Feedback Intensity Research Articles

Broadband laser chaos generation using a quantum cascade laser with optical feedback.

We propose a method to generate broadband laser chaos using a quantum cascade laser (QCL). Through numerical simulation, we give the evidence that the QCL with optical feedback can route to chaos through the quasi-periodic path. Furthermore, we investigate the influence of the feedback intensity and the bias current on the chaos bandwidth. Final results demonstrate that the chaos bandwidth can headily reach 43.1 GHz due to the lack of relaxation oscillation phenomena in QCLs.

Second-Order Correlation Function Supported Optical Sensing for Particle Detection

We propose a new sensing method based on the measurement of the second-order autocorrelation of the output of micro- and nanolasers with intensity feedback. The sensing function is implemented through the feedback-induced threshold shift, whose photon statistics is controlled by the feedback level in a characteristic way for different laser sizes. The specific response offers performances which can be adapted to different kinds of sensors. We propose the implementation of two schemes capable of providing a quantitative sensing signal and covering a broad range of feedback levels: one is utilizing the evolution of g <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(2)</sup> (0), the other one is the ratio between central and side peaks in g <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(2)</sup> ( τ). Laser-threshold-based sensing could, thanks to its potential sensitivity, gain relevance in biomolecular diagnostics and security monitoring.

Dynamical behavior of simplified FitzHugh–Nagumo neural system with time delay driven by Lévy noise

In this paper, the dynamical behavior of the FitzHugh–Nagumo (FHN) neural system with time delay driven by Lévy noise is studied from two aspects: the mean first-passage time (MFPT) and the probability density function (PDF) of the first-passage time (FPT). Using the Janicki–Weron algorithm to generate the Lévy noise, and through the order-4 Runge–Kutta algorithm to simulate the FHN system response, the time that the system needs from one stable state to the other one is tracked in the process. Using the MATLAB software to simulate the process above 20,000 times and recording the PFTs, the PDF of the FPT and the MFPT is obtained. Finally, the effects of the Lévy noise and time-delay on the FPT are discussed. It is found that the increase of both time-delay feedback intensity and Lévy noise intensity can promote the transition of the particle from the resting state to the excited state. However, the two parameters produce the opposite effects in the other direction.

A Robust Relaxation-free Multiphysics Iteration Scheme for CMFD–Accelerated Neutron Transport k–eigenvalue Calculation–II: Numerical Results

In a companion paper, we present the theoretical development of a new robust, relaxation-free iteration scheme for multiphysics -eigenvalue problems. These types of problems are essential to the study of computational reactor physics and in particular whole-core, high-fidelity simulation codes. The deterministic whole-core simulation tools invariably rely on the coarse mesh finite difference (CMFD) acceleration for fast convergence. However, the use of CMFD-accelerated transport in multiphysics problems coupled via Picard iteration is not robust and is frequently treated with relaxation. In this paper, we build on our previous theoretical work that uses Fourier analysis to prove how stability and efficient convergence can be achieved in the multiphysics problem by appropriately loosening the convergence criteria of the low-order diffusion acceleration equations. Specifically, we develop a methodology for estimating a key problem-dependent parameter, the feedback intensity, required by the nearly optimally partially converged coarse mesh finite difference (NOPC-CMFD) method. We then describe the implementation of NOPC-CMFD in the Michigan Parallel Characteristics Transport (MPACT) code and perform several numerical calculations. Problems ranging from a single pressurized water reactor (PWR) fuel rod to a full-core PWR cycle depletion are analyzed to assess the performance and robustness of NOPC-CMFD over a wide range of conditions that consider multiple forms of multiphysics feedback. The results verify the theoretical predictions of our companion paper, illustrating that the NOPC-CMFD is superior to current CMFD or nonlinear diffusion acceleration schemes that use relaxation. Overall, the method is able to recover the performance of traditional CMFD in problems without feedback for a wide range of conditions. This was observed to result in a substantial reduction, up to 40%, of the run time in whole-core cycle depletion problems.

Effect of time-delayed feedback in a bistable system inferred by logic operation

• The effect of time delay in bistable system can be inferred by logic operation. • Time-delayed negative feedback can reduce the width of bistable region. • There is an unstable limit cycle on the directly connected boundary between the oscillatory and suprathreshold region. • In the alternate region, the system is sensitive to parameters and can enter two potential wells alternately with the slight variation in sensitive parameters. The effect of time delay is inferred by studying the influence of time-delayed feedback on the signal threshold of logic input signal, which reflects the width of the bistable region. Time-delayed positive feedback does not alter the width of the bistable region but increases the switching time. Time-delayed negative feedback leads to decreases in the depth of two potential wells and the width of the bistable region of the system, resulting in instability and oscillation of the system. Then, the parameter plane of the system can be divided into suprathreshold, subthreshold, oscillatory and alternate regions. With increasing time delay and negative feedback intensity, the suprathreshold and oscillatory regions continuously squeeze the middle subthreshold region until they are connected. One part of the oscillatory region is directly connected with the suprathreshold region, while the other part is transiently connected with the alternate region. There is an unstable limit cycle on the directly connected boundary. In the alternate region, the system is sensitive to initial values and system parameters and can enter two potential wells alternately with slight variations in sensitive parameters.

