Negative Pulse Research Articles

A Light‐Stimulus Flexible Synaptic Transistor Based on Ion‐Gel Side‐Gated Graphene for Neuromorphic Computing

Optogenetic technology is to express the channel proteins that can be act on light for realizing the activity of neurons activated and inhibited. Here, inspired by optogenetics, a flexible side‐gate artificial synaptic transistor based on ion gel and graphene is demonstrated, where the long‐term remembering or forgetting could be activated by the 450 nm light stimulus. Taking advantage of in‐plane‐field tunable carrier transport in graphene and the high ionic motion of ion gels, various synaptic functions under flatting or bending conditions by electric stimuli are successfully mimicked, including inhibition postsynaptic current, excitatory postsynaptic current, and paired‐pulse facilitation. A light‐induced forgetting or remembering is demonstrated by long‐term synaptic plasticity under 20 s and 10 Hz positive or negative gate pulse stimulus in the dark and 4 min recovery with light illumination. Moreover, the light stimulus promotes the associative learning and remembering function, which is demonstrated by Pavlov's dog experiment with electrical pulses and light stimulus. Such light‐assisted learning and memory function on synaptic plasticity can be attributed to the photogenerated electrons trapping effects in our device. The authors’ results provide a feasible strategy for realizing flexible light–electrical‐stimulus synaptic transistors and developing the low‐energy flexible neuromorphic optoelectronic hardware platform.

Gait regulation using monopolar intraspinal micro-stimulation of spinal cord central pattern generator: New insights for improving Hodgkin–Huxley model

Restoring the motor function of paralyzed limbs has always been an important aim in the field of biomedical engineering. In view of the discovery of the repeatable experimental phenomenon that positive and negative stimulation pulses applied to specific points, identified as central pattern generator (CPG) sites, could induce switching of the movement patterns of bilateral hindlimbs, an improved Hodgkin–Huxley (HH) neuron model was established by introducing the electric field effect principle. A CPG neural network model comprising 12 neural units in six joints of the bilateral hindlimbs was modeled. The simulation results showed the alternating movement patterns of the bilateral hindlimbs through the action potential release of extensor and flexor neurons. The explosive electromyogram of the gastrocnemius (GM) and quadriceps femoris (QF) when stimulating the CPG sites with intraspinal micro-stimulation (ISMS) was consistent with the action potential diagram of the flexor and extensor neurons obtained via simulation. Our research considers the neural network model of electric field radiation, which can facilitate a deep understanding of the dynamic characteristics of neurons in the electric field environment, and verifies the correlation between the location of CPG sites, stimulus polarity and movement patterns to induce alternating left–right coordinated movements.

Laser-induced shock-wave-expanded nanobubbles in spherical geometry

The secondary cavitation generation following laser-induced breakdown in aqueous media in spherical geometry, mimicking the geometry of the frontal part of the human eye, was studied. A numerical simulation of the shock wave propagation was performed, yielding peak-pressure maps, correctly predicting the location of the secondary cavitation onset for different shock wave source positions. The comparison between the simulation results and the experiments, performed with a high-precision, multiple-illumination technique, supports the suggested description of the nature of the secondary cavitation onset. It is shown that large transient negative pressures are created at the location of the acoustic image of the shock wave source, which is different from the optical focus. After the passage of the shock wave, abundant secondary cavitation is generated there. Additionally, the existence of an important contributing factor to the reduction of the secondary cavitation threshold is supported by the experimental results, namely the pre-illumination of the water by the breakdown-generating laser pulse, playing a crucial role in conditioning the medium. There is strong experimental evidence of the existence of another mechanism of pre-conditioning the water for the secondary cavitation onset, namely in the form of repetitive negative pressure pulse passage through the same volume, an indication of a possible two- or multiple-stage process.

