Pulses In Range Research Articles

Dependence of interfacial mixing for thermally induced magnetization switching in Gd/Fe multilayers

The use of femtosecond laser pulses for ultrafast triggering of magnetization switching is of great interest in multilayer systems with great tunability. At present, the impact of interfacial mixing on magnetization switching has not been thoroughly investigated. In this paper, the impact of interfacial mixing on magnetization dynamics in multilayer systems is investigated by a combination of atomic spin dynamics and two-temperature models. Our results show that interfacial mixing in multilayer systems not only reduces the energy density required for magnetization switching but also expands the range of pulse durations that can trigger magnetization switching. In addition, we have investigated the dependence of the switching time on the interfacial mixing in multilayer systems. The results show that interfacial mixing can accelerate the process of magnetization dynamics, thus providing a theoretical basis for the design of faster speed optically controlled magnetic tunnel junctions.

Nanosecond Structural Dynamics during Electrical Melting of Charge Density Waves in 1T-TaS_{2}.

Electrical control of charge density waves has been of immense interest, as the strong underlying electron-lattice interactions potentially open new, efficient pathways for manipulating their ordering and, consequently, their electronic properties. However, the transition mechanisms are often unclear as electric field, current, carrier injection, heat, and strain can all contribute and play varying roles across length scales and timescales. Here, we provide insight on how electrical stimulation melts the room temperature charge density wave order in 1T-TaS_{2} by visualizing the atomic and mesoscopic structural dynamics from quasi-static to nanosecond pulsed melting. Using a newly developed ultrafast electron microscope setup with electrical stimulation, we reveal the order and strain dynamics during voltage pulses as short as 20ns. The order parameter dynamics across a range of pulse amplitudes and durations support a thermally driven mechanism even for fields as high as 19 kV cm^{-1}. In addition, time-resolved imaging reveals a heterogeneous, mesoscopic strain response across the flake, including MHz-scale acoustic resonances that emerge during sufficiently short pulsed excitation which may modulate the order. These results suggest that metallic charge density wave phases like studied here may be more robust to electronic switching pathways than insulating ones, motivating further investigations at higher fields and currents in this and other related systems.

Quantitative investigation on the effects of eyeball geometry, blood perfusion and natural convection in retinal laser surgery

The photothermal effects of laser on tissue are widely used in ophthalmology to treat retinal diseases. The accurate modelling of retinal laser surgery will prove valuable guidance for clinic treatment. There are several important issues should be carefully evaluated during retinal laser surgery modelling, including the eye geometry (whole eye or fundus only, retinal pigment epithelium layer incorporated or not), blood perfusion and natural convection. In previous publications, the existence of the anterior part of eyeball and retinal pigment epithelium layer is neglected to simply the eye geometry due to low laser light absorption (anterior part of eyeball) or small volume occupation (retinal pigment epithelium layer), respectively. However, the justification of this treatment has not been conducted. In this study, we will quantitatively investigate these factors systemically in a large pulse duration range that covers all the retinal laser surgery used in clinic. To do this, we present a bioheat transfer model for the simulation of the thermal response of the eye to laser irradiation. In the simulation, the 3D whole-eye geometry is considered. The Pennes bioheat transfer equation is adopted for the whole-eye temperature modelling. Simultaneously, we treat the fundus as a multilayered medium that all primary components, including RPE layer, are considered for first time in whole eye modelling. Our model calculates the thermal responses of the eye during laser retinal surgery with the pulse duration from nanosecond to tens of second. The effects of eye geometry, blood perfusion and natural convection are clearly clarified based on the laser pulse duration and incident energy used. The results show that neglecting the anterior part of eyeball will introduce the computational error more than 27 %. The existence of the retinal pigment epithelium layer should always be considered in retinal laser surgery modelling in all pulse durations used in clinic, otherwise more than 20 % computational error will be generated. When the pulse duration is longer than 10s, the effect of blood perfusion and natural convection in vitreous body should both be considered.

