but also creates new, discrete, toroidicity-induced shear Alfven eigenmodes with frequencies inside the continuum gaps. Potential applications of the low-n toroidicity-induced shear Alfven eigenmodes on plasma heating and instabilities are addressed. 17 refs., 4 figs.

  7. Riemann solvers and Alfven waves in black hole magnetospheres

    Science.gov (United States)

    Punsly, Brian; Balsara, Dinshaw; Kim, Jinho; Garain, Sudip

    2016-09-01

    In the magnetosphere of a rotating black hole, an inner Alfven critical surface (IACS) must be crossed by inflowing plasma. Inside the IACS, Alfven waves are inward directed toward the black hole. The majority of the proper volume of the active region of spacetime (the ergosphere) is inside of the IACS. The charge and the totally transverse momentum flux (the momentum flux transverse to both the wave normal and the unperturbed magnetic field) are both determined exclusively by the Alfven polarization. Thus, it is important for numerical simulations of black hole magnetospheres to minimize the dissipation of Alfven waves. Elements of the dissipated wave emerge in adjacent cells regardless of the IACS, there is no mechanism to prevent Alfvenic information from crossing outward. Thus, numerical dissipation can affect how simulated magnetospheres attain the substantial Goldreich-Julian charge density associated with the rotating magnetic field. In order to help minimize dissipation of Alfven waves in relativistic numerical simulations we have formulated a one-dimensional Riemann solver, called HLLI, which incorporates the Alfven discontinuity and the contact discontinuity. We have also formulated a multidimensional Riemann solver, called MuSIC, that enables low dissipation propagation of Alfven waves in multiple dimensions. The importance of higher order schemes in lowering the numerical dissipation of Alfven waves is also catalogued.

  8. Low-frequency noise from large wind turbines.

    Science.gov (United States)

    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.

  9. Radiative cooling and broadband phenomenon in low-frequency waves

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    In this paper, we analyze the effects of radiative cooling on the pure baroclinic low-frequency waves under the approximation of equatorial -plane and semi-geostrophic condition. The results show that radiative cooling does not, exclusively, provide the damping effects on the development of low-frequency waves. Under the delicate radiative-convective equilibrium, radiative effects will alter the phase speed and wave period, and bring about the broadband of phase velocity and wave period by adjusting the vertical profiles of diabatic heating. when the intensity of diabatic heating is moderate and appropriate, it is conductive to the development and sustaining of the low-frequency waves and their broadband phenomena, not the larger, the better. The radiative cooling cannot be neglected in order to reach the moderate and appropriate intensity of diabatic heating.

  10. Behavioral estimates of human frequency selectivity at low frequencies

    DEFF Research Database (Denmark)

    Orellana, Carlos Andrés Jurado

    A fundamental property of our hearing organ is its ability to break down sound into different spectral components, allowing us to make use of the richness in natural sound phenomena. Auditory filters, which conceptualize this property of the ear, however, have not been appropriately described...... at low sound frequencies. As a consequence of our lack of knowledge, we cannot accurately model our perception of complex low-frequency sound (such as that emitted by wind turbines or industrial processes, which can easily produce annoyance) nor make meaningful predictions of our perception based...... on physical sound measurements. In this PhD thesis a detailed description of frequency selectivity at low frequencies is given. Different experiments have been performed to determine the properties of human auditory filters. Besides, loudness perception of low-frequency sinusoidal signals has been evaluated...

  11. Present and Future Modes of Low Frequency Climate Variability

    Energy Technology Data Exchange (ETDEWEB)

    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.

  12. Spontaneous low-frequency oscillations in cerebral vessels

    DEFF Research Database (Denmark)

    Schytz, Henrik W; Hansson, Andreas; Phillip, Dorte

    2010-01-01

    The etiology behind and physiological significance of spontaneous oscillations in the low-frequency spectrum in both systemic and cerebral vessels remain unknown. Experimental studies have proposed that spontaneous oscillations in cerebral blood flow reflect impaired cerebral autoregulation (CA......). Analysis of CA by measurement of spontaneous oscillations in the low-frequency spectrum in cerebral vessels might be a useful tool for assessing risk and investigating different treatment strategies in carotid artery disease (CAD) and stroke. We reviewed studies exploring spontaneous oscillations...... coefficients in the time domain are the most frequently used parameters for analyzing spontaneous oscillations in systemic and cerebral vessels. At present, there is no gold standard for analyzing spontaneous oscillations in the low-frequency spectrum, and simplistic models of CA have failed to predict...

  13. EFFECTS OF LOW FREQUENCY ELECTROMAGNETIC FIELDON THE HUMAN BODY

    Directory of Open Access Journals (Sweden)

    PETRICA POPOV

    2016-06-01

    Full Text Available International standardization institutions, which play an important role in assessing the effects o f the field and determining the need to take protective measures for the human factor, developed safety standards on human exposure to electromagnetic field, differentiated for electric and magnetic fields of low frequency ( near fields, as well as to ele ctromagnetic radiation fields (far fields. Until recently, many studies has shown that the main harmful effect on the human body was produced by high frequency electromagnetic field, but in recent years, more and more information also reveals that the serious damage can be caused by low frequency electric and magnetic fields. These low -frequency electromagnetic fields interact with human tissue causing harmful effects, the degree of destruction depending on factors such as: intensity, frequency, energy f ield level and duration of exposure.

  14. Detection of Ionospheric Alfven Resonator Signatures Onboard C/NOFS: Implications for IRI Modeling

    Science.gov (United States)

    Simoes, F.; Klenzing, J.; Ivanov, S.; Pfaff, R.; Rowland, D.; Bilitza, D.

    2011-01-01

    The 2008-2009 long-lasting solar minimum activity has been the one of its kind since the dawn of space age, offering exceptional conditions for investigating space weather in the near-Earth environment. First ever detection of Ionospheric Alfven Resonator (IAR) signatures in orbit offers new means for investigating ionospheric electrodynamics, namely MHD (MagnetoHydroDynamics) wave propagation, aeronomy processes, ionospheric dynamics, and Sun-Earth connection mechanisms at a local scale. Local and global plasma density heterogeneities in the ionosphere and magnetosphere allow for formation of waveguides and resonators where magnetosonic and shear Alfven waves propagate. The ionospheric magnetosonic waveguide results from complete magnetosonic wave reflection about the ionospheric F-region peak, where the Alfven index of refraction presents a maximum. MHD waves can also be partially trapped in the vertical direction between the lower boundary of the ionosphere and the magnetosphere, a resonance mechanism known as IAR. In this work we present C/NOFS (Communications/Navigation Outage Forecasting System) Extremely Low Frequency (ELF) electric field measurements related to IAR signatures, discuss the resonance and wave propagation mechanisms in the ionosphere, and address the electromagnetic inverse problem from which electron/ion distributions can be derived. These peculiar IAR electric field measurements provide new, complementary methodologies for inferring ionospheric electron and ion density profiles, and also contribute for the investigation of ionosphere dynamics and space weather monitoring. Specifically, IAR spectral signatures measured by C/NOFS contribute for improving the International Reference Ionosphere (IRI) model, namely electron density and ion composition.

  15. Low frequency noise reduction using stiff light composite panels

    Institute of Scientific and Technical Information of China (English)

    DENG Yongchang; LIN Weizheng

    2003-01-01

    The experiment presented in this paper is to investigate and analyze the noise reduction at low frequency using stiff light composite panels. Since these composite panels are made of lightweight and stiff materials, this actuation strategy will enable the creation of composite panels for duct noise control without using traditional heavy structural mass. The results suggest that the mass-spring resonance absorption in the case of a comparatively stiff thick panel with a thin flexible plate is more efficient with minimum weight, when subjected to low-frequency (<500 Hz). The efficiency of the panel absorber depends on the mass of the thin flexible plate and the stiffness of the panel.

  16. Simulation of the low-frequency collimator impedance

    CERN Document Server

    Kroyer, T

    2008-01-01

    The low-frequency transverse collimator impedance constitutes a major part of the LHC impedance budget. In this paper numerical simulations for frequencies below 1 MHz using a commercial package are presented. From the 3D field solution of the two-wire simulations the transverse impedance is directly calculated. After a cross-check with theory for rotationally symmetric structures a geometry with two jaws and an LHC graphite collimator is examined. Furthermore, a simple physics picture that explains the principal characteristics of the impedance at high and low frequencies is given.

  17. Mixed Discretization of the Time Domain MFIE at Low Frequencies

    KAUST Repository

    Ulku, Huseyin Arda

    2017-01-10

    Solution of the magnetic field integral equation (MFIE), which is obtained by the classical marching on-in-time (MOT) scheme, becomes inaccurate when the time step is large, i.e., under low-frequency excitation. It is shown here that the inaccuracy stems from the classical MOT scheme’s failure to predict the correct scaling of the current’s Helmholtz components for large time steps. A recently proposed mixed discretization strategy is used to alleviate the inaccuracy problem by restoring the correct scaling of the current’s Helmholtz components under low-frequency excitation.

  18. Resonances in low frequency ionization by periodic electric fields

    Energy Technology Data Exchange (ETDEWEB)

    Dando, P.A.; Richards, D. (Open Univ., Milton Keynes (United Kingdom). Mathematics Faculty)

    1993-09-28

    The behaviour of a one-dimensional system perturbed by a low frequency, periodic electric field is examined in the limit as the field frequency, [Omega], tends to zero, that is the static field limit. In particular we obtain estimates of the widths of each member of the infinite set of resonances between any finite value of [Omega] and 0. In order to obtain this estimate we derive a new analytic approximation of the two-state equations of motion. Our analysis shows why recent experiments on the ionization of excited hydrogen atoms by low frequency fields failed to observe any resonances. (author).

  19. DATA ACQUISITION AND ANALYSIS OF LOW FREQUENCY ELECTROMAGNETIC FIELD

    Directory of Open Access Journals (Sweden)

    PETRICA POPOV

    2016-06-01

    Full Text Available In recent years more and more studies have shown that, the low frequency field strength (particularly magnetic, 50 / 60Hz are a major risk factor; according to some specialists - even more important as the radiation field. As a result, the personnel serving equipment and facilities such as: electric generators, synchronous, the motors, the inverters or power transformers is subjected continually to intense fields, in their vicinity, with possible harmful effects in the long term by affecting metabolism cell, espectively, the biological mechanisms.Therefore, finding new methods and tools for measurement and analysis of low frequency electromagnetic fields may lead to improved standards for exposure limits of the human body.

  20. Investigation on upsetting assisted by low-frequency vibration

    Directory of Open Access Journals (Sweden)

    Zhang M.

    2015-01-01

    Full Text Available The application of vibration load in metal forming processes has been demonstrated to be effective in reducing the forming load. In this paper, upsetting processes assisted by low-frequency vibration at room temperature was investigated based on finite element simulations. The vibration load was applied by the reciprocating movement of the upsetting punch. The influence of vibration frequency and feeding rate were analysed. It was revealed that low-frequency vibration was effective to reduce the mean forming load and increase the friction between billets and tools.

  1. An analysis of low frequency noise from large wind turbines

    DEFF Research Database (Denmark)

    Pedersen, Christian Sejer; Møller, Henrik

    2010-01-01

    between 75 kW and 3.6 MW was analyzed. The apparent sound power, LWA, increases with electric power at a rate close to 3 dB per doubling of electric power. The low-frequency proportion (10-160 Hz) increases more rapidly, and the difference in slope is statistically significant. A comparison of one-third-octave......As wind turbines get larger, worries have emerged, that the noise emitted by the turbines would move down in frequency, and that the contents of low-frequency noise would be enough to cause significant annoyance for the neighbors. The sound emission from 48 wind turbines with nominal electric power...

  2. Nonlinear Low Frequency Water Waves in a Cylindrical Shell

    Science.gov (United States)

    Peng, H. W.; Wang, D. J.; Lee, C. B.

    The experiment was carried out to study the low frequency surface waves due to the horizontal high frequency excitation. The feature of the phenomenon was that the big amplitude axisymmetric surface wave frequency was typically about 1/50 of the excitation frequency. The viscous effect of water was neglected as a first approximation in the earlier papers on this subject. In contrast, we found the viscosity was important to achieve the low frequency water wave with the cooperation of hundreds of "finger" waves. Photographs were taken with stroboscopic lighting and thereafter relevant quantitative results were obtained based on the measurements with Polytec Scanning Vibrometer PSV 400.

  3. Low-Frequency Relaxation Oscillations in Capacitive Discharge Processes

    Institute of Scientific and Technical Information of China (English)

    ZHOU Zhu-Wen; M.A.LIEBERMAN; Sungjin KIM; JI Shi-Yin; DENG Ming-Sen; SUN Guang-Yu

    2008-01-01

    Low-frequency (2.72-3.70 Hz) relaxation oscillations at 100m Tort at higher absorbed power were observed from time-varying optical emission of the main discharge chamber and the periphery.We interpret the low frequency oscillations using an electromagnetic model of the slot impedance with parallel connection variational peripheral capacitance,coupled to a circuit analysis of the system including the matching network.The model results are in general agreement with the experimental observations,and indicate a variety of bchaviours dependent on the matching conditions.

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

    Science.gov (United States)

    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.

  5. Kinetic Alfv\\'{e}n turbulence below and above ion-cyclotron frequency

    CERN Document Server

    Zhao, J S; Wu, D J; Yu, M Y

    2015-01-01

    Alfv\\'{e}nic turbulent cascade perpendicular and parallel to the background magnetic field is studied accounting for anisotropic dispersive effects and turbulent intermittency. The perpendicular dispersion and intermittency make the perpendicular-wavenumber magnetic spectra steeper and speed up production of high ion-cyclotron frequencies by the turbulent cascade. On the contrary, the parallel dispersion makes the spectra flatter and decelerate the frequency cascade above the ion-cyclotron frequency. Competition of the above factors results in spectral indices distributed in the interval [-2,-3], where -2 is the index of high-frequency space-filling turbulence, and -3 is the index of low-frequency intermittent turbulence formed by tube-like fluctuations. Spectra of fully intermittent turbulence fill a narrower range of spectral indices [-7/3,-3], which almost coincides with the range of indexes measured in the solar wind. This suggests that the kinetic-scale turbulent spectra are shaped mainly by dispersion a...

  6. Nonlinear propagation of short wavelength drift-Alfven waves

    DEFF Research Database (Denmark)

    Shukla, P. K.; Pecseli, H. L.; Juul Rasmussen, Jens

    1986-01-01

    Making use of a kinetic ion and a hydrodynamic electron description together with the Maxwell equation, the authors derive a set of nonlinear equations which governs the dynamics of short wavelength ion drift-Alfven waves. It is shown that the nonlinear drift-Alfven waves can propagate as two...

  7. Alfven cyclotron instability and ion cyclotron emission

    Energy Technology Data Exchange (ETDEWEB)

    Gorelenkov, N.N.; Cheng, C.Z.

    1995-07-01

    Two-dimensional solutions of compressional Alfven eigenmodes (CAE) are studied in the cold plasma approximation. For finite inverse aspect ratio tokamak plasmas the two-dimensional eigenmode envelope is localized at the low magnetic field side with the radial and poloidal localization on the order of a/{radical}m and a/(fourth root of m), respectively, where m is the dominant poloidal mode number. Charged fusion product driven Alfven Cyclotron Instability (ACI) of the compressional Alfven eigenmodes provides the explanation for the ion cyclotron emission (ICE) spectrum observed in tokamak experiments. The ACI is excited by fast charged fusion products via Doppler shifted cyclotron wave-particle resonances. The ion cyclotron and electron Landau dampings and fast particle instability drive are calculated perturbatively for deuterium-deuterium (DD) and deuterium-tritium (DT) plasmas. Near the plasma edge at the low field side the velocity distribution function of charged fusion products is localized in both pitch angle and velocity. The poloidal localization of the eigenmode enhances the ACI growth rates by a factor of {radical}m in comparison with the previous results without poloidal envelope. The thermal ion cyclotron damping determines that only modes with eigenfrequencies at multiples of the edge cyclotron frequency of the background ions can be easily excited and form an ICE spectrum similar to the experimental observations. Theoretical understanding is given for the results of TFTR DD and DT experiments with {upsilon}{sub {alpha}0}/{upsilon}{sub A} < 1 and JET experiments with {upsilon}{sub {alpha}0}/{upsilon}{sub A} > 1.

  8. Roles of Fast-Cyclotron and Alfven-Cyclotron Waves for the Multi-Ion Solar Wind

    CERN Document Server

    Xiong, Ming

    2012-01-01

    Using linear Vlasov theory of plasma waves and quasi-linear theory of resonant wave-particle interaction, the dispersion relations and the electromagnetic field fluctuations of fast and Alfven waves are studied for a low-beta multi-ion plasma in the inner corona. Their probable roles in heating and accelerating the solar wind via Landau and cyclotron resonances are quantified. We assume that (1) low-frequency Alfven and fast waves have the same spectral shape and the same amplitude of power spectral density; (2) these waves eventually reach ion cyclotron frequencies due to a turbulence cascade; (3) kinetic wave-particle interaction powers the solar wind. The existence of alpha particles in a dominant proton/electron plasma can trigger linear mode conversion between oblique fast-whistler and hybrid alpha-proton cyclotron waves. The fast-cyclotron waves undergo both alpha and proton cyclotron resonances. The alpha cyclotron resonance in fast-cyclotron waves is much stronger than that in Alfven-cyclotron waves. ...

  9. HLL Riemann Solvers and Alfven Waves in Black Hole Magnetospheres

    CERN Document Server

    Punsly, Brian; Kim, Jinho; Garain, Sudip

    2016-01-01

    In the magnetosphere of a rotating black hole, an inner Alfven critical surface (IACS) must be crossed by inflowing plasma. Inside the IACS, Alfven waves are inward directed toward the black hole. The majority of the proper volume of the active region of spacetime (the ergosphere) is inside of the IACS. The charge and the totally transverse momentum flux (the momentum flux transverse to both the wave normal and the unperturbed magnetic field) are both determined exclusively by the Alfven polarization. However, numerical simulations of black hole magnetospheres are often based on 1-D HLL Riemann solvers that readily dissipate Alfven waves. Elements of the dissipated wave emerge in adjacent cells regardless of the IACS, there is no mechanism to prevent Alfvenic information from crossing outward. Thus, it is unclear how simulated magnetospheres attain the substantial Goldreich-Julian charge density associated with the rotating magnetic field. The HLL Riemann solver is also notorious for producing large recurring...

  10. Damping of visco-resistive Alfven waves in solar spicules

    Directory of Open Access Journals (Sweden)

    Z Fazel

    2014-12-01

    Full Text Available Interaction of Alfven waves with plasma inhomogeneity generates phase mixing which can cause the dissipation of Alfven waves. We investigated the dissipation of standing Alfven waves due to phase mixing at the presence of steady flow and sheared magnetic field in solar spicules. Moreover, the transition region between chromosphere and corona was considered. Our numerical simulation showed that the phase mixing and dissipation rate of Alfven waves are enhanced relative to viscosity and resistivity gradients. Comparison of the results of our models with and without these gradients illustrated a significant difference between them. In other words, with these assumptions, Alfven waves may transfer the photospheric energy to the corona during timescales corresponding to the observed lifetimes of spicules. It should be noted that the results of our numerical simulation were in good agreement with observational scaling law obtained by Kuridze et al. [1

  11. Low frequency fluctuation with two external cavity reflectors

    Institute of Scientific and Technical Information of China (English)

    王春林; 伍剑; 林金桐

    2003-01-01

    The dynamics of a semiconductor laser with two optical feedbacks is studied in this paper. A new set of nonlinear rate equations that can describe external cavity semiconductor lasers with any amount of two optical feedbacks is proposed. It is found that when the laser is biased above the threshold and subjected to one feedback, the other feedback can induce low-frequency fluctuations.

  12. Low-frequency scattering from two-dimensional perfect conductors

    DEFF Research Database (Denmark)

    Hansen, Thorkild; Yaghjian, A.D

    1991-01-01

    Exact expressions have been obtained for the leading terms in the low-frequency expansions of the far fields scattered from three different types of two-dimensional perfect conductors: a cylinder with finite cross section, a cylindrical bump on an infinite ground plane, and a cylindrical dent...

  13. Subpixel edge detection method based on low-frequency filtering

    Science.gov (United States)

    Bylinsky, Yosip Y.; Kotyra, Andrzej; Gromaszek, Konrad; Iskakova, Aigul

    2016-09-01

    A method of edge detection in images is proposed basing that based on low-frequency filtering. The method uses polynomial interpolation to determine the coordinates of the edge point with subpixel accuracy. Some experiments have been results also have been provided.

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

    DEFF Research Database (Denmark)

    León-Tavares, J.; Falvella, M.C.; Stompor, R.

    2011-01-01

    We describe the processing of data from the Low Frequency Instrument (LFI) used in production of the Planck Early Release Compact Source Catalogue (ERCSC). In particular, we discuss the steps involved in reducing the data from telemetry packets to cleaned, calibrated, time-ordered data (TOD) and ...

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

    DEFF Research Database (Denmark)

    León-Tavares, J.; Falvella, M.C.; Stompor, R.;

    2011-01-01

    We describe the processing of data from the Low Frequency Instrument (LFI) used in production of the Planck Early Release Compact Source Catalogue (ERCSC). In particular, we discuss the steps involved in reducing the data from telemetry packets to cleaned, calibrated, time-ordered data (TOD) and ...

  16. Low frequency interference between short synchrotron radiation sources

    Directory of Open Access Journals (Sweden)

    F. Méot

    2001-06-01

    Full Text Available A recently developed analytical formalism describing low frequency far-field synchrotron radiation (SR is applied to the calculation of spectral angular radiation densities from interfering short sources (edge, short magnet. This is illustrated by analytical calculation of synchrotron radiation from various assemblies of short dipoles, including an “isolated” highest density infrared SR source.

  17. Intrinsic low-frequency variability of the Gulf Stream

    NARCIS (Netherlands)

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

    2012-01-01

    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 schem

  18. Intrinsic low-frequency variability of the Gulf Stream

    Science.gov (United States)

    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.

  19. Intrinsic low-frequency variability of the Gulf Stream

    Directory of Open Access Journals (Sweden)

    G. Quattrocchi

    2012-03-01

    Full Text Available 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.

  20. Low-frequency noise in planar Hall effect bridge sensors

    DEFF Research Database (Denmark)

    Persson, Anders; Bejhedb, R.S.; Bejhed, R.S.

    2011-01-01

    The low-frequency characteristics of planar Hall effect bridge sensors are investigated as function of the sensor bias current and the applied magnetic field. The noise spectra reveal a Johnson-like spectrum at high frequencies, and a 1/f-like excess noise spectrum at lower frequencies, with a knee...

  1. Intrinsic low-frequency variability of the Gulf Stream

    NARCIS (Netherlands)

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

    2012-01-01

    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

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

    NARCIS (Netherlands)

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

    2010-01-01

    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 an

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

    NARCIS (Netherlands)

    Sterk, A. E.; Vitolo, R.; Broer, H.W.; Simó, C.; Dijkstra, H.A.|info:eu-repo/dai/nl/073504467

    2010-01-01

    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 a

  4. Musculoskeletal modelling of low-frequency whole-body vibrations

    DEFF Research Database (Denmark)

    Rasmussen, John; Andersen, Michael Skipper

    2012-01-01

    This paper presents a musculoskeletal model for assessment of the effect of low-frequency whole-body vibrations on the human body. It is a basic assumption behind the model that the vibrations are slow enough to allow the central nervous system to respond to them in terms of muscle activations...

  5. Twentesat - the first low-frequency interferometer in space

    NARCIS (Netherlands)

    Bentum, Marinus Jan

    2012-01-01

    Low frequency radio astronomy, observing at frequencies below 30 MHz, is one of the last unexplored frequency ranges, and is one of the topics receiving increased interest in astronomy. Since Earth-based observations at those frequencies are not possible, observations have to be done in space. In th

  6. Short wave breaking effects on low frequency waves

    NARCIS (Netherlands)

    Daly, C.; Roelvink, J.A.; Van Dongeren, A.; Van Thiel de Vries, J.S.M.; McCall, R.T.

    2010-01-01

    The effect of short wave breaking on low frequency waves is investigated using two breaker formulations implemented in a time-dependent numerical model (XBeach): (1) an advective-deterministic approach (ADA) and (2) the probabilistic breaker formulation of Roelvink (1993). Previous research has show

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

    DEFF Research Database (Denmark)

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

    2016-01-01

    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...

  8. Mitigation of low-frequency groundnoise from runways

    NARCIS (Netherlands)

    Eerden, F.J.M. van der; Salomons, E.M.; Beeks, A.A.F.M.

    2007-01-01

    With the extra runway at Amsterdam Schiphol Airport, introduced in 2003, the noise nuisance for local residents increased due to increased groundnoise. In a case study the effect of enhanced ground absorption on the propagation of low-frequency noise from aircraft ground operations, e.g. departing a

  9. Twenty-two cases of low-frequency noise complaints

    DEFF Research Database (Denmark)

    Pedersen, Christian Sejer; Møller, Henrik; Persson-Waye, Kerstin

    2006-01-01

    In Denmark and in other industrialized countries there are cases where people complain about annoying low-frequency or infrasonic noise in their homes. Besides noise annoyance people often report other adverse effects such as insomnia, headache, lack of concentration etc. In many cases the noise...

  10. Dynamic Range Improvement of GMRT Low Frequency Images

    CERN Document Server

    Prasad, Peeyush

    2011-01-01

    This paper outlines some new observational and data processing techniques for enhancing the dynamic range of low frequency images obtained with the Giant Metrewave Radio Telescope. We illustrate new software tools developed to facilitate visibility editing and calibration as well as other preprocessing required to enhance the dynamic range of images from a planned survey.

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

    Science.gov (United States)

    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.

  12. Ultra low frequency waves at Venus: Observations by the Venus Express spacecraft

    Science.gov (United States)

    Fränz, M.; Echer, E.; Marques de Souza, A.; Dubinin, E.; Zhang, T. L.

    2017-10-01

    The generation of waves with low frequencies (below 100 mHz) has been observed in the environment of most bodies in the solar system and well studied at Earth. These waves can be generated either upstream of the body in the solar wind by ionization of planetary exospheres or ions reflected from a bow shock or in the magnetosheath closer to the magnetic barrier. For Mars and Venus the waves may have special importance since they can contribute to the erosion of the ionopause and by that enhance atmospheric escape. While over the past years many case studies on wave phenomena observed at Venus have been published most statistical studies have been based on magnetic observations only. On the other hand the generation mechanisms and transport of these waves through the magnetosphere can only be quantified using both magnetic and particle observations. We use the long time observations of Venus Express (2006-2014) to determine the predominant processes and transport parameters. First we demonstrate the analysis methods in four case studies, then we present a statistical analysis by determining transport ratios from the complete Venus Express dataset. We find that Alfvenic waves are very dominant (>80%) in the solar wind and in the core magnetosheath. Fast waves are observed mainly at the bow shock (around 40%) but also at the magnetic barrier where they may be most important for the energy transfer into the ionosphere. Their occurrence in the magnetotail may be an artifact of the detection of individual plasma jets in this region. Slow mode waves are rarely dominating but occur with probability of about 10% at the bow shock and in the pile-up-region. Mirror mode waves have probability <20% in the magnetosheath slightly increasing towards the pile-up-boundary.

  13. Alfv\\'en QPOs in Magnetars

    CERN Document Server

    Sotani, Hajime; Stergioulas, Nikolaos

    2007-01-01

    We investigate torsional Alfv\\'en oscillations of relativistic stars with a global dipole magnetic field, via two-dimensional numerical simulations. We find that a) there exist two families of quasi-periodic oscillations (QPOs) with harmonics at integer multiples of the fundamental frequency, b) the lower-frequency QPO is related to the region of closed field lines, near the equator, while the higher-frequency QPO is generated near the magnetic axis, c) the QPOs are long-lived, d) for the chosen form of dipolar magnetic field, the frequency ratio of the lower to upper fundamental QPOs is ~0.6, independent of the equilibrium model or of the strength of the magnetic field, and e) within a representative sample of equations of state and of various magnetar masses, the Alfv\\'en QPO frequencies are given by accurate empirical relations that depend only on the compactness of the star and on the magnetic field strength. The lower and upper QPOs can be interpreted as corresponding to the edges or turning points of an...

  14. Alfven wave in higher dimensional space time

    CERN Document Server

    Panigrahi, D; Chatterjee, S

    2009-01-01

    Following the wellknown spacetime decomposition technique as applied to (d+1) dimensions we write down the equations of magnetohydrodynamics (MHD) in a spatially at generalised FRW universe. Assuming an equation of state for the background cosmic fluid we find solutions in turn for acous- tic waves and also for Alfven waves in a warm (cold) magnetised plasma. Interestingly the different plasma modes closely resemble the at space coun- terparts except that here the field variables all redshift with their time due to the expansion of the background. It is observed that in the ultrarelativistic limit the field parameters all scale as the free photon. The situation changes in the prerelativistic limit where the frequencies change in a bizarre fashion depending on initial conditions. It is observed that for a fixed magnetic field in a particular medium the Alfven wave velocity decreases with the number of dimensions, being the maximum in the usual 4D. Further for a fixed dimension the velocity attenuation is more ...

  15. Low-Frequency Gravitational Radiation from Coalescing Massive Black Holes

    CERN Document Server

    Sesana, A; Madau, P; Volonteri, M

    2005-01-01

    We compute the expected low-frequency gravitational wave signal from coalescing massive black hole (MBH) binaries at the center of galaxies. We follow the merging history of halos and associated holes via cosmological Monte Carlo realizations of the merger hierarchy from early times to the present in a LCDM cosmology. MBHs get incorporated through a series of mergers into larger and larger halos, sink to the centre owing to dynamical friction, accrete a fraction of the gas in the merger remnant to become more massive, and form a binary system. Stellar dynamical processes dominates the orbital evolution of the binary at large separations, while gravitational wave emission takes over at small radii, causing the final coalescence of the system. We discuss the observability of inspiraling MBH binaries by a low-frequency gravitational wave experiment such as the planned Laser Interferometer Space Antenna (LISA), discriminating between resolvable sources and unresolved confusion noise. Over a 3-year observing perio...

  16. Numerical and experimental characterizations of low frequency MEMS AE sensors

    Science.gov (United States)

    Saboonchi, Hossain; Ozevin, Didem

    2013-04-01

    In this paper, new MEMS Acoustic Emission (AE) sensors are introduced. The transduction principle of the sensors is capacitance due to gap change. The sensors are numerically modeled using COMSOL Multiphysics software in order to estimate the resonant frequencies and capacitance values, and manufactured using MetalMUMPS process. The process includes thick metal layer (20 μm) made of nickel for freely vibration layer and polysilicon layer as the stationary layer. The metal layer provides a relatively heavy mass so that the spring constant can be designed high for low frequency sensor designs in order to increase the collapse voltage level (proportional to the stiffness), which increases the sensor sensitivity. An insulator layer is deposited between stationary layer and freely vibration layer, which significantly reduces the potential of stiction as a failure mode. As conventional AE sensors made of piezoelectric materials cannot be designed for low frequencies (vacuum packaging. The MEMS sensor responses are compared with similar frequency piezoelectric AE sensors.

  17. Extremely low frequency magnetic fields and health risks

    Directory of Open Access Journals (Sweden)

    M.I. Buzdugan

    2009-10-01

    Full Text Available In a world abounding in artificially created electromagnetic fields, we consider that a new approach regarding their possible harmful effects on living beings becomes mandatory. The paper reviews briefly the results of some epidemiological studies, the ICNIRP (International Committee on Non-Ionizing Radiation Protection Guidelines and the latest document of the SCENIHR (an organism of the European Commission regarding extremely low frequency (ELF magnetic fields. We are convinced that the best conduct that might be adopted on this matter is the policy of the prudential avoidance. Several examples of possible harmful effects determined by extremely low frequency magnetic fields dedicated to building services engineering in residences are presented, along with several methods of mitigating them.

  18. Low-frequency Raman scattering in alkali tellurite glasses

    Indian Academy of Sciences (India)

    Angelos G Kalampounias

    2008-10-01

    Raman scattering has been employed to study the alkali-cation size dependence and the polarization characteristics of the low-frequency modes for the glass-forming tellurite mixtures, 0.1M2O–0.9TeO2 (M = Na, K, Rb and Cs). The analysis has shown that the Raman coupling coefficient alters by varying the type of the alkali cation. The addition of alkali modifier in the tellurite network leads to the conversion of the TeO4 units to TeO3 units with a varying number of non-bridging oxygen atoms. Emphasis has also been given to the lowfrequency modes and particular points related to the low-frequency Raman phenomenology are discussed in view of the experimental findings.

  19. Low-frequency noise reduction of lightweight airframe structures

    Science.gov (United States)

    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.

  20. Measurement of low-frequency noise in rooms

    DEFF Research Database (Denmark)

    Pedersen, Steffen; Møller, Henrik; Persson-Waye, Kerstin

    2006-01-01

    to the highest level present in a room, rather than a room average level. In order to ensure representative noise measurements, different positions were investigated based on theoretical considerations and observations from numerical room simulations. In addition measurements were performed in three different......Measurement of low-frequency noise in rooms is problematic due to standing wave patterns. The spatial variation in the sound pressure level can typically be as much as 20-30 dB. For assessment of annoyance from low-frequency noise in dwellings, it is important to measure a level close...... rooms. The sound pressure level was measured 1) in three-dimensional corners and 2) according to current Swedish and Danish measurement methods. Furthermore, the entire sound pressure distributions were measured by scanning. The Swedish and Danish measurement methods include a corner measurement...

  1. Relativistic runaway breakdown in low-frequency radio

    DEFF Research Database (Denmark)

    Fullekrug, M.; Roussel-Dupre, R.; Symbalisty, E.M.D.

    2011-01-01

    is characterized by consecutive broadband pulses in the low-frequency radio range from similar to 10 to 300 kHz at a distance of similar to 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 similar to 550 km. The measured broadband pulses occur similar to 4-9 ms after the sprite-producing lightning discharge, they exhibit electromagnetic radiation which mainly spans the frequency range from similar to 50 to 350 kHz, and they exhibit complex waveforms without the typical...... ionospheric reflection of the first hop sky wave. Two consecutive pulses occur similar to 4.5 ms and similar to 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...

  2. Fabrication of SU-8 low frequency electrostatic energy harvester

    KAUST Repository

    Ramadan, Khaled S.

    2011-11-01

    A 1500μm × 1500μm × 150μm out-of-plane, gap closing, electrostatic energy harvester is designed and fabricated to harvest low-frequency ambient vibrations. SU-8 is used to fabricate the proof mass (1200μm × 1200μm × 150μm) and the 5 m springs. Different harvesters were designed to harvest at 50, 75 and 110 Hz. At 110 Hz, Simulations show that with an input vibration of 10 μm amplitude at the frequency of resonance of the structure, the energy harvester should generate an average output power density of 0.032μW/mm3. This is the most area-efficient low-frequency electrostatic harvester to-date. © 2011 IEEE.

  3. Low-Frequency Waves in HF Heating of the Ionosphere

    Science.gov (United States)

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

    2016-02-01

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

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  6. Planck 2013 results. II. The Low Frequency Instrument data processing

    DEFF Research Database (Denmark)

    Aghanim, N.; Armitage-Caplan, C.; Arnaud, M.

    2013-01-01

    We describe the data processing pipeline of the Planck Low Frequency Instrument (LFI) data processing centre (DPC) to create and characterize full-sky maps based on the first 15.5 months of operations at 30, 44, and 70 GHz. In particular, we discuss the various steps involved in reducing the data...... using Jupiter transits, which are also used for the geometrical calibration of the focal plane....

  7. Evaluation of annoyance from low frequency noise under laboratory conditions

    Directory of Open Access Journals (Sweden)

    Malgorzata Pawlaczyk-Luszczynska

    2010-01-01

    Full Text Available The aim of the study was to investigate the annoyance of low frequency noise (LFN at levels normally prevailing at workplaces in control rooms and office-like areas. Two different laboratory experiments were carried out. The first experiment included 55 young volunteers and the second one comprised 70 older volunteers, categorized in terms of sensitivity to noise. The subjects listened to noise samples with different spectra, including LFNs at sound pressure level (SPL of 45-67 dBA, and evaluated annoyance using a 100-score graphical rating scale. The subjective ratings of annoyance were compared to different noise metrics. In both the experiments, there were no differences in annoyance assessments between females and males. A significant influence of individual sensitivity to noise on annoyance rating was observed for some LFNs. Annoyance of LFN was not rated higher than annoyance from broadband noises without or with less prominent low frequencies at similar A-weighted SPLs. In both the experiments, median annoyance rating of LFN highly correlated with A-weighted SPL (L Aeq,T , low frequency A-weighted SPL (L LFAeq,T and C-weighted SPL (L Ceq,T . However, it is only the two latter noise metrics (i.e. L LFAeq,T and L Ceq,T which seem to be reliable predictors of annoyance exclusively from LFN. The young and older participants assessed similar annoyance from LFN at similar L LFAeq,T or L Ceq,T levels. Generally, over half of the subjects were predicted to be highly annoyed by LFN at the low frequency A-weighted SPL or C-weighted SPL above 62 and 83 dB, respectively.

  8. Offshore windfarm connection with low frequency AC transmission technology

    DEFF Research Database (Denmark)

    Qin, Nan; Xu, Zhao; You, Shi

    2009-01-01

    This paper investigates the feasibility of using the low frequency AC transmission (LFAC) system, e.g. fraction of 50 Hz or 60 Hz, for connecting the large offshore wind farm to the grid by modelling and simulation. The LFAC system improves the transmission capacity and distance compared to the c...... to the reduced inductive reactance of the grid. Moreover, the harmonics introduced by the frequency converter may require extra filters to be installed in such system....

  9. Low Frequency Variability In Globally Integrated Tropical Cyclone Power Dissipation

    OpenAIRE

    Sriver, Ryan; Huber, Matthew

    2006-01-01

    Surface wind and temperature records from the European Centre for Medium- Range Weather Forecasts 40 Year Reanalysis (ERA-40) Project are used to estimate low-frequency variations in globally integrated tropical cyclone (TC) intensity from 1958 to 2001. For the first time, the annually integrated power dissipation (PD) is explicitly calculated on a global scale, and results show an upward trend in PD during much of the ERA-40 project period, although we argue this is at least partially due to...

  10. Low-frequency electromagnetic field in a Wigner crystal

    CERN Document Server

    Stupka, Anton

    2016-01-01

    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.

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

    Science.gov (United States)

    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. Ultra-low frequency shock dynamics in degenerate relativistic plasmas

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

  15. Low-frequency noise from large wind turbines

    DEFF Research Database (Denmark)

    Møller, Henrik; Pedersen, Christian Sejer

    2011-01-01

    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...

  16. Relativistic runaway breakdown in low-frequency radio

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  18. Charge density fluctuation of low frequency in a dusty plasma

    Institute of Scientific and Technical Information of China (English)

    李芳; 吕保维; O.Havnes

    1997-01-01

    The charge density fluctuation of low frequency in a dusty plasma, which is derived from the longitudinal dielectric permittivity of the dusty plasma, has been studied by kinetic theory. The results show that the P value, which describes the relative charge density on the dust in the plasma, and the charging frequency of a dust particle Ωc, which describes the ratio of charge changing of the dust particles, determine the character of the charge density fluctuation of low frequency. For a dusty plasma of P<<1, when the charging frequency Ωc is much smaller than the dusty plasma frequency wd, there is a strong charge density fluctuation which is of character of dust acoustic eigen wave. For a dusty plasma of P>>1, when the frequency Ωc, is much larger than wd there are weaker fluctuations with a wide spectrum. The results have been applied to the ionosphere and the range of radius and density of dust particles is found, where a strong charge density fluctuation of low frequency should exist.

  19. Full waveform inversion with extrapolated low frequency data

    CERN Document Server

    Li, Yunyue Elita

    2016-01-01

    The availability of low frequency data is an important factor in the success of full waveform inversion (FWI) in the acoustic regime. The low frequencies help determine the kinematically relevant, low-wavenumber components of the velocity model, which are in turn needed to avoid convergence of FWI to spurious local minima. However, acquiring data below 2 or 3 Hz from the field is a challenging and expensive task. In this paper we explore the possibility of synthesizing the low frequencies computationally from high-frequency data, and use the resulting prediction of the missing data to seed the frequency sweep of FWI. As a signal processing problem, bandwidth extension is a very nonlinear and delicate operation. It requires a high-level interpretation of bandlimited seismic records into individual events, each of which is extrapolable to a lower (or higher) frequency band from the non-dispersive nature of the wave propagation model. We propose to use the phase tracking method for the event separation task. The...

  20. GMRT Low Frequency Observations of Extrasolar Planetary Systems

    CERN Document Server

    George, Samuel

    2007-01-01

    Extrasolar planets are expected to emit detectable low frequency radio emission. In this paper we present results from new low frequency observations of two extrasolar planetary systems (Epsilon Eridani and HD 128311) taken at 150 MHz with the Giant Metrewave Radio Telescope (GMRT). These two systems have been chosen because the stars are young (with ages < 1 Gyr) and are likely to have strong stellar winds, which will increase the expected radio flux. The planets are massive (presumably) gas giant planets in longer period orbits, and hence will not be tidally locked to their host star (as is likely to be the case for short period planets) and we would expect them to have a strong planetary dynamo and magnetic field. We do not detect either system, but are able to place tight upper limits on their low frequency radio emission, at levels comparable to the theoretical predictions for these systems. From these observations we have a 2.5sigma limit of 7.8 mJy for Epsilon Eri and 15.5 mJy for HD 128311. In addi...

