External Pulse Research Articles

Neuromorphic-computing-based adaptive learning using ion dynamics in flexible energy storage devices.

High-accuracy neuromorphic devices with adaptive weight adjustment are crucial for high-performance computing. However, limited studies have been conducted on achieving selective and linear synaptic weight updates without changing electrical pulses. Herein, we propose high-accuracy and self-adaptive artificial synapses based on tunable and flexible MXene energy storage devices. These synapses can be adjusted adaptively depending on the stored weight value to mitigate time and energy loss resulting from recalculation. The resistance can be used to effectively regulate the accumulation and dissipation of ions in single devices, without changing the external pulse stimulation or preprogramming, to ensure selective and linear synaptic weight updates. The feasibility of the proposed neural network based on the synapses of flexible energy devices was investigated through training and machine learning. The results indicated that the device achieved a recognition accuracy of ∼95% for various neural network calculation tasks such as numeric classification.

Estimation of impulse action parameters using a network of neuronlike oscillators

Aim of the study is to develop a method for estimating the parameters of an external periodic impulse action using a spiking network of neuronlike oscillators. Methods. The spiking activity of a network consisting of coupled nonidentical neuronlike FitzHugh–Nagumo oscillators was studied, depending on the parameters of the periodic impulse action. To estimate the amplitude of the external impulse signal, we detuned the FitzHugh–Nagumo oscillators, which were in a stable state of equilibrium in the absence of an external action, by the threshold parameter responsible for the excitation of the oscillator. To estimate the frequency of excitatory pulses, we detuned the FitzHugh–Nagumo oscillators by the parameter characterizing the ratio of time scales, the value of which determines the natural frequency of oscillators. We also changed the duration of external pulses. Results. It is shown that the number of spikes generated by a network of nonidentical FitzHugh–Nagumo oscillators has a monotonic dependence on the amplitude of the external pulse signal and a nonmonotonic dependence on the frequency of the pulse signal. The number of spikes generated by the network remains constant over a wide range of external pulse durations. A method for estimating the amplitude and frequency of impulse action is proposed. The method efficiency is demonstrated in numerical simulations and in a radio physical experiment. Conclusion. The proposed method allows one to estimate the amplitude of an external pulse signal, knowing its frequency, and estimate the frequency of this signal, knowing its amplitude. The method can be used in robotics when solving the problems of information processing related to the motion control of mobile robots.

Dynamical generation of chiral W and Greenberger-Horne-Zeilinger states in laser-controlled Rydberg-atom trimers

Motivated by the significantly improved scalability of optically trapped neutral-atom systems, extensive efforts have been devoted in recent years to quantum-state engineering in Rydberg-atom ensembles. Here we investigate the problem of engineering generalized (``twisted'') $W$ states, as well as Greenberger-Horne-Zeilinger (GHZ) states, in the strongly interacting regime of a neutral-atom system. We assume that each atom in the envisioned system initially resides in its ground state and is subject to several external laser pulses that are close to being resonant with the same internal atomic transition. In particular, in the special case of a three-atom system (Rydberg-atom trimer) we determine configurations of field alignments and atomic positions that enable the realization of chiral $W$ states---a special type of twisted three-qubit $W$ states of interest for implementing noiseless-subsystem qubit encoding. Using chiral $W$ states as an example we also address the problem of deterministically converting twisted $W$ states into their GHZ counterparts in the same three-atom system, thus significantly generalizing recent works that involve only ordinary $W$ states. We show that starting from twisted---rather than ordinary---$W$ states is equivalent to renormalizing downward the relevant Rabi frequencies. While this leads to somewhat longer state-conversion times, we also demonstrate that those times are at least two orders of magnitude shorter than typical lifetimes of relevant Rydberg states.

