Pulse Phenomena Research Articles

Mechanism Analysis and Elimination of Multiple Pulse Phenomenon of Active Rectifier in Wireless Power Transfer Systems

Mechanism Analysis and Elimination of Multiple Pulse Phenomenon of Active Rectifier in Wireless Power Transfer Systems

Exponential stability of switched systems with state-dependent delayed impulses via B-equivalent method

This paper studies the stability problem of switched systems with state-dependent delayed impulses (SDDIs), where switching times satisfy the definition of average dwell-time. Firstly, the pulse phenomenon of the systems with SDDIs is avoided under some necessary assumptions. Subsequently, the state-dependent delayed impulsive switched systems can be transformed into the corresponding time-dependent ones by using the B-equivalent method. Furthermore, the stability of stable and unstable systems with time-dependent delayed impulses (TDDIs) are analyzed, where the limitation that the impulsive delays are less than the impulsive intervals is relaxed. Based on the equivalence of the original system and the corresponding switched system with TDDIs, some new stability conditions for the switched systems with SDDIs are derived. Finally, the theoretical results are applied to a switched neural network with SDDIs to demonstrate the validity of the results.

Detection‐based compound event‐triggered secure control for nonlinear multiagent systems

SummaryThis paper designs a distributed dynamic‐detection‐based event‐triggered control method to address the secure tracking control problem. A distributed online iterative dynamic detection mechanism is designed to detect denial‐of‐service (DoS) attacks. The detection results are transmitted into a proposed ET method to adjust the triggering threshold, which can mitigate the impact of DoS attacks. Moreover, the signals of state, observations of disturbance observers and adaptive laws are calculated to generate the trigger signals in the control signal simultaneously, which can help conserve communication resources and reduce the occurrence of pulse phenomenon. Meanwhile, since the predictor exists certain prediction errors that will reduce the tracking performance, a speed function is introduced to ensure the achievement of the control objective. The designed solution guarantees semiglobally uniformly ultimately bounded for all signals within the closed‐loop system. Finally, the effectiveness of control scheme is demonstrated through several simulation results.

Composite adaptive fuzzy bipartite consensus of fractional-order multiagent systems with a switched event-triggered mechanism

This paper focuses on online recorded-data-based composite adaptive fuzzy bipartite consensus control for uncertain fractional-order multiagent systems with interconnected terms and external disturbances by employing a switched-threshold-based event-triggered mechanism (ETM) under the backstepping structure. Fuzzy logic system is used as a universal function approximation to deal with function uncertainties that are not prone to model in the system. A new composite learning adaptive parameter design scheme that synthesizes both prediction error and tracking error is developed to enhance the tracking performance, where the prediction error is raised from the utilization of online recorded data and instantaneous data. A unique switched-threshold-based ETM is introduced, in which the information transmission between the sensor and the controller is imposed on one of the individuals. One merit of this work consists in that it can automatically and rapidly switch and adjust between the fixed threshold and relative threshold ETM according to the amplitude of input signals to balance the network resources and impede the occurrence of pulse phenomenon. In addition, it is theoretically proven that the proposed scheme can ensure that all internal signals of the closed-loop system are bounded and achieve local bipartite consistent errors through the fractional Lyapunov stability criterion. Finally, a numerical example is provided to confirm the feasibility of the proposed approach.

All-multimode fiber spatiotemporal mode-locked figure-eight laser based on multimode gain fiber.

In this paper, we report for the first time on an all-multimode fiber spatiotemporal mode-locked figure-eight laser operating at 1.0µm. This laser utilizes a multimode gain fiber and a nonlinear amplifying loop mirror mechanism. It can generate mode-locked noise-like pulses at different central wavelengths. Additionally, we observed the presence of a multi-soliton state within the cavity by reducing intracavity gain. This study contributes to a broader investigation of various pulse phenomena in spatiotemporal mode-locked lasers and provides valuable insights into further exploring the evolution of spatiotemporal dynamics in such systems.

Numerical simulation of the early startup period of heat pipe cooled reactor system from the room temperature state

Heat pipe cooled reactor has unique characteristics during reactor startup and power operation due to the design of solid reactor and heat pipes heat transportation. In this paper, numerical simulation of the early startup period of typical heat pipe cooled reactor is carried out. Based on the calculation, it can be found that it takes about 6000s to complete startup from the room temperature, and fuel temperature reaches about 730 K. Important phenomenon of power pulse is also discovered. For power pulse, reactor power can rapidly increase from 80 wt to 40kWt with about 220 s, leading to rapid increase in fuel temperature from 300 K to 420 K. It is also found that heat pipes may cool down again if reactor power is low enough. Studies carried out in this paper show the dynamic characteristics and point out the key issues that need to be focused on during the reactor early startup period.

