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Sample records for stabilization technique low-frequency

  1. 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 (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 discussed. With the optimized

  2. Voltage stabilizer of the asynchronous low-frequency generator

    Directory of Open Access Journals (Sweden)

    Berzan V.P.

    2008-08-01

    Full Text Available The new method of output voltage stabilization of the asynchronous generator with capacitor excitation is offered. Value of the basic magnetic stream of the three-phase generator is adjusted by consecutive connection of excitation winding outputs to a zero point. In result it is received more high-speed and exact system of stabilization of voltage in independence of the reason of a preset value deviation. Experimental check has confirmed efficiency of the offered way of asynchronous generator voltage stabilization and an opportunity of its use in independent wind power installations

  3. 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.

  4. Equilibrium and low-frequency stability of a uniform density, collisionless, spherical Vlasov system

    International Nuclear Information System (INIS)

    Barnes, D.C.; Chacon, L.; Finn, J.M.

    2002-01-01

    Equilibrium and stability of a collisionless, spherical Vlasov system with uniform density are considered. Such an electron system is useful for the Periodically Oscillating Plasma Sphere (POPS) fusion system. In POPS the space charge of a uniform-density spherical electron cloud provides a harmonic well for an under-dense thermal ion population. Previous special solutions [D. C. Barnes, Phys. Plasmas 6, 4472 (1999)] are extended to arbitrary energy dependence. These equilibrium distribution functions and their first derivatives may be made nonsingular, in contrast to the previous solutions. Linear stability of general spherical equilibria is considered, and reduced to a one-dimensional calculation by the introduction of a spherical harmonic decomposition. All azimuthal mode numbers are degenerate. Using this formalism, the low-frequency stability of a collisionless, spherical Vlasov electron system coupled to a minority ion cloud is studied for the class of uniform-density electron equilibria found. In the low-frequency (adiabatic) limit, the general kinetic stability formalism can be integrated to find a closed form for the response of electron number density. The adiabatic response operator is shown to be self-adjoint. Computation of its eigenvalues proves the constant-density electrons/thermal ions system in POPS to be mostly stable to ion-electron electrostatic modes. Unstable modes are avoided unless central electrons have an extremely small energy spread. These results may also be useful for the consideration of gravitational and beam systems

  5. Instrumentation, computer software and experimental techniques used in low-frequency internal friction studies at WNRE

    International Nuclear Information System (INIS)

    Sprugmann, K.W.; Ritchie, I.G.

    1980-04-01

    A detailed and comprehensive account of the equipment, computer programs and experimental methods developed at the Whiteshell Nuclear Research Estalbishment for the study of low-frequency internal friction is presented. Part 1 describes the mechanical apparatus, electronic instrumentation and computer software, while Part II describes in detail the laboratory techniques and various types of experiments performed together with data reduction and analysis. Experimental procedures for the study of internal friction as a function of temperature, strain amplitude or time are described. Computer control of these experiments using the free-decay technique is outlined. In addition, a pendulum constant-amplitude drive system is described. (auth)

  6. A Touch Sensing Technique Using the Effects of Extremely Low Frequency Fields on the Human Body.

    Science.gov (United States)

    Elfekey, Hatem; Bastawrous, Hany Ayad; Okamoto, Shogo

    2016-12-02

    Touch sensing is a fundamental approach in human-to-machine interfaces, and is currently under widespread use. Many current applications use active touch sensing technologies. Passive touch sensing technologies are, however, more adequate to implement low power or energy harvesting touch sensing interfaces. This paper presents a passive touch sensing technique based on the fact that the human body is affected by the surrounding extremely low frequency (ELF) electromagnetic fields, such as those of AC power lines. These external ELF fields induce electric potentials on the human body-because human tissues exhibit some conductivity at these frequencies-resulting in what is called AC hum. We therefore propose a passive touch sensing system that detects this hum noise when a human touch occurs, thus distinguishing between touch and non-touch events. The effectiveness of the proposed technique is validated by designing and implementing a flexible touch sensing keyboard.

  7. A Touch Sensing Technique Using the Effects of Extremely Low Frequency Fields on the Human Body

    Directory of Open Access Journals (Sweden)

    Hatem Elfekey

    2016-12-01

    Full Text Available Touch sensing is a fundamental approach in human-to-machine interfaces, and is currently under widespread use. Many current applications use active touch sensing technologies. Passive touch sensing technologies are, however, more adequate to implement low power or energy harvesting touch sensing interfaces. This paper presents a passive touch sensing technique based on the fact that the human body is affected by the surrounding extremely low frequency (ELF electromagnetic fields, such as those of AC power lines. These external ELF fields induce electric potentials on the human body—because human tissues exhibit some conductivity at these frequencies—resulting in what is called AC hum. We therefore propose a passive touch sensing system that detects this hum noise when a human touch occurs, thus distinguishing between touch and non-touch events. The effectiveness of the proposed technique is validated by designing and implementing a flexible touch sensing keyboard.

  8. CONSIDERATIONS ON CONTACTLESS MEASUREMENTS IN HYDROGEOLOGY USING VERY LOW FREQUENCY ELECTROMAGNETIC TECHNIQUES

    Directory of Open Access Journals (Sweden)

    Tudor BURLAN-ROTAR

    2017-05-01

    Full Text Available Studies of groundwater consist in data acquisition, their processing and interpretation. In areas of interest hydrogeological is assumed that there is a network of wells drilled. This network provides a first in the hydrogeological information. Electromagnetic (EM mapping through the use of such areas, using data obtained from existing network of wells drilled, calibration and confirmation. Measurements using the EM can highlight the existence of several layers with different characteristics: clay, limestone, sand, etc. Studies of groundwater interpretation are used for developing a regional hydrogeologic model. The application of electromagnetic techniques for measuring soil resistivity or conductivity has been known for a long time. Conductivity is preferable in inductive techniques, as instrumentation readings are generally directly proportional to conductivity and inversely proportional to resistivity. The operating principle of this method is: a Tx coil transmitter, supplied with alternating current at an audio frequency, is placed on the ground. An Rx coil receiver is located at a short distance, s, away from the Tx coil. The magnetic field varies in time and the Tx coil induces very small currents in the ground. These currents generate a secondary magnetic field, Hs, which is sensed by the Rx receiver coil, together, with primary magnetic field Hp. The ratio of the secondary field, Hs, to the primary magnetic field, Hp, (Hs/Hp is directly proportional to terrain conductivity. Measuring this ratio, it is possible to construct a device which measures the terrain conductivity by contactless, direct-reading electromagnetic technique (linear meter. This technique for measuring conductivity by electromagnetic induction, using Very Low Frequency (VLF, is a non-intrusive, non-destructive sampling method. The measurements can be done quickly and are not expensive. The Electromagnetic induction technology was originally developed for the mining

  9. Neonatal total liquid ventilation: is low-frequency forced oscillation technique suitable for respiratory mechanics assessment?

    Science.gov (United States)

    Bossé, Dominick; Beaulieu, Alexandre; Avoine, Olivier; Micheau, Philippe; Praud, Jean-Paul; Walti, Hervé

    2010-08-01

    This study aimed to implement low-frequency forced oscillation technique (LFFOT) in neonatal total liquid ventilation (TLV) and to provide the first insight into respiratory impedance under this new modality of ventilation. Thirteen newborn lambs, weighing 2.5 + or - 0.4 kg (mean + or - SD), were premedicated, intubated, anesthetized, and then placed under TLV using a specially design liquid ventilator and a perfluorocarbon. The respiratory mechanics measurements protocol was started immediately after TLV initiation. Three blocks of measurements were first performed: one during initial respiratory system adaptation to TLV, followed by two other series during steady-state conditions. Lambs were then divided into two groups before undergoing another three blocks of measurements: the first group received a 10-min intravenous infusion of salbutamol (1.5 microg x kg(-1) x min(-1)) after continuous infusion of methacholine (9 microg x kg(-1) x min(-1)), while the second group of lambs was chest strapped. Respiratory impedance was measured using serial single-frequency tests at frequencies ranging between 0.05 and 2 Hz and then fitted with a constant-phase model. Harmonic test signals of 0.2 Hz were also launched every 10 min throughout the measurement protocol. Airway resistance and inertance were starkly increased in TLV compared with gas ventilation, with a resonant frequency < or = 1.2 Hz. Resistance of 0.2 Hz and reactance were sensitive to bronchoconstriction and dilation, as well as during compliance reduction. We report successful implementation of LFFOT to neonatal TLV and present the first insight into respiratory impedance under this new modality of ventilation. We show that LFFOT is an effective tool to track respiratory mechanics under TLV.

  10. The low-frequency sound power measuring technique for an underwater source in a non-anechoic tank

    Science.gov (United States)

    Zhang, Yi-Ming; Tang, Rui; Li, Qi; Shang, Da-Jing

    2018-03-01

    In order to determine the radiated sound power of an underwater source below the Schroeder cut-off frequency in a non-anechoic tank, a low-frequency extension measuring technique is proposed. This technique is based on a unique relationship between the transmission characteristics of the enclosed field and those of the free field, which can be obtained as a correction term based on previous measurements of a known simple source. The radiated sound power of an unknown underwater source in the free field can thereby be obtained accurately from measurements in a non-anechoic tank. To verify the validity of the proposed technique, a mathematical model of the enclosed field is established using normal-mode theory, and the relationship between the transmission characteristics of the enclosed and free fields is obtained. The radiated sound power of an underwater transducer source is tested in a glass tank using the proposed low-frequency extension measuring technique. Compared with the free field, the radiated sound power level of the narrowband spectrum deviation is found to be less than 3 dB, and the 1/3 octave spectrum deviation is found to be less than 1 dB. The proposed testing technique can be used not only to extend the low-frequency applications of non-anechoic tanks, but also for measurement of radiated sound power from complicated sources in non-anechoic tanks.

  11. Stabilization and Low-Frequency Oscillation of Capillary Bridges with Modulated Acoustic Radiation Pressure

    Science.gov (United States)

    Marston, Philip L.; Marr-Lyon, Mark J.; Morse, S. F.; Thiessen, David B.

    1996-01-01

    In the work reported here it is demonstrated that acoustic radiation pressure may be used in simulated low gravity to produce stable bridges significantly beyond the Rayleigh limit with S as large as 3.6. The bridge (PDMS mixed with a dense liquid) has the same density as the surrounding water bath containing an ultrasonic standing wave. Modulation was first used to excite specific bridge modes. In the most recent work reported here the shape of the bridge is optically sensed and the ultrasonic drive is electronically adjusted such that the radiation stress distribution dynamically quenches the most unstable mode. This active control simulates passive stabilization suggested for low gravity. Feedback increases the mode frequency in the naturally stable region since the effective stiffness of the mode is increased.

  12. Low frequency noise fiber delay stabilized laser with reduced sensitivity to acceleration

    Science.gov (United States)

    Argence, B.; Clivati, C.; Dournaux, J.-L.; Holleville, D.; Faure, B.; Lemonde, P.; Santarelli, G.

    2017-11-01

    Lasers with sub-hertz line-width and fractional frequency instability around 1×10-15 for 0.1 s to 10 s averaging time are currently realized by locking onto an ultra-stable Fabry-Perot cavity using the Pound-Drever-Hall method. This powerful method requires tight alignment of free space optical components, precise polarization adjustment and spatial mode matching. To circumvent these issues, we use an all-fiber Michelson interferometer with a long fiber spool as a frequency reference and a heterodyne detection technique with a fibered acousto optical modulator (AOM)1. At low Fourier frequencies, the frequency noise of our system is mainly limited by mechanical vibrations, an issue that has already been explored in the field of optoelectronic oscillators.2,3,4

  13. Characterization of exposure to extremely low frequency magnetic fields using multidimensional analysis techniques.

    Science.gov (United States)

    Verrier, A; Souques, M; Wallet, F

    2005-05-01

    Our lack of knowledge about the biological mechanisms of 50 Hz magnetic fields makes it hard to improve exposure assessment. To provide better information about these exposure measures, we use multidimensional analysis techniques to examine the relations between different exposure metrics for a group of subjects. We used a combination of a two stage Principal Component Analysis (PCA) followed by an ascending hierarchical classification (AHC) to identify a set of measures that would capture the characteristics of the total exposure. This analysis gives an indication of the aspects of the exposure that are important to capture to get a complete picture of the magnetic field environment. We calculated 44 metrics of exposure measures from 16 exposed EDF employees and 15 control subjects, containing approximately 20,000 recordings of magnetic field measurements, taken every 30 s for 7 days with an EMDEX II dosimeter. These metrics included parameters used routinely or occasionally and some that were new. To eliminate those that expressed the least variability and that were most highly correlated to one another, we began with an initial Principal Component Analysis (PCA). A second PCA of the remaining 12 metrics enabled us to identify from the foreground 82.7% of the variance: the first component (62.0%) was characterized by central tendency metrics, and the second (20.7%) by dispersion characteristics. We were able to use AHC to divide the entire sample (of individuals) into four groups according to the axes that emerged from the PCA. Finally, discriminant analysis tested the discriminant power of the variables in the exposed/control classification as well as those from the AHC classification. The first showed that two subjects had been incorrectly classified, while no classification error was observed in the second. This exploratory study underscores the need to improve exposure measures by using at least two dimensions: intensity and dispersion. It also indicates the

  14. Low frequency radioastronomy

    International Nuclear Information System (INIS)

    Zarka, Philippe; Cecconi, Baptiste; Tagger, Michel; Torchinsky, Steve; Picard, Philippe; Pezzani, Jacques; Cognard, Ismael; Boone, Frederic; Woan, Graham; Weber, Rodolphe; Gousset, Thierry; Lautridou, Pascal; Dallier, Richard

    2011-07-01

    Low frequency radioastronomy deals with the direct detection (below 100 MHz) and heterodyne detection (up to few GHz) of electromagnetic waves (phase and amplitude) followed by a time or spectral analysis. The 30. Goutelas school covered several aspects of radioastronomy involving various aspects of physics: non-thermal phenomena in plasmas and physics of magnetized plasmas, atomic and molecular physics, and particle physics. These proceedings comprise 17 lectures dealing with: 1 - Low-Frequency Radioastronomy Basics (P. Zarka); 2 - Radioastronomy Historical Highlights (S. A. Torchinsky); 3 - Antennas (P. Picard, J. Pezzani); 4 - Receptors (P. Picard, J. Pezzani); 5 - Pulsars chronometry: metrology in radioastronomy (I. Cognard); 6 - Interferometry as imaging technique (F. Boone); 7 - Radio propagation and scintillation (G. Woan); 8 - Square Kilometer Array (S. A. Torchinsky); 9 - Techniques against radio-electrical interferences in low-frequency radioastronomy (R. Weber); 10 - Introduction to poly-phase filtering (R. Weber); 11 - Three decades of Jupiter's radio-emission studies: from the Nancay deca-meter network to LOFAR (P. Zarka); 12 - Atmospheric showers and their radio counterpart (T. Gousset); 13 - From cosmic rays radio-detection to pulse radioastronomy (P. Lautridou, R. Dallier); 14 - The CODALEMA project (R. Dallier, P. Lautridou); 15 - Space-based radio measurements: Gonio-polarimetry (B. Cecconi); 16 - Radio astronomy from space (G. Woan); 17 - LOFAR: the Low Frequency Array and the French FLOW consortium (M. Tagger, P. Zarka)

  15. Controlled drug release under a low frequency magnetic field: effect of the citrate coating on magnetoliposomes stability

    KAUST Repository

    Nappini, Silvia

    2011-01-01

    The paper describes the effect of a low-frequency alternating magnetic field (LF-AMF) on the permeability and release properties of large (LUVs) and giant (GUVs) unilamellar vesicles loaded with citrate coated cobalt ferrite nanoparticles (NPs). The citrate shell allows a high loading of NPs in lipid vesicles without modifying their magnetic properties. The increase of magnetic LUVs permeability upon exposure to LF-AMF has been evaluated as the fluorescence self-quenching of carboxyfluorescein (CF) entrapped inside the liposome aqueous pool. Liposome leakage has been monitored as a function of field frequency, time exposure and concentration of the citrate coated NPs. Confocal Laser Scanning Microscopy (CLSM) experiments performed on magnetic GUVs labeled with the fluorescent probe DiIC18 and loaded with Alexa 488-C5-maleimide fluorescent dye provided insights on the release mechanism induced by LF-AMF. The results show that LF-AMF strongly affects vesicles permeability, suggesting the formation of pores in the lipid bilayer due to both hyperthermic effects and nanoparticle oscillations in the vesicles pool at the applied frequency. The behaviour of these magnetic vesicles in the presence of LF-AMF makes this system a good candidate for controlled drug delivery. © 2011 The Royal Society of Chemistry.

  16. COMPARISON OF DIFFERENT TECHNIQUES FOR DESIGN OF POWER SYSTEM STABILIZER

    OpenAIRE

    M. Ravindra Babu,; A. Ramulu; B. Durga Prasad,; Doradla. Prathap Hari Krishna,

    2011-01-01

    The major problem in power system operation is related to small signal instability caused by insufficient damping in the system. The most effective way of countering this instability is to use auxiliary controllers called power system stabilizers, to produce additional damping during low frequency oscillations in the system. Heffron-Phillip’s Model of a synchronous machine is commonly used in small signal stability analysis. Different techniques for designing of power system stabilizer is pro...

  17. The design of delay-dependent wide-area DOFC with prescribed degree of stability α for damping inter-area low-frequency oscillations in power system.

    Science.gov (United States)

    Sun, Miaoping; Nian, Xiaohong; Dai, Liqiong; Guo, Hua

    2017-05-01

    In this paper, the delay-dependent wide-area dynamic output feedback controller (DOFC) with prescribed degree of stability is proposed for interconnected power system to damp inter-area low-frequency oscillations. Here, the prescribed degree of stability α is used to maintain all the poles on the left of s=-α in the s-plane. Firstly, residue approach is adopted to select input-output control signals and the schur balanced truncation model reduction method is utilized to obtain the reduced power system model. Secondly, based on Lyapunov stability theory and transformation operation in complex plane, the sufficient condition of asymptotic stability for closed-loop power system with prescribed degree of stability α is derived. Then, a novel method based on linear matrix inequalities (LMIs) is presented to obtain the parameters of DOFC and calculate delay margin of the closed-loop system considering the prescribed degree of stability α. Finally, case studies are carried out on the two-area four-machine system, which is controlled by classical wide-area power system stabilizer (WAPSS) in reported reference and our proposed DOFC respectively. The effectiveness and advantages of the proposed method are verified by the simulation results under different operating conditions. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.

  18. The kinetic theory and stability of a stochastic plasma with respect to low frequency perturbations and magnetospheric convection

    International Nuclear Information System (INIS)

    Hurricane, O.A.

    1994-09-01

    In this dissertation, a new linear Vlasov kinetic theory is developed for calculating the plasma response to perturbing electromagnetic fields in cases where the particle dynamics are stochastic; for modes with frequencies less than the typical particle bounce frequency. A variational form is arrived at which allows one to properly perform a stability analysis for a stochastic plasma. In the case of stochastic dynamics, the authors demonstrate that the plasma responds to the flux tube volume average of the perturbing potentials as opposed to the usual case of adiabatic dynamics where plasma responds to the bounce average of the perturbed potentials. They show that for the stochastic plasma, the kinetic variational form maps into the Bernstein energy principle if the perturbation frequency is large compared to all drift frequencies, the perpendicular wavelength is large compared to the Larmor radius, and vanishing of the potentials associated with the parallel electric field are all assumed. By explicit minimization of the energy principle, it is established that the stochastic plasma is always less stable than an adiabatic plasma. Lastly, the effect of strictly enforcing the quasi-neutrality (QN) condition upon a gyro-kinetic type stability analysis is explored. From simple mathematical considerations, it is shown that when the QN condition is imposed convective type modes that are equipotentials along magnetic field lines are created that alter the stability properties of the plasma. The pertinent modifications to the Bernstein energy principle are given

  19. LOW FREQUENCY DAMPER

    Directory of Open Access Journals (Sweden)

    Radu BOGATEANU

    2009-09-01

    Full Text Available The low frequency damper is an autonomous equipment for damping vibrations with the 1-20Hz range.Its autonomy enables the equipment to be located in various mechanical systems, without requiring special hydraulic installations.The low frequency damper was designed for damping the low frequency oscillations occurring in the circuit controls of the upgraded IAR-99 Aircraft.The low frequency damper is a novelty in the aerospace field ,with applicability in several areas as it can be built up in an appropriate range of dimensions meeting the requirements of different beneficiaries. On this line an equipment able to damp an extended frequency range was performed for damping oscillations in the pipes of the nuclear power plants.This damper, tested in INCAS laboratories matched the requirements of the beneficiary.The low frequency damper is patented – the patent no. 114583C1/2000 is held by INCAS.

  20. Low frequency electromagnetic field sensor

    International Nuclear Information System (INIS)

    Zhu Min; Zhou Yan; He Yicheng; Zheng Zhenxing; Liu Sunkun

    2000-01-01

    The measurement technique of low frequency electromagnetic field is reported. According to this principle, the authors have designed a sensor, which is used to measure the natural electromagnetic field, SLEMP and electromagnetic signals generated by some explosions. The frequency band of this sensor is from 0.08 Hz to 2 MHz

  1. Minimization of nanosatellite low frequency magnetic fields

    Science.gov (United States)

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

    2016-03-01

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

  2. Minimization of nanosatellite low frequency magnetic fields

    International Nuclear Information System (INIS)

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

    2016-01-01

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

  3. 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.

  4. Observations and Analyses of Heliospheric Faraday Rotation of a Coronal Mass Ejection (CME) Using the LOw Frequency ARray (LOFAR) and Space-Based Imaging Techniques

    Science.gov (United States)

    Bisi, Mario Mark; Jensen, Elizabeth; Sobey, Charlotte; Fallows, Richard; Jackson, Bernard; Barnes, David; Giunta, Alessandra; Hick, Paul; Eftekhari, Tarraneh; Yu, Hsiu-Shan; Odstrcil, Dusan; Tokumaru, Munetoshi; Wood, Brian

    2017-04-01

    Geomagnetic storms of the highest intensity are general driven by coronal mass ejections (CMEs) impacting the Earth's space environment. Their intensity is driven by the speed, density, and, most-importantly, their magnetic-field orientation and magnitude of the incoming solar plasma. The most-significant magnetic-field factor is the North-South component (Bz in Geocentric Solar Magnetic - GSM - coordinates). At present, there are no reliable prediction methods available for this magnetic-field component ahead of the in-situ monitors around the Sun-Earth L1 point. Observations of Faraday rotation (FR) can be used to attempt to determine average magnetic-field orientations in the inner heliosphere. Such a technique has already been well demonstrated through the corona, ionosphere, and also the interstellar medium. Measurements of the polarisation of astronomical (or spacecraft in superior conjunction) radio sources (beacons/radio frequency carriers) through the inner corona of the Sun to obtain the FR have been demonstrated but mostly at relatively-high radio frequencies. Here we show some initial results of true heliospheric FR using the Low Frequency Array (LOFAR) below 200 MHz to investigate the passage of a coronal mass ejection (CME) across the line of sight. LOFAR is a next-generation low-frequency radio interferometer, and a pathfinder to the Square Kilometre Array (SKA) - LOW telescope. We demonstrate preliminary heliospheric FR results through the analysis of observations of pulsar J1022+1001, which commenced on 13 August 2014 at 13:00UT and spanned over 150 minutes in duration. We also show initial comparisons to the FR results via various modelling techniques and additional context information to understand the structure of the inner heliosphere being detected. This observation could indeed pave the way to an experiment which might be implemented for space-weather purposes that will eventually lead to a near-global method for determining the magnetic

  5. LOFAR, the low frequency array

    Science.gov (United States)

    Vermeulen, R. C.

    2012-09-01

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

  6. Using a modified time-reverse imaging technique to locate low-frequency earthquakes on the San Andreas Fault near Cholame, California

    Science.gov (United States)

    Horstmann, Tobias; Harrington, Rebecca M.; Cochran, Elizabeth S.

    2015-01-01

    We present a new method to locate low-frequency earthquakes (LFEs) within tectonic tremor episodes based on time-reverse imaging techniques. The modified time-reverse imaging technique presented here is the first method that locates individual LFEs within tremor episodes within 5 km uncertainty without relying on high-amplitude P-wave arrivals and that produces similar hypocentral locations to methods that locate events by stacking hundreds of LFEs without having to assume event co-location. In contrast to classic time-reverse imaging algorithms, we implement a modification to the method that searches for phase coherence over a short time period rather than identifying the maximum amplitude of a superpositioned wavefield. The method is independent of amplitude and can help constrain event origin time. The method uses individual LFE origin times, but does not rely on a priori information on LFE templates and families.We apply the method to locate 34 individual LFEs within tremor episodes that occur between 2010 and 2011 on the San Andreas Fault, near Cholame, California. Individual LFE location accuracies range from 2.6 to 5 km horizontally and 4.8 km vertically. Other methods that have been able to locate individual LFEs with accuracy of less than 5 km have mainly used large-amplitude events where a P-phase arrival can be identified. The method described here has the potential to locate a larger number of individual low-amplitude events with only the S-phase arrival. Location accuracy is controlled by the velocity model resolution and the wavelength of the dominant energy of the signal. Location results are also dependent on the number of stations used and are negligibly correlated with other factors such as the maximum gap in azimuthal coverage, source–station distance and signal-to-noise ratio.

  7. Auditory filters at low-frequencies

    DEFF Research Database (Denmark)

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

    2009-01-01

    Hz. The notched-noise method was used, with the noise masker at 40 dB spectral density. A rounded exponential auditory filter model (roex(p,r)) was used to fit the masking data. Preliminary data on 1 subject is discussed. Considering the system as a whole (e.g. without removing the assumed middle......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...... 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. 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....

  9. Optical metrology techniques for dimensional stability measurements

    NARCIS (Netherlands)

    Ellis, Jonathan David

    2010-01-01

    This thesis work is optical metrology techniques to determine material stability. In addition to displacement interferometry, topics such as periodic nonlinearity, Fabry-Perot interferometry, refractometry, and laser stabilization are covered.

  10. Controlled Pilot Study of High-Impact Low-Frequency Exercise on Bone Loss and Vital-Sign Stabilization in Adolescents With Eating Disorders.

    Science.gov (United States)

    Martin, Susanne P K; Bachrach, Laura K; Golden, Neville H

    2017-01-01

    Adolescents with anorexia nervosa (AN) face an increased lifetime risk of bone fragility. This randomized controlled study examined the efficacy and safety of a high-impact activity program on markers of bone turnover and stabilization of vital signs (VSS). Forty-one hospitalized adolescents with AN were randomly assigned to routine care or routine care plus 20 jumps twice daily. Bone markers were measured at baseline days 1-3 (T1), days 4-6 (T2), and days 7-9 (T3). The primary outcome was change in bone-specific alkaline phosphatase (BSAP) at T3 adjusted for BSAP and % median body mass index at T1. Secondary outcomes were serum N-telopeptide (NTX) and osteocalcin at T3. Safety was determined by comparing weight gain, time to VSS and length of stay for each group. BSAP, NTX, or osteocalcin did not differ between groups at baseline or at T3. BSAP and NTX at T3 were not associated with group of enrollment or % median body mass index. VSS was significantly reduced in the intervention group compared with the control group (11.6 ± 5.7 days vs. 17 ± 10.5 days, p = .049). There was no significant difference in weight gain or length of stay between groups. Twice-daily jumping activity failed to influence markers of bone turnover in adolescents with AN but was well tolerated, shortened time to vital-sign stabilization and did not slow weight gain. Copyright © 2016 Society for Adolescent Health and Medicine. Published by Elsevier Inc. All rights reserved.

  11. Comparison of Different Techniques For Tuning of Power System Stabilizer

    OpenAIRE

    BAYAT, Ehsan; DELAVARİ, Hadi

    2015-01-01

    Abstract. The power system is subjected to different types of disturbances such as small changes in the load that affects its efficiency and sometimes leads to unstable system. These disturbances cause oscillations at low frequencies that are undesirable since it affects the amount of transferred power through the transmission lines and leads to external stress to the mechanical shaft. In order to compress low-frequency oscillations, a common solution is use the power system stabilizer (PSS)....

  12. Low-frequency noise complaints

    DEFF Research Database (Denmark)

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

    2006-01-01

    is only heard by a single person in the household. This raises the fundamental question whether the complainants are annoyed by an external physical sound, or if other explanations such as low-frequency tinnitus must be sought. The main aim of this study is to answer this fundamental question...

  13. 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 (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.

  14. Evaluation and Improvement of Liquid Propellant Rocket Chugging Analysis Techniques. Part 1: A One-Dimensional Analysis of Low Frequency Combustion Instability in the Fuel Preburner of the Space Shuttle Main Engine. Final Report M.S. Thesis - Aug. 1986

    Science.gov (United States)

    Lim, Kair Chuan

    1986-01-01

    Low frequency combustion instability, known as chugging, is consistently experienced during shutdown in the fuel and oxidizer preburners of the Space Shuttle Main Engines. Such problems always occur during the helium purge of the residual oxidizer from the preburner manifolds during the shutdown sequence. Possible causes and triggering mechanisms are analyzed and details in modeling the fuel preburner chug are presented. A linearized chugging model, based on the foundation of previous models, capable of predicting the chug occurrence is discussed and the predicted results are presented and compared to experimental work performed by NASA. Sensitivity parameters such as chamber pressure, fuel and oxidizer temperatures, and the effective bulk modulus of the liquid oxidizer are considered in analyzing the fuel preburner chug. The computer program CHUGTEST is utilized to generate the stability boundary for each sensitivity study and the region for stable operation is identified.

  15. Low frequency noise of gallium nitride-based deep ultraviolet light emitting diodes

    Science.gov (United States)

    Sawyer, Shayla Maya Louise

    This study covers the investigation of deep UV GaN-based light emitting diodes using low frequency noise characterization. Using this technique, device improvements were analyzed as feedback to developers and practical parameters were created for system use. AlGaN LEDs emit wavelengths into the deep UV spectral region (lambda food and water sterilization, non-line-of-sight short range communication, counterfeit identification, photolithography, and general white lighting. The current technological trend demonstrates a decrease in material quality and device performance with decreasing wavelength. However, progress has allowed for its commercialization in a relatively short period of time. Characterization of material and device improvements provides feedback for changes in development. Secondly, methods to determine the reliability and stability of these devices are essential to the applications for which they are used. One such method is through optical and current low frequency noise (LFN) measurements in which both system related parameters such as a signal-to-noise ratio for light sources and insight into the fundamental physics within the devices can be determined. The quality of the device can be compared before costly integration into systems that require low noise, high reliability, and optical stability. It not only quantifies performance limiting noise levels, but it is known to be a sensitive, nondestructive measure of material quality and reliability. The research highlighted in this thesis demonstrates a new measurement technique in analyzing the light intensity fluctuations through low frequency optical noise. From this work, a proposed figure-of-merit is presented. Low frequency current noise was performed as a well known indicator of material quality. Each technique compares LEDs grown by SET Inc. LEDs of varying wavelengths along the UV spectrum, with different growth methods and device structures. The cross-correlation between optical and current

  16. Low-frequency fields - sources and exposure

    International Nuclear Information System (INIS)

    Kunsch, B.

    1993-01-01

    The author briefly discusses definition of terms, gives an introduction to measurement techniques and describes the characteristics of various low-frequency fields and their causes using typical examples: natural electric fields (thunderstroms), natural magnetic fields, technical electric constant fields (urban transportation, households), static magnetic fields (urban transportation, nuclear magnetic resonance imaging), technical electric alternating fields (high-voltage transmission lines, households), and magnetic alternating fields (high-voltage transmission lines). The author discusses both occupational exposure and that of the general public while underpinning his statements by numerous tables, measurement diagrams and charts. (Uhe) [de

  17. Review of subsidence and stabilization techniques

    International Nuclear Information System (INIS)

    Fernando, D.A.

    1988-01-01

    In Britain the damage caused by underground coal mining operations approximates to about 100 million pounds Sterling per annum, most of the damage resulting from longwall mining operations. Causes of subsidence can be attributed to the following factors: (1) roof failure (2) pillar failure (3) floor movements. Currently, in Britain, the mining industry is undergoing a state of decline for economic reasons. Consequently, the number of old coal sites available for development schemes has increased. Therefore, the problems associated with subsidence can be segregated into two parts. The first being the mitigation of the effects of subsidence on structures on actively mined areas. The second being the stabilization and rehabilitation of ground over and around old mine sites for new development schemes. In the former case the stabilization techniques employed may be local or global, depending on the problems encountered in any particular area. In the latter case, generally, grouting techniques are employed. This paper aims to review the causes of subsidence and the techniques used to minimize its effect on structures. Also, more economic alternative methods of ground stabilization techniques are described and proposed, to be used in this area of ground engineering

  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 (fsonophoresis). This review summarizes mechanisms and applications of low-frequency sonophoresis. In vitro, in vivo, as well as clinical studies demonstrating the effect of low-frequency ultrasound on transdermal drug delivery and glucose extraction are summarized. Mechanistic insights gained through a number of investigations are also reviewed. Finally, reports on the synergistic effect of low-frequency ultrasound with other enhancers including chemicals and iontophoresis are summarized.

  19. Robust Coordinated Design of PSS and TCSC using PSO Technique for Power System Stability Enhancement

    Directory of Open Access Journals (Sweden)

    S. Panda

    2007-06-01

    Full Text Available Power system stability improvement by coordinated design of a Power System Stabilizer (PSS and a Thyristor Controlled Series Compensator (TCSC controller is addressed in this paper. Particle Swarm Optimization (PSO technique is employed for optimization of the parameterconstrained nonlinear optimization problem implemented in a simulation environment. The proposed controllers are tested on a weakly connected power system. The non-linear simulation results are presented for wide range of loading conditions with various fault disturbances and fault clearing sequences as well as for various small disturbances. The eigenvalue analysis and simulation results show the effectiveness and robustness of proposed controllers to improve the stability performance of power system by efficient damping of low frequency oscillations under various disturbances.

  20. Stabilizing Rabi oscillation of a charge qubit via the atomic clock technique

    Science.gov (United States)

    Yu, Deshui; Landra, Alessandro; Kwek, Leong Chuan; Amico, Luigi; Dumke, Rainer

    2018-02-01

    We propose a superconducting circuit-atom hybrid, where the Rabi oscillation of single excess Cooper pair in the island is stabilized via the common atomic clock technique. The noise in the superconducting circuit is mapped onto the voltage source which biases the Cooper-pair box via an inductor and a gate capacitor. The fast fluctuations of the gate charge are significantly suppressed by an inductor-capacitor resonator, leading to a long-relaxation-time Rabi oscillation. More importantly, the residual low-frequency fluctuations are further reduced by using the general feedback-control method, in which the voltage bias is stabilized via continuously measuring the dc-Stark-shift-induced atomic Ramsey signal. The stability and coherence time of the resulting charge-qubit Rabi oscillation are both enhanced. The principal structure of this Cooper-pair-box oscillator is studied in detail.

  1. Effective masking bandwidths at low frequencies.

    Science.gov (United States)

    Fidell, S; Horonjeff, R; Teffeteller, S; Green, D M

    1983-02-01

    Masking of low-frequency sinusoids of varying durations by Gaussian noise of varying spectral shape was measured in three different studies. Common solutions to technical problems associated with control and specification of low-frequency signals were used in the three studies. If interpreted in terms of Fletcher's critical ratio assumptions, data from the first study lead to the inference that the masking bandwidth is inversely related to signal frequency below about 200 Hz. Data from the second study rule out the likelihood that the apparent increase in masking bandwidth is attributable to changes in auditory integration times at low frequencies. The data of the third study suggest that the apparent increase in auditory filter bandwidth at low frequencies is more adequately explained by a decrease in observers' detection efficiency than by broadening of the filter bandpass.

  2. Passive Shielding for Low Frequency Magnetic Films

    National Research Council Canada - National Science Library

    Damaskos, Nickander

    1997-01-01

    Report developed under SBIR Contract. An approach to low frequency shielding is shown with application to suppression of electromagnetic fields emanating from rail gun barrels and power cable busses. Damaskos, Inc...

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

    Science.gov (United States)

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

    2008-07-01

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

  4. The reduction of low frequency fluctuations in RFP experiments

    Energy Technology Data Exchange (ETDEWEB)

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

    1998-09-01

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

  5. The reduction of low frequency fluctuations in RFP experiments

    International Nuclear Information System (INIS)

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

    1998-01-01

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

  6. 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

  7. 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

  8. 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...

  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

  11. Low-frequency fields - health risk assessment

    International Nuclear Information System (INIS)

    Bernhardt, J.

    1993-01-01

    The author briefly reviews the biological actions and effects of low-frequency fields, epidemiological studies and discusses health risks in detail. He describes the assessment principles of the International Commission on Non-ionizing Radiation Protection (ICNIRP), medical principles for risk assessment, determination of limits and thesholds, and aspects of prevention. This is supplemented to by several fables and literature list. (Uhe) [de

  12. 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...

  13. The Astronomical Low-Frequency Array

    Science.gov (United States)

    Jones, D. L.; Allen, R. J.; Blume, W. H.; Desch, M. M.; Erickson, W. C.; Kaiser, M. L.; Kassim, N. E.; Kuiper, T. B. H.; Mahoney, M. J.; Marsh, K. A.; hide

    1996-01-01

    An array of satellites is proposed to make astronomic observations in the low frequency range of a few tens of MHz down to roughly 100 kHz, a range that cannot be observed through the ionosphere. The array would be in a solar orbit to avoid radio interference from Earth and to simplify trajectory tracking and control.

  14. Seabed Scattering from Low Frequency Reverberation Measurements

    Science.gov (United States)

    2015-09-30

    bottom element dA at a grazing angle h, the backward scattering intensity at one me- ter from an elementary area in the u direction can be written as...X.Z. Zhang, " Low frequency seabed scattering at low grazing angles," Journal of the Acoustical Society of America, 131 (4), 261 1-2621 (Apr 2012). 2...reverberation, shallow water acoustics, low grazing angles scattering, shear waves 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF a . REPORT b

  15. 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.

  16. Sensors for low frequency electromagnetic radiation

    International Nuclear Information System (INIS)

    Huber, E.; Urban, M.

    1996-01-01

    For estimating the personal exposure from low fequency electric and magnetic fields suitable measurement systems are necessary. Investigations of appropriate magnetic and electric field probes and sensors have been done as a basis for a pocket sized personal dosimeter. There exist many different sensors, which can be used for the measurement of static and low frequency magnetic fields, such as inductive transducers, hall generators, tunnel diode oscillators, flux gate sensors and magnetoresistive sensors. In contrast to the magnetic sensors there are less different sensor types based on different physical detection principles available showing a sufficient sensitivity for low frequency electrical fields. Important is the knowledge on the feed back of the sensor itself on the detected field strength. Whether a sensor is suitable for a certain application is depending on its frequency related sensitivity, its signal to noise ratio, linearity and detection range, sensitivity to environmental influences as temperature, humidity etc. This presentation will focus on some important basic aspects of the measurement of low frequency electrical and magnetic fields for radiation protection purposes. (author)

  17. An agile laser with ultra-low frequency noise and high sweep linearity.

    Science.gov (United States)

    Jiang, Haifeng; Kéfélian, Fabien; Lemonde, Pierre; Clairon, André; Santarelli, Giorgio

    2010-02-15

    We report on a fiber-stabilized agile laser with ultra-low frequency noise. The frequency noise power spectral density is comparable to that of an ultra-stable cavity stabilized laser at Fourier frequencies higher than 30 Hz. When it is chirped at a constant rate of approximately 40 MHz/s, the max non-linearity frequency error is about 50 Hz peak-to-peak over more than 600 MHz tuning range. The Rayleigh backscattering is found to be a significant frequency noise source dependent on fiber length, chirping rate and the power imbalance of the interferometer arms. We analyze this effect both theoretically and experimentally and put forward techniques to reduce this noise contribution.

  18. Status of the low frequency facility experiment

    Energy Technology Data Exchange (ETDEWEB)

    Bracci, L [Dipartimento di Fisica, Universita di Firenze, Florence (Italy); Calamai, G [Istituto Nazionale di Fisica Nucleare, Sez Firenze/Urbino (Italy); Cuoco, E [Istituto Nazionale di Fisica Nucleare, Sez Firenze/Urbino (Italy); Dominici, P [Dipartimento di Fisica, Universita di Firenze, Firenze (Italy); Fabbroni, L [Istituto Nazionale di Fisica Nucleare, Sez Firenze/Urbino (Italy); Guidi, G [Dipartimento di Fisica, Universita di Urbino, Urbino (Italy); Losurdo, G [Istituto Nazionale di Fisica Nucleare, Sez Firenze/Urbino (Italy); Martelli, F [Istituto Nazionale di Fisica Nucleare, Sez Firenze/Urbino (Italy); Mazzoni, M [Istituto Nazionale di Fisica Nucleare, Sez Firenze/Urbino (Italy); Stanga, R [Istituto Nazionale di Fisica Nucleare, Sez Firenze/Urbino (Italy); Vetrano, F [Dipartimento di Fisica, Universita di Urbino, Urbino (Italy); Porzio, A [Istituto Nazionale di Fisica Nucleare, Sez Naples (Italy); Ricciardi, I [Istituto Nazionale di Fisica Nucleare, Sez Naples (Italy); Solimeno, S [Istituto Nazionale di Fisica Nucleare, Sez Naples (Italy); Ballardin, G [Istituto Nazionale di Fisica Nucleare, Sez Pisa (Italy); Braccini, S [Istituto Nazionale di Fisica Nucleare, Sez Pisa (Italy); Bradaschia, C [Istituto Nazionale di Fisica Nucleare, Sez Pisa (Italy); Casciano, C [Istituto Nazionale di Fisica Nucleare, Sez Pisa (Italy); Cavalieri, R [Istituto Nazionale di Fisica Nucleare, Sez Pisa (Italy); Cecchi, R [Istituto Nazionale di Fisica Nucleare, Sez Pisa (Italy); Cella, G [Istituto Nazionale di Fisica Nucleare, Sez Pisa (Italy); Dattilo, V [Istituto Nazionale di Fisica Nucleare, Sez Pisa (Italy); Virgilio, A Di [Istituto Nazionale di Fisica Nucleare, Sez Pisa (Italy); Fazzi, M [Istituto Nazionale di Fisica Nucleare, Sez Pisa (Italy); Ferrante, I [Istituto Nazionale di Fisica Nucleare, Sez Pisa (Italy); Fidecaro, F [Istituto Nazionale di Fisica Nucleare, Sez Pisa (Italy)] [and others

    2002-04-07

    The low frequency facility is a VIRGO R and D experiment having the goal of performing a direct measurement of the thermal noise of the VIRGO suspensions by means of a two-mirror Fabry-Perot cavity suspended to the last stage of the attenuating chain. The present status of advancement of this experiment is reported: the apparatus, including mechanical and optical parts, has been completely built and put into operation. Vacuum facilities and the first control loops are active. First measurements on the suspended cavity are in progress.

  19. A variable passive low-frequency absorber

    DEFF Research Database (Denmark)

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

    2005-01-01

    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...

  20. Status of the low frequency facility experiment

    International Nuclear Information System (INIS)

    Bracci, L; Calamai, G; Cuoco, E; Dominici, P; Fabbroni, L; Guidi, G; Losurdo, G; Martelli, F; Mazzoni, M; Stanga, R; Vetrano, F; Porzio, A; Ricciardi, I; Solimeno, S; Ballardin, G; Braccini, S; Bradaschia, C; Casciano, C; Cavalieri, R; Cecchi, R; Cella, G; Dattilo, V; Virgilio, A Di; Fazzi, M; Ferrante, I; Fidecaro, F; Frasconi, F; Gennaro, G; Giazotto, A; Holloway, L; Penna, P La; Lomtadze, T; Nenci, F; Nicolosi, L; Lelli, F; Paoletti, F; Pasqualetti, A; Passaquieti, R; Passuello, D; Poggiani, R; Raffaelli, F; Taddei, R; Vicere, A; Zhang, Z; Frasca, S; Majorana, E; Palomba, C; Perciballi, M; Puppo, P; Rapagnani, P; Ricci, F

    2002-01-01

    The low frequency facility is a VIRGO R and D experiment having the goal of performing a direct measurement of the thermal noise of the VIRGO suspensions by means of a two-mirror Fabry-Perot cavity suspended to the last stage of the attenuating chain. The present status of advancement of this experiment is reported: the apparatus, including mechanical and optical parts, has been completely built and put into operation. Vacuum facilities and the first control loops are active. First measurements on the suspended cavity are in progress

  1. Suspension for the low frequency facility

    CERN Document Server

    Cella, G; Di Virgilio, A; Gaddi, A; Viceré, A

    2000-01-01

    We introduce the working principles of the VIRGO Low Frequency Facility (LFF), whose main aim is the measurement of the thermal noise in the VIRGO suspension system. We evaluate the displacement thermal noise of a mirror, which is an intermediate element of a double pendulum suspension system. This double pendulum will be suspended to the last stage of a VIRGO Super-Attenuator (SA), the prototype VIRGO suspension system being tested at the Pisa section of INFN. In the proposed configuration, we evaluate the spectrum of the thermal noise for different choices of the parameters: based on this study, we comment on the future directions to be undertaken in the LFF experiment.

  2. Child leukaemia and low frequency electromagnetic fields

    International Nuclear Information System (INIS)

    Clavel, J.

    2009-01-01

    The author discusses the possible causes of child leukaemia: exposure to natural ionizing radiation (notably radon), to pesticides, and to hydrocarbons emitted by road traffic. Some studies suggested that an inadequate reaction of the immune system to an ordinary infection could result in leukaemia. Other factors are suspected, notably extremely low frequency electromagnetic fields, the influence of which is then discussed by the author. She evokes and discusses results of different investigations on this topic which have been published since the end of the 1970's. It appears that a distance less than 50 meters from high voltage lines or the vicinity of transformation stations may double the risk of child leukaemia

  3. A low frequency RFI monitoring system

    Science.gov (United States)

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

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

  4. Power system stabilizers based on modern control techniques

    Energy Technology Data Exchange (ETDEWEB)

    Malik, O.P.; Chen, G.P.; Zhang, Y.; El-Metwally, K. [Calgary Univ., AB (Canada). Dept. of Electrical and Computer Engineering

    1994-12-31

    Developments in digital technology have made it feasible to develop and implement improved controllers based on sophisticated control techniques. Power system stabilizers based on adaptive control, fuzzy logic and artificial networks are being developed. Each of these control techniques possesses unique features and strengths. In this paper, the relative performance of power systems stabilizers based on adaptive control, fuzzy logic and neural network, both in simulation studies and real time tests on a physical model of a power system, is presented and compared to that of a fixed parameter conventional power system stabilizer. (author) 16 refs., 45 figs., 3 tabs.

  5. Dual-Phase Lock-In Amplifier Based on FPGA for Low-Frequencies Experiments

    Directory of Open Access Journals (Sweden)

    Gonzalo Macias-Bobadilla

    2016-03-01

    Full Text Available Photothermal techniques allow the detection of characteristics of material without invading it. Researchers have developed hardware for some specific Phase and Amplitude detection (Lock-In Function applications, eliminating space and unnecessary electronic functions, among others. This work shows the development of a Digital Lock-In Amplifier based on a Field Programmable Gate Array (FPGA for low-frequency applications. This system allows selecting and generating the appropriated frequency depending on the kind of experiment or material studied. The results show good frequency stability in the order of 1.0 × 10−9 Hz, which is considered good linearity and repeatability response for the most common Laboratory Amplitude and Phase Shift detection devices, with a low error and standard deviation.

  6. Dual-Phase Lock-In Amplifier Based on FPGA for Low-Frequencies Experiments.

    Science.gov (United States)

    Macias-Bobadilla, Gonzalo; Rodríguez-Reséndiz, Juvenal; Mota-Valtierra, Georgina; Soto-Zarazúa, Genaro; Méndez-Loyola, Maurino; Garduño-Aparicio, Mariano

    2016-03-16

    Photothermal techniques allow the detection of characteristics of material without invading it. Researchers have developed hardware for some specific Phase and Amplitude detection (Lock-In Function) applications, eliminating space and unnecessary electronic functions, among others. This work shows the development of a Digital Lock-In Amplifier based on a Field Programmable Gate Array (FPGA) for low-frequency applications. This system allows selecting and generating the appropriated frequency depending on the kind of experiment or material studied. The results show good frequency stability in the order of 1.0 × 10(-9) Hz, which is considered good linearity and repeatability response for the most common Laboratory Amplitude and Phase Shift detection devices, with a low error and standard deviation.

  7. Low frequency electromagnetic fields and health problems

    International Nuclear Information System (INIS)

    Zahedi, A.; Cosic, I.

    1996-01-01

    Full text: Electromagnetic fields developed around the electric circuits are considered as magnetic pollution and these fields are produced wherever electric appliances or machinery are used at home as well as at workplace. Electric fields and magnetic fields around the home are produced by anything with electric current flowing through it including: the street power lines, the home wiring system, electric ovens, refrigerators, washing machines, electric clothes dryers, vacuum cleaners, television sets, video cassette recorders, toasters, light bulbs, clock radios, electric blankets, mobile phones, etc. In the workplace they would be produced by: nearby power lines, factory machinery, computers/video display units, lights, photocopiers, electrical cabling etc. As one can see, human life is strongly dependent on using-electric appliance. A large number of studies have been undertaken to find out the correlation between electromagnetic fields and health problems. The following significant results have been reported [Lerner E.J., IEEE Spectrum, 57-67, May 1984]: (a) Induction of chromosomal defects in mice spermatogenetic cells following microwave radiation in the Ghz range; (b) Changes in the calcium balance of living cats' brains exposed to microwaves modulated at extremely low frequencies; (c) Alternation of nerve and bone cells exposed to extremely low frequency fields; (d) Decreased activity of the immune cells of mice exposed to modulated microwaves; (e) Apparent increase in deformed foetuses among miniature swine exposed to intense power-line frequency fields. The mostly investigated effect is the effect of electromagnetic irradiation in particular one produced by power lines, and cancer. More than 100 epidemiological studies have been reported but no conclusive result was achieved. A number of studies with laboratory animals were also inconclusive. However, some of these experiments have shown improvements in immune system and tumour suppression when

  8. 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.

