Increasing Number Of Pulses Research Articles

Experimental study on multi-point ignition of NH3/air by high-frequency nanosecond dielectric barrier discharge

Non-equilibrium plasma ignition technology, with its ability to expand ignition limits and increase ignition volume, is considered an important development direction of advanced ignition systems, and has significant advantages in improving ignition stability and combustion rate. This study investigates the ignition and combustion assistance effect of high-frequency nanosecond surface dielectric barrier discharge (nSDBD) on NH3/air mixture in a constant volume combustion chamber (CVCC). The study reveals the influence of high-frequency nSDBD on the growth process of the flame kernel in NH3/air mixture. As the discharge pulse number (PN) increases, the flame kernel develops from the middle position of the discharge filament to the head of the discharge filament, while there is no obvious flame at the root and middle of the discharge filament. Continuous discharge causes the flame kernel to appear concave and the center of the flame kernel to shift towards the wall of the CVCC. In the NH3/air mixture, the initial flame kernels exhibit dissipation phenomenon, resulting in a discrepancy between the number of initial flame kernels and the number of stable combustion flame kernels. As the discharge frequency or pulse number increases, and the number of stable combustion flame kernel increases. The adjustment of discharge frequency and pulse number can effectively control the flame development time (FDT) and flame rise time (FRT) of NH3/air mixture. As PN increases, both FDT and FRT are shortened. When discharge frequency is 20 kHz, the maximum shortening of FDT and FRT are 30 ms and 14 ms, respectively, about 55 % and 30 %. The effects of discharge frequency on FDT and FRT exhibit a non-monotonic variation pattern, and it is necessary to comprehensively consider various discharge parameters to achieve the best ignition effect. The ignition success rate curve of high-frequency nSDBD in NH3/air mixture is steep. The study results of this paper provide new discoveries and experimental data for advanced ignition systems.

Interplay between Electric Field Strength and Number of Short-Duration Pulses for Efficient Gene Electrotransfer.

Electroporation is a method that shows great promise as a non-viral approach for delivering genes by using high-voltage electric pulses to introduce DNA into cells to induce transient gene expression. This research aimed to evaluate the interplay between electric pulse intensity and 100 µs-duration pulse numbers as an outcome of gene electrotransfer efficacy and cell viability. Our results indicated a close relationship between pulse number and electric field strength regarding gene electrotransfer efficacy; higher electric pulse intensity resulted in fewer pulses needed to achieve the same gene electrotransfer efficacy. Subsequently, an increase in pulse number had a more negative impact on overall gene electrotransfer by significantly reducing cell viability. Based on our data, the best pulse parameters to transfect CHO cells with the pMax-GFP plasmid were using 5 HV square wave pulses of 1000 V/cm and 2 HV of 1600 V/cm, correspondingly resulting in 55 and 71% of transfected cells and maintaining 79 and 54% proliferating cells. This shows ESOPE-like 100 µs-duration pulse protocols can be used simultaneously to deliver cytotoxic drugs as well as immune response regulating genetically encoded cytokines.

The ablation threshold and incubation effect in picosecond laser surface treatment of CFRP

The ablation threshold of carbon fiber is a critical parameter to consider in the laser surface treatment of carbon fiber reinforced polymers (CFRP), as it is necessary to design process parameters based on the threshold fluence to ensure process quality and efficiency. The incubation effect is a key factor influencing the ablation threshold, and a more rational incubation model contributes to a more accurate prediction of the ablation threshold. The conventional incubation model describes the regular decrease of the ablation threshold with an increasing pulse number. However, experimental findings show that the time interval of pulses is also a significant factor affecting the ablation and incubation process. In this study, the conventional incubation model was improved by comprehensively considering the time interval and space interval of pulses, which shows better prediction ability of ablation threshold under different parameter sets. The temperature history of CFRP under picosecond laser irradiation was calculated to support the rationality of the optimized incubation model. In addition, the laser-induced periodic surface structures (LIPSS) and the ablation of carbon fibers and resin were investigated based on the ablation threshold.