Large-energy mode-locked Er-doped fiber laser based on indium antimonide as a modulator

Large energy mode-locked pulsed fiber lasers have great potential, especially for a wide range of applications in human eye safety lidar. In our work, we have obtained stable large-energy mode-locking pulse phenomena by making saturable absorbers (SA) from indium antimonized (InSb). InSb-SA was obtained by liquid-phase exfoliation method. A large energy mode-locked pulse of 10.89 nJ was obtained at a pump pulse of 620 mW and a repetition frequency of 469 kHz, with an output power of 5.09 mW. Our research shows that InSb has more advantages compared with commonly used optical modulators. The experimental results can provide a reference for future research on large-energy mode-locked pulses.

Multiple Bound State Soliton Pulses in the All Polarization Maintaining Fiber Laser.

The bound state soliton pulse, a novel mode-locked output state of fiber lasers, has been studied extensively to gain a better understanding of soliton interactions and to explain the mechanism behind the generation of mode-locked pulses. In this particular research, we utilized a self-made saturable absorber (SA) consisting of single-walled carbon nanotubes (SWCNT) in a fully polarization maintaining (PM) erbium-doped fiber optical path. Through this setup, we observed various bound state pulse phenomena, including the double bound state with different phase differences, the bound state formed by two double pulse bound states, the multi-pulse bound state, etc. The abundant bound soliton pulse states demonstrated the excellent nonlinear absorption characteristics of the SA as well as the excellent optical properties of the all-PM fiber laser. It contributed to exploring the relationship between sub pulses and mode-locked pulses in the future. Additionally, due to the strong interaction between bound state solitons and the inherent stability of the PM optical path, there was potential for utilizing this setup as a seed source to enhance the stability of high-power fiber lasers.

Dynamic behavior of outburst two-phase flow in a coal mine T-shaped roadway: The formation of impact airflow and its disaster-causing effect

The study of the dynamic disaster mechanism of coal and gas outburst two-phase flow is crucial for improving disaster reduction and rescue ability of coal mine outburst accidents. An outburst test in a T-shaped roadway was conducted using a self-developed large-scale outburst dynamic disaster test system. We investigated the release characteristics of main energy sources in coal seam, and obtained the dynamic characteristics of outburst two-phase flow in a roadway. Additionally, we established a formation model for outburst impact flow and a model for its flow in a bifurcated structure. The results indicate that the outburst process exhibits pulse characteristics, and the rapid destruction process of coal seam and the blocking state of gas flow are the main causes of the pulse phenomenon. The outburst energy is released in stages, and the elastic potential energy is released in the vertical direction before the horizontal direction. In a straight roadway, the impact force oscillates along the roadway. With an increase in the solid–gas ratio, the two-phase flow impact force gradually increases, and the disaster range extends from the middle of the roadway to the coal seam. In the area near the coal seam, the disaster caused by the two-phase flow impact is characterized by intermittent recovery. In a bifurcated roadway, the effect of impact airflow on impact dynamic disaster is much higher than that of two-phase flow, and the impact force tends to weaken with increasing solid-gas ratio. The impact force is asymmetrically distributed; it is higher on the left of the bifurcated roadway. With an increase in the solid-gas ratio, the static pressure rapidly decreases, and the bifurcated structure accelerates the attenuation of static pressure. Moreover, secondary acceleration is observed when the shock wave moves along the T-shaped roadway, indicating that the bifurcated structure increases the shock wave velocity.

Exponential stability of delayed nonlinear systems with state-dependent delayed impulses and its application in delayed neural networks

This paper mainly studies stability of delayed nonlinear systems (DNSs) under state-dependent delayed impulses (SDDIs). Firstly, under some appropriate hypotheses, it is proved that the pulse phenomenon can be avoided. Then, by the method of comparison principle, new theoretical frameworks are established for stability of DNSs under state-dependent delayed impulsive control and delayed impulsive interference, respectively. Furthermore, the proposed criteria are applied in the stability of delayed neural networks (DNNs) under SDDIs. Finally, examples are provided to illustrate the correctness of obtained results.

A renewed search for radio emission from the variable γ-ray pulsar PSR J2021+4026

ABSTRACT We undertake the first targeted search at 1.5 GHz for radio emission from the variable γ-ray pulsar PSR J2021+4026. This radio-quiet pulsar assumes one of two stable γ-ray emission states, between which it transitions on a time-scale of years. These transitions, in both γ-ray flux and pulse profile shape, are accompanied by contemporaneous changes to the pulsar’s spin-down rate. A number of radio pulsars are known to exhibit similar correlated variability, which in some cases involves an emission state in which the radio emission ceases to be detectable. In this paper, we perform a search for radio emission from PSR J2021+4026, using archival radio observations recorded when the pulsar was in each of its emission/spin-down states. Using improved techniques, we search for periodic radio emission as well as single pulse phenomena such as giant radio pulses and RRAT-like emission. Our search reveals no evidence of radio emission from PSR J2021+4026. We estimate that the flux density for periodic emission from PSR J2021+4026 does not exceed 0.2 mJy at this frequency. We also estimate single-pulse flux limits for RRAT-like bursts and giant radio pulses to be 0.3 and 100 Jy, respectively. We discuss the transitioning behaviour of PSR J2021+4026 in the context of pulsar glitches, intermittent pulsars and the increasingly common emission-rotation correlation observed in radio pulsars.

