Change In Phase Difference Research Articles

Radio Frequency FBG-Based Interferometer for Remote Adaptive Strain Monitoring

A radio frequency (RF) optical fiber interferometer based on dual-fiber Bragg grating is proposed for a few to tens of kilometers distance remote measurements. The interference spectrum is observed in the microwave domain by sweeping the frequency using a network analyzer. The wavelength-difference variation is naturally transferred to the RF phase-difference change after the long round-trip of the optical carriers shifting the microwave interference pattern. The sensor exhibits important advantages of easy multiplexing, stability against random perturbations, self-adaptation to temperature, and mostly importantly, a potentially much higher sensitivity compared with common wavelength-modulated optic sensors. A measurement of a strain-turned grating was accomplished with a $\sim 6.5$ -km long single-mode fiber, where a high maximum sensitivity of 53.57 kHz/ $\mu \varepsilon $ was realized, which can easily be further improved by more than two orders of magnitude through various low-cost fiber dispersion components.

Differential control of temporal and spatial aspects of cockroach leg coordination

Ensembles of neuronal networks and sensory pathways participate in controlling the kinematic and dynamic parameters of animal movement necessary to achieve motor coordination. Determining the relative contribution of proprioceptive feedback is essential for understanding how animals sustain stable, coordinated locomotion in complex natural environments. Here, we focus on the role of chordotonal organs (COs), proprioceptors found in insect legs, in the spatial and temporal regulation of walking. We compare gait parameters of intact cockroaches (Periplaneta americana) and sensory-impaired ones, injected with pymetrozine, a chemical previously shown to abolish CO function in locusts. We verify that afferent CO activity in pymetrozine-treated cockroaches is inhibited, and analyze the effect of this sensory deprivation on inter-leg coordination. We find significant changes in tarsi placement and leg path trajectories after pymetrozine treatment. Leg touchdown accuracy, measured from relative tarsi positions of adjacent legs, is reduced in treated animals. Interestingly, despite poorer spatial coordination in both stance and swing, temporal properties of the gait remain largely the same as in the intact preparations, apart from changes in ipsilateral phase differences between front and middle legs. These findings provide insights into the role of COs in insect gait control and establish pymetrozine as a useful tool for further studies of insect locomotion.

The phase difference between neural drives to antagonist muscles in essential tremor is associated with the relative strength of supraspinal and afferent input.

The pathophysiology of essential tremor (ET), the most common movement disorder, is not fully understood. We investigated which factors determine the variability in the phase difference between neural drives to antagonist muscles, a long-standing observation yet unexplained. We used a computational model to simulate the effects of different levels of voluntary and tremulous synaptic input to antagonistic motoneuron pools on the tremor. We compared these simulations to data from 11 human ET patients. In both analyses, the neural drive to muscle was represented as the pooled spike trains of several motor units, which provides an accurate representation of the common synaptic input to motoneurons. The simulations showed that, for each voluntary input level, the phase difference between neural drives to antagonist muscles is determined by the relative strength of the supraspinal tremor input to the motoneuron pools. In addition, when the supraspinal tremor input to one muscle was weak or absent, Ia afferents provided significant common tremor input due to passive stretch. The simulations predicted that without a voluntary drive (rest tremor) the neural drives would be more likely in phase, while a concurrent voluntary input (postural tremor) would lead more frequently to an out-of-phase pattern. The experimental results matched these predictions, showing a significant change in phase difference between postural and rest tremor. They also indicated that the common tremor input is always shared by the antagonistic motoneuron pools, in agreement with the simulations. Our results highlight that the interplay between supraspinal input and spinal afferents is relevant for tremor generation.