  9. Glenohumeral internal rotation measurements differ depending on stabilization techniques.

    Science.gov (United States)

    Wilk, Kevin E; Reinold, Michael M; Macrina, Leonard C; Porterfield, Ron; Devine, Kathleen M; Suarez, Kim; Andrews, James R

    2009-03-01

    The loss of glenohumeral internal rotation range of motion in overhead athletes has been well documented in the literature. Several different methods of assessing this measurement have been described, making comparison between the results of studies difficult. Significant differences in the amount of internal rotation range of motion exist when using different methods of stabilization. Descriptive laboratory study. THREE TECHNIQUES WERE USED BILATERALLY IN RANDOM FASHION TO MEASURE GLENOHUMERAL INTERNAL ROTATION RANGE OF MOTION: stabilization of the humeral head, stabilization of the scapula, and visual inspection without stabilization. An initial study on 20 asymptomatic participants was performed to determine the intrarater and interrater reliability for each measurement technique. Once complete, measurements were performed on 39 asymptomatic professional baseball players to determine if a difference existed in measurement techniques and if there was a significant side-to-side difference. A 2-way repeated-measures analysis of variance was used. While interrater reliability was fair between all 3 methods, scapular stabilization provided the best intrarater reliability. A statistically significant difference was observed between all 3 methods (P < .001). Internal rotation was significantly less in the dominant shoulder than in the nondominant shoulder (P < .001). Differences in internal rotation range of motion measurements exist when using different methods. The scapula stabilization method displayed the highest intrarater reproducibility and should be considered when evaluating internal rotation passive range of motion of the glenohumeral joint. A standardized method of measuring internal rotation range of motion is required to accurately compare physical examinations of patients. The authors recommend the use of the scapula stabilization method to assess internal rotation range of motion by allowing normal glenohumeral arthrokinematics while stabilizing the

  10. Effects of Preservative Techniques on the Storage Stability of ...

    African Journals Online (AJOL)

    The effect of different preservative techniques on the storage stability of sorghum stem sheath beverage was studied. A portion of the beverage samples were pasteurized at 75oC for 15 mins, another pasteurized and refrigerated and the other pasteurized and preserved with 0.1% sodium benzoate and they were studied at ...

  11. 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.

  12. Dissipative elastic metamaterial with a low-frequency passband

    Science.gov (United States)

    Liu, Yongquan; Yi, Jianlin; Li, Zheng; Su, Xianyue; Li, Wenlong; Negahban, Mehrdad

    2017-06-01

    We design and experimentally demonstrate a dissipative elastic metamaterial structure that functions as a bandpass filter with a low-frequency passband. The mechanism of dissipation in this structure is well described by a mass-spring-damper model that reveals that the imaginary part of the wavenumber is non-zero, even in the passband of dissipative metamaterials. This indicates that transmittance in this range can be low. A prototype for this viscoelastic metamaterial model is fabricated by 3D printing techniques using soft and hard acrylics as constituent materials. The transmittance of the printed metamaterial is measured and shows good agreement with theoretical predictions, demonstrating its potential in the design of compact waveguides, filters and other advanced devices for controlling mechanical waves.

  13. Dissipative elastic metamaterial with a low-frequency passband

    Directory of Open Access Journals (Sweden)

    Yongquan Liu

    2017-06-01

    Full Text Available We design and experimentally demonstrate a dissipative elastic metamaterial structure that functions as a bandpass filter with a low-frequency passband. The mechanism of dissipation in this structure is well described by a mass-spring-damper model that reveals that the imaginary part of the wavenumber is non-zero, even in the passband of dissipative metamaterials. This indicates that transmittance in this range can be low. A prototype for this viscoelastic metamaterial model is fabricated by 3D printing techniques using soft and hard acrylics as constituent materials. The transmittance of the printed metamaterial is measured and shows good agreement with theoretical predictions, demonstrating its potential in the design of compact waveguides, filters and other advanced devices for controlling mechanical waves.

  14. A ratchet mechanism for low-frequency hearing in mammals

    Science.gov (United States)

    Reichenbach, Tobias; Hudspeth, A. J.

    2010-03-01

    The sensitivity and frequency selectivity of hearing result from tuned amplification by an active process in the mechanoreceptive hair cells. The nature of the active process in the mammalian cochlea is intensely debated, for outer hair cells exhibit two forms of mechanical activity, active hair-bundle motility and membrane-based electromotility. Here we show theoretically that active hair-bundle motility and electromotility can together implement an efficient mechanism for amplification that functions like a ratchet: sound-evoked forces acting on the basilar membrane are transmitted to the hair bundles while electromotility decouples the active hair-bundle forces from the basilar membrane. Through a combination of analytical and computational techniques we demonstrate that the ratchet mechanism can naturally account for a variety of unexplained experimental observations from low-frequency hearing.

  15. Techniques for the reduction of low frequency noise in buildings

    NARCIS (Netherlands)

    Zuada Coelho, B.A.; Koopman, A.

    2012-01-01

    Vibration isolation of buildings is often achieved by introducing spring systems at the foundation level. This can be an effective measure, especially against vibrations induced by noise, but it is also very costly. Due to the current usage of the cities space, where buildings and infrastructures

  16. 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

  17. Voltage Stabilizer Based on SPWM technique Using Microcontroller

    Directory of Open Access Journals (Sweden)

    K. N. Tarchanidis

    2013-01-01

    Full Text Available This paper presents an application of the well known SPWM technique on a voltage stabilizer, using a microcontroller. The stabilizer is AC/DC/AC type. So, the system rectifies the input AC voltage to a suitable DC level and the intelligent control of an embedded microcontroller regulates the pulse width of the output voltage in order to produce through a filter a perfect sinusoidal AC voltage. The control program on the microcontroller has the ability to change the FET transistor firing in order to compensate any input voltage variation. The applied software using the microcontroller’s interrupts managed to achieve concurrency on the running program.

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

    Science.gov (United States)

    Ogura, Makoto; Paliwal, Sumit; Mitragotri, Samir

    2008-06-30

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

  19. The Radio And Very Low Frequency (VLF) Electromagnetic ...

    African Journals Online (AJOL)

    The Radio And Very Low Frequency (VLF) Electromagnetic Response Of A Layered Earth Media With Variable Dielectric Permittivity. ... A radio frequency of 125 KHz and a very low frequency (VLF) of 20 KHz were used in the computations and the field parameters studied over a dimensionless induction number, B. The ...

  20. Behavioral estimates of human frequency selectivity at low frequencies

    DEFF Research Database (Denmark)

    Orellana, Carlos Andrés Jurado

    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...

  1. Measurement of low-frequency noise in rooms

    DEFF Research Database (Denmark)

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

    2006-01-01

    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 to the high...

  2. Low-frequency Raman scattering in alkali tellurite glasses

    Indian Academy of Sciences (India)

    Wintec

    TeO3 units with a varying number of non-bridging oxygen atoms. Emphasis has also been given to the low- frequency modes and particular points related to the low-frequency Raman phenomenology are discussed in view of the experimental findings. Keywords. Tellurites; Raman spectroscopy; alkali tellurite glasses. 1.

  3. Annoyance of low frequency noise and traffic noise

    DEFF Research Database (Denmark)

    Mortensen, Frank Rysgaard; Poulsen, Torben

    2000-01-01

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

  4. 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...

  5. Design and optimization of the low frequency eddy current technique for the volumetric inspection of austenitic small diameter tubes with a wall thickness up to 12 mm; Auslegung und Optimierung des Niederfrequenz-Wirbelstrom-Verfahrens fuer die volumetrische Pruefung von austenitischen Neben- und Kleinleitungen mit Wandstaerken bis 12 mm

    Energy Technology Data Exchange (ETDEWEB)

    Becker, R.; Bessert, S.; Disque, M.; Weiss, R. [Fraunhofer-Institut fuer Zerstoerungsfreie Pruefverfahren, Saarbruecken (Germany)

    1998-11-01

    The low-frequency eddy current technique discussed is a suitable external inspection technique detecting defects at the inner walls of small-diameter tubes and measuring their depths via the ligament. A testing system with optimized sensor lus software for image recording, evaluation, display and documentation is available. The current state of development of the system permits detection and measurement of defects up to 20 mm in size in austenitic inner walls 12.5 mm thick down to a depth of 3 mm. This applies both to the homogenous base metal and the weld with {delta} ferrite. (orig./CB) [Deutsch] Das vorgestellte Niederfrequenz-Wirbelstrom-Verfahren ist geeignet, bei Pruefung von aussen Fehler an der Innenseite von Klein- und Nebenleitungen nachzuweisen und ueber das Ligament deren Tiefe zu bestimmen. Ein entsprechendes Pruefsystem mit optimiertem Sensor und der Software zur Aufnahme, Auswertung, Darstellung und Dokumentation der Wirbelstrom-Urdaten steht zur Verfuegung. Beim jetzigen Entwicklungsstand liegt die Nachweisgrenze fuer einen 20 mm langen Innenfehler in einer 12.5 mm dicken austenitischen Wandung bei einer Fehlertiefe von 3 mm. Dies gilt sowohl fuer den homogenen Grundwerkstoff als auch fuer Schweissgefuege mit {delta}-Ferrit. (orig./MM)

  6. Low-frequency scaling applied to stochastic finite-fault modeling

    Science.gov (United States)

    Crane, Stephen; Motazedian, Dariush

    2014-01-01

    Stochastic finite-fault modeling is an important tool for simulating moderate to large earthquakes. It has proven to be useful in applications that require a reliable estimation of ground motions, mostly in the spectral frequency range of 1 to 10 Hz, which is the range of most interest to engineers. However, since there can be little resemblance between the low-frequency spectra of large and small earthquakes, this portion can be difficult to simulate using stochastic finite-fault techniques. This paper introduces two different methods to scale low-frequency spectra for stochastic finite-fault modeling. One method multiplies the subfault source spectrum by an empirical function. This function has three parameters to scale the low-frequency spectra: the level of scaling and the start and end frequencies of the taper. This empirical function adjusts the earthquake spectra only between the desired frequencies, conserving seismic moment in the simulated spectra. The other method is an empirical low-frequency coefficient that is added to the subfault corner frequency. This new parameter changes the ratio between high and low frequencies. For each simulation, the entire earthquake spectra is adjusted, which may result in the seismic moment not being conserved for a simulated earthquake. These low-frequency scaling methods were used to reproduce recorded earthquake spectra from several earthquakes recorded in the Pacific Earthquake Engineering Research Center (PEER) Next Generation Attenuation Models (NGA) database. There were two methods of determining the stochastic parameters of best fit for each earthquake: a general residual analysis and an earthquake-specific residual analysis. Both methods resulted in comparable values for stress drop and the low-frequency scaling parameters; however, the earthquake-specific residual analysis obtained a more accurate distribution of the averaged residuals.

  7. Effects of low-frequency pulsed electromagnetic fields on plateau frostbite healing in rats.

    Science.gov (United States)

    Jiao, Mingke; Lou, Lin; Jiao, Lin; Hu, Jie; Zhang, Peng; Wang, Zhongming; Xu, Wenjuan; Geng, Xiliang; Song, Hongping

    2016-11-01

    Plateau frostbite (PF) treatments have remained a clinical challenge because this condition injures tissues in deep layers and affected tissues exhibit unique pathological characteristics. For instance, low-frequency pulsed electromagnetic field (PEMF) can affect tissue restoration and penetrate tissues. Therefore, the effect of PEMF on PF healing should be investigated. This study aimed to evaluate the effects of low-frequency PEMF on PF healing systematically. Ninety-six Sprague-Dawley rats were randomly and equally divided into three groups: normal control, partial thickness plateau frostbite (PTPF), and PTPF with low-frequency PEMF exposure (PTPF + PEMF). PTPF wounds were induced in the dorsum of the rats. The PTPF + PEMF group was exposed to low-frequency PEMF daily. During PF healing, wound microcirculation in each group was monitored through contrast ultrasonography. Wound appearance, histological observation, and wound tensile strength were also evaluated. Results showed that the rate of the microcirculation restoration of the PTPF + PEMF group was nearly 25% faster than that of the PTPF group, and wound appearance suggested that the healing of the PTPF group was slower than that of the PTPF + PEMF group. Histological observation revealed that PEMF accelerated the growth of different deep tissues, as confirmed by tensile strength examination. Low-frequency PEMF could penetrate PF tissues, promote their restoration, and provide a beneficial effect on PF healing. Therefore, this technique may be a potential alternative to treat PF. © 2016 by the Wound Healing Society.

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

    DEFF Research Database (Denmark)

    Christensen, Anders Tornvig

    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......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...

  9. The role of low-frequency intraseasonal oscillations in the ...

    Indian Academy of Sciences (India)

    frequency intraseasonal modulations with significant impact on the onset and active/break phases occurred in 2002 which were manifested as a good association between low-frequency intraseasonal oscillations and the onset and active/break spells.

  10. Energy harvesting from low frequency applications using piezoelectric materials

    International Nuclear Information System (INIS)

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

    2014-01-01

    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

  11. Passive Acoustic Thermometry Using Low-Frequency Deep Water Noise

    Science.gov (United States)

    2015-09-30

    1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Passive Acoustic Thermometry Using Low-Frequency Deep... thermometry using Cross-correlation processing of deep water ambient noise. OBJECTIVE Our previous research effort has demonstrated that coherent... thermometry using low-frequency deep water ambient noise recorded on the global IMS- CTBTO network Results from this study are expected to help guide the

  12. The use of low frequency AC for offshore wind power

    Energy Technology Data Exchange (ETDEWEB)

    Schuette, T.; Stroem, M.; Gustavsson, Bo [Balfour Beatty Rail AB, Vaesteraas (Sweden)

    2001-07-01

    Low frequency AC, that means AC with a frequency well below the usual frequencies 50 or 60 Hz, has today its main use in single phase AC electrified railways in a number of European countries (16 2/3 Hz), USA (25 Hz) and Costa Rica (20 Hz). Offshore wind power is well suited to 'join the club' as low frequency AC has a number of advantages for that use: Low frequency AC better fits the low revolution frequency of wind power rotors. This can either be used for reduction of pole number for direct generation machines or for a reduction of the gear ratio for conventional machines, resulting in simpler, lighter and more reliable gearboxes. Low frequency AC gives rise to lower charging current/reactive power production, which restricts the maximum cable length for 50 - 60 Hz heavily due to the high specific capacitance of power cables. For low frequency AC, cables longer than 100 km are possible, which is necessary for many future offshore wind power sites. Low frequency AC enables for the use of (air insulated) transmission lines at loads well above their characteristic power, often up to their thermal maximum load. This means that weak 50 or 60 Hz lines between the shore and consumers or stronger parts of a national grid can transfer more power when operated with low frequency AC. On all aspects of low frequency AC, profound knowledge has been accumulated the last century in the railway sector and can be made available for wind power.

  13. Static and low frequency electric and magnetic fields

    International Nuclear Information System (INIS)

    Thommesen, G.; Tynes, T.

    1994-01-01

    The biological effects of exposure to low frequency electric and magnetic fields are reviewed with the objective of summarizing effects directly relevant to considerations of the health and safety of exposed people. Static and low frequency electric and magnetic fields may elicit biological reactions. Whether exposure to such fields may affect human health at field strengths present in everyday or occupational life is still unsettled. There is unsufficient knowledge to establish any dose concept relevant to health risk. 196 refs., 6 tabs

  14. Transdermal drug delivery using low-frequency sonophoresis.

    Science.gov (United States)

    Mitragotri, S; Blankschtein, D; Langer, R

    1996-03-01

    Application of therapeutic ultrasound (frequency: 1-3 MHz and intensity: 0-2 W/cm2) enhances transdermal drug transport, although typically by a factor of less than 10. In this paper, we show that application of ultrasound at 20 KHz induces transdermal transport enhancements of up to 1000 times higher than those induced by therapeutic ultrasound. In vitro (human cadaver epidermis) as well as in vivo (hairless rat skin) permeation experiments were performed to assess the effect of low-frequency ultrasound on transdermal transport. Application of low-frequency ultrasound (20 KHz, 125 mW/cm2, 100 msec pulses applied every second) enhanced transdermal transport of several permeants, including estradiol, salicylic acid, corticosterone, sucrose, aldosterone, water, and butanol, across human cadaver skin by a factor in the range of 3 to 3000 and that of salicylic acid across hairless rat skin in vivo by a factor of up to 300. Low-frequency ultrasound did not induce a long-term loss of the barrier properties of the skin (in vitro) or damage to living skin of hairless rats. At a mechanistic level, it is hypothesized that application of low-frequency ultrasound enhances transdermal transport through aqueous channels in the SC generated by cavitation-induced bilayer disordering. Support for this hypothesis is provided using experimental and theoretical analyses of low-frequency sonophoresis. Low-frequency ultrasound enhances transdermal transport of drugs more effectively than that induced by therapeutic ultrasound.

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

    Science.gov (United States)

    LoVerde, John J.; Dong, David W.

    2002-11-01

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

  16. 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. © 2011 Acoustical Society of America

  17. Performance enhancement of pneumatic vibration isolation tables in low frequency range by time delay control

    Science.gov (United States)

    Shin, Yun-Ho; Kim, Kwang-Joon

    2009-04-01

    As environmental vibration requirements on precision equipment become more stringent, the use of pneumatic isolators has become more popular and their performance is subsequently required to be further improved. Dynamic performance of passive pneumatic isolators is related to various design parameters in a complicated manner and that in low-frequency range is limited by resonance frequency or volume of pneumatic chambers in practice. In this study, an active control technique, called as time delay control, is applied to a pneumatic isolator to enhance the isolation performance in the low frequency range where the passive techniques have difficulties. This time delay control technique is taken especially because it is known to be useful for the low frequency control. The procedure of applying the time delay control technique to the pneumatic isolator is presented, together with how to resolve distortion problems in actuator dynamics in implementing the active control technique into a pneumatic system. Effectiveness of the technique in enhancement of transmissibility performance is shown based on simulation as well as experiments. Comparisons with passive pneumatic isolators are also presented.

  18. 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.

  19. 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.

  20. Low frequency electrostatic modes in a magnetized dusty plasma

    International Nuclear Information System (INIS)

    Salimullah, M.; Hassan, M.H.A.

    1991-09-01

    The dispersion properties of low frequency electrostatic modes in a dusty plasma in the presence of a static homogeneous magnetic field are examined. It is found that the presence of the dust particles and the static magnetic field have significant effects on the dispersion relations. For the parallel propagation the electrostatic mode is slightly modified by the magnetic field for the ion acoustic branch. A new longitudinal mode arises at the extreme low frequency limit, which is unaffected by the magnetic field for the parallel propagation. For the transverse propagation the ion acoustic mode is not affected by the magnetic field. However, the undamped extreme low frequency mode is significantly modified by the presence of the magnetic field for the propagation transverse to the direction of the magnetic field. (author). 23 refs

  1. 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.

  2. Effect of low-frequency vibrations on speckle interferometry fringes

    International Nuclear Information System (INIS)

    Vikram, C.S.; Pechersky, M.J.

    1998-01-01

    The effects of low-frequency vibrations on speckle correlation fringes have been investigated. The relatively short capture time of the camera in the low-frequency case may yield usable fringe contrast in spite of vibration. It has been shown that the fringes also shift due to the vibration. The study is in agreement with experimental observations of good-contrast correlation fringes even if the object is not on a vibration-isolated table. Some such experimental observations are also presented. copyright 1998 Society of Photo-Optical Instrumentation Engineers

  3. 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.

  4. 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.

  5. 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...

  6. Characteristics of low frequency oscillations of the atmosphere ...

    Indian Academy of Sciences (India)

    R.Narasimhan(krishtel emaging)1461 1996 Oct 15 13:05:22

    The low frequency oscillation of latent heat flux over the tropical oceans has been studied. The. NCEP reanalyzed fields of wind and humidity alongwith Reynolds SST are used to compute the instantaneous as well as monthly mean surface latent heat fluxes (LHF) for the year 1999. The procedure of LHF computation is ...

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

    NARCIS (Netherlands)

    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.

    2006-01-01

    The authors have studied low-frequency resistance fluctuations in shadow-evaporated Al/AlOx/Al tunnel junctions. Between 300 and 5?K the spectral density follows a 1/f law. Below 5?K, individual defects distort the 1/f shape of the spectrum. The spectral density decreases linearly with temperature

  8. 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...

  9. 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...

  10. Indoor measurements of low-frequency noise for annoyance assessment

    DEFF Research Database (Denmark)

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

    2007-01-01

    The sound pressure level within a room may vary as much as 20-30 dB at low frequencies. Mainly the highest levels are of concern with regards to annoyance assessment, rather than a room average. The highest levels can however be very difficult to find. Sound fields in rooms were investigated usin...

  11. Low frequency wave resonance in fringing reef environments

    NARCIS (Netherlands)

    Pomeroy, A.W.M.; van Dongeren, A.; Lowe, R.J.; Van Thiel de Vries, J.S.M.; Roelvink, J.A.

    2012-01-01

    Low frequency wave resonance has been postulated to enhance damage to coral reef protected coastlines during storm events. This paper uses the numerical model XBeach to examine the dynamics that contribute to resonance that have been previously observed on a fringing reef on Guam during tropical

  12. The role of low-frequency intraseasonal oscillations in the ...

    Indian Academy of Sciences (India)

    We analyze the dynamical features and responsible factors of the low-frequency intraseasonal time scales which influenced the nature of onset, intensity and duration of active/break phases and withdrawal of the monsoon during the anomalous Indian summer monsoon of 2002 – the most severe drought recorded in recent ...

  13. 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.

  14. OLFAR - Orbiting low frequency antennas for radio astronomy

    NARCIS (Netherlands)

    Bentum, Marinus Jan

    2013-01-01

    One of the last unexplored frequency ranges in radio astronomy is the frequency band below 30 MHz. New interesting astronomical science drivers for low frequency radio astronomy have emerged, ranging from studies of the astronomical dark ages, the epoch of reionization, exoplanets, to ultra-high

  15. Olfar: orbiting low frequency antenna for radio astronomy

    NARCIS (Netherlands)

    Bentum, Marinus Jan; Boonstra, Albert Jan

    2009-01-01

    New interesting astronomical science drivers for very low frequency radio astronomy have emerged, ranging from studies of the astronomical dark ages, the epoch of reionization, exoplanets, to ultra-high energy cosmic rays. However, astronomical observations with Earth-bound radio telescopes at very

  16. Tracking Galaxy Evolution Through Low-Frequency Radio ...

    Indian Academy of Sciences (India)

    energetic, it is extremely short-lived. This justify focussing on transitio- nal galaxies to find relic-evidences of the immediate past AGN-feedback which decide the future course of evolution of a galaxy. Relic radio lobes can be best detected in low frequency observations with the GMRT,. LOFAR and in future SKA. The age of ...

  17. Low Frequency Radio Emission from the 'Quiet' Sun

    Indian Academy of Sciences (India)

    tribpo

    Astr. (2000) 21, 237 240. Low Frequency Radio Emission from the 'Quiet' Sun. R. Ramesh, Indian Institute of Astrophysics, Bangalore 560034, India, e mail: ramesh@iiap. ernet. in. Abstract. We present observations of the 'quiet' Sun close to the recent solar minimum (Cycle 22), with the Gauribidanur radioheliograph. Our.

  18. Excitation of low-frequency electrostatic instability on the auroral ...

    African Journals Online (AJOL)

    Low-Frequency Electrostatic Instability That Is Observed By Both Ground Facilities And Satellites Have Been Studied In The Auroral Acceleration Region Consisting Of Hot Precipitating Electron Beam From The Magnetosphere, Cold Background Electron And Ion Beam Moving Upward Away From The Earth Along The ...

  19. 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

  20. 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

  1. The low frequency vibrations of hydrogen bonded adipic acid crystals

    Science.gov (United States)

    Yaremko, A. M.; Silvi, B.; Zelsmann, H. R.

    2000-03-01

    The low frequency vibrational spectrum of crystalline adipic acid has been investigated in the range 20-450 cm -1 at room and low temperatures. The experimental results are compared to ab initio results on a model asymmetric unit. It is shown that the doublet and quartet structures observed for several bands are due to Davydov splitting and Fermi resonance effects.

  2. Effects of very low frequency electromagnetic method (VLFEM) and ...

    African Journals Online (AJOL)

    The study examined the impact of livestock dung on ground water status in the study area. To achieve this, a very low frequency EM survey was conducted; the aim and objective was to detect fractures in the subsurface. VLF data were acquired at 5m intervals along two profiles, with maximum length of 60m in the ...

  3. 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 kn...

  4. 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

  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

  6. Low-frequency noise phenomena in switched MOSFETs

    NARCIS (Netherlands)

    van der Wel, A.P.; Klumperink, Eric A.M.; Kolhatkar, J.S.; Hoekstra, E.; Snoeij, Martijn F.; Salm, Cora; Wallinga, Hans; Nauta, Bram

    2007-01-01

    In small-area MOSFETs widely used in analog and RF circuit design, low-frequency (LF) noise behavior is increasingly dominated by single-electron effects. In this paper, we review the limitations of current compact noise models which do not model such single-electron effects. We present measurement

  7. 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

  8. Burn Control in Fusion Reactors via Nonlinear Stabilization Techniques

    International Nuclear Information System (INIS)

    Schuster, Eugenio; Krstic, Miroslav; Tynan, George

    2003-01-01

    Control of plasma density and temperature magnitudes, as well as their profiles, are among the most fundamental problems in fusion reactors. Existing efforts on model-based control use control techniques for linear models. In this work, a zero-dimensional nonlinear model involving approximate conservation equations for the energy and the densities of the species was used to synthesize a nonlinear feedback controller for stabilizing the burn condition of a fusion reactor. The subignition case, where the modulation of auxiliary power and fueling rate are considered as control forces, and the ignition case, where the controlled injection of impurities is considered as an additional actuator, are treated separately.The model addresses the issue of the lag due to the finite time for the fresh fuel to diffuse into the plasma center. In this way we make our control system independent of the fueling system and the reactor can be fed either by pellet injection or by puffing. This imposed lag is treated using nonlinear backstepping.The nonlinear controller proposed guarantees a much larger region of attraction than the previous linear controllers. In addition, it is capable of rejecting perturbations in initial conditions leading to both thermal excursion and quenching, and its effectiveness does not depend on whether the operating point is an ignition or a subignition point.The controller designed ensures setpoint regulation for the energy and plasma parameter β with robustness against uncertainties in the confinement times for different species. Hence, the controller can increase or decrease β, modify the power, the temperature or the density, and go from a subignition to an ignition point and vice versa

  9. Polymorph characterization of active pharmaceutical ingredients (APIs) using low-frequency Raman spectroscopy.

    Science.gov (United States)

    Larkin, Peter J; Dabros, Marta; Sarsfield, Beth; Chan, Eric; Carriere, James T; Smith, Brian C

    2014-01-01

    Polymorph detection, identification, and quantitation in crystalline materials are of great importance to the pharmaceutical industry. Vibrational spectroscopic techniques used for this purpose include Fourier transform mid-infrared (FT-MIR) spectroscopy, Fourier transform near-infrared (FT-NIR) spectroscopy, Raman spectroscopy, and terahertz (THz) and far-infrared (FIR) spectroscopy. Typically, the fundamental molecular vibrations accessed using high-frequency Raman and MIR spectroscopy or the overtone and combination of bands in the NIR spectra are used to monitor the solid-state forms of active pharmaceutical ingredients (APIs). The local environmental sensitivity of the fundamental molecular vibrations provides an indirect probe of the long-range order in molecular crystals. However, low-frequency vibrational spectroscopy provides access to the lattice vibrations of molecular crystals and, hence, has the potential to more directly probe intermolecular interactions in the solid state. Recent advances in filter technology enable high-quality, low-frequency Raman spectra to be acquired using a single-stage spectrograph. This innovation enables the cost-effective collection of high-quality Raman spectra in the 200-10 cm(-1) region. In this study, we demonstrate the potential of low-frequency Raman spectroscopy for the polymorphic characterization of APIs. This approach provides several benefits over existing techniques, including ease of sampling and more intense, information-rich band structures that can potentially discriminate among crystalline forms. An improved understanding of the relationship between the crystalline structure and the low-frequency vibrational spectrum is needed for the more widespread use of the technique.

  10. 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.

  11. TorPeDO: A Low Frequency Gravitational Force Sensor

    Science.gov (United States)

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

    2016-05-01

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

  12. 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...

  13. A lunar far-side very low frequency array

    Science.gov (United States)

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

    1989-01-01

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

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

    Science.gov (United States)

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

    2009-09-01

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

  15. 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.

  16. Low-frequency sonophoresis: pathologic and thermal effects in dogs.

    Science.gov (United States)

    Singer, A J; Homan, C S; Church, A L; McClain, S A

    1998-01-01

    Low-frequency sonophoresis has recently been shown to significantly facilitate transdermal permeability of various substances (e.g., insulin) in animal models, thus eliminating the need to inject such agents. Prior to human trials, the authors studied the safety profile of low-frequency sonophoresis in dogs by evaluating microscopic and temperature changes in the skin after sonophoresis. An evaluator-blinded canine study of sonophoresis using different energy intensities and probe diameters was performed. Low-frequency ultrasound was applied for 60 seconds to the clipped abdominal skin of 3 anesthetized adult mongrel dogs using a sonicator operating at a frequency of 20 KHz with a maximal energy output of 400 W. The sonicator was immersed in normal saline, and intensities of 4%, 10%, 20%, 30%, and 50% were applied during 600 msec of every second (pulsed mode). Three probes, 1-cm cylindrical, 5-cm cylindrical, and 10-cm disc-shaped, were evaluated. Each experimental condition was performed twice. Subcutaneous temperatures were measured by temperature probe before and after sonophoresis. At 30 minutes post-sonophoresis, full-thickness skin biopsies were taken for blinded histopathologic evaluation. Minimal urticarial reactions were noted with the 1-cm probe at intensities of < or = 20% and with the 5-cm probe at 4% intensity. With higher intensity, thermal injuries were observed grossly with erythema and vesicles. The microscopic correlates were papillary and dermal edema with neutrophils and telangiectasia. The conditions producing vesicles grossly had foci of epidermal necrosis, subepidermal vesicles, and degeneration of papillary dermal collagen. With still higher intensities, confluent epidermal necrosis became apparent. Use of the 10-cm probe did not result in any injury. Low-frequency ultrasound at low intensities appears safe for use to enhance the topical delivery of medications, producing only minimal urticarial reactions. Higher-intensity conditions

  17. Study on low frequency probe characterization for concrete application

    International Nuclear Information System (INIS)

    Amry Amin Abas; Mohd Pauzi Ismail

    2002-01-01

    Ultrasonic testing has been widely used in metal and non-metal material. For non-metal material such as concrete, a probe emitting low frequency ultrasonic wave is applied. This paper describes the comparison between three custom made probes using same design and piezoelectric crystal. The only difference is the backing material, which comprise of three different materials. Characterization of each transducer is compared in order to understand the effects of backing material in the probe. (Author)

  18. Preamplifier with ultra low frequency cutoff for infrasonic condenser microphone

    DEFF Research Database (Denmark)

    Kinnerup, Rasmus Trock; Marbjerg, Kresten; Rasmussen, Per

    2012-01-01

    B. Being able to measure down to ultra low frequencies in the infrasonic frequency range will aid actors in the debate on wind turbine noise. Sonic booms from supersonic flights include frequencies down to 10 mHz and the preamplifier proposed in this paper will aid scientists trying to modify the N......-shaped shock wave at high level which prohibits flights in land zones....

  19. Determination of low-frequency vibrational states in glasses

    International Nuclear Information System (INIS)

    Ahmad, N.; Hasan, M.M.

    1996-01-01

    It is shown that density of low frequency (v < 1 THz) vibrational states g(v) in glasses can be determined from heat capacities measured at low temperature. These g(v) are identical to those determined from inelastic neutron scattering studies. The form of g(v) is non quadratic and therefore the Debye density of states may not be used to interpret the Raman, and infrared absorption in glasses. (author)

  20. Renormalized theory of low-frequency hydrodynamic fluctuations in plasmas

    International Nuclear Information System (INIS)

    Sitenko, A.G.; Sosenko, P.P.

    1989-01-01

    The basic statement of the renormalized statistical theory of low-frequency hydrogynamic fluctuations in magnetized plasmas are formulated. Stationary fluctuation spectra are calculated with account for the nonlinear interaction of fluctuations within the context of the theory developed for the general case of electromagnetic interaction. It is demonstrated that electromagnetic effects may influence essentially the spectral characteristics of the convective fluctuations and the relevant anomalous transport in plasmas. 82 refs

  1. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    López, Rodrigo A.; Yoon, Peter H. [Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742 (United States); Viñas, Adolfo F. [NASA Goddard Space Flight Center, Heliophysics Science Division, Geospace Physics Laboratory, Mail Code 673, Greenbelt, MD 20771 (United States); Araneda, Jaime A., E-mail: rlopezh@umd.edu, E-mail: yoonp@umd.edu [Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Concepción, Concepción (Chile)

    2017-08-10

    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.

  3. 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...

  4. Static and low frequency noise characterization of ultra-thin body InAs MOSFETs

    Science.gov (United States)

    Karatsori, T. A.; Pastorek, M.; Theodorou, C. G.; Fadjie, A.; Wichmann, N.; Desplanque, L.; Wallart, X.; Bollaert, S.; Dimitriadis, C. A.; Ghibaudo, G.

    2018-05-01

    A complete static and low frequency noise characterization of ultra-thin body InAs MOSFETs is presented. Characterization techniques, such as the well-known Y-function method established for Si MOSFETs, are applied in order to extract the electrical parameters and study the behavior of these research grade devices. Additionally, the Lambert-W function parameter extraction methodology valid from weak to strong inversion is also used in order to verify its applicability in these experimental level devices. Moreover, a low-frequency noise characterization of the UTB InAs MOSFETs is presented, revealing carrier trapping/detrapping in slow oxide traps and remote Coulomb scattering as origin of 1/f noise, which allowed for the extraction of the oxide trap areal density. Finally, Lorentzian-like noise is also observed in the sub-micron area devices and attributed to both Random Telegraph Noise from oxide individual traps and g-r noise from the semiconductor interface.

  5. Impact of self-assembled monolayer on low frequency noise of organic thin film transistors

    International Nuclear Information System (INIS)

    Ke Lin; Dolmanan, Surani Bin; Shen Lu; Vijila, Chellappan; Chua, Soo Jin; Png, R.-Q.; Chia, P.-J.; Chua, L.-L.; Ho, Peter K-H.

    2008-01-01

    Bottom-contact organic field-effect transistors (FETs) based on regioregular poly(3-hexylthiophene) were fabricated with different surface treatments and were evaluated using a low frequency noise (LFN) spectroscopy. The oxygen-plasma (OP) treated device shows the highest mobility with the lowest current fluctuation. Octadecyltrichlorosilane and perfluorodecyldimetylchlorosilane treated device gives a higher noise compared with the OP treated device. Hexamethyldisilazane treated devices show the highest noise but the lowest mobility. The LFN results are correlated with organic FET device mobility and stability, proved by channel material crystallinity and degree of dislocations analysis. LFN measurement provides a nondisruptive and direct methodology to characterize device performance

  6. The low frequency facility Fabry-Perot cavity used as a speed-meter

    Energy Technology Data Exchange (ETDEWEB)

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

    2003-09-15

    Fabry-Perot cavities have many different applications as scientific instruments. In the gravitational waves research field they are extensively used to frequency stabilize lasers and to measure very small distance variations. In the present Letter a method to evaluate from the transmitted power only the relative speed and position of the mirrors of a cavity, having finesse F>40, is described. A displacement spectral sensitivity of the order of about 3x10{sup -10} m/Hz{sup -1/2} at 10 Hz is obtained with the cavity of the low frequency facility.

  7. Characterisation of hole traps in GaAs Fets by DLTS, low frequency noise and g sub M dispersion methods

    International Nuclear Information System (INIS)

    Iqbal, M.A.; Kaya, L.; Jones, B.K.

    1997-01-01

    Deep level effects in GaAs MOSFET have been characterised in the ohmic channel using DLTS, low frequency excess noise and dispersion technique. An isothermal multi exponential curve fitting method has been devised and implanted into the DLTS system. Multi exponential curve fitting method used to decompose a multi exponential transient into its constituents so that the peak signature can be better characterised for the case whereas several peaks are closely spaced. Low frequency excess noise and dispersion techniques also confirm the trap in signature of the same traps observed in the DLTS measurements. (author)

  8. Growth inhibition of Staphylococcus aureus induced by low-frequency electric and electromagnetic fields.

    Science.gov (United States)

    Obermeier, Andreas; Matl, Florian Dominik; Friess, Wolfgang; Stemberger, Axel

    2009-05-01

    Magnetic field therapy is an established technique in the treatment of pseudarthrosis. In cases of osteomylitis, palliation is also observed. This study focuses on the impact of different electric and electromagnetic fields on the growth of Staphylococcus aureus by in vitro technologies. Cultures of Staphylococcus aureus in fluid and gel-like medium were exposed to a low-frequency electromagnetic field, an electromagnetic field combined with an additional electric field, a sinusoidal electric field and a static electric field. In gel-like medium no significant difference between colony-forming units of exposed samples and non-exposed references was detected. In contrast, Staphylococcus aureus concentrations in fluid medium could clearly be reduced under the influence of the four different applied fields within 24 h of experiment. The strongest effects were observed for the direct current electric field which could decrease CFU/ml of 37%, and the low-frequency electromagnetic field with additional induced electric alternating field with a decrease of Staphylococci concentration by 36%. The effects of the electromagnetic treatment on Staphylococci within fluid medium are significantly higher than in gel-like medium. The application of low-frequency electromagnetic fields corroborates clinical situations of bone infections during magnetic field therapy. Copyright 2009 Wiley-Liss, Inc.

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

    DEFF Research Database (Denmark)

    Poutanen, T.; Lähteenmäki, A.; León-Tavares, J.

    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 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...

  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.; 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.

    2016-01-01

    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. High-efficiency ventilated metamaterial absorber at low frequency

    Science.gov (United States)

    Wu, Xiaoxiao; Au-Yeung, Ka Yan; Li, Xin; Roberts, Robert Christopher; Tian, Jingxuan; Hu, Chuandeng; Huang, Yingzhou; Wang, Shuxia; Yang, Zhiyu; Wen, Weijia

    2018-03-01

    We demonstrate a ventilated metamaterial absorber operating at low frequency (90%) has been achieved in both simulations and experiments. This high-efficiency absorption under the ventilation condition originates from the weak coupling of two identical split tube resonators constituting the absorber, which leads to the hybridization of the degenerate eigenmodes and breaks the absorption upper limit of 50% for conventional transmissive symmetric acoustic absorbers. The absorber can also be extended to an array and work in free space. The absorber should have potential applications in acoustic engineering where both noise reduction and ventilation are required.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2004-02-23

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

  13. High and low frequency Alfven modes in tokamaks

    International Nuclear Information System (INIS)

    Briguglio, S.; Fogaccia, G.; Vlad, G.; Zonca, F.; Chen, L.; Dong, J.Q.; Santoro, R.A.

    2001-01-01

    We present an analysis of the typical features of shear Alfven waves in tokamak plasmas in a frequency domain ranging from the ''high'' frequencies (ω ≅ ν A /2qR 0 ; ν A being the Alfven speed and qR 0 the tokamak connection length) of the toroidal gap to the ''low'' frequencies, comparable with the thermal ion diamagnetic frequency, ω *pi and/or the thermal ion transit frequency ω ti = ν ti /qR 0 (ν ti being the ion thermal speed). (author)

  14. Fetal exposure to low frequency electric and magnetic fields

    International Nuclear Information System (INIS)

    Cech, R; Leitgeb, N; Pediaditis, M

    2007-01-01

    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

  15. Robust design of decentralized power system stabilizers using meta-heuristic optimization techniques for multimachine systems

    Directory of Open Access Journals (Sweden)

    Jeevanandham Arumugam

    2009-01-01

    Full Text Available In this paper a classical lead-lag power system stabilizer is used for demonstration. The stabilizer parameters are selected in such a manner to damp the rotor oscillations. The problem of selecting the stabilizer parameters is converted to a simple optimization problem with an eigen value based objective function and it is proposed to employ simulated annealing and particle swarm optimization for solving the optimization problem. The objective function allows the selection of the stabilizer parameters to optimally place the closed-loop eigen values in the left hand side of the complex s-plane. The single machine connected to infinite bus system and 10-machine 39-bus system are considered for this study. The effectiveness of the stabilizer tuned using the best technique, in enhancing the stability of power system. Stability is confirmed through eigen value analysis and simulation results and suitable heuristic technique will be selected for the best performance of the system.

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

    Science.gov (United States)

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

    2012-02-28

    The objective of this study was to test low frequency sonophoresis at 20 kHz for delivery of ketoprofen into and across the skin. Permeation studies were carried out in vitro on excised hairless rat skin over a period of 24h using Franz diffusion cells after which, skin samples were subjected to skin extraction to quantify the amount of drug present in skin. Parameters like ultrasound application time, duty cycle coupling medium and distance of ultrasound horn from skin were optimized. Transepidermal water loss (TEWL) was measured to indicate the extent of barrier disruption following sonophoresis. Confocal microscopy was used to visualize dye penetration through sonophoresis treated skin. Application of ultrasound significantly enhanced permeation of ketoprofen from 74.87 ± 5.27 μg/cm(2) for passive delivery to 491.37 ± 48.78 μg/cm(2) for sonophoresis. Drug levels in skin layers increased from 34.69 ± 7.25 μg following passive permeation to 212.62 ± 45.69 μg following sonophoresis. TEWL increased from 31.6 ± 0.02 (passive) to 69.5 ± 12.60 (sonophoresis) indicating disruption of barrier properties. Confocal microscopy images depicted enhanced dye penetration through sonophoresis treated skin confirming barrier disruption. Low frequency sonophoresis with optimized ultrasound parameters can be effectively used to actively enhance transdermal and topical delivery of ketoprofen. Copyright © 2011 Elsevier B.V. All rights reserved.

  17. Low-Frequency Electromagnetic Thermal Fluctuations in the Solar Wind

    Science.gov (United States)

    Gaelzer, R.; Yoon, P. H.; Ziebell, L. F.; Pavan, J.

    2012-12-01

    It is well known that the solar wind proton temperature anisotropy is constrained in the temperature ratio vs. beta parameter space by the mirror/proton-cyclotron and parallel/oblique firehose instability threshold conditions (Hellinger et al., 2006). However, the actual solar wind is found in the parameter regime stable to these instabilities (Bale et al., 2009). Since no waves can be generated in the purely collisionless and stable plasma, the source of the low-frequency electromagnetic fluctuations in the solar wind must be owing to spontaneous thermal effects. The problem of the spontaneously emitted electromagnetic waves from magnetized plasmas is generally poorly understood (Araneda et al., 2011). In the present paper, we formulate the theory of spontaneous thermal emission of electromagnetic radiation in the vicinity of the low-frequency modes of Alfvén, ion-cyclotron, and whistler modes. We carry out a statistical analysis by varying the temperature anisotropy and parallel beta and compare the theoretical fluctuation intensity against the observation such as that reported by Bale et al. (2009). Hellinger et al., GRL, 33, L09101 (2006). Bale et al., PRL, 103, 211101 (2009). Araneda et al., Space Sci. Rev., DOI:10.1007/s11214-011-9773-0 (2011).

  18. 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.

  19. A new hybrid phononic crystal in low frequencies

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Z., E-mail: zhangz@dlut.edu.cn; Han, X.K.

    2016-11-25

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

  20. 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.

  1. 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.

  2. Current Status of The Low Frequency All Sky Monitor

    Science.gov (United States)

    Dartez, Louis; Creighton, Teviet; Jenet, Fredrick; Dolch, Timothy; Boehler, Keith; Bres, Luis; Cole, Brent; Luo, Jing; Miller, Rossina; Murray, James; Reyes, Alex; Rivera, Jesse

    2018-01-01

    The Low Frequency All Sky Monitor (LoFASM) is a distributed array of cross-dipole antennas that are sensitive to radio frequencies from 10 to 88 MHz. LoFASM consists of antennas and front end electronics that were originally developed for the Long Wavelength Array by the U.S. Naval Research Lab, the University of New Mexico, Virginia Tech, and the Jet Propulsion Laboratory. LoFASM, funded by the U.S. Department of Defense, will initially consist of 4 stations, each consisting of 12 dual- polarization dipole antenna stands. The primary science goals of LoFASM will be the detection and study of low-frequency radio transients, a high priority science goal as deemed by the National Research Council’s ASTRO2010 decadal survey. The data acquisition system for the LoFASM antenna array uses Field Programmable Gate Array (FPGA) technology to implement a real time full Stokes spectrometer and data recorder. This poster presents an overview of the LoFASM Radio Telescope as well as the status of data analysis of initial commissioning observations.

  3. Low frequency RFQ linacs for heavy ion fusion

    International Nuclear Information System (INIS)

    Moretti, A.; Watson, J.M.; Martin, R.L.; Lari, R.J.; Stockley, R.L.

    1982-01-01

    Low frequency, radio frequency quadrupole (RFQ) structures are under study at Argonne National Laboratory (ANL) as the low-velocity portion of an rf linac driver for heavy ion inertial confinement fusion. Besides offering a direct comparison with the present ANL front end, it would provide a second low-velocity Xe +1 linac for funneling experiments at 22.9 MeV. Heavy ion RFQ accelerators are characterized by their low rf operating frequency of about 10 MHz. The large size of a manifold-fed four-vane, 10 MHz RFQ resonator structure (about 6 m in diameter) makes it unacceptable for heavy ions; therefore, alternate structures are under study at Argonne. The structures under study are: (1) a Wideroe-type structure with external stub lines, (2) a Wideroe-type structure with the stub lines internal to the structure, (3) a split coaxial line resonator with modulated vanes, and (4) a interdigital line resonator with modulated cylindrical rods. The split coaxial line resonator seems best at this low frequency. It is compact and very efficient. About 15.5 m of linac structure excited with 560 kW of rf power is sufficient to accelerate 30 mA of Xe +1 with 97% transmission efficiency from 250 keV to 3 MeV

  4. 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

  5. Techniques for Liquid Rocket Combustion Spontaneous Stability and Rough Combustion Assessments

    Science.gov (United States)

    Kenny, R. J.; Giacomoni, C.; Casiano, M. J.; Fischbach, S. R.

    2016-01-01

    This work presents techniques for liquid rocket engine combustion stability assessments with respect to spontaneous stability and rough combustion. Techniques covering empirical parameter extraction, which were established in prior works, are applied for three additional programs: the F-1 Gas Generator (F1GG) component test program, the RS-84 preburner component test program, and the Marshall Integrated Test Rig (MITR) program. Stability assessment parameters from these programs are compared against prior established spontaneous stability metrics and updates are identified. Also, a procedure for comparing measured with predicted mode shapes is presented, based on an extension of the Modal Assurance Criterion (MAC).

  6. Methods of reducing low frequency cabin noise and sonically induced stresses, based on the intrinsic structural tuning concept

    Science.gov (United States)

    Sengupta, G.

    1977-01-01

    Control of low frequency interior noise has been difficult in all commercial and general aviation aircraft, since the existing sound attenuation techniques are less effective at these frequencies. Therefore low frequency cabin noise and sonically induced stresses can be reduced mainly by a proper design of the fuselage structure. For this purpose, a concept based on intrinsic tuning and damping of fuselage structural elements has been under development at Boeing for the past three years. This paper describes the results of some laboratory and field tests that were conducted for evaluation of the concept.

  7. Extremely low frequencies. Health effects of extremely low frequency electromagnetic fields. Opinion of the Afsset. Collective expertise report

    International Nuclear Information System (INIS)

    Bounouh, Alexandre; Brugere, Henri; Clavel, Jacqueline; Febvre, Pascal; Lagroye, Isabelle; Vecchia, Paolo; Dore, Jean-Francois; Anfosso-Ledee, Fabienne; Berengier, Michel; Cesarini, Jean-Pierre; Cohen, Jean-Claude; Planton, Serge; Courant, Daniel; Tardif, Francois; Couturier, Frederic; Debouzy, Jean-Claude; El Khatib, Aicha; Flahaut, Emmanuel; Gaffet, Eric; Hours, Martine; Lambert, Jacques; Vallet, Michel; Job, Agnes; Labeyrie, Antoine; Laurier, Dominique; Le Bihan, Olivier; Lepoutre, Philippe; Marchal, Didier; Moch, Annie; Pirard, Philipe; Rumeau, Michel; De Seze, Rene; Attia, Dina; Merckel, Olivier; Fite, Johanna; Guichard, Alexandra; Saihi, Myriam; Guitton, Sophie; Saddoki, Sophia

    2010-03-01

    This report aims at proposing a synthesis of works of international expertise on the health effect of extremely low frequency electromagnetic fields, at performing a methodological analysis of the 'Expers' study (a study on the exposure of individuals), at performing a methodological analysis of a study performed by the Criirem in the western part of France, at assessing the contribution of different equipment and situations to the exposure of population to extremely-low-frequency electromagnetic fields, at making recommendations and proposals for a better assessment of the exposure level, and at proposing topics of investigation and research to improve knowledge on these issues. The report recalls the context, scope and modalities of the study, gives an overview of generalities on electromagnetic fields (nature, physical values, electromagnetic spectrum, artificial and natural electromagnetic field sources, exposure threshold values and regulatory context), addresses the assessment of exposure (notion of exposure, exposure assessment methods, analysis of available data, analysis of recent or current studies), gives an overview of biological and health effects of these electromagnetic fields (methodological aspects, interaction between fields and biological tissues, synthesis of the international expertise on health impacts). Recommendations are formulated

  8. Enhancing the beamforming map of spherical arrays at low frequencies using acoustic holography

    DEFF Research Database (Denmark)

    Tiana Roig, Elisabet; Torras Rosell, Antoni; Fernandez Grande, Efren

    2014-01-01

    Recent studies have shown that the localization of acoustic sources based on circular arrays can be improved at low frequencies by combining beamforming with acoustic holography. This paper extends this technique to the three dimensional case by making use of spherical arrays. The pressure captured...... by a rigid spherical array under free-field conditions is used to compute the expected pressure on a virtual and larger sphere by means of acoustic holography. Beamforming is then applied with the pressure predicted at the virtual array. Since the virtual array has a larger radius compared to the one...

  9. 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.

  10. Method for imaging with low frequency electromagnetic fields

    Science.gov (United States)

    Lee, Ki H.; Xie, Gan Q.