  1. Nonlinear evolution of parallel propagating Alfven waves: Vlasov - MHD simulation

    CERN Document Server

    Nariyuki, Y; Kumashiro, T; Hada, T

    2009-01-01

    Nonlinear evolution of circularly polarized Alfv\\'en waves are discussed by using the recently developed Vlasov-MHD code, which is a generalized Landau-fluid model. The numerical results indicate that as far as the nonlinearity in the system is not so large, the Vlasov-MHD model can validly solve time evolution of the Alfv\\'enic turbulence both in the linear and nonlinear stages. The present Vlasov-MHD model is proper to discuss the solar coronal heating and solar wind acceleration by Alfve\\'n waves propagating from the photosphere.

  2. Low frequency signals analysis from broadband seismometers records

    Science.gov (United States)

    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

  3. Advances in Fluid Modeling of the Solar Wind. Part 1: Electron and Anisotropic Proton Temperatures from the Collisionless Dissipation of Alfven Wave Turbulence

    CERN Document Server

    Chandran, Benjamin D G; Quataert, Eliot; Bale, Stuart D

    2011-01-01

    We develop a 1D solar-wind model that includes separate energy equations for the electrons and protons, proton temperature anisotropy, collisional and collisionless heat flux, and an analytical treatment of low-frequency, reflection-driven, Alfven-wave turbulence. To partition the turbulent heating between electron heating, parallel proton heating, and perpendicular proton heating, we employ results from the theories of linear wave damping and nonlinear stochastic heating. We account for mirror and oblique firehose instabilities by increasing the proton pitch-angle scattering rate when the proton temperature anisotropy exceeds the threshold for either instability. We numerically integrate the equations of the model forward in time until a steady state is reached, focusing on two fast-solar-wind-like solutions. These solutions are consistent with a number of observations, supporting the idea that Alfven-wave turbulence plays an important role in the origin of the solar wind.

  4. Numerical Simulation of Solitary Kinetic Alfven Waves

    Institute of Scientific and Technical Information of China (English)

    DING Jian; LI Yi; WANG Shui

    2008-01-01

    Using the two-fluid model in the case of α1 (α=β/2Q, β is the ratio of thermal pressure to magnetic pressure, and Q=m,e/m,I), we numerically investigate the interactions between two solitary kinetic Alfven waves (SKAWs) and between an SKAW and a density discontinuity. The results show that the two SKAWs would remain in their original shapes and propagate at their initiating speeds, which indicates that SKAWs behave just like standard solitons. The simulation also shows that SKAWs will reflect and refract when crossing a discontinuity and propagating into a higher density region. The transmission wave is an SKAW with increasing density, and the reverberation is a disturbance with lower amplitude.

  5. A laboratory search for plasma erosion by Alfven waves

    Science.gov (United States)

    Vincena, S.; Gekelman, W.; Pribyl, P.

    2007-12-01

    Obliquely propagating shear Alfven waves with transverse wavelengths on the order of the electron inertial length or even the ion gyro-radius are commonly observed in the earth's low-altitude auroral zones. These regions are also replete with observations of electron beams and transversely heated ions. A kinetic treatment of shear Alfven wave-particle interaction reveals how these waves can be responsible for some of the observed particle acceleration. The auroral plasma environment is further enriched by the presence of field-aligned depletions in plasma density, and it has been suggested* that the Alfven waves may, in fact, be the cause of the erosion of ionospheric density. In this laboratory experiment, shear waves will be launched using a variety of proven antennas, and also allowed to grow spontaneously as Drift-Alfven modes in seeded density depletions**. Detailed measurements of the wave magnetic fields in the perpendicular density gradient regions will be presented which demonstrate the generation of short perpendicular wave scales due to the perpendicular gradient in parallel wave phase speed. Miniature in-situ particle diagnostics will also be used to look for electron and ion acceleration. The waves will also be launched into an increasing region of background magnetic field in an attempt to model the ratios of Alfven speed to electron thermal speed, and density gradient scale length to electron inertial length appropriate to the earth's auroral zone. Preliminary results will be presented on the efficacy of shear Alfven waves to self-generate plasma density depletions, or deepen ambient density inhomogeneities. The experiments are conducted at UCLA's Basic Plasma Science Facility in the Large Plasma Device. *Chaston, et al., "Ionospheric erosion by Alfven Waves," JGR, V 111, A03206, 2006. **Penano, et al., "Drift-Alfven fluctuations associated with a narrow pressure striation," Phys. Plasmas, V 7, Issue 1, pp. 144-157 (2000).

  6. Emission of radiation induced by pervading Alfven waves

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, G. Q. [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Wu, C. S. [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing (China); Institute of Space Science, National Central University, Zhongli, Taiwan (China)

    2013-03-15

    It is shown that under certain conditions, propagating Alfven waves can energize electrons so that consequently a new cyclotron maser instability is born. The necessary condition is that the plasma frequency is lower than electron gyrofrequency. This condition implies high Alfven speed, which can pitch-angle scatter electrons effectively and therefore the electrons are able to acquire free energy which are needed for the instability.

  7. Low-frequency fatigue at maximal and submaximal muscle contractions

    Directory of Open Access Journals (Sweden)

    R.R. Baptista

    2009-04-01

    Full Text Available Skeletal muscle force production following repetitive contractions is preferentially reduced when muscle is evaluated with low-frequency stimulation. This selective impairment in force generation is called low-frequency fatigue (LFF and could be dependent on the contraction type. The purpose of this study was to compare LFF after concentric and eccentric maximal and submaximal contractions of knee extensor muscles. Ten healthy male subjects (age: 23.6 ± 4.2 years; weight: 73.8 ± 7.7 kg; height: 1.79 ± 0.05 m executed maximal voluntary contractions that were measured before a fatigue test (pre-exercise, immediately after (after-exercise and after 1 h of recovery (after-recovery. The fatigue test consisted of 60 maximal (100% or submaximal (40% dynamic concentric or eccentric knee extensions at an angular velocity of 60°/s. The isometric torque produced by low- (20 Hz and high- (100 Hz frequency stimulation was also measured at these times and the 20:100 Hz ratio was calculated to assess LFF. One-way ANOVA for repeated measures followed by the Newman-Keuls post hoc test was used to determine significant (P < 0.05 differences. LFF was evident after-recovery in all trials except following submaximal eccentric contractions. LFF was not evident after-exercise, regardless of exercise intensity or contraction type. Our results suggest that low-frequency fatigue was evident after submaximal concentric but not submaximal eccentric contractions and was more pronounced after 1-h of recovery.

  8. Low-Frequency Electromagnetic Exploration for Groundwater on Mars

    Science.gov (United States)

    Grimm, Robert E.

    2002-01-01

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

  9. LOW-FREQUENCY DIELECTRIC RELAXATION IN SILVER STEARATE LAYERS

    Directory of Open Access Journals (Sweden)

    Smirnov, A.P.

    2016-05-01

    Full Text Available The low-frequency dielectric relaxation process in silver stearate layers was studied. The increasing of dielectric permittivity with frequency decreasing and temperature increasing in studied sample are associated with the dipole-relaxation polarization mechanisms. The dispersion of loss factor could be connected with the contribution of relaxation mechanism and conductivity. The shape of the Cole-Cole diagram shows that silver stearate is a non-Debye dielectric material characterized by a wide distribution of relaxators, according to the Cole-Cole relaxation model.

  10. Planck 2015 results. II. Low Frequency Instrument data processing

    CERN Document Server

    Ade, P A R; 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; 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; 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; 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

    2015-01-01

    We present an updated description of the Planck Low Frequency (LFI) data processing pipeline, associated with the 2015 data release. We point out the places in which 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. We refer to other related papers where more detailed descriptions on the LFI data processing pipeline may be found if needed.

  11. Low-frequency measurements of the CMB spectrum

    Energy Technology Data Exchange (ETDEWEB)

    Kogut, A.; Bensadoun, M.; Amici, G.D.; Levin, S.; Limon, M.; Smoot, G. (U. C. Berkeley, Berkeley, CA (USA) Lawrence Berkeley Laboratory, Berkeley, CA (USA) Space Sciences Laboratory, Berkeley, CA (USA)); Sironi, G. (Physics Department, University of Milano (Italy)); Bersanelli, M.; Bonelli, G. (IFCTR/CNR-Milano (Italy))

    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.

  12. Low-Frequency Measurements of the CMB Spectrum

    Energy Technology Data Exchange (ETDEWEB)

    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.

  13. Fabrication and characterization of a low frequency electromagnetic energy harvester

    Institute of Scientific and Technical Information of China (English)

    Abu Riduan Md.Foisal; Gwiy-Sang Chung

    2012-01-01

    This paper presents the fabrication and characterization of an AA size electromagnetic energy transducer based on vibration.A magnetic spring technique is used to scavenge energy from low frequency external vibration.The output of the harvester is maximized by optimizing the mass of moving and fixed magnets,coil width,coil position and load resistance through a comprehensive experimental analysis.The prototype can generate an open circuit voltage of 3.961 V and 1.18 mW average power at a load resistance of 97 Ω with 9 Hz resonance frequency and 0.5 mm displacement.

  14. Ultra low frequency waves impact on radiation belt energetic particles

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    One of the most fundamental important issues in the space physics is to understand how solar wind energy transports into the inner magnetosphere.Ultra low frequency(ULF)wave in the magnetosphere and its impact on energetic particles,such as the wave-particle resonance,modulation,and particle acceleration,are extremely important topics in the Earth’s radiation belt dynamics and solar wind― magnetospheric coupling.In this review,we briefly introduce the recent advances on ULF waves study. Further,we will explore the density structures and ion compositions around the plasmaspheric boundary layer(PBL)and discuss its possible relation to the ULF waves.

  15. Ultra low frequency waves impact on radiation belt energetic particles

    Institute of Scientific and Technical Information of China (English)

    ZONG QiuGang; HAO YongQiang; WANG YongFu

    2009-01-01

    One of the most fundamental important issues in the space physics is to understand how solar wind energy transports into the inner magnetosphere.Ultra low frequency(ULF)wave in the magnetosphere and its impact on energetic particles,such as the wave-particle resonance,modulation,and particle acceleration,are extremely important topics in the Earth's radiation belt dynamics and solar windmagnetospheric coupling.In this review,we briefly introduce the recent advances on ULF waves study.Further,we will explore the density structures and ion compositions around the plasmaspheric boundary layer(PBL)and discuss its possible relation to the ULF waves.

  16. Homogenization of Two-Dimensional Phononic Crystals at Low Frequencies

    Institute of Scientific and Technical Information of China (English)

    NI Qing; CHENG Jian-Chun

    2005-01-01

    @@ Effective velocities of elastic waves propagating in two-dimensional phononic crystal at low frequencies are analysed theoretically, and exact analytical formulas for effective velocities of elastic waves are derived according to the method presented by Krokhin et al. [Phys. Rev. Lett. 91 (2003) 264302]. Numerical calculations for phononic crystals consisted of array of Pb cylinders embedded in epoxy show that the composites have distinct anisotropy at low filling fraction. The anisotropy increases as the filling fraction increases, while as the filling fraction closes to the limitation, the anisotropy decreases.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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

  19. Low-frequency fluid waves in fractures and pipes

    Energy Technology Data Exchange (ETDEWEB)

    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.

  20. Fetal exposure to low frequency electric and magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Cech, R; Leitgeb, N; Pediaditis, M [Institute of Clinical Engineering, Graz University of Technology, Inffeldgasse 18, 8010 Graz (Austria)

    2007-02-21

    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.

  1. Fetal exposure to low frequency electric and magnetic fields

    Science.gov (United States)

    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.

  2. Study of low frequency acoustic signals from superheated droplet detector

    CERN Document Server

    Mondal, P K; Das, M; Bhattacharjee, P

    2013-01-01

    The bubble nucleation process in superheated droplet detector (SDD) is associated with the emission of an acoustic pulse that can be detected by an acoustic sensor. We have studied the neutron and gamma-ray induced nucleation events in a SDD with the active liquid R-12 (CCl2F2, b.p. -29.8oC) using a condenser microphone sensor. A comparative study in the low frequency region (~ 0-10kHz) for the neutron and gamma-ray induced nucleation is presented here. From the analysis of the waveforms we observe a significant difference between the neutron and gamma-ray induced acoustic events.

  3. Low-frequency quadrupole impedance of undulators and wigglers

    Science.gov (United States)

    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 ).

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

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

    Directory of Open Access Journals (Sweden)

    Armstrong J. W.

    2006-01-01

    Full Text Available 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 $2 Delta v/c = Delta u/ u_0$, where $Delta u$ is the Doppler shift and $ u_0$ 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 $Delta u/ u_0$. 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.

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

    Science.gov (United States)

    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.

  9. Low-frequency electromagnetic technique for nondestructive evaluation

    Science.gov (United States)

    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.

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

    Science.gov (United States)

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

    2017-06-01

    Piezoelectric Zinc Oxide (ZnO) nanogenerators (NGs) have been fabricated for low frequency (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.

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

    Science.gov (United States)

    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.

  12. Low-frequency gravitational-wave science frontiers

    Science.gov (United States)

    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.

  13. Alternative source models of very low frequency events

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    Frederiksen, Jorgen S.; Webster, Peter J.

    1988-08-01

    Observational studies have revealed a rich low-frequency structure in the atmosphere. A review of the theories, observations, and model studies of this low-frequency atmospheric variability is presented. On time scales of weeks or longer the atmosphere appears to possess distinct oscillatory behavior in well-defined and persistent "centers of action." This behavior is also an endemic feature of surrogate atmospheric data sets emerging from experiments with complicated climate models. Many theories have attempted to determine the dominant physical processes responsible for the low-frequency variance but have usually failed when compared carefully with observations. For example, simple linear steady state and Rossby wave dispersion theories have been used in an attempt to explain the observed global response to low-latitude perturbation. However, the observed structures of mature anomalies are often quite distinct from the vertical structures of disturbances predicted in these theories. Also, in general circulation and model studies, the sign of the nonlinear response is not simply related to the sign of the forcing as predicted by linear steady state theories. It is argued that the theories fail because either the full three-dimensional complexity of the basic state is not considered or its inherent instability structure is not recognized or is, in fact, ignored. It is shown that three-dimensional instability theory provides a natural generalization and marriage of the zonally averaged instability theory of Charney and Eady and the Rossby wave dispersion theory of Rossby and Yeh. As such, it provides a formalism which may be used to understand a wide variety of atmospheric fluctuations including the locations of eddy flux covariance maxima and storm tracks in both the tropics and extratropics and the generation of blocking, teleconnection patterns, and other quasi-stationary anomaly features. Attention is focused on two particular mechanisms within this formalism

  15. On reflection of Alfven waves in the solar wind

    Science.gov (United States)

    Krogulec, M.; Musielak, Z. E.; Suess, S. T.; Moore, R. L.; Nerney, S. F.

    1993-01-01

    We have revisited the problem of propagation of toroidal and linear Alfven waves formulated by Heinemann and Olbert (1980) to compare WKB and non-WKB waves and their effects on the solar wind. They considered two solar wind models and showed that reflection is important for Alfven waves with periods of the order of one day and longer, and that non-WKB Alfven waves are no more effective in accelerating the solar wind than WKB waves. There are several recently published papers which seem to indicate that Alfven waves with periods of the order of several minutes should be treated as non-WKB waves and that these non-WKB waves exert a stronger acceleration force than WKB waves. The purpose of this paper is to study the origin of these discrepancies by performing parametric studies of the behavior of the waves under a variety of different conditions. In addition, we want to investigate two problems that have not been addressed by Heinemann and Olbert, namely, calculate the efficiency of Alfven wave reflection by using the reflection coefficient and identify the region of strongest wave reflection in different wind models. To achieve these goals, we investigated the influence of temperature, electron density distribution, wind velocity and magnetic field strength on the waves. The obtained results clearly demonstrate that Alfven wave reflection is strongly model dependent and that the strongest reflection can be expected in models with the base temperatures higher than 10(exp 6) K and with the base densities lower than 7 x 10(exp 7) cm(exp -3). In these models as well as in the models with lower temperatures and higher densities, Alfven waves with periods as short as several minutes have negligible reflection so that they can be treated as WKB waves; however, for Alfven waves with periods of the order of one hour or longer reflection is significant, requiring a non-WKB treatment. We also show that non-WKB, linear Alfven waves are always less effective in accelerating the

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

    Science.gov (United States)

    Grimm, R. E.

    2013-12-01

    EM sounding is divided by loss tangent 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 nuclear magnetic

  17. Low Frequency Variability and the Eastern Mediterranean Teleconnection Pattern

    Science.gov (United States)

    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

  18. Time domain acoustic contrast control implementation of sound zones for low-frequency input signals

    DEFF Research Database (Denmark)

    Schellekens, Daan H. M.; Møller, Martin Bo; Olsen, Martin

    2016-01-01

    Sound zones are two or more regions within a listening space where listeners are provided with personal audio. Acoustic contrast control (ACC) is a sound zoning method that maximizes the average squared sound pressure in one zone constrained to constant pressure in other zones. State-of-the-art t......Sound zones are two or more regions within a listening space where listeners are provided with personal audio. Acoustic contrast control (ACC) is a sound zoning method that maximizes the average squared sound pressure in one zone constrained to constant pressure in other zones. State......-of-the-art time domain broadband acoustic contrast control (BACC) methods are designed for anechoic environments. These methods are not able to realize a flat frequency response in a limited frequency range within a reverberant environment. Sound field control in a limited frequency range is a requirement...... to accommodate the effective working range of the loudspeakers. In this paper, a new BACC method is proposed which results in an implementation realizing a flat frequency response in the target zone. This method is applied in a bandlimited low-frequency scenario where the loudspeaker layout surrounds two...

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

    Science.gov (United States)

    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. Low-Frequency Radio Bursts and Space Weather

    Science.gov (United States)

    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. Low frequency wave modes of liquid-filled flexible tubes

    Science.gov (United States)

    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.

  2. Observation of low frequency electromagnetic activity at 1000 km altitude

    Directory of Open Access Journals (Sweden)

    N. Ivchenko

    Full Text Available We present a statistical study of low frequency fluctuations of electric and magnetic fields, commonly interpreted as Alfvénic activity. The data base consists of six months of electric and magnetic field measurements by the Astrid-2 microsatellite. The occurrence of the events is studied with respect to the location and general activity. Large regions of broadband Alfvénic activity are persistently observed in the cusp/cleft and, during the periods of high geo-magnetic activity, also in the pre-midnight sector of the auroral oval.

    Key words. Ionosphere (auroral ionosphere – Space plasma physics (waves and instabilities – Magnetospheric physics (magnetosphere-ionosphere interactions

  3. Low-frequency quadrupole impedance of undulators and wigglers

    Directory of Open Access Journals (Sweden)

    A. Blednykh

    2016-10-01

    Full Text Available 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 μ_{r}. 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 (μ_{r}→∞, and the case in which the magnets are fully saturated (μ_{r}=1.

  4. Low-frequency noise in Josephson junctions for superconducting qubits

    Science.gov (United States)

    Eroms, J.; van Schaarenburg, L. C.; Driessen, E. F. C.; Plantenberg, J. H.; Huizinga, C. M.; Schouten, R. N.; Verbruggen, A. H.; Harmans, C. J. P. M.; Mooij, J. E.

    2006-09-01

    The authors have studied low-frequency resistance fluctuations in shadow-evaporated Al /AlOx/Al tunnel junctions. Between 300 and 5K the spectral density follows a 1/f law. Below 5K, individual defects distort the 1/f shape of the spectrum. The spectral density decreases linearly with temperature between 150 and 1K and saturates below 0.8K. At 4.2K, it is about two orders of magnitude lower than expected from a recent survey [D. J. Van Harlingen et al., Phys. Rev. B 70, 064510 (2004)]. Due to saturation below 0.8K the estimated qubit dephasing times at 100mK are only about two times longer than calculated by Van Harlingen et al.

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

    Directory of Open Access Journals (Sweden)

    Fufei Liu

    2017-01-01

    Full Text Available 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.

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

    Science.gov (United States)

    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.

  7. Low-frequency fluctuations in a pure toroidal magnetized plasma

    Indian Academy of Sciences (India)

    P K Sharma; R Singh; D Bora

    2009-12-01

    A magnetized, low- plasma in pure toroidal configuration is formed and extensively studied with ion mass as control parameter. Xenon, krypton and argon plasmas are formed at a fixed toroidal magnetic field of 0.024 T, with a peak density of ∼ 1011 cm-3, ∼ 4 × 1010 cm-3 and ∼ 2 × 1010 cm−3 respectively. The experimental investigation of time-averaged plasma parameter reveals that their profiles remain insensitive to ion mass and suggests that saturated slab equilibrium is obtained. Low-frequency (LF) coherent fluctuations ( < ci) are observed and identified as flute modes. Here ci represents ion cyclotron frequency. Our results indicate that these modes get reduced with ion mass. The frequency of the fluctuating mode decreases with increase in the ion mass. Further, an attempt has been made to discuss the theory of flute modes to understand the relevance of some of our experimental observations.

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

    Science.gov (United States)

    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.

  9. The Low Frequency Sensitivity to Gravitational Waves for ASTROD

    CERN Document Server

    Paton, Antonio Pulido

    2007-01-01

    ASTROD is a relativity mission concept encompassing multi-purposes. One of its main purposes is to detect gravitational waves sensitive to low-frequency band similar to LISA, but shifted to lower frequencies. In this aspect, ASTROD would complement LISA in probing the Universe and study strong-field black hole physics. Since ASTROD will be after LISA, in the Cosmic Vision time-frame 2015-2025, a ten-fold improvement over LISA accelerometer noise goal would be possible, allowing us to test relativistic gravity to 1 ppb and improve the gravitational-wave sensitivity. In this paper, we address to this possible improvement, especially in the frequency range below 0.1 mHz. We look into possible thermal noise improvement, magnetic noise improvement, spurious discharging noise improvement and local gravitational noise improvement. We discuss various possibilities of lower-frequency gravitational-wave responses and their significance to potential astrophysical sources.

  10. Electrodialytic soil remediation enhanced by low frequency pulse current

    DEFF Research Database (Denmark)

    Mortensen, John; Sun, Tian Ran; Ottosen, Lisbeth M.

    2013-01-01

    The effect of low frequency pulse current on decreasing the polarization and energy consumption during the process of electrodialytic soil remediation was investigated in the present work. The results indicated that the transportation of cations through the cation exchange membrane was the rate...... current experiment compared to the constant current experiment. At the cation exchange membrane, only the resistance caused by concentration polarization decreased. In the soil compartment, an average of +60 mV overpotential caused by the polarization of the electric double layer of the clay particles...... controlling step both in constant and pulse current experiments, thus responsible for the major energy consumption. After 180 h, a decrease in both the initial ohmic resistance in each pulse cycle and the resistance caused by concentration polarization of the anion exchange membrane were seen in the pulse...

  11. Man-induced low-frequency seismic events in Italy

    Science.gov (United States)

    Latorre, Diana; Amato, Alessandro; Cattaneo, Marco; Carannante, Simona; Michelini, Alberto

    2014-12-01

    Unconventional seismic events in Italy are detected by scanning three years of continuous waveforms recorded by the Italian National Seismic Network. Cross correlation of signal templates with continuous seismic records has evidenced unusual events with similar low-frequency characteristics in several Italian regions. Spectral analysis and spatiotemporal distribution of these events, some of which are previously interpreted as tectonic long-period transients, suggest that they are not natural, but produced by huge cement factories. Since there are at least 57 full-cycle cement plants operating in Italy, each affecting areas of about 1250 to 2800 km2, we argue that significant portions of the Italian territory (23% to 51%) can be affected by this man-made noise. Seismic noise analyses, such as those used for microzonation or crustal structure investigations, as well as data mining techniques used to retrieve anomalous transient signals, should thus take into account this peculiar and pervasive source of seismic waves.

  12. An Architecture for High Data Rate Very Low Frequency Communication

    Directory of Open Access Journals (Sweden)

    Arun Kumar

    2013-01-01

    Full Text Available Very low frequency (VLF communication is used for long range shore-to-ship broadcasting applications. This paper proposes an architecture for high data rate VLF communication using Gaussian minimum shift keying (GMSK modulation and low delay parity check (LDPC channel coding. Non-data aided techniques are designed and used for carrier phase synchronization, symbol timing recovery, and LDPC code frame synchronization. These require the estimation of the operative Eb/N0 for which a kurtosis based algorithm is used. Also, a method for modeling the probability density function of the received signal under the bit condition is presented in this regard. The modeling of atmospheric radio noise (ARN that corrupts VLF signals is described and an algorithm for signal enhancement in the presence of ARN in given. The BER performance of the communication system is evaluated for bit rates of 400 bps, 600 bps, and 800 bps for communication bandwidth of ~200 Hz.

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

    Science.gov (United States)

    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.

  14. EXTREMELY LOW FREQUENCY MAGNETIC FIELD SUSCEPTIBILITY OF VISUAL DISPLAY UNITS

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Extremely low frequency (ELF) magnetic field susceptibility is an index of visual display unit (VDU) quality and performance. This paper provided field measured data on the susceptibility for a large variety of VDUs. A test rig was built to study the susceptibility of VDUs to magnetic fields at fundamental and third harmonic frequencies. It was found that the susceptibility level is largely dependent on refresh rate of the VDU and the orientation of the external ELF field. It was also found that the VDU susceptibility is significantly increased in the presence of harmonic frequency magnetic fields. About 30% of the tested samples have susceptibility levels higher than that stated in IEC 1000-4-8 standard.

  15. Behavior of radon progeny in low frequency electromagnetic fields

    CERN Document Server

    Oda, K; Yamamoto, T

    1999-01-01

    Whether the electro-magnetic (EM) fields are carcinogenic or not still remains to be discussed from scientific point of view. Recently a possibility was pointed out that increased deposition of radon progeny in the EM-fields should enhance exposure dose to internal body. We investigated the behavior of charged sup 2 sup 2 sup 2 Rn progeny and aerosols containing them by measuring the pattern and the magnitude of the deposition rate of decay products on both CR-39 track detectors and imaging plates under various conditions. We concluded that the attachment to wire cables should be increased mainly by electric component of low frequency EM-fields and possibly by electric field induced by strong changing magnetic ones.

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

    Science.gov (United States)

    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.

  17. Sound field control for a low-frequency test facility

    DEFF Research Database (Denmark)

    Pedersen, Christian Sejer; Møller, Henrik

    2013-01-01

    The two largest problems in controlling the reproduction of low-frequency sound for psychoacoustic experiments is the effect of the room due to standing waves and the relatively large sound pressure levels needed. Anechoic rooms are limited downward in frequency and distortion may be a problem even...... at moderate levels, while pressure-field playback can give higher sound pressures but is limited upwards in frequency. A new solution that addresses both problems has been implemented in the laboratory of Acoustics, Aalborg University. The solution uses one wall with 20 loudspeakers to generate a plane wave...... that is actively absorbed when it reaches the 20 loudspeakers on the opposing wall. This gives a homogeneous sound field in the majority of the room with a flat frequency response in the frequency range 2-300 Hz. The lowest frequencies are limited to sound pressure levels in the order of 95 dB. If larger levels...

  18. Planck 2013 results. II. Low Frequency Instrument data processing

    CERN Document Server

    Aghanim, N; Arnaud, M; Ashdown, M; Atrio-Barandela, F; Aumont, J; Baccigalupi, C; Banday, A J; Barreiro, R B; Battaner, E; Benabed, K; Benoît, A; Benoit-Lévy, A; Bernard, J -P; Bersanelli, M; Bielewicz, P; Bobin, J; Bock, J J; Bonaldi, A; Bonavera, L; Bond, J R; Borrill, J; Bouchet, F R; Bridges, M; Bucher, M; Burigana, C; Butler, R C; Cappellini, B; Cardoso, J -F; Catalano, A; Chamballu, A; Chen, X; Chiang, L -Y; Christensen, P R; Church, S; Colombi, S; Colombo, L P L; Crill, B P; Cruz, M; 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; Dupac, X; Efstathiou, G; Enßlin, T A; Eriksen, H K; Falvella, M C; Finelli, F; Forni, O; Frailis, M; Franceschi, E; Gaier, T C; Galeotta, S; Ganga, K; Giard, M; Giardino, G; Giraud-Héraud, Y; Gjerløw, E; González-Nuevo, J; Górski, K M; Gratton, S; Gregorio, A; Gruppuso, A; Hansen, F K; Hanson, D; Harrison, D; Henrot-Versillé, S; Hernández-Monteagudo, C; Herranz, D; Hildebrandt, S R; Hivon, E; Hobson, M; Holmes, W A; Hornstrup, A; Hovest, W; Huffenberger, K M; Jaffe, T R; Jaffe, A H; Jewell, J; Jones, W C; Juvela, M; Kangaslahti, P; Keihänen, E; Keskitalo, R; Kiiveri, K; Kisner, T S; Knoche, J; Knox, L; Kunz, M; Kurki-Suonio, H; Lagache, G; Lähteenmäki, A; Lamarre, J -M; Lasenby, A; Lattanzi, M; Laureijs, R J; Lawrence, C R; Leach, S; Leahy, J P; Leonardi, R; Lesgourgues, J; Liguori, M; Lilje, P B; Lindholm, V; Linden-Vørnle, M; López-Caniego, M; Lubin, P M; Macías-Pérez, J F; Maggio, G; Maino, D; Mandolesi, N; Maris, M; Marshall, D J; Martin, P G; Martínez-González, E; Masi, S; Matarrese, S; Matthai, F; Mazzotta, P; Meinhold, P R; Melchiorri, A; Mendes, L; Mennella, A; Migliaccio, M; Mitra, S; Moneti, A; Montier, L; Morgante, G; Mortlock, D; Moss, A; Munshi, D; Naselsky, P; Natoli, P; Netterfield, C B; Nørgaard-Nielsen, H U; Novikov, D; Novikov, I; O'Dwyer, I J; Osborne, S; Paci, F; Pagano, L; Paladini, R; Paoletti, D; Partridge, B; Pasian, F; Patanchon, G; Peel, M; Perdereau, O; Perotto, L; Perrotta, F; Pierpaoli, E; Pietrobon, D; Plaszczynski, S; Platania, P; Pointecouteau, E; Polenta, G; Ponthieu, N; Popa, L; Poutanen, T; Pratt, G W; Prézeau, G; Prunet, S; Puget, J -L; Rachen, J P; Reach, W T; Rebolo, R; Reinecke, M; Remazeilles, M; Ricciardi, S; Riller, T; Rocha, G; Rosset, C; Rossetti, M; Roudier, G; Rubiño-Martín, J A; Rusholme, B; Salerno, E; Sandri, M; Santos, D; Scott, D; Seiffert, M D; Shellard, E P S; Spencer, L D; Starck, J -L; Stolyarov, V; Stompor, R; Sureau, F; 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; Varis, J; Vielva, P; Villa, F; Vittorio, N; Wade, L A; Wandelt, B D; Watson, R; Wehus, I K; White, S D M; Wilkinson, A; Yvon, D; Zacchei, A; Zonca, A

    2014-01-01

    We describe the data processing pipeline of the Planck Low Frequency Instrument (LFI) data processing centre (DPC) to create and characterize full-sky maps based on the first 15.5 months of operations at 30, 44 and 70 GHz. In particular, we discuss the various steps involved in reducing the data, starting from telemetry packets through to the production of cleaned, calibrated timelines and calibrated frequency maps. Data are continuously calibrated using the modulation induced on the mean temperature of the cosmic microwave background radiation by the proper motion of the spacecraft. Sky signals other than the dipole are removed by an iterative procedure based on simultaneous fitting of calibration parameters and sky maps. Noise properties are estimated from time-ordered data after the sky signal has been removed, using a generalized least square map-making algorithm. A destriping code (Madam) is employed to combine radiometric data and pointing information into sky maps, minimizing the variance of correlated...

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

    Science.gov (United States)

    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 (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 efficient vibration energy harvesting using the VDL system, ways to mitigate eddy current damping and a coil geometry for transduction were critically

  20. Bayesian inference on EMRI signals using low frequency approximations

    CERN Document Server

    Ali, Asad; Meyer, Renate; Röver, Christian; 10.1088/0264-9381/29/14/145014

    2013-01-01

    Extreme mass ratio inspirals (EMRIs) are thought to be one of the most exciting gravitational wave sources to be detected with LISA. Due to their complicated nature and weak amplitudes the detection and parameter estimation of such sources is a challenging task. In this paper we present a statistical methodology based on Bayesian inference in which the estimation of parameters is carried out by advanced Markov chain Monte Carlo (MCMC) algorithms such as parallel tempering MCMC. We analysed high and medium mass EMRI systems that fall well inside the low frequency range of LISA. In the context of the Mock LISA Data Challenges, our investigation and results are also the first instance in which a fully Markovian algorithm is applied for EMRI searches. Results show that our algorithm worked well in recovering EMRI signals from different (simulated) LISA data sets having single and multiple EMRI sources and holds great promise for posterior computation under more realistic conditions. The search and estimation meth...

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

    Science.gov (United States)

    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. Compact Polarimetry in a Low Frequency Spaceborne Context

    Science.gov (United States)

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

    2011-01-01

    Compact polarimetry has been shown to be an interesting alternative mode to full polarimetry when global coverage and revisit time are key issues. It consists on transmitting a single polarization, while receiving on two. Several critical points have been identified, one being the Faraday rotation (FR) correction and the other the calibration. When a low frequency electromagnetic wave travels through the ionosphere, it undergoes a rotation of the polarization plane about the radar line of sight for a linearly polarized wave, and a simple phase shift for a circularly polarized wave. In a low frequency radar, the only possible choice of the transmit polarization is the circular one, in order to guaranty that the scattering element on the ground is illuminated with a constant polarization independently of the ionosphere state. This will allow meaningful time series analysis, interferometry as long as the Faraday rotation effect is corrected for the return path. In full-polarimetric (FP) mode, two techniques allow to estimate the FR: Freeman method using linearly polarized data, and Bickel and Bates theory based on the transformation of the measured scattering matrix to a circular basis. In CP mode, an alternate procedure is presented which relies on the bare surface scattering properties. These bare surfaces are selected by the conformity coefficient, invariant with FR. This coefficient is compared to other published classifications to show its potential in distinguishing three different scattering types: surface, doublebounce and volume. The performances of the bare surfaces selection and FR estimation are evaluated on PALSAR and airborne data. Once the bare surfaces are selected and Faraday angle estimated over them, the correction can be applied over the whole scene. The algorithm is compared with both FP techniques. In the last part of the paper, the calibration of a CP system from the point of view of classical matrix transformation methods in polarimetry is

  3. Low frequency signal spectrum analysis for strong earthquakes

    Directory of Open Access Journals (Sweden)

    Masashi Hayakawa

    2012-04-01

    Full Text Available

    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.

     

  4. Clamped seismic metamaterials: ultra-low frequency stop bands

    Science.gov (United States)

    Achaoui, Y.; Antonakakis, T.; Brûlé, S.; Craster, R. V.; Enoch, S.; Guenneau, S.

    2017-06-01

    The regularity of earthquakes, their destructive power, and the nuisance of ground vibration in urban environments, all motivate designs of defence structures to lessen the impact of seismic and ground vibration waves on buildings. Low frequency waves, in the range 1-10 Hz for earthquakes and up to a few tens of Hz for vibrations generated by human activities, cause a large amount of damage, or inconvenience; depending on the geological conditions they can travel considerable distances and may match the resonant fundamental frequency of buildings. The ultimate aim of any seismic metamaterial, or any other seismic shield, is to protect over this entire range of frequencies; the long wavelengths involved, and low frequency, have meant this has been unachievable to date. Notably this is scalable and the effects also hold for smaller devices in ultrasonics. There are three approaches to obtaining shielding effects: bragg scattering, locally resonant sub-wavelength inclusions and zero-frequency stop-band media. The former two have been explored, but the latter has not and is examined here. Elastic flexural waves, applicable in the mechanical vibrations of thin elastic plates, can be designed to have a broad zero-frequency stop-band using a periodic array of very small clamped circles. Inspired by this experimental and theoretical observation, all be it in a situation far removed from seismic waves, we demonstrate that it is possible to achieve elastic surface (Rayleigh) wave reflectors at very large wavelengths in structured soils modelled as a fully elastic layer periodically clamped to bedrock. We identify zero frequency stop-bands that only exist in the limit of columns of concrete clamped at their base to the bedrock. In a realistic configuration of a sedimentary basin 15 m deep we observe a zero frequency stop-band covering a broad frequency range of 0-30 Hz.

  5. Compact Polarimetry in a Low Frequency Spaceborne Context

    Science.gov (United States)

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

    2011-01-01

    Compact polarimetry has been shown to be an interesting alternative mode to full polarimetry when global coverage and revisit time are key issues. It consists on transmitting a single polarization, while receiving on two. Several critical points have been identified, one being the Faraday rotation (FR) correction and the other the calibration. When a low frequency electromagnetic wave travels through the ionosphere, it undergoes a rotation of the polarization plane about the radar line of sight for a linearly polarized wave, and a simple phase shift for a circularly polarized wave. In a low frequency radar, the only possible choice of the transmit polarization is the circular one, in order to guaranty that the scattering element on the ground is illuminated with a constant polarization independently of the ionosphere state. This will allow meaningful time series analysis, interferometry as long as the Faraday rotation effect is corrected for the return path. In full-polarimetric (FP) mode, two techniques allow to estimate the FR: Freeman method using linearly polarized data, and Bickel and Bates theory based on the transformation of the measured scattering matrix to a circular basis. In CP mode, an alternate procedure is presented which relies on the bare surface scattering properties. These bare surfaces are selected by the conformity coefficient, invariant with FR. This coefficient is compared to other published classifications to show its potential in distinguishing three different scattering types: surface, doublebounce and volume. The performances of the bare surfaces selection and FR estimation are evaluated on PALSAR and airborne data. Once the bare surfaces are selected and Faraday angle estimated over them, the correction can be applied over the whole scene. The algorithm is compared with both FP techniques. In the last part of the paper, the calibration of a CP system from the point of view of classical matrix transformation methods in polarimetry is

  6. Toward an adjustable nonlinear low frequency acoustic absorber

    Science.gov (United States)

    Mariani, R.; Bellizzi, S.; Cochelin, B.; Herzog, P.; Mattei, P. O.

    2011-10-01

    A study of the targeted energy transfer (TET) phenomenon between an acoustic resonator and a thin viscoelastic membrane has recently been presented in the paper [R. Bellet et al., Experimental study of targeted energy transfer from an acoustic system to a nonlinear membrane absorber, Journal of Sound and Vibration 329 (2010) 2768-2791], providing a new path to passive sound control in the low frequency domain where no efficient dissipative device exists. This paper presents experimental results showing that a loudspeaker used as a suspended piston working outside its range of linearity can also be used as a nonlinear acoustic absorber. The main advantage of this technology of absorber is the perspective to adjust independently the device parameters (mass, nonlinear stiffness and damping) according to the operational conditions. To achieve this purpose, quasi-static and dynamic tests have been performed on three types of commercial devices (one with structural modifications), in order to define the constructive characteristics that it should present. An experimental setup has been developed using a one-dimensional acoustic linear system coupled through a box (acting as a weak spring) to a loudspeaker used as a suspended piston acting as an essentially nonlinear oscillator. The tests carried out on the whole vibro-acoustic system have showed the occurrence of the acoustic TET from the acoustic media to the suspended piston and demonstrated the efficiency of this new kind of absorber at low frequencies over a wide frequency range. Moreover, the experimental analyses conducted with different NES masses have confirmed that it is possible to optimize the noise absorption with respect to the excitation level of the acoustic resonator.

  7. Excitation of global Alfven Eigenmodes by RF heating in JET

    Energy Technology Data Exchange (ETDEWEB)

    Kerner, W.; Borba, D.; Gormezano, C.; Huysmans, G.; Porcelli, F.; Start, D. [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking; Fasoli, A. [Ecole Polytechnique Federale, Lausanne (Switzerland). Centre de Recherche en Physique des Plasma (CRPP); Sharapov, S. [Kurchatov Institute, Moscow (Russian Federation)

    1994-07-01

    The alpha-particle confinement of future D-T experiments at JET can be severely degraded by Global Alfven Eigenmodes (AE). Scenarios for the excitation of Alfven Eigenmodes in usual (e.g. D-D) plasmas are proposed, which provide a MHD diagnostic and allow the study of the transport of super-Alfvenic ions. Active studies with separate control of TAE amplitude and energetic particle destabilization, measuring the plasma response, give more information than passive studies, in particular concerning the damping mechanisms. The TAE excitation can be achieved by means of the saddle coil and the ICRH antenna. The experimental method is introduced together with a theoretical model for RF excitation. (authors). 6 refs., 3 figs.

  8. Diffusive shock acceleration with magnetic field amplification and Alfvenic drift

    CERN Document Server

    Kang, Hyesung

    2012-01-01

    We explore how wave-particle interactions affect diffusive shock acceleration (DSA) at astrophysical shocks by performing time-dependent kinetic simulations, in which phenomenological models for magnetic field amplification (MFA), Alfvenic drift, thermal leakage injection, Bohm-like diffusion, and a free escape boundary are implemented. If the injection fraction of cosmic-ray (CR) particles is greater than 2x10^{-4}, for the shock parameters relevant for young supernova remnants, DSA is efficient enough to develop a significant shock precursor due to CR feedback, and magnetic field can be amplified up to a factor of 20 via CR streaming instability in the upstream region. If scattering centers drift with Alfven speed in the amplified magnetic field, the CR energy spectrum can be steepened significantly and the acceleration efficiency is reduced. Nonlinear DSA with self-consistent MFA and Alfvenic drift predicts that the postshock CR pressure saturates roughly at 10 % of the shock ram pressure for strong shocks...

