Number Of Pulses Research Articles

Effect of pulsed electric field processing on the quality characteristics and enzyme activity of tender coconut water.

Tender coconut water (TCW) is a natural drink rich in natural electrolytes, minerals, salts and sugars; it has good health benefits. But, its shelf-life is very limited because of the active nature of enzymes present in it when exposed to air. Therefore, the processing of TCW is necessary to inactivate the enzymes. So, this study aims to observe the effect of various process parameters of pulsed electric field (PEF) on the quality parameters of TCW. For the treatment of TCW with PEF, a full-factorial design of experiments was followed with process parameters such as three levels of electric field intensity (8, 12, and 16 kV/cm), two levels of pulse width (PW) (50 and 70 μs), and six levels of the number of pulses (2000 to 12,000 pulses) were considered at a constant pulse OFF time of 75 ms. PEF treatment did not significantly change pH, total soluble solids, and viscosity. However, it significantly affected vitamin C, colour, and total and reducing sugars. PEF treatment significantly enhanced the total phenolic content and antioxidant activity by 23.17% and 42.49%, respectively. At the same time, significant inactivation of polyphenol oxidase (100%) and peroxidase (60.2%) was observed at PEF treatment conditions of 16 kV/cm, 70 μs PW, and 12,000 pulses. Moreover, no significant change in the sensory acceptability of PEF-treated TCW (16 kV/cm, 70 μs PW, 12,000 pulses) when compared to the untreated/fresh TCW, which is a promising sign.

Effect of Picosecond Laser Irradiation on the Properties of Nanostructured Zinc Oxide Thin Films

In this article, a picosecond laser source was employed to irradiate the nanostructured ZnO thin film prepared by the sol-gel method. The impact of laser irradiation on the characteristics of a nanostructured ZnO thin film was investigated. Analysis using X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy confirmed a significant influence on the structure of the ZnO thin film. As the duration of laser irradiation (the number of laser pulses) increased, there was a remarkable decrease in both the electronic and photoluminescence intensities of the nanostructured film. Tauc's plot indicates a noticeable change in the optical band gaps of the thin film with the increase in irradiation time. The morphological image suggests that the laser irradiation energy induces both degradation and modification of the film surface, consequently causing changes in the structural, absorption, and photoluminescence properties of nanostructured ZnO. The observed effects are attributed to alterations in the crystal structure and size of the nanostructured ZnO film, as confirmed by XRD. The reduction in photoluminescence intensity observed over the laser irradiation times may be a result of potential degradation in the crystalline structure of the nanostructured ZnO film.

Colloidal synthesis of ZnTe nanocrystals by laser ablation and fabrication of hybrid light emitting device

Zinc telluride (ZnTe) nanocrystals (NCs) have generated the interest of researchers as an electrode material in hybrid light emitting devices (HLEDs) due to its potentially high capacity. However, due to the restricted fundamental charging capacity of the electrode materials, the available energy of existing nanomaterial light emitting devices remains enough for a wide range of applications. In this research, ZnTe nanocrystals were synthesized using Nd: YAG laser at energy 600 mJ by 150 pulse number to form a battery device out of ITO/ZnTe/TPD/Ni. The spectra of the ZnTe NCs were assessed using ultraviolet-visible (UV-VIS) and photoluminescence (PL). The results proved that the synthesized NCs were nanocrystalline structures. The energy gap (Eg) within ZnTe NCs regarded as (PL) spectrum has been identified to be about 3.6 eV. ZnTe NCs produced via laser ablation enhance the functionality of the HLEDs by increasing the carrier's charge mobility and, as a further benefit, by facilitating recombination processes inside ZnTe NCs with TPD organic polymer. In addition to lighting at 3V, current-voltage (I-V) specifications establish suitable environment as well as formation.

