Sample records for high frequency oscillation

  1. High-frequency resonant-tunneling oscillators

    NASA Technical Reports Server (NTRS)

    Brown, E. R.; Parker, C. D.; Calawa, A. R.; Manfra, M. J.; Chen, C. L.

    1991-01-01

    Advances in high-frequency resonant-tunneling-diode (RTD) oscillators are described. Oscillations up to a frequency of 420 GHz have been achieved in the GaAs/AlAs system. Recent results obtained with In0.53Ga0.47As/AlAs and InAs/AlSb RTDs show a greatly increased power density and indicate the potential for fundamental oscillations up to about 1 THz. These results are consistent with a lumped-element equivalent circuit model of the RTD. The model shows that the maximum oscillation frequency of the GaAs/AlAs RTDs is limited primarily by series resistance, and that the power density is limited by low peak-to-valley current ratio.

  2. High frequency pressure oscillator for microcryocoolers.

    PubMed

    Vanapalli, S; ter Brake, H J M; Jansen, H V; Zhao, Y; Holland, H J; Burger, J F; Elwenspoek, M C

    2008-04-01

    Microminiature pulse tube cryocoolers should operate at a frequency of an order higher than the conventional macro ones because the pulse tube cryocooler operating frequency scales inversely with the square of the pulse tube diameter. In this paper, the design and experiments of a high frequency pressure oscillator is presented with the aim to power a micropulse tube cryocooler operating between 300 and 80 K, delivering a cooling power of 10 mW. Piezoelectric actuators operate efficiently at high frequencies and have high power density making them good candidates as drivers for high frequency pressure oscillator. The pressure oscillator described in this work consists of a membrane driven by a piezoelectric actuator. A pressure ratio of about 1.11 was achieved with a filling pressure of 2.5 MPa and compression volume of about 22.6 mm(3) when operating the actuator with a peak-to-peak sinusoidal voltage of 100 V at a frequency of 1 kHz. The electrical power input was 2.73 W. The high pressure ratio and low electrical input power at high frequencies would herald development of microminiature cryocoolers.

  3. High frequency pressure oscillator for microcryocoolers

    NASA Astrophysics Data System (ADS)

    Vanapalli, S.; ter Brake, H. J. M.; Jansen, H. V.; Zhao, Y.; Holland, H. J.; Burger, J. F.; Elwenspoek, M. C.

    2008-04-01

    Microminiature pulse tube cryocoolers should operate at a frequency of an order higher than the conventional macro ones because the pulse tube cryocooler operating frequency scales inversely with the square of the pulse tube diameter. In this paper, the design and experiments of a high frequency pressure oscillator is presented with the aim to power a micropulse tube cryocooler operating between 300 and 80K, delivering a cooling power of 10mW. Piezoelectric actuators operate efficiently at high frequencies and have high power density making them good candidates as drivers for high frequency pressure oscillator. The pressure oscillator described in this work consists of a membrane driven by a piezoelectric actuator. A pressure ratio of about 1.11 was achieved with a filling pressure of 2.5MPa and compression volume of about 22.6mm3 when operating the actuator with a peak-to-peak sinusoidal voltage of 100V at a frequency of 1kHz. The electrical power input was 2.73W. The high pressure ratio and low electrical input power at high frequencies would herald development of microminiature cryocoolers.

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

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Liqiu, Wei, E-mail: weiliqiu@gmail.com, E-mail: weiliqiu@hit.edu.cn; Liang, Han; Ziyi, Yang

    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.

  5. High-frequency gamma oscillations coexist with low-frequency gamma oscillations in the rat visual cortex in vitro.

    PubMed

    Oke, Olaleke O; Magony, Andor; Anver, Himashi; Ward, Peter D; Jiruska, Premysl; Jefferys, John G R; Vreugdenhil, Martin

    2010-04-01

    Synchronization of neuronal activity in the visual cortex at low (30-70 Hz) and high gamma band frequencies (> 70 Hz) has been associated with distinct visual processes, but mechanisms underlying high-frequency gamma oscillations remain unknown. In rat visual cortex slices, kainate and carbachol induce high-frequency gamma oscillations (fast-gamma; peak frequency approximately 80 Hz at 37 degrees C) that can coexist with low-frequency gamma oscillations (slow-gamma; peak frequency approximately 50 Hz at 37 degrees C) in the same column. Current-source density analysis showed that fast-gamma was associated with rhythmic current sink-source sequences in layer III and slow-gamma with rhythmic current sink-source sequences in layer V. Fast-gamma and slow-gamma were not phase-locked. Slow-gamma power fluctuations were unrelated to fast-gamma power fluctuations, but were modulated by the phase of theta (3-8 Hz) oscillations generated in the deep layers. Fast-gamma was spatially less coherent than slow-gamma. Fast-gamma and slow-gamma were dependent on gamma-aminobutyric acid (GABA)(A) receptors, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and gap-junctions, their frequencies were reduced by thiopental and were weakly dependent on cycle amplitude. Fast-gamma and slow-gamma power were differentially modulated by thiopental and adenosine A(1) receptor blockade, and their frequencies were differentially modulated by N-methyl-D-aspartate (NMDA) receptors, GluK1 subunit-containing receptors and persistent sodium currents. Our data indicate that fast-gamma and slow-gamma both depend on and are paced by recurrent inhibition, but have distinct pharmacological modulation profiles. The independent co-existence of fast-gamma and slow-gamma allows parallel processing of distinct aspects of vision and visual perception. The visual cortex slice provides a novel in vitro model to study cortical high-frequency gamma oscillations.

  6. Data mining neocortical high-frequency oscillations in epilepsy and controls

    PubMed Central

    Stead, Matt; Krieger, Abba; Stacey, William; Maus, Douglas; Marsh, Eric; Viventi, Jonathan; Lee, Kendall H.; Marsh, Richard; Litt, Brian; Worrell, Gregory A.

    2011-01-01

    Transient high-frequency (100–500 Hz) oscillations of the local field potential have been studied extensively in human mesial temporal lobe. Previous studies report that both ripple (100–250 Hz) and fast ripple (250–500 Hz) oscillations are increased in the seizure-onset zone of patients with mesial temporal lobe epilepsy. Comparatively little is known, however, about their spatial distribution with respect to seizure-onset zone in neocortical epilepsy, or their prevalence in normal brain. We present a quantitative analysis of high-frequency oscillations and their rates of occurrence in a group of nine patients with neocortical epilepsy and two control patients with no history of seizures. Oscillations were automatically detected and classified using an unsupervised approach in a data set of unprecedented volume in epilepsy research, over 12 terabytes of continuous long-term micro- and macro-electrode intracranial recordings, without human preprocessing, enabling selection-bias-free estimates of oscillation rates. There are three main results: (i) a cluster of ripple frequency oscillations with median spectral centroid = 137 Hz is increased in the seizure-onset zone more frequently than a cluster of fast ripple frequency oscillations (median spectral centroid = 305 Hz); (ii) we found no difference in the rates of high frequency oscillations in control neocortex and the non-seizure-onset zone neocortex of patients with epilepsy, despite the possibility of different underlying mechanisms of generation; and (iii) while previous studies have demonstrated that oscillations recorded by parenchyma-penetrating micro-electrodes have higher peak 100–500 Hz frequencies than penetrating macro-electrodes, this was not found for the epipial electrodes used here to record from the neocortical surface. We conclude that the relative rate of ripple frequency oscillations is a potential biomarker for epileptic neocortex, but that larger prospective studies

  7. Data mining neocortical high-frequency oscillations in epilepsy and controls.

    PubMed

    Blanco, Justin A; Stead, Matt; Krieger, Abba; Stacey, William; Maus, Douglas; Marsh, Eric; Viventi, Jonathan; Lee, Kendall H; Marsh, Richard; Litt, Brian; Worrell, Gregory A

    2011-10-01

    Transient high-frequency (100-500 Hz) oscillations of the local field potential have been studied extensively in human mesial temporal lobe. Previous studies report that both ripple (100-250 Hz) and fast ripple (250-500 Hz) oscillations are increased in the seizure-onset zone of patients with mesial temporal lobe epilepsy. Comparatively little is known, however, about their spatial distribution with respect to seizure-onset zone in neocortical epilepsy, or their prevalence in normal brain. We present a quantitative analysis of high-frequency oscillations and their rates of occurrence in a group of nine patients with neocortical epilepsy and two control patients with no history of seizures. Oscillations were automatically detected and classified using an unsupervised approach in a data set of unprecedented volume in epilepsy research, over 12 terabytes of continuous long-term micro- and macro-electrode intracranial recordings, without human preprocessing, enabling selection-bias-free estimates of oscillation rates. There are three main results: (i) a cluster of ripple frequency oscillations with median spectral centroid = 137 Hz is increased in the seizure-onset zone more frequently than a cluster of fast ripple frequency oscillations (median spectral centroid = 305 Hz); (ii) we found no difference in the rates of high frequency oscillations in control neocortex and the non-seizure-onset zone neocortex of patients with epilepsy, despite the possibility of different underlying mechanisms of generation; and (iii) while previous studies have demonstrated that oscillations recorded by parenchyma-penetrating micro-electrodes have higher peak 100-500 Hz frequencies than penetrating macro-electrodes, this was not found for the epipial electrodes used here to record from the neocortical surface. We conclude that the relative rate of ripple frequency oscillations is a potential biomarker for epileptic neocortex, but that larger prospective studies correlating high-frequency

  8. High frequency inductive lamp and power oscillator

    DOEpatents

    MacLennan, Donald A.; Dymond, Jr., Lauren E.; Gitsevich, Aleksandr; Grimm, William G.; Kipling, Kent; Kirkpatrick, Douglas A.; Ola, Samuel A.; Simpson, James E.; Trimble, William C.; Tsai, Peter; Turner, Brian P.

    2001-01-01

    A high frequency inductively coupled electrodeless lamp includes an excitation coil with an effective electrical length which is less than one half wavelength of a driving frequency applied thereto, preferably much less. The driving frequency may be greater than 100 MHz and is preferably as high as 915 MHz. Preferably, the excitation coil is configured as a non-helical, semi-cylindrical conductive surface having less than one turn, in the general shape of a wedding ring. At high frequencies, the current in the coil forms two loops which are spaced apart and parallel to each other. Configured appropriately, the coil approximates a Helmholtz configuration. The lamp preferably utilizes an bulb encased in a reflective ceramic cup with a pre-formed aperture defined therethrough. The ceramic cup may include structural features to aid in alignment and I or a flanged face to aid in thermal management. The lamp head is preferably an integrated lamp head comprising a metal matrix composite surrounding an insulating ceramic with the excitation integrally formed on the ceramic. A novel solid-state oscillator preferably provides RF power to the lamp. The oscillator is a single active element device capable of providing over 70 watts of power at over 70% efficiency. Various control circuits may be employed to adjust the driving frequency of the oscillator.

  9. High frequency inductive lamp and power oscillator

    DOEpatents

    MacLennan, Donald A.; Turner, Brian P.; Dolan, James T.; Kirkpatrick, Douglas A.; Leng, Yongzhang

    2000-01-01

    A high frequency inductively coupled electrodeless lamp includes an excitation coil with an effective electrical length which is less than one half wavelength of a driving frequency applied thereto, preferably much less. The driving frequency may be greater than 100 MHz and is preferably as high as 915 MHz. Preferably, the excitation coil is configured as a non-helical, semi-cylindrical conductive surface having less than one turn, in the general shape of a wedding ring. At high frequencies, the current in the coil forms two loops which are spaced apart and parallel to each other. Configured appropriately, the coil approximates a Helmholtz configuration. The lamp preferably utilizes an bulb encased in a reflective ceramic cup with a pre-formed aperture defined therethrough. The ceramic cup may include structural features to aid in alignment and/or a flanged face to aid in thermal management. The lamp head is preferably an integrated lamp head comprising a metal matrix composite surrounding an insulating ceramic with the excitation integrally formed on the ceramic. A novel solid-state oscillator preferably provides RF power to the lamp. The oscillator is a single active element device capable of providing over 70 watts of power at over 70% efficiency. Various control circuits may be employed to match the driving frequency of the oscillator to a plurality of tuning states of the lamp.

  10. Coexistence of gamma and high-frequency oscillations in rat medial entorhinal cortex in vitro

    PubMed Central

    Cunningham, M O; Halliday, David M; Davies, Ceri H; Traub, Roger D; Buhl, Eberhard H; Whittington, Miles A

    2004-01-01

    High frequency oscillations (> 80–90 Hz) occur in neocortex and hippocampus in vivo where they are associated with specific behavioural states and more classical EEG frequency bands. In the hippocampus in vitro these oscillations can occur in the absence of pyramidal neuronal somatodendritic compartments and are temporally correlated with on-going, persistent gamma frequency oscillations. Their occurrence in the hippocampus is dependent on gap-junctional communication and it has been suggested that these high frequency oscillations originate as collective behaviour in populations of electrically coupled principal cell axonal compartments. Here we demonstrate that the superficial layers of medial entorhinal cortex can also generate high frequency oscillations associated with gamma rhythms. During persistent gamma frequency oscillations high frequency oscillations occur with a high bispectral coherence with the field gamma activity. Bursts of high frequency oscillations are temporally correlated with both the onset of compound excitatory postsynaptic potentials in fast-spiking interneurones and spikelet potentials in both pyramidal and stellate principal neurones. Both the gamma frequency and high frequency oscillations were attenuated by the gap junction blocker carbenoxolone. These data suggest that high frequency oscillations may represent the substrate for phasic drive to interneurones during persistent gamma oscillations in the medial entorhinal cortex. PMID:15254156

  11. Parkinsonian Rest Tremor Is Associated With Modulations of Subthalamic High-Frequency Oscillations.

    PubMed

    Hirschmann, Jan; Butz, Markus; Hartmann, Christian J; Hoogenboom, Nienke; Özkurt, Tolga E; Vesper, Jan; Wojtecki, Lars; Schnitzler, Alfons

    2016-10-01

    High frequency oscillations (>200 Hz) have been observed in the basal ganglia of PD patients and were shown to be modulated by the administration of levodopa and voluntary movement. The objective of this study was to test whether the power of high-frequency oscillations in the STN is associated with spontaneous manifestation of parkinsonian rest tremor. The electromyogram of both forearms and local field potentials from the STN were recorded in 11 PD patients (10 men, age 58 [9.4] years, disease duration 9.2 [6.3] years). Patients were recorded at rest and while performing repetitive hand movements before and after levodopa intake. High-frequency oscillation power was compared across epochs containing rest tremor, tremor-free rest, or voluntary movement and related to the tremor cycle. We observed prominent slow (200-300 Hz) and fast (300-400 Hz) high-frequency oscillations. The ratio between slow and fast high-frequency oscillation power increased when tremor became manifest. This increase was consistent across nuclei (94%) and occurred in medication ON and OFF. The ratio outperformed other potential markers of tremor, such as power at individual tremor frequency, beta power, or low gamma power. For voluntary movement, we did not observe a significant difference when compared with rest or rest tremor. Finally, rhythmic modulations of high-frequency oscillation power occurred within the tremor cycle. Subthalamic high-frequency oscillation power is closely linked to the occurrence of parkinsonian rest tremor. The balance between slow and fast high-frequency oscillation power combines information on motor and medication state. © 2016 International Parkinson and Movement Disorder Society. © 2016 International Parkinson and Movement Disorder Society.

  12. Sustainable limitation of high-frequency oscillations of elevator cabin

    NASA Astrophysics Data System (ADS)

    Kaytukov, Batraz

    2017-10-01

    In this paper, a problem of sustainable limitation of vertical high-frequency oscillations of elevator cabin in buildings with various number of storeys is considered. To solve this problem, dynamic model of the elevator movement was developed. In the course of analytical and experimental studies, the main cause for emergence of undesirable high-frequency oscillations of a cabin was defined. The amplification factor which is the function of λ and length of cable was determined. The λ parameter is variable, and length of the cable changes depending on length passed by the cabin and is an amplification factor argument. For sustainable limitation of oscillations, use of dynamic dumper of lever type is proposed. Adjustment of the dumper natural vibration frequency in such a way that it is equal to the excitation frequency allows limiting of oscillations of the cabin and the elevator machine to reasonable value irrespective to position of a moving cabin in the shaft. Using dependences and plots which were obtained in the course of scientific analysis and experimental studies, reasonability of dumper application for sustainable limitation of high-frequency influence of the elevator machine on the base and obtaining of solutions of inertial forces equilibration problem was proved.

  13. Analysis of high-frequency oscillations in mutually-coupled nano-lasers.

    PubMed

    Han, Hong; Shore, K Alan

    2018-04-16

    The dynamics of mutually coupled nano-lasers has been analyzed using rate equations which include the Purcell cavity-enhanced spontaneous emission factor F and the spontaneous emission coupling factor β. It is shown that in the mutually-coupled system, small-amplitude oscillations with frequencies of order 100 GHz are generated and are maintained with remarkable stability. The appearance of such high-frequency oscillations is associated with the effective reduction of the carrier lifetime for larger values of the Purcell factor, F, and spontaneous coupling factor, β. In mutually-coupled nano-lasers the oscillation frequency changes linearly with the frequency detuning between the lasers. For non-identical bias currents, the oscillation frequency of mutually-coupled nano-lasers also increases with bias current. The stability of the oscillations which appear in mutually coupled nano-lasers offers opportunities for their practical applications and notably in photonic integrated circuits.

  14. High frequency nanotube oscillator

    DOEpatents

    Peng, Haibing [Houston, TX; Zettl, Alexander K [Kensington, TX

    2012-02-21

    A tunable nanostructure such as a nanotube is used to make an electromechanical oscillator. The mechanically oscillating nanotube can be provided with inertial clamps in the form of metal beads. The metal beads serve to clamp the nanotube so that the fundamental resonance frequency is in the microwave range, i.e., greater than at least 1 GHz, and up to 4 GHz and beyond. An electric current can be run through the nanotube to cause the metal beads to move along the nanotube and changing the length of the intervening nanotube segments. The oscillator can operate at ambient temperature and in air without significant loss of resonance quality. The nanotube is can be fabricated in a semiconductor style process and the device can be provided with source, drain, and gate electrodes, which may be connected to appropriate circuitry for driving and measuring the oscillation. Novel driving and measuring circuits are also disclosed.

  15. Ictal high frequency oscillations distinguish two types of seizure territories in humans

    PubMed Central

    Weiss, Shennan A.; Banks, Garrett P.; McKhann, Guy M.; Goodman, Robert R.; Emerson, Ronald G.; Trevelyan, Andrew J.

    2013-01-01

    High frequency oscillations have been proposed as a clinically useful biomarker of seizure generating sites. We used a unique set of human microelectrode array recordings (four patients, 10 seizures), in which propagating seizure wavefronts could be readily identified, to investigate the basis of ictal high frequency activity at the cortical (subdural) surface. Sustained, repetitive transient increases in high gamma (80–150 Hz) amplitude, phase-locked to the low-frequency (1–25 Hz) ictal rhythm, correlated with strong multi-unit firing bursts synchronized across the core territory of the seizure. These repetitive high frequency oscillations were seen in recordings from subdural electrodes adjacent to the microelectrode array several seconds after seizure onset, following ictal wavefront passage. Conversely, microelectrode recordings demonstrating only low-level, heterogeneous neural firing correlated with a lack of high frequency oscillations in adjacent subdural recording sites, despite the presence of a strong low-frequency signature. Previously, we reported that this pattern indicates a failure of the seizure to invade the area, because of a feedforward inhibitory veto mechanism. Because multi-unit firing rate and high gamma amplitude are closely related, high frequency oscillations can be used as a surrogate marker to distinguish the core seizure territory from the surrounding penumbra. We developed an efficient measure to detect delayed-onset, sustained ictal high frequency oscillations based on cross-frequency coupling between high gamma amplitude and the low-frequency (1–25 Hz) ictal rhythm. When applied to the broader subdural recording, this measure consistently predicted the timing or failure of ictal invasion, and revealed a surprisingly small and slowly spreading seizure core surrounded by a far larger penumbral territory. Our findings thus establish an underlying neural mechanism for delayed-onset, sustained ictal high frequency oscillations, and

  16. High-frequency neural oscillations and visual processing deficits in schizophrenia

    PubMed Central

    Tan, Heng-Ru May; Lana, Luiz; Uhlhaas, Peter J.

    2013-01-01

    Visual information is fundamental to how we understand our environment, make predictions, and interact with others. Recent research has underscored the importance of visuo-perceptual dysfunctions for cognitive deficits and pathophysiological processes in schizophrenia. In the current paper, we review evidence for the relevance of high frequency (beta/gamma) oscillations towards visuo-perceptual dysfunctions in schizophrenia. In the first part of the paper, we examine the relationship between beta/gamma band oscillations and visual processing during normal brain functioning. We then summarize EEG/MEG-studies which demonstrate reduced amplitude and synchrony of high-frequency activity during visual stimulation in schizophrenia. In the final part of the paper, we identify neurobiological correlates as well as offer perspectives for future research to stimulate further inquiry into the role of high-frequency oscillations in visual processing impairments in the disorder. PMID:24130535

  17. A Resonantly Excited Disk-Oscillation Model of High-Frequency QPOs of Microquasars

    NASA Astrophysics Data System (ADS)

    Kato, Shoji

    2012-12-01

    A possible model of twin high-frequency QPOs (HF QPOs) of microquasars is examined. The disk is assumed to have global magnetic fields and to be deformed with a two-armed pattern. In this deformed disk, a set of a two-armed (m = 2) vertical p-mode oscillation and an axisymmetric (m = 0) g-mode oscillation is considered. They resonantly interact through the disk deformation when their frequencies are the same. This resonant interaction amplifies the set of the above oscillations in the case where these two oscillations have wave energies of opposite signs. These oscillations are assumed to be excited most efficiently in the case where the radial group velocities of these two waves vanish at the same place. The above set of oscillations is not unique, depending on the node number n, of oscillations in the vertical direction. We consider that the basic two sets of oscillations correspond to the twin QPOs. The frequencies of these oscillations depend on the disk parameters, such as the strength of the magnetic fields. For observational mass ranges of GRS 1915+ 105, GRO J1655-40, XTE J1550-564, and HEAO H1743-322, the spins of these sources are estimated. High spins of these sources can be described if the disks have weak poloidal magnetic fields as well as toroidal magnetic fields of moderate strength. In this model the 3:2 frequency ratio of high-frequency QPOs is not related to their excitation, but occurs by chance.

  18. High spectral purity Kerr frequency comb radio frequency photonic oscillator

    PubMed Central

    Liang, W.; Eliyahu, D.; Ilchenko, V. S.; Savchenkov, A. A.; Matsko, A. B.; Seidel, D.; Maleki, L.

    2015-01-01

    Femtosecond laser-based generation of radio frequency signals has produced astonishing improvements in achievable spectral purity, one of the basic features characterizing the performance of an radio frequency oscillator. Kerr frequency combs hold promise for transforming these lab-scale oscillators to chip-scale level. In this work we demonstrate a miniature 10 GHz radio frequency photonic oscillator characterized with phase noise better than −60 dBc Hz−1 at 10 Hz, −90 dBc Hz−1 at 100 Hz and −170 dBc Hz−1 at 10 MHz. The frequency stability of this device, as represented by Allan deviation measurements, is at the level of 10−10 at 1–100 s integration time—orders of magnitude better than existing radio frequency photonic devices of similar size, weight and power consumption. PMID:26260955

  19. High frequency oscillations are associated with cognitive processing in human recognition memory.

    PubMed

    Kucewicz, Michal T; Cimbalnik, Jan; Matsumoto, Joseph Y; Brinkmann, Benjamin H; Bower, Mark R; Vasoli, Vincent; Sulc, Vlastimil; Meyer, Fred; Marsh, W R; Stead, S M; Worrell, Gregory A

    2014-08-01

    High frequency oscillations are associated with normal brain function, but also increasingly recognized as potential biomarkers of the epileptogenic brain. Their role in human cognition has been predominantly studied in classical gamma frequencies (30-100 Hz), which reflect neuronal network coordination involved in attention, learning and memory. Invasive brain recordings in animals and humans demonstrate that physiological oscillations extend beyond the gamma frequency range, but their function in human cognitive processing has not been fully elucidated. Here we investigate high frequency oscillations spanning the high gamma (50-125 Hz), ripple (125-250 Hz) and fast ripple (250-500 Hz) frequency bands using intracranial recordings from 12 patients (five males and seven females, age 21-63 years) during memory encoding and recall of a series of affectively charged images. Presentation of the images induced high frequency oscillations in all three studied bands within the primary visual, limbic and higher order cortical regions in a sequence consistent with the visual processing stream. These induced oscillations were detected on individual electrodes localized in the amygdala, hippocampus and specific neocortical areas, revealing discrete oscillations of characteristic frequency, duration and latency from image presentation. Memory encoding and recall significantly modulated the number of induced high gamma, ripple and fast ripple detections in the studied structures, which was greater in the primary sensory areas during the encoding (Wilcoxon rank sum test, P = 0.002) and in the higher-order cortical association areas during the recall (Wilcoxon rank sum test, P = 0.001) of memorized images. Furthermore, the induced high gamma, ripple and fast ripple responses discriminated the encoded and the affectively charged images. In summary, our results show that high frequency oscillations, spanning a wide range of frequencies, are associated with memory processing and

  20. Graphene-hexagonal boron nitride resonant tunneling diodes as high-frequency oscillators

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Gaskell, J.; Fromhold, T. M.; Greenaway, M. T.

    We assess the potential of two-terminal graphene-hexagonal boron nitride-graphene resonant tunneling diodes as high-frequency oscillators, using self-consistent quantum transport and electrostatic simulations to determine the time-dependent response of the diodes in a resonant circuit. We quantify how the frequency and power of the current oscillations depend on the diode and circuit parameters including the doping of the graphene electrodes, device geometry, alignment of the graphene lattices, and the circuit impedances. Our results indicate that current oscillations with frequencies of up to several hundred GHz should be achievable.

  1. High frequency oscillations in brain hemodynamic response

    NASA Astrophysics Data System (ADS)

    Akin, Ata; Bolay, Hayrunnisa

    2007-07-01

    Tight autoregulation of vessel tone guarantees proper delivery of nutrients to the tissues. This regulation is maintained at a more delicate level in the brain since any decrease in the supply of glucose and oxygen to neuronal tissues might lead to unrecoverable injury. Functional near infrared spectroscopy has been proposed as a new tool to monitor the cerebrovascular response during cognitive activity. We have observed that during a Stroop task three distinct oscillatory patterns govern the control of the cerebrovascular reactivity: very low frequency (0.02-0.05 Hz), low frequency (0.08-0.12 Hz) and high frequency (0.12-0.18 Hz). High frequency oscillations have been shown to be related to stress level of the subjects. Our findings indicate that as the stress level is increased so does the energy of the high frequency component indicating a higher stimulation from the autonomic nervous system.

  2. Photoinduced High-Frequency Charge Oscillations in Dimerized Systems

    NASA Astrophysics Data System (ADS)

    Yonemitsu, Kenji

    2018-04-01

    Photoinduced charge dynamics in dimerized systems is studied on the basis of the exact diagonalization method and the time-dependent Schrödinger equation for a one-dimensional spinless-fermion model at half filling and a two-dimensional model for κ-(bis[ethylenedithio]tetrathiafulvalene)2X [κ-(BEDT-TTF)2X] at three-quarter filling. After the application of a one-cycle pulse of a specifically polarized electric field, the charge densities at half of the sites of the system oscillate in the same phase and those at the other half oscillate in the opposite phase. For weak fields, the Fourier transform of the time profile of the charge density at any site after photoexcitation has peaks for finite-sized systems that correspond to those of the steady-state optical conductivity spectrum. For strong fields, these peaks are suppressed and a new peak appears on the high-energy side, that is, the charge densities mainly oscillate with a single frequency, although the oscillation is eventually damped. In the two-dimensional case without intersite repulsion and in the one-dimensional case, this frequency corresponds to charge-transfer processes by which all the bonds connecting the two classes of sites are exploited. Thus, this oscillation behaves as an electronic breathing mode. The relevance of the new peak to a recently found reflectivity peak in κ-(BEDT-TTF)2X after photoexcitation is discussed.

  3. High-frequency voltage oscillations in cultured astrocytes

    PubMed Central

    Fleischer, Wiebke; Theiss, Stephan; Slotta, Johannes; Holland, Christine; Schnitzler, Alfons

    2015-01-01

    Because of their close interaction with neuronal physiology, astrocytes can modulate brain function in multiple ways. Here, we demonstrate a yet unknown astrocytic phenomenon: Astrocytes cultured on microelectrode arrays (MEAs) exhibited extracellular voltage fluctuations in a broad frequency spectrum (100–600 Hz) after electrical stimulation. These aperiodic high-frequency oscillations (HFOs) could last several seconds and did not spread across the MEA. The voltage-gated calcium channel antagonist cilnidipine dose-dependently decreased the power of the oscillations. While intracellular calcium was pivotal, incubation with bafilomycin A1 showed that vesicular release of transmitters played only a minor role in the emergence of HFOs. Gap junctions and volume-regulated anionic channels had just as little functional impact, which was demonstrated by the addition of carbenoxolone (100 μmol/L) and NPPB (100 μmol/L). Hyperpolarization with low potassium in the extracellular solution (2 mmol/L) dramatically raised oscillation power. A similar effect was seen when we added extra sodium (+50 mmol/L) or if we replaced it with NMDG+ (50 mmol/L). The purinergic receptor antagonist PPADS suppressed the oscillation power, while the agonist ATP (100 μmol/L) had only an increasing effect when the bath solution pH was slightly lowered to pH 7.2. From these observations, we conclude that astrocytic voltage oscillations are triggered by activation of voltage-gated calcium channels and driven by a downstream influx of cations through channels that are permeable for large ions such as NMDG+. Most likely candidates are subtypes of pore-forming P2X channels with a low affinity for ATP. PMID:25969464

  4. High frequency oscillations evoked by peripheral magnetic stimulation.

    PubMed

    Biller, S; Simon, L; Fiedler, P; Strohmeier, D; Haueisen, J

    2011-01-01

    The analysis of somatosensory evoked potentials (SEP) and / or fields (SEF) is a well-established and important tool for investigating the functioning of the peripheral and central human nervous system. A standard technique to evoke SEPs / SEFs is the stimulation of the median nerve by using a bipolar electrical stimulus. We aim at an alternative stimulation technique enabling stimulation of deep nerve structures while reducing patient stress and error susceptibility. In the current study, we apply a commercial transcranial magnetic stimulation system for peripheral magnetic stimulation of the median nerve. We compare the results of simultaneously recorded EEG signals to prove applicability of our technique to evoke SEPs including low frequency components (LFC) as well as high frequency oscillations (HFO). Therefore, we compare amplitude, latency and time-frequency characteristics of the SEP of 14 healthy volunteers after electric and magnetic stimulation. Both low frequency components and high frequency oscillations were detected. The HFOs were superimposed onto the primary cortical response N20. Statistical analysis revealed significantly lower amplitudes and increased latencies for LFC and HFO components after magnetic stimulation. The differences indicate the inability of magnetic stimulation to elicit supramaximal responses. A psycho-perceptual evaluation showed that magnetic stimulation was less unpleasant for 12 out of the 14 volunteers. In conclusion, we showed that LFC and HFO components related to median nerve stimulation can be evoked by peripheral magnetic stimulation.

  5. High-frequency Oscillations in the Atmosphere above a Sunspot Umbra

    NASA Astrophysics Data System (ADS)

    Wang, Feng; Deng, Hui; Li, Bo; Feng, Song; Bai, Xianyong; Deng, Linhua; Yang, Yunfei; Xue, Zhike; Wang, Rui

    2018-03-01

    We use high spatial and temporal resolution observations, simultaneously obtained with the New Vacuum Solar Telescope and Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, to investigate the high-frequency oscillations above a sunspot umbra. A novel time–frequency analysis method, namely, the synchrosqueezing transform (SST), is employed to represent their power spectra and to reconstruct the high-frequency signals at different solar atmospheric layers. A validation study with synthetic signals demonstrates that SST is capable of resolving weak signals even when their strength is comparable to the high-frequency noise. The power spectra, obtained from both SST and the Fourier transform, of the entire umbral region indicate that there are significant enhancements between 10 and 14 mHz (labeled as 12 mHz) at different atmospheric layers. Analyzing the spectrum of a photospheric region far away from the umbra demonstrates that this 12 mHz component exists only inside the umbra. The animation based on the reconstructed 12 mHz component in AIA 171 Å illustrates that an intermittently propagating wave first emerges near the footpoints of coronal fan structures, and then propagates outward along the structures. A time–distance diagram, coupled with a subsonic wave speed (∼49 km s‑1), highlights the fact that these coronal perturbations are best described as upwardly propagating magnetoacoustic slow waves. Thus, we first reveal the high-frequency oscillations with a period around one minute in imaging observations at different height above an umbra, and these oscillations seem to be related to the umbral perturbations in the photosphere.

  6. Stereotyped high-frequency oscillations discriminate seizure onset zones and critical functional cortex in focal epilepsy.

    PubMed

    Liu, Su; Gurses, Candan; Sha, Zhiyi; Quach, Michael M; Sencer, Altay; Bebek, Nerses; Curry, Daniel J; Prabhu, Sujit; Tummala, Sudhakar; Henry, Thomas R; Ince, Nuri F

    2018-01-30

    High-frequency oscillations in local field potentials recorded with intracranial EEG are putative biomarkers of seizure onset zones in epileptic brain. However, localized 80-500 Hz oscillations can also be recorded from normal and non-epileptic cerebral structures. When defined only by rate or frequency, physiological high-frequency oscillations are indistinguishable from pathological ones, which limit their application in epilepsy presurgical planning. We hypothesized that pathological high-frequency oscillations occur in a repetitive fashion with a similar waveform morphology that specifically indicates seizure onset zones. We investigated the waveform patterns of automatically detected high-frequency oscillations in 13 epilepsy patients and five control subjects, with an average of 73 subdural and intracerebral electrodes recorded per patient. The repetitive oscillatory waveforms were identified by using a pipeline of unsupervised machine learning techniques and were then correlated with independently clinician-defined seizure onset zones. Consistently in all patients, the stereotypical high-frequency oscillations with the highest degree of waveform similarity were localized within the seizure onset zones only, whereas the channels generating high-frequency oscillations embedded in random waveforms were found in the functional regions independent from the epileptogenic locations. The repetitive waveform pattern was more evident in fast ripples compared to ripples, suggesting a potential association between waveform repetition and the underlying pathological network. Our findings provided a new tool for the interpretation of pathological high-frequency oscillations that can be efficiently applied to distinguish seizure onset zones from functionally important sites, which is a critical step towards the translation of these signature events into valid clinical biomarkers.awx374media15721572971001. © The Author(s) (2018). Published by Oxford University Press on

  7. Thin-film piezoelectric-on-silicon resonators for high-frequency reference oscillator applications.

    PubMed

    Abdolvand, Reza; Lavasani, Hossein M; Ho, Gavin K; Ayazi, Farrokh

    2008-12-01

    This paper studies the application of lateral bulk acoustic thin-film piezoelectric-on-substrate (TPoS) resonators in high-frequency reference oscillators. Low-motional-impedance TPoS resonators are designed and fabricated in 2 classes--high-order and coupled-array. Devices of each class are used to assemble reference oscillators and the performance characteristics of the oscillators are measured and discussed. Since the motional impedance of these devices is small, the transimpedance amplifier (TIA) in the oscillator loop can be reduced to a single transistor and 3 resistors, a format that is very power-efficient. The lowest reported power consumption is approximately 350 microW for an oscillator operating at approximately 106 MHz. A passive temperature compensation method is also utilized by including the buried oxide layer of the silicon-on-insulator (SOI) substrate in the structural resonant body of the device, and a very small (-2.4 ppm/ degrees C) temperature coefficient of frequency is obtained for an 82-MHz oscillator.

  8. Twin peak high-frequency quasi-periodic oscillations as a spectral imprint of dual oscillation modes of accretion tori

    NASA Astrophysics Data System (ADS)

    Bakala, P.; Goluchová, K.; Török, G.; Šrámková, E.; Abramowicz, M. A.; Vincent, F. H.; Mazur, G. P.

    2015-09-01

    Context. High-frequency (millisecond) quasi-periodic oscillations (HF QPOs) are observed in the X-ray power-density spectra of several microquasars and low-mass X-ray binaries. Two distinct QPO peaks, so-called twin peak QPOs, are often detected simultaneously exhibiting their frequency ratio close or equal to 3:2. A widely discussed class of proposed QPOs models is based on oscillations of accretion toroidal structures orbiting in the close vicinity of black holes or neutron stars. Aims: Following the analytic theory and previous studies of observable spectral signatures, we aim to model the twin peak QPOs as a spectral imprint of specific dual oscillation regime defined by a combination of the lowest radial and vertical oscillation mode of slender tori. We consider the model of an optically thick slender accretion torus with constant specific angular momentum. We examined power spectra and fluorescent Kα iron line profiles for two different simulation setups with the mode frequency relations corresponding to the epicyclic resonance HF QPOs model and modified relativistic precession QPOs model. Methods: We used relativistic ray-tracing implemented in the parallel simulation code LSDplus. In the background of the Kerr spacetime geometry, we analyzed the influence of the distant observer inclination and the spin of the central compact object. Relativistic optical projection of the oscillating slender torus is illustrated by images in false colours related to the frequency shift. Results: We show that performed simulations yield power spectra with the pair of dominant peaks that correspond to the frequencies of radial and vertical oscillation modes and with the peak frequency ratio equal to the proper value 3:2 on a wide range of inclinations and spin values. We also discuss exceptional cases of a very low and very high inclination, as well as unstable high spin relativistic precession-like configurations that predict a constant frequency ratio equal to 1:2. We

  9. Somatic evoked high-frequency magnetic oscillations reflect activity of inhibitory interneurons in the human somatosensory cortex.

    PubMed

    Hashimoto, I; Mashiko, T; Imada, T

    1996-05-01

    High-frequency potential oscillations in the range of 300-900 Hz have recently been shown to concur with the primary response (N20) of the somatosensory cortex in awake humans. However, the physiological mechanisms of the high-frequency oscillations remained undetermined. We addressed the issue by analyzing magnetic fields during wakefulness and sleep over the left hemisphere to right median nerve stimulation with a wide bandpass (0.1-2000 Hz) recording with subsequent high-pass (> 300 Hz) and low-pass (< 300 Hz) filtering. With wide bandpass recordings, high-frequency magnetic oscillations with the main signal energy at 580-780 Hz were superimposed on the N20m during wakefulness. Isofield mapping at each peak of the high-pass filtered and isolated high-frequency oscillations showed a dipolar pattern and the estimated source for these peaks was the primary somatosensory cortex (area 3b) very close to that for the N20m peak. During sleep, the high-frequency oscillations showed dramatic diminution in amplitude while the N20m amplitude exhibited a moderate increment. This reciprocal relation between the high-frequency oscillations and the N20m during a wake-sleep cycle suggests that they represent different generator substrates. We speculate that the high-frequency oscillations represent a localized activity of the GABAergic inhibitory interneurons of layer 4, which have been shown in animal experiments to respond monosynaptically to thalamo-cortical input with a high-frequency (600-900 Hz) burst of short duration spikes. On the other hand, the underlying N20m represents activity of pyramidal neurons which receive monosynaptic excitatory input from the thalamus as well as a feed-forward inhibition from the interneurons.

  10. Atomic fountain clock with very high frequency stability employing a pulse-tube-cryocooled sapphire oscillator.

    PubMed

    Takamizawa, Akifumi; Yanagimachi, Shinya; Tanabe, Takehiko; Hagimoto, Ken; Hirano, Iku; Watabe, Ken-ichi; Ikegami, Takeshi; Hartnett, John G

    2014-09-01

    The frequency stability of an atomic fountain clock was significantly improved by employing an ultra-stable local oscillator and increasing the number of atoms detected after the Ramsey interrogation, resulting in a measured Allan deviation of 8.3 × 10(-14)τ(-1/2)). A cryogenic sapphire oscillator using an ultra-low-vibration pulse-tube cryocooler and cryostat, without the need for refilling with liquid helium, was applied as a local oscillator and a frequency reference. High atom number was achieved by the high power of the cooling laser beams and optical pumping to the Zeeman sublevel m(F) = 0 employed for a frequency measurement, although vapor-loaded optical molasses with the simple (001) configuration was used for the atomic fountain clock. The resulting stability is not limited by the Dick effect as it is when a BVA quartz oscillator is used as the local oscillator. The stability reached the quantum projection noise limit to within 11%. Using a combination of a cryocooled sapphire oscillator and techniques to enhance the atom number, the frequency stability of any atomic fountain clock, already established as primary frequency standard, may be improved without opening its vacuum chamber.

  11. Beta-gamma burst stimulations of the inferior olive induce high-frequency oscillations in the deep cerebellar nuclei.

    PubMed

    Cheron, Julian; Cheron, Guy

    2018-02-20

    The cerebellum displays various sorts of rhythmic activities covering both low- and high-frequency oscillations. These cerebellar high-frequency oscillations were observed in the cerebellar cortex. Here, we hypothesised that not only is the cerebellar cortex a generator of high-frequency oscillations but also that the deep cerebellar nuclei may also play a similar role. Thus, we analysed local field potentials and single-unit activities in the deep cerebellar nuclei before, during and after electric stimulation in the inferior olive of awake mice. A high-frequency oscillation of 350 Hz triggered by the stimulation of the inferior olive, within the beta-gamma range, was observed in the deep cerebellar nuclei. The amplitude and frequency of the oscillation were independent of the frequency of stimulation. This oscillation emerged during the period of stimulation and persisted after the end of the stimulation. The oscillation coincided with the inhibition of deep cerebellar neurons. As the inhibition of the deep cerebellar nuclei is related to inhibitory inputs from Purkinje cells, we speculate that the oscillation represents the unmasking of the synchronous activation of another subtype of deep cerebellar neuronal subtype, devoid of GABA receptors and under the direct control of the climbing fibres from the inferior olive. Still, the mechanism sustaining this oscillation remains to be deciphered. Our study sheds new light on the role of the olivo-cerebellar loop as the final output control of the intercerebellar circuitry. © 2018 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

  12. 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.

  13. Phase reduction of a limit cycle oscillator perturbed by a strong amplitude-modulated high-frequency force.

    PubMed

    Pyragas, Kestutis; Novičenko, Viktor

    2015-07-01

    The phase reduction method for a limit cycle oscillator subjected to a strong amplitude-modulated high-frequency force is developed. An equation for the phase dynamics is derived by introducing a new, effective phase response curve. We show that if the effective phase response curve is everywhere positive (negative), then an entrainment of the oscillator to an envelope frequency is possible only when this frequency is higher (lower) than the natural frequency of the oscillator. Also, by using the Pontryagin maximum principle, we have derived an optimal waveform of the perturbation that ensures an entrainment of the oscillator with minimal power. The theoretical results are demonstrated with the Stuart-Landau oscillator and model neurons.

  14. Cannabinoid Receptors Mediate Methamphetamine Induction of High Frequency Gamma Oscillations in the Nucleus Accumbens

    PubMed Central

    Morra, Joshua T.; Glick, Stanley D.; Cheer, Joseph F.

    2012-01-01

    Patients suffering from amphetamine---induced psychosis display repetitive behaviors, partially alleviated by antipsychotics, which are reminiscent of rodent stereotypies. Due to recent evidence implicating endocannabinoid involvement in brain disorders, including psychosis, we studied the effects of endocannabinoid signaling on neuronal oscillations of rats exhibiting methamphetamine stereotypy. Neuronal network oscillations were recorded with multiple single electrode arrays aimed at the nucleus accumbens of freely moving rats. During the experiments, animals were dosed intravenously with the CB1 receptor antagonist rimonabant (0.3 mg/kg) or vehicle followed by an ascending dose regimen of methamphetamine (0.01, 0.1, 1, and 3 mg/kg; cumulative dosing). The effects of drug administration on stereotypy and local gamma oscillations were evaluated. Methamphetamine treatment significantly increased high frequency gamma oscillations (~ 80 Hz). Entrainment of a subpopulation of nucleus accumbens neurons to high frequency gamma was associated with stereotypy encoding in putative fast-spiking interneurons, but not in putative medium spiny neurons. The observed ability of methamphetamine to induce both stereotypy and high frequency gamma power was potently disrupted following CB1 receptor blockade. The present data suggest that CB1 receptor-dependent mechanisms are recruited by methamphetamine to modify striatal interneuron oscillations that accompany changes in psychomotor state, further supporting the link between endocannabinoids and schizophrenia spectrum disorders. PMID:22609048

  15. High-frequency sarcomeric auto-oscillations induced by heating in living neonatal cardiomyocytes of the rat

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Shintani, Seine A.; Oyama, Kotaro; Fukuda, Norio, E-mail: noriof@jikei.ac.jp

    2015-02-06

    Highlights: • We tested the effects of infra-red laser irradiation on cardiac sarcomere dynamics. • A rise in temperature (>∼38 °C) induced high-frequency sarcomeric auto-oscillations. • These oscillations occurred with and without blockade of intracellular Ca{sup 2+} stores. • Cardiac sarcomeres can play a role as a temperature-dependent rhythm generator. - Abstract: In the present study, we investigated the effects of infra-red laser irradiation on sarcomere dynamics in living neonatal cardiomyocytes of the rat. A rapid increase in temperature to >∼38 °C induced [Ca{sup 2+}]{sub i}-independent high-frequency (∼5–10 Hz) sarcomeric auto-oscillations (Hyperthermal Sarcomeric Oscillations; HSOs). In myocytes with the intactmore » sarcoplasmic reticular functions, HSOs coexisted with [Ca{sup 2+}]{sub i}-dependent spontaneous beating in the same sarcomeres, with markedly varying frequencies (∼10 and ∼1 Hz for the former and latter, respectively). HSOs likewise occurred following blockade of the sarcoplasmic reticular functions, with the amplitude becoming larger and the frequency lower in a time-dependent manner. The present findings suggest that in the mammalian heart, sarcomeres spontaneously oscillate at higher frequencies than the sinus rhythm at temperatures slightly above the physiologically relevant levels.« less

  16. Respiratory Control in Stuttering Speakers: Evidence from Respiratory High-Frequency Oscillations.

    ERIC Educational Resources Information Center

    Denny, Margaret; Smith, Anne

    2000-01-01

    This study examined whether stuttering speakers (N=10) differed from fluent speakers in relations between the neural control systems for speech and life support. It concluded that in some stuttering speakers the relations between respiratory controllers are atypical, but that high participation by the high frequency oscillation-producing circuitry…

  17. Cannabinoid receptors mediate methamphetamine induction of high frequency gamma oscillations in the nucleus accumbens.

    PubMed

    Morra, Joshua T; Glick, Stanley D; Cheer, Joseph F

    2012-09-01

    Patients suffering from amphetamine-induced psychosis display repetitive behaviors, partially alleviated by antipsychotics, which are reminiscent of rodent stereotypies. Due to recent evidence implicating endocannabinoid involvement in brain disorders, including psychosis, we studied the effects of endocannabinoid signaling on neuronal oscillations of rats exhibiting methamphetamine stereotypy. Neuronal network oscillations were recorded with multiple single electrode arrays aimed at the nucleus accumbens of freely-moving rats. During the experiments, animals were dosed intravenously with the CB1 receptor antagonist rimonabant (0.3 mg/kg) or vehicle followed by an ascending dose regimen of methamphetamine (0.01, 0.1, 1, and 3 mg/kg; cumulative dosing). The effects of drug administration on stereotypy and local gamma oscillations were evaluated. Methamphetamine treatment significantly increased high frequency gamma oscillations (∼80 Hz). Entrainment of a subpopulation of nucleus accumbens neurons to high frequency gamma was associated with stereotypy encoding in putative fast-spiking interneurons, but not in putative medium spiny neurons. The observed ability of methamphetamine to induce both stereotypy and high frequency gamma power was potently disrupted following CB1 receptor blockade. The present data suggest that CB1 receptor-dependent mechanisms are recruited by methamphetamine to modify striatal interneuron oscillations that accompany changes in psychomotor state, further supporting the link between endocannabinoids and schizophrenia spectrum disorders. Copyright © 2012 Elsevier Ltd. All rights reserved.

  18. Temporal Characteristics of High-Frequency Lower-Limb Oscillation during Freezing of Gait in Parkinson's Disease

    PubMed Central

    Yungher, Don A.; Morris, Tiffany R.; Dilda, Valentina; Shine, James M.; Naismith, Sharon L.; Lewis, Simon J. G.; Moore, Steven T.

    2014-01-01

    A cardinal feature of freezing of gait (FOG) is high frequency (3–8 Hz) oscillation of the legs, and this study aimed to quantify the temporal pattern of lower-body motion prior to and during FOG. Acceleration data was obtained from sensors attached to the back, thighs, shanks, and feet in 14 Parkinson's disease patients performing timed-up-and-go tasks, and clinical assessment of FOG was performed by two experienced raters from video. A total of 23 isolated FOG events, defined as occurring at least 5 s after gait initiation and with no preceding FOG, were identified from the clinical ratings. The corresponding accelerometer records were analyzed within a 4 s window centered at the clinical onset of freezing. FOG-related high-frequency oscillation (an increase in power in the 3–8 Hz band >3 SD from baseline) followed a distal to proximal onset pattern, appearing at the feet, shanks, thighs, and then back over a period of 250 ms. Peak power tended to decrease as the focus of oscillation moved from feet to back. There was a consistent delay (mean 872 ms) between the onset of high frequency oscillation at the feet and clinical onset of FOG. We infer that FOG is characterized by high frequency oscillation at the feet, which progresses proximally and is mechanically damped at the torso. PMID:25101189

  19. Brain state-dependent recruitment of high-frequency oscillations in the human hippocampus.

    PubMed

    Billeke, Pablo; Ossandon, Tomas; Stockle, Marcelo; Perrone-Bertolotti, Marcela; Kahane, Philippe; Lachaux, Jean-Philippe; Fuentealba, Pablo

    2017-09-01

    Ripples are high-frequency bouts of coordinated hippocampal activity believed to be crucial for information transfer and memory formation. We used intracortical macroelectrodes to record neural activity in the human hippocampus of awake subjects undergoing surgical treatment for refractory epilepsy and distinguished two populations of ripple episodes based on their frequency spectrum. The phase-coupling of one population, slow ripples (90-110 Hz), to cortical delta oscillations was differentially modulated by cognitive task; whereas the second population, fast ripples (130-170 Hz), was not seemingly correlated to local neural activity. Furthermore, as cognitive tasks changed, the ongoing coordination of neural activity associated to slow ripples progressively augmented along the parahippocampal axis. Thus, during resting states, slow ripples were coordinated in restricted hippocampal territories; whereas during active states, such as attentionally-demanding tasks, high frequency activity emerged across the hippocampus and parahippocampal cortex, that was synchronized with slow ripples, consistent with ripples supporting information transfer and coupling anatomically distant regions. Hence, our results provide further evidence of neural diversity in hippocampal high-frequency oscillations and their association to cognitive processing in humans. Copyright © 2017 Elsevier Ltd. All rights reserved.

  20. High-frequency large-amplitude oscillations of a non-isothermal N/S boundary

    NASA Astrophysics Data System (ADS)

    Bezuglyj, A. I.; Shklovskij, V. A.

    2016-10-01

    Within the framework of a phenomenological approach based on the heat balance equation and the current dependence of the critical temperature of the superconductor, the effect of high-frequency current of large amplitude and arbitrary waveform on the non-isothermal balance of an oscillating N/S interface in a long superconductor was studied. Self-consistent average temperature field of the rapidly oscillating non-isothermal N/S boundary (heat kink) was introduced, which allowed us to go beyond the well-known concept of mean-square heating and consider the effect of the current waveform. With regard to experiments on the effects of high-power microwave radiation on the current-voltage (IV) characteristics of superconducting films, their classification was performed and the families of IV curves of inhomogeneous superconductors carrying a current containing a high-frequency component of large amplitude. Several IV curves exhibited a hysteresis of thermal nature.

  1. Dynamic modulation of epileptic high frequency oscillations by the phase of slower cortical rhythms.

    PubMed

    Ibrahim, George M; Wong, Simeon M; Anderson, Ryan A; Singh-Cadieux, Gabrielle; Akiyama, Tomoyuki; Ochi, Ayako; Otsubo, Hiroshi; Okanishi, Tohru; Valiante, Taufik A; Donner, Elizabeth; Rutka, James T; Snead, O Carter; Doesburg, Sam M

    2014-01-01

    Pathological high frequency oscillations (pHFOs) have been proposed to be robust markers of epileptic cortex. Oscillatory activity below this frequency range has been shown to be modulated by phase of lower frequency oscillations. Here, we tested the hypothesis that dynamic cross-frequency interactions involving pHFOs are concentrated within the epileptogenic cortex. Intracranial electroencephalographic recordings from 17 children with medically-intractable epilepsy secondary to focal cortical dysplasia were obtained. A time-resolved analysis was performed to determine topographic concentrations and dynamic changes in cross-frequency amplitude-to-phase coupling (CFC). CFC between pHFOs and the phase of theta and alpha rhythms was found to be significantly elevated in the seizure-onset zone compared to non-epileptic regions (p<0.01). Data simulations showed that elevated CFC could not be attributed to the presence of sharp transients or other signal properties. The phase of low frequency oscillations at which pHFO amplitudes were maximal was inconsistent at seizure initiation, yet consistently at the trough of the low frequency rhythm at seizure termination. Amplitudes of pHFOs were most significantly modulated by the phase of alpha-band oscillations (p<0.01). These results suggest that increased CFC between pHFO amplitude and alpha phase may constitute a marker of epileptogenic brain areas and may be relevant for understanding seizure dynamics. Copyright © 2013 Elsevier Inc. All rights reserved.

  2. High repetition frequency PPMgOLN mid-infrared optical parametric oscillator

    NASA Astrophysics Data System (ADS)

    Liu, J.; Liu, Q.; Yan, X.; Chen, H.; Gong, M.

    2010-09-01

    A mid-infrared optical parametric oscillator (OPO) with the idler wavelengths of 3591 nm, 3384 nm, and 3164 nm at the repetition of 76.8 kHz is reported, and a high repetition frequency acousto-optic Q-switched Nd:YVO4 laser is used as the pump source. The OPO is designed as an external non-colinear single-resonator optical parametric oscillator. When the power of the pump light is 25.1 W, the idler with the wavelength of 3164 nm and the power of 4.3 W is generated. The corresponding signal light is 1603 nm with the power of 3.1 W. The efficiency from 1064 nm to 3160 nm can reach as high as 17.1%, and the efficiency of the OPO is 29.5%.

  3. The detection and characterization of high frequency and high wavenumber solar oscillations. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Fernandes, David Neil

    1992-01-01

    Doppler shift measurements of the Na D(sub 1) absorption line have revealed solar oscillations in a new regime of frequency and wavenumber. Oscillations of vertical velocities in the temperature minimum and low chromosphere of the Sun are observed with frequencies ranging up to 9.5 mHz. There is no evidence for chromospheric modes of 3 minute period. This indicates that the chromosphere does not form a good cavity for acoustic waves. The fundamental-modes appear with wavenumbers up to 5.57 M per m (equivalent spherical harmonic degree, 3877). The frequencies lie below the predicted values at wavenumbers above 1 M per m. The values are in agreement with previous measurements that exist for wavenumbers up to 2.67 M per m. Spatial maps of velocity power show that high wavenumber oscillations are suppressed in active regions. The shape of the power depression indicates that wave motion is affected in the layer of atmosphere where the measurement is made. The f-modes are suppressed in the same way as p-modes, indicating that the mechanism for wave suppression affects velocity fluctuations. Mode frequencies are not affected by the magnetic fields by more than 50 micro Hz, the precision of the measurement.

  4. Detection of High-Frequency Oscillations and Damping from Multi-slit Spectroscopic Observations of the Corona

    NASA Astrophysics Data System (ADS)

    Samanta, T.; Singh, J.; Sindhuja, G.; Banerjee, D.

    2016-01-01

    During the total solar eclipse of 11 July 2010, multi-slit spectroscopic observations of the solar corona were performed from Easter Island, Chile. To search for high-frequency waves, observations were taken at a high cadence in the green line at 5303 Å that is due to [Fe xiv] and the red line at 6374 Å that is due to [Fe x]. The data were analyzed to study the periodic variations in intensity, Doppler velocity, and line width using wavelet analysis. The data with high spectral and temporal resolution enabled us to study the rapid dynamical changes within coronal structures. We find that at certain locations, each parameter shows significant oscillation with periods ranging from 6 - 25 s. For the first time, we were able to detect damping of high-frequency oscillations with periods of about 10 s. If the observed damped oscillations are due to magnetohydrodynamic waves, then they can contribute significantly to the heating of the corona. From a statistical study we try to characterize the nature of the observed oscillations while considering the distribution of power in different line parameters.

  5. Frequency quenching of microwave-induced resistance oscillations in a high-mobility two-dimensional electron gas

    NASA Astrophysics Data System (ADS)

    Studenikin, S. A.; Sachrajda, A. S.; Gupta, J. A.; Wasilewski, Z. R.; Fedorych, O. M.; Byszewski, M.; Maude, D. K.; Potemski, M.; Hilke, M.; West, K. W.; Pfeiffer, L. N.

    2007-10-01

    The frequency dependence of microwave-induced resistance oscillations (MIROs) has been studied experimentally in high-mobility electron GaAs/AlGaAs structures to explore the limits at which these oscillations can be observed. It is found that in dc transport experiments at frequencies above 120GHz , MIROs start to quench, while above 230GHz , they completely disappear. The results will need to be understood theoretically but are qualitatively discussed within a model in which forced electronic charge oscillations (plasmons) play an intermediate role in the interaction process between the radiation and the single-particle electron excitations between Landau levels.

  6. Novel high-frequency, high-power, pulsed oscillator based on a transmission line transformer.

    PubMed

    Burdt, R; Curry, R D

    2007-07-01

    Recent analysis and experiments have demonstrated the potential for transmission line transformers to be employed as compact, high-frequency, high-power, pulsed oscillators with variable rise time, high output impedance, and high operating efficiency. A prototype system was fabricated and tested that generates a damped sinusoidal wave form at a center frequency of 4 MHz into a 200 Omega load, with operating efficiency above 90% and peak power on the order of 10 MW. The initial rise time of the pulse is variable and two experiments were conducted to demonstrate initial rise times of 12 and 3 ns, corresponding to a spectral content from 4-30 and from 4-100 MHz, respectively. A SPICE model has been developed to accurately predict the circuit behavior and scaling laws have been identified to allow for circuit design at higher frequencies and higher peak power. The applications, circuit analysis, test stand, experimental results, circuit modeling, and design of future systems are all discussed.

  7. Frequency-locked chaotic opto-RF oscillator.

    PubMed

    Thorette, Aurélien; Romanelli, Marco; Brunel, Marc; Vallet, Marc

    2016-06-15

    A driven opto-RF oscillator, consisting of a dual-frequency laser (DFL) submitted to frequency-shifted feedback, is experimentally and numerically studied in a chaotic regime. Precise control of the reinjection strength and detuning permits isolation of a parameter region of bounded-phase chaos, where the opto-RF oscillator is frequency-locked to the master oscillator, in spite of chaotic phase and intensity oscillations. Robust experimental evidence of this synchronization regime is found, and phase noise spectra allow us to compare phase-locking and bounded-phase chaos regimes. In particular, it is found that the long-term phase stability of the master oscillator is well transferred to the opto-RF oscillator, even in the chaotic regime.

  8. Low-frequency oscillations in Hall thrusters

    NASA Astrophysics Data System (ADS)

    Wei, Li-Qiu; Han, Liang; Yu, Da-Ren; Guo, Ning

    2015-05-01

    In this paper, we summarize the research development of low-frequency oscillations in the last few decades. The findings of physical mechanism, characteristics and stabilizing methods of low-frequency oscillations are discussed. It shows that it is unreasonable and incomplete to model an ionization region separately to analyze the physical mechanism of low-frequency oscillations. Electro-dynamics as well as the formation conditions of ionization distribution play an important role in characteristics and stabilizing of low-frequency oscillations. Understanding the physical mechanism and characteristics of low- frequency oscillations thoroughly and developing a feasible method stabilizing this instability are still important research subjects. Project supported by the National Natural Science Foundation of China (Grant No. 51477035), the Fundamental Research Funds for the Central Universities, China (Grant No. HIT.NSRIF 2015064), and the Open Research Fund Program of State Key Laboratory of Cryogenic Vacuum Technology and Physics, China (Grant No. ZDK201304).

  9. The dark side of high-frequency oscillations in the developing brain.

    PubMed

    Le Van Quyen, Michel; Khalilov, Ilgam; Ben-Ari, Yehezkel

    2006-07-01

    Adult brain networks generate a wide range of oscillations. Some of these are behaviourally relevant, whereas others occur during seizures and other pathological conditions. This raises the question of how physiological oscillations differ from pathogenic ones. In this review, this issue is discussed from a developmental standpoint. Indeed, both epileptic and physiological high-frequency oscillations (HFOs) appear progressively during maturation, and it is therefore possible to determine how this program corresponds to maturation of the neuronal populations that generate these oscillations. We review here important differences in the development of neuronal populations that might contribute to their different oscillatory properties. In particular, at an early stage, the density of glutamatergic synapses is too low for physiological HFOs but an additional drive can be provided by excitatory GABA, triggering epileptic HFOs and the cascades involved in long-lasting epileptogenic transformations. This review is part of the INMED/TINS special issue "Nature and nurture in brain development and neurological disorders", based on presentations at the annual INMED/TINS symposium (http://inmednet.com/).

  10. Measurement of high-degree solar oscillation frequencies

    NASA Technical Reports Server (NTRS)

    Bachmann, K. T.; Duvall, T. L., Jr.; Harvey, J. W.; Hill, F.

    1995-01-01

    We present m-averaged solar p- and f-mode oscillation frequencies over the frequency range nu greater than 1.8 and less than 5.0 mHz and the spherical harmonic degree range l greater than or equal to 100 and less than or equal to 1200 from full-disk, 1000 x 1024 pixel, Ca II intensity images collected 1993 June 22-25 with a temporal cadence of 60 s. We itemize the sources and magnitudes of statistical and systematic uncertainties and of small frequency corrections, and we show that our frequencies represent an improvement in accuracy and coverage over previous measurements. Our frequencies agree at the 2 micro Hz level with Mount Wilson frequencies determined for l less than or equal to 600 from full-disk images, and we find systematic offsets of 10-20 micro Hz with respect to frequencies measured from Big Bear and La Palma observations. We give evidence that these latter offsets are indicative of spatial scaling uncertainties associated with the analysis of partial-disk images. In comparison with theory, our p-mode frequencies agree within 10 micro Hz of frequencies predicted by the Los Alamos model but are as much as 100 micro Hz smaller than frequencies predicted by the Denmark and Yale models at degrees near 1000. We also find systematic differences between our n = 0 frequencies and the frequencies closely agreed upon by all three models.

  11. Coherent Phonon Rabi Oscillations with a High-Frequency Carbon Nanotube Phonon Cavity.

    PubMed

    Zhu, Dong; Wang, Xin-He; Kong, Wei-Cheng; Deng, Guang-Wei; Wang, Jiang-Tao; Li, Hai-Ou; Cao, Gang; Xiao, Ming; Jiang, Kai-Li; Dai, Xing-Can; Guo, Guang-Can; Nori, Franco; Guo, Guo-Ping

    2017-02-08

    Phonon-cavity electromechanics allows the manipulation of mechanical oscillations similar to photon-cavity systems. Many advances on this subject have been achieved in various materials. In addition, the coherent phonon transfer (phonon Rabi oscillations) between the phonon cavity mode and another oscillation mode has attracted many interest in nanoscience. Here, we demonstrate coherent phonon transfer in a carbon nanotube phonon-cavity system with two mechanical modes exhibiting strong dynamical coupling. The gate-tunable phonon oscillation modes are manipulated and detected by extending the red-detuned pump idea of photonic cavity electromechanics. The first- and second-order coherent phonon transfers are observed with Rabi frequencies 591 and 125 kHz, respectively. The frequency quality factor product fQ m ∼ 2 × 10 12 Hz achieved here is larger than k B T base /h, which may enable the future realization of Rabi oscillations in the quantum regime.

  12. Sustaining GHz oscillation of carbon nanotube based oscillators via a MHz frequency excitation

    NASA Astrophysics Data System (ADS)

    Motevalli, Benyamin; Taherifar, Neda; Zhe Liu, Jefferson

    2016-05-01

    There have been intensive studies to investigate the properties of gigahertz nano-oscillators based on multi-walled carbon nanotubes (MWCNTs). Many of these studies, however, revealed that the unique telescopic translational oscillations in such devices would damp quickly due to various energy dissipation mechanisms. This challenge remains the primary obstacle against its practical applications. Herein, we propose a design concept in which a GHz oscillation could be re-excited by a MHz mechanical motion. This design involves a triple-walled CNT, in which sliding of the longer inner tube at a MHz frequency can re-excite and sustain a GHz oscillation of the shorter middle tube. Our molecular dynamics (MD) simulations prove this design concept at ˜10 nm scale. A mathematical model is developed to explore the feasibility at a larger size scale. As an example, in an oscillatory system with the CNT’s length above 100 nm, the high oscillatory frequency range of 1.8-3.3 GHz could be excited by moving the inner tube at a much lower frequency of 53.4 MHz. This design concept together with the mechanical model could energize the development of GHz nano-oscillators in miniaturized electro-mechanical devices.

  13. [Low-Frequency Flow Oscillation

    NASA Technical Reports Server (NTRS)

    Bragg, Michael B.

    1997-01-01

    The results of the research conducted under this grant are presented in detail in three Master theses, by Heinrich, Balow, and Broeren. Additional analysis of the experimental data can be found in two AIAA Journal articles and two conference papers. Citations for all of the studies' publications can be found in the bibliography which is attached. The objective of Heinrich's study was to document the low-frequency flow oscillation on the LRN-1007 airfoil, which had been previously observed at low Reynolds number, to determine its origin, and explore the phenomenon at higher Reynolds number. Heinrich performed detailed flow visualization on the airfoil using surface fluorescent oil and laser-sheet off-body visualization. A large leading-edge separation bubble and trailing-edge separation was identified on the airfoil just prior to the onset of the unsteady stall flow oscillation. From the laser-sheet data, the unsteady flow appeared as a massive boundary-layer separation followed by flow reattachment. Hot-wire data were taken in the wake to identify the presence of the flow oscillation and the dominant frequency. The oscillation was found in the flow from a Reynolds number of 0.3 to 1.3 x 10 exp 6. The Strouhal number based on airfoil projected height was nominally 0.02 and increased slightly with increasing Reynolds number and significantly with increasing airfoil angle of attack. Balow focused his research on the leading-edge separation bubble which was hypothesized to be the origin of the low-frequency oscillation. Initially, experimental measurements in the bubble at the onset of the low-frequency oscillation were attempted to study the characteristics of the bubble and explain possible relationships to the shear-layer-flapping phenomena. Unfortunately, the bubble proved to be extremely sensitive to the probe interference and it drastically reduced the size of the bubble. These detailed measurements were then abandoned by Balow. However, this led to a series of

  14. Energy Spectra and High Frequency Oscillations in 4U 0614+091

    NASA Technical Reports Server (NTRS)

    Ford, E. C.; Kaaret, P.; Chen, K.; Tavani, M.; Barret, D.; Bloser, P.; Grindlay, J.; Harmon, B. A.; Paciesas, W. S.; Zhang, S. N.

    1997-01-01

    We investigate the behavior of the high frequency quasi-periodic oscillations (QPOs) in 4U 0614+091, combining timing and spectral analysis of RXTE (Rossi X-ray Timing Explorer) observations. The energy spectrum of the source can be described by a power law plus a blackbody component. The blackbody has a variable temperature (kT approximately 0.8 to 1.4 keV) and accounts for 10 to 25% of the total energy flux. The power law flux and photon index also vary (F approximately 0.8 to 1.6 x 10(exp -9) erg/sq cm.s and alpha approximately 2.0 to 2.8 respectively). We find a robust correlation of the frequency of the higher frequency QPO with the flux of the blackbody. The source follows the same relation even in observations separated by several months. The QPO frequency does not have a similarly unique correlation with the total flux or the flux of the power law component. The RMS amplitudes of the higher frequency QPO rise with energy but are consistent with a constant for the lower frequency QPO. These results may be interpreted in terms of a beat frequency model for the production of the high frequency QPOs.

  15. High-Frequency Network Oscillations in Cerebellar Cortex

    PubMed Central

    Middleton, Steven J.; Racca, Claudia; Cunningham, Mark O.; Traub, Roger D.; Monyer, Hannah; Knöpfel, Thomas; Schofield, Ian S.; Jenkins, Alistair; Whittington, Miles A.

    2016-01-01

    SUMMARY Both cerebellum and neocortex receive input from the somatosensory system. Interaction between these regions has been proposed to underpin the correct selection and execution of motor commands, but it is not clear how such interactions occur. In neocortex, inputs give rise to population rhythms, providing a spatiotemporal coding strategy for inputs and consequent outputs. Here, we show that similar patterns of rhythm generation occur in cerebellum during nicotinic receptor subtype activation. Both gamma oscillations (30–80 Hz) and very fast oscillations (VFOs, 80–160 Hz) were generated by intrinsic cerebellar cortical circuitry in the absence of functional glutamatergic connections. As in neocortex, gamma rhythms were dependent on GABAA receptor-mediated inhibition, whereas VFOs required only nonsynaptically connected intercellular networks. The ability of cerebellar cortex to generate population rhythms within the same frequency bands as neocortex suggests that they act as a common spatiotemporal code within which corticocerebellar dialog may occur. PMID:18549787

  16. High-frequency oscillations mirror disease activity in patients with epilepsy.

    PubMed

    Zijlmans, M; Jacobs, J; Zelmann, R; Dubeau, F; Gotman, J

    2009-03-17

    High-frequency oscillations (HFOs) can be recorded in epileptic patients with clinical intracranial EEG. HFOs have been associated with seizure genesis because they occur in the seizure focus and during seizure onset. HFOs are also found interictally, partly co-occurring with epileptic spikes. We studied how HFOs are influenced by antiepileptic medication and seizure occurrence, to improve understanding of the pathophysiology and clinical meaning of HFOs. Intracerebral depth EEG was partly sampled at 2,000 Hz in 42 patients with intractable focal epilepsy. Patients with five or more usable nights of recording were selected. A sample of slow-wave sleep from each night was analyzed, and HFOs (ripples: 80-250 Hz, fast ripples: 250-500 Hz) and spikes were identified on all artifact-free channels. The HFOs and spikes were compared before and after seizures with stable medication dose and during medication reduction with no intervening seizures. Twelve patients with five to eight nights were included. After seizures, there was an increase in spikes, whereas HFO rates remained the same. Medication reduction was followed by an increase in HFO rates and mean duration. Contrary to spikes, high-frequency oscillations (HFOs) do not increase after seizures, but do so after medication reduction, similarly to seizures. This implies that spikes and HFOs have different pathophysiologic mechanisms and that HFOs are more tightly linked to seizures than spikes. HFOs seem to play an important role in seizure genesis and can be a useful clinical marker for disease activity.

  17. Multimode and multistate ladder oscillator and frequency recognition device

    NASA Technical Reports Server (NTRS)

    Aumann, Herbert M. (Inventor)

    1976-01-01

    A ladder oscillator composed of capacitive and inductive impedances connected together to form a ladder network which has a chosen number N oscillation modes at N different frequencies. Each oscillation mode is characterized by a unique standing wave voltage pattern along the nodes of the ladder oscillator, with the mode in which the ladder oscillator is oscillating being determinable from the amplitudes or phase of the oscillations at the nodes. A logic circuit may be connected to the nodes of the oscillator to compare the phases of selected nodes and thereby determine which mode the oscillator is oscillating in. A ladder oscillator composed of passive capacitive and inductive impedances can be utilized as a frequency recognition device, since the passive ladder oscillator will display the characteristic standing wave patterns if an input signal impressed upon the ladder oscillator is close to one of the mode frequencies of the oscillator. A CL ladder oscillator having series capacitive impedances and shunt inductive impedances can exhibit sustained and autonomous oscillations if active nonlinear devices are connected in parallel with the shunt inductive impedances. The active CL ladder oscillator can be synchronized to input frequencies impressed upon the oscillator, and will continue to oscillate after the input signal has been removed at a mode frequency which is, in general, nearest to the input signal frequency. Autonomous oscillations may also be obtained as desired from the active CL ladder oscillator at the mode frequencies.

  18. Synchronization of electrically coupled micromechanical oscillators with a frequency ratio of 3:1

    NASA Astrophysics Data System (ADS)

    Pu, Dong; Wei, Xueyong; Xu, Liu; Jiang, Zhuangde; Huan, Ronghua

    2018-01-01

    In this Letter, synchronization of micromechanical oscillators with a frequency ratio of 3:1 is reported. Two electrically coupled piezoresistive micromechanical oscillators are built for the study, and their oscillation frequencies are tuned via the Joule heating effect to find out the synchronization region. Experimental results show that the larger coupling strength or bias driving voltage is applied and a wider synchronization region is obtained. Interestingly, however, the oscillator's frequency tunability is dramatically reduced from -809.1 Hz/V to -23.1 Hz/V when synchronization is reached. A nearly 10-fold improvement of frequency stability at 1 s is observed from one of the synchronized oscillators, showing a comparable performance of the other. The stable high order synchronization of micromechanical oscillators is helpful to design high performance resonant sensors with a better frequency resolution and a larger scale factor.

  19. Servo-controlled pneumatic pressure oscillator for respiratory impedance measurements and high-frequency ventilation.

    PubMed

    Kaczka, David W; Lutchen, Kenneth R

    2004-04-01

    The ability to provide forced oscillatory excitation of the respiratory system can be useful in mechanical impedance measurements as well as high frequency ventilation (HFV). Experimental systems currently used for generating forced oscillations are limited in their ability to provide high amplitude flows or maintain the respiratory system at a constant mean pressure during excitation. This paper presents the design and implementation of a pneumatic pressure oscillator based on a proportional solenoid valve. The device is capable of providing forced oscillatory excitations to the respiratory system over a bandwidth suitable for mechanical impedance measurements and HVF. It delivers high amplitude flows (> 1.4 l/s) and utilizes a servo-control mechanism to maintain a load at a fixed mean pressure during simultaneous oscillation. Under open-loop conditions, the device exhibited a static hysteresis of approximately 7%, while its dynamic magnitude and phase responses were flat out to 10 Hz. Broad-band measurement of total harmonic distortion was approximately 19%. Under closed-loop conditions, the oscillator was able to maintain a mechanical test load at both positive and negative mean pressures during oscillatory excitations from 0.1 to 10.0 Hz. Impedance of the test load agreed closely with theoretical predictions. We conclude that this servo-controlled oscillator can be a useful tool for respiratory impedance measurements as well as HFV.

  20. Automatic oscillator frequency control system

    NASA Technical Reports Server (NTRS)

    Smith, S. F. (Inventor)

    1985-01-01

    A frequency control system makes an initial correction of the frequency of its own timing circuit after comparison against a frequency of known accuracy and then sequentially checks and corrects the frequencies of several voltage controlled local oscillator circuits. The timing circuit initiates the machine cycles of a central processing unit which applies a frequency index to an input register in a modulo-sum frequency divider stage and enables a multiplexer to clock an accumulator register in the divider stage with a cyclical signal derived from the oscillator circuit being checked. Upon expiration of the interval, the processing unit compares the remainder held as the contents of the accumulator against a stored zero error constant and applies an appropriate correction word to a correction stage to shift the frequency of the oscillator being checked. A signal from the accumulator register may be used to drive a phase plane ROM and, with periodic shifts in the applied frequency index, to provide frequency shift keying of the resultant output signal. Interposition of a phase adder between the accumulator register and phase plane ROM permits phase shift keying of the output signal by periodic variation in the value of a phase index applied to one input of the phase adder.