  9. Convective and Diffusive Energetic Particle Losses Induced by Shear Alfven Waves in the ASDEX Upgrade Tokamak

    NARCIS (Netherlands)

    Garcia-Munoz, M.; Hicks, N.; van Voornveld, R.; Classen, I.G.J.; Bilato, R.; Bobkov, V.; Bruedgam, M.; Fahrbach, H. U.; Igochine, V.; Jaemsae, S.; Maraschek, M.; Sassenberg, K.

    2010-01-01

    We present here the first phase-space characterization of convective and diffusive energetic particle losses induced by shear Alfven waves in a magnetically confined fusion plasma. While single toroidal Alfven eigenmodes (TAE) and Alfven cascades (AC) eject resonant fast ions in a convective process

  10. Spontaneous low frequency oscillation studies in gallium arsenide fast photoconductors

    CERN Document Server

    Foulon, F; Brullot, B; Petit, P; Bergonzo, P; Rubbelynck, C

    1999-01-01

    We have investigated the influence of spontaneous low frequency oscillations (LFO, f approx 0.01 Hz) occurring at high electric field (>1 kV/cm) in resistive photoconductors (PCD) made from semi-insulating GaAs on the response of the PCDs under pulsed gamma-ray irradiation (E approx 1.2 MeV, tau sub F sub W sub H sub M =30 ns). The PCDs were fabricated using GaAs from five commercially available sources. The PCDs were irradiated with fission neutrons in order to reduce their response time down to less than 100 ps. The amplitude of the LFOs was found to be related to the carrier lifetime, and thus defect concentration in the GaAs material. It was larger for material exhibiting high carrier lifetime. Increasing the localised defect concentration, such as EL2 type defect, through GaAs irradiation with fission neutrons was found to decrease the amplitude of the LFOs. PCDs irradiated at high neutron doses (>1x10 sup 1 sup 5 neutrons/cm sup 2) showed no LFOs. It is suggested that interactions between the propagatin...

  11. Low Frequency Spectral Structure of X-shaped Radio Sources

    Science.gov (United States)

    Lal, D. V.; Rao, A. P.

    2005-12-01

    X-shaped radio galaxies are attributed to be formed by galactic mergers as the black holes of two galaxies fall into the merged system and form a bound system. Recent analysis of Giant Metrewave Radio Telescope low frequency data for an X-shaped source, 3C 223.1 has revealed an unusual result (Lal & Rao 2004). The radio morphologies of it at 240 and 610 MHz show well defined X-shape with a pair of active jets along the north-south axis and a pair of wings along the east-west axis, that pass symmetrically through the undetected radio core. The wings (or low surface brightness jets) have flatter spectral indices with respect to the high surface brightness jets, which confirms the earlier marginal result obtained at high frequency by Dennett-Thorpe et al. (2002). Although unusual, it is a valuable result which puts stringent constraints on the formation models and nature of these sources. We present preliminary results for two such sources.

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

    Science.gov (United States)

    Asami, Koji

    2014-07-01

    Dielectric spectra of Escherichia coli cells suspended in 0.1-10 mM NaCl were measured over a frequency range of 10 Hz to 10 MHz. Low-frequency dielectric dispersion, so-called the α-dispersion, was found below 10 kHz in addition to the β-dispersion, due to interfacial polarization, appearing above 100 kHz. When the cells were killed by heating at 60°C for 30 min, the β-dispersion disappeared completely, whereas the α-dispersion was little influenced. This suggests that the plasma (or inner) membranes of the dead cells are no longer the permeability barrier to small ions, and that the α-dispersion is not related to the membrane potential due to selective membrane permeability of ions. The intensity of the α-dispersion depended on both of the pH and ionic strength of the external medium, supporting the model that the α-dispersion results from the deformation of the ion clouds formed outside and inside the cell wall containing charged residues. Copyright © 2014 Elsevier B.V. All rights reserved.

  13. Low frequency seabed scattering at low grazing angles.

    Science.gov (United States)

    Zhou, Ji-Xun; Zhang, Xue-Zhen

    2012-04-01

    Low-frequency (LF) seabed scattering at low grazing angles (LGA) is almost impossible to directly measure in shallow water (SW), except through inversion from reverberation. The energy flux method for SW reverberation is briefly introduced in this paper. The closed-form expressions of reverberation in an isovelocity waveguide, derived from this method, indicate that in the three-halves law range interval multimode/ray sea bottom scattering with different incident and scattering angles in forming the reverberation may equivalently be represented by the bottom backscattering at a single range-dependent angle. This equivalent relationship is used to derive the bottom backscattering strength (BBS) as a function of angle and frequency. The LF&LGA BBS is derived in a frequency band of 200-2500 Hz and in a grazing angle range of 1.1°-14.0° from reverberation measurements at three sites with sandy bottoms. This is based on three previous works: (1) The closed-form expressions of SW reverberation [Zhou, (Chinese) Acta Acustica 5, 86-99 (1980)]; (2) the effective geo-acoustic model of sandy bottoms that follows the Biot model [Zhou et al., J. Acoust. Soc. Am. 125, 2847-2866 (2009)] and (3) A quality database of wideband reverberation level normalized to source level [Zhou and Zhang, IEEE J. Oceanic Eng. 30, 832-842 (2005)].

  14. Unusual Low-frequency Magnetic Perturbations in TFTR

    Energy Technology Data Exchange (ETDEWEB)

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

    2001-02-12

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

  15. Response growth using a low-frequency suppressor.

    Science.gov (United States)

    DiGiovanni, Jeffrey J; Nair, Padmaja

    2007-12-01

    Numerous psychophysical studies on two-tone suppression have been carried out. More recently, researchers have attempted to relate the magnitude of suppression to the level of suppressee. [Wojtczak, M., Viemeister, N.F., 2005. Psychophysical response growth under suppression. In: Pressnitzer, D., de Cheveigne, A., McAdams, S., Collet, L. (Eds.), Auditory Signal Processing: Physiology, Psychoaccoustics, and Models. Springer, New York, pp. 67-74] demonstrated that the magnitude of suppression for a higher-frequency, fixed-level suppressor decreases with increasing level of the suppressee. This suggests a linearization of the basilar membrane response in presence of a high-frequency suppressor. The present study expands these results to a low-frequency suppressor of varying intensity levels. Detection of a 10-ms, 4.0-kHz probe was measured under different forward-masking conditions: one with a 200-ms, 4.0-kHz masker (suppressee) presented with no suppressor and another with the same masker paired with a 2.2-kHz, 200-ms suppressor. The 4.0-kHz masker level was varied adaptively and a range of probe levels was used to measure the growth of suppression. Results indicate that (1) the magnitude of suppression increases with increasing suppressor level and (2) generally, the probe level was not related to the magnitude of suppression.

  16. Low-frequency oscillations in radiative-convective models

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Qi; Randall, D.A.

    1991-12-31

    Although eastward propagation is usually regarded as an essential feature of the low-frequency ``Madden-Julian oscillation`` observed in the tropical atmosphere, many observations indicate that there is an important stationary or quasi-stationary component of the oscillation. Yasunari (1979), for example, investigated the stationary 30--60 day variation in upper tropospheric cloudiness in the Asian summer monsoon region. In a case study of the 30--60 day oscillation. Hsu et al. (1990) found a strong stationary oscillation of the divergence, outgoing longwave mdiadon and other fields. A recent observational study by Weickmann and Khalsa (1990) offers further evidence that the Madden-Julian oscillation has an important stationary component. In this paper, we present evidence that intraseasonal oscillations can be produced by local radiative and convective processes. This suggests that the observed propagating Madden-Julian wave is produced by interactions between these local processes and the large scale motion field, and is not essential for the existence of the observed oscillation.

  17. Low-frequency oscillations in radiative-convective models

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Qi; Randall, D.A.

    1991-01-01

    Although eastward propagation is usually regarded as an essential feature of the low-frequency Madden-Julian oscillation'' observed in the tropical atmosphere, many observations indicate that there is an important stationary or quasi-stationary component of the oscillation. Yasunari (1979), for example, investigated the stationary 30--60 day variation in upper tropospheric cloudiness in the Asian summer monsoon region. In a case study of the 30--60 day oscillation. Hsu et al. (1990) found a strong stationary oscillation of the divergence, outgoing longwave mdiadon and other fields. A recent observational study by Weickmann and Khalsa (1990) offers further evidence that the Madden-Julian oscillation has an important stationary component. In this paper, we present evidence that intraseasonal oscillations can be produced by local radiative and convective processes. This suggests that the observed propagating Madden-Julian wave is produced by interactions between these local processes and the large scale motion field, and is not essential for the existence of the observed oscillation.

  18. Collagen and component polypeptides: Low frequency and amide vibrations

    Science.gov (United States)

    Fontaine-Vive, F.; Merzel, F.; Johnson, M. R.; Kearley, G. J.

    2009-01-01

    Collagen is a fibrous protein, which exists widely in the human body. The biomechanical properties of collagen depend on its triple helix structure and the corresponding low frequency vibrations. We use first-principles, density functional theory methods and analytical force fields to investigate the molecular vibrations of a model collagen compound, the results being validated by comparison with published, inelastic neutron scattering data. The results from these atomistic simulations are used at higher frequency to study the Amide I and V vibrations and therefore the vibrational signature of secondary and tertiary structure formation. In addition to collagen, its component homopolymers, poly-glycine and poly-proline are also studied. The Amide V vibration of glycine is strongly modified in going from the single helix of poly-glycine II to the triple helix of collagen. The collagen models are hydrated and this work allows us to discuss the relative merits of density functional theory and force field methods when tackling complex, partially crystalline systems.

  19. An Architecture for High Data Rate Very Low Frequency Communication

    Directory of Open Access Journals (Sweden)

    Arun Kumar

    2013-01-01

    Full Text Available Very low frequency (VLF communication is used for long range shore-to-ship broadcasting applications. This paper proposes an architecture for high data rate VLF communication using Gaussian minimum shift keying (GMSK modulation and low delay parity check (LDPC channel coding. Non-data aided techniques are designed and used for carrier phase synchronization, symbol timing recovery, and LDPC code frame synchronization. These require the estimation of the operative Eb/N0 for which a kurtosis based algorithm is used. Also, a method for modeling the probability density function of the received signal under the bit condition is presented in this regard. The modeling of atmospheric radio noise (ARN that corrupts VLF signals is described and an algorithm for signal enhancement in the presence of ARN in given. The BER performance of the communication system is evaluated for bit rates of 400 bps, 600 bps, and 800 bps for communication bandwidth of ~200 Hz.Defence Science Journal, 2013, 63(1, pp.25-33, DOI:http://dx.doi.org/10.14429/dsj.63.3760

  20. Progress on the Low Frequency All Sky Monitor

    Science.gov (United States)

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

    2015-01-01

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

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

    Science.gov (United States)

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

    2015-12-01

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

  2. Low-frequency deep brain stimulation for movement disorders.

    Science.gov (United States)

    Baizabal-Carvallo, José Fidel; Alonso-Juarez, Marlene

    2016-10-01

    Traditionally, deep brain stimulation (DBS) for movement disorders (MDs) is provided using stimulation frequencies equal to or above 100 Hz. However, recent evidence suggests that relatively low-frequency stimulation (LFS) below 100 Hz is an option to treat some patients with MDs. We aimed to review the clinical and pathophysiological evidence supporting the use of stimulation frequencies below 100 Hz in different MDs. Stimulation of the subthalamic nucleus at 60 Hz has provided benefit in gait and other axial symptoms such as swallowing and speech. Stimulation of the pedunculopontine nucleus between 20 and 45 Hz can provide benefit in freezing of gait, cognition, and sleep quality in select patients with Parkinson's disease. Stimulation of the globus pallidus internus below 100 Hz in patients with dystonia has provided benefit at the beginning of the therapy, although progressively higher stimulation frequencies seem to be necessary to maintain the clinical benefit. Relative LFS can lower energy requirements and reduce battery usage-a useful feature, particularly in patients treated with high current energy. DBS at frequencies below 100 Hz is a therapeutic option in select cases of Parkinson's disease with freezing of gait and other axial symptoms, and in select patients with dystonia and other hyperkinetic movements, particularly those requiring an energy-saving strategy. Copyright © 2016 Elsevier Ltd. All rights reserved.

  3. Planck 2013 results. II. Low Frequency Instrument data processing

    Science.gov (United States)

    Planck Collaboration; Aghanim, N.; Armitage-Caplan, C.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Battaner, E.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bobin, J.; Bock, J. J.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Bridges, M.; Bucher, M.; Burigana, C.; Butler, R. C.; Cappellini, B.; Cardoso, J.-F.; Catalano, A.; Chamballu, A.; Chen, X.; Chiang, L.-Y.; Christensen, P. R.; Church, S.; Colombi, S.; Colombo, L. P. L.; Crill, B. P.; Cruz, M.; 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.; Dupac, X.; Efstathiou, G.; Enßlin, T. A.; Eriksen, H. K.; Falvella, M. C.; Finelli, F.; Forni, O.; Frailis, M.; Franceschi, E.; Gaier, T. C.; Galeotta, S.; Ganga, K.; Giard, M.; Giardino, G.; Giraud-Héraud, Y.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Hansen, F. K.; Hanson, D.; Harrison, D.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huffenberger, K. M.; Jaffe, A. H.; Jaffe, T. R.; Jewell, J.; Jones, W. C.; Juvela, M.; Kangaslahti, P.; Keihänen, E.; Keskitalo, R.; Kiiveri, K.; Kisner, T. S.; Knoche, J.; Knox, L.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lähteenmäki, A.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Laureijs, R. J.; Lawrence, C. R.; Leach, S.; Leahy, J. P.; Leonardi, R.; Lesgourgues, J.; 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.; Maris, M.; Marshall, D. J.; Martin, P. G.; Martínez-González, E.; Masi, S.; Massardi, M.; Matarrese, S.; Matthai, F.; Mazzotta, P.; Meinhold, P. R.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Moneti, A.; Montier, L.; Morgante, G.; Morisset, N.; Mortlock, D.; Moss, A.; Munshi, D.; Naselsky, P.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Novikov, D.; Novikov, I.; O'Dwyer, I. J.; Osborne, S.; Paci, F.; Pagano, L.; Paladini, R.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Peel, M.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Platania, P.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Popa, L.; Poutanen, T.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reach, W. T.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Ricciardi, S.; Riller, T.; Robbers, G.; Rocha, G.; Rosset, C.; Rossetti, M.; Roudier, G.; Rubiño-Martín, J. A.; Rusholme, B.; Salerno, E.; Sandri, M.; Santos, D.; Scott, D.; Seiffert, M. D.; Shellard, E. P. S.; Spencer, L. D.; Starck, J.-L.; Stolyarov, V.; Stompor, R.; Sureau, F.; 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.; Varis, J.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L. A.; Wandelt, B. D.; Watson, R.; Wehus, I. K.; White, S. D. M.; Wilkinson, A.; Yvon, D.; Zacchei, A.; Zonca, A.

    2014-11-01

    We describe the data processing pipeline of the Planck Low Frequency Instrument (LFI) data processing centre (DPC) to create and characterize full-sky maps based on the first 15.5 months of operations at 30, 44, and 70 GHz. In particular, we discuss the various steps involved in reducing the data, from telemetry packets through to the production of cleaned, calibrated timelines and calibrated frequency maps. Data are continuously calibrated using the modulation induced on the mean temperature of the cosmic microwave background radiation by the proper motion of the spacecraft. Sky signals other than the dipole are removed by an iterative procedure based on simultaneous fitting of calibration parameters and sky maps. Noise properties are estimated from time-ordered data after the sky signal has been removed, using a generalized least squares map-making algorithm. A destriping code (Madam) is employed to combine radiometric data and pointing information into sky maps, minimizing the variance of correlated noise. Noise covariance matrices, required to compute statistical uncertainties on LFI and Planck products, are also produced. Main beams are estimated down to the ≈- 20 dB level using Jupiter transits, which are also used for the geometrical calibration of the focal plane.

  4. Planck Early Results: The Low Frequency Instrument data processing

    CERN Document Server

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

    2011-01-01

    We describe the data processing pipeline employed by the Low Frequency Instrument (LFI) Data Processing Centre (DPC) to create and characterize the frequency maps used by the ERCSC (Early Release Compact Source Catalogue) first product of Planck to become public. In particular, we discuss the various steps involved in reducing the data, starting from telemetry (TM)packets through to the production of cleaned calibrated timelines and calibrated frequency maps. Data are continuously calibrated using the modulation induced on the mean temperature of the Cosmic Microwave Background Radiation by the proper motion of the spacecraft. The sky signals other than the dipole are removed by an iterative procedure based on simultaneous fitting of calibration parameters and sky maps. Noise properties are estimated from time-ordered data where the sky signal is removed using a Generalized Least Square map-making algorithm. The measured 1/f noise knee-frequencies range from \\sim 100 mHz at 30 GHz to a few tens of mHz at 70 G...

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

    Science.gov (United States)

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

    2011-12-01

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

  6. Low-frequency meandering piezoelectric vibration energy harvester.

    Science.gov (United States)

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

    2012-05-01

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

  7. Energy harvesting from low frequency applications using piezoelectric materials

    Energy Technology Data Exchange (ETDEWEB)

    Li, Huidong; Tian, Chuan; Deng, Z. Daniel, E-mail: zhiqun.deng@pnnl.gov [Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352 (United States)

    2014-12-15

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Chang, J.W.

    1991-07-01

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

  9. High Sensitivity Very Low Frequency Receiver for Earthquake Data Acquisition.

    Science.gov (United States)

    Munir, A.; Najmurrokhman, A.

    2017-03-01

    high sensitivity very low frequency (VLF) receiver is developed based on AD744 monolithic operational amplifier (Op-Amp) for earthquake data acquisition. In research related natural phenomena such as atmospheric noise, lightning and earthquake, a VLF receiver particularly with high sensitivity is utterly required due to the low power of VLF wave signals received by the antenna. The developed receiver is intended to have high sensitivity reception for the signals in frequency range of 10-30kHz allocated for earthquake observation. The VLF receiver which is portably designed is also equipped with an output port connectable to the soundcard of personal computer for further data acquisition. After obtaining the optimum design, the hardware realization is implemented on a printed circuit board (PCB) for experimental characterization. It shows that the sensitivity of realized VLF receiver is almost linear in the predefined frequency range for the input signals lower than -12dBm and to be quadratic for the higher level input signals.

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

    Science.gov (United States)

    Chang, J. W.

    1991-07-01

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

  11. MYOELECTRIC ALTERATIONS AFTER VOLUNTARY INDUCED HIGH - AND LOW - FREQUENCY FATIGUE

    Directory of Open Access Journals (Sweden)

    Vojko Strojnik

    2008-06-01

    Full Text Available The aim of the study was to find whether voluntary induced high- and low-frequency peripheral fatigue exhibit specific alteration in surface EMG signal (SEMG during evoked and maximum voluntary contractions. Ten male students of physical education performed 60 s long stretch-shortening cycle (SSC exercise with maximal intensity and 30 s long concentric (CON exercise with maximal intensity. To verify voluntary induced peripheral fatigue, knee torques during low- (T20 and high-frequency electrical stimulation (T100 of relaxed vastus lateralis muscle (VL were obtained. Contractile properties of the VL were measured with passive twitch and maximal voluntary knee extension test (MVC. Changes in M-waves and SEMG during MVC test were used to evaluate the differences in myoelectrical signals. T100/T20 ratio decreased by 10.9 ± 8.4 % (p < 0.01 after the SSC exercise and increased by 35.9 ± 17.5 % (p < 0.001 after the CON exercise. Significant SEMG changes were observed only after the CON exercise where peak to peak time of the M-waves increased by 9.2 ± 13.3 % (p < 0.06, SEMG amplitude during MVC increased by 32.9 ± 21.6 % (p < 0.001 and SEMG power spectrum median frequency decreased by 11.0 ± 10.5 % (p < 0.05. It is concluded that high frequency fatigue wasn't reflected in SEMG, however the SEMG changes after the CON seemed to reflect metabolic changes due to acidosis

  12. Low Frequency Shadowing of the Parkes Superb Survey

    Science.gov (United States)

    Bhat, N. D. R.; Kaplan, D. L.; Williams, A.; Wayth, R.

    2017-01-01

    The field of Fast Radio Bursts (FRBs) is rapidly gaining momentum. Since their discovery in the Parkes high time resolution survey (Thornton et al. 2013), the number of reported FRB detections has more than tripled, and measurements have been made of their scattering, scintillation, polarisation and Faraday rotation properties, all of which helped to establish their astrophysical nature. Obser- vational evidence continues to mount in support of their extragalactic origin, and the world-wide competitive race is ramping up as a suite of new and existing instruments are gearing up to find them in large numbers. The SUPERB survey at Parkes has been conceived to realise the important goal of understanding the origin and progenitors of FRBs. An integral part of this survey is co-ordinated multi-wavelength follow-ups and shadowing. Our MWA-based shadowing efforts last year resulted in the first simultaneous multi-frequency observation of an FRB (albeit a non-detection at the MWA), and hence the first broadband limit on the spectral index, as reported in our Nature publication (Keane at al. 2016). After an year-long hiatus the SUPERB survey is scheduled to resume in December 2016. We propose to resume our MWA-based efforts by undertaking effective low-frequency shadowing that is uniquely possible with the MWA. Simultaneous detection of even a single a self-same FRB would bring in a huge science payoff and will yield the first unambiguous constraints on the spectral and scattering properties of FRBs, besides the prospects of sub-arc minute localisation that will be possible with the long baseline array of Phase 2 MWA. We propose to make use of unallocated blocks of time within the schedule, available outside the approved programs and the planned commissioning activities relating to Phase 2. This proposal will thus make excellent use of idle time for an exciting and very important science goal in the nascent field of FRB science.

  13. A Wire Grid Paraboloid for Large Low Frequency Telescopes

    Science.gov (United States)

    Kuiper, Tom

    2017-05-01

    Planetary magnetic fields are usually studied remotely through their electron cyclotron maser (ECM) emission from electrons trapped in their magnetic fields. Jupiter has been well studied since the 1960's because its strong magnetic field allows emissions up to about 40 MHz to be observed. The emission from Earth and other outer planets is mostly below 1 MHz and can only be observed from space. It is reasonable to assume that most exoplanets with ECM must be observed at low frequencies from space. Even optimistic assumptions about the strength of such emission leads one to conclude that very large filled aperture telescopes, with a diameters of a kilometer or more, will be needed.This paper reports on a study of a copper wire reflector with a diameter of 1 km operating between 100 kHz and 3.75 MHz. It would require 200 kg of 0.5 mm diameter copper wire (AWG 24)) to be lifted to and deployed in space. For aluminum, the mass would be about 100 kg. By optimizing the wire spacing the mass can be reduced to 80% of a simple radial-azimuthal arrangement. A relatively flat reflector (0.6 ≤ f/D ≤ 1.0) needs to be anchored at about 5 points from center to ring along 24 radii. Station-keeping CubeSats could serve as anchors. A total of about 100-120 anchors would be needed for an f/D = 1 reflector, adding 200-300 kg. to the mass of the reflector. It would be possible to carry several such reflectors into space in a single payload.The Deep Space Network is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract to the National Aeronautics and Space Administration.

  14. Low-frequency Fresnel mirrors for fluorescence detectors

    Science.gov (United States)

    Diaz-Anzures, J.; Cordero-Davila, A.; Gonzalez-Garcia, J.; Martinez-Bravo, O.; Robledo-Sanchez, C.; Khrenov, B. A.; Garipov, G. K.

    2004-07-01

    In this work we present several designs of a Fresnel mirror with small number of rings (low frequency) to be used in fluorescence detectors aimed for study of ultra high energy cosmic rays. Being segmented the Fresnel mirror has an advantage of simple development from a compact package to a "plane" large area mirror-concentrator. This advantage is important for detectors in space and detectors at remote mountain sites. In this work, we investigated four possible ways of generating a focusing surface. In the first (main) design, the mirror consists of sections belonging to several parabolic surfaces. In this case the best focusing of a source on optical axis is achieved--the Fresnel mirror operates as parabolic mirror. This design is the best for a space "telescope", observing a source from large distances. Close to this design are mirror options with sections of a common parabolic surface and with sections of several spherical surfaces. The simplest for construction is the mirror with sections of a common spherical surface. In this design, focusing of a source on optical axis is much poorer than in previous options, but the mirror may be used in the experiments needed a wide field of view (FOV) with rough angular resolution. An advantage of this design is simplicity of the mirror construction which is shown in the mirror prototype construction and its testing. Results of the focal spot measurements are presented. This simple design of the Fresnel mirror is planned for use in the Pico de Orizaba mountain hybrid array where the wide field of view is important.

  15. Constraints on Subduction Zone Processes from Low Frequency Earthquakes

    Science.gov (United States)

    Bostock, M. G.

    2015-12-01

    The discovery of tectonic tremor and constituent low-frequency earthquakes (LFEs) offers seismologists new opportunities to study both deformational processes and structure within the subduction zone forearc. This assertion is especially true for northern Cascadia where i) regular seismicity is sparse, and ii) a relatively transparent overriding plate inflicts minimal distortion upon direct P and S wave arrivals from LFEs. Despite low signal-to-noise ratios, LFEs are highly repetitive and signal can be enhanced through construction of stacked templates. Studies in both Cascadia and Nankai reveal an association between LFE hypocenters and a high Vp/Vs, low-velocity zone (LVZ) that is inferred to represent overpressured upper oceanic crust. Scattered signals within Vancouver Island templates, interpreted to originate at boundaries of the LVZ, place LFEs within the LVZ and suggest that this structure may define a distributed (several km) zone of deformation. A recent analysis of LFE magnitudes indicates that LFEs exhibit scaling relations distinct from both regular earthquakes and longer period (10's of seconds to days) phenomena associated with slow slip. Regular earthquakes generally obey a scaling of moment proportional to duration cubed consistent with self similarity, whereas long period slow slip phenomena exhibit a linear scaling between moment and duration that can be accommodated through constant slip or constant stress drop models. In contrast, LFE durations are nearly constant suggesting that moment is governed by slip alone and that asperity size remains approximately constant. The implied dimensions (~1 km2), the persistance of LFEs in time and their stationarity in space point to structural heterogeneity, perhaps related to pockets of upper oceanic crust impervious to hydrothermal circulation, as a fundamental control.

  16. Reduced models of extratropical low-frequency variability

    Science.gov (United States)

    Strounine, Kirill

    Low-frequency variability (LFV) of the atmosphere refers to its behavior on time scales of 10-100 days, longer than the life cycle of a mid-latitude cyclone but shorter than a season. This behavior is still poorly understood and hard to predict. It has been helpful in gaining understanding that might improve prediction to use various simplified models. The present study compares and contrasts various mode reduction strategies that help derive systematically such simplified models of LFV. Three major strategies have been applied to reduce a fairly realistic, high-dimensional, quasi-geostrophic, 3-level (QG3) atmospheric model to lower dimensions: (i) a purely empirical, multi-level regression procedure, which specifies the functional form of the reduced model and finds the model coefficients by multiple polynomial regression; (ii) an empirical-dynamical method, which retains only a few components in the projection of the full QG3 model equations onto a specified basis (the so-called bare truncation), and finds the linear deterministic and additive stochastic corrections empirically; and (iii) a dynamics-based technique, employing the stochastic mode reduction strategy of Majda et al. (2001; MTV). Subject to the assumption of significant time-scale separation in the physical system under consideration, MTV derives the form of the reduced model and finds its coefficients with minimal statistical fitting. The empirical-dynamical and dynamical reduced models were further improved by sequential parameter estimation and benchmarked against multi-level regression models; the extended Kalman filter (EKF) was used for the parameter estimation. In constructing the reduced models, the choice of basis functions is also important. We considered as basis functions a set of empirical orthogonal functions (EOFs). These EOFs were computed using (a) an energy norm; and (b) a potential-enstrophy norm. We also devised a method, using singular value decomposition of the full

  17. Kinetic Alfven wave instability in a Lorentzian dusty plasma: Non-resonant particle approach

    Energy Technology Data Exchange (ETDEWEB)

    Rubab, N.; Biernat, H. K. [Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz (Austria); Institute of Physics, University of Graz, Universitaetplatz 5, A-8010 Graz (Austria); Erkaev, V. [Institute of Computational Modelling, 660036 Krasnoyarsk, Russia and Siberian Federal University, 660041 Krasnoyarsk (Russian Federation); Langmayr, D. [Virtual Vehicle Competence Center (vif), Inffeldgasse 21a, 8010 Graz (Austria)

    2011-07-15

    Analysis of the electromagnetic streaming instability is carried out which is related to the cross field drift of kappa distributed ions. The linear dispersion relation for electromagnetic wave using Vlasov-fluid equations in a dusty plasma is derived. Modified two stream instability (MTSI) in a dusty plasma has been discussed in the limit {omega}{sub pd}{sup 2}/c{sup 2}k{sub perpendicular}{sup 2}<<1. Numerical calculations of the growth rate of instability have been carried out. Growth rates of kinetic Alfven instability are found to be small as compared to MTSI. Maximum growth rates for both instabilities occur in oblique directions for V{sub 0}{>=}V{sub A}. It is shown that the presence of both the charged dust particles and perpendicular ion beam sensibly modify the dispersion relation of low-frequency electromagnetic wave. The dispersion characteristics are found to be insensible to the superthermal character of the ion distribution function. Applications to different intersteller regions are discussed.

  18. Alfven eigenmode structure during off-axis neutral beam injection

    NARCIS (Netherlands)

    Tobias, B.; Bass, E. M.; Classen, I.G.J.; Domier, C.W.; Grierson, B. A.; Heidbrink, W. W.; N C Luhmann Jr.,; Nazikian, R.; Park, H. K.; Spong, D. A.; VanZeeland, M. A.

    2012-01-01

    The spatial structure of Alfven eigenmodes on the DIII-D tokamak is compared for contrasting fast ion deposition profiles resulting from on- and off-axis neutral beam injection (NBI). In both cases, poloidal mode rotation and eigenmode twist, or radial phase variation, are correlated with the direct

  19. Quantum effects on compressional Alfven waves in compensated semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Amin, M. R. [Department of Electronics and Communications Engineering, East West University, Aftabnagar, Dhaka 1212 (Bangladesh)

    2015-03-15

    Amplitude modulation of a compressional Alfven wave in compensated electron-hole semiconductor plasmas is considered in the quantum magnetohydrodynamic regime in this paper. The important ingredients of this study are the inclusion of the particle degeneracy pressure, exchange-correlation potential, and the quantum diffraction effects via the Bohm potential in the momentum balance equations of the charge carriers. A modified nonlinear Schrödinger equation is derived for the evolution of the slowly varying amplitude of the compressional Alfven wave by employing the standard reductive perturbation technique. Typical values of the parameters for GaAs, GaSb, and GaN semiconductors are considered in analyzing the linear and nonlinear dispersions of the compressional Alfven wave. Detailed analysis of the modulation instability in the long-wavelength regime is presented. For typical parameter ranges of the semiconductor plasmas and at the long-wavelength regime, it is found that the wave is modulationally unstable above a certain critical wavenumber. Effects of the exchange-correlation potential and the Bohm potential in the wave dynamics are also studied. It is found that the effect of the Bohm potential may be neglected in comparison with the effect of the exchange-correlation potential in the linear and nonlinear dispersions of the compressional Alfven wave.

  20. Direct excitation of resonant torsional Alfven waves by footpoint motions

    NARCIS (Netherlands)

    Ruderman, M. S.; Berghmans, D.; Goossens, M.; Poedts, S.

    1997-01-01

    The present paper studies the heating of coronal loops by linear resonant Alfven waves that are excited by the motions of the photospheric footpoints of the magnetic field lines. The analysis is restricted to torsionally polarised footpoint motions in an axially symmetric system so that only

  1. The role of torsional Alfven waves in coronal heating

    CERN Document Server

    Antolin, P

    2009-01-01

    In the context of coronal heating, among the zoo of MHD waves that exist in the solar atmosphere, Alfven waves receive special attention. Indeed, these waves constitute an attractive heating agent due to their ability to carry over the many different layers of the solar atmosphere sufficient energy to heat and maintain a corona. However, due to their incompressible nature these waves need a mechanism such as mode conversion (leading to shock heating), phase mixing, resonant absorption or turbulent cascade in order to heat the plasma. New observations with polarimetric, spectroscopic and imaging instruments such as those on board of the japanese satellite Hinode, or the SST or CoMP, are bringing strong evidence for the existence of energetic Alfven waves in the solar corona. In order to assess the role of Alfven waves in coronal heating, in this work we model a magnetic flux tube being subject to Alfven wave heating through the mode conversion mechanism. Using a 1.5-dimensional MHD code we carry out a paramete...

  2. Swirling astrophysical flows - efficient amplifiers of Alfven waves

    CERN Document Server

    Rogava, A D; Bodo, G; Massaglia, S; Rogava, Andria D.; Mahajan, Swadesh M.; Bodo, Gianluigi; Massaglia, Silvano

    2003-01-01

    We show that a helical shear flow of a magnetized plasma may serve as an efficient amplifier of Alfven waves. We find that even when the flow is purely ejectional (i.e., when no rotation is present) Alfven waves are amplified through the transient, shear-induced, algebraic amplification process. Series of transient amplifications, taking place sequentially along the flow, may result in a cascade amplification of these waves. However, when a flow is swirling or helical (i.e., some rotation is imposed on the plasma motion), Alfven waves become subject to new, much more powerful shear instabilities. In this case, depending on the type of differential rotation, both usual and parametric instabilities may appear. We claim that these phenomena may lead to the generation of large amplitude Alfven waves and the mechanism may account for the appearance of such waves in the solar atmosphere, in accretion-ejecion flows and in accretion columns. These processes may also serve as an important initial (linear and nonmodal)...

  3. Planck 2015 results: XXV. Diffuse low-frequency Galactic foregrounds

    DEFF Research Database (Denmark)

    Ade, P. A R; Aghanim, N.; Alves, M. I R

    2016-01-01

    component-separation tool has been used to separate the various astrophysical processes in total intensity. Comparison with radio recombination line templates verifies the recovery of the free-free emission along the Galactic plane. Comparison of the high-latitude Hα emission with our free-free map shows...... the nebulae. The emissivity of spinning dust in these diffuse regions is of the same order as previous detections in the literature. Over the entire sky, the Commander solution finds more anomalous microwave emission (AME) than the WMAP component maps, at the expense of synchrotron and free-free emission....... This can be explained by the difficulty in separating multiple broadband components with a limited number of frequency maps. Future surveys, particularly at 5-20 GHz, will greatly improve the separation by constraining the synchrotron spectrum. We combine Planck and WMAP data to make the highest signal...

  4. Manipulating neuronal activity with low frequency transcranial ultrasound

    Science.gov (United States)

    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.

  5. Low Frequency Radio-wave System for subsurface investigation

    Science.gov (United States)

    Soldovieri, Francesco; Gennarelli, Gianluca; Kudelya, Anatoliy; Denisov, Alexander

    2015-04-01

    Low frequency radio-wave methods (RWM) allow subsurface investigations in terms of lithological structure characterization, detection of filtration flows of ground water, anthropogenic and natural cavities. In this contribution, we present a RWM that exploits two coils working at frequencies of few MHz as transmitting and receiving antennas. The basic principle of this inductive method is as follows. The primary alternating electromagnetic field radiated by the transmitting coil induces eddy currents in the subsurface mainly due to the conductivity anomalies. These eddy currents generate a secondary (scattered) magnetic field which overlaps to the incident magnetic field and is detected by the receiving coil. Despite the simple operation of the system, the complexity of the electromagnetic scattering phenomenon at hand must be properly modeled to achieve adequate performance. Therefore, an advanced data processing technique, belonging to the class of the inverse scattering approaches, has been developed by the authors in a full 3D geometry. The proposed method allows to deal with data collected on a scanning surface under a dipole inductive profiling (DIP) modality, where the transmitting/receiving coils are moved simultaneously with fixed offset (multi-bistatic configuration). The hardware, called Dipole Inductive Radio-wave System (DIRS), is composed by an electronic unit and transmitting and receiving loop antennas radiating at frequencies of few MHz (2-4 MHz), which are installed on theodolite supports. The compactness of DIRS and its robustness to external electromagnetic interference offers the possibility to perform geophysical research up to the depth of some tens of meters and under several types of ground and water surfaces, vegetation, and weather conditions. The light weight and small size of system (the single antenna with support weights about 5 kg and has a diameter of 0.5m) allows two operators to perform geophysical research without disturbing the

  6. PageRank for low frequency earthquake detection

    Science.gov (United States)

    Aguiar, A. C.; Beroza, G. C.

    2013-12-01

    We have analyzed Hi-Net seismic waveform data during the April 2006 tremor episode in the Nankai Trough in SW Japan using the autocorrelation approach of Brown et al. (2008), which detects low frequency earthquakes (LFEs) based on pair-wise waveform matching. We have generalized this to exploit the fact that waveforms may repeat multiple times, on more than just a pair-wise basis. We are working towards developing a sound statistical basis for event detection, but that is complicated by two factors. First, the statistical behavior of the autocorrelations varies between stations. Analyzing one station at a time assures that the detection threshold will only depend on the station being analyzed. Second, the positive detections do not satisfy "closure." That is, if window A correlates with window B, and window B correlates with window C, then window A and window C do not necessarily correlate with one another. We want to evaluate whether or not a linked set of windows are correlated due to chance. To do this, we map our problem on to one that has previously been solved for web search, and apply Google's PageRank algorithm. PageRank is the probability of a 'random surfer' to visit a particular web page; it assigns a ranking for a webpage based on the amount of links associated with that page. For windows of seismic data instead of webpages, the windows with high probabilities suggest likely LFE signals. Once identified, we stack the matched windows to improve the snr and use these stacks as template signals to find other LFEs within continuous data. We compare the results among stations and declare a detection if they are found in a statistically significant number of stations, based on multinomial statistics. We compare our detections using the single-station method to detections found by Shelly et al. (2007) for the April 2006 tremor sequence in Shikoku, Japan. We find strong similarity between the results, as well as many new detections that were not found using

  7. Does Cooling Magma Drive Deep Low-Frequency Earthquakes?

    Science.gov (United States)

    Aso, N.; Ide, S.; Tsai, V. C.

    2013-12-01

    = Introduction = One major type of deep low-frequency earthquakes (LFEs) is tectonic LFEs that locate around plate boundaries, and are thought to be slip events. Another type of LFEs is volcanic LFEs that locate around the Moho mostly beneath active or Quaternary volcanoes, and their physical mechanism is not well established. We recently suggested that the volcanic LFEs in eastern Shimane can be interpreted as a resonant oscillation within an old magma conduit of 1600 m in length, which produces a focal mechanism that is equivalent to a compensated linear vector dipole (CLVD) oriented in the direction of the conduit [Aso et al., in prep. for re-submission]. However, a remaining question is what excites the resonance. In the present study, we suggest that cooling magma acts as a trigger for the resonant oscillation of volcanic LFEs, with the idea that thermal contraction of magma produces an anisotropic strain rate and the resulting brittle failure would trigger oscillation. To verify this, we calculated strain rates produced by this effect both analytically and numerically. = Model Setting and Method = We set the initial extent of magma as a 1600-m-long 400-m-wide pipe as is inferred from the distribution of hypocenters in eastern Shimane. The initial perturbation is set to be 400 K uniformly within the pipe. Thermal strain rate is calculated using the thermal stress potential of Timoshenko and Goodier [1970]. First, we estimated the strain rate without the effect of latent heat release. Assuming a cuboid pipe, it can be solved easily analytically. Next, to account for latent heat release, we use the enthalpy method [Eyres et al., 1946] to numerically solve the problem, assuming a cylindrical pipe. = Results = For the case without latent heat release, the strain rate remains higher than than 10-14/s for 600 years at the center of the pipe. For the case with latent heat release, although the latent heat delays the thermal evolution and decreases the strain rate, it

  8. Cellular studies and interaction mechanisms of extremely low frequency fields

    Science.gov (United States)

    Liburdy, Robert P.

    1995-01-01

    Worldwide interest in the biological effects of ELF (extremely low frequency, electromagnetic fields has grown significantly. Health professionals and government administrators and regulators, scientists and engineers, and, importantly, an increasing number of individuals in the general public are interested in this health issue. The goal of research at the cellular level is to identify cellular responses to ELF fields, to develop a dose threshold for such interactions, and with such information to formulate and test appropriate interaction mechanisms. This review is selective and will discuss the most recent cellular studies directed at these goals which relate to power line, sinusoidal ELF fields. In these studies an interaction site at the cell membrane is by consensus a likely candidate, since changes in ion transport, ligand-receptor events such as antibody binding, and G protein activation have been reported. These changes strongly indicate that signal transduction (ST) can be influenced. Also, ELF fields are reported to influence enzyme activation, gene expression, protein synthesis, and cell proliferation, which are triggered by earlier ST events at the cell membrane. The concept of ELF fields altering early cell membrane events and thereby influencing intracellular cell function via the ST cascade is perhaps the most plausible biological framework currently being investigated for understanding ELF effects on cells. For example, the consequence of an increase due to ELF fields in mitogenesis, the final endpoint of the ST cascade, is an overall increase in the probability of mutagenesis and consequently cancer, according to the Ames epigenetic model of carcinogenesis. Consistent with this epigenetic mechanism and the ST pathway to carcinogenesis is recent evidence that ELF fields can alter breast cancer cell proliferation and can act as a copromoter in vitro. The most important dosimetric question being addressed currently is whether the electric (E) or the

  9. Sub-Alfvenic inlet boundary conditions for axisymmetric MHD nozzles

    Energy Technology Data Exchange (ETDEWEB)

    Cassibry, J T [Propulsion Research Center, University of Alabama in Huntsville, Huntsville, AL 35899 (United States); Wu, S T [Center for Space Plasma and Aeronomy Research, University of Alabama in Huntsville, Huntsville, AL 35899 (United States)

    2007-09-07

    There are numerous electromagnetic accelerator concepts which require plasma expansion through a magnetic nozzle. If the inlet flow is slower than one or all of the outgoing characteristics, namely, the Alfven, slow and fast magnetosonic speeds, then the number of inlet conditions which could be arbitrarily specified are reduced by the number of outgoing characteristics (up to three). We derive the axisymmetric compatibility equations using the method of projected characteristics for the inlet conditions in the z-plane to assure the boundary conditions being consistent with flow properties. We make simplifications to the equations assuming that the inlet Alfven speed is much faster than the sonic and slow magnetosonic speeds. We compare results for various inlet boundary conditions, including a modified Lax-Wendroff implementation of the compatibility equations, first order extrapolation and arbitrarily specifying the inlet conditions, in order to assess the stability and accuracy of various approaches.