Polarization-sensitive optical phase modulators based on aperiodic multilayers containing nano-scale fullerene and semiconductor layers

The band characteristics and the phase shift of electromagnetic waves in one-dimensional Fibonacci photonic structures composed of nano-scale fullerene and semiconductor layers are investigated theoretically in detail for both TE and TM polarizations and for different incident angles. We adopt the transmission matrix method to analyze the transmission properties of supposed sub-wavelength structure. We observe that within the stop band, the reflection phase difference changes smoothly and increases with the increasing of the incident angle. Furthermore, the phase shift decreases with the incident angle increasing for TE mode, and increases with the incident angle increasing for TM mode. Especially, at both the edges of the gap, the reflection phase difference keeps zero in spite of the change of incident angle. Based on our results, the supposed structure provides a convenient way to design very compact phase controllers such as phase retarders.

Markers of criticality in phase synchronization.

The concept of the brain as a critical dynamical system is very attractive because systems close to criticality are thought to maximize their dynamic range of information processing and communication. To date, there have been two key experimental observations in support of this hypothesis: (i) neuronal avalanches with power law distribution of size and (ii) long-range temporal correlations (LRTCs) in the amplitude of neural oscillations. The case for how these maximize dynamic range of information processing and communication is still being made and because a significant substrate for information coding and transmission is neural synchrony it is of interest to link synchronization measures with those of criticality. We propose a framework for characterizing criticality in synchronization based on an analysis of the moment-to-moment fluctuations of phase synchrony in terms of the presence of LRTCs. This framework relies on an estimation of the rate of change of phase difference and a set of methods we have developed to detect LRTCs. We test this framework against two classical models of criticality (Ising and Kuramoto) and recently described variants of these models aimed to more closely represent human brain dynamics. From these simulations we determine the parameters at which these systems show evidence of LRTCs in phase synchronization. We demonstrate proof of principle by analysing pairs of human simultaneous EEG and EMG time series, suggesting that LRTCs of corticomuscular phase synchronization can be detected in the resting state and experimentally manipulated. The existence of LRTCs in fluctuations of phase synchronization suggests that these fluctuations are governed by non-local behavior, with all scales contributing to system behavior. This has important implications regarding the conditions under which one should expect to see LRTCs in phase synchronization. Specifically, brain resting states may exhibit LRTCs reflecting a state of readiness facilitating rapid task-dependent shifts toward and away from synchronous states that abolish LRTCs.

The effects of interactions between intrinsic properties and network parameters on bilateral phasing in a reduced leech heartbeat system

The leech heartbeat central pattern generator (CPG) consists of a network of heart interneurons (HN) that coordinate heart excitor (HE) motor neuron activity via inhibitory chemical synapses. Each segmental pair of HE’s is connected to one another via electrical coupling. Depending on the segment, the pair of motor neurons in the living system is active across a wide range of phase differences from nearly in-phase to anti-phase [1]. Prior efforts to model this complete network have not quantitatively matched all contralateral phase values observed [2]. We have created a reduced network model in Simulink to explore parameters that contribute to these phase differences. This parameter search has been analyzed in MATLAB using the PANDORA toolbox [3]. In our network model, we implemented known neuronal properties and synaptic connections from a single segmental ganglion. The HN’s were modeled as endogenous bursters as previously described with a network cycle period of 9.45 ± 0.11 sec [4]; in previous studies [5], the HE’s were modeled as tonic firers. We varied three network parameters shown in Figure ​Figure11 in this study: phased delay of the right HN synaptic input [ΦSyn], the maximum conductances of the inhibitory synapse [gSyn], and electrical coupling strength [gcoup]. We varied ΦSyn to emulate the variable timing of inhibition onto HE’s in the full network of the living system. In addition, we varied the set of maximum conductances for the HE neurons in a linear fashion from classical HE (tonic firing) to HN (endogenous bursting) values to ascertain the role of intrinsic properties on phase-shifts. Figure 1 Leech heartbeat circuit diagram showing identified CPG heart interneurons (HN) and heart excitor motor neurons (HE). This linear variation of HE properties from tonic firing towards endogenous bursting led to a step-wise phase advance up to ~0.10 for both neurons. In-phase (ΦSyn: 0.0) and anti-phase (0.5) values of ΦSyn produced expected HE phase differences. However, intermediate synaptic delays (0.25, 0.75) caused a reduction in phase differences as the two motor neurons pull towards one another due to their electrical coupling. The amount of phase difference reduction was directly impacted in a nonlinear manner by the intrinsic properties of these HE neurons. Duty cycle (burst duration / cycle period) was not significantly impacted by intrinsic properties. In summary, increases in ΦSyn led to non-monotonic changes in HE motor neuron contralateral phase differences. Our search of parameter space continues to provide a foundation for understanding the mechanisms underlying variable phase differences in neuronal networks and reinforces the importance of interactions between endogenous properties and synaptic connections for producing functional motor patterns. The project described was supported by Vermont Genetics Network through an NIGMS (NIH) Institutional Development Award P20 {type:entrez-nucleotide,attrs:{text:GM103449,term_id:221402118,term_text:GM103449}}GM103449.

