Small Phase Lag Research Articles

1P1-F03 A Realtime Quadratic Sliding Mode Filter for Removing Noise(3D Measurement/Sensor Fusion)

This paper presents a sliding mode filter that effectively removes impulsive noise and high-frequency noise with producing much smaller phase lag than linear filters. It is less prone to overshoot than previous sliding mode filters and it does not produce chattering. In addition, it is computationally inexpensive, and thus suitable for realtime applications. The proposed sliding mode filter employs a quadratic surface as its sliding surface, which is designed so that the output converges to the input in finite time if the input value is constant. Its algorithm is derived by using the backward Euler discretization, which prevents chattering. The effectiveness of the filter was shown by experiments by using an ultrasonic sensor and an optical encoder.

Photothermal radiometry and modulated luminescence examination of demineralized and remineralized dental lesions

Dental caries involves continuous challenges of acid-induced mineral loss and a counteracting process of mineral recovery. As an emerging non-destructive methodology, photothermal radiometry and modulated luminescence (PTR-LUM) has shown promise in measuring changes in tooth mineral content. Human molars (n=37) were subjected to demineralization in acid gel (pH 4.5, 10 days), followed by incubation in remineralisation solutions (pH 6.7, 4 weeks) without or with fluoride (1 or 1000 ppm). PTR-LUM frequency scans (1 Hz – 1 kHz) were performed prior to and during demineralization and remineralization treatments. Transverse Micro-Radiography (TMR) analysis followed at treatment conclusion. The non-fluoridated group exhibited opposite amplitude and phase trends to those of the highly fluoridated group: smaller phase lag and larger amplitude. These results point to a complex interplay between surface and subsurface processes during remineralization, confining the thermal-wave centroid toward the dominating layer.

Phase locking of pulse-coupled oscillators with delays is determined by the phase response curve

Event Abstract Back to Event Phase locking of pulse-coupled oscillators with delays is determined by the phase response curve Gamma oscillations (30-70 Hz) can synchronize with near zero phase lag over multiple cortical regions and between hemispheres, and between two distal sites in hippocampal slices in which gamma was induced by tetanus. Additionally, oscillations the gamma band can synchronize with nonzero phase lag between pairs of EEG electrodes. There are two mechanisms by which long range synchronization could occur: by locking to a common input or via reciprocal coupling. Here we address phase-locking that arises via bidirectional coupling of two limit cycle oscillators with a conduction delay. It is often implied that for two distal oscillators, phase lags equal to the conduction delay are expected, and how synchronization can take place over long distances in a stable manner is considered an open question. Here we assume that under conditions in which two local circuit generators of gamma oscillations arise separated by some distance, these circuits function as intrinsic nonlinear oscillators that are bidirectionally coupled with a conduction delay. Nothing is assumed regarding the oscillators other than that the phase response curve (PRC) can be measured using an input that approximates the one received from the other oscillator, and that the effect of the coupling is dissipated within one network period such that the coupling is effectively pulsatile. Here we derive existence and stability criteria based on the PRC for phase locking with delays of any length, and test them on oscillators with a wide variety of PRCs and varying levels of heterogeneity. The method is accurate for any shape PRC that we examined and therefore very general. For identical frequencies, identical coupling strength, and identical delays, synchrony emerges as a consequence of symmetry. We show that for both homogenous and heterogenous networks, in phase synchronization alternates with out of phase synchronization as the delay is increased, with regions of bistability in the intermediate values. In practice, the frequencies of the local circuits are unlikely to be identical; therefore, the cycle periods need to be altered via phase resetting in order to reach a common frequency. If the coupling is strong, as it must be in order for synchronization to occur rapidly, and the frequencies, conduction delays and PRCs of the oscillators are similar, then the input to each neuron will arrive at a similar phase, resulting in a small phase lag in the firing times. The stability of the phase locking depends upon the slope of the phase resetting curve at the phase at which the input is received in the phase locked mode. In other circuits, the conduction delays are asymmetric, in which case additional mechanisms may be required to achieve near zero phase lag. Having an explicit and general solution for the existence and stability of in phase locking with delay can provide insight into how such locking is achieved in the brain. Conference: Computational and systems neuroscience 2009, Salt Lake City, UT, United States, 26 Feb - 3 Mar, 2009. Presentation Type: Poster Presentation Topic: Poster Presentations Citation: (2009). Phase locking of pulse-coupled oscillators with delays is determined by the phase response curve. Front. Syst. Neurosci. Conference Abstract: Computational and systems neuroscience 2009. doi: 10.3389/conf.neuro.06.2009.03.139 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 02 Feb 2009; Published Online: 02 Feb 2009. Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Google Google Scholar PubMed Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Nearly instantaneous brightness induction

