Influence Of Pulse Duration Research Articles

Influence of pulse duration on the fatigue behavior of a carbon‐fiber‐reinforced composite under cyclic three‐point bending at 20 kHz

AbstractVery high cycle fatigue (VHCF) experiments are limited in practice due to their long testing times. In ultrasonic fatigue test (UFT) systems, the cyclic oscillation is applied using resonance at 20 kHz with a pulse and pause sequence. However, determining optimal pulse durations to achieve minimal testing time and avoid thermal‐induced fatigue damage in fiber‐reinforced polymer composites remains a challenge. In this work, several fatigue experiments, temperature analyses, and digital light optical microscopy were carried out to evaluate the influence of pulse duration on the fatigue behavior of a carbon‐fiber fabric reinforced in polyether‐ketone‐ketone (CF‐PEKK) composite. A shorter pulse duration with the same pulse–pause ratio as the longer pulse duration is proposed for higher stress amplitudes to avoid any thermal influence during mechanical fatigue without altering the underlying fatigue damage mechanisms.

Effects of Nanosecond Pulsed Electric Field (nsPEF) on a Multicellular Spheroid Tumor Model: Influence of Pulse Duration, Pulse Repetition Rate, Absorbed Energy, and Temperature.

Cellular response upon nsPEF exposure depends on different parameters, such as pulse number and duration, the intensity of the electric field, pulse repetition rate (PRR), pulsing buffer composition, absorbed energy, and local temperature increase. Therefore, a deep insight into the impact of such parameters on cellular response is paramount to adaptively optimize nsPEF treatment. Herein, we examined the effects of nsPEF ≤ 10 ns on long-term cellular viability and growth as a function of pulse duration (2-10 ns), PRR (20 and 200 Hz), cumulative time duration (1-5 µs), and absorbed electrical energy density (up to 81 mJ/mm3 in sucrose-containing low-conductivity buffer and up to 700 mJ/mm3 in high-conductivity HBSS buffer). Our results show that the effectiveness of nsPEFs in ablating 3D-grown cancer cells depends on the medium to which the cells are exposed and the PRR. When a medium with low-conductivity is used, the pulses do not result in cell ablation. Conversely, when the same pulse parameters are applied in a high-conductivity HBSS buffer and high PRRs are applied, the local temperature rises and yields either cell sensitization to nsPEFs or thermal damage.

Using the numerical simulation and artificial neural network (ANN) to evaluate temperature distribution in pulsed laser welding of different alloys

The temperature field during laser welding process plays an important role on determining the quality and quantity of the weld bead size, microstructure characterizations and mechanical properties of the welding interface in the thermal engineering applications. In this study, using the numerical simulation, the influence of pulse duration and frequency on the temperature distribution and velocity field in distinctive laser welding of stainless steel 420 (S.S 420)/stainless steel 304 (S.S 304), and Bohler 303 (B 303)/stainless steel 304 (S.S 304) was examined. The results of numerical modeling illustrated that shear stress of Marangoni and buoyancy force are the most curtail aspects in the formation of the flow of liquid metal. A novel artificial intelligence method is proposed to optimally predict the melting ratio, and maximum temperature of the materials. To this end, a combination of ANN and Particle Swarm Optimization (PSO) algorithms are employed. The PSO algorithm is used to optimize the architecture and training algorithm of the ANN, while the ANN is employed for the regression problem. Based on the results, a three-layer feed-forward architecture with sigmoid transfer functions having 17 and 8 neurons in the hidden layers combined with the scaled conjugate gradient backpropagation training scheme is recognized by the PSO as the optimal configuration. Application of optimal ANN to the regression problem results in an acceptable level of error for the training, validation, and test datasets. Finally, the optimized ANN can be utilized to anticipate the melting ratio and thereby the resultant temperature.

