Pulsed Wave Mode Research Articles

Integrated Control of Thermal Residual Stress and Mechanical Properties by Adjusting Pulse-Wave Direct Energy Deposition.

Directed energy deposition with laser beam (DED-LB) components experience significant residual stress due to rapid heating and cooling cycles. Excessive residual tensile stress can lead to cracking in the deposited sample, resulting in service failure. This study utilized digital image correlation (DIC) and thermal imaging to observe the in situ temporal evolution of strain and temperature gradients across all layers of a deposited 316 L stainless steel thin wall during DED-LB. Both continuous-wave (CW) and pulsed-wave (PW) laser modes were employed. Additionally, the characteristics of thermal cracks and geometric dislocation density were examined. The results reveal that PW mode generates a lower temperature gradient, which in turn reduces thermal strain. In CW mode, the temperature-stress relationship curve of the additive manufacturing sample enters the "brittleness temperature zone", leading to the formation of numerous hot cracks. In contrast, PW mode samples are almost free of cracks, as the metal avoids crack-sensitive regions during solidification, thereby minimizing hot crack formation. Overall, these factors collectively contribute to reduced residual stress and improved mechanical properties through the adjustment of pulsed-wave laser deposition.

Pulsed Wave Mode of Fractional Radiofrequency Microneedling as a New Advance in the Treatment of Inflammatory Acne Vulgaris

Inflammatory acne vulgaris (IAV) is a common skin condition characterized by the presence of reddish, inflamed, and painful lesions on the skin. IAV can drastically affect individuals, specifically their self-esteem, psychological health, and quality of their life in general. Despite new advances in the field, traditional treatment modalities withstand many challenges. Hence, in the current study, we sought to assess the efficacy and safety of a new pulsed wave mode of the fractional microneedling radiofrequency device in the treatment of IAV. This advanced technique employs insulated microneedles to administer energy to the deep dermis without causing damage to the epidermis. Eighty patients (40 males, 40 females, age 21 ± 3, Fitzpatrick skin type III and IV), with acne severity ranging from moderate to severe, were employed in this trial. They were randomly assigned into two groups, 40 patients each. The treated group (A) underwent four sessions of fractionated microneedle RF, 1.5-month apart, whereas group B was designated as the control group that received placebo treatment. Six months following the last session, the degree of improvement assessed by the quantity of IAV lesions and the overall skin appearance in terms of facial pores, sebum excretion, scar, skin tone, and texture. The RF-treated group showed significant improvement compared to the control group after the follow-up period (p-value = 0.0071). Regarding safety, very mild adverse effects were reported, such as discomfort during the session, pinpoint hemorrhage, and erythema, with no major side effects such as burns, scarring, hyperpigmentation, or hypopigmentation were reported. Thus, our data suggest a potential role of the fractional microneedling radiofrequency device in IAV treatment that is both effective and safe.

Dose-dependent effects of transcranial photobiomodulation on brain temperature in patients with major depressive disorder: a spectroscopy study.

This study aimed to evaluate the dose-dependent brain temperature effects of transcranial photobiomodulation (t-PBM). Thirty adult subjects with major depressive disorder were randomized to three t-PBM sessions with different doses (low: 50 mW/cm2, medium: 300 mW/cm2, high: 850 mW/cm2) and a sham treatment. The low and medium doses were administered in continuous wave mode, while the high dose was administered in pulsed wave mode. A 3T MRI scanner was used to perform proton magnetic resonance spectroscopy (1H-MRS). A voxel with a volume of 30 × 30 × 15 mm3 was placed on the left prefrontal region. Brain temperature (°C) was derived by analyzing 1H-MRS spectrum chemical shift differences between the water (~ 4.7 ppm) and N-acetyl aspartate (NAA) (~ 2.01 ppm) peaks. After quality control of the data, the following group numbers were available for both pre- and post-temperature estimations: sham (n = 10), low (n = 11), medium (n = 10), and high (n = 8). We did not detect significant temperature differences for any t-PBM-active or sham groups post-irradiation (p-value range = 0.105 and 0.781). We also tested for potential differences in the pre-post variability of brain temperature in each group. As for t-PBM active groups, the lowest fluctuation (variance) was observed for the medium dose (σ2 = 0.29), followed by the low dose (σ2 = 0.47), and the highest fluctuation was for the high dose (σ2 = 0.67). t-PBM sham condition showed the overall lowest fluctuation (σ2 = 0.11). Our 1H-MRS thermometry results showed no significant brain temperature elevations during t-PBM administration.

