317 results for qubit oscillator frequency
Data from: Input-dependent frequency modulation of cortical gamma oscillations shapes spatial synchronization and enables phase coding
Contributors: Lowet, Eric, Roberts, Mark, Hadjipapas, Avgis, Peter, Alina, van der Eerden, Jan, De Weerd, Peter
phase-oscillator model part 1...phase-oscillator model part 2...phase-oscillator model part 3...phase-oscillator model part 4...oscillation frequencies at nearby spatial locations. Similarly to cortical...oscillation phase codes, may resolve conflicting experimental observations...frequency with increasing input drive. The relates to the experimental...oscillators. The gamma phase-locking, the precise phase relation and the...oscillators, where input drive determines the intrinsic (natural) frequency...Frequency Modulation of Cortical Gamma Oscillations Shapes Spatial Synchronization...oscillation...frequency of gamma oscillations varies with input drive (e.g. visual contrast ... 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 or slower oscillation phase codes, may resolve conflicting experimental observations on gamma phase coding. Our modeling results offer clear testable experimental predictions. We conclude that input-dependency of gamma frequencies could be essential rather than detrimental for meaningful gamma-mediated temporal organization of cortical activity.
Data from: Detection of transient synchrony across oscillating receptors by the central electrosensory system of mormyrid fish
Contributors: Vélez, Alejandro, Carlson, Bruce A.
oscillations among receptors. We found that electrosensory stimulation...oscillating electroreceptors in weakly electric fish (Mormyridae) respond...oscillation frequencies of the receptors. These frequencies are lower ...Frequency tuning in the midbrain resembled peripheral frequency tuning ... Recently, we reported evidence for a novel mechanism of peripheral sensory coding based on oscillatory synchrony. Spontaneously oscillating electroreceptors in weakly electric fish (Mormyridae) respond to electrosensory stimuli with a phase reset that results in transient synchrony across the receptor population (Baker et al., 2015). Here, we asked whether the central electrosensory system actually detects the occurrence of synchronous oscillations among receptors. We found that electrosensory stimulation elicited evoked potentials in the midbrain exterolateral nucleus at a short latency following receptor synchronization. Frequency tuning in the midbrain resembled peripheral frequency tuning, which matches the intrinsic oscillation frequencies of the receptors. These frequencies are lower than those in individual conspecific signals, and instead match those found in collective signals produced by groups of conspecifics. Our results provide further support for a novel mechanism for sensory coding based on the detection of oscillatory synchrony among peripheral receptors.
Data for: A Low Phase Noise Super–Harmonic Coupling Quadrature VCO Using an Additional Double Frequency Oscillator
Contributors: Samad Sheikhaei, bahram jafari
oscillator, proposed in the paper. The files are related to the Cadence ... These files are the schematic files of the quadrature oscillator, proposed in the paper. The files are related to the Cadence integrated circuit design environment.
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Contributors: João Casaleiro, Luís B. Oliveira, Igor M. Filanovsky
oscillation frequency and the coupling strength. ...frequency, phase error and amplitude mismatch that are validated by simulations...RC-oscillator with capacitive coupling fabricated in 130nm CMOS circuit...RC-oscillators...RC-oscillators is investigated. The capacitive coupling has the advantages...Frequency of oscillation with the oscillators uncoupled and coupled (CX...RC-oscillators with the same circuit topology. ...RC-oscillators. ...RC-oscillators, yet the dissipated power is about four times less. We ...frequency. ...oscillator...oscillators ... In this paper the capacitive coupling in quadrature RC-oscillators is investigated. The capacitive coupling has the advantages of being noiseless with a small area penalty and without increasing the power dissipation. The results show that a phase error below 1° and an amplitude mismatch lower than 1% are obtained with a coupling capacitance about 20% of the oscillator׳s capacitance value. Due to this kind of coupling, the phase-noise improves by 3dB (to −115.1 dBc/Hz @ 10MHz) and the increase of power requirement is only marginal leading to a figure-of-merit of −154.8dBc/Hz. This is comparable to the best state-of-the-art RC-oscillators, yet the dissipated power is about four times less. We present calculations of frequency, phase error and amplitude mismatch that are validated by simulations. The theory shows that phase error is proportional to the amplitude mismatch, indicating that an automatic phase error minimization based on the amplitude mismatches is possible. The measurements on a 2.4GHz voltage-controlled quadrature RC-oscillator with capacitive coupling fabricated in 130nm CMOS circuit prototypes validate the theory.