Enhancement of hole mobility in high-rate reactively sputtered Cu2O thin films induced by laser thermal annealing

In presented work, a reactive high-power impulse magnetron sputtering (r-HiPIMS) was used for high-rate deposition (≈ 170 nm/min) of Cu2O films. Films were deposited on a standard soda-lime glass (SLG) substrate at a temperature of 190 °C. As-deposited films exhibit poor hole mobility in the orders of ≈ 1 cm2/Vs. We have systematically studied the effect of laser thermal annealing (LTA) procedure performed using high-power infrared laser under different laser parameters (number of pulses, length of the pulse). We have found, LTA procedure could significantly enhance the hole mobility (up to 24 cm2/Vs in our case). We have also fitted the results of a temperature-dependent Hall measurement to clarify the mechanism of the reported increase in hole mobility. Moreover, we have discussed the effect of the LTA procedure on microstructure (crystallinity, surface morphology) and on the value of optical band gap.

Finite Element Analysis and Experimental Verification of Thermal Fatigue of W-PFM with Stacked Structure

As the prime candidate for plasma-facing materials (PFM), the response of tungsten (W) to thermal shock loads is an important research topic for future fusion devices. Under heat loads, the surface of tungsten plasma-facing materials (W-PFM) can experience thermal damage, including brittle cracking and fatigue cracks. Therefore, exploring solutions for thermal damage of W-PFM remains one of the current research focuses. We propose a novel approach to mitigate thermal radiation damage in PFM, namely, the stacked structure W-PFM. The surface thermal stress distribution of the stacked structure W-PFM under heat loads was simulated and analyzed by the finite element method. As the foil thickness decreases, both the peak thermal stresses in the normal direction (ND) and rolling direction (RD) decrease. When the thickness decreases to a certain value, the peak thermal stress in the RD decreases to about 1384 MPa and no longer decreases; while the peak thermal stress in the ND approaches 0 MPa and can be neglected. In the range of approximately 5–100 mm, the accumulated equivalent plastic strain decreases sharply as the thickness decreases; in other thickness ranges, it decreases slowly. Thermal fatigue experiments were conducted on the stacked structure W composed of W foils with different thicknesses and bulk W using an electron beam facility. The samples were applied with a power density of 30 MW/m2 for 10,000 and 20,000 pulses. The cracks on the surface of the stacked structure W extended along the ND direction, while on the surface of bulk W, besides the main crack in the ND direction, a crack network also formed. The experimental results were consistent with finite element simulations. When the pulse number was 10,000, as the thickness of the W foil decreased, the number and width of the cracks on the surface of the stacked structure W decreased. Only four small cracks were present on the surface of stacked structure W (0.05 mm). When the pulse number increased to 20,000, the plastic deformation and number of cracks on the surface of all samples increased. However, the stacked structure W (0.05 mm) only added one small crack and had the smallest surface roughness (Ra = 1.536 μm). Quantitative analysis of the fatigue cracks showed that the stacked structure W-PFM (0.05 mm) exhibited superior thermal fatigue performance.

Nanosecond repetitively pulsed plasmas with MHz bursts for CO2 dissociation

A novel pulsed power source capable of nanosecond pulses with burst frequencies up to 1 MHz is employed to create atmospheric pressure pulsed plasma in pure CO2 gas. The short bursts contain up to four nanosecond pulses. The CO2 conversion and corresponding energy efficiency are measured ex-situ with Fourier-transform infrared absorption spectroscopy. Trends in the absorption line profile of in-situ quantum cascade laser infrared absorption spectroscopy indicate an elevated vibrational temperature of CO2 with an increasing number of pulses per burst. The key result of this paper is that the dissociation energy efficiency is higher when operating the plasma in burst mode. Furthermore, a larger number of pulses in a burst is associated with a further increase of the dissociation efficiency. The highest efficiency measured is (17.7±0.3) % for single pulses spaced 2 ms apart, and (20.0±0.3) % for bursts of three pulses, with an in-burst frequency of 1 MHz and bursts spaced 4 ms apart.

Fast Stator Flux Trajectory Control for PMSM Operating Under Low Switching Frequency

In rail transit traction field, the traction motor needs to operate at a very low switching frequency to decrease the switching loss. Hybrid pulse-width modulation scheme is usually applied for decreasing switching frequency and providing good harmonic performance. However, when the transition between different modulation schemes occurs or the voltage command steps, the stator flux would deviate from the expected trajectory, which would lead to current/torque shock even overcurrent. This paper proposes a method which can provide more flexible choice of voltage vector and can fast eliminate the stator flux deviation. Compared with the previous method, the proposed one can provide better dynamic performance (less oscillation in current/torque and less settling time), especially when the pulse number is relatively low, like square-wave mode, and is easy to implement. The effectiveness of the proposed method is verified by the simulation and experimental results.