The influence of pulse duration and duty cycle on the energy flux to the substrate in high power impulse magnetron sputtering

The paper focuses on measurements of the total energy flux and normalized energy flux onto the substrate during high power impulse magnetron sputtering (HiPIMS) in a wide range of the pulse duration and discharge current. Al, Cr and Ti targets with a diameter 76 mm are used for sputtering. HiPIMS parameters include 1 kW discharge power, 15 to 150 А discharge current, 0.4–10 kHz pulse frequency, and 5–100 μs pulse duration. It is shown that the use of short pulses leads to ∼40 and 70% growth in the total energy flux onto floating and biased (−100 V) substrates, respectively. The energy per unit volume of the deposited coating increases by several times, if the pulse duration and the duty cycle are reduced. The paper examines reasons for the increased total and normalized energy fluxes onto the substrate observed after the pulse parameter modulation in the sputtering process.

Effect of physical parameters of laser radiation on the process of weld formation in transparent dielectrics

The article determines the influence of pulse duration, energy density and focusing parameters on the process of formation of a weld of transparent dielectrics. A comparative analysis of laser welding of borosilicate and quartz glass with different pulse durations and energies of picosecond and femtosecond fiber lasers was carried out. Basic regularities of weld shape change depending on pulse duration and energy are obtained. The combination of physical parameters of laser radiation and focusing allows welding along gaps up to 6 μm.

Investigation of the Influence of Pulse Duration and Application Mode on Microsecond Laser Microsurgery of the Retinal Pigment Epithelium.

Optical microsurgery confined to the retinal pigment epithelium (RPE) requires locally optimized laser parameters and reliable real-time feedback dosimetry (RFD) to prevent unwanted neuroretinal overexposure. This study aimed to compare pulses of different durations and application modes (single, ramp, burst). Moreover, optical coherence tomography (OCT)-based RFD was investigated in an ex vivo experiment, utilizing nine porcine eyes that were exposed to laser pulses of 8, 12, 16 and 20 µs duration (wavelength: 532 nm, exposure area: 90 × 90 µm2, radiant exposure: 247 to 1975 mJ/µm2). Simultaneously, time-resolved OCT M-scans were recorded (central wavelength: 870 nm, scan rate: 85 kHz) for RFD. Post irradiation, retinal changes were assessed with color fundus photography (CFP) and cross-sectional OCT B-scans. RPE cell damage was quantified via fluorescence-based cell viability assay and compared to the OCT dosimetry feedback. Our experiments indicate cumulative RPE damage for pulse bursts of 16 µs and 20 µs, whereas no cumulative effects were found for pulse durations of 8 µs and 12 µs applied in ramp mode. According to statistical analysis, OCT-RFD correctly detected RPE cell damage with 96% sensitivity and 97% specificity using pulses of 8 µs duration in ramp mode.

A 3-D Multiphysics Modeling of Electroporation Excited by a Single Pulse

Three-dimensional multiphysics modeling of electroporation (EP), including asymptotic electroporation (AEP), dielectric dispersion (DP), and evolution of pore radii, is proposed in this article. A boundary equivalent method is introduced to replace the membrane region with a surface boundary, which reduces the mesh generation inside the membrane and makes it possible to build a 3-D realistic irregularly shaped cell model and accurately calculate the distribution of the EP area related to the evolution of pore radii and cell surface shape. The applicable range of the equivalent boundary is discussed, and the equivalent model is verified through theoretical analysis and numerical simulation. Based on this model, the difference between the models including AEP and DP with and without the pore radii evolution submodel was investigated. A numerical analysis was performed by applying a single rectangular pulse with a duration of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1~\mu \text{s}$ </tex-math></inline-formula> to biological cells. The results show the significant effects of variable pore radii on the EP process. In addition, a double-shell geometry model is built to discuss the influence of pulse duration and intensity on outer and inner membrane responses related to EP and intracellular electromanipulation (IEM).