Closed-Loop Estimation Method of Neurostimulation Strength-Duration Curve Using Fisher Information Optimization.

Strength-duration (SD) curve, rheobase and chronaxie parameters provide insights about neural activation dynamics and interdependence between pulse amplitude and duration, for diagnostics and therapeutic applications. The existing SD curve estimation methods are based on open-loop uniform and/or random pulse durations, which are chosen without feedback from neuronal data. To develop a method for closed-loop estimation of the SD curve, where the pulse durations are adjusted iteratively using the neuronal data. In the proposed method, after the selection of each pulse duration through Fisher information matrix (FIM) optimization, the corresponding motor threshold (MT) is computed, the SD curve estimation is updated, and the process continues until satisfaction of a stopping rule based on the successive convergence of the SD curve parameters. The results are compared with various iterative uniform and random sampling techniques, where the SD curve estimation is updated after each sample. 250 simulation cases were run. The FIM method satisfied the stopping rule in 225 (90%) runs, and estimated the rheobase (chronaxie in parenthesis) with an average absolute relative error (ARE) of 1.57% (2.15%), with an average of 85 samples. At the FIM termination sample, methods with two and all random pulse durations, and uniform methods with descending, ascending and random orders led to 5.69% (20.09%), 2.22% (3.93%), 7.34% (40.90%), 3.10% (4.44%), and 2.05% (3.45%) AREs. In all 250 runs, the FIM method has chosen the minimum and maximum pulse durations as the optimal pulse durations for the SD curve estimation. As proposed by the FIM method, the SD curve is identifiable by fitting to the data of the minimum and maximum pulse durations. However, the range of pulse duration should cover the vertical and horizontal parts of the SD curve. Also, iterative random or uniform samples from only the vertical or horizontal areas of the curve might not result in satisfactory estimation. This paper provides insights about pulse durations selection for closed-loop and open-loop SD curve estimation.

Maps of Membrane Pore Dynamics From Picosecond to Millisecond Pulse Durations.

Electroporation occurs when cells are exposed to an electric pulse of sufficient intensity E0 and pulse duration τ. Many studies have attempted to develop universal scaling laws to predict membrane pore dynamics for pulsed electric fields (PEFs) of different durations; however, the differences in pore dynamics across these parameters makes this difficult both experimentally and numerically. This study uses the asymptotic Smoluchowski equation (ASME) to quantify the number of pores, average pore radius, and fractional pore area (FPA) during exposure to PEFs with durations from hundreds of picoseconds to a millisecond. We highlight pulse parameter regimes that favor increases in pore radius and number and show that the FPA is dominated by the number of pores formed on the cell membrane. Furthermore, the number of pores and the FPA depend almost entirely on E0 for τ exceeding the charging time of the cell and both E0 and τ for τ shorter than the charging time. Finally, the maps of pore number, average radius, and FPA demonstrate that a universal scaling law for pore dynamics across a wide range of pulse durations does not exist, although certain scaling behaviors may be valuable over narrow regimes. Practically, these maps provide a guideline for selecting PEF parameters to achieve desired membrane permeabilization.

Towards a more accurate quasi-static approximation of the electric potential for neurostimulation with kilohertz-frequency sources * *This work has been partially supported by ANID Millennium Science Initiative Program through Millennium Nucleus for Applied Control and Inverse Problems NCN19-161.

