Pulsed Mode Research Articles

Laser Powder Bed Fusion and Heat Treatment of the Martensitic Age‐Hardenable Steel (1.2709)

The primary objective of this study is to clarify the fundamental question of whether, in principle, it is possible to dispense with a prior solution annealing process in favor of a direct aging heat treatment for specimens of maraging stainless steel grade X3NiCoMoTi18‐9‐5 (1.2709) produced by laser powder bed fusion (LPBF). The waiver of a solution annealing process would significantly increase the process efficiency and thus support a sustainable and resource‐friendly production of such components. Therefore, the hardness, microstructure, and the present phases of specimens in as‐built + aged condition (AB + A) and solution‐annealed + aged (SOL + A) are examined during this study. Initially, an extended parameter study is performed using a Renishaw AM 250 LPBF system equipped with a pulsed mode laser system to achieve the highest possible apparent density. As test specimens, small cubes are produced for parameter study and are analyzed for porosity by means of optical microscopy. To investigate the relationship between microstructure and hardness in different material states, one series of specimens is aged directly after LPBF processing in the as‐built state (AB + A). For comparison, the other series was solution annealed at 820 °C for 60 min, quenched in water and then aged (SOL + A). A maximum hardness value of 614 HV1.0 is achieved for specimen aged at 490 °C for 120 min in as built condition (AB + A), while 624 HV1.0 was measured for specimen aged at 490 °C for 180 min in conventionally solution annealed + aged (SOL + A) condition. Significant austenite reversion is not observed at aging temperature of 490 °C in both cases. Aging of specimens at temperatures of 540 and 600 °C resulted in reduction of specimen hardness due to higher percentage of austenite reversion. No significant difference between the hardness values of AB + A and SOL + A specimens is observed. It can therefore be concluded that, in principle, conventional solution annealing and ageing can be dispensed with in favor of direct aging. However, as the results are based on small sized specimens, further investigations into the scalability are needed.

Effect of Er:YAG laser on debonding zirconia and lithium disilicate crowns bonded with 2- and 1-bottle adhesive resin cements.

Erbium-doped yttrium-aluminum-garnet (Er:YAG) laser debonding of zirconia and lithium disilicate restorations is increasingly used for a range of clinical applications. Using rotary instruments to remove such restorations for any purpose has proven to be challenging. Erbium laser has been reported to be a conservative method for removing ceramic restorations. There is little data in the literature about the effect of adhesive resin cement type on the debonding time of the ceramic restoration using the Er:YAG laser. To evaluate and compare the time required for the Er:YAG laser to debond zirconia and lithium disilicate crowns bonded with a 2- and 1-bottle adhesive resin cement systems. Forty extracted premolar teeth were prepared and scanned for milled 40 CAD/CAM crowns. Teeth were randomly assigned into groups (n = 10 per group): 3 mol% yttria-partially stabilized zirconia crowns 3Y-PSZ (G1a) bonded with Panavia™ V5 (2-bottle adhesive resin cement), Zirconia 3Y-PSZ crowns (G1b) bonded with RelyX™ Ultimate (1-bottle adhesive resin cement), and for the lithium disilicate crowns bonded with the two types of cements (G2a, G2b). Each specimen was irradiated with an Er:YAG laser at 335 mJ, 15 Hz, 5.0 W, and 50-ms pulse duration (super short pulse mode). The irradiation time required for crowns to be successfully debonded was recorded for each specimen. Data were statistically analyzed using ANOVA and Tukey HSD post-hoc test (p < 0.05), at the 95 percent level of confidence. The intaglio surface of the debonded crown was analyzed using scanning electron microscopy (SEM). The mean ± standard deviation times needed for crown debonding were 5.75 ± 2.00 min for the G1a group, 4.79 ± 1.20 min for group G1b, 1.69 ± 0.49 min for group G2a, and 1.12 ± 0.17 for group G2b. There was no statistically significant difference in debonding time between the 2- and 1- bottle adhesive resin cement within the groups G1a and b (p = 0.2914), or between groups G2a b (p = 0.7116). A statistically significant difference (p < 0.05) was found between groups G1a and G2a and b and between groups G1b and G2a and b were SEM analysis showed no changes in the microstructure of the ceramic surface after Er:YAG laser irradiation. Zirconia and lithium disilicate restorations can be debonded using Er:YAG lasers in a safe and efficient manner. There is no significant difference in the debonding time between the 2- and 1- bottle adhesive resin cement systems used in this study. Retrieving zirconia and lithium disilicate ceramics can be a challenging process when using diamond rotary instruments. ER:YAG lasers may efficiently debond these ceramics from the tooth structure, independent of the bonding process used for bonding them.

