Contributors: Feng Liu, JiaFu Wang, Wei Wang

Date: 1999-05-31

(a) The SNR vs noise intensity D for fs=30,15, and 100 Hz, respectively. (b) The mean synaptic input Isyn(t) vs time for fs=30 Hz and D=0.15 and 6, respectively. (c) The SNR for various frequencies for the cases of D=0.5 and 5, respectively, in the case of I0i=0.8 and I1=0.11, and Jij∈[−4,20]. (d) The SNR vs signal frequency for D=0.5 and 5, respectively, for the case of I0i∈[0,1] and I1=0.072. ...Intrinsic oscillations...The 40 Hz oscillation...The frequency sensitivity...The frequency fi and the corresponding height H of the main peak in PSD of Isyn(t) vs (a) A for the case of I0i∈[0,3.5]; (b) M in the case of Jij∈[−5,10]. ...The phenomena of frequency sensitivity in weak signal detection and the 40 Hz oscillation in a neuronal network have been interpreted based on the intrinsic oscillations of the system. There exists a most sensitive frequency range of 20–60 Hz, over which the signal-to-noise ratio has a large value. This results from the resonance between the subthreshold intrinsic oscillation and the periodic signal. The network can exhibit the synchronous 40 Hz oscillation only with constant bias, which is due to the intrinsic features of neurons and long-range interactions between them....I0i∈[0,2] and Jij∈[−1,10]. (a) The spatiotemporal firing pattern is plotted by recording the firing time tni defined by Xi(tni)>0 and Xi(tni−)frequency fi and the corresponding height H of the main peak in PSD of Isyn(t) for different coupling strength. ... The phenomena of frequency sensitivity in weak signal detection and the 40 Hz oscillation in a neuronal network have been interpreted based on the intrinsic oscillations of the system. There exists a most sensitive frequency range of 20–60 Hz, over which the signal-to-noise ratio has a large value. This results from the resonance between the subthreshold intrinsic oscillation and the periodic signal. The network can exhibit the synchronous 40 Hz oscillation only with constant bias, which is due to the intrinsic features of neurons and long-range interactions between them.

Contributors: Weixiong Chen, Quanbin Zhao, Yingchun Wang, Palash Kumar Sen, Daotong Chong, Junjie Yan

Date: 2016-09-01

Submerged steam jet condensation is widely applied in various fields because of its high heat transfer efficiency. Condensation oscillation is a major character of submerged steam turbulent jet, and it significantly affects the design and safe operation of industrial equipment. This study is designed to reveal the mechanism of the low-frequency pressure oscillation of steam turbulent jet condensation and determine its affected region. First, pressure oscillation signals with low frequency are discovered in the downstream flow field through oscillation frequency spectrogram and power analysis. The oscillation frequency is even lower than the first dominant frequency. Moreover, the critical positions, where the low-frequency pressure oscillation signals appear, move downstream gradually with radial distance and water temperature. However, these signals are little affected by the steam mass flux. Then, the regions with low-frequency pressure oscillation occurring are identified experimentally. The affected width of the low-frequency pressure oscillation is similar to the turbulent jet width. Turbulent jet theory and the experiment results collectively indicate that the low-frequency pressure oscillation is generated by turbulent jet vortexes in the jet wake region. Finally, the angular coefficients of the low-frequency affected width are obtained under different water temperatures. Angular coefficients, ranging from 0.2268 to 0.2887, decrease with water temperature under test conditions....Frequency spectrograms distribution along the axial direction (R/D=2). ...Frequency spectrograms of condensation oscillation [21]. ...Frequency spectrograms under radial position of R/D=3.0 and R/D=4.0. ...Half affected width of pressure oscillation. ...Pressure oscillation...Oscillation power axial distribution for low frequency region. ... Submerged steam jet condensation is widely applied in various fields because of its high heat transfer efficiency. Condensation oscillation is a major character of submerged steam turbulent jet, and it significantly affects the design and safe operation of industrial equipment. This study is designed to reveal the mechanism of the low-frequency pressure oscillation of steam turbulent jet condensation and determine its affected region. First, pressure oscillation signals with low frequency are discovered in the downstream flow field through oscillation frequency spectrogram and power analysis. The oscillation frequency is even lower than the first dominant frequency. Moreover, the critical positions, where the low-frequency pressure oscillation signals appear, move downstream gradually with radial distance and water temperature. However, these signals are little affected by the steam mass flux. Then, the regions with low-frequency pressure oscillation occurring are identified experimentally. The affected width of the low-frequency pressure oscillation is similar to the turbulent jet width. Turbulent jet theory and the experiment results collectively indicate that the low-frequency pressure oscillation is generated by turbulent jet vortexes in the jet wake region. Finally, the angular coefficients of the low-frequency affected width are obtained under different water temperatures. Angular coefficients, ranging from 0.2268 to 0.2887, decrease with water temperature under test conditions.