Numerical simulation and experimental study on the heat and mass transfer behavior during the pulsed laser cladding process

Compared with continuous wave (CW), pulse wave (PW) perturbation results in a larger temperature change rate inside the cladding layer, which leads to a higher quality cladding layer. In this paper, a three-dimensional numerical model of laser cladding Fe60 powder was established. The multiphysics field coupling transient evolution and solute distribution under PW and CW operating modes were studied. The problem of lack of theoretical support for laser cladding process under different working modes in heat source was solved. Calculations show that at 1970 ms when the temperature is stable, the maximum temperature, flow rate, and stress under the PW mode are 2660 K, 0.34 m/s, and 354 MPa, respectively, which are smaller than those under the CW mode. The four solute distributions at stable temperature are as follows: The minimum mass fractions of Fe and Mn are 87% and 0.49% in the CW mode, and the maximum mass fractions of Cr and Ni are 11% and 5%. In the PW mode, the minimum mass fractions of Fe and Mn are 82% and 0.44%, and the maximum mass fractions of Cr and Ni are 14% and 5%. PW has a smaller heat input than CW, resulting in a smaller molten pool, so the elements in the molten pool are more fully mixed with other alloying elements. Metallographic experiments were performed using a scanning electron microscope to examine the mechanical properties on the fusion cladding layer, and the accuracy of the model was verified by combining numerical simulations with experimental studies for comparative analysis.

Initial description of the novel handheld wireless ultrasound device TE Air with Doppler and Color Duplex imaging.

To test and initially describe a new handheld wireless ultrasound technique (TE Air) for clinical use. In this pilot study, the new ultrasound device TE Air from Mindray was used to examine the hepatic and renal vessels of healthy volunteers for first impressions. The probe has a sector transducer with a frequency range of 1.8-4.5 MHz. The B-mode and color-coded doppler sonography (CCDS) scanning methods were used. A high-end device from the same company (Resona 9, Mindray) was used as a reference. The results were evaluated using an image rating scale ranging from 0 to 5, with 0 indicating not assessable and 5 indicating without limitations. Altogether, 61 participants (n = 34 female [55.7%], n = 27 male [44.3%]), age range 18-83 years, mean age 37.9±16.5 years) could be adequately studied using TE AIR and the high-end device. With one exception, the image quality score for TE Air never fell below 3 and had a mean/median scored of 4.97/5.00 for the B-mode, 4.92/5.00 for the color flow (CF) mode, and 4.89/5.00 for the pulse wave (PW) mode of the hepatic vein, 4.90/5.00 for the portal vein, 4.11/4.00 for the hepatic artery, and 4.57/5.00 for the renal segmental artery. A significant difference in the assessment of flow measurement of the hepatic artery and renal segmental arteries was found between TE AIR and the high-end device. TE Air represents a new dimension in point-of-care ultrasound via wireless handheld devices. Especially, its flow measurement ability offers a relevant advantage over other available handheld models. TE Air provides a formally sufficient image quality in terms of diagnostic significance.

Laser Technology Advancements in the Treatment of Benign Prostatic Hypertrophy.

Lasers have had a significant impact on the treatment of benign prostatic hypertrophy. This article attempts to distill the advancements in laser technology for the treatment of benign prostatic hypertrophy (BPH) into key and understandable points to help make this topic more accessible to urologists. The holmium:yttrium-aluminum-garnet (YAG) laser, one of the most significant lasers in the field of urology, has recently been improved with pulse modulating technology (Moses™ technology). New thulium:YAG technology allows both pulsed and continuous wave modes. The thulium fiber laser is one of the newer lasers to come to market and has been shown to have effective and safe outcomes. GreenLight™ lasers are predominantly used in photovaporization procedures and have also been studied extensively, although less in recent years. The modern urologist is fortunate to have many high-quality lasers and a wide variety of surgical techniques to choose from when treating BPH. Understanding the basic laser principles and applications will help urologists to select the best treatment options for their patients with BPH.

