Pulse Frequency Research Articles

Exploring the machining characteristics of aluminum 6061 using nanosecond pulse fiber laser machine

The present study aims to probe the influence of nanosecond laser parameters on the surface quality of aluminum material (Al 6061) using a full factorial design approach. Additionally, the study utilizes the Harris Hawks optimization (HHO) algorithm to determine the optimized laser parameters for achieving desirable surface features on straight-cut aluminum samples. Subsequently, the machined samples are analyzed through optical microscopy, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The evaluation criteria for the present study are taper, surface roughness, and heat-affected zone (HAZ) thickness. The results revealed that average laser power significantly impacted the taper (17.01%), and scanning speed contributed significantly to the taper (26.62%). The average power and scanning speed combined showed the most substantial influence on taper (47.76%). Furthermore, the average power had the most significant effect on the heat-affected zone (77.76%) and surface roughness (SR) (72.22%). The optimal conditions determined by the HHO were a pulse frequency of 100 Hz, a scanning speed of 10 mm/s, and an average power of 40 W, resulting in heat-affected zone = 36.047, surface roughness = 5.496, and taper angle = 23.188. These findings hold significant implications for enhancing the surface characteristics of aluminum in laser machining processes, thereby benefiting industries such as aerospace, automotive, and electronics.

The Effects of Bipolar Cancellation Phenomenon on Nano-Electrochemotherapy of Melanoma Tumors: In Vitro and In Vivo Pilot.

The phenomenon known as bipolar cancellation is observed when biphasic nanosecond electric field pulses are used, which results in reduced electroporation efficiency when compared to unipolar pulses of the same parameters. Basically, the negative phase of the bipolar pulse diminishes the effect of the positive phase. Our study aimed to investigate how bipolar cancellation affects Ca2+ electrochemotherapy and cellular response under varying electric field intensities and pulse durations (3-7 kV/cm, 100, 300, and 500 ns bipolar 1 MHz repetition frequency pulse bursts, n = 100). As a reference, standard microsecond range parametric protocols were used (100 µs × 8 pulses). We have shown that the cancellation effect is extremely strong when the pulses are closely spaced (1 MHz frequency), which results in a lack of cell membrane permeabilization and consequent failure of electrochemotherapy in vitro. To validate the observations, we have performed a pilot in vivo study where we compared the efficacy of monophasic (5 kV/cm × ↑500 ns × 100) and biphasic sequences (5 kV/cm × ↑500 ns + ↓500 ns × 100) delivered at 1 MHz frequency in the context of Ca2+ electrochemotherapy (B16-F10 cell line, C57BL/6 mice, n = 24). Mice treated with bipolar pulses did not exhibit prolonged survival when compared to the untreated control (tumor-bearing mice); therefore, the bipolar cancellation phenomenon was also occurrent in vivo, significantly impairing electrochemotherapy. At the same time, the efficacy of monophasic nanosecond pulses was comparable to 1.4 kV/cm × 100 µs × 8 pulses sequence, resulting in tumor reduction following the treatment and prolonged survival of the animals.

The deletion of nuclear progesterone receptors from kisspeptin cells does not impair negative feedback in female mice.

Reproductive function in mammals depends on the ability of progesterone to suppress pulsatile gonadotrophin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion in a homeostatic negative feedback loop. Previous research identified that cells upstream from GnRH neurons expressing the nuclear progesterone receptor (PGR) are required for progesterone-negative feedback. However, the identity of these cells and the mechanism by which they reduce GnRH/LH pulsatile secretion is unknown. We aimed to address the hypothesis that PGR expressed by a neural population in the arcuate nucleus recently identified as the GnRH pulse generator, cells expressing Kisspeptin, Neurokinin B, and Dynorphin (KNDy cells), mediate progesterone negative feedback. To achieve this, we utilized female mice with the PGR gene conditionally deleted from kisspeptin cells (KPRKO mice) and observed a substantial decrease in the percentage of KNDy neurons co-expressing PGR mRNA (11% in KPRKO mice versus 86% in wildtype mice). However, KPRKO mice did not display changes in the frequency or amplitude of LH pulses in diestrus or estrus, nor in the ability of exogenous progesterone to blunt a post-castration rise in LH. Further, mRNA expression of arcuate kisspeptin and dynorphin, which are excitatory and inhibitory to GnRH secretion, respectively, remained unaltered in KPRKO mice compared to wildtype controls. Together, these findings show that the near-complete loss of PGR signaling from KNDy cells does not impact negative feedback regulation of GnRH pulse generation in mice, suggesting that feedback through this receptor can occur via a small number of KNDy cells or a yet unidentified cell population.