Objective. Our goal was to determine the conditions for which a more precise calculation of the electric potential than the quasi-static approximation may be needed in models of electrical neurostimulation, particularly for signals with kilohertz-frequency components. Approach. We conducted a comprehensive quantitative study of the differences in nerve fiber activation and conduction block when using the quasi-static and Helmholtz approximations for the electric potential in a model of electrical neurostimulation. Main results. We first show that the potentials generated by sources of unbalanced pulses exhibit different transients as compared to those of charge-balanced pulses, and this is disregarded by the quasi-static assumption. Secondly, relative errors for current-distance curves were below 3%, while for strength-duration curves these ranged between 1%–17%, but could be improved to less than 3% across the range of pulse duration by providing a corrected quasi-static conductivity. Third, we extended our analysis to trains of pulses and reported a ‘congruence area’ below 700 Hz, where the fidelity of fiber responses is maximal for supra-threshold stimulation. Further examination of waveforms and polarities revealed similar fidelities in the congruence area, but significant differences were observed beyond this area. However, the spike-train distance revealed differences in activation patterns when comparing the response generated by each model. Finally, in simulations of conduction-block, we found that block thresholds exhibited errors above 20% for repetition rates above 10 kHz. Yet, employing a corrected value of the conductivity improved the agreement between models, with errors no greater than 8%. Significance. Our results emphasize that the quasi-static approximation cannot be naively extended to electrical stimulation with high-frequency components, and notable differences can be observed in activation patterns. As well, we introduce a methodology to obtain more precise model responses using the quasi-static approach, retaining its simplicity, which can be a valuable resource in computational neuroengineering.

Accelerating Xinomavro Red Wine Flavor Aging Using a Pulsed Electric Field and Various Wood Chips

Pulsed electric field (PEF) treatment has gained significant attention within the food industry. This study examines the application of PEF combined with wood chips of diverse species to expedite the flavor aging process of Xinomavro red wine. Various wood chip species, including black locust, common juniper, apricot, sweet chestnut, cherry, apple, peach, and European oak, sourced from pruning residues were immersed in the wine prior to subjecting it to PEF treatment. The samples underwent a range of pulse durations and intervals during treatment. Comparative preparations encompassing wine without chips and wine infused with each wood type left at ambient temperature for 5 days were also examined. The sensory attributes and the volatile compounds (VC) were assessed through the utilization of headspace solid-phase microextraction and GC-MS. In the control sample, 12 VCs were identified, whereas in the samples, 22 distinct VCs were identified. Favorable sensory attributes across all PEF conditions were associated with the incorporation of cherry wood chips. These findings highlight the potential of PEF treatment to enhance the quality parameters of the aging process in Xinomavro red wine, capitalizing on the synergistic interaction between PEF and various wood chip species. This innovative approach holds promise for augmenting crucial oenological parameters of red wine, strengthening the use of PEF as an efficient technique to enhance the overall quality.

Probing thermal dissipation dimensionality to laser ablation in the pulse duration range from 300 fs to 1 µs.

We propose a quantitative method to determine the thermal dissipation dimensionality to laser ablation. We derived an analytical expression for the melting condition due to a single pulse for arbitrary spot diameters and pulse durations, which explicitly contains the dimensionality of the thermal diffusion process. As a demonstration, we compared the analytical expression with multi-shot ablation thresholds measured over pulse durations of more than six orders of magnitude for copper. The result shows that the thermal dissipation processes dominate for pulse durations longer than 5 ps, while nonthermal processes begin to dominate for shorter pulse durations.

Pulse duration dependent optical nonlinearities of Bi2Se3 thin films.

Topological insulators, such as the Bi2Se3 material, exhibit significant optical nonlinearities. This work investigates the impact of the pulse duration on the nonlinear optical responses of Bi2Se3 layers. Scanning electron microscopy studies have been performed to reveal the crystalline structure of the samples. The nonlinear optical performance has been investigated for a wide range of pulse durations, from 400 fs to 10 ps, using 1030 nm laser excitation. The nonlinear absorption coefficients recorded in this study range from -1.45 x10-7 m/W to -4.86 x10-7 m/W. The influence of two different mechanisms on optical nonlinearities was observed and discussed. Identical experimental conditions have been employed throughout the studies allowing a direct comparison of the results.