Adjustment of high-energy ion flux in BP-HiPIMS via pulsed coil magnetic field: plasma dynamics and film deposition

As an emerging and extraordinary plasma source, bipolar pulsed high power impulse magnetron sputtering (BP-HiPIMS) discharge has been widely concerned by academia and industry due to the ability to control the deposited ion energy. In the present work, with the intension of increasing the high-energy ion fraction and flux during deposition, the BP-HiPIMS is operated together with a solenoidal coil installed in front of the target. This intension is achieved by applying a pulsed coil current so that the ions generated during the high-power negative pulse can be manipulated to diffuse towards substrate and then arrive at the substrate surface during the positive pulse. Systematic investigations of discharge characteristics and plasma parameters for Ti target discharge in Ar gas have been made, illustrating that applying a pulsed coil current prior to the positive pulse onset for ∼50 μs is an optimal selection to obtain a larger fraction of high-energy ions. The complex plasma dynamics has also been explored using the particle-in-cell/Monte Carlo collision approach. To verify the statements realized by plasma measurements, the Ti films have been deposited on a floating Si substrate, whose microstructure and surface morphology are characterized by field emission scanning electron microscope and atomic force microscope. The deposition illustrates that applying a pulsed coil current prior to the positive pulse onset for ∼50 μs can prepare a thicker, denser, and smoother Ti film. The link between the plasma parameters and film microstructure is studied using the molecular dynamics simulations which show that the high-energy ions contribute to optimizing the adatom diffusion and mobility on growing film surface, which is more beneficial to get a smaller grain size and decrease the film surface roughness.

Characterization of the effects of high-intensity negative current pulses on metal transfer and melting rate in the AC-GMAW process

The use of variants of the gas metal arc welding (GMAW) process has become an affordable option in industry. Alternating current–gas metal arc welding (AC-GMAW) arises as one of them, providing additional degrees of freedom for process controllability and versatility. This study focused on the analysis of a complex waveform of the AC-GMAW process for welding stainless steel, employed in modern synergic programs, which has not been widely disseminated in the technical literature and assessed scientifically. The main objective was to characterize the effects of high-intensity pulses in negative polarity over the process and to discuss the potential of this strategy, since it has not been used in conventional AC synergic programs. In order to bring to light information on the phenomena involved, such as the arc climbing on the wire electrode, advanced techniques of high-speed videography were used, synchronized with the acquisition of electrical welding process signals, as well as infrared thermography, to verify the evolution of the cooling of the piece after welding. The results grounded discussions on different AC-GMAW waveforms. The process’ electrical data, along with images of the arc and analysis of the wire melting and workpiece thermal behavior, showed that there was a significant visible increase in wire melting during the negative pulse. In addition, it evidenced how the negative electrode increment contributed to the increase in wire melting even at lower power and also showed the thermal effects on the workpiece.

Influence of unipolar pulse time offset between Ti and Zr dual cathodes in closed magnetic field high power impulse magnetron sputtering

Titanium/zirconium dual cathodes with a closed magnetic field configuration were used in unipolar high power impulse magnetron sputtering (HiPIMS). Different pulse width (pulse on time) and pulse time offset between the negative voltage pulses of two targets were applied. The target discharge current waveforms and consequent substrate current waveforms were recorded and compared. The results show that both ion fluxes emitted from the Ti and Zr cathodes increase with the argon pressure. However, the ion flux emitted from the Zr cathode increases more substantially at high argon pressure. The closed magnetic field raises the target discharge current and ion flux to the substrate when the pulses of the two targets are simultaneous synchronized, or followed closely. The TiZr film composition is influenced by the HiPIMS discharge behavior of each target material more than by the average power ratio of each target. For low working pressure and short pulse width, simultaneous synchronization of the pulses on the two targets might effectively use the electrons drifting between the dual targets to enhance the generation of ions from both targets. For high working pressure and long target pulse width, setting pulses on two targets following closely is recommended to additionally utilize the runaway ions as pre-ionized media for the follow-up pulse on the adjacent target.