Article - Simulation of Spontaneous Ca2+ Oscillations in Astrocytes Mediated by Voltage-Gated Calcium Channels
Contributors: Shuai Zeng, Bing Li, Shaoqun Zeng, Shangbin Chen
frequency-encoded in signaling. Moreover, the properties of Ca2+ oscillations...oscillation. Within −70.0 to −64.9 mV, the frequency and amplitude of ...oscillations in astrocytes....oscillations in silico. Our model could mimic the oscillatory phenomenon...oscillations of astrocytes. By incorporating different types of voltage-gated...frequency (dotted line) decreased with temperature. ...frequency of Ca2+ oscillations increased with a rise in extracellular ...Frequency of Ca2+ oscillations versus membrane potential. ...oscillations changed slightly (both frequency changed...frequency of Ca2+ oscillations versus temperature. In the temperature ... The purpose of this computational study was to investigate the possible role of voltage-gated Ca2+ channels in spontaneous Ca2+ oscillations of astrocytes. By incorporating different types of voltage-gated Ca2+ channels and a previous model, this study reproduced typical Ca2+ oscillations in silico. Our model could mimic the oscillatory phenomenon under a wide range of experimental conditions, including resting membrane potential (−75 to −60 mV), extracellular Ca2+ concentration (0.1 to 1500 μM), temperature (20 to 37°C), and blocking specific Ca2+ channels. By varying the experimental conditions, the amplitude and duration of Ca2+ oscillations changed slightly (both <25%), while the frequency changed significantly (∼400%). This indicates that spontaneous Ca2+ oscillations in astrocytes might be an all-or-none process, which might be frequency-encoded in signaling. Moreover, the properties of Ca2+ oscillations were found to be related to the dynamics of Ca2+ influx, and not only to a constant influx. Therefore, calcium channels dynamics should be used in studying Ca2+ oscillations. This work provides a platform to explore the still unclear mechanism of spontaneous Ca2+ oscillations in astrocytes.
A better oscillation detection method robustly extracts EEG rhythms across brain state changes: The human alpha rhythm as a test case
Contributors: Tara A. Whitten, Adam M. Hughes, Clayton T. Dickson, Jeremy B. Caplan
oscillation detection across frequency, region and task. Here we show ...oscillations at the alpha frequency (9.5Hz) highlighted in red, using ...OSCillation detection) method. This method produces systematic, objective...Oscillations detected across all frequencies by the oscillatory episode...oscillations were detected at each frequency. (E) The raw signal from ...Oscillation...frequencies, brain regions and tasks. It does so by modeling the functional ... Oscillatory activity is a principal mode of operation in the brain. Despite an intense resurgence of interest in the mechanisms and functions of brain rhythms, methods for the detection and analysis of oscillatory activity in neurophysiological recordings are still highly variable across studies. We recently proposed a method for detecting oscillatory activity from time series data, which we call the BOSC (Better OSCillation detection) method. This method produces systematic, objective, and consistent results across frequencies, brain regions and tasks. It does so by modeling the functional form of the background spectrum by fitting the empirically observed spectrum at the recording site. This minimizes bias in oscillation detection across frequency, region and task. Here we show that the method is also robust to dramatic changes in state that are known to influence the shape of the power spectrum, namely, the presence versus absence of the alpha rhythm, and can be applied to independent components, which are thought to reflect underlying sources, in addition to individual raw signals. This suggests that the BOSC method is an effective tool for measuring changes in rhythmic activity in the more common research scenario wherein state is unknown.
Contributors: Tolga Esat Özkurt, Alfons Schnitzler
frequency) and 15Hz (phase frequency). The simulated signal contained ...Cross-frequency coupling...oscillations (at 20, 25, 30, 40 and 100Hz) having no coupling relation...oscillations and noise. ...Oscillations ... Recent studies have observed the ubiquity of phase–amplitude coupling (PAC) phenomenon in human and animal brain recordings. While various methods were performed to quantify it, a rigorous analytical definition of PAC is lacking. This paper yields an analytical definition and accordingly offers theoretical insights into some of the current methods. A direct PAC estimator based on the given definition is presented and shown theoretically to be superior to some of the previous methods such as general linear model (GLM) estimator. It is also shown that the proposed PAC estimator is equivalent to GLM estimator when a constant term is removed from its formulation. The validity of the derivations is demonstrated with simulated data of varying noise levels and local field potentials recorded from the subthalamic nucleus of a Parkinson's disease patient.