Automated verification of countermeasure against detector-control attack in quantum key distribution

Attacks that control single-photon detectors in quantum key distribution using tailored bright illumination are capable of eavesdropping the secret key. Here we report an automated testbench that checks the detector’s vulnerabilities against these attacks. We illustrate its performance by testing a free-running detector that includes a rudimentary countermeasure measuring an average photocurrent. While our testbench automatically finds the detector to be controllable in a continuous-blinding regime, the countermeasure registers photocurrent significantly exceeding that in a quantum regime, thus revealing the attack. We then perform manually a pulsed blinding attack, which controls the detector intermittently. This attack is missed by the countermeasure in a wide range of blinding pulse durations and powers, still allowing to eavesdrop the key. We make recommendations for improvement of both the testbench and countermeasure.

Parametric Analysis of Surface Roughness and Metal Removal Rate during Electrical Discharge Machining of O1 Tool Steel

This work studies the impact of input machining parameters of Electrical Discharge Machining (EDM) on the machining process performance. Tool steel O1 was selected as the workpiece material, copper as the electrode material, and kerosene as the dielectric medium. Experimental runs have been carried out with a Design of Experiment (DOE) technique. Twenty tests are accomplished with the current range of (18 to 24 Ampere), a pulse duration range of (150 to 200 µs), and a pulse-off time range of (25 to 75 µs). Based upon the experimental study's output results, the EDM parameter's effect (voltage of power supply, discharge current, pulse duration, and pulse pause interval) on the responses of the process represented by surface roughness value Ra and Metal Removal MR rate. The results obtained by the DOE approach are analyzed by STATISTICA software. It has been concluded that an increase in the current and pulse duration maximizes both metal removal rate and surface roughness. At the same time, they are minimized by maximizing the pulse pause interval.

Efficient Generation of Axial Magnetic Field by Multiple Laser Beams with Twisted Pointing Directions.

Strong laser-driven magnetic fields are crucial for high-energy-density physics and laboratory astrophysics research, but generation of axial multikilotesla fields remains a challenge. The difficulty comes from the inability of a conventional linearly polarized laser beam to induce the required azimuthal current or, equivalently, angular momentum (AM). We show that several laser beams can overcome this difficulty. Our three-dimensional kinetic simulations demonstrate that a twist in their pointing directions enables them to carry orbital AM and transfer it to the plasma, thus generating a hot electron population carrying AM needed to sustain the magnetic field. The resulting multikilotesla field occupies a volume that is tens of thousands of cubic microns and it persists on a picosecond timescale. The mechanism can be realized for a wide range of laser intensities and pulse durations. Our scheme is well suited for implementation using multikilojoule petawatt-class lasers, because, by design, they have multiple beamlets and because the scheme requires only linear polarization.

Response of Human Malignant Glioma Cells to Asymmetric Bipolar Electrical Impulses

Electric and electromagnetic pulses have been shown to enhance the endocytosis rate, with all-or-nothing responses beyond a field strength threshold and linear responses as a function of field strength and treatment duration utilizing bipolar symmetrical and monopolar pulses, respectively. Malignant glioma (MG) is resistant to chemotherapy. The present study looked for a new electrical impulse that can aid electrochemotherapy to deliver anticancer drugs while using less electrical energy. Bipolar asymmetric electric pulses were applied to U251MG cells suspended in physiologically conductive media in the presence of molecular probes, including Bleomycin. The delivered electric pulses with a pulse duration range of 180-500 µs and a frequency range of 100-400 Hz had a low field intensity ranging from 1.5 V/cm to 7.3 V/cm. Spectrophotometric and spectrofluorometric measurements were used to investigate the impact of these variables on cancer cell survival and the molecular probe uptake induced by the electric pulses. An all-or-nothing response was observed above a specified threshold of electric field intensity of 4 V/cm. This threshold was unaffected by changes in repetition frequency or pulse duration. It was not a temperature effect that caused the molecular probe uptake to increase. When bipolar asymmetric electric pulses were applied just before electroporation, the effectiveness of the cytotoxic impact of bleomycin was increased from 80%, when employing electroporation pulses alone, to 100%.