  1. A novel optogenetically tunable frequency modulating oscillator

    PubMed Central

    2018-01-01

    Synthetic biology has enabled the creation of biological reconfigurable circuits, which perform multiple functions monopolizing a single biological machine; Such a system can switch between different behaviours in response to environmental cues. Previous work has demonstrated switchable dynamical behaviour employing reconfigurable logic gate genetic networks. Here we describe a computational framework for reconfigurable circuits in E.coli using combinations of logic gates, and also propose the biological implementation. The proposed system is an oscillator that can exhibit tunability of frequency and amplitude of oscillations. Further, the frequency of operation can be changed optogenetically. Insilico analysis revealed that two-component light systems, in response to light within a frequency range, can be used for modulating the frequency of the oscillator or stopping the oscillations altogether. Computational modelling reveals that mixing two colonies of E.coli oscillating at different frequencies generates spatial beat patterns. Further, we show that these oscillations more robustly respond to input perturbations compared to the base oscillator, to which the proposed oscillator is a modification. Compared to the base oscillator, the proposed system shows faster synchronization in a colony of cells for a larger region of the parameter space. Additionally, the proposed oscillator also exhibits lesser synchronization error in the transient period after input perturbations. This provides a strong basis for the construction of synthetic reconfigurable circuits in bacteria and other organisms, which can be scaled up to perform functions in the field of time dependent drug delivery with tunable dosages, and sets the stage for further development of circuits with synchronized population level behaviour. PMID:29389936

  2. A novel optogenetically tunable frequency modulating oscillator.

    PubMed

    Mahajan, Tarun; Rai, Kshitij

    2018-01-01

    Synthetic biology has enabled the creation of biological reconfigurable circuits, which perform multiple functions monopolizing a single biological machine; Such a system can switch between different behaviours in response to environmental cues. Previous work has demonstrated switchable dynamical behaviour employing reconfigurable logic gate genetic networks. Here we describe a computational framework for reconfigurable circuits in E.coli using combinations of logic gates, and also propose the biological implementation. The proposed system is an oscillator that can exhibit tunability of frequency and amplitude of oscillations. Further, the frequency of operation can be changed optogenetically. Insilico analysis revealed that two-component light systems, in response to light within a frequency range, can be used for modulating the frequency of the oscillator or stopping the oscillations altogether. Computational modelling reveals that mixing two colonies of E.coli oscillating at different frequencies generates spatial beat patterns. Further, we show that these oscillations more robustly respond to input perturbations compared to the base oscillator, to which the proposed oscillator is a modification. Compared to the base oscillator, the proposed system shows faster synchronization in a colony of cells for a larger region of the parameter space. Additionally, the proposed oscillator also exhibits lesser synchronization error in the transient period after input perturbations. This provides a strong basis for the construction of synthetic reconfigurable circuits in bacteria and other organisms, which can be scaled up to perform functions in the field of time dependent drug delivery with tunable dosages, and sets the stage for further development of circuits with synchronized population level behaviour.

  3. Interplay of intrinsic and synaptic conductances in the generation of high-frequency oscillations in interneuronal networks with irregular spiking.

    PubMed

    Baroni, Fabiano; Burkitt, Anthony N; Grayden, David B

    2014-05-01

    High-frequency oscillations (above 30 Hz) have been observed in sensory and higher-order brain areas, and are believed to constitute a general hallmark of functional neuronal activation. Fast inhibition in interneuronal networks has been suggested as a general mechanism for the generation of high-frequency oscillations. Certain classes of interneurons exhibit subthreshold oscillations, but the effect of this intrinsic neuronal property on the population rhythm is not completely understood. We study the influence of intrinsic damped subthreshold oscillations in the emergence of collective high-frequency oscillations, and elucidate the dynamical mechanisms that underlie this phenomenon. We simulate neuronal networks composed of either Integrate-and-Fire (IF) or Generalized Integrate-and-Fire (GIF) neurons. The IF model displays purely passive subthreshold dynamics, while the GIF model exhibits subthreshold damped oscillations. Individual neurons receive inhibitory synaptic currents mediated by spiking activity in their neighbors as well as noisy synaptic bombardment, and fire irregularly at a lower rate than population frequency. We identify three factors that affect the influence of single-neuron properties on synchronization mediated by inhibition: i) the firing rate response to the noisy background input, ii) the membrane potential distribution, and iii) the shape of Inhibitory Post-Synaptic Potentials (IPSPs). For hyperpolarizing inhibition, the GIF IPSP profile (factor iii)) exhibits post-inhibitory rebound, which induces a coherent spike-mediated depolarization across cells that greatly facilitates synchronous oscillations. This effect dominates the network dynamics, hence GIF networks display stronger oscillations than IF networks. However, the restorative current in the GIF neuron lowers firing rates and narrows the membrane potential distribution (factors i) and ii), respectively), which tend to decrease synchrony. If inhibition is shunting instead of

  4. Interplay of Intrinsic and Synaptic Conductances in the Generation of High-Frequency Oscillations in Interneuronal Networks with Irregular Spiking

    PubMed Central

    Baroni, Fabiano; Burkitt, Anthony N.; Grayden, David B.

    2014-01-01

    High-frequency oscillations (above 30 Hz) have been observed in sensory and higher-order brain areas, and are believed to constitute a general hallmark of functional neuronal activation. Fast inhibition in interneuronal networks has been suggested as a general mechanism for the generation of high-frequency oscillations. Certain classes of interneurons exhibit subthreshold oscillations, but the effect of this intrinsic neuronal property on the population rhythm is not completely understood. We study the influence of intrinsic damped subthreshold oscillations in the emergence of collective high-frequency oscillations, and elucidate the dynamical mechanisms that underlie this phenomenon. We simulate neuronal networks composed of either Integrate-and-Fire (IF) or Generalized Integrate-and-Fire (GIF) neurons. The IF model displays purely passive subthreshold dynamics, while the GIF model exhibits subthreshold damped oscillations. Individual neurons receive inhibitory synaptic currents mediated by spiking activity in their neighbors as well as noisy synaptic bombardment, and fire irregularly at a lower rate than population frequency. We identify three factors that affect the influence of single-neuron properties on synchronization mediated by inhibition: i) the firing rate response to the noisy background input, ii) the membrane potential distribution, and iii) the shape of Inhibitory Post-Synaptic Potentials (IPSPs). For hyperpolarizing inhibition, the GIF IPSP profile (factor iii)) exhibits post-inhibitory rebound, which induces a coherent spike-mediated depolarization across cells that greatly facilitates synchronous oscillations. This effect dominates the network dynamics, hence GIF networks display stronger oscillations than IF networks. However, the restorative current in the GIF neuron lowers firing rates and narrows the membrane potential distribution (factors i) and ii), respectively), which tend to decrease synchrony. If inhibition is shunting instead of

  5. High-Frequency Oscillations Recorded on the Scalp of Patients With Epilepsy Using Tripolar Concentric Ring Electrodes.

    PubMed

    Besio, Walter G; Martínez-Juárez, Iris E; Makeyev, Oleksandr; Gaitanis, John N; Blum, Andrew S; Fisher, Robert S; Medvedev, Andrei V

    2014-01-01

    Epilepsy is the second most prevalent neurological disorder ([Formula: see text]% prevalence) affecting [Formula: see text] million people worldwide with up to 75% from developing countries. The conventional electroencephalogram is plagued with artifacts from movements, muscles, and other sources. Tripolar concentric ring electrodes automatically attenuate muscle artifacts and provide improved signal quality. We performed basic experiments in healthy humans to show that tripolar concentric ring electrodes can indeed record the physiological alpha waves while eyes are closed. We then conducted concurrent recordings with conventional disc electrodes and tripolar concentric ring electrodes from patients with epilepsy. We found that we could detect high frequency oscillations, a marker for early seizure development and epileptogenic zone, on the scalp surface that appeared to become more narrow-band just prior to seizures. High frequency oscillations preceding seizures were present in an average of 35.5% of tripolar concentric ring electrode data channels for all the patients with epilepsy whose seizures were recorded and absent in the corresponding conventional disc electrode data. An average of 78.2% of channels that contained high frequency oscillations were within the seizure onset or irritative zones determined independently by three epileptologists based on conventional disc electrode data and videos.

  6. Experiments on Suppression of Thermocapillary Oscillations in Sodium Nitrate Floating Half-Zones by High-frequency End-wall Vibrations

    NASA Technical Reports Server (NTRS)

    Anilkumar, A.; Grugel, R. N.; Bhowmick, J.; Wang, T.

    2004-01-01

    Experiments to suppress thermocapillary oscillations using high-frequency vibrations were carried out in sodium nitrate floating half-zones. Such a half-zone is formed by melting one end of a vertically held sodium nitrate crystal rod in contact with a hot surface at the top. Thermocapillary convection occurs in the melt because of the temperature gradient at the free surface of the melt. In the experiments, when thermocapillary oscillations occurred, the bottom end of the crystal rod was vibrated at a high frequency to generate a streaming flow in a direction opposite to that of the thermocapillary convection. It is observed that, by generating a sufficiently strong streaming flow, the thermocapillary flow can be offset enough such that the associated thermocapillary oscillations can be quenched.

  7. HIGH POWER PULSED OSCILLATOR

    DOEpatents

    Singer, S.; Neher, L.K.

    1957-09-24

    A high powered, radio frequency pulse oscillator is described for generating trains of oscillations at the instant an input direct voltage is impressed, or immediately upon application of a light pulse. In one embodiment, the pulse oscillator comprises a photo-multiplier tube with the cathode connected to the first dynode by means of a resistor, and adjacent dynodes are connected to each other through adjustable resistors. The ohmage of the resistors progressively increases from a very low value for resistors adjacent the cathode to a high value adjacent the plate, the last dynode. Oscillation occurs with this circuit when a high negative voltage pulse is applied to the cathode and the photo cathode is bombarded. Another embodiment adds capacitors at the resistor connection points of the above circuit to increase the duration of the oscillator train.

  8. Frequency jumps in single chip microwave LC oscillators

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Gualco, Gabriele; Grisi, Marco; Boero, Giovanni, E-mail: giovanni.boero@epfl.ch

    2014-12-15

    We report on the experimental observation of oscillation frequency jumps in microwave LC oscillators fabricated using standard complementary metal-oxide-semiconductor technologies. The LC oscillators, operating at a frequency of about 20 GHz, consist of a single turn planar coil, a metal-oxide-metal capacitor, and two cross-coupled metal-oxide-semiconductor field effect transistors used as negative resistance network. At 300 K as well as at 77 K, the oscillation frequency is a continuous function of the oscillator bias voltage. At 4 K, frequency jumps as large as 30 MHz are experimentally observed. This behavior is tentatively attributed to the emission and capture of single electrons from defects andmore » dopant atoms.« less

  9. Frequency stability improvement for piezoresistive micromechanical oscillators via synchronization

    NASA Astrophysics Data System (ADS)

    Pu, Dong; Huan, Ronghua; Wei, Xueyong

    2017-03-01

    Synchronization phenomenon first discovered in Huygens' clock shows that the rhythms of oscillating objects can be adjusted via an interaction. Here we show that the frequency stability of a piezoresistive micromechanical oscillator can be enhanced via synchronization. The micromechanical clamped-clamped beam oscillator is built up using the electrostatic driving and piezoresistive sensing technique and the synchronization phenomenon is observed after coupling it to an external oscillator. An enhancement of frequency stability is obtained in the synchronization state. The influences of the synchronizing perturbation intensity and frequency detuning applied on the oscillator are studied experimentally. A theoretical analysis of phase noise leads to an analytical formula for predicting Allan deviation of the frequency output of the piezoresistive oscillator, which successfully explains the experimental observations and the mechanism of frequency stability enhancement via synchronization.

  10. High-frequency sediment-level oscillations in the swash zone

    USGS Publications Warehouse

    Sallenger, A.H.; Richmond, B.M.

    1984-01-01

    Sediment-level oscillations with heights of about 6 cm and shore-normal lengths of order 10 m have been measured in the swash zone of a high-energy, coarse-sand beach. Crests of oscillations were shore parallel and continuous alongshore. The oscillations were of such low steepness (height-to-length ratio approximately 0.006) that they were difficult to detect visually. The period of oscillation ranged between 6 and 15 min and decreased landward across the swash zone. The sediment-level oscillations were progressive landward with an average migration rate in the middle to upper swash zone of 0.8 m min-1. Migration was caused mostly by erosion on the seaward flank of the crest of an oscillation during a period of net seaward sediment transport. Thus, the observed migration was a form migration landward rather than a migration involving net landward sediment transport. The observed sediment-level oscillations were different than sand waves or other swash-zone bedforms previously described. ?? 1984.

  11. A PK-PD Model of Ketamine-Induced High-Frequency Oscillations

    PubMed Central

    Flores, Francisco J.; Ching, ShiNung; Hartnack, Katharine; Fath, Amanda B.; Purdon, Patrick L.; Wilson, Matthew A.; Brown, Emery N.

    2017-01-01

    Objective Ketamine is a widely used drug with clinical and research applications, and also known to be used as a recreational drug. Ketamine produces conspicuous changes in the electrocorticographic (ECoG) signals observed both in humans and rodents. In rodents, the intracranial ECoG displays a High-Frequency Oscillation (HFO) which power is modulated non-linearly by ketamine dose. Despite the widespread use of ketamine there is no model description of the relationship between the pharmacokinetic-pharmacodynamics (PK-PD) of ketamine and the observed HFO power. Approach In the present study, we developed a PK-PD model based on estimated ketamine concentration, its known pharmacological actions, and observed ECoG effects. The main pharmacological action of ketamine is antagonism of the NMDA receptor (NMDAR), which in rodents is accompanied by a high-frequency oscillation (HFO) observed in the ECoG. At high doses, however, ketamine also acts at non-NMDAR sites, produces loss of consciousness, and the transient disappearance of the HFO. We propose a two-compartment PK model that represents the concentration of ketamine, and a PD model based in opposing effects of the NMDAR and non-NMDAR actions on the HFO power. Main results We recorded ECoG from the cortex of rats after two doses of ketamine, and extracted the HFO power from the ECoG spectrograms. We fit the PK-PD model to the time course of the HFO power, and showed that the model reproduces the dose-dependent profile of the HFO power. The model provides good fits even in the presence of high variability in HFO power across animals. As expected, the model does not provide good fits to the HFO power after dosing the pure NMDAR antagonist MK-801. Significance Our study provides a simple model to relate the observed electrophysiological effects of ketamine to its actions at the molecular level at different concentrations. This will improve the study of ketamine and rodent models of schizophrenia to better understand the

  12. Magnetoquantum Oscillations at THz Frequencies in InSb.

    PubMed

    Gogoi, P; Kamenskyi, D; Arslanov, D D; Jongma, R T; van der Zande, W J; Redlich, B; van der Meer, A F G; Engelkamp, H; Christianen, P C M; Maan, J C

    2017-10-06

    The ac magnetoconductance of bulk InSb at THz frequencies in high magnetic fields, as measured by the transmission of THz radiation, shows a field-induced transmission, which at high temperatures (≈100  K) is well explained with classical magnetoplasma effects (helicon waves). However, at low temperatures (4 K), the transmitted radiation intensity shows magnetoquantum oscillations that represent the Shubnikov-de Haas effect at THz frequencies. At frequencies above 0.9 THz, when the radiation period is shorter than the Drude scattering time, an anomalously high transmission is observed in the magnetic quantum limit that can be interpreted as carrier localization at high frequencies.

  13. Magnetoquantum Oscillations at THz Frequencies in InSb

    NASA Astrophysics Data System (ADS)

    Gogoi, P.; Kamenskyi, D.; Arslanov, D. D.; Jongma, R. T.; van der Zande, W. J.; Redlich, B.; van der Meer, A. F. G.; Engelkamp, H.; Christianen, P. C. M.; Maan, J. C.

    2017-10-01

    The ac magnetoconductance of bulk InSb at THz frequencies in high magnetic fields, as measured by the transmission of THz radiation, shows a field-induced transmission, which at high temperatures (≈100 K ) is well explained with classical magnetoplasma effects (helicon waves). However, at low temperatures (4 K), the transmitted radiation intensity shows magnetoquantum oscillations that represent the Shubnikov-de Haas effect at THz frequencies. At frequencies above 0.9 THz, when the radiation period is shorter than the Drude scattering time, an anomalously high transmission is observed in the magnetic quantum limit that can be interpreted as carrier localization at high frequencies.

  14. 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.

  15. Highly Stable Wideband Microwave Extraction by Synchronizing Widely Tunable Optoelectronic Oscillator with Optical Frequency Comb

    PubMed Central

    Hou, D.; Xie, X. P.; Zhang, Y. L.; Wu, J. T.; Chen, Z. Y.; Zhao, J. Y.

    2013-01-01

    Optical frequency combs (OFCs), based on mode-locked lasers (MLLs), have attracted considerable attention in many fields over recent years. Among the applications of OFCs, one of the most challenging works is the extraction of a highly stable microwave with low phase noise. Many synchronisation schemes have been exploited to synchronise an electronic oscillator with the pulse train from a MLL, helping to extract an ultra-stable microwave. Here, we demonstrate novel wideband microwave extraction from a stable OFC by synchronising a single widely tunable optoelectronic oscillator (OEO) with an OFC at different harmonic frequencies, using an optical phase detection technique. The tunable range of the proposed microwave extraction extends from 2 GHz to 4 GHz, and in a long-term synchronisation experiment over 12 hours, the proposed synchronisation scheme provided a rms timing drift of 18 fs and frequency instabilities at 1.2 × 10−15/1 s and 2.2 × 10−18/10000 s. PMID:24336459

  16. Highly Stable Wideband Microwave Extraction by Synchronizing Widely Tunable Optoelectronic Oscillator with Optical Frequency Comb

    NASA Astrophysics Data System (ADS)

    Hou, D.; Xie, X. P.; Zhang, Y. L.; Wu, J. T.; Chen, Z. Y.; Zhao, J. Y.

    2013-12-01

    Optical frequency combs (OFCs), based on mode-locked lasers (MLLs), have attracted considerable attention in many fields over recent years. Among the applications of OFCs, one of the most challenging works is the extraction of a highly stable microwave with low phase noise. Many synchronisation schemes have been exploited to synchronise an electronic oscillator with the pulse train from a MLL, helping to extract an ultra-stable microwave. Here, we demonstrate novel wideband microwave extraction from a stable OFC by synchronising a single widely tunable optoelectronic oscillator (OEO) with an OFC at different harmonic frequencies, using an optical phase detection technique. The tunable range of the proposed microwave extraction extends from 2 GHz to 4 GHz, and in a long-term synchronisation experiment over 12 hours, the proposed synchronisation scheme provided a rms timing drift of 18 fs and frequency instabilities at 1.2 × 10-15/1 s and 2.2 × 10-18/10000 s.

  17. Disordered high-frequency oscillation in face processing in schizophrenia patients

    PubMed Central

    Liu, Miaomiao; Pei, Guangying; Peng, Yinuo; Wang, Changming; Yan, Tianyi; Wu, Jinglong

    2018-01-01

    Abstract Schizophrenia is a complex disorder characterized by marked social dysfunctions, but the neural mechanism underlying this deficit is unknown. To investigate whether face-specific perceptual processes are influenced in schizophrenia patients, both face detection and configural analysis were assessed in normal individuals and schizophrenia patients by recording electroencephalogram (EEG) data. Here, a face processing model was built based on the frequency oscillations, and the evoked power (theta, alpha, and beta bands) and the induced power (gamma bands) were recorded while the subjects passively viewed face and nonface images presented in upright and inverted orientations. The healthy adults showed a significant face-specific effect in the alpha, beta, and gamma bands, and an inversion effect was observed in the gamma band in the occipital lobe and right temporal lobe. Importantly, the schizophrenia patients showed face-specific deficits in the low-frequency beta and gamma bands, and the face inversion effect in the gamma band was absent from the occipital lobe. All these results revealed face-specific processing in patients due to the disorder of high-frequency EEG, providing additional evidence to enrich future studies investigating neural mechanisms and serving as a marked diagnostic basis. PMID:29419668

  18. 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

  19. Variations in High-frequency Oscillations of Tropical Cyclones over the Western North Pacific

    NASA Astrophysics Data System (ADS)

    Chen, Shumin; Li, Weibiao; Wen, Zhiping; Zhou, Mingsen; Lu, Youyu; Qian, Yu-Kun; Liu, Haoya; Fang, Rong

    2018-04-01

    Variations in the high-frequency oscillations of tropical cyclones (TCs) over the western North Pacific (WNP) are studied in numerical model simulations. Power spectrum analysis of maximum wind speeds at 10 m (MWS10) from an ensemble of 15 simulated TCs shows that oscillations are significant for all TCs. The magnitudes of oscillations in MWS10 are similar in the WNP and South China Sea (SCS); however, the mean of the averaged significant periods in the SCS (1.93 h) is shorter than that in the open water of the WNP (2.83 h). The shorter period in the SCS is examined through an ensemble of simulations, and a case simulation as well as a sensitivity experiment in which the continent is replaced by ocean for Typhoon Hagupit (2008). The analysis of the convergence efficiency within the boundary layer suggests that the shorter periods in the SCS are possibly due to the stronger terrain effect, which intensifies convergence through greater friction. The enhanced convergence strengthens the disturbance of the gradient and thermal wind balances, and then contributes to the shorter oscillation periods in the SCS.

  20. A method for the topographical identification and quantification of high frequency oscillations in intracranial electroencephalography recordings

    PubMed Central

    Waldman, Zachary J.; Shimamoto, Shoichi; Song, Inkyung; Orosz, Iren; Bragin, Anatol; Fried, Itzhak; Engel, Jerome; Staba, Richard; Sperling, Michael R.; Weiss, Shennan A.

    2018-01-01

    Objective To develop a reliable software method using a topographic analysis of time-frequency plots to distinguish ripple (80–200 Hz) oscillations that are often associated with EEG sharp waves or spikes (RonS) from sinusoid-like waveforms that appear as ripples but correspond with digital filtering of sharp transients contained in the wide bandwidth EEG. Methods A custom algorithm distinguished true from false ripples in one second intracranial EEG (iEEG) recordings using wavelet convolution, identifying contours of isopower, and categorizing these contours into sets of open or closed loop groups. The spectral and temporal features of candidate groups were used to classify the ripple, and determine its duration, frequency, and power. Verification of detector accuracy was performed on the basis of simulations, and visual inspection of the original and band-pass filtered signals. Results The detector could distinguish simulated true from false ripple on spikes (RonS). Among 2934 visually verified trials of iEEG recordings and spectrograms exhibiting RonS the accuracy of the detector was 88.5% with a sensitivity of 81.8% and a specificity of 95.2%. The precision was 94.5% and the negative predictive value was 84.0% (N = 12). Among, 1,370 trials of iEEG recording exhibiting RonS that were reviewed blindly without spectrograms the accuracy of the detector was 68.0%, with kappa equal to 0.01 ± 0.03. The detector successfully distinguished ripple from high spectral frequency ‘fast ripple’ oscillations (200–600 Hz), and characterize ripple duration and spectral frequency and power. The detector was confounded by brief bursts of gamma (30–80 Hz) activity in 7.31 ± 6.09% of trials, and in 30.2 ± 14.4% of the true RonS detections ripple duration was underestimated. Conclusions Characterizing the topographic features of a time-frequency plot generated by wavelet convolution is useful for distinguishing true oscillations from false oscillations generated by

  1. U.S. Hail Frequency and the Global Wind Oscillation

    NASA Astrophysics Data System (ADS)

    Gensini, Vittorio A.; Allen, John T.

    2018-02-01

    Changes in Earth relative atmospheric angular momentum can be described by an index known as the Global Wind Oscillation. This global index accounts for changes in Earth's atmospheric budget of relative angular momentum through interactions of tropical convection anomalies, extratropical dynamics, and engagement of surface torques (e.g., friction and mountain). It is shown herein that U.S. hail events are more (less) likely to occur in low (high) atmospheric angular momentum base states when excluding weak Global Wind Oscillation days, with the strongest relationships found in the boreal spring and fall. Severe, significant severe, and giant hail events are more likely to occur during Global Wind Oscillation phases 8, 1, 2, and 3 during the peak of U.S. severe weather season. Lower frequencies of hail events are generally found in Global Wind Oscillation phases 4-7 but vary based on Global Wind Oscillation amplitude and month. In addition, probabilistic anomalies of atmospheric ingredients supportive of hail producing supercell thunderstorms closely mimic locations of reported hail frequency, helping to corroborate report results.

  2. High-Frequency Oscillations Recorded on the Scalp of Patients With Epilepsy Using Tripolar Concentric Ring Electrodes

    PubMed Central

    Martínez-Juárez, Iris E.; Makeyev, Oleksandr; Gaitanis, John N.; Blum, Andrew S.; Fisher, Robert S.; Medvedev, Andrei V.

    2014-01-01

    Epilepsy is the second most prevalent neurological disorder (\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{upgreek} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} }{}\\(\\sim 1\\) \\end{document}% prevalence) affecting \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{upgreek} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} }{}\\(\\sim 67\\) \\end{document} million people worldwide with up to 75% from developing countries. The conventional electroencephalogram is plagued with artifacts from movements, muscles, and other sources. Tripolar concentric ring electrodes automatically attenuate muscle artifacts and provide improved signal quality. We performed basic experiments in healthy humans to show that tripolar concentric ring electrodes can indeed record the physiological alpha waves while eyes are closed. We then conducted concurrent recordings with conventional disc electrodes and tripolar concentric ring electrodes from patients with epilepsy. We found that we could detect high frequency oscillations, a marker for early seizure development and epileptogenic zone, on the scalp surface that appeared to become more narrow-band just prior to seizures. High frequency oscillations preceding seizures were present in an average of 35.5% of tripolar concentric ring electrode data channels for all the patients with epilepsy whose seizures were recorded and absent in the corresponding conventional disc electrode data. An average of 78.2% of channels that contained high frequency oscillations were within the seizure onset or irritative zones determined independently by three epileptologists based on conventional disc electrode data and videos. PMID:27170874

  3. Frequency transitions in odor-evoked neural oscillations.

    PubMed

    Ito, Iori; Bazhenov, Maxim; Ong, Rose Chik-ying; Raman, Baranidharan; Stopfer, Mark

    2009-12-10

    In many species, sensory stimuli elicit the oscillatory synchronization of groups of neurons. What determines the properties of these oscillations? In the olfactory system of the moth, we found that odors elicited oscillatory synchronization through a neural mechanism like that described in locust and Drosophila. During responses to long odor pulses, oscillations suddenly slowed as net olfactory receptor neuron (ORN) output decreased; thus, stimulus intensity appeared to determine oscillation frequency. However, changing the concentration of the odor had little effect upon oscillatory frequency. Our recordings in vivo and computational models based on these results suggested that the main effect of increasing odor concentration was to recruit additional, less well-tuned ORNs whose firing rates were tightly constrained by adaptation and saturation. Thus, in the periphery, concentration is encoded mainly by the size of the responsive ORN population, and oscillation frequency is set by the adaptation and saturation of this response.

  4. Parametric Oscillation, Frequency Mixing, and Injection Locking of Strongly Coupled Nanomechanical Resonator Modes.

    PubMed

    Seitner, Maximilian J; Abdi, Mehdi; Ridolfo, Alessandro; Hartmann, Michael J; Weig, Eva M

    2017-06-23

    We study locking phenomena of two strongly coupled, high quality factor nanomechanical resonator modes to a common parametric drive at a single drive frequency in different parametric driving regimes. By controlled dielectric gradient forces we tune the resonance frequencies of the flexural in-plane and out-of-plane oscillation of the high stress silicon nitride string through their mutual avoided crossing. For the case of the strong common parametric drive signal-idler generation via nondegenerate parametric two-mode oscillation is observed. Broadband frequency tuning of the very narrow linewidth signal and idler resonances is demonstrated. When the resonance frequencies of the signal and idler get closer to each other, partial injection locking, injection pulling, and complete injection locking to half of the drive frequency occurs depending on the pump strength. Furthermore, satellite resonances, symmetrically offset from the signal and idler by their beat note, are observed, which can be attributed to degenerate four-wave mixing in the highly nonlinear mechanical oscillations.

  5. Frequency transitions in odor-evoked neural oscillations

    PubMed Central

    Ito, Iori; Bazhenov, Maxim; Ong, Rose Chik-ying; Raman, Baranidharan; Stopfer, Mark

    2009-01-01

    Summary In many species sensory stimuli elicit the oscillatory synchronization of groups of neurons. What determines the properties of these oscillations? In the olfactory system of the moth we found that odors elicited oscillatory synchronization through a neural mechanism like that described in locust and Drosophila. During responses to long odor pulses, oscillations suddenly slowed as net olfactory receptor neuron (ORN) output decreased; thus, stimulus intensity appeared to determine oscillation frequency. However, changing the concentration of the odor had little effect upon oscillatory frequency. Our recordings in vivo and computational models based on these results suggested the main effect of increasing odor concentration was to recruit additional, less well-tuned ORNs whose firing rates were tightly constrained by adaptation and saturation. Thus, in the periphery, concentration is encoded mainly by the size of the responsive ORN population, and oscillation frequency is set by the adaptation and saturation of this response. PMID:20005825

  6. Improving the frequency precision of oscillators by synchronization.

    PubMed

    Cross, M C

    2012-04-01

    Improving the frequency precision by synchronizing a lattice of N oscillators with disparate frequencies is studied in the phase reduction limit. In the general case where the coupling is not purely dissipative the synchronized state consists of targetlike waves radiating from a local source, which is a region of higher-frequency oscillators. In this state the improvement of the frequency precision is shown to be independent of N for large N, but instead depends on the disorder and reflects the dependence of the frequency of the synchronized state on just those oscillators in the source region of the waves. These results are obtained by a mapping of the nonlinear phase dynamics onto the linear Anderson problem of the quantum mechanics of electrons on a random lattice in the tight-binding approximation.

  7. The role of high-frequency oscillations in epilepsy surgery planning.

    PubMed

    Gloss, David; Nolan, Sarah J; Staba, Richard

    2014-01-15

    Epilepsy is a serious brain disorder characterized by recurrent unprovoked seizures. Approximately two-thirds of seizures can be controlled with antiepileptic medications (Kwan 2000). For some of the others, surgery can completely eliminate or significantly reduce the occurrence of disabling seizures. Localization of epileptogenic areas for resective surgery is far from perfect, and new tools are being investigated to more accurately localize the epileptogenic zone (the zone of the brain where the seizures begin) and improve the likelihood of freedom from postsurgical seizures. Recordings of pathological high-frequency oscillations (HFOs) may be one such tool. To assess the ability of HFOs to improve the outcomes of epilepsy surgery by helping to identify more accurately the epileptogenic areas of the brain. We searched the Cochrane Epilepsy Group Specialized Register (15 April 2013), the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library (2013, Issue 3), MEDLINE (Ovid) (1946 to 15 April 2013), CINAHL (EBSCOhost) (15 April 2013), Web of Knowledge (Thomson Reuters) (15 April 2013), www.clinicaltrials.gov (15 April 2013), and the World Health Organization International Clinical Trials Registry Platform (15 April 2013). We included studies that provided information on the outcomes of epilepsy surgery at at least six months and which used high-frequency oscillations in making decisions about epilepsy surgery. The primary outcome of the review was the Engel Class Outcome System. Secondary outcomes were responder rate, International League Against Epilepsy (ILAE) epilepsy surgery outcome, frequency of adverse events from any source and quality of life outcomes. We intended to analyse outcomes via an aggregated data fixed-effect model meta-analysis. Two studies met the inclusion criteria. Both studies were small non-randomised trials, with no control group and no blinding. The quality of evidence for all outcomes was very low. The combination

  8. High frequency stimulation abolishes thalamic network oscillations: an electrophysiological and computational analysis

    NASA Astrophysics Data System (ADS)

    Lee, Kendall H.; Hitti, Frederick L.; Chang, Su-Youne; Lee, Dongchul C.; Roberts, David W.; McIntyre, Cameron C.; Leiter, James C.

    2011-08-01

    Deep brain stimulation (DBS) of the thalamus has been demonstrated to be effective for the treatment of epilepsy. To investigate the mechanism of action of thalamic DBS, we examined the effects of high frequency stimulation (HFS) on spindle oscillations in thalamic brain slices from ferrets. We recorded intracellular and extracellular electrophysiological activity in the nucleus reticularis thalami (nRt) and in thalamocortical relay (TC) neurons in the lateral geniculate nucleus, stimulated the slice using a concentric bipolar electrode, and recorded the level of glutamate within the slice. HFS (100 Hz) of TC neurons generated excitatory post-synaptic potentials, increased the number of action potentials in both TC and nRt neurons, reduced the input resistance, increased the extracellular glutamate concentration, and abolished spindle wave oscillations. HFS of the nRt also suppressed spindle oscillations. In both locations, HFS was associated with significant and persistent elevation in extracellular glutamate levels and suppressed spindle oscillations for many seconds after the cessation of stimulation. We simulated HFS within a computational model of the thalamic network, and HFS also disrupted spindle wave activity, but the suppression of spindle activity was short-lived. Simulated HFS disrupted spindle activity for prolonged periods of time only after glutamate release and glutamate-mediated activation of a hyperpolarization-activated current (Ih) was incorporated into the model. Our results suggest that the mechanism of action of thalamic DBS as used in epilepsy may involve the prolonged release of glutamate, which in turn modulates specific ion channels such as Ih, decreases neuronal input resistance, and abolishes thalamic network oscillatory activity.

  9. Optoelectronic oscillator with improved phase noise and frequency stability

    NASA Astrophysics Data System (ADS)

    Eliyahu, Danny; Sariri, Kouros; Taylor, Joseph; Maleki, Lute

    2003-07-01

    In this paper we report on recent improvements in phase noise and frequency stability of a 10 GHz opto-electronic oscillator. In our OEO loop, the high Q elements (the optical fiber and the narrow bandpass microwave filter) are thermally stabilized using resistive heaters and temperature controllers, keeping their temperature above ambient. The thermally stabilized free running OEO demonstrates a short-term frequency stability of 0.02 ppm (over several hours) and frequency vs. temperature slope of -0.1 ppm/°C (compared to -8.3 ppm/°C for non thermally stabilized OEO). We obtained an exceptional spectral purity with phase noise level of -143 dBc/Hz at 10 kHz of offset frequency. We also describe the multi-loop configuration that reduces dramatically the spurious level at offset frequencies related to the loop round trip harmonic frequency. The multi-loop configuration has stronger mode selectivity due to interference between signals having different cavity lengths. A drop of the spurious level below -90 dBc was demonstrated. The effect of the oscillator aging on the frequency stability was studied as well by recording the oscillator frequency (in a chamber) over several weeks. We observed reversal in aging direction with logarithmic behavior of A ln(B t+1)-C ln(D t+1), where t is the time and A, B, C, D are constants. Initially, in the first several days, the positive aging dominates. However, later the negative aging mechanism dominates. We have concluded that the long-term aging behavioral model is consistent with the experimental results.

  10. High-frequency optical oscillation during the flare phase of the red dwarf EV Lac

    NASA Astrophysics Data System (ADS)

    Contadakis, M.; Avgoloupis, S.; Seiradakis, J.

    2006-01-01

    The observational support of the presence of high frequency low amplitude oscillations reported by Zhillyaev et al. 2000 and Contadakis et al. 2004, is highly demanding and will be done by the future observations and by carefully reanalysing the data from our files. In this paper we present the results of the analysis of the B-light curve for a flare of magnitude 1.01,which was observed on September,1993. Despite the low time resolution (sampling interval 12s) we were able to detect transient low amplitude oscillations with period ranging between 30s and 125s with a confidence level higher than 70%. This result is in favour of (or does not contradict) the suggested explanation i.e the evolution of a fast mode magneto-acoustic wave generated at the impulsive phase of the flare and travelling through the magnetic loop From: Michael E.Contadakis Address: kodadaki@vergina.eng.auth.gr Database: phy

  11. High-frequency modulation of ion-acoustic waves.

    NASA Technical Reports Server (NTRS)

    Albright, N. W.

    1972-01-01

    A large amplitude, high-frequency electromagnetic oscillation is impressed on a nonrelativistic, collisionless plasma from an external source. The frequency is chosen to be far from the plasma frequency (in fact, lower). The resulting electron velocity distribution function strongly modifies the propagation of ion-acoustic waves parallel to the oscillating electric field. The complex frequency is calculated numerically.

  12. Localization of beta and high-frequency oscillations within the subthalamic nucleus region.

    PubMed

    van Wijk, B C M; Pogosyan, A; Hariz, M I; Akram, H; Foltynie, T; Limousin, P; Horn, A; Ewert, S; Brown, P; Litvak, V

    2017-01-01

    Parkinsonian bradykinesia and rigidity are typically associated with excessive beta band oscillations in the subthalamic nucleus. Recently another spectral peak has been identified that might be implicated in the pathophysiology of the disease: high-frequency oscillations (HFO) within the 150-400 Hz range. Beta-HFO phase-amplitude coupling (PAC) has been found to correlate with severity of motor impairment. However, the neuronal origin of HFO and its usefulness as a potential target for deep brain stimulation remain to be established. For example, it is unclear whether HFO arise from the same neural populations as beta oscillations. We intraoperatively recorded local field potentials from the subthalamic nucleus while advancing DBS electrodes in 2 mm steps from 4 mm above the surgical target point until 2 mm below, resulting in 4 recording sites. Data from 26 nuclei from 14 patients were analysed. For each trajectory, we identified the recording site with the largest spectral peak in the beta range (13-30 Hz), and the largest peak in the HFO range separately. In addition, we identified the recording site with the largest beta-HFO PAC. Recording sites with largest beta power and largest HFO power coincided in 50% of cases. In the other 50%, HFO was more likely to be detected at a more superior recording site in the target area. PAC followed more closely the site with largest HFO (45%) than beta power (27%). HFO are likely to arise from spatially close, but slightly more superior neural populations than beta oscillations. Further work is necessary to determine whether the different activities can help fine-tune deep brain stimulation targeting.

  13. Dependence of the colored frequency noise in spin torque oscillators on current and magnetic field

    NASA Astrophysics Data System (ADS)

    Eklund, Anders; Bonetti, Stefano; Sani, Sohrab R.; Majid Mohseni, S.; Persson, Johan; Chung, Sunjae; Amir Hossein Banuazizi, S.; Iacocca, Ezio; Östling, Mikael; Åkerman, Johan; Gunnar Malm, B.

    2014-03-01

    The nano-scale spin torque oscillator (STO) is a compelling device for on-chip, highly tunable microwave frequency signal generation. Currently, one of the most important challenges for the STO is to increase its longer-time frequency stability by decreasing the 1/f frequency noise, but its high level makes even its measurement impossible using the phase noise mode of spectrum analyzers. Here, we present a custom made time-domain measurement system with 150 MHz measurement bandwidth making possible the investigation of the variation of the 1/f as well as the white frequency noise in a STO over a large set of operating points covering 18-25 GHz. The 1/f level is found to be highly dependent on the oscillation amplitude-frequency non-linearity and the vicinity of unexcited oscillation modes. These findings elucidate the need for a quantitative theoretical treatment of the low-frequency, colored frequency noise in STOs. Based on the results, we suggest that the 1/f frequency noise possibly can be decreased by improving the microstructural quality of the metallic thin films.

  14. Transport of pulmonary secretions by asymmetric high frequency oscillation

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Gruenauer, L.M.

    1987-01-01

    Asymmetric high frequency oscillation (AHFO) was investigated as a mechanism for augmenting the clearance of excess pulmonary secretions from the airways of the lungs. In vitro and in vivo models were developed to test its ability to predictably transport pulmonary secretions. The augmentation of mucus transport by 10 Hz AHFO was investigated in the canine trachea. Ventilation of eight dogs (2 studies each) was performed with three AHFO power settings in random order and conventional mechanical ventilation (CMV) before or after the AHFO trials. Prior to each trial, 35-45 ..mu..l of canine muscus mixed with a radiotagged colloid (/sup 99/Tc/supmore » m/) was instilled in the distal trachea. As the radiotagged mixture traveled up the trachea, tracheal muscus velocities (TMV) were recorded on six channels with a multidetector probe. CMV mean TMVs before and after AHFO were not significantly different. The mean TMV of 6.3 +/- 2.6 mm/min at 30% power AHFO was faster than the CMV mean TVM of 4.1 +/- 2.1 mm/min (p <0.05).« less

  15. Serotonergic hallucinogens differentially modify gamma and high frequency oscillations in the rat nucleus accumbens.

    PubMed

    Goda, Sailaja A; Piasecka, Joanna; Olszewski, Maciej; Kasicki, Stefan; Hunt, Mark J

    2013-07-01

    The nucleus accumbens (NAc) is a site critical for the actions of many drugs of abuse. Psychoactive compounds, such as N-methyl-D-aspartate receptor (NMDAR) antagonists, modify gamma (40-90) and high frequency oscillations (HFO, 130-180 Hz) in local field potentials (LFPs) recorded in the NAc. Lysergic acid diethylamide (LSD) and 2,5-dimethoxy-4-iodoamphetamine (DOI) are serotonergic hallucinogens and activation of 5HT2A receptors likely underlies their hallucinogenic effects. Whether these compounds can also modulate LFP oscillations in the NAc is unclear. This study aims to examine the effect of serotonergic hallucinogens on gamma and HFO recorded in the NAc and to test whether 5HT2A receptors mediate the effects observed. LFPs were recorded from the NAc of freely moving rats. Drugs were administered intraperitoneally. LSD (0.03-0.3 mg/kg) and DOI (0.5-2.0 mg/kg) increased the power and reduced the frequency of HFO. In contrast, the hallucinogens produced a robust reduction in the power of low (40-60 Hz), but not high gamma oscillations (70-90 Hz). MDL 11939 (1.0 mg/kg), a 5HT2A receptor antagonist, fully reversed the changes induced by DOI on HFO but only partially for the low gamma band. Equivalent increases in HFO power were observed after TCB-2 (5HT2A receptor agonist, 0.1-1.5 mg/kg), but not CP 809101 (5H2C receptor agonist, 0.1-3 mg/kg). Notably, hallucinogen-induced increases in HFO power were smaller than those produced by ketamine (25 mg/kg). Serotonergic hallucinogen-induced changes in HFO and gamma are mediated, at least in part, by stimulation of 5HT2A receptors. Comparison of the oscillatory changes produced by serotonergic hallucinogens and NMDAR antagonists are also discussed.

  16. Synchronous Oscillations in Van Der Pol Generator with Modulated Natural Frequency

    NASA Astrophysics Data System (ADS)

    Nimets, A. Yu.; Vavriv, D. M.

    2015-12-01

    The synchronous operation of Van Der Pole generator with the low-frequency modulated natural frequency has been investigated. The presence of low-frequency modulation is shown to lead to formation of additional synchronization regions. The appearance of such regions is found to be caused by threefrequency resonances resulted from the interaction between oscillations of the generator natural frequency, modulation frequency and synchronized signal frequency. Characteristics of synchronous oscillations due to the below mentioned three-frequency interaction are obtained and comparison with the case of synchronization of oscillator on the main mode made.

  17. The role of high-frequency oscillations in epilepsy surgery planning

    PubMed Central

    Gloss, David; Nolan, Sarah J; Staba, Richard

    2014-01-01

    Background Epilepsy is a serious brain disorder characterized by recurrent unprovoked seizures. Approximately two-thirds of seizures can be controlled with antiepileptic medications (Kwan 2000). For some of the others, surgery can completely eliminate or significantly reduce the occurrence of disabling seizures. Localization of epileptogenic areas for resective surgery is far from perfect, and new tools are being investigated to more accurately localize the epileptogenic zone (the zone of the brain where the seizures begin) and improve the likelihood of freedom from postsurgical seizures. Recordings of pathological high-frequency oscillations (HFOs) may be one such tool. Objectives To assess the ability of HFOs to improve the outcomes of epilepsy surgery by helping to identify more accurately the epileptogenic areas of the brain. Search methods We searched the Cochrane Epilepsy Group Specialized Register (15 April 2013), the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library (2013, Issue 3), MEDLINE (Ovid) (1946 to 15 April 2013), CINAHL (EBSCOhost) (15 April 2013), Web of Knowledge (Thomson Reuters) (15 April 2013), www.clinicaltrials.gov (15 April 2013), and the World Health Organization International Clinical Trials Registry Platform (15 April 2013). Selection criteria We included studies that provided information on the outcomes of epilepsy surgery at at least six months and which used high-frequency oscillations in making decisions about epilepsy surgery. Data collection and analysis The primary outcome of the review was the Engel Class Outcome System. Secondary outcomes were responder rate, International League Against Epilepsy (ILAE) epilepsy surgery outcome, frequency of adverse events from any source and quality of life outcomes. We intended to analyse outcomes via an aggregated data fixed-effect model meta-analysis. Main results Two studies met the inclusion criteria. Both studies were small non-randomised trials, with no

  18. The role of high-frequency oscillations in epilepsy surgery planning.

    PubMed

    Gloss, David; Nevitt, Sarah J; Staba, Richard

    2017-10-05

    Epilepsy is a serious brain disorder characterized by recurrent unprovoked seizures. Approximately two-thirds of seizures can be controlled with antiepileptic medications (Kwan 2000). For some of the others, surgery can completely eliminate or significantly reduce the occurrence of disabling seizures. Localization of epileptogenic areas for resective surgery is far from perfect, and new tools are being investigated to more accurately localize the epileptogenic zone (the zone of the brain where the seizures begin) and improve the likelihood of freedom from postsurgical seizures. Recordings of pathological high-frequency oscillations (HFOs) may be one such tool. To assess the ability of HFOs to improve the outcomes of epilepsy surgery by helping to identify more accurately the epileptogenic areas of the brain. For the latest update, we searched the Cochrane Epilepsy Group Specialized Register (25 July 2016), the Cochrane Central Register of Controlled Trials (CENTRAL) via the Cochrane Register of Studies Online (CRSO, 25 July 2016), MEDLINE (Ovid, 1946 to 25 July 2016), CINAHL Plus (EBSCOhost, 25 July 2016), Web of Science (Thomson Reuters, 25 July 2016), ClinicalTrials.gov (25 July 2016), and the World Health Organization International Clinical Trials Registry Platform ICTRP (25 July 2016). We included studies that provided information on the outcomes of epilepsy surgery for at least six months and which used high-frequency oscillations in making decisions about epilepsy surgery. The primary outcome of the review was the Engel Class Outcome System (class I = no disabling seizures, II = rare disabling seizures, III = worthwhile improvement, IV = no worthwhile improvement). Secondary outcomes were responder rate, International League Against Epilepsy (ILAE) epilepsy surgery outcome, frequency of adverse events from any source and quality of life outcomes. We intended to analyse outcomes via an aggregated data fixed-effect model meta-analysis. Two studies representing

  19. Study on ion energy distribution in low-frequency oscillation time scale of Hall thrusters

    NASA Astrophysics Data System (ADS)

    Wei, Liqiu; Li, Wenbo; Ding, Yongjie; Han, Liang; Yu, Daren; Cao, Yong

    2017-11-01

    This paper reports on the dynamic characteristics of the distribution of ion energy during Hall thruster discharge in the low-frequency oscillation time scale through experimental studies, and a statistical analysis of the time-varying peak and width of ion energy and the ratio of high-energy ions during the low-frequency oscillation. The results show that the ion energy distribution exhibits a periodic change during the low-frequency oscillation. Moreover, the variation in the ion energy peak is opposite to that of the discharge current, and the variations in width of the ion energy distribution and the ratio of high-energy ions are consistent with that of the discharge current. The variation characteristics of the ion density and discharge potential were simulated by one-dimensional hybrid-direct kinetic simulations; the simulation results and analysis indicate that the periodic change in the distribution of ion energy during the low-frequency oscillation depends on the relationship between the ionization source term and discharge potential distribution during ionization in the discharge channel.

  20. SPH simulation of turbulent flow past a high-frequency in-line oscillating cylinder near free-surface

    NASA Astrophysics Data System (ADS)

    Ghazanfarian, Jafar; Saghatchi, Roozbeh; Gorji-Bandpy, Mofid

    2016-08-01

    This paper studies a two-dimensional incompressible viscous flow past a circular cylinder with in-line oscillation close to a free-surface. The sub-particle scale (SPS) turbulence model of a Lagrangian particle-based smoothed-particle hydrodynamics (SPH) method has been used to solve the full Navier-Stokes equations together with the continuity equation. The accuracy of numerical code has been verified using two cases consisting of an oscillating cylinder placed in the stationary fluid, and flow over a fixed cylinder close to a free-surface. Simulations are conducted for the Froude number of 0.3, the Reynolds numbers of 40 and 80, various gap ratios for fully-submerged and half-submerge cylinders. The dimensionless frequency and amplitude of oscillating have been chosen as 0.5, 0.8 and 10, 15, respectively. The selection of such a high oscillating frequency causes the flow regime to become turbulent. It is seen that the gap ratio defined as the ratio of cylinder distance from free-surface and its diameter, strongly affects the flow pattern and the magnitude of the drag and lift coefficients. The jet-like flow (the region above the cylinder and beneath the free-surface) creation is discussed in detail and showed that the strength of this jet-like flow is weakened when the gap ratio shrinks. It is seen that by decreasing the gap ratio, the lift and drag coefficients increase and decrease, respectively. It is found that the Reynolds number has an inverse effect on the drag and lift coefficients. Also, it is concluded that by increasing the amplitude of oscillation the drag coefficient increases.

  1. High frequency optoelectronic oscillators based on the optical feedback of semiconductor mode-locked laser diodes.

    PubMed

    Haji, Mohsin; Hou, Lianping; Kelly, Anthony E; Akbar, Jehan; Marsh, John H; Arnold, John M; Ironside, Charles N

    2012-01-30

    Optical self seeding feedback techniques can be used to improve the noise characteristics of passively mode-locked laser diodes. External cavities such as fiber optic cables can increase the memory of the phase and subsequently improve the timing jitter. In this work, an improved optical feedback architecture is proposed using an optical fiber loop delay as a cavity extension of the mode-locked laser. We investigate the effect of the noise reduction as a function of the loop length and feedback power. The well known composite cavity technique is also implemented for suppressing supermode noise artifacts presented due to harmonic mode locking effects. Using this method, we achieve a record low radio frequency linewidth of 192 Hz for any high frequency (>1 GHz) passively mode-locked laser to date (to the best of the authors' knowledge), making it promising for the development of high frequency optoelectronic oscillators.

  2. High-frequency oscillations in human and monkey neocortex during the wake–sleep cycle

    PubMed Central

    Le Van Quyen, Michel; Muller, Lyle E.; Telenczuk, Bartosz; Halgren, Eric; Cash, Sydney; Hatsopoulos, Nicholas G.; Dehghani, Nima; Destexhe, Alain

    2016-01-01

    Beta (β)- and gamma (γ)-oscillations are present in different cortical areas and are thought to be inhibition-driven, but it is not known if these properties also apply to γ-oscillations in humans. Here, we analyze such oscillations in high-density microelectrode array recordings in human and monkey during the wake–sleep cycle. In these recordings, units were classified as excitatory and inhibitory cells. We find that γ-oscillations in human and β-oscillations in monkey are characterized by a strong implication of inhibitory neurons, both in terms of their firing rate and their phasic firing with the oscillation cycle. The β- and γ-waves systematically propagate across the array, with similar velocities, during both wake and sleep. However, only in slow-wave sleep (SWS) β- and γ-oscillations are associated with highly coherent and functional interactions across several millimeters of the neocortex. This interaction is specifically pronounced between inhibitory cells. These results suggest that inhibitory cells are dominantly involved in the genesis of β- and γ-oscillations, as well as in the organization of their large-scale coherence in the awake and sleeping brain. The highest oscillation coherence found during SWS suggests that fast oscillations implement a highly coherent reactivation of wake patterns that may support memory consolidation during SWS. PMID:27482084

  3. High-frequency oscillations in human and monkey neocortex during the wake-sleep cycle.

    PubMed

    Le Van Quyen, Michel; Muller, Lyle E; Telenczuk, Bartosz; Halgren, Eric; Cash, Sydney; Hatsopoulos, Nicholas G; Dehghani, Nima; Destexhe, Alain

    2016-08-16

    Beta (β)- and gamma (γ)-oscillations are present in different cortical areas and are thought to be inhibition-driven, but it is not known if these properties also apply to γ-oscillations in humans. Here, we analyze such oscillations in high-density microelectrode array recordings in human and monkey during the wake-sleep cycle. In these recordings, units were classified as excitatory and inhibitory cells. We find that γ-oscillations in human and β-oscillations in monkey are characterized by a strong implication of inhibitory neurons, both in terms of their firing rate and their phasic firing with the oscillation cycle. The β- and γ-waves systematically propagate across the array, with similar velocities, during both wake and sleep. However, only in slow-wave sleep (SWS) β- and γ-oscillations are associated with highly coherent and functional interactions across several millimeters of the neocortex. This interaction is specifically pronounced between inhibitory cells. These results suggest that inhibitory cells are dominantly involved in the genesis of β- and γ-oscillations, as well as in the organization of their large-scale coherence in the awake and sleeping brain. The highest oscillation coherence found during SWS suggests that fast oscillations implement a highly coherent reactivation of wake patterns that may support memory consolidation during SWS.

  4. 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.

  5. Frequency stabilization in nonlinear MEMS and NEMS oscillators

    DOEpatents

    Lopez, Omar Daniel; Antonio, Dario

    2014-09-16

    An illustrative system includes an amplifier operably connected to a phase shifter. The amplifier is configured to amplify a voltage from an oscillator. The phase shifter is operably connected to a driving amplitude control, wherein the phase shifter is configured to phase shift the amplified voltage and is configured to set an amplitude of the phase shifted voltage. The oscillator is operably connected to the driving amplitude control. The phase shifted voltage drives the oscillator. The oscillator is at an internal resonance condition, based at least on the amplitude of the phase shifted voltage, that stabilizes frequency oscillations in the oscillator.

  6. Stabilizing Microwave Frequency of a Photonic Oscillator

    NASA Technical Reports Server (NTRS)

    Maleki, Lute; Yu, Nan; Tu, Meirong

    2006-01-01

    A scheme for stabilizing the frequency of a microwave signal is proposed that exploits the operational characteristics of a coupled optoelectronic oscillator (COEO) and related optoelectronic equipment. An essential element in the scheme is a fiber mode-locked laser (MLL), the optical frequency of which is locked to an atomic transition. In this scheme, the optical frequency stability of the mode-locked laser is transferred to that of the microwave in the same device. Relative to prior schemes for using wideband optical frequency comb to stabilize microwave signals, this scheme is simpler and lends itself more readily to implementation in relatively compact, rugged equipment. The anticipated development of small, low-power, lightweight, highly stable microwave oscillators based on this scheme would afford great benefits in communication, navigation, metrology, and fundamental sciences. COEOs of various designs, at various stages of development, in some cases called by different names, have been described in a number of prior NASA Tech Briefs articles. A COEO is an optoelectronic apparatus that generates both short (picosecond) optical pulses and a steady microwave signal having an ultrahigh degree of spectral purity. The term "coupled optoelectronic" in the full name of such an apparatus signifies that its optical and electronic oscillations are coupled to each other in a single device. The present frequency-stabilization scheme is best described indirectly by describing the laboratory apparatus used to demonstrate it. The apparatus (see figure) includes a COEO that generates a comb-like optical spectrum, the various frequency components of which interfere, producing short optical pulses. This spectrum is centered at a nominal wavelength of 1,560 nm. The spectrum separation of this comb is about 10 GHz, as determined primarily by the length of an optical loop and the bandpass filter in the microwave feedback loop. The optical loop serves as microwave resonator

  7. Frequency-stabilization of mode-locked laser-based photonic microwave oscillator

    NASA Technical Reports Server (NTRS)

    Yu, Nan; Tu, Meirong; Salik, Ertan; Maleki, Lute

    2005-01-01

    In this paper, we will describe our recent phase-noise measurements of photonic microwave oscillators. We will aslo discuss our investigation of the frequency stability link between the optical and microwave frequencies in the coupled oscillator.

  8. Modulation linearization of a frequency-modulated voltage controlled oscillator, part 3

    NASA Technical Reports Server (NTRS)

    Honnell, M. A.

    1975-01-01

    An analysis is presented for the voltage versus frequency characteristics of a varactor modulated VHF voltage controlled oscillator in which the frequency deviation is linearized by using the nonlinear characteristics of a field effect transistor as a signal amplifier. The equations developed are used to calculate the oscillator output frequency in terms of pertinent circuit parameters. It is shown that the nonlinearity exponent of the FET has a pronounced influence on frequency deviation linearity, whereas the junction exponent of the varactor controls total frequency deviation for a given input signal. A design example for a 250 MHz frequency modulated oscillator is presented.

  9. High-frequency oscillations (HFOs) in clinical epilepsy

    PubMed Central

    Jacobs, J.; Staba, R.; Asano, E.; Otsubo, H.; Wu, J.Y.; Zijlmans, M.; Mohamed, I.; Kahane, P.; Dubeau, F.; Navarro, V.; Gotman, J.

    2013-01-01

    Epilepsy is one of the most frequent neurological diseases. In focal medically refractory epilepsies, successful surgical treatment largely depends on the identification of epileptogenic zone. High-frequency oscillations (HFOs) between 80 and 500 Hz, which can be recorded with EEG, may be novel markers of the epileptogenic zone. This review discusses the clinical importance of HFOs as markers of epileptogenicity and their application in different types of epilepsies. HFOs are clearly linked to the seizure onset zone, and the surgical removal of regions generating them correlates with a seizure free post-surgical outcome. Moreover, HFOs reflect the seizure-generating capability of the underlying tissue, since they are more frequent after the reduction of antiepileptic drugs. They can be successfully used in pediatric epilepsies such as epileptic spasms and help to understand the generation of this specific type of seizures. While mostly recorded on intracranial EEGs, new studies suggest that identification of HFOs on scalp EEG or magnetoencephalography (MEG) is possible as well. Thus not only patients with refractory epilepsies and invasive recordings but all patients might profit from the analysis of HFOs. Despite these promising results, the analysis of HFOs is not a routine clinical procedure; most results are derived from relatively small cohorts of patients and many aspects are not yet fully understood. Thus the review concludes that even if HFOs are promising biomarkers of epileptic tissue, there are still uncertainties about mechanisms of generation, methods of analysis, and clinical applicability. Large multicenter prospective studies are needed prior to widespread clinical application. PMID:22480752

  10. He's Frequency Formulation for Nonlinear Oscillators

    ERIC Educational Resources Information Center

    Geng, Lei; Cai, Xu-Chu

    2007-01-01

    Based on an ancient Chinese algorithm, J H He suggested a simple but effective method to find the frequency of a nonlinear oscillator. In this paper, a modified version is suggested to improve the accuracy of the frequency; two examples are given, revealing that the obtained solutions are of remarkable accuracy and are valid for the whole solution…

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

    PubMed

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

    2014-08-06

    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.

  12. Interrater reliability of visually evaluated high frequency oscillations.

    PubMed

    Spring, Aaron M; Pittman, Daniel J; Aghakhani, Yahya; Jirsch, Jeffrey; Pillay, Neelan; Bello-Espinosa, Luis E; Josephson, Colin; Federico, Paolo

    2017-03-01

    High frequency oscillations (HFOs) and interictal epileptiform discharges (IEDs) have been shown to be markers of epileptogenic regions. However, there is currently no 'gold standard' for identifying HFOs. Accordingly, we aimed to formally characterize the interrater reliability of HFO markings to validate the current practices. A morphology detector was implemented to detect events (candidate HFOs, lower-threshold events, and distractors) from the intracranial EEG (iEEG) of ten patients. Six electroencephalographers visually evaluated these events for the presence of HFOs and IEDs. Interrater reliability was calculated using pairwise Cohen's Kappa (κ) and intraclass correlation coefficients (ICC). The HFO evaluation distributions were significantly different for most pairs of reviewers (p<0.05; 11/15 pairs). Interrater reliability was poor for HFOs alone (κ mean =0.403; ICC=0.401) and HFO+IEDs (κ mean =0.568; ICC=0.570). The current practice of using two visual reviewers to identify HFOs is prone to bias arising from the poor agreement between reviewers, limiting the extrinsic validity of studies using these markers. The poor interrater reliability underlines the need for a framework to reconcile the important findings of existing studies. The present epoched design is an ideal candidate for the implementation of such a framework. Copyright © 2017 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.

  13. Trapped Ion Oscillation Frequencies as Sensors for Spectroscopy

    PubMed Central

    Vogel, Manuel; Quint, Wolfgang; Nörtershäuser, Wilfried

    2010-01-01

    The oscillation frequencies of charged particles in a Penning trap can serve as sensors for spectroscopy when additional field components are introduced to the magnetic and electric fields used for confinement. The presence of so-called “magnetic bottles” and specific electric anharmonicities creates calculable energy-dependences of the oscillation frequencies in the radiofrequency domain which may be used to detect the absorption or emission of photons both in the microwave and optical frequency domains. The precise electronic measurement of these oscillation frequencies therefore represents an optical sensor for spectroscopy. We discuss possible applications for precision laser and microwave spectroscopy and their role in the determination of magnetic moments and excited state life-times. Also, the trap-assisted measurement of radiative nuclear de-excitations in the X-ray domain is discussed. This way, the different applications range over more than 12 orders of magnitude in the detectable photon energies, from below μeV in the microwave domain to beyond MeV in the X-ray domain. PMID:22294921

  14. A high-overtone bulk acoustic wave resonator-oscillator-based 4.596 GHz frequency source: Application to a coherent population trapping Cs vapor cell atomic clock.

    PubMed

    Daugey, Thomas; Friedt, Jean-Michel; Martin, Gilles; Boudot, Rodolphe

    2015-11-01

    This article reports on the design and characterization of a high-overtone bulk acoustic wave resonator (HBAR)-oscillator-based 4.596 GHz frequency source. A 2.298 GHz signal, generated by an oscillator constructed around a thermally controlled two-port aluminum nitride-sapphire HBAR resonator with a Q-factor of 24,000 at 68 °C, is frequency multiplied by 2-4.596 GHz, half of the Cs atom clock frequency. The temperature coefficient of frequency of the HBAR is measured to be -23 ppm/ °C at 2.298 GHz. The measured phase noise of the 4.596 GHz source is -105 dB rad(2)/Hz at 1 kHz offset and -150 dB rad(2)/Hz at 100 kHz offset. The 4.596 GHz output signal is used as a local oscillator in a laboratory-prototype Cs microcell-based coherent population trapping atomic clock. The signal is stabilized onto the atomic transition frequency by tuning finely a voltage-controlled phase shifter implemented in the 2.298 GHz HBAR-oscillator loop, preventing the need for a high-power-consuming direct digital synthesis. The short-term fractional frequency stability of the free-running oscillator is 1.8 × 10(-9) at one second integration time. In locked regime, the latter is improved in a preliminary proof-of-concept experiment at the level of 6.6 × 10(-11) τ(-1/2) up to a few seconds and found to be limited by the signal-to-noise ratio of the detected CPT resonance.

  15. A high-overtone bulk acoustic wave resonator-oscillator-based 4.596 GHz frequency source: Application to a coherent population trapping Cs vapor cell atomic clock

    NASA Astrophysics Data System (ADS)

    Daugey, Thomas; Friedt, Jean-Michel; Martin, Gilles; Boudot, Rodolphe

    2015-11-01

    This article reports on the design and characterization of a high-overtone bulk acoustic wave resonator (HBAR)-oscillator-based 4.596 GHz frequency source. A 2.298 GHz signal, generated by an oscillator constructed around a thermally controlled two-port aluminum nitride-sapphire HBAR resonator with a Q-factor of 24 000 at 68 °C, is frequency multiplied by 2-4.596 GHz, half of the Cs atom clock frequency. The temperature coefficient of frequency of the HBAR is measured to be -23 ppm/ °C at 2.298 GHz. The measured phase noise of the 4.596 GHz source is -105 dB rad2/Hz at 1 kHz offset and -150 dB rad2/Hz at 100 kHz offset. The 4.596 GHz output signal is used as a local oscillator in a laboratory-prototype Cs microcell-based coherent population trapping atomic clock. The signal is stabilized onto the atomic transition frequency by tuning finely a voltage-controlled phase shifter implemented in the 2.298 GHz HBAR-oscillator loop, preventing the need for a high-power-consuming direct digital synthesis. The short-term fractional frequency stability of the free-running oscillator is 1.8 × 10-9 at one second integration time. In locked regime, the latter is improved in a preliminary proof-of-concept experiment at the level of 6.6 × 10-11 τ-1/2 up to a few seconds and found to be limited by the signal-to-noise ratio of the detected CPT resonance.

  16. Frequency control of a spin-torque oscillator using magnetostrictive anisotropy

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Park, Min Gyu Albert; Lee, Seok-Hee, E-mail: bgpark@kaist.ac.kr, E-mail: shlee@kaist.edu; Baek, Seung-heon Chris

    2016-01-11

    We report the working principle of a spin-torque oscillator, of which the frequency is efficiently controlled by manipulating the magnetostrictive anisotropy. To justify the scheme, we simulate a conventional magnetic-tunnel junction-based oscillator which is fabricated on a piezoelectric material. By applying mechanical stress to a free layer using a piezoelectric material, the oscillation frequency can be controlled to ensure a broad tuning range without a significant reduction of the dynamic resistance variation. Such controllability, which appears in the absence of an external magnetic field, will not only enable the integration of spin-torque oscillators and conventional complimentary metal-oxide semiconductor technology butmore » will also broaden the applicability of spin-torque oscillators.« less

  17. High frequency inductive lamp and power oscillator

    DOEpatents

    Kirkpatrick, Douglas A.; Gitsevich, Aleksandr

    2005-09-27

    An oscillator includes an amplifier having an input and an output, a feedback network connected between the input of the amplifier and the output of the amplifier, the feedback network being configured to provide suitable positive feedback from the output of the amplifier to the input of the amplifier to initiate and sustain an oscillating condition, and a tuning circuit connected to the input of the amplifier, wherein the tuning circuit is continuously variable and consists of solid state electrical components with no mechanically adjustable devices including a pair of diodes connected to each other at their respective cathodes with a control voltage connected at the junction of the diodes. Another oscillator includes an amplifier having an input and an output, a feedback network connected between the input of the amplifier and the output of the amplifier, the feedback network being configured to provide suitable positive feedback from the output of the amplifier to the input of the amplifier to initiate and sustain an oscillating condition, and transmission lines connected to the input of the amplifier with an input pad and a perpendicular transmission line extending from the input pad and forming a leg of a resonant "T", and wherein the feedback network is coupled to the leg of the resonant "T".

  18. Endogenous modulation of low frequency oscillations by temporal expectations

    PubMed Central

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

    2011-01-01

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

  19. Fast oscillations in cortical-striatal networks switch frequency following rewarding events and stimulant drugs.

    PubMed

    Berke, J D

    2009-09-01

    Oscillations may organize communication between components of large-scale brain networks. Although gamma-band oscillations have been repeatedly observed in cortical-basal ganglia circuits, their functional roles are not yet clear. Here I show that, in behaving rats, distinct frequencies of ventral striatal local field potential oscillations show coherence with different cortical inputs. The approximately 50 Hz gamma oscillations that normally predominate in awake ventral striatum are coherent with piriform cortex, whereas approximately 80-100 Hz high-gamma oscillations are coherent with frontal cortex. Within striatum, entrainment to gamma rhythms is selective to fast-spiking interneurons, with distinct fast-spiking interneuron populations entrained to different gamma frequencies. Administration of the psychomotor stimulant amphetamine or the dopamine agonist apomorphine causes a prolonged decrease in approximately 50 Hz power and increase in approximately 80-100 Hz power. The same frequency switch is observed for shorter epochs spontaneously in awake, undrugged animals and is consistently provoked for < 1 s following reward receipt. Individual striatal neurons can participate in these brief high-gamma bursts with, or without, substantial changes in firing rate. Switching between discrete oscillatory states may allow different modes of information processing during decision-making and reinforcement-based learning, and may also be an important systems-level process by which stimulant drugs affect cognition and behavior.

  20. Cross-frequency coupling of brain oscillations in studying motivation and emotion.

    PubMed

    Schutter, Dennis J L G; Knyazev, Gennady G

    2012-03-01

    Research has shown that brain functions are realized by simultaneous oscillations in various frequency bands. In addition to examining oscillations in pre-specified bands, interactions and relations between the different frequency bandwidths is another important aspect that needs to be considered in unraveling the workings of the human brain and its functions. In this review we provide evidence that studying interdependencies between brain oscillations may be a valuable approach to study the electrophysiological processes associated with motivation and emotional states. Studies will be presented showing that amplitude-amplitude coupling between delta-alpha and delta-beta oscillations varies as a function of state anxiety and approach-avoidance-related motivation, and that changes in the association between delta-beta oscillations can be observed following successful psychotherapy. Together these studies suggest that cross-frequency coupling of brain oscillations may contribute to expanding our understanding of the neural processes underlying motivation and emotion.

  1. The Phosphorylation State of the Drosophila TRP Channel Modulates the Frequency Response to Oscillating Light In Vivo

    PubMed Central

    Rhodes-Mordov, Elisheva; Katz, Ben; Oberegelsbacher, Claudia; Yasin, Bushra; Tzadok, Hanan; Huber, Armin

    2017-01-01

    Drosophila photoreceptors respond to oscillating light of high frequency (∼100 Hz), while the detected maximal frequency is modulated by the light rearing conditions, thus enabling high sensitivity to light and high temporal resolution. However, the molecular basis for this adaptive process is unclear. Here, we report that dephosphorylation of the light-activated transient receptor potential (TRP) ion channel at S936 is a fast, graded, light-dependent, and Ca2+-dependent process that is partially modulated by the rhodopsin phosphatase retinal degeneration C (RDGC). Electroretinogram measurements of the frequency response to oscillating lights in vivo revealed that dark-reared flies expressing wild-type TRP exhibited a detection limit of oscillating light at relatively low frequencies, which was shifted to higher frequencies upon light adaptation. Strikingly, preventing phosphorylation of the S936-TRP site by alanine substitution in transgenic Drosophila (trpS936A) abolished the difference in frequency response between dark-adapted and light-adapted flies, resulting in high-frequency response also in dark-adapted flies. In contrast, inserting a phosphomimetic mutation by substituting the S936-TRP site to aspartic acid (trpS936D) set the frequency response of light-adapted flies to low frequencies typical of dark-adapted flies. Light-adapted rdgC mutant flies showed relatively high S936-TRP phosphorylation levels and light–dark phosphorylation dynamics. These findings suggest that RDGC is one but not the only phosphatase involved in pS936-TRP dephosphorylation. Together, this study indicates that TRP channel dephosphorylation is a regulatory process that affects the detection limit of oscillating light according to the light rearing condition, thus adjusting dynamic processing of visual information under varying light conditions. SIGNIFICANCE STATEMENT Drosophila photoreceptors exhibit high temporal resolution as manifested in frequency response to oscillating

  2. Numerical study of low-frequency discharge oscillations in a 5 kW Hall thruster

    NASA Astrophysics Data System (ADS)

    Le, YANG; Tianping, ZHANG; Juanjuan, CHEN; Yanhui, JIA

    2018-07-01

    A two-dimensional particle-in-cell plasma model is built in the R–Z plane to investigate the low-frequency plasma oscillations in the discharge channel of a 5 kW LHT-140 Hall thruster. In addition to the elastic, excitation, and ionization collisions between neutral atoms and electrons, the Coulomb collisions between electrons and electrons and between electrons and ions are analyzed. The sheath characteristic distortion is also corrected. Simulation results indicate the capability of the built model to reproduce the low-frequency oscillation with high accuracy. The oscillations of the discharge current and ion density produced by the model are consistent with the existing conclusions. The model predicts a frequency that is consistent with that calculated by the zero-dimensional theoretical model.

  3. Numerical simulation of the transition to chaos in a dissipative Duffing oscillator with two-frequency excitation

    NASA Astrophysics Data System (ADS)

    Zavrazhina, T. V.

    2007-10-01

    A mathematical modeling technique is proposed for oscillation chaotization in an essentially nonlinear dissipative Duffing oscillator with two-frequency excitation on an invariant torus in ℝ2. The technique is based on the joint application of the parameter continuation method, Floquet stability criteria, bifurcation theory, and the Everhart high-accuracy numerical integration method. This approach is used for the numerical construction of subharmonic solutions in the case when the oscillator passes to chaos through a sequence of period-multiplying bifurcations. The value of a universal constant obtained earlier by the author while investigating oscillation chaotization in dissipative oscillators with single-frequency periodic excitation is confirmed.

  4. A high-overtone bulk acoustic wave resonator-oscillator-based 4.596 GHz frequency source: Application to a coherent population trapping Cs vapor cell atomic clock

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Daugey, Thomas; Friedt, Jean-Michel; Martin, Gilles

    2015-11-15

    This article reports on the design and characterization of a high-overtone bulk acoustic wave resonator (HBAR)-oscillator-based 4.596 GHz frequency source. A 2.298 GHz signal, generated by an oscillator constructed around a thermally controlled two-port aluminum nitride-sapphire HBAR resonator with a Q-factor of 24 000 at 68 °C, is frequency multiplied by 2–4.596 GHz, half of the Cs atom clock frequency. The temperature coefficient of frequency of the HBAR is measured to be −23 ppm/ °C at 2.298 GHz. The measured phase noise of the 4.596 GHz source is −105 dB rad{sup 2}/Hz at 1 kHz offset and −150 dB rad{sup 2}/Hz at 100more » kHz offset. The 4.596 GHz output signal is used as a local oscillator in a laboratory-prototype Cs microcell-based coherent population trapping atomic clock. The signal is stabilized onto the atomic transition frequency by tuning finely a voltage-controlled phase shifter implemented in the 2.298 GHz HBAR-oscillator loop, preventing the need for a high-power-consuming direct digital synthesis. The short-term fractional frequency stability of the free-running oscillator is 1.8 × 10{sup −9} at one second integration time. In locked regime, the latter is improved in a preliminary proof-of-concept experiment at the level of 6.6 × 10{sup −11} τ{sup −1/2} up to a few seconds and found to be limited by the signal-to-noise ratio of the detected CPT resonance.« less

  5. Dominant side in single-leg stance stability during floor oscillations at various frequencies

    PubMed Central

    2014-01-01

    Background We investigated lateral dominance in the postural stability of single-leg stance with anteroposterior floor oscillations at various frequencies. Methods Thirty adults maintained a single-leg stance on a force platform for 20 seconds per trial. Trials were performed with no oscillation (static condition) and with anteroposterior floor oscillations (2.5-cm amplitude) at six frequencies: 0.25, 0.5, 0.75, 1.0, 1.25 and 1.5 Hz (dynamic condition). A set of three trials was performed on each leg in each oscillation frequency in random order. The mean speed of the center of pressure in the anteroposterior direction (CoPap) was calculated as an index of postural stability, and frequency analysis of CoPap sway was performed. Footedness for carrying out mobilizing activities was assessed with a questionnaire. Results CoPap speed exponentially increased as oscillation frequency increased in both legs. The frequency analysis of CoPap showed a peak <0.3 Hz at no oscillation. The frequency components at 0.25-Hz oscillation included common components with no oscillation and those at 1.5-Hz oscillation showed the maximum amplitude among all conditions. Postural stability showed no significant difference between left- and right-leg stance at no oscillation and oscillations ≤1.25 Hz, but at 1.5-Hz oscillation was significantly higher in the right-leg stance than in the left-leg stance. For the lateral dominance of postural stability at individual levels, the lateral difference in postural stability at no oscillation was positively correlated with that at 0.25-Hz oscillation (r = 0.51) and negatively correlated with that at 1.5-Hz oscillation (r = -0.53). For 70% of subjects, the dominant side of postural stability was different at no oscillation and 1.5-Hz oscillation. In the subjects with left- or right-side dominance at no oscillation, 94% or 38% changed their dominant side at 1.5-Hz oscillation, with a significant difference between these percentages. In

  6. Direct measurement of density oscillation induced by a radio-frequency wave.

    PubMed

    Yamada, T; Ejiri, A; Shimada, Y; Oosako, T; Tsujimura, J; Takase, Y; Kasahara, H

    2007-08-01

    An O-mode reflectometer at a frequency of 25.85 GHz was applied to plasmas heated by the high harmonic fast wave (21 MHz) in the TST-2 spherical tokamak. An oscillation in the phase of the reflected microwave in the rf range was observed directly for the first time. In TST-2, the rf (250 kW) induced density oscillation depends mainly on the poloidal rf electric field, which is estimated to be about 0.2 kV/m rms by the reflectometer measurement. Sideband peaks separated in frequency by ion cyclotron harmonics from 21 MHz, and peaks at ion cyclotron harmonics which are suggested to be quasimodes generated by parametric decay, were detected.

  7. 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.