Dynamic Characteristics of Pressure-Balanced Metal Bellows in Fluid–Structure Interaction

As a flexible component in high-pressure vessels and pipeline systems, bellows experience significant fluid–structure interaction effects under high-speed internal fluids and external vibrations. Nevertheless, their dynamic response mechanisms coupled with fluid–structure interaction mentioned below have not yet been clarified so far. In this work, a novel pressure-balanced metal bellow (PBMB) for low-stiffness and high-pressure resistance is firstly proposed. Several fluid–structure interaction models were considered to study the dynamic response characteristics of the PBMB. An experimental platform associated with fluid–structure interaction was established to validate the effectiveness of its vibration attenuation performance. The results indicate that the PBMB has an obvious vibration attenuation effect in the range of 5–90[Formula: see text]Hz, and super-harmonic and sub-harmonic resonance phenomena occur in the range of 90–200[Formula: see text]Hz. Under constant fluid conditions, fluid density, viscosity, flow velocity, and pressure are positively correlated with the response amplitude of the PBMB. The response of the PBMB oscillates at the fluid entry point due to both pulsating flow velocity and pulsating pressure. After several cycles, the response caused by pulsating flow velocity gradually decays and stabilizes. Thus, the impact of pulsating frequency on the stability of the response of bellows is insignificant during the initial cycles.

Large eddy simulation of turbulent transport and thermal enhancement in a steam-cooled ribbed channel

Pulsating flow, as an active heat transfer enhancement technique, is expected to further improve thermal performance. To demonstrate the potential value of pulsating flow in blade cooling, a numerical investigation is conducted on the flow and heat transfer in a steam-cooled ribbed channel under steady and pulsating inflow at Re = 12000. LES, based on OpenFOAM-8, is employed and precursor simulation method is used to generate fully developed turbulent inflow. Three operating conditions, steady inflow (StF = 0), low frequency pulsation (StF = 0.02) and medium frequency pulsation (StF = 0.08), are studied. The features under steady inflow condition (StF = 0) are firstly discussed, indicating that, due to the entry effect, the ribbed channel can be divided into two regions with different vortex motion behaviors. The ejections induced by vortex evolution enhance turbulent and energy transport between the sidewall and mainstream. Two cases of pulsating inflow are then carried out, finding that stronger ejections appear and low heat transfer area is significantly improved. Corresponding to low frequency pulsation (StF = 0.02) and medium frequency pulsation (StF = 0.08), the Nusselt number has an increase of 3.511 % and 14.242 %, respectively, and friction factor has a rise of 3.934 % and 8.253 %, compared with steady inflow. The thermal performance factor is increased by 11.262 % at StF = 0.08, indicating better cooling performance than the rise of 2.188 % at StF = 0.02. It is suggested that pulsating flow with medium frequency pulsation has positive performance in a steam-cooled ribbed channel.

Long-living periodic solutions of complex cubic-quintic Ginzburg-Landau equation in the presence of intrapulse Raman scattering: A bifurcation and numerical study.

