Frequency Jitter Research Articles

Active fluctuations of axoneme oscillations scale with number of dynein motors

Fluxes of energy generate active forces in living matter, yet also active fluctuations. As a canonical example, collections of molecular motors exhibit spontaneous oscillations with frequency jitter caused by nonequilibrium phase fluctuations. We investigate phase fluctuations in reactivated Chlamydomonas reinhardtii axonemes, which are accessible to direct manipulation. We quantify the precision of axonemal oscillations after controlled chemical removal of dynein motors, providing an experimental test for the theory prediction that the quality factor of motor oscillations should increase with motor number. Our quantification reveals specialized roles of inner and outer arm dynein motors. This supports a model in which inner dyneins serve as master pace-makers, to which outer arm dyneins become entrained, consistent with recent insight provided by structural biology.

How changes in the mean latency, jitter amplitude, and jitter frequency impact target acquisition performance

Interactive technologies require the user to frequently generate purposeful movements, where actions are guided towards targets. While delays between the movement onset and the corresponding update within the virtual space have been shown to impair target acquisition, the relative contribution of the individual latency parameters remains unclear. This paper investigates how changes in latency, the moment-by-moment variability in the latency (jitter amplitude) and the rate of variability (jitter frequency), affect the speed and accuracy of target acquisition at different mean latencies. Experiment 1 explored changes in the mean latency and jitter amplitude. As the mean latency increased, we observed substantial impairments in completion time and accuracy, with increased variability in performance. There was also an interaction between the mean latency and jitter amplitude: although large jitter amplitudes caused a small completion time impairment, this effect decreased as the mean latency increased. Experiment 2 isolated the effect of the jitter by investigating changes in the jitter amplitude and jitter frequency at a fixed mean latency. Here, we observed completion time impairments from 67ms amplitude and accuracy impairments from 134ms amplitude. Like Experiment 1, the effect of the amplitude was small. Notably, we found no evidence that changes in the jitter frequency significantly influenced performance. Overall, increases in the mean latency contributed most to the impairment, disrupting acquisition speed and accuracy as it increased. Large jitter amplitudes also disrupted speed and accuracy, but this was a comparatively small effect that was mediated by the mean latency.

Controllable lasing characteristics in Brillouin random fiber lasers by tailoring gain and random feedback fibers

Brillouin random fiber lasers (BRFLs), the combination of stimulated Brillouin scattering (SBS) gain and random distributed feedback, offer narrow linewidth lasing with simplicity and flexibility. However, BRFLs may not gain broad acceptance unless the fundamental lasing mechanisms governing their operation are fully understood and the lasing properties are effectively manipulated. Here, we demonstrate the control of lasing characteristics in BRFLs by tailoring the SBS gain fiber and the scattering pattern of the random feedback fiber. Experimental results show that BRFLs with 5 cm random fiber gratings (RFGs) feedback exhibit lower intensity fluctuation, longer coherence time, and more stable frequency compared to those with 6 km Rayleigh scattering fiber (RSF) feedback thanks to more correlated phase, lower mode density, and weaker dependence on external variations of RFGs. The low-randomness RFG feedback further improves the coherence time and intensity fluctuation attributed to the small period variation of sub-gratings. Moreover, the BRFL based on the high gain fiber and the strong scattering RFG feedback with low loss achieves high lasing efficiency and low threshold. The frequency jitter, intensity noise, and coherence time are also improved by reducing the gain fiber from 20 km to 1 km due to decreased mode hopping from mode competition. These results clarify the impact of gain and random feedback fibers on BRFL performance, offering insights for optimizing complex laser design for applications requiring high frequency stability and long coherence time.