  8. Effects of dendritic load on the firing frequency of oscillating neurons.

    PubMed

    Schwemmer, Michael A; Lewis, Timothy J

    2011-03-01

    We study the effects of passive dendritic properties on the dynamics of neuronal oscillators. We find that the addition of a passive dendrite can sometimes have counterintuitive effects on firing frequency. Specifically, the addition of a hyperpolarized passive dendritic load can either increase, decrease, or have negligible effects on firing frequency. We use the theory of weak coupling to derive phase equations for "ball-and-stick" model neurons and two-compartment model neurons. We then develop a framework for understanding how the addition of passive dendrites modulates the frequency of neuronal oscillators. We show that the average value of the neuronal oscillator's phase response curves measures the sensitivity of the neuron's firing rate to the dendritic load, including whether the addition of the dendrite causes an increase or decrease in firing frequency. We interpret this finding in terms of to the slope of the neuronal oscillator's frequency-applied current curve. We also show that equivalent results exist for constant and noisy point-source input to the dendrite. We note that the results are not specific to neurons but are applicable to any oscillator subject to a passive load.

  9. Information coding with frequency of oscillations in Belousov-Zhabotinsky encapsulated disks

    NASA Astrophysics Data System (ADS)

    Gorecki, J.; Gorecka, J. N.; Adamatzky, Andrew

    2014-04-01

    Information processing with an excitable chemical medium, like the Belousov-Zhabotinsky (BZ) reaction, is typically based on information coding in the presence or absence of excitation pulses. Here we present a new concept of Boolean coding that can be applied to an oscillatory medium. A medium represents the logical TRUE state if a selected region oscillates with a high frequency. If the frequency fails below a specified value, it represents the logical FALSE state. We consider a medium composed of disks encapsulating an oscillatory mixture of reagents, as related to our recent experiments with lipid-coated BZ droplets. We demonstrate that by using specific geometrical arrangements of disks containing the oscillatory medium one can perform logical operations on variables coded in oscillation frequency. Realizations of a chemical signal diode and of a single-bit memory with oscillatory disks are also discussed.

  10. Frequency modulation of neural oscillations according to visual task demands.

    PubMed

    Wutz, Andreas; Melcher, David; Samaha, Jason

    2018-02-06

    Temporal integration in visual perception is thought to occur within cycles of occipital alpha-band (8-12 Hz) oscillations. Successive stimuli may be integrated when they fall within the same alpha cycle and segregated for different alpha cycles. Consequently, the speed of alpha oscillations correlates with the temporal resolution of perception, such that lower alpha frequencies provide longer time windows for perceptual integration and higher alpha frequencies correspond to faster sampling and segregation. Can the brain's rhythmic activity be dynamically controlled to adjust its processing speed according to different visual task demands? We recorded magnetoencephalography (MEG) while participants switched between task instructions for temporal integration and segregation, holding stimuli and task difficulty constant. We found that the peak frequency of alpha oscillations decreased when visual task demands required temporal integration compared with segregation. Alpha frequency was strategically modulated immediately before and during stimulus processing, suggesting a preparatory top-down source of modulation. Its neural generators were located in occipital and inferotemporal cortex. The frequency modulation was specific to alpha oscillations and did not occur in the delta (1-3 Hz), theta (3-7 Hz), beta (15-30 Hz), or gamma (30-50 Hz) frequency range. These results show that alpha frequency is under top-down control to increase or decrease the temporal resolution of visual perception.

  11. 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.

  12. Oscillator or Amplifier With Wide Frequency Range

    NASA Technical Reports Server (NTRS)

    Kleinberg, L.; Sutton, J.

    1987-01-01

    Inductive and capacitive effects synthesized with feedback circuits. Oscillator/amplifier resistively tunable over wide frequency range. Feedback circuits containing operational amplifiers, resistors, and capacitors synthesize electrical effects of inductance and capacitance in parallel between input terminals. Synthetic inductance and capacitance, and, therefore, resonant frequency of input admittance, adjusted by changing potentiometer setting.

  13. 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.

  14. High-frequency Oscillations in Small Magnetic Elements Observed with Sunrise/SuFI

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Jafarzadeh, S.; Solanki, S. K.; Cameron, R. H.

    2017-04-01

    We characterize waves in small magnetic elements and investigate their propagation in the lower solar atmosphere from observations at high spatial and temporal resolution. We use the wavelet transform to analyze oscillations of both horizontal displacement and intensity in magnetic bright points found in the 300 nm and the Ca ii H 396.8 nm passbands of the filter imager on board the Sunrise balloon-borne solar observatory. Phase differences between the oscillations at the two atmospheric layers corresponding to the two passbands reveal upward propagating waves at high frequencies (up to 30 mHz). Weak signatures of standing as well as downward propagating waves are alsomore » obtained. Both compressible and incompressible (kink) waves are found in the small-scale magnetic features. The two types of waves have different, though overlapping, period distributions. Two independent estimates give a height difference of approximately 450 ± 100 km between the two atmospheric layers sampled by the employed spectral bands. This value, together with the determined short travel times of the transverse and longitudinal waves provide us with phase speeds of 29 ± 2 km s{sup −1} and 31 ± 2 km s{sup −1}, respectively. We speculate that these phase speeds may not reflect the true propagation speeds of the waves. Thus, effects such as the refraction of fast longitudinal waves may contribute to an overestimate of the phase speed.« less

  15. Wideband-frequency tunable optoelectronic oscillator based on injection locking to an electronic oscillator.

    PubMed

    Fleyer, Michael; Sherman, Alexander; Horowitz, Moshe; Namer, Moshe

    2016-05-01

    We experimentally demonstrate a wideband-frequency tunable optoelectronic oscillator (OEO) based on injection locking of the OEO to a tunable electronic oscillator. The OEO cavity does not contain a narrowband filter and its frequency can be tuned over a broad bandwidth of 1 GHz. The injection locking is based on minimizing the injected power by adjusting the frequency of one of the OEO cavity modes to be approximately equal to the frequency of the injected signal. The phase noise that is obtained in the injection-locked OEO is similar to that obtained in a long-cavity self-sustained OEO. Although the cavity length of the OEO was long, the spurious modes were suppressed due to the injection locking without the need to use a narrowband filter. The spurious level was significantly below that obtained in a self-sustained OEO after inserting a narrowband electronic filter with a Q-factor of 720 into the cavity.

  16. Electromagnetic inhibition of high frequency thermal bonding machine

    NASA Astrophysics Data System (ADS)

    He, Hong; Zhang, Qing-qing; Li, Hang; Zhang, Da-jian; Hou, Ming-feng; Zhu, Xian-wei

    2011-12-01

    The traditional high frequency thermal bonding machine had serious radiation problems at dominant frequency, two times frequency and three times frequency. Combining with its working principle, the problems of electromagnetic compatibility were studied, three following measures were adopted: 1.At the head part of the high frequency thermal bonding machine, resonant circuit attenuator was designed. The notch groove and reaction field can make the radiation being undermined or absorbed; 2.The electromagnetic radiation shielding was made for the high frequency copper power feeder; 3.Redesigned the high-frequency oscillator circuit to reduce the output of harmonic oscillator. The test results showed that these measures can make the output according with the national standard of electromagnetic compatibility (GB4824-2004-2A), the problems of electromagnetic radiation leakage can be solved, and good social, environmental and economic benefits would be brought.

  17. The measurement of linear frequency drift in oscillators

    NASA Astrophysics Data System (ADS)

    Barnes, J. A.

    1985-04-01

    A linear drift in frequency is an important element in most stochastic models of oscillator performance. Quartz crystal oscillators often have drifts in excess of a part in ten to the tenth power per day. Even commercial cesium beam devices often show drifts of a few parts in ten to the thirteenth per year. There are many ways to estimate the drift rates from data samples (e.g., regress the phase on a quadratic; regress the frequency on a linear; compute the simple mean of the first difference of frequency; use Kalman filters with a drift term as one element in the state vector; and others). Although most of these estimators are unbiased, they vary in efficiency (i.e., confidence intervals). Further, the estimation of confidence intervals using the standard analysis of variance (typically associated with the specific estimating technique) can give amazingly optimistic results. The source of these problems is not an error in, say, the regressions techniques, but rather the problems arise from correlations within the residuals. That is, the oscillator model is often not consistent with constraints on the analysis technique or, in other words, some specific analysis techniques are often inappropriate for the task at hand. The appropriateness of a specific analysis technique is critically dependent on the oscillator model and can often be checked with a simple whiteness test on the residuals.

  18. Influence of the oscillation frequency of different side-to-side toothbrushes on noncontact biofilm removal.

    PubMed

    Schmidt, Julia C; Astasov-Frauenhoffer, Monika; Waltimo, Tuomas; Weiger, Roland; Walter, Clemens

    2018-01-22

    The objective of this study was to investigate the influence of different oscillation frequencies of three powered toothbrushes with side-to-side action for noncontact biofilm removal in an artificial interdental space model. A three-species biofilm (Porphyromonas gingivalis, Fusobacterium nucleatum and Streptococcus sanguinis) was formed in vitro on protein-coated titanium disks using a flow chamber system combined with a static biofilm growth model. The oscillation frequencies of three commercial side-to-side toothbrushes were evaluated by means of a dose response. The frequency was decreased in steps (100, 85, 70, 55, and 40%). Subsequently, the biofilm-coated substrates were exposed to the side-to-side toothbrushes. The biofilm volumes were measured using volumetric analyses (Imaris 8.1.2) with confocal laser scanning microscope images (Zeiss LSM700). Compared to maximum oscillation frequency (100%), lower oscillation frequencies (up to 40%) resulted in reduced median percentages of biofilm reduction (median biofilm reduction up to 53% for maximum oscillation frequency, and up to 13% for 40% oscillation frequency) (p ≥ 0.03). In addition, decreasing the oscillation frequencies of the side-to-side toothbrushes showed an enhanced variety in the results of repeated experiments. The oscillation frequency of the tested side-to-side toothbrushes affected the biofilm reduction in an interdental space model. Within a toothbrush, higher oscillation frequencies may lead to beneficial effects on interdental biofilm removal by noncontact brushing.

  19. 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.

  20. Exploring the time-frequency content of high frequency oscillations for automated identification of seizure onset zone in epilepsy.

    PubMed

    Liu, Su; Sha, Zhiyi; Sencer, Altay; Aydoseli, Aydin; Bebek, Nerse; Abosch, Aviva; Henry, Thomas; Gurses, Candan; Ince, Nuri Firat

    2016-04-01

    High frequency oscillations (HFOs) in intracranial electroencephalography (iEEG) recordings are considered as promising clinical biomarkers of epileptogenic regions in the brain. The aim of this study is to improve and automatize the detection of HFOs by exploring the time-frequency content of iEEG and to investigate the seizure onset zone (SOZ) detection accuracy during the sleep, awake and pre-ictal states in patients with epilepsy, for the purpose of assisting the localization of SOZ in clinical practice. Ten-minute iEEG segments were defined during different states in eight patients with refractory epilepsy. A three-stage algorithm was implemented to detect HFOs in these segments. First, an amplitude based initial detection threshold was used to generate a large pool of HFO candidates. Then distinguishing features were extracted from the time and time-frequency domain of the raw iEEG and used with a Gaussian mixture model clustering to isolate HFO events from other activities. The spatial distribution of HFO clusters was correlated with the seizure onset channels identified by neurologists in seven patient with good surgical outcome. The overlapping rates of localized channels and seizure onset locations were high in all states. The best result was obtained using the iEEG data during sleep, achieving a sensitivity of 81%, and a specificity of 96%. The channels with maximum number of HFOs identified epileptogenic areas where the seizures occurred more frequently. The current study was conducted using iEEG data collected in realistic clinical conditions without channel pre-exclusion. HFOs were investigated with novel features extracted from the entire frequency band, and were correlated with SOZ in different states. The results indicate that automatic HFO detection with unsupervised clustering methods exploring the time-frequency content of raw iEEG can be efficiently used to identify the epileptogenic zone with an accurate and efficient manner.

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

    PubMed

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

    2017-09-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Zhang, Junfeng; Zhang, Chunwang; Ma, Daqing

    2018-01-01

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

  3. Comparing performance of three oscillating positive expiratory pressure devices at similar amplitude and frequencies of oscillations on displacement of mucus inside trachea during cough.

    PubMed

    Ragavan, Anpalaki J

    2012-03-13

    generate high amplitude oscillations at moderate frequencies, increasing frontal depths of mucus facing airflow and slightly increasing resistance to airflow in airways in COPD patients.

  4. Realization of Ultra-High Spectral Purity with the Opto-Electronic Oscillator

    NASA Technical Reports Server (NTRS)

    Yao, Steve; Maleki, Lute; Ji, Yu; Dick, John

    2000-01-01

    Recent results with the Opto-Electronic Oscillator (OEO) have led to the realization of very high spectral purity. Experimental results have produced a performance characterized by a noise as low as by -50 dBc/Hz at 10 Hz for a 10 GHz OEO. The unit was built in a compact package containing an integrated DFB laser and the modulator. This performance is significant because the oscillator is free running, and since the noise in an OEO is independent of the oscillation frequency, the same result can also be obtained at higher frequencies. The result also demonstrates that high frequency, high performance, low cost, and miniature OEO can be realized with the integrated photonic technology. We have also developed a novel carrier suppression technique to reduce the 1/f phase noise of the oscillator even further. The technique is based on the use of a long fiber delay, in place of the high Q cavity, to implement carrier suppression. Our preliminary experimental results indicate an extra 10 to 20 dB phase noise reduction of the OEO with this novel technique. Further noise reduction beyond this value is expected with improved circuit design and longer reference fiber.

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

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    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 ofmore » hourly averages for the various observational days. Both signal frequencies are apparently due to odd-degree spherical harmonic oscillations of the sun.« less

  6. Low frequency oscillations in total ozone measurements

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

    Low frequency oscillations with periods of approximately one to two months are found in eight years of global grids of total ozone data from the Total Ozone Mapping Spectrometer (TOMS) satellite instrument. The low frequency oscillations corroborate earlier analyses based on four years of data. In addition, both annual and seasonal one-point correlation maps based on the 8-year TOMS data are presented. The results clearly show a standing dipole in ozone perturbations, oscillating with 35 to 50 day periods over the equatorial Indian Ocean-west Pacific region. This contrasts with the eastward moving dipole reported in other data sets. The standing ozone dipole appears to be a dynamical feature associated with vertical atmospheric motions. Consistent with prior analyses based on lower stratospheric temperature fields, large-scale standing patterns are also found in the extratropics of both hemispheres, correlated with ozone fluctuations over the equatorial west Pacific. In the Northern Hemisphere, a standing pattern is observed extending from the tropical Indian Ocean to the north Pacific, across North America, and down to the equatorial Atlantic Ocean region. This feature is most pronounced in the NH summer.

  7. Frequency and amplitude stabilization in MEMS and NEMS oscillators

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Chen, Changyao; Lopez, Omar Daniel; Czaplewski, David A.

    This invention comprises a nonlinear micro- and nano-mechanical resonator that can maintain frequency of operation and amplitude of operation for a period of time after all external power has been removed from the device. Utilizing specific nonlinear dynamics of the micromechanical resonator, mechanical energy at low frequencies can be input and stored in higher frequencies modes, thus using the multiple degrees of freedom of the resonator to extend its energy storage capacity. Furthermore, the energy stored in multiple vibrational modes can be used to maintain the resonator oscillating for a fixed period of time, even without an external power supply.more » This is the first demonstration of an "autonomous" frequency source that can maintain a constant frequency and vibrating amplitude when no external power is provided, making it ideal for applications requiring an oscillator in low power, or limited and intermittent power supplies.« less

  8. Fluidic Oscillator Having Decoupled Frequency and Amplitude Control

    NASA Technical Reports Server (NTRS)

    Koklu, Mehti (Inventor)

    2016-01-01

    A fluidic oscillator having independent frequency and amplitude control includes a fluidic-oscillator main flow channel having a main flow inlet, a main flow outlet, and first and second control ports disposed at opposing sides thereof. A fluidic-oscillator controller has an inlet and outlet. A volume defined by the main flow channel is greater than the volume defined by the controller. A flow diverter coupled to the outlet of the controller defines a first fluid flow path from the controller's outlet to the first control port and defines a second fluid flow path from the controller's outlet to the second control port.

  9. Fluidic Oscillator Having Decoupled Frequency and Amplitude Control

    NASA Technical Reports Server (NTRS)

    Koklu, Mehti (Inventor)

    2017-01-01

    A fluidic oscillator having independent frequency and amplitude control includes a fluidic-oscillator main flow channel having a main flow inlet, a main flow outlet, and first and second control ports disposed at opposing sides thereof. A fluidic-oscillator controller has an inlet and outlet. A volume defined by the main flow channel is greater than the volume defined by the controller. A flow diverter coupled to the outlet of the controller defines a first fluid flow path from the controller's outlet to the first control port and defines a second fluid flow path from the controller's outlet to the second control port.

  10. Effect of low-frequency oscillation on performance of Hall thrusters

    NASA Astrophysics Data System (ADS)

    Liqiu, WEI; Wenbo, LI; Yongjie, DING; Daren, YU

    2018-07-01

    In this paper, a direct connection between the discharge current amplitude and the thruster performance is established by varying solely the capacitance of the filter unit of the Hall thrusters. To be precise, the variation characteristics of ion current, propellant utilization efficiency, and divergence angle of plume at different low-frequency oscillation amplitudes are measured. The findings demonstrate that in the case of the propellant in the discharge channel just meets or falls below the full ionization condition, the increase of low-frequency oscillation amplitude can significantly enhance the ionization degree of the neutral gas in the channel and increase the thrust and anode efficiency of thruster. On the contrary, the increase in the amplitude of low-frequency oscillation will lead to increase the loss of plume divergence, therefore the thrust and anode efficiency of thruster decrease.

  11. Frequency equation for the submicron CMOS ring oscillator using the first order characterization

    NASA Astrophysics Data System (ADS)

    Koithyar, Aravinda; Ramesh, T. K.

    2018-05-01

    By utilizing the first order behavior of the device, an equation for the frequency of operation of the submicron CMOS ring oscillator is presented. A 5-stage ring oscillator is utilized as the initial design, with different Beta ratios, for the computation of the operating frequency. Later on, the circuit simulation is performed from 5-stage till 23-stage, with the range of oscillating frequency being 3.0817 and 0.6705 GHz respectively. It is noted that the output frequency is inversely proportional to the square of the device length, and when the value of Beta ratio is used as 2.3, a difference of 3.64% is observed on an average, in between the computed and the simulated values of frequency. As an outcome, the derived equation can be utilized, with the inclusion of an empirical constant in general, for arriving at the ring oscillator circuit’s output frequency.

  12. Impact of excitation waveform on the frequency stability of electrostatically-actuated micro-electromechanical oscillators

    NASA Astrophysics Data System (ADS)

    Juillard, J.; Brenes, A.

    2018-05-01

    In this paper, the frequency stability of high-Q electrostatically-actuated MEMS oscillators with cubic restoring forces, and its relation with the amplitude, the phase and the shape of the excitation waveform, is studied. The influence on close-to-the carrier frequency noise of additive processes (such as thermomechanical noise) or parametric processes (bias voltage fluctuations, feedback phase fluctuations, feedback level fluctuations) is taken into account. It is shown that the optimal operating conditions of electrostatically-actuated MEMS oscillators are highly waveform-dependent, a factor that is largely overlooked in the existing literature. This simulation-based study covers the cases of harmonic and pulsed excitation of a parallel-plate capacitive MEMS resonator.

  13. Regulation of NF-κB Oscillation by Nuclear Transport: Mechanisms Determining the Persistency and Frequency of Oscillation

    PubMed Central

    Ohshima, Daisuke; Ichikawa, Kazuhisa

    2015-01-01

    The activated transcription factor NF-κB shuttles between the cytoplasm and the nucleus resulting in the oscillation of nuclear NF-κB (NF-κBn). The oscillation pattern of NF-κBn is implicated in the regulation of gene expression profiles. Using computational models, we previously reported that spatial parameters, such as the diffusion coefficient, nuclear to cytoplasmic volume ratio, transport through the nuclear envelope, and the loci of translation of IκB protein, modified the oscillation pattern of NF-κBn. In a subsequent report, we elucidated the importance of the “reset” of NF-κBn (returning of NF-κB to the original level) and of a “reservoir” of IκB in the cytoplasm. When the diffusion coefficient of IκB was large, IκB stored at a distant location from the nucleus diffused back to the nucleus and “reset” NF-κBn. Herein, we report mechanisms that regulate the persistency and frequency of NF-κBn oscillation by nuclear transport. Among the four parameters of nuclear transport tested in our spatio-temporal computational model, the export of IκB mRNA from the nucleus regulated the persistency of oscillation. The import of IκB to the nucleus regulated the frequency of oscillation. The remaining two parameters, import and export of NF-κB to and from the nucleus, had virtually no effect on the persistency or frequency. Our analyses revealed that lesser export of IκB mRNA allowed NF-κBn to transcript greater amounts of IκB mRNA, which was retained in the nucleus, and was subsequently exported to the cytoplasm, where large amounts of IκB were synthesized to “reset” NF-κBn and drove the persistent oscillation. On the other hand, import of greater amounts of IκB led to an increase in the influx and the efflux of NF-κB to and from the nucleus, resulting in an increase in the oscillation frequency. Our study revealed the importance of nuclear transport in regulating the oscillation pattern of NF-κBn. PMID:26042739

  14. Vigabatrin therapy implicates neocortical high frequency oscillations in an animal model of infantile spasms.

    PubMed

    Frost, James D; Le, John T; Lee, Chong L; Ballester-Rosado, Carlos; Hrachovy, Richard A; Swann, John W

    2015-10-01

    Abnormal high frequency oscillations (HFOs) in EEG recordings are thought to be reflections of mechanisms responsible for focal seizure generation in the temporal lobe and neocortex. HFOs have also been recorded in patients and animal models of infantile spasms. If HFOs are important contributors to infantile spasms then anticonvulsant drugs that suppress these seizures should decrease the occurrence of HFOs. In experiments reported here, we used long-term video/EEG recordings with digital sampling rates capable of capturing HFOs. We tested the effectiveness of vigabatrin (VGB) in the TTX animal model of infantile spasms. VGB was found to be quite effective in suppressing spasms. In 3 of 5 animals, spasms ceased after a daily two week treatment. In the other 2 rats, spasm frequency dramatically decreased but gradually increased following treatment cessation. In all animals, hypsarrhythmia was abolished by the last treatment day. As VGB suppressed the frequency of spasms, there was a decrease in the intensity of the behavioral spasms and the duration of the ictal EEG event. Analysis showed that there was a burst of high frequency activity at ictal onset, followed by a later burst of HFOs. VGB was found to selectively suppress the late HFOs of ictal complexes. VGB also suppressed abnormal HFOs recorded during the interictal periods. Thus VGB was found to be effective in suppressing both the generation of spasms and hypsarrhythmia in the TTX model. Vigabatrin also appears to preferentially suppress the generation of abnormal HFOs, thus implicating neocortical HFOs in the infantile spasms disease state. Copyright © 2015 Elsevier Inc. All rights reserved.

  15. Vigabatrin Therapy Implicates Neocortical High Frequency Oscillations in an Animal Model of Infantile Spasms

    PubMed Central

    Frost, James D.; Le, John T.; Lee, Chong L.; Ballester-Rosado, Carlos; Hrachovy, Richard A.; Swann, John W.

    2015-01-01

    Abnormal high frequency oscillations (HFOs) in EEG recordings are thought to be reflections of mechanisms responsible for focal seizure generation in the temporal lobe and neocortex. HFOs have also been recorded in patients and animal models of infantile spasms. If HFOs are important contributors to infantile spasms then anticonvulsant drugs that suppress these seizures should decrease the occurrence of HFOs. In experiments reported here, we used long-term video/EEG recordings with digital sampling rates capable of capturing HFOs. We tested the effectiveness of vigabatrin (VGB) in the TTX animal model of infantile spasms. VGB was found to be quite effective in suppressing spasms. In 3 of 5 animals, spasms ceased after a daily two week treatment. In the other 2 rats, spasm frequency dramatically decreased but gradually increased following treatment cessation. In all animals, hypsarrhythmia was abolished by the last treatment day. As VGB suppressed the frequency of spasms, there was a decrease in the intensity of the behavioral spasms and the duration of the ictal EEG event. Analysis showed that there was a burst of high frequency activity at ictal onset, followed by a later burst of HFOs. VGB was found to selectively suppress the late HFOs of ictal complexes. VGB also suppressed abnormal HFOs recorded during the interictal periods. Thus VGB was found to be effective in suppressing both the generation of spasms and hypsarrhythmia in the TTX model. Vigabatrin also appears to preferentially suppress the generation of abnormal HFOs, thus implicating neocortical HFOs in the infantile spasms disease state. PMID:26026423

  16. Dependence of synchronization on frequency mismatch and network configuration in chemo-mechanical oscillators

    NASA Astrophysics Data System (ADS)

    Kumar, Pawan; Parmananda, P.

    2018-04-01

    In this paper, synchronization among the mercury beating heart (MBH) oscillators is studied. In the first set of experiments, two MBH oscillators were taken. Frequency of one oscillator is kept constant and that of the other is increased monotonically. These were then coupled using bidirectional and unidirectional coupling mechanisms separately. Dependence of synchronization on the frequency difference between the two oscillators is investigated. For the second set of experiments involving unidirectional coupling, an ensemble of fifteen oscillators was taken and different configurations of these oscillators were considered. These include an all-to-all network and fractionally distributed master slave configurations. The effect of both the extent of coupling and network configuration on synchronization among these oscillators was investigated.

  17. 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

  18. Design considerations of Miller oscillators for high-sensitivity QCM sensors in damping media.

    PubMed

    Rodriguez-Pardo, Loreto; Fariña, Jose; Gabrielli, Claude; Perrot, Hubert; Brendel, Remi

    2007-10-01

    In this paper, a new contribution to the design of quartz crystal oscillators for high-sensitivity microbalance sensors used in liquid media is presented. The oscillation condition for a Miller configuration was studied to work in a wide dynamic range of the resonator losses. The equations relating the values of the active and passive components with the maximum supported damping and mass were obtained. Also, the conditions to obtain a stable frequency according to the resonator damping (R(Q)), the static capacity (Cp) and the filter frequency (f(F)) were found. Under these conditions, the circuit oscillation frequency will be proportional to the resonant series frequency and does not depend on the previous parameters (R(Q), f(F), and Cp). If these conditions cannot be satisfied, the expression of the oscillation frequency is given and the discrimination of these effects is obtained through resonator frequency measurements.

  19. Black hole spin inferred from 3:2 epicyclic resonance model of high-frequency quasi-periodic oscillations

    NASA Astrophysics Data System (ADS)

    Šrámková, E.; Török, G.; Kotrlová, A.; Bakala, P.; Abramowicz, M. A.; Stuchlík, Z.; Goluchová, K.; Kluźniak, W.

    2015-06-01

    Estimations of black hole spin in the three Galactic microquasars GRS 1915+105, GRO J1655-40, and XTE J1550-564 have been carried out based on spectral and timing X-ray measurements and various theoretical concepts. Among others, a non-linear resonance between axisymmetric epicyclic oscillation modes of an accretion disc around a Kerr black hole has been considered as a model for the observed high-frequency quasi-periodic oscillations (HF QPOs). Estimates of spin predicted by this model have been derived based on the geodesic approximation of the accreted fluid motion. Here we assume accretion flow described by the model of a pressure-supported torus and carry out related corrections to the mass-spin estimates. We find that for dimensionless black hole spin a ≡ cJ/GM2 ≲ 0.9, the resonant eigenfrequencies are very close to those calculated for the geodesic motion. Their values slightly grow with increasing torus thickness. These findings agree well with results of a previous study carried out in the pseudo-Newtonian approximation. The situation becomes different for a ≳ 0.9, in which case the resonant eigenfrequencies rapidly decrease as the torus thickness increases. We conclude that the assumed non-geodesic effects shift the lower limit of the spin, implied for the three microquasars by the epicyclic model and independently measured masses, from a ~ 0.7 to a ~ 0.6. Their consideration furthermore confirms compatibility of the model with the rapid spin of GRS 1915+105 and provides highly testable predictions of the QPO frequencies. Individual sources with a moderate spin (a ≲ 0.9) should exhibit a smaller spread of the measured 3:2 QPO frequencies than sources with a near-extreme spin (a ~ 1). This should be further examined using the large amount of high-resolution data expected to become available with the next generation of X-ray instruments, such as the proposed Large Observatory for X-ray Timing (LOFT).

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

    DOE Office of Scientific and Technical Information (OSTI.GOV)

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

    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 foundmore » 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.« less

  1. Effect of section shape on frequencies of natural oscillations of tubular springs

    NASA Astrophysics Data System (ADS)

    Pirogov, S. P.; Chuba, A. Yu; Cherentsov, D. A.

    2018-05-01

    The necessity of determining the frequencies of natural oscillations of manometric tubular springs is substantiated. Based on the mathematical model and computer program, numerical experiments were performed that allowed us to reveal the effect of geometric parameters on the frequencies of free oscillations of manometric tubular springs.

  2. Submillimeter sources for radiometry using high power Indium Phosphide Gunn diode oscillators

    NASA Technical Reports Server (NTRS)

    Deo, Naresh C.

    1990-01-01

    A study aimed at developing high frequency millimeter wave and submillimeter wave local oscillator sources in the 60-600 GHz range was conducted. Sources involved both fundamental and harmonic-extraction type Indium Phosphide Gunn diode oscillators as well as varactor multipliers. In particular, a high power balanced-doubler using varactor diodes was developed for 166 GHz. It is capable of handling 100 mW input power, and typically produced 25 mW output power. A high frequency tripler operating at 500 GHz output frequency was also developed and cascaded with the balanced-doubler. A dual-diode InP Gunn diode combiner was used to pump this cascaded multiplier to produce on the order of 0.5 mW at 500 GHz. In addition, considerable development and characterization work on InP Gunn diode oscillators was carried out. Design data and operating characteristics were documented for a very wide range of oscillators. The reliability of InP devices was examined, and packaging techniques to enhance the performance were analyzed. A theoretical study of a new class of high power multipliers was conducted for future applications. The sources developed here find many commercial applications for radio astronomy and remote sensing.

  3. Investigation of non-uniform airflow signal oscillation during high frequency chest compression

    PubMed Central

    Sohn, Kiwon; Warwick, Warren J; Lee, Yong W; Lee, Jongwon; Holte, James E

    2005-01-01

    Background High frequency chest compression (HFCC) is a useful and popular therapy for clearing bronchial airways of excessive or thicker mucus. Our observation of respiratory airflow of a subject during use of HFCC showed the airflow oscillation by HFCC was strongly influenced by the nonlinearity of the respiratory system. We used a computational model-based approach to analyse the respiratory airflow during use of HFCC. Methods The computational model, which is based on previous physiological studies and represented by an electrical circuit analogue, was used for simulation of in vivo protocol that shows the nonlinearity of the respiratory system. Besides, airflow was measured during use of HFCC. We compared the simulation results to either the measured data or the previous research, to understand and explain the observations. Results and discussion We could observe two important phenomena during respiration pertaining to the airflow signal oscillation generated by HFCC. The amplitudes of HFCC airflow signals varied depending on spontaneous airflow signals. We used the simulation results to investigate how the nonlinearity of airway resistance, lung capacitance, and inertance of air characterized the respiratory airflow. The simulation results indicated that lung capacitance or the inertance of air is also not a factor in the non-uniformity of HFCC airflow signals. Although not perfect, our circuit analogue model allows us to effectively simulate the nonlinear characteristics of the respiratory system. Conclusion We found that the amplitudes of HFCC airflow signals behave as a function of spontaneous airflow signals. This is due to the nonlinearity of the respiratory system, particularly variations in airway resistance. PMID:15904523

  4. NMDA receptor antagonist-enhanced high frequency oscillations: are they generated broadly or regionally specific?

    PubMed

    Olszewski, Maciej; Dolowa, Wioleta; Matulewicz, Pawel; Kasicki, Stefan; Hunt, Mark J

    2013-12-01

    Systemic administration of NMDA receptor antagonists, used to model schizophrenia, increase the power of high-frequency oscillations (130-180Hz, HFO) in a variety of neuroanatomical and functionally distinct brain regions. However, it is unclear whether HFO are independently and locally generated or instead spread from a distant source. To address this issue, we used local infusion of tetrodotoxin (TTX) to distinct brain areas to determine how accurately HFO recorded after injection of NMDAR antagonists reflect the activity actually generated at the electrode tip. Changes in power were evaluated in local field potentials (LFPs) recorded from the nucleus accumbens (NAc), prefrontal cortex and caudate and in electrocorticograms (ECoGs) from visual and frontal areas. HFO recorded in frontal and visual cortices (ECoGs) or in the prefrontal cortex, caudate (LFPs) co-varied in power and frequency with observed changes in the NAc. TTX infusion to the NAc immediately and profoundly reduced the power of accumbal HFO which correlated with changes in HFO recorded in distant cortical sites. In contrast, TTX infusion to the prefrontal cortex did not change HFO power recorded locally, although gamma power was reduced. A very similar result was found after TTX infusion to the caudate. These findings raise the possibility that the NAc is an important neural generator. Our data also support existing studies challenging the idea that high frequencies recorded in LFPs are necessarily generated at the recording site. Copyright © 2013 Elsevier B.V. and ECNP. All rights reserved.

  5. Resonance frequencies of lipid-shelled microbubbles in the regime of nonlinear oscillations

    PubMed Central

    Doinikov, Alexander A.; Haac, Jillian F.; Dayton, Paul A.

    2009-01-01

    Knowledge of resonant frequencies of contrast microbubbles is important for the optimization of ultrasound contrast imaging and therapeutic techniques. To date, however, there are estimates of resonance frequencies of contrast microbubbles only for the regime of linear oscillation. The present paper proposes an approach for evaluating resonance frequencies of contrast agent microbubbles in the regime of nonlinear oscillation. The approach is based on the calculation of the time-averaged oscillation power of the radial bubble oscillation. The proposed procedure was verified for free bubbles in the frequency range 1–4 MHz and then applied to lipid-shelled microbubbles insonified with a single 20-cycle acoustic pulse at two values of the acoustic pressure amplitude, 100 kPa and 200 kPa, and at four frequencies: 1.5, 2.0, 2.5, and 3.0 MHz. It is shown that, as the acoustic pressure amplitude is increased, the resonance frequency of a lipid-shelled microbubble tends to decrease in comparison with its linear resonance frequency. Analysis of existing shell models reveals that models that treat the lipid shell as a linear viscoelastic solid appear may be challenged to provide the observed tendency in the behavior of the resonance frequency at increasing acoustic pressure. The conclusion is drawn that the further development of shell models could be improved by the consideration of nonlinear rheological laws. PMID:18977009

  6. Spectral modification of seismic waves propagating through solids exhibiting a resonance frequency: a 1-D coupled wave propagation-oscillation model

    NASA Astrophysics Data System (ADS)

    Frehner, Marcel; Schmalholz, Stefan M.; Podladchikov, Yuri

    2009-02-01

    A 1-D model is presented that couples the microscale oscillations of non-wetting fluid blobs in a partially saturated poroelastic medium with the macroscale wave propagation through the elastic skeleton. The fluid oscillations are caused by surface tension forces that act as the restoring forces driving the oscillations. The oscillations are described mathematically with the equation for a linear oscillator and the wave propagation is described with the 1-D elastic wave equation. Coupling is done using Hamilton's variational principle for continuous systems. The resulting linear system of two partial differential equations is solved numerically with explicit finite differences. Numerical simulations are used to analyse the effect of solids exhibiting internal oscillations, and consequently a resonance frequency, on seismic waves propagating through such media. The phase velocity dispersion relation shows a higher phase velocity in the high-frequency limit and a lower phase velocity in the low-frequency limit. At the resonance frequency a singularity in the dispersion relation occurs. Seismic waves can initiate oscillations of the fluid by transferring energy from solid to fluid at the resonance frequency. Due to this transfer, the spectral amplitude of the solid particle velocity decreases at the resonance frequency. After initiation, the oscillatory movement of the fluid continuously transfers energy at the resonance frequency back to the solid. Therefore, the spectral amplitude of the solid particle velocity is increased at the resonance frequency. Once initiated, fluid oscillations decrease in amplitude with increasing time. Consequently, the spectral peak of the solid particle velocity at the resonance frequency decreases with time.

  7. 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.

  8. Predicting the onset of high-frequency self-excited oscillations in a channel with an elastic wall

    NASA Astrophysics Data System (ADS)

    Ward, Thomas; Whittaker, Robert

    2016-11-01

    Flow-induced oscillations of fluid-conveying elastic-walled channels arise in many industrial and biological systems including the oscillation of the vocal cords during phonation. We derive a system of equations that describes the wall displacement in response to the steady and oscillatory components of the fluid pressure derived by Whittaker et al. (2010). We show that the steady pressure component results in a base state deformation assumed to be small in magnitude relative to the length of the channel. The oscillation frequency of the elastic wall is determined by an eigenvalue problem paramterised by the shape of the base state deformation, the strength of axial tension relative to azimuthal bending, F , and the size of non-linear stretching effects from the wall's initial deformation, K . We determine the slow growth or decay of the normal modes in each by considering the energy budget of the system. The amplitude of the oscillations grow or decay exponentially with a growth rate Λ, which may be expressed in terms of a critical Reynolds number Rec . We use numerical simulations to identify three distinct regions in parameter regimes space and determine the stability of oscillations in each.

  9. Antiferromagnetic THz-frequency Josephson-like Oscillator Driven by Spin Current.

    PubMed

    Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasyl; Ivanov, Boris A; Slavin, Andrei

    2017-03-06

    The development of compact and tunable room temperature sources of coherent THz-frequency signals would open a way for numerous new applications. The existing approaches to THz-frequency generation based on superconductor Josephson junctions (JJ), free electron lasers, and quantum cascades require cryogenic temperatures or/and complex setups, preventing the miniaturization and wide use of these devices. We demonstrate theoretically that a bi-layer of a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can be a source of a coherent THz signal. A spin-current flowing from a DC-current-driven Pt layer and polarized along the hard AFM anisotropy axis excites a non-uniform in time precession of magnetizations sublattices in the AFM, due to the presence of a weak easy-plane AFM anisotropy. The frequency of the AFM oscillations varies in the range of 0.1-2.0 THz with the driving current in the Pt layer from 10 8  A/cm 2 to 10 9  A/cm 2 . The THz-frequency signal from the AFM with the amplitude exceeding 1 V/cm is picked up by the inverse spin-Hall effect in Pt. The operation of a room-temperature AFM THz-frequency oscillator is similar to that of a cryogenic JJ oscillator, with the energy of the easy-plane magnetic anisotropy playing the role of the Josephson energy.

  10. Antiferromagnetic THz-frequency Josephson-like Oscillator Driven by Spin Current

    NASA Astrophysics Data System (ADS)

    Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasyl; Ivanov, Boris A.; Slavin, Andrei

    2017-03-01

    The development of compact and tunable room temperature sources of coherent THz-frequency signals would open a way for numerous new applications. The existing approaches to THz-frequency generation based on superconductor Josephson junctions (JJ), free electron lasers, and quantum cascades require cryogenic temperatures or/and complex setups, preventing the miniaturization and wide use of these devices. We demonstrate theoretically that a bi-layer of a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can be a source of a coherent THz signal. A spin-current flowing from a DC-current-driven Pt layer and polarized along the hard AFM anisotropy axis excites a non-uniform in time precession of magnetizations sublattices in the AFM, due to the presence of a weak easy-plane AFM anisotropy. The frequency of the AFM oscillations varies in the range of 0.1-2.0 THz with the driving current in the Pt layer from 108 A/cm2 to 109 A/cm2. The THz-frequency signal from the AFM with the amplitude exceeding 1 V/cm is picked up by the inverse spin-Hall effect in Pt. The operation of a room-temperature AFM THz-frequency oscillator is similar to that of a cryogenic JJ oscillator, with the energy of the easy-plane magnetic anisotropy playing the role of the Josephson energy.

  11. Resection of ictal high-frequency oscillations leads to favorable surgical outcome in pediatric epilepsy

    PubMed Central

    Fujiwara, Hisako; Greiner, Hansel M.; Lee, Ki Hyeong; Holland-Bouley, Katherine D.; Seo, Joo Hee; Arthur, Todd; Mangano, Francesco T.; Leach, James L.; Rose, Douglas F.

    2012-01-01

    Summary Purpose Intracranial electroencephalography (EEG) is performed as part of an epilepsy surgery evaluation when noninvasive tests are incongruent or the putative seizure-onset zone is near eloquent cortex. Determining the seizure-onset zone using intracranial EEG has been conventionally based on identification of specific ictal patterns with visual inspection. High-frequency oscillations (HFOs, >80 Hz) have been recognized recently as highly correlated with the epileptogenic zone. However, HFOs can be difficult to detect because of their low amplitude. Therefore, the prevalence of ictal HFOs and their role in localization of epileptogenic zone on intracranial EEG are unknown. Methods We identified 48 patients who underwent surgical treatment after the surgical evaluation with intracranial EEG, and 44 patients met criteria for this retrospective study. Results were not used in surgical decision making. Intracranial EEG recordings were collected with a sampling rate of 2,000 Hz. Recordings were first inspected visually to determine ictal onset and then analyzed further with time-frequency analysis. Forty-one (93%) of 44 patients had ictal HFOs determined with time-frequency analysis of intracranial EEG. Key Findings Twenty-two (54%) of the 41 patients with ictal HFOs had complete resection of HFO regions, regardless of frequency bands. Complete resection of HFOs (n = 22) resulted in a seizure-free outcome in 18 (82%) of 22 patients, significantly higher than the seizure-free outcome with incomplete HFO resection (4/19, 21%). Significance Our study shows that ictal HFOs are commonly found with intracranial EEG in our population largely of children with cortical dysplasia, and have localizing value. The use of ictal HFOs may add more promising information compared to interictal HFOs because of the evidence of ictal propagation and followed by clinical aspect of seizures. Complete resection of HFOs is a favorable prognostic indicator for surgical outcome. PMID

  12. Temperature and frequency dependence of anelasticity in a nickel oscillator

    NASA Astrophysics Data System (ADS)

    Berg, Robert F.

    1995-09-01

    The frequency dependence of the real and imaginary parts of a nickel oscillator's transfer function is described over 3 decades in frequency by the use of simple expressions. These expressions incorporate only the resonance frequency ω0, the quality factor Q, and a characteristic exponent β determined by a single measurement of creep. They are based on the ansatz φ(ω)=Q-1(ω/ω0)-β, where φ is the imaginary part of the spring constant. Over a 100 K range of temperature T, the exponent β≂0.18 was constant even though Q(T) changed by a factor of 8. These expressions are potentially useful for accurately describing a mechanical oscillator whose transfer function must be modeled at frequencies far below ω0. Examples include accelerometers based on a flexure element and suspensions for interferometric gravitational wave detectors.

  13. El Niño$-$Southern Oscillation frequency cascade

    DOE PAGES

    Stuecker, Malte F.; Jin, Fei -Fei; Timmermann, Axel

    2015-10-19

    The El Niño$-$Southern Oscillation (ENSO) phenomenon, the most pronounced feature of internally generated climate variability, occurs on interannual timescales and impacts the global climate system through an interaction with the annual cycle. The tight coupling between ENSO and the annual cycle is particularly pronounced over the tropical Western Pacific. In this paper, we show that this nonlinear interaction results in a frequency cascade in the atmospheric circulation, which is characterized by deterministic high-frequency variability on near-annual and subannual timescales. Finally, through climate model experiments and observational analysis, it is documented that a substantial fraction of the anomalous Northwest Pacific anticyclonemore » variability, which is the main atmospheric link between ENSO and the East Asian Monsoon system, can be explained by these interactions and is thus deterministic and potentially predictable.« less

  14. El Niño$-$Southern Oscillation frequency cascade

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Stuecker, Malte F.; Jin, Fei -Fei; Timmermann, Axel

    The El Niño$-$Southern Oscillation (ENSO) phenomenon, the most pronounced feature of internally generated climate variability, occurs on interannual timescales and impacts the global climate system through an interaction with the annual cycle. The tight coupling between ENSO and the annual cycle is particularly pronounced over the tropical Western Pacific. In this paper, we show that this nonlinear interaction results in a frequency cascade in the atmospheric circulation, which is characterized by deterministic high-frequency variability on near-annual and subannual timescales. Finally, through climate model experiments and observational analysis, it is documented that a substantial fraction of the anomalous Northwest Pacific anticyclonemore » variability, which is the main atmospheric link between ENSO and the East Asian Monsoon system, can be explained by these interactions and is thus deterministic and potentially predictable.« less

  15. Trains of electrical stimulation of the trapezius muscles redistribute the frequencies of body oscillations during stance.

    PubMed

    Nhouvannasak, V; Clément, S; Manto, M

    2015-09-01

    We investigated the postural effects of trains of electrical stimulation (TES) applied unilaterally or bilaterally on the trapezius muscle in 20 healthy subjects (mean age: 23.1 ± 1.33 years; F/M: 8/12). The anterior-posterior (AP) displacements (AP axis), medio-lateral displacements (ML axis) and total travelled distances (TTW) of the centre of pressure (COP) remained unchanged with TES. However, detailed spectral analysis of COP oscillations revealed a marked decrease of the magnitudes of peak power spectral density (peak PSD) following application of TES. Peak PSD was highly correlated with the intensity of stimulation (P < 0.001 both the AP and ML axes). For the AP axis, the integrals of the sub-bands 0-0.4, 0.4-1.5, 1.5-3 Hz were significantly decreased (P < 0.001), the integrals of the sub-bands 3-5 and 5-8 Hz were not significantly affected (P>0.30) and the integrals of the sub-band 8-10 Hz were significantly increased (P < 0.001). The ratios of the integrals of sub-bands 8-10 Hz/0-3 Hz were markedly enhanced with bilateral TES (P < 0.001). For the ML axis, the effects were striking (P < 0.001) for the sub-bands 0-0.4, 0.4-1.5 and 8-10 Hz. For both the AP and ML axes, a significant inverse linear relationship was found between the intensity of TES and the average speed of COP. We show that TES applied over the trapezius muscles exerts significant and so far unrecognised effects upon oscillations of the COP, decreasing low-frequency oscillations and enhancing high-frequency oscillations. Our data unravel a novel property of the trapezius muscles upon postural control. We suggest that this muscle plays a role of a distributor of low-frequency versus high-frequency sub-bands of frequency during stance. Previous studies have shown that patients with supra-tentorial stroke show an increased peak PSD in low frequencies of body oscillations. Therefore, our findings provide a rationale to assess neurostimulation of the

  16. Network Mechanisms Generating Abnormal and Normal Hippocampal High-Frequency Oscillations: A Computational Analysis1,2,3

    PubMed Central

    Catoni, Nicholas

    2015-01-01

    Abstract High-frequency oscillations (HFOs) are an intriguing potential biomarker for epilepsy, typically categorized according to peak frequency as either ripples (100–250 Hz) or fast ripples (>250 Hz). In the hippocampus, fast ripples were originally thought to be more specific to epileptic tissue, but it is still very difficult to distinguish which HFOs are caused by normal versus pathological brain activity. In this study, we use a computational model of hippocampus to investigate possible network mechanisms underpinning normal ripples, pathological ripples, and fast ripples. Our results unify several prior findings regarding HFO mechanisms, and also make several new predictions regarding abnormal HFOs. We show that HFOs are generic, emergent phenomena whose characteristics reflect a wide range of connectivity and network input. Although produced by different mechanisms, both normal and abnormal HFOs generate similar ripple frequencies, underscoring that peak frequency is unable to distinguish the two. Abnormal ripples are generic phenomena that arise when input to pyramidal cells overcomes network inhibition, resulting in high-frequency, uncoordinated firing. In addition, fast ripples transiently and sporadically arise from the precise conditions that produce abnormal ripples. Lastly, we show that such abnormal conditions do not require any specific network structure to produce coherent HFOs, as even completely asynchronous activity is capable of producing abnormal ripples and fast ripples in this manner. These results provide a generic, network-based explanation for the link between pathological ripples and fast ripples, and a unifying description for the entire spectrum from normal ripples to pathological fast ripples. PMID:26146658

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

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wang, Chunsheng, E-mail: wangcs@hit.edu.cn; 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.

  18. Oscillator circuit for use with high loss quartz resonator sensors

    DOEpatents

    Wessendorf, Otto

    1995-01-01

    The disclosure is directed to a Lever oscillator for use in high resistance resonator applications, especially for use with quartz resonator sensors. The oscillator is designed to operate over a wide dynamic range of resonator resistance due to damping of the resonator in mediums such as liquids. An oscillator design is presented that allows both frequency and loss (R.sub.m) of the resonator to be determined over a wide dynamic range of resonator loss. The Lever oscillator uses negative feedback in a differential amplifier configuration to actively and variably divide (or leverage) the resonator impedance such that the oscillator can maintain the phase and gain of the loop over a wide range of resonator resistance.

  19. Frequency modulation entrains slow neural oscillations and optimizes human listening behavior

    PubMed Central

    Henry, Molly J.; Obleser, Jonas

    2012-01-01

    The human ability to continuously track dynamic environmental stimuli, in particular speech, is proposed to profit from “entrainment” of endogenous neural oscillations, which involves phase reorganization such that “optimal” phase comes into line with temporally expected critical events, resulting in improved processing. The current experiment goes beyond previous work in this domain by addressing two thus far unanswered questions. First, how general is neural entrainment to environmental rhythms: Can neural oscillations be entrained by temporal dynamics of ongoing rhythmic stimuli without abrupt onsets? Second, does neural entrainment optimize performance of the perceptual system: Does human auditory perception benefit from neural phase reorganization? In a human electroencephalography study, listeners detected short gaps distributed uniformly with respect to the phase angle of a 3-Hz frequency-modulated stimulus. Listeners’ ability to detect gaps in the frequency-modulated sound was not uniformly distributed in time, but clustered in certain preferred phases of the modulation. Moreover, the optimal stimulus phase was individually determined by the neural delta oscillation entrained by the stimulus. Finally, delta phase predicted behavior better than stimulus phase or the event-related potential after the gap. This study demonstrates behavioral benefits of phase realignment in response to frequency-modulated auditory stimuli, overall suggesting that frequency fluctuations in natural environmental input provide a pacing signal for endogenous neural oscillations, thereby influencing perceptual processing. PMID:23151506

  20. Effects of aberrant gamma frequency oscillations on prepulse inhibition.

    PubMed

    Jones, Nigel C; Anderson, Paul; Rind, Gil; Sullivan, Caley; van den Buuse, Maarten; O'Brien, Terence J

    2014-10-01

    Emerging literature implicates abnormalities in gamma frequency oscillations in the pathophysiology of schizophrenia, with hypofunction of N-methyl-D-aspartate (NMDA) receptors implicated as a key factor. Prepulse inhibition (PPI) is a behavioural measure of sensorimotor gating, which is disrupted in schizophrenia. We studied relationships between ongoing and sensory-evoked gamma oscillations and PPI using pharmacological interventions designed to increase gamma oscillations (ketamine, MK-801); reduce gamma oscillations (LY379268); or disrupt PPI (amphetamine). We predicted that elevating ongoing gamma power would lead to increased 'neural noise' in cortical circuits, dampened sensory-evoked gamma responses and disrupted behaviour. Wistar rats were implanted with EEG recording electrodes. They received ketamine (5 mg/kg), MK-801 (0.16 mg/kg), amphetamine (0.5 mg/kg), LY379268 (3 mg/kg) or vehicle and underwent PPI sessions with concurrent EEG recording. Ketamine and MK-801 increased the power of ongoing gamma oscillations and caused time-matched disruptions of PPI, while amphetamine marginally affected ongoing gamma power. In contrast, LY379268 reduced ongoing gamma power, but had no effect on PPI. The sensory gamma response evoked by the prepulse was reduced following treatment with all psychotomimetics, associating with disruptions in PPI. This was most noticeable following treatment with NMDA receptor antagonists. We found that ketamine and MK-801 increase ongoing gamma power and reduce evoked gamma power, both of which are related to disruptions in sensorimotor gating. This appears to be due to antagonism of NMDA receptors, since amphetamine and LY379268 differentially impacted these outcomes and possess different neuropharmacological substrates. Aberrant gamma frequency oscillations caused by NMDA receptor hypofunction may mediate the sensory processing deficits observed in schizophrenia.

  1. Study of Oscillating Electroosmotic Flows with High Temporal and Spatial Resolution.

    PubMed

    Zhao, Wei; Liu, Xin; Yang, Fang; Wang, Kaige; Bai, Jintao; Qiao, Rui; Wang, Guiren

    2018-02-06

    Near-wall velocity of oscillating electroosmotic flow (OEOF) driven by an AC electric field has been investigated using a laser-induced fluorescence photobleaching anemometer (LIFPA). For the first time, an up to 3 kHz velocity response of OEOF has been successfully measured experimentally, even though the oscillating velocity is as low as 600 nm/s. It is found that the oscillating velocity decays with the forcing frequency f f as f f -0.66 . In the investigated range of electric field intensity (E A ), below 1 kHz, the linear relation between oscillating velocity and E A is also observed. Because the oscillating velocity at high frequency is very small, the contribution of noise to velocity measurement is significant, and it is discussed in this manuscript. The investigation reveals the instantaneous response of OEOF to the temporal change of electric fields, which exists in almost all AC electrokinetic flows. Furthermore, the experimental observations are important for designing OEOF-based micro/nanofluidics systems.

  2. Recent progress in opto-electronic oscillator

    NASA Technical Reports Server (NTRS)

    Maleki, Lute

    2005-01-01

    The optoelectronic oscillator (OEO) is a unique device based on photonics techniques to generate highly spectrally pure microwave signals [1]. The development of the OEO was motivated by the need for high performance oscillators in the frequency range larger than 10 GHz, where conventional electronic oscillators have a number of limitations. These limitations typically stem from the product of fQ, where f is the oscillator frequency and Q is the quality factor of the resonator in the oscillator. In conventional resonators, whether electromagnetic or piezoelectric, this product is usually a constant. Thus, as the oscillator frequency is pushed higher, the quality factor degrades, resulting in degradation of the phase noise of the oscillator. An approach to mitigate the problem is to start with a very high quality signal in the 5 to 100 MHz range generated by a quartz oscillator and multiply the frequency to achieve the desired microwave signal. Here again, frequency multiplication also results in an increase of the phase noise by a factor of 2010gN, where N is the multiplication factor.

  3. High-frequency response and the possibilities of frequency-tunable narrow-band terahertz amplification in resonant tunneling nanostructures

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kapaev, V. V., E-mail: kapaev@sci.lebedev.ru; Kopaev, Yu. V.; Savinov, S. A.

    2013-03-15

    The characteristics of the high-frequency response of single- and double-well resonant tunneling structures in a dc electric field are investigated on the basis of the numerical solution of a time-dependent Schroedinger equation with open boundary conditions. The frequency dependence of the real part of high frequency conductivity (high-frequency response) in In{sub 0.53}Ga{sub 0.47}As/AlAs/InP structures is analyzed in detail for various values of the dc voltage V{sub dc} in the negative differential resistance (NDR) region. It is shown that double-well three-barrier structures are promising for the design of terahertz-band oscillators. The presence of two resonant states with close energies in suchmore » structures leads to a resonant (in frequency) response whose frequency is determined by the energy difference between these levels and can be controlled by varying the parameters of the structure. It is shown that, in principle, such structures admit narrow-band amplification, tuning of the amplification frequency, and a fine control of the amplification (oscillation) frequency in a wide range of terahertz frequencies by varying a dc electric voltage applied to the structure. Starting from a certain width of the central intermediate barrier in double-well structures, one can observe a collapse of resonances, where the structure behaves like a single-well system. This phenomenon imposes a lower limit on the oscillation frequency in three-barrier resonant tunneling structures.« less

  4. ELISA: a cryocooled 10 GHz oscillator with 10(-15) frequency stability.

    PubMed

    Grop, S; Bourgeois, P Y; Bazin, N; Kersalé, Y; Rubiola, E; Langham, C; Oxborrow, M; Clapton, D; Walker, S; De Vicente, J; Giordano, V

    2010-02-01

    This article reports the design, the breadboarding, and the validation of an ultrastable cryogenic sapphire oscillator operated in an autonomous cryocooler. The objective of this project was to demonstrate the feasibility of a frequency stability of 3x10(-15) between 1 and 1000 s for the European Space Agency deep space stations. This represents the lowest fractional frequency instability ever achieved with cryocoolers. The preliminary results presented in this paper validate the design we adopted for the sapphire resonator, the cold source, and the oscillator loop.

  5. Frequency adjustment and synchrony in networks of delayed pulse-coupled oscillators

    NASA Astrophysics Data System (ADS)

    Nishimura, Joel

    2015-01-01

    We introduce a system of pulse-coupled oscillators that can change both their phases and frequencies and prove that when there is a separation of time scales between phase and frequency adjustment the system converges to exact synchrony on strongly connected graphs with time delays. The analysis involves decomposing the network into a forest of tree-like structures that capture causality. These results provide a robust method of sensor net synchronization as well as demonstrate a new avenue of possible pulse-coupled oscillator research.

  6. Frequency comb based on a narrowband Yb-fiber oscillator: pre-chirp management for self-referenced carrier envelope offset frequency stabilization.

    PubMed

    Lim, Jinkang; Chen, Hung-Wen; Chang, Guoqing; Kärtner, Franz X

    2013-02-25

    Laser frequency combs are normally based on mode-locked oscillators emitting ultrashort pulses of ~100-fs or shorter. In this paper, we present a self-referenced frequency comb based on a narrowband (5-nm bandwidth corresponding to 415-fs transform-limited pulses) Yb-fiber oscillator with a repetition rate of 280 MHz. We employ a nonlinear Yb-fiber amplifier to both amplify the narrowband pulses and broaden their optical spectrum. To optimize the carrier envelope offset frequency (fCEO), we optimize the nonlinear pulse amplification by pre-chirping the pulses at the amplifier input. An optimum negative pre-chirp exists, which produces a signal-to-noise ratio of 35 dB (100 kHz resolution bandwidth) for the detected fCEO. We phase stabilize the fCEO using a feed-forward method, resulting in 0.64-rad (integrated from 1 Hz to 10 MHz) phase noise for the in-loop error signal. This work demonstrates the feasibility of implementing frequency combs from a narrowband oscillator, which is of particular importance for realizing large line-spacing frequency combs based on multi-GHz oscillators usually emitting long (>200 fs) pulses.

  7. Human gamma-frequency oscillations associated with attention and memory.

    PubMed

    Jensen, Ole; Kaiser, Jochen; Lachaux, Jean-Philippe

    2007-07-01

    Both theoretical and experimental animal work supports the hypothesis that transient oscillatory synchronization of neuronal assemblies at gamma frequencies (30-100 Hz) is closely associated with sensory processing. Recent data from recordings in animals and humans have suggested that gamma-frequency activity also has an important role in attention and both working and long-term memory. The involvement of gamma-band synchronization in various cognitive paradigms in humans is currently being investigated using intracranial and high-density electro- and magnetoencephalography recordings. Here, we discuss recent findings demonstrating human gamma-frequency activity associated with attention and memory in both sensory and non-sensory areas. Because oscillatory gamma-frequency activity has an important role in neuronal communication and synaptic plasticity, it could provide a key for understanding neuronal processing in both local and distributed cortical networks engaged in complex cognitive functions. This review is part of the INMED/TINS special issue Physiogenic and pathogenic oscillations: the beauty and the beast, based on presentations at the annual INMED/TINS symposium (http://inmednet.com).

  8. A frequency doubled pressure-tunable oscillator-amplifier dye laser system

    NASA Technical Reports Server (NTRS)

    Moriarty, A.; Heaps, W.; Davis, D. D.

    1976-01-01

    A tunable high-repetition-rate oscillator-amplifier dye-laser system is reported. The dye laser described was longitudinally pumped with the second harmonic of a Nd-YAG laser operating at 10 Hz. Using three Faraday-Perot etalons and pressure tuning, a maximum fundamental output power of the order of 6 MW with a corresponding spectral width of less than 0.003 nm at 564 nm was obtained. The fundamental at 564 nm was frequency doubled to give a maximum power level of 0.6 MW of second-harmonic output power with a spectral width less than 0.0015 nm at 282 nm. Frequency stability could be maintained to within approximately 15% of the line-width.

  9. Electrodiagnostic applications of somatosensory evoked high-frequency EEG oscillations: Technical considerations.

    PubMed

    Simpson, A J; Cunningham, M O; Baker, M R

    2018-03-01

    High frequency oscillations (HFOs) embedded within the somatosensory evoked potential (SEP) are not routinely recorded/measured as part of standard clinical SEPs. However, HFOs could provide important additional diagnostic/prognostic information in various patient groups in whom SEPs are tested routinely. One area is the management of patients with hypoxic ischaemic encephalopathy (HIE) in the intensive care unit (ICU). However, the sensitivity of standard clinical SEP recording techniques for detecting HFOs is unknown. SEPs were recorded using routine clinical methods in 17 healthy subjects (median nerve stimulation; 0.5 ms pulse width; 5 Hz; maximum 4000 stimuli) in an unshielded laboratory. Bipolar EEG recordings were acquired (gain 50 k; bandpass 3Hz-2 kHz; sampling rate 5 kHz; non-inverting electrode 2 cm anterior to C3/C4; inverting electrode 2 cm posterior to C3/C4). Data analysis was performed in MATLAB. SEP-HFOs were detected in 65% of controls using standard clinical recording techniques. In 3 controls without significant HFOs, experiments were repeated using a linear electrode array with higher spatial sampling frequency. SEP-HFOs were observed in all 3 subjects. Currently standard clinical methods of recording SEPs are not sufficiently sensitive to permit the inclusion of SEP-HFOs in routine clinical diagnostic/prognostic assessments. Whilst an increase in the number/density of EEG electrodes should improve the sensitivity for detecting SEP-HFOs, this requires confirmation. By improving and standardising clinical SEP recording protocols to permit the acquisition/analysis of SEP-HFOs, it should be possible to gain important insights into the pathophysiology of neurological disorders and refine the management of conditions such as HIE. Copyright © 2018. Published by Elsevier Inc.

  10. Detecting and characterizing high-frequency oscillations in epilepsy: a case study of big data analysis

    NASA Astrophysics Data System (ADS)

    Huang, Liang; Ni, Xuan; Ditto, William L.; Spano, Mark; Carney, Paul R.; Lai, Ying-Cheng

    2017-01-01

    We develop a framework to uncover and analyse dynamical anomalies from massive, nonlinear and non-stationary time series data. The framework consists of three steps: preprocessing of massive datasets to eliminate erroneous data segments, application of the empirical mode decomposition and Hilbert transform paradigm to obtain the fundamental components embedded in the time series at distinct time scales, and statistical/scaling analysis of the components. As a case study, we apply our framework to detecting and characterizing high-frequency oscillations (HFOs) from a big database of rat electroencephalogram recordings. We find a striking phenomenon: HFOs exhibit on-off intermittency that can be quantified by algebraic scaling laws. Our framework can be generalized to big data-related problems in other fields such as large-scale sensor data and seismic data analysis.

  11. 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

  12. 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. Copyright © 2013. Published by Elsevier Inc.

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

    PubMed Central

    Ekstrom, Arne D.; Watrous, Andrew J.

    2014-01-01

    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 arm to explore). 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. PMID:23792985

  14. Forced Longitudinal Oscillations of a Gas in an Open Pipe Near the Resonance Excitation Frequency

    NASA Astrophysics Data System (ADS)

    Zaripov, R. G.; Tkachenko, L. A.; Shaidullin, L. R.

    2017-11-01

    Results of theoretical and experimental investigations of forced longitudinal oscillations of a homogeneous gas in an open pipe near the first natural frequency are presented. It has been established that at the resonance frequency the shape of the gas pressure wave changes with time by a law different from the harmonic one. The amplitude-frequency characteristics of the indicated oscillations have been derived. Satisfactory agreement of the theoretical calculation of the gas pressure oscillation range with experimental data has been obtained.

  15. Investigation of high frequency oscillations in the OV102 elevon actuation subsystems using continuous system modeling program simulation

    NASA Technical Reports Server (NTRS)

    Powell, W. W., Sr.

    1979-01-01

    Two theories emerged as the cause of undesired oscillations at frequencies between 40 and 60 Hz in the Orbiter Vehicle inboard and outboard elevon actuation subsystems during hardware testing. Both the "hardover feedback" and "deadspace" theories were examined using continuous system modeling program simulation. Results did not support the "hardover feedback" theory but showed that deadspace in the torque feedback spring connections to the servospools must be considered to be a possible cause of the oscillations. Further investigation is recommended.

  16. Super-spinning compact objects and models of high-frequency quasi-periodic oscillations observed in Galactic microquasars. II. Forced resonances

    NASA Astrophysics Data System (ADS)

    Kotrlová, A.; Šrámková, E.; Török, G.; Stuchlík, Z.; Goluchová, K.

    2017-11-01

    In our previous work (Paper I) we applied several models of high-frequency quasi-periodic oscillations (HF QPOs) to estimate the spin of the central compact object in three Galactic microquasars assuming the possibility that the central compact body is a super-spinning object (or a naked singularity) with external spacetime described by Kerr geometry with a dimensionless spin parameter a ≡ cJ/GM2 > 1. Here we extend our consideration, and in a consistent way investigate implications of a set of ten resonance models so far discussed only in the context of a < 1. The same physical arguments as in Paper I are applied to these models, I.e. only a small deviation of the spin estimate from a = 1, a ≳ 1, is assumed for a favoured model. For five of these models that involve Keplerian and radial epicyclic oscillations we find the existence of a unique specific QPO excitation radius. Consequently, there is a simple behaviour of dimensionless frequency M × νU(a) represented by a single continuous function having solely one maximum close to a ≳ 1. Only one of these models is compatible with the expectation of a ≳ 1. The other five models that involve the radial and vertical epicyclic oscillations imply the existence of multiple resonant radii. This signifies a more complicated behaviour of M × νU(a) that cannot be represented by single functions. Each of these five models is compatible with the expectation of a ≳ 1.

  17. Action potentials contribute to epileptic high-frequency oscillations recorded with electrodes remote from neurons.

    PubMed

    Kobayashi, Katsuhiro; Akiyama, Tomoyuki; Ohmori, Iori; Yoshinaga, Harumi; Gotman, Jean

    2015-05-01

    The importance of epileptic high-frequency oscillations (HFOs) in electroencephalogram (EEG) is growing. Action potentials generating some HFOs are observed in the vicinity of neurons in experimental animals. However electrodes that are remote from neurons, as in case of clinical situations, should not record action potentials. We propose to resolve this question by a realistic simulation of epileptic neuronal network. The rat dentate gyrus with sclerosis was simulated in silico. We computed the current dipole moment generated by each granule cell and the field potentials in a measurement area far from neurons. The dentate gyrus was stimulated through synaptic input to evoke discharges resembling interictal epileptiform discharges, which had superimposed HFOs⩽295Hz that were recordable with remote electrodes and represented bursts of action potentials of granule cells. The increase in power of HFOs was associated with the progression of sclerosis, the reduction of GABAergic inhibition, and the increase in cell connectivity. Spectral frequency of HFOs had similar tendencies. HFOs recorded with electrodes remote from neurons could actually be generated by clusters of action potentials. The phenomenon of action potentials recorded with remote electrodes can possibly extend the clinical meaning of EEG. Copyright © 2014 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

  18. A microwave exciter for Cs frequency standards based on a sapphire-loaded cavity oscillator.

    PubMed

    Koga, Y; McNeilage, C; Searls, J H; Ohshima, S

    2001-01-01

    A low noise and highly stable microwave exciter system has been built for Cs atomic frequency standards using a tunable sapphire-loaded cavity oscillator (SLCO), which works at room temperature. This paper discusses the successful implementation of a control system for locking the SLCO to a long-term reference signal and reports an upper limit of the achieved frequency tracking error 6 x 10(-15) at tau = 1 s.

  19. Effective deep brain stimulation suppresses low-frequency network oscillations in the basal ganglia by regularizing neural firing patterns.

    PubMed

    McConnell, George C; So, Rosa Q; Hilliard, Justin D; Lopomo, Paola; Grill, Warren M

    2012-11-07

    Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an effective treatment for the motor symptoms of Parkinson's disease (PD). The effects of DBS depend strongly on stimulation frequency: high frequencies (>90 Hz) improve motor symptoms, while low frequencies (<50 Hz) are either ineffective or exacerbate symptoms. The neuronal basis for these frequency-dependent effects of DBS is unclear. The effects of different frequencies of STN-DBS on behavior and single-unit neuronal activity in the basal ganglia were studied in the unilateral 6-hydroxydopamine lesioned rat model of PD. Only high-frequency DBS reversed motor symptoms, and the effectiveness of DBS depended strongly on stimulation frequency in a manner reminiscent of its clinical effects in persons with PD. Quantification of single-unit activity in the globus pallidus externa (GPe) and substantia nigra reticulata (SNr) revealed that high-frequency DBS, but not low-frequency DBS, reduced pathological low-frequency oscillations (∼9 Hz) and entrained neurons to fire at the stimulation frequency. Similarly, the coherence between simultaneously recorded pairs of neurons within and across GPe and SNr shifted from the pathological low-frequency band to the stimulation frequency during high-frequency DBS, but not during low-frequency DBS. The changes in firing patterns in basal ganglia neurons were not correlated with changes in firing rate. These results indicate that high-frequency DBS is more effective than low-frequency DBS, not as a result of changes in firing rate, but rather due to its ability to replace pathological low-frequency network oscillations with a regularized pattern of neuronal firing.

  20. Effective deep brain stimulation suppresses low frequency network oscillations in the basal ganglia by regularizing neural firing patterns

    PubMed Central

    McConnell, George C.; So, Rosa Q.; Hilliard, Justin D; Lopomo, Paola; Grill, Warren M.

    2012-01-01

    Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an effective treatment for the motor symptoms of Parkinson’s disease (PD). The effects of DBS depend strongly on stimulation frequency: high frequencies (>90Hz) improve motor symptoms, while low frequencies (<50Hz) are either ineffective or exacerbate symptoms. The neuronal basis for these frequency-dependent effects of DBS is unclear. The effects of different frequencies of STN-DBS on behavior and single-unit neuronal activity in the basal ganglia were studied in the unilateral 6-hydroxydopamine lesioned rat model of PD. Only high frequency DBS reversed motor symptoms and the effectiveness of DBS depended strongly on stimulation frequency in a manner reminiscent of its clinical effects in persons with PD. Quantification of single-unit activity in the globus pallidus externa (GPe) and substantia nigra reticulata (SNr) revealed that high frequency DBS, but not low frequency DBS, reduced pathological low frequency oscillations (~9Hz) and entrained neurons to fire at the stimulation frequency. Similarly, the coherence between simultaneously recorded pairs of neurons within and across GPe and SNr shifted from the pathological low frequency band to the stimulation frequency during high frequency DBS, but not during low frequency DBS. The changes in firing patterns in basal ganglia neurons were not correlated with changes in firing rate. These results indicate that high frequency DBS is more effective than low frequency DBS, not as a result of changes in firing rate, but rather due to its ability to replace pathological low frequency network oscillations with a regularized pattern of neuronal firing. PMID:23136407

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

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

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

  2. Frequency-Temperature Compensation Techniques for High-Q Microwave Resonators

    NASA Astrophysics Data System (ADS)

    Hartnett, John G.; Tobar, Michael E.

    Low-noise high-stability resonator oscillators based on high-Q monolithic sapphire ``Whispering Gallery'' (WG)-mode resonators have become important devices for telecommunication, radar and metrological applications. The extremely high quality factor of sapphire, of 2 x10^5 at room temperature, 5 x10^7 at liquid nitrogen temperature and 5 x10^9 at liquid helium temperature has enabled the lowest phase noise and highly frequency-stable oscillators in the microwave regime to be constructed. To create an oscillator with exceptional frequency stability, the resonator must have its frequency-temperature dependence annulled at some temperature, as well as a high quality factor. The Temperature Coefficient of Permittivity (TCP) for sapphire is quite large, at 10-100parts per million/K above 77K. This mechanism allows temperature fluctuations to transform to resonator frequency fluctuations.A number of research groups worldwide have investigated various methods of compensating the TCP of a sapphire dielectric resonator at different temperatures. The usual electromagnetic technique of annulment involves the use of paramagnetic impurities contributing an opposite temperature coefficient of the magnetic susceptibility to the TCP. This technique has only been realized successfully in liquid helium environments. Near 4K the thermal expansion and permittivity effects are small and only small quantities of the paramagnetic ions are necessary to compensate the mode frequency. Compensation is due to impurity ions that were incidentally left over from the manufacturing process.Recently, there has been an effort to dispense with the need for liquid helium and make a compact flywheel oscillator for the new generation of primary frequency standards such as the cesium fountain at the Laboratoire Primaire du Temps et des Fréquences (LPTF), France. To achieve the stability limit imposed

  3. A PK-PD model of ketamine-induced high-frequency oscillations

    NASA Astrophysics Data System (ADS)

    Flores, Francisco J.; Ching, ShiNung; Hartnack, Katharine; Fath, Amanda B.; Purdon, Patrick L.; Wilson, Matthew A.; Brown, Emery N.

    2015-10-01

    Objective. Ketamine is a widely used drug with clinical and research applications, and also known to be used as a recreational drug. Ketamine produces conspicuous changes in the electrocorticographic (ECoG) signals observed both in humans and rodents. In rodents, the intracranial ECoG displays a high-frequency oscillation (HFO) which power is modulated nonlinearly by ketamine dose. Despite the widespread use of ketamine there is no model description of the relationship between the pharmacokinetic-pharmacodynamics (PK-PDs) of ketamine and the observed HFO power. Approach. In the present study, we developed a PK-PD model based on estimated ketamine concentration, its known pharmacological actions, and observed ECoG effects. The main pharmacological action of ketamine is antagonism of the NMDA receptor (NMDAR), which in rodents is accompanied by an HFO observed in the ECoG. At high doses, however, ketamine also acts at non-NMDAR sites, produces loss of consciousness, and the transient disappearance of the HFO. We propose a two-compartment PK model that represents the concentration of ketamine, and a PD model based in opposing effects of the NMDAR and non-NMDAR actions on the HFO power. Main results. We recorded ECoG from the cortex of rats after two doses of ketamine, and extracted the HFO power from the ECoG spectrograms. We fit the PK-PD model to the time course of the HFO power, and showed that the model reproduces the dose-dependent profile of the HFO power. The model provides good fits even in the presence of high variability in HFO power across animals. As expected, the model does not provide good fits to the HFO power after dosing the pure NMDAR antagonist MK-801. Significance. Our study provides a simple model to relate the observed electrophysiological effects of ketamine to its actions at the molecular level at different concentrations. This will improve the study of ketamine and rodent models of schizophrenia to better understand the wide and divergent

  4. Short-term variability in QT interval and ventricular arrhythmias induced by dofetilide are dependent on high-frequency autonomic oscillations

    PubMed Central

    Champeroux, P; Thireau, J; Judé, S; Laigot-Barbé, C; Maurin, A; Sola, M L; Fowler, J S L; Richard, S; Le Guennec, J Y

    2015-01-01

    Background and Purpose The present study was undertaken to investigate an effect of dofetilide, a potent arrhythmic blocker of the voltage-gated K+ channel, hERG, on cardiac autonomic control. Combined with effects on ardiomyocytes, these properties could influence its arrhythmic potency. Experimental Approach The short-term variability of beat-to-beat QT interval (STVQT), induced by dofetilide is a strong surrogate of Torsades de pointes liability. Involvement of autonomic modulation in STVQT was investigated in healthy cynomolgus monkeys and beagle dogs by power spectral analysis under conditions of autonomic blockade with hexamethonium. Key Results Increase in STVQT induced by dofetilide in monkeys and dogs was closely associated with an enhancement of endogenous heart rate and QT interval high-frequency (HF) oscillations. These effects were fully suppressed under conditions of autonomic blockade with hexamethonium. Ventricular arrhythmias, including Torsades de pointes in monkeys, were prevented in both species when HF oscillations were suppressed by autonomic blockade. Similar enhancements of heart rate HF oscillations were found in dogs with other hERG blockers described as causing Torsades de pointes in humans. Conclusions and Implications These results demonstrate for the first time that beat-to-beat ventricular repolarization variability and ventricular arrhythmias induced by dofetilide are dependent on endogenous HF autonomic oscillations in heart rate. When combined with evidence of hERG-blocking properties, enhancement of endogenous HF oscillations in heart rate could constitute an earlier and more sensitive biomarker than STVQT for Torsades de pointes liability, applicable to preclinical regulatory studies conducted in healthy animals. PMID:25625756

  5. Short-term variability in QT interval and ventricular arrhythmias induced by dofetilide are dependent on high-frequency autonomic oscillations.