We have found long-living periodic solutions of the complex cubic-quintic Ginzburg-Landau equation (CCQGLE) perturbed with intrapulse Raman scattering. To achieve this we have applied a model system of ordinary differential equations (SODE). A set of the fixed points of the system has been described. A complete phase portrait as well as phase portraits near the fixed points have been built for a proper choice of parameters. The behavior of the model system near the fixed points has been determined. We have presented a detailed description of the subcritical Poincaré-Andronov-Hopf bifurcation due to the intrapulse Raman scattering that appears at one of the fixed points. We have established that there appears an unstable limit cycle in the SODE. To check the validity of the obtained results from the model system we have compared them with the results of the numerical solution of the CCQGLE perturbed with intrapulse Raman scattering. There has been found a remarkable correspondence between the obtained numerical results for the amplitude and frequency of the soliton pulses and the results for these parameters of the bifurcation theory. We have observed that the numerical characteristics of the propagating solitonlike pulses-amplitude, frequency, width, and position-periodically change if we change the distance with a period determined by the bifurcation analysis.

Soft‐switching boundary and piecewise control of LLC converter with hybrid modulation

AbstractThe voltage gain range of LLC converter can be effectively broadened by using the hybrid modulation of phase‐shift modulation (PSM) and pulse frequency modulation (PFM). However, the harmonic of resonant tank increases dramatically in PSM mode, and the first harmonic approximation is no longer suitable for solving the voltage gain. Moreover, the conditions for soft switching in PSM mode are not clear. Meanwhile, the small‐signal models of the converter in different modulation modes are quite different, and it is difficult for a fixed controller to ensure a good dynamic performance of the converter in both modulation modes. To address above issues, a voltage gain modeling method of PSM mode LLC converter is proposed. By establishing the function between input current and resonant current, the voltage gain model of the converter is obtained according to the power conservation. Moreover, considering the parasitic capacitance charge and resonant current commutation time, the condition for soft switching is derived. Furthermore, a control strategy of LLC converter in hybrid modulation is proposed. The piecewise proportional integral (PI) controller is adopted, and the parameters of the controller are dynamically adjusted with the modulation mode, so that the converter has excellent dynamic performance in both modes. And the hysteresis control is used to ensure the stability of mode switching. An experimental prototype with 200–340 V input and 28 V/1 kW output was built based on gallium nitride (GaN) devices. The peak efficiency was 97.82%, and the power density was 65.76 w/in3.

Advancements in Non-Thermal Processing Technologies for Enhancing Safety and Quality of Infant and Baby Food Products: A Review.

Breast milk is the main source of nutrition during early life, but both infant formulas (Ifs; up to 12 months) and baby foods (BFs; up to 3 years) are also important for providing essential nutrients. The infant food industry rigorously controls for potential physical, biological, and chemical hazards. Although thermal treatments are commonly used to ensure food safety in IFs and BFs, they can negatively affect sensory qualities, reduce thermosensitive nutrients, and lead to chemical contaminant formation. To address these challenges, non-thermal processing technologies such as high-pressure processing, pulsed electric fields, radio frequency, and ultrasound offer efficient pathogen destruction similar to traditional thermal methods, while reducing the production of key process-induced toxicants such as furan and 5-hydroxymethyl-2-furfural (HMF). These alternative thermal processes aim to overcome the drawbacks of traditional methods while retaining their advantages. This review paper highlights the growing global demand for healthy, sustainable foods, driving food manufacturers to adopt innovative and efficient processing techniques for both IFs and BFs. Based on various studies reviewed for this work, the application of these novel technologies appears to reduce thermal processing intensity, resulting in products with enhanced sensory properties, comparable shelf life, and improved visual appeal compared to conventionally processed products.

Vibration and Flow Characteristics of a 200 MW Kaplan Turbine Unit under Off-Cam Conditions

Kaplan turbine units can adjust their blades to achieve wider outputs without a significant loss of efficiency. The combination of guide vane angle (GVA) and blade angle (BA) is selected based on efficiency curves obtained from cam tests. However, the vibration characteristics are not considered in the test. The vibration and flow characteristics are complex with different combinations of guide vane and blade angles. Different cam relation selection principles lead to varying machine vibration and flow characteristics. In this research, the flow and vibration characteristics were obtained by means of field test and numerical simulation. Vibration, pressure pulsation, and other stability indicators have been extracted and investigated under off-cam conditions. The flow and variation rules of different indicators have been thoroughly researched. The findings suggest that the magnitude of vibration in the X direction surpassed that in the Y direction for the head cover, upper frame, and lower frame under 22 experimental conditions. The disparity between the head cover and upper frame in both directions was not significant, whereas a substantial contrast existed between the lower frame in the X and Y directions. The calculation results indicate that when the guide vane angle was small, vortices appeared near the high-pressure edge of the runner in the vaneless region and caused disorganized flow lines in the runner, and this complex vortex behavior led to multiple frequency components in the pressure pulsation frequency domain. The conclusions provide references for the designers of Kaplan turbine units and improves the operating safety of Kaplan turbine power stations.