DRiFT current mode, trigger settings and flexible detector specifications applied to scintillator arrays

MCNP radiation transport output is post-processed by DRiFT, a Detector Response Function Toolkit to simulate detailed nuclear instrumentation response. DRiFT can be used to assess the performance and potential limitations of scintillator, gas, and semiconductor detectors under a variety of simulated conditions not easily achievable in a laboratory setting. This work describes new updates in DRiFT for scintillator simulations which focus on the capability to simulate scintillators in current mode, an expansion of trigger options, and the ability to customize individual detector properties in a simulation. These improvements are designed to facilitate the ability to model large arrays of scintillator detectors with higher fidelity than was previously possible and are demonstrated in three examples. The first shows the difference between operating DRiFT in current and pulse mode. In the second example, which is intended to demonstrate deviations in individual detector performance, each detector has properties (PMT gain, optical transport, scintillation yield, etc.) that vary between detectors and are specified in DRiFT. A final example examines how DRiFT could be used to optimize digitizer settings in high rate measurements with split signals using the new common trigger option.

Nanoscale Analysis of Frozen Water by Atom Probe Tomography Using Graphene Encapsulation and Cryo-Workflows.

There has been an increasing interest in atom probe tomography (APT) to characterize hydrated and biological materials. A major benefit of APT compared to microscopy techniques more commonly used in biology is its combination of outstanding three-dimensional (3D) spatial resolution and mass sensitivity. APT has already been successfully used to characterize biominerals, revealing key structural information at the atomic scale, however there are many challenges inherent to the analysis of soft hydrated materials. New preparation protocols, often involving specimen preparation and transfer at cryogenic temperature, enable APT analysis of hydrated materials and have the potential to enable 3D atomic scale characterization of biological materials in the near-native hydrated state. In this study, samples of pure water at the tips of tungsten needle specimens were prepared at room temperature by graphene encapsulation. A comparative study was conducted where specimens were transferred at either room temperature or cryo-temperature and analyzed by APT by varying the flight path and pulsing mode. The differences between the analysis workflows are presented along with recommendations for future studies, and the compatibility between graphene coating and cryogenic workflows is demonstrated.

Performance evaluation of GaN etching using Cl2-based plasma with bias pulsing

Reducing plasma-induced damage (PID) is one of the most challenging goals for the fabrication of GaN-based MOS-HEMT. In this paper, we propose a performance evaluation of a Cl2-based etching chemistry using bias pulsing mode for GaN applications. The plasma-induced damage using bias pulsing has been compared to conventional reactive ion etching (RIE) and atomic layer etching (ALE) processes using sheet resistance (Rsheet) measurements. This pulsing mode showed low plasma-induced damage, similar to ALE. In addition, it keeps an acceptable GaN etching rate, showing that pulsing mode has potential for industrial applications.

Study of a Laboratory Circuit with a Warm Baseboard in Pulse Mode

The increasing global energy demand is a problem that people have been paying attention to, people's demand for energy is increasingly urgent, and improving energy efficiency has become a hot topic in this century. Studies have shown that pulsating flow has an important effect on heat transfer, and it has been concluded in most literatures that turbulent pulsation can enhance heat transfer in different degrees. Pulsation heat transfer is a comprehensive heat transfer process, and the best heat transfer performance can be achieved only when the thermal resistance of each part is reasonably coordinated. Based on the principle of hydraulic shock, this paper develops a device with warm substrate which can be used to increase the pulsating pressure and enhance the heat transfer efficiency of pulsating flow. Firstly, the construction scheme of the experimental device is proposed, and the working principle of the experimental device is described in detail. The complex impedance, frequency function, amplitude-frequency characteristic and phase-frequency characteristic are obtained by mathematical transformation of power supply circuit. Finally, the frequency response of the circuit is constructed.