Early Detection of Parkinson Disease Throughbiomedical Speech and Voice Analysis

Parkinson's disease, widely recognized as a neurodegenerative condition characterized by subtle changes in voice, has spurred an investigation into voice analysis for diagnostic purposes. This study is dedicated to the early detection of Parkinson's disease through a comprehensive examination of biomedical speech attributes. Parameters such as fundamental frequency range, jitter, shimmer, noise-to-harmonics ratio, and features derived from nonlinear analysis are considered, alongside variables like status, indicating the presence of neurological disorders, and class for classification purposes. Together, these attributes provide a detailed representation of voice signals, offering valuable insights into both neurological and voice disorders for research purposes. The dataset exhibits promising potential for applications in medical diagnostics and voice analysis. In the pursuit of accurate disease detection, various machine learning methodologies are employed, including Support Vector Machines (SVM), Random Forest (RF), Decision Tree (DT), Neural Networks (NN), and state- of-the-art Convolutional Neural Networks (CNNs). The incorporation of CNNs is pivotal, signifying a significantleap in accuracy of 100%for disease detection. The results showcase a model adept at discerning subtle changesassociated with Parkinson's disease, with SVM achieving 96%, Decision Tree demonstrating a perfect 100%, Neural Network attaining 98%, and Random Forest showcasing an accuracy of 99%. This innovative approach not only transforms early Parkinson's disease identification through voice analysis, setting a precision benchmark, but also underscores the transformative potential of cutting-edge technologies in healthcare practices. The study positions the model as a reliable diagnostic tool, capable of advancing medical diagnosticsthrough the seamless integration of biomedical research and machine learning, contributing to the broader fieldof neurodegenerative disease diagnostics.

Oscillator design for high efficiency DC-DC of micro direct methanol fuel cell

This paper develops a novel oscillator with wide output frequency range, continuous frequency adoption, anti-electromagnetic interference (EMI), and high precision in order to achieve the high energy conversion efficiency of DC-DC for micro direct methanol fuel cell (μDMFC). The oscillator employs the state of art including frequency jitter, slope compensation, and digital trimming to perform the load mode control and detection module, thus linearly adjusting the operating frequency and modulation according to the load. Based on the 0.18 μm microelectronics process, the transient output of the presented oscillator during continuously turning on exports a stable voltage square wave. The jitter frequency ranges only about −1.66% to +4.3% of the base frequency. Moreover, the oscillator can adjust the typical output frequency linearly from 100 kHz to 1 MHz continuously based on the light or heavy load state. The oscillator yields stable performance under EMI with the jittering rate ranges from −31.82% to 36.2%. The quantitative results validates the wide frequency range, continuous frequency adoption, anti-EMI, and high precision of the oscillator. The oscillator solves the low energy conversion efficiency of the μDMFC DC-DC. The oscillator will achieve high energy conversion efficiency and stable output voltage of μDMFC for practical application.

Composite control of anti-drone platform for stable tracking under disturbance.

First, focused on the complex problem that a U-shaped tracking frame is unreachable to obtain the pointing angles of an unmanned aerial vehicle target, a novel coordinate transformation method is proposed in this paper. The fixed transformation relationship between the intermediate links is deduced by establishing a unified coordinate system, simplifying the algorithm conversion process, and saving computing resources and time. Furthermore, the accuracy of the proposed method has been verified in both aspects of theory and experiment. Then, in order to achieve smooth motion performance between target pointing strategy and stable tracking strategy, a mode switching method based on hysteresis intervals is developed. Compared with the traditional single-point threshold method, the switching method overcomes the high frequency jitter problem. The experimental results validate the consistency between practical effects and theoretical expectations. Finally, to improve the disturbance rejection performance of the platform, a composite control method integrating the information from the gyroscope and circular grating is proposed. The corresponding control scheme and the compensation principle are conceived and explained. The experimental results show the anti-interference performance of the proposed composite control method is five times that of the closed-loop method based on the gyroscope speed signal and two times that of the disturbance observer control method.