The Hemodynamic Effect of Phase Differences Between the BJUT‐II Ventricular Assist Device and Native Heart on the Cardiovascular System

The BJUT-II VAD (which was previously called the intra-aorta pump) is a novel left ventricular assist device (LVAD) with a special structure and connection with the native heart. The hemodynamic effect of the phase difference of this pump on the cardiovascular system is still unclear. In this work, seven speed waveforms, whose phase differences vary from 0° to 180°, are used to evaluate the hemodynamic effect of change in phase difference on the cardiovascular system. The external work (EW), equivalent afterload (EAL), pulsatile ratio (PR), and mean aortic pressure during diastolic period (MAPD) are chosen to evaluate the hemodynamic state of the circulatory system. Mathematical study results show that the support levels generated by the BJUT-II VAD under various phase differences are comparable. In contrast, EW, EAL, PR, and MAPD are significantly affected by change in phase difference. It is found that EW reaches its maximum value when the phase difference equals 30°. Similarly, EAL declines with increasing phase difference. PR reaches its maximum value when the phase difference is at 60°. In addition, MAPD decreases with increasing phase difference and then achieves its maximum value at 30°. To obtain comprehensive evaluation of the hemodynamic effects of phase difference on the cardiovascular system, a weight detection algorithm (WDA) whose output indicates the hemodynamic state of the circulatory system is also designed, with EW, PR, and MAPD chosen as the inputs. The minimum value of the output of the WDA indicates the optimal hemodynamic state and optimal phase difference for the BJUT-II VAD. According to the output of the WDA, 30° is considered to be the optimal phase difference for the BJUT-II VAD.

Measurement of the internal stress and electric field in a resonating piezoelectric transformer for high-voltage applications using the electro-optic and photoelastic effects

The high output voltages from piezoelectric transformers are currently being used to accelerate charged particle beams for x-ray and neutron production. Traditional methods of characterizing piezoelectric transformers (PTs) using electrical probes can decrease the voltage transformation ratio of the device due to the introduction of load impedances on the order of hundreds of kiloohms to hundreds of megaohms. Consequently, an optical diagnostic was developed that used the photoelastic and electro-optic effects present in piezoelectric materials that are transparent to a given optical wavelength to determine the internal stress and electric field. The combined effects of the piezoelectric, photoelastic, and electro-optic effects result in a time-dependent change the refractive indices of the material and produce an artificially induced, time-dependent birefringence in the piezoelectric material. This induced time-dependent birefringence results in a change in the relative phase difference between the ordinary and extraordinary wave components of a helium-neon laser beam. The change in phase difference between the wave components was measured using a set of linear polarizers. The measured change in phase difference was used to calculate the stress and electric field based on the nonlinear optical properties, the piezoelectric constitutive equations, and the boundary conditions of the PT. Maximum stresses of approximately 10 MPa and electric fields of as high as 6 kV/cm were measured with the optical diagnostic. Measured results were compared to results from both a simple one-dimensional (1D) model of the piezoelectric transformer and a three-dimensional (3D) finite element model. Measured stresses and electric fields along the length of an operating length-extensional PT for two different electrical loads were within at least 50 % of 3D finite element simulated results. Additionally, the 3D finite element results were more accurate than the results from the 1D model for a wider range of electrical load impedances under test.