Atomistic-Continuum Study of an Ultrafast Melting Process Controlled by a Femtosecond Laser-Pulse Train.

In femtosecond laser fabrication, the laser-pulse train shows great promise in improving processing efficiency, quality, and precision. This research investigates the influence of pulse number, pulse interval, and pulse energy ratio on the lateral and longitudinal ultrafast melting process using an experiment and the molecular dynamics coupling two-temperature model (MD-TTM model), which incorporates temperature-dependent thermophysical parameters. The comparison of experimental and simulation results under single and double pulses proves the reliability of the MD-TTM model and indicates that as the pulse number increases, the melting threshold at the edge region of the laser spot decreases, resulting in a larger diameter of the melting region in the 2D lateral melting results. Using the same model, the lateral melting results of five pulses are simulated. Moreover, the longitudinal melting results are also predicted, and an increasing pulse number leads to a greater early-stage melting depth in the melting process. In the case of double femtosecond laser pulses, the pulse interval and pulse energy ratio also affect the early-stage melting depth, with the best enhancement observed with a 2 ps interval and a 3:7 energy ratio. However, pulse number, pulse energy ratio, and pulse interval do not affect the final melting depth with the same total energies. The findings mean that the phenomena of melting region can be flexibly manipulated through the laser-pulse train, which is expected to be applied to improve the structural precision and boundary quality.

Digital and Analog Resistive Switching Behavior in Si-NCs Embedded in a Si/SiO2 Multilayer Structure for Neuromorphic Systems

In this work, we report the digital and analog resistive-switching (RS) characteristics in a memristor based on silicon nanocrystals (Si-NCs) integrated into a complementary metal-oxide-semiconductor (MOS) structure. Si-NCs with a diameter of 5.48 ± 1.24 nm embedded in a SiO2/Si-NCs/SiO2 multilayer structure acts as an RS layer. These devices exhibit bipolar RS with an intermediate resistance step during SET and RESET processes, which is believed to lie in the Si-NCs layer acting as charge-trapping nodes. The endurance studies of about 70 DC cycles indicate an ON/OFF ratio of ~106 and a retention time larger than 104 s. Long-term potentiation (LTP, -2 V) and long-term depression (LTD, +4 V) are obtained by applying consecutive identical pulse voltages of 150 ms duration. The current value gradually increases/decreases (LTP/LTD) as the pulse number increases. Three consecutive identical pulses of -2 V/150 ms (LTP) separated by 5 and 15 min show that the last current value obtained at the end of each pulse train is kept, confirming an analog RS behavior. These characteristics provide a possible way to mimic biological synapse functions for applications in neuromorphic computing in Si-NCs-based CMOS structures.

Laser ablation of RB-SiC composite by femtosecond laser irradiation

Reaction-bonded silicon carbide composites (RB-SiC), consisting of SiC grains and Si matrix, have a complex ablation mechanism as two-phase composites under femtosecond laser irradiation. The ablation threshold of RB-SiC was calculated, which decreases (from 1.01 J/cm2 to 0.56 J/cm2) with increasing pulse number N and finally stabilized. At low fluence (F/Fth ≤ 5) and a low number of pulses, photochemical ablation dominates. For a higher number of pulses and high fluence (5 <F/Fth ≤ 50), photothermal ablation dominates with photochemical ablation. The results show that structures such as pits, convex, and holes exist on the surface of Crater I, while Laser-induced Periodic Surface Structures (LIPSS), and condensation structures exist on the surface of Crater II. In both types of ablation craters, the SiC grain surface produces the Low Spatial Frequency LIPSS (LSFL) with a period of about 900 nm and the High Spatial Frequency LIPSS (HSFL) with a period of about 300 nm. Based on the surface morphology, microstructure, and physical phase analysis of the ablation craters, a preliminary model of the removal mechanism of the ablation craters by femtosecond laser irradiation was established. These findings are expected to provide theoretical and experimental support for the precision processing of RB-SiC by femtosecond laser.