Kinematic of the Position and Orientation Synchronization of the Posture of a n DoF Upper-Limb Exoskeleton with a Virtual Object in an Immersive Virtual Reality Environment

Exoskeletons are an external structural mechanism with joints and links that work in tandem with the user, which increases, reinforces, or restores human performance. Virtual Reality can be used to produce environments, in which the intensity of practice and feedback on performance can be manipulated to provide tailored motor training. Will it be possible to combine both technologies and have them synchronized to reach better performance? This paper consists of the kinematics analysis for the position and orientation synchronization between an n DoF upper-limb exoskeleton pose and a projected object in an immersive virtual reality environment using a VR headset. To achieve this goal, the exoskeletal mechanism is analyzed using Euler angles and the Pieper technique to obtain the equations that lead to its orientation, forward, and inverse kinematic models. This paper extends the author’s previous work by using an early stage upper-limb exoskeleton prototype for the synchronization process.

Speech Intensity Response to Altered Intensity Feedback in Individuals With Parkinson's Disease.

Purpose Hypophonia (low speech intensity) is the most common speech symptom experienced by individuals with Parkinson's disease (IWPD). Previous research suggests that, in IWPD, there may be abnormal integration of sensory information for motor production of speech intensity. In the current study, intensity of auditory feedback was systematically manipulated (altered in both positive and negative directions) during sensorimotor conditions that are known to modulate speech intensity in everyday contexts in order to better understand the role of auditory feedback for speech intensity regulation. Method Twenty-six IWPD and 24 neurologically healthy controls were asked to complete the following tasks: converse with the experimenter, start vowel production, and read sentences at a comfortable loudness, while hearing their own speech intensity randomly altered. Altered intensity feedback conditions included 5-, 10-, and 15-dB reductions and increases in the feedback intensity. Speech tasks were completed in no noise and in background noise. Results IWPD displayed a reduced response to the altered intensity feedback compared to control participants. This reduced response was most apparent when participants were speaking in background noise. Specific task-based differences in responses were observed such that the reduced response by IWPD was most pronounced during the conversation task. Conclusions The current study suggests that IWPD have abnormal processing of auditory information for speech intensity regulation, and this disruption particularly impacts their ability to regulate speech intensity in the context of speech tasks with clear communicative goals (i.e., conversational speech) and speaking in background noise.

The Continental-Scale Soil-Moisture Precipitation Feedback in Europe with Parameterized and Explicit Convection

AbstractSoil moisture atmosphere interactions are key elements of the regional climate system. There is a well-founded hope that a more accurate representation of the soil moisture-precipitation feedback would improve the simulation of summer precipitation on daily to seasonal, to climate time scales. However, uncertainties have persistently remained as the simulated feedback is strongly sensitive to the model representation of deep convection. Here we assess the feedback representation using a GPU-accelerated version of the regional climate model COSMO. We simulate and compare the impact of continental-scale springtime soil-moisture anomalies on summer precipitation at convection-resolving (2.2 km) and convection-parameterizing resolution (12 km). We conduct re-analysis-driven simulations of 10 summer seasons (1999-2008) in continental Europe. While both simulations qualitatively agree on a positive sign of soil moisture-induced precipitation, they strongly differ in precipitation frequency: When convection is parameterized, wetter soil predominantly leads to more frequent precipitation events, and when convection is treated explicitly, they primarily become more intense. The results indicate that the sensitivity to soil moisture is stronger with parameterized convection, suggesting that the land surface-atmosphere coupling may be overestimated. In addition, the feedback’s sensitivity in complex terrain is assessed for soil perturbations of different horizontal scales. The convection-resolving simulations confirm a negative feedback for sub-continental soil moisture anomalies, which manifests itself in a local decrease of wet-hour frequency. However, the intensity feedback reinforces precipitation events at the same time (positive feedback). The two processes are represented differently in simulations with explicit and parameterized convection, explaining much of the difference between the two simulations.