The influence of pulse duration and exposure time of Er,Cr:YSGG laser on lithium disilicate laminate debonding, an in vitro study

Problem statementGrinding restorations, such as veneers, with rotary instruments, is the conventional removal approach. It may be accompanied by micro-fractures that affect the adjacent healthy dental structures. Differentiation of the veneer from the dental structure, as well as the resin cement, is not a highly selective procedure when rotary instruments are used. Moreover, the rotary instruments may lead to scratches and overheating of the enamel. Patient discomfort is another disadvantage, due to the noise of the drill. PurposeThe purpose of this in vitro study was to examine the effectiveness of a 2790 nm Er,Cr:YSGG laser to debond lithium disilicate laminate, utilizing two distinct pulse durations and various exposure times. The shear bond strength, intrapulpal temperature, and adhesive remaining index were evaluated. Methods and materialsThis study included three groups of 75 extracted permanent mandibular incisors: G1, G2 (laser-treated groups were classified according to the pulse duration) and C (control group). Twenty five samples were regarded for each group. Both test groups were irradiated with a 3 W output power of Er,Cr:YSGG laser, for a variety of time intervals (20 s, 30 s, 40 s, 50 s, and 60 s). Five samples were tested for each time interval. During irradiation, the temperature in the pulp chamber was monitored using a K-type thermocouple connected to a digital multilogger thermometer that was introduced into the prepared sample pulp chamber. Subsequently, the shear bond strength was measured for G1 and G2, in addition to the control group (no irradiation). The adhesive remaining index was examined microscopically. The area was measured and analysed, and then, transformed into scores for comparisons. Finally, One untreated sample and two other samples of the highest power value from laser-treated groups were examined for their surface morphology by scanning electron microscope (SEM). ResultsThe debonding protocols were safe relative to the intrapulpal protocol. The temperature rise after an exposure time of 50 s and 60 s was significantly different from an exposure time of 20 s, 30 s, and 40 s, in both groups (p < 0.05). Both G1 and G2 significantly outperformed the control group in shear bond strength. There was no significant difference between G1 and G2 at any of the tested exposure times (p > 0.05). Nevertheless, the 60 s exposure time showed the lowest shear bond strength. ConclusionRegarding intralpulpal temperature, both modes can be safely used to remove laminate veneers. In sum, an exposure time of 50 s and a pulse duration of 60 μs demonstrated superior results for SBS, adhesive remaining index, and temperature values. Clinical implicationLithium disilicate laminate veneers may be removed quickly, safely, and comfortably. Laser-assisted debonding of porcelain laminate veneer is recommended and does not cause any damage to the veneer or enamel surface.

Ultra-Short Pulse Laser Cleaning of Contaminated Pleistocene Bone: A Comprehensive Study on the Influence of Pulse Duration and Wavelength

The impact of wavelength and pulse duration in laser cleaning of hard blackish contaminants crust from archaeologically significant Pleistocene bone is investigated in this research. The objective is to determine the practical cleaning procedures and identify adequate laser parameters for cleaning archaeological bone from Sima de los Huesos (Spain) based on conservation and restoration perspectives. Bone surface cleaning was performed utilizing two Q-switched Nd:YAG lasers: sub-nanosecond pulsed lasers with emission wavelengths at 355 nm and 1064 nm, respectively, and a Yb:KGW femtosecond pulsed laser with an emission wavelength in the third harmonic at 343 nm. In all experiments, the laser beam scanning mode was applied to measure cleaning efficiency in removing contaminants and degradation products while assessing the underlying substrate surface damage. Several properties, including wavelength-dependent absorption, pulse repetition rate, and thermal properties of the material, are analyzed when evaluating the ability of these lasers to boost the cleaning efficiency of the deteriorated bone surface. Bone surface morphology and composition were studied and compared before and after laser irradiation, using Optical Microscopy, Scanning Electron Microscopy with Energy Dispersive X-ray Spectrometry (SEM-EDS), Fourier Transform Infrared Spectroscopy (FTIR), and X-ray Photoelectron Spectroscopy (XPS) characterization methods. The results indicate that 238-femtosecond UV laser irradiation with 2.37 TWcm−2 is significantly safer and more efficient toward surface contaminant desorption than sub-nanosecond laser irradiation. The results herein presented suggest that these types of fs lasers may be considered for realistic laser conservation of valuable historic and archaeological museum artifacts.