Contributors: Andrada Ianuş, Bernard Siow, Ivana Drobnjak, Hui Zhang, Daniel C. Alexander
oscillation frequency for four different sizes of the restricted compartment...oscillation frequency for (a) several values of Δ, R=5μm and G=0.1T/m;...Oscillating gradient...oscillations. Restricted diffusion as a function of (c) gradient strength...oscillations have been popular for some time, recent work suggests additional...oscillating gradient spin echo (OGSE) sequences using the Gaussian phase...frequencies, R=5μm and Δ=45ms; (d) cylinder radius for several frequencies...oscillating waveforms. This paper presents analytical expressions of the...oscillation frequency and are accurate to within a few percent. Finally...oscillations...oscillation frequency. ...Oscillating gradients provide an optimal probe of small pore sizes in ... Oscillating gradients provide an optimal probe of small pore sizes in diffusion MRI. While sinusoidal oscillations have been popular for some time, recent work suggests additional benefits of square or trapezoidal oscillating waveforms. This paper presents analytical expressions of the free and restricted diffusion signal for trapezoidal and square oscillating gradient spin echo (OGSE) sequences using the Gaussian phase distribution (GPD) approximation and generalises existing similar expressions for sinusoidal OGSE. Accurate analytical models are necessary for exploitation of these pulse sequences in imaging studies, as they allow model fitting and parameter estimation in reasonable computation times. We evaluate the accuracy of the approximation against synthesised data from the Monte Carlo (MC) diffusion simulator in Camino and Callaghan’s matrix method and we show that the accuracy of the approximation is within a few percent of the signal, while providing several orders of magnitude faster computation. Moreover, since the expressions for trapezoidal wave are complex, we test sine and square wave approximations to the trapezoidal OGSE signal. The best approximations depend on the gradient amplitude and the oscillation frequency and are accurate to within a few percent. Finally, we explore broader applications of trapezoidal OGSE, in particular for non-model based applications, such as apparent diffusion coefficient estimation, where only sinusoidal waveforms have been considered previously. We show that with the right apodisation, trapezoidal waves also have benefits by virtue of the higher diffusion weighting they provide compared to sinusoidal gradients.
Contributors: R. Kalter, M.J. Tummers, S. Kenjereš, B.W. Righolt, C.R. Kleijn
oscillations kosc,2D. The inlet velocity is vin=0.4m/s (Rein=3.1×103, ...oscillations. The low frequency self-sustained jet oscillations induce...oscillations of turbulent jets (Re=3.1×103) issuing from a submerged bifurcated...Frequency peaks are found at fPOD=0.027Hz (FL<0), fPOD=0.046Hz (FL=0) ...frequency peaks are in reasonable agreement with the frequencies found...oscillation. When FLoscillation is...oscillation amplitude is enhanced by a factor of 1.5....frequency fTS of the free surface oscillation at a monitoring point at...frequency fPOD from the power spectrum of the first chrono mode of the...oscillations ... The effect of Lorentz forcing on self-sustained oscillations of turbulent jets (Re=3.1×103) issuing from a submerged bifurcated nozzle into a thin rectangular liquid filled cavity was investigated using free surface visualization and time-resolved particle image velocimetry (PIV). A Lorentz force is produced by applying an electrical current across the width of the cavity in conjunction with a magnetic field. As a working fluid a saline solution is used. The Lorentz force can be directed downward (FL0), to weaken or strengthen the self-sustained jet oscillations. The low frequency self-sustained jet oscillations induce a free surface oscillation. When FL0 the free surface oscillation amplitude is enhanced by a factor of 1.5.
Contributors: S. Sutradhar, R. Paul
oscillation. It turns out that, various modes of oscillation can be fully...oscillation is the signature of a bioriented chromosome. ...oscillation is observed when the kinetochore, a specific protein structure...oscillation of the mono-oriented chromosome, monotonic migration of the...oscillation. The model is robust and is not restricted to any particular...oscillation up to ~1000s is mono-oriented and from ~1200s onwards it is...oscillation, we compare numerical results with the available experimental...oscillations triggered by the capture of an uncaptured kinetochore by ...oscillation, a monotonic increase followed by an irregular oscillation ... Chromosomes move towards and away from the centrosomes during the mitosis. This oscillation is observed when the kinetochore, a specific protein structure on the chromosome is captured by centrosome-nucleated polymer called microtubules. We present a computational model, incorporating activities of various molecular motors and microtubule dynamics, to demonstrate the observed oscillation. The model is robust and is not restricted to any particular cell type. Quantifying the average velocity, amplitude and periodicity of the chromosomal oscillation, we compare numerical results with the available experimental data. Our analysis supports a tug-of-war like mechanism between opposing motors that changes the course of chromosomal oscillation. It turns out that, various modes of oscillation can be fully understood by assembling the dynamics of molecular motors. Near the stall regime, when opposing motors are engaged in a tug-of-war, sufficiently large kinetochore–microtubule generated force may prolong the stall durations.