Theoretical and Experimental Studies on Ultraviolet Nanosecond Laser Micromachining of Sapphire

The micromachining of sapphire by laser has dominated research in resent years. This paper provided theoretical and experimental studies of the micromachining of sapphire based on the UV nanosecond laser. The results indicate that the ablation is dominated by the photochemical and photo-thermal through a finite element analysis. The single-pulse ablation threshold of UV nanosecond on sapphire is 15.58 J/cm2, and the ablation threshold gradually decreases and tends to stable finally with the increase of pulse number. Furthermore, the experiment proves that the ablation morphology with a smooth surface and little molten sediment can be realized by optimizing laser processing parameters.

Survival model database of human digestive system cells exposed to electroporation pulses: An in vitro and in silico study.

Background and objectivesThis study aimed to establish a mathematical survival model database containing cell-specific coefficients from human digestive system cells exposed to electroporation pulses (EPs).Materials and methodsA total of 20 types of human digestive system cell lines were selected to investigate the effect of EPs on cell viability. Cell viability was measured after exposure to various pulse settings, and a cell survival model was established using the Peleg–Fermi model. Next, the cell-specific coefficients of each cell line were determined.ResultsCell viability tended to decrease when exposed to stronger electric field strength (EFS), longer pulse duration, and more pulse number, but the decreasing tendency varied among different cell lines. When exposed to a lower EFS (<1,000 V/cm), only a slight decrease in cell viability occurred. All cell lines showed a similar tendency: the extent of electrical injury (EI) increased with the increase in pulse number and duration. However, there existed differences in heat sensitivity among organs.ConclusionsThis database can be used for the application of electroporation-based treatment (EBT) in the digestive system to predict cell survival and tissue injury distribution during the treatment.

Theoretical analysis on the forced ignition of a quiescent mixture by repetitive heating pulse

Recently, forced ignition by nanosecond-repetitive-pulsed-discharge (NRPD) has received great attention since it can greatly promote ignition. However, there is no theoretical analysis on ignition induced by multiple heating pulses such as NRPD. Therefore, this work attempts to provide a theoretical interpretation on the ignition of a quiescent, flammable mixture by multiple discharges and to assess the effects of repetitive pulse on ignition characteristics. Based on fully transient formulation, analytical expressions describing ignition kernel propagation induced by multiple pulses are derived. The key parameters of multiple pulse heating, such as energy distribution among individual pulse, intermittent duration between neighboring pulse and total pulse numbers are appropriately incorporated, and their effects on ignition characteristics are assessed. It is found that because of memory effect, the flame kernel continues to propagate after switching off the external heating source. Sequentially introducing identical heating pulses at appropriate intermittent duration repetitively exploits the memory effect during ignition kernel development and thus extends propagating distance of the flame front. The repetitive pulse heating can promote ignition capability due to the flame revitalization effect, i.e., ignition reinforcement to the flame front thanks to additional thermal energy supplied by subsequent pulse. This is consistent with the synergistic effect of NRPD observed in previous experimental studies. In particular, as the pulse number increases, the minimum ignition energy decreases and approaches to an asymptotic value. In the limit of large pulse number, it is found that the integration of the implicit expressions describing the ignition kernel evolution does not depend on the pulse number explicitly. This substantiates the invariance of minimum ignition energy with heating pulse number. The present theory explains the effects of multiple discharges on ignition and provides insights on ignition enhancement.

POLARIZATION CONTROLLED BIREFRINGENCE IN LITHIUM ALUMINOSILI-CATE GLASS

The rise of polarization-controlled birefringence under a series of femtosecond laser pulses in the bulk of lithium silicate and lithium aluminosilicate glasstentatively attributed to the formation of nanogratings is demonstrated. The dependences of the retardance of the light passing through the modified regions on the parameter of laser radiation and the chemical composition of the glass are determined. It is shown that an increase of Al2O3 content at the expense of alkali content in glass composition leads to an increase in the minimum number of pulses for the formation of a birefringent region, as well as an increase in the retardance.