Brightness induction is the modulation of the perceived intensity of a region by the luminance of surrounding regions and reveals fundamental properties of neural organization in the visual system. Grating induction affords a unique opportunity to precisely measure the temporal properties of induction using a quadrature motion technique. Contrary to previous reports that induction is a sluggish process with temporal frequency cutoffs of 2-5 Hz (R. L. DeValois, M. A. Webster, K. K. DeValois, & B. Lingelbach, 1986; A. F. Rossi & M. A. Paradiso, 1996), we find that induction is nearly instantaneous. The temporal response of induced brightness differs from that of luminance gratings by a small time lag (<1 ms), or by a small temporal phase lag (<0.016 cycle), and remains relatively constant across wide variations in test field height. These data are not easily explained by an edge-dependent, homogeneous filling-in process (A. F. Rossi & M. A. Paradiso, 1996); however, they are consistent with an explanation of brightness induction based on spatial filtering by cortical simple cells (B. Blakeslee & M. E. McCourt, 1999).

Analytic Theory of the YORP Effect for Near-Spherical Objects

The YORP effect is produced when the surface of a small object in interplanetary space is heated by sunlight and reradiates the absorbed energy in thermal wavelengths. The absorbed, reflected, and emitted photons produce tiny torques on the small body that can change its spin rate and obliquity over planetary timescales. Previous theories of the YORP effect relied on numerical or seminumerical evaluation of the radiation torques. Here we develop an alternative approach and calculate the YORP torques analytically. Our theory is limited to near-spherical objects. While unsuitable for a precise determination of torques on elongated and/or highly irregular objects, the analytic theory helps to explain several general properties of the YORP torques that were identified in previous numerical works. For example, we demonstrate that the component of the YORP torque that affects the spin rate, s, can vanish for obliquity values ≈ 55° (and ≈ 125°). As discussed by Vokrouhlický and coworkers, this property of s is important for establishing the so-called Slivan states, which arise as evolutionary end states of spin vectors of small solar system bodies such as asteroids. We show that s (averaged over spin and orbit periods) is a second-order quantity in the small parameter that describes the deviation of the shape from an ideal sphere. We calculate s explicitly as polynomials of cos . These expressions show that the YORP torque arises from coupled deformations of the body's shape in topographic longitude and latitude. Moreover, by introducing a small phase lag to mimic the delay between the absorption and reemission of photons we demonstrate that s is insensitive to the exact value of the surface thermal conductivity. These and other analytic results described here provide a baseline for understanding the YORP effect on bodies with more complicated surface shapes and properties other than the ones considered here. We discuss applications of the analytic theory on near-spherical asteroids like 1998 KY26 and on more elongated and/or irregular objects like (1862) Apollo and (25143) Itokawa.

Angular acceleration estimation and feedback control: An experimental investigation

Angular acceleration estimation and its application in acceleration feedback control are investigated experimentally in the paper. In combination of Newton Predictor (NP) with Kalman Filter (KF), a new predictive estimator for angular acceleration, called Newton Predictor Enhanced Kalman Filter (NPEKF) is proposed. This estimator provides a wide bandwidth and a small phase lag of the estimated acceleration while attenuating noises. Based on the estimated acceleration an acceleration feedback control (AFC) is presented for multiple degree-of-freedom (DOF) mechatronic system. The design of AFC is specified in terms of its stability and ability in suppressing dynamic disturbances. Experiments are conducted on a 2-DOF direct-drive manipulator. The frequency responses of the acceleration estimated by NP, KF and NPEKF are compared with those of the measured acceleration via linear accelerometer. The performance of AFC using the estimated acceleration is assessed against that using the measured acceleration. This study has shown that the proposed NPEKF estimator is able to supply the AFC with reliable required acceleration.