  10. Alfven frequency modes at the edge of TFTR plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Z.; Fredrickson, E.D.; Zweben, S.J. [and others

    1995-07-01

    An Alfven frequency mode (AFM) is very often seen in TFTR neutral beam heated plasmas as well as ohmic plasmas. This quasi-coherent mode is so far only seen on the magnetic fluctuation diagnostics (Mirnov coils). A close correlation between the plasma edge density and the mode activity (frequency and amplitude) has been observed, which indicates that the AFM is an edge localized mode with r/a > 0.85. No direct impact of this mode on the plasma global performance or fast ion loss (e.g., the {alpha}-particles in DT experiments) has been observed. This mode is apparently not the conventional TAE (toroidicity-induced Alfven eigenmodes). The present TAE theory cannot explain the observation. Other possible explanations are discussed.

  11. Phase Mixing of Alfv\\'en Waves Near a 2D Magnetic Null Point

    CERN Document Server

    McLaughlin, J A

    2014-01-01

    The propagation of linear Alfv\\'en wave pulses in an inhomogeneous plasma near a 2D coronal null point is investigated. When a uniform plasma density is considered, it is seen that an initially planar Alfv\\'en wavefront remains planar, despite the varying equilibrium Alfv\\'en speed, and that all the wave collects at the separatrices. Thus, in the non-ideal case, these Alfv\\'enic disturbances preferentially dissipate their energy at these locations. For a non-uniform equilibrium density, it is found that the Alfv\\'en wavefront is significantly distorted away from the initially planar geometry, inviting the possibility of dissipation due to phase mixing. Despite this however, we conclude that for the Alfv\\'en wave, current density accumulation and preferential heating still primarily occur at the separatrices, even when an extremely non-uniform density profile is considered.

  12. Resonant energy conversion of 3-minute intensity oscillations into Alfven waves in the solar atmosphere

    CERN Document Server

    Kuridze, D

    2007-01-01

    Nonlinear coupling between 3-minute oscillations and Alfven waves in the solar lower atmosphere is studied. 3-minute oscillations are considered as acoustic waves trapped in a chromospheric cavity and oscillating along transversally inhomogeneous vertical magnetic field. It is shown that under the action of the oscillations the temporal dynamics of Alfven waves is governed by Mathieu equation. Consequently, the harmonics of Alfven waves with twice period and wavelength of 3-minute oscillations grow exponentially in time near the layer where the sound and Alfven speeds equal. Thus the 3-minute oscillations are resonantly absorbed by pure Alfven waves near this resonant layer. The resonant Alfven waves may penetrate into the solar corona taking energy from the chromosphere. Therefore the layer c_s=v_A may play a role of energy channel for otherwise trapped acoustic oscillations.

  13. Attractors of magnetohydrodynamic flows in an Alfvenic state

    Energy Technology Data Exchange (ETDEWEB)

    Nunez, Manuel; Sanz, Javier [Departamento de Analisis Matematico, Universidad de Valladolid, Valladolid (Spain)

    1999-08-13

    We present a simplified form of the magnetohydrodynamic system which describes the evolution of a plasma where the small-scale velocity and magnetic field are aligned in the form of Alfven waves, such as happens in several turbulent situations. Bounds on the dimension of the global attractor are found, and are shown to be an improvement of the standard ones for the full magnetohydrodynamic equations. (author)

  14. Nonlinear Alfv\\'en waves in extended magnetohydrodynamics

    CERN Document Server

    Abdelhamid, Hamdi M

    2015-01-01

    Large-amplitude Alfv\\'en waves are observed in various systems in space and laboratories, demonstrating an interesting property that the wave shapes are stable even in the nonlinear regime. The ideal magnetohydrodynamics (MHD) model predicts that an Alfv\\'en wave keeps an arbitrary shape constant when it propagates on a homogeneous ambient magnetic field. However, such arbitrariness is an artifact of the idealized model that omits the dispersive effects. Only special wave forms, consisting of two component sinusoidal functions, can maintain the shape; we derive fully nonlinear Alfv\\'en waves by an extended MHD model that includes both the Hall and electron inertia effects. Interestingly, these \\small-scale effects" change the picture completely; the large-scale component of the wave cannot be independent of the small scale component, and the coexistence of them forbids the large scale component to have a free wave form. This is a manifestation of the nonlinearity-dispersion interplay, which is somewhat differ...

  15. Low frequency vibration tests on a floating slab track in an underground laboratory

    Institute of Scientific and Technical Information of China (English)

    De-yun DING; Wei-ning LIU; Ke-fei LI; Xiao-jing SUN; Wei-feng LIU

    2011-01-01

    Low frequency vibrations induced by underground railways have attracted increasing attention in recent years. To obtain the characteristics of low frequency vibrations and the low frequency performance of a floating slab track (FST), low frequency vibration tests on an FST in an underground laboratory at Beijing Jiaotong University were carried out. The FST and an unbalanced shaker SBZ30 for dynamic simulation were designed for use in low frequency vibration experiments. Vibration measurements were performed on the bogie of the unbalanced shaker, the rail, the slab, the tunnel invert, the tunnel wall, the tunnel apex, and on the ground surface at distances varying from 0 to 80 m from the track. Measurements were also made on several floors of an adjacent building. Detailed results of low frequency vibration tests were reported. The attenuation of low frequency vibrations with the distance from the track was presented, as well as the responses of different floors of the building. The experimental results could be regarded as a reference for developing methods to control low frequency vibrations and for adopting countermeasures.

  16. The Effect of Low-Frequency Sound Stimulation on Patients with Fibromyalgia: A Clinical Study

    Directory of Open Access Journals (Sweden)

    Lili Naghdi

    2015-01-01

    Full Text Available Researchers have hypothesized that thalamocortical dysfunction plays a role in fibromyalgia. The use of low-frequency sound stimulation to ameliorate thalamocortical dysfunction has also been investigated, and has shown promise in treating certain pain conditions. Accordingly, the authors of this study aimed to assess the effects of treatment with low-frequency sound stimulation among patients with fibromyalgia.

  17. Stimulated low frequency Raman scattering in cupric oxide nanoparticles water suspension

    Science.gov (United States)

    Averyushkin, A. S.; Baranov, A. N.; Bulychev, N. A.; Kazaryan, M. A.; Kudryavtseva, A. D.; Strokov, M. A.; Tcherniega, N. V.; Zemskov, K. I.

    2017-04-01

    Cupric oxide nanoparticles with average size of 213.2 nm, were synthesized in acoustoplasma discharge for investigating their vibrational properties. The low-frequency acoustic mode in cupric oxide (CuO) nanoparticles has been studied by stimulated low-frequency Raman scattering (SLFRS). SLFRS conversion efficiency, threshold and frequency shift of the scattered light are measured.

  18. Low frequency sound reproduction in irregular rooms using CABS (Control Acoustic Bass System)

    DEFF Research Database (Denmark)

    Celestinos, Adrian; Nielsen, Sofus Birkedal

    2011-01-01

    Early investigations on low frequency sound reproduction in rectangular rooms using CABS (Controlled Acoustic Bass System) have shown good results on simulations and measurements in real rooms. CABS takes the advantage of having a rectangular room with parallel walls. By using two low frequency l...

  19. An investigation of twenty-one cases of low-frequency noise complaints

    DEFF Research Database (Denmark)

    Pedersen, Christian Sejer; Møller, Henrik; Persson-Waye, Kerstin

    2007-01-01

    Twenty-one cases of low-frequency noise complaints were thoroughly investigated with the aim of answering the question whether it is real physical sound or low-frequency tinnitus that causes the annoyance. Noise recordings were made in the homes of the complainants taking the spatial variation...

  20. Large Amplitude Low Frequency Waves in a Magnetized Nonuniform Electron-Positron-Ion Plasma

    Institute of Scientific and Technical Information of China (English)

    Q. Haque; H. Saleem

    2004-01-01

    @@ It is shown that the large amplitude low-frequency electromagnetic drift waves in electron-positron-ion plasmas might give rise to dipolar vortices. A linear dispersion relation of several coupled electrostatic and electromagnetic low-frequency modes is obtained. The relevance of this work to both laboratory and astrophysical situations is pointed out.

  1. Development of a rating procedure for low frequency noise : Results of measurements near runways

    NARCIS (Netherlands)

    Buikema, E.; Vercammen, M.; Ploeg, F. van der; Granneman, J.; Vos, J.

    2010-01-01

    Recent issues concerning low frequency aircraft noise around airports (groundnoise) and a legal verdict about the application of low frequency noise criteria in the Netherlands have been the motivation to start a research commissioned by the Dutch Ministry of Housing, Spatial Planning and the Enviro

  2. Averaged two-dimensional low-frequency wave spectrum of wind waves

    NARCIS (Netherlands)

    Kimura, A.

    1984-01-01

    This report deals with second order, two-dimensional low frequency waves induced by the non-linear interactions of the first order component waves in a two-dimensional short wave field. The convolution to calculate the averaged two-dimensional low frequency wave spectrum is developed. Any given two-

  3. 77 FR 52317 - Record of Decision for Surveillance Towed Array Sensor System Low Frequency Active Sonar

    Science.gov (United States)

    2012-08-29

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF DEFENSE Department of the Navy Record of Decision for Surveillance Towed Array Sensor System Low Frequency Active... Array Sensor System Low Frequency Active (SURTASS LFA) sonar systems with certain geographical...

  4. An acoustic vector based approach to locate low frequency noise sources in 3D

    NARCIS (Netherlands)

    Bree, H.-E. de; Ostendorf, C.; Basten, T.

    2009-01-01

    Although low frequency noise is an issue of huge societal importance, traditional acoustic testing methods have limitations in finding the low frequency source. It is hard to determine the direction of the noise using traditional microphones. Three dimensional sound probes capturing the particle vel

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

    Science.gov (United States)

    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.

  6. How to measure the thickness of dirty, wet Himalayan glaciers with low-frequency radar

    Science.gov (United States)

    Pritchard, Hamish; Mayer, Christoph; Lambrecht, Astrid

    2017-04-01

    High Mountain Asia holds 90,000 glaciers of which only around ten have any ice thickness measurements at all, and on any one glacier these tend to be sparsely distributed and not well suited to calculating glacier ice volume. Existing regional ice volume estimates come from indirect methods (based on area-volume scaling or modelled ice flux) that are poorly constrained in this region and so have a wide spread (e.g., 1670 to 6500 km3 (Bolch et al., 2012; Huss and Faranotti, 2012)). Sufficiently extensive measurements of ice thickness can be used to calculate ice volumes directly, or can be used to calibrate and hence improve the indirect estimates. Unfortunately, measuring ice thickness on such glaciers on a useful scale is difficult. They are often remote with very rough, water-logged and debris-covered ablation areas, a lossy environment for radar and quite different to clean and cold polar glaciers that lend themselves well to rapid radar surveying by snowmobile or aeroplane. A possible solution is to develop a low-frequency, helicopter-borne radar that can access remote mountain valleys and penetrate to the beds of the thickest of these mountain glaciers. But the lower the frequency, the longer the dipole and the more cumbersome the radar: what frequency do we need to detect the bed? Here we report results from pilot studies on the ground in the Langtang Valley and on Ngozumpa, Nepal's largest glacier, that show how bed detectability depends on frequency both in terms of signal attenuation and clutter, and what this means for a planned regional-scale glacier thickness surveys.

  7. Low-frequency Periodic Error Identification and Compensation for Star Tracker Attitude Measurement

    Institute of Scientific and Technical Information of China (English)

    WANG Jiongqi; XIONG Kai; ZHOU Haiyin

    2012-01-01

    The low-frequency periodic error of star tracker is one of the most critical problems for high-accuracy satellite attitude determination.In this paper an approach is proposed to identify and compensate the low-frequency periodic error for star tracker in attitude measurement.The analytical expression between the estimated gyro drift and the low-frequency periodic error of star tracker is derived firstly.And then the low-frequency periodic error,which can be expressed by Fourier series,is identified by the frequency spectrum of the estimated gyro drift according to the solution of the first step.Furthermore,the compensated model of the low-frequency periodic error is established based on the identified parameters to improve the attitude determination accuracy.Finally,promising simulated experimental results demonstrate the validity and effectiveness of the proposed method.The periodic error for attitude determination is eliminated basically and the estimation precision is improved greatly.

  8. Kelvin-Helmholtz instability in an Alfven resonant layer of a solar coronal loop

    Science.gov (United States)

    Uchimoto, E.; Strauss, H. R.; Lawson, W. S.

    1991-01-01

    A Kelvin-Helmholtz instability has been identified numerically on an azimuthally symmetric Alfven resonant layer in an axially bounded, straight cylindrical coronal loop. The set of equations is solved numerically as an initial value problem. The linear growth rate of this instability is shown to be approximately proportional to the Alfven driving amplitude and inversely proportional to the width of the Alfven resonant layer. It is also shown that the linear growth rate increases linearly with m - 1 up to a certain m, reaches its maximum value for the mode whose half wavelength is comparable to the Alfven resonant layer width, and decreases at higher azimuthal mode number.

  9. Simulation of the interaction between Alfven waves and fast particles

    Energy Technology Data Exchange (ETDEWEB)

    Feher, Tamas Bela

    2014-02-18

    There is a wide variety of Alfven waves in tokamak and stellarator plasmas. While most of them are damped, some of the global eigenmodes can be driven unstable when they interact with energetic particles. By coupling the MHD code CKA with the gyrokinetic code EUTERPE, a hybrid kinetic-MHD model is created to describe this wave-particle interaction in stellarator geometry. In this thesis, the CKA-EUTERPE code package is presented. This numerical tool can be used for linear perturbative stability analysis of Alfven waves in the presence of energetic particles. The equations for the hybrid model are based on the gyrokinetic equations. The fast particles are described with linearized gyrokinetic equations. The reduced MHD equations are derived by taking velocity moments of the gyrokinetic equations. An equation for describing the Alfven waves is derived by combining the reduced MHD equations. The Alfven wave equation can retain kinetic corrections. Considering the energy transfer between the particles and the waves, the stability of the waves can be calculated. Numerically, the Alfven waves are calculated using the CKA code. The equations are solved as an eigenvalue problem to determine the frequency spectrum and the mode structure of the waves. The results of the MHD model are in good agreement with other sophisticated MHD codes. CKA results are shown for a JET and a W7-AS example. The linear version of the EUTERPE code is used to study the motion of energetic particles in the wavefield with fixed spatial structure, and harmonic oscillations in time. In EUTERPE, the gyrokinetic equations are discretized with a PIC scheme using the delta-f method, and both full orbit width and finite Larmor radius effects are included. The code is modified to be able to use the wavefield calculated externally by CKA. Different slowing-down distribution functions are also implemented. The work done by the electric field on the particles is measured to calculate the energy transfer

  10. Low frequency sound field enhancement system for rectangular rooms, using multiple loudspeakers

    DEFF Research Database (Denmark)

    Celestinos, Adrian

    2007-01-01

    and solving it in the time domain. Loudspeakers are the last link in the sound reproduction chain, and they are typically placed in small or medium size rooms. When low frequency sound is radiated by a loudspeaker the sound level distribution along the room presents large deviations. This is due...... of low frequency sound in rooms both in the time and the frequency domain. This is done by implementing the finite-difference time-domain method (FDTD) in order to simulate and predict the sound field produced by loudspeakers in rooms at low frequencies. The outcome of this work is a novel and effective...

  11. Compound Effect of Alfv\\'en Waves and Ion-cyclotron Waves on Heating/Acceleration of Minor Ions via the Pickup Process

    CERN Document Server

    Wang, C B; Lee, L C

    2014-01-01

    A scenario is proposed to explain the preferential heating of minor ions and differential streaming velocity between minor ions and protons observed in the solar corona and in the solar wind. It is demonstrated by test particle simulations that minor ions can be nearly fully picked up by intrinsic Alfv\\'en-cyclotron waves observed in the solar wind based on the observed wave energy density. Both high frequency ion-cyclotron waves and low frequency Alfv\\'en waves play crucial roles in the pickup process. A minor ion can first gain a high magnetic moment through the resonant wave-particle interaction with ion-cyclotron waves, and then this ion with a large magnetic moment can be trapped by magnetic mirror-like field structures in the presence of the lower-frequency Alfv\\'en waves. As a result, the ion is picked up by these Alfv\\'en-cyclotron waves. However, minor ions can only be partially picked up in the corona due to low wave energy density and low plasma beta. During the pickup process, minor ions are stoch...

  12. Destabilization of Alfven eigenmodes by fast particles in W7-AS

    Energy Technology Data Exchange (ETDEWEB)

    Zegenhagen, S.

    2006-02-15

    In the present thesis, a systematic study of beam driven Alfven eigenmodes in high-density and low-temperature plasmas of the W7-AS stellarator is performed. The goal of this thesis is twofold: (I) identification and description of fast particle driven Alfven instabilities in W7-AS, and (II) study of energetic particle losses induced by Alfven instabilities. A total of 133 different Alfven eigenmodes is studied in discharges from different experimental campaigns. The discharges are characterized by high density, n{sub e}=5 x 1019 m{sup -3} to 2.5 x 1020 m{sup -3} at relatively low temperatures of T{sub e}=T{sub i}=150..600 eV. Additional 13 events are found to have frequencies inside the EAE gap and could possibly be EAEs. Evidence for high-frequency Alfven eigenmodes (mirror- and helicity-induced Alfven eigenmodes) is seen, but can not be proven rigorously due to uncertain mode numbers and the complexity of the Alfven continuum. The remaining 41 Alfven eigenmodes can not be classified to be one of the above cases. (orig.)

  13. Amplification of exo-hiss into low-frequency chorus following substorm injection

    Science.gov (United States)

    Gao, Z.; Su, Z.

    2016-12-01

    Whistler-mode chorus waves contribute significantly to the acceleration of radiation belt electrons. Chorus with frequency below 0.1 fce (fce is the equatorial electron gyro-frequency) has been identified as the low-frequency chorus. How such low-frequency chorus waves are generated remains an unanswered question. Here we propose a new candidate generation mechanism that exo-hiss waves can serve as the source of low-frequency chorus. Exo-hiss is usually believed to be the leaked plasmaspheric hiss from the high-density plasmasphere into the low-density plasmatrough. Both Van Allen Probes observations and linear instability analyses support that exo-hiss can be effectively amplified into low-frequency chorus by the substorm-injected anisotropic electrons at energies around 100 keV.

  14. Power system low frequency oscillation monitoring and analysis based on multi-signal online identification

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The advance in the wide-area measurement system (WAMS) is driving the power system to the trend of wide-area monitoring and control.The Prony method is usually used for low frequency oscillation online identification.However,the identified amplitude and phase information is not sufficiently used.In this paper,the amplitude is adopted to detect the occurrence of the oscillation and to obtain the mode observability of the sites.The phase is adopted to identify the oscillation generator grouping and to obtain the mode shapes.The time varying characteristics of low frequency oscillations are studied.The behaviors and the characters of low frequency oscillations are displayed by dynamic visual techniques.Demonstrations on the "11.9" low frequency oscillation of the Guizhou Power Grid substantiate the feasibility and the validation of the proposed methods.

  15. A lightweight low-frequency sound insulation membrane-type acoustic metamaterial

    Science.gov (United States)

    Lu, Kuan; Wu, Jiu Hui; Guan, Dong; Gao, Nansha; Jing, Li

    2016-02-01

    A novel membrane-type acoustic metamaterial with a high sound transmission loss (STL) at low frequencies (⩽500Hz) was designed and the mechanisms were investigated by using negative mass density theory. This metamaterial's structure is like a sandwich with a thin (thickness=0.25mm) lightweight flexible rubber material within two layers of honeycomb cell plates. Negative mass density was demonstrated at frequencies below the first natural frequency, which results in the excellent low-frequency sound insulation. The effects of different structural parameters of the membrane on the sound-proofed performance at low frequencies were investigated by using finite element method (FEM). The numerical results show that, the STL can be modulated to higher value by changing the structural parameters, such as the membrane surface density, the unite cell film shape, and the membrane tension. The acoustic metamaterial proposed in this study could provide a potential application in the low-frequency noise insulation.

  16. Low-Frequency, All Digital Radar (ADR) for Biomass and Ice-sheet Investigations Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Low-Frequency, All Digital Radar (ADR) can be a key component for NASA Phased-array and tomographic Radar systems spanning multiple earth-science measurement...

  17. A study of twenty-one cases of low-frequency noise complaints

    DEFF Research Database (Denmark)

    Pedersen, Christian Sejer; Møller, Henrik; Persson-Waye, Kerstin

    2008-01-01

    -frequency tinnitus. Noise recordings were made in the homes of the complainants, and the complainants were exposed to these in blind test listening experiments. Furthermore, the low-frequency hearing function of the complainants was investigated, and characteristics of the annoying sound was matched. The results...... showed that some of the complainants are annoyed by a physical sound (20-180 Hz), while others suffer from low-frequency tinnitus (perceived frequency 40-100 Hz). Physical sound at frequencies below 20 Hz (infrasound) is not responsible for the annoyance - or at all audible - in any of the investigated...... cases, and none of the complainants has extraordinary hearing sensitivity at low frequencies. For comparable cases of low-frequency noise complaints in general, it is anticipated that physical sound is responsible in a substantial part of the cases, while lowfrequency tinnitus is responsible in another...

  18. An Ultra-low Frequency Modal Testing Suspension System for High Precision Air Pressure Control

    National Research Council Canada - National Science Library

    Qiaoling Yuan; Jianhui Sun; Xiaohang Shan; Biqing Ye

    2014-01-01

      In this paper, as a resolution for air pressure control challenges in ultra-low frequency modal testing suspension systems, an incremental PID control algorithm with a dead band is applied to achieve...

  19. Low frequency band gaps below 10 Hz in radial flexible elastic metamaterial plate

    Science.gov (United States)

    Gao, Nansha; Hou, Hong; Wu, Jiu Hui; Cheng, Baozhu

    2016-11-01

    This paper presents the low frequency acoustic properties of a new proposed elastic metamaterial, which is arranged in the axial coordinate. The band structures, transmission spectra, and eigenmode displacement fields of this metamaterial are different from previous elastic metamaterial structures. Numerical calculation results show that the first order band gap of the radial flexible elastic metamaterial plate is below 10 Hz. A multiple-vibration coupling mechanism is proposed to explain the low frequency band gaps. By changing the geometrical dimensions h 1, h 2, b 1, and b 1 of the centre part, the location and width of the low frequency band gaps can be varied easily. The effects of density and Young’s modulus are also discussed in detail. In summary, the radial flexible elastic metamaterial plate can restrain low frequency vibration, owing to which it can potentially be used to protect infrasound, generate filters, and design acoustic devices.

  20. Direct CFD Predictions of Low Frequency Sounds Generated by Helicopter Main Rotors

    Science.gov (United States)

    Sim, Ben W.; Potsdam, Mark; Conner, Dave; Watts, Michael E.

    2010-01-01

    This proposed paper will highlight the application of a CSD/CFD methodology currently inuse by the US Army Aerfolightdynamics Directorate (AFDD) to assess the feasibility and fidelity of directly predicting low frequency sounds of helicopter rotors.

  1. Improving room acoustics at low frequencies with multiple loudspeakers and time based room correction

    DEFF Research Database (Denmark)

    Nielsen, Sofus Birkedal; Celestinos, Adrian

    2008-01-01

    Small and medium size rectangular rooms are often used for sound reproduction. These rooms have substantial acoustical problems at low frequencies primarily caused by the reflections from the room boundaries. The spatial variation in sound pressure level (SPL) can be up to 30 dB in a room at low...... frequencies, and appear not only at modal frequencies. The problem is an acoustical issue in time, and should therefore be analyzed in the time-domain, instead of the traditional steady state frequency domain. The construction of a finite-difference time-domain approximation program (FDTD) has lead...... to a simple and untraditional solution called CABS (Controlled Acoustical Bass System) that makes use of multiple loudspeakers. With the proper placement of low frequency loudspeakers, CABS can create a plane wave from the front wall which will be absorbed by additional low frequency loudspeakers at the back...

  2. Low frequency voltage noise in current biased HTCS thin films. [BiSrCaCuO

    Energy Technology Data Exchange (ETDEWEB)

    Gierlowski, P. (Inst. Fizyki PAN, Warszawa (Poland)); Jung, G. (Inst. Fizyki PAN, Warszawa (Poland) Physics Dept., Ben Gurion Univ. of the Negev, Beer-Sheva (Israel) Dipt. di Fisica, Univ. di Salerno (Italy)); Kula, W. (Inst. Fizyki PAN, Warszawa (Poland) Electrical Engineering Dept., Univ. of Rochester, NY (United States)); Lewandowski, S.J. (Inst. Fizyki PAN, Warszawa (Poland)); Savo, B. (Dipt. di Fisica, Univ. di Salerno (Italy)); Sobolewski, R. (Inst. Fizyki PAN, Warszawa (Poland) Electrical Engineering Dept., Univ. of Rochester, NY (United States)); Tebano, A. (Dipt. di Ingegneria Meccanica, Univ. di Roma Tor-Vergata (Italy)); Vecchione, A. (Physics Dept., Ben Gurion Univ. of the Negev, Beer-Sheva (Israel) Dipt. di Fisica, Univ. di Salerno (Italy))

    1994-02-01

    Pronounced changes in low-frequency noise power spectra have been observed, close to the transition temperature, in current biased high-T[sub c] superconducting thin films. Generally, the spectra scale as 1/f[sup [alpha

  3. Small foamed polystyrene shield protects low-frequency microphones from wind noise

    Science.gov (United States)

    Tedrick, R. N.

    1964-01-01

    A foamed polystyrene noise shield for microphones has been designed in teardrop shape to minimize air turbulence. The shield slips on and off the microphone head easily and is very effective in low-frequency sound intensity measurements.

  4. Improving room acoustics at low frequencies with multiple loudspeakers and time based room correction

    DEFF Research Database (Denmark)

    Nielsen, Sofus Birkedal; Celestinos, Adrian

    2008-01-01

    to a simple and untraditional solution called CABS (Controlled Acoustical Bass System) that makes use of multiple loudspeakers. With the proper placement of low frequency loudspeakers, CABS can create a plane wave from the front wall which will be absorbed by additional low frequency loudspeakers at the back......Small and medium size rectangular rooms are often used for sound reproduction. These rooms have substantial acoustical problems at low frequencies primarily caused by the reflections from the room boundaries. The spatial variation in sound pressure level (SPL) can be up to 30 dB in a room at low...... frequencies, and appear not only at modal frequencies. The problem is an acoustical issue in time, and should therefore be analyzed in the time-domain, instead of the traditional steady state frequency domain. The construction of a finite-difference time-domain approximation program (FDTD) has lead...

  5. Relativistic particle acceleration in developing Alfv\\'{e}n turbulence

    CERN Document Server

    Matsukiyo, S; 10.1088/0004-637X/692/2/1004

    2009-01-01

    A new particle acceleration process in a developing Alfv\\'{e}n turbulence in the course of successive parametric instabilities of a relativistic pair plasma is investigated by utilyzing one-dimensional electromagnetic full particle code. Coherent wave-particle interactions result in efficient particle acceleration leading to a power-law like energy distribution function. In the simulation high energy particles having large relativistic masses are preferentially accelerated as the turbulence spectrum evolves in time. Main acceleration mechanism is simultaneous relativistic resonance between a particle and two different waves. An analytical expression of maximum attainable energy in such wave-particle interactions is derived.

  6. Measurements and modeling of Alfven eigenmode induced fast ion transport and loss in DIII-D and ASDEX Upgrade

    NARCIS (Netherlands)

    VanZeeland, M. A.; Heidbrink, W. W.; Fisher, R. K.; Munoz, M. G.; Kramer, G. J.; Pace, D. C.; White, R. B.; Akaslompolo, S.; Austin, M. E.; Boom, J. E.; Classen, I.G.J.; da Graca, S.; Geiger, B.; Gorelenkova, M.; Gorelenkov, N. N.; Hyatt, A. W.; Luhmann, N.; Maraschek, M.; McKee, G. R.; Moyer, R. A.; Muscatello, C. M.; Nazikian, R.; Park, H.; Sharapov, S.; Suttrop, W.; Tardini, G.; Tobias, B. J.; Zhu, Y. B.

    2011-01-01

    Neutral beam injection into reversed magnetic shear DIII-D and ASDEX Upgrade plasmas produces a variety of Alfvenic activity including toroidicity-induced Alfven eigenmodes and reversed shear Alfven eigenmodes (RSAEs). These modes are studied during the discharge current ramp phase when incomplete c

  7. 69. Impact of low frequency ultrasound and lymphatic drainage on triglycerides in chronic atherosclerotic patients

    OpenAIRE

    M. Badawy

    2016-01-01

    The aim of this study was to evaluate the effect of low frequency ultrasound plus lymphatic drainage on Blood Triglycerides in Cardiac patients (chronic coronary atherosclerosis patients, with high triglycerides and fat mass body composition). Low frequency ultrasound plus lymphatic drainage as a technique could be used as an alternative to conventional exercise and alternative to many obesity surgery as Liposuction surgery and thus provide an opportunity to improve the quality of obese cardi...

  8. The relation of low frequency restoration methods to the Gerchberg-Papoulis algorithm.

    Science.gov (United States)

    Yan, H; Mao, J T

    1990-10-01

    In magnetic resonance imaging, low frequency components can be allowed to saturate the analog to digital converter to reduce the quantization noise. These components can be estimated using least squares error estimation based low frequency restoration methods or the iterative Gerchberg-Papoulis algorithm. In this paper, we show the relationship between the closed form estimation methods and the iterative algorithm, propose a method for improving the speed of iteration, and discuss the advantages and disadvantages of two types of methods.

  9. Algorithm and Software for Landslide Slopes Stability Estimation with Online Very Low Frequency Monitoring

    Science.gov (United States)

    Gordeev, V. F.; Kabanov, M. M.; Kapustin, S. N.

    2017-04-01

    In addition to preliminary surveying, landslide slopes stability estimation problems require online real-time monitoring alerting about potential emergencies. Very low frequency monitoring data provided by geodynamic processes automated control system provides a solution to that problem. Authors describe the software and algorithms implemented for that system, make conclusions on the efficiency of applied solutions and propose options for the further development of online very low frequency monitoring system.

  10. Destabilization kinetics of polyvinylpyrrolidone-iodine in a field of low frequency impacts

    Science.gov (United States)

    Fadeev, G. N.; Ermolaeva, V. I.; Boldyrev, V. S.; Sinkevich, V. V.

    2016-09-01

    Experimental results on the destabilization kinetics of compounds with chelate structure (polyvinylpyrrolidone-iodine) in the field of the impact of low-frequency vibrations (from 2 to 45 Hz) are presented. The optimum frequencies at which the process rate is greatest are found for different impact modes. Based on the experimental data, conclusions are drawn as to the effect the energy of low-frequency impacts has on the studied clathrate and chelate structures.

  11. Subjective evaluation of noise from neighbours with focus on low frequencies

    DEFF Research Database (Denmark)

    Mortensen, Frank Rysgaard

    1999-01-01

    There is a growing tendency to use lightweight constructions in the building industry. One unwanted side effect of this tendency is poor sound insulation at low frequencies. The purpose of this investigation has been to examine the subjective effects of the resulting increase of low frequency noi...... from neighbours in dwellings using listening tests. The results of the experiments confirm that noise from neighbours transmitted through light constructions is indeed rated more annoying than noise transmitted through heavier constructions....

  12. Subjective evaluation of noise from neighbours with focus on low frequencies

    DEFF Research Database (Denmark)

    Mortensen, Frank Rysgaard

    1999-01-01

    There is a growing tendency to use lightweight constructions in the building industry. One unwanted side effect of this tendency is poor sound insulation at low frequencies. The purpose of this investigation has been to examine the subjective effects of the resulting increase of low frequency noise...... from neighbours in dwellings using listening tests. The results of the experiments confirm that noise from neighbours transmitted through light constructions is indeed rated more annoying than noise transmitted through heavier constructions....

  13. Noncontact, Low Frequency Ultrasound as an Effective Therapy against Pseudomonas aeruginosa-infected Biofilm Wounds

    Science.gov (United States)

    2013-03-01

    effective. Previous studies have shown physical effects on cells and their surrounding matrix due to ultrasound energy, termed cavitation and...Noncontact, low-frequency ultrasound as an effective therapy against Pseudomonas aeruginosa–infected biofilm wounds Akhil K. Seth, MD1; Khang T...devices may potentially improve healing, but with no evidence of efficacy against biofilms. This study evaluates noncontact, low-frequency ultrasound

  14. A piezoelectric spring-mass system as a low-frequency energy harvester.

    Science.gov (United States)

    Hu, Hongping; Hu, Lin; Yang, Jiashi; Wang, Hairen; Chen, Xuedong

    2013-04-01

    We propose a new structure consisting of a piezoelectric spring-mass system as a low-frequency piezoelectric energy harvester. A theoretical model is developed for the system from the theory of piezoelectricity. An analysis is performed to demonstrate the low-frequency nature of the system. Other basic characteristics of the energy harvester, including the output power, voltage, and efficiency, are also calculated and examined.

  15. THE DAMAGING EFFECTS OF EXPOSURE TO EXTREMELY LOW FREQUENCES OF ELECTROMAGNETIC FIELDS

    OpenAIRE

    Dejan Petković; Dejan Krstić; Dušan Sokolović; Boris Đinđić; Jovica Jovanović; Petar Babović

    2010-01-01

    In both living and working environment, apart from the ever present Earth's atmospheric and magnetic fields, very often there is an existing very low- frequency electromagnetic field emitted by energy plants, home, radio and TV appliances, public transport vehicles and video terminals. Low-frequency electromagnetic fields (30-300 Hz) are also present in the vicinity of high-voltage transmission lines, high and middle voltage conductors, sub-stations and industry. A large number of people who ...

  16. Alfven waves in the solar atmosphere. III - Nonlinear waves on open flux tubes

    Science.gov (United States)

    Hollweg, J. V.; Jackson, S.; Galloway, D.

    1982-01-01

    Consideration is given the nonlinear propagation of Alfven waves on solar magnetic flux tubes, where the tubes are taken to be vertical, axisymmetric and initially untwisted and the Alfven waves are time-dependent axisymmetric twists. The propagation of the waves into the chromosphere and corona is investigated through the numerical solution of a set of nonlinear, time-dependent equations coupling the Alfven waves into motions that are parallel to the initial magnetic field. It is concluded that Alfven waves can steepen into fast shocks in the chromosphere, pass through the transition region to produce high-velocity pulses, and then enter the corona, which they heat. The transition region pulses have amplitudes of about 60 km/sec, and durations of a few tens of seconds. In addition, the Alfven waves exhibit a tendency to drive upward flows, with many of the properties of spicules.

  17. The Design and Implementation of Instruments for Low-Frequency Electromagnetic Sounding of the Martian Subsurface

    Science.gov (United States)

    Delory, G. T.; Grimm, R. E.

    2003-01-01

    Low-frequency electromagnetic soundings of the subsurface can identify liquid water at depths ranging from hundreds of meters to approx. 10 km in an environment such as Mars. Among the tools necessary to perform these soundings are low-frequency electric and magnetic field sensors capable of being deployed from a lander or rover such that horizontal and vertical components of the fields can be measured free of structural or electrical interference. Under a NASA Planetary Instrument Definition and Development Program (PIDDP), we are currently engaged in the prototype stages of low frequency sensor implementations that will enable this technique to be performed autonomously within the constraints of a lander platform. Once developed, this technique will represent both a complementary and alternative method to orbital radar sounding investigations, as the latter may not be able to identify subsurface water without significant ambiguities. Low frequency EM methods can play a crucial role as a ground truth measurement, performing deep soundings at sites identified as high priority areas by orbital radars. Alternatively, the penetration depth and conductivity discrimination of low-frequency methods may enable detection of subsurface water in areas that render radar methods ineffective. In either case, the sensitivity and depth of penetration inherent in low frequency EM exploration makes this tool a compelling candidate method to identify subsurface liquid water from a landed platform on Mars or other targets of interest.

  18. Low-Frequency Radio Observations of the Solar Corona with Arcminute Angular Resolution: Implications for Coronal Turbulence and Weak Energy Releases

    Science.gov (United States)

    Mugundhan, V.; Ramesh, R.; Barve, Indrajit V.; Kathiravan, C.; Gireesh, G. V. S.; Kharb, P.; Misra, Apurva

    2016-11-01

    We report on the first long baseline interferometer (length ≈8 km) observations of the solar corona at 37 MHz that were carried out recently with an angular resolution of ≈ {1}\\prime . The results indicate that, (1) discrete radio sources of the aforesaid angular size or even lesser are present in the solar corona from where radiation at the above frequency originates. This constrains the angular broadening of radio sources at low frequencies due to scattering by density turbulence in the solar corona; and (2) the observed sources in the present case correspond to the weakest energy releases in the solar atmosphere reported so far.

  19. Effects of compressional magnetic perturbation on kinetic Alfven waves

    Science.gov (United States)

    Dong, Ge; Bhattacharjee, Amitava; Lin, Zhihong

    2016-10-01

    Kinetic Alfven waves play a very important role in the dynamics of fusion as well as space and astrophysical plasmas. The compressional magnetic perturbation δB|| can play important role in kinetic Alfven waves (KAW) and various instabilities at large plasma β. It could affect the nonlinear behavior of these modes significantly even at small β. In this study, we have implemented δB|| in gyrokinetic toroidal code (GTC). The perpendicular Ampere's law is solved as a force balance equation. Double gyroaveraging is incorporated in the code to treat the finite Larmor radius effects related to δB|| terms. KAW is studied in slab geometry as a benchmark case. A scan in β for the KAW dispersion relation shows that as β approaches 1 (>0.3), the effects of δB|| becomes important. Connections are made with other existing studies of KAWs in the fusion and space plasma literature. This new capability of including δB|| in GTC could be applied to nonlinear simulations of modes such as kinetic ballooning and tearing modes. This research is supported by DOE Contract No. DE-AC02-09CH11466.

  20. Cosmic Ray propagation in sub-Alfvenic magnetohydrodynamic turbulence

    CERN Document Server

    Cohet, Romain

    2016-01-01

    This work has the main objective to provide a detailed investigation of cosmic ray propagation in magnetohydrodynamic turbulent fields generated by forcing the fluid velocity field at large scales. It provides a derivation of the particle mean free path dependences in terms of the turbulence level described by the Alfv\\'enic Mach number and in terms of the particle rigidity. We use an upgrade version of the magnetohydrodynamic code {\\tt RAMSES} which includes a forcing module and a kinetic module and solve the Lorentz equation for each particle. The simulations are performed using a 3 dimension periodical box in the test-particle and magnetostatic limits. The forcing module is implemented using an Ornstein-Uhlenbeck process. An ensemble average over a large number of particle trajectories is applied to reconstruct the particle mean free paths. We derive the cosmic ray mean free paths in terms of the Alfv\\'enic Mach numbers and particle reduced rigidities in different turbulence forcing geometries. The reduced...

  1. Clustered frequency analysis of shear Alfven modes in stellarators

    Energy Technology Data Exchange (ETDEWEB)

    Spong, Donald A [ORNL; D' Azevedo, Ed F [ORNL; Todo, Yasushi [National Institute for Fusion Science, Toki, Japan

    2010-01-01

    The shear Alfven spectrum in three-dimensional configurations, such as stellarators and rippled tokamaks, is more densely populated due to the larger number of mode couplings caused by the variation in the magnetic field in the toroidal dimension. This implies more significant computational requirements that can rapidly become prohibitive as more resolution is requested. Alfven eigenfrequencies and mode structures are a primary point of contact between theory and experiment. A new algorithm based on the Jacobi-Davidson method is developed here and applied for a reduced magnetohydrodynamics model to several stellarator configurations. This technique focuses on finding a subset of eigenmodes clustered about a specified input frequency. This approach can be especially useful in modeling experimental observations, where the mode frequency can generally be measured with good accuracy and several different simultaneous frequency lines may be of interest. For cases considered in this paper, it can be a factor of 10{sup 2}-10{sup 3} times faster than more conventional methods.

  2. Characteristics of Short-wavelength Oblique Alfven and Slow waves

    CERN Document Server

    Zhao, J S; Yu, M Y; Lu, J Y; Wu, D J

    2014-01-01

    Linear properties of kinetic Alfv\\'en waves (KAWs) and kinetic slow waves (KSWs) are studied in the framework of two-fluid magnetohydrodynamics. We obtain the wave dispersion relations that are valid in a wide range of the wave frequency {\\omega} and plasma-to-magnetic pressure ratio {\\beta}. The KAW frequency can reach and exceed the ion cyclotron frequency at ion kinetic scales, whereas the KSW frequency remains sub-cyclotron. At {\\beta}\\sim1, the plasma and magnetic pressure perturbations of both modes are in anti-phase, so that there is nearly no total pressure perturbations. However, these modes exhibit several different properties. At high {\\beta}, the electric field polarization of KAW and KSW is opposite at the ion gyroradius scale, where KAWs are polarized in sense of electron gyration (right-hand polarized) and KSWs are left-hand polarized. The magnetic helicity {\\sigma}\\sim1 for KAWs and {\\sigma}\\sim-1 for KSWs, and the ion Alfv\\'en ratio R_{Ai}\\ll 1 for KAWs and R_{Ai}\\gg 1 for KSWs. We also found...