The jitter frequency domain of long-span railway cable-stayed bridges considering the influence of pneumatic admittance

The long-span bridge is highly sensitive to wind loads, and their random vibration response under static wind deformation and fluctuating wind load are relatively complex. The analysis of jitter response has become a key issue in the design. Taking the Hanjiatuo Yangtze River Bridge in the chongqing-lichuan railway as the engineering background, the influence of different aerodynamic admittance functions on the main girder jitter response is studied through frequency domain analysis. The results show that aerodynamic admittance has a great influence on the jitter response. Considering that the jitter displacement response of the aerodynamic admittance function is obviously smaller than the calculated results, the influence of aerodynamic admittance should be considered in the calculation and analysis.

Voltage fluctuations and probe frequency jitter in electric force microscopy of a conductor.

Electric force microscopy probes the statistics of electric field fluctuations from a sample surface, both through measurement of the noncontact friction exerted on the oscillating charged probe and by determination of the power spectrum of stochastic probe frequency fluctuations, referred to as "jitter." Here we calculate the frequency jitter power spectrum determined over a conducting sample of finite thickness, whose response is characterized by a dielectric function that is wavevector-dependent. These calculations complement previous predictions of the coefficient of noncontact friction in an electric force microscopy measurement for the same model, and also previous predictions of the jitter power spectrum for a dielectric continuum. The inclusion both of a finite sample thickness and a wavevector-dependent dielectric response can significantly enhance the magnitude of the predicted jitter spectrum for a conductor, relative to a simpler model of an infinitely thick dielectric continuum. These calculations provide a baseline prediction of the jitter power spectrum generated by the dynamics of conduction electrons in a metal sample.

Ultrahigh bandwidth measuring approach of an I-FOG based on axial magnetic sensitivity.

The bandwidth is one of the key indicators of the interferometric fiber optic gyroscope (I-FOG) in the application with high frequency jitter. The traditional bandwidth measurement equipment, such as the angular vibration table, can only provide angular vibrations of hundreds of hertz and cannot meet the measurement needs of a high bandwidth gyro. We propose an approach, with which a signal of several thousand hertz can be provided and can measure a high bandwidth of I-FOGs. The bandwidth measurement approach is based on the axial magnetic sensitivity. We present the measurement principle, derive the axial magnetic sensitivity expression of the fiber coil in I-FOGs, and demonstrate the bandwidth measuring system. With this system, the bandwidth of an I-FOG is measured and the experimental result shows that the bandwidth is ∼10 kHz. It is proved that this new, to the best of our knowledge, approach is capable of testing the bandwidth of the I-FOG at ultrahigh frequencies.

A 10-Gb/s 275-fsec Jitter Cryo-CMOS Charge-Sampling CDR for Quantum Computing Application

This letter presents the first clock and data recovery (CDR) system operating at 4.2 K designed for quantum computing (QC) applications. By considering the benefits and challenges of cryogenic operation, a dedicated analog CDR structure is employed so as to maintain high performance at 300 and 4.2 K. The CDR incorporates a new complementary charge-sampling phase detector (PD) that achieves low power and low jitter. Fabricated in 40-nm CMOS, the proposed CDR operates at 10 Gb/s, achieving a recovered clock jitter of 260 fs and a jitter tolerance of 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\rm UI}_{{\rm PP}}$</tex-math> </inline-formula> at a 5-MHz jitter frequency while consuming 4.7 mW at room temperature (RT). At 4.2 K, the power consumption reduces to 3.1 mW with a recovered clock jitter of 275 fs and a jitter tolerance of 0.85 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\rm UI}_{{\rm PP}}$</tex-math> </inline-formula> at a 5-MHz jitter frequency, demonstrating its functionality for a high-speed cryogenic wireline link.

A Self-Oscillating Driving Circuit for Low-Q MEMS Vibratory Gyroscopes.

This article establishes a circuit model with which to analyze the difficulty of auto-gain control driving for low-Q micromechanical gyroscopes at room temperature and normal pressure. It also proposes a driving circuit based on frequency modulation to eliminate the same-frequency coupling between the drive signal and displacement signal using a second harmonic demodulation circuit. The results of the simulation indicate that a closed-loop driving circuit system based on the frequency modulation principle can be established within 200 ms with a stable average frequency of 4504 Hz and a frequency deviation of 1 Hz. After the system was stabilized, the root mean square of the simulation data was taken, and the frequency jitter was 0.0221 Hz.