Role of the Gouy Phase in the Coherent Phase Control of the Photoionization and Photodissociation of Vinyl Chloride

We demonstrate theoretically and experimentally that the Gouy phase of a focused laser beam may be used to control the photoinduced reactions of a polyatomic molecule. Quantum mechanical interference between one- and three-photon excitation of vinyl chloride produces a small phase lag between the dissociation and ionization channels on the axis of the molecular beam. Away from the axis, the Gouy phase introduces a much larger phase lag that agrees quantitatively with theory without any adjustable parameters.

Synchronization Properties of Slow Cortical Oscillations

During slow-wave sleep, the brain shows slow oscillatory activity with remarkable long-range synchrony. Intracellular recordings show that the slow oscillation consists of two phases: an up state and a down state. Deriving the phase-response function of simplified neuronal systems, we examine the synchronization properties on slow oscillations between the up state and the down state. As a result, the strange interaction functions are found in some parameter ranges. These functions indicate that the states with the smaller phase lag than a critical value are all stable.

Interannual Variation of Freshwater in the Yellow and East China Seas: Roles of the Changjiang Discharge and Wind Forcing

The interannual variation of the behavior of Changjiang freshwater has been investigated using the Princeton Ocean Model (POM). Five experiments are described in this study. Three basic experiments (Exps. B1, B2 and B3) were performed to examine the freshwater behavior in response to annual variations of the Changjiang discharge in normal, wet and dry years, respectively. Thereafter, the freshwater variation was investigated with the model forced by primary-interannual variations of river discharge with an 8-year period (Exp. I1) and a wind field with a 3.6-year period (Exp. I2). In Exp. B1, the average residence time of freshwater is roughly estimated to be 681.4 days in the Yellow Sea (YS) and 353.4 days in the combined area of the East China Sea (ECS) and the Chinese Coast (CC). This difference is attributed to the current pattern in each region and freshwater exchange among the regions. The interannual variation of freshwater volume in Exp. I1 has a large amplitude and long phase lag in the YS (38 km3 and 1.6-year against primary-interannual discharge variation), while there are relatively small amplitudes and short phase lags in the ECS (18 km3 and 0.7-year) and the CC (14 km3 and 0.5-year). It is concluded that the difference in the freshwater behavior results from the difference in the average residence time in each region.

Gravitational waves in magnetized relativistic plasmas

We study the propagation of gravitational waves (GW's) in a uniformly magnetized plasma at arbitrary angles to the magnetic field. No a priori assumptions are made about the temperature, and we consider both a plasma at rest and a plasma flowing out at ultrarelativistic velocities. In the $3+1$ orthonormal tetrad description, we find that all three fundamental low-frequency plasma wave modes are excited by the GW's. Alfv\'en waves are excited by a \ifmmode\times\else\texttimes\fi{} polarized GW, whereas the slow and fast magnetoacoustic modes couple to the + polarization. The slow mode, however, does not interact coherently with the GW. The most relevant wave mode is the fast magnetoacoustic mode which in a strongly magnetized plasma has a vanishingly small phase lag with respect to the GW allowing for coherent interaction over large length scales. When the background magnetic field is almost, but not entirely, parallel to the GW's direction of propagation even the Alfv\'en waves grow to first order in the GW amplitude. Finally, we calculate the growth of the magnetoacoustic waves and the damping of the GW.

Basin‐scale internal wave dynamics during a winter cooling period in a large lake

Basin‐scale internal waves are examined using a combined field observation and 3‐D numerical approach. The field site, Lake Tahoe (CA‐NV) during winter, is characterized by the presence of a weak density stratification and the passage of several storm fronts of varying character. Under these conditions internal waves with periods greater than 5 days and displacements of 30 m are possible. The model used is shown to have negligible numerical dissipation and sufficiently small phase lag over the time periods needed to represent basin‐scale waves. Both the numerical results and the observations identify the presence of three Kelvin modes and one Poincaré mode. While the wave periods are consistent with theoretical predictions, the spatial characteristics are far more complex than theory can predict. The spatial features are revealed through analysis of the integrated potential and kinetic energy fields yielded by the model. This shows that the basin topography exerts an influence on both Kelvin and Poincaré waves. The effect of the variable storms and, in particular, the phasing of the storms with respect to the internal waves is shown to be responsible for the amplification and annihilation of the basin‐scale waves.