    1994-01-01

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

  11. Investigating low-frequency compression using the Grid method

    DEFF Research Database (Denmark)

    Fereczkowski, Michal; Dau, Torsten; MacDonald, Ewen

    2016-01-01

    in literature. Moreover, slopes of the low-level portions of the BM I/O functions estimated at 500 Hz were examined, to determine whether the 500-Hz off-frequency forward masking curves were affected by compression. Overall, the collected data showed a trend confirming the compressive behaviour. However......There is an ongoing discussion about whether the amount of cochlear compression in humans at low frequencies (below 1 kHz) is as high as that at higher frequencies. It is controversial whether the compression affects the slope of the off-frequency forward masking curves at those frequencies. Here......, the Grid method with a 2-interval 1-up 3-down tracking rule was applied to estimate forward masking curves at two characteristic frequencies: 500 Hz and 4000 Hz. The resulting curves and the corresponding basilar membrane input-output (BM I/O) functions were found to be comparable to those reported...

  12. 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...

  13. Characteristics of low frequency MHD fluctuations in the PRETEXT tokamak

    International Nuclear Information System (INIS)

    Kochanski, T.P.

    1981-05-01

    The temporal and spectral characteristics of low frequency (< 100KHz) MHD fluctuations, which are commonly associated with disruptions, have been investigated in the PRETEXT tokamak. There exists rigid phase coherence between the internal m = 1, and externally detected m = 2 modes indicative of strong mode coupling. A parametric study of the frequency of the mode, in the saturated state, indicates that the frequency scales with the toroidal magnetic field, and is inversely proportional to the plasma current. The frequency is observed to decrease abruptly as the mode amplitude rapidly increases prior to a plasma disruption. The burst type growth of the m = 2 mode appears to be inextricably linked to the occurrence of the disruptive instability

  14. 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.

  15. Stimulated low-frequency Raman scattering in plant virus suspensions

    Science.gov (United States)

    Donchenko, E. K.; Karpova, O. V.; Kudryavtseva, A. D.; Pershin, S. M.; Savichev, V. I.; Strokov, M. A.; Tcherniega, N. V.; Zemskov, K. I.

    2017-11-01

    The study deals with laser pulse interaction with plant viruses: we investigated tobacco mosaic virus (TMV) and two types of potato viruses (PVX and PVA) in Tris-HCl pH7.5 buffer and in water. We used 20 ns ruby laser pulses for excitation. We employed Fabry–Pérot interferometers to record spectra of the light passing through the sample and reflected from it. For TMV and PVX in Tris-HCl pH7.5 buffer, same as for PVA in water, we observed additional spectral lines corresponding to the stimulated low-frequency Raman scattering (SLFRS). We believe we were the first to measure SLFRS frequency shifts, conversion efficiency and threshold. High conversion efficiency of the scattered light is evidence of laser pulses efficiently exciting gigahertz vibrations in viruses. SLFRS can be used to identify and affect biological nanoparticles.

  16. 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.

  17. WHO's health risk assessment of extremely low frequency electric fields

    International Nuclear Information System (INIS)

    Repacholi, M.H.

    2003-01-01

    The World Health Organization (WHO), the International Commission on Non-Ionizing Radiation Protection (ICNIRP), WHOs scientific collaborating centres (including the UKs National Radiological Protection Board (NRPB) and over 50 participating Member States are participants of WHOs International EMF Project. As part of WHOs health risk assessment process for extremely low frequency fields (ELFs), this workshop was convened by NRPB to assist WHO in evaluating potential health impacts of electrical currents and fields induced by ELF in molecules, cells, tissues and organs of the body. This paper describes the process by which WHO will conduct its health risk assessment. WHO is also trying to provide information on why exposure to ELF magnetic fields seems to be associated with an increased incidence of childhood leukaemia. Are there mechanisms that could lead to this health outcome or does the epidemiological evidence incorporate biases or other factors that need to be further explored? (author)

  18. 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

  19. Electrodialytic soil remediation enhanced by low frequency pulse current

    DEFF Research Database (Denmark)

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

    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...... 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...... 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...

  20. Nonlinear beat excitation of low frequency wave in degenerate plasmas

    Science.gov (United States)

    Mir, Zahid; Shahid, M.; Jamil, M.; Rasheed, A.; Shahbaz, A.

    2018-03-01

    The beat phenomenon due to the coupling of two signals at slightly different frequencies that generates the low frequency signal is studied. The linear dispersive properties of the pump and sideband are analyzed. The modified nonlinear dispersion relation through the field coupling of linear modes against the beat frequency is derived in the homogeneous quantum dusty magnetoplasmas. The dispersion relation is used to derive the modified growth rate of three wave parametric instability. Moreover, significant quantum effects of electrons through the exchange-correlation potential, the Bohm potential, and the Fermi pressure evolved in macroscopic three wave interaction are presented. The analytical results are interpreted graphically describing the significance of the work. The applications of this study are pointed out at the end of introduction.

  1. 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.

  2. Very low frequency noise reduction in orthogonal fluxgate

    Science.gov (United States)

    Butta, Mattia; Janosek, Michal

    2018-04-01

    In this paper we present a simple, cheap and effective method to obtain reduction of very low frequency noise in an orthogonal fluxgate in fundamental mode. This method consists in the application of a layer of silicone over the magnetic core of the sensor filling the whole space inside the pick-up coil. In this way we avoid fast variations of temperature to affect the offset of the sensor (which is very sensitive to temperature changes). Eventually the offset will still drift to the same value, but it will do it slower, thus reducing the component of the noise in the sub-Hz region. Using this method we could simply reduce the noise at 100 mHz from 23 to 8 pT/√Hz, with no additional hardware on the excitation or signal conditioning circuits.

  3. Multimode/Multifrequency Low Frequency Airborne Radar Design

    Directory of Open Access Journals (Sweden)

    Sandra Costanzo

    2013-01-01

    Full Text Available This work deals with the design of multimode/multifrequency airborne radar suitable for imaging and subsurface sounding. The system operates at relatively low frequencies in the band ranging from VHF to UHF. It is able to work in two different modalities: (i nadir-looking sounder in the VHF band (163 MHz and (ii side-looking imager (SAR in the UHF band with two channels at 450 MHz and 860 MHz. The radar has been completely designed by CO.Ri.S.T.A. for what concerns the RF and the electronic aspect, and by the University of Calabria for what concerns the design, realization, and test of SAR antennas. The radar has been installed on a civil helicopter and its operation has been validated in flight in both sounder and imager modality. Preliminary surveys have been carried out over different areas of Campania region, South Italy.

  4. 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.

  5. Biological actions and effects of low-frequency fields

    International Nuclear Information System (INIS)

    Brix, J.

    1993-01-01

    Cell culture studies have shown that low-frequency electromagnetic fields may affect cell behaviour. The fact that the corresponding field strengths are too weak to affect membrane potential, suggests that these fields trigger enzymatic reactions at the outer face of the membrane, i.e. cell-intrinsic reaction cascades and a biological modification of the affected biological system take place. These are working models and hypotheses which need to substantiated by further studies in this field. Epidemiological studies suggest that electromagnetic fields influence cancer development in man. However there is no action model indicating exposure to fields to be a genotoxic agent possible triggering a direct genetic modification which precludesr any initialization. (orig.) [de

  6. 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.

  7. 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 > 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 resonance. This is a

  8. Software Toolbox for Low-Frequency Conductivity and Current Density Imaging Using MRI.

    Science.gov (United States)

    Sajib, Saurav Z K; Katoch, Nitish; Kim, Hyung Joong; Kwon, Oh In; Woo, Eung Je

    2017-11-01

    Low-frequency conductivity and current density imaging using MRI includes magnetic resonance electrical impedance tomography (MREIT), diffusion tensor MREIT (DT-MREIT), conductivity tensor imaging (CTI), and magnetic resonance current density imaging (MRCDI). MRCDI and MREIT provide current density and isotropic conductivity images, respectively, using current-injection phase MRI techniques. DT-MREIT produces anisotropic conductivity tensor images by incorporating diffusion weighted MRI into MREIT. These current-injection techniques are finding clinical applications in diagnostic imaging and also in transcranial direct current stimulation (tDCS), deep brain stimulation (DBS), and electroporation where treatment currents can function as imaging currents. To avoid adverse effects of nerve and muscle stimulations due to injected currents, conductivity tensor imaging (CTI) utilizes B1 mapping and multi-b diffusion weighted MRI to produce low-frequency anisotropic conductivity tensor images without injecting current. This paper describes numerical implementations of several key mathematical functions for conductivity and current density image reconstructions in MRCDI, MREIT, DT-MREIT, and CTI. To facilitate experimental studies of clinical applications, we developed a software toolbox for these low-frequency conductivity and current density imaging methods. This MR-based conductivity imaging (MRCI) toolbox includes 11 toolbox functions which can be used in the MATLAB environment. The MRCI toolbox is available at http://iirc.khu.ac.kr/software.html . Its functions were tested by using several experimental datasets, which are provided together with the toolbox. Users of the toolbox can focus on experimental designs and interpretations of reconstructed images instead of developing their own image reconstruction softwares. We expect more toolbox functions to be added from future research outcomes. Low-frequency conductivity and current density imaging using MRI includes

  9. Stability assessment for underground excavations and key construction techniques

    CERN Document Server

    Zhu, Hanhua; Zhao, Yu; Niu, Fusheng

    2017-01-01

    This book examines how the state of underground structures can be determined with the assistance of force, deformation and energy. It then analyzes mechanized shield methods, the New Austrian tunneling method (NATM) and conventional methods from this new perspective. The book gathers a wealth of cases reflecting the experiences of practitioners and administrators alike. Based on statistical and engineering studies of these cases, as well as lab and field experiments, it develops a stability assessment approach incorporating a stable equilibrium, which enables engineers to keep the structure and surrounding rocks safe as long as the stable equilibrium and deformation compliance are maintained. The book illustrates the implementation of the method in various tunneling contexts, including soil-rock mixed strata, tunneling beneath operating roads, underwater tunnels, and tunnel pit excavation. It offers a valuable guide for researchers, designers and engineers, especially those who are seeking to understand the u...

  10. New Technique for Soil Reclamation and Conservation: In Situ Stabilization of Trace Elements in Contaminated Soils

    OpenAIRE

    Negim, Osama

    2009-01-01

    The accumulation of toxic metals in the soil is mainly inherited from parent materials or inputs through human activities. New techniques are being developed to remediate trace elements in contaminated soils such as phytoremediation and in situ stabilization. In situ stabilization technique is one of the common practices for reducing negative effects of metals and metalloids such as As, Cr, Cu and Zn in contaminated soils by adding amendments. The application of alkaline materials such as bas...

  11. Immobilization, stabilization and patterning techniques for enzyme based sensor systems.

    Energy Technology Data Exchange (ETDEWEB)

    Flounders, A.W.; Carichner, S.C.; Singh, A.K.; Volponi, J.V.; Schoeniger, J.S.; Wally, K.

    1997-01-01

    Sandia National Laboratories has recently opened the Chemical and Radiation Detection Laboratory (CRDL) in Livermore CA to address the detection needs of a variety of government agencies (e.g., Department of Energy, Environmental Protection Agency, Department of Agriculture) as well as provide a fertile environment for the cooperative development of new industrial technologies. This laboratory consolidates a variety of existing chemical and radiation detection efforts and enables Sandia to expand into the novel area of biochemically based sensors. One aspect of this biosensor effort is further development and optimization of enzyme modified field effect transistors (EnFETs). Recent work has focused upon covalent attachment of enzymes to silicon dioxide and silicon nitride surfaces for EnFET fabrication. They are also investigating methods to pattern immobilized proteins; a critical component for development of array-based sensor systems. Novel enzyme stabilization procedures are key to patterning immobilized enzyme layers while maintaining enzyme activity. Results related to maximized enzyme loading, optimized enzyme activity and fluorescent imaging of patterned surfaces will be presented.

  12. Potassium-cobalt sulphate crystal growth assisted by low frequency vibrations

    Science.gov (United States)

    Sadovsky, A.; Ermochenkov, I.; Dubovenko, E.; Sukhanova, E.; Bebyakin, M.; Dubov, V.; Avetissov, I.

    2018-02-01

    Single crystals of K2Co(SO4)2·6H2O were grown from solution using the temperature reduction method enhanced by the axial low frequency vibration control technique (AVC-technique). Physical modeling of heat-mass transfer in solution under the AVC action was performed. The growth rate of the AVC grown crystal was found to be twice that of the crystal grown under natural convection conditions. Analysis of spectral characteristics (absorption and Raman spectra) as well as structural properties (dislocation density and microhardness) of the grown crystals showed the significant superiority of the AVC technique for the growth of K2Co(SO4)2·6H2O crystals.

  13. Stabilizing operation point technique based on the tunable distributed feedback laser for interferometric sensors

    Science.gov (United States)

    Mao, Xuefeng; Zhou, Xinlei; Yu, Qingxu

    2016-02-01

    We describe a stabilizing operation point technique based on the tunable Distributed Feedback (DFB) laser for quadrature demodulation of interferometric sensors. By introducing automatic lock quadrature point and wavelength periodically tuning compensation into an interferometric system, the operation point of interferometric system is stabilized when the system suffers various environmental perturbations. To demonstrate the feasibility of this stabilizing operation point technique, experiments have been performed using a tunable-DFB-laser as light source to interrogate an extrinsic Fabry-Perot interferometric vibration sensor and a diaphragm-based acoustic sensor. Experimental results show that good tracing of Q-point was effectively realized.

  14. Application of Arma Technique For Operation Stability of RSG-Gas

    International Nuclear Information System (INIS)

    Djudjuratisbela, Udju

    2000-01-01

    Application Of Arma Technique For Operation Stability Of RSG-Gas. Application of Fast Fourier Transport (FFT) method in the noise experiments data had been conducted to reactor kinetic parameter determination of RSG-Gas. Reactor stability that has closed relation to operation safety has not been measured yet. Noise analysis method and ARMA (Auto Regressive Moving Average) technique that has capability to identify mathematical model of the noise experimental data can be used for determination of kinetic/dynamic characteristic equation and its roots. From the roots of reactor characteristic equation, magnitude of natural frequency (fn), damping ratio (xi), damping frequency (fd), decay ratio (delta) and then reactor stability can be calculated

  15. The improvement of phycocyanin stability extracted from Spirulina sp using extrusion encapsulation technique

    Science.gov (United States)

    Suzery, Meiny; Hadiyanto, Sutanto, Heri; Soetrisnanto, Danny; Majid, Dian; Setyawan, Deny; Azizah, Nur

    2015-12-01

    The stability of phycocyanin extracted from microalgae Spirulina has been evaluated and it showed that the stability of this antioxidant was affected by temperature and pH changes. The encapsulation technique was of the alternatives to overcome this stability changes. The objective of this paper was to investigate the effects of coating materials (alginate and chitosan) during encapsulation by using extrusion technique. The experiments were conducted with variation of alginate as coating materials. The size of each microcapsules was evaluated by using SEM/XRD for its size and homogeneity.

  16. Spots of Seismic Danger Extracted by Properties of Low-Frequency Seismic Noise

    Science.gov (United States)

    Lyubushin, Alexey

    2013-04-01

    A new method of seismic danger estimate is presented which is based on using properties of low-frequency seismic noise from broadband networks. Two statistics of noise waveforms are considered: multi-fractal singularity spectrum support width D and minimum normalized entropy En of squared orthogonal wavelet coefficients. The maps of D and En are plotted in the moving time window. Let us call the regions extracted by low values of D and high values of En as "spots of seismic danger" - SSD. Mean values of D and En are strongly anti-correlated - that is why statistics D and En extract the same SSD. Nevertheless their mutual considering is expedient because these parameters are based on different approaches. The physical mechanism which underlies the method is consolidation of small blocks of the Earth's crust into the large one before the strong earthquake. This effect has a consequence that seismic noise does not include spikes which are connected with mutual movements of small blocks. The absence of irregular spikes in the noise follows the decreasing of D and increasing of entropy En. The stability in space and size of the SSD provides estimates of the place and energy of the probable future earthquake. The increasing or decreasing of SSD size and minimum or maximum values of D and En within SSD allows estimate the trend of seismic danger. The method is illustrating by the analysis of seismic noise from broadband seismic network F-net in Japan [1-5]. Statistically significant decreasing of D allowed a hypothesis about approaching Japan to a future seismic catastrophe to be formulated at the middle of 2008. The peculiarities of correlation coefficient estimate within 1 year time window between median values of D and generalized Hurst exponent allowed to make a decision that starting from July of 2010 Japan come to the state of waiting strong earthquake [3]. The method extracted a huge SSD near Japan which includes the region of future Tohoku mega-earthquake and the

  17. Thermal analyses of in vitro low frequency sonophoresis.

    Science.gov (United States)

    Peng, Han-Min; Zhu, Pan-Cheng; Chen, Zhi-Jun

    2017-03-01

    As a type of transdermal drug delivery method, low frequency sonophoresis (LFS) has been investigated during the last twenty years and is currently being attempted in a clinical setting. However, the safety of low frequency ultrasound on humans has not been completely guaranteed with high-intensity ultrasound. Thermal damage, one of the challenges in the LFS process, e.g., burns, epidermal detachment and necrosis of tissues, hinders its widespread applications. To predict and impede the overheating problems in LFS, an acoustic-flow-thermal finite element method (FEM) based on COMSOL Multiphysics software is proposed in this paper to achieve thermal analyses. The temperature distribution and its rising curves in in vitro LFS are obtained by the FEM method and experimental measurements. Both simulated and experimental maximum temperatures are larger than the safety value (e.g., 42°C on human tissues) when the driving voltage is higher than 40V (5.5W input electric power), which proves that the overheating problem really exists in high-intensity ultrasound. Furthermore, the results show that the calculated temperature rising curves in in vitro LFS correspond to the experimental results, proving the effectiveness of this FEM method. In addition, several potential thermal influence factors have been studied, including a duty ratio and amplitude of the driving voltage, and liquid height in the donor, which may be helpful in restraining the temperature increase to limit thermal damage. According to the calculated and experimental results, the former two factors are sensitive to the rise in temperature, but a small scale of liquid volume increase can enhance the permeation of Calcein without obvious temperature change. Hence, the above factors can be synthetically utilized to restrain the rise in temperature with little sacrifice of permeation ability. So this acoustic-flow-thermal FEM method could be applied to an optimized LFS system design and simulating the thermal

  18. Suppression of the Leidenfrost effect via low frequency vibrations.

    Science.gov (United States)

    Ng, Boon T; Hung, Yew M; Tan, Ming K

    2015-01-28

    The ability to suppress the Leidenfrost effect is of significant importance in applications that require rapid and efficient cooling of surfaces with temperature higher than the Leidenfrost point TSL. The Leidenfrost effect will result in substantial reduction in cooling efficiency and hence there have been a few different approaches to suppress the Leidenfrost effect. The majority of these approaches relies on fabricating micro/nano-structures on heated surfaces, others rely on inducing an electric field between the droplets and the heated surfaces. In this paper, we present an approach that induces low frequency vibrations (f∼10(2) Hz) on a heated surface to suppress the effect. By mapping the different magnitudes of surface acceleration [greek xi with two dots above]sversus different initial surface temperatures Ts of the substrate, three regimes that represent three distinct impact dynamics are analyzed. Regime-I represents gentle film boiling ([greek xi with two dots above]s∼10(2) m s(-2) and Ts∼TSL), which is associated with the formation of thin spreading lamella around the periphery of the impinged droplet; Regime-II ([greek xi with two dots above]s∼10(2) m s(-2) and Ts>TSL) represents film boiling, which is associated with the rebound of the impinged droplet due to the presence of a thick vapor layer; Regime-III ([greek xi with two dots above]s∼10(3) m s(-2) and Ts∼TSL) represents contact boiling, which is associated with the ejection of tiny droplets due to the direct contact between the droplet and the heated surface. The estimated cooling enhancement for Regime-I is between 10% and 95%, Regime-II is between 5% and 15%, and Regime-III is between 95% and 105%. The improvement in cooling enhancement between Regime-I (strong Leidenfrost effect) and Regime-III (suppressed Leidenfrost effect) is more than 80%, demonstrating the effectiveness of using low frequency vibrations to suppress the Leidenfrost effect.

  19. Controlling low frequency noise using a passive silencer

    Energy Technology Data Exchange (ETDEWEB)

    DeGagne, D.C.; Faszer, A.C. [Noise Solutions Inc., Calgary, AB (Canada)

    2009-07-01

    Nearly 85 per cent of all the oil and natural gas recovered in Canada comes from Alberta where noise emissions from energy facilities are regulated by the Energy Resources Conservation Board (ERCB) and the Alberta Utilities Commission (AUC) through Noise Control Directive D-038. Operators of energy facilities in Alberta must meet the Permissible Sound Level (PSL) established for industrial facilities that are established for receptor locations such as nearby residences. Despite efforts to manage noise, complaints from nearby residents continue to occur even if the facility is in compliance. This is because high and mid frequency components can decay or be absorbed by air and ground conditions leaving mostly low frequency noise (LFN) at the residence. This paper explored the significance of LFN and how some facility operators are dealing with this problem. The impacts of LFN can range from creating a sensation of pressure in the ear, disturbing normal conversation, to creating secondary vibrating effects within homes. If severe enough, it can also result in potential behavioural dysfunction such as task performance deterioration, sleep disturbance and headaches. In 2006, Noise Solutions Inc. was approached by Hunt Oil Company regarding the installation of a new compressor at their Caroline site. The proposal posed a serious noise problem for the community which requested that the new compressor unit be developed without any additional noise impact on the area. Noise Solutions Inc. used a multi-phased approach to develop the most effective LFN silencer using best practical technology and materials. In an effort to fully attenuate both the high frequency noise (dBA) and the low frequency noise (dBC) of the new compressor unit, Noise Solutions and Hunt Oil agreed that a significant level of sound-suppression would be necessary. The entire noise-suppression unit was specially designed to compensate for the sheer size of the compressor building. The first step to

  20. Evaluation and characterization of fetal exposures to low frequency magnetic fields generated by laptop computers.

    Science.gov (United States)

    Zoppetti, Nicola; Andreuccetti, Daniele; Bellieni, Carlo; Bogi, Andrea; Pinto, Iole

    2011-12-01

    Portable - or "laptop" - computers (LCs) are widely and increasingly used all over the world. Since LCs are often used in tight contact with the body even by pregnant women, fetal exposures to low frequency magnetic fields generated by these units can occur. LC emissions are usually characterized by complex waveforms and are often generated by the main AC power supply (when connected) and by the display power supply sub-system. In the present study, low frequency magnetic field emissions were measured for a set of five models of portable computers. For each of them, the magnetic flux density was characterized in terms not just of field amplitude, but also of the so called "weighted peak" (WP) index, introduced in the 2003 ICNIRP Statement on complex waveforms and confirmed in the 2010 ICNIRP Guidelines for low frequency fields. For the model of LC presenting the higher emission, a deeper analysis was also carried out, using numerical dosimetry techniques to calculate internal quantities (current density and in-situ electric field) with reference to a digital body model of a pregnant woman. Since internal quantities have complex waveforms too, the concept of WP index was extended to them, considering the ICNIRP basic restrictions defined in the 1998 Guidelines for the current density and in the 2010 Guidelines for the in-situ electric field. Induced quantities and WP indexes were computed using an appropriate original formulation of the well known Scalar Potential Finite Difference (SPFD) numerical method for electromagnetic dosimetry in quasi-static conditions. Copyright © 2011 Elsevier Ltd. All rights reserved.

  1. Extremely low frequency electric fields and cancer: assessing the evidence.

    Science.gov (United States)

    Kheifets, Leeka; Renew, David; Sias, Glenn; Swanson, John

    2010-02-01

    Much of the research and reviews on extremely low frequency (ELF) electric and magnetic fields (EMFs) have focused on magnetic rather than electric fields. Some have considered such focus to be inappropriate and have argued that electric fields should be part of both epidemiologic and laboratory work. This paper fills the gap by systematically and critically reviewing electric-fields literature and by comparing overall strength of evidence for electric versus magnetic fields. The review of possible mechanisms does not provide any specific basis for focusing on electric fields. While laboratory studies of electric fields are few, they do not indicate that electric fields should be the exposure of interest. The existing epidemiology on residential electric-field exposures and appliance use does not support the conclusion of adverse health effects from electric-field exposure. Workers in close proximity to high-voltage transmission lines or substation equipment can be exposed to high electric fields. While there are sporadic reports of increase in cancer in some occupational studies, these are inconsistent and fraught with methodologic problems. Overall, there seems little basis to suppose there might be a risk for electric fields, and, in contrast to magnetic fields, and with a possible exception of occupational epidemiology, there seems little basis for continued research into electric fields. (c) 2009 Wiley-Liss, Inc.

  2. Electric and magnetic fields at extremely low frequencies

    International Nuclear Information System (INIS)

    Anderson, L.E.; Kaune, W.T.

    1989-01-01

    Whole-body exposure to extremely low frequency (ELF, 30-300 Hz) electric fields may involve effects related to stimulation of the sensory apparatus at the body surface (hair vibration, possible direct neural stimulation) and effects within the body caused by the flow of current. Magnetic fields may interact predominantly by the induction of internal current flow. Biological effects observed in a living organism may depend on the electric fields induced inside the body, possibly on the magnetic fields penetrating into the body, and on the fields acting at the surface of the body. Areas in which effects have been observed often appear to be associated with the nervous system, including altered neuronal excitability and neurochemical changes, altered hormone levels, changes in behavioural responses, and changes in biological rhythms. No studies unequivocably demonstrate deleterious effects of ELF electric or magnetic field exposure on mammalian reproduction and development, but several suggest such effects. Exposure to ELF electric and magnetic fields does produce biological effects. However, except for fields strong enough to induce current densities above the threshold for the stimulation of nerve tissues, there is no consensus as to whether these effects constitute a hazard to human health. Human data from epidemiological studies, including reported effects on cancer promotion, congenital malformations, reproductive performance and general health, though somewhat suggestive of adverse health effects, are not conclusive. 274 refs, 13 figs, 6 tabs

  3. Counterion vibrations in the DNA low-frequency spectra

    Science.gov (United States)

    Perepelytsya, S. M.; Volkov, S. N.

    2007-11-01

    The vibrations of univalent metal cations with respect to phosphate groups of the DNA backbone are described using the four-mass model approach (S.N. Volkov, S.N. Kosevich, J. Biomol. Struct. Dyn. 8, 1069 (1991)) extended in this paper. The force constant of the counterion-phosphate interaction is determined by considering the DNA with counterions as a lattice of ion crystal. For such ion-phosphate lattice the Madelung constant and the dielectric constant are estimated. The obtained value of the Madelung constant is lower than for the NaCl crystal, and its value is about 1.3. The dielectric constant is within 2.3-2.7 depending on the counterion type and form of the double helix. The calculations of the low-frequency spectra show that for the DNA with metal cations Na+ , K+ , Rb+ and Cs+ the frequency of ion-phosphate vibrations decreases from 174 to 96cm^-1 as the counterion mass increases. The obtained frequencies agree well with the vibrational spectra of polynucleotides in a dry state which prove our suggestion about the existence of the ion-phosphate lattice around the DNA double helix. The amplitudes of conformational vibrations for DNA in B -form are calculated as well. The results demonstrate that light counterions ( Na+ do not disturb the internal dynamics of the DNA. However, heavy counterions ( Cs+ have effect on the internal vibrations of the DNA structural elements.

  4. Broadband low-frequency sound isolation by lightweight adaptive metamaterials

    Science.gov (United States)

    Liao, Yunhong; Chen, Yangyang; Huang, Guoliang; Zhou, Xiaoming

    2018-03-01

    Blocking broadband low-frequency airborne noises is highly desirable in lots of engineering applications, while it is extremely difficult to be realized with lightweight materials and/or structures. Recently, a new class of lightweight adaptive metamaterials with hybrid shunting circuits has been proposed, demonstrating super broadband structure-borne bandgaps. In this study, we aim at examining their potentials in broadband sound isolation by establishing an analytical model that rigorously combines the piezoelectric dynamic couplings between adaptive metamaterials and acoustics. Sound transmission loss of the adaptive metamaterial is investigated with respect to both the frequency and angular spectrum to demonstrate their sound-insulation effects. We find that efficient sound isolation can indeed be pursued in the broadband bi-spectrum for not only the case of the small resonator's periodicity where only one mode relevant to the mass-spring resonance exists, but also for the large-periodicity scenario, so that the total weight can be even lighter, in which the multiple plate-resonator coupling modes appear. In the latter case, the negative spring stiffness provided by the piezoelectric stack has been utilized to suppress the resonance-induced high acoustic transmission. Such kinds of adaptive metamaterials could open a new approach for broadband noise isolation with extremely lightweight structures.

  5. Funnel-shaped, low-frequency equatorial waves

    Science.gov (United States)

    Boardsen, S. A.; Gallagher, D. L.; Gurnett, D. A.; Peterson, W. K.; Green, J. L.

    1992-01-01

    Funnel-shaped, low-frequency radiation, as observed in frequency time spectrograms, is frequently found at the earth's magnetic equator which extends from the proton-cyclotron frequency up to the lower hybrid frequency. Ray-tracing calculations can qualitatively reproduce the observed frequency-time characteristics of these emissions if the waves are propagating in the fast magnetosonic mode starting with wave normal angles of about 88 deg at the magnetic equator. The funnel-shaped emissions are consistent with generation by protons with a ring-type velocity space distribution. A ring-shaped region of positive slope in the velocity space density distribution of protons is observed near the Alfven velocity, indicating that the ring protons strongly interact with the waves. Ray-tracing calculations show that for similar equatorial wave normal angles lower-frequency fast magnetosonic waves are more closely confined to the magnetic equator than higher-frequency fast magnetosonic waves. For waves refracted back toward the equator at similar magnetic latitudes, the lower-frequency waves experience stronger damping in the vicinity of the equator than higher-frequency waves. Also, wave growth is restricted to higher frequencies at larger magnetic latitudes. Wave damping at the equator and wave growth off the equator favors equatorial wave normal angle distributions which lead to the funnel-shaped frequency time characteristic.

  6. 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...

  7. HERA Broadband Feed Design for Low-Frequency Radio Astronomy

    Science.gov (United States)

    Garza, Sierra; Trung, Vincent; Ewall-Wice, Aaron Michael; Li, Jianshu; Hewitt, Jacqueline; Riley, Daniel; Bradley, Richard F.; Makhija, Krishna

    2018-01-01

    As part of the Hydrogen Epoch of Reionization Array (HERA) project, we are designing a broadband low-frequency radio feed to extend the bandwidth from 100-200 MHz to 50-220 MHz. By extending the lower-limit to 50 MHz, we hope to detect the signatures of the first black holes heating the hydrogen gas in the intergalactic medium.The isolation of a very faint signal from vastly brighter foregrounds sets strict requirements on antenna spectral smoothness, polarization purity, forward gain, and internal reflections. We are currently working to meet these requirements with a broad-band sinuous antenna feed suspended over the 14-m parabolic HERA dish, using a combination of measurements and simulations to verify the performance of our design.A sinuous feed has been designed and simulated with Computer Simulation Technology (CST) software. We will present the construction of a prototype sinuous antenna and measurements of its reflection coefficient, S11, including laboratory characterization of baluns. Our measurements agree well with the CST simulations of the antenna’s performance, giving us confidence in our ability to model the feed and ensure that it meets the requirements of a 21cm cosmology measurement.

  8. Unusual Low-frequency Magnetic Perturbations in TFTR

    International Nuclear Information System (INIS)

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

    2001-01-01

    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

  9. Earless toads sense low frequencies but miss the high notes

    DEFF Research Database (Denmark)

    Womack, Molly C; Christensen-Dalsgaard, Jakob; Coloma, Luis A

    2017-01-01

    Sensory losses or reductions are frequently attributed to relaxed selection. However, anuran species have lost tympanic middle ears many times, despite anurans' use of acoustic communication and the benefit of middle ears for hearing airborne sound. Here we determine whether pre-existing alternat......Sensory losses or reductions are frequently attributed to relaxed selection. However, anuran species have lost tympanic middle ears many times, despite anurans' use of acoustic communication and the benefit of middle ears for hearing airborne sound. Here we determine whether pre......-existing alternative sensory pathways enable anurans lacking tympanic middle ears (termed earless anurans) to hear airborne sound as well as eared species or to better sense vibrations in the environment. We used auditory brainstem recordings to compare hearing and vibrational sensitivity among 10 species (six eared......, four earless) within the Neotropical true toad family (Bufonidae). We found that species lacking middle ears are less sensitive to high-frequency sounds, however, low-frequency hearing and vibrational sensitivity are equivalent between eared and earless species. Furthermore, extratympanic hearing...

  10. Cellular effects of extremely low frequency (ELF) electromagnetic fields.

    Science.gov (United States)

    Santini, Maria T; Rainaldi, Gabriella; Indovina, Pietro L

    2009-04-01

    The major areas of research that have characterised investigation of the impact of extremely low frequency (ELF) electromagnetic fields on living systems in the past 50 years are discussed. In particular, selected studies examining the role of these fields in cancer, their effects on immune and nerve cells, and the positive influence of these ELF fields on bone and nerve cells, wound healing and ischemia/reperfusion injury are explored. The literature indicates that there is still no general agreement on the exact biological detrimental effects of ELF fields, on the physical mechanisms that may be behind these effects or on the extent to which these effects may be harmful to humans. Nonetheless, the majority of the in vitro experimental results indicate that ELF fields induce numerous types of changes in cells. Whether or not the perturbations observed at the cellular level can be directly extrapolated to negative effects in humans is still unknown. However, the myriad of effects that ELF fields have on biological systems should not be ignored when evaluating risk to humans from these fields and, consequently, in passing appropriate legislation to safeguard both the general public and professionally-exposed workers. With regard to the positive effects of these fields, the possibility of testing further their efficacy in therapeutic protocols should also not be overlooked.

  11. Effect of extremely low frequency electromagnetic fields on bacterial membrane.

    Science.gov (United States)

    Oncul, Sule; Cuce, Esra M; Aksu, Burak; Inhan Garip, Ayse

    2016-01-01

    The effect of extremely low frequency electromagnetic fields (ELF-EMF) on bacteria has attracted attention due to its potential for beneficial uses. This research aimed to determine the effect of ELF-EMF on bacterial membrane namely the membrane potential, surface potential, hydrophobicity, respiratory activity and growth. Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli were subjected to ELF-EMF, 50 Hz, 1 mT for 2 h. Membrane potential was determined by fluorescence spectroscopy with or without EDTA (Ethylenediaminetetraacetic acid) with DisC3(5) (3,3-dipropylthiacarbocyanine iodide), zeta potential measurements were performed by electrophoretic mobility, hydrophobicity of the membrane was measured with MATH (Microbial Adhesion to Hydrocarbons) test, respiratory activity was determined with CTC (5-Cyano-2,3-ditolyl tetrazolium chloride), colony forming unit (CFU) and DAPI (4',6-diamidino-2-phenylindole, dihydrochloride) was used for growth determinations. ELF-EMF caused changes in physicochemical properties of both Gram-positive and Gram-negative bacteria. Hyperpolarization was seen in S. aureus and EDTA-treated E. coli. Surface potential showed a positive shift in S. aureus contrariwise to the negative shift seen in EDTA-untreated E. coli. Respiratory activity increased in both bacteria. A slight decrease in growth was observed. These results show that ELF-EMF affects the crucial physicochemical processes in both Gram-positive and Gram-negative bacteria which need further research.

  12. 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.

  13. Ionization of atoms in strong low-frequency electromagnetic field

    International Nuclear Information System (INIS)

    Krainov, V. P.

    2010-01-01

    The ionization of atoms in a low-frequency linearly polarized electromagnetic field (the photon energy is much lower than the ionization potential of an atom) is considered under new conditions, in which the Coulomb interaction of an electron with the atomic core in the final state of the continuum cannot be considered in perturbation theory in the interaction of the electron with the electromagnetic field. The field is assumed to be much weaker that the atomic field. In these conditions, the classical motion of the electron in the final state of the continuum becomes chaotic (so-called dynamic chaos). Using the well-known Chirikov method of averaging over chaotic variations of the phase of motion, the problem can be reduced to non-linear diffusion on the energy scale. We calculate the classical electron energy in the final state, which is averaged over fast chaotic oscillations and takes into account both the Coulomb field and the electromagnetic field. This energy is used to calculate the probability of ionization from the ground state of the atom to a lower-lying state in the continuum using the Landau-Dykhne approximation (to exponential accuracy). This ionization probability noticeably depends on the field frequency. Upon a decrease in frequency, a transition to the well-known tunnel ionization limit with a probability independent of the field frequency is considered.

  14. 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.

  15. 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.

  16. Considerations on collected data with the Low Frequency Facility experiment

    Energy Technology Data Exchange (ETDEWEB)

    Di Virgilio, A [Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, Polo Fibonacci Ed. C, via F. Buonarrori 2, Pisa (Italy); Cella, G [Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, Polo Fibonacci Ed. C, via F. Buonarrori 2, Pisa (Italy); Dattilo, V [EGO, European, Gravitational Observatory, Cascina (Italy); Frasconi, F [Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, Polo Fibonacci Ed. C, via F. Buonarrori 2, Pisa (Italy); Gennai, A [Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, Polo Fibonacci Ed. C, via F. Buonarrori 2, Pisa (Italy); Penna, P La [EGO, European, Gravitational Observatory, Cascina (Italy); Losurdo, G [INFN Sezione di Firenze, Sesto Fiorentino (Italy); Pasqualetti, A [EGO, European, Gravitational Observatory, Cascina (Italy); Passuello, D [Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, Polo Fibonacci Ed. C, via F. Buonarrori 2, Pisa (Italy); Piergiovanni, F [Universita di Urbino, Urbino (Italy); Porzio, A [Coherentia, CNR-INFM Napoli (Italy); Raffaelli, F [Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, Polo Fibonacci Ed. C, via F. Buonarrori 2, Pisa (Italy); Rapagnani, P [Universita di Roma, Roma1, Rome (Italy); Ricci, F [Universita di Roma, Roma1, Rome (Italy); Solimeno, S [Coherentia, CNR-INFM Napoli (Italy); Istituto Nazionale di Fisica Nucleare, Sez. Napoli, and Dipartimento di Scienze Fisiche, Universita di Napoli ' Federico II' (Italy); Zhang, Z [EGO, European, Gravitational Observatory, Cascina (Italy)

    2006-03-02

    The Low Frequency Facility consists of a 1 cm Fabry-Perot cavity suspended to a single SuperAttenuator, which is the mechanical system adopted to isolate the test masses of the Virgo interferometer. In this paper we present the preliminary results of measurements performed with a cavity of finesse 4000 and lasting 1-2 hours in different working conditions. The analysis presented here is focused mainly on the region below 100 Hz, and uses data collected with longitudinal control bandwidth below 150 Hz. A calibration test confirmed that the collected data are in good agreement with the model of the longitudinal control loop based on the open loop measurements. In addition to this, above 2 Hz the power spectrum of the two mirrors relative displacement shows a stationary noise floor and few peaks with high mechanical quality factor. Studying these peaks in the time domain, it has been observed that the energy associated with a single peak is Boltzman distributed, whether the oscillations are not excited. The measured upper limit of the seismic noise contamination at 10 Hz is around 2 x 10{sup -14} m/{radical}Hz.

  17. Health effects of low frequency electric and magnetic fields

    International Nuclear Information System (INIS)

    1992-06-01

    The US Department of Labor and the President's Office of Science and Technology Policy (STP) requested that the Committee on interagency Radiation Research and Policy Coordination (CIRRPC) conduct an independent evaluation of the reported health effects from exposure to low-frequency electric and magnetic fields (ELF-EMF), especially reports of carcinogenesis and reproductive and neurophysiological effects focusing on frequencies which appeared to be of greatest public concern. Oak Ridge Associated Universities (ORAU) was tasked by the CIRRPC to oversee the review by a panel of independent, non-Federal, scientists. Following their review of over 1000 journal articles, the ORAU Panel concluded ''... that there is no convincing evidence ... to support the contention that exposure to ELF-EMF generated by sources such as household appliances, video display terminals (10 to 30 KHz), and local power lines (15 to 180 Hz) are demonstrable health hazards.'' Although the Panel noted that some biological effects produced by these fields may be of scientific interest and warrant consideration for future research, it concluded that ''... in the broad scope of research needs in basic science and health research, any health concerns over exposures to these fields should not receive a high priority.'' This executive summary outlines the panel's investigation

  18. Low frequency noise in tunneling field effect transistors

    Science.gov (United States)

    Bu, S. T.; Huang, D. M.; Jiao, G. F.; Yu, H. Y.; Li, Ming-Fu

    2017-11-01

    An analytical model is developed for the fluctuation of the electrostatic potential induced by a charged trap in the gate oxide in tunneling field effect transistor (TFET). The model is applied to get the fluctuation of the drain current induced by an interface trap in TFET. A low frequency noise model based on the current transportation through the tunneling and the channel is proposed. The dependency of the normalized power spectra SId/Id2 on the frequency f and the gate bias Vg for TFET is obtained. The noise spectra in TFET are found to be very different from those of conventional MOSFETs, and have the superposition of Lorentzian and 1/f lineshapes with the former associated with tunneling and the later with channel transportation. The potential and current models are compared with TCAD simulation. The calculated IdVg and the noise spectra are also compared with our experimental observations. The results show that the normalized spectra of the current noise due to the tunneling are more significantly affected by Vg than that due to the transportation through the channel. The results also show that the noise from the channel is dominated by the mobility fluctuation rather than the carrier number fluctuation.

  19. Doppler spectral line shapes in low frequency turbulent plasmas

    International Nuclear Information System (INIS)

    Marandet, Y.; Godbert-Mouret, L.; Koubiti, M.; Stamm, R.; Capes, H.; Guirlet, R.

    2003-01-01

    In this paper we investigate the influence of low frequency, i.e. drift wave like turbulence on the spectral line shapes in magnetized plasmas. The measured spectrum, which is obtained through both spatial and time averaging processes, is shown to contain information on turbulence. Using a statistical description of the turbulent fluctuations, we investigate the effects of density, fluid velocity and temperature fluctuations on the Doppler profile of a spectral line. The model we built, relies on 2 separations of scales, first between the atomic processes and the turbulence, allowing the use of a simple LTE model for the VDF (velocity distribution function) of the emitters. Then between turbulent scales and the measurement scales, allowing a statistical treatment of the turbulent fluctuations. The relevant quantity pertaining to turbulence for line shape calculations is found to be the joint PDF (probability distribution function) of the fluctuating plasma parameters. Using our model, we were able to investigate the limiting cases where only one variable fluctuates. At this level of approximation, the Doppler line does not contain information on the density fluctuations. A non-Gaussian PDF leads to a profile which is also non-Gaussian. Thus information on this PDF might be obtained from the measured line shape

  20. Latitudinal beaming of Jupiter's low frequency radio emissions

    International Nuclear Information System (INIS)

    Alexander, J.K.; Desch, M.D.; Kaiser, M.L.; Thieman, J.R.

    1979-01-01

    By comparing Rae 1 and Imp 6 satelite measurements of Jupiter's radio emissions near 1 MHz with recent Voyager 1 and 2 observations in the same frequency range it is now possible to study the properties of the low frequency radiation pattern over a 10 0 range of latitudes with respect to the Jovian rotation equator. These observations, which cover a wider latitudinal range than is possible from the earth, are consistent with many aspect of earlier ground-based measurements that have been used to infer a sharp beaming pattern for the decameter wavelength emissions. We find marked, systematic changes in the statistical occurrence probability distributions with system III central meridian longitude as the Jovigraphic latitude of the observer changes over this range. Moreover, simultaneous observations by the two Voyager spacecraft, which are separated by up to 3 0 in Jovigraphic latitude, suggest that the instantaneous beam width may be no more than a few degrees at times. The new hectometer wave results can be interpreted in terms of a narrow, curved sheet at a fixed magnetic latitude into which the emission is beamed to escape the planet

  1. Establishing the Response of Low Frequency Auditory Filters

    Science.gov (United States)

    Rafaelof, Menachem; Christian, Andrew; Shepherd, Kevin; Rizzi, Stephen; Stephenson, James

    2017-01-01

    The response of auditory filters is central to frequency selectivity of sound by the human auditory system. This is true especially for realistic complex sounds that are often encountered in many applications such as modeling the audibility of sound, voice recognition, noise cancelation, and the development of advanced hearing aid devices. The purpose of this study was to establish the response of low frequency (below 100Hz) auditory filters. Two experiments were designed and executed; the first was to measure subject's hearing threshold for pure tones (at 25, 31.5, 40, 50, 63 and 80 Hz), and the second was to measure the Psychophysical Tuning Curves (PTCs) at two signal frequencies (Fs= 40 and 63Hz). Experiment 1 involved 36 subjects while experiment 2 used 20 subjects selected from experiment 1. Both experiments were based on a 3-down 1-up 3AFC adaptive staircase test procedure using either a variable level narrow-band noise masker or a tone. A summary of the results includes masked threshold data in form of PTCs, the response of auditory filters, their distribution, and comparison with similar recently published data.

  2. Analysis of hysteresis characteristics and low frequency oscillation in gas discharge plasma

    International Nuclear Information System (INIS)

    Matsunaga, Yasushi; Kato, Tomokazu

    1997-01-01

    Hysteresis of gas discharge plasma and nonlinear oscillation of low frequency, caused by the trapped ion, are analyzed. Mainly, the hysteresis and emergence of multiple-steady states are discussed by a simple model of chemical-reaction system. It is shown that a function describing the energy balance has three different real roots. The condition for plural roots depends on the ratio of the bulk energy increase to the surface energy loss of plasma. The criterion contains the non-thermodynamic variables such as conductivity and surface quantities. Examination of stabilities of three-obtained solutions by using linear analysis of differential equations manifests that a root represents a saddle point and other two roots represent stable points. (author)

  3. The Neuroprotective Mechanism of Low-Frequency rTMS on Nigral Dopaminergic Neurons of Parkinson’s Disease Model Mice

    Directory of Open Access Journals (Sweden)

    Qiaoyun Dong

    2015-01-01

    Full Text Available Background. Parkinson’s disease is a neurodegenerative disease in elder people, pathophysiologic basis of which is the severe deficiency of dopamine in the striatum. The purpose of the present study was to evaluate the neuroprotective effect of low-frequency rTMS on Parkinson’s disease in model mice. Methods. The effects of low-frequency rTMS on the motor function, cortex excitability, neurochemistry, and neurohistopathology of MPTP-induced Parkinson’s disease mice were investigated through behavioral detection, electrophysiologic technique, high performance liquid chromatography-electrochemical detection, immunohistochemical staining, and western blot. Results. Low-frequency rTMS could improve the motor coordination impairment of Parkinson’s disease mice: the resting motor threshold significantly decreased in the Parkinson’s disease mice; the degeneration of nigral dopaminergic neuron and the expression of tyrosine hydroxylase were significantly improved by low-frequency rTMS; moreover, the expressions of brain derived neurotrophic factor and glial cell line derived neurotrophic factor were also improved by low-frequency rTMS. Conclusions. Low-frequency rTMS had a neuroprotective effect on the nigral dopaminergic neuron which might be due to the improved expressions of brain derived neurotrophic factor and glial cell line-derived neurotrophic factor. The present study provided a theoretical basis for the application of low-frequency rTMS in the clinical treatment and recovery of Parkinson’s disease.

  4. Low frequency noise sources and mechanisms in semiconductor nanowire transistors

    Science.gov (United States)

    Delker, Collin James

    Semiconductor nanowires are attractive candidates for use in future high-speed electronics, transparent/flexible devices, and chemical sensors. Among other materials, III-V semiconductors have gained considerable interest for their high bulk mobility and low band gap, making them promising for high-speed nanoscale devices. However, nanowire devices also exhibit high levels of low-frequency noise due to their low band gap and high surface-to-volume ratio. The sources and mechanisms of this noise must be understood and controlled in order to realize practical applications of nanowire electronics. This work seeks to understand the underlying noise mechanisms of nanowire transistors in order discover ways to reduce noise levels. It also demonstrates how noise can provide a spectroscopy for analyzing device quality. Most traditional noise studies tend to apply standard MOSFET models to nanowire noise and transport, which lump together all possible independent noise sources in a nanowire, ignoring effects of the contacts or multiple gates, and could lead to misestimation of the noise figures for a device. This work demonstrates how noise in a nanowire transistor can stem from the channel, ungated access regions, metal- semiconductor contacts, and tunnel barriers, all independently adding to the total noise. Each source of noise can contribute and may dominate the overall noise behavior under certain bias regimes and temperatures, as demonstrated in this work through various device structures and measurements. For example, the contacts can influence noise even below the threshold voltage under certain conditions, emphasizing the need for high-quality metal-semiconductor interface technology.

  5. Natural very-low-frequency sferics and headache

    Science.gov (United States)

    Vaitl, D.; Propson, N.; Stark, R.; Schienle, A.

      Very-low-frequency (VLF) atmospherics or sferics are pulse-shaped alternating electric and magnetic fields which originate from atmospheric discharges (lightning). The objective of the study was threefold: (i) to analyse numerous parameters characterizing the sferics activity with regard to their suitability for field studies, (ii) to identify meteorological processes related to the sferics activity and (iii) to investigate the possible association of sferics with pain processes in patients suffering from migraine- and tension-type headaches. Over a period of 6 months (July through December) the sferics activity in the area of Giessen (Germany) was recorded. Three sferics parameters were chosen. The number of sferics impulses per day, the variability of the impulse rate during a day and the variability in comparison to the preceding day were correlated with weather processes (thunderstorm, temperature, vapour pressure, barometric pressure, humidity, wind velocity, warm sector). Significant correlations were obtained during the summer months (July, August) but not during the autumn months (October, November, December). During autumn, however, the sferics activity was correlated with the occurrence of migraine-type headaches (r=0.33, Pheadache diary over a period of 6 months (July-December). While the thunderstorm activity was very intense during July and August, no relationship between sferics and migraine was found. In summer, tension-type headaches were associated with meteorological parameters such as temperature (r=0.42, P<0.01) and vapour pressure (r=0.28, P<0.05). Although the sferics activity can explain a small percentage of the variation in migraine occurrence, a direct influence was more likely exerted by visible or otherwise perceptible weather conditions (thunderstorms, humidity, vapour pressure, warm sector, etc.) than by the sferics activity itself.

  6. MASER: Measuring, Analysing, Simulating low frequency Radio Emissions.

    Science.gov (United States)

    Cecconi, B.; Le Sidaner, P.; Savalle, R.; Bonnin, X.; Zarka, P. M.; Louis, C.; Coffre, A.; Lamy, L.; Denis, L.; Griessmeier, J. M.; Faden, J.; Piker, C.; André, N.; Genot, V. N.; Erard, S.; King, T. A.; Mafi, J. N.; Sharlow, M.; Sky, J.; Demleitner, M.