Understanding the microstructural evolution and tensile characteristics of low nickel austenitic stainless-steel welds fabricated by diode LASER

In the present investigation, the utilization of diode laser welding in both continuous wave (CW) and pulse wave (PW) modes was applied to weld sections of 4 mm thick low nickel austenitic stainless steel (LNiASS) material. Subsequently, a comprehensive examination of the microstructural attributes of these welds was conducted by X-ray diffraction, electron backscatter diffraction (EBSD), and electron channeling contrast imaging (ECCI). The microstructural assessment was performed at both as-welded state and after the tensile deformation at three discrete strain rates ranging from 3.3 × 10−4 to 1.0 × 10−2. Furthermore, an investigation into the influence of strain rate variations on the tensile behavior of the two aforementioned types of welded joints, along with an exploration of the occurrence of strain-induced martensitic transformation, was carried out. The outcomes revealed that the PW welds yielded finer grain sizes in comparison to CW welds. It was observed that the martensite content within both CW and PW welds exhibited an augmentation with increasing strain rates. Furthermore, the PW welds exhibited a higher martensite content when compared to the CW welds under all examined strain rates. The PW welds consistently demonstrated higher UTS and total elongation across all three strain rates, while the CW welds exhibited a higher YS. Furthermore, as the strain rates increased, a decline in the strength ratio was observed for both weld types, accompanied by an increasing disparity between UTS and YS, indicative of work hardening phenomena.

Understanding the effect of Mn2+ on Yb3+/Er3+ co-doped NaYF4 upconversion and obtaining the optimal combination of these tridoping

In this work, we investigated in detail the upconversion properties of several types of nanoparticles, including NaYF4:5%Yb3+/30%Mn2+, NaYF4:40%Mn2+/x%Yb3+ (x% = 1, 5, 10, 20, 30, and 40), NaYF4:2%Er3+/x%Mn2+ (x% = 20, 30, 40, 50, 60, and 70), NaYF4:40%Mn2+/x%Er3+ (x% = 1, 2, 5, and 10), and NaYF4:40%Mn2+/1%Yb3+/x%Er3+ (x% = 0, 2, 5, and 10). We studied their upconversion emission under 980 nm excitation in both pulsed and continuous wave modes at different synthesis temperatures. The nanoparticles were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), and photoluminescence (PL) spectroscopy. The doping of Yb3+ and Mn2+ ions resulted in the nanoparticles assuming cubic and hexagonal crystal structures. The emission intensity increased (106.4 (a.u.*103) to 334.4(a.u.*103)) with increasing synthesis temperature from 120 to 140 °C, while a sharp decrease was observed when the synthesis temperature was increased to 200 °C. The gradual decrease in peak intensity with increasing Mn2+ concentration from 20 to 70% was attributed to energy transfer from Mn2+ to Yb3+. In NaYF4:Mn2+/Yb3+/Er3+ UCNPs, increasing the Er3+ concentration from 0 to 10% led to the disappearance of the blue, orange, and green emission bands. The intense upconversion luminescence pattern with high spatial resolution indicates excellent potential for applications in displays, biological sensors, photodetectors, and solar energy converters.

Pulsing the Passive RF Identification Technology: The Pulsed Wave Mode

Pulsing the Passive RF Identification Technology: The Pulsed Wave Mode

Study on pulsed wave mode laser welding of Nb-Zr-C alloy and many-objective optimization using meta-heuristic techniques

Study on pulsed wave mode laser welding of Nb-Zr-C alloy and many-objective optimization using meta-heuristic techniques

Control of thermal strain and residual stress in pulsed-wave direct laser deposition

Components manufactured by direct laser deposition (DED) are prone to produce excessive residual stress due to its rapid heating by laser and cooling. Excessive residual tensile stress leads to cracking of deposited sample, even cause failure to serve. Understanding thermodynamic behavior during processing is critical for controlling residual stress. In this study, in-situ transient strain and temperature gradient evolution of each layer on deposited sample 316L stainless steel thin wall during DED using both continuous-wave (CW) and pulsed-wave (PW) laser modes were emerged by digital image correlation (DIC) method and thermal imager. The longitudinal residual stress of deposited sample was evaluated using two laser modes. The results demonstrated that the PW mode creates a smaller temperature gradient and hence a lesser thermal strain than the CW mode. Furthermore, the cyclic thermal stress characteristics of PW mode was observed. All these factors contribute to the reduction of residual stress.