Эволюция транспупиллярной лазерной коагуляции сетчатки в лечении активной ретинопатии недоношенных: от режима одиночного импульса до навигационного сопровождения

Abstract Evolution of transpupillary laser coagulation of the retina in the treatment of active retinopathy of prematurity: from single pulse mode to navigational support A.V. Tereshchenko, I.G. Trifanenkova, Yu.A. Sidorova, V.V. Firsova, V.V. Shaulov S. Fyodorov Eye Microsurgery Federal State Institution, Kaluga branch, Kaluga, Russian Federation K.E. Tsiolkovski Kaluga State University, Kaluga, Russian Federation Purpose. To present the development stages and results of 18 years of experience in laser technologies application for the treatment of premature infants with active ROP in the Kaluga branch of S. Fyodorov Eye Microsurgery Federal State Institution. Material and methods. Transpupillary laser coagulation of the retina (LCR) was performed in 1583 children (2537 eyes) with active ROP for the period from 2004 to 2021. LCR was carried out with various stationary laser ophthalmocoagulators. Stages 2 and 3 of active ROP with an unfavorable disease course, stage of early clinical manifestations, manifestation of aggressive posterior ROP were indications for laser treatment. Results. Transpupillary LCR began to be performed for children with active ROP with a stationary ophthalmic coagulator for the first time in Kaluga branch of the S. Fyodorov Eye Microsurgery in 2004. The technology of patterned LCR in active ROP was applied for the first time at domestic and international clinical practice, in the Kaluga branch of Eye Microsurgery in 2009. Pattern LCR began to be performed on the Integre Pro Scan device in 2016. Pattern with the most dense and uniform arrangement of laser applications – hexagonal – was identified. In 2021 transpupillary LCR of the avascular zone of the retina was performed in automatic mode with navigation support on the Navilas 577s laser system. It was possible to perform LCR of the avascular zone of the retina up to the dentate line in all cases. Regression of disease was achieved in 100% of cases. Conclusion. Evolution of laser technologies and the experience of their use demonstrate the high efficacy, safety and predictability of the results of laser treatment of active ROP. Modern pattern laser techniques are highly effective, safe, dosed and tissue-saving, which can serve as the basis for standardization of retinal laser coagulation technology in the treatment of active ROP. Key words: retinopathy of prematurity, unfavorable type of course, laser coagulation of the retina, hexagonal pattern, navigation system

Void closure in a pulsed complex plasma in microgravity

A new experimental method for creating void-free complex (dusty) plasmas under microgravity conditions is presented. The method is based on a pulsed operation mode of a four-channel radio frequency generator for plasma sustainment. A dust cloud of micrometer-sized particles can be immersed in the bulk of a low temperature plasma under microgravity conditions. It typically contains a central volume depleted of particles—the void—that prevents the generation of large, continuous clouds. Experiments performed at different neutral gas pressures and discharge volumes during the microgravity phase of a parabolic flight show that the central void is closed completely once the pulsed operation mode is applied. The particle cloud shape and the density distribution within the cloud are practically independent of the pulse period within the investigated parameter range and mainly depend on the overall discharge parameters neutral gas pressure and discharge volume. This indicates that the pulsed operation of the plasma source does not introduce new physical effects on the particles aside from the void closure. The proposed method has great potential for future application in experimental facilities dedicated to fundamental studies of large three-dimensional, homogeneous complex plasma systems in microgravity.