Self-injection locking of a low-noise erbium-doped random fiber laser by a random fiber grating ring.

We demonstrate a self-injection locking (SIL) in an Er-doped random fiber laser by a high quality factor (high-Q) random fiber grating ring (RFGR) resonator, which enables a single-mode narrow-linewidth lasing with ultra-low intensity and frequency noise. The RFGR resonator includes a fiber ring with a random fiber grating to provide random feedback modes and noise suppression filters with self-adjusted peak frequency adaptable to small perturbations allowing single longitudinal mode over 7000 s with frequency jitter below 3.0 kHz. Single-mode operation is accomplished by carefully controlling phase delays and mode coupling of resonant modes between main ring and RFGR with a side-mode suppression ratio of 70 dB and narrow linewidth of 1.23 kHz. The relative intensity noise is -140 dB/Hz above 100 kHz and the frequency noise is 1 Hz/Hz1/2 above 10 kHz.

Sine-Cosine Techniques for Detecting Fast Optical Frequency Variations With Ultra-High Resolution

We introduce the concept of sine-cosine optical frequency detection (OFD) for measuring fast optical frequency variations with the ultra-high spectral resolution for applications requiring rapidly tunable or low frequency-jitter lasers, including coherent detection based distributed sensing and communication systems and tunable diode laser spectroscopy (TDLS) systems, for which conventional spectral measurement techniques cannot meet the speed and spectral resolution requirements. The concept relies on representing the frequency-dependent differential phase of the laser light passing through two different optical paths as sine and cosine functions to calculate the optical frequency, similar to the sine-cosine encoder concept commonly used for obtaining the rotation information of a motor, which can simultaneously achieve both high spectral resolution and wide frequency range without mutual constraints. We present multiple schemes, some are seemingly very different, for implementing the concept and demonstrate that all frequency-related parameters of a tunable light source, including frequency tuning rate, nonlinearity, ripple, range, duty cycle, repeatability, and power swing can be precisely characterized. In addition, the frequency jitter of a fixed narrow line-width laser can also be accurately measured. Ultra-fast optical frequency sweep with a rate in excess of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> nm/s and a resolution down to MHz is demonstrated with a differential delay of only 0.8 mm, suggesting that the concept is feasible to be implemented with photonic integrated circuit (PIC). Our work is attractive for applications such as coherent distributed sensing (OCT, OFDR and FMCW lidar), coherent detection, FBG sensing interrogation and TDLS, especially considering that some schemes can be integrated on PIC chips.

High-Resolution Random Laser Dynamic-Strain Sensor Based on Two-Cavity FBG-FP Interferometer

A high-resolution optic fiber dynamic strain sensor based on a two-cavity fiber Bragg grating Fabry-Perot (FBG-FP) interferometer and random fiber laser (RFL) is demonstrated. The specially designed two-cavity FBG-FP interferometer acts as a sensing element and can effectively suppress the competition-induced multi-spike lasing modes and frequency jitter, which contributes to establish single-wavelength laser and suppress frequency noise of RFL. The frequency noise is reduced from about 12 to 3 Hz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\surd $ </tex-math></inline-formula> Hz above 4 kHz. An ultrahigh dynamic-strain detecting resolution of 30 femto-strain ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{f}\varepsilon)/\surd $ </tex-math></inline-formula> Hz is achieved. To the best of our knowledge, it is the first time that two-cavity FBG-FP interferometer has been used in sensing field.

