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Sample records for low-frequency mammalian oscillator

  1. A synthetic low-frequency mammalian oscillator

    PubMed Central

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

    2010-01-01

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

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

    PubMed Central

    Lodha, Neha; Christou, Evangelos A.

    2017-01-01

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

  3. High vs low frequency neural oscillations in schizophrenia.

    PubMed

    Moran, Lauren V; Hong, L Elliot

    2011-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

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

    SciTech Connect

    Wang, Chunsheng Wang, Huashan

    2016-08-15

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

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

    SciTech Connect

    Sonin, E.B.

    1983-01-20

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

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

    NASA Astrophysics Data System (ADS)

    Tesař, Václav

    2016-03-01

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

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

    PubMed

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

    2012-10-01

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

  9. Weak low-frequency electromagnetic oscillations in water.

    PubMed

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

    2017-01-01

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

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

    PubMed

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

    1990-03-01

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

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

    SciTech Connect

    Barral, S.; Ahedo, E.

    2008-03-19

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

  12. Possible feedback path for low-frequency atmospheric oscillations

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

  13. Modulating action of low frequency oscillations on high frequency instabilities in Hall thrusters

    SciTech Connect

    Liqiu, Wei E-mail: weiliqiu@hit.edu.cn; Liang, Han; Ziyi, Yang; Jing, Li; Yong, Cao; Daren, Yu; Jianhua, Du

    2015-02-07

    It is found that the low frequency oscillations have modulating action on high frequency instabilities in Hall thrusters. The physical mechanism of this modulation is discussed and verified by numerical simulations. Theoretical analyses indicate that the wide-range fluctuations of plasma density and electric field associated with the low frequency oscillations affect the electron drift velocity and anomalous electron transport across the magnetic field. The amplitude and frequency of high frequency oscillations are modulated by low frequency oscillations, which show the periodic variation in the time scale of low frequency oscillations.

  14. Low Frequency High Amplitude Temperature Oscillations in Loop Heat Pipe Operation

    NASA Technical Reports Server (NTRS)

    Ku, Jentung; Rodriguez, Jose

    2003-01-01

    This paper presents viewgraphs on the low frequency high amplitude temperature oscillations observed in loop heat pipe operations. The topics include: 1) Proposed Theory; 2) Test Loop and Test Results; and 3) Effects of Various Parameters. The author also presents a short summary on the conditiions that must be met in order to sustain a low frequency high amplitude temperature oscillation.

  15. Hydrodynamic Force on a Cylinder Oscillating at Low Frequency

    NASA Technical Reports Server (NTRS)

    Berg, Robert F.; Yao, Minwu; Panzarella, Charles H.

    2007-01-01

    The hydrodynamic force on a cylinder oscillating transversely to its axis is a nonlinear function of the displacement amplitude x0. We report measurements and numerical calculations of the force at frequencies low enough that delta > R, where delta is the viscous penetration length and R is the cylinder radius. For small amplitudes, the numerically calculated Fourier transform of the force per unit length, F(sub small), agrees with Stokes' analytical calculation. For larger amplitudes, the force per unit length found by both calculation and measurement is F = F(sub small)C (x(sub 0)/delta,R/delta). The complex function C depends only weakly on R/delta, indicating that x0/delta is more appropriate as a scaling variable than the Keulegan-Carpenter number KC = pi*x(sub 0)/R. The measurements used a torsion oscillator driven at frequencies from 1 to 12 Hz while immersed in dense xenon. The oscillator comprised cylinders with an effective radius of R = 13.4 micron and oscillation amplitudes as large as x(sub 0)/delta = 4 (corresponding to KC as large as 71). The calculations used similar conditions except that the amplitudes were as large as x0/delta = 28.

  16. Stimulus-dependent modulation of spontaneous low-frequency oscillations in the rat visual cortex.

    PubMed

    Huang, Liangming; Liu, Yadong; Gui, Jianjun; Li, Ming; Hu, Dewen

    2014-06-09

    Research on spontaneous low-frequency oscillations is important to reveal underlying regulatory mechanisms in the brain. The mechanism for the stimulus modulation of low-frequency oscillations is not known. Here, we used the intrinsic optical imaging technique to examine stimulus-modulated low-frequency oscillation signals in the rat visual cortex. The stimulation was presented monocularly as a flashing light with different frequencies and intensities. The phases of low-frequency oscillations in different regions tended to be synchronized and the rhythms typically accelerated within a 30-s period after stimulation. These phenomena were confined to visual stimuli with specific flashing frequencies (12.5-17.5 Hz) and intensities (5-10 mA). The acceleration and synchronization induced by the flashing frequency were more marked than those induced by the intensity. These results show that spontaneous low-frequency oscillations can be modulated by parameter-dependent flashing lights and indicate the potential utility of the visual stimulus paradigm in exploring the origin and function of low-frequency oscillations.

  17. Synchronization of low-frequency oscillations in the human cardiovascular system

    NASA Astrophysics Data System (ADS)

    Karavaev, A. S.; Prokhorov, M. D.; Ponomarenko, V. I.; Kiselev, A. R.; Gridnev, V. I.; Ruban, E. I.; Bezruchko, B. P.

    2009-09-01

    We investigate synchronization between the low-frequency oscillations of heart rate and blood pressure having in humans a basic frequency close to 0.1 Hz. A method is proposed for quantitative estimation of synchronization between these oscillating processes based on calculation of relative time of phase synchronization of oscillations. It is shown that healthy subjects exhibit on average substantially longer epochs of internal synchronization between the low-frequency oscillations in heart rate and blood pressure than patients after acute myocardial infarction.

  18. Seismology and geodesy of the sun: Low-frequency oscillations.

    PubMed

    Dicke, R H

    1981-04-01

    The hourly averages of the solar ellipticity measured from June 13 to Sept. 17, 1966, are analyzed for indications of solar oscillations with periods in excess of 2 hr nu < 0.5 hr(-1). Nothing significant is found for frequencies nu > 0.1 hr(-1) but for lower frequencies the power spectrum shows a very complex structure containing about 20 strong narrow peaks. The complexity is illusionary. The signal apparently consists of only two frequencies. The complexity is due to aliasing by the window function with its basic 24-hr period, with many observational days missing, and with different numbers of hourly averages for the various observational days. Both signal frequencies are apparently due to odd-degree spherical harmonic oscillations of the sun.

  19. Seismology and geodesy of the sun: low-frequency oscillations

    SciTech Connect

    Dicke, R.H.

    1981-04-01

    The hourly averages of the solar ellipticity measured from June 13 to September 17, 1966, are analyzed for indications of solar oscillations with periods in excess of 2 h ..nu.. < 0.5 h/sup -1/. Nothing significant is found for frequencies ..nu.. > 0.1 hr/sup -1/ but for lower frequencies the power spectrum shows a very complex structure containing about 20 strong narrow peaks. The complexity is illusionary. The signal apparently consists of only two frequencies. The complexity is due to aliasing by the window function with its basic 24-h period, with many observational days missing, and with different numbers of hourly averages for the various observational days. Both signal frequencies are apparently due to odd-degree spherical harmonic oscillations of the sun.

  20. Low-frequency calcium oscillations accompany deoxyhemoglobin oscillations in rat somatosensory cortex

    PubMed Central

    Du, Congwu; Volkow, Nora D.; Koretsky, Alan P.; Pan, Yingtian

    2014-01-01

    Spontaneous low-frequency oscillations (LFOs) of blood-oxygen-level-dependent (BOLD) signals are used to map brain functional connectivity with functional MRI, but their source is not well understood. Here we used optical imaging to assess whether LFOs from vascular signals covary with oscillatory intracellular calcium (Ca2+i) and with local field potentials in the rat’s somatosensory cortex. We observed that the frequency of Ca2+i oscillations in tissue (∼0.07 Hz) was similar to the LFOs of deoxyhemoglobin (HbR) and oxyhemoglobin (HbO2) in both large blood vessels and capillaries. The HbR and HbO2 fluctuations within tissue correlated with Ca2+i oscillations with a lag time of ∼5–6 s. The Ca2+i and hemoglobin oscillations were insensitive to hypercapnia. In contrast, cerebral-blood-flow velocity (CBFv) in arteries and veins fluctuated at a higher frequency (∼0.12 Hz) and was sensitive to hypercapnia. However, in parenchymal tissue, CBFv oscillated with peaks at both ∼0.06 Hz and ∼0.12 Hz. Although the higher-frequency CBFv oscillation (∼0.12 Hz) was decreased by hypercapnia, its lower-frequency component (∼0.06 Hz) was not. The sensitivity of the higher CBFV oscillations to hypercapnia, which triggers blood vessel vasodilation, suggests its dependence on vascular effects that are distinct from the LFOs detected in HbR, HbO2, Ca2+i, and the lower-frequency tissue CBFv, which were insensitive to hypercapnia. Hemodynamic LFOs correlated both with Ca2+i and neuronal firing (local field potentials), indicating that they directly reflect neuronal activity (perhaps also glial). These findings show that HbR fluctuations (basis of BOLD oscillations) are linked to oscillatory cellular activity and detectable throughout the vascular tree (arteries, capillaries, and veins). PMID:25313035

  1. Low-frequency oscillation in a narrow vibrated granular system

    NASA Astrophysics Data System (ADS)

    Oyarte Gálvez, Loreto; van der Meer, Devaraj

    2015-11-01

    The analogy of the behaviour of granular materials with that of fluids has motivated much appealing research. An important example is a vertically shaken granular bed which exhibits fluid-like behavior, such as the Leidenfrost effect where a dense layer of grains floats on top of a gaseous layer, just like when a liquid droplet floats on its own vapour above a hot plate. When the shaking energy is increased the granular bed transits from the Leidenfrost to the convection state, for which a precursor is expected in the form of an oscillation of the bed as a whole. This precursor was observed numerically like an oscillation in the motion of the dense part, where the frequency of this oscillation is much lower than the frequency of the injected energy, and appears more relevant when the system is getting closer to the convective state. We built a setup that permits the observation of the granular Leidenfrost effect for a wide range of driving parameters. More specifically, a monodisperse granular material is contained in a transparent box and vertically shaken, and a fast camera is used to study its dynamics. The presence of a LFO is directly measured by images analysis and shows a good agreement with the previous numerical and experimental works.

  2. Analytical theory of low-frequency space charge oscillations in gyrotrons

    SciTech Connect

    Yan Ran; Antonsen, T. M. Jr.; Nusinovich, G. S.

    2008-10-15

    Low-frequency oscillations attributed to reflected electrons bouncing adiabatically between the electron gun and the interaction space have been observed in many gyrotrons. An analytical model is considered which allows one to apply space-charge wave theory to the analysis of these oscillations. In the framework of the small-signal theory, the regions of low-frequency oscillations, the oscillation frequency and the temporal and spatial growth rates of low-frequency oscillations are determined in the relevant parameter space. The mode frequency is determined not only by the particle travel time, but by the travel time of charge waves on the reflected electron beam. This explains the existence of modes with noncommensurate frequencies.

  3. Numerical Investigation of the Low-Frequency Flow Oscillation over NACA-0012 Aerofoil

    NASA Astrophysics Data System (ADS)

    Elawad, Yasir A.; Eljack, Eltayeb M.

    2017-03-01

    The present study investigates the low-frequency flow oscillation phenomenon near stall conditions for NACA0012 aerofoil at Reynolds number of 9 × 104, Mach number of and angle of attack of 11.0°. The phenomenon is clearly captured in the time histories of aerodynamic coefficients. Statistical and spectral analysis are carried out for time histories of aerodynamic coefficients. Qualitative study is performed to investigate the unsteady behaviour of laminar separation bubble over one low-frequency cycle.

  4. Voluntary reduction of force variability via modulation of low-frequency oscillations.

    PubMed

    Park, Seoung Hoon; Casamento-Moran, Agostina; Yacoubi, Basma; Christou, Evangelos A

    2017-06-12

    Visual feedback can influence the force output by changing the power in frequencies below 1 Hz. However, it remains unknown whether visual guidance can help an individual reduce force variability voluntarily. The purpose of this study, therefore, was to determine whether an individual can voluntarily reduce force variability during constant contractions with visual guidance, and whether this reduction is associated with a decrease in the power of low-frequency oscillations (0-1 Hz) in force and muscle activity. Twenty young adults (27.6 ± 3.4 years) matched a force target of 15% MVC (maximal voluntary contraction) with ankle dorsiflexion. Participants performed six visually unrestricted contractions, from which we selected the trial with the least variability. Following, participants performed six visually guided contractions and were encouraged to reduce their force variability within two guidelines (±1 SD of the least variable unrestricted trial). Participants decreased the SD of force by 45% (P < 0.001) during the guided condition, without changing mean force (P > 0.2). The decrease in force variability was associated with decreased low-frequency oscillations (0-1 Hz) in force (R (2) = 0.59), which was associated with decreased low-frequency oscillations in EMG bursts (R (2) = 0.35). The reduction in low-frequency oscillations in EMG burst was positively associated with power in the interference EMG from 35 to 60 Hz (R (2) = 0.47). In conclusion, voluntary reduction of force variability is associated with decreased low-frequency oscillations in EMG bursts and consequently force output. We provide novel evidence that visual guidance allows healthy young adults to reduce force variability voluntarily likely by adjusting the low-frequency oscillations in the neural drive.

  5. Self-modulation of low-frequency oscillations in a plasma

    NASA Astrophysics Data System (ADS)

    Honzawa, Tadao

    1990-04-01

    Experimental results are reported on the self-modulation of low-frequency oscillations in a plasma. The phenomenon is observed to occur at large amplitudes above a threshold. This is clearly shown by violent changes in the envelope form of externally modulated oscillations. Resultant spiky forms of the oscillation envelopes are observed to change strongly depending on parameters such as the rf frequency, the rf amplitude, and so on. Furthermore, spectral observations give additional information on the properties of the spiky oscillations. Finally, the observed phenomenon is qualitatively interpreted using a theory on the parametric process.

  6. Amplitude of low-frequency oscillations in schizophrenia: A resting state fMRI study

    PubMed Central

    Hoptman, Matthew J.; Zuo, Xi-Nian; Butler, Pamela D.; Javitt, Daniel C.; D’Angelo, Debra; Mauro, Cristina J.; Milham, Michael P.

    2009-01-01

    Recently, a great deal of interest has arisen in resting state fMRI as a measure of tonic brain function in clinical populations. Most studies have focused on the examination of temporal correlation between resting state fMRI low-frequency oscillations (LFOs). Studies on the amplitudes of these low-frequency oscillations are rarely reported. Here, we used amplitude of low-frequency fluctuations (ALFF) and fractional ALFF (fALFF; the relative amplitude that resides in the low frequencies) to examine the amplitude of LFO in schizophrenia. Twenty-six healthy controls and 29 patients with schizophrenia or schizoaffective disorder participated. Our findings show that patients showed reduced low-frequency amplitude in proportion to the total frequency band investigated (i.e., fALFF) in the lingual gyrus, left cuneus, left insula/superior temporal gyrus, and right caudate and increased fALFF in the medial prefrontal cortex and the right parahippocampal gyrus. ALFF was reduced in patients in the lingual gyrus, cuneus, and precuneus and increased in the left parahippocampal gyrus. These results suggest LFO abnormalities in schizophrenia. The implication of these abnormalities for schizophrenic symptomatology is further discussed. PMID:19854028

  7. Synchronization of low-frequency oscillations in the cardiovascular system: Application to medical diagnostics and treatment

    NASA Astrophysics Data System (ADS)

    Ponomarenko, V. I.; Prokhorov, M. D.; Karavaev, A. S.; Kiselev, A. R.; Gridnev, V. I.; Bezruchko, B. P.

    2013-10-01

    We investigate synchronization between the low-frequency oscillations of heart rate and blood pressure having in humans a basic frequency close to 0.1 Hz. A quantitative estimation of this synchronization based on calculation of relative time of phase synchronization of oscillations is proposed. We show that assessment of synchronization between the considered oscillations can be useful for selecting an optimal dose of beta-blocker treatment in patients after acute myocardial infarction. It is found out that low value of synchronization between the low-frequency rhythms in heart rate and blood pressure at the first week after acute myocardial infarction is a sensitive marker of high risk of mortality during the subsequent 5 years.

  8. Oscillating bubble as a sensor of low frequency electro-acoustic signals in electrolytes.

    PubMed

    Tankovsky, N; Baerner, K; Barey, Dooa Abdel

    2006-08-16

    Small air-bubble deformations, caused by electro-acoustic signals generated in electrolytic solutions have been detected by angle-modulation of a refracted He-Ne laser beam. The observed electromechanical resonance at low frequency, below 100 Hz, has proved to be directly related to the oscillations of characteristic ion-doped water structures when driven by an external electric field. The presence of structure-breaking or structure-making ions modifies the water structure, which varies the mechanical losses of the oscillating system and can be registered as changes in the width of the observed resonance curves.

  9. Linkages between the North Pacific Oscillation and central tropical Pacific SSTs at low frequencies

    NASA Astrophysics Data System (ADS)

    Furtado, Jason C.; Di Lorenzo, Emanuele; Anderson, Bruce T.; Schneider, Niklas

    2012-12-01

    The North Pacific Oscillation (NPO) recently (re-)emerged in the literature as a key atmospheric mode in Northern Hemisphere climate variability, especially in the Pacific sector. Defined as a dipole of sea level pressure (SLP) between, roughly, Alaska and Hawaii, the NPO is connected with downstream weather conditions over North America, serves as the atmospheric forcing pattern of the North Pacific Gyre Oscillation (NPGO), and is a potential mechanism linking extratropical atmospheric variability to El Niño events in the tropical Pacific. This paper explores further the forcing dynamics of the NPO and, in particular, that of its individual poles. Using observational data and experiments with a simple atmospheric general circulation model (AGCM), we illustrate that the southern pole of the NPO (i.e., the one near Hawaii) contains significant power at low frequencies (7-10 years), while the northern pole (i.e., the one near Alaska) has no dominant frequencies. When examining the low-frequency content of the NPO and its poles separately, we discover that low-frequency variations (periods >7 years) of the NPO (particularly its subtropical node) are intimately tied to variability in central equatorial Pacific sea surface temperatures (SSTs) associated with the El Niño-Modoki/Central Pacific Warming (CPW) phenomenon. This result suggests that fluctuations in subtropical North Pacific SLP are important to monitor for Pacific low-frequency climate change. Using the simple AGCM, we also illustrate that variability in central tropical Pacific SSTs drives a significant fraction of variability of the southern node of the NPO. Taken together, the results highlight important links between secondary modes (i.e., CPW-NPO-NPGO) in Pacific decadal variability, akin to already established relationships between the primary modes of Pacific climate variability (i.e., canonical El Niño, the Aleutian Low, and the Pacific Decadal Oscillation).

  10. Mechanisms underlying very-low-frequency RR-interval oscillations in humans

    NASA Technical Reports Server (NTRS)

    Taylor, J. A.; Carr, D. L.; Myers, C. W.; Eckberg, D. L.

    1998-01-01

    BACKGROUND: Survival of post-myocardial infarction patients is related inversely to their levels of very-low-frequency (0.003 to 0.03 Hz) RR-interval variability. The physiological basis for such oscillations is unclear. In our study, we used blocking drugs to evaluate potential contributions of sympathetic and vagal mechanisms and the renin-angiotensin-aldosterone system to very-low-frequency RR-interval variability in 10 young healthy subjects. METHODS AND RESULTS: We recorded RR intervals and arterial pressures during three separate sessions, with the patient in supine and 40 degree upright tilt positions, during 20-minute frequency (0.25 Hz) and tidal volume-controlled breathing after intravenous injections: saline (control), atenolol (0.2 mg/kg, beta-adrenergic blockade), atropine sulfate (0.04 mg/kg, parasympathetic blockade), atenolol and atropine (complete autonomic blockade), and enalaprilat (0.02 mg/kg, ACE blockade). We integrated fast Fourier transform RR-interval spectral power at very low (0.003 to 0.03 Hz), low (0.05 to 0. 15 Hz), and respiratory (0.2 to 0.3 Hz) frequencies. Beta-adrenergic blockade had no significant effect on very-low- or low-frequency RR-interval power but increased respiratory frequency power 2-fold. ACE blockade had no significant effect on low or respiratory frequency RR-interval power but modestly (approximately 21%) increased very-low-frequency power in the supine (but not upright tilt) position (P<0.05). The most profound effects were exerted by parasympathetic blockade: Atropine, given alone or with atenolol, abolished nearly all RR-interval variability and decreased very-low-frequency variability by 92%. CONCLUSIONS: Although very-low-frequency heart period rhythms are influenced by the renin-angiotensin-aldosterone system, as low and respiratory frequency RR-interval rhythms, they depend primarily on the presence of parasympathetic outflow. Therefore the prognostic value of very-low-frequency heart period oscillations may

  11. Mechanisms underlying very-low-frequency RR-interval oscillations in humans

    NASA Technical Reports Server (NTRS)

    Taylor, J. A.; Carr, D. L.; Myers, C. W.; Eckberg, D. L.

    1998-01-01

    BACKGROUND: Survival of post-myocardial infarction patients is related inversely to their levels of very-low-frequency (0.003 to 0.03 Hz) RR-interval variability. The physiological basis for such oscillations is unclear. In our study, we used blocking drugs to evaluate potential contributions of sympathetic and vagal mechanisms and the renin-angiotensin-aldosterone system to very-low-frequency RR-interval variability in 10 young healthy subjects. METHODS AND RESULTS: We recorded RR intervals and arterial pressures during three separate sessions, with the patient in supine and 40 degree upright tilt positions, during 20-minute frequency (0.25 Hz) and tidal volume-controlled breathing after intravenous injections: saline (control), atenolol (0.2 mg/kg, beta-adrenergic blockade), atropine sulfate (0.04 mg/kg, parasympathetic blockade), atenolol and atropine (complete autonomic blockade), and enalaprilat (0.02 mg/kg, ACE blockade). We integrated fast Fourier transform RR-interval spectral power at very low (0.003 to 0.03 Hz), low (0.05 to 0. 15 Hz), and respiratory (0.2 to 0.3 Hz) frequencies. Beta-adrenergic blockade had no significant effect on very-low- or low-frequency RR-interval power but increased respiratory frequency power 2-fold. ACE blockade had no significant effect on low or respiratory frequency RR-interval power but modestly (approximately 21%) increased very-low-frequency power in the supine (but not upright tilt) position (P<0.05). The most profound effects were exerted by parasympathetic blockade: Atropine, given alone or with atenolol, abolished nearly all RR-interval variability and decreased very-low-frequency variability by 92%. CONCLUSIONS: Although very-low-frequency heart period rhythms are influenced by the renin-angiotensin-aldosterone system, as low and respiratory frequency RR-interval rhythms, they depend primarily on the presence of parasympathetic outflow. Therefore the prognostic value of very-low-frequency heart period oscillations may

  12. Stabilizing low-frequency oscillation with two-stage filter in Hall thrusters

    NASA Astrophysics Data System (ADS)

    Wei, Liqiu; Han, Liang; Ding, Yongjie; Yu, Daren; Zhang, Chaohai

    2017-07-01

    The use of a filter is the most common method to suppress low-frequency discharge current oscillation in Hall thrusters. The only form of filter in actual use involves RLC networks, which serve the purpose of reducing the level of conducted electromagnetic interference returning to the power processing unit, which is the function of a filter. Recently, the role of the filter in the oscillation control was introduced. It has been noted that the filter regulates the voltage across itself according to the variation of discharge current so as to decrease its fluctuation in the discharge circuit, which is the function of a controller. Therefore, a kind of two-stage filter is proposed to fulfill these two purposes, filtering and controlling, and the detailed design methods are discussed and verified. A current oscillation attenuation ratio of 10 was achieved by different capacitance and inductance combinations of the filter stage, and the standard deviation of low-frequency oscillations decreased from 3 A-1 A by the control stage in our experiment.

  13. A theoretical investigation of low frequency diameter oscillations of muscular arteries.

    PubMed

    Achakri, H; Rachev, A; Stergiopulos, N; Meister, J J

    1994-01-01

    Spontaneous low frequency diameter oscillations have been observed in vivo in some muscular arteries. The aim of this paper is to propose a possible mechanism for their appearance. A lumped parameter mathematical model for the mechanical response of an artery perfused with constant flow is proposed, which takes into account the active behavior of the vascular smooth muscle. The system of governing equations is reduced into two nonlinear autonomous differential equations for the arterial circumferential stretch ratio, and the concentration of calcium ions, Ca2+, within the smooth muscle cells. Factors controlling the muscular tone are taken into account by assuming that the rate of change of Ca2+ depends on arterial pressure and on shear stress acting on the endothelium. Using the theory of dynamical systems, it was found that the stationary solution of the set of governing equations may become unstable and a periodic solution arises, yielding self-sustained diameter oscillations. It is found that a necessary condition for the appearance of diameter oscillations is the existence of a negative slope of the steady state pressure-diameter relationship, a phenomenon known to exist in arterioles. A numerical parametric study was performed and bifurcation diagrams were obtained for a typical muscular artery. Results show that low frequency diameter oscillations develop when the magnitude of the perfused inflow, the distal resistance, as well as the length of the artery are within a range of critical values.

  14. A preliminary analysis of low frequency pressure oscillations in hybrid rocket motors

    NASA Astrophysics Data System (ADS)

    Jenkins, Rhonald M.

    1994-10-01

    Past research with hybrid rockets has suggested that certain motor operating conditions are conducive to the formation of pressure oscillations, or flow instabilities, within the motor combustion chamber. These combustion-related vibrations or pressure oscillations may be encountered in virtually any type of rocket motor and typically fall into three frequency ranges: low frequency oscillations (0-300 Hz); intermediate frequency oscillations (400-1000 Hz); and high frequency oscillations (greater than 1000 Hz). In general, combustion instability is characterized by organized pressure oscillations occurring at well-defined intervals with pressure peaks that may maintain themselves, grow, or die out. Usually, such peaks exceed +/- 5% of the mean chamber pressure. For hybrid motors, these oscillations have been observed to grow to a limiting amplitude which may be dependent on factors such as fuel characteristics, oxidizer injector characteristics, average chamber pressure, oxidizer mass flux, combustion chamber length, and grain geometry. The approach taken in the present analysis is to develop a modified chamber length, L, instability theory which accounts for the relationship between pressure and oxidizer to fuel concentration ratio in the motor.

  15. A preliminary analysis of low frequency pressure oscillations in hybrid rocket motors

    NASA Technical Reports Server (NTRS)

    Jenkins, Rhonald M.

    1994-01-01

    Past research with hybrid rockets has suggested that certain motor operating conditions are conducive to the formation of pressure oscillations, or flow instabilities, within the motor combustion chamber. These combustion-related vibrations or pressure oscillations may be encountered in virtually any type of rocket motor and typically fall into three frequency ranges: low frequency oscillations (0-300 Hz); intermediate frequency oscillations (400-1000 Hz); and high frequency oscillations (greater than 1000 Hz). In general, combustion instability is characterized by organized pressure oscillations occurring at well-defined intervals with pressure peaks that may maintain themselves, grow, or die out. Usually, such peaks exceed +/- 5% of the mean chamber pressure. For hybrid motors, these oscillations have been observed to grow to a limiting amplitude which may be dependent on factors such as fuel characteristics, oxidizer injector characteristics, average chamber pressure, oxidizer mass flux, combustion chamber length, and grain geometry. The approach taken in the present analysis is to develop a modified chamber length, L, instability theory which accounts for the relationship between pressure and oxidizer to fuel concentration ratio in the motor.

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

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

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

  17. Increased Amplitude of Thalamocortical Low-Frequency Oscillations in Patients with Migraine

    PubMed Central

    Wilcox, Sophie L.; Veggeberg, Rosanna; Noseda, Rodrigo; Burstein, Rami; Borsook, David; Becerra, Lino

    2016-01-01

    For many years, neurobiological theories have emphasized the importance of neuronal oscillations in the emergence of brain function. At the same time, clinical studies have shown that disturbances or irregularities in brain rhythms may relate to various common neurological conditions, including migraine. Increasing evidence suggests that the CNS plays a fundamental role in the predisposition to develop different forms of headache. Here, we present human imaging data that strongly support the presence of abnormal low-frequency oscillations (LFOs) in thalamocortical networks of patients in the interictal phase of migraine. Our results show that the main source of arrhythmic activity was localized to the higher-order thalamic relays of the medial dorsal nucleus. In addition, spontaneous LFOs in the thalamus were selectively associated with the headache attack frequency, meaning that the varying amplitude of dysrhythmia could predispose patients to recurrent attacks. Rhythmic cortical feedback to the thalamus is a major factor in the amplification of thalamocortical oscillations, making it a strong candidate for influencing neuronal excitability. We further speculate that the intrinsic dynamics of thalamocortical network oscillations are crucial for early sensory processing and therefore could underlie important pathophysiological processes involved in multisensory integration. SIGNIFICANCE STATEMENT In many cases, migraine attacks are thought to begin centrally. A major obstacle to studying intrinsic brain activity has been the identification of the precise anatomical structures and functional networks that are involved in migraine. Here, we present imaging data that strongly support the presence of abnormal low-frequency oscillations in thalamocortical networks of patients in the interictal phase of migraine. This arrhythmic activity was localized to the higher-order thalamic relays of the medial dorsal nucleus and was selectively associated with headache attack

  18. A precluding but not ensuring role of entrained low-frequency oscillations for auditory perception.

    PubMed

    Ng, Benedict Shien Wei; Schroeder, Tim; Kayser, Christoph

    2012-08-29

    Oscillatory activity in sensory cortices reflects changes in local excitation-inhibition balance, and recent work suggests that phase signatures of ongoing oscillations predict the perceptual detection of subsequent stimuli. Low-frequency oscillations are also entrained by dynamic natural scenes, suggesting that the chance of detecting a brief target depends on the relative timing of this to the entrained rhythm. We tested this hypothesis in humans by implementing a cocktail-party-like scenario requiring subjects to detect a target embedded in a cacophony of background sounds. Using EEG to measure auditory cortical oscillations, we find that the chance of target detection systematically depends on both power and phase of theta-band (2-6 Hz) but not alpha-band (8-12 Hz) oscillations before target. Detection rates were higher and responses faster when oscillatory power was low and both detection rate and response speed were modulated by phase. Intriguingly, the phase dependency was stronger for miss than for hit trials, suggesting that phase has a inhibiting but not ensuring role for detection. Entrainment of theta range oscillations prominently occurs during the processing of attended complex stimuli, such as vocalizations and speech. Our results demonstrate that this entrainment to attended sensory environments may have negative effects on the detection of individual tokens within the environment, and they support the notion that specific phase ranges of cortical oscillations act as gatekeepers for perception.

  19. Comparison between simultaneous GOLF and MDI observations in search of low frequency solar oscillations

    NASA Astrophysics Data System (ADS)

    Henney, Carl John

    One of the mission objectives of both the Global Oscillations at Low Frequency (GOLF) and the Michelson Doppler Imager (MDI) instruments aboard the Solar and Heliospheric Observatory (SOHO) is the detection of new low frequency globally coherent solar oscillation modes. After more than two years of nearly continuous observing by both instruments, the clear detection of modes below 1200 μHz has still proven to be elusive. The search for new modes is aided here by combining the high duty cycle of GOLF with the spatial resolution and various data products of MDI. By combining the two data sets, a signal enhancement is anticipated since both instruments provide a low noise data stream and their sources of solar and instrumental noise are expected to be different from each other. Presented here is a comparison between the observed GOLF signal and a selection of spatially masked MDI full-disk signals for a 759 day period from May 25, 1996 through June 22, 1998. The signal-to-background ratio is compared between the various signals for low degree (l <= 3) and low frequency (<2000 μHz) p-modes. It was found that signals from both MDI and GOLF are beneficial for detecting these p-modes. Cross-analysis between GOLF and MDI signals is done to enhance the ability to detect low frequency solar oscillations. Using cross-amplitude and averaged power spectra, an unique list of low degree modes is presented here, along with three new low frequency acoustic mode candidates. Finally, the effects of early main sequence cometary mass accretion with heavy-element diffusion on the solar interior are investigated. For solar models with element diffusion, the addition of mass accretion with a rate suggested by observations of other stars has a negligible effect on the predicted p-mode frequencies for the cases investigated here. The predicted g-mode frequencies exhibit a slight shift of approximately 0.1 μHz with the addition of mass accretion. Compared to previous work, the squared

  20. A dual resonant rectilinear-to-rotary oscillation converter for low frequency broadband electromagnetic energy harvesting

    NASA Astrophysics Data System (ADS)

    Deng, Wei; Wang, Ya

    2017-09-01

    This paper reports a dual resonant rectilinear-to-rotary oscillation converter (RROC) for low frequency broadband electromagnetic energy harvesting from ambient vibrations. An approximate theoretical model has been established to integrate the electromechanical coupling into a comprehensive electromagnetic-dynamic model of the dual resonant RROC. Numerical simulation has proved the nature of dual resonances by revealing that both the rectilinear resonance and the rotary resonance could be achieved when the stand-alone rectilinear oscillator (RLO) and the stand-alone rotary oscillator (RTO) were excited independently. Simulation on the magnetically coupled RROC has also shown that the rectilinear resonance and the rotary resonance could be obtained simultaneously in the low-frequency region (2-14 Hz) with well-defined restoring torque (M r ) and the initial rotation angle of the RLO (ψ). The magnetic interaction patterns between the rectilinear and the RTOs have been categorized based on aforementioned simulation results. Both simulation and experimental results have demonstrated broadband output attributing from the dual resonances. Experimental results have also indicated that the RROC could have wide bandwidth in a much lower frequency region (2-8 Hz) even without the rotary resonance as long as the system parameters are carefully tuned. Parameter analysis on different values of M r and ψ are experimentally carried out to provide a quantitative guidance of designing the RROC to achieve an optimal power density.

  1. Low Frequency High Amplitude Temperature Oscillations in Loop Heat Pipe Operation

    NASA Technical Reports Server (NTRS)

    Ku, Jentung; Rodriquez, Jose; Simpson, Alda D. (Technical Monitor)

    2003-01-01

    This paper presents a theory that explains low frequency, high amplitude temperature oscillations in loop heat pipe (LHP) operation. Oscillations of the CC temperature with amplitudes on the order of tens of degrees Kelvin and periods on the order of hours have been observed in some LHPs during ambient testing. There are presently no satisfactory explanations for such a phenomenon in the literature. It is well-known that the operating temperature of an LHP with a single evaporator is governed by the compensation chamber (CC) temperature, which in turn is a function of the evaporator heat load, sink temperature, and ambient temperature. As the operating condition changes, the CC temperature will change during the transient but eventually reach a new steady temperature. Under certain conditions, however, the LHP never really reaches a true steady state, but instead displays an oscillatory behavior. The proposed new theory describes why low frequency, high amplitude oscillations may occur when the LHP has a low evaporator power, a low heat sink temperature (below ambient temperature), and a large thermal mass attached to the evaporator. When this condition prevails, there are some complex interactions between the CC, condenser, thermal mass and ambient. The temperature oscillation is a result of the large movement of the vapor front inside the condenser, which is caused by a change in the net evaporator power modulated by the large thermal mass through its interaction with the sink and CC. The theory agrees very well with previously published test data. Effects of various parameters on the amplitude and frequency of the temperature oscillation are also discussed.

  2. Measurements of the Plasma Parameters and Low Frequency Oscillations in the Fisk Plasma Source

    NASA Technical Reports Server (NTRS)

    Thomas, Edward, Jr.; Wallace, Kent; Lampkin, Gregory; Watson, Michael

    1998-01-01

    A new plasma device, the Fisk Plasma Source (FPS), has been developed at Fisk University. This plasma device is used to study the physics of low temperature plasmas and plasma-material interactions. The FPS device is a stainless steel vacuum 6-way cross vacuum vessel with at 10-inch inner diameter. Low temperature argon plasmas are generated using DC glow discharge and thermionic filament techniques. Spatial profiles of the plasma density, plasma potential, and electron temperature are measured using Langmuir probes. We present initial experimental measurements of density and temperature profiles in the FPS device. Experimental and theoretical studies of low frequency oscillations observed in the FPS device are also presented.