Control over Amplification in Exciton Polariton Condensate

Exciton polariton condensates are the most well-studied case of Bose-Einstein condensation (BEC) of quasiparticles. Together with their prominent fundamental importance, the exciton-polariton condensates have a wide spectrum of engineering applications covering interferometry and metrology, different types of SQUIDs and accelerometers, and forming a universal gate set for quantum computing via the control with external laser pulses. The efficient experimental manipulation with the polariton BEC can be realized via the bosonic final-state stimulation, matter-wave amplification, or by lasing of polaritons, but a satisfactory theoretical model for such control has not been developed yet. Here we study the polariton matter-wave amplifier based on the stimulated scattering of massive particles. The amplification of the injected quasiparticles is achieved through an elastic scattering of so-called lower polaritons (LPs). Such an amplifier has many advantages compared with a standard lasing or using a photon amplifier: it can provide a sufficient gain coefficient. To develop an efficient control algorithm for the polariton amplifier we use here the dynamical model for the LP population proposed by Ciuti, Savona, et al. in 1998. The phenomenological model for the gain coefficient is based on the experiments with cold collisions of polaritons performed by Deng, Haug, and Yamamoto in 2010 and later. We use different feedback algorithms (speed gradient vs target attractor) to track efficiently the polariton population in the amplifier. We compare the pros and cons of our alternative approaches and discuss their possible engineering applications.

Role of External Stimuli in Engineering Magnetic Phases and Real-Time Spin Dynamics of Co/Mn Oxides.

Magnetism in atomically thin two-dimensional (2D) materials can be easily manipulated by alloying, functionalization, external ultrafast laser pulse, strain, electric field, etc. In this work, we have performed a series of spin-resolved density functional theory calculations on 2D magnetic hexagonal transition-metal oxide alloys, CoMnO4. We have explored different alloy patterns and found the most stable magnetic phases in each pattern, resulting in a stable ferromagnetic (FM) ground state depending upon the pattern. We have used Janus functionalization in these materials to tune the magnetic nature of the system from FM to antiferromagnetic (AFM) states. To further control the spin dynamics, we have applied an ultrafast laser pulse to the Janus systems to explore an AFM-to-FM transition process. Finally, applying strain and electric field to the Janus alloys allows us to tune the structure-property relationship in the 2D layers to obtain desirable spin arrangements.

Optimal entrainment for removal of pinned spiral waves.

Cardiac fibrillation is caused by self-sustaining spiral waves that occur in the myocardium, some of which can be pinned to anatomical obstacles, making them more difficult to eliminate. A small electrical stimulation is often sufficient to unpin these spirals but only if it is applied during the vulnerable unpinning window. Even if these unpinning windows can be inferred from data, when multiple pinned spirals exist, their unpinning windows will not generally overlap. Using phase-based reduction techniques, we formulate and solve an optimal control problem to yield a time-varying external voltage gradient that can synchronize a collection of spiral waves that are pinned to a collection of heterogeneous obstacles. Upon synchronization, the unpinning windows overlap so that they can be simultaneously unpinned by applying an external voltage gradient pulse at an appropriate moment. Numerical validation is presented in bidomain model simulations. Results represent a proof-of-concept illustration of the proposed unpinning strategy which explicitly incorporates heterogeneity in the problem formulation and requires no real-time feedback about the system state.

Percutaneous Neuromodulation of the Brachial Plexus and Sciatic Nerve for the Treatment of Acute Pain Following Surgery: Secondary Outcomes From a Multicenter, Randomized, Controlled Pilot Study