Tungsten trioxide nanocomposite for conventional soliton and noise-like pulse generation in anomalous dispersion laser cavity

Abstract This work demonstrates the employment of tungsten trioxide/polydimethylsiloxane nanocomposite saturable absorber (WO3/PDMS-SA) in realizing mode-locked conventional soliton (CS) and noise-like pulse (NLP) laser generation in net anomalous dispersion. The switching formation from CS regime of 970.0 fs pulse duration to NLP regime of 182.0 fs coherent spike with 65.3 ps pedestal was achieved by varying its pump power. The pulse laser exhibited good stability of 50.76 and 49.82 dB signal-to-noise ratio at 9.09 MHz fundamental repetition rate and trivial variation during stability test for CS and NLP regime, respectively. This work expresses the feasibility of WO3/PDMS-SA in attaining various types of mode-locked pulse phenomena using a fixed cavity configuration conceivably beneficial for compact dual-purpose laser systems.

Observation of low-frequency oscillation in argon helicon discharge

We present here a kind of low-frequency oscillation in argon helicon discharge with a half helical antenna. This time-dependent instability shows a global quasi-periodic oscillation of plasma density and electron temperature, with a typical frequency of a few tens of Hz which increases with external magnetic field as well as radiofrequency (RF) power. The relative oscillation amplitude decreases with magnetic field and RF power, but the rising time and pulse width do not change significantly under different discharge conditions. The oscillation can only be observed in some specific conditions of low magnetic fields and low RF power when the gas flows in from one end of the discharge area and out from another end. This global instability is suggested to be attributed to the pressure instability of neutral depletion, which is the result of compound action of gas depletion by heating expansion and gas replenishment from upstream. There are two kinds of oscillations, large and small amplitude oscillations, occurring in different discharge modes. This study could be a good verification of and complement to earlier experiments. This kind of spontaneous pulse phenomenon is also helpful in realizing a pulsing plasma source without a pulsed power supply.

Event-Triggered Impulsive Control for Nonlinear Systems With Actuation Delays

This article studies impulsive stabilization of nonlinear systems. We propose two types of event-triggering algorithms to update the impulsive control signals with actuation delays. The first algorithm is based on continuous event detection, while the second type makes decision about updating the impulsive control inputs according to periodic event detection. Sufficient conditions are derived to ensure asymptotic stability of the impulsive control systems with the designed event-triggering algorithms. Lower bounds of the time period between two consecutive events are also obtained, so that the closed-loop impulsive systems are free of Zeno behavior. That is to say that the pulse phenomena are excluded from the event-triggered impulsive control systems, in the community of impulsive differential equations. An illustrative example demonstrates effectiveness of the proposed algorithms and our theoretical results.

The low frequency pressure pulsation and control of the open-jet wind tunnel

An open jet wind tunnel has low-frequency pressure pulsation in common wind speed range due to its unique structural form, which seriously damages the quality of flow field in the test section. The low-frequency pressure fluctuation performance and control mechanism of Jilin University open jet and return flow wind tunnel are investigated by experiments and numerical simulation. The results show that the low-frequency pressure fluctuation is a narrow pulse phenomenon that only occurs in certain intervals, and several velocity intervals may be found in the same wind tunnel. The reliability of the numerical simulation is verified by comparing the peak frequency and amplitude of pressure fluctuation in numerical simulation and wind tunnel tests. A simplified model similar to and amplifying the phenomenon is established. The flow structure and vortex evolution are analyzed via detached eddy simulation. In the test section, large-scale shedding vortices are formed at the nozzle exit, introducing periodic pulsating instantaneous velocity and acting with the collector to form an edge-feedback. This acoustic feedback forms resonance with the pipeline circuit, resulting in poor flow field quality. In accordance with the mechanism of nozzle jet, two methods of controlling pulsation are proposed: spoiler and flow-follow device. The study shows that the effects of two methods are abrupt, and the frequency of pressure pulsation is changed. The spoiler destroys the complete structure of vortex ring in free jet and develops into a complementary double vortex ring structure, which is highly sensitive to size factors. The flow-follow device supplements the velocity loss of the free jet at the nozzle and develops into a double vortex ring with master–slave structure in the middle of the test section. Its vibration reduction effect is greatly affected by the flow velocity. It takes effect in an appropriate range where the flow velocity is higher than the nozzle velocity. If the follow velocity is extremely low, the flow-follow device cannot change the original jet structure. If the follow velocity is extremely high, the momentum of the fan will be greatly reduced, the flow field will be unstable, and another order of pulsation may be induced. This work lays a solid foundation for further understanding the aerodynamic characteristics and optimization mechanism of open jet wind tunnel.