  3. Distinguishing low frequency oscillations within the 1/f spectral behaviour of electromagnetic brain signals

    PubMed Central

    Demanuele, Charmaine; James, Christopher J; Sonuga-Barke, Edmund JS

    2007-01-01

    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. PMID:18070337

  4. Multifaceted roles for low-frequency oscillations in bottom-up and top-down processing during navigation and memory.

    PubMed

    Ekstrom, Arne D; Watrous, Andrew J

    2014-01-15

    A prominent and replicated finding is the correlation between running speed and increases in low-frequency oscillatory activity in the hippocampal local field potential. A more recent finding concerns low-frequency oscillations that increase in coherence between the hippocampus and neocortical brain areas such as prefrontal cortex during memory-related behaviors (i.e., remembering the correct location to visit). In this review, we tie together movement-related and memory-related low-frequency oscillations in the rodent with similar findings in humans. We argue that although movement-related low-frequency oscillations, in particular, may have slightly different characteristics in humans than rodents, placing important constraints on our thinking about this issue, both phenomena have similar functional foundations. We review four prominent theoretical models that provide partially conflicting accounts of movement-related low-frequency oscillations. We attempt to tie together these theoretical proposals, and existing data in rodents and humans, with memory-related low-frequency oscillations. We propose that movement-related low-frequency oscillations and memory-related low-frequency oscillatory activity, both of which show significant coherence with oscillations in other brain regions, represent different facets of "spectral fingerprints," or different resonant frequencies within the same brain networks underlying different cognitive processes. Together, movement-related and memory-related low-frequency oscillatory coupling may be linked by their distinct contributions to bottom-up, sensorimotor driven processing and top-down, controlled processing characterizing aspects of memory encoding and retrieval.

  5. Low-frequency theta oscillations in the human hippocampus during real-world and virtual navigation

    PubMed Central

    Bohbot, Véronique D.; Copara, Milagros S.; Gotman, Jean; Ekstrom, Arne D.

    2017-01-01

    Low-Frequency Oscillations (LFO) in the range of 7–9 Hz, or theta rhythm, has been recorded in rodents ambulating in the real world. However, intra-hippocampus EEG recordings during virtual navigation in humans have consistently reported LFO that appear to predominate around 3–4 Hz. Here we report clear evidence of 7–9 Hz rhythmicity in raw intra-hippocampus EEG traces during real as well as virtual movement. Oscillations typically occur at a lower frequency in virtual than real world navigation. This study highlights the possibility that human and rodent hippocampal EEG activity are not as different as previously reported and this difference may arise, in part, due to the lack of actual movement in previous human navigation studies, which were virtual. PMID:28195129

  6. Low frequency oscillations in semi-insulating GaAs: a nonlinear analysis.

    PubMed

    Rubinger, R M; da Silva, R L; de Oliveira, A G; Ribeiro, G M; Albuquerque, H A; Rodrigues, W N; Moreira, M V B

    2003-06-01

    We have observed low frequency current oscillations in a semi-insulating GaAs sample grown by low temperature molecular beam epitaxy. For this, an experimental setup proper to measure high impedance samples with small external noise was developed. Spontaneous oscillations in the current were observed for some bias conditions. Although measurements were carried out from room temperature down to liquid helium, the dynamical analysis was carried out around 200 K where the signal to noise ratio was fairly favorable. To increase the data quality we have also used a noise reduction algorithm suitably developed for nonlinear systems. We observed attractors having low embedding dimension, limit cycle bifurcations, and chaotic behavior characteristic of nonlinear dynamical processes in route to chaos. Attractor reconstruction, Poincare sections, Lyapunov exponents, and correlation dimension were also analyzed.

  7. Low-frequency theta oscillations in the human hippocampus during real-world and virtual navigation.

    PubMed

    Bohbot, Véronique D; Copara, Milagros S; Gotman, Jean; Ekstrom, Arne D

    2017-02-14

    Low-Frequency Oscillations (LFO) in the range of 7-9 Hz, or theta rhythm, has been recorded in rodents ambulating in the real world. However, intra-hippocampus EEG recordings during virtual navigation in humans have consistently reported LFO that appear to predominate around 3-4 Hz. Here we report clear evidence of 7-9 Hz rhythmicity in raw intra-hippocampus EEG traces during real as well as virtual movement. Oscillations typically occur at a lower frequency in virtual than real world navigation. This study highlights the possibility that human and rodent hippocampal EEG activity are not as different as previously reported and this difference may arise, in part, due to the lack of actual movement in previous human navigation studies, which were virtual.

  8. Comparing origins of low-frequency quasi-periodic oscillations with spectral-timing

    NASA Astrophysics Data System (ADS)

    Stevens, Abigail L.; Uttley, Phil

    2017-08-01

    The light curves of low-mass X-ray binaries show variability on timescales from milliseconds to months. The rapid (sub-second) variability is particularly interesting because it is thought to probe the inner region of the accretion disk and the central compact object. Observations suggest that different types of low-frequency quasi-periodic oscillations (QPOs) are associated with different emitting-region geometries (e.g., disk-like or jet-like) in the innermost part of the X-ray binary, that are varying possibly due to general relativistic precession. A new way to analyze QPOs is with spectral-timing, which seeks to investigate how matter behaves in the strong gravitational field around the compact object by causally linking the variations from different spectral components. We developed a technique for phase-resolved spectroscopy of QPOs, and are applying it to two types of low-frequency QPOs from the black hole X-ray binary GX 339-4. Over a QPO “period”, we find that the energy spectrum changes not only in normalization, but also in spectral shape. We can quantify how the spectral shape changes as a function of QPO phase, and the two different QPOs show markedly different spectral changes. The "Type B" low-frequency QPO shows evidence of a large-scale-height (jet-like) power-law- emitting precessing region, while in the same outburst the "Type C" low-frequency QPO shows evidence of a small-scale-height (disk-like) power-law-emitting precessing region. These interpretations can be used to look into the evolution of matter in the strong-gravity regime.

  9. Proteomic response of Schizosaccharomyces pombe to static and oscillating extremely low-frequency electromagnetic fields.

    PubMed

    Sinclair, John; Weeks, Mark; Butt, Amna; Worthington, Jessica L; Akpan, Akunna; Jones, Nic; Waterfield, Mike; Allanand, Donald; Timms, John F

    2006-09-01

    There is considerable public concern regarding the health effects of exposure to low-frequency electromagnetic fields. In addition, the association between exposure and disease incidence or the possible biological effects of exposure are unclear. Using 2D-DIGE and MS in a blind study, we have investigated the effects of static and oscillating extremely low-frequency electromagnetic fields (ELF EMFs) on the proteomes of wild type Schizosaccharomyces pombe and a Sty1p deletion mutant which displays increased sensitivity to a variety of cellular stresses. Whilst this study identifies a number of protein isoforms that display significant differential expression across experimental conditions, there was no correlation between their patterns of expression and the ELF EMF exposure regimen. We conclude that there are no significant effects of either static or oscillating EMF on the yeast proteome at the sensitivity afforded by 2D-DIGE. We hypothesise that the proteins identified must be sensitive to subtle changes in culture and/or handling conditions, and that the identification of these proteins in other proteomic studies should be treated with some caution when the results of such studies are interpreted in a biological context.

  10. Hemodynamic low-frequency oscillation reflects resting-state neuronal activity in rodent brain

    NASA Astrophysics Data System (ADS)

    Chen, Wei; Liu, Peng; Li, James; Pan, Yingtian; Du, Congwu

    2015-03-01

    Brain functional connectivity is mapped using spontaneous low-frequency oscillations (LFOs) in blood-oxygen-leveldependent (BOLD) signals using fMRI. However, the origin of spontaneous BOLD oscillations remains elusive. Specifically, the coupling of regional hemodynamic LFOs to neuronal activity in a resting brain is rarely examined directly. Here we present a method based on instantaneous-frequency (IF) analysis to detect regional LFOs of cerebral blood flow (CBF) along with local-field potential (LFP) changes of neurons in resting state to study neurovascular coupling. CBF and LFP were simultaneously acquired using laser Doppler flowmetry (LDF) and electroencephalography in the rat's somatosensory cortex with high temporal resolution (i.e., 20Hz for CBF and 2kHz for LDF, respectively). Instead of fast Fourier transform analysis, a peak-detection algorithm was used to define the LFP activities and CBF spontaneous oscillations in the time domain and the time lapses were used to calculate the IFs of hemodynamic (i.e., CBF) oscillations and neuronal (i.e., LFP) activities. Our results showed that the CBF mostly oscillated at ~0.1Hz with a full-half-bandwidth of [0.08Hz, 0.15Hz]. In addition, the maximal frequency of LFP firings was also approximately at 0.1Hz, which collaborated with to the frequency of CBF oscillations. Interestingly, CBF increased linearly with the LFP activity up to 0.15Hz (r=0.93), and both signals then decreased rapidly as a function of activity frequency. This indicates the spontaneous hemodynamic LFOs were associated with neuronal activities, thus confirming the neuronal origin of the hemodynamic oscillations.

  11. Low Frequency Plasma Oscillations in a 6-kW Magnetically Shielded Hall Thruster

    NASA Technical Reports Server (NTRS)

    Jorns, Benjamin A.; Hofery, Richard R.

    2013-01-01

    The oscillations from 0-100 kHz in a 6-kW magnetically shielded thruster are experimen- tally characterized. Changes in plasma parameters that result from the magnetic shielding of Hall thrusters have the potential to significantly alter thruster transients. A detailed investigation of the resulting oscillations is necessary both for the purpose of determin- ing the underlying physical processes governing time-dependent behavior in magnetically shielded thrusters as well as for improving thruster models. In this investigation, a high speed camera and a translating ion saturation probe are employed to examine the spatial extent and nature of oscillations from 0-100 kHz in the H6MS thruster. Two modes are identified at 8 kHz and 75-90 kHz. The low frequency mode is azimuthally uniform across the thruster face while the high frequency oscillation is concentrated close to the thruster centerline with an m = 1 azimuthal dependence. These experimental results are discussed in the context of wave theory as well as published observations from an unshielded variant of the H6MS thruster.

  12. Relating Intrinsic Low-Frequency BOLD Cortical Oscillations to Cognition in Schizophrenia

    PubMed Central

    Fryer, Susanna L; Roach, Brian J; Ford, Judith M; Turner, Jessica A; van Erp, Theo G M; Voyvodic, James; Preda, Adrian; Belger, Aysenil; Bustillo, Juan; O'Leary, Daniel; Mueller, Bryon A; Lim, Kelvin O; McEwen, Sarah C; Calhoun, Vince D; Diaz, Michelle; Glover, Gary; Greve, Douglas; Wible, Cynthia G; Vaidya, Jatin; Potkin, Steven G; Mathalon, Daniel H

    2015-01-01

    The amplitude of low-frequency fluctuations (ALFF) in the blood oxygenation level-dependent (BOLD) signal during resting-state fMRI reflects the magnitude of local low-frequency BOLD oscillations, rather than interregional connectivity. ALFF is of interest to studies of cognition because fluctuations in spontaneous intrinsic brain activity relate to, and possibly even constrain, task-evoked brain responses in healthy people. Lower ALFF has been reported in schizophrenia, but the cognitive correlates of these reductions remain unknown. Here, we assess relationships between ALFF and attention and working memory in order to establish the functional relevance of intrinsic BOLD oscillatory power alterations with respect to specific cognitive impairments in schizophrenia. As part of the multisite FBIRN study, resting-state fMRI data were collected from schizophrenia subjects (SZ; n=168) and healthy controls (HC; n=166). Voxelwise fractional ALFF (fALFF), a normalized ALFF measure, was regressed on neuropsychological measures of sustained attention and working memory in SZ and HC to identify regions showing either common slopes across groups or slope differences between groups (all findings p<0.01 height, p<0.05 family-wise error cluster corrected). Poorer sustained attention was associated with smaller fALFF in the left superior frontal cortex and bilateral temporoparietal junction in both groups, with additional relationships in bilateral posterior parietal, posterior cingulate, dorsal anterior cingulate (ACC), and right dorsolateral prefrontal cortex (DLPFC) evident only in SZ. Poorer working memory was associated with smaller fALFF in bilateral ACC/mPFC, DLPFC, and posterior parietal cortex in both groups. Our findings indicate that smaller amplitudes of low-frequency BOLD oscillations during rest, measured by fALFF, were significantly associated with poorer cognitive performance, sometimes similarly in both groups and sometimes only in SZ, in regions known to

  13. Relating Intrinsic Low-Frequency BOLD Cortical Oscillations to Cognition in Schizophrenia.

    PubMed

    Fryer, Susanna L; Roach, Brian J; Ford, Judith M; Turner, Jessica A; van Erp, Theo G M; Voyvodic, James; Preda, Adrian; Belger, Aysenil; Bustillo, Juan; O'Leary, Daniel; Mueller, Bryon A; Lim, Kelvin O; McEwen, Sarah C; Calhoun, Vince D; Diaz, Michelle; Glover, Gary; Greve, Douglas; Wible, Cynthia G; Vaidya, Jatin; Potkin, Steven G; Mathalon, Daniel H

    2015-11-01

    The amplitude of low-frequency fluctuations (ALFF) in the blood oxygenation level-dependent (BOLD) signal during resting-state fMRI reflects the magnitude of local low-frequency BOLD oscillations, rather than interregional connectivity. ALFF is of interest to studies of cognition because fluctuations in spontaneous intrinsic brain activity relate to, and possibly even constrain, task-evoked brain responses in healthy people. Lower ALFF has been reported in schizophrenia, but the cognitive correlates of these reductions remain unknown. Here, we assess relationships between ALFF and attention and working memory in order to establish the functional relevance of intrinsic BOLD oscillatory power alterations with respect to specific cognitive impairments in schizophrenia. As part of the multisite FBIRN study, resting-state fMRI data were collected from schizophrenia subjects (SZ; n=168) and healthy controls (HC; n=166). Voxelwise fractional ALFF (fALFF), a normalized ALFF measure, was regressed on neuropsychological measures of sustained attention and working memory in SZ and HC to identify regions showing either common slopes across groups or slope differences between groups (all findings p<0.01 height, p<0.05 family-wise error cluster corrected). Poorer sustained attention was associated with smaller fALFF in the left superior frontal cortex and bilateral temporoparietal junction in both groups, with additional relationships in bilateral posterior parietal, posterior cingulate, dorsal anterior cingulate (ACC), and right dorsolateral prefrontal cortex (DLPFC) evident only in SZ. Poorer working memory was associated with smaller fALFF in bilateral ACC/mPFC, DLPFC, and posterior parietal cortex in both groups. Our findings indicate that smaller amplitudes of low-frequency BOLD oscillations during rest, measured by fALFF, were significantly associated with poorer cognitive performance, sometimes similarly in both groups and sometimes only in SZ, in regions known to

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

    NASA Astrophysics Data System (ADS)

    Windows-Yule, C. R. K.; Rivas, N.; Parker, D. J.; Thornton, A. R.

    2014-12-01

    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 and amplitudes, with particles of varying material and using containers of differing material properties. The experimentally acquired results show a close qualitative and quantitative agreement with both theory and simulations across the range of parameters tested. Strong agreement between experimental and simulation results was also observed when investigating the influence of sidewall dissipation on LFOs and vertical density profiles. This paper additionally provides evidence of two phenomena present in the Leidenfrost state: a circulatory motion over extended time periods in near-crystalline configurations, and a Leidenfrost-like state in which the dense upper region displays an unusual inverse thermal convection.

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

    PubMed

    Windows-Yule, C R K; Rivas, N; Parker, D J; Thornton, A R

    2014-12-01

    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 and amplitudes, with particles of varying material and using containers of differing material properties. The experimentally acquired results show a close qualitative and quantitative agreement with both theory and simulations across the range of parameters tested. Strong agreement between experimental and simulation results was also observed when investigating the influence of sidewall dissipation on LFOs and vertical density profiles. This paper additionally provides evidence of two phenomena present in the Leidenfrost state: a circulatory motion over extended time periods in near-crystalline configurations, and a Leidenfrost-like state in which the dense upper region displays an unusual inverse thermal convection.

  16. The signature of low-frequency oceanic forcing in the Atlantic Multidecadal Oscillation

    NASA Astrophysics Data System (ADS)

    O'Reilly, Christopher H.; Huber, Markus; Woollings, Tim; Zanna, Laure

    2016-03-01

    The Atlantic Multidecadal Oscillation (AMO) significantly influences the climate of the surrounding continents and has previously been attributed to variations in the Atlantic Meridional Overturning Circulation. Recently, however, similar multidecadal variability was reported in climate models without ocean circulation variability. We analyze the relationship between turbulent heat fluxes and sea surface temperatures (SSTs) over the midlatitude North Atlantic in observations and coupled climate model simulations, both with and without ocean circulation variability. SST anomalies associated with the AMO are positively correlated with heat fluxes on decadal time scales in both observations and models with varying ocean circulation, whereas in models without ocean circulation variability the anomalies are negatively correlated when heat flux anomalies lead. These relationships are captured in a simple stochastic model and rely crucially on low-frequency forcing of SST. The fully coupled models that better capture this signature more effectively reproduce the observed impact of the AMO on European summertime temperatures.

  17. WAMS measurements pre-processing for detecting low-frequency oscillations in power systems

    NASA Astrophysics Data System (ADS)

    Kovalenko, P. Y.

    2017-07-01

    Processing the data received from measurement systems implies the situation when one or more registered values stand apart from the sample collection. These values are referred to as “outliers”. The processing results may be influenced significantly by the presence of those in the data sample under consideration. In order to ensure the accuracy of low-frequency oscillations detection in power systems the corresponding algorithm has been developed for the outliers detection and elimination. The algorithm is based on the concept of the irregular component of measurement signal. This component comprises measurement errors and is assumed to be Gauss-distributed random. The median filtering is employed to detect the values lying outside the range of the normally distributed measurement error on the basis of a 3σ criterion. The algorithm has been validated involving simulated signals and WAMS data as well.

  18. Low-frequency cortical oscillations entrain to sub-threshold rhythmic auditory stimuli.

    PubMed

    Ten Oever, Sanne; Schroeder, Charles E; Poeppel, David; van Atteveldt, Nienke; Mehta, Ashesh D; Mégevand, Pierre; Groppe, David M; Zion-Golumbic, Elana

    2017-04-14

    Many environmental stimuli contain temporal regularities, a feature which can help predict forthcoming input. Phase-locking (entrainment) of ongoing low-frequency neuronal oscillations to rhythmic stimuli is proposed as a potential mechanism for enhancing neuronal responses and perceptual sensitivity, by aligning high-excitability phases to events within a stimulus stream. Previous experiments show that rhythmic structure has a behavioral benefit even when the rhythm itself is below perceptual detection thresholds (Ten Oever et al., 2014). It is not known whether this "inaudible" rhythmic sound stream also induces entrainment. Here we tested this hypothesis using magnetoencephalography (MEG) and electrocorticography (ECoG) in humans to record changes in neuronal activity as subthreshold rhythmic stimuli gradually became audible. We found that significant phase-locking to the rhythmic sounds preceded participants' detection of them. Moreover, no significant auditory-evoked responses accompanied this pre-threshold entrainment. These auditory-evoked responses, distinguished by robust, broad-band increases in inter-trial coherence (ITC), only appeared after sounds were reported as audible. Taken together with the reduced perceptual thresholds observed for rhythmic sequences, these findings support the proposition that entrainment of low-frequency oscillations serves a mechanistic role in enhancing perceptual sensitivity for temporally-predictive sounds. This framework has broad implications for understanding the neural mechanisms involved in generating temporal predictions and their relevance for perception, attention, and awareness.SIGNIFICANCE STATEMENTThe environment is full of rhythmically structured signals that the nervous system can exploit for information processing. Thus it is important to understand how the brain processes such temporally structured, regular features of external stimuli. Here we report the alignment of slowly fluctuating oscillatory brain

  19. 3D CFDTD PIC Simulation Study on Low-Frequency Oscillations in a Gyrotron

    NASA Astrophysics Data System (ADS)

    Lin, M. C.; Smithe, D. N.

    2011-10-01

    Low-frequency oscillations (LFOs) have been observed in a high average power gyrotron and the trapped electron population contributing to the oscillation has been measured. As high average power gyrotrons are the most promising millimeter wave source for thermonuclear fusion research, it is important to get a better understanding of this parasitic phenomenon to avoid any deterioration of the electron beam quality thus reducing the gyrotron efficiency. However, understanding of the LFOs remains incomplete and a full picture of this parasitic phenomenon has not been seen yet. In this work, we use a 3D conformal finite-difference time-domain (CFDTD) particle-in-cell (PIC) method to accurately and efficiently study the LFOs in a magnetron injection gun (MIG) of a high average power gyrotron. Employing a highly parallelized computation, the model can be simulated in time domain more realistically. LFOs have been obtained in a 3D time domain simulation for the first time. From our preliminary simulation studies, it is found that not only magnetic compression profile but initial velocity or velocity ratio play an important role in the operation of a MIG electron gun. In addition, the secondary emission effects on the LFOs are also studied. Detailed results will be presented. Work supported by the U.S. Department of Energy under Grant No. DE-SC0004436.

  20. Frequency-shift vibro-acoustic modulation driven by low-frequency broadband excitations in a bistable cantilever oscillator

    NASA Astrophysics Data System (ADS)

    He, Qingbo; Xu, Yanyan; Lu, Siliang; Shao, Yong

    2017-03-01

    This paper reports a frequency-shift vibro-acoustic modulation (VAM) effect in a bistable microcracked cantilever oscillator. Low-frequency broadband excitations induced a VAM effect with a shifted modulation frequency through involving a microcracked metal beam in a bistable oscillator model. We used nonlinear dynamics equations and principles to describe the mechanism of a bistable oscillator whose natural frequency varied as the oscillation amplitude increased. We demonstrated this frequency-shift VAM effect using a prototype bistable oscillator model designed to efficiently detect microcracks in solid materials via the VAM effect using ambient vibration excitations.

  1. Low-Frequency Flow Oscillations on Stalled Wings Exhibiting Cellular Separation Topology

    NASA Astrophysics Data System (ADS)

    Disotell, Kevin James

    One of the most pervasive threats to aircraft controllability is wing stall, a condition associated with loss of lift due to separation of air flow from the wing surface at high angles of attack. A recognized need for improved upset recovery training in extended-envelope flight simulators is a physical understanding of the post-stall aerodynamic environment, particularly key flow phenomena which influence the vehicle trajectory. Large-scale flow structures known as stall cells, which scale with the wing chord and are spatially-periodic along the span, have been previously observed on post-stall airfoils with trailing-edge separation present. Despite extensive documentation of stall cells in the literature, the physical mechanisms behind their formation and evolution have proven to be elusive. The undertaken study has sought to characterize the inherently turbulent separated flow existing above the wing surface with cell formation present. In particular, the question of how the unsteady separated flow may interact with the wing to produce time-averaged cellular surface patterns is considered. Time-resolved, two-component particle image velocimetry measurements were acquired at the plane of symmetry of a single stall cell formed on an extruded NACA 0015 airfoil model at chord Reynolds number of 560,000 to obtain insight into the time-dependent flow structure. The evolution of flow unsteadiness was analyzed over a static angle-of-attack range covering the narrow post-stall regime in which stall cells have been observed. Spectral analysis of velocity fields acquired near the stall angle confirmed a low-frequency flow oscillation previously detected in pointwise surface measurements by Yon and Katz (1998), corresponding to a Strouhal number of 0.042 based on frontal projected chord height. Probability density functions of the streamwise velocity component were used to estimate the convective speed of this mode at approximately half the free-stream velocity, in agreement

  2. The effect of low-frequency oscillations on cardio-respiratory synchronization. Observations during rest and exercise

    NASA Astrophysics Data System (ADS)

    Kenwright, D. A.; Bahraminasab, A.; Stefanovska, A.; McClintock, P. V. E.

    2008-10-01

    We show that the transitions which occur between close orders of synchronization in the cardiorespiratory system are mainly due to modulation of the cardiac and respiratory processes by low-frequency components. The experimental evidence is derived from recordings on healthy subjects at rest and during exercise. Exercise acts as a perturbation of the system that alters the mean cardiac and respiratory frequencies and changes the amount of their modulation by low-frequency oscillations. The conclusion is supported by numerical evidence based on a model of phase-coupled oscillators, with white noise and lowfrequency noise. Both the experimental and numerical approaches confirm that low-frequency oscillations play a significant role in the transitional behavior between close orders of synchronization.

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

    PubMed

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

    2015-12-01

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

  4. Pressure oscillation induced by composite fluid flow - Physical picture generating low frequency earthquake -

    NASA Astrophysics Data System (ADS)

    Takashima, S.; Kurita, K.

    2006-12-01

    Recently low frequency (LF) earthquakes have been found to occur in various geophysical settings. Structural inspection of the source region and analysis of focal mechanism suggest the possible role of fluid in the generation process. The nature of fluid expected in the source region should be characterized by multiphase system such as magma and gas bubble, magma and crystal and aqueous fluid and gas bubble, for example. In this system the physical properties of this composite depends on the mutual volume fraction. The volume fraction is variable depending on the flow situation. We consider the link between the flow situation and the volume fraction is an essential part of the composite flow. Here based on the concept that nature of the composite flow plays a central role in the generation of pressure oscillation, we report a simple laboratory model to demonstrate LF earthquakes. The multiphase system in the source region of the LF earthquakes is modeled here as a composite of viscous fluid and incompressible granular phase. plastic particles made of polystyrene (0.5 mm in diameter) and glycerol solution is packed into a cylindrical case (60 mm in diameter). The packing state of the solid phase is near random closed packing state. The glycerol solution flows into the case from the pressure reservoir and it goes out from exit tube with 60 mm in length and 3 mm in diameter. The pressure is measured using a pressure sensor. The control parameter is fluid pressure (1 atm plus 300 Pa to 1500 Pa) and its viscosity (30 mPas to 100 mPas) in this experiment. When the pressure difference between the case is low, the flow is characterized as a permeable flow. Only the interstitial fluid of the glycerol solution flows out depending on the pressure difference. When the pressure difference is above the critical value, both fluid and particles flow out as a composite flow. In this state the output pressure was observed to oscillate. In the diagram of power spectrum of the

  5. Enhanced detection of a low-frequency signal by using broad squeezed light and a bichromatic local oscillator

    NASA Astrophysics Data System (ADS)

    Li, Wei; Jin, Yuanbin; Yu, Xudong; Zhang, Jing

    2017-08-01

    We experimentally study a protocol of using the broadband high-frequency squeezed vacuum to detect the low-frequency signal. In this scheme, the lower sideband field of the squeezed light carries the low-frequency modulation signal, and the two strong coherent light fields are applied as the bichromatic local oscillator in the homodyne detection to measure the quantum entanglement of the upper and lower sideband for the broadband squeezed light. The power of one of the local oscillators for detecting the upper sideband can be adjusted to optimize the conditional variance in the low-frequency regime by subtracting the photocurrent of the upper sideband field of the squeezed light from that of the lower sideband field. By means of the quantum correlation of the upper and lower sideband for the broadband squeezed light, the low-frequency signal beyond the standard quantum limit is measured. This scheme is appropriate for enhancing the sensitivity of the low-frequency signal by the aid of the broad squeezed light, such as gravitational waves detection, and does not need to directly produce the low-frequency squeezing in an optical parametric process.

  6. Utrophin suppresses low frequency oscillations and coupled gating of mechanosensitive ion channels in dystrophic skeletal muscle.

    PubMed

    Lansman, Jeffry B

    2015-01-01

    An absence of utrophin in muscle from mdx mice prolongs the open time of single mechanosensitive channels. On a time scale much longer than the duration of individual channel activations, genetic depletion of utrophin produces low frequency oscillations of channel open probability. Oscillatory channel opening occurred in the dystrophin/utrophin mutants, but was absent in wild-type and mdx fibers. By contrast, small conductance channels showed random gating behavior when present in the same patch. Applying a negative pressure to a patch on a DKO fiber produced a burst of mode II activity, but channels subsequently closed and remained silent for tens of seconds during the maintained pressure stimulus. In addition, simultaneous opening of multiple MS channels could be frequently observed in recordings from patches on DKO fibers, but only rarely in wild-type and mdx muscle. A model which accounts for the single-channel data is proposed in which utrophin acts as gating spring which maintains the mechanical stability a caveolar-like compartment. The state of this compartment is suggested to be dynamic; its continuity with the extracellular surface varying over seconds to minutes. Loss of the mechanical stability of this compartment contributes to pathogenic Ca(2+) entry through MS channels in Duchenne dystrophy.

  7. Observation of low-frequency oscillations in LDX with an angular electrostatic probe

    NASA Astrophysics Data System (ADS)

    Bergmann, R. M.; Boxer, A. C.; Ellsworth, J. L.; Kesner, J.; Garnier, D. T.; Mauel, M. E.

    2008-11-01

    Previous computational models using magnetic configurations similar to LDX have yielded results where convective cells transport particles without transporting energy [1], and this would prove useful in a fusion reactor since it could remove ash from the core without cooling it. A vertically adjustable angular electrostatic probe array has been designed to observe the previously seen low-frequency oscillations [2] with better resolution and to identify if they are related to the expected convective cells. The array will rest one meter from the centerline of the device and measure edge fluctuations on field lines near the separatrix that are mapped to 1.7m to 1.85m at midplane. It will cover ninety degrees angularly and have 24 probes mounted on it for total probe tip separation of 7.1cm. Each probe will consist of a 1cm tungsten electrode inside an alumina tube in series with a one mega-ohm resistor located 50 cm from the probe tip. The array can be fitted with an extension to provide radial sampling at a later date. [0pt] [1] J. Tonge, N. Leboeuf, C. Huang, and J.M. Dawson Phys. Plasmas 10 (2003) 9.[0pt] [2] D. Garnier et al., J. Plasma Phys. 74 (2008).

  8. Noninvasive optical evaluation of low frequency oscillations in prefrontal cortex hemodynamics during verbal working memory

    NASA Astrophysics Data System (ADS)

    Li, Ting; Zhao, Yue; Li, Kai; Sun, Yunlong

    2014-03-01

    The low frequency oscillation (LFO) around 0.1 Hz has been observed recently in cerebral hemodynamic signals during rest/sleep, enhanced breathing, and head- up-tilting, showing that cerebral autoregulation can be accessed by LFOs. However, many brain function researches require direct measurement of LFOs during specified brain function activities. This pilot study explored using near-infrared spectroscopy/imaging (NIRS) to noninvasively and simultaneously detect LFOs of prefrontal cerebral hemodynamics (i.e., oxygenated/deoxygenated/total hemoglobin concentration: △[oxy-Hb]/ △[deoxy-Hb]/ △[tot-Hb]) during N-back visual verbal working memory task. The LFOs were extracted from the measured variables using power spectral analysis. We found the brain activation sites struck clear LFOs while other sites did not. The LFO of △[deoxy-Hb] acted as a negative pike and ranged in (0.05, 0.1) Hz, while LFOs of △[oxy-Hb] and △[tot-Hb] acted as a positive pike and ranged in (0.1, 0.15) Hz. The amplitude difference and frequency lag between △[deoxy-Hb] and △[oxy-Hb]/ △[tot-Hb] produced a more focused and sensitive activation map compare to hemodynamic amplitude-quantified activation maps. This study observed LFOs in brain activities and showed strong potential of LFOs in accessing brain functions.

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

    PubMed

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

    2014-01-15

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

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

    PubMed

    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.

  11. Low-frequency, broadband vibration energy harvester using coupled oscillators and frequency up-conversion by mechanical stoppers

    NASA Astrophysics Data System (ADS)

    Dechant, Eduard; Fedulov, Feodor; Chashin, Dmitrii V.; Fetisov, Leonid Y.; Fetisov, Yuri K.; Shamonin, Mikhail

    2017-06-01

    The frequencies of ambient vibrations are often low (below 30 Hz). A broadband (3 dB bandwidth is larger than 10 Hz at an acceleration amplitude of 9.81 m s-2) vibration based energy harvester is proposed for transducing mechanical energy at such low frequencies into electrical energy. The mechanical setup converts low frequency mechanical vibrations into high frequency resonance oscillations of the transducer. This conversion is done by mechanical impacts on two mechanical stoppers. The originality of the presented design is that both low-frequency and high-frequency oscillators are permanently mechanically coupled. In the equivalent mechanical circuit, this coupling is achieved by connecting the ends of the stiff spring to both seismic masses, whereas one seismic mass (collison member) is also attached to the soft spring used as the constitutive element of a low-frequency oscillator. Further, both mechanical oscillators are not realized as conventional cantilever beams. In particular, the high frequency oscillator with the natural frequency of 340 Hz is a disc-shaped diaphragm with attached piezoelectric elements and a seismic mass. It is shown that it is possible to convert mechanical vibrations with acceleration amplitude of 9.81 m s-2 in the region between approximately 7 and 25 Hz into electrical power larger than 0.1 mW with the maximum value of 0.8 mW. A simplified mathematical model based on piecewise linear coupled oscillators shows good agreement with experimental results. The ways to enhance the performance of the harvester and improve agreement with experiments are discussed.

  12. A newly designed experimental system for exposure of mammalian cells to extremely low frequency magnetic fields.

    PubMed

    Miyakoshi, J; Ohtsu, S; Tatsumi-Miyajima, J; Takebe, H

    1994-03-01

    To examine the biological effects of extremely low frequency magnetic field (ELFMF), we have designed and manufactured a new equipment for long-term and high-density exposure of cells to ELFMF. The ELFMF exposure system consists of a generator of magnets with a built-in CO2 incubator, an alternating current (AC) power supply, a gas compressor and a thermocontroller for the incubator, and a cooling unit for the magnets. The CO2 incubator made of acrylic resin is inserted into the inner-space of the silicon steel strip-cores. In this system, the temperature of the incubator is maintained at 37 +/- 0.5 degrees C. The maximum magnetic flux density on the exposure area of the incubator is 500 mT (T; tesla) at a current of 556 Arms (rms; root mean square) at 50 Hz. The long-term (up to 120 hr) exposure of 400 mT ELFMF did not affect the growth of both HL60RG and CCRF-CEM cells originated from human leukemia. The post-X-irradiation exposure of 400 mT ELFMF for 2 hr also did not affect the radiation sensitivity of GM0637 and TAT2SF cells originated from a normal human and an ataxia telangiectasia patient.

  13. Motor dysfunction in the tottering mouse is linked to cerebellar spontaneous low frequency oscillations revealed by flavoprotein autofluorescence optical imaging

    NASA Astrophysics Data System (ADS)

    Chen, Gang; Popa, Laurentiu S.; Wang, Xinming; Gao, Wangcai; Barnes, Justin; Hendrix, Claudia M.; Hess, Ellen J.; Ebner, Timothy J.

    2009-02-01

    Flavoprotein autofluorescence optical imaging is developing into a powerful research tool to study neural activity, particularly in vivo. In this study we used this imaging technique to investigate the neuronal mechanism underlying the episodic movement disorder that is characteristic of the tottering (tg) mouse, a model of episodic ataxia type 2. Both EA2 and the tg mouse are caused by mutations in the gene encoding Cav2.1 (P/Q-type) voltage-gated Ca2+ channels. These mutations result in a reduction in P/Q Ca2+ channel function. Both EA2 patients and tg mice have a characteristic phenotype consisting of transient motor attacks triggered by stress, caffeine or ethanol. The neural events underlying these episodes of dystonia are unknown. Flavoprotein autofluorescence optical imaging revealed spontaneous, transient, low frequency oscillations in the cerebellar cortex of the tg mouse. Lasting from 30 - 120 minutes, the oscillations originate in one area then spread to surrounding regions over 30 - 60 minutes. The oscillations are reduced by removing extracellular Ca2+ and blocking Cav 1.2/1.3 (L-type) Ca2+ channels. The oscillations are not affected by blocking AMPA receptors or by electrical stimulation of the parallel fiber - Purkinje cell circuit, suggesting the oscillations are generated intrinsically in the cerebellar cortex. Conversely, L-type Ca2+ agonists generate oscillations with similar properties. In the awake tg mouse, transcranial flavoprotein imaging revealed low frequency oscillations that are accentuated during caffeine induced attacks of dystonia. The oscillations increase during the attacks of dystonia and are coupled to oscillations in face and hindlimb EMG activity. These transient oscillations and the associated cerebellar dysfunction provide a novel mechanism by which an ion channel disorder results in episodic motor dysfunction.

  14. In vivo imaging of spontaneous low-frequency oscillations in cerebral hemodynamics with a digital red-green-blue camera

    NASA Astrophysics Data System (ADS)

    Mustari, Afrina; Nakamura, Naoki; Nishidate, Izumi; Kawauchi, Satoko; Sato, Shunichi; Sato, Manabu; Kokobo, Yasuaki

    2017-04-01

    Nervous system relies on a continuous and adequate supply of blood flow, bringing the nutrients that it needs and removing the waste products of metabolism. Failure of these mechanisms is found in a number of devastating cerebral diseases, including stroke, vascular dementia, brain injury and trauma. Vasomotion which is the spontaneous low-frequency oscillation derived by the contraction and relaxation of arterioles and appears to be an intrinsic property of the cerebral vasculature, is important for monitoring the cerebral flow, tissue metabolism and health status of brain tissue. In the present study, we investigated a method to visualize the spontaneous low-frequency oscillation of cerebral blood volume based on the sequential RGB images of exposed brain.

  15. Frontal top-down signals increase coupling of auditory low-frequency oscillations to continuous speech in human listeners.