ObjectivesWe recently reported that percutaneous peripheral nerve stimulation (PNS or “neuromodulation”) decreased pain and opioid consumption within the first two weeks following ambulatory surgery. However, the anatomic lead locations were combined for the analysis, and benefits for each location remain unknown. We therefore now report the effects of percutaneous PNS for brachial plexus and sciatic nerve leads separately. Materials and MethodsBefore surgery, leads were implanted percutaneously to target the brachial plexus (N = 21) for rotator cuff repair or sciatic nerve (N = 40) for foot/ankle surgery, followed by a single injection of local anesthetic. Postoperatively, subjects were randomized in a double masked fashion to 14 days of electrical stimulation (N = 30) or sham/placebo (N = 31) using an external pulse generator. The primary outcome of interest was opioid consumption and pain scores evaluated jointly. Thus, stimulation was deemed effective if superior on either outcome and at least noninferior on the other. ResultsFor brachial plexus leads, during the first seven postoperative days pain measured with the numeric rating scale in participants given active stimulation was a median [interquartile range] of 0.8 [0.5, 1.6] versus 3.2 [2.7, 3.5] in patients given sham (p < 0.001). For this same group, opioid consumption in participants given active stimulation was 10 mg [5, 20] versus 71 mg [35, 125] in patients given sham (p = 0.043). For sciatic nerve leads, pain scores for the active treatment group were 0.7 [0, 1.4] versus 2.8 [1.6, 4.6] in patients given sham (p < 0.001). During this same period, participants given active stimulation consumed 5 mg [0, 30] of opioids versus 40 mg [20, 105] in patients given sham (p = 0.004). Treatment effects did not differ statistically between the two locations. ConclusionsAmbulatory percutaneous PNS of both the brachial plexus and sciatic nerve is an effective treatment for acute pain free of systemic side effects following painful orthopedic surgery.

Numerical investigation on fluidization characteristics of binary particles in supercritical water fluidized bed reactor under pulsed conditions

The fluidization properties of binary particles in a supercritical water fluidized bed reactor (SCWFBR) are numerically investigated based on coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) simulations. The accuracy and effectiveness of the CFD-DEM model is firstly validated via previously published experimental data. Then, the model is adopted to study the effect of flow velocities and sinusoidal pulse on the mixing of the binary particles. Numerical results show that it is effective to promote mixing of binary particles in SCWFBR by introducing external energy pulses, which cannot be achieved by simply increasing the flow velocities without pulses. Compared to high frequency pulses, low frequency pulses are more effective in promoting mixing. Within the parameters considered here, it is also found that the pulse amplitude is almost positively correlated with the effect on the promotion of particle mixing when it is smaller than the fixed flow velocity. In addition, an efficient and economical method based on Fast Fourier Transform (FFT) on the bed pressure drop is given to determine the optimal pulse frequency, which can prevent the waste of manpower and the physical resources from happening. This study can provide technical guidance to achieve optimal mixing of binary particles in SCWFBR and offer theoretical support for the design and optimization.

The equivalent method for arbitrary pulses loaded on the elastic-brittle panel

The risk of urban blasts is rising nowadays. As the most fragile component in modern buildings, glass may cause casualties when it fails in a blast. Thus, being able to accurately predict the average splash speed of fragments is of great significance. In almost all the published studies on glass blast-resistance, the blast pulses are treated as monotonously decaying pulses, which is somewhat oversimplified for the pulses with complex shapes in urban blasts.In this study, for the pulses applied to the elastic panels, the applicability of the Youngdahl Equivalent Method (Y-EM), which is usually adopted in plastic analysis, is checked by employing our previous finite deformation approximate solutions. It is confirmed that Y-EM is applicable for the pulses loaded on an elastic-brittle panel when the finish time in Y-EM is set as the time at which the deflection reaches its maximum, rather than the duration of the external pulse. Furthermore, based on the combination of Y-EM and saturation analysis, an equivalent method for arbitrary pulses loaded on the elastic-brittle panel is proposed. Adopting this method, the average splash speed of glass fragments is predicted, which is proved to be accurate by comparison with the published experimental data. As the theoretical basis of the prediction, the pulse equivalent method proposed here is also proved to be effective.

Angle selective piezoelectric strain-controlled magnetization switching in artificial spin ice based multiferroic system