Laser damage threshold of Ge8As23S69 films irradiated under single- and multiple-pulse femtosecond laser

In this study, the single- and multiple-pulse laser-induced surface damage characteristics of the Ge8As23S69 chalcogenide film under the femtosecond laser irradiation were experimentally investigated. The 1-on-1 and S-on-1 methods were utilized to measure the femtosecond laser damage by using single and multiple pulses, respectively. The femtosecond laser-induced damage threshold (LIDT) was obtained using linear regression method by measuring the damage morphology under different pulse energies and pulse numbers of the femtosecond laser. Results show that the LIDT of the film under single-pulse radiation is higher than that under multiple-pulse radiation because of accumulation and defect effects. For the single-pulse radiation, LIDT is attributed to the field enhancement effect, multiphoton ionization, and avalanche ionization. The single-pulse damage threshold of Ge8As23S69 films is 232.548 mJ/cm2. For the multiple-pulse radiation, the LIDT of the film decreases with increasing pulse number due to accumulation and defect effects.

High Transient-Thermal-Shock Resistant Nanochannel Tungsten Films.

Developing high-performance tungsten plasma-facing materials for fusion reactors is an urgent task. In this paper, novel nanochannel structural W films prepared by magnetron sputtering deposition were irradiated using a high-power pulsed electron beam or ion beam to study their edge-localized modes, such as transient thermal shock resistance. Under electron beam irradiation, a 1 μm thick nanochannel W film with 150 watt power showed a higher absorbed power density related cracking threshold (0.28–0.43 GW/m2) than the commercial bulk W (0.16–0.28 GW/m2) at room temperature. With ion beam irradiation with an energy density of 1 J/cm2 for different pulses, the bulk W displayed many large cracks with the increase of pulse number, while only micro-crack networks with a width of tens of nanometers were found in the nanochannel W film. For the mechanism of the high resistance of nanochannel W films to transient thermal shock, a residual stress analysis was made by Grazing-incidence X-ray diffraction (GIXRD), and the results showed that the irradiated nanochannel W films had a much lower stress than that of the irradiated bulk W, which indicates that the nanochannel structure can release more stress, due to its special nanochannel structure and ability for the annihilation of irradiation induced defects.

Determining tissue conductivity in tissue ablation by nanosecond pulsed electric fields

Nanosecond pulsed electric field (nsPEF) causes the permeabilization of the cell membrane and has been used to non-thermally treat cancerous tissues. As increased permeabilization in membranes were reported to be accompanied by impedance changes, the ablation effect of nsPEF on tissues can be monitored via the changes in tissue conductivity. In this study, effects of nsPEF on biological tissues were evaluated by determining the conductivities of potato and 4 T1-luc breast tumor tissues ex vivo from a murine model subjected to multiple 100-ns, 1–10 kV pulses. Using a four-needle electrode system with a calibrated electrode constant of 1.1 ± 0.1 cm, the conductivities of tissues was determined from both the network-analyzer measurement, before and after treatment, and voltage-current measurement in real-time. The conductivity of the potato tissue was measured for a frequency range of 0.1–3 MHz, and it increased with increasing pulse number and voltage amplitude. The conductivity of the tumor tissue was also observed to increase with pulse number and pulse voltage over a similar frequency range. In addition, the linear correlation between the ablation area in a treated potato tissue and the conductivity change in the tissue suggests that conductivity analysis of biological tissue under treatment could be a fast and sensitive approach to evaluate the effectiveness of a nsPEF treatment.