    PubMed

    Park, Hyojin; Ince, Robin A A; Schyns, Philippe G; Thut, Gregor; Gross, Joachim

    2015-06-15

    Humans show a remarkable ability to understand continuous speech even under adverse listening conditions. This ability critically relies on dynamically updated predictions of incoming sensory information, but exactly how top-down predictions improve speech processing is still unclear. Brain oscillations are a likely mechanism for these top-down predictions [1, 2]. Quasi-rhythmic components in speech are known to entrain low-frequency oscillations in auditory areas [3, 4], and this entrainment increases with intelligibility [5]. We hypothesize that top-down signals from frontal brain areas causally modulate the phase of brain oscillations in auditory cortex. We use magnetoencephalography (MEG) to monitor brain oscillations in 22 participants during continuous speech perception. We characterize prominent spectral components of speech-brain coupling in auditory cortex and use causal connectivity analysis (transfer entropy) to identify the top-down signals driving this coupling more strongly during intelligible speech than during unintelligible speech. We report three main findings. First, frontal and motor cortices significantly modulate the phase of speech-coupled low-frequency oscillations in auditory cortex, and this effect depends on intelligibility of speech. Second, top-down signals are significantly stronger for left auditory cortex than for right auditory cortex. Third, speech-auditory cortex coupling is enhanced as a function of stronger top-down signals. Together, our results suggest that low-frequency brain oscillations play a role in implementing predictive top-down control during continuous speech perception and that top-down control is largely directed at left auditory cortex. This suggests a close relationship between (left-lateralized) speech production areas and the implementation of top-down control in continuous speech perception.

  16. α-Adrenergic effects on low-frequency oscillations in blood pressure and R-R intervals during sympathetic activation.

    PubMed

    Kiviniemi, Antti M; Frances, Maria F; Tiinanen, Suvi; Craen, Rosemary; Rachinsky, Maxim; Petrella, Robert J; Seppänen, Tapio; Huikuri, Heikki V; Tulppo, Mikko P; Shoemaker, J Kevin

    2011-08-01

    The present study was designed to address the contribution of α-adrenergic modulation to the genesis of low-frequency (LF; 0.04-0.15 Hz) oscillations in R-R interval (RRi), blood pressure (BP) and muscle sympathetic nerve activity (MSNA) during different sympathetic stimuli. Blood pressure and RRi were measured continuously in 12 healthy subjects during 5 min periods each of lower body negative pressure (LBNP; -40 mmHg), static handgrip exercise (HG; 20% of maximal force) and postexercise forearm circulatory occlusion (PECO) with and without α-adrenergic blockade by phentolamine. Muscle sympathetic nerve activity was recorded in five subjects during LBNP and in six subjects during HG and PECO. Low-frequency powers and median frequencies of BP, RRi and MSNA were calculated from power spectra. Low-frequency power during LBNP was lower with phentolamine versus without for both BP and RRi oscillations (1.6 ± 0.6 versus 1.2 ± 0.7 ln mmHg(2), P = 0.049; and 6.9 ± 0.8 versus 5.4 ± 0.9 ln ms(2), P = 0.001, respectively). In contrast, the LBNP with phentolamine increased the power of high-frequency oscillations (0.15-0.4 Hz) in BP and MSNA (P < 0.01 for both), which was not observed during saline infusion. Phentolamine also blunted the increases in the LBNP-induced increase in frequency of LF oscillations in BP and RRi. Phentolamine decreased the LF power of RRi during HG (P = 0.015) but induced no other changes in LF powers or frequencies during HG. Phentolamine resulted in decreased frequency of LF oscillations in RRi (P = 0.004) during PECO, and a similar tendency was observed in BP and MSNA. The power of LF oscillation in MSNA did not change during any intervention. We conclude that α-adrenergic modulation contributes to LF oscillations in BP and RRi during baroreceptor unloading (LBNP) but not during static exercise. Also, α-adrenergic modulation partly explains the shift to a higher frequency of LF oscillations during baroreceptor unloading and muscle

  17. Quantifying the correlation between photoplethysmography and laser Doppler flowmetry microvascular low-frequency oscillations

    NASA Astrophysics Data System (ADS)

    Mizeva, Irina; Di Maria, Costanzo; Frick, Peter; Podtaev, Sergey; Allen, John

    2015-03-01

    Photoplethysmography (PPG) and laser Doppler flowmetry (LDF) are two recognized optical techniques that can track low-frequency perfusion changes in microcirculation. The aim of this study was to determine, in healthy subjects, the correlation between the techniques for specific low-frequency bands previously defined for microcirculation. Twelve healthy male subjects (age range 18 to 50 years) were studied, with PPG and LDF signals recorded for 20 min from their right and left index (PPG) and middle (LDF) fingers. Wavelet analysis comprised dividing the low-frequency integral wavelet spectrum (IWS) into five established physiological bands relating to cardiac, respiratory, myogenic, neurogenic, and endothelial activities. The correlation between PPG and LDF was quantified using wavelet correlation analysis and Spearman correlation analysis of the median IWS amplitude. The median wavelet correlation between signals (right-left side average) was 0.45 (cardiac), 0.49 (respiratory), 0.86 (myogenic), 0.91 (neurogenic), and 0.91 (endothelial). The correlation of IWS amplitude values (right-left side average) was statistically significant for the cardiac (ρ=0.64, p<0.05) and endothelial (ρ=0.62, p<0.05) bands. This pilot study has shown good correlation between PPG and LDF for specific physiological frequency bands. In particular, the results suggest that PPG has the potential to be a low-cost replacement for LDF for endothelial activity assessments.

  18. Low-frequency oscillations of a cylinder in a viscous fluid

    NASA Astrophysics Data System (ADS)

    Amin, Norsarahaida

    1988-05-01

    The flow induced by a circular cylinder oscillating in a viscous fluid when the amplitude of the oscillation is small and the frequecy is low is considered. This solution, obtained by the method of matched asymptotic expansions, is compared with the solution obtained from an Oseen approximation to the governing equations by Andres and Ingard (1953).

  19. Discomfort of seated persons exposed to low frequency lateral and roll oscillation: effect of seat cushion.

    PubMed

    Beard, George F; Griffin, Michael J

    2014-11-01

    The discomfort caused by lateral oscillation, roll oscillation, and fully roll-compensated lateral oscillation has been investigated at frequencies between 0.25 and 1.0 Hz when sitting on a rigid seat and when sitting on a compliant cushion, both without a backrest. Judgements of vibration discomfort and the transmission of lateral and roll oscillation through the seat cushion were obtained with 20 subjects. Relative to the rigid seat, the cushion increased lateral acceleration and roll oscillation at the lower frequencies and also increased discomfort during lateral oscillation (at frequencies less than 0.63 Hz), roll oscillation (at frequencies less than 0.4 Hz), and fully roll-compensated lateral oscillation (at frequencies between 0.315 and 0.5 Hz). The root-sums-of-squares of the frequency-weighted lateral and roll acceleration at the seat surface predicted the greater vibration discomfort when sitting on the cushion. The frequency-dependence of the predicted discomfort may be improved by adjusting the frequency weighting for roll acceleration at frequencies between 0.25 and 1.0 Hz. Copyright © 2014 Elsevier Ltd and The Ergonomics Society. All rights reserved.

  20. A periodic foundation with rotational oscillators for extremely low-frequency seismic isolation: analysis and experimental verification

    NASA Astrophysics Data System (ADS)

    Huang, Jiankun; Shi, Zhifei; Huang, Weixin; Chen, Xinhua; Zhang, Zhiwei

    2017-03-01

    A new type of periodic foundation (PF) with rotational oscillators was developed, and its locally resonant attenuation feature was analyzed numerically and experimentally. The proposed PF was composed of a concrete matrix in which local resonators consisting of steel cores with rubber linkers were attached. Finite element method was employed to comprehensively investigate influences of material and geometrical parameters on the attenuation zones. Furthermore, a scaled PF was fabricated and shake tests were performed. The locally resonant mechanism within the rotational resonator can produce extremely low-frequency wave-forbidding capability. The results demonstrated that a PF can isolate seismic waves with frequencies lower than 10 Hz, sufficient to serve as a seismic isolation foundation for civil engineering structures. This kind of foundation system opens up new perspectives for the development of seismic isolation foundations for low-frequency applications.

  1. Ultra Low-Frequency Oscillations of a Solar Filament Observed by the GONG Network

    NASA Astrophysics Data System (ADS)

    Efremov, V. I.; Parfinenko, L. D.; Solov'ev, A. A.

    2016-11-01

    The data of ground-based telescopes of the Global Oscillation Network Group (GONG) obtained in the Hα line provide an opportunity to study the long-period oscillations of chromospheric filaments (quiescent prominences). For the first time, on the basis of time series of 5 days duration that we combined from the observations of three observatories of the GONG network, a new ultra-low mode with a period of between 20 and 30 hours was reliably detected in oscillations of a long-lived dark filament on the solar disk.

  2. Optical parametric amplification and oscillation assisted by low-frequency stimulated emission.

    PubMed

    Longhi, Stefano

    2016-04-15

    Optical parametric amplification and oscillation provide powerful tools for coherent light generation in spectral regions inaccessible to lasers. Parametric gain is based on a frequency down-conversion process and, thus, it cannot be realized for signal waves at a frequency ω3 higher than the frequency of the pump wave ω1. In this Letter, we suggest a route toward the realization of upconversion optical parametric amplification and oscillation, i.e., amplification of the signal wave by a coherent pump wave of lower frequency, assisted by stimulated emission of the auxiliary idler wave. When the signal field is resonated in an optical cavity, parametric oscillation is obtained. Design parameters for the observation of upconversion optical parametric oscillation at λ3=465 nm are given for a periodically poled lithium-niobate (PPLN) crystal doped with Nd(3+) ions.

  3. Oscillations Go the Distance: Low-Frequency Human Hippocampal Oscillations Code Spatial Distance in the Absence of Sensory Cues during Teleportation.

    PubMed

    Vass, Lindsay K; Copara, Milagros S; Seyal, Masud; Shahlaie, Kiarash; Farias, Sarah Tomaszewski; Shen, Peter Y; Ekstrom, Arne D

    2016-03-16

    Low-frequency (delta/theta band) hippocampal neural oscillations play prominent roles in computational models of spatial navigation, but their exact function remains unknown. Some theories propose they are primarily generated in response to sensorimotor processing, while others suggest a role in memory-related processing. We directly recorded hippocampal EEG activity in patients undergoing seizure monitoring while they explored a virtual environment containing teleporters. Critically, this manipulation allowed patients to experience movement through space in the absence of visual and self-motion cues. The prevalence and duration of low-frequency hippocampal oscillations were unchanged by this manipulation, indicating that sensorimotor processing was not required to elicit them during navigation. Furthermore, the frequency-wise pattern of oscillation prevalence during teleportation contained spatial information capable of classifying the distance teleported. These results demonstrate that movement-related sensory information is not required to drive spatially informative low-frequency hippocampal oscillations during navigation and suggest a specific function in memory-related spatial updating.

  4. Photothermal fluctuations as a fundamental limit to low-frequency squeezing in a degenerate optical parametric oscillator

    SciTech Connect

    Goda, Keisuke; Mikhailov, Eugeniy E.; Mavalvala, Nergis; McKenzie, Kirk; McClelland, David E.; Lam, Ping Koy

    2005-10-15

    We study the effect of photothermal fluctuations on squeezed states of light through the photo-refractive effect and thermal expansion in a degenerate optical parametric oscillator (OPO). We also discuss the effect of the photothermal noise in various cases and how to minimize its undesirable consequences. We find that the photothermal noise in the OPO introduces a significant amount of noise on phase squeezed beams, making them less than ideal for low-frequency applications such as gravitational wave (GW) interferometers, whereas amplitude squeezed beams are relatively immune to the photothermal noise and may represent the best choice for application in GW interferometers.

  5. Low-frequency, self-sustained oscillations in inductively coupled plasmas used for optical pumping

    NASA Astrophysics Data System (ADS)

    Coffer, J.; Encalada, N.; Huang, M.; Camparo, J.

    2014-10-01

    We have investigated very low frequency, on the order of one hertz, self-pulsing in alkali-metal inductively-coupled plasmas (i.e., rf-discharge lamps). This self-pulsing has the potential to significantly vary signal-to-noise ratios and (via the ac-Stark shift) resonant frequencies in optically pumped atomic clocks and magnetometers (e.g., the atomic clocks now flying on GPS and Galileo global navigation system satellites). The phenomenon arises from a nonlinear interaction between the atomic physics of radiation trapping and the plasma's electrical nature. To explain the effect, we have developed an evaporation/condensation theory (EC theory) of the self-pulsing phenomenon.

  6. Low-frequency, self-sustained oscillations in inductively coupled plasmas used for optical pumping

    SciTech Connect

    Coffer, J.; Encalada, N.; Huang, M.; Camparo, J.

    2014-10-28

    We have investigated very low frequency, on the order of one hertz, self-pulsing in alkali-metal inductively-coupled plasmas (i.e., rf-discharge lamps). This self-pulsing has the potential to significantly vary signal-to-noise ratios and (via the ac-Stark shift) resonant frequencies in optically pumped atomic clocks and magnetometers (e.g., the atomic clocks now flying on GPS and Galileo global navigation system satellites). The phenomenon arises from a nonlinear interaction between the atomic physics of radiation trapping and the plasma's electrical nature. To explain the effect, we have developed an evaporation/condensation theory (EC theory) of the self-pulsing phenomenon.

  7. Short Meditation Trainings Enhance Non-REM Sleep Low-Frequency Oscillations.

    PubMed

    Dentico, Daniela; Ferrarelli, Fabio; Riedner, Brady A; Smith, Richard; Zennig, Corinna; Lutz, Antoine; Tononi, Giulio; Davidson, Richard J

    2016-01-01

    We have recently shown higher parietal-occipital EEG gamma activity during sleep in long-term meditators compared to meditation-naive individuals. This gamma increase was specific for NREM sleep, was present throughout the entire night and correlated with meditation expertise, thus suggesting underlying long-lasting neuroplastic changes induced through prolonged training. The aim of this study was to explore the neuroplastic changes acutely induced by 2 intensive days of different meditation practices in the same group of practitioners. We also repeated baseline recordings in a meditation-naive cohort to account for time effects on sleep EEG activity. High-density EEG recordings of human brain activity were acquired over the course of whole sleep nights following intervention. Sound-attenuated sleep research room. Twenty-four long-term meditators and twenty-four meditation-naïve controls. Two 8-h sessions of either a mindfulness-based meditation or a form of meditation designed to cultivate compassion and loving kindness, hereafter referred to as compassion meditation. We found an increase in EEG low-frequency oscillatory activities (1-12 Hz, centered around 7-8 Hz) over prefrontal and left parietal electrodes across whole night NREM cycles. This power increase peaked early in the night and extended during the third cycle to high-frequencies up to the gamma range (25-40 Hz). There was no difference in sleep EEG activity between meditation styles in long-term meditators nor in the meditation naïve group across different time points. Furthermore, the prefrontal-parietal changes were dependent on meditation life experience. This low-frequency prefrontal-parietal activation likely reflects acute, meditation-related plastic changes occurring during wakefulness, and may underlie a top-down regulation from frontal and anterior parietal areas to the posterior parietal and occipital regions showing chronic, long-lasting plastic changes in long-term meditators.

  8. Short Meditation Trainings Enhance Non-REM Sleep Low-Frequency Oscillations

    PubMed Central

    Dentico, Daniela; Ferrarelli, Fabio; Riedner, Brady A.; Smith, Richard; Zennig, Corinna; Lutz, Antoine; Tononi, Giulio; Davidson, Richard J.

    2016-01-01

    Study Objectives We have recently shown higher parietal-occipital EEG gamma activity during sleep in long-term meditators compared to meditation-naive individuals. This gamma increase was specific for NREM sleep, was present throughout the entire night and correlated with meditation expertise, thus suggesting underlying long-lasting neuroplastic changes induced through prolonged training. The aim of this study was to explore the neuroplastic changes acutely induced by 2 intensive days of different meditation practices in the same group of practitioners. We also repeated baseline recordings in a meditation-naive cohort to account for time effects on sleep EEG activity. Design High-density EEG recordings of human brain activity were acquired over the course of whole sleep nights following intervention. Setting Sound-attenuated sleep research room. Patients or Participants Twenty-four long-term meditators and twenty-four meditation-naïve controls. Interventions Two 8-h sessions of either a mindfulness-based meditation or a form of meditation designed to cultivate compassion and loving kindness, hereafter referred to as compassion meditation. Measurements and Results We found an increase in EEG low-frequency oscillatory activities (1–12 Hz, centered around 7–8 Hz) over prefrontal and left parietal electrodes across whole night NREM cycles. This power increase peaked early in the night and extended during the third cycle to high-frequencies up to the gamma range (25–40 Hz). There was no difference in sleep EEG activity between meditation styles in long-term meditators nor in the meditation naïve group across different time points. Furthermore, the prefrontal-parietal changes were dependent on meditation life experience. Conclusions This low-frequency prefrontal-parietal activation likely reflects acute, meditation-related plastic changes occurring during wakefulness, and may underlie a top-down regulation from frontal and anterior parietal areas to the posterior

  9. Design of a Low-Frequency Oscillator with PTC Memristor and an Inductor

    NASA Astrophysics Data System (ADS)

    Rajamani, Vetriveeran; Yang, Changju; Kim, Hyongsuk; Chua, Leon

    An electronic oscillator circuit is designed by connecting an inductor in series with a locally-active PTC Memristor and a battery. The PTC Memristor is locally active on the negative resistance region of its DC VM-IM curve. A DC operating point Q is chosen on the locally-active region of the PTC Memristor and a small-signal equivalent circuit at Q is derived via Taylor series. The small-signal admittance YCM(s; V ) of the composite one-port in Fig. 1 is derived using the small-signal equivalent circuit at Q, in series with an inductor whose value is chosen such that YCM(iω0; V ) = 0 at some s = iω0. The sinusoidal oscillation computed numerically from this circuit is shown to emerge from a supercritical Hopf bifurcation.

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

    PubMed

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

    2014-01-01

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

  11. Low-frequency Intensity Variation of the South Asian High and its relationship to Boreal Summer Intraseasonal Oscillation

    NASA Astrophysics Data System (ADS)

    Shang, Wei; Ren, Xuejuan

    2016-04-01

    The South Asian High (SAH) is an important member among the Asian summer monsoon circulations in the upper troposphere located over the Tibean Plateau and its surrounding areas during boreal summer. This research attempts to study the characteristics and mechanisms of low-frequency oscillation of SAH, using daily ERA-Interim reanalysis dataset and NECP/NCAR OLR data. The empirical orthogonal function (EOF)analysis is performed on 200hPa geopotential height low-frequency anomalies over the 20°-35°N, 35°-110°E for June, July and August from 1979 to 2013. The first EOF mode shows a monopole pattern capturing the strengthening or weakening of the SAH's body. The power spectrum analysis of the corresponding principal component (PC1) time series shows that the first mode has a period about 10-30 days. Positive anomalies appear in the 200hPa geopotential height and negative anomalies appear in their north side when SAH is in positive low-frequency phase. A band with negative outgoing longwave radiation (OLR) anomalies presents from the Arabian Sea, north of Indian Peninsula to Southeast China and Japan Island. Correspondingly, positive anomalous rainfall are contiguous in the north of Indian Peninsula, south of Tibetan Plateau, Southeast China and Japan Island. The lead-lag regression analysis demonstrates that from day -12 to day 0, negative OLR anomalies band move northward and northwest from the equatorial Indian Ocean, the Bay of Bengals, the South China sea and Western North Pacific to the Arabian Sea, north of Indian Peninsula, south of Tibetan Plateau, Southeast China and Japan Island. Corresponding to OLR anomalies, positive rainfall anomalies band have the similar evolution. The spatial pattern of anomalies in integrated apparent heat source and integrated apparent moisture sink resemble that of rainfall and OLR, which correspond more anomalous condensation heat release. The lead-lag regression analysis also shows that the OLR band moving northward

  12. Application of the floating-potential probe for studies of low frequency oscillations in a plasma

    NASA Technical Reports Server (NTRS)

    Dzhakov, B. Y.

    1973-01-01

    The proper interpretation of the results obtained from measurements of the floating potential of an electrostatic probe may cause difficulties in time varying plasmas. The following limitations of the method are considered: the charge separation in the plasma, the influence of the input capacity of the measuring circuit, and the influence of the layer capacity near the probe. A detailed analysis is carried out in the cases of moving striations and ion acoustic waves. A simple measuring technique is suggested for ion acoustic studies, giving detailed information about ion density oscillations.

  13. Midline Frontal Cortex Low-Frequency Activity Drives Subthalamic Nucleus Oscillations during Conflict

    PubMed Central

    Zavala, Baltazar A.; Tan, Huiling; Little, Simon; Ashkan, Keyoumars; Hariz, Marwan; Foltynie, Thomas; Zrinzo, Ludvic; Zaghloul, Kareem A.

    2014-01-01

    Making the right decision from conflicting information takes time. Recent computational, electrophysiological, and clinical studies have implicated two brain areas as being crucial in assuring sufficient time is taken for decision-making under conditions of conflict: the medial prefrontal cortex and the subthalamic nucleus (STN). Both structures exhibit an elevation of activity at low frequencies (<10 Hz) during conflict that correlates with the amount of time taken to respond. This suggests that the two sites could become functionally coupled during conflict. To establish the nature of this interaction we recorded from deep-brain stimulation electrodes implanted bilaterally in the STN of 13 Parkinson's disease patients while they performed a sensory integration task involving randomly moving dots. By gradually increasing the number of dots moving coherently in one direction, we were able to determine changes in the STN associated with response execution. Furthermore, by occasionally having 10% of the dots move in the opposite direction as the majority, we were able to identify an independent increase in STN theta-delta activity triggered by conflict. Crucially, simultaneous midline frontal electroencephalographic recordings revealed an increase in the theta-delta band coherence between the two structures that was specific to high-conflict trials. Activity over the midline frontal cortex was Granger causal to that in STN. These results establish the cortico-subcortical circuit enabling successful choices to be made under conditions of conflict and provide support for the hypothesis that the brain uses frequency-specific channels of communication to convey behaviorally relevant information. PMID:24849364

  14. Midline frontal cortex low-frequency activity drives subthalamic nucleus oscillations during conflict.

    PubMed

    Zavala, Baltazar A; Tan, Huiling; Little, Simon; Ashkan, Keyoumars; Hariz, Marwan; Foltynie, Thomas; Zrinzo, Ludvic; Zaghloul, Kareem A; Brown, Peter

    2014-05-21

    Making the right decision from conflicting information takes time. Recent computational, electrophysiological, and clinical studies have implicated two brain areas as being crucial in assuring sufficient time is taken for decision-making under conditions of conflict: the medial prefrontal cortex and the subthalamic nucleus (STN). Both structures exhibit an elevation of activity at low frequencies (<10 Hz) during conflict that correlates with the amount of time taken to respond. This suggests that the two sites could become functionally coupled during conflict. To establish the nature of this interaction we recorded from deep-brain stimulation electrodes implanted bilaterally in the STN of 13 Parkinson's disease patients while they performed a sensory integration task involving randomly moving dots. By gradually increasing the number of dots moving coherently in one direction, we were able to determine changes in the STN associated with response execution. Furthermore, by occasionally having 10% of the dots move in the opposite direction as the majority, we were able to identify an independent increase in STN theta-delta activity triggered by conflict. Crucially, simultaneous midline frontal electroencephalographic recordings revealed an increase in the theta-delta band coherence between the two structures that was specific to high-conflict trials. Activity over the midline frontal cortex was Granger causal to that in STN. These results establish the cortico-subcortical circuit enabling successful choices to be made under conditions of conflict and provide support for the hypothesis that the brain uses frequency-specific channels of communication to convey behaviorally relevant information. Copyright © 2014 Zavala et al.

  15. Sixty-hertz stimulation improves bradykinesia and amplifies subthalamic low-frequency oscillations.

    PubMed

    Blumenfeld, Zack; Koop, Mandy Miller; Prieto, Thomas E; Shreve, Lauren A; Velisar, Anca; Quinn, Emma J; Trager, Megan H; Brontë-Stewart, Helen

    2017-01-01

    The objective of this study was to investigate the hypothesis that attenuation of subthalamic nucleus (STN) alpha-/beta-band oscillations is causal to improvement in bradykinesia. STN local field potentials from a sensing neurostimulator (Activa(®) PC+S; Medtronic, Inc.) and kinematics from wearable sensors were recorded simultaneously during 60- and 140-Hz deep brain stimulation (DBS) in 9 freely moving PD subjects (15 STNs) performing repetitive wrist flexion-extension. Kinematics were recorded during 20-Hz DBS in a subgroup. Both 60- and 140-Hz DBS improved the angular velocity and frequency of movement (P = 0.002 and P = 0.029, respectively, for 60 Hz; P < 0.001 and P < 0.001, respectively, for 140 Hz), but 60-Hz DBS did not attenuate beta-band power (13-30 Hz). In fact, 60-Hz DBS amplified alpha/low-beta (11-15 Hz, P = 0.007) and attenuated high-beta power (19-27 Hz, P < 0.001), whereas 140-Hz DBS broadly attenuated beta power (15-30 Hz, P < 0.001). Only 60-Hz DBS improved the regularity of angular range (P = 0.046) and 20-Hz DBS did not worsen bradykinesia. There was no correlation between beta-power modulation and bradykinesia. These novel results obtained from freely moving PD subjects demonstrated that both 140- and 60-Hz DBS improved bradykinesia and attenuated high beta oscillations; however, 60-Hz DBS amplified a subband of alpha/low-beta oscillations, and DBS at a beta-band frequency did not worsen bradykinesia. Based on recent literature, we suggest that both 140- and 60-Hz DBS decouple the cortico-STN hyperdirect pathway, whereas 60-Hz DBS increases coupling within striato-STN circuitry. These results inform future algorithms for closed-loop DBS in PD. © 2016 International Parkinson and Movement Disorder Society. © 2016 International Parkinson and Movement Disorder Society.

  16. Fatigue Effect on Low-Frequency Force Fluctuations and Muscular Oscillations during Rhythmic Isometric Contraction

    PubMed Central

    Lin, Yen-Ting; Kuo, Chia-Hua; Hwang, Ing-Shiou

    2014-01-01

    Continuous force output containing numerous intermittent force pulses is not completely smooth. By characterizing force fluctuation properties and force pulse metrics, this study investigated adaptive changes in trajectory control, both force-generating capacity and force fluctuations, as fatigue progresses. Sixteen healthy subjects (20–24 years old) completed rhythmic isometric gripping with the non-dominant hand to volitional failure. Before and immediately following the fatigue intervention, we measured the gripping force to couple a 0.5 Hz sinusoidal target in the range of 50–100% maximal voluntary contraction. Dynamic force output was off-line decomposed into 1) an ideal force trajectory spectrally identical to the target rate; and 2) a force pulse trace pertaining to force fluctuations and error-correction attempts. The amplitude of ideal force trajectory regarding to force-generating capacity was more suppressed than that of the force pulse trace with increasing fatigue, which also shifted the force pulse trace to lower frequency bands. Multi-scale entropy analysis revealed that the complexity of the force pulse trace at high time scales increased with fatigue, contrary to the decrease in complexity of the force pulse trace at low time scales. Statistical properties of individual force pulses in the spatial and temporal domains varied with muscular fatigue, concurrent with marked suppression of gamma muscular oscillations (40–60 Hz) in the post-fatigue test. In conclusion, this study first reveals that muscular fatigue impairs the amplitude modulation of force pattern generation more than it affects the amplitude responsiveness of fine-tuning a force trajectory. Besides, motor fatigue results disadvantageously in enhancement of motor noises, simplification of short-term force-tuning strategy, and slow responsiveness to force errors, pertaining to dimensional changes in force fluctuations, scaling properties of force pulse, and muscular oscillation

  17. Increased Low-Frequency Oscillation Amplitude of Sensorimotor Cortex Associated with the Severity of Structural Impairment in Cervical Myelopathy

    PubMed Central

    Zhou, Fuqing; Gong, Honghan; Liu, Xiaojia; Wu, Lin; Luk, Keith Dip-Kei; Hu, Yong

    2014-01-01

    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. PMID:25111566

  18. The quasi-periodic oscillations and very low frequency noise of Scorpius X-1 as transient chaos - A dripping handrail?

    NASA Technical Reports Server (NTRS)

    Scargle, Jeffrey D.; Steiman-Cameron, Thomas; Young, Karl; Donoho, David L.; Crutchfield, James P.; Imamura, James

    1993-01-01

    We present evidence that the quasi-periodic oscillations (QPO) and very low frequency noise (VLFN) characteristic of many accretion sources are different aspects of the same physical process. We analyzed a long, high time resolution EXOSAT observation of the low-mass X-ray binary (LMXB) Sco X-1. The X-ray luminosity varies stochastically on time scales from milliseconds to hours. The nature of this variability - as quantified with both power spectrum analysis and a new wavelet technique, the scalegram - agrees well with the dripping handrail accretion model, a simple dynamical system which exhibits transient chaos. In this model both the QPO and VLFN are produced by radiation from blobs with a wide size distribution, resulting from accretion and subsequent diffusion of hot gas, the density of which is limited by an unspecified instability to lie below a threshold.

  19. The quasi-periodic oscillations and very low frequency noise of Scorpius X-1 as transient chaos - A dripping handrail?

    NASA Technical Reports Server (NTRS)

    Scargle, Jeffrey D.; Steiman-Cameron, Thomas; Young, Karl; Donoho, David L.; Crutchfield, James P.; Imamura, James

    1993-01-01

    We present evidence that the quasi-periodic oscillations (QPO) and very low frequency noise (VLFN) characteristic of many accretion sources are different aspects of the same physical process. We analyzed a long, high time resolution EXOSAT observation of the low-mass X-ray binary (LMXB) Sco X-1. The X-ray luminosity varies stochastically on time scales from milliseconds to hours. The nature of this variability - as quantified with both power spectrum analysis and a new wavelet technique, the scalegram - agrees well with the dripping handrail accretion model, a simple dynamical system which exhibits transient chaos. In this model both the QPO and VLFN are produced by radiation from blobs with a wide size distribution, resulting from accretion and subsequent diffusion of hot gas, the density of which is limited by an unspecified instability to lie below a threshold.

  20. Alleviation SSR and Low Frequency Power Oscillations in Series Compensated Transmission Line using SVC Supplementary Controllers

    NASA Astrophysics Data System (ADS)

    Kumar, Sanjiv; Kumar, Narendra

    2016-07-01

    In this work, supplementary sub-synchronous damping controllers (SSDC) are proposed for damping sub-synchronous oscillations in power systems with series compensated transmission lines. Series compensation have extensively been used as effective means of increasing the power transfer capability of a transmission lines and improving transient stability limits of power systems. Series compensation with transmission lines may cause sub-synchronous resonance (SSR). The eigenvalue investigation tool is used to ascertain the existence of SSR. It is shown that the addition of supplementary controller is able to stabilize all unstable modes for T-network model. Eigenvalue investigation and time domain transient simulation of detailed nonlinear system are considered to investigate the performance of the controllers. The efficacies of the suggested supplementary controllers are compared on the IEEE first benchmark model for computer simulations of SSR by means of time domain simulation in Matlab/Simulink environment. Supplementary SSDC are considered in order to compare effectiveness of SSDC during higher loading in alleviating the small signal stability problem.

  1. Alleviation SSR and Low Frequency Power Oscillations in Series Compensated Transmission Line using SVC Supplementary Controllers

    NASA Astrophysics Data System (ADS)

    Kumar, Sanjiv; Kumar, Narendra

    2017-06-01

    In this work, supplementary sub-synchronous damping controllers (SSDC) are proposed for damping sub-synchronous oscillations in power systems with series compensated transmission lines. Series compensation have extensively been used as effective means of increasing the power transfer capability of a transmission lines and improving transient stability limits of power systems. Series compensation with transmission lines may cause sub-synchronous resonance (SSR). The eigenvalue investigation tool is used to ascertain the existence of SSR. It is shown that the addition of supplementary controller is able to stabilize all unstable modes for T-network model. Eigenvalue investigation and time domain transient simulation of detailed nonlinear system are considered to investigate the performance of the controllers. The efficacies of the suggested supplementary controllers are compared on the IEEE first benchmark model for computer simulations of SSR by means of time domain simulation in Matlab/Simulink environment. Supplementary SSDC are considered in order to compare effectiveness of SSDC during higher loading in alleviating the small signal stability problem.

  2. Low Frequency Oscillations in Assimilated Global Datasets Using TRMM Rainfall Observations

    NASA Technical Reports Server (NTRS)

    Tao, Li; Yang, Song; Zhang, Zhan; Hou, Arthur; Olson, William S.

    2004-01-01

    Global datasets for the period May-August 1998 from the Goddard Earth Observing System (GEOS) data assimilation system (DAS) with/without assimilated Tropical Rainfall Measuring Mission (TRMM) precipitation are analyzed against European Center for Medium-Range Weather Forecast (ECMWF) output, NOAA observed outgoing longwave radiation (OLR) data, and TRMM measured rainfall. The purpose of this study is to investigate the representation of the Madden-Julian Oscillation (MJO) in GEOS assimilated global datasets, noting the impact of TRMM observed rainfall on the MJO in GEOS data assimilations. A space-time analysis of the OLR data indicates that the observed OLR exhibits a spectral maximum for eastward-propagating wavenumber 1-3 disturbances with periods of 20-60 days in the 0deg-30degN latitude band. The assimilated OLR has a similar feature but with a smaller magnitude. However, OLR spectra from assimilations including TRMM rainfall data show better agreement with observed OLR spectra than spectra from assimilations without TRMM rainfall. Similar results are found for wavenumber 4-6 disturbances. There is a spectral peak for eastward-propagating wavenumber 4-6 disturbances with periods of 20-40 days near the equator, while for westward-moving disturbances, a spectral peak is noted for periods of 30-50 days near 25degN. To isolate the MJO, a 30-50 day band filter is selected for this study. It was found that the eastward-propagating waves from the band-filtered observed OLR between 10degs- 10degN are located in the eastern hemisphere. Similar patterns are evident in surface rainfall and the 850 hPa wind field. Assimilation of TRMM-observed rainfall reveals more distinct MJO features in the analysis than without rainfall assimilation. Similar analyses are also conducted over the Indian summer monsoon and East Asia summer monsoon regions, where the MJO is strongly related to the summer monsoon active-break patterns.

  3. Low Frequency Oscillations in Assimilated Global Datasets Using TRMM Rainfall Observations

    NASA Technical Reports Server (NTRS)

    Tao, Li; Yang, Song; Zhang, Zhan; Hou, Arthur; Olson, William S.

    2004-01-01

    Global datasets for the period May-August 1998 from the Goddard Earth Observing System (GEOS) data assimilation system (DAS) with/without assimilated Tropical Rainfall Measuring Mission (TRMM) precipitation are analyzed against European Center for Medium-Range Weather Forecast (ECMWF) output, NOAA observed outgoing longwave radiation (OLR) data, and TRMM measured rainfall. The purpose of this study is to investigate the representation of the Madden-Julian Oscillation (MJO) in GEOS assimilated global datasets, noting the impact of TRMM observed rainfall on the MJO in GEOS data assimilations. A space-time analysis of the OLR data indicates that the observed OLR exhibits a spectral maximum for eastward-propagating wavenumber 1-3 disturbances with periods of 20-60 days in the 0deg-30degN latitude band. The assimilated OLR has a similar feature but with a smaller magnitude. However, OLR spectra from assimilations including TRMM rainfall data show better agreement with observed OLR spectra than spectra from assimilations without TRMM rainfall. Similar results are found for wavenumber 4-6 disturbances. There is a spectral peak for eastward-propagating wavenumber 4-6 disturbances with periods of 20-40 days near the equator, while for westward-moving disturbances, a spectral peak is noted for periods of 30-50 days near 25degN. To isolate the MJO, a 30-50 day band filter is selected for this study. It was found that the eastward-propagating waves from the band-filtered observed OLR between 10degs- 10degN are located in the eastern hemisphere. Similar patterns are evident in surface rainfall and the 850 hPa wind field. Assimilation of TRMM-observed rainfall reveals more distinct MJO features in the analysis than without rainfall assimilation. Similar analyses are also conducted over the Indian summer monsoon and East Asia summer monsoon regions, where the MJO is strongly related to the summer monsoon active-break patterns.

