Energy Distribution Research Articles

Investigating episodic mass loss in evolved massive stars

Mass loss during the red supergiant (RSG) phase plays a crucial role in the evolution of an intermediate-mass star; however, the underlying mechanism remains unknown. We aim to increase the sample of well-characterized RSGs at subsolar metallicity by deriving the physical properties of 127 RSGs in nine nearby southern galaxies. For each RSG, we provide spectral types and used MARCS atmospheric models to measure stellar properties from their optical spectra, such as the effective temperature, extinction, and radial velocity. By fitting the spectral energy distribution, we obtained the stellar luminosity and radius for 92 RSGs, finding that ~50% of them have log(L/L⊙) ≥ 5.0 and six RSGs have R ≳ 1400 R⊙. We also find a correlation between the stellar luminosity and mid-IR excess of 33 dusty variable sources. Three of these dusty RSGs have luminosities exceeding the revised Humphreys-Davidson limit. We then derived a metallicity-dependent J − Ks color versus temperature relation from synthetic photometry and two new empirical J − Ks color versus temperature relations calibrated on literature TiO and J-band temperatures. To scale our derived cool TiO temperatures to values that are in agreement with the evolutionary tracks, we derived two linear scaling relations calibrated on J-band and i-band temperatures. We find that the TiO temperatures are more discrepant as a function of the mass-loss rate, and discuss future prospects of the TiO bands as a mass-loss probe. Finally, we speculate that three hot dusty RSGs may have experienced a recent mass ejection (12% of the K-type sample) and classify them as candidate Levesque-Massey variables.

Dynamic response characteristics of backfill under blasting disturbance simulated through a three-dimensional model

During mining operations, the backfill body is subject to significant disturbance due to large-volume blasting, resulting in stress concentration and vibration response within the backfill. This alters energy distribution, leading to the continuous development, expansion, and accumulation of damage, potentially culminating in instability and collapse. Blasting disturbance in stopes is the main cause of filling instability and ore dilution. It is crucial to study the failure mechanism of filling bodies under blasting load to guide actual mine production. In this study, a custom mold was created to establish an innovative three-dimensional model of an ore-backfill system subject to explosion loading. Simultaneous detonation was selected as the control group and delayed detonation was selected as the experimental group. Monitoring and analysis methods, such as a high-speed camera system, MATLAB software, and vibration monitors, were utilized to investigate the impact of delay time on the dynamic response characteristics of the backfill. The results show that the dynamic fracture process of the backfill is mainly divided into four stages: initial crack initiation stage, crack development stage, crack expansion stage, and backfill collapse stage. The difference in delay time on the dynamic fracture process of the backfill is mainly reflected in two aspects: time effect and crack distribution. The surface flatness after delayed detonation is higher by 20.5% as compared with that after simultaneous detonation. The average damping rate during delayed detonation decreases by 19.7% as compared with that after simultaneous detonation, the frequency distribution of the single stage is more uniform, and the instantaneous peak energy during delayed detonation is 0.76 times that during simultaneous detonation. The maximum crushing size, average crushing size, and bulk crushing size after delayed detonation are reduced by 25%, 15.26%, and 9.23%, respectively, compared with that after simultaneous blasting. Thus, delayed detonation effectively improves the crushing effect while reducing the degree of damage to the backfill.

Quantum Informative Analysis in Smart Power Distribution

Advancements in the Internet of Things (IoT) paradigm have greatly improved the quality of services in the electricity industry through the integration of smart energy distribution and dependable electric devices. Conspicuously, the current research introduces a method for managing electricity consumption in smart residences using IoT-Fog technology, focusing on efficient energy allocation and real-time energy needs. The study specifically examines the effectiveness of electricity grid sub-stations in distributing energy using fog computing technology. By utilizing a Quantum Computing-assisted approach, optimal energy distribution is achieved by calculating a novel Electricity Usage Measure (EUM) based on actual energy usage patterns of smart homes. Furthermore, the Quantumized Neural Network (QiM-NN) technique is developed to forecast the electricity distribution over grid substations. For performance assessment, 4-month data is collected using four smart houses. Comparative analysis with existing data assessment techniques illustrates the effectiveness in terms of Temporal Delay (6.33 ms), Optimization Performance (Specificity (93.00%), Sensitivity (90.86%), Precision (96.66%), Coverage (96.66 %)), Reliability (93.76%), and Stability (71%).