Effects of Activation of the Histaminergic Tuberomammillary Nucleus on Visual Responses of Neurons in the Dorsal Lateral Geniculate Nucleus

We investigated the effects of the central histaminergic system on afferent sensory signals in the retinogeniculocortical pathway in the intact brain. Extracellular physiological recordings in vivo were obtained from neurons in the cat dorsal lateral geniculate nucleus (LGN) in conjunction with electrical activation of the histamine-containing cells in the tuberomammillary nucleus of the hypothalamus. Tuberomammillary activation resulted in a rapid and significant increase in the amplitude of baseline activity and visual responses in LGN neurons. Geniculate X- and Y-cells were affected similarly. LGN cells that exhibited a burst pattern of activity in the control condition switched to a tonic firing pattern during tuberomammillary activation. Effects on visual response properties were assessed using drifting sinusoidal gratings of varied spatial frequency. The resultant spatial tuning curves were elevated by tuberomammillary activation, but there was no change in tuning curve shape. Rather, the effect was proportionate to the control response, with the greatest tuberomammillary effects at spatial frequencies already optimal for the cell. Tuberomammillary activation caused a small phase lag in the visual response that was similar at all spatial frequencies, consistent with the induced shift from burst to tonic firing mode. These results indicate a significant histaminergic effect on LGN thalamocortical cells, with no clear effect on thalamic inhibitory neurons. The histaminergic system appears to strengthen central transmission of afferent information, intensifying but not transforming the retinally derived signals. Promoting sensory input may be one way in which the histaminergic system plays a role in arousal.

Electroacoustic Properties of Barium Sulfate Particles Coated with a Conductive Layer of Antimony/Tin(IV) Oxides

The dynamic mobility of barium sulfate particles coated with a conducting layer of antimony/tin oxides has been measured with the technique of electroacoustics. Differences between the dynamic mobility spectra of uncoated barium sulfate suspensions and those of the coated particles are observed and attributed to the presence of the conducting surface layer. The magnitude of the complex mobility of the coated particles decreases monotonically with increasing frequency, just as for a nonconducting particle; however, the magnitudes appear to be independent of electrolyte conductivity. The phase angle behavior is also different from that of a low dielectric particle. The change in the phase angle behavior is most obvious at low suspension conductivities and high frequencies where the phase angles show a much smaller phase lag than at higher conductivities. Reasonable agreement between the experimental dynamic mobility spectra and calculated mobilities was found with O'Brien's theory for the enhanced permittiv...

The Dynamic Mobility of Colloidal Semiconducting Antimony-Doped Tin(IV) Oxide Particles

The dynamic mobility spectra of suspensions of semiconducting tin(IV) oxide particles doped with antimony have been measured with the technique of electroacoustics. The magnitude of the complex mobility decreases essentially monotonically with increasing frequency, just as for a nonconducting (dielectric) particle under the same conditions. Unlike the case for a dielectric particle, however, the magnitudes at low frequency increase with increasing conductivity. The phase angle behavior is also different from that of a normal dielectric particle. The change in the phase angle behavior is most obvious at low suspension conductivity and high frequency where the phase angles showed a much smaller phase lag than at high conductivities. Reasonable agreement was found between the experimental mobility and the theoretical dynamic mobility spectra obtained with O'Brien's theory for the enhanced permittivity of semiconductors.