  4. Low-frequency respiratory mechanics using ventilator-driven forced oscillations.

    PubMed

    Lutchen, K R; Kaczka, D W; Suki, B; Barnas, G; Cevenini, G; Barbini, P

    1993-12-01

    We evaluated the potential for using a fast Fourier transform (FFT) analysis applied to a standard ventilator waveform to estimate (< 2 Hz) frequency dependence of respiratory or lung resistance (R) and elastance (E). In four healthy humans we measured pressure and flow at the airway opening while applying sine wave forcing from 0.2 to 0.6 Hz at two tidal volumes (VT; 250 and 500 ml). We then applied a step inspiratory ventilator flow wave with relaxed expiration at the same VT and only 0.2 Hz. Step waveform data were also acquired from nine mechanically ventilated patients under intensive care unit conditions. Finally, we simultaneously measured total respiratory (rs), lung (L), and chest wall (cw) impedance data from two dogs (0.156-2 Hz) before and after severe pulmonary edema. Rrs and Ers were estimated by the FFT approach. Humans displayed a small frequency dependence in Rrs and Ers from 0.2 to 0.6 Hz, and both Rrs and Ers decreased at the higher VT. The spectral estimates of Rrs and Ers with the step ventilator wave were often qualitatively comparable to sine wave results below 0.6 Hz but became extremely erratic above the third harmonic. Conversely, in dogs the step wave produced reliable and stable estimates up to 2 Hz in all conditions. Nevertheless, Ecw and Ers still displayed clear and correlated oscillations with increasing frequency, whereas EL showed none. This suggests that nonlinear processes, most likely at the chest wall, contribute to periodic-like fluctuations in respiratory mechanical properties when estimated by applying FFT to a step ventilator wave. Moreover, in humans, but not dogs, a ventilator flow cycle contains insufficient signal energy beyond the third harmonic. We show that the amount of energy available at higher frequencies is largely governed by the mechanical time constant contributing to passive expiratory flow. In dogs the shorter time constant contributes to increased energy. In essence, the frequency content of the flow is

  5. Evaluation of spontaneous low-frequency oscillations in cerebral hemodynamics with time-series red-green-blue images

    NASA Astrophysics Data System (ADS)

    Nishidate, Izumi; Mustari, Afrina; Nakamura, Naoki; Kawauchi, Satoko; Sato, Shunichi; Sato, Manabu; Kokubo, Yasuaki

    2017-02-01

    The brain relies on a continuous and adequate supply of blood flow, bringing the nutrients that it needs and removing the waste products of metabolism. It is thus one of the most tightly regulated systems in the body, whereby a whole range of mechanisms act to maintain this supply, despite changes in blood pressure etc. Failure of these mechanisms is found in a number of devastating cerebral diseases, including stroke, vascular dementia and brain injury and trauma. Spontaneous contraction and relaxation of arterioles (and in some instances venules) termed vasomotion has been observed in an extensive variety of tissues and species. Vasomotion has a beneficial effect on tissue oxygenation and enhance blood flow. Although vasomotion is strictly a local phenomenon, the regulation of contractile activity of vascular smooth muscle cells is dependent on the complex interplay between vasodilator and vasoconstrictor stimuli from circulating hormones, neurotransmitters, endothelial derived factors, and blood pressure. Therefore, evaluation of the spontaneous oscillations in cerebral vasculatures might be a useful tool for assessing risk and investigating different treatment strategies in neurological disorders, such as traumatic brain injury, seizure, ischemia, and stroke. In the present study, we newly propose a method to visualize the spontaneous low-frequency oscillation of cerebral blood volume based on the sequential RGB images of exposed brain.

  6. LOW-FREQUENCY QUASI-PERIODIC OSCILLATION FROM THE 11 Hz ACCRETING PULSAR IN TERZAN 5: NOT FRAME DRAGGING

    SciTech Connect

    Altamirano, D.; Van der Klis, M.; Wijnands, R.; Ingram, A.; Linares, M.; Homan, J.

    2012-11-01

    We report on six RXTE observations taken during the 2010 outburst of the 11 Hz accreting pulsar IGR J17480-2446 located in the globular cluster Terzan 5. During these observations we find power spectra which resemble those seen in Z-type high-luminosity neutron star low-mass X-ray binaries, with a quasi-periodic oscillation (QPO) in the 35-50 Hz range simultaneous with a kHz QPO and broadband noise. Using well-known frequency-frequency correlations, we identify the 35-50 Hz QPOs as the horizontal branch oscillations, which were previously suggested to be due to Lense-Thirring (LT) precession. As IGR J17480-2446 spins more than an order of magnitude more slowly than any of the other neutron stars where these QPOs were found, this QPO cannot be explained by frame dragging. By extension, this casts doubt on the LT precession model for other low-frequency QPOs in neutron stars and perhaps even black hole systems.

  7. Low-frequency oscillations in R-R interval and blood pressure across the continuum of cardiovascular risk.

    PubMed

    Kiviniemi, Antti M; Tiinanen, Suvi; Hautala, Arto J; Seppänen, Tapio; Norton, Katelyn N; Frances, Maria F; Nolan, Robert P; Huikuri, Heikki V; Tulppo, Mikko P; Shoemaker, J Kevin

    2010-12-08

    The purpose of this study was to assess the power and the frequency of low-frequency (LF; 0.04-<0.15 Hz) oscillations in systolic blood pressure (SBP) and R-R interval (RRi) across the continuum of risk of cardiovascular disease, including age. A potential confound in such determinations is low spontaneous breathing frequency in some individuals. We measured beat-to-beat SBP, RRi and respiration in healthy YOUNG (33±3 years) and OLDER subjects (62±5 years) and older patients with hypertension (HT, 61±5 years), coronary artery disease without (CAD, 62±5 years) and with type 2 diabetes (CAD+DM, 62±4 years, n=28 for all groups) during spontaneous breathing at supine rest. Power (Power(LF)) and median frequency (Med(LF)) of LF oscillations were calculated by power spectral analysis after removing respiratory effects by least-mean-square adaptive filtering. OLDER had higher Power(LF-SBP) (5.5±3.0 vs. 3.4±2.5 mmHg(2), p=0.002) and lower Power(LF-RRi) than YOUNG (339±460 vs. 575±422 ms(2), p=0.001) whereas neither variable differed between OLDER and patient groups. Med(LF-SBP) (0.072±0.009 vs. 0.080±0.011 Hz, p=0.005) and Med(LF-RRi) (0.072±0.010 vs. 0.079±0.013 Hz, p=0.027) were lower in OLDER compared with YOUNG. Compared with OLDER, Med(LF-RRi) was lower in CAD (0.065±0.006 Hz, p=0.015) and CAD +DM (0.066±0.008 Hz, p=0.012); whereas CAD+DM had also lower Med(LF-SBP) (0.065±0.006 Hz, p=0.012). No differences were observed between OLDER and HT and between CAD and CAD+DM in these variables. We concluded that age is major determinant of the power of LF oscillations in SBP and RRi at rest, whereas the median frequency of these oscillations is altered also by coronary artery disease.

  8. Comparison between Spontaneous Low-Frequency Oscillations in Regional Cerebral Blood Volume, and Cerebral and Plethysmographic Pulsations

    NASA Astrophysics Data System (ADS)

    Yamazaki, Kyoko; Uchida, Mariko; Obata, Akiko; Katura, Takusige; Sato, Hiroki; Tanaka, Naoki; Maki, Atsushi

    2007-07-01

    The brain plays a crucial role in maintaining systemic functions. Hence, the cerebral circulation is important because the tissue in the brain cannot store energy sources within it and has to constantly obtain them with oxygen from the blood flow. The mean cerebral blood flow is kept constant over a wide range of blood pressure levels by the regulation of the cerebral circulation. However, the regional cerebral blood flow (rCBF) and volume (rCBV) exhibit strong low-frequency oscillations (LFOs) such as arterial blood pressure and heart rate, which may reflect the interaction of the cerebral and systemic circulation. To gain an insight into the regulation of the cerebral circulation, we investigated LFOs in the rCBV, cerebral pulsation (CP) and plethysmographic pulsation (PP) particularly on their spectral properties. The rCBV and PP signals were simultaneously measured by optical topography (OT: multi-channel near infra-red spectroscopy) and plethysmography with the subject in a resting, seated state. The CP signals were obtained from the pulsatile component contained in the OT signals. When we compared the spectra of LFOs, we found that the spectral peak for LFOs tended to distinctly appear in the order of rCBV, PP, and CP. This distinctness might reflect the regulation of the cerebral circulation. OT signals are considered to contain a contribution from the skin tissue. We also demonstrate that CP is different from the pulsation observed from the skin tissue.

  9. Low-frequency oscillations in black holes: a spectral-timing approach to the case of GX 339-4

    NASA Astrophysics Data System (ADS)

    Motta, S.; Muñoz-Darias, T.; Casella, P.; Belloni, T.; Homan, J.

    2011-12-01

    We analysed Rossi X-ray Timing Explorer (RXTE)/PCA and HEXTE data of the transient black hole binary GX 339-4, collected over a time-span of 8 years. We studied the properties and the behaviour of low-frequency quasi-periodic oscillations (QPOs) as a function of the integrated broad-band variability and the spectral parameters during four outbursts (2002, 2004, 2007 and 2010). Most of the QPOs could be classified following the ABC classification which has been proposed before. Our results show that the ABC classification can be extended to include spectral dependencies and that the three QPO types have indeed intrinsically different properties. In terms of the relation between QPO frequency and power-law flux, types A and C QPOs may follow the same relation, whereas the type B QPOs trace out a very different relation. Type B QPO frequencies clearly correlate with the power-law flux and are connected to local increases of the count rate. The frequencies of all QPOs observed in the rising phase of the 2002, 2007 and 2010 outbursts correlate with the disc flux. Our results can be interpreted within the framework of the recently proposed QPO models involving Lense-Thirring precession. We suggest that types C and A QPOs might be connected and could be interpreted as being the result of the same phenomenon observed at different stages of the outburst evolution, while a different physical process produces type B QPOs.

  10. Hemodynamic and electrophysiological spontaneous low-frequency oscillations in the cortex: directional influences revealed by Granger causality.

    PubMed

    Huang, Liangming; Liu, Yadong; Li, Ming; Hu, Dewen

    2014-01-15

    We used a combined electrophysiological/hemodynamic system to examine low-frequency oscillations (LFOs) in spontaneous neuronal activities (spike trains and local field potentials) and hemodynamic signals (cerebral blood flow) recorded from the anesthetized rat somatosensory and visual cortices. The laser Doppler flowmetry (LDF) probe was tilted slightly to approach the area in which a microelectrode array (MEA) was implanted for simultaneous recordings. Spike trains (STs) were converted into continuous-time rate functions (CRFs) using the ST instantaneous firing rates. LFOs were detected for all three of the components using the multi-taper method (MTM). The frequencies of these LFOs ranged from 0.052 to 0.167 Hz (mean±SD, 0.10±0.026 Hz) for cerebral blood flow (CBF), from 0.027 to 0.26 Hz (mean±SD, 0.12±0.041 Hz) for the CRFs of the STs and from 0.04 to 0.19 Hz (mean±SD, 0.11±0.035 Hz) for local field potentials (LFPs). We evaluated the Granger causal relationships of spontaneous LFOs among CBF, LFPs and CRFs using Granger causality (GC) analysis. Significant Granger causal relationships were observed from LFPs to CBF, from STs to CBF and from LFPs to STs at approximately 0.1 Hz. The present results indicate that spontaneous LFOs exist not only in hemodynamic components but also in neuronal activities of the rat cortex. To the best of our knowledge, the present study is the first to identify Granger causal influences among CBF, LFPs and STs and show that spontaneous LFOs carry important Granger causal influences from neural activities to hemodynamic signals.

  11. Motor network plasticity and low-frequency oscillations abnormalities in patients with brain gliomas: a functional MRI study.

    PubMed

    Niu, Chen; Zhang, Ming; Min, Zhigang; Rana, Netra; Zhang, Qiuli; Liu, Xin; Li, Min; Lin, Pan

    2014-01-01

    Brain plasticity is often associated with the process of slow-growing tumor formation, which remodels neural organization and optimizes brain network function. In this study, we aimed to investigate whether motor function plasticity would display deficits in patients with slow-growing brain tumors located in or near motor areas, but who were without motor neurological deficits. We used resting-state functional magnetic resonance imaging to probe motor networks in 15 patients with histopathologically confirmed brain gliomas and 15 age-matched healthy controls. All subjects performed a motor task to help identify individual motor activity in the bilateral primary motor cortex (PMC) and supplementary motor area (SMA). Frequency-based analysis at three different frequencies was then used to investigate possible alterations in the power spectral density (PSD) of low-frequency oscillations. For each group, the average PSD was determined for each brain region and a nonparametric test was performed to determine the difference in power between the two groups. Significantly reduced inter-hemispheric functional connectivity between the left and right PMC was observed in patients compared with controls (P<0.05). We also found significantly decreased PSD in patients compared to that in controls, in all three frequency bands (low: 0.01-0.02 Hz; middle: 0.02-0.06 Hz; and high: 0.06-0.1 Hz), at three key motor regions. These findings suggest that in asymptomatic patients with brain tumors located in eloquent regions, inter-hemispheric connection may be more vulnerable. A comparison of the two approaches indicated that power spectral analysis is more sensitive than functional connectivity analysis for identifying the neurological abnormalities underlying motor function plasticity induced by slow-growing tumors.

  12. Non-contact magnetically coupled rectilinear-rotary oscillations to exploit low-frequency broadband energy harvesting with frequency up-conversion

    NASA Astrophysics Data System (ADS)

    Deng, Wei; Wang, Ya

    2016-09-01

    Ambient vibrations have a rectilinear and broadband nature and are particularly rich in the low-frequency regions. This letter reports an electromagnetic energy harvester to transform low-frequency broadband rectilinear vibrations into electricity with frequency up-conversion. The harvester consists of a rectilinear oscillator and a rotary oscillator coupled through magnetic force induced by four arc permanent magnets centrosymmetrically distributed on each oscillator. The rotary oscillator also includes two repulsive magnets and six stationary coils with steel screws inside to obtain and maintain four equilibrium positions with shallowed potential wells. The magnetic interaction between the rectilinear oscillator and the rotary oscillator is formulated using a magnetic dipole model. The restoring torque induced by the steel screws on the rotor is experimentally measured. Magnetically coupled governing equations are derived and their numerical solutions are used to characterize the dynamic response of the harvester under chirp excitations. Experimental results demonstrate its excellent harvesting capability of scavenging low-frequency wideband vibrational energy under slow-frequency-drifted excitations, simple harmonic excitations, and mixed-frequency excitations. Under harmonic excitations, the rectilinear oscillator vibrates non-harmonically but approximately periodically, while the rotary counterpart oscillates in a more complex pattern varying with the excitation frequency, which leads to the frequency up-conversion (up to 10 times increase) and broadened bandwidth (25% increase from its resonant frequency). Experiments show an output voltage of 5 V (RMS)/40 V (Peak to Peak) and an output power of 55 mW (RMS)/950 mW (Peak) at an optimal load of 465 Ω under harmonic excitation of 4 Hz at 0.7 g.

  13. Controversial cytogenetic observations in mammalian somatic cells exposed to extremely low frequency electromagnetic radiation: a review and future research recommendations.

    PubMed

    Vijayalaxmi; Obe, Guenter

    2005-07-01

    During the years 1990-2003, a large number of investigations were conducted using animals, cultured rodent and human cells as well as freshly collected human blood lymphocytes to determine the genotoxic potential of exposure to nonionizing radiation emitted from extremely low frequency electromagnetic fields (EMF). Among the 63 peer reviewed scientific reports, the conclusions from 29 studies (46%) did not indicate increased damage to the genetic material, as assessed from DNA strand breaks, incidence of chromosomal aberrations (CA), micronuclei (MN), and sister chromatid exchanges (SCE), in EMF exposed cells as compared with sham exposed and/or unexposed cells, while those from 14 investigations (22%) have suggested an increase in such damage in EMF exposed cells. The observations from 20 other studies (32%) were inconclusive. This study reviews the investigations published in peer reviewed scientific journals during 1990-2003 and attempts to identify probable reason(s) for the conflicting results. Recommendations are made for future research to address some of the controversial observations.

  14. Oscillations in motor unit discharge are reflected in the low-frequency component of rectified surface EMG and the rate of change in force.

    PubMed

    Yoshitake, Yasuhide; Shinohara, Minoru

    2013-11-01

    Common drive to a motor unit (MU) pool manifests as low-frequency oscillations in MU discharge rate, producing fluctuations in muscle force. The aim of the study was to examine the temporal correlation between instantaneous MU discharge rate and rectified EMG in low frequencies. Additionally, we attempted to examine whether there is a temporal correlation between the low-frequency oscillations in MU discharge rate and the first derivative of force (dF/dt). Healthy young subjects produced steady submaximal force with their right finger as a single task or while maintaining a pinch-grip force with the left hand as a dual task. Surface EMG and fine-wire MU potentials were recorded from the first dorsal interosseous muscle in the right hand. Surface EMG was band-pass filtered (5-1,000 Hz) and full-wave rectified. Rectified surface EMG and the instantaneous discharge rate of MUs were smoothed by a Hann-window of 400 ms duration (equivalent to 2 Hz low-pass filtering). In each of the identified MUs, the smoothed MU discharge rate was positively correlated with the rectified-and-smoothed EMG as confirmed by the distinct peak in cross-correlation function with greater values in the dual task compared with the single task. Additionally, the smoothed MU discharge rate was temporally correlated with dF/dt more than with force and with rectified-and-smoothed EMG. The results indicated that the low-frequency component of rectified surface EMG and the first derivative of force provide temporal information on the low-frequency oscillations in the MU discharge rate.

  15. Reproducing the Correlations of Type C Low-frequency Quasi-periodic Oscillation Parameters in XTE J1550–564 with a Spiral Structure

    NASA Astrophysics Data System (ADS)

    Varniere, Peggy; Vincent, Frederic H.

    2017-01-01

    While it has been observed that the parameters intrinsic to the type C low-frequency quasi-periodic oscillations are related in a nonlinear manner among themselves, there has been, up to now, no model to explain or reproduce how the frequency, the FWHM, and the rms amplitude of the type C low-frequency quasi-periodic oscillations behave with respect to one another. Here we are using a simple toy model representing the emission from a standard disk and a spiral such as that caused by the accretion–ejection instability to reproduce the overall observed behavior and shed some light on its origin. This allows us to prove the ability of such a spiral structure to be at the origin of flux modulation over more than an order of magnitude in frequency.

  16. LOW-FREQUENCY (11 mHz) OSCILLATIONS IN H1743-322: A NEW CLASS OF BLACK HOLE QUASI-PERIODIC OSCILLATIONS?

    SciTech Connect

    Altamirano, D.; Strohmayer, T.

    2012-08-01

    We report the discovery of quasi-periodic oscillations (QPOs) at {approx}11 mHz in two RXTE and one Chandra observations of the black hole candidate H1743-322. The QPO is observed only at the beginning of the 2010 and 2011 outbursts at similar hard color and intensity, suggestive of an accretion state dependence for the QPO. Although its frequency appears to be correlated with X-ray intensity on timescales of a day, in successive outbursts eight months apart, we measure a QPO frequency that differs by less than Almost-Equal-To 2.2 mHz while the intensity had changed significantly. We show that this {approx}11 mHz QPO is different from the so-called Type C QPOs seen in black holes and that the mechanisms that produce the two flavors of variability are most probably independent. After comparing this QPO with other variability phenomena seen in accreting black holes and neutron stars, we conclude that it best resembles the so-called 1 Hz QPOs seen in dipping neutron star systems, although having a significantly lower (1-2 orders of magnitude) frequency. If confirmed, H1743-322 is the first black hole showing this type of variability. Given the unusual characteristics and the hard-state dependence of the {approx}11 mHz QPO, we also speculate whether these oscillations could instead be related to the radio jets observed in H1743-322. A systematic search for this type of low-frequency QPOs in similar systems is needed to test this speculation. In any case, it remains unexplained why these QPOs have only been seen in the last two outbursts of H1743-322.

  17. An experimental investigation of low-frequency noise in 8-mm-band Gunn-diode oscillators

    NASA Astrophysics Data System (ADS)

    Kravtsov, I. A.; Malyshev, V. M.; Meshcheriakov, A. V.

    1989-07-01

    The noise characteristics of Ka-band Gunn oscillators are studied. The dependences of the frequency fluctuations on the SWR and load phases are analyzed. A comparison of the noise characteristics of Ka- and X-band Gunn oscillators shows that their fluctuation levels are about the same if they are calculated at the same oscillation frequency. The amplitude fluctuation is 10 dB lower in Ka-band oscillators.

  18. Low Frequency Quasi-periodic Oscillations in the High-eccentric LMXB Cir X-1: Extending the WK Correlation for Z Sources

    NASA Astrophysics Data System (ADS)

    Bu, Qingcui; Belloni, T. M.; Chen, Li; Qu, Jinlu

    2017-06-01

    Using archival Rossi X-ray Timing Explorer (RXTE) data, we studied the low-frequency quasi-periodic oscillations (LFQPOs) in the neutron star low-mass X-ray binary (LMXB) Cir X-1 and examined their contribution to frequency-frequency correlations for Z sources. We also studied the orbital phase effects on the LFQPO properties and found them to be phase independent. Comparing LFQPO frequencies in different classes of LMXBs, we found that systems that show both Z and atoll states form a common track with atoll/BH sources in the so-called WK correlation, while persistent Z systems are offset by a factor of about two. We found that neither source luminosity nor mass accretion rate is related to the shift of persistent Z systems. We discuss the possibility of a misidentification of fundamental frequency for horizontal branch oscillations from persistent Z systems and interpreted the oscillations in terms of models based on relativistic precession.

  19. Electromagnetic fluctuation spectra of collective oscillations in magnetized Maxwellian equal mass plasmas for low-frequency waves

    SciTech Connect

    Vafin, S.; Schlickeiser, R.; Yoon, P. H.

    2016-05-15

    Recently, the general electromagnetic fluctuation theory for magnetized plasmas has been used to study the steady-state fluctuation spectra and the total intensity of low-frequency collective weakly damped modes for parallel wave vectors in Maxwellian plasmas. Now, we address the same question with respect to an arbitrary direction of the wave-vector. Here, we analyze this problem for equal mass plasmas. These plasmas are a very good tool to study various plasma phenomena, as they considerably facilitate the theoretical consideration and at the same time provide with their clear physical picture. Finally, we compare our results in the limiting case of parallel wave vectors with the previous study.

  20. Deep brain stimulation of the globus pallidus internus in the parkinsonian primate: local entrainment and suppression of low-frequency oscillations.

    PubMed

    McCairn, Kevin W; Turner, Robert S

    2009-04-01

    Competing theories seek to account for the therapeutic effects of high-frequency deep brain stimulation (DBS) of the internal globus pallidus (GPi) for medically intractable Parkinson's disease. To investigate this question, we studied the spontaneous activity of 102 pallidal neurons during GPiDBS in two macaques rendered parkinsonian by administration of MPTP. Stimulation through macroelectrodes in the GPi (> or =200 microA at 150 Hz for 30 s) reduced rigidity in one animal and increased spontaneous movement in both. Novel artifact subtraction methods allowed uninterrupted single-unit recording during stimulation. GPiDBS induced phasic (78% of cells) or sustained (22%) peristimulus changes in firing in both pallidal segments. A subset of cells responded at short latency (<2 ms) in a manner consistent with antidromic driving. Later phasic increases clustered at 3- to 5-ms latency. Stimulation-induced decreases were either phasic, clustered at 1-3 ms, or sustained, showing no peristimulus modulation. Response latency and magnitude often evolved over 30 s of stimulation, but responses were relatively stable by the end of that time. GPiDBS reduced mean firing rates modestly and only in GPi (-6.9 spikes/s). Surprisingly, GPiDBS had no net effect on the prevalence or structure of burst firing. GPiDBS did reduce the prevalence of synchronized low-frequency oscillations. Some cell pairs became synchronized instead at the frequency of stimulation. Suppression of low-frequency oscillations did not require high-frequency synchronization, however, or even the presence of a significant peristimulus response. In summary, the therapeutic effects of GPiDBS may be mediated by an abolition of low-frequency synchronized oscillations as a result of phasic driving.

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

    NASA Astrophysics Data System (ADS)

    Meehan, Aidan; Connelly, Michael J.

    2014-05-01

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

  2. Phase-amplitude investigation of spontaneous low-frequency oscillations of cerebral hemodynamics with near-infrared spectroscopy: A sleep study in human subjects

    PubMed Central

    Pierro, Michele; Sassaroli, Angelo; Bergethon, Peter R.; Ehrenberg, Bruce L.; Fantini, Sergio

    2012-01-01

    We have investigated the amplitude and phase of spontaneous low-frequency oscillations (LFOs) of the cerebral deoxy- and oxy-hemoglobin concentrations ([Hb] and [HbO]) in a human sleep study using near-infrared spectroscopy (NIRS). Amplitude and phase analysis was based on the analytic signal method, and phasor algebra was used to decompose measured [Hb] and [HbO] oscillations into cerebral blood volume (CBV) and flow velocity (CBFV) oscillations. We have found a greater phase lead of [Hb] vs. [HbO] LFOs during non-REM sleep with respect to the awake and REM sleep states (maximum increase in [Hb] phase lead: ~π/2). Furthermore, during non-REM sleep, the amplitudes of [Hb] and [HbO] LFOs are suppressed with respect to the awake and REM sleep states (maximum amplitude decrease: 87%). The associated cerebral blood volume and flow velocity oscillations are found to maintain their relative phase difference during sleep, whereas their amplitudes are attenuated during non-REM sleep. These results show the potential of phase-amplitude analysis of [Hb] and [HbO] oscillations measured by NIRS in the investigation of hemodynamics associated with cerebral physiology, activation, and pathological conditions. PMID:22820416

  3. Low-Frequency Oscillations and Transport Processes Induced by Multiscale Transverse Structures in the Polar Wind Outflow: A Three-Dimensional Simulation

    NASA Technical Reports Server (NTRS)

    Ganguli, Supriya B.; Gavrishchaka, Valeriy V.

    1999-01-01

    Multiscale transverse structures in the magnetic-field-aligned flows have been frequently observed in the auroral region by FAST and Freja satellites. A number of multiscale processes, such as broadband low-frequency oscillations and various cross-field transport effects are well correlated with these structures. To study these effects, we have used our three-dimensional multifluid model with multiscale transverse inhomogeneities in the initial velocity profile. Self-consistent-frequency mode driven by local transverse gradients in the generation of the low field-aligned ion flow and associated transport processes were simulated. Effects of particle interaction with the self-consistent time-dependent three-dimensional wave potential have been modeled using a distribution of test particles. For typical polar wind conditions it has been found that even large-scale (approximately 50 - 100 km) transverse inhomogeneities in the flow can generate low-frequency oscillations that lead to significant flow modifications, cross-field particle diffusion, and other transport effects. It has also been shown that even small-amplitude (approximately 10 - 20%) short-scale (approximately 10 km) modulations of the original large-scale flow profile significantly increases low-frequency mode generation and associated cross-field transport, not only at the local spatial scales imposed by the modulations but also on global scales. Note that this wave-induced cross-field transport is not included in any of the global numerical models of the ionosphere, ionosphere-thermosphere, or ionosphere-polar wind. The simulation results indicate that the wave-induced cross-field transport not only affects the ion outflow rates but also leads to a significant broadening of particle phase-space distribution and transverse particle diffusion.

  4. Synchronization, non-linear dynamics and low-frequency fluctuations: Analogy between spontaneous brain activity and networked single-transistor chaotic oscillators

    SciTech Connect

    Minati, Ludovico E-mail: ludovico.minati@unitn.it

    2015-03-15

    In this paper, the topographical relationship between functional connectivity (intended as inter-regional synchronization), spectral and non-linear dynamical properties across cortical areas of the healthy human brain is considered. Based upon functional MRI acquisitions of spontaneous activity during wakeful idleness, node degree maps are determined by thresholding the temporal correlation coefficient among all voxel pairs. In addition, for individual voxel time-series, the relative amplitude of low-frequency fluctuations and the correlation dimension (D{sub 2}), determined with respect to Fourier amplitude and value distribution matched surrogate data, are measured. Across cortical areas, high node degree is associated with a shift towards lower frequency activity and, compared to surrogate data, clearer saturation to a lower correlation dimension, suggesting presence of non-linear structure. An attempt to recapitulate this relationship in a network of single-transistor oscillators is made, based on a diffusive ring (n = 90) with added long-distance links defining four extended hub regions. Similarly to the brain data, it is found that oscillators in the hub regions generate signals with larger low-frequency cycle amplitude fluctuations and clearer saturation to a lower correlation dimension compared to surrogates. The effect emerges more markedly close to criticality. The homology observed between the two systems despite profound differences in scale, coupling mechanism and dynamics appears noteworthy. These experimental results motivate further investigation into the heterogeneity of cortical non-linear dynamics in relation to connectivity and underline the ability for small networks of single-transistor oscillators to recreate collective phenomena arising in much more complex biological systems, potentially representing a future platform for modelling disease-related changes.

  5. Synchronization, non-linear dynamics and low-frequency fluctuations: Analogy between spontaneous brain activity and networked single-transistor chaotic oscillators

    NASA Astrophysics Data System (ADS)

    Minati, Ludovico; Chiesa, Pietro; Tabarelli, Davide; D'Incerti, Ludovico; Jovicich, Jorge

    2015-03-01

    In this paper, the topographical relationship between functional connectivity (intended as inter-regional synchronization), spectral and non-linear dynamical properties across cortical areas of the healthy human brain is considered. Based upon functional MRI acquisitions of spontaneous activity during wakeful idleness, node degree maps are determined by thresholding the temporal correlation coefficient among all voxel pairs. In addition, for individual voxel time-series, the relative amplitude of low-frequency fluctuations and the correlation dimension (D2), determined with respect to Fourier amplitude and value distribution matched surrogate data, are measured. Across cortical areas, high node degree is associated with a shift towards lower frequency activity and, compared to surrogate data, clearer saturation to a lower correlation dimension, suggesting presence of non-linear structure. An attempt to recapitulate this relationship in a network of single-transistor oscillators is made, based on a diffusive ring (n = 90) with added long-distance links defining four extended hub regions. Similarly to the brain data, it is found that oscillators in the hub regions generate signals with larger low-frequency cycle amplitude fluctuations and clearer saturation to a lower correlation dimension compared to surrogates. The effect emerges more markedly close to criticality. The homology observed between the two systems despite profound differences in scale, coupling mechanism and dynamics appears noteworthy. These experimental results motivate further investigation into the heterogeneity of cortical non-linear dynamics in relation to connectivity and underline the ability for small networks of single-transistor oscillators to recreate collective phenomena arising in much more complex biological systems, potentially representing a future platform for modelling disease-related changes.

  6. Synchronization, non-linear dynamics and low-frequency fluctuations: analogy between spontaneous brain activity and networked single-transistor chaotic oscillators.

    PubMed

    Minati, Ludovico; Chiesa, Pietro; Tabarelli, Davide; D'Incerti, Ludovico; Jovicich, Jorge

    2015-03-01

    In this paper, the topographical relationship between functional connectivity (intended as inter-regional synchronization), spectral and non-linear dynamical properties across cortical areas of the healthy human brain is considered. Based upon functional MRI acquisitions of spontaneous activity during wakeful idleness, node degree maps are determined by thresholding the temporal correlation coefficient among all voxel pairs. In addition, for individual voxel time-series, the relative amplitude of low-frequency fluctuations and the correlation dimension (D2), determined with respect to Fourier amplitude and value distribution matched surrogate data, are measured. Across cortical areas, high node degree is associated with a shift towards lower frequency activity and, compared to surrogate data, clearer saturation to a lower correlation dimension, suggesting presence of non-linear structure. An attempt to recapitulate this relationship in a network of single-transistor oscillators is made, based on a diffusive ring (n = 90) with added long-distance links defining four extended hub regions. Similarly to the brain data, it is found that oscillators in the hub regions generate signals with larger low-frequency cycle amplitude fluctuations and clearer saturation to a lower correlation dimension compared to surrogates. The effect emerges more markedly close to criticality. The homology observed between the two systems despite profound differences in scale, coupling mechanism and dynamics appears noteworthy. These experimental results motivate further investigation into the heterogeneity of cortical non-linear dynamics in relation to connectivity and underline the ability for small networks of single-transistor oscillators to recreate collective phenomena arising in much more complex biological systems, potentially representing a future platform for modelling disease-related changes.

  7. Low Frequency (11 mHz) Oscillations in H1743-322: A New Class of Black Hole QPOs?

    NASA Technical Reports Server (NTRS)

    Altamirano, D.; Strohmayer, T.

    2012-01-01

    We report the discovery of quasi-periodic oscillations (QPO) at approx 11 mHz in two RXTE observations and one Chandra observation of the black hole candidate HI743-322. The QPO is observed only at the beginning of the 2010 and 2011 outbursts at similar hard color and intensity, suggestive of an accretion state dependence for the QPO. Although its frequency appears to be correlated with Xray intensity on timescales of a day, in successive outbursts eight months apart we measure a QPO frequency that differs by less than approximately equals 0.0015 Hz while the intensity had changed significantly. We show that this 11 mHz QPO is different from the so-called Type-C QPOs seen in black holes and that the mechanisms that produce the two flavors of variability are most probably independent. We compare the 11 mHz QPO with other variability phenomena seen in accreting black holes and neutron stars and conclude that although at 1-2 orders of magnitude lower in frequency, they best resemble the so-called "1 Hz" QPOs seen in dipping neutron star systems. If confirmed, H1743-322 is the first black hole showing this type of variability. Given the unusual characteristics and the hard-state dependence of the 11 mHz QPO, we speculate that these oscillations might instead be related to the radio jets observed in HI743-322. It remains unexplained, however, why similar QPOs have not yet been identified in other black holes and why they have only been seen in the last two outbursts of HI743-322.

  8. Detection of Very Low-frequency, Quasi-periodic Oscillations in the 2015 Outburst of V404 Cygni

    NASA Astrophysics Data System (ADS)

    Huppenkothen, D.; Younes, G.; Ingram, A.; Kouveliotou, C.; Göğüş, E.; Bachetti, M.; Sánchez-Fernández, C.; Chenevez, J.; Motta, S.; van der Klis, M.; Granot, J.; Gehrels, N.; Kuulkers, E.; Tomsick, J. A.; Walton, D. J.

    2017-01-01

    In 2015 June, the black hole X-ray binary (BHXRB) V404 Cygni went into outburst for the first time since 1989. Here, we present a comprehensive search for quasi-periodic oscillations (QPOs) of V404 Cygni during its recent outburst, utilizing data from six instruments on board five different X-ray missions: Swift/XRT, Fermi/GBM, Chandra/ACIS, INTEGRAL’s IBIS/ISGRI and JEM-X, and NuSTAR. We report the detection of a QPO at 18 mHz simultaneously with both Fermi/GBM and Swift/XRT, another example of a rare but slowly growing new class of mHz-QPOs in BHXRBs linked to sources with a high orbital inclination. Additionally, we find a duo of QPOs in a Chandra/ACIS observation at 73 mHz and 1.03 Hz, as well as a QPO at 136 mHz in a single Swift/XRT observation that can be interpreted as standard Type-C QPOs. Aside from the detected QPOs, there is significant structure in the broadband power, with a strong feature observable in the Chandra observations between 0.1 and 1 Hz. We discuss our results in the context of current models for QPO formation.

  9. The influence of sea surface temperature anomalies on low-frequency variability of the North Atlantic Oscillation

    NASA Astrophysics Data System (ADS)

    Manganello, Julia V.

    2008-05-01

    The influence of sea surface temperature anomalies (SSTA) on multi-year persistence of the North Atlantic Oscillation (NAO) during the second half of the twentieth century is investigated using the Center for Ocean-Land-Atmosphere Studies (COLA) Atmospheric GCM (AGCM) with an emphasis on isolating the geographic location of the SSTA that produce this influence. The present study focuses on calculating the atmospheric response to the SSTA averaged over 1988 1995 (1961 1968) corresponding to the observed period of strong persistence of the positive (negative) phase of the decadal NAO. The model response to the global 1988 1995 average SSTA shows a statistically significant large-scale pattern characteristic of the positive phase of the NAO. Forcing with the global 1961 1968 average SSTA generates a NAO of the opposite polarity compared to observations. However, all large-scale features both in the model and observations during this period are weaker in magnitude and less significant compared to 1988 1995. Additional idealized experiments show that over the northern center of the NAO the non-linear component of the forced response appears to be quite important and acts to enhance the positive NAO signal. On the other hand, over the southern center where the model response is the strongest, it is also essentially linear. The 1988 1995 average SSTA restricted to the western tropical Pacific region produce a positive NAO remarkably similar in structure but stronger in magnitude than the model response to the global and tropical Indo-Pacific 1988 1995 forcing. A 200-hPa geopotential height response in these experiments shows a positive anomaly over the southern center of the NAO embedded in the Rossby wave trains propagating from the western tropical Pacific. Indian Ocean SSTA lead to much weaker positive NAO primarily through the effect on its northern center. SST forcing confined to the North Atlantic north of equator does not produce a response statistically different

  10. Low-frequency oscillations of the East Asia-Pacific teleconnection pattern and their impacts on persistent heavy precipitation in the Yangtze-Huai River valley

    NASA Astrophysics Data System (ADS)

    Li, Lei; Zhai, Panmao; Chen, Yang; Ni, Yunqi

    2016-06-01

    Based on the daily reanalysis data from NCEP-NCAR and daily precipitation data from the China National Meteorological Information Center, an ensemble empirical mode decomposition method is employed to extract the predominant oscillation modes of the East Asia-Pacific (EAP) teleconnection pattern. The influences of these low-frequency modes on persistent heavy precipitation in the Yangtze-Huai River (YHR) valley are investigated. The results indicate that the EAP pattern and rainfall in YHR valley both exhibit remarkable 10-30- and 30-60-day oscillations. The impacts of the EAP pattern on the YHR persistent heavy precipitation can be found on both the 10-30- and 30-60-day timescales—the 10-30-day scale for most cases. Composite analysis indicates that, on the 10-30-day timescale, formation of the EAP pattern in the lower and middle troposphere is determined by convective systems near the tropical western Pacific; whereas in the middle troposphere, the phase transition is jointly contributed by both the dispersion of zonal wave energies at higher latitudes and convective systems over the South China Sea. In the context of the 10-30-day EAP pattern, the anomalously abundant moisture is transported by an anomalous subtropical anticyclone system, and strong moisture convergence results from that anomalous anticyclone system and a cyclonic system in the midlatitude East Asia. Such a combination of systems persists for at least three days, contributing to the formation of persistent heavy precipitation in the YHR valley.