Metabolic Allometric Scaling of Multicellular Organisms as a Product of Evolutionary Development and Optimization of Food Chains

Production of energy is a foundation of life. The metabolic rate of organisms (amount of energy produced per unit time) generally increases slower than organisms’ mass, which has important implications for life organization. This phenomenon, when considered across different taxa, is called interspecific allometric scaling. Its origin has puzzled scientists for many decades, and still is considered unknown. In this paper, we posit that natural selection, as determined by evolutionary pressures, leads to distribution of resources, and accordingly energy, within a food chain, which is optimal from the perspective of stability of the food chain, when each species has sufficient amount of resources for continuous reproduction, but not too much to jeopardize existence of other species. Metabolic allometric scaling (MAS) is then a quantitative representation of this optimal distribution. Taking locomotion and the primary mechanism for distribution of energy, we developed a biomechanical model to find energy expenditures, considering limb length, skeleton mass and speed. Using the interspecific allometric exponents for these three measures and substituting them into the locomotion-derived model for energy expenditure, we calculated allometric exponents for mammals, reptiles, fish, and birds, and compared these values with allometric exponents derived from experimental observations. The calculated allometric exponents were nearly identical to experimentally observed exponents for mammals, and very close for fish, reptiles and the basal metabolic rate (BMR) of birds. The main result of the study is that the MAS is a function of a mechanism of optimal energy distribution between the species of a food chain. This optimized sharing of common resources provides stability of a food chain for a given habitat and is guided by evolutionary pressures and natural selection.

The progenitor star of SN 2023ixf: A massive red supergiant with enhanced, Episodic Pre-Supernova mass loss

Abstract We identify the progenitor star of SN 2023ixf in Messier 101 using Keck/NIRC2 adaptive optics imaging and pre-explosion HST/ACS images. The supernova, localized with diffraction spikes and high-precision astrometry, unambiguously coincides with a progenitor candidate of mF814W = 24.87 ± 0.05 (AB). Given its reported infrared excess and semi-regular variability, we fit a time-dependent spectral energy distribution (SED) model of a dusty red supergiant (RSG) to a combined dataset of HST optical, ground-based near-infrared, and Spitzer/IRAC [3.6], [4.5] photometry. The progenitor resembles a RSG of Teff = 3488 ± 39 K and log (L/L⊙) = 5.15 ± 0.02, with a 0.13 ± 0.01 dex (31.1 ± 1.7 per cent) luminosity variation at a period of P = 1144.7 ± 4.8 days, obscured by a dusty envelope of τ = 2.92 ± 0.02 at 1 μm in optical depth (or AV = 8.43 ± 0.11 mag). The signatures match a post-main sequence star of $18.2_{-0.6}^{+1.3}\, \mathrm{M}_\odot$ in Zero-Age Main Sequence mass, among the most massive SN II progenitor, with a pulsation-enhanced mass-loss rate of $\dot{M}=(4.32\pm 0.26)\times 10^{-4} \, \mathrm{M}_\odot \, \text{yr}^{-1}$. The dense and confined circumstellar material is ejected during the last episode of radial pulsation before the explosion. Notably, we find strong evidence for variations of τ or Teff along with luminosity, a necessary assumption to reproduce the wavelength-dependent variability, which implies periodic dust sublimation and condensation. Given the observed SED, partial dust obscuration remains possible, but any unobstructed binary companion over 5.6 M⊙ can be ruled out.