Predicting radiative intensity in transient radiative transfer with an inhomogeneous medium by spectral element discontinuous Galerkin method

Accurate prediction of the transient radiative intensity within an inhomogeneous medium is very useful in laser pulse technology. In the present work, a spectral element discontinuous Galerkin method (SEDGM) is proposed to solve transient radiative transfer with two kinds of boundary conditions, i.e., intense diffuse irradiation and short square laser irradiation. In the solving processing, the discontinuous elements are adopted to capture the large variety of radiative intensity on the element boundary. Then, the implicit temporal differencing scheme is introduced to deal with the time discretization. Several test cases are chosen to test the accuracy of the SEDGM. Results show that: (1) the SEDGM can provide good accuracy and efficiency for transient radiative transfer in an inhomogeneous medium; (2) the SEDGM has h-p convergence characteristics. Otherwise, the angle-time distributions of radiative intensities at boundaries are exhibited, and the influences of pulse duration and scattering phase function are investigated.

Mechanical and Thermal Properties of W-Ta-B Coatings Deposited by High-Power Impulse Magnetron Sputtering (HiPIMS).

We present the deposition and characterization of tungsten-tantalum diboride (W,Ta)B2 coatings prepared by the high-power impulse magnetron sputtering technique. We evaluated the influence of pulse duration and substrate bias on the properties of (W,Ta)B2 films. A high hardness of up to 35 GPa measured by nanoindentation was simultaneously obtained with good elastic properties. Changing the pulse duration greatly affected the B/(W+Ta) atomic ratio, which influenced the properties of the coatings. The deposited films are thermally stable at up to 1000 °C in vacuum and are able to withstand oxidation at 500 °C.

INFLUENCE OF PULSE DURATION ON SURFACE ROUGHNESS IN ASSISTING ELECTRODE ELECTRIC DISCHARGE MACHINING

Electrical discharge machining (EDM) is an unconventional machining process that can machine all electrically conductive materials, regardless of their physical and metallurgical properties. Due to the efficiency of machining modern engineering materials, existing EDM methods are constantly being researched and improved or developed. This paper deals with an innovative method that enables EDM machining of non-conductive ceramic material, named Assisting Electrode Electrical Discharge Machining (AEEDM). It combines electrical discharge machining with a hybrid assisting electrode. The aim of the study is to find the influence of pulse duration on surface roughness. For the set machining conditions, it was found that the surface roughness was increased by increasing the pulse duration. It should be emphasized that the supporting electrode method is used only in the electroerosion of electrically non-conductive materials.

Characterization of a Modulated X-ray Source for Ion Mobility Spectrometry.

As a highly deployed field instrument for the detection of narcotics, explosives, and chemical warfare agents, drift tube ion mobility spectrometry relies heavily upon the performance of the ionization source and mechanism of ion beam modulation. For this instrumental platform, ion chemistry plays a critical role in the performance of the instrument from a sensitivity and selectivity perspective; however, a range of instrumental components also occupy pivotal roles. Most notably, the mechanism of ion modulation or ion gating is a primary contributor to peak width in a drift tube ion mobility experiment. Unfortunately, physical ion gates rarely perform perfectly, and in addition to serving as physical impediments to ion transmission, their modulation also has undesirable field effects. Using a recently developed modulated, non-radioactive X-ray source, we detail the performance of an ion mobility spectrometry (IMS) system that is free of a gating structure and utilizes the pulsed nature of the modulated X-ray source (MXS) for both ion generation and initiation of the IMS experiment. After investigating the influence of pulse duration and spatial X-ray beam width on the analytical performance of the instrument, the possibility of using multiplexing with a shutterless system is explored. By increasing ion throughput, the observed multiplexing gain compared to a signal-averaged spectrum approaches the theoretical maximum and illustrates the capability of the MXS-IMS system to realize significant signal to noise improvements.

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.