    PubMed

    Champeroux, P; Thireau, J; Judé, S; Laigot-Barbé, C; Maurin, A; Sola, M L; Fowler, J S L; Richard, S; Le Guennec, J Y

    2015-06-01

    The present study was undertaken to investigate an effect of dofetilide, a potent arrhythmic blocker of the voltage-gated K(+) channel, hERG, on cardiac autonomic control. Combined with effects on ardiomyocytes, these properties could influence its arrhythmic potency. The short-term variability of beat-to-beat QT interval (STVQT ), induced by dofetilide is a strong surrogate of Torsades de pointes liability. Involvement of autonomic modulation in STVQT was investigated in healthy cynomolgus monkeys and beagle dogs by power spectral analysis under conditions of autonomic blockade with hexamethonium. Increase in STVQT induced by dofetilide in monkeys and dogs was closely associated with an enhancement of endogenous heart rate and QT interval high-frequency (HF) oscillations. These effects were fully suppressed under conditions of autonomic blockade with hexamethonium. Ventricular arrhythmias, including Torsades de pointes in monkeys, were prevented in both species when HF oscillations were suppressed by autonomic blockade. Similar enhancements of heart rate HF oscillations were found in dogs with other hERG blockers described as causing Torsades de pointes in humans. These results demonstrate for the first time that beat-to-beat ventricular repolarization variability and ventricular arrhythmias induced by dofetilide are dependent on endogenous HF autonomic oscillations in heart rate. When combined with evidence of hERG-blocking properties, enhancement of endogenous HF oscillations in heart rate could constitute an earlier and more sensitive biomarker than STVQT for Torsades de pointes liability, applicable to preclinical regulatory studies conducted in healthy animals. © 2015 The British Pharmacological Society.

  6. 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.

  7. Electro-opto-mechanical radio-frequency oscillator driven by guided acoustic waves in standard single-mode fiber

    NASA Astrophysics Data System (ADS)

    London, Yosef; Diamandi, Hilel Hagai; Zadok, Avi

    2017-04-01

    An opto-electronic radio-frequency oscillator that is based on forward scattering by the guided acoustic modes of a standard single-mode optical fiber is proposed and demonstrated. An optical pump wave is used to stimulate narrowband, resonant guided acoustic modes, which introduce phase modulation to a co-propagating optical probe wave. The phase modulation is converted to an intensity signal at the output of a Sagnac interferometer loop. The intensity waveform is detected, amplified, and driven back to modulate the optical pump. Oscillations are achieved at a frequency of 319 MHz, which matches the resonance of the acoustic mode that provides the largest phase modulation of the probe wave. Oscillations at the frequencies of competing acoustic modes are suppressed by at least 40 dB. The linewidth of the acoustic resonance is sufficiently narrow to provide oscillations at a single longitudinal mode of the hybrid cavity. Competing longitudinal modes are suppressed by at least 38 dB as well. Unlike other opto-electronic oscillators, no radio-frequency filtering is required within the hybrid cavity. The frequency of oscillations is entirely determined by the fiber opto-mechanics.

  8. System for adjusting frequency of electrical output pulses derived from an oscillator

    DOEpatents

    Bartholomew, David B.

    2006-11-14

    A system for setting and adjusting a frequency of electrical output pulses derived from an oscillator in a network is disclosed. The system comprises an accumulator module configured to receive pulses from an oscillator and to output an accumulated value. An adjustor module is configured to store an adjustor value used to correct local oscillator drift. A digital adder adds values from the accumulator module to values stored in the adjustor module and outputs their sums to the accumulator module, where they are stored. The digital adder also outputs an electrical pulse to a logic module. The logic module is in electrical communication with the adjustor module and the network. The logic module may change the value stored in the adjustor module to compensate for local oscillator drift or change the frequency of output pulses. The logic module may also keep time and calculate drift.

  9. Detection With Rhessi of High Frequency X-ray Oscillations in the Tail of the 2004 Hyperflare From SGR 1806-20

    NASA Technical Reports Server (NTRS)

    Watts, Anna L.; Strohmayer, Tod E.

    2005-01-01

    The recent discovery of high frequency oscillations in giant flares from SGR 1806-20 and SGR 1900+14 may be the first direct detection of vibrations in a neutron star crust. If this interpretation is correct it offers a novel means of testing the neutron star equation of state, crustal breaking strain, and magnetic field configuration. Using timing data from RHESSI, we have confirmed the detection of a 92.5 Hz Quasi-Periodic Oscillation (QPO) in the tail of the SGR 1806-20 giant flare. We also find another, stronger, QPO at higher energies, at 626.5 Hz. Both QPOs are visible only at particular (but different) rotational phases, implying an association with a specific area of the neutron star surface or magnetosphere. At lower frequencies we confirm the detection of an 18 Hz QPO, at the same rotational phase as the 92.5 Hz QPO, and report the additional presence of a broad 26 Hz QPO. We are however unable to make a robust confirmation of the presence of a 30 Hz QPO, despite higher count rates. We discuss our results in the light of neutron star vibration models.

  10. Fast Dynamical Coupling Enhances Frequency Adaptation of Oscillators for Robotic Locomotion Control

    PubMed Central

    Nachstedt, Timo; Tetzlaff, Christian; Manoonpong, Poramate

    2017-01-01

    Rhythmic neural signals serve as basis of many brain processes, in particular of locomotion control and generation of rhythmic movements. It has been found that specific neural circuits, named central pattern generators (CPGs), are able to autonomously produce such rhythmic activities. In order to tune, shape and coordinate the produced rhythmic activity, CPGs require sensory feedback, i.e., external signals. Nonlinear oscillators are a standard model of CPGs and are used in various robotic applications. A special class of nonlinear oscillators are adaptive frequency oscillators (AFOs). AFOs are able to adapt their frequency toward the frequency of an external periodic signal and to keep this learned frequency once the external signal vanishes. AFOs have been successfully used, for instance, for resonant tuning of robotic locomotion control. However, the choice of parameters for a standard AFO is characterized by a trade-off between the speed of the adaptation and its precision and, additionally, is strongly dependent on the range of frequencies the AFO is confronted with. As a result, AFOs are typically tuned such that they require a comparably long time for their adaptation. To overcome the problem, here, we improve the standard AFO by introducing a novel adaptation mechanism based on dynamical coupling strengths. The dynamical adaptation mechanism enhances both the speed and precision of the frequency adaptation. In contrast to standard AFOs, in this system, the interplay of dynamics on short and long time scales enables fast as well as precise adaptation of the oscillator for a wide range of frequencies. Amongst others, a very natural implementation of this mechanism is in terms of neural networks. The proposed system enables robotic applications which require fast retuning of locomotion control in order to react to environmental changes or conditions. PMID:28377710

  11. Rapid, high-frequency, and theta-coupled gamma oscillations in the inferior occipital gyrus during face processing.

    PubMed

    Sato, Wataru; Kochiyama, Takanori; Uono, Shota; Matsuda, Kazumi; Usui, Keiko; Inoue, Yushi; Toichi, Motomi

    2014-11-01

    Neuroimaging studies have found greater activation in the inferior occipital gyrus (IOG), or occipital face area, in response to faces relative to non-facial stimuli. However, the temporal, frequency, and functional profiles of IOG activity during face processing remain unclear. Here, this issue was investigated by recording intracranial field potentials in the IOG during the presentation of faces, mosaics, and houses in upright and inverted orientations. Time-frequency statistical parametric mapping analyses revealed greater gamma-band activation in the IOG beginning at 110 msec and covering 40-300 Hz in response to upright faces relative to upright houses and mosaics. Phase-amplitude cross-frequency coupling analyses revealed more evident theta-gamma couplings at 115-256 msec during the processing of upright faces as compared with that of upright houses and mosaics. Comparable gamma-band activity was observed during the processing of inverted and upright faces at about 100-200 msec, but weaker activity and different coupling with theta-band activity after 200 msec. These patterns of activity were more evident in the right than in the left IOG. These results, together with other evidence on neural communication, suggest that broadband gamma oscillations in the right IOG conduct rapid and multistage (i.e., both featural and configural) face processing in collaboration with theta oscillations transmitted from other brain regions. Copyright © 2014 Elsevier Ltd. All rights reserved.

  12. A novel photonic oscillator

    NASA Technical Reports Server (NTRS)

    Yao, X. S.; Maleki, L.

    1995-01-01

    We report a novel oscillator for photonic RF systems. This oscillator is capable of generating high-frequency signals up to 70 GHz in both electrical and optical domains and is a special voltage-controlled oscillator with an optical output port. It can be used to make a phase-locked loop (PLL) and perform all functions that a PLL is capable of for photonic systems. It can be synchronized to a reference source by means of optical injection locking, electrical injection locking, and PLL. It can also be self-phase locked and self-injection locked to generate a high-stability photonic RF reference. Its applications include high-frequency reference regeneration and distribution, high-gain frequency multiplication, comb-frequecy and square-wave generation, carrier recovery, and clock recovery. We anticipate that such photonic voltage-controlled oscillators (VCOs) will be as important to photonic RF systems as electrical VCOs are to electrical RF systems.

  13. Pulse-coupled Belousov-Zhabotinsky oscillators with frequency modulation

    NASA Astrophysics Data System (ADS)

    Horvath, Viktor; Epstein, Irving R.

    2018-04-01

    Inhibitory perturbations to the ferroin-catalyzed Belousov-Zhabotinsky (BZ) chemical oscillator operated in a continuously fed stirred tank reactor cause long term changes to the limit cycle: the lengths of the cycles subsequent to the perturbation are longer than that of the unperturbed cycle, and the unperturbed limit cycle is recovered only after several cycles. The frequency of the BZ reaction strongly depends on the acid concentration of the medium. By adding strong acid or base to the perturbing solutions, the magnitude and the direction of the frequency changes concomitant to excitatory or inhibitory perturbations can be controlled independently of the coupling strength. The dynamics of two BZ oscillators coupled through perturbations carrying a coupling agent (activator or inhibitor) and a frequency modulator (strong acid or base) was explored using a numerical model of the system. Here, we report new complex temporal patterns: higher order, partially synchronized modes that develop when inhibitory coupling is combined with positive frequency modulation (FM), and complex bursting patterns when excitatory coupling is combined with negative FM. The role of time delay between the peak and perturbation (the analog of synaptic delays in networks of neurons) has also been studied. The complex patterns found under inhibitory coupling and positive FM vanish when the delay is significant, whereas a sufficiently long time delay is required for the complex temporal dynamics to occur when coupling is excitatory and FM is negative.

  14. High-frequency neural activity predicts word parsing in ambiguous speech streams

    PubMed Central

    Basirat, Anahita; Azizi, Leila; van Wassenhove, Virginie

    2016-01-01

    During speech listening, the brain parses a continuous acoustic stream of information into computational units (e.g., syllables or words) necessary for speech comprehension. Recent neuroscientific hypotheses have proposed that neural oscillations contribute to speech parsing, but whether they do so on the basis of acoustic cues (bottom-up acoustic parsing) or as a function of available linguistic representations (top-down linguistic parsing) is unknown. In this magnetoencephalography study, we contrasted acoustic and linguistic parsing using bistable speech sequences. While listening to the speech sequences, participants were asked to maintain one of the two possible speech percepts through volitional control. We predicted that the tracking of speech dynamics by neural oscillations would not only follow the acoustic properties but also shift in time according to the participant's conscious speech percept. Our results show that the latency of high-frequency activity (specifically, beta and gamma bands) varied as a function of the perceptual report. In contrast, the phase of low-frequency oscillations was not strongly affected by top-down control. Whereas changes in low-frequency neural oscillations were compatible with the encoding of prelexical segmentation cues, high-frequency activity specifically informed on an individual's conscious speech percept. PMID:27605528

  15. Coupled opto-electronic oscillator

    NASA Technical Reports Server (NTRS)

    Yao, X. Steve (Inventor); Maleki, Lute (Inventor)

    1999-01-01

    A coupled opto-electronic oscillator that directly couples a laser oscillation with an electronic oscillation to simultaneously achieve a stable RF oscillation at a high frequency and ultra-short optical pulsation by mode locking with a high repetition rate and stability. Single-mode selection can be achieved even with a very long opto-electronic loop. A multimode laser can be used to pump the electronic oscillation, resulting in a high operation efficiency. The optical and the RF oscillations are correlated to each other.

  16. Gap Junction Modulation of Low-Frequency Oscillations in the Cerebellar Granule Cell Layer.

    PubMed

    Robinson, Jennifer Claire; Chapman, C Andrew; Courtemanche, Richard

    2017-08-01

    Local field potential (LFP) oscillations in the granule cell layer (GCL) of the cerebellar cortex have been identified previously in the awake rat and monkey during immobility. These low-frequency oscillations are thought to be generated through local circuit interactions between Golgi cells and granule cells within the GCL. Golgi cells display rhythmic firing and pacemaking properties, and also are electrically coupled through gap junctions within the GCL. Here, we tested if gap junctions in the rat cerebellar cortex contribute to the generation of LFP oscillations in the GCL. We recorded LFP oscillations under urethane anesthesia, and examined the effects of local infusion of gap junction blockers on 5-15 Hz oscillations. Local infusion of the gap junction blockers carbenoxolone and mefloquine resulted in significant decreases in the power of oscillations over a 30-min period, but the power of oscillations was unchanged in control experiments following vehicle injections. In addition, infusion of gap junction blockers had no significant effect on multi-unit activity, suggesting that the attenuation of low-frequency oscillations was likely due to reductions in electrical coupling rather than a decreased excitability within the granule cell layer. Our results indicate that electrical coupling among the Golgi cell networks in the cerebellar cortex contributes to the local circuit mechanisms that promote the occurrence of GCL LFP slow oscillations in the anesthetized rat.

  17. 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.

  18. High Speed Laser with 100 Ghz Resonance Frequency

    DTIC Science & Technology

    2014-02-28

    applications, such as opto - electronic oscillators . Recently, however, by optimizing the detuning frequency and injection ratio, we have shown enhanced...semiconductor lasers has been limited by relaxation oscillation frequency to < 40 GHz. By using strong optical injection locking, we report resonance...direct modulation bandwidth of semiconductor lasers. In a typical laser, the relaxation oscillation [resonance] frequency is a figure-of-merit that is a

  19. Frequency spectrum of transepithelial potential difference reveals transport-related oscillations.

    PubMed

    Montalbetti, Nicolás; Fischbarg, Jorge

    2009-09-16

    How epithelia transport fluid is a fundamental issue that is unresolved. Explanations offered include molecular engines, local transcellular osmosis, local paracellular osmosis, and paracellular fluid transport. On the basis of experimental and theoretical work done on corneal endothelium, a fluid transporting epithelium, we suggest electroosmotic coupling at the level of the intercellular junctions driven by the transendothelial electrical potential difference as an explanation of paracellular fluid transport. We collect frequency spectra of that potential difference in real-time. For what we believe is the first time for any epithelium, we report that, unexpectedly, the potential difference displays oscillations at many characteristic frequencies. We also show that on both stimulating cell activity and inhibiting ion transport mechanisms, there are corresponding changes in the oscillations amplitudes that mirror changes known previously in rates of fluid transport. We believe these findings provide a novel tool to study the kinetics of electrogenic elements such as channels and transporters, which from this evidence would give rise to current oscillations with characteristic periods going from 150 ms to 8 s.

  20. Unprecedented long-term frequency stability with a microwave resonator oscillator.

    PubMed

    Grop, Serge; Schafer, Wolfgang; Bourgeois, Pierre-Yves; Kersale, Yann; Oxborrow, Mark; Rubiola, Enrico; Giordano, Vincent

    2011-08-01

    This article reports on the long-term frequency stability characterization of a new type of cryogenic sapphire oscillator using an autonomous pulse-tube cryocooler as its cold source. This new design enables a relative frequency stability of better than 4.5 x 10(-15) over one day of integration. To the best of our knowledge, this represents the best long-term frequency stability ever obtained with a signal source based on a macroscopic resonator.

  1. Phase inversion and frequency doubling of reflection high-energy electron diffraction intensity oscillations in the layer-by-layer growth of complex oxides

    NASA Astrophysics Data System (ADS)

    Mao, Zhangwen; Guo, Wei; Ji, Dianxiang; Zhang, Tianwei; Gu, Chenyi; Tang, Chao; Gu, Zhengbin; Nie*, Yuefeng; Pan, Xiaoqing

    In situ reflection high-energy electron diffraction (RHEED) and its intensity oscillations are extremely important for the growth of epitaxial thin films with atomic precision. The RHEED intensity oscillations of complex oxides are, however, rather complicated and a general model is still lacking. Here, we report the unusual phase inversion and frequency doubling of RHEED intensity oscillations observed in the layer-by-layer growth of SrTiO3 using oxide molecular beam epitaxy. In contacts to the common understanding that the maximum(minimum) intensity occurs at SrO(TiO2) termination, respectively, we found that both maximum or minimum intensities can occur at SrO, TiO2, or even incomplete terminations depending on the incident angle of the electron beam, which raises a fundamental question if one can rely on the RHEED intensity oscillations to precisely control the growth of thin films. A general model including surface roughness and termination dependent mean inner potential qualitatively explains the observed phenomena, and provides the answer to the question how to prepare atomically and chemically precise surface/interfaces using RHEED oscillations for complex oxides. We thank National Basic Research Program of China (No. 11574135, 2015CB654901) and the National Thousand-Young-Talents Program.

  2. Inspiratory High Frequency Airway Oscillation Attenuates Resistive Loaded Dyspnea and Modulates Respiratory Function in Young Healthy Individuals

    PubMed Central

    Morris, Theresa; Sumners, David Paul; Green, David Andrew

    2014-01-01

    Direct chest-wall percussion can reduce breathlessness in Chronic Obstructive Pulmonary Disease and respiratory function may be improved, in health and disease, by respiratory muscle training (RMT). We tested whether high-frequency airway oscillation (HFAO), a novel form of airflow oscillation generation can modulate induced dyspnoea and respiratory strength and/or patterns following 5 weeks of HFAO training (n = 20) compared to a SHAM-RMT (conventional flow-resistive RMT) device (n = 15) in healthy volunteers (13 males; aged 20–36 yrs). HFAO causes oscillations with peak-to-peak amplitude of 1 cm H2O, whereas the SHAM-RMT device was identical but created no pressure oscillation. Respiratory function, dyspnoea and ventilation during 3 minutes of spontaneous resting ventilation, 1 minute of maximal voluntary hyperventilation and 1 minute breathing against a moderate inspiratory resistance, were compared PRE and POST 5-weeks of training (2×30 breaths at 70% peak flow, 5 days a week). Training significantly reduced NRS dyspnoea scores during resistive loaded ventilation, both in the HFAO (p = 0.003) and SHAM-RMT (p = 0.005) groups. Maximum inspiratory static pressure (cm H2O) was significantly increased by HFAO training (vs. PRE; p<0.001). Maximum inspiratory dynamic pressure was increased by training in both the HFAO (vs. PRE; p<0.001) and SHAM-RMT (vs. PRE; p = 0.021) groups. Peak inspiratory flow rate (L.s−1) achieved during the maximum inspiratory dynamic pressure manoeuvre increased significantly POST (vs. PRE; p = 0.001) in the HFAO group only. HFAO reduced inspiratory resistive loading–induced dyspnoea and augments static and dynamic maximal respiratory manoeuvre performance in excess of flow-resistive IMT (SHAM-RMT) in healthy individuals without the respiratory discomfort associated with RMT. PMID:24651392

  3. A MEMS-based high frequency x-ray chopper.

    PubMed

    Siria, A; Dhez, O; Schwartz, W; Torricelli, G; Comin, F; Chevrier, J

    2009-04-29

    Time-resolved x-ray experiments require intensity modulation at high frequencies (advanced rotating choppers have nowadays reached the kHz range). We here demonstrate that a silicon microlever oscillating at 13 kHz with nanometric amplitude can be used as a high frequency x-ray chopper. We claim that using micro-and nanoelectromechanical systems (MEMS and NEMS), it will be possible to achieve higher frequencies in excess of hundreds of megahertz. Working at such a frequency can open a wealth of possibilities in chemistry, biology and physics time-resolved experiments.

  4. Frequency stability degradation of an oscillator slaved to a periodically interrogated atomic resonator.

    PubMed

    Santarelli, G; Audoin, C; Makdissi, A; Laurent, P; Dick, G J; Clairon, A

    1998-01-01

    Atomic frequency standards using trapped ions or cold atoms work intrinsically in a pulsed mode. Theoretically and experimentally, this mode of operation has been shown to lead to a degradation of the frequency stability due to the frequency noise of the interrogation oscillator. In this paper a physical analysis of this effect has been made by evaluating the response of a two-level atom to the interrogation oscillator phase noise in Ramsey and multi-Rabi interrogation schemes using a standard quantum mechanical approach. This response is then used to calculate the degradation of the frequency stability of a pulsed atomic frequency standard such as an atomic fountain or an ion trap standard. Comparison is made to an experimental evaluation of this effect in the LPTF Cs fountain frequency standard, showing excellent agreement.

  5. Humidification during high-frequency oscillation ventilation is affected by ventilator circuit and ventilatory setting.

    PubMed

    Chikata, Yusuke; Imanaka, Hideaki; Onishi, Yoshiaki; Ueta, Masahiko; Nishimura, Masaji

    2009-08-01

    High-frequency oscillation ventilation (HFOV) is an accepted ventilatory mode for acute respiratory failure in neonates. As conventional mechanical ventilation, inspiratory gas humidification is essential. However, humidification during HFOV has not been clarified. In this bench study, we evaluated humidification during HFOV in the open circumstance of ICU. Our hypothesis is that humidification during HFOV is affected by circuit design and ventilatory settings. We connected a ventilator with HFOV mode to a neonatal lung model that was placed in an infant incubator set at 37 degrees C. We set a heated humidifier (Fisher & Paykel) to obtain 37 degrees C at the chamber outlet and 40 degrees C at the distal temperature probe. We measured absolute humidity and temperature at the Y-piece using a rapid-response hygrometer. We evaluated two types of ventilator circuit: a circuit with inner heating wire and another with embedded heating element. In addition, we evaluated three lengths of the inspiratory limb, three stroke volumes, three frequencies, and three mean airway pressures. The circuit with embedded heating element provided significantly higher absolute humidity and temperature than one with inner heating wire. As an extended tube lacking a heating wire was shorter, absolute humidity and temperature became higher. In the circuit with inner heating wire, absolute humidity and temperature increased as stroke volume increased. Humidification during HFOV is affected by circuit design and ventilatory settings.

  6. KvN mechanics approach to the time-dependent frequency harmonic oscillator.

    PubMed

    Ramos-Prieto, Irán; Urzúa-Pineda, Alejandro R; Soto-Eguibar, Francisco; Moya-Cessa, Héctor M

    2018-05-30

    Using the Ermakov-Lewis invariants appearing in KvN mechanics, the time-dependent frequency harmonic oscillator is studied. The analysis builds upon the operational dynamical model, from which it is possible to infer quantum or classical dynamics; thus, the mathematical structure governing the evolution will be the same in both cases. The Liouville operator associated with the time-dependent frequency harmonic oscillator can be transformed using an Ermakov-Lewis invariant, which is also time dependent and commutes with itself at any time. Finally, because the solution of the Ermakov equation is involved in the evolution of the classical state vector, we explore some analytical and numerical solutions.

  7. On-clip high frequency reliability and failure test structures

    DOEpatents

    Snyder, Eric S.; Campbell, David V.

    1997-01-01

    Self-stressing test structures for realistic high frequency reliability characterizations. An on-chip high frequency oscillator, controlled by DC signals from off-chip, provides a range of high frequency pulses to test structures. The test structures provide information with regard to a variety of reliability failure mechanisms, including hot-carriers, electromigration, and oxide breakdown. The system is normally integrated at the wafer level to predict the failure mechanisms of the production integrated circuits on the same wafer.

  8. On-clip high frequency reliability and failure test structures

    DOEpatents

    Snyder, E.S.; Campbell, D.V.

    1997-04-29

    Self-stressing test structures for realistic high frequency reliability characterizations. An on-chip high frequency oscillator, controlled by DC signals from off-chip, provides a range of high frequency pulses to test structures. The test structures provide information with regard to a variety of reliability failure mechanisms, including hot-carriers, electromigration, and oxide breakdown. The system is normally integrated at the wafer level to predict the failure mechanisms of the production integrated circuits on the same wafer. 22 figs.

  9. High Frequency Chandler Wobble Excitation

    NASA Astrophysics Data System (ADS)

    Seitz, F.; Stuck, J.; Thomas, M.

    2003-04-01

    Variations of Earth rotation on sub-daily to secular timescales are caused by mass redistributions in the Earth system as a consequence of geophysical processes and gravitational influences. Forced oscillations of polar motion are superposed by free oscillations of the Earth, i.e. the Chandler wobble and the free core nutation. In order to study the interactions between externally induced polar motion and the Earth's free oscillations, a non-linear gyroscopic model has been developed. In most of the former investigations on polar motion, the Chandler wobble is introduced as a damped oscillation with predetermined frequency and amplitude. However, as the effect of rotational deformation is a backcoupling mechanism of polar motion on the Earth's rotational dynamics, both period and amplitude of the Chandler wobble are time-dependent when regarding additional excitations from, e.g., atmospheric or oceanic mass redistributions. The gyroscopic model is free of any explicit information concerning amplitude, phase, and period of free oscillations. The characteristics of the Earth's free oscillation is reproduced by the model from rheological and geometrical parameters and rotational deformation is taken into account. This enables to study the time variable Chandler oscillation when the gyro is forced with atmospheric and oceanic angular momentum from the global atmospheric ECHAM3-T21 general circulation model together with the ocean model for circulation and tides OMCT driven by ECHAM including surface pressure. Besides, mass redistributions in the Earth's body due to gravitational and loading deformations are regarded and external torques exerted by Moon and Sun are considered. The numerical results of the gyro are significantly related with the geodetically observed time series of polar motion published by the IERS. It is shown that the consistent excitation is capable to counteract the damping and thus to maintain the Chandler amplitude. Spectral analyses of the ECHAM

  10. High-frequency oscillations in epilepsy and surgical outcome. A meta-analysis

    PubMed Central

    Höller, Yvonne; Kutil, Raoul; Klaffenböck, Lukas; Thomschewski, Aljoscha; Höller, Peter M.; Bathke, Arne C.; Jacobs, Julia; Taylor, Alexandra C.; Nardone, Raffaele; Trinka, Eugen

    2015-01-01

    High frequency oscillations (HFOs) are estimated as a potential marker for epileptogenicity. Current research strives for valid evidence that these HFOs could aid the delineation of the to-be resected area in patients with refractory epilepsy and improve surgical outcomes. In the present meta-analysis, we evaluated the relation between resection of regions from which HFOs can be detected and outcome after epilepsy surgery. We conducted a systematic review of all studies that related the resection of HFO-generating areas to postsurgical outcome. We related the outcome (seizure freedom) to resection ratio, that is, the ratio between the number of channels on which HFOs were detected and, among these, the number of channels that were inside the resected area. We compared the resection ratio between seizure free and not seizure free patients. In total, 11 studies were included. In 10 studies, ripples (80–200 Hz) were analyzed, and in 7 studies, fast ripples (>200 Hz) were studied. We found comparable differences (dif) and largely overlapping confidence intervals (CI) in resection ratios between outcome groups for ripples (dif = 0.18; CI: 0.10–0.27) and fast ripples (dif = 0.17; CI: 0.01–0.33). Subgroup analysis showed that automated detection (dif = 0.22; CI: 0.03–0.41) was comparable to visual detection (dif = 0.17; CI: 0.08–0.27). Considering frequency of HFOs (dif = 0.24; CI: 0.09–0.38) was related more strongly to outcome than considering each electrode that was showing HFOs (dif = 0.15; CI = 0.03–0.27). The effect sizes found in the meta-analysis are small but significant. Automated detection and application of a detection threshold in order to detect channels with a frequent occurrence of HFOs is important to yield a marker that could be useful in presurgical evaluation. In order to compare studies with different methodological approaches, detailed and standardized reporting is warranted. PMID:26539097

  11. Dynamics of multi-frequency oscillator ensembles with resonant coupling

    NASA Astrophysics Data System (ADS)

    Lück, S.; Pikovsky, A.

    2011-07-01

    We study dynamics of populations of resonantly coupled oscillators having different frequencies. Starting from the coupled van der Pol equations we derive the Kuramoto-type phase model for the situation, where the natural frequencies of two interacting subpopulations are in relation 2:1. Depending on the parameter of coupling, ensembles can demonstrate fully synchronous clusters, partial synchrony (only one subpopulation synchronizes), or asynchrony in both subpopulations. Theoretical description of the dynamics based on the Watanabe-Strogatz approach is developed.

  12. Laser Raman spectroscopy of the effect of solvent on the low-frequency oscillations of organic molecules

    NASA Astrophysics Data System (ADS)

    Brandt, N. N.; Chikishev, A. Yu.; Dolgovskii, V. I.; Lebedenko, S. I.

    2007-09-01

    The effect of solvent on low-frequency oscillations is studied using an example of the 1,1,2,2-tetrachloroethane (TCE) and 1,1,2,2-tetrabromoethane (TBE) molecules, which exhibit torsional oscillations in the terahertz range. Dimethylsulfoxide (DMSO) and carbon tetrachloride (CTC) are used as solvents. It is demonstrated that a decrease in the concentration of the substance under study in the TBE/CTC, TCE/DMSO, and TCE/CTC mixtures leads to a frequency shift of the low-frequency oscillation. The shift is not observed in the TBE/DMSO mixture but a decrease in the TBE concentration causes significant broadening of the low-frequency line.

  13. Integrated optoelectronic oscillator.

    PubMed

    Tang, Jian; Hao, Tengfei; Li, Wei; Domenech, David; Baños, Rocio; Muñoz, Pascual; Zhu, Ninghua; Capmany, José; Li, Ming

    2018-04-30

    With the rapid development of the modern communication systems, radar and wireless services, microwave signal with high-frequency, high-spectral-purity and frequency tunability as well as microwave generator with light weight, compact size, power-efficient and low cost are increasingly demanded. Integrated microwave photonics (IMWP) is regarded as a prospective way to meet these demands by hybridizing the microwave circuits and the photonics circuits on chip. In this article, we propose and experimentally demonstrate an integrated optoelectronic oscillator (IOEO). All of the devices needed in the optoelectronic oscillation loop circuit are monolithically integrated on chip within size of 5×6cm 2 . By tuning the injection current to 44 mA, the output frequency of the proposed IOEO is located at 7.30 GHz with phase noise value of -91 dBc/Hz@1MHz. When the injection current is increased to 65 mA, the output frequency can be changed to 8.87 GHz with phase noise value of -92 dBc/Hz@1MHz. Both of the oscillation frequency can be slightly tuned within 20 MHz around the center oscillation frequency by tuning the injection current. The method about improving the performance of IOEO is carefully discussed at the end of in this article.

  14. Internal Fluid Dynamics and Frequency Scaling of Sweeping Jet Fluidic Oscillators

    NASA Astrophysics Data System (ADS)

    Seo, Jung Hee; Salazar, Erik; Mittal, Rajat

    2017-11-01

    Sweeping jet fluidic oscillators (SJFOs) are devices that produce a spatially oscillating jet solely based on intrinsic flow instability mechanisms without any moving parts. Recently, SJFOs have emerged as effective actuators for flow control, but the internal fluid dynamics of the device that drives the oscillatory flow mechanism is not yet fully understood. In the current study, the internal fluid dynamics of the fluidic oscillator with feedback channels has been investigated by employing incompressible flow simulations. The study is focused on the oscillation mechanisms and scaling laws that underpin the jet oscillation. Based on the simulation results, simple phenomenological models that connect the jet deflection to the feedback flow are developed. Several geometric modifications are considered in order to explore the characteristic length scales and phase relationships associated with the jet oscillation and to assess the proposed phenomenological model. A scaling law for the jet oscillation frequency is proposed based on the detailed analysis. This research is supported by AFOSR Grant FA9550-14-1-0289 monitored by Dr. Douglas Smith.

  15. The forgotten role of central volume in low frequency oscillations of heart rate variability.

    PubMed

    Ferrario, Manuela; Moissl, Ulrich; Garzotto, Francesco; Cruz, Dinna N; Tetta, Ciro; Signorini, Maria G; Ronco, Claudio; Grassmann, Aileen; Cerutti, Sergio; Guzzetti, Stefano

    2015-01-01

    The hypothesis that central volume plays a key role in the source of low frequency (LF) oscillations of heart rate variability (HRV) was tested in a population of end stage renal disease patients undergoing conventional hemodialysis (HD) treatment, and thus subject to large fluid shifts and sympathetic activation. Fluid overload (FO) in 58 chronic HD patients was assessed by whole body bioimpedance measurements before the midweek HD session. Heart Rate Variability (HRV) was measured using 24-hour Holter electrocardiogram recordings starting before the same HD treatment. Time domain and frequency domain analyses were performed on HRV signals. Patients were retrospectively classified in three groups according to tertiles of FO normalized to the extracellular water (FO/ECW%). These groups were also compared after stratification by diabetes mellitus. Patients with the low to medium hydration status before the treatment (i.e. 1st and 2nd FO/ECW% tertiles) showed a significant increase in LF power during last 30 min of HD compared to dialysis begin, while no significant change in LF power was seen in the third group (i.e. those with high pre-treatment hydration values). In conclusion, several mechanisms can generate LF oscillations in the cardiovascular system, including baroreflex feedback loops and central oscillators. However, the current results emphasize the role played by the central volume in determining the power of LF oscillations.

  16. High-frequency neural activity predicts word parsing in ambiguous speech streams.

    PubMed

    Kösem, Anne; Basirat, Anahita; Azizi, Leila; van Wassenhove, Virginie

    2016-12-01

    During speech listening, the brain parses a continuous acoustic stream of information into computational units (e.g., syllables or words) necessary for speech comprehension. Recent neuroscientific hypotheses have proposed that neural oscillations contribute to speech parsing, but whether they do so on the basis of acoustic cues (bottom-up acoustic parsing) or as a function of available linguistic representations (top-down linguistic parsing) is unknown. In this magnetoencephalography study, we contrasted acoustic and linguistic parsing using bistable speech sequences. While listening to the speech sequences, participants were asked to maintain one of the two possible speech percepts through volitional control. We predicted that the tracking of speech dynamics by neural oscillations would not only follow the acoustic properties but also shift in time according to the participant's conscious speech percept. Our results show that the latency of high-frequency activity (specifically, beta and gamma bands) varied as a function of the perceptual report. In contrast, the phase of low-frequency oscillations was not strongly affected by top-down control. Whereas changes in low-frequency neural oscillations were compatible with the encoding of prelexical segmentation cues, high-frequency activity specifically informed on an individual's conscious speech percept. Copyright © 2016 the American Physiological Society.

  17. Transonic streamline of symmetric wing under the influence unilateral oscillations characterized by the spectrum of two frequencies

    NASA Astrophysics Data System (ADS)

    Zamuraev, V. P.; Kalinina, A. P.

    2017-10-01

    Forced high-frequency vibrations of the airfoil surface part with the amplitude almost equal to the sound velocity can change significantly the lift force of the symmetric profile streamlined at zero angle of attack. The oscillation consists of two harmonics. The ratio of harmonics frequencies values is equal to 2. The present work shows that the aerodynamic properties depend significantly on the specific energy contribution of each frequency.

  18. The effects of high-frequency oscillations in hippocampal electrical activities on the classification of epileptiform events using artificial neural networks

    NASA Astrophysics Data System (ADS)

    Chiu, Alan W. L.; Jahromi, Shokrollah S.; Khosravani, Houman; Carlen, Peter L.; Bardakjian, Berj L.

    2006-03-01

    The existence of hippocampal high-frequency electrical activities (greater than 100 Hz) during the progression of seizure episodes in both human and animal experimental models of epilepsy has been well documented (Bragin A, Engel J, Wilson C L, Fried I and Buzsáki G 1999 Hippocampus 9 137-42 Khosravani H, Pinnegar C R, Mitchell J R, Bardakjian B L, Federico P and Carlen P L 2005 Epilepsia 46 1-10). However, this information has not been studied between successive seizure episodes or utilized in the application of seizure classification. In this study, we examine the dynamical changes of an in vitro low Mg2+ rat hippocampal slice model of epilepsy at different frequency bands using wavelet transforms and artificial neural networks. By dividing the time-frequency spectrum of each seizure-like event (SLE) into frequency bins, we can analyze their burst-to-burst variations within individual SLEs as well as between successive SLE episodes. Wavelet energy and wavelet entropy are estimated for intracellular and extracellular electrical recordings using sufficiently high sampling rates (10 kHz). We demonstrate that the activities of high-frequency oscillations in the 100-400 Hz range increase as the slice approaches SLE onsets and in later episodes of SLEs. Utilizing the time-dependent relationship between different frequency bands, we can achieve frequency-dependent state classification. We demonstrate that activities in the frequency range 100-400 Hz are critical for the accurate classification of the different states of electrographic seizure-like episodes (containing interictal, preictal and ictal states) in brain slices undergoing recurrent spontaneous SLEs. While preictal activities can be classified with an average accuracy of 77.4 ± 6.7% utilizing the frequency spectrum in the range 0-400 Hz, we can also achieve a similar level of accuracy by using a nonlinear relationship between 100-400 Hz and <4 Hz frequency bands only.

  19. Frequency Regulation and Oscillation Damping Contributions of Variable-Speed Wind Generators in the U.S. Eastern Interconnection (EI)

    DOE PAGES

    Liu, Yong; Gracia, Jose R,; King, Jr, Thomas J.; ...

    2014-05-16

    The U.S. Eastern Interconnection (EI) is one of the largest electric power grids in the world and is expected to have difficulties in dealing with frequency regulation and oscillation damping issues caused by the increasing wind power. On the other side, variable-speed wind generators can actively engage in frequency regulation or oscillation damping with supplementary control loops. This paper creates a 5% wind power penetration simulation scenario based on the 16 000-bus EI system dynamic model and developed the user-defined wind electrical control model in PSS (R) E that incorporates additional frequency regulation and oscillation damping control loops. We evaluatedmore » the potential contributions of variable-speed wind generations to the EI system frequency regulation and oscillation damping, and simulation results demonstrate that current and future penetrations of wind power are promising in the EI system frequency regulation and oscillation damping.« less

  20. Emergence of amplitude and oscillation death in identical coupled oscillators.

    PubMed

    Zou, Wei; Senthilkumar, D V; Duan, Jinqiao; Kurths, Jürgen

    2014-09-01

    We deduce rigorous conditions for the onset of amplitude death (AD) and oscillation death (OD) in a system of identical coupled paradigmatic Stuart-Landau oscillators. A nonscalar coupling and high frequency are beneficial for the onset of AD. In strong contrast, scalar diffusive coupling and low intrinsic frequency are in favor of the emergence of OD. Our finding contributes to clearly distinguish intrinsic geneses for AD and OD, and further substantially corroborates that AD and OD are indeed two dynamically distinct oscillation quenching phenomena due to distinctly different mechanisms.

  1. A study on the high-order mode oscillation in a four-cavity intense relativistic klystron amplifier

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Liu, Ying-Hui; Niu, Xin-Jian; Wang, Hui

    The high-order mode oscillation is studied in designing a four-cavity intense relativistic klystron amplifier. The reason for the oscillation caused by high-order modes and a method to suppress these kinds of spurious modes are found through theoretical analyses and the study on the influence of major parameters of a high frequency structure (such as the oscillation frequency of cavities, the cavity Q value, the length of drift tube section, and the characteristic impedance). Based on much simulation, a four-cavity intense relativistic klystron amplifier with a superior performance has been designed, built, and tested. An output power of 2.22 GW corresponding tomore » 27.4% efficiency and 61 dB gain has been obtained. Moreover, the high-order mode oscillation is suppressed effectively, and an output power of 1.95 GW corresponding to 26% efficiency and 62 dB gain has been obtained in our laboratory.« less

  2. Input-dependent frequency modulation of cortical gamma oscillations shapes spatial synchronization and enables phase coding.

    PubMed

    Lowet, Eric; Roberts, Mark; Hadjipapas, Avgis; Peter, Alina; van der Eerden, Jan; De Weerd, Peter

    2015-02-01

    Fine-scale temporal organization of cortical activity in the gamma range (∼25-80Hz) may play a significant role in information processing, for example by neural grouping ('binding') and phase coding. Recent experimental studies have shown that the precise frequency of gamma oscillations varies with input drive (e.g. visual contrast) and that it can differ among nearby cortical locations. This has challenged theories assuming widespread gamma synchronization at a fixed common frequency. In the present study, we investigated which principles govern gamma synchronization in the presence of input-dependent frequency modulations and whether they are detrimental for meaningful input-dependent gamma-mediated temporal organization. To this aim, we constructed a biophysically realistic excitatory-inhibitory network able to express different oscillation frequencies at nearby spatial locations. Similarly to cortical networks, the model was topographically organized with spatially local connectivity and spatially-varying input drive. We analyzed gamma synchronization with respect to phase-locking, phase-relations and frequency differences, and quantified the stimulus-related information represented by gamma phase and frequency. By stepwise simplification of our models, we found that the gamma-mediated temporal organization could be reduced to basic synchronization principles of weakly coupled oscillators, where input drive determines the intrinsic (natural) frequency of oscillators. The gamma phase-locking, the precise phase relation and the emergent (measurable) frequencies were determined by two principal factors: the detuning (intrinsic frequency difference, i.e. local input difference) and the coupling strength. In addition to frequency coding, gamma phase contained complementary stimulus information. Crucially, the phase code reflected input differences, but not the absolute input level. This property of relative input-to-phase conversion, contrasting with latency codes

  3. Input-Dependent Frequency Modulation of Cortical Gamma Oscillations Shapes Spatial Synchronization and Enables Phase Coding

    PubMed Central

    Lowet, Eric; Roberts, Mark; Hadjipapas, Avgis; Peter, Alina; van der Eerden, Jan; De Weerd, Peter

    2015-01-01

    Fine-scale temporal organization of cortical activity in the gamma range (∼25–80Hz) may play a significant role in information processing, for example by neural grouping (‘binding’) and phase coding. Recent experimental studies have shown that the precise frequency of gamma oscillations varies with input drive (e.g. visual contrast) and that it can differ among nearby cortical locations. This has challenged theories assuming widespread gamma synchronization at a fixed common frequency. In the present study, we investigated which principles govern gamma synchronization in the presence of input-dependent frequency modulations and whether they are detrimental for meaningful input-dependent gamma-mediated temporal organization. To this aim, we constructed a biophysically realistic excitatory-inhibitory network able to express different oscillation frequencies at nearby spatial locations. Similarly to cortical networks, the model was topographically organized with spatially local connectivity and spatially-varying input drive. We analyzed gamma synchronization with respect to phase-locking, phase-relations and frequency differences, and quantified the stimulus-related information represented by gamma phase and frequency. By stepwise simplification of our models, we found that the gamma-mediated temporal organization could be reduced to basic synchronization principles of weakly coupled oscillators, where input drive determines the intrinsic (natural) frequency of oscillators. The gamma phase-locking, the precise phase relation and the emergent (measurable) frequencies were determined by two principal factors: the detuning (intrinsic frequency difference, i.e. local input difference) and the coupling strength. In addition to frequency coding, gamma phase contained complementary stimulus information. Crucially, the phase code reflected input differences, but not the absolute input level. This property of relative input-to-phase conversion, contrasting with latency

  4. High frequency oscillations in intracranial EEGs mark epileptogenicity rather than lesion type

    PubMed Central

    Jacobs, Julia; LeVan, Pierre; Châtillon, Claude-Édouard; Olivier, André; Dubeau, François; Gotman, Jean

    2013-01-01

    High frequency oscillations (HFOs) called ripples (80–250 Hz) and fast ripples (FR, 250–500 Hz) can be recorded from intracerebral EEG macroelectrodes in patients with intractable epilepsy. HFOs occur predominantly in the seizure onset zone (SOZ) but their relationship to the underlying pathology is unknown. It was the aim of this study to investigate whether HFOs are specific to the SOZ or result from pathologically changed tissue, whether or not it is epileptogenic. Patients with different lesion types, namely mesial temporal atrophy (MTA), focal cortical dysplasia (FCD) and nodular heterotopias (NH) were investigated. Intracranial EEG was recorded from depth macroelectrodes with a sampling rate of 2000 Hz. Ripples (80–250 Hz) and Fast Ripples (250–500 Hz) were visually marked in 12 patients: five with MTA, four with FCD and three with NH. Rates of events were statistically compared in channels in four areas: lesional SOZ, non-lesional SOZ, lesional non-SOZ and non-lesional non-SOZ. HFO rates were clearly more linked to the SOZ than to the lesion. They were highest in areas in which lesion and SOZ overlap, but in patients with a SOZ outside the lesion, such as in NHs, HFO rates were clearly higher in the non-lesional SOZ than in the inactive lesions. No specific HFO pattern could be identified for the different lesion types. The findings suggest that HFOs represent a marker for SOZ areas independent of the underlying pathology and that pathologic tissue changes alone do not lead to high rates of HFOs. PMID:19297507

  5. Nanoconstriction spin-Hall oscillator with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Divinskiy, B.; Demidov, V. E.; Kozhanov, A.; Rinkevich, A. B.; Demokritov, S. O.; Urazhdin, S.

    2017-07-01

    We experimentally study spin-Hall nano-oscillators based on [Co/Ni] multilayers with perpendicular magnetic anisotropy. We show that these devices exhibit single-frequency auto-oscillations at current densities comparable to those for in-plane magnetized oscillators. The demonstrated oscillators exhibit large magnetization precession amplitudes, and their oscillation frequency is highly tunable by the electric current. These features make them promising for applications in high-speed integrated microwave circuits.

  6. High-frequency filtering of strong-motion records

    USGS Publications Warehouse

    Douglas, J.; Boore, D.M.

    2011-01-01

    The influence of noise in strong-motion records is most problematic at low and high frequencies where the signal to noise ratio is commonly low compared to that in the mid-spectrum. The impact of low-frequency noise (5 Hz) on computed pseudo-absolute response spectral accelerations (PSAs). In contrast to the case of low-frequency noise our analysis shows that filtering to remove high-frequency noise is only necessary in certain situations and that PSAs can often be used up to 100 Hz even if much lower high-cut corner frequencies are required to remove the noise. This apparent contradiction can be explained by the fact that PSAs are often controlled by ground accelerations associated with much lower frequencies than the natural frequency of the oscillator because path and site attenuation (often modelled by Q and κ, respectively) have removed the highest frequencies. We demonstrate that if high-cut filters are to be used, then their corner frequencies should be selected on an individual basis, as has been done in a few recent studies.

  7. Frequency of gamma oscillations in humans is modulated by velocity of visual motion

    PubMed Central

    Butorina, Anna V.; Sysoeva, Olga V.; Prokofyev, Andrey O.; Nikolaeva, Anastasia Yu.; Stroganova, Tatiana A.

    2015-01-01

    Gamma oscillations are generated in networks of inhibitory fast-spiking (FS) parvalbumin-positive (PV) interneurons and pyramidal cells. In animals, gamma frequency is modulated by the velocity of visual motion; the effect of velocity has not been evaluated in humans. In this work, we have studied velocity-related modulations of gamma frequency in children using MEG/EEG. We also investigated whether such modulations predict the prominence of the “spatial suppression” effect (Tadin D, Lappin JS, Gilroy LA, Blake R. Nature 424: 312-315, 2003) that is thought to depend on cortical center-surround inhibitory mechanisms. MEG/EEG was recorded in 27 normal boys aged 8–15 yr while they watched high-contrast black-and-white annular gratings drifting with velocities of 1.2, 3.6, and 6.0°/s and performed a simple detection task. The spatial suppression effect was assessed in a separate psychophysical experiment. MEG gamma oscillation frequency increased while power decreased with increasing velocity of visual motion. In EEG, the effects were less reliable. The frequencies of the velocity-specific gamma peaks were 64.9, 74.8, and 87.1 Hz for the slow, medium, and fast motions, respectively. The frequency of the gamma response elicited during slow and medium velocity of visual motion decreased with subject age, whereas the range of gamma frequency modulation by velocity increased with age. The frequency modulation range predicted spatial suppression even after controlling for the effect of age. We suggest that the modulation of the MEG gamma frequency by velocity of visual motion reflects excitability of cortical inhibitory circuits and can be used to investigate their normal and pathological development in the human brain. PMID:25925324

  8. Frequency comb generation in a continuously pumped optical parametric oscillator

    NASA Astrophysics Data System (ADS)

    Mosca, S.; Parisi, M.; Ricciardi, I.; Leo, F.; Hansson, T.; Erkintalo, M.; Maddaloni, P.; De Natale, P.; Wabnitz, S.; De Rosa, M.

    2018-02-01

    We demonstrate optical frequency comb generation in a continuously pumped optical parametric oscillator, in the parametric region around half of the pump frequency. We also model the dynamics of such quadratic combs using a single time-domain mean-field equation, and obtain simulation results that are in good agreement with experimentally observed spectra. Moreover, we numerically investigate the coherence properties of simulated combs, showing the existence of correlated and phase-locked combs. Our work could pave the way for a new class of frequency comb sources, which may enable straightforward access to new spectral regions and stimulate novel applications of frequency combs.

  9. Acetylcholine modulates gamma frequency oscillations in the hippocampus by activation of muscarinic M1 receptors.

    PubMed

    Betterton, Ruth T; Broad, Lisa M; Tsaneva-Atanasova, Krasimira; Mellor, Jack R

    2017-06-01

    Modulation of gamma oscillations is important for the processing of information and the disruption of gamma oscillations is a prominent feature of schizophrenia and Alzheimer's disease. Gamma oscillations are generated by the interaction of excitatory and inhibitory neurons where their precise frequency and amplitude are controlled by the balance of excitation and inhibition. Acetylcholine enhances the intrinsic excitability of pyramidal neurons and suppresses both excitatory and inhibitory synaptic transmission, but the net modulatory effect on gamma oscillations is not known. Here, we find that the power, but not frequency, of optogenetically induced gamma oscillations in the CA3 region of mouse hippocampal slices is enhanced by low concentrations of the broad-spectrum cholinergic agonist carbachol but reduced at higher concentrations. This bidirectional modulation of gamma oscillations is replicated within a mathematical model by neuronal depolarisation, but not by reducing synaptic conductances, mimicking the effects of muscarinic M1 receptor activation. The predicted role for M1 receptors was supported experimentally; bidirectional modulation of gamma oscillations by acetylcholine was replicated by a selective M1 receptor agonist and prevented by genetic deletion of M1 receptors. These results reveal that acetylcholine release in CA3 of the hippocampus modulates gamma oscillation power but not frequency in a bidirectional and dose-dependent manner by acting primarily through muscarinic M1 receptors. © 2017 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

  10. Phase and frequency structure of superradiance pulses generated by relativistic Ka-band backward-wave oscillator

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Rostov, V. V.; Romanchenko, I. V.; Elchaninov, A. A.

    2016-08-15

    Phase and frequency stability of electromagnetic oscillations in sub-gigawatt superradiance (SR) pulses generated by an extensive slow-wave structure of a relativistic Ka-band backward-wave oscillator were experimentally investigated. Data on the frequency tuning and radiation phase stability of SR pulses with a variation of the energy and current of electron beam were obtained.

  11. Nature's Autonomous Oscillators

    NASA Technical Reports Server (NTRS)

    Mayr, H. G.; Yee, J.-H.; Mayr, M.; Schnetzler, R.

    2012-01-01

    Nonlinearity is required to produce autonomous oscillations without external time dependent source, and an example is the pendulum clock. The escapement mechanism of the clock imparts an impulse for each swing direction, which keeps the pendulum oscillating at the resonance frequency. Among nature's observed autonomous oscillators, examples are the quasi-biennial oscillation and bimonthly oscillation of the Earth atmosphere, and the 22-year solar oscillation. The oscillations have been simulated in numerical models without external time dependent source, and in Section 2 we summarize the results. Specifically, we shall discuss the nonlinearities that are involved in generating the oscillations, and the processes that produce the periodicities. In biology, insects have flight muscles, which function autonomously with wing frequencies that far exceed the animals' neural capacity; Stretch-activation of muscle contraction is the mechanism that produces the high frequency oscillation of insect flight, discussed in Section 3. The same mechanism is also invoked to explain the functioning of the cardiac muscle. In Section 4, we present a tutorial review of the cardio-vascular system, heart anatomy, and muscle cell physiology, leading up to Starling's Law of the Heart, which supports our notion that the human heart is also a nonlinear oscillator. In Section 5, we offer a broad perspective of the tenuous links between the fluid dynamical oscillators and the human heart physiology.

  12. Ultrastable Cryogenic Microwave Oscillators

    NASA Astrophysics Data System (ADS)

    Mann, Anthony G.

    Ultrastable cryogenic microwave oscillators are secondary frequency standards in the microwave domain. The best of these oscillators have demonstrated a short term frequency stability in the range 10-14 to a few times 10-16. The main application for these oscillators is as flywheel oscillators for the next generation of passive atomic frequency standards, and as local oscillators in space telemetry ground stations to clean up the transmitter close in phase noise. Fractional frequency stabilities of passive atomic frequency standards are now approaching 3 x10^-14 /τ where τ is the measurement time, limited only by the number of atoms that are being interrogated. This requires an interrogation oscillator whose short-term stability is of the order of 10-14 or better, which cannot be provided by present-day quartz technology. Ultrastable cryogenic microwave oscillators are based on resonators which have very high electrical Q-factors. The resolution of the resonator's linewidth is typically limited by electronics noise to about 1ppm and hence Q-factors in excess of 108 are required. As these are only attained in superconducting cavities or sapphire resonators at low temperatures, use of liquid helium cooling is mandatory, which has so far restricted these oscillators to the research or metrology laboratory. Recently, there has been an effort to dispense with the need for liquid helium and make compact flywheel oscillators for the new generation of primary frequency standards. Work is under way to achieve this goal in space-borne and mobile liquid-nitrogen-cooled systems. The best cryogenic oscillators developed to date are the ``whispering gallery'' (WG) mode sapphire resonator-oscillators of NASA's Jet Propulsion Laboratory (JPL) and the University of Western Australia (UWA), as well as Stanford University's superconducting cavity stabilized oscillator (SCSO). All of these oscillators have demonstrated frequency

  13. RF Frequency Oscillations in the Early Stages of Vacuum Arc Collapse

    NASA Technical Reports Server (NTRS)

    Griffin, Steven T.; Thio, Y. C. Francis

    2003-01-01

    RF frequency oscillations may be produced in a typical capacitive charging / discharging pulsed power system. These oscillations may be benign, parasitic, destructive or crucial to energy deposition. In some applications, proper damping of oscillations may be critical to proper plasma formation. Because the energy deposited into the plasma is a function of plasma and circuit conditions, the entire plasma / circuit system needs to be considered as a unit To accomplish this, the initiation of plasma is modeled as a time-varying, non-linear element in a circuit analysis model. The predicted spectra are compared to empirical power density spectra including those obtained from vacuum arcs.

  14. Seizure-induced alterations in fast-spiking basket cell GABA currents modulate frequency and coherence of gamma oscillation in network simulations

    NASA Astrophysics Data System (ADS)

    Proddutur, Archana; Yu, Jiandong; Elgammal, Fatima S.; Santhakumar, Vijayalakshmi

    2013-12-01

    Gamma frequency oscillations have been proposed to contribute to memory formation and retrieval. Fast-spiking basket cells (FS-BCs) are known to underlie development of gamma oscillations. Fast, high amplitude GABA synapses and gap junctions have been suggested to contribute to gamma oscillations in FS-BC networks. Recently, we identified that, apart from GABAergic synapses, FS-BCs in the hippocampal dentate gyrus have GABAergic currents mediated by extrasynaptic receptors. Our experimental studies demonstrated two specific changes in FS-BC GABA currents following experimental seizures [Yu et al., J. Neurophysiol. 109, 1746 (2013)]: increase in the magnitude of extrasynaptic (tonic) GABA currents and a depolarizing shift in GABA reversal potential (EGABA). Here, we use homogeneous networks of a biophysically based model of FS-BCs to examine how the presence of extrasynaptic GABA conductance (gGABA-extra) and experimentally identified, seizure-induced changes in gGABA-extra and EGABA influence network activity. Networks of FS-BCs interconnected by fast GABAergic synapses developed synchronous firing in the dentate gamma frequency range (40-100 Hz). Systematic investigation revealed that the biologically realistic range of 30 to 40 connections between FS-BCs resulted in greater coherence in the gamma frequency range when networks were activated by Poisson-distributed dendritic synaptic inputs rather than by homogeneous somatic current injections, which were balanced for FS-BC firing frequency in unconnected networks. Distance-dependent conduction delay enhanced coherence in networks with 30-40 FS-BC interconnections while inclusion of gap junctional conductance had a modest effect on coherence. In networks activated by somatic current injections resulting in heterogeneous FS-BC firing, increasing gGABA-extra reduced the frequency and coherence of FS-BC firing when EGABA was shunting (-74 mV), but failed to alter average FS-BC frequency when EGABA was depolarizing

  15. Metastability and Inter-Band Frequency Modulation in Networks of Oscillating Spiking Neuron Populations

    PubMed Central

    Bhowmik, David; Shanahan, Murray

    2013-01-01

    Groups of neurons firing synchronously are hypothesized to underlie many cognitive functions such as attention, associative learning, memory, and sensory selection. Recent theories suggest that transient periods of synchronization and desynchronization provide a mechanism for dynamically integrating and forming coalitions of functionally related neural areas, and that at these times conditions are optimal for information transfer. Oscillating neural populations display a great amount of spectral complexity, with several rhythms temporally coexisting in different structures and interacting with each other. This paper explores inter-band frequency modulation between neural oscillators using models of quadratic integrate-and-fire neurons and Hodgkin-Huxley neurons. We vary the structural connectivity in a network of neural oscillators, assess the spectral complexity, and correlate the inter-band frequency modulation. We contrast this correlation against measures of metastable coalition entropy and synchrony. Our results show that oscillations in different neural populations modulate each other so as to change frequency, and that the interaction of these fluctuating frequencies in the network as a whole is able to drive different neural populations towards episodes of synchrony. Further to this, we locate an area in the connectivity space in which the system directs itself in this way so as to explore a large repertoire of synchronous coalitions. We suggest that such dynamics facilitate versatile exploration, integration, and communication between functionally related neural areas, and thereby supports sophisticated cognitive processing in the brain. PMID:23614040

  16. High-frequency autonomic modulation: a new model for analysis of autonomic cardiac control.

    PubMed

    Champéroux, Pascal; Fesler, Pierre; Judé, Sebastien; Richard, Serge; Le Guennec, Jean-Yves; Thireau, Jérôme

    2018-05-03

    Increase in high-frequency beat-to-beat heart rate oscillations by torsadogenic hERG blockers appears to be associated with signs of parasympathetic and sympathetic co-activation which cannot be assessed directly using classic methods of heart rate variability analysis. The present work aimed to find a translational model that would allow this particular state of the autonomic control of heart rate to be assessed. High-frequency heart rate and heart period oscillations were analysed within discrete 10 s intervals in a cohort of 200 healthy human subjects. Results were compared to data collected in non-human primates and beagle dogs during pharmacological challenges and torsadogenic hERG blockers exposure, in 127 genotyped LQT1 patients on/off β-blocker treatment and in subgroups of smoking and non-smoking subjects. Three states of autonomic modulation, S1 (parasympathetic predominance) to S3 (reciprocal parasympathetic withdrawal/sympathetic activation), were differentiated to build a new model of heart rate variability referred to as high-frequency autonomic modulation. The S2 state corresponded to a specific state during which both parasympathetic and sympathetic systems were coexisting or co-activated. S2 oscillations were proportionally increased by torsadogenic hERG-blocking drugs, whereas smoking caused an increase in S3 oscillations. The combined analysis of the magnitude of high-frequency heart rate and high-frequency heart period oscillations allows a refined assessment of heart rate autonomic modulation applicable to long-term ECG recordings and offers new approaches to assessment of the risk of sudden death both in terms of underlying mechanisms and sensitivity. © 2018 The Authors. British Journal of Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.

  17. Single frequency 1083nm ytterbium doped fiber master oscillator power amplifier laser.

    PubMed

    Huang, Shenghong; Qin, Guanshi; Shirakawa, Akira; Musha, Mitsuru; Ueda, Ken-Ichi

    2005-09-05

    Single frequency 1083nm ytterbium fiber master oscillator power amplifier system was demonstrated. The oscillator was a linear fiber cavity with loop mirror filter and polarization controller. The loop mirror with unpumped ytterbium fiber as a narrow bandwidth filter discriminated and selected laser longitudinal modes efficiently. Spatial hole burning effect was restrained by adjusting polarization controller appropriately in the linear cavity. The amplifier was 5 m ytterbium doped fiber pumped by 976nm pigtail coupled laser diode. The linewidth of the single frequency laser was about 2 KHz. Output power up to 177 mW was produced under the launched pump power of 332 mW.

  18. Measurement of the Bs0-Bs0 oscillation frequency.

    PubMed

    Abulencia, A; Acosta, D; Adelman, J; Affolder, T; Akimoto, T; Albrow, M G; Ambrose, D; Amerio, S; Amidei, D; Anastassov, A; Anikeev, K; Annovi, A; Antos, J; Aoki, M; Apollinari, G; Arguin, J-F; Arisawa, T; Artikov, A; Ashmanskas, W; Attal, A; Azfar, F; Azzi-Bacchetta, P; Azzurri, P; Bacchetta, N; Bachacou, H; Badgett, W; Barbaro-Galtieri, A; Barnes, V E; Barnett, B A; Baroiant, S; Bartsch, V; Bauer, G; Bedeschi, F; Behari, S; Belforte, S; Bellettini, G; Bellinger, J; Belloni, A; Ben Haim, E; Benjamin, D; Beretvas, A; Beringer, J; Berry, T; Bhatti, A; Binkley, M; Bisello, D; Blair, R E; Blocker, C; Blumenfeld, B; Bocci, A; Bodek, A; Boisvert, V; Bolla, G; Bolshov, A; Bortoletto, D; Boudreau, J; Boveia, A; Brau, B; Bromberg, C; Brubaker, E; Budagov, J; Budd, H S; Budd, S; Burkett, K; Busetto, G; Bussey, P; Byrum, K L; Cabrera, S; Campanelli, M; Campbell, M; Canelli, F; Canepa, A; Carlsmith, D; Carosi, R; Carron, S; Casal, B; Casarsa, M; Castro, A; Catastini, P; Cauz, D; Cavalli-Sforza, M; Cerri, A; Cerrito, L; Chang, S H; Chapman, J; Chen, Y C; Chertok, M; Chiarelli, G; Chlachidze, G; Chlebana, F; Cho, I; Cho, K; Chokheli, D; Chou, J P; Chu, P H; Chuang, S H; Chung, K; Chung, W H; Chung, Y S; Ciljak, M; Ciobanu, C I; Ciocci, M A; Clark, A; Clark, D; Coca, M; Compostella, G; Convery, M E; Conway, J; Cooper, B; Copic, K; Cordelli, M; Cortiana, G; Crescioli, F; Cruz, A; Cuenca Almenar, C; Cuevas, J; Culbertson, R; Cyr, D; DaRonco, S; D'Auria, S; D'Onofrio, M; Dagenhart, D; de Barbaro, P; De Cecco, S; Deisher, A; De Lentdecker, G; Dell'Orso, M; Delli Paoli, F; Demers, S; Demortier, L; Deng, J; Deninno, M; De Pedis, D; Derwent, P F; Di Giovanni, G P; Di Ruzza, B; Dionisi, C; Dittmann, J R; DiTuro, P; Dörr, C; Donati, S; Donega, M; Dong, P; Donini, J; Dorigo, T; Dube, S; Ebina, K; Efron, J; Ehlers, J; Erbacher, R; Errede, D; Errede, S; Eusebi, R; Fang, H C; Farrington, S; Fedorko, I; Fedorko, W T; Feild, R G; Feindt, M; Fernandez, J P; Field, R; Flanagan, G; Flores-Castillo, L R; Foland, A; Forrester, S; Foster, G W; Franklin, M; Freeman, J C; Frisch, H J; Furic, I; Gallinaro, M; Galyardt, J; Garcia, J E; Garcia Sciveres, M; Garfinkel, A F; Gay, C; Gerberich, H; Gerdes, D; Giagu, S; Giannetti, P; Gibson, A; Gibson, K; Ginsburg, C; Giokaris, N; Giolo, K; Giordani, M; Giromini, P; Giunta, M; Giurgiu, G; Glagolev, V; Glenzinski, D; Gold, M; Goldschmidt, N; Goldstein, J; Gomez, G; Gomez-Ceballos, G; Goncharov, M; González, O; Gorelov, I; Goshaw, A T; Gotra, Y; Goulianos, K; Gresele, A; Griffiths, M; Grinstein, S; Grosso-Pilcher, C; Group, R C; Grundler, U; Guimaraes da Costa, J; Gunay-Unalan, Z; Haber, C; Hahn, S R; Hahn, K; Halkiadakis, E; Hamilton, A; Han, B-Y; Han, J Y; Handler, R; Happacher, F; Hara, K; Hare, M; Harper, S; Harr, R F; Harris, R M; Hatakeyama, K; Hauser, J; Hays, C; Heijboer, A; Heinemann, B; Heinrich, J; Herndon, M; Hidas, D; Hill, C S; Hirschbuehl, D; Hocker, A; Holloway, A; Hou, S; Houlden, M; Hsu, S-C; Huffman, B T; Hughes, R E; Huston, J; Incandela, J; Introzzi, G; Iori, M; Ishizawa, Y; Ivanov, A; Iyutin, B; James, E; Jang, D; Jayatilaka, B; Jeans, D; Jensen, H; Jeon, E J; Jindariani, S; Jones, M; Joo, K K; Jun, S Y; Junk, T R; Kamon, T; Kang, J; Karchin, P E; Kato, Y; Kemp, Y; Kephart, R; Kerzel, U; Khotilovich, V; Kilminster, B; Kim, D H; Kim, H S; Kim, J E; Kim, M J; Kim, S B; Kim, S H; Kim, Y K; Kirsch, L; Klimenko, S; Klute, M; Knuteson, B; Ko, B R; Kobayashi, H; Kondo, K; Kong, D J; Konigsberg, J; Korytov, A; Kotwal, A V; Kovalev, A; Kraan, A; Kraus, J; Kravchenko, I; Kreps, M; Kroll, J; Krumnack, N; Kruse, M; Krutelyov, V; Kuhlmann, S E; Kusakabe, Y; Kwang, S; Laasanen, A T; Lai, S; Lami, S; Lammel, S; Lancaster, M; Lander, R L; Lannon, K; Lath, A; Latino, G; Lazzizzera, I; LeCompte, T; Lee, J; Lee, J; Lee, Y J; Lee, S W; Lefèvre, R; Leonardo, N; Leone, S; Levy, S; Lewis, J D; Lin, C; Lin, C S; Lindgren, M; Lipeles, E; Liss, T M; Lister, A; Litvintsev, D O; Liu, T; Lockyer, N S; Loginov, A; Loreti, M; Loverre, P; Lu, R-S; Lucchesi, D; Lujan, P; Lukens, P; Lungu, G; Lyons, L; Lys, J; Lysak, R; Lytken, E; Mack, P; MacQueen, D; Madrak, R; Maeshima, K; Maki, T; Maksimovic, P; Malde, S; Manca, G; Margaroli, F; Marginean, R; Marino, C; Martin, A; Martin, V; Martínez, M; Maruyama, T; Mastrandrea, P; Matsunaga, H; Mattson, M E; Mazini, R; Mazzanti, P; McFarland, K S; McIntyre, P; McNulty, R; Mehta, A; Menzemer, S; Menzione, A; Merkel, P; Mesropian, C; Messina, A; von der Mey, M; Miao, T; Miladinovic, N; Miles, J; Miller, R; Miller, J S; Mills, C; Milnik, M; Miquel, R; Mitra, A; Mitselmakher, G; Miyamoto, A; Moggi, N; Mohr, B; Moore, R; Morello, M; Movilla Fernandez, P; Mülmenstädt, J; Mukherjee, A; Muller, Th; Mumford, R; Murat, P; Nachtman, J; Naganoma, J; Nahn, S; Nakano, I; Napier, A; Naumov, D; Necula, V; Neu, C; Neubauer, M S; Nielsen, J; Nigmanov, T; Nodulman, L; Norniella, O; Nurse, E; Ogawa, T; Oh, S H; Oh, Y D; Okusawa, T; Oldeman, R; Orava, R; Osterberg, K; Pagliarone, C; Palencia, E; Paoletti, R; Papadimitriou, V; Paramonov, A A; Parks, B; Pashapour, S; Patrick, J; Pauletta, G; Paulini, M; Paus, C; Pellett, D E; Penzo, A; Phillips, T J; Piacentino, G; Piedra, J; Pinera, L; Pitts, K; Plager, C; Pondrom, L; Portell, X; Poukhov, O; Pounder, N; Prakoshyn, F; Pronko, A; Proudfoot, J; Ptohos, F; Punzi, G; Pursley, J; Rademacker, J; Rahaman, A; Rakitin, A; Rappoccio, S; Ratnikov, F; Reisert, B; Rekovic, V; van Remortel, N; Renton, P; Rescigno, M; Richter, S; Rimondi, F; Ristori, L; Robertson, W J; Robson, A; Rodrigo, T; Rogers, E; Rolli, S; Roser, R; Rossi, M; Rossin, R; Rott, C; Ruiz, A; Russ, J; Rusu, V; Saarikko, H; Sabik, S; Safonov, A; Sakumoto, W K; Salamanna, G; Saltó, O; Saltzberg, D; Sanchez, C; Santi, L; Sarkar, S; Sartori, L; Sato, K; Savard, P; Savoy-Navarro, A; Scheidle, T; Schlabach, P; Schmidt, E E; Schmidt, M P; Schmitt, M; Schwarz, T; Scodellaro, L; Scott, A L; Scribano, A; Scuri, F; Sedov, A; Seidel, S; Seiya, Y; Semenov, A; Sexton-Kennedy, L; Sfiligoi, I; Shapiro, M D; Shears, T; Shepard, P F; Sherman, D; Shimojima, M; Shochet, M; Shon, Y; Shreyber, I; Sidoti, A; Sinervo, P; Sisakyan, A; Sjolin, J; Skiba, A; Slaughter, A J; Sliwa, K; Smith, J R; Snider, F D; Snihur, R; Soderberg, M; Soha, A; Somalwar, S; Sorin, V; Spalding, J; Spezziga, M; Spinella, F; Spreitzer, T; Squillacioti, P; Stanitzki, M; Staveris-Polykalas, A; St Denis, R; Stelzer, B; Stelzer-Chilton, O; Stentz, D; Strologas, J; Stuart, D; Suh, J S; Sukhanov, A; Sumorok, K; Sun, H; Suzuki, T; Taffard, A; Takashima, R; Takeuchi, Y; Takikawa, K; Tanaka, M; Tanaka, R; Tanimoto, N; Tecchio, M; Teng, P K; Terashi, K; Tether, S; Thom, J; Thompson, A S; Thomson, E; Tipton, P; Tiwari, V; Tkaczyk, S; Toback, D; Tokar, S; Tollefson, K; Tomura, T; Tonelli, D; Tönnesmann, M; Torre, S; Torretta, D; Tourneur, S; Trischuk, W; Tsuchiya, R; Tsuno, S; Turini, N; Ukegawa, F; Unverhau, T; Uozumi, S; Usynin, D; Vaiciulis, A; Vallecorsa, S; Varganov, A; Vataga, E; Velev, G; Veramendi, G; Veszpremi, V; Vidal, R; Vila, I; Vilar, R; Vine, T; Vollrath, I; Volobouev, I; Volpi, G; Würthwein, F; Wagner, P; Wagner, R G; Wagner, R L; Wagner, W; Wallny, R; Walter, T; Wan, Z; Wang, S M; Warburton, A; Waschke, S; Waters, D; Wester, W C; Whitehouse, B; Whiteson, D; Wicklund, A B; Wicklund, E; Williams, G; Williams, H H; Wilson, P; Winer, B L; Wittich, P; Wolbers, S; Wolfe, C; Wright, T; Wu, X; Wynne, S M; Yagil, A; Yamamoto, K; Yamaoka, J; Yamashita, T; Yang, C; Yang, U K; Yang, Y C; Yao, W M; Yeh, G P; Yoh, J; Yorita, K; Yoshida, T; Yu, G B; Yu, I; Yu, S S; Yun, J C; Zanello, L; Zanetti, A; Zaw, I; Zetti, F; Zhang, X; Zhou, J; Zucchelli, S

    2006-08-11

    We present the first precise measurement of the Bs0-Bs0 oscillation frequency Deltams. We use 1 fb-1 of data from pp collisions at sqrts=1.96 TeV collected with the CDF II detector at the Fermilab Tevatron. The sample contains signals of 3600 fully reconstructed hadronic Bs decays and 37,000 partially reconstructed semileptonic Bs decays. We measure the probability as a function of proper decay time that the Bs decays with the same, or opposite, flavor as the flavor at production, and we find a signal consistent with Bs0-Bs0 oscillations. The probability that random fluctuations could produce a comparable signal is 0.2%. Under the hypothesis that the signal is due to Bs0-Bs0 oscillations, we measure Deltams=17.31(-0.18)+0.33(stat)+/-0.07(syst) ps-1 and determine |Vtd/Vts|=0.208(-0.002)+0.001(expt)-0.006(+0.008)(theor).

  19. Wavelet based comparison of high frequency oscillations in the geodetic and fluid excitation functions of polar motion

    NASA Astrophysics Data System (ADS)

    Kosek, W.; Popinski, W.; Niedzielski, T.

    2011-10-01

    It has been already shown that short period oscillations in polar motion, with periods less than 100 days, are very chaotic and are responsible for increase in short-term prediction errors of pole coordinates data. The wavelet technique enables to compare the geodetic and fluid excitation functions in the high frequency band in many different ways, e.g. by looking at the semblance function. The waveletbased semblance filtering enables determination the common signal in both geodetic and fluid excitation time series. In this paper the considered fluid excitation functions consist of the atmospheric, oceanic and land hydrology excitation functions from ECMWF atmospheric data produced by IERS Associated Product Centre Deutsches GeoForschungsZentrum, Potsdam. The geodetic excitation functions have been computed from the combined IERS pole coordinates data.

  20. Detection of frequency-mode-shift during thermoacoustic combustion oscillations in a staged aircraft engine model combustor

    NASA Astrophysics Data System (ADS)

    Kobayashi, Hiroaki; Gotoda, Hiroshi; Tachibana, Shigeru; Yoshida, Seiji

    2017-12-01

    We conduct an experimental study using time series analysis based on symbolic dynamics to detect a precursor of frequency-mode-shift during thermoacoustic combustion oscillations in a staged aircraft engine model combustor. With increasing amount of the main fuel, a significant shift in the dominant frequency-mode occurs in noisy periodic dynamics, leading to a notable increase in oscillation amplitudes. The sustainment of noisy periodic dynamics during thermoacoustic combustion oscillations is clearly shown by the multiscale complexity-entropy causality plane in terms of statistical complexity. A modified version of the permutation entropy allows us to detect a precursor of the frequency-mode-shift before the amplification of pressure fluctuations.

  1. Multi-photon Rabi oscillations in high spin paramagnetic impurity

    NASA Astrophysics Data System (ADS)

    Bertaina, S.; Groll, N.; Chen, L.; Chiorescu, I.

    2011-10-01

    We report on multiple photon monochromatic quantum oscillations (Rabi oscillations) observed by pulsed EPR (Electron Paramagnetic Resonance) of Mn2+ (S = 5/2) impurities in MgO. We find that when the microwave magnetic field is similar or large than the anisotropy splitting, the Rabi oscillations have a spectrum made of many frequencies not predicted by the S = l/2 Rabi model. We show that these new frequencies come from multiple photon coherent manipulation of the multi-level spin impurity. We develop a model based on the crystal field theory and the rotating frame approximation, describing the observed phenomenon with a very good agreement.