POROSITY DISTRIBUTION AND MICROHARDNESS OF A COLD ARC PULSE™ WIRE ARC ADDITIVELY MANUFACTURED AlSix MECHANICAL PLATE

Porosity is known as the main problem of aluminum alloys regardless of the method for formation of aluminum components due to the unique thermophysical properties of this metal. The larger the heat input is, the higher the likelihood is of formation of pores within the structure of the components, whether be they caused by the gas adsorption or due to the expansion and then shrinkage of the material during the heating/cooling cycle. Since the pore formation mechanisms of additively manufactured specimens is still unclear, during the present work a wire arc additively manufactured specimen was used in order to study the concentration of pores within the structure of the last along its volume. Additionally, the less studied cold arc pulse (CAP) mode was employed during the specimens manufacturing. Since the structure directly influences the mechanical properties of the components, a microhardness map was prepared as well as investigation of the microhardness as a function of the specimen’s height. The results were summarized and indicated an increasing trend of the porosity of the specimen towards its top section. The larger defects were observed closer towards the bottom of the specimen due to the lower interpass temperature, this the worse fusion of the aluminum. Despite this the microhardness along the face-wall of the specimen and its cross section remained the same within the margin of error. The possibility of decreasing the porosity and increasing the quality of the deposited components was discussed.

Exploring the bias: how skin color influences oxygen saturation readings via Monte Carlo simulations.

Our goal is to understand the root cause of reported oxygen saturation ( ) overestimation in heavily pigmented skin types to devise solutions toward enabling equity in pulse oximeter designs. We aim to gain theoretical insights into the effect of skin tone on curves using a three-dimensional, four-layer tissue model representing a finger. A finger tissue model, comprising the epidermis, dermis, two arteries, and a bone, was developed using a Monte Carlo-based approach in the MCmatlab software. Two skin tones-light and dark-were simulated by adjusting the absorption and scattering properties within the epidermal layer. Following this, curves were generated in various tissue configurations, including transmission and reflection modes using red and infrared wavelengths. In addition, the influence of source-detector (SD) separation distances on both light and dark skin tissue models was studied. In transmission mode, curves did not deviate with changes in skin tones because both pulsatile and non-pulsatile terms experienced equal attenuation at red and infrared wavelengths. However, in reflection mode, measurable variations in curves were evident. This was due to differential attenuation of the red components, which resulted in a lower perfusion index at the red wavelength in darker skin. As the SD separation increased, the effect of skin tone on curves in reflection mode became less pronounced, with the largest SD separation exhibiting effects similar to those observed in transmission mode. Monte Carlo simulations have demonstrated that different light pathlengths within the tissue contribute to the overestimation of in people with darker skin in reflection mode pulse oximetry. Increasing the SD separation may mitigate the effect of skin tone on readings. These trends were not observed in transmission mode; however, further planned research using more complex models of the tissue is essential.

Evaluation of Cutting Parameters on Heat-Affected Zone in Wood Plastic Composites by Pulsed Fiber Laser

Biodegradable and environmentally friendly composite materials such as wood plastic composites (WPCs) have gained attention in industrial applications due to environmental concerns and global sustainability goals. However, owing to their unique structures and properties, cutting on WPCs can be challenging. Continuous wave (CW) mode laser may result in heat build-up and easily warp the WPCs during laser cutting. Therefore, minimizing these defects and determining the cutting parameters that influence the heat-affected zone (HAZ) by pulsed mode laser is essential. In this present work, 1 mm thickness of WPC 30 wt.% of wood fiber (WF) filled with recycled high-density polyethylene (rHDPE) has been experimentally cut by single-mode pulsed fiber laser to evaluate the minimum laser energy required to cut the WPC and the influence of cutting parameters on the HAZ. The HAZ was measured using a digital microscope, and the statistical significance of the cutting parameters to HAZ was determined by analysis of variance (ANOVA). The results confirmed that a minimum linear energy of more than 9 J/mm is required to cut the WPC. It has been found that the cutting speed is the major influence on the HAZ, followed by pulse width. Adequate interaction time by cutting speed and duration of the single-laser pulse also significantly affects the cutting process. The higher gas pressure could minimize the HAZ at the surrounding cutting region of the WPCs. Understanding the influence of these parameters could minimize the thermal effect of HAZ and improve the laser cut quality.