    2017-12-01

    The MASER (Measuring, Analysing and Simulating Radio Emissions) project provides a comprehensive infrastructure dedicated to low frequency radio emissions (typically Earth, the Sun, Jupiter and Saturn. They are observed either from ground (down to 10 MHz) or from space. Ground observatories are more sensitive than space observatories and capture high resolution data streams (up to a few TB per day for modern instruments). Conversely, space-borne instruments can observe below the ionospheric cut-off (10 MHz) and can be placed closer to the studied object. Several tools have been developed in the last decade for sharing space physcis data. Data visualization tools developed by The CDPP (http://cdpp.eu, Centre de Données de la Physique des Plasmas, in Toulouse, France) and the University of Iowa (Autoplot, http://autoplot.org) are available to display and analyse space physics time series and spectrograms. A planetary radio emission simulation software is developed in LESIA (ExPRES: Exoplanetary and Planetary Radio Emission Simulator). The VESPA (Virtual European Solar and Planetary Access) provides a search interface that allows to discover data of interest for scientific users, and is based on IVOA standards (astronomical International Virtual Observatory Alliance). The University of Iowa also develops Das2server that allows to distribute data with adjustable temporal resolution. MASER is making use of all these tools and standards to distribute datasets from space and ground radio instruments available from the Observatoire de Paris, the Station de Radioastronomie de Nançay and the CDPP deep archive. These datasets include Cassini/RPWS, STEREO/Waves, WIND/Waves, Ulysses/URAP, ISEE3/SBH, Voyager/PRA, Nançay Decameter Array (Routine, NewRoutine, JunoN), RadioJove archive, swedish Viking mission, Interball/POLRAD... MASER also includes a Python software library for reading raw data.

  7. Effects of extremely low frequency electromagnetic fields on human beings

    International Nuclear Information System (INIS)

    Lilien, J.L.; Dular, P.; Sabariego, R.; Beauvois, V.; Barbier, P.P.; Lorphevre, R.

    2010-01-01

    Since the early seventies, potential health risks from ELF (Extremely Low frequency electromagnetic Fields) exposure (50 Hz) have been extensively treated in the literature (more than 1000 references registered by WHO (World Health Organisation), 2007). After 30 years of worldwide research, the major epidemiological output is the possible modest increased risk (by a factor 2) of childhood leukaemia in case of a long exposure to an ambient magnetic flux density (B-field) higher than 0.4 μT. However, this fact has not been confirmed by in vivo and in vitro studies. Moreover it has not been validated by any adverse health biological mechanisms neither for adults nor for children. International recommendations (ICNIRP, International Commission on Non-Ionising Radiation Protection) are currently, for general public, not to exceed a B-field of 100 μT (50 Hz) and an E-field of 5 kV/m (50 Hz). Herein, a rough overview of typical values of ELF fields will be presented followed by a brief literature survey on childhood leukaemia and ELF The potential carcinogenic effect of ELF would be linked to electrical disturbances in cell behaviour. The major concern linking child-hood leukaemia and ELF is thus to determine the response of bone marrow cells under ELF fields. With that purpose, transmembrane potential will be targeted and linked to the E-field at that level. This paper is three-folded: (1) the electric interactions between ambient ELF fields and the body are studied both qualitatively and quantitatively. Different sources of internal E-field are analysed and classified according to their potential risk; (2) the hypothesis of contact current is detailed; (3) key actions to undertake are highlighted. Based on the current state of the art and some authors' own developments, this paper proposes simple low cost enhancements of private electrical installations in order to annihilate the major source of potential effects of ELF. (authors)

  8. 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

  9. 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.

  10. A Model for Low-Frequency Earthquake Slip

    Science.gov (United States)

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

    2017-12-01

    Using high-resolution relative low-frequency earthquake (LFE) locations, we calculate the patch areas (Ap) of LFE families. During episodic tremor and slip (ETS) events, we define AT as the area that slips during LFEs and ST as the total amount of summed LFE slip. Using observed and calculated values for AP, AT, and ST, we evaluate two end-member models for LFE slip within an LFE family patch. In the ductile matrix model, LFEs produce 100% of the observed ETS slip (SETS) in distinct subpatches (i.e., AT ≪ AP). In the connected patch model, AT = AP, but ST ≪ SETS. LFEs cluster into 45 LFE families. Spatial gaps (˜10 to 20 km) between LFE family clusters and smaller gaps within LFE family clusters serve as evidence that LFE slip is heterogeneous on multiple spatial scales. We find that LFE slip only accounts for ˜0.2% of the slip within the slow slip zone. There are depth-dependent trends in the characteristic (mean) moment and in the number of LFEs during both ETS events (only) and the entire ETS cycle (Mcets and NTets and Mcall and NTall, respectively). During ETS, Mc decreases with downdip distance but NT does not change. Over the entire ETS cycle, Mc decreases with downdip distance, but NT increases. These observations indicate that deeper LFE slip occurs through a larger number (800-1,200) of small LFEs, while updip LFE slip occurs primarily during ETS events through a smaller number (200-600) of larger LFEs. This could indicate that the plate interface is stronger and has a higher stress threshold updip.

  11. 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.

  12. Low-frequency vibration control of floating slab tracks using dynamic vibration absorbers

    Science.gov (United States)

    Zhu, Shengyang; Yang, Jizhong; Yan, Hua; Zhang, Longqing; Cai, Chengbiao

    2015-09-01

    This study aims to effectively and robustly suppress the low-frequency vibrations of floating slab tracks (FSTs) using dynamic vibration absorbers (DVAs). First, the optimal locations where the DVAs are attached are determined by modal analysis with a finite element model of the FST. Further, by identifying the equivalent mass of the concerned modes, the optimal stiffness and damping coefficient of each DVA are obtained to minimise the resonant vibration amplitudes based on fixed-point theory. Finally, a three-dimensional coupled dynamic model of a metro vehicle and the FST with the DVAs is developed based on the nonlinear Hertzian contact theory and the modified Kalker linear creep theory. The track irregularities are included and generated by means of a time-frequency transformation technique. The effect of the DVAs on the vibration absorption of the FST subjected to the vehicle dynamic loads is evaluated with the help of the insertion loss in one-third octave frequency bands. The sensitivities of the mass ratio of DVAs and the damping ratio of steel-springs under the floating slab are discussed as well, which provided engineers with the DVA's adjustable room for vibration mitigation. The numerical results show that the proposed DVAs could effectively suppress low-frequency vibrations of the FST when tuned correctly and attached properly. The insertion loss due to the attachment of DVAs increases as the mass ratio increases, whereas it decreases with the increase in the damping ratio of steel-springs.

  13. Tuning and sensitivity of the human vestibular system to low-frequency vibration.

    Science.gov (United States)

    Todd, Neil P McAngus; Rosengren, Sally M; Colebatch, James G

    2008-10-17

    Mechanoreceptive hair-cells of the vertebrate inner ear have a remarkable sensitivity to displacement, whether excited by sound, whole-body acceleration or substrate-borne vibration. In response to seismic or substrate-borne vibration, thresholds for vestibular afferent fibre activation have been reported in anamniotes (fish and frogs) in the range -120 to -90 dB re 1g. In this article, we demonstrate for the first time that the human vestibular system is also extremely sensitive to low-frequency and infrasound vibrations by making use of a new technique for measuring vestibular activation, via the vestibulo-ocular reflex (VOR). We found a highly tuned response to whole-head vibration in the transmastoid plane with a best frequency of about 100 Hz. At the best frequency we obtained VOR responses at intensities of less than -70 dB re 1g, which was 15 dB lower than the threshold of hearing for bone-conducted sound in humans at this frequency. Given the likely synaptic attenuation of the VOR pathway, human receptor sensitivity is probably an order of magnitude lower, thus approaching the seismic sensitivity of the frog ear. These results extend our knowledge of vibration-sensitivity of vestibular afferents but also are remarkable as they indicate that the seismic sensitivity of the human vestibular system exceeds that of the cochlea for low-frequencies.

  14. A New Method for Maintaining Constant Dither Amplitude in Low Frequency PWM

    Directory of Open Access Journals (Sweden)

    KANG, H.

    2017-02-01

    Full Text Available Various controls for fluid flow and pressure are now required in related industries, and the pulse width modulation (PWM and dithering techniques have become essential for the proportional control of solenoids. However, there is a fatal drawback when the dither current signals are generated as a by-product of low frequency PWM. That is, the average current and the dither amplitude in low frequency PWM cannot be controlled independently. Therefore, a new method for maintaining constant dither amplitudes is proposed in this paper. Throughout the mathematical analysis, the effect of PWM frequency and duty cycle on the average current and dither amplitude was investigated, and the analysis result was validated by electrical experiments. Based on the mathematical analysis, a new method that properly varies both the duty cycle and the PWM frequency to obtain the desired average current and constant dither amplitude was established and verified. This method requires only the calculations for determining the proper PWM frequency and duty cycle, so it is possible to improve the performance of a proportional solenoid valve without additional devices or cost.

  15. Trend extraction of rail corrugation measured dynamically based on the relevant low-frequency principal components reconstruction

    International Nuclear Information System (INIS)

    Li, Yanfu; Liu, Hongli; Ma, Ziji

    2016-01-01

    Rail corrugation dynamic measurement techniques are critical to guarantee transport security and guide rail maintenance. During the inspection process, low-frequency trends caused by rail fluctuation are usually superimposed on rail corrugation and seriously affect the assessment of rail maintenance quality. In order to extract and remove the nonlinear and non-stationary trends from original mixed signals, a hybrid model based ensemble empirical mode decomposition (EEMD) and modified principal component analysis (MPCA) is proposed in this paper. Compared with the existing de-trending methods based on EMD, this method first considers low-frequency intrinsic mode functions (IMFs) thought to be underlying trend components that maybe contain some unrelated components, such as white noise and low-frequency signal itself, and proposes to use PCA to accurately extract the pure trends from the IMFs containing multiple components. On the other hand, due to the energy contribution ratio between trends and mixed signals is prior unknown, and the principal components (PCs) decomposed by PCA are arranged in order of energy reduction without considering frequency distribution, the proposed method modifies traditional PCA and just selects relevant low-frequency PCs to reconstruct the trends based on the zero-crossing numbers (ZCN) of each PC. Extensive tests are presented to illustrate the effectiveness of the proposed method. The results show the proposed EEMD-PCA-ZCN is an effective tool for trend extraction of rail corrugation measured dynamically. (paper)

  16. Characterization of indoor extremely low frequency and low frequency electromagnetic fields in the INMA-Granada cohort.

    Science.gov (United States)

    Calvente, Irene; Dávila-Arias, Cristina; Ocón-Hernández, Olga; Pérez-Lobato, Rocío; Ramos, Rosa; Artacho-Cordón, Francisco; Olea, Nicolás; Núñez, María Isabel; Fernández, Mariana F

    2014-01-01

    To characterize the exposure to electric fields and magnetic fields of non-ionizing radiation in the electromagnetic spectrum (15 Hz to 100 kHz) in the dwellings of children from the Spanish Environment and Childhood-"INMA" population-based birth cohort. The study sample was drawn from the INMA-Granada cohort. Out of 300 boys participating in the 9-10 year follow-up, 123 families agreed to the exposure assessment at home and completed a specific ad hoc questionnaire gathering information on sources of non-ionizing radiation electric and magnetic fields inside the homes and on patterns of use. Long-term indoor measurements were carried out in the living room and bedroom. Survey data showed a low exposure in the children's homes according to reference levels of the International Commission on Non-Ionizing Radiation Protection but with large differences among homes in mean and maximum values. Daytime electrostatic and magnetic fields were below the quantification limit in 78.6% (92 dwellings) and 92.3% (108 dwellings) of houses, with an arithmetic mean value (± standard deviation) of 7.31±9.32 V/m and 162.30±91.16 nT, respectively. Mean magnetic field values were 1.6 lower during the night than the day. Nocturnal electrostatic values were not measured. Exposure levels were influenced by the area of residence (higher values in urban/semi-urban versus rural areas), type of dwelling, age of dwelling, floor of the dwelling, and season. Given the greater sensitivity to extremely low-frequency electromagnetic fields of children and following the precautionary principle, preventive measures are warranted to reduce their exposure.

  17. A Sub-Hertz, Low-Frequency Vibration Isolation Platform

    Science.gov (United States)

    Ortiz, Gerardo, G.; Farr, William H.; Sannibale, Virginio

    2011-01-01

    One of the major technical problems deep-space optical communication (DSOC) systems need to solve is the isolation of the optical terminal from vibrations produced by the spacecraft navigational control system and by the moving parts of onboard instruments. Even under these vibration perturbations, the DSOC transceivers (telescopes) need to be pointed l000 fs of times more accurately than an RF communication system (parabolic antennas). Mechanical resonators have been extensively used to provide vibration isolation for groundbased, airborne, and spaceborne payloads. The effectiveness of these isolation systems is determined mainly by the ability of designing a mechanical oscillator with the lowest possible resonant frequency. The Low-Frequency Vibration Isolation Platform (LFVIP), developed during this effort, aims to reduce the resonant frequency of the mechanical oscillators into the sub-Hertz region in order to maximize the passive isolation afforded by the 40 dB/decade roll-off response of the resonator. The LFVIP also provides tip/tilt functionality for acquisition and tracking of a beacon signal. An active control system is used for platform positioning and for dampening of the mechanical oscillator. The basic idea in the design of the isolation platform is to use a passive isolation strut with an approximately equal to 100-mHz resonance frequency. This will extend the isolation range to lower frequencies. The harmonic oscillator is a second-order lowpass filter for mechanical disturbances. The resonance quality depends on the dissipation mechanisms, which are mainly hysteretic because of the low resonant frequency and the absence of any viscous medium. The LFVIP system is configured using the well-established Stewart Platform, which consists of a top platform connected to a base with six extensible struts (see figure). The struts are attached to the base and to the platform via universal joints, which permit the extension and contraction of the struts. The

  18. 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

  19. Accelerated Minority Institution Low Frequency OdontoceteHearing

    National Research Council Canada - National Science Library

    Losey, George

    1998-01-01

    We have tested the hearing of bottlenose dolphins, Risso's dolphins, and False killer whales using both the behavioral techniques and the envelope following response evoked auditory potential procedure...

  20. Characterization of piezoelectric materials for simultaneous strain and temperature sensing for ultra-low frequency applications

    International Nuclear Information System (INIS)

    Islam, Mohammad Nouroz; Seethaler, Rudolf; Alam, M Shahria

    2015-01-01

    Piezoelectric materials are used extensively in a number of sensing applications ranging from aerospace industries to medical diagnostics. Piezoelectric materials generate charge when they are subjected to strain. However, since measuring charge is difficult at low frequencies, traditional piezoelectric sensors are limited to dynamic applications. In this research an alternative technique is proposed to determine static strain that relies upon the measurement of piezoelectric capacitance and resistance using piezoelectric sensors. To demonstrate the validity of this approach, the capacitance and resistance of a piezoelectric patch sensor was characterized for a wide range of strain and temperature. The study shows that the piezoelectric capacitance is sensitive to both strain and temperature while the resistance is mostly dependent on the temperature variation. The findings can be implemented to obtain thermally compensated static strain from piezoelectric sensors, which does not require an additional temperature sensor. (paper)

  1. Pulsars Probe the Low-Frequency Gravitational Sky: Pulsar Timing Arrays Basics and Recent Results

    Science.gov (United States)

    Tiburzi, Caterina

    2018-03-01

    Pulsar Timing Array experiments exploit the clock-like behaviour of an array of millisecond pulsars, with the goal of detecting low-frequency gravitational waves. Pulsar Timing Array experiments have been in operation over the last decade, led by groups in Europe, Australia, and North America. These experiments use the most sensitive radio telescopes in the world, extremely precise pulsar timing models and sophisticated detection algorithms to increase the sensitivity of Pulsar Timing Arrays. No detection of gravitational waves has been made to date with this technique, but Pulsar Timing Array upper limits already contributed to rule out some models of galaxy formation. Moreover, a new generation of radio telescopes, such as the Five hundred metre Aperture Spherical Telescope and, in particular, the Square Kilometre Array, will offer a significant improvement to the Pulsar Timing Array sensitivity. In this article, we review the basic concepts of Pulsar Timing Array experiments, and discuss the latest results from the established Pulsar Timing Array collaborations.

  2. Modelling and design of planar Hall effect bridge sensors for low-frequency applications

    DEFF Research Database (Denmark)

    Persson, Åsa; Bejhed, R.S.; Østerberg, Frederik Westergaard

    2013-01-01

    and moderate noise figure. In this work, the applicability of such PHEB sensors to different areas is investigated. An analytical model is constructed to estimate the performance of an arbitrary PHEB sensor geometry in terms of, e.g., sensitivity and detectivity. The model is valid for an ideal case, e......The applicability of miniaturized magnetic field sensors is being explored in several areas of magnetic field detection due to their integratability, low mass, and potentially low cost. In this respect, different thin-film technologies, especially those employing magnetoresistance, show great...... potential, being compatible with batch micro- and nanofabrication techniques. For low-frequency magnetic field detection, sensors based on the planar Hall effect, especially planar Hall effect bridge (PHEB) sensors, show promising performance given their inherent low-field linearity, limited hysteresis...

  3. Temporal Activity Modulation of Deep Very Low Frequency Earthquakes in Shikoku, Southwest Japan

    Science.gov (United States)

    Baba, Satoru; Takeo, Akiko; Obara, Kazushige; Kato, Aitaro; Maeda, Takuto; Matsuzawa, Takanori

    2018-01-01

    We investigated long-term changes in the activity of deep very low frequency earthquakes (VLFEs) in western Shikoku, southwest part of the Nankai subduction zone in Japan for 13 years by the matched-filter technique. VLFE activity is expected to be a proxy of interplate slips. In the Bungo channel, where long-term slow slip events (SSEs) occurred frequently, the cumulative number of detected VLFEs increased rapidly in 2010 and 2014, which were modulated by long-term SSEs. In the neighboring inland region near the Bungo channel, the cumulative number increased steeply every 6 months. This stepwise change was accompanied by episodic tremors and slips. Deep VLFE activity in western Shikoku has been low since the latter half of 2014. This decade-scale quiescence may be attributed to the change in interplate coupling strength in the Nankai subduction zone.

  4. Comparison of pulse characteristic of low frequency ultrasonic probes for concrete application

    International Nuclear Information System (INIS)

    Amry Amin Abas; Suhairy Sani; Muhammad Pauzi Ismail

    2006-01-01

    Ultrasonic testing of concrete or large volume of composites usually is done in low frequency range. To obtain low frequency pulse, a low frequency pulser/receiver is used attached to a low frequency probe as transmitter/receiver. Concrete is highly attenuative and a high energy pulse is essential to ensure good penetration of test samples. High energy pulse can be obtained by producing low frequency ultrasonic waves.To achieve high penetration in concrete, a low frequency probe is fabricated with the centre frequency lying at around 100 kHz. The probe is fabricated with single crystal of 18 mm thickness without any backing material to obtain wider pulse and higher pulse power. Then, comparison of pulse characteristic is done between the fabricated probe and a commercially available probe to determine the quality of the probe fabricated. (Author)

  5. Power System Transient Stability Enhancement By Tuning Of SSSC And PSS Parameters Using PSO Technique

    Directory of Open Access Journals (Sweden)

    Hashim Dhahir Mohammed

    2018-03-01

    Full Text Available In this paper, the tuning design of  SSSC and PSS was examined in increasing the damping of system oscillations and improve the stability of the power system during disturbances. The design problem of the SSSC controller and PSS is designed as problem of optimization and the technique uses (PSO technique to find for optimal control parameters. By minimizing the objective function based on the speed deviation and time domain, which deliberately deviates at the oscillation angle of the alternator rotor to improve performance of transient stability of the system. The proposed controllers are tested on the system of weak bonding ability exposed to severe disturbance. Nonlinear simulation results are presented to demonstrate the proposed controller's effectiveness and its ability to give efficient damping. It is also noted that the proposed controllers  of SSSC and PSS greatly improves the power system stability.

  6. Complementary analysis techniques applied on optimizing suspensions of yttria stabilized zirconia

    DEFF Research Database (Denmark)

    Della Negra, Michela; Foghmoes, Søren Preben Vagn; Klemensø, Trine

    2016-01-01

    Three different polymers with different functional groups and similar molecular weight were tested as dispersing agents for suspensions of yttria stabilized zirconia in ethanol: polyvinyl pyrrolidone, polyethylene imine, polyvinyl butyral/acetal. The stability of the system was assessed consideri...... excellent performance of polyvinyl pyrrolidone and polyethylene imine as dispersing agents. The stability and dispersing power were finally utilized for preparing concentrated suspensions for tape casting and subsequently to sinter the tapes into dense ceramic pieces......., in details, all the processing steps, including suspension de-agglomeration, slurry manipulation, quality of sintered tapes microstructure, and final layer leak tightness. Different analytical techniques were used to monitor ceramic de-agglomeration and stability as a function of time, for different types...

  7. Tuning of SVC Stabilizers over a Wide Range of Load Parameters Using Pole-Placement Technique

    Directory of Open Access Journals (Sweden)

    K. Ellithy

    2008-12-01

    Full Text Available This paper investigates the effect of typical load model parameters on the static var compensator (SVC stabilizers tuning. A proportional-Integral (PI type stabilizer is considered and its gain-settings are tuned using the pole-placement technique to improve the damping of power systems. Tuning of SVC stabilizers (damping controllers traditionally assumes that the system loads are voltage dependent with fixed parameters. However, the load parameters are generally uncertain. This uncertain behavior of the load parameters can de-tune the gains of the stabilizer; consequently the SVC stabilizer with fixed gain-settings can be adequate for some load parameters but contrarily can reduce system damping and contribute to system instability with loads having other parameters. The effect of typical load model parameters on the tuning gains of the SVC PI stabilizer is examined and it is found the load parameters have a considerable influence on the tuning gains. The time domain simulations performed on the system show that the SVC stabilizer tuned at fixed load parameters reduce the system damping under other load parameters and could lead system instability.

  8. A fiber-optic interferometer with subpicometer resolution for dc and low-frequency displacement measurement

    International Nuclear Information System (INIS)

    Smith, D. T.; Pratt, J. R.; Howard, L. P.

    2009-01-01

    We have developed a fiber-optic interferometer optimized for best performance in the frequency range from dc to 1 kHz, with displacement linearity of 1% over a range of ± 25 nm, and noise-limited resolution of 2 pm. The interferometer uses a tunable infrared laser source (nominal 1550 nm wavelength) with high amplitude and wavelength stability, low spontaneous self-emission noise, high sideband suppression, and a coherence control feature that broadens the laser linewidth and dramatically lowers the low-frequency noise in the system. The amplitude stability of the source, combined with the use of specially manufactured ''bend-insensitive'' fiber and all-spliced fiber construction, results in a robust homodyne interferometer system, which achieves resolution of 40 fm Hz -1/2 above 20 Hz and approaches the shot-noise-limit of 20 fm Hz -1/2 at 1 kHz for an optical power of 10 μW, without the need for differential detection. Here we describe the design and construction of the interferometer, as well as modes of operation, and demonstrate its performance.

  9. Slow slip rate and excitation efficiency of deep low-frequency tremors beneath southwest Japan

    Science.gov (United States)

    Daiku, Kumiko; Hiramatsu, Yoshihiro; Matsuzawa, Takanori; Mizukami, Tomoyuki

    2018-01-01

    We estimated the long-term average slip rate on the plate interface across the Nankai subduction zone during 2002-2013 using deep low-frequency tremors as a proxy for short-term slow slip events based on empirical relations between the seismic moment of short-term slow slip events and tremor activities. The slip rate in each region is likely to compensate for differences between the convergence rate and the slip deficit rate of the subducting Philippine Sea plate estimated geodetically, although the uncertainty is large. This implies that the strain because of the subduction of the plate is partially stored as the slip deficit and partially released by slow slip events during the interseismic period. The excitation efficiency of the tremors for the slow slip events differs among regions: it is high in the northern Kii region. Some events in the western Shikoku region show a somewhat large value. Antigorite serpentinite of two types exists in the mantle wedge beneath southwest Japan. Slips with more effective excitation of tremors presumably occur in high-temperature conditions in the antigorite + olivine stability field. Other slip events with low excitation efficiency are distributed in the antigorite + brucite stability field. Considering the formation reactions of these minerals and their characteristic structures, events with high excitation efficiency can be correlated with a high pore fluid pressure condition. This result suggests that variation in pore fluid pressure on the plate interface affects the magnitude of tremors excited by slow slip events.

  10. An offset tone based gain stabilization technique for mixed-signal RF measurement systems

    International Nuclear Information System (INIS)

    Joshi, Gopal; Motiwala, Paresh D.; Randale, G.D.; Singh, Pitamber; Agarwal, Vivek; Kumar, Girish

    2015-01-01

    This paper describes a gain stabilization technique for a RF signal measurement system. A sinusoidal signal of known amplitude, phase and close enough in frequency is added to the main, to be measured RF signal at the input of the analog section. The system stabilizes this offset tone in the digital domain, as it is sampled at the output of the analog section. This process generates a correction factor needed to stabilize the magnitude of the gain of the analog section for the main RF signal. With the help of a simple calibration procedure, the absolute amplitude of the main RF signal can be measured. The technique is especially suited for a system that processes signals around a single frequency, employs direct signal conversion into the digital domain, and processes subsequent steps in an FPGA. The inherent parallel signal processing in an FPGA-based implementation allows a real time stabilization of the gain. The effectiveness of the technique is derived from the fact, that the gain stabilization stamped to the main RF signal measurement branch requires only a few components in the system to be inherently stable. A test setup, along with experimental results is presented from the field of RF instrumentation for particle accelerators. Due to the availability of a phase synchronized RF reference signal in these systems, the measured phase difference between the main RF and the RF reference is also stabilized using this technique. A scheme of the signal processing is presented, where a moving average filter has been used to filter out not only the unwanted frequencies, but also to separate the main RF signal from the offset tone signal. This is achieved by a suitable choice of sampling and offset tone frequencies. The presented signal processing scheme is suitable to a variety of RF measurement applications

  11. An offset tone based gain stabilization technique for mixed-signal RF measurement systems

    Energy Technology Data Exchange (ETDEWEB)

    Joshi, Gopal, E-mail: gjos@barc.gov.in [BARC, Mumbai 400085 (India); Motiwala, Paresh D.; Randale, G.D.; Singh, Pitamber [BARC, Mumbai 400085 (India); Agarwal, Vivek; Kumar, Girish [IIT Bombay, Powai, Mumbai 400076 (India)

    2015-09-21

    This paper describes a gain stabilization technique for a RF signal measurement system. A sinusoidal signal of known amplitude, phase and close enough in frequency is added to the main, to be measured RF signal at the input of the analog section. The system stabilizes this offset tone in the digital domain, as it is sampled at the output of the analog section. This process generates a correction factor needed to stabilize the magnitude of the gain of the analog section for the main RF signal. With the help of a simple calibration procedure, the absolute amplitude of the main RF signal can be measured. The technique is especially suited for a system that processes signals around a single frequency, employs direct signal conversion into the digital domain, and processes subsequent steps in an FPGA. The inherent parallel signal processing in an FPGA-based implementation allows a real time stabilization of the gain. The effectiveness of the technique is derived from the fact, that the gain stabilization stamped to the main RF signal measurement branch requires only a few components in the system to be inherently stable. A test setup, along with experimental results is presented from the field of RF instrumentation for particle accelerators. Due to the availability of a phase synchronized RF reference signal in these systems, the measured phase difference between the main RF and the RF reference is also stabilized using this technique. A scheme of the signal processing is presented, where a moving average filter has been used to filter out not only the unwanted frequencies, but also to separate the main RF signal from the offset tone signal. This is achieved by a suitable choice of sampling and offset tone frequencies. The presented signal processing scheme is suitable to a variety of RF measurement applications.

  12. A Reconstructive Stabilization Technique for Nontraumatic or Chronic Traumatic Extensor Tendon Subluxation.

    Science.gov (United States)

    Lee, Jae Hoon; Baek, Jong Hun; Lee, Jung Seok

    2017-01-01

    Subluxation of the extensor tendon results from a disruption to the sagittal band at the metacarpophalangeal joint. When conservative treatment fails to correct the subluxation, surgical treatment may be necessary. Surgical techniques for chronic cases vary in graft source and graft pathway. We present a surgical technique to recentralize and stabilize the extensor tendon using a residual ruptured sagittal band. This technique is simple and effective without donor site morbidity and seems to provide potential biomechanical advantages by restoring nearly normal anatomy. Copyright © 2017 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.

  13. Performance Comparison of Adaptive Estimation Techniques for Power System Small-Signal Stability Assessment

    Directory of Open Access Journals (Sweden)

    E. A. Feilat

    2010-12-01

    Full Text Available This paper demonstrates the assessment of the small-signal stability of a single-machine infinite- bus power system under widely varying loading conditions using the concept of synchronizing and damping torques coefficients. The coefficients are calculated from the time responses of the rotor angle, speed, and torque of the synchronous generator. Three adaptive computation algorithms including Kalman filtering, Adaline, and recursive least squares have been compared to estimate the synchronizing and damping torque coefficients. The steady-state performance of the three adaptive techniques is compared with the conventional static least squares technique by conducting computer simulations at different loading conditions. The algorithms are compared to each other in terms of speed of convergence and accuracy. The recursive least squares estimation offers several advantages including significant reduction in computing time and computational complexity. The tendency of an unsupplemented static exciter to degrade the system damping for medium and heavy loading is verified. Consequently, a power system stabilizer whose parameters are adjusted to compensate for variations in the system loading is designed using phase compensation method. The effectiveness of the stabilizer in enhancing the dynamic stability over wide range of operating conditions is verified through the calculation of the synchronizing and damping torque coefficients using recursive least square technique.

  14. Experimental demonstration of the existence of highly permeable localized transport regions in low-frequency sonophoresis.

    Science.gov (United States)

    Kushner, Joseph; Blankschtein, Daniel; Langer, Robert

    2004-11-01

    Recent advances in low-frequency sonophoresis have focused on the existence of hypothesized localized transport regions (LTRs). However, there has been no actual experimental demonstration that the hypothesized LTRs are, in fact, localized regions of high permeability. Through a series of low-frequency sonophoresis experiments conducted with full-thickness pig skin, in the presence of the surfactant sodium lauryl sulfate (SLS), in which we have separately measured the transport of calcein through the LTRs, which have areas ranging from 10 to 40 mm(2), and the surrounding regions of the skin (the non-LTRs) by means of a novel masking technique, we demonstrate that the calcein permeability through the LTRs is approximately 80-fold higher than the calcein permeability through the non-LTRs, suggesting that the LTRs are structurally perturbed to a greater extent than the non-LTRs from the exposure to the ultrasound/SLS system. In addition, we propose basic models to predict the total skin transdermal permeability from the transdermal permeabilities of the LTRs and the non-LTRs, and then compare the predictions to the experimental data obtained from the masking experiments. We also demonstrate that both the LTRs and the non-LTRs exhibit significant decreases in skin electrical resistivity relative to untreated skin ( approximately 5000-fold and approximately 170-fold, respectively), suggesting the existence of two levels of significant skin structural perturbation due to ultrasound exposure in the presence of SLS. Finally, an analysis of the porosity/tortuosity ratio (epsilon/tau) values suggests that trans-cellular transdermal transport pathways are present within the highly permeable, and highly structurally perturbed, LTRs.

  15. Topology optimization and fabrication of low frequency vibration energy harvesting microdevices

    International Nuclear Information System (INIS)

    Deng, Jiadong; Rorschach, Katherine; Baker, Evan; Sun, Cheng; Chen, Wei

    2015-01-01

    Topological design of miniaturized resonating structures capable of harvesting electrical energy from low frequency environmental mechanical vibrations encounters a particular physical challenge, due to the conflicting design requirements: low resonating frequency and miniaturization. In this paper structural static stiffness to resist undesired lateral deformation is included into the objective function, to prevent the structure from degenerating and forcing the solution to be manufacturable. The rational approximation of material properties interpolation scheme is introduced to deal with the problems of local vibration and instability of the low density area induced by the design dependent body forces. Both density and level set based topology optimization (TO) methods are investigated in their parameterization, sensitivity analysis, and applicability for low frequency energy harvester TO problems. Continuum based variation formulations for sensitivity analysis and the material derivative based shape sensitivity analysis are presented for the density method and the level set method, respectively; and their similarities and differences are highlighted. An external damper is introduced to simulate the energy output of the resonator due to electrical damping and the Rayleigh proportional damping is used for mechanical damping. Optimization results for different scenarios are tested to illustrate the influences of dynamic and static loads. To demonstrate manufacturability, the designs are built to scale using a 3D microfabrication method and assembled into vibration energy harvester prototypes. The fabricated devices based on the optimal results from using different TO techniques are tested and compared with the simulation results. The structures obtained by the level set based TO method require less post-processing before fabrication and the structures obtained by the density based TO method have resonating frequency as low as 100 Hz. The electrical voltage response

  16. Real-time stability in power systems techniques for early detection of the risk of blackout

    CERN Document Server

    Savulescu, Savu

    2014-01-01

    This pioneering volume has been updated and enriched to reflect the state-of-the-art in blackout prediction and prevention. It documents and explains background and algorithmic aspects of the most successful steady-state, transient and voltage stability solutions available today in real-time. It also describes new, cutting-edge stability applications of synchrophasor technology, and captures industry acceptance of metrics and visualization tools that quantify and monitor the distance to instability. Expert contributors review a broad spectrum of additionally available techniques, such as traje

  17. Energy Harvesting From Low Frequency Applications Using Piezoelectric Materials

    Energy Technology Data Exchange (ETDEWEB)

    Li, Huidong; Tian, Chuan; Deng, Zhiqun

    2014-11-06

    This paper reviewed the state of research on piezoelectric energy harvesters. Various types of harvester configurations, piezoelectric materials, and techniques used to improve the mechanical-to-electrical energy conversion efficiency were discussed. Most of the piezoelectric energy harvesters studied today have focused on scavenging mechanical energy from vibration sources due to their abundance in both natural and industrial environments. Cantilever beams have been the most studied structure for piezoelectric energy harvester to date because of the high responsiveness to small vibrations.

  18. Evaluation of the color stability of two techniques for reproducing artificial irides after microwave polymerization.

    Science.gov (United States)

    Goiato, Marcelo Coelho; Santos, Daniela Micheline dos; Moreno, Amália; Gennari-Filho, Humberto; Pellizzer, Eduardo Piza

    2011-01-01

    The use of ocular prostheses for ophthalmic patients aims to rebuild facial aesthetics and provide an artificial substitute to the visual organ. Natural intemperate conditions promote discoloration of artificial irides and many studies have attempted to produce irides with greater chromatic paint durability using different paint materials. The present study evaluated the color stability of artificial irides obtained with two techniques (oil painting and digital image) and submitted to microwave polymerization. Forty samples were fabricated simulating ocular prostheses. each sample was constituted by one disc of acrylic resin N1 and one disc of colorless acrylic resin with the iris interposed between the discs. The irides in brown and blue color were obtained by oil painting or digital image. The color stability was determined by a reflection spectrophotometer and measurements were taken before and after microwave polymerization. Statistical analysis of the techniques for reproducing artificial irides was performed by applying the normal data distribution test followed by 2-way ANOVA and Tukey HSD test (α=.05). Chromatic alterations occurred in all specimens and statistically significant differences were observed between the oil-painted samples and those obtained by digital imaging. There was no statistical difference between the brown and blue colors. Independently of technique, all samples suffered color alterations after microwave polymerization. The digital imaging technique for reproducing irides presented better color stability after microwave polymerization.

  19. Dimensional Stability and Acuracy of Silicone - Based Impression Materials Using Different Impression Techniques - A Literature Review.

    Science.gov (United States)

    Naumovski, Borjan; Kapushevska, Biljana

    2017-09-01

    A quality-made dental impression is a prerequisite for successful fixed-prosthodontic fabrication and is directly dependent on the dimensional stability, accuracy and flexibility of the elastomeric impression materials, as well as on the appropriately used impression techniques. The purpose of this paper is to provide a literature review of relevant scientific papers which discuss the use of various silicone impression materials, different impression techniques and to evaluate their impact on the dimensional stability and accuracy of the obtained impressions. Scientific papers and studies were selected according to the materials used, the sample size, impression technique, storage time, type of measurements and use of spacer for the period between 2002 and 2016. In the reviewed literature several factors that influence the dimensional stability and accuracy of silicone impression molds, including the choice of the type of viscosity, impression material thickness, impression technique, retention of the impression material on the tray, storage time before the casting, number of castings, hydrophilicity of the material, release of byproducts, contraction after polymerization, thermal contraction and incomplete elastic recovery were presented. The literature review confirmed the lack of standardization of methodologies applied in the research and their great diversity. All findings point to the superiority of the addition silicone compared to the condensation silicone.

  20. 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...

  1. 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...

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

    Indian Academy of Sciences (India)

    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 ...

  3. Extracting Low-Frequency Information from Time Attenuation in Elastic Waveform Inversion

    Science.gov (United States)

    Guo, Xuebao; Liu, Hong; Shi, Ying; Wang, Weihong

    2017-03-01

    Low-frequency information is crucial for recovering background velocity, but the lack of low-frequency information in field data makes inversion impractical without accurate initial models. Laplace-Fourier domain waveform inversion can recover a smooth model from real data without low-frequency information, which can be used for subsequent inversion as an ideal starting model. In general, it also starts with low frequencies and includes higher frequencies at later inversion stages, while the difference is that its ultralow frequency information comes from the Laplace-Fourier domain. Meanwhile, a direct implementation of the Laplace-transformed wavefield using frequency domain inversion is also very convenient. However, because broad frequency bands are often used in the pure time domain waveform inversion, it is difficult to extract the wavefields dominated by low frequencies in this case. In this paper, low-frequency components are constructed by introducing time attenuation into the recorded residuals, and the rest of the method is identical to the traditional time domain inversion. Time windowing and frequency filtering are also applied to mitigate the ambiguity of the inverse problem. Therefore, we can start at low frequencies and to move to higher frequencies. The experiment shows that the proposed method can achieve a good inversion result in the presence of a linear initial model and records without low-frequency information.

  4. Millisecond and binary pulsars as nature's frequency standards - II. The effects of low-frequency timing noise on residuals and measured parameters

    Science.gov (United States)

    Kopeikin, Sergei M.

    1999-05-01

    Millisecond and binary pulsars are the most stable natural frequency standards. They can be applied to a number of principal problems in modern astronomy and time-keeping metrology, including the search for a stochastic gravitational wave background in the early Universe, testing general relativity and establishing a new ephemeris time-scale. The full exploration of pulsar properties requires that proper unbiased estimates of the spin and orbital parameters be obtained, a problem which deserves special investigation. These estimates depend essentially on the random noise component being revealed in the residuals of time of arrival (TOA) and having various physical origins. In the present paper, the influence of low-frequency (`red') timing noise with spectral indices from 1 to 6 on TOA residuals, variances, and covariances of the estimates of measured parameters of single and binary pulsars is studied. In order to determine the functional dependence of these quantities on time, an analytical technique for processing observational data in the time domain is developed. Data processing in the time domain is more informative, because it takes into account both the stationary and non-stationary components of noise. Data processing in the frequency domain is valid if and only if the noise is stationary. Our analysis includes a simplified timing model of a binary pulsar in a circular orbit and a procedure for estimating pulsar parameters and residuals under the influence of red noise. We reconfirm, in accordance with the results of previous authors, that uncorrelated white noise in the errors of measurements of TOA causes gradually decreasing residuals, variances and covariances of all parameters. On the other hand, we show that any low-frequency, correlated noise of terrestrial or/and astrophysical origin that is present causes the residuals, variances and covariances of certain parameters to increase with time. Hence, the low-frequency noise corrupts our observations

  5. Efficient fast multipole method for low-frequency scattering

    International Nuclear Information System (INIS)

    Darve, Eric; Have, Pascal

    2004-01-01

    The solution of the Helmholtz and Maxwell equations using integral formulations requires to solve large complex linear systems. A direct solution of those problems using a Gauss elimination is practical only for very small systems with few unknowns. The use of an iterative method such as GMRES can reduce the computational expense. Most of the expense is then computing large complex matrix vector products. The cost can be further reduced by using the fast multipole method which accelerates the matrix vector product. For a linear system of size N, the use of an iterative method combined with the fast multipole method reduces the total expense of the computation to NlogN. There exist two versions of the fast multipole method: one which is based on a multipole expansion of the interaction kernel expιkr/r and which was first proposed by V. Rokhlin and another based on a plane wave expansion of the kernel, first proposed by W.C. Chew. In this paper, we propose a third approach, the stable plane wave expansion (SPW-FMM), which has a lower computational expense than the multipole expansion and does not have the accuracy and stability problems of the plane wave expansion. The computational complexity is NlogN as with the other methods

  6. Biomechanical stability of intramedullary technique for fixation of joint depressed calcaneus fracture.

    Science.gov (United States)

    Nelson, Joshua D; McIff, Terence E; Moodie, Patrick G; Iverson, Jamey L; Horton, Greg A

    2010-03-01

    Internal fixation of the os calcis is often complicated by prolonged soft tissue management and posterior facet disruption. An ideal calcaneal construct would include minimal hardware prominence, sturdy posterior facet fixation and nominal soft tissue disruption. The purpose of this study was to develop such a construct and provide a biomechanical analysis comparing our technique to a standard internal fixation technique. Twenty fresh-frozen cadaver calcanei were used to create a reproducible Sanders type-IIB calcaneal fracture pattern. One calcaneus of each pair was randomly selected to be fixed using our compressive headless screw technique. The contralateral matched calcaneus was fixed with a nonlocking calcaneal plate in a traditional fashion. Each calcaneus was cyclically loaded at a frequency of 1 Hz for 4000 cycles using an increasing force from 250 N to 1000 N. An Optotrak motion capturing system was used to detect relative motion of the three fracture fragments at eight different points along the fracture lines. Horizontal separation and vertical displacement at the fracture lines was recorded, as well as relative rotation at the primary fracture line. When the data were averaged, there was more horizontal displacement at the primary fracture line of the plate and screw construct compared to the headless screw construct. The headless screw construct also had less vertical displacement at the primary fracture line at every load. On average those fractures fixed with the headless screw technique had less rotation than those fixed with the side plate technique. A new headless screw technique for calcaneus fracture fixation was shown to provide stability as good as, or better than, a standard side plating technique under the axial loading conditions of our model. Although further testing is needed, the stability of the proposed technique is similar to that typically provided by intramedullary fixation. This fixation technique provides a biomechanically stable

  7. [The progress of research on low-frequency sonophoresis and its applications].

    Science.gov (United States)

    Tu, Xi; Yin, Qinqin; Zhang, Wensheng; Huang, Hua

    2008-12-01

    Low-frequency ultrasound can increase the transdermal delivery of many drugs, including macromolecular drugs. The main mechanism is ultrasonic cavitation. Most researchers pointed out that it could change the form-structure of stratum corneum keratinocytes and, in this way, it can improve the permeability of skin. Low-frequency sonophoresis has been in use for in-vitro experiments and in-vivo animal experiments, and so far, both small-molecules transdermal delivery and macromolecules transdermal delivery have been successfully performed in many experiments. However, there are few reports about the real low-frequency sonophoresis for clinical treatment. A large number of clinical trials are necessary to confirm its safety and practicality. Once its safety is confirmed and the suitable low-frequency sonophoresis devices are developed successfully, Low-frequency Sonophoresis will come to be a safe, effective, controllable, and economic new delivery method.

  8. Determination of pelvic ring stability: a new technique using a composite hemi-pelvis.

    Science.gov (United States)

    Clements, J P; Moriaty, N; Chesser, T J S; Ward, A J; Cunningham, J L

    2008-07-01

    Traumatic disruption of the pelvic ring caused by high-energy impact is associated with significant mortality and morbidity. A variety of fixation techniques have been developed for treating these injuries with the main aims of restoring the stability of the pelvic ring and promoting recovery of normal function. The stability of fixation of these techniques is often analysed by cadaveric studies, which can introduce high variability into the results and have small sample numbers. This study presents a new method that uses a composite hemi-pelvis to enable stabilization of the pelvic ring to be accurately determined. The pelvis was loaded cyclically to simulate walking conditions and to assess the stability of the fixation, which was measured using a displacement transducer that monitors the motion of the pelvis in six degrees of freedom. The motions measured showed comparable results with previously published cadaveric studies. This reproducible method of testing with a hemi-pelvis composite model and rig allows valid analysis of pubic symphysis implants, obviating the difficulties of performing a cadaveric study.

  9. Alternative procedure to improve the stability of mandibular complete dentures: a modified neutral zone technique.

    Science.gov (United States)

    Rehmann, Peter; Zenginel, Martha; Wostmann, Bernd

    2012-01-01

    The aim of this report is to describe an alternative technique to record the neutral zone. An acrylic resin base with posterior occlusal rims was applied using a thermoplastic denture adhesive. After being worn for 2 days, the base was transferred into an acrylic resin complete denture. Most patients reported an improvement in denture stability and a reduction of pressure sores. This procedure seems to be helpful to improve denture function, especially in the mandible, in patients who cannot be treated with implants. However, because of its complexity, this neutral zone technique cannot be recommended for routine clinical use.

  10. Accuracy Enhanced Stability and Structure Preserving Model Reduction Technique for Dynamical Systems with Second Order Structure

    DEFF Research Database (Denmark)

    Tahavori, Maryamsadat; Shaker, Hamid Reza

    gramians within the time interval to build the appropriate Petrov-Galerkin projection for dynamical systems within the time interval of interest. The bound on approximation error is also derived. The numerical results are compared with the counterparts from other techniques. The results confirm......A method for model reduction of dynamical systems with the second order structure is proposed in this paper. The proposed technique preserves the second order structure of the system, and also preserves the stability of the original systems. The method uses the controllability and observability...

  11. Scalping injuries: new technique for stabilization of flaps to the skull.

    Science.gov (United States)

    Schubert, W; Guzman-Stein, G; Hope, R; Ahrenholz, D H; Solem, L D; Cunningham, B L

    1988-05-01

    Extensive scalping injuries offer a unique challenge for tissue coverage because of the wide expanse of bone and lack of deep soft tissue or significant perforating vessels. For smaller injuries, pedicle flaps offer ideal coverage. Larger defects can be covered by omental flaps. Coverage with a free muscle flap followed by split-thickness skin grafting offers optimal long-term coverage. Two new techniques are introduced. The wire-button technique offers stabilization, and the halo frame provides good support and protection for a new free-flap graft and may increase the success rate of flaps in patients with scalping injuries.

  12. Stability analysis of nonlinear Roesser-type two-dimensional systems via a homogenous polynomial technique

    International Nuclear Information System (INIS)

    Zhang Tie-Yan; Zhao Yan; Xie Xiang-Peng

    2012-01-01

    This paper is concerned with the problem of stability analysis of nonlinear Roesser-type two-dimensional (2D) systems. Firstly, the fuzzy modeling method for the usual one-dimensional (1D) systems is extended to the 2D case so that the underlying nonlinear 2D system can be represented by the 2D Takagi—Sugeno (TS) fuzzy model, which is convenient for implementing the stability analysis. Secondly, a new kind of fuzzy Lyapunov function, which is a homogeneous polynomially parameter dependent on fuzzy membership functions, is developed to conceive less conservative stability conditions for the TS Roesser-type 2D system. In the process of stability analysis, the obtained stability conditions approach exactness in the sense of convergence by applying some novel relaxed techniques. Moreover, the obtained result is formulated in the form of linear matrix inequalities, which can be easily solved via standard numerical software. Finally, a numerical example is also given to demonstrate the effectiveness of the proposed approach. (general)

  13. Low-frequency Raman spectra of sub- and supercritical CO2: qualitative analysis of the diffusion coefficient behavior.

    Science.gov (United States)

    Idrissi, A; Longelin, S; Damay, P; Leclercq, F

    2005-09-01

    We report the results of the low-frequency Raman experiments on CO(2) which were carried out in a wide density range, along the liquid-gas coexistence curve in a temperature range of 293-303 K, and on the critical isochore of 94.4 cm(3) mol(-1) in a temperature range of 304-315 K. In our approach, the qualitative behavior of the diffusion coefficient D is predicted, assuming the following: first, that the low-frequency Raman spectra can be interpreted in terms of the translation rotation motions; second, that the random force could be replaced by the total force to calculate the friction coefficient; and finally, that the Einstein frequency is associated with the position of the maximum of the low-frequency Raman spectrum. The results show that the diffusion coefficient increases along the coexistence curve, and its values are almost constant on the critical isochore. The predicted values reproduce qualitatively those obtained by other techniques. The values of D were also calculated by molecular-dynamics simulation and they qualitatively reproduce the behavior of D.

  14. Optimizing an integrated waveguide modulator for sensitive low-frequency alternating-current electric-field sensors

    Science.gov (United States)

    Al-Tarawni, Musab A. M.; Bakar, A. Ashrif A.; Zain, Ahmad Rifqi Md; Tarawneh, Mou'ad A.; Ahmad, Sahrim Hj.

    2017-06-01

    The use of integrated waveguide modulators is a common technique in electric-field sensing. However, the distortion in the modulated signal caused by high half-voltage Vπ and the difficulty in obtaining low-frequency responses are challenging issues for the use of low-frequency alternating-current (AC) electric-field sensors. This study investigates the use of an optimized segmented slot waveguide as the core of a sensor to determine the sensor features that produce useful frequency responses and sensitivity. The segmented slot waveguide is optimized in terms of periodicity and segment width to produce low Vπ and electrical bandwidth before testing the sensor sensitivity. The results show that reducing the segment width achieves a low Vπ of 0.32 V and a very low electrical bandwidth of 4.3 kHz. Our study provides evidence of the feasibility of using a segmented slot waveguide as the primary element for highly sensitive, low-frequency AC electric-field sensors.

  15. Study on The Extended Range Weather Forecast of Low Frequency Signal Based on Period Analysis Method

    Science.gov (United States)

    Li, X.