Semi-analytical modeling of prompt redeposition in a steady-state plasma

Abstract A steady-state, 1D semi-analytical model for prompt redeposition based on the separation between redeposition caused by the electric field in the sheath and redeposition related to gyromotion is here described. The model allows for the estimation of not only the fraction of promptly redeposited flux but also the energy and angular distribution of the non-promptly redeposited population, along with their average charge state. Thus, the temperature and mean parallel-to-B velocity of the non-promptly redeposited flux are also available. The semi-analytical model was validated against equivalent Monte Carlo simulations across a broad range of input parameters. In this paper the eroded material under exam was tungsten (W) for which the code demonstrated consistent agreement with respect to numerical results, within its defined validity limits. The model can theoretically provide a solution for any material, temperature and electron density profile in the sheath, monotonic potential drop profile, and sputtered particles energy and angular distribution at the wall. As such, this code emerges as a potential tool for addressing the boundary redeposition phenomenon in fluid impurity transport simulations.

Study of the Management of the Electrical Energy Production and Distribution System Within the National School of Teachers of Mamou, Guinea

With the energy transition, marked essentially by the mass integration of energy production based on renewable resources, the missions and challenges of electrical energy distribution networks are evolving. This study is part of this dynamic, its objective is the study of the management of the production and distribution system of electrical energy within the National School of Teachers of Mamou. It emerges from this study that the supply of electrical energy to the National School of Teachers of Mamou is ensured by a hybrid system of three power sources: photovoltaic solar fields, Generator Group and Electricity of Guinea. The current electrical energy requirements of the Mamou NST are 40 kW. The total power of the installed photovoltaic solar fields is 70 kWp; the Generator used has a power of 10 kVA; the site’s Electricity of Guinea network is made up of transformers, cabin substations and protective equipment. The electricity distribution network is characterized by: Four (4) 250 A circuit breakers; a 32 A circuit breaker for the departure of lamps, sockets and fans; a 10 A circuit breaker for the lamps; a 10 A circuit breaker for the fans; a 16 A circuit breaker for the sockets and an 800 A mechanical inverter. The study shows that the power of photovoltaic solar fields is largely sufficient to cover the current electrical energy needs of the National School of Teachers of Mamou.

Dry Reforming of Methane to Syngas Mediated by Rhodium-Cobalt Oxide Cluster Anions Rh2CoO.

Dry reforming of methane (DRM) to syngas is an important route to co-convert CH4 and CO2. However, the highly endothermic nature of DRM induces the thermocatalysis to commonly operate at high temperatures that inevitably causes coke deposition through pyrolysis of methane. Herein, benefiting from the mass spectrometric experiments complemented with quantum chemical calculations, we have discovered that the bimetallic oxide cluster Rh2CoO- can mediate the co-conversion of CH4 and CO2 at room temperature giving rise to two free H2 molecules and two adsorbed CO molecules (COads). The only elementary step requiring the input of external energy (e.g., high temperature) is desorption of COads from the reaction intermediate Rh2CoOC2O2-. The doping effect of Co has also been clarified that the Co could tune the charge distribution and orbital energy of the active metal Rh, enabling the enhancement of cluster reactivity toward C-H activation, which is essential to facilitating the DRM to syngas. This work not only underlines the importance of temperature control over elementary steps in practical thermocatalysis but also identifies a promising active species containing the late 3d transition metal to drive DRM to syngas. The findings could provide novel insights into design of bimetallic catalysts for co-conversion of CH4 and CO2 at low temperatures.

Wake Dynamics of Complex Turning Vanes Using Time-Resolved Particle Image Velocimetry Measurements

Abstract The use of turning vanes spans multiple engineering disciplines such as aerospace, ocean, and biomedical to effectively turn an otherwise uniform flowfield and achieve desired downstream flow angles. The presented work investigates the wake dynamics generated by sets of complex turning vanes which contained nonaxisymmetric geometries, spanwise variations in turning angle, and multiple vane junctions. Time-resolved particle image velocimetry (TR-PIV) measurements were performed to collect three-component velocity data downstream of the vane pack geometries. As the vanes contained blunt trailing edges (TEs), large-scale periodic structures (von Kármán vortices) dominated the unsteady wakes. Two postprocessing methods, proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD), were employed to extract the wake energy or enstrophy content, corresponding spatial modes, and associated frequencies. This was completed for various parameters such as Reynolds number, vane turning angle, and vane trailing edge thickness. Spatial POD analyses showed that zero-turning vanes contained similar dynamics to that of a circular cylinder, and the total wake energy distributions were affected by freestream velocity. A spectral POD analysis in the wake of vane junctions found that the junction flow contained significant coherent content and gave some insight into the mean flow. Finally, vane parameters such as turning angle and TE thickness were found to play a large role in modifying the enstrophy content of the large-scale shedding modes.