  11. "Can waiting awaken the resting brain?" A comparison of waiting- and cognitive task-induced attenuation of very low frequency neural oscillations.

    PubMed

    Hsu, Chia-Fen; Broyd, Samantha J; Helps, Suzannah K; Benikos, Nicholas; Sonuga-Barke, Edmund J S

    2013-08-02

    The default mode network (DMN) is characterised by coherent very low frequency (VLF) neural oscillations in the resting brain. The attenuation of this activity has been demonstrated following the transition from rest to performance of a broad range of cognitive goal-directed tasks. Whether the activity of resting state VLF oscillations is attenuated during non-cognitive goal-directed tasks such as waiting for rewarding outcomes is not known. This study examined the VLF EEG power from resting to performance of attention demanding task and two types of goal-directed waiting tasks. The association between the attenuation of VLF EEG power and Attention-Deficit/Hyperactivity Disorder (ADHD) symptoms was examined. Direct current EEG (DC-EEG) data were collected from 32 healthy young adults (half high and half low ADHD symptom scorers) during (i) a rest state, (ii) while performing a cognitive demanding reaction time task (2CRT), and (iii) while undertaking each of two different goal-directed waiting conditions: "forced-to-wait (FW)" and "choose-to-wait (CW)" tasks. The spatial distribution of VLF EEG power across scalp was similar to that seen in previous resting VLF EEG studies. Significant rest-to-task attenuation of VLF EEG power occurred during the 2CRT and the CW task, but not during the FW task. The association between self-ratings of ADHD symptoms and waiting-induced attenuation was not significant. This study suggests VLF EEG power attenuation that occurs following rest-to-task transition is not simply determined by changes in cognitive load. The goal-directed nature of a task, its motivated nature and/or the involvement of effortful attention may also contribute. Future studies should explore the attenuation of resting state VLF oscillations during waiting and impulsive choice.

  12. Amplitude of Low-Frequency Oscillations in First-Episode, Treatment-Naive Patients with Major Depressive Disorder: A Resting-State Functional MRI Study

    PubMed Central

    Wang, Li; Dai, Wenji; Su, Yunai; Wang, Gang; Tan, Yunlong; Jin, Zhen; Zeng, Yawei; Yu, Xin; Chen, Wei; Wang, Xiaodong; Si, Tianmei

    2012-01-01

    Background Resting-state fMRI is a novel approach to measure spontaneous brain activity in patients with major depressive disorder (MDD). Although most resting-state fMRI studies have focused on the examination of temporal correlations between low-frequency oscillations (LFOs), few studies have explored the amplitude of these LFOs in MDD. In this study, we applied the approaches of amplitude of low-frequency fluctuation (ALFF) and fractional ALFF to examine the amplitude of LFOs in MDD. Methodology/Principal Findings A total of 36 subjects, 18 first-episode, treatment-naive patients with MDD matched with 18 healthy controls (HCs) completed the fMRI scans. Compared with HCs, MDD patients showed increased ALFF in the right fusiform gyrus and the right anterior and posterior lobes of the cerebellum but decreased ALFF in the left inferior temporal gyrus, bilateral inferior parietal lobule, and right lingual gyrus. The fALFF in patients was significantly increased in the right precentral gyrus, right inferior temporal gyrus, bilateral fusiform gyrus, and bilateral anterior and posterior lobes of the cerebellum but was decreased in the left dorsolateral prefrontal cortex, bilateral medial orbitofrontal cortex, bilateral middle temporal gyrus, left inferior temporal gyrus, and right inferior parietal lobule. After taking gray matter (GM) volume as a covariate, the results still remained. Conclusions/Significance These findings indicate that MDD patients have altered LFO amplitude in a number of regions distributed over the frontal, temporal, parietal, and occipital cortices and the cerebellum. These aberrant regions may be related to the disturbances of multiple emotion- and cognition-related networks observed in MDD and the apparent heterogeneity in depressive symptom domains. Such brain functional alteration of MDD may contribute to further understanding of MDD-related network imbalances demonstrated in previous fMRI studies. PMID:23119084

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

    PubMed

    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.

  14. ON THE GEOMETRIC NATURE OF LOW-FREQUENCY QUASI-PERIODIC OSCILLATIONS IN NEUTRON-STAR LOW-MASS X-RAY BINARIES

    SciTech Connect

    Homan, Jeroen; Remillard, Ronald A.; Fridriksson, Joel K.

    2015-10-10

    We report on a detailed analysis of the so-called ∼1 Hz quasi-periodic oscillation (QPO) in the eclipsing and dipping neutron-star low-mass X-ray binary EXO 0748–676. This type of QPO has previously been shown to have a geometric origin. Our study focuses on the evolution of the QPO as the source moves through the color–color diagram in which it traces out an atoll-source-like track. The QPO frequency increases from ∼0.4 Hz in the hard state to ∼25 Hz as the source approaches the soft state. Combining power spectra based on QPO frequency reveals additional features that strongly resemble those seen in non-dipping/eclipsing atoll sources. We show that the low-frequency QPOs in atoll sources and the ∼1 Hz QPO in EXO 0748–676 follow similar relations with respect to the noise components in their power spectra. We conclude that the frequencies of both types of QPOs are likely set by (the same) precession of a misaligned inner accretion disk. For high-inclination systems like EXO 0748–676 this results in modulations of the neutron-star emission due to obscuration or scattering, while for lower-inclination systems the modulations likely arise from relativistic Doppler-boosting and light-bending effects.

  15. Low-frequency oscillations measured in the periphery with near-infrared spectroscopy are strongly correlated with blood oxygen level-dependent functional magnetic resonance imaging signals

    NASA Astrophysics Data System (ADS)

    Tong, Yunjie; Hocke, Lia Maria; Licata, Stephanie C.; deB. Frederick, Blaise

    2012-10-01

    Low-frequency oscillations (LFOs) in the range of 0.01-0.15 Hz are commonly observed in functional imaging studies, such as blood oxygen level-dependent functional magnetic resonance imaging (BOLD fMRI) and functional near-infrared spectroscopy (fNIRS). Some of these LFOs are nonneuronal and are closely related to autonomic physiological processes. In the current study, we conducted a concurrent resting-state fMRI and NIRS experiment with healthy volunteers. LFO data was collected simultaneously at peripheral sites (middle fingertip and big toes) by NIRS, and centrally in the brain by BOLD fMRI. The cross-correlations of the LFOs collected from the finger, toes, and brain were calculated. Our data show that the LFOs measured in the periphery (NIRS signals) and in the brain (BOLD fMRI) were strongly correlated with varying time delays. This demonstrates that some portion of the LFOs actually reflect systemic physiological circulatory effects. Furthermore, we demonstrated that NIRS is effective for measuring the peripheral LFOs, and that these LFOs and the temporal shifts between them are consistent in healthy participants and may serve as useful biomarkers for detecting and monitoring circulatory dysfunction.

  16. Low frequency cauterization.

    PubMed

    Sawatzky, G; Wiest, P P

    1993-01-01

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

  17. Energy dependence of r.m.s amplitude of low frequency broadband noise and kHz quasi periodic oscillations in 4U 1608-52

    NASA Astrophysics Data System (ADS)

    Mandal, Soma

    2016-07-01

    The neutron star low mass X-ray binary 4U 1608-52 is known to show kHz QPOs as well as low frequency broad band noise. The energy dependence of the fractional r.m.s of these variations reflect the underlying radiative mechanism responsible for the phenomena. In this work we compute the energy depedence for 26 instances of kHz QPO observed by RXTE. We typically find as reported before, that the r.m.s increases with energy with slope of ˜0.5. This indicates that the variation is in the hot thermal compotonization component and in particular the QPO is likely to be driven by variation in the thermal heating rate of the hot plasma. For the same data, we compute the energy dependent r.m.s variability of the low frequency broad band noise component by considering the light curves. In contrast to the behaviour seen for the kHz QPO, the energy dependence is nearly flat i.e. the r.m.s. is energy independent. This indicates that the driver here may be the soft photon source. Thus the radiative mechanism driving the low frequency broad band noise and the high frequency QPO are different in nature.

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

    PubMed

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

    2016-02-01

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

  19. Noncontact imaging of plethysmographic pulsation and spontaneous low-frequency oscillation in skin perfusion with a digital red-green-blue camera

    NASA Astrophysics Data System (ADS)

    Nishidate, Izumi; Hoshi, Akira; Aoki, Yuta; Nakano, Kazuya; Niizeki, Kyuichi; Aizu, Yoshihisa

    2016-03-01

    A non-contact imaging method with a digital RGB camera is proposed to evaluate plethysmogram and spontaneous lowfrequency oscillation. In vivo experiments with human skin during mental stress induced by the Stroop color-word test demonstrated the feasibility of the method to evaluate the activities of autonomic nervous systems.

  20. Low Frequency Acoustics

    DTIC Science & Technology

    2016-06-13

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

  1. Coordinated infraslow neural and cardiac oscillations mark fragility and offline periods in mammalian sleep.

    PubMed

    Lecci, Sandro; Fernandez, Laura M J; Weber, Frederik D; Cardis, Romain; Chatton, Jean-Yves; Born, Jan; Lüthi, Anita

    2017-02-01

    Rodents sleep in bouts lasting minutes; humans sleep for hours. What are the universal needs served by sleep given such variability? In sleeping mice and humans, through monitoring neural and cardiac activity (combined with assessment of arousability and overnight memory consolidation, respectively), we find a previously unrecognized hallmark of sleep that balances two fundamental yet opposing needs: to maintain sensory reactivity to the environment while promoting recovery and memory consolidation. Coordinated 0.02-Hz oscillations of the sleep spindle band, hippocampal ripple activity, and heart rate sequentially divide non-rapid eye movement (non-REM) sleep into offline phases and phases of high susceptibility to external stimulation. A noise stimulus chosen such that sleeping mice woke up or slept through at comparable rates revealed that offline periods correspond to raising, whereas fragility periods correspond to declining portions of the 0.02-Hz oscillation in spindle activity. Oscillations were present throughout non-REM sleep in mice, yet confined to light non-REM sleep (stage 2) in humans. In both species, the 0.02-Hz oscillation predominated over posterior cortex. The strength of the 0.02-Hz oscillation predicted superior memory recall after sleep in a declarative memory task in humans. These oscillations point to a conserved function of mammalian non-REM sleep that cycles between environmental alertness and internal memory processing in 20- to 25-s intervals. Perturbed 0.02-Hz oscillations may cause memory impairment and ill-timed arousals in sleep disorders.

  2. Coordinated infraslow neural and cardiac oscillations mark fragility and offline periods in mammalian sleep

    PubMed Central

    Lecci, Sandro; Fernandez, Laura M. J.; Weber, Frederik D.; Cardis, Romain; Chatton, Jean-Yves; Born, Jan; Lüthi, Anita

    2017-01-01

    Rodents sleep in bouts lasting minutes; humans sleep for hours. What are the universal needs served by sleep given such variability? In sleeping mice and humans, through monitoring neural and cardiac activity (combined with assessment of arousability and overnight memory consolidation, respectively), we find a previously unrecognized hallmark of sleep that balances two fundamental yet opposing needs: to maintain sensory reactivity to the environment while promoting recovery and memory consolidation. Coordinated 0.02-Hz oscillations of the sleep spindle band, hippocampal ripple activity, and heart rate sequentially divide non–rapid eye movement (non-REM) sleep into offline phases and phases of high susceptibility to external stimulation. A noise stimulus chosen such that sleeping mice woke up or slept through at comparable rates revealed that offline periods correspond to raising, whereas fragility periods correspond to declining portions of the 0.02-Hz oscillation in spindle activity. Oscillations were present throughout non-REM sleep in mice, yet confined to light non-REM sleep (stage 2) in humans. In both species, the 0.02-Hz oscillation predominated over posterior cortex. The strength of the 0.02-Hz oscillation predicted superior memory recall after sleep in a declarative memory task in humans. These oscillations point to a conserved function of mammalian non-REM sleep that cycles between environmental alertness and internal memory processing in 20- to 25-s intervals. Perturbed 0.02-Hz oscillations may cause memory impairment and ill-timed arousals in sleep disorders. PMID:28246641

  3. Amplitude of Low-frequency Oscillations in Parkinson's Disease: A 2-year Longitudinal Resting-state Functional Magnetic Resonance Imaging Study

    PubMed Central

    Hu, Xiao-Fei; Zhang, Jiu-Quan; Jiang, Xiao-Mei; Zhou, Chao-Yang; Wei, Lu-Qing; Yin, Xun-Tao; Li, Jing; Zhang, Yan-Ling; Wang, Jian

    2015-01-01

    Background: Neuroimaging studies have found that functional changes exist in patients with Parkinson's disease (PD). However, the majority of functional magnetic resonance imaging (fMRI) studies in patients with PD are task-related and cross-sectional. This study investigated the functional changes observed in patients with PD, at both baseline and after 2 years, using resting-state fMRI. It further investigated the relationship between whole-brain spontaneous neural activity of patients with PD and their clinical characteristics. Methods: Seventeen patients with PD underwent an MRI procedure at both baseline and after 2 years using resting-state fMRI that was derived from the same 3T MRI. In addition, 20 age- and sex-matched, healthy controls were examined using resting-state fMRI. The fractional amplitude of low-frequency fluctuation (fALFF) approach was used to analyze the fMRI data. Nonlinear registration was used to model within-subject changes over the scanning interval, as well as changes between the patients with PD and the healthy controls. A correlative analysis between the fALFF values and clinical characteristics was performed in the regions showing fALFF differences. Results: Compared to the control subjects, the patients with PD showed increased fALFF values in the left inferior temporal gyrus, right inferior parietal lobule (IPL) and right middle frontal gyrus. Compared to the baseline in the 2 years follow-up, the patients with PD presented with increased fALFF values in the right middle temporal gyrus and right middle occipital gyrus while also having decreased fALFF values in the right cerebellum, right thalamus, right striatum, left superior parietal lobule, left IPL, left precentral gyrus, and left postcentral gyrus (P < 0.01, after correction with AlphaSim). In addition, the fALFF values in the right cerebellum were positively correlated with the Unified PD Rating Scale (UPDRS) motor scores (r = 0.51, P < 0.05, uncorrected) and the change in

  4. Low-Frequency Repetitive Transcranial Magnetic Stimulation (rTMS) Modulates Evoked-Gamma Frequency Oscillations in Autism Spectrum Disorder (ASD)

    PubMed Central

    Baruth, Joshua M.; Casanova, Manuel F.; El-Baz, Ayman; Horrell, Tim; Mathai, Grace; Sears, Lonnie; Sokhadze, Estate

    2010-01-01

    Introduction It has been reported that individuals with Autism Spectrum Disorder (ASD) have abnormal reactions to the sensory environment and visuo-perceptual abnormalities. Electrophysiological research has provided evidence that gamma band activity (30-80 Hz) is a physiological indicator of the co-activation of cortical cells engaged in processing visual stimuli and integrating different features of a stimulus. A number of studies have found augmented and indiscriminative gamma band power at early stages of visual processing in ASD; this may be related to decreased inhibitory processing and an increase in the ratio of cortical excitation to inhibition. Low frequency or ‘slow’ (≤1HZ) repetitive transcranial magnetic stimulation (rTMS) has been shown to increase inhibition of stimulated cortex by the activation of inhibitory circuits. Methods We wanted to test the hypothesis of gamma band abnormalities at early stages of visual processing in ASD by investigating relative evoked (i.e. ~ 100 ms) gamma power in 25 subjects with ASD and 20 age-matched controls using Kanizsa illusory figures. Additionally, we wanted to assess the effects of 12 sessions of bilateral ‘slow’ rTMS to the dorsolateral prefrontal cortex (DLPFC) on evoked gamma activity using a randomized controlled design. Results In individuals with ASD evoked gamma activity was not discriminative of stimulus type, whereas in controls early gamma power differences between target and non-target stimuli were highly significant. Following rTMS individuals with ASD showed significant improvement in discriminatory gamma activity between relevant and irrelevant visual stimuli. We also found significant improvement in the responses on behavioral questionnaires (i.e., irritability, repetitive behavior) as a result of rTMS. Conclusion We proposed that ‘slow’ rTMS may have increased cortical inhibitory tone which improved discriminatory gamma activity at early stages of visual processing. rTMS has the

  5. Transport in GaAs/Al{sub x}Ga{sub 1-x}As superlattices with narrow forbidden minibands: Low-frequency negative differential conductivity and current oscillations

    SciTech Connect

    Andronov, A. A. Dodin, E. P.; Zinchenko, D. I.; Nozdrin, Yu. N.

    2009-02-15

    Current-voltage characteristics have been measured and low-frequency current instabilities have been studied for GaAs/Al{sub x}Ga{sub 1-x}As superlattices with narrow forbidden minibands. At relatively low electric fields, a saw-like structure for current-voltage characteristics with alternating portions of positive and negative differential conductivity and spontaneous generation of low-frequency current oscillations with a complex frequency spectrum (varying from discrete to continuous) are observed. It is shown that the observed specific features of electron transport are caused by the spatial-temporal dynamics of electric-field domains (dipoles and monopoles). The effects of the bifurcation, hysteresis, and multistability of current-voltage characteristics are also observed. At high fields, regular features are observed and identified in the current-voltage characteristics; these features are caused by resonance tunneling of electrons between the levels of the Wannier-Stark ladders belonging to quantum wells separated by several periods.

  6. From quiescence to proliferation: Cdk oscillations drive the mammalian cell cycle.

    PubMed

    Gérard, Claude; Goldbeter, Albert

    2012-01-01

    We recently proposed a detailed model describing the dynamics of the network of cyclin-dependent kinases (Cdks) driving the mammalian cell cycle (Gérard and Goldbeter, 2009). The model contains four modules, each centered around one cyclin/Cdk complex. Cyclin D/Cdk4-6 and cyclin E/Cdk2 promote progression in G1 and elicit the G1/S transition, respectively; cyclin A/Cdk2 ensures progression in S and the transition S/G2, while the activity of cyclin B/Cdk1 brings about the G2/M transition. This model shows that in the presence of sufficient amounts of growth factor the Cdk network is capable of temporal self-organization in the form of sustained oscillations, which correspond to the ordered, sequential activation of the various cyclin/Cdk complexes that control the successive phases of the cell cycle. The results suggest that the switch from cellular quiescence to cell proliferation corresponds to the transition from a stable steady state to sustained oscillations in the Cdk network. The transition depends on a finely tuned balance between factors that promote or hinder progression in the cell cycle. We show that the transition from quiescence to proliferation can occur in multiple ways that alter this balance. By resorting to bifurcation diagrams, we analyze the mechanism of oscillations in the Cdk network. Finally, we show that the complexity of the detailed model can be greatly reduced, without losing its key dynamical properties, by considering a skeleton model for the Cdk network. Using such a skeleton model for the mammalian cell cycle we show that positive feedback (PF) loops enhance the amplitude and the robustness of Cdk oscillations with respect to molecular noise. We compare the relative merits of the detailed and skeleton versions of the model for the Cdk network driving the mammalian cell cycle.

  7. Low frequency cavitation erosion

    NASA Astrophysics Data System (ADS)

    Pardue, Sally J.; Chandekar, Gautam

    2002-11-01

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

  8. Testing the relativistic precession model using low-frequency and kHz quasi-periodic oscillations in neutron star low-mass X-ray binaries with known spin

    NASA Astrophysics Data System (ADS)

    van Doesburgh, Marieke; van der Klis, Michiel

    2017-03-01

    We analyse all available RXTE data on a sample of 13 low-mass X-ray binaries with known neutron star spin that are not persistent pulsars. We carefully measure the correlations between the centroid frequencies of the quasi-periodic oscillations (QPOs). We compare these correlations to the prediction of the relativistic precession model that, due to frame dragging, a QPO will occur at the Lense-Thirring precession frequency νLT of a test-particle orbit whose orbital frequency is the upper kHz QPO frequency νu. Contrary to the most prominent previous studies, we find two different oscillations in the range predicted for νLT that are simultaneously present over a wide range of νu. Additionally, one of the low-frequency noise components evolves into a (third) QPO in the νLT range when νu exceeds 600 Hz. The frequencies of these QPOs all correlate to νu following power laws with indices between 0.4 and 3.3, significantly exceeding the predicted value of 2.0 in 80 per cent of the cases (at 3 to >20σ). Also, there is no evidence that the neutron star spin frequency affects any of these three QPO frequencies, as would be expected for frame dragging. Finally, the observed QPO frequencies tend to be higher than the νLT predicted for reasonable neutron star specific moment of inertia. In the light of recent successes of precession models in black holes, we briefly discuss ways in which such precession can occur in neutron stars at frequencies different from test-particle values and consistent with those observed. A precessing torus geometry and other torques than frame dragging may allow precession to produce the observed frequency correlations, but can only explain one of the three QPOs in the νLT range.

  9. Robust synchronization of coupled circadian and cell cycle oscillators in single mammalian cells.

    PubMed

    Bieler, Jonathan; Cannavo, Rosamaria; Gustafson, Kyle; Gobet, Cedric; Gatfield, David; Naef, Felix

    2014-07-15

    Circadian cycles and cell cycles are two fundamental periodic processes with a period in the range of 1 day. Consequently, coupling between such cycles can lead to synchronization. Here, we estimated the mutual interactions between the two oscillators by time-lapse imaging of single mammalian NIH3T3 fibroblasts during several days. The analysis of thousands of circadian cycles in dividing cells clearly indicated that both oscillators tick in a 1:1 mode-locked state, with cell divisions occurring tightly 5 h before the peak in circadian Rev-Erbα-YFP reporter expression. In principle, such synchrony may be caused by either unidirectional or bidirectional coupling. While gating of cell division by the circadian cycle has been most studied, our data combined with stochastic modeling unambiguously show that the reverse coupling is predominant in NIH3T3 cells. Moreover, temperature, genetic, and pharmacological perturbations showed that the two interacting cellular oscillators adopt a synchronized state that is highly robust over a wide range of parameters. These findings have implications for circadian function in proliferative tissues, including epidermis, immune cells, and cancer.

  10. Robust synchronization of coupled circadian and cell cycle oscillators in single mammalian cells

    PubMed Central

    Bieler, Jonathan; Cannavo, Rosamaria; Gustafson, Kyle; Gobet, Cedric; Gatfield, David; Naef, Felix

    2014-01-01

    Circadian cycles and cell cycles are two fundamental periodic processes with a period in the range of 1 day. Consequently, coupling between such cycles can lead to synchronization. Here, we estimated the mutual interactions between the two oscillators by time-lapse imaging of single mammalian NIH3T3 fibroblasts during several days. The analysis of thousands of circadian cycles in dividing cells clearly indicated that both oscillators tick in a 1:1 mode-locked state, with cell divisions occurring tightly 5 h before the peak in circadian Rev-Erbα-YFP reporter expression. In principle, such synchrony may be caused by either unidirectional or bidirectional coupling. While gating of cell division by the circadian cycle has been most studied, our data combined with stochastic modeling unambiguously show that the reverse coupling is predominant in NIH3T3 cells. Moreover, temperature, genetic, and pharmacological perturbations showed that the two interacting cellular oscillators adopt a synchronized state that is highly robust over a wide range of parameters. These findings have implications for circadian function in proliferative tissues, including epidermis, immune cells, and cancer. PMID:25028488

  11. Human PLCζ exhibits superior fertilization potency over mouse PLCζ in triggering the Ca2+ oscillations required for mammalian oocyte activation

    PubMed Central

    Nomikos, Michail; Theodoridou, Maria; Elgmati, Khalil; Parthimos, Dimitris; Calver, Brian L.; Buntwal, Luke; Nounesis, George; Swann, Karl; Lai, F. Anthony

    2014-01-01

    A sperm-specific phospholipase C-zeta (PLCζ) is believed to play an essential role in oocyte activation during mammalian fertilization. Sperm PLCζ has been shown to trigger a prolonged series of repetitive Ca2+ transients or oscillations in oocytes that precede activation. This remarkable intracellular Ca2+ signalling phenomenon is a distinctive characteristic observed during in vitro fertilization by sperm. Previous studies have notably observed an apparent differential ability of PLCζ from disparate mammalian species to trigger Ca2+ oscillations in mouse oocytes. However, the molecular basis and confirmation of the apparent PLCζ species difference in activity remains to be provided. In the present study, we provide direct evidence for the superior effectiveness of human PLCζ relative to mouse PLCζ in generating Ca2+ oscillations in mouse oocytes. In addition, we have designed and constructed a series of human/mouse PLCζ chimeras to enable study of the potential role of discrete PLCζ domains in conferring the enhanced Ca2+ signalling potency of human PLCζ. Functional analysis of these human/mouse PLCζ domain chimeras suggests a novel role of the EF-hand domain in the species-specific differences in PLCζ activity. Our empirical observations are compatible with a basic mathematical model for the Ca2+ dependence of generating cytoplasmic Ca2+ oscillations in mammalian oocytes by sperm PLCζ. PMID:24478462

  12. Whole blood of mammalian species in the oscillating shear field: influence of erythrocyte aggregation

    NASA Astrophysics Data System (ADS)

    Windberger, U.; Pöschl, Ch; Peters, S.; Huber, J.; van den Hoven, R.

    2017-02-01

    This is the rheologicalanalysis of mammalian blood of species with a high (horse), medium (man), and low (sheep) erythrocyte (RBC) aggregability by small amplitude oscillation technique. Amplitude and frequency sweep tests in linear mode were performed with blood from healthy adult volunteers, horses, and sheep in CSS-mode. Blood samples were hematocrit (HCT) adjusted (40%, 50%, 60%) and tested at 7°C, 22°C, and 37°C. Storage modulus (G‧) increased with HCT and decreased with temperature in each species, but the gradient of this increase was species-specific. The lower dependency of G‧ on the equine HCT value could be a benefit during physical performance when high numbers of RBCs are released from the spleen in the horse. In sheep, a HCT-threshold had to be overcome before elasticity of the blood sample could be measured, suggesting that the cohesive forces between RBCs, and between RBCs and plasma molecules must be very low. The frequencies for tests under quasi-staticcondition were in a narrow range around the physiologic heart rate of the species. In horse, time-dependent influences concurred at frequencies lower than 3 rad.s-1 probably due to sedimentation of RBC aggregates. In conclusion, elasticity of blood depends not only on the amount of blood cells, but also on their mechanical and functional properties.

  13. Oscillating Evolution of a Mammalian Locus with Overlapping Reading Frames: An XLαs/ALEX Relay

    PubMed Central

    Nekrutenko, Anton; Wadhawan, Samir; Goetting-Minesky, Paula; Makova, Kateryna D

    2005-01-01

    XLαs and ALEX are structurally unrelated mammalian proteins translated from alternative overlapping reading frames of a single transcript. Not only are they encoded by the same locus, but a specific XLαs/ALEX interaction is essential for G-protein signaling in neuroendocrine cells. A disruption of this interaction leads to abnormal human phenotypes, including mental retardation and growth deficiency. The region of overlap between the two reading frames evolves at a remarkable speed: the divergence between human and mouse ALEX polypeptides makes them virtually unalignable. To trace the evolution of this puzzling locus, we sequenced it in apes, Old World monkeys, and a New World monkey. We show that the overlap between the two reading frames and the physical interaction between the two proteins force the locus to evolve in an unprecedented way. Namely, to maintain two overlapping protein-coding regions the locus is forced to have high GC content, which significantly elevates its intrinsic evolutionary rate. However, the two encoded proteins cannot afford to change too quickly relative to each other as this may impair their interaction and lead to severe physiological consequences. As a result XLαs and ALEX evolve in an oscillating fashion constantly balancing the rates of amino acid replacements. This is the first example of a rapidly evolving locus encoding interacting proteins via overlapping reading frames, with a possible link to the origin of species-specific neurological differences. PMID:16110341

  14. The Low Frequency Space Array

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

  15. Low-frequency electrical properties.

    USGS Publications Warehouse

    Olhoeft, G.R.

    1985-01-01

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

  16. Low Frequency Sonar Signal Simulation

    DTIC Science & Technology

    2010-04-14

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

  17. Low Frequency Geoacoustic Inversion Method

    DTIC Science & Technology

    2011-09-01

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

  18. Low Frequency Geoacoustic Inversion Method

    DTIC Science & Technology

    2012-09-30

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

  19. LOFAR, the low frequency array

    NASA Astrophysics Data System (ADS)

    Vermeulen, R. C.

    2012-09-01

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

  20. Digital Signal Processing Reveals Circadian Baseline Oscillation in Majority of Mammalian Genes

    PubMed Central

    Ptitsyn, Andrey A; Zvonic, Sanjin; Gimble, Jeffrey M

    2007-01-01

    In mammals, circadian periodicity has been described for gene expression in the hypothalamus and multiple peripheral tissues. It is accepted that 10%–15% of all genes oscillate in a daily rhythm, regulated by an intrinsic molecular clock. Statistical analyses of periodicity are limited by the small size of datasets and high levels of stochastic noise. Here, we propose a new approach applying digital signal processing algorithms separately to each group of genes oscillating in the same phase. Combined with the statistical tests for periodicity, this method identifies circadian baseline oscillation in almost 100% of all expressed genes. Consequently, circadian oscillation in gene expression should be evaluated in any study related to biological pathways. Changes in gene expression caused by mutations or regulation of environmental factors (such as photic stimuli or feeding) should be considered in the context of changes in the amplitude and phase of genetic oscillations. PMID:17571920

  1. PERIOD1-associated proteins modulate the negative limb of the mammalian circadian oscillator.

    PubMed

    Brown, Steven A; Ripperger, Juergen; Kadener, Sebastian; Fleury-Olela, Fabienne; Vilbois, Francis; Rosbash, Michael; Schibler, Ueli

    2005-04-29

    The clock proteins PERIOD1 (PER1) and PERIOD2 (PER2) play essential roles in a negative transcriptional feedback loop that generates circadian rhythms in mammalian cells. We identified two PER1-associated factors, NONO and WDR5, that modulate PER activity. The reduction of NONO expression by RNA interference (RNAi) attenuated circadian rhythms in mammalian cells, and fruit flies carrying a hypomorphic allele were nearly arrhythmic. WDR5, a subunit of histone methyltransferase complexes, augmented PER-mediated transcriptional repression, and its reduction by RNAi diminished circadian histone methylations at the promoter of a clock gene.

  2. Low frequency ac waveform generator

    DOEpatents

    Bilharz, O.W.

    1983-11-22

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

  3. Low frequency AC waveform generator

    DOEpatents

    Bilharz, Oscar W.

    1986-01-01

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

  4. Low Frequency Radio Experiment (LORE)

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  5. Low-frequency sonophoresis: a review.

    PubMed

    Mitragotri, Samir; Kost, Joseph

    2004-03-27

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

  6. Low Frequency Radio Experiment (LORE)

    NASA Astrophysics Data System (ADS)

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

    High temporal and frequency resolution observations of solar generated disturbances below 15 MHz in the near-Sun region and at Sun-Earth distances in conjunction with optical and high energy observations of Sun are essential to understand the structure and evolution of eruptions, such as, flares, coronal mass ejections (CMEs), and their associated solar wind disturbances at heights above the photosphere and their consequences in the interplanetary medium. This talk presents a case study of Low Frequency Radio Experiment (LORE) payload to probe the corona and the solar disturbances at solar offsets greater than 2 solar radii below 30 MHz. The LORE, although not part of Aditya-L1 mission, can be complimentary to planned Aditya-L1 coronagraph and its other on-board payloads as well as synergistic to ground based observations, which are routinely carried out by Ooty Radio Telescope. We discuss the baseline design and technical details of the proposed LORE and it is particularly suitable for providing data on the detailed time and frequency structure of fast drifting Type-III and slow drifting Type-II radio bursts with unprecedented time and frequency resolution as well as goniopolarimetry, made possible with better designed antennas and state-of-art electronics, employing FPGAs and an intelligent data management system. This would enable wide ranging studies such as studies of nonlinear plasma processes, CME in-situ radio emission, CME driven phenomena, interplanetary CME driven shocks, ICMEs driven by decelerating IP shocks and space weather effects of Solar Wind interaction regions. The talk will highlight the science objectives as well as the proposed technical design features.

  7. Ionospheric very low frequency transmitter

    SciTech Connect

    Kuo, Spencer P.

    2015-02-15

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

  8. Low frequency gravitational wave astrophysics

    NASA Astrophysics Data System (ADS)

    Larson, Shane

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

  9. Simulated body temperature rhythms reveal the phase-shifting behavior and plasticity of mammalian circadian oscillators

    PubMed Central

    Saini, Camille; Morf, Jörg; Stratmann, Markus; Gos, Pascal; Schibler, Ueli

    2012-01-01

    The circadian pacemaker in the suprachiasmatic nuclei (SCN) of the hypothalamus maintains phase coherence in peripheral cells through metabolic, neuronal, and humoral signaling pathways. Here, we investigated the role of daily body temperature fluctuations as possible systemic cues in the resetting of peripheral oscillators. Using precise temperature devices in conjunction with real-time monitoring of the bioluminescence produced by circadian luciferase reporter genes, we showed that simulated body temperature cycles of mice and even humans, with daily temperature differences of only 3°C and 1°C, respectively, could gradually synchronize circadian gene expression in cultured fibroblasts. The time required for establishing the new steady-state phase depended on the reporter gene, but after a few days, the expression of each gene oscillated with a precise phase relative to that of the temperature cycles. Smooth temperature oscillations with a very small amplitude could synchronize fibroblast clocks over a wide temperature range, and such temperature rhythms were also capable of entraining gene expression cycles to periods significantly longer or shorter than 24 h. As revealed by genetic loss-of-function experiments, heat-shock factor 1 (HSF1), but not HSF2, was required for the efficient synchronization of fibroblast oscillators to simulated body temperature cycles. PMID:22379191

  10. Simulated body temperature rhythms reveal the phase-shifting behavior and plasticity of mammalian circadian oscillators.

    PubMed

    Saini, Camille; Morf, Jörg; Stratmann, Markus; Gos, Pascal; Schibler, Ueli

    2012-03-15

    The circadian pacemaker in the suprachiasmatic nuclei (SCN) of the hypothalamus maintains phase coherence in peripheral cells through metabolic, neuronal, and humoral signaling pathways. Here, we investigated the role of daily body temperature fluctuations as possible systemic cues in the resetting of peripheral oscillators. Using precise temperature devices in conjunction with real-time monitoring of the bioluminescence produced by circadian luciferase reporter genes, we showed that simulated body temperature cycles of mice and even humans, with daily temperature differences of only 3°C and 1°C, respectively, could gradually synchronize circadian gene expression in cultured fibroblasts. The time required for establishing the new steady-state phase depended on the reporter gene, but after a few days, the expression of each gene oscillated with a precise phase relative to that of the temperature cycles. Smooth temperature oscillations with a very small amplitude could synchronize fibroblast clocks over a wide temperature range, and such temperature rhythms were also capable of entraining gene expression cycles to periods significantly longer or shorter than 24 h. As revealed by genetic loss-of-function experiments, heat-shock factor 1 (HSF1), but not HSF2, was required for the efficient synchronization of fibroblast oscillators to simulated body temperature cycles.

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

    SciTech Connect

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

    1995-12-31

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

  12. Low-frequency electromagnetic field in a Wigner crystal

    SciTech Connect

    Stupka, Anton

    2013-03-15

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

  13. Study of low frequency hydromagnetic waves using ATS-1 data

    NASA Technical Reports Server (NTRS)

    Cummings, W. D.; Mason, F.; Coleman, P. J., Jr.

    1976-01-01

    Low frequency oscillations of the magnetic field at ATS-1 were analyzed for the 25 month data interval, Dec., 1966 through 1968. Irregular oscillations and those associated with magnetic storms were excluded from the analysis. Of the 222 events identified, 170 were found to be oscillating predominantly transverse to the background magnetic field. The oscillations were observed to occur most frequently in the early afternoon hours. They also seemed to occur more frequently during Dec., Jan., and Feb. than at any other time of the year. During a given event, the frequency was fairly constant. The event duration varied between a minimum of 10 min. and a maximum of 14 hrs and 26 min. During a given event the amplitude varied.