Reducing backscattering and the Kerr noise in a resonant micro-optic gyro using two independent lasers

In a resonator micro-optic gyroscope (R-MOG), backscattering noise and Kerr noise have been key issues affecting the optical gyro output that are difficult to completely suppress. A method is proposed to suppress backscattering noise in a R-MOG. It uses two independent lasers and, by locking the two optical signals at different resonance peaks, a differential output of the two optical signals is achieved that successfully suppresses the backscattering noise. At the same time, a light intensity feedback loop based on a light intensity modulator is added to the loop to ensure the same optical power into the cavity. Experimental results show that the light intensity fluctuation into the gyro system is reduced nearly two orders of magnitude and the bias stability is improved to 9.06 deg/h by using a light intensity feedback loop with two independent lasers.

Complex Dynamics and Hard Limiter Control of a Fractional-Order Buck-Boost System

Chaos and control analysis for the fractional-order nonlinear circuits is a recent hot topic. In this study, a fractional-order model is deduced from a Buck-Boost converter, and its discrete solution is obtained based on the Adomian decomposition method (ADM). Chaotic dynamic characteristics of the fractional-order system are investigated by the bifurcation diagram, 0-1 test, spectral entropy (SE) algorithm, and NIST test. Meanwhile, the control of the fractional-order Buck-Boost model is discussed through two different ways, namely, the intensity feedback and the hard limiter control. Specifically, the hard limiter control can be realized using a current limiter in the circuit, where the current limiter device is applied to control the branch current. The results show that the proposed fractional-order system has complex dynamic behaviors and potential application values in the engineering field.

Coherent laser detection of the femtowatt-level frequency-shifted optical feedback based on a DFB fiber laser.

The theoretical basis and experimental realization of an all-fiber self-mixing laser Doppler velocimetry based on frequency-shifted feedback in a distributed feedback (DFB) fiber laser are presented, which employs a pair of fiber-coupled acousto-optic modulators to adjust the modulation intensity and frequency of the laser self-mixing effect. Moreover, the minimum optical feedback intensity for the velocity signal successfully measured by the interferometer is 5.12 fW, corresponding to 0.16 photons per Doppler cycle. The results demonstrate that the proposed scheme can adapt to the non-contact measurement requirements of the wide-range speed and weak feedback level in the complex environment.

Interactions of diffusion and nonlocal delay give rise to vegetation patterns in semi-arid environments

Vegetation pattern is caused by local instability in phase space, which can reflect the distribution characteristics of vegetation in the studied space. In semi-arid environment, the vegetation roots will not only absorb the water resources near themselves, but also absorb the water resources in the whole study area, that is to say, the absorption of water resources by vegetation roots is a nonlocal process. Meanwhile, the feedback mechanism of soil-water diffusion plays an important role in the process of water absorption by vegetation roots. However, it is not clear that how the feedback mechanism of nonlocal water absorption by vegetation roots and soil-water diffusion affects vegetation pattern. In this paper, we construct a positive feedback vegetation-water model with nonlocal delay. The instability of Turing pattern is analyzed by analytical method, and the conditions of stable pattern occurrence are obtained. At the same time, we use multi-scale analysis method to obtain the amplitude equation of vegetation-water system. We found that the non-local water absorption intensity of vegetation roots and the feedback of soil-water diffusion can cause the phase change of vegetation pattern. The change of nonlocal water absorption intensity will produce mixed vegetation pattern structure. The enhancement of soil-water diffusion feedback intensity will change the vegetation pattern structure: low density cold spot patterns → mixed patterns → high density hot spot patterns. The isolation between vegetation patches will be increased as that nonlocal water absorption intensity is enhanced or the feedback intensity of soil-water diffusion is increased. We also revealed that increasing the feedback intensity of soil water diffusion or nonlocal strength within a certain range is helpful to increase the vegetation density, while excessive feedback intensity or nonlocal strength will induce land desertification.

Chaotic Macropulse Green Laser Beam Generated by Modulating a 520 nm Laser Diode with Optical Feedback

We describe a novel chaotic macropulse green laser designed employing the pulse modulation of a 520 nm laser diode with optical feedback. We analyze the characteristics of these chaotic macropulses, in view of effects of the feedback intensity, injection current, modulation voltage, duty cycle, and modulation frequency on the pulses, including their full width at half maximum (FWHM) values and peak side-lobe levels (PSLs). We determine an optimum feedback intensity of 11.7% based on the maximum peak optical power and the scope of the amplitude jitter of the chaotic macropulse. The optimum injection currents are approximately between 60 and 70 mA, and the modulation voltages between 2.0 and 3.0 V are limited by the radio-frequency (RF) power. We found that chaos also occurred at the bottom of the macropulse when the duty cycle was less than approximately 30%. The modulation frequencies were loaded from 4 to 20 MHz; this range was restricted by the performance of the RF input port on the laser diode mount. The range resolution of the chaotic macropulses is approximately 3 cm in seawater; it is achieved with lower power consumption than a continuous wave chaotic laser.