Revealing kinetics of a diode-pumped metastable Ar laser in pulsed and CW lasing.

We have experimentally investigated the kinetics of a diode-pumped metastable Ar laser by simultaneously monitoring the population evolution of 1s5 and 1s4 states during lasing. A comparison between the two cases with the pump laser on and off revealed the cause for the transition from pulsed to CW lasing. The depletion of 1s5 atoms was responsible for the pulsed lasing phenomenon, while increasing the duration and density of 1s5 atoms resulted in CW lasing. Furthermore, population accumulation of the 1s4 state was observed.

Semiconductor Core Optical Fibers for the Purpose of Nonlinear pulse Reshaping

In this work, we design semiconductor core normal dispersion optical fibers in the single-mode regime to observe the phenomena of nonlinear pulse reshaping through them. Initially, a Ge-core fiber is proposed, considering pure silica material as the cladding of the fiber. It is observed that the designed fiber is capable of generating a semi-parabolic pulse (SPP) (misfit value ≤ 4%) within a much shorter fiber length (~ 5 cm) while a Sech pulse of very low peak power (~100 mW) is taken as input at the operating wavelength of 2.8 μm. Various fiber parameters and pulse parameters are optimized next for the betterment of the generated pulse. Finally, a comparative study between the Ge-core and Si-core fibers is accomplished to identify the best possible fiber for the generation of efficient SPP at a sufficiently small fiber length.

Investigation of the temporal behavior of the self-Q-switched Ho:GdVO4 laser pumped by a Tm-doped fiber laser

We investigate the temporal behavior of a self-Q-switched Ho:GdVO4 laser at 2074 nm by analyzing the variation of reabsorption region with the incident pump power. The different temporal behaviors of self-Q-switched Ho:GdVO4 laser are observed by changing the incident pump power. When the incident pump power is below 11.7 W, the self-Q-switching pulse train are stable and fully modulated. However, once the incident pump power exceeds 11.7 W, the modulation depth of output laser pulse train drops sharply with the increase of incident pump power until the pulsing phenomenon disappears. Under considering the ground state reabsorption effect, the temporal behavior of self-Q-switched Ho:GdVO4 laser is discussed by calculating the variation of reabsorption region with the incident pump power, and the theoretical analysis can explain the experimental results very well. The maximum average output power of self-Q-switched Ho:GdVO4 laser reaches 1.07 W at the incident pump power of 11.7 W, with a pulse width of 1.808 µs and a pulse repetition frequency of 56.53 kHz. To the best of our knowledge, this is the first Ho doped self-Q-switched solid state laser.

Passively mode-locked Ho-doped fiber laser with soliton rain and noise-like pulse regime

A passively Ho-doped fiber laser at 2 μm with soliton rain and noise-like pulse (NLP) operation regime has been realized by using nonlinear polarization rotation (NPR) technology. By adjusting the polarization state, the evolution phenomenon of soliton rain pulse and the NLP are obtained. The typical NLP mode-locking operation regime is achieved by finely adjusting pump power and polarization state, which delivers a corresponding pulse energy of 8.93 nJ with pulse width of 1.31 ps. The soliton rain operation regime with multiple solitons is achieved by finely adjusting pump power, which delivers a corresponding pulse energy of 22.98 nJ with pulse width of 1.21 ps. In addition, a NLP mode-locking operation regime is obtained again under a proper pump power and polarization state with a corresponding pulse energy of 34.14 nJ and pulse width of 1.18 ps. The experimental results well demonstrate the evolution of ultrashort pulse regime with the pump power and polarization state in passively mode-locked Ho-doped fiber lasers at 2 μm.

Theoretical characteristics of mid-infrared gain switched pulsed iron-doped ZnSe laser

We report a four-level theoretical model revealing the laser kinetics of a gain-switched pulsed Fe2+:ZnSe laser that is established for the first time, to the best of our knowledge. The experimental results agree with the theoretical primary spike pulse and relaxation oscillation phenomenon of pulse. Furthermore, the effects of temperature, doping concentration, and the output coupler reflectivity on the performance of the pulsed Fe2+:ZnSe laser are simulated using the proposed model. The simulated results indicate that the laser efficiency is higher at low temperature and high Fe2+ concentrations, and the optimal output coupler reflectivity is ∼23% at 77 K.