    2016-12-01

    Although many studies have explored the MJO and its application for weather forecasting, low-frequency oscillation has been insufficiently studied for the extend range weather forecasting over middle and high latitudes. In China, low-frequency synoptic map is a useful tool for meteorological operation department to forecast extend range weather. It is therefore necessary to develop objective methods to serve the need for finding low-frequency signal, interpretation and application of this signal in the extend range weather forecasting. In this paper, method of Butterworth band pass filter was applied to get low-frequency height field at 500hPa from 1980 to 2014 by using NCEP/NCAR daily grid data. Then period analysis and optimal subset regression methods were used to process the low frequency data of 150 days before the first forecast day and extend the low frequency signal of 500hPa low-frequency high field to future 30 days in the global from June to August during 2011-2014. Finally, the results were test. The main results are as follows: (1) In general, the fitting effect of low frequency signals of 500hPa low-frequency height field by period analysis in the northern hemisphere was better than that in the southern hemisphere, and was better in the low latitudes than that in the high latitudes. The fitting accuracy gradually reduced with the increase of forecast time length, which tended to be stable during the late forecasting period. (2) The fitting effects over the 6 key regions in China showed that except filtering result over Xinjiang area in the first 10 days and 30 days, filtering results over the other 5 key regions throughout the whole period have passed reliability test with level more than 95%. (3) The center and scope of low and high low frequency systems can be fitted well by using the methods mentioned above, which is consist with the corresponding use of the low-frequency synoptic map for the prediction of the extended period. Application of the

  16. Air-Coupled Low Frequency Ultrasonic Transducers and Arrays with PMN-32%PT Piezoelectric Crystals

    Directory of Open Access Journals (Sweden)

    Rymantas J. Kazys

    2017-01-01

    Full Text Available Air-coupled ultrasonic techniques are being increasingly used for material characterization, non-destructive evaluation of composite materials using guided waves as well as for distance measurements. Application of those techniques is mainly limited by the big losses of ultrasonic signals due to attenuation and mismatch of the acoustic impedances of ultrasonic transducers and air. One of the ways to solve this problem is by application of novel more efficient piezoelectric materials like lead magnesium niobate-lead titanate (PMN-PT type crystals. The objective of this research was the development and investigation of low frequency (<50 kHz wide band air-coupled ultrasonic transducers and arrays with an improved performance using PMN-32%PT crystals. Results of finite element modelling and experimental investigations of the developed transducers and arrays are presented. For improvement of the performance strip-like matching elements made of low acoustic impedance, materials such as polystyrene foams were applied. It allowed to achieve transduction losses for one single element transducer −11.4 dB, what is better than of commercially available air-coupled ultrasonic transducers. Theoretical and experimental investigations of the acoustic fields radiated by the eight element ultrasonic array demonstrated not only a good performance of the array in a pulse mode, but also very good possibilities to electronically focus and steer the ultrasonic beam in space.

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

    Directory of Open Access Journals (Sweden)

    M. Badawy

    2016-07-01

    Methods: Forty female patients with age ranges from 40 to 50 years were selected from Palestine Hospital, they were chronic atherosclerotic patients and were assigned into 2 groups according to their BMI based on the classification of the world health organization, each patient in the two groups (Group A and Group B was evaluated before and after 24 sessions treatment program by using the combination of ultrasound and lymphatic drainage machine, the assessment of blood serum triglycerides by UDICHEM-310 ANALYSER have been done before and after the end of 24 sessions and Re-assessment after 2 months from the last treatment session. The collected raw data of the current patients were statistically analyzed to evaluate the results of the two groups to investigate the effect of using the combination of ultrasound and lymphatic drainage machine on blood serum triglycerides, the data obtained in the current stud revealed statistical significance changes in blood serum triglycerides, and revealed that, there was a significant improvement (reduction in the total blood serum triglycerides for the Group A (Class I and, Group B (Class II groups at the three stages of the measurements (Pre, Post, and Post II, and revealed that there was a strong significant correlation between, the reduction of fat mass post-treatment and the reduction of the total body triglycerides (Post II treatment (two months after the last session. Low frequency ultrasound technique plus lymphatic drainage technique improve blood serum triglycerides of chronic cardiac patients.

  18. Amplatzer Vascular Plug Anchoring Technique to Stabilize the Delivery System for Microcoil Embolization

    International Nuclear Information System (INIS)

    Onozawa, Shiro; Murata, Satoru; Mine, Takahiko; Sugihara, Fumie; Yasui, Daisuke; Kumita, Shin-ichiro

    2016-01-01

    PurposeTo evaluate the feasibility of a novel embolization technique, the Amplatzer vascular plug (AVP) anchoring technique, to stabilize the delivery system for microcoil embolization.Materials and methodsThree patients were enrolled in this study, including two cases of internal iliac artery aneurysms and one case of internal iliac arterial occlusion prior to endovascular aortic repair. An AVP was used in each case for embolization of one target artery, and the AVP was left in place. The AVP detachment wire was then used as an anchor to stabilize the delivery system for microcoil embolization to embolize the second target artery adjacent to the first target artery. The microcatheter for the microcoils was inserted parallel to the AVP detachment wire in the guiding sheath or catheter used for the AVP.ResultsThe AVP anchoring technique was achieved and the microcatheter was easily advanced to the second target artery in all three cases.ConclusionThe AVP anchoring technique was found to be feasible to advance the microcatheter into the neighboring artery of an AVP-embolized artery.

  19. Amplatzer Vascular Plug Anchoring Technique to Stabilize the Delivery System for Microcoil Embolization

    Energy Technology Data Exchange (ETDEWEB)

    Onozawa, Shiro, E-mail: onozawa@nms.ac.jp; Murata, Satoru, E-mail: genji@nms.ac.jp [Nippon Medical School, Department of Radiology/Center for Advanced Medical Technology (Japan); Mine, Takahiko, E-mail: takahikomine@gmail.com [Tokai University School of Medicine, Department of Radiology, Tokai University Hachioji Hospital (Japan); Sugihara, Fumie, E-mail: giorcubgogo@yahoo.co.jp; Yasui, Daisuke, E-mail: ledhotcp@nms.ac.jp; Kumita, Shin-ichiro, E-mail: s-kumita@nms.ac.jp [Nippon Medical School, Department of Radiology/Center for Advanced Medical Technology (Japan)

    2016-05-15

    PurposeTo evaluate the feasibility of a novel embolization technique, the Amplatzer vascular plug (AVP) anchoring technique, to stabilize the delivery system for microcoil embolization.Materials and methodsThree patients were enrolled in this study, including two cases of internal iliac artery aneurysms and one case of internal iliac arterial occlusion prior to endovascular aortic repair. An AVP was used in each case for embolization of one target artery, and the AVP was left in place. The AVP detachment wire was then used as an anchor to stabilize the delivery system for microcoil embolization to embolize the second target artery adjacent to the first target artery. The microcatheter for the microcoils was inserted parallel to the AVP detachment wire in the guiding sheath or catheter used for the AVP.ResultsThe AVP anchoring technique was achieved and the microcatheter was easily advanced to the second target artery in all three cases.ConclusionThe AVP anchoring technique was found to be feasible to advance the microcatheter into the neighboring artery of an AVP-embolized artery.

  20. The Effect of High Pressure Techniques on the Stability of Anthocyanins in Fruit and Vegetables

    Directory of Open Access Journals (Sweden)

    Krystian Marszałek

    2017-01-01

    Full Text Available Anthocyanins are a group of phenolic compounds responsible for red, blue and violet colouration of many fruits, vegetables and flowers. The high content of these pigments is important as it influences directly their health promoting properties as well as the sensory quality of the product; however they are prone to degradation by, inter alia, elevated temperature and tissue enzymes. The traditional thermal methods of food preservation cause significant losses of these pigments. Thus, novel non-thermal techniques such as high pressure processing, high pressure carbon dioxide and high pressure homogenization are under consideration. In this review, the authors attempted to summarize the current knowledge of the impact of high pressure techniques on the stability of anthocyanins during processing and storage of fruit and vegetable products. Furthermore, the effect of the activity of enzymes involved in the degradation of these compounds has been described. The conclusions including comparisons of pressure-based methods with high temperature preservation techniques were presented.

  1. Low-frequency RF Coupling To Unconventional (Fat Unbalanced) Dipoles

    Energy Technology Data Exchange (ETDEWEB)

    Ong, M M; Brown, C G; Perkins, M P; Speer, R D; Javedani, J B

    2010-12-07

    The report explains radio frequency (RF) coupling to unconventional dipole antennas. Normal dipoles have thin equal length arms that operate at maximum efficiency around resonance frequencies. In some applications like high-explosive (HE) safety analysis, structures similar to dipoles with ''fat'' unequal length arms must be evaluated for indirect-lightning effects. An example is shown where a metal drum-shaped container with HE forms one arm and the detonator cable acts as the other. Even if the HE is in a facility converted into a ''Faraday cage'', a lightning strike to the facility could still produce electric fields inside. The detonator cable concentrates the electric field and carries the energy into the detonator, potentially creating a hazard. This electromagnetic (EM) field coupling of lightning energy is the indirect effect of a lightning strike. In practice, ''Faraday cages'' are formed by the rebar of the concrete facilities. The individual rebar rods in the roof, walls and floor are normally electrically connected because of the construction technique of using metal wire to tie the pieces together. There are two additional requirements for a good cage. (1) The roof-wall joint and the wall-floor joint must be electrically attached. (2) All metallic penetrations into the facility must also be electrically connected to the rebar. In this report, it is assumed that these conditions have been met, and there is no arcing in the facility structure. Many types of detonators have metal ''cups'' that contain the explosives and thin electrical initiating wires, called bridge wires mounted between two pins. The pins are connected to the detonator cable. The area of concern is between the pins supporting the bridge wire and the metal cup forming the outside of the detonator. Detonator cables usually have two wires, and in this example, both wires generated the same voltage at the

  2. Control of Full-Scale Converter based Wind Power Plants for damping of low frequency system oscillations

    DEFF Research Database (Denmark)

    Adamczyk, Andrzej Grzegorz; Teodorescu, Remus; Rodriguez, Pedro

    2011-01-01

    Damping of low frequency power oscillations is one of essential aspects of maintaining power system stability. In literature can be found publications on damping capability of Doubly Fed Induction Generator based wind turbines. This paper extends discussion on Wind Power Plant damping capability...... and design is based on modal analysis, therefore matching modeling approach for wind power plant is proposed. Finally, performance of Wind Power Plant damping control is compared to a regular power system stabilizer installed on a synchronous generator....... to Full-Scale Converter based type. Moreover resemblance of such Wind Power Plant to modern FACTS devices is recognized and exploited. Paper discusses many aspect of damping controller design, including feedback signal selection and control effectiveness with respect to wind farm location. Analysis...

  3. Development of Technique for Testing the Long-Term Stability of Silicon Microstrip Detectors

    International Nuclear Information System (INIS)

    Kosinov, A.V.; Maslov, N.I.; Naumov, S.V.; Ovchinnik, V.D.; Starodubtsev, A.F.; Vasiliev, G.P.; Yalovenko, V.I.; Bosisio, L.

    2006-01-01

    An automatic multi-channel set-up prototype for simultaneous testing of the Long-Term Stability (LTS) of more than ten detectors is described. The Inner Tracking System of the ALICE experiment will include about two thousand Double-sided Microstrip Detectors (DSMD). Efficient automatic measurement techniques are crucial for the LTS test, because the corresponding test procedure should be performed on each detector and requires long time, at least two days. By using special adapters for supporting and connecting the bare DSMDs, failing detectors can be screened out before module assembly, thus minimizing the cost. Automated probe stations developed for a special purpose or for microelectronics industry are used for measuring physical static DSMD characteristics and check good-to-bad elements ratio for DSMD. However, automated (or semi-automatic)test benches for studying LTS or testing DSMD long-term stability before developing a detecting module are absent

  4. Porous resins as a cavitation enhancer for low-frequency sonophoresis.

    Science.gov (United States)

    Terahara, Takaaki; Mitragotri, Samir; Langer, Robert

    2002-03-01

    The application of low-frequency ultrasound enhances drug transport through the skin, a phenomenon referred to as low-frequency sonophoresis. This enhancement is mediated through cavitation, the formation and collapse of gaseous bubbles. We hypothesized that the efficacy of low-frequency sonophoresis can be significantly enhanced by provision of nuclei for cavitation. In this study, we used two porous resins, Diaion HP20 and Diaion HP2MG (2MG), as cavitation nuclei. We measured the effect of these resins on cavitation using pitting of aluminum foil. 2MG showed a higher efficacy in enhancing cavitation compared with Diaion HP20. 2MG was also effective in enhancing transdermal mannitol transport. These results confirm that the addition of cavitation nuclei such as porous resins further increases the effect of low-frequency ultrasound on skin permeability. Copyright 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association.

  5. Biological effects of exposure to low frequency electric and magnetic fields

    International Nuclear Information System (INIS)

    Ahnstroem, G.

    1992-10-01

    The biological effects of exposure to low frequency electric and magnetic fields are reviewed with the objective of summarizing effects directly relevant to considerations of the health and safety of exposed people

  6. Analysis of Power System Low Frequency Oscillation Based on Energy Shift Theory

    Science.gov (United States)

    Zhang, Junfeng; Zhang, Chunwang; Ma, Daqing

    2018-01-01

    In this paper, a new method for analyzing low-frequency oscillation between analytic areas based on energy coefficient is proposed. The concept of energy coefficient is proposed by constructing the energy function, and the low-frequency oscillation is analyzed according to the energy coefficient under the current operating conditions; meanwhile, the concept of model energy is proposed to analyze the energy exchange behavior between two generators. Not only does this method provide an explanation of low-frequency oscillation from the energy point of view, but also it helps further reveal the dynamic behavior of complex power systems. The case analysis of four-machine two-area and the power system of Jilin Power Grid proves the correctness and effectiveness of the proposed method in low-frequency oscillation analysis of power system.

  7. Low Frequency Activity of Cortical Networks on Microelectrode Arrays is Differentially Altered by Bicuculline and Carbaryl

    Science.gov (United States)

    Thousands of chemicals need to be characterized for their neurotoxicity potential. Neurons grown on microelectrode arrays (MEAs) are an in vitro model used to screen chemicals for functional effects on neuronal networks. Typically, after removal of low frequency components, effec...

  8. 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...

  9. Low-Frequency, All Digital Radar (ADR) for Biomass and Ice-sheet Investigations, Phase I

    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...

  10. 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.

  11. Voltage Stabilization of a Wind Turbine with STATCOM Using Intelligent Control Techniques

    Directory of Open Access Journals (Sweden)

    S. A. Gawish

    2016-03-01

    Full Text Available Application of FACTS controller called Static Synchronous Compensator STATCOM to improve the performance of power grid with Wind System is investigated. The essential feature of the STATCOM is that it has the ability to absorb or inject fastly reactive power with power grid. Therefore the voltage regulation of the power grid with STATCOM FACTS device is achieved. Moreover restoring the stability of the wind system at suddenly step up or down in wind speed is obtained with STATCOM. This paper describes a complete simulation of voltage regulation of a wind system using STATCOM. Conventional control technique as proportional plus integral controller , and intelligent techniques as FLC and ANFIS are used in this work. The control technique is performed using MATLAB package software. The dynamic response of uncontrolled system is also investigated under wide range of disturbances. The voltage regulation by using STATCOM whose output is varied so as to maintain or control output voltage in the system. The dynamic response of controlled system is shown and comparison between the uncontrolled system and the controlled system is described to assure the validity of the proposed controller. Also comparison between the proposed control methods scheme is presented. To validate the powerful of the STATCOM FACTS controllers, the studied power system is simulated and subjected to different severe disturbances. The results prove the effectiveness of the proposed STATCOM controller in terms of fast damping the power system oscillations and restoring the power system stability and voltage.

  12. Postoperative stabilization of the posttraumatic thoracic and lumbar spine: a review of concepts and orthotic techniques.

    Science.gov (United States)

    Benzel, E C; Larson, S J

    1989-03-01

    A review of 109 case histories of patients who had undergone a spine fusion and/or posterior instrumentation procedure for thoracic and/or lumbar spine trauma was performed with respect to efficacy of several postoperative external splinting techniques. These data formed the basis for a review of external spinal splinting techniques. The type of orthosis that appears to offer the most efficacious immobilization and maximum patient comfort for fractures in the upper thoracic region in a body shell jacket extending from the submental and suboccipital regions to the lumbar region (modified Minerva jacket). To gain a lower point of fixation in patients with mid-to-low lumbar fractures, it was found that an extended body shell or an extension of a body jacket to one leg (hip spica) was necessary. Thoracic and thoracolumbar injuries may be stabilized with either a Jewett brace or a body jacket. The lack of maintenance of the cylindrical body shell, as well as excessive discomfort, make the Jewett brace and similar orthotic devices a second choice to body shell jackets for fractures in this region. The application of plastic polymer (Thermoplast) to spine splinting techniques offers the patient increased comfort and stability, as well as facilitating easy application and a more snug fit.

  13. Application of low-frequency sonophoresis and reduction of antibiotics in the aquatic systems.

    Science.gov (United States)

    Cobo Labarca, C; Radinger, J; Schöning, V; Ariav, R; Jung, R; Thompson, K D; Kloas, W; Knopf, K

    2017-11-01

    A major concern in aquaculture is the use of chemical therapeutics, such as antibiotics, because of their impact on the environment as well as on the fish product. As a potential tool for reducing antibiotic use, we tested the application of low-frequency ultrasound as a method for enhancing antibiotic uptake. Rainbow trout juveniles (Oncorhynchus mykiss) were exposed to two different concentrations of oxytetracycline (OTC), flumequine (FLU) and florfenicol (FLO), administered by bath after the application of ultrasound. After exposure, concentrations of these substances were measured in the liver and blood of treated fish. Results showed that the ultrasound treatment can significantly increase the uptake for all three antibiotics. The uptake of OTC for example, in fish exposed to an OTC concentration of 20 mg L -1 after prior treatment with ultrasound, was similar to the OTC concentrations in their liver and blood to fish exposed to 100 mg L -1 without sonication. For FLU and FLO, the use of ultrasound caused significant differences of uptake in the liver at high antibiotic concentrations. This suggests that the use of ultrasound as a technique to deliver antibiotics to fish can ultimately reduce the amount of antibiotics discharged into the aquatic environment. © 2017 John Wiley & Sons Ltd.

  14. Extremely low-frequency magnetic fields of transformers and possible biological and health effects.

    Science.gov (United States)

    Sirav, Bahriye; Sezgin, Gaye; Seyhan, Nesrin

    2014-12-01

    Physiological processes in organisms can be influenced by extremely low-frequency (ELF) electromagnetic energy. Biological effect studies have great importance; as well as measurement studies since they provide information on the real exposure situations. In this study, the leakage magnetic fields around a transformer were measured in an apartment building in Küçükçekmece, Istanbul, and the measurement results were evaluated with respect to the international exposure standards. The transformer station was on the bottom floor of a three-floor building. It was found that people living and working in the building were exposed to ELF magnetic fields higher than the threshold magnetic field value of the International Agency for Research on Cancer (IARC). Many people living in this building reported health complaints such as immunological problems of their children. There were child-workers working in the textile factories located in the building. Safe distances or areas for these people should be recommended. Protective measures could be implemented to minimize these exposures. Further residential exposure studies are needed to demonstrate the exposure levels of ELF magnetic fields. Precautions should, therefore, be taken either to reduce leakage or minimize the exposed fields. Shielding techniques should be used to minimize the leakage magnetic fields in such cases.

  15. Zygosaccharomyces bailii inactivation by means of UV light and low-frequency ultrasound treatments.

    Science.gov (United States)

    Gómez-Díaz, J J; Santiesteban-López, A; Palou, E; López-Malo, A

    2011-10-01

    Zygosaccharomyces bailii inactivation suspended in apple juice was evaluated under the effects of selected treatments: short-wave UV light (UVC, using one or two lamps), or low-frequency ultrasound (US), or their simultaneous combination. US treatments (20 kHz, 120-μm wave amplitude) were performed at 35°C in a double-wall vessel by using a 13-mm probe. The UVC device consists of two 90-cm-long stainless steel tubes with 40-W UVC lamps covered with quartz tubes, each one inside a stainless steel tube (annular inside diameter of 2.6 cm) connected to a peristaltic pump. Inoculated systems were recirculated through individual or simultaneous US and UVC treatments, samples were taken periodically, and yeast survivors were determined by the plate-count technique. Yeast survival curves demonstrated that UVC alone or in combination with US produced higher inactivation than US alone. Survival curves were appropriately described by the Weibull distribution of resistances model, obtaining model parameter values that adequately reflected the effect of the studied treatments. For every tested case, the distribution of resistances model revealed an absence of mode, while mean values and variances decreased when simultaneous UVC irradiation with two lamps and US were applied, reaching a 7-log cycle reduction after 40 min of treatment. Combined treatment was more effective than individual US or UVC treatments.

  16. In situ monitoring of cocrystals in formulation development using low-frequency Raman spectroscopy.

    Science.gov (United States)

    Otaki, Takashi; Tanabe, Yuta; Kojima, Takashi; Miura, Masaru; Ikeda, Yukihiro; Koide, Tatsuo; Fukami, Toshiro

    2018-03-07

    In recent years, to guarantee a quality-by-design approach to the development of pharmaceutical products, it is important to identify properties of raw materials and excipients in order to determine critical process parameters and critical quality attributes. Feedback obtained from real-time analyses using various process analytical technology (PAT) tools has been actively investigated. In this study, in situ monitoring using low-frequency (LF) Raman spectroscopy (10-200 cm -1 ), which may have higher discriminative ability among polymorphs than near-infrared spectroscopy and conventional Raman spectroscopy (200-1800 cm -1 ), was investigated as a possible application to PAT. This is because LF-Raman spectroscopy obtains information about intermolecular and/or lattice vibrations in the solid state. The monitoring results obtained from Furosemide/Nicotinamide cocrystal indicate that LF-Raman spectroscopy is applicable to in situ monitoring of suspension and fluidized bed granulation processes, and is an effective technique as a PAT tool to detect the conversion risk of cocrystals. LF-Raman spectroscopy is also used as a PAT tool to monitor reactions, crystallizations, and manufacturing processes of drug substances and products. In addition, a sequence of conversion behaviors of Furosemide/Nicotinamide cocrystals was determined by performing in situ monitoring for the first time. Copyright © 2018 Elsevier B.V. All rights reserved.

  17. Low-Frequency Internal Friction Study on the Structural Changes in Polymer Melts

    International Nuclear Information System (INIS)

    Xue-Bang, Wu; Qiao-Ling, Xu; Shu-Ying, Shang; Jia-Peng, Shui; Chang-Song, Liu; Zhen-Gang, Zhu

    2008-01-01

    With the help of the low-frequency internal friction method, we investigate the structural properties of polymer melts, such as amorphous polystyrene (PS), poly(methyl methacrylate) (PMMA), and semi-crystalline poly(ethylene oxide) (PEO). An obvious peak of relaxation type is found in each of the internal friction curves. The peak temperature T p follows the relation T p ≈ (1.15 – 1.18) T g for PS and PMMA melts, while it follows T p ≈ 1.22T m for PEO melt, with T g being the glass transition temperature and T m the melting temperature. Based on the analysis of the features of this peak, it is found that this peak is related to the liquid-liquid transition temperature T u of polymer melts. Mechanism of the liquid-liquid transition is suggested to be thermally-activated collective relaxation through cooperation. This finding may be helpful to understand the structural changes in polymer melts. In addition, the internal friction technique proves to be effective in studying dynamics in polymer melts

  18. Acoustic characterization of a nonlinear vibroacoustic absorber at low frequencies and high sound levels

    Science.gov (United States)

    Chauvin, A.; Monteil, M.; Bellizzi, S.; Côte, R.; Herzog, Ph.; Pachebat, M.

    2018-03-01

    A nonlinear vibroacoustic absorber (Nonlinear Energy Sink: NES), involving a clamped thin membrane made in Latex, is assessed in the acoustic domain. This NES is here considered as an one-port acoustic system, analyzed at low frequencies and for increasing excitation levels. This dynamic and frequency range requires a suitable experimental technique, which is presented first. It involves a specific impedance tube able to deal with samples of sufficient size, and reaching high sound levels with a guaranteed linear response thank's to a specific acoustic source. The identification method presented here requires a single pressure measurement, and is calibrated from a set of known acoustic loads. The NES reflection coefficient is then estimated at increasing source levels, showing its strong level dependency. This is presented as a mean to understand energy dissipation. The results of the experimental tests are first compared to a nonlinear viscoelastic model of the membrane absorber. In a second step, a family of one degree of freedom models, treated as equivalent Helmholtz resonators is identified from the measurements, allowing a parametric description of the NES behavior over a wide range of levels.

  19. Measurement of misalignment in a journal bearing with low frequency ultrasound

    International Nuclear Information System (INIS)

    Kim, Noh Nu

    1998-01-01

    Misalignment of a shaft in journal bearing of rotary compressor was measured and analyzed for the study on the effect of misalignment on the performance of the rotary compressor using a new ultrasonic pulse-echo technique. Two low-frequency ultrasonic transducers(10Mhz) were mounted on the outer surface of the bearing in X and Y axis to receive the reflection signals from each axis and to obtain the amplitude of a modified reflection wave defined as the total reflection wave minus the first reflection wave from a thin layer which is inversely proportional to the thickness of the layer in the region where h/λ is approximately less than 1/4. The relationship of the amplitude of the modified reflection wave to the thickness of the oil layer was shown both in mathematical form and in graph. Gap clearances between the bearing and the shaft in the horizontal and vertical axis were determined directly by the relationship and used to evaluate the misalignment of the journal bearing. Several intentional misalignments in a test compressor were made to measure and show the misalignment and the effect of the misalignment on the efficiency of the rotary compressor. A fast quantitative evaluation of the misalignment of journal bearing was possible using the amplitude of the modified reflection signal without any inversion process to extract thickness information from waveforms of the reflected waves.

  20. Tumor therapy by fast moving magnetic nanoparticle under low-frequency alternating magnetic field

    Directory of Open Access Journals (Sweden)

    Yangyang Liu

    2015-03-01

    Full Text Available Magnetic nanoparticle plays an important role in biomedical engineering, especially in tumor therapy. In this paper, a new technique has been developed by using the rapid moving magnetic nanoparticle under a low-frequency alternating magnetic field (LFAMF to kill tumor cells. The LFAMF system which was used to drive magnetic nanoparticles (MNPs was setup with the magnetic field frequency and power range at ∼ 10–100 Hz and ∼ 10–200 mT, respectively. During the experiment, the LFAMF was adjusted at different frequencies and power levels. The experimental results show that the liver tumor cells (HepG2 mixed with MNPs (10 μg/mL became partial fragments when exposed in the LFAMF with different frequencies (∼ 10–100 Hz and power (∼ 10–200 mT, and the higher the frequency or the power, the more the tumor cells were killed at the same magnetic nanoparticle concentration. Conclusion: Tumor cells were effectively damaged by MNPs under LFAMF, which suggests that they had great potential to be applied in tumor therapy.

  1. The ultra low frequency electromagnetic radiation observed in the topside ionosphere above boundaries of tectonic plates

    Directory of Open Access Journals (Sweden)

    Michael A. Athanasiou

    2015-01-01

    Full Text Available In this paper we present results of a comparison between ultra low frequency (ULF electromagnetic (EM radiation, recorded by an electric field instrument onboard the satellite detection of electromagnetic emissions transmitted from earthquake regions in the topside ionosphere, and the seismicity of regions with high and low seismic activity. In particular, we evaluated the energy variations of the ULF Ezelectric field component during a period of four years (2006-2009, in order to examine the possible relation of ULF EM radiation with seismogenic regions located in Central America, Indonesia, the Eastern Mediterranean Basin and Greece. As a tool for evaluating the ULF Ez energy variations we used singular spectrum analysis techniques. The results of our analysis clearly show a significant increase of the ULF EM energy emitted from regions of highest seismic activity at the boundaries tectonic plates. Furthermore, we found that higher electromagnetic radiation was detected in a region above the northern- western Greek Arc (R1 than above the adjacent region including Athens and its urban area. We interpret these results of the present study as suggesting that: i the seismogenic regions at the boundary of tectonic plates radiate ULF EM emissions observed by satellites in the topside ionosphere; and ii that this EM radiation is not only related with the occurrence time of great (M≥5 earthquakes, but it is often present in intermediate times and it appears as a quasi-permanent phenomenon.

  2. Low-frequency magnetohydrodynamics and geodesic acoustic modes in toroidally rotating tokamak plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Wahlberg, C, E-mail: Christer.Wahlberg@fysast.uu.s [Department of Physics and Astronomy, EURATOM/VR Fusion Association, PO Box 516, Uppsala University, SE-751 20 Uppsala (Sweden)

    2009-08-15

    This paper analyses low-frequency magnetohydrodynamic (MHD) modes, especially the geodesic acoustic modes (GAMs), in toroidal plasmas with large aspect ratio and circular cross section, including the effects of toroidal plasma rotation. A system of equations describing MHD modes with frequency of the order of the sound frequency in such plasmas is derived from the Frieman-Rotenberg equation, using a technique where the plasma perturbation xi and the perturbed magnetic field Q are expanded separately in the inverse aspect ratio epsilon = r/R, where r and R denote the minor and major radii of the plasma torus, respectively. The large-scale, ideal MHD properties of the GAM induced by toroidal rotation (Wahlberg 2008 Phys. Rev. Lett. 101 115003) are thereafter analysed in more detail employing this system of equations. It is shown that both the axisymmetric GAMs existing in rotating plasmas are localized on a specific magnetic surface only to leading order in epsilon, and that a 'halo' consisting of finite components of both xi and Q with dominant poloidal mode numbers m = +-2 appears outside this magnetic surface to higher orders in epsilon.

  3. Development of Lightweight, Compact, Structurally-Integrated Acoustic Liners for Broadband Low-Frequency Noise Mitigation

    Science.gov (United States)

    Chambers, Andrew T.

    Airborne noise with a low dominant frequency content (software tool is developed to determine optimal 3D cavity packing for a prescribed liner volume and target frequency range. ZKTL-based parametric studies on core dimensions and face sheet porosity are utilized for detailed design of test articles. Experimental verification of absorption coefficient spectra conducted using 3D printed test articles in a normal incidence acoustic impedance tube yield good correlation with simulations. More than 100 Hz of continuous bandwidth with an absorption coefficient greater than 0.6 is shown to be possible in the 300 to 400 Hz range with a 38.1-mm (1.5-inch) thick liner. Further, the influence of face sheet type, Mach number, and sound pressure level on the attenuation across folded core liners is evaluated using grazing flow impedance tube tests. Up to 20 dB of attenuation is observed in the targeted frequency range in these tests indicating potential for performance retention in an operational scenario. With current additive and hybrid manufacturing techniques attaining critical commercial maturity, lightweight and compact acoustic liners employing folded cores could provide a promising practical solution to mitigate low-frequency airborne noise, especially in aerospace applications.

  4. Analytical and numerical calculations of resistive wall impedances for thin beam pipe structures at low frequencies

    Energy Technology Data Exchange (ETDEWEB)

    Niedermayer, U., E-mail: u.niedermayer@gsi.de [Technische Universitaet Darmstadt, Institut fuer Theorie Elektromagnetischer Felder, Schlossgartenstrasse 8, 64289 Darmstadt (Germany); Boine-Frankenheim, O. [Technische Universitaet Darmstadt, Institut fuer Theorie Elektromagnetischer Felder, Schlossgartenstrasse 8, 64289 Darmstadt (Germany)

    2012-09-21

    The resistive wall impedance is one of the main sources for beam instabilities in synchrotrons and storage rings. The fast ramped SIS18 synchrotron at GSI and the projected SIS100 synchrotron for FAIR both employ thin (0.3 mm) stainless steel beam pipes in order to reduce eddy current effects. The lowest betatron sidebands are at about 100 kHz, which demands accurate impedance predictions in the low frequency (LF) range where the beam pipe and possibly also the structures behind the pipe are the dominating impedance sources. The longitudinal and transverse resistive wall impedances of a circular multi-layer pipe are calculated analytically using the field matching technique. We compare the impedances obtained from a radial wave model, which corresponds to the setup used in bench measurements, with the axial wave model, which corresponds to an actual beam moving with relativistic velocity. For thin beam pipes the induced wall current and the corresponding shielding properties of the pipe are important. In both models the wall current is obtained analytically. The characteristic frequencies for the onset of the wall current are calculated from equivalent lumped element circuits corresponding to the radial model. For more complex structures, like the SIS100 beam pipe, we use a numerical method, in which the impedance is obtained from the total power loss. The method is validated by the analytic expressions for circular beam pipes.

  5. Towards assessing cortical bone porosity using low-frequency quantitative acoustics: A phantom-based study.

    Directory of Open Access Journals (Sweden)

    Florian Vogl

    Full Text Available Cortical porosity is a key characteristic governing the structural properties and mechanical behaviour of bone, and its quantification is therefore critical for understanding and monitoring the development of various bone pathologies such as osteoporosis. Axial transmission quantitative acoustics has shown to be a promising technique for assessing bone health in a fast, non-invasive, and radiation-free manner. One major hurdle in bringing this approach to clinical application is the entanglement of the effects of individual characteristics (e.g. geometry, porosity, anisotropy etc. on the measured wave propagation. In order to address this entanglement problem, we therefore propose a systematic bottom-up approach, in which only one bone property is varied, before addressing interaction effects. This work therefore investigated the sensitivity of low-frequency quantitative acoustics to changes in porosity as well as individual pore characteristics using specifically designed cortical bone phantoms.14 bone phantoms were designed with varying pore size, axial-, and radial pore number, resulting in porosities (bone volume fraction between 0% and 15%, similar to porosity values found in human cortical bone. All phantoms were manufactured using laser sintering, measured using axial-transmission acoustics and analysed using a full-wave approach. Experimental results were compared to theoretical predictions based on a modified Timoshenko theory.A clear dependence of phase velocity on frequency and porosity produced by increasing pore size or radial pore number was demonstrated, with the velocity decreasing by between 2-5 m/s per percent of additional porosity, which corresponds to -0.5% to -1.0% of wave speed. While the change in phase velocity due to axial pore number was consistent with the results due to pore size and radial pore number, the relative uncertainties for the estimates were too high to draw any conclusions for this parameter.This work has

  6. 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...... traveling-wave model. The dynamics of the low-frequency fluctuations are explained qualitatively in terms of bistability through an iterative description...

  7. Ultra-low-frequency wave-driven diffusion of radiation belt relativistic electrons

    OpenAIRE

    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.

    2015-01-01

    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 ha...

  8. Effect of dynamic muscular stabilization technique on low back pain of different durations.

    Science.gov (United States)

    Kumar, Suraj; Sharma, Vijai P; Aggarwal, Anoop; Shukla, Rakesh; Dev, Ravi

    2012-01-01

    Low back pain (LBP) has multi-factorial origin and its treatment varies considerably. Multidisciplinary pain programs have shown their effectiveness in the management of LBP but it is not documented whether subjects with difference in chronicity (duration) of pain will respond differently to these regimes. Dynamic muscular stabilization technique (DMST) is an active approach of stabilizing training for lumbar area which involves the training for the co-contraction of the transverse abdominis and multifidus muscles. This study determines the efficacy of Dynamic Muscular Stabilization Technique (DMST) in LBP of different durations. Follow-up, comparative study. Physical medicine and rehabilitation department (PMR) of university. Total 72 patients were categorized in 5 groups on the basis of duration (chronicity) of their low back pain. The documentation of chronicity was done on the basis of subjective questionnaire. All subjects were treated with DMST. Pain was the primary outcome measure while physical strength (back pressure change: BPC, abdominal pressure changes: APC), physical ability (walking, stair climbing, stand ups) and quality of life (QOL) were the secondary. Variables were assessed at baseline (day 0), 3 months (day 90) and at the end of the follow up (day 180). Variables (Pain, BPC, APC, Walking, Stair climbing, Stand ups and QOL) significantly improved on 90th and 180th day while compared to the baseline. Therefore irrespective of the chronicity of pain, all chronic pain patients will respond positively to the DMST treatment. This study concludes that DMST intervention is an effective rehabilitation technique for all chronic low back pain patients irrespective of the duration (chronicity) of their pain.

  9. Effects on Performance and Work Quality due to Low Frequency Ventilation Noise

    Science.gov (United States)

    Persson Waye, K.; Rylander, R.; Benton, S.; Leventhall, H. G.

    1997-08-01

    A pilot study was carried out to assess method evaluating effects of low frequency noise on performance. Of special interest was to study objective and subjective effects over time. Two ventilation noises were used, one of a predominantly mid frequency character and the other of a predominantly low frequency character. Both had an NC value of 35. For the study, 50 students were recruited and 30 selected on the basis of subjective reports of pressure on the eardrum after exposure to a low frequency noise. Of these, 14 randomly selected subjects aged 21 and 34 took part. The subjects performed three computerized cognitive tests in the mid frequency or the low frequency noise condition alternatively. Tests I and II were performed together with a secondary task.Questionnaires were used to evaluate subjective symptoms, effects on mood and estimated interference with the test results due to temperature, light and noise. The results showed that the subjective estimations of noise interference with performance were higher for the low frequency noise (psocial orientation (pstudied. The results further indicate that the NC curves do not fully assess the negative effects of low frequency noise on work performance.

  10. Dispersive properties and attraction instability of low-frequency collective modes in dusty plasmas

    International Nuclear Information System (INIS)

    Tsytovich, V.N.; Rezendes, D.

    1998-01-01

    A dispersion relation for low-frequency collective modes in dusty plasmas is derived with allowance for attractive and repulsive forces arising between the dust grains due to dissipative fluxes of plasma particles onto the grain surfaces. It is shown that these fluxes give rise to dust attraction instabilities, which are similar to the gravitational instability. In the range of wave numbers corresponding to the stability domain, two types of dust sound waves arise, depending on whether the wavelengths of the collective modes are longer or shorter than the mean free path of the plasma particles (i.e., the distance they travel before they collide with dust grains). The dispersion relation derived is valid for any ratio between the wavelength of the perturbations and the mean free path and encompasses the entire range of intermediate wave numbers. The critical wave numbers that determine the threshold for the onset of attraction instability, which is similar to the Jeans instability, can, in particular, lie within this range. The thresholds for attraction instability and the instability growth rates are obtained numerically for a wide range of the plasma parameters (such as the ratio of the ion temperature to the electron temperature) that are of interest for present-day experiments with dust crystals, plasma etching, and space plasma studies. Computer simulation shows that, in the nonlinear stage, the attraction instability causes the dust cloud to collapse, which leads to the formation of dust plasma crystals. Our investigation makes it possible to trace the processes in the initial stage of dust crystallization. Results are obtained for hydrogen and silicon plasmas, which are most typical of laboratory experiments

  11. A very low noise, high accuracy, programmable voltage source for low frequency noise measurements

    Science.gov (United States)

    Scandurra, Graziella; Giusi, Gino; Ciofi, Carmine

    2014-04-01

    In this paper an approach for designing a programmable, very low noise, high accuracy voltage source for biasing devices under test in low frequency noise measurements is proposed. The core of the system is a supercapacitor based two pole low pass filter used for filtering out the noise produced by a standard DA converter down to 100 mHz with an attenuation in excess of 40 dB. The high leakage current of the supercapacitors, however, introduces large DC errors that need to be compensated in order to obtain high accuracy as well as very low output noise. To this end, a proper circuit topology has been developed that allows to considerably reduce the effect of the supercapacitor leakage current on the DC response of the system while maintaining a very low level of output noise. With a proper design an output noise as low as the equivalent input voltage noise of the OP27 operational amplifier, used as the output buffer of the system, can be obtained with DC accuracies better that 0.05% up to the maximum output of 8 V. The expected performances of the proposed voltage source have been confirmed both by means of SPICE simulations and by means of measurements on actual prototypes. Turn on and stabilization times for the system are of the order of a few hundred seconds. These times are fully compatible with noise measurements down to 100 mHz, since measurement times of the order of several tens of minutes are required in any case in order to reduce the statistical error in the measured spectra down to an acceptable level.

  12. Impression techniques for the resorbed mandibular arch: A guide to increased stability

    Directory of Open Access Journals (Sweden)

    Manish Jain

    2015-01-01

    Full Text Available All clinicians face the common problems in making complete denture prosthesis for patients exhibiting high degree of bone resorption. Though resorption can be prevented to an extent but sooner or later it comes back to haunt the clinician. The result is a dis-satisfied patient with a loose prosthesis ready for a new one. The real problem lies in the capturing the oral tissues and using them for creating retention and stability in the prosthesis. Though ultimate success also depends on many other factors such as the occlusal scheme used and patient adaptability yet the most important step still remains the impression technique employed. A few impression techniques are suggested for increasing the success rates in such patients.

  13. Effect of meniscus replacement fixation technique on restoration of knee contact mechanics and stability.

    Science.gov (United States)

    D'Lima, D D; Chen, P C; Kessler, O; Hoenecke, H R; Colwell, C W

    2011-06-01

    The menisci are important biomechanical components of the knee. We developed and validated a finite element model of meniscal replacement to assess the effect of surgical fixation technique on contact behavior and knee stability. The geometry of femoral and tibial articular cartilage and menisci was segmented from magnetic resonance images of a normal cadaver knee using MIMICS (Materialise, Leuven, Belgium). A finite element mesh was generated using HyperWorks (Altair Inc, Santa Ana, CA). A finite element solver (Abaqus v6.9, Simulia, Providence, RI) was used to compute contact area and stresses under axial loading and to assess stability (reaction force generated during anteroposterior translation of the femur). The natural and surgical attachments of the meniscal horns and peripheral rim were simulated using springs. After total meniscectomy, femoral contact area decreased by 26% with a concomitant increase in average contact stresses (36%) and peak contact stresses (33%). Replacing the meniscus without suturing the horns did little to restore femoral contact area. Suturing the horns increased contact area and reduced peak contact stresses. Increasing suture stiffness correlated with increased meniscal contact stresses as a greater proportion of tibiofemoral load was transferred to the meniscus. A small incremental benefit was seen of simulated bone plug fixation over the suture construct with the highest stiffness (50 N/mm). Suturing the rim did little to change contact conditions. The nominal anteroposterior stiffness reduced by 3.1 N/mm after meniscectomy. In contrast to contact area and stress, stiffness of the horn fixation sutures had a smaller effect on anteroposterior stability. On the other hand suturing the rim of the meniscus affected anteroposterior stability to a much larger degree. This model emphasizes the importance of the meniscus in knee biomechanics. Appropriate meniscal replacement fixation techniques are likely to be critical to the clinical

  14. Sparse blind deconvolution based low-frequency seismic data reconstruction for multiscale full waveform inversion

    Science.gov (United States)

    Zhang, Pan; Han, Liguo; Xu, Zhuo; Zhang, Fengjiao; Wei, Yajie

    2017-04-01

    Full waveform inversion (FWI) reconstructs the underground velocity structures by minimizing the data residual between calculated wavefields and observed wavefileds. The conventional FWI usually uses some local optimization algorithms which lead to a strong dependency on initial velocity model. The objective function corresponding to low-frequency data components has less local minima. Reconstructing low-frequency information from recorded seismic data and using it in FWI can reduce cycle-skipping and thus weaken the dependency of inversion process on initial model. In this paper, based on the conventional frequency down-shifting method, we propose a sparse blind deconvolution-convolution low-frequency data reconstruction method, which can simultaneously update the wavelet and reconstruct the low-frequency components. First, we extract the subsurface reflection impulse responses (SRIR) by solving a L1 norm sparse constraint problem using the Fast Iterative Shrinkage-Thresholding Algorithm (FISTA). Then we test the accuracy of our algorithm, and discuss the effect of wavelet error and noises on the reconstruction result. When the wavelet is inaccurate, we update the amplitude of wavelet by alternately inverting L1 norm constraint and Tikhonov regularization problems, and correct the time-shift error by cross-correlating the direct waves. After that we can get the accurate wavelet and SRIR simultaneously. Then using the reconstructed data successively as observed data, combining it with dynamic random sources and layer-stripping methods, we propose a new strategy for the fast multiscale FWI. We test our method by numerical examples in several cases including blended acquisition cases. The results show that it has good anti-noise property and it can reconstruct valid low-frequency components when the observed data lacking low-frequency information. The example using inaccurate wavelet shows that the blind deconvolution-convolution algorithm is able to obtain accurate

  15. 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)

  16. 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...

  17. Dependence of low-frequency sonophoresis on ultrasound parameters; distance of the horn and intensity.

    Science.gov (United States)

    Terahara, T; Mitragotri, S; Kost, J; Langer, R

    2002-03-20

    Sonophoresis at a frequency of 20 kHz has been shown to enhance transdermal drug delivery, a phenomenon referred to as low-frequency sonophoresis. This study provides an investigation of the dependence of low-frequency sonophoresis on various ultrasound parameters, including the distance of the horn from the skin, intensity, and frequency. We performed in vitro experiments with full thickness pig skin to measure enhancements of skin conductivity and drug permeability. Ultrasound was applied to pretreat the skin using a sonicator operating at a frequency of either 20 or 40 kHz. We also measured pitting of aluminum foil to measure cavitation, which is the principal mechanism of low-frequency sonophoresis. The skin conductivity enhancement was found to be inversely proportional to the distance of the horn from the skin. As the intensity increased, skin conductivity enhancement also increased up to a certain threshold, and then dropped off. The intensities (I(max)) at which maximum enhancement occur are about 14 W/cm2 for 20 kHz and 17 W/cm2 for 40 kHz. These findings may be useful in optimizing low-frequency sonophoresis. Overall, the dependence of transport on ultrasound parameters is similar to that of aluminum foil pitting. These results support the role of cavitation in low-frequency sonophoresis.

  18. 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.

  19. Phonons in models for icosahedral quasicrystals : low frequency behaviour and inelastic scattering properties

    Science.gov (United States)

    Los, J.; Janssen, T.; Gähler, F.

    1993-06-01

    A detailed study of the low frequency behaviour of the phonon spectrum for 3-dimensional tiling models of icosahedral quasicrystals is presented, in commensurate approximations with up to 10 336 atoms per unit cell. The scaling behaviour of the lowest phonon branches shows that the widths of the gaps relative to the bandwidths vanish in the low frequency limit. The density of states at low frequencies is calculated by Brillouin zone integration, using either local linear or local quadratic interpolation of the branch surface. For perfect approximants it appears that there is a deviation from the normal ω^2-behaviour already at relatively low frequencies, in the form of pseudogaps. Also randomized approximants are considered, and it turns out that the pseudogaps in the density of states are flattened by randomization. When approaching the quasiperiodic limit, the dispersion of the acoustic branches becomes more and more isotropic, and the two transversal sound velocities tend to the same value. The dynamical structure factor is determined for several approximants, and it is shown that the linearity and the isotropy of the dispersion are extended far beyond the range of the acoustic branches inside the Brillouin zone. A sharply peaked response is observed at low frequencies, and broadening at higher frequencies. To obtain these results, an efficient algorithm based on Lanczos tridiagonalisation is used.

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

    Science.gov (United States)

    Nakajima, Yoshie; Tanaka, Naofumi; Mima, Tatsuya; Izumi, Shin-Ichi

    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.

  1. Low frequency repetitive transcranial magnetic stimulation improves motor dysfunction after cerebral infarction

    Directory of Open Access Journals (Sweden)

    Zhi-yong Meng

    2017-01-01

    Full Text Available Low frequency (≤ 1 Hz repetitive transcranial magnetic stimulation (rTMS can affect the excitability of the cerebral cortex and synaptic plasticity. Although this is a common method for clinical treatment of cerebral infarction, whether it promotes the recovery of motor function remains controversial. Twenty patients with cerebral infarction combined with hemiparalysis were equally and randomly divided into a low frequency rTMS group and a control group. The patients in the low frequency rTMS group were given 1-Hz rTMS to the contralateral primary motor cortex with a stimulus intensity of 90% motor threshold, 30 minutes/day. The patients in the control group were given sham stimulation. After 14 days of treatment, clinical function scores (National Institute of Health Stroke Scale, Barthel Index, and Fugl-Meyer Assessment improved significantly in the low frequency rTMS group, and the effects were better than that in the control group. We conclude that low frequency (1 Hz rTMS for 14 days can help improve motor function after cerebral infarction.

  2. Low frequency repetitive transcranial magnetic stimulation improves motor dysfunction after cerebral infarction.

    Science.gov (United States)

    Meng, Zhi-Yong; Song, Wei-Qun

    2017-04-01

    Low frequency (≤ 1 Hz) repetitive transcranial magnetic stimulation (rTMS) can affect the excitability of the cerebral cortex and synaptic plasticity. Although this is a common method for clinical treatment of cerebral infarction, whether it promotes the recovery of motor function remains controversial. Twenty patients with cerebral infarction combined with hemiparalysis were equally and randomly divided into a low frequency rTMS group and a control group. The patients in the low frequency rTMS group were given 1-Hz rTMS to the contralateral primary motor cortex with a stimulus intensity of 90% motor threshold, 30 minutes/day. The patients in the control group were given sham stimulation. After 14 days of treatment, clinical function scores (National Institute of Health Stroke Scale, Barthel Index, and Fugl-Meyer Assessment) improved significantly in the low frequency rTMS group, and the effects were better than that in the control group. We conclude that low frequency (1 Hz) rTMS for 14 days can help improve motor function after cerebral infarction.

  3. Increased low-frequency oscillation amplitude of sensorimotor cortex associated with the severity of structural impairment in cervical myelopathy.

    Directory of Open Access Journals (Sweden)

    Fuqing Zhou

    Full Text Available Decreases in metabolites and increased motor-related, but decreased sensory-related activation of the sensorimotor cortex (SMC have been observed in patients with cervical myelopathy (CM using advanced MRI techniques. However, the nature of intrinsic neuronal activity in the SMC, and the relationship between cerebral function and structural damage of the spinal cord in patients with CM are not fully understood. The purpose of this study was to assess intrinsic neuronal activity by calculating the regional amplitude of low frequency fluctuations (ALFF using resting-state functional MRI (rs-fMRI, and correlations with clinical and imaging indices. Nineteen patients and 19 age- and sex-matched healthy subjects underwent rs-fMRI scans. ALFF measurements were performed in the SMC, a key brain network likely to impaired or reorganized patients with CM. Compared with healthy subjects, increased amplitude of cortical low-frequency oscillations (LFO was observed in the right precentral gyrus, right postcentral gyrus, and left supplementary motor area. Furthermore, increased z-ALFF values in the right precentral gyrus and right postcentral gyrus correlated with decreased fractional anisotropy values at the C2 level, which indicated increased intrinsic neuronal activity in the SMC corresponding to the structural impairment in the spinal cord of patients with CM. These findings suggest a complex and diverging relationship of cortical functional reorganization and distal spinal anatomical compression in patients with CM and, thus, add important information in understanding how spinal cord integrity may be a factor in the intrinsic covariance of spontaneous low-frequency fluctuations of BOLD signals involved in cortical plasticity.