A chaos control method of single-phase H-bridge photovoltaic inverter

There are complex nonlinear behaviors such as bifurcation and chaos in a single-phase H-bridge photovoltaic inverter under proportional integral control, which will increase the harmonic content of the output current greatly and reduce the stability of system operation and reliability of power supply. There are the problems suffering the complicated modeling and difficulty in determining the control coefficients in existing chaos control methods. The exponential delay feedback control is a further development of the delay feedback control, which has the advantages of requiring no precise mathematical model of the system and simple implementation. However, our research shows that when the exponential delay feedback control is directly applied to the system, the feedback intensity cannot be controlled, which will bring too big a disturbance to the system. Based on it, an improved exponential delayed feedback control method is proposed in this paper. Firstly, a feedback signal is formed by the difference between the output current of the system and its own delay, then the feedback signal is used to obtain the control signal through an exponential link, a subtraction link and an proportion link, and the control signal is applied to the controlled system in the form of a feedback. At the same time, the discrete mapping model of the system is established and its Jacobian matrix expression is determined. Finally, the limiting conditions of the feedback control coefficient of the control signal are derived based on the stability criterion, and the control is applied to the system. In order to verify the control effect of this method, a lot of simulation experiments are conducted. The results show that the problems that the exponential delay feedback cannot control the feedback strength and causes excessive disturbance to the system will be effectively solved by this method. When the bifurcation parameters vary greatly, the chaos behaviors in the system will be suppressed effectively, the stable operating domain of the system will be expanded greatly and the harmonic content of the output current will be reduced.

Comparative Evaluation of the Effectiveness of Rotary Instrumentation over Manual Instrumentation with Ultrasonic Irrigation on Incidence, Duration, and Intensity of Postendodontic Pain: An In vivo Study.

Aim:The aim of this study was to compare the effectiveness of rotary instrumentation over manual instrumentation with ultrasonic irrigation on incidence, duration, and intensity of postendodontic pain (PEP).Subjects and Methods:Eighty patients, with asymptomatic irreversible pulpitis in maxillary anterior teeth, were selected and treated with single-visit endodontic treatment. Patients were randomly divided into 2 groups (40 each), Group A (K files using step-back technique) and Group B (ProTaper Next using crown-down technique) along with passive ultrasonic irrigation. Patients were recalled, examined, and asked to fill up questionnaire after 24 h, 48 h, and 7 days. On the basis of response given in the feedback forms, incidence, duration, and intensity of PEP were evaluated.Results:Statistical analysis of the data was carried out using Chi-square test, and level of significance (P < 0.05) was evaluated. More incidence of pain was noticed in Group A when compared with Group B. Significant difference found between two groups (χ2 = 22.759; P = 0.001). There was also statistically significant difference between two groups at different time intervals.Conclusion:Both instrumentation techniques under investigation cause PEP. The incidence of pain was more in manual technique than rotary technique. The duration of pain was higher in manual group than rotary group at different time intervals.

EFFICIENT MULTIPHYSICS ITERATIONS IN MPACT WITH PARTIALLY CONVERGENT CMFD

Partial convergence of CMFD can help to stabilize multiphysics iteration schemes. In this paper, an efficient multiphysics iteration scheme with near-optimal partially convergent CMFD implemented in MPACT is presented. In the new scheme, the feedback intensity of the problem is automatically estimated, and the relative convergence of CMFD solver is adjusted accordingly. Numerical results show that MPACT with near-optimal partially convergent CMFD can have almost the same convergence rate in problems with feedback as those without feedback. For the problems tested here the run time may be reduced by more than 20% and up to 49% compared with that of current MPACT.

Coherent beam combining of a nine-fiber laser array using an all-optical ring cavity feedback loop based on diffractive optical element

Our study describes the development of coherent beam combining of an array of nine fiber lasers using an all-optical ring cavity feedback loop based on a diffractive optical element to achieve a single-aperture output. Nine 300-mW Yb-doped fiber amplifier beams arranged in a 1 × 9 end-cap array were combined to achieve a single-aperture beam with a power of 739 mW and a beam quality (M2) of 1.18 with 21.5% combining efficiency. The optical spectra, far-field distributions, and time-domain characteristics of the combined beams were investigated under open- and closed-loop conditions. Under open-loop conditions, the far-field coherent visibility changed constantly from 72.1% to 90.9% and the fluctuation intensity was strong. Under closed-loop conditions, the system achieved a steady state with a visibility of 98.6% and an average feedback intensity of 0.4 V, indicating the occurrence of phase locking. Furthermore, mode hopping was observed when there were more than four channels in a combination. However, the system interference pattern remained stable. Comprehensive research on the relevant literature indicated that novel filled-aperture CBC was achieved using an all-optical ring cavity feedback loop based on a DOE.