EPA-1603 - Changes of resting-state eeg and functional connectivity in the sensor and source space of patients with major depression

Introduction Dyfunctions of prefrontal neuronal circuits contribute to the pathophysiology of depression. Previous studies showed increased functional MRI and EEG connectivity in patients with depression. In this study we investigated a large sample of patients with major depression (n=228) and healthy subjects (n=215). Methods Spectrotemporal dynamics during resting state with closed eyes were analyzed in sensor and source space to examine functional EEG connectivity (fcEEG) alterations between groups. Quantitative measures of delta, theta, alpha, beta and gamma power, hemispheric asymmetry, coherence, phase and current source density (CSD, eLORETA) analyses were calculated from artifact-free EEG recordings. Results EEG theta power was increased in all brain regions in the group of patients with a focus in frontal regions and increased frontal theta and alpha power. Excessive coherence differences were detected in the delta, theta and alpha-bands in frontal, frontal-temporal and frontal-parietal regions. There were changes in phase differences in the delta, theta, alpha-bands between patients and healthy subjects. Differences in CSD were found for the delta, theta, alpha-band in the (rostral and subgenual) anterior cingulate cortex (ACC) with increased CSD in the patients. Conclusion The main finding of the present study was an increase in cortical slow-wave activity in sensor and source space in patients with depression revealing marked differences in prefrontal cortical networks. Functional delta, theta and alpha connectivity (coherence and phase) were altered with a predominance in the left hemisphere. Dysfunctions of the ACC, together with alterations in fcEEG may contribute to the pathophysiology of major depression.

Simultaneous recording of brain responses indicating sensation and perception of changes in interaural phase differences

Changing the interaural phase difference (IPD) between binaurally presented tones induces the sensation of a change of the sound source in space and elicits auditory brain responses specific for sound localization. We recorded neuromagnetic responses to IPD changes in young, middle-aged, and older listeners at various tonal frequencies. Young listeners showed brain responses below 1500 Hz according to the behavioral findings of using IPD for sound localization at low frequencies only. The upper limit for IPD detection decreased with age, and older listeners (mean age of 71 years) could make use of IPD changes only for tonal sounds below 750 Hz. The stimuli were amplitude modulated at 40 Hz and elicited synchronized brain activity at the rhythm of the amplitude modulation. Thus, 40-Hz brain activity was recorded simultaneously with the IPD change responses. Although the amplitude modulation as continuous and specifically did not change the interaural phase relation, the 40-Hz brain response was reset at the IPD change. We interpret the 40-Hz brain responses as related to sensory binding for perception. Each change in the auditory environment requires a reset and reconfiguration of the binding network, which can be observed in the reset of 40-Hz brain oscillations. Recording simultaneously brain responses to sensation and perception of IPD changes gives insight into the temporal dynamics of binaural auditory processing.

A Landslide Monitoring Technique Based on Dual-Receiver and Phase Difference Measurements

A new landslide detection technique that installs a transmitter (Tx) array at the area of interest to transmit signals to two receivers is presented. It detects the phase difference change, due to the Tx displacement, at the dual-receiver system to monitor near real time of small but critical area landslide in centimeter range. The dual-receiver system, apart at a small distance, demodulates the receiving signals independently but coherently. An ambiguity route, which corresponds to a landslide's movement without change on phase difference, is defined and must be avoided. No field test was tried, but three simulated examples are given to illustrate the technique.