The effect of pulse duration on the Brillouin frequency shift accuracy in the differential cross-spectrum BOTDR (DCS-BOTDR) fiber sensor

• The cross-correlation between short and long pulses in BOTDR results in a narrow Brillouin spectrum width. • The subtraction between two optical pulses with slightly different duration offers sub-meter spatial resolution measurement. • The DCS-BOTDR technique offers a potential application for long distance fiber measurement with high measurement accuracy. In this paper, we report the effect of pulse duration on the Brillouin frequency shift (BFS) accuracy measurement in our previously proposed differential cross-spectrum Brillouin optical time domain reflectometry (DCS-BOTDR) fiber sensing technique. The DCS-BOTDR uses a pair of optical pulsed probes generated via intensity modulation scheme, in which the first probe consists of a long- and short duration of pulses separated by a short interval, while the second probe only has the long pulse with the same duration as the first one. From the experimental analysis, by varying the duration of the long pulse between 6 and 60 ns, we found that an optimum range of the long pulse duration between 14 and 22 ns provided good measurement of BFS accuracy around 5.3 MHz. Furthermore, by heating up a 2 m fiber section at the end of a 4 km test fiber, by using long- and short pulse durations of 18 ns and 4 ns respectively, we have successfully demonstrated 40 cm spatial resolution and 4 °C of temperature resolution measurement.

Influence of pulse duration on mechanical properties and dislocation density of dry laser peened aluminum alloy using ultrashort pulsed laser-driven shock wave

This study aims to investigate the influence of the pulse duration on the mechanical properties and dislocation density of an aluminum alloy treated using dry laser peening (DLP), which is a laser peening technique that uses ultrashort pulsed laser-driven shock wave to eliminate the need for a sacrificial overlay under atmospheric conditions. The results of the micro-Vickers hardness test, residual stress measurement, and dislocation density measurement demonstrate that over a pulse duration range of 180 fs to 10 ps, the maximum peening effects are achieved with a pulse duration of 1 ps. Moreover, the most significant DLP effects are obtained by choosing a pulse duration that achieves a laser intensity that simultaneously generates the strongest shock pressure, suppresses optical nonlinear effects, and realizes the least thermal effects, which weaken the shock effects. Shock temperature calculations based on thermodynamic equations also suggest that a laser intensity driving a shock pressure less than 80 GPa, as in the case of a pulse duration of 1 ps in this study, maintains the solid state of the material throughout the process, resulting in significant DLP effects.

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.

Yttrium Oxide (Y2O3) as a Pulse Initiator in a Mode-Locking Erbium-Doped Fiber Laser

Mode-locking is an ultra-short pulse laser generation technique. The range of pulse duration may vary from picoseconds to femtoseconds. Yttrium Oxide (Y2O3) based saturable absorber (SA) was appropriately revealed in the mode-locked method within the 1.55-micron regime. Y2O3 is perfect for strength, melting point, and chemical stability and can be used as a laminated insulator due to its properties. Moreover, Y2O3 also owns broadband service, switching speed, and engineering features. The Y2O3-PVA film was produced by combining the 50 mg Y2O3 powder into a 50 mL polyvinyl alcohol (PVA) solution and stirring it at room temperature for about 24 h. A mode-locked pulse was recorded with the integrated Y2O3-PVA SA in the erbium-doped fiber laser (EDFL) cavity, and the output spectrum optical spectrum analyzer displayed was around 1560.66 nm. In addition to the sustained mode-locked pulse, a nearly constant repetition rate of 1.01 MHz at a specific pump power begins from 175.87 mW to 228.04 mW while the pulse duration is 4.15 ps. Lastly, the mode-locked pulse had been evaluated, which showed the peak power started from 4.94 kW to 6.07 kW.