Recent experiments on photo-assisted negative ion production in caesium sputter ion source at the JYFL Pelletron facility

We have measured the effect of a 15 W, 445 nm laser on Br− beam current produced by a SNICS ion source by systematically varying the ion source parameters, most importantly the target holder material, and temperatures of the ioniser and Cs oven. The target holder material has no significant effect on the observed photoenhancement of the beam current. The evidence shows that the laser allows reaching higher beam currents at low ioniser temperatures compared to running the source without the laser but at higher ioniser temperature. We have observed a priming effect, i.e. applying a number of laser pulses at certain ion source settings causes the beam current measured without the laser to increase significantly and remain high after ceasing the laser pulsing. These observations suggest that the photo-assisted effect is related to changes of the cathode caesium coverage. Finally, we report the results of our first attempts to sustain a stable beam current at the elevated level over several hours, achieved through active control of the laser power.

Self-pulsing of dielectric barrier discharges at low driving frequencies

This paper investigates the self-pulsing of dielectric barrier discharges (DBDs) at low driving frequencies. In particular, (a) the dependence of current on the product pd of gas pressure p and the gas gap length d, (b) the effects of lossy dielectrics (in resistive discharges) and large dielectric permittivity (in ferroelectrics) on current dynamics, (c) the transition from Townsend to a dynamic capacitively coupled plasma (CCP) discharge with changing pd values, and (d) the transition from Townsend to a high-frequency CCP regime with increasing the driving frequency. A one-dimensional fluid model of argon plasma is coupled to an equivalent RC circuit for lossy dielectrics. Our results show multiple current pulses per AC period in Townsend and CCP discharge modes which are explained by uncoupled electron–ion transport in the absence of quasineutrality and surface charge deposition at dielectric interfaces. The number of current pulses decreases with an increasing applied frequency when the Townsend discharge transforms into the CCP discharge. The resistive barrier discharge with lossy dielectrics exhibits Townsend and glow modes for the same pd value (7.6 Torr cm) for higher and lower resistances, respectively. Finally, we show that ferroelectric materials can amplify discharge current in DBDs. Similarities between current pulsing in DBD, Trichel pulses in corona discharges, and subnormal oscillations in DC discharges are discussed.

Temperature and strain gradient monitoring of the buoyancy material curing reaction with a submillimeter spatial resolution fs-FBG array

Millimeter-scale temperature and strain gradient measurements are crucial for understanding the mechanical properties of buoyancy materials. In this paper, we successfully fabricated ultrashort and high-density fiber Bragg grating (FBG) array based on femtosecond laser point-by-point writing technology. By optimizing the energy and number of femtosecond laser pulse, and introducing secondary tilt apodization technology, submillimeter-spatial-resolution FBG arrays were prepared. To the best of our knowledge, this is the first application of femtosecond FBG array for high spatial resolution temperature and strain gradient in situ monitoring of buoyancy materials. FBGs exhibit excellent anti-chirp performance and achieve submillimeter spatial resolution curing monitoring under temperature and strain monitoring gradients of 2.6 °C/mm and 231 με/mm, respectively.

Development of a dose-rate dosimeter using a silicon photodiode for a medical linear accelerator in a 10 MV flattening filter-free mode.