Efeitos da estimulação transcraniana por corrente contínua (ETCC) na voz e fala na doença de Parkinson: relato de caso

ABSTRACT This study describes the results of two different interventions for dysarthria in Parkinson’s disease (PD). It concerns two male patients with PD and hypokinetic dysarthria who underwent speech and voice assessment. The first (S1) received ten 20-minute sessions of transcranial direct current stimulation (tDCS), while the second (S2) received ten 20-minute sessions of tDCS as well as speech therapy. The patients were re-evaluated immediately after the intervention and again after 30 days. Improvements in phonation time, velar movement, and other measures of dysarthria were more significant in S1. According to the acoustic analysis source parameters, improvements in the frequency measurements and Jitter, Shimmer, and noise measurements were greater in S2 in both the immediate post-intervention and 30-day postintervention assessments, followed by S1 in the immediate post-intervention assessment. S1 showed better results in the auditory-perceptual evaluation of speech and voice, whereas S2 obtained better scores in acoustic analysis. These findings suggest that conventional speech therapy combined with tDCS has a more significant impact on speech and voice than tDCS alone, demonstrating the potential of tDCS as an adjuvant treatment for patients with PD.

Single-longitudinal-mode short-cavity Brillouin random fiber laser via frequency auto-tracking with unpumped-EDF sagnac loop

A single-longitudinal-mode high-coherence Brillouin random fiber laser (BRFL) with low-noise and narrow linewidth is proposed and experimentally demonstrated, which owns the shortest cavity structure ever reported in BRFL configuration by the combined utilization of highly nonlinear fiber (HNLF) and unpumped Er-doped-fiber sagnac loop (UESL). In this BRFL, stimulated Brillouin scattering and Rayleigh scattering are exploited to provide the resonant gain and random distributed feedback, respectively. The UESL, with a narrow bandpass width and a capability of auto-tracking the center frequency of the transmitted light, is realized by forming a dynamic fiber grating (DFG) filter with periodically modulated refractive index through the saturable absorption effect and hole-burning effect along the Er-doped fiber. The UESL can effectively act as a center-frequency-auto-tracking bandpass filter with narrow bandwidth to filter out the undesired dense random modes and simultaneously restrict the resonant modes within a very limited frequency range. It thus suppresses the modes hopping and multi-mode resonances within the Brillouin gain bandwidth so that the frequency jitter and instability of laser output are greatly alleviated. The short cavity was realized by utilizing a section of HNLF with high nonlinearity coefficient (≥10 W−1·km−1 @1550 nm), which can provide enough Brillouin gain for the BRFL when short length is employed. Compared with the currently prevalent BRFLs based on long-cavity configurations, the short-cavity structure enables a significant reduction in the number of random cavity modes so as to guarantee a high probability for the single-longitudinal-mode random lasing output. In the experiment, a stable single-longitudinal-mode lasing output with an ultra-narrow linewidth of ∼802.42 Hz is obtained from the proposed BRFL. Statistical characteristics of the mode resonances, laser noise performance and statistical analysis of the lasing output are also experimentally investigated for the proposed BRFL. In addition, broadband wavelength-tunable output is realized in the proposed BRFL.

Towards optimal conversion efficiency of Brillouin random fiber lasers in a half-open linear cavity.

We proposed and demonstrated an unprecedented high-efficiency Brillouin random fiber laser (BRFL) by fiber length optimization in a half-open linear cavity. In terms of the trade-off between Brillouin gain saturation and weak distributed Rayleigh feedback strength, optimal laser efficiency associated to proper fiber length in a BRFL was theoretically predicted. As a proof-of-concept, a unidirectional-pumped BRFL with a half-open linear cavity was experimentally conducted, in which a fiber Bragg grating at one end of gain fiber served as a high-reflection mirror while Rayleigh scattering enabled distributed feedback for random lasing resonance. Results show that the optimal fiber length of ∼3.4 km in the BRFL offers sufficient Rayleigh scattered random feedback whilst alleviating the Brillouin gain saturation to a large extent. Consequently, an optimal laser efficiency of 77.0% in the BRFL was experimentally demonstrated, which reaches the state-of-the-art high record. Laser characteristics, including the linewidth, statistics and frequency jitter were also systematically investigated. It is believed that such efficient BRFL could provide a promising platform for inspiring new explorations of laser physics as well as potentials in long-haul coherent communication and fiber-optic sensing.