  3. Superdiffusion versus Alfvenic collapse: plasma flow bounding and penetration

    Science.gov (United States)

    Savin, S.; Amata, A.; Zelenyi, L.; Budaev, V.; Kuznetsov, E. A.; Consolini, G.; Blecki, J.; Buechner, J.; Rauch, J. L.

    2009-04-01

    A geophysical flow is the solar plasma one around the Earth's magnetosphere. We discuss an anomalous MHD plasma mixing with concentrated kinetic energy bursts - ‘plasma jets' - in view of common features of the geophysical flows, along with the laboratory and astrophysical plasma ones. While the plasma flows are quite dilute, they probably can lead to electric power system collapses on the ground, radiation hazards in space, including geostationary spacecraft faults, and communication interrupts etc. We would like to concentrate on a unique case of plasma mixing by the jets in the streamlining flow with quite effective transport barrier , most probably, due to Alfvenic collapse of the magnetic field at the interface of their streaming and stagnant plasma ahead the Earth magnetopause on February 2, 2003 from the Cluster spacecraft data. On the basis of outer magnetospheric spacecraft observations in the magnetosheath (MSH) we provide evidence for the temporary existence of the anomalously concentrated plasma jets as well in the region close to the bow shock (BS) as near the magnetopause (MP). Disturbed zones of duration of up to 2 hours are regularly detected in the MSH, preferably downstream of the quasi-parallel and oblique BS with average energy density well above that of the un-shocked solar wind (SW). These zones are similar to high-latitude MSH near the MP, known as the ‘turbulent boundary layer' (TBL), which is the result of the interaction of the MSH flow with the throat of the cusp. In both these disturbed zones the field and plasma fluctuations have comparable intensity and similar spectral properties. Determination of the structure functions of the magnetic field and ion flux also reveals similar multifractal and intermittent properties. The same holds for fitting a Log-Poisson cascade model. A new phenomenon - Alfvenic collapse - is discussed as a ‘tool' for separating of the MHD flows: in the MHD limit it predicts infinite field rising due to

  4. The role of low-frequency variation in the manifestation of warming trend and ENSO amplitude

    Science.gov (United States)

    Yeo, Sae-Rim; Yeh, Sang-Wook; Kim, Kwang-Yul; Kim, WonMoo

    2017-08-01

    Despite the increase in greenhouse gas concentration, the sea surface temperature (SST) over the tropical eastern Pacific during the period of 1999-2014 exhibits less warming trend compared to the earlier decades. It has been noted that this warming hiatus is accompanied by a negative phase of the Pacific Decadal Oscillation (PDO), which represents low-frequency variability over the Pacific. On the other hand, the 2015/2016 El Niño is among the strongest comparable to the 1997/1998 event, which coincides with the recently altered PDO phase from negative to positive. These observational evidences have generated substantial interest in the role of low-frequency variations in modulating El Niño-Southern Oscillation amplitude as well as manifestation of warming signal in the tropical Pacific. Therefore, it is necessary to appropriately separate low-frequency variability and global warming signal from SST records. Here, we present three primary modes of global SST that include secular warming trend, low-frequency variability, and biennial oscillation. Based on the independent behavior of these three modes, global warming is clearly continuing but its manifestation is enhanced (depressed) when the low-frequency variation is in the positive (negative) phase. Further, possibility of strong El Niño increases under the positive phase of the low-frequency mode, which amplifies warming over the tropical eastern Pacific. Indeed, the strong 2015/2016 El Niño is largely attributed to the positive phase of the low-frequency mode. In order to examine the climate models' ability to simulate the three SST modes as obtained in the observational record, the Coupled Model Intercomparison Project phase 5 (CMIP5) datasets are also analyzed. The spatial and temporal characteristics of the three modes have been replicated closely by the selected CMIP5 models forced by the historical condition, which provides an analogy of the interplay of three modes in the observed tropical Pacific SST.

  5. Low frequency noise from large wind turbines - updated 2011; Lavfrekvent stoej fra store vindmoeller - opdateret 2011

    Energy Technology Data Exchange (ETDEWEB)

    Moeller, H.; Sejer Pedersen, C.; Pedersen, Steffen

    2011-07-01

    The study analyzed measurements of noise from 65 wind turbines, 25 large turbines (2.3 to 3.6 MW) and 40 small ones (up to 2 MW). The large mills (2.3 to 3.6 MW) emit relatively more low frequency noise than the small ones (up to 2 MW). The difference is statistically significant for the frequency range 63-250 Hz, regardless of whether calculations are performed on all the large mills or only on new wind turbines. There are no significant differences between prototype turbines and the new mills. Because of wind noise in the measurements of the small mills, it is not possible to determine whether the difference between small and large turbines continues further down in frequency. Looking at the A-weighted sound pressure in relevant neighbor distances, the lower frequencies constitute an essential part of the noise from the large mills, and there is no doubt that the low frequency noise is both audible and annoying. When the total A-weighted sound pressure level is the same, there will on average be about 3 dB more low frequency noise from large turbines than from small ones. At large distances the noise character becomes yet more low frequency because atmospheric absorption reduces the high frequencies more than the low frequencies. Depending on the sound insulation the low frequency noise can also be annoying indoors. If the total A-weighted sound pressure level outdoors is 44 dB, the low frequency noise can be heard indoors in all the houses and for all the large turbines. The sound pressure level will in many cases exceed the indoor limit for evening night at 20 dB. (ln)

  6. Low-frequency earthquakes at the Torfajökull volcano, south Iceland

    Science.gov (United States)

    Soosalu, Heidi; Lippitsch, Regina; Einarsson, Páll

    2006-05-01

    Torfajökull is a large rhyolitic volcanic edifice with a 12-km-diameter caldera and abundant high-temperature geothermal activity. It is located in the neovolcanic zone in south Iceland, at the junction of the eastern rift zone and a transform zone with the intraplate volcanic flank zone of south Iceland. The latest eruption at Torfajökull occurred about 500 years ago. Torfajökull is a source of persistent small-scale seismicity, where two types of earthquakes occur. High-frequency events are concentrated in the western part of the caldera and low-frequency events cluster in the south. Small low-frequency earthquakes have been observed at Torfajökull since the installation of a local analogue seismograph station in 1985. They typically occur in swarms; up to 300 earthquakes per day have been observed. The low-frequency events have a frequency content of about 1-3 Hz, and are difficult to locate, because of the emergent nature of their phases. The 160 events located during the years 1994-2000 using the permanent Icelandic seismic network cluster in the southern part of the Torfajökull caldera. A closer study of low-frequency events was carried out between May and October 2002, with a dense network of twenty Güralp 6TD broadband seismometers in the Torfajökull area. No distinct swarm activity was observed during this period, but small low-frequency events occurred almost on a daily basis. About 330 low-frequency events were detected during the study period. They are located in the southern part of the caldera, between two small glaciers. Areas of intensive geothermal activity surround the cluster of low-frequency events. It is argued that these earthquakes are associated with active magma in the south part of the Torfajökull caldera, possibly a rising cryptodome.

  7. Transformed eddy-PV flux and positive synoptic eddy feedback onto low-frequency flow

    Energy Technology Data Exchange (ETDEWEB)

    Ren, Hong-Li [University of Hawaii, School of Ocean and Earth Sciences and Technology, Honolulu, HI (United States); China Meteorological Administration, Laboratory for Climate Studies, National Climate Center, Beijing (China); Jin, Fei-Fei [University of Hawaii, School of Ocean and Earth Sciences and Technology, Honolulu, HI (United States); Kug, Jong-Seong [Korea Ocean Research and Development Institute, Ansan (Korea, Republic of); Gao, Li [University of Hawaii, School of Ocean and Earth Sciences and Technology, Honolulu, HI (United States); China Meteorological Administration, Numerical Prediction Center, National Meteorological Center, Beijing (China)

    2011-06-15

    Interaction between synoptic eddy and low-frequency flow (SELF) has been the subject of many studies. In this study, we further examine the interaction by introducing a transformed eddy-potential-vorticity (TEPV) flux that is obtained from eddy-potential-vorticity flux through a quasi-geostrophic potential-vorticity inversion. The main advantage of using the TEPV flux is that it combines the effects of the eddy-vorticity and heat fluxes into the net acceleration of the low-frequency flow in such a way that the TEPV flux tends to be analogous to the eddy-vorticity fluxes in the barotropic framework. We show that the anomalous TEPV fluxes are preferentially directed to the left-hand side of the low-frequency flow in all vertical levels throughout the troposphere for monthly flow anomalies and for climate modes such as the Arctic Oscillation (AO). Furthermore, this left-hand preference of the TEPV flux direction is a convenient three-dimensional indicator of the positive reinforcement of the low-frequency flow by net eddy-induced acceleration. By projecting the eddy-induced net accelerations onto the low-frequency flow anomalies, we estimate the eddy-induced growth rates for the low frequency flow anomalies. This positive eddy-induced growth rate is larger (smaller) in the lower (upper) troposphere. The stronger positive eddy feedback in the lower troposphere may play an important role in maintaining an equivalent barotropic structure of the low-frequency atmospheric flow by balancing some of the strong damping effect of surface friction. (orig.)

  8. Transformed eddy-PV flux and positive synoptic eddy feedback onto low-frequency flow

    Science.gov (United States)

    Ren, Hong-Li; Jin, Fei-Fei; Kug, Jong-Seong; Gao, Li

    2011-06-01

    Interaction between synoptic eddy and low-frequency flow (SELF) has been the subject of many studies. In this study, we further examine the interaction by introducing a transformed eddy-potential-vorticity (TEPV) flux that is obtained from eddy-potential-vorticity flux through a quasi-geostrophic potential-vorticity inversion. The main advantage of using the TEPV flux is that it combines the effects of the eddy-vorticity and heat fluxes into the net acceleration of the low-frequency flow in such a way that the TEPV flux tends to be analogous to the eddy-vorticity fluxes in the barotropic framework. We show that the anomalous TEPV fluxes are preferentially directed to the left-hand side of the low-frequency flow in all vertical levels throughout the troposphere for monthly flow anomalies and for climate modes such as the Arctic Oscillation (AO). Furthermore, this left-hand preference of the TEPV flux direction is a convenient three-dimensional indicator of the positive reinforcement of the low-frequency flow by net eddy-induced acceleration. By projecting the eddy-induced net accelerations onto the low-frequency flow anomalies, we estimate the eddy-induced growth rates for the low frequency flow anomalies. This positive eddy-induced growth rate is larger (smaller) in the lower (upper) troposphere. The stronger positive eddy feedback in the lower troposphere may play an important role in maintaining an equivalent barotropic structure of the low-frequency atmospheric flow by balancing some of the strong damping effect of surface friction.

  9. Annoyance of low frequency noise (LFN) in the laboratory assessed by LFN-sufferers and non-sufferers

    DEFF Research Database (Denmark)

    Poulsen, Torben

    2007-01-01

    , for the first time in one set of covers, over thirty papers on the effects of low frequency noise and vibration on people. The papers are arranged under five headings: • Perception thresholds for low frequency noise • Effect of low frequency noise on people in terms of annoyance and sleep deprivation...

  10. Annoyance of low frequency noise (LFN) in the laboratory assessed by LFN-sufferers and non-sufferers

    DEFF Research Database (Denmark)

    Poulsen, Torben

    2007-01-01

    , for the first time in one set of covers, over thirty papers on the effects of low frequency noise and vibration on people. The papers are arranged under five headings: • Perception thresholds for low frequency noise • Effect of low frequency noise on people in terms of annoyance and sleep deprivation...

  11. Comparison of objective methods for assessment of annoyance of low frequency noise with the results of a laboratory listening test

    DEFF Research Database (Denmark)

    Poulsen, Torben

    2007-01-01

    , for the first time in one set of covers, over thirty papers on the effects of low frequency noise and vibration on people. The papers are arranged under five headings: • Perception thresholds for low frequency noise • Effect of low frequency noise on people in terms of annoyance and sleep deprivation...

  12. Stress Recovery Effects of High- and Low-Frequency Amplified Music on Heart Rate Variability

    Directory of Open Access Journals (Sweden)

    Yoshie Nakajima

    2016-01-01

    Full Text Available Sounds can induce autonomic responses in listeners. However, the modulatory effect of specific frequency components of music is not fully understood. Here, we examined the role of the frequency component of music on autonomic responses. Specifically, we presented music that had been amplified in the high- or low-frequency domains. Twelve healthy women listened to white noise, a stress-inducing noise, and then one of three versions of a piece of music: original, low-, or high-frequency amplified. To measure autonomic response, we calculated the high-frequency normalized unit (HFnu, low-frequency normalized unit, and the LF/HF ratio from the heart rate using electrocardiography. We defined the stress recovery ratio as the value obtained after participants listened to music following scratching noise, normalized by the value obtained after participants listened to white noise after the stress noise, in terms of the HFnu, low-frequency normalized unit, LF/HF ratio, and heart rate. Results indicated that high-frequency amplified music had the highest HFnu of the three versions. The stress recovery ratio of HFnu under the high-frequency amplified stimulus was significantly larger than that under the low-frequency stimulus. Our results suggest that the high-frequency component of music plays a greater role in stress relief than low-frequency components.

  13. Design and initial characterization of a compact, ultra high vacuum compatible, low frequency, tilt accelerometer

    Science.gov (United States)

    O'Toole, A.; Peña Arellano, F. E.; Rodionov, A. V.; Shaner, M.; Sobacchi, E.; Dergachev, V.; DeSalvo, R.; Asadoor, M.; Bhawal, A.; Gong, P.; Kim, C.; Lottarini, A.; Minenkov, Y.; Murphy, C.

    2014-07-01

    A compact tilt accelerometer with high sensitivity at low frequency was designed to provide low frequency corrections for the feedback signal of the Advanced Laser Interferometer Gravitational Wave Observatory active seismic attenuation system. It has been developed using a Tungsten Carbide ceramic knife-edge hinge designed to avoid the mechanical 1/f noise believed to be intrinsic in polycrystalline metallic flexures. Design and construction details are presented; prototype data acquisition and control limitations are discussed. The instrument's characterization reported here shows that the hinge is compatible with being metal-hysteresis-free, and therefore also free of the 1/f noise generated by the dislocation Self-Organized Criticality in the metal. A tiltmeter of this kind will be effective to separate the ground tilt component from the signal of horizontal low frequency seismometers, and to correct the ill effects of microseismic tilt in advanced seismic attenuation systems.

  14. Human hippocampal increases in low-frequency power during associative prediction violations.

    Science.gov (United States)

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

    2013-10-01

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

  15. Method for Estimating Low-Frequency Return Current of DC Electric Railcar

    Science.gov (United States)

    Hatsukade, Satoru

    The Estimation of the harmonic current of railcars is necessary for achieving compatibility between train signaling systems and railcar equipment. However, although several theoretical analyses methods for estimating the harmonic current of railcars using switching functions exist, there are no theoretical analysis methods estimating a low-frequency current at a frequency less than the power converter's carrier frequency. This paper describes a method for estimating the spectrum (frequency and amplitude) of the low-frequency return current of DC electric railcars. First, relationships between the return current and characteristics of the DC electric railcars, such as mass and acceleration, are determined. Then, the mathematical (not numerical) calculation results for low-frequency current are obtained from the time-current curve for a DC electric railcar by using Fourier series expansions. Finally, the measurement results clearly show the effectiveness of the estimation method development in this study.

  16. Damping Of Low Frequency Oscillations In Power System Using Device Upfc With Fuzzy Logic

    Directory of Open Access Journals (Sweden)

    B.Divya Lakshmi

    2014-04-01

    Full Text Available Power stability is an important issue that is becoming increasingly important to an power systems at all levels. We are unable to achieve the stability of the system due to some factors. Low frequency oscillation’s is one of the major factors that affect the transmission line capacity. Traditionally power system stabilizers(PSS are being used to damp these inevitable oscillations. In advanced technology FACTS devices such as unified power flow controllers (UPFC are used to control the power flow in transmission lines. They can also replace the PSS to damp the low frequency oscillations effectively through direct control of voltage and power. In our model, single machine infinite bus power system with UPFC is considered. The designed FUZZY based UPFC controllers adjusts four UPFC inputs by appropriately processing of input error signal and provides an efficient damping. The results of the simulation show that the UPFC with FUZZY LOGIC controller is effectively damping the LOW FREQUENCY OSCILLATIONS.

  17. Design and initial characterization of a compact, ultra high vacuum compatible, low frequency, tilt accelerometer

    Energy Technology Data Exchange (ETDEWEB)

    O’Toole, A., E-mail: amandajotoole@gmail.com, E-mail: riccardo.desalvo@gmail.com [Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, 405 Hilgard Ave, Los Angeles, California 90095 (United States); Peña Arellano, F. E. [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Rodionov, A. V.; Kim, C. [California Institute of Technology, Pasadena, California 91125 (United States); Shaner, M.; Asadoor, M. [Mayfield Senior School, 500 Bellefontaine Street Pasadena, California 91105 (United States); Sobacchi, E. [Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa (Italy); Dergachev, V.; DeSalvo, R., E-mail: amandajotoole@gmail.com, E-mail: riccardo.desalvo@gmail.com [LIGO Laboratory, California Institute of Technology, MS 100-36, Pasadena, California 91125 (United States); Bhawal, A. [Arcadia High School, 180 Campus Drive, Arcadia, California 91007 (United States); Gong, P. [Department of Precision Instrument, Tsinghua University, Beijing 100084 (China); Lottarini, A. [Department of Computer Science, University of Pisa, Largo B. Pontecorvo 3, 56127 Pisa (Italy); Minenkov, Y. [Sezione INFN Tor Vergata, via della Ricerca Scientfica 1, 00133 Roma (Italy); Murphy, C. [School of Physics, The University of Western Australia, 35 Stirling Highway, Crawley, Perth, Western Australia 6009 (Australia)

    2014-07-15

    A compact tilt accelerometer with high sensitivity at low frequency was designed to provide low frequency corrections for the feedback signal of the Advanced Laser Interferometer Gravitational Wave Observatory active seismic attenuation system. It has been developed using a Tungsten Carbide ceramic knife-edge hinge designed to avoid the mechanical 1/f noise believed to be intrinsic in polycrystalline metallic flexures. Design and construction details are presented; prototype data acquisition and control limitations are discussed. The instrument's characterization reported here shows that the hinge is compatible with being metal-hysteresis-free, and therefore also free of the 1/f noise generated by the dislocation Self-Organized Criticality in the metal. A tiltmeter of this kind will be effective to separate the ground tilt component from the signal of horizontal low frequency seismometers, and to correct the ill effects of microseismic tilt in advanced seismic attenuation systems.

  18. Inductive phenomena at low frequencies in impedance spectra of proton exchange membrane fuel cells - A review

    Science.gov (United States)

    Pivac, Ivan; Barbir, Frano

    2016-09-01

    The results of electrochemical impedance spectroscopy of proton exchange membrane (PEM) fuel cells may exhibit inductive phenomena at low frequencies. The occurrence of inductive features at high frequencies is explained by the cables and wires of the test system. However, explanation of inductive loop at low frequencies requires a more detailed study. This review paper discusses several possible causes of such inductive behavior in PEM fuel cells, such as side reactions with intermediate species, carbon monoxide poisoning, and water transport, also as their equivalent circuit representations. It may be concluded that interpretation of impedance spectra at low frequencies is still ambiguous, and that better equivalent circuit models are needed with clearly defined physical meaning of each of the circuit elements.

  19. The history of early low frequency radio astronomy in Australia. 2: Tasmania

    Science.gov (United States)

    George, Martin; Orchiston, Wayne; Slee, Bruce; Wielebinski, Richard

    2015-03-01

    Significant contributions to low frequency radio astronomy were made in the Australian state of Tasmania after the arrival of Grote Reber in 1954. Initially, Reber teamed with Graeme Ellis, who was then working with the Ionospheric Prediction Service, and they carried out observations as low as 0.52 MHz during the 1955 period of exceptionally low sunspot activity. In the early 1960s, Reber established a 2.085 MHz array in the southern central region of the State and used this to make the first map of the southern sky at this frequency. In addition, in the 1960s the University of Tasmania constructed several low frequency arrays near Hobart, including a 609m × 609m array designed for operation between about 2 MHz and 20 MHz. In this paper we present an overview of the history of low frequency radio astronomy in Tasmania.

  20. Low frequency sound field control for loudspeakers in rectangular rooms using CABS (Controlled Acoustical Bass System)

    DEFF Research Database (Denmark)

    Nielsen, Sofus Birkedal; Celestinos, Adrian

    2010-01-01

    Rectangular rooms are the most common shape for sound reproduction, but at low frequencies the reflections from the boundaries of the room cause large spatial variations in the sound pressure level.  Variations up to 30 dB are normal, not only at the room modes, but basically at all frequencies....... As sound propagates in time, it seems natural that the problems can best be analyzed and solved in the time domain. A time based room correction system named CABS (Controlled Acoustical Bass System) has been developed for sound reproduction in rectangular listening rooms. It can control the sound...... distribution in the room at low frequencies by using multiple loudspeakers together with an optimal placement of the loudspeakers.  At low frequencies CABS will create a plane wave from the front wall loudspeakers which will be absorbed by additional loudspeakers at the rear wall giving an almost homogeneous...

  1. Data-driven prediction strategies for low-frequency patterns of North Pacific climate variability

    CERN Document Server

    Comeau, Darin; Giannakis, Dimitrios; Majda, Andrew J

    2015-01-01

    The North Pacific exhibits patterns of low-frequency variability on the intra-annual to decadal time scales, which manifest themselves in both model data and the observational record, and prediction of such low-frequency modes of variability is of great interest to the community. While parametric models, such as stationary and non-stationary autoregressive models, possibly including external factors, may perform well in a data-fitting setting, they may perform poorly in a prediction setting. Ensemble analog forecasting, which relies on the historical record to provide estimates of the future based on past trajectories of those states similar to the initial state of interest, provides a promising, nonparametric approach to forecasting that makes no assumptions on the underlying dynamics or its statistics. We apply such forecasting to low-frequency modes of variability for the North Pacific sea surface temperature and sea ice concentration fields extracted through Nonlinear Laplacian Spectral Analysis. We find ...

  2. Low-frequency electrostatic dust-modes in a non-uniform magnetized dusty plasma

    Indian Academy of Sciences (India)

    S S Duha; S K Paul; A K Banerjee; A A Mamun

    2004-11-01

    A self-consistent and general description of obliquely propagating low-frequency electrostatic dust-modes in a non-uniform magnetized dusty plasma system has been presented. A number of different situations, which correspond to different low-frequency electrostatic dust-modes, namely, dust-acoustic mode, dust-drift mode, dust-cyclotron mode, dust-lower-hybrid mode, and other associated modes (such as, accelerated and retarded dust-acoustic modes, accelerated and retarded dust-lower-hybrid modes, etc.), have also been investigated. It has been shown that the effects of obliqueness and inhomogeneities in plasma particle number densities introduce new electrostatic dust modes as well as significantly modify the dispersion properties of the other low-frequency electrostatic dust associated modes. The implications of these results to some space and astrophysical dusty plasma systems, especially to planetary ring-systems and cometary tails, are briefly mentioned.

  3. Energy dissipation of Alfven wave packets deformed by irregular magnetic fields in solar-coronal arches

    Science.gov (United States)

    Similon, Philippe L.; Sudan, R. N.

    1989-01-01

    The importance of field line geometry for shear Alfven wave dissipation in coronal arches is demonstrated. An eikonal formulation makes it possible to account for the complicated magnetic geometry typical in coronal loops. An interpretation of Alfven wave resonance is given in terms of gradient steepening, and dissipation efficiencies are studied for two configurations: the well-known slab model with a straight magnetic field, and a new model with stochastic field lines. It is shown that a large fraction of the Alfven wave energy flux can be effectively dissipated in the corona.

  4. Behavior of Torsional Alfven Waves and Field Line Resonance on Rotating Magnetars

    CERN Document Server

    Kojima, T O Y

    2005-01-01

    Torsional Alfven waves are likely excited with bursts in rotating magnetars. These waves are probably propagated through corotating atmospheres toward a vacuum exterior. We have studied the physical effects of the azimuthal wave number and the characteristic height of the plasma medium on wave transmission. In this work, explicit calculations were carried out based on the three-layered cylindrical model. We found that the coupling strength between the internal shear and the external Alfven modes is drastically enhanced, when resonance occurs in the corotating plasma cavity. The spatial structure of the electromagnetic fields in the resonance cavity is also investigated when Alfven waves exhibit resonance.

  5. Low-frequency high-definition power Doppler in visualizing and defining fetal pulmonary venous connections.

    Science.gov (United States)

    Liu, Lin; He, Yihua; Li, Zhian; Gu, Xiaoyan; Zhang, Ye; Zhang, Lianzhong

    2014-07-01

    The use of low-frequency high-definition power Doppler in assessing and defining pulmonary venous connections was investigated. Study A included 260 fetuses at gestational ages ranging from 18 to 36 weeks. Pulmonary veins were assessed by performing two-dimensional B-mode imaging, color Doppler flow imaging (CDFI), and low-frequency high-definition power Doppler. A score of 1 was assigned if one pulmonary vein was visualized, 2 if two pulmonary veins were visualized, 3 if three pulmonary veins were visualized, and 4 if four pulmonary veins were visualized. The detection rate between Exam-1 and Exam-2 (intra-observer variability) and between Exam-1 and Exam-3 (inter-observer variability) was compared. In study B, five cases with abnormal pulmonary venous connection were diagnosed and compared to their anatomical examination. In study A, there was a significant difference between CDFI and low-frequency high-definition power Doppler for the four pulmonary veins observed (P frequency high-definition power Doppler was higher than that when employing two-dimensional B-mode imaging or CDFI. There was no significant difference between the intra- and inter-observer variabilities using low-frequency high-definition power Doppler display of pulmonary veins (P > 0.05). The coefficient correlation between Exam-1 and Exam-2 was 0.844, and the coefficient correlation between Exam-1 and Exam-3 was 0.821. In study B, one case of total anomalous pulmonary venous return and four cases of partial anomalous pulmonary venous return were diagnosed by low-frequency high-definition power Doppler and confirmed by autopsy. The assessment of pulmonary venous connections by low-frequency high-definition power Doppler is advantageous. Pulmonary venous anatomy can and should be monitored during fetal heart examination.

  6. Balloon observations of ultra-low-frequency waves in the electric field above the South Pole

    Energy Technology Data Exchange (ETDEWEB)

    Liao, B.; Benbrrook, J.R.; Bering E.A. III; Byrne, G.J.; Theall, J.R. (Univ. of Houston, TX (USA))

    1988-01-01

    The physics of ultra-low-frequency waves in the magnetosphere, near the cusp and in the polar cap, is important because this region is one where ultra-low-frequency wave energy from the magnetopause can most easily enter the magnetosphere. During the 1985-1986 South Pole balloon campaign, eight stratospheric balloon payloads were launched from Amundsen-Scott Station, South Geographic Pole, Antarctica, to record data on ultra-low-frequency waves. The payloads were instrumented with three-axis double-probe electric field detectors and X-ray scintillation counters. This paper concentrates on the third flight of this series, which was launched at 2205 universal time on 21 December 1985. Good data were received from the payload until the transmitter failed at 0342 universal time on 22 December. During most of the four hours that the balloon was afloat, an intense ultra-low-frequency wave event was in progress. The electric-field data from this period have been examined in detail and compared with magnetic field data, obtained with ground-based fluxgate and induction magnetometers to determine the characteristics of the waves. After float was reached, the electric-field data in figure 1 show large-amplitude, quasi-periodic fluctuations suggesting the presence of intense ultra-low-frequency wave activity. In conclusion, the electric-field signature observed from flight 3 appears to have been essentially an electrostatic event or possibly a short-wavelength hydromagnetic wave with a varying and interesting polarization character. The authors are continuing the analysis of the data to determine the source of the observed ultra-low-frequency waves.

  7. Acoustic properties of pistonphones at low frequencies in the presence of pressure leakage and heat conduction

    Science.gov (United States)

    Zhang, Fan; He, Wen; He, Longbiao; Rong, Zuochao

    2015-12-01

    The wide concern on absolute pressure calibration of acoustic transducers at low frequencies prompts the development of the pistonphone method. At low frequencies, the acoustic properties of pistonphones are governed by the pressure leakage and the heat conduction effects. However, the traditional theory for these two effects applies a linear superposition of two independent correction models, which differs somewhat from their coupled effect at low frequencies. In this paper, acoustic properties of pistonphones at low frequencies in full consideration of the pressure leakage and heat conduction effects have been quantitatively studied, and the explicit expression for the generated sound pressure has been derived. With more practical significance, a coupled correction expression for these two effects of pistonphones has been derived. In allusion to two typical pistonphones, the NPL pistonphone and our developed infrasonic pistonphone, comparisons were done for the coupled correction expression and the traditional one, whose results reveal that the traditional one produces maximum insufficient errors of about 0.1 dB above the lower limiting frequencies of two pistonphones, while at lower frequencies, excessive correction errors with an explicit limit of about 3 dB are produced by the traditional expression. The coupled correction expression should be adopted in the absolute pressure calibration of acoustic transducers at low frequencies. Furthermore, it is found that the heat conduction effect takes a limiting deviation of about 3 dB for the pressure amplitude and a small phase difference as frequency decreases, while the pressure leakage effect remarkably drives the pressure amplitude to attenuate and the phase difference tends to be 90° as the frequency decreases. The pressure leakage effect plays a more important role on the low frequency property of pistonphones.

  8. Flextensional fiber Bragg grating-based accelerometer for low frequency vibration measurement

    Institute of Scientific and Technical Information of China (English)

    Jinghua Zhang; Xueguang Qiao; Manli Hu; Zhongyao Feng; Hong Gao; Yang Yang; Rui Zhou

    2011-01-01

    @@ The intelligent structural health monitoring method,which uses a fiber Bragg grating(FBG)sensor,is a new approach in the field of civil engineering.However,it lacks a reliable FBG-based accelerometer for taking structural low frequency vibration measurements.In this letter,a flextensional FBG-based accelerometer is proposed and demonstrated.The experimental results indicate that the natural frequency of the developed accelerometer is 16.7 Hz,with a high sensitivity of 410.7 pm/g.In addition,it has a broad and flat response over low frequencies ranging from 1 to 10 Hz.The natural frequency and sensitivity of the accelerometer can be tuned by adding mass to tailor the sensor performance to specific applications.Experimental results are presented to demonstrate the good performance of the proposed FBG-based accelerometer.These results show that the proposed accelerometer is satisfactory for low frequency vibration measurements.%The intelligent structural health monitoring method, which uses a fiber Bragg grating {FBG} sensor, ie a new approach in the field of civil engineering. However, it lacks a reliable FBG-based accelerometer for taking structural low frequency vibration measurements. In this letter, a flextensional FBG-based accelerometer is proposed and demonstrated. The experimental results indicate that the natural frequency of the developed accelerometer is 16.7 Hz, with a high sensitivity of 410.7 pm/g. In addition, it has a broad and flat response over low frequencies ranging from 1 to 10 Hz. The natural frequency and sensitivity of the accelerometer can be tuned by adding mass to tailor the sensor performance to specific applications. Experimental results are presented to demonstrate the good performance of the proposed FBG-based accelerometer. These results show that the proposed accelerometer is satisfactory for low frequency vibration measurements.

  9. Effect of Low Frequency Electromagnetic Field on Macrosegregation of Horizontal Direct Chill Casting Aluminum Alloys

    Institute of Scientific and Technical Information of China (English)

    Zhihao ZHAO; Jianzhong CUI; Jie DONG; Beijiang ZHANG

    2005-01-01

    The horizontal direct chill (HDC) casting process is a well-established production route for aluminum alloy ingot but the ingot may suffer from macrosegregation sometimes. In order to control the defect, a low frequency electromagnetic field has been applied in HDC casting process and the relevant influence has been studied. The results show that application of low frequency electromagnetic field can reduce macrosegregation in HDC casting process; and two main parameters of electromagnetic field density and frequency, have great influences on the solution distribution along the diameter of ingot. Moreover, the mechanisms of reduction of macrosegregation by electromagnetic field have been discussed.

  10. Numerical and experimental investigation of nonlinear ultrasonic Lamb waves at low frequency

    Science.gov (United States)

    Zuo, Peng; Zhou, Yu; Fan, Zheng

    2016-07-01

    Nonlinear ultrasonic Lamb waves are popular to characterize the nonlinearity of materials. However, the widely used nonlinear Lamb mode suffers from two associated complications: inherent dispersive and multimode natures. To overcome these, the symmetric Lamb mode (S0) at low frequency region is explored. At the low frequency region, the S0 mode is little dispersive and easy to generate. However, the secondary mode still exists, and increases linearly for significant distance. Numerical simulations and experiments are used to validate the nonlinear features and therefore demonstrate an easy alternative for nonlinear Lamb wave applications.

  11. The GMRT Radio Halo Survey and low frequency follow-up

    CERN Document Server

    Venturi, T; Cassano, R; Brunetti, G; Dallacasa, D; Macario, G; Setti, G; Bardelli, S; Athreya, R

    2009-01-01

    The GMRT Radio Halo Survey, carried out at 610 MHz to investigate the statistical properties of cluster radio halos in a complete cluster sample selected in the redshift interval z=0.2-0.4, has significantly improved our understanding of the origin of cluster radio halos and relics. Here we briefly summarize the most relevant results of our investigation. A low frequency follow-up is in progress with the GMRT at 325 MHz and 240 MHz on the diffuse sources and candidated found at 610 MHz. We briefly report some preliminary results on these low frequency observations. Cluster radio halos with different radio spectral properties have been unexpectedly found.

  12. Low-frequency relaxation modes and structural disorder in KTa1-xNbxO3

    Science.gov (United States)

    Sokoloff, J. P.; Chase, L. L.; Boatner, L. A.

    1990-02-01

    A light-scattering study of the low-frequency excitations in single crystals of cubic and tetragonal KTa1-xNbxO3 (x=0.26 and 0.28) has been carried out by employing a technique which uses an Iodine filter to remove elastically scattered light. Low-frequency Raman and Fabry-Pérot components related to structural disorder in the mixed-crystal tantalate-niobate system were observed. The spectral shape, symmetry properties, and thermal behavior of these components are consistent with an eight-site order-disorder model of the sequence of structural phase transitions observed in ferrodistortive perovskites.

  13. A Low-Frequency and Refinement Stable Impedance Boundary Condition EFIE

    CERN Document Server

    Dely, Alexandre; Cools, Kristof

    2016-01-01

    In this contribution, a discretisation of the IBC EFIE is introduced that (i) yields the correct solution at arbitrarily small frequencies, (ii) requires for its solution a number of matrix vector products bounded as the frequency tends to zero and as the mesh density increases. The low frequency stabilisation is based on a projector-based discrete Helmholtz splitting, rescaling, and recombination that depends on the low frequency behaviour of both the EFIE operator and the surface impedance condition. The dense mesh stabilisation is a modifcation of the Perfect Electric Conductor operator preconditioning approach taking into account the effect on the singular value spectrum of the IBC term.

  14. The statistics of low frequency radio interference at the Murchison Radio-astronomy Observatory

    CERN Document Server

    Sokolowski, Marcin; Lewis, Morgan

    2016-01-01

    We characterize the low frequency radio-frequency interference (RFI) environment at the Murchison Radio-astronomy Observatory (MRO), the location selected for the low-frequency component of the Square Kilometre Array. Data were collected from the BIGHORNS instrument, located at the MRO, which records a contiguous bandwidth between 70 and 300 MHz, between November 2014 to March 2015 inclusive. The data were processed to identify RFI, and we describe a series of statistics in both the time and frequency domain, including modeling of the RFI occupancy and signal power as a series of distribution functions, with the goal of aiding future scientists and operation staff in observation planning.

  15. Development of a low-frequency physiotherapeutic device for diabetes manipulated by microcontroller.

    Science.gov (United States)

    Guo, Jin-Song; Gong, Jian

    2001-01-01

    OBJECTIVE: To develop a physiotherapeutic device for diabetes that generates special low-frequency waveform manipulated by a microcontroller. METHODS: A microcontoller and a digital-to-analog converter were utilized along with a keyboard and LED display circuit, to generate desired low-frequecy waveform with the assistance of a software. RESULTS: The complex waveform generated by this device met the demands for diabetes physiotherapy, and the frequency and amplitude could be freely adjusted. CONCLUSIONS: The utilization of a digital-to-analog converter controlled by a microcontroller can very well serve the purpose of a low-frequency physiotherapy for diabetes.

  16. Combined Ideal and Kinetic Effects on Reversed Shear Alfven Eigenmodes

    Energy Technology Data Exchange (ETDEWEB)

    N.N. Gorelenkov, G.J. Kramer, and R. Nazikian

    2011-05-23

    A theory of Reversed Shear Alfven Eigenmodes (RSAEs) is developed for reversed magnetic field shear plasmas when the safety factor minimum, qmin, is at or above a rational value. The modes we study are known sometimes as either the bottom of the frequency sweep or the down sweeping RSAEs. We show that the ideal MHD theory is not compatible with the eigenmode solution in the reversed shear plasma with qmin above integer values. Corrected by special analytic FLR condition MHD dispersion of these modes nevertheless can be developed. Large radial scale part of the analytic RSAE solution can be obtained from ideal MHD and expressed in terms of the Legendre functions. The kinetic equation with FLR effects for the eigenmode is solved numerically and agrees with the analytic solutions. Properties of RSAEs and their potential implications for plasma diagnostics are discussed.

  17. Alfven Wave Collisions, The Fundamental Building Block of Plasma Turbulence IV: Laboratory Experiment

    CERN Document Server

    Drake, D J; Howes, G G; Kletzing, C A; Skiff, F; Carter, T A; Auerbach, D W

    2013-01-01

    Turbulence is a phenomenon found throughout space and astrophysical plasmas. It plays an important role in solar coronal heating, acceleration of the solar wind, and heating of the interstellar medium. Turbulence in these regimes is dominated by Alfven waves. Most turbulence theories have been established using ideal plasma models, such as incompressible MHD. However, there has been no experimental evidence to support the use of such models for weakly to moderately collisional plasmas which are relevant to various space and astrophysical plasma environments. We present the first experiment to measure the nonlinear interaction between two counterpropagating Alfven waves, which is the building block for astrophysical turbulence theories. We present here four distinct tests that demonstrate conclusively that we have indeed measured the daughter Alfven wave generated nonlinearly by a collision between counterpropagating Alfven waves.

  18. Drift-Alfven instabilities of a finite beta plasma shear flow along a magnetic field

    Science.gov (United States)

    Mikhailenko, V. V.; Mikhailenko, V. S.; Lee, Hae June

    2016-02-01

    It was derived that the drift-Alfven instabilities with the shear flow parallel to the magnetic field have significant difference from the drift-Alfven instabilities of a shearless plasma when the ion temperature is comparable with electron temperature for a finite plasma beta. The velocity shear not only modifies the frequency and the growth rate of the known drift-Alfven instability, which develops due to the inverse electron Landau damping, but also triggers a combined effect of the velocity shear and the inverse ion Landau damping, which manifests the development of the ion kinetic shear-flow-driven drift-Alfven instability. The excited unstable waves have the phase velocities along the magnetic field comparable with the ion thermal velocity, and the growth rate is comparable with the frequency. The development of this instability may be the efficient mechanism of the ion energization in shear flows.

  19. Pressure-gradient-induced Alfven eigenmodes: 2. Kinetic excitation with ion temperature gradient

    CERN Document Server

    Bierwage, Andreas; Zonca, Fulvio

    2009-01-01

    The kinetic excitation of ideal magnetohydrodynamic (MHD) discrete Alfven eigenmodes in the second MHD ballooning stable domain is studied in the presence of a thermal ion temperature gradient (ITG), using linear gyrokinetic particle-in-cell simulations of a local flux tube in shifted-circle tokamak geometry. The instabilities are identified as alpha-induced toroidal Alfven eigenmodes (alphaTAE); that is, bound states trapped between pressure-gradient-induced potential barriers of the Schroedinger equation for shear Alfven waves. Using numerical tools, we examine in detail the effect of kinetic thermal ion compression on alphaTAEs; both non-resonant coupling to ion sound waves and wave-particle resonances. It is shown that the Alfvenic ITG instability thresholds (e.g., the critical temperature gradient) are determined by two resonant absorption mechanisms: Landau damping and continuum damping. The numerical results are interpreted on the basis of a theoretical framework previously derived from a variational f...

  20. Parametric instabilities of large-amplitude parallel propagating Alfven waves: 2-D PIC simulation

    CERN Document Server

    Nariyuki, Yasuhiro; Hada, Tohru

    2008-01-01

    We discuss the parametric instabilities of large-amplitude parallel propagating Alfven waves using the 2-D PIC simulation code. First, we confirmed the results in the past study [Sakai et al, 2005] that the electrons are heated due to the modified two stream instability and that the ions are heated by the parallel propagating ion acoustic waves. However, although the past study argued that such parallel propagating longitudinal waves are excited by transverse modulation of parent Alfven wave, we consider these waves are more likely to be generated by the usual, parallel decay instability. Further, we performed other simulation runs with different polarization of the parent Alfven waves or the different ion thermal velocity. Numerical results suggest that the electron heating by the modified two stream instability due to the large amplitude Alfven waves is unimportant with most parameter sets.