An Energy Efficient Process for Degrading Perfluorooctanoic Acid (PFOA) Using Strip Fountain Dielectric Barrier Discharge Plasma

Perfluorooctanoic acid (PFOA) is an artificially synthesized per-fluorinated chemical widely used in industry. It is often released into the environment without treatment and causes pollution in groundwater. In this paper, we employed a strip fountain dielectric barrier discharge (SF-DBD) plasma source to degrade PFOA from the water. The effects of power supply mode, discharge gases, pH, the conductivity of the solution, concentration, etc., on the degradation efficiency were studied. For a 200 mL sample of 75 mg/L PFOA, a 99% degradation efficiency with a 204.5 μg/kJ energy production rate was achieved using an average power of 43 W negative pulse argon plasma for 50 min at atmospheric pressure. The total organic carbon concentration (TOC) decreased by 63% after a 60 min treatment. The SF-DBD proves to be a promising and energy-saving technique to efficiently remove PFOA from water.

Braiding Operations for a Topological Josephson Junction Array using SFQ Current Pulses

Majorana bound states (MBSs) can occur in topological Josephson junction (JJ) arrays with the presence of a fractional vortex with 2π-phase winding. It has been theoretically shown that the braiding operation can be achieved by using current pulses, compatible with single flux quantum (SFQ) technology. Therefore, we designed an SFQ logic circuit for the braiding operations of the topological JJ array using single flux quanta in a conventional JJ array. Braiding operations could be realized by an SFQ logic circuit with double flux quantum driver. To obtain positive and negative current pulses using the SFQ logic circuit, we used SFQ logic circuits with ac biasing for simulation. Finally, we confirmed the CNOT operation using an array-type SFQ circuit by means of simulation and estimated the CNOT operation speed.

Application of positive pulse to extract ions from HiPIMS ionization region

High power impulse magnetron sputtering (HiPIMS) is a promising physical vapor deposition technique with one of the main drawbacks being its relatively low deposition rate. In this article, a method was propose by using a positive ions extraction pulse (Uextract) which would be immediately applied to the sputtering target after the HiPIMS negative pulse to extract out the ions from the ionization region near the HiPIMS target. The Particle-In-Cell/Monte Carlo Collision (PIC-MCC) simulation, experiments, and theoretical study were conducted to investigate the ions extraction process. It is demonstrated that the higher potential moved from the target area to the substrate direction and the peak ion density was driven to the substrate direction, after applying the positive ions extraction pulse to the target. The measured ion-energy distribution function (IEDF) characteristics verified that the ions extraction method works. The experimental results indicated that the Ti + ion flux dramatically increased when the Uextract was over 50 V. Good agreement between the experimental and simulation results was obtained, validating the simulation conclusion. Finally, the microscopic mechanism of ions extraction is proposed.

Windmill discharge migration pattern during plasma electrolytic oxidation of aluminium

Plasma electrolytic oxidation process is a surface modification technique using plasma-assisted oxidation to prepare the protective layers that improve the surface performances of valve metals such as aluminium, magnesium, and titanium. However, there is poor understanding and ability to control the process, and many uncertainties. The main objective of this paper is to present the discharge behavior with windmill structure, stable group movement and long-term stability. All processes were carried out on 6061 aluminium alloy by applying a bipolar pulsed current with a frequency of 200 Hz, positive and negative pulse durations of 2 ms, and equal pulse pauses. Utilizing current pulses having equal amplitudes between the positive and negative periods resulted in destructive discharges in the late stage. By adjusting the average positive current at a certain time, destructive discharges were eliminated. Meanwhile, various windmill discharge migration patterns were established, in which collective discharges aggregated into several clusters and rotated as a whole on the sample surface. The number of the clusters was correlated to the average positive current. A complete plasma electrolytic oxidation process was proposed to produce a series of coatings, in which the average positive current was reduced at a rate of 0.1 A·min−1 from 95 min to 100 min, and the windmill discharge migration pattern gradually emerged after 100 min. The proposed method increased the treatment duration from ~95 min to ~180 min compared to the process with no current adjustment. In addition, the thickness, relative content of α- and γ-Al2O3 phases, and Vickers hardness of the coatings were significantly enhanced, allowing for the preparation of high-quality coatings.

Induced voltage at two poles of 10kV parallel distribution line caused by direct lightning strike on the phase wire of adjacent line

Triggered lightning was used to strike different phase wires of a 10 kV double circuit distribution line in 2018. The induced voltage on two poles of the other circuit is analyzed. When it struck on phase A, for the pole close to the strike point, the induced voltage of the lowest phase C is different from that of the two phases, with three obvious negative pulses and one prominent positive pulse. The negative peak of three-phase overvoltage ranges from -11.7 kV to -65.2 kV corresponding to lightning current from -8.3 kA to -18.1 kA. For the three-phase voltage on the pole far away from the strike point, its negative peak is between -10.5 kV and -42.8 kV corresponding to lightning current from -8.3 kA to -26.7 kA. The test method and results proposed in this paper will be helpful to the research on the lightning overvoltage response of parallel power distribution lines.

Spatial inhomogeneous effect on single-order harmonic enhancement

The spatial inhomogeneous effect of the laser pulse on the enhancement of the single-order harmonic has been theoretically investigated. It is shown that the single-order harmonic enhancement from the symmetric and negative inhomogeneous laser pulses presented the similar phenomena. Specifically, as the inhomogeneous parameter increases, the blue-shift of the single-order harmonic enhancement can be found. While in the case of the positive inhomogeneous effect, as the inhomogeneous parameter increases, the multiple harmonic enhancements can be found instead of the single-order harmonic enhancement. Finally, the reason behind the change of the single-order harmonic enhancement with the inhomogeneous effect is given by the time–frequency analyses of the harmonic emission process.

Hybrid electrochemical additive and subtractive manufacturing (HEASM) based on simultaneous mask electrochemical deposition and dissolution

This paper proposed a method for hybrid electrochemical additive and subtractive manufacturing (HEASM) to fabricate microstructures with high-dimensional accuracy and good surface quality. Electrochemical additive manufacturing is achieved by applying positive pulses between the electrodes and then negative pulses are subsequently applied to achieve electrochemical finishing of the shape and surface. In this study, the formation of irregular surface defects was investigated, and a verification experiment was carried out. The inter-electrode pulse waveform and machining process were observed to characterize the electrochemical deposition and dissolution machining. The effects of pure electrodeposition, HEASM, and excessive electrolysis on the surface morphology were compared experimentally. The results indicate that HEASM can reduce the surface roughness by 45.5% but excessive electrolysis can cause a collapse of edge regions. Finally, Taguchi optimization experiments were carried out, and an optimized parameter combination for HEASM was obtained. A microstructure manufactured with an optimized pulse number ratio 0.6 × 10−2, peak current ratio 0.5, and pulse width ratio 1.0 had the best surface morphology and dimensional accuracy. And its surface roughness and height were 0.343 μm and 33.563 μm, respectively.

New Architecture of Solid-State High-Voltage Pulse Generators

The application of the nanosecond pulsed electric field (nsPEF) for biomedical treatments has gained more interest in recent decades due to the development of pulsed power technologies which provides the ability to control the electric field dose applied during tests. In this context, the proposed paper describes a new architecture of solid-state high-voltage pulse generators (SS-HVPG) designed to generate fully customised sequences of quasi-rectangular pulses. The idea is based on the combination of semiconductor switches (IGBT/MOSFET) known for their flexibility and controllability with special magnetic switches to build compact and modular generators. The proposed structure is inspired by the most known pulse generator of Marx, but mixes its two variants for negative and positive polarities. Thus, the polarity of the generated pulses can be freely selected. In addition to that, the use of IGBTs/MOSFET ensures a tunable repetition rate and pulse width. The capacitors are charged via a series of magnetic switches and a flyback DC–DC converter which provides fast and efficient charging and also an adjustable amplitude of the output pulses. The design can be easily simplified giving two other modified structures, based on the same idea, for mono-polar operating (only positive or only negative pulses) with a reduced number of switches. A SPICE simulation of the generator and results of experimental tests carried out on a three stages generator are presented. The obtained results confirm the operating principle and the claimed performances of the new structure.

High voltage pulser for ion shutters in ion mobility spectrometry based on an optocoupler.

A novel high voltage pulser for an ion shutter used in drift-tube ion-mobility spectrometers is described. The simple design suitable for the in-house construction of these spectrometers relies on a special optocoupler to isolate the triggering circuitry from the high voltage at the ion shutter. The device was tested with an electrospray-ionization ion-mobility device with a 10cm drift tube operated at 4kV into which a standard test mixture of four tetraalkylamines was injected with a negative going gating pulse of about 50V on top of 4kV. A fall time of 15.7 µs and a rise time of 2.0 µs were determined for the pulse, which was adequate for the required injection pulse width of 450 µs. Resolving powers between 61 and 81 were determined for the four quaternary amines, which were found to be comparable to the performance obtained with a previously reported pulser circuitry of a different design used as a reference.

Analysis of discharge characteristics of pulsed plasma power source in the microsecond scale

The characteristics test of plasma discharge is an essential physical basis for studying plasma flow control. The power consumption of pulsed plasma aerodynamic actuation is 30% lower than when the actuation voltage is a continuous sine wave. This paper uses a self-developed pulsed plasma power source to superimpose DC. The power source conducts the discharge measurement on the sliding discharge plasma. The experimental results show that the power source effectively outputs 0-20 kV pulsed high voltage. The superimposed DC power source generates a negative DC high voltage, accelerating the drift speed of positive ions in the plasma and forming a stable and uniform surface discharge. But the essence of pulse discharge is still filamentary discharge. In a cycle, the plasma discharge is mainly concentrated on the rising edge of the pulse. In contrast, the pulse current is bipolar, and the negative pulse current has a more obvious growth trend, which is more effective for improving the flow control ability.

Regional genioglossus reflex responses to negative pressure pulses in people with obstructive sleep apnea.

Tongue and upper airway dilator muscle movement patterns during quiet breathing vary in people with obstructive sleep apnea (OSA). Many patients have inadequate or counterproductive responses to inspiratory negative airway pressure that likely contributes to their OSA. This may be due, at least in part, to inadequate or nonhomogeneous reflex drive to different regions of the largest upper airway dilator, genioglossus. To investigate potential regional heterogeneity of genioglossus reflex responses in OSA, brief suction pulses were applied via a nasal breathing mask and an electromyogram (EMG) was recorded in four regions (anterior oblique, anterior horizontal, posterior oblique, and posterior horizontal) using intramuscular fine wire electrodes in 15 people with OSA. Genioglossus short-latency reflex excitation amplitude had regional heterogeneity (horizontal vs. oblique regions) when expressed in absolute units but homogeneity when normalized as a percentage of the immediate (100 ms) prestimulus EMG. Regional variability in reflex morphology (excitation and inhibition) was present in one-third of the participants. The minimum cross-sectional area (CSA) of the pharyngeal airway was quantified using MRI and may be related to the amplitude of the short-latency reflex response to negative pressure as we found that people with a smaller CSA tended to have a greater reflex amplitude (e.g., horizontal region r2=0.41, P = 0.01). These findings highlight the complexity of genioglossus reflex control, the potential for regional heterogeneity, and the functional importance of upper airway anatomy in mediating genioglossus reflex responses to rapid changes in negative pressure in OSA.NEW & NOTEWORTHY Our findings indicate that 30% of participants had regional heterogeneity in reflex morphology (excitation/inhibition) to brief pulses of negative upper-airway pressure across anterior oblique, anterior horizontal, posterior oblique, and posterior horizontal regions of the genioglossus muscle. Reflex excitation amplitude was proportional to prestimulus drive, with increased activation in oblique compared with horizontal regions of the posterior tongue. People with narrower upper-airway anatomy tended to have increased genioglossus reflex amplitude to negative pressure pulses during wakefulness.

Agricultural Diversification in Tamil Nadu – An Economic analysis

In comparison to other Indian states, Tamil Nadu has unique agro-climatic and cropping patterns, which have caused a lot of concern, both environmentally and in terms of food security. From 2001 to 2020, the study examines changes in land use and cropping patterns in Tamil Nadu. Secondary data on area under major crops was gathered from various sources. To assess the expansion of area under major crops over time, the compound growth rate was calculated (2001-2020). In cropping pattern, direction of changes was investigated using Markov chain analysis and for each year, crop diversification index was calculated. The results indicated that land classified as land put to non-agricultural uses and fallow land recorded positive expansion in area. The area under paddy, bajra, sugarcane, groundnut, and gingelly are growing at a negative rate, but maize, pulses, fruits, vegetables, coconut, and cotton are growing at a positive rate. It can be stated that net sown area in Tamil Nadu is declining, with shift in food crops being hurt worse than non-food crops. Based on Crop Diversification Index score, crop intensification has increased in the state over time, helping to reduce failure of crop and income loss while also creating jobs for rural people.

Experimental study on multi-channel ignition of propane-air by transient repetitive nanosecond surface dielectric barrier discharge

Multi-channel ignition by nanosecond surface dielectric barrier discharge (nSDBD) offers potential for efficiency boost in spark ignition engines. In this paper, transient repetitive nSDBD ignition is proposed using a simple pulse forming circuit to make multi-channel ignition more feasible, considering that nSDBD can be enhanced by high frequency pulses and that convenient discharge energy control can be achieved by adjusting pulse number. Ignition experiments for propane/air mixtures were carried out in a constant volume combustion chamber under stoichiometric conditions at ambient initial temperature and pressure. Discharge channel transformation and flame propagation were captured by a high-speed camera. For 20 kHz negative pulses, discharge energy rose from 4 mJ to 8 mJ as pulse number increases from 1 to 12, and filaments grew from 2 mm to 12 mm. Partially overlapping filaments formed a tree-like discharge pattern with divergent roots and a concentrated middle part. Multiple flame kernels were generated in the middle region of the filaments and then greatly promoted by subsequent discharges, resulting in a petaloid flame. Ignition probability has been tested and the minimum ignition energy of repetitive nSDBD is obtained. The influence of discharge energy on flame propagation speed and combustion characteristics were analyzed.

Ion energy analysis of a bipolar HiPIMS discharge using a retarding field energy analyser

The time evolution of the positive ion energy distribution functions (IEDF’s) at the substrate position in an asymmetric bipolar high-power impulse magnetron sputtering (HiPIMS) system was determined using a gridded energy analyser. This was done for a range of operating conditions, namely the positive voltage U rev and ‘on-time’ negative pulse duration τ neg. The magnetron sputtering discharge was equipped with a Nb target. Based on the knowledge of the IEDF’s, the bombarding ion flux density Γi and energy flux density Q i to a grounded surface were calculated. Time-resolved IEDF measurements showed that ions with energies approaching the equivalent of the positive pulse voltage U rev were generated as the reverse positive voltage phase developed. On time-average, we observed that increasing the set U rev value (from 0 to 100 V), resulted in a marginal decrease in the ion flux density Γi to the analyser. However, this is accompanied by a five-fold increase in the ion energy flux density Q i compared to the unipolar, U rev = 0 V case. Reducing the negative HiPIMS pulse duration τ neg (from 130 to 40 μs) at a constant discharge power leads to a modest increase in Γi, but a four-fold increase in Q i. The results reveal the benefit of the bipolar HiPIMS technique, in which it is possible to control and enhance the power density of ions bombarding a grounded (or fixed bias) substrate, for potentially better tailoring of thin film properties.