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

    NASA Astrophysics Data System (ADS)

    Dubinin, E.; Fraenz, M.

    2016-02-01

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

  15. Robust network oscillations during mammalian respiratory rhythm generation driven by synaptic dynamics.

    PubMed

    Guerrier, Claire; Hayes, John A; Fortin, Gilles; Holcman, David

    2015-08-04

    How might synaptic dynamics generate synchronous oscillations in neuronal networks? We address this question in the preBötzinger complex (preBötC), a brainstem neural network that paces robust, yet labile, inspiration in mammals. The preBötC is composed of a few hundred neurons that alternate bursting activity with silent periods, but the mechanism underlying this vital rhythm remains elusive. Using a computational approach to model a randomly connected neuronal network that relies on short-term synaptic facilitation (SF) and depression (SD), we show that synaptic fluctuations can initiate population activities through recurrent excitation. We also show that a two-step SD process allows activity in the network to synchronize (bursts) and generate a population refractory period (silence). The model was validated against an array of experimental conditions, which recapitulate several processes the preBötC may experience. Consistent with the modeling assumptions, we reveal, by electrophysiological recordings, that SF/SD can occur at preBötC synapses on timescales that influence rhythmic population activity. We conclude that nondeterministic neuronal spiking and dynamic synaptic strengths in a randomly connected network are sufficient to give rise to regular respiratory-like rhythmic network activity and lability, which may play an important role in generating the rhythm for breathing and other coordinated motor activities in mammals.

  16. Characterization of Low-Frequency Combustion Stability of the Fastrac Engine

    NASA Technical Reports Server (NTRS)

    Rocker, Marvin; Jones, Preston (Technical Monitor)

    2002-01-01

    A series of tests were conducted to measure the combustion performance of the Fastrac engine thrust chamber. During mainstage, the thrust chamber exhibited no large-amplitude chamber pressure oscillations that could be identified as low-frequency combustion instability or 'chug'. However, during start-up and shutdown, the thrust chamber very briefly exhibited large-amplitude chamber pressure oscillations that were identified as chug. These instabilities during start-up and shutdown were regarded as benign due to their brevity. Linear models of the thrust chamber and the propellant feed systems were formulated for both the thrust chamber component tests and the flight engine tests. These linear models determined the frequency and decay rate of chamber pressure oscillations given the design and operating conditions of the thrust chamber and feed system. The frequency of chamber pressure oscillations determined from the model closely matched the frequency of low-amplitude, low-frequency chamber pressure oscillations exhibited in some of the later thrust chamber mainstage tests. The decay rate of the chamber pressure oscillations determined from the models indicated that these low-frequency oscillations were stable. Likewise, the decay rate, determined from the model of the flight engine tests indicated that the low-frequency chamber pressure oscillations would be stable.

  17. Measurement of whole blood of different mammalian species in the oscillating shear field: influence of erythrocyte aggregation

    NASA Astrophysics Data System (ADS)

    Windberger, U.; Pöschl, Ch; Peters, S.; Huber, J.; van den Hoven, R.

    2017-01-01

    This is the first systematic analysis of mammalian blood of species with a high (horse), medium (man), and low (sheep) erythrocyte (RBC) aggregability by small amplitude oscillation technique. Amplitude and frequency sweep tests (linear viscoelastic mode) were performed with blood from healthy adult volunteers, horses, and sheep in CSS-mode. Blood samples were hematocrit (HCT) adjusted (40%, 50%, 60%) and tested at 7°C, 22°C, and 37°C. Generally, storage modulus (G´) increased with HCT and decreased with temperature in each species, but the gradient of this increase was species-specific. The lower dependency of G´ on the equine HCT value could be a benefit during physical performance when high numbers of RBCs are released from the spleen. In sheep, an HCT-threshold had to be overcome before the desired quasi-static condition of the blood sample could be achieved, suggesting that the contact between RBCs, and between RBCs and plasma molecules must be very low. The frequencies for tests under linear viscoelastic condition were in a narrow range around the physiologic heart rate of the species. In horse, time-dependent influences concurred at frequencies lower than 3 rad.s-1probably due to sedimentation of RBC aggregates. In conclusion, blood is a fragile suspension that shows its best stability around the resting heart rate of the species.

  18. Online detection of low-frequency functional connectivity

    NASA Astrophysics Data System (ADS)

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

    2004-04-01

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

  19. CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: A new mammalian circadian oscillator model including the cAMP module

    NASA Astrophysics Data System (ADS)

    Wang, Jun-Wei; Zhou, Tian-Shou

    2009-12-01

    In this paper, we develop a new mathematical model for the mammalian circadian clock, which incorporates both transcriptional/translational feedback loops (TTFLs) and a cAMP-mediated feedback loop. The model shows that TTFLs and cAMP signalling cooperatively drive the circadian rhythms. It reproduces typical experimental observations with qualitative similarities, e.g. circadian oscillations in constant darkness and entrainment to light-dark cycles. In addition, it can explain the phenotypes of cAMP-mutant and Rev-erbα-/--mutant mice, and help us make an experimentally-testable prediction: oscillations may be rescued when arrhythmic mice with constitutively low concentrations of cAMP are crossed with Rev-erbα-/- mutant mice. The model enhances our understanding of the mammalian circadian clockwork from the viewpoint of the entire cell.

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

    NASA Astrophysics Data System (ADS)

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

    2012-11-01

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

  1. Low frequency electromagnetic fields and the Belousov-Zhabotinsky reaction.

    PubMed

    Sontag, W

    2006-05-01

    Low frequency magnetic fields can influence biochemical reactions and consequently physiological rhythms and oscillations. To test this for a model reaction we used the chemical Belousov-Zhabotinsky (BZ) reaction, which is one of the simplest chemical oscillators. The oscillation frequency of the reaction was tracked optically by the absorption of blue light. Field treatment was carried out at room temperature in the middle of two Helmholtz coils. After starting the reaction, for 5 min the oscillations were monitored as control measurement, then during the next 10 min monitoring was with a magnetic field switched on, followed by a period of 5 min with the field switched off. A variety of exposure conditions have been tested: the frequency was varied between 5 and 1000 Hz, the field strength was varied up to 2.7 mT, different pulse shapes were used, the influence of the exposure temperature was tested, and the influence of the optimum exposure conditions (static magnetic field and the frequency of the dynamic field) as predicted by the ion parametric resonance (IPR) model has been measured. In conclusion, in no case any statistical significant influence of the magnetic treatment on the oscillation frequency of the BZ reaction could be detected (P > .05, t-test).

  2. The LWA1 Low Frequency Sky Survey

    NASA Astrophysics Data System (ADS)

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

    2017-08-01

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

  3. Low frequency acoustic and electromagnetic scattering

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  4. Low frequency acoustic and electromagnetic scattering

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

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

  5. Low frequency Raman study of the nucleosides

    NASA Astrophysics Data System (ADS)

    Koontz, Craig; Lee, Scott

    2011-03-01

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

  6. Low frequency Raman study of the nucleosides

    NASA Astrophysics Data System (ADS)

    Koontz, Craig; Lee, Scott

    2010-10-01

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

  7. Low frequency Raman study of the nucleosides

    NASA Astrophysics Data System (ADS)

    Koontz, Craig; Lee, Scott

    2011-04-01

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

  8. Hearing Foreign Languages through Low Frequencies.

    ERIC Educational Resources Information Center

    Roberge, Claude

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

  9. Low Frequency Rada Sounding Through Martian Ionosphere

    NASA Technical Reports Server (NTRS)

    Safaeinili, A.; Jordan, R.

    2000-01-01

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

  10. Is low frequency ocean sound increasing globally?

    PubMed

    Miksis-Olds, Jennifer L; Nichols, Stephen M

    2016-01-01

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

  11. Low frequency dielectric relaxation in boracites

    NASA Technical Reports Server (NTRS)

    Kim, Q.; Somoano, R.

    1983-01-01

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

  12. Extreme Low Frequency Acoustic Measurement System

    NASA Technical Reports Server (NTRS)

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

    2017-01-01

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

  13. Extreme low frequency acoustic measurement system

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

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

  14. Analysis of Jovian low frequency radio emissions

    NASA Technical Reports Server (NTRS)

    Gurnett, D. A.

    1985-01-01

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

  15. Seabed Scattering from Low Frequency Reverberation Measurements

    DTIC Science & Technology

    2015-09-30

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

  16. An Overview of Low Frequency Communications

    DTIC Science & Technology

    1992-06-01

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

  17. Low frequency sound propagation in activated carbon.

    PubMed

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

    2012-07-01

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

  18. LOFAR: The LOw-Frequency ARray

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

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

  19. A variable passive low-frequency absorber

    NASA Astrophysics Data System (ADS)

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

    2005-04-01

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

  20. Complex Systems Theory to understand extremely low frequency magnetic fields interaction with immune cells

    NASA Astrophysics Data System (ADS)

    Vázquez-Coutiño, G. A.; Serrano-Luna, G.; Cañedo-Dorantes, L.; Godina-Nava, J. J.; Rodríguez-Segura, M. A.

    2003-09-01

    Well-documented studies about the interaction of extremely low frequency electromagnetic fields (ELF) with lymphocytes provide elements for the development of non-linear theoretical models. The Eichwald-Kaiser model of calcium oscillations was tested with a rectified cosine function at a frequency of 120 Hz. A change in dynamical behavior of calcium oscillations, from periodic in the normal case (without perturbation, what corresponds to a limit cycle) to the existence of very small micro-oscillations and a strange attractor in the perturbed case was found. It is concluded that the ELF configuration used in this model, alters the dynamical behavior of calcium oscillations in lymphocytes.

  1. Transient Modeling of Hybrid Rocket Low Frequency Instabilities

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

  3. Low Frequency Plasma Turbulence as a Source of Clutter in Surveillance and Communication

    DTIC Science & Technology

    2012-09-01

    shear, whereas interchange or flute type oscillations in magnetized plasma are associated with Rayleigh-Taylor type instability. These types of density...density irregularities are excited by plasma flows with velocity shear, whereas interchange or flute type oscillations in magnetized plasma are...equations will be used to describe low-frequency interchange modes ( ,i   where  is the frequency of the flute mode and 0zi i ZeB m c  is the

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

    NASA Astrophysics Data System (ADS)

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

    2017-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  6. Low frequency electric and magnetic fields

    NASA Technical Reports Server (NTRS)

    Spaniol, Craig

    1989-01-01

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

  7. Low-frequency vibrational modes of glutamine

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  8. Low frequency ionic conduction across liquid interfaces

    NASA Astrophysics Data System (ADS)

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

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

  9. Minimization of nanosatellite low frequency magnetic fields.

    PubMed

    Belyayev, S M; Dudkin, F L

    2016-03-01

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

  10. Minimization of nanosatellite low frequency magnetic fields

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  11. Minimization of nanosatellite low frequency magnetic fields

    SciTech Connect

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

    2016-03-15

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

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

    SciTech Connect

    Niklas Schneider

    2009-06-17

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

  13. Low Frequency Variability and the Eastern Mediterranean Teleconnection Pattern

    NASA Astrophysics Data System (ADS)

    Hatzaki, M.; Flocas, H. A.

    2007-12-01

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

  14. Simple Low-Frequency Beam Pickup

    SciTech Connect

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

    2011-10-12

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

  15. Low frequency variability of Southern Ocean jets

    NASA Astrophysics Data System (ADS)

    Thompson, Andrew F.; Richards, Kelvin J.

    2011-09-01

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

  16. Low frequency variability of Southern Ocean jets

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  17. Low-Frequency Waves in Space Plasmas

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  18. Low Frequency Observations of Galactic Supernova Remnants

    NASA Astrophysics Data System (ADS)

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

    2001-12-01

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

  19. Low Frequency Interstellar Scattering and Pulsar Observations

    NASA Technical Reports Server (NTRS)

    Cordes, James M.

    1992-01-01

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

  20. LOFAR: A LOw Frequency radio ARray

    NASA Astrophysics Data System (ADS)

    Hewitt, Jacqueline

    2001-04-01

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

  1. A low frequency RFI monitoring system

    NASA Astrophysics Data System (ADS)

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

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

  2. Low frequency acoustic resonances in urban courtyards.

    PubMed

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

    2014-01-01

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

  3. Low-frequency radio navigation system

    NASA Technical Reports Server (NTRS)

    Wallis, D. E. (Inventor)

    1983-01-01

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

  4. Sporadically Emitting Pulsars at Low Frequencies

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  5. Time evolution of low frequency plasma modes

    NASA Astrophysics Data System (ADS)

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

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

  6. Extremely Low Frequency Electromagnetic Investigation on Mars

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

  7. Low Frequency Electromagnetic Pulse and Explosions

    SciTech Connect

    Sweeney, J J

    2011-02-01

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

  8. Chimeras of sperm PLCζ reveal disparate protein domain functions in the generation of intracellular Ca2+ oscillations in mammalian eggs at fertilization

    PubMed Central

    Theodoridou, Maria; Nomikos, Michail; Parthimos, Dimitris; Gonzalez-Garcia, J. Raul; Elgmati, Khalil; Calver, Brian L.; Sideratou, Zili; Nounesis, George; Swann, Karl; Lai, F. Anthony

    2013-01-01

    Phospholipase C-zeta (PLCζ) is a sperm-specific protein believed to cause Ca2+ oscillations and egg activation during mammalian fertilization. PLCζ is very similar to the somatic PLCδ1 isoform but is far more potent in mobilizing Ca2+ in eggs. To investigate how discrete protein domains contribute to Ca2+ release, we assessed the function of a series of PLCζ/PLCδ1 chimeras. We examined their ability to cause Ca2+ oscillations in mouse eggs, enzymatic properties using in vitro phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis and their binding to PIP2 and PI(3)P with a liposome interaction assay. Most chimeras hydrolyzed PIP2 with no major differences in Ca2+ sensitivity and enzyme kinetics. Insertion of a PH domain or replacement of the PLCζ EF hands domain had no deleterious effect on Ca2+ oscillations. In contrast, replacement of either XY-linker or C2 domain of PLCζ completely abolished Ca2+ releasing activity. Notably, chimeras containing the PLCζ XY-linker bound to PIP2-containing liposomes, while chimeras containing the PLCζ C2 domain exhibited PI(3)P binding. Our data suggest that the EF hands are not solely responsible for the nanomolar Ca2+ sensitivity of PLCζ and that membrane PIP2 binding involves the C2 domain and XY-linker of PLCζ. To investigate the relationship between PLC enzymatic properties and Ca2+ oscillations in eggs, we have developed a mathematical model that incorporates Ca2+-dependent InsP3 generation by the PLC chimeras and their levels of intracellular expression. These numerical simulations can for the first time predict the empirical variability in onset and frequency of Ca2+ oscillatory activity associated with specific PLC variants. PMID:24152875

  9. USP7 and TDP-43: Pleiotropic Regulation of Cryptochrome Protein Stability Paces the Oscillation of the Mammalian Circadian Clock.

    PubMed

    Hirano, Arisa; Nakagawa, Tomoki; Yoshitane, Hikari; Oyama, Masaaki; Kozuka-Hata, Hiroko; Lanjakornsiripan, Darin; Fukada, Yoshitaka

    2016-01-01

    Mammalian Cryptochromes, CRY1 and CRY2, function as principal regulators of a transcription-translation-based negative feedback loop underlying the mammalian circadian clockwork. An F-box protein, FBXL3, promotes ubiquitination and degradation of CRYs, while FBXL21, the closest paralog of FBXL3, ubiquitinates CRYs but leads to stabilization of CRYs. Fbxl3 knockout extremely lengthened the circadian period, and deletion of Fbxl21 gene in Fbxl3-deficient mice partially rescued the period-lengthening phenotype, suggesting a key role of CRY protein stability for maintenance of the circadian periodicity. Here, we employed a proteomics strategy to explore regulators for the protein stability of CRYs. We found that ubiquitin-specific protease 7 (USP7 also known as HAUSP) associates with CRY1 and CRY2 and stabilizes CRYs through deubiquitination. Treatment with USP7-specific inhibitor or Usp7 knockdown shortened the circadian period of the cellular rhythm. We identified another CRYs-interacting protein, TAR DNA binding protein 43 (TDP-43), an RNA-binding protein. TDP-43 stabilized CRY1 and CRY2, and its knockdown also shortened the circadian period in cultured cells. The present study identified USP7 and TDP-43 as the regulators of CRY1 and CRY2, underscoring the significance of the stability control process of CRY proteins for period determination in the mammalian circadian clockwork.

  10. USP7 and TDP-43: Pleiotropic Regulation of Cryptochrome Protein Stability Paces the Oscillation of the Mammalian Circadian Clock

    PubMed Central

    Yoshitane, Hikari; Oyama, Masaaki; Kozuka-Hata, Hiroko; Lanjakornsiripan, Darin; Fukada, Yoshitaka

    2016-01-01

    Mammalian Cryptochromes, CRY1 and CRY2, function as principal regulators of a transcription-translation-based negative feedback loop underlying the mammalian circadian clockwork. An F-box protein, FBXL3, promotes ubiquitination and degradation of CRYs, while FBXL21, the closest paralog of FBXL3, ubiquitinates CRYs but leads to stabilization of CRYs. Fbxl3 knockout extremely lengthened the circadian period, and deletion of Fbxl21 gene in Fbxl3-deficient mice partially rescued the period-lengthening phenotype, suggesting a key role of CRY protein stability for maintenance of the circadian periodicity. Here, we employed a proteomics strategy to explore regulators for the protein stability of CRYs. We found that ubiquitin-specific protease 7 (USP7 also known as HAUSP) associates with CRY1 and CRY2 and stabilizes CRYs through deubiquitination. Treatment with USP7-specific inhibitor or Usp7 knockdown shortened the circadian period of the cellular rhythm. We identified another CRYs-interacting protein, TAR DNA binding protein 43 (TDP-43), an RNA-binding protein. TDP-43 stabilized CRY1 and CRY2, and its knockdown also shortened the circadian period in cultured cells. The present study identified USP7 and TDP-43 as the regulators of CRY1 and CRY2, underscoring the significance of the stability control process of CRY proteins for period determination in the mammalian circadian clockwork. PMID:27123980

  11. Imaging Jupiter Radiation Belts At Low Frequencies

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

  12. Toward an adjustable nonlinear low frequency acoustic absorber

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

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

  13. Interim prediction method for low frequency core engine noise

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

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

  14. The LWA1 Low Frequency Sky Survey

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  16. Low frequency earthquakes below southern Vancouver Island

    NASA Astrophysics Data System (ADS)

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

    2012-11-01

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

  17. Low frequency electromagnetic radiation and hearing.

    PubMed

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

    2009-11-01

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

  18. Seismic moment tensor recovery at low frequencies

    NASA Astrophysics Data System (ADS)

    Riedesel, M. A.

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

  19. A low frequency rotational energy harvesting system

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

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

    PubMed

    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.

  1. Squeezing-enhanced fiber Mach-Zehnder interferometer for low-frequency phase measurement

    NASA Astrophysics Data System (ADS)

    Liu, Fang; Zhou, Yaoyao; Yu, Juan; Guo, Jiale; Wu, Yang; Xiao, Shixiong; Wei, Dan; Zhang, Yong; Jia, Xiaojun; Xiao, Min

    2017-01-01

    We propose and experimentally demonstrate a quantum-enhanced fiber Mach-Zehnder interferometer for low-frequency phase measurement beyond the shot-noise limit using a high-frequency squeezing technique. The local oscillator field is amplitude-modulated in the MHz range and is then demodulated to avoid the technical noise that occurs at low frequencies. After measurement of the phase noise at a frequency of tens of kHz, an improvement of ˜2 dB relative to the shot-noise level is achieved. Additionally, the amplitude modulation depth has no significant effect on the phase noise improvement of the interferometer when deployed in our experimental configuration. The current scheme introduces a quantum technique into the fiber-based measurements, particularly for the low frequency range, and this scheme has potential applications in the high-precision fiber sensing of temperature, strain, and various other parameters.

  2. Effect of positive feedback loops on the robustness of oscillations in the network of cyclin-dependent kinases driving the mammalian cell cycle.

    PubMed

    Gérard, Claude; Gonze, Didier; Goldbeter, Albert

    2012-09-01

    The transitions between the G(1), S, G(2) and M phases of the mammalian cell cycle are driven by a network of cyclin-dependent kinases (Cdks), whose sequential activation is regulated by intertwined negative and positive feedback loops. We previously proposed a detailed computational model for the Cdk network, and showed that this network is capable of temporal self-organization in the form of sustained oscillations, which govern ordered progression through the successive phases of the cell cycle [Gérard and Goldbeter (2009) Proc Natl Acad Sci USA 106, 21643-21648]. We subsequently proposed a skeleton model for the cell cycle that retains the core regulatory mechanisms of the detailed model [Gérard and Goldbeter (2011) Interface Focus 1, 24-35]. Here we extend this skeleton model by incorporating Cdk regulation through phosphorylation/dephosphorylation and by including the positive feedback loops that underlie the dynamics of the G(1)/S and G(2)/M transitions via phosphatase Cdc25 and via phosphatase Cdc25 and kinase Wee1, respectively. We determine the effects of these positive feedback loops and ultrasensitivity in phosphorylation/dephosphorylation on the dynamics of the Cdk network. The multiplicity of positive feedback loops as well as the existence of ultrasensitivity promote the occurrence of bistability and increase the amplitude of the oscillations in the various cyclin/Cdk complexes. By resorting to stochastic simulations, we further show that the presence of multiple, redundant positive feedback loops in the G(2)/M transition of the cell cycle markedly enhances the robustness of the Cdk oscillations with respect to molecular noise. © 2012 The Authors Journal compilation © 2012 FEBS.

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

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

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

  4. Transformed Eddy-PV Flux and Positive Synoptic Eddy Feedback onto Low-Frequency Flow

    NASA Astrophysics Data System (ADS)

    Ren, H.; Jin, F.; Kug, J.; Gao, L.

    2010-12-01

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

  5. Electrophysiological low-frequency coherence and cross-frequency coupling contribute to BOLD connectivity.

    PubMed

    Wang, Liang; Saalmann, Yuri B; Pinsk, Mark A; Arcaro, Michael J; Kastner, Sabine

    2012-12-06

    Brain networks are commonly defined using correlations between blood oxygen level-dependent (BOLD) signals in different brain areas. Although evidence suggests that gamma-band (30-100 Hz) neural activity contributes to local BOLD signals, the neural basis of interareal BOLD correlations is unclear. We first defined a visual network in monkeys based on converging evidence from interareal BOLD correlations during a fixation task, task-free state, and anesthesia, and then simultaneously recorded local field potentials (LFPs) from the same four network areas in the task-free state. Low-frequency oscillations (<20 Hz), and not gamma activity, predominantly contributed to interareal BOLD correlations. The low-frequency oscillations also influenced local processing by modulating gamma activity within individual areas. We suggest that such cross-frequency coupling links local BOLD signals to BOLD correlations across distributed networks.

  6. Electrophysiological low-frequency coherence and cross-frequency coupling contributes to BOLD connectivity

    PubMed Central

    Wang, Liang; Saalmann, Yuri B.; Pinsk, Mark A.; Arcaro, Michael J.; Kastner, Sabine

    2012-01-01

    SUMMARY Brain networks are commonly defined using correlations between blood oxygen level-dependent (BOLD) signals in different brain areas. Although evidence suggests that gamma band (30–100 Hz) neural activity contributes to local BOLD signals, the neural basis of inter-areal BOLD correlations is unclear. We first defined a visual network in monkeys based on converging evidence from inter-areal BOLD correlations during a fixation task, task-free state and anesthesia, and then simultaneously recorded local field potentials (LFPs) from the same four network areas in the task-free state. Low frequency oscillations (< 20 Hz), and not gamma activity, predominantly contributed to inter-areal BOLD correlations. The low frequency oscillations also influenced local processing by modulating gamma activity within individual areas. We suggest that such cross-frequency coupling links local BOLD signals to BOLD correlations across distributed networks. PMID:23217748

  7. Investigating Low-Frequency Earthquake Properties

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    SciTech Connect

    Krainov, V. P.

    2010-08-15

    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.

  9. Extremely Low Frequency Signal Acquisition, Recording and Analysis

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  10. Unusual ultra-low frequency fluctuations in freestanding graphene

    NASA Astrophysics Data System (ADS)

    Barber, Steven; Xu, Peng; Neek-Amal, Mehdi; Ackerman, Matthew; Schoelz, James; Thibado, Paul; Sadeghi, Ali; Peeters, Francois

    2014-03-01

    Intrinsic ripples in freestanding graphene have been difficult to study with common experimental methods. In notable breakthroughs, ripple geometry was recently imaged using scanning electron microscopy as well as scanning tunneling microscopy (STM), but these measurements are thus far limited to static configurations. Thermally-activated flexural phonon modes could generate dynamic changes in curvature which would be of great interest to observe. Here, we present how to track the vertical movement of a one-square-angstrom region of suspended graphene using STM. This allows a direct measurement of the out-of-plane trajectory at one point in space over long periods of time. Based on these data, we present a model from elasticity theory to explain the very-low frequency oscillations that are observed. Unexpectedly, we sometimes detect a sudden colossal jump, which we interpret as due to mirror buckling. This innovative technique provides a much needed atomic-scale probe for the time-dependent behaviors of intrinsic ripples in freestanding graphene, and it represents a fundamental advance in the use of STM. Financial support was provided by the Office of Naval Research, the National Science Foundation, the EU-Marie Curie IIF Postdoc Fellowship, the ESF-EuroGRAPHENE project CONGRAN, the Flemish Science Foundation, and the Methusalem Foundation.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

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

    NASA Astrophysics Data System (ADS)

    Nakamura, Mamoru

    2017-04-01

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

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

    PubMed

    Ogura, Makoto; Paliwal, Sumit; Mitragotri, Samir

    2008-06-30

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

  14. Electroporation of mammalian cells by nanosecond electric field oscillations and its inhibition by the electric field reversal

    PubMed Central

    Gianulis, Elena C.; Lee, Jimo; Jiang, Chunqi; Xiao, Shu; Ibey, Bennet L.; Pakhomov, Andrei G.

    2015-01-01

    The present study compared electroporation efficiency of bipolar and unipolar nanosecond electric field oscillations (NEFO). Bipolar NEFO was a damped sine wave with 140 ns first phase duration at 50% height; the peak amplitude of phases 2–4 decreased to 35%, 12%, and 7% of the first phase. This waveform was rectified to produce unipolar NEFO by cutting off phases 2 and 4. Membrane permeabilization was quantified in CHO and GH3 cells by uptake of a membrane integrity marker dye YO-PRO-1 (YP) and by the membrane conductance increase measured by patch clamp. For treatments with 1–20 unipolar NEFO, at 9.6–24 kV/cm, 10 Hz, the rate and amount of YP uptake were consistently 2-3-fold higher than after bipolar NEFO treatments, despite delivering less energy. However, the threshold amplitude was about 7 kV/cm for both NEFO waveforms. A single 14.4 kV/cm unipolar NEFO caused a 1.5–2 times greater increase in membrane conductance (p < 0.05) than bipolar NEFO, along with a longer and less frequent recovery. The lower efficiency of bipolar NEFO was preserved in Ca2+-free conditions and thus cannot be explained by the reversal of electrophoretic flows of Ca2+. Instead, the data indicate that the electric field polarity reversals reduced the pore yield. PMID:26348662

  15. Electroporation of mammalian cells by nanosecond electric field oscillations and its inhibition by the electric field reversal.

    PubMed

    Gianulis, Elena C; Lee, Jimo; Jiang, Chunqi; Xiao, Shu; Ibey, Bennet L; Pakhomov, Andrei G

    2015-09-08

    The present study compared electroporation efficiency of bipolar and unipolar nanosecond electric field oscillations (NEFO). Bipolar NEFO was a damped sine wave with 140 ns first phase duration at 50% height; the peak amplitude of phases 2-4 decreased to 35%, 12%, and 7% of the first phase. This waveform was rectified to produce unipolar NEFO by cutting off phases 2 and 4. Membrane permeabilization was quantified in CHO and GH3 cells by uptake of a membrane integrity marker dye YO-PRO-1 (YP) and by the membrane conductance increase measured by patch clamp. For treatments with 1-20 unipolar NEFO, at 9.6-24 kV/cm, 10 Hz, the rate and amount of YP uptake were consistently 2-3-fold higher than after bipolar NEFO treatments, despite delivering less energy. However, the threshold amplitude was about 7 kV/cm for both NEFO waveforms. A single 14.4 kV/cm unipolar NEFO caused a 1.5-2 times greater increase in membrane conductance (p<0.05) than bipolar NEFO, along with a longer and less frequent recovery. The lower efficiency of bipolar NEFO was preserved in Ca2+-free conditions and thus cannot be explained by the reversal of electrophoretic flows of Ca2+. Instead, the data indicate that the electric field polarity reversals reduced the pore yield.

  16. Sources and effects of low-frequency noise.

    PubMed

    Berglund, B; Hassmén, P; Job, R F

    1996-05-01

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

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

    DTIC Science & Technology

    2014-09-30

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

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

    PubMed

    Ricketts, Todd; Henry, Paula

    2002-06-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  20. High- and low-frequency noise in Cs and in liquid metal ion sources.

    PubMed

    Rüdenauer, F; Mitterauer, J; Genovese, A

    2009-04-01

    Fundamental Physics space missions set rigid thrust noise limits for liquid metal ion thrusters used as actuators on drag-free platforms aboard the spacecraft. We have measured current-, voltage- and thrust noise of Cs and In LMIS, foreseen as prime candidates in these missions. In the high-frequency range, quasiperiodic oscillations around approximately 10(5)Hz can be observed for both types of emitters with frequency depending on emission current. In the low-frequency range (1-10(-3)Hz), which is particularly important for drag-free control, different types of noise events are observed, which in some instances show definite signs of deterministic chaos (period doubling, self-similarity). High-frequency current oscillations are generally ascribed to electro-hydrodynamic oscillations of the TAYLOR cone and the jet at its apex, with concomitant emission of charged nanodroplets. Comparison of theory and experiment shows unsatisfactory agreement in predicted vs. measured current oscillation frequencies and large disagreement in droplet emission frequencies. No theory is presently available for describing low-frequency noise events. In terms of a linearized Mair theory it is, however, shown that these noise events can be efficiently described by spontaneous variations in electrical emitter impedance. In spite of this impedance noise, the mission requirements for thrust noise (<0.1microN/Hz(1/2)) can be met by a thrust-stabilized In emitter.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  2. Dynamics of Synoptic Eddy and Low-Frequency Flow Interaction. Part III: Baroclinic Model Results.

    NASA Astrophysics Data System (ADS)

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

    2006-07-01

    In this three-part study, a linear closure has been developed for the synoptic eddy and low-frequency flow (SELF) interaction and demonstrated that internal dynamics plays an important role in generating the leading low-frequency modes in the extratropical circulation anomalies during cold seasons.In Part III, a new linearized primitive equation system is first derived for time-mean flow anomalies. The dynamical operator of the system includes a traditional part depending on the observed climatological mean state and an additional part from the SELF feedback closure utilizing the observed climatological properties of synoptic eddy activity. The latter part relates nonlocally all the anomalous eddy-forcing terms in equations of momentum, temperature, and surface pressure to the time-mean flow anomalies. Using the observational data, the closure was validated with reasonable success, and it was found that terms of the SELF feedback in the momentum and pressure equations tend to reinforce the low-frequency modes, whereas those in the thermodynamic equation tends to damp the temperature anomalies to make the leading modes equivalent barotropic. Through singular vector analysis of the linear dynamical operator, it is highlighted that the leading modes of the system resemble the observed patterns of the Arctic Oscillation, Antarctic Oscillation, and Pacific North American pattern, in which the SELF feedback plays an essential role, consistent with the finding of the barotropic model study in Part II.


  3. Assessing Low Frequency Climate Signals in Global Circulation Models using an Integrated Hydrologic Model

    NASA Astrophysics Data System (ADS)

    Niswonger, R. G.; Huntington, J. L.

    2010-12-01

    Climate signals with periodicities of approximately one decade are pervasive in long-term streamflow records for streams in the western United States that receive significant baseflow. The driver of these signals is unknown but hypotheses have been presented, such as variations in solar input to the Earth, or harmonics of internal (i.e., processes in the ocean and troposphere) forcings like the Pacific Decadal Oscillation (PDO) and El Niño Southern Oscillation (ENSO). Climate signals of about 1 decade are important for several reasons, including their relation to climate extremes (i.e., droughts and floods), and because the drivers of these climate signals are clearly important for projecting future climate conditions. Furthermore, identifying the drivers of these climate signals is important for separating the relative impacts of human production of greenhouse gases on global warming verses external drivers of climate change, such as sunspot cycles. Studies using Global Circulation Models (GCMs) that do not incorporate solar forcings associated with sun spots have identified oscillations of about a decade long in certain model output. However, these oscillations can be difficult to identify in simulated precipitation data due to high frequency variations (less than 1 year) that obscure low frequency (decade) signals. We have found that simulations using an integrated hydrologic model (IHM) called GSFLOW reproduce decade-long oscillations in streamflow when driven by measured precipitation records, and that these oscillations are also present in simulated streamflow when driven by temperature and precipitation data projected by GCMs. Because the IHM acts as a low-pass filter that reveals low frequency signals (i.e. decadal oscillations), they can be used to assess GCMs in terms of their ability to reproduce important low-frequency climate oscillations. We will present results from GSFLOW applied to three basins in the eastern Sierra Nevada driven by 100 years of

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

    NASA Astrophysics Data System (ADS)

    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. The low frequency 2D vibration sensor based on flat coil element

    SciTech Connect

    Djamal, Mitra; Sanjaya, Edi; Islahudin; Ramli

    2012-06-20

    Vibration like an earthquake is a phenomenon of physics. The characteristics of these vibrations can be used as an early warning system so as to reduce the loss or damage caused by earthquakes. In this paper, we introduced a new type of low frequency 2D vibration sensor based on flat coil element that we have developed. Its working principle is based on position change of a seismic mass that put in front of a flat coil element. The flat coil is a part of a LC oscillator; therefore, the change of seismic mass position will change its resonance frequency. The results of measurements of low frequency vibration sensor in the direction of the x axis and y axis gives the frequency range between 0.2 to 1.0 Hz.

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

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

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

  7. Searching for Low-Frequency Radio Transients from Supernovae

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

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

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

    NASA Astrophysics Data System (ADS)

    Wang, Jianrong; Wang, Renxiang; Hu, Xin

    2016-06-01

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

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

    NASA Astrophysics Data System (ADS)

    LoVerde, John J.; Dong, David W.

    2002-11-01

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

  10. The vestibular system mediates sensation of low-frequency sounds in mice.

    PubMed

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

    2010-12-01

    The mammalian inner ear contains sense organs responsible for detecting sound, gravity and linear acceleration, and angular acceleration. Of these organs, the cochlea is involved in hearing, while the sacculus and utriculus serve to detect linear acceleration. Recent evidence from birds and mammals, including humans, has shown that the sacculus, a hearing organ in many lower vertebrates, has retained some of its ancestral acoustic sensitivity. Here we provide not only more evidence for the retained acoustic sensitivity of the sacculus, but we also found that acoustic stimulation of the sacculus has behavioral significance in mammals. We show that the amplitude of an elicited auditory startle response is greater when the startle stimuli are presented simultaneously with a low-frequency masker, including masker tones that are outside the sensitivity range of the cochlea. Masker-enhanced auditory startle responses were also observed in otoconia-absent Nox3 mice, which lack otoconia but have no obvious cochlea pathology. However, masker enhancement was not observed in otoconia-absent Nox3 mice if the low-frequency masker tones were outside the sensitivity range of the cochlea. This last observation confirms that otoconial organs, most likely the sacculus, contribute to behavioral responses to low-frequency sounds in mice.

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

    SciTech Connect

    Ghosh, Samiran; Chakrabarti, Nikhil

    2016-08-15

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

  12. Low frequency spectrum of vacuum squeezed radiation to be used in GW antennas

    NASA Astrophysics Data System (ADS)

    Fiorentino, M.; Maddalena, P.; Porzio, A.; Romano, R.; Solimeno, S.

    1997-02-01

    We generalize the Collett and Gardiner model for the generation of vacuum squeezed radiation by degenerate optical parametric oscillators. We account for fluctuating pump, cavity with time varying length and nonlinear crystal phase matching temperature. The equation of motion of the intracavity field is integrated by WKB approximation by introducing a set of random functions. Relying on this result we calculate the low frequency spectrum of the quadrature amplitude, a quantity essential for assessing the photon noise reduction in interferometric gravitational wave antennas using vacuum squeezed light.

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

    NASA Astrophysics Data System (ADS)

    Konovalenko, A. A.