  1. Alfven. Symphony No 5 in A minor, Op. 54 / Robert Layton

    Index Scriptorium Estoniae

    Layton, Robert

    1994-01-01

    Uuest heliplaadist "Alfven. Symphony No 5 in A minor, Op. 54. The Mountain King - Suite, Gustav II Adolf, Op. 49 - Elegy. Royal Stockholm Philarmonic Orchestra / Neeme Järvi. BIS CD 585 (68 minutes) Recorded in association with Trygg Hansa"

  2. Alfven. Symphony No 5 in A minor, Op. 54 / Robert Layton

    Index Scriptorium Estoniae

    Layton, Robert

    1994-01-01

    Uuest heliplaadist "Alfven. Symphony No 5 in A minor, Op. 54. The Mountain King - Suite, Gustav II Adolf, Op. 49 - Elegy. Royal Stockholm Philarmonic Orchestra / Neeme Järvi. BIS CD 585 (68 minutes) Recorded in association with Trygg Hansa"

  3. Alfven Waves in a Plasma Sheet Boundary Layer Associated with Near-Tail Magnetic Reconnection

    Institute of Scientific and Technical Information of China (English)

    YUAN Zhi-Gang; DENG Xiao-Hua; PANG Ye; LI Shi-You; WANG Jing-Fang

    2007-01-01

    We report observations from Geotail satellite showing that large Poynting fluxes associated with Alfven waves in the plasma sheet boundary layer(PSBL) occur in the vicinity of the near-tail reconnection region on 10 December 1996.During the period of large Poynting fluxex,Geotail also observed strong tailward plasma flws.These observations demonstrate the importance of near-tail reconnection process as the energy source of Alfven waves in the PSBL.Strong tailward(Earthward)plasma flows ought to be an important candidate in generating Alfven waves.Furthermore,the strong pertutbations not only of the magnetic field but also of the electric field observed in the PSBL indicate that the PSBL plays an important role in the generation and propagation of the energy flux associated with Alfven waves.

  4. Heating of the Solar Corona by Alfven Waves: Self-Induced Opacity

    CERN Document Server

    Zahariev, N I

    2011-01-01

    There have been derived equations describing the static distributions of temperature and wind velocity at the transition region within the framework of the magnetohydrodynamics (MHD) of fully ionized hydrogen plasma . We have also calculated the width of the transition between the chromosphere and corona as a self-induced opacity of the high-frequency Alfven waves (AWs). The domain wall is a direct consequence of the self-consistent MHD treatment of AWs propagation. We predict considerable spectral density of the high-frequency AWs in the photosphere. The idea that Alfven waves might heat the solar corona belong to Alfven - we simply derived the corresponding MHD equations. The comparison of the solutions to those equations with the observational/measured data will be crucial for revealing the heating mechanism. The analysis of those solutions will explain how Alfven waves brick unto the corona and dissipate their energy there.

  5. Transfer of Energy, Potential, and Current by Alfv\\'en Waves in Solar Flares

    CERN Document Server

    Melrose, D B

    2013-01-01

    Alfv\\'en waves play three related roles in the impulsive phase of a solar flare: they transport energy from a generator region to an acceleration region; they map the cross-field potential (associated with the driven energy release) from the generator region onto the acceleration region; and within the acceleration region they damp by setting up a parallel electric field that accelerates electrons and transfers the wave energy to them. The Alfv\\'en waves may also be regarded as setting up new closed current loops, with field-aligned currents that close across field lines at boundaries. A model is developed for large-amplitude Alfv\\'en waves that shows how Alfv\\'en waves play these roles in solar flares. A picket-fence structure for the current flow is incorporated into the model to account for the "number problem" and the energy of the accelerated electrons.

  6. The Low-Frequency Array (LOFAR) and EoR Key-Science Project

    NARCIS (Netherlands)

    Brentjens, Michiel; Koopmans, L. V. E.; de Bruyn, A. G.; Zaroubi, S.

    The Low-Frequency ARray (LOFAR) is a novel radio-telescope facility with its core and operation center in the Netherlands. LOFAR is one of several current pathfinders toward SKA. One of LOFAR's key science projects is the detection and characterization of the redshifted 21-cm emission from neutral

  7. Global low-frequency modes in weakly ionized magnetized plasmas: effects of equilibrium plasma rotation

    Energy Technology Data Exchange (ETDEWEB)

    Sosenko, P.; Pierre, Th. [Universite Marseille, Lab. PIIM - UMR6633 CNRS, Centre Saint Jerome, 13 - Marseille (France); Zagorodny, A. [Nancy-1 Univ. Henri Poincare, Lab. de Physique des Milieux Ionises (LPMIA, UPRES-A), Nancy 54 (France); International Centre of Physics, Kyiv (Ukraine)

    2004-07-01

    The linear and non-linear properties of global low-frequency oscillations in cylindrical weakly ionized magnetized plasmas are investigated analytically for the conditions of equilibrium plasma rotation. The theoretical results are compared with the experimental observations of rotating plasmas in laboratory devices, such as Mistral and Mirabelle in France, and KIWI in Germany. (authors)

  8. A lightweight low-frequency sound insulation membrane-type acoustic metamaterial

    Directory of Open Access Journals (Sweden)

    Kuan Lu

    2016-02-01

    Full Text Available A novel membrane-type acoustic metamaterial with a high sound transmission loss (STL at low frequencies (⩽500Hz was designed and the mechanisms were investigated by using negative mass density theory. This metamaterial’s structure is like a sandwich with a thin (thickness=0.25mm lightweight flexible rubber material within two layers of honeycomb cell plates. Negative mass density was demonstrated at frequencies below the first natural frequency, which results in the excellent low-frequency sound insulation. The effects of different structural parameters of the membrane on the sound-proofed performance at low frequencies were investigated by using finite element method (FEM. The numerical results show that, the STL can be modulated to higher value by changing the structural parameters, such as the membrane surface density, the unite cell film shape, and the membrane tension. The acoustic metamaterial proposed in this study could provide a potential application in the low-frequency noise insulation.

  9. S-shape spring sensor: Sensing specific low-frequency vibration by energy harvesting

    Science.gov (United States)

    Zhang, Lan; Lu, Jian; Takei, Ryohei; Makimoto, Natsumi; Itoh, Toshihiro; Kobayashi, Takeshi

    2016-08-01

    We have developed a Si-based microelectromechanical systems sensor with high sensitivity for specific low-frequency vibration-sensing and energy-harvesting applications. The low-frequency vibration sensor contains a disk proof mass attached to two or three lead zirconate titanate (PZT) S-shape spring flexures. To obtain a faster and less expensive prototype, the design and optimization of the sensor structure are studied via finite-element method analysis. To validate the sensor structure to detect low-frequency vibration, the effects of geometrical dimensions, including the width and diameter of the S-shape spring of the proof mass, were analyzed and measured. The functional features, including the mechanical property and electrical performance of the vibration sensor, were evaluated. The results demonstrated that a very low resonant frequency of 0.2g can be typically achieved. Given a low-frequency vibration sensor with ideal performance and mass fabrication, many advanced civilian and industrial applications can be possibly realized.

  10. Planck early results. III. First assessment of the Low Frequency Instrument in-flight performance

    DEFF Research Database (Denmark)

    León-Tavares, J.; Falvella, M.C.; Hughes, N.;

    2011-01-01

    The scientific performance of the Planck Low Frequency Instrument (LFI) after one year of in-orbit operation is presented. We describe the main optical parameters and discuss photometric calibration, white noise sensitivity, and noise properties. A preliminary evaluation of the impact of the main...

  11. Assessment of extremely low frequency magnetic field exposure from GSM mobile phones

    NARCIS (Netherlands)

    Calderón, Carolina; Addison, Darren; Mee, Terry; Findlay, Richard; Maslanyj, Myron; Conil, Emmanuelle; Kromhout, Hans; Lee, Ae Kyoung; Sim, Malcolm R.; Taki, Masao; Varsier, Nadège; Wiart, Joe; Cardis, Elisabeth

    2014-01-01

    Although radio frequency (RF) electromagnetic fields emitted by mobile phones have received much attention, relatively little is known about the extremely low frequency (ELF) magnetic fields emitted by phones. This paper summarises ELF magnetic flux density measurements on global system for mobile c

  12. Extremely low-frequency magnetic field exposure, electrical shocks and risk of Parkinson's disease

    NARCIS (Netherlands)

    van der Mark, Marianne; Vermeulen, Roel; Nijssen, Peter C. G.; Mulleners, Wim M.; Sas, Antonetta M. G.; van Laar, Teus; Kromhout, Hans; Huss, Anke

    2015-01-01

    Previous studies did not provide strong evidence for an increased Parkinson's disease (PD) risk after exposure to extremely low-frequency magnetic fields (ELF-MF), but were limited in their scope to address other exposures related to the use of electricity such as electrical shocks. We evaluated the

  13. Wind Turbine Infra and Low-Frequency Sound: Warning Signs that Were Not Heard

    Science.gov (United States)

    James, Richard R.

    2012-01-01

    Industrial wind turbines are frequently thought of as benign. However, the literature is reporting adverse health effects associated with the implementation of industrial-scale wind developments. This article explores the historical evidence about what was known regarding infra and low-frequency sound from wind turbines and other noise sources…

  14. Chiral Low Frequency Resonance on an Anisotropically Conductive Cylinder with a Thin Longitudinal Slot

    Science.gov (United States)

    2000-09-29

    electromagnetic waves by a Narrow anisotropically conductive strip," Radiotekh. Elektron ., vol. 44, no. 7, pp. 800-805, 1999. [3] A. N. Sivov, A. D...Chuprin, and A. D. Shatrov, "Low-frequency resonance in a hollow circular cylinder with perfect conductivity along helical lines," Radiotekh. Elektron

  15. Low-Frequency Variants in HMGA1 Are Not Associated With Type 2 Diabetes Risk

    NARCIS (Netherlands)

    Marquez, Marcel; Huyvaert, Marlene; Perry, John R. B.; Pearson, Richard D.; Falchi, Mario; Morris, Andrew P.; Vivequin, Sidonie; Lobbens, Stephane; Yengo, Loic; Gaget, Stefan; Pattou, Francois; Poulain-Godefroy, Odile; Charpentier, Guillaume; Carlsson, Lena M. S.; Jacobson, Peter; Sjostrom, Lars; Lantieri, Olivier; Heude, Barbara; Walley, Andrew; Balkau, Beverley; Marre, Michel; Froguel, Philippe; Cauchi, Stephane

    2012-01-01

    It has recently been suggested that the low-frequency c.136-14_136-13insC variant in high-mobility group Al (HMGA1) may strongly contribute to insulin resistance and type 2 diabetes risk. In our study, we attempted to confirm that HMGA1 is a novel type 2 diabetes locus in French Caucasians. The gene

  16. A New Ultra-low Frequency Passive Vertical Vibration Isolation System

    Institute of Scientific and Technical Information of China (English)

    赵鹏飞; 黄玉盈; 唐孟希

    2002-01-01

    A new ultra-low frequency passive vertical vibration isolation system is constructed by connecting the torsion spring isolator with a reverse pendulum. The theoretical analysis shows that the new system can achieve a much longer resonant period and have a smaller size than the current torsion spring isolators with the same geometric parameters.

  17. A New Ultra-low Frequency Passive Vertical Vibration Isolation System

    Science.gov (United States)

    Zhao, Peng-Fei; Huang, Yu-Ying; Tang, Meng-Xi

    2002-02-01

    A new ultra-low frequency passive vertical vibration isolation system is constructed by connecting the torsion spring isolator with a reverse pendulum. The theoretical analysis shows that the new system can achieve a much longer resonant period and have a smaller size than the current torsion spring isolators with the same geometric parameters.

  18. Inactivation of Enterobacter aerogenes in reconstituted skim milk by high- and low-frequency ultrasound.

    Science.gov (United States)

    Gao, Shengpu; Hemar, Yacine; Lewis, Gillian D; Ashokkumar, Muthupandian

    2014-11-01

    The inactivation of Enterobacter aerogenes in skim milk using low-frequency (20kHz) and high-frequency (850kHz) ultrasonication was investigated. It was found that low-frequency acoustic cavitation resulted in lethal damage to E. aerogenes. The bacteria were more sensitive to ultrasound in water than in reconstituted skim milk having different protein concentrations. However, high-frequency ultrasound was not able to inactivate E. aerogenes in milk even when powers as high as 50W for 60min were used. This study also showed that high-frequency ultrasonication had no influence on the viscosity and particle size of skim milk, whereas low-frequency ultrasonication resulted in the decrease in viscosity and particle size of milk. The decrease in particle size is believed to be due to the breakup of the fat globules, and possibly to the cleavage of the κ-casein present at the surface of the casein micelles. Whey proteins were also found to be slightly affected by low-frequency ultrasound, with the amounts of α-lactalbumin and β-lactoglobulin slightly decreasing.

  19. Daris, a low-frequency distributed aperture array for radio astronomy in space

    NARCIS (Netherlands)

    Boonstra, A.J.; Saks, N.; Bentum, Marinus Jan; van 't Klooster, K.; Falcke, H.

    2010-01-01

    DARIS (Distributed Aperture Array for Radio Astronomy in Space) is a radio astronomy space mission concept aimed at observing the low-frequency radio sky in the range 1-10 MHz. Because of the Earth's ionospheric disturbances and opaqueness, this frequency range can only be observed from space. The a

  20. A dedicated pistonphone for absolute calibration of infrasound sensors at very low frequencies

    Science.gov (United States)

    He, Wen; He, Longbiao; Zhang, Fan; Rong, Zuochao; Jia, Shushi

    2016-02-01

    Aimed at the absolute calibration of infrasound sensors at very low frequencies, an upgraded and improved infrasonic pistonphone has been developed. The pistonphone was designed such that a very narrow clearance between the piston and its guide was realized based on an automatically-centered clearance-sealing structure, and a large volume rigid-walled chamber was also adopted, which improved the leakage time-constant of the chamber. A composite feedback control system was applied to the electromagnetic vibrator to control the precise motion of the piston. Performance tests and uncertainty analysis show that the leakage time-constant is so large, and the distortion of the sound pressure is so small, that the pistonphone can be used as a standard infrasound source in the frequency range from 0.001 Hz to 20 Hz. The low frequency property of the pistonphone has been verified through calibrating low frequency microphones. Comparison tests with the reciprocity method have shown that the pressure sensitivities from the pistonphone are not only reliable at common frequencies but also have smaller uncertainties at low frequencies.

  1. Simulation of Low frequency Noise from a Downwind Wind Turbine Rotor

    DEFF Research Database (Denmark)

    Madsen, Helge Aa.; Johansen, Jeppe; Sørensen, Niels

    2007-01-01

    One of the major drawbacks of a wind turbine with a downwind rotor is the generation of considerable low frequency noise (so-called thumping noise) which can cause annoyance of people at a considerable distance. This was experienced on a number of full-scale turbines in e.g. US and Sweden in the ...

  2. Low-Frequency Variants in HMGA1 Are Not Associated With Type 2 Diabetes Risk

    NARCIS (Netherlands)

    Marquez, Marcel; Huyvaert, Marlene; Perry, John R. B.; Pearson, Richard D.; Falchi, Mario; Morris, Andrew P.; Vivequin, Sidonie; Lobbens, Stephane; Yengo, Loic; Gaget, Stefan; Pattou, Francois; Poulain-Godefroy, Odile; Charpentier, Guillaume; Carlsson, Lena M. S.; Jacobson, Peter; Sjostrom, Lars; Lantieri, Olivier; Heude, Barbara; Walley, Andrew; Balkau, Beverley; Marre, Michel; Froguel, Philippe; Cauchi, Stephane

    2012-01-01

    It has recently been suggested that the low-frequency c.136-14_136-13insC variant in high-mobility group Al (HMGA1) may strongly contribute to insulin resistance and type 2 diabetes risk. In our study, we attempted to confirm that HMGA1 is a novel type 2 diabetes locus in French Caucasians. The gene

  3. Measurements of Low Frequency Noise of Infrared Photo-Detectors with Transimpedance Detection System

    Directory of Open Access Journals (Sweden)

    Ciura Łukasz

    2014-08-01

    Full Text Available The paper presents the method and results of low-frequency noise measurements of modern mid-wavelength infrared photodetectors. A type-II InAs/GaSb superlattice based detector with nBn barrier architecture is compared with a high operating temperature (HOT heterojunction HgCdTe detector. All experiments were made in the range 1 Hz - 10 kHz at various temperatures by using a transimpedance detection system, which is examined in detail. The power spectral density of the nBn’s dark current noise includes Lorentzians with different time constants while the HgCdTe photodiode has more uniform 1/f - shaped spectra. For small bias, the low-frequency noise power spectra of both devices were found to scale linearly with bias voltage squared and were connected with the fluctuations of the leakage resistance. Leakage resistance noise defines the lower noise limit of a photodetector. Other dark current components give raise to the increase of low-frequency noise above this limit. For the same voltage biasing devices, the absolute noise power densities at 1 Hz in nBn are 1 to 2 orders of magnitude lower than in a MCT HgCdTe detector. In spite of this, low-frequency performance of the HgCdTe detector at ~ 230K is still better than that of InAs/GaSb superlattice nBn detector.

  4. Study on Low-Frequency TEM Effect of Coal during Dynamic Rupture

    Directory of Open Access Journals (Sweden)

    Cheng-wu Li

    2015-01-01

    Full Text Available Dynamic loads provided by the SHPB test system were applied to coal specimens, and the TEM signals that emerged during coal rupture were recorded by the TMVT system. Experiments on coal-mass blasting rupture in excavating workface were also carried out, and the emerged TEM signal was analyzed. The results indicate that the low-frequency TEM signals were detected close to the coal specimens under high strain dynamic load applied by the SHPB, initially rising sharply and dropping rapidly, followed by a small tailing turbulence. And the field test results obtained during coal blasting process coincided with the results from the SHPB tests. Furthermore, its initial part shaped like a pulse cluster had a more pronounced tail and lasted even longer. And the generation mechanism of the low-frequency TEM effect was analyzed. It suggests that the low-frequency TEM effect of coal during dynamic rupture is contributed by the fractoemission mechanism and the resonance or waveguide effects. Because its wavelength is longer than the higher ones, the low-frequency TEM has a good anti-interference performance. That can expand the scope and performance of the coal-rock dynamic disaster electromagnetic monitoring technique.

  5. Extremely low-frequency magnetic field exposure, electrical shocks and risk of Parkinson's disease

    NARCIS (Netherlands)

    van der Mark, Marianne; Vermeulen, Roel; Nijssen, Peter C. G.; Mulleners, Wim M.; Sas, Antonetta M. G.; van Laar, Teus; Kromhout, Hans; Huss, Anke

    Previous studies did not provide strong evidence for an increased Parkinson's disease (PD) risk after exposure to extremely low-frequency magnetic fields (ELF-MF), but were limited in their scope to address other exposures related to the use of electricity such as electrical shocks. We evaluated the

  6. Wind Turbine Acoustic Investigation: Infrasound and Low-Frequency Noise--A Case Study

    Science.gov (United States)

    Ambrose, Stephen E.; Rand, Robert W.; Krogh, Carmen M. E.

    2012-01-01

    Wind turbines produce sound that is capable of disturbing local residents and is reported to cause annoyance, sleep disturbance, and other health-related impacts. An acoustical study was conducted to investigate the presence of infrasonic and low-frequency noise emissions from wind turbines located in Falmouth, Massachusetts, USA. During the…

  7. Proposed Criteria for Assessing Low Frequency Noise Annoyance in Occupational Settings

    National Research Council Canada - National Science Library

    Pawlaczyk-Łuszczyńska, Maĺgorzata; Szymczak, Wiesłaaw; Dudarewicz, Adam; Śliwińska-Kowalska, Mariola

    2006-01-01

    ...: (i) method I - frequency analysis in 1/3-octave bands within the range of 10-250 Hz, (ii) method II - consisting in 1/3-octave band measurements and determination of low frequency equivalentcontinuous A-weighted sound pressure level (SPL...

  8. Wind Turbine Infra and Low-Frequency Sound: Warning Signs that Were Not Heard

    Science.gov (United States)

    James, Richard R.

    2012-01-01

    Industrial wind turbines are frequently thought of as benign. However, the literature is reporting adverse health effects associated with the implementation of industrial-scale wind developments. This article explores the historical evidence about what was known regarding infra and low-frequency sound from wind turbines and other noise sources…

  9. Wind model for low frequency power fluctuations in offshore wind farms

    DEFF Research Database (Denmark)

    Vigueras-Rodríguez, A.; Sørensen, Poul Ejnar; Cutululis, Nicolaos Antonio

    2010-01-01

    into an aggregated model which is used for estimating some electrical parameters as power ramps and reserves requirements, showing a quite good agreement between simulations and measurement. The comparison with measurements generally show that the inclusion of the correlation between low frequency components...

  10. Applications of a plane wave based room correction system for low frequencies using multiple loudspeakers

    DEFF Research Database (Denmark)

    Celestinos, Adrian; Nielsen, Sofus Birkedal

    2008-01-01

    System (CABS) produces uniform sound field at low frequencies. This is performed by utilizing loudspeakers at the front wall and extra loudspeakers at the opposite wall, processed to remove the rear-wall reflection of a rectangular room. Effectiveness of CABS on different room scenarios has been...

  11. Multiple sessions of low-frequency repetitive transcranial magnetic stimulation in focal hand dystonia

    DEFF Research Database (Denmark)

    Kimberley, Teresa Jacobson; Borich, Michael R; Arora, Sanjeev

    2013-01-01

    Purpose: The ability of low-frequency repetitive transcranial magnetic stimulation (rTMS) to enhance intracortical inhibition has motivated its use as a potential therapeutic intervention in focal hand dystonia (FHD). In this preliminary investigation, we assessed the physiologic and behavioral...

  12. Predictability and Diagnosis of Low Frequency Climate Processes in the Pacific, Final Technical Report

    Energy Technology Data Exchange (ETDEWEB)

    Niklas Schneider

    2009-06-17

    The report summarized recent findings with respect to Predictability and Diagnosis of Low Frequency Climate Processes in the Pacific, with focus on the dynamics of the Pacific Decadal Oscillation, oceanic adjustments and the coupled feedback in the western boundary current of the North and South Pacific, decadal dynamics of oceanic salinity, and tropical processes with emphasis on the Indonesian Throughflow.

  13. Extremely low-frequency magnetic field exposure, electrical shocks and risk of Parkinson's disease

    NARCIS (Netherlands)

    van der Mark, Marianne; Vermeulen, Roel; Nijssen, Peter C G; Mulleners, Wim M; Sas, Antonetta M G; van Laar, Teus; Kromhout, Hans; Huss, Anke

    2015-01-01

    PURPOSE: Previous studies did not provide strong evidence for an increased Parkinson's disease (PD) risk after exposure to extremely low-frequency magnetic fields (ELF-MF), but were limited in their scope to address other exposures related to the use of electricity such as electrical shocks. We eval

  14. Low-frequency signals produced by Northeast Atlantic killer whales (Orcinus orca).

    Science.gov (United States)

    Samarra, Filipa I P; Deecke, Volker B; Miller, Patrick J O

    2016-03-01

    Killer whale acoustic behavior has been extensively investigated; however, most studies have focused on pulsed calls and whistles. This study reports the production of low-frequency signals by killer whales at frequencies below 300 Hz. Recordings were made in Iceland and Norway when killer whales were observed feeding on herring and no other marine mammal species were nearby. Low-frequency sounds were identified in Iceland and ranged in duration between 0.14 and 2.77 s and in frequency between 50 and 270 Hz, well below the previously reported lower limit for killer whale tonal sounds of 500 Hz. Low-frequency sounds appeared to be produced close in time to tail slaps, which are indicative of feeding attempts, suggesting that these sounds may be related to a feeding context. However, their precise function is unknown, and they could be the by-product of a non-vocal behavior rather than a vocal signal deliberately produced by the whales. Although killer whales in Norway exhibit similar feeding behavior, this sound has not been detected in recordings from Norway to date. This study suggests that, like other delphinids, killer whales produce low-frequency sounds, but further studies will be required to understand whether similar sounds exist in other killer whale populations.

  15. Wind Turbine Acoustic Investigation: Infrasound and Low-Frequency Noise--A Case Study

    Science.gov (United States)

    Ambrose, Stephen E.; Rand, Robert W.; Krogh, Carmen M. E.

    2012-01-01

    Wind turbines produce sound that is capable of disturbing local residents and is reported to cause annoyance, sleep disturbance, and other health-related impacts. An acoustical study was conducted to investigate the presence of infrasonic and low-frequency noise emissions from wind turbines located in Falmouth, Massachusetts, USA. During the…

  16. Tuning Range Optimization of a Planar Inverted F Antenna for LTE Low Frequency Bands

    DEFF Research Database (Denmark)

    Barrio, Samantha Caporal Del; Pelosi, Mauro; Franek, Ondrej

    2011-01-01

    This paper presents a Planar Inverted F Antenna (PIFA) tuned with a fixed capacitor to the low frequency bands supported by the Long Term Evolution (LTE) technology. The tuning range is investigated and optimized with respect to the bandwidth and the efficiency of the resulting antenna. Simulations...

  17. Tuning Range Optimization of a Planar Inverted F Antenna for LTE Low Frequency Bands

    DEFF Research Database (Denmark)

    Barrio, Samantha Caporal Del; Pelosi, Mauro; Franek, Ondrej

    2011-01-01

    This paper presents a Planar Inverted F Antenna (PIFA) tuned with a fixed capacitor to the low frequency bands supported by the Long Term Evolution (LTE) technology. The tuning range is investigated and optimized with respect to the bandwidth and the efficiency of the resulting antenna. Simulatio...... and mock-ups are presented....

  18. FR II radio galaxies at low frequencies - I. Morphology, magnetic field strength and energetics

    NARCIS (Netherlands)

    Harwood, Jeremy J.; Croston, Judith H.; Intema, Huib T.; Stewart, Adam J.; Ineson, Judith; Hardcastle, Martin J.; Godfrey, Leith; Best, Philip; Brienza, Marisa; Heesen, Volker; Mahony, Elizabeth K.; Morganti, Raffaella; Murgia, Matteo; Orrú, Emanuela; Röttgering, Huub; Shulevski, Aleksandar; Wise, Michael W.

    2016-01-01

    Due to their steep spectra, low-frequency observations of Fanaroff-Riley type II (FR II) radio galaxies potentially provide key insights in to the morphology, energetics and spectrum of these powerful radio sources. However, limitations imposed by the previous generation of radio interferometers at

  19. Low-frequency variability of surface air temperature over the Barents Sea

    NARCIS (Netherlands)

    Linden, van der Eveline C.; Bintanja, Richard; Hazeleger, Wilco; Graversen, R.G.

    2016-01-01

    The predominant decadal to multidecadal variability in the Arctic region is a feature that is not yet well-understood. It is shown that the Barents Sea is a key region for Arctic-wide variability. This is an important topic because low-frequency changes in the ocean might lead to large variations

  20. The Effects of Visual Complexity for Japanese Kanji Processing with High and Low Frequencies

    Science.gov (United States)

    Tamaoka, Katsuo; Kiyama, Sachiko

    2013-01-01

    The present study investigated the effects of visual complexity for kanji processing by selecting target kanji from different stroke ranges of visually simple (2-6 strokes), medium (8-12 strokes), and complex (14-20 strokes) kanji with high and low frequencies. A kanji lexical decision task in Experiment 1 and a kanji naming task in Experiment 2…

  1. A barrier for low frequency noise from starting aircraft: comparison between numerical and scale model results

    NARCIS (Netherlands)

    Bosschaart, C.; Eisses, A.R.; Eerden, F.J.M. van der

    2010-01-01

    Amsterdam Airport Schiphol has organized a competition to design a noise mitigating measure along the 'Polderbaan' runway. Its main goal is to reduce the low frequency (LF) ground noise from starting aircraft. The winning concept is a flexible parabolic shaped noise barrier positioned relatively clo

  2. Whole-exome sequencing identifies rare and low-frequency coding variants associated with LDL cholesterol

    NARCIS (Netherlands)

    L.A. Lange (Leslie); Y. Hu (Youna); H. Zhang (He); C. Xue (Chenyi); E.M. Schmidt (Ellen); Z.-Z. Tang (Zheng-Zheng); C. Bizon (Chris); E.M. Lange (Ethan); G.D. Smith; E.H. Turner (Emily); Y. Jun (Yang); H.M. Kang (Hyun Min); G.M. Peloso (Gina); P. Auer (Paul); K.-P. Li (Kuo-Ping); J. Flannick (Jason); J. Zhang (Ji); C. Fuchsberger (Christian); K. Gaulton (Kyle); C.M. Lindgren (Cecilia); A. Locke (Adam); A.K. Manning (Alisa); X. Sim (Xueling); M.A. Rivas (Manuel); O.L. Holmen (Oddgeir); R.F. Gottesman (Rebecca); Y. Lu (Yingchang); D. Ruderfer (Douglas); E.A. Stahl (Eli); Q. Duan (Qing); Y. Li (Yun); P. Durda (Peter); S. Jiao (Shuo); A.J. Isaacs (Aaron); A. Hofman (Albert); J.C. Bis (Joshua); D.D. Correa; M.D. Griswold (Michael); M. Jakobsdottir (Margret); G.D. Smith; P.J. Schreiner (Pamela); M.F. Feitosa (Mary Furlan); Q. Zhang (Qunyuan); J.E. Huffman (Jennifer); S. Crosby; C.L. Wassel (Christina); R. Do (Ron); N. Franceschini (Nora); L.W. Martin (Lisa); J.G. Robinson (Jennifer); T.L. Assimes (Themistocles); D.R. Crosslin (David); E.A. Rosenthal (Elisabeth); M.Y. Tsai (Michael); M. Rieder (Mark); D.N. Farlow (Deborah); A.R. Folsom (Aaron); T. Lumley (Thomas); E.R. Fox (Ervin); C.S. Carlson (Christopher); U. Peters (Ulrike); R.D. Jackson (Rebecca); C.M. van Duijn (Cock); A.G. Uitterlinden (André); D. Levy (Daniel); J.I. Rotter (Jerome); H.A. Taylor (Herman); V. Gudnason (Vilmundur); D.S. Siscovick (David); M. Fornage (Myriam); I.B. Borecki (Ingrid); C. Hayward (Caroline); I. Rudan (Igor); Y.E. Chen (Y. Eugene); E.P. Bottinger (Erwin); R.J.F. Loos (Ruth); P. Sætrom (Pål); K. Hveem (Kristian); M. Boehnke (Michael); L. Groop (Leif); M.I. McCarthy (Mark); T. Meitinger (Thomas); C. Ballantyne (Christie); S.B. Gabriel (Stacey); C.J. O'Donnell (Christopher); W.S. Post (Wendy S.); K.E. North (Kari); A. Reiner (Alexander); E.A. Boerwinkle (Eric); B.M. Psaty (Bruce); D. Altshuler (David); S. Kathiresan (Sekar); D.Y. Lin (Dan); G.P. Jarvik (Gail); L.A. Cupples (Adrienne); C. Kooperberg (Charles); J.G. Wilson (James); D.A. Nickerson (Deborah); G.R. Abecasis (Gonçalo); S.S. Rich (Stephen); R.P. Tracy (Russell); C.J. Willer (Cristen)

    2014-01-01

    textabstractElevated low-density lipoprotein cholesterol (LDL-C) is a treatable, heritable risk factor for cardiovascular disease. Genome-wide association studies (GWASs) have identified 157 variants associated with lipid levels but are not well suited to assess the impact of rare and low-frequency

  3. Topology Optimization of Distributed Mass Dampers for Low-frequency Vibration Suppression

    DEFF Research Database (Denmark)

    Jensen, Jakob Søndergaard; Lazarov, Boyan Stefanov

    2007-01-01

    In this paper the method of topology optimization is used to find optimized parameter distributions for a multiple mass damper system with the purpose of minimizing the low-frequency steady-state response of a carrier structure. An effective density model that describes the steady-state effect...

  4. Coordinated observations using the world largest low-frequency radio telescopes and space misiions

    Science.gov (United States)

    Konovalenko, A. A.; Zarka, Ph.; Kolyadin, V. L.; Zakharenko, V. V.; Stepkin, S. V.; Panchenko, M.; Lecacheux, A.; Rucker, H. O.; Fischer, G.; Ulyanov, O. M.; Melnik, V. N.; Litvinenko, G. V.; Sidorchuk, M. A.; Bubnov, I. N.; Vasilyeva, Ya. Yu.; Bojko, A. I.; Shaposhnikov, V.; Mann, G.; Kalinichenko, N. N.; Falkovich, I. S.; Koval, A. A.; Mylostna, K.; Pylaev, O. S.; Shepelev, V. A.; Reznik, A. P.

    2013-09-01

    The positive possibilities of astrophysical objects studies(including the Solar system investigations) using coordinated observations with the largest existing and coming low frequency radio telescopes are shown. The observations of the Sun, Jupiter, Saturn, ant others with UTR-2, URAN, NDA radio telescopes, and WIND, Cassini and STEREO space missions at frequencies lower than 40 MHz have been carried out.

  5. Consideration of some factors affecting low-frequency fuselage noise transmission for propeller aircraft

    Science.gov (United States)

    Mixson, J. S.; Roussos, L. A.

    1986-01-01

    Possible reasons for disagreement between measured and predicted trends of sidewall noise transmission at low frequency are investigated using simplified analysis methods. An analytical model combining incident plane acoustic waves with an infinite flat panel is used to study the effects of sound incidence angle, plate structural properties, frequency, absorption, and the difference between noise reduction and transmission loss. Analysis shows that these factors have significant effects on noise transmission but they do not account for the differences between measured and predicted trends at low frequencies. An analytical model combining an infinite flat plate with a normally incident acoustic wave having exponentially decaying magnitude along one coordinate is used to study the effect of a localized source distribution such as is associated with propeller noise. Results show that the localization brings the predicted low-frequency trend of noise transmission into better agreement with measured propeller results. This effect is independent of low-frequency stiffness effects that have been previously reported to be associated with boundary conditions.

  6. On the influence of heat transport on low- frequency paramagnetic spin-Lattice relaxation experiments

    NARCIS (Netherlands)

    Flokstra, Jakob; Gerritsma, G.J.; Hartemink, G.A.; van der Marel, L.C.

    1974-01-01

    In low-frequency relaxation experiments on paramagnetic crystals, placed in liquid helium, often dispersion- and absorption curves are found, strongly deviating from those following from the thermodynamic theory of Casimir and Du Pré. For the relaxation time τabs, related to the maximum in the

  7. Rare and low-frequency variants in human common diseases and other complex traits.

    Science.gov (United States)

    Lettre, Guillaume

    2014-11-01

    In humans, most of the genetic variation is rare and often population-specific. Whereas the role of rare genetic variants in familial monogenic diseases is firmly established, we are only now starting to explore the contribution of this class of genetic variation to human common diseases and other complex traits. Such large-scale experiments are possible due to the development of next-generation DNA sequencing. Early findings suggested that rare and low-frequency coding variation might have a large effect on human phenotypes (eg, PCSK9 missense variants on low-density lipoprotein-cholesterol and coronary heart diseases). This observation sparked excitement in prognostic and diagnostic medicine, as well as in genetics-driven strategies to develop new drugs. In this review, I describe results and present initial conclusions regarding some of the recent rare and low-frequency variant discoveries. We can already assume that most phenotype-associated rare and low-frequency variants have modest-to-weak phenotypical effect. Thus, we will need large cohorts to identify them, as for common variants in genome-wide association studies. As we expand the list of associated rare and low-frequency variants, we can also better recognise the current limitations: we need to develop better statistical methods to optimally test association with rare variants, including non-coding variation, and to account for potential confounders such as population stratification.

  8. Waves of change: immunomodulation of the innate immune response by low frequency electromagnetic field exposure

    NARCIS (Netherlands)

    Golbach, L.A.

    2015-01-01

      In this thesis we investigated possible modulatory roles of low frequency electromagnetic fields (LF EMFs) exposure on the innate immune system. Recent decades have seen a huge increase in the use of electronic devices that nowadays enable us to communicate with distant family, enjoy music ev

  9. Low-frequency songs lose their potency in noisy urban conditions

    Science.gov (United States)

    Halfwerk, Wouter; Bot, Sander; Buikx, Jasper; van der Velde, Marco; Komdeur, Jan; ten Cate, Carel; Slabbekoorn, Hans

    2011-01-01

    Many animal species communicate with their mates through acoustic signals, but this communication seems to become a struggle in urbanized areas because of increasing anthropogenic noise levels. Several bird species have been reported to increase song frequency by which they reduce the masking impact of spectrally overlapping noise. However, it remains unclear whether such behavioral flexibility provides a sufficient solution to noisy urban conditions or whether there are hidden costs. Species may rely on low frequencies to attract and impress females, and the use of high frequencies may, therefore, come at the cost of reduced attractiveness. We studied the potential tradeoff between signal strength and signal detection in a successful urban bird species, the great tit (Parus major). We show that the use of low-frequency songs by males is related to female fertility as well as sexual fidelity. We experimentally show that urban noise conditions impair male–female communication and that signal efficiency depends on song frequency in the presence of noise. Our data reveal a response advantage for high-frequency songs during sexual signaling in noisy conditions, whereas low-frequency songs are likely to be preferred. These data are critical for our understanding of the impact of anthropogenic noise on wild-ranging birds, because they provide evidence for low-frequency songs being linked to reproductive success and to be affected by noise-dependent signal efficiency. PMID:21876157

  10. Considerations on low frequency high gradient cavities for muon capture and cooling

    Energy Technology Data Exchange (ETDEWEB)

    Spazzaro, B.; Tazzioli, F. [Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati, Rome (Italy)

    2001-01-01

    In this note are discussed some alternatives in the design of low frequency cavities for Muon capture and cooling in a Neutrino Factory. Both solutions with closed and open irises are considered. The comparison between the various solutions is based on dimensions and power per unit length, for a given accelerating gradient.

  11. The Growth and Decay of Low-Frequency Anomalies in a GCM.

    Science.gov (United States)

    Feldstein, Steven

    1998-02-01

    The temporal evolution of a regional-scale persistent low-frequency anomaly is examined with data from a 2100-day perpetual January general circulation model. The persistent episodes are determined with an objective analysis of the low-pass (>10 day) 350-mb streamfunction field that uses both pattern correlations and empirical orthogonal function (EOF) analysis.The composite evolution of each term in the streamfunction tendency equation is calculated relative to the onset day (the first day of the persistent episode). By projecting each term in the streamfunction tendency equation onto an EOF (the EOF is associated with a particular low-frequency anomaly), the contribution of these terms toward the tendency of the corresponding principal component can be obtained. It is found that the sum of the linear terms dominates during most of the growth and the decay of the low-frequency anomaly. The linear term that accounts for the growth and maintenance of the low-frequency anomaly is the interaction between the anomaly and the time-mean zonally asymmetric flow. After the anomaly attains sufficient amplitude, its decay is accomplished through the divergence term. For one phase of the EOF, it is found that the high-frequency transients prolong the anomaly, whereas in the other phase they do not.Implications of this study for examining monthly averaged anomalies are also discussed.

  12. Bistability and low-frequency fluctuations in semiconductor lasers with optical feedback: a theoretical analysis

    DEFF Research Database (Denmark)

    Mørk, Jesper; Tromborg, Bjarne; Christiansen, Peter Leth

    1988-01-01

    Near-threshold operation of a semiconductor laser exposed to moderate optical feedback may lead to low-frequency fluctuations. In the same region, a kink is observed in the light-current characteristic. Here it is demonstrated that these nonlinear phenomena are predicted by a noise driven multimode...

  13. Extremely low-frequency magnetic fields and survival from childhood acute lymphoblastic leukemia

    DEFF Research Database (Denmark)

    Schüz, J; Grell, K; Kinsey, S

    2012-01-01

    A previous US study reported poorer survival in children with acute lymphoblastic leukemia (ALL) exposed to extremely low-frequency magnetic fields (ELF-MF) above 0.3 μT, but based on small numbers. Data from 3073 cases of childhood ALL were pooled from prospective studies conducted in Canada...

  14. Low Frequency Noise Measurement and Analysis of Capacitive Micro-Accelerometers: Temperature Effect

    Science.gov (United States)

    Mohd-Yasin, Faisal; Nagel, David J.; Ong, D. S.; Korman, Can E.; Chuah, H. T.

    2008-06-01

    A noise measurements of micro-accelerometers were performed using a special measurement system. A common spectral behavior of noise is found, with 1/ f noise dominating at low frequencies and white thermal noise being the limiting factor at higher frequencies. A temperature dependent and an acceleration dependant of the noise are found in the accelerometers, in agreement and contract of the theories, respectively.

  15. S-shape spring sensor: Sensing specific low-frequency vibration by energy harvesting.

    Science.gov (United States)

    Zhang, Lan; Lu, Jian; Takei, Ryohei; Makimoto, Natsumi; Itoh, Toshihiro; Kobayashi, Takeshi

    2016-08-01

    We have developed a Si-based microelectromechanical systems sensor with high sensitivity for specific low-frequency vibration-sensing and energy-harvesting applications. The low-frequency vibration sensor contains a disk proof mass attached to two or three lead zirconate titanate (PZT) S-shape spring flexures. To obtain a faster and less expensive prototype, the design and optimization of the sensor structure are studied via finite-element method analysis. To validate the sensor structure to detect low-frequency vibration, the effects of geometrical dimensions, including the width and diameter of the S-shape spring of the proof mass, were analyzed and measured. The functional features, including the mechanical property and electrical performance of the vibration sensor, were evaluated. The results demonstrated that a very low resonant frequency of 0.2g can be typically achieved. Given a low-frequency vibration sensor with ideal performance and mass fabrication, many advanced civilian and industrial applications can be possibly realized.