Ultra-high intensity temporally oscillatory optical Kerr effect in Carbon Disulfide arising from electronic and molecular distortions

Temporal oscillatory structure of Kerr induced birefringence is revealed in Carbon Disulfide (CS2) using an intense femtosecond optical pump pulse. The optical Kerr effect using temporal gates were experimentally investigated using a 300 fs 600 nm probe and a 1200 nm pump pulses. Several input pump powers and focusing lenses were used to show how the oscillator nature of Kerr Gating scales with input pump intensity. Temporal curves were also simulated using the two primary Kerr (n2) mechanisms: the ultrafast electron cloud (n2(e)) and the slower molecular motion (n2(m)) distortions. Results reveal high level oscillatory structure in CS2 that had been previously unreported and show the influence of pulse duration on relaxation processes. The discrepancies between high intensity gates and corresponding simulated curves display the impactful role of plasma generation in Kerr processes at extreme intensities.

Influence of pulse duration and water/air cooling ratio on the efficiency of Er:YAG 2940 nm laser in debonding of porcelain laminate veneers: An in vitro study.

ObjectiveTo determine the effectiveness of different pulse durations (PD) and the water/air (W/A) cooling ratio of the Er:YAG 2940 nm laser that are required for debonding porcelain laminate veneers (PLV), by investigation of the needed time for PLV debonding (DT) and the changes in dental pulp temperature.Materials and MethodsThirty‐six extracted noncarious human maxillary premolars were prepared for receiving PLV. Samples were randomly assigned to six different groups, based on PD and the W/A ratio: Groups A (50 µs, 1:1), B (50 µs, 3:3), C (100 µs, 1:1), D (100 µs, 3:3), E (300 µs, 1:1), and F (300 µs, 3:3). Veneers were debonded using laser irradiation by the same parameters (270 mJ, 15 Hz) with noncontact application mode.ResultsAll 36 veneers were debonded. Samples of the 50 and 100 µs PDs showed significantly shorter DT (7.4−17 s) than that of the 300 µs which showed significantly the longest DT (104 s) among all other groups (p < .001). However, the highest elevation of pulp temperature was observed in Group E (300 µs, 1:1) which reached (3.4°C).ConclusionUsing the 50 or 100 µs PD of the Er:YAG laser was more efficient than 300 µs in reducing DT of PLVs with minimal change in pulp temperature. W/A cooling ratio had minimal influence on the DT of PLV.

Influence of Pulse Duration on X-ray Emission during Industrial Ultrafast Laser Processing.

Soft X-ray emissions during the processing of industrial materials with ultrafast lasers are of major interest, especially against the background of legal regulations. Potentially hazardous soft X-rays, with photon energies of >5 keV, originate from the fraction of hot electrons in plasma, the temperature of which depends on laser irradiance. The interaction of a laser with the plasma intensifies with growing plasma expansion during the laser pulse, and the fraction of hot electrons is therefore enhanced with increasing pulse duration. Hence, pulse duration is one of the dominant laser parameters that determines the soft X-ray emission. An existing analytical model, in which the fraction of hot electrons was treated as a constant, was therefore extended to include the influence of the duration of laser pulses on the fraction of hot electrons in the generated plasma. This extended model was validated with measurements of H (0.07) dose rates as a function of the pulse duration for a constant irradiance of about 3.5 × 1014 W/cm2, a laser wavelength of 800 nm, and a pulse repetition rate of 1 kHz, as well as for varying irradiance at the laser wavelength of 1030 nm and pulse repetition rates of 50 kHz and 200 kHz. The experimental data clearly verified the predictions of the model and confirmed that significantly decreased dose rates are generated with a decreasing pulse duration when the irradiance is kept constant.

Effect of Pulse Duration and Direction on Plasticity Induced by 5 Hz Repetitive Transcranial Magnetic Stimulation in Correlation With Neuronal Depolarization.