Constraining Near-simultaneous Radio Emission from Short Gamma-Ray Bursts Using CHIME/FRB

We use the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Fast Radio Burst (FRB) Project to search for FRBs that are temporally and spatially coincident with gamma-ray bursts (GRBs) occurring between 2018 July 7 and 2023 August 3. We do not find any temporal (within 1 week) and spatial (within overlapping 3σ localization regions) coincidences between any CHIME/FRB candidates and all GRBs with 1σ localization uncertainties <1°. As such, we use CHIME/FRB to constrain the possible FRB-like radio emission for 27 short gamma-ray bursts (SGRBs) that were within 17° of CHIME/FRB’s meridian at a point either 6 hr prior up to 12 hr after the high-energy emission. Two SGRBs, GRB 210909A and GRB 230208A, were above the horizon at CHIME at the time of their high-energy emission and we place some of the first constraints on simultaneous FRB-like radio emission from SGRBs. While neither of these two SGRBs have known redshifts, we construct a redshift range for each GRB based on their high-energy fluence and a derived SGRB energy distribution. For GRB 210909A, this redshift range corresponds to z = [0.009, 1.64] with a mean of z = 0.13. Thus, for GRB 210909A, we constrain the radio luminosity at the time of the high-energy emission to L < 2 × 1046 erg s−1, L < 5 × 1044 erg s−1, and L < 3 × 1042 erg s−1 assuming redshifts of z = 0.85, z = 0.16, and z = 0.013, respectively. We compare these constraints with the predicted simultaneous radio luminosities from different compact object merger models.

Euclid preparation. XLIX. Selecting active galactic nuclei using observed colours

The space mission will cover over $14\,000\ $ with two optical and near-infrared spectro-photometric instruments, and is expected to detect around ten million active galactic nuclei (AGN). This unique data set will make a considerable impact on our understanding of galaxy evolution in general, and AGN in particular. For this work we identified the best colour selection criteria for AGN, based only on photometry or including ancillary photometric observations, such as the data that will be available with the Rubin Legacy Survey of Space and Time (LSST) and observations already available from Spitzer /IRAC. The analysis was performed for unobscured AGN, obscured AGN, and composite (AGN and star-forming) objects. We made use of the spectro-photometric realisations of infrared-selected targets at all-$z$ ( ) to create mock catalogues mimicking both the Euclid Wide Survey (EWS) and the Euclid Deep Survey (EDS). Using these mock catalogues, we estimated the best colour selection, maximising the harmonic mean (F1) of: (a) completeness, that is, the fraction of AGN correctly selected with respect to the total AGN sample; and (b) purity, that is, the fraction of AGN inside the selection with respect to the selected sample. The selection of unobscured AGN in both surveys (Wide and Deep) is possible with photometry alone with $ F1=0.22$--0.23 (Wide and Deep), which can increase to $ F1=0.43$--0.38 (Wide and Deep) if we limit out study to objects at $z&gt;0.7$. Such a selection is improved once the Rubin/LSST filters, that is, a combination of the $u$, $g$, $r$, or $z$ filters, are considered, reaching an F1 score of 0.84 and 0.86 for the EDS and EWS, respectively. The combination of a colour with the $ colour, which is possible only in the EDS, results in an F1 score of 0.59, improving the results using only filters, but worse than the selection combining and LSST colours. The selection of composite AGN =0.05$--0.65 at 8--40$\ and obscured AGN is challenging, with $ F1 even when including Rubin/LSST or IRAC filters. This is unsurprising since it is driven by the similarities between the broad-band spectral energy distribution of these AGN and star-forming galaxies in the wavelength range 0.3--5\,micron

A Lightweight Pathological Gait Recognition Approach Based on a New Gait Template in Side-View and Improved Attention Mechanism