This study was aimed at developing a dose-rate dosimeter to measure the instantaneous dose rate of a commercially available medical linear accelerator. A dose-rate dosimeter composed of a silicon photodiode (Si-PD), a complementary metal-oxide semiconductor single operational amplifier, a resistor of 20 MΩ, a capacitor of 100 pF, and a mini-substrate measuring 16 × 16mm2 was evaluated. Voltage outputs from the proposed dosimeter were measured using an analog-to-digital converter on a microcomputer. A custom-made x-ray tube generator at an energy of 120kV with a tube current ranging from 0.1 to 2.0 mA was used for the dose-rate calibration. Dose-rate calibration was performed 83.3mm from an x-ray source using a commercially available semiconductor dosimeter. The developed Si-PD dosimeter could measure up to 0.6 Gy/s at a distance of 19.3mm from the x-ray source. Measurements were also performed using a medical linear accelerator in a 10 MV flattening filter-free mode at depths of 0, 25, 50, and 100mm with an irradiation field of 100 × 100mm2 at a constant distance of 1000mm from the source to the dosimeter. A peak voltage variation corresponding to the instantaneous dose rate was observed using a sampling period of 1.0ms, and the peak voltages decreased with the depth. The detected pulse numbers were 512, 484, 491, and 511 at depths of 0, 25, 50, and 100mm, respectively.

Controlling the morphologies of femtosecond laser-induced periodic surface structure on silicon by combining deep learning with energy deposition model

As an important patterning method, femtosecond laser-induced periodic surface structure (LIPSS) has attracted widespread attention in recent years. Due to the complex physical processes involved in the femtosecond laser scanning process, it is difficult to predict the required LIPSS morphologies, which hinders rapid customization of the large-area LIPSS patterns. In this study, a structural optimization method combining data-driven deep learning with energy deposition model was proposed to control LIPSS morphologies of silicon. After femtosecond laser processing under dynamic irradiation condition, four LIPSS morphological types were well defined based on experimental results. Deep learning model was constructed to extract data features by labeling and encoding sample data. The accuracy of self-correlation validation reached 98.0% and the accuracy of cross-correlation validation reached 91.9%. Our results show that the distribution of LIPSS morphological types exhibits the dependence of energy deposition, which is the joint effect of the effective pulse number and accumulative fluence. Moreover, the period of groove (super-wavelength LIPSS) increases with the increase of energy deposition, while the period of LSFL (low spatial frequency LIPSS) slightly decreases with the increase of energy deposition. Through this structural optimization method, customization and online monitoring of large-area LIPSS patterns in the future industrial applications.

Experimental investigation and optimization of modification during coaxial waterjet-assisted femtosecond laser drilling

Waterjet-assisted laser drilling technology facilitates the fabrication of high-quality micro-holes by utilizing the collaborative benefits of waterjets and lasers. In this study, the coaxial waterjet-assisted laser drilling (CWALD) technique was employed to improve the properties of micro-holes during femtosecond laser drilling. Based on computational fluid dynamics (CFD) simulations, the stability of the waterjet was initially verified by optimizing the structure of the watercourse and nozzle shape in the CWALD device. Furthermore, a comparative experiment between laser direct drilling (LDD) and CWALD revealed that while CWALD can produce well-rounded micro-holes with a high aspect ratio, it exhibits lower efficiency and results in a larger heat-affected zone (HAZ). To address these drawbacks associated with CWALD, a two-step coaxial waterjet-assisted composite laser drilling (TS-CWALD) method was proposed. TS-CWALD involves applying CWALD for secondary modification of micro-hole shape following LDD with punching. This modification process is pivotal for enhancing drilling accuracy but requires consideration of multiple parameters. For this purpose, regression models were established for the inlet diameter, outlet diameter, and taper; response surface methodology was then employed to optimize these parameters. Subsequently, interactive effects analysis was conducted on different responses based on laser pulse energy, frequency, modification speed, and number of modification cycles. The adequacy of the developed models was subsequently verified using analysis of variance methods. Finally, the successful fabrication of a film hole with an inlet diameter of 205 μm and an outlet diameter of 200 μm, featuring a taper of only 0.2°, was achieved ultimately through meticulous parameter optimization. Furthermore, the micro-hole retained a minimal HAZ. The optimized parameters encompassed a pulse energy of 20.6 μJ, frequency of 127 kHz, modification speed of 3 mm/s, and shape modification carried out over 335 cycles.

Pulsed electric field-assisted extraction of hesperidin from tangerine peel and its technological optimization through response surface methodology.