  16. Dipole AlfvenVortex with Finite Ion Larmor Radius in a Low-Beta Plasma

    Institute of Scientific and Technical Information of China (English)

    WANG Xu-Yu; HE Xian-Tu; LIU Zhen-Xing; CAO Jin-Bin

    2000-01-01

    A set of nonlinear fluid equations which include the effects of ion gyroradius is derived to describe Alfven vortex. The correction of finite ion gyroradius to the Alfven vortex in the inertial region is much more significant than that in the kinetic region. The amplitude of the vortex is enhanced in both regions. The scale of the vortex in the kinetic region becomes larger whereas it becomes smaller in the inertial region.

  17. Existence of Weakly Damped Kinetic Alfven Eigenmodes in Reversed Shear Tokamak

    Energy Technology Data Exchange (ETDEWEB)

    N. N. Gorelenkov

    2008-08-12

    A kinetic theory of weakly damped Alfven Eigenmode (AE) solutions strongly interacting with the continuum is developed for tokamak plasmas with reversed magnetic shear. We show that the ideal MHD model is not sufficient for the eigenmode solutions if the standard causality condition bypass rule is applied. Finite Larmor radius effects are required, which introduce multiple kinetic subeigenmodes and collisionless radiative damping. The theory explains the existence of experimentally observed Alfvenic instabilities with frequencies sweeping down and reaching their minimum (bottom).

  18. Impact of visual repetition rate on intrinsic properties of low frequency fluctuations in the visual network.

    Directory of Open Access Journals (Sweden)

    Yi-Chia Li

    Full Text Available BACKGROUND: Visual processing network is one of the functional networks which have been reliably identified to consistently exist in human resting brains. In our work, we focused on this network and investigated the intrinsic properties of low frequency (0.01-0.08 Hz fluctuations (LFFs during changes of visual stimuli. There were two main questions to be discussed in this study: intrinsic properties of LFFs regarding (1 interactions between visual stimuli and resting-state; (2 impact of repetition rate of visual stimuli. METHODOLOGY/PRINCIPAL FINDINGS: We analyzed scanning sessions that contained rest and visual stimuli in various repetition rates with a novel method. The method included three numerical approaches involving ICA (Independent Component Analyses, fALFF (fractional Amplitude of Low Frequency Fluctuation, and Coherence, to respectively investigate the modulations of visual network pattern, low frequency fluctuation power, and interregional functional connectivity during changes of visual stimuli. We discovered when resting-state was replaced by visual stimuli, more areas were involved in visual processing, and both stronger low frequency fluctuations and higher interregional functional connectivity occurred in visual network. With changes of visual repetition rate, the number of areas which were involved in visual processing, low frequency fluctuation power, and interregional functional connectivity in this network were also modulated. CONCLUSIONS/SIGNIFICANCE: To combine the results of prior literatures and our discoveries, intrinsic properties of LFFs in visual network are altered not only by modulations of endogenous factors (eye-open or eye-closed condition; alcohol administration and disordered behaviors (early blind, but also exogenous sensory stimuli (visual stimuli with various repetition rates. It demonstrates that the intrinsic properties of LFFs are valuable to represent physiological states of human brains.

  19. Characteristics of low-frequency oscillation intensity of air-sea turbulent heat fluxes over the northwest Pacific

    Institute of Scientific and Technical Information of China (English)

    LI Gen; REN BaoHua; ZHENG JianOiu; WANG Jun

    2009-01-01

    Based on the daily turbulent heat fluxes and related meteorological variables dataeets (1985-2006) from Objectively Analyzed air-sea Fluxes (OAFlux) Project of Woods Hole Oceanographic Institution (WHOI), characteristics of low-frequency oscillation intensity of air-sea turbulent heat fluxes over the northwest Pacific are analyzed by linear perturbation method and correlation analysis. It can be concluded that: 1) the distribution of low-frequency oscillation intensity of latent heat flux (LHF) over the northwest Pacific is mainly affected by that of low-frequency oscillation intensity of anomalous air-eea humidity gradient (△q') as well as mean air-eea humidity gradient (△q), while the distribution of low-frequency oscillation Intensity of sensible heat flux (SHF) is mainly affected by that of low-frequency oscillation intensity of anomalous air-sea temperature gradient (△T'). 2) The low-frequency oscillation of turbulent heat fluxes over the northwest Pacific is the strongest in winter and the weakest in summer. And the seasonal transition of low-frequency oscillation intensity of LHF is jointly influenced by those of low-frequency oscillation intensity of △q', low-frequency oscillation intensity of anomalous wind speed (U'), △q and mean wind speed (U), while the seasonal transition of low-frequency oscillation intensity of SHF is mainly influenced by those of low-frequency oscillation Intensity of △T' and U. 3) Over the tropical west Pacific and sea areas north of 20ON, the low-frequency oscillation of LHF (SHF) is mainly influenced by atmospheric variables qa' (Ta') and U', indicating an oceanic response to overlying atmospheric forcing. In contrast, over the tropical eastern and central Pacific south of 20°N, qs' (Ts') also greatly influences the low-frequency oscillation of LHF (SHF).

  20. Global Structures of Alfven-Ballooning Modes in Magnetospheric Plasmas.

    Science.gov (United States)

    Vetoulis, Georgios

    1995-01-01

    The problem of radial localization of kinetically excited Alfven-type waves in the terrestial magnetosphere is examined using WKB approximations in the radial direction. These modes have been called drift Alfven ballooning modes (DABM) by CHEN and HASEGAWA, (1991)^1 and are the prime candidates to explain Pc4-Pc5 waves observed during storms. Pc4-5 type geomagnetic oscillations are long-lasting pulsations with large amplitudes and periods on the order of 500 sec. They are typically observed in the inner magnetosphere. Up to now, work on the theory of these pulsations has been done in one dimension, along the equilibrium magnetic field. In this dissertation, we include the effects of both parallel and perpendicular plasma inhomogeneities and investigate the issue of whether such a wave can be radially localized. In the first part, we formulate the theoretical approach neglecting the wave -particle resonances and using the one-fluid MHD limit. A local dispersion relationship is found on each flux surface of the equilibrium, and a global quantization condition is derived. To each flux surface correspond certain characteristic frequencies, (determined as eigenvalues of appropriate one-dimensional problems along the equilibrium magnetic field), and if the appropriate frequency matches the global mode frequency, then this surface is called resonant. In the picture developed here, the global mode is trapped at the outer side of a storm-time ring current by a steep pressure gradient. At the same time, energy from it tunnels through a barrier, and gets absorbed at its corresponding resonant flux surface, which in space physics terminology is called field line resonance. This energy absorption would lead to the damping of the mode, in the absence of an excitation mechanism. A strong dependence of the damping rate on the azimuthal wave number m is established, as well as on the equilibrium profile. First, it is found that the equilibrium pressure gradient has to be steeper

  1. Low-frequency blood pressure oscillations and inotrope treatment failure in premature infants.

    Science.gov (United States)

    Vesoulis, Zachary A; Hao, Jessica; McPherson, Christopher; El Ters, Nathalie M; Mathur, Amit M

    2017-07-01

    The underlying mechanism as to why some hypotensive preterm infants do not respond to inotropic medications remains unclear. For these infants, we hypothesize that impaired vasomotor function is a significant factor and is manifested through a decrease in low-frequency blood pressure variability across regulatory components of vascular tone. Infants born ≤28 wk estimated gestational age underwent prospective recording of mean arterial blood pressure for 72 h after birth. After error correction, root-mean-square spectral power was calculated for each valid 10-min data frame across each of four frequency bands (B1, 0.005-0.0095 Hz; B2, 0.0095-0.02 Hz; B3, 0.02-0.06 Hz; and B4, 0.06-0.16) corresponding to different components of vasomotion control. Forty infants (twenty-nine normotensive control and eleven inotrope-exposed) were included with a mean ± SD estimated gestational age of 25.2 ± 1.6 wk and birth weight 790 ± 211 g. 9.7/11.8 Million (82%) data points were error-free and used for analysis. Spectral power across all frequency bands increased with time, although the magnitude was 20% less in the inotrope-exposed infants. A statistically significant increase in spectral power in response to inotrope initiation was noted across all frequency bands. Infants with robust blood pressure response to inotropes had a greater increase compared with those who had limited or no blood pressure response. In this study, hypotensive infants who require inotropes have decreased low-frequency variability at baseline compared with normotensive infants, which increases after inotrope initiation. Low-frequency spectral power does not change for those with inotrope treatment failure, suggesting dysfunctional regulation of vascular tone as a potential mechanism of treatment failure.NEW & NOTEWORTHY In this study, we examine patterns of low-frequency oscillations in blood pressure variability across regulatory components of vascular tone in normotensive and

  2. Effects of low-frequency magnetic field on grain boundary segregation in horizontal direct chill casting of 2024 aluminum alloy

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    Effects of low frequency electromagnetic field on grain boundary segregation in horizontal direct chill (HDC)casting process was investigated experimentally. The grain boundary segregation and microstructures of the ingots,which manufactured by conventional HDC casting and low frequency electromagnetic HDC casting were compared.Results show that low frequency electromagnetic field significantly refines the microstructures and reduces grain boundary segregation. Decreasing electromagnetic frequency or increasing electromagnetic intensity has great effects in reducing grain boundary segregation. Meanwhile, the governing mechanisms were discussed.

  3. Low-Frequency Foam Insulator (LOFFI) Accelerometer Mount Characterization Results and Analysis for Phase I (FY2013)

    Science.gov (United States)

    2014-06-01

    Low-Frequency Foam Insulator (LOFFI) Accelerometer Mount Characterization Results and Analysis for Phase I (FY2013) by Andrew Drysdale...Proving Ground, MD 21005-5068 ARL-TR-6977 June 2014 Low-Frequency Foam Insulator (LOFFI) Accelerometer Mount Characterization Results...4. TITLE AND SUBTITLE Low-Frequency Foam Insulator (LOFFI) Accelerometer Mount Characterization Results and Analysis for Phase I (FY2013) 5a

  4. Association studies of low-frequency coding variants in nonsyndromic cleft lip with or without cleft palate

    DEFF Research Database (Denmark)

    Leslie, Elizabeth J; Carlson, Jenna C; Shaffer, John R

    2017-01-01

    Test (SKAT) and Combined Multivariate and Collapsing (CMC) method using two minor allele frequency cutoffs (1% and 5%). We found that a burden of low-frequency coding variants in N4BP2, CDSN, PRTG, and AHRR were associated with increased risk of NSCL/P. Low-frequency variants in other genes were...... associated with decreased risk of NSCL/P. These results demonstrate that low-frequency variants contribute to the genetic etiology of NSCL/P....

  5. Alfven waves in a cold plasma with curved magnetic fields. Final report, 1 January 1985-31 December 1986

    Energy Technology Data Exchange (ETDEWEB)

    Carrion, P.M.; Hasegawa, A.; Patton, W.; Prakash, M.

    1988-06-01

    A set of linearized magnetohydrodynamic equations was reduced to the reflectivity equation for the compressional magnetic perturbations in the framework of the Radoski model. It is shown that the reflection coeficient is a function of the inhomogeneities of the magnetic field, and the inhomogeneities of the Alfven velocity. An interesting property of the reflectivity equation is that, near Alfven resonant magnetic-force lines, this equation reduces to the curvature-free Budden equation. Near Alfven resonances, the curvature does not play a significant role and Budden's asymptotics in time can be applied to the wave field near the magnetic-force lines where the Alfven dispersion relation holds.

  6. Nonlinear coupling of kinetic Alfven waves with acoustic waves in a self-gravitating dusty plasma with adiabatic trapping

    Science.gov (United States)

    Sabeen, A.; Masood, W.; Qureshi, M. N. S.; Shah, H. A.

    2017-07-01

    In this paper, linear and nonlinear coupling of kinetic Alfven and acoustic waves has been studied in a dusty plasma in the presence of trapping and self-gravitation effects. In this regard, we have derived the linear dispersion relations for positively and negatively coupled dust kinetic Alfven-acoustic waves. Stability analysis of the coupled dust kinetic Alfven-acoustic wave has also been presented. The formation of solitary structures has been investigated following the Sagdeev potential approach by using the two-potential theory. Numerical results show that the solitary structures can be obtained only for sub-Alfvenic regimes in the scenario of space plasmas.

  7. A mixed method for measuring low-frequency acoustic properties of macromolecular materials

    Institute of Scientific and Technical Information of China (English)

    LIU; Hongwei; YAO; Lei; ZHAO; Hong; ZHANG; Jichuan; XUE; Zhaohong

    2006-01-01

    A mixed method for measuring low-frequency acoustic properties of macromolecular materials is presented.The dynamic mechanical parameters of materials are first measured by using Dynamic Mechanical Thermal Apparatus(DMTA) at low frequencies,usually less than 100 Hz; then based on the Principles of Time-Temperature Super position (TTS),these parameters are extended to the frequency range that acousticians are concerned about,usually from hundreds to thousands of hertz; finally the extended dynamic mechanical parameters are transformed into acoustic parameters with the help of acoustic measurement and inverse analysis.To test the feasibility and accuracy,we measure a kind of rubber sample in DMTA and acquire the basic acoustic parameters of the sample by using this method.While applying the basic parameters to calculating characteristics of the sample in acoustic pipe,a reasonable agreement of sound absorption coefficients is obtained between the calculations and measurements in the acoustic pipe.

  8. Towards noise engineering: Recent insights in low-frequency excess flux noise of superconducting quantum devices

    Science.gov (United States)

    Kempf, Sebastian; Ferring, Anna; Enss, Christian

    2016-10-01

    The comprehensive analysis of low-frequency excess flux noise both in terms of magnetic flux noise S Φ , 1 / f and energy sensitivity ɛ1/f of 84 superconducting quantum devices studied at temperatures below 1 K reveals a universal behavior. When analyzing data in terms of ɛ1/f, we find that noise spectra of independent devices cross each other all at certain crossing frequencies fc. Besides this main result of our paper, we further show that superconducting quantum interference device (SQUID) arrays systematically feature higher noise exponents than single SQUIDs and give evidence for a material and device type dependence of low-frequency excess flux noise. The latter results facilitate to engineer the shape of magnetic flux noise spectra and thus to experimentally modify key properties such as coherence or measurement times of superconducting quantum devices.

  9. Effect of low frequency noise on the evolution of the emittance and halo population

    CERN Document Server

    Fitterer, Miriam; Antoniou, Fanouria; Bravin, Enrico; Bruce, Roderik; Fartoukh, Stephane; Fuchsberger, Kajetan; Hofle, Wolfgang; Gasior, Marek; Jaussi, Michael; Jacquet, Delphine; Kotzian, Gerd; Olexa, Jakub; Papadopoulou, Parthena Stefania; Papotti, Giulia; Papaphilippou, Yannis; Redaelli, Stefano; Salvachua Ferrando, Belen Maria; Stancari, Giulio; Trad, Georges; Valuch, Daniel; Valentino, Gianluca; Wagner, Joschka; Wenninger, Jorg; CERN. Geneva. ATS Department

    2016-01-01

    For the High Luminosity upgrade the β* in IR1 and IR5 will be further reduced compared to the current LHC. As the β* decreases the β-functions in the inner triplet (IT) increase resulting in a higher sensitivity of the HL-LHC to ground motion in the IT region or to increases of the low frequency noise. Noise can in general lead to emittance growth and higher halo population and diffusion rate. However, it is usually assumed in the literature that only frequencies close to the betatron frequencies and sidebands have an effect on the emittance and tail population. To test this theory, an MD was carried out to observe if also low frequency noise can lead to emittance growth and stronger halo population and diffusion.

  10. Fractal EEG analysis with Higuchi's algorithm of low-frequency noise exposition on humans

    Science.gov (United States)

    Panuszka, Ryszard; Damijan, Zbigniew; Kasprzak, Cezary

    2004-05-01

    Authors used methods based on fractal analysis of EEG signal to assess the influence of low-frequency sound field on the human brain electro-potentials. The relations between LFN (low-frequency noise) and change in fractal dimension EEG signal were measured with stimulations tones. Three types of LFN stimuli were presented; each specified dominant frequency and sound-pressure levels (7 Hz at 120 dB, 18 Hz at 120 dB, and 40 Hz at 110 dB). Standard EEG signal was recorded before, during, and after subject's exposure for 35 min. LFN. Applied to the analysis fractal dimension of EEG-signal Higuchis algorithm. Experiments show LFN influence on complexity of EEG-signal with calculated Higuchi's algorithm. Observed increase of mean value of Higuchi's fractal dimension during exposition to LFN.

  11. A new method for calculation of low-frequency coupling impedance

    Energy Technology Data Exchange (ETDEWEB)

    Kurennoy, S.S.; Stupakov, G.V.

    1993-05-01

    In high-energy proton accelerators and storage rings the bunch length is typically at least a few times larger than the radius of the vacuum chamber. For example, the SSC will have an rms bunch length above 6 cm and a beam-pipe radius below 2 cm. The main concern for beam stability in such a machine is the low-frequency impedance, i.e., the coupling impedance at frequencies wen below the cut-off frequency of the vacuum chamber. In the present paper we develop a new analytical approach for calculation of the low-frequency impedance of axisymmetric structures that allows us to give quick and reliable estimates of contributions to the impedance from various chamber discontinuities. Simple formulae for the longitudinal impedance of some typical discontinuities are obtained.

  12. Low Frequency Carbon Radio Recombination Lines II: The Diffuse Interstellar Medium

    CERN Document Server

    Salgado, F; Oonk, J B R; Salas, P; Toribio, M C; Rottgering, H J A; Tielens, A G G M

    2016-01-01

    In the second paper of the series, we have modeled low frequency carbon radio recombination lines (CRRL) from the interstellar medium. Anticipating the LOw Frequency ARray (LOFAR) survey of Galactic CRRLs, we focus our study on the physical conditions of the diffuse cold neutral medium (CNM). We have used the improved departure coefficients computed in the first paper of the series to calculate line-to-continuum ratios. The results show that the line width and integrated optical depths of CRRL are sensitive probes of the electron density, gas temperature, and the emission measure of the cloud. Furthermore, the ratio of CRRL to the [CII] at 158 $\\mu$m line is a strong function of the temperature and density of diffuse clouds. Guided by our calculations, we analyze CRRL observations and illustrate their use with data from the literature.

  13. Low-frequency features of the ultrasound echo from an adhesively bonded layer-substrate structure

    Institute of Scientific and Technical Information of China (English)

    WANG Xiaomin; LI Mingxuan; MAO Jie; LIAN Guoxuan

    2005-01-01

    The low-frequency features of the ultrasound reflection spectra from the structure of a single layer on a substrate bonded by a thin adhesive layer are theoretically studied; the low-frequency here means the frequency of the interrogating ultrasonic wave is less than the quart-wavelength resonance frequency of the adhesive layer. The possibility of the inversion of the thickness and the evaluation of the cohesion strength of the adhesive layer from the resonance frequency shifts of the layered system is indicated. An analytic solution to the nonlinear equation satisfied by the resonance frequency is presented by Taylor expansion method showing satisfactory agreement with the numerical results by Newton iterative method. The results indicate larger range for application than the traditional spring model for the thin adhesive layer. In a much lower frequency range the thin adhesive layer may be regarded to be a spring.

  14. Ultra-low-frequency wave-driven diffusion of radiation belt relativistic electrons.

    Science.gov (United States)

    Su, Zhenpeng; Zhu, Hui; Xiao, Fuliang; Zong, Q-G; Zhou, X-Z; Zheng, Huinan; Wang, Yuming; Wang, Shui; Hao, Y-X; Gao, Zhonglei; He, Zhaoguo; Baker, D N; Spence, H E; Reeves, G D; Blake, J B; Wygant, J R

    2015-12-22

    Van Allen radiation belts are typically two zones of energetic particles encircling the Earth separated by the slot region. How the outer radiation belt electrons are accelerated to relativistic energies remains an unanswered question. Recent studies have presented compelling evidence for the local acceleration by very-low-frequency (VLF) chorus waves. However, there has been a competing theory to the local acceleration, radial diffusion by ultra-low-frequency (ULF) waves, whose importance has not yet been determined definitively. Here we report a unique radiation belt event with intense ULF waves but no detectable VLF chorus waves. Our results demonstrate that the ULF waves moved the inner edge of the outer radiation belt earthward 0.3 Earth radii and enhanced the relativistic electron fluxes by up to one order of magnitude near the slot region within about 10 h, providing strong evidence for the radial diffusion of radiation belt relativistic electrons.

  15. AN ALTERNATIVE APPROACH TO LOW FREQUENCY RF ACCELERATORS AND POWER SOURCES.

    Energy Technology Data Exchange (ETDEWEB)

    ZHAO, Y.

    2001-06-18

    The Muon Collider and Neutrino Factory projects require low frequency rf cavities because the size and emittance of the muon beam is much larger than is usual for electron or proton beams. The range of 30 MHz to 200 MHz is of special interest. However, the size of an accelerator with low frequency will be impractically large if it is simply scaled up from usual designs. In addition, to get very high peak power in this range is difficult. Presented in this paper is an alternative structure that employs a quasi-lumped inductance that can significantly reduce the transverse size while keeping high gradient. Also addressed is a power compression scheme with a thyratron. This gives a possible solution to provide very high peak power.

  16. Low-frequency vibration isolation in sandwich plates by piezoelectric shunting arrays

    Science.gov (United States)

    Chen, Shengbing; Wang, Gang; Song, Yubao

    2016-12-01

    Piezoelectric shunting arrays are proposed to isolate low-frequency vibrations transmitted in sandwich plates. The performance is characterized through application of finite element method. The numerical result shows that a complete band gap, whose width is about 20 Hz, is produced in the desired low-frequency ranges. The band gap is induced by local resonances of the shunting circuits, whose location is strongly related to the inductance, while the resistance can broaden the band gap to some extent. Vibration experiments are conducted on a 1200 × 1000 × 15 mm aluminum honeycomb plate with two arrays of 5 × 5 shunted piezoelectric patches bonded on the surface panels. Significant attenuation is found in the experimental results, which agree well with the theoretical predictions. Consequently, the proposed idea is feasible and effective.

  17. Measurement of low-frequency ultrasonic wave in water using an acoustic fiber sensor.

    Science.gov (United States)

    Sakoda, Tatsuya; Sonoda, Yoshito

    2006-04-01

    An acoustic fiber sensor for measurement of ultrasonic waves, which used the approximate Raman-Nath diffraction effect where light diffraction waves were generated in an optical fiber by strain due to the ultrasonic waves, was proposed and examined. In order to characterize the acoustic fiber sensor as a basic study, measurements of low-frequency ultrasonic waves in water were examined using a step index fiber operating as a detection sensor. The results showed that characteristics of detected signals agreed with the theoretical prediction based on Fraunhofer diffraction. This indicates that our proposed fiber sensor can be used for the detection of low-frequency ultrasonic waves as well as the transmission of light diffraction signals.

  18. Low-Frequency Volatility in China’s Gold Futures Market and Its Macroeconomic Determinants

    Directory of Open Access Journals (Sweden)

    Song Liu

    2015-01-01

    Full Text Available We extract low- and high-frequency volatility from China’s Shanghai gold futures market using an asymmetric Spline-GARCH (ASP-GARCH model. We then regress monthly low-frequency volatility on selected monthly macroeconomic indicators to study the impact of macroeconomy on gold futures market and to test for excess volatility. Our main result is volatility in China’s Shanghai gold futures market resulting from both macroeconomic fluctuations and investor behaviour. Chinese Consumer Price Index Volatility and US dollar volatility are the two main determinants of low-frequency gold volatility. We also find significant evidence of excess volatility, which can in part be explained in terms of loss-aversive investor behaviour.

  19. Damping of Inter-Area Low Frequency Oscillation Using an Adaptive Wide-Area Damping Controller

    DEFF Research Database (Denmark)

    Yao, Wei; Jiang, L.; Fang, Jiakun

    2013-01-01

    This paper presents an adaptive wide-area damping controller (WADC) based on generalized predictive control (GPC) and model identification for damping the inter-area low frequency oscillations in large-scale inter-connected power system. A recursive least-squares algorithm (RLSA) with a varying...... forgetting factor is applied to identify online the reduced-order linearlized model which contains dominant inter-area low frequency oscillations. Based on this linearlized model, the generalized predictive control scheme considering control output constraints is employed to obtain the optimal control signal...... in each sampling interval. Case studies are undertaken on a two-area fourmachine power system and the New England 10-machine 39-bus power system, respectively. Simulation results show that the proposed adaptive WADC not only can damp the inter-area oscillations effectively under a wide range of operation...

  20. An approach to global equalisation in a rectangular room at low frequencies

    DEFF Research Database (Denmark)

    Orozco, Arturo

    1999-01-01

    The motivation of this study is the fact that sound reproduced in a room undergoes a spectral colouration, which is undesirable. This effect is particularly severe at low frequencies in small enclosures.A theoretical study based on computer simulations is presented. The listening area is a contin......The motivation of this study is the fact that sound reproduced in a room undergoes a spectral colouration, which is undesirable. This effect is particularly severe at low frequencies in small enclosures.A theoretical study based on computer simulations is presented. The listening area...... domain. Modelling delay is used in the time domain to obtain the optimal values of the control filter coefficients in the least-square sense. The sound field can be estimated with sensors placed closed to the walls and the ceiling....

  1. Low-frequency 1/f fluctuations in hydrodynamic and magnetohydrodynamic turbulence.

    Science.gov (United States)

    Dmitruk, Pablo; Matthaeus, W H

    2007-09-01

    We investigate the occurrence of 1/f spectra of low-frequency fluctuations in numerical simulations of three-dimensional hydrodynamic and magnetohydrodynamic turbulence driven by a random forcing with a controlled correlation time. A range of one decade of 1/f spectrum is observed when a strong background magnetic field is present. The frequency spectra of individual Fourier modes is also analyzed and it is observed that the 1/f range is present in the largest available wavelength mode for the magnetohydrodynamic simulations with and without a background magnetic field and it is not observed (or is less clear) for the hydrodynamic case. The presence of 1/f spectra of low-frequency fluctuations is also analyzed for two-dimensional magnetohydrodynamic and hydrodynamic turbulence simulations and it is observed in both cases. The origin of these long period fluctuations is discussed.

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

    Directory of Open Access Journals (Sweden)

    John G. Baker

    2013-09-01

    Full Text Available 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.

  3. Health risks associated with residential exposure to extremely low frequency electromagnetic radiation.

    Science.gov (United States)

    Lamarine, R J; Narad, R A

    1992-10-01

    Extremely low frequency electromagnetic radiation has received considerable attention recently as a possible threat to the health of persons living near high tension electric power lines, distribution substations, and even in close proximity to common household electric appliances. Results of epidemiological and laboratory research are examined to assess risks associated with magnetic fields generated by extremely low frequency electromagnetic sources. Health risks associated with such fields include a wide variety of ills ranging from disruption of normal circadian rhythms to childhood cancers. Risk assessment has been particularly difficult to determine in light of an ostensible lack of a dose-response relationship. Current media sensation fueled in part by an equivocal position adopted by the United States Environmental Protection Agency has contributed to the controversy. Recommendations for prudent avoidance of possible dangers are presented along with policy implications concerning health risks associated with magnetic fields.

  4. MODELING AND EXPERIMENTAL RESEARCH OF FOUR-STRAND LOW-FREQUENCY ELECTROMAGNETIC CASTING ALUMINUM ALLOY

    Institute of Scientific and Technical Information of China (English)

    J.C. Li; B.F. Wang; J.Z. Cui

    2007-01-01

    With the aid of ANSYS software, the effect of different mould external part materials on magnetic flux density in the aluminum melt and magnetic field interaction of four coils applied with same currents were investigated. Calculating results showed that magnetic flux density in the aluminum melt was greatly improved and the magnetic field interaction among different coils was decreased when external part of mould is made of soft magnetic material. Based on the finding, a four-strand low-frequency electromagnetic casting 6063 aluminum alloy experiment was carried out in the laboratory. The experiment showed that the surface of the billet was smooth and had no exudations and cold shuts, the as-cast microstructures were fine, uniform, equiaxed, net-globular or globular under low-frequency electromagnetic field. The microstructure becomes finer with increased current value.

  5. Suppression of low-frequency charge noise in gates-defined GaAs quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    You, Jie; Li, Hai-Ou, E-mail: haiouli@ustc.edu.cn, E-mail: gpguo@ustc.edu.cn; Wang, Ke; Cao, Gang; Song, Xiang-Xiang; Xiao, Ming; Guo, Guo-Ping, E-mail: haiouli@ustc.edu.cn, E-mail: gpguo@ustc.edu.cn [Key Laboratory of Quantum Information, Chinese Academy of Sciences, University of Science and Technology of China, Hefei, Anhui 230026 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2015-12-07

    To reduce the charge noise of a modulation-doped GaAs/AlGaAs quantum dot, we have fabricated shallow-etched GaAs/AlGaAs quantum dots using the wet-etching method to study the effects of two-dimensional electron gas (2DEG) underneath the metallic gates. The low-frequency 1/f noise in the Coulomb blockade region of the shallow-etched quantum dot is compared with a non-etched quantum dot on the same wafer. The average values of the gate noise are approximately 0.5 μeV in the shallow-etched quantum dot and 3 μeV in the regular quantum dot. Our results show the quantum dot low-frequency charge noise can be suppressed by the removal of the 2DEG underneath the metallic gates, which provides an architecture for noise reduction.

  6. An oscillation phenomenon of low frequency reverberation in the shallow water and its physical explanation

    Institute of Scientific and Technical Information of China (English)

    LI Fenghua; LIU Jianjun; LI Zhenglin; ZHANG Renhe

    2005-01-01

    An oscillation phenomenon of the low frequency reverberation intensity was observed in several shallow water reverberation experiments. This phenomenon cannot be explained by the widely used incoherent reverberation theory. In this paper, to explain the observed oscillation phenomenon, a normal mode based coherent reverberation theory is presented. The theoretical analysis and numerical results show that modal interference can cause the regular oscillation phenomenon of the low frequency reverberation intensity, and the oscillation frequency is determined by the normal mode eigen-values. A new method to estimate the bottom sound speed based on the oscillation frequency of reverberation intensity was presented in this paper. The experimental results at three different sites indicate that the bottom sound speed estimated from the oscillation frequency of reverberation intensity agrees with that inverted from Matched Field Processing (MFP) well.

  7. Analytical Method for Reduction of Residual Stress Using Low Frequency and Ultrasonic Vibrations

    Science.gov (United States)

    Aoki, Shigeru; Kurita, Katsumi; Koshimizu, Shigeomi; Nishimura, Tadashi; Hiroi, Tetsumaro; Hirai, Seiji

    Welding is widely used for construction of many structures. It is well known that residual stress is generated near the bead because of locally given heat. Tensile residual stress on the surface degrades fatigue strength. On the other hand, welding is used for repair of mold and die. In this case, reduction of residual stress is required because of protection from crack of welded part in mold and die. In this paper, a new method for reduction of residual stress of welded joint is proposed for repair welding of mold and die. In this method, low frequency and ultrasonic vibrations are used during welding. Thick plates are used as specimens of mold and die. Residual stresses are reduced when low frequency and ultrasonic vibrations are used during welding. Experimental results are examined by simulation method using an analytical model. One mass model considering plastic deformation is used as an analytical model. Experimental results are demonstrated by simulation method.

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

    CERN Document Server

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

    2012-01-01

    We review the tests of general relativity that will become possible with space-based gravitational-wave detectors operating in the ~0.01mHz - 1Hz low-frequency band. The fundamental aspects of gravitation that can be tested include the presence of additional gravitational fields other than the metric; the number and tensorial nature of gravitational-wave polarization states; the velocity of propagation of gravitational waves; the binding energy and gravitational-wave radiation of binaries, and therefore the time evolution of binary inspirals; the strength and shape of the waves emitted from binary mergers and ringdowns; the true nature of astrophysical black holes; and much more. The strength of this science alone calls for the swift implementation of a space-based detector; the remarkable richness of astrophysics, astronomy, and cosmology in the low-frequency gravitational-wave band make the case even stronger.

  9. Ultra-low-frequency dust-electromagnetic modes in self-gravitating magnetized dusty plasmas

    Indian Academy of Sciences (India)

    A K Banerjee; M N Alam; A A Mamun

    2001-05-01

    Obliquely propagating ultra-low-frequency dust-electromagnetic waves in a self-gravitating, warm, magnetized, two fluid dusty plasma system have been investigated. Two special cases, namely, dust-Alfvén mode propagating parallel to the external magnetic field and dust-magnetosonic mode propagating perpendicular to the external magnetic field have also been considered. It has been shown that effects of self-gravitational field, dust fluid temperature, and obliqueness significantly modify the dispersion properties of these ultra-low-frequency dust-electromagnetic modes. It is also found that in parallel propagating dust-Alfvén mode these effects play no role, but in obliquely propagating dust-Alfvén mode or perpendicular propagating dust-magnetosonic mode the effect of self-gravitational field plays destabilizing role whereas the effect of dust/ion fluid temperature plays stabilizing role.

  10. Thickness Measurement of a Film on a Substrate by Low-Frequency Ultrasound

    Institute of Scientific and Technical Information of China (English)

    LI Ming-Xuan; WANG Xiao-Min; MAO Jie

    2004-01-01

    @@ We describe a new simple technique for the low-frequency ultrasonic thickness measurement of an air-backed soft thin layer attached on a hard substrate of finite thickness through the frequency-shifts of the substrate resonances by the substrate-side insonification. A plane compressive wave impinging normally on the substrate surface from a liquid is studied. Low frequency here means an interrogating acoustical wave frequency of less than half of coating to the substrate. Equations for the frequency-shifts are derived and solved by the Newton iterative method and the Taylor expansion method, respectively, indicating satisfactory agreement within the range of interest of thickness ratio of the thin layer to the substrate for a polymer-aluminium structure. An experimental setup is constructed to verify the validity of the technique.

  11. Direct CFD Predictions of Low Frequency Sounds Generated by a Helicopter Main Rotor

    Science.gov (United States)

    Sim, Ben W.; Potsdam, Mark A.; Conner, Dave A.; Conner, Dave A.; Watts, Michael E.

    2010-01-01

    The use of CFD to directly predict helicopter main rotor noise is shown to be quite promising as an alternative mean for low frequency source noise evaluation. Results using existing state-of-the-art grid structures and finite-difference schemes demonstrated that small perturbation pressures, associated with acoustics radiation, can be extracted with some degree of fidelity. Accuracy of the predictions are demonstrated via comparing to predictions from conventional acoustic analogy-based models, and with measurements obtained from wind tunnel and flight tests for the MD-902 helicopter at several operating conditions. Findings show that the direct CFD approach is quite successfully in yielding low frequency results due to thickness and steady loading noise mechanisms. Mid-to-high frequency contents, due to blade-vortex interactions, are not predicted due to CFD modeling and grid constraints.

  12. The Response of Long-Span Bridges to Low Frequency, Near-Fault Earthquake Ground Motions

    Energy Technology Data Exchange (ETDEWEB)

    McCallen, David; Astaneh-Asl, A.; Larsen, S.C.; Hutchings, Larry

    2009-02-27

    Historical seismic hazard characterizations did not include earthquake ground motion waveforms at frequencies below approximately 0.2 Hz (5 seconds period). This resulted from limitations in early strong motion instrumentation and signal processing techniques, a lack of measurements in the near-field of major earthquakes and therefore no observational awareness, and a delayed understanding in the engineering community of the potential significance of these types of motions. In recent years, there is a growing recognition of the relevance of near-fault, low frequency motions, particularly for long-period structures such as large bridges. This paper describes a computationally based study of the effects of low frequency (long-period) near-fault motions on long-span bridge response. The importance of inclusion of these types of motions for long span cable supported bridges is demonstrated using actual measured broad-band, near-fault motions from large earthquakes.

  13. Low frequency sound reproduction in irregular rooms using CABS (Control Acoustic Bass System)

    DEFF Research Database (Denmark)

    Celestinos, Adrian; Nielsen, Sofus Birkedal

    2011-01-01

    loudspeakers well positioned at the end of the room a virtual array is formed propagating plane waves along the length of the room in one direction. This will correct the sound field distribution in the room. When plane wave arrives to the end wall two more loudspeakers have to be placed connected......Early investigations on low frequency sound reproduction in rectangular rooms using CABS (Controlled Acoustic Bass System) have shown good results on simulations and measurements in real rooms. CABS takes the advantage of having a rectangular room with parallel walls. By using two low frequency...... with the same signal in counter phase and with a delay corresponding to approximately the length of the room. This is to cancel the reflection and maintain the plane wave propagating along the room. Real life rooms are not necessary rectangular and can be of different shapes. In this paper simulations...

  14. Multichannel Recorder for Low Frequency Signals: Application of Oscilloscope as Integrated Mobile Service for a Smartphone

    Directory of Open Access Journals (Sweden)

    Michal Kochlan

    2016-01-01

    Full Text Available Data acquisition and processing are well known for some time. Many applications use powerful hardware to acquire, process, and visualize signal waveforms. But there are some applications that do not have to perform high resolution signal acquisition and process large amount of data, for example, low frequency applications of embedded design and applications for remote power grid monitoring. The paper describes special system for low frequency signal data sample acquisition, processing, and visualization implemented as a service on Android-based smart device. The service makes smart device functioning as an oscilloscope or arbitrary waveform generator which is accessible remotely through Bluetooth. The design respects low power consumption requirements, simplicity, and user friendliness in application design. Application scenario was implemented as wireless data acquisition system for power grid monitoring.

  15. Low-frequency suppression of random-telegraph-noise spectra in high-temperature superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Ashkenazy, V.D. (Department of Physics, Bar-Ilan University, 52100, Ramat Gan (Israel)); Jung, G. (Department of Physics, Ben Gurion University of the Negev, 84105 Beer-Sheva (Israel) Instytut Fizuki, Polish Academy of Sciences, 02668 Warszawa (Poland)); Khalfin, I.B. (Department of Physics, Bar-Ilan University, 52100, Ramat Gan (Israel)); Shapiro, B.Y. (Jack and Pearl Resnik Institute of Advanced Technology, Bar-Ilan University, 52100, Ramat Gan (Israel) Department of Physics, Bar-Ilan University, 52100, Ramat Gan (Israel))

    1995-01-01

    Interaction of the random-telegraph-noise signals with pinned Abrikosov vortices in granular high-temperature superconductors is investigated. It is shown that the low-frequency part of random-noise spectra is suppressed due to interaction of Abrikosov vortices with pinning centers at low magnetic fields and/or due to mutual interactions of vortices in an Abrikosov lattice at high magnetic fields. Values of characteristic frequencies below which spectra are suppressed are evaluated for various experimental configurations including a typical experimental thin-film strip geometry. It is shown that characteristic frequencies and the functional dependence of the low-frequency part of the noise spectra strongly depend on the external magnetic field.

  16. Low-frequency noise characterization of a magnetic field monitoring system using an anisotropic magnetoresistance

    CERN Document Server

    Mateos, I; Lobo, A

    2016-01-01

    A detailed study about magnetic sensing techniques based on anisotropic magnetoresistive sensors shows that the technology is suitable for low-frequency space applications like the eLISA mission. Low noise magnetic measurements at the sub-millihertz frequencies were taken by using different electronic noise reduction techniques in the signal conditioning circuit. We found that conventional modulation techniques reversing the sensor bridge excitation do not reduce the potential $1/f$ noise of the magnetoresistors, so alternative methods such as flipping and electro-magnetic feedback are necessary. In addition, a low-frequency noise analysis of the signal conditioning circuits has been performed in order to identify and minimize the different main contributions from the overall noise. The results for chip-scale magnetoresistances exhibit similar noise along the eLISA bandwidth ($0.1\\,{\\rm mHz}-1\\,{\\rm Hz}$) to the noise measured by means of the voluminous fluxgate magnetometers used in its precursor mission, kn...

  17. An Extraction Method of Weak Low-Frequency Magnetic Communication Signals Based on Multisensor

    Directory of Open Access Journals (Sweden)

    Chao Huang

    2015-01-01

    Full Text Available It is a technical challenge to effectively remove the influence of magnetic noise from the vicinity of the receiving sensors on low-frequency magnetic communication. The traditional denoising methods are difficult to extract high-quality original signals under the condition of low SNR (the signal-to-noise ratio. In this paper, we analyze the numerical characteristics of the low-frequency magnetic field and propose the algorithms of the fast optimization of blind source separation (FOBSS and the frequency-domain correlation extraction (FDCE. FOBSS is based on blind source separation (BSS. Signal extraction of low SNR can be implemented through FOBSS and FDCE. This signal extraction method is verified in multiple field experiments which can remove the magnetic noise by about 25 dB or more.

  18. Low frequency sound field control for loudspeakers in rectangular rooms using CABS (Controlled Acoustical Bass System)

    DEFF Research Database (Denmark)

    Nielsen, Sofus Birkedal; Celestinos, Adrian

    2010-01-01

    . As sound propagates in time, it seems natural that the problems can best be analyzed and solved in the time domain. A time based room correction system named CABS (Controlled Acoustical Bass System) has been developed for sound reproduction in rectangular listening rooms. It can control the sound...... distribution in the room at low frequencies by using multiple loudspeakers together with an optimal placement of the loudspeakers.  At low frequencies CABS will create a plane wave from the front wall loudspeakers which will be absorbed by additional loudspeakers at the rear wall giving an almost homogeneous...... sound field in the whole room, and short impulse response.  In a standard listening room (180 m3) only 4 loudspeakers are needed, 2 more than a traditional stereo setup. CABS is controlled by a developed DSP system. The time based approached might help with the understanding of sound field control...

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

    Science.gov (United States)

    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.