Contributors: M.R. Qader

Date: 2013-01-01

Driven qubit...The transient scattered radiation due to interaction of a short laser pulse (of rectangular shape) with a qubit is studied through the Haar wavelet window spectrum. Asymmetrical structure in the spectrum is shown due to frequency miss-match of the laser and qubit frequencies and the shift window parameter. ... The transient scattered radiation due to interaction of a short laser pulse (of rectangular shape) with a qubit is studied through the Haar wavelet window spectrum. Asymmetrical structure in the spectrum is shown due to frequency miss-match of the laser and qubit frequencies and the shift window parameter.

Contributors: D. Sugny, M. Ndong, D. Lauvergnat, Y. Justum, M. Desouter-Lecomte

Date: 2007-08-15

We examine the effect of dissipation on the laser control of a process that transforms a state into a superposed state. We consider a two-dimensional double well of a single potential energy surface. In the context of reactivity, the objective of the control is the localization in a given well, for instance the creation of an enantiomeric form whereas for quantum gates, this control corresponds to one of the transformation of the Hadamard gate. The environment is either modelled by coupling few harmonic oscillators (up to five) to the system or by an effective interaction with an Ohmic bath. In the discrete case, dynamics is carried out exactly by using the coupled harmonic adiabatic channels. In the continuous case, Markovian and non-Markovian dynamics are considered. We compare two laser control strategies: the Stimulated Raman Adiabatic Passage (STIRAP) method and the optimal control theory. Analytical estimations for the control by adiabatic passage in a Markovian environment are also derived....Dynamics controlled by f-STIRAP strategy for the preparation of the superposed state |R〉. Panels (a) and (b) show, respectively, the evolution of the localization in the right well for different values of λ and the Rabi frequencies of the different pulses. Rabi frequencies are in atomic units. The solid line of panel (b) corresponds to the Stokes pulse and the dashed one to the pump pulse. The total duration of the process is of the order of 4.5ps. ...Qubit...Half-live time τ1/2 in fs and the time τmax for which C(t) (Eq. (12)) vanishes for the two reference frequencies (Eq. (7)) and temperatures used in the simulations ...Robustness of the f-STIRAP process as a function of the peak Rabi frequency and the delay between the pulses for a total duration of 4.5ps of the overall field. Rabi frequency and delay are in atomic units. The upper and the lower part of the figure correspond, respectively, to λ=5×10−4 and λ=2×10−3. ... We examine the effect of dissipation on the laser control of a process that transforms a state into a superposed state. We consider a two-dimensional double well of a single potential energy surface. In the context of reactivity, the objective of the control is the localization in a given well, for instance the creation of an enantiomeric form whereas for quantum gates, this control corresponds to one of the transformation of the Hadamard gate. The environment is either modelled by coupling few harmonic oscillators (up to five) to the system or by an effective interaction with an Ohmic bath. In the discrete case, dynamics is carried out exactly by using the coupled harmonic adiabatic channels. In the continuous case, Markovian and non-Markovian dynamics are considered. We compare two laser control strategies: the Stimulated Raman Adiabatic Passage (STIRAP) method and the optimal control theory. Analytical estimations for the control by adiabatic passage in a Markovian environment are also derived.

Contributors: Uwe Starossek

Date: 2015-01-01

Free oscillation response of pendulum mechanism. ...Free oscillation response...Low frequency...A pendulum mechanism is presented whose natural frequency of oscillation is distinctly lower than that of a conventional pendulum of comparable size. Furthermore, its natural frequency is approximately proportional to its amplitude of oscillation. The mechanism can thus be tuned to extremely low frequencies by using small amplitudes. The undamped free oscillation response of the mechanism is studied. The derivation of the equation of motion is outlined for both large and, after neglecting higher order terms, small displacements. In both cases, a second-order nonlinear differential equation results. When higher order terms are neglected, the equation of motion is of simple form and can be solved symbolically in terms of a Jacobi elliptic function. Based on this solution, a closed-form expression for the natural frequency is derived and the characteristics of the free oscillation response are discussed. ... A pendulum mechanism is presented whose natural frequency of oscillation is distinctly lower than that of a conventional pendulum of comparable size. Furthermore, its natural frequency is approximately proportional to its amplitude of oscillation. The mechanism can thus be tuned to extremely low frequencies by using small amplitudes. The undamped free oscillation response of the mechanism is studied. The derivation of the equation of motion is outlined for both large and, after neglecting higher order terms, small displacements. In both cases, a second-order nonlinear differential equation results. When higher order terms are neglected, the equation of motion is of simple form and can be solved symbolically in terms of a Jacobi elliptic function. Based on this solution, a closed-form expression for the natural frequency is derived and the characteristics of the free oscillation response are discussed.

Contributors: Howan Leung, Cannon X.L. Zhu, Danny T.M. Chan, Wai S. Poon, Lin Shi, Vincent C.T. Mok, Lawrence K.S. Wong

Date: 2015-01-01

High-frequency oscillations...An example of the implantation schedule (patient #1) demonstrating areas with conventional frequency ictal patterns, ictal high-frequency oscillations, hyperexcitability, and radiological lesions. ...An example of the implantation schedule (patient #7) demonstrating areas with conventional frequency ictal patterns, ictal high-frequency oscillations, hyperexcitability, and radiological lesions. ...High-frequency oscillations (HFOs, 80–500Hz) from intracranial electroencephalography (EEG) may represent a biomarker of epileptogenicity for epilepsy. We explored the relationship between ictal HFOs and hyperexcitability with a view to improving surgical outcome....Summary table for statistical analysis. HFO=high frequency oscillations, CFIP=conventional frequency ictal patterns. ... High-frequency oscillations (HFOs, 80–500Hz) from intracranial electroencephalography (EEG) may represent a biomarker of epileptogenicity for epilepsy. We explored the relationship between ictal HFOs and hyperexcitability with a view to improving surgical outcome.

Contributors: M.E. Leser, S. Acquistapace, A. Cagna, A.V. Makievski, R. Miller

Date: 2005-07-01

Apparent dilational elasticity modulus as a function of oscillation frequency for drops of water (♦), water/ethanol 86:14 (■), ethanol (▴), amplitude of volume oscillations 8%. ...Surface tension and apparent dilational elasticity modulus E as a function of oscillation frequency for an air bubble in pure water. ...Oscillating drops and bubbles...Surface tension and apparent dilational elasticity modulus E as a function of oscillation frequency for a drop of pure water in air. ...Apparent dilational elasticity modulus as a function of oscillation frequency for drops of silicon oil (●), paraffin oil (■), amplitude of volume oscillations 2%. ...Limiting frequency...To determine the dilational rheology of surface layers, the profile analysis tensiometry can be used with oscillating drops or bubbles. The methodology limits for these oscillations depend on the liquids’ properties, such as density, viscosity and surface tension. For the most frequently studied water/air interface, the maximum oscillation frequency is of the order of 1Hz, although much higher frequencies are technically feasible by the existing profile analysis tensiometers. For f>1Hz, deviations of the drops/bubbles from the Laplacian shape mimic non-zero dilational elasticities for the pure water/air and ethanol/air interface. For liquids of higher viscosity, the critical frequency is much lower....Apparent dilational elasticity modulus as a function of oscillation frequency for drops of water (♦), water/ethanol 86:14 (■), ethanol (▴), amplitude of volume oscillations 2%. ... To determine the dilational rheology of surface layers, the profile analysis tensiometry can be used with oscillating drops or bubbles. The methodology limits for these oscillations depend on the liquids’ properties, such as density, viscosity and surface tension. For the most frequently studied water/air interface, the maximum oscillation frequency is of the order of 1Hz, although much higher frequencies are technically feasible by the existing profile analysis tensiometers. For f>1Hz, deviations of the drops/bubbles from the Laplacian shape mimic non-zero dilational elasticities for the pure water/air and ethanol/air interface. For liquids of higher viscosity, the critical frequency is much lower.

Contributors: Fatema F. Ghasia, Aasef G. Shaikh

Date: 2014-01-01

(A) Comparison of the frequency of oscillations during oblique, pure horizontal and pure vertical saccades. Number of observations is plotted on y-axis, while x-axis represents bins of oscillation frequency. Each data point represents the number of observations in a given frequency bin. Black trace suggests oblique saccade, Gray traces with circular symbols are horizontal saccades and triangular symbols represent vertical saccade. Dashed lines depict median oscillation frequency. (B) Comparison of frequency oblique saccade oscillations with the frequency of orthogonal saccadic oscillations during pure horizontal and vertical saccades. Each data point depicts one subject. Black data points are comparison with pure horizontal saccade, gray data points are comparison with vertical saccade. Dashed gray line is an equality line. (C) Comparison of the amplitude of the sinusoidal modulation of oblique, horizontal, and vertical saccade trajectories. Number of samples is plotted on y-axis, while x-axis represents the amplitude bins. Each data point depicts number of observations in a given bin of the histogram. Black trace shows oblique saccade, Gray trace with circuit symbol is a horizontal saccade and the triangular symbol is a vertical saccade. Dashed lines represent median values. ...Most common eye movements, oblique saccades, feature rapid velocity, precise amplitude, but curved trajectory that is variable from trial-to-trial. In addition to curvature and inter-trial variability, the oblique saccade trajectory also features high-frequency oscillations. A number of studies proposed the physiological basis of the curvature and inter-trial variability of the oblique saccade trajectory, but kinematic characteristics of high-frequency oscillations are yet to be examined. We measured such oscillations and compared their properties with orthogonal pure horizontal and pure vertical oscillations generated during pure vertical and pure horizontal saccades, respectively. We found that the frequency of oscillations during oblique saccades ranged between 15 and 40 Hz, consistent with the frequency of orthogonal saccadic oscillations during pure horizontal or pure vertical saccades. We also found that the amplitude of oblique saccade oscillations was larger than pure horizontal and pure vertical saccadic oscillations. These results suggest that the superimposed high-frequency sinusoidal oscillations upon the oblique saccade trajectory represent reverberations of disinhibited circuit of reciprocally innervated horizontal and vertical burst generators....An example of horizontal, vertical, and oblique saccade from one healthy subject. The left column depicts horizontal saccade; central column vertical, and right column is oblique saccade. Panels A, B and C illustrate eye position vector plotted along y-axis. Panels D, E and F represent eye velocity vector plotted along y-axis while ordinate in panels G, H and I illustrate eye acceleration. In each panel, x-axis represents corresponding time. Arrows in panels C, F, I show oscillations in oblique saccade trajectory. ... Most common eye movements, oblique saccades, feature rapid velocity, precise amplitude, but curved trajectory that is variable from trial-to-trial. In addition to curvature and inter-trial variability, the oblique saccade trajectory also features high-frequency oscillations. A number of studies proposed the physiological basis of the curvature and inter-trial variability of the oblique saccade trajectory, but kinematic characteristics of high-frequency oscillations are yet to be examined. We measured such oscillations and compared their properties with orthogonal pure horizontal and pure vertical oscillations generated during pure vertical and pure horizontal saccades, respectively. We found that the frequency of oscillations during oblique saccades ranged between 15 and 40 Hz, consistent with the frequency of orthogonal saccadic oscillations during pure horizontal or pure vertical saccades. We also found that the amplitude of oblique saccade oscillations was larger than pure horizontal and pure vertical saccadic oscillations. These results suggest that the superimposed high-frequency sinusoidal oscillations upon the oblique saccade trajectory represent reverberations of disinhibited circuit of reciprocally innervated horizontal and vertical burst generators.

Contributors: György Buzsáki, Fernando Lopes da Silva

Date: 2012-09-01

Spontaneously occurring fast ‘ripple’ oscillations (400–500Hz) in the neocortex of the rat during high-voltage spindles. (A) Averaged high-voltage spindles and associated unit firing histograms from layers IV–VI. (B) Wide-band (a and a′; 1Hz–5kHz), filtered field (b and b′; 200–800Hz), and filtered unit (c and c′; 0.5–5kHz) traces from layers IV and V, respectively. (C) Averaged fast waves and corresponding unit histograms. The field ripples are filtered (200–800Hz) derivatives of the wide-band signals recorded from 16 sites. Note the sudden phase-reversal of the oscillating waves (arrows) but locking of unit discharges (dashed lines). These phase reversed dipoles likely reflect synchronous discharge of layer 5 neurons in the vicinity of the recording electrode. ...Self-organized burst of activity in the CA3 region of the hippocampus produces a sharp wave sink in the apical dendrites of CA1 pyramidal neurons and also discharge interneurons. The interactions between the discharging pyramidal cells and interneurons give rise to a short-lived fast oscillation (‘ripple’; 140–200Hz), which can be detected as a field potential in the somatic layer. The strong CA1 population burst brings about strongly synchronized activity in the target populations of parahippocampal structures as well. These parahippocampal ripples are slower and less synchronous, compared to CA1 ripples. ...High frequency oscillations (HFOs) constitute a novel trend in neurophysiology that is fascinating neuroscientists in general, and epileptologists in particular. But what are HFOs? What is the frequency range of HFOs? Are there different types of HFOs, physiological and pathological? How are HFOs generated? Can HFOs represent temporal codes for cognitive processes? These questions are pressing and this symposium volume attempts to give constructive answers. As a prelude to this exciting discussion, we summarize the physiological high frequency patterns in the intact brain, concentrating mainly on hippocampal patterns, where the mechanisms of high frequency oscillations are perhaps best understood. ... High frequency oscillations (HFOs) constitute a novel trend in neurophysiology that is fascinating neuroscientists in general, and epileptologists in particular. But what are HFOs? What is the frequency range of HFOs? Are there different types of HFOs, physiological and pathological? How are HFOs generated? Can HFOs represent temporal codes for cognitive processes? These questions are pressing and this symposium volume attempts to give constructive answers. As a prelude to this exciting discussion, we summarize the physiological high frequency patterns in the intact brain, concentrating mainly on hippocampal patterns, where the mechanisms of high frequency oscillations are perhaps best understood.

Contributors: Sven P. Heinrich, Michael Bach

Date: 2004-10-07

High-frequency oscillations...Time–frequency distributions. On the left side, the full 20–1000 Hz range is displayed for three exemplary subjects. The two graphs per subject show the ERG and VEP activity, respectively. The high-frequency oscillations appear as a distinct area which in most cases is around or above 100 Hz. The flash was given at t=0. Those parts of the time–frequency diagram which would be contaminated by edge effects are displayed in white. Their spread is due to the inevitable frequency-dependent finite time resolution, which also causes the spurious pre-stimulus activity at low frequencies. The white rectangles in the diagrams mark the regions of interest, which are shown enlarged on the right side for all 7 subjects. The arrows link the high-frequency maxima of ERG and VEP. Most subjects produced activity around or above 100 Hz in both VEP and ERG. However, only in one subject (S1) the frequencies matched. Asterisks indicate the significance levels of frequency differences in standard notation, based on a sequential Bonferroni adjustment. No significance value could be obtained for subject S3. ...Flash stimulation elicits oscillatory responses above 100 Hz in human visual cortex. It has been proposed that these are the result of retinal oscillations being directly relayed through the visual pathway to area V1. Experimental evidence, however, is scarce and contradictory. To address this issue, we performed a time–frequency analysis of simultaneously recorded retinal and cortical potentials. Matching frequencies would support the assumption of a direct relationship between retinal and cortical activities. In 4 of 7 subjects the frequency was significantly lower in the cortex than in the retina and in one subject it was significantly higher. The differences were in the range of 10–34 Hz and suggest that the cortical oscillations are not a simple echo of their retinal counterparts. ... Flash stimulation elicits oscillatory responses above 100 Hz in human visual cortex. It has been proposed that these are the result of retinal oscillations being directly relayed through the visual pathway to area V1. Experimental evidence, however, is scarce and contradictory. To address this issue, we performed a time–frequency analysis of simultaneously recorded retinal and cortical potentials. Matching frequencies would support the assumption of a direct relationship between retinal and cortical activities. In 4 of 7 subjects the frequency was significantly lower in the cortex than in the retina and in one subject it was significantly higher. The differences were in the range of 10–34 Hz and suggest that the cortical oscillations are not a simple echo of their retinal counterparts.