Neutron emission characterization of IPR 14 MeV neutron generator

Accelerator-based neutron sources are being developed worldwide due to their wide applications. Institute for Plasma Research in India has developed an accelerator-based high-yield 14 MeV neutron generator based on deuterium-tritium (D-T) reaction to perform fusion-related benchmark experiments. This neutron generator is designed to produce 1012 neutrons per second in both mode continuous and pulse. The emission of neutrons from an accelerator-based neutron generator is not isotropic due to target geometry and angular dependency of reaction cross-section. A detailed and accurate description of neutron source emission and distribution is required to use such a neutron generator for various experiments. The neutron generator is characterized using experiments and simulations to accomplish the request. Energy and angular distributions of emitted neutrons are measured using a calibrated single crystal diamond (SCD) detector. Experimental data of neutron distributions are used to validate source neutron definition for Monte Carlo N Particle (MCNP) simulation. An accurate model of the Titanium Tritide (TiT) target and its holder geometry is prepared for the simulation. Finally, to validate the simulation model, simulated neutron fluxes are compared with measured ones by the SCD detector. This paper discusses the methodology adopted to characterize emitted neutrons and its results.

When is it safe to operate after the failure of therapeutic steroid injections in carpal tunnel syndrome?

Carpal Tunnel Syndrome (CTS) is a multifactorial neuropathy caused by the compression of the median nerve due to its entrapment as it passes through the carpal tunnel in the wrist. It accounts for nearly 90% of neuropathies and usually presents as numbness, tingling, weakness, and pain. These symptoms are predominantly present in the thumb, second finger, third finger, and radial half of the hand's fourth finger. In the US, CTS has a prevalence of 50 per 1,000, which is similar to the prevalence in other developed countries.1 Overall, the prevalence of CTS in the general population in developed countries ranges from 3% to 6%, whereas the prevalence of CTS in developing countries like Pakistan has been reported to be from 10% to 15%.2 The management of mild to moderate CTS ranges from conservative management, including ultrasound therapy using the pulsed mode, wrist splinting, and tendon gliding exercises, to Neuro-mobilization.3 On the other hand, the management of moderate to severe CTS, which is unresponsive to the above-mentioned therapies comprises therapeutic steroid injections and surgical decompression of the median nerve. In many cases, surgical decompression is used as a last resort after the failure of therapeutic steroid injections. However, studies have shown that surgical decompression in these cases is associated with poor postoperative outcomes, including increased risk of pain and paresthesia.4 Furthermore, such cases are also associated with an increased risk of surgical site infections, non-infectious wound complications, and 1 year-reoperation. The risk of these complications is maximum when surgery is performed within 30 days of the last therapeutic steroid injection along with a high number of therapeutic steroid injections (infections 1.77%, non-infectious complications 1.12%, 1-year re-operation 2.09%), and is minimal when performed from 90 to 180 days of the last therapeutic steroid injection with a low number of therapeutic steroid injections (infections 1.19%, non-infectious complications 0.44%, 1-year re-operation 1.58%). Therefore, surgical decompression of the median nerve should be delayed for 90 to 180 days after the last therapeutic steroid injection, depending on the severity.5 There is a high prevalence of CTS in developing countries like Pakistan and therapeutic steroid injections are frequently prescribed as first-line treatment for moderate to severe CTS. ---Continue

#1755 Cardio-protective effect of soy proteins during long-term consumption of Cynomolgus Monkeys high-saline diet