    2017-03-01

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

  14. Low-frequency noise from large wind turbines.

    PubMed

    Møller, Henrik; Pedersen, Christian Sejer

    2011-06-01

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

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

    PubMed

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

    2014-10-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

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

  18. Atomic Oxygen Energy in Low Frequency Hyperthermal Plasma Ashers

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Finch, James

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

  20. Low-Frequency Vibration Drilling of Titanium Alloy

    NASA Astrophysics Data System (ADS)

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

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

  1. Present and Future Modes of Low Frequency Climate Variability

    SciTech Connect

    Cane, Mark A.

    2014-02-20

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

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

    PubMed

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

    2016-07-26

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

  3. Minimal basilar membrane motion in low-frequency hearing

    PubMed Central

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

  5. Reducing low-frequency noise during reversible fluctuations

    NASA Astrophysics Data System (ADS)

    Chamberlin, Ralph V.

    2017-02-01

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

  6. Energy harvesting from aperiodic low-frequency motion using reverse electrowetting.

    PubMed

    Hsu, Tsung-Hsing; Taylor, J A; Krupenkin, T N

    2017-07-01

    Mechanical energy harvesting can provide a promising alternative to electrochemical batteries, which are currently widely utilized to power mobile electronics. In this work we present a theoretical analysis of a recently proposed method of mechanical energy harvesting, which combines a reverse electrowetting phenomenon with the fast self-oscillating process of bubble growth and collapse. We investigate the details of the bubble dynamics and analyze the dependence of the energy generation process on the system parameters. The results demonstrate that self-oscillation frequencies of several kHz are possible, which can lead to very high power generation densities in excess of 10(4) W m(-2). The obtained results indicate the possibility of high-power energy harvesting from mechanical energy sources with very low frequencies, well below 1 Hz.

  7. Experimental results for oscillatory water flow in 10-ppi metal foam at low-frequencies

    NASA Astrophysics Data System (ADS)

    Bağcı, Ö.; Arbak, A.; De Paepe, M.; Dukhan, N.

    2016-09-01

    This experimental study presents results and interpretation of oscillatory water flow in open-cell metal foam. The tested foam had 10 pores per inch and a porosity of 88%. At relatively low frequencies, three flow displacements were employed in the experiment. The influence of frequency and displacement on pressure loss and friction factor is discussed. A correlation of friction factor as a function of the kinetic Reynolds number was determined. Porous media parameters, permeability and drag coefficient, were also found for the same foam via steady-state flow experiments in the Darcy and Forchheimer regimes. The friction factor of oscillating flow was found to be higher than that of steady state. The findings of this study are considered important for oscillating heat transfer in metal foam.

  8. Low-frequency optical dielectric response and rigidity transitions in network glasses

    SciTech Connect

    Gonzalez-Leal, J. M.; Angel, J. A.; Marquez, E.; Jimenez-Garay, R.; Krecmer, P.

    2006-11-15

    Self-organization occurring in As{sub x}S{sub 1-x} and As{sub x}Se{sub 1-x} glass alloy films reflects in their low-frequency optical dielectric response, and valuable information about the building blocks conforming their structure, can be derived from the analysis of the refractive-index dispersion data. The experimental results are discussed in the framework of the single-oscillator approach proposed by Wemple and DiDomenico, which provides a meaningful parametrization of the phenomena ruling the coupling between the photon-probe and the electron plasma in the near-infrared spectral region. Rigidity transitions occurring in both binary glassy systems are discussed in terms of the differences observed in the oscillator parameters, and these electronic evidences are linked to those arguments found in the literature, based on calorimetric and Raman measurements, that point to a segregated-phase view of glass materials.

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

    NASA Technical Reports Server (NTRS)

    Stec, Robert C.

    1999-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Hughes, Scott

    2016-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  12. The auditory nerve overlapped waveform (ANOW): A new objective measure of low-frequency hearing

    NASA Astrophysics Data System (ADS)

    Lichtenhan, Jeffery T.; Salt, Alec N.; Guinan, John J.

    2015-12-01

    One of the most pressing problems today in the mechanics of hearing is to understand the mechanical motions in the apical half of the cochlea. Almost all available measurements from the cochlear apex of basilar membrane or other organ-of-Corti transverse motion have been made from ears where the health, or sensitivity, in the apical half of the cochlea was not known. A key step in understanding the mechanics of the cochlear base was to trust mechanical measurements only when objective measures from auditory-nerve compound action potentials (CAPs) showed good preparation sensitivity. However, such traditional objective measures are not adequate monitors of cochlear health in the very low-frequency regions of the apex that are accessible for mechanical measurements. To address this problem, we developed the Auditory Nerve Overlapped Waveform (ANOW) that originates from auditory nerve output in the apex. When responses from the round window to alternating low-frequency tones are averaged, the cochlear microphonic is canceled and phase-locked neural firing interleaves in time (i.e., overlaps). The result is a waveform that oscillates at twice the probe frequency. We have demonstrated that this Auditory Nerve Overlapped Waveform - called ANOW - originates from auditory nerve fibers in the cochlear apex [8], relates well to single-auditory-nerve-fiber thresholds, and can provide an objective estimate of low-frequency sensitivity [7]. Our new experiments demonstrate that ANOW is a highly sensitive indicator of apical cochlear function. During four different manipulations to the scala media along the cochlear spiral, ANOW amplitude changed when either no, or only small, changes occurred in CAP thresholds. Overall, our results demonstrate that ANOW can be used to monitor cochlear sensitivity of low-frequency regions during experiments that make apical basilar membrane motion measurements.

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

    ERIC Educational Resources Information Center

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

    2013-01-01

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

  14. Intrinsic low-frequency variability of the Gulf Stream

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

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

    ERIC Educational Resources Information Center

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

    2013-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Delombard, R.

    1984-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2004-03-01

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

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

    DTIC Science & Technology

    2015-06-01

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

  19. Ionization oscillations in Hall accelerators

    NASA Astrophysics Data System (ADS)

    Barral, S.; Peradzyński, Z.

    2010-01-01

    The underlying mechanism of low-frequency oscillations in Hall accelerators is investigated theoretically. It is shown that relaxation oscillations arise from a competition between avalanche ionization and the advective transport of the working gas. The model derived recovers the slow progression and fast recession of the ionization front. Analytical approximations of the shape of current pulses and of the oscillation frequency are provided for the case of large amplitude oscillations.

  20. Vertical amplitude phase structure of a low-frequency acoustic field in shallow water

    NASA Astrophysics Data System (ADS)

    Kuznetsov, G. N.; Lebedev, O. V.; Stepanov, A. N.

    2016-11-01

    We obtain in integral and analytic form the relations for calculating the amplitude and phase characteristics of an interference structure of orthogonal projections of the oscillation velocity vector in shallow water. For different frequencies and receiver depths, we numerically study the source depth dependences of the effective phase velocities of an equivalent plane wave, the orthogonal projections of the sound pressure phase gradient, and the projections of the oscillation velocity vector. We establish that at low frequencies in zones of interference maxima, independently of source depth, weakly varying effective phase velocity values are observed, which exceed the sound velocity in water by 5-12%. We show that the angles of arrival of the equivalent plane wave and the oscillation velocity vector in the general case differ; however, they virtually coincide in the zone of the interference maximum of the sound pressure under the condition that the horizontal projections of the oscillation velocity appreciably exceed the value of the vertical projection. We give recommendations on using the sound field characteristics in zones with maximum values for solving rangefinding and signal-detection problems.

  1. Probing a chemical compass: novel variants of low-frequency reaction yield detected magnetic resonance.

    PubMed

    Maeda, Kiminori; Storey, Jonathan G; Liddell, Paul A; Gust, Devens; Hore, P J; Wedge, C J; Timmel, Christiane R

    2015-02-07

    We present a study of a carotenoid-porphyrin-fullerene triad previously shown to function as a chemical compass: the photogenerated carotenoid-fullerene radical pair recombines at a rate sensitive to the orientation of an applied magnetic field. To characterize the system we develop a time-resolved Low-Frequency Reaction Yield Detected Magnetic Resonance (tr-LF-RYDMR) technique; the effect of varying the relative orientation of applied static and 36 MHz oscillating magnetic fields is shown to be strongly dependent on the strength of the oscillating magnetic field. RYDMR is a diagnostic test for involvement of the radical pair mechanism in the magnetic field sensitivity of reaction rates or yields, and has previously been applied in animal behavioural experiments to verify the involvement of radical-pair-based intermediates in the magnetic compass sense of migratory birds. The spectroscopic selection rules governing RYDMR are well understood at microwave frequencies for which the so-called 'high-field approximation' is valid, but at lower frequencies different models are required. For example, the breakdown of the rotating frame approximation has recently been investigated, but less attention has so far been given to orientation effects. Here we gain physical insights into the interplay of the different magnetic interactions affecting low-frequency RYDMR experiments performed in the challenging regime in which static and oscillating applied magnetic fields as well as internal electron-nuclear hyperfine interactions are of comparable magnitude. Our observations aid the interpretation of existing RYDMR-based animal behavioural studies and will inform future applications of the technique to verify and characterize further the biological receptors involved in avian magnetoreception.

  2. Fine structure of the low-frequency spectra of heart rate and blood pressure

    PubMed Central

    Kuusela, Tom A; Kaila, Timo J; Kähönen, Mika

    2003-01-01

    Background The aim of this study was to explore the principal frequency components of the heart rate and blood pressure variability in the low frequency (LF) and very low frequency (VLF) band. The spectral composition of the R–R interval (RRI) and systolic arterial blood pressure (SAP) in the frequency range below 0.15 Hz were carefully analyzed using three different spectral methods: Fast Fourier transform (FFT), Wigner-Ville distribution (WVD), and autoregression (AR). All spectral methods were used to create time–frequency plots to uncover the principal spectral components that are least dependent on time. The accurate frequencies of these components were calculated from the pole decomposition of the AR spectral density after determining the optimal model order – the most crucial factor when using this method – with the help of FFT and WVD methods. Results Spectral analysis of the RRI and SAP of 12 healthy subjects revealed that there are always at least three spectral components below 0.15 Hz. The three principal frequency components are 0.026 ± 0.003 (mean ± SD) Hz, 0.076 ± 0.012 Hz, and 0.117 ± 0.016 Hz. These principal components vary only slightly over time. FFT-based coherence and phase-function analysis suggests that the second and third components are related to the baroreflex control of blood pressure, since the phase difference between SAP and RRI was negative and almost constant, whereas the origin of the first component is different since no clear SAP–RRI phase relationship was found. Conclusion The above data indicate that spontaneous fluctuations in heart rate and blood pressure within the standard low-frequency range of 0.04–0.15 Hz typically occur at two frequency components rather than only at one as widely believed, and these components are not harmonically related. This new observation in humans can help explain divergent results in the literature concerning spontaneous low-frequency oscillations. It also raises methodological

  3. A method for sputtering with low frequency alternating current

    SciTech Connect

    Timberlake, J.R.

    1993-12-31

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

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

    NASA Astrophysics Data System (ADS)

    Zarka, P.; Mottez, F.

    2016-12-01

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

  5. An evolutionary sequence of low frequency radio astronomy missions

    NASA Technical Reports Server (NTRS)

    Jones, Dayton L.

    1990-01-01

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

  6. Method for sputtering with low frequency alternating current

    DOEpatents

    Timberlake, John R.

    1996-01-01

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

  7. Method for sputtering with low frequency alternating current

    DOEpatents

    Timberlake, J.R.

    1996-04-30

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

  8. A lunar far-side very low frequency array

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

  9. Computer simulation of low-frequency electromagnetic data acquisition

    SciTech Connect

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

    1982-02-01

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

  10. Theory of low frequency noise transmission through turbines

    NASA Technical Reports Server (NTRS)

    Matta, R. K.; Mani, R.

    1979-01-01

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

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

    PubMed

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

    2009-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-03-01

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

  13. Low-frequency computational electromagnetics for antenna analysis

    SciTech Connect

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

    1991-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

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

    PubMed

    Malaescu, I; Marin, C N

    2002-07-01

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

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

    NASA Astrophysics Data System (ADS)

    Poole, Travis L.; Frisk, George V.

    2002-11-01

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

  17. Low-frequency noise reduction of lightweight airframe structures

    NASA Technical Reports Server (NTRS)

    Getline, G. L.

    1976-01-01

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

  18. Low frequency electrorotation of fixed red blood cells.

    PubMed Central

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

    1998-01-01

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

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

    PubMed

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

    2016-11-15

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

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

    NASA Astrophysics Data System (ADS)

    Sau, Jay D.; Setiawan, F.

    2017-02-01

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

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

    PubMed

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

    2004-07-01

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

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

    PubMed Central

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

    1989-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Foster, Griffin

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

  4. The reduction of low frequency fluctuations in RFP experiments

    SciTech Connect

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

    1998-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-06-01

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

  6. Length sensing and control for Einstein Telescope Low Frequency

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

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

    DTIC Science & Technology

    1991-04-01

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

  8. A kinetic-MHD model for low frequency phenomena

    SciTech Connect

    Cheng, C.Z.

    1991-07-01

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

  9. Low-frequency creep in CoNiFe films.

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

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

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

    SciTech Connect

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

    2004-12-01

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

  11. Low-frequency creep in CoNiFe films.

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-09-01

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

  13. Spatial structure of low-frequency wind noise.

    PubMed

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

    2007-12-01

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

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

    DTIC Science & Technology

    2011-05-01

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

  15. Relativistic runaway breakdown in low-frequency radio

    NASA Astrophysics Data System (ADS)

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

    2010-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

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

    PubMed Central

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Patil, Ajinkya; Fisher, R.

    2012-01-01

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

  20. Impact of low-frequency sound on historic structures

    NASA Astrophysics Data System (ADS)

    Sutherland, Louis C.; Horonjeff, Richard D.

    2005-09-01

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

  1. Solar observations with a low frequency radio telescope

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2004-01-01

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

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

    SciTech Connect

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

    1995-12-31

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

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

    SciTech Connect

    Beckham, Richard Edward; Amr, Abdel - Fattah I; Peter, Roberts M; Reem, Ibrahim; Tarimala, Sowmitri

    2009-01-01

    Naturally occurring seismic events and artificially generated low-frequency (1 to 500 Hertz) elastic waves have been observed to alter the production rates of oil and water wells, sometimes increasing and sometimes decreasing production, and to influence the turbidity of surface and well water. The decreases in production are of particular concern - especially when artificially generated elastic waves are applied as a method for enhanced oil recovery. The exact conditions that result in a decrease in production remain unknown. While the underlying environment is certainly complex, the observed increase in water well turbidity after natural seismic events suggests the existence of a mechanism that can affect both the subsurface flow paths and mobilization of in-situ colloidal particles. This paper explores the macroscopic and microscopic effects of low-frequency dynamic stress stimulations on the release of colloidal particles from an analog core representing an infinitesimal section along the propagation paths of an elastic wave. Experiments on a column packed with 1-mm borosilicate beads and loaded with polystyrene microspheres demonstrate that axial mechanical stress oscillations enhance the mobilization of captured microspheres. Increasing the amplitude of the oscillations increases the number of microspheres released and can also result in cyclical spikes in effluent microsphere concentration during stimulation. Under a prolonged period of stimulation, the cyclical effluent spikes coincided with fluctuations in the column pressure data, and continue at a diminished level after stimulation. This behavior can be attributed to rearrangements of the beads in the column, resulting in possible changes to the void space and/or tortuosity of the packing. Optical microscopy observations of the beads during low frequency oscillations reveal that individual beads rotate, thereby rubbing against each other and scraping away portions of the adsorbed microspheres. These

  5. Low frequency signals analysis from broadband seismometers records

    NASA Astrophysics Data System (ADS)

    Hsu, Po-Chin

    2016-04-01

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

  6. Brain alterations in low-frequency fluctuations across multiple bands in obsessive compulsive disorder.

    PubMed

    Giménez, Mònica; Guinea-Izquierdo, Andrés; Villalta-Gil, Victoria; Martínez-Zalacaín, Ignacio; Segalàs, Cinto; Subirà, Marta; Real, Eva; Pujol, Jesús; Harrison, Ben J; Haro, Josep Maria; Sato, Joao R; Hoexter, Marcelo Q; Cardoner, Narcís; Alonso, Pino; Menchón, José Manuel; Soriano-Mas, Carles

    2016-10-22

    The extent of functional abnormalities in frontal-subcortical circuits in obsessive-compulsive disorder (OCD) is still unclear. Although neuroimaging studies, in general, and resting-state functional Magnetic Resonance Imaging (rs-fMRI), in particular, have provided relevant information regarding such alterations, rs-fMRI studies have been typically limited to the analysis of between-region functional connectivity alterations at low-frequency signal fluctuations (i.e., <0.08 Hz). Conversely, the local attributes of Blood Oxygen Level Dependent (BOLD) signal across different frequency bands have been seldom studied, although they may provide valuable information. Here, we evaluated local alterations in low-frequency fluctuations across different oscillation bands in OCD. Sixty-five OCD patients and 50 healthy controls underwent an rs-fMRI assessment. Alterations in the fractional amplitude of low-frequency fluctuations (fALFF) were evaluated, voxel-wise, across four different bands (from 0.01 Hz to 0.25 Hz). OCD patients showed decreased fALFF values in medial orbitofrontal regions and increased fALFF values in the dorsal-medial prefrontal cortex (DMPFC) at frequency bands <0.08 Hz. This pattern was reversed at higher frequencies, where increased fALFF values also appeared in medial temporal lobe structures and medial thalamus. Clinical variables (i.e., symptom-specific severities) were associated with fALFF values across the different frequency bands. Our findings provide novel evidence about the nature and regional distribution of functional alterations in OCD, which should contribute to refine neurobiological models of the disorder. We suggest that the evaluation of the local attributes of BOLD signal across different frequency bands may be a sensitive approach to further characterize brain functional alterations in psychiatric disorders.

  7. Low-frequency elastic waves alter pore-scale colloid mobilization

    SciTech Connect

    Beckham, Richard Edward; Abdel-fattah, Amr I; Roberts, Peter M; Ibrahim, Reem; Tarimala, Sownitri

    2009-01-01

    Naturally occurring seismic events and artificially generated low-frequency elastic waves have been observed to alter the production rates of oil and water wells, sometimes increasing and sometimes decreasing production, and to influence the turbidity of water wells. TEe decreases in production are of particular concern - especially when artificially generated elastic waves are applied as a method for enhanced oil recovery. The exact conditions that result in a decrease in production remain unknown. While the underlying environment is certainly complex, the observed increase in water well turbidity after seismic events suggests the existence of a mechanism that can affect both the subsurface flow paths and mobilization of in-situ colloidal particles. This paper explores the macroscopic and microscopic effects of elastic wave stimulations on the release of colloidal particles and investigates the microscopic mechanism of particle release during stimulation. Experiments on a column packed with 1-mm borosilicate beads loaded with polystyrene microspheres demonstrate that low-frequency elastic wave stimulations enhance the mobilization of captured microspheres. Increasing the intensity of the stimulations increases the number of microspheres released and can also result in cyclical variations in effluent microsphere concentration during and after stimulations. Under a prolonged period of stimulation, the cyclical effluent variations coincided with fluctuations in the column pressure data. This behavior can be attributed to flow pathways fouling and/or rearrangements of the beads in the column. Optical microscopy observations of the beads during low frequency oscillations reveal that the individual beads rotate, thereby rubbing against each other and scraping off portions of the adsorbed microspheres. These results support the theory that mechanical interactions between soil grains are important mechanisms in flow path alteration and the mobilization of naturally

  8. Cold-Flow Study of Low Frequency Pressure Instability in Hybrid Rocket Motors

    NASA Technical Reports Server (NTRS)

    Jenkins, Rhonald M.

    1997-01-01

    Past experience with hybrid rockets has shown that certain motor operating conditions are conducive to the formation of low frequency pressure oscillations, or flow instabilities, within the motor. Both past and present work in the hybrid propulsion community acknowledges deficiencies in the understanding of such behavior, though it seems probable that the answer lies in an interaction between the flow dynamics and the combustion heat release. Knowledge of the fundamental flow dynamics is essential to the basic understanding of the overall stability problem. A first step in this direction was a study conducted at NASA Marshall Space Flight Center (MSFC), centered around a laboratory-scale two dimensional water flow model of a hybrid rocket motor. Principal objectives included: (1) visualization of flow and measurement of flow velocity distributions: (2) assessment of the importance of shear layer instabilities in driving motor pressure oscillations; (3) determination of the interactions between flow induced shear layers with the mainstream flow, the secondary (wall) throughflow, and solid boundaries; (4) investigation of the interactions between wall flow oscillations and the mainstream flow pressure distribution.

  9. Numerical prediction of low frequency combustion instability in a model ramjet combustor

    SciTech Connect

    Shang, H.M.; Chen, Y.S.; Shih, M.S.; Farmer, R.C.

    1996-12-31

    A numerical analysis has been conducted for low-frequency combustion instability in a model ramjet combustor. The facility is two-dimensional, and is comprised of a long inlet duct, a dump combustor chamber, and an exhaust nozzle. The experiments observed that the combustor pressure oscillation under the particular operating condition did not have much cycle-to-cycle variation. The main resonant frequency occurs at about 65 Hz for this case. In the numerical analysis, a time accurate Computational Fluid Dynamics (CFD) code with a pressure-correction algorithm is used, and the combustion process was modeled with a single step chemistry model and a modified eddy breakup model. A high-order upwind scheme with flux limiter is used for convection terms. The convergence of the linear algebraic equations is accelerated through a preconditioned conjugate gradient matrix solver. The numerical predictions show that the flame oscillates in the combustion chamber at the calculation condition and are justified by the experimental schlieren photographs. The numerical analyses correctly predict the chamber pressure oscillation frequency is over-predicted compared with the experimental data. The discrepancy can be explained by the simplified turbulence and combustion model used in this study, and the uncertainty of the inlet boundary conditions.

  10. Causal Modes in the Low-frequency variability of Mediterranean and Middle-Eastern climates

    NASA Astrophysics Data System (ADS)

    Casagrande, Erik; Zampieri, Matteo; Artale, Vincenzo; Gualdi, Silvio; Molini, Annalisa

    2015-04-01

    In the last three decades, the Mediterranean and the Middle East experienced a phase of warming larger than the one that could be expected from global warming, and largely ascribable to natural (e.g. internal) climate variability. To better understand this process we explore here the presence of causal relationships among the diverse modes of variability of the climate system, focusing in particular on inter-annual and decadal scales of variability, influencing the climate of Mediterranean and Middle-Eastern regions. Causality measures used in this study include time and frequency-domain Granger causality (GC) and the phase slope index (Ψ), a directional coupling statistic developed by Nolte et. al. in 2007. GC metrics are applied to signals before and after the filtering of high frequency (inter-annual) components, while Ψ is designed to discern between low-frequency causal flow and higher frequency components. To assure the necessary sample size, the analysis is based on the preindustrial runs of the Fifth Coupled Model Intercomparison Project (CMIP5), which are free from external perturbation and last some hundred years. We selected the runs based on ENSO stationarity - to ensure that the simulations reached the equilibrium - and the consistent representation of the Atlantic Multidecadal Oscillation (AMO), which is considered one of the main drivers for the low-frequency (decadal) climate variability of the Mediterranean and the Middle East in summer. Finally, we discuss the potential of causality metrics for the predictability of future decadal variability in these regions.

  11. Kinetic theory of low-frequency cross-field instability in a weakly ionized plasma. I

    SciTech Connect

    Dimant, Y.S.; Sudan, R.N.

    1995-04-01

    A consistent kinetic theory is developed for the description of electrons under conditions of a low-frequency two-stream {bold E}{times}{bold B} instability in collisionally dominated, weakly ionized plasmas. Starting from the Boltzmann collision integral, a simplified kinetic equation for the electron distribution function has been derived, which takes into account strong pitch-angle scattering of electrons by neutrals, velocity dependence of the electron--neutral collision frequency, etc. Linearized equations describing small oscillations of the electron distribution function and ion density are presented. For the asymptotic case of short waves, the dispersion relation of the {bold E}{times}{bold B} instability has been obtained and analyzed under conditions typical for the lower ionosphere. Under certain conditions, the rigorous kinetic consideration yields substantial changes in results compared to previous theories. The general approach may be applied to other linear and nonlinear low-frequency processes in a weakly ionized plasma. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  12. A high figure of merit vibrational energy harvester for low frequency applications

    NASA Astrophysics Data System (ADS)

    Nico, V.; Boco, E.; Frizzell, R.; Punch, J.

    2016-01-01

    Small-scale vibration energy harvesters that respond efficiently at low frequencies are challenging to realize. This paper describes the design and implementation of one such harvester, which achieves a high volumetric Figure of Merit (FoMv = 2.6% at 11.50 Hz) at the scale of a C-type battery and outperforms other state-of-the-art devices in the sub 20 Hz frequency range. The device employs a 2 Degree-of-Freedom velocity-amplified approach and electromagnetic transduction. The harvester comprises two masses oscillating one inside the other, between four sets of magnetic springs. Collisions between the two masses transfer momentum from the heavier to the lighter mass, exploiting velocity amplification. The paper first presents guidelines for designing and optimizing the transduction mechanism, before a nonlinear numerical model for the system dynamics is developed. Experimental characterisation of the harvester design is then presented to validate both the transducer optimization and the dynamics model. The resulting high FoMV demonstrates the effectiveness of the device for low frequency applications, such as human motion.

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

    PubMed

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

    2016-01-01

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

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

    PubMed

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

    2014-02-01

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

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

    PubMed

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

    2015-03-15

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

  16. Low-frequency and wideband vibration energy harvester with flexible frame and interdigital structure

    SciTech Connect

    Li, Pengwei Wang, Yanfen; Luo, Cuixian; Li, Gang; Hu, Jie; Zhang, Wendong; Liu, Ying; Liu, Wei

    2015-04-15

    As an alternative to traditional cantilever beam structures and their evolutions, a flexible beam based, interdigital structure, vibration energy harvester has been presented and investigated. The proposed interdigital-shaped oscillator consists of a rectangular flexible frame and series of cantilever beams interdigitally bonded to it. In order to achieve low frequency and wide-bandwidth harvesting, Young’s modulus of materials, frame size and the amount of the cantilevers have been studied systematically. The measured frequency responses of the designed device (PDMS frame, quintuple piezoelectric cantilever beams) show a 460% increase in bandwidth below 80Hz. When excited at an acceleration of 1.0 g, the energy harvester achieves to a maximum open-circuit voltage of 65V, and the maximum output power 4.5 mW.

  17. A common structure underlies low-frequency cortical dynamics in movement, sleep, and sedation.

    PubMed

    Hall, Thomas M; de Carvalho, Felipe; Jackson, Andrew

    2014-09-03

    Upper-limb movements are often composed of regular submovements, and neural correlates of submovement frequencies between 1 and 4 Hz have been found in the motor cortex. The temporal profile of movements is usually assumed to be determined by extrinsic factors such as limb biomechanics and feedback delays, but another possibility is that an intrinsic rhythmicity contributes to low frequencies in behavior. We used multielectrode recordings in monkeys performing an isometric movement task to reveal cyclic activity in primary motor cortex locked to submovements, and a distinct oscillation in premotor cortex. During ketamine sedation and natural sleep, cortical activity traversed similar cycles and became synchronized across areas. Because the same cortical dynamics are coupled to submovements and also observed in the absence of behavior, we conclude that the motor networks controlling the upper limb exhibit an intrinsic periodicity at submovement frequencies that is reflected in the speed profile of movements.

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

    PubMed Central

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

    2017-01-01

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

  19. Low-Frequency Electromagnetic Exploration for Groundwater on Mars

    NASA Technical Reports Server (NTRS)

    Grimm, Robert E.

    2002-01-01

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

  20. Low Frequency Radio Astronomical Antennas for the Lunar Environment

    NASA Astrophysics Data System (ADS)

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

    2009-01-01

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

  1. Low-Frequency Electromagnetic Exploration for Groundwater on Mars

    NASA Technical Reports Server (NTRS)

    Grimm, Robert E.

    2002-01-01

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

  2. Low-frequency combustion instability mechanisms in a side-dump combustor

    SciTech Connect

    Samaniego, J.M.; Yip, B.; Poinsot, T.; Candel, S. . E.M2.C Lab.)

    1993-09-01

    This article describes a study of a two-dimensional two-inlet side-dump combustor fed with a mixture of air and propane. The present results concern symmetric operating conditions with respect to the two inlets. Stable and unstable regimes which depend on the inlet velocity and the equivalence ratio have been identified. Schlieren visualization, radical imaging with an intensified CCD camera, and simultaneous pressure, inlet velocity and C[sub 2] emission light measurements, have been used to characterize the combustor behavior. Imaging of the flowfield has provided an insight on the flame structure and its interaction with the entering jets. Two low-frequency unstable modes (a fuel-rich regime and a fuel-lean regime with an instability frequency around 500 Hz) were studied using a conditional imaging technique. It was found that unsteady heat release occurs in two different ways: pulsating combustion in the dome region and convection of reaction zones downstream of the jet-impingement region. Flame oscillations were induced by a periodic impingement of the jets on the centerplane of the chamber. Pressure fluctuations in the test section were roughly in phase with the global C[sub 2] emission, indicating that the instabilities were sustained by energy addition to the acoustic field. A two-dimensional distribution of the Rayleigh index computed for each unstable mode indicated that the fuel-lean mode was driven by the unsteady heat release in the dome region whereas the fuel-rich mode was driven by the flame oscillations downstream of the jet-impingement region. The transition from the fuel-lean to the fuel-rich instability featured a shift of driving mechanism. This study shows that even in the idealized geometry the coupling mechanisms leading to low-frequency combustion instabilities are not unique and illustrates the difficulty of devising predictive models.

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

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

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

  5. Fetal exposure to low frequency electric and magnetic fields

    NASA Astrophysics Data System (ADS)

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

    2007-02-01

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

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

    PubMed

    McDonald, B Edward; Calvo, David C

    2007-12-01

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

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

    PubMed

    Dykeman, Eric C; Sankey, Otto F

    2008-01-18

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

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

    NASA Astrophysics Data System (ADS)

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

    2004-02-01

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

  9. Angular structure of extragalactic radio sources at low frequencies

    NASA Astrophysics Data System (ADS)

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

    2005-06-01

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

  10. Low-Frequency Measurements of the CMB Spectrum

    SciTech Connect

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

    1989-10-01

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

  11. Low-frequency measurements of the CMB spectrum

    SciTech Connect

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

    1990-01-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

  14. Low-frequency quadrupole impedance of undulators and wigglers

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

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

    PubMed Central

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

    2017-01-01

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

  16. Upgrading Emma to Use Low-Frequency RF Cavities

    NASA Astrophysics Data System (ADS)

    Ohmori, Chihiro; Berg, J. Scott

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-08-01

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

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

    PubMed

    Kuehler, Robert; Fedtke, Thomas; Hensel, Johannes

    2015-04-01

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

  19. A new hybrid phononic crystal in low frequencies

    NASA Astrophysics Data System (ADS)

    Zhang, Z.; Han, X. K.

    2016-11-01

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

  20. Low-frequency fluid waves in fractures and pipes

    SciTech Connect

    Korneev, Valeri

    2010-09-01

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

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

    SciTech Connect

    Stevens, R.G.

    1988-12-01

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

  2. Sympathetically-induced changes in microvascular cerebral blood flow and in the morphology of its low-frequency waves.

    PubMed

    Deriu, F; Roatta, S; Grassi, C; Urciuoli, R; Micieli, G; Passatore, M

    1996-06-10

    The effect of bilateral cervical sympathetic nerve stimulation on microvascular cerebral blood flow, recorded at various depths in the parietal lobe and in ponto-mesencephalic areas, was investigated by laser-Doppler flowmetry in normotensive rabbits. These areas were chosen as representative of the vascular beds supplied by the carotid and vertebro-basilar systems, which exhibit different degrees of sympathetic innervation, the former being richer than the latter. Sympathetic stimulation at 30 imp/s affects cerebral blood flow in 77% of the parietal lobe and in 43% of the ponto-mesencephalic tested areas. In both cases the predominant effect was a reduction in blood flow (14.7 +/- 5.1% and 4.1 +/- 2.4%, respectively). The extent of the reduction in both areas was less if the stimulation frequency was decreased. Sometimes mean cerebral blood flow showed a small and transient increase, mainly in response to low-frequency stimulation. The morphology was analysed of low-frequency spontaneous oscillations in cerebral blood flow, attributed to vasomotion. Present in 41% of the tested areas (frequency 4-12 cycles/min, peak-to-peak amplitude 10-40% of mean value), these waves decreased in amplitude and increased in frequency during sympathetic stimulation, irrespective of changes in mean flow. The possibility has been proposed that the sympathetic action on low-frequency spontaneous oscillations may contribute to the protective influence that this system is known to exert on the blood-brain barrier in hypertension.

  3. Concurrent Acoustic Activation of the Medial Olivocochlear System Modifies the After-Effects of Intense Low-Frequency Sound on the Human Inner Ear.

    PubMed

    Kugler, Kathrin; Wiegrebe, Lutz; Gürkov, Robert; Krause, Eike; Drexl, Markus

    2015-12-01

    >Human hearing is rather insensitive for very low frequencies (i.e. below 100 Hz). Despite this insensitivity, low-frequency sound can cause oscillating changes of cochlear gain in inner ear regions processing even much higher frequencies. These alterations outlast the duration of the low-frequency stimulation by several minutes, for which the term 'bounce phenomenon' has been coined. Previously, we have shown that the bounce can be traced by monitoring frequency and level changes of spontaneous otoacoustic emissions (SOAEs) over time. It has been suggested elsewhere that large receptor potentials elicited by low-frequency stimulation produce a net Ca(2+) influx and associated gain decrease in outer hair cells. The bounce presumably reflects an underdamped, homeostatic readjustment of increased Ca(2+) concentrations and related gain changes after low-frequency sound offset. Here, we test this hypothesis by activating the medial olivocochlear efferent system during presentation of the bounce-evoking low-frequency (LF) sound. The efferent system is known to modulate outer hair cell Ca(2+) concentrations and receptor potentials, and therefore, it should modulate the characteristics of the bounce phenomenon. We show that simultaneous presentation of contralateral broadband noise (100 Hz-8 kHz, 65 and 70 dB SPL, 90 s, activating the efferent system) and ipsilateral low-frequency sound (30 Hz, 120 dB SPL, 90 s, inducing the bounce) affects the characteristics of bouncing SOAEs recorded after low-frequency sound offset. Specifically, the decay time constant of the SOAE level changes is shorter, and the transient SOAE suppression is less pronounced. Moreover, the number of new, transient SOAEs as they are seen during the bounce, are reduced. Taken together, activation of the medial olivocochlear system during induction of the bounce phenomenon with low-frequency sound results in changed characteristics of the bounce phenomenon. Thus, our data provide experimental support

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

    NASA Astrophysics Data System (ADS)

    Dartez, L. P.

    2014-04-01

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

  5. Alternative source models of very low frequency events

    USGS Publications Warehouse

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Barklow, William E.

    2004-05-01

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

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

    NASA Astrophysics Data System (ADS)

    Barklow, William E.

    2001-05-01

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

  8. Low-frequency Raman scattering from silicon nanostructures

    NASA Astrophysics Data System (ADS)

    Shukla, A. K.; Kumar, Vivek

    2011-09-01

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

  9. Alternative source models of very low frequency events

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

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

    PubMed

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

    2012-02-28

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

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

    PubMed

    Wallace, M N; Palmer, A R

    2009-04-01

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

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

    PubMed

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

    2008-08-01

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

  13. Low-frequency terrestrial tensor gravitational-wave detector

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

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

    PubMed

    Armstrong, J W

    2006-01-01

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

  15. Low-frequency gravitational-wave science frontiers

    NASA Astrophysics Data System (ADS)

    Hughes, Scott

    2017-01-01

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

  16. Low-frequency electromagnetic technique for nondestructive evaluation

    NASA Astrophysics Data System (ADS)

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

    2000-05-01

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

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

    NASA Technical Reports Server (NTRS)

    Jones, Dayton L.

    2014-01-01

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

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

    PubMed Central

    Olson, P.

    2007-01-01

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

  19. Passive Super-Low Frequency electromagnetic prospecting technique

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

  20. Very low frequency earthquakes in Cascadia migrate with tremor

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  1. The low frequency vibrational modes of green fluorescent proteins

    NASA Astrophysics Data System (ADS)

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

    2003-02-01

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

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

    NASA Technical Reports Server (NTRS)

    Jones, Dayton L.

    2014-01-01

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

  3. Sensitive ultrasonic vibrometer for very low frequency applications.

    PubMed

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

    2007-08-01

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

  4. Characterizing low frequency plasma waves at Mars with MAVEN

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  5. Micromachined low frequency rocking accelerometer with capacitive pickoff

    DOEpatents

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

    2001-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    PubMed

    Olson, P

    2007-12-18

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Balandin, Alexander A.