  2. 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.

  3. Weld pool oscillation during pulsed GTA welding

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Aendenroomer, A.J.R.; Ouden, G. den

    1996-12-31

    This paper deals with weld pool oscillation during pulsed GTA welding and with the possibility to use this oscillation for in-process control of weld penetration. Welding experiments were carried out under different welding conditions. During welding the weld pool was triggered into oscillation by the normal welding pulses or by extra current pulses. The oscillation frequency was measured both during the pulse time and during the base time by analyzing the arc voltage variation using a Fast Fourier Transformation program. Optimal results are obtained when full penetration occurs during the pulse time and partial penetration during the base time. Undermore » these conditions elliptical overlapping spot welds are formed. In the case of full penetration the weld pool oscillates in a low frequency mode (membrane oscillation), whereas in the case of partial penetration the weld pool oscillates in a high frequency mode (surface oscillation). Deviation from the optimal welding conditions occurs when high frequency oscillation is observed during both pulse time and base time (underpenetration) or when low frequency oscillation is observed during both pulse time and base time (overpenetration). In line with these results a penetration sensing system with feedback control was designed, based on the criterion that optimal weld penetration is achieved when two peaks are observed in the frequency distribution. The feasibility of this sensing system for orbital tube welding was confirmed by the results of experiments carried out under various welding conditions.« less

  4. Radio Frequency Transistors Using Aligned Semiconducting Carbon Nanotubes with Current-Gain Cutoff Frequency and Maximum Oscillation Frequency Simultaneously Greater than 70 GHz.

    PubMed

    Cao, Yu; Brady, Gerald J; Gui, Hui; Rutherglen, Chris; Arnold, Michael S; Zhou, Chongwu

    2016-07-26

    In this paper, we report record radio frequency (RF) performance of carbon nanotube transistors based on combined use of a self-aligned T-shape gate structure, and well-aligned, high-semiconducting-purity, high-density polyfluorene-sorted semiconducting carbon nanotubes, which were deposited using dose-controlled, floating evaporative self-assembly method. These transistors show outstanding direct current (DC) performance with on-current density of 350 μA/μm, transconductance as high as 310 μS/μm, and superior current saturation with normalized output resistance greater than 100 kΩ·μm. These transistors create a record as carbon nanotube RF transistors that demonstrate both the current-gain cutoff frequency (ft) and the maximum oscillation frequency (fmax) greater than 70 GHz. Furthermore, these transistors exhibit good linearity performance with 1 dB gain compression point (P1dB) of 14 dBm and input third-order intercept point (IIP3) of 22 dBm. Our study advances state-of-the-art of carbon nanotube RF electronics, which have the potential to be made flexible and may find broad applications for signal amplification, wireless communication, and wearable/flexible electronics.

  5. High efficiency and output power from second- and third-harmonic millimeter-wave InP-TED oscillators at frequencies above 170 GHz

    NASA Astrophysics Data System (ADS)

    Rydberg, Anders

    1990-10-01

    InP TED (transferred electron device) oscillators have been experimentally investigated for frequencies between 170 and 279 GHz. It has been found that output powers of more than 7 and 0.2 mW are possible at 180 and 272 GHz using second- and third-harmonic mode operation, respectively. Conversion efficiencies of more than 13 percent and 0.3 percent between fundamental and second harmonic and fundamental and third harmonic, respectively, have been found. The conversion efficiencies are comparable to GaAs TEDs. The output powers, conversion efficiencies, and tuning ranges (more than 22 percent) are the largest reported for InP TEDs at these frequencies. The output power at third harmonic was sufficient for supplying a superconducting mixer with local oscillator power.

  6. Injection locked coupled opto-electronic oscillator for optical frequency comb generation

    NASA Astrophysics Data System (ADS)

    Williams, Charles; Mandridis, Dimitrios; Davila-Rodriguez, Josue; Delfyett, Peter J.

    2011-06-01

    A CW injection locked Coupled Opto-Electronic Oscillator (COEO) is presented with a 10.24 GHz spaced optical frequency comb output as well as a low noise RF output. A modified Pound-Drever-Hall scheme is employed to ensure long-term stability of the injection lock, feeding back into the cavity length to compensate for cavity resonance drifts relative to the injection seed frequency. Error signal comparison to an actively mode-locked injection locked laser is presented. High optical signal-to-noise ratio of ~35 dB is demonstrated with >20 comblines of useable bandwidth. The optical linewidth, in agreement with injection locking theory, reduces to that of the injection seed frequency, <5 kHz. Low amplitude and absolute phase noise are presented from the optical output of the laser system. The integrated pulse-to-pulse energy fluctuation was found to be reduced by up to a factor of two due to optical injection. Additional decreases were shown for varying injection powers.

  7. Coherent frequency division with a degenerate synchronously pumped optical parametric oscillator.

    PubMed

    Wan, Chenchen; Li, Peng; Ruehl, Axel; Hartl, Ingmar

    2018-03-01

    Synchronously pumped optical parametric oscillators (OPOs) are important tools for frequency comb (FC) generation in the mid-IR spectral range, where few suitable laser gain materials exist. For degenerate OPOs, self-phase-locking to the pump FC has been demonstrated. Here, we present a phase noise study of the carrier envelope offset frequency, revealing a -6  dB reduction compared to the pump FC over a wide Fourier frequency range. These results demonstrate that a degenerate OPO can be an ideal coherent frequency divider without any excess noise.

  8. High Resolution Switching Mode Inductance-to-Frequency Converter with Temperature Compensationti

    PubMed Central

    Matko, Vojko; Milanović, Miro

    2014-01-01

    This article proposes a novel method for the temperature-compensated inductance-to-frequency converter with a single quartz crystal oscillating in the switching oscillating circuit to achieve better temperature stability of the converter. The novelty of this method lies in the switching-mode converter, the use of additionally connected impedances in parallel to the shunt capacitances of the quartz crystal, and two inductances in series to the quartz crystal. This brings a considerable reduction of the temperature influence of AT-cut crystal frequency change in the temperature range between 10 and 40 °C. The oscillator switching method and the switching impedances connected to the quartz crystal do not only compensate for the crystal's natural temperature characteristics but also any other influences on the crystal such as ageing as well as from other oscillating circuit elements. In addition, the method also improves frequency sensitivity in inductance measurements. The experimental results show that through high temperature compensation improvement of the quartz crystal characteristics, this switching method theoretically enables a 2 pH resolution. It converts inductance to frequency in the range of 85–100 μH to 2–560 kHz. PMID:25325334

  9. 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

  10. Movement-related beta oscillations show high intra-individual reliability.

    PubMed

    Espenhahn, Svenja; de Berker, Archy O; van Wijk, Bernadette C M; Rossiter, Holly E; Ward, Nick S

    2017-02-15

    Oscillatory activity in the beta frequency range (15-30Hz) recorded from human sensorimotor cortex is of increasing interest as a putative biomarker of motor system function and dysfunction. Despite its increasing use in basic and clinical research, surprisingly little is known about the test-retest reliability of spectral power and peak frequency measures of beta oscillatory signals from sensorimotor cortex. Establishing that these beta measures are stable over time in healthy populations is a necessary precursor to their use in the clinic. Here, we used scalp electroencephalography (EEG) to evaluate intra-individual reliability of beta-band oscillations over six sessions, focusing on changes in beta activity during movement (Movement-Related Beta Desynchronization, MRBD) and after movement termination (Post-Movement Beta Rebound, PMBR). Subjects performed visually-cued unimanual wrist flexion and extension. We assessed Intraclass Correlation Coefficients (ICC) and between-session correlations for spectral power and peak frequency measures of movement-related and resting beta activity. Movement-related and resting beta power from both sensorimotor cortices was highly reliable across sessions. Resting beta power yielded highest reliability (average ICC=0.903), followed by MRBD (average ICC=0.886) and PMBR (average ICC=0.663). Notably, peak frequency measures yielded lower ICC values compared to the assessment of spectral power, particularly for movement-related beta activity (ICC=0.386-0.402). Our data highlight that power measures of movement-related beta oscillations are highly reliable, while corresponding peak frequency measures show greater intra-individual variability across sessions. Importantly, our finding that beta power estimates show high intra-individual reliability over time serves to validate the notion that these measures reflect meaningful individual differences that can be utilised in basic research and clinical studies. Copyright © 2016 The

  11. Recent Developments in the Analysis of Couple Oscillator Arrays

    NASA Technical Reports Server (NTRS)

    Pogorzelski, Ronald J.

    2000-01-01

    This presentation considers linear arrays of coupled oscillators. Our purpose in coupling oscillators together is to achieve high radiated power through the spatial power combining which results when the oscillators are injection locked to each other. York, et. al. have shown that, left to themselves, the ensemble of injection locked oscillators oscillate at the average of the tuning frequencies of all the oscillators. Coupling these arrays achieves high radiated power through coherent spatial power combining. The coupled oscillators are usually designed to produce constant aperture phase. Oscillators are injection locked to each other or to a master oscillator to produce coherent radiation. Oscillators do not necessarily oscillate at their tuning frequency.

  12. High power pumped MID-IR wavelength devices using nonlinear frequency mixing (NFM)

    NASA Technical Reports Server (NTRS)

    Sanders, Steven (Inventor); Lang, Robert J. (Inventor); Waarts, Robert G. (Inventor)

    2001-01-01

    Laser diode pumped mid-IR wavelength sources include at least one high power, near-IR wavelength, injection and/or sources wherein one or both of such sources may be tunable providing a pump wave output beam to a quasi-phase matched (QPM) nonlinear frequency mixing (NFM) device. The NFM device may be a difference frequency mixing (DFM) device or an optical parametric oscillation (OPO) device. Wavelength tuning of at least one of the sources advantageously provides the ability for optimizing pump or injection wavelengths to match the QPM properties of the NFM device enabling a broad range of mid-IR wavelength selectivity. Also, pump powers are gain enhanced by the addition of a rare earth amplifier or oscillator, or a Raman/Brillouin amplifier or oscillator between the high power source and the NFM device. Further, polarization conversion using Raman or Brillouin wavelength shifting is provided to optimize frequency conversion efficiency in the NFM device.

  13. The Effect of Doppler Frequency Shift, Frequency Offset of the Local Oscillators, and Phase Noise on the Performance of Coherent OFDM Receivers

    NASA Technical Reports Server (NTRS)

    Xiong, Fuqin; Andro, Monty

    2001-01-01

    This paper first shows that the Doppler frequency shift affects the frequencies of the RF carrier, subcarriers, envelope, and symbol timing by the same percentage in an Orthogonal Frequency Division Multiplexing (OFDM) signal or any other modulated signals. Then the SNR degradation of an OFDM system due to Doppler frequency shift, frequency offset of the local oscillators and phase noise is analyzed. Expressions are given and values for 4-, 16-, 64-, and 256-QAM OFDM systems are calculated and plotted. The calculations show that the Doppler shift of the D3 project is about 305 kHz, and the degradation due to it is about 0.01 to 0.04 dB, which is negligible. The degradation due to frequency offset and phase noise of local oscillators will be the main source of degradation. To keep the SNR degradation under 0.1 dB, the relative frequency offset due to local oscillators must be below 0.01 for the 16 QAM-OFDM. This translates to an offset of 1.55 MHz (0.01 x 155 MHz) or a stability of 77.5 ppm (0.01 x 155 MHz/20 GHz) for the DI project. To keep the SNR degradation under 0.1 dB, the relative linewidth (0) due to phase noise of the local oscillators must be below 0.0004 for the 16 QAM-OFDM. This translates to a linewidth of 0.062 MHz (0.0004 x 155 MHz) of the 20 GHz RIF carrier. For a degradation of 1 dB, beta = 0.04, and the linewidth can be relaxed to 6.2 MHz.

  14. Seizure-induced alterations in fast-spiking basket cell GABA currents modulate frequency and coherence of gamma oscillation in network simulations

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Proddutur, Archana; Yu, Jiandong; Elgammal, Fatima S.

    2013-12-15

    Gamma frequency oscillations have been proposed to contribute to memory formation and retrieval. Fast-spiking basket cells (FS-BCs) are known to underlie development of gamma oscillations. Fast, high amplitude GABA synapses and gap junctions have been suggested to contribute to gamma oscillations in FS-BC networks. Recently, we identified that, apart from GABAergic synapses, FS-BCs in the hippocampal dentate gyrus have GABAergic currents mediated by extrasynaptic receptors. Our experimental studies demonstrated two specific changes in FS-BC GABA currents following experimental seizures [Yu et al., J. Neurophysiol. 109, 1746 (2013)]: increase in the magnitude of extrasynaptic (tonic) GABA currents and a depolarizing shiftmore » in GABA reversal potential (E{sub GABA}). Here, we use homogeneous networks of a biophysically based model of FS-BCs to examine how the presence of extrasynaptic GABA conductance (g{sub GABA-extra}) and experimentally identified, seizure-induced changes in g{sub GABA-extra} and E{sub GABA} influence network activity. Networks of FS-BCs interconnected by fast GABAergic synapses developed synchronous firing in the dentate gamma frequency range (40–100 Hz). Systematic investigation revealed that the biologically realistic range of 30 to 40 connections between FS-BCs resulted in greater coherence in the gamma frequency range when networks were activated by Poisson-distributed dendritic synaptic inputs rather than by homogeneous somatic current injections, which were balanced for FS-BC firing frequency in unconnected networks. Distance-dependent conduction delay enhanced coherence in networks with 30–40 FS-BC interconnections while inclusion of gap junctional conductance had a modest effect on coherence. In networks activated by somatic current injections resulting in heterogeneous FS-BC firing, increasing g{sub GABA-extra} reduced the frequency and coherence of FS-BC firing when E{sub GABA} was shunting (−74 mV), but failed to alter

  15. Dawn- Dusk Auroral Oval Oscillations Associated with High- Speed Solar Wind

    NASA Technical Reports Server (NTRS)

    Liou, Kan; Sibeck, David G.

    2018-01-01

    We report evidence of global-scale auroral oval oscillations in the millihertz range, using global auroral images acquired from the Ultraviolet Imager on board the decommissioned Polar satellite and concurrent solar wind measurements. On the basis of two events (15 January 1999 and 6 January 2000) studied, it is found that (1) quasi-periodic auroral oval oscillations (approximately 3 megahertz) can occur when solar wind speeds are high at northward or southward interplanetary magnetic field turning, (2) the oscillation amplitudes range from a few to more than 10 degrees in latitudes, (3) the oscillation frequency is the same for each event irrespective of local time and without any azimuthal phase shift (i.e., propagation), (4) the auroral oscillations occur in phase within both the dawn and dusk sectors but 180 degrees out of phase between the dawn and dusk sectors, and (5) no micropulsations on the ground match the auroral oscillation periods. While solar wind conditions favor the growth of the Kelvin-Helmholtz (K-H) instability on the magnetopause as often suggested, the observed wave characteristics are not consistent with predictions for K-H waves. The in-phase and out-of-phase features found in the dawn-dusk auroral oval oscillations suggest that wiggling motions of the magnetotail associated with fast solar winds might be the direct cause of the global-scale millihertz auroral oval oscillations. Plain Language Summary: We utilize global auroral image data to infer the motion of the magnetosphere and show, for the first time, the entire magnetospheric tail can move east-west in harmony like a windsock flapping in wind. The characteristic period of the flapping motion may be a major source of global long-period ULF (Ultra Low Frequency) waves, adding an extra source of the global mode ULF waves.

  16. Computational Re-design of Synthetic Genetic Oscillators for Independent Amplitude and Frequency Modulation.

    PubMed

    Tomazou, Marios; Barahona, Mauricio; Polizzi, Karen M; Stan, Guy-Bart

    2018-04-25

    To perform well in biotechnology applications, synthetic genetic oscillators must be engineered to allow independent modulation of amplitude and period. This need is currently unmet. Here, we demonstrate computationally how two classic genetic oscillators, the dual-feedback oscillator and the repressilator, can be re-designed to provide independent control of amplitude and period and improve tunability-that is, a broad dynamic range of periods and amplitudes accessible through the input "dials." Our approach decouples frequency and amplitude modulation by incorporating an orthogonal "sink module" where the key molecular species are channeled for enzymatic degradation. This sink module maintains fast oscillation cycles while alleviating the translational coupling between the oscillator's transcription factors and output. We characterize the behavior of our re-designed oscillators over a broad range of physiologically reasonable parameters, explain why this facilitates broader function and control, and provide general design principles for building synthetic genetic oscillators that are more precisely controllable. Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.

  17. Force Control Is Related to Low-Frequency Oscillations in Force and Surface EMG

    PubMed Central

    Moon, Hwasil; Kim, Changki; Kwon, Minhyuk; Chen, Yen Ting; Onushko, Tanya; Lodha, Neha; Christou, Evangelos A.

    2014-01-01

    Force variability during constant force tasks is directly related to oscillations below 0.5 Hz in force. However, it is unknown whether such oscillations exist in muscle activity. The purpose of this paper, therefore, was to determine whether oscillations below 0.5 Hz in force are evident in the activation of muscle. Fourteen young adults (21.07±2.76 years, 7 women) performed constant isometric force tasks at 5% and 30% MVC by abducting the left index finger. We recorded the force output from the index finger and surface EMG from the first dorsal interosseous (FDI) muscle and quantified the following outcomes: 1) variability of force using the SD of force; 2) power spectrum of force below 2 Hz; 3) EMG bursts; 4) power spectrum of EMG bursts below 2 Hz; and 5) power spectrum of the interference EMG from 10–300 Hz. The SD of force increased significantly from 5 to 30% MVC and this increase was significantly related to the increase in force oscillations below 0.5 Hz (R 2 = 0.82). For both force levels, the power spectrum for force and EMG burst was similar and contained most of the power from 0–0.5 Hz. Force and EMG burst oscillations below 0.5 Hz were highly coherent (coherence = 0.68). The increase in force oscillations below 0.5 Hz from 5 to 30% MVC was related to an increase in EMG burst oscillations below 0.5 Hz (R 2 = 0.51). Finally, there was a strong association between the increase in EMG burst oscillations below 0.5 Hz and the interference EMG from 35–60 Hz (R 2 = 0.95). In conclusion, this finding demonstrates that bursting of the EMG signal contains low-frequency oscillations below 0.5 Hz, which are associated with oscillations in force below 0.5 Hz. PMID:25372038

  18. High-Frequency Oscillations and Seizure Generation in Neocortical Epilepsy

    ERIC Educational Resources Information Center

    Worrell, Greg A.; Parish, Landi; Cranstoun, Stephen D.; Jonas, Rachel; Baltuch, Gordon; Litt, Brian

    2004-01-01

    Neocortical seizures are often poorly localized, explosive and widespread at onset, making them poorly amenable to epilepsy surgery in the absence of associated focal brain lesions. We describe, for the first time in an unselected group of patients with neocortical epilepsy, the finding that high-frequency (60--100 Hz) epileptiform oscillations…

  19. An L-band transit-time oscillator with mechanical frequency tunability

    NASA Astrophysics Data System (ADS)

    Song, Lili; He, Juntao; Ling, Junpu; Cao, Yibing

    2017-02-01

    An L-band coaxial Transit-time Oscillator (TTO) with mechanical frequency tunability is introduced in this paper. Particle-in-cell simulations have been done. The output power efficiency has been improved at least 20% under a 10.2 GW input power and with a tunable range from 1.57 GHz to 1.90 GHz by modulating the outer conductor. It is worth to note that the efficiency can reach as high as 41% at 1.75 GHz. The mechanical engineering method is also detailed in this work. The frequency tuning range of the coaxial TTO is 22.6% of the central frequency. On the other hand, the frequency can be tuned from 1.6 GHz to 1.85 GHz by modulating the inner conductor. The author highlights a hollow structure of the L-band coaxial TTO which can work from 1.03 GHz to 1.31 GHz via modulating the outer conductor in the rest of the article. The frequency tuning range of the hollow TTO is 21.4% of the central frequency. More importantly, the hollow TTO can be easily achieved after the inner conductor is removed from the coaxial TTO. The electric field distributions of the coaxial and hollow TTOs are analyzed, resulting in that the longitudinal and transverse working modes are TM01 and π mode, respectively. The same working mode from these two structures implies the stability of the TTOs mentioned above.

  20. Fishbone Oscillations in the Experimental Advanced Superconductivity Tokamak

    NASA Astrophysics Data System (ADS)

    Xu, Li-Qing; Hu, Li-Qun; Yuan, Yi; Li, Ying-Ying; Zhong, Guo-Qiang; Liu, Hai-Qing; Chen, Kai-Yun; Shi, Tong-Hui; Duan, Yan-Min

    2018-03-01

    A fishbone oscillation was observed in the neutral beam injection plasma at Experimental Advanced Superconductivity Tokamak (EAST). This m = 1/n = 1 ( m, n: poloidal, toroidal mode numbers, respectively) typical internal kink mode travels in the ion-diamagnetism direction in the poloidal section with a rotation speed close to the ion diamagnetic drift frequency. A high thermal plasma beta and high amounts of energetic ions are necessary for the mode to develop. Fishbone oscillations can expel heavy impurities in the core, which favors sustaining a high-performance plasma. The born frequency of the fishbone oscillation is the ion diamagnetic drift frequency and the chirping down of the frequency during the initial growth phase is the result of a drop in iondiamagnetic drift frequency. The excitation energy is thought to be due to the thermal plasma pressure gradient; however, the development of a fishbone oscillation is related to energetic ions.

  1. Generation of mechanical oscillation applicable to vibratory rate gyroscopes

    NASA Technical Reports Server (NTRS)

    Lemkin, Mark A. (Inventor); Juneau, Thor N. (Inventor); Clark, William A. (Inventor); Roessig, Allen W. (Inventor)

    2001-01-01

    To achieve a drive-axis oscillation with improved frequency and amplitude stability, additional feedback loops are used to adjust force-feedback loop parameters. An amplitude-control loop measures oscillation amplitude, compares this value to the desired level, and adjusts damping of the mechanical sense-element to grow or shrink oscillation amplitude as appropriate. A frequency-tuning loop measures the oscillation frequency, compares this value with a highly stable reference, and adjusts the gain in the force-feedback loop to keep the drive-axis oscillation frequency at the reference value. The combined topology simultaneously controls both amplitude and frequency. Advantages of the combined topology include improved stability, fast oscillation start-up, low power consumption, and excellent shock rejection.

  2. High-energy terahertz wave parametric oscillator with a surface-emitted ring-cavity configuration.

    PubMed

    Yang, Zhen; Wang, Yuye; Xu, Degang; Xu, Wentao; Duan, Pan; Yan, Chao; Tang, Longhuang; Yao, Jianquan

    2016-05-15

    A surface-emitted ring-cavity terahertz (THz) wave parametric oscillator has been demonstrated for high-energy THz output and fast frequency tuning in a wide frequency range. Through the special optical design with a galvano-optical scanner and four-mirror ring-cavity structure, the maximum THz wave output energy of 12.9 μJ/pulse is achieved at 1.359 THz under the pump energy of 172.8 mJ. The fast THz frequency tuning in the range of 0.7-2.8 THz can be accessed with the step response of 600 μs. Moreover, the maximum THz wave output energy from this configuration is 3.29 times as large as that obtained from the conventional surface-emitted THz wave parametric oscillator with the same experimental conditions.

  3. High-frequency and high-quality silicon carbide optomechanical microresonators

    PubMed Central

    Lu, Xiyuan; Lee, Jonathan Y.; Lin, Qiang

    2015-01-01

    Silicon carbide (SiC) exhibits excellent material properties attractive for broad applications. We demonstrate the first SiC optomechanical microresonators that integrate high mechanical frequency, high mechanical quality, and high optical quality into a single device. The radial-breathing mechanical mode has a mechanical frequency up to 1.69 GHz with a mechanical Q around 5500 in atmosphere, which corresponds to a fm · Qm product as high as 9.47 × 1012 Hz. The strong optomechanical coupling allows us to efficiently excite and probe the coherent mechanical oscillation by optical waves. The demonstrated devices, in combination with the superior thermal property, chemical inertness, and defect characteristics of SiC, show great potential for applications in metrology, sensing, and quantum photonics, particularly in harsh environments that are challenging for other device platforms. PMID:26585637

  4. High frequency oscillations (80–500 Hz) in the preictal period in patients with focal seizures

    PubMed Central

    Jacobs, Julia; Zelmann, Rina; Jirsch, Jeffrey; Chander, Rahul; Châtillon, Claude-Édouard; Dubeau, François; Gotman, Jean

    2013-01-01

    Summary Purpose Intracranial depth macroelectrode recordings from patients with focal seizures demonstrate interictal and ictal high frequency oscillations (HFOs, 80–500 Hz). These HFOs are more frequent in the seizure-onset zone (SOZ) and reported to be linked to seizure genesis. We evaluated whether HFO activity changes in a systematic way during the preictal period. Methods Fifteen minutes of preictal intracranial electroencephalography (EEG) recordings were evaluated in seven consecutive patients with well-defined SOZ. EEG was filtered at 500 Hz and sampled at 2,000 Hz. Ripples (80–250 Hz) and fast ripples (250–500 Hz) were visually marked, and spectral analysis was performed in seizure-onset as well as nonseizure-onset channels. Linear regressions fitted to the power trends corresponding to intervals of 1, 5, and 15 min before the seizure onset was calculated. Results Total rates of HFOs were significantly higher in the SOZ than outside. Preictal increases and decreases in HFO rates and band power could be detected in all patients, and they were not limited to the SOZs. These measures were very variable, and nosystematic trends were observed when comparing patients or seizures in the same patient. Discussion High frequencies in the range of 80–500 Hz are present during the preictal period and are more prominent in the SOZ. They do not change in a systematic way before seizure onset for the horizons we tested. The 80–500 Hz band may be used for the localization of seizure-onset areas but may be more difficult to use for seizure prediction purposes. PMID:19400871

  5. Properties and Frequency Conversion of High-Brightness Diode-Laser Systems

    NASA Astrophysics Data System (ADS)

    Boller, Klaus-Jochen; Beier, Bernard; Wallenstein, Richard

    An overview of recent developments in the field of high-power, high-brightness diode-lasers, and the optically nonlinear conversion of their output into other wavelength ranges, is given. We describe the generation of continuous-wave (CW) laser beams at power levels of several hundreds of milliwatts to several watts with near-perfect spatial and spectral properties using Master-Oscillator Power-Amplifier (MOPA) systems. With single- or double-stage systems, using amplifiers of tapered or rectangular geometry, up to 2.85 W high-brightness radiation is generated at wavelengths around 810nm with AlGaAs diodes. Even higher powers, up to 5.2W of single-frequency and high spatial quality beams at 925nm, are obtained with InGaAs diodes. We describe the basic properties of the oscillators and amplifiers used. A strict proof-of-quality for the diode radiation is provided by direct and efficient nonlinear optical conversion of the diode MOPA output into other wavelength ranges. We review recent experiments with the highest power levels obtained so far by direct frequency doubling of diode radiation. In these experiments, 100mW single-frequency ultraviolet light at 403nm was generated, as well as 1W of single-frequency blue radiation at 465nm. Nonlinear conversion of diode radiation into widely tunable infrared radiation has recently yielded record values. We review the efficient generation of widely tunable single-frequency radiation in the infrared with diode-pumped Optical Parametric Oscillators (OPOs). With this system, single-frequency output radiation with powers of more than 0.5W was generated, widely tunable around wavelengths of 2.1,m and 1.65,m and with excellent spectral and spatial quality. These developments are clear indicators of recent advances in the field of high-brightness diode-MOPA systems, and may emphasize their future central importance for applications within a vast range of optical

  6. Altered modulation of gamma oscillation frequency by speed of visual motion in children with autism spectrum disorders.

    PubMed

    Stroganova, Tatiana A; Butorina, Anna V; Sysoeva, Olga V; Prokofyev, Andrey O; Nikolaeva, Anastasia Yu; Tsetlin, Marina M; Orekhova, Elena V

    2015-01-01

    Recent studies link autism spectrum disorders (ASD) with an altered balance between excitation and inhibition (E/I balance) in cortical networks. The brain oscillations in high gamma-band (50-120 Hz) are sensitive to the E/I balance and may appear useful biomarkers of certain ASD subtypes. The frequency of gamma oscillations is mediated by level of excitation of the fast-spiking inhibitory basket cells recruited by increasing strength of excitatory input. Therefore, the experimental manipulations affecting gamma frequency may throw light on inhibitory networks dysfunction in ASD. Here, we used magnetoencephalography (MEG) to investigate modulation of visual gamma oscillation frequency by speed of drifting annular gratings (1.2, 3.6, 6.0 °/s) in 21 boys with ASD and 26 typically developing boys aged 7-15 years. Multitaper method was used for analysis of spectra of gamma power change upon stimulus presentation and permutation test was applied for statistical comparisons. We also assessed in our participants visual orientation discrimination thresholds, which are thought to depend on excitability of inhibitory networks in the visual cortex. Although frequency of the oscillatory gamma response increased with increasing velocity of visual motion in both groups of participants, the velocity effect was reduced in a substantial proportion of children with ASD. The range of velocity-related gamma frequency modulation correlated inversely with the ability to discriminate oblique line orientation in the ASD group, while no such correlation has been observed in the group of typically developing participants. Our findings suggest that abnormal velocity-related gamma frequency modulation in ASD may constitute a potential biomarker for reduced excitability of fast-spiking inhibitory neurons in a subset of children with ASD.

  7. Parameters affecting the frequency of a fluid oscillator

    NASA Astrophysics Data System (ADS)

    Cheng, R. M. H.; Kwok, C. K.; Lee, R. S.

    1983-06-01

    A new type of liquid-operated low-frequency oscillator is introduced. The oscillator consists of a cone-shaped housing with a fluid inlet and two outlet discharging tubes. The fluid discharge is controlled by a ball which blocks one of the outlet tubes. A strong vacuum develops due to the inertial effect of the column of liquid moving downward in the blocked tube. When the initial energy and velocity of the liquid slug are reduced to zero, it starts to return toward the ball. Eventually the combined force of the pressure inside the housing and the momentum of the upcoming slug is large enough to displace the ball to the other outlet tube, and the same procedure is then repeated. The main part of the paper consists of an analysis of the time required for the forward and reverse motion of the slug and for the ball to move from one discharge hole to the other.

  8. A wide-range variable-frequency resonant tunneling diode oscillator using a variable resonator suitable for simple MEMS process

    NASA Astrophysics Data System (ADS)

    Yamashita, Takashi; Nakano, Daisuke; Mori, Masayuki; Maezawa, Koichi

    2018-04-01

    A resonant tunneling diode oscillator having a wide frequency variation range based on a novel MEMS resonator was proposed, which exploits the change in the signal propagation velocity on a coplanar waveguide according to a movable ground plane. First, we discussed the velocity modulation mechanism, and clarified the importance of the dielectric constant of the substrate. Then, a prototype device oscillating in a 10 to 20 GHz frequency range was fabricated to demonstrate the basic operation. A large and continuous increase in the oscillation frequency of about two times was achieved with this device. This is promising for various applications including THz spectroscopy.

  9. High power pumped mid-IR wavelength systems using nonlinear frequency mixing (NFM) devices

    NASA Technical Reports Server (NTRS)

    Sanders, Steven (Inventor); Lang, Robert J. (Inventor); Waarts, Robert G. (Inventor)

    1999-01-01

    Laser diode pumped mid-IR wavelength systems include at least one high power, near-IR wavelength, injection and/or sources wherein one or both of such sources may be tunable providing a pump wave output beam to a quasi-phase matched (QPM) nonlinear frequency mixing (NFM) device. The NFM device may be a difference frequency mixing (DFM) device or an optical parametric oscillation (OPO) device. Wavelength tuning of at least one of the sources advantageously provides the ability for optimizing pump or injection wavelengths to match the QPM properties of the NFM device enabling a broad range of mid-IR wavelength selectivity. Also, pump powers are gain enhanced by the addition of a rare earth amplifier or oscillator, or a Raman/Brillouin amplifier or oscillator between the high power source and the NFM device. Further, polarization conversion using Raman or Brillouin wavelength shifting is provided to optimize frequency conversion efficiency in the NFM device.

  10. Completely monolithic linearly polarized high-power fiber laser oscillator

    NASA Astrophysics Data System (ADS)

    Belke, Steffen; Becker, Frank; Neumann, Benjamin; Ruppik, Stefan; Hefter, Ulrich

    2014-03-01

    We have demonstrated a linearly polarized cw all-in-fiber oscillator providing 1 kW of output power and a polarization extinction ratio (PER) of up to 21.7 dB. The design of the laser oscillator is simple and consists of an Ytterbium-doped polarization maintaining large mode area (PLMA) fiber and suitable fiber Bragg gratings (FBG) in matching PLMA fibers. The oscillator has nearly diffraction-limited beam quality (M² < 1.2). Pump power is delivered via a high power 6+1:1 pump coupler. The slope efficiency of the laser is 75 %. The electro/optical efficiency of the complete laser system is ~30 % and hence in the range of Rofin's cw non-polarized fiber lasers. Choosing an adequate bending diameter for the Yb-doped PLMA fiber, one polarization mode as well as higher order modes are sufficiently supressed1. Resulting in a compact and robust linearly polarized high power single mode laser without external polarizing components. Linearly polarized lasers are well established for one dimensional cutting or welding applications. Using beam shaping optics radially polarized laser light can be generated to be independent from the angle of incident to the processing surface. Furthermore, high power linearly polarized laser light is fundamental for nonlinear frequency conversion of nonlinear materials.

  11. Low-frequency oscillations in default mode subnetworks are associated with episodic memory impairments in Alzheimer's disease.

    PubMed

    Veldsman, Michele; Egorova, Natalia; Singh, Baljeet; Mungas, Dan; DeCarli, Charles; Brodtmann, Amy

    2017-11-01

    Disruptions to functional connectivity in subsystems of the default mode network are evident in Alzheimer's disease (AD). Functional connectivity estimates correlations in the time course of low-frequency activity. Much less is known about other potential perturbations to this activity, such as changes in the amplitude of oscillations and how this relates to cognition. We examined the amplitude of low-frequency fluctuations in 44 AD patients and 128 cognitively normal participants and related this to episodic memory, the core deficit in AD. We show higher amplitudes of low-frequency oscillations in AD patients. Rather than being compensatory, this appears to be maladaptive, with greater amplitude in the ventral default mode subnetwork associated with poorer episodic memory. Perturbations to default mode subnetworks in AD are evident in the amplitude of low-frequency oscillations in the resting brain. These disruptions are associated with episodic memory demonstrating their behavioral and clinical relevance in AD. Copyright © 2017 Elsevier Inc. All rights reserved.

  12. Frequency stability and offset locking of a laser-diode-pumped Nd:YAG monolithic nonplanar ring oscillator

    NASA Technical Reports Server (NTRS)

    Kane, Thomas J.; Nilsson, Alan C.; Byer, Robert L.

    1987-01-01

    The frequency stability of laser-diode-pumped, monolithic Nd:YAG solid-state unidirectional nonplanar ring oscillators was studied by heterodyne measurements. CW single-axial- and transverse-mode power of 25 mW at 1064 nm was obtained at a slope efficiency of 19 percent. Two independent oscillators were offset-locked at 17 MHz with frequency fluctuations of less than + or - 40 kHz for periods of 8 min.

  13. Feasibility of recording high frequency oscillations with tripolar concentric ring electrodes during pentylenetetrazole-induced seizures in rats.

    PubMed

    Makeyev, Oleksandr; Liu, Xiang; Wang, Liling; Zhu, Zhenghan; Taveras, Aristides; Troiano, Derek; Medvedev, Andrei V; Besio, Walter G

    2012-01-01

    As epilepsy remains a refractory condition in about 30% of patients with complex partial seizures, electrical stimulation of the brain has recently shown potential for additive seizure control therapy. Previously, we applied noninvasive transcranial focal stimulation via novel tripolar concentric ring electrodes (TCREs) on the scalp of rats after inducing seizures with pentylenetetrazole (PTZ). We developed a close-loop system to detect seizures and automatically trigger the stimulation and evaluated its effect on the electrographic activity recorded by TCREs in rats. In our previous work the detectors of seizure onset were based on seizure-induced changes in signal power in the frequency range up to 100 Hz, while in this preliminary study we assess the feasibility of recording high frequency oscillations (HFOs) in the range up to 300 Hz noninvasively with scalp TCREs during PTZ-induced seizures. Grand average power spectral density estimate and generalized likelihood ratio tests were used to compare power of electrographic activity at different stages of seizure development in a group of rats (n= 8). The results suggest that TCREs have the ability to record HFOs from the scalp as well as that scalp-recorded HFOs can potentially be used as features for seizure onset detection.

  14. A Constant Energy-Per-Cycle Ring Oscillator Over a Wide Frequency Range for Wireless Sensor Nodes

    PubMed Central

    Lee, Inhee; Sylvester, Dennis; Blaauw, David

    2016-01-01

    This paper presents an energy-efficient oscillator for wireless sensor nodes (WSNs). It avoids short-circuit current by minimizing the time spent in the input voltage range from Vthn to [Vdd − |Vthp|]. A current-feeding scheme with gate voltage control enables the oscillator to operate over a wide frequency range. A test chip is fabricated in a 0.18 μm CMOS process. The measurements show that the proposed oscillator achieves a constant energy-per-cycle (EpC) of 0.8 pJ/cycle over the 21–60 MHz frequency range and is more efficient than a conventional current-starved ring oscillator (CSRO) below 300 kHz at 1.8 V supply voltage. As an application example, the proposed oscillator is implemented in a switched-capacitor DC–DC converter. The converter is 11%–56% more efficient for load power values ranging from 583 pW to 2.9 nW than a converter using a conventional CSRO. PMID:27546899

  15. A Constant Energy-Per-Cycle Ring Oscillator Over a Wide Frequency Range for Wireless Sensor Nodes.

    PubMed

    Lee, Inhee; Sylvester, Dennis; Blaauw, David

    2016-03-01

    This paper presents an energy-efficient oscillator for wireless sensor nodes (WSNs). It avoids short-circuit current by minimizing the time spent in the input voltage range from V thn to [ V dd - | V thp |]. A current-feeding scheme with gate voltage control enables the oscillator to operate over a wide frequency range. A test chip is fabricated in a 0.18 μm CMOS process. The measurements show that the proposed oscillator achieves a constant energy-per-cycle (EpC) of 0.8 pJ/cycle over the 21-60 MHz frequency range and is more efficient than a conventional current-starved ring oscillator (CSRO) below 300 kHz at 1.8 V supply voltage. As an application example, the proposed oscillator is implemented in a switched-capacitor DC-DC converter. The converter is 11%-56% more efficient for load power values ranging from 583 pW to 2.9 nW than a converter using a conventional CSRO.

  16. Downstream boundary effects on the frequency of self-excited oscillations in transonic diffuser flows

    NASA Astrophysics Data System (ADS)

    Hsieh, T.

    1986-10-01

    Investigation of downstream boundary effects on the frequency of self-excited oscillations in two-dimensional, separated transonic diffuser flows were conducted numerically by solving the compressible, Reynolds-averaged, thin-layer Navier-Stokes equation with two equation turbulence models. It was found that the flow fields are very sensitive to the location of the downstream boundary. Extension of the diffuser downstream boundary significantly reduces the frequency and amplitude of oscillations for pressure, velocity, and shock. The existence of a suction slot in the experimental setpup obscures the physical downstream boundary and therefore presents a difficulty for quantitative comparisons between computation and experiment.

  17. Constraining properties of high-density matter in neutron stars with magneto-elastic oscillations

    NASA Astrophysics Data System (ADS)

    Gabler, Michael; Cerdá-Durán, Pablo; Stergioulas, Nikolaos; Font, José A.; Müller, Ewald

    2018-05-01

    We discuss torsional oscillations of highly magnetized neutron stars (magnetars) using two-dimensional, magneto-elastic-hydrodynamical simulations. Our model is able to explain both the low- and high-frequency quasi-periodic oscillations (QPOs) observed in magnetars. The analysis of these oscillations provides constraints on the breakout magnetic-field strength, on the fundamental QPO frequency, and on the frequency of a particularly excited overtone. By performing a new set of simulations, we are able to derive for the first time empirical relations for a self consistent model including a superfluid core which describe these constraints quantitatively. We use these relations to generically constrain properties of high-density matter in neutron stars, employing Bayesian analysis. In spite of current uncertainties and computational approximations, our model-dependent Bayesian posterior estimates for SGR 1806-20 yield a magnetic-field strength \\bar{B}˜ 2.1^{+1.3}_{-1.0}× 10^{15} G and a crust thickness of Δ r = 1.6^{+0.7}_{-0.6} km, which are both in remarkable agreement with observational and theoretical expectations, respectively (1σ error bars are indicated). Our posteriors also favour the presence of a superfluid phase in the core, a relatively low stellar compactness, M/R < 0.19, indicating a relatively stiff equation of state and/or low-mass neutron star, and high shear speeds at the base of the crust, cs > 1.4 × 108 cm s-1. Although the procedure laid out here still has large uncertainties, these constraints could become tighter when additional observations become available.

  18. Novel High Temperature Capacitive Pressure Sensor Utilizing SiC Integrated Circuit Twin Ring Oscillators

    NASA Technical Reports Server (NTRS)

    Scardelletti, M.; Neudeck, P.; Spry, D.; Meredith, R.; Jordan, J.; Prokop, N.; Krasowski, M.; Beheim, G.; Hunter, G.

    2017-01-01

    This paper describes initial development and testing of a novel high temperature capacitive pressure sensor system. The pressure sensor system consists of two 4H-SiC 11-stage ring oscillators and a SiCN capacitive pressure sensor. One oscillator has the capacitive pressure sensor fixed at one node in its feedback loop and varies as a function of pressure and temperature while the other provides a pressure-independent reference frequency which can be used to temperature compensate the output of the first oscillator. A two-day repeatability test was performed up to 500C on the oscillators and the oscillator fundamental frequency changed by only 1. The SiCN capacitive pressure sensor was characterized at room temperature from 0 to 300 psi. The sensor had an initial capacitance of 3.76 pF at 0 psi and 1.75 pF at 300 psi corresponding to a 54 change in capacitance. The integrated pressure sensor system was characterized from 0 to 300 psi in steps of 50 psi over a temperature range of 25 to 500C. The pressure sensor system sensitivity was 0.113 kHzpsi at 25C and 0.026 kHzpsi at 500C.

  19. Frequency response of nonlinear oscillations of air column in a tube with an array of Helmholtz resonators.

    PubMed

    Sugimoto, N; Masuda, M; Hashiguchi, T

    2003-10-01

    Nonlinear cubic theory is developed to obtain a frequency response of shock-free, forced oscillations of an air column in a closed tube with an array of Helmholtz resonators connected axially. The column is assumed to be driven by a plane piston sinusoidally at a frequency close or equal to the lowest resonance frequency with its maximum displacement fixed. By applying the method of multiple scales, the equation for temporal modulation of a complex pressure amplitude of the lowest mode is derived in a case that a typical acoustic Mach number is comparable with the one-third power of the piston Mach number, while the relative detuning of a frequency is comparable with the quadratic order of the acoustic Mach number. The steady-state solution gives the asymmetric frequency response curve with bending (skew) due to nonlinear frequency upshift in addition to the linear downshift. Validity of the theory is checked against the frequency response obtained experimentally. For high amplitude of oscillations, an effect of jet loss at the throat of the resonator is taken into account, which introduces the quadratic loss to suppress the peak amplitude. It is revealed that as far as the present check is concerned, the weakly nonlinear theory can give quantitatively adequate description up to the pressure amplitude of about 3% to the equilibrium pressure.

  20. High power, high frequency helix TWT's

    NASA Astrophysics Data System (ADS)

    Sloley, H. J.; Willard, J.; Paatz, S. R.; Keat, M. J.

    The design and performance characteristics of a 34-GHz pulse tube capable of 75 W peak power output at 30 percent duty cycle and a broadband CW tube are presented. Particular attention is given to the engineering problems encountered during the development of the tubes, including the suppression of backward wave oscillation, the design of electron guns for small-diameter high-current beams, and the thermal capability of small helix structures. The discussion also covers the effects of various design parameters and choice of engineering materials on the ultimate practical limit of power and gain at the operating frequencies. Measurements are presented for advanced experimental tubes.

  1. Observation of millimeter-wave oscillations from resonant tunneling diodes and some theoretical considerations of ultimate frequency limits

    NASA Technical Reports Server (NTRS)

    Sollner, T. C. L. G.; Brown, E. R.; Goodhue, W. D.; Le, H. Q.

    1987-01-01

    Recent observations of oscillation frequencies up to 56 GHz in resonant tunneling structures are discussed in relation to calculations by several authors of the ultimate frequency limits of these devices. It is found that calculations relying on the Wentzel-Kramers-Brillouin (WKB) approximation give limits well below the observed oscillation frequencies. Two other techniques for calculating the upper frequency limit were found to give more reasonable results. One method employs the solution of the time-dependent Schroedinger equation obtained by Kundrotas and Dargys (1986); the other uses the energy width of the transmission function for electrons through the double-barrier structure. This last technique is believed to be the most accurate since it is based on general results for the lifetime of any resonant state. It gives frequency limits on the order of 1 THz for two recently fabricated structures. It appears that the primary limitation of the oscillation frequency for double-barrier resonant-tunneling diodes is imposed by intrinsic device circuit parameters and by the transit time of the depletion layer rather than by time delays encountered in the double-barrier region.

  2. VO2 film temperature dynamics at low-frequency current self-oscillations

    NASA Astrophysics Data System (ADS)

    Bortnikov, S. G.; Aliev, V. Sh.; Badmaeva, I. A.; Mzhelskiy, I. V.

    2018-02-01

    Low-frequency (˜2 Hz) current self-oscillations were first obtained in a millimeter-sized two-terminal planar device with a vanadium dioxide (VO2) film. The film temperature distribution dynamics was investigated within one oscillation period. It was established that the formation and disappearance of a conductive channel occur in a film in less than 60 ms with oscillation period 560 ms. The experimentally observed temperature in the channel region reached 413 K, being understated due to a low infrared microscope performance (integration time 10 ms). The VO2 film temperature distribution dynamics was simulated by solving a 2D problem of the electric current flow and heat transfer in the film. The calculation showed that the thermally initiated resistance switching in the film occurs in less than 4 ms at a channel temperature reaching ˜1000 K. The experimental results and simulation are consistent with the current self-oscillation mechanism based on the current pinching and dielectric relaxation in the VO2 film at the metal-insulator phase transition.

  3. Investigation of low-frequency-oscillating water flow in metal foam with 10 pores per inch

    NASA Astrophysics Data System (ADS)

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

    2018-01-01

    In this study, oscillating water flow in metal foam with open cells is investigated experimentally. The metal foam sample has a porosity of 88% and 10 pores. The water was oscillated in the test section with three frequencies between 0.116 Hz and 0.348 Hz, which are considered low for water oscillation, and three flow displacements ranging between 74.35 mm and 111.53 mm. The combinations of frequencies of displacements were studied for their impacts of dimensional and non-dimensional pressure loss quantities. To this purpose, friction factor was correlated as a function of kinetic Reynolds number. The same metal foam sample was studied by exposing it to steady-state water flow to investigate its permeability and drag coefficient in low-velocity flow regimes. The friction factor distribution for oscillating flow was found to be over that found for steady state. The outcomes of the study are important for studying heat transfer under the same flow conditions.

  4. North-south asymmetry of ultra-low-frequency oscillations of Earth's electromagnetic field

    NASA Astrophysics Data System (ADS)

    Guglielmi, Anatol; Klain, Boris; Potapov, Alexander

    2017-12-01

    In the paper, we present the result of an experimental study of north-south asymmetry of ultralow-frequency electromagnetic oscillations IPCL. This study is based on observations made at Mirny Observatory (Antarctica). IPCLs are excited in the dayside sector of the auroral oval in the range 3-10 min periods and represent one of the most powerful types of oscillations of Earth's magnetosphere. These oscillations were discovered in the 1970s during IPhE AS USSR polar expeditions organized by Prof. V.A. Troitskaya. We have shown that IPCL activity in Mirny depends on the inclination (north-south asymmetry) of interplanetary magnetic field (IMF) lines to the plane of the geomagnetic equator before the front of the magnetosphere. The result suggests a controlling exposure of IMF on the magnetospheric oscillations and gives rise to the hypothesis that IPCLs are forced oscillations of a nonlinear dynamical system whose major structural elements are dayside polar cusps. The paper is dedicated to the memory of Professor V.A. Troitskaya (1917-2010).

  5. Rabi-Bloch oscillations in spatially distributed systems: Temporal dynamics and frequency spectra

    NASA Astrophysics Data System (ADS)

    Levie, Ilay; Kastner, Raphael; Slepyan, Gregory

    2017-10-01

    We consider one-dimensional chains of two-level quantum systems coupled via tunneling. The chain is driven by the superposition of dc and ac fields in the strong coupling regime. Based on the fundamental principles of electrodynamics and quantum theory, we have developed a generalized model of quantum dynamics for such interactions, free of rotating-wave approximation. The system of equations of motion was studied numerically. We analyzed the dynamics and spectra of the inversion density, dipole current density, and tunneling current density. In the case of resonant interaction with the ac component, the particle dynamics exhibits itself in the oscillatory regime, which may be interpreted as a combination of Rabi and Bloch oscillations with their strong mutual influence. Such scenario for an obliquely incident ac field dramatically differs from the individual picture of both types of oscillations due to the interactions. This effect is counterintuitive because of the existence of markedly different frequency ranges for such two types of oscillations. These dynamics manifest themselves in multiline spectra in different combinations of Rabi and Bloch frequencies. The effect is promising as a framework of a new type of spectroscopy in nanoelectronics and electrical control of nanodevices.

  6. Opto-electronic microwave oscillator

    NASA Astrophysics Data System (ADS)

    Yao, X. Steve; Maleki, Lute

    1996-12-01

    Photonic applications are important in RF communication systems to enhance many functions including remote transfer of antenna signals, carrier frequency up or down conversion, antenna beam steering, and signal filtering. Many of these functions require reference frequency oscillators. However, traditional microwave oscillators cannot meet all the requirements of photonic communication systems that need high frequency and low phase noise signal generation. Because photonic systems involve signals in both optical and electrical domains, an ideal signal source should be able to provide electrical and optical signals. In addition, it should be possible to synchronize or control the signal source by both electrical and optical means. We present such a source1-2 that converts continuous light energy into stable and spectrally pure microwave signals. This Opto-Electronic Oscillator, OEO, consists of a pump laser and a feedback circuit including an intensity modulator, an optical fiber delay line, a photodetector, an amplifier, and a filter, as shown in Figure 1a. Its oscillation frequency, limited only by the speed of the modulator, can be up to 75 GHz.

  7. Evolutionary Model and Oscillation Frequencies for α Ursae Majoris: A Comparison with Observations

    NASA Astrophysics Data System (ADS)

    Guenther, D. B.; Demarque, P.; Buzasi, D.; Catanzarite, J.; Laher, R.; Conrow, T.; Kreidl, T.

    2000-02-01

    Inspired by the observations of low-amplitude oscillations of α Ursae Majoris A by Buzasi et al. using the WIRE satellite, a grid of stellar evolutionary tracks has been constructed to derive physically consistent interior models for the nearby red giant. The pulsation properties of these models were then calculated and compared with the observations. It is found that, by adopting the correct metallicity and for a normal helium abundance, only models in the mass range of 4.0-4.5 Msolar fall within the observational error box for α UMa A. This mass range is compatible, within the uncertainties, with the mass derived from the astrometric mass function. Analysis of the pulsation spectra of the models indicates that the observed α UMa oscillations can be most simply interpreted as radial (i.e., l=0) p-mode oscillations of low radial order n. The lowest frequencies observed by Buzasi et al. are compatible, within the observational errors, with model frequencies of radial orders n=0, 1, and 2 for models in the mass range of 4.0-4.5 Msolar. The higher frequencies observed can also be tentatively interpreted as higher n-valued radial p-modes, if we allow that some n-values are not presently observed. The theoretical l=1, 2, and 3 modes in the observed frequency range are g-modes with a mixed mode character, that is, with p-mode-like characteristics near the surface and g-mode-like characteristics in the interior. The calculated radial p-mode frequencies are nearly equally spaced, separated by 2-3 μHz. The nonradial modes are very densely packed throughout the observed frequency range and, even if excited to significant amplitudes at the surface, are unlikely to be resolved by the present observations.

  8. THEORETICAL p-MODE OSCILLATION FREQUENCIES FOR THE RAPIDLY ROTATING {delta} SCUTI STAR {alpha} OPHIUCHI

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Deupree, Robert G., E-mail: bdeupree@ap.smu.ca

    2011-11-20

    A rotating, two-dimensional stellar model is evolved to match the approximate conditions of {alpha} Oph. Both axisymmetric and nonaxisymmetric oscillation frequencies are computed for two-dimensional rotating models which approximate the properties of {alpha} Oph. These computed frequencies are compared to the observed frequencies. Oscillation calculations are made assuming the eigenfunction can be fitted with six Legendre polynomials, but comparison calculations with eight Legendre polynomials show the frequencies agree to within about 0.26% on average. The surface horizontal shape of the eigenfunctions for the two sets of assumed number of Legendre polynomials agrees less well, but all calculations show significant departuresmore » from that of a single Legendre polynomial. It is still possible to determine the large separation, although the small separation is more complicated to estimate. With the addition of the nonaxisymmetric modes with |m| {<=} 4, the frequency space becomes sufficiently dense that it is difficult to comment on the adequacy of the fit of the computed to the observed frequencies. While the nonaxisymmetric frequency mode splitting is no longer uniform, the frequency difference between the frequencies for positive and negative values of the same m remains 2m times the rotation rate.« less

  9. Cholinergic enhancement of visual attention and neural oscillations in the human brain.

    PubMed

    Bauer, Markus; Kluge, Christian; Bach, Dominik; Bradbury, David; Heinze, Hans Jochen; Dolan, Raymond J; Driver, Jon

    2012-03-06

    Cognitive processes such as visual perception and selective attention induce specific patterns of brain oscillations. The neurochemical bases of these spectral changes in neural activity are largely unknown, but neuromodulators are thought to regulate processing. The cholinergic system is linked to attentional function in vivo, whereas separate in vitro studies show that cholinergic agonists induce high-frequency oscillations in slice preparations. This has led to theoretical proposals that cholinergic enhancement of visual attention might operate via gamma oscillations in visual cortex, although low-frequency alpha/beta modulation may also play a key role. Here we used MEG to record cortical oscillations in the context of administration of a cholinergic agonist (physostigmine) during a spatial visual attention task in humans. This cholinergic agonist enhanced spatial attention effects on low-frequency alpha/beta oscillations in visual cortex, an effect correlating with a drug-induced speeding of performance. By contrast, the cholinergic agonist did not alter high-frequency gamma oscillations in visual cortex. Thus, our findings show that cholinergic neuromodulation enhances attentional selection via an impact on oscillatory synchrony in visual cortex, for low rather than high frequencies. We discuss this dissociation between high- and low-frequency oscillations in relation to proposals that lower-frequency oscillations are generated by feedback pathways within visual cortex. Copyright © 2012 Elsevier Ltd. All rights reserved.

  10. Fast, precise, and widely tunable frequency control of an optical parametric oscillator referenced to a frequency comb.

    PubMed

    Prehn, Alexander; Glöckner, Rosa; Rempe, Gerhard; Zeppenfeld, Martin

    2017-03-01

    Optical frequency combs (OFCs) provide a convenient reference for the frequency stabilization of continuous-wave lasers. We demonstrate a frequency control method relying on tracking over a wide range and stabilizing the beat note between the laser and the OFC. The approach combines fast frequency ramps on a millisecond timescale in the entire mode-hop free tuning range of the laser and precise stabilization to single frequencies. We apply it to a commercially available optical parametric oscillator (OPO) and demonstrate tuning over more than 60 GHz with a ramping speed up to 3 GHz/ms. Frequency ramps spanning 15 GHz are performed in less than 10 ms, with the OPO instantly relocked to the OFC after the ramp at any desired frequency. The developed control hardware and software are able to stabilize the OPO to sub-MHz precision and to perform sequences of fast frequency ramps automatically.

  11. Self-entrainment to optimal gaits of an underactuated biomimetic swimming robot using adaptive frequency oscillators.

    PubMed

    Alessi, Alessio; Accoto, Dino; Guglielmelli, Eugenio

    2015-08-01

    Underactuated compliant swimming robots are characterized by a simple mechanical structure, capable to mimic the body undulation of many fish species. One of the design issue for these robots is the generation and control of best performing swimming gaits. In this paper we propose a new controller, based on AFO oscillators, to address this issue. After analyzing the effects of the motion on the robot natural frequencies, we show that the closed loop system is able to generate self-sustained oscillations, at a characteristic frequency, while maximizing swimming velocity.

  12. Frequency hopping due to acousto-electric interaction in ZnO based surface acoustic wave oscillator

    NASA Astrophysics Data System (ADS)

    Dasgupta, Daipayan; Sreenivas, K.

    2011-08-01

    A 36 MHz surface acoustic wave delay line based oscillator has been used to study the effect of acousto-electric interaction due to photo generated charge carriers in rf sputtered ZnO film under UV illumination (λ = 365 nm, 20-100 μW/cm2). Design aspects for developing a delay line based SAW oscillator are specified. The observed linear downshift in frequency (2.2 to 19.0 kHz) with varying UV intensity (20-100 μW/cm2) is related to the fractional velocity change due to acousto-electric interaction. UV illumination level of 100 μW/cm2 leads to a characteristic frequency hopping behavior arising due to a change in the oscillation criteria, and is attributed to the complex interplay between the increased attenuation and velocity shift.

  13. Comparing Optical Oscillators across the Air to Milliradians in Phase and 10^{-17} in Frequency.

    PubMed

    Sinclair, Laura C; Bergeron, Hugo; Swann, William C; Baumann, Esther; Deschênes, Jean-Daniel; Newbury, Nathan R

    2018-02-02

    We demonstrate carrier-phase optical two-way time-frequency transfer (carrier-phase OTWTFT) through the two-way exchange of frequency comb pulses. Carrier-phase OTWTFT achieves frequency comparisons with a residual instability of 1.2×10^{-17} at 1 s across a turbulent 4-km free space link, surpassing previous OTWTFT by 10-20 times and enabling future high-precision optical clock networks. Furthermore, by exploiting the carrier phase, this approach is able to continuously track changes in the relative optical phase of distant optical oscillators to 9 mrad (7 as) at 1 s averaging, effectively extending optical phase coherence over a broad spatial network for applications such as correlated spectroscopy between distant atomic clocks.

  14. Photonic harmonic up-converter based on a self-oscillating optical frequency comb using a DP-DPMZM

    NASA Astrophysics Data System (ADS)

    Xiao, Xuedi; Li, Shangyuan; Xie, Zhengyang; Peng, Shaowen; Wu, Dexin; Xue, Xiaoxiao; Zheng, Xiaoping; Zhou, Bingkun

    2018-04-01

    A photonic harmonic up-converter based on a self-oscillating optical frequency comb (OFC) utilizing an integrated dual-polarization dual-parallel Mach-Zehnder Modulator (DP-DPMZM) is proposed and experimentally demonstrated. One DPMZM is used to generate the optoelectronic oscillator (OEO)-based OFC, and the rest one is used to generate the optical-modulated intermediate frequency (IF) signal. Beating these two signals, the up-converted signals at different bands would be obtained. As the OFC is generated based on the OEO loop, phase noise can be very low, ensuring good phase noise properties of the up-converted signals. Moreover, frequency spacing between the combs is dependent on oscillating frequency of the OEO, which can be as large as tens of gigahertz. Thus IF signals with large bandwidth can be up-converted to RF bands without aliasing. Experimentally, the 2.5 GHz IF signal is simultaneously up-converted to 13.3, 24.1, and 34.9 GHz by a self-oscillating 7-line OFC spacing at 10.8 GHz. Owing to good phase noise property of the OEO, the up-converted signals at 13.3 and 24.1 GHz maintain the phase noise of the IF signal from 1 KHz to 100 KHz offset. The results show that the converter is promising for multi-band radar and satellite navigation applications.

  15. Detecting phase-amplitude coupling with high frequency resolution using adaptive decompositions

    PubMed Central

    Pittman-Polletta, Benjamin; Hsieh, Wan-Hsin; Kaur, Satvinder; Lo, Men-Tzung; Hu, Kun

    2014-01-01

    Background Phase-amplitude coupling (PAC) – the dependence of the amplitude of one rhythm on the phase of another, lower-frequency rhythm – has recently been used to illuminate cross-frequency coordination in neurophysiological activity. An essential step in measuring PAC is decomposing data to obtain rhythmic components of interest. Current methods of PAC assessment employ narrowband Fourier-based filters, which assume that biological rhythms are stationary, harmonic oscillations. However, biological signals frequently contain irregular and nonstationary features, which may contaminate rhythms of interest and complicate comodulogram interpretation, especially when frequency resolution is limited by short data segments. New method To better account for nonstationarities while maintaining sharp frequency resolution in PAC measurement, even for short data segments, we introduce a new method of PAC assessment which utilizes adaptive and more generally broadband decomposition techniques – such as the empirical mode decomposition (EMD). To obtain high frequency resolution PAC measurements, our method distributes the PAC associated with pairs of broadband oscillations over frequency space according to the time-local frequencies of these oscillations. Comparison with existing methods We compare our novel adaptive approach to a narrowband comodulogram approach on a variety of simulated signals of short duration, studying systematically how different types of nonstationarities affect these methods, as well as on EEG data. Conclusions Our results show: (1) narrowband filtering can lead to poor PAC frequency resolution, and inaccuracy and false negatives in PAC assessment; (2) our adaptive approach attains better PAC frequency resolution and is more resistant to nonstationarities and artifacts than traditional comodulograms. PMID:24452055

  16. Modulation characteristics of a high-power semiconductor Master Oscillator Power Amplifier (MOPA)

    NASA Technical Reports Server (NTRS)

    Cornwell, Donald Mitchell, Jr.

    1992-01-01

    A semiconductor master oscillator-power amplifier was demonstrated using an anti-reflection (AR) coated broad area laser as the amplifier. Under CW operation, diffraction-limited single-longitudinal-mode powers up to 340 mW were demonstrated. The characteristics of the far-field pattern were measured and compared to a two-dimensional reflective Fabry-Perot amplifier model of the device. The MOPA configuration was modulated by the master oscillator. Prior to injection into the amplifier, the amplitude and frequency modulation properties of the master oscillator were characterized. The frequency response of the MOPA configuration was characterized for an AM/FM modulated injection beam, and was found to be a function of the frequency detuning between the master oscillator and the resonant amplifier. A shift in the phase was also observed as a function of frequency detuning; this phase shift is attributed to the optical phase shift imparted to a wave reflected from a Fabry-Perot cavity. Square-wave optical pulses were generated at 10 MHz and 250 MHz with diffraction-limited peak powers of 200 mW and 250 mW. The peak power for a given modulation frequency is found to be limited by the injected power and the FM modulation at that frequency. The modulation results make the MOPA attractive for use as a transmitter source in applications such as free-space communications and ranging/altimetry.

  17. Initial high-degree p-mode frequency splittings from the 1988 Mt. Wilson 60-foot Tower Solar Oscillation Program

    NASA Technical Reports Server (NTRS)

    Rhodes, Edward J., Jr.; Cacciani, Alessandro; Korzennik, Sylvain G.

    1988-01-01

    The initial frequency splitting results of solar p-mode oscillations obtained from the 1988 helioseismology program at the Mt. Wilson Observatory are presented. The frequency splittings correspond to the rotational splittings of sectoral harmonics which range in degree between 10 and 598. They were obtained from a cross-correlation analysis of the prograde and retrograde portions of a two-dimensional (t - v) power spectrum. This power spectrum was computed from an eight-hour sequence of full-disk Dopplergrams obtained on July 2, 1988, at the 60-foot tower telescope with a Na magneto-optical filter and a 1024x1024 pixel CCD camera. These frequency splittings have an inherently larger scatter than did the splittings obtained from earlier 16-day power spectra. These splittings are consistent with an internal solar rotational velocity which is independent of radius along the equatorial plane. The normalized frequency splittings averaged 449 + or - 3 nHz, a value which is very close to the observed equatorial rotation rate of the photospheric gas of 451.7 nHz.

  18. Ultra-high-frequency chaos in a time-delay electronic device with band-limited feedback.

    PubMed

    Illing, Lucas; Gauthier, Daniel J

    2006-09-01

    We report an experimental study of ultra-high-frequency chaotic dynamics generated in a delay-dynamical electronic device. It consists of a transistor-based nonlinearity, commercially-available amplifiers, and a transmission-line for feedback. The feedback is band-limited, allowing tuning of the characteristic time-scales of both the periodic and high-dimensional chaotic oscillations that can be generated with the device. As an example, periodic oscillations ranging from 48 to 913 MHz are demonstrated. We develop a model and use it to compare the experimentally observed Hopf bifurcation of the steady-state to existing theory [Illing and Gauthier, Physica D 210, 180 (2005)]. We find good quantitative agreement of the predicted and the measured bifurcation threshold, bifurcation type and oscillation frequency. Numerical integration of the model yields quasiperiodic and high dimensional chaotic solutions (Lyapunov dimension approximately 13), which match qualitatively the observed device dynamics.

  19. Exoskeleton control for lower-extremity assistance based on adaptive frequency oscillators: adaptation of muscle activation and movement frequency.

    PubMed

    Aguirre-Ollinger, Gabriel

    2015-01-01

    In this article, we analyze a novel strategy for assisting the lower extremities based on adaptive frequency oscillators. Our aim is to use the control algorithm presented here as a building block for the control of powered lower-limb exoskeletons. The algorithm assists cyclic movements of the human extremities by synchronizing actuator torques with the estimated net torque exerted by the muscles. Synchronization is produced by a nonlinear dynamical system combining an adaptive frequency oscillator with a form of adaptive Fourier analysis. The system extracts, in real time, the fundamental frequency component of the net muscle torque acting on a specific joint. Said component, nearly sinusoidal in shape, is the basis for the assistive torque waveform delivered by the exoskeleton. The action of the exoskeleton can be interpreted as a virtual reduction in the mechanical impedance of the leg. We studied the ability of human subjects to adapt their muscle activation to the assistive torque. Ten subjects swung their extended leg while coupled to a stationary hip joint exoskeleton. The experiment yielded a significant decrease, with respect to unassisted movement, of the activation levels of an agonist/antagonist pair of muscles controlling the hip joint's motion, which suggests the exoskeleton control has potential for assisting human gait. A moderate increase in swing frequency was observed as well. We theorize that the increase in frequency can be explained by the impedance model of the assisted leg. Per this model, subjects adjust their swing frequency in order to control the amount of reduction in net muscle torque. © IMechE 2015.

  20. Electric-field assisted spin torque nano-oscillator and binary frequency shift keying modulation

    NASA Astrophysics Data System (ADS)

    Zhang, Xiangli; Chen, Hao-Hsuan; Zhang, Zongzhi; Liu, Yaowen

    2018-04-01

    Electric-controlled magnetization precession introduces technologically relevant possibility for developing spin torque nano-oscillators (STNO) with potential applications in microwave emission. Using the perpendicularly magnetized magnetic tunnel junction (MTJ), we show that the magnetization oscillation frequency can be tuned by the co-action of electric field and spin polarized current. The dynamical phase diagram of MTJ-based STNO is analytically predicted through coordinate transformation from the laboratory frame to the rotation frame, by which the nonstationary out-of-plane magnetization precession process is therefore transformed into the stationary process in the rotation frame. Furthermore, using this STNO as a microwave source, we numerically demonstrate that the bit signal can be transmitted by a binary frequency shift keying (BFSK) modulation technique. The BFSK scheme shows good modulation features with no transient state.

  1. Low-Frequency Cortical Oscillations Entrain to Subthreshold Rhythmic Auditory Stimuli

    PubMed Central

    Schroeder, Charles E.; Poeppel, David; van Atteveldt, Nienke

    2017-01-01

    Many environmental stimuli contain temporal regularities, a feature that 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 and electrocorticography 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 prethreshold entrainment. These auditory-evoked responses, distinguished by robust, broad-band increases in intertrial coherence, 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 STATEMENT The 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 activity to

  2. AlGaN/GaN-HEMTs with a breakdown voltage higher than 100 V and maximum oscillation frequency f{sub max} as high as 100 GHz

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Mokerov, V. G., E-mail: vgmokerov@yandex.ru; Kuznetsov, A. L.; Fedorov, Yu. V.

    2009-04-15

    The N-Al{sub 0.27}Ga{sub 0.73}N/GaN High Electron Mobility Transistors (HEMTs) with different gate lengths L{sub g} (ranging from 170 nm to 0.5 {mu}m) and gate widths W{sub s} (ranging from 100 to 1200 {mu}m) have been studied. The S parameters have been measured; these parameters have been used to determine the current-gain cutoff frequency f{sub t}, the maximum oscillation frequency f{sub max}, and the power gain MSG/MAG and Mason's coefficients were investigated in the frequency range from 10 MHz to 67 GHz in relation to the gate length and gate width. It was found that the frequencies f{sub t} and f{submore » max} attain their maximum values of f{sub t} = 48 GHz and f{sub max} = 100 GHz at L{sub g} = 170 nm and W{sub g} = 100 {mu}m. The optimum values of W{sub g} and output power P out of the basic transistors have been determined for different frequencies of operation. It has also been demonstrated that the 170 nm Al{sub 0.27}Ga{sub 0.73}N/GaN HEMT technology provides both good frequency characteristics and high breakdown voltages and is very promising for high-frequency applications (up to 40 GHz)« less

  3. High frequency vibration analysis by the complex envelope vectorization.

    PubMed

    Giannini, O; Carcaterra, A; Sestieri, A

    2007-06-01

    The complex envelope displacement analysis (CEDA) is a procedure to solve high frequency vibration and vibro-acoustic problems, providing the envelope of the physical solution. CEDA is based on a variable transformation mapping the high frequency oscillations into signals of low frequency content and has been successfully applied to one-dimensional systems. However, the extension to plates and vibro-acoustic fields met serious difficulties so that a general revision of the theory was carried out, leading finally to a new method, the complex envelope vectorization (CEV). In this paper the CEV method is described, underlying merits and limits of the procedure, and a set of applications to vibration and vibro-acoustic problems of increasing complexity are presented.

  4. Frequency-agile terahertz-wave parametric oscillator in a ring-cavity configuration.

    PubMed

    Minamide, Hiroaki; Ikari, Tomofumi; Ito, Hiromasa

    2009-12-01

    We demonstrate a frequency-agile terahertz wave parametric oscillator (TPO) in a ring-cavity configuration (ring-TPO). The TPO consists of three mirrors and a MgO:LiNbO(3) crystal under noncollinear phase-matching conditions. A novel, fast frequency-tuning method was realized by controlling a mirror of the three-mirror ring cavity. The wide tuning range between 0.93 and 2.7 THz was accomplished. For first demonstration using the ring-TPO, terahertz spectroscopy was performed as the verification of the frequency-agile performance, measuring the transmission spectrum of the monosaccharide glucose. The spectrum was obtained within about 8 s in good comparison to those of Fourier transform infrared spectrometer.

  5. Membrane Properties and the Balance between Excitation and Inhibition Control Gamma-Frequency Oscillations Arising from Feedback Inhibition

    PubMed Central

    Economo, Michael N.; White, John A.

    2012-01-01

    Computational studies as well as in vivo and in vitro results have shown that many cortical neurons fire in a highly irregular manner and at low average firing rates. These patterns seem to persist even when highly rhythmic signals are recorded by local field potential electrodes or other methods that quantify the summed behavior of a local population. Models of the 30–80 Hz gamma rhythm in which network oscillations arise through ‘stochastic synchrony’ capture the variability observed in the spike output of single cells while preserving network-level organization. We extend upon these results by constructing model networks constrained by experimental measurements and using them to probe the effect of biophysical parameters on network-level activity. We find in simulations that gamma-frequency oscillations are enabled by a high level of incoherent synaptic conductance input, similar to the barrage of noisy synaptic input that cortical neurons have been shown to receive in vivo. This incoherent synaptic input increases the emergent network frequency by shortening the time scale of the membrane in excitatory neurons and by reducing the temporal separation between excitation and inhibition due to decreased spike latency in inhibitory neurons. These mechanisms are demonstrated in simulations and in vitro current-clamp and dynamic-clamp experiments. Simulation results further indicate that the membrane potential noise amplitude has a large impact on network frequency and that the balance between excitatory and inhibitory currents controls network stability and sensitivity to external inputs. PMID:22275859

  6. Hippocampal Ripple Oscillations and Inhibition-First Network Models: Frequency Dynamics and Response to GABA Modulators.

    PubMed

    Donoso, José R; Schmitz, Dietmar; Maier, Nikolaus; Kempter, Richard

    2018-03-21

    consolidation of memories. During deep sleep and resting periods, the hippocampus generates high-frequency (∼200 Hz) oscillations called ripples, which are important for memory consolidation. The mechanisms underlying ripple generation are not well understood. A prominent hypothesis holds that the ripples are generated by local recurrent networks of inhibitory neurons. Using computational models and experiments in brain slices from rodents, we show that the dynamics of interneuron networks clarify several previously unexplained characteristics of ripple oscillations, which advances our understanding of hippocampus-dependent memory consolidation. Copyright © 2018 the authors 0270-6474/18/383125-23$15.00/0.

  7. Asymptotic theory of intermediate- and high-degree solar acoustic oscillations

    NASA Technical Reports Server (NTRS)

    Brodsky, M.; Vorontsov, S. V.

    1993-01-01

    A second-order asymptotic approximation is developed for adiabatic nonradial p-modes of a spherically symmetric star. The exact solutions of adiabatic oscillations are assumed in the outermost layers, where the asymptotic description becomes invalid, which results in a eigenfrequency equation with model-dependent surface phase shift. For lower degree modes, the phase shift is a function of frequency alone; for high-degree modes, its dependence on the degree is explicitly taken into account.

  8. Effect of artificially lengthened vocal tract on vocal fold oscillation's fundamental frequency.

    PubMed

    Hanamitsu, Masakazu; Kataoka, Hideyuki

    2004-06-01

    The fundamental frequency of vocal fold oscillation (F(0)) is controlled by laryngeal mechanics and aerodynamic properties. F(0) change per unit change of transglottal pressure (dF/dP) using a shutter valve has been studied and found to have nonlinear, V-shaped relationship with F(0). On the other hand, the vocal tract is also known to affect vocal fold oscillation. This study examined the effect of artificially lengthened vocal tract length on dF/dP. dF/dP was measured in six men using two mouthpieces of different lengths. The dF/dP graph for the longer vocal tract was shifted leftward relative to the shorter one. Using the one-mass model, the nadir of the "V" on the dF/dP graph was strongly influenced by the resonance around the first formant frequency. However, a more precise model is needed to account for the effects of viscosity and turbulence.

  9. Carrier-envelope frequency stabilization of a Ti:sapphire oscillator using different pump lasers.

    PubMed

    Vernaleken, Andreas; Schmidt, Bernhard; Wolferstetter, Martin; Hänsch, Theodor W; Holzwarth, Ronald; Hommelhoff, Peter

    2012-07-30

    We investigate the suitability of various commercially available pump lasers for operation with a carrier-envelope offset frequency stabilized Ti:sapphire oscillator. Although the tested pump lasers differ in their setup and properties (e.g., single vs. multi-mode), we find that they are all well-suited for the purpose. The residual rms phase noise (integrated between 20 Hz and 5 MHz) of the stabilized oscillator is found to be below 160 mrad with each pump laser, corresponding to less than 1/40 of an optical cycle. Differences in performance vary slightly. In particular, our results indicate that the latest generation of multi-mode pump lasers can be used for applications where precise phase control of the oscillator is strictly required.