  20. Characteristics of Large Low-frequency Debris Flow Hazards and Mitigation Strategies

    Institute of Scientific and Technical Information of China (English)

    WANG Shige

    2005-01-01

    A low-frequency debris flow took place in the north coastal range of Venezuela on Dec. 16, 1999,and scientists all over the world paid attention to this catastrophe. Four characteristics of low-frequency debris hazard are discussed: long return period and extreme catastrophe, special rare triggering factors,difficulty in distinguishing and a series of small hazards subsequent to the catastrophe. Different measures, such as preventing, forecast - warning,engineering, can be used for mitigating and controlling the catastrophe. In engineering practice, it is a key that large silt-trap dams are used to control rare large debris flow. A kind of low dam with cheap cost can be used to replace high dam in developing countries. A planning for controlling debris flow hazard in Cerro Grande stream of Venezuela is presented at the end of this paper.

  1. Evolution of a low frequency QPO during the 2000 outburst of XTE J1550-564

    CERN Document Server

    Rodríguez, J; Kalemci, E; Tomsick, J A; Tagger, M

    2002-01-01

    We follow the evolution of a low frequency QPO during the 2000 outburst of the microquasar XTE J1550-564, which was found to be present in the PCA energy range (2-65 keV) in 19 of 43 observations. The frequency of the QPO varies from 0.1 Hz to 6 Hz, and appears to follow the evolution of the soft X-ray flux. If we assume the soft X-rays represent the behavior of an accretion disk, the relation indicates that this low frequency QPO is linked to the accretion disk. We show that the non-trivial relation between the QPO frequency and the soft flux may be as expected from the Accretion Ejection Instability (AEI), when the disk approaches its last stable orbit. Furthermore, the energy dependence of the QPO may indicate the presence of a hot spot rotating in the disk as predicted by the AEI.

  2. Planck early results: First assessment of the Low Frequency Instrument in-flight performance

    CERN Document Server

    Mennella, A; Butler, R C; Curto, A; Cuttaia, F; Davis, R J; Dick, J; Frailis, M; Galeotta, S; Gregorio, A; Kurki-Suonio, H; Lawrence, C R; Leach, S; Leahy, J P; Lowe, S; Maino, D; Mandolesi, N; Maris, M; Mart\\'\\inez-González, E; Meinhold, P R; Morgante, G; Pearson, D; Perrotta, F; Polenta, G; Poutanen, T; Sandri, M; Seiffert, M D; Suur-Uski, A -S; Tavagnacco, D; Terenzi, L; Tomasi, M; Valiviita, J; Villa, F; Watson, R; Wilkinson, A; Zacchei, A; Zonca, A; Aja, B; Artal, E; Baccigalupi, C; Banday, A J; Barreiro, R B; Bartlett, J G; Bartolo, N; Battaglia, P; Bennett, K; Bonaldi, A; Bonavera, L; Borrill, J; Bouchet, F R; Burigana, C; Cabella, P; Cappellini, B; Chen, X; Colombo, L; Cruz, M; Danese, L; D'Arcangelo, O; Davies, R D; de Gasperis, G; de Rosa, A; de Zotti, G; Dickinson, C; Diego, J M; Donzelli, S; Efstathiou, G; En\\sslin, T A; Eriksen, H K; Falvella, M C; Finelli, F; Foley, S; Franceschet, C; Franceschi, E; Gaier, T C; Génova-Santos, R T; George, D; Gómez, F; González-Nuevo, J; Górski, K M; Gruppuso, A; Hansen, F K; Herranz, D; Herreros, J M; Hoyland, R J; Hughes, N; Jewell, J; Jukkala, P; Juvela, M; Kangaslahti, P; Keihänen, E; Keskitalo, R; Kilpia, V -H; Kisner, T S; Knoche, J; Knox, L; Laaninen, M; Lähteenmäki, A; Lamarre, J -M; Leonardi, R; León-Tavares, J; Leutenegger, P; Lilje, P B; López-Caniego, M; Lubin, P M; Malaspina, M; Marinucci, D; Massardi, M; Matarrese, S; Matthai, F; Melchiorri, A; Mendes, L; Miccolis, M; Migliaccio, M; Mitra, S; Moss, A; Natoli, P; Nesti, R; N\\orgaard-Nielsen, H U; Pagano, L; Paladini, R; Paoletti, D; Partridge, B; Pasian, F; Pettorino, V; Pietrobon, D; Pospieszalski, M; Prézeau, G; Prina, M; Procopio, P; Puget, J -L; Quercellini, C; Rachen, J P; Rebolo, R; Reinecke, M; Ricciardi, S; Robbers, G; Rocha, G; Roddis, N; Rubi\; Savelainen, M; Scott, D; Silvestri, R; Simonetto, A; Sjoman, P; Smoot, G F; Sozzi, C; Stringhetti, L; Tauber, J A; Tofani, G; Tuovinen, J; Türler, M; Umana, G; Valenziano, L; Varis, J; Vielva, P; Vittorio, N; Wade, L A; Watson, C; White, S; Winder, F

    2011-01-01

    The scientific performance of the Planck Low Frequency Instrument (LFI) after one year of in-orbit operation is presented. We describe the main optical parameters and discuss photometric calibration, white noise sensitivity, and noise properties. A preliminary evaluation of the impact of the main systematic effects is presented. For each of the performance parameters, we outline the methods used to obtain them from the flight data and provide a comparison with pre-launch ground assessments, which are essentially confirmed in flight.

  3. Collapsed methylation quantitative trait loci analysis for low frequency and rare variants.

    Science.gov (United States)

    Richardson, Tom G; Shihab, Hashem A; Hemani, Gibran; Zheng, Jie; Hannon, Eilis; Mill, Jonathan; Carnero-Montoro, Elena; Bell, Jordana T; Lyttleton, Oliver; McArdle, Wendy L; Ring, Susan M; Rodriguez, Santiago; Campbell, Colin; Smith, George Davey; Relton, Caroline L; Timpson, Nicholas J; Gaunt, Tom R

    2016-10-01

    Single variant approaches have been successful in identifying DNA methylation quantitative trait loci (mQTL), although as with complex traits they lack the statistical power to identify the effects from rare genetic variants. We have undertaken extensive analyses to identify regions of low frequency and rare variants that are associated with DNA methylation levels. We used repeated measurements of DNA methylation from five different life stages in human blood, taken from the Avon Longitudinal Study of Parents and Children (ALSPAC) cohort. Variants were collapsed across CpG islands and their flanking regions to identify variants collectively associated with methylation, where no single variant was individually responsible for the observed signal. All analyses were undertaken using the sequence kernel association test. For loci where no individual variant mQTL was observed based on a single variant analysis, we identified 95 unique regions where the combined effect of low frequency variants (MAF ≤ 5%) provided strong evidence of association with methylation. For loci where there was previous evidence of an individual variant mQTL, a further 3 regions provided evidence of association between multiple low frequency variants and methylation levels. Effects were observed consistently across 5 different time points in the lifecourse and evidence of replication in the TwinsUK and Exeter cohorts was also identified. We have demonstrated the potential of this novel approach to mQTL analysis by analysing the combined effect of multiple low frequency or rare variants. Future studies should benefit from applying this approach as a complementary follow up to single variant analyses. © The Author 2016. Published by Oxford University Press.

  4. Stillbirth and residential proximity to extremely low frequency power transmission lines: a retrospective cohort study.

    Science.gov (United States)

    Auger, Nathalie; Park, Alison L; Yacouba, Soumana; Goneau, Marc; Zayed, Joseph

    2012-02-01

    The relationship between electromagnetic field exposure and stillbirth has not been evaluated. We assessed associations between residential proximity to extremely low frequency power transmission lines and stillbirth across gestational age. Data included singleton live births (N=514,826) and stillbirths (N=2033) for 1998-2007 in metropolitan areas of Québec, Canada. Using power transmission line maps, the distances between lines and residential six-digit postal codes (rule out a possible link.

  5. Study on forming directivity with constant beam width in low frequency based on small sensor

    Institute of Scientific and Technical Information of China (English)

    HUI Junying; LIU Hong; YU Huabing; LIANG Guolong

    2001-01-01

    Based on a combined sensor with the size of 10 cm, a narrow beam with a constant receiving beam width of 20 degree has been formed in low frequency from several Hz to thousands of Hz by using simple adaptive algorithm. The results of theoretical simulation,laboratory experiment and lake experiment with one-dimension and two-dimension combined sensors have been given.

  6. Advanced finite element methodology for low-frequency and static electromagnetic modeling

    OpenAIRE

    Li, Yanlin; 黎燕林

    2015-01-01

    The design of state-of-the-art microelectronic devices poses unprecedented challenges to computational electromagnetics (CEM), which is cursed by the null space of curl operator. Both the low-frequency catastrophe for dynamic electromagnetic problems and non-uniqueness for magnetostatic problems originate from the null space. Although a few remedies are proposed during the last decade, a theoretically rigorous and numerically efficient solution is still on its way. Toward this end, this t...

  7. Low-frequency sheath instability in a non-Maxwellian plasma with energetic ions.

    Science.gov (United States)

    Starodubtsev, Mikhail; Kamal-Al-Hassan, Md; Ito, Hiroaki; Yugami, Noboru; Nishida, Yasushi

    2004-01-30

    Spontaneous low-frequency oscillations have been observed in the circuit of a positively biased electrode when the ambient nonuniform plasma is irradiated by a microwave pulse of short duration, which is approximately equal to the ion-plasma period. The instability with its characteristic frequency below the ion-plasma frequency is driven by an accelerated ion component interacting with the sheath of the electrode. A qualitative model of the instability is suggested.

  8. Weak-Coupling Theory for Low-Frequency Periodically Driven Two-Level Systems

    Institute of Scientific and Technical Information of China (English)

    CHEN Ai-Xi; HUANG Ke-Lin; WANG Zhi-Ping

    2008-01-01

    We generalize the Wu-Yang strong-coupling theory to solve analytically periodically driven two-level systems in the weak-coupling and low-frequency regimes for single- and multi-period periodic driving of continuous-wave-type and pulse-type including ultrashort pulses of a few cycles. We also derive a general formula of the AC Stark shift suitable for such diverse situations.

  9. A low frequency piezoelectric power harvester using a spiral-shaped bimorph

    Institute of Scientific and Technical Information of China (English)

    HU Yuantai; HU Hongping; YANG Jiashi

    2006-01-01

    We propose a spiral-shaped piezoelectric bimorph power harvester operating with coupled flexural and extensional vibration modes for applications to low frequency energy sources.A theoretical analysis is performed and the computational results show that the spiral structure has relatively low operating frequency compared to beam power harvesters of the same size.It is found that to optimize the performance of a piezoelectric spiral-shaped harvester careful design is needed.

  10. ELF (extremely-low-frequency) field interactions at the animal, tissue and cellular levels

    Energy Technology Data Exchange (ETDEWEB)

    Tenforde, T.S.

    1990-10-01

    A description is given of the fundamental physical properties of extremely-low-frequency (ELF) electromagnetic fields, and the mechanisms through which these fields interact with the human body at a macroscopic level. Biological responses to ELF fields at the tissue, cellular and molecular levels are summarized, including new evidence that ELF field exposure produces alterations in gene expression and the cytoplasmic concentrations of specific proteins.

  11. Effects of Extremely Low Frequency Electromagnetic Fields on Growth and Differentiation of ’Physarum polycephalum’

    Science.gov (United States)

    1975-04-01

    AD-AO10 187 EFFECTS OF EXTREMELY LOW FREQUENCY ELECTRO- MAGNETIC FIELDS ON GROWTH AND DIFFERENTIATION OF ’ PHYSARUM POLYCEPHALUM ’ E. M. Guodman, et al...LExtremely Low Prequency Electromagnetic Fields on Growth and Differentiation of Physarum polycephalum Technical Report Phase I (Continuous Wave) by...that weak, alternating electromagnetic fields (60 or 75 Hz, 2.0 G, 0.7 V/n) affect the cell cycle of Physarum polycephalum by increasing the interval

  12. Toward Low-Frequency Mechanical Energy Harvesting Using Energy-Dense Piezoelectrochemical Materials.

    Science.gov (United States)

    Cannarella, John; Arnold, Craig B

    2015-12-02

    The piezoelectrochemical coupling between mechanical stress and electrochemical potential is explored in the context of mechanical energy harvesting and shown to have promise in developing high-energy-density harvesters for low-frequency applications (e.g., human locomotion). This novel concept is demonstrated experimentally by cyclically compressing an off-the-shelf lithium-ion battery and measuring the generated electric power output.

  13. Modeling drug release from functionalized magnetic nanoparticles actuated by non-heating low frequency magnetic field

    Science.gov (United States)

    Golovin, Y.; Golovin, D.; Klyachko, N.; Majouga, A.; Kabanov, A.

    2017-02-01

    Various plausible acceleration mechanisms of drug release from nanocarriers composed of a single-domain magnetic nanoparticle core with attached long macromolecule chains activated by low frequency non-heating alternating magnetic field (AMF) are discussed. The most important system characteristics affecting the AMF exposure impact are determined. Impact of several reasonable mechanisms is estimated analytically or obtained using numerical modeling. Some conditions providing manifold release acceleration as a result from exposure in AMF are found.

  14. Integrated circuit for processing a low-frequency signal from a seismic detector

    Energy Technology Data Exchange (ETDEWEB)

    Malashevich, N. I.; Roslyakov, A. S.; Polomoshnov, S. A., E-mail: S.Polomoshnov@tsen.ru; Fedorov, R. A. [Research and Production Complex ' Technological Center' of the Moscow Institute of Electronic Technology (Russian Federation)

    2011-12-15

    Specific features for the detection and processing of a low-frequency signal from a seismic detector are considered in terms of an integrated circuit based on a large matrix crystal of the 5507 series. This integrated circuit is designed for the detection of human movements. The specific features of the information signal, obtained at the output of the seismic detector, and the main characteristics of the integrated circuit and its structure are reported.

  15. Comparing origins of low-frequency quasi-periodic oscillations with spectral-timing

    Science.gov (United States)

    Stevens, Abigail L.; Uttley, Phil

    2017-08-01

    The light curves of low-mass X-ray binaries show variability on timescales from milliseconds to months. The rapid (sub-second) variability is particularly interesting because it is thought to probe the inner region of the accretion disk and the central compact object. Observations suggest that different types of low-frequency quasi-periodic oscillations (QPOs) are associated with different emitting-region geometries (e.g., disk-like or jet-like) in the innermost part of the X-ray binary, that are varying possibly due to general relativistic precession. A new way to analyze QPOs is with spectral-timing, which seeks to investigate how matter behaves in the strong gravitational field around the compact object by causally linking the variations from different spectral components. We developed a technique for phase-resolved spectroscopy of QPOs, and are applying it to two types of low-frequency QPOs from the black hole X-ray binary GX 339-4. Over a QPO “period”, we find that the energy spectrum changes not only in normalization, but also in spectral shape. We can quantify how the spectral shape changes as a function of QPO phase, and the two different QPOs show markedly different spectral changes. The "Type B" low-frequency QPO shows evidence of a large-scale-height (jet-like) power-law- emitting precessing region, while in the same outburst the "Type C" low-frequency QPO shows evidence of a small-scale-height (disk-like) power-law-emitting precessing region. These interpretations can be used to look into the evolution of matter in the strong-gravity regime.

  16. Stress Recovery Effects of High- and Low-Frequency Amplified Music on Heart Rate Variability

    OpenAIRE

    2016-01-01

    Sounds can induce autonomic responses in listeners. However, the modulatory effect of specific frequency components of music is not fully understood. Here, we examined the role of the frequency component of music on autonomic responses. Specifically, we presented music that had been amplified in the high- or low-frequency domains. Twelve healthy women listened to white noise, a stress-inducing noise, and then one of three versions of a piece of music: original, low-, or high-frequency amplifi...

  17. Low-frequency acoustic atomization with oscillatory flow around micropillars in a microfluidic device

    Energy Technology Data Exchange (ETDEWEB)

    Cheung, Yin Nee, E-mail: mailccheung@gmail.com, E-mail: mtnwong@ntu.edu.sg; Wong, Teck Neng, E-mail: mailccheung@gmail.com, E-mail: mtnwong@ntu.edu.sg [School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, Singapore 639798 (Singapore); Nguyen, Nam Trung, E-mail: nam-trung.nguyen@griffith.edu.au [Queensland Micro- and Nanotechnology Centre, Griffith University, Brisbane QLD 4111 (Australia)

    2014-10-06

    This letter reports a low frequency acoustic atomization technique with oscillatory extensional flow around micropillars. Large droplets passing through two micropillars are elongated. Small droplets are then produced through the pinch-off process at the spindle-shape ends. As the actuation frequency increases, the droplet size decreases with increasing monodispersity. This method is suitable for in-situ mass production of fine droplets in a multi-phase environment without external pumping. Small particles encapsulation was demonstrated with the current technique.

  18. Resource Letter BELFEF-1: Biological effects of low-frequency electromagnetic fields

    Science.gov (United States)

    Hafemeister, David

    1996-08-01

    This Resource Letter provides a guide to the literature on the interaction of extremely low-frequency electromagnetic field (ELF/EMF) interactions with biological matter, and on the possibility that such interactions could have a harmful effect on human health. Journal articles and books are cited for the following topics: ELF/EMF theoretical interactions with biological cells, organs and organisms, magnetic dipole interactions, sensing by animals, biomedical-biophysical experiments, epidemiology, and litigation-mitigation risk issues.

  19. Detection of low frequency impulsive noise from large wind turbine generators

    Science.gov (United States)

    Shepherd, K. P.

    1985-01-01

    The thresholds of detection of low frequency, impulsive wind turbine sounds in the presence of background noise were examined. Seven wind turbine sounds, six of which were synthesized, were used in conjunction with three background noise conditions; quiet, 35, and 45 dB(A). The results indicate that thresholds of detection are predictable based on assumed characteristics of the auditory system. The synthesized wind turbine sounds were found to adequately represent a real recording.

  20. FR II radio galaxies at low frequencies - I. Morphology, magnetic field strength and energetics

    Science.gov (United States)

    Harwood, Jeremy J.; Croston, Judith H.; Intema, Huib T.; Stewart, Adam J.; Ineson, Judith; Hardcastle, Martin J.; Godfrey, Leith; Best, Philip; Brienza, Marisa; Heesen, Volker; Mahony, Elizabeth K.; Morganti, Raffaella; Murgia, Matteo; Orrú, Emanuela; Röttgering, Huub; Shulevski, Aleksandar; Wise, Michael W.

    2016-06-01

    Due to their steep spectra, low-frequency observations of Fanaroff-Riley type II (FR II) radio galaxies potentially provide key insights in to the morphology, energetics and spectrum of these powerful radio sources. However, limitations imposed by the previous generation of radio interferometers at metre wavelengths have meant that this region of parameter space remains largely unexplored. In this paper, the first in a series examining FR IIs at low frequencies, we use LOFAR (LOw Frequency ARray) observations between 50 and 160 MHz, along with complementary archival radio and X-ray data, to explore the properties of two FR II sources, 3C 452 and 3C 223. We find that the morphology of 3C 452 is that of a standard FR II rather than of a double-double radio galaxy as had previously been suggested, with no remnant emission being observed beyond the active lobes. We find that the low-frequency integrated spectra of both sources are much steeper than expected based on traditional assumptions and, using synchrotron/inverse-Compton model fitting, show that the total energy content of the lobes is greater than previous estimates by a factor of around 5 for 3C 452 and 2 for 3C 223. We go on to discuss possible causes of these steeper-than-expected spectra and provide revised estimates of the internal pressures and magnetic field strengths for the intrinsically steep case. We find that the ratio between the equipartition magnetic field strengths and those derived through synchrotron/inverse-Compton model fitting remains consistent with previous findings and show that the observed departure from equipartition may in some cases provide a solution to the spectral versus dynamical age disparity.

  1. Development and application of a low-frequency FBG vibration sensor

    Science.gov (United States)

    Nan, Qiu-ming

    2010-10-01

    Dynamic monitoring is part of bridge structural health monitoring. Real-time and online monitoring for bridge's dynamic performance is an important technology means for model updating, damage detection of structure and security evaluation of bridge. Nowadays dynamic monitoring system is generally installed on new long-span bridges. Vibration sensor is key part of the technology means. Vibration of a large-scale bridge belongs to low frequency one, but traditional electromagnetic vibration sensors are restricted for use in the field due to such defects as signal unable to long distance transmission, hard to measure ultra-low frequency vibration, so it is inevitable and imminent to develop a novel-type vibration sensor instead of them. Aiming at the above-mentioned problems, the author in the paper develops a low-frequency vibration sensor with double-cantilever beam structure, based on fiber Bragg grating (FBG) and matching filtering demodulation. Some experiments are done to study its sensing properties and the results indicate that it has good temperature compensation, its natural frequency is about 35Hz, measurement bandwidth from 0.1Hz to 20Hz, sensitivity is 1000mv/g or so, linearity degree is over 0.9992, repeatability is superior to 2.4%, acceleration measurement range is 1g, and cross anti-interference is 5.6%. Such sensors have been successfully used on Wuhan Tianxingzhou Yangtze River Bridge(WTYRB). The most transmission distance of measurement signal is 10km or so and the lowest measurement frequency is 0.24 Hz. The application results show it can detect accurately dynamic properties of vital areas of the bridge and can meet the demands for dynamic measurement. To sum up, the sensor developed in the paper can overcome the shortcomings of electromagnetic sensors and has very good sensing properties, so it is very suitable to be used for low-frequency vibration measurement.

  2. FR II radio galaxies at low frequencies - I. Morphology, magnetic field strength and energetics.

    Science.gov (United States)

    Harwood, Jeremy J; Croston, Judith H; Intema, Huib T; Stewart, Adam J; Ineson, Judith; Hardcastle, Martin J; Godfrey, Leith; Best, Philip; Brienza, Marisa; Heesen, Volker; Mahony, Elizabeth K; Morganti, Raffaella; Murgia, Matteo; Orrú, Emanuela; Röttgering, Huub; Shulevski, Aleksandar; Wise, Michael W

    2016-06-01

    Due to their steep spectra, low-frequency observations of Fanaroff-Riley type II (FR II) radio galaxies potentially provide key insights in to the morphology, energetics and spectrum of these powerful radio sources. However, limitations imposed by the previous generation of radio interferometers at metre wavelengths have meant that this region of parameter space remains largely unexplored. In this paper, the first in a series examining FR IIs at low frequencies, we use LOFAR (LOw Frequency ARray) observations between 50 and 160 MHz, along with complementary archival radio and X-ray data, to explore the properties of two FR II sources, 3C 452 and 3C 223. We find that the morphology of 3C 452 is that of a standard FR II rather than of a double-double radio galaxy as had previously been suggested, with no remnant emission being observed beyond the active lobes. We find that the low-frequency integrated spectra of both sources are much steeper than expected based on traditional assumptions and, using synchrotron/inverse-Compton model fitting, show that the total energy content of the lobes is greater than previous estimates by a factor of around 5 for 3C 452 and 2 for 3C 223. We go on to discuss possible causes of these steeper-than-expected spectra and provide revised estimates of the internal pressures and magnetic field strengths for the intrinsically steep case. We find that the ratio between the equipartition magnetic field strengths and those derived through synchrotron/inverse-Compton model fitting remains consistent with previous findings and show that the observed departure from equipartition may in some cases provide a solution to the spectral versus dynamical age disparity.

  3. Assessment of waveform control method for mitigation of low-frequency current ripple

    OpenAIRE

    Zhu, GR; Wang, HR; Xiao, CY; Kang, Y.; Tan, SC

    2013-01-01

    Waveform control method can mitigate such a low-frequency ripple current being drawn from the DC distribution while the DC distribution system delivers AC power to the load through a differential inverter. Assessment on the waveform control method and comparative study between with and without waveform control method are proposed in this paper1. Experimental results are provided to explain the operation and showcase the performance between with and without the waveform control method. Results...

  4. A magnetic-spring-based, low-frequency-vibration energy harvester comprising a dual Halbach array

    Science.gov (United States)

    Salauddin, M.; Halim, M. A.; Park, J. Y.

    2016-09-01

    Energy harvesting that uses low-frequency vibrations is attractive due to the availability of such vibrations throughout the ambient environment. Significant power generation at low-frequency vibrations, however, is challenging because the power flow decreases as the frequency decreases; moreover, designing a spring-mass system that is suitable for low-frequency-vibration energy harvesting is difficult. In this work, our proposed device overcomes both of these challenges by using a dual Halbach array and magnetic springs. Each Halbach array concentrates the magnetic-flux lines on one side of the array while suppressing the flux lines on the other side; therefore, a dual Halbach array allows for an interaction between the concentrated magnetic-flux lines and the same coil so that the maximum flux linkage occurs. During the experiment, vibration was applied in a horizontal direction to reduce the gravity effect on the Halbach-array structure. To achieve an increased power generation at low-amplitude and low-frequency vibrations, the magnetic structure of the dual Halbach array and the magnetic springs were optimized in terms of the operating frequency and the power density; subsequently, a prototype was fabricated and tested. The prototype device offers a normalized power density of 133.45 μW cm-3 g-2 that is much higher than those of recently reported electromagnetic energy harvesters; furthermore, it is capable of delivering a maximum average power of 1093 μW to a 44 Ω optimum load, at an 11 Hz resonant frequency and under a 0.5 g acceleration.

  5. Design and performance of a low frequency cross-polarized log-periodic dipole antenna

    CERN Document Server

    Raja, K Sasikumar; Ramesh, R; Rajalingam, M; Barve, Indrajit V

    2016-01-01

    We report the design and performance of a cross-polarized log-periodic dipole (CLPD) antenna for observations of polarized radio emission from the solar corona at low frequencies. The measured isolation between the two mutually orthogonal log periodic dipole antennas was as low as $\\approx$ -43 dBm in the 65-95 MHz range. We carried out observations of the solar corona at 80 MHz with the above CLPD and successfully recorded circularly polarized emission.

  6. Exome genotyping arrays to identify rare and low frequency variants associated with epithelial ovarian cancer risk

    DEFF Research Database (Denmark)

    Permuth, Jennifer B; Pirie, Ailith; Ann Chen, Y

    2016-01-01

    that is in LD (r(2 )=( )0.90) with a previously identified 'best hit' (rs7651446) mapping to an intron of TIPARP. Suggestive associations (5.0 × 10 (-)  (5 )>( )P≥5.0 ×10 (-)  (7)) were detected for rare and low-frequency variants at 16 novel loci. Four rare missense variants were identified (ACTBL2 rs73757391...

  7. Low-Frequency Surface Backscattering Strengths Measured in the Critical Sea Test Experiments

    Science.gov (United States)

    2017-01-19

    Naval Research Laboratory Washington, DC 20375-5320 NRL/MR/7160--17-9702 Low-Frequency Surface Backscattering Strengths Measured in the Critical Sea...including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing...control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 5d. PROJECT NUMBER 5e

  8. Ultrawide low frequency band gap of phononic crystal in nacreous composite material

    Energy Technology Data Exchange (ETDEWEB)

    Yin, J.; Huang, J.; Zhang, S., E-mail: zhangs@dlut.edu.cn; Zhang, H.W.; Chen, B.S.

    2014-06-27

    The band structure of a nacreous composite material is studied by two proposed models, where an ultrawide low frequency band gap is observed. The first model (tension-shear chain model) with two phases including brick and mortar is investigated to describe the wave propagation in the nacreous composite material, and the dispersion relation is calculated by transfer matrix method and Bloch theorem. The results show that the frequency ranges of the pass bands are quite narrow, because a special tension-shear chain motion in the nacreous composite material is formed by some very slow modes. Furthermore, the second model (two-dimensional finite element model) is presented to investigate its band gap by a multi-level substructure scheme. Our findings will be of great value to the design and synthesis of vibration isolation materials in a wide and low frequency range. Finally, the transmission characteristics are calculated to verify the results. - Highlights: • A Brick-and-Mortar structure is used to discuss wave propagation through nacreous materials. • A 1D Bloch wave solution of nacreous materials with a tension-shear chain model is obtained. • The band structure and transmission characteristics of nacreous materials with the FE model are examined. • An ultrawide low frequency band gap is found in nacreous materials with both theory and FE model.

  9. Strong Coulomb scattering effects on low frequency noise in monolayer WS2 field-effect transistors

    Science.gov (United States)

    Joo, Min-Kyu; Yun, Yoojoo; Yun, Seokjoon; Lee, Young Hee; Suh, Dongseok

    2016-10-01

    When atomically thin semiconducting transition metal dichalcogenides are used as a channel material, they are inevitably exposed to supporting substrates. This situation can lead to masking of intrinsic properties by undesired extrinsic doping and/or additional conductance fluctuations from the largely distributed Coulomb impurities at the interface between the channel and the substrate. Here, we report low-frequency noise characteristics in monolayer WS2 field-effect transistors on silicon/silicon-oxide substrate. To mitigate the effect of extrinsic low-frequency noise sources, a nitrogen annealing was carried out to provide better interface quality and to suppress the channel access resistance. The carrier number fluctuation and the correlated mobility fluctuation (CNF-CMF) model was better than the sole CNF one to explain our low-frequency noise data, because of the strong Coulomb scattering effect on the effective mobility caused by carrier trapping/detrapping at oxide traps. The temperature-dependent field-effect mobility in the four-probe configuration and the Coulomb scattering parameters are presented to support this strong Coulomb scattering effect on carrier transport in monolayer WS2 field-effect transistor.

  10. Extremely Low Frequency Magnetic Fields Induce Spermatogenic Germ Cell Apoptosis: Possible Mechanism

    Directory of Open Access Journals (Sweden)

    Sang-Kon Lee

    2014-01-01

    Full Text Available The energy generated by an extremely low frequency electromagnetic field (ELF-EMF is too weak to directly induce genotoxicity. However, it is reported that an extremely low frequency magnetic field (ELF-MF is related to DNA strand breakage and apoptosis. The testes that conduct spermatogenesis through a dynamic cellular process involving meiosis and mitosis seem vulnerable to external stress such as heat, MF exposure, and chemical or physical agents. Nevertheless the results regarding adverse effects of ELF-EMF on human or animal reproductive functions are inconclusive. According to the guideline of the International Commission on Non-Ionizing Radiation Protection (ICNIRP; 2010 for limiting exposure to time-varying MF (1 Hz to 100 kHz, overall conclusion of epidemiologic studies has not consistently shown an association between human adverse reproductive outcomes and maternal or paternal exposure to low frequency fields. In animal studies there is no compelling evidence of causal relationship between prenatal development and ELF-MF exposure. However there is increasing evidence that EL-EMF exposure is involved with germ cell apoptosis in testes. Biophysical mechanism by which ELF-MF induces germ cell apoptosis has not been established. This review proposes the possible mechanism of germ cell apoptosis in testes induced by ELF-MF.

  11. Band-gap tunable dielectric elastomer filter for low frequency noise

    Science.gov (United States)

    Jia, Kun; Wang, Mian; Lu, Tongqing; Zhang, Jinhua; Wang, Tiejun

    2016-05-01

    In the last decades, diverse materials and technologies for sound insulation have been widely applied in engineering. However, suppressing the noise radiation at low frequency still remains a challenge. In this work, a novel membrane-type smart filter, consisting of a pre-stretched dielectric elastomer membrane with two compliant electrodes coated on the both sides, is presented to control the low frequency noise. Since the stiffness of membrane dominates its acoustic properties, sound transmission band-gap of the membrane filter can be tuned by adjusting the voltage applied to the membrane. The impedance tube experiments have been carried out to measure the sound transmission loss (STL) of the filters with different electrodes, membrane thickness and pre-stretch conditions. The experimental results show that the center frequency of sound transmission band-gap mainly depends on the stress in the dielectric elastomer, and a large band-gap shift (more than 60 Hz) can be achieved by tuning the voltage applied to the 85 mm diameter VHB4910 specimen with pre-stretch {λ }0=3. Based on the experimental results and the assumption that applied electric field is independent of the membrane behavior, 3D finite element analysis has also been conducted to calculate the membrane stress variation. The sound filter proposed herein may provide a promising facility to control low frequency noise source with tonal characteristics.

  12. Response Identification in the Extremely Low Frequency Region of an Electret Condenser Microphone

    Science.gov (United States)

    Jeng, Yih-Nen; Yang, Tzung-Ming; Lee, Shang-Yin

    2011-01-01

    This study shows that a small electret condenser microphone connected to a notebook or a personal computer (PC) has a prominent response in the extremely low frequency region in a specific environment. It confines most acoustic waves within a tiny air cell as follows. The air cell is constructed by drilling a small hole in a digital versatile disk (DVD) plate. A small speaker and an electret condenser microphone are attached to the two sides of the hole. Thus, the acoustic energy emitted by the speaker and reaching the microphone is strong enough to actuate the diaphragm of the latter. The experiments showed that, once small air leakages are allowed on the margin of the speaker, the microphone captured the signal in the range of 0.5 to 20 Hz. Moreover, by removing the plastic cover of the microphone and attaching the microphone head to the vibration surface, the low frequency signal can be effectively captured too. Two examples are included to show the convenience of applying the microphone to pick up the low frequency vibration information of practical systems. PMID:22346594

  13. Response Identification in the Extremely Low Frequency Region of an Electret Condenser Microphone

    Directory of Open Access Journals (Sweden)

    Shang-Yin Lee

    2011-01-01

    Full Text Available This study shows that a small electret condenser microphone connected to a notebook or a personal computer (PC has a prominent response in the extremely low frequency region in a specific environment. It confines most acoustic waves within a tiny air cell as follows. The air cell is constructed by drilling a small hole in a digital versatile disk (DVD plate. A small speaker and an electret condenser microphone are attached to the two sides of the hole. Thus, the acoustic energy emitted by the speaker and reaching the microphone is strong enough to actuate the diaphragm of the latter. The experiments showed that, once small air leakages are allowed on the margin of the speaker, the microphone captured the signal in the range of 0.5 to 20 Hz. Moreover, by removing the plastic cover of the microphone and attaching the microphone head to the vibration surface, the low frequency signal can be effectively captured too. Two examples are included to show the convenience of applying the microphone to pick up the low frequency vibration information of practical systems.

  14. Tolerance of low-frequency ultrasound sonophoresis: a double-blind randomized study on humans.

    Science.gov (United States)

    Maruani, Annabel; Vierron, Emilie; Machet, Laurent; Giraudeau, Bruno; Halimi, Jean-Michel; Boucaud, Alain

    2012-05-01

    Sonophoresis [low-frequency ultrasound (US)] has been used in animals and in vitro to investigate enhanced percutaneous absorption of drugs. No study focused on its clinical human tolerance has been published as yet. We aimed to assess the bioeffects of low-frequency US in vivo on human skin in a double-blind randomized-controlled study. We applied pulse-mode US at 36 kHz for 5 min in a step procedure of increasing dosage, from 1.57 to 3.50 W/cm(2), and placebo. The primary outcome was toxic effects of the procedure, defined as a pain score >40 on a 0-100 mm visual analogue scale or necrosis. Erythema (scored from 0 to 3 in severity) was also evaluated. The secondary outcomes were measurements of skin thickness by high-resolution skin imaging, of skin capacitance and temperature. We included 34 healthy volunteers. We found no pain score >38 and no skin necrosis with either US or placebo. Erythema was systematically observed immediately after US application, but after 1 day, we observed three cases in the knee group. The most frequent adverse effect was tinnitus. We observed no marked increase in temperature or cutaneous thickness after US or placebo. Cutaneous capacitance increased immediately after both applications. Such data demonstrating good tolerance of sonophoresis can be useful before the initiation of a clinical trial of the therapeutic use of low-frequency sonophoresis in humans. © 2011 John Wiley & Sons A/S.

  15. Low-frequency heroin injection among out-of-treatment, street-recruited injection drug users.

    Science.gov (United States)

    Harris, Jennie L; Lorvick, Jennifer; Wenger, Lynn; Wilkins, Tania; Iguchi, Martin Y; Bourgois, Philippe; Kral, Alex H

    2013-04-01

    In this paper, we explore the understudied phenomenon of "low-frequency" heroin injection in a sample of street-recruited heroin injectors not in drug treatment. We conducted a cross-sectional study of 2,410 active injection drug users (IDUs) recruited in San Francisco, California from 2000 to 2005. We compare the sociodemographic characteristics and injection risk behaviors of low-frequency heroin injectors (low-FHI; one to 10 self-reported heroin injections in the past 30 days) to high-frequency heroin injectors (high-FHI; 30 or more self-reported heroin injections in the past 30 days). Fifteen percent of the sample met criteria for low-FHI. African American race, men who have sex with men (MSM) behavior, and injection and noninjection methamphetamine use were independently associated with low-FHI. Compared to high-FHI, low-FHI were less likely to report syringe sharing and nonfatal heroin overdose. A small but significant proportion of heroin injectors inject heroin 10 or less times per month. Additional research is needed to qualitatively examine low-frequency heroin injection and its relationship to drug use trajectories.

  16. Low-frequency repetitive transcranial magnetic simulation prevents chronic epileptic seizure*

    Institute of Scientific and Technical Information of China (English)

    Yinxu Wang; Xiaoming Wang; Sha Ke; Juan Tan; Litian Hu; Yaodan Zhang; Wenjuan Cui

    2013-01-01

    Although low-frequency repetitive transcranial magnetic simulation can potentially treat epilepsy, its underlying mechanism remains unclear. This study investigated the influence of low-frequency re-petitive transcranial magnetic simulation on changes in several nonlinear dynamic electroenceph-alographic parameters in rats with chronic epilepsy and explored the mechanism underlying repeti-tive transcranial magnetic simulation-induced antiepileptic effects. An epilepsy model was estab-lished using lithium-pilocarpine intraperitoneal injection into adult Sprague-Dawley rats, which were then treated with repetitive transcranial magnetic simulation for 7 consecutive days. Nonlinear elec-electroencephalographic parameters were obtained from the rats at 7, 14, and 28 days post-stimulation. Results showed significantly lower mean correlation-dimension and Kolmogo-rov-entropy values for stimulated rats than for non-stimulated rats. At 28 days, the complexity and point-wise correlation dimensional values were lower in stimulated rats. Low-frequency repetitive transcranial magnetic simulation has suppressive effects on electrical activity in epileptic rats, thus explaining its effectiveness in treating epilepsy.

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

    Science.gov (United States)

    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 (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.

  18. What can we Learn From Dynamic Triggering of Low-Frequency Earthquakes?

    Science.gov (United States)

    Miyazawa, M.; Brodsky, E. E.; Mori, J.

    2008-12-01

    Remote triggering of small low-frequency seismic events near the seismic-aseismic transition zone of subduction zones, by surface waves from large distant earthquakes, has been reported in southwest Japan and the Cascadia region. Recent observed triggering in southwest Japan from three large earthquakes (2003 Tokachi-oki (Mw 8.1), 2007 Solomon (Mw 8.1), and 2008 Wenchuan (Mw 7.9)) covering wide azimuthal information that is necessary to distinguish the triggering processes, shows significant triggering from Rayleigh waves rather than Love waves. This observation provides strong evidence for the influence of fluids in the source area because fluid can be affected by normal stress changes and not by shear stress changes. In the Cascadia region, it has been reported that seismic tremor associated with episodic slip is triggered by shear stress changes from Love waves. The low-frequency events both in southwest Japan and the Cascade region are though to be fluid related events. The Coulomb failure stress analyses suggest the effective friction coefficient is large for southwest Japan and small for the Cascadia region, which could be related to the amount of fluid in the source regions of the low-frequency events.

  19. Biological and clinical effects of low-frequency magnetic and electric fields

    Energy Technology Data Exchange (ETDEWEB)

    Llaurado, J.G.; Sances, A. Jr.; Battocletti, J. (eds.)

    1974-01-01

    The blurb on this book states that it has been written for physicians, biologists, psychologists, engineers and those persons interested in the interaction of low frequency electric and magnetic fields upon animals and man. Certainly, the content of this book--which comprises papers presented by specialists at a symposium on The Effects of Low Frequency Magnetic Fields on Biological Communication Processes held in Aspen, Colorado--does not make simple reading and those lacking the necessary background are unlikely to make much progress. This said, however, the book can be recommended to those with the necessary interest, knowledge and perseverance. The book provides a great deal of information in a convenient manner and all those concerned with its production are to be congratulated on their work. Articles are well set out, illustrated and supported by abstracts, extensive references and discussions. As indicated above, the range of the subjects covered is large and includes such varied items as acupuncture, bird communication and some details of the U.S.A. Navy's extra low frequency communication system known as Project Sanguine. Finally, it is a pleasure to say that the book has been attractively produced and contains an excellent index.

  20. Effect of Intermittent Low-Frequency Electrical Stimulation on the Rat Gastrocnemius Muscle

    Directory of Open Access Journals (Sweden)

    Arata Tsutaki

    2013-01-01

    Full Text Available Low-frequency neuromuscular electrical stimulation (NMES has been used as an endurance exercise model. This study aimed to test whether low-frequency NMES increases the phosphorylation of anabolic signaling molecules and induces skeletal muscle hypertrophy, as seen with high-frequency NMES. Using Sprague-Dawley rats, 1 bout of exercise (with dissection done immediately (Post0 and 3 h (Post3 after exercise and another 6 sessions of training were performed. All experimental groups consisted of high- and low-frequency stimulation (HFS: 100 Hz; LFS: 10 Hz. Periodic acid-Schiff (PAS staining was conducted to investigate type II fiber activation, and western blot analysis (WB was conducted to examine whether NMES leads to anabolic intracellular signaling. At first, we examined the acute effect of exercise. PAS staining revealed that glycogen depletion occurred in both type I and type II fibers. WB results demonstrated that p70S6K phosphorylation was significantly increased by HFS, but there was no significant difference with LFS. In contrast, ERK 1/2 phosphorylation was increased by LFS at Post0. In the 6-session training, the wet weight and myofibrillar protein were significantly increased by both HFS and LFS. In conclusion, LFS has a similar anabolic effect for skeletal muscle hypertrophy as HFS, but the mediating signaling pathway might differ.