The Effects of Pulsed Electrospinning Process Variables on the Size of Polymer Fibers Established with a 23 Factorial Design.

In the present study, the influence of the electrical parameters of the pulsed electrospinning process, such as the electrical voltage, the frequency of pulses, and the pulse duration, on the structure of obtained nonwovens was determined for the first time. It was found that all the parameters studied strongly influence the average diameter of the obtained fibers and that the pulsed electrospinning process carried out under specific conditions makes it possible to obtain, among other things, bimodal nonwovens. A 23 factorial design was used to determine how the selected electrical parameters of the pulsed electrospinning process affect the structure of the resulting electrospun mats. It is shown, among other things, that by appropriately selecting the parameters of the electrospinning process, the thickness of fibers can be controlled, resulting in nonwovens with a desired morphology.

Artificial intelligence based experimental investigation of underwater fiber laser transmission process during micro-channelling operation on PMMA

Industries that engage in laser-based material processing are increasingly turning to fiber lasers as one of the most effective laser systems available. Using a pulsed fiber laser system, an experimental investigation of underwater laser micro-channelling on hard to machine thick PMMA has been conducted in this research work. Submerged laser transmission cutting which is also known as underwater laser induced backside machining helps to generate clean kerf edge without presence of mushy region, which is very common during laser machining of thick PMMA with wavelength of near infrared region. Submerged conditions are used here for laser transmission micromachining in order to reduce adverse thermal effects and microcracking or charring inside the material. Pulse frequency, working power, and cutting speed have been selected as the input parameters. As machining responses, the depth of the micro-channel, the width of the kerf, and the width of the heat affected zone (HAZ) have been considered. To find the ideal parametric condition for simultaneously achieving numerous goals, Response Surface Methodology (RSM) and AI-based Teaching Learning-Based Optimisation (TLBO) have been used. The TLBO technique determined that the optimal laser machining settings are a power setting of 13.98 %, a pulse frequency of 50 kHz, and a cutting speed of 0.20 mm/sec. These parameters result in a minimum HAZ width of 4.1874 µm, a minimum kerf width of 22.3698 µm, and a maximum depth of cut of 37.1478 µm. Underwater laser processing reduces heat affected zone and redeposition surrounding micro-channels, creating a cleaner, finer structure.

Effects of growth rate and dynamic substrate tilt on properties of Au-Ta alloy films deposited by high-power impulse magnetron sputtering

Gold‑tantalum (AuTa) alloys are promising for next-generation hohlraums for magnetically-assisted indirect-drive inertial confinement fusion. Hohlraum fabrication involves sputter deposition of ultrathick coatings on sphero-cylindrical substrates. The control of physical properties of such coatings remains a challenge. Here, we systematically study effects of the growth rate and dynamic substrate tilt on properties of AuTa4 films deposited onto rotating planar substrates mounted at different tilt angles to mimic different regions of the sphero-cylindrical surface of a hohlraum. We use high-power impulse magnetron sputtering (HiPIMS) in the constant charge per pulse mode with a pulse duration of 100 μs, a charge per pulse of 190 μC, a peak target current of about 3 A, and the pulse frequency varied in the range of 400–1400 Hz. The Langmuir probe, mass-resolved ion energy spectrometry, and optical emission spectroscopy are used to monitor plasma discharge characteristics in order to isolate and study effects of the growth rate. The deposition rate and the ballistics and energetics of depositing species are estimated by Monte Carlo simulations. Results show that the film microstructure, crystallographic phase, residual stress, and electrical resistivity strongly depend on both the deposition rate and substrate tilt, highlighting their critical role in tailoring properties of AuTa films during hohlraum fabrication.