The prospect of electrically controlled writing of ferromagnetic bits is highly desirable for developing scalable and energy-efficient spintronics devices. In this direction, various efforts have been made to achieve electrically controlled magnetization switching utilizing an artificial multiferroic system. To date, the magnetization switching has been realized in a diverse nanopatterned magnetic system. However, the demonstration of electric field-induced strain-controlled magnetization switching in artificial spin ice (ASI) coupled with a piezoelectric material is still unexplored. In the present work, we perform micromagnetic simulations to investigate the electric field-induced strain-mediated magnetization switching in an ASI based multiferroic system. Here, the piezoelectric strain-controlled magnetization switching has been studied by applying the electric-field pulse at different angles with respect to the axes of the system. Remarkably, magnetization switches by 180° only if the external electric-field pulse is applied at some specific angles, close to the anisotropy axis of the system (≈30°–60°). Our detailed analysis of the demagnetization energy variation reveals that the energy barrier becomes antisymmetric in such cases, facilitating complete magnetization reversal. Moreover, we have also proposed a possible magnetization reversal mechanism with two sequential electric-field pulses of a relatively smaller magnitude. We believe that the present work could pave the way for a future ASI-based multiferroic system for scalable magnetic field-free low power spintronics devices.

Coherence and de-coherence in the Time-Resolved ARPES of realistic materials: An ab-initio perspective

Coherence and de-coherence are the most fundamental steps that follow the initial photo-excitation occurring in typical pump-and-probe experiments. Indeed, the initial external laser pulse transfers coherence to the system in terms of creation of multiple electron–hole pairs excitation. The excitation concurs both to the creation of a finite carriers density and to the appearance of induced electromagnetic fields. The two effects, to a very first approximation, can be connected to the simple concepts of populations and oscillations. The dynamics of the system following the initial photo-excitation is, thus, entirely dictated by the interplay between coherence and de-coherence. This interplay and the de-coherence process itself, is due to the correlation effects stimulated by the photo-excitation. Single-particle, like the electron–phonon, and two-particles, like the electron–electron, scattering processes induce a complex dynamics of the electrons that, in turn, makes the description of the correlated and photo-excited system in terms of pure excitonic and/or carriers populations challenging.

Peculiar Features of Quantum Oscillator Excitation by Pulses with Different Envelopes

We investigate the excitation of a quantum harmonic oscillator by pulses with different envelopes in terms of the excitation probability during the action of a pulse. The majority of attention is given to the dependence of the probability on the pulse duration and the pulse carrier frequency for three envelopes: exponential, double exponential, and rectangular. The choice of these envelopes makes it possible to cover various features of the excitation of a quantum oscillator by an external pulse. In particular, the presence of weak and strong excitation modes is established, for each of which the dependences of the process probability on pulse parameters are studied.

Reconfigurable and real-time high-bandwidth Nyquist signal detection with low-bandwidth in silicon photonics.

We demonstrate for the first time, to the best of our knowledge, reconfigurable and real-time orthogonal time-domain detection of a high-bandwidth Nyquist signal with a low-bandwidth silicon photonics Mach-Zehnder modulator based receiver. As the Nyquist signal has a rectangular bandwidth, it can be multiplexed in the wavelength domain without any guardband as a part of a Nyquist-WDM superchannel. These superchannels can be additionally multiplexed in space and polarization. Thus, the presented demonstration can open a new possibility for the detection of multidimensional parallel data signals with silicon photonics. No external pulse source is needed for the receiver, and frequency-time coherence is used to sample the incoming Nyquist signal with orthogonal sinc-shaped Nyquist pulse sequences. All parameters are completely tunable in the electrical domain. The feasibility of the scheme is demonstrated through a proof-of-concept experiment over the entire C-band (1530 nm-1560 nm), employing a 24 Gbaud Nyquist QPSK signal due to experimental constraints on the transmitter side electronics. However, the silicon Mach-Zehnder modulator with a 3-dB bandwidth of only 16 GHz can process Nyquist signals of 90 GHz optical bandwidth, suggesting a possibility to detect symbol rates up to 90 GBd in an integrated Nyquist receiver.