Experimental study on the accumulative effect of multiple pulses on acceleration sensor

Intentional electromagnetic interference is a serious threat to the safety of electronic devices. Multiple electromagnetic pulses will be coupled and transmitted to electronic devices through the cables. Accumulative effects are generated, which make it easier for damage to occur in the electronic devices. In this article, the working principle of micro-silicon acceleration sensors is introduced. The accumulative effects of multiple pulses on acceleration sensors is studied by a large number of injection experiments. The accumulation trends of multiple pulses with different pulse numbers and intervals are analyzed. The damaged structures inside abnormal sensor amplifiers were observed via optical microscopy and scanning electron microscopy. The experimental results show that the accumulative effect is strengthened with increased pulse number or decreased pulse interval, and the threshold voltage for multiple pulses on the acceleration sensor decreases. The threshold voltage for a single pulse is 321.57 V. When the pulse interval is 1 μs and the pulse number is 5, the threshold voltage for multiple pulses is 163.42 V, which is reduced by 49.12% compared with a single pulse. These results provide a reference for the damage design of electromagnetic pulse weapons.

Picosecond laser induced periodic surface structures on K9 glass

In this paper, LIPSS (laser-induced periodic surface structures) are generated on the K9 glass surface by using an ultrashort pulsed laser with pulse width of 8 ps, wavelength of 532 nm and repetition frequency of 1 KHz. Two kinds of LIPSS are generated on the surface of K9 glass, in the laser fluence range from 1.52 J/cm 2 to 9.38 J/cm 2 and pulse number from 1 to 50, namely low space frequency LIPSS (LSFL) and supra-wavelength periodic surface structures (SWPSS). When the laser fluence is increased, LSFL ( F = 1.9 J/cm 2 ~ 9.38 J/cm 2 ) can be generated on the surface of K9 glass. LSFL with a period in the range of 480 nm to 510 nm are found with 1 to 20 pulses when the laser fluences higher than 1.9 J/cm 2 . For low pulse numbers, the depth of the LSFL structures grows with increasing pulse number. It is noticed that when the laser fluence reaches the threshold of the LIPSS (LSFL), the formation of the LIPSS happened together with the removal of the material surface. In other words, the ablation craters are formed gradually at higher pulse numbers with the laser fluence above the LIPSS formation threshold. Furthermore, the depth of the ablation crater is increased with higher pulse numbers, and SWPSS appear at the bottom of the crater. The period of SWPSS is 1.2 μm to 1.5 μm. The LSFL found in this paper can be used to reduce the reflection coefficient of the K9 material from 4% to less than 2.2 % at wavelengths above 1.2 μm.

Amorphization and Nano-Crystallization of Ni-Nb Coating on GH3039 Alloys by High Current Pulsed Electron Beam.

In this paper, the Ni-Nb coatings were successfully prepared onto the GH3039 alloys by High current pulsed electron beam (HCPEB). The transmission electron microscopy (TEM) results confirmed that the Ni-Nb layer of 10-pulsed samples exhibited partial amorphization, which was consisted of γ-Ni particles, rod-like Ni3Nb particles and nano Ni3Nb with 30 nm in size. After 20-pulsed irradiation, the results show that only Ni3Nb clusters with around 3 nm in size were dispersed in fully amorphization layer. With increased pulse number to 30, the nano-particles embedded into the amorphous layer were grown up, the size of which was about 8 nm. The microstructure evolution during HCPEB irradiation was from the partial amorphous to fully amorphous and then to nano-crystallization. The 20-pulsed samples possessed the best hardness and corrosion resistance. The ultrafine clusters uniformly embedded into amorphous layer were main reason for improving properties.