Chaotic Behavior and Heat Transfer Analysis of Pulsating Flows with Different Frequencies

Due to the rapid development of electronic devices, the improvement of air–cooling methods for thermal management is urgent. In the present work, a promising way of coupling pulsating flow and vortex generators is proposed to eliminate the impacts of severe local high-temperature regions behind the vortex generators. Different from the traditional qualitative analysis, chaos is introduced to identify the quantitative impacts of the nonlinear dynamics of the coupling system. Particularly, the flow field was examined using the line stretching and the Poincaré map, and the chaotic characteristics of high-frequency pulsating flow were investigated. The results show that high-frequency pulsating flow enhances heat transfer mainly by promoting chaotic mixing. The chaotic fluid repeatedly stretches and folds, which increases the line stretching. Thus, the line stretching distribution can represent the heat transfer. Compared to the steady flow case, at Reynolds number of 1024 and pulsation frequency of 250 Hz, pulsating flow improves the Nusselt number by 5.82% and reduces friction factor by 2.62%, resulting in an improvement of thermal performance factor by 6.76%.

Positional Regulation, Sucking Reflex and Incidence When Given Nutrition Through OGT in High-Risk Infants with Low Birth Weight Infants in the Nicu Room: A Case Study of Waled Hospital

High-risk babies are babies born at 32 – 36 weeks of gestation/prematurely, babies whose mothers suffer from Diabetes Mellitus, babies with a history of apnea, babies with seizures, sepsis, asphyxia, babies with bleeding disorders or breathing problems. Problems that often arise in cases of LBW babies include unstable body temperature, breathing problems, digestive and nutritional disorders, liver immaturity, anaemia, intraventricular bleeding, seizures, infections, hypoglycemia, hyperglycemia and hypocalcemia. This study aims to provide nursing care to babies at high risk in the Nicu Room at Waled Hospital, Cirebon Regency, on 27 December 2023. Examination of the sucking reflex is recommended as a screening that shows intact motor neuron function in neonates. The sucking reflex is well-developed in normal babies and is coordinated with breathing. Inhibition of the sucking reflex in the first hours of life will affect the ability to suck at the beginning of life and will directly hinder the nutritional intake received by the baby. Arranging sleeping positions for newborn babies is the role of the neonatal nurse in providing routine daily care. Positioning, especially for premature babies, is not easy. Positioning errors can result in changes in physiological status (increased respiratory rate, pulse frequency, and decreased oxygen saturation), disturbed comfort and quality of sleep, drinking intolerance, hip joint deformity, and bleeding in the brain. The issues affecting all three clients have not been resolved. However, interventions such as positioning, assessing sucking reflexes in high-risk babies, and providing nutrition through OGT are ongoing, with efforts to set the supine sleep position during enteral nutrition. While the problems faced by the high-risk infants in this study are not yet resolved, ongoing nursing interventions are crucial in managing their care. Continued attention to proper positioning, monitoring of sucking reflexes, and nutritional support through OGT is vital for improving the health outcomes of these vulnerable infants.

Effect of liquid level monitor gas injection point size on information source amplitude-frequency characteristics

In order to analyse the effect of the injection point size of the CBM (Coalbed Methane) well level monitor on the amplitude and frequency of pressure pulsations in the wellhead manifold, numerical simulations and experiments were carried out to investigate the effect of different injection point sizes on the amplitude and frequency of pressure pulsations downstream of the sudden expansion structure. Using compressed air as the fluid and the size of the injection point as the variable, the amplitude and frequency of pressure pulsations at different locations downstream of the sudden expansion structure were tested. The results show that the pressure pulsation amplitude is affected by the size of the injection point, and the larger the injection point is, the larger the pressure pulsation amplitude is; the size of the injection point has less influence on the pressure pulsation frequency downstream of the protruding and expanding structure, and the pressure pulsation frequency at 0.5 m and 1 m downstream of the protruding and expanding structure is in the vicinity of 76 Hz. Therefore, the echo signal processing should be filtered around this frequency to obtain accurate liquid level echo signals, so as to improve the accuracy of liquid level monitoring and realise the efficient development of coalbed methane wells.