Element-selective ultrafast magnetization dynamics of hybrid Stoner-Heisenberg magnets

Stoner and Heisenberg excitations in magnetic materials are inherently different. The first involves an effective reduction of the exchange splitting, whereas the second comprises excitation of spin waves. In this work, we test the impact of these two excitations in the hybrid Stoner-Heisenberg system of FePd. We present a microscopic picture of ultrafast demagnetization dynamics in this alloy, which represents both components of strong local exchange splitting in Fe and induced polarization in Pd. We identify the spin-orbit coupling (SOC) and the optical intersite spin transfer (OISTR) as the two dominant factors for demagnetization at ultrashort timescales. Remarkably, the drastic difference in the origin of the magnetic moment of the Fe and Pd species is not deciding the initial magnetization dynamics in this alloy. By tuning the external laser pulse, the extrinsic OISTR can be manipulated for site-selective demagnetization on femtosecond timescales providing the fastest way for optical and selective control of the magnetization dynamics in alloys. Saliently, our results signify why various experiments demonstrating OISTR might obtain conflicting results.

Characterization of bilateral, pudendal nerve-evoked, urethral rhabdosphincter contractions in anesthetized cats

Pudendal (PUD) efferent activity contracts urethral rhabdosphincters to resist urine leakage. This study evaluates the potential for PUD nerve stimulation to provide benefit for urinary incontinence. Acute responses of the urethral rhabdosphincter to modulation of current amplitude, pulse duration (PD), and frequency of stimulation were examined. Urethral pressure was measured using a microtip catheter in chloralose-anesthetized, male cats with or without acute spinalization at T10. Stimulation was applied from an external pulse generator coupled to cuff electrodes placed around left and right PUD nerves in the ischiorectal fossa, central to its branching. Bladder pressure clamp techniques were used for testing effects of stimulation on time and rate of leakage during PUD stimulation. Single pulses (0.1 ms) produced single transient increases in urethral pressure that peaked at 50 ms and diminished to 50% of peak at 90 ms. Threshold current was 88 ± 30μA with maximal responses occurring with 50% increases in current. Peak pressures increased with increasing PDs between 40–180μs. Summation, tetany, peak pressures, and fatigue of responses to increasing stimulation frequencies during 2 min periods of stimulation are described. Stimulation under pressures that are typical during bladder filling or during bladder contractions (30–40 cm H2O) prevented leakage up to an hour in some animals, increased the median time to leak from 0.3 min to 56.0 min, and decreased the median rate of leakage from 1.44 ml/min to 0.04 ml/min when leakage did occur in less than hour. During rapid elevations in bladder pressure to simulate a Valsalva-like bladder pressure (120 cm H2O), PUD stimulation increased the median time to leak from 9 s to 93 s and decreased the median rate of leakage from 5.5 ml/min to 3.4 ml/min. These results support future studies of bilateral PUD stimulation in a clinically-relevant, animal model of urinary incontinence.

Impact of the structure on the thermal burnout effect induced by microwave pulses of PIN limiter diodes

Positive-intrinsic-negative (PIN) limiters are widely used to protect sensitive components from leakage power itself and adjacent high-power injection. Being the core of a PIN limiter, the PIN diode is possible to be burnt out by the external microwave pulses. Here, using a parallel computing program for semiconductor multi-physics effects designed by ourselves, we studied the influence of the thickness of the I layer and the anode diameter of the PIN diode on the maximum temperature change curve of the PIN diode limiter. The damage threshold criterion in the numerical simulation was first studied by comparing experimental results with simulation results. Then, we determined the impact of the structure on the thermal burnout effect induced by microwave pulses of PIN limiter diodes.

Advanced Stabilization Methods of Plasma Devices for Plasma-Based Acceleration

Towards the next generation of compact plasma-based accelerators, useful in several fields, such as basic research, medicine and industrial applications, a great effort is required to control the plasma creation, the necessity of producing a time-jitter free channel, and its stability namely uniformity and reproducibility. In this Letter, we describe an experimental campaign adopting a gas-filled discharge-capillary where the plasma and its generation are stabilized by triggering its ignition with an external laser pulse or an innovative technique based on the primary dark current (DC) in the accelerating structure of a linear accelerator (LINAC). The results show an efficient stabilization of the discharge pulse and plasma density with both pre-ionizing methods turning the plasma device into a symmetrical stable accelerating environment, especially when the external voltage is lowered near the breakdown value of the gas. The development of tens of centimeter long capillaries is enabled and, in turn, longer acceleration lengths can be adopted in a wide range of plasma-based acceleration experiments.