  10. Synchronous high-frequency oscillations in inhibitory-dominant network motifs consisting of three dentate gyrus-CA3 systems

    NASA Astrophysics Data System (ADS)

    Zhang, Liyuan; Fan, Denggui; Wang, Qingyun

    2018-06-01

    Studies on the structural-functional connectomes of the human brain have demonstrated the existence of synchronous firings in a specific brain network motif. In particular, synchronization of high-frequency oscillations (HFOs) has been observed in the experimental data sets of temporal lobe epilepsy (TLE). In addition, both clinical and experimental evidences have accumulated to demonstrate the effect of electrical stimulation on TLE, which, however, remains largely unexplored. In this work, we first employ our previously proposed dentate gyrus (DG)-CA3 network model to investigate the influence of an external electrical stimulus on the HFO transitions. The results indicate that the reinforcing stimulus can induce the HFO transitions of the DG-CA3 system from the gamma band to the fast ripples band. Along with that, the consistent oscillations of neurons within DG-CA3 can also be enhanced with the increasing of stimulus. Then, we expand into a simple motif of three coupled DG-CA3 systems in both the feedforward inhibition and feedback inhibition connections, to investigate the synchronous evolutions of HFOs by regulating both the stimulation strength and inhibitory function. It is shown that the comprehensive effects, which lead to band transition, are independent of the motif configurations. The enhanced external electrical stimulus weakens the synchronism and correlation of connected motifs. In contrast, we demonstrate that the increased inhibitory coupling could facilitate correlation to some extent. Overall, our work highlights the possible origin of synchronous HFOs of hippocampal motifs governed by external inputs and inhibitory connection, which might contribute to a better understanding of the interplay between synchronization dynamics and epileptic structure in the human brain.

  11. Super-spinning compact objects and models of high-frequency quasi-periodic oscillations observed in Galactic microquasars

    NASA Astrophysics Data System (ADS)

    Kotrlová, Andrea; Török, Gabriel; Šrámková, Eva; Stuchlík, Zdeněk

    2014-12-01

    We have previously applied several models of high-frequency quasi-periodic oscillations (HF QPOs) to estimate the spin of the central Kerr black hole in the three Galactic microquasars, GRS 1915+105, GRO J1655-40, and XTE J1550-564. Here we explore the alternative possibility that the central compact body is a super-spinning object (or a naked singularity) with the external space-time described by Kerr geometry with a dimensionless spin parameter a ≡ cJ/GM2> 1. We calculate the relevant spin intervals for a subset of HF QPO models considered in the previous study. Our analysis indicates that for all but one of the considered models there exists at least one interval of a> 1 that is compatible with constraints given by the ranges of the central compact object mass independently estimated for the three sources. For most of the models, the inferred values of a are several times higher than the extreme Kerr black hole value a = 1. These values may be too high since the spin of superspinars is often assumed to rapidly decrease due to accretion when a ≫ 1. In this context, we conclude that only the epicyclic and the Keplerian resonance model provides estimates that are compatible with the expectation of just a small deviation from a = 1.

  12. Abnormal excitability and episodic low-frequency oscillations in the cerebral cortex of the tottering mouse.

    PubMed

    Cramer, Samuel W; Popa, Laurentiu S; Carter, Russell E; Chen, Gang; Ebner, Timothy J

    2015-04-08

    The Ca(2+) channelopathies caused by mutations of the CACNA1A gene that encodes the pore-forming subunit of the human Cav2.1 (P/Q-type) voltage-gated Ca(2+) channel include episodic ataxia type 2 (EA2). Although, in EA2 the emphasis has been on cerebellar dysfunction, patients also exhibit episodic, nonmotoric abnormalities involving the cerebral cortex. This study demonstrates episodic, low-frequency oscillations (LFOs) throughout the cerebral cortex of tottering (tg/tg) mice, a widely used model of EA2. Ranging between 0.035 and 0.11 Hz, the LFOs in tg/tg mice can spontaneously develop very high power, referred to as a high-power state. The LFOs in tg/tg mice are mediated in part by neuronal activity as tetrodotoxin decreases the oscillations and cortical neuron discharge contain the same low frequencies. The high-power state involves compensatory mechanisms because acutely decreasing P/Q-type Ca(2+) channel function in either wild-type (WT) or tg/tg mice does not induce the high-power state. In contrast, blocking l-type Ca(2+) channels, known to be upregulated in tg/tg mice, reduces the high-power state. Intriguingly, basal excitatory glutamatergic neurotransmission constrains the high-power state because blocking ionotropic or metabotropic glutamate receptors results in high-power LFOs in tg/tg but not WT mice. The high-power LFOs are decreased markedly by acetazolamide and 4-aminopyridine, the primary treatments for EA2, suggesting disease relevance. Together, these results demonstrate that the high-power LFOs in the tg/tg cerebral cortex represent a highly abnormal excitability state that may underlie noncerebellar symptoms that characterize CACNA1A mutations. Copyright © 2015 the authors 0270-6474/15/355664-16$15.00/0.

  13. Plasma Oscillation Characterization of NASA's HERMeS Hall Thruster via High Speed Imaging

    NASA Technical Reports Server (NTRS)

    Huang, Wensheng; Kamhawi, Hani; Haag, Thomas W.

    2016-01-01

    The performance and facility effect characterization tests of NASA's 12.5-kW Hall Effect Rocket with Magnetic Shielding had been completed. As a part of these tests, three plasma oscillation characterization studies were performed to help determine operation settings and quantify margins. The studies included the magnetic field strength variation study, background pressure effect study, and cathode flow fraction study. Separate high-speed videos of the thruster including the cathode and of only the cathode were recorded. Breathing mode at 10-15 kHz and cathode gradient-driven mode at 60-75 kHz were observed. An additional high frequency (40-70 kHz) global oscillation mode with sinusoidal probability distribution function was identified.

  14. Automated Detector of High Frequency Oscillations in Epilepsy Based on Maximum Distributed Peak Points.

    PubMed

    Ren, Guo-Ping; Yan, Jia-Qing; Yu, Zhi-Xin; Wang, Dan; Li, Xiao-Nan; Mei, Shan-Shan; Dai, Jin-Dong; Li, Xiao-Li; Li, Yun-Lin; Wang, Xiao-Fei; Yang, Xiao-Feng

    2018-02-01

    High frequency oscillations (HFOs) are considered as biomarker for epileptogenicity. Reliable automation of HFOs detection is necessary for rapid and objective analysis, and is determined by accurate computation of the baseline. Although most existing automated detectors measure baseline accurately in channels with rare HFOs, they lose accuracy in channels with frequent HFOs. Here, we proposed a novel algorithm using the maximum distributed peak points method to improve baseline determination accuracy in channels with wide HFOs activity ranges and calculate a dynamic baseline. Interictal ripples (80-200[Formula: see text]Hz), fast ripples (FRs, 200-500[Formula: see text]Hz) and baselines in intracerebral EEGs from seven patients with intractable epilepsy were identified by experienced reviewers and by our computer-automated program, and the results were compared. We also compared the performance of our detector to four well-known detectors integrated in RIPPLELAB. The sensitivity and specificity of our detector were, respectively, 71% and 75% for ripples and 66% and 84% for FRs. Spearman's rank correlation coefficient comparing automated and manual detection was [Formula: see text] for ripples and [Formula: see text] for FRs ([Formula: see text]). In comparison to other detectors, our detector had a relatively higher sensitivity and specificity. In conclusion, our automated detector is able to accurately calculate a dynamic iEEG baseline in different HFO activity channels using the maximum distributed peak points method, resulting in higher sensitivity and specificity than other available HFO detectors.

  15. Adaptive Injection-locking Oscillator Array for RF Spectrum Analysis

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Leung, Daniel

    2011-04-19

    A highly parallel radio frequency receiver using an array of injection-locking oscillators for on-chip, rapid estimation of signal amplitudes and frequencies is considered. The oscillators are tuned to different natural frequencies, and variable gain amplifiers are used to provide negative feedback to adapt the locking band-width with the input signal to yield a combined measure of input signal amplitude and frequency detuning. To further this effort, an array of 16 two-stage differential ring oscillators and 16 Gilbert-cell mixers is designed for 40-400 MHz operation. The injection-locking oscillator array is assembled on a custom printed-circuit board. Control and calibration is achievedmore » by on-board microcontroller.« less

  16. Stabilising high energy orbit oscillations by the utilisation of centrifugal effects for rotating-tyre-induced energy harvesting

    NASA Astrophysics Data System (ADS)

    Zhang, Yunshun; Zheng, Rencheng; Nakano, Kimihiko; Cartmell, Matthew P.

    2018-04-01

    Nonlinear energy harvesters are frequently considered in preference to linear devices because they can potentially overcome the narrow frequency bandwidth limitations inherent to linear variants; however, the possibility of variable harvesting efficiency is raised for the nonlinear case. This paper proposes a rotational energy harvester which may be fitted into an automobile tyre, with the advantage that it may broaden the rotating frequency bandwidth and simultaneously stabilise high-energy orbit oscillations. By consideration of the centrifugal effects due to rotation, the overall restoring force will potentially be increased for a cantilever implemented within the harvester, and this manifests as an increase in its equivalent elastic stiffness. In addition, this study reveals that the initial potential well barriers become as shallow as those for a bistable system. When the rotational frequency increases beyond an identifiable boundary frequency, the system transforms into one with a potential barrier of a typical monostable system. On this basis, the inter-well motion of the bistable system can provide sufficient kinetic energy so that the cantilever maintains its high-energy orbit oscillation for monostable hardening behaviour. Furthermore, in a vehicle drive experiment, it has been shown that the effective rotating frequency bandwidth can be widened from 15 km/h-25 km/h to 10 km/h-40 km/h. In addition, it is confirmed that the centrifugal effects can improve the harvester performance, producing a mean power of 61 μW at a driving speed of 40 km/h, and this is achieved by stabilising the high-energy orbit oscillations of the rotational harvester.

  17. An X-band phase-locked relativistic backward wave oscillator

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wu, Y.; Science and Technology on High Power Microwave Laboratory, Mianyang 621900; Li, Z. H.

    2015-08-15

    For the purpose of coherent high power microwave combining at high frequency band, an X-band phase-locked relativistic backward wave oscillator is presented and investigated. The phase-locking of the oscillator is accomplished by modulation of the electron beam before it reaches the oscillator. To produce a bunched beam with an acceptable injected RF power requirement, an overmoded input cavity is employed to provide initial density modulation. And a buncher cavity is introduced to further increase the modulation depth. When the beam enters the oscillator, the modulation depth is enough to lock the frequency and phase of the output microwave generated bymore » the oscillator. Particle-in-cell simulation shows that an input power of 90 kW is sufficient to lock the frequency and phase of 1.5 GW output microwave with locking bandwidth of 60 MHz.« less

  18. GNSS Signal Tracking Performance Improvement for Highly Dynamic Receivers by Gyroscopic Mounting Crystal Oscillator

    PubMed Central

    Abedi, Maryam; Jin, Tian; Sun, Kewen

    2015-01-01

    In this paper, the efficiency of the gyroscopic mounting method is studied for a highly dynamic GNSS receiver’s reference oscillator for reducing signal loss. Analyses are performed separately in two phases, atmospheric and upper atmospheric flights. Results show that the proposed mounting reduces signal loss, especially in parts of the trajectory where its probability is the highest. This reduction effect appears especially for crystal oscillators with a low elevation angle g-sensitivity vector. The gyroscopic mounting influences frequency deviation or jitter caused by dynamic loads on replica carrier and affects the frequency locked loop (FLL) as the dominant tracking loop in highly dynamic GNSS receivers. In terms of steady-state load, the proposed mounting mostly reduces the frequency deviation below the one-sigma threshold of FLL (1σFLL). The mounting method can also reduce the frequency jitter caused by sinusoidal vibrations and reduces the probability of signal loss in parts of the trajectory where the other error sources accompany this vibration load. In the case of random vibration, which is the main disturbance source of FLL, gyroscopic mounting is even able to suppress the disturbances greater than the three-sigma threshold of FLL (3σFLL). In this way, signal tracking performance can be improved by the gyroscopic mounting method for highly dynamic GNSS receivers. PMID:26404286

  19. GNSS Signal Tracking Performance Improvement for Highly Dynamic Receivers by Gyroscopic Mounting Crystal Oscillator.

    PubMed

    Abedi, Maryam; Jin, Tian; Sun, Kewen

    2015-08-31

    In this paper, the efficiency of the gyroscopic mounting method is studied for a highly dynamic GNSS receiver's reference oscillator for reducing signal loss. Analyses are performed separately in two phases, atmospheric and upper atmospheric flights. Results show that the proposed mounting reduces signal loss, especially in parts of the trajectory where its probability is the highest. This reduction effect appears especially for crystal oscillators with a low elevation angle g-sensitivity vector. The gyroscopic mounting influences frequency deviation or jitter caused by dynamic loads on replica carrier and affects the frequency locked loop (FLL) as the dominant tracking loop in highly dynamic GNSS receivers. In terms of steady-state load, the proposed mounting mostly reduces the frequency deviation below the one-sigma threshold of FLL (1σ(FLL)). The mounting method can also reduce the frequency jitter caused by sinusoidal vibrations and reduces the probability of signal loss in parts of the trajectory where the other error sources accompany this vibration load. In the case of random vibration, which is the main disturbance source of FLL, gyroscopic mounting is even able to suppress the disturbances greater than the three-sigma threshold of FLL (3σ(FLL)). In this way, signal tracking performance can be improved by the gyroscopic mounting method for highly dynamic GNSS receivers.

  20. Wavelet transform analysis to assess oscillations in pial artery pulsation at the human cardiac frequency.

    PubMed

    Winklewski, P J; Gruszecki, M; Wolf, J; Swierblewska, E; Kunicka, K; Wszedybyl-Winklewska, M; Guminski, W; Zabulewicz, J; Frydrychowski, A F; Bieniaszewski, L; Narkiewicz, K

    2015-05-01

    Pial artery adjustments to changes in blood pressure (BP) may last only seconds in humans. Using a novel method called near-infrared transillumination backscattering sounding (NIR-T/BSS) that allows for the non-invasive measurement of pial artery pulsation (cc-TQ) in humans, we aimed to assess the relationship between spontaneous oscillations in BP and cc-TQ at frequencies between 0.5 Hz and 5 Hz. We hypothesized that analysis of very short data segments would enable the estimation of changes in the cardiac contribution to the BP vs. cc-TQ relationship during very rapid pial artery adjustments to external stimuli. BP and pial artery oscillations during baseline (70s and 10s signals) and the response to maximal breath-hold apnea were studied in eighteen healthy subjects. The cc-TQ was measured using NIR-T/BSS; cerebral blood flow velocity, the pulsatility index and the resistive index were measured using Doppler ultrasound of the left internal carotid artery; heart rate and beat-to-beat systolic and diastolic blood pressure were recorded using a Finometer; end-tidal CO2 was measured using a medical gas analyzer. Wavelet transform analysis was used to assess the relationship between BP and cc-TQ oscillations. The recordings lasting 10s and representing 10 cycles with a frequency of ~1 Hz provided sufficient accuracy with respect to wavelet coherence and wavelet phase coherence values and yielded similar results to those obtained from approximately 70cycles (70s). A slight but significant decrease in wavelet coherence between augmented BP and cc-TQ oscillations was observed by the end of apnea. Wavelet transform analysis can be used to assess the relationship between BP and cc-TQ oscillations at cardiac frequency using signals intervals as short as 10s. Apnea slightly decreases the contribution of cardiac activity to BP and cc-TQ oscillations. Copyright © 2015 Elsevier Inc. All rights reserved.

  1. Observation of beat oscillation generation by coupled waves associated with parametric decay during radio frequency wave heating of a spherical tokamak plasma.

    PubMed

    Nagashima, Yoshihiko; Oosako, Takuya; Takase, Yuichi; Ejiri, Akira; Watanabe, Osamu; Kobayashi, Hiroaki; Adachi, Yuuki; Tojo, Hiroshi; Yamaguchi, Takashi; Kurashina, Hiroki; Yamada, Kotaro; An, Byung Il; Kasahara, Hiroshi; Shimpo, Fujio; Kumazawa, Ryuhei; Hayashi, Hiroyuki; Matsuzawa, Haduki; Hiratsuka, Junichi; Hanashima, Kentaro; Kakuda, Hidetoshi; Sakamoto, Takuya; Wakatsuki, Takuma

    2010-06-18

    We present an observation of beat oscillation generation by coupled modes associated with parametric decay instability (PDI) during radio frequency (rf) wave heating experiments on the Tokyo Spherical Tokamak-2. Nearly identical PDI spectra, which are characterized by the coexistence of the rf pump wave, the lower-sideband wave, and the low-frequency oscillation in the ion-cyclotron range of frequency, are observed at various locations in the edge plasma. A bispectral power analysis was used to experimentally discriminate beat oscillation from the resonant mode for the first time. The pump and lower-sideband waves have resonant mode components, while the low-frequency oscillation is exclusively excited by nonlinear coupling of the pump and lower-sideband waves. Newly discovered nonlocal transport channels in spectral space and in real space via PDI are described.

  2. Effect of High-Frequency Oscillations on Cough Peak Flows Generated by Mechanical In-Exsufflation in Medically Stable Subjects With Amyotrophic Lateral Sclerosis.

    PubMed

    Sancho, Jesús; Bures, Enric; de La Asunción, Saray; Servera, Emilio

    2016-08-01

    Mechanically assisted coughing with mechanical in-exsufflation (MI-E) is recommended for noninvasive management of respiratory secretions in amyotrophic lateral sclerosis (ALS). To improve the effectiveness of the technique, a new device combining MI-E with high-frequency oscillations (HFO) has been developed. This work aimed to assess the effect of HFO on the cough peak flow generated by MI-E in medically stable subjects with ALS. This was a prospective study that included subjects with ALS in a medically stable condition. Cough peak flow generated by MI-E was measured in 4 situations: without HFO, with HFO during insufflation, with HFO during exsufflation, and with HFO in both cycles. The parameters used were: insufflation pressure of +40 cm H2O, exsufflation pressure of -40 cm H2O, insufflation time 2 s, exsufflation time 3 s, amplitude of oscillations 10 cm H2O, and frequency of oscillations 15 Hz. Forty-seven subjects with ALS were included: 66% males, 68.2 ± 9.2 y, 40% with bulbar onset, FVC = 1.7 ± 1.1 L, percent-of-predicted FVC = 54.4 ± 26.6%, cough peak flow = 3.8 ± 2.2 L/s, PImax = -39.4 ± 26.4 cm H2O, revised ALS scale = 28.5 ± 9.3, Norris bulbar subscore = 26.1 ± 10.4. No statistical differences were found in cough peak flow generated by MI-E in the 4 situations (without HFO = 4.0 ± 1.2 L/s, with insufflation HFO = 3.9 ± 1.2 L/s, with exsufflation HFO = 4.1 ± 1.2 L/s, with in-exsufflation HFO = 3.9 ± 1.1 L/s). The addition of HFO to mechanically assisted coughing with MI-E does not have an effect on the cough peak flow of medically stable subjects with ALS. Copyright © 2016 by Daedalus Enterprises.

  3. Self-shielding printed circuit boards for high frequency amplifiers and transmitters

    NASA Technical Reports Server (NTRS)

    Galvin, D.

    1969-01-01

    Printed circuit boards retaining as much copper as possible provide electromagnetic shielding between stages of the high frequency amplifiers and transmitters. Oscillation is prevented, spurious output signals are reduced, and multiple stages are kept isolated from each other, both thermally and electrically.

  4. An integrated low phase noise radiation-pressure-driven optomechanical oscillator chipset

    PubMed Central

    Luan, Xingsheng; Huang, Yongjun; Li, Ying; McMillan, James F.; Zheng, Jiangjun; Huang, Shu-Wei; Hsieh, Pin-Chun; Gu, Tingyi; Wang, Di; Hati, Archita; Howe, David A.; Wen, Guangjun; Yu, Mingbin; Lo, Guoqiang; Kwong, Dim-Lee; Wong, Chee Wei

    2014-01-01

    High-quality frequency references are the cornerstones in position, navigation and timing applications of both scientific and commercial domains. Optomechanical oscillators, with direct coupling to continuous-wave light and non-material-limited f × Q product, are long regarded as a potential platform for frequency reference in radio-frequency-photonic architectures. However, one major challenge is the compatibility with standard CMOS fabrication processes while maintaining optomechanical high quality performance. Here we demonstrate the monolithic integration of photonic crystal optomechanical oscillators and on-chip high speed Ge detectors based on the silicon CMOS platform. With the generation of both high harmonics (up to 59th order) and subharmonics (down to 1/4), our chipset provides multiple frequency tones for applications in both frequency multipliers and dividers. The phase noise is measured down to −125 dBc/Hz at 10 kHz offset at ~400 μW dropped-in powers, one of the lowest noise optomechanical oscillators to date and in room-temperature and atmospheric non-vacuum operating conditions. These characteristics enable optomechanical oscillators as a frequency reference platform for radio-frequency-photonic information processing. PMID:25354711

  5. 1645-nm single-frequency, injection-seeded Q-switched Er:YAG master oscillator and power amplifier

    NASA Astrophysics Data System (ADS)

    Wang, Shuo; Gao, Chunqing; Shi, Yang; Song, Rui; Na, Quanxin; Gao, Mingwei; Wang, Qing

    2018-02-01

    A 1645-nm injection-seeded Q-switched Er:YAG master oscillator and power amplifier system is reported. The master oscillator generates single-frequency pulse energy of 11.10 mJ with a pulse width of 188.8 ns at 200 Hz. An Er:YAG monolithic nonplanar ring oscillator is employed as a seed laser. The output pulse from the master oscillator is amplified to 14.33-mJ pulse energy through an Er:YAG amplifier, with a pulse width of 183.3 ns. The M2-factors behind the amplifier are 1.14 and 1.23 in x- and y-directions, respectively. The full width at half maximum of the fast Fourier transformation spectrum of the heterodyne beating signal is 2.84 MHz.

  6. High frequency estimation of 2-dimensional cavity scattering

    NASA Astrophysics Data System (ADS)

    Dering, R. S.

    1984-12-01

    This thesis develops a simple ray tracing approximation for the high frequency scattering from a two-dimensional cavity. Whereas many other cavity scattering algorithms are very time consuming, this method is very swift. The analytical development of the ray tracing approach is performed in great detail, and it is shown how the radar cross section (RCS) depends on the cavity's length and width along with the radar wave's angle of incidence. This explains why the cavity's RCS oscillates as a function of incident angle. The RCS of a two dimensional cavity was measured experimentally, and these results were compared to computer calculations based on the high frequency ray tracing theory. The comparison was favorable in the sense that angular RCS minima and maxima were exactly predicted even though accuracy of the RCS magnitude decreased for incident angles far off-axis. Overall, once this method is extended to three dimensions, the technique shows promise as a fast first approximation of high frequency cavity scattering.

  7. Filterless low-phase-noise frequency-quadrupled microwave generation based on a multimode optoelectronic oscillator

    NASA Astrophysics Data System (ADS)

    Teng, Yichao; Zhang, Pin; Zhang, Baofu; Chen, Yiwang

    2018-02-01

    A scheme to realize low-phase-noise frequency-quadrupled microwave generation without any filter is demonstrated. In this scheme, a multimode optoelectronic oscillator is mainly contributed by dual-parallel Mach-Zehnder modulators, fiber, photodetector, and microwave amplifier. The local source signal is modulated by a child MZM (MZMa), which is worked at maximum transmission point. Through properly adjusting the bias voltages of the other child MZM (MZMb) and the parent MZM (MZMc), optical carrier is effectively suppressed and second sidebands are retained, then the survived optical signal is fed back to the photodetector and MZMb to form an optoelectronic hybrid resonator and realize frequency-quadrupled signal generation. Due to the high Q-factor and mode selection effect of the optoelectronic hybrid resonator, compared with the source signal, the generated frequency-quadrupled signal has a lower phase noise. The approach has verified by experiments, and 18, 22, and 26 GHz frequency-quadrupled signal are generated by 4.5, 5.5, and 6.5 GHz local source signals. Compared with 4.5 GHz source signal, the phase noise of generated 18 GHz signal at 10 kHz frequency offset has 26.5 dB reduction.

  8. 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. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.

  9. Frontal Top-Down Signals Increase Coupling of Auditory Low-Frequency Oscillations to Continuous Speech in Human Listeners

    PubMed Central

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

    2015-01-01

    Summary 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. PMID:26028433

  10. Differential Resonant Ring YIG Tuned Oscillator

    NASA Technical Reports Server (NTRS)

    Parrott, Ronald A.

    2010-01-01

    A differential SiGe oscillator circuit uses a resonant ring-oscillator topology in order to electronically tune the oscillator over multi-octave bandwidths. The oscillator s tuning is extremely linear, because the oscillator s frequency depends on the magnetic tuning of a YIG sphere, whose resonant frequency is equal to a fundamental constant times the DC magnetic field. This extremely simple circuit topology uses two coupling loops connecting a differential pair of SiGe bipolar transistors into a feedback configuration using a YIG tuned filter creating a closed-loop ring oscillator. SiGe device technology is used for this oscillator in order to keep the transistor s 1/f noise to an absolute minimum in order to achieve minimum RF phase noise. The single-end resonant ring oscillator currently has an advantage in fewer parts, but when the oscillation frequency is greater than 16 GHz, the package s parasitic behavior couples energy to the sphere and causes holes and poor phase noise performance. This is because the coupling to the YIG is extremely low, so that the oscillator operates at near the unloaded Q. With the differential resonant ring oscillator, the oscillation currents are just in the YIG coupling mechanisms. The phase noise is even better, and the physical size can be reduced to permit monolithic microwave integrated circuit oscillators. This invention is a YIG tuned oscillator circuit making use of a differential topology to simultaneously achieve an extremely broadband electronic tuning range and ultra-low phase noise. As a natural result of its differential circuit topology, all reactive elements, such as tuning stubs, which limit tuning bandwidth by contributing excessive open loop phase shift, have been eliminated. The differential oscillator s open-loop phase shift is associated with completely non-dispersive circuit elements such as the physical angle of the coupling loops, a differential loop crossover, and the high-frequency phase shift of the n

  11. Pyramidal cell-interneuron interactions underlie hippocampal ripple oscillations.

    PubMed

    Stark, Eran; Roux, Lisa; Eichler, Ronny; Senzai, Yuta; Royer, Sebastien; Buzsáki, György

    2014-07-16

    High-frequency ripple oscillations, observed most prominently in the hippocampal CA1 pyramidal layer, are associated with memory consolidation. The cellular and network mechanisms underlying the generation, frequency control, and spatial coherence of the rhythm are poorly understood. Using multisite optogenetic manipulations in freely behaving rodents, we found that depolarization of a small group of nearby pyramidal cells was sufficient to induce high-frequency oscillations, whereas closed-loop silencing of pyramidal cells or activation of parvalbumin- (PV) or somatostatin-immunoreactive interneurons aborted spontaneously occurring ripples. Focal pharmacological blockade of GABAA receptors abolished ripples. Localized PV interneuron activation paced ensemble spiking, and simultaneous induction of high-frequency oscillations at multiple locations resulted in a temporally coherent pattern mediated by phase-locked interneuron spiking. These results constrain competing models of ripple generation and indicate that temporally precise local interactions between excitatory and inhibitory neurons support ripple generation in the intact hippocampus. Copyright © 2014 Elsevier Inc. All rights reserved.

  12. Pyramidal Cell-Interneuron Interactions Underlie Hippocampal Ripple Oscillations

    PubMed Central

    Stark, Eran; Roux, Lisa; Eichler, Ronny; Senzai, Yuta; Royer, Sebastien; Buzsáki, György

    2015-01-01

    SUMMARY High-frequency ripple oscillations, observed most prominently in the hippocampal CA1 pyramidal layer, are associated with memory consolidation. The cellular and network mechanisms underlying the generation, frequency control, and spatial coherence of the rhythm are poorly understood. Using multisite optogenetic manipulations in freely behaving rodents, we found that depolarization of a small group of nearby pyramidal cells was sufficient to induce high-frequency oscillations, whereas closed-loop silencing of pyramidal cells or activation of parvalbumin-(PV) or somatostatin-immunoreactive interneurons aborted spontaneously occurring ripples. Focal pharmacological blockade of GABAA receptors abolished ripples. Localized PV inter-neuron activation paced ensemble spiking, and simultaneous induction of high-frequency oscillations at multiple locations resulted in a temporally coherent pattern mediated by phase-locked inter-neuron spiking. These results constrain competing models of ripple generation and indicate that temporally precise local interactions between excitatory and inhibitory neurons support ripple generation in the intact hippocampus. PMID:25033186

  13. Mechanisms of high-frequency song generation in brachypterous crickets and the role of ghost frequencies.

    PubMed

    Robillard, Tony; Montealegre-Z, Fernando; Desutter-Grandcolas, Laure; Grandcolas, Philippe; Robert, Daniel

    2013-06-01

    Sound production in crickets relies on stridulation, the well-understood rubbing together of a pair of specialised wings. As the file of one wing slides over the scraper of the other, a series of rhythmic impacts causes harmonic oscillations, usually resulting in the radiation of pure tones delivered at low frequencies (2-8 kHz). In the short-winged crickets of the Lebinthini tribe, acoustic communication relies on signals with remarkably high frequencies (>8 kHz) and rich harmonic content. Using several species of the subfamily Eneopterinae, we characterised the morphological and mechanical specialisations supporting the production of high frequencies, and demonstrated that higher harmonics are exploited as dominant frequencies. These specialisations affect the structure of the stridulatory file, the motor control of stridulation and the resonance of the sound radiator. We placed these specialisations in a phylogenetic framework and show that they serve to exploit high-frequency vibrational modes pre-existing in the phylogenetic ancestor. In Eneopterinae, the lower frequency components are harmonically related to the dominant peak, suggesting they are relicts of ancestral carrier frequencies. Yet, such ghost frequencies still occur in the wings' free resonances, highlighting the fundamental mechanical constraints of sound radiation. These results support the hypothesis that such high-frequency songs evolved stepwise, by a form of punctuated evolution that could be related to functional constraints, rather than by only the progressive increase of the ancestral fundamental frequency.

  14. Cryogenic Pound Circuits for Cryogenic Sapphire Oscillators

    NASA Technical Reports Server (NTRS)

    Dick, G. John; Wang, Rabi

    2006-01-01

    Two modern cryogenic variants of the Pound circuit have been devised to increase the frequency stability of microwave oscillators that include cryogenic sapphire-filled cavity resonators. The original Pound circuit is a microwave frequency discriminator that provides feedback to stabilize a voltage-controlled microwave oscillator with respect to an associated cavity resonator. In the present cryogenic Pound circuits, the active microwave devices are implemented by use of state-of-the-art commercially available tunnel diodes that exhibit low flicker noise (required for high frequency stability) and function well at low temperatures and at frequencies up to several tens of gigahertz. While tunnel diodes are inherently operable as amplitude detectors and amplitude modulators, they cannot, by themselves, induce significant phase modulation. Therefore, each of the present cryogenic Pound circuits includes passive circuitry that transforms the AM into the required PM. Each circuit also contains an AM detector that is used to sample the microwave signal at the input terminal of the high-Q resonator for the purpose of verifying the desired AM null at this point. Finally, each circuit contains a Pound signal detector that puts out a signal, at the modulation frequency, having an amplitude proportional to the frequency error in the input signal. High frequency stability is obtained by processing this output signal into feedback to a voltage-controlled oscillator to continuously correct the frequency error in the input signal.

  15. A high-performance Hg(+) trapped ion frequency standard

    NASA Technical Reports Server (NTRS)

    Prestage, J. D.; Tjoelker, R. L.; Dick, G. J.; Maleki, L.

    1992-01-01

    A high-performance frequency standard based on (199)Hg(+) ions confined in a hybrid radio frequency (RF)/dc linear ion trap is demonstrated. This trap permits storage of large numbers of ions with reduced susceptibility to the second-order Doppler effect caused by the RF confining fields. A 160-mHz-wide atomic resonance line for the 40.5-GHz clock transition is used to steer the output of a 5-mHz crystal oscillator to obtain a stability of 2 x 10(exp -15) for 24,000-second averaging times. Measurements with a 37-mHz line width for the Hg(+) clock transition demonstrate that the inherent stability for this frequency standard is better than 1 x 10(exp -15) at 10,000-second averaging times.

  16. A Biochemical Oscillator Using Excitatory Molecules for Nanonetworks.

    PubMed

    Shitiri, Ethungshan; Cho, Ho-Shin

    2016-10-01

    For nanonetworks to be able to achieve large-scale functionality, such as to respond collectively to a trigger, synchrony between nanomachines is essential. However, to facilitate synchronization, some sort of physical clocking mechanism is required, such as the oscillators driven by auto-inhibitory molecules or by auto-inducing molecules. In this study, taking inspiration from the widely studied biological oscillatory phenomena called Calcium (Ca 2+ ) oscillations, we undertake a different approach to design an oscillator. Our model employs three different types of excitatory molecules that work in tandem to generate oscillatory phenomenon in the concentration levels of the molecule of interest. The main objective of the study is to model a high frequency biochemical oscillator, along with the investigations to identify and determine the parameters that affect the period of the oscillations. The investigations entail and highlight the design of the reserve unit, a reservoir of the molecule of interest, as a key factor in realizing a high frequency stable biochemical oscillator.

  17. Combustor oscillating pressure stabilization and method

    DOEpatents

    Gemmen, R.S.; Richards, G.A.; Yip, M.T.J.; Robey, E.H.; Cully, S.R.; Addis, R.E.

    1998-08-11

    High dynamic pressure oscillations in hydrocarbon-fueled combustors typically occur when the transport time of the fuel to the flame front is at some fraction of the acoustic period. These oscillations are reduced to acceptably lower levels by restructuring or repositioning the flame front in the combustor to increase the transport time. A pilot flame front located upstream of the oscillating flame and pulsed at a selected frequency and duration effectively restructures and repositions the oscillating flame in the combustor to alter the oscillation-causing transport time. 7 figs.

  18. Investigation of a High Voltage, High Frequency Power Conditioning System for Use with Flux Compression Generators

    DTIC Science & Technology

    2007-06-01

    missouri.edu Abstract The University of Missouri-Columbia is developing a compact pulsed power system to condition the high current signal from a...flux compression generator (FCG) to the high voltage, high frequency signal required for many pulsed power applications. The system consists of a...non-magnetic core, spiral-wound transformer, series exploding wire fuse, and an oscillating mesoband source. The flux compression generator is being

  19. Spatiotemporal frequency characteristics of cerebral oscillations during the perception of fundamental frequency contour changes in one-syllable intonation.

    PubMed

    Ueno, Sanae; Okumura, Eiichi; Remijn, Gerard B; Yoshimura, Yuko; Kikuchi, Mitsuru; Shitamichi, Kiyomi; Nagao, Kikuko; Mochiduki, Masayuki; Haruta, Yasuhiro; Hayashi, Norio; Munesue, Toshio; Tsubokawa, Tsunehisa; Oi, Manabu; Nakatani, Hideo; Higashida, Haruhiro; Minabe, Yoshio

    2012-05-02

    Accurate perception of fundamental frequency (F0) contour changes in the human voice is important for understanding a speaker's intonation, and consequently also his/her attitude. In this study, we investigated the neural processes involved in the perception of F0 contour changes in the Japanese one-syllable interjection "ne" in 21 native-Japanese listeners. A passive oddball paradigm was applied in which "ne" with a high falling F0 contour, used when urging a reaction from the listener, was randomly presented as a rare deviant among a frequent "ne" syllable with a flat F0 contour (i.e., meaningless intonation). We applied an adaptive spatial filtering method to the neuromagnetic time course recorded by whole-head magnetoencephalography (MEG) and estimated the spatiotemporal frequency dynamics of event-related cerebral oscillatory changes in the oddball paradigm. Our results demonstrated a significant elevation of beta band event-related desynchronization (ERD) in the right temporal and frontal areas, in time windows from 100 to 300 and from 300 to 500 ms after the onset of deviant stimuli (high falling F0 contour). This is the first study to reveal detailed spatiotemporal frequency characteristics of cerebral oscillations during the perception of intonational (not lexical) F0 contour changes in the human voice. The results further confirmed that the right hemisphere is associated with perception of intonational F0 contour information in the human voice, especially in early time windows. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

  20. Ionospheric modifications in high frequency heating experiments

    NASA Astrophysics Data System (ADS)

    Kuo, Spencer P.

    2015-01-01

    Featured observations in high-frequency (HF) heating experiments conducted at Arecibo, EISCAT, and high frequency active auroral research program are discussed. These phenomena appearing in the F region of the ionosphere include high-frequency heater enhanced plasma lines, airglow enhancement, energetic electron flux, artificial ionization layers, artificial spread-F, ionization enhancement, artificial cusp, wideband absorption, short-scale (meters) density irregularities, and stimulated electromagnetic emissions, which were observed when the O-mode HF heater waves with frequencies below foF2 were applied. The implication and associated physical mechanism of each observation are discussed and explained. It is shown that these phenomena caused by the HF heating are all ascribed directly or indirectly to the excitation of parametric instabilities which instigate anomalous heating. Formulation and analysis of parametric instabilities are presented. The results show that oscillating two stream instability and parametric decay instability can be excited by the O-mode HF heater waves, transmitted from all three heating facilities, in the regions near the HF reflection height and near the upper hybrid resonance layer. The excited Langmuir waves, upper hybrid waves, ion acoustic waves, lower hybrid waves, and field-aligned density irregularities set off subsequent wave-wave and wave-electron interactions, giving rise to the observed phenomena.

  1. Spontaneous switching of frequency-locking by periodic stimulus in oscillators of plasmodium of the true slime mold.

    PubMed

    Takamatsu, A; Yamamoto, T; Fujii, T

    2004-01-01

    Microfabrication technique was used to construct a model system with a living cell of plasmodium of the true slime mold, Physarum polycephalum, a living coupled oscillator system. Its parameters can be systematically controlled as in computer simulations, so that results are directly comparable to those of general mathematical models. As the first step, we investigated responses in oscillatory cells, the oscillators of the plasmodium, to periodic stimuli by temperature changes to elucidate characteristics of the cells as nonlinear systems whose internal dynamics are unknown because of their complexity. We observed that the forced oscillator of the plasmodium show 1:1, 2:1, 3:1 frequency locking inside so-called Arnold tongues regions as well as in other nonlinear systems such as chemical systems and other biological systems. In addition, we found spontaneous switching behavior from certain frequency locking states to other states, even under certain fixed parameters. This technique can be applied to more complex systems with multiple elements, such as coupled oscillator systems, and would be useful to investigate complicated phenomena in biological systems such as information processing.

  2. An Optimal Frequency in Ca2+ Oscillations for Stomatal Closure Is an Emergent Property of Ion Transport in Guard Cells.

    PubMed

    Minguet-Parramona, Carla; Wang, Yizhou; Hills, Adrian; Vialet-Chabrand, Silvere; Griffiths, Howard; Rogers, Simon; Lawson, Tracy; Lew, Virgilio L; Blatt, Michael R

    2016-01-01

    Oscillations in cytosolic-free Ca(2+) concentration ([Ca(2+)]i) have been proposed to encode information that controls stomatal closure. [Ca(2+)]i oscillations with a period near 10 min were previously shown to be optimal for stomatal closure in Arabidopsis (Arabidopsis thaliana), but the studies offered no insight into their origins or mechanisms of encoding to validate a role in signaling. We have used a proven systems modeling platform to investigate these [Ca(2+)]i oscillations and analyze their origins in guard cell homeostasis and membrane transport. The model faithfully reproduced differences in stomatal closure as a function of oscillation frequency with an optimum period near 10 min under standard conditions. Analysis showed that this optimum was one of a range of frequencies that accelerated closure, each arising from a balance of transport and the prevailing ion gradients across the plasma membrane and tonoplast. These interactions emerge from the experimentally derived kinetics encoded in the model for each of the relevant transporters, without the need of any additional signaling component. The resulting frequencies are of sufficient duration to permit substantial changes in [Ca(2+)]i and, with the accompanying oscillations in voltage, drive the K(+) and anion efflux for stomatal closure. Thus, the frequency optima arise from emergent interactions of transport across the membrane system of the guard cell. Rather than encoding information for ion flux, these oscillations are a by-product of the transport activities that determine stomatal aperture. © 2016 American Society of Plant Biologists. All Rights Reserved.

  3. Widely tunable opto-electronic oscillator based on a dual frequency laser

    NASA Astrophysics Data System (ADS)

    Maxin, J.; Saleh, K.; Pillet, G.; Morvan, L.; Llopis, O.; Dolfi, D.

    2013-03-01

    We present the stabilization of the beatnote of an Er,Yb:glass Dual Frequency Laser at 1.53 μm with optical fiber delay lines. Instead of standard optoelectronics oscillators, this architecture does not need RF filter and offers a wide tunability from 2.5 to 5.5 GHz. Thank to a fine analysis of the laser RIN to phase noise conversion in the photodiodes, the expected RF-amplifiers noise limit is reached with a phase noise power spectral density of -25 dBc/Hz at 10 Hz (respectively -110 dBc/Hz at 10 kHz) from the carrier over the whole tuning range. Implementation of a double fiber coil architecture improves the oscillator spectral purity: the phase noise reaches a level of -35 dBc/Hz at 10 Hz (respectively -112 dBc/Hz respectively 10 kHz) from the carrier.

  4. High Power Local Oscillator Sources for 1-2 THz

    NASA Technical Reports Server (NTRS)

    Mehdi, Imran; Thomas, Bertrand; Lin, Robert; Maestrini, Alain; Ward, John; Schlecht, Erich; Gill, John; Lee, Choonsup; Chattopadhyay, Goutam; Maiwald, Frank

    2010-01-01

    Recent results from the Heterodyne Instrument for Far-Infrared (HIFI) on the Herschel Space Telescope have confirmed the usefulness of high resolution spectroscopic data for a better understanding of our Universe. This paper will explore the current status of tunable local oscillator sources beyond HIFI and provide demonstration of how power combining of GaAs Schottky diodes can be used to increase both power and upper operating frequency for heterodyne receivers. Availability of power levels greater than 1 watt in the W-band now makes it possible to design a 1900 GHz source with more than 100 microwatts of expected output power.

  5. Regenerator Operation at Very High Frequencies for Microcryocoolers

    NASA Astrophysics Data System (ADS)

    Radebaugh, Ray; O'Gallagher, Agnes

    2006-04-01

    The size of Stirling and Stirling-type pulse tube cryocoolers is dominated by the size of the pressure oscillator. Such cryocoolers typically operate at frequencies up to about 60 Hz for cold-end temperatures above about 60 K. Higher operating frequencies would allow the size and mass of the pressure oscillator to be reduced for a given power input. However, simply increasing the operating frequency leads to large losses in the regenerator. The simple analytical equations derived here show how the right combination of frequency and pressure, along with optimized regenerator geometry, can lead to successful regenerator operation at frequencies up to 1 kHz. Efficient regenerator operation at such high frequencies is possible only with pressures of about 5 to 8 MPa and with very small hydraulic diameters and lengths. Other geometrical parameters must also be optimized for such conditions. The analytical equations are used to provide guidance to the right combination of parameters. We give example numerical calculations with REGEN3.2 in the paper for 60 Hz, 400 Hz, and 1000 Hz operation of optimized screen regenerators and show that the coefficient of performance at 400 Hz and 1000 Hz is about 78 % and 68 %, respectively, of that for 60 Hz when an average pressure of 7 MPa is used with the higher frequency, compared with 2.5 MPa for 60 Hz operation. The 1000 Hz coefficient of performance for parallel tubes is about the same as that of the screen geometry at 60 Hz. The compressor and cold-end swept volumes are reduced by a factor of 47 at 1000 Hz, compared with the 60 Hz case for the same input acoustic power, which can enable the development of microcryocoolers for MEMS applications.

  6. 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.

  7. Electronically tunable phase locked loop oscillator

    NASA Astrophysics Data System (ADS)

    Balasis, M.; Davis, M. R.; Jackson, C. R.

    1982-02-01

    This report describes the design and development of a low noise, high power, variable oscillator incorporating a high 'Q' electronically tunable resonator as the frequency determining element. The VCO provides improved EMC performance in phase locked synthesizers which are a part of communications equipments. The oscillator combines a low noise VMOS transistor with the selectivity and out-of-band attenuation of a coaxial resonator to provide superior EMC performance. Several oscillator designs were examined and the basis for the final configuration is presented. Oscillator noise is discussed and models for analysis are explained. A brass board model was constructed and tested and the technical results are presented.

  8. A revisit to self-excited push pull vacuum tube radio frequency oscillator for ion sources and power measurements

    NASA Astrophysics Data System (ADS)

    Hlondo, L. R.; Lalremruata, B.; Punte, L. R. M.; Rebecca, L.; Lalnunthari, J.; Thanga, H. H.

    2016-04-01

    Self-excited push-pull vacuum tube oscillator is one of the most commonly used oscillators in radio frequency (RF)-ion plasma sources for generation of ions using radio frequency. However, in spite of its fundamental role in the process of plasma formation, the working and operational characteristics are the most frequently skip part in the descriptions of RF ion sources in literatures. A more detailed treatment is given in the present work on the RF oscillator alone using twin beam power tetrodes 829B and GI30. The circuit operates at 102 MHz, and the oscillation conditions, stability in frequency, and RF output power are studied and analyzed. A modified form of photometric method and RF peak voltage detection method are employed to study the variation of the oscillator output power with plate voltage. The power curves obtained from these measurements are quadratic in nature and increase with increase in plate voltage. However, the RF output power as measured by photometric methods is always less than the value calculated from peak voltage measurements. This difference is due to the fact that the filament coil of the ordinary light bulb used as load/detector in photometric method is not a perfect inductor. The effect of inductive reactance on power transfer to load was further investigated and a technique is developed to estimate the amount of power correction needed in the photometric measurement result.

  9. A revisit to self-excited push pull vacuum tube radio frequency oscillator for ion sources and power measurements

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hlondo, L. R.; Lalremruata, B.; Punte, L. R. M.

    Self-excited push-pull vacuum tube oscillator is one of the most commonly used oscillators in radio frequency (RF)-ion plasma sources for generation of ions using radio frequency. However, in spite of its fundamental role in the process of plasma formation, the working and operational characteristics are the most frequently skip part in the descriptions of RF ion sources in literatures. A more detailed treatment is given in the present work on the RF oscillator alone using twin beam power tetrodes 829B and GI30. The circuit operates at 102 MHz, and the oscillation conditions, stability in frequency, and RF output power aremore » studied and analyzed. A modified form of photometric method and RF peak voltage detection method are employed to study the variation of the oscillator output power with plate voltage. The power curves obtained from these measurements are quadratic in nature and increase with increase in plate voltage. However, the RF output power as measured by photometric methods is always less than the value calculated from peak voltage measurements. This difference is due to the fact that the filament coil of the ordinary light bulb used as load/detector in photometric method is not a perfect inductor. The effect of inductive reactance on power transfer to load was further investigated and a technique is developed to estimate the amount of power correction needed in the photometric measurement result.« less

  10. A revisit to self-excited push pull vacuum tube radio frequency oscillator for ion sources and power measurements.

    PubMed

    Hlondo, L R; Lalremruata, B; Punte, L R M; Rebecca, L; Lalnunthari, J; Thanga, H H

    2016-04-01

    Self-excited push-pull vacuum tube oscillator is one of the most commonly used oscillators in radio frequency (RF)-ion plasma sources for generation of ions using radio frequency. However, in spite of its fundamental role in the process of plasma formation, the working and operational characteristics are the most frequently skip part in the descriptions of RF ion sources in literatures. A more detailed treatment is given in the present work on the RF oscillator alone using twin beam power tetrodes 829B and GI30. The circuit operates at 102 MHz, and the oscillation conditions, stability in frequency, and RF output power are studied and analyzed. A modified form of photometric method and RF peak voltage detection method are employed to study the variation of the oscillator output power with plate voltage. The power curves obtained from these measurements are quadratic in nature and increase with increase in plate voltage. However, the RF output power as measured by photometric methods is always less than the value calculated from peak voltage measurements. This difference is due to the fact that the filament coil of the ordinary light bulb used as load/detector in photometric method is not a perfect inductor. The effect of inductive reactance on power transfer to load was further investigated and a technique is developed to estimate the amount of power correction needed in the photometric measurement result.

  11. Analysis of skin blood microflow oscillations in patients with rheumatic diseases

    NASA Astrophysics Data System (ADS)

    Mizeva, Irina; Makovik, Irina; Dunaev, Andrey; Krupatkin, Alexander; Meglinski, Igor

    2017-07-01

    Laser Doppler flowmetry (LDF) has been applied for the assessment of variation in blood microflows in patients with rheumatic diseases and healthy volunteers. Oscillations of peripheral blood microcirculation observed by LDF have been analyzed utilizing a wavelet transform. A higher amplitude of blood microflow oscillations has been observed in a high frequency band (over 0.1 Hz) in patients with rheumatic diseases. Oscillations in the high frequency band decreased in healthy volunteers in response to the cold pressor test, whereas lower frequency pulsations prevailed in patients with rheumatic diseases. A higher perfusion rate at normal conditions was observed in patients, and a weaker response to cold stimulation was observed in healthy volunteers. Analysis of blood microflow oscillations has a high potential for evaluation of mechanisms of blood flow regulation and diagnosis of vascular abnormalities associated with rheumatic diseases.

  12. Continuous High-Frequency Oscillation Therapy in Invasively Ventilated Pediatric Subjects in the Critical Care Setting.

    PubMed

    Morgan, Stephen; Hornik, Christoph P; Patel, Niyati; Williford, Walter L; Turner, David A; Cheifetz, Ira M

    2016-11-01

    Continuous high-frequency oscillation (CHFO) creates a pressure gradient in the small airways that accelerates expiratory flow. The intended use of CHFO therapy is to facilitate secretion removal and treat atelectasis. Our objective was to assess the feasibility, safety, and efficacy of CHFO in the mechanically ventilated pediatric population. After institutional review board approval, we retrospectively reviewed medical records of mechanically ventilated children treated with CHFO (the MetaNeb system) at our institution from July 1, 2007 through August 31, 2012. Patients supported with extracorporeal membrane oxygenation were excluded. We evaluated changes in ventilator settings in subjects with ventilator data documented within 6 h pre- and post-treatment. We evaluated arterial blood gas (ABG) results for individual treatments, comparing ABG results within 8 h pre-therapy to ABG results within 3 h post-treatment. Oxygen index and P aO 2 /F IO 2 were calculated. Demographic data, blood pressure, heart rate, and development of new air leak while being treated with CHFO were recorded. Pre- and post-CHFO measurements were compared using Wilcoxon signed-rank testing. Our cohort included 59 invasively ventilated subjects. Median age was 2 y (range 1 month to 19 y), and median weight was 14 kg (2-81 kg). We evaluated data on 528 total treatments (range per subject 1-39 treatments). Peak inspiratory pressure significantly decreased with CHFO, whereas other parameters, including P aCO 2 and breathing frequency, remained stable. There was no significant change in systolic blood pressure, diastolic blood pressure, or heart rate following treatment with CHFO. One subject (2%) developed a clinically insignificant pneumothorax during CHFO. CHFO is feasible and seems safe in our cohort of mechanically ventilated pediatric subjects. The rate of pneumothorax was consistent with that seen in similar pediatric ICU populations. These preliminary results suggest that CHFO may be

  13. Triple inverter pierce oscillator circuit suitable for CMOS

    DOEpatents

    Wessendorf,; Kurt, O [Albuquerque, NM

    2007-02-27

    An oscillator circuit is disclosed which can be formed using discrete field-effect transistors (FETs), or as a complementary metal-oxide-semiconductor (CMOS) integrated circuit. The oscillator circuit utilizes a Pierce oscillator design with three inverter stages connected in series. A feedback resistor provided in a feedback loop about a second inverter stage provides an almost ideal inverting transconductance thereby allowing high-Q operation at the resonator-controlled frequency while suppressing a parasitic oscillation frequency that is inherent in a Pierce configuration using a "standard" triple inverter for the sustaining amplifier. The oscillator circuit, which operates in a range of 10 50 MHz, has applications for use as a clock in a microprocessor and can also be used for sensor applications.

  14. Note: An approach to measurement of low frequency oscillation amplitude of discharge current of in-orbit Hall thruster.

    PubMed

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

    2014-06-01

    This paper provides a method to measure the amplitude of low frequency oscillation under the on-track working condition, and realizes the sampling by means of adding the circuit design of sampling, low pass filtering by 3 dB at 48.2 kHz, detection and integrating in the filtering unit. The experimental results prove that the measuring device of merely 0.8 g can quantitatively reflect the amplitude of low frequency oscillation in Hall thruster and the maximum deviation of experiment data and theory data is 10% FS.

  15. 80-GHz MMIC HEMT Voltage-Controlled Oscillator

    NASA Technical Reports Server (NTRS)

    Samoska, Lorene; Radisic, Vesna; Micovic, Miro; Hu, Ming; Janke, Paul; Ngo, Catherine; Nguyen, Loi

    2003-01-01

    A voltage-controlled oscillator (VCO) that operates in the frequency range from 77.5 to 83.5 GHz has been constructed in the form of a monolithic microwave integrated circuit (MMIC) that includes high-electron-mobility transistors (HEMTs). This circuit is a prototype of electronically tunable signal sources in the 75-to-110-GHz range, needed for communication, imaging, and automotive radar applications, among others. This oscillator (see Figure 1) includes two AlInAs/GaInAs/InP HEMTs. One HEMT serves mainly as an oscillator gain element. The other HEMT serves mainly as a varactor for controlling the frequency: the frequency-control element is its gate-to-source capacitance, which is varied by changing its gate supply voltage. The gain HEMT is biased for class-A operation (meaning that current is conducted throughout the oscillation cycle). Grounded coplanar waveguides are used as impedance-matching transmission lines, the input and output matching being chosen to sustain oscillation and maximize output power. Air bridges are placed at discontinuities to suppress undesired slot electromagnetic modes. A high density of vias is necessary for suppressing a parallel-plate electromagnetic mode that is undesired because it can propagate energy into the MMIC substrate. Previous attempts at constructing HEMT-based oscillators yielded circuits with relatively low levels of output power and narrow tuning ranges. For example, one HEMT VCO reported in the literature had an output power of 7 dBm (.5 mW) and a tuning range 2-GHz wide centered approximately at a nominal frequency of 77 GHz. In contrast, as shown in Figure 2, the present MMIC HEMT VCO puts out a power of 12.5 dBm (.18 mW) or more over the 6-GHz-wide frequency range from 77.5 to 83.5 GHz

  16. Generation of a tunable environment for electrical oscillator systems.

    PubMed

    León-Montiel, R de J; Svozilík, J; Torres, Juan P

    2014-07-01

    Many physical, chemical, and biological systems can be modeled by means of random-frequency harmonic oscillator systems. Even though the noise-free evolution of harmonic oscillator systems can be easily implemented, the way to experimentally introduce, and control, noise effects due to a surrounding environment remains a subject of lively interest. Here, we experimentally demonstrate a setup that provides a unique tool to generate a fully tunable environment for classical electrical oscillator systems. We illustrate the operation of the setup by implementing the case of a damped random-frequency harmonic oscillator. The high degree of tunability and control of our scheme is demonstrated by gradually modifying the statistics of the oscillator's frequency fluctuations. This tunable system can readily be used to experimentally study interesting noise effects, such as noise-induced transitions in systems driven by multiplicative noise, and noise-induced transport, a phenomenon that takes place in quantum and classical coupled oscillator networks.

  17. The Autonomous Cryocooled Sapphire Oscillator: A Reference for Frequency Stability and Phase Noise Measurements

    NASA Astrophysics Data System (ADS)

    Giordano, V.; Grop, S.; Fluhr, C.; Dubois, B.; Kersalé, Y.; Rubiola, E.

    2016-06-01

    The Cryogenic Sapphire Oscillator (CSO) is the microwave oscillator which feature the highest short-term stability. Our best units exhibit Allan deviation σy (τ) of 4.5x10-16 at 1s, ≈ 1.5x10-16 at 100 s ≤ t ≤ 5,000 s (floor), and ≤ 5x10-15 at one day. The use of a Pulse-Tube cryocooler enables full two year operation with virtually no maintenance. Starting with a short history of the CSO in our lab, we go through the architecture and we provide more details about the resonator, the cryostat, the oscillator loop, and the servo electronics. We implemented three similar oscillators, which enable the evaluation of each with the three- cornered hat method, and provide the potential for Allan deviation measurements at parts of 10-17 level. One of our CSOs (ULISS) is transportable, and goes with a small customized truck. The unique feature of ULISS is that its σy (τ) can be validated at destination by measuring before and after the roundtrip. To this extent, ULISS can be regarded as a traveling standard of frequency stability. The CSOs are a part of the Oscillator IMP project, a platform dedicated to the measurement of noise and short-term stability of oscillators and devices in the whole radio spectrum (from MHz to THz), including microwave photonics. The scope spans from routine measurements to the research on new oscillators, components, and measurement methods.

  18. A low power cryocooled autonomous ultra-stable oscillator

    NASA Astrophysics Data System (ADS)

    Fluhr, C.; Dubois, B.; Grop, S.; Paris, J.; Le Tetû, G.; Giordano, V.

    2016-12-01

    We present the design and the preliminary evaluation of a cryostat equipped with a low power pulse-tube cryocooler intended to maintain near 5 K a high-Q factor sapphire microwave resonator. This cooled resonator constitutes the frequency reference of an ultra-stable oscillator presenting a short term fractional frequency stability of better than 1 ×10-15 . The proposed design enables to reach a state-of-the-art frequency stability with a cryogenic oscillator consuming only 3 kW of electrical power.

  19. Plasma oscillations in a 6-kW magnetically shielded Hall thruster

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Jorns, Benjamin A., E-mail: benjamin.a.jorns@jpl.nasa.gov; Hofer, Richard R.

    2014-05-15

    Plasma oscillations from 0–100 kHz in a 6-kW magnetically shielded Hall thruster are experimentally characterized with a high-speed, optical camera. Two modes are identified at 7–12 kHz and 70–90 kHz. The low frequency mode is found to be azimuthally uniform across the thruster face, while the high frequency oscillation is peaked close to the centerline-mounted cathode with an m = 1 azimuthal dependence. An analysis of these results in the context of wave-based theory suggests that the low frequency wave is the breathing mode oscillation, while the higher frequency mode is gradient-driven. The effect of these oscillations on thruster operation is examined through an analysismore » of thruster discharge current and a comparison with published observations from an unshielded variant of the thruster. Most notably, it is found that although the oscillation spectra of the two thrusters are different, they exhibit nearly identical steady-state behavior.« less

  20. Resonant-tunneling oscillators and multipliers for submillimeter receivers

    NASA Technical Reports Server (NTRS)

    Sollner, T. C. L. Gerhard

    1988-01-01

    Resonant tunneling through double-barrier heterostructures has attracted increasing interest recently, largely because of the fast charge transport it provides. In addition, the negative differential resistance regions that exist in the current-voltage (I-V) curve (peak-to-valley ratios of 3.5:1 at room temperature, and nearly 10:1 at 77 K, were measured) suggest that high-speed devices based on the character of the I-V curve should be possible. For example, the negative differential resistance region is capable of providing the gain necessary for high-frequency oscillations. In the laboratory attempts were made to increase the frequency and power of these oscillators and to demonstrate several different high-frequency devices.

  1. Optical distribution of local oscillators in future telecommunication satellite payloads

    NASA Astrophysics Data System (ADS)

    Benazet, Benoît; Sotom, Michel; Maignan, Michel; Berthon, Jacques

    2017-11-01

    The distribution of high spectral purity reference signals over optical fibre in future telecommunication satellite payloads is presented. Several types of applications are considered, including the distribution of a reference frequency at 10 MHz (Ultra-Stable Reference Oscillator) as well as the distribution of a radiofrequency oscillator around 800 MHz (Master Local Oscillator). The results of both experimental and theoretical studies are reported. In order to meet phase noise requirements for the USRO distribution, the use of an optimised receiver circuit based on an optically synchronised oscillator is investigated. Finally, the optical distribution of microwave local oscillators at frequencies exceeding 20 GHz is described. Such a scheme paves the way to more advanced sub-systems involving optical frequency-mixing and optical transmission of microwave signals, with applications to multiple-beam active antennas.

  2. Demonstration of a Submillimeter-Wave HEMT Oscillator Module at 330 GHz

    NASA Technical Reports Server (NTRS)

    Radisic, Vesna; Deal, W. R.; Mei, X. B.; Yoshida, Wayne; Liu, P. H.; Uyeda, Jansen; Lai, Richard; Samoska, Lorene; Fung, King Man; Gaier, Todd; hide

    2010-01-01

    In this work, radial transitions have been successfully mated with a HEMT-based MMIC (high-electron-mobility-transistor-based monolithic microwave integrated circuit) oscillator circuit. The chip has been assembled into a WR2.2 waveguide module for the basic implementation with radial E-plane probe transitions to convert the waveguide mode to the MMIC coplanar waveguide mode. The E-plane transitions have been directly integrated onto the InP substrate to couple the submillimeter-wave energy directly to the waveguides, thus avoiding wire-bonds in the RF path. The oscillator demonstrates a measured 1.7 percent DC-RF efficiency at the module level. The oscillator chip uses 35-nm-gate-length HEMT devices, which enable the high frequency of oscillation, creating the first demonstration of a packaged waveguide oscillator that operates over 300 GHz and is based on InP HEMT technology. The oscillator chip is extremely compact, with dimensions of only 1.085 x 320 sq mm for a total die size of 0.35 sq mm. This fully integrated, waveguide oscillator module, with an output power of 0.27 mW at 330 GHz, can provide low-mass, low DC-power-consumption alternatives to existing local oscillator schemes, which require high DC power consumption and large mass. This oscillator module can be easily integrated with mixers, multipliers, and amplifiers for building high-frequency transmit and receive systems at submillimeter wave frequencies. Because it requires only a DC bias to enable submillimeter wave output power, it is a simple and reliable technique for generating power at these frequencies. Future work will be directed to further improving the applicability of HEMT transistors to submillimeter wave and terahertz applications. Commercial applications include submillimeter-wave imaging systems for hidden weapons detection, airport security, homeland security, and portable low-mass, low-power imaging systems

  3. Discriminator Stabilized Superconductor/Ferroelectric Thin Film Local Oscillator

    NASA Technical Reports Server (NTRS)

    Romanofsky, Robert R. (Inventor); Miranda, Felix A. (Inventor)

    2000-01-01

    A tunable local oscillator with a tunable circuit that includes a resonator and a transistor as an active element for oscillation. Tuning of the circuit is achieved with an externally applied dc bias across coupled lines on the resonator. Preferably the resonator is a high temperature superconductor microstrip ring resonator with integral coupled lines formed over a thin film ferroelectric material. A directional coupler samples the output of the oscillator which is fed into a diplexer for determining whether the oscillator is performing at a desired frequency. The high-pass and lowpass outputs of the diplexer are connected to diodes respectively for inputting the sampled signals into a differential operational amplifier. The amplifier compares the sampled signals and emits an output signal if there is a difference between the resonant and crossover frequencies. Based on the sampled signal, a bias supplied to the ring resonator is either increased or decreased for raising or lowering the resonant frequency by decreasing or increasing, respectively, the dielectric constant of the ferroelectric.

  4. Tremor amplitude and tremor frequency variability in Parkinson's disease is dependent on activity and synchronisation of central oscillators in basal ganglia.

    PubMed

    Bartolić, Andrej; Pirtosek, Zvezdan; Rozman, Janez; Ribaric, Samo

    2010-02-01

    Rest tremor is one of the four main clinical features of Parkinson's disease (PD), besides rigidity, bradykinesia and postural instability. While rigidity, bradykinesia and postural instability can be explained with changes in neurotransmitter concentrations and neuronal activity in basal ganglia, the pathogenesis of parkinsonian tremor is not fully understood. According to the leading hypothesis tremor is generated by neurons or groups of neurons in the basal ganglia which act as central oscillators and generate repetitive impulses to the muscles of the body parts involved. The exact morphological substrate for central oscillators and the mechanisms leading to their activation are still an object of debate. Peripheral neural structures exert modulatory influence on tremor amplitude, but not on tremor frequency. We hypothesise that rest tremor in PD is the result of two mechanisms: increased activity and increased synchronisation of central oscillators. We tested our hypothesis by demonstrating that the reduction in rest tremor amplitude is accompanied by increased variability of tremor frequency. The reduction of tremor amplitude is attributed to decreased activity and poor synchronisation of central oscillators in basal ganglia; the increased variability of tremor frequency is attributed to poor synchronisation of the central oscillators. In addition, we demonstrated that the recurrence of clinically visible rest tremor is accompanied by a reduction in tremor frequency variability. This reduction is attributed to increased synchronisation of central oscillators in basal ganglia. We argue that both mechanisms, increased activity of central oscillators and increased synchronisation of central oscillators, are equally important and we predict that tremor becomes clinically evident only when both mechanisms are active at the same time. In circumstances when one of the mechanisms is suppressed tremor amplitude becomes markedly reduced. On the one hand, if the number

  5. STUDIES OF THE ORIGIN OF HIGH-FREQUENCY QUASI-PERIODIC OSCILLATIONS OF MASS-ACCRETING BLACK HOLES IN X-RAY BINARIES WITH NEXT-GENERATION X-RAY TELESCOPES

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Beheshtipour, Banafsheh; Hoormann, Janie K.; Krawczynski, Henric, E-mail: b.beheshtipour@wustl.edu

    Observations with RXTE ( Rossi X-ray Timing Explorer ) revealed the presence of high-frequency quasi-periodic oscillations (HFQPOs) of the X-ray flux from several accreting stellar-mass black holes. HFQPOs (and their counterparts at lower frequencies) may allow us to study general relativity in the regime of strong gravity. However, the observational evidence today does not yet allow us to distinguish between different HFQPO models. In this paper we use a general-relativistic ray-tracing code to investigate X-ray timing spectroscopy and polarization properties of HFQPOs in the orbiting Hotspot model. We study observational signatures for the particular case of the 166 Hz quasi-periodicmore » oscillation (QPO) in the galactic binary GRS 1915+105. We conclude with a discussion of the observability of spectral signatures with a timing-spectroscopy experiment such as the LOFT ( Large Observatory for X-ray Timing ) and polarization signatures with space-borne X-ray polarimeters such as IXPE ( Imaging X-ray Polarimetry Explorer ), PolSTAR ( Polarization Spectroscopic Telescope Array ), PRAXyS ( Polarimetry of Relativistic X-ray Sources ), or XIPE ( X-ray Imaging Polarimetry Explorer ). A mission with high count rate such as LOFT would make it possible to get a QPO phase for each photon, enabling the study of the QPO-phase-resolved spectral shape and the correlation between this and the flux level. Owing to the short periods of the HFQPOs, first-generation X-ray polarimeters would not be able to assign a QPO phase to each photon. The study of QPO-phase-resolved polarization energy spectra would thus require simultaneous observations with a first-generation X-ray polarimeter and a LOFT -type mission.« less

  6. On-chip microfluid induced by oscillation of microrobot for noncontact cell transportation

    NASA Astrophysics Data System (ADS)

    Feng, Lin; Liang, Shuzhang; Zhou, Xiangcong; Yang, Jianlei; Jiang, Yonggang; Zhang, Deyuan; Arai, Fumihito

    2017-11-01

    The importance of cell manipulation and cultivation is increasing rapidly in various fields, such as drug discovery, regenerative medicine, and investigation of new energy sources. This paper presents a method to transport cells in a microfluidic chip without contact. A local vortex was generated when high-frequency oscillation of a microtool was induced in a microfluidic chip. The vortex was controlled by tuning the tool's oscillation parameters, such as the oscillation amplitude and frequency. The cells were then transported in the chip based on the direction of the tool's movement, and their position, posture, and trajectories were controlled. Bovine oocyte manipulations, that is, transportation and rotation, were conducted to demonstrate the capability of the proposed method, without any contact by the microrobot with high-frequency oscillation.

  7. Power enhanced frequency conversion system

    NASA Technical Reports Server (NTRS)

    Sanders, Steven (Inventor); Lang, Robert J. (Inventor); Waarts, Robert G. (Inventor)

    2001-01-01

    A frequency conversion system includes at least one source providing a first near-IR wavelength output including a gain medium for providing high power amplification, such as double clad fiber amplifier, a double clad fiber laser or a semiconductor tapered amplifier to enhance the power output level of the near-IR wavelength output. The NFM device may be a difference frequency mixing (DFM) device or an optical parametric oscillation (OPO) device. Pump powers are gain enhanced by the addition of a rare earth amplifier or oscillator, or a Ra-man/Brillouin amplifier or oscillator between the high power source and the NFM device.

  8. Activity patterns in networks stabilized by background oscillations.

    PubMed

    Hoppensteadt, Frank

    2009-07-01

    The brain operates in a highly oscillatory environment. We investigate here how such an oscillating background can create stable organized behavior in an array of neuro-oscillators that is not observable in the absence of oscillation, much like oscillating the support point of an inverted pendulum can stabilize its up position, which is unstable without the oscillation. We test this idea in an array of electronic circuits coming from neuroengineering: we show how the frequencies of the background oscillation create a partition of the state space into distinct basins of attraction. Thus, background signals can stabilize persistent activity that is otherwise not observable. This suggests that an image, represented as a stable firing pattern which is triggered by a voltage pulse and is sustained in synchrony or resonance with the background oscillation, can persist as a stable behavior long after the initial stimulus is removed. The background oscillations provide energy for organized behavior in the array, and these behaviors are categorized by the basins of attraction determined by the oscillation frequencies.

  9. Active power control of solar PV generation for large interconnection frequency regulation and oscillation damping

    DOE PAGES

    Liu, Yong; Zhu, Lin; Zhan, Lingwei; ...

    2015-06-23

    Because of zero greenhouse gas emission and decreased manufacture cost, solar photovoltaic (PV) generation is expected to account for a significant portion of future power grid generation portfolio. Because it is indirectly connected to the power grid via power electronic devices, solar PV generation system is fully decoupled from the power grid, which will influence the interconnected power grid dynamic characteristics as a result. In this study, the impact of solar PV penetration on large interconnected power system frequency response and inter-area oscillation is evaluated, taking the United States Eastern Interconnection (EI) as an example. Furthermore, based on the constructedmore » solar PV electrical control model with additional active power control loops, the potential contributions of solar PV generation to power system frequency regulation and oscillation damping are examined. The advantages of solar PV frequency support over that of wind generator are also discussed. Finally, simulation results demonstrate that solar PV generations can effectively work as ‘actuators’ in alleviating the negative impacts they bring about.« less

  10. AUTOMATIC FREQUENCY CONTROL SYSTEM

    DOEpatents

    Hansen, C.F.; Salisbury, J.D.

    1961-01-10

    A control is described for automatically matching the frequency of a resonant cavity to that of a driving oscillator. The driving oscillator is disconnected from the cavity and a secondary oscillator is actuated in which the cavity is the frequency determining element. A low frequency is mixed with the output of the driving oscillator and the resultant lower and upper sidebands are separately derived. The frequencies of the sidebands are compared with the secondary oscillator frequency. deriving a servo control signal to adjust a tuning element in the cavity and matching the cavity frequency to that of the driving oscillator. The driving oscillator may then be connected to the cavity.

  11. Sea level oscillations over minute timescales: a global perspective

    NASA Astrophysics Data System (ADS)

    Vilibic, Ivica; Sepic, Jadranka

    2016-04-01

    Sea level oscillations occurring over minutes to a few hours are an important contributor to sea level extremes, and a knowledge on their behaviour is essential for proper quantification of coastal marine hazards. Tsunamis, meteotsunamis, infra-gravity waves and harbour oscillations may even dominate sea level extremes in certain areas and thus pose a great danger for humans and coastal infrastructure. Aside for tsunamis, which are, due to their enormous impact to the coastlines, a well-researched phenomena, the importance of other high-frequency oscillations to the sea level extremes is still underrated, as no systematic long-term measurements have been carried out at a minute timescales. Recently, Intergovernmental Oceanographic Commission (IOC) established Sea Level Monitoring Facility portal (http://www.ioc-sealevelmonitoring.org), making 1-min sea level data publicly available for several hundred tide gauge sites in the World Ocean. Thereafter, a global assessment of oscillations over tsunami timescales become possible; however, the portal contains raw sea level data only, being unchecked for spikes, shifts, drifts and other malfunctions of instruments. We present a quality assessment of these data, estimates of sea level variances and contributions of high-frequency processes to the extremes throughout the World Ocean. This is accompanied with assessment of atmospheric conditions and processes which generate intense high-frequency oscillations.

  12. The Influence of the External Signal Modulation Waveform and Frequency on the Performance of a Photonic Forced Oscillator.

    PubMed

    Sánchez-Castro, Noemi; Palomino-Ovando, Martha Alicia; Estrada-Wiese, Denise; Valladares, Nydia Xcaret; Del Río, Jesus Antonio; de la Mora, Maria Beatriz; Doti, Rafael; Faubert, Jocelyn; Lugo, Jesus Eduardo

    2018-05-21

    Photonic crystals have been an object of interest because of their properties to inhibit certain wavelengths and allow the transmission of others. Using these properties, we designed a photonic structure known as photodyne formed by two porous silicon one-dimensional photonic crystals with an air defect between them. When the photodyne is illuminated with appropriate light, it allows us to generate electromagnetic forces within the structure that can be maximized if the light becomes localized inside the defect region. These electromagnetic forces allow the microcavity to oscillate mechanically. In the experiment, a chopper was driven by a signal generator to modulate the laser light that was used. The driven frequency and the signal modulation waveform (rectangular, sinusoidal or triangular) were changed with the idea to find optimal conditions for the structure to oscillate. The microcavity displacement amplitude, velocity amplitude and Fourier spectrum of the latter and its frequency were measured by means of a vibrometer. The mechanical oscillations are modeled and compared with the experimental results and show good agreement. For external frequency values of 5 Hz and 10 Hz, the best option was a sinusoidal waveform, which gave higher photodyne displacements and velocity amplitudes. Nonetheless, for an external frequency of 15 Hz, the best option was the rectangular waveform.

  13. The Influence of the External Signal Modulation Waveform and Frequency on the Performance of a Photonic Forced Oscillator

    PubMed Central

    Sánchez-Castro, Noemi; Palomino-Ovando, Martha Alicia; Estrada-Wiese, Denise; Valladares, Nydia Xcaret; del Río, Jesus Antonio; Doti, Rafael; Faubert, Jocelyn; Lugo, Jesus Eduardo

    2018-01-01

    Photonic crystals have been an object of interest because of their properties to inhibit certain wavelengths and allow the transmission of others. Using these properties, we designed a photonic structure known as photodyne formed by two porous silicon one-dimensional photonic crystals with an air defect between them. When the photodyne is illuminated with appropriate light, it allows us to generate electromagnetic forces within the structure that can be maximized if the light becomes localized inside the defect region. These electromagnetic forces allow the microcavity to oscillate mechanically. In the experiment, a chopper was driven by a signal generator to modulate the laser light that was used. The driven frequency and the signal modulation waveform (rectangular, sinusoidal or triangular) were changed with the idea to find optimal conditions for the structure to oscillate. The microcavity displacement amplitude, velocity amplitude and Fourier spectrum of the latter and its frequency were measured by means of a vibrometer. The mechanical oscillations are modeled and compared with the experimental results and show good agreement. For external frequency values of 5 Hz and 10 Hz, the best option was a sinusoidal waveform, which gave higher photodyne displacements and velocity amplitudes. Nonetheless, for an external frequency of 15 Hz, the best option was the rectangular waveform. PMID:29883393

  14. Oscillations During Thermonuclear X-ray Bursts

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod E.; White, Nicholas E. (Technical Monitor)

    2001-01-01

    High amplitude, nearly coherent X-ray brightness oscillations during thermonuclear X-ray bursts were discovered with the Rossi X-ray Timing Explorer (RXTE) in early 1996. Spectral and timing evidence strongly supports the conclusion that these oscillations are caused by rotational modulation of the burst emission and that they reveal the spin frequency of neutron stars in low mass X-ray binaries, a long sought goal of X-ray astronomy. Studies carried out over the past year have led to the discovery of burst oscillations in four new sources, bringing to ten the number with confirmed burst oscillations. I review the status of our knowledge of these oscillations and indicate how they can be used to probe the physics of neutron stars. For a few burst oscillation sources it has been proposed that the strongest and most ubiquitous frequency is actually the first overtone of the spin frequency and hence that two nearly antipodal hot spots are present on the neutron star. This inference has important implications for both the physics of thermonuclear burning as well as the mass - radius relation for neutron stars, so its confirmation is crucial. I discuss recent attempts to confirm this hypothesis for 4U 1636-53, the source for which a signal at the putative fundamental (290Hz) has, been claimed.