The influence of magnetic fields and fluctuating currents in the complex of medical rehabilitation on the state of peripheral blood flow in the early postoperative period of breast cancer

Abstract. Taking into account the high prevalence of complications after radical surgical treatment of breast cancer, medical rehabilitation courses were developed and conducted in the early postoperative period (2–4 days after surgery) with the inclusion of physical factors: fluctuating currents, extended local magnetic therapy, general magnetic therapy, as well as physical therapy, training with biofeedback on the support reaction (balance therapy) and individual sessions with a medical psychologist. Purpose. In a comparative aspect, study the indicators of peripheral microcirculation to assess the effectiveness of various methods of magnetic therapy and fluctuarization in patients operated on for breast cancer in the early postoperative period. Material and methods. The study included 107 women operated on for breast cancer 2–4 days after surgery. Using simple randomization, the patients were divided into 3 groups, comparable in age, clinical and functional indicators; at all stages of the study, the patients underwent clinical, functional and laboratory examinations, and questionnaires. In the 1st group (n=35), in the early postoperative period, in the complex of medical rehabilitation, 10 fluctuarization procedures were carried out using an expanded technique; in the 2nd group (n=35), patients received 10 procedures of expanded magnetic therapy; in the 3rd group (n =37) patients received 10 procedures of general magnetic therapy. In addition to physiotherapy, all patients received a complex of physical therapy, balance therapy and classes with a medical psychologist. Results. In the early stages, fluctuating currents seemed more effective, which, due to chaotic changes in the frequency and amplitude of current pulses, help restore conduction along peripheral nerves and activate muscle fiber contractility, improving hemodynamics. It should be noted the effect of extended and general magnetic therapy on improving the contractility of the muscles of the upper limb and the conductivity of peripheral nerve fibers, as well as on the restoration of capillary blood flow. Early signs of the regeneration process are a restructuring of microvascular regulation, namely an increase in the contribution of nutritional blood flow, the activity of myogenic and neurogenic oscillations in hemodynamics, and an increase in blood flow activity.

Feasibility of capturing vessel expansion with 4D-CTA: Phantom study to determine reproducibility, spatial and temporal resolution.

Dynamic Computed Tomography Angiography (4D CTA) has the potential of providing insight into the biomechanical properties of the vessel wall, by capturing motion of the vessel wall. For vascular pathologies, like intracranial aneurysms, this could potentially refine diagnosis, prognosis, and treatment decision-making. The objective of this research is to determine the feasibility of a 4D CTA scanner for accurately measuring harmonic diameter changes in an in-vitro simulated vessel. A silicon tube was exposed to a simulated heartbeat. Simulated heart rates between 40 and 100 beats-per-minute (bpm) were tested and the flow amplitude was varied, resulting in various changes of tube diameter. A 320-detector row CT system with ECG-gating captured three consecutive cycles of expansion. Image registration was used to calculate the diameter change. A vascular echography set-up was used as a reference, using a 9MHz linear array transducer. The reproducibility of 4D CTA was represented by the Pearson correlation (r) between the three consecutive diameter change patterns, captured by 4D CTA. The peak value similarity (pvs) was calculated between the 4D CTA and US measurements for increasing frequencies and was chosen as a measure of temporal resolution. Spatial resolution was represented by the Sum of the Relative Percentual Difference (SRPD) between 4D CTA and US diameter change patterns for increasing amplitudes. The reproducibility of 4D CTA measurements was good (r ≥ 0.9) if the diameter change was larger than 0.3mm, moderate (0.7 ≤ r<0.9) if the diameter change was between 0.1 and 0.3mm, and low (r<0.7) if the diameter change was smaller than 0.1mm. Regarding the temporal resolution, the amplitude of 4D CTA was similar to the US measurements (pvs ≥ 90%) for the frequencies of 40 and 50bpm. Frequencies between 60 and 80bpm result in a moderate similarity (70% ≤ pvs<90%). A low similarity (pvs<70%) is observed for 90 and 100bpm. Regarding the spatial resolution, diameter changes above 0.30mm result in SRPDs consistently below 50%. In a phantom setting, 4D CTA can be used to reliably capture reproducible tube diameter changes exceeding 0.30mm. Low pulsation frequencies (40 or 50bpm) provide an accurate measurement of the maximum tube diameter change.