Sixth order non-dissipative C 1 spline collocation method for oscillatory ordinary initial value problems

In this paper we construct a global method, based on quintic C 1-spline, for the integration of first order ordinary initial value problems (IVPs) including stiff equations and those possessing oscillatory solutions as well. The method will be shown to be of order six and in particular is A-stable. Attention is also paid for the phase error (or dispersion) and it is proved that the method is dispersive and has dispersion order six with small phase-lag (compared with the extant methods having the same order (cf. [7])). Moreover, the method may be regarded as a continuous extension of the closed four-panel Newton–Cotes formula (NC4) (typically it is a continuous extension of an implicit Runge–Kutta method). In additiona priori error estimates, in the uniform norm, together with illustrative test examples will also be presented.

Three-dimensional eye-movement responses to off-vertical axis rotations in humans.

We recorded three-dimensional eye movements elicited by velocity steps about axes that were tilted with respect to the earth-vertical. Subjects were accelerated in 1 s from zero to 100 degrees/s, and the axis of rotation was tilted by 15 degrees, 30 degrees, 60 degrees, or 90 degrees. This stimulus induced a constant horizontal velocity component that was directed opposite to the direction of rotation, as well as a modulation of the horizontal, vertical and torsional components with the frequency of the rotation. The maximum steady-state response in the horizontal constant-velocity component was much smaller than in other species (about 6 degrees/s), reaching a maximum at a tilt angle of about 60 degrees. While the amplitude of the horizontal modulation component increased up to a tilt angle of 90 degrees (8.4 degrees/s), the vertical and torsional modulation amplitudes saturated around 60 degrees (ca. 2.5 degrees/s). At small tilt angles, the horizontal modulation component showed a small phase lag with respect to the chair position, which turned into a small phase lead at large tilt angles. The torsional component showed a phase lead that increased with increasing tilt angle. The vertical and torsional velocity modulation at large tilt angles was not predicted by a recent model of otolith-canal interaction by Merfeld. Agreement between model and experimental data could be achieved, however, by introducing a constant force along the body's z-axis to compensate for the gravitational pull on the otoliths in the head-upright position. This approach had been suggested previously to explain the direction of the perceived subjective vertical during roll under different g-levels, and produced in our model the observed vertical and torsional modulation components at large tilt angles.

A classroom jumping ring

We present the design of a compact alternating current jumping ring apparatus which can electromagnetically launch conducting rings across a classroom. Jump energy and height are calculated for core and thin ring length, radius, thickness, and material. The effects of core saturation, permeability, hysteresis and demagnetizing field, ring shielding, and convective derivative are described. Rings with even small phase lag can pass by the magnetic pole of the primary in one-quarter of a cycle. Large ring size relative to skin depth delays the ring current close to the 180 deg of Lenz’s law. Contactless jump height measurement enables ring resistivity determination. Demonstrating the effects of voltage, frequency, conductivity, permeability, and geometry contributes to understanding electromagnetism in the classroom.

Spatiotemporal patterns of gamma frequency oscillations tetanically induced in the rat hippocampal slice.

1. We used transverse and longitudinal rat hippocampal slices to study the synchronization of gamma frequency (> 20 Hz) oscillations, across distances of up to 4.5 mm. gamma oscillations were evoked in the CA1 region by tetanic stimulation at one or two sites simultaneously, and were associated with population spikes. Tetanic stimuli that were strong enough to induce oscillations were associated with depolarization of both pyramidal cells and interneurones, largely produced by activation of metabotropic glutamate receptors. 2. Computer simulations of gamma oscillations were also performed in a model with pyramidal cells and interneurones, arranged in a chain of five cell groups. This model had suggested previously that interneurone networks alone could generate synchronous gamma oscillations locally, but that pyramidal cell firing, by inducing spike doublets in interneurones, was necessary for the occurrence of highly correlated oscillations with small phase lag (< 2.5 ms), in a distributed network possessing long axon conduction delays. 3. In both experiment and model, pyramidal cell spikes occurred in phase with local population spikes, as did the first spike of the interneurone doublet. 4. The conductance of the interneurone alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor-mediated conductance was manipulated in the model, while the relation between oscillations at opposite ends of the chain was examined. When the conductance was large enough for doublet firing to be synaptically induced in interneurones, oscillation phase lags were < 2.25 ms across the chain. As predicted, experimental blockade of AMPA receptors resulted in increased phase lags between two sites oscillating simultaneously, compared with control conditions. 5. Both in model and in experiment, when stimuli to the two ends of the network were slightly different, cross-network synchronization occurred with a shorter phase lag at high frequencies than at lower frequencies. 6. These data suggest that, while interneurone networks alone can generate locally synchronized gamma oscillations, firing of pyramidal cells, and the synaptically induced doublet firing in interneurones, contribute to the stability and tight synchrony of the oscillations in distributed networks.