Abstract Background and Aims High salt intake is accompanied by the development of cardiovascular disorders, not always associated with an increase in blood pressure (BP). Recently, it has been found that the introduction of soy protein into the diet can have some nephroprotective and cardioprotective effects in chronic kidney disease. Considering the cardioprotective effect of soy proteins in chronic kidney disease, the question arose about the possibility of using soy proteins to neutralize the damaging effect of a high-salt diet on the cardiovascular system. This work aims to study the effect of long-term use of a diet high in NaCl and soy protein on myocardial remodeling in monkeys. Method The study was performed on male Macaca fascicularis. The animals were divided into three groups (6 animals each), comparable in weight and age (6-8 years, body weight - 5.15-9.7 kg). The control group received a standard diet (2 g NaCl/kg feed). The second was a high salt diet (8 g NaCl/kg feed), and the third was a high salt diet and SUPRO760 soy protein (200 g/kg feed). Echocardiography (EchoCG), registration of BP and heart rate were performed at baseline, after 4 and 12 months. EchoCG was performed with a sector transducer with a frequency of 3–5 MHz on the Chison SonoTouch 60 ultrasound system (China). EchoCG was performed in B_mode (two-dimensional scanning), M_mode (one-dimensional scanning), as well as in pulse and tissue Doppler modes. Statistical analysis was performed using parametric statistics: mixed ANOVA in comparing data from 3 study groups (with post hoc analysis using Tukey criterion) and single factor variance analysis for related samples in studying the dynamics of one or another index in each group during the 12-month follow-up. Differences were considered significant at p &amp;lt; 0.05. Results In animals of all three groups for 12 months, blood pressure (BPsis-109±10.09, BPdias – 60 ± 7.42 mm Hg) and heart rate (77 ± 12.61 min-1) did not change significantly (p&amp;gt;0. 05). However, in macaques on a high-salt diet, deterioration in left ventricular (LV) systolic and diastolic function was noted by the end of the study. Macaques of this group had a decrease in the LV shortening fraction (27.9±2.69%) and an increase in the thickness of the posterior wall of the LV in systole (0.69±0.039 cm), LV mass (19.60±2.83 g), compared with animals additionally receiving soy proteins (34.9±6.57%; 0.57 0.0559 cm; 14.86±2.94 g, respectively; all p &amp;lt; 0.05). In addition, the monkeys receiving soy isolate did not differ from the control in these parameters. By the time the study was completed, the animals in this group had significantly increased the magnitude of systolic excursion of the mitral annulus plane, and signs of improvement in LV diastolic function appeared in the form of an increase in the maximum rate of excursion of the mitral valve fibrous annulus in early diastole, as well as a decrease in the E/e' ratio. The thickness of the interventricular septum also decreased (0.42±0.04 cm; in the high-salt group - 0.51±0.08 cm), which can be interpreted as a sign of positive myocardial remodeling. Conclusion Thus, high salt intake leads to adverse structural and functional disorders of the heart in cynomolgus monkeys, not associated with an increase in blood pressure. The inclusion of soy isolate in the diet reduces the negative effects of a high-salt diet on the cardiovascular system.

Utilizing the Sentinel-6 Michael Freilich Equivalent Number of Looks for Sea State Applications

Sentinel-6 Michael Freilich (S6-MF) is the first altimeter operating in a continuous high-rate pulse mode, i.e., interleaved mode. This ensures the generation of low-resolution (LR) mode measurements with a pulse repetition frequency (PRF) of ∼9 kHz (variable along the orbit) for the Ku-band as well as the processing of high-resolution (HR) echoes on ground. This operating mode provides an elevated number of highly correlated single looks with respect to the fewer number, weakly correlated echoes of Jason-3 altimeter. A theoretical model is exploited to envisage the correlation properties of S6-MF pulse limited waveform echoes for different sea-state conditions; after that, the model is validated by comparison with the equivalent number of looks (ENL) empirically estimated from real data. The existence of a significant dependence of the statistical properties on the range is verified, and its impact on the precision and on the accuracy in the estimation of the geophysical parameters is assessed in case of the 9 kHz PRF of S6-MF. By applying pulse decimation before the multilook processing, an investigation on new processing techniques is performed, aimed at exploiting the higher ENL in S6-MF low-resolution mode waveforms. It is shown that a bias of less than 0.4 cm is found for SSH and about 1.5 cm for SWH at SWH = 2 m when the decimated waveforms processing is compared with full high-PRF processing.

Vinyl-based interlayers synthesized by variable pulsed plasma for polymer composites

The low-pressure pulsed plasma is a crucial tool for the construction of materials in the form of coatings with variable properties. The pulsed mode is characterized by many parameters such as pulse on-time, off-time, pulse period, pulse frequency, duty cycle, and using the total power, the average power during the pulse can be introduced as the effective power. Based on a pulse period ranging from 2 to 100 ms and a total power of 10–500 W, it is demonstrated that the effective power is the key parameter responsible for the properties of the synthesized coatings independent of the total power. When an organosilicon precursor with a vinyl functional group, this parameter allows the chemical and physical properties of vinyl-based coatings to be controlled over a wide range, allowing to optimize their properties as functional interlayers in polymer composites to control their performance.