Research on Polarization Modulation of Electro-Optical Crystals for 3D Imaging Reconstruction.

A method for enhancing the resolution of 3D imaging reconstruction by employing the polarization modulation of electro-optical crystals is proposed. This technique utilizes two polarizers oriented perpendicular to each other along with an electro-optical modulation crystal to achieve high repetition frequency and narrow pulse width gating. By varying the modulation time series of the electro-optical crystal, three-dimensional gray images of the laser at different distances are acquired, and the three-dimensional information of the target is reconstructed using the range energy recovery algorithm. This 3D imaging system can be implemented with large area detectors, independent of the an Intensified Charge-Coupled Device (ICCD) manufacturing process, resulting in improved lateral resolution. Experimental results demonstrate that when imaging a target at the distance of 20 m, the lateral resolution within the region of interest is 2560 × 2160, with a root mean square error of 3.2 cm.

Study on Pulsed Gas Tungsten Arc Lap Welding Techniques for 304L Austenitic Stainless Steel

The lap welding process for 304L stainless steel welded using the pulsed gas tungsten arc welding (P-GTAW) procedure was studied, and the effects of the pulse welding parameters (the peak current, background current, duty cycle, pulse frequency, and welding speed) on the macroscopic morphology, microstructure, and mechanical properties of the resultant lap joints were investigated. Tensile tests, hardness measurements, and SEM/EDS/XRD analyses were conducted to reveal the characterization of the joint. The relationships between the welding parameters; certain joint characteristic dimensions (the weld width, D; the weld width on the lower plate, La; the weld depth on the lower plate, P; and the minimum fusion radius, R); and the maximum tensile bearing capacity were studied. The weld zone was primarily composed of vermicular ferrite, skeletal ferrite, and austenite, and no obvious welding defects, precipitation, or phase transformations were evident in the weld. Microhardness tests demonstrated that the weld microhardness was highest in the base metal zone and lowest in the weld zone. As the heat input increased, the average microhardness decreased. The hardness difference reached 17.6 Hv10 due to the uneven grain size and the transformation of the structure to ferrite in the weld. The fracture location in welded joints varied as the heat input changed. In some parameter combinations, the weld tensile strength was significantly higher than that of the base material, with fractures occurring in the weld. Scanning electron microscopy results exhibited an obvious dimple morphology, which is a typical form of ductile fracture. XRD revealed no significant phase changes in the weld zone, with a higher intensity of the austenite diffraction peaks compared to the ferrite diffraction peaks.

Noncirculating current series resonant converter with pulse frequency modulation

SummaryIn this paper, an asymmetric pulse frequency modulation (APFM) is applied to the full‐bridge series resonant converter with a secondary LC resonant tank. Different from the traditional PFM, the upper and lower switches have complementary gate drivers and the lower switches have constant on time of half‐resonant period in this paper. Thanks to the resonant tank moved to the secondary side with the adopted APFM, the maximum magnetic flux density Bm of a high‐frequency transformer (HFT) is only concerned with the fixed resonant frequency rather than the variable switching frequency. Hence, the switching frequency can be widely regulated, as well as the voltage gain. Furthermore, the circulating current flowing back to the input voltage source in the traditional LC series resonant converter can be eliminated by the APFM, leading to a low resonant current peak value. The operation principles and characteristics of the adopted method are analyzed in detail. Finally, a 500 W/70–120 V to 300 V/21–180 kHz prototype is built, and the experimental results verified the theoretical analysis well.