As people age, abnormal gait recognition becomes a critical problem in the field of healthcare. Currently, some algorithms can classify gaits with different pathologies, but they cannot guarantee high accuracy while keeping the model lightweight. To address these issues, this paper proposes a lightweight network (NSVGT-ICBAM-FACN) based on the new side-view gait template (NSVGT), improved convolutional block attention module (ICBAM), and transfer learning that fuses convolutional features containing high-level information and attention features containing semantic information of interest to achieve robust pathological gait recognition. The NSVGT contains different levels of information such as gait shape, gait dynamics, and energy distribution at different parts of the body, which integrates and compensates for the strengths and limitations of each feature, making gait characterization more robust. The ICBAM employs parallel concatenation and depthwise separable convolution (DSC). The former strengthens the interaction between features. The latter improves the efficiency of processing gait information. In the classification head, we choose to employ DSC instead of global average pooling. This method preserves the spatial information and learns the weights of different locations, which solves the problem that the corner points and center points in the feature map have the same weight. The classification accuracies for this paper’s model on the self-constructed dataset and GAIT-IST dataset are 98.43% and 98.69%, which are 0.77% and 0.59% higher than that of the SOTA model, respectively. The experiments demonstrate that the method achieves good balance between lightweightness and performance.

Dynamics of the Cl + CH3CN reaction on an automatically-developed full-dimensional abinitio potential energy surface.

A full-dimensional analytical potential energy surface (PES) is developed for the Cl + CH3CN reaction following our previous work on the benchmark abinitio characterization of the stationary points. The spin-orbit-corrected PES is constructed using the Robosurfer program and a fifth-order permutationally invariant polynomial method for fitting the high-accuracy energy points determined by a ManyHF-based coupled-cluster/triple-zeta-quality composite method. Quasi-classical trajectory simulations are performed at six collision energies between 10 and 60kcal mol-1. Multiple low-probability product channels are found, including isomerization to isonitrile (CH3NC), but out of the eight possible channels, only the H-abstraction has significant reaction probability; thus, detailed dynamics studies are carried out only for this reaction. The cross sections and opacity functions show that the probability of the H-abstraction reaction increases with increasing collision energy (Ecoll). Scattering angle, initial attack angle, and product relative translational energy distributions indicate that the mechanism changes with the collision energy from indirect/rebound to direct stripping. The distribution of initial attack angles shows a clear preference for methyl group attack but with different angles at different Ecoll values. Post-reaction energy distributions show that the energy transfer is biased toward the products' relative translational energy instead of their internal energy. Rotational and vibrational energy have about the same amount of contribution to the internal energy in the case of both products (HCl and CH2CN), i.e., both of them are formed with high rotational excitations. HCl is produced mostly in the ground vibrational state, while a notable fraction of CH2CN is formed with vibrational excitation.

Numerical Study of an Energy Storage Container with a Flat Plate Phase Change Unit Characterized by an S-Shaped Flow Channel

China’s rapid economic development and rising energy consumption have led to significant challenges in energy supply and demand. While wind and solar energy are clean alternatives, they do not always align with the varying energy needs across different times and regions. Concurrently, China produces substantial amounts of industrial waste heat annually. Effective recycling of this waste heat could substantially mitigate energy supply and demand issues. The Mobile Thermal Energy Storage (M-TES) system is a key solution to address these challenges, as it helps manage the uneven distribution of energy over time and space. This article establishes a packaged M-TES based on a plate-type phase change unit. Based on different placement methods of the plate-type phase change unit, different inlet temperatures and phase change temperature differences, and different inlet and outlet directions, the complete charging and discharging process of the packaged phase change thermal storage system was simulated using ANSYS FLUENT 2022 R1 software. The results showed that during the heating process of the entire system, the horizontal placement of the plate-type phase change unit and the inlet and outlet methods of the heat transfer fluid (HTF) significantly improved the heating effect of the system, increasing it by 15.9%. Increasing the temperature difference between the inlet temperature of the heat transfer fluid and the melting temperature of the phase change material (PCM) from 4 K to 19 K can increase the melting rate of PCM by approximately 54.9%

Single-pulse three-dimensional parallel recording in glass using a feedback system.