  15. A novel model of interaction between high frequency electromagnetic non-ionizing fields and microtubules viewed as coupled two-degrees of freedom harmonic oscillators.

    PubMed

    Caligiuri, Luigi Maxmilian

    2015-01-01

    The question regarding the potential biological and adverse health effects of non-ionizing electromagnetic fields on living organisms is of primary importance in biophysics and medicine. Despite the several experimental evidences showing such occurrence in a wide frequency range from extremely low frequency to microwaves, a definitive theoretical model able to explain a possible mechanism of interaction between electromagnetic fields and living matter, especially in the case of weak and very weak intensities, is still missing. In this paper it has been suggested a possible mechanism of interaction involving the resonant absorption of electromagnetic radiation by microtubules. To this aim these have been modeled as non-dissipative forced harmonic oscillators characterized by two coupled "macroscopic" degrees of freedom, respectively describing longitudinal and transversal vibrations induced by the electromagnetic field. We have shown that the proposed model, although at a preliminary stage, is able to explain the ability of even weak electromagnetic radiating electromagnetic fields to transfer high quantities of energy to living systems by means of a resonant mechanism, so capable to easily damage microtubules structure.

  16. High Power and Frequency-Agile Optical Parametric Oscillators for Airborne DIAL Measurements of CH4 and H2O

    NASA Astrophysics Data System (ADS)

    Nehrir, A. R.; Shuman, T.; Chuang, T.; Hair, J. W.; Refaat, T. F.; Ismail, S.; Kooi, S. A.; Notari, A.

    2014-12-01

    Atmospheric methane (CH4) has the second largest radiative forcing of the long-lived greenhouse gasses (GHG) after carbon dioxide. However, methane's much shorter atmospheric lifetime and much stronger warming potential make its radiative forcing equivalent to that for CO2 over a 20-year time horizon which makes CH4 a particularly attractive target for mitigation strategies. Similar to CH4, water vapor (H2O) is the most dominant of the short-lived GHG in the atmosphere and plays a key role in many atmospheric processes. Atmospheric H2O concentrations span over four orders of magnitude from the planetary boundary layer where high impact weather initiates to lower levels in the upper troposphere and lower stratosphere (UTLS) where water vapor has significant and long term impacts on the Earth's radiation budget. NASA Langley has fostered the technology development with Fibertek, Inc. to develop frequency agile and high power (> 3 W) pulsed lasers using similar architectures in the 1645 nm and 935 nm spectral bands for DIAL measurements of CH4 and H2O, respectively. Both systems utilize high power 1 kHz pulse repetition frequency Nd:YAG lasers to generate high power laser emission at the desired wavelength via optical parametric oscillators (OPO). The CH4 OPO, currently in its final build stage in a SBIR Phase II program has demonstrated >2 W average power with injection seeding from a distributed feedback (DFB) laser during risk reduction experiments. The H2O OPO has demonstrated high power operation (>2 W) during the SBIR Phase I program while being injection seeded with a DFB laser, and is currently funded via an SBIR Phase II to build a robust system for future integration into an airborne water vapor DIAL system capable of profiling from the boundary layer up to the UTLS. Both systems have demonstrated operation with active OPO wavelength control to allow for optimization of the DIAL measurements for operation at different altitudes and geographic regions. An

  17. Gravitational wave-Gauge field oscillations

    NASA Astrophysics Data System (ADS)

    Caldwell, R. R.; Devulder, C.; Maksimova, N. A.

    2016-09-01

    Gravitational waves propagating through a stationary gauge field transform into gauge field waves and back again. When multiple families of flavor-space locked gauge fields are present, the gravitational and gauge field waves exhibit novel dynamics. At high frequencies, the system behaves like coupled oscillators in which the gravitational wave is the central pacemaker. Due to energy conservation and exchange among the oscillators, the wave amplitudes lie on a multidimensional sphere, reminiscent of neutrino flavor oscillations. This phenomenon has implications for cosmological scenarios based on flavor-space locked gauge fields.

  18. Frequency conversion system

    NASA Technical Reports Server (NTRS)

    Sanders, Steven (Inventor); Lang, Robert J. (Inventor)

    2001-01-01

    Laser diode pumped mid-IR wavelength sources include at least one high power, near-IR wavelength, injection and/or sources wherein one or both of such sources may be tunable providing a pump wave output beam to a quasi-phase matched (QPM) nonlinear frequency mixing (NFM) device. The NFM device may be a difference frequency mixing (DFM) device or an optical parametric oscillation (OPO) device. Wavelength tuning of at least one of the sources advantageously provides the ability for optimizing pump or injection wavelengths to match the QPM properties of the NFM device enabling a broad range of mid-IR wavelength selectivity. Also, pump powers are gain enhanced by the addition of a rare earth amplifier or oscillator, or a Raman/Brillouin amplifier or oscillator between the high power source and the NFM device. Further, polarization conversion using Raman or Brillouin wavelength shifting is provided to optimize frequency conversion efficiency in the NFM device.

  19. Temperature Oscillations in Loop Heat Pipes - A Revisit

    NASA Technical Reports Server (NTRS)

    Ku, Jentung

    2018-01-01

    Three types of temperature oscillation have been observed in the loop heat pipes. The first type is an ultra-high frequency temperature oscillation with a period on the order of seconds or less. This type of temperature oscillation is of little significance in spacecraft thermal control because the amplitude is in the noise level. The second type is a high frequency, low amplitude temperature oscillation with a period on the order of seconds to minutes and an amplitude on the order of one Kelvin. It is caused by the back-and-forth movement of the vapor front near the inlet or outlet of the condenser. The third type is a low frequency, high amplitude oscillation with a period on the order of hours and an amplitude on the order of tens of Kelvin. It is caused by the modulation of the net heat load into the evaporator by the attached large thermal mass which absorbs and releases energy alternately. Several papers on LHP temperature oscillation have been published. This paper presents a further study on the underlying physical processes during the LHP temperature oscillation, with an emphasis on the third type of temperature oscillation. Specifically, equations governing the thermal and hydraulic behaviors of LHP operation will be used to describe interactions among LHP components, heat source, and heat sink. The following sequence of events and their interrelationship will also be explored: 1) maxima and minima of reservoir and thermal mass temperatures; 2) the range of the vapor front movement inside the condenser; 3) rates of change of the reservoir and thermal mass temperatures; 4) the rate of heat absorption and heat release by the thermal mass and the rate of vapor front movement; and 5) inflection points of the reservoir and thermal mass temperatures.

  20. Stable And Oscillating Acoustic Levitation

    NASA Technical Reports Server (NTRS)

    Barmatz, Martin B.; Garrett, Steven L.

    1988-01-01

    Sample stability or instability determined by levitating frequency. Degree of oscillation of acoustically levitated object along axis of levitation chamber controlled by varying frequency of acoustic driver for axis above or below frequency of corresponding chamber resonance. Stabilization/oscillation technique applied in normal Earth gravity, or in absence of gravity to bring object quickly to rest at nominal levitation position or make object oscillate in desired range about that position.

  1. Frequency conversion system

    NASA Technical Reports Server (NTRS)

    Sanders, Steven (Inventor); Waarts, Robert G. (Inventor)

    2001-01-01

    A frequency conversion system comprises first and second gain sources providing first and second frequency radiation outputs where the second gain source receives as input the output of the first gain source and, further, the second gain source comprises a Raman or Brillouin gain fiber for wave shifting a portion of the radiation of the first frequency output into second frequency radiation output to provided a combined output of first and second frequencies. Powers are gain enhanced by the addition of a rare earth amplifier or oscillator, or a Raman/Brillouin amplifier or oscillator between the high power source and the NFM device. Further, polarization conversion using Raman or Brillouin wavelength shifting is provided to optimize frequency conversion efficiency in the NFM device.

  2. Identified Cellular Correlates of Neocortical Ripple and High-Gamma Oscillations during Spindles of Natural Sleep.

    PubMed

    Averkin, Robert G; Szemenyei, Viktor; Bordé, Sándor; Tamás, Gábor

    2016-11-23

    Ultra-high-frequency network events in the hippocampus are instrumental in a dialogue with the neocortex during memory formation, but the existence of transient ∼200 Hz network events in the neocortex is not clear. Our recordings from neocortical layer II/III of freely behaving rats revealed field potential events at ripple and high-gamma frequencies repeatedly occurring at troughs of spindle oscillations during sleep. Juxtacellular recordings identified subpopulations of fast-spiking, parvalbumin-containing basket cells with epochs of firing at ripple (∼200 Hz) and high-gamma (∼120 Hz) frequencies detected during spindles and centered with millisecond precision at the trough of spindle waves in phase with field potential events but phase shifted relative to pyramidal cell firing. The results suggest that basket cell subpopulations are involved in spindle-nested, high-frequency network events that hypothetically provide repeatedly occurring neocortical temporal reference states potentially involved in mnemonic processes. Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.

  3. MMIC Replacement for Gunn Diode Oscillators

    NASA Technical Reports Server (NTRS)

    Crowe, Thomas W.; Porterfield, David

    2011-01-01

    An all-solid-state replacement for high-frequency Gunn diode oscillators (GDOs) has been proposed for use in NASA s millimeter- and submillimeter-wave sensing instruments. Highly developed microwave oscillators are used to achieve a low-noise and highly stable reference signal in the 10-40-GHz band. Compact amplifiers and high-power frequency multipliers extend the signal to the 100-500-GHz band with minimal added phase noise and output power sufficient for NASA missions. This technology can achieve improved output power and frequency agility, while maintaining phase noise and stability comparable to other GDOs. Additional developments of the technology include: a frequency quadrupler to 145 GHz with 18 percent efficiency and 15 percent fixed tuned bandwidth; frequency doublers featuring 124, 240, and 480 GHz; an integrated 874-GHz subharmonic mixer with a mixer noise temperature of 3,000 K DSB (double sideband) and mixer conversion loss of 11.8 dB DSB; a high-efficiency frequency tripler design with peak output power of 23 mW and 14 mW, and efficiency of 16 and 13 percent, respectively; millimeter-wave integrated circuit (MMIC) power amplifiers to the 30-40 GHz band with high DC power efficiency; and an 874-GHz radiometer suitable for airborne observation with state-of-the-art sensitivity at room temperature and less than 5 W of total power consumption.

  4. Time delay generation at high frequency using SOA based slow and fast light.

    PubMed

    Berger, Perrine; Bourderionnet, Jérôme; Bretenaker, Fabien; Dolfi, Daniel; Alouini, Mehdi

    2011-10-24

    We show how Up-converted Coherent Population Oscillations (UpCPO) enable to get rid of the intrinsic limitation of the carrier lifetime, leading to the generation of time delays at any high frequencies in a single SOA device. The linear dependence of the RF phase shift with respect to the RF frequency is theoretically predicted and experimentally evidenced at 16 and 35 GHz. © 2011 Optical Society of America

  5. 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.

  6. Morse oscillator propagator in the high temperature limit I: Theory

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Toutounji, Mohamad, E-mail: Mtoutounji@uaeu.ac.ae

    2017-02-15

    In an earlier work of the author the time evolution of Morse oscillator was studied analytically and exactly at low temperatures whereupon optical correlation functions were calculated using Morse oscillator coherent states were employed. Morse oscillator propagator in the high temperature limit is derived and a closed form of its corresponding canonical partition function is obtained. Both diagonal and off-diagonal forms of Morse oscillator propagator are derived in the high temperature limit. Partition functions of diatomic molecules are calculated. - Highlights: • Derives the quantum propagator of Morse oscillator in the high temperature limit. • Uses the resulting diagonal propagatormore » to derive a closed form of Morse oscillator partition function. • Provides a more sophisticated formula of the quantum propagator to test the accuracy of the herein results.« less

  7. Discovery of Nearly Coherent Oscillations with a Frequency of approximately 567 Hz During Type I X-ray Bursts of the X-ray Transient and Eclipsing Binary X1658-298

    NASA Technical Reports Server (NTRS)

    Wijnands, Rudy; Strohmayer, Tod; Franco, Lucia M.; White, Nicholas E. (Technical Monitor)

    2001-01-01

    We report the discovery of nearly coherent oscillations with a frequency of approximately 567 Hz during type I X-ray bursts from the X-ray transient and eclipsing binary X1658-298. If these oscillations are directly related to the neutron star rotation, then the spin period of the neutron star in X1658-298 is approximately 1.8 ms. The oscillations can be present during the rise or decay phase of the bursts. Oscillations during the decay phase of the bursts show an increase in frequency of approximately 0.5-1 Hz. However, in one particular burst the oscillations reappear at the end of the decay phase at about 571.5 Hz. This represents an increase in oscillation frequency of about 5 Hz, which is the largest frequency change seen so far in a burst oscillation. It is unclear if such a large change can be accommodated by present models used to explain the frequency evolution of the oscillations. The oscillations at 571.5 Hz are unusually soft compared to the oscillations found at 567 Hz. We also observed several bursts during which the oscillations are detected at much lower significance or not at all. Most of these bursts happen during periods of X-ray dipping behavior, suggesting that the X-ray dipping might decrease the amplitude of the oscillations (although several complications exist with this simple picture). We discuss our discovery in the framework of the neutron star spin interpretation.

  8. Prediction of high frequency combustion instability in liquid propellant rocket engines

    NASA Technical Reports Server (NTRS)

    Kim, Y. M.; Chen, C. P.; Ziebarth, J. P.; Chen, Y. S.

    1992-01-01

    The present use of a numerical model developed for the prediction of high-frequency combustion stabilities in liquid propellant rocket engines focuses on (1) the overall behavior of nonlinear combustion instabilities (2) the effects of acoustic oscillations on the fuel-droplet vaporization and combustion process in stable and unstable engine operating conditions, oscillating flowfields, and liquid-fuel trajectories during combustion instability, and (3) the effects of such design parameters as inlet boundary conditions, initial spray conditions, and baffle length. The numerical model has yielded predictions of the tangential-mode combustion instability; baffle length and droplet size variations are noted to have significant effects on engine stability.

  9. Investigation of a compact coaxially fed switched oscillator

    NASA Astrophysics Data System (ADS)

    Wang, Yuwei; Chen, Dongqun; Zhang, Jiande; Cao, Shengguang; Li, Da; Liu, Chebo

    2013-09-01

    To generate a relative high frequency mesoband microwave, a compact coaxially fed transmission line switched oscillator with high voltage capability is investigated. The characteristic impedance and voltage capability of the low impedance transmission line (LITL) have been analyzed. It is shown that the working voltage of the oscillator can reach up to 200 kV when it is filled by pressurized nitrogen and charged by a nanosecond driving source. By utilizing a commercial electromagnetic simulation code, the transient performance of the switched oscillator with a lumped resistance load is simulated. It is illustrated that the center frequency of the output signal reaches up to ˜0.6 GHz when the spark gap practically closes with a single channel. Besides, the influence of the closing mode and rapidity of the spark gap, the permittivity of the insulator at the output end of the LITL, and the load impedance on the transient performance of the designed oscillator has been analyzed in quantification. Finally, the good transient performance of the switched oscillator has been preliminarily proved by the experiment.

  10. Investigation of a compact coaxially fed switched oscillator.

    PubMed

    Wang, Yuwei; Chen, Dongqun; Zhang, Jiande; Cao, Shengguang; Li, Da; Liu, Chebo

    2013-09-01

    To generate a relative high frequency mesoband microwave, a compact coaxially fed transmission line switched oscillator with high voltage capability is investigated. The characteristic impedance and voltage capability of the low impedance transmission line (LITL) have been analyzed. It is shown that the working voltage of the oscillator can reach up to 200 kV when it is filled by pressurized nitrogen and charged by a nanosecond driving source. By utilizing a commercial electromagnetic simulation code, the transient performance of the switched oscillator with a lumped resistance load is simulated. It is illustrated that the center frequency of the output signal reaches up to ~0.6 GHz when the spark gap practically closes with a single channel. Besides, the influence of the closing mode and rapidity of the spark gap, the permittivity of the insulator at the output end of the LITL, and the load impedance on the transient performance of the designed oscillator has been analyzed in quantification. Finally, the good transient performance of the switched oscillator has been preliminarily proved by the experiment.

  11. The dynamics of a stabilised Wien bridge oscillator

    NASA Astrophysics Data System (ADS)

    Lerner, L.

    2016-11-01

    We present for the first time analytic solutions for the nonlinear dynamics of a Wien bridge oscillator stabilised by three common methods: an incandescent lamp, signal diodes, and the field effect transistor. The results can be used to optimise oscillator design, and agree well with measurements. The effect of operational amplifier marginal nonlinearity on oscillator performance at high frequencies is clarified. The oscillator circuits and their analysis can be used to demonstrate nonlinear dynamics in the undergraduate laboratory.

  12. Monolithic fiber laser oscillator with record high power

    NASA Astrophysics Data System (ADS)

    Yang, Baolai; Shi, Chen; Zhang, Hanwei; Ye, Qing; Pi, Haoyang; Tao, Rumao; Wang, Xiaolin; Ma, Pengfei; Leng, Jinyong; Chen, Zilun; Zhou, Pu; Xu, Xiaojun; Chen, Jinbao; Liu, Zejin

    2018-07-01

    With an increasing output power, the power scaling of monolithic fiber laser oscillators faces the severe limitations of stimulated Raman scattering (SRS) and the transverse mode instability (TMI) effect. In this work, we report a high power monolithic fiber laser oscillator with a maximum output power of 5.2 kW, which is realized with a trade-off design between the SRS and TMI. The monolithic fiber laser oscillator is constructed with ytterbium-doped fiber with a core/inner cladding diameter of 25/400 µm and corresponding home-made FBG. High-power 915 nm laser diodes are employed as a pump source and are distributed in a bidirectional-pump configuration. By optimizing the bidirectional pump proportion, the monolithic fiber laser oscillator is scaled up to 5.2 kW with a slope efficiency of ~63%. Operating at 5.2 kW, the intensity of the Raman stokes light is ~22 dB below the signal laser and the beam quality (M2-factor) is ~2.2. To the best of our knowledge, this is a record high power for monolithic fiber laser oscillators.

  13. Oscillating Permanent Magnets.

    ERIC Educational Resources Information Center

    Michaelis, M. M.; Haines, C. M.

    1989-01-01

    Describes several ways to partially levitate permanent magnets. Computes field line geometries and oscillation frequencies. Provides several diagrams illustrating the mechanism of the oscillation. (YP)

  14. Resonance condition and low-frequency quasi-periodic oscillations of the outbursting source H1743-322

    NASA Astrophysics Data System (ADS)

    Chakrabarti, Sandip K.; Mondal, Santanu; Debnath, Dipak

    2015-10-01

    It has long been proposed that low-frequency quasi-periodic oscillations (QPOs) in stellar-mass black holes or their equivalents in supermassive black holes are the result of resonances between infall and cooling timescales. We explicitly compute these two timescales in a generic situation to show that resonances are easily achieved. During an outburst of a transient black hole candidate, the accretion rate of the Keplerian disc as well as the geometry of the Comptonizing cloud change very rapidly. During some period, a resonance condition between the cooling timescale (predominantly by Comptonization) and the infall timescale of the Comptonizing cloud is roughly satisfied. This leads to low-frequency quasi-periodic oscillations (LFQPOs) of the Compton cloud and the consequent oscillation of hard X-rays. In this paper, we explicitly follow black hole candidate H1743-322 during its 2010 outburst. We compute the Compton cooling time and infall time over several days and show that QPOs take place when these two roughly agree within ˜50 per cent, i.e., the resonance condition is generally satisfied. We also confirm that for the sharper LFQPOs (i.e. higher Q-factors) the ratio of the two timescales is very close to 1.

  15. A narrow-band injection-seeded pulsed titanium:sapphire oscillator-amplifier system with on-line chirp analysis for high-resolution spectroscopy.

    PubMed

    Hannemann, S; van Duijn, E-J; Ubachs, W

    2007-10-01

    A narrow-band tunable injection-seeded pulsed titanium:sapphire laser system has been developed for application in high-resolution spectroscopic studies at the fundamental wavelengths in the near infrared as well as in the ultraviolet, deep ultraviolet, and extreme ultraviolet after upconversion. Special focus is on the quantitative assessment of the frequency characteristics of the oscillator-amplifier system on a pulse-to-pulse basis. Frequency offsets between continuous-wave seed light and the pulsed output are measured as well as linear chirps attributed mainly to mode pulling effects in the oscillator cavity. Operational conditions of the laser are found in which these offset and chirp effects are minimal. Absolute frequency calibration at the megahertz level of accuracy is demonstrated on various atomic and molecular resonance lines.

  16. A statistical study on the occurrence of discrete frequencies in the high velocity solar wind and in the magnetosphere

    NASA Astrophysics Data System (ADS)

    Di Matteo, Simone; Villante, Umberto

    2016-04-01

    The possible occurrence of oscillations at discrete frequencies in the solar wind and their possible correspondence with magnetospheric field oscillations represent an interesting aspect of the solar wind/magnetopheric research. We analyze a large set of high velocity streams following interplanetary shocks in order to ascertain the possible occurrence of preferential sets of discrete frequencies in the oscillations of the solar wind pressure in such structures. We evaluate, for each event, the power spectrum of the dynamic pressure by means of two methods (Welch and multitaper windowing) and accept the common spectral peaks that also pass a harmonic F-test at the 95% confidence level. We compare these frequencies with those detected at geosynchronous orbit in the magnetospheric field components soon after the manifestation of the corresponding Sudden Impulses.

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

    PubMed Central

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

    2015-01-01

    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. PMID:25833429

  18. Fully stabilized mid-infrared frequency comb for high-precision molecular spectroscopy.

    PubMed

    Vainio, Markku; Karhu, Juho

    2017-02-20

    A fully stabilized mid-infrared optical frequency comb spanning from 2.9 to 3.4 µm is described in this article. The comb is based on half-harmonic generation in a femtosecond optical parametric oscillator, which transfers the high phase coherence of a fully stabilized near-infrared Er-doped fiber laser comb to the mid-infrared region. The method is simple, as no phase-locked loops or reference lasers are needed. Precise locking of optical frequencies of the mid-infrared comb to the pump comb is experimentally verified at sub-20 mHz level, which corresponds to a fractional statistical uncertainty of 2 × 10-16 at the center frequency of the mid-infrared comb. The fully stabilized mid-infrared comb is an ideal tool for high-precision molecular spectroscopy, as well as for optical frequency metrology in the mid-infrared region, which is difficult to access with other stabilized frequency comb techniques.

  19. Low-cost FM oscillator for capacitance type of blade tip clearance measurement system

    NASA Technical Reports Server (NTRS)

    Barranger, John P.

    1987-01-01

    The frequency-modulated (FM) oscillator described is part of a blade tip clearance measurement system that meets the needs of a wide class of fans, compressors, and turbines. As a result of advancements in the technology of ultra-high-frequency operational amplifiers, the FM oscillator requires only a single low-cost integrated circuit. Its carrier frequency is 42.8 MHz when it is used with an integrated probe and connecting cable assembly consisting of a 0.81 cm diameter engine-mounted capacitance probe and a 61 cm long hermetically sealed coaxial cable. A complete circuit analysis is given, including amplifier negative resistance characteristics. An error analysis of environmentally induced effects is also derived, and an error-correcting technique is proposed. The oscillator can be calibrated in the static mode and has a negative peak frequency deviation of 400 kHz for a rotor blade thickness of 1.2 mm. High-temperature performance tests of the probe and 13 cm of the adjacent cable show good accuracy up to 600 C, the maximum permissible seal temperature. The major source of error is the residual FM oscillator noise, which produces a clearance error of + or - 10 microns at a clearance of 0.5 mm. The oscillator electronics accommodates the high rotor speeds associated with small engines, the signals from which may have frequency components as high as 1 MHz.

  20. An Optimal Frequency in Ca2+ Oscillations for Stomatal Closure Is an Emergent Property of Ion Transport in Guard Cells1[CC-BY

    PubMed Central

    Minguet-Parramona, Carla; Hills, Adrian; Vialet-Chabrand, Silvere; Griffiths, Howard; Lawson, Tracy; Lew, Virgilio L.; Blatt, Michael R.

    2016-01-01

    Oscillations in cytosolic-free Ca2+ concentration ([Ca2+]i) have been proposed to encode information that controls stomatal closure. [Ca2+]i oscillations with a period near 10 min were previously shown to be optimal for stomatal closure in Arabidopsis (Arabidopsis thaliana), but the studies offered no insight into their origins or mechanisms of encoding to validate a role in signaling. We have used a proven systems modeling platform to investigate these [Ca2+]i oscillations and analyze their origins in guard cell homeostasis and membrane transport. The model faithfully reproduced differences in stomatal closure as a function of oscillation frequency with an optimum period near 10 min under standard conditions. Analysis showed that this optimum was one of a range of frequencies that accelerated closure, each arising from a balance of transport and the prevailing ion gradients across the plasma membrane and tonoplast. These interactions emerge from the experimentally derived kinetics encoded in the model for each of the relevant transporters, without the need of any additional signaling component. The resulting frequencies are of sufficient duration to permit substantial changes in [Ca2+]i and, with the accompanying oscillations in voltage, drive the K+ and anion efflux for stomatal closure. Thus, the frequency optima arise from emergent interactions of transport across the membrane system of the guard cell. Rather than encoding information for ion flux, these oscillations are a by-product of the transport activities that determine stomatal aperture. PMID:26628748

  1. Local oscillator induced degradation of medium-term stability in passive atomic frequency standards

    NASA Technical Reports Server (NTRS)

    Dick, G. John; Prestage, John D.; Greenhall, Charles A.; Maleki, Lute

    1990-01-01

    As the performance of passive atomic frequency standards improves, a new limitation is encountered due to frequency fluctuations in an ancillary local oscillator (L.O.). The effect is due to time variation in the gain of the feedback which compensates L.O. frequency fluctuations. The high performance promised by new microwave and optical trapped ion standards may be severely compromised by this effect. Researchers present an analysis of this performance limitation for the case of sequentially interrogated standards. The time dependence of the sensitivity of the interrogation process to L.O. frequency fluctuations is evaluated for single-pulse and double-pulse Ramsey RF interrogation and for amplitude modulated pulses. The effect of these various time dependencies on performance of the standard is calculated for an L.O. with frequency fluctuations showing a typical 1/f spectral density. A limiting 1/sq. root gamma dependent deviation of frequency fluctuations is calculated as a function of pulse lengths, dead time, and pulse overlap. Researchers also present conceptual and hardware-oriented solutions to this problem which achieve a much more nearly constant sensitivity to L.O. fluctuations. Solutions involve use of double-pulse interrogation; alternate interrogation of multiple traps so that the dead time of one trap can be covered by operation of the other; and the use of double-pulse interrogation for two traps, so that during the time of the RF pulses, the increasing sensitivity of one trap tends to compensate for the decreasing sensitivity of the other. A solution making use of amplified-modulated pulses is also presented which shows nominally zero time variation.

  2. New Insights of High-precision Asteroseismology: Acoustic Radius and χ2-matching Method for Solar-like Oscillator KIC 6225718

    NASA Astrophysics Data System (ADS)

    Wu, Tao; Li, Yan

    2017-10-01

    Asteroseismology is a powerful tool for probing stellar interiors and determining stellar fundamental parameters. In the present work, we adopt the χ2-minimization method but only use the observed high-precision seismic observations (i.e., oscillation frequencies) to constrain theoretical models for analyzing solar-like oscillator KIC 6225718. Finally, we find the acoustic radius τ0 is the only global parameter that can be accurately measured by the χ2-matching method between observed frequencies and theoretical model calculations for a pure p-mode oscillation star. We obtain seconds for KIC 6225718. It leads that the mass and radius of the CMMs are degenerate with each other. In addition, we find that the distribution range of acoustic radius is slightly enlarged by some extreme cases, which posses both a larger mass and a higher (or lower) metal abundance, at the lower acoustic radius end.

  3. Gigahertz Electromagnetic Structures via Direct Ink Writing for Radio-Frequency Oscillator and Transmitter Applications.

    PubMed

    Zhou, Nanjia; Liu, Chengye; Lewis, Jennifer A; Ham, Donhee

    2017-04-01

    Radio-frequency (RF) electronics, which combine passive electromagnetic devices and active transistors to generate and process gigahertz (GHz) signals, provide a critical basis of ever-pervasive wireless networks. While transistors are best realized by top-down fabrication, relatively larger electromagnetic passives are within the reach of printing techniques. Here, direct writing of viscoelastic silver-nanoparticle inks is used to produce a broad array of RF passives operating up to 45 GHz. These include lumped devices such as inductors and capacitors, and wave-based devices such as transmission lines, their resonant networks, and antennas. Moreover, to demonstrate the utility of these printed RF passive structures in active RF electronic circuits, they are combined with discrete transistors to fabricate GHz self-sustained oscillators and synchronized oscillator arrays that provide RF references, and wireless transmitters clocked by the oscillators. This work demonstrates the synergy of direct ink writing and RF electronics for wireless applications. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. A one-parametric formula relating the frequencies of twin-peak quasi-periodic oscillations

    NASA Astrophysics Data System (ADS)

    Török, Gabriel; Goluchová, Kateřina; Šrámková, Eva; Horák, Jiří; Bakala, Pavel; Urbanec, Martin

    2017-12-01

    Timing analysis of X-ray flux in more than a dozen low-mass X-ray binary systems containing a neutron star reveals remarkable correlations between frequencies of two characteristic peaks present in the power-density spectra. We find a simple analytic relation that well reproduces all these individual correlations. We link this relation to a physical model which involves accretion rate modulation caused by an oscillating torus.

  5. Heartbeat of the Southern Oscillation explains ENSO climatic resonances

    NASA Astrophysics Data System (ADS)

    Bruun, John T.; Allen, J. Icarus; Smyth, Timothy J.