Minimizing Thermal Damage During Thulium Laser-Assisted Partial Arytenoidectomy: Pulsed Versus Continuous Cutting in an Ex-Vivo Calf Model.

The 2 µm-wavelength thulium laser is an effective cutter during partial arytenoidectomy, but thermal trauma can damage adjacent laryngeal tissue. Pulsing laser energy may reduce trauma when compared to continuous-wave cutting. This study measured temperature changes, thermal trauma, and time to complete partial arytenoidectomy, with and without pulsing, in an ex-vivo calf model. Tissue temperature and time to complete a trans-cartilaginous cut were measured during partial arytenoidectomy on ex-vivo calf vocal folds (N = 24) using a thulium laser in continuous-wave (CW, N = 12) and pulsed-wave (PW, N = 12) modes. Energy was 5 W for CW and PW cuts; pulse-widths were 250, 500, and 750 ms. Thermal damage was analyzed histologically by measuring the depth of lactate dehydrogenase (LDH) inactivation perpendicular to the laser-cut edge at the vocal process. Paired t-tests compared CW and PW modes. Change in temperature was lower using CW (6.5°C) compared to PW modes (250 ms = 18°; 500 ms = 16°; 750 = 19°; P < .05). Trans-cartilaginous cuts were completed faster using CW (37 seconds) compared to PW (250 ms = 136 seconds; 500 ms = 61 seconds; 750 = 44 seconds; P < .05), and both modes delivered the same total Joules. The average depth of LDH depletion (thermal damage) was similar for all cuts. 1. Thulium laser cuts in continuous-mode unexpectedly produced less tissue heating yet created similar thermal damage than pulsed-mode cuts during simulated partial arytenoidectomy. 2. Trans-cartilaginous cuts were completed significantly faster in continuous-mode as compared to pulsed-mode cutting. 3. Pulsing the thulium laser does not minimize thermal damage compared to continuous wave cutting during thulium laser-assisted partial arytenoidectomy.

Роль комплексной эхографии печени в ранней диагностике преэклампсии и HELLP-синдрома

Objective. To study the possibilities of comprehensive ultrasound imaging with pulsed wave mode and Doppler color flow mapping in evaluation of hepatic blood flow and its compensatory capabilities in pre-eclampsia (PE) of different severity. Patients and methods. Complex liver ultrasonography combined with Doppler assessment of arterial and venous blood flow was performed in 87 pregnant women at 28–40 weeks’ gestation. The study group comprised 59 women with PE of varying severity and 12 women with HELLP syndrome. The control group included 30 women with normal pregnancy. Results. Doppler assessment of blood flow in the hepatic artery and in the maternal-placental-fetal system arteries in patients with moderate and severe PE revealed similar changes, which were manifested by elevated vascular resistance in these vessels and correlated with the severity of PE. The maximum values of pulsatility index and resistance index in the hepatic artery were observed in patients with HELLP syndrome – 1.6 ± 0.11 and 0.74 ± 0.08, respectively. Qualitative and quantitative characteristics of blood flow in the portal vein in patients with moderate PE did not statistically differ from those in the control group, while patients with severe PE and HELLP syndrome showed statistically significant disturbances of portal vein blood flow manifested by an increase in portal vein diameter and a decrease in maximum linear velocity of blood flow in the portal vein. Changes in hepatic arterial blood flow were found in patients with moderate PE in the absence of clinical and laboratory manifestations of liver dysfunction. Already in the early stages of PE, a shift of hemodynamic indices toward an increase in peripheral vascular resistance was determined. The increase in hepatic artery vascular resistance was observed in parallel with the increase of similar indices in the uterine-placental-fetal blood flow. Disturbance of blood flow in the portal vein was determined only in patients with severe PE and HELLP syndrome. Conclusion. Vascular disorders of the liver can serve as an additional diagnostic method for early diagnosis of liver involvement in the pathological process, while the signs of portal vein blood flow disorders are a criterion of extremely severe PE course, prognostically unfavorable regarding HELLP syndrome development. Key words: resistance index, liver dysfunction, hepatic artery, pre-eclampsia, hepatic blood flow, pulsatility index, HELLP syndrome