High-quality three-dimensional computer-generated holograms (3D-CGHs) are crucial for programmable 3D femtosecond laser parallel recording (3D-FLPR). In this study, we introduced an innovative feedback approach for the rapid optimization of 3D-CGHs by incorporating the superposition of the calculated lens phases (CLPs) onto the 3D-CGHs within a feedback system. This feedback system, governed by coordinated control of a spatial light modulator (SLM) and a camera, served to avoid the poor quality of the ordinary CGH system. As a result, we successfully demonstrated coaxial 3D-FLPR in Ag-doped phosphate glass solely using a single fs laser pulse. Additionally, we regulated the energy distribution of the generated 3D multi-focus (3D-MF) to compensate the laser energy losses inside the glass. The presented single-pulse 3D parallel recording indicated the significant advancement facilitated by our method, particularly in enhancing the writing efficiency of optical storage.

The Simons Observatory: Combining cross-spectral foreground cleaning with multitracer B -mode delensing for improved constraints on inflation

The Simons Observatory (SO), due to start full science operations in early 2025, aims to set tight constraints on inflationary physics by inferring the tensor-to-scalar ratio r from measurements of cosmic microwave background (CMB) polarization B-modes. Its nominal design including three small-aperture telescopes (SATs) targets a precision σ(r=0)≤0.003 without delensing. Achieving this goal and further reducing uncertainties requires a thorough understanding and mitigation of other large-scale B-mode sources such as Galactic foregrounds and weak gravitational lensing. We present an analysis pipeline aiming to estimate r by including delensing within a cross-spectral likelihood, and demonstrate it for the first time on SO-like simulations accounting for various levels of foreground complexity, inhomogeneous noise and partial sky coverage. As introduced in an earlier SO delensing paper, lensing B-modes are synthesized using internal CMB lensing reconstructions as well as -like cosmic infrared background maps and LSST-like galaxy density maps. We then extend SO’s power-spectrum-based foreground-cleaning algorithm to include all auto- and cross-spectra between the lensing template and the SAT B-modes in the likelihood function. This allows us to constrain r and the parameters of our foreground model simultaneously. Within this framework, we demonstrate the equivalence of map-based and cross-spectral delensing and use it to motivate an optimized pixel-weighting scheme for power spectrum estimation. We start by validating our pipeline in the simplistic case of uniform foreground spectral energy distributions. In the absence of primordial B-modes, we find that the 1σ statistical uncertainty on r, σ(r), decreases by 37% as a result of delensing. Tensor modes at the level of r=0.01 are successfully detected by our pipeline. Even when using more realistic foreground models including spatial variations in the dust and synchrotron spectral properties, we obtain unbiased estimates of r both with and without delensing by employing the moment-expansion method. In this case, uncertainties are increased due to the higher number of model parameters, and delensing-related improvements range between 27% and 31%. These results constitute the first realistic assessment of the delensing performance at SO’s nominal sensitivity level. Published by the American Physical Society 2024

Comparative Studies of the Properties of Copper Components: Conventional vs. Additive Manufacturing Technologies

This article presents a comparative analysis of the crucial physical properties of electrically conductive components made of pure copper, produced by various additive manufacturing technologies such as binder jetting (BJ) and direct metal laser sintering (DMLS). The comparison concerned the assessment of critical parameters important from the application point of view, such as: electrical conductivity, hardness, yield point, microstructure and the occurrence of internal material defects. Same-sized components made in a conventional casting and subtractive method (machining) were used as a reference material. Comprehensive tests and the comparison of a wide range of parameters allowed us to determine that among the selected methods, printing using the DMLS technique allowed for obtaining arcing contact with mechanical and electrical parameters very similar to the reference element. Therefore, the obtained results showed the possibility of using the copper elements made by additive manufacturing for the switching and protection devices used in electrification and energy distribution industrial sectors.