Introduction: High frequency repetitive transcranial magnetic stimulation applied to the motor cortex causes an increase in the amplitude of motor evoked potentials (MEPs) that persists after stimulation. Here, we focus on the aftereffects generated by high frequency controllable pulse TMS (cTMS) with different directions, intensities, and pulse durations.Objectives: To investigate the influence of pulse duration, direction, and amplitude in correlation to induced depolarization on the excitatory plastic aftereffects of 5 Hz repetitive transcranial magnetic stimulation (rTMS) using bidirectional cTMS pulses.Methods: We stimulated the hand motor cortex with 5 Hz rTMS applying 1,200 bidirectional pulses with the main component durations of 80, 100, and 120 μs using a controllable pulse stimulator TMS (cTMS). Fourteen healthy subjects were investigated in nine sessions with 80% resting motor threshold (RMT) for posterior-anterior (PA) and 80 and 90% RMT anterior-posterior (AP) induced current direction. We used a model approximating neuronal membranes as a linear first order low-pass filter to estimate the strength–duration time constant and to simulate the membrane polarization produced by each waveform.Results: PA and AP 5 Hz rTMS at 80% RMT produced no significant excitation. An exploratory analysis indicated that 90% RMT AP stimulation with 100 and 120 μs pulses but not 80 μs pulses led to significant excitation. We found a positive correlation between the plastic outcome of each session and the simulated peak neural membrane depolarization for time constants >100 μs. This correlation was strongest for neural elements that are depolarized by the main phase of the AP pulse, suggesting the effects were dependent on pulse direction.Conclusions: Among the tested conditions, only 5 Hz rTMS with higher intensity and wider pulses appeared to produce excitatory aftereffects. This correlated with the greater depolarization of neural elements with time constants slower than the directly activated neural elements responsible for producing the motor output (e.g., somatic or dendritic membrane).Significance: Higher intensities and wider pulses seem to be more efficient in inducing excitation. If confirmed, this observation could lead to better results in future clinical studies performed with wider pulses.

Performance enhancement of intermittent spray cooling with a self-rewetting fluid for relatively high-temperature applications

Comparing to continuous spray, intermittent spray is able to offer effective cooling by consuming less liquid. Targeting at relatively high-temperature applications, this study explores the influences of pulse duration and duty cycle (DC) in the cooling performance of the intermittent spray of a self-rewetting fluid, the 1.5% wt.% aqueous solution of 1-pentanol. Unlike water, using the self-rewetting fluid in intermittent spray is able to induce the inverse Marangoni convection which helps to replenish the hot spot with cool liquid even though the surface temperature exceeds 145°C. This leads to a further reduction in fluid consumption because comparable cooling rate can be delivered by spraying the self-rewetting fluid at a much lower frequency. Although dryout can still occur in the low DC regime, the inverse Marangoni convection is proven to sustain effective cooling during spray-off period in the high DC regime. As a result, cooling rate is nearly independent of DC in the high DC regime. For the self-rewetting fluid, cooling performance is not benefited from increasing the pulse duration as excess fluid simply drains out without contributing much to heat removal. Hence, a pulse duration of 1.5 s with a DC of 15% is recommended for the intermittent spray cooling of 1-pentanol/water mixtures at high wall superheats. Since the spray cooling efficiency of the self-rewetting fluid is always higher than that of water in this study, it opens up new possibility in spray quenching with more rapid cooling, better thermal uniformity, and further reduction in liquid consumption.

Measurements of acoustic radiation force of ultrahigh frequency ultrasonic transducers using model-based approach.

Even though ultrahigh frequency ultrasonic transducers over 60 MHz have been used for single-cell-level manipulation such as intracellular delivery, acoustic tweezers, and stimulation to investigate cell phenotype and cell mechanics, no techniques have been available to measure the actual acoustic radiation force (ARF) applied to target cells. Therefore, we have developed an approach to measure the ARF of ultrahigh frequency ultrasonic transducers using a theoretical model of the dynamics of a solid sphere in a gelatin phantom. To estimate ARF at the focus of a 130 MHz transducer, we matched measured maximum displacements of a solid sphere with theoretical calculations. We selected appropriate ranges of input voltages and pulse durations for single-cell applications, and the estimated ARF was in the range of tens of μN. To gauge the influence of pulse duration, an impulse of different pulse durations was estimated. Fluorescence resonance energy transfer live cell imaging was demonstrated to visualize calcium transport between cells after a target single cell was stimulated by the developed ultrasonic transducer.