Low Frequency-Noise Ring Random Fiber Laser With a Dual-Cavity FBG Fabry-Perot Filter

A low frequency-noise ring random fiber laser (RFL) based on random Bragg grating array (RBGA) feedback is proposed. A dual-cavity fiber Bragg grating Fabry-Perot (FBG-FP) filter, which matches the wavelength of RBGA, is specially designed. Due to the narrower bandwidth, flatter response and steeper rolloff, the dual-cavity FBG-FP filter can significantly suppress the competition-induced frequency jitter and undesired residual random lasing modes, and contribute to establish stable lasing and further reduce frequency noise of RFL. The frequency noise of the proposed RFL is ∼3 Hz/√Hz above 1 kHz, and the frequency jitter is ∼3.11 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−11</sup> over 10 s. The 3-dB linewidth is ∼490 Hz with a ∼40 dB of optical signal-to-noise ratio.

Stabilized Narrow-Linewidth Brillouin Random Fiber Laser With a Double-Coupler Fiber Ring Resonator

A stabilized coherent narrow-linewidth Brillouin random fiber laser with low lasing noise is proposed and investigated experimentally, which employs stimulated Brillouin scattering and Rayleigh scattering in optical fibers to provide the gain and the random distributed feedback, respectively. The stabilized lasing output with suppressed noise is realized utilizing a simple structure of a double-coupler fiber ring resonator, which is composed of a section of single-mode fiber and two optical couplers with different coupling ratios. Compared with the existing free-running Brillouin random fiber lasers, much more stabilized laser output can be obtained as the double-coupler fiber ring resonator effectively acts as a narrow-bandwidth mode filter through the Vernier effect that constrains the dense random longitudinal modes competition within a small frequency range. In the experiment, a stable ultra-narrow linewidth of approximately 586.4 Hz is obtained from the laser output. Statistical analysis of mode hopping in the proposed laser indicates a great improvement in multi-mode resonances and frequency jitters with the imbedding of the ring resonator. In addition, measurement results of relative intensity noise and frequency noise of the proposed laser showcase a great suppression in mode-competition-induced lasing instability and a significant improvement in the noise level compared to the free-running Brillouin random fiber lasers. The proposed all-fiber-based stabilization technique makes a step forward for developing practically robust and reliable Brillouin random fiber lasers. Such a stabilized highly coherent narrow-linewidth laser source with low cost and low power consumption will find promising applications in high-resolution spectrometers, microwave photonics, and optical sensing.

Exploring the Common Mechanisms of Motion-Based Visual Prediction

Human vision supports prediction for moving stimuli. Here we take an individual differences approach to investigate whether there could be a common processing rate for motion-based visual prediction across diverse motion phenomena. Motion Induced Spatial Conflict (MISC) refers to an incongruity arising from two edges of a combined stimulus, moving rigidly, but with different apparent speeds. This discrepancy induces an illusory jitter that has been attributed to conflict within a motion prediction mechanism. Its apparent frequency has been shown to correlate with the frequency of alpha oscillations in the brain. We asked what other psychophysical measures might correlate positively with MISC frequency. We measured the correlation between MISC jitter frequency and another three measures that might be linked to motion-based spatial prediction. We demonstrate that the illusory jitter frequency in MISC correlates significantly with the accrual rate of the Motion Induced Position Shift (MIPS) effect - the well-established observation that a carrier movement in a static envelope of a Gabor target leads to an apparent position shift of the envelope in the direction of motion. We did not observe significant correlations with the other two measures – the Adaptation Induced Spatial Shift accrual rate (AISS) and the Smooth Motion Threshold (SMT). These results suggest a shared perceptual rate between MISC and MIPS, implying a common periodic mechanism for motion-based visual prediction.