Tangerine peel is rich in flavonoids, particularly hesperidin, which has anti-inflammatory, antioxidant and anticancer biological activities. However, it is often wasted during citrus processing. The current common extraction method for hesperidin is solvent extraction, which has the characteristics of low extraction rate and high contamination. The aim of this study was to investigate the effect of pulsed electric field-assisted alkali dissolution extraction, followed by an acidification precipitation method, on the extraction rate and structure of hesperidin from tangerine peel. The results showed that the selected factors (material/liquid ratio, electric field intensity and pulse number) had a significant effect on the extraction yield. An optimum condition of 66.00 mL g-1, 4.00 kV cm-1 and 35.00 pulses gave the maximum amount (669.38 μg mL-1), which was consistent with the theoretically predicted value by software (672.10 μg mL-1), indicating that the extraction process was feasible. In addition, the purified extract was further identified as hesperidin from UV and NMR spectra. An appropriate strength of pulsed electric field-assisted alkali dissolution extraction followed by an acidification precipitation method can effectively improve the extraction rate of orange peel, and the purity of the extracted orange peel is higher. Compared with the traditional extraction, the pulsed electric field-assisted extraction method may be a potential technology for hesperidin extraction, which is beneficial for the high-value utilization of citrus resources. © 2024 Society of Chemical Industry.

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.

Employing Atmospheric Pressure Plasma Jet Technology in Surface Treatment Iron Oxide Films for Industrial Applications

In this study, pure iron oxide nanostructures were prepared by a physical method (laser-induced plasma) inside a vacuum using a second harmonic laser Nd: YAG with a wavelength of 532 nm, a laser energy of 500 mJ and a number of pulses of 300 pulses per second. The effect of the plasma generated from argon gas under normal atmospheric pressure was studied using a "cold plasma jet" system with an output voltage of 13 kV and a frequency of 50 Hz. Iron oxide nanostructures were exposed to cold plasma for different periods. The optical and structural properties of the nanostructures were measured before and after exposure, and there was a clear change in them, thus improving the properties of the nanostructures for use in industrial applications such as gas sensors, photovoltaic cells, diodes, detectors, and solar cells.

The role of absorption mechanism on the optimization of processing commercial polymers under high repetition rate femtosecond laser irradiation

The response of three of the most used commercial polymers (poly(vinyl chloride) (PVC), poly(ethylene terephthalate) (PET) and polypropylene (PP)) under irradiation with high repetition rate (1 kHz-1 MHz) femtosecond (450 fs) multi-pulse (N=10-1500) laser at λ=343 nm, 515 nm (1.40 J/cm2 for both former wavelengths) and 1030 nm (1.70 J/cm2) is reported, obtaining a study on how the absorption mechanism influences the processing efficiency for these materials. Tunable ablation depth and diameters are accomplished by modifying repetition rates at a constant fluence and number of pulses. The results highlight the role of absorption mechanism, repetition rate ranges and thermal properties of the materials for benefiting ablation efficiency. Furthermore, the use of high repetition rates improves the laser processing, reducing extended thermal effects and increasing ablation uniformity

Multi-pulse Ramsey interferometry of a double-well Bose–Einstein condensate in a cavity

Ramsey interferometry as one of the most important high-precision measurement methods has prospects for inferring various properties of ultracold atoms and molecules. We investigate the multi-pulse Ramsey interferometry of a double-well Bose–Einstein condensate (BEC) in an optical cavity. Compared with the standard two-pulse Ramsey scheme, our multi-pulse Ramsey proposal greatly relaxes the requirements for both intensity and width of the pulses, allowing the interferometry to be achieved using weak and narrow pulses. When the pumping pulses characterizing the coupling between the cavity field and the atomic BEC are applied to the zero background field, we demonstrate the atomic Ramsey fringes in the time domain for different pulse numbers and different pulse widths. We find that although the multi-pulse Ramsey fringes are no longer sensitive to cavity-pump detuning, they can still record the information of the interaction between coherent atoms. We obtain the fundamental frequency of the multi-pulse Ramsey fringes analytically and find that it is proportional to the number of pulses. Particularly, it is shown that the minimum of the fundamental frequency is exactly the critical point of the phase transition of the system. For a nonzero background field, the results indicate that a nondestructive observation of atomic Ramsey fringes by cavity transmission spectroscopy is feasible. Our findings provide insights for improving the accuracy of Ramsey interferometry and for using interferometry to observe phase transitions.