A New Puzzling Periodic Signal in GeV Energies of the γ-Ray Binary LS I+61°303

LS I+61°303 is a high-mass X-ray binary system comprising a massive Be star and a rapidly rotating neutron star. Its spectral energy distribution across multiwavelengths categorizes it as a γ-ray binary system. In our analysis of LS I+61°303 using Fermi Large Area Telescope observations, we not only confirmed the three previously discussed periodicities of orbital, superorbital, and orbital–superorbital beat periods observed in multiwavelength observations, but also identified an additional periodic signal. This newly discovered signal exhibits a period of ∼26.3 days at a ∼7σ confidence level. Moreover, the power spectrum peak of the new signal gradually decreases as the energy increases across the energy ranges of 0.1–0.3, 0.3–1.0, and 1.0–500.0 GeV. Interestingly, a potential signal with a similar period was found in data obtained from the Owens Valley Radio Observatory 40 m telescope. We suggest that the newly discovered periodic signal may originate from a coupling between the orbital period and the retrograde stellar precession period.

Effect of oscillation parameters on weld surface morphology during laser beam oscillation welding of stainless steel

During laser beam oscillation welding (LBOW), the weld surface morphology is important because it influences the appearance of the workpiece and reflects the welding quality, and the oscillation parameters have an important effect on the weld surface morphology. Therefore, a combination of experimental research and numerical simulation is conducted to investigate the influence of oscillation parameters, including oscillation mode, oscillation frequency, and oscillation amplitude, on the weld surface morphology during LBOW. The calculation encompasses the oscillation trajectory, combined velocity, and energy distribution on the weld surface, varying with different oscillation parameters. A three-dimensional heat transfer and fluid flow model with the oscillation heat source is established to simulate the temperature and fluid flow behavior inside the weld pool. When the heat input is constant, an increase in oscillation frequency results in a decrease in weld width and a smoother surface. As the oscillation frequency increases, the weld width decreases, the surface becomes smooth, and the energy distribution on the weld surface becomes more uniform. The fact that the period of the surface pattern is almost equal to the oscillation period indicates a direct correlation between the formation of weld surface pattern and the oscillation trajectory in LBOW. Among all the oscillation modes, the minimum combined velocity which is equal to the welding velocity occurs at the inflection point in the linear oscillation mode, and the variation in combined velocity of the laser beam is the smallest for circular oscillation mode. The surface pattern is primarily influenced by the oscillation trajectory and fluid flow within the weld pool. Under conditions of lower oscillation frequencies or larger oscillation amplitudes, the fluid flow is weaker, and the surface pattern is primarily influenced by the oscillation trajectory. Conversely, when the fluid flow is stronger, the surface pattern is mainly determined by the fluid flow within the weld pool under conditions of higher oscillation frequencies or smaller oscillation amplitudes. This study explains the formation mechanisms of weld surface patterns and provides insights and guidance for selecting optimal oscillation parameters in LBOW.

Enhanced performance of all-PM Ho-doped fiber oscillator using NPE-SESAM hybrid mode-locking

We demonstrate a 2.08 µm all-polarization-maintaining (PM) holmium-doped fiber oscillator using a hybrid mode-locking technique with nonlinear polarization evolution (NPE) and a semiconductor saturable absorber mirror (SESAM). This oscillator features a linear structure with dual output ports. It initiates stable single-pulse mode-locking at a fundamental repetition rate of 57.86 MHz, requiring only about 400 mW of pump power. However, removing SESAM requires increasing the pump power to about 2.2 W—about a 5.8-fold increase—to initiate mode-locking, which starts in a multi-pulse state. Additionally, the oscillator can operate in two distinct states by adjusting the phase bias, ensuring that the main output port delivers high-quality, soliton-like femtosecond pulses. The other port, known as the rejection port, emits lower-quality pulses with different spectral and temporal characteristics. However, in one state, the pulse quality at the rejection port is significantly enhanced, approaching the high quality of the main output port. Theoretical analysis indicates that the pulse quality at the rejection port strongly relies on the energy distribution between the two orthogonally polarized pulses in the PM fiber. Another advantage of the hybrid mode-locking configuration is that it allows a pump power tuning range to maintain single-pulse operation as high as 220 mW. It is ∼4 times higher than that of the NPE-only configuration which is about 60 mW. These results indicate that oscillators using hybrid mode-locking exhibit much greater flexibility and reliability than those using PM-NPE alone. The hybrid mode-locking technique shows potential in addressing the self-starting challenges inherent in PM-NPE lasers, thereby advancing their applicability in practical scenarios.