A Novel Millimeter-Wave Dual-Fed Phased Array for Beam Steering

A novel beam-steering approach is presented based on the superposition of two squinted antenna beams. The two antenna beams are realized by exciting the opposite feeds of a dual-fed array antenna. A change in phase difference and amplitude ratio between the input signals, possibly using only one phase shifter and one variable gain amplifier, steers the main beam in different directions. Additionally, sum and difference patterns can be obtained using this concept, allowing for a monopulse operation with a broad peak or a deep null at broadside. Using this approach, beam nulls can also be steered toward interference directions, while keeping the shape and direction of the main beam unchanged. To verify the concept, a 77-GHz demonstrator using a linear patch array antenna and monolithic microwave integrated circuit in-phase/quadrature modulators has been designed and fabricated. The measurement results show a beam-scanning range of 16 °, well in accord with the simulation results.

Nonparametric Estimation of Power Quantities in the Frequency Domain Using Rife-Vincent Windows

This paper presents algorithms for fast measurement and the nonparametric estimation of the unknown changing frequency, amplitude, and phase difference of the signals from two channels with the same frequency, as well as other power quantities, such as the apparent, the active, and the reactive power. The possibilities for systematic error reduction through use of the interpolated discrete Fourier transform using the Rife-Vincent windows class I (RV-I) are described. RV-I windows are designed for maximization of the window spectrum side-lobes fall-off and owing to their minimal leakage, minimal systematic bias curves can be evaluated as a function of the measurement interval duration expressed in signal cycles. Parameters are calculated from the discrete Fourier transform coefficients around the component peaks by summation to reduce the leakage effects. The optimum for reducing the time of measurement and for reducing systematic errors under non-coherent conditions of sampling real noisy signals could be the estimation with the three cycles window using the three-point interpolation and the RV-I window order 3.

Relationship between the Earth tidal factor and phase lag of groundwater levels in confined aquifers and the Wenchuan M s8.0 earthquake of 2008

This work focuses on variations of the Earth tidal factor and phase lag derived from groundwater observations before and after major earthquakes. It is based on an analysis of the data from four observational wells at boundaries between distinct active blocks of China mainland. These wells are also situated on several active fault zones and have exhibited considerable responses to the Wenchuan Ms8.0 earthquake of 2008 in China. We collected hourly records of water levels of these wells from 2007 to 2009 and processed these data for analysis. The tidal factors, phase lags, and phase-difference changes of tidal residuals of each well were calculated. We found that when the Wenchuan quake happened, the tidal factors of the 4 wells were changing rapidly, while their phase lags and phase differences of tidal residuals declined swiftly, which may reflect the stress and strain changes of the well-aquifer system during the seismic generation.

Nonspecific detection of lead ions in water using a simple integrated optical polarimetric interferometer

Real-time detection of heavy metal ions in water was implemented by using a composite optical waveguide (COWG) based polarimetric interferometer. The COWG was made by local deposition of a tapered nanometric layer of high-index materials onto a single-mode slab glass waveguide, and it is a low-cost robust waveguide with a locally large modal birefringence. The COWG-based polarimetric interferometer operates with a single incident laser beam and uses the transverse electric and transverse magnetic modes as the sensing and reference beams, respectively, and it can easily detect 0.1 ppm lead(II) ions in water via nonspecific adsorption on the tapered layer of TiO2. The excellent linearity was obtained between the lead(II) concentration and the ratio of concentration to the phase-difference change (Δϕ), suggesting that adsorption of lead(II) ions on the TiO2 film follows the Langmuir isotherm model. The saturation adsorption leads to Δϕmax = 7.485π. By use of the eigenvalue equations for a homogeneous waveguide to fit the measured refractive-index (RI) sensitivity of the interferometer, the equivalent thickness of Teq = 26.05 nm for the tapered TiO2 layer used was achieved. With Teq = 26.05 nm and Δϕmax = 7.485π and the thickness of 0.264 nm for the lead(II) adlayer, the adlayer RI was derived to be nad ≈ 1.945 at the maximum coverage.