Coupling Sub-nanoliter BDPA Organic Radical Spin Ensembles with YBCO Inverse Anapole Resonators

We report the development and test of planar microwave Inverse Anapole Resonators (IARs) made of superconducting Yttrium Barium Copper Oxide (YBCO) for electron spin resonance spectroscopy on small samples. We first characterize our resonators in zero field and then by carrying out transmission spectroscopy on a diluted $$\alpha ,\gamma $$ -bisdiphenylene- $$\beta $$ -phenylally (BDPA) organic radical spin ensemble in an applied magnetic field. These IARs allow us to carry out electron spin resonance spectroscopy both in continuous-wave and pulsed-wave mode, and to estimate the spin memory time of BDPA. The comparison with the results obtained for the same sample on typical linear coplanar resonators shows an improvement by $$\approx 2\text { - up to}\,3$$ – orders of magnitude in spin sensitivity, with effective sensing volumes below 1 nanoliter. The best sensitivity we achieved is $$S\approx \,10^{7}\,\text {spin}/\sqrt{\mathrm{Hz}}$$ in the pulsed-wave regime. These results compare well with similar experiments reported in the literature.

Photobiomodulation in Acute Traumatic Brain Injury: A Systematic Review and Meta-Analysis.

Photobiomodulation (PBM) is a therapeutic modality that has gained increasing interest in neuroscience applications, including acute traumatic brain injury (TBI). Its proposed mechanisms for therapeutic effect when delivered to the injured brain include antiapoptotic and anti-inflammatory effects. This systematic review summarizes the available evidence for the value of PBM in improving outcomes in acute TBI and presents a meta-analysis of the pre-clinical evidence for neurological severity score (NSS) and lesion size in animal models of TBI. A systematic review of the literature was performed, with searches and data extraction performed independently in duplicate by two authors. Eighteen published articles were identified for inclusion: seventeen pre-clinical studies of in vivo animal models and one clinical study in human patients. The available human study supports safety and feasibility of PBM in acute moderate TBI. For pre-clinical studies, meta-analysis for NSS and lesion size were found to favor intervention versus control. Subgroup analysis based on PBM parameter variables for these outcomes was performed. Favorable parameters were identified as: wavelengths in the region of 665 nm and 810 nm; time to first administration of PBM ≤4 h; total number of daily treatments ≤3. No differences were identified between pulsed and continuous wave modes or energy delivery. Mechanistic substudies within included in vivo studies are presented and were found to support hypotheses of antiapoptotic, anti-inflammatory, and pro-proliferative effects, and a modulation of cellular metabolism. This systematic review provides substantial meta-analysis evidence of the benefits of PBM on functional and histological outcomes of TBI in in vivo mammalian models. Study design and PBM parameters should be closely considered for future human clinical studies.

A Study on the Photoelectric Properties of Dual Ridge Terahertz Quantum Cascade Lasers at 3.1 THz.

High-power, incoherent THz array sources are widely desired in some applications due to their low energy, unique terahertz fingerprint, and image. In this work, a dual ridge terahertz quantum cascade laser lasing at 3.1 THz is presented, and the device’s performance is analyzed in detail. The maximum output power can reach 512 mW when the two ridges work simultaneously in continuous-wave mode, with a threshold current density of 281 A/cm2 at 15 K. While the peak power is approximately 704 mW in pulse-wave mode at 15 K, the lasing still could be observed approximately 7 mW at 125 K. The far-field pattern of the dual ridge THz QCL is detected by a THz camera; two light spots typically show a single-lobe Gaussian distribution. The experimental results provide a reference for realizing high-power THz quantum cascade lasers, and they will provide some guidance for the structural design of multiple ridges or laser arrays.