Steering the structure and selectivity of CO2 electroreduction catalysts by potential pulses

Convoluted selectivity trends and a missing link between reaction product distribution and catalyst properties hinder practical applications of the electrochemical CO2 reduction reaction (CO2RR) for multicarbon product generation. Here we employ operando X-ray absorption and X-ray diffraction methods with subsecond time resolution to unveil the surprising complexity of catalysts exposed to dynamic reaction conditions. We show that by using a pulsed reaction protocol consisting of alternating working and oxidizing potential periods that dynamically perturb catalysts derived from Cu2O nanocubes, one can decouple the effect of the ensemble of coexisting copper species on the product distribution. In particular, an optimized dynamic balance between oxidized and reduced copper surface species achieved within a narrow range of cathodic and anodic pulse durations resulted in a twofold increase in ethanol production compared with static CO2RR conditions. This work thus prepares the ground for steering catalyst selectivity through dynamically controlled structural and chemical transformations.

Acousto-optically driven lensless single-shot ultrafast optical imaging

Driven by many applications in a wide span of scientific fields, a myriad of advanced ultrafast imaging techniques have emerged in the last decade, featuring record-high imaging speeds above a trillion-frame-per-second with long sequence depths. Although bringing remarkable insights into various ultrafast phenomena, their application out of a laboratory environment is however limited in most cases, either by the cost, complexity of the operation or by heavy data processing. We then report a versatile single-shot imaging technique combining sequentially timed all-optical mapping photography (STAMP) with acousto-optics programmable dispersive filtering (AOPDF) and digital in-line holography (DIH). On the one hand, a high degree of simplicity is reached through the AOPDF, which enables full control over the acquisition parameters via an electrically driven phase and amplitude spectro-temporal tailoring of the imaging pulses. Here, contrary to most single-shot techniques, the frame rate, exposure time, and frame intensities can be independently adjusted in a wide range of pulse durations and chirp values without resorting to complex shaping stages, making the system remarkably agile and user-friendly. On the other hand, the use of DIH, which does not require any reference beam, allows to achieve an even higher technical simplicity by allowing its lensless operation but also for reconstructing the object on a wide depth of field, contrary to classical techniques that only provide images in a single plane. The imaging speed of the system as well as its flexibility are demonstrated by visualizing ultrashort events on both the picosecond and nanosecond timescales. The virtues and limitations as well as the potential improvements of this on-demand ultrafast imaging method are critically discussed.

Micro- and Nanosecond Pulses Used in Doxorubicin Electrochemotherapy in Human Breast and Colon Cancer Cells with Drug Resistance.

(1) Background: Pulsed electric field (PEF) techniques are commonly used to support the delivery of various molecules. A PEF seems a promising method for low permeability drugs or when cells demonstrate therapy resistance and the cell membrane becomes an impermeable barrier. (2) Methods: In this study, we have used doxorubicin-resistant and sensitive models of human breast cancer (MCF-7/DX, MCF-7/WT) and colon cancer cells (LoVo, LoVoDX). The study aimed to investigate the susceptibility of the cells to doxorubicin (DOX) and electric fields in the 20–900 ns pulse duration range. The viability assay was utilized to evaluate the PEF protocols’ efficacy. Cell confluency and reduced glutathione were measured after PEF protocols. (3) Results: The obtained results showed that PEFs significantly supported doxorubicin delivery and cytotoxicity after 48 and 72 h. The 60 kV/cm ultrashort pulses × 20 ns × 400 had the most significant cytotoxic anticancer effect. The increase in DOX concentration provokes a decrease in cell viability, affected cell confluency, and reduced GSSH when combined with the ESOPE (European Standard Operating Procedures of Electrochemotherapy) protocol. Additionally, reactive oxygen species after PEF and PEF-DOX were detected. (4) Conclusions: Ultrashort electric pulses with low DOX content or ESOPE with higher DOX content seem the most promising in colon and breast cancer treatment.