    2017-08-01

    The El Niño-Southern Oscillation (ENSO) nonlinear oscillator phenomenon has a far reaching influence on the climate and human activities. The up to 10 year quasi-period cycle of the El Niño and subsequent La Niña is known to be dominated in the tropics by nonlinear physical interaction of wind with the equatorial waveguide in the Pacific. Long-term cyclic phenomena do not feature in the current theory of the ENSO process. We update the theory by assessing low (>10 years) and high (<10 years) frequency coupling using evidence across tropical, extratropical, and Pacific basin scales. We analyze observations and model simulations with a highly accurate method called Dominant Frequency State Analysis (DFSA) to provide evidence of stable ENSO features. The observational data sets of the Southern Oscillation Index (SOI), North Pacific Index Anomaly, and ENSO Sea Surface Temperature Anomaly, as well as a theoretical model all confirm the existence of long-term and short-term climatic cycles of the ENSO process with resonance frequencies of {2.5, 3.8, 5, 12-14, 61-75, 180} years. This fundamental result shows long-term and short-term signal coupling with mode locking across the dominant ENSO dynamics. These dominant oscillation frequency dynamics, defined as ENSO frequency states, contain a stable attractor with three frequencies in resonance allowing us to coin the term Heartbeat of the Southern Oscillation due to its characteristic shape. We predict future ENSO states based on a stable hysteresis scenario of short-term and long-term ENSO oscillations over the next century.Plain Language SummaryThe Pacific El Niño-Southern <span class="hlt">Oscillation</span> (ENSO) nonlinear <span class="hlt">oscillator</span> phenomenon has a far reaching influence on the climate and our human activities. This work can help predict both long-term and short-term future ENSO events and to assess the risk of future climate hysteresis changes: is the elastic band that regulates the ENSO</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19950053970&hterms=tunnel+diodes&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dtunnel%2Bdiodes','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19950053970&hterms=tunnel+diodes&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dtunnel%2Bdiodes"><span>Fundamental and subharmonic excitation for an <span class="hlt">oscillator</span> with several tunneling diodes in series</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Boric-Lubecke, Olga; Pan, Dee-Son; Itoh, Tatsuo</p> <p>1995-01-01</p> <p>Connecting several tunneling diodes in series shows promise as a method for increasing the output power of these devices as millimeter-wave <span class="hlt">oscillators</span>. However, due to the negative differential resistance (NDR) region in the dc I-V curve of a single tunneling diode, a circuit using several devices connected in series, and biased simultaneously in the NDR region, is dc unstable. Because of this instability, an <span class="hlt">oscillator</span> with several tunneling diodes in series has a demanding excitation condition. Excitation using an externally applied RF signal is one approach to solving this problem. This is experimentally demonstrated using an RF source, both with <span class="hlt">frequency</span> close to as well as with <span class="hlt">frequency</span> considerably lower than the <span class="hlt">oscillation</span> <span class="hlt">frequency</span>. Excitation by an RF (radio <span class="hlt">frequency</span>) source with a <span class="hlt">frequency</span> as low as one sixth of the <span class="hlt">oscillation</span> <span class="hlt">frequency</span> was demonstrated in a proof-of-principle experiment at 2 GHz, for an <span class="hlt">oscillator</span> with two tunnel diodes connected in series. Strong harmonics of the <span class="hlt">oscillation</span> signal were generated as a result of the <span class="hlt">highly</span> nonlinear dc I-V curve of the tunnel diode and a large signal <span class="hlt">oscillator</span> design. Third harmonic output power comparable to that of the fundamental was observed in one <span class="hlt">oscillator</span> circuit. If submillimeter wave resonant-tunneling diodes (RTD's) are used instead of tunnel diodes, this harmonic output may be useful for generating signals at <span class="hlt">frequencies</span> well into the terahertz range.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4490899','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4490899"><span>Continuous <span class="hlt">High</span> <span class="hlt">Frequency</span> Activity: A peculiar SEEG pattern related to specific brain regions</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Melani, Federico; Zelmann, Rina; Mari, Francesco; Gotman, Jean</p> <p>2015-01-01</p> <p>Objective While visually marking the <span class="hlt">high</span> <span class="hlt">frequency</span> <span class="hlt">oscillations</span> in the stereo-EEG of epileptic patients, we observed a continuous/semicontinuous activity in the ripple band (80–250 Hz), which we defined continuous <span class="hlt">High</span> <span class="hlt">Frequency</span> Activity (HFA). We aim to analyze in all brain regions the occurrence and significance of this particular pattern. Methods Twenty patients implanted in mesial temporal and neocortical areas were studied. One minute of slow-wave sleep was reviewed. The background was classified as continuous/semicontinuous, irregular, or sporadic based on the duration of the fast <span class="hlt">oscillations</span>. Each channel was classified as inside/outside the seizure onset zone (SOZ) or a lesion. Results The continuous/semicontinuous HFA occurred in 54 of the 790 channels analyzed, with a clearly higher prevalence in hippocampus and occipital lobe. No correlation was found with the SOZ or lesions. In the occipital lobe the continuous/semicontinuous HFA was present independently of whether eyes were open or closed. Conclusions We describe what appears to be a new physiological <span class="hlt">High</span> <span class="hlt">Frequency</span> Activity, independent of epileptogenicity, present almost exclusively in the hippocampus and occipital cortex but independent of the alpha rhythm. Significance The continuous HFA may be an intrinsic characteristic of specific brain regions, reflecting a particular type of physiological neuronal activity. PMID:23768436</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19730028746&hterms=film+movies&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dfilm%2Bmovies','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19730028746&hterms=film+movies&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dfilm%2Bmovies"><span><span class="hlt">Oscillation</span> effects upon film boiling from a sphere.</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Schmidt, W. E.; Witte, L. C.</p> <p>1972-01-01</p> <p>Heat transfer rates from a silver-plated copper sphere, 0.75 in. in diameter, were studied by <span class="hlt">high</span> speed photography during <span class="hlt">oscillations</span> of the sphere in saturated liquid nitrogen and Freon-11. The <span class="hlt">oscillation</span> <span class="hlt">frequencies</span> ranged from zero to 13 Hz, and the amplitude-to-diameter ratio varied from zero to 2.67. The sphere was supported by a thin-walled stainless steel tube and carried a thermocouple attached near the lower stagnation point. A Fastax WF-3 16mm movie camera was used at about 2000 frames/sec. The differences in the vapor removal process at lower and higher <span class="hlt">oscillation</span> <span class="hlt">frequencies</span> are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/22525282-aspects-neutrino-oscillation-alternative-gravity-theories','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/22525282-aspects-neutrino-oscillation-alternative-gravity-theories"><span>Aspects of neutrino <span class="hlt">oscillation</span> in alternative gravity theories</span></a></p> <p><a target="_blank" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Chakraborty, Sumanta, E-mail: sumantac.physics@gmail.com</p> <p>2015-10-01</p> <p>Neutrino spin and flavour <span class="hlt">oscillation</span> in curved spacetime have been studied for the most general static spherically symmetric configuration. Having exploited the spherical symmetry we have confined ourselves to the equatorial plane in order to determine the spin and flavour <span class="hlt">oscillation</span> <span class="hlt">frequency</span> in this general set-up. Using the symmetry properties we have derived spin <span class="hlt">oscillation</span> <span class="hlt">frequency</span> for neutrino moving along a geodesic or in a circular orbit. Starting from the expression of neutrino spin <span class="hlt">oscillation</span> <span class="hlt">frequency</span> we have shown that even in this general context, in <span class="hlt">high</span> energy limit the spin <span class="hlt">oscillation</span> <span class="hlt">frequency</span> for neutrino moving along circular orbit vanishes.more » We have verified previous results along this line by transforming to Schwarzschild coordinates under appropriate limit. This finally lends itself to the probability of neutrino helicity flip which turns out to be non-zero. While for neutrino flavour <span class="hlt">oscillation</span> we have derived general results for <span class="hlt">oscillation</span> phase, which subsequently have been applied to three different gravity theories. One, of them appears as low-energy approximation to string theory, where we have an additional field, namely, dilaton field coupled to Maxwell field tensor. This yields a realization of Reissner-Nordström solution in string theory at low-energy. Next one corresponds to generalization of Schwarzschild solution by introduction of quadratic curvature terms of all possible form to the Einstein-Hilbert action. Finally, we have also discussed regular black hole solutions. In all these cases the flavour <span class="hlt">oscillation</span> probabilities can be determined for solar neutrinos and thus can be used to put bounds on the parameters of these gravity theories. While for spin <span class="hlt">oscillation</span> probability, we have considered two cases, Gauss-Bonnet term added to the Einstein-Hilbert action and the f(R) gravity theory. In both these cases we could impose bounds on the parameters which are consistent with previous considerations. In a</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Nanot..28o5701C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Nanot..28o5701C"><span>Rotation-excited perfect <span class="hlt">oscillation</span> of a tri-walled nanotube-based <span class="hlt">oscillator</span> at ultralow temperature</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cai, Kun; Zhang, Xiaoni; Shi, Jiao; Qin, Qing H.</p> <p>2017-04-01</p> <p>In recent years, carbon-nanotube (CNT)-based gigahertz <span class="hlt">oscillators</span> have been widely used in numerous areas of practical engineering such as <span class="hlt">high</span>-speed digital, analog circuits, and memory cells. One of the major challenges to practical applications of the gigahertz <span class="hlt">oscillator</span> is generating a stable <span class="hlt">oscillation</span> process from the gigahertz <span class="hlt">oscillators</span> and then maintaining the stable process for a specified period of time. To address this challenge, an <span class="hlt">oscillator</span> from a triple-walled CNT-based rotary system is proposed and analyzed numerically in this paper, using a molecular dynamics approach. In this system, the outer tube is fixed partly as a stator. The middle tube, with a constant rotation, is named Rotor 2 and runs in the stator. The inner tube acts as Rotor 1, which can rotate freely in Rotor 2. Due to the friction between the two rotors when they have relative motion, the rotational <span class="hlt">frequency</span> of Rotor 1 increases continuously and tends to converge with that of Rotor 2. During rotation, the <span class="hlt">oscillation</span> of Rotor 1 may be excited owing to both a strong end barrier at Rotor 2 and thermal vibration of atoms in the tubes. From the discussion on the effects of length of Rotor 1, temperature, and input rotational <span class="hlt">frequency</span> of Rotor 2 on the dynamic response of Rotor 1, an effective way to control the <span class="hlt">oscillation</span> of Rotor 1 is found. Being much longer than Rotor 2, Rotor 1 will have perfect <span class="hlt">oscillation</span>, i.e., with both stable (or nearly constant) period and amplitude—especially at relatively low temperature. This discovery can be taken as a useful guidance for the design of an <span class="hlt">oscillator</span> from CNTs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28303802','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28303802"><span>Rotation-excited perfect <span class="hlt">oscillation</span> of a tri-walled nanotube-based <span class="hlt">oscillator</span> at ultralow temperature.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Cai, Kun; Zhang, Xiaoni; Shi, Jiao; Qin, Qing H</p> <p>2017-04-18</p> <p>In recent years, carbon-nanotube (CNT)-based gigahertz <span class="hlt">oscillators</span> have been widely used in numerous areas of practical engineering such as <span class="hlt">high</span>-speed digital, analog circuits, and memory cells. One of the major challenges to practical applications of the gigahertz <span class="hlt">oscillator</span> is generating a stable <span class="hlt">oscillation</span> process from the gigahertz <span class="hlt">oscillators</span> and then maintaining the stable process for a specified period of time. To address this challenge, an <span class="hlt">oscillator</span> from a triple-walled CNT-based rotary system is proposed and analyzed numerically in this paper, using a molecular dynamics approach. In this system, the outer tube is fixed partly as a stator. The middle tube, with a constant rotation, is named Rotor 2 and runs in the stator. The inner tube acts as Rotor 1, which can rotate freely in Rotor 2. Due to the friction between the two rotors when they have relative motion, the rotational <span class="hlt">frequency</span> of Rotor 1 increases continuously and tends to converge with that of Rotor 2. During rotation, the <span class="hlt">oscillation</span> of Rotor 1 may be excited owing to both a strong end barrier at Rotor 2 and thermal vibration of atoms in the tubes. From the discussion on the effects of length of Rotor 1, temperature, and input rotational <span class="hlt">frequency</span> of Rotor 2 on the dynamic response of Rotor 1, an effective way to control the <span class="hlt">oscillation</span> of Rotor 1 is found. Being much longer than Rotor 2, Rotor 1 will have perfect <span class="hlt">oscillation</span>, i.e., with both stable (or nearly constant) period and amplitude-especially at relatively low temperature. This discovery can be taken as a useful guidance for the design of an <span class="hlt">oscillator</span> from CNTs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1989ApOpt..28.1579R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1989ApOpt..28.1579R"><span>Relationship between cutoff <span class="hlt">frequency</span> and accuracy in time-interval photon statistics applied to <span class="hlt">oscillating</span> signals</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rebolledo, M. A.; Martinez-Betorz, J. A.</p> <p>1989-04-01</p> <p>In this paper the accuracy in the determination of the period of an <span class="hlt">oscillating</span> signal, when obtained from the photon statistics time-interval probability, is studied as a function of the precision (the inverse of the cutoff <span class="hlt">frequency</span> of the photon counting system) with which time intervals are measured. The results are obtained by means of an experiment with a square-wave signal, where the Fourier or square-wave transforms of the time-interval probability are measured. It is found that for values of the <span class="hlt">frequency</span> of the signal near the cutoff <span class="hlt">frequency</span> the errors in the period are small.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100019594','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100019594"><span>A 311-GHz Fundamental <span class="hlt">Oscillator</span> Using InP HBT Technology</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Gaier, Todd; Fung, King Man; Samoska, Lorene; Radisic, Vesna; Sawdai, Donald; Scott, Dennis; Deal, W.R.</p> <p>2010-01-01</p> <p>This <span class="hlt">oscillator</span> uses a single-emitter 0.3- m InP heterojunction bipolar transistor (HBT) device with maximum <span class="hlt">frequency</span> of <span class="hlt">oscillation</span> (fmax) greater than 500 GHz. Due to <span class="hlt">high</span> conductor and substrate losses at submillimeterwave <span class="hlt">frequencies</span>, a primary challenge is to efficiently use the intrinsic device gain. This was done by using a suitable transmission-line media and circuit topology. The passive components of the <span class="hlt">oscillator</span> are realized in a twometal process with benzocyclobutene (BCB) used as the primary transmission line dielectric. The circuit was designed using microstrip transmission lines. The <span class="hlt">oscillator</span> is implemented in a common-base topology due to its inherent instability, and the design includes an on-chip resonator, outputmatching circuitry, and an injection-locking port, the port being used to demonstrate the injection-locking prin ciple. A free-running <span class="hlt">frequency</span> of 311.6 GHz has been measured by down-converting the signal. Ad di tionally, injection locking has been successfully demonstrated with up to 17.8 dB of injection-locking gain. The injection-locking reference signal is generated using a 2 20 GHz <span class="hlt">frequency</span> synthesizer, followed by a doubler, active tripler, a W-band amplifier, and then a passive tripler. Therefore, the source <span class="hlt">frequency</span> is multiplied 18 times to obtain a signal above 300 GHz that can be used to injection lock the <span class="hlt">oscillator</span>. Measurement shows that injection locking has improved the phase noise of the <span class="hlt">oscillator</span> and can be also used for synchronizing a series of <span class="hlt">oscillators</span>. A signal conductor is implemented near the BCP -InP interface and the topside of the BCB layer is fully metallized as a signal ground. Because the fields are primarily constrained in the lower permittivity BCB region, this type of transmission line is referred to as an inverted microstrip. In addition, both common-emitter and commonbase circuits were investigated to determine optimum topology for <span class="hlt">oscillator</span> design. The common -base topology required smaller</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050060736','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050060736"><span><span class="hlt">High</span>-Speed Rainbow Schlieren Visualization of an <span class="hlt">Oscillating</span> Helium Jet Undergoing Gravitational Change</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Leptuch, Peter A.; Agrawal, Ajay K.</p> <p>2005-01-01</p> <p>Rainbow schlieren deflectometry combined with <span class="hlt">high</span>-speed digital imaging was used to study buoyancy effects on flow structure of a helium jet discharged vertically into air. The experimental data were taken using the 2.2-sec drop tower facility at the NASA John H. Glenn Research Center in Cleveland, Ohio. The test conditions pertained to jet Reynolds number of 490 and jet Richardson number of 0.11, for which buoyancy is often considered unimportant. Experimental results show global <span class="hlt">oscillations</span> at a <span class="hlt">frequency</span> of 27 Hz in Earth gravity. In microgravity, the jet <span class="hlt">oscillations</span> vanished and the jet width increased. Results provide a direct physical evidence of the importance of buoyancy on the flow structure of low-density gas jets at a Richardson number considered too small to account for gravity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017SPIE10251E..0XM','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017SPIE10251E..0XM"><span>In vivo imaging of spontaneous low-<span class="hlt">frequency</span> <span class="hlt">oscillations</span> in cerebral hemodynamics with a digital red-green-blue camera</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mustari, Afrina; Nakamura, Naoki; Nishidate, Izumi; Kawauchi, Satoko; Sato, Shunichi; Sato, Manabu; Kokobo, Yasuaki</p> <p>2017-04-01</p> <p>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-<span class="hlt">frequency</span> <span class="hlt">oscillation</span> 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-<span class="hlt">frequency</span> <span class="hlt">oscillation</span> of cerebral blood volume based on the sequential RGB images of exposed brain.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18436196','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18436196"><span>The hallucinogen DOI reduces low-<span class="hlt">frequency</span> <span class="hlt">oscillations</span> in rat prefrontal cortex: reversal by antipsychotic drugs.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Celada, Pau; Puig, M Victoria; Díaz-Mataix, Llorenç; Artigas, Francesc</p> <p>2008-09-01</p> <p>Perceptual and psychic alterations and thought disorder are fundamental elements of schizophrenia symptoms, a pathology associated with an abnormal macro- and microcircuitry of several brain areas including the prefrontal cortex (PFC). Alterations in information processing in PFC may partly underlie schizophrenia symptoms. The 5-HT(2A/2C) agonist DOI and antipsychotic drugs were administered to anesthetized rats. Single unit and local field potential (LFP) extracellular recordings were made in medial PFC (mPFC). Electrolytic lesions were performed in the thalamic nuclei. DOI markedly disrupts cellular and network activity in rat PFC. DOI altered pyramidal discharge in mPFC (39% excited, 27% inhibited, 34% unaffected; n = 51). In all instances, DOI concurrently reduced low-<span class="hlt">frequency</span> <span class="hlt">oscillations</span> (.3-4 Hz; power spectrum: .25 +/- .02 and .14 +/- .01 microV(2) in basal conditions and after 50-300 microg/kg intravenous (i.v.) DOI, respectively; n = 51). Moreover, DOI disrupted the temporal association between the active phase of LFP and pyramidal discharge. Both effects were reversed by M100907 (5-HT(2A) receptor antagonist) and were not attenuated by thalamic lesions, supporting an intracortical origin of the effects of DOI. The reduction in low-<span class="hlt">frequency</span> <span class="hlt">oscillations</span> induced by DOI was significantly reversed by the antipsychotic drugs haloperidol (.1-.2 mg/kg i.v.) and clozapine (1 mg/kg i.v.). DOI disorganizes network activity in PFC, reducing low-<span class="hlt">frequency</span> <span class="hlt">oscillations</span> and desynchronizing pyramidal discharge from active phases of LFP. These effects may underlie DOI's psychotomimetic action. The reversal by clozapine and haloperidol indicates that antipsychotic drugs may reduce psychotic symptoms by normalizing an altered PFC function.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24062700','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24062700"><span>Chronic Ketamine Reduces the Peak <span class="hlt">Frequency</span> of Gamma <span class="hlt">Oscillations</span> in Mouse Prefrontal Cortex Ex vivo.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>McNally, James M; McCarley, Robert W; Brown, Ritchie E</p> <p>2013-01-01</p> <p>Abnormalities in EEG gamma band <span class="hlt">oscillations</span> (GBO, 30-80 Hz) serve as a prominent biomarker of schizophrenia (Sz), associated with positive, negative, and cognitive symptoms. Chronic, subanesthetic administration of antagonists of N-methyl-D-aspartate receptors (NMDAR), such as ketamine, elicits behavioral effects, and alterations in cortical interneurons similar to those observed in Sz. However, the chronic effects of ketamine on neocortical GBO are unknown. Thus, here we examine the effects of chronic (five daily i.p. injections) application of ketamine (5 and 30 mg/kg) and the more specific NMDAR antagonist, MK-801 (0.02, 0.5, and 2 mg/kg), on neocortical GBO ex vivo. <span class="hlt">Oscillations</span> were generated by focal application of the glutamate receptor agonist, kainate (KA), in coronal brain slices containing the prelimbic cortex. This region constitutes the rodent analog of the human dorsolateral prefrontal cortex, a brain region strongly implicated in Sz-pathophysiology. Here we report the novel finding that chronic ketamine elicits a reduction in the peak oscillatory <span class="hlt">frequency</span> of KA-elicited <span class="hlt">oscillations</span> (from 47 to 40 Hz at 30 mg/kg). Moreover, the power of GBO in the 40-50 Hz band was reduced. These findings are reminiscent of both the reduced resonance <span class="hlt">frequency</span> and power of cortical <span class="hlt">oscillations</span> observed in Sz clinical studies. Surprisingly, MK-801 had no significant effect, suggesting care is needed when equating Sz-like behavioral effects elicited by different NMDAR antagonists to alterations in GBO activity. We conclude that chronic ketamine in the mouse mimics GBO abnormalities observed in Sz patients. Use of this ex vivo slice model may be useful in testing therapeutic compounds which rescue these GBO abnormalities.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3699652','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3699652"><span>Dynamic Interaction of Spindles and Gamma Activity during Cortical Slow <span class="hlt">Oscillations</span> and Its Modulation by Subcortical Afferents</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Valencia, Miguel; Artieda, Julio; Bolam, J. Paul; Mena-Segovia, Juan</p> <p>2013-01-01</p> <p>Slow <span class="hlt">oscillations</span> are a hallmark of slow wave sleep. They provide a temporal framework for a variety of phasic events to occur and interact during sleep, including the expression of <span class="hlt">high-frequency</span> <span class="hlt">oscillations</span> and the discharge of neurons across the entire brain. Evidence shows that the emergence of distinct <span class="hlt">high-frequency</span> <span class="hlt">oscillations</span> during slow <span class="hlt">oscillations</span> facilitates the communication among brain regions whose activity was correlated during the preceding waking period. While the <span class="hlt">frequencies</span> of <span class="hlt">oscillations</span> involved in such interactions have been identified, their dynamics and the correlations between them require further investigation. Here we analyzed the structure and dynamics of these signals in anesthetized rats. We show that spindles and gamma <span class="hlt">oscillations</span> coexist but have distinct temporal dynamics across the slow <span class="hlt">oscillation</span> cycle. Furthermore, we observed that spindles and gamma are functionally coupled to the slow <span class="hlt">oscillations</span> and between each other. Following the activation of ascending pathways from the brainstem by means of a carbachol injection in the pedunculopontine nucleus, we were able to modify the gain in the gamma <span class="hlt">oscillations</span> that are independent of the spindles while the spindle amplitude was reduced. Furthermore, carbachol produced a decoupling of the gamma <span class="hlt">oscillations</span> that are dependent on the spindles but with no effect on their amplitude. None of the changes in the <span class="hlt">high-frequency</span> <span class="hlt">oscillations</span> affected the onset or shape of the slow <span class="hlt">oscillations</span>, suggesting that slow <span class="hlt">oscillations</span> occur independently of the phasic events that coexist with them. Our results provide novel insights into the regulation, dynamics and homeostasis of cortical slow <span class="hlt">oscillations</span>. PMID:23844020</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21219970','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21219970"><span>Induction of θ-<span class="hlt">frequency</span> <span class="hlt">oscillations</span> in the rat medial septal diagonal band slice by metabotropic glutamate receptor agonists.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lu, C B; Ouyang, G; Henderson, Z; Li, X</p> <p>2011-03-17</p> <p>The aim of this study was to examine the role of metabotropic glutamate receptors (mGluR) in the generation of oscillatory field activity at theta <span class="hlt">frequency</span> (4-12 Hz) in the medial septal slice prepared from rat brain. Bath application of mGluR agonists and antagonists showed that activation of mGluR1-type receptors produces persistent theta <span class="hlt">frequency</span> <span class="hlt">oscillations</span> in a dose-responsive manner. This activity, induced by the group I mGluR agonist (RS)-3,5-dihydroxyphenylglycine (DHPG), was reduced by ionotropic glutamate receptor antagonists and abolished by further addition of a GABAA receptor antagonist. However, addition of a GABAA receptor antagonist on its own converted the DHPG-induced <span class="hlt">oscillations</span> to intermittent episodes of accentuated theta <span class="hlt">frequency</span> activity following a burst. In a proportion of slices, DHPG induced large amplitude field population spiking activity (100-300 μV) which is correlated linearly with the field theta <span class="hlt">oscillations</span> and is sensitive to glutamate receptor antagonists, suggesting a role of this type of spikes in theta generation induced by DHPG. These data demonstrate that DHPG-sensitive neuronal networks within medial septum generate theta rhythmic activity and are differentially modulated by excitatory and inhibitory ionotropic neurotransmissions. Copyright © 2011 IBRO. Published by Elsevier Ltd. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018ApPhL.112c2901F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018ApPhL.112c2901F"><span><span class="hlt">High</span>-performance gap-closing vibrational energy harvesting using electret-polarized dielectric <span class="hlt">oscillators</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Feng, Yue; Yu, Zejie; Han, Yanhui</p> <p>2018-01-01</p> <p>In conventional gap-closing electret-biased electrostatic energy harvesting (EEEH) schemes, electrets with a very low ratio of electret thickness to permittivity are in great demand to allow the attainment of <span class="hlt">high</span> power output. However, in practice, pursuing such a low ratio introduces unwanted burdens on the electret stability and therefore the reliability of the EEEH devices. In this paper, we propose a dielectric-<span class="hlt">oscillator</span>-based electrostatic EH (DEEH) scheme as an alternative approach to harvesting electret-biased electrostatic energy. This approach permits the fabrication of an electret-free closed EH circuit. The DEEH architecture directly collects the electrical energy exclusively through the <span class="hlt">oscillating</span> dielectric body and thus completely circumvents the restrictions imposed by the electret parameters (thickness and permittivity) on power generation. Significantly, without considering the electret thickness and permittivity, both theoretical analysis and experiments have verified the effectiveness of this DEEH strategy, and a <span class="hlt">high</span> figure of merit (on the order of 10-8 mW cm-2 V-2 Hz-1) was achieved for low-<span class="hlt">frequency</span> movements.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010SPIE.7579E..1BL','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010SPIE.7579E..1BL"><span><span class="hlt">High</span>-Q optical resonators: characterization and application to stabilization of lasers and <span class="hlt">high</span> spectral purity microwave <span class="hlt">oscillators</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Llopis, O.; Merrer, P. H.; Bouchier, A.; Saleh, K.; Cibiel, G.</p> <p>2010-02-01</p> <p>Microwave optical systems for <span class="hlt">frequency</span> generation are described in this paper. The goal is to reach <span class="hlt">high</span> spectral purity in the microwave <span class="hlt">frequency</span> range using ultra <span class="hlt">high</span> Q optical resonators. The resonators investigated are of two types : resonant (passive) fiber rings and WGM tridimensional resonators. They all feature ultra <span class="hlt">high</span> optical Q factors, in excess of 108 or 109 near 1550 nm. These resonators also sustain a large number of optical resonances, and the microwave signal is stabilized on two (or more) resonances of this optical comb. Different problems have to be overcome in order to reach a functional system, such as : resonator design and coupling, laser stabilization on a resonance, overall system design, noise optimization... This paper gives an overlook on these problems, and on some solutions we found to work towards a compact and efficient microwave opto-electronic <span class="hlt">oscillator</span> (OEO). A first result is presented on a 10 GHz OEO based on a resonant fiber ring.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AIPC..676..230T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AIPC..676..230T"><span>Control of <span class="hlt">Oscillation</span> Patterns in a Symmetric Coupled Biological <span class="hlt">Oscillator</span> System</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Takamatsu, Atsuko; Tanaka, Reiko; Yamamoto, Takatoki; Fujii, Teruo</p> <p>2003-08-01</p> <p>A chain of three-<span class="hlt">oscillator</span> system was constructed with living biological <span class="hlt">oscillators</span> of phasmodial slime mold, Physarum polycehalum and the <span class="hlt">oscillation</span> patterns were analyzed by the symmetric Hopf bifurcation theory using group theory. Multi-stability of <span class="hlt">oscillation</span> patterns was observed, even when the coupling strength was fixed. This suggests that the coupling strength is not an effective parameter to obtain a desired <span class="hlt">oscillation</span> pattern among the multiple patterns. Here we propose a method to control <span class="hlt">oscillation</span> patterns using resonance to external stimulus and demonstrate pattern switching induced by <span class="hlt">frequency</span> resonance given to only one of <span class="hlt">oscillators</span> in the system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19890048882&hterms=astronomia+espacio&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dastronomia%2By%2Bespacio','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19890048882&hterms=astronomia+espacio&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dastronomia%2By%2Bespacio"><span><span class="hlt">Oscillations</span> in stellar atmospheres</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Costa, A.; Ringuelet, A. E.; Fontenla, J. M.</p> <p>1989-01-01</p> <p>Atmospheric excitation and propagation of <span class="hlt">oscillations</span> are analyzed for typical pulsating stars. The linear, plane-parallel approach for the pulsating atmosphere gives a local description of the phenomenon. From the local analysis of <span class="hlt">oscillations</span>, the minimum <span class="hlt">frequencies</span> are obtained for radially propagating waves. The comparison of the minimum <span class="hlt">frequencies</span> obtained for a variety of stellar types is in good agreement with the observed periods of the <span class="hlt">oscillations</span>. The role of the atmosphere in the globar stellar pulsations is thus emphasized.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017OptLT..96...65L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017OptLT..96...65L"><span>Terahertz generation by difference <span class="hlt">frequency</span> generation from a compact optical parametric <span class="hlt">oscillator</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Zhongyang; Wang, Silei; Wang, Mengtao; Wang, Weishu</p> <p>2017-11-01</p> <p>Terahertz (THz) generation by difference <span class="hlt">frequency</span> generation (DFG) processes with dual idler waves is theoretically analyzed. The dual idler waves are generated by a compact optical parametric <span class="hlt">oscillator</span> (OPO) with periodically poled lithium niobate (PPLN). The phase-matching conditions in a same PPLN for the optical parametric <span class="hlt">oscillation</span> generating signal and idler waves and for the DFG generating THz waves can be simultaneously satisfied by selecting the poling period of PPLN. Moreover, 3-order cascaded DFG processes generating THz waves can be realized in the same PPLN. To take an example of 8.341 THz which locates in the vicinity of polariton resonances, THz intensities and quantum conversion efficiencies are calculated. Compared with non-cascaded DFG processes, THz intensities of 8.341 THz in 3-order cascaded DFG processes increase to 2.57 times. When the pump intensity equals to 20 MW/mm2, the quantum conversion efficiency of 106% in 3-order cascaded DFG processes can be realized, which exceeds the Manley-Rowe limit.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015MNRAS.448.1298P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015MNRAS.448.1298P"><span>On the modulation of low-<span class="hlt">frequency</span> quasi-periodic <span class="hlt">oscillations</span> in black hole transients</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pawar, Devraj D.; Motta, Sara; Shanthi, K.; Bhattacharya, Dipankar; Belloni, Tomaso</p> <p>2015-04-01</p> <p>We studied the properties of the low-<span class="hlt">frequency</span> quasi-periodic <span class="hlt">oscillations</span> detected in a sample of six black hole candidates (XTE J1550-564, H 1743-322, XTE J1859+226, 4U 1630-47, GX 339-4, XTE J1650-500) observed by the Rossi XTE satellite. We analysed the relation between the full width at half-maximum and the <span class="hlt">frequency</span> of all the narrow peaks detected in power density spectra where a type-C QPO is observed. Our goal was to understand the nature of the modulation of the signal by comparing the properties of different harmonic peaks in the power density spectrum. We find that for the sources in our sample the width of the fundamental and of the first harmonic are compatible with a <span class="hlt">frequency</span> modulation, while that of the sub-harmonic is independent of <span class="hlt">frequency</span>, possibly indicating the presence of an additional modulation in amplitude. We compare our results with those obtained earlier from GRS 1915+105 and XTE J1550-564.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3846747','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3846747"><span>A Daily <span class="hlt">Oscillation</span> in the Fundamental <span class="hlt">Frequency</span> and Amplitude of Harmonic Syllables of Zebra Finch Song</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Wood, William E.; Osseward, Peter J.; Roseberry, Thomas K.; Perkel, David J.</p> <p>2013-01-01</p> <p>Complex motor skills are more difficult to perform at certain points in the day (for example, shortly after waking), but the daily trajectory of motor-skill error is more difficult to predict. By undertaking a quantitative analysis of the fundamental <span class="hlt">frequency</span> (FF) and amplitude of hundreds of zebra finch syllables per animal per day, we find that zebra finch song follows a previously undescribed daily <span class="hlt">oscillation</span>. The FF and amplitude of harmonic syllables rises across the morning, reaching a peak near mid-day, and then falls again in the late afternoon until sleep. This <span class="hlt">oscillation</span>, although somewhat variable, is consistent across days and across animals and does not require serotonin, as animals with serotonergic lesions maintained daily <span class="hlt">oscillations</span>. We hypothesize that this <span class="hlt">oscillation</span> is driven by underlying physiological factors which could be shared with other taxa. Song production in zebra finches is a model system for studying complex learned behavior because of the ease of gathering comprehensive behavioral data and the tractability of the underlying neural circuitry. The daily <span class="hlt">oscillation</span> that we describe promises to reveal new insights into how time of day affects the ability to accomplish a variety of complex learned motor skills. PMID:24312654</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18542516','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18542516"><span><span class="hlt">High</span>-order dispersion in chirped-pulse <span class="hlt">oscillators</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kalashnikov, Vladimir L; Fernández, Alma; Apolonski, Alexander</p> <p>2008-03-17</p> <p>The effects of <span class="hlt">high</span>-order dispersion on a chirped-pulse <span class="hlt">oscillator</span> operating in the positive dispersion regime were studied both theoretically and experimentally. It was found that odd and negative even <span class="hlt">high</span>-order dispersions impair the <span class="hlt">oscillator</span> stability owing to resonance with the dispersion waves, but can broaden the spectrum as in the case of continuum generation in the fibers. Positive fourth-order dispersion enhances the stability and shifts the stability range into negative dispersion. The destabilization mechanism was found to be a parametrical instability which causes noisy mode locking around zero dispersion.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29092187','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29092187"><span>Supermode noise suppression with mutual injection locking for coupled optoelectronic <span class="hlt">oscillator</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Dai, Jian; Liu, Anni; Liu, Jingliang; Zhang, Tian; Zhou, Yue; Yin, Feifei; Dai, Yitang; Liu, Yuanan; Xu, Kun</p> <p>2017-10-30</p> <p>The coupled optoelectronic <span class="hlt">oscillator</span> (COEO) is typically used to generate <span class="hlt">high</span> <span class="hlt">frequency</span> spectrally pure microwave signal with serious sidemodes noise. We propose and experimentally demonstrate a simple scheme for supermode suppression with mutual injection locking between the COEO (master <span class="hlt">oscillator</span> with multi-modes <span class="hlt">oscillation</span>) and the embedded free-running <span class="hlt">oscillator</span> (slave <span class="hlt">oscillator</span> with single-mode <span class="hlt">oscillation</span>). The master and slave <span class="hlt">oscillators</span> share the same electrical feedback path, which means that the mutually injection-locked COEO brings no additional hardware complexity. Owing to the mode matching and mutually injection locking effect, 9.999 GHz signal has been successfully obtained by the mutually injection-locked COEO with the phase noise about -117 dBc/Hz at 10 kHz offset <span class="hlt">frequency</span>. Besides, the supermode noise can be significantly suppressed more than 50 dB to below -120 dBc.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5367085','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5367085"><span>Communication between Brain Areas Based on Nested <span class="hlt">Oscillations</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Kastner, Sabine</p> <p>2017-01-01</p> <p>Abstract Unraveling how brain regions communicate is crucial for understanding how the brain processes external and internal information. Neuronal <span class="hlt">oscillations</span> within and across brain regions have been proposed to play a crucial role in this process. Two main hypotheses have been suggested for routing of information based on <span class="hlt">oscillations</span>, namely communication through coherence and gating by inhibition. Here, we propose a framework unifying these two hypotheses that is based on recent empirical findings. We discuss a theory in which communication between two regions is established by phase synchronization of <span class="hlt">oscillations</span> at lower <span class="hlt">frequencies</span> (<25 Hz), which serve as temporal reference frame for information carried by <span class="hlt">high-frequency</span> activity (>40 Hz). Our framework, consistent with numerous recent empirical findings, posits that cross-<span class="hlt">frequency</span> interactions are essential for understanding how large-scale cognitive and perceptual networks operate. PMID:28374013</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110022592','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110022592"><span>Nonlinear <span class="hlt">Oscillators</span> in Space Physics</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Lester,Daniel; Thronson, Harley</p> <p>2011-01-01</p> <p>We discuss dynamical systems that produce an <span class="hlt">oscillation</span> without an external time dependent source. Numerical results are presented for nonlinear <span class="hlt">oscillators</span> in the Em1h's atmosphere, foremost the quasi-biennial <span class="hlt">oscillation</span> (QBOl. These fluid dynamical <span class="hlt">oscillators</span>, like the solar dynamo, have in common that one of the variables in a governing equation is strongly nonlinear and that the nonlinearity, to first order, has particular form. of 3rd or odd power. It is shown that this form of nonlinearity can produce the fundamental li'equency of the internal <span class="hlt">oscillation</span>. which has a period that is favored by the dynamical condition of the fluid. The fundamental <span class="hlt">frequency</span> maintains the <span class="hlt">oscillation</span>, with no energy input to the system at that particular <span class="hlt">frequency</span>. Nonlinearities of 2nd or even power could not maintain the <span class="hlt">oscillation</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PhRvE..97d2901O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PhRvE..97d2901O"><span>Experiments and characterization of low-<span class="hlt">frequency</span> <span class="hlt">oscillations</span> in a granular column</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Oyarte Gálvez, Loreto; Rivas, Nicolás; van der Meer, Devaraj</p> <p>2018-04-01</p> <p>The behavior of a vertically vibrated granular bed is reminiscent of a liquid in that it exhibits many phenomena such as convection and Faraday-like surface waves. However, when the lateral dimensions of the bed are confined such that a quasi-one-dimensional geometry is formed, the only phenomena that remain are bouncing bed and the granular Leidenfrost effect. This permits the observation of the granular Leidenfrost state for a wide range of energy injection parameters and more specifically allows for a thorough characterization of the low-<span class="hlt">frequency</span> <span class="hlt">oscillation</span> (LFO) that is present in this state. In both experiments and particle simulations we determine the LFO <span class="hlt">frequency</span> from the power spectral density of the center-of-mass signal of the grains, varying the amplitude and <span class="hlt">frequency</span> of the driving, the particle diameter, and the number of layers in the system. We thus find that the LFO <span class="hlt">frequency</span> (i) is inversely proportional to the fast inertial timescale and (ii) decorrelates with a typical decay time proportional to the slow dissipative timescale in the system. The latter is consistent with the view that the LFO is driven by the inherent noise that is present in the granular Leidenfrost state with a low number of particles.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1405296-precise-measurement-meson-oscillation-frequency','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1405296-precise-measurement-meson-oscillation-frequency"><span>A precise measurement of the $B^0$ meson <span class="hlt">oscillation</span> <span class="hlt">frequency</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Aaij, R.; Abellán Beteta, C.; Adeva, B.; ...</p> <p>2016-07-21</p> <p>The <span class="hlt">oscillation</span> <span class="hlt">frequency</span>, Δm d, of B 0 mesons is measured using semileptonic decays with a D – or D* – meson in the final state. The data sample corresponds to 3.0fb –1 of pp collisions, collected by the LHCb experiment at centre-of-mass energies √s = 7 and 8TeV. A combination of the two decay modes gives Δm d=(505.0±2.1±1.0)ns –1, where the first uncertainty is statistical and the second is systematic. This is the most precise single measurement of this parameter. It is consistent with the current world average and has similar precision.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/15890781','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/15890781"><span>The <span class="hlt">frequencies</span> of calcium <span class="hlt">oscillations</span> are optimized for efficient calcium-mediated activation of Ras and the ERK/MAPK cascade.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kupzig, Sabine; Walker, Simon A; Cullen, Peter J</p> <p>2005-05-24</p> <p>Ras proteins are binary switches that, by cycling through inactive GDP- and active GTP-bound conformations, regulate multiple cellular signaling pathways, including those that control growth and differentiation. For some time, it has been known that receptor-mediated increases in the concentration of intracellular free calcium ([Ca(2+)](i)) can modulate Ras activation. Increases in [Ca(2+)](i) often occur as repetitive Ca(2+) spikes or <span class="hlt">oscillations</span>. Induced by electrical or receptor stimuli, these repetitive Ca(2+) <span class="hlt">oscillations</span> increase in <span class="hlt">frequency</span> with the amplitude of receptor stimuli, a phenomenon critical for the induction of selective cellular functions. Here, we show that Ca(2+) <span class="hlt">oscillations</span> are optimized for Ca(2+)-mediated activation of Ras and signaling through the extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) cascade. We present additional evidence that Ca(2+) <span class="hlt">oscillations</span> reduce the effective Ca(2+) threshold for the activation of Ras and that the oscillatory <span class="hlt">frequency</span> is optimized for activation of Ras and the ERK/MAPK pathway. Our results describe a hitherto unrecognized link between complex Ca(2+) signals and the modulation of the Ras/ERK/MAPK signaling cascade.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/1174504','DOE-PATENT-XML'); return false;" href="https://www.osti.gov/servlets/purl/1174504"><span>Active shunt capacitance cancelling <span class="hlt">oscillator</span> circuit</span></a></p> <p><a target="_blank" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Wessendorf, Kurt O.</p> <p>2003-09-23</p> <p>An <span class="hlt">oscillator</span> circuit is disclosed which can be used to produce <span class="hlt">oscillation</span> using a piezoelectric crystal, with a <span class="hlt">frequency</span> of <span class="hlt">oscillation</span> being largely independent of any shunt capacitance associated with the crystal (i.e. due to electrodes on the surfaces of the crystal and due to packaging and wiring for the crystal). The <span class="hlt">oscillator</span> circuit is based on a tuned gain stage which operates the crystal at a <span class="hlt">frequency</span>, f, near a series resonance <span class="hlt">frequency</span>, f.sub.S. The <span class="hlt">oscillator</span> circuit further includes a compensation circuit that supplies all the ac current flow through the shunt resistance associated with the crystal so that this ac current need not be supplied by the tuned gain stage. The compensation circuit uses a current mirror to provide the ac current flow based on the current flow through a reference capacitor that is equivalent to the shunt capacitance associated with the crystal. The <span class="hlt">oscillator</span> circuit has applications for driving piezoelectric crystals for sensing of viscous, fluid or solid media by detecting a change in the <span class="hlt">frequency</span> of <span class="hlt">oscillation</span> of the crystal and a resonator loss which occur from contact of an exposed surface of the crystal by the viscous, fluid or solid media.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018AIPC.1942m0030B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018AIPC.1942m0030B"><span>Microwave <span class="hlt">frequency</span> tuning in heterogeneous spin torque <span class="hlt">oscillator</span> with perpendicular polarizer: A macrospin study</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bhoomeeswaran, H.; Vivek, T.; Sabareesan, P.</p> <p>2018-04-01</p> <p>In this article, we have theoretically devised a Spin Torque Nano <span class="hlt">Oscillator</span> (STNO) with perpendicular polarizer using macro spin model. The devised spin valve structure is heterogeneous (i.e.) it is made of two different ferromagnetic materials [Co and its alloy CoFeB]. The dynamics of magnetization provoked by spin transfer torque is studied numerically by solving the famous Landau-Lifshitz-Gilbert-Slonczewski [LLGS] equation. The results are obtained for the perpendicular polarizer and for that particular out of plane orientation we vary the free layer angle from 10° to 90°. The obtained results are <span class="hlt">highly</span> appealing, because <span class="hlt">frequency</span> range is available in all the tilt angles of free layer and it is exceptionally tunable in all free layer tilt angles with zero applied field. Moreover, the utmost operating <span class="hlt">frequency</span> of about 83.3 GHz and its corresponding power of 4.488 µW/mA2/GHz is acquired for the free layer tilt angle θ = 90° with the solid applied current density of 10 × 1010 A/m2. Also, our device emits <span class="hlt">high</span> quality factor of about 396, which is remarkably desirable for making devices. These pioneering results provides a significant development for future spintronic based devices.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050136663','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050136663"><span>How to Distinguish Neutron Star and Black Hole X-ray Binaries? Spectral Index and Quasi-Periodic <span class="hlt">Oscillation</span> <span class="hlt">Frequency</span> Correlation</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Titarchuk, Lev; Shaposhnikov, Nickolai</p> <p>2005-01-01</p> <p>Recent studies have revealed strong correlations between 1-10 Hz <span class="hlt">frequencies</span> of quasiperiodic <span class="hlt">oscillations</span> (QPOs) and the spectral power law index of several Black Hole (BH) candidate sources when seen in the low/hard state, the steep power-law (soft) state, and in transition between these states. In the soft state these index-QPO <span class="hlt">frequency</span> correlations show a saturation of the photon index GAMMA approximately equal to 2.7 at <span class="hlt">high</span> values of the low <span class="hlt">frequency</span> nu(sub L). This saturation effect was previously identified as a black hole signature. In this paper we argue that this saturation does not occur, at least for one neutron star (NS) source 4U 1728-34, for which the index GAMMA monotonically increases with nu(sub L) to the values of 6 and higher. We base this conclusion on our analysis of approximately 1.5 Msec of RXTE archival data for 4U 1728-34. We reveal the spectral evolution of the Comptonized blackbody spectra when the source transitions from the hard to soft states. The hard state spectrum is a typical thermal Comptonization spectrum of the soft photons which originate in the disk and the NS outer photospheric layers. The hard state photon index is GAMMA approximately 2. The soft state spectrum consists of two blackbody components which are only slightly Comptonized. Thus we can claim (as expected from theory) that in NS sources thermal equilibrium is established for the soft state. To the contrary in BH sources, the equilibrium is never established due to the presence of the BH horizon. The emergent BH spectrum, even in the <span class="hlt">high</span>/soft state, has a power law component. We also identify the low QPO <span class="hlt">frequency</span> nu(sub L) as a fundamental <span class="hlt">frequency</span> of the quasi-spherical component of the transition layer (presumably related to the corona and the NS and disk magnetic closed field lines). The lower <span class="hlt">frequency</span> nu(sub SL) is identified as the <span class="hlt">frequency</span> of <span class="hlt">oscillations</span> of a quasi-cylindrical configuration of the TL (presumably related to the NS and disk magnetic</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/4281653','DOE-PATENT-XML'); return false;" href="https://www.osti.gov/biblio/4281653"><span>VOLTAGE-CONTROLLED TRANSISTOR <span class="hlt">OSCILLATOR</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Scheele, P.F.</p> <p>1958-09-16</p> <p>This patent relates to transistor <span class="hlt">oscillators</span> and in particular to those transistor <span class="hlt">oscillators</span> whose <span class="hlt">frequencies</span> vary according to controlling voltages. A principal feature of the disclosed transistor <span class="hlt">oscillator</span> circuit resides in the temperature compensation of the <span class="hlt">frequency</span> modulating stage by the use of a resistorthermistor network. The resistor-thermistor network components are selected to have the network resistance, which is in series with the modulator transistor emitter circuit, vary with temperature to compensate for variation in the parameters of the transistor due to temperature change.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018E%26ES..114a2012C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018E%26ES..114a2012C"><span>Design of c-band telecontrol transmitter local <span class="hlt">oscillator</span> for UAV data link</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cao, Hui; Qu, Yu; Song, Zuxun</p> <p>2018-01-01</p> <p>A C-band local <span class="hlt">oscillator</span> of an Unmanned Aerial Vehicle (UAV) data link radio <span class="hlt">frequency</span> (RF) transmitter unit with <span class="hlt">high</span>-stability, <span class="hlt">high</span>-precision and lightweight was designed in this paper. Based on the <span class="hlt">highly</span> integrated broadband phase-locked loop (PLL) chip HMC834LP6GE, the system performed fractional-N control by internal modules programming to achieve low phase noise and small <span class="hlt">frequency</span> resolution. The simulation and testing methods were combined to optimize and select the loop filter parameters to ensure the <span class="hlt">high</span> precision and stability of the <span class="hlt">frequency</span> synthesis output. The theoretical analysis and engineering prototype measurement results showed that the local <span class="hlt">oscillator</span> had stable output <span class="hlt">frequency</span>, accurate <span class="hlt">frequency</span> step, <span class="hlt">high</span> spurious suppression and low phase noise, and met the design requirements. The proposed design idea and research method have theoretical guiding significance for engineering practice.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..MARB46013S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..MARB46013S"><span>Enthalpy of sublimation as measured using a silicon <span class="hlt">oscillator</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shakeel, Hamza; Pomeroy, J. M.</p> <p></p> <p>In this study, we report the enthalpy of sublimation of common gases (nitrogen, oxygen, argon, carbon dioxide, neon, krypton, xenon, and water vapor) using a large area silicon <span class="hlt">oscillator</span> with a sub-ng (~0.027 ng/cm2) mass sensitivity. The double paddle <span class="hlt">oscillator</span> design enables <span class="hlt">high</span> <span class="hlt">frequency</span> stability (17 ppb) at cryogenic temperatures and provides a consistent technique for enthalpy measurements. The enthalpies of sublimation are derived from the rate of mass loss during programmed thermal desorption and are detected as a change in the resonance <span class="hlt">frequency</span> of the self-tracking <span class="hlt">oscillator</span>. These measured enthalpy values show excellent agreement with the accepted literature values.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26976199','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26976199"><span><span class="hlt">Frequency</span> and amplitude modulation of ultra-compact terahertz quantum cascade lasers using an integrated avalanche diode <span class="hlt">oscillator</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Castellano, Fabrizio; Li, Lianhe; Linfield, Edmund H; Davies, A Giles; Vitiello, Miriam S</p> <p>2016-03-15</p> <p>Mode-locked comb sources operating at optical <span class="hlt">frequencies</span> underpin applications ranging from spectroscopy and ultrafast physics, through to absolute <span class="hlt">frequency</span> measurements and atomic clocks. Extending their operation into the terahertz <span class="hlt">frequency</span> range would greatly benefit from the availability of compact semiconductor-based sources. However, the development of any compact mode-locked THz laser, which itself is inherently a <span class="hlt">frequency</span> comb, has yet to be achieved without the use of an external stimulus. <span class="hlt">High</span>-power, electrically pumped quantum cascade lasers (QCLs) have recently emerged as a promising solution, owing to their octave spanning bandwidths, the ability to achieve group-velocity dispersion compensation and the possibility of obtaining active mode-locking. Here, we propose an unprecedented compact architecture to induce both <span class="hlt">frequency</span> and amplitude self-modulation in a THz QCL. By engineering a microwave avalanche <span class="hlt">oscillator</span> into the laser cavity, which provides a 10 GHz self-modulation of the bias current and output power, we demonstrate multimode laser emission centered around 3 THz, with distinct multiple sidebands. The resulting microwave amplitude and <span class="hlt">frequency</span> self-modulation of THz QCLs opens up intriguing perspectives, for engineering integrated self-mode-locked THz lasers, with impact in fields such as nano- and ultrafast photonics and optical metrology.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_23 --> <div id="page_24" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="461"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4792146','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4792146"><span><span class="hlt">Frequency</span> and amplitude modulation of ultra-compact terahertz quantum cascade lasers using an integrated avalanche diode <span class="hlt">oscillator</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Castellano, Fabrizio; Li, Lianhe; Linfield, Edmund H.; Davies, A. Giles; Vitiello, Miriam S.</p> <p>2016-01-01</p> <p>Mode-locked comb sources operating at optical <span class="hlt">frequencies</span> underpin applications ranging from spectroscopy and ultrafast physics, through to absolute <span class="hlt">frequency</span> measurements and atomic clocks. Extending their operation into the terahertz <span class="hlt">frequency</span> range would greatly benefit from the availability of compact semiconductor-based sources. However, the development of any compact mode-locked THz laser, which itself is inherently a <span class="hlt">frequency</span> comb, has yet to be achieved without the use of an external stimulus. <span class="hlt">High</span>-power, electrically pumped quantum cascade lasers (QCLs) have recently emerged as a promising solution, owing to their octave spanning bandwidths, the ability to achieve group-velocity dispersion compensation and the possibility of obtaining active mode-locking. Here, we propose an unprecedented compact architecture to induce both <span class="hlt">frequency</span> and amplitude self-modulation in a THz QCL. By engineering a microwave avalanche <span class="hlt">oscillator</span> into the laser cavity, which provides a 10 GHz self-modulation of the bias current and output power, we demonstrate multimode laser emission centered around 3 THz, with distinct multiple sidebands. The resulting microwave amplitude and <span class="hlt">frequency</span> self-modulation of THz QCLs opens up intriguing perspectives, for engineering integrated self-mode-locked THz lasers, with impact in fields such as nano- and ultrafast photonics and optical metrology. PMID:26976199</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DFDG21008C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DFDG21008C"><span>Nonlinear <span class="hlt">oscillation</span> and interfacial stability of an encapsulated microbubble under dual-<span class="hlt">frequency</span> ultrasound</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Calvisi, Michael; Liu, Yunqiao; Wang, Qianxi</p> <p>2016-11-01</p> <p>Encapsulated microbubbles (EMBs) are widely used in medical ultrasound imaging as contrast-enhanced agents. However, the potential damaging effects of violent, collapsing EMBs to cells and tissues in clinical practice have remained a concern. Dual-<span class="hlt">frequency</span> ultrasound is a promising technique for improving the efficacy and safety of sonography. The EMB system modeled consists of the external liquid, membrane, and internal gases. The microbubble dynamics are simulated using a simple nonlinear interactive theory, considering the compressibility of the internal gas, viscosity of the liquid flow, and elasticity of the membrane. The radial <span class="hlt">oscillation</span> and interfacial stability of an EMB under single and dual-<span class="hlt">frequency</span> excitations are compared. The simulation results show that the dual-<span class="hlt">frequency</span> technique produces larger backscatter pressure at higher harmonics of the primary driving <span class="hlt">frequency</span>. This enriched acoustic spectrum can enhance blood-tissue contrast and improve sonographic image quality. The results further show that the acoustic pressure threshold associated with the onset of shape instability is greater for dual-<span class="hlt">frequency</span> driving. This suggests that the dual-<span class="hlt">frequency</span> technique stabilizes the EMB, thereby improving the efficacy and safety of contrast-enhanced agents.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3862267','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3862267"><span>Membrane Resonance Enables Stable and Robust Gamma <span class="hlt">Oscillations</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Moca, Vasile V.; Nikolić, Danko; Singer, Wolf; Mureşan, Raul C.</p> <p>2014-01-01</p> <p>Neuronal mechanisms underlying beta/gamma <span class="hlt">oscillations</span> (20–80 Hz) are not completely understood. Here, we show that in vivo beta/gamma <span class="hlt">oscillations</span> in the cat visual cortex sometimes exhibit remarkably stable <span class="hlt">frequency</span> even when inputs fluctuate dramatically. Enhanced <span class="hlt">frequency</span> stability is associated with stronger <span class="hlt">oscillations</span> measured in individual units and larger power in the local field potential. Simulations of neuronal circuitry demonstrate that membrane properties of inhibitory interneurons strongly determine the characteristics of emergent <span class="hlt">oscillations</span>. Exploration of networks containing either integrator or resonator inhibitory interneurons revealed that: (i) Resonance, as opposed to integration, promotes robust <span class="hlt">oscillations</span> with large power and stable <span class="hlt">frequency</span> via a mechanism called RING (Resonance INduced Gamma); resonance favors synchronization by reducing phase delays between interneurons and imposes bounds on <span class="hlt">oscillation</span> cycle duration; (ii) Stability of <span class="hlt">frequency</span> and robustness of the <span class="hlt">oscillation</span> also depend on the relative timing of excitatory and inhibitory volleys within the <span class="hlt">oscillation</span> cycle; (iii) RING can reproduce characteristics of both Pyramidal INterneuron Gamma (PING) and INterneuron Gamma (ING), transcending such classifications; (iv) In RING, robust gamma <span class="hlt">oscillations</span> are promoted by slow but are impaired by fast inputs. Results suggest that interneuronal membrane resonance can be an important ingredient for generation of robust gamma <span class="hlt">oscillations</span> having stable <span class="hlt">frequency</span>. PMID:23042733</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5226354','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5226354"><span>Interictal <span class="hlt">High</span> <span class="hlt">Frequency</span> <span class="hlt">Oscillations</span> Detected with Simultaneous Magnetoencephalography and Electroencephalography as Biomarker of Pediatric Epilepsy</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Papadelis, Christos; Tamilia, Eleonora; Stufflebeam, Steven; Grant, Patricia E.; Madsen, Joseph R.; Pearl, Phillip L.; Tanaka, Naoaki</p> <p>2016-01-01</p> <p>Crucial to the success of epilepsy surgery is the availability of a robust biomarker that identifies the Epileptogenic Zone (EZ). <span class="hlt">High</span> <span class="hlt">Frequency</span> <span class="hlt">Oscillations</span> (HFOs) have emerged as potential presurgical biomarkers for the identification of the EZ in addition to Interictal Epileptiform Discharges (IEDs) and ictal activity. Although they are promising to localize the EZ, they are not yet suited for the diagnosis or monitoring of epilepsy in clinical practice. Primary barriers remain: the lack of a formal and global definition for HFOs; the consequent heterogeneity of methodological approaches used for their study; and the practical difficulties to detect and localize them noninvasively from scalp recordings. Here, we present a methodology for the recording, detection, and localization of interictal HFOs from pediatric patients with refractory epilepsy. We report representative data of HFOs detected noninvasively from interictal scalp EEG and MEG from two children undergoing surgery. The underlying generators of HFOs were localized by solving the inverse problem and their localization was compared to the Seizure Onset Zone (SOZ) as this was defined by the epileptologists. For both patients, Interictal Epileptogenic Discharges (IEDs) and HFOs were localized with source imaging at concordant locations. For one patient, intracranial EEG (iEEG) data were also available. For this patient, we found that the HFOs localization was concordant between noninvasive and invasive methods. The comparison of iEEG with the results from scalp recordings served to validate these findings. To our best knowledge, this is the first study that presents the source localization of scalp HFOs from simultaneous EEG and MEG recordings comparing the results with invasive recordings. These findings suggest that HFOs can be reliably detected and localized noninvasively with scalp EEG and MEG. We conclude that the noninvasive localization of interictal HFOs could significantly improve the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SPIE.9728E..1VW','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SPIE.9728E..1VW"><span><span class="hlt">High</span> power, <span class="hlt">high</span> signal-to-noise ratio single-<span class="hlt">frequency</span> 1μm Brillouin all-fiber laser</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Jing; Hou, Yubin; Zhang, Qian; Jin, Dongchen; Sun, Ruoyu; Shi, Hongxing; Liu, Jiang; Wang, Pu</p> <p>2016-03-01</p> <p>We demonstrate a <span class="hlt">high</span>-power, <span class="hlt">high</span> signal-to-noise ratio single-<span class="hlt">frequency</span> 1 μm Brillouin all-fiber laser with <span class="hlt">high</span> slope efficiency. The Brillouin laser system consists of a <span class="hlt">high</span>-power single-<span class="hlt">frequency</span> fiber laser and a single-pass Brillouin ring cavity. The <span class="hlt">high</span>-power single-<span class="hlt">frequency</span> fiber laser is one-stage master-<span class="hlt">oscillator</span> power amplifier with the maximum output power of 10.33 W, the signal-to-noise ratio of 50 dB and the slope efficiency of 46%. The Brillouin fiber laser is pumped by the amplified laser with a linewidth of 33 kHz and an output power of 2.61 W limited by the damage threshold of the optical isolator. By optimizing the length of the Brillouin ring cavity to 10 m, stable singlefrequency Brillouin fiber laser is obtained with 3 kHz linewidth owing to the linewidth narrowing effect. At the launched pump power of 2.15 W, the Brillouin fiber laser generates maximum output power of 1.4 W with a slope efficiency of 79% and the optical signal-to-noise ratio of 77 dB.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006OExpr..1412341L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006OExpr..1412341L"><span>Mid-infrared wavelength- and <span class="hlt">frequency</span>-modulation spectroscopy with a pump-modulated singly-resonant optical parametric <span class="hlt">oscillator</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lindsay, I. D.; Groß, P.; Lee, C. J.; Adhimoolam, B.; Boller, K.-J.</p> <p>2006-12-01</p> <p>We describe the implementation of the wavelength- and <span class="hlt">frequency</span>-modulation spectroscopy techniques using a singly-resonant optical parametric <span class="hlt">oscillator</span> (OPO) pumped by a fiber-amplified diode laser. <span class="hlt">Frequency</span> modulation of the diode laser was transferred to the OPO’s mid-infrared idler output, avoiding the need for external modulation devices. This approach thus provides a means of implementing these important techniques with powerful, widely tunable, mid-infrared sources while retaining the simple, flexible modulation properties of diode lasers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AIPC..985..622G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AIPC..985..622G"><span>Piezo-Hydraulic Actuation for Driving <span class="hlt">High</span> <span class="hlt">Frequency</span> Miniature Split-Stirling Pulse Tube Cryocoolers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Garaway, I.; Grossman, G.</p> <p>2008-03-01</p> <p>In recent years piezoelectric actuation has been identified as a promising means of driving miniature Stirling devices. It supports miniaturization, has a <span class="hlt">high</span> power to volume ratio, can operate at almost any <span class="hlt">frequency</span>, good electrical to mechanical efficiencies, and potentially has a very long operating life. The major drawback of piezoelectric actuation, however, is the very small displacements that this physical phenomenon produces. This study shows that by employing valve-less hydraulic amplification an <span class="hlt">oscillating</span> pressure wave can be created that is sufficiently large to drive a <span class="hlt">high</span> <span class="hlt">frequency</span> miniature pulse tube cryocooler (as <span class="hlt">high</span> as 500 Hz in our experiments and perhaps higher). Beyond the direct benefits derived from using piezoelectric actuation, there are further benefits derived from using the piezo-hydraulic arrangement with membranes. Due to the incompressibility of the hydraulic fluid, the actuator may be separated from the main body of the cryocooler by relatively large distances with almost no detrimental effects, and the complete lack of rubbing parts in the power conversion processes makes this type of cryocooler extremely robust. The design and experimental device, coined the "Piezo-Hydraulic Membrane <span class="hlt">Oscillator</span>", are presented along with some test results.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1297914-nonequilibrium-simulations-model-ionomers-oscillating-electric-field','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1297914-nonequilibrium-simulations-model-ionomers-oscillating-electric-field"><span>Nonequilibrium simulations of model ionomers in an <span class="hlt">oscillating</span> electric field</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Ting, Christina L.; Sorensen-Unruh, Karen E.; Stevens, Mark J.; ...</p> <p>2016-07-25</p> <p>Here, we perform molecular dynamics simulations of a coarse-grained model of ionomer melts in an applied <span class="hlt">oscillating</span> electric field. The <span class="hlt">frequency</span>-dependent conductivity and susceptibility are calculated directly from the current density and polarization density, respectively. At <span class="hlt">high</span> <span class="hlt">frequencies</span>, we find a peak in the real part of the conductivity due to plasma <span class="hlt">oscillations</span> of the ions. At lower <span class="hlt">frequencies</span>, the dynamic response of the ionomers depends on the ionic aggregate morphology in the system, which consists of either percolated or isolated aggregates. We show that the dynamic response of the model ionomers to the applied <span class="hlt">oscillating</span> field can be understoodmore » by comparison with relevant time scales in the systems, obtained from independent calculations.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/1297914','SCIGOV-STC'); return false;" href="https://www.osti.gov/servlets/purl/1297914"><span>Nonequilibrium simulations of model ionomers in an <span class="hlt">oscillating</span> electric field</span></a></p> <p><a target="_blank" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Ting, Christina L.; Sorensen-Unruh, Karen E.; Stevens, Mark J.</p> <p></p> <p>Here, we perform molecular dynamics simulations of a coarse-grained model of ionomer melts in an applied <span class="hlt">oscillating</span> electric field. The <span class="hlt">frequency</span>-dependent conductivity and susceptibility are calculated directly from the current density and polarization density, respectively. At <span class="hlt">high</span> <span class="hlt">frequencies</span>, we find a peak in the real part of the conductivity due to plasma <span class="hlt">oscillations</span> of the ions. At lower <span class="hlt">frequencies</span>, the dynamic response of the ionomers depends on the ionic aggregate morphology in the system, which consists of either percolated or isolated aggregates. We show that the dynamic response of the model ionomers to the applied <span class="hlt">oscillating</span> field can be understoodmore » by comparison with relevant time scales in the systems, obtained from independent calculations.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/1439588','SCIGOV-STC'); return false;" href="https://www.osti.gov/servlets/purl/1439588"><span>Nonlinearity induced synchronization enhancement in mechanical <span class="hlt">oscillators</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Czaplewski, David A.; Lopez, Omar; Guest, Jeffrey R.</p> <p></p> <p>An autonomous <span class="hlt">oscillator</span> synchronizes to an external harmonic force only when the forcing <span class="hlt">frequency</span> lies within a certain interval, known as the synchronization range, around the <span class="hlt">oscillator</span>'s natural <span class="hlt">frequency</span>. Under ordinary conditions, the width of the synchronization range decreases when the <span class="hlt">oscillation</span> amplitude grows, which constrains synchronized motion of micro- and nano-mechanical resonators to narrow <span class="hlt">frequency</span> and amplitude bounds. The present invention shows that nonlinearity in the <span class="hlt">oscillator</span> can be exploited to manifest a regime where the synchronization range increases with an increasing <span class="hlt">oscillation</span> amplitude. The present invention shows that nonlinearities in specific configurations of <span class="hlt">oscillator</span> systems, as described herein,more » are the key determinants of the effect. The present invention presents a new configuration and operation regime that enhances the synchronization of micro- and nano-mechanical <span class="hlt">oscillators</span> by capitalizing on their intrinsic nonlinear dynamics.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20130009405','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20130009405"><span>Real-Time Distributed Embedded <span class="hlt">Oscillator</span> Operating <span class="hlt">Frequency</span> Monitoring</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Pollock, Julie; Oliver, Brett; Brickner, Christopher</p> <p>2012-01-01</p> <p>A document discusses the utilization of embedded clocks inside of operating network data links as an auxiliary clock source to satisfy local <span class="hlt">oscillator</span> monitoring requirements. Modem network interfaces, typically serial network links, often contain embedded clocking information of very tight precision to recover data from the link. This embedded clocking data can be utilized by the receiving device to monitor the local <span class="hlt">oscillator</span> for tolerance to required specifications, often important in <span class="hlt">high</span>-integrity fault-tolerant applications. A device can utilize a received embedded clock to determine if the local or the remote device is out of tolerance by using a single link. The local device can determine if it is failing, assuming a single fault model, with two or more active links. Network fabric components, containing many operational links, can potentially determine faulty remote or local devices in the presence of multiple faults. Two methods of implementation are described. In one method, a recovered clock can be directly used to monitor the local clock as a direct replacement of an external local <span class="hlt">oscillator</span>. This scheme is consistent with a general clock monitoring function whereby clock sources are clocking two counters and compared over a fixed interval of time. In another method, overflow/underflow conditions can be used to detect clock relationships for monitoring. These network interfaces often provide clock compensation circuitry to allow data to be transferred from the received (network) clock domain to the internal clock domain. This circuit could be modified to detect overflow/underflow conditions of the buffering required and report a fast or slow receive clock, respectively.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19571944','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19571944"><span>Compact, passively Q-switched, all-solid-state master <span class="hlt">oscillator</span>-power amplifier-optical parametric <span class="hlt">oscillator</span> (MOPA-OPO) system pumped by a fiber-coupled diode laser generating <span class="hlt">high</span>-brightness, tunable, ultraviolet radiation.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Peuser, Peter; Platz, Willi; Fix, Andreas; Ehret, Gerhard; Meister, Alexander; Haag, Matthias; Zolichowski, Paul</p> <p>2009-07-01</p> <p>We report on a compact, tunable ultraviolet laser system that consists of an optical parametric <span class="hlt">oscillator</span> (OPO) and a longitudinally diode-pumped Nd:YAG master <span class="hlt">oscillator</span>-power amplifier (MOPA). The pump energy for the whole laser system is supplied via a single delivery fiber. Nanosecond pulses are produced by an <span class="hlt">oscillator</span> that is passively Q-switched by a Cr(4+):YAG crystal. The OPO is pumped by the second harmonic of the Nd:YAG MOPA. Continuously tunable radiation is generated by an intracavity sum-<span class="hlt">frequency</span> mixing process within the OPO in the range of 245-260 nm with <span class="hlt">high</span> beam quality. Maximum pulse energies of 1.2 mJ were achieved, which correspond to an optical efficiency of 3.75%, relating to the pulse energy of the MOPA at 1064 nm.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2885579','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2885579"><span>W-Band <span class="hlt">Frequency</span>-Swept EPR</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Hyde, James S.; Strangeway, Robert A.; Camenisch, Theodore G.; Ratke, Joseph J.; Froncisz, Wojciech</p> <p>2010-01-01</p> <p>This paper describes a novel experiment on nitroxide radical spin labels using a multiarm EPR W-band bridge with a loop-gap resonator (LGR). We demonstrate EPR spectroscopy of spin labels by linear sweep of the microwave <span class="hlt">frequency</span> across the spectrum. The <span class="hlt">high</span> bandwidth of the LGR, about 1 GHz between 3 dB points of the microwave resonance, makes this new experiment possible. A <span class="hlt">frequency</span>-tunable yttrium iron garnet (YIG) <span class="hlt">oscillator</span> provides sweep rates as <span class="hlt">high</span> as 1.8 × 105 GHz/s, which corresponds to 6.3 kT/s in magnetic field-sweep units over a 44 MHz range. Two experimental domains were identified. In the first, linear <span class="hlt">frequency</span> sweep rates were relatively slow, and pure absorption and pure dispersion spectra were obtained. This appears to be a practical mode of operation at the present level of technological development. The main advantage is the elimination of sinusoidal magnetic field modulation. In the second mode, the <span class="hlt">frequency</span> is swept rapidly across a portion of the spectrum, and then the <span class="hlt">frequency</span> sweep is stopped for a readout period; FID signals from a swept line <span class="hlt">oscillate</span> at a <span class="hlt">frequency</span> that is the difference between the spectral position of the line in <span class="hlt">frequency</span> units and the readout position. If there is more than one line, <span class="hlt">oscillations</span> are superimposed. The sweep rates using the YIG <span class="hlt">oscillator</span> were too slow, and the portion of the spectrum too narrow to achieve the full EPR equivalent of Fourier transform (FT) NMR. The paper discusses technical advances required to reach this goal. The hypothesis that trapezoidal <span class="hlt">frequency</span> sweep is an enabling technology for FT EPR is supported by this study. PMID:20462775</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1999IJBm...43...31D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1999IJBm...43...31D"><span>The effects of extra-low-<span class="hlt">frequency</span> atmospheric pressure <span class="hlt">oscillations</span> on human mental activity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Delyukov, A. A.; Didyk, L.</p> <p></p> <p>Slight atmospheric pressure <span class="hlt">oscillations</span> (APO) in the extra-low-<span class="hlt">frequency</span> range below 0.1 Hz, which frequently occur naturally, can influence human mental activity. This phenomenon has been observed in experiments with a group of 12 healthy volunteers exposed to experimentally created APO with amplitudes 30-50 Pa in the <span class="hlt">frequency</span> band 0.011-0.17 Hz. Exposure of the subjects to APO for 15-30 min caused significant changes in attention and short-term memory functions, performance rate, and mental processing flexibility. The character of the response depended on the APO <span class="hlt">frequency</span> and coherence. Periodic APO promoted purposeful mental activity, accompanied by an increase in breath-holding duration and a slower heart rate. On the other hand, quasi-chaotic APO, similar to the natural perturbations of atmospheric pressure, disrupted mental activity. These observations suggest that APO could be partly responsible for meteorosensitivity in humans.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19780033599&hterms=wave+oscillation&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dwave%2Boscillation','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19780033599&hterms=wave+oscillation&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dwave%2Boscillation"><span>Thermally driven <span class="hlt">oscillations</span> and wave motion of a liquid drop</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Baumeister, K. J.; Hendricks, R. C.; Schoessow, G. J.</p> <p>1977-01-01</p> <p>In the state of Leidenfrost boiling, liquid drops are observed to vibrate in a variety of modal patterns. Theories are presented which predict the <span class="hlt">frequency</span> of <span class="hlt">oscillation</span> and show that the observed modal patterns of drops correspond to the minimum energy oscillatory excitation state. <span class="hlt">High</span>-speed photographic techniques were used to record these motions and substantiate the theories. An incipient temperature was also found for water drops in film boiling below which free <span class="hlt">oscillations</span> do not exist. In addition to these <span class="hlt">oscillations</span>, photographic sequences are presented which show that wave motion can exist along the circumference of the drop. Following the study of free <span class="hlt">oscillations</span>, the system was mounted on a shaker table and the drop subjected to a range of forced <span class="hlt">frequencies</span> and accelerations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19770021491','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19770021491"><span>Thermally Driven <span class="hlt">Oscillations</span> and Wave Motion of a Liquid Drop</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Baumeister, K. J.; Hendricks, R. C.; Schoessow, G. J.</p> <p>1977-01-01</p> <p>In the state of Leidenfrost boiling, liquid drops are observed to vibrate in a variety of modal patterns. Theories are presented which predict the <span class="hlt">frequency</span> of <span class="hlt">oscillation</span> and show that the observed model patterns of drops correspond to the minimum energy oscillatory excitation state. <span class="hlt">High</span>-speed photographic techniques were used to record these motions and substantiate the theories. An incipient temperature was also found for water drops in film boiling below which free <span class="hlt">oscillations</span> do not exist. In addition to these <span class="hlt">oscillations</span>, photographic sequences are presented which show that wave motion can exist along the circumference of the drop. Following the study of free <span class="hlt">oscillations</span>, the system was mounted on a shaker table and the drop subjected to a range of forced <span class="hlt">frequencies</span> and accelerations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110012594','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110012594"><span>Early <span class="hlt">Oscillation</span> Detection Technique for Hybrid DC/DC Converters</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wang, Bright L.</p> <p>2011-01-01</p> <p><span class="hlt">Oscillation</span> or instability is a situation that must be avoided for reliable hybrid DC/DC converters. A real-time electronics measurement technique was developed to detect catastrophic <span class="hlt">oscillations</span> at early stages for hybrid DC/DC converters. It is capable of identifying low-level <span class="hlt">oscillation</span> and determining the degree of the <span class="hlt">oscillation</span> at a unique <span class="hlt">frequency</span> for every individual model of the converters without disturbing their normal operations. This technique is specially developed for space-used hybrid DC/DC converters, but it is also suitable for most of commercial and military switching-mode power supplies. This is a weak-electronic-signal detection technique to detect hybrid DC/DC converter <span class="hlt">oscillation</span> presented as a specific noise signal at power input pins. It is based on principles of feedback control loop <span class="hlt">oscillation</span> and RF signal modulations, and is realized by using signal power spectral analysis. On the power spectrum, a channel power amplitude at characteristic <span class="hlt">frequency</span> (CPcf) and a channel power amplitude at switching <span class="hlt">frequency</span> (CPsw) are chosen as <span class="hlt">oscillation</span> level indicators. If the converter is stable, the CPcf is a very small pulse and the CPsw is a larger, clear, single pulse. At early stage of <span class="hlt">oscillation</span>, the CPcf increases to a certain level and the CPsw shows a small pair of sideband pulses around it. If the converter <span class="hlt">oscillates</span>, the CPcf reaches to a higher level and the CPsw shows more <span class="hlt">high</span>-level sideband pulses. A comprehensive stability index (CSI) is adopted as a quantitative measure to accurately assign a degree of stability to a specific DC/DC converter. The CSI is a ratio of normal and abnormal power spectral density, and can be calculated using specified and measured CPcf and CPsw data. The novel and unique feature of this technique is the use of power channel amplitudes at characteristic <span class="hlt">frequency</span> and switching <span class="hlt">frequency</span> to evaluate stability and identify <span class="hlt">oscillations</span> at an early stage without interfering with a DC/DC converter s</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007JaJAP..46.5865O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007JaJAP..46.5865O"><span>Linearly Polarized Single-<span class="hlt">Frequency</span> <span class="hlt">Oscillations</span> of Laser-Diode-Pumped Microchip Ceramic Nd:YAG Lasers with Forced Ince-Gaussian Mode Operations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Otsuka, Kenju; Nemoto, Kana; Kamikariya, Koji; Miyasaka, Yoshihiko; Chu, Shu-Chun</p> <p>2007-09-01</p> <p>Detailed <span class="hlt">oscillation</span> spectra and polarization properties have been examined in laser-diode-pumped (LD-pumped) microchip ceramic (i.e., polycrystalline) Nd:YAG lasers and the inherent segregation of lasing patterns into local modes possessing different polarization states was observed. Single-<span class="hlt">frequency</span> linearly-polarized stable <span class="hlt">oscillations</span> were realized by forcing the laser to Ince-Gaussian mode operations by adjusting azimuthal cavity symmetry.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018ApJ...860L..10S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018ApJ...860L..10S"><span>Evidence for an Optical Low-<span class="hlt">frequency</span> Quasi-periodic <span class="hlt">Oscillation</span> in the Kepler Light Curve of an Active Galaxy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smith, Krista Lynne; Mushotzky, Richard F.; Boyd, Patricia T.; Wagoner, Robert V.</p> <p>2018-06-01</p> <p>We report evidence for a quasi-periodic <span class="hlt">oscillation</span> (QPO) in the optical light curve of KIC 9650712, a narrow-line Seyfert 1 galaxy in the original Kepler field. After the development and application of a pipeline for Kepler data specific to active galactic nuclei (AGNs), one of our sample of 21 AGNs selected by infrared photometry and X-ray flux demonstrates a peak in the power spectrum at log ν = ‑6.58 Hz, corresponding to a temporal period of t = 44 days. We note that although the power spectrum is well fit by a model consisting of a Lorentzian and a single power law, alternative continuum models cannot be ruled out. From optical spectroscopy, we measure the black hole mass of this AGN as log (M BH/M ⊙) = 8.17. We find that this <span class="hlt">frequency</span> lies along a correlation between low-<span class="hlt">frequency</span> QPOs and black hole mass from stellar and intermediate mass black holes to AGNs, similar to the known correlation in <span class="hlt">high-frequency</span> QPOs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2000JMagR.146..132J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2000JMagR.146..132J"><span>Recoupling of Heteronuclear Dipolar Interactions with Rotational-Echo Double-Resonance at <span class="hlt">High</span> Magic-Angle Spinning <span class="hlt">Frequencies</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jaroniec, Christopher P.; Tounge, Brett A.; Rienstra, Chad M.; Herzfeld, Judith; Griffin, Robert G.</p> <p>2000-09-01</p> <p>Heteronuclear dipolar recoupling with rotational-echo double-resonance (REDOR) is investigated in the rapid magic-angle spinning regime, where radiofrequency irradiation occupies a significant fraction of the rotor period (10-60%). We demonstrate, in two model 13C-15N spin systems, [1-13C, 15N] and [2-13C, 15N]glycine, that REDOR ΔS/S0 curves acquired at <span class="hlt">high</span> MAS rates and relatively low recoupling fields are nearly identical to the ΔS/S0 curve expected for REDOR with ideal δ-function pulses. The only noticeable effect of the finite π pulse length on the recoupling is a minor scaling of the dipolar <span class="hlt">oscillation</span> <span class="hlt">frequency</span>. Experimental results are explained using both numerical calculations and average Hamiltonian theory, which is used to derive analytical expressions for evolution under REDOR recoupling sequences with different π pulse phasing schemes. For xy-4 and extensions thereof, finite pulses scale only the dipolar <span class="hlt">oscillation</span> <span class="hlt">frequency</span> by a well-defined factor. For other phasing schemes (e.g., xx-4 and xx¯-4) both the <span class="hlt">frequency</span> and amplitude of the <span class="hlt">oscillation</span> are expected to change.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_24 --> <div id="page_25" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="481"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AcAau.133..158X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AcAau.133..158X"><span>Experimental study on the flow separation and self-excited <span class="hlt">oscillation</span> phenomenon in a rectangular duct</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xiong, Bing; Wang, Zhen-Guo; Fan, Xiao-Qiang; Wang, Yi</p> <p>2017-04-01</p> <p>To study the characteristics of flow separation and self-excited <span class="hlt">oscillation</span> of a shock train in a rectangular duct, a simple test case has been conducted and analyzed. The <span class="hlt">high</span>-speed Schlieren technique and <span class="hlt">high-frequency</span> pressure measurements have been adopted to collect the data. The experimental results show that there are two separation modes in the duct under M3 incoming condition. The separation mode switch has great effects on the flow effects, such as the pressure distribution, the standard deviation distribution and so on. The separation mode switch can be judged by the history of pressure standard deviation. When it comes to the self-excited <span class="hlt">oscillation</span> of a shock train, the <span class="hlt">frequency</span> contents in the undisturbed region, the intermittent region, and the separated bubble have been compared. It was found that the low-<span class="hlt">frequency</span> disturbance induced by the upstream shock foot motions can travel downstream and the <span class="hlt">frequency</span> will be magnified by the separation bubble. The <span class="hlt">oscillation</span> of the small shock foot and the <span class="hlt">oscillation</span> of the large shock foot are associated with each other rather than <span class="hlt">oscillating</span> independently.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28286415','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28286415"><span>A precise measurement of the [Formula: see text] meson <span class="hlt">oscillation</span> <span class="hlt">frequency</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Aaij, R; Abellán Beteta, C; Adeva, B; Adinolfi, M; Affolder, A; Ajaltouni, Z; Akar, S; Albrecht, J; Alessio, F; Alexander, M; Ali, S; Alkhazov, G; Alvarez Cartelle, P; Alves, A A; Amato, S; Amerio, S; Amhis, Y; An, L; Anderlini, L; Anderson, J; Andreassi, G; Andreotti, M; Andrews, J E; Appleby, R B; Aquines Gutierrez, O; Archilli, F; d'Argent, P; Artamonov, A; Artuso, M; Aslanides, E; Auriemma, G; Baalouch, M; Bachmann, S; Back, J J; Badalov, A; Baesso, C; Baldini, W; Barlow, R J; Barschel, C; Barsuk, S; Barter, W; Batozskaya, V; Battista, V; Bay, A; Beaucourt, L; Beddow, J; Bedeschi, F; Bediaga, I; Bel, L J; Bellee, V; Belloli, N; Belyaev, I; Ben-Haim, E; Bencivenni, G; Benson, S; Benton, J; Berezhnoy, A; Bernet, R; Bertolin, A; Bettler, M-O; van Beuzekom, M; Bien, A; Bifani, S; Billoir, P; Bird, T; Birnkraut, A; Bizzeti, A; Blake, T; Blanc, F; Blouw, J; Blusk, S; Bocci, V; Bondar, A; Bondar, N; Bonivento, W; Borghi, S; Borsato, M; Bowcock, T J V; Bowen, E; Bozzi, C; Braun, S; Britsch, M; Britton, T; Brodzicka, J; Brook, N H; Buchanan, E; Bursche, A; Buytaert, J; Cadeddu, S; Calabrese, R; Calvi, M; Calvo Gomez, M; Campana, P; Campora Perez, D; Capriotti, L; Carbone, A; Carboni, G; Cardinale, R; Cardini, A; Carniti, P; Carson, L; Carvalho Akiba, K; Casse, G; Cassina, L; Castillo Garcia, L; Cattaneo, M; Cauet, Ch; Cavallero, G; Cenci, R; Charles, M; Charpentier, Ph; Chefdeville, M; Chen, S; Cheung, S-F; Chiapolini, N; Chrzaszcz, M; Cid Vidal, X; Ciezarek, G; Clarke, P E L; Clemencic, M; Cliff, H V; Closier, J; Coco, V; Cogan, J; Cogneras, E; Cogoni, V; Cojocariu, L; Collazuol, G; Collins, P; Comerma-Montells, A; Contu, A; Cook, A; Coombes, M; Coquereau, S; Corti, G; Corvo, M; Couturier, B; Cowan, G A; Craik, D C; Crocombe, A; Cruz Torres, M; Cunliffe, S; Currie, R; D'Ambrosio, C; Dall'Occo, E; Dalseno, J; David, P N Y; Davis, A; De Aguiar Francisco, O; De Bruyn, K; De Capua, S; De Cian, M; De Miranda, J M; De Paula, L; De Simone, P; Dean, C-T; Decamp, D; Deckenhoff, M; Del Buono, L; Déléage, N; Demmer, M; Derkach, D; Deschamps, O; Dettori, F; Dey, B; Di Canto, A; Di Ruscio, F; Dijkstra, H; Donleavy, S; Dordei, F; Dorigo, M; Dosil Suárez, A; Dossett, D; Dovbnya, A; Dreimanis, K; Dufour, L; Dujany, G; Dupertuis, F; Durante, P; Dzhelyadin, R; Dziurda, A; Dzyuba, A; Easo, S; Egede, U; Egorychev, V; Eidelman, S; Eisenhardt, S; Eitschberger, U; Ekelhof, R; Eklund, L; El Rifai, I; Elsasser, Ch; Ely, S; Esen, S; Evans, H M; Evans, T; Falabella, A; Färber, C; Farley, N; Farry, S; Fay, R; Ferguson, D; Fernandez Albor, V; Ferrari, F; Ferreira Rodrigues, F; Ferro-Luzzi, M; Filippov, S; Fiore, M; Fiorini, M; Firlej, M; Fitzpatrick, C; Fiutowski, T; Fohl, K; Fol, P; Fontana, M; Fontanelli, F; C Forshaw, D; Forty, R; Frank, M; Frei, C; Frosini, M; Fu, J; Furfaro, E; Gallas Torreira, A; Galli, D; Gallorini, S; Gambetta, S; Gandelman, M; Gandini, P; Gao, Y; García Pardiñas, J; Garra Tico, J; Garrido, L; Gascon, D; Gaspar, C; Gauld, R; Gavardi, L; Gazzoni, G; Gerick, D; Gersabeck, E; Gersabeck, M; Gershon, T; Ghez, Ph; Gianì, S; Gibson, V; Girard, O G; Giubega, L; Gligorov, V V; Göbel, C; Golubkov, D; Golutvin, A; Gomes, A; Gotti, C; Grabalosa Gándara, M; Graciani Diaz, R; Granado Cardoso, L A; Graugés, E; Graverini, E; Graziani, G; Grecu, A; Greening, E; Gregson, S; Griffith, P; Grillo, L; Grünberg, O; Gui, B; Gushchin, E; Guz, Yu; Gys, T; Hadavizadeh, T; Hadjivasiliou, C; Haefeli, G; Haen, C; Haines, S C; Hall, S; Hamilton, B; Han, X; Hansmann-Menzemer, S; Harnew, N; Harnew, S T; Harrison, J; He, J; Head, T; Heijne, V; Heister, A; Hennessy, K; Henrard, P; Henry, L; Hernando Morata, J A; van Herwijnen, E; Heß, M; Hicheur, A; Hill, D; Hoballah, M; Hombach, C; Hulsbergen, W; Humair, T; Hussain, N; Hutchcroft, D; Hynds, D; Idzik, M; Ilten, P; Jacobsson, R; Jaeger, A; Jalocha, J; Jans, E; Jawahery, A; Jing, F; John, M; Johnson, D; Jones, C R; Joram, C; Jost, B; Jurik, N; Kandybei, S; Kanso, W; Karacson, M; Karbach, T M; Karodia, S; Kecke, M; Kelsey, M; Kenyon, I R; Kenzie, M; Ketel, T; Khanji, B; Khurewathanakul, C; Kirn, T; Klaver, S; Klimaszewski, K; Kochebina, O; Kolpin, M; Komarov, I; Koopman, R F; Koppenburg, P; Kozeiha, M; Kravchuk, L; Kreplin, K; Kreps, M; Krocker, G; Krokovny, P; Kruse, F; Krzemien, W; Kucewicz, W; Kucharczyk, M; Kudryavtsev, V; K Kuonen, A; Kurek, K; Kvaratskheliya, T; Lacarrere, D; Lafferty, G; Lai, A; Lambert, D; Lanfranchi, G; Langenbruch, C; Langhans, B; Latham, T; Lazzeroni, C; Le Gac, R; van Leerdam, J; Lees, J-P; Lefèvre, R; Leflat, A; Lefrançois, J; Lemos Cid, E; Leroy, O; Lesiak, T; Leverington, B; Li, Y; Likhomanenko, T; Liles, M; Lindner, R; Linn, C; Lionetto, F; Liu, B; Liu, X; Loh, D; Longstaff, I; Lopes, J H; Lucchesi, D; Lucio Martinez, M; Luo, H; Lupato, A; Luppi, E; Lupton, O; Lusardi, N; Lusiani, A; Machefert, F; Maciuc, F; Maev, O; Maguire, K; Malde, S; Malinin, A; Manca, G; Mancinelli, G; Manning, P; Mapelli, A; Maratas, J; Marchand, J F; Marconi, U; Marin Benito, C; Marino, P; Marks, J; Martellotti, G; Martin, M; Martinelli, M; Martinez Santos, D; Martinez Vidal, F; Martins Tostes, D; Massafferri, A; Matev, R; Mathad, A; Mathe, Z; Matteuzzi, C; Mauri, A; Maurin, B; Mazurov, A; McCann, M; McCarthy, J; McNab, A; McNulty, R; Meadows, B; Meier, F; Meissner, M; Melnychuk, D; Merk, M; Michielin, E; Milanes, D A; Minard, M-N; Mitzel, D S; Molina Rodriguez, J; Monroy, I A; Monteil, S; Morandin, M; Morawski, P; Mordà, A; Morello, M J; Moron, J; Morris, A B; Mountain, R; Muheim, F; Müller, D; Müller, J; Müller, K; Müller, V; Mussini, M; Muster, B; Naik, P; Nakada, T; Nandakumar, R; Nandi, A; Nasteva, I; Needham, M; Neri, N; Neubert, S; Neufeld, N; Neuner, M; Nguyen, A D; Nguyen, T D; Nguyen-Mau, C; Niess, V; Niet, R; Nikitin, N; Nikodem, T; Novoselov, A; O'Hanlon, D P; Oblakowska-Mucha, A; Obraztsov, V; Ogilvy, S; Okhrimenko, O; Oldeman, R; Onderwater, C J G; Osorio Rodrigues, B; Otalora Goicochea, J M; Otto, A; Owen, P; Oyanguren, A; Palano, A; Palombo, F; Palutan, M; Panman, J; Papanestis, A; Pappagallo, M; Pappalardo, L L; Pappenheimer, C; Parkes, C; Passaleva, G; Patel, G D; Patel, M; Patrignani, C; Pearce, A; Pellegrino, A; Penso, G; Pepe Altarelli, M; Perazzini, S; Perret, P; Pescatore, L; Petridis, K; Petrolini, A; Petruzzo, M; Picatoste Olloqui, E; Pietrzyk, B; Pilař, T; Pinci, D; Pistone, A; Piucci, A; Playfer, S; Plo Casasus, M; Poikela, T; Polci, F; Poluektov, A; Polyakov, I; Polycarpo, E; Popov, A; Popov, D; Popovici, B; Potterat, C; Price, E; Price, J D; Prisciandaro, J; Pritchard, A; Prouve, C; Pugatch, V; Puig Navarro, A; Punzi, G; Qian, W; Quagliani, R; Rachwal, B; Rademacker, J H; Rama, M; Rangel, M S; Raniuk, I; Rauschmayr, N; Raven, G; Redi, F; Reichert, S; Reid, M M; Dos Reis, A C; Ricciardi, S; Richards, S; Rihl, M; Rinnert, K; Rives Molina, V; Robbe, P; Rodrigues, A B; Rodrigues, E; Rodriguez Lopez, J A; Rodriguez Perez, P; Roiser, S; Romanovsky, V; Romero Vidal, A; W Ronayne, J; Rotondo, M; Rouvinet, J; Ruf, T; Ruiz Valls, P; Saborido Silva, J J; Sagidova, N; Sail, P; Saitta, B; Salustino Guimaraes, V; Sanchez Mayordomo, C; Sanmartin Sedes, B; Santacesaria, R; Santamarina Rios, C; Santimaria, M; Santovetti, E; Sarti, A; Satriano, C; Satta, A; Saunders, D M; Savrina, D; Schael, S; Schiller, M; Schindler, H; Schlupp, M; Schmelling, M; Schmelzer, T; Schmidt, B; Schneider, O; Schopper, A; Schubiger, M; Schune, M-H; Schwemmer, R; Sciascia, B; Sciubba, A; Semennikov, A; Sergi, A; Serra, N; Serrano, J; Sestini, L; Seyfert, P; Shapkin, M; Shapoval, I; Shcheglov, Y; Shears, T; Shekhtman, L; Shevchenko, V; Shires, A; Siddi, B G; Silva Coutinho, R; Silva de Oliveira, L; Simi, G; Sirendi, M; Skidmore, N; Skwarnicki, T; Smith, E; Smith, E; Smith, I T; Smith, J; Smith, M; Snoek, H; Sokoloff, M D; Soler, F J P; Soomro, F; Souza, D; Souza De Paula, B; Spaan, B; Spradlin, P; Sridharan, S; Stagni, F; Stahl, M; Stahl, S; Stefkova, S; Steinkamp, O; Stenyakin, O; Stevenson, S; Stoica, S; Stone, S; Storaci, B; Stracka, S; Straticiuc, M; Straumann, U; Sun, L; Sutcliffe, W; Swientek, K; Swientek, S; Syropoulos, V; Szczekowski, M; Szczypka, P; Szumlak, T; T'Jampens, S; Tayduganov, A; Tekampe, T; Teklishyn, M; Tellarini, G; Teubert, F; Thomas, C; Thomas, E; van Tilburg, J; Tisserand, V; Tobin, M; Todd, J; Tolk, S; Tomassetti, L; Tonelli, D; Topp-Joergensen, S; Torr, N; Tournefier, E; Tourneur, S; Trabelsi, K; Tran, M T; Tresch, M; Trisovic, A; Tsaregorodtsev, A; Tsopelas, P; Tuning, N; Ukleja, A; Ustyuzhanin, A; Uwer, U; Vacca, C; Vagnoni, V; Valenti, G; Vallier, A; Vazquez Gomez, R; Vazquez Regueiro, P; Vázquez Sierra, C; Vecchi, S; van Veghel, M; Velthuis, J J; Veltri, M; Veneziano, G; Vesterinen, M; Viaud, B; Vieira, D; Vieites Diaz, M; Vilasis-Cardona, X; Vollhardt, A; Volyanskyy, D; Voong, D; Vorobyev, A; Vorobyev, V; Voß, C; de Vries, J A; Waldi, R; Wallace, C; Wallace, R; Walsh, J; Wandernoth, S; Wang, J; Ward, D R; Watson, N K; Websdale, D; Weiden, A; Whitehead, M; Wilkinson, G; Wilkinson, M; Williams, M; Williams, M P; Williams, M; Williams, T; Wilson, F F; Wimberley, J; Wishahi, J; Wislicki, W; Witek, M; Wormser, G; Wotton, S A; Wright, S; Wyllie, K; Xie, Y; Xu, Z; Yang, Z; Yu, J; Yuan, X; Yushchenko, O; Zangoli, M; Zavertyaev, M; Zhang, L; Zhang, Y; Zhelezov, A; Zhokhov, A; Zhong, L; Zhukov, V; Zucchelli, S</p> <p>2016-01-01</p> <p>The <span class="hlt">oscillation</span> <span class="hlt">frequency</span>, [Formula: see text], of [Formula: see text] mesons is measured using semileptonic decays with a [Formula: see text] or [Formula: see text] meson in the final state. The data sample corresponds to 3.0[Formula: see text] of pp collisions, collected by the LHCb experiment at centre-of-mass energies [Formula: see text] = 7 and 8[Formula: see text]. A combination of the two decay modes gives [Formula: see text], where the first uncertainty is statistical and the second is systematic. This is the most precise single measurement of this parameter. It is consistent with the current world average and has similar precision.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018AIPA....8d5312X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018AIPA....8d5312X"><span>Nonuniform gyrotropic <span class="hlt">oscillation</span> of skyrmion in a nanodisk</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xuan, Shengjie; Liu, Yan</p> <p>2018-04-01</p> <p>It was predicted that magnetic skyrmions have potential application in the spin nano-<span class="hlt">oscillators</span>. The <span class="hlt">oscillation</span> <span class="hlt">frequency</span> is a key parameter. In this paper, we study the skyrmion relaxation in a FeGe nanodisk and find that the <span class="hlt">oscillation</span> <span class="hlt">frequency</span> depends on the skyrmion position. The relaxation process is associated with the variation of skyrmion diameter. By analyzing the system energy, we believe that the nonuniform gyrotropic <span class="hlt">oscillation</span> <span class="hlt">frequency</span> is due to the change of the skyrmion diameter.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29715868','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29715868"><span>Phase measurement by using a forced delay-line <span class="hlt">oscillator</span> and its application for an acoustic fiber sensor.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Fleyer, Michael; Horowitz, Moshe</p> <p>2018-04-02</p> <p>We demonstrate, theoretically and experimentally, a new method to measure small changes in the cavity length of <span class="hlt">oscillators</span>. The method is based on the <span class="hlt">high</span> sensitivity of the phase of forced delay-line <span class="hlt">oscillators</span> to changes in their cavity length. The <span class="hlt">oscillator</span> phase is directly detected by mixing the <span class="hlt">oscillator</span> output with the injected signal. We describe a comprehensive theoretical model for studying the signal and the noise at the output of a general forced delay-line <span class="hlt">oscillator</span> with an instantaneous gain saturation and an amplitude-to-phase conversion. The results indicate that the magnitude and the bandwidth of the <span class="hlt">oscillator</span> response to a small perturbation can be controlled by adjusting the injection ratio and the injected <span class="hlt">frequency</span>. For signals with a <span class="hlt">frequency</span> that is smaller than the device bandwidth, the <span class="hlt">oscillator</span> noise is dominated by the noise of the injected signal. This noise is <span class="hlt">highly</span> suppressed by mixing the <span class="hlt">oscillator</span> output with the injected signal. Hence, the device sensitivity at <span class="hlt">frequencies</span> below its bandwidth is limited only by the internal noise that is added in a single roundtrip in the <span class="hlt">oscillator</span> cavity. We demonstrate the use of a forced <span class="hlt">oscillator</span> as an acoustic fiber sensor in an optoelectronic <span class="hlt">oscillator</span>. A good agreement is obtained between theory and experiments. The magnitude of the output signal can be controlled by adjusting the injection ratio while the noise power at low <span class="hlt">frequencies</span> is not enhanced as in sensors that are based on a free-running <span class="hlt">oscillator</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017FlDyR..49b5518L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017FlDyR..49b5518L"><span>Nonlinear <span class="hlt">oscillation</span> and interfacial stability of an encapsulated microbubble under dual-<span class="hlt">frequency</span> ultrasound</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, Yunqiao; Calvisi, Michael L.; Wang, Qianxi</p> <p>2017-04-01</p> <p>Encapsulated microbubbles (EMBs) are widely used in medical ultrasound imaging as contrast-enhanced agents. However, the potential damaging effects of violent collapsing EMBs to cells and tissues in clinical settings have remained a concern. Dual-<span class="hlt">frequency</span> ultrasound is a promising technique for improving the efficacy and safety of sonography. The system modeled consists of the external liquid, membrane and internal gases of an EMB. The microbubble dynamics are simulated using a simple nonlinear interactive theory, considering the compressibility of the internal gas, viscosity of the liquid flow and viscoelasticity of the membrane. The radial <span class="hlt">oscillation</span> and interfacial stability of an EMB under single- and dual-<span class="hlt">frequency</span> excitations are compared. The simulation results show that the dual-<span class="hlt">frequency</span> technique produces larger backscatter pressure at higher harmonics of the primary driving frequency—this enriched acoustic spectrum can enhance blood-tissue contrast and improve the quality of sonographic images. The results further show that the acoustic pressure threshold associated with the onset of shape instability is greater for dual-<span class="hlt">frequency</span> driving. This suggests that the dual-<span class="hlt">frequency</span> technique stabilizes the encapsulated bubble, thereby improving the efficacy and safety of contrast-enhanced agents.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940011393','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940011393"><span>Effect of wind tunnel acoustic modes on linear <span class="hlt">oscillating</span> cascade aerodynamics</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Buffum, Daniel H.; Fleeter, Sanford</p> <p>1993-01-01</p> <p>The aerodynamics of a biconvex airfoil cascade <span class="hlt">oscillating</span> in torsion is investigated using the unsteady aerodynamic influence coefficient technique. For subsonic flow and reduced <span class="hlt">frequencies</span> as large as 0.9, airfoil surface unsteady pressures resulting from <span class="hlt">oscillation</span> of one of the airfoils are measured using flush-mounted <span class="hlt">high-frequency</span>-response pressure transducers. The influence coefficient data are examined in detail and then used to predict the unsteady aerodynamics of a cascade <span class="hlt">oscillating</span> at various interblade phase angles. These results are correlated with experimental data obtained in the traveling-wave mode of <span class="hlt">oscillation</span> and linearized analysis predictions. It is found that the unsteady pressure disturbances created by an <span class="hlt">oscillating</span> airfoil excite wind tunnel acoustic modes which have detrimental effects on the experimental data. Acoustic treatment is proposed to rectify this problem.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3775780','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3775780"><span>Value of electrical stimulation and <span class="hlt">high</span> <span class="hlt">frequency</span> <span class="hlt">oscillations</span> (80–500 Hz) in identifying epileptogenic areas during intracranial EEG recordings</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Jacobs, Julia; Zijlmans, Maeike; Zelmann, Rina; Olivier, André; Hall, Jeffery; Gotman, Jean; Dubeau, François</p> <p>2013-01-01</p> <p>Summary Purpose Electrical stimulation (ES) is used during intracranial electroencephalography (EEG) investigations to delineate epileptogenic areas and seizure-onset zones (SOZs) by provoking afterdischarges (ADs) or patients’ typical seizure. <span class="hlt">High</span> <span class="hlt">frequency</span> <span class="hlt">oscillations</span> (HFOs—ripples, 80–250 Hz; fast ripples, 250–500 Hz) are linked to seizure onset. This study investigates whether interictal HFOs are more frequent in areas with a low threshold to provoke ADs or seizures. Methods Intracranial EEG studies were filtered at 500 Hz and sampled at 2,000 Hz. HFOs were visually identified. Twenty patients underwent ES, with gradually increasing currents. Results were interpreted as agreeing or disagreeing with the intracranial study (clinical-EEG seizure onset defined the SOZ). Current thresholds provoking an AD or seizure were correlated with the rate of HFOs of each channel. Results ES provoked a seizure in 12 and ADs in 19 patients. Sixteen patients showed an ES response inside the SOZ, and 10 had additional areas with ADs. The response was more specific for mesiotemporal than for neocortical channels. HFO rates were negatively correlated with thresholds for ES responses; especially in neo-cortical regions; areas with low threshold and <span class="hlt">high</span> HFO rate were colocalized even outside the SOZ. Discussion Areas showing epileptic HFOs colocalize with those reacting to ES. HFOs may represent a pathologic correlate of regions showing an ES response; both phenomena suggest a more widespread epileptogenicity. PMID:19845730</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/4343311','DOE-PATENT-XML'); return false;" href="https://www.osti.gov/biblio/4343311"><span>STABILIZED <span class="hlt">OSCILLATOR</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Jessen, P.L.; Price, H.J.</p> <p>1958-03-18</p> <p>This patent relates to sine-wave generators and in particular describes a generator with a novel feedback circuit resulting in improved <span class="hlt">frequency</span> stability. The generator comprises two triodes having a common cathode circuit connected to <span class="hlt">oscillate</span> at a <span class="hlt">frequency</span> and amplitude at which the loop galn of the circutt ls unity, and another pair of triodes having a common cathode circuit arranged as a conventional amplifier. A signal is conducted from the osciliator through a <span class="hlt">frequency</span> selective network to the amplifier and fed back to the osciliator. The unique feature of the feedback circuit is the amplifier operates in the nonlinear portion of its tube characteristics thereby providing a relatively constant feedback voltage to the <span class="hlt">oscillator</span> irrespective of the amplitude of its input signal.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22088663','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22088663"><span>Direct EPR irradiation of a sample using a quartz <span class="hlt">oscillator</span> operating at 250 MHz for EPR measurements.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Yokoyama, Hidekatsu</p> <p>2012-01-01</p> <p>Direct irradiation of a sample using a quartz <span class="hlt">oscillator</span> operating at 250 MHz was performed for EPR measurements. Because a quartz <span class="hlt">oscillator</span> is a <span class="hlt">frequency</span> fixed <span class="hlt">oscillator</span>, the operating <span class="hlt">frequency</span> of an EPR resonator (loop-gap type) was tuned to that of the quartz <span class="hlt">oscillator</span> by using a single-turn coil with a varactor diode attached (<span class="hlt">frequency</span> shift coil). Because the <span class="hlt">frequency</span> shift coil was mobile, the distance between the EPR resonator and the coil could be changed. Coarse control of the resonant <span class="hlt">frequency</span> was achieved by changing this distance mechanically, while fine <span class="hlt">frequency</span> control was implemented by changing the capacitance of the varactor electrically. In this condition, EPR measurements of a phantom (comprised of agar with a nitroxide radical and physiological saline solution) were made. To compare the presented method with a conventional method, the EPR measurements were also done by using a synthesizer at the same EPR <span class="hlt">frequency</span>. In the conventional method, the noise level increased at <span class="hlt">high</span> irradiation power. Because such an increase in the noise was not observed in the presented method, <span class="hlt">high</span> sensitivity was obtained at <span class="hlt">high</span> irradiation power. Copyright © 2011 Elsevier Inc. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013APS..MAR.Q1317E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013APS..MAR.Q1317E"><span><span class="hlt">High</span> <span class="hlt">Frequency</span> Supercapacitors for Piezo-based Energy Harvesting</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ervin, Matthew; Pereira, Carlos; Miller, John; Outlaw, Ronald; Rastegar, Jay; Murray, Richard</p> <p>2013-03-01</p> <p>Energy harvesting is being investigated as an alternative to batteries for powering munition guidance and fuzing functions during flight. A piezoelectric system that generates energy from the <span class="hlt">oscillation</span> of a mass on a spring (set in motion by the launch acceleration) is being developed. Original designs stored this energy in an electrolytic capacitor for use during flight. Here we replace the electrolytic capacitor with a smaller, lighter, and potentially more reliable electrochemical double layer capacitor (aka, supercapacitor). The potential problems with using supercapacitors in this application are that the piezoelectric output greatly exceeds the supercapacitor electrolyte breakdown voltage, and the <span class="hlt">frequency</span> greatly exceeds the operating <span class="hlt">frequency</span> of commercial supercapacitors. Here we have investigated the use of ultrafast vertically oriented graphene array-based supercapacitors for storing the energy in this application. We find that the electrolyte breakdown is not a serious limitation as it is either kinetically limited by the relatively <span class="hlt">high</span> <span class="hlt">frequency</span> of the piezoelectric output, or it is overcome by the self-healing nature of supercapacitors. We also find that these supercapacitors have sufficient dynamic response to efficiently store the generated energy.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018MNRAS.473L.136T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018MNRAS.473L.136T"><span>On one-parametric formula relating the <span class="hlt">frequencies</span> of twin-peak quasi-periodic <span class="hlt">oscillations</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Török, Gabriel; Goluchová, Kateřina; Šrámková, Eva; Horák, Jiří; Bakala, Pavel; Urbanec, Martin</p> <p>2018-01-01</p> <p>Twin-peak quasi-periodic <span class="hlt">oscillations</span> (QPOs) are observed in several low-mass X-ray binary systems containing neutron stars. Timing the analysis of X-ray fluxes of more than dozen of such systems reveals remarkable correlations between the <span class="hlt">frequencies</span> of two characteristic peaks present in the power density spectra. The individual correlations clearly differ, but they roughly follow a common individual pattern. <span class="hlt">High</span> values of measured QPO <span class="hlt">frequencies</span> and strong modulation of the X-ray flux both suggest that the observed correlations are connected to orbital motion in the innermost part of an accretion disc. Several attempts to model these correlations with simple geodesic orbital models or phenomenological relations have failed in the past. We find and explore a surprisingly simple analytic relation that reproduces individual correlations for a group of several sources through a single parameter. When an additional free parameter is considered within our relation, it well reproduces the data of a large group of 14 sources. The very existence and form of this simple relation support the hypothesis of the orbital origin of QPOs and provide the key for further development of QPO models. We discuss a possible physical interpretation of our relation's parameters and their links to concrete QPO models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5244383','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5244383"><span>Reference-free, <span class="hlt">high</span>-resolution measurement method of timing jitter spectra of optical <span class="hlt">frequency</span> combs</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Kwon, Dohyeon; Jeon, Chan-Gi; Shin, Junho; Heo, Myoung-Sun; Park, Sang Eon; Song, Youjian; Kim, Jungwon</p> <p>2017-01-01</p> <p>Timing jitter is one of the most important properties of femtosecond mode-locked lasers and optical <span class="hlt">frequency</span> combs. Accurate measurement of timing jitter power spectral density (PSD) is a critical prerequisite for optimizing overall noise performance and further advancing comb applications both in the time and <span class="hlt">frequency</span> domains. Commonly used jitter measurement methods require a reference mode-locked laser with timing jitter similar to or lower than that of the laser-under-test, which is a demanding requirement for many laser laboratories, and/or have limited measurement resolution. Here we show a <span class="hlt">high</span>-resolution and reference-source-free measurement method of timing jitter spectra of optical <span class="hlt">frequency</span> combs using an optical fibre delay line and optical carrier interference. The demonstrated method works well for both mode-locked <span class="hlt">oscillators</span> and supercontinua, with 2 × 10−9 fs2/Hz (equivalent to −174 dBc/Hz at 10-GHz carrier <span class="hlt">frequency</span>) measurement noise floor. The demonstrated method can serve as a simple and powerful characterization tool for timing jitter PSDs of various comb sources including mode-locked <span class="hlt">oscillators</span>, supercontinua and recently emerging Kerr-<span class="hlt">frequency</span> combs; the jitter measurement results enabled by our method will provide new insights for understanding and optimizing timing noise in such comb sources. PMID:28102352</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017SPIE10453E..2QW','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017SPIE10453E..2QW"><span>Resonant tunneling diode <span class="hlt">oscillators</span> for optical communications</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Watson, Scott; Zhang, Weikang; Wang, Jue; Al-Khalidi, Abdullah; Cantu, Horacio; Figueiredo, Jose; Wasige, Edward; Kelly, Anthony E.</p> <p>2017-08-01</p> <p>The ability to use resonant tunneling diodes (RTDs) as both transmitters and receivers is an emerging topic, especially with regards to wireless communications. Successful data transmission has been achieved using electronic RTDs with carrier <span class="hlt">frequencies</span> exceeding 0.3 THz. Specific optical-based RTDs, which act as photodetectors, have been developed by adjusting the device structure to include a light absorption layer and small optical windows on top of the device to allow direct optical access. This also allows the optical signal to directly modulate the RTD <span class="hlt">oscillation</span>. Both types of RTD <span class="hlt">oscillators</span> will allow for seamless integration of <span class="hlt">high</span> <span class="hlt">frequency</span> radio and optical fiber networks.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3712982','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3712982"><span><span class="hlt">High-frequency</span> <span class="hlt">oscillations</span>, extent of surgical resection, and surgical outcome in drug-resistant focal epilepsy</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Haegelen, Claire; Perucca, Piero; Châtillon, Claude-Edouard; Andrade-Valença, Luciana; Zelmann, Rina; Jacobs, Julia; Collins, D. Louis; Dubeau, François; Olivier, André; Gotman, Jean</p> <p>2013-01-01</p> <p>Summary Purpose Removal of areas generating <span class="hlt">high-frequency</span> <span class="hlt">oscillations</span> (HFOs) recorded from the intracerebral electroencephalography (iEEG) of patients with medically intractable epilepsy has been found to be correlated with improved surgical outcome. However, whether differences exist according to the type of epilepsy is largely unknown. We performed a comparative assessment of the impact of removing HFO-generating tissue on surgical outcome between temporal lobe epilepsy (TLE) and extratemporal lobe epilepsy (ETLE). We also assessed the relationship between the extent of surgical resection and surgical outcome. Methods We studied 30 patients with drug-resistant focal epilepsy, 21 with TLE and 9 with ETLE. Two thirds of the patients were included in a previous report and for these, clinical and imaging data were updated and follow-up was extended. All patients underwent iEEG investigations (500 Hz <span class="hlt">high</span>-pass filter and 2,000 Hz sampling rate), surgical resection, and postoperative magnetic resonance imaging (MRI). HFOs (ripples, 80–250 Hz; fast ripples, >250 Hz) were identified visually on a 5–10 min interictal iEEG sample. HFO rates inside versus outside the seizure-onset zone (SOZ), in resected versus nonresected tissue, and their association with surgical outcome (ILAE classification) were assessed in the entire cohort, and in the TLE and ETLE subgroups. We also tested the correlation of resected brain hippocampal and amygdala volumes (as measured on postoperative MRIs) with surgical outcome. Key Findings HFO rates were significantly higher inside the SOZ than outside in the entire cohort and TLE subgroup, but not in the ETLE subgroup. In all groups, HFO rates did not differ significantly between resected and nonresected tissue. Surgical outcome was better when higher HFO rates were included in the surgical resection in the entire cohort and TLE subgroup, but not in the ETLE subgroup. Resected brain hippocampal and amygdala volumes were not correlated with</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015IAUGA..2255391M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015IAUGA..2255391M"><span><span class="hlt">Oscillation</span> spectrum of WASP-33 from the MOST photometry</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mkrtichian, David</p> <p>2015-08-01</p> <p>We present results of extended continuous time series photometry of the Delta Scuti type pulsating exoplanet host star WASP-33 obtained in two seasons (2011 and 2013) with the MOST space telescope. Our <span class="hlt">frequency</span> analysis yealds rich, low-amplitude multi-<span class="hlt">frequency</span> spectrum of <span class="hlt">oscillation</span> modes. We discuss possible resonances between the orbiital period of the planet and <span class="hlt">frequencies</span> of the <span class="hlt">oscillation</span> modes. We present results of our measurements of planets orbital O-C variations and analyze possible existence of invisible planets in the system. We review recent results of the <span class="hlt">high</span>-resolution spectroscopic campaign on WASP-33 and confirm the retrograde orbital motion of the planet WASP-33b.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19870011799','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19870011799"><span>Low phase noise <span class="hlt">oscillator</span> using two parallel connected amplifiers</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kleinberg, Leonard L.</p> <p>1987-01-01</p> <p>A <span class="hlt">high</span> <span class="hlt">frequency</span> <span class="hlt">oscillator</span> is provided by connecting two amplifier circuits in parallel where each amplifier circuit provides the other amplifier circuit with the conditions necessary for <span class="hlt">oscillation</span>. The inherent noise present in both amplifier circuits causes the quiescent current, and in turn, the generated <span class="hlt">frequency</span>, to change. The changes in quiescent current cause the transconductance and the load impedance of each amplifier circuit to vary, and this in turn results in opposing changes in the input susceptance of each amplifier circuit. Because the changes in input susceptance oppose each other, the changes in quiescent current also oppose each other. The net result is that <span class="hlt">frequency</span> stability is enhanced.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050244990','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050244990"><span>Evidence for Harmonic Content and <span class="hlt">Frequency</span> Evolution of <span class="hlt">Oscillations</span> During the Rising Phase of X-ray Bursts From 4U 1636-536</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bgattacharyya, Sudip; Strohmayer, E.</p> <p>2005-01-01</p> <p>We report on a study of the evolution of burst <span class="hlt">oscillation</span> properties during the rising phase of X-ray bursts from 4U 1636-536 observed with the proportional counter array (PCA) on board the Rossi X-Ray Timing Explorer (RXTE) . We present evidence for significant harmonic structure of burst <span class="hlt">oscillation</span> pulses during the early rising phases of bursts. This is the first such detection in burst rise <span class="hlt">oscillations</span>, and is very important for constraining neutron star structure parameters and the equation of state models of matter at the core of a neutron star. The detection of harmonic content only during the initial portions of the burst rise is consistent with the theoretical expectation that with time the thermonuclear burning region becomes larger, and hence the fundamental and harmonic amplitudes both diminish. We also find, for the first time from this source, strong evidence of <span class="hlt">oscillation</span> <span class="hlt">frequency</span> increase during the burst rise. The timing behavior of harmonic content, amplitude, and <span class="hlt">frequency</span> of burst rise <span class="hlt">oscillations</span> may be important in understanding the spreading of thermonuclear flames under the extreme physical conditions on neutron star surfaces.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20060013336','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20060013336"><span>Comprehensive Analysis of RXTE Data from Cyg X-1. Spectral Index-Quasi-Periodic <span class="hlt">Oscillation</span> <span class="hlt">Frequency</span>-Luminosity Correlations</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Shaposhnikov, Nickolai; Titarchuk, Lev</p> <p>2006-01-01</p> <p>We present timing and spectral analysis of approx. 2.2 Ms of Rossi X-ray Time Explorer (RXTE) archival data from Cyg X-1. Using the generic Comptonization model we reveal that the spectrum of Cyg X-1 consists of three components: a thermal seed photon spectrum, a Comptonized part of the seed photon spectrum and the iron line. We find a strong correlation between 0.1-20 Hz <span class="hlt">frequencies</span> of quasiperiodic <span class="hlt">oscillations</span> (QPOs) and the spectral power-law index. Presence of two spectral phases (states) are clearly seen in the data when the spectral indices saturate at low and <span class="hlt">high</span> values of QPO <span class="hlt">frequencies</span>. This saturation effect was discovered earlier in a number of black hole candidate (BHC) sources and now we strongly confirm this phenomenon in Cyg X-1. In the soft state this index- QPO <span class="hlt">frequency</span> correlation shows a saturation of the photon index Gamma approx. 2.1 at <span class="hlt">high</span> values of the low <span class="hlt">frequency</span> upsilon(sub L). The saturation level of Gamma approx. 2.1 is the lowest value found yet in BHCs. The bolometric luminosity does not show clear correlation with the index. We also show that Fe K(sub alpha) emission line strength (equivalent width, EW) correlates with the QPO <span class="hlt">frequency</span>. EW increases from 200 eV in the low/hard state to 1.5 keV in the <span class="hlt">high</span>/soft state. The revealed observational correlations allow us to propose a scenario for the spectral transition and iron line formation which occur in BHC sources. We also present the spectral state (the power-law index) evolution for eight years of Cyg X-1 observations by RXTE.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19950020839','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950020839"><span><span class="hlt">High</span>-precision buffer circuit for suppression of regenerative <span class="hlt">oscillation</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Tripp, John S.; Hare, David A.; Tcheng, Ping</p> <p>1995-01-01</p> <p>Precision analog signal conditioning electronics have been developed for wind tunnel model attitude inertial sensors. This application requires low-noise, stable, microvolt-level DC performance and a <span class="hlt">high</span>-precision buffered output. Capacitive loading of the operational amplifier output stages due to the wind tunnel analog signal distribution facilities caused regenerative <span class="hlt">oscillation</span> and consequent rectification bias errors. <span class="hlt">Oscillation</span> suppression techniques commonly used in audio applications were inadequate to maintain the performance requirements for the measurement of attitude for wind tunnel models. Feedback control theory is applied to develop a suppression technique based on a known compensation (snubber) circuit, which provides superior <span class="hlt">oscillation</span> suppression with <span class="hlt">high</span> output isolation and preserves the low-noise low-offset performance of the signal conditioning electronics. A practical design technique is developed to select the parameters for the compensation circuit to suppress regenerative <span class="hlt">oscillation</span> occurring when typical shielded cable loads are driven.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012cosp...39.2138W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012cosp...39.2138W"><span>Surface <span class="hlt">oscillation</span> of levitated liquid droplets under microgravity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Watanabe, Masahito; Hibiya, Taketoshi; Ozawa, Shumpei; Mizuno, Akitoshi</p> <p>2012-07-01</p> <p>Microgravity conditions have advantages of measurement of surface tension and viscosity of metallic liquids by the <span class="hlt">oscillating</span> drop method with an electromagnetic levitation (EML) device. Thus, we are now planning the thermophysical properties, the surface tension, viscosity, density and etc., measurements of liquid alloys using the electromagnetic levitator named MSL-EML (Materials Science Laboratory Electromagnetic Levitator), which ahs been developed by the European Space Agency (ESA), installed in the International Space Station (ISS). The surface tension and the viscosity of liquid samples by the <span class="hlt">oscillating</span> drop method are obtained from the surface <span class="hlt">oscillation</span> <span class="hlt">frequency</span> and damping time of surface <span class="hlt">oscillation</span> respectively. However, analysis of <span class="hlt">oscillating</span> drop method in EML must be improved even in the microgravity conditions, because on the EML conditions the electromagnetic force (EMF) cannot generate the surface <span class="hlt">oscillation</span> with discretely <span class="hlt">oscillation</span> mode. Since under microgravity the levitated droplet shape is completely spherical, the surface <span class="hlt">oscillation</span> <span class="hlt">frequency</span> with different <span class="hlt">oscillation</span> modes degenerates into the single <span class="hlt">frequency</span>. Therefore, surface tension will be not affected the EML condition under microgravity, but viscosity will be affected on the different <span class="hlt">oscillation</span> mode of surface <span class="hlt">oscillations</span>. Because dumping time of surface <span class="hlt">oscillation</span> of liquid droplets depends on the <span class="hlt">oscillation</span> modes, the case of surface <span class="hlt">oscillation</span> including multi <span class="hlt">oscillation</span> modes the viscosity values obtained from dumping time will be modified from the correct viscosity. Therefore, we investigate the dumping time of surface <span class="hlt">oscillation</span> of levitated droplets with different <span class="hlt">oscillation</span> modes and also with including multi <span class="hlt">oscillation</span> modes using the electrostatic levitation (ESL) on ground and EML under microgravity conditions by the parabolic flight of airplane. The ESL can discretely generate the surface <span class="hlt">oscillation</span> with different <span class="hlt">oscillation</span> modes by the change of</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_25 --> <div class="footer-extlink text-muted" style="margin-bottom:1rem; text-align:center;">Some links on this page may take you to non-federal websites. 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