    2013-08-01

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

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

    NASA Astrophysics Data System (ADS)

    Palagummi, Sri Vikram

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

  11. Negative feedback system reduces pump oscillations

    NASA Technical Reports Server (NTRS)

    Rosenmann, W.

    1967-01-01

    External negative feedback system counteracts low frequency oscillations in rocket engine propellant pumps. The system uses a control piston to sense pump discharge fluid on one side and a gas pocket on the other.

  12. Shear-flow trapped-ion-mode interaction revisited. II. Intermittent transport associated with low-frequency zonal flow dynamics

    SciTech Connect

    Ghizzo, A.; Palermo, F.

    2015-08-15

    We address the mechanisms underlying low-frequency zonal flow generation in turbulent system and the associated intermittent regime of ion-temperature-gradient (ITG) turbulence. This model is in connection with the recent observation of quasi periodic zonal flow oscillation at a frequency close to 2 kHz, at the low-high transition, observed in the ASDEX Upgrade [Conway et al., Phys. Rev. Lett. 106, 065001 (2011)] and EAST tokamak [Xu et al., Phys. Rev. Lett 107, 125001 (2011)]. Turbulent bursts caused by the coupling of Kelvin-Helmholtz (KH) driven shear flows with trapped ion modes (TIMs) were investigated by means of reduced gyrokinetic simulations. It was found that ITG turbulence can be regulated by low-frequency meso-scale zonal flows driven by resonant collisionless trapped ion modes (CTIMs), through parametric-type scattering, a process in competition with the usual KH instability.

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

    NASA Astrophysics Data System (ADS)

    Grimm, R. E.

    2013-12-01

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

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

    NASA Technical Reports Server (NTRS)

    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.

  15. Oscillations of a vertically stratified dissipative atmosphere. II. Low frequency trapped modes

    NASA Astrophysics Data System (ADS)

    Rudenko, G. V.; Dmitrienko, I. S.

    2016-05-01

    Trapped atmosphere waves, such as IGW waveguide modes and Lamb modes, are described using dissipative solution above source (DSAS) (Dmitrienko and Rudenko, 2016). According to this description, the modes are disturbances penetrating without limit in the upper atmosphere and dissipating their energy throughout the atmosphere; leakage from a trapping region to the upper atmosphere is taken into consideration. The DSAS results are compared to those based on both accurate and WKB approximated dissipationless equations. It is shown that the spatial and frequency characteristics of modes in the upper atmosphere calculated by any of the methods are close to each other and are in good agreement with the observed characteristics of traveling ionospheric disturbances.

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

    NASA Astrophysics Data System (ADS)

    Miller, Robert E. (Robin)

    2005-04-01

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

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

    SciTech Connect

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

    2010-08-15

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

  18. In vivo Recordings from Low-Frequency Nucleus Laminaris in the Barn Owl.

    PubMed

    Palanca-Castan, Nicolas; Köppl, Christine

    2015-01-01

    Localization of sound sources relies on 2 main binaural cues: interaural time differences (ITD) and interaural level differences. ITD computing is first carried out in tonotopically organized areas of the brainstem nucleus laminaris (NL) in birds and the medial superior olive (MSO) in mammals. The specific way in which ITD are derived was long assumed to conform to a delay line model in which arrays of systematically arranged cells create a representation of auditory space, with different cells responding maximally to specific ITD. This model conforms in many details to the particular case of the high-frequency regions (above 3 kHz) in the barn owl NL. However, data from recent studies in mammals are not consistent with a delay line model. A new model has been suggested in which neurons are not topographically arranged with respect to ITD and coding occurs through assessment of the overall response of 2 large neuron populations – 1 in each brainstem hemisphere. Currently available data comprise mainly low-frequency (<1,500 Hz) recordings in the case of mammals and higher-frequency recordings in the case of birds. This makes it impossible to distinguish between group-related adaptations and frequency-related adaptations. Here we report the first comprehensive data set from low-frequency NL in the barn owl and compare it to data from other avian and mammalian studies. Our data are consistent with a delay line model, so differences between ITD processing systems are more likely to have originated through divergent evolution of different vertebrate groups. © 2015 S. Karger AG, Basel.

  19. Viscometer for low frequency, low shear rate measurements

    NASA Technical Reports Server (NTRS)

    Berg, R. F.; Moldover, M. R.

    1986-01-01

    A computer-controlled torsion-oscillator viscometer with low 0.5 Hz frequency and very low 0.05/s shear rate is designed to precisely study shear-sensitive fluids such as microemulsions, gels, polymer solutions and melts, colloidal solutions undergoing coagulation, and liquid mixtures near critical points. The viscosities are obtained from measurements of the logarithmic decrement of an underdriven oscillator. The viscometer is found to have a resolution of 0.2 percent when used with liquid samples and a resolution of 0.4 percent when used with a dense gaseous sample. The design is compatible with submillikelvin temperature control.

  20. The effect of islands on low frequency equatorial motions

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

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

  1. The Noisiness of Low Frequency Bands of Noise

    NASA Technical Reports Server (NTRS)

    Lawton, B. W.

    1975-01-01

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

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

    DOE PAGES

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

    2016-09-20

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

  3. Low Frequency NQR using Double Contact Cross-relaxation

    NASA Astrophysics Data System (ADS)

    Stephenson, David; Smith, John A. S.

    2000-02-01

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

  4. Method for imaging with low frequency electromagnetic fields

    DOEpatents

    Lee, Ki H.; Xie, Gan Q.

    1994-01-01

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

  5. Low frequency/high sensitivity triaxial monolithic sensor

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  7. Low frequency/high sensitivity triaxial monolithic inertial sensor

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

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

    PubMed

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

    2012-09-06

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

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

    NASA Astrophysics Data System (ADS)

    Gascon, Nicolas; Cappelli, Mark

    2001-10-01

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

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

    PubMed

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

    2011-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

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

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

    NASA Technical Reports Server (NTRS)

    Douglas, James N.; Smith, Harlan J.

    1988-01-01

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

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

    PubMed Central

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

    2017-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

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

  16. Robust Audio Watermarking by Using Low-Frequency Histogram

    NASA Astrophysics Data System (ADS)

    Xiang, Shijun

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

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

    NASA Astrophysics Data System (ADS)

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

    1984-12-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Kaye, H. M.

    1982-10-01

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

  20. Low-frequency switching in a transistor amplifier.

    PubMed

    Carroll, T L

    2003-04-01

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

  1. Modeling and investigative studies of Jovian low frequency emissions

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  2. High Sensitive Scintillation Observations At Very Low Frequencies

    NASA Astrophysics Data System (ADS)

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

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

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

    PubMed Central

    Oster, G; Jaffe, J S

    1980-01-01

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

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

    PubMed

    Bernau, A; Kruppa, G

    1981-02-01

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

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

    SciTech Connect

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

    2005-11-19

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

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

    NASA Astrophysics Data System (ADS)

    Chou, Yuan-Fang; Peng, Tzu-Huan

    2015-09-01

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

  7. Space applications of superconductivity - Low frequency superconducting sensors

    NASA Technical Reports Server (NTRS)

    Zimmerman, J. E.

    1980-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  9. Space applications of superconductivity - Low frequency superconducting sensors

    NASA Technical Reports Server (NTRS)

    Zimmerman, J. E.

    1980-01-01

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

  10. Method for imaging with low frequency electromagnetic fields

    DOEpatents

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

    1994-12-13

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

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

    SciTech Connect

    Tenforde, T.S.

    1991-07-01

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

  15. The spectral evolution of low-frequency variable radio sources

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

    The dynamic spectra of several low frequency extragalactic radio sources are presented. The observations were made at 318, 430, 606, 880, and 1400 MHz at several different radio observatories around the U.S. Two outbursts were observed in AO 0235 + 16 at 1.4 GHz, followed by a diminished variation at the lower frequencies. The dynamic frequencies of NRAO 140, PKS 1117 + 14, DA 406, CTA 102, and 3C 454.3 do not fit the same pattern. These radio sources displayed the following characteristics: (1) departure from straight or curved spectra at the frequencies of variation; (2) no obvious frequency drifting; and (3) negligible variation at 1.4 GHz. Possible explanations for this behavior are briefly discussed.

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

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

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

  17. A Low Frequency Study of Rotating Radio Transients

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    Rotating radio transients (RRATs) are neutron stars whose radio emission is typically detectable as sporadic emission (as opposed to periodic emission). This RRAT study will observe two RRATs (J0614-03, J0545-03) which have low to moderate dispersion measures and should be detectable with the MWA. Nominally, both RRATs should be within a single pointing, due to the increased field-of-view provided by the compact hex-tile core. Given our first concrete detection of the RRAT J2325-0530 with the recently implemented coherent beamformer, we expect that these sources will also be detectable. Observations below 300MHz of these RRATs have not been reported, thus the MWA provides an opportunity to perform the first low-frequency, high time resolution studies of these objects.

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

    NASA Astrophysics Data System (ADS)

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

    2006-09-01

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

  19. Masking in three pinnipeds: underwater, low-frequency critical ratios.

    PubMed

    Southall, B L; Schusterman, R J; Kastak, D

    2000-09-01

    Behavioral techniques were used to determine underwater masked hearing thresholds for a northern elephant seal (Mirounga angustirostris), a harbor seal (Phoca vitulina), and a California sea lion (Zalophus californianus). Octave-band white noise maskers were centered at five test frequencies ranging from 200 to 2500 Hz; a slightly wider noise band was used for testing at 100 Hz. Critical ratios were calculated at one masking noise level for each test frequency. Above 200 Hz, critical ratios increased with frequency. This pattern is similar to that observed in most animals tested, and indicates that these pinnipeds lack specializations for detecting low-frequency tonal sounds in noise. However, the individual pinnipeds in this study, particularly the northern elephant seal, detected signals at relatively low signal-to-noise ratios. These results provide a means of estimating zones of auditory masking for pinnipeds exposed to anthropogenic noise sources.

  20. Thermocapillary Flows with Low Frequency g-Jitter

    NASA Technical Reports Server (NTRS)

    Grassia, P.; Homsy, G. M.

    1999-01-01

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

  1. Imaging and data processing with the Low Frequency Space Array

    NASA Technical Reports Server (NTRS)

    Simon, R. S.; Spencer, J. H.; Dennison, B. K.; Weiler, K. W.; Johnston, K. J.; Kaiser, M. L.; Desch, M. D.; Fainberg, J.; Brown, L. W.; Stone, R. G.

    1987-01-01

    The Low Frequency Space Array (LFSA) is being designed to image the entire sky at extremely low radio frequencies with arcmin to subarcmin resolution. To accomplish this goal, data from LFSA will be continuously integrated for many months and then be used with aperture synthesis techniques to produce images. The three dimensional nature of LFSA and the effects of orbital geometry make LFSA a continuously evolving array which has an excellent synthesized point-response function. After transforming the data to produce an initial image, it is possible to remove low-level sidelobe responses remaining in the image and thereby produce a high dynamic-range image. Interference (both man-made and from solar-system objects) is a potential problem for LFSA, but appropriate data handling techniques are available which should eliminate any of its effects.

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

    PubMed

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

    2017-01-22

    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.

  3. Low-frequency macroscopic instabilities of fully ionized magnetoplasma

    NASA Technical Reports Server (NTRS)

    Rognlien, T. D.

    1972-01-01

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

  4. Dissipative elastic metamaterial with a low-frequency passband

    NASA Astrophysics Data System (ADS)

    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.

  5. Low-frequency microwave radiometer for N-ROSS

    NASA Technical Reports Server (NTRS)

    Hollinger, J. P.; Lo, R. C.

    1985-01-01

    The all weather, global determination of sea surface temperature (SST) has been identified as a requirement needed to support naval operations. The target SST accuracy is + or - 1.0 K with a surface resolution of 10 km. Investigations of the phenomenology and technology of remote passive microwave sensing of the ocean environment over the past decade have demonstrated that this objective is presently attainable. Preliminary specification and trade off studies were conducted to define the frequency, polarization, scan geometry, antenna size, and other esstential parameters of the low frequency microwave radiometer (LFMR). It will be a dual polarized, dual frequency system at 5.2 and 10.4 GHz using a 4.9 meter deployable mesh surface antenna. It is to be flown on the Navy-Remote Ocean Sensing System (N-ROSS) satellite scheduled to be launched in late 1988.

  6. Low-Frequency Radio Bursts and Space Weather

    NASA Technical Reports Server (NTRS)

    Gopalswamy, N.

    2016-01-01

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

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

    SciTech Connect

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

    2011-04-15

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

  8. Low frequency mechanical modes of viruses with atomic detail

    NASA Astrophysics Data System (ADS)

    Dykeman, Eric; Sankey, Otto

    2008-03-01

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

  9. Theory for low-frequency modulated Langmuir wave packets

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

  10. Characterization of microstructure with low frequency electromagnetic techniques

    SciTech Connect

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

    2014-02-18

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

  11. Low frequency azimuthal stability of the ionization region of the Hall thruster discharge. II. Global analysis

    SciTech Connect

    Escobar, D.; Ahedo, E.

    2015-10-15

    The linear stability of the Hall thruster discharge is analysed against axial-azimuthal perturbations in the low frequency range using a time-dependent 2D code of the discharge. This azimuthal stability analysis is spatially global, as opposed to the more common local stability analyses, already afforded previously (D. Escobar and E. Ahedo, Phys. Plasmas 21(4), 043505 (2014)). The study covers both axial and axial-azimuthal oscillations, known as breathing mode and spoke, respectively. The influence on the spoke instability of different operation parameters such as discharge voltage, mass flow, and thruster size is assessed by means of different parametric variations and compared against experimental results. Additionally, simplified models are used to unveil and characterize the mechanisms driving the spoke. The results indicate that the spoke is linked to azimuthal oscillations of the ionization process and to the Bohm condition in the transition to the anode sheath. Finally, results obtained from local and global stability analyses are compared in order to explain the discrepancies between both methods.

  12. Ultra-low frequency vertical vibration isolator based on LaCoste spring linkage

    NASA Astrophysics Data System (ADS)

    Li, G.; Hu, H.; Wu, K.; Wang, G.; Wang, L. J.

    2014-10-01

    For the applications in precision measurement such as absolute gravimeter, we have designed and built an ultra-low frequency vertical vibration isolator based on LaCoste spring linkage. In the system, an arm with test mass is suspended by a mechanical extension spring, and one end of the arm is connected to the frame with flexible pivots. The displacement of the arm is detected by an optical reflection method. With the displacement signal, a feedback control force is exerted on the arm to keep it at the balance position. This method can also correct the systematic drift caused by temperature change. In order to study the vibration isolation performance of the system, we analyze the dynamic characteristics of the spring linkage in the general case, and present key methods to adjust the natural oscillating period of the system. With careful adjustment, the system can achieve a steady oscillation with a natural period up to 32 s. This isolator has been tested based on the T-1 absolute gravimeter. A statistical uncertainty of 2 μGal has been achieved within a typical 12 h measurement. The experimental results verify that the isolator has significant vibration isolation performance, and it is very suitable for applications in high precision absolute gravity measurement.

  13. Ultra-low frequency vertical vibration isolator based on LaCoste spring linkage.

    PubMed

    Li, G; Hu, H; Wu, K; Wang, G; Wang, L J

    2014-10-01

    For the applications in precision measurement such as absolute gravimeter, we have designed and built an ultra-low frequency vertical vibration isolator based on LaCoste spring linkage. In the system, an arm with test mass is suspended by a mechanical extension spring, and one end of the arm is connected to the frame with flexible pivots. The displacement of the arm is detected by an optical reflection method. With the displacement signal, a feedback control force is exerted on the arm to keep it at the balance position. This method can also correct the systematic drift caused by temperature change. In order to study the vibration isolation performance of the system, we analyze the dynamic characteristics of the spring linkage in the general case, and present key methods to adjust the natural oscillating period of the system. With careful adjustment, the system can achieve a steady oscillation with a natural period up to 32 s. This isolator has been tested based on the T-1 absolute gravimeter. A statistical uncertainty of 2 μGal has been achieved within a typical 12 h measurement. The experimental results verify that the isolator has significant vibration isolation performance, and it is very suitable for applications in high precision absolute gravity measurement.

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

    NASA Astrophysics Data System (ADS)

    Saboonchi, Hossain; Ozevin, Didem

    2013-04-01

    In this paper, new MEMS Acoustic Emission (AE) sensors are introduced. The transduction principle of the sensors is capacitance due to gap change. The sensors are numerically modeled using COMSOL Multiphysics software in order to estimate the resonant frequencies and capacitance values, and manufactured using MetalMUMPS process. The process includes thick metal layer (20 μm) made of nickel for freely vibration layer and polysilicon layer as the stationary layer. The metal layer provides a relatively heavy mass so that the spring constant can be designed high for low frequency sensor designs in order to increase the collapse voltage level (proportional to the stiffness), which increases the sensor sensitivity. An insulator layer is deposited between stationary layer and freely vibration layer, which significantly reduces the potential of stiction as a failure mode. As conventional AE sensors made of piezoelectric materials cannot be designed for low frequencies (<300 kHz) with miniature size, the MEMS sensor frequencies are tuned to 50 kHz and 200 kHz. The each sensor contained several parallel-connected cells with an overall size of approximately 250μm × 500 μm. The electromechanical characterizations are performed using high precision impedance analyzer and compared with the numerical results, which indicate a good fit. The initial mechanical characterization tests in atmospheric pressure are conducted using pencil lead break simulations. The proper sensor design reduces the squeeze film damping so that it does not require any vacuum packaging. The MEMS sensor responses are compared with similar frequency piezoelectric AE sensors.

  15. Thermal analyses of in vitro low frequency sonophoresis.

    PubMed

    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

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

    USGS Publications Warehouse

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

    2008-01-01

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

  17. Compact Polarimetry in a Low Frequency Spaceborne Context

    NASA Technical Reports Server (NTRS)

    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

  18. Low frequency signal spectrum analysis for strong earthquakes

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  19. Compact Polarimetry in a Low Frequency Spaceborne Context

    NASA Technical Reports Server (NTRS)

    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

  20. Remote tracking of a magnetic receiver using low frequency beacons

    NASA Astrophysics Data System (ADS)

    Sheinker, Arie; Ginzburg, Boris; Salomonski, Nizan; Frumkis, Lev; Kaplan, Ben-Zion

    2014-10-01

    Low frequency magnetic fields feature high penetration ability, which allows communication, localization, and tracking in environments where radio or acoustic waves are blocked or distorted by multipath interferences. In the present work, we propose a method for tracking a magnetic receiver using beacons of low frequency magnetic field, where the receiver includes a tri-axial search-coil magnetometer. Measuring the beacons’ magnetic fields and calculating the total-field signals enables localization without restrictions on magnetometer orientation, allowing on-the-move tracking. The total-field signals are used by a global search method, e.g., simulated annealing (SA) algorithm, to localize the receiver. The magnetic field produced by each beacon has a dipole structure and is governed by the beacon’s position and magnetic moment. We have investigated two different methods for estimating beacons’ magnetic moments prior to localization. The first method requires directional measurements, whereas for the second method the total-field signal is used. Effectiveness of these methods has been proved in numerous field tests. In the present work, we introduce a method for tracking a moving receiver by successive localizations. Using previous localization as a starting point of the search method for the next localization can reduce execution time and chances for divergence. The proposed method has been tested using numerous computer simulations. Successful system operation has been verified in field conditions. The good tracking capability together with simple implementation makes the proposed method attractive for real-time, low power field applications, such as mobile robots navigation.

  1. Concealed weapons detection using low-frequency magnetic imaging

    NASA Astrophysics Data System (ADS)

    Zollars, Byron G.; Sallee, Bradley; Durrett, Michael G.; Cruce, Clay; Hallidy, William

    1997-02-01

    Military personnel, law-enforcement officers, and civilians face ever-increasing dangers from persons carrying concealed handguns and other weapons. In direct correspondence with this danger is a need for more sophisticated means of detecting concealed weapons. We have developed a novel concealed-weapons detector based on the principle of low- frequency magnetic imaging. The detector is configured as a portal, and constructs an image of electrically conductive objects transported through it with a potential spatial resolution of approximately 1 inch. Measurements on a breadboard version of the weapons detector have, to date, yielded a resolution of 2 inches. In operation, magnetic dipole radiation, emitted by transmitting antennas in the perimeter of the portal, is scattered from conductive objects and is picked up by receive antennas, also positioned around the portal. With sufficient measurements, each with a different geometry, a solution to the inverse scattering problem can be found. The result is an image of conductive objects in the detector. The detector is sensitive to all metals, semiconductors, and conductive composites. The measured conductivity image formed by the detector is combined with the video signal from a visible CCD camera to form a composite image of persons transiting the detector portal and the conductive objects they are carrying. Accompanying image recognition software could be used to determine the threat level of objects based upon shape, conductivity, and placement on the person of the carrier, and provide cueing, logging, or alarm functions to the operator if suspect weapons are identified. The low- power, low-frequency emissions from the detector are at levels considered safe to humans and medical implants..

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

    NASA Astrophysics Data System (ADS)

    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.

  3. Reduced event-related low frequency EEG activity in patients with early onset schizophrenia and their unaffected siblings.

    PubMed

    Simmonite, Molly; Bates, Alan Thomas; Groom, Madeleine; Hollis, Chris; Liddle, Peter Francis

    2015-04-30

    Low-frequency oscillations in the electroencephalogram (EEG) have been found to be abnormal in patients with schizophrenia. It is unclear, however, whether these abnormalities are related to severity of illness or are a marker for risk. This study investigated total and evoked theta and delta activity in schizophrenia patients, unaffected siblings, and healthy controls (HCs). EEG data were recorded whilst 24 individuals with schizophrenia, 26 unaffected siblings of individuals with schizophrenia and 26 healthy control participants completed a Go/No-Go task. Event-related total activity and evoked theta and delta activity were calculated for correct hits (CH), failed inhibitions (FI) and correct inhibitions (CI) trials. Patients displayed significantly less total delta, evoked delta, total theta and evoked theta activity when compared with healthy controls. Unaffected siblings displayed abnormalities of evoked delta, but other measures were similar to those in control participants. The findings of this study add to evidence that abnormal low-frequency EEG oscillations contribute to impairments in information processing seen in schizophrenia. These findings also suggest abnormal evoked delta oscillations are associated with an increased familial risk of developing the disorder. Copyright © 2015. Published by Elsevier Ireland Ltd.

  4. Low-frequency ultrasound attenuation in sodium chlorate crystals

    NASA Astrophysics Data System (ADS)

    Igisheva, AL; Soboleva, EG; Krit, TB

    2016-11-01

    The authors study reduction of longitudinal ultrasonic oscillations in sodium chlorate crystals within the temperature range of 78 - 525 K and relative amplitudes of oscillatory deformation of 10-7 - 10-5 according to the method of compound piezoelectric vibrator at the frequencies of ≈ 10 5 Hz.

  5. WIND OSCILLATIONS BETWEEN 30 AND 60 KILOMETERS OVER WHITE SANDS MISSILE RANGE, NEW MEXICO,

    DTIC Science & Technology

    STRATOSPHERE, WIND), OSCILLATION, ERRORS, SOUNDING ROCKETS, NEW MEXICO , DIURNAL VARIATIONS, MEASUREMENT, SOLAR RADIATION, MEASUREMENT, SOLAR RADIATION, OZONE, LOW FREQUENCY, ROTATION, HARMONIC ANALYSIS, RADIOSONDES.

  6. Low-Frequency Fluctuations of the Resting Brain: High Magnitude Does Not Equal High Reliability

    PubMed Central

    Jia, Wenbin; Liao, Wei; Li, Xun; Huang, Huiyuan; Yuan, Jianhua; Zang, Yu-Feng; Zhang, Han

    2015-01-01

    The amplitude of low-frequency fluctuation (ALFF) measures low-frequency oscillations of the blood-oxygen-level-dependent signal, characterizing local spontaneous activity during the resting state. ALFF is a commonly used measure for resting-state functional magnetic resonance imaging (rs-fMRI) in numerous basic and clinical neuroscience studies. Using a test-retest rs-fMRI dataset consisting of 21 healthy subjects and three repetitive scans, we found that several key brain regions with high ALFF intensities (or magnitude) had poor reliability. Such regions included the posterior cingulate cortex, the medial prefrontal cortex in the default mode network, parts of the right and left thalami, and the primary visual and motor cortices. The above finding was robust with regard to different sample sizes (number of subjects), different scanning parameters (repetition time) and variations of test-retest intervals (i.e., intra-scan, intra-session, and inter-session reliability), as well as with different scanners. Moreover, the qualitative, map-wise results were validated further with a region-of-interest-based quantitative analysis using “canonical” coordinates as reported previously. Therefore, we suggest that the reliability assessments be incorporated in future ALFF studies, especially for the brain regions with a large ALFF magnitude as listed in our paper. Splitting single data into several segments and assessing within-scan “test-retest” reliability is an acceptable alternative if no “real” test-retest datasets are available. Such evaluations might become more necessary if the data are collected with clinical scanners whose performance is not as good as those that are used for scientific research purposes and are better maintained because the lower signal-to-noise ratio may further dampen ALFF reliability. PMID:26053265

  7. Simulating 3D Spacecraft Constellations for Low Frequency Radio Imaging

    NASA Astrophysics Data System (ADS)

    Hegedus, A. M.; Amiri, N.; Lazio, J.; Belov, K.; Kasper, J. C.

    2016-12-01

    Constellations of small spacecraft could be used to realize a low-frequency phased array for either heliophysics or astrophysics observations. However, there are issues that arise with an orbiting array that do not occur on the ground, thus rendering much of the existing radio astronomy software inadequate for data analysis and simulation. In this work we address these issues and consider the performance of two constellation concepts. The first is a 32-spacecraft constellation for astrophysical observations, and the second is a 5-element concept for pointing to the location of radio emission from coronal mass ejections (CMEs). For the first, we fill the software gap by extending the APSYNSIM software to simulate the aperture synthesis for a radio interferometer in orbit. This involves using the dynamic baselines from the relative motion of the individual spacecraft as well as the capability to add galactic noise. The ability to simulate phase errors corresponding to positional uncertainty of the antennas was also added. The upgraded software was then used to model the imaging of a 32 spacecraft constellation that would orbit the moon to image radio galaxies like Cygnus A at .3-30 MHz. Animated images showing the improvement of the dirty image as the orbits progressed were made. RMSE plots that show how well the dirty image matches the input image as a function of integration time were made. For the second concept we performed radio interferometric simulations of the Sun Radio Interferometer Space Experiment (SunRISE) using the Common Astronomy Software Applications (CASA) package. SunRISE is a five spacecraft phased array that would orbit Earth to localize the low frequency radio emission from CMEs. This involved simulating the array in CASA, creating truth images for the CMEs over the entire frequency band of SunRISE, and observing them with the simulated array to see how well it could localize the true position of the CME. The results of our analysis show that we

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

    PubMed

    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.

  9. Low-Frequency Electromagnetic Backscatter from Buried Tunnels

    SciTech Connect

    Casey, K; Pao, H

    2006-06-21

    This progress report is submitted under a contract between the Special Project Office of DARPA and Lawrence Livermore National Laboratory. The Project Manager at DARPA is Dr. Michael Zatman. Our purpose under this contract is to investigate interactions between electromagnetic waves and a class of buried targets located in multilayered media with rough interfaces. In this report, we investigate three preliminary problems. In each case our specific goal is to understand various aspects of the electromagnetic wave interaction mechanisms with targets in layered media. The first problem, discussed in Section 2, is that of low-frequency electromagnetic backscattering from a tunnel that is cut into a lossy dielectric half-space. In this problem, the interface between the upper (free space) region and the lower (ground) region is smooth. The tunnel is assumed to be a cylindrical free-space region of infinite extent in its axial direction and with a diameter that is small in comparison to the free-space wavelength. Because its diameter is small, the tunnel can be modeled as a buried ''wire'' described by an equivalent impedance per unit length. In Section 3 we extend the analysis to include a statistically rough interface between the air and ground regions. The interface is modeled as a random-phase screen. Such a screen reduces the coherent power in a plane wave that is transmitted through it, scattering some of the total power into an incoherent field. Our analysis of this second problem quantifies the reduction in the coherent power backscattered from the buried tunnel that is caused by the roughness of the air-ground interface. The problem of low-frequency electromagnetic backscattering from two buried tunnels, parallel to each other but at different locations in the ground, is considered in Section 4. In this analysis, we wish to determine the conditions under which the presence of more than one tunnel can be detected via backscattering. Section 5 concludes the report

  10. Low-frequency modes and nonbarotropic effects in pseudo-Newtonian accretion disks

    NASA Technical Reports Server (NTRS)

    Ipser, James R.

    1994-01-01

    A recently developed formalism is used to reexamine the question of the existence of hydrodynamical modes that pulsate with very low frequencies in the inner regions of accretion disks. The formalism is valid in an exact sense for the adiabatic pulsations of rotating Newtonian fluids that are generally nonbarotropic (such as those with 'nonadiabatic temperature gradients,' for example), and hence its application in the present context represents an improvement over previous analyses that are more approximate. The formalism is applied to thin non-self-gravitating disks, with the gravitational potential of the central source modified in the usual way in order to simulate relativistic effects. In the barotropic limit, the analyses indicate that in many cases nearly Keplerian disks exhibit nonaxisymmetric modes of pulsation that are trapped in the inner disk regions, with pulsation periods much longer than the dynamical timescale. These results are similar to those of earlier calculations that assume disks pulsate without changing the temperature distribution. A method is developed for including lowest order nonbarotropic effects. Previous analyses have been incapable of accurately treating the nonbarotropic regime. The application of the present method to the low-frequency modes reveals that, due to unexpected cancellations among terms, the nonbarotropic correction to the pusation frequency omega is only of order tilde-omega(sub BV exp 2) omega, where tilde-omega(sub BV) is the appropriate dimensionless Brunt-Vaisala frequency. This correction is much smaller than the expected correction of order tilde-omega(sub BV) Omega, where Omega is the rotation angular velocity. The important conclusion drawn from this is that nonbarotropic corrections are generally small and hence that low-frequency modes persist into the nonbarotropic regime. For disk temperatures appropriate to X-ray emission, the adiabatic frequencies of trapped modes are of the same order as the frequencies

  11. Low-frequency modes and nonbarotropic effects in pseudo-Newtonian accretion disks

    NASA Technical Reports Server (NTRS)

    Ipser, James R.

    1994-01-01

    A recently developed formalism is used to reexamine the question of the existence of hydrodynamical modes that pulsate with very low frequencies in the inner regions of accretion disks. The formalism is valid in an exact sense for the adiabatic pulsations of rotating Newtonian fluids that are generally nonbarotropic (such as those with 'nonadiabatic temperature gradients,' for example), and hence its application in the present context represents an improvement over previous analyses that are more approximate. The formalism is applied to thin non-self-gravitating disks, with the gravitational potential of the central source modified in the usual way in order to simulate relativistic effects. In the barotropic limit, the analyses indicate that in many cases nearly Keplerian disks exhibit nonaxisymmetric modes of pulsation that are trapped in the inner disk regions, with pulsation periods much longer than the dynamical timescale. These results are similar to those of earlier calculations that assume disks pulsate without changing the temperature distribution. A method is developed for including lowest order nonbarotropic effects. Previous analyses have been incapable of accurately treating the nonbarotropic regime. The application of the present method to the low-frequency modes reveals that, due to unexpected cancellations among terms, the nonbarotropic correction to the pusation frequency omega is only of order tilde-omega(sub BV exp 2) omega, where tilde-omega(sub BV) is the appropriate dimensionless Brunt-Vaisala frequency. This correction is much smaller than the expected correction of order tilde-omega(sub BV) Omega, where Omega is the rotation angular velocity. The important conclusion drawn from this is that nonbarotropic corrections are generally small and hence that low-frequency modes persist into the nonbarotropic regime. For disk temperatures appropriate to X-ray emission, the adiabatic frequencies of trapped modes are of the same order as the frequencies

  12. Low-frequency low-field magnetic susceptibility of ferritin and hemosiderin.

    PubMed

    Allen, P D; St Pierre, T G; Chua-anusorn, W; Ström, V; Rao, K V

    2000-02-21

    Low-frequency low-field magnetic susceptibility measurements were made on four samples of mammalian tissue iron oxide deposits. The samples comprised: (1) horse spleen ferritin; (2) dugong liver hemosiderin; (3) thalassemic human spleen ferritin; and (4) crude thalassemic human spleen hemosiderin. These samples were chosen because Mössbauer spectroscopic measurements on the samples indicated that they exemplified the variation in magnetic and mineral structure found in mammalian tissue iron oxide deposits. The AC-magnetic susceptometry yielded information on the magnetization kinetics of the four samples indicating samples 1, 2, and 3 to be superparamagnetic with values of around 10(11) s(-1) for the pre-exponential frequency factor in the Néel-Arrhenius equation and values for characteristic magnetic anisotropy energy barriers in the range 250-400 K. Sample 4 was indicated to be paramagnetic at all temperatures above 1.3 K. The AC-magnetic susceptometry data also indicated a larger magnetic anisotropy energy distribution in the dugong liver sample compared with samples 1 and 3 in agreement with previous Mössbauer spectroscopic data on these samples. At temperatures below 200 K, samples 1-3 exhibited Curie-Weiss law behavior, indicating weak particle-particle interactions tending to favor antiparallel alignment of the particle magnetic moments. These interactions were strongest for the dugong liver hemosiderin, possibly reflecting the smaller separation between mineral particles in this sample. This is the first magnetic susceptometry study of hemosiderin iron deposits and demonstrates that the AC-magnetic susceptometry technique is a fast and informative method of studying such tissue iron oxide deposits.

  13. The functional spectrum of low-frequency coding variation.

    PubMed

    Marth, Gabor T; Yu, Fuli; Indap, Amit R; Garimella, Kiran; Gravel, Simon; Leong, Wen Fung; Tyler-Smith, Chris; Bainbridge, Matthew; Blackwell, Tom; Zheng-Bradley, Xiangqun; Chen, Yuan; Challis, Danny; Clarke, Laura; Ball, Edward V; Cibulskis, Kristian; Cooper, David N; Fulton, Bob; Hartl, Chris; Koboldt, Dan; Muzny, Donna; Smith, Richard; Sougnez, Carrie; Stewart, Chip; Ward, Alistair; Yu, Jin; Xue, Yali; Altshuler, David; Bustamante, Carlos D; Clark, Andrew G; Daly, Mark; DePristo, Mark; Flicek, Paul; Gabriel, Stacey; Mardis, Elaine; Palotie, Aarno; Gibbs, Richard

    2011-09-14

    Rare coding variants constitute an important class of human genetic variation, but are underrepresented in current databases that are based on small population samples. Recent studies show that variants altering amino acid sequence and protein function are enriched at low variant allele frequency, 2 to 5%, but because of insufficient sample size it is not clear if the same trend holds for rare variants below 1% allele frequency. The 1000 Genomes Exon Pilot Project has collected deep-coverage exon-capture data in roughly 1,000 human genes, for nearly 700 samples. Although medical whole-exome projects are currently afoot, this is still the deepest reported sampling of a large number of human genes with next-generation technologies. According to the goals of the 1000 Genomes Project, we created effective informatics pipelines to process and analyze the data, and discovered 12,758 exonic SNPs, 70% of them novel, and 74% below 1% allele frequency in the seven population samples we examined. Our analysis confirms that coding variants below 1% allele frequency show increased population-specificity and are enriched for functional variants. This study represents a large step toward detecting and interpreting low frequency coding variation, clearly lays out technical steps for effective analysis of DNA capture data, and articulates functional and population properties of this important class of genetic variation.

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

    SciTech Connect

    Chang, J.W.

    1991-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

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

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

    PubMed

    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.

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

    SciTech Connect

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

    1992-05-01

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

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

    SciTech Connect

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

    1992-01-01

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

  19. Bioparticles assembled using low frequency vibration immune to evacuation drifts.

    PubMed

    Shao, Fenfen; Whitehill, James David; Ng, Tuck Wah

    2012-08-01

    The use of low frequency vibration on suspensions of glass beads in a droplet has been shown to develop a strong degree of patterning (to a ring) due to the manner with which the surface waves are modified. Functionalized glass beads that serve as bioparticles permit for sensitive readings when concentrated at specific locations. However, a time controlled exposure with analytes is desirable. The replacement of the liquid medium with analyte through extraction is needed to conserve time. Nevertheless, we show here that extraction with a porous media, which is simple and useable in the field, will strongly displace the patterned beads. The liquid removal was found to be dependent on two mechanisms that affect the shape of the droplet, one of contact hysteresis due to the outer edge pinning, and the other of liquid being drawn into the porous media. From this, we developed and demonstrated a modified well structure that prevented micro-bead displacement during evacuation. An added strong advantage with this approach lies with its ability to require only analytes to be dispensed at the location of aggregated particles, which minimizes analyte usage. This was analytically established here.

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

    PubMed

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

    2015-12-01

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