  4. Assessment of Crack Detection in Heavy-Walled Cast Stainless Steel Piping Welds Using Advanced Low-Frequency Ultrasonic Methods

    Energy Technology Data Exchange (ETDEWEB)

    Anderson, Michael T.; Crawford, Susan L.; Cumblidge, Stephen E.; Denslow, Kayte M.; Diaz, Aaron A.; Doctor, Steven R.

    2007-03-01

    Studies conducted at the Pacific Northwest National Laboratory in Richland, Washington, have focused on assessing the effectiveness and reliability of novel approaches to nondestructive examination (NDE) for inspecting coarse-grained, cast stainless steel reactor components. The primary objective of this work is to provide information to the U.S. Nuclear Regulatory Commission on the effectiveness and reliability of advanced NDE methods as related to the inservice inspection of safety-related components in pressurized water reactors (PWRs). This report provides progress, recent developments, and results from an assessment of low frequency ultrasonic testing (UT) for detection of inside surface-breaking cracks in cast stainless steel reactor piping weldments as applied from the outside surface of the components. Vintage centrifugally cast stainless steel piping segments were examined to assess the capability of low-frequency UT to adequately penetrate challenging microstructures and determine acoustic propagation limitations or conditions that may interfere with reliable flaw detection. In addition, welded specimens containing mechanical and thermal fatigue cracks were examined. The specimens were fabricated using vintage centrifugally cast and statically cast stainless steel materials, which are typical of configurations installed in PWR primary coolant circuits. Ultrasonic studies on the vintage centrifugally cast stainless steel piping segments were conducted with a 400-kHz synthetic aperture focusing technique and phased array technology applied at 500 kHz, 750 kHz, and 1.0 MHz. Flaw detection and characterization on the welded specimens was performed with the phased array method operating at the frequencies stated above. This report documents the methodologies used and provides results from laboratory studies to assess baseline material noise, crack detection, and length-sizing capability for low-frequency UT in cast stainless steel piping.

  5. Effect of shading technique and thickness on color stability and translucency of new generation translucent zirconia.

    Science.gov (United States)

    Alp, Gülce; Subaşı, Meryem Gülce; Seghi, Robert R; Johnston, William M; Yilmaz, Burak

    2018-03-27

    To evaluate the effect of shading technique and thickness on the color stability and translucency of translucent zirconia after coffee thermocycling. Specimens in different thicknesses (1; 1.5; 2 mm) (n = 4 for each thickness) were sectioned from translucent preshaded zirconia (Pre) and externally shaded zirconia (Ext). After sintering, specimens were glazed and subjected to 10,000 thermocycling in coffee solution. The color coordinates of specimens were measured with a spectroradiometer before and after coffee thermocyling. Color differences and relative translucency parameter (RTP) values were calculated with CIEDE2000 color difference and TP CIEDE2000 formulas. ANOVA was used to analyze the CIEDE2000 color difference and RTP values (α = 0.05). According to 2-way ANOVA, no significant effect of shading technique and thickness on the color difference values was found (P > .05). According to 3-way ANOVA, a significant interaction between the shading technique and thickness (P < .0001) was found for RTP. The RTP parameter decreased with the increase in the thickness. Ext specimens presented significantly higher RTP than Pre specimens (P < .0001), except for between Ext 1 mm and Pre 1 mm (P = .179). Neither shading technique nor tested thicknesses affected the color of translucent zirconia. Shading technique and thickness affected the RTP of translucent zirconia. The RTP was inversely affected with the thickness of the material. Externally shaded zirconia presented higher RTP than preshaded zirconia for specimens thicker than 1 mm. Discoloration with coffee was insignificant for the tested translucent zirconia in tested thicknesses (1, 1.5, 2 mm). When a translucent restoration is intended, thinner externally shaded translucent zirconia restorations should be preferred instead of preshaded translucent zirconia. Copyright © 2018 Elsevier Ltd. All rights reserved.

  6. Trends in Shoulder Stabilization Techniques Used in the United States Based on a Large Private-Payer Database

    Science.gov (United States)

    Riff, Andrew J.; Frank, Rachel M.; Sumner, Shelby; Friel, Nicole; Bach, Bernard R.; Verma, Nikhil N.; Romeo, Anthony A.

    2017-01-01

    Background: Arthroscopic stabilization is the most broadly used surgical procedure in the United States for management of recurrent shoulder instability. Latarjet coracoid transfer has been considered a salvage surgical procedure for failed arthroscopic repairs or cases of significant glenoid bone loss; however, with recent literature suggesting reduced risk of recurrent instability with Latarjet, several surgeons have advocated its broader utilization as a primary operation for treatment of shoulder instability. Purpose: To determine trends in shoulder stabilization techniques used in the United States. Study Design: Cross-sectional study. Methods: A retrospective analysis of a publicly available national insurance database was performed to identify shoulder stabilization procedures performed over 9 years (2007-2015). The following Current Procedural Terminology codes were searched: 29806 (arthroscopic stabilization), 23455 (open capsulolabral repair), 23466 (open capsular shift), 23462 (Latarjet coracoid transfer), and 23460 (open anterior capsulorrhaphy with other bone block augmentation). Outcomes of interest included (1) trends in the use of each technique throughout the study interval, (2) age and sex distributions of patients undergoing each technique, and (3) regional predilections for the use of each technique. Results: Arthroscopic stabilization was the most broadly used shoulder stabilization procedure in the database (87%), followed by open Bankart (7%), Latarjet (3.2%), open capsular shift (2.6%), and alternative bone block procedure (0.8%). Throughout the study period, the incidence of arthroscopic stabilization and Latarjet increased (8% and 15% per year, respectively); the incidence of open capsular shift remained relatively constant; and the incidence of open Bankart decreased (9% per year). Arthroscopic stabilization, open Bankart, and Latarjet each had similar sex-based distributions (roughly 70% male), while open capsular shift and alternative

  7. Intradermal drug delivery by low-frequency sonophoresis (25 kHz).

    Science.gov (United States)

    Santoianni, Pietro; Nino, Massimiliano; Calabro, Gabriella

    2004-10-15

    Ultrasound waves (US) have been proposed to facilitate the absorption of active compounds (transdermal delivery) stimulating some disaggregation of the horny layer and promoting convective movements within the epidermis. Drugs used for alopecia areata, melasma, and lentigo, although proved effective, have limited effects resulting from only partial penetration into the skin. This study has evaluated the efficacy of low-frequency sonophoresis (LFS) at 25 kHz produced by a sonicator apparatus for treatment of alopecia areata, melasma, and solar lentigo. Thirty patients affected by alopecia areata were treated by application of methylprednisolone or cyclosporine solution followed by LFS. In a case-control study 48 women with melasma and 48 with solar lentigo were also treated by depigmenting emulsion and LFS application. For alopecia areata after 36 applications with LFS and 3-month treatment, the results were 57 percent partial regrowth and 29 percent total with methylprednisolone, and 33 percent partial regrowth and 34 percent total when cyclosporine was used. For melasma and solar lentigines the results when the drug application was followed by LFS, were (after twice-a-week application for 3 months) 75 percent complete depigmentation and 25 percent partial for melasma, 43 percent total regression and 57 percent partial for solar lentigo. This is the first report of sonophoresis at a frequency of 25 kHz in dermatocosmetology. The study shows that LFS, a not aggressive technique, enhance penetration of topic agents obtaining effects at the level of the epidermis, dermis and appendages (intradermal delivery), giving better results in the treatment of some cosmetic skin disorders.

  8. Abnormal functional integration of thalamic low frequency oscillation in the BOLD signal after acute heroin treatment.

    Science.gov (United States)

    Denier, Niklaus; Schmidt, André; Gerber, Hana; Vogel, Marc; Huber, Christian G; Lang, Undine E; Riecher-Rossler, Anita; Wiesbeck, Gerhard A; Radue, Ernst-Wilhelm; Walter, Marc; Borgwardt, Stefan

    2015-12-01

    Heroin addiction is a severe relapsing brain disorder associated with impaired cognitive control, including deficits in attention allocation. The thalamus has a high density of opiate receptors and is critically involved in orchestrating cortical activity during cognitive control. However, there have been no studies on how acute heroin treatment modulates thalamic activity. In a cross-over, double-blind, vehicle-controlled study, 29 heroin-maintained outpatients were studied after heroin and placebo administration, while 20 healthy controls were included for the placebo condition only. Resting-state functional magnetic resonance imaging was used to analyze functional integration of the thalamus by three different resting state analysis techniques. Thalamocortical functional connectivity (FC) was analyzed by seed-based correlation, while intrinsic thalamic oscillation was assessed by analysis of regional homogeneity (ReHo) and the fractional amplitude of low frequency fluctuations (fALFF). Relative to the placebo treatment and healthy controls, acute heroin administration reduced thalamocortical FC to cortical regions, including the frontal cortex, while the reductions in FC to the mediofrontal cortex, orbitofrontal cortex, and frontal pole were positively correlated with the plasma level of morphine, the main psychoactive metabolite of heroin. Furthermore, heroin treatment was associated with increased thalamic ReHo and fALFF values, whereas fALFF following heroin exposure correlated negatively with scores of attentional control. The heroin-associated increase in fALFF was mainly dominated by slow-4 (0.027-0.073 Hz) oscillations. Our findings show that there are acute effects of heroin within the thalamocortical system and may shed new light on the role of the thalamus in cognitive control in heroin addiction. Future research is needed to determine the underlying physiological mechanisms and their role in heroin addiction. © 2015 Wiley Periodicals, Inc.

  9. Vascular gene transfer and drug delivery in vitro using low-frequency ultrasound and microbubbles

    Science.gov (United States)

    Yang, Hong; Liu, Zhong-hua; Liu, Yi-yao; Lou, Chang-chun; Ren, Zheng-long; Miyoshi, Hirokazu

    2010-01-01

    Aim: To determine the effects of ultrasound exposure in combination with a microbubble contrast agent (SonoVue) on the cellular uptake and delivery of drugs/genes into human umbilical vein endothelial cells (HUVECs) as well as their biological effects on migration. Methods: HUVECs in suspension were exposed to pulsed ultrasound with a 10% duty cycle in combination with various concentrations of a microbubble contrast agent (SonoVue) using a digital sonifier at a frequency of 20 kHz and an intensity of 3.77 W/cm2 on the surface of a horn tip. Cell culture inserts were used to determine the cell migration ability. Results: Exposure to pulsed ultrasound resulted in enhanced green fluorescent protein (EGFP) gene transfection efficiencies ranging from 0.2% to 2%. The transfection efficiency of HUVECs was approximately 3-fold higher in the presence of SonoVue than in its absence at the effective exposure time of 6 s. For drug delivery to HUVECs using ultrasound, the delivery efficiencies of a low-molecular-weight model drug (TO-PRO®−1, MW 645.38) were significantly higher when compared to drug delivery without ultrasound, with a maximum efficiency of approximately 34%. However, the delivery efficiencies of a high-molecular-weight model drug (Dextran-Rhodamine B, MW 70 000) were low, with a maximum delivery efficiency of nearly 0.5%, and gene transfection results were similarly poor. The migration ability of HUVECs exposed to ultrasound was also lower than that of the control (no exposure). Conclusion: The use of low-frequency and low-energy ultrasound in combination with microbubbles could be a potent physical method of increasing drug/gene delivery efficiency. This technique is a promising nonviral approach that can be used in cardiovascular disease therapy. PMID:20348943

  10. Characterization of ultra low frequency (ULF pulsations and the investigation of their possible source

    Directory of Open Access Journals (Sweden)

    S. H. Mthembu

    2009-08-01

    Full Text Available In this paper we present the results from the observation of ultra low frequency (ULF pulsations in the Doppler velocity data from SuperDARN HF radar located at Goose Bay (61.94° N, 23.02° E, geomagnetic. Fourier spectral techniques were used to determine the spectral content of the data and the results show Pc 5 ULF pulsations (with a frequency range of 1 to 4 mHz where the magnetic field lines were oscillating at discrete frequencies of about 1.3 and 1.9 mHz. These pulsations are classified as field lines resonance (FLR since the 1.9 mHz component exhibited an enhancement in amplitude with an associated phase change of approximately 180° across a resonance latitude of 71.3°. The spatial and temporal structure of the ULF pulsations was examined by investigating their instantaneous amplitude which was calculated as the amplitude of the analytic signal. The results presented a full field of view which exhibit pulsations activity simultaneously from all beams. This representation shows that the peak amplitude of the 1.9 mHz component was observed over the longitudinal range of 13°. The temporal structure of the pulsations was investigated from the evolution of the 1.9 mHz component and the results showed that the ULF pulsations had a duration of about 1 h. Wavelet analysis was used to investigate solar wind as a probable source of the observed ULF pulsations. The time delay compared well with the solar wind travel time estimates and the results suggest a possible link between the solar wind and the observed pulsations. The sudden change in dynamic pressure also proved to be a possible source of the observed ULF pulsations.

  11. Low frequency ultrasound and UV-C for elimination of pathogens in recirculating aquaculture systems.

    Science.gov (United States)

    Bazyar Lakeh, Amir Abbas; Kloas, Werner; Jung, Rainer; Ariav, Ra'anan; Knopf, Klaus

    2013-09-01

    Low frequency ultrasound (LFUS) was evaluated as a novel disinfection technique within recirculating aquaculture systems both individually and combined with UV-C. Dose-dependent inactivation rates were determined for the total viable counts and model organisms representing different taxa of common fish parasites: the ciliate Paramecium sp., second larval stage (L2) of the nematode Anguillicola crassus and metanauplii of Artemia sp. Application of LFUS up to 19 kJ/L did not reduce the number of colony forming units (CFU), whilst UV-C irradiation was highly effective. Pre-treatment with LFUS reduced the mean size of suspended solids in aquaculture water and thus increased the germicidal effect of UV-C by up to 0.6 log units. LFUS was effective against the eukaryotic organisms, and the dose-dependent inactivation could be well described by functions of an exponential decay. However, the efficiency of LFUS differed greatly between species. A LFUS dose of 1.9 kJ/L (consumed energy) was sufficient to inactivate Artemia by 99%, but a ten times higher dose was necessary to inactivate 95% and 81% of Paramecium and Anguillicola larvae, respectively. In clear water, the energetic efficiency of UV-C (emitted by a low pressure lamp) against Paramecium and Anguillicola larvae was higher compared to LFUS, but LFUS was more efficient against Artemia. However, the efficiency of LFUS against ciliates or nematode larvae would be similar or even higher than UV-C in highly turbid water or if less efficient medium pressure lamps are used. This study shows that LFUS can be applied safely at energy densities that are effective against a wide range of parasites like ciliates, nematodes and crustaceans. The combination of LFUS and UV-C could provide an appropriate water treatment with regards to all relevant pathogens in recirculating aquaculture systems. Copyright © 2013 Elsevier B.V. All rights reserved.

  12. Identification and classification of very low frequency waves on a coral reef flat

    Science.gov (United States)

    Gawehn, Matthijs; van Dongeran, Ap; van Rooijen, Arnold; Storlazzi, Curt; Cheriton, Olivia; Reniers, Ad

    2016-01-01

    Very low frequency (VLF, 0.001–0.005 Hz) waves are important drivers of flooding of low-lying coral reef-islands. In particular, VLF wave resonance is known to drive large wave runup and subsequent overwash. Using a 5 month data set of water levels and waves collected along a cross-reef transect on Roi-Namur Island in the Republic of the Marshall Islands, the observed VLF motions were categorized into four different classes: (1) resonant, (2) (nonresonant) standing, (3) progressive-growing, and (4) progressive-dissipative waves. Each VLF class is set by the reef flat water depth and, in the case of resonance, the incident-band offshore wave period. Using an improved method to identify VLF wave resonance, we find that VLF wave resonance caused prolonged (∼0.5–6.0 h), large-amplitude water surface oscillations at the inner reef flat ranging in wave height from 0.14 to 0.83 m. It was induced by relatively long-period, grouped, incident-band waves, and occurred under both storm and nonstorm conditions. Moreover, observed resonant VLF waves had nonlinear, bore-like wave shapes, which likely have a larger impact on the shoreline than regular, sinusoidal waveforms. As an alternative technique to the commonly used Fast Fourier Transformation, we propose the Hilbert-Huang Transformation that is more computationally expensive but can capture the wave shape more accurately. This research demonstrates that understanding VLF waves on reef flats is important for evaluating coastal flooding hazards.

  13. Investigations of the role of cavitation in low-frequency sonophoresis using acoustic spectroscopy.

    Science.gov (United States)

    Tezel, Ahmet; Sens, Ashley; Mitragotri, Samir

    2002-02-01

    Application of low-frequency ultrasound significantly enhances skin permeability. The enhancement of skin permeability is mediated by cavitation, oscillation, and collapse of gaseous cavities. In this article, we report detailed investigations of the occurrence of cavitation during low-frequency sonophoresis. Cavitation was monitored by recording pressure amplitudes of subharmonic emission and broadband noise at four different ultrasound frequencies in the range of 20-100 kHz and at various intensities in the range of 0-2.6 W/cm(2). Enhancement of skin conductivity, in the presence of sodium lauryl sulfate (SLS), was also measured under the same ultrasound conditions. Enhancement of skin conductivity correlated well with the amplitude of broadband noise, which suggests the role of transient cavitation in low-frequency sonophoresis. No correlation was found between the subharmonic pressure amplitude and conductivity enhancement. Copyright 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:444-453, 2002

  14. Deletion method of image low-frequency components using fast median filter algorithm

    Directory of Open Access Journals (Sweden)

    N. V. Bilous

    2016-12-01

    Full Text Available This article proposes a computational method for removing low-frequency component of the raster image. Development of a calculation method is based on the fast median filtering. Presented method implementation removes low-frequency component for a larger image by dividing the image into sections for eliminating of the edge effect. The method can be usedfor enhancing the signal / noise ratio, reducing the dynamic range of images and processing time of large images, as well as allow for section-by-section filtering without the influence of the edge effect. Article also represents quality indicators of luminance image alignment. It was shown that a computer implementation of the proposed modification of the method of removing the low-frequency component of a larger image using a fast median filtering were made on FrameSmooth software.

  15. 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.

  16. 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.

  17. 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...

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

    DEFF Research Database (Denmark)

    Celestinos, Adrian

    2007-01-01

    to the multiple reflection of sound at the rigid walls of the room. This may cause level differences of up to 20 dB in the room. Some of these deviations are associated with the standing waves, resonances or anti resonances of the room. The understanding of the problem is accomplished by analyzing the behavior......The scope of this PhD dissertation is within the performance of loudspeakers in rooms at low frequencies. The research concentrates on the improvement of the sound level distribution in rooms produced by loudspeakers at low frequencies. The work focuses on seeing the problem acoustically...... 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...

  19. Low frequency forces on tubular spaceframe towers: Analysis of Cognac data

    Energy Technology Data Exchange (ETDEWEB)

    Conte, J.P. [Rice Univ., Houston, TX (United States). Dept. of Civil Engineering; Marshall, P.W. [Univ. of Newcastle upon Tyne (United Kingdom). Dept. of Civil Engineering

    1994-12-31

    The ultimate objective of the study presented here was to identify if field data collected from the Cognac platform can be used to discriminate between the empirical Wheeler and Delta stretching schemes to approximate near surface kinematics, in terms of the low-frequency forces which are potentially important in the design of compliant towers. Previous studies focusing on the peak hydrodynamic forces, as used for the design of fixed platforms, have shown a significant difference between predictions based on Wheeler and Delta stretching. The cognac field data indicate that the low-frequency force components are not negligible and are significantly correlated to the wave envelope process. Simulation studies based on a vertical rigid cylinder subjected to Hurricane Frederic sea states show significant differences in applied low-frequency drag forces obtained using Wheeler versus Delta stretching.

  20. Reduction of low frequency error for SED36 and APS based HYDRA star trackers

    Science.gov (United States)

    Ouaknine, Julien; Blarre, Ludovic; Oddos-Marcel, Lionel; Montel, Johan; Julio, Jean-Marc

    2017-11-01

    In the frame of the CNES Pleiades satellite, a reduction of the star tracker low frequency error, which is the most penalizing error for the satellite attitude control, was performed. For that purpose, the SED36 star tracker was developed, with a design based on the flight qualified SED16/26. In this paper, the SED36 main features will be first presented. Then, the reduction process of the low frequency error will be developed, particularly the optimization of the optical distortion calibration. The result is an attitude low frequency error of 1.1" at 3 sigma along transverse axes. The implementation of these improvements to HYDRA, the new multi-head APS star tracker developed by SODERN, will finally be presented.

  1. A space-coiled acoustic metamaterial with tunable low-frequency sound absorption

    Science.gov (United States)

    Wang, Yang; Zhao, Honggang; Yang, Haibin; Zhong, Jie; Wen, Jihong

    2017-12-01

    A novel low-frequency absorber composed a perforated panel and a cavity with a coiled-up channel is presented and demonstrated. Both theoretical analysis and finite element method are utilized to reveal that the absorber possesses a low-frequency absorption with deep-subwavelength thickness. The effect of the folding number of a space-coiled channel on the absorption peak position is discussed and the result shows that a greater folding number can reduce the absorption peak frequency dramatically without sacrificing the total thickness of the absorber. In order to broaden the absorption bandwidth, an absorber combining two units with different folding number is constructed to further enhance the low-frequency absorption performance.

  2. A new low-frequency power unit based on principle of converting phase condenser

    International Nuclear Information System (INIS)

    Liu Lianye; Zhu Yulong

    1988-02-01

    While a magnetic reluctance motor is used for driving a reactor control rod, it needs a low-frequency power unit. In this case it's phase sequence can be positive or negative. In a project this power unit is a frequency converter based on principle of converting phase resistance from a alternative current frequency to another one controlled by silicon controlled rectifier. But in practical use, it often broke down due to fusing of fuses or malfunction of silicon controlled rectifiers and converting phase resistances and so on. A new low-frequency power unit based on principle of converting phase condenser instead of converting phase resistance is described. It stood up to all tests of laboratory and actual application, it is proved that the new low-frequency power unit has the advantage over the old one in many sides, such as simpler circuit, smaller heat generating, higher lifting power of drive mechanism, and increased reliability

  3. Observational study of generation conditions of substorm-associated low-frequency AKR emissions

    Directory of Open Access Journals (Sweden)

    A. Olsson

    2004-11-01

    Full Text Available It has lately been shown that low-frequency bursts of auroral kilometric radiation (AKR are nearly exclusively associated with substorm expansion phases. Here we study low-frequency AKR using Polar PWI and Interball POLRAD instruments to constrain its possible generation mechanisms. We find that there are more low-frequency AKR emission events during wintertime and equinoxes than during summertime. The dot-AKR emission radial distance range coincides well with the region where the deepest density cavities are seen statistically during Kp>2. We suggest that the dot-AKR emissions originate in the deepest density cavities during substorm onsets. The mechanism for generating dot-AKR is possibly strong Alfvén waves entering the cavity from the magnetosphere and changing their character to more inertial, which causes the Alfvén wave associated parallel electric field to increase. This field may locally accelerate electrons inside the cavity enough to produce low-frequency AKR emission. We use Interball IESP low-frequency wave data to verify that in about half of the cases the dot-AKR is accompanied by low-frequency wave activity containing a magnetic component, i.e. probably inertial Alfvén waves. Because of the observational geometry, this result is consistent with the idea that inertial Alfvén waves might always be present in the source region when dot-AKR is generated. The paper illustrates once more the importance of radio emissions as a powerful remote diagnostic tool of auroral processes, which is not only relevant for the Earth's magnetosphere but may be relevant in the future in studying extrasolar planets.

  4. The effects of finishing and polishing techniques on surface roughness and color stability of nanocomposites.

    Science.gov (United States)

    Gönülol, Nihan; Yilmaz, Fikret

    2012-12-01

    The aim of this in vitro study was to evaluate the effects of different finishing and polishing techniques on the surface roughness and color stability of nanocomposites. Two nanohybrid (Grandio, Aelite Aesthetic Enamel), two nanofill (Filtek Supreme XT Dentin and Translucent), and a microhybrid (Filtek Z250) composites were used. Two hundred and eighty disc-shaped specimens were cured under a mylar strip. Seven specimens of each resin composite were randomly assigned to one of the seven polishing systems. A profilometer was used for assessing surface roughness. ΔE was calculated with a colorimeter at baseline and 48 h after storage in a coffee solution. The results were analysed by two-way ANOVA and Tukey's HSD test (α=0.05). Regression analysis was used to examine the correlation between surface roughness and color stability (α=0.01). There was no significant difference in R(a) values between mylar strips and Sof-Lex polishing discs (p>0.05). The highest ΔE and R(a) values were obtained from Grandio (pGrandio presented the highest surface roughness and staining susceptibility after storage in coffee solution. Aelite Aesthetic Enamel, which did not include TEGDMA in its composition, showed the least discoloration. The composites with smaller filler size did not necessarily show low surface roughness and discoloration. Staining of composite resins was dependent on monomer structure, as well as surface irregularities. Copyright © 2012 Elsevier Ltd. All rights reserved.

  5. Synthesis, microstructure and mechanical properties of ceria stabilized tetragonal zirconia prepared by spray drying technique

    International Nuclear Information System (INIS)

    Sharma, S.C.; Gokhale, N.M.; Dayal, Rajiv; Lazl, Ramji

    2002-01-01

    Ceria stabilized zirconia powders with ceria concentration varying from 6 to 16 mol% were synthesized using spray drying technique. Powders were characterized for their particle size distribution and specific surface area. The dense sintered ceramics fabricated using these powders were characterized for their microstructure, crystallite size and phase composition. The flexural strength, fracture toughness and micro-hardness of sintered ceramics were measured. High fracture toughness and flexural strength were obtained for sintered bodies with 12 mol% of CeO 2 . Flexural strength and fracture toughness were dependent on CeO 2 concentration, crystallite size and phase composition of sintered bodies. Correlation of data has indicated that the transformable tetragonal phase is the key factor in controlling the fracture toughness and strength of ceramics. It has been demonstrated that the synthesis method is effective to prepare nanocrystalline tetragonal ceria stabilized zirconia powders with improved mechanical properties. Ce-ZrO 2 with 20 wt% alumina was also prepared with flexural strength, 1200 MPa and fracture toughness 9.2 MPa√m. (author)

  6. On the Decay Ratio Determination in BWR Stability Analysis by Auto-Correlation Function Techniques

    International Nuclear Information System (INIS)

    Behringer, K.; Hennig, D.

    2002-11-01

    A novel auto-correlation function (ACF) method has been investigated for determining the oscillation frequency and the decay ratio in BWR stability analyses. The neutron signals are band-pass filtered to separate the oscillation peak in the power spectral density (PSD) from background. Two linear second-order oscillation models are considered. These models, corrected for signal filtering and including a background term under the peak in the PSD, are then least-squares fitted to the ACF of the previously filtered neutron signal, in order to determine the oscillation frequency and the decay ratio. Our method uses fast Fourier transform techniques with signal segmentation for filtering and ACF estimation. Gliding 'short-term' ACF estimates on a record allow the evaluation of uncertainties. Numerical results are given which have been obtained from neutron data of the recent Forsmark I and Forsmark II NEA benchmark project. Our results are compared with those obtained by other participants in the benchmark project. The present PSI report is an extended version of the publication K. Behringer, D. Hennig 'A novel auto-correlation function method for the determination of the decay ratio in BWR stability studies' (Behringer, Hennig, 2002)

  7. Simulation on a new method of low-frequency phase aberration correction

    CERN Document Server

    Deng Qing Hua; Jing Feng; LiuLanQin

    2002-01-01

    A kind of new phase aberration correcting method is introduced--using a phase countervailing mirror to correct the low-frequency phase error. This method is mainly aimed to correct the static phase aberration caused by the fishing error on the optics. With random phase screen simulating the low-frequency phase aberration of the amplifiers, and the other effect of amplifiers on the beam is neglected, a beam propagation is set up. A new concept of equivalent phase plate is introduced and the phase of the mirror, as the invert phase of the equivalent phase plate, is easy to get. Finally, simulation of the correcting course was done

  8. Low frequency torsional vibration gaps in the shaft with locally resonant structures

    International Nuclear Information System (INIS)

    Yu Dianlong; Liu Yaozong; Wang Gang; Cai Li; Qiu Jing

    2006-01-01

    The propagation of torsional wave in the shaft with periodically attached local resonators is studied with the transfer matrix theory and the finite element method. The analytical dispersion relation and the complex band structure of such a structure is presented for the first time, which indicates the existence of low frequency gaps. The effect of shaft material on the vibration attenuation in band gap is investigated. The frequency response function of the shaft with finite periodic locally resonant oscillators is simulated with finite element method, which shows large vibration attenuation in the frequency range of the gap as expected. The low frequency torsional gap in shafts provides a new idea for vibration control

  9. Global low-frequency motions in protein allostery: CAP as a model system.

    Science.gov (United States)

    Townsend, Philip D; Rodgers, Thomas L; Pohl, Ehmke; Wilson, Mark R; McLeish, Tom C B; Cann, Martin J

    2015-06-01

    Allostery is a fundamental process by which ligand binding to a protein alters its activity at a distant site. There is considerable evidence that allosteric cooperativity can be communicated by the modulation of protein dynamics without conformational change. The Catabolite Activator Protein (CAP) of Escherichia coli is an important experimental exemplar for entropically driven allostery. Here we discuss recent experimentally supported theoretical analysis that highlights the role of global low-frequency dynamics in allostery in CAP and identify how allostery arises as a natural consequence of changes in global low-frequency protein fluctuations on ligand binding.

  10. Research of hydroelectric generating set low-frequency vibration monitoring system based on optical fiber sensing

    Science.gov (United States)

    Min, Li; Zhang, Xiaolei; Zhang, Faxiang; Sun, Zhihui; Li, ShuJuan; Wang, Meng; Wang, Chang

    2017-10-01

    In order to satisfy hydroelectric generating set low-frequency vibration monitoring, the design of Passive low-frequency vibration monitoring system based on Optical fiber sensing in this paper. The hardware of the system adopts the passive optical fiber grating sensor and unbalanced-Michelson interferometer. The software system is used to programming by Labview software and finishing the control of system. The experiment show that this system has good performance on the standard vibration testing-platform and it meets system requirements. The frequency of the monitoring system can be as low as 0.2Hz and the resolution is 0.01Hz.

  11. On low-frequency errors of uniformly modulated filtered white-noise models for ground motions

    Science.gov (United States)

    Safak, Erdal; Boore, David M.

    1988-01-01

    Low-frequency errors of a commonly used non-stationary stochastic model (uniformly modulated filtered white-noise model) for earthquake ground motions are investigated. It is shown both analytically and by numerical simulation that uniformly modulated filter white-noise-type models systematically overestimate the spectral response for periods longer than the effective duration of the earthquake, because of the built-in low-frequency errors in the model. The errors, which are significant for low-magnitude short-duration earthquakes, can be eliminated by using the filtered shot-noise-type models (i. e. white noise, modulated by the envelope first, and then filtered).

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

    OpenAIRE

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

    2016-01-01

    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 of killer whales were made in Iceland and Norway when whales were observed feeding on herring, and no other cetacean species were nearby. Low-frequency sounds were identified in Iceland and ranged in duration between 0.14 and 2.77 seconds and in frequ...

  13. Return-map for low-frequency fluctuations in semiconductor lasers with optical feedback

    DEFF Research Database (Denmark)

    Mørk, Jesper; Sabbatier, H.; Sørensen, Mads Peter

    1999-01-01

    We show that the phenomenon of low-frequency fluctuations (LFF) , commonly observed in semiconductor lasers with optical feedback, can be explained by a simple return-map, implying a tremendous simplification in the description of the slow time-scale dynamics of the system. Experimentally observed...... parameter dependencies are simply explained by the calculated return-maps. Our approach partly decouples the slow and the fast time-scale behaviour. The latter is often described in terms of chaotic itinerary, but this does not provide an explanation for the low-frequency fluctuations themselves....

  14. Fine Structure of the Low-Frequency Raman Phonon Bands of Single-Wall Carbon Nanotubes

    Science.gov (United States)

    Iliev, M. N.; Litvinchuk, A. P.; Arepalli, S.; Nikolaev, P.; Scott, C. D.

    1999-01-01

    The Raman spectra of singled-wall carbon nanotubes (SWNT) produced by laser and are process were studied between 5 and 500 kappa. The line width vs. temperature dependence of the low-frequency Raman bands between 150 and 200/ cm deviates from that expected for phonon decay through phonon-phonon scattering mechanism. The experimental results and their analysis provided convincing evidence that each of the low-frequency Raman lines is a superposition of several narrower Raman lines corresponding to tubes of nearly the same diameter. The application of Raman spectroscopy to probe the distribution of SWNT by both diameter and chirality is discussed.

  15. The impact of different peripheral suture techniques on the biomechanical stability in flexor tendon repair.

    Science.gov (United States)

    Wieskötter, B; Herbort, M; Langer, M; Raschke, M J; Wähnert, D

    2018-01-01

    Flexor tendon repair consists of circumferential peripheral sutures in combination with core sutures to avoid fraying and reduces the exposure of suture material on tendon surface. The peripheral suture adds up to a tenfold increase of the biomechanical stability compared to the core suture alone. The purpose of our study was to determine the most favourable peripheral repair technique for tendon repair. Seventy-two porcine flexor tendons underwent standardized tenotomy and repair using one of the following six methods (n = 12): simple-running (SR), simple-locking (SL), Halsted-mattress (HM), lin-locking (LL), Lembert-mattress (LM), and Silfverskiöld cross-stich (SCS) suture technique. The SL- suture was placed 2 mm; the HM, LM, SC, and LL suture were placed 5 mm from the tendon gap. The SR suture was placed 1, 2, and 3 mm from tendon ends; no additional core suture was applied. For cyclic testing (1000 cycles), elongation was calculated; for load to failure construct stiffness, yield load and maximum load were determined. The mean cyclic elongation for all tested suture techniques was less than 2 mm; there was no significant difference between the groups regarding elongation as well as yield load. The HM, LM, SCS, and LL suture techniques presented significantly higher maximum loads compared to the SR- and SL-sutures. The 3 mm SR showed significantly higher maximum loads compared to the 2 and 1 mm SR. Beside the distance from tendon gap, the type of linkage of the suture material across and beneath the epitendineum is important for biomechanical stability. Simple-running suture is easy to use, even with a slight increase of the distance from tendon gap significantly increases biomechanical strength. For future repairs of flexor tendon injuries, 3 mm stitch length is highly recommended for simple peripheral suture, while the Halsted-mattress suture unites the most important qualities: biomechanically strong, most part of suture material placed

  16. Vibro-Shock Dynamics Analysis of a Tandem Low Frequency Resonator—High Frequency Piezoelectric Energy Harvester

    Directory of Open Access Journals (Sweden)

    Darius Žižys

    2017-04-01

    Full Text Available Frequency up-conversion is a promising technique for energy harvesting in low frequency environments. In this approach, abundantly available environmental motion energy is absorbed by a Low Frequency Resonator (LFR which transfers it to a high frequency Piezoelectric Vibration Energy Harvester (PVEH via impact or magnetic coupling. As a result, a decaying alternating output signal is produced, that can later be collected using a battery or be transferred directly to the electric load. The paper reports an impact-coupled frequency up-converting tandem setup with different LFR to PVEH natural frequency ratios and varying contact point location along the length of the harvester. RMS power output of different frequency up-converting tandems with optimal resistive values was found from the transient analysis revealing a strong relation between power output and LFR-PVEH natural frequency ratio as well as impact point location. Simulations revealed that higher power output is obtained from a higher natural frequency ratio between LFR and PVEH, an increase of power output by one order of magnitude for a doubled natural frequency ratio and up to 150% difference in power output from different impact point locations. The theoretical results were experimentally verified.

  17. Normal and friction stabilization techniques for interactive rigid body constraint-based contact force computations

    DEFF Research Database (Denmark)

    Silcowitz-Hansen, Morten; Abel, Sarah Maria Niebe; Erleben, Kenny

    2010-01-01

    We present a novel, yet simple, method for stabilization of normal forces. A normal stabilization term, carefully designed from hypotheses about interactive usability, is added to the contact force problem. Further, we propose friction stabilization as a completely new stabilization paradigm in i...

  18. Temperature-dependent thermal conductivity of flexible yttria-stabilized zirconia substrate via 3ω technique

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Shivkant; Yarali, Milad; Mavrokefalos, Anastassios [Department of Mechanical Engineering, University of Houston, Houston, TX (United States); Shervin, Shahab [Materials Science and Engineering Program, University of Houston, Houston, TX (United States); Venkateswaran, Venkat; Olenick, Kathy; Olenick, John A. [ENrG Inc., Buffalo, NY (United States); Ryou, Jae-Hyun [Department of Mechanical Engineering, University of Houston, Houston, TX (United States); Materials Science and Engineering Program, University of Houston, Houston, TX (United States); Texas Center for Superconductivity, University of Houston (TcSUH), Houston, TX (United States)

    2017-10-15

    Thermal management in flexible electronic has proven to be challenging thereby limiting the development of flexible devices with high power densities. To truly enable the technological implementation of such devices, it is imperative to develop highly thermally conducting flexible substrates that are fully compatible with large-scale fabrication. Here, we present the thermal conductivity of state-of-the-art flexible yttria-stabilized zirconia (YSZ) substrates measured using the 3ω technique, which is already commercially manufactured via roll-to-roll technique. We observe that increasing the grain size increases the thermal conductivity of the flexible 3 mol.% YSZ, while the flexibility and transparency of the sample are hardly affected by the grain size enlargement. We exhibit thermal conductivity values of up to 4.16 Wm{sup -1}K {sup -1} that is at least 4 times higher than state-of-the-art polymeric flexible substrates. Phonon-hopping model (PHM) for granular material was used to fit the measured thermal conductivity and accurately define the thermal transport mechanism. Our results show that through grain size optimization, YSZ flexible substrates can be realized as flexible substrates, that pave new avenues for future novel application in flexible electronics through the utilization of both their ceramic structural flexibility and high heat dissipating capability. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  19. Neural robust stabilization via event-triggering mechanism and adaptive learning technique.

    Science.gov (United States)

    Wang, Ding; Liu, Derong

    2018-06-01

    The robust control synthesis of continuous-time nonlinear systems with uncertain term is investigated via event-triggering mechanism and adaptive critic learning technique. We mainly focus on combining the event-triggering mechanism with adaptive critic designs, so as to solve the nonlinear robust control problem. This can not only make better use of computation and communication resources, but also conduct controller design from the view of intelligent optimization. Through theoretical analysis, the nonlinear robust stabilization can be achieved by obtaining an event-triggered optimal control law of the nominal system with a newly defined cost function and a certain triggering condition. The adaptive critic technique is employed to facilitate the event-triggered control design, where a neural network is introduced as an approximator of the learning phase. The performance of the event-triggered robust control scheme is validated via simulation studies and comparisons. The present method extends the application domain of both event-triggered control and adaptive critic control to nonlinear systems possessing dynamical uncertainties. Copyright © 2018 Elsevier Ltd. All rights reserved.

  20. Estimation of Power System Stabilizer Parameters Using Swarm Intelligence Techniques to Improve Small Signal Stability of Power System

    Directory of Open Access Journals (Sweden)

    Hossein Soleymani

    2017-08-01

    Full Text Available Interconnection of the power system utilities and grids offers a formidable dispute in front of design engineers. With the interconnections, power system has emerged as a more intricate and nonlinear system. Recent years small signal stability problems have achieved much significance along with the conventional transient constancy problems. Transient stability of the power system can be attained with high gain and fast acting Automatic Voltage Regulators (AVRs. Yet, AVRs establish negative damping in the system. Propagation of small signals is hazardous for system’s health and offers a potential threat to system’s oscillatory stability. These small signals have magnitude of 0.2 to 2 Hz. The professional control tactic to develop system damping is Power System Stabilizer (PSS.This paper presents application of swarm intelligence for PSS parameter estimation issue on standard IEEE 10 Generator 39 Bus power network (New England. Realization of the objective function is done with the help of interpolation investigation using MATLAB. The system performance is compared with the conventional optimization algorithms like Genetic Algorithm (GA and Particle Swarm Optimization (PSO based PSS controller. The strength of proposed controller is tested by examining various operating conditions. An Eigen property analysis is done on this system i.e. before installing PSS, and after the employment of GA and PSO tuned PSSs. A significant comparison is carried out with GA and PSO on the basis of convergence uniqueness and dynamic response of speed deviation curves of various generators.

  1. Identification and classification of very low frequency waves on a coral reef flat

    NARCIS (Netherlands)

    Gawehn, M.; van Dongeren, AR; van Rooijen, A.A.; Storlazzi, C.D.; Cheriton, O.M.; Reniers, A.J.H.M.

    2016-01-01

    Very low frequency (VLF, 0.001–0.005 Hz) waves are important drivers of flooding of low-lying coral reef-islands. In particular, VLF wave resonance is known to drive large wave runup and subsequent overwash. Using a 5 month data set of water levels and waves collected along a cross-reef transect on

  2. Hydrogen Cosmology from the Deep Space Gateway: Data Analysis Pipeline for Low-Frequency Radio Telescopes

    Science.gov (United States)

    Rapetti, D.; Tauscher, K.; Burns, J. O.; Switzer, E.; Mirocha, J.; Furlanetto, S.; Monsalve, R.

    2018-02-01

    The Deep Space Gateway will provide a unique opportunity for low-frequency radio telescopes shielded by the Moon to study the unexplored Cosmic Dawn, which our novel pipeline is able to constrain by extracting the spectrum of a neutral hydrogen line.

  3. Low frequency photoacoustics for monitoring the photobaric component in vivo of green leaves

    NARCIS (Netherlands)

    Frandas, A.; Jalink, H.; Schoor, van der R.

    1997-01-01

    The photoacoustic frequency spectrum under steady-state conditions from Philodendron green leaves attached to the plant was measured in the 0.2-200 Hz frequency range. The PA amplitude spectrum showed a maximum at low frequency (around 1 Hz) which was attributed to an optimum frequency for oxygen

  4. 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…

  5. 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…

  6. Low-frequency dust-lower-hybrid modes in a dusty plasma

    International Nuclear Information System (INIS)

    Salimullah, M.

    1995-10-01

    The existence of low-frequency dust-lower-hybrid modes in a magnetized dusty plasma has been examined. These modes arise on account of the inequalities of charge and number densities of electrons, ions, and dust particles, and finite Larmor radius effects in a dusty plasma. (author). 14 refs

  7. 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 (Cornelia); 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

  8. Low-Frequency Interlayer Raman Modes to Probe Interface of Twisted Bilayer MoS2.

    Science.gov (United States)

    Huang, Shengxi; Liang, Liangbo; Ling, Xi; Puretzky, Alexander A; Geohegan, David B; Sumpter, Bobby G; Kong, Jing; Meunier, Vincent; Dresselhaus, Mildred S

    2016-02-10

    van der Waals homo- and heterostructures assembled by stamping monolayers together present optoelectronic properties suitable for diverse applications. Understanding the details of the interlayer stacking and resulting coupling is crucial for tuning these properties. We investigated the low-frequency interlayer shear and breathing Raman modes (<50 cm(-1)) in twisted bilayer MoS2 by Raman spectroscopy and first-principles modeling. Twisting significantly alters the interlayer stacking and coupling, leading to notable frequency and intensity changes of low-frequency modes. The frequency variation can be up to 8 cm(-1) and the intensity can vary by a factor of ∼5 for twisting angles near 0° and 60°, where the stacking is a mixture of high-symmetry stacking patterns and is thus sensitive to twisting. For twisting angles between 20° and 40°, the interlayer coupling is nearly constant because the stacking results in mismatched lattices over the entire sample. It follows that the Raman signature is relatively uniform. Note that for some samples, multiple breathing mode peaks appear, indicating nonuniform coupling across the interface. In contrast to the low-frequency interlayer modes, high-frequency intralayer Raman modes are much less sensitive to interlayer stacking and coupling. This research demonstrates the effectiveness of low-frequency Raman modes for probing the interfacial coupling and environment of twisted bilayer MoS2 and potentially other two-dimensional materials and heterostructures.

  9. 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

  10. Equivalent circuit modeling of the dielectric properties of rubber wood at low frequency

    Science.gov (United States)

    Wan M. Daud; Kaida B. Khalid; Aziz H.A. Sidek

    2000-01-01

    Dielectric properties of rubber wood were studied at various moisture contents and grain directions at low frequencies from 10-2 to 105 Hz. Results showed that the moisture content of wood affected the dielectric properties considerably. Dielectric data at different anisotropic directions, i.e., longitudinal, radial, and...

  11. Low-frequency oscillations and convective phenomena in a density-inverted vibrofluidized granular system

    NARCIS (Netherlands)

    Windows-Yule, Kit; Rivas Abud, Nicolás; Parker, D.J.; Thornton, Anthony Richard

    2014-01-01

    Low-frequency oscillations (LFOs) are thought to play an important role in the transition between the Leidenfrost and convective states of a vibrated granular bed. This work details the experimental observation of LFOs, which are found to be consistently present for a range of driving frequencies

  12. 77 FR 52317 - Record of Decision for Surveillance Towed Array Sensor System Low Frequency Active Sonar

    Science.gov (United States)

    2012-08-29

    ... Sonar AGENCY: Department of the Navy, DoD. ACTION: Notice of decision and availability. SUMMARY: The... Array Sensor System Low Frequency Active (SURTASS LFA) sonar systems with certain geographical.... This decision, which pertains to the employment of up to four SURTASS LFA sonar systems (as originally...

  13. The influence of low frequencies on the assessment of noise from neighbours

    DEFF Research Database (Denmark)

    Rindel, Jens Holger; Rasmussen, Birgit; Nielsen, Jesper Rye

    1996-01-01

    Lightweight building constructions often suffer from insufficient sound insulation at low frequencies. In order to investigate the degree of the problems, a laboratory experiment has been carried out. Twenty test persons have been asked to evaluate series of typical noise from neighbours, ie, two...

  14. 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.

  15. 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.

  16. Low-Frequency Noise Reduction by Earmuffs with Flax Fibre-Reinforced Polypropylene Ear Cups

    Directory of Open Access Journals (Sweden)

    Linus Yinn Leng Ang

    2018-01-01

    Full Text Available Soldiers and supporting engineers are frequently exposed to high low-frequency (<500 Hz cabin noise in military vehicles. Despite the use of commercial hearing protection devices, the risk of auditory damage is still imminent because the devices may not be optimally customised for such applications. This study considers flax fibre-reinforced polypropylene (Flax-PP as an alternative to the material selection for the ear cups of commercial earmuffs, which are typically made of acrylonitrile butadiene styrene (ABS. Different weaving configurations (woven and nonwoven and various noise environments (pink noise, cabin booming noise, and firing noise were considered to investigate the feasibility of the proposed composite earmuffs for low-frequency noise reduction. The remaining assembly components of the earmuff were kept consistent with those of a commercial earmuff, which served as a benchmark for results comparison. In contrast to the commercial earmuff, the composite earmuffs were shown to be better in mitigating low-frequency noise by up to 16.6 dB, while compromising midfrequency acoustical performance. Consequently, the proposed composite earmuffs may be an alternative for low-frequency noise reduction in vehicle cabins, at airports, and at construction sites involving heavy machineries.

  17. DARIS, a fleet of passive formation flying small satellites for low frequency radio astronomy

    NARCIS (Netherlands)

    Saks, Noah; Boonstra, Albert Jan; Rajan, Raj Thilak; Rajan, Raj; Bentum, Marinus Jan; Beliën, Frederik; van 't Klooster, Kees

    2010-01-01

    DARIS (Distributed Aperture Array for Radio Astronomy In Space) is a mission to conduct radio astronomy in the low frequency region from 1-10MHz. This region has not yet been explored, as the Earth's ionosphere is opaque to those frequencies, and so a space based observatory is the only solution.

  18. Effects of Removing Low-Frequency Electric Information on Speech Perception with Bimodal Hearing

    Science.gov (United States)

    Fowler, Jennifer R.; Eggleston, Jessica L.; Reavis, Kelly M.; McMillan, Garnett P.; Reiss, Lina A. J.

    2016-01-01

    Purpose: The objective was to determine whether speech perception could be improved for bimodal listeners (those using a cochlear implant [CI] in one ear and hearing aid in the contralateral ear) by removing low-frequency information provided by the CI, thereby reducing acoustic-electric overlap. Method: Subjects were adult CI subjects with at…

  19. 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

  20. 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

  1. Experiments with a Ship-Mounted Low Frequency SAS for the Detection of Buried Objects

    NARCIS (Netherlands)

    Colin, M.E.G.D.; Quesson, B.A.J.; Hetet, A.; Groen, J.; Sabel, J.C.; Zerr, B.; Brusieux, M.; Legris, M.

    2004-01-01

    In September 2002, GESMA and TNO-FEL carried out a sea trial with a low frequency (20 kHz) sonar mounted on a mine hunter. The objective of the experiments was to collect sonar echoes from proud and buried objects for subsequent synthetic aperture processing. A large data set was collected,

  2. 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.

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

    DEFF Research Database (Denmark)

    Poutanen, T.; Lähteenmäki, A.; León-Tavares, J.

    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...

  4. Creating poloidal flux in a tokamak plasma with low frequency waves

    International Nuclear Information System (INIS)

    Kirkwood, R.K.; Capewell, D.L.; Bellan, P.M.

    1993-01-01

    Using a fully toroidal, collisionless, low frequency model, we show that low amplitude, circularly polarized waves can, depending on antenna geometry (i) drive the toroidal EMF necessary to sustain a tokamak reactor, or (ii) shift the internal current profile. Measurements on a small tokamak to test (ii) agree with the model predictions. (orig.)

  5. 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

    When low frequency sound is radiated inside small listening spaces by loudspeakers, large uniformities occur over the sound field. This is due to the multiple reflection and diffraction of sound on the walls and different objects in the room. A developed system named Controlled Acoustically Bass ...

  6. 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....

  7. Towards an enhanced performance of uniform circular arrays at low frequencies

    DEFF Research Database (Denmark)

    Tiana Roig, Elisabet; Torras Rosell, Antoni; Fernandez Grande, Efren

    2013-01-01

    of the acoustic information captured by the microphones to the virtual array is based on acoustic holography. The predicted pressure is then used as input of the beamforming procedure. The combination of holography and beamforming for enhancing the beamforming output at low frequencies is examined with computer...