Selective tuning of order parameters of multiferroicBiFeO3in picoseconds using midinfrared terahertz laser pulses

Selectively tuning the properties of a material with multiple order parameters, such as polarization and magnetization, requires precise control of the crystal structure. Recently developed midinfrared THz laser techniques provide an efficient way to manipulate the structure of materials at an ultrafast rate. This paper presents a methodology to evaluate the possibility of picosecond multiple switching of order parameters in perovskite structure oxides using first-principles calculations. With multiferroic ${\mathrm{BiFeO}}_{3}$ as a model system, we demonstrate that the desired property can be tuned by an external laser pulse's perturbation with frequency 15.2 THz. The dynamics of phonon modes are illustrated, revealing that lasers enable switching of polarization and magnetization within 1 ps. The switching mechanisms can be attributed to the nonlinear coupling of the pumped infrared-active mode with the ferroelectric and antiferrodistortive modes. Our work provides an initiative for more detailed experimental investigations to explore light control orders and dynamic material design.

Interactions of the second-order solitons with an external probe pulse in the optical event horizon

We demonstrate manipulating the interactions of a second-order soliton with a weak probe pulse under the condition of group velocity match and group velocity mismatch (GVMM). During these interactions, the second-order soliton acting as an effective periodic refractive-index barrier leads to the polychromatic scattering of the probe pulse, which is represented as unequally spaced narrow-band sources with adjustable spectral width. In the case of GVMM, almost all the spectral components of the narrow-band sources meet the nonlinear frequency conversion relationship by using the wavenumber-matching relationship due to the robustness of the second-order soliton under moderate high-order-dispersion perturbations, so this case is more conducive to the study of the soliton wells. In addition, different transmission states of a soliton well are demonstrated under different probe pulse properties in the fiber-optical analog of the event horizon. When the power of the probe pulse is strong enough, a dispersive wave can be generated from the collision of two fundamental solitons split from the two second-order solitons. These interesting phenomena investigated in this work as a combination of white- and black-hole horizons can be considered as promising candidates for frequency conversion and broadband supercontinuum generation.

Real world experience with minimally invasive wireless percutaneous neuromodulation in a tertiary care centre.

Wireless percutaneous nerve stimulation (PNS) for chronic pain is rapidly evolving in the ever expanding neuromodulation paradigm. Safety and lower risks with a potential of long-term analgesia cannot be over emphasised especially with the ongoing opioid pandemic. PNS with an implanted pulse generator (IPG) has also been shown to provide good benefit, without often unpleasant widespread paraesthesia from conventional spinal cord stimulators. We retrospectively extracted data on all wireless PNS implants in our highly specialised pain neuromodulation centre since initiation of wireless PNS service in August 2019. Patient demographics, pain history, analgesic intake and details on implant follow-up data within 1year post-implant including pain relief, EuroQol-5 Dimension (EQ-5D) and Patients' Global Impression of Change (PGIC) scores were extracted. The cases are presented in a narrative format. A total of five patients were implanted with wireless (Stimwave®) PNS from August 2019 to February 2020. Neuropathic pain was the most common presenting diagnosis. All patients showed >50% pain relief at 3months. EQ-5D and PGIC did not show any improvement in the subjects. Two of the patients managed to decrease their analgesics after implantation. Similar sustained benefits could not be demonstrated after 1year. PNS can provide analgesia in appropriately selected cases. Naivety of the technique and procedure might cause some degree of uncertainty. External pulse generator with wireless transmission avoids IPG and tunnelling related side effects, but requires individualised special wearable technology to power the lead. Minimally invasive nature of the technique might be attractive and preferable for patients with complex medical issues, nickel allergy and poor general health who may otherwise be unsuitable for Spinal Cord Stimulation (SCS) with conventional hardware. Robust prospective controlled studies and RCTs in future might provide further insights on utility in other neuropathic pain diagnosis, long-term outcomes and acceptability compared to conventional SCS.