Stability of transcranial magnetic stimulation electroencephalogram evoked potentials in pediatric epilepsy

Transcranial magnetic stimulation paired with electroencephalography (TMS–EEG) can measure local excitability and functional connectivity. To address trial-to-trial variability, responses to multiple TMS pulses are recorded to obtain an average TMS evoked potential (TEP). Balancing adequate data acquisition to establish stable TEPs with feasible experimental duration is critical when applying TMS–EEG to clinical populations. Here we aim to investigate the minimum number of pulses (MNP) required to achieve stable TEPs in children with epilepsy. Eighteen children with Self-Limited Epilepsy with Centrotemporal Spikes, a common epilepsy arising from the motor cortices, underwent multiple 100-pulse blocks of TMS to both motor cortices over two days. TMS was applied at 120% of resting motor threshold (rMT) up to a maximum of 100% maximum stimulator output. The average of all 100 pulses was used as a “gold-standard” TEP to which we compared “candidate” TEPs obtained by averaging subsets of pulses. We defined TEP stability as the MNP needed to achieve a concordance correlation coefficient of 80% between the candidate and “gold-standard” TEP. We additionally assessed whether experimental or clinical factors affected TEP stability. Results show that stable TEPs can be derived from fewer than 100 pulses, a number typically used for designing TMS-EEG experiments. The early segment (15–80 ms) of the TEP was less stable than the later segment (80–350 ms). Global mean field amplitude derived from all channels was less stable than local TEP derived from channels overlying the stimulated site. TEP stability did not differ depending on stimulated hemisphere, block order, or antiseizure medication use, but was greater in older children. Stimulation administered with an intensity above the rMT yielded more stable local TEPs. Studies of TMS-EEG in pediatrics have been limited by the complexity of experimental set-up and time course. This study serves as a critical starting point, demonstrating the feasibility of designing efficient TMS–EEG studies that use a relatively small number of pulses to study pediatric epilepsy and potentially other pediatric groups.

The effectiveness of a virtual fencing technology to allocate pasture and herd cows to the milking shed.

Virtual fencing technology provides an opportunity to rethink the management of intensive grazing systems in general, yet most studies have used products developed and applied to more extensive livestock systems. This research aimed to assess the application of a virtual fencing technology developed for the intensive pastoral dairy industry. The Halter system uses 2 primary cues, sound and vibration, and one aversive secondary cue, a low energy electrical pulse, to confine cows to a pasture allocation and remotely herd cows. Two groups of 40 mid-lactation multiparous dairy cows were studied (Bos taurus, predominantly Friesian and Friesian × Jersey, parity 1-8). Cows were milked twice per day and provided 9 kg pasture DM/day in a 24-h allocation, supplemented with 7 kg silage and 6 kg grain DM/day. Training to the Halter system occurred over 10 d after which cows were managed with the technology for a further 28 d. The type and time of cues delivered was recorded by each collar and communicated via a base-station to cloud data storage. Cows took less than a day to start responding to the sound cues delivered while held on a pasture allocation and were moving to the milking parlor without human intervention by d 4 of training. On training d 1, at least 60% of sound cues resulted in an electrical pulse. Across training d 2-10, 6.4% of sound cues resulted in a pulse. After the 10-d training period, 2.6% of sound cues resulted in a pulse. During the management period, 90% of cows spent ≤1.7 min/d beyond the virtual fence, received ≤ 0.71 pulse/d in the paddock and received ≤ 1 pulse/d during virtual herding to the parlor. By the final week of the management period, 50% of cows received zero pulses/week in the paddock and 35% received zero pulses/week during virtual herding. The number of pulses delivered per day and the pulse:sound cue ratio was lower in this study than that previously reported using other virtual fencing technologies. We conclude that the Halter technology is successful at containing lactating dairy cows in an intensive grazing system as well as at remotely herding animals to the milking parlor.