  8. Rare and low-frequency coding variants alter human adult height

    DEFF Research Database (Denmark)

    Marouli, Eirini; Graff, Mariaelisa; Medina-Gómez, Carolina

    2017-01-01

    as proteoglycan and glycosaminoglycan synthesis) involved in growth. Our results demonstrate that sufficiently large sample sizes can uncover rare and low-frequency variants of moderate-to-large effect associated with polygenic human phenotypes, and that these variants implicate relevant genes and pathways....

  9. 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.

  10. Orbiting low frequency antennas for radio astronomy(OLFAR): Distributing signal processing

    NARCIS (Netherlands)

    Rajan, Raj; Rajan, R.T.; Budianu, A.; Engelen, Steven; van der Veen, Alle-Jan; Bentum, Marinus Jan; Boonstra, Albert Jan; Verhoeven, Chris

    2011-01-01

    Recently, new and interesting science drivers have emerged in the ultra low frequency range of 0.3-30 MHz ranging from the epoch of re-ionization, exo-planets, ultra-high energy cosmic rays and studies of the astronomical dark ages. However at these wavelengths, ground based observations are

  11. Dynamical systems modeling of low-frequency variability in low-order atmospheric models

    NARCIS (Netherlands)

    Broer, H.W.; Vitolo, R.

    2008-01-01

    The understanding of atmospheric and oceanic low-frequency variability is an old problem having both theoretical interest and practical importance, e.g., for the assessment of climate change. In this paper possible relations with dynamical systems theory are given, in particular through bifurcation

  12. 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 f...

  13. 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 ...

  14. Time based room correction system for low frequencies using multiple loudspeakers

    DEFF Research Database (Denmark)

    Nielsen, Sofus Birkedal; Celestinos, Adrian

    2007-01-01

      Improving sound from loudspeakers in a room is a big issue. We are facing a rather complicated and serious problem, as one can experience very big variations in sound pressure level - up to 30 dB - in a room, especially at low frequencies. An innovative way of looking at the problem in the time...... from scratch for further development of CABS....

  15. 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

  16. Simulation of low frequency noise from a downwind wind turbine rotor

    DEFF Research Database (Denmark)

    Madsen Aagaard, Helge; Johansen, Jeppe; Sørensen, Niels N.

    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 ...

  17. Effects of low-frequency magnetic fields on the viability of yeast Saccharomyces cerevisiae

    Czech Academy of Sciences Publication Activity Database

    Novák, Jan; Strašák, Luděk; Fojt, Lukáš; Slaninová, I.; Vetterl, Vladimír

    2007-01-01

    Roč. 70, č. 1 (2007), s. 115-121 ISSN 1567-5394 R&D Projects: GA AV ČR(CZ) IAA4004404; GA AV ČR(CZ) IBS5004107 Institutional research plan: CEZ:AV0Z50040702 Keywords : low-frequency electromagnetic field * yeast * Saccharomyces cerevisiae Subject RIV: BO - Biophysics Impact factor: 2.992, year: 2007

  18. Extremely low-frequency magnetic fields and risk of childhood leukemia

    DEFF Research Database (Denmark)

    Schüz, Joachim; Dasenbrock, Clemens; Ravazzani, Paolo

    2016-01-01

    Exposure to extremely low-frequency magnetic fields (ELF-MF) was evaluated in an International Agency for Research on Cancer (IARC) Monographs as "possibly carcinogenic to humans" in 2001, based on increased childhood leukemia risk observed in epidemiological studies. We conducted a hazard assess...

  19. Setting the Frame: The Human Brain Activates a Basic Low-Frequency Network for Language Processing

    NARCIS (Netherlands)

    Lohmann, G.; Hoehl, S.; Brauer, J.; Danielmeier, C.; Bornkessel, I.D.; Bahlmann, J.; Turner, R.; Friederici, A.D.

    2010-01-01

    Low-frequency fluctuations (LFFs) are a major source of variation in fMRI data. This has been established in numerous experiments-particularly in the resting state. Here we investigate LFFs in a task-dependent setting. We hypothesized that LFFs may contain information about cognitive networks that

  20. Low-frequency electrostatic dust-modes in a non-uniform ...

    Indian Academy of Sciences (India)

    tures in Saturn's rings (revealed by Voyager space mission [8]). Angelis et al [6] investigated the propagation of ion-acoustic waves in a dusty plasma, in which a spatial inhomogeneity is created by a distribution of immobile dust particles [9]. They [6] applied their results in interpreting the low frequency noise enhancement.

  1. STABILITY OF PATTERNS OF BEHAVIOR IN THE BUTTERFLY TECHNIQUE OF THE ELITE SWIMMERS

    Directory of Open Access Journals (Sweden)

    Hugo Louro

    2010-09-01

    Full Text Available The purpose of this study was to find patterns in the butterfly swimming technique, with an adaptation of the Behavioral Observation System Tech. This, as an instrument for ad-hoc qualitative analysis, enables the study of the stability of the technical implementation. When used in the training of swimmers, analysis can reduce the variability of behavioral tuning swimming technique. Through the analysis of temporal patterns (T-pattern and a sequence of five cycles running at hand maximum speed, the behavior of four technical Portuguese elite swimmers, with a record of 259 alphanumeric codes and a total of 160 configurations, were studied. The structure of the original instrument, based on a mixed system of categories and formats Field, can record technical features, observed during the execution of hand cycles. The validity was ensured through the index of intra-observer reliability (95% and inter-observer accuracy (96%. To detect patterns in each swimmer, the Theme 5.0 software was used, which allowed to identify the stable structures of technical performance within a critical interval of time (p <0.05 - t-patterns. The patterns were different, adjusting to the characteristics of technical implementation of the swimmers. It was found that the swimmer can create settings with different levels of structure complexity, depending on the implementation of changes within the hand cycle. Variations of codes in each configuration obtained using the SOCTM, allowed determining the differences between swimmers. However, the records showed a clear behavioral similarity when comparing the result with a general pattern of the butterfly technique. The potential quality of this instrument seems to be important due to the patterns obtained from a temporal sequence

  2. Low-Frequency Pulsed Current Versus Kilohertz-Frequency Alternating Current: A Scoping Literature Review.

    Science.gov (United States)

    Vaz, Marco Aurélio; Frasson, Viviane Bortoluzzi

    2017-12-14

    To compare the effectiveness of low-frequency pulsed current versus kilohertz-frequency alternating current in terms of evoked force, discomfort level, current intensity, and muscle fatigability; to discuss the physiological mechanisms of each neuromuscular electrical stimulation type; and to determine if kilohertz-frequency alternating current is better than low-frequency pulsed current for clinical treatment. Articles were obtained from PubMed, Scopus, Cochrane Central Register of Controlled Trials, CINAHL, MEDLINE, and SPORTSDiscus databases using the terms Russian current or kilohertz current or alternating current or pulsed current or Aussie current and torque or discomfort or fatigue or current intensity, and through citation tracking up to July 2017. Two independent reviewers selected studies comparing the use of the 2 neuromuscular electrical stimulation currents. Studies describing maximal current intensity tolerated and the main effects of the 2 different current types on discomfort, muscle force, and fatigability were independently reviewed. Data were systematized according to (1) methodology; (2) electrical current characteristics; and (3) outcomes on discomfort level, evoked force, current intensity, and muscle fatigability. The search revealed 15 articles comparing the 2 current types. Kilohertz-frequency alternated current generated equal or less force, similar discomfort, similar current intensity for maximal tolerated neuromuscular electrical stimulation, and more fatigue compared with low-frequency pulsed current. Similar submaximal levels of evoked force revealed higher discomfort and current intensity for kilohertz-frequency alternated current compared with low-frequency pulsed current. Available evidence does not support the idea that kilohertz-frequency alternated current is better than low-frequency pulsed current for strength training and rehabilitation. Copyright © 2017 American Congress of Rehabilitation Medicine. Published by Elsevier

  3. Adiabatic perturbation theory for atoms and molecules in the low-frequency regime

    Science.gov (United States)

    Martiskainen, Hanna; Moiseyev, Nimrod

    2017-12-01

    There is an increasing interest in the photoinduced dynamics in the low frequency, ω, regime. The multiphoton absorptions by molecules in strong laser fields depend on the polarization of the laser and on the molecular structure. The unique properties of the interaction of atoms and molecules with lasers in the low-frequency regime imply new concepts and directions in strong-field light-matter interactions. Here we represent a perturbational approach for the calculations of the quasi-energy spectrum in the low-frequency regime, which avoids the construction of the Floquet operator with extremely large number of Floquet channels. The zero-order Hamiltonian in our perturbational approach is the adiabatic Hamiltonian where the atoms/molecules are exposed to a dc electric field rather than to ac-field. This is in the spirit of the first step in the Corkum three-step model. The second-order perturbation correction terms are obtained when i ℏ ω ∂/∂ τ serves as a perturbation and τ is a dimensionless variable. The second-order adiabatic perturbation scheme is found to be an excellent approach for calculating the ac-field Floquet solutions in our test case studies of a simple one-dimensional time-periodic model Hamiltonian. It is straightforward to implement the perturbation approach presented here for calculating atomic and molecular energy shifts (positions) due to the interaction with low-frequency ac-fields using high-level electronic structure methods. This is enabled since standard quantum chemistry packages allow the calculations of atomic and molecular energy shifts due to the interaction with dc-fields. In addition to the shift of the energy positions, the energy widths (inverse lifetimes) can be obtained at the same level of theory. These energy shifts are functions of the laser parameters (low frequency, intensity, and polarization).

  4. 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.

  5. Low-frequency instabilities of a warm plasma in a magnetic field

    International Nuclear Information System (INIS)

    Smith, D.F.; Hollweg, J.V.

    1977-01-01

    The marginal stability of a plasma carrying current along the static magnetic field with isotropic Maxwellian ions and isotropic Maxwellian electrons drifting relative to the ions is investigated. The complete electromagnetic dispersion relation is studied using numerical techniques; the electron sums are restricted to three terms which limits the analysis to frequencies much less than the electron gyro-frequency, but includes frequencies somewhat above the ion gyro-frequency. A 'kink-like' instability and an instability of the Alfven mode are found to have the lowest threshold drift velocities in most cases. In fact the threshold drift for the kink-like instability can be significantly less than the ion thermal speed. Electrostatic and electromagnetic ion-cyclotron instabilities are also found as well as the electro-static ion-acoustic instability. No instability of the fast magnetosonic mode was found. The stability analysis provides only threshold drift velocities and gives no information about growth rates. (author)

  6. Improved current-regulated delta modulator for reducing switching frequency and low-frequency current error in permanent magnet brushless AC drives \\ud

    OpenAIRE

    Wipasuramonton, P.; Zhu, Z.Q.; Howe, D.

    2005-01-01

    The conventional current-regulated delta modulator (CRDM) results in a high current ripple and a high switching frequency at low rotational speeds, and in low-frequency current harmonics, including a fundamental current error, at high rotational speeds. An improved current controller based on CRDM is proposed which introduces a zero-vector zone and a current error correction technique. It reduces the current ripple and switching frequency at low speeds, without the need to detect the back-emf...

  7. Robust design of decentralized power system stabilizers using meta-heuristic optimization techniques for multimachine systems

    OpenAIRE

    Jeevanandham Arumugam; Thanushkodi Gowder Keppana

    2009-01-01

    In this paper a classical lead-lag power system stabilizer is used for demonstration. The stabilizer parameters are selected in such a manner to damp the rotor oscillations. The problem of selecting the stabilizer parameters is converted to a simple optimization problem with an eigen value based objective function and it is proposed to employ simulated annealing and particle swarm optimization for solving the optimization problem. The objective function allows the selection of the stabilizer ...

  8. Interface studies of N2 plasma-treated ZnSnO nanowire transistors using low-frequency noise measurements

    International Nuclear Information System (INIS)

    Kim, Seongmin; Janes, David B; Kim, Hwansoo; Ju, Sanghyun

    2013-01-01

    Due to the large surface-to-volume ratio of nanowires, the quality of nanowire–insulator interfaces as well as the nanowire surface characteristics significantly influence the electrical characteristics of nanowire transistors (NWTs). To improve the electrical characteristics by doping or post-processing, it is important to evaluate the interface characteristics and stability of NWTs. In this study, we have synthesized ZnSnO (ZTO) nanowires using the chemical vapor deposition method, characterized the composition of ZTO nanowires using x-ray photoelectron spectroscopy, and fabricated ZTO NWTs. We have characterized the current–voltage characteristics and low-frequency noise of ZTO NWTs in order to investigate the effects of interface states on subthreshold slope (SS) and the noise before and after N 2 plasma treatments. The as-fabricated device exhibited a SS of 0.29 V/dec and Hooge parameter of ∼1.20 × 10 −2 . Upon N 2 plasma treatment with N 2 gas flow rate of 40 sccm (20 sccm), the SS improved to 0.12 V/dec (0.21 V/dec) and the Hooge parameter decreased to ∼4.99 × 10 −3 (8.14 × 10 −3 ). The interface trap densities inferred from both SS and low-frequency noise decrease upon plasma treatment, with the highest flow rate yielding the smallest trap density. These results demonstrate that the N 2 plasma treatment decreases the interface trap states and defects on ZTO nanowires, thereby enabling the fabrication of high-quality nanowire interfaces. (paper)

  9. OBTAINING HYSTERESIS LOOPS AT LOW FREQUENCY FOR CHARACTERIZATION OF MATERIALS TO BE USED IN BIOMEDICAL APPLICATIONS

    Directory of Open Access Journals (Sweden)

    Atika Arshad

    2015-05-01

    Full Text Available The promising development of magnetic sensors in biomedical field demands an appropriate level of understanding of the magnetic properties of the materials used in their fabrication. To date only few of the types of magnetic materials are encountered where their magnetic properties, characterization techniques and magnetization behavior are yet to be explored more suitably in the light of their applications. This research work studies the characterization of materials by using a cost effective and simple circuit consisting of inductive transducer and an OP-AMP as a voltage integrator. In this approach the circuit was simulated using PSPICE and experiments have been conducted to achieve the desired results. The simulation and experimental results are obtained for three test materials namely iron, steel and plastic. The novelty lies in applying the simple circuit for material testing and characterization via obtaining simulation results and validating these results through experiment. The magnetic properties in low external magnetic field are studied with materials under test. The magnetization effect of a magneto-inductive sensor is detected in low frequency range for different magnetic core materials. The results have shown magnetization behaviour of magnetic materials due to the variation of permeability and magnetism. The resulted hysteresis loops appeared to have different shapes for different materials. The magnetic hysteresis loop found for iron core demonstrated a bigger coercive force and larger reversals of magnetism than these of steel core, thus obtaining its magnetic saturation at a larger magnetic field strength. The shape of the hysteresis loop itself is found to be varying upon the nature of the material in use. The resulted magnetization behaviors of the materials proved their possible applicability for use in sensing devices. The key concern of this work is found upon selecting the appropriate magnetic materials at the desired

  10. Design of Weighted Wide Area Damping Controller (WWADC Based PSS for Damping Inter-Area Low Frequency Oscillations

    Directory of Open Access Journals (Sweden)

    Saleh M. Bamasak

    2017-09-01

    Full Text Available Wide Area Measurement System (WAMS can extend and effectively improve the power system stabilizers (PSS capability in damping the inter-area low frequency oscillations in interconnected bulk power systems. This paper proposes the implementation of Weighted Wide Area Damping Controller (WWADC in which weighted factors are introduced for each remote feedback signals. Modal analysis approach is implemented for the purpose of identifying the optimal location as well as the input signals’ optimal combination of WWADC. Based on the linearized model, Differential Evolution (DE algorithm is applied to search for optimal controller parameters and optimal weighted factors. The successful application of the proposed approach is achieved in two power networks; the two-area 4-machine system and the IEEE-39 bus 10-machine system. The analysis of the eigenvalue and non-linear time domain simulations indicate that damping the inter-area oscillations and improving the system stability irrespective of the severity and the location of the disturbances can be effectively achieved by WADC

  11. Low frequency acoustic properties of bilayer membrane acoustic metamaterial with magnetic oscillator

    Directory of Open Access Journals (Sweden)

    Nansha Gao

    2017-07-01

    Full Text Available A bilayer membrane acoustic metamaterial was proposed to overcome the influence of the mass law on traditional acoustic materials and obtain a lightweight thin-layer structure that can effectively isolate low frequency noise. The finite element analysis (FEA results agree well with the experimental results. It is proved that the sound transmission losses (STLs of the proposed structures are higher than those of same surface density acoustic materials. The introduction of the magnetic mass block is different from the traditional design method, in which only a passive mass block is fixed on the membrane. The magnetic force will cause tension in the membrane, increase membrane prestress, and improve overall structural stiffness. The effects of the geometry size on the STLs are discussed in detail. The kind of method presented in this paper can provide a new means for engineering noise control. Keywords: Bilayer membrane acoustic metamaterial, Low frequency sound insulation, Sound transmission loss, Magnet oscillator

  12. Low-frequency sonophoresis: a noninvasive method of drug delivery and diagnostics.

    Science.gov (United States)

    Mitragotri, S; Kost, J

    2000-01-01

    Transdermal drug delivery offers an attractive alternative to injections and oral medications. However, applications of transdermal drug delivery are limited to only a few drugs as a result of low skin permeability. Application of low-frequency ultrasound enhances skin permeability, a phenomenon referred to as low-frequency sonophoresis. In this method, a short application of ultrasound is used to permeabilize skin for a prolonged period of time. During this period, ultrasonically permeabilized skin may be utilized for drug delivery. In addition, a sample of interstitial fluid or its components may be extracted through permeabilized skin for diagnostic applications. In this paper, we report our in vivo studies that demonstrate the principles of both of these concepts. Detailed studies on drug delivery are performed using inulin and mannitol as model drugs. Studies on diagnostics are performed using glucose as a model analyte. Applications of this technology to drug delivery and diagnostics are discussed.

  13. A low-frequency vibration energy harvester based on diamagnetic levitation

    Science.gov (United States)

    Kono, Yuta; Masuda, Arata; Yuan, Fuh-Gwo

    2017-04-01

    This article presents 3-degree-of-freedom theoretical modeling and analysis of a low-frequency vibration energy harvester based on diamagnetic levitation. In recent years, although much attention has been placed on vibration energy harvesting technologies, few harvesters still can operate efficiently at extremely low frequencies in spite of large potential demand in the field of structural health monitoring and wearable applications. As one of the earliest works, Liu, Yuan and Palagummi proposed vertical and horizontal diamagnetic levitation systems as vibration energy harvesters with low resonant frequencies. This study aims to pursue further improvement along this direction, in terms of expanding maximum amplitude and enhancing the flexibility of the operation direction for broader application fields by introducing a new topology of the levitation system.

  14. Low frequency electric and magnetic fields - effect on fertility and fetal development

    International Nuclear Information System (INIS)

    Thommesen, G.

    1989-01-01

    The epidemiological as well as the experimental data are still inconclusive. Inconsistencies within and between research reports make it impossible to state whether, or under what circumstances, low frequency fields may be harmful to reproduction by reducing fertility or by causing fetal malformations or death. The data indicate, however, that a certain care should be exercised in the case of NMR diagnostic imaging, industrial magnetic field exposure, and paramedical pulsed magnetic field therapy on women who might be expected to be in the first trimester of pregnancy, particularly in the unindentified initial phase. Work in connection with visual display units, living in the neighbourhood of overhead high-voltage powerlines, or other every-day sources of exposure to low frequency fields seem, however, to be an insignificant or non-existent threat to an unborn life. 147 refs

  15. 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.

  16. Coupled electromechanical modeling of piezoelectric disc transducers for low-frequency ultrasonic collimated beam generation

    Science.gov (United States)

    Chillara, Vamshi Krishna; Pantea, Cristian; Sinha, Dipen N.

    2017-04-01

    Low-frequency ultrasonic collimated beam generation from radial modes of piezoelectric disc transducers is studied using a coupled electromechanical finite element approach. First, resonance and vibration characteristics of the radial modes of the disc transducers are obtained using an eigenfrequency analysis. The vibration patterns obtained from numerical simulation are compared with those obtained from experiments and are in good agreement. Next, ultrasonic beam profiles in water generated from the radial modes of a piezo-disc are studied. It was found that a free piezo-disc generates a Bessel-beam with multiple side-lobes. In contrast, clamping the lateral edges of the piezo-disc results in a well-collimated central beam with reduced side-lobes. This provides a novel transducer design for low-frequency collimated beam generation for imaging through highly attenuating materials

  17. MD1271: Effect of low frequency noise on the evolution of the emittance and halo population

    CERN Document Server

    Fitterer, Miriam; Valishev, Alexander; Bruce, Roderik; Hofle, Wolfgang; Hostettler, Michi; Papadopoulou, Parthena Stefania; Papotti, Giulia; Papaphilippou, Yannis; Pellegrini, Dario; Trad, Georges; Valuch, Daniel; Valentino, Gianluca; Wagner, Joschka; Cai, Xu; CERN. Geneva. ATS Department

    2018-01-01

    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. This MD conducted on 24.08.2016 follows a previous MD on 05.11.2015/06.11.2015

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

    International Nuclear Information System (INIS)

    Hwang, Y.S.; Okuda, H.

    1989-02-01

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

  19. Modeling of Low Frequency MHD Induced Beam Ion Transport In NSTX

    International Nuclear Information System (INIS)

    Gorelenkov, N.N.; Medley, S.S.

    2004-01-01

    Beam ion transport in the presence of low frequency MHD activity in National Spherical Tokamak Experiment (NSTX) plasma is modeled numerically and analyzed theoretically in order to understand basic underlying physical mechanisms responsible for the observed fast ion redistribution and losses. Numerical modeling of the beam ions flux into the NPA in NSTX shows that after the onset of low frequency MHD activity high energy part of beam ion distribution, E b > 40keV, is redistributed radially due to stochastic diffusion. Such diffusion is caused by high order harmonics of the transit frequency resonance overlap in the phase space. Large drift orbit radial width induces such high order resonances. Characteristic confinement time is deduced from the measured NPA energy spectrum and is typically ∼ 4msec. Considered MHD activity may induce losses on the order of 10% at the internal magnetic field perturbation (delta)B/B = Ο (10 -3 ), which is comparable to the prompt orbit losses

  20. 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.

  1. Influence of a Low Frequency Electromagnetic field in the Microbial Flora of a Mango Nectar

    Directory of Open Access Journals (Sweden)

    Yaima Torres-Ferrer

    2016-07-01

    Full Text Available In this work an evaluation of the influence of a low frequency electromagnetic field on the microbial flora of mango nectar in order to study their behavior after each treatment is presented. Experiments are designed and implemented with one factor in which the influence of a low frequency electromagnetic field is determined at various levels (0, 90, 95 Gauss, in a homogeneous and completely randomized unit on the microbial load of nectar mango. Magnetic conditioning device used in the tests with approximate average values of magnetic induction of 90 to 95 characterized Gauss. It is established that the application of the magnetic field in the range of values used (90, 95 Gauss causes a stimulation in the values of total count of mesophilic, leading to increased microbial load present in mango nectar studied.

  2. Effect of Seafloor Current on low Frequency Seismic Noise Observed in the Seafloor

    Science.gov (United States)

    Araki, E.; Kawaguchi, K.; Matsumoto, H.; Sugioka, H.; Ito, A.; Suetsugu, D.; Kaneda, Y.

    2008-12-01

    Seismometer installed in the seafloor is affected by water flow in the seafloor. Such effect is significant especially for low frequencies below 0.1 Hz. Burial of seismometer, or installation using deep borehole, is suggested to reduce effect of seafloor current. There are a number of examples showing burial in the seafloor significantly reduce low frequency seismic noise. The reason for such improvement is explained by improved seafloor coupling of seismometer and reduction of tilting effect due to force from water flow by minimizing area of seismometer exposed in the water flow. Another mechanism is that turbulence in the seafloor current impose load on the seafloor that deforms and tilt the seafloor. There are few example, though, to demonstrate a model which explain relationship between speed of seafloor water flow and expected low frequency seismic noise quantitatively. We are currently planning to build seafloor broadband seismic network off Kii Peninsula, Honshu, Japan, where recurrence of magnitude 8 class earthquake is expected in the future. In such location, a network of broadband seismometer will be deployed in the seafloor. In order to design for optimum low frequency performance of seismometers, we conducted test installation of three broadband seismometers (Guralp CMG3T) closely, within 150m distances from each other. The test observation was conducted in the Kumano Basin, from late December, 2007 to early February, 2008. The one cylindrical seismometer was buried in the seafloor, while the other two sit on the seafloor. The seafloor seismometers were different in that the one had grid type anchor and the other had wide planar anchor. Difference in these arrangements was intended to find optimum design of seismometer package and installation method. Differential pressure gauges, a seafloor current meter, thermometers were installed to monitor environmental change during the test observation. Observation data from deployed broadband seismometers

  3. 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...

  4. Low-frequency band gap mechanism of torsional vibration of lightweight elastic metamaterial shafts

    Science.gov (United States)

    Li, Lixia; Cai, Anjiang

    2016-07-01

    In this paper, the low-frequency band gap mechanism of torsional vibration is investigated for a kind of light elastic metamaterial (EM) shafts architecture comprised of a radial double-period element periodically as locally resonant oscillators with low frequency property. The dispersion relations are calculated by a method combining the transfer matrix and a lumped-mass method. The theoretical results agree well with finite method simulations, independent of the density of the hard material ring. The effects of the material parameters on the band gaps are further explored numerically. Our results show that in contrast to the traditional EM shaft, the weight of our proposed EM shaft can be reduced by 27% in the same band gap range while the vibration attenuation is kept unchanged, which is very convenient to instruct the potential engineering applications. Finally, the band edge frequencies of the lower band gaps for this light EM shaft are expressed analytically using physical heuristic models.

  5. Identification of low-frequency variants associated with gout and serum uric acid levels

    DEFF Research Database (Denmark)

    Sulem, Patrick; Gudbjartsson, Daniel F; Walters, G Bragi

    2011-01-01

    ,506 individuals for whom serum uric acid measurements were available. We identified a low-frequency missense variant (c.1580C>G) in ALDH16A1 associated with gout (OR = 3.12, P = 1.5 × 10(-16), at-risk allele frequency = 0.019) and serum uric acid levels (effect = 0.36 s.d., P = 4.5 × 10(-21)). We confirmed.......48 s.d., P = 4.5 × 10(-16)). This variant is close to a common variant previously associated with serum uric acid levels. This work illustrates how whole-genome sequencing data allow the detection of associations between low-frequency variants and complex traits....

  6. 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.

  7. 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

    of hours, taking into account the spectral correlation between different wind turbines. The modelling is supported by measurements from two large wind farms, namely Nysted and Horns Rev. Measurements from individual wind turbines and meteorological masts are used. Finally, the models are integrated...... 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...... is an improvement, but the effect is relatively small. The effect of including the low frequency components in the model is much more significant. Therefore, that aggregated model is useful in the power system planning and operation, e.g. regarding load following and regulation. Copyright © 2009 John Wiley & Sons...

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

    Directory of Open Access Journals (Sweden)

    Qiaoling YUAN

    2014-05-01

    Full Text Available As a resolution for air pressure control challenges in ultra-low frequency modal testing suspension systems, an incremental PID control algorithm with dead band is applied to achieve high-precision pressure control. We also develop a set of independent hardware and software systems for high-precision pressure control solutions. Taking control system versatility, scalability, reliability, and other aspects into considerations, a two-level communication employing Ethernet and CAN bus, is adopted to complete such tasks as data exchange between the IPC, the main board and the control board ,and the pressure control. Furthermore, we build a single set of ultra-low frequency modal testing suspension system and complete pressure control experiments, which achieve the desired results and thus confirm that the high-precision pressure control subsystem is reasonable and reliable.

  9. Low-frequency analogue Hawking radiation: The Bogoliubov-de Gennes model

    Science.gov (United States)

    Coutant, Antonin; Weinfurtner, Silke

    2018-01-01

    We analytically study the low-frequency properties of the analogue Hawking effect in Bose-Einstein condensates. We show that in one-dimensional flows displaying an analogue horizon, the Hawking effect is dominant in the low-frequency regime. This happens despite nonvanishing grey-body factors, that is, the coupling of the Hawking mode and its partner to the mode propagating with the flow. To show this, we obtained analytical expressions for the scattering coefficients, in general flows and taking into account the full Bogoliubov dispersion relation. We discuss the obtained expressions for the grey-body factors. In particular, we show that they can be significantly decreased if the flow obeys a conformal coupling condition. We argue that in the presence of a small but non-zero temperature, reducing grey-body factors greatly facilitates the observation of entanglement, that is, establishing that the state of the Hawking mode and its partner is non-separable.

  10. 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.

  11. Resonant scattering of energetic electrons by unusual low-frequency hiss

    Science.gov (United States)

    Ni, Binbin; Li, Wen; Thorne, Richard M.; Bortnik, Jacob; Ma, Qianli; Chen, Lunjin; Kletzing, Craig A.; Kurth, William S.; Hospodarsky, George B.; Reeves, Geoffrey D.; Spence, Harlan E.; Bernard Blake, J.; Fennell, Joseph F.; Claudepierre, Seth G.

    2014-03-01

    We quantify the resonant scattering effects of the unusual low-frequency dawnside plasmaspheric hiss observed on 30 September 2012 by the Van Allen Probes. In contrast to normal (~100-2000 Hz) hiss emissions, this unusual hiss event contained most of its wave power at ~20-200 Hz. Compared to the scattering by normal hiss, the unusual hiss scattering speeds up the loss of ~50-200 keV electrons and produces more pronounced pancake distributions of ~50-100 keV electrons. It is demonstrated that such unusual low-frequency hiss, even with a duration of a couple of hours, plays a particularly important role in the decay and loss process of energetic electrons, resulting in shorter electron lifetimes for ~50-400 keV electrons than normal hiss, and should be carefully incorporated into global modeling of radiation belt electron dynamics during periods of intense injections.

  12. 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.

  13. Suppression of low-frequency charge noise in gates-defined GaAs quantum dots

    International Nuclear Information System (INIS)

    You, Jie; Li, Hai-Ou; Wang, Ke; Cao, Gang; Song, Xiang-Xiang; Xiao, Ming; Guo, Guo-Ping

    2015-01-01

    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

  14. Low-frequency flux noise in YBCO dc SQUIDs cooled in static magnetic fields

    International Nuclear Information System (INIS)

    Sager, M.P.; Bindslev Hansen, J.; Petersen, P.R.E.; Holst, T.; Shen, Y.Q.

    1999-01-01

    The low-frequency flux noise in bicrystal and step-edge YBa 2 Cu 3 O x dc SQUIDs has been investigated. The width, w, of the superconducting strips forming the SQUID frame was varied from 4 to 42 μm. The SQUIDs were cooled in static magnetic fields up to 150 μT. Two types of low-frequency noise dominated, namely 1/f-like noise and random telegraph noise giving a Lorentzian frequency spectrum. The 1/f noise performance of the w = 4, 6 and 7 μm SQUIDs was almost identical, while the SQUIDs with w = 22 and 42 μm showed an order of magnitude higher noise level. Our analysis of the data suggests an exponential increase of the 1/f noise versus the cooling field, exhibiting a characteristic magnetic field around 40 μT. (author)

  15. Infrasound and low frequency noise from wind turbines: exposure and health effects

    Energy Technology Data Exchange (ETDEWEB)

    Bolin, Karl [Marcus Wallenberg Laboratory, Department of Aeronautical and Vehicle Engineering, Kungliga Tekniska Hoegskolan (Sweden); Bluhm, Goesta; Nilsson, Mats E [Institute of Environmental Medicine, Karolinska Institutet (Sweden); Eriksson, Gabriella, E-mail: kbolin@kth.se [Swedish National Road and Transport Research Institute and Linkoeping University (Sweden)

    2011-07-15

    Wind turbines emit low frequency noise (LFN) and large turbines generally generate more LFN than small turbines. The dominant source of LFN is the interaction between incoming turbulence and the blades. Measurements suggest that indoor levels of LFN in dwellings typically are within recommended guideline values, provided that the outdoor level does not exceed corresponding guidelines for facade exposure. Three cross-sectional questionnaire studies show that annoyance from wind turbine noise is related to the immission level, but several explanations other than low frequency noise are probable. A statistically significant association between noise levels and self-reported sleep disturbance was found in two of the three studies. It has been suggested that LFN from wind turbines causes other, and more serious, health problems, but empirical support for these claims is lacking.

  16. 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.

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

    Science.gov (United States)

    Yu, Yueyue; Cai, Ming; Ren, Rongcai

    2017-08-01

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

  18. Computational Electromagnetic Studies for Low-Frequency Compensation of the Reflector Impulse-radiating Antenna

    Science.gov (United States)

    2015-03-26

    can speed up simulations by employing a short-duration Gaussian pulse that may reduce the overall number of time steps required. How- ever, this...and structures that tend to store some energy, reducing the DC and low frequency content can speed up the simulation, as the field energy in the domain...these images, 56 Figure 4.6. Boresight gain of the standard IRA designs. the sidelobes are also lower in amplitude. This agrees with the findings of Tyo

  19. Low-frequency dielectric dispersion of brain tissue due to electrically long neurites

    Science.gov (United States)

    Monai, Hiromu; Inoue, Masashi; Miyakawa, Hiroyoshi; Aonishi, Toru

    2012-12-01

    The dielectric properties of brain tissue are important for understanding how neural activity is related to local field potentials and electroencephalograms. It is known that the permittivity of brain tissue exhibits strong frequency dependence (dispersion) and that the permittivity is very large in the low-frequency region. However, little is known with regard to the cause of the large permittivity in the low-frequency region. Here, we postulate that the dielectric properties of brain tissue can be partially accounted for by assuming that neurites are of sufficient length to be “electrically long.” To test this idea, we consider a model in which a neurite is treated as a long, narrow body, and it is subjected to a stimulus created by electrodes situated in the region external to it. With regard to this electric stimulus, the neurite can be treated as a passive cable. Assuming adequate symmetry so that the tissue packed with multiple cables is equivalent to an isolated system consisting of a single cable and a surrounding extracellular resistive medium, we analytically calculate the extracellular potential of the tissue in response to such an externally created alternating-current electric field using a Green's function that we obtained previously. Our results show that brain tissue modeled by such a cable existing within a purely resistive extracellular medium exhibits a large effective permittivity in the low-frequency region. Moreover, we obtain results suggesting that an extremely large low-frequency permittivity can coexist with weak low-pass filter characteristics in brain tissue.

  20. Connecting structural relaxation with the low frequency modes in a hard-sphere colloidal glass.

    Science.gov (United States)

    Ghosh, Antina; Chikkadi, Vijayakumar; Schall, Peter; Bonn, Daniel

    2011-10-28

    Structural relaxation in hard-sphere colloidal glasses has been studied using confocal microscopy. The motion of individual particles is followed over long time scales to detect the rearranging regions in the system. We have used normal mode analysis to understand the origin of the rearranging regions. The low-frequency modes, obtained over short time scales, show strong spatial correlation with the rearrangements that happen on long time scales.

  1. [Effect of extremely low frequency magnetic field on glutathione in rat muscles].

    Science.gov (United States)

    Ciejka, Elzbieta; Jakubowska, Ewa; Zelechowska, Paulina; Huk-Kolega, Halina; Kowalczyk, Agata; Goraca, Anna

    2014-01-01

    Free radicals (FR) are atoms, molecules or their fragments. Their excess leads to the development of oxidizing stress, the cause of many neoplastic, neurodegenerative and inflammatory diseases, and aging of the organism. Industrial pollution, tobacco smoke, ionizing radiation, ultrasound and magnetic field are the major FR exogenous sources. The low frequency magnetic field is still more commonly applied in the physical therapy. The aim of the presented study was to evaluate the effect of extremely low frequency magnetic field used in the magnetotherapy on the level of total glutathione, oxidized and reduced, and the redox state of the skeletal muscle cells, depending on the duration of exposure to magnetic field. The male rats, weight of 280-300 g, were randomly devided into 3 experimental groups: controls (group I) and treatment groups exposed to extremely low frequency magnetic field (ELF-MF) (group II exposed to 40 Hz, 7 mT for 0.5 h/day for 14 days and group III exposed to 40 Hz, 7 mT for 1 h/day for 14 days). Control rats were kept in a separate room not exposed to extremely low frequency magnetic field. Immediately after the last exposure, part of muscles was taken under pentobarbital anesthesia. Total glutathione, oxidized and reduced, and the redox state in the muscle tissue of animals were determined after exposure to magnetic fields. Exposure to low magnetic field: 40 Hz, 7 mT for 30 min/day and 60 min/day for 2 weeks significantly increased the total glutathione levels in the skeletal muscle compared to the control group (p magnetic therapy plays an important role in the development of adaptive mechanisms responsible for maintaining the oxidation-reduction balance in the body and depends on exposure duration.

  2. Numerical modelling of complex resistivity effects on a homogeneous half-space at low frequencies

    DEFF Research Database (Denmark)

    Ingeman-Nielsen, Thomas; Baumgartner, François

    2006-01-01

    half-space with CR effects and study some aspects of the complex coupling function. We advocate the use of the CR based coupling function in the interpretation process, in order to obtain a better understanding of the physical processes involved in CR effects. Application of the model to real field...... that the use of a second Cole-Cole model to describe EM coupling may corrupt the interpretation of the low frequency dispersion, even when only the normal range of frequencies (...

  3. Intermittency in low frequency current oscillations in semi-insulating GaAs

    CERN Document Server

    Samuilov, V; Cenys, A; Kyritsi, K G; Anagnostopoulos, A N; Bleris, G L

    2003-01-01

    Spontaneous low frequency current oscillations were observed in semi-insulating crystalline GaAs. If the value of the applied voltage U was increased, a crisis induced intermittency was observed. The time intervals between successive transitions were measured. For values of the control parameter U larger than a critical value two interacting chaotic subattractors were observed. The average time intervals are scaling with the control parameter with a critical exponent very close to -1/2.

  4. Effect of porosity and pore morphology on the low-frequency ...

    Indian Academy of Sciences (India)

    Effect of porosity and pore morphology on the low-frequency dielectric response in sintered. ZrO2–8 mol% Y2O3 ceramic compact. D SEN1, T MAHATA2, A K PATRA1, S MAZUMDER1 and B P SHARMA2. 1Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400 085, India. 2Powder Metallurgy Division ...

  5. Peculiarities of low-frequency dielectric spectra and domain wall motion in gadolinium molybdate

    International Nuclear Information System (INIS)

    Galiyarova, N.M.; Gorin, S.V.; Dontsova, L.I.; Shil'nikov, A.V.; Shuvalov, L.A.

    1994-01-01

    Low-frequency Debye dispersion of dielectric permeability in GMO with the low values of high-frequency limit ε ∞ was investigated in a wide temperature range as well as in fields of variable amplitude. The features of domain boundaries motion were studied at the partial repolarization in monopolar P-pulsed fields. The model of cooperationrelaxation motion brifing in parallel with positive to negative contribution to polarization that explained the low values of ε ∞ was suggested

  6. 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...... of the dampers is derived based on a continuous approximation of the damper distribution. The dampers are optimized with respect to the point-wise distribution of mass ratio, natural frequency, and damping ratio....

  7. Low frequency complex dielectric (conductivity) response of dilute clay suspensions: Modeling and experiments.

    Science.gov (United States)

    Hou, Chang-Yu; Feng, Ling; Seleznev, Nikita; Freed, Denise E

    2018-04-11

    In this work, we establish an effective medium model to describe the low-frequency complex dielectric (conductivity) dispersion of dilute clay suspensions. We use previously obtained low-frequency polarization coefficients for a charged oblate spheroidal particle immersed in an electrolyte as the building block for the Maxwell Garnett mixing formula to model the dilute clay suspension. The complex conductivity phase dispersion exhibits a near-resonance peak when the clay grains have a narrow size distribution. The peak frequency is associated with the size distribution as well as the shape of clay grains and is often referred to as the characteristic frequency. In contrast, if the size of the clay grains has a broad distribution, the phase peak is broadened and can disappear into the background of the canonical phase response of the brine. To benchmark our model, the low-frequency dispersion of the complex conductivity of dilute clay suspensions is measured using a four-point impedance measurement, which can be reliably calibrated in the frequency range between 0.1 Hz and 10 kHz. By using a minimal number of fitting parameters when reliable information is available as input for the model and carefully examining the issue of potential over-fitting, we found that our model can be used to fit the measured dispersion of the complex conductivity with reasonable parameters. The good match between the modeled and experimental complex conductivity dispersion allows us to argue that our simplified model captures the essential physics for describing the low-frequency dispersion of the complex conductivity of dilute clay suspensions. Copyright © 2018 Elsevier Inc. All rights reserved.

  8. Acute neuroprotective effects of extremely low-frequency electromagnetic fields after traumatic brain injury in rats.

    Science.gov (United States)

    Yang, Yang; Li, Ling; Wang, Yan-Gang; Fei, Zhou; Zhong, Jun; Wei, Li-Zhou; Long, Qian-Fa; Liu, Wei-Ping

    2012-05-10

    Traumatic brain injury commonly has a result of a short window of opportunity between the period of initial brain injury and secondary brain injury, which provides protective strategies and can reduce damages of brain due to secondary brain injury. Previous studies have reported neuroprotective effects of extremely low-frequency electromagnetic fields. However, the effects of extremely low-frequency electromagnetic fields on neural damage after traumatic brain injury have not been reported yet. The present study aims to investigate effects of extremely low-frequency electromagnetic fields on neuroprotection after traumatic brain injury. Male Sprague-Dawley rats were used for the model of lateral fluid percussion injury, which were placed in non-electromagnetic fields and 15 Hz (Hertz) electromagnetic fields with intensities of 1 G (Gauss), 3 G and 5 G. At various time points (ranging from 0.5 to 30 h) after lateral fluid percussion injury, rats were treated with kainic acid (administered by intraperitoneal injection) to induce apoptosis in hippocampal cells. The results were as follows: (1) the expression of hypoxia-inducible factor-1α was dramatically decreased during the neuroprotective time window. (2) The kainic acid-induced apoptosis in the hippocampus was significantly decreased in rats exposed to electromagnetic fields. (3) Electromagnetic fields exposure shortened the escape time in water maze test. (4) Electromagnetic fields exposure accelerated the recovery of the blood-brain barrier after brain injury. These findings revealed that extremely low-frequency electromagnetic fields significantly prolong the window of opportunity for brain protection and enhance the intensity of neuroprotection after traumatic brain injury. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

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

    Energy Technology Data Exchange (ETDEWEB)

    Moradi, Afshin, E-mail: a.moradi@kut.ac.ir [Department of Engineering Physics, Kermanshah University of Technology, Kermanshah (Iran, Islamic Republic of)

    2016-08-15

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

  10. Study of the low-frequency Raman scattering in NaNbO sub 3 crystal

    CERN Document Server

    Bouziane, E; Ayadi, M

    2003-01-01

    The Raman scattering spectrum of the sodium niobate crystal, in both P and R phases, has been investigated from room temperature up to 440 sup d eg C. The dependence of the low-frequency (LF) spectrum clearly reveals, for the first time, over a wide temperature range, the presence of a strong quasi-elastic scattering below a LF zone centre phonon. The phase transition mechanism is discussed, considering an order-disorder process induced by the relaxation of the Nb ions.

  11. Stabilization

    Directory of Open Access Journals (Sweden)

    Muhammad H. Al-Malack

    2016-07-01

    Full Text Available Fuel oil flyash (FFA produced in power and water desalination plants firing crude oils in the Kingdom of Saudi Arabia is being disposed in landfills, which increases the burden on the environment, therefore, FFA utilization must be encouraged. In the current research, the effect of adding FFA on the engineering properties of two indigenous soils, namely sand and marl, was investigated. FFA was added at concentrations of 5%, 10% and 15% to both soils with and without the addition of Portland cement. Mixtures of the stabilized soils were thoroughly evaluated using compaction, California Bearing Ratio (CBR, unconfined compressive strength (USC and durability tests. Results of these tests indicated that stabilized sand mixtures could not attain the ACI strength requirements. However, marl was found to satisfy the ACI strength requirement when only 5% of FFA was added together with 5% of cement. When the FFA was increased to 10% and 15%, the mixture’s strength was found to decrease to values below the ACI requirements. Results of the Toxicity Characteristics Leaching Procedure (TCLP, which was performed on samples that passed the ACI requirements, indicated that FFA must be cautiously used in soil stabilization.

  12. 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.

  13. Skin permeability enhancement by low frequency sonophoresis: lipid extraction and transport pathways.

    Science.gov (United States)

    Alvarez-Román, R; Merino, G; Kalia, Y N; Naik, A; Guy, R H

    2003-06-01

    The objective of this study was to shed light on the mechanism(s) by which low-frequency ultrasound (20 KHz) enhances the permeability of the skin. The physical effects on the barrier and the transport pathway, in particular, were examined. The amount of lipid removed from the intercellular domains of the stratum corneum following sonophoresis was determined by infrared spectroscopy. Transport of the fluorescent probes nile red and calcein, under the influence of ultrasound, was evaluated by laser-scanning confocal microscopy. The results were compared with the appropriate passive control data and with data obtained from experiments in which the skin was exposed simply to the thermal effects induced by ultrasound treatment. A significant fraction ( approximately 30%) of the intercellular lipids of the stratum corneum, which are principally responsible for skin barrier function, were removed during the application of low-frequency sonophoresis. Although the confocal images from the nile red experiments were not particularly informative, ultrasound clearly and significantly (again, relative to the corresponding controls) facilitated transport of the hydrophilic calcein via discrete permeabilized regions, whereas other areas of the barrier were apparently unaffected. Lipid removal from the stratum corneum is implicated as a factor contributing the observed permeation enhancement effects of low-frequency ultrasound. However, microscopic observations imply that sonophoresis induces localized (aqueous?) permeation pathways at discrete sites. Copyright 2003 Wiley-Liss, Inc.

  14. Source of low frequency modulation of ENSO amplitude in a CGCM

    Energy Technology Data Exchange (ETDEWEB)

    Moon, Byung-Kwon [Chonbuk National University, Division of Science Education/Institute of Science Education, Jeonju (Korea); Yeh, Sang-Wook [Korea Ocean Research and Development Institute, Ansan (Korea); Dewitte, Boris [Laboratoire d' Etude en Geophysique et Oceanographie Spatiale, Toulouse (France); Jhun, Jong-Ghap [Seoul National University, School of Earth and Environmental Sciences, Seoul (Korea); Kang, In-Sik [Seoul National University, Climate Environment System Research Center (CES), Seoul (Korea)

    2007-07-15

    We study the relationship between changes in equatorial stratification and low frequency El Nino/Southern Oscillation (ENSO) amplitude modulation in a coupled general circulation model (CGCM) that uses an anomaly coupling strategy to prevent climate drifts in the mean state. The stratification is intensified at upper levels in the western and central equatorial Pacific during periods of high ENSO amplitude. Furthermore, changes in equatorial stratification are connected with subsurface temperature anomalies originating from the central south tropical Pacific. The correlation analysis of ocean temperature anomalies against an index for the ENSO modulation supports the hypothesis of the existence of an oceanic ''tunnel'' that connects the south tropical Pacific to the equatorial wave guide. Further analysis of the wind stress projection coefficient onto the oceanic baroclinic modes suggests that the low frequency modulation of ENSO amplitude is associated with a significant contribution of higher-order modes in the western and central equatorial Pacific. In the light of these results, we suggest that, in the CGCM, change in the baroclinic mode energy distribution associated with low frequency ENSO amplitude modulation have its source in the central south tropical Pacific. (orig.)

  15. Low-Frequency Ultrasound Therapy in Combination Treatment of Patients with Type 2 Diabetes Mellitus

    Directory of Open Access Journals (Sweden)

    YE.E. LAVRINENKO

    2013-04-01

    Results. The beginning of therapeutic effect was observed after 2 procedures of the ultrasound exposure. The maximum effect is appeared after 8–10 treatment sessions. The positive dynamics of complex treatment is improving the general state of health, a disappearance of asthenization, and a decrease in the symptoms of cardiovascular disorders, achieving faster compensation of carbohydrate metabolism. The course of treatment contributed to the hyperglycemia reduction in patients with newly detected type 2 DM. After ultrasound treatment, the authors noted a positive dynamics of clinical symptoms: an improvement of the general health status, a decrease in fatigue, an improvement of psycho-emotional indices, disappearance of pain in the right upper quadrant, and a decrease in liver size in all the patients under study. Conclusions. The use of low-frequency ultrasound therapy on cutaneous projection of the liver in patients with type 2 DM promotes the normalization both fasting and postprandial glycemia. The effect of low-frequency ultrasound on cutaneous projection of the liver is significantly decreasing parameters that characterize the pancreatic insulin synthesizing function (immunoreactive insulin, C-peptide in patients with newly diagnosed type 2 DM and a BMI > 25 kg/m2. Low-frequency ultrasound reduces the glucagon secretion and thereby positively affects the hepatic gluconeogenesis. Ultrasound therapy can be used in the complex treatment of patients with newly diagnosed type 2 DM.

  16. 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.

  17. Experimental Observation of a Large Low-Frequency Band Gap in a Polymer Waveguide

    Directory of Open Access Journals (Sweden)

    Marco Miniaci

    2018-02-01

    Full Text Available The quest for large and low-frequency band gaps is one of the principal objectives pursued in a number of engineering applications, ranging from noise absorption to vibration control, and to seismic wave abatement. For this purpose, a plethora of complex architectures (including multiphase materials and multiphysics approaches have been proposed in the past, often involving difficulties in their practical realization. To address the issue of proposing a material design that enables large band gaps using a simple configuration, in this study we propose an easy-to-manufacture design able to open large, low-frequency complete Lamb band gaps exploiting a suitable arrangement of masses and stiffnesses produced by cavities in a monolithic material. The performance of the designed structure is evaluated by numerical simulations and confirmed by scanning laser Doppler vibrometer (SLDV measurements on an isotropic polyvinyl chloride plate in which a square ring region of cross-like cavities is fabricated. The full wave field reconstruction clearly confirms the ability of even a limited number of unit cell rows of the proposed design to efficiently attenuate Lamb waves. In addition, numerical simulations show that the structure allows to shift the central frequency of the BG through geometrical modifications. The design may be of interest for applications in which large BGs at low frequencies are required.