Dynamic Transitions in Neuronal Network Firing Sustained by Abnormal Astrocyte Feedback.

Astrocytes play a crucial role in neuronal firing activity. Their abnormal state may lead to the pathological transition of neuronal firing patterns and even induce seizures. However, there is still little evidence explaining how the astrocyte network modulates seizures caused by structural abnormalities, such as gliosis. To explore the role of gliosis of the astrocyte network in epileptic seizures, we first established a direct astrocyte feedback neuronal network model on the basis of the hippocampal CA3 neuron-astrocyte model to simulate the condition of gliosis when astrocyte processes swell and the feedback to neurons increases in an abnormal state. We analyzed the firing pattern transitions of the neuronal network when astrocyte feedback starts to change via increases in both astrocyte feedback intensity and the connection probability of astrocytes to neurons in the network. The results show that as the connection probability and astrocyte feedback intensity increase, neuronal firing transforms from a nonepileptic synchronous firing state to an asynchronous firing state, and when astrocyte feedback starts to become abnormal, seizure-like firing becomes more severe and synchronized; meanwhile, the synchronization area continues to expand and eventually transforms into long-term seizure-like synchronous firing. Therefore, our results prove that astrocyte feedback can regulate the firing of the neuronal network, and when the astrocyte network develops gliosis, there will be an increase in the induction rate of epileptic seizures.

Large eddy simulation of the unstable flame structure and gas-to-liquid thermal feedback in a medium-scale methanol pool fire

The objective of the present study is to perform fine-grained Large Eddy Simulations (LES) of a canonical 30-cm-diameter methanol pool fire configuration in order to evaluate the ability of current fire models to predict the flame structure and the rate of heat transfer to the liquid fuel surface. The simulations are performed using an LES solver called FireFOAM, a prescribed fuel evaporation rate, and a “wall-resolved” approach; the simulations also include a description of the fuel pan lip. Great attention is paid to the design of the computational grid and to the control of spatial resolution. Less attention is paid to the LES model formulation: except for the treatment of radiation for which we consider both a simplified model using a prescribed global radiant fraction and a more advanced model based on the Weighted-Sum-of-Gray-Gases approach, the simulations use baseline FireFOAM treatments to describe subgrid-scale turbulence and combustion. Results suggest that grid-converged solutions are achieved at a spatial resolution of 2 mm in the near-pool-surface region and 5 mm in the bulk of the flame region. Consistent with experimental observations, the simulated flames feature a strong instability characterized by the cyclic formation of thin boundary layer flames at the liquid pool surface and vortex rings at the burner rim that grow into large puffs and determine the structure of the entire flame. Predictions of the mean and root-mean-square temperature and velocity are found to be in good agreement with measurements taken from the literature. Equally encouraging results are obtained for the mean radiative and convective heat fluxes near the pool surface; quantitatively, simulations are found to overestimate the intensity of the thermal feedback by 25%. These results suggest that provided that the computational grid is fine enough, current fire models can be used to predict the gas-to-fuel thermal feedback.

Examining the links between active Facebook use, received likes, self-esteem and happiness: A study using objective social media data

For social media users, profile updating and receiving Likes may feel like a reward, and elicit positive emotions, reinforcing use of the platform. Could this mechanism have consequences for users’ self-esteem and happiness? Previous findings on the topic are mixed, and typically limited by use of self-reports of online activity. In the present study, we used objective behavioral data to examine the hypotheses that receiving Likes on Facebook would relate to 1) users’ level of perceived self-esteem, and 2) increased happiness via the mediating role of self-esteem. We recruited 2,349 adult Facebook users (589 men, 1,760 women; 67% aged 18–25, 26% aged 26–35, 7% aged > 35 years). Participants answered an online survey and provided access to their objective Facebook data (i.e., profile updates and received Likes). We found that frequency of users updating their profile and sharing personal content (e.g., self-generated texts, images, friends and location tags) had a direct effect on the frequency and intensity of the feedback (i.e., Likes) they received from other users in their online social network. Additionally, analyses supported a positive link between the frequency and intensity of positive feedback received by users and perceived happiness that was mediated in part by an increase in self-esteem. Overall, findings demonstrate a process linking positive online social feedback and perceived well-being.