Numerical study of thermal fluid dynamics and solidification characteristics during continuous wave and pulsed wave laser welding

Pulsed wave (PW) mode laser welding is often preferred under conditions where specific heat input and tailorable cooling rate are required. Previous works on numerical modelling of laser welding mainly focus on continuous wave (CW) mode, while physical understanding of PW mode from numerical investigation is scarce. In this work, a 3D multi-physics thermal fluid model is developed considering both CW and PW modes laser welding. The main physical factors involving heat transfer, thermal fluid flow, Fresnel absorption, recoil pressure induced by metal evaporation, Marangoni effect driven by surface tension, free surface tracing, and laser multiple reflections inside the keyhole are included in this model. The model is tested and validated against the corresponding experimental results for laser welds of stainless steel 316 L. The simulated weld fusion cross sections and surface molten pool agree well with the experimentally observed results for both CW and PW modes. The results show that PW mode exhibits a higher depth of penetration and a smaller molten pool at the same heat input with CW mode. In CW mode laser welding, the shape of keyhole is unstable, while its depth keeps relatively stable. There are two main flow patterns in the molten pool of CW mode welding: an outward flow from keyhole outlet to the rear weld pool and a clockwise flow from the keyhole tip to the rear weld pool. While for PW mode, keyhole and molten pool show periodic behaviors with a period of the laser energy output used. The periodic fluid flow pattern is mainly affected by the gradually changed surface tension and suddenly changed recoil pressure. Furthermore, it is found that a finer microstructure with a smaller secondary dendrite arm spacing is obtained in PW mode due to a higher cooling rate from both the calculated and experimentally measured results.

High-Power Terahertz Quantum Cascade Lasers Based on High-Al-Composition Four Quantum Wells

High-power terahertz frequency quantum cascade lasers operating in both pulsed and continuous wave (CW) modes are demonstrated. High Al composition four quantum wells active region based on diagonal structure are employed to suppress the escape of electrons into continuum and thermally activated LO-phonon scattering, as evidenced by the activation energy value of ~14.4 meV extracted from the experimental data. The devices operate in a frequency range of 3.8 - 4.05 THz and have a pulsed maximum operating temperature of ~119 K. The total optical output power from an uncoated laser is 1.57 W and the maximum single-facet emission power from an HR coated one is 1.03 W in pulsed mode at 7 K. The maximum output power of ~256 mW is obtained by a 2.5-mm-long device operating in CW mode with a low threshold current density of 188.6 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 15 K.

Experiments of Microwave Ablation Based on Dual-Frequency Antenna Under Pulsed Mode

In this letter, we review the microwave ablation (MWA) under pulsed wave (PW) mode and perform the experiments by using a dual-frequency antenna. Parameters such as frequency (915 MHz or 2450 MHz), excitation power (40 W or 60 W), duty cycle (40%–60%), cycle (10 ms–100 s), and durations (5 min or 10) min are variably combined in different experimental schemes for investigation. Based on the results of these experiments, which use our super compact dual-frequency antenna and egg white as a reference tissue environment, it can be seen that PW MWA may reduce backward heating and increase ablation roundness to 0.964 (compared to a traditional continuous wave (CW) ablation roundness of 0.5). For further verification of these results and for comparison, a single-frequency antenna is also used under PW mode and the achieved ablation roundness is 0.91, which is also greater than that of 0.55 under CW mode. PW MWA can thus be considered as an effective candidate for tissue ablation during the treatment of tumors.

Residual stress control of 316 L stainless steel using pulsed-wave laser additive manufacturing

In this paper, 316 L stainless steel were fabricated by direct laser deposition (DED) using both continuous-wave (CW) and pulsed-wave (PW) laser modes. Effects of laser modes on residual stress, geometric dislocation density (GND) and solid phase transformation with a given heat energy input were investigated. Results showed that PW mode tends to generate less concentrated, lower residual stress than that CW mode does, which the decline range was reached about 42% at the joint of the deposition and the substrate and approximately 75% on the deposition respectively. This is determined by the process characteristics of PW mode. Firstly, the relatively small temperature gradient in PW mode directly causes small thermal stress. Secondly, the characteristic of periodic temperature history and an improved cooling rate of molten pool in PW mode leads to more thermal stress relaxation. The released thermal stress can be used as a driving force for the formation of dislocations at grain boundaries. In addition, solid phase transformation does not occur with PW mode, which has little contribution to the reduction of residual stress.