Temperature restrictions at generation of the second harmonica of powerful lasers in periodically polarized gradient crystals of LiNbO3

The research examines the possibility of increasing of Periodically poled lithium niobate (PPLN) converters efficiency due to application of gradient nonlinear and optical environments. Use efficiency for radiation transformation of the powerful continuous PPLN lasers made of gradient niobate lithium crystals, can be several times higher, than PPLN made of uniform traditional optically niobate lithium crystals. However, such high efficiency values of transformation are observed at gradient PPLN in more limited interval of rating capacities, than at PPLN made of optically uniform niobate lithium crystals because of possibility of nonlinear change in phase difference of interacting waves.

Frequency discontinuity and amplitude death with time-delay asymmetry

We consider oscillators coupled with asymmetric time delays, namely, when the speed of information transfer is direction dependent. As the coupling parameter is varied, there is a regime of amplitude death within which there is a phase-flip transition. At this transition the frequency changes discontinuously, but unlike the equal delay case when the relative phase difference changes by π, here the phase difference changes by an arbitrary value that depends on the difference in delays. We consider asymmetric delays in coupled Landau-Stuart oscillators and Rössler oscillators. Analytical estimates of phase synchronization frequencies and phase differences are obtained by separating the evolution equations into phase and amplitude components. Eigenvalues and eigenvectors of the Jacobian matrix in the neighborhood of the transition also show an "avoided crossing," as has been observed in previous studies with symmetric delays.

Respiration drives phase synchronization between blood pressure and R‐R interval following loss of cardiovagal baroreflex during vasovagal syncope

Thoracic hypovolemia and hyperpnea contribute to the nonlinear time‐dependent hemodynamic instability of vasovagal syncope. We used a phase synchronization index (PhSI) to describe coupling between systolic BP (SBP), RR‐interval (RR), and ventilation, and a directional index (DI) of coupling. We hypothesized normal AP‐RR PhSI during early 70° head‐up tilt, indicating intact cardiovagal baroreflex (CVB), but decrease as faint approached. Data were recorded supine and upright in 15 control (C) and 15 fainters (F). Data were evaluated during baseline, early tilt, late tilt, faint, and recovery. During late tilt to faint, F but not C showed SBP‐RR PhSI decrease (from 0.65±0.04 to 0.24±0.03) which increased at faint (0.80±0.03) coinciding with a change in phase difference from positive to negative. Starting in late tilt and through faint, F but not C exhibited increasing phase coupling between respiration and AP and between respiration and RR. DI indicated respiratory driven AP and RR in F. The initial drop in the SBP‐RR PhSI and directional change of phase difference at late tilt indicates loss of cardiovagal baroreflex. The subsequent increase in SBP‐RR PhSI is due to a respiratory synchronization and drive on both AP and RR. Cardiovagal baroreflex is lost prior to syncope and supplanted by respiratory reflexes, producing hypotension and bradycardia.

An Improved Airborne Single Observer Passive Location

Using phase difference change rate’s augmentation to angular velocity, an improved passive location is developed,which solves the high precision parameter measurement problem of angular velocity in passive location and tracking via spatial-frequency domain information. The simulation shows that this method can reduce the difficulties of parameter measurement. The ranging error is mainly affected by the measurement error of phase difference change rate and doppler frequency change rate. Compared with the original method, it has higher passive location precision.

Polymer Electro-optic Modulator Linear Bias Using the Thermo-optic Effect

A quasi-rectangular waveguide polymer Mach—Zehnder (M-Z) electro-optic (EO) modulator based on an organic/inorganic hybrid material with thermal bias control is fabricated and demonstrated. Linear bias for the modulator is obtained through thermo-optic effect. The optical output is adjusted by changing phase difference between the two arms of the M-Z interferometer. A power consumption of 16.1 mW for π phase change is observed owing to the application of silica cladding. This approach is proved to be effective to suppress direct current drift in polymer EO modulators.