Enhancing selective production of atomic oxygen through nanosecond pulse-burst driven mode in a He/O2 dielectric barrier discharge

In this study, the temporal evolution of O atoms in a nanosecond burst-pulsed dielectric barrier discharge (DBD) is measured by two-photon absorption laser-induced fluorescence spectroscopy. The experiment is conducted at burst conditions of 50, 100, and 200 kHz pulse frequency, 10 Hz burst frequency, and 20–400 pulses in 0.1%–2% O2 + He mixtures. The accumulation effect of O atoms in the burst mode is observed and the density gradually saturates at around 100 pulses. Increasing the pulse frequency effectively enhances the O saturation density. The 0-dimensional kinetic model reveals that the saturation effect is primarily balanced by the formation and loss characteristics of O atoms. Similar saturation effect is also observed in the typical continuous periodic pulse mode (one pulse each cycle), but with a saturation density about one order of magnitude lower than that in the burst case, highlighting the burst excitation mode as an effective method for enhancing the instantaneous peak production of O atoms. Further investigations into the influence of O2 proportion on the selective production of O atoms are also performed. The results suggest that a low O2 proportion (<2%) and pulse-burst driven mode for the He/O2 DBD facilitates the selective production of O atoms while competing with O3 formation.

A High-Energy, Wide-Spectrum, Spatiotemporal Mode-Locked Fiber Laser.

In this article, we demonstrate a high-energy, wide-spectrum, spatiotemporal mode-locked (STML) fiber laser. Unlike traditional single-mode fiber lasers, STML fiber lasers theoretically enable mode-locking with various combinations of transverse modes. The laser can deliver two different STML pulse sequences with different pulse widths, spectra and beam profiles, due to the different compositions of transverse modes in the output pulses. Moreover, we achieve a wide-spectrum pulsed output with a single-pulse energy of up to 116 nJ, by weakening the spectral filtering and utilizing self-cleaning. Strong spatial and spectral filtering are usually thought to be necessary for achieving STML. Our experiment verifies the necessity of spatial filtering for achieving STML, and we show that weakening unnecessary spectral filtering provides an effective way to increase the pulse energy and spectrum width of mode-locked fiber lasers.

Enhancing corrosion resistance and microstructure of the PEO coating layer on 6061 aluminium alloy: The role of first step voltage in plasma electrolytic oxidation

In this study, a novel two-step hybrid PEO technique was used to produce an alumina(Al2O3) on an Al6061 alloy. The research emphasizes the influence of the microstructure of the initial thin layer on the amount of defects such as microcracks and micropores in the final coating. Initially, a thin alumina layer was formed at 400 ∼ 600 V using a pulsed unipolar mode, followed by a thicker layer at 500 V using a pulsed bipolar mode. The results indicate that a sound PEO coating with fewer defects markedly enhances the corrosion resistance of the Al6061 alloy.

Enhancing tensile properties of MIG welded AA6061 joints: Effect of pulse mode and post-weld heat treatment

Metal-Inert Gas (MIG) welding is one of the most important welding technologies commonly used in the manufacturing industry due to its high degree of automation and welding adaptability. However, softening is prone to occur in fusion zone (FZ) and heat affected zone (HAZ) of AA6061 MIG welded joint, which limits its application. In this work, AA6061 was welded by MIG welding with different pulse modes, and the post-welding heat treatment was carried out. The results show that the dual pulse MIG (DP-MIG) and PWHT can significantly improve the mechanical properties of AA6061 butt joint, and its ultimate tensile strength (UTS) is 331.3 MPa, even more than 90% of the base material (BM). In this paper, the microstructure of welded joints under different pulse conditions before and after PWHT was compared, and the relationship between the welding process, microstructure, and mechanical properties was established Furthermore, the influence mechanisms of pulse mode and PWHT on the mechanical properties of welded joints were explained in detail.