Analysis on reversible/irreversible electroporation region in lung adenocarcinoma cell model in vitro with electric pulses delivered by needle electrodes

Irreversible electroporation (IRE) is a minimally invasive tumor therapy using pulsed electric field with high intensity while the important tissues such as blood vessel, bile duct, and nerve are preserved. In addition to ablation area, reversible electroporation (RE) region is also generated using needle electrodes for pulse delivery. The goal of this work is to study the generation of RE region and ablation region on a 2D lung adenocarcinoma cell model in vitro. The tumor model is exposed to electric pulses with various number. The calcium AM and propidium iodide (PI) are examined to detect the ablation area and electroporation area, respectively. The results show that electroporation area firstly tends to plateau after approximately 50 pulses, while the ablation area continues to increase. The percentage of IRE area in total electroporation area increases with additional pulses, which means that RE region could be gradually turned into ablation area with increased pulse number. However, the percentage of IRE area only achieves to 54% for 200 pulses, which indicates that RE region still cannot be completely removed. RE and IRE thresholds appear to converge as the number of pulses increases. An equation between pulse number and the electric field threshold of ablation including the electric field threshold of RE is also provided for lung adenocarcinoma cell ablation. This work may have the value for the optimization of IRE protocols on tumor ablation.

Pre-weakening behavior of magnetite quartzite based on high-voltage pulse discharge

To ascertain the mechanism that the ore grinding characteristics were improved by high-voltage pulse discharge (HVPD) pre-treatment, an innovative experiment system was performed on magnetite quartzite. The HVPD pre-treatment improved the −0.074 mm mass fraction in ground products, and the increase in pulse number effectively enhanced the mass fraction. The values of relative grindability (K1 and K2) increased with the pulse number significantly, whereas their value reduced as the grinding fineness and grinding time extended. A laser particle size analysis showed that the distribution of HVPD pre-treatment products was uniform. The particle size distribution and cumulative distribution curves satisfied the lognormal distribution function and power function, respectively. The Brunauer–Emmett–Teller (BET) analysis indicated that the specific surface area, total pore volume, and the porosity of crushed products were improved effectively by the HVPD pre-treatment. The internal ore structure became loosened, resulting in the decline in the mechanical properties of the ore; this is conducive to improve the grinding efficiency. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses indicated that the grain-boundary breakage was obtained via the HVPD pre-treatment selectivity.

Nanosecond Laser Ablation of Ti–6Al–4V under Different Temperature

Multi-pulse nanosecond laser ablation of Ti–6Al–4V is a complex process. In this study, the effect of substrate temperature on the nanosecond laser ablation of Ti–6Al–4V was investigated. Morphology, diameter and depth of ablation craters were observed; ablation efficiency ω (μm3/mJ) was proposed to analyzes the ablation process. The results showed that, with the increasing of substrate temperature, the ablation craters’ diameter increased and depth decreased, while ω initially increased, but then decreased rapidly. Furthermore, with increasing pulse number, the depth of ablation crater increased linearly, while the growth of the diameter gradually slowed down and tended to be stable after the 16th irradiation. The above changes were different in details at different substrate temperatures.

Effect of the streamwise pulsed arc discharge array on shock wave/boundary layer interaction control

The streamwise pulsed arc discharge array (S-PADA), in which five actuators are connected in series with adjustable frequency, is employed to control the shock wave/boundary layer interaction (SWBLI) at a 24° compression ramp in a M = 2.0 flow and under two Reynolds numbers based on boundary layer thickness (Re1 = 46 800 and Re2 = 11 700). High-speed schlieren imaging at 50 000 fps is used for flow visualization. The schlieren snapshots, as well as the statistics of the image sequence, namely, mean and root-mean-square, are examined to reveal the control outcome. The results show that the separated wave foot gradually presents bifurcation and partial disappearance under Re1 with the increasing pulse number of the S-PADA, indicating the decline in the shock intensity. The increase in frequency does affect the control outcome remarkably because shock weakening effect can be achieved under Re1 through 10 kHz and 20 kHz actuations, while no obvious change can be observed by the 5 kHz actuation. The experiments under Re2, where little control effect is exerted by the same methods, are also discussed. It is believed that the separated wave under a lower Reynolds number of Re2 presents the poorly developed turbulent boundary layer; hence, the effective SWBLI control is difficult to be ensured.