  18. Multi-cavity locally resonant structure with the low frequency and broad band-gaps

    Directory of Open Access Journals (Sweden)

    Jiulong Jiang

    2016-11-01

    Full Text Available A multi-cavity periodic structure with the characteristic of local resonance was proposed in the paper. The low frequency band-gap structure was comparatively analyzed by the finite element method (FEM and electric circuit analogy (ECA. Low frequency band-gap can be opened through the dual influence of the coupling’s resonance in the cavity and the interaction among the couplings between structures. Finally, the influence of the structural factors on the band-gap was analyzed. The results show that the structure, which is divided into three parts equally, has a broader effective band-gap below the frequency of 200 Hz. It is also proved that reducing the interval between unit structures can increase the intensity of the couplings among the structures. And in this way, the width of band-gap would be expanded significantly. Through the parameters adjustment, the structure enjoys a satisfied sound insulation effect below the frequency of 500Hz. In the area of low frequency noise reduction, the structure has a lot of potential applications.

  19. Plate-type metamaterials for extremely broadband low-frequency sound insulation

    Science.gov (United States)

    Wang, Xiaopeng; Guo, Xinwei; Chen, Tianning; Yao, Ge

    2018-01-01

    A novel plate-type acoustic metamaterial with a high sound transmission loss (STL) in the low-frequency range ( ≤1000 Hz) is designed, theoretically proven and then experimentally verified. The thin plates with large modulus used in this paper mean that we do not need to apply tension to the plates, which is more applicable to practical engineering, the achievement of noise reduction is better and the installation of plates is more user-friendly than that of the membranes. The effects of different structural parameters of the plates on the sound-proofed performance at low-frequencies were also investigated by experiment and finite element method (FEM). The results showed that the STL can be modulated effectively and predictably using vibration theory by changing the structural parameters, such as the radius and thickness of the plate. Furthermore, using unit cells of different geometric sizes which are responsible for different frequency regions, the stacked panels with thickness ≤16 mm and weight ≤5 kg/m2 showed high STL below 2000 Hz. The acoustic metamaterial proposed in this study could provide a potential application in the low-frequency noise insulation.

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

    Science.gov (United States)

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

    2009-12-01

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

  1. [Effects of extremely low frequency electromagnetic radiation on cardiovascular system of workers].

    Science.gov (United States)

    Zhao, Long-yu; Song, Chun-xiao; Yu, Duo; Liu, Xiao-liang; Guo, Jian-qiu; Wang, Chuan; Ding, Yuan-wei; Zhou, Hong-xia; Ma, Shu-mei; Liu, Xiao-dong; Liu, Xin

    2012-03-01

    To observe the exposure levels of extremely low frequency electromagnetic fields in workplaces and to analyze the effects of extremely low frequency electromagnetic radiation on cardiovascular system of occupationally exposed people. Intensity of electromagnetic fields in two workplaces (control and exposure groups) was detected with EFA-300 frequency electromagnetic field strength tester, and intensity of the noise was detected with AWA5610D integral sound level. The information of health physical indicators of 188 controls and 642 occupationally exposed workers was collected. Data were analyzed by SPSS17.0 statistic software. The intensity of electric fields and the magnetic fields in exposure groups was significantly higher than that in control group (P 0.05). The results of physical examination showed that the abnormal rates of HCY, ALT, AST, GGT, ECG in the exposure group were significantly higher than those in control group (P 0.05). Exposure to extremely low frequency electromagnetic radiation may have some effects on the cardiovascular system of workers.

  2. Low-frequency forces on tubular spaceframe towers: Analysis of Cognac data

    Energy Technology Data Exchange (ETDEWEB)

    Conte, J.P. (Rice Univ., Houston, TX (United States). Dept. of Civil Engineering); Marshall, P.W. (Univ. of Newcastle upon Tyne (United Kingdom). Dept. of Civil Engineering)

    1994-08-01

    The Cognac field data indicate that the low-frequency force response components are not negligible and are significantly correlated to the wave envelope process. Although this is a well-known phenomenon in floating structures, it had previously not been validated from data recorded on fixed platforms. Simulation studies based on a vertical rigid cylinder subjected to Hurricane Frederic sea states show significant differences in applied low-frequency drag forces obtained using the Wheeler and Delta stretching schemes used to approximate near-surface fluid kinematics. Previous studies focusing on the peak hydrodynamic forces, as used for the design of fixed platforms, have shown a significant difference between predictions based on Wheeler and Delta stretching. The present study reveals that the Cognac field data could be used to discriminate between the Wheeler and Delta stretching schemes in terms of the low-frequency forces, which are potentially important in the design of compliant towers. However, such a discriminatory study would require detailed structural and hydrodynamic modeling of the Cognac tower.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2007-02-01

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

  4. Adaptation of the vertical vestibulo-ocular reflex in cats during low-frequency vertical rotation.

    Science.gov (United States)

    Fushiki, Hiroaki; Maruyama, Motoyoshi; Shojaku, Hideo

    2018-04-01

    We examined plastic changes in the vestibulo-ocular reflex (VOR) during low-frequency vertical head rotation, a condition under which otolith inputs from the vestibular system are essential for VOR generation. For adaptive conditioning of the vertical VOR, 0.02Hz sinusoidal pitch rotation for one hour about the earth's horizontal axis was synchronized with out-of-phase vertical visual stimulation from a random dot pattern. A vertical VOR was well evoked when the upright animal rotated around the earth-horizontal axis (EHA) at low frequency due to the changing gravity stimulus and dynamic stimulation of the otoliths. After adaptive conditioning, the amplitude of the vertical VOR increased by an average of 32.1%. Our observations showing plasticity in the otolithic contribution to the VOR may provide a new strategy for visual-vestibular mismatch training in patients with otolithic disorders. This low-frequency vertical head rotation protocol also provides a model for investigating the mechanisms underlying the adaptation of VORs mediated by otolith activation. Copyright © 2017 Elsevier B.V. All rights reserved.

  5. Powering autonomous sensors with miniaturized piezoelectric based energy harvesting devices operating at very low frequency

    International Nuclear Information System (INIS)

    Ferin, G; Bantignies, C; Khanh, H Le; Flesch, E; Nguyen-Dinh, A

    2015-01-01

    Harvesting energy from ambient mechanical vibrations is a smart and efficient way to power autonomous sensors and support innovative developments in IoT (Internet of Things), WSN (Wireless Sensor Network) and even implantable medical devices. Beyond the environmental operating conditions, efficiency of such devices is mainly related to energy source properties like the amplitude of vibrations and its spectral contain and some of these applications exhibit a quite low frequency spectrum where harvesting surrounding mechanical energy make sense, typically 5-50Hz for implantable medical devices or 50Hz-150Hz for industrial machines. Harvesting such low frequency vibrations is a challenge since it leads to adapt the resonator geometries to the targeted frequency or to use out-off band indirect harvesting strategies. In this paper we present a piezoelectric based vibrational energy harvesting device (PEH) which could be integrated into a biocompatible package to power implantable sensor or therapeutic medical devices. The presented architecture is a serial bimorph laminated with ultra-thinned (ranging from 15μm to 100μm) outer PZT “skins” that could operate at a “very low frequency”, below 25Hz typically. The core process flow is disclosed and performances highlighted with regards to other low frequency demonstrations. (paper)

  6. Low-frequency, high-density, inductively coupled plasma sources: Operation and applications

    Science.gov (United States)

    Xu, S.; Ostrikov, K. N.; Li, Y.; Tsakadze, E. L.; Jones, I. R.

    2001-05-01

    Operation regimes, plasma parameters, and applications of the low-frequency (˜500 kHz) inductively coupled plasma (ICP) sources with a planar external coil are investigated. It is shown that highly uniform, high-density (ne˜9×1012 cm-3) plasmas can be produced in low-pressure argon discharges with moderate rf powers. The low-frequency ICP sources operate in either electrostatic (E) or electromagnetic (H) regimes in a wide pressure range without any Faraday shield or an external multipolar magnetic confinement, and exhibit high power transfer efficiency, and low circuit loss. In the H mode, the ICP features high level of uniformity over large processing areas and volumes, low electron temperatures, and plasma potentials. The low-density, highly uniform over the cross-section, plasmas with high electron temperatures and plasma and sheath potentials are characteristic to the electrostatic regime. Both operation regimes offer great potential for various plasma processing applications. As examples, the efficiency of the low-frequency ICP for steel nitriding and plasma-enhanced chemical vapor deposition of hydrogenated diamond-like carbon (DLC) films, is demonstrated. It appears possible to achieve very high nitriding rates and dramatically increase micro-hardness and wear resistance of the AISI 304 stainless steel. It is also shown that the deposition rates and mechanical properties of the DLC films can be efficiently controlled by selecting the discharge operating regime.

  7. Low-frequency electrohydrodynamic convection patterns in nematic liquid crystal aligned using parallel-oriented nanofiber

    Science.gov (United States)

    Mahendra, Bhisma; Nugroho, Fahrudin; Yusuf, Yusril

    2018-02-01

    Parallel-aligned poly(vinyl alcohol) (PVA) nanofiber with a diameter of 240 ± 60 nm and an alignment parameter (S) of 0.95 ± 0.16 was obtained by a gap collector electrospinning that used copper (Cu) as a collector. The sandwiched cells (the horizontal-view and longitudinal-view) nematic liquid crystal was prepared by treating glass surfaces with the aligned PVA nanofiber to provide uniform anchoring of the director. When an electric field was applied to these samples, the electrohydrodynamic convection (EHC) pattern was observed. In the longitudinal-view cells, above a threshold voltage at low frequency, a typically low-frequency EHC rolls i.e., a Williams domain (WD) pattern was observed. By increasing the voltage, a fluctuating Williams domain (FWD) and grid patterns (GPs) could also be observed. In the transverse-view cells, at low-frequency regimes, WD, sawtooth patterned (STP), and dynamic scattering mode (DSM) patterns were observed. By replacing the conventional rubbing method with the use of parallel-aligned nanofibers, the well-known EHC phenomenon also could be observed.

  8. Powering autonomous sensors with miniaturized piezoelectric based energy harvesting devices operating at very low frequency

    Science.gov (United States)

    Ferin, G.; Bantignies, C.; Le Khanh, H.; Flesch, E.; Nguyen-Dinh, A.

    2015-12-01

    Harvesting energy from ambient mechanical vibrations is a smart and efficient way to power autonomous sensors and support innovative developments in IoT (Internet of Things), WSN (Wireless Sensor Network) and even implantable medical devices. Beyond the environmental operating conditions, efficiency of such devices is mainly related to energy source properties like the amplitude of vibrations and its spectral contain and some of these applications exhibit a quite low frequency spectrum where harvesting surrounding mechanical energy make sense, typically 5-50Hz for implantable medical devices or 50Hz-150Hz for industrial machines. Harvesting such low frequency vibrations is a challenge since it leads to adapt the resonator geometries to the targeted frequency or to use out-off band indirect harvesting strategies. In this paper we present a piezoelectric based vibrational energy harvesting device (PEH) which could be integrated into a biocompatible package to power implantable sensor or therapeutic medical devices. The presented architecture is a serial bimorph laminated with ultra-thinned (ranging from 15μm to 100μm) outer PZT “skins” that could operate at a “very low frequency”, below 25Hz typically. The core process flow is disclosed and performances highlighted with regards to other low frequency demonstrations.

  9. Distinguishing low frequency oscillations within the 1/f spectral behaviour of electromagnetic brain signals

    Directory of Open Access Journals (Sweden)

    Sonuga-Barke Edmund JS

    2007-12-01

    Full Text Available Abstract Background It has been acknowledged that the frequency spectrum of measured electromagnetic (EM brain signals shows a decrease in power with increasing frequency. This spectral behaviour may lead to difficulty in distinguishing event-related peaks from ongoing brain activity in the electro- and magnetoencephalographic (EEG and MEG signal spectra. This can become an issue especially in the analysis of low frequency oscillations (LFOs – below 0.5 Hz – which are currently being observed in signal recordings linked with specific pathologies such as epileptic seizures or attention deficit hyperactivity disorder (ADHD, in sleep studies, etc. Methods In this work we propose a simple method that can be used to compensate for this 1/f trend hence achieving spectral normalisation. This method involves filtering the raw measured EM signal through a differentiator prior to further data analysis. Results Applying the proposed method to various exemplary datasets including very low frequency EEG recordings, epileptic seizure recordings, MEG data and Evoked Response data showed that this compensating procedure provides a flat spectral base onto which event related peaks can be clearly observed. Conclusion Findings suggest that the proposed filter is a useful tool for the analysis of physiological data especially in revealing very low frequency peaks which may otherwise be obscured by the 1/f spectral activity inherent in EEG/MEG recordings.

  10. Inverted pendulum as low-frequency pre-isolation for advanced gravitational wave detectors

    International Nuclear Information System (INIS)

    Takamori, A.; Raffai, P.; Marka, S.; DeSalvo, R.; Sannibale, V.; Tariq, H.; Bertolini, A.; Cella, G.; Viboud, N.; Numata, K.; Takahashi, R.; Fukushima, M.

    2007-01-01

    We have developed advanced seismic attenuation systems for Gravitational Wave (GW) detectors. The design consists of an Inverted Pendulum (IP) holding stages of Geometrical Anti-Spring Filters (GASF) and pendula, which isolate the test mass suspension from ground noise. The ultra-low-frequency IP suppresses the horizontal seismic noise, while the GASF suppresses the vertical ground vibrations. The three legs of the IP are supported by cylindrical maraging steel flexural joints. The IP can be tuned to very low frequencies by carefully adjusting its load. As a best result, we have achieved an ultra low, ∼12 mHz pendulum frequency for the system prototype made for Advanced LIGO (Laser Interferometer Gravitational Wave Observatory). The measured quality factor, Q, of this IP, ranging from Q∼2500 (at 0.45 Hz) to Q∼2 (at 12 mHz), is compatible with structural damping, and is proportional to the square of the pendulum frequency. Tunable counterweights allow for precise center-of-percussion tuning to achieve the required attenuation up to the first leg internal resonance (∼60 Hz for advanced LIGO prototype). All measurements are in good agreement with our analytical models. We therefore expect good attenuation in the low-frequency region, from ∼0.1to ∼50 Hz, covering the micro-seismic peak. The extremely soft IP requires minimal control force, which simplifies any needed actuation

  11. Characterization of low-frequency acoustic wave propagation through a periodic corrugated waveguide

    Science.gov (United States)

    Jiang, Changyong; Huang, Lixi

    2018-03-01

    In this paper, a periodic corrugated waveguide structure is proposed, and its unit-cell is analyzed by the wave finite element method. In low-frequency range, the unit-cell is treated as an equivalent fluid through a homogenization process, and the equivalent acoustic parameters are obtained, which are validated by finite structure simulations and experiments. The proposed structure is shown to add tortuosity to the waveguide, hence higher equivalent fluid density is achieved, while the system elastic modulus remains unchanged. As a result, the equivalent speed of sound is smaller than normal air. The application of such change of speed of sound is demonstrated in the classic quarter-wavelength resonator based on the corrugated waveguide, which gives a lower resonance frequency with the same side branch length. When the waveguide is filled with porous materials, the added tortuosity enhances the broadband, low-frequency sound absorption by increasing the equivalent mass without bringing in excess damping, the latter being partly responsible for the poor performance of usual porous materials in the low-frequency region. Therefore, the proposed structure provides another dimension for the design and optimization of porous sound absorption materials.

  12. 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.

  13. Advanced techniques for the analysis of crisis stability, deterrence, and latency

    Energy Technology Data Exchange (ETDEWEB)

    Canavan, G.H.

    1997-12-01

    Studies on crisis stability, deterrence, and latency are presented in chronological order, which also reflects their logical order of development, captures the main features of stability analysis; relates first strike, crisis, and arms control stability as seen from US and Russian perspective; and addresses questions such as whether uncertainty in damage preference or defense deployment can be destabilizing. It illustrates the problems with alternative metrics, latency and reconstitution, and deep unilateral and proportional force reductions.

  14. Advanced techniques for the analysis of crisis stability, deterrence, and latency

    Energy Technology Data Exchange (ETDEWEB)

    Canavan, G.H.

    1998-12-31

    This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The principal results of studies on crisis stability, deterrence, and latency are presented in their order of development. They capture the main features of stability analysis; relate first strike, crisis, and arms control stability as seen from US and Russian perspective; and address whether different metrics, uncertain damage preferences, or the deployment of defenses can be destabilizing. The report explores differences between unilateral and proportional force reductions in the region of deep reductions where concern shifts from stability to latency.

  15. Perception of force and stiffness in the presence of low-frequency haptic noise.

    Directory of Open Access Journals (Sweden)

    Netta Gurari

    Full Text Available This work lays the foundation for future research on quantitative modeling of human stiffness perception. Our goal was to develop a method by which a human's ability to perceive suprathreshold haptic force stimuli and haptic stiffness stimuli can be affected by adding haptic noise.Five human participants performed a same-different task with a one-degree-of-freedom force-feedback device. Participants used the right index finger to actively interact with variations of force (∼5 and ∼8 N and stiffness (∼290 N/m stimuli that included one of four scaled amounts of haptically rendered noise (None, Low, Medium, High. The haptic noise was zero-mean Gaussian white noise that was low-pass filtered with a 2 Hz cut-off frequency; the resulting low-frequency signal was added to the force rendered while the participant interacted with the force and stiffness stimuli.We found that the precision with which participants could identify the magnitude of both the force and stiffness stimuli was affected by the magnitude of the low-frequency haptically rendered noise added to the haptic stimulus, as well as the magnitude of the haptic stimulus itself. The Weber fraction strongly correlated with the standard deviation of the low-frequency haptic noise with a Pearson product-moment correlation coefficient of ρ > 0.83. The mean standard deviation of the low-frequency haptic noise in the haptic stimuli ranged from 0.184 N to 1.111 N across the four haptically rendered noise levels, and the corresponding mean Weber fractions spanned between 0.042 and 0.101.The human ability to perceive both suprathreshold haptic force and stiffness stimuli degrades in the presence of added low-frequency haptic noise. Future work can use the reported methods to investigate how force perception and stiffness perception may relate, with possible applications in haptic watermarking and in the assessment of the functionality of peripheral pathways in individuals with haptic impairments.

  16. Evaluation of low-frequency operational limit of proposed ITER low-field-side reflectometer waveguide run including miter bends

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Guiding [Univ. of California, Los Angeles, CA (United States). Dept. of Physics and Astronomy and Plasma Science and Technology Inst. (PSTI); Peebles, W. A. [Univ. of California, Los Angeles, CA (United States). Dept. of Physics and Astronomy and Plasma Science and Technology Inst. (PSTI); Doyle, E. J. [Univ. of California, Los Angeles, CA (United States). Dept. of Physics and Astronomy and Plasma Science and Technology Inst. (PSTI); Crocker, N. A. [Univ. of California, Los Angeles, CA (United States). Dept. of Physics and Astronomy and Plasma Science and Technology Inst. (PSTI); Wannberg, C. [Univ. of California, Los Angeles, CA (United States). Dept. of Physics and Astronomy and Plasma Science and Technology Inst. (PSTI); Lau, Cornwall H. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Hanson, Gregory R. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Doane, John L. [General Atomics, San Diego, CA (United States)

    2017-10-19

    The present design concept for the ITER low-field-side reflectometer transmission line (TL) consists of an ~40 m long, 6.35 cm diameter helically corrugated waveguide (WG) together with ten 90° miter bends. This paper presents an evaluation of the TL performance at low frequencies (33-50 GHz) where the predicted HE11 mode ohmic and mode conversion losses start to increase significantly. Quasi-optical techniques were used to form a near Gaussian beam to efficiently couple radiation in this frequency range into the WG. We observed that the output beams from the guide remained linearly polarized with cross-polarization power levels of ~1.5%-3%. The polarization rotation due to the helical corrugations was in the range ~1°-3°. The radiated beam power profiles typically show excellent Gaussian propagation characteristics at distances >20 cm from the final exit aperture. The round trip propagation loss was found to be ~2.5 dB at 50 GHz and ~6.5 dB at 35 GHz, showing an inverse increase with frequency. This was consistent with updated calculations of miter bend and ohmic losses. At low frequencies (33-50 GHz), the mode purity remained very good at the exit of the waveguide, and the losses are perfectly acceptable for operation in ITER. Finally, the primary challenge may come from the future addition of a Gaussian telescope and other filter components within the corrugated guide, which will likely introduce additional perturbations to the beam profile and an increase in mode-conversion loss.

  17. The impact research of control modes in steam turbine control system (digital electric hydraulic to the low-frequency oscillation of grid

    Directory of Open Access Journals (Sweden)

    Yanghai Li

    2016-01-01

    Full Text Available Through the analysis of the control theory for steam turbine, the transfer function of the steam turbine control modes in the parallel operation was obtained. The frequency domain analysis indicated that different control modes of turbine control system have different influence on the damping characteristics of the power system. The comparative analysis shows the direction and the degree of the influence under the different oscillation frequency range. This can provide the theory for the suppression of the low-frequency oscillation from turbine side and has a guiding significance for the stability of power system. The results of simulation tests are consistent with the theoretic analysis.

  18. Delineation of Gold Mineralization Zone using Resistivity and Very Low Frequency Electromagnetic Methods around, North Singhbhum Mobile Belt, India.

    Science.gov (United States)

    Upadhyay, A.; Panda, K. P.; Singh, A.; Sharma, S. P.

    2017-12-01

    The results of electrical resistivity and VLF electromagnetic surveys are presented in this study to delineate the suitable geological structure associated with gold mineralization near Lawa Village (Seraikela-Kharsawan, Jharkhand), India. The area under observation lies in North Singhbhum Mobile Belt (NSMB) which is bounded by Chotanagpur Gneiss Complex in north and Archean Singhbhum Craton in the south. Shear zone of the study area, trending E-W, is mainly associated with Cu-U mineralization which is also associated with gold. Previous geological studies have revealed that this region can be a potential site for gold prospects within NSMB. A comprehensive electrical resistivity imaging and very low frequency surveys have been performed around Lawa village to outline appropriate conducting zones, with their lateral extension and depth extent, which may be associated with gold mineralization. Resistivity survey done using Dipole-Dipole multi-electrode array reveals multiple zones of mineralization separated by variable distances. The VLF data in the current study was tainted by non-stationary and non-linear noises which cannot be eliminated by standard filtering techniques. Therefore to restore signals with significant geologic information empirical mode decomposition (EMD) technique was used. The noise free data obtained was then processed using Fast Imaging technique to obtain apparent current density pseudo-sections for interpretation. Interpretation and analysis of results from each investigating survey demonstrate a steeply dipping conductor with E-W strike direction along the shear zone. These conductive zones are characterized by low resistivity and high current density values.

  19. On radiation stability of the advanced for nuclear technique of the construction oxides material

    International Nuclear Information System (INIS)

    Abdukadirova, I.Kh.

    2004-01-01

    Full text: Al 2 O 3 oxide (as some metal oxides) is one of the prospective high-k electro-insulators and construction oxides materials, in particular, for the ceramics fuel material and the first wall of thermonuclear reactor. Besides, this oxide is used widely as an active element or substrate for lasers and MOS systems, as a film coating and receiver of IR-radiation. From here this work is aimed at investigation of radiation stability of the physical properties and structure of Al 2 O 3 oxide after irradiation to a high fluence in the reactor. In this connection the peculiarities of radiation effect on lattice parameters (a,c), form and position of several reflections, reflection coefficient and frequency of valence and deformation oscillations of Al-O bonds, electric characteristics of the oxide were studied with techniques of X-diffraction, dielectric and IR-reflection spectroscopy. For example, this communication presents the results on X-ray structure investigation of σ after irradiation to high neutron doses (F). X-diffraction patterns were obtained using a roentgen diffractometer. Particular attention was paid to dynamics of form and positions some representative reflexes. The diffraction patterns showed essential changes of peak intensity and position depending upon F, the Bragg angle 2 Θ decreases with an increase in dose, the lattice parameters of crystals ( a, c ) was undergone anisotropy expansion, at very high dose of change this parameters is not so much as Δc= 0,0038 nm and Δa = 0,0014 nm. Besides, it is shown that at these doses some halo appears at the diffraction patterns. The mechanism of atom displacement out of lattice knots plays the main role in radiation damage of crystals irradiated to high doses. The optical characteristics - a reflection coefficient and frequency of valence (736, 614 cm -1 ) and deformation (464 cm -1 ) oscillations of Al-O bonds of the oxide were studied with techniques of IR-reflection spectroscopy in region of

  20. Determination of stability constants of iron(III and chromium(III-nitrilotriacetate-methyl cysteine mixed complexes by electrophoretic technique

    Directory of Open Access Journals (Sweden)

    Brij Bhushan Tewari

    2004-06-01

    Full Text Available The stability constants of Fe(III and Cr(III with methyl cysteine and nitrilotriacetate (NTA were determined by paper electrophoretic technique. Beside binary ternary complexes have also been studied, in which nitrilotriacetate and methyl cysteine acts as primary and secondary ligand, respectively. The stability constants of mixed ligand complexes metal (M-nitrilotriacetate-methyl cysteine have been found to be 5.72 plus or minus 0.09 and 5.54 plus or minus 0.11 (log K values for Fe(III and Cr(III complexes, respectively, at 35 oC and ionic strength 0.1 M.

  1. ANALYSIS OF MONTE CARLO SIMULATION SAMPLING TECHNIQUES ON SMALL SIGNAL STABILITY OF WIND GENERATOR- CONNECTED POWER SYSTEM

    Directory of Open Access Journals (Sweden)

    TEMITOPE RAPHAEL AYODELE

    2016-04-01

    Full Text Available Monte Carlo simulation using Simple Random Sampling (SRS technique is popularly known for its ability to handle complex uncertainty problems. However, to produce a reasonable result, it requires huge sample size. This makes it to be computationally expensive, time consuming and unfit for online power system applications. In this article, the performance of Latin Hypercube Sampling (LHS technique is explored and compared with SRS in term of accuracy, robustness and speed for small signal stability application in a wind generator-connected power system. The analysis is performed using probabilistic techniques via eigenvalue analysis on two standard networks (Single Machine Infinite Bus and IEEE 16–machine 68 bus test system. The accuracy of the two sampling techniques is determined by comparing their different sample sizes with the IDEAL (conventional. The robustness is determined based on a significant variance reduction when the experiment is repeated 100 times with different sample sizes using the two sampling techniques in turn. Some of the results show that sample sizes generated from LHS for small signal stability application produces the same result as that of the IDEAL values starting from 100 sample size. This shows that about 100 sample size of random variable generated using LHS method is good enough to produce reasonable results for practical purpose in small signal stability application. It is also revealed that LHS has the least variance when the experiment is repeated 100 times compared to SRS techniques. This signifies the robustness of LHS over that of SRS techniques. 100 sample size of LHS produces the same result as that of the conventional method consisting of 50000 sample size. The reduced sample size required by LHS gives it computational speed advantage (about six times over the conventional method.

  2. Effects of low-frequency stimulation of the subthalamic nucleus on movement in Parkinson's disease.

    Science.gov (United States)

    Eusebio, Alexandre; Chen, Chiung Chu; Lu, Chin Song; Lee, Shih Tseng; Tsai, Chon Haw; Limousin, Patricia; Hariz, Marwan; Brown, Peter

    2008-01-01

    Excessive synchronization of basal ganglia neural activity at low frequencies is considered a hallmark of Parkinson's disease (PD). However, few studies have unambiguously linked this activity to movement impairment through direct stimulation of basal ganglia targets at low frequency. Furthermore, these studies have varied in their methodology and findings, so it remains unclear whether stimulation at any or all frequencies < or = 20 Hz impairs movement and if so, whether effects are identical across this broad frequency band. To address these issues, 18 PD patients chronically implanted with deep brain stimulation (DBS) electrodes in both subthalamic nuclei were stimulated bilaterally at 5, 10 and 20 Hz after overnight withdrawal of their medication and the effects of the DBS on a finger tapping task were compared to performance without DBS (0 Hz). Tapping rate decreased at 5 and 20 Hz compared to 0 Hz (by 11.8+/-4.9%, p=0.022 and 7.4+/-2.6%, p=0.009, respectively) on those sides with relatively preserved baseline task performance. Moreover, the coefficient of variation of tap intervals increased at 5 and 10 Hz compared to 0 Hz (by 70.4+/-35.8%, p=0.038 and 81.5+/-48.2%, p=0.043, respectively). These data suggest that the susceptibility of basal ganglia networks to the effects of excessive synchronization may be elevated across a broad low-frequency band in parkinsonian patients, although the nature of the consequent motor impairment may depend on the precise frequencies at which synchronization occurs.

  3. Low-frequency electroacupuncture suppresses focal epilepsy and improves epilepsy-induced sleep disruptions.

    Science.gov (United States)

    Yi, Pei-Lu; Lu, Chin-Yu; Jou, Shuo-Bin; Chang, Fang-Chia

    2015-07-07

    The positive effects of acupuncture at Feng-Chi acupoints on treating epilepsy and insomnia have been well-documented in ancient Chinese literature. However, there is a lack of scientific evidence to elucidate the underlying mechanisms behind these effects. Our previous study demonstrated that high-frequency (100 Hz) electroacupuncture (EA) at Feng-Chi acupoints deteriorates both pilocarpine-induced focal epilepsy and sleep disruptions. This study investigated the effects of low-frequency (10 Hz) EA on epileptic activities and epilepsy-induced sleep disruptions. In rats, the Feng-Chi acupoint is located 3 mm away from the center of a line between the two ears. Rats received 30 min of 10 Hz EA stimuli per day before each day's dark period for three consecutive days. Our results indicated that administration of pilocarpine into the left CeA at the beginning of the dark period induced focal epilepsy and decreased both rapid eye movement (REM) sleep and non-REM (NREM) sleep during the consequent light period. Low-frequency (10 Hz) EA at Feng-Chi acupoints suppressed pilocarpine-induced epileptiform EEGs, and this effect was in turn blocked by naloxone (a broad-spectrum opioid receptor antagonist), but not by naloxonazine (a μ-receptor antagonist), naltrindole (a δ-receptor antagonist) and nor-binaltorphimine (a κ-receptor antagonist). Ten Hz EA enhanced NREM sleep during the dark period, and this enhancement was blocked by all of the opioid receptor antagonists. On the other hand, 10 Hz EA reversed pilocarpine-induced NREM suppression during the light period, and the EA's effect on the sleep disruption was only blocked by naloxonazine. These results indicate that low-frequency EA stimulation of Feng-Chi acupoints is beneficial in improving epilepsy and epilepsy-induced sleep disruptions, and that opioid receptors in the CeA mediate EA's therapeutic effects.

  4. The frequency dependence of friction in experiment, theory, and observations of low frequency earthquakes

    Science.gov (United States)

    Thomas, A.; Beeler, N. M.; Burgmann, R.; Shelly, D. R.

    2011-12-01

    Low frequency earthquakes (LFEs) are small amplitude, short duration events composing tectonic tremor, probably generated by shear slip on asperities downdip of the seismogenic zone. In Parkfield, Shelly and Hardebeck [2010] have identified 88 LFE families, or hypocentral locations, that contain over half a million LFEs since 2001 on a 160-km-long section of the San Andreas fault between 16 and 30 km depth. A number of studies have demonstrated the extreme sensitivity of low frequency earthquakes (LFEs) near Parkfield to stress changes ranging from contingent upon the amplitude and frequency content of the applied stress. We attempt to test this framework by comparing observations of LFEs triggered in response to stresses spanning several orders of magnitude in both frequency and amplitude (e.g. tides, teleseismic surface waves, static stress changes, etc.) to the predicted response of a single degree of freedom slider block model with rate and state dependent strength. The sensitivity of failure time in the friction model as developed in previous studies does not distinguish between shear and normal stresses; laboratory experiments show a more complicated sensitivity of failure time to normal stress change than in the published model. Because the shear and normal tidal stresses at Parkfield have different amplitudes and are not in phase, we have modified the model to include the expected sensitivity to normal stress. Our prior investigations of the response of both regular and low frequency earthquakes to tidal stresses [Thomas et al., 2009; Shelly and Johnson, 2011] are qualitatively consistent with the predictions of the friction model , as both the timing and degree (probability) of correlation are in agreement.

  5. Dynamic microparticle manipulation with an electroosmotic flow gradient in low-frequency alternating current dielectrophoresis.

    Science.gov (United States)

    Gencoglu, Aytug; Olney, David; LaLonde, Alexandra; Koppula, Karuna S; Lapizco-Encinas, Blanca H

    2014-02-01

    In this study, the potential of low-frequency AC insulator-based DEP (iDEP) was explored for the separation of polystyrene microparticles and yeast cells. An EOF gradient was generated by employing an asymmetrical, 20 Hz AC electrical signal in an iDEP device consisting of a microchannel with diamond-shaped insulating posts. Two types of samples were analyzed, the first sample contained three types of polystyrene particles with different diameters (0.5, 1.0, and 2.0 μm) and the second sample contained two types of polystyrene particles (1.0 and 2 μm) and yeast cells (6.3 μm). This particular scheme uses a tapered AC signal that allows for all particles to be trapped and concentrated at the insulating post array, as the signal becomes asymmetrical (more positive), particles are selectively released. The smallest particles in each sample were released first, since they require greater dielectrophoretic forces to remain trapped. The largest particles in each sample were released last, when the applied signal became cyclical. A dielectropherogram, which is analogous to a chromatogram, was obtained for each sample, demonstrating successful separation of the particles by showing "peaks" of the released particles. These separations were achieved at lower applied potentials than those reported in previous studies that used solely direct current electrical voltages. Additionally, mathematical modeling with COMSOL Multiphysics was carried out to estimate the magnitude of the dielectrophoretic and EOF forces acting on the particles considering the low-frequency, asymmetrical AC signal used in the experiments. The results demonstrated the potential of low-frequency AC-iDEP systems for handling and separating complex mixtures of microparticles and biological cells. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Effects of swallowing training combined with low-frequency electrical stimulation on dysphagia after ischemic stroke

    Directory of Open Access Journals (Sweden)

    Zhi-zhong ZHU

    2015-04-01

    Full Text Available Objective To investigate the effects of swallowing training combined with low-frequency electrical stimulation on dysphagia after ischemic stroke.  Methods A total of 68 patients with dysphagia after ischemic stroke were divided into control group (N = 34, receiving swallowing training and feeding strategies and combined treatment group (N = 34, receiving swallowing training, feeding strategies and low-frequency electrical stimulation. Video Fluoroscopic Swallowing Study (VFSS and Standardized Swallowing Assessment (SSA were used to evaluate the swallowing function of patients in 2 groups before and after 15 d of treatment. Results According to Oxfordshire Community Stroke Project (OCSP classification, 34 patients in control group were classified into 12 cases with total anterior circulation infarct (TACI, 8 cases with partial anterior circulation infarct (PACI, 10 cases with posterior circulation infarct (POCI and 4 cases with lacunar infarct (LACI; 34 patients in combined treatment group were classified into 10 cases with TACI, 7 cases with PACI, 11 cases with POCI and 6 cases with LACI. Compared with before treatment, the VFSS score increased (P = 0.003, 0.000, while SSA score decreased (P = 0.003, 0.000 in both groups. Compared with control group, the VFSS score increased (P = 0.004, while SSA score decreased (P = 0.020 in combined treatment group.  Conclusions Swallowing training combined with low-frequency electrical stimulation can significantly improve the swallowing capacity of patients with acute ischemic stroke, and the effect is better than mere swallowing training. DOI: 10.3969/j.issn.1672-6731.2015.04.007

  7. Low-frequency excess contribution in simple liquids revealed by fast field cycling NMR

    Energy Technology Data Exchange (ETDEWEB)

    Meier, Roman; Herrmann, Axel; Kahlau, Robert; Kruk, Danuta; Roessler, Ernst [Experimentalphysik II, Universitaet Bayreuth (Germany)

    2010-07-01

    The main relaxation ({alpha}-relaxation) of simple liquids studied by dielectric spectroscopy is well described by a Cole-Davidson (CD) susceptibility. In particular the low-frequency limit follows a Debye behavior {chi}{sub DS}''{proportional_to}{omega}{sup 1}. Applying fast field cycling (FFC) {sup 1}H NMR and transforming the spin-lattice dispersion data T{sub 1} into the susceptibility representation {chi}{sub NMR}''{proportional_to}{nu}/T{sub 1} we have discovered a low-frequency excess contribution for systems like glycerol and its homologues as well as fluoroaniline. The CD function fails to describe the data due to a retarded transition to the limit {omega}{sup 1}, i.e., a ''shoulder'' is observed on the low frequency side of the a-relaxation peak ({omega}{tau}{sub {alpha}}<1) possibly reflecting a slower relaxation process. Actually only a few liquids like o-terphenyl and tristyrene studied by FFC NMR do not show this phenomenon. Collecting dispersion data over a large temperature range, the relaxation strength of the excess contribution is specified quantitatively. Measurements of dilution series of propylene glycol in deuterated chloroform proved an intermolecular origin of the excess contribution. Dilution experiments of deuterated in protonated glycerol suggest this additional contribution being also fully reflected by sole intramolecular spin-spin vectors. A possible explanation of this effect are transient molecular clusters due to chemical interactions (e.g. H-bonds).

  8. Tumor-specific mutations in low-frequency genes affect their functional properties.

    Science.gov (United States)

    Erdem-Eraslan, Lale; Heijsman, Daphne; de Wit, Maurice; Kremer, Andreas; Sacchetti, Andrea; van der Spek, Peter J; Sillevis Smitt, Peter A E; French, Pim J

    2015-05-01

    Causal genetic changes in oligodendrogliomas (OD) with 1p/19q co-deletion include mutations in IDH1, IDH2, CIC, FUBP1, TERT promoter and NOTCH1. However, it is generally assumed that more somatic mutations are required for tumorigenesis. This study aimed to establish whether genes mutated at low frequency can be involved in OD initiation and/or progression. We performed whole-genome sequencing on three anaplastic ODs with 1p/19q co-deletion. To estimate mutation frequency, we performed targeted resequencing on an additional 39 ODs. Whole-genome sequencing identified a total of 55 coding mutations (range 8-32 mutations per tumor), including known abnormalities in IDH1, IDH2, CIC and FUBP1. We also identified mutations in genes, most of which were previously not implicated in ODs. Targeted resequencing on 39 additional ODs confirmed that these genes are mutated at low frequency. Most of the mutations identified were predicted to have a deleterious functional effect. Functional analysis on a subset of these genes (e.g. NTN4 and MAGEH1) showed that the mutation affects the subcellular localization of the protein (n = 2/12). In addition, HOG cells stably expressing mutant GDI1 or XPO7 showed altered cell proliferation compared to those expressing wildtype constructs. Similarly, HOG cells expressing mutant SASH3 or GDI1 showed altered migration. The significantly higher rate of predicted deleterious mutations, the changes in subcellular localization and the effects on proliferation and/or migration indicate that many of these genes functionally may contribute to gliomagenesis and/or progression. These low-frequency genes and their affected pathways may provide new treatment targets for this tumor type.

  9. Locating Very-Low-Frequency Earthquakes in the San Andreas Fault.

    Science.gov (United States)

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

    2016-12-01

    The portion of tectonic fault where rheological properties transtition from brittle to ductile hosts a variety of seismic signals suggesting a range of slip velocities. In subduction zones, the two dominantly observed seismic signals include very-low frequency earthquakes ( VLFEs), and low-frequency earthquakes (LFEs) or tectonic tremor. Tremor and LFE are also commonly observed in transform faults, however, VLFEs have been reported dominantly in subduction zone environments. Here we show some of the first known observations of VLFEs occurring on a plate boundary transform fault, the San Andreas Fault (SAF) between the Cholame-Parkfield segment in California. We detect VLFEs using both permanent and temporary stations in 2010-2011 within approximately 70 km of Cholame, California. We search continous waveforms filtered from 0.02-0.05 Hz, and remove time windows containing teleseismic events and local earthquakes, as identified in the global Centroid Moment Tensor (CMT) and the Northern California Seismic Network (NCSN) catalog. We estimate the VLFE locations by converting the signal into envelopes, and cross-correlating them for phase-picking, similar to procedures used for locating tectonic tremor. We first perform epicentral location using a grid search method and estimate a hypocenter location using Hypoinverse and a shear-wave velocity model when the epicenter is located close to the SAF trace. We account for the velocity contrast across the fault using separate 1D velocity models for stations on each side. Estimated hypocentral VLFE depths are similar to tremor catalog depths ( 15-30 km). Only a few VLFEs produced robust hypocentral locations, presumably due to the difficulty in picking accurate phase arrivals with such a low-frequency signal. However, for events for which no location could be obtained, the moveout of phase arrivals across the stations were similar in character, suggesting that other observed VLFEs occurred in close proximity.

  10. Effect of hydrate formation-dissociation on emulsion stability using DSC and visual techniques

    Energy Technology Data Exchange (ETDEWEB)

    Lachance, J.W.; Dendy Sloan, E.; Koh, C.A. [Colorado School of Mines, Golden, CO (United States). Center for Hydrates Research

    2008-07-01

    Many flow assurance operators are now focusing on preventing hydrates from agglomerating and forming plugs within pipelines. A key factor in reducing plug formation in oil-dominated systems is the stability of emulsified water in gas hydrate formation. In this study, differential scanning calorimetry (DSC) studies were used to show that gas hydrate formation has a destabilizing effect on water and oil emulsions, and can result in a free water phase through the coalescence and agglomeration of dissociated hydrate particles. The study focused on investigating the ability of the hydrates to stay segregated with hydrate formation. The stability of water-in-oil emulsions with hydrate formation was investigated with a range of different crude oils with varying emulsion stability levels. Thermal properties were measured at both atmospheric and pressurized conditions. Thermocouples in the calorimetric furnace were used to measure the temperature difference between reference and sample cells. Emulsion stability was measured over a 1-month time period. Results of the study showed that hydrate formation and dissociation destabilizes emulsions. However, the asphaltene fraction in crude oils resists hydrate-induced destabilization. The stability of the emulsion increased when asphaltene content increased. It was concluded that emulsion stability is a key factor in preventing agglomeration in flow lines. 14 refs., 3 tabs., 8 figs.

  11. Unified model of low-frequency electromagnetic modes in the anisotropic current sheet of the Earth's magnetotail.

    Science.gov (United States)

    Zelenyi, Lev; Malova, H.; Artemyev, A.; Popov, V.

    Experimental investigation of the Earth's magnetosphere indicates that there is close coupling between the global magnetospheric dynamics and characteristic properties of the magnetotail current sheet (CS). The investigation of CS stability is developed in a frame of analytical self-consistent model of a thin anisotropic current sheet with anisotropic pressure tensor. Ion population is considered in quasiadiabatic approximation, electrons are taken into account in Boltzman approximation. The general case of oblique perturbations with an arbitrary polarization is studied including tearing, kink, sausage and twist modes. In a frame of the linear perturbation theory it is shown that thin current sheets have larger free energy than the well known isotropic ones. It is demonstrated that, contrary to stable Harris-type current sheets, there exists certain "gaps" in the parameter space where system could become unstable for tearing perturbation. The investigation of the development of an oblique perturbation modes demonstrated the possibility of the growth of other low frequency electromagnetic instabilities such kink and sausage modes. Generally, unstable modes exist for any arbitrary angle of propagation while tearing and twist modes are most unstable for propagation along Bx, while kink and sausage modes have maximum growth rate for propagation along current. Our studies might have important implications for understanding magnetospheric dynamics during substorm activization, e.g. current sheet evolution, destruction, flapping and other dynamic plasma processes in the Earth's magnetotail.

  12. Changes in low-frequency fluctuations in patients with antisocial personality disorder revealed by resting-state functional MRI.

    Directory of Open Access Journals (Sweden)

    Huasheng Liu

    Full Text Available Antisocial Personality Disorder (APD is a personality disorder that is most commonly associated with the legal and criminal justice systems. The study of the brain in APD has important implications in legal contexts and in helping ensure social stability. However, the neural contribution to the high prevalence of APD is still unclear. In this study, we used resting-state functional magnetic resonance imaging (fMRI to investigate the underlying neural mechanisms of APD. Thirty-two healthy individuals and thirty-five patients with APD were recruited. The amplitude of low-frequency fluctuations (ALFF was analyzed for the whole brain of all subjects. Our results showed that APD patients had a significant reduction in the ALFF in the right orbitofrontal cortex, the left temporal pole, the right inferior temporal gyrus, and the left cerebellum posterior lobe compared to normal controls. We observed that the right orbitofrontal cortex had a negative correlation between ALFF values and MMPI psychopathic deviate scores. Alterations in ALFF in these specific brain regions suggest that APD patients may be associated with abnormal activities in the fronto-temporal network. We propose that our results may contribute in a clinical and forensic context to a better understanding of APD.

  13. Effects of low-frequency ultrasound on microcirculation in venous leg ulcers

    Directory of Open Access Journals (Sweden)

    Uwe Wollina

    2011-01-01

    Full Text Available Background: Therapeutic low-frequency ultrasound (US has been used for many years to improve wound healing in chronic wounds like venous leg ulcers. No human data are available for the possible effects of single US applications on microcirculation and their frequency-dependency. Aims: To investigated the role of therapeutic low-frequency US on microcirculation of venous leg ulcers in vivo. Patients and Methods: This is a pilot study on an inpatient basis. We use a newly developed low-frequency continuous-wave US-equipment composed of a US transducer based on piezo-fiber composites that allow the change of frequency. In this study, we apply US of 34 kHz, 53.5 kHz, and 75 kHz respectively. Twelve patients with chronic venous leg ulcers are analyzed. As an adjunct to good ulcer care, therapeutic US is applied, non-contacting, once a day, in a subaqual position for 10 minutes. Microcirculation is assessed in the ulcers adjacent to skin before US-therapy, immediately after the treatment and 30 minutes later. We use a micro-light guide spectrophotometer (O2C, LEA Medizintechnik GmbH, Gieίen, Germany for calculation of blood flow velocity, hemoglobin oxygen saturation (SCO 2 and relative hemoglobin concentration (rHb in 2 and 8 mm depth. Contact-free remission spectroscopy (SkinREM3, Color Control Chemnitz GmbH, Chemnitz, Germany allows contact free measurements in the VIS-NIR range of the spectrum (400 ± 1600 nm. Results: It is seen that therapeutic US is well tolerated. One patient dropped out from a treatment series since he developed erysipelas responding to standard antibiotic. Effects were seen at 34 kHz only. The SO 2 values increased after single US application. The values for rHb were higher in the superficial layer of the wound bed (depth 2 mm compared to deeper parts (8 mm depth. US treatment did not result in significant changes of rHb and blood cell velocity. The data obtained by remission spectroscopy disclose an increase of oxygenized

  14. Low frequency oscillations in cephalic vessels assessed by near infrared spectroscopy

    DEFF Research Database (Denmark)

    Phillip, Dorte; Schytz, Henrik W; Selb, Juliette

    2012-01-01

    BACKGROUND AND METHODS: Low frequency oscillations (LFO) of cerebral vessels are believed to reflect cerebral autoregulation. We investigated day-to-day and hemispheric variations in 0.1 Hz LFO with near infrared spectroscopy (NIRS) and transcranial Doppler (TCD) to determine phase shift and gain...... breathing at 6 breaths per minute on two separate days. RESULTS: The variation between hemispheres had a prediction interval (PI) of ± 39° for ABP-oxyHb phase shift and ± 69% for gain. ABP-Vmca showed ± 57° PI phase shift and ± 158% PI for gain. The variation from day to day showed ± 61° PI for ABP...

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

    International Nuclear Information System (INIS)

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

    2015-01-01

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

  16. Ultra-low-frequency electromagnetic waves in the Earth's crust and magnetosphere

    International Nuclear Information System (INIS)

    Guglielmi, A V

    2007-01-01

    Research on natural intra- and extraterrestrially produced electromagnetic waves with periods ranging from 0.2 to 600 s is reviewed. The way in which the energy of rock movements transforms into the energy of an alternating magnetic field is analyzed. Methods for detecting seismomagnetic signals against a strong background are described. In discussing the physics of ultra-low-frequency waves in the magnetosphere, the 11-year activity modulation of 1-Hz waves and ponderomotive forces affecting plasma distribution are emphasized. (reviews of topical problems)

  17. Vital functions of organisms in infra-low frequency magnetic fields 1. The bacteriostatic effect

    Energy Technology Data Exchange (ETDEWEB)

    Khizhenkov, P.K.; Bilobrov, V.M.; Chugai, A.V.

    1994-10-01

    The effect of infra-low frequency variable magnetic fields H on a culture of Staph. aureus was studied experimentally. Dependencies of the bacteria number growth on the field action duration and on the frequency f were obtained. It was shown that the maximum bacteriostatic effect of H occurs in the f {approx} 0.1-10.0 Hz interval. It was noted that the action of H does not result in the death of the bacteria, and that in the absence of a field, the bacterial fission exceeds the control case.

  18. Low-frequency electrical dosimetry: research agenda of the IEEE International Committee on Electromagnetic Safety.

    Science.gov (United States)

    Reilly, J Patrick; Hirata, Akimasa

    2016-06-21

    This article treats unsettled issues in the use of numerical models of electrical dosimetry as applied to international limits on human exposure to low-frequency (typically  IEEE-ICES (International Committee on Electromagnetic Safety) Technical Committee 95. The paper discusses 25 issues needing attention, fitting into three general categories: induction models; electrostimulation models; and human exposure limits. Of these, 9 were voted as 'high priority' by members of Subcommittee 6. The list is presented as a research agenda for refinements in numerical modeling with applications to human exposure limits. It is likely that such issues are also important in medical and electrical product safety design applications.

  19. Monitoring the photobaric component of green leaves by low frequency photoacoustics

    Science.gov (United States)

    Frandas, A.; Jalink, H.; van der Schoor, R.

    1999-03-01

    The photoacoustic spectrum in the 0.2÷200 Hz frequency range of Philodendron leaves was measured under steady-state conditions. The photoacoustic signal amplitude showed a maximum at low frequencies (around 1Hz) which was attributed to an optimum frequency for oxygen evolution. The signal decreased at lower frequencies where the oxygen uptake becomes important. At higher frequencies, the transition in the dominant component from photobaric to photothermal was evidenced. Efficiency of the oxygen evolution as a function of excitation intensity was determined for different levels of background light. The effect of lowering the temperature was also discussed.

  20. Medium Band Least Squares Estimation of Fractional Cointegration in the Presence of Low-Frequency Contamination

    DEFF Research Database (Denmark)

    Christensen, Bent Jesper; Varneskov, Rasmus T.

    This paper introduces a new estimator of the fractional cointegrating vector between stationary long memory processes that is robust to low-frequency contamination such as level shifts, i.e., structural changes in the means of the series, and deterministic trends. In particular, the proposed medium...... the cointegration strength and testing MBLS against the existing narrow band least squares estimator are developed. Finally, the asymptotic framework for the MBLS estimator is used to provide new perspectives on volatility factors in an empirical application to long-span realized variance series for S&P 500...