Age scale of the air in the summit ice: Implication for glacial‐interglacial temperature change

The air occluded in ice sheets and glaciers has, in general, a younger age (defined as the time after its isolation from the atmosphere) than the surrounding ice matrix because snow is first transformed into open porous firn, in which the air can exchange with the atmosphere. Only at a certain depth (firn‐ice transition) the pores are pinched off and the air is definitely isolated from the atmosphere. The firn‐ice transition depth is at around 70 m under present climatic conditions at Summit, central Greenland. The air at this depth is roughly 10 years old due to diffusive mixing, whereas the ice is about 220 years old. This results in an age difference between the air and the ice of 210 years. This difference depends on temperature and accumulation rate and did thus not remain constant during the past. We used a dynamic firn densification model to calculate the firn‐ice transition depth and the age of the ice at this depth and an air diffusion model to determine the age of the air at the transition. Past temperatures and accumulation rates have been deduced from the δ18O record using time independent functions. We present the results of model calculations of two paleotemperature scenarios yielding a record of the age difference between the air and the ice for the Greenland Ice Core Project (GRIP) and the Greenland Ice Sheet Project Two (GISP2) ice cores for the last 100,000 years. During the Holocene, the age difference stayed rather stable around 200 years, while it reached values up to 1400 years during the last glaciation for the colder scenario. The model results are compared with age differences obtained independently by matching corresponding climate events in the methane and δ18O records assuming a very small phase lag between variations in the Greenland surface temperature and the atmospheric methane. The past firn‐ice transition depths are compared with diffusive column heights obtained from δ15N of N2 measurements. The results of this study corroborate the large temperature change of 20 to 25 K from the coldest glacial to Holocene climate found by evaluating borehole temperature profiles.

Prediction of complex two-dimensional trajectories by a cerebellar model of smooth pursuit eye movement.

A neural network model based on the anatomy and physiology of the cerebellum is presented that can generate both simple and complex predictive pursuit, while also responding in a feedback mode to visual perturbations from an ongoing trajectory. The model allows the prediction of complex movements by adding two features that are not present in other pursuit models: an array of inputs distributed over a range of physiologically justified delays, and a novel, biologically plausible learning rule that generated changes in synaptic strengths in response to retinal slip errors that arrive after long delays. To directly test the model, its output was compared with the behavior of monkeys tracking the same trajectories. There was a close correspondence between model and monkey performance. Complex target trajectories were created by summing two or three sinusoidal components of different frequencies along horizontal and/or vertical axes. Both the model and the monkeys were able to track these complex sum-of-sines trajectories with small phase delays that averaged 8 and 20 ms in magnitude, respectively. Both the model and the monkeys showed a consistent relationship between the high- and low-frequency components of pursuit: high-frequency components were tracked with small phase lags, whereas low-frequency components were tracked with phase leads. The model was also trained to track targets moving along a circular trajectory with infrequent right-angle perturbations that moved the target along a circle meridian. Before the perturbation, the model tracked the target with very small phase differences that averaged 5 ms. After the perturbation, the model overshot the target while continuing along the expected nonperturbed circular trajectory for 80 ms, before it moved toward the new perturbed trajectory. Monkeys showed similar behaviors with an average phase difference of 3 ms during circular pursuit, followed by a perturbation response after 90 ms. In both cases, the delays required to process visual information were much longer than delays associated with nonperturbed circular and sum-of-sines pursuit. This suggests that both the model and the eye make short-term predictions about future events to compensate for visual feedback delays in receiving information about the direction of a target moving along a changing trajectory. In addition, both the eye and the model can adjust to abrupt changes in target direction on the